The glass transition temperature of PET is about 165°C, and the material crystallization temperature range is 120~220°C. PET has a strong hygroscopicity at high temperatures. For glass fiber-reinforced PET materials, bending deformation is also very easy to occur at high temperatures. The degree of crystallinity of the material can be increased by adding crystallization enhancers. Transparent articles processed with PET have gloss and heat distortion temperatures.
PET mould is a kind of special mold in the plastic mold. There are many precautions in the design, processing, and adjustment of the mold. Because PET macromolecules contain lipid groups and have a certain degree of hydrophilicity, the pellets are sensitive to water at high temperatures. When the moisture content exceeds the limit, the molecular weight will decrease during the processing of PET, and the products will become discolored and brittle. Therefore, the material must be dried before processing. Its drying temperature is 150° C. for more than 4 hours; it is generally 170° C. for 3-4 hours. Air ejection can be used to check if the material is completely dry. The proportion of recycled PET bottles should not exceed 25%, and the recycled materials should be thoroughly dried.
PET has a short melting point and a high melting point. Therefore, it is necessary to use injection systems with more temperature control sections and less self-heating during plasticization. The actual weight of the product should not be less than two-fold of the injection volume of the machine. three. PET preforms are generally formed by hot runner molds. It is better to have heat insulation plates between the molds and the injection molding machine template. The thickness of the PET preforms is about 12 mm, and the heat insulation plates must be able to withstand high pressure. Exhaust must be sufficient to avoid local overheating or fragmentation, but the depth of the exhaust port generally should not exceed 0.03mm, otherwise it is prone to flash.
Do not use excessive residence time when making PET Mould to prevent the decrease of the molecular weight and try to avoid temperatures above 300°C. If the shutdown is less than 15 minutes, only an empty shot is required; if it exceeds 15 minutes, use a viscous PE to clean and lower the barrel temperature to the PE temperature until it is turned on again.