PETG is an amorphous copolyester material with high transparency, high toughness, good chemical resistance and easy molding, which is widely used in transparent parts, cosmetic packaging, electronic housings and daily necessities. However, PETG is very sensitive to moisture, temperature, shear force and mold conditions, and improper control in any link can easily lead to product defects, such as silver streaks, bubbles, flow marks, surface fogging, brittleness, cracking and mold sticking. Therefore, strict control of each production link is required to ensure the appearance and quality of PETG products. The following are the key precautions in the whole process of PETG injection molding, covering raw material treatment, temperature control, process setting, mold requirements and on-site environment management.
Raw Material DryingPETG has strong hygroscopicity and can absorb moisture quickly in the air, so it is strictly forbidden to directly put the undried raw material into the injection molding machine for production. Before molding, a special hot air dryer or dehumidifying dryer must be used for drying treatment. The drying temperature is controlled at 60-70℃, too high temperature will cause the raw material to stick and agglomerate, affecting normal feeding.
The drying time is 3-4 hours to ensure that the residual moisture in the raw material is completely removed. After drying, the hopper holding temperature is set at 50-60℃ to prevent the dried raw material from absorbing moisture again. The drying effect is directly related to the product appearance: only when the injection molded product has no silver streaks, no bubbles and bright surface, can it be judged that the drying is qualified.
Temperature ControlPETG is not resistant to high temperature, and excessive temperature will lead to material degradation, yellowing, brittleness and peculiar smell, so the temperature of each section of the barrel must be strictly controlled. The barrel temperature is generally set at 220-240℃, thin-walled products can take the upper limit, thick-walled products take the lower limit, and the maximum temperature must not exceed 250℃. The nozzle temperature should be slightly lower than the front end of the barrel to prevent melt drooling and wire drawing, affecting product appearance. Before shutting down the machine, the barrel temperature must be reduced first, and the residual melt in the barrel must be completely shot out to avoid carbonization of the residual material at high temperature, which will affect the next production and cause black spots on the product.
Injection Molding Process SettingPETG molding needs to adopt medium speed and medium pressure for stable filling to avoid defects caused by excessive shear force. Adopt medium injection speed, too fast speed will produce shear overheating, leading to surface flow marks and fogging, too slow speed will cause insufficient filling and cold marks. Apply moderate and low holding pressure to reduce the internal stress of the product and prevent cracking and deformation after demolding. Appropriately increase the back pressure to help improve the uniformity of melt plasticization and remove gas, thereby improving the transparency of the product. Select low screw speed to reduce shear heat and avoid material degradation. Reserve sufficient cooling time to ensure the product is fully shaped in the mold and avoid deformation during ejection.
Mold RequirementsThe mold cavity surface must be highly polished to ensure the transparency and surface gloss of PETG products. The exhaust system of the mold must be smooth, and exhaust grooves should be set at the melt flow end, dead corner and weld line position to prevent gas retention from causing gas marks and scorching. The cooling water circuit should be evenly arranged to ensure uniform cooling of the product, and the mold temperature is controlled at 20-40℃. Too high mold temperature will cause the product to stick to the mold, and too low mold temperature will lead to excessive internal stress of the product. In addition, sufficient demolding draft angle should be set, and the ejection system should be balanced to avoid scratching the transparent surface during ejection.
Production Site and Environment ControlThe production workshop should be kept clean and dust-free, because PETG is a transparent material, dust and oil stains on the mold or raw material will be clearly reflected on the product surface, directly leading to product scrapping. Avoid mixing PETG with other plastic materials, and the barrel must be thoroughly cleaned when changing materials to prevent material contamination. Try to avoid using release agent, especially oily release agent, which will cause surface fogging and affect the adhesion of subsequent surface treatment. The proportion of recycled material should be controlled within 20%, and the recycled material must be re-dried before use.
