JP2008149607A - Clear-coated stainless steel plate and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a clear-coated stainless steel plate prevented from the peeling of a clear-coated film, and its manufacturing method. <P>SOLUTION: The clear-coated stainless steel plate 10 has a stainless steel base plate 11, the chemical treatment coated film 12 formed on one side of the stainless steel base plate 11 and the clear-coated film 13 formed on the surface of the chemical treatment coated film 12 and the area ratio of the surface oil-contaminated part of the stainless steel base plate 11 is 2% or below. The clear-coated stainless steel plate is manufactured by joining the coils of two stainless steel base plates 11, subsequently subjecting the joined coils to degreasing treatment, coating the degreased coils with a chemical treatment liquid to form the chemical treatment coated film 12 and coating the surface of the chemical treatment coated film 12 with clear coat to form the clear-coated film 13. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a clear-coated stainless steel sheet having a clear coating film and a method for producing the same.

In recent years, a clear-coated stainless steel sheet in which a clear coating film is formed on the surface of a stainless steel sheet original plate via a chemical conversion coating film is sometimes used as a housing material for home appliances and electronic devices (Patent Documents 1 to 5). reference).
JP 2001-149860 A JP 2001-316845 A JP 2003-154309 A JP 2005-153168 A JP 2006-142642 A

Usually, before forming a clear coated stainless steel sheet into a desired shape, a protective film may be attached to the surface of the clear coating film. However, when the protective film is peeled off after molding, the clear coating film may be peeled off from the stainless steel sheet original plate together with the protective film. In particular, exfoliation was likely to occur in severe press forming conditions, for example, press forming with complex shapes of clear-coated stainless steel sheets, deep drawing in integral forming of large panels, and bending with a small curvature radius. . When the chemical conversion coating film and the clear coating film are peeled off, the appearance is impaired, and the stainless steel plate becomes easily rusted. Therefore, a clear coated stainless steel plate in which the clear coating film is prevented from peeling is desired.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a clear-coated stainless steel sheet in which peeling of the clear coating film after forming is prevented and a method for producing the same.

  The inventor investigated the cause of peeling of the chemical conversion coating and the clear coating when a clear-coated stainless steel sheet was formed. As a result, the Joiner oil (hereinafter referred to as oil) used in the coil joining process when producing the clear coated stainless steel plate remains on the surface of the stainless steel plate, and the remaining oil causes peeling. I found it. In particular, when a stainless steel plate is wound in a coil shape, the oil is transferred to a portion where no oil adheres, and the portion contaminated with the oil spreads, and it is found that peeling is more likely to occur. It was. And based on the knowledge, as a result of investigating the clear coated stainless steel sheet in which the chemical conversion coating film and the clear coating film are difficult to peel, the following clear coated stainless steel sheet and the manufacturing method thereof were invented.

That is, the present invention includes the following configurations.
[1] A stainless steel sheet original plate, a chemical conversion coating film formed on one surface of the stainless steel sheet original plate, and a clear coating film formed on the surface of the chemical conversion coating film,
A clear-coated stainless steel sheet, characterized in that the area ratio of oil-contaminated parts on the surface of the stainless steel sheet is 2% or less.
[2] The chemical conversion coating is a coating containing one or both of an aminosilane-based silane coupling agent and an epoxysilane-based silane coupling agent, and the adhesion amount of the chemical conversion coating is ² to 50 mg / m ^2. And
The clear coating film has a crosslinkable functional group, and is a thermosetting resin composition in which an acrylic resin having a glass transition point of 30 to 90 ° C. and a number average molecular weight of 3000 to 50000 is crosslinked with a blocked isocyanate compound. The clear-coated stainless steel sheet according to [1].
[3] The clear coating according to [2], wherein the clear coating film contains 0.25 to 10 parts by mass of a polyolefin-based wax with respect to 100 parts by mass of the solid material of the thermosetting resin composition. Stainless steel sheet.
[4] The clear coated stainless steel sheet according to [2] or [3], wherein the acrylic resin in the clear coating film is also crosslinked with an amino resin.
[5] The clear coating film contains 2 to 10 parts by mass of silica sol with respect to 100 parts by mass of the solid material of the thermosetting resin composition, according to any one of [2] to [4]. Clear-coated stainless steel sheet.
[6] The clear coating film contains 0.5 to 5 parts by mass of amorphous silica with respect to 100 parts by mass of the solid of the thermosetting resin composition [2] to [5] A clear-coated stainless steel sheet according to any one of the above.
[7] The clear coated stainless steel plate according to any one of [2] to [6], wherein the chemical conversion coating film contains 0.1 to 30% by mass of chain-like water-dispersible silica.
[8] After joining the coils of the two stainless steel plate, and then degreasing, apply a chemical conversion liquid to form a chemical conversion coating film, and apply a clear coating on the surface of the chemical conversion coating film. A method for producing a clear-coated stainless steel sheet, characterized by forming a clear coating film.

