JPS59201832A - Preparation of injection molded article - Google Patents

Abstract

PURPOSE:To improve the surface gloss of a molded article, by performing injection molding by using a mold of which the cavity surface is coated with a cured silicone varnish film with a thickness of 5-100mum. CONSTITUTION:Silicone varnish is applied to the vavity surfaces of a mold and cured to form a cured film with a thickness of 5-100mum. In the next step, for example, a thermoplastic resin obtained by graft polymerizing one or more of a monomer selected from an aromatic vinyl compound, a vinyl cyanide compound and alkyl methacrylate with an alkyl acrylate polymer is subjected to injection molding in the coated cavity.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing an injection molded article with excellent surface gloss and no uneven gloss.

Conventionally, when injection molding thermoplastic resins such as olefin and styrene, the cavity surface of the mold is subjected to surface treatment such as hard chrome plating in order to improve the surface gloss of the injection molded product. However, with conventional metal plating methods, it is often the case that sufficient gloss cannot be obtained depending on the molding material. For this reason, methods are used to improve the overall gloss by increasing the molding conditions, especially the mold temperature.

If the mold temperature is raised, the molding time becomes longer, which significantly reduces productivity, and depending on the shape of the molded product, the so-called sink mark phenomenon, which causes depressions on the surface of the molded product, is more likely to occur, so its practical use is limited. It's just a method. On the other hand, molded products with a textured pattern on the surface of the molded product are often used due to design needs, but in conventional metal plating processes, when the textured pattern is present, the gate area and weld line of the textured surface are The unevenness of gloss tends to occur in some areas, which seriously impairs the appearance of the molded product.This unevenness of gloss cannot be solved by conventional metal plating treatment, improvement of molding conditions, etc.

Conventionally, a method of applying an oil-type or emulsion-type silicone mold release agent (non-curing) to the mold surface has been used, but this method prevents the resin from sticking to the mold during molding. This prevents molding from occurring and makes it easier to take out the molded product, but it does not have the effect of improving the appearance of the molded product.

The present invention solves this problem.

That is, the present invention is characterized in that, in injection molding of thermoplastic resin, the injection molding is carried out using a mold in which the cavity of the mold is coated with a cured coating film of silicone face having a thickness of 5 to 100 μm. The present invention relates to a method for manufacturing injection molded products.

The thermoplastic resin of the present invention includes a polymer obtained by radical copolymerization. Among these, ov-fin type thermoplastic resins include polyethylene, polypropylene,
Ethylene-propylene copolymer, ethylene-propylene-diene copolymer.

Examples include polybutadiene. In addition, examples of styrene-based thermoplastic resins include sunalene and chlorostyrene.

Polymers or copolymers of styrenic monomers such as vinyltoluene, α-methylstyrene, α-ethylstyrene, etc.
Copolymers of styrene monomers with other monomers such as acrylonitrile and methacrylic acid alkyl esters (e.g. styrene-acrylonitrile copolymers), polybutadiene, ethylene-propylene copolymer, ethylene-propylene-diene copolymer, acrylic acid Products obtained by graft polymerizing a styrene monomer and other monomers as necessary to a rubber component such as an alkyl ester polymer (
Examples include acrylonitrile-polybutadiene comb-styrene terpolymer, acrylonitrile-acrylic acid alkyl ester polymer-styrene copolymer, etc. In addition, here, the acrylic acid alkyl ester polymer is
If necessary, add acrylic alkyl esters such as butyl acrylate, divinylbenzene, ethylene glycol dimethacrylate, triallyl in cyanurate.

It is obtained by polymerization in the presence of a polyfunctional monomer such as triallyl cyanurate or tris(2-acryloyloxyethyl)in cyanurate and, if necessary, polybutadiene rubber. -Again.

The acrylic acid alkyl ester polymer may be crosslinked with a peroxide such as benzoyl peroxide.

The thermoplastic resin of the present invention includes at least one selected from the above-mentioned acrylic acid alkyl ester polymer, an aromatic vinyl compound such as a styrene monomer, a vinyl cyanide compound such as acrylonitrile, and a methacrylic acid alkyl ester such as methyl methacrylate. Particularly preferably, a product obtained by polymerizing at least two or more monomers including a styrene monomer has an excellent improvement effect in that an injection molded product with no surface gloss and no uneven gloss can be obtained.

