A comprehensive analysis of TPU films: characteristics, processing and applications

About TPU film
TPU, or thermoplastic polyurethane elastomer, is a linear block copolymer consisting of oligomeric polyol soft segments and diisocyanate-chain extender hard segments. It is carefully made into a film through special processes such as calendering, casting, blown film, coating, etc., and has become a key application form of TPU material. This kind of film not only has good moisture permeability and air permeability, but also has multiple excellent characteristics such as cold resistance, heat resistance, wear resistance, high tension, high tensile force, high load support force, etc., so that its application in the field of plastics can be widely expanded. Especially in recent decades, TPU has become one of the fastest-growing polymer materials.
It is worth mentioning that the composition of TPU has been rigorously tested by SGS ASTM F963, which proves that it does not contain harmful substances such as cadmium, lead, mercury, arsenic, chromium and barium, and fully meets environmental protection standards. With the global implementation of environmental protection policies, TPU film is gradually replacing non-environmentally friendly films, which has become an inevitable trend in the development of the industry.
In addition, TPU also shows great potential in the field of hot melt adhesives. The newly developed TPU hot melt adhesive film not only satisfies the customer's pursuit of high viscosity, but also shines in many fields where traditional hot melt adhesives are difficult to apply with its excellent physical properties, such as good elasticity and mechanical strength. It is foreseeable that TPU hot melt adhesive film will become one of the important development directions for the combination of plastic film and hot melt adhesive in the future.
As a new type of industrial material that can be sustainably modified, the performance of TPU film can be further optimized through raw material modification, material formula adjustment and production process optimization, and the application field can be continuously expanded. This strong vitality is not only reflected in the field of plastics, but also widely used in many other fields.
In terms of processing technology, at present, TPU film mainly adopts film blowing method, casting method, coating method and calendering method. Among them, the blown film method and the casting method are favored because of their mature process and high efficiency. With the continuous innovation and progress of technology, the application prospect of TPU film will be broader.
Due to the excellent elongation and elasticity of TPU films, it is difficult to form them individually due to the challenges of blown film processing. Therefore, the usual method is to combine it with an easy-to-form PE material and process it through a co-extrusion process. Specifically, TPU and PE raw materials are plasticized and extruded using different extruders, and then composite molding is carried out at the co-extrusion die. In actual use, the PE layer only needs to be peeled off to achieve recycling.
【Cast coating method】
TPU extrusion coating is a production process in which molten TPU is tightly bonded to a substrate. In this process, the TPU resin is first extruded and melted in the extruder barrel and then evenly extruded through a flat die head into the space between the two rollers. At the same time, the substrate is pulled through the area between the molten plasticized TPU material and the rubber pressurized rollers. By adjusting the pressure of the pressurized rollers, it is ensured that the plasticized TPU material can be tightly attached to the substrate. Subsequently, the hot adhesive tape is cooled by a metal roller, and then through the trimming and winding steps to obtain an application product that can be processed and formed in a single time.
【Processing characteristics of TPU film】
Due to the significant hygroscopicity of TPU resin, if the moisture content of the granular material is too high, it will cause a series of processing problems and directly affect the quality of the finished product. Therefore, it is particularly important to carry out the necessary drying treatment of TPU materials and their related processing aids before starting processing. The moisture content of the dried granular material should be strictly controlled below 02% (in terms of weight percentage). To ensure the drying effect, the dried resin should be properly stored in an airtight and dry container to prevent re-hygroscopicity. Normally, if the plasticized TPU film is foaming or bubbles, it often means that the drying process is not ideal.
Drying parameters of TPU resins with different hardnesses
Due to the high density and elasticity of TPU granular resin, as well as the high temperature after drying, these characteristics make the resin easy to bridge and difficult to cut in ordinary hoppers. Therefore, the blanking opening of the hopper and barrel needs to be specially designed to solve this problem. At the same time, considering that the price of TPU resin is relatively expensive, the configuration of weighing and feeding system can effectively save raw materials.
Key points of TPU processing:
TPU melts are very sensitive to shear and temperature. Too high a shear can lead to a decrease in product performance, while too high a temperature can cause the melt to break down. Therefore, special attention needs to be paid to the design of the extruder and screw during the processing process to ensure that the processing temperature and shear rate are controlled within the appropriate range. In general, reducing the screw speed is an effective way to control these parameters, but this can also affect the amount of extrusion. To solve this problem, it is recommended to adopt a barrier-type force-feed screw equipped with a smooth barrel to maintain a stable extrusion volume.