The clear-coated stainless steel sheet of the present invention is prevented from peeling off the clear coating film after forming.
According to the method for producing a clear coated stainless steel sheet of the present invention, it is possible to produce a clear coated stainless steel sheet in which peeling of the clear coating film after forming is prevented.

(Clear coated stainless steel sheet)
An embodiment of the clear coated stainless steel sheet of the present invention will be described.
FIG. 1 shows a clear-coated stainless steel sheet according to this embodiment. The clear-coated stainless steel plate 10 of the present embodiment was formed on the surface of the stainless steel plate 11, the chemical conversion coating 12 formed on one surface of the stainless steel plate 11, and the surface of the chemical conversion coating 12. It has a clear coating film 13.

The stainless steel plate 11 in the clear coated stainless steel plate 10 has a total area ratio of oil-contaminated parts on the surface of 2% or less, and preferably 1% or less. When the area ratio of the oil-contaminated portion on the surface of the stainless steel plate 11 is 2% or less, peeling of the chemical conversion coating film 12 and the clear coating film 13 can be prevented.
Here, the area ratio of the oil-contaminated portion is obtained as follows by a normal image analysis apparatus.
First, a part of the surface of the stainless steel plate 11 is photographed with a scanning electron microscope (SEM), and the obtained image is binarized into a black oil-contaminated part and other non-contaminated parts, and the entire image measurement is performed. Obtain the percentage of the area of the oil contaminated part relative to the area. This is performed at a plurality of locations (three locations), and the average value thereof is defined as the area ratio of the oil contaminated portion.
FIG. 2 shows the relationship between the area ratio of oil stains on various clear-coated stainless steel sheets and clear coating film peeling. When the oil stain area ratio of the stainless steel plate before clear coating is 2% or less, peeling at the time of processing the clear coating film is remarkably reduced. In addition, the measuring method of the area ratio of the oil stain in the illustrated example is a method described in Examples described later.

[Chemical conversion coating]
As the chemical conversion coating film 12, a coating film containing one or both of an aminosilane-based silane coupling agent and an epoxysilane-based silane coupling agent is preferable. If the chemical conversion coating film 12 containing these silane coupling agents is present between the stainless steel plate 11 and the clear coating 13, the chromate-free and non-polluting and the stainless steel plate 11 and the clear coating are applied. Adhesiveness with the film 13 can be increased.
Here, as the aminosilane coupling agent, for example, N-2 (aminoethyl) 3-aminopropylmethyldimethoxysilane, N-2 (aminoethyl) 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane Etc.
Examples of the epoxy-based silane coupling agent include 2- (3,4 epoxycyclohexyl) ethyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, and the like.

The adhesion amount of the chemical conversion coating film 12 is preferably ² to 50 mg / m ² . When the adhesion amount of the chemical conversion coating film 12 is less than 2 mg / m ² , the gloss and corrosion resistance are liable to decrease, and when the adhesion amount exceeds 50 mg / m ² , blisters are formed on the coating film surface after the boiling water test. Sometimes. The upper limit with the preferable adhesion amount of the chemical conversion coating film 12 is 30 mg / m < ² >, More preferably, it is 10 mg / m < ² >.
The adhesion amount of the chemical conversion coating film 12 can be determined by measuring the amount of SiO ₂ by fluorescent X-ray analysis.

The chemical conversion coating film 12 of the present invention preferably contains chain-like water-dispersible silica in that the gloss of the clear-coated stainless steel sheet 10 can be increased.
The content of the chain water-dispersible silica in the chemical conversion coating film 12 is preferably 0.1 to 30% by mass (solid content ratio). If the content of the chain water-dispersible silica is less than 0.1% by mass, the effect of improving the glossiness is insufficient, and if the content exceeds 30% by mass, the chemical conversion treatment liquid used for forming the chemical conversion coating film 12 is used. May be less stable.

