TWI569955B - Stainless steel plate covered with clear coat - Google Patents

Description

Colorless coated stainless steel plate Technical field

The present invention relates to a colorless coated stainless steel sheet having corrosion resistance.

The present application claims priority on Japanese Patent Application No. 2013-188828, filed on Sep.

Background technique

A colorless coated stainless steel sheet having a colorless coating film formed on the surface of the stainless steel sheet, and a high-grade appearance having a beautiful metallic luster peculiar to stainless steel can be obtained (see, for example, Patent Documents 1 and 2). Therefore, colorless coated stainless steel sheets are widely used for housings or interior materials and exterior materials of home electric appliances. Further, the colorless coated stainless steel sheet has corrosion resistance and durability as compared with a coated steel sheet having a base material such as a galvanized steel sheet classified into ordinary steel or a composite material in which the ordinary steel is bonded with a film material. The advantage of excellent sex.

From the viewpoint of cost, the coated steel sheet for household appliances uses a representative ferrite-based iron-based stainless steel such as SUS430 (18Cr). However, in the stainless steel, the ferrite-based stainless steel has a low rust-preventing power as compared with the Worstian iron-based stainless steel which is representative of SUS304 (18Cr-8Ni).

It is well known that the rust of stainless steel is caused by halide ions such as chloride ions. In household appliances such as air conditioners and electric cookers, liquids rich in salt such as seasonings are attached. Therefore, the use of household appliances having coated stainless steel sheets causes a decrease in appearance due to rust or a decrease in durability.

Further, the colorless coated stainless steel sheet used in the home appliance can be processed into a cylindrical resin shape after being bent into a cylindrical shape, and then subjected to processing such as fitting a resin molded component by the anvil joint end faces or after bending the end face portion. However, slit corrosion occurs in the anvil or the fitting.

A method of improving the corrosion resistance of a colorless coated stainless steel sheet is known as a method of adding a rust preventive pigment to a colorless paint (Patent Document 3). Although the method of using the rust preventive pigment is effective for a general paint system, since the rust preventive pigment itself has low transparency, when the rust preventive pigment is added to the colorless paint, the resulting colorless paint film will have a cloudy or hazy appearance. Therefore, the high design property of the surface appearance of the stainless steel sheet which is characteristic of the colorless coated stainless steel sheet is impaired.

Moreover, a method of improving the corrosion resistance is known as a method of coating an epoxy resin-containing primer coating having excellent corrosion resistance (Patent Document 4). However, when the primer is applied, the coating step is increased to complicate the work. Further, since the top coating layer is colorless (transparent), it can transmit ultraviolet rays satisfactorily. However, since the epoxy resin has low light resistance, the undercoating film is remarkably discolored or peeled off when used for a long period of time, and corrosion resistance is lowered.

Prior technical literature Patent literature

Patent Document 1: Japanese Patent Laid-Open No. 02-111865

Patent Document 2: Japanese Patent Laid-Open Publication No. 2002-143764

Patent Document 3: Japanese Patent No. 4027848

Patent Document 4: Japanese Patent Laid-Open Publication No. 2002-187234

Summary of invention

An object of the present invention is to provide a colorless coated stainless steel sheet which is excellent in corrosion resistance and design and can maintain corrosion resistance for a long period of time.

The present invention has the following aspects.

[1] A colorless coated stainless steel sheet having: a stainless steel sheet; a chemical conversion treatment film formed by chemical conversion treatment of at least one of the stainless steel sheets; and a colorless coating film formed on the chemical conversion treatment film Further, the chemical conversion treatment film contains a coupling agent and a liquid rust inhibitor, and the content of the liquid rust inhibitor is 10 to 250 parts by mass with respect to 100 parts by mass of the coupling agent; and the colorless coating film containing liquid The cured coating film of the thermosetting resin of the rust preventive agent is contained in an amount of 0.2 to 20 parts by mass based on 100 parts by mass of the colorless coating film from which the liquid rust preventive agent has been deducted.

[2] A colorless coated stainless steel plate comprising: a stainless steel plate; a chemical conversion treatment film formed by chemical conversion treatment of at least one of the stainless steel plates; and a colorless coating film formed on the chemical conversion treatment film Further, the chemical conversion treatment film contains a coupling agent and a liquid rust inhibitor, and the content of the liquid rust inhibitor is 10 to 250 parts by mass based on 100 parts by mass of the coupling agent.

