Method for molding article in plurality of colors

Abstract

A method and apparatus for molding plastic articles in two colors, particularly, the bodies of magnetic tape cassettes, in which a strong bonding force is provided between the two portions without having to form a recess and projection on the joining edges of the two portions. A slide core, which is moved in and out of a primary mold cavity between the mold of the two portions of the article, is provided with a tubular passage having an opening within the primary mold cavity along edge portions of the slide core. The slide core is fully inserted into the primary mold cavity to mold the first portion, then partially withdrawn to form a seconary mold cavity in which the second portion is subsequently molded. After molding the first portion, an adhesive is injected through the tubular passage along the edges of the first portion which will join corresponding edges of the second portion to thereby firmly join the two portions.

Description

BACKGROUND OF THE INVENTIONThe present invention relates to a method and apparatus for molding a plastic article in a plurality of colors, and more particularly to a method and apparatus for molding an article in a plurality of colors in such a manner that the strength of a joint between primary and secondary molded pieces made of plastics of respective two different colors is enhanced.Products made of injection-molded plastics are widely used, and various methods for injection molding have been cassette.A magnetic tape cassette generally employs a pair of hubs on which a magnetic tape is wound rotatably supported in the body of the cassette. The cassette body is composed of upper and lower half portions manufactured by the injection molding of a plastic material such as ABS resin. Each of the upper and lower half portions has a transparent or translucent window through which the state of winding of the magnetic tape or the like can be observed from the outside. The window portion, ...

AI Technical Summary

Benefits of technology

Accordingly, it is an object of the present invention to provide a method and apparatus for molding plastic articles in a plurality of colors in which the bonding force between the mutually joined surfaces of two different types of plastics sufficiently high enough to provide the joint with sufficient strength, even if the surfaces are not provided with an engaging projection and recess.

Problems solved by technology

This results in less than desirable productivity and a high cost of production.

However, the bonding force between the mutually joined surfaces of the two types of plastic used in the two-color molding process to constitute the window portion and the half portions of the body of the magnetic tape cassette strongly depends on the temperature and injection pressure of the later-injected plastic material, and the strength of the joint of the mutually joined surfaces is generally less than desirable.

This is a problem particularly if the magnetic tape cassette is of a type having a relatively small body thickness and is made of two different types of plastic materials which are not soluble in each other.

The problem is very serious because it affects the quality and service life of the whole cassette.

However, the bonding force is still generally insufficient.

However, this approach is still disadvantageous in that the size of the projection is limited, and hence the bonding force is still insufficient.

When the slide core is moved, if the molded projection is large, the recess in the slide core will greatly strain the projection molded therein when the slide core is moved.

That is, if the size of the projection is made large enough to sufficiently increase the bonding force between the window portion and the body portion, the projection will undergo strain or deformation due to the movement of the slide core, thus again decreasing the strength of the joined surfaces.

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