As the plastic has a light weight, Clear Corrugated Plastic Sheets good toughness, easy molding. Low cost, so in modern industrial and household products, more and more use of plastic instead of glass, especially for optical instruments and packaging industry, the development is particularly rapid. But because of its requirements for its transparency is good, high wear resistance, impact toughness is better, so the composition of plastic, plastic injection of the entire process, equipment, mold, etc., have to make a lot of work to ensure that these are used to replace the glass Plastic (hereinafter referred to as transparent plastic), Clear Corrugated Plastic Sheets the surface quality is good, so as to achieve the requirements.
Currently on the market generally use transparent plastic polymethyl methacrylate (commonly known as acrylic or plexiglass, code pmma), polycarbonate (code pc). Clear Corrugated Plastic Sheets Polyethylene terephthalate (code pet), transparent nylon. Asp (styrene-styrene-styrene copolymer), polysulfone (code psf), etc., which we have the most contact is pmma, pc and pet three kinds of plastic, due to limited space, the following three kinds of plastic as an example to discuss Transparent plastic properties and injection molding process.
Transparent plastic must first have a high degree of transparency, followed by a certain degree of strength and wear resistance, to impact resistance, Clear Corrugated Plastic Sheets heat resistance is better, chemical resistance is excellent, water absorption is small, only in order to use, to meet the transparency Requirements and long-term change, the following list of Table 1, compare the performance of pmma, pc and pet.
Transparent plastic due to high transmittance, plastic products must be required to meet the quality of surface quality, can not have any markings, stomata, whitening. Fog halo, Clear Corrugated Plastic Sheets black spots, discoloration, poor gloss and other defects, and thus in the entire injection process on raw materials, equipment. Mold, and even product design, should be very careful and put forward strict or even special requirements. Second, Clear Corrugated Plastic Sheets because the transparent plastic is mostly high melting point, poor mobility, so in order to ensure the quality of the product surface, often in the machine high temperature, Clear Corrugated Plastic Sheets injection pressure, injection speed and other technical parameters for minor adjustments, so that when the injection molding material is full of mold, Will produce internal stress caused by product deformation and cracking.
In order to prevent the contamination of raw materials and the presence of old materials or impurities in the depression of the screw and accessories, the resin with special thermal stability is present. Therefore, before using, all the parts are cleaned with the screw cleaning agent, Clear Corrugated Plastic Sheets When there is no screw cleaning agent, pe, ps and other resin can be used to clean the screw. When the temporary shutdown, in order to prevent the raw material at high temperatures for a long time to stay, causing degradation, should the dryer and barrel temperature, such as pc, pmma and other barrel temperature should be reduced to 160 ℃ below. (Hopper temperature for pc should be reduced to 100 ℃ below)
Pm-ma viscosity, poor mobility, it must be high temperature, high injection pressure injection Caixing, which injection temperature is greater than the injection pressure, Clear Corrugated Plastic Sheets but the injection pressure increased, is conducive to improving the product shrinkage. Injection temperature range is wide, melting temperature of 160 ℃, and decomposition temperature of 270 ℃, Clear Corrugated Plastic Sheets so the temperature range of a wide range of materials, the process is better. So improve the mobility, from the injection temperature to start. Poor impact, wear resistance is not good, easy to draw flowers, easy to crack, it should improve the mold temperature, improve the condensation process, to overcome these defects.
Pc viscosity, high melting temperature, poor mobility, it must be higher temperature injection (270-320 ℃ between), relatively narrow range of temperature adjustment, Clear Corrugated Plastic Sheets the process is not as good as pmma. Injection pressure on the mobility of small, but because of the viscosity, still larger injection pressure, the corresponding in order to prevent the internal stress, the holding time to be as short as possible. Shrinkage rate, size and stability, but the product stress, easy to crack, Clear Corrugated Plastic Sheets it is appropriate to improve the temperature rather than pressure to improve the mobility, and from improving the mold temperature, improve the mold structure and post-processing to reduce the possibility of cracking. When the injection speed is low, the gate prone to ripple and other defects, radiation nozzle temperature to separate control, Clear Corrugated Plastic Sheets mold temperature should be high, the flow channel, gate resistance to be small.
Pet molding temperature is high, and the temperature adjustment range is narrow (260-300 ℃), but after melting, good liquidity, so the process is poor, Clear Corrugated Plastic Sheets and often in the nozzle to increase the anti-flow device. Mechanical strength and performance after injection is not high, must be through the drawing process and modification in order to improve performance. Mold temperature control, is to prevent warping, Clear Corrugated Plastic Sheets deformation of the important element, back to the proposed hot runner mold. Mold temperature is high, otherwise it will cause the surface gloss difference and stripping difficult.
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