As the chain water-dispersible silica, those having a small amount of sodium are preferably used. Examples of commercial products of chain-like water-dispersible silica include Snowtex UP, Snowtex OUP (manufactured by Nissan Chemical Industries, Ltd.) and the like.
In addition to the chain water-dispersible silica, spherical water-dispersible silica is known as the water-dispersible silica, but high gloss cannot be obtained even when spherical water-dispersible silica is contained. The reason why chain water-dispersible silica is suitable is not clear, but it is considered that it is because of its good film formability, good bondability, and high viscosity and high film-forming gel property.

  In order to further improve the corrosion resistance, the chemical conversion coating film 12 includes phosphoric acids such as phosphates, condensed phosphoric acid, polyphosphoric acid, metaphosphoric acid, pyrophosphoric acid or salts thereof, acrylic resin, urethane resin, epoxy resin, phenol. Resins such as resin, polyester, polyolefin, and alkyd resin may be included.

[Clear coating]
The clear coating film 13 in the present embodiment is a coating film containing a thermosetting resin composition such as an acrylic resin, a urethane resin, an epoxy resin, a phenol resin, or a fluororesin.
The thermosetting resin composition contained in the clear coating film 13 is preferably a resin obtained by crosslinking an acrylic resin having a crosslinkable functional group (hereinafter abbreviated as “acrylic resin”) with a blocked isocyanate compound.
Here, the crosslinkable functional group is one or more functional groups selected from a hydroxyl group, a carboxy group, an alkoxysilane group, and the like. The acrylic resin preferably has two or more crosslinkable functional groups per molecule.

The acrylic resin is a copolymer of at least one non-functional acrylic monomer and at least one functional monomer.
Nonfunctional acrylic monomers include, for example, methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, methacrylic acid Examples include aliphatic acrylates or cyclic acrylates such as n-butyl, n-hexyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, and lauryl methacrylate.
Examples of the functional monomer include a monomer having a hydroxyl group, a monomer having a carboxy group, and a monomer having an alkoxysilane group.

  Examples of the monomer having a hydroxyl group include hydroxyalkyl esters such as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, hydroxypropyl acrylate, and hydroxypropyl methacrylate, and lactone-modified hydroxyl group-containing acrylic monomers (Daicel Chemical). Industrial trade name Plaxels FM1-5, FA-1-5).

  Examples of the monomer having a carboxy group include acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid and the like.

  Examples of the monomer having an alkoxysilane group include vinyltrimethoxysilane, vinyltriethoxysilane, methacryloxypropyltrimethoxysilane, and the like.

  Other monomers other than the non-functional acrylic monomer and the functional monomer may be copolymerized in the acrylic resin. Examples of other monomers include methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, n-butyl vinyl ethers; styrenes such as styrene and α-methyl styrene; acrylamide, N-methylol acrylamide, diacetone acrylamide, and the like. Examples include acrylamide monomers.

The glass transition point of the acrylic resin is preferably 30 to 90 ° C, and more preferably 50 to 90 ° C. When the clear coated stainless steel sheet 10 is continuously pressed, friction and processing heat are generated, and the surface temperature rises to 80 to 100 ° C. Therefore, when the glass transition point of the acrylic resin is less than 30 ° C., the clear coating film 13 May soften and adhere to the mold. In addition, when the glass transition temperature of the acrylic resin exceeds 90 ° C., pinholes and insufficient leveling tend to occur.
In order to set the glass transition temperature of the acrylic resin within the above range, the composition of the acrylic resin may be appropriately selected.

The number average molecular weight of the acrylic resin is preferably 3000 to 50000, and more preferably 4000 to 10,000. When the number average molecular weight of the acrylic resin is less than 3000, the reactivity with the blocked isocyanate compound becomes low, and the clear coating film 13 is difficult to form. When the acrylic resin exceeds 50000, the solvent solubility becomes low. It becomes difficult to obtain.
The number average molecular weight of the acrylic resin can be adjusted by conditions (for example, polymerization temperature, type and amount of polymerization initiator, etc.) when the acrylic resin is produced.

