Description
Title of Invention
PRE-COATED METAL SHEET, METHOD FOR MANUFACTURING PRE-
5 COATED METAL SHEET, AND CONTINUOUS COATING APPAMTUS
Technical Field
[OOOl]
The present invention relates to a pre-coated metal sheet, a method for
10 manufacturing a pre-coated metal sheet, and a continuous coating apparatus that are
capable of achieving both high glossiness and high adhesion between film layers.
Background Art
[0002]
15 Pre-coated metal sheets, which are coated in advance at steelworks, for
example, are used as coated metal sheets for various uses, such as home appliances,
building materials, civil works, machines, automobiles, furniture, and containers. A
pre-coated metal sheet is obtained by coating a surface (one surface or both surfaces)
of a metal sheet, such as a steel sheet or a plated steel sheet, with one or a plurality of
20 films. For example, a pre-coated steel sheet is obtained by coating a surface of a
plated steel sheet with multiple films (e.g., a primer film, a colored film, and a clear
film).
[OOO3]
Examples of a conventional continuous coating method for continuously
25 coating a long metal sheet (metal strip) with multiple layers by using a continuous
coating line include (1) successive coating and baking method, (2) wet-on-wet
method, and (3) multilayer simultaneous coating method.
[0004]
(1) Successive coating and baking method is a coating method that
30 successively performs, film by film, application (coat) and baking (bake) of a coating
material (e.g., see Patent Literature 1). For example, a coating method that
performs the application and baking of an upper layer film after the application and
baking of a lower layer film is called a two-coat two-bake (2C2B) method. (2) Weton-
wet method is a coating method that applies an upper layer film before a lower
layer film is dried, by utilizing a difference in surface tension between coating
5 materials, for example, without performing baking, drying, and the like after the
application of the lower layer film (e.g., see Patent Literature 2). This wet-on-wet
method is also called a two-coat one-bake (2ClB) method or a three-coat one-bake
(3ClB) method, depending on the number of lower layer films. (3) Multilayer
simultaneous coating method is a coating method that simultaneously applies a
10 plurality of films by using a multilayer coater, such as a slide curtain coater (e.g., see
Patent Literature 2).
[OOOS]
Besides the above-described methods that continuously coat a long metal
strip by using a continuous coating line, there is also a method that individually coats
15 outer parts of an automobile body, for example, by using an air spray or the like. It
is known that a wet-on-wet method of this individual coating method uses preheating.
To prevent mixing of coating materials in upper and lower layers, the weton-
wet method using pre-heating applies the upper layer after the lower layer is
applied and pre-heated at a relatively low temperature to be semi-cured. For
20 example, Patent Literatures 3 and 4 disclose applying a colored base coating material
in a lower layer onto an outer part of an automobile body made of metal or plastic,
by electrostatic coating or by using an air spray, for example, then pre-heating the
lower layer (80 "C, ten minutes), applying a clear coating material in an upper layer
onto the uncured coating surface, and then simultaneously baking the upper and
25 lower layers (140 "C, 30 minutes).
Citation List
Patent Literature
[0006]
30 Patent Literature 1 :
Patent Literature 2:
Patent Literature 3:
Patent Literaturc 4:
Summary of Invention
5 Technical Problem
[0007]
In general, to obtain a inultilayer pre-coated metal sheet, a colored film is
formed as a lower layer by applying a colored coating material containing a color
pigment, and then a clear film is formed as an upper layer by applying a clear coating
10 material not containing a color pigment. In this case, in the successive coating and
baking method (2C2B) according to Patent Literature 1, the clear film in the upper
layer is applied and baked after the colored film in the lower layer is baked to be
completely dried; thus, coating steps are independent from each other. This is
advantageous in that the clear film in the upper layer and the colored film in the
15 lower layer do not mix with each other, and the clear film not containing a color
pigment can have a sufficient thickness, so that the gloss of the clear film can be
ensured. There is a problem, however, in that when the upper layer is applied, the
clear coating material in the upper layer does not easily conform to the completely
dried and cured colored film in the lower layer, and the adhesion between the upper
20 and lower layers decreases, which makes peeling likely to occur at the interface
between the films in the two layers.
[0008]
In the wet-on-wet method and the multilayer simultaneous coating method
according to Patent Literature 2, the coating materials in the upper and lower layers
25 easily conform to each other at the interface between the films, and high adhesion is
obtained between the upper and lower layers. When the upper layer is applied,
however, the colored film in a wet state in the lower layer and the clear coating
material in the upper layer mix with each other to form a mixed layer. This causes a
problem in that the clear film not containing a color pigment cannot have a sufficient
30 thickness, so that the gloss of the pre-coated metal sheet significantly decreases.
[0009]
On this point, in the wet-on-wet method using pre-heating according to
Patent Literatures 3 and 4, the colored film in the lower layer is semi-cured by preheating,
which prevents mixing of the colored film and the clear film in the upper
layer; thus, the gloss can be high to some extent.
5 [OOlO]
However, also in the wet-on-wet method using pre-heating, a color pigment
contained in the colored film in the lower layer diffuses into the clear film in the
upper layer, affecting the gloss of the pre-coated metal sheet after baking. The
present inventors have found through extensive research that when heating
10 conditions at the time of pre-heating are inappropriate, the color pigment
concentration distribution at the boundary portion between the pre-heated colored
film and the clear film becomes inappropriate, owing to diffusion and convection of
the color pigment from the lower layer to the upper layer, thus causing a decrease in
the gloss of the pre-coated metal sheet.
15 [ O O l l ]
Nevertheless, the effects of heating conditions at the time of pre-heating and
the color pigment concentration distribution at the boundary portion between the
colored film and the clear film on the gloss of the pre-coated metal sheet have not
been clarified in detail. Hence, the glossiness of the pre-coated metal sheet has
20 sufficient room for improvement if it is possible to appropriately control the heating
conditions at the time of pre-heating and the color pigment concentration distribution
at the boundary portion.
[OO12]
Furtl~ermore, the coating method using pre-heating according to Patent
25 Literatures 3 and 4 is applied not to the case of continuously coating a metal strip
using a continuous coating line, but to the case of individually coating outer parts of
an automobile body, for example, and the time for pre-heating the lower layer is as
long as several minutes to scveral tens of minutes. Therefore, with regard to a
multilayer pre-coated metal sheet manufactured by continuously coating a metal strip
30 using a continuous coating line, appropriate heating conditions at the time of preheatirig
and appropriate color pigment concentration distribution at the boundary
portion between the colored film and the clear film have not been clarified.
[0013]
Hence, the present invention, which has been made in view of the above
problems, aims to achieve both the glossiness and the adhesion between films of a
5 mdtilayer pre-coated metal sheet manufactured in a continuous coating line at high
levels.
Solution to Problem
[0014]
10 According to an aspect of the present invention in order to achieve the
above-mentioned object, there is provided a pre-coated metal sheet including a
pl~irality of film layers on one surface or both surfaces of a metal sheet, the film
layers including a colored film layer that is placed on the metal sheet side and
contains a color pigment, a pigment-concentrated layer that is formed on the colored
15 film layer, and whose color pigment concentration is equal to or greater than an
average value of color pigment concentration in the colored film layer and increases
toward an outer layer side, a diffusion layer that is formed on the pigmentconcentrated
layer, and whose color pigment concentration decreases toward the
outer layer side, and a clear layer that is formed on the diffusion layer and does not
20 contain the color pigment. A ratio dlld2 between a thickness dl of the clear layer
and a thickness d2 of the pigment-concentrated layer satisfies 1.7 5 dlld2 5 4.7.
[00 1-51
A ratio cllc2 between a maximum value cl and a minimum value c2 of a
color pigment concentration ratio c in the pigment-concentrated layer based on the
25 average value of the color pigment concentration in the colored film layer may
satisfy 1.04 i clIc2 5 2.0.
[OOI 61
The ratio dlld2 may satisfy 2.0 5 dlld2 5 4.7.
[0017]
30 The thickness d2 of the pigment-concentrated layer may be equal to or
greater than 2.2 pm and equal to or less than 8.0 pm.
[OO 181
The thickness dl of the clear layer may be equal to or greater than 5.0 pin
and equal to or less than 12.3 pm.
[0019]
5 According to another aspect of the present invention in order to achieve the
above-mentioned object, there is provided a method for manufacturing a pre-coated
metal sheet, in which the pre-coated metal sheet is manufactured by continuously
coating a surface of a strip-shaped metal sheet, the method including: a first coating
step of, by a first coating device, applying a colored coating material containing a
10 color pigment onto the surface of the metal sheet or onto another film applied onto
the surface of the metal sheet, to form a colored film; a pre-heating step of, by a
heating device, heating the colored film at a heating temperature of 60 to 150 "C for
a heating time of 1 to 10 seconds to bring the colored film into a half-dried state; a
second coating step of, by a second coating device, applying a clear coating material
15 not containing the color pigment onto the colored film in a half-dried state to form a
clear film; and a baking step of, by a baking device, simultaneously baking the
colored film and the clear film.
[0020]
According to another aspect of the present invention in order to achieve the
20 above-mentioned object, there is provided a continuous coating apparatus, in which
the pre-coated metal sheet is manufactured by continuously coating a surface of a
strip-shaped metal sheet, the continuous coating apparatus including: a first coating
device configured to apply a colored coatii~g material containing a color pigment
onto the surface of the metal sheet or onto another film applied onto the surface of
25 the metal sheet, to form a colored film; a heating device configured to heat the
colored film at a heating temperature of 60 to 150 OC for a heating time of 1 to 10
seconds to bring the colored film into a half-dried state; a second coating device
configured to apply a clear coating material not coiltailling the color pigment onto the
colored film in a half-dried state to form a clear film; and a baking device configured
30 to simultaneously bake the colored film and the clear film.
Advantageous Effects of Invention
[002 11
According to the present invention, both the glossiness and the adhesion
between films of a multilayer pre-coated metal sheet manufactured in a continuous
5 coating line can be achieved at high levels.
Brief Description of Drawings
[0022]
[FIG. 11 FIG. 1 is a schematic diagram illustrating a line configuration of a
10 continuous coating apparatus according to a first embodiment of the present
invention.
[FIG. 2A] FIG. 2A is an explanatory diagram illustrating a stacked state of films and
color pigment concentration distribution in a first coating step according to the
embodiment.
15 [FIG. 2B] FIG 2B is an explanatory diagram illustrating a stacked state of films and
color pigment concentration distribution in a pre-heating step according to the
embodiment.
[FIG. 2C] FIG. 2C is an explanatory diagram illustrating a stacked state of films and
color pigment concentration distribution in a second coating step according to the
20 embodiment.
[FIG. 201 FIG. 2D is an explanato~yd iagram illustrating a stacked state of films and
color pigment concentration distribution after the second coating step according to
the embodiment.
[FIG. 2E] FIG. 2E is an explanatory diagram illustrating a stacked state of films and
26 color pigment concentration distribution in a baking step according to the
embodiment.
[FIG. 3A] FIG. 3A is a schematic diagram illustrating a step of applying an upper
layer coating material onto a lower layer film by a conventional 2C2B method.
[FIG. 3B] FIG. 3B is a schematic diagram illustrating a step of applying an upper
30 layer coating material onto a lower layer film by a conventional wet-on-wet method.
[FIG. 3C] FIG. 3C is a schematic diagram illustrating a step of applying an upper
layer coating material onto a lower layer film by a pre-heating method according to
the present embodiment.
[FIG. 41 FIG. 4 is a graph showing an example of the color pigment concentration
distribution in films of a pre-coated steel sheet manufactured by each of conventio~ial
5 coating methods.
[FIG. 51 FIG. 5 is a graph showing an example of the color pigment conccntration
distribution in film layers of a pre-coated steel sheet according to the embodiment.
[FIG. 61 FIG. 6 is a graph showing a modification example of the color pigment
concentration distribution in film layers of a pre-coated steel sheet according to the
10 embodiment.
[FIG. 71 FIG. 7 is a schematic diagram illustrating a line configuration of a
continuous coating apparatus according to a second embodiment of the present
invention.
[FIG. 81 FIG. 8 is a schematic diagram illustrating a line configuration of a
15 continuous coating apparatus according to a third embodiment of the present
invention.
[FIG 91 FIG. 9 is a schematic diagram illustrating a line configuration of a
continuous coating apparatus according to a fourth embodiment of the present
invention.
20 [FIG. 101 FIG. 10 is a schematic diagram illustrating a method for bending a precoated
steel sheet.
[FIG. 111 FIG. 11 is a graph showing the Ti concentration ratio distribution in the film
thickness direction of Comparative Examples 1 to 3.
[FIG. 121 FIG. 12 is a graph showing the Ti concentration ratio distribution in the
25 film thickness direction of Examples 1 to 4 and Comparative Example 1.
[FIG. 131 FIG. 13 is a graph obtained by partially enlarging FIG. 12.
[FIG. 141 FIG. 14 is a graph showing the relation between dlld2 and the test results
of 60-degree gloss.
[FIG. 151 FIG. 15 is a graph showing the relation between heating temperature T, and
30 dl, d2, and the test results of 60-degree gloss.
[FIG. 16A] FIG. 16A is an enlarged photograph of a bent portion of a pre-coated steel
sheet according to Comparative Example.
[FIG. 16Bl FIG. 16B is an enlarged photograph of a bent portion of a pre-coated steel
sheet according to Example.
Description of Embodiments
5 [0023]
Hereinafter, (a) preferred embodiment(s) of the present disclosure will be
described in detail with reference to the appended drawings. In this specification
and the drawings, elements that have substantially the same function and structure
are denoted with the same reference signs, and repeated explanation is omitted.
10 [0024]
[l. Overview of method for manufacturing pre-coated metal sheet]
First, an overview of a method for manufacturing a pre-coated metal sheet
according to a first embodiment of the present invention will be described.
[0025]
15 As described above, examples of a conventional coating method for
continuously coating a strip-shaped long metal sheet (metal strip) include a
successive coating and baking method, a wet-on-wet method, and a multilayer
simultaneous coating method. These conventional coating methods, however, have
a problem in that high glossiness and high adhesion between films of a pre-coated
20 metal sheet cannot both be achieved.
