JP2019006036A - Clear-coated stainless steel sheet - Google Patents

Abstract

To provide a clear-coated stainless steel sheet which allows a clear resin layer to be easily removed by an alkali solution, and is excellent in workability and water resistance.SOLUTION: A clear-coated stainless steel sheet 10 includes a stainless steel sheet 11, and a clear resin layer 13 formed on at least one surface of the stainless steel sheet 11, where the clear resin layer 13 contains a core-shell type acrylic emulsion resin and neutralized amine having a boiling point of 50-130°C, the core part of the core-shell type acrylic emulsion resin has a number average molecular weight of 300,000 to 400,000 and a glass transition temperature of -40 to 0°C, the shell part of the core-shell type acrylic emulsion resin has a number average molecular weight of 8,000 to 15,000 and a glass transition temperature of 50-120°C, and a surface of the clear resin layer 13 is an uneven surface.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a clear-coated stainless steel sheet.

Stainless steel sheets are widely used in housings, interior materials, and cover materials for household and commercial appliances because they have a high-grade appearance that takes advantage of the beautiful metallic luster unique to stainless steel.
A stainless steel plate is likely to be scratched on the surface due to friction generated between the press die and the stainless steel plate during press working, and tends to reduce the commercial value. For this reason, a method has been proposed in which lubricating oil is applied to the inner surface of a press die to enhance lubricity.
However, although the method of applying the lubricating oil to the press mold is effective from the viewpoint of preventing scratches, it is necessary to continuously apply the lubricating oil to the press mold, and the productivity tends to be lowered.

Thus, methods have been proposed in which a protective film is attached to the surface of a stainless steel plate or a clear resin layer is formed as a protective film. Hereinafter, a stainless steel plate having a clear resin layer formed on the surface is also referred to as a “clear coated stainless steel plate”.
However, the method of sticking a protective film on the surface of a stainless steel plate is insufficient in lubricity, and part of the protective film may be damaged and peeled off from the stainless steel plate, leaving fragments in the press mold. . If the next stainless steel plate is pressed with fragments remaining, the surface of the stainless steel plate may be damaged by the fragments. Moreover, it is necessary to peel off a protective film after press work, and it takes time and effort.

On the other hand, the method of forming a clear resin layer on the surface of a stainless steel plate can prevent scratches during press working without impairing the appearance of the stainless steel plate if the clear resin layer is a thin film. Therefore, a method of forming a clear resin layer on the surface of a stainless steel plate has been widely used in recent years as a simple and excellent technique.
However, when the welding process is performed after pressing, or when the clear-coated stainless steel sheet is used as a product and exposed to high heat or exposed to direct fire, the clear resin layer may burn or burn. Odor may be generated and the appearance of the clear coated stainless steel sheet may be impaired.

  Therefore, in recent years, a stainless steel plate (a delamination-type clear-coated stainless steel plate) having a clear resin layer that can be peeled off by degreasing has been proposed (Patent Documents 1 to 6). The film-removed clear-coated stainless steel sheet is designed so that the clear resin layer can be easily peeled off by being immersed in an alkaline solution after press working. The film-removed clear-coated stainless steel sheet is the same as the method of applying lubricant to the press mold in terms of increasing the number of processes because the number of degreasing processes is increased, but the lubricant is applied to the press mold. Unlike the method, it is excellent in productivity in that it is not necessary to continuously apply lubricating oil to the press die.

JP-A-10-1114013 JP 2000-280400 A JP 2000-160096 A JP 2002-120323 A JP 2002-144478 A JP 2005-161562 A

However, conventional film-removed clear-coated stainless steel sheets are inferior in lubricity compared to non-film-removed clear-coated stainless steel sheets. In addition, when the workability is insufficient, the clear resin layer may be stretched and whitened during press working.
If the clear resin layer is peeled off after pressing, there is no problem even if the clear resin layer is whitened, but all stainless steel plates are used in locations where they are exposed to high heat as described above or are exposed to direct fire. I don't mean. Therefore, the film-removal type clear-coated stainless steel sheet used in places that are not exposed to high heat or exposed to direct fire will be used without de-filming, and it will be a problem if the clear resin layer is whitened. .
To eliminate the problem of whitening, use a film-removed, clear-coated stainless steel sheet in locations exposed to high heat or direct fire, and non-film-removed, clear-coated stainless steel sheets in other locations. However, it is necessary to prepare both a film-removal type clear-coated stainless steel plate and a non-film-removed type clear-coated stainless steel plate, which is a factor for reducing productivity.

