JPS5921336B2 - Method of forming a cured film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a coating film curing method for forming a coating film on the surface of a plastic molded product to obtain a product with excellent surface hardness. The present invention relates to a method for providing cured coatings with smooth surface properties.

Plastic molded products generally have characteristics such as easy moldability, impact resistance, colorability, and light weight, and are used in a wide range of fields. However, it had the disadvantage that the surface hardness was low and the surface of the plastic molded product was easily scratched. In order to eliminate these drawbacks, a coating method is known in which a hydrolyzed condensate of organosiloxane is applied to the surface of a plastic molded product and heated. It is also known to use a coating liquid to which a curing agent such as organic sodium carboxylate is added for this purpose. However, in the conventional method of using a coating liquid containing such a hardening agent, even if the coated product is excellent, the life of the coating liquid, so-called pot life, is short and the coating liquid is relatively short. It had a tendency to gel over time. For this reason, it is difficult to manufacture products with stable coating performance, which causes variations in coating thickness, smoothness, transparency, etc. Furthermore, as a matter of course, the usage rate of the coating liquid was also poor, which was a major drawback in manufacturing. In general, the more excellent the catalyst has a curing effect, the greater the drawbacks, and for this reason, the catalyst has been plagued by a contradiction between the surface hardness of the product and the pot life of the coating liquid. In the past, in order to solve this drawback, an anti-gelling agent was sometimes added to the coating solution, but this did not sufficiently solve the above-mentioned drawback. An object of the present invention is to eliminate the above-mentioned drawbacks and provide a method for forming a cured film that does not cause problems in the pot life of the coating liquid.

That is, the present invention applies a hydrolyzed condensate solution of organosiloxane to the surface of a plastic molded article, pre-dries it to form a film of the condensate, and then applies a curing catalyst that penetrates into the film but does not dissolve it. This method of forming a cured film is characterized by applying a solution onto the film and curing it.

The hydrolyzed condensate of organosiloxane used in the present invention has the general formula R'Si(OR2)3 (where R' is methyl, ethyl, propyl, butyl, phenyl, vinyl,
aryl, R2 is a C1-C4 alkyl group), as described in U.S. Patent No. 34513
5 by adding water and a trace amount of acid as described in No. 88.
It is an initial hydrolysis condensate obtained by heating at a temperature of 0 to 80°C for 1 to 10 hours, and also includes a cocondensation product obtained by hydrolysis with tetraalkoxysilane, bifunctional siloxane, etc.

A solution of the hydrolyzed condensate of organosiloxane, ie, a coating liquid, is prepared by dissolving the condensate in a C, to C4 alcohol, preferably ethyl alcohol.

This solution contains a solvent that is compatible with the plastic substrate in order to improve the adhesion between the surface of the plastic molded product and the coating film, and an appropriate medium boiling point to prevent condensation that can cause clouding due to rapid evaporation of the solvent. It is also possible to add solvents such as solvents and high boiling point solvents. The ratio of the organosiloxane hydrolyzed condensate to the solvent, the so-called solid content concentration, varies depending on the purpose, but the solid content concentration is usually 10 to 5.
About 0% is used. Furthermore, leveling agents, surfactants, ultraviolet absorbers, dyes and pigments, antistatic agents, etc. can also be added as appropriate to the coating liquid. The coating solution prepared in this manner may be applied to the surface of the plastic molded article by any conventional method, such as dipping, spraying, roll coater, flow coater, etc.

The thickness of the coating film varies depending on the use of the plastic molded product, but it is usually 1 to 20 μm, preferably 3 to 20 μm.
It is about 10μ.

For example, when a dipping method is used, the film thickness is controlled by the viscosity of the coating liquid, and the viscosity is controlled by the amount of solvent and the degree of condensation of the alkyltrialkoxysilane partial condensate. The coated molded article is pre-dried to form a film of the organosiloxane hydrolysis condensate.

Drying conditions vary depending on the type of plastic, the composition of the coating liquid, the purpose, etc., and are carried out at room temperature or any temperature below the heat distortion temperature of the plastic substrate. If drying is insufficient, the film of the organosiloxane hydrolyzed condensate will dissolve in the catalyst solution or fall off when immersed in the catalyst solution, resulting in poor appearance of the product. The curing reaction of the condensate proceeds due to heat, resulting in insufficient penetration of the subsequent catalyst solution, and as a result, the surface hardness of the product does not increase. In the present invention, such drawbacks have been solved by appropriately selecting pre-drying conditions of 15 minutes or less at 50 to 120°C. The curing catalyst solution used in the present invention consists of a curing catalyst and a solvent for dissolving the curing catalyst, and any curing catalyst known as a curing catalyst for organosiloxane may be used.

