Critical Considerations for the Injection Molding of Transparent TPE Materials
Time of issue:2024-09-14
Title: Critical Considerations for the Injection Molding of Transparent TPE Materials
Due to the high light transmittance requirements of transparent TPE materials, the surface quality of the final product must be stringent, avoiding any defects such as spots, voids, whitening, shrinkage marks, black spots, discoloration, or poor gloss. Throughout the injection molding process, strict and sometimes special requirements must be placed on the TPE material, equipment, molds, and even product design. Here, we will analyze the precautions for the molding process of transparent TPE materials in terms of material preparation, equipment requirements, injection molding process, and material handling.
1. Preparation and Drying of Materials
Since any impurities in TPR/TPE materials can affect the transparency of the product, care must be taken to keep the material clean during storage, transportation, and feeding. Moisture in TPR/TPE materials can cause degradation upon heating, so drying is essential. During injection molding, a dry hopper must be used. It is also important that the air supplied during the drying process is filtered and dehumidified to prevent contamination of the material.
2. Cleaning of Cylinders, Screws, and Accessories
To prevent contamination of TPR/TPE materials and to remove old materials or impurities that may reside in the recesses of screws and accessories (especially those with poor thermal stability), thorough cleaning of all components should be performed before use and after shutdown. This daily cleaning work must be done meticulously.
3. Considerations for Injection Molding Process (Including Machine Requirements)
To improve internal stress and surface quality, the following points should be considered in the injection molding process:
1. Use a specialized screw and an injection molding machine with a separately temperature-controlled nozzle.
2. Use a higher injection temperature, provided the material does not decompose.
3. Use generally high injection pressure to overcome the high viscosity of the melt, but excessively high pressure can cause internal stress, leading to ejection difficulties and deformation.
4. Use a slower injection speed when possible, ideally employing a multi-stage injection process (slow-fast-slow).
5. Keep the holding time and cycle time as short as possible while ensuring the part is fully filled and free of sink marks or bubbles, to minimize the melt's residence time in the barrel.
6. Keep the screw rotation speed and backpressure as low as possible to prevent degradation.
7. Mold temperature plays a critical role in the cooling of the part and its quality; if possible, maintain a higher mold temperature for better quality.
4. Additional Precautions
To ensure surface quality, use minimal release agents during injection molding. When recycling TPE, use no more than 5-10%, and never exceed 20%.
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