For this reason, the film removal type clear coated stainless steel sheet is required to have excellent workability. If the processability is excellent, the clear resin layer will not be easily whitened during press processing, so a film-removable clear-coated stainless steel sheet is used where it is not exposed to high heat or exposed to direct fire without peeling off the clear resin layer. It is not necessary to use a non-delaminating clear-coated stainless steel sheet.
Further, when the clear resin layer is formed on the surface of the stainless steel plate, it is usually dried at a high temperature of 100 ° C. or higher. Therefore, the clear coated stainless steel plate may be water-cooled after the clear resin layer is formed. Therefore, the film-removed clear-coated stainless steel sheet is required to have excellent water resistance.

  An object of the present invention is to provide a clear-coated stainless steel sheet in which a clear resin layer is easily removed by an alkaline solution and is excellent in workability and water resistance.

The present invention has the following aspects.
[1] A stainless steel plate and a clear resin layer formed on at least one surface of the stainless steel plate, the clear resin layer having a core-shell type acrylic emulsion resin and a boiling point of 50 to 130 ° C. The core-shell type acrylic emulsion resin has a number average molecular weight of 300,000 to 400,000, a glass transition temperature of −40 to 0 ° C., and the core / shell. A clear coated stainless steel sheet having a number average molecular weight of 8,000 to 15,000 in the shell part of the acrylic emulsion resin of the mold, a glass transition temperature of 50 to 120 ° C., and a surface of the clear resin layer being an uneven surface .
[2] The clear coated stainless steel sheet according to [1], wherein the surface of the clear resin layer has an arithmetic average roughness Ra of 0.04 to 0.50 μm.
[3] The clear-coated stainless steel sheet according to [1] or [2], wherein the clear resin layer further includes a lubricant.

  According to the present invention, it is possible to provide a clear-coated stainless steel sheet in which a clear resin layer is easily removed by an alkaline solution and excellent in workability and water resistance.

It is sectional drawing which shows typically the example of 1 embodiment of the clear coated stainless steel plate of this invention. It is a top view which shows typically the example of 1 embodiment of a mode that the clear coated stainless steel plate of this invention was planarly viewed from the clear resin layer side. It is sectional drawing which shows typically one example of embodiment of the core-shell type acrylic emulsion resin contained in the clear resin layer of the clear coating stainless steel plate of this invention.

Hereinafter, an embodiment of the clear coated stainless steel sheet of the present invention will be described.
FIG. 1 is a cross-sectional view schematically showing an embodiment of a clear-coated stainless steel sheet according to the present invention, and FIG. 2 is an embodiment of a plan view of the clear-coated stainless steel sheet according to the present invention from the clear resin layer side. It is a top view which shows the example of a form typically.
A clear-coated stainless steel plate 10 according to this embodiment includes a stainless steel plate 11, a chemical conversion coating film 12 formed on one surface of the stainless steel plate 11, and a clear resin formed on the surface of the chemical conversion coating film 12. And a layer 13.

In FIGS. 1 to 3, the dimensional ratio is different from the actual one for convenience of explanation.
In the following description, one surface of the stainless steel plate 11 is referred to as a “surface of the stainless steel plate”, and the surface opposite to the one surface (surface) of the stainless steel plate 11, that is, the other surface of the stainless steel plate 11 is “ "Back side of stainless steel sheet".

In the present invention, “clear” means that the light transmittance in the visible light region is 30% or more. The light transmittance in the visible light region is a light transmittance measured in a wavelength range of 380 nm to 750 nm using a spectrophotometer.
When the light transmittance in the visible light region of the clear resin layer 13 is less than 30%, visible light is slightly transmitted, but the stainless steel plate 11 can hardly be visually observed. Therefore, a design that takes advantage of the beautiful appearance of stainless steel cannot be obtained.
In particular, the visible light transmittance of the clear resin layer 13 is preferably 40% or more, and more preferably 50% or more.

Further, in the present invention, “powder” means an aggregate of particles, and includes fine particles, fine particles, granules, powder particles in which these are mixed, and the like.
In the present invention, the “average particle diameter” is a value measured by a laser diffraction scattering method.

"Stainless steel plate"
As the stainless steel plate 11, known stainless steel plates that are generally used, such as ferrite, martensite, austenite, and austenite / ferrite (two-phase), can be used.
The surface of the stainless steel plate 11 may be subjected to polishing treatment. As the polishing treatment, Commonly used polishing methods such as 4 polishing, hairline (HL) polishing, 2B polishing and the like can be mentioned.

"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 provided between the stainless steel plate 11 and the clear resin layer 13, it can be made harmless and chromate-free, and the stainless steel plate 11 and the clear resin layer 13. Adhesion with 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 silane coupling agent include 2- (3,4 epoxycyclohexyl) ethyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, and 3-glycidoxypropylmethyldiethoxysilane.

