JP3305913B2 - Alkali-soluble protective coating-coated stainless steel sheet with excellent galling resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stainless steel sheet coated with a protective film, wherein the protective film is excellent in galling resistance and which can be removed with an alkaline solution.

[0002]

2. Description of the Related Art Stainless steel sheets are excellent in corrosion resistance and appearance, and are used as they are in kitchen equipment and building materials, making use of the skin peculiar to stainless steel sheets in many applications. However, the stainless steel sheet has a drawback that when a change occurs in the surface state, even a part thereof is extremely noticeable. For this reason, when manufacturing a member that uses the surface of a stainless steel plate as it is by pressing, a protection film of a vinyl chloride resin is stuck to prevent galling that the surface of the steel plate is worn by a mold. In addition, the protective film of vinyl chloride resin has lubricity,
Because the workability is insufficient, press oil is applied on the protective film and processed.After the protective film is manually peeled off, the surface of the processed product is washed with a chlorine-based solvent such as trichloroethane or an alkaline aqueous solution. I was

[0003] However, since the protective film of a vinyl chloride resin has insufficient lubricating properties, a partial breakage of the film may occur at the time of pressing a stainless steel plate, causing galling on the surface of the steel plate. In addition, peeling the protective film by hand requires a lot of labor, time and expense, and since the part that has been ironed by processing is firmly adhered to the stainless steel plate, the film may be broken at the time of peeling, There were portions that could not be peeled and remained. Therefore, in order to prevent film breakage during peeling as much as possible, the thickness of the protective film was conventionally increased.However, even when manufacturing a member that is not severely pressed, the protective film must be thickened, which increases the material cost. I was further,
The application and removal of the press oil deteriorates the working environment.

[0004]

SUMMARY OF THE INVENTION The present invention provides a stainless steel sheet coated with a protective film, which solves these problems.

[0005]

The protective coating-coated stainless steel sheet of the present invention has an acid value of 40 to 40 on the surface of the stainless steel sheet.
At 300, a lower coating of an epoxy-modified acrylic resin obtained by modifying an acrylic resin having a glass transition temperature of 0 ° C. to 20 ° C. with an epoxy oligomer having a molecular weight of 500 to 2000 by 3 to 20% by mass, and an acid value of 40 to 300 And an upper layer film of an acrylic resin having a glass transition temperature of 40 ° C. to 80 ° C. is sequentially formed, the total thickness of the upper and lower layer films is 1 to 20 μm, and the upper layer film has an average particle size of 0.1 to 10 μm.
m is contained in 1 to 25% by mass of a polymer resin powder.

[0006]

The present inventors have conducted various studies to develop a polymer protective film material which is excellent in galling resistance during press working and can be chemically removed. As a result, the acid value of acrylic resin, glass transition temperature and film It has been found that, by adjusting the thickness, the adhesiveness is excellent and can be dissolved and removed with an alkaline solution. However, if the adhesion and alkali solubility are increased with a single coating, the adhesion of the coating increases, and when stainless steel sheets are stacked, blocking occurs and the galling resistance during press working is insufficient. There was found. Therefore, the present inventors have studied to solve this problem by forming a film having a two-layer structure in which the lower layer has excellent galling resistance and the upper layer has excellent blocking resistance.

[0007] Table 1 shows that a plurality of acrylic resins having different acid values and glass transition temperatures were prepared by changing and copolymerizing each component of methyl methacrylate, butyl acrylate, and methacrylic acid, and then forming them on stainless steel. It was applied to the surface of a steel sheet and dried, and the solubility of the film with an aqueous alkali solution, the film adhesion, the galling resistance, and the blocking resistance were investigated. There is a need to. Further, it is necessary to lower the glass transition temperature in order to improve the adhesion to the stainless steel plate. However, in order to improve blocking resistance, it is necessary to increase the glass transition temperature. Therefore,
If the upper and lower layers have a large acid value, the lower layer has a lower glass transition temperature and the upper layer has a higher one, the film structure has excellent alkali solution solubility, excellent adhesion and blocking resistance. become. In addition, the test method and evaluation method of the film physical property in Table 1 were based on the method described in Example 1 described later.

[0008]

[Table 1] (Note) The film thickness is 10 μm.

However, it can be seen from Table 1 that the glass transition temperature should not be too high or low and should be 10 to 20 ° C. in order to improve the galling resistance. Even if the temperature is in this temperature range, the problem of galling resistance cannot be fundamentally solved. Then, the present inventors have found that when the acrylic resin is modified with epoxy, the galling resistance is improved. Table 2 is Table 1
An epoxy-modified acrylic resin obtained by reacting an epoxy resin having a different molecular weight with an acrylic resin having an acid value of 100 and a glass transition temperature of 10 ° C synthesized in the same manner as described above is applied to the surface of a stainless steel plate and dried. The same performance as in Table 1 was investigated, but the molecular weight was 500 to 20.
When an epoxy-modified acrylic resin modified with an epoxy oligomer of No. 00 is used, the galling resistance is improved.