Note that the thermoplastic resin of the present invention may be a blend of two or more of the above-mentioned resins.

The silicone varnish in the present invention includes a silanol group at the end of methyl silicone varnish, methyl phenyl silicone varnish, etc., which undergoes a crosslinking reaction at room temperature or under heating in the presence or absence of a catalyst, resulting in a three-dimensional structure. A cured product is used.

To form a hardened silicone varnish film on the cavity surface of the mold, first, coat the cavity of the mold with silicone varnish, spray paint, etc.
It can be cured at room temperature or by heating. The preferred curing conditions at this time vary depending on the type of silicone face, but 1. Usually, it is cured by heating to 100 to 250°C. 2. It improves the adhesion of the cured film to the mold surface, 1. It improves the surface hardness, and This is preferable for improving the gloss of molded products.

The thickness of the cured film is 5 to 100 μm, preferably 10 to 100 μm.
5 Q It is made ltm. If it is less than 5 μm, the gloss improvement effect will be low, and if it exceeds 100 μm, the cooling process after injection molding will be long, resulting in a longer molding cycle.

An injection molding machine for injection molding according to the present invention.

There are no restrictions on injection molding conditions and molding materials.

It should be selected based on the shape of the molded product, etc.

For example, as the injection molding machine, a conventional one-screw or one-plunger injection molding machine can be used. It was a long time ago. The molding temperature is determined by the melting temperature of the resin, and is set at a temperature at which the resin is sufficiently melted within the cylinder and at which it does not deteriorate due to thermal decomposition or the like. The injection pressure is determined by the molding temperature.

The pressure is set above the pressure necessary to prevent short shots and sink marks, and below the pressure that does not cause flash. The mold temperature is generally 20 to 100°C, but depending on the flowability of the resin,
It is selected as appropriate based on conditions such as molding temperature, wall thickness, and molding cycle.

Next [Example is shown]

Example 1 The cavity surface of the mold was spray coated with silicone face (50 Tittle Melt iM) - Re Silicone SR, 2410° Tone Silicone (trade name).

It was baked at 200° C. for 30 minutes to form a hardened film of 30 μm. Using this mold, an acrylonitrile-acrylic acid alkyl ester polymer was molded using an injection molding machine (model V36A-450 manufactured by Nikko Ankelberg ■) under the following conditions: resin temperature 240°C, mold temperature 50°C, injection field pressure 500, and 97cm2. A polymerized styrene copolymer (Pitax V6700.Hitachi Chemical Co., Ltd. trade name) was injection molded.

Table IVC shows the results of measuring the glossiness (reflection angle of 60°) of the surface of the molded product using a crossmeter. In addition, injection molding was performed in the same manner using a mold in which no cured film of the silicone face was formed, and evaluation was made. The results are shown in Table 1.

Table 1 Measurement Results Example 2 Silicone face (50% toluene solution) was spray-painted on a flat plate mold with a grain pattern (FNDB2 and UNDAx manufactured by Tanazawa Hakkosha Co., Ltd.) on the surface of the injection mold. It was baked at ℃ for 30 minutes to form a hardened film with a thickness of 20 μm. Using this mold, injection molding was carried out using the same molding machine and molding conditions as in Example 1.

This flat plate has a game of 3 points and a weld line of 2
It is a ridge that occurs in several places. On the other hand, the same material was injection molded under the same conditions using a different mold. Table 2 shows the results of evaluating the molded appearance of the injection molded product.

Table 2 Molding appearance As in Example 1, by using a mold with a hardened silicone face coating applied to the cavity surface of the injection mold, the surface gloss of the injection molded product was improved, and the gloss on the grained surface was improved. The effect of eliminating unevenness can be obtained.

Claims (1)

[Scope of Claims] 1. In injection molding of thermoplastic resin, injection molding is performed using a mold whose cavity surface is coated with a cured coating film of silicone varnish having a thickness of 5 to 100 μm. A method for manufacturing an injection molded product characterized by: 2. A patent claim in which the thermoplastic resin is obtained by graft polymerizing an acrylic acid alkyl ester polymer with one or more monomers selected from aromatic vinyl compounds, vinyl cyanide compounds, and methacrylic acid alkyl esters. A method for producing an injection molded product according to item 1.