  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, polyesters, polyolefins, alkyd resins and other resins may be included.

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 likely to be lowered. On the other hand, when the adhesion amount exceeds 50 mg / m ² , blisters may be formed on the surface of the coating film after the boiling water test. 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.

"Clear resin layer"
The clear resin layer 13 is a coating film containing a core-shell type acrylic emulsion resin and a neutralized amine having a boiling point of 50 to 130 ° C.
The clear resin layer 13 preferably contains a lubricant and the like in addition to the acrylic emulsion resin and the neutralized amine.

<Acrylic emulsion resin>
For example, as shown in FIG. 3, the acrylic emulsion resin is a core-shell type resin having a laminated structure including a central portion called a core portion 14 and an outer portion called a shell portion 15 formed around the core portion 14. It is. The core part 14 and the shell part 15 are made of different resins, and the core part 14 and the shell part 15 have different functions. Specifically, workability is expressed by the core portion 14 and blocking resistance is expressed by the shell portion 15.

The number average molecular weight of the core part 14 is 300,000-400,000, and 300,000-350,000 are preferable. If the number average molecular weight of the core part 14 is 300,000 or more, workability will improve, and if it is 400,000 or less, film removal property will improve. The number average molecular weight of the core part 14 can be adjusted by conditions (for example, polymerization temperature, type and amount of polymerization initiator, etc.) when the core part 14 is produced.
The number average molecular weight of the core part 14 is a value in terms of standard polystyrene measured by gel filtration chromatography (GPC). Specifically, the monomer component (c) used as the material of the core part 14 is polymerized, the number average molecular weight of the obtained polymer is measured by GPC, and the value converted to standard polystyrene is the number average of the core part 14. Considered molecular weight.

The glass transition temperature of the core part 14 is −40 to 0 ° C., and preferably −30 to −10 ° C. If the glass transition temperature of the core part 14 is −40 ° C. or higher, the tackiness after drying is excellent, and if it is 0 ° C. or lower, the film forming property is excellent. In order to set the glass transition temperature of the core portion 14 within the above range, the composition of the core portion 14 may be appropriately selected.
The glass transition temperature of the core part 14 is a value obtained by measurement with a differential scanning calorimeter (DSC). Specifically, the value obtained by polymerizing the monomer component (c) and measuring the number average molecular weight of the obtained polymer by DSC is regarded as the glass transition temperature of the core portion 14.

The core part 14 is an acrylic resin made of a polymer obtained by polymerizing the monomer component (c). The monomer component (c) includes, for example, at least one of a non-functional acrylic monomer and a 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.
A non-functional acrylic monomer may be used individually by 1 type, and may use 2 or more types together.

Examples of the functional monomer include a monomer having a hydroxy group, a monomer having a carboxy group, and a monomer having an alkoxysilane group.
Examples of the monomer having a hydroxy 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). Examples include trade name Plaxels FM1-5, FA-1-5) manufactured by Chemical Industries.
Examples of the monomer having a carboxy group include acrylic acid, methacrylic acid, itaconic acid, maleic acid, and fumaric acid.
Examples of the monomer having an alkoxysilane group include vinyltrimethoxysilane, vinyltriethoxysilane, methacryloxypropyltrimethoxysilane, and the like.
These monomers having a hydroxy group, monomers having a carboxy group, and monomers having an alkoxysilane group may be used alone or in combination of two or more. .

The monomer component (c) may contain a monomer other than the non-functional acrylic monomer and the functional monomer.
Examples of other monomers include vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, and n-butyl vinyl ether; styrenes such as styrene and α-methyl styrene; acrylamide, N-methylol acrylamide, and diacetone. Examples include acrylamide monomers such as acrylamide.
Another monomer may be used individually by 1 type and may use 2 or more types together.

The number average molecular weight of the shell portion 15 is 8,000 to 15,000, preferably 8,000 to 10,000. If the number average molecular weight of the shell part 15 is 8,000 or more, processability will improve, and if it is 15,000 or less, film removal property will improve. The number average molecular weight of the shell part 15 can be adjusted by conditions (for example, polymerization temperature, type and amount of polymerization initiator, etc.) when the shell part 15 is manufactured.
The number average molecular weight of the shell part 15 is a standard polystyrene conversion value measured by gel filtration chromatography (GPC). Specifically, the monomer component (s) used as the material of the shell portion 15 is polymerized, the number average molecular weight of the obtained polymer is measured by GPC, and the value converted to standard polystyrene is the number average of the shell portion 15. Considered molecular weight.

