JPS5850267B2 - Coating material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a coating composition for improving surface properties such as surface hardness and chemical resistance of plastic products.

In general, plastic molded products, such as thermoplastic resins such as polymethyl methacrylate, polystyrene, polyvinyl chloride, and polycarbonate, have advantages such as light weight, easy processability, and impact resistance. It has drawbacks such as being susceptible to swelling and dissolution upon contact with other materials.

A number of methods have been proposed to improve these drawbacks, such as a method of hardening the plastic surface by coating with a coating agent made of a hydrolyzate of tetraalkoxysilane and an organic polymer or a hydrolyzate of alkyltrialkoxysilane.

However, methods using such compositions generally require a high curing temperature (120'C to 170°C), which is unsuitable for processing thermoplastic resins as it may cause deformation of the molded product, and is not suitable for widespread practical use. Not yet reached.

In order to improve the above-mentioned drawbacks, the present inventors have conducted extensive research on low-temperature curing methods for compositions containing hydrolysates of alkoxysilanes as main components. At least one of a partial hydrolyzate of an alkoxysilane, a co-partial hydrolyzate of a tetraalkoxysilane and an alkyltrialkoxysilane, and a mixture of a partial hydrolyzate of a tetraalkoxysilane and a partial hydrolyzate of an alkyltrialkoxysilane; It has been discovered that a composition obtained by dissolving an alkali metal borate salt in a solvent can provide a coating film that can be cured at low temperatures and has excellent practicality.

The tetraalkoxysilane used in the present invention is one in which the alkoxy group is methoxy, ethoxy, propoxy, butoxy, or the like.

Furthermore, alkyltrialkoxysilanes include those in which the alkyl group is methyl, ethyl, propyl, butyl, pentyl, hexyl, etc., and the alkoxy group is methoxy, ethoxy, propoxy, butoxy, etc.

Partially hydrolyzed products of these silane compounds can be obtained by preparing an alcohol solution of tetraalkoxysilane or alkyltrialkoxysilane separately or by mixing them, and adding water in an amount equal to or more than the mole amount removed based on the total mole amount of alkoxy groups present. Obtained by hydrolysis in the presence of acid.

In some cases, partial hydrolysates of these silane compounds can also be obtained by directly hydrolyzing tetrachlorosilane or alkyltrichlorosilane.

Generally, it is often better to mix these silane compounds and co-hydrolyze them simultaneously than to hydrolyze them separately.

In the present invention, the alkali metal boric acid salts are salts of metaboric acid, tetraboric acid, etc., and lithium, sodium, potassium, etc.

In addition, its use is limited to silicon (
Si) is 1 to 100% heavier on a weight basis.

If the amount of the alkali metal borate is less than this range, the effect will be insufficient, and if it is more than this range, the adhesion and water resistance of the coating film will tend to deteriorate.

Organic polymers such as alkyl acrylate or alkyl methacrylate/hydroxyalkyl acrylate or hydroxyalkyl methacrylate copolymer or etherified methylolmelamine may be added to the composition of the present invention for the purpose of improving the physical properties of the coating film, particularly heat cycle resistance. is also possible.

Furthermore, it is possible to add surfactants to prevent surface defects such as peeling and shrinkage of the paint film, as well as to prevent repellency and pinholes in the paint film. A good film is produced by adding a small amount of the bookmark copolymer.

Further, it is also possible to further improve the practicality of the composition as a coating agent by dissolving an ultraviolet absorber, an antistatic agent, or a dye in the composition of the present invention.

Solvents used in the production of coating compositions include alcohols, ketones, esters, ethers,
Cellosolves, halides, carboxylic acids, aromatic compounds, etc. can be used, but the selection depends on factors such as the base material such as the polymeric material used and the evaporation rate, and the It is mixed with various ingredients in a wide range of proportions.

In particular, the use of lower alkylcarboxylic acids such as formic acid and acetic acid is effective in improving the adhesion between the substrate and the coating film, the hot water resistance of the coating film, and preventing increases in liquid viscosity and gelation after the composition is prepared. .

Generally lower alcohols (e.g. methanol, ethanol, propatool, butanol), lower alkyl carboxylic acids (e.g. formic acid, acetic acid, propionic acid), aromatic compounds (e.g. benzene, toluene, xylene) and cellosolves (e.g. It is particularly useful to use a combination of evapolymer methyl cellosolve, butyl cellosolve, and the like.

The amount of solvent used can be appropriately selected depending on the required thickness of the coating film, coating method, etc.

Coating with the composition of the present invention can be done by any of the commonly used methods such as spraying, dipping, brushing, and roll coating, and it can be made transparent by heating it after being applied to the surface of the thermoplastic resin product. It is possible to form a coating film with excellent hardness, scratch resistance, and chemical resistance.

The environmental conditions in the coating step are preferably 20° C.±3° C. and a relative humidity of 60% or less under clean air from which dust has been removed, from the viewpoint of transparency of the coated product.