[0026]
To solve this problem, in the present embodiment, in a continuous coating
line for coating a metal sheet with a plurality of films, a heating device for preheating
(hereinafter called a pre-heating device) is placed to follow a first coating
25 device that applies a colored coating material in a first layer (lower layer), and to
precede a second coating device that applies a clear coating material in a second
layer (upper layer). This pre-heating device is a simple heating device having lower
output and heating temperature and smaller installation space than a conventional
baking device.
30 [0027]
In the methcd for manufacturing a pre-coated metal sheet according to the
present embodiment, in continuously coating a strip-shaped metal sheet by thc
continuous coating line, first, a colored film in the lower layer is applied onto the
mctal sheet. Then, the colored film is pre-heated under appropriate heating
conditions to be brought into a half-dried state by the pre-heating device.
5 Furthermore, without the colored film in a half-dried state being subjected to cooling
and drying, a clear coating material in the uppcr layer is applied to form a clear film.
Afterthat, the colored film in the lower layer and the clear film in the uppcr layer arc
simultaneously baked.
[0028]
10 This continuous coating method by a wet-on-wet method using pre-heating
can form four characteristic film layers (clear layer, diffusion layer, pigmentconcentrated
layer, and colored film layer) having different color pigment
concentration distribution characteristics in the colored film and the clear film of the
pre-coated metal sheet. This makes it possible to manufacture a pre-coated metal
15 sheet having high glossiness and having high adhesion between the colored film in
the lower layer and the clear film in the upper layer.
[0029]
Hereinafter, detailed description will be given on a continuous coating
apparatus for implementing the wet-on-wet method using pre-heating (hereinafter
20 called a pre-heating method) and a method for manufacturing a pre-coated metal
shcet using the apparatus. In the example described below, a pre-coated steel shect
in which a steel sheet is coated with upper and lower two films, a colored film and a
clear film, is manufactured as a pre-coated mctal sheet, but a pre-coated mctal shect
of the prcsent invention is not limited to this example. For example, a mctal shect
25 made of any material other than a steel shcet may be used as a base material (mctal
sheet) to be coated. In addition, the present invention can also be applied to a case
of manufacturing a pre-coated metal shcet in which a metal shect is coated with three
or more films.
[0030]
30 [2. Confi yration of continuous coating apparatus]
Next, an entire configuration of a continuous coating apparatus according to
the first embodiment of thc present invention will be described with refcrcnce to FIG.
1. FIG. 1 is a schematic diagram illustrating a line configuration of the continuous
coating appalatus according to the present embodiment.
[003 11
5 As illustrated in FIG. 1, the continuous coating apparatus according to the
present embodiment is a coating line for continuously coating a surface of a strip-
,shaped steel sheet 10 (steel strip) with a predetermined width to manufacture a
multilayer pre-coated metal sheet. While passing the steel sheet 10 at a constant
line speed ill the sheet-passing direction, the continuous coatiug apparatus
10 continuously applies a plurality of films 11 and 12 onto at least one surface of the
steel sheet 10, and further, bakes, cools, and dries the plurality of films 11 and 12
simultaneously. The line speed in passing the steel sheet 10 is, for example, 30 to
200 mlmin.
[0032]
15 Such a continuous coating apparatus includes a roll coater 13
(corresponding to a first coating device of the present invention), a pre-heating
device 14 (corresponding to a heating device of the present invention), a curtain
coater 15 (corresponding to a second coating device of the present invention), a
baking device 16 (corresponding to a baking device of the present invention), a
20 cooling device 17, and a drying device 18.
100331
The roll coater 13 is an example of the first coating device that applies a
coloied coating material containing a color pigment onto the surface of the steel
sheet 10. The colored coating material is a coating material for forming a colored
25 fill11 11 in a lower layel; and contains the color pigment. The roll coater 13 causes a
roll holding the colored coating material to come in contact with the surface of the
steel sheet 10 while rotating the roll, thereby applying the colored coating material
onto the surface of the steel sheet 10. Thus, the colored film 11 is foimed as a first
layer (lower layer) on the surface of the steel sheet 10.
30 [0034]
As the first coating device, either of a contact-type coating device (e.g., roll
coater) and a non-contact-type coating device (e.g., curtain coatcr) may be uscd; as
illustrated in FIG. 1, the roll coater 13, which is of a contact type, is preferably used.
In general, it is difficult for a curtain coater to control thickuess. In contrast, the roll
coater 13 can control thickness relatively easily and highly precisely by adjusting a
5 roll rotation speed and a gap between rolls, and thus can control the thickness of the
colored film 11 in the lower layer highly precisely. In addition, the use of the roll
coater 13 broadens a viscosity range of coating materials that can be applied.
[0035]
The pre-heating device 14 is an example of a heating device that heats the
10 colored film 11 at a predetermined heating temperature T. The pre-heating device
14 is placed to follow the above-described roll coater 13 (the first coating device)
and to precede the curtain coater 15 (the second coating device) on the coating line.
As illustrated in FIG. 1, on the coating line between these two coating devices, only
the pre-heating device 14 is installed, and a baking device, a cooling device, a drying
15 device, or the like for the colored film 11 is not installed. On this point, the
continuous coating line according to the present embodiment has a device
configuration and an arrangement different from those of a continuous coating line of
a conventional 2C2B method.
[0036]
20 The pre-heating device 14 is configured with, for example, a hot air drying
furnace, an induction heating furnace, an infrared heating furnace, or a furnace using
any of these in combination, any heating device capable of heating a coating material
call be used. This pre-heating device 14 does not bake the colored film 11 on the
steel sheet 10 by heating it for a long time at a high temperature, but heats the
25 colored film 11 for a short time at the predetermiued heating tempeiature T (e.g., 60
to 150 "C) lower than a baking temperature by a general baking device. This
heating temperature T is, for example, equal to or lower than the boiling point of a
volatile content of the colored coating material. Note that the heating temperature T
is expressed by a peak metal temperature (PMT) of the steel sheet 10 heated by the
30 pre-heating device 14.
[0037]
For the above reason, the pre-heating device 14 is configured with a heating
device having lower output, lower heating temperature, smaller size, and less
installation space than a baking device generally used in a conventional coating line.
For example, the output (necessary electric energy per unit mass of the steel sheet
5 10) of the baking device 16, which is of a conventional general IH type, is 11 to 24
kWldton. In contrast, the output of the pre-heating device 14 can be 3 to 17
kWh/ton, which is as low as approximately 27 to 70 % of the output of the general
baking device 16. In addition, the heating temperature of the baking device 16 is
200 "C or higher in many cases. In contrast, the heating temperature T of the pre-
10 heating device 14 can be as low as approximately 60 to 150 OC. Furthermore, the
total length of the baking device 16 in the sheet-passing direction is generally 30 m
or greater. In contrast, the total length of the pre-heating device 14 can be
approximately 1 to 5 m.
[0038]
15 This pre-heating device 14 is used to heat the colored film 11 to the low
heating temperature T equal to or lower than the boiling point of the volatile content
of the colored coating material. This brings the colored film 11 into a "half-dried
state" in which it is not completely dried by volatilization of all of the volatile
content of the coating material (i.e., not baked), but partially dried by volatilization
20 of part of the volatile content of the coating material.
[0039]
The curtain coater 15 is an example of the second coating device that
applies a clear coating material onto the colored film 11. The curtain coater 15
applies the clear coating material onto the colored film 11 that has been brought into
25 a half-dried state by being heated by the above-described pre-heating device 14, to
form a clear film 12.
[0040]
As the curtain coater 15, for example, a known curtain coater, such as a
curtain flow coater or a roller curtain coater, can be used. This curtain coater 15
30 causes the clear coating material to flow down, from above the steel sheet 10 being
passed, in the form of a curtain with a width larger than a sheet width of the steel
sheet 10, thereby applying thc clear coating material onto the colored film 11 without
contact. Thus, the clear film 12 in an upper layer is formcd on the colorcd film 11
in the lower layer.
[0041]
5 As the second coating device, either of a contact-type coating device (e.g.,
roll coater) and a non-contact-type coating device (e.g., curtain coater) may be used;
as illustrated in FIG. 1, a non-contact-type coating device, such as the curtain coater
15, is preferably used. This is because when the clear coating material is applied
onto the colored film I1 in a half-dried state by using a roll coater, which is of a
10 contact type, there is a possibility of peeling of the colored film 11.
100421
The use of a non-contact-type coating device, such as the curtain coater 15,
as the second coating device prevents peeling of the colored film 11 and enables
stable formation of the films in the upper and lower layers with desired thicknesses.
15 In addition, the use of the non-contact-type coating device provides the clear film 12
with a smooth and beautiful appearance, and further, enables application of a coating
material that is likely to cause uneven transfer from a roll, and allows high-speed
coating.
[0043]
20 In addition, as illustrated in FIG. 1, the curtain coater 15 is placed to follow
the pre-heating device 14 on the coating line, and a cooling device and a drying
device for forced cooling and drying of the colored film 11 are not provided between
the pre-heating device 14 and the curtain coater 15. Therefore, the curtain coater 15
applies the clear coating material onto the colored film 11 that is not subjected to
25 forced cooling and drying after being heated by the pre-heating device 14. Such a
configuration of the coating line enables the curtain coater 15 to apply the clear
coating material onto the colored film I1 before the temperature of the colored film
11 in a half-dried state ejected from the pre-heating device 14 decreases, to make the
colored film 11 and the clear film 12 confornl to each other appropriately.
30 [0044]
The baking device 16 is placed to follow the curtain coater 15, and
simultaneously bakes the colored film 11 and the clear film 12 applied onto ihe stecl
sheet 10. This baking device 16 is configured with a general coating material
baking furnace, for example, a hot air drying furnace, an induction heating furnace,
an infrared heating furnace, or a furnace using any of these in combination.
5 [0045]
As described above, the baking device 16 illustrated in FIG. 1 is equivalent
to a baking device generally used in a conventional coating line, and has significantly
higher output, heating temperature, and the like and larger installation space than the
pre-heating device 14. The heating temperature by the baking device 16 is higher
10 than the boiling points of volatile contents of the colored coating material and the
clear coating material (e.g., the heating temperature is 200 "C or higher), and the
heating time by the baking device 16 is longer than that by the pre-heating device 14.
Consequently, by passing the steel sheet 10 into the baking device 16, the colored
film 11 and the clear film 12 are heated to a high heating temperature, and the two
15 films 11 and 12 are baked onto the steel sheet 10 simultaneously.
[0046]
In addition, the cooling device 17 and the drying device 18 are placed to
follow the baking device 16. The cooling device 17 water-cools the steel sheet 10
onto which the colored film 11 and the clear film 12 have been baked by the baking
20 device 16. The drying device 18 is configured with a drier or the like, and dries the
steel sheet 10 after the cooling by the cooling device 17.
[0047]
[3. Specific examples of coating materials]
Next, definitions and specific examples of coating materials used for the
25 colored film 11 (intermediate coat film) and the clear film 12 (topcoat film) will be
described.
[0048]
[3.1. Definitions of ternls]
First, terms related to coating materials will be defined.
30 A coating material includes a solid content and a volatile content. The
solid content is a component that constitutes a fill11 by baking, among coinponents of
the coating material, and is uscd to offer various functions of the coating material.
This solid content includes a dissolved component that is dissolved in the volatile
content and a suspcnded component that is suspended in a state of being dispersed in
the form of fine particles without being dissolved in the volatile content. The
5 volatile content of the coating material is a component that is volatilized by baking,
among components of the coating material, and is used to impart flowability to the
solid content to make it easy to apply. This volatile content is volatilized at the time
of heating after the application, and does not constitute the film after the baking.
Note that in this specification, volatilization of the volatile content of the coating
10 material encompasses not only the volatilization of the volatile content at a
temperature lower than its boiling point, but also vaporization of the volatile content
at a temperature equal to or higher than its boiling point.
100491
An oil-based coating material is a coating material using an organic solvent
15 as the volatile content. The solid content of the oil-based coating material includes
various resins (dissolved conlponent) and fine particles (suspended component) of
wax, a pigment, a crosslinking agent, a matting agent, an extender pigment, an
ultraviolet absorber, a curing agent, a corrosion inhibitol; or the like. In the volatile
content (organic solvent) of the oil-based coating material, as the solid content, the
20 various resins (dissolved component) are dissolved and the fine particles (suspended
component) of wax, a pigment, or the like are dispersed. Examples of the oil-based
coating material include an oil-based colored coating material and an oil-based clear
coating material.
[OOSO]
25 A water-based coating material is a coating material using a liquid mainly
constituted by water as thc volatile content. The solid content of the water-based
coating material includes various resins (suspended component) and fine particles
(suspended component) of wax, a pigment, a crosslinking agent, a matting agent, an
extender pigment, an ultraviolet absorber, a curing agent, a corrosion inhibitor, or the
30 like. In the volatile content (liquid mainly constituted by water) of the water-based
coating material, as the solid content, fine particles of the various resins (suspended
conlponent) are dispersed without being dissolved and the fine particles (suspended
componcnt) of wax, a pigment, or the like are also dispersed. Examples of the
water-based coating material include a water-based colored coating material and a
water-based clear coating material.
5 [0051]
Iiere, the volatile content of the water-based coating material may be only
water, or may be a mixture of an organic solvent and water (e.g., lower alcohol). In
the latter case, a mass proportion of water in the volatile content of the water-based
coating material is 95 mass% or greater, for example, but a mixture in which the
10 mass proportion of water is less than 95 mass% may also serve as the volatile content
of the water-based coating material.
[0052]
A volatile content coneentration is a proportion of a mass B of the volatile
content in the total mass (the sum of a mass A of the solid content and the mass B of
15 the volatile content) of a coating material (volatile content concentration = B/(A+B)
[mass%]). The volatile content concentration of a coating material forming a film
is highest at the time when the coating material is applied, and the volatile content
concentration decreases as the applied film dries (i.e., as the volatile content in the
film is volatilized).