The glass transition temperature of the shell portion 15 is 50 to 120 ° C, preferably 50 to 100 ° C, and more preferably 50 to 80 ° C. If the glass transition temperature of the shell part 15 is 50 ° C. or higher, the tackiness after drying is excellent, and if it is 120 ° C. or lower, the film forming property is excellent. In order to set the glass transition temperature of the shell portion 15 within the above range, the composition of the shell portion 15 may be appropriately selected.
The glass transition temperature of the shell portion 15 is a value obtained by measurement with a differential scanning calorimeter (DSC). Specifically, the value obtained by polymerizing the monomer component (s) and measuring the number average molecular weight of the obtained polymer by DSC is regarded as the glass transition temperature of the shell portion 15.

The shell portion 15 is an acrylic resin made of a polymer obtained by polymerizing the monomer component (s). The monomer component (s) includes, for example, at least one of a non-functional acrylic monomer and a functional monomer. The monomer component (s) may contain a monomer other than the non-functional acrylic monomer and the functional monomer.
Examples of the non-functional acrylic monomer, the functional monomer, and the other monomer include the non-functional acrylic monomer, the functional monomer, and the like exemplified above in the description of the monomer component (c). Other monomers may be mentioned.

<Neutralized amine>
The neutralized amine neutralizes an acrylic emulsion resin that is acidic. By neutralizing the acrylic emulsion resin, that is, by reacting the acrylic emulsion resin with the neutralized amine, the functional group contained in the acrylic emulsion resin (for example, a monomer having a hydroxy group, a single amount having a carboxy group) Body, a functional group derived from a functional monomer such as alkoxysilane group) and an amino group contained in the neutralized amine form a salt, and the acrylic emulsion resin is difficult to gel.

The boiling point of the neutralized amine has a great influence on the film removal property of the clear resin layer 13. The reason why the boiling point of the neutralized amine affects the film removal property is considered to be because the amount (remaining amount) of the neutralized amine remaining in the clear resin layer 13 changes according to the boiling point of the neutralized amine.
As will be described in detail later, in the process of applying a clear coating containing a core / shell type acrylic emulsion resin and a neutralized amine to the stainless steel plate 11 and then drying it, the solvent water evaporates. Even try to evaporate. Since the evaporation amount of the neutralized amine varies depending on the boiling point of the neutralized amine, the remaining amount of the neutralized amine remaining in the clear resin layer 13 after the drying step increases as the boiling point increases. As the remaining amount of neutralized amine increases, the alkaline solution used in the step of removing the clear-coated stainless steel sheet 10 acts more strongly on the clear resin layer 13, the resin skeleton is easily broken, and the film removal property is improved. . However, if the neutralized amine remains excessively in the clear resin layer 13, the water resistance decreases.

  The boiling point of the neutralized amine is 50 to 130 ° C, preferably 55 to 100 ° C, and more preferably 60 to 80 ° C. When the boiling point of the neutralized amine is 50 ° C. or higher, the film removal property is improved, and when it is 130 ° C. or lower, the water resistance is improved.

Examples of the neutralized amine include triethylamine, N, N-diisopropylethylamine, diethylamine, di (2-ethylhexyl) amine, and 3-methoxypropylamine.
Neutralized amines may be used alone or in combination of two or more.
The neutralized amine in the clear resin layer 13 can be qualitatively obtained by, for example, extracting the neutralized amine from the clear resin layer 13 with a solvent and measuring the extract by gas chromatography (GC).

<Lubricant>
Examples of the lubricant include a fluororesin, an olefin lubricant, and a non-polyolefin wax other than the fluororesin (hereinafter also referred to as “other non-polyolefin wax”).
One type of lubricant may be used alone, or two or more types may be used in combination.

Examples of fluororesins include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), tetrafluoroethylene-ethylene copolymer (ETFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer ( PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP) and the like.
Examples of commercially available fluororesins include FLUON PTFE L150J, L169J, L170J, L172J, and L-173J (above, manufactured by Asahi Glass Co., Ltd.); Lubron L-2, L-5, L-5F (above, manufactured by Daikin Industries, Ltd.); KTL-1N, 2N, 4N, 8N, 8HM, 8F, 10N, 20N, 500F (above, manufactured by Kitamura Co., Ltd.), etc. Is mentioned.
A fluororesin may be used individually by 1 type, and may use 2 or more types together.

The fluororesin may be in the form of powder or liquid, but is preferably in the form of powder from the viewpoint of being easily dispersed uniformly in the thickness direction of the clear resin layer 13.
When the fluororesin is powdery, the average particle size of the fluororesin is preferably 1 to 100 μm, more preferably 1 to 20 μm, and even more preferably 1 to 10 μm.

