Technical Field
[0001]
The present invention relates to a coated metal sheet for automobile having
10 chipping resistance and being excellent in rust resistance in low temperature running
environments.
15
Background Art
[0002]
The background art of the present invention will now be described.
[0003]
Most automobile body members are formed of metal sheets such as steel
sheets; and are produced by undergoing many processes of [1] a blank process that
cuts a metal sheet to a prescribed size, [2] an oil cleaning process that cleans the
20 metal sheet with oil, [3] a process that press-molds the blank, [4] a joining process
that fashions the molded material into a member with a desired shape by spot
welding, adhesion, or the like, [5] a process that removes the press oil of the surface
of the member for cleaning, [ 6] a chemical conversion treatment process, and [7] an
electrodeposition coating process. A car body member used as an outer sheet
25 generally further undergoes coating processes such as [8] an intermediate coating
process and [9] an topcoat process. Therefore, in the automotive industry, the needs
for cost reduction by omitting or simplifying production processes, in particular the
chemical conversion treatment process and the coating process, are high.
30
[0004]
In response to these needs, studies have been made on using a coated metal
sheet (a pre-coated metal sheet) for automobile body members in order to omit the
5
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chemical conversiOn treatment process, omit or simplifY the electrodeposition
coating process, and omit or reduce the amount of subsidiary materials during
automobile manufacturing.
[0005]
One of the important performance required for automobile body members is
chipping resistance. Chipping refers to a phenomenon in which stones and the like
spattered during the running of an automobile collide with the car body and at this
time a coating film and a plating film are broken and peeled off. The phenomenon
is a major problem in cold districts, and is called a low temperature chipping
10 phenomenon. In cold districts, the coating film is exposed to low temperatures, and
is affected by internal stress that is prone to contract. When the impact of stone
spattering or. the like. is given to the coating film, not only is the . coating film
damaged, but also the underlying plating film is damaged, and furthermore cracking
may occur up to the interface between the plating film and the steel sheet. This is
15 considered to be due to the fact that the internal stress of the coating film acts on the
plating film. The peeled portion of the plating film like this immediately leads to a
reduction in corrosion resistance, and constitutes a serious problem with the
automobile body coating system.
20
[0006]
A measure that has been taken to cope with the chipping of automobile body
members is to insert a chipping primer between an electrodeposition coating film and
an intermediate coating film. The object of the chipping primer is to mitigate the
impact on the coating film at the time of the collision of a stone by its function as a
cushion layer. Hence, as the propetiies of the chipping primer, a high elasticity of
25 the coating film, a large rate of extension of the coating film, and a high strength of
the coating film are required.
[0007]
As a chipping primer with a large rate of extension of the coating film, an
aqueous chipping primer in which a glass transition temperature (T g) is adjusted to 0
30 to -75°C is described in Patent Literature l (JP 2003-251272A).
[0008]
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On the other hand, in the automotive industry, the needs for cost reduction
by omitting or simplifying production processes, in pmiicular the coating process, are
high as described above, and an automobile body coating system by which an
attached process such as chipping primer coating can be omitted is required.
5 [0009]
For example, Patent Literature 2 (JP 2003-245605A) and Patent Literature 3
(JP 2005-15516A) describe a method for fmming a laminated coating film in which
rubber pmiicles that absorb the impact of chipping are put into an intermediate
coating film to provide chipping resistance, and thus the application of a chipping
10 primer is omitted.
[0010]
Patent Literature. 4 (JP 2003-253211A) discloses an aqueous int~rmediate
coating composition that is composed of a coating-formable resin, a hardener, a
coloring pigment, talc, and a silane coupling agent and has chipping resistance.
15 [0011]
All of Patent Literatures 2 to 4 aim to omit a chipping primer by a method in
which, after an under-coating material such as an electrodeposition coating material
is applied to an automotive steel sheet, an intermediate coating layer to be laminated
is provided with chipping resistance. In contrast, there is not yet an automobile
20 body coating system in which a coated metal sheet is used for an automobile body
member and the coating film itself of the coated metal sheet is provided with
chipping resistance, and thus a chipping primer is omitted.
25 Patent Literature
[0012]
Patent Literature 1:
Patent Literature 2:
Patent Literature 3:
30 Patent Literature 4:
Citation List
JP 2003-251272A
JP 2003-245605A
JP 2005-15516A
JP 2003-253211A
Technical Problem
[0013]
4/69
Summary oflnvention
PCT/JP2015/077845
The present invention has been made in view of the issue mentioned above,
5 and relates to a coated metal sheet for automobile having chipping resistance and
being excellent in rust resistance in low temperature rmming environments.
10
Solution to Problem
[0014]
The present inventors have found that a chipping primer can be omitted by a
method in which an organic resin used for conventional chipping primers that has a
high rate of extension and a glass transition temperature Tg.of 0°C or Jess is used as
a coating film of a coated metal sheet and thus chipping resistance is provided.
However, the coating film formed of an organic resin with a glass transition
15 temperature Tg of 0°C or less has adhesiveness at normal temperature, and has had a
problem that, when coated metal sheets are stored while being stacked, over- and
underlying coated metal sheets adhere. The present inventors further conducted
studies, and have solved the problem by putting particles having a specific hardness
into the coating film and have been able to obtain a coated metal sheet for
20 automobile having chipping resistance of the present invention.
[0015]
[1]
25
30
The present invention is specifically described below.
A coated metal sheet for automobile comprising:
a metal sheet; and
a coating film (a) present on at least one surface of the metal sheet,
wherein the coating film (a) contains
an organic resin (A),
electrically conductive pigments (B), and
anti-corrosion pigments (C), and
a Martens micro-hardness HM at -20°C of the surface of the coating film (a)
5
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is 10 to 200 (mg/mm2
) at 20 points or more when measured at 100 points, and a
Martens micro-hardness HM at 40°C of the surface of the coating film (a) is 200 to
200,000 (mg/mm2
) at 5 points or more when measured at I 00 points.
[2]
The coated metal sheet for automobile according to [1], wherein a glass
transition temperature Tg of the organic resin (A) is -80°C to -20°C.
[3]
The coated metal sheet for automobile according to [I], wherein the organic
resin (A) is selected from the group consisting of a polyester resin, a polyurethane
10 resin, and an acrylic resin, and a modified product thereof.
[4]
The coated metal. sheet for automobile .according to [1],. w.herein. the
electrically conductive pigments (B) are non-oxide ceramic particles with an
electrical resistivity at 25°C of 0.1 X 10'6 tO 185 X 10'6 flcm, the electrically
15 conductive pigments being at least one selected from a boride, a carbide, a nitride,
and a silicide.
[5]
The coated metal sheet for automobile according to [1], wherein the coating
film (a) contains 0.5 vol% to 65 vol% of the electrically conductive pigments (B).
20 [6]
25
The coated metal sheet for automobile according to [1], wherein the anticmTosion
pigments (C) contain
one or more selected from a compound capable of releasing a silicate ion, a
phosphate ion, a vanadate ion, a tungstate ion, or a molybdate ion,
one or more particles containing a metal element selected from the group
consisting of Si, Ti, AI, and Zr, or
both thereof.
[7]
The coated metal sheet for automobile according to [1], wherein the coating
30 film (a) contains I vol% to 40 vol% of the anti-corrosion pigments (C).
[8]
5
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The coated metal sheet for automobile according to [I]; comprising, in the
coating film, granular patiicles (D) with a Martens hardness at 40°C of 200 mg/mm2
to 200,000 mg/mm2
.
[9]
An automobile component formed by processing and shaping the coated
metal sheet for automobile according to [I].
[I 0]
An automobile component formed by further applying one or more of an
electrodeposition coating layer, an intermediate coating layer, and an topcoat layer to
10 the automobile component according to [9].
Advantageous Effects ofinvention
[0016]
In the coated metal sheet for automobile of the present invention, since the
15 coating film itself has chipping resistance, the process of applying a chipping primer
does not need to be provided in the coating process after the coated metal sheet is
processed and shaped into an automobile component. Furthermore, the chipping
resistance of the coating film is effective particularly in low temperature
environments of -l5°C or less, and a coated metal sheet for automobile excellent in
20 cmmsion resistance can be provided.
Brief Description of Drawings
[0017]
[FIG. 1] FIG. 1 shows a schematic diagram of a cross section of the configuration of
25 a conventional automobile coating film comprising a chipping primer.
[FIG. 2] FIG. 2 shows a schematic diagram of a cross section of a coating film on the
occasion when a flying object collides with an automobile body member and the
surface of a metal sheet is exposed.
[FIG. 3] FIG. 3 shows a schematic diagram of a cross section of a coating film on the
30 occasion when a flying object collides with an automobile body member that uses a
coated metal sheet for automobile of the present invention and the metal sheet is
PCT/JP2015/077845
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exposed, and then an antirust component that is dissolved out from a coating film (a)
due to wetting with water reacts on the exposed surface of the metal sheet to form a
protective covering film.
[FIG. 4] FIG. 4 shows a schematic diagram of a cross section of a coating film on the
5 occasion when a flying object collides with an automobile body member that uses a
coated metal sheet for automobile of which the properties of a coating film (a) do not
conform to the range of the present invention, thus the overlying covering film,
comprising a plating layer, is largely peeled off due to a large intemal stress of- the
coating film (a), and the surface of the metal sheet is, even upon subsequent wetting
10 with water, not sufficiently covered with a protective covering film formed of an
antirust component that is derived from the coating film (a), because of the large
exposure of the surface of the metal sheet.
[FIG. 5] FIG. 5 shows a schematic diagram of a cross section of a coated metal sheet
for automobile of the present invention in the case where underlayer treatment is
15 performed.
[FIG. 6] FIG. 6 shows a schematic diagram of a cross section of a coated metal sheet
for automobile of the present invention in the case where underlayer treatment is not
performed.
[FIG. 7] FIG. 7 shows a schematic diagram showing states of distribution of particles
20 (P) in a cross section of a coated metal sheet for automobile of the present invention.
Description of Embodiments
[0018]
Hereinbelow, the present invention is described in detail.
25 [0019]

A coated metal sheet for automobile of the present invention is, for example,
a plating film-equipped metal sheet in which at least part of the surface is covered
with a specific electrically conductive coating film. In the metal sheet, depending
30 on the use, it is possible for both surfaces of the metal sheet to be covered with the
electrically conductive coating film, or for only one surface to be covered, and it is
5
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possible for part of the surface to be covered, or for the entire surface to be covered.
The part covered with the electrically conductive coating film of the metal sheet is
excellent in resistance weldability and corrosion resistance.
[0020]
Examples of the constituent metal of the plating film-equipped metal sheet
that can be used for the coated metal sheet of the present invention comprise
aluminum, titanium, zinc, copper, nickel, steel, and the like. The components of
these metals are not particularly limited; for example, in the case of using steel,
common steel or steel containing an additive element such as chromium maybe used.
10 However, since the metal sheet of the present invention is to be press-molded, in all
cases of metal sheets it is preferable to appropriately control the type and the amount
15
of addition of additive ylernents and the metal structure. so that desired .shaping
processing followability is provided.
[0021]
In the case where a steel sheet is used as the metal sheet, the type of the
surface plating film is not particularly limited. Examples of the usable plating film
include plating containing one of zinc, aluminum, cobalt, tin, and nickel, alloy
plating containing any of these metal elements and another metal element and/or a
non-metal element, and the like. In particular, examples of the zinc-based plating
20 film include plating of zinc, alloy plating of zinc and at least one of aluminum, cobalt,
tin, nickel, iron, chromium, titanium, magnesium, and manganese, and various zincbased
alloy platings further containing another metal element and/or non-metal
element (e.g., quaternary alloy plating of zinc, aluminum, magnesium, and silicon);
and the alloy components other than zinc are not particularly limited. Fmiher, these
25 plating films may contain, as a small amount of a different metal element or impurity,
cobalt, molybdenum, tungsten, nickel, titanium, chromium, aluminum, manganese,
iron, magnesium, lead, bismuth, antimony, tin, copper, cadmium, arsenic, or the like,
and may contain a material in which an inorganic substance such as silica, alumina,
or titania is dispersed.
30 [0022]
Examples of the aluminum-based plating film include plating of aluminum,
5
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alloy plating of aluminum and at least one of silicon, zinc, and magnesium (e.g.,
alloy plating of aluminum and silicon, alloy plating of aluminum and zinc, and
te1tiary alloy plating of aluminum, silicon, and magnesium), and the like.
[0023]
Further, also multiple-layer plating in which the plating mentioned above
and another type of plating, such as iron plating, alloy plating of iron and phosphorus,
nickel plating, and cobalt plating, are combined may be used.