20 [0053]
[3.2. Specific examples of colored coating material]
The colored film 11 is an intermediate coal film, and is used to implement
the design (e.g., color) of a pre-coated steel sheet and the functionality (e.g.,
improved hardness, chemical resistance, stain resistance, and corrosion prevention)
25 of a film. The colored coating material is a coating material containing a color
pigment, and is used to fom~th e colored film 11. As the colored coating material, a
generally known coating resin to which a color pigment and the like are added can be
used, and for example, a resin co~mnerciallya vailable as a coating material for precoating,
such as a resin for anti-corrosive films, can be used.
30 [0054]
As a resin of the colored coating material, for example, a general-use resin
used for a coating material for pre-coating, such as a polyester resin, a polyurethane
resin, an epoxy resin, or a fluorocarbon polymel; can be used. As needed, two or
more kinds of these resins may be mixed to be used, or a crosslinking agent, such as
a melamine resin or an isocyanate resin, may be used. In particular, a resin of a
5 type in which a polyester resin is cross-linked with a melamine resin or an isocyanate
has excellent workability.
[0055]
As a color pigment contained in the colored coating material, for example, a
general-use color pigment, such as titanium oxide, zinc oxide, iron oxide, aluminum
10 oxide, barium sulfate, aluminum, or carbon black, can be used. It is particularly
preferable to use a color pigment whose refractive index differs greatly from that of
the above resin.
[0056]
In addition, as needed, a known leveling agent, pigment dispersant, wax,
15 matting agent, or the like can be added to the colored coating material. The kinds
and addition amounts of these additives are not particularly limited, and can be
selected as needed. The colored coating material may be either of an oil-based
coating material and a water-based coating material.
[0057]
20 An oil-based colored coating material is a colored coating material using an
organic solvent as the volatile content. The solid content of the oil-based colored
coating material is, for example, a color pigment, silica, or a lubricant. The volatile
content (organic solvent) of the oil-based coating material is, for example, xylene,
cyclohexanone, or methyl ethyl ketone. The volatile content concentration of the
25 oil-based coating material (i.e., the concentration of the organic solvent) is, for
example, 30 to 70 mass%, particularly 40 to 65 mass%. A specific example of the
oil-based colored coating material is a colored coating material obtained by adding a
white pigment (titanium oxide) or a black pigment (carbon black) to a clear coating
material and stirring the mixture. The clear coating material is obtained by adding
30 an acid catalyst to a mixed solution of a polyester resin and a melamine resin (a
solution in which a polyester resin is cross-linked with a melamine resin) and stirring
the mixture.
[OOSS]
A water-based colored coating material is a colored coating material using a
liquid mainly constituted by water as the volatile content. The proportion of water
5 in the water-based colored coating material is, for example, 40 to 90 mass%. A
specific example of the water-based colored coating material is a colored coating
material obtained by adding a curing agent (e.g., a melamine resin or a
polyisocyanate compound), a color pigment (e.g., carbon black), silica particles (e.g.,
spherical silica particles), and a lubricant (e.g., polyethylene resin particles) to an
10 aqueous resin (e.g., a polyester resin, a urethane resin, or an acrylic resin).
[0059]
[3.3. Clear coating material]
The clear film 12 is a topcoat film forming the outermost layer of a precoated
steel sheet, and is used to implement the design (e.g., gloss) of the pre-coated
15 steel sheet and the functionality (e.g., improved hardness, chemical resistance, stain
resistance, and corrosion prevention) of a film. The clear coating material is a
coating material not containing a color pigment, and is used to form the clear film 12.
As the clear coating material, a generally known coating resin to which a lubricant
and the like are added can be used, and for example, a resin commercially available
20 as a coating material for pre-coating, such as a resin for anti-corrosive films, can be
used.
[0060]
As a resin of the clear coating material, for example, a general-use resin
used for a coating material for pre-coating, such as a polyester resin, a polyurethane
25 resin, an epoxy resin, or a fluorocarbon polymel; can be used. As needed, two or
more kinds of these resins may be mixed to be used, or a crosslinking agent, such as
a mclanline resin or an isocyanate resin, may be used. In particular, a resin of a
type in which a polyester resin is cross-linked with a melamine resin or an isocyanate
has excellent workability.
30 [0061]
A lubricant can bc added to the clear coating material as needed.
Components of the lubricant are not particularly limited, and polytetrafluoroethylene
(PTFE), polyethylene, microcrystalline, or the like can bc used.
[0062]
In addition, as needed, a known leveling agent, wax, matting agent, or the
5 like can be added to the clear coating material. The kinds and addition amounts of
these additives are not particularly limited, and can be selected as needed. The
clear coating material may be either of an oil-based coating material and a waterbased
coating material.
[0063]
10 An oil-based clear coating material is a clear coating material using an
organic solvent as the volatile content. The solid content of the oil-based clear
coating material is, for example, silica or a lubricant. The volatile content (organic
solvent) of the oil-based clear coating material is, for example, xylene,
cyclohexanone, or methyl ethyl ketone. The volatile content concentration of the
15 oil-based coating material (i.e., the concentration of the organic solvent) is, for
example, 30 to 70 mass%, particularly 40 to 65 mass%. A specific example of the
oil-based clear coating material is a clear coating material obtained by adding an acid
catalyst to a mixed solution of a polyester resin and a melamine resin (a solution in
which a polyester resin is cross-linked with a melamine resin) and stirring the
20 mixture.
[0064]
A water-based clear coating material is a clear coating material using a
liquid mainly constituted by water as the volatile content. The proportion of water
in the water-based clear coating material is, for exaillple, 40 to 90 mass%. A
25 specific example of the water-based clear coating material is a clear coating material
obtained by adding a curing agent (e.g., a melamine resin or a polyisocyanate
compound), silica particles (e.g., spherical silica particles), and a lubricant (e.g.,
polyethylene resin particles) to an aqueous resin (e.g., a polyester resin, a urethane
resin, or an acrylic resin).
30 [0065]
[4. Method for manufacturing pre-coated metal sheet]
Next, the method for manufacturing a pre-coated metal sheet according to
the present embodiment will he described. Described below is a method for
manufacturing a pre-coated steel sheet by co~~tinuouslcyo ating a steel sheet with
multiple layers by using the continuous coating apparatus (coating line) illustrated in
5 FIG. 1. Description is also given as appropriate on a stacked state of films in each
step of the manufacturing method and the distribution of color pigment concentration
in films, with reference to FIG. 2.
[0066]
The method for manufacturing a pre-coated metal sheet according to the
10 present embodiment includes (1) First coating step, (2) Pre-heating step, (3) Second
coating step, (4) Baking step, (5) Cooling step, and (6) Drying step. Each step is
described below.
[0067]
(1) First coating step
15 The steel sheet 10 is a hot dip galvanized steel sheet, an electro galvanized
steel sheet, a cold-rolled steel sheet, or the like, and has a sheet thickness of 0.3 to
3.2 mm, for example, and a sheet width of 600 to 1828 mm, for example.
[0068]
As illustrated in FIG. 1, first, the strip-shaped steel sheet 10 passed on the
20 coating line is introduced into the roll coater 13 (the first coating device). This roll
coater 13 applies a colored coating material onto a surface of the steel sheet 10 to
form the colored film 11 (lower layer film) on the surface of the steel sheet 10. A
thickness Dl of the colored film 11 at the time of this application may be 5 to 50 pn~,
for example; described below is an example in which Dl = 24 pm. Note that it is
25 possible to form a chemical conversion treatment layer on the surface of the steel
sheet 10, in advance, by a chemical conversion treatment device (not illustrated)
before applying the colored coating material, and form the colored film 11 on the
chemical conversion treatment layer. It is also possible to form a primer film, in
advance, by applying a primer coating material onto the steel sheet 10 or a chenlical
30 conversion treatment layel; and form the colored film 11 on the primer film.
[0069]
The colored film 11 applied in the above manner contains a color pigment at
a substantially uniform concentration in the thickness direction. Therefore, as
illustrated in FIG. 2A, within the colored film 11, the color pigment concentration is
substantially constant from the base material (the steel sheet 10) side to the outer
5 layer side.
[0070]
(2) Pre-heating step
Then, the steel sheet 10 on which the colored film 11 is formed is
introduced into the pre-heating device 14 (heating device). This pre-heating device
10 14 pre-heats the colored film 11 on the steel sheet 10. On this occasion, the preheating
device 14 does not bake the colored film 11 by heating it for a long time to a
high heating temperature, but heats the colored film 11 at the low heating
temperature T (e.g., 60 to 150 OC) equal to or lower than the boiling point of the
volatile content of the colored coating material. A heating time t of the steel sheet
15 10 by the pre-heating device 14 is very short, and is preferably 1.0 to 10 seconds, for
example. For example, in the case where the pre-heating device 14 has a length of
installation of 5 m and the steel sheet 10 is passed at a line speed of 100 m/min, ihe
heating time of the steel sheet 10 by the pre-heating device 14 is three seconds.
[0071]
20 Such heating (pre-heating) at low temperature for a short time by the preheating
device 14 volatilizes part of the volatile content (e.g., an organic solvent or
water) of thc colored coating material from the colored filin 11, causing the volatile
content concentration in the colored film 11 to decrease, which brings the colored
film 11 into a "half-dried state".
25 [0072]
In the case where the colored coating material is an oil-based colored
coating material, its boiling point is 150 to 160 OC; hence, the heating temperature T
by the pre-heating device 14 is preferably PMT 60 to 150 OC, which is equal to or
lower than the boiling point, further preferably PMT 90 to 140 OC . In the case
30 where the colored coating material is a water-based colored coating material, its
boiling point is 90 to 120 "C; hence, the heating temperature T by the pre-heating
device 14 is preferably PMT 50 to 80 "C, which is equal to or lower than the boiling
point. In this mannel; the pre-heating device 14 heats the colored film 11 to the
appropriate heating temperature T equal to or lower than the boiling point of the
volatile content of the colored coating material, thereby drying the colored film 11 to
5 an appropriate level to bring it into a half-dried state in which mixing of an upper
layer coating material can be prevented. Note that this pre-heating slightly reduces
the thickness Dl of the colored film 11 (e.g., from 24 pm to 22 pm).
100731
In addition, since the colored film 11 is only heated for a short time at low
10 temperature in the pre-heating step, the color pigment contained in the colored film
11 hardly moves inside the colored film 11. Therefore, as illustrated in FIG. 2B,
within the pre-heated colored film 11, the color pigment concentration is still
substantially constant in the thickness direction.
[0074]
15 (3) Second coating step
Then, the steel sheet 10 where the colored film 11 in a half-dried state is
applied is introduced into the curtain coater 15 (the second coating device). This
curtain coater 15 applies a clear coating material onto the colored film 11 in a halfdried
state to form the clear film 12 (upper layer film) on the colored film 11 (lower
20 layer film). That is, a clear film is a "film formed by applying a clear coating
material", and partly contains a color pigment as will be described later. A
thickness D2 of the clear film 12 at the time of this application may be 10 to 100 pnl,
for example; described below is an example in which D2 = 40 pm.
[0075]
25 As illustrated in FIG. 1, the curtain coater 15 is placed to immediately
follow the pre-heating device 14 on the coating line. Therefore, the second coating
step by the curtain coater 15 is performed right after the heating step by the preheating
device 14, and between the two steps, the colored film 11 is not subjected to
forced cooling and drying using a cooling device and a drying device.
30 Consequently, in the second coating step, the clear film 12 is applied onto the colored
film 11 still in a half-dried state.
[0076]
In the above manner, the clear film 12 is applied onto the colored film 11 in
a half-dried statc. At the time when the clear film 12 is applied, as illustrated in FIG.
2C, the color pigment concentration of the colored film 11 is constant as in the case
5 of FIG. 2B, and the color pigment concentration of the clear film 12 is zero.
However, as time elapses after the application of the clear film 12, mass transfer
occurs at the interface between the colored film 11 and the clear film 12, and thus a
pigment-concentrated layer 123 and a diffusion layer 122 are formed in the clear film
12. That is, the color pigment contained in the colored film 11 in the lower layer
10 moves to the upper layer side by convection and concentration diffusion, and enters
thc clear film 12 in the upper layer to be diffused. As a result, as illustrated in FIG.
2D, the color pigment concentration in the colored film 11 decreases, and the
pigment-concentrated layer 123 and the diffusion layer 122 containing the color
pigment and a clear layer 121 not containing the color pigment are formed in the
15 clear film 12.
[0077]
The pigment-concentrated layer 123 is formed on the base material side in
the clear film 12, right above the colored film 11. This pigment-concentrated layer
123 is a portion where the color pigment concentration continuously increases
20 toward the outer layer side of the clear film 12. The color pigment concentration
reaches its highest peak at the outer layer side of the pigmen-concentrated layer 123.
[0078]
The diffusion layer 122 is formed right above the pigment-concentratcd
layer 123 (on the outer layer side) in the clear film 12. This diffusion layer 122 is a
25 portion of the clear film 12 where the color pigment concentration continuously
decreases toward the outer layer side of the clear film 12.
[0079]
Furthermore, the clear layer 121 containing substantially no color pigment is
formed on the outermost layer side in the clear film 12. In the present embodiment,
30 the colored film 11 is pre-heated before the application of the clear film 12 to be
brought into an appropriate half-dried state. Thus, the color pigment moves and
diffuses from the colored film 11 to the clcar film 12, but its diffusion range is
limited, and the color pigment does not reach the outermost layer portion of the clear
film 12. Consequently, the clear layer 121 containing substantially no color
pigment is formed in the outermost layer portion in the clear film 12.
5 [0080]
In addition, since the color pigment moves from the colored film 11 to the
pigment-concentrated layer 123 and the diffusion layer 122 of the clear film 12 as
described above, the color pigment concentration in the colored film 11 decreases as
a whole. In particular, in the outer-layer-side portion of the colored film 11, which
10 is adjacent to the pigment-concentrated layer 123, the color pigment concentration
greatly decreases, and there may occur a valley where the color pigment
concentration is lower than in the central portion in the thickness direction of the
colored film 11. In this manner, the applying of the clear film 12 in the upper layer
causes a decrease in the color pigment concentration of the colored film I1 in the
15 lower layer; the colored film ,ll whose color pigment concentration has decreased
after the application of the clear film 12 will be called a colored film layer 111.