A blocked isocyanate compound which is a crosslinking agent for crosslinking an acrylic resin is a compound having two or more isocyanate groups in one molecule. Specifically, aromatic diisocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate and naphthalene diisocyanate, aliphatic diisocyanates such as hexamethylene diisocyanate and dimer acid diisocyanate, alicyclic diisocyanates such as isophorone diisocyanate and cyclohexane diisocyanate, Polyisocyanate burette type adducts, isocyanuric ring type adducts, etc., blocked with blocking agents such as phenols, oximes, active methylenes, ε-caprolactams, triazoles, pyrazoles, etc. It is done. An organotin catalyst such as dibutyltin dilaurate is used as a dissociation accelerator for the blocking agent.
Examples of commercially available blocked isocyanate compounds include Desmodur BL1100, BL1265MPA / X, VPLS2253, BL3475BS / SN, BL3272MPA, BL3370MPA, BL4265SN, Desmosum 2170, Sumidur 3175 (manufactured by Sumika Bayer Urethane Co., Ltd.), Duranate. 17B-60PX, TPA-B80X, MF-B60X, MF-K60X (manufactured by Asahi Kasei Chemicals Corporation), Barnock DB-980K, D-550, B3-867, B7-887-60 (all, Dainippon Ink and Chemical Kogyo Co., Ltd.), Coronate 2515, 2507, 2513 (Nippon Polyurethane Industry Co., Ltd.). These blocked isocyanate compounds may be used alone or in combination.

The acrylic resin is preferably cross-linked using not only the above-mentioned blocked isocyanate compound but also an amino resin (melamine resin) as the clear coating film 13 becomes hard and the wrinkle resistance becomes higher. .
Amino resin is a general term for resins modified with alcohol by addition reaction of amino compounds (melamine, guanamine, urea) and formaldehyde (formalin). Specific examples include melamine resin, benzoguanamine resin, urea resin, butylated urea resin, butylated urea melamine resin, glycoluril resin, acetoguanamine resin, cyclohexylguanamine resin, and the like. Among these, melamine resin is preferable from the viewpoints of fingerprint stain resistance, wrinkle resistance, and chemical resistance.
Melamine resins are classified into, for example, methylated melamine resins, n-butylated melamine resins, isobutylated melamine resins, mixed alkylated melamine resins, and the like depending on the type of alcohol to be modified.

Specifically, as the methylated melamine resin, Cymel 300, 301, 303, 350, 370, 771, 325, 327, 703, 712, 715, 701, 267, 285, 232, 235, 236, 238, 211 254, 204, 212, 202, 207 (Mitsui Cytec Co., Ltd.), LUWIPAL 063, 066, 068, 069, 072, 073 (BASF), Super Becamine L-105 (Dainippon Ink, Ltd.) Chemical Industry Co., Ltd.), Melan 522, 523, 620, 622, 623 (above, manufactured by Hitachi Chemical Co., Ltd.).
As n-butylated melamine resin, My Coat 506, 508 (Mitsui Cytec Co., Ltd.), Uban 20SB, 20SE, 21R, 22R, 122, 125, 128, 220, 225, 228, 28-60, 20HS 2020, 2021, 2028, 120 (above, manufactured by Mitsui Chemicals), PLASTOPAL EBS 100A, 100B, 400B, 600B, CB (above, manufactured by BASF), Super Becamine J-820, L-109, L-117 , L-127, L-164 (manufactured by Dainippon Ink & Chemicals, Inc.), Melan 21A, 22, 220, 2000, 8000 (manufactured by Hitachi Chemical Co., Ltd.), Tesazine 3020, 3021, 3036 (and above) And Hitachi Chemical Polymer Co., Ltd.).
Examples of isobutylated melamine resins include Yuban 60R, 62, 62E, 360, 361, 165, 166-60, 169, 2061 (manufactured by Mitsui Chemicals, Inc.), Super Becamine G-821, L-145, L- 110, L-125 (above, Dainippon Ink & Chemicals, Inc.), PLASTOPAL EBS 4001, FIB, H731B, LR8824 (above, made by BASF), Melan 27, 28, 28D, 245, 265, 269, 289 (above , Hitachi Chemical Co., Ltd.), Tesazine 3027, 3028, 3029, 3030, 3037 (above, Hitachi Chemical Polymer Co., Ltd.) and the like.
Examples of the mixed alkylated melamine resin include Cymel 267, 285, 232, 235, 236, 238, 211, 254, 204, 212, 202, 207 (manufactured by Mitsui Cytec Co., Ltd.).
An amino resin may be used individually by 1 type, and may use 2 or more types together.

Other components The clear coating film 13 preferably contains a polyolefin wax. If the clear coating film 13 contains a polyolefin-based wax, the lubricity becomes higher than that when an oil-based lubricant or the like is applied, and the clear coated stainless steel sheet 10 is excellent in workability.