[0024]
The method for forming the plating film ·is not patticularly limited.
10 Examples include electroplating, electroless plating, hot dipping, vapor deposition
plating, dispersion plating, and the like. The plating treatment method may be
.. either the continuous system. .or the batch system.. In.the .. case of using a.steel .. sheet,
the treatment after plating may be zero spangle treatment that is an external
appearance uniformity treatment after hot dipping, annealing treatment that is a
15 modification treatment of the plating film, temper rolling for adjusting the surface
condition or the material quality, etc.; but the treatment is not particularly limited to
these in the present invention, and any appropriate treatment may be used.
20
[0025]

A coating film (a) that covers the metal sheet of the present invention
contains an organic resin (A), electrically conductive pigments (B), and anticorrosion
pigments (C), and a Martens micro-hardness HM at -20°C of the surface of
the coating film (a) is 10 to 200 (mg/mm2
) at 20 points or more out of 100 points
measured, and a Martens micro-hardness HM at 40°C of the surface of the coating
25 film (a) is 200 to 200,000 (mg/mrn2
) at 5 points or more out of 100 points measured.
[0026]
The Martens micro-hardness HM is usually an indicator indicating the
hardness, and prescribes the hardness of the surface of the coating film (a) in the
present invention. The Martens micro-hardness HM can be measured by using
30 Nanoindcnter HM 500 manufactured by Fischer Instruments K.K. and setting the
indentation depth to 5 J.Lm or less in a coating film with a thickness of I 0 J.Lm or more.
PCT/JP2015/077845
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In a coating film with a thickness of less than I 0 f!m, measurement may be
performed by setting the indentation depth to 1/5 of the coating film thickness; but in
this case, since the variation in measurement is large, the number of times of
measurement is increased as appropriate, and the average value thereof is taken as
5 the measurement value. In the present invention, a sheet that falls under both of the
following cases is taken as the coated metal sheet for automobile of the present
invention: when the Martens micro-hardness HM at -20°C is measured at I 00
random points of the surface of the <:oating film (a) of the coated metal sheet, HM is
I 0 to 200 (mg/mm2
) at 20 points or more of the I 00 points; and when the Martens
10 micro-hardness HM at 40°C is measured at I 00 random points, HM is 200 to
200,000 (mg/mm2
) at 5 points or more of the I 00 points. Further, the case where
the. measurement of the Martens micro-hardness HM atc20°C.at 100 random points
yields an HM of 10 to 200 (mg/mm2
) at 40 points or more of the I 00 points and
fnrthetmore the measurement of the Martens micro-hardness HM at 40°C at I 00
15 random points yields an HM of 200 to 200,000 (mg/mm2
) at I 0 points or more of the
I 00 points is preferable, and the case where the measurement of the Martens microhardness
HM at -20°C at 100 random points yields an HM of 10 to 200 (mg/mm2
) at
60 points or more of the I 00 points and fntihermore the measurement of the Martens
micro-hardness HM at 40°C at I 00 random points yields an HM of 200 to 200,000
20 (mg/mm2
) at 20 points or more ofthe I 00 points is more preferable.
[0027]
Here, "random" refers to excluding, in the choice of I 00 points that are
measurement points, arbitrariness that leads to a biased measurement result. For
example, cetiain 2 points may be set, and I 00 points may be chosen at equal intervals
25 or random intervals between the points; and then the Martens micro-hardness HM at
20°C and the Martens micro-hardness HM at 40°C may be measured. In this case,
the interval between adjacent measurement points is preferably set so that the
measurement points are not influenced by the each other's hardness. Although I 00
points are chosen in the above, it is presumed that, as the number of measurement
30 points increases, the measurement value is averaged more, and precision is improved.
[0028)
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The inventors have found that, when a metal sheet that compnses the
coating film (a) of the present invention and is provided with electrodeposition
coating, intermediate coating, and topcoat for automobile receives the spattering of a
flying stone in a low temperature environment, significant flaw marking due to the
5 impact of stone spattering that would lead to the peeling of the plating layer is
suppressed in the case where the coating film (a) is sufficiently flexible even in a low
temperature environment, as compared to other cases. Fmiher, the inventors have
found that significant flaw marking is suppressed in the case where the Martens
micro-hardness of the coating film (a) in a low temperature environment is in a low
10 range of 10 to 200 (mg/mm2
).
[0029]
In the.case where .the coating film (a) is not .sufficiently flexible.at .low
temperature, the topcoat film, the intermediate coating film, and the electrodeposition
coating film are broken by the impact of stone spattering, and in addition the coating
15 film (a) is broken. It has been found that, in this case, the contraction stress of these
coating films released by the breaking is transferred as stress that peels off the
plating layer, and consequently the plating layer is largely peeled off. On the other
hand, it has been found that, in the case where the coating film (a) has sufficient
flexibility at low temperature, even when the coating film lying on the coating film
20 (a) is broken by the impact of stone spattering, the contraction stress is absorbed by
the deformation of the coating film (a) and is not transfeJTed to the plating layer, and
consequently the peeling of the plating layer is suppressed. Thus, it has been found
that, in the case where the peeling of the plating layer is suppressed even when the
overlying coating film is flawed, the corrosion of the surfaces of the plating layer and
25 the underlayer metal sheet exposed in the flawed pmiion is suppressed by the action
of the anti-con·osion pigments contained in the coating film (a), and therefore
chipping corrosion resistance is high.
[0030]
According to the investigation by the inventors, it has been found that the
30 coating film (a) was flexible enough to sufficiently exhibit the effect described above
in the case where the Martens micro-hardness HM measured from the surface of the
PCT/JP2015/077845
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coating film (a) was 10 to 200 at -20°C at 20 points or more among 100 random
measurement points. It has been found that, if HM was more than 200, the coating
film (a) was not flexible, and the effect of suppressing the transfer of the contraction
stress of the coating film to the plating layer was insufficient. The lower limit of
5 HM at -20°C is not particularly specified; but since a resin that provides a coating
film (a) with an I-IM at -20°C of less than 10 cannot be obtained at ordinary
industrial costs, this value serves as the practical lower limit.
[0031]
In the case of a coating film (a) that is flexible at low temperature to such a
10 degree as to have a part with an HM at -20 of 200 or less, when coating filmequipped
metal sheets are held so as to be superimposed in a situation of storage,
transportation,.etc. at what is .. called normal temperature of approximately.20 to 40°C,
it is likely that coating films (a) will mutually adhere or fuse and industrial handling
will be interfered with. According to the investigation by the inventors, it has been
15 found that the mutual adhesion or fusion between coating films (a) mentioned above
was sufficiently suppressed in the case where the Martens micro-hardness HM
measured from the surface of the coating film (a) was 200 to 200,000 at 40°C at 5
points or more among 1 00 random measurement points. It is presumed that, when
coating film-equipped metal sheets are held so as to be superimposed in a situation of
20 storage, transportation, etc. at what is called normal temperature of approximately 20
to 40°C, the contact of parts with a low HM at -20°C of 10 to 200 described above is
suppressed by the presence of a part with a high HM at 40°C on the surface of the
coating film (a) like the above, and consequently the adhesion or fusion of coating
films (a) is prevented. The effect described above is reduced in the case where the
25 number of points at which the Martens micro-hardness HM at 40°C is 200 to
200,000 is less than 5 among 100 random measurement points.
[0032]
The Martens micro-hardness I-IM at -20°C of the coating film (a) can
generally be controlled by appropriately selecting the organic resin (A) and a
30 hardener of the composition for the coating film. Specific examples of the method
include a method in which the resin molecular structure is formed so as to include an
PCT/JP2015/077845
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easy-to-deform, flexible structure in which the molecular weight of the part between
crosslinking points is large, a method in which the type and the amount of addition of
the hardener are adjusted to keep low the density of crosslinks between molecular
chains of the resin, and a method in which the baking temperature of the coating fihn
5 is reduced or the baking time is shortened and thereby the crosslinking reaction
produced by the hardener is mitigated.
[0033]
Hereinafter,. the coating composition for obtaining the coating film (a) in the
present invention is referred to as a coating composition (~). Examples of the
10 coating composition (~) include a water-based coating composition and an organic
solvent-based coating composition.
[0034] '- . ,_,) .,_'
In the present invention, the "water-based coating composition" refers to a
composition composed using a "water-based solvent" in which water accounts for 50
15 mass% or more of the entire solvent. Further, the "organic solvent-based coating
composition" refers to a composition composed using an "organic solvent-based
solvent" in which an organic solvent accounts for 50 mass% or more of the entire
solvent.
20
[0035]
Examples of the constituent component other than water of the "water-based
solvent" mentioned above include an inorganic acid that mixes with water well, such
as sulfuric acid, nitric acid, hydrochloric acid, phosphoric acid, boric acid, and
hydrofluoric acid, an inorganic salt that is soluble in water, such as water-soluble
metal salts and ammonium salts of the inorganic acids mentioned above, an inorganic
25 compound that is soluble in water, such as silicates, thiosulfates, and thiocyanates,
and an organic compound that mixes with water. Further, an organic solvent may
be added to the "water-based solvent" mentioned above as necessary. However, in
the "water-based coating composition" of the present invention, it is preferable from
the viewpoint of labor hygiene that the type and the amount of addition of the
30 organic solvent be adjusted so as to obtain a coating composition that does not fall
under the organic solvents etc. (class I organic solvents, class 2 organic solvents, or
PCT/JP2015/077845
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class 3 organic solvents, or materials containing more than 5 mass% of the organic
solvent mentioned above) defined in Enforcement Ordinance of Industrial Safety and
Health Law (Ordinance on the Prevention of Organic Solvent Poisoning, Chapter 1,
Section 1).
5 [0036]
Preferred examples of the method for producing a film on the metal sheet in
the case of a water-based or solvent-based coating composition include a method in
which the coating composition (p) is applied onto the metal sheet by a known coating
method such as roll coating, groove roll coating, curtain flow coating, roller curtain
10 coating, dipping, or air knife squeezing, and then the water or solvent of the wet
coating film is removed to dryness. Preferred examples of the method for curing
these dried coating films.indnde curing by polymerization by heating and baking the
organic resin in the coating film; for example, polymerization or curing by ultraviolet
irradiation may be used when the resin in the coating film can be polymerized by
15 ultraviolet light, and polymerization or curing by electron beam irradiation may be
used when the resin in the coating film can be polymerized by an electron beam.
[0037]
An underlayer treatment covering film may be provided between the coating
film (a) and the surface of the metal sheet for the purposes of further improving the
20 adhesiveness to the metal sheet, the corrosion resistance, etc. of the coating film. In
the case where an underlayer treatment covering film is provided, the number and
composition of the layer is not limited; but in order not to impair the processing
followability and con·osion resistance of the coating film (a) at the time of shapingprocessing
the metal sheet, it is necessary that the underlayer treatment covering film
25 be excellent in adhesiveness to the metal sheet and the overlying coating film (a).
In view of the compatibility with the environment, the underlayer treatment covering
film preferably has a chromate-free composition. Further, in order to ensure
sufficient electrical conductivity in the thickness direction ofthe covering film, the
thickness of the underlayer treatment covering film is preferably set to 0.5 J.!m or less.
30 [0038]
In the case of providing the underlayer treatment covering film, the method
PCT/JP20 15/077845
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for producing the underlayer treatment covering film is not limited as long as it is an
industrially applicable film production method. Examples of the method for
producing the underlayer treatment covering film include forming a film out of a
composition for underlayer treatment by application, vapor deposition, film sticking,
5 etc.; fi'om the viewpoints of film production cost (productivity), versatility, etc., a
method based on the application and drying of a water-based or solvent-based
composition for underlayer treatment is preferable. In the case of using a waterbased
or solvent-based composition for underlayer treatment, a multiple-layer
coating film may be formed by repeating the application and drying of each layer
10 from the lowermost layer to the outermost layer of a plurality of coating films
comprising the underlayer treatment covering film (a successive coating method).