[0081]
As described above, by convection and diffusion actions of substances (e.g.,
color pigment) between the clear film 12 in the upper layer and the colored film 11 in
20 the lower layer, three layers (the pigment-concentrated layer 123, the diffusion layer
122, and the clear layer 121) are formed in the clear film 12. In addition, the
colored film 11 becomes the colored film layer 111 whose color pigment
concentration has decreased after the application of the clcar film 12. As a result,
film layers of a two-layer structure of the colored film 11 and the clear film 12
25 changes to film layers of a four-layer structure (the colored film layer 11 1, the
pigment-concentrated layer 123, the diffusion layer 122, and the clcar layer 121 in
that order from the lower layer side).
[0082]
(4) Baking step
30 After that, the steel sheet 10 on which the colored film 11 and the clear fihn
12 are formed is introduced into the baking device 16. This baking device 16 heats
the colored film 11 and the clear film 12 on thc steel sheet 10 to a heating
temperature (c.g., 200 "C or higher) significantly higher than the boiling points of
volatile contents of the coating materials, to simultaneously bake the colored film 11
and the clear film 12.
5 [0083]
Such high-temperature heating (baking) by the baking device 16 completely
volatilizes the volatile content of the colored coating material from the colored film
11, and completely volatilizes the volatile content of the clear coating material from
the clear film 12. This causes the volatile content concentration in the two films 11
10 and 12 to decrease to substantially zero, bringing the two films 11 and 12 into a
completely dried, cured state.
[0084]
As a result, as illustrated in FIG. 2E, the colored film 11 and the clear film
12 are reduced in thickness. The thickness Dl of the colored film 11 is reduced
15 from 22 pm to 15 pm, for example, and the thickness D2 of the clear film 12 is
reduced from 40 pm to 15 pm, for example. This results in a reduction in the
thickness of each of the clear layer 121, the diffusion layer 122, the pigmentconcentrated
layer 123, and the colored film layer 111. Note that the color pigment
concentration distribution of each layer does not change.
20 [0085]
(5) Cooling step
Then, the high-temperature steel sheet 10 onto which the colored film 11
and the clear film 12 have been baked in the above manner is introduced into the
cooling device 17. This cooling device 17 sprays cooling water on the steel sheet
25 10 to cool it to a temperature close to ordinary temperature.
[0086]
(6) Drying step
Afier that, the steel sheet 10 cooled in the above manner is introduced into
the drying device 18. This drying device 18 vaporizes moisture attached to a
30 surface of the clear film 12 of the stecl sheet 10 to dry the stecl sheet 10.
[0087]
Through the above steps, the long steel sheet 10 is continuously coated with
the colored film 11 and the clear film 12, so that a two-layer pre-coated metal sheet is
manufactured. Described above is an example in which a front surface of the steel
sheet 10 is coated with two layers, but a rear surface of the steel sheet 10 may also be
5 coated with one layer or multiple layers by a known coating method
[OOSS]
Next, description is given on the reuse of the clear coating material in the
second coating step and on the adhesion between the colored film 11 in the lower
layer and the clear film 12 in the upper layer, with reference to FIGS. 3A to 3C.
10 FIGS. 3A to 3C are schematic diagrams each illustrating a step of applying a clear
coating material onto the colored film 11 by using the curtain coater 15.
[0089]
FIG. 3A illustrates a step of applying a clear coating material by a
conventional 2C2B method (successive coating and baking method). In the case of
15 applying the clear coating material in the upper layer by using a curtain coater after
completely baking the colored film 11 in the lower layer, as illustrated in FIG. 3A,
the coating material of the colored film 11 and the applied clear coating material do
not mix with each other. That is, the clear coating material in a flowing state flows
down in the form of a curtain from the curtain coater, to be attached onto the colored
20 film 11 of the steel sheet 10 passing under the curtain coater, so that the clear film 12
is formed. Concurrently, an excess clear coating material 12a flows down
downward from both sides in the width direction of the steel sheet 10. On this
occasion, since the colored film 11 is in a completely dried state, the clear coating
material does not mix with the coating material of the colored film 11.
25 Consequently, the clear coating material 12a flowing down from the both sides in the
width direction of the steel sheet 10 can be collected to be reused.
[0090]
However, in the 2C2B method illustrated in FIG. 3A, the clear coating
material in the upper layer does not conforin to the colored film 11 in the lower layer,
30 which has been baked to be completely dried and cured. This causes a probleill in
that, after the clear film 12 is baked, the adhesion between the colored film 11 and
the clear film 12 decreases, making the clear film 12 likely to pccl off from the
colored film 11 at the interface between the two films.
[0091]
FIG. 3B illustrates a step of applying a clear coating material by a
5 conventional multilayer simultaneous coating method. In the case of
sin~ultaneouslya pplying a colored coating material in the lower layer and the clear
coating material in the upper layer by using a multilayer curtain coater, as illustrated
in FIG. 3B, the two coating materials mix with each other because they are in a wet
state. Consequently, even if an excess colored coating material 1 la and the clear
10 coating material 12a flowing down downward from both sides in the width direction
of the steel sheet 10 are collected, they cannot be reused and must be disposed of
because they are mixed with each other. As described above, the multilayer
simultaneous coating method illustrated in FIG. 3B has a problem in that, since the
coating materials cannot be collected to be reused, disposal volume of the coating
15 materials increases and causes an increase in coating cost.
[0092]
In contrast, FIG. 3C illustrates a step of applying a clear coating material by
a wet-on-wet method using pre-heating (hereinafter called a pre-heating method)
according to the present embodiment. In the present embodiment, the curtain coater
20 15 applies the clear coating material in the upper layer onto the colored film 11 in a
half-dried state in the lower layer. As illustrated in FIG. 3C, the clear coating
material flowing down in the form of a curtain from the curlain coater 15 is attached
onto the colored film 11 to foim the clear film 12, and the excess clear coating
material 1221 flows down downward from both sides in the width direction of the
25 steel sheet 10 to be collected. On this occasion, since the colored film 11 is in a
half-dried statc, the clear coating material does not mix with the colored film 11.
Consequently, the collected excess clear coating material 12a can be reused because
it is not mixed with the colored coating material. This produces an effect of
reducing disposal volume of the coating materials and coating cost.
30 [0093]
Furthernlore, the applying of the clear coating illaterial in a wet state onto
the colored film 11 in a half-dried state makes the two coating ~uaterials conform to
each other at the interface between the colored film 11 and the clear film 12, and
makes the roughness of the interface higher than that in the case of FIG. 3A.
Consequently, after the colored film 11 and the clear film 12 are baked
5 simultaneously, the adhesion between the colored film 11 and the clear film 12 is
improved. This produces an effect of making the clear film 12 unlikely to peel off
from the colored film 11 at the interface between the two films.
[0094]
As described above, according to the method for manufacturing a pre-coated
10 metal sheet according to the present embodiment, the pre-heating device 14 brings
the colored film 11 in the lower layer into a half-dried state, and the clear coating
material in the upper layer is applied onto the colored film 11 without the colored
film 11 being subjected to cooling and drying. This improves the adhesion between
the colored film 11 in the lower layer and the clear film 12 in the upper layer, and
15 improves the reusability of the clear coating material in the lower layer, thus
reducing disposal volume of the coating materials.
LO0951
15. Appropriate range of volatile content concentration of film in half-dried state]
Next, description is given on an appropriate range of the volatile content
20 concentration of the colored film 11 that is brought into a half-dried state by the preheating
device 14.
[0096]
As described above, in the case where the colored film 11 in the lower layer
has a high volatile content concentration and its state is close to a wet state, when the
25 clear coating material in the upper layer is applied, the two films 11 and 12 easily
conform to each other and their adhesion is improved. On the other hand, the
colored film 11 in a state close to a wet state and the clear film 12 mix with each
other to form a mixed layer, making it difficult to folm the clear layer 121 not
containing the color pigment.
30 [0097]
In the case where the colored film 11 in the lower layer has a low volatile
content concentration and its state is close to a dried state, the two fi1111s 11 and 12 do
not easily conform to each other and their adhesion decreases. Furthermore, since it
is difficult for the color pigment to move from the colored film 11 in a state close to a
dried state to the clear film 12, the clear layer 121 is easily formed, but the pigment-
5 concentrated layer 123 and the diffusion layer 122 are difficult to form in the clear
film 12.
100981
As described above, the adhesion between the films and the formability of
the clear layer 121 have a trade-off relationship. The formability of the clear layer
10 121 and the formability of the pigment-concentrated layer 123 and the diffusion layer
122 also have a trade-off relationship. Hence, to appropriately form the three layers
of the clear layer 121, the diffusion layer 122, and the pigment-concentrated layer
123 in the clear film 12 and to ensure the adhesion between the films, it is preferable
to control heating conditions at the time of pre-heating so that the volatile content
15 concentration of the colored film 11 in a half-dried state is adjusted to fall within an
appropriate range.
COO991
Hence, in the present embodiment, when the colored film 11 is heated by
the pre-heating device 14 to be brought into a half-dried state, heating conditions are
20 controlled so that the volatile content concentration of the colored film 11 becomes
22 to 64 mass%. Note that the volatile content concentration of the colored film 11
is the volatile content concentration of the colored coating material forming the
colored film 1 1.
[OlOOj
25 In the case where the colored coating material in the lower layer is an oilbased
colored coating material, the volatile content concentration (the concentration
of the organic solvent) of the colored film 11 in a half-dried state is preferably 22 to
55 mass%. When the volatile content concentration of the colored film 11 in a halfdried
state is 55 mass% or less, the oil-based colored coating material of the colored
30 film 1 1 and the clear coating material in the upper layer do not mix with each other.
This allows the clear layer 121 to be formed appropriately in the clear film 12.
When the volatile content concentration of the colored film 11 is 22 mass% or greater,
the oil-based colored coating material of the colored film 11 in a half-dried state and
the clear coating material easily conform to each other, which improves the adhesion
between the films in the two layers, and the pigment-concentrated layer 123 and the
5 diffusion layer 122 can be formed appropriately in the clear film 12. Furthermore,
as compared with a conventional successive coating and baking method, the output
specification and installation space of the pre-heating device 14 according to the
present embodiment can be reduced by approximately 40 to 50 %, which makes it
possible to save the space and energy of the continuous coating apparatus.
10 [OlOl]
In the case where the colored coating material in the lower layer is a waterbased
colored coating material, the volatile content concentration (the concentration
of water, or the concentration of the mixture of water and the organic solvent) of the
colored film 11 in a half-dried state is preferably 25 to 64 mass%. When the
15 volatile content concentration of the colored film 11 in a half-dried state is 64 mass%
or less, the water-based colored coating material of the colored film 11 and the clear
coating material in the upper layer do not mix with each other. This allows the clear
layer 121 to be formed appropriately in the clear film 12. When the volatile content
concentration of the colored film 11 in a half-dried state is 25 mass% or greater, the
20 water-based colored coating material of the colored film 11 and the clear coating
material easily conform to each othel; which improves the adhesion between the
films in the two layers, and the pigment-concentrated layer 123 and the diffusion
layer 122 can be formed appropriately in the clear film 12. Furthermore, as in the
case of the oil-based colored coating material, the output specification and
25 installation space of the pre-heating device 14 can be reduced by approximately 40 to
50 %, which makes it possible to save the space and energy of the continuous coating
apparatus.
[O 1021
[6. Characteristics of pre-coated steel sheet]
30 Next, description is given on characteristics of a pre-coated steel sheet
manufactured by the abovc-described method for manufacturing a pre-coated steel
sheet according to the present embodiment.
[0103]
The pre-coated steel sheet is coated by the pre-heating method (wet-on-wet
method using pre-coating) according to the present embodiment, and is manufactured
5 by coating one surface or both swfaces of the steel sheet 10 serving as a base
material with at least two films. The pre-coated steel sheet according to the present
embodiment is, as described above, obtained by coating one surface of the steel sheet
10 with the colored film 11 in the lower layer and the clear film 12 in the upper layer.
[0 1041
10 Furthermore, as illustrated in FIG. 2, the pre-coated steel sheet according to
the present embodiment includes the pigment-concentrated layer 123 and the
diffusion layer 122 between the colored film layer 1 11 and the clear layer 121. As
described with reference to FIG. 2, the clear film 12 applied onto the colored film 11
is divided into three layers of the clear layer 121, the diffusion layer 122, and the
16 pigment-concentrated layer 123, in accordance with the color pigment concentration
distribution. In the clear film 12, the outermost layer portion not containing the
color pigment is the clear layer 121, the base-material-side portion containing the
color pigment at a high concentration is the pigment-concentrated layer 123, and the
portion between the clear layer 121 and the pigment-concentrated layer 123 is the
20 diffusion layer 122. In addition, the colored film 11 whose color pigment
concentration has decreased owing to the application of the clear film 12 becomes
the colored film layer 11 1.
[0105]
In this manner, in the pre-coated steel sheet according to the present
25 embodiment, the films in the upper and lower two layers (the colored film 11 and the
clear film 12) formed by the two coating steps are divided into four layers (the
colored film layer 111, the pigment-concentrated layer 123, the diffusion layer 122,
and the clear layer 121 in that order fiom the lower layer side), in accordance with
the color pigment concentration distribution.
30 [0106]
The colored film layer 111 is a layer containing the color pigment at a .
substantially constant concentration in the thickness direction. A thickness d4 of
the colored film layer 11 1 is, for example, 8 to 13 pm. The pigment-concentrated
layer 123 is a layer containing the color pigment that has moved from the colored
film 11 at a high concentration, and a thickness d2 of the pigment-concentrated layer
5 123 is, for example, 2.2 to 8 pm. The diffusion layer 122 is a layer containing the
color pigment that has diffused from the colored film 11 into the clear film 12, and a
thickness d3 of the diffusion layer 122 is, for example, 3 to 12 pm. The clear layer
121 is a transparent layer not containing the color pigment, and a thickness dl of the
clear layer 121 is, for example, 5 to 12.3 pm.
lo [0107]
Here, detailed description is given on the color pigment concentration
distribution in the film layers of the pre-coated steel sheet according to the present
embodiment, with reference to FIGS. 4 to 6. FIG. 4 is a graph showing an example
of the color pigment concentration distribution in film layers of a pre-coated steel
15 sheet manufactured by each of conventional methods, a 2C2B method and a wet-onwet
method. FIGS. 5 and 6 are graphs showing examples of the color pigment
concentration distribution in the film layers of the pre-coated steel sheet according to
the present embodiment. Note that the graphs of FIGS. 5 and 6 show the color
pigment concentration ratio of each layer when the average value of the color
20 pigment concentration in the colored film layer 11 1 is defined as 1 .O.
[0108]
First, dcscription is given-on the color pigment concentration distribution of
the pre-coated steel sheet according to each of the conventional coating methods, and
problems thereof, with reference to FIG. 4.
25 [0109]
In a conventional 2C2B method, since the clear film in the upper layer is
applied after the colored film in the lower layer is baked, the color pigment does not
move between the two films. Therefore, as illustrated in FIG. 4, the color pigment
concentration of the colored film in the lower layer (thickness: Dl) is constant in the
30 thickness direction, and the color pigment concentration of the clear film in the upper
layer (thickness: D2) is zero. In the case of this 2C2B method, the clear film not
containing the color pigment can have a large thickness D2, but unlike in the present
embodiment, the pigment-concentrated layer 123 having a high color pigment
concentration cannot be formed. Consequently, the colored film cannot diffusely
reflect light efficiently, which leaves room for improvement in the gloss of the pre-
5 coated steel sheet. In addition, in the 2C2B method, the adhesion between the
colored film and the clear film is very low.
[Ol lo]
In a conventional wet-on-wet method, since the clear film in a wet state in
the upper layer is applied onto the colored film in a wet state in the lower layer, the
10 two films mix with each other to form a mixed layer. Therefore, as illustrated in
FIG. 4, the color pigment is contained across the entire thickness direction from the
colored film in the lower layer (thickness: Dl) to the clear film in the upper layer
(thickness: D2), and the color pigment concentration gradually decreases toward the
outer layer side. In this manner, in the wet-on-wet method, a clear layer not
15 containing the color pigment is not formed. Consequently, incident light cannot
appropriately pass through the outer layer portion of the film, and further, the colored
film cannot specularly and diffusely reflect the incident light appropriately, which
result in a significant decrease in the gloss of the pre-coated steel sheet.
[Olll]
20 In contrast, description is given on the color pigment concentration
distribution of the pre-coated steel sheet according to the present embodiment, with
reference to FIGS. 5 and 6.
[0112]
As illustrated in FIG. 5, in the colored film layer 11 1 (thickness: d4) of the
25 pre-coated steel sheet according to the present embodiment, the color pigment
concentration is substantially constant in the central portion in the thickness direction
of the colored film layer 11 1, but decreases from the central portion toward the outer
layer side. On the basis of an average value CAvE of the color pigment
concentration in this colored film layer 111, the distribution of a color pigment
30 concentration C of each of the other layers is evaluated relatively. A color pigment
concentration ratio c used below is the ratio between C and CAVE(C = CJCAVE).
[0113]
The pigment-concentrated layer 123 (thickness: d2) has a color piginent
concentration equal to or greater than the average value CAVEo f the color piginent
concentration in the colored film layer 11 1. In this pigmen-conccntrated layer 123,
5 the color pigment concentration continuously increases from the base material side
toward the outer layer side. The color pigment concentration ratio c becomes a
minimum value c2 at the interface between the pigment-concentrated layer 123 and
the colored film layer 11 1, and becomes a maximum value cl at the interface
between the pigment-concentrated layer 123 and the diffusion layer 122. The color
10 pigment concentration ratio c of the pigmen-concentrated layer 123 is, for example,
within a range of 1.0 to 1.2. The boundary portion between the pigmentconcentrated
layer 123 and the colored film layer 111 has a color pigment
concentration lower than that around the boundary portion. This is because, at the
time of pre-heating, the color pigment that had existed in a portion of the colored
15 film 11 corresponding to the boundary portion has moved to the outer layer side (the
clear film 12 side) by convection and concentration diffusion, and the pigmentconcentrated
layer 123 has been formed.
[0114]
As illustrated in FIG. 5, in the diffusion layer 122 (thickness: d3), the color
20 pigment concentration continuously decreases from the base material side toward the
outer layer side, and the color pigment concentration is zero at the boundaly between
the diffusion layer 122 and the clear layer 121. The color pigment concentration
ratio c of the diffusion layer 122 is, for example, within a rangc of 0 to 1.2. Not
containing the color pigment, the clear layer 121 (thickness: dl) has a color pigment
25 concentration of zero.
[0115]
As described above, the pre-coated steel sheet according to the present
embodiment has a feature in the color pigment concentration distribution of the fourlayer
structure in the film layers. In particular, the clear layer 121 containing
30 substantially no color pigment is formed on the outermost layer side of the clear film
12, and the pigme~lt-concentrated layer 123 having a markedly high color pigment
concentration is formed on the base material side of the clear film 12. Such
combination of the clear layer 121 and the pigment-concentrated layer 123
significantly improves the glossiness of the pre-coated steel sheet for the following
reasons.
5 [0116]
In general, when light falls on a pre-coated steel sheet, light that has passed
through a clear film in the outermost layer is reflected by a colored film in the lower
layer. Here, the amount of reflected light increases with an increase in the color
pigment concentration of the colored film. However, an increase in color pigment
10 concentration of a colored coating material causes problems of a decrease in the
storage stability of the colored coating material, and deterioration of the adhesion of
the colored film at the time of steel sheet working.
[0117]
In contrast, in the present embodiment, in manufacturing the pre-coated
15 steel sheet, the colored film 11 in the lower layer is pre-heated for a short time, as
described above, unlike in a conventional technology. Thus, the clear layer 121
with an appropriate thickness dl not containing the color pigment can be formed on
the outermost layer side of the clear film 12 more stably than in a conventional weton-
wet method. In addition, the pigment-concentrated layer 123 having a markedly
20 high color pigment concentration can be formed on the base material side of the clear
film 12 (in the neighborhood of the boundary with the colored film 11).
Consequently, the pigment-concentrated layer 123 can diffusely reflect light that has
passed through the clear layer 121 and the diffusion layer 122 efficiently to the outer
layer side. Therefore, according to the present embodiment, the gloss of the pre-
25 coated steel sheet as an end-product can be significantly improved.
[0118]
Note that the technical scope of the present invention encompasses the case
of a concentration distribution in which, as illustrated in FIG. 6, the boundary portion
between the pigment-concentrated layer 123 and the colored film layer 11 1 does not
30 have a color pigment concentration lower than that around the boundary portion.
Also in this case, the pigment-concentrated layer 123 has a color pigment
concentration equal to or greater than the average value CAVEo f the color pigment
concentration in the colored film layer 11 1, and the color pigment concentration
continuously increases toward the outer layer side. Consequently, the pigmentconcentrated
layer 123 of FIG. 6 can diffusely reflect incident light as efficiently as
5 the pigment-concentrated layer 123 of FIG. 5 can, which provides a pre-coated stccl
sheet with high glossiness.
[0119]
In addition, in manufacturing the pre-coated steel sheet according to the
present embodiment, the clear film 12 in the upper layer is applied in a state where
10 the colored film 11 in the lower layer is brought into a half-dried state by the abovedescribed
pre-heating; therefore, the two films conform to each other favorably at the
interface between the colored film 11 and the clear film 12. Consequently, after the
colored film 11 and the clear film 12 are baked simultaneously, the adhesion between
the colored film 11 and the clear film 12 is significantly improved. Therefore, the
15 pre-coated steel sheet according to the present embodiment has sufficiently high
adhesion (working adhesion) between films subjected to working (e.g., bending or
press working).
[O 1201
As described above, the pre-coated steel sheet according to the present
20 embodiment has advantages of high adhesion between the films in the upper and
lower layers, and a high gloss of the surface of the steel sheet. Furthermore, in
manufacturing the pre-coated steel sheet, the thickness dl of the clear layer 121 not
containing the color pigment and the thickness d2 of thc pigment-concentrated layer
123 can be controlled by adjusting the heating conditions (e.g., heating time t and
25 heating temperature T) of the pre-heating of the colored film 11. This control
makes it possible to achieve both the adhesion between the upper and lower layers
and the glossiness of the pre-coated steel sheet at high levels. As a result, the precoated
steel sheet manuhctured by the pre-heating method according to the present
embodiment can have a higher gloss than that in the case of a conventional wet-on-
30 wet method. Furthermore, when the heating conditions of the pre-heating and dl
and d2 are controlled favorably, the pre-coated steel sheet according to the present
embodiment can have a higher gloss than that in the case of a successive coating and
baking method (e.g., 2C2B).
[O121]
Here, in view of enhancing the gloss of the pre-coated steel sheet, more
5 detailed description is given on the interrelation between the thicknesses of the clear
layer 121 (thickness: dl), the diffusion layer 122 (thickness: d3), the pigmentconcentrated
layer 123 (thickness: d2), and the colored film layer 111 (thickness: d4)
according to the present embodiment.
[0 1221
10 (1) Appropriate range of dlld2
First, description is given on an appropriate range of a ratio dlld2 between
the thicknesses of the clear layer 121 and the pigment-concentrated layer 123
according to the present embodiment. When dl/d2 is controlled to be equal to or
greater than 1.7 and equal to or less than 4.7 as expressed by the following formula
15 (I), both the adhesion between the upper and lower layers and the gloss of the precoated
steel sheet can be achieved at high levels.
1.7 5 dl/d2 5 4.7 ...( I)
[0 1231
If dlId2 is less than 1.7, the clear layer 121 does not have a sufficient
20 thickness dl, and thus a target gloss (e.g., a gloss that is 1.7 times or more higher
than that in the case of a wet-on-wet method) is not obtained. On the other hand, if
dlld2 is greater than 4.7, the pigment-concentrated layer 123 does not have a
sufficient thickness d2, and thus the adhesion between the films deteriorate, and a
gloss higher than that in the case of a successive coating and baking method (e.g.,
25 2C2B) is difficult to obtain. Hence, to ensure high adhesion between the films and
obtain a gloss sufficiently higher than that in the case of a wet-on-wet method, dlld2
is preferably controlled to be 1.7 to 4.7.
[0 1241
Furthermore, as expressed by the following formula (2), dlld2 is further
30 preferably controlled to be 2.0 or greater. In this case, the 60-degree gloss of the
pre-coated steel sheet according to the present embodiment can be improved to be
100 or highel; which means that a gloss higher than a gloss (60-degree gloss:
approximately 90) in the case of a successive coating and baking method (e.g.,
2C2B) can he obtained.
2.0 5 dlld2 i 4.7 ...( 2)
5 [0125]
(2) Appropriate range ofclIc2
Next, description is given on an appropriate range of a ratio clIc2 between
the maximum value cl and the mininlum value c2 of the color pigment concentration
ratio c in the pigment-concentrated layer 123. As expressed by the following
10 for~nula(3 ), clIc2 is preferahly equal to or greater than 1.04 and equal to or less than
2.0.
1.04 5 clIc2 5 2.0 ...( 3)
[0126]
When clIc2 is 1.04 or greater, diffuse reflection of incident light easily
15 occurs at a high-concentration portion (peak portion) of the color pigment extending
across the pigment-concentrated layer 123 and the diffusion layer 122, which
increases the amount of light incident on an optical receiver of a glossmeter.
Consequently, the 60-degree gloss of the pre-coated steel sheet according to the
present embodiment can be improved to be 100 or higher, which means that a gloss
20 higher than a gloss (60-degree gloss: approximately 90) in the case of a successive
coating and baking method (e.g., 2C2B) can be obtained. If clIc2 is less than 1.04,
a gloss higher than that in the case of a wet-on-wet method can he obtained, but the
high-concentration portion has an insufficient peak value and a gloss higher than that
in a successive coating and baking method (e.g., 2C2B) cannot be obtained in some
25 cases.
[0 1271
If clIc2 is greater than 2.0, the elxichment degree of the color pigment in
the pigment-concentrated layer 123 gets too intense. This may cause emhrittlement
of the pigment-concentrated layer 123 and deterioration of the working adhesion
30 between the films. Hence, to maintain working adhesion, clIc2 is preferably 2.0 or
less.
[0128]
(3) Appropriate range of d2
Next, description is given 011 an appropriate range of the thickness d2 of the
pigment-concentrated layer 123. As expressed by the following formula (4), d2 is
5 preferably equal to or greater than 2.2 pm and equal to or less than 8.0 pm.
2.2 pm 5 d2 5 8.0 pm ...( 4)
[O 1291
When d2 is 2.2 pm or greater, the pigment-concentrated layer 123 can
diffusely reflect incident light appropriately, which provides a pre-coated steel sheet
10 having a higher gloss than a conventional one. If d2 is less than 2.2 pm, diffuse
reflection by the pigment-concentrated layer 123 is insufficient, which causes a
decrease in the gloss of the pre-coated steel sheet.
[0130]
If d2 is greater than 8.0 pm, a gloss improvement effect by the pigment-
15 concentrated layer 123 is saturated, bringing the gloss of the pre-coated steel sheet to
an upper limit value, and the working adhesion between the film layers decreases.
Hence, to ensure the working adhesion between the film layers while obtaining a
high gloss of the pre-coated steel sheet, d2 is preferably 2.2 to 8.0 pm.
[0131]
20 (4) Appropriate range of dl
Next, description is given on an appropriate range of the thickness dl of the
clear layer 121. As expressed by the following formula (5), dl is preferably equal
to or greater than 5.0 pm and equal to or less than 12.3 pm.
5.0 pm 5 dl 5 12.3 pm ...( 5)
25 [0132]
In order for the pre-coated steel sheet to have a high gloss, the clear layer
121 not containing the color pigment needs to exist on the outermost layer side of the
film layer. If the thickness dl of this clear layer 121 is less than 5.0 pm, the clear
layer 121 cannot have a thickness needed to diffusely reflect incident light, which
30 makes the gloss of the pre-coated steel sheet insufficient. On the other hand, if dl
is greater than 12.3 pni, the amount of light that reaches the pigment-concentrated
layer 123 below the clear layer 121 decreases, so that a sufficient gloss cannot be
obtained. Hence, to obtain a high gloss of the pre-coated steel sheet, dl is
preferably 5.0 to 12.3 pnl.
[0133]
5 Described above using the formulas (1) to (5) are appropriate ranges of
parameters, such as dl/d2, clIc2, d2, and dl, according to the present embodiment.
In the method for manufacturing a pre-coated steel sheet according to the present
embodiment, these parameters can be controlled by controlling the heating
conditions (e.g., heating temperature T and heating time t) of the colored film 11 in
10 the pre-heating step.
[0134]
According to the method for manufacturing a pre-coated steel sheet
according to the present embodiment, when the heating temperature T and the
heating time t are set to 60 to 150 OC and 1 to 10 seconds, respectively, in the pre-
15 heating step, a pre-coated steel sheet satisfying the above formulas (1) and (3) to (5)
can be manufactured. Furthermore, when the heating temperature T and the heating
time t are set to 90 to 150 "C and 1.9 to 10 seconds, respectively, a pre-coated steel
sheet satisfying all of the above formulas (1) to (5) can be manufactured.
101351
20 [7. Conclusion]
Detailed description has been given above on the pre-coated metal sheet
according to the first embodiment of the present invention, the method for
manufacturing the pre-coated metal sheet, and the continuous coating apparatus.
According to the present embodiment, the colored film 11 in the lower layer is
25 heated for a short time at low temperature by the pre-heating device 14 to be brought
into a half-dried state, and then the clear coating material in the upper layer is applied
to form the clear film 12 in the upper layer on the colored film 11 in a half-dried state.
[0136]
In this manner, both the adhesion between the films in the upper and lower
30 layers and the gloss of the pre-coated steel sheet can be achieved at high levels.
That is, by appropriately controlling heating conditions at the time of pre-heating, the
clear layer 121 not containing the color pigment (thickness: dl) can be stably formed
in the outermost layer of the clear film 12, and the pigment-concentrated layer 123
having a markedly high color pigment concentration (thickness: d2) can be formed
below the clear layer 121. Furthermore, the ratio dl/d2 between the thicknesses of
5 the clear layer 121 and the pigment-concentrated layer 123 can be controlled to be
within a favorable range (1.7 5 dlld2 5 4.7). Consequently, the pigmentconcentrated
layer 123 can diffusely reflect incident light that has passed through the
clear layer 121 efficiently to the outer layer side, so that the gloss of the pre-coated
steel sheet can be significantly improved. Therefore, the pre-coated steel sheet
10 according to the present embodiment achieves significantly higher glossiness than a
pre-coated steel sheet manufactured by a conventional wet-on-wet method.
[0137]
Furthermore, by further appropriately controlling heating conditions at the
time of pre-heating, the ratio cl/c2 between the maximum value cl and the minimum
15 value c2 of the color pigment concentration ratio c in the pigment-concentrated layer
123 is controlled to be within a favorable range (clIc2 ? 1.04). This further
improves the function of the pigment-concentrated layer 123 diffusely reflecting
incident light. Consequently, the pre-coated steel sheet according to the present
embodiment can have higher glossiness than a pre-coated steel sheet manufactured
20 by a conventional successive coating and baking method (2C2B method).
[0138]
In addition, the above manufacturing method makes the films in the upper
and lower layers easily conform to each other, and increases the roughness of thc
interface between the films in the two layers; thus, the adhesion between the two
25 layers is improved after the two layers are completely dried in final baking.
Consequently, the adhesion between the films in the upper and lower layers can be
significantly improved as compared with a conventional successive coating and
baking method (2C2B method), in which a coating material in the upper layer is
applied and baked after a film in the lower layer is completely dried. This makes
30 peeling unlikely to occur at the interface between the films in the two layers, and
facilitates layer mixing control.
[0139]
In addition, when the clear film 12 in the upper layer is applied by using the
curtain coater 15, the colored film 11 in the lower layer (half-dried state) and the
clear coating material in the upper layer (wet state) do not mix with each other; thus,
5 only the clear coating material can be collected to be reused. This enables recycled
use of the clear coating material, thus reducing disposal volun~ea nd coating cost of
the clear coating material and offering excellent compatibility with the environment.
[0 1401
Furthermore, as compared with a baking device of a conventional
10 successive coating and baking method, the pre-heating device 14 can be reduced in
output and installation space, and there is no need to install a plurality of sets of a
cooling device and a drying device in the coating line. Consequently, as compared
with a conventional successive coating and baking method, facilities of the coating
line can be simplified and their space and energy can be saved. This facilitates
15 multilayer coating on the steel sheet 10 using a simple continuous coating line, in a
plating step of the steel sheet 10.
[0141]
[8. Other embodiments]
Next, other embodiments of the present invention will be described.
20 Described in the first embodiment is an example of two-layer coating, but the present
invention can be applied to a case of multilayer coating with thee or more films.
[0 1421
[8.1. Second embodiment]
FIG. 7 is a schematic diagram illustrating a line configuration of a
25 continuous coating apparatus according to a second embodiment of the present
invention. As illustrated in FIG. 7, the continuous coating apparatus according to
the second embodiment has a line configuration in which coating facilities for
coating wit11 a film in a third layer (a curtain coater 21, a baking device 22, a cooling
device 23, and a drying device 24) are additionally installed to follow the coating line
30 (see FIG. 1) of the continuous coating apparatus according to the first cmbodiment,
[0143]
In the second embodiment, first, the roll coater 13 (the first coating device)
applies a colored coating material onto the steel sheet 10 to form the colored film 11
in a first layer, and the pre-heating device 14 heats the colored film 11 to bring it into
a half-dried state.
5 [0144]
Then, the curtain coater 15 (the second coating device) applies a clear
coating material onto the colored film 11 in a half-dried state to form the clear film
12 in a second layer. Furthermore, the baking device 16 simultaneously bakes the
film 11 in the first layer and the film 12 in the second layer, then the cooling device
10 17 water-cools the steel sheet 10 onto which the films 11 and 12 have been baked,
and the drying device 18 dries the steel sheet 10.
[O 1451
After that, the curtain coater 21 (the third coating device) applies a clear
coating material onto the clear film 12 in a dried state to form a clear film 20 in the
15 third layer. Note that as the third coating device, a roll coater or another coating
device may be used instead of the curtain coater 21. Furthermore, the baking
device 22 bakes the film 20 in the third layer, then the cooling device 23 water-cools
the steel sheet 10 onto which the film 20 has been baked, and the drying device 24
dries the steel sheet 10.
20 [0146]
In the above manner, in the second embodiment, a pre-coated steel sheet
coated with the films 11, 12, and 20 in the three layers is manufactured. According
to the second embodiment, the clear layer 121, the diffusion layer 122, the pigmentconcentrated
layer 123, and the colored film layer 11 1 are formed in the colored film
25 11 in the first layer and the clear film 12 in the second layer. A total thickness dl of
a clear layer (= dl' + D2'), which is the sum of a thickness dl' ofthe clear layer 121
and a thickness D2' of the clear film 20 in the third layel; is preferably controlled to
satisfy 1.7 i dl/d2 5 4.7. In this case, like the two-layer pre-coated steel sheet in
the first embodiment, the three-layer pre-coated steel sheet can also have high
30 glossiness owing to the above four-layer structwe.
[O 1471
Like the first embodiment, the second embodiment provides excellent
adhesion between the colored film 11 in the first layer and the clear film 12 in the
second layer. In addition, in the second coating step using the curtain coater 15, the
clear coating material in the second layer can be collected to be reused.
5 Furlhermore, in the second embodiment, in the third coating step using the curtain
coater 21, the clear coating material in the third layer can be collected to be reused.
[0148]
In the second embodiment, after the application of the clear film 12 in the
second layer, the third layer is applied after the first and second layers are baked by
10 the baking device 16. Without being limited to this example, it is possible not to
install the baking device 16, the cooling device 17, and the drying device 18
illustrated in FIG. 7 and to perform coating with the clear films 12 and 20 in the
second and third layers by a wet-on-wet method by using the two curtain coaters 15
and 2 1, for example.
15 [0149]
L8.2. Third embodiment]
FIG. 8 is a schematic diagram illustrating a line configuration of a
continuous coating apparatus according to a third embodiment of the present
invention. As illustrated in FIG. 8, the continuous coating apparatus according to
20 the third embodiment has a line configuration in which coating facilities for coating
with a film in a lower layer (a curtain coater 34, a baking device 35, a cooling device
36, and a drying device 37) are additionally installed to precede the coating line (see
FIG. 1) of the continuous coating apparatus according to the first embodiment.
[OI 501
25 In the third embodiment, first, the curtain coater 34 (the third coating
device) applies a primer coating material onto the steel sheet 10 to form a primer film
31 in a first layer. Note that as the third coating device, a roll coater or another
coating device may be used instead of the curlain coater 34. Furthermore, the
baking device 35 bakes the primer film 31 onto the stcel sheet 10, then the cooling
30 device 36 water-cools the steel sheet 10, and the drying device 37 dries the steel
sheet 10.
[0151]
Then, the roll coater 13 (the first coating device) applies a colored coating
material onto the primer film 3 1 in a dried state to form a colored film 32 in a second
layer. Then, the pre-heating device 14 heats the colored film 32 to bring it into a
5 half-dried state.
[0152]
Then, the curtain coater 15 (the second coating device) applies a clear
coating material onto the colored film 32 in a half-dried state to form a clear film 33
in a third layer. Furthermore, the baking device 16 simultaneously bakes the films
10 32 and 33 in the second and third layers. After that, the cooling device 17 watercools
the steel sheet 10 onto which the films 32 and 33 have been baked, and the
drying device 18 dries the steel sheet 10.
101531
In the above manner, in the third embodiment, a pre-coated steel sheet
15 coated with the films 3 1, 32, and 33 in the three layers is manufactured. According
to the third embodiment, the four-layer structure (the clear layer 121, the diffusion
layer 122, the pigment-concentrated layer 123, and the colored film layer 111) can be
foimed in the colored film 32 in the second layer and the clear film 33 in the third
layer. This four-layer structure allows a pre-coated steel sheet with high glossiness
20 to be manufactured. Furthermore, as in the first embodiment, the adhesion between
the colored film 32 in the second layer and the clear film 33 in the third layer is
excellent, and the clear coating material in the third layer can be collected to be
reused. The primer coating material in the first layer can also be collected to be
reused.
25 101541
In the third embodiment, the second layer is applied after the primer film 3 1
in the first layer is baked by the baking device 35. Without being limited to this
example, it is possible not to install the baking device 35, the cooling device 36, and
the drying device 37 illustrated in FIG. 8 and to perform coating with the primer film
30 31 in the first layer and the colored film 32 in the second layer by a wet-on-wet
method by using the curtain coater 34 and the roll coater 13, for example.
[0155]
[8.3. Fourth embodiment]
FIG. 9 is a schematic diagram illustrating a line configuration of a
continuous coating apparatus according to a fourth embodiment of the present
5 invention. As illustrated in FIG. 9, the continuous coating apparatus according to
the fourth embodiment has a line configuration in which coating facilities for coating
with a film in a second layer (a curtain coater 44 and a pre-heating device 45) are
additionally installed in the middle of the coating line (see FIG. 1) of the continuous
coating apparatus according to the first embodiment.
10 [0156]
In the fourth embodiment, first, the roll coater 13 (the third coating device)
applies a primer coating material onto the steel sheet 10 to form a primer film 41 in a
first layer, and the pre-heating device 14 heats the primer film 41 to bring it into a
half-dried state.
15 [0157]
Then, the curtain coater 44 (the first coating device) applies a colored
coating material onto the primer film 41 in a half-dried state to form a colored film
42 in a second layer. Furthermore, the pre-heating device 45 heats the colored film
42 in the second layer to bring it into a half-dried state.
20 [0158]
After that, the curtain coater 15 (the second coating device) applies a clear
coating material onto the colored film 42 in a half-dried state to form a clear film 43
in a third layer. Furthermore, the baking device 16 simultaneously bakes the films
41, 42, and 43 in the first to third layers, then the cooling device 17 water-cools the
25 steel sheet 10 onto which the films 41, 42, and 43 have been baked, and the drying
device 18 dries the steel sheet 10.
[0159]
In the above.manne1; in the fourth embodiment, a pre-coated steel sheet
coated with the films 41, 42, and 43 in the three layers is manufactured. According
30 to the fourth embodiment, the four-layer structure (the clear layer 121, the diffusion
laycr 122, the pigment-concentratcd layer 123, and the colored film layer 11 1) can be
formed in the colored film 32 in the second layer and the clear film 33 in the third
layer. This four-layer structure allows a pre-coated steel sheet with high glossiness
to be manufactured.
[0160]
5 Furthermore, excellent adhesion between the primer film 41 in the first laycr
and the colored film 42 in the second layer is achieved as well as excellent adhesion
between the colored film 42 in the second layer and the clear film 43 in the third
layer. In addition to the clear coating material in the third layer, the colored coating
material in the second layer can be collected to be reused. Moreover, since only
10 one baking device 16, which performs final baking, one cooling device 17, and one
drying device 18 need to be installed, facilities of the coating line for three-layer
coating can be significantly simplified and space can he saved, as compared with a
coating line for a conventional three-coat three-hake method.
[0161]
15 [8.4. Additional embodiments]
Described in the above first to fourth embodiments are examples in which
one surface of the steel sheet 10 is coated, but the present invention is not limited to
these examples. A coating method of the present invention can be applied to
coating of either of one surface and both surfaces of the steel sheet 10.