Examples of the polyolefin wax include hydrocarbon waxes such as paraffin, microcrystalline, polyethylene, and polyethylene-fluorine.
When the clear coated stainless steel plate 10 is processed, the coating film temperature rises due to heat generated by processing and frictional heat, and therefore the melting point of the polyolefin wax is preferably 70 to 160 ° C. When the melting point of the polyolefin wax is less than 70 ° C., it may be softened and melted during processing, and the excellent characteristics as a solid lubricating additive may not be exhibited. When the melting point of the polyolefin wax exceeds 160 ° C., hard particles are present on the surface and the frictional characteristics are deteriorated, so that high workability may not be obtained.
The acid value of the polyolefin wax is preferably 0-30. If the acid value of the polyolefin wax exceeds 30, the compatibility with the thermosetting resin composition increases, and the polyolefin wax does not easily float on the surface of the coating film. May be insufficient.

  The polyolefin wax content in the clear coating film 13 is preferably 0.25 to 10 parts by mass with respect to 100 parts by mass of the solid material of the thermosetting resin composition. If the content of the polyolefin wax is less than 0.25 parts by mass, the processability may be insufficient, and if it exceeds 10 parts by mass, unevenness occurs on the surface of the coated film, and the appearance of the clear coated stainless steel sheet 10 May be damaged.

The clear coating film 13 preferably contains silica sol because it has higher hardness and scratch resistance, and higher fingerprint stain resistance.
Silica sol is silica particles composed of nanometer-sized particles.

  The content of the silica sol in the clear coating film 13 is preferably 2 to 10 parts by mass and more preferably 3 to 8 parts by mass with respect to 100 parts by mass of the solid material of the thermosetting resin composition. When the content of the silica sol is less than 2 parts by mass, the scratch resistance and hardness tend to be insufficient, and when it exceeds 10 parts by mass, the workability of the clear coated stainless steel sheet 10 tends to be lowered.

  The clear coating film 13 preferably contains amorphous silica. If the clear coating film 13 contains amorphous silica, the resistance to fingerprint contamination can be further improved. This is considered to be based on the porosity and surface hydrophilicity of amorphous silica.

  Amorphous silica is a fluid powder having porosity. Specific examples of the amorphous silica include silicia 250, 250N, 256, 256N, 310P, 320, 350, 370, 380, 420, 430, 440, 450, 470, 435, 445, 436, 446, 456, 476. 530, 550, 710, 730, 740, 770, 780 (above, manufactured by Fuji Silysia Chemical Ltd.), Mizukasil P-801, P-802, P-526, P-527, P-603, P-604, P-554A, P-73, P-78A, P-78D, P-78F, P-707, P-740, P-752, P-50, P-766 (manufactured by Mizusawa Chemical Co., Ltd.), Carplex FPS-1, FPS-2, FPS-3, FPS-4, FPS-5, FPS-101, CS-5, CS-7, CS-8, CS-701, C -801 (manufactured by Shionogi & Co., Ltd.), and the like. Amorphous silica may be used alone or in combination of two or more.

  The content of the amorphous silica in the clear coating film 13 is preferably 0.5 to 5 parts by mass, and 1 to 4 parts by mass with respect to 100 parts by mass of the solid material of the thermosetting resin composition. It is more preferable. When the content of amorphous silica is less than 0.5 parts by mass, the antifouling resistance to fingerprints is reduced. Fingerprints are easily attached when directly touching the coating film, and fingerprints are difficult to remove even if wiped off with gauze. Tend to be. When the content of amorphous silica exceeds 5 parts by mass, the gloss of the clear coating film 13 becomes too low, and the appearance of the clear coated stainless steel sheet 10 tends to be impaired.

  The clear coating film 13 may further contain a leveling agent, an antifoaming agent, an antioxidant, an ultraviolet absorber, a matting agent, a silane coupling agent, and the like as additives. Moreover, an epoxy resin, a silicon resin, a fluororesin, polyester, etc. may be included.

  The film thickness of the clear coating film 13 is preferably 1 to 10 μm. When the film thickness of the clear coating film 13 is less than 1 μm, the function of the clear coating film is not sufficiently exhibited and workability is deteriorated. When the film thickness exceeds 10 μm, the function of the clear coating film is saturated and it may be difficult to form the clear coating film.

