Injection molding knowledge

What are the precautions for TPU material injection molding?

Among the raw materials for injection molding products, TPU material is a frequently used raw material. Its high tension, high pulling force, strong and aging-resistant characteristics make it very popular in plastic products. At present, TPU has been widely used in medical and health, electronic appliances, industry and sports. It has the characteristics of high strength, good toughness, wear resistance, cold resistance, oil resistance, water resistance, aging resistance, and weather resistance that other plastic materials cannot match. At the same time, it has many excellent functions such as high waterproofness, moisture permeability, windproof, cold resistance, antibacterial, mildew resistance, warmth retention, UV resistance, and energy release.


What are the things you need to pay attention to when injecting TPU materials? Today, engineers from Baitao Technology will introduce them to you.


  1. Material coloring

    Except for some special needs, TPU is usually provided in natural color. Users can easily color TPU. The direct, simple and reliable method is to add toner or masterbatch for coloring. The recommended dosage is as follows: Toner: 0.2-0.5%, Masterbatch: 1-4%.

  2. Material drying

    Since TPU easily absorbs moisture and is easily hydrolyzed, incompletely dried TPU raw materials can easily lead to processing difficulties. The surface of the injection product will have bubbles or silver streaks, and the surface of the extruded product will show unevenness, dullness, blistering and foaming. In order to ensure zero defects in production and product quality, it is recommended that the TPU raw materials must be fully dried to a moisture content of less than 0.05% before processing. If toner or masterbatch is used for dyeing, it must be mixed with TPU natural colorant and dried together. Generally, a circulating air dryer or a dehumidifying dryer is used to dry TPU. Depending on the hardness, the recommended drying temperature is 80-110℃ and the drying time is about 3 hours.

  3. Injection molding

    Generally, a single-screw three-stage injection molding machine is suitable for TPU injection molding. Compared with other plastics, since TPU has a very high viscosity when melted, it is easy to generate high shear force in the barrel and destroy the physical properties of TPU itself. Generally, an injection molding machine with a screw L/D ratio of about 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. Good products are crushed and then mixed with new materials, but they must be dried again before use. For some mechanical and physical requirements, recycled materials are not allowed to be used in the injection molding process. It accounts for more than 30% of all raw materials. Extruded recycled materials should be processed separately or added to new injection molding materials. In addition, recycled materials should not be stored for too long. Use dry top. Waste that cannot be recycled can be incinerated to obtain heat.

  5. Extrusion Processing

    The regulation and control of injection pressure, holding pressure, injection speed and back pressure are very important for product dimensional stability and release performance. If the holding pressure is too low, it is easy to cause product sagging; if the pressure is too high, it is easy to cause product release. The injection pressure holding pressure should be adjustable within the range of 100-1200bar, and the injection pressure should be set to only eliminate product pressure drop, usually setting the holding pressure to 50% of the injection pressure. In order to ensure uniform plasticization, the back pressure should be controlled within 10-25% of the injection pressure.

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