PET plastic material production process
The rheology of PET in molten state is better, and the effect of pressure on viscosity is greater than temperature. Therefore, the fluidity of the melt is mainly changed from pressure.
1. Processing of plastics Because PET macromolecules contain a lipid group and have certain hydrophilicity, the 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, and its drying temperature is 150 ° C, 4 hours or more, generally 170 ° C, 3-4 hours. Airborne methods can be used to verify that the material is completely dry. The proportion of recycled materials should not exceed 25%, and the recycled materials should be thoroughly dried.
2. The selection of PET for injection molding machine is short due to the short time after melting point, and the melting point is higher. Therefore, it is necessary to select an injection system with more temperature control sections and less self-friction heat during plasticization, and the actual product (aqueous slag) The weight should not be less than 2/3 of the machine's injection volume. Based on these requirements, Ramada has developed a small and medium series of PET plasticizing systems in recent years. The clamping force is selected to be greater than 6300t/m2.
3, mold and gate design PET 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.
4, the melting temperature can be measured by the air-launch method. Between 270 and 295 ° C, the enhanced grade GF-PET can be set to 290-315 ° C and the like.
5, the injection speed is generally faster, to prevent premature coagulation during injection. But too fast, the high shear rate makes the material brittle. The shot is usually completed in 4 seconds.
6, the lower the back pressure, the better, so as not to wear. Generally no more than 100bar. Usually no need to use.
7. Do not use excessive residence time for the residence time to prevent molecular weight from falling. 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.
Common in mineral water bottles, carbonated beverage bottles, etc. When the temperature reaches 70 °C, it is easy to deform, and it cannot be filled with alcohol or oil at high temperature.
(1) General properties PET resin is a milky white translucent or colorless transparent body with a relative density of 1.38 and a light transmittance of 90%. PET is a medium barrier material having a permeability coefficient of 50 to 90 cm 3 · mm / (m 2 · d · MPa) for O 2 and a transmission coefficient of CO 2 of 180 cm 3 · mm / (m 2 · d · MPa). The water absorption rate of PET is 0.6%, and the water absorption is large.
(2) Mechanical properties The tensile strength of PET film is very high, comparable to aluminum foil, 9 times that of HDPE film, and 3 times that of PC and PA film. Reinforced PET has low creep, excellent fatigue resistance (better than PC and PA), good abrasion resistance and abrasion resistance. The mechanical properties of PET are less affected by temperature.
(3) Thermal properties The heat resistance of pure PET plastics is not high, but it is greatly improved after the reinforced treatment. The mechanical properties at 180 °C are better than those of PF laminates, and it is a heat-resistant variety of reinforced thermoplastic engineering plastics. PET has good heat aging resistance, and the embrittlement temperature is -70 ° C, and it still has certain toughness at -30 ° C. PET is not easy to burn, the flame is yellow, and there is dripping.
(4) Electrical properties Although PET is a polar polymer, it has excellent electrical insulation and can be well maintained at high frequencies. PET has poor corona resistance and cannot be used for high voltage insulation; electrical insulation is affected by temperature and humidity, and is affected by humidity.
(5) Environmental properties PET contains ester bonds and is not resistant to water, acids, and alkalis under high temperature and water vapor conditions. PET is stable to organic solvents such as acetone, benzene, toluene, trichloroethane, carbon tetrachloride and oils, and is also highly resistant to some oxidizing agents such as hydrogen peroxide, sodium hypochlorite and potassium dichromate. PET has excellent weather resistance and can be used outdoors for a long time.
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