Further, as .a .method. for forming the coating film on the surface of the metal sheet
simply and efficiently, film production may be performed by a laminating method
that comprises the following processes in this order: a process in which a plurality of
15 coating films of the lowermost layer in contact with the surface of the metal sheet to
the outermost layer are applied for covering successively or simultaneously in a wet
state (the process of wet-on-wet application or multiple-layer simultaneous
application of a coating composition); a drying process in which the water or solvent
of the covering films in a wet state is removed to dryness simultaneously; and a film
20 production process in which the multiple-layer coating film mentioned above is
cured. Here, the wet-on-wet coating method is a method in which a coating liquid
is applied onto the metal sheet, then another coating liquid is applied onto the coating
liquid in a solvent-containing state while the preceding coating liquid is not yet dried
(in a wet state), the solvents of the resulting laminate coating liquid are
25 simultaneously removed to dryness for curing, and thus a film is produced. The
multiple-layer simultaneous coating method is a method in which, using a multiplelayer
slide-type curtain coater, a slot die coater, or the like, a plurality of layers of
coating liquids are simultaneously applied in a laminate state onto the metal sheet,
then the solvents of the laminate coating liquid are simultaneously removed to
30 dryness for curing, and thus a film is produced.
[0039]
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The average thickness of the coating film (u) that covers the metal sheet of
the present invention is preferably in the range of 0.5 to 30 [!ill, and more preferably
in the range of I to 15 flm. At thicknesses less than 0.5 f!ID, the coating film is too
thin to hold a sufficient amount of the anti-corrosion pigments, and corrosion
5 resistance may not be obtained. If the coating film thickness is more than 30 [!ill,
the amount of the coating composition (~) used is increased and production cost is
increased, and furthermore the coating film may aggregate and break or be peeled off
during press molding. In addition, due to the thick film, the electrical insulation in
the film thickness direction is increased, and resistance welding becomes difficult.
10 Furthermore, in the case where a water-based coating composition is used, it is
highly likely that a coating defect such as toaming will occur, and it is not easy to
stably obtain an external appearance necessary as an industrial product. .
[0040]
The thickness of the coating film (a) can be measured by the cross-sectional
15 observation of the coating film or the like. Alternatively, based on the fact that the
calculation value obtained by a method in which the mass of the coating film
attached to unit area of the metal sheet is divided by the specific gravity of the
coating film or the specific gravity after drying of the coating composition (~) is
expected to be a value close to the measurement value obtained by cross-sectional
20 observation, a method of performing calculation simply using specific gravity is
possible. The method for determining the mass of the coating film attached may be
appropriately selected from existing methods, such as measuring the mass difference
between before and after coating, measuring the mass difference between before and
after the peeling of the coating tilm after coating, or performing X-ray fluorescence
25 analysis on the coating film to measure the amount of existence of an element of
which the amount contained in the coating film has been found in advance. The
method for determining the specific gravity of the coating film or the specific gravity
after drying of the coating composition (~) may be appropriately selected from
existing methods, such as measuring the capacity and mass of the isolated coating
30 film, measuring the capacity and mass of the dried coating composition (~) obtained
by putting a suitable amount of it into a container and performing drying, or
PCT/JP2015/077845
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performing calculation from the amounts of the blended constituent components of
the coating film and the known specific gravity of each component.
[0041]

5 The organic resin (A) of the present invention is a binder component of the
coating film (a); by appropriately selecting this, the Martens micro-hardness HM at-
20°C and Tg necessary for the coating film of the coated metal sheet for automobile
of the present invention can be obtained. The organic resin (A) may be either of a
water-based resin and an organic solvent-based resin, and is particularly a resin (AI)
10 described later. The organic resin (A) may further contain a reaction derivative
(A2) of the resin (AI).
[0042] ·. .
The orgamc resm (A) of the present invention preferably has a glass
transition temperature Tg of -80°C to -20°C, as described in detail below.
15 [0043]
The coating composition (p) used to form the coating film (a) in the present
invention may be either of a water-based composition and an organic solvent-based
composition, and contains 50 to 100 mass% of a resin (A 1) described later based on
its nonvolatile content. The resin (AI) exists stably in the coating composition (p).
20 When such coating composition (p) is applied to the metal sheet and heating is
perfmmed, in many cases, the resin (A I) does not react but dries as it is. In the case
where a silane coupling agent, a hardener, a crosslinker, or the like is contained in
the coating composition (p), at least part of the resin (AI) reacts with them to form a
derivative (A2) of the resin (AI). Thus, in this case, the material comprising the
25 umeacted resin (AI) and the reaction derivative (A2) of the resin (AI) serves as the
organic resin (A) that is a binder component of the coating film (a).
[0044]
The type of the resm (AI) is not particularly limited, and may be, for
example, a polyurethane resin, a polyester resin, an epoxy resin, a (meth)acrylic resin,
30 or a polyolefin resin, a modified product thereof, or the like as long as it has a
necessary Martens micro-hardness HM and a necessary glass transition temperature
5
PCT/JP2015/077845
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Tg. One of or a mixture of two or more of these may be used as the resin (Al), or
at least one organic resin may be modified and one of or a mixture of two or more of
the resulting organic resin(s) may be used as the resin (Al).
[0045]
Preferred examples of the resm (Al) include a polyurethane resin, a
polyurethane resin modified product, and a polyurethane resin composite, a mixture
of these and another resin, and the like. The urethane group (-NHCOO-) in a
polyurethane resin has ~ higher molecular aggregation energy (8.74 kcal/mol) than
many other organic groups; therefore, when a polyurethane resin is contained in the
10 resin (Al ), the adhesiveness of the coating film is increased, the peeling and galling
of the coating film are less likely to occur during press molding, and in addition the
effect of improving corrosion fRctor blocking properties (the denseness of the coating
film ) to enhance corrosion resistance is exhibited by virtue of the relatively high
aggregation energy. The molecular aggregation energies of organic groups other
15 than the urethane group, for example a methylene group ( -CH2-), an ether group ( -0-
), a secondary amino group (an imino group, -NH-), an ester group (-COO-), and a
benzene ring, are 0.68 kcal/mol, 1.00 kcal/mol, 1.50 kcal/mol, 2.90 kcal/mol, and
3.90 kcal/mol, respectively; thus, the molecular aggregation energy of the urethane
group ( -NHCOO-) is much higher than these. Hence, in many cases, a coating film
20 containing a polyurethane resin has higher adhesiveness than a coating film made of
many other resins, such as a polyester resin, a (meth)acrylic resin, and a polyolefin
resin, and has high corrosion resistance.
[0046]
As described above, the type of the resin (Al) is not particularly limited as
25 long as it has a necessary glass transition temperature Tg. It is preferable that the
resin (Al) be a resin containing, in its structure, at least one functional group selected
from a carboxyl group (-COOH), a carboxylate group (-Coo·M+; M+ represents a
monovalent cation), a sulfonic acid group (-S03H), a sulfonate group (-S03-M+; M+
represents a monovalent cation), a primary amino group ( -NH2), a secondary amino
30 group (-NHR1
; R1 represents a hydrocarbon group), a tertiary amino group (-NR1R2
;
R 1 and R2 individually represent a hydrocarbon group), a quaternary ammonium salt
PCT/JP2015/077845
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group (-N+R1R2R3X; R1
, R2
, and R3 individually represent a hydrocarbon group, and
X represents a monovalent anion), a sulfonium salt group (-S+R1R2X; R1 and R2
individually represent a hydrocarbon group, and X represents a monovalent anion),
and a phosphonium salt group (-P+H1R2R3X; R1
, R2
, and R3 individually represent a
5 hydrocarbon group, and x· represents a monovalent anion). Details and specific
examples of these are described later.
[0047]
Examples of the resin used for the coating composition (~) for obtaining the
coating film (a) in the present invention may include a water-soluble or solvent-
10 soluble resin that is completely dissolved in water or an organic solvent, and a resin
that is dispersed in water or a solvent uniformly and finely in the form of emulsion,
suspension, .or the .like {a wat~r dispersible resin or. a solvent dispersible. resin).
Here, the "(meth)acrylic resin" refers to an acrylic resin and a methacrylic resin.
15
[0048]
Among the examples of the resin (A.l) mentioned above, examples of the
polyurethane resin include a material obtained by reacting a polyol compound and a
polyisocyanate compound together and then performing chain extension using a
chain extender, and the like. The polyol compound is not particularly limited as
long as it is a compound containing two or more hydroxyl groups per molecule, and
20 examples include ethylene glycol, propylene glycol, diethylene glycol, 1,6-
hexanediol, neopentyl glycol, triethylene glycol, glycerin, trimethylolethane,
trimethylolpropane, a polycarbonate polyol, a polyester polyol, a polyether polyol
such as bisphenol hydroxypropyl ether, a polyesteramide polyol, an acrylic polyol,
and a polyurethane polyol, and a mixture thereof. The polyisocyanate compound is
25 not particularly limited as long as it is a compound containing two or more
isocyanate groups per molecule, and examples include an aliphatic isocyanate such
as hexamethylene diisocyanate (HDI), an alicyclic diisocyanate such as isophorone
diisocyanate (IPDI), an aromatic diisocyanate such as tolylene diisocyanate (TDI),
and an aromatic aliphatic diisocyanate such as diphenylmethane diisocyanate (MDI),
30 and a mixture thereof. The chain extender is not particularly limited as long as it is
a compound containing one or more active hydrogen atoms in a molecule, and water
PCT/JP2015/077845
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or an amine compound may be used. Examples of the amine compound include an
aliphatic polyamine such as ethylenediamine, propylenediamine,
hexamethylenediamine, diethylenetriamine, dipropylenetriamine,
triethylenetetramine, and tetraethylenepentamine, an aromatic polyamine such as
5 tolylenediamine, xylylenediamine, and diaminodiphenylmethane, an alicyclic
polyamine such as diaminocyclohexylmethanc, piperazine, 2,5-dimethylpiperazine,
and isophoronediamine, a hydrazine-based compound such as hydrazine, dihydrazide
succinate, dihydrazide adipate, and dihydrazide phthalate; an alkanolamine such as
hydroxyethyldiethylenetriarr\ine, 2-[(2-aminoethyl)amino ]ethanol, and 3-
10 aminopropanediol, and the like.
[0049]
In tb~ case where it. is desired to obtain a water, based polyurethane .. .resin,
for example, a method in which, during resin production, at least part of the pol yo!
compounds mentioned above are replaced with a carboxyl group-containing polyol
15 compound, the carboxyl group-containing polyol compound is reacted with a
polyisocyanate compound to introduce a carboxyl group into the resin chain, and
then the carboxyl group is neutralized with a base to produce a water-based resin
may be used. Alternatively, a method in which, during resin production, at least
part of the polyol compounds mentioned above are replaced with a polyol compound
20 having a secondary amino group or a tertiary amino group in a molecule, the polyol
compound is reacted with a polyisocyanate compound to introduce a secondary
amino group or a tertiary amino group into the resin chain, and then neutralization is
performed with an acid to produce a water-based resin may be used. In the case
where a tertiary amino group is present on the resin chain, an alkyl group may be
25 introduced into the tertiary amino group to produce a quaternary amino group, and
thereby a water-based cationic resin having a quaternary ammonium salt group can
be obtained. These compounds may be used singly or in a mixture of two or more.
[0050]
As mentioned above, the polyurethane resin that can be used as the resin
30 (Al) is preferably a polyurethane resin containing a large amount of aromatic rings
in the molecular structure. In such a polyurethane resin, a glass transition
PCT/JP2015/077845
21169
temperature is higher than that of a polyurethane resin having no aromatic ring or
having a limited amount of aromatic rings in the molecular structure, the molecular
chain is rigid and the resistance to the deformation of the coating film is strong, and
the rate of extension deformation of the coating film is low; therefore, the hardness
5 and brittleness of the coating film (a) needed in the present invention are higher than
in a polyurethane resin having no aromatic ring or a limited amount of aromatic rings.
Thus, although there is no particular limit on the polyol compound, the
polyisocyanate · compound, and the chain extender used for resin production, it is
preferable to use an aromatic aliphatic or aromatic alicyclic compound or the like
10 containing a large amount of aromatic rings.