  In the clear-coated stainless steel plate 10 described above, the oil-contaminated portion on the surface of the stainless steel plate 11 is less than a specific range, so that the adhesion of the chemical conversion coating film 12 is excellent. As a result, the chemical conversion coating film 12 and the clear coating film 13 are difficult to peel from the stainless steel plate 11. Such a clear-coated stainless steel sheet 10 is suitable for applications such as press molding with a complicated shape, deep drawing in integral molding of a large panel, and bending with a small radius of curvature.

(Manufacturing method of clear coated stainless steel sheet)
Next, an embodiment of a method for producing the clear coated stainless steel sheet of the present invention will be described. However, the manufacturing method of the clear coated stainless steel sheet 10 is not limited to this embodiment.
In the manufacturing method of this embodiment, first, two coils of stainless steel plate are joined. Thereafter, the surface of the stainless steel plate 11 is washed with an aqueous solution of an alkaline compound, a solvent, or the like and degreased.
Examples of the alkali compound used for the degreasing treatment include sodium hydroxide, sodium carbonate, sodium silicate, sodium phosphate and the like.
Examples of the solvent include industrial gasoline, kerosene, light oil, benzene, toluene, xylene, solvent naphtha, methyl ethyl ketone, acetone, 1,1,1-trichloroethane, trichlorotrifluoroethane, trichloroethylene, perchloroethylene, methylene chloride (methylene chloride). ), Carbon tetrachloride, methanol, isopropanol and the like.
Examples of the cleaning method include a method of spraying an aqueous alkali solution or solvent onto the surface of the stainless steel plate original plate 11 by spraying, a method of immersing the stainless steel plate original plate 11 in a container storing the alkaline aqueous solution or solvent, and the like.

It is disclosed in Patent Documents 4 and 5 that the stainless steel plate is degreased before chemical conversion treatment. However, in any of the prior documents including Patent Documents 4 and 5, the correlation between degreasing and the adhesion of the clear coating film, that is, the peeling resistance of the coating film is not pointed out. That is, conventionally, the relationship between the oil stain on the stainless steel plate and the peel resistance of the clear coating film after processing into a product has not been known.
What is important in the actual machine manufacturing process is that oil stains on the stainless steel plate do not occur even after joining the two coils. Therefore, it is very important to perform a degreasing process after coil joining.

Next, a chemical conversion treatment liquid containing one or both of an aminosilane coupling agent and an epoxysilane coupling agent is applied to the degreased stainless steel plate 11 and dried to form a chemical conversion coating film 12.
A commercial item can be used as said chemical conversion liquid. Examples of commercially available chemical conversion treatment liquid include Palcoat E305, 3750, 3751, 3753, 3756, 3757, 3970 (manufactured by Nippon Parkerizing Co., Ltd.), Alsurf 440 (manufactured by Nippon Paint Co., Ltd.), and the like.
As a method for applying the chemical conversion liquid, for example, spraying, roll coating, bar coating, curtain flow coating, electrostatic coating, or the like can be employed.
The drying temperature (surface temperature) of the chemical conversion liquid is preferably 60 to 140 ° C.

Next, a clear paint is applied to the surface of the chemical conversion coating film 12 and dried (baked). During this drying, the acrylic resin is crosslinked with the blocked isocyanate compound to form a thermosetting resin composition. Thereby, the clear coating film 13 containing a thermosetting resin composition is formed, and the clear coating stainless steel plate 10 is obtained.
Here, the clear paint contains an acrylic resin, a blocked isocyanate compound, and a solvent as essential components, and includes a curing catalyst for the blocked isocyanate compound, an amino resin, a polyolefin wax, silica sol, amorphous silica, an acrylic resin bead, and the like. It is a paint containing as an optional component.

  The ratio between the acrylic resin and the blocked isocyanate in the clear coating is preferably such that the isocyanate group is 0.1 to 2.0 moles per mole of the crosslinkable functional group of the acrylic resin. It is more preferable that the isocyanate group has a ratio of 0.1 to 1.0 mol with respect to 1 mol of the functional group, and the isocyanate group has an amount of 0.2 to 0.00 with respect to 1 mol of the crosslinkable functional group of the acrylic resin. A ratio of 8 mol is particularly preferable.

The clear paint can contain a curing catalyst for a blocked isocyanate compound in order to shorten the formation time of the clear coating film 13.
As a curing catalyst for the blocked isocyanate compound, di-n-butyltin oxide, n-dibutyltin chloride, di-n-butyltin dilaurate, di-n-butyltin diacetate, di-n-octyltin oxide, di- Examples include n-octyltin dilaurate and tetra-n-butyltin.

