About TPU thin film
TPU, short for thermoplastic polyurethane elastomer (Thermoplastic polyurethanes), also known as PU thermoplastic. It is a linear block copolymer composed of soft segment of oligomer polyol and hard segment of diisocyanate-chain extender. TPU film is a kind of thin film based on TPU granular material, which is prepared by special processes such as calendering, casting, blowing and coating. TPU film is an important application form of TPU material.
TPU film produced by TPU granular extrusion casting has the characteristics of high moisture permeability, air permeability, cold resistance, heat resistance, wear resistance, high tension, high tension and high load support. So that its application can be extended to the field of plastics. Especially in recent decades, TPU has become one of the fastest growing polymer materials.
TPU components tested by SGS ASTM F963 do not contain cadmium, lead, mercury, arsenic, chromium and barium, and meet environmental protection standards. With the alternate development of industry technology, replacing non-environmental protection film with TPU film has become the trend of implementing environmental protection policy all over the world.
Compared with EVA hot melt adhesives and synthetic rubber hot melt adhesives, TPU hot melt adhesives can not only meet the needs of customers for high viscosity, but also have good physical properties of TPU, such as good elasticity and mechanical strength. TPU hot melt adhesive film is suitable for many traditional hot-melt adhesives. TPU hot melt adhesive film will be one of the important development directions of plastic film and hot melt adhesive field in the future.
TPU film is a new type of industrial material with sustainable modification. It can be further optimized by modifying raw materials, adjusting material formulation and optimizing production process. It can expand the application field and give it strong and sustained vitality. In addition to other fields of plastics, it is also widely used.
TPU thin film processing technology
At present, the main processing methods of TPU films include blowing film, tape casting, coating and calendering. Blowing film method and tape casting process are the most common TPU films.
Blown film method
Because the film has high elongation and elasticity, it is relatively complex in the process of blown film processing, and it is difficult to process separately. So the common process is co-extrusion processing with easy-formed PE as backing, i.e. plasticizing and extruding TPU and PE raw materials respectively through different extruders, and The compound die is formed in the co extrusion die, and the PE layer is stripped and reused.
[tape casting method]
TPU extrusion coating is a production process that melted the TPU on the substrate. TPU resin is extruded and melted in the barrel of the extruder, and extruded downward through a flat die head to the two barrels. At the same time, the base material is pulled between the melted plasticized material and the rubber pressure roller. Controlling the pressure of pressure roll, plasticized TPU material and base material are bonded together. After the hot rubber cloth is cooled by the metal roll, it is trimmed, coiled and processed once to form the applied products.
Processing characteristics of TPU thin films
TPU resin has a strong hygroscopicity. If the granular material contains too much water, it will cause processing problems and reduce the quality of finished products. Therefore, TPU materials and processing aids must be dried before processing. The moisture content of dry granular material should not exceed 0.02% (weight%). The dried resin should be immediately stored in a dry container that can be safely sealed to avoid re-hygroscopicity. Generally speaking, if the TPU film after plasticization has foaming site or air bubbles, it means that the drying effect is not good.
Because TPU granular resin has high density, elasticity and high temperature after drying, it is easy to build bridges without cutting materials in ordinary hoppers. Therefore, it is necessary to make special design for the discharge outlet of hoppers and barrels. Considering the high price of TPU resin, the effect of weighing and feeding system can effectively save material consumption.
Points for attention in TPU processing
TPU melt is sensitive to shear and temperature, too high shear will lead to product performance degradation, too high temperature will lead to melt decomposition, so there are certain requirements for extruder and screw design. Generally, the processing temperature and shear rate in extrusion process are controlled by reducing the screw speed, but this will lead to the decrease of extrusion volume. Therefore, it is suggested to adopt barrier-type forced feed screw with smooth barrel to solve the extrusion volume problem.
TPU film has good stretching elasticity, so in the process of traction and winding, we must pay attention to maintaining the stability of tension and reducing the traction force as much as possible. Therefore, some devices adopt tension closed-loop control to achieve constant tension of traction, ensure the stability of tension, and winding through clearance. Way to do the winding up.
Ten properties of TPU thin films
Ten properties of TPU thin films
Source: comprehensive innovation of functional membrane materials innovation area