[0051]
Among. the. examples of the resin (Al) mentioned a hove,. the .polyesterxesin
is not particularly limited as long as it has a necessary HM and a necessary glass
transition temperature Tg. Examples include a material obtained by the dehydration
15 condensation polymerization of a polyol such as ethylene glycol, 1 ,3-propanediol,
1 ,2-propanediol, propylene glycol, diethylene glycol, 1,6-hexanediol, neopentyl
glycol, triethylene glycol, bisphenol hydroxypropyl ether, 2-methyl-1,3-propanediol,
2,2-dimethyl-1,3-propanediol, 2-butyl-2-ethyl-1 ,3-propanediol, 1,4-butanediol, 2-
methyl-1 ,4-butanediol, 2-methyl-3-methyl-1 ,4-butanediol, 1,5-pentanediol, 3-
20 methyl-! ,5-pentanediol, 1,6-hexanediol, 1 ,4-cyclohexanedimethanol, I ,3-
cyclohexanedimethanol, I ,2-cyclohexanedimethanol, hydrogenated bisphenol A, a
dimer diol, trimethylolethane, trimethylolpropane, glycerin, and pentaerythritol, and
a polyvalent carboxylic acid such as phthalic acid, phthalic anhydride,
tetrahydrophthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic acid,
25 hexahydrophthalic anhydride, methyltetraphthalic acid, methyltetrahydrophthalic
anhydride, isophthalic acid, terephthalic acid, succinic anhydride, adipic acid,
sebacic acid, maleic acid, maleic anhydride, itaconic acid, fumaric acid, Himic
Anhydride, trim ell itic acid, trimellitic anhydride, pyromellitic acid, pyromellitic
anhydride, azelaic acid, succm1c acid, succ1mc anhydride, lactic acid,
30 dodecenylsuccinic acid, dodecenylsuccinic anhydride, cyclohexane-1,4-dicarboxylic
acid, and an acid anhydride in the endo form. Also a water-based resin obtained by
PCT/JP2015/077845
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neutralizing these with ammonia, an amine compound, or the like, etc. may be given.
[0052]
Among the examples of the resin (A 1) mentioned above, the epoxy resin is
not particularly limited as long as it has a necessary HM and a necessary glass
5 transition temperature Tg. For example, it is obtained by reacting an epoxy resin
such as a bisphenol A type epoxy resin, a bisphenol F type epoxy resin, a resorcin
type epoxy resin, a hydrogenated bisphenol A type epoxy resin, a hydrogenated
bisphenol F type epoxy resin, a resorcin type epoxy resin, and a novo lac type epoxy
resin with an amine compound such as diethanolamine and N-methylethanolamine.
10 Further, a water-based resin obtained by neutralizing these with an organic acid or an
inorganic acid, a water-based material obtained by radically polymerizing a high acid
value acrylic resin in .the presence of the epoxy resin mentioned above, and .. th~n
performing neutralization with ammonia, an amine compound, or the like, etc. may
be given.
15 [0053]
Among the examples of the resin (Al) mentioned above, the (meth)acrylic
resin is not particularly limited as long as it has a necessary HM and a necessary
glass transition temperature Tg. Examples include a material obtained by radically
polymerizing an alkyl (meth)acrylate such as ethyl (meth)acrylate, 2-ethylhexyl
20 (meth)acrylate, and n-butyl (meth)acrylate, a hydroxyalkyl (meth)acrylate such as 2-
hydroxyethyl (meth)acrylate, or a (meth)acrylic acid ester such as an alkoxysilane
(meth)acrylate together with (meth)acrylic acid in water using a polymerization
initiator. The polymerization initiator is not pmiicularly limited, and examples
include a persulfate such as potassium persulfate and ammonium persulfate, an azo
25 compound such as azobis( cyanovaleric acid) and azobisisobutyronitrile, and the like.
Here, the "(meth)acrylate" refers to an acrylate and a methacrylate, and
"(meth)acrylic acid" refers to acrylic acid and methacrylic acid.
[0054]
Among the examples of the resin (A I) mentioned above, the polyolefin
30 resm is not particularly limited as long as it has a necessary glass transition
temperature Tg. Examples include a material obtained by radically polymerizing
PCT/JP2015/077845
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ethylene and an unsaturated carboxylic acid such as methacrylic acid, acrylic acid,
maleic acid, fumaric acid, itaconic acid, or crotonic acid under high temperature and
high pressure. Further, a water-based resin obtained by neutralizing these with
ammonia, an amine compound, a basic metal compound such as KOH, NaOH, or
5 LiOH, ammonia, an amine compound, or the like containing the metal compound
mentioned above, or the like, etc. may be given.
[0055]
The above examples of the resin (AI) may be used singly or in a mixture of
two or more. Further, as a main component of the coating composition (~), one
10 ormore components of a composite resin that is obtained by modifying at least part
of at least one of the examples of the resin (A I) in the presence of the same resin
(AI) may be used as the resin (A I) as a whole.
[0056]

15 A glass transition temperature Tg of the organic resin (A) is preferably -
sooc to -20°C. The glass transition temperature Tg can be measured by a method
in which the organic resin that forms the coating film is cured by heating at a
maximum heating temperature of 200°C to form a film with a film thickness of 15
11m, and the maximum heating temperature of a differential scanning calorimeter
20 (DSC) or the transition temperature in a dynamic viscoelasticity measuring apparatus
is taken as the transition temperature Tg. Tg is preferably not less than -80°C and
not more than -20°C. A resin with a Tg higher than -20°C has low flexibility, and
therefore has limited capability to mitigate the transfer to the plating layer of the
contraction stress of the coating film that is released in association with the flaw
25 marking of the coating film due to the collision of stone spattering. The lower limit
of Tg is not particularly prescribed, but an organic resin having a Tg lower than -
80°C is difficult to industrially obtain at low cost. Tg is more preferably not less
than -60°C and not more than -30°C.
[0057]
30
As the electrically conductive pigments (B), one or more selected from a
PCT/JP2015/077845
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metal", an alloy, electrically conductive carbon, iron phosphide, a carbide, and a
semiconductor oxide are preferably used. Examples include a metal such as zinc,
nickel, iron, aluminum, cobalt, manganese, copper, tin, and cru·omium, a powder of
an alloy thereof, electrically conductive carbon, an electrically conductive carbon
5 powder such as graphite powder, iron phosphide powder, a powder of a carbide such
as titanium carbide and silicon carbide, an electrically conductive semiconductor
powder, ceramic pmiicles, and the like. Among these, non-oxide ceramic particles
are particularly preferable in the coated metal sheet of the present invention.
10
[0058]
In the case where non-oxide ceramic particles are used, even when the
coating composition (p) for obtaining the coating film (a) is a water-based
composition, these non-oxide cermnic pmiicles are not degraded in the composition,
and maintain high electrical conductivity permanently. Hence, excellent resistance
weldability can be maintained for a very long period of time as compared to
15 electrically conductive pmiicles that are degraded due to water, such as base metal
pmiicles and fen·osilicon pmiicles.
[0059]
The non-oxide ceramic that forms the non-oxide cermnic particle contained
in the coating film (a) of the present invention is a boride ceramic, a carbide ceramic,
20 a nitride ceramic, or a silicide ceramic of which the electrical resistivity (volume
resistivity, specific resistance) at 25°C is in the range of 0.1 x 1 o·6 to 185 x 1 o-6 Ocm.
The non-oxide cermnic herein is a ceramic made of an element other than oxygen or
a compound not containing oxygen. The boride ceramic, the carbide ceramic, the
nitride ceramic, and the silicide ceramic herein are non-oxide ceramics containing
25 boron B, carbon C, nitrogen N, and silicon Si as a main non-metal constituent
element, respectively. Among these, one having an electrical resistivity at 25°C of
less than 0.1 x 10·6 Ocm is not found. In the case where the electrical resistivity
(volume resistivity, specific resistance) at 25°C of the non-oxide ceramic is more
than 185 x 1 o·6 em, a large amount of addition to the coating film is needed in order
30 to provide the resin coating film with sufficient electrical conductivity, and
significant peeling and galling of the coating film occur during the press molding of
PCT/JP2015/077845
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the coated metal sheet of the present invention and conosion resistance is reduced;
thus, this is not suitable.
[0060]
Since the non-oxide ceramic particle contained in the coating film (a) of the
5 present invention has high electrical conductivity, the amount of addition for
providing the resin coating film with sufficient electrical conductivity is allowed to
be a smaller amount, and consequently the bad influence on the corrosion resistance
and. moldability of the coated metal sheet is reduced. For reference; the electrical
resistivity of pure metals is in the range of 1.6 x 10·6 Ocm (Ag simple substance) to
10 185 x 1 o-6 Ocm (Mn simple substance), and it can be seen thatthe non-oxide ceramic
used as the electrically conductive particle in the present invention (electrical
resistivity:. 0.1. x .10-6 to 1.85x 10-6 Ocm) has excellent.e!t;ctrical conductivity at ~
level subsmntially equal to that of pure metals.
15
[0061]
Examples of the non-oxide ceramic that can be used in the present invention
include the following. That is, examples of the boride ceramic include a boride of
each transition metal of groups IV (Ti, Zr, and Hf), V (V, Nb, and Ta), and VI (Cr,
Mo, and W) of the periodic table, Mn, Fe, Co, Ni, a rare eatih element, and an
alkaline earth metal (Ca, Sr, and Ba) other than Be or Mg.
20 [0062]
Some borides of Be having an electrical resistivity at 25°C of more than 185
x 10-6 Ocm (e.g., Be2B, BeB6, etc.) are not suitable for use in the present invention
because the electrical conductivity is not sufficient. Further, borides of Mg (Mg3B2,
MgB2, etc.) are not suitable for use in the present invention because they are unstable
25 to water and acid.
[0063]
Examples of the carbide ceramic include a carbide of each transition metal
of groups IV, V, and VI, Mn, Fe, Co, and Ni. Carbides of rare earth elements and
alkaline earth metals (e.g., YC2, LaC2, CeC2, PrC2, Be2C, Mg2C3, SrC2, etc.) that
30 may be hydrolyzed in a moist atmosphere are not suitable for use in the present
invention.
PCT/JP2015/077845
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[0064]
Examples of the nitride ceramic include a nitride of each transition metal of
groups IV, V, and VI, Mn, Fe, Co, and Ni. Nitrides of rare earth elements and
alkaline emih metals (e.g., LaN, Mg3N2, Ca3N2, etc.) that may be hydrolyzed in a
5 moist atmosphere are not suitable for use in the present invention. Examples of the
· silicide ceramic include a silicide of each transition metal of groups IV, V, and VI,
Mn, Fe, Co, and Ni. Silicides of rare earth elements and alkaline earth metals (e.g.,
LaSi, Mg2Si, SrSh, BaSh, etc.) that may react with water to produce hydrogen in a
moist atmosphere are not suitable for use in the present invention. Further,
10 examples include a mixture of two or more selected from these borides, carbides,
nitrides, and silicides, a cermet obtained by mixing these ceramics with a metal
bonding material and performing sintering, and the like ..
[0065]
In the case of producing the coating film (a) out of a water-based coating
15 composition, the standard electrode potential of the metal constituting a part of the
cermet is preferably -0.3 V or more to provide water degradation resistance. This is
because, in the case where the standard electrode potential of the metal constituting a
part of the ce1met is less than -0.3 V, when the cermet particle exists in the waterbased
coating composition for a long period of time, a rust layer or a thick oxide
20 insulating layer may be produced on the surface of the pmiicle and the electrical
conductivity of the particle may be lost. Examples of the water degradation
resistant cermet particle include WC-12Co, WC-12Ni, TiC-20TiN-15WC-10Mo2C-
5Ni, and the like. The standard electrode potentials of Co and Ni are -0.28 V and -
0.25 V, respectively, both of which are nobler than -0.3 V, and both metals are
25 resistant to water degradation.
[0066]
Among the non-oxide ceramics mentioned above, Cr-based ceramics (CrB,
CrB2, Cr3C2, Cr2N, CrSi, etc.) have a concern about environmental burdens, and Hfbased
ceramics (HfBz, HfC, HfN, etc.) and most of the ceramics based on rare earth
30 elements on the heavier rare emih side than Tb are expensive and are not
commercially available; hence, in the present invention it is preferable to use a nonPCT/
JP2015/077845
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oxide ceramic other than these among the group mentioned above, or a mixture of
two or more selected from these picked out ceramics.