Examples of the olefin-based lubricant include polyolefin wax and polyolefin powder (powdered polyolefin). Among these, polyolefin waxes are preferable from the viewpoint of improving processability.
Examples of the polyolefin wax include hydrocarbon waxes such as paraffin, microcrystalline, polyethylene, and polyethylene-fluorine.
One type of polyolefin wax may be used alone, or two or more types may be used in combination.

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 70 ° C. or higher, it is difficult to soften and melt during processing, and the excellent characteristics as a solid lubricating additive can be sufficiently exhibited. On the other hand, if the melting point of the polyolefin-based wax is 160 ° C. or less, hard particles are unlikely to be present on the surface, so that the friction characteristics are not easily lowered and high workability can be maintained satisfactorily.
The acid value of the polyolefin wax is preferably 0 to 30 mg KOH / g. If the acid value of the polyolefin wax is 30 mgKOH / g or less, the compatibility with the acrylic emulsion resin does not become too high, and the polyolefin wax tends to float uniformly on the surface of the coating film. Tend to be more improved.
The average particle diameter of the polyolefin-based wax is preferably 0.1 to 7.0 μm, and more preferably 1.0 to 5.0 μm. If the average particle diameter of the polyolefin wax is 0.1 μm or more, the workability of the clear coated stainless steel sheet 10 obtained can be maintained well. On the other hand, when the average particle size of the polyolefin wax exceeds 7.0 μm, the dispersibility of the polyolefin wax in the clear resin layer 13 tends to be low.

Examples of the polyolefin powder include powders of polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-propylene-butene copolymer, and the like.
One type of polyolefin powder may be used alone, or two or more types may be used in combination.

  The average particle size of the polyolefin powder is preferably 1 to 100 μm, more preferably 5 to 50 μm, and even more preferably 5 to 20 μm.

Examples of other non-polyolefin waxes include carnauba wax, lanolin, polyamide, silicone-modified additive, liquid fluororesin (fluorine-modified additive), and the like.
Other non-polyolefin waxes may be used alone or in combination of two or more.

  The content of the lubricant in the clear resin layer 13 is preferably 1 to 10 parts by mass and more preferably 1 to 5 parts by mass with respect to 100 parts by mass of the solid content of the acrylic emulsion resin. If the content of the lubricant is 1 part by mass or more, a sufficient lubricity improving effect is obtained, and if it exceeds 10 parts by mass, the film formability is lowered and the coating workability may be lowered.

<Optional component>
The clear resin layer 13 includes pigments, leveling agents, antifoaming agents, antioxidants, UV absorbers, matting agents, silane coupling agents, brightening agents, silica sol, amorphous silica, acrylic resin beads, antibacterial agents, Additives such as fungicides, and other resins such as epoxy resins, silicone resins, polyesters and amino resins may be included.

<Surface structure>
The surface of the clear resin layer 13 is an uneven surface. That is, the surface of the cut surface obtained by cutting the clear resin layer 13 in the film thickness direction is uneven. For example, as illustrated in FIGS. 1 and 2, the clear resin layer 13 has a concavo-convex structure including a plurality of concave portions 16 and convex portions 17 formed between the plurality of concave portions 16 on the surface.
Since the surface of the clear resin layer 13 is an uneven surface, the contact area with the alkaline solution increases when the film is removed as compared with the case where the surface is flat. Therefore, the film removal rate is increased and the film removal is easily performed.

The arithmetic average roughness Ra of the surface of the clear resin layer 13 is preferably 0.04 to 0.50 μm, and more preferably 0.04 to 0.20 μm. When the arithmetic average roughness Ra of the surface of the clear resin layer 13 is 0.04 μm or more, the lubricity of the clear resin layer 13 is sufficiently exhibited, the workability is further improved, and when the surface is 0.50 μm or less, film removal is performed. More improved. The arithmetic average roughness Ra of the surface of the clear resin layer 13 can be controlled by the type and content of the acrylic emulsion resin and the neutralized amine contained in the clear resin layer 13 and the clear paint application method and application speed described later.
The arithmetic average roughness Ra of the surface of the clear resin layer 13 is a value measured according to JIS B0601-2001.

<Film thickness>
The film thickness of the clear resin layer 13 is preferably 0.5 to 1 μm. If the thickness of the clear resin layer 13 is 0.5 μm or more, workability and lubricity can be maintained well, and if it is 1 μm or less, the surface of the clear resin layer 13 tends to be uneven.
In the present invention, the film thickness of the clear resin layer 13 refers to the apex of the convex portion 17 from the interface between the clear resin layer 13 and a layer adjacent to the clear resin layer 13 (the chemical conversion coating film 12 in this embodiment). Is the vertical distance d.