  When the clear paint contains an amino resin in addition to the blocked isocyanate compound as a crosslinking agent, the content of the amino resin in the clear paint is preferably 10 to 40 parts by mass with respect to 100 parts by mass of the acrylic resin solid content. More preferably, it is 15-30 mass parts. If the content of the amino resin in the clear paint is less than 10 parts by mass, the scratch resistance cannot be sufficiently improved, and if it exceeds 40 parts by mass, it becomes difficult to form the clear coating film 13. There is.

In addition, when the clear coating contains an amino resin, the curing time (baking time) of the acrylic resin tends to be long, and therefore a curing catalyst for the amino resin can be contained. If the clear paint contains an amino resin curing catalyst, the curing time can be shortened.
As the curing catalyst for the amino resin, for example, a sulfonic acid catalyst or an amine catalyst is used, and a p-toluenesulfonic acid catalyst is preferable because it is particularly effective for shortening the curing time.
The amount of the curing catalyst for the amino resin is preferably 0.5 to 5 parts by mass, and is 1 to 2 parts by mass when the total amount of the acrylic resin, the blocked isocyanate compound and the amino resin is 100 parts by mass. It is more preferable.
If the amount of the curing catalyst for the amino resin is less than 0.5 parts by mass when the total amount of the acrylic resin, the blocked isocyanate compound and the amino resin is 100 parts by mass, the curing time may not be shortened. When it exceeds the mass part, the workability of the clear coated stainless steel plate 10 obtained tends to be low.

  When the clear paint contains a polyolefin wax, the polyolefin wax preferably has an average particle size of 0.1 to 7.0 μm. If the average particle diameter of the polyolefin wax exceeds 7.0 μm, the dispersibility of the polyolefin wax in the clear coating film 13 tends to be low, and if it is less than 0.1 μm, the resulting clear coated stainless steel sheet 10 There is a tendency that the workability of the steel becomes low.

When the clear paint contains silica sol, the clear paint may be prepared by adding organosilica sol.
The organosilica sol is a colloidal solution in which nanometer-sized colloidal silica is stably dispersed in an organic solvent.
The organosilica sol includes MA-ST-M, IPA-ST, EG-ST, EG-ZL, NPC-ST, DMAC-ST, DMAC-ST-ZL, XBA-ST, MIBK-ST (and above, Nissan Chemical Industries). Etc.). An organosilica sol may be used individually by 1 type, and may use 2 or more types together.

  In the manufacturing method of the clear coated stainless steel plate 10 described above, since the surface of the stainless steel plate original plate 11 is degreased, the chemical conversion coating film 12 can be formed on the surface of the stainless steel plate original plate 11 with high adhesion. Therefore, the clear coated stainless steel sheet 10 in which peeling of the chemical conversion coating film 12 and the clear coating film 13 is prevented can be manufactured.

(Production Example 1)
In a four-necked flask equipped with a thermometer, reflux condenser, stirrer, dropping funnel, and nitrogen gas inlet tube, toluene and butyl acetate are added in the amounts shown in Table 1, and the temperature is raised to 110 ° C. and nitrogen gas is supplied. The mixture was stirred while blowing, and a mixture of methyl methacrylate, styrene, n-butyl methacrylate, 2-hydroxyethyl methacrylate, methyl acrylate, and azobisisobutyronitrile (AIBN) was added dropwise over 3 hours. After the addition was completed, AIBN was further added and reacted at the same temperature for further 3 hours to obtain an acrylic resin solution having a nonvolatile content of 50%.
Next, a block isocyanate “Desmodur VPLS 2253” (manufactured by Sumika Bayer Urethane Co., Ltd., NCO content 10.5% by mass) as a curing agent and a melamine resin (manufactured by Mitsui Cytec Co., Ltd.) as an amino resin are added to the acrylic resin solution. The clear paint was obtained by blending Cymel 327) as shown in Table 1.
Next, 4 parts by mass of polyethylene wax was added to the clear paint with respect to 100 parts by mass of the solid material of the thermosetting resin composition.

  Also, two stainless steel plate precursors (SUS304 No. 4 polished finish product) were joined, and then the surface of the joined stainless steel plate precursor was FC-L4434 (sodium silicate 45-50% by mass) manufactured by Nihon Parkerizing. And degreasing treatment with trisodium phosphate (25-30% by mass), surfactant (5-10% by mass, condensed sodium phosphate (5-10% by mass)). The area ratio of the oil-contaminated portion on the surface of the stainless steel plate after degreasing was 0.5% or less. The area ratio of the oil-contaminated part was determined by image analysis using LUZEX-F manufactured by Nireco. In addition, the area ratio of the oil-contaminated part was calculated | required from the result of having observed the peeling surface after peelability evaluation of the clear coating film mentioned later with the scanning electron microscope (SEM).