[3] A colorless coated stainless steel plate having: a stainless steel plate; a chemical conversion treatment film formed by chemical conversion treatment of at least one of the stainless steel plates: and a colorless coating film formed on the chemical conversion treatment film Further, the colorless coating film is a cured coating film of a thermosetting resin containing a liquid rust preventive agent, and is a liquid rust inhibitor with respect to 100 parts by mass of the colorless coating film after the liquid rust inhibitor has been deducted. The content is 0.2 to 20 parts by mass.

[4] The colorless coated stainless steel sheet according to any one of [1] to [3] wherein the liquid rust inhibitor has a pH of 7.0 or more.

The colorless coated stainless steel sheet of the present invention is excellent in corrosion resistance and designability, and can maintain corrosion resistance for a long period of time.

Form for implementing the invention

Hereinafter, an embodiment of the present invention will be described.

<Colorless coated stainless steel plate>

The colorless coated stainless steel sheet according to the embodiment has a stainless steel sheet, a chemical conversion treatment film formed on at least one surface of the stainless steel sheet, and a colorless coating film formed on the surface of the chemical conversion treatment film.

The chemical conversion treatment film is a coating film containing a coupling agent.

The chemical conversion treatment film is preferably a coating film containing one or both of an amino decane decane coupling agent and an epoxy decane decane coupling agent. Between the stainless steel plate and the colorless coating film by chemical conversion containing the decane coupling agent The film can be non-polluting and non-chromic, and can improve the adhesion of the stainless steel plate and the colorless film.

Here, the amino decane-based coupling agent may, for example, be N-2 (aminoethyl) 3-aminopropylmethyldimethoxydecane or N-2 (aminoethyl) 3-amino group. Propyltriethoxydecane, 3-aminopropyltrimethoxydecane, and the like.

The epoxy decane coupling agent may, for example, be 2-(3,4 epoxycyclohexyl)ethyltrimethoxydecane, 3-glycidoxypropyltrimethoxydecane or 3-epoxypropoxy group. Propylmethyldiethoxydecane, and the like.

The amount of the chemical conversion treatment film attached to the stainless steel plate is preferably 2 to 50 mg/m ² . When the adhesion amount of the chemical conversion treatment film to the stainless steel plate is less than 2 mg/m ² , the gloss and the corrosion resistance are liable to lower, and when the adhesion amount is more than 50 mg/m ² , bubbles are generated on the surface of the coating film after the boiling water test. A preferred upper limit of the amount of the chemical conversion treatment film to the stainless steel plate is 30 mg/m ² , and more preferably 10 mg/m ² .

The amount of adhesion of the chemical conversion treatment film can be determined by measuring the amount of SiO ₂ by fluorescent X-ray analysis.

The chemical conversion treatment film of the present invention contains a liquid rust inhibitor. Here, "liquid" means that it is liquid at 10 to 40 ° C even if it is not dissolved in a solvent.

The liquid rust inhibitor may, for example, be a metal salt or an amine salt of zinc, calcium, barium or magnesium, a phosphate of a higher alcohol, an amine salt of a polyoxyalkynsulfonic acid, an organic phosphate, or a fatty acid. Amine salts and the like. These may be used alone or in combination of two or more.

The aforementioned liquid rust inhibitor is usually applied as a metal material or a metal zero. The rust preventive oil used for rust prevention, etc., is not included in the coating film.

The liquid rust preventive agent preferably has a pH of 7 or more at 25 ° C, and preferably 7 to 8 is used. When the pH of the liquid rust inhibitor is less than 7, the rust preventive force will become slightly lower. Further, there is a concern that it reacts with other components in the chemical conversion treatment liquid.

The content of the liquid rust inhibitor in the chemical conversion treatment film is 10 to 250 parts by mass, preferably 50 to 200 parts by mass, based on 100 parts by mass of the coupling agent in the chemical conversion treatment film.

When the content of the liquid rust inhibitor of the chemical conversion treatment film is less than the above lower limit value, the rust prevention effect is not sufficiently exhibited. On the other hand, when the content of the liquid rust preventive agent is larger than the above upper limit value, the rust preventive effect will rise to the apex, and even if the content is increased, it only increases the cost and does not contribute.

In the chemical conversion treatment film, the rust preventive effect is further enhanced, and the solid rust preventive agent may be contained in a range in which the transparency is not significantly lowered. The content of the solid rust inhibitor is preferably 4.0 parts by mass or less based on 100 parts by mass of the coupling agent in the chemical conversion treatment film.

The solid rust inhibitor is a solid rust inhibitor at 10 to 40 ° C.