"Production method of clear coated stainless steel sheet"
Next, an example of a method for manufacturing the above-described clear-coated stainless steel sheet 10 will be described. In addition, the manufacturing method of the clear coating stainless steel plate 10 is not limited to the following examples.
In the manufacturing method of this example, first, the stainless steel plate 11 is subjected to a known pretreatment such as alkali degreasing, acid or alkali etching.
Next, a chemical conversion treatment liquid is applied to the stainless steel plate 11 and dried to form a chemical conversion coating film 12.
As said chemical conversion liquid, what contains one or both of an aminosilane coupling agent and an epoxysilane coupling agent, for example is preferable. Moreover, a commercial item can be used as a chemical conversion liquid. Examples of commercially available chemical conversion treatment liquids 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 12 and dried (baked) to form a clear resin layer 13 having a concavo-convex structure on the surface, whereby a clear coated stainless steel plate 10 is obtained.
As the clear paint application method, the same method as the chemical conversion liquid application method is applied.
The coating amount of the clear paint is preferably such that the thickness of the clear resin layer 13 after drying is 0.5 to 1 μm. If the application amount of the clear paint is within the above range, the surface of the clear resin layer 13 tends to be uneven.

The clear paint includes the core-shell type acrylic emulsion resin described above and a neutralized amine. The clear paint preferably contains a lubricant. Further, the clear coating material may contain the above-described crosslinking agent, optional component, solvent, and the like, if necessary.
When the clear coating contains a cross-linking agent, the acrylic emulsion resin forms a cross-linked structure by the cross-linking agent during the drying.

  The ratio of the lubricant in the clear paint is preferably 1 to 10 parts by mass and more preferably 1 to 5 parts by mass with respect to 100 parts by mass of the solid content of the acrylic emulsion resin.

The drying temperature (surface temperature) of the clear paint is preferably 100 to 200 ° C.
After drying, the clear-coated stainless steel sheet may be cooled by water cooling. Since the clear resin layer formed according to the present invention is excellent in water resistance, whitening or the like hardly occurs even when cooled with water. Further, since the clear-coated stainless steel sheet can be cooled with water, for example, the clear-coated stainless steel sheet can be collected by high-speed coil winding.

"Effect"
Since the clear-coated stainless steel sheet described above includes a clear resin layer containing an acrylic emulsion resin having a core / shell structure, it is excellent in workability and blocking resistance. Moreover, since the surface of this clear resin layer is an uneven surface, and the clear resin layer contains a neutralized amine having a boiling point of 50 to 130 ° C., the clear resin layer is easily dissolved when immersed in an alkaline solution, and is wiped off. The clear resin layer can be removed easily by cleaning or washing. In addition, the clear resin layer is selectively dissolved in an alkaline solution, hardly dissolved in water, and excellent in water resistance.
Therefore, the clear-coated stainless steel sheet of the present invention is easy to remove the clear resin layer with an alkaline solution and is excellent in workability and water resistance.

"Use"
The clear-coated stainless steel sheet of the present invention is suitably used as a housing or interior material or a cover material for household or business appliances and electronic equipment products.
Since the clear-coated stainless steel plate of the present invention is a delamination-type clear-coated stainless steel plate, the clear resin layer is used after removing the clear resin layer, for example, when used in a place exposed to high heat or exposed to direct fire. Moreover, since the clear coated stainless steel sheet of the present invention is excellent in workability, the clear resin layer is hardly whitened during press working. Therefore, when it is used in a place where it is not exposed to high heat or exposed to direct fire, it can be used as it is without removing the clear resin layer. As described above, the clear-coated stainless steel sheet of the present invention can be applied to both a location where the clear resin layer needs to be removed and a location where no removal is required.

"Other embodiments"
The clear-coated stainless steel sheet of the present invention is not limited to the above-described one. For example, in the embodiment described above, the clear resin layer is formed only on the surface of the stainless steel plate, but the clear resin layer may be formed on the back surface of the stainless steel plate. Moreover, although it had a chemical conversion treatment film between the stainless steel plate and the clear resin layer, it does not need to have a chemical conversion treatment film.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited only to this Example.