[0067]
Further, from the viewpoints of the presence or absence of industrial
5 products, stable distribution on home and abroad markets, prices, electrical resistivity,
etc., the following non-oxide ceramics are more preferable. That is, it is preferable
to use BaB6 (electrical resistivity: 77 x 10-6 !1cm), CeB6 (the same: 30 x 10-6 !1cm),
Co2B (the same: 33 x 1 o-6 !1cm), CoB (the same: 76 x 1 o-6 !1cm), FeB (the same: 80
X 10'6 !1cm), GdB4 (the same: 31 X 10'6 !1cm), GdB6 (the same: 45 X 10'6 !1cm),
10 LaB4 (the same: 12 x 10-6 !1cm), LaB6 (the same: 15 x 10-6 !1cm), Mo2B (the same:
40 X 10'6 !1cm), MoB (the same: 35 X 10'6 !1cm), MoB2 (the same: 45 X 10'6 !1cm),
Mo2B5 .{the same: 26 x l0'6 Dcm), Nb3B2 (the same: 45 ,x 10-6 !1cm),.NhB (the same:
6.5 X 10'6 !1cm), Nb3B4 (the same: 34 X 10'6 !1cm), NbB2 (the same: 10 X 10'6 !1cm),
NdB4 (the same: 39 x 10-6 !1cm), NdB6 (the same: 20 x 10-6 !1cm), PrB4 (the same:
15 40 X 10'6 !1cm), PrB6 (the same: 20 X 10'6 !1cm), SrB6 (the same: 77 X 10'6 !1cm),
TaB (the same: 100 x 10-6 !1cm), TaB2 (the same: 100 x 10-6 !1cm), TiB (the same:
40 X 10'6 !1cm), TiB2 (the same: 28 X 10'6 !1cm), VB (the same: 35 X 10'6 !1cm),
VB2 (the same: 150 x 10-6 !1cm), W2B5 (the same: 80 x 10-6 !1cm), YB4 (the same:
29 X 10'6 !1cm), YB6 (the same: 40 X 10'6 !1cm), YBI2 (the same: 95 X 10'6 !1cm),
20 ZrB2 (the same: 60 x 10-6 !1cm), MoC (the same: 97 x 10-6 !1cm), Mo2C (the same:
100 X 10'6 !1cm), Nb2C (the same: 144 X 10'6 !1cm), NbC (the same: 74 X 10'6 !1cm),
Ta2C (the same: 49 x 10-6 !1cm), TaC (the same: 30 x 10-6 !1cm), TiC (the same: 180
X 10'6 Qcm), V2C (the Same: 140 X J0-6 Qcm), VC (the Same: 150 X 10'6 Qcm), WC
(the same: 80 X 10'6 !1cm), w2c (the same: 80 X 10'6 Qcm), ZrC (the same: 70 X 10'6
25 !1cm), Mo2N (the same: 20 x 10-6 !1cm), Nb2N (the same: 142 x 10-6 !1cm), NbN
(the same: 54 X 10'6 !1cm), SeN (the same: 25 X 10'6 !1cm), Ta2N (the same: 135 X
10'6 !1cm), TiN (the same: 22 X 10'6 !1cm), ZrN (the same: 14 X 10'6 !1cm), CoSi2
(the same: 18 x 10-6 !1cm), Mo3Si (the same: 22 x 10'6 !1cm), Mo5Sh (the same: 46
X 10'6 !1cm), MoSi2 (the same: 22 X 10'6 !1cm), NbSi2 (the same: 6.3 X 10'6 !1cm),
30 Ni2Si (the same: 20 x 10-6 !1cm), Ta2Si (the same: 124 x 10-6 !1cm), TaSi2 (the same:
8.5 X 10'6 !1cm), TiSi (the same: 63 X 10'6 !1cm), TiSh (the same: 123 X 10'6 !1cm),
PCT/JP2015/077845
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V5Si3 (the same: 115 x 10-6 Qcm), VSi2 (the same: 9.5 x 10-6 Qcm), W3Si (the same:
93 X 10'6 Qcm), WSi2 (the same: 33 X 10'6 Qcm), ZrSi (the same: 49 X 10'6 Qcm), or
ZrSi2 (the same: 76 x 10-6 Qcm), or a mixture of two or more selected from these.
[0068]
5 Among these, non-oxide ceramics of which the electrical resistivity at 25°C
is in the range of 0.1 X 10'6 to 100 X 10'6 Qcm are particularly preferable. This is
because these have higher electrical conductivity than non-oxide ceramics having an
electrical resistivity at 25?C ·in the range of more. than 100 x 10-6 Qcm up to 185 x
10·6 Qcm; therefore, the ainount of particles added to provide the resin coating film
10 with sufficient electrical conductivity is allowed to be smaller, thus only a limited
number of conduction paths of corrosion current that penetrate through the coating
. _film are formed, and._conseqnently corrosion resistance. is hardly reduced. In
addition, this is because, due to the limited amount of particles added, the peeling
and galling of the coating film are not brought about during press molding and
15 moldability is hardly reduced.
[0069]
The electrical resistivities additionally written in the parentheses of the nonoxide
ceramics mentioned above are representative values (literature values) of those
on the market and in use as industrial materials. These electrical resistivities
20 increase or decrease with the type and amount of impurity elements that have entered
the crystal lattice of the non-oxide ceramic; hence, in the present invention these
materials may be used after checking that the electrical resistivity is in the range of
0.1 x 10·6 to 185 x 10-6 Qcm by, for example, actually measuring the electrical
resistivity at 25°C using the four-terminal four-probe method and the constant
25 current application system in accordance with JIS K7194, using a resistivity meter
Loresta EP (MCP-T360 type) and ESP probes (the diameter of the flat head portion
of the terminal: 2 mm) manufactured by Mitsubishi Chemical Analytech Co.,Ltd.
[0070]
The shape of the particle of the electrically conductive pigments (B) is
30 preferably a shape close to a sphere, such as a spherical particle or a quasi-spherical
particle (e.g., an ellipsoidal shape, a hen's egg-like shape, a rugby ball-like shape,
PCT/JP2015/077845
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etc.) and a polyhedral particle (e.g., a soccer ball-like shape, a die-like shape, brilliant
cut shapes of various jewels, etc.). Particles of a long, thin shape (e.g., a bar-like
shape, a needle-like shape, a fibrous shape, etc.) and a planar shape (e.g., a flake-like
shape, a flat sheet-like shape, a thin leaf-like shape, etc.) are not suitable for use in
5 the present invention because, in the coating process, they may be ananged parallel
to the surface of the coating film or be deposited near the interface between the metal
sheet (in the case where underlayer treatment is performed on the metal surface, the
underlayer treatment layer) that is the substrate for coating and the coating 'film, and
this makes it difficult to form an effective cunent path penetrating in the thickness
10 direction of the coating film.
[0071]
. The. average. particle diameter of the electrically conductive pigments .(B) is
not particularly limited; but the pigments are preferably present in the form of
particles with a volume average diameter of 0.2 to 20 11m, more preferably present in
15 the form of particles with a volume average diameter of 0.5 to 12 !lll1, and
particularly preferably present in the form of particles with a volume average
diameter of l to 8 11m in the coating composition (~) of the present invention. The
dispersed particle having a volume average diameter in the above range may be
either a single particle or a secondary particle in which a plurality of single particles
20 are strongly aggregated as long as they stably exist in the coating composition (~)
during the production process, storage, and transportation of the coating composition
(~), in the process of application to the metal sheet that is the substrate for coating (in
the case where underlayer treatment is performed on the metal surface, the
underlayer treatment layer), or in other like events. In the process of the application
25 of the coating composition to the substrate, it is possible for the (B) particles to be
aggregated and for the volume average diameter in the coating film to be increased
during the drying of the coating film and film production.
[0072]
The volume average diameter herein refers to the average diameter on a
30 volumetric basis found from volume distribution data of particles. This may be
found using any commonly known particle diameter distribution measurement
PCT/JP2015/077845
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method, and it is preferable to use the average value of a sphere volume-equivalent
diameter distribution measured by the Coulter method (the aperture electrical
resistance method). This is because the Coulter method has little difference in
measurement value between manufacturers and types of the measuring apparatus,
5 and can make accurate, high precision measurement as compared to other pmiicle
diameter distribution measurement methods (for exmnple, (a) calculation from a
volume distribution obtained by the laser diffi'action scattering method, (b)
conversion of a circle area-equivalent diameter distribution obtained by the image
analysis method to a volume distribution, (c) calculation from a mass distribution
10 obtained by the centrifugal sedimentation method, etc.). In the Coulter method, test
particles are suspended in an electrolyte aqueous solution, a fixed current is passed
through an aperture .of a .glass tube, and negative pressure is set so th4t particles are
made to pass through the aperture. When a particle passes through the aperture, the
electrical resistance of the aperture is increased due to the volume of the electrolyte
15 aqueous solution that is forced out by the particle (= the volume of the particle).
When a fixed cunent is applied, the resistance change at the time of the passage of
the particle is reflected in the voltage pulse change; thus, the volume of the
individual pmiicle can be directly measured by measuring the height of the voltage
pulse for each particle. Since pmiicles have irregular shapes in many cases, a
20 spherical body with the smne volume as the particle is imaginarily set, and the
particle size is converted to the diameter of the spherical body (= sphere volumeequivalent
diameter). Such a method for measuring the sphere volume-equivalent
dimneter by the Coulter method is well known; for example, details are described in
the literature of a web page on the official Internet site of Beckman Coulter, Inc.,
25 [http://www. beckmancoulter.co.jp/product/product03/Multisizer3 .html (Multisizer 3,
a precise particle size distribution measuring apparatus)].
[0073]
Non-oxide ceramic particles with a volume average diameter less than 0.2
f!m are generally more expensive than non-oxide ceramic pmiicles with a volume
30 average diameter higher than that, and are not distributed much on markets as
industrial products. Furthermore, since the specific surface area is relatively large,
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when preparing a water-based or organic solvent-based coating composition, it is
difficult to disperse particles while wetting the entire surface of the particle, even
using a moisture dispersant, and undissolved lumps or unmixed-in lumps not
compatible with water or organic solvents occur in many cases; hence, it is
5 preferable not to use the above-mentioned particles in the present invention.
Further, non-oxide ceramic particles with a volume average diameter more than 20
flm are likely to sediment faster in a water-based or organic solvent-based coating
composition than non-oxide ceramic particles with a volume· average ·diameter
smaller than that (as is clear from the Stokes equation). Therefore, it is difficult to
10 ensure dispersion stability, even when the dispersant is modified, and troubles such
as an event in which particles do not float but sediment in a short time, are
aggregated and solidified, .and are consequently difficultto .. re-disperse may. occur;
hence, it is preferable not to use the above-mentioned particles in the present
invention.
15 [0074]
In general, most electrically conductive pigments (B) available are prepared
with a prescribed particle diameter by pulverizing the source material and classifYing
the resulting particles as necessary, and therefore have a particle diameter
distribution in which particles with different patiicle diameters are mixed.
20 Therefore, even when the volume average diameter is within the patiicle diameter
range described above, weldability is influenced depending on the particle diameter
distribution. Among the examples of the electrically conductive pigments (B),
particularly (B 1) in which the volume particle diatneter of each patiicle is 0.25 to 24
flm exhibits effect for good weldability.
25 [0075]
The amount of the electrically conductive pigments (B) contained in the
coating film (a) at 25°C is preferably 0.5 to 65 volume%, more preferably 1 to 40
volume% from the viewpoints of electrical conduction capability during resistance
welding, the ensuring of moldability, and cost increase due to the increase in the
30 amount of the electrically conductive pigments, and still more preferably 2 to 20
volume%. The range of 4 to 20 volume% is particularly preferable from the
PCT/JP2015/077845
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viewpoints of ensunng sufficient cmTOSion resistance and moldability, and m
addition ensuring sufficient resistance weldability.
[0076]
The reason why the coating film (a) exhibits good electrical conductivity in
5 the coated metal sheet of the present invention is presumably that, in the coating film
(a), the electrically conductive pigments (B), which are electrically conductive
particles, is hardly aggregated and is sufficiently uniformly dispersed over the entire
surface of the coating film, and electrical conduction paths leading to the underlying
metal sheet do not exist locally in the coating film. ·If electrically conductive
10 particles have been aggregated in the coating film, electrical conduction paths in a
state of being uniformly scattered over the entire surface of the coating film are less
likely to he formed in the coating film, and an art;
The type of the anti-corrosion pigments (C) used in the present invention is
25 not patiicularly limited, but is preferably one containing one or more selected from a
silicate compound, a phosphate compound, a vanadate compound, and metal oxide
fine patiicles.
[0081]
A silicate compound, a phosphate compound, and a vanadate compound can,
30 m the coating composition (~) or the coating film ( u), release a silicate ion, a
phosphate ion, and a vanadate ion, and counter-cations of these anions (e.g., an
PCT/JP2015/077845
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alkaline earth metal ion, a Zn ion, an AI ion, etc.), respectively, in accordance with
the environmental change of water in the composition or the coating film, contact
with a coexisting substance or the substrate surface, pH, etc. It is presumed that, of
these ions, the ions that have already been dissolved out in the coating composition
5 (~) are incorporated into the coating film (a.) during film production; and in
accordance with the increase or decrease in the amount of water in the coating film,
contact with a coexisting substance or the substrate surface, pH change, etc., the ions
form a covering film of an insoluble salt or oxide together with another coexisting
atom or atomic group, and thus suppress corrosion: Similarly, it is presumed that,
10 in accordance with the environmental change after coating film formation, also the
silicate compound, the phosphate compound, and the vanadate conipound
.incorporated inthe.coatinf'film (a) gradually release.the anion and cation mentioned
above and form a covering film of an insoluble salt or oxide, and thus suppress
cmmswn. Also in the case where the coating film is flawed and the plating film of
15 the metal sheet or the underlayer metal below the plating is exposed, the action
mentioned above is brought out by silicate ions, phosphate ions, and vanadate ions,
and counter-cations of these anions being released and arriving at the exposed
surface of the plating film or the underlayer metal. The action is exhibited more
effectively in the case where the degree of flawing is suppressed to a low level and
20 the exposed area of the plating film or the underlayer metal is limited to a low level.