Specific solid rust inhibitors, for example, zinc chromate, strontium chromate, lead dan, lead oxynitride, lead dicyandiamide, lead chromate, lead sulphate, calcium lead phosphate, zinc phosphate, calcium phosphate, phosphoric acid Aluminum, aluminum tripolyphosphate, calcium tripolyphosphate, zinc molybdate, calcium zinc molybdate, calcium molybdate, zinc phosphomolybdate, calcium phosphomolybdate, and the like. However, from the point of view of environmental load, it is not preferable to use a solid rust inhibitor containing chromium or lead.

(colorless film)

A colorless coating film is a hard coating film of a thermosetting resin, specifically, heat The curable resin is a coating film which is crosslinked by a crosslinking agent. The colorless coating film is usually formed as a single layer on the surface of the chemical conversion treatment film, but may be laminated in a plurality of layers.

The thermosetting resin is not particularly limited as long as it has surface hardness, transparency, and adhesion to stainless steel, and examples thereof include an acrylic resin, an alkyd resin, a polyester resin, an epoxy resin, and a fluororesin. . Among these, acrylic resin is preferred from the viewpoint of easily obtaining high surface hardness.

The acrylic resin of the present invention is polymerized with a polymer of a non-crosslinkable acrylic monomer and a crosslinkable acrylic monomer.

As the non-crosslinkable acrylic monomer, for example, methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, methyl methacrylate, and A can be used. An aliphatic or cyclic acrylate such as ethyl acrylate, isopropyl methacrylate, n-butyl methacrylate, n-hexyl methacrylate, cyclohexyl methacrylate or lauryl methacrylate.

The crosslinkable acrylic monomer may, for example, be an alkyl acrylate or an alkyl methacrylate having a crosslinkable functional group such as a hydroxyl group, a carboxyl group or an alkoxyalkyl group.

Further, the acrylic resin of the present invention may be copolymerized, if necessary, with a styrene selected from the group consisting of methyl vinyl ether, styrene, and α-methylstyrene, acrylamide, N-methylol acrylamide, and diacetone propylene oxime. One type of acrylamide-based monomer such as an amine, or two or more other monomers.

The crosslinkable acrylic monomer, the non-crosslinkable acrylic monomer, and the other monomer may be used alone or in combination of two or more.

The acrylic resin has a crosslinkable functional group such as a hydroxyl group, a carboxyl group or an alkoxyalkyl group, and may have two or more such crosslinkable functional groups in one molecule.

Further, the glass transition temperature of the acrylic resin is preferably from 30 to 90 °C. When the glass transition temperature is less than 30 ° C, the surface hardness of the colorless coating film obtained by the crosslinking reaction will become low. Further, when the processing such as press-coating of a steel sheet is performed, the coating film is softened by heat, and there is a problem that a peeled coating film called a galling adheres to the mold. On the other hand, when the glass transition temperature is more than 90 ° C, the flatness of the colorless coating film or the like tends to be low, and the appearance of the beautiful surface of the colorless stainless steel sheet itself is impaired. Further, the glass transition temperature can be measured by, for example, differential thermal analysis or the like.

The number average molecular weight of the acrylic resin is preferably from 3,000 to 50,000.

When the number average molecular weight is less than 3,000, the reactivity with the crosslinking agent is lowered, so that the crosslinking reaction is not sufficiently performed, and the resin after the reaction fails to form a film. On the other hand, when the number average molecular weight is more than 50,000, the solubility in a solvent is insufficient, and the resin solution cannot be used, and it may not be used as a coating resin.

The crosslinking agent may, for example, be a polyfunctional isocyanate compound having two or more isocyanate groups in one molecule, an amine-based resin, or a polyfunctional epoxy compound having two or more epoxy groups in one molecule. Among these, a polyfunctional isocyanate compound is preferred from the viewpoint of versatility. In particular, when the thermosetting resin is an acrylic resin, when a polyfunctional isocyanate compound is used as a crosslinking agent, the intended properties (rust resistance and design properties) are easily obtained.

The polyfunctional isocyanate compound is not particularly limited as long as it is a crosslinkable thermosetting resin. Specifically, examples of the polyfunctional isocyanate compound include toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), meta-indole diisocyanate (XDI), naphthalene diisocyanate (NDI), and the like. Aromatic diisocyanate, hexamethylene diisocyanate (HDI), etc. An alicyclic diisocyanate such as an aliphatic diisocyanate, isophorone diisocyanate (IPDI) or cyclohexane diisocyanate. From the viewpoint of sufficiently ensuring the high designability of the colorless coated stainless steel sheet to have a transparent feeling, it is preferable to refer to a non-yellowing type, and specifically, HDI, IPDI, and XDI are preferable.

The polyfunctional isocyanate compound is thermally crosslinked as a premise to suppress reactivity under non-heating, and may be a general-purpose blocked isocyanate in which an isocyanate group is sealed by a blocking agent.