"Acrylic emulsion resin"
The following compounds were used as the acrylic emulsion resin.
Acrylic emulsion resin A1: An acrylic emulsion resin comprising a core portion having a glass transition temperature of −40 ° C. and a shell portion having a glass transition temperature of 100 ° C.
Acrylic emulsion resin A2: An acrylic emulsion resin comprising a core part having a glass transition temperature of −40 ° C. and a shell part having a glass transition temperature of 120 ° C.
Acrylic emulsion resin A3: an acrylic emulsion resin composed of a core portion having a glass transition temperature of −20 ° C. and a shell portion having a glass transition temperature of 100 ° C.
Acrylic emulsion resin A4: an acrylic emulsion resin comprising a core portion having a glass transition temperature of −20 ° C. and a shell portion having a glass transition temperature of 120 ° C.
Acrylic emulsion resin A5: an acrylic emulsion resin comprising a core part having a glass transition temperature of −60 ° C. and a shell part having a glass transition temperature of 100 ° C.
Acrylic emulsion resin A6: an acrylic emulsion resin comprising a core portion having a glass transition temperature of −40 ° C. and a shell portion having a glass transition temperature of 140 ° C.
In addition, in acrylic emulsion resin A1-A6, both a core part and a shell part are acrylic resins. Moreover, in acrylic emulsion resin A1-A6, the number average molecular weight of a core part exists in the range of 300,000-400,000, and the number average molecular weight of a shell part exists in the range of 8,000-15,000.

"Neutralized amine"
The following compounds were used as neutralizing amines.
-Neutralized amine B1: Ammonia water having a boiling point of 36 ° C.
Neutralizing amine B2: Diethylamine having a boiling point of 55.4 ° C.
Neutralized amine B3: Triethylamine having a boiling point of 90 ° C.
Neutralizing amine B4: N, N-dimethylethanolamine having a boiling point of 134 ° C.

"lubricant"
As the lubricant, the following compounds were used.
Lubricant C1: Powdered polytetrafluoroethylene (PTFE) (manufactured by 3M Japan, trade name “DYNEON PTFE micropowder TF9201Z”, average particle size 6 μm).
Lubricant C2: Polyethylene wax (manufactured by Gifu Serask Manufacturing Co., Ltd., trade name “High Flat X15P-2”, average particle size 3.5 μm).
Lubricant C3: Carnauba wax (manufactured by Koyo Chemical Co., Ltd., trade name “Microflat”).

"Example 1"
<Preparation of clear paint>
100 parts by mass of acrylic emulsion resin A1 in terms of solids, 5 parts by mass of neutralized amine B2 and lubricant C1 were mixed to prepare a clear paint.

<Manufacture of clear coated stainless steel sheet>
As the stainless steel plate, a SUS430 / 2B abrasive was used.
The chemical conversion solution containing an aminosilane coupling agent is coated on the surface of this stainless steel plate with a roll coater so that the SiO ₂ becomes ₂ to 10 mg / m ² with fluorescent X-rays, and the maximum material temperature (PMT) is increased. It dried so that it might become 100 degreeC, and formed the chemical conversion coating film on the surface of a stainless steel plate.
Next, a clear paint was applied to the surface of the chemical conversion coating film with a bar coater and baked to a surface temperature of 130 ° C. to form a clear resin layer having a thickness of 1 μm, thereby obtaining a clear coated stainless steel sheet.
The surface of the clear resin layer was observed based on the following measurement method. Further, the arithmetic average roughness Ra of the surface was measured. The results are shown in Table 1.
The clear coated stainless steel sheet was evaluated for blocking resistance, film removal, water resistance and workability based on the following evaluation methods. The results are shown in Table 1.

<Measurement / Evaluation>
(1) Surface observation The surface of the clear resin layer was observed with a scanning electron microscope to confirm the presence or absence of irregularities.

(2) Measurement of Arithmetic Average Roughness Ra The arithmetic average roughness Ra of the surface of the clear resin layer is based on JIS B0601-2001, a surface roughness measuring instrument (product name “Surf Test SJ-201, manufactured by Mitutoyo Corporation”). )).

(3) Evaluation of blocking resistance A clear coated stainless steel plate was wound around a stainless steel coil having a single weight of 2 t and left for one week. The clear coated stainless steel sheet after standing was visually observed, and the blocking resistance was evaluated according to the following evaluation criteria.
5: Generation | occurrence | production of blocking is not seen.
4: Although blocking occurs slightly, the blocking trace disappears within one day.
3: Blocking occurs slightly, and the blocking marks do not disappear.
2: Strong blocking occurs, and when peeling from the coiled state, it peels off while producing a sound.
1: Extremely blocking occurs, and the first clear resin layer peels off when extended from the coiled state.

