Hot film material: TPU film, how much do you know?
About TPU film
TPU, short for Thermoplastic Polyurethane Elastomer (Thermoplastic polyurethanes), is also called PU Thermoplastic. It is a linear block copolymer composed of oligomer polyol soft segment and diisocyanate-chain extender hard segment. TPU film is a film made by special processes such as calendering, casting, blown film, coating on the basis of TPU pellets. TPU film is an important application form of TPU material.
The TPU film produced by TPU pellet extrusion casting has the characteristics of high moisture permeability, air permeability, cold resistance, heat resistance, wear resistance, high tension, high tensile force, and high load supporting force. As a result, its application can be extended to the field of plastics. Especially in recent decades, TPU has become one of the fastest growing polymer materials.
The composition of TPU is tested by SGS ASTM F963. It does not contain cadmium, lead, mercury, arsenic, chromium, and barium, and meets environmental protection standards. With the development of industry technology, the replacement of non-environment-friendly films with TPU films has become the trend of implementing environmental protection policies around the world.
The use of TPU to make new products in hot-melt adhesives, hot-melt adhesive films, has also started and developed gradually. Compared with the currently dominant EVA hot-melt adhesives and synthetic rubber-based hot-melt adhesives, TPU hot-melt adhesive films are not only It can meet customers' needs for high viscosity, and also has good physical properties of TPU, such as good elasticity and high mechanical strength. TPU hot-melt adhesive films can be used in many areas where traditional hot-melt adhesives are difficult to use. TPU hot melt adhesive film will be one of the important development directions of the future combination of plastic film and hot melt adhesive field.
TPU film is a new type of industrial material that can be continuously modified. The raw materials can be modified, material formulations can be adjusted, and production processes can be optimized to further optimize performance and expand application fields, which can give it a strong and sustainable vitality. In addition to plastics, other fields are also widely used.
TPU film processing technology
At present, the main processing methods of TPU film include blown film method, casting method, coating method, and calendering method. Among them, blown film method and cast method for processing TPU film are the most common.
[Blow film method]
Because the film has high extensibility and elasticity, it is relatively complicated in the blown film processing process, and it is difficult to carry out separate molding processing. Therefore, the common process is co-extrusion molding with easy-to-form PE as the backing, that is, different The extruder respectively plasticizes and extrudes the TPU raw material and the PE raw material, and compound-molds them in a co-extrusion die. When used, the PE layer is peeled off and recycled.
[Cast coating method]
TPU extrusion coating is a production process of laminating molten TPU on a substrate. TPU resin is extruded and melted in the barrel of the extruder, extruded downward between two rollers through a flat die, and simultaneously draws the substrate between the molten plasticized material and the rubber pressure roller. The pressure of the pressure roller is controlled, and the plasticized TPU material is bonded to the substrate. After the hot tape is cooled by the metal roller, it is trimmed, rolled, and processed into a single application product.
Processing characteristics of TPU film
TPU resin has strong hygroscopicity. If the granular material contains too much moisture, it will cause processing problems and reduce the quality of the finished product. Therefore, both the TPU material and the processing aid must be dried before processing. The moisture content of the dried granular material should not exceed 0.02% by weight. The dried resin should be stored immediately in a dry container that can be safely sealed to prevent it from absorbing moisture again. In general, if the plasticized TPU film has foaming sites or air bubbles, it means that the drying effect is not good.
Because TPU pellet resin has high density, elasticity, and high temperature characteristics after drying, it will cause the resin to be bridged in the ordinary hopper without being discharged. Therefore, the special design of the hopper and barrel blanking port is needed. Considering that TPU resin is expensive, the effect of configuring a weighing and feeding system can effectively save raw material consumption.
TPU processing attention points
The TPU melt is sensitive to both shear and temperature. Excessive shear will cause the performance of the product to decrease, and excessive temperature will cause the melt to decompose. Therefore, there are certain requirements for the design of the extruder and screw. Generally, the processing temperature and shear rate in the extrusion process are controlled by reducing the rotation speed of the screw, but this will lead to a reduction in the amount of extrusion. Therefore, it is recommended to use a barrier-type forced-feed screw and a smooth barrel to solve the extrusion problem.
TPU film has good tensile elasticity, so we must pay attention during traction and rewinding. Generally, we must maintain the stability of tension and reduce the traction force as much as possible during the traction process. Therefore, some devices use tension closed-loop control to achieve traction. Constant tension, to ensure the stability of tension, and rewinding by means of gap winding.
Ten characteristics of TPU film
Ten characteristics of TPU film
Source: Comprehensive finishing of functional membrane material innovation domain
Chinese TPU film manufacturers and their characteristics