Among the blocked isocyanates, the higher the dissociation temperature of the blocking agent, the lower the surface hardness of the colorless coating film. Therefore, the dissociation temperature of the blocking agent is preferably 130 ° C or less.

The amine-based resin may, for example, be a melamine resin, a urea resin or a benzoguanamine resin.

Among the amine-based resins, a melamine resin is preferred from the viewpoint of improving workability and reactivity.

The combination of the thermosetting resin and the crosslinking agent is not particularly limited, and may be appropriately selected depending on the desired workability, chemical resistance, weather resistance and the like. Each of the thermosetting resin and the crosslinking agent may be used alone or in combination of two or more.

The colorless coating film of the present invention contains a liquid rust inhibitor. By containing a liquid rust preventive agent in the colorless coating film, color retention and corrosion resistance can be maintained.

A liquid rust inhibitor contained in a colorless coating film can be used and chemical conversion The liquid rust inhibitor contained in the film is the same. Further, the liquid rust preventive agent contained in the colorless coating film is the same as the liquid rust preventive agent contained in the chemical conversion treatment film, and preferably has a pH of 7 or more at 25 ° C, and preferably 7 to 8 is preferable. When the pH of the liquid rust preventive agent is less than 7, the rust preventive force is slightly lowered. Further, there are concerns that other components in the colorless paint (for example, coloring pigments) react and other components are aggregated.

Further, when an amine-based resin is used as the crosslinking agent, the acidic rust inhibitor exhibits an effect similar to an acid catalyst, and the crosslinking reaction of the amine-based resin is excessively performed, so that the workability is deteriorated. Therefore, the use of an amine-based resin as a crosslinking agent is not preferable.

The content of the liquid rust preventive agent of the colorless coating film is 0.2 to 20.0 parts by mass, preferably 1.0 to 10.0 parts by mass, based on 100 parts by mass of the colorless coating film after the liquid rust inhibitor has been deducted, and is preferably 2.0 to 6.0. The mass portion is preferred.

When the content of the liquid rust preventive agent in the colorless coating film is less than the above lower limit value, the rust preventing effect is not sufficiently exhibited. On the other hand, when the content of the liquid rust preventive agent is larger than the above upper limit value, the rust preventive effect will rise to the apex, and even if the content is increased, it only increases the cost and does not contribute.

In the colorless coating film, in order to further improve the rust preventing effect, a solid rust preventive agent may be contained in a range in which the transparency is not significantly lowered. The content of the solid rust preventive agent is preferably 2.0 parts by mass or less based on 100 parts by mass of the colorless coating film obtained by subtracting the liquid rust preventive agent.

The solid rust preventive agent contained in the colorless coating film can be the same as the solid rust preventive agent contained in the chemical conversion treatment film.

The colorless coating film may also contain a coloring pigment, an extender pigment, a delustering agent, and a luminescent material (for example, aluminum powder, pearl pigment, glass flake, etc.). Moreover, for the purpose of adjusting the surface gloss or appearance, it is also possible to contain a resin particle in the colorless coating film. grain. Further, the colorless coating film may contain an antioxidant, a preservative, a lubricant, a conductive agent, an ultraviolet absorber, a light stabilizer, and the like.

However, the above-mentioned components which may be contained in the colorless coating film are contained in a range which does not impair the colorlessness of the colorless coating film. The component is preferably 0.1 to 18.0 parts by mass, and more preferably 0.1 to 10.0 parts by mass, based on 100 parts by mass of the colorless coating film from which the liquid rust preventive agent has been removed.

Since the colorless coating film of the present invention is colorless, the colorless coated stainless steel sheet of the present invention can exhibit a high-grade design with a beautiful appearance of stainless steel using a substrate.

Here, "colorless" means that the light transmittance in the visible light region is more than 30%. The light transmittance in the visible light region is a light transmittance measured by a spectrophotometer in a wavelength range of 380 nm to 750 nm.

When the light transmittance in the visible light region of the colorless coating film is less than 30%, the visible light can be slightly transmitted, but the stainless steel plate is hardly visible by visual observation. Therefore, it has not been possible to obtain a design that uses the beautiful appearance of stainless steel.

The visible light transmittance of the colorless coating film is preferably 40% or more, more preferably 50% or more.

Further, the most characteristic effect of the present invention is that the colorless coating film does not turbid even if it does not contain a rust preventive agent, and the transparency can be maintained. Specifically, in the colorless coating film containing the liquid rust inhibitor of the present invention, the attenuation rate of the visible light transmittance defined below is 90% or more.