(4) Evaluation of film removal property A clear-coated stainless steel sheet was immersed in a sodium orthosilicate aqueous solution having a concentration of 8% by mass for 2 minutes. About the state of the clear resin layer immediately after pulling up the clear coated stainless steel plate from the sodium orthosilicate aqueous solution, the film removal property was evaluated according to the following evaluation criteria. A score of 4 or more is accepted.
5: The clear resin layer is easily peeled off by running water.
4: When the clear resin layer is rubbed with a finger, the clear resin layer is peeled off.
3: When the clear resin layer is strongly rubbed with a finger, the clear resin layer is peeled off.
2: When the nail is raised on the clear resin layer, the clear resin layer is peeled off.
1: Clear resin layer does not peel off.

(5) Evaluation of water resistance 2-3 ml of tap water was dropped on the clear resin layer of the clear coated stainless steel plate and left for 2 minutes. After leaving, water drops on the clear resin layer were wiped off with a waste cloth. The appearance of the clear resin layer where the tap water was dropped was visually observed, and the water resistance was evaluated according to the following evaluation criteria. A score of 4 or more is accepted.
5: No change.
4: Slight whitening can be confirmed.
3: Although whitening can be confirmed, the whitened part does not peel off.
2: Whitening can be confirmed and the whitened part peels off.
1: The clear resin layer of the part which dripped tap water disappeared.

(6) Evaluation of workability A rectangular clear-coated stainless steel sheet was prepared as a test object. In the clear-coated stainless steel plate, one side with the center in the longitudinal direction as a boundary was sandwiched between two plates having the same thickness as the clear-coated stainless steel plate. Next, the clear-coated stainless steel plate was folded 180 degrees with the center in the longitudinal direction as the bent portion, the folded clear-coated stainless steel plate and the two plates were overlapped, and firmly tightened with a vise.
The degree of cracks in the processed portion thus stretched was magnified with a 30-fold magnifier and visually observed, and the workability was evaluated according to the following evaluation criteria. A score of 4 or more is accepted.
5: A crack is not seen in a process location.
4: Several fine cracks are seen in the processed part.
3: A large number of small cracks can be visually confirmed in the processed portion.
2: A large crack can be confirmed together with a small crack in the processed portion.
1: A lot of large cracks enter the processed part, and the coating film is turned up.

"Examples 2-9, Comparative Examples 1-6"
Example 1 and a clear paint were prepared except that the types of acrylic emulsion resin, neutralized amine and lubricant were changed to Tables 1-3.
A clear-coated stainless steel sheet was obtained in the same manner as in Example 1 except that the clear coating material thus obtained was used and the thickness of the clear resin layer and the arithmetic average roughness Ra of the surface were changed to the values shown in Tables 1 to 3. And various measurements and evaluations were made. The results are shown in Tables 1-3. The arithmetic average roughness Ra of the surface was controlled by the type of bar coater and the coating speed.

  From the results shown in Tables 1 and 2, the clear-coated stainless steel sheet obtained in each example had a clear resin layer that was easily removed with an alkaline solution, and was excellent in workability, water resistance, and blocking resistance.

On the other hand, from the results in Table 3, in the case of Comparative Example 1 using a neutralized amine having a boiling point of 134 ° C., the water resistance was poor.
In the case of Comparative Example 2 using a neutralized amine having a boiling point of 36 ° C., the film removal property was inferior.
In Comparative Examples 3 and 4 where the surface of the clear resin layer was not an uneven surface, the film removal property was inferior.
In the case of the comparative example 5 using the acrylic emulsion resin whose glass transition temperature of a core part is -60 degreeC, it was inferior to water resistance and blocking resistance.
In the case of the comparative example 6 using the acrylic emulsion resin whose glass transition temperature of a shell part is 140 degreeC, it was inferior to film removal property and workability.

DESCRIPTION OF SYMBOLS 10 Clear painted stainless steel plate 11 Stainless steel plate 12 Chemical conversion coating film 13 Clear resin layer 14 Core part 15 Shell part 16 Concave part 17 Convex part

Claims (3)

Comprising a stainless steel plate and a clear resin layer formed on at least one surface of the stainless steel plate,
The clear resin layer includes a core-shell type acrylic emulsion resin and a neutralized amine having a boiling point of 50 to 130 ° C.
The number average molecular weight of the core part of the core-shell type acrylic emulsion resin is 300,000 to 400,000, and the glass transition temperature is −40 to 0 ° C.,
The number average molecular weight of the shell part of the core-shell type acrylic emulsion resin is 8,000 to 15,000, the glass transition temperature is 50 to 120 ° C.,
A clear-coated stainless steel sheet, wherein the surface of the clear resin layer is an uneven surface.   The clear-coated stainless steel sheet according to claim 1, wherein an arithmetic average roughness Ra of the surface of the clear resin layer is 0.04 to 0.50 µm.   The clear coated stainless steel sheet according to claim 1, wherein the clear resin layer further contains a lubricant.

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