How to improve the transparency of plastic products

Because plastic has light weight, good toughness, and easy molding. Because of its advantages such as low cost, in modern industry and daily products, more and more plastics are used instead of glass, especially in optical instruments and packaging industries, and the development is particularly rapid. However, because it requires good transparency, high abrasion resistance, and good impact resistance, it is necessary for the composition of the plastic, the process and equipment of the entire injection molding process. A lot of work has to be done for molds, etc., to ensure that these plastics used to replace glass (hereinafter referred to as transparent plastics) have good surface quality, so as to meet the requirements of use.

Currently, the transparent plastics generally used in the market are polymethyl methacrylate (commonly known as acrylic or plexiglass, code PMMA) and polycarbonate (code PC). Polyethylene terephthalate (code-named PET), transparent nylon. AS (acrylonitrile-styrene copolymer), polysulfone (code-named PSF), etc., among which we are more exposed to PMMA.Take these three plastics as examples to discuss the characteristics of transparent plastics and the injection molding process.
1. The performance of transparent plasticTransparent plastics must first have high transparency, and secondly they must have a certain degree of strength and wear resistance, impact resistance, heat-resistant parts, excellent chemical resistance, and low water absorption. Only in this way can they meet the requirements of transparency in use. Requirement and lasting unchanged. PC is a more ideal choice, but mainly because of its high raw material price and difficult injection molding process, PMMA is still the main choice (for products with general requirements), and PPT has to be stretched to obtain good mechanical properties. Therefore, it is mostly used in packaging and containers.

2. Common issues that should be paid attention to in the process of transparent plastic injection moldingBecause of the high light transmittance of transparent plastic, strict requirements on the surface quality of plastic products must be required, without any markings, pores, and whitening. Defects such as haze, black spots, discoloration, poor gloss and so on, so the raw materials and equipment are affected during the entire injection molding process. The design of molds and even products must pay great attention to and put forward strict and even special requirements.Secondly, because transparent plastics mostly have high melting point and poor fluidity, in order to ensure the surface quality of the product, it is often necessary to make fine adjustments to the barrel temperature, injection pressure, injection speed and other process parameters, so that the mold can be filled with the plastic during injection. Will produce internal stress and cause product deformation and cracking.

In terms of equipment and mold requirements, injection molding process and product raw material processing, talk about the matters that should be paid attention to:DryingPreparation and drying of raw materials because any impurity in the plastic may affect the transparency of the product, it is stored and transported.During the feeding process, attention must be paid to sealing to ensure that the raw materials are clean. Especially the raw material contains moisture, which will cause the raw material to deteriorate after heating, so it must be dried, and when injection molding, a drying hopper must be used for feeding. It should also be noted that during the drying process, it is recommended that the input air should be filtered and dehumidified to ensure that the raw materials will not be polluted.

Cleaning of barrel, screw and accessoriesIn order to prevent the contamination of raw materials and the presence of old materials or impurities in the recesses of the screw and accessories, especially the presence of resin with poor thermal stability, screw cleaning agents should be used to clean all parts before use and after shutdown to prevent impurities from sticking. When there is no screw cleaner, PE, PS and other resins can be used to clean the screw.When temporarily shutting down, in order to prevent the raw material from staying at high temperature for a long time and cause the solution to drop, the temperature of the dryer and barrel should be lowered. For example, the temperature of the barrel of PC, PMMA, etc. should be reduced to below 160°C. (The temperature of the hopper should be lowered to below 100°C for PC)