The attenuation rate of the visible light transmittance is a percentage of the visible light transmittance of the colorless coating film containing the rust preventive agent with respect to the visible light transmittance of the colorless coating film containing no rust inhibitor. The visible light transmittance here is based on a spectrophotometer. Light transmittance measured in the wavelength range of 380 nm to 750 nm.

The attenuation rate of the visible light transmittance is preferably 95% or more.

The colorless coating film may be formed only on the surface side of the stainless steel sheet, or may be formed on both the surface side and the back side.

The film thickness of the colorless coating film formed on the surface side of the stainless steel plate is preferably 1 to 25 μm. When the film thickness of the colorless coating film formed on the surface side of the stainless steel plate is less than 1 μm, it is difficult to adjust the film thickness, and the content of the liquid rust inhibitor in the coating film is small, and the corrosion resistance cannot be sufficiently exhibited. When the film thickness of the colorless coating film formed on the surface side of the stainless steel plate is more than 25 μm, not only the coating cost increases, but also the surface hardness tends to be low. In addition, the light transmittance in the visible light region is degraded, and the design with the appearance of stainless steel is detrimental. When the colorless pigment is contained in the colorless coating film, the design deterioration caused by the decrease in light transmittance is more remarkable.

The film thickness of the colorless coating film on the back surface is not particularly limited, but may be 1 μm or more.

<Manufacturing method of colorless coated stainless steel plate>

The method for producing a colorless coated stainless steel sheet according to the present embodiment includes a chemical conversion treatment film forming step and a colorless coating film forming step.

The chemical conversion treatment film formation step is a step of forming a chemical conversion treatment film by applying a chemical conversion treatment liquid to at least one of the stainless steel sheets and hardening it.

The chemical conversion treatment liquid includes a coupling agent, a crosslinking agent, a liquid rust inhibitor, and a solvent.

The solvent contained in the chemical conversion treatment liquid is not particularly limited, and examples thereof include hydrocarbons (toluene, xylene, benzene, cyclohexane, hexane, etc.) and alcohols. Compounds (methanol, ethanol, propanol, butanol, etc.), ester compounds (ethyl acetate, butyl acetate, etc.), ether compounds (diethyl ether, etc.), ketones (acetone, methyl ethyl ketone, methyl isobutyl ketone, etc.) Other polar solvents (dimethylformamide, dimethylhydrazine, etc.), and are appropriately selected.

The coating method of the chemical conversion treatment liquid is not particularly limited, and for example, spray, roll coating, bar coating, curtain flow coating, electrostatic coating, or the like can be used.

After the chemical conversion treatment liquid is applied, it is preferred to bake and dry the stainless steel plate to a surface reaching temperature (PMT) of 60 to 140 °C. Pretreatment such as etching by alkaline degreasing or acid may be performed as needed before the baking treatment.

The colorless coating film forming step is a step of coating a surface of the chemical conversion treatment film with a colorless coating and hardening it to form a colorless coating film.

The colorless coating material includes a thermosetting resin, a crosslinking agent, a liquid rust inhibitor, and a solvent.

In the colorless paint, the composition ratio of the thermosetting resin and the crosslinking agent other than the amine resin is 1 mol per mol of the total of the crosslinkable functional groups contained in the thermosetting resin, and the crosslinking agent is used. The reactive group such as an isocyanate group is preferably 0.1 to 2.0 mols, more preferably 0.1 to 1.0 mol.

The solvent contained in the colorless paint is not particularly limited, and the same solvent as that contained in the chemical conversion treatment liquid can be used.

The colorless coating may further contain a catalyst as a reaction accelerator for the thermosetting resin and the crosslinking agent. In particular, when a blocked isocyanate is selected as the crosslinking agent, it is preferred to contain a catalyst in the colorless coating. If the catalyst is contained in the colorless paint, the dissociation of the plugging agent is promoted, and the cross-linking reaction can be uniformly performed on the coating film.

The catalyst may be exemplified by a metal catalyst such as a tin-based or an organic catalyst such as an amine, and the types thereof are not particularly limited.

In order to improve the workability during painting, an antifoaming agent, a leveling agent, a rheology control agent, and an anti-settling agent may be contained in the colorless paint.

The coating method of the colorless paint is not particularly limited, and for example, spray, roll coating, bar coating, curtain flow coating, electrostatic coating, or the like can be used.

The hardening condition after application of the colorless paint is preferably 190 to 250 ° C by heating to a maximum material reaching temperature (PMT). When the maximum temperature of the material is less than 190 ° C, the hardening reaction is not sufficiently performed, and not only the surface hardness of the colorless coating film is lowered, but also the adhesion between the stainless steel plate and the colorless coating film is lowered. On the other hand, when the maximum temperature of the material reaches more than 250 ° C, not only the hardening reaction is saturated, but also the colorless stainless steel plate is yellowed, resulting in a decrease in design.

<Action effect>

The solid rust preventive used in the past has a low transparency and does not have solubility in a solvent in the paint, so that the appearance of the stainless steel plate cannot be utilized, and the design property is lowered. In particular, when the coating film is thin, the solid rust preventive agent protrudes from the surface of the coating film to impair the appearance of the surface, and the design property is liable to be lowered.

On the other hand, the chemical conversion treatment film and the colorless coating film of the present embodiment contain a liquid rust preventive agent, and the colorless coated stainless steel sheet is excellent in corrosion resistance. In addition, corrosion resistance can be maintained for a long time.

Further, the liquid rust preventive agent can be easily dissolved in the solvent of the coating material in addition to its own transparency, and is easily dispersed uniformly in the coating film. Therefore, it is excellent in transparency, does not impair the aesthetics of a stainless steel plate, and is excellent in design.

In particular, in the colorless coated stainless steel sheet having a large color of the colored pigment, the rust-preventing force tends to decrease. However, according to the present invention, the design deterioration can be suppressed even in the case of rich color, and the corrosion resistance can be ensured.

Further, the present invention is not limited by the foregoing embodiments. The liquid rust inhibitor may be contained in at least one of the chemical conversion treatment film and the colorless coating film, or may be contained only in the chemical conversion treatment film or only in the colorless coating film. However, the liquid rust inhibitor is preferably contained in both the chemical conversion treatment film and the colorless coating film from the viewpoint of obtaining sufficient corrosion resistance. The liquid rust preventive agent is contained in only one of the chemical conversion treatment film and the colorless coating film, and the liquid rust inhibitor is more likely to improve the corrosion resistance in the case of both the chemical conversion treatment film and the colorless coating film. Therefore, when the liquid rust preventive agent is contained in both of the chemical conversion treatment film and the colorless coating film, the total content of the liquid rust preventive agent can be reduced.

Example

Hereinafter, the present invention will be more specifically described by way of examples and comparative examples. However, the invention is not limited by the following examples.

(Examples 1 to 25 and Comparative Examples 1 to 6)

A stainless steel plate NSSC FW1/No. 4 ground material made of Nippon Steel & Sumitomo Gold Stainless Steel Co., Ltd. was used as the stainless steel plate. The mixed chemical conversion treatment liquid shown in Tables 1 to 4 was applied to both surfaces of the stainless steel plate by a roll coater, and the SiO ₂ system was 2 to 10 mg/m ² as measured by fluorescent X-ray. Next, baking and drying were carried out so that the surface reaching temperature (PMT) was 100 °C.

Next, the mixed colorless paints shown in Tables 1 to 4 were applied by a bar coater to have a film thickness of 3 to 5 μm when dried. Thereafter, heating to a surface reaching temperature (PMT) of 216 to 235 ° C, cross-linked acrylic resin by diisocyanate Form a film. Thereby, a colorless coated stainless steel plate was obtained.

Further, the acrylic resin to be used used was a number average molecular weight of 5,000, a glass transition temperature of 60 ° C, and an OH value of 60 mgKOH/g. The diisocyanate is an amine-blocked HDI having an NCO price of 10%.

The following are used for the rust preventive.

Liquid rust inhibitor A: alkane aryl sulfonate zinc salt (pH 6.0 at 25 ° C)

Liquid rust inhibitor B: polyoxyalkynylamine salt (pH 7.0 at 25 ° C)

Liquid rust inhibitor C: organic phosphate (pH 7.3 at 25 ° C)

Liquid rust inhibitor D: fatty acid amine salt (pH 8.4 at 25 ° C)

Solid rust inhibitor A: strontium chromate

Solid rust inhibitor B: aluminum dihydrogen phosphate

Further, in Tables 1 to 4, the liquid rust inhibitor content in the coating film of the colorless coating film is the liquid rust inhibitor content in 100 parts by mass of the colorless coating film containing the liquid rust inhibitor.

3.7 parts by mass of Examples 1 to 4 and Examples 9 to 12 and 3.7 parts by mass of Examples 5 to 8 with respect to the liquid rust inhibitor content of 100 parts by mass of the colorless coating film after the liquid rust inhibitor was removed. Examples 17 to 21 are 7.6 parts by mass.

