Progress in polyurethane waterproof and breathable coated fabrics

This article mainly introduces the research on the production process of polyurethane PU coating, effectively solving the “skin hanging” phenomenon of coating slurry during the production process; improving the fluidity of slurry, solving problems such as high thickness coating and knife distance selection to meet the needs of Customer demand. 0. Introduction Polyurethane PU water-based coating has become one of the new methods for textile finishing today. Because this product has many functions, high performance and great changes, it occupies an important position in the domestic and foreign textile fabric markets.

Because it is completely water-based instead of solvent-based, it not only changes the working environment of operators, but also eliminates safety hazards and environmental issues. Polyurethane coating can form multifunctional and high value-added textiles, and can be widely used in various fields such as clothing, decoration, industry, and military industry. Its prospects are very broad. The research of this project was listed as the “National New Product Plan” of the National Science and Technology Commission in 1995. This product was rated as “Excellent New Product of Jiangsu Province” in 1996. More than 300,000 meters of this product were trial-produced and processed into garments. Mainly sold in the United States, Japan, and Southeast Asia, and has been well received by customers. 1. Main issues 1.1 Solve the problem of slurry “hanging skin” in production. The polymer of water-dispersed polyurethane is in granular form, and higher temperatures must be used to produce a continuous film with better performance. During the production and use process, this material will produce local cross-links with changes in time and climate. After the cross-linking change occurs, a thick layer of skin forms on the surface of the slurry, commonly known as “hanging skin”. These crusting slurries are brought to the cloth surface during coating to form color (spots), which directly affects the quality of the finished product. After careful observation and analysis, it was found that under certain conditions, the slurry first produced self-crosslinking and then increased in viscosity, followed by “hanging skin”. After many selection experiments, we finally decided to add a moisturizing agent to the slurry to delay the “skin hanging” of the slurry to meet the needs of production. However, we have conducted many tests on the appropriate amount of moisturizer, as shown in Table 1: Table 1: Comparison table of moisturizer dosage and slurry hanging time

It can be clearly seen that adding moisturizer to the slurry has an obvious effect, but when the dosage reaches 6%, even if the dosage is increased, the effect will not be great. Therefore, we choose 6% moisturizer to be placed in the slurry. The material effectively solves the problem of “hanging skin” in production. 1.2 Improve the fluidity of slurry. The solid content of the polyurethane PU coating slurry used in our factory is as high as 50%, and the thickness is also high, which brings about the problem of poor fluidity during coating; when the coating was first started during production, it was normal, but After driving for several hundred meters, “fish scale-like” stripes and horizontal block marks will appear on the cloth surface, which seriously affects the coating quality of the cloth surface. Can you add suitable media to the slurry and improve the slurry? To improve the coating quality, we tried several media according to the performance of the slurry. The results are as shown in Table 2: Table 2: Comparison of different media added to the slurry.
It can be concluded from Table 2 that only organic solvents that are soluble in the slurry can improve and increase the fluidity of the slurry during coating, thereby solving the above-mentioned defects. 1.3 Solve the problem of high thickness coating. