[Technical Field]
5 [0001]
The present invention relates to a pre-painted metal sheet, a burn-prevention cover,
and a manufacturing method of the pre-painted metal sheet.
[Background Art]
[0002]
10 Conventionally, foam has been formed on a metal sheet surface to reduce weight
and cost, and add functionality and design. In particular, foam of a thermoplastic resin
generally has excellent flexibility, impact absorbency, a heat-insulating property, and other
properties. Therefore, the foam of the thermoplastic resin is widely used, for example, as
vehicle interior materials such as ceilings, doors, and instrument panels, and as
15 heat-insulating materials. However, it is difficult to make a foamed metal sheet by
combining a metal sheet formed into a complex shape by press molding and foam. The
reason for the difficulty is that even if a metal sheet formed into a complex shape is joined
to be integrated with foam having increased rigidity by foaming, the foam cannot be neatly
aligned with the molded surface of the metal sheet and peeling occurs from a bonding
20 interface, resulting in loss of integrity.
[0003]
As a technology for solving such difficulties, for example, the following Patent
Document 1 discloses a technology for using a paint component in which a foaming agent
forms voids during baking and curing of a paint in a paint film of a pre-painted metal sheet.
25 [0004]
Further, the following Patent Document 2 discloses a heat foaming pre-painted
2
metal sheet and a manufacturing method thereof, in which a paint film on a surface of a
pre-painted metal sheet is foamed and a primer layer is further provided.
[Prior Art Document]
[Patent Document]
5 [0005]
Patent Document 1: Japanese Laid-open Patent Publication No. 2005-206736
Patent Document 2: Japanese Laid-open Patent Publication No. 2018-126900
[Disclosure of the Invention]
[Problems to Be Solved by the Invention]
10 [0006]
However, the pre-painted metal sheet disclosed in the above Patent Document 1
tends to have continuous voids formed by foaming in the paint film, and sufficient paint
film adhesiveness cannot be obtained. In particular, when such technology is applied to a
pre-painted steel sheet that is processed after film formation, the paint film tends to peel off
15 at the processed portion.
[0007]
The pre-painted metal sheet disclosed in the above Patent Document 2 uses
thermally expandable microcapsules as foaming particles dispersed in the paint, thereby
suppressing the presence of continuous voids in the paint film and improving the paint film
20 adhesiveness, which had been a problem. However, pressure that the paint film is
subjected to during storage, transportation, and press working destroys the voids in the
paint film, resulting in insufficient effectiveness. In particular, the paint film is subjected
to high pressure when the pre-painted metal sheet is wound into a coil, which easily
destroys the voids. Thus, the paint film with destroyed voids did not provide sufficient
25 performance.
[0008]
3
The present invention has been made in view of the above problems, and an object
of the present invention is to provide a pre-painted metal sheet and a manufacturing
method of the pre-painted metal sheet capable of retaining voids in the paint film even if
the paint film is subjected to pressure during storage, transportation, and press working,
5 and a burn-prevention cover using such a pre-painted metal sheet.
[Means for Solving the Problems]
[0009]
The inventors have diligently studied to solve the above problems and arrived at
the idea of dispersing fine particles with appropriate size in a paint film with voids, and
10 have completed the present invention.
The gist of the invention completed based on such knowledge is as follows.
[0010]
[1] A pre-painted metal sheet including: a metal sheet; and a void-containing paint
film, which is a paint film located on at least one surface of the metal sheet, with dispersed
15 fine particles and voids, wherein when a cross-section of the void-containing paint film cut
in a thickness direction of the void-containing paint film is observed, the voids are present
in 40 to 95 area% of a total area of the cross-section of the void-containing paint film,
when an average particle diameter of the fine particles is t [μm] and an average film
thickness of the void-containing paint film is T [μm], a ratio t/T is in a range of 0.7 to 3.0,
20 and an elastic modulus of the fine particles, when compressed by 10% from the thickness
direction, is 30 MPa or more.
[2] The pre-painted metal sheet according to [1], wherein the average film
thickness T of the void-containing paint film is larger than an average diameter dV of the
voids.
25 [3] The pre-painted metal sheet according to [1] or [2], wherein when the average
diameter of the voids is dV [μm], the average film thickness T of the void-containing paint
4
film and the average diameter dV of the voids satisfy a relationship expressed by the
following inequality (1).
T ≥ 1.1dV ... (1)
[4] The pre-painted metal sheet according to any one of [1] to [3], wherein when a
5 presence ratio of the voids in the void-containing paint film relative to the total area of the
cross-section is PV [area%], the presence ratio PV [area%] of the voids, the average particle
diameter t of the fine particles, the average film thickness T, and a predetermined
measurement width W satisfy a relationship expressed by the following inequality (2).
(t2/8)π/(W‧T) ≤ PV ≤ 10t2π/(W‧T) ... (2)
10 [5] The pre-painted metal sheet according to any one of [1] to [4], wherein the
average film thickness T of the void-containing paint film is in a range of 50 to 1000 μm.
[6] The pre-painted metal sheet according to any one of [1] to [5], wherein a
second paint film that does not contain voids and has an average film thickness of 0.5 to
20.0 μm is present on an upper layer of the void-containing paint film.
15 [7] The pre-painted metal sheet according to any one of [1] to [6], wherein the fine
particles are at least either one of polyacrylonitrile or vinylbenzene polymer.
[8] The pre-painted metal sheet according to any one of [1] to [7], wherein a
content of the fine particles is in a range of 1 to 40 area% of the total area of the
cross-section of the void-containing paint film when cut in the thickness direction of the
20 void-containing paint film.
[9] The pre-painted metal sheet according to any one of [1] to [8], wherein the
metal sheet is any of a galvanized steel sheet, a zinc-aluminum alloy-plated steel sheet, a
zinc-aluminum-magnesium alloy-plated steel sheet, an aluminum plated steel sheet, a
zinc-nickel alloy-plated steel sheet, a zinc-iron alloy-plated steel sheet, a copper sheet, a
25 magnesium sheet, an aluminum sheet, or a stainless sheet
[10] The pre-painted metal sheet according to any one of [1] to [9], wherein an
5
emissivity of a surface of the metal sheet opposite the void-containing paint film is 0.30 or
less.
[11] A burn-prevention cover, which is a cover formed by the pre-painted metal
sheet according to any one of [1] to [10], wherein a heat source is used to be located on an
5 opposite side of the void-containing paint film.
[12] A manufacturing method of a pre-painted metal sheet having a
void-containing paint film, which is a paint film with dispersed fine particles and voids, on
at least one surface of a metal sheet, including: forming the void-containing paint film by
coating a first paint, which contains the fine particles, a resin, a curing agent, hollow
10 microcapsules, and a solvent, on at least one surface of the metal sheet and heating the
metal sheet coated with the first paint to be cured, wherein the hollow microcapsules
contain an organic solvent, a content of the hollow microcapsules in the first paint is in a
range of 5 to 50 mass% of a solid content mass of the first paint, and when an average
particle diameter of the fine particles is t [μm] and an average film thickness of the
15 void-containing paint film after dried and cured is T [μm], the first paint is coated so that a
ratio t/T is in a range of 0.7 to 3.0.
[13] The manufacturing method of the pre-painted metal sheet according to [12],
wherein an average paint film thickness of the first paint is larger than an average diameter
of the hollow microcapsules.
20 [14] The manufacturing method of the pre-painted metal sheet according to [12]
or [13], wherein the average paint film thickness of the first paint is 1.1 times or more the
average diameter of the hollow microcapsules.
[15] The manufacturing method of the pre-painted metal sheet according to any
one of [12] to [14], wherein the first paint is cured at a temperature in a range of 150 to
25 250°C and the hollow microcapsules containing the organic solvent are foamed at a
temperature in a range of 130 to 190°C.
6
[16] The manufacturing method of the pre-painted metal sheet according to any
one of [12] to [15], wherein the metal sheet coated with the first paint is heated at a heating
rate of 70 to 750°C/min to reach a peak metal temperature of 200 to 250°C, the peak metal
temperature is held for 0.5 to 10 s, and then the metal sheet is cooled to 60°C or less at a
5 cooling rate of 3 to 230°C/min.
[17] The manufacturing method of the pre-painted metal sheet according to any
one of [12] to [16], wherein the fine particles are at least either one of polyacrylonitrile or
vinylbenzene polymer.
[18] The manufacturing method of the pre-painted metal sheet according to any
10 one of [12] to [17], wherein a multilayer curtain film is formed by the first paint and a
second paint that does not contain the hollow microcapsules and coated on a surface of the
metal sheet.
[Effect of the Invention]
[0011]
15 As explained above, the present invention makes it possible to provide a
pre-painted metal sheet, even a pre-painted metal sheet equipped with a paint film with
voids, in which the voids in the paint film are difficult to be destroyed by pressure due to
transportation, storage, and processing of the paint film, and having a heat-insulating
property, and a burn-prevention cover using such a pre-painted metal sheet.
20 [Brief Description of the Drawings]
[0012]
[FIG. 1] FIG. 1 is a diagram when a cross-section of an example of a
void-containing paint film held by a pre-painted metal sheet according to an embodiment
of the present invention is observed.
25 [FIG. 2A] FIG. 2A is an explanatory diagram to explain a finger contact
temperature measuring method in examples.
7
[FIG. 2B] FIG. 2B is an explanatory diagram to explain a finger contact
temperature measuring method in examples.
[Embodiments for Carrying out the Invention]
[0013]
5 Hereinafter, preferred embodiments of the present invention are explained in
detail.
[0014]
(Pre-painted metal sheet)
A pre-painted metal sheet according to an embodiment of the present invention is
10 a pre-painted metal sheet including: a metal sheet; and a void-containing paint film, which
is a paint film located on at least one surface of the metal sheet, with dispersed fine
particles P and voids (hereinafter, sometimes abbreviated as a "paint film A"), wherein
when a cross-section of the void-containing paint film cut in a thickness direction of the
void-containing paint film is observed, the voids are present in 40 to 95 area% of a total
15 area of the cross-section of the void-containing paint film, when an average particle
diameter of the fine particles is t [μm] and an average film thickness of the void-containing
paint film is T [μm], a ratio t/T is in a range of 0.7 to 3.0, and an elastic modulus of the fine
particles P, when compressed by 10% from the thickness direction, is 30 MPa or more.
[0015]
20
Examples of the metal sheets used as base sheets for coating in this embodiment
include various steel sheets, nonferrous metal sheets, and the like including alloys, to
which various known plating treatments, and the like, are applied as necessary. Such
metal sheets include, for example, cold-rolled steel sheets, galvanized steel sheets,
25 zinc-aluminum alloy-plated steel sheets, zinc-aluminum-magnesium alloy-plated steel
sheets, aluminum-plated steel sheets, zinc-nickel alloy-plated steel sheets, zinc-iron
8
alloy-plated steel sheets, zinc-vanadium-plated steel sheets, zinc-zirconium-plated steel
sheets, aluminum sheets, aluminum alloy sheets, copper sheets, copper alloy sheets,
magnesium sheets, magnesium alloy sheets, stainless sheets, and so on.
[0016]
5 Here, in the metal sheet of this embodiment, an emissivity of a surface of the
metal sheet opposite the void-containing paint film (paint film A), which is described in
detail below, is preferably 0.30 or less. By setting the emissivity to 0.30 or less, a
temperature rise of the paint film A can be more reliably suppressed when heat is applied to
the surface of the metal sheet opposite the paint film A. As a result, the pre-painted metal
10 sheet of this embodiment can be used more suitably as a material for a burn-prevention
cover. In the metal sheet, the emissivity of the surface opposite the paint film A is more
preferably 0.25 or less. The lower the emissivity of the surface, the better in terms of
suppressing the temperature rise mentioned above, and a lower limit value is not specified,
but approximately 0.03 is a practical lower limit value.
15 [0017]
A thickness of the metal sheet of this embodiment may be set appropriately
according to mechanical strength (for example, tensile strength, or other strengths)
required for the pre-painted metal sheet of this embodiment.
[0018]
20
The void-containing paint film (paint film A) of this embodiment is a paint film
located on at least one surface of the metal sheet as described above, in which the fine
particles P are dispersed and voids are contained. In addition to the above-mentioned fine
particles P and voids, the paint film A preferably contains a binder resin composed of, for
25 example, various thermoplastic resins, thermosetting resins, and the like. The paint film
A may also contain fine particles other than the fine particles P.
9
[0019]
In the paint film A of this embodiment, the binder resin is more preferably
composed of the thermosetting resin. By using the thermosetting resin, baking and curing
of the paint film and formation of voids can be performed simultaneously. A type of the
5 thermosetting resin is not limited, and various known resins such as a polyester resin,
polyurethane resin, acrylic resin, and epoxy resin can be used.
[0020]
Known curing agents such as melamine resins and isocyanates may be used as
curing agents. These resins may be used alone or in combination. For example,
10 methyl-melamine formaldehyde (Cymel 303, manufactured by Nippon Cytec Industries
Co., Ltd.), imino group melamine (Cymel 327, manufactured by Nippon Cytec Co., Ltd.),
butyl group melamine (Super Beckamine, manufactured by DIC Corporation), and the like
can be used as the melamine resins. The melamine resin can also be used together with
an acid catalyst (Catalyst 600, manufactured by Nippon Cytec Industries Co., Ltd.), if
15 necessary. For example, block isocyanate (Coronate, manufactured by Tosoh
Corporation) or the like can be used as isocyanates. These curing agents and additives
may be used alone or in combination.
[0021]
When the cross-section of the paint film A of this embodiment cut in a thickness
20 direction of the paint film A is observed, the voids are present in 40 to 95 area% of a total
area of the cross-section of the paint film A. Here, when the cross-section is observed by
using a microscope through the following method, the "void" in this embodiment
corresponds to a portion where an embedded resin exists when resin-embedded polishing is
performed, and to a depressed portion with respect to a polished surface when microtome
25 processing is performed or Cryo-FIB-SEM is used.
[0022]
10
In the following, a percentage of the voids to the total area of the cross-section is
also referred to as a presence ratio PV [area%]. When the presence ratio PV of such voids
is less than 40 area%, it is difficult to provide a heat-insulating property to the paint film A.
By setting the presence ratio PV of the voids to 40 area% or more, it is possible to provide
5 the heat-insulating property to the paint film A. The presence ratio PV of the voids is
preferably 50 area% or more. On the other hand, when the presence ratio PV of the voids
exceeds 95 area%, adhesiveness of the paint film A may decrease and the paint film may
peel off from the metal sheet. The presence ratio PV of the voids is preferably 85 area%
or less.
10 [0023]
Here, the presence ratio PV of the voids can be measured as follows. That is, the
pre-painted metal sheet is polished and a flat cross-section formed by the polishing is
observed under a microscope. The voids in the paint film can be easily distinguished
because of their different focal points. A microscope image is binarized and a void area is
15 determined by image processing. The void area% changes with each polishing cycle and
eventually reaches a maximum value. This maximum value is taken as the void area%.
An average of the area% of the voids at 10 arbitrarily selected locations is used as a
percentage of the voids. Note that when the void area of the first observed cross-section
is the maximum value, it is excluded from the average value determination.
20 [0024]
A polishing method is not limited, and known methods can be employed, such as
the resin-embedded polishing and the microtome processing, for example. For
particularly high precision, Cryo-FIB-SEM (Cryo scanning electronscopy combined with
focused ion beam) can be suitably used as the polishing method. Since a sample
25 temperature is set at about -100°C and the sample is processed by an ion beam, there is
little damage to the paint film due to heat generated by ion beam irradiation, and polishing
11
on a sub-nanometer scale is possible.
[0025]
In this embodiment, such "voids" are contained inside the paint film A. When an
average film thickness of the paint film A described below is T [μm] and an average
diameter of the void 5 s is dV [μm], a relationship T > dV is established. Furthermore, in this
embodiment, the average film thickness T of the paint film A and the average diameter dV
of the voids preferably satisfy a relationship expressed by the following inequality (1).
By satisfying the relationship expressed by the following inequality (1), it is possible to
further improve paint film adhesiveness after processing.
10 [0026]
T ≥ 1.1dV ... (1)
[0027]
The average film thickness T of the paint film A and the average diameter dV of
the voids more preferably satisfy a relationship of T ≥ 1.4dV. An upper limit value of a
15 ratio (the average film thickness T of the paint film A/the average diameter dV of the voids)
is not specified, but in terms of efficiently obtaining desired burn-prevention properties, an
upper limit of the ratio (the average film thickness T of the paint film A/the average
diameter dV of the voids) is substantially about 3.0.
[0028]
20 Here, the average diameter dV of the voids can be measured as follows. That is,
an average area ratio PV' per void is obtained regarding the voids that were binarized when
determining the void presence ratio PV. Here, continuous voids are counted as one void.
Then, the average diameter dV of the voids is calculated using the following formula.
dV = (4‧PV'/π)0.5
25 [0029]
The fine particles P are dispersed inside the paint film A as described above. By
12
providing the fine particles P inside the paint film A, stress concentration in the paint film
A can be dispersed and collapse of the voids can be suppressed even if the paint film A is
subjected to pressure. Such fine particles P are preferably made of polyacrylonitrile or
vinylbenzene polymer, or both. Other possible candidates for the fine particles P include,
5 for example, those made of various nitrides, such as titanium nitride and boron nitride, and
various metals, such as stainless steel. However, because of their high specific gravity,
these nitrides and metals tend to make sediment in the paint used to form the paint film A,
and the nitrides and metals may not be dispersed in the paint film A to be formed. It is
also possible to consider using nylon polymer, acrylic polymer, urethane polymer, or
10 fluoropolymer as the material for the fine particles P. However, these materials are
undesirable because they are deformed by a surface pressure caused by coiling tension of a
coil. For these reasons, it is preferable to use polyacrylonitrile or vinylbenzene polymer
with low specific gravity as the material for the fine particles P.
[0030]
15 The average particle diameter t of the fine particles P is set so that the ratio t/T to
the average film thickness T of the paint film A is 0.7 to 3.0, as detailed below. By setting
the average particle diameter t of the fine particles P so that the above relationship is
satisfied, it is possible to retain the voids even if the paint film A is under pressure. The
average particle diameter t of the fine particles P is more preferably a value such that the
20 ratio t/T is in a range of 0.8 to 2.0. Even if the ratio t/T of the fine particles P to the
average film thickness T of the paint film A is in the above range, the paint film A exists
above the fine particles P, and the fine particles P do not protrude from a surface of the
paint film A.
[0031]
25 Here, the average particle diameter t of the fine particles P can be measured as
follows. That is, the pre-painted metal sheet is polished, and a flat cross-section formed
13
by polishing is observed under a microscope to determine a cross-sectional diameter of the
fine particles P. The cross-sectional diameter changes with each repetition of polishing
and eventually reaches a maximum value. This maximum value is taken as the particle
diameter of the fine particles P. An average of the particle diameters of the fine particles
5 P at 10 arbitrarily selected locations is the average particle diameter t of the fine particles P.
Note that when the first cross-sectional diameter observed is the maximum value, it is
excluded from the average determination because it may be smaller than an actual particle
diameter.
[0032]
10 The polishing method is not limited and known methods can be employed, such as
the resin-embedded polishing and the microtome processing, for example. For
particularly high precision, Cryo-FIB-SEM is the preferred polishing method. Since the
sample temperature is set at about -100°C and the sample is processed by the ion beam,
there is little damage to the paint film due to heat generated by the ion beam irradiation,
15 and polishing on a sub-nanometer scale is possible. An example of a microscope image
of the flat cross-section obtained by the above method is presented in FIG. 1.
[0033]
Furthermore, in this embodiment, the presence ratio PV [area%] of the voids and
the average particle diameter t of the fine particles P preferably satisfy a relationship
20 expressed by the following inequality (2). By satisfying the relationship expressed by the
following inequality (2), it is possible to further keep the heat-insulating properties and
retain the voids in the paint film.
(t2/8)π ≤ PV ≤ 10t2π ... (2)
[0034]
25 The presence ratio PV [area%] of the voids and the average particle diameter t of
the fine particles P preferably satisfy a relationship expressed by the following inequality
14
(2)'.
(t2/4)π ≤ PV ≤ 6t2π ... (2)'
[0035]
A content of the fine particles P in the paint film A is preferably in a range of 1 to
5 40 area% of a total area of the cross-section of the paint film A when the paint film A is cut
in the thickness direction. By setting the content of the fine particles P in the above range,
it is possible to properly disperse the fine particles P in the paint film A. The content of
the fine particles P is more preferably in a range of 2 to 30 area%.
[0036]
10 Here, the content of the fine particles P in the already formed paint film A can be
measured as follows. That is, an area S of an entire paint film A and the number of fine
particles P, NP, are determined by any cross-sectional observation image in the thickness
direction as described above. The content of the fine particles P, Cp, can be obtained by
the following formula.
15 Cp = {NP × π × (t/2)2}/S
[0037]
In the pre-painted metal sheet of this embodiment, when the average film
thickness of the paint film A is T [μm], the ratio t/T of the average particle diameter t of the
fine particles P to the average film thickness T of the paint film A is set in the range of 0.7
20 to 3.0. When the ratio t/T is less than 0.7, the pressure applied to the paint film A cannot
be kept by the fine particles P, and the voids may be destroyed. The ratio t/T is preferably
0.8 or more. On the other hand, when the ratio t/T exceeds 3.0, the fine particles P may
drop out of the paint film A. The ratio t/T is preferably 2.5 or less and more preferably
2.0 or less.
25 [0038]
Here, in this embodiment, the average film thickness T of the paint film A is
15
preferably, for example, in a range of 50 μm or more and 1000 μm or less. By setting the
average film thickness T to 50 μm or more, more sufficient heat-insulating performance
can be obtained. The average film thickness T of the paint film A is more preferably 70
μm or more. On the other hand, by setting the average film thickness T of the paint film
5 A to 1000 μm or less, a decrease in process adhesiveness of the paint film A can be
suppressed more certainly. The average film thickness T of the paint film A is more
preferably 700 μm or less.
[0039]
The average film thickness T of the paint film A can be measured as follows. A
10 vertical cross-section of the pre-painted metal sheet (a cross-section parallel to the
thickness direction of the pre-painted metal sheet) is observed under a microscope. Then,
a maximum thickness in an area where there is no fine particle P (that is, an area where a
surface of the paint film is approximately parallel to a surface of the metal sheet) is
determined. Ten views are arbitrarily observed, and the average (arithmetic mean) of the
15 ten observations is taken as the average film thickness T.
[0040]
In the pre-painted metal sheet of this embodiment, when the fine particles P are
compressed by 10% (more precisely, when the fine particles P are compressed from the
thickness direction of the paint film A by 10%), an elastic modulus is 30 MPa or more.
20 When the elastic modulus of the fine particles P at 10% compression is less than 30 MPa,
the fine particles P may not be able to keep the pressure applied to the paint film A, and the
voids may be destroyed. An upper limit of the elastic modulus of the fine particles P at
10% compression is not limited but is substantially approximately 100 MPa.
[0041]
25 Here, the elastic modulus at 10% compression of the fine particles P can be
measured as follows. The pre-painted metal sheet is embedded in resin and polished.
16
Then, a nanoindenter (TI premier multi scale, manufactured by Bruker Corporation) is
used to apply a force in a compression direction to the fine particles from the vertical
cross-section (a cross-section parallel to the thickness direction of the pre-painted metal
sheet) to investigate a relationship between displacement and load. The elastic modulus
5 can be obtained from the load at which the displacement of the fine particles P becomes
1/10 of the average particle diameter t of the fine particles P. When the fine particles P
are destroyed before 10% compression, a maximum load is determined and used as the
elastic modulus.
[0042]
10 The void-containing paint film (paint film A) of this embodiment has been
described in detail above.
[0043]

In the pre-painted metal sheet of this embodiment, it is preferable to further form a
15 second paint film that does not contain voids (hereinafter sometimes abbreviated as a
"paint film B") on an upper layer of the above-mentioned void-containing paint film (paint
film A). The presence of the second paint film (paint film B) that does not contain voids
improves the process adhesiveness of the pre-painted metal sheet.
[0044]
20 Here, various known thermoplastic and thermosetting resins can be used for a
resin forming the paint film B. However, the same type of resin as the binder resin
forming the paint film A is preferably used and the same resin as the binder resin forming
the paint film A is more preferably used in consideration of adhesiveness with the paint
film A.
25 [0045]
An average film thickness of the paint film B is preferably in a range of 0.5 to
17
20.0 μm. By setting the average film thickness of the paint film B to 0.5 μm or more, it is
possible to uniformly cover the paint film A without creating uncoated areas. The
average film thickness of the paint film B is more preferably 1.0 μm or more. On the
other hand, by reducing the average film thickness of the paint film B to 20.0 μm or less, it
5 is possible to control an increase in cost. In addition, when attempting to increase the
average film thickness, popping, which is a coating defect caused by solvent bumping in a
paint, may occur. It is necessary to reduce a sheet-passage rate and increase a heating rate
to suppress popping, but such measures will result in a decrease in productivity. However,
it is possible to prevent the occurrence of popping without causing the decrease in
10 productivity by setting the average film thickness of the paint film B to 20.0 μm or less.
The average film thickness of the paint film B is more preferably less than 15.0 μm.
[0046]
The average film thickness of the paint film B can be measured in the same way
as the average film thickness of the paint film A.
15 [0047]
In the pre-painted metal sheet of this embodiment, various known additives may
be contained in the paint film A and paint film B to an extent that the above effects are not
impaired.
[0048]
20 For example, various color pigments may be dispersed in the paint films A and B,
if necessary. As such color pigments, known pigments can be used. For example,
carbon black (furnace black, Ketjen black, acetylene black, channel black), red iron oxide,
aluminum, mica, titanium oxide, and the like can be used as color pigments.
[0049]
25 In the pre-painted metal sheet of this embodiment, a chemical treatment layer
and/or a primer layer may be provided between the metal sheet and the paint film A. By
18
providing the chemical treatment layer and/or the primer layer, adhesiveness between the
metal sheet and the paint film A can be improved and corrosion resistance of the
pre-painted metal sheet can be enhanced. Various known products can be used for such
chemical treatment layer and primer layer.
5 [0050]
Hereinabove, the pre-painted metal sheet of this embodiment has been described
in detail.
[0051]
(Manufacturing method of pre-painted metal sheet)
10 Next, a manufacturing method of the pre-painted metal sheet of this embodiment
will be described in detail.
The manufacturing method of the pre-painted metal sheet of this embodiment is a
manufacturing method of a pre-painted metal sheet having a void-coating paint film (paint
film A), which is a paint film with dispersed fine particles and voids, on at least one
15 surface of the metal sheet.
[0052]
More precisely, in the manufacturing method of the pre-painted metal sheet of this
embodiment, a first paint containing fine particles P, a resin, a curing agent, hollow
microcapsules, and a solvent is coated on at least one surface of the metal sheet. The
20 metal sheet coated with the first paint is then heated to cure the first paint to form the
void-containing paint film (paint film A). Here, the hollow microcapsules contain an
organic solvent.
[0053]
Here, the fine particles P used in the first paint have been mentioned earlier. The
25 resin and curing agent used in the first paint are preferably the above-mentioned resin and
curing agent for producing the binder resin of the paint film A.
19
[0054]
Furthermore, the solvent used for the first paint is not limited and various known
solvents such as pure water and organic solvents can be used, as long as the solvent can
properly disperse the fine particles P, resin, curing agent, and hollow microcapsules.
5 [0055]
The hollow microcapsules used in the first paint should consist of a liquid that
gasifies (more precisely, an organic solvent) and a capsule wall that encapsulates the liquid,
and expand upon heating as the liquid gasifies and the capsule wall softens. In such
hollow microcapsules, the organic solvent inside the capsule gasifies and expands during
10 the curing process of the first paint. In parallel with such expansion, the paint film cures
to form voids. The organic solvent gas or atmospheric gas components may remain
inside the voids formed in this manner, or organic solvent or other substances may remain
in a liquid state to an extent that they are not observed in the cross-sectional observation as
described above. Various types of known thermal expansion microcapsules may be used.
15 Examples of such thermal expansion microcapsules include Advancell (registered
trademark) series manufactured by Sekisui Chemical Co., Ltd., Matsumoto Microsphere
(registered trademark) series manufactured by Matsumoto Yushi-Seiyaku Co., Ltd.,
Expancell (registered trademark) series manufactured by Japan Fillite Co., Ltd, and the like,
for example. These may be used alone or in a combination of two or more types. An
20 average particle diameter of the hollow microcapsules is not limited, but in consideration
of coating properties and volume after heating, for example, the particle diameter in a
range of 15 to 30 μm is preferable. An average paint film thickness of the first paint is
preferably larger than an average diameter of the hollow microcapsules to more reliably
enable the relationship between the average film thickness T of the paint film A and the
25 average diameter dV of the voids (T > dV) as described above.
[0056]
20
A content of the hollow microcapsules in the first paint is in a range of 5 to 50
mass%, considering a percentage of the voids in the paint film A to be formed. By setting
the content of the hollow microcapsules in the above range, the percentage of the voids
(presence ratio PV) in the paint film A to be formed can be more reliably set to 45 to 95
5 area%. The content of the hollow microcapsules is preferably in a range of 10 to 40
mass%.