20 [0162]
For example, in the continuous coating apparatus according to the first
embodiment (see FIG. I), in addition to the first coating device (the roll coater 13)
and the second coating device (the curtain coater 15) for coating a surface (one
surfacc) of the steel sheet 10, there may be installed a third coating device for coating
25 a surface on the other side (rear surface) of the steel sheet 10. Concurrently with
the first coating step of applying a first film (the colored film 11) by using the first
coating device, the heating step of bringing the colored film 11 into a half-dried state
by using the pre-heating device 14, and the second coating step of applying a second
film (the clear film 12) by using the sccond coating device, which are performed on
30 the one surface of the steel sheet 10, a third coating step of forming a third film by
using a third coating device may be performed on the surface on the other side of the
steel sheet 10. After that, a baking step of si~nultancouslyb aking the iirst to third
films on the both surfaces of the steel sheet 10 may be performed. Note that also in
the second to fourth embodiments (see FIGS. 7 to 9), the surface on the other side
(rear surface) of the steel sheet 10 may be coated by using an additional coating
5 device concurrently with the coating of the one surface of the steel sheet 10
described above.
[Examples]
[0163]
10 Next, Examples of the present invention will be described. Note that
Examples described below are only condition examples employed to assess the
feasibility and effect of the present invention, and the present invention is not limited
to the conditions of Examples described below.
101641
15 <1. Overview of tesV
Chemical conversion treatment liquids, a colored coating material, and a
clear coating material were prepared and two-layer coating was performed on steel
sheets, whereby samples of pre-coated steel sheets were fabricated. Here, samples
obtained by coating a steel sheet with a colored film and a clear film by the pre-
20 heating method according to an embodiment of the present invention are Examples
of the present invention. Samples obtained by coating a steel sheet with a colored
film and a clear film by conventional methods, a 2C2B method and a wet-on-wet
method, are Comparative Examples. Samples obtained by the pre-heating method
hut subjected to pre-heating under heating conditions (heating temperature T and
25 heating time t) falling outside an appropriate range are also Comparative Examples.
[0165]
With regard to the samples of Examples and Comparative Examples,
elementary analysis in the film thickness direction was performed, and thicknesses
dl, d3, d2, and d4 of a clear layer, a diffusion layer, a pigment-concentrated layer,
30 and a colored film layer and a maximum value cl and a minimum value c2 of a color
pigmcnt concentration ratio c of the pigment-concentrated layer were measured.
[0 1 661
Fui-thel-more, the 60-degee gloss of each sample was measured by using a
glossmeter, and glossiness was evaluated. In addition, the adhcsion between the
films in the upper and lower layers of each sample was evaluated by a 180-degree
5 adhesion bending (OT bending) lest.
[0 1671
Table 1 shows the test conditions and evaluation results ofthis test.
[Ol68]
[Table 11

[0169]
<2. Preparation of samples>
<2.1. Preparation of coating materials to be used>
(1) Chemical conversion treatment liquid 1
5 Chemical conversion treatment liquids used for the samples were prepared
as follows.
An aqueous solution containing 5glL of "3-
Glycidoxypropyltrimethoxysilane" available from Shin-Etsu Chemical Co., Ltd., as a
silane coupling agent, l.Og/L of "Snowtex-N" available from Nissan Chemical
10 Industries, Ltd., as water-dispersed silica, 0.5gIL (zirconium ion basis) of zirconyl
ammonium carbonate, as a zirconium compound, and 25glL of polyacrylic acid, as
an aqueous acrylic resin, was prepared as Chemical conversion treatment liquid 1.
[0 1701
(2) Chemical conversion treatment liquid 2
15 After blending 80 parts by mass of "HUX-320" available from ADEKA
CORPORATION, as a urethane resin, 15 parts by mass of "Snowtex-N available
from Nissan Chemical Industries, Ltd., as silica sol, and 5 parts by mass of
CHEMIPEARL (W500) available from Mitsui Chemicals, Inc., as aqueous wax, ionexchanged
water was added and the solid content of the blend was adjusted to be
20 20 %; thus, Chemical conversion treatment liquid 2 for a rear surface was prepared.
[0171]
(3) Clear coating material (upper-layer coating material)
First, "VYLON (registered trademark) 270" (hereinafter called PES), which
is an amorphous polyester resin available from Toyoboseki Co., Ltd., was dissolved
25 in an organic solvent (cyclohexanone and Solvesso 150 (product name) were mixed
at a mass ratio of 1:1 to be used). Next, a melamine resin "CYMEL (registered
trademark) 303" available from Mitsui Cytec Ltd., as a curing agent, was added to
the organic solvent in which the polyester resin was dissolved. On this occasion,
the melamine resin was added in a manner that the resin solid contents satisfy the
30 following mass ratio: the polyester resin solid content: the melamine resin solid
content = 100: 35. Furthcrmorc, 0.5 mass% of an acid catalyst "Catalyst 600"
available fiom Mitsui Cytec Ltd. was added to the mixed solution of the polyester
resin the melamine resin. In this manner, a polyesterlmelamine-based coating
material was prepared as a clear coating material not containing a color pigment.
[0 1721
5 (4) Colored coating material (lower-layer coating material)
Polytetrafluoroethylene (hereinafter called PTFE), which is a commercially
available lubricant, was added, to the clear coating material obtained in (3) above so
as to account for 2 mass% in a dried film. Next, titanium oxide "Multi-rack 106
white" available from TOYOCOLOR CO., LTD. was added so as to account for 60
10 mass% in a dried film. After that, titanium oxide was dispersed in the clear coating
material by using a disperser; thus, a white coating material was obtained. In this
manner, a polyesterlmelamine-based coating material (containing titanium oxide as a
color pigment) was prepared as a colored coating material.
[0 1731
15 12.2. Preparation of samples of pre-coated steel sheets>
(1) Base material
An electroplated steel sheet was used as a base material (metal sheet) to be
coated.
[0 1741
20 (2) Coating and dryinglcuring
Chemical conversion treatment liquids 1 and 2 were applied respectively
onto a front surface and a rear surface of the base material to form chemical
conversion treatment layers. Then, the colored coating material in the lower layer
was applied onto the front surface of the base material by bar coating under
25 conditions such that a dried film thickness Dl would be 15 pm, and the colored film
was pre-heated at a predetermined heating temperature T (PMT) for a heating time t.
Furthermore, the steel sheet after the pre-heating of the colored film was placed on a
hot plate held at the same temperature as the heating temperature T of the lower layer,
and the clear coating material in thc upper layer was applied onto the colored film by
30 blade coating under conditions such that a dried film thickness D2 would be 15 pm.
After that, the colored coating material and the clear coating material applied onto
the steel sheet were baked at PMT 230 "C (drying and curing). In this manner,
samples were prepared.
[0175]
(3) Heating conditions for lower layer film
5 As shown in Table 1, for Examples 1 to 7 of the pre-heating method, the
heating temperature T (PMT) at the time of pre-heating the colored film in the lower
layer was sel to 60 OC (Example I), 90 "C (Example 2), 120 "C (Example 3), 150 "C
(Example 4), 120 "C (Example 5 to 7), and 150 "C (Example 8). For Comparative
Examples 3 to 8 of the pre-heating method, the heating temperature T (PMT) at the
10 time of pre-heating the colored film in the lower layer was set to 40 O.C (Comparative
Example 3), 50 "C (Comparative Example 4), 160 "C (Comparative Example 5),
150 "C (Comparative Examples 6 and 7), and 60 "C (Comparative Example 8).
[0 1761
Samples of a 2C2B method (Comparative Example 1) and a wet-on-wet
15 method (Comparative Example 2) were also fabricated. In the 2C2B method
(Comparative Example I), the heating temperature of the colored film in the lower
layer was set to 230 "C, and the colored film was completely dried and cured. In
the wet-on-wet method (Comparative Example 2), after the colored film was applied,
the clear coating material was applied onto the colored film in a wet state without
20 heating the colored film.
[0177]
<3. Test method>
<3.1. Titanium concentration ratio measurement test>
(1) Measurement method
25 Elementary analysis in the film thickness direction was performed, while
etching the films and a galvanized layer, from the outernlost layer of each sample
coated with the colored film and the clear film, by argon sputtering of glow discharge
emission spectrometry (GDS). The measured elements were C, N, 0, Si, Ti, Zn,
and Fe. As a glow discharge enlission spectrometer, "GD-PROFILER2" available
30 ftom HORIBA, Ltd. was used.
[0178]
(2) Ti concentration ratio measurement
The thicknesses dl, d3, d2, and d4 of the respective layers (clear layer,
difhsion layer, pigment-concentrated layer, and colored film layer) of the four-layer
structure were determined, on the basis of the sample of Comparative Example 1
5 (2C2B) prepared with a thickness configuration similar to those of the samples of
Examples (pre-heating method). On this occasion, the distribution of Ti
concentration ratio (see the following formula) when the Ti molar concentration of
the colored film layer is defined as 1 was measured for each sample.
Ti concentration ratio = (Ti molar concentration)/(maximum Ti molar concentration
10 of the colored film layer)
[0 1791
(3) Thickness measurement
Since titanium oxide is a white color pigment, measurement of the Ti
concentration ratio in the thickness direction allows measurement of the color
15 pigment concentration distribution and the thickness of each layer. Hence, the
thickness of a layer not containing the color pigment (Ti) from the outermost surface
of the film was determined, as the thickness dl of the clear layer. In addition, the
thickness of a layer from a local maximum value (when a plurality of local maximum
values exist, the local maximum value of the concentration distribution that is closest
20 to the outermost layer) of the Ti concentration distribution in the clear film to a local
minimum value on the base material side was determined, as the thickness d2 of the
pigment-concentrated layer. The thickness of a layer between the clear layer and
the pigment-concentrated layer was determined, as the thickness d3 of the diffusion
layer. The thickness of a layer between the pigment-concentrated layer and the base
25 material was determined, as the thickness d4 of the colored film layer.
[Ol 801
<3.2. Gloss measurement test>
As an indicator of the glossiness of a sample surface, 60-dcgree gloss
according to "JIS Z 8741" was measured. As a glossnleter of 60-degree gloss, a
30 glossmeter "UGV-6P" available f?om Suga Test Instruments Co., Ltd. was used. In
the measu~ement, an incidence angle and an acceptance angle were each adjusted to
be 60 degrees. That is, out of the total reflected light reflected by the sample (total
reflection), only the intensity of a specular reflection component, which is generally
determined as the gloss of a pre-coated steel sheet, was measured. Note that diffuse
reflectivity and total reflectivity are known as ways to measure light reflectivity; ill
5 general, the relation of "total reflectivity = specular reflectivity + diffuse reflectivity"
is satisfied. These values are different from 60-degrec gloss measured in the
present application.
[0181]
<3.3. Working adhesion evaluation test>
10 As illustrated in FIG. 10, each of the samples of pre-coated steel sheets was
worked into a 50 rnm x 100 mm rectangular sheet and was subjected to bending in a
manner that an evaluation surface 10a faces outward. This bending, carried out in a
20 "C atmosphere, was "adhesion bending (OT)", in which a spacer is not placed
between portions of the steel sheet 10. After that, "Cellotape (registered
15 trademark)", available from Nichiban Co., Ltd., with a width of 24 mm was attached
onto the film at a bent portion and then peeled off; thus, the film at the bent portion
was attempted to be peeled off, and the residual state of the film was visually
observed. The residual degree of the film was evaluated in five levels, and when
the score was 5 or more, indicating no occurrence of the peeling of the film, it was
20 determined that the working adhesion between the films in the upper and lower
layers was favorable. ("Good" in Table 1). When the score was 4 or less, it was
k
determined that the working adhesion was unfavorable ("No Good" in Table 1).
[0182]
<3.4. Cross-sectional SEM observation>
25 Gold evaporation was performed on each sample, then the sample was
embedded in a resin, and a cross section of the sample was polished together with the
resin. After that, the state of the cross section (polished surface) of the sample was
observed with a FE-SEM.
[O 1831
30 <4. Evaluation results>
Next, the results of the above tests will be described referring to Table 1 as
appropriate.
[O 1 841
<4.1. Measurement results of titanium concentration ratio>
FIG 11 is a graph showing the Ti concentration ratio distribution in the film
5 thickness direction of Comparative Examples 1 to 3 of Table 1. FIG. 12 is a graph
showing the Ti concentration ratio distribution in the film thickness direction of
Examples 1 to 4 and Comparative Example 1 of Table 1. FIG. 13 is a graph
obtained by partially enlarging FIG. 12.
[0185]
10 As shown in FIG. 11, in Comparative Example 1 (2C2B method), Ti does
not exist on the outer layer side, and a layer with high Ti concentration exists on the
base material side. In other words, in Comparative Example 1, a clear layer with
zero Ti concentration and a colored film layer with high Ti concentration exist, but a
pigment-concentrated layer and a diffusion layer do not exist.
15 [0186]
In Comparative Example 2 (wet-on-wet method), Ti exists in a large amount
on the outer layer side of the film, and Ti reaches the outermost layer of the film.
This is presumably because the clear film and the colored film in a wet state mixed
with each other to form a mixed layer, and thus Ti of the colored film moved to the
20 clear film. As described above, in Comparative Example 2, a clear layer with zero
Ti concentration does not exist and the Ti concentration distribution is ununiform.
[01'87]
In Co~uparative Example 3 (pre-heating method), as compared with
Comparative Example 2, a large amount of Ti is distributed in the central portion in
25 the film thickness direction, but Ti has moved to the neighborhood of the outermost
layer of the film, and a definite clear layer and pigment-concentrated layer do not
exist, presumably for the following reason. That is, in Con~parativeE xample 3, the
heating temperature T at the time of pre-heating the colored film in the lower layer
was 40 "C, which is too low, and the heating time t was 0.4 seconds, which is too
30 short; therefore, the colored film in the lower layer was not brought into an
appropriate half-dried state by the pre-heating. Consequently, when the clear
coating material in the upper layer was applied, the colored film and the clear film
mixed with each othel; and a definite clear layer and pigment-concentrated layer
were not formed.
[0188]
5 In contrast, in Examples 1 to 4 (pre-heating method), as shown in FIGS. 12
and 13, the amount of movement of Ti to the outer layer side is smaller than those of
Comparative Examples 2 and 3, and Ti does not exist, i.e., a clear layer not
containing Ti is formed, in a range of at least 5 pm from the outermost layer. A
peak of Ti concentration exists around film thicknesses of 14 to 17 pm. On the
10 outer layer side of the peak, a diffusion layer in which Ti concentration continuously
decreases from the peak toward the outer layer side is formed. In addition, on the
base material side of the peak, a pigment-concentrated layer in which Ti
concentration continuously increases toward the outer layer side to reach the peak is
formed. On the base material side of the pigment-concentrated layer, a colored film
15 layer having a substantially constant Ti concentration is formed.