In addition, when towing and winding TPU films, attention is also required to maintain the stability of tension and minimize traction. Some equipment adopts tension closed-loop control technology to achieve constant tension of traction, and winding is carried out by gap winding to ensure the quality and processing efficiency of the film.
Top 10 characteristics of TPU films
Hardness: The higher the hardness grade of TPU film, the stronger its puncture resistance and abrasion resistance. At the same time, the TPU film with low hardness grades shows a supple texture and soft feel.
Abrasion resistance: TPU film is more abrasion resistant than many other polymers, and even more than five times more abrasion resistant than natural rubber, making it an ideal choice for wear-resistant products.
Stretchability: TPU film has excellent tensile strength and elongation at break, and its tensile ability is impressive.
Weather resistance: TPU film outperforms natural rubber and other synthetic rubbers in terms of weather aging resistance.
Low-temperature flexibility: TPU films remain flexible even at temperatures as low as -30 degrees Celsius, making them an ideal material for demanding environments.
Temperature resistance: The temperature resistance of TPU film can reach 130 degrees Celsius, and the temperature resistance of polyether series can also reach 90 degrees Celsius.
Oil and chemical resistance: As a highly polar polymer material, TPU has little affinity for non-polar mineral oils, so it is almost impervious to erosion in fuel oil and mechanical oil. In particular, TPU products of the polyester series have better oil resistance.
Biomedical performance: TPU also has a wide range of applications in the biomedical field.
TPU film not only has excellent biocompatibility, non-toxic, non-allergic, non-local irritation and non-pyrogens, but also has environmental protection and degradability. When burned, it does not produce air pollution and biodegrades in the soil for only 3-5 years. In addition, the polyester series can be completely hydrolyzed after soaking at a certain temperature for a certain period of time, which further reflects its environmental performance.
TPU films are also extremely versatile, allowing them to be processed vacuum or thermally while still maintaining their flexibility and performance, while also being welded into irregular shapes to meet a wide range of application needs.
In terms of performance, TPU films perform well. Its transparency is excellent, and it can achieve intuitive and transparent results at different thicknesses. At the same time, the yellowing resistance level is quite high, and the color can be maintained stable even after continuous exposure to ultraviolet light. In addition, there are also colored TPU films that can be customized according to the color standards specified by the customer.
In terms of physical properties, the resilience and deformation rate of TPU film are also commendable. It has excellent deformation and rebound ability, and can quickly return to its original shape after the application of external force. At the same time, the friction resistance is also quite excellent, and the wear resistance and thermal properties of the wear-resistant material polyurethane particles are closely related, which can effectively evaluate the wear and ability of the product to adapt to high temperature environments.
Finally, TPU film also has excellent tear resistance, further enhancing its durability in real-world applications.
The tear resistance of TPU film is its strength to resist notched tensile tearing, which reflects the physical properties of the material in the transverse direction. Different notch tear strengths and notch angles can lead to different tear standards. In addition, polyether-based TPU films exhibit excellent hydrolysis and antibacterial and mildew resistance, making them stable even in harsh environments.
At present, the number of TPU film manufacturers in China is relatively small, but the industry concentration is high. This is mainly due to the late start of Chinese manufacturers, mainly focusing on the low-end market, and facing the challenge of technology and production experience thresholds. In contrast, foreign companies such as South Korea's Jinxing Industry, Taiwan's Kunzhong and Samhwang, and European and American companies represented by BASF and Bayer occupy the high-end market.
In the TPU industry competition pattern, Taiwan, China and Chinese mainland are the three main regions. From a geographical point of view, Taiwan, Europe and the United States occupy an important position in the mid-to-high-end of the Chinese market with their more than 30 years of development history and mature technology. The products of these enterprises have stable performance, so they can successfully occupy the mid-to-high-end market.
Foreign companies often have diversified production capacity in the polyurethane industry chain, and their products cover multiple links. For example, BASF, as one of the world's leading chemical companies, not only provides TPU upstream raw materials such as MDI and polyols, but also produces TPU pellets and further processes them into TPU films. Bayer MaterialScience is also strong, with its TPU film products such as the Dureflex series, while Bayer also produces other polyurethane products, demonstrating its comprehensive strength. Huntsman focuses on the R&D and production of TPU glass sheets, and also provides basic chemical raw materials such as MDI. Lubrizol is committed to producing a variety of TPU pellets and films to meet the needs of different customers. Therefore, these foreign companies show a strong comprehensiveness in product structure, and TPU film is only one of them.