[0057]
A content of the fine particles P in the first paint is preferably in a range of 1 to 40
area% in an area ratio when coated. By setting the content of the fine particles P in the
10 above range, a dispersion state of the fine particles P can be more reliably set to a desired
state. The content of the fine particles P is more preferably in a range of 3 to 30 area%.
[0058]
A method of coating the first paint is not limited, and various known methods
such as, for example, a roll coating method, a curtain coating method, and a spraying
15 method can be used. Using these methods, the first paint should be coated in an adhesion
amount such that the average film thickness after dried and cured is in the above range.
Among these methods, the curtain coating method is particularly preferred because it
allows uniform coating.
[0059]
20 A heating temperature for drying and curing the above first paint is preferably set
according to the solvent used, a boiling point of the organic solvent held inside the hollow
microcapsules, and the like. In this case, the average paint film thickness of the first paint
is preferably 1.1 times or more the average diameter of the hollow microcapsules, and
more preferably 1.4 times or more.
25 [0060]
For example, when drying and curing the first paint, it is preferable to cure the
21
first paint at a temperature in a range of 150 to 250°C and to foam the above hollow
microcapsules at a temperature in a range of 130 to 190°C. By setting the curing
temperature of the first paint and the foaming temperature of the hollow microcapsules in
the above ranges, it is possible to more reliably set the presence ratio PV of the voids
5 formed to be in the previously described range. The curing temperature of the first paint
is more preferably 170°C or more, and even more preferably 180°C or more. The curing
temperature of the first paint is more preferably 240°C or less, and even more preferably
230°C or less. The foaming temperature of the hollow microcapsules is more preferably
135°C or more, and even more preferably 140°C or more. The foaming temperature of
10 the hollow microcapsules is more preferably 180°C or less, and even more preferably
170°C or less.
[0061]
It is preferable that the metal sheet coated with the first paint is heated at a heating
rate of 70 to 750°C/min to reach a peak metal temperature of 200 to 250°C, the peak metal
15 temperature is held for 0.1 to 10 s, and then the metal sheet is cooled to 60°C or less at a
cooling rate of 3 to 460°C/s. By drying and curing the first paint along a heat pattern as
described above, the pre-painted metal sheet with the void-containing paint film (paint film
A) as described above can be manufactured more reliably.
[0062]
20 The heating rate is more preferably 140 to 700°C/min, and even more preferably
210 to 600°C/min. The peak metal temperature is more preferably 210 to 240°C, and
even more preferably 215 to 230°C. The holding time at the peak metal temperature is
more preferably 0.2 to 5.0 s, and even more preferably 0.4 to 3.0 s. The cooling rate is
more preferably 150 to 350°C/s, and even more preferably 200 to 300°C/s.
25 [0063]
In the case of forming the second paint film (paint film B) that does not contain
22
the voids, a second paint that does not contain the hollow microcapsules is prepared, then
the second paint is coated using the same coating method as the first paint and then dried
and cured.
[0064]
5 For example, it is preferable to form a multilayer curtain film formed by the first
paint and second paint and coat the surface of the metal sheet by the curtain coating
method.
[0065]
The chemical treatment layer and/or the primer layer may also be provided to
10 improve the adhesiveness and corrosion resistance of the pre-painted metal sheet. In this
case, a chemical treatment solution to form the chemical treatment layer or a treatment
solution to form the primer layer can be coated by various known methods, such as, for
example, the roll coating method, the curtain coating method, and the spraying method.
[0066]
15 Hereinabove, the manufacturing method of the pre-painted metal sheet of this
embodiment has been described in detail.
[0067]
(Burn-prevention cover)
As described above, the pre-painted metal sheet of this embodiment has the paint
20 film A and thus can achieve a heat-insulating effect. Therefore, a burn-prevention cover
can be obtained by using such a pre-painted metal sheet.
[0068]
In this case, the pre-painted metal sheet is placed so that a heat source is located
on an opposite side of the paint film A. This makes it possible to effectively insulate heat
25 generated from the heat source.
[Examples]
23
[0069]
The pre-painted metal sheet and the manufacturing method of the pre-painted
metal sheet according to the present invention will be concretely described by presenting
examples and comparative examples below. The examples presented below are only one
5 example of the pre-painted metal sheet and the manufacturing method of the pre-painted
metal sheet according to the present invention, and the pre-painted metal sheet and the
manufacturing method of the pre-painted metal sheet of the present invention are not
limited to the following examples.
[0070]
10 <1. Preparation of varnish paint>
«Varnish formulation-1»
"Byron (registered trademark) 270", an amorphous polyester resin manufactured
by Toyobo Co., Ltd., was dissolved in an organic solvent (a mixture of cyclohexanone:
Sorbeso 150 (product name) = 1:1 by mass ratio). Next, "Cymel (registered trademark)
15 303", a methyl-melamine formaldehyde resin manufactured by Allnex Japan Inc., and
"Mycoat (registered trademark) 506", a butyl group melamine resin manufactured by
Allnex Japan Inc., were added as curing agents to the above solution. The
methyl-melamine formaldehyde resin and butyl group melamine resin were mixed 1:1 in a
resin solid mass ratio to adjust a mixed melamine resin. The polyester resin and mixed
20 melamine resin were then adjusted to a solid mass ratio of 100:30. In addition, 0.5
mass% of "Catalyst 600", an acid catalyst manufactured by Allnex Japan Inc., was further
added to the mixed solution of the polyester resin and melamine resin. The mixed
solution was then stirred to obtain varnish formulation-1.
[0071]
25 «Varnish formulation-2»
"UWR (registered trademark) S-2818", an acrylic resin manufactured by Nippon
24
Shokubai Co., Ltd., was dissolved in the organic solvent (the mixture of cyclohexanone:
Solvesso 150 (product name) = 1:1 by mass ratio). Next, "Cymel (registered trademark)
303", the methyl-melamine formaldehyde resin manufactured by Allnex Japan Inc., and
"Mycoat (registered trademark) 506", the butyl group melamine resin manufactured by
5 Allnex Japan Inc., were added as the curing agents to the above solution. The
methyl-melamine formaldehyde resin and butyl group melamine resin were mixed 1:1 in a
resin solid mass ratio to adjust the mixed melamine resin. The acrylic resin and mixed
melamine resin were then adjusted to a solid mass ratio of 100:30. In addition, 0.5
mass% of "Catalyst 600", the acid catalyst manufactured by Allnex Japan Inc., was further
10 added to this mixed solution of the acrylic resin and melamine resin. The mixed solution
was then stirred to obtain varnish formulation-2.
