JPH08281864A - Clear coating stainless steel panel - Google Patents

Abstract

PURPOSE: To provide a coated stainless steel panel having a clear coating film protecting the surface of a stainless steel panel having beautiful surface appearance such as a brilliant stainless steel panel having metal gloss or a stainless steel panel having design surface finish without damaging the appearance thereof and excellent in scratch resistance and antistaining properties. CONSTITUTION: A chemical forming tretment soln. consisting of phosphoric acid and a silica sol is applied to at least one surface of a stainless steel panel and dried to form a chemical forming treatment film thereon and paint containing an acrylic org. polymer, a siloxane inorg. polymer and a curing agent is further applied thereto and dried to form a colorless transparent clear film with a thickness of 2-50μm thereon to obtain a clear coating stainless steel panel.

Description

Detailed Description of the Invention

[0001]

This invention relates to a stainless steel plate having a beautiful surface appearance, such as a bright stainless steel plate having metallic luster and a stainless steel plate having a designed surface finish, and protects the surface without impairing its beautiful appearance. Then
Further, the present invention relates to a clear-painted stainless steel plate having excellent scratch resistance and stain resistance, and particularly to a clear-painted stainless steel plate suitable for use in building materials and kitchen applications.

[0002]

2. Description of the Related Art Stainless steel sheets have been used for various purposes since they are excellent in corrosion resistance, heat resistance, brilliance of metallic luster, and beautiful appearance such as design surface finish. Applications in which the above-mentioned beautiful appearance of stainless steel sheets can be utilized include, for example, building materials and kitchen applications. However, when a bare stainless steel plate is used in such an application, contaminants such as fingerprints are likely to be attached, and the contaminated part is conspicuous, and the surface of the stainless steel plate is easily soiled due to rusting. However, there is a problem in that the beautiful appearance of is impaired remarkably.

Therefore, a technique of baking organic resin paint, for example, fluororesin clear paint on a stainless steel plate to reduce contamination such as fingerprints and prevent rust while maintaining the beautiful appearance of the stainless steel plate. It has been known.

For example, Japanese Patent Laid-Open No. 63-242379 discloses a technique for improving weather resistance and corrosion resistance by coating an acrylic resin clear paint on a stainless steel plate and then applying a fluororesin clear paint. ing.

Further, in Japanese Patent Laid-Open No. 106057/1993, a chromate-treated film is formed on a stainless steel sheet which has been subjected to a phosphate treatment by a coating type chromate treatment liquid, and then a transparent fluororesin paint is applied. , Techniques for improving stain resistance are disclosed.

[0006]

However, in all of the above techniques, a fluororesin is used as the clear coating film, but the clear coating film of the fluororesin is slightly whitish. Appearance, slightly less clear. Further, since this coating film is soft and inferior in scratch resistance, there are problems that fine scratches are generated on the surface when wiping off surface deposits, the clearness deteriorates with time, and the appearance of the stainless steel sheet is impaired.

Further, in the technique disclosed in Japanese Patent Laid-Open No. 5-106057, there is a chromate-treated film as a base film of a clear coating film. The chromate-treated film is colored yellow due to Cr ⁶⁺ in the film, and even if the content of Cr ⁶⁺ is reduced to suppress the coloring, it is colored yellow due to heat applied during use. For this reason, when a chromate-treated film is provided as a lower layer and clear coating is performed on it, it is inevitable that the chromate-treated film has a yellowish appearance and the appearance of the stainless steel sheet is impaired. Further, when the coating film is cracked, chromium may be eluted from the portion during use, which may cause an environmental problem.

An object of the present invention is to provide a clear-painted stainless steel plate that solves the above problems.

[0009]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present inventors formed a chemical conversion treatment film of a specific composition containing no chromium as the first layer, and It has been found that a stainless steel sheet having excellent scratch resistance and stain resistance can be obtained by forming a clear film having a specific composition on the second layer. The present invention has been made on the basis of such knowledge, and the characteristic configuration is as follows.