[0082]
Examples of the silicate compound that can be used in the present invention
include a silicate of an alkaline earth metal such as magnesium silicate and calcium
silicate, a silicate of an alkali metal such as lithium silicate, sodium silicate, and
25 potassium silicate, aluminum silicate, and the like. Of these, examples of the ·
lith.ium silicate, the sodium silicate, and the potassium silicate include a lithium
silicate in which the composition molar ratio between silicon oxide (Si02) and
lithium oxide (Li20) is 0.5 <:: (Si02/Liz0) <:: 8, a sodium silicate in which the
composition molar ratio between silicon oxide (Si02) and sodium oxide (Na20) is
30 0.5 <:: (SiOz/NazO) <:: 4, and a potassium silicate in which the composition molar ratio
between silicon oxide (SiOz) and potassium oxide (K20) is 0.5 <:: (Si02/K20) <:: 4,
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and a hydrate of these silicates. Specific examples of these include lithium
orthosilicate (Li4Si04; 2Li20·Si02), hexalithium diorthosilicate (Li6Sh07;
3Liz0·2Si02), lithium metasilicate (LhSi03; Li20·Si02), lithium disilicate (Li2Si20 5;
Liz0·2Si02), tetralithium heptasilicate (2Li20·7Si02), lithium tetrasilicate (LhSi40 9;
5 Lh0·4Si02), tetralithium nonasi!icate (2Li20·9Si02), tetralithium pentadecasilicate
(2Lh0·15Si02), sodium orthosilicate (Na4Si04; 2Na20·Si02), sodium metasilicate
(Na2Si03; NazO·SiOz), sodium disilicate (Na2Sh05; Na20·2Si02), sodium
tetrasilicate (NazSi:109; Na20·4Si0z), potassium orthosilicate (K4Si04; · 2K20,Si02),
potassium metasilicate (K2Si03; K20·Si02), potassium disilicate (K2Si20 5;
10 K20·2Si0z), and potassium tetrasilicate (K2Si40 9; K20·4Si02), and a hydrate of
these silicates. Most of the hydrates of these silicates easily tum into a gel in a
hydrated state as it. is due .to. the environmental change of pH, _temperatury, etc .. , and
part of them may turn into a macromolecule to form a polysilicate. Also such a
polysilicate is included in the silicate compound that can be used in the present
15 invention.
[0083]
Examples of the phosphate compound that can be used in the present
invention include a metal salt of orthophosphoric acid, polyphosphoric acid (the
simple substances of linear polymers in which the degree of polymerization of
20 orthophosphoric acid is up to 6, or a mixture of two or more of these),
metaphosphoric acid (the simple substances of cyclic polymers in which the degree
of polymerization of orthophosphoric acid is 3 to 6, or a mixture of two or more of
these), tetrametaphosphoric acid, hexametaphosphoric acid, and the like, a phosphate
mineral such as phosphorus pentoxide, monetite, triphylite, whitlockite, xenotime,
25 stercorite, struvite, and vivianite, a commercially available composite phosphate
pigments such as silica polyphosphate and a tripolyphosphate, and a metal salt of
phytic acid, phosphonic acid (phosphorous acid), phosphinic acid (hypophosphoric
acid), and the like, a mixture of two or more of these, and the like. The
orthophosphate herein includes a monohydric salt (HPO/-) and a dihydric salt
30 (H2P04-) of orthophosphoric acid. Further, the polyphosphate includes a hydric salt.
The type of the cation for forming the phosphate is not particularly limited; examples
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include a metal ion of Co, Cu, Fe, Mn, Nb, Ni, Sn, Ti, V, Y, Zr, AI, Ba, Ca, Mg, Sr,
Zn, and the like, and an oxocation such as vanadyl, titanyl, and zirconyl; and AI, Ca,
Mg, Mn, and Ni are preferably used. The phosphate compounds mentioned above
may be used singly or in combination of two or more.
5 [0084]
It is not preferable to use a large amount of an alkali· metal as the type of the
cation for forming the phosphate. In the case where a phosphate of an alkali metal
is used, a product obtained by firing in an industrial production process tends to be
dissolved in water excessively. However, a phosphate of an alkali metal may be
10 used in a slightly larger amount when the solubility in water can be controlled during
the production of the anti -corrosion pigments, the production of the coating
composition, the production of a film on the metal sheet, the use of the coated metal
sheet, etc. Examples of such control include a method in which an anti-corrosion
pigments are made to coexist with another additive that restrains the solubility in
15 water or made to coexist with a resin-based or inorganic-based macromolecule that is
crosslinked to a high degree, and the rate of dissolving-out in water is controlled, and
the like.
[0085]
The vanadate compound that can be used in the present invention is a
20 compound in which the valence of vanadium is one of 0, 2, 3, 4, and 5 or a
composite compound having two or more of these valences, and examples include an
oxide, a hydroxide, an oxyacid salt of various metals, a vanadyl compound, a halide,
a sulfate, a metal powder, etc. of vanadium having the above valences. These
decompose during heating or in the presence of water, and react with coexisting
25 oxygen. For example, a metal powder or a divalent compound of vanadium
changes to a compound with a valence of one of 3, 4, and 5 in the end. A zerovalent
compound, for example vanadium metal powder, can be used for the reason
mentioned above, but has a problem such as oxidation reaction being insufficient and
is therefore not preferable in practical terms. A pentavalent vanadium compound
30 has a vanadate ion, and is likely to react with a phosphate ion by heating to fmm a
heteropolymer that contributes to rust resistance; thus, containing a pentavalent
PCT/JP2015/077845
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vanadium compound as a component is preferable. Specific examples of the
vanadium compound include a vanadium(II) compound such as vanadium(II) oxide
and vanadium(II) hydroxide, a vanadium(Jll) compound such as vanadium(III) oxide,
a vanadium(IV) compound such as vanadium(IV) oxide and a vanadyl halide, and a
5 vanadium(V) compound such as vanadium(V) oxide and a vanadate (an
orthovanadate, a metavanadate, and a pyrovanadate of various metals, etc.), and a
mixture thereof. The preferred type of metal for forming the vanadate is the same
as the metals described for the phosphate.
10
[0086]
In the case where a vanadate of an alkali metal is used, a product obtained
by firing in an industrial production process tends to be dissolved in water
excessively; thus, like in.th~:.case of the phosphate, it is not preferable to use a large
amount of a vanadate of an alkali metal. However, these may be used when the
solubility in water can be controlled, like in the case where a phosphate of an alkali
15 metal is used. This similarly applies to the cases of a halide and a sulfate of
vanadium.
[0087]
In the coated metal sheet of the present invention, the total amount of the
silicate compound, the phosphate compound, and the vanadate compound mentioned
20 above is I to 40 volume%, preferably 1 to 20 volume%, and more preferably 2 to 15
volume% of the coating film ( u). If the total amount is less than I volume%, the
action of the silicate compound, the phosphate compound, and the vanadate
compound is insufficient, and therefore cmmsion resistance may be reduced. If the
total amount is more than 20 volume%, the coating film is embrittled; hence, by the
25 cohesion failure of the coating film, the adhesiveness and followability of the coating
film during shaping may be reduced and weldability may be reduced.
[0088]
The anti-corrosion pigments (C) preferably contain one or more of a silicate
compound, a phosphate compound, and a vanadate compound, and more preferably
30 has a composition in which a phosphate compound (a phosphate ion source) and at
least one of a silicate compound (a silicate ion source) and a vanadate compound (a
PCT/JP2015/077845
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vanadate ion source) coexist, m te1ms of enhancing the antirust effect. The
blending ratio between the amount of the phosphate ion source and the total amount
of the silicate ion source and the vanadate ion source is preferably set to [the number
of moles ofP20s]:[the total number of moles of Si02 and V20s] being 25:75 to 99: I.
5 If the molar ratio of the total amount of the silicate ion source and the vanadate ion
source to the total amount of the phosphate ion source, the silicate ion source, and the
vanadate ion source is more than 75%, the antirust effect by phosphate ions may be
reduced; and if the molar ratio of the total amount of the silicate ion source and the
vanadate ion source is smaller than 1%, the effect of oxidizing and fixing
10 neighboring chemical components by silicate ions (or vanadate ions) may be
insufficient.
[0089] -·.- ... ,. '
Other than the above, metal oxide fine particles made of one or more metal
elements selected from the group consisting of Si, Ti, AI, and Zr may be used as the
15 anti-corrosion pigments (C) used in the present invention. These metal oxide fine
particles may be used singly, or may be blended together with a silicate compound, a
phosphate compound, and a vanadate compound; thereby, corrosion resistance can
further be enhanced. When a silicate compound, a phosphate compound, and a
vanadate compound, and silica coexist, con·osion resistance is improved even more;
20 thus, this is preferable. Examples of the silica include fumed silica, colloidal silica,
aggregated silica, etc. Also calcareous silica may be used.
[0090]
Examples of the metal oxide fine particles mentioned above that can be used
in the present invention include silica fine pmticles, alumina fine particles, titania
25 fine particles, zirconia fine particles, and the like in which the volume average
diameter is approximately 0.2 to 10 J.Lm; and metal oxide fine nanopmticles in which
the volume average diameter is approximately 0.5 to 30 nm are more preferable.
These may be used singly, or may be used in combination of two or more. Among
these, silica fine nanoparticles may be added in the case where both the improvement
30 in corrosion resistance and the toughening of the coating film aTe needed.
[0091]
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As the metal oxide fine nanoparticles with a particle diameter of not less
than 0.5 nm and less than 30 nm, for example, colloidal silica, colloidal titania, and
colloidal zirconia may be used. These are produced by a different method from the
metal oxide mentioned above that is prepared in a fine particle form by pulverization,
5 and are therefore easily dispersed in the coating material and in the coating film of
the coated metal member after coating, while having a particle diameter of fine
primary particles (0.5 nm to 30 nm) as they are. These metal oxide fine
nanoparticles have higher antirust effect than metal oxide fine particles of. the same
composition having a larger particle diameter. However, such metal oxide fine
10 nanoparticles may inhibit weldability in energization resistance welding in which a
current is passed while a load is applied with electrodes, and the resulting Joule heat
is utilized to perfmm welding, sneh as spot welding.
[0092]
For the amount of metal oxide fine nanoparticles, it is preferable that the
15 ratio of the total volume of the metal oxide fine nanoparticles in the coating film to
the total volume of the non-oxide ceramic particles (B) (metal oxide fine
nanoparticles/B) be 20 or less. In the case where importance is attached to
weldability, the ratio is more preferably I 0 or less. The lower limit of (metal oxide
fine nanoparticles/B) is preferably 0.1 or more. The case where (metal oxide fine
20 nanoparticles/B) is less than 0.1 is a state where the amount of non-oxide ceramic
patiicles (B) in the coating film is too large, or the amount of metal oxide fine
nanoparticles is too small. In the former, since the amount of non-oxide ceramic
particles (B) in the coating film is too large, the coating film is embrittled, and the
cracking and falling off of the coating film during shaping may occur. The cracking
25 atld falling off of the coating film lead to a reduction in corrosion resistance provided
by the coating film and a defective external appearance of the coated metal sheet.
In the latter, since the amount of metal oxide fine nanopatiicles in the coating film is
insufficient, the effect of enhancing corrosion resistance may not be obtained
sufficiently. The rust resistance that is reduced by suppressing the amount of metal
30 oxide fine nanoparticles in order to ensure weldability can be compensated for by
adding anti-corrosion pigments (C) with a patiicle diameter of I 00 run or more.
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The anti-corrosion pigments (C) with a particle diameter of I 00 nm or more are less
likely to get between an electrode and (B), between (B) and (B), or between (B) and
the metal sheet in a state where the coating film is applied on the metal sheet or a
state where the coating film is deformed by the load applied by the welding
5 electrodes, and therefore has little bad influence on energization resistance welding
as compared to metal oxide fine nanoparticles.