[0072]
«Varnish formulation-3»
"EPICLON (registered trademark) EXA-123", an epoxy resin manufactured by
15 DIC Corporation, was dissolved in the organic solvent (the mixture of cyclohexanone:
Solvesso 150 (product name) = 1:1 by mass ratio). Next, block isocyanate "CORONATE
(registered trademark) 2507" manufactured by Tosoh Corporation was added to the above
solution as the curing agent. The epoxy resin and block isocyanate were then adjusted to
a solid mass ratio of 100:20. The mixed solution was then stirred to obtain varnish
20 formulation-3.
[0073]
<2. Preparation of paint for steel sheet coating>
Hollow microcapsules A: "Advancell (registered trademark) EHM303", B:
"Advancell (registered trademark) EM306", C: "Advancell (registered trademark) EM406",
25 D: Advancell (registered trademark) EHM303, or E: Advancell (registered trademark)
HB-2051" manufactured by Sekisui Chemical Co., Ltd. was added to the above varnish
25
paint. Types of hollow microcapsules added and their mass concentrations to the paint
solid content were listed in Table 1 below.
[0074]
A: Divinylbenzene polymer (Micropearl (registered trademark)) manufactured by
5 Sekisui Chemical Co., Ltd. and/or B: polyacrylonitrile (Torayca (registered trademark)
matting) manufactured by Toray Industries, Inc., which were crushed and classified with a
sieve, were used as the fine particles.
[0075]
C: Acrylic beads (MBX-20, manufactured by Sekisui Chemical Co., Ltd.) and D:
10 urethane beads (Art pearl (registered trademark)-C, manufactured by Negami Chemical
Industrial Co., Ltd.) were dispersed in ratios listed in Table 1, respectively as other fine
particles, to prepare predetermined paints for steel sheet coating.
[0076]
<3. Preparation of test materials>
15 Then, an electrogalvanized steel sheet (manufactured by Nippon Steel Corporation,
a plating weight of 20 g/m2 per side, hereafter abbreviated as "EG") was prepared and a
chemical conversion treatment paint film was formed on both sides of the steel sheet.
The chemical conversion treatment paint film was formed by coating a chromate-free
chemical treatment solution "CT-E300 N" manufactured by Nihon Parkerizing Co., Ltd.,
20 under a condition of a deposition amount to be 300 mg/m2 after dried and drying at a steel
sheet temperature of 60°C. Subsequently, the paint described above was coated and
dried.
[0077]
Various types of metal sheets listed below were also prepared, and test materials
25 were prepared in the same manner as above.
‧ Sn-plated steel sheet (manufactured by Nippon Steel Corporation, a plating
26
weight of 3 g/m2 per side, hereafter abbreviated as "Sn")
‧ Zn-55% Al plated steel sheet (manufactured by Nippon Steel Coated Sheet
Corporation, a plating weight of 90 g/m2 per side)
‧ Zn-11% Al-3% Mg plated steel sheet (manufactured by Nippon Steel
5 Corporation, a plating weight of 60 g/m2 per side)
‧ Al-10% Si plated steel sheet (manufactured by Nippon Steel Corporation, a
plating weight of 40 g/m2 per side)
‧ Zn-10% Ni plated steel sheet (manufactured by Nippon Steel Corporation, a
plating weight of 20 g/m2 per side)
10 ‧ Zn-10% Fe plated steel sheet (manufactured by Nippon Steel Corporation, a
plating weight of 45 g/m2 per side)
‧ Aluminum plate (AL 1050)
‧ Stainless plate (SUS 304)
‧ Copper plate (Cu C1100P)
15 ‧ Magnesium plate (Mg AZ31B)
[0078]
Several types of test materials #1 to #66 were thereby prepared with various
parameters changed as listed in Table 1-1 and Table 1-2 below.
[0079]
20 Test material #1 did not contain the hollow microcapsules.
Test materials #2 to #7 were those in which the type and concentration of the
hollow microcapsules dispersed in the paint film were changed. Test materials #8 to #13
were those in which the fine particles of different types and average particle diameters
were dispersed in the paint film of Test material #10. Test materials #14 to #18 were
25 those in which the paint film thickness and the average particle diameter of the fine
particles were changed.
27
[0080]
Test materials #19 to #22 were those in which the paint film without the voids was
formed on a surface of Test material #10 as the second coating layer. Test materials #23
and #24 were those in which the type of the fine particles was changed. Test materials
5 #25 to #31 were those in which the type of the base sheet (metal sheet) was changed.
[0081]
Test material #32 was the one in which the chemical conversion treatment paint
film on a rear surface of Test material #30 was omitted. Test material #33 was the one in
which the deposition amount of the chemical conversion treatment paint film on a rear
10 surface of Test material #10 was set to 2 g/m2.
[0082]
Test material #34 was the one in which the base sheet of Test material #7 was
changed to an Sn-plated steel sheet. Test material #35 was the one in which 60 parts by
mass of titanium oxide were added to the paint film of Test material #7 as the color
15 pigment. Test material #36 was the one in which 10 parts by mass of carbon black were
added to the paint film of Test material #7 as the color pigment.
[0083]
Test materials #37 and #39 were those in which the type of varnish of Test
material #10 was changed. Test materials #38 and #40 were those in which the type of
20 varnish forming a first paint film layer of Test material #20 was changed. Test material
#41 was the one in which the type of varnish forming a second paint film layer of Test
material #20 was changed.
[0084]
Test materials #42 and #43 were those in which the emissivity on the rear surface
25 of the base sheet was changed. More precisely, they were each coated with a paint film in
which 2 parts by mass of carbon black were added to the varnish formulation-1 as the color
28
pigment. In this case, film thicknesses were adjusted so that the emissivities of the rear
surfaces were 0.4 and 0.3, respectively.