[0010]

[Table 2] (Note) The film thickness is 10 μm.

In the present invention, based on the above findings, both the upper and lower coatings are made to have a large acid value, and the lower coating is an epoxy-modified acrylic resin coating having a low glass transition temperature, the epoxy-modified amount of which is 3 to 20% by mass. In addition, the upper layer film is made of a high acrylic resin film so as to balance the solubility of the film in an aqueous alkali solution, the galling resistance and the blocking resistance.

The underlayer coating of the present invention has an acid value of 40 to 30.
0, an acrylic resin having a glass transition temperature of 0 to 20 ° C. is modified by an epoxy oligomer into an epoxy-modified acrylic resin film having an acid value of 40 to 3%.
The reason for setting the value to 00 is that if it is less than 40, it is difficult to dissolve and remove it with an alkaline aqueous solution, and if it exceeds 300, the film strength is reduced and the film may be scraped off during processing. In order to balance alkali solubility with film strength, the acid value is preferably in the range of 100 to 300.
The acid value refers to the number of milligrams of potassium hydroxide required to neutralize the free fatty acids contained in 1 g of the acrylic resin. When the glass transition temperature is set to 0 to 20 ° C., if the temperature is lower than 0 ° C., the coating hardness at room temperature becomes insufficient, and the galling resistance is reduced. This is because they cannot be obtained. Further, when the temperature is set to 10 to 20 ° C., the blocking resistance becomes better.

The reason why the molecular weight of the epoxy oligomer for modifying the acrylic resin is set to 500 to 2,000 is that
If it is less than 0, the galling resistance is insufficient, and if it exceeds 2,000, the alkali solubility is impaired. Also,
The reason why the epoxy modification amount is 3 to 20% by mass is that 3% by mass.
If the amount is less than the above, sufficient galling resistance cannot be obtained, and if it exceeds 20% by mass, the alkali solubility is impaired. To harmonize galling resistance and alkali solubility,
It is preferred that the molecular weight of the epoxy oligomer be 800 to 1200 and the modification amount be 3 to 10% by mass.

An acrylic resin having an acid value of 40 to 300 and a glass transition temperature of 0 to 20 ° C. has a molecular weight of 500 to 2,000.
There are various methods for modifying the epoxy oligomer by 3 to 20% by mass. A typical method is to first synthesize an acrylic resin having an acid value of 40 to 300 and a glass transition temperature of 0 to 20 ° C. Then, an epoxy oligomer having a molecular weight of 500 to 2,000 is added thereto, and after heating to around 100 ° C. after the addition of the amine, a carboxyl group of the acrylic resin reacts with the epoxy group of the epoxy oligomer. After reacting a carboxyl compound having an unsaturated bond, such as acrylic acid, methacrylic acid, maleic anhydride or unsaturated fatty acid,
There is a method of polymerizing while dropping an acrylic monomer.

The upper film is made of an acrylic resin having an acid value of 40 to 300 and a glass transition temperature of 40 to 80 ° C. The acid value of 40 to 300 is different from that of the lower film described above. The same is true. On the other hand, when the glass transition temperature is
The reason why the temperature is set to 80 ° C. is that if the temperature is lower than 40 ° C., the temperature in the factory rises to near 40 ° C. in summer, and if the temperature rises, the film becomes sticky. This is because the film becomes brittle, and cracking or peeling may occur during film formation.

The acrylic resin of the lower layer and the upper layer film is obtained by copolymerizing a polymer or copolymer of acrylic acid and / or methacrylic acid or a monomer thereof with an acrylate or methacrylate as required. It is possible to use those obtained by adjusting the acid value and the glass transition temperature according to the polymerization amount, the copolymerization component and the like. Here, examples of the (meth) acrylate include methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, and 2-ethylhexyl acrylate. The copolymerizable monomer may further be copolymerized with a monomer copolymerizable with the (meth) acrylic acid ester, for example, styrene, acrylonitrile, acrylamide, butadiene, vinyl acetate, and the like.

The total thickness of the lower film and the upper film is 1 μm
If it is less than, it is not possible to prevent galling on the surface of the steel sheet during press working, and if it exceeds 20 μm, the amount of film shaved off by the mold is significantly increased, and frequent maintenance of the mold is required. And reduce productivity. For this reason, it is desirable that the thickness be 1 to 20 μm, preferably 1 to 5 μm. When the glass transition temperature of the lower layer coating is low,
When the thickness of the upper film is half or more of that of the lower film, the blocking resistance is improved.