In the case of the composition of the present invention, the heating temperature can be much lower and for a shorter time than in the case of conventional methods, and the heating temperature is 70 to 90°C and 30°C.
Since about 120 minutes is sufficient, it is suitable for coating resins with low heat distortion temperatures such as polymethyl methacrylate.

The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited by these Examples.

Note that all parts in the examples indicate parts by weight unless otherwise specified.

Examples 1 to 8 (1) Preparation of partial hydrolyzate solution of tetraethoxysilane (
Ingredients ■) 46g of isopropyl alcohol and 12g of tetraethoxysilane
5 g was dissolved, and 43 g of a 0.05N aqueous hydrochloric acid solution was further added, followed by stirring at room temperature to effect hydrolysis.

After the reaction, the mixture was aged for 20 hours or more. (2) Preparation of partial hydrolyzate solution of methyltriethoxysilane (component ■) 103g of isopropyl alcohol and 96g of methyltriethoxysilane were charged into a hydrolysis container equipped with a reflux condenser, mixed and dissolved, and further 0.05 N Hydrochloric acid aqueous solution 15g
was added and the solution was heated under reflux for 5 hours while stirring to effect hydrolysis.

After the reaction, the mixture was cooled to room temperature to obtain a partial hydrolyzate solution.

(3) Preparation of co-partial hydrolysis solution of tetraethoxysilane and methyltriethoxysilane (component ■) As the hydrolysis reaction solution, 68 g of isopropyl alcohol, 38 g of tetraethoxysilane, 72 g of methyltriethoxysilane, and 36 g of a 0.05N hydrochloric acid aqueous solution were used. A copartial hydrolyzate solution was obtained in the same manner as in (2).

(4) Preparation of paint The above-mentioned component I, component ■, component ■ solution and potassium tetraborate (
80 parts of n-butanol and 4 parts of acetic acid in the proportions shown in Table 1.
It was dissolved in 0 parts.

In addition, if necessary, butyl acrylate/2-hydroxyethyl methacrylate copolymer (weight composition ratio 4/1) was added and dissolved to prepare a paint. 3 (5) Performance test of coating and coated products 3. After washing a methacrylate cast plate (product name SUMIPEX-〇〇〇, manufactured by Sumitomo Chemical Co., Ltd.) with water and ethanol, the above paint was heated at 21.5℃ and humidity 5.
The coating was applied under the environmental conditions of 5 minutes, and cured by heating and drying in a hot air dryer at 80° C. for 1 hour.

The painted polymethyl methacrylate cast board was subjected to the following tests.

a) Appearance: Transparency and other defects in the coating film were examined by visual observation.

b) Adhesion: After using a steel knife to make 100 incisions on the paint film, each extending one square inch into the material, and pasting cellophane tape (manufactured by Sekisui Chemical Co., Ltd.) on top of the incisions, The evaluation was made based on the number of stitches remaining when the cellophane tape was strongly peeled off in an upward direction of 90°.

C) Abrasion resistance: Rubbed with #000 steel wool to examine scratch resistance.

The judgment was as follows.

A...It won't get scratched even if it is rubbed strongly.

B: If you rub it too hard, it will be slightly scratched.

C: Damage occurs even with weak friction.

Note that the polymethyl methacrylate cast plate that was not coated at all was graded C.

Comparative Example 4 100 parts of the same partial hydrolyzate solution of tetraethoxysilane (ff part I) as in Example 1, 80 parts of n-butanol, 40 parts of acetic acid, butyl acrylate/2-hydroxyethyl methacrylate copolymer (weight composition A paint was prepared by adding and dissolving 20 parts (ratio 4/1) and 1 part of boric acid.

This paint was coated in the same manner as in the examples and performance tests were conducted on coated products, and the following results were obtained.

Performance of painted product Appearance Good Good adhesion 89/100 Abrasion resistance C Comparative example 5 100 parts of the same partial hydrolyzate solution of tetraethoxysilane (component I) as in Example 1, 80 parts of n-butanol, and 4 parts of acetic acid.
0 parts, butyl acrylate/2-hydroxyethyl methacrylate copolymer (weight composition ratio 4/1) 1.0 part of sodium tetraborate was added and dissolved in 20 parts and charged into a flask equipped with a reflux device.

After that, the internal temperature was raised to 70℃ without stirring.
After 5 minutes, the liquid became viscous and contained gel-insoluble matter, making it unusable as a coating liquid.

Claims (1)

[Claims] 1 (A) Partial hydrolyzate of tetraalkoxysilane, partial hydrolyzate of alkyltrialkoxysilane, copartial hydrolyzate of tetraalkoxysilane and alkyltrialkoxysilane, and partial hydrolyzate of tetraalkoxysilane and alkyltrialkoxy Obtained by dissolving at least one kind of a mixture of partial hydrolysates of silane and a heavy alkali metal salt in an amount of 1 to 100 weight tons based on the weight of silicon (Si) in the AJ (B) component in a solvent. Coating composition for thermoplastic resin.