<evaluation>

The corrosion resistance of the obtained coated stainless steel sheet, the attenuation rate of visible light transmittance, the visual evaluation of the design, the pencil hardness of the coating film, the adhesion of the coating film, and the workability of the coating film were measured or evaluated as follows. The results are shown in Tables 1~4.

(1) Corrosion resistance

The corrosion resistance was subjected to the following tests and evaluations. First, the test plate of the colorless coated stainless steel plate was subjected to JIS K 5600-7-1 (corresponding to international standard: ISO 7253, Paints and varnishes-Determination of resistance to neutral salt spray)/neutral salt spray test for 24 hours. It can be placed in the environment of 23 ° C for 24 hours without washing the test plate. This cycle was repeated 15 times, and the thus obtained test plate was evaluated by the following methods (i) to (iii).

The test plate thus obtained was evaluated by the following methods (i) to (iii).

(i) Aaronson dent

The colorless coated stainless steel plate was extruded by 8 mm using a DuPont-type Alice Indentation Tester, and a neutral salt spray test was performed on the colorless coated stainless steel plate to visually confirm the presence or absence of rust.

5: No rust was observed from the extrusion processing section. (qualified)

4: It is possible to confirm the slight rust of the self-pressing portion. (qualified)

3: There is obvious rust in the self-extrusion processing section. (failed)

2: The self-pressing portion is rusted, and the rust flows out to the lower end portion. (failed)

1: There was significant rust in the self-extruding portion, and the coating film was peeled off. (failed)

(ii) 90 degree bending

A neutral salt spray test was conducted on a colorless coated stainless steel plate bent at a right angle with a bending radius of R = 0.5 mm, and the presence or absence of rust was visually confirmed.

5: No rust was found in the processing department. (qualified)

4: A slight rust can be confirmed in the processing department. (qualified)

3: Several points of rust can be confirmed from the processing department. (failed)

2: The workpiece is largely rusted and the rust flows out. (failed)

1: Most of the coating film peeled off due to significant rust in the self-processing part. (failed)

(iii) cutting off the lower end

The colorless coated stainless steel plate was cut by applying a force from the surface of the surface of the coating film toward the back surface portion, and the cut portion was placed at the lower end portion. After the neutral salt spray test, the presence or absence of rust was visually confirmed.

5: Almost no rust was found from the lower end. (qualified)

4: It is possible to confirm the slight rust from the lower end. (qualified)

3: It is possible to confirm the rust and slight rust from the lower end. (failed)

2: Residue caused by large rust at the lower end (failed)

1: Significantly rusted, and most of the coating film at the lower end peeled off. (failed)

(2) Attenuation rate of visible light transmittance

The ratio of the visible light transmittance of the colorless coating film containing the rust preventive agent was determined with respect to the visible light transmittance of the colorless coating film containing no rust preventive agent, and the obtained value was used as the attenuation rate of the visible light transmittance. The smaller the attenuation rate, the more design Excellent.

Specifically, it is measured as follows.

First, a non-coated colorless coating containing a rust preventive agent is applied to a non-coated glass plate having a thickness of 2 mm to a thickness of 3 to 5 μm to form a coating film after hardening. With respect to this coating film, the transmittance curve in the visible light region was measured, and the integrated value of the curve was calculated.

Next, the uncoated glass plate having a thickness of 2 mm was coated with a colorless colorless paint containing no rust inhibitor, and the film thickness was 3 to 5 μm, which was hardened to form a coating film. With respect to this coating film, the transmittance curve in the visible light region was measured, and the integrated value of the curve was calculated.

Further, the transmittance curve in the visible light region was measured in the same manner in the uncoated glass plate, and the integrated value was calculated.

Based on these numerical values, the attenuation rate of the visible light transmittance is calculated by the following formulas (1) to (4).

Further, the light transmittance was measured in a wavelength range of 380 nm to 750 nm using a spectrophotometer (V670 manufactured by JASCO Corporation).

The attenuation rate is above 90%: qualified, more than 95% are excellent

Attenuation rate less than 90%: unqualified

[Number 1]

x: calculated integral value of uncoated glass plate

X: Transmittance of uncoated glass plate (%)

y: calculated integral value of the laminated body containing the rust preventive coating film and the uncoated glass plate

Y: light transmittance of the coating film containing the rust preventive agent (%)

z: Calculated integral value of the laminate of the coating film containing no rust inhibitor and the uncoated glass plate

Z: Transmittance of coating film without rust inhibitor (%)

(3) Design visual evaluation

The design of the obtained colorless coated stainless steel sheet was evaluated by visual observation and on the following basis.

At this time, under the fluorescent light, the distance from the distance steel plate is about 20~30cm.