[0085]
Test materials #44, #45, and #46 were those in which the content of the fine
5 particles P of Test material #11 was changed.

What Is Claimed is
[Claim 1]
A pre-painted metal sheet comprising:
a metal sheet; and
5 a void-containing paint film, which is a paint film located on at least one surface
of the metal sheet, with dispersed fine particles and voids, wherein
when a cross-section of the void-containing paint film cut in a thickness direction
of the void-containing paint film is observed, the voids are present in 40 to 95 area% of a
total area of the cross-section of the void-containing paint film,
10 when an average particle diameter of the fine particles is t [μm] and an average
film thickness of the void-containing paint film is T [μm], a ratio t/T is in a range of 0.7 to
3.0, and
an elastic modulus of the fine particles, when compressed by 10% from the
thickness direction, is 30 MPa or more.
15 [Claim 2]
The pre-painted metal sheet according to claim 1, wherein
the average film thickness of the void-containing paint film is larger than an
average diameter of the voids.
[Claim 3]
20 The pre-painted metal sheet according to claim 1 or 2, wherein
when the average diameter of the voids is dV [μm], the average film thickness T of
the void-containing paint film and the average diameter dV of the voids satisfy a
relationship expressed by the following inequality (1).
T ≥ 1.1dV ... (1)
25 [Claim 4]
The pre-painted metal sheet according to any one of claims 1 to 3, wherein
39
when a presence ratio of the voids in the void-containing paint film relative to the
total area of the cross-section is PV [area%], the presence ratio PV [area%] of the voids, the
average particle diameter t of the fine particles, the average film thickness T, and a
predetermined measurement width W satisfy a relationship expressed by the following
5 inequality (2).
(t2/8)π/(W‧T) ≤ PV ≤ 10t2π/(W‧T) ... (2)
[Claim 5]
The pre-painted metal sheet according to any one of claims 1 to 4, wherein
the average film thickness T of the void-containing paint film is in a range of 50 to
10 1000 μm.
[Claim 6]
The pre-painted metal sheet according to any one of claims 1 to 5, wherein
a second paint film that does not contain voids and has an average film thickness
of 0.5 to 20.0 μm is present on an upper layer of the void-containing paint film.
15 [Claim 7]
The pre-painted metal sheet according to any one of claims 1 to 6, wherein
the fine particles are at least either one of polyacrylonitrile or vinylbenzene
polymer.
[Claim 8]
20 The pre-painted metal sheet according to any one of claims 1 to 7, wherein
a content of the fine particles is in a range of 1 to 40 area% of the total area of the
cross-section of the void-containing paint film when cut in the thickness direction of the
void-containing paint film.
[Claim 9]
25 The pre-painted metal sheet according to any one of claims 1 to 8, wherein
the metal sheet is any of a galvanized steel sheet, a zinc-aluminum alloy-plated
40
steel sheet, a zinc-aluminum-magnesium alloy-plated steel sheet, an aluminum plated steel
sheet, a zinc-nickel alloy-plated steel sheet, a zinc-iron alloy-plated steel sheet, a copper
sheet, a magnesium sheet, an aluminum sheet, or a stainless sheet
[Claim 10]
5 The pre-painted metal sheet according to any one of claims 1 to 9, wherein
an emissivity of a surface of the metal sheet opposite the void-containing paint
film is 0.30 or less.
[Claim 11]
A burn-prevention cover, which is a cover formed by the pre-painted metal sheet
10 according to any one of claims 1 to 10, wherein
a heat source is used to be located on an opposite side of the void-containing paint
film.
[Claim 12]
A manufacturing method of a pre-painted metal sheet having a void-containing
15 paint film, which is a paint film with dispersed fine particles and voids, on at least one
surface of a metal sheet, the manufacturing method comprising:
forming the void-containing paint film by coating a first paint, which contains the
fine particles, a resin, a curing agent, hollow microcapsules, and a solvent, on at least one
surface of the metal sheet and heating the metal sheet coated with the first paint to be cured,
20 wherein
the hollow microcapsules contain an organic solvent and a content of the hollow
microcapsules in the first paint is in a range of 5 to 50 mass% of a solid content mass of the
first paint, and
when an average particle diameter of the fine particles is t [μm] and an average
25 film thickness of the void-containing paint film after dried and cured is T [μm], the first
paint is coated so that a ratio t/T is in a range of 0.7 to 3.0.
41
[Claim 13]
The manufacturing method of the pre-painted metal sheet according to claim 12,
wherein
an average paint film thickness of the first paint is larger than an average diameter
5 of the hollow microcapsules.
[Claim 14]
The manufacturing method of the pre-painted metal sheet according to claim 12 or
13, wherein
the average paint film thickness of the first paint is 1.1 times or more the average
10 diameter of the hollow microcapsules.
[Claim 15]
The manufacturing method of the pre-painted metal sheet according to any one of
claims 12 to 14, wherein
the first paint is cured at a temperature in a range of 150 to 250°C, and
15 the hollow microcapsules containing the organic solvent are foamed at a
temperature in a range of 130 to 190°C.
[Claim 16]
The manufacturing method of the pre-painted metal sheet according to any one of
claims 12 to 15, wherein
20 the metal sheet coated with the first paint is heated at a heating rate of 70 to
750°C/min to reach a peak metal temperature of 200 to 250°C, the peak metal temperature
is held for 0.5 to 10 s, and then the metal sheet is cooled to 60°C or less at a cooling rate of
3 to 230°C/min.
[Claim 17]
25 The manufacturing method of the pre-painted metal sheet according to any one of
claims 12 to 16, wherein
42
the fine particles are at least either one of polyacrylonitrile or vinylbenzene
polymer.
[Claim 18]
The manufacturing method of the pre-painted metal sheet according to any one of
5 claims 12 to 17, wherein
a multilayer curtain film is formed by the first paint and a second paint that does
not contain the hollow microcapsules and coated on a surface of the metal sheet.