Injection molding method for thermoplastic resin

Abstract

The invention provides an injection molding method capable of further increasing the replicability and glossiness during the injection molding of carbon dioxide. The method of injection molding includes that resin (a) is filled in a die cavity (1), then in the process from the starting to die opening, the replicability and the glossiness are increased by injecting the carbon dioxide between the resin and the surface of the die cavity, wherein after a filling procedure that the resin with a just-designed amount is filled in the die cavity is finished, a procedure aiming to decrease the pressure of the resin through temporarily stopping the filling of the resin is provided, and then a pressure keeping procedure is carried out by increasing the pressure of the resin. The carbon dioxide can be uniformly distributed everywhere in the cavity (1) through employing the method, and thereby the replicability and the glossiness of the integral visual surface of molding products can be uniformly increased.

Description

technical field [0001] The present invention relates to an injection molding method for thermoplastic resins, and more specifically to an injection molding method as follows: in order to improve reproducibility (writing property) and glossiness, carbon dioxide, etc. The surface softens and enters the holding process, thereby improving reproducibility and gloss. Background technique [0002] In general, injection molding is to fill the molten resin into the cavity of the mold and cool it in the mold to obtain the molded product. In this injection molding, the mold is kept below the solidification temperature of the resin before filling the resin. Therefore, the solidification of the resin proceeds from the moment the molten resin is filled into the cavity, and a solidified layer called a skin layer is formed on the surface. In particular, the flow front of the molten resin is replicated on the surface of the molded article due to the action of the fountain flow. Curing also...

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Problems solved by technology

[0003] However, in this method, although the reproducibility is improved, shrinkage cavities (ヒケ) and warpage tend to occur in the molded product due to uneven shrinkage when the resin is cured

And the following problems arise: the molding cycle becomes longer, the production efficiency is lowered, and thus the molding cost is increased

However, these methods have the following problems: Although the reproducibility is improved, special equipment is required for each, and the molding cost is increased because the molding cycle becomes longer and the production efficiency is lowered.

[0009] However, in the invention described in the aforementioned Japanese Patent Laid-Open No. 2000-244610, when the thickness of the molded article is thin or the shape is complex, there may be a transfer defect as follows: the carbon dioxide does not permeate the surface layer uniformly, and the transfer cannot be improved as a whole. , or cannot locally improve replicability

As one of the reasons, the problem is that after the filling process of the molten resin is completed, the molten resin in the cavity of the mold remains under the high resin pressure during filling, and even if carbon dioxide is injected, the injected carbon dioxide cannot be sufficiently spread to be compatible with the entire product. Between the cavity surface corresponding to the viewing surface and the molten resin

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