[0093]
It is preferable that the amount of the anti-con·osion pigments (C) be 1 to 40
volume% of the coating film (a) and that the total amount of the anti-corrosion
10 pigments (C) and the electrically conductive pigments (B) not exceed 80 volume%.
In the case where importance is attached to the corrosion resistance of the coated
metalsheet, the ammmt of the anti-corrosion pigments (C) is more preferablyJ to 40
volume%, and still more preferably 7.5 to 40 volume%. In the case where
importance is attached to achieving even more corrosion resistance of the coated
15 metal sheet, the amount of the anti-corrosion pigments (C) is more preferably 13 to
40 volume%. If the amount is less than I volume%, the amount of the anticorrosion
pigments (C) is insufficient, and therefore the effect of enhancing
corrosion resistance may not be obtained sufficiently. If the amount is more than 40
volume%, the coating film may be embrittled and the adhesiveness of the coating
20 film to the metal sheet may be reduced; consequently, the metal sheet may be
exposed due to the breaking and peeling of the coating film during shaping, and the
external appearance of the coated metal sheet may be degraded and the effect of
improving corrosion resistance provided by the coating film may be reduced.
25
[0094]
The amount of the electrically conductive pigments (B) and the amount of
the anti-corrosion pigments (C) can be calculated by observing a cross section of the
coating film with an electron microscope to identifY each particle, counting the
number of particles per cross section, and converting the resulting number to the
number per volume of the coating film. In this case, each particle may be identified
30 using an EDX spectrometer or the like, as necessary. It is also possible to calculate
the amount of particles in the coating film from the amounts of(B) and (C) contained
PCT/JP2015/077845
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in the coating material before coating and the amount of the coating film attached to
the metal sheet. When the amounts of (B) and (C) incorporated in the coating
material before coating have been found, the amount of particles in the coating film
can be calculated from the amounts of incorporation and the amount of the coating
5 material attached to the metal sheet. When the amounts of incorporation are
unknown, calculation may be made by, for example, identifying and counting
individual particles in a coating material that have been diluted to an appropriate
concentration, using image analysis with an apparatus such as Morphologi G3, a
particle image analyzer manufactured by Malvern Instruments Ltd. This method
10 may be used also in the case where the coating film attached to the metal sheet is
dissolved and the nnmber of particles is counted. However, based on the fact that
.. the .calculation values of.the.amount of the electrically .conductive pigments. (B.). and
the amount of the anti-corrosion pigments (C) in the coating film (a) obtained by
calculation based on the blending ratio between the organic resin (A), the electrically
15 conductive pigments (B), and the anti-corrosion pigments (C) and the specific
gravities of them after drying are expected to be values close to the measurement
values obtained by cross-sectional observation, also a method of performing
calculation simply from the blending ratio is possible.
20
[0095]
The various anti-corrosion pigments mentioned above are introduced into
the organic resin (A) in the coating film (a) preferably by dissolving, or dispersing
and stabilizing a suitable amount of the anti-corrosion pigments in the coating
composition CP) in advance.
[0096]
25
In addition to the electrically conductive pigments (B) and the anticonosion
pigments (C), particles (D) such as granular wax or resin beads in which
the Martens hardness at 40°C is 200 mg/mm2 to 200,000 mg/mm2 may be contained
as particles in the coating film of the present invention. The granular wax and the
30 resin beads with a Martens hardness at 40°C of 200 mg/mm2 to 200,000 mg/mm2
may be arbitrarily selected in view of the ease of addition to the coating material, etc.
5
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Examples include polyolefin wax, polyethylene wax, polypropylene wax,
polybutylene wax, modified polyolefin wax, acrylic resin particles, silicon resm
particles, fluorine resin particles, a polyacrylonitrile resin, and the like.
[0097]
In the case where the Martens hardness at 40°C of the particles (D) is less
than 200 mg/mm2
, when surfaces of coated metal sheets of the present invention
come into contact with each other or the surface of the coated metal sheet comes into
contact with another material, instrument, or tool, the effect of particles (D) coming
into contact more preferentially than the resin (A) and thereby preventing the coating
10 film (a) from adhering to or melting with them is small. It is difficult to industrially
find particles (D) with a Martens hardness at 40°C of more than 200,000 mg/mm2
,
and this value practically. serves as the upper limit .of .. HM. The .xange. of the
Martens hardness is more preferably not less than 300 mg/m2 and not more than
2000 mg/m2
.
15 [0098]
Particles that are selected from the electrically conductive pigments (B), the
anti-corrosion pigments (C), and the particles (D) mentioned above and have a
diameter of the primary particle of I J.lm to I 0 J.lm are defined as particles (P). The
particles (P) are composed of at least one of the electrically conductive pigments (B)
20 and the anti-cmmsion pigments (C), and may include particles (D) as necessary.
[0099]
The exposure state and the pmiicle diameter of the particles (P) can be
found by microscopic observation from above the coated metal sheet or the
microscopic observation of a cross section of the coated metal sheet. Also the
25 density of exposed particles (P) can be found by observation from above the coated
metal sheet. Alternatively, when the pmiicle diameter and the number of pmiicles
of the source material of the particles (P) are known, the density may be calculated
from the amount of blending in the coating material. The particles (P) exposed on
the surface of the coating film (a) have a Mmiens micro-hardness HM at 40°C of200
30 to 200,000 (mg/mm2
), and constitute at least part of the surface of the coating film
(a). According to the investigation by the inventors, the pmiicles (P) exposed on
PCT/JP2015/077845
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the surface of the coating film ( u) are less likely to deform than the resin (A) forming
the coating film (u); therefore, when surfaces of coated metal sheets of the present
invention come into contact with each other or the surface of the coated metal sheet
comes into contact with another material, instrument, or tool, particles (P) come into
5 contact more preferentially than the coating film (u), and can thereby prevent the
coating film (u) from adhering to or melting with them.
10
15
[0 1 00]
FIG. 7 shows a state where partides (P) are exposed from the coating film
(u), as a schematic diagram. In order for particles (P) to come into contact with
another material more preferentially than the coating film ( u ), it is preferable that the
relationship between the thickness (T) of the coating film after drying and the
.· pmiicle diameter (R) of the particle (P) satisfy the following. formula:
T/R = 0.6 to 2.5
(where R represents the volume average particle diameter (11m) of the particle P).
If T/R is less than 0.6, most part of the individual pmiicle (P) protrudes from the
coating film (u); therefore, particles (P) are likely to fall off and the particles (P) do
not exhibit the effect sufficiently, or the particles (P) that have fallen off are likely to
get mixed in the process and cause a problem with quality; hence, this is not
preferable. If T/R is more than 2.5, the exposure of particles (P) from the coating
20 film ( u) is insufficient, and the effect of preventing adhesion or melting is low; hence,
this is not preferable.
[0101]
The effect was found to be significant in the case where the diameter of the
primary particle of the particles (P) was I 11m to I 0 11m and the exposure density was
25 100 to 2.0 x 106/mm2
. The case where the exposure density is 1.0 x 103 to 2.0 x
105/mm2 is preferable, and the case where the exposure density is 5.0 x 103 to 2.0 x
104/mm2 is more preferable. In the case where the diameter of the primary particle
is less than I Jlm, particles (P) are buried in the coating film (u), and therefore it is
difficult to bring out the action of particles (P) coming into contact preferentially.
30 In the case where the diameter of the primary particle is more than I 0 11m, it is
difficult for particles (P) to stably exist in the coating material for forming the
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coating film (u), and the economical efficiency of the storage of the coating material
and coating is poor. In the case where the exposure density of particles (P) is less
than 1 00/md, the density is too low, and therefore it is difficult to bring out the
action of particles (P) coming into contact preferentially. In the case where the
5 amount is large enough for the exposure density to be more than 2.0 x l06/mm2
, the
amount of particles (P) in the coating film (u) is too large, and therefore the problems
that the coating film is likely to be peeled off and that coating is difficult, etc. arise.
10
[01 02]

The method for producing the coating composition (p) used to form the
coating film (u) of the present invention is not particularly limited. Examples
include. a method in whichJhe components for forming the coating film ( u) are. added
into water or an organic solvent, and stirring is performed with a dispersing machine
such as a disperser to perform dissolution, dispersion, or pulverization dispersion.
15 In the case of a water-based coating composition, a known hydrophilic solvent or the
like may be added in order to improve the solubility or dispersibility of the
components for forming the coating film (a), as necessary.
[0103]
In particular, in the case of a water-based coating composition (p), in
20 addition to the pmiicles (D), various water-soluble or water dispersible additives may
be added to the resin (AI), the electrically conductive pigments (B), and the anticorrosion
pigments (C) to the extent that the aqueous nature and coatability of the
coating material are not impaired, as necessary. For example, various water-soluble
or water dispersible antirust agents not having the form of pigments, a surfactant
25 such as an antifoaming agent, an anti -setting agent, a leveling agent, and a moisture
dispersant, a thickener, a viscosity modifier, etc. may be added. Further, for the
purposes of the stabilization of constituent components of the coating composition
(p) such as a resin or another organic compound etc., a small amount of an organic
solvent may be added to the extent that it does not fall under the organic solvents etc.
30 (class I organic solvents, class 2 organic solvents, or class 3 organic solvents, or
materials containing more than 5 mass% of the organic solvent mentioned above)
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defined in Enforcement Ordinance of Industrial Safety and Health Law (Ordinance
on the Prevention of Organic Solvent Poisoning, Chapter 1, Section 1 ).
[0104]
In the case where the coating film (a) of the present invention is formed of a
5 water-based coating composition (p), because of the water-based prope1iies, the
surface tension is high as compared to organic solvent-based coating compositions;
thus, the wettability to the metal sheet that is the substrate (in the case where
underlayer treatment is performed, the underlayer treatment layer), the electrically
conductive pigments (B), the anti-corrosion pigments (C), the particles (D), etc. is
10 poor, and uniform coatability and particle dispersibility may not be obtained when a
prescribed amount of coating is performed on the substrate. In such a case, the
moisture dispersant and- the thickener mentioned .above may be added ... As the
moisture dispersant, a surfactant that reduces the surface tension may be used, and a
macromolecular surfactant with a molecular weight of 2000 or more (a
15 macromolecular dispersant) is preferably used. A low-molecular surfactant can
move through the resin coating film containing moisture relatively easily, and is
therefore likely to bring, to the metal surface, water adsorbed on a polar group of the
surfactant and corrosion factors such as dissolved oxygen and dissolved salts coming
via the water, and fmihermore likely to bleed out for itself and dissolve out;
20 consequently, often degrades the rust resistance of the coating film. In contrast, a
macromolecular surfactant can adsorb on the surface of a metal, a ceramic particle,
and a pigment by multipoint adsorption, and is therefore hardly detached once it is
adsorbed; thus, it is effective in wettability improvement even at low concentration.
In addition, molecules are voluminous, and are therefore less likely to move through
25 the resin coating film and less likely to bring corrosion factors to the metal surface.
Some of the acrylic resins of which the addition to the organic resin (A) is
recommended in the item of mentioned above have the function
of a macromolecular surfactant like the above, and have the effects of restraining the
sedimentation of the electrically conductive pigments (B), the anti-corrosion
30 pigments (C), the particles (D), etc. and uniformity dispersing them in the waterbased
coating composition.
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(0105]
A thickener may be added as a measure in the case where a moisture
dispersant by itself cannot provide the repulsive portion of the substrate surface with
sufficient surface covering condition or in the case where the viscosity of the water-
5 based coating composition is too low to ensure a necessary coating film thickness.
Many thickeners have a molecular weight of several thousand to several ten
thousand; and molecules of a thickener adsorb on the surface of a pigment etc. by
·multipoint adsorption and are associated with each other to form a weak network
structure, and can thus enhance the viscosity of the coating composition.
10 (0106]
In the case where the water-based coating composition (~) contains
electrically conductive pigments (B), anti-corrosion pigments (C), .and particles.(D)
with a high specific gravity, a viscosity modifier that can provide thixotropic
properties (thixotropy) may be added to the coating material, as necessary. Like in
15 the case of the thickener mentioned above, molecules of a viscosity modifier adsorb
on the surface of a pigment etc. by multipoint adsorption in the water-based coating
composition, and form a network structure. The molecular weight of such a
viscosity modifier is several hundred thousand to several million, which is very high,
and therefore the viscosity modifier forms a strong network structure having a large
20 yield value in the water-based coating composition (~); thus, the coating composition
(~) is, at a low shear rate, less likely to deform, and has a high viscosity. When a
large shear stress more than the yield value is applied to the coating composition (~),
the network structure collapses and the viscosity decreases rapidly. Thus, when a
viscosity modifier is added, the following effects are exhibited: during storage and
25 transportation in which the water-based coating composition (~) generally keeps a
stationary state, the viscosity of the coating composition (~) is enhanced and the
sedimentation of heavy pigments is restrained; and when a high shear stress (high
shear rate) is applied, such as when the composition flows through pipes in a coating
factory and when the composition is applied to the substrate, the viscosity of the
30 coating composition (~) is reduced and flowing is made easier.
