JPH0768217A - Metal surface coating method - Google Patents

Abstract

(57) [Summary] [Objective] To provide a coating method for obtaining a metal surface excellent in weather resistance, acid resistance, stain resistance and scratch resistance. [Composition] In a method for coating a metal surface,
A method for coating a metal surface, which comprises applying a liquid composition containing a hydrolyzate of an alkoxysilane and a polyester resin to the metal surface, and then drying.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for coating a metal surface.

[0002]

2. Description of the Related Art In the manufacture of transportation machines, especially passenger cars, after assembling the machine, a paint dissolved in a solvent or the like is applied to the surface of the machine to form a coating film.・ It is actually practiced to improve the stain resistance and corrosion resistance and maintain the aesthetic appearance. Further, demands for weather resistance, acid resistance, stain resistance, and scratch resistance are extremely high also in the fields of home appliances and building exteriors.

Generally, these automobiles, home electric appliances and building material products are applied after assembling, but if it is possible to increase the proportion of applying and drying before assembling and bending it to the final product, productivity of them can be increased. Will improve accordingly. Therefore, if it is possible to form a coating on a metal flat plate and then bend it, the application to home electric appliances and building materials, and further to the outer panels of automobiles can be expanded. Therefore, there is a strong demand for improvement in coating flexibility.

Further, at present, the problem of acid rain is drawing attention, and there is a demand for improvement of a technique for keeping a coating film more beautiful. Various methods have been proposed to meet this demand, but these requirements are not always sufficiently satisfied.

[0005]

Therefore, the present inventor has reached various aspects of the present invention by conducting various studies in order to find a coating method for a metal surface which meets the above-mentioned demands and has improved flexibility.

[0006]

That is, the gist of the present invention is, in a method for coating a metal surface, applying a liquid composition containing a hydrolyzate of an alkoxysilane and a polyester resin to the metal surface and then drying. A method of coating a metal surface is characterized by that. Hereinafter, the present invention will be described in detail.

First, as the alkoxysilane hydrolyzate in the present invention, a tetraalkoxysilane partial hydrolyzate such as tetramethoxysilane, tetraethoxysilane, or tetrapropoxysilane is usually used.
The hydrolysis reaction itself can be carried out by a known method. For example, a predetermined amount of water is added to the above tetraalkoxysilane in the presence of an acid catalyst to distill off the by-produced alcohol, and usually about room temperature to 100%. React at ℃. The alkoxysilane is hydrolyzed by this reaction, and a liquid silicate oligomer having two or more hydroxyl groups by a condensation reaction (usually an average degree of polymerization of about 2 to 8, preferably about 3).
~ 6) are obtained as hydrolysates.

The degree of hydrolysis can be appropriately adjusted depending on the amount of water used, but in the present invention, it is usually 4
It is selected from about 0 to 90%, preferably about 60 to 80%. This tetramethoxysilane hydrolyzate is usually 2 to
Although it contains 10% by weight of the monomer, the monomer content is removed by a known method such as flash distillation or vacuum distillation so that the content of the monomer is 1% or less, preferably 0.3% or less. The storage stability of the compounded liquid is also improved. In the present invention, in this hydrolyzate,
A polyester resin is blended to obtain a liquid blend.

Examples of the polyester resin include polybasic acids such as phthalic anhydride, isophthalic acid, terephthalic acid, fumaric acid, adipic acid and succinic acid, monobasic acids such as lauric acid and stearic acid, and ethylene glycol, propylene glycol, Butylene glycol, diethylene glycol,
A condensate with a polyhydric alcohol such as trimethylolpropane, glycerin, neopentyl glycol, pentaerythritol, 1,4-butanediol, and 1,6-hexanediol, which can be used as a coating resin on the market. .

The above-mentioned hydrolyzate and polyester resin are compounded as follows. That is, although an organic solvent is preferably used, it is preferable that the organic solvent is compatible with both the hydrolyzate and the polyester resin, such as alcohols, glycol derivatives, hydrocarbons, esters, One kind or a mixture of two or more kinds of ketones and ethers can be used.

Specific examples of alcohols include methanol, ethanol, isopropyl alcohol, n-butanol, isobutanol and octanol, and examples of glycol derivatives include ethylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether and ethylene glycol. Examples include mono n-propyl ether and ethylene glycol mono n-butyl ether. Of these, if ethanol or methanol is used, it is possible to obtain a coating of high hardness, which is particularly excellent in scratch resistance.

The hydrocarbons include benzene, kerosene,
Toluene, xylene, etc. can be used, and as esters,
Methyl acetate, ethyl acetate, butyl acetate, methyl acetoacetate, ethyl acetoacetate and the like can be used. Ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and acetylacetone, and ethers such as ethyl ether, butyl ether, methyl cellosolve, ethyl cellosolve, dioxane, furan and tetrahydrofuran can be used.

The amount of the organic solvent used is preferably about 1 to 10 times the weight of the polyester resin in terms of operability. When compounding, a catalyst is added before the coating on the metal surface, which will be described later. For example, inorganic acids such as hydrochloric acid, acetic acid, nitric acid, formic acid, sulfuric acid, phosphoric acid, paratoluenesulfonic acid, benzoic acid, phthalic acid, etc. Organic acids, dibutyltin dilaurate, dibutyltin dioctiate, dibutyltin diacetate and other organic tin compounds, potassium hydroxide, sodium hydroxide and other alkali catalysts are effective, but especially inorganic acids, organic tin compounds and organic acids Is effective.