When a polymer resin powder is added as a lubricant to the upper layer coating, lubricity is improved, processing without oil coating is possible, and an oil coating step and a degreasing step can be omitted. Also improve. However, when the addition amount of the resin powder is less than 1% by mass, the lubricating property is inferior to the case where the press oil is applied, and when it exceeds 25% by mass, dispersion in the treatment liquid becomes difficult and gelation occurs. . For this reason, the addition amount is 1-2.
The content is preferably 5% by mass, and when considering the long-term stability of the processing solution, it is preferably 1 to 10% by mass. Also,
If the average particle size of the resin powder is less than 0.1 μm, the coefficient of friction of the film becomes small, but the lubricating property is not sufficiently obtained.
If it exceeds 0 μm, the resin powder will fall off during processing and will not exhibit lubricity. For this reason, the average particle size is 0.1 to 10 μm
To

The resin powder is not particularly limited, but may be a powder of a fluorine resin, a polyethylene resin, a polyester resin, or the like. These resin powders may be used alone or in combination, or may be melt-blended. In order to enhance the lubricity of the film, it is preferable to use a mixture of a fluororesin powder having excellent lubricity and a polyethylene resin powder which is not easily deformed under a high surface pressure.

The lower and upper coatings are formed on the surface of the stainless steel sheet by applying an emulsion of an epoxy-modified acrylic resin by a coating method such as a roll coater capable of obtaining a uniform coating, drying and then subjecting to an acid value. Acrylic resin emulsion having a glass transition temperature of 40 to 300C and a glass transition temperature of 40 to 80C may be similarly applied and dried.

[0021]

【Example】

Example 1 A plurality of emulsion treatment liquids of an acrylic resin having different acid values and glass transition temperatures were prepared by changing each component of methyl methacrylate, butyl acrylate, and methacrylic acid and copolymerizing them. Bisphenol A type epoxy oligomer was reacted with one having a low glass transition temperature to carry out epoxy modification. Next, the emulsion of the epoxy-modified acrylic resin was coated on a stainless steel plate (steel type: SUS304, finish: BA, plate thickness: 0.6 m).
m) was coated on the surface with a bar coater and dried in an oven to form an underlayer film. Thereafter, an acrylic resin having a glass transition temperature higher than that of the acrylic resin before the epoxy modification was applied and dried on the lower film by the same method to form an upper film. Tables 3 and 4 show the obtained acrylic resin film-coated stainless steel sheets. Next, the following characteristics were investigated for this steel sheet. Table 5 shows the results.

(1) Solubility of film The test piece was immersed in a NaOH solution (pH: 12, liquid temperature: 40 ° C), and the time required for the film to completely dissolve was 2 hours.
Those with less than minutes were evaluated with a symbol ○, those with 2 minutes or more and less than 5 minutes were evaluated with a symbol Δ, and those with 5 minutes or more were evaluated with a symbol X. (2) Adhesion to film The test piece was subjected to a DuPont impact test (weight drop height: 500 m
m, weight of the weight; 500 g), and serothe
A tape test was conducted in which the tape was once adhered and then peeled off.
Those with less than 0% were evaluated with the symbol 、, those with less than 40 to 60% were evaluated with the symbol △, those with less than 20 to 40% were evaluated with the symbol X, and those with less than 20% were evaluated with the symbol XX.

(3) Resistance to galling A test piece (30 mm × 250 mm) was subjected to a draw test as shown in FIG. 1 (pressing force: 1500 N, drawing speed: 8.3 × 10 ⁻² m / sec). ), The symbol 記号 indicates that the residual ratio of the film in the test portion is 80% or more, the symbol を indicates that the residual ratio is less than 60 to 80%, and the symbol △ indicates that the residual ratio is less than 40 to 60%.
Those with 0 to less than 40% were evaluated with the symbol x, and those with less than 20% were evaluated with the symbol xx. (4) Blocking resistance The test pieces were stacked so that the surfaces of the protective coatings matched each other, and allowed to stand at a temperature of 40 ° C. and a pressure of 1200 N / cm ² for 24 hours. , The test piece was forcibly peeled off, the symbol ○ indicates that no peeling was observed on the protective film, and the symbol を indicates that the peeling was partially observed.
Those in which film peeling due to blocking was recognized on the entire surface were evaluated with the symbol x.

[0024]

[Table 3]

[0025]

[Table 4]

[0026]

[Table 5]

EXAMPLE 2 Methyl methacrylate, butyl acrylate, acrylic acid and methacrylic acid were copolymerized to synthesize an acrylic resin having an acid value of 100 and a glass transition temperature of 10 ° C. 1,000 bisphenol A type epoxy oligomers were reacted to obtain an epoxy-modified acrylic resin having a modification amount of 10% by mass. Then, an emulsion treatment liquid of this resin was applied to the same stainless steel plate surface as in Example 1 by barco coating.
The mixture was applied with a tar and dried in an oven to form a lower layer film having a thickness of 5 μm. Thereafter, an acrylic resin having an acid value of 100 and a glass transition temperature of 40 ° C. was treated with methyl methacrylate.
Butyl acrylate and methacrylic acid were copolymerized, and a polyethylene resin powder and / or a fluororesin powder were added to the emulsion treatment liquid, and the mixture was sealed in a glass container and kept in a 40 ° C. atmosphere for 10 days. Or left for 20 days. Then, after standing, the treatment liquid was applied on the lower layer coating in the same manner as described above and dried to form an upper layer coating. Table 6 shows the results of the following tests performed on the emulsion treatment liquid for the upper layer coating and the obtained acrylic resin film-coated stainless steel sheet.

(1) Stability of treatment liquid Acrylic resin for the upper layer film is sealed in a glass container,
If the treatment liquid was not allowed to stand for 20 days in an atmosphere at 0 ° C. for 20 days, a symbol indicating no thickening or gelling was observed. Before a lapse of days, the occurrence of thickening or gelation was evaluated by the symbol x. (2) Workability Cylindrical drawing test using a disk test piece (punch diameter: 40
φ, drawing ratio: 2.35, wrinkle holding force: 2.5 × 10
⁴ N) performs, before processing of the specimen diameter L _1, a test piece average diameter after working as L ₂ / L ₁ of the case of the L ₂ is less than 0.88 symbol ◎, 0.88～ Those with a value of less than 0.90 are marked with the symbol 、,
Those with 90 to 0.94 were evaluated with the symbol △, and those with more than 0.94 were evaluated with the symbol x. (3) Galling resistance The same as in Example 1.

[0029]

[Table 6] (Note 1) A of the resin powder is a polyethylene resin powder, B is a fluororesin powder, and C is a mixture of polyethylene resin powder / fluororesin powder = 9/1 (weight ratio). (Note 2) In Comparative Examples 21 and 26, the treatment liquid was gelled.
Application was difficult.

[0030]

As described above, the stainless steel sheet coated with a protective film of the present invention has good adhesion and strength of the protective film, so that no galling occurs during processing even if it is a thin film. In addition, since the protective film can be dissolved and removed by immersing it in an alkaline solution, complicated manual peeling is released, and workability is significantly improved. Furthermore, if a polymer resin powder is added to the protective film, the lubricity is improved, so that press oil application before processing and deoiling after processing are unnecessary.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a mold for a test for a test used in a galling resistance test of a film in Example 1.

────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Hirofumi Takezu 5 Ishizu Nishimachi, Sakai City, Osaka Prefecture Nisshin Steel Co., Ltd. Inside the Surface Treatment Laboratory, Steel Research Laboratory (72) Inventor Masaya Yamamoto 5 Ishizu Nishimachi, Sakai City, Osaka Prefecture No. Nisshin Steel Co., Ltd.Steel Research Laboratory Surface Treatment Research Department (72) Inventor Takeshi Masuda 12 Yawata Kaigan-dori, Ichihara-shi, Chiba Dainichi Ink Chemical Industry Co., Ltd. (56) References JP 50-89427 (JP, A) JP-A-55-18238 (JP, A) JP-A-63-44969 (JP, A) JP-A-60-42469 (JP, A) JP-A-52-124032 (JP, A) ( 58) Field surveyed (Int. Cl. ⁷ , DB name) B32B 15/08 B05D ⁷ /14-7/24

Claims (3)

(57) [Claims] An acid value of 40 to 3 on the surface of a stainless steel plate.
An acrylic resin having a glass transition temperature of 0 ° C. to 20 ° C. and an epoxy oligomer having a molecular weight of 500 to 2,000.
A lower layer film of an epoxy-modified acrylic resin modified with 3 to 20% by mass and an upper layer film of an acrylic resin having an acid value of 40 to 300 and a glass transition temperature of 40 to 80 ° C. are sequentially formed. Is an alkali-soluble protective film-coated stainless steel sheet excellent in galling resistance, having a total thickness of 1 to 20 µm. 2. The acrylic resin of the lower layer coating and the upper layer coating is a polymer of acrylic acid and / or methacrylic acid or a copolymer of at least one of these monomers with an acrylate and / or methacrylate. The stainless steel sheet coated with an alkali-soluble protective film having excellent galling resistance according to claim 1. 3. The stainless steel sheet according to claim 1, wherein the upper coating is a polymer resin powder having an average particle size of 0.1 to 10 μm.
An alkali-soluble protective coating-coated stainless steel sheet with excellent galling resistance, characterized by containing by mass%.