(1) A chemical conversion treatment film formed by applying a chemical conversion treatment liquid containing phosphoric acid and silica to at least one surface of a stainless steel plate and drying it, and an acrylic organic polymer and a siloxane inorganic polymer on the chemical conversion treatment film. And a coating containing a curing agent are applied and dried to a film thickness of 2μ
Clear coated stainless steel sheet with a colorless and transparent clear film of m or more and 50 μm or less.

(2) In the clear-coated stainless steel sheet according to (1) above, the weight ratio of phosphoric acid and silica in the chemical conversion treatment liquid is H ₃ PO ₄ / SiO ₂ of 1/10 or more and 5/1 or less, and The amount of chemical conversion coating adhered is ₂ mg in terms of SiO 2.
/ M ² or more and 200 mg / m ² or less, clear coated stainless steel sheet.

(3) In the clear-coated stainless steel sheet of (1) or (2) above, the thickness of the clear film is 5
Clear-painted stainless steel plate with a size of μm or more and 20 μm or less.

(4) In the clear-coated stainless steel sheets of (1) to (3) above, the content of the siloxane-based inorganic polymer in the coating material containing the acrylic organic polymer and the siloxane-based inorganic polymer and the curing agent is the acrylic-based A clear-coated stainless steel plate having a content of organic polymer and a content of siloxane-based inorganic polymer of 10 wt% or more and 50 wt% or less.

[0014]

The present invention will be described below.

The first layer of the present invention comprises a chemical conversion treatment film formed by applying a chemical conversion treatment liquid comprising phosphoric acid and silica sol on the surface of a stainless steel plate and drying it. With this film, excellent adhesion between the stainless steel plate and the clear film can be obtained. This adhesion does not decrease even under high temperature or wet environment. Further, since this film is colorless and transparent and does not contain chromium, there is no environmental problem.

The reason why the adhesion is improved is considered as follows. Anchor effect due to the etching of the stainless steel plate surface by phosphoric acid to create fine irregularities,
It is considered that the adhesiveness between the stainless steel sheet and the clear film is improved by the effect of the chemical bond generated between the precipitated phosphate and the surface of the stainless steel sheet. Furthermore, it is considered that the silica contained in the coating strengthens the chemical conversion coating and the action of the silanol groups in the silica further improves the adhesion between the stainless steel sheet and the clear coating.

The weight ratio of phosphoric acid and silica in the chemical conversion treatment liquid is preferably 1/10 or more and 5/1 or less. H
_{When 3} PO ₄ / SiO ₂ is less than 1/10, it is not possible to secure strong adhesion between the treated film and the stainless steel sheet, and when it exceeds 5/1, it becomes difficult to obtain a stable treated film. The adhesion of the film is reduced.

Further coating weight of treated film is desirably 2 mg / m ² or more 200 mg / m ² or less.
If it is less than 2 mg / m ² , the film will be unevenly formed, and the adhesion between the clear film and the stainless steel plate will decrease.
If it exceeds 00 mg / m ² , cohesive failure is likely to occur inside the coating, resulting in poor adhesion.

As the phosphoric acid, any water-soluble one can be used, and examples thereof include orthophosphoric acid and phosphoric anhydride.

As the silica sol, a commercially available one may be used, and either a dry method or a wet method may be used.

The treatment liquid can be prepared by mixing a phosphoric acid aqueous solution adjusted to a predetermined concentration according to the amount of the treatment layer adhered with a predetermined amount of silica sol, stirring the mixture, and forming a uniform solution.

The treatment liquid can be applied by a commonly used method such as spraying, roll coating, curtain flow coating or electrostatic coating. Drying may be carried out by evaporating water, and the temperature is suitably 50 to 150 ° C.

In this treatment, known pretreatments such as degreasing with an alkali or a solvent and etching with an alkali or an acid may be carried out, if necessary.

After forming the chemical conversion coating of the first layer consisting of phosphoric acid and silica sol, a coating containing an organic polymer, an inorganic polymer and a curing agent is applied and dried to form a clear coating. This film is colorless and transparent and has excellent clearness.

