Processing of plastics Due to the fatty base and relative hydrophilicity in the macromolecules of the preform, the particles are more sensitive to water at high temperatures. When the water content is greater than the limit, the molecular weight decreases during processing, and the product becomes discolored and brittle. Therefore, the material is dried before processing. The drying temperature is 150℃ for more than 4 hours, generally 170℃ for 3-4 hours. The air jet method can be used to check that the material is completely dry. In general, the proportion of recycled materials should not exceed 25%, and the recycled materials should be thoroughly dried. 2. Selection of injection molding machine Due to the short stabilization time after the melting point of pet and the high melting point, an injection system with more temperature control sections and less self-friction heating during the plasticizing process should be selected. The actual weight of the product (water-containing material) should not be less than the injection volume of the machine 2/3 of . 3. Mold and gate design
The preform is generally formed by a hot runner mold. There is a heat shield between the mold and the injection molding machine template, the thickness is about 12 mm, and the heat shield can withstand high pressure. The exhaust should be enough to avoid local overheating or fragmentation, but the depth of the exhaust port should not be greater than 0.03mm, otherwise it is easy to produce flash. 4. Melt temperature It can be measured by aerial shot. The temperature range is 270-295°C, and the temperature range of the enhanced gf-pet is 290-315°C. 5. Injection rate Generally speaking, the injection rate should be fast to prevent premature solidification during injection. But too fast shear rates can make the material brittle. Injections are usually completed within 4 seconds
. 6. Back pressure The lower the better, to avoid wear. Generally no more than 100 bar. Usually not needed. 7. Residence time Do not use too long residence time to prevent the molecular weight from decreasing. Try to avoid temperatures exceeding 300°C. If the downtime is less than 15 minutes. If more than 15 minutes, rinse with viscosity PE and lower the barrel temperature to PE temperature until start up again. 8. Precautions for injection molding of bottle embryos a. The recycled material should not be too large, otherwise it is easy to cause "bridge" at the blanking place, which will affect the plasticization. b. If the mold temperature is not well controlled or the material temperature is not properly controlled, it is easy to produce "white fog" and opacity. The mold temperature is low and uniform, the cooling speed is fast, and the crystallization is less to make the product transparent.