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What are the precautions for injection molding of TPU materials?
2023-04-26
1. Material coloring Except for certain special needs, TPUs are usually provided in natural colors . Users can easily color TPUs. The direct, simple, and reliable method is to add carbon powder or color masterbatch for coloring. The recommended dosage is as follows: color powder: 0.2-0.5%, color masterbatch: 1-4% Due to the easy absorption of moisture and hydrolysis of TPU, incomplete drying of TPU raw materials can easily lead to processing difficulties. The surface of the injection product will have bubbles or silver lines, and the surface of the extruded product will show uneven, dull, bubbling, and bubbling. In order to ensure zero defects in production and product quality, it is recommended to fully dry the TPU raw material until the moisture content is less than 0.05% before processing. If carbon powder or masterbatch is used for dyeing, it must be mixed with TPU natural colorant and dried together. Usually, a circulating air dryer or dehumidifier is used to dry TPUs. Based on the hardness, the recommended drying temperature is 80-110 ℃ and the drying time is about 3 hours. 3. Injection Molding Usually, a single screw three stage injection molding machine is suitable for TPU injection molding processing. Compared with other plastics, due to the high viscosity of TPU during melting, it is easy to generate high shear forces in the material barrel and damage the physical properties of TPU itself. Usually, an injection molding machine with a screw L/D ratio of approximately 16-20 and a compression ratio of 2.0-25 is more suitable. 4. Processing recycled materials It can be nozzle material or washing machine material that crushes the finished product and mixes it with new materials, but it must be dried again before use. For certain mechanical and physical requirements, the use of recycled materials during injection molding is not allowed. It accounts for over 30% of all raw materials. The extruded recycled material should be processed separately or added to the new injection molding material. In addition, recycled materials should not be stored for too long. Use a dry top. Unrecyclable waste can be incinerated to obtain heat.
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