Air-auxiliary injection forming process of thermoplastic resin product

Abstract

A gas-aided injection moulding technology for manufacturing thermoplastic resin products includes such steps as adding supercritical N2 and / or CO2 to fused resin, stirring, filling compressed air in mould, injecting said resin mixture in the mould while controlling air pressure, cooling, and demoulding.

Description

technical field [0001] The invention relates to a gas-assisted injection molding method for thermoplastic resin products, in particular to a method of adding compressed nitrogen into the molten resin before the molten resin material enters the cavity of the mold, and injecting it after forming a uniform molten resin / gas mixture In-cavity molding methods to a molding mold in which a sufficiently stable gas backpressure has been established with compressed gas. technical background [0002] In recent years, with the wide application of injection molded products in various fields, such as household appliances (such as televisions, telephones, etc.) and mobile electronic equipment (such as laptops, mobile phones, etc.) industry, commercial equipment, auto parts manufacturing, and In the daily industrial field, etc., due to the cost and function considerations of the products, there is an increasing demand for thinner and lighter products. At the same time, due to the need for c...

AI Technical Summary

Problems solved by technology

By adding less than 0.08% by weight of blowing agent or between 1% and 25% of blowing agent (nitrogen and / or carbon dioxide) into the molten resin in the plasticizing unit in a supercritical state, a homogeneous mixture or a single phase solution, and then nucleated by rapid pressure drop in the nucleation path, and finally injected into the cavity, because the viscosity of the mixture is significantly reduced after the carbon dioxide and / or nitrogen are fully mixed with the molten resin, and this mixture is injected into the mold In the process, the jet flow is very easy to occur, so there are defects such as jet spots and surface foaming on the surface of the product; at the same time, because the bubble nuclei will grow during the flow of the resin flow in the mold, the bubble holes will burst at the flow peak, so it is inevitable to appear The appearance of defects in traditional foaming processes such as swirling and splayed patterns

On the other hand, as the flow length ratio increases, the cells grow up during the flow process, resulting in serious defects such as inner bubbles, shrinkage, bursting and short shots. The existence of these defects limits the application of this technology, especially for products with a larger area

In the patent publication CN1325337A, some methods similar to co-injection are disclosed to try to solve these surface defects, but it is difficult to control the amount of resin in the skin layer and prevent the skin layer from being burst by the foam layer

[0009] In the Chinese patent document CN1104316C, a method is disclosed to try to solve the problems of surface quality and the like, using supercritical carbon dioxide and / or nitrogen to join in the continuous plasticizer by weight between 0.1-30 to form mutual dissolution state, It is then injected into the mold cavity that is pre-pressed at a pressure higher than the supercritical state to control nucleation and foaming in the cavity. However, as a result, a very high injection pressure is required to overcome such a high gas back pressure to achieve filling, and the weight loss is limited, so the molded product has a large residual stress, and a large amount of gas is consumed to pre-cavity. pressure, increasing production costs

[0010] A foaming process disclosed in Chinese patent document CN01821564.5 claims that the foaming agent (carbon dioxide or nitrogen) content is between 0.05% and 10%, but also adopts 7MPa or higher pressure carbon dioxide pre-compression mold type The cavity is used to control the foaming of the flow peak of the cavity; at the same time, the overflow well technology is used to relieve the foaming pressure, shorten the molding cycle and achieve weight reduction, but it is difficult to achieve in thin-walled products or products with a large flow-to-length ratio Function of the overflow well

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