The content of the hydrolyzate is preferably 50 to 300 parts by weight, more preferably 1 part by weight, based on 100 parts by weight.
It is from 00 to 250 parts by weight. If it is less than 50 parts by weight, the bending rigidity is lowered, which is not preferable. The composition containing the above hydrolyzate, polyester resin, (catalyst) and solvent is a substantially uniform liquid substance having a two-phase separation of 10,000 cps or less at room temperature (25 ° C.).

In the present invention, the liquid composition is coated on the metal surface. Examples of the metal include plate-shaped bodies such as mild steel, aluminum and stainless steel. The coating is carried out by a general liquid coating method such as ordinary atomization coating, roll coater, curtain flow coater and dip coating. The thickness of the coating film varies depending on the purpose of use, but is usually selected from about 10 to 50 μm.

The coated metal is then dried. Drying is possible at room temperature, but usually -20 to 300 ° C
From the viewpoint of efficiency and efficiency, heating is preferably performed to about 150 ° C. The drying furnace can use forced air blowing or an open type. Drying volatilizes the organic solvent, completes the dehydration condensation reaction of the hydrolyzate and the polyester resin, and volatilizes water.

The metal surface coated as described above has good weather resistance, acid resistance, stain resistance, and high flexibility, and therefore can sufficiently withstand bending after coating.

[0018]

EXAMPLES The present invention will be described in more detail below with reference to examples. Parts and% are parts by weight and% by weight, unless otherwise specified. Examples 1-3 500 equipped with stirrer, condenser for reflux and thermometer
Tetramethoxysilane 2 was added to a 3 ml round bottom flask.
After adding 34 gr and 74 gr of methanol and mixing,
22.2 gr of 0.05% hydrochloric acid was added, and the internal temperature was 65 ° C, and 2
The hydrolysis reaction was performed for a time.

Then replace the condenser with an extraction tube,
The internal temperature was raised to 150 ° C, extraction was performed with methanol, and the mixture was further heated at 150 ° C for 3 hours for condensation. In this way, a hydrolyzate was obtained. The degree of polymerization was 3 to 6 and the hydroxyl group was 10 or more. A mixture of 200 parts by weight of this alkoxysilane hydrolyzate and 100 parts by weight of any of the following polyester resins A to C (Examples 1 to 3) is a mixed solvent of xylene / butyl acetate = 50/50 (weight ratio). Ford Cup No. No. 4 was diluted so that the flow-down time would be about 20 seconds and chromated stainless steel plate (SUS 304 HL size 70
(× 150 × 0.3 mm) coated on one side with an air spray gun to a dry film thickness of about 20 μm,
After leaving it for a minute, it was baked and dried for 20 minutes in an electric heating type hot air drying furnace kept at about 180 ° C., left for 24 hours at room temperature, and then subjected to various tests.

(1) Polyester resin Polyester resin A ("Byron" 20 from Toyobo Co., Ltd.)
0) Polyester resin B (Hitachi Chemical Co., Ltd. "Esper")
1102) Polyester resin C (Dainippon Ink and Chemicals, Inc. "Super Beckolite" M-6803-40)

(2) Test method Pencil hardness: JIS K5400 8.4.2 Evaluation by scratches Bending test: The test piece was bent 180 ° with the coated surface facing outward, and an unpainted test plate of the same thickness was applied inside. Displayed with the minimum number of test plates that will not crack or peel when completely bent with a vise. Adhesion: JIS K5400 8.5.2 Cross-cut tape method Clearance 1 mm Acid resistance: 5% H ₂ SO ₄ spot Test, 1 month Contamination resistance: According to JIS K5400 8.10. However, wipe with a clean gauze soaked in water. Contamination material is oil-based black accelerated weathering resistance of marking pen specified in JIS S6037: JIS K5400 9.8.1 Sunshine carbon arc lamp type, gloss retention rate after 3000 hours. The test results obtained are shown in Table 1.

[0022]

[Table 1]

[Example 4] The monomer content of the tetramethoxysilane hydrolyzate obtained in Example 1 was 5%. Subsequently, the jacket heated to 100 to 150 ° C. is boiled with tetramethoxysilane oligomer, and the vaporized monomer is discharged out of the system together with the inert gas. The amount of monomers in the tetramethoxysilane oligomer thus obtained was 0.2%. Then, a compounded solution was obtained in exactly the same manner as in Example 1 using a polyester resin and a xylene / butyl acetate solvent. This liquid did not show thickening even after 6 months. The viscosity of the mixed liquid obtained in Example 1 doubled in February.

[0024]

According to the method of the present invention, the metal surface obtained has excellent weather resistance and acid resistance and has high flexibility.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tana 邉 ▼ Yasuo Marunouchi 2-5-2, Chiyoda-ku, Tokyo Sanryo Kasei Co., Ltd. (72) Inventor Nobuyuki Matsuzoe 2-5 Marunouchi, Chiyoda-ku, Tokyo No. 2 Sanritsu Kasei Co., Ltd.

Claims (2)

[Claims] 1. A method for coating a metal surface, which comprises coating a liquid composition containing a hydrolyzate of an alkoxysilane and a polyester resin on the metal surface and then drying. 2. The method for coating a metal surface according to claim 1, wherein the amount of the monomer in the hydrolyzate is 1% by weight or less.