5: The coating film is completely transparent, and the polishing marks of the base stainless steel are clearly visible. (qualified)

4: A slight dim can be confirmed from the angle of observation. (qualified)

3: It can be confirmed from any angle that the film is turbid or faint (not qualified)

2: Only the substrate can be confirmed, but the substrate cannot be discerned after slightly lengthening the visual distance. (failed)

1: It is completely obscured and completely obscured. (failed)

(4) Pencil hardness (surface hardness) of the coating film

The surface hardness of the coating film is based on JIS K5600-5-4 (corresponding to international specifications: ISO/DIS 15184, Paints and varnishes-Determination of film hardness by pencil test) scratch hardness (pencil method), using Mitsubishi pencil pencil scratches The value test was evaluated by pencil hardness.

Pencil hardness H or more: qualified, more than 2H is excellent

Pencil hardness below F: unqualified

(5) Adhesion of the coating film

The test was carried out in accordance with JIS K5600-5-6 (corresponding to international specifications: ISO 2409, Paints and varnishes-Cross cut test) / adhesion (cross-cut method), and was evaluated on the basis of the following criteria.

5: The intersection of the cut was included, and no peeling was found at all. (qualified)

4: Very slight peeling was observed at the intersection or edge of the cut. (qualified)

3: Nearly 20% of the cross-section of the cut or edge stripping. (failed)

2: A large defect is produced along the edge of the cut, and nearly 50% of the square is peeled off. (failed)

1: The cut portion is completely peeled off. (failed)

(6) Processability of coating film

A rectangular coated stainless steel plate was prepared as the test object. In the above-mentioned coated stainless steel sheet, one side of the longitudinal direction was sandwiched by two sheets of the same thickness as the coated stainless steel sheet. Next, the stainless steel plate was bent 180 degrees with the center of the longitudinal direction as a curved portion, and the bent stainless steel plate and the two plates were laminated, and then tightly locked with a vise.

The thus-extended processing portion was magnified with a magnifying glass of 30 times, and visually observed, and the degree of the crack was evaluated on the basis of the following.

5: No cracks were found in the processing. (qualified)

4: Several small cracks were found at the processing site. (qualified)

3: Many small cracks can be visually confirmed at the processing site. (failed)

2: Size cracks can be confirmed at the processing site. (failed)

1: Many large cracks were produced at the processing site, and the coating film was turned upside down. (failed)

In Examples 1 to 25 in which at least one of the colorless coating film and the chemical conversion treatment film contained a liquid rust inhibitor, the corrosion resistance and the design property were excellent. Further, the surface hardness of the coating film, the adhesion of the coating film, and the processability of the coating film are also excellent.

In Comparative Example 1 in which the colorless coating film and the chemical conversion treatment film were completely free of the rust preventive agent, the corrosion resistance was low.

Although Comparative Examples 2 to 6 which did not contain a liquid rust preventive agent contained a solid rust preventive agent were low in design.

Claims (4)

a colorless coated stainless steel plate having: a stainless steel plate; a chemical conversion treatment film formed by chemical conversion treatment of at least one side of the stainless steel plate; and a colorless coating film formed on a surface of the chemical conversion treatment film; Further, the chemical conversion treatment film contains a coupling agent and a liquid rust inhibitor, and the content of the liquid rust inhibitor is 10 to 250 parts by mass based on 100 parts by mass of the coupling agent; and the colorless coating film contains liquid prevention The cured coating film of the thermosetting resin of the rust agent is contained in an amount of 0.2 to 20 parts by mass based on 100 parts by mass of the colorless coating film from which the liquid rust preventive agent has been deducted. a colorless coated stainless steel plate having: a stainless steel plate; a chemical conversion treatment film formed by chemical conversion treatment of at least one side of the stainless steel plate; and a colorless coating film formed on a surface of the chemical conversion treatment film; Further, the chemical conversion treatment film contains a coupling agent and a liquid rust inhibitor, and the content of the liquid rust inhibitor is 10 to 250 parts by mass based on 100 parts by mass of the coupling agent. A colorless coated stainless steel plate having: a stainless steel plate; a chemical conversion treatment film formed by chemical conversion treatment of at least one of the stainless steel plates; and a colorless coating film formed on the surface of the chemical conversion treatment film; and the colorless coating film containing liquid The cured coating film of the thermosetting resin of the rust preventive agent is contained in an amount of 0.2 to 20 parts by mass based on 100 parts by mass of the colorless coating film from which the liquid rust preventive agent has been deducted. The colorless coated stainless steel sheet according to any one of claims 1 to 3, wherein the liquid rust inhibitor has a pH of 7.0 or more.