Matters needing attention in injection molding of TPU materials


Its high tension, high tensile force, toughness and aging resistance make it very popular in plastic products. At present, TPU has been widely used in medical and health, electronic appliances, industry and sports, etc. 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 waterproof and moisture permeability, windproof, cold proof, antibacterial, mildew proof, warmth retention, UV resistance and energy release.

What are the matters needing attention when TPU material injection molding?

1. Material coloring

Except for some special needs, TPU is usually provided in natural colors. Users can easily shade the TPU. The straightforward, simple and reliable method is to add toner or color 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 injected product will have air bubbles or silver streaks, and the surface of the extruded product will show unevenness, dullness, blistering and blistering. In order to ensure zero defects in production and product quality, it is recommended that 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 coloring, it must be mixed with TPU natural colorant and dried together. Typically, circulating air dryers or dehumidifying dryers are used to dry TPU. Depending on the hardness, the recommended drying temperature is 80-110°C, 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, due to the high viscosity of TPU when melted, it is easy to generate high shear forces 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 to crush a good product and then mix it with new material but have to dry it again before use. For certain mechanical and physical requirements, the use of recycled materials in the injection molding process is not allowed. It accounts for more than 30% of all raw materials. Extruded recycled material should be processed separately or added to new injection molding material. Also, recycled materials should not be stored for too long. Use a dry top. Unrecyclable waste can be incinerated to obtain heat.


5. Extrusion processing

The adjustment 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 the product to sag; If the pressure is too high, it can easily lead to product release. The injection pressure holding pressure shall be adjustable in the range of 100-1200bar, and the injection pressure shall be set to eliminate only the product pressure drop. Generally, the holding pressure shall be set 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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Post time: Apr-22-2022