PET plastic box in the molten state of rheology is better, the impact of pressure on the viscosity is greater than the temperature, therefore, mainly from the pressure to change the melt fluidity.
1. Plastics treatment Because PET macromolecules contain lipid groups and have a certain degree of hydrophilicity, pellets are sensitive to water at high temperatures. When the moisture content exceeds the limit, the molecular weight of PET decreases during processing and the product is colored. Become brittle. Therefore, the material must be dried before processing. Its drying temperature is 150°C, more than 4 hours, usually 170°C, 3-4 hours. Air ejection can be used to check if the material is completely dry. The proportion of recycled materials should not exceed 25%, and the recycled materials should be thoroughly dried.
2. The PET machine used in injection molding machine has a short stabilization time after melting point and a higher melting point. Therefore, it is necessary to use injection systems with more temperature control sections and less self-heating friction during plasticization, and the actual product (water-containing material) is used. The weight should not be less than 2/3 of the injection volume of the machine. Based on these requirements, Ramada has developed a small and medium-sized PET special plasticizing system in recent years. The clamping force is greater than 6300t/m2.
3, PET plastic box mold and gate design PET bottle embryos generally use hot runner mold, the mold and the injection molding machine template between the best insulation board, its thickness is about 12mm, and the insulation board can 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.
4 Melt temperature can be measured by air jet method. Different from 270-295°C, the reinforced grade GF-PET can be set to 290-315°C.
5, PET plastic box injection speed is generally faster, can prevent premature coagulation during injection. But too fast, the high shear rate makes the material fragile. The shot is usually completed within 4 seconds.
6. The lower the back pressure of the PET plastic box, the better so as not to wear out. Generally does not exceed 100bar. Usually do not need to use.
7. Do not use long residence time to prevent the decrease of molecular weight. Try to avoid temperatures above 300°C. If the stoppage is less than 15 minutes. Only air shot processing is required; if it exceeds 15 minutes, it is cleaned with viscosity PE and the barrel temperature is lowered to PE temperature until it is turned on again.