[0189]
As described above, in Examples 1 to 4, a definite four-layer structure of the
clear layer, the diffusion layer, the pigment-concentrated layer, and the colored film
layer exists. Particularly in Example 4 (T = 150 "C), as shown in FIG. 13, a peak
20 with a markedly high Ti concentration ratio exists around a film thickness of 16 pm,
and a valley with a markedly low Ti concentration ratio exists around a film
thickness of 21 pm. This proves the existence of a marked pigment-concentrated
layer in Example 4.
[0 1901
25 As shown in Table 1, in Examples 1 to 8, the ratio dlld2 between the
thickness dl of the clear layer and the thickness d2 of the pigment-concentrated layer
is equal to or greater than 1.7 and equal to or less than 4.7, and falls within the
aforementioned appropriate range of dlld2 (1.7 5 dlld2 5 4.7) for obtaining a high
gloss. This is presumably because in Exanlples 1 to 8, the pre-heating of the
30 colored film in the lower layer was performed under appropriate heating conditions
(i.e., heating temperature T = 60 to 150 OC, heating time t = 1.0 to 10 seconds),
which allowed dlld2 to fall within the appropriate range. Furthermore, in
Examples 2 to 8, in which T = 90 to 150 OC, dlld2 falls within a more favorable
appropriate range of dlld2 (2.0 r_< dlld2 < 4.7).
[0191]
5 In contrast, dlld2 of Comparative Examples 4 and 6 to 8 fall outside the
above appropriate range of dlld2. In Comparative Example 4, the short heating
time t of 0.7 seconds and the too low heating temperature T of 50 "C presumably
made the pre-heating of the colored film insufficient. In Comparative Examples 6
and 7, T was 150 "C, which is within the appropriate range, but the too long heating
10 times t of 11 seconds and 20 seconds presumably caused the colored film to be
excessively pre-heated to be dried more than necessary. In Comparative Example 8,
despite T being a low temperature of 60 "C, the markedly too long heating time t of
600 seconds presumably caused the colored film to be excessively pre-heated to be
dried more than necessary. Furthermore, in Comparative Example 5, the too high
15 heating temperature T of 160 "C made the amount of the solvent volatilized from the
colored coating material at the time of pre-heating excessively large, so that the tests
were not able to be performed.
[0192]
The above results prove that, in the method for manufacturing a pre-coated
20 steel sheet according to the embodiment, by heating the colored film in the lower
layer under appropriate heating conditions (T = 60 to 150 OC, t = 1.0 to 10 seconds)
at the time of pre-heating, the definite four-layer structure can be formed in the film
layers of the pre-coated steel sheet after final baking, and dlld2 can be controlled to
fall within an appropriate range.
25 [0193]
14.2. Evaluation results of gloss:
FIG. 14 is a graph showing the relation between dlld2 and the test results of
60-degree gloss of Table 1. FIG. 15 is a graph showing the relation between the
heating temperature T, and dl, d2, and the test results of 60-degree gloss of Table 1.
30 Note that FIG. 15 shows the results when a rate of temperature rise "= (PMT ["C] -
25 ["C])/heating time 1 [s]" at the time of pre-heating the lower layer film was
approximately 35 "CIS.
[O 1 941
As shown in Table 1 and FIG. 14, in Examples 1 to 8, which satisfy 1.7 5
dlld2 < 4.7, the 60-degree gloss is 85 or higher, which mcans that a gloss
5 significantly higher (1.7 times or more higher) than the 60-degree gloss (= 50) in the
case of Comparative Example 2 (wet-on-wet method) is obtained. Furthermore, in
Examples 2 to 8, which satisfy 2.0 5 dlld2 < 4.7, the 60-degree gloss is 103 or higher,
which means that a gloss higher than the 60-degree gloss (= 90) in the case of
Comparative Example 1 (2C2B method) is obtained.
10 [0195]
In addition, the results of Comparative Examples 3 and 4 (pre-heating
method) show that as the heating temperature T of the colored film in the lower layer
decreases from 60 "C, the 60-degree gloss decreases to approach the 60-degree gloss
in the case of Comparative Example 2 (wet-on-wet method). In Examples 2 to 8, in
15 which T 1 90 "C, the 60-degree gloss is substantially constant at 100 or higher. In
Comparative Examples 6 to 8 (pre-hcating method), which do not satisfy appropriate
conditions (1 second 5 t 5 10 seconds) of the heating time t at the time of pre-heating,
a gloss higher than that of Comparative Example 2 (wet-on-wet method) is obtained,
hut the gloss is lower than that of Comparative Example 1 (2C2B method). Note
20 that these Comparative Examples 6 to 8 have a problem of low adhesion between the
films, as will be described later (see Table 1).
[0196]
The above results prove that satisfying 1.7 5 dlld2 5 4.7 results in at least a
gloss significantly higher than that in the case of a conventional wet-on-wet method,
25 and further, satisfying 2.0 5 dlld2 5 4.7 results in a gloss higher than that in the case
of a conventional 2C2B method.
[O 1971
As shown in Table 1 and FIG. 15, in Examples 1 to 8 (pre-heating method),
when "60 "C 5 T 5 150 "C", "d2 > 2.2 pm", and "5.0 pnl < dl < 12.3 pm" are
30 satisfied, the 60-degree gloss is 85 or higher, which means that a gloss significantly
higher than that of Comparative Example 2 (wet-on-wet method) is obtained.
Furthermore, in Examples 2 to 8 (pre-heating method), when "90 "C 5 T 5 150 "C",
"d2 2 2.8 pm", and "8.0 pm i dl 5 12.3 pm" are satisfied, the 60-degree gloss is 100
or highel; which means that a gloss higher than that of Comparative Example 1
(2C2B method) is obtained.
5 [0198]
<4.3. Evaluation results of working adhesion>
Next, description is given on the results of evaluating the working adhesion
betwcen the films in the upper and lower layers by the "adhesion bending (OT)" test
illustrated in FIG. 10. FIG. 16A is an enlarged photograph of the bent portion of the
10 pre-coated steel sheet according to Comparative Example 1 (2C2B). FIG. 16B is an
enlarged photograph of the bent portion of the pre-coated steel sheet according to
Example 1 (heating temperature T = 60 OC).
[O 1991
As shown in Table 1, in Comparative Example 1 (2C2B), the clear film in
15 the upper layer peeled off from the colored film in the lower layer as shown in FIG.
15A. Peeling occurred similarly in Comparative Examples 6 to 8 (pre-heating
method) as well. This is presumably because in Comparative Examples 1 and 6 to
8, the lower layer film was dried and cured at the time of heating the lower layer film,
which made the adhesion low between the upper and lower layer films
20 [0200]
In contrast, in Examples 1 to 8 (pre-heating method), Comparative Example
2 (wet-on-wet method), and Comparative Examples 3 and 4 (pre-heating method),
the clear film in the upper layer did not peel off from the colored film in the lower
layer as shown in FIG. 15B. This is presumably because in Comparative Example 2,
25 the lower layer film was not pre-heated, which made the adhesion high between the
upper and lower films in a wet state, and because in Exanlples 1 to 8 (pre-heating
method) and Comparative Examples 3 and 4 (pre-heating method), the upper layer
film was applied after the lower layer film was brought into an appropriate half-dried
state by pre-heating, which resulted in a significant improvement in the adhesion
30 between the films in the upper and lower layers, as compared with Comparative
Examples 1 and 6 to 8.
[0201]
In addition, according to the evaluation test results of 60-degree gloss and
the test results of working adhesion, which are described above, in Examples 1 to 8
@re-heating method), which satisfy appropriate conditions of dlid2 (1.7 i dlid2 5
5 4.7), a high 60-degree gloss of 85 or higher and high working adhesion are both
achieved. In contrast, in Comparative Example 2 (wet-on-wet method), and in
Comparative Examples 3 and 4 @re-heating method), which do not satisfy 1.7 i
dlid2 4.7, working adhesion is high, but 60-degree gloss is as low as
approximately 50 to 70. In Comparative Examples 6 to 8 @re-heating method), 60-
10 degree gloss is high to some extent, but the adhesion between the films is low.
[0202]
The above results prove that the pre-heating method of the method for
manufacturing a pre-coated steel sheet according to the embodiment makes it
possible to form the above four-layer structure in the film layers of the pre-coated
15 steel sheet after final baking, and satisfying 1.7 5 dlld2 i 4.7 makes it possible to
achieve both high glossiness and high working adhesion between the films.
[0203]
<4.4. Evaluation results of cross-sectional SEM observation>
Next, description is given on the results of observing and evaluating a cross-
20 sectional SEM image of each sample it1 the above cross-sectional SEM observation
test.
[0204]
In the sample of Comparative Example 2 (wet-on-wet method), the colored
film in the lower layer and the clear film in the upper layer lnixed with each other to
25 folm a mixed layer. In Comparative Example 3 (pre-heating method, T = 40°), the
interface between the colored film in the lower layer and the clear film in the upper
layer was greatly curved. Hence, it is presumed that in these Comparative
Examples 2 and 3, the clear layer and the pigment-concentrated layer are not formed.
Consequently, incident light cannot appropriately pass through the outer layer portion
30 of the film having no clear layer, and is not diffusely reflected by a pigmentconcentrated
layer, which is presumably the reason for the low 60-degee gloss of thc
samples of Comparative Examples 2 and 3.
[0205]
In contrast, in Examples 1 to 4 (pre-heating method), the interface between
the colored film in the layer and the clear film in the upper layer was smoother than
5 those of Comparative Examples 2 and 3. Hence, it is presumed that in Examples 1
to 4, the clear layer and the pigment-concentrated layer are appropriately fo~med.
Consequently, incident light appropriately passes through the clear layer and is
diffusely reflected efficiently by the pigment-concentrated layer, which is
presumably the reason for the 60-degree gloss of the samples of Examples 1 to 4
10 being significantly higher than those of Comparative Examples 2 and 3.
[0206]
The preferred embodiment(s) of the present disclosure haslhave been
described above with reference to the accompanying drawings, whilst the present
disclosure is not limited to the above examples. Aperson skilled in the art may find
15 various alterations and modifications within the scope of the appended claims, and it
should be understood that they will naturally come under the technical scope of the
present disclosure.
Reference Signs List
20 [0207]
10 steel sheet, metal sheet
11, 32,42 colored film
12,20, 33,43 clear film
13 roll coater
25 14,45 pre-heating device
15,21, 34,44 curtain coater
16, 22, 35 baking device
17,23,36 cooling device
18,24,37 drying device
30 31,41 primer film
11 1 colored film layer
121 clear layer
122 diffusion layer
123 pigment-concentrated layer
CLAlMS
Claim 1
A pre-coated metal sheet comprising a plurality of film layers on one
surface or both surfaces of a metal sheet, the film layers including
5 a colored film layer that is placed on the metal sheet side and contains a
color pigment,
a pigment-concentrated layer that is formed on the colored film layer, and
whose color pigment concentration is equal to or greater than an average value of
color pigment concentration in the colored film layer and increases toward an outer
10 layer side,
a diffusion layer that is formed on the pigment-concentrated layer, and
whose color pigment concentration decreases toward the outer layer side, and
a clear layer that is formed on the diffusion layer and does not contain the
color pigment,
15 wherein a ratio dlld2 between a thickness dl of the clear layer and a
thickness d2 of the pigment-concentrated layer satisfies 1.7 5 dlld2 i 4.7.
Claim 2
The pre-coated metal sheet according to claim 1, wherein a ratio clIc2
20 between a maximum value cl and a minimum value c2 of a color pigment
concentration ratio c in the pigment-concentrated layer based on the average value of
the color pigment concentration in the colored film layer satisfies 1.04 i clIc2 5 2.0.
Claim 3
25 The pre-coated metal sheet according to claim 1 or 2, wherein the ratio
dlld2 satisfies 2.0 5 dlld2 i 4.7.
Claim 4
The pre-coated metal sheet according to claim 1 or 2, wherein the thickness
30 d2 of the pigment-concentrated layer is equal to or greater than 2.2 pm and equal to
or less than 8.0 pm.
Claim 5
The pre-coated metal sheet according to claim 1 or 2, wherein the thickness
dl of the clear layer is equal to or greater than 5.0 pm and equal to or less than 12.3
6 pm.
Claim 6
A method for manufacturing a pre-coated metal sheet, wherein the precoated
metal sheet according to any one of claims 1 to 5 is manufactured by
10 continuously coating a surface of a strip-shaped metal sheet, the method comprising:
a first coating step of, by a first coating device, applying a colored coating
material containing a color pigment onto the surface of the metal sheet or onto
another film applied onto the surface of the metal sheet, to form a colored film;
a pre-heating step of, by a heating device, heating the colored film at a
15 heating temperature of 60 to 150 O C for a heating time of 1 to 10 seconds to bring the
colored film into a half-dried state;
a second coating step of, by a second coating device, applying a clear
coating material not containing the color pigment onto the colored film in a halfdried
state to form a clear film; and
20 a baking step of, by a baking device, simultaneously baking the colored film
and the clear film.
Claim 7
A continuous coating apparatus, wherein the pre-coated metal sheet
25 according to any one of claims 1 to 5 is manufactured by continuously coating a
surface of a strip-shaped metal sheet, the continuous coating apparatus comprising:
a first coating device configured to apply a colored coating material
containing a color pigment onto the surface of the metal sheet or onto another film
applied onto the surface of the metal sheet, to form a colored film;
30 a heating device configured to heat the colored film at a heating temperature
of 60 to 150 "C for a heating time of 1 to 10 seconds to bring the colored film into a
half-dried statc;
a second coating device configured to apply a clear coating matcrial irot
coniai~urrgt he color pignlent onto the coloied iilnl in a hall-dtied state to for111 a
P
clear film; and
6 a baliiilg dcvice configured to simultaneously halie the colored fill11 and the
clear film.