Because of its light weight, good toughness and easy molding. The advantages of low cost, etc., in the modern industry and daily products, more and more plastics instead of glass, especially in the optical instrument and packaging industry, the development is particularly rapid. However, due to the requirement for transparency, the wear resistance is high, and the impact toughness is better, so the composition of the plastic, the process of the injection molding process, equipment. Molds, etc., have to do a lot of work to ensure that these plastics used to replace glass (hereinafter referred to as transparent plastics) have good surface quality and thus meet the requirements for use.
Transparent plastics currently used on the market are polymethyl methacrylate (commonly known as acrylic or plexiglass, codenamed PMMA) and polycarbonate (codenamed PC). Polyethylene terephthalate (code name PET), transparent nylon. AS (acrylonitrile-styrene copolymer), polysulfone (code name PSF), etc., of which we contact more PMMA. PC and PET plastics, due to limited space, the following three plastics as an example to discuss the characteristics of transparent plastics and injection molding process.
First, the performance of transparent plastic
Transparent plastic must first have high transparency. Secondly, it must have certain strength and wear resistance. It can resist impact, heat-resistant parts, chemical resistance and water absorption. Only in this way can it meet the transparency. Requires and remains unchanged for a long time. PC is an ideal choice, but it is mainly because of its expensive raw materials and injection molding process, so it is still mainly based on PMMA (for general requirements), and PPT can get good mechanical properties due to stretching. Therefore, it is mostly used in packaging and containers.
Second, the common problems that should be paid attention to during the process of transparent plastic injection molding。
Due to the high light transmittance of transparent plastics, the surface quality of plastic products must be strict, and there must be no markings, pores or whitening. Fog, black spots, discoloration, poor gloss and other defects, so the raw materials, equipment throughout the injection process. Molds and even product designs must pay great attention to and impose strict or even special requirements.
Secondly, since transparent plastics have high melting point and poor fluidity, in order to ensure the surface quality of the products, the process parameters such as barrel temperature, injection pressure and injection speed are often finely adjusted so that the plastic can be filled with the mold without Internal stress is generated to cause deformation and cracking of the product.