PETplasticbottlespecificproductionprocess,petinjectionmoldingmachine
The production process of plastic bottles: PET plastic bottles have better rheology in the molten state, and the influence of pressure on viscosity is greater than temperature. Therefore, the fluidity of the melt is mainly changed from pressure. Plastic bottles have different states of use in different environments, so the rheology and viscosity are effectively controlled in the molten state of the plastic bottle.
1. The PET plastic bottle used in the injection molding machine has a short melting time after melting point and a high melting point. Therefore, it is necessary to use an injection system with more temperature control sections and less self-friction heat during plasticization, and the product (water content) Material) The actual weight cannot be less than 2/3 of the machine injection volume. The selection of injection molding machine needs reasonable control according to the injection quantity of the machine and the injection system. Based on these requirements, China has developed a small and medium series PET special plasticizing system in recent years, and the clamping force is selected to be greater than 6300t/m2.
2, plastic processing Because the PET plastic bottle contains a lipid base in the macromolecule, has a certain hydrophilicity, the pellet is more sensitive to water at high temperature, when the moisture content exceeds the limit, the molecular weight of the PET plastic bottle decreases during processing. The product is colored and brittle. In this case, the material must be dried before processing, and the drying temperature is 150 ° C, more than 4 hours, generally 170 ° C, 3-4 hours. Airborne methods can be used to verify that the material is completely dry. When using the materials, the raw materials should be dried to a certain extent. Pay attention to different drying temperatures and time limits to ensure that the produced plastic bottles have good product performance. The proportion of recycled materials should not exceed 25%, and the recycled materials should be thoroughly dried.
3. Residence time Do not use excessive residence time to prevent molecular weight loss. Try to avoid temperatures above 300 °C. If the shutdown is less than 15 minutes. Only need to be air-blasted; if it is more than 15 minutes, clean it with viscosity PE and reduce the temperature of the barrel to PE temperature until it is turned on again. Strict control should be carried out when the plastic bottle is used for residence time. Different treatments are required at different temperatures, and the time limit must be strictly controlled.
4, mold and gate design PET plastic preforms are generally formed by hot runner mold, between the mold and the injection molding machine template should have a heat insulation board, the thickness of about 12mm, and the insulation board must be able to withstand high pressure. Exhaust gas must be sufficient to avoid local overheating or chipping, but the depth of the exhaust port should not exceed 0.03mm, otherwise it will easily produce flash.
5, the back pressure is as low as possible to avoid wear. Generally no more than 100bar. Usually no need to use.
6, injection speed Generally, the injection speed is fast, which can prevent premature coagulation during injection. But too fast, the high shear rate makes the material brittle. The shot is usually completed in 4 seconds.
7. Precautions (1) Recycled materials should not be too large, otherwise it will easily cause "bridge" at the blanking part and affect plasticization. When recycling plastics, the quantity of recycled materials should be strictly controlled to ensure the plasticizing quality of plastics. (2) If the mold temperature is not well controlled or the material temperature is not properly controlled, it is easy to produce "white fog" and is opaque. It is necessary to strictly control the mold temperature, otherwise there will be events that you do not want to see. The mold temperature is low and uniform, the cooling speed is fast, and the product is less transparent when the crystal is less. The production process of plastic bottles requires strict quality system inspection to ensure that the plastic bottles produced have good product quality and guarantee. The production process is complex and requires different production processes to be strictly controlled to ensure that each process is carried out in strict accordance with standards.