The organic polymer is indispensable for obtaining a film excellent in processing adhesion. However, since the organic polymer is soft, when the organic polymer is used alone, the scratch resistance of the clear film is inferior, but when the inorganic polymer having high hardness is used together, the scratch resistance of the clear film can be made excellent.

Further, the inorganic polymer also contributes to the improvement of the adhesiveness between the chemical conversion treatment film of the first layer and the clear coating film. The reason for this is considered to be that the inorganic polymer in the coating film forms a strong chemical bond with phosphoric acid or silica sol in the chemical conversion treatment film during curing.

The content of the inorganic polymer is 10 with respect to the total of the content of the organic polymer and the content of the inorganic polymer.
It is desirable that the content is not less than wt% and not more than 50 wt%. If it is less than 10 wt%, excellent scratch resistance cannot be exhibited, and 50 w
If it exceeds t%, the viscosity of the coating material is reduced, and a stable film thickness cannot be obtained in the coating work, and the clear coating film is likely to be cracked during the processing, and the adhesiveness of the coating film is deteriorated.

As the organic polymer used in the present invention, it is desirable to select an acrylic resin from the viewpoint of increasing the hardness of the coating film, durability and easiness of binding with the inorganic polymer.
Acrylic resins include acrylic acid esters such as methyl acrylate, ethyl acrylate, propyl acrylate, 2-ethylhexyl acrylate, or methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate. It can be produced by polymerizing a methacrylic acid ester such as the above as a main component and various monomers described below or a mixed monomer in which a plurality of these are combined by a conventional method.

As various monomers to be mixed with acrylic acid ester or methacrylic acid ester, acrylic acid,
Α, β-monoethylenically unsaturated carboxylic acids such as methacrylic acid, itaconic acid, maleic acid, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, etc. Α, β-containing the hydroxyl group of
Monoethylenically unsaturated carboxylic acid ester, acrylamide, N-methylol acrylamide, N-butoxymethyl methacrylamide, diacetone acrylamide, N
-Amino group-containing monoethylenically unsaturated compounds such as methylol methacrylamide, N-butoxymethyl methacrylamide, diacetone methacrylamide, diethylaminoethyl acrylate and dimethylaminoethyl methacrylate, glycidyl such as glycidyl esters of acrylic acid and methacrylic acid Group-containing monoethylenically unsaturated compound,
Examples thereof include styrene, acrylonitrile, and methacrylonitrile.

The inorganic polymer is a polymer in which a silicon atom forms a long chain polymer such as -Si-O-Si-O-Si- through oxygen, and a methyl group, an ethyl group, a propyl group, and a butyl group are formed on the side chains. A siloxane-based inorganic polymer having an organic group consisting of an alkyl group such as a group, an alkoxy group such as a methoxy group and an ethoxy group, an aryl group such as a phenyl group, a fluoro-substituted alkyl group and an aryl group is preferable.
Since the siloxane-based inorganic polymer lowers the surface energy of the clear film and imparts excellent water-repelling property and oil-repelling property to the film, the stain resistance is improved.

The curing agent added together with these organic polymer and inorganic polymer contributes to the improvement of the adhesiveness of the coating by making the coating into a network structure and making it stronger. As the curing agent, for example, various isocyanate compounds, blocked isocyanate compounds, benzoguanamine, melamine resins, and amino resins such as urea resins can be applied. Further, a binder that shares an organic group and an inorganic group, such as a silane coupling agent containing an acrylic group, may be used. It is also possible to use an acrylic resin containing an inorganic group by copolymerizing a siloxane polymer containing an acrylic group with an acrylic monomer such as methacrylic acid.

The thickness of the clear film layer is 2 μm or more and 50 μm or more.
It must be m or less. When the film thickness is less than 2 μm, the coating property of the coating film is poor and the scratch resistance is reduced. Film thickness is 50
If it exceeds μm, the workability is deteriorated. A more preferable film thickness is 5 μm or more and 20 μm or less.

Since the above-mentioned film is excellent in clearness, it does not impair the appearance of the surface of the stainless steel plate. In addition, various additives such as a leveling agent, a thickener, and a stabilizer may be added in a small amount within a range that does not impair the clearness.