Next, a chemical conversion treatment solution containing an aminosilane coupling agent is applied to one side of the degreased stainless steel plate by a roll coater and dried so that the surface temperature becomes 100 ° C., and the SiO ₂ adhesion amount is 10 mg / m ^2. The chemical conversion coating film was formed.
Next, a clear paint was applied to the surface of the chemical conversion coating film with a bar coater, baked to a surface temperature of 193 ° C., and a clear coating film having a thickness of 3 μm was formed to obtain a clear coated stainless steel sheet.

About the obtained clear coating stainless steel plate, the peelability of the chemical conversion treatment film and clear film after forming was evaluated. The evaluation results are shown in Table 2.
(Peelability evaluation method)
The clear coated stainless steel plate was bent under the condition of a curvature radius of 4 mm, and an adhesive tape (C330 manufactured by Hitachi Chemical Co., Ltd.) was attached to the bent portion, and then the adhesive tape was peeled off. And the presence or absence of peeling of the chemical conversion coating film and clear coating film after peeling off an adhesive tape was observed visually.

(Production Example 2)
A clear-coated stainless steel sheet was obtained in the same manner as in Production Example 1 except that the surface was not degreased and a stainless steel sheet original plate with an oil contaminated area ratio of 2.054% was used. The peelability was evaluated in the same manner as in Production Example 1. The evaluation results are shown in Table 2.

The clear coated stainless steel plate of Production Example 1 in which the surface of the stainless steel plate was degreased was prevented from peeling off the chemical conversion coating film and the clear coating film.
In the clear-coated stainless steel plate of Production Example 2 in which the surface of the stainless steel plate was not degreased, peeling of the chemical conversion coating film and the clear coating film was not prevented.

It is sectional drawing which shows one embodiment of the clear coated stainless steel plate of this invention. It is a figure which shows the relationship between the area ratio of the oil stain of the clear coating stainless steel plate of this invention, and clear coating film peeling.

Explanation of symbols

  10 Clear painted stainless steel plate, 11 Stainless steel plate, 12 Chemical conversion coating, 13 Clear coating

Claims (8)

A stainless steel plate, a chemical conversion coating film formed on one or both surfaces of the stainless steel plate, and a clear coating film formed on the surface of the chemical conversion coating;
A clear-coated stainless steel sheet, characterized in that the area ratio of oil-contaminated parts on the surface of the stainless steel sheet is 2% or less. The chemical conversion coating is a coating containing one or both of an aminosilane-based silane coupling agent and an epoxysilane-based silane coupling agent, and the amount of the chemical conversion coating is ² to 50 mg / m ² ,
The clear coating film has a crosslinkable functional group, and is a thermosetting resin composition in which an acrylic resin having a glass transition point of 30 to 90 ° C. and a number average molecular weight of 3000 to 50000 is crosslinked with a blocked isocyanate compound. The clear-coated stainless steel sheet according to claim 1.   The clear coated stainless steel sheet according to claim 2, wherein the clear coating film contains 0.25 to 10 parts by mass of a polyolefin-based wax with respect to 100 parts by mass of the solid material of the thermosetting resin composition.   The clear-coated stainless steel sheet according to claim 2 or 3, wherein the acrylic resin in the clear coating film is also crosslinked with an amino resin.   The clear coated stainless steel sheet according to any one of claims 2 to 4, wherein the clear coating film contains 2 to 10 parts by mass of silica sol with respect to 100 parts by mass of the solid material of the thermosetting resin composition. .   The clear coating film contains 0.5 to 5 parts by mass of amorphous silica with respect to 100 parts by mass of the solid material of the thermosetting resin composition. Clear-coated stainless steel sheet.   The clear coating stainless steel sheet according to any one of claims 2 to 6, wherein the chemical conversion coating film contains 0.1 to 30% by mass (solid content ratio) of chain-like water-dispersible silica.   After joining the two stainless steel plate coils and then degreasing, a chemical conversion solution is applied to form a chemical conversion coating, and a clear coating is applied to the surface of the chemical conversion coating. A method for producing a clear-coated stainless steel sheet, comprising forming a film.

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