[0107]
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In the case of an organic solvent-based coating composition (~), the coating
composition in which a resin is dissolved in an organic solvent has a relatively high
viscosity, and the viscosity is easy to adjust. Hence, the viscosity of the coating
composition can be easily and stably maintained at I 00 mPa·s or more, which is
5 advantageous to suppress the sedimentation of pigments. Fmiher, a non-oxide
ceramic used as an electrically conductive material is a substance having also a
hydrophobic pmi on its surface, and is therefore easily dispersed in an organic
solvent-based coating -composition (~), in general; therefore, . coating can be
perfmmed without causing the sedimentation of the electrically conductive -pigments
10 (B) in the coating composition (~); thus, this is preferable.
[01 08]
When a. coating cqmposition in which .the organic. solvent-b[!s.ed .coating
composition (~) that forms the coating film has a viscosity of I 00 to 2000 mPa·s is
applied onto the metal sheet with a roll coater or a curtain coater and then drying and
15 baking are performed, the electrically conductive pigments (B) are less likely to
sediment; thus, this is more preferable. If the viscosity of the coating composition
(~) is less than I 00 mPa·s, the electrically conductive pigments (B) are likely to
sediment; and if the viscosity is more than 2000 mPa·s, the viscosity is too high and a
defective external appearance during coating commonly called ribbing or the like
20 may be brought about. The viscosity is more preferably 250 to 1000 mPa·s. The
viscosity of the organic solvent-based coating composition(~) can be measured using
a Brookfield viscometer at the same temperature as the temperature of the coating
composition at the time of coating with a roll coater or a curtain coater.
25
[0109]
The viscosity can be adjusted by the type of the organic solvent used and the
amount of the solvent. As the organic solvent, a known solvent may generally be
used, but an organic solvent with a high boiling point is preferable. Since the
baking time is short in the production line of the metal sheet of the present invention,
using a solvent with a low boiling point may cause a coating defect commonly called
30 boiling. A solvent with a boiling point of 120°C or more is preferably used. As
organic solvents with a high boiling point like the above, a known solvent such as
5
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cyclohexane or Solvesso (product name of ExxonMobile Yugen Kaisha), which is an
aromatic hydrocarbon-based organic solvent, may be used.
[0 11 0]

As described in the item of , in the case where the
coating composition (~) is a water-based or organic solvent-based composition, the
coating film (a) of the present invention is preferably produced by a film production
method in which the coating composition (~) is applied onto the metal sheet using a
known coating method such as roll coating, groove roll coating; curtain flow coating,
10 roller curtain coating, dipping, or air knife squeezing, and then the water or solvent
of the wet coating film is removed to dryness. In the case of, among the above
compositions, a water-based .or organic solvent-based .ultraviolet curabl~. or. electron
beam curable composition, it is preferable to apply the composition onto the metal
sheet by the coating method mentioned above, then remove the water or solvent to
15 dryness, and apply ultraviolet light or an electron beam to perform polymerization.
[0 111]
A baking drying method in the case where the coating composition (~) is a
water-based or organic solvent-based bake hardenable composition will now be
specifically described. In the case where the coating composition (~) is a water-
20 based or organic solvent-based bake curable composition, the baking drying method
is not particularly limited; the metal sheet may be heated in advance or the metal
sheet may be heated after coating, or these may be combined to perform drying.
The heating method is not particularly limited; hot air, induction heating, nearinfrared
light, direct fire, etc. may be used singly or in combination.
25 [0112]
In the case where the coating composition (~) is a water-based bake curable
composition, the baking drying temperature is preferably 120°C to 250°C as the
maximum heating temperature of the surface of the metal sheet. If the maximum
heating temperature is less than 120°C, the curing of the coating film may be
30 insufficient and corrosion resistance may be reduced; and if the maximum heating
temperature is more than 250°C, bake curing may be excessive, and conosion
PCT/JP2015/077845
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resistance and moldability may be reduced. The baking drying time is preferably 1
to 60 seconds, and more preferably 3 to 20 seconds. If the time is less than I
second, bake curing may be insufficient, and conosion resistance may be reduced;
and if the time is more than 60 seconds, productivity may be reduced.
5 [0113]
In the case where the coating composition (~) is an organic solvent-based
bake curable composition, the maximum heating temperature of the surface of the
metal sheet is preferably 180°C to 260°C. If the maximum heating temperature is
less than 180°C, the curing of the coating film may be insufficient, and corrosion
10 resistance may be reduced; and if the maximum heating temperature is more than
260°C, bake curing may be excessive, and conosion resistance and moldability may
be reduced. The baking . .drying time is preferably .10 to 80 seconds, and more
preferably 40 to 60 seconds. If the time is less than I 0 seconds, bake curing may be
insufficient, and conosion resistance may be reduced; and if the time is more than 80
15 seconds, productivity may be reduced.
[0114]
A film production method in the case where the coating composition(~) is a
water-based or organic solvent-based ultraviolet curable or electron beam curable
composition will now be specifically described. Any of these compositions is
20 applied by a similar method to the case of the water-based or organic solvent-based
composition mentioned above, then the water or solvent of the wet coating film is
removed to dryness, and after that ultraviolet light or an electron beam is applied.
The coating film is produced by being cured mainly from, as a starting point, radicals
generated by ultraviolet or electron beam in·adiation; hence, the drying temperature
25 is allowed to be lower than in the case of a bake curable composition. Ultraviolet or
electron beam irradiation is preferably perfmmed after most of the water or solvent is
volatilized in a drying process at a relatively low maximum heating temperature of
the metal surface of approximately 80 to 120°C.
30
[0115]
The ultraviolet irradiation for radically polymerizing and cunng an
ultraviolet curable resin in the coating film is usually performed in the air atmosphere,
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an inert gas atmosphere, a mixed atmosphere of the air and an inert gas, or the like.
In the ultraviolet ewing of the present invention, ultraviolet irradiation is performed
preferably in a mixed atmosphere of the air and an inert gas in which the oxygen
concentration is adjusted to I 0 volume% or less or in an inert gas atmosphere.
5 Since oxygen acts as an inhibitor of radical polymerization, in the case where the
concentration of atmospheric oxygen during ultraviolet inadiation is low,
deactivation and crosslinking reaction inhibition due to the addition of oxygen to the
generated radicals are suppressed, and the ultraviolet cmable composition used in the
present invention experiences radical polymerization and crosslinking and is
10 sufficiently tuned into macromolecules. Hence, the adhesiveness to the electrically
conductive pigments (B) and the surface of the metal sheet is enhanced, and as a
result .the conosion resistance of the coating film is. improved over .. t)le ... C!JSe of
ultraviolet curing in the air atmosphere. Examples of the inert gas used herein
include nitrogen gas, carbon dioxide gas, and argon gas, a mixed gas thereof, and the
15 like.
[0116]
Ultraviolet light can be applied by using an ultraviolet light source such as a
high pressure mercury lamp of a metal vapor discharge system, a metal halide lamp
or the like, a xenon lamp or the like of a rare gas discharge system, or an
20 electrodeless lamp using a microwave. In the coated metal sheet of the present
invention, any lamp may be used as long as the ultraviolet curable coating film can
be sufficiently cured and desired resistance weldability, corrosion resistance, and
moldability can be obtained. In general, the peak illuminance and the integrated
amount of ultraviolet light received by the coating film in±1uence the curability of the
25 coating film; but the conditions of ultraviolet irradiation are not particularly limited
as long as the ultraviolet curable coating film can be sufficiently cured and desired
corrosion resistance and moldability can be obtained.
[0 117]
In the case where the coating composition (~) is an electron beam curable
30 composition, an ordinary electron beam irradiation apparatus used in the fields of
printing, coating, film coating, wrapping, sterilization, etc. may be used for electron
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beam curing. These are an apparatus that applies a high voltage to thermoelectrons
generated from a hot filament in a high vacuum to accelerate them, extracts the
resulting electron current into an inert gas atmosphere, and applies the current to a
polymerizable substance. In the coated metal sheet of the present invention, any
5 apparatus may be used as long as the electron beam curable coating film can be
sufficiently cured and desired resistance weldability, corrosion resistance, and
moldability can be obtained. In general, the acceleration voltage of the electron
beam absorbed by th~ coating film influences the depth to which the. electron beam
permeates through the coating film and the absorbed dose influences the rate of
10 polymerization (the curability of the coating film); but the conditions of electron
beam irradiation are not particularly limited as long as the electron beam curable
coating .film can . be. suffkiently cured and . desired corrosion resistance. and
moldability can be obtained. However, in the case of radical polymerization with
an electron beam, the presence of even a minute amount of oxygen causes
15 deactivation and crosslinking reaction inhibition due to the addition of oxygen to the
generated radicals, and makes curing insufficient; hence, electron beam irradiation is
performed preferably in an inert gas atmosphere in which the oxygen concentration
is 500 ppm or less. Examples of the inert gas used herein include nitrogen gas,
carbon dioxide gas, and argon gas, a mixed gas of these, and the like.
20 [Examples]
[0118]
Example I
The present invention will now be specifically described with Example I
using a water-based coating composition.
25 [0119]
1. Preparation of metal sheet
The following five types of zinc-based plated steel sheets were prepared,
and were dipped in an aqueous solution at 40°C containing 2.5 mass% of a waterbased
alkaline degreasing agent (FC-301 produced by Nihon Parkerizing Co.,Ltd.)
30 for 2 minutes to degrease the surface, and then water washing and drying were
performed; thus, metal sheets for coating were formed.

Claim 1
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CLAIMS
A coated metal sheet for automobile comprising:
a metal sheet; and
PCT/JP2015/077845
a coating film (a) present on at least one surface of the metal sheet,
wherein the coating film (a) contains
an organic resin (A),
electrically conductive pigments (B), and
anti-corrosion pigments (C), and
a Matiens micro-hardness HM at -20°C of the surface of the coating film (a)
IS 10 to 200 (mg/mm2
) at 20 points or more when measured at 100 points, and a
Mmiens micro-hardness HM at 40°C of the surface of the c0ating film (a) i~ 200 to . .
200,000 (mg/mm2
) at 5 points or more when measured at 100 points.
15 Claim 2
20
25
30
The coated metal sheet for automobile according to claim 1, wherein a glass
transition temperature Tg of the organic resin (A) is -80°C to -20°C.
Claim 3
The coated metal sheet for automobile according to claim 1, wherein the
orgamc resin (A) is selected from the group consisting of a polyester resm, a
polyurethane resin, md an acrylic resin, and a modified product thereof.
Claim 4
The coated metal sheet for automobile according to claim I, wherein the
electrically conductive pigments (B) are non-oxide ceramic particles with an
electrical resistivity at 25°C of 0.1 x 10·6 to 185 x 10·6 Ocm, the electrically
conductive pigments being at least one selected fi·om a boride, a carbide, a nitride,
and a silicide.
Claim 5
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The coated metal sheet for automobile according to claim I, wherein the
coating film (a) contains 0.5 vol% to 65 vol% of the electrically conductive pigments
(B).
5 Claim 6
10
15
The coated metal sheet for automobile according to claim 1, wherein the
anti-corrosion pigments (C) contain
.one or more ~elected from a compound capable of releasing a silicate ion, a
phosphate ion, a vanadate ion, a tungstate ion, or a molybdate ion,
particles containing a metal element selected from the group consisting of Si,
Ti, AI, and Zr, or
both thereof. · .... ~- ,.,,.,_ :.
Claim 7
The coated metal sheet for automobile according to claim 1, wherein the
coating film (a) contains 1 vol% to 40 vol% of the anti-corrosion pigments (C).
Claim 8
The coated metal sheet for automobile according to claim 1, comprising, in
20 the coating film, granular particles (D) with a Martens hardness at 40°C of 200
mg/mm2 to 200,000 mg/mm2
.
Claim 9
An automobile component formed by processing and shaping the coated
25 metal sheet for automobile according to claim 1.
Claim 10
An automobile component formed by further applying .one or more of an
electrodeposition coating layer, an intetmediate coating layer, and an topcoat layer to
30 the automobile component according to claim 9.