An example is an alkali metal salt of an organic carboxylic acid. The solvent must be a solvent that dissolves the curing catalyst and penetrates into the pre-dried organosiloxane hydrolyzed condensate film, but does not dissolve it. In such a case, the curing catalyst will penetrate into the coating together with the solvent, but the coating will not dissolve and fall off and the appearance will not be impaired. An effective example of such a curing catalyst solution is a combination of acetic acid, water, and curing catalyst. During implementation, the film thickness of the coating, the degree of pre-drying, the composition of the catalyst solution, the temperature of the catalyst solution, the time of immersion in the catalyst solution, and the temperature of the molded product during immersion are interrelated, and the optimal conditions are determined by combining these appropriate conditions. It is important to find out. The molded article immersed in the curing catalyst solution is finally dried and cured.

The higher the drying temperature, the shorter the drying time, which is preferable, but if it is too high, the molded product will deform, so it must be lower than the heat deformation temperature of the plastic substrate. Usually, in the case of thermoplastics, the temperature is 50 to 120°C for about 1 to 12 hours. A surfactant can also be added to the catalyst solution to prevent repellency.

Other additives such as ultraviolet absorbers, dyes and pigments, antistatic agents, and other additives can also be added as appropriate. Plastic base materials include polystyrene, acrylonitrile, styrene copolymer, polymethyl methacrylate, styrene methyl methacrylate copolymer, polyvinyl chloride, polycarbonate, ABS resin, high impact polystyrene, transparent ABS resin, cellulose acetate, cellulose propionate, Examples include cellulose butyrate, diallyl phthalate resin, and diethylene glycol bisallyl carbonate resin.

The present invention will be explained below with reference to Examples. Example 1 Methyltriethoxysilane was put into a reactor at a ratio of 120f1 water was 301ml, and hydrochloric acid was put in a ratio of 3 millionths of the total weight of methyltriethoxysilane and water, and heated at 50°C for 4 hours.
A partial hydrolyzate of methyltriethoxysilane was obtained.

The mixture was further heated to expel water and by-produced ethanol, and then cooled. Ethanol was added to prepare a 20% solution of a methyltriethoxysilane partial hydrolysis condensate, which was used as a coating liquid. After degreasing and washing a polymethyl methacrylic molded lens with a detergent, it was immersed in the above coating solution, and the composition solution was applied by pulling it up at a speed of 40 (1-J mo V!) for 1 minute. It was pre-dried for 2 minutes at 90°C.

Separately, prepare a catalyst solution consisting of 80 Y of acetic acid, 207 V of water, 2 V of sodium acetate, and 0.57 V of surfactant, and add the previously pre-dried lens to this catalyst solution (2 V) without cooling.
0° C.) for 5 seconds, left at room temperature for 2 minutes, placed in the dryer again, and dried and hardened at 90° C. for 10 hours.

The pencil hardness, adhesion, and scratch resistance (steel wool test) of the product thus obtained were measured.

The measurement method is as follows. Pencil hardness: Measured using a pencil hardness meter (manufactured by Toyo Seiki) with a load of 10007.

Adhesion: I used a razor to make 11 incisions vertically and horizontally at 1mm intervals to create base marks, and once the Zero Tape was adhered, I peeled it off strongly.

The peeling of the base grain was observed. Scratch resistance - (
Steel wool test) The surface was scratched with steel wool and the degree of damage was observed.

Lens appearance: Judgment was made with the naked eye.

The test results are as follows. Comparative example 1 of scratch level Sodium acetate 17 was added and dissolved in the coating liquid used in Example 1 to prepare a coating liquid.

Claims (1)

[Claims] 1. A solution of a hydrolyzed condensate of organosiloxane is applied to the surface of a plastic molded product, pre-dried to form a film of the condensate, and then penetrates into the film but does not dissolve it. A method for forming a cured film, comprising applying a curing catalyst solution onto the film and curing it. 2. The method for forming a cured film according to claim 1, wherein the curing catalyst solution contains an alkali metal salt of an organic carboxylic acid, acetic acid, and water.