TPU film summary
Thermoplastic polyurethanes, referred to as TPU, also known as PU thermoplastics, are linear block copolymers composed of a soft segment of an oligomer polyol and a hard segment of a diisocyanate-chain extender. Excellent elongation and recovery elasticity, good softness and biocompatibility, waterproof and moisture permeable, abrasion resistance, flexural resistance, low temperature resistance, oil resistance, UV radiation resistance, hardness range from 60HA to 85HD. It is widely used in various fields, such as: various footwear, clothing, diaper fabrics and lining materials in daily life; surgical gowns in medical and health fields, medical mattresses, ice bags, bandages, medical breathable tapes, surgical use Wraps fabrics and lining materials; in the field of national defense, it can be used as a weapon to seal film, field tents, life jackets, inflatable boats and other fabrics and lining materials; in the industrial field, it is often used for fireproof, heat insulation, sound insulation materials, aircraft parts And decoration, auto parts, waterproof stickers, compression glands, drive belts, insulation boards, safety bulletproof glass, etc.
Processing characteristics of TPU film
TPU resin is highly hygroscopic, and its granular material, if it contains too much moisture, will cause processing problems and reduce the quality of the finished product. Therefore, it is necessary to dry the TPU material and processing aid before processing. The moisture content of the dried particulate 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 a foaming site or bubbles, it means that the drying effect is not good.
At the same time, due to the high density, elasticity, and high temperature characteristics of the TPU granule resin, the resin can be easily bridged in the ordinary hopper without cutting, so the hopper and the barrel of the barrel need to be specially designed. Considering the high price of TPU resin, the effect of configuring the weighing feeding system can effectively save raw material consumption.
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, the blown film method and the casting method for processing TPU film are the most common. Because the film has high elongation 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 processing by easily forming PE as a substrate, that is, by different The extruder separately plasticizes and extrudes the TPU raw material and the PE raw material, and performs compound molding in the co-extrusion die. When used, the PE layer is peeled off and recycled.
In the cast coating process, TPU extrusion coating is a production process in which molten TPU is attached to a substrate. The TPU resin is extruded and melted in an extruder barrel, and is extruded downwardly between two rolls by a flat die while pulling the substrate between the molten plasticized material and the rubber pressure roll. The pressure of the pressure roller is controlled, and the plasticized TPU material is bonded to the substrate, and the hot rubber cloth is cooled by the metal roller, trimmed, coiled, and processed at one time.
TPU processing attention points
The TPU melt is sensitive to shear and temperature. Excessive shearing leads to a decrease in product performance. Excessive temperatures can cause melt decomposition. Therefore, there are certain requirements for extruder and screw design. Generally, the processing temperature and shear rate during the extrusion process are controlled by reducing the rotation speed of the screw, but this will result in a decrease in the amount of extrusion. Therefore, it is recommended to use a barrier type forced feed screw to support the extrusion amount with a smooth barrel. problem.
Because TPU film has good tensile elasticity, it must be paid attention to during the traction and winding process. Generally, the tension stability should be maintained during the traction process and the traction force should be reduced as much as possible. Therefore, some equipment adopts tension closed-loop control to realize traction. The constant tension ensures the stability of the tension and is wound up by winding the gap.