The coating composition can be obtained by blending a predetermined amount of an organic polymer, an inorganic polymer and a curing agent with stirring.

The coating method is as follows, using the above coating composition.
As in the case of the treatment liquid for the first layer, a commonly used method such as spraying, roll coating, curtain flow coating, or electrostatic coating can be used. Dry baking can be performed by a commonly used method using a hot air heating furnace, an infrared heating furnace, an induction heating furnace, or the like.

The above-mentioned coating can be appropriately formed on one side or both sides of the stainless steel plate, if necessary.

The stainless steel plate used in the present invention is
Various stainless steel plates can be applied regardless of steel type and surface finish.

[0038]

Example The following stainless steel plate was used as the stainless steel plate to be the substrate.

A: SUS304, B: SUS430,
C: SUS316, D: SUS444 On the above stainless steel plate, H in the range of 0.02 to 10
_A treatment liquid consisting of phosphoric acid and silica sol adjusted to have a ₃ PO ₄ / SiO ₂ ratio (weight ratio) was applied by spraying, and dried in a hot air drying oven at a plate temperature of 80 ° C. Subsequently, a coating material in which an acrylic organic polymer, a siloxane inorganic polymer and a curing agent are mixed is roll-coated on it and baked under the condition that the plate temperature is 270 ° C. 1
-No. 23 clear-painted stainless steel plates were obtained.

The acrylic organic polymer is acrylic resin "Acridic A801" manufactured by Dainippon Ink and Chemicals, Inc., and the siloxane inorganic polymer is Toray.
Dimethyl siloxane "Silicone resin SR2408" manufactured by Dow Corning Silicone Co., Ltd.
Methylated melamine manufactured by Mitsui Cyanamid Co., Ltd. was used. The mixing ratio of the acrylic organic polymer and the siloxane inorganic polymer is as shown in Table 1, and the curing agent was mixed with this organic-inorganic mixed resin at a ratio of 1/5.

For comparison, a coated stainless steel plate having a clear film outside the scope of the present invention (Comparative Example No. 5),
Painted stainless steel sheet with a chemical conversion coating different from that of the present invention (Comparative Examples No. 1 to No. 3), coated stainless steel sheet without a chemical conversion coating (Comparative Example No. 4), coated stainless steel sheet with a clear coating composition different from that of the present invention (Comparative Examples No. 6 to N
o. 8) was obtained in the same manner as in the above-mentioned invention example.

For these test materials, the clearness of the coating film,
The stain resistance, scratch resistance, paint adhesion, corrosion resistance, and heat resistance were investigated. The test conditions for each property are as follows. [1] Clearness of coating film The colored state of the coating film or the white turbidity state of the coating film was visually evaluated according to the following criteria. ⊚: No color change, ○: Slightly colored, Δ: Yellow or white colored, ×: Significantly colored

[2] Contamination resistance A fingertip was pressed against the surface of the sample material, and the state of adhesion of fingerprints after the fingertip was released was evaluated according to the following criteria. ⊚: No fingerprint adhered, ○: Slight fingerprint imprint, Δ: Clearly fingerprint imprint, ×: Vigorous fingerprint imprint

[3] Scratch resistance test The test materials were evaluated according to the pencil scratch test method according to JIS K 5400. If it is 7H or more, the hardness is good.

[4] Paint Adhesion Test (Primary Adhesion) The test material was made into 100 squares according to the JIS K 5400 cross-cut test, and cellophane tape was pressure-bonded and then rapidly peeled off. I counted the number of eyes. The smaller the number, the better the paint adhesion.

(Secondary Adhesion) After the test material was immersed in boiling water for 2 hours, an adhesion test was conducted in the same manner as the above primary adhesion test.

[5] Corrosion resistance test After cross-cutting the surface of the test material, JIS K 2371
Based on the above, salt water was sprayed for 2000 hours, and the peeled state of the coating film was visually evaluated. ⊚: Peeling rate less than 5%, ◯: Peeling rate 5% or more and 10% or less,
Δ: Peeling rate 10% or more and 25% or less, ×: Peeling rate 25% or more

[6] Heat resistance test The test material was kept in a furnace at 200 ° C. for 8 hours, air-cooled, and then visually evaluated to evaluate the degree of coloring and paint adhesion. The degree of coloring was evaluated by the same method as the clearness of the coating film. The paint adhesion was evaluated by a cross-cut test in the same manner as the paint adhesion test in [4] above.

Table 1 shows the manufacturing conditions and test results of the test materials.

[0050]

[Table 1]

The examples of the present invention are all excellent in the clearness, scratch resistance and stain resistance of the coating film. No discoloration is observed even after the heat resistance test.

When the weight ratio of phosphoric acid and silica in the chemical conversion treatment liquid is H ₃ PO ₄ / SiO ₂ of 1/10 or more and 5/1 or less, the adhesion amount of the chemical conversion coating is ₂ mg / m ^{2 in} terms of SiO ^2. Above 200 mg / m ² (Invention Example No. 1,
2, 4, 7, 8, 10 to 23), and the paint adhesion is more excellent. When the film thickness of the clear film is 5 μm or more and 20 μm or less (Invention Examples Nos. 1 to 15 and 18 to 23), scratch resistance and paint adhesion are more excellent. The content of the siloxane-based inorganic polymer in the coating material containing the acrylic organic polymer and the siloxane-based inorganic polymer and the curing agent is 10 wt% or more and 50 wt% or more based on the total of the content of the acrylic-based organic polymer and the content of the siloxane-based inorganic polymer. %
In the case of the following (invention examples Nos. 1 to 11 and 14 to 2)
3) The paint adhesion is more excellent.

On the other hand, when the thickness of the clear film is below the range of the present invention (Comparative Example No. 5), scratch resistance and stain resistance are poor. Chemical treatment different from that of the present invention (Comparative Example N
o. Nos. 1 to 4) are inferior in clearness and / or scratch resistance of the coating film. The clear coating film containing no inorganic polymer or curing agent (Comparative Examples Nos. 6 and 7) has poor stain resistance. The clear coating film made of a fluororesin (Comparative Example No. 8) is inferior in the coating film clear property, scratch resistance and stain resistance.

[0054]

As described above, according to the present invention, it is possible to obtain a coated stainless steel sheet excellent in stain resistance and scratch resistance of the coating film without impairing the appearance of the base stainless steel sheet.

Further, the weight ratio of phosphoric acid and silica in the chemical conversion treatment liquid and the adhesion amount of the chemical conversion treatment film are specified in a specific range, the thickness of the clear film is specified to be 5 to 20 μm, and the siloxane-based inorganic material in the clear paint is specified. By controlling the content of the polymer within a specific range, the paint adhesion is more excellent.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Saburo Ito 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Steel Pipe Co., Ltd.

Claims (4)

[Claims] 1. A chemical conversion treatment film formed by applying a chemical conversion treatment liquid consisting of phosphoric acid and silica sol to at least one surface of a stainless steel plate and drying it, and an acrylic organic polymer and a siloxane inorganic polymer on the chemical conversion treatment film. A film thickness of 2μ formed by applying a coating material containing a curing agent and drying.
A clear-painted stainless steel sheet having a colorless and transparent clear film of m or more and 50 μm or less. 2. A weight ratio of phosphoric acid and silica in the chemical conversion treatment liquid.
Is H₃PO_Four/ SiO ₂Is 1/10 or more and 5/1 or less
And the amount of chemical conversion coating adhered is SiO₂2 mg in conversion
/ M²200 mg / m or more²Characterized by
The clear-painted stainless steel plate according to claim 1. 3. The thickness of the clear film is 5 μm or more and 20 μm or more.
It is the following, The clear coating stainless steel plate of Claim 1 or Claim 2 characterized by the following. 4. The content of the siloxane-based inorganic polymer in the coating material containing the acrylic organic polymer and the siloxane-based inorganic polymer and the curing agent is based on the total content of the acrylic organic polymer and the siloxane-based inorganic polymer. It is 10 wt% or more and 50 wt% or less, and the clear coated stainless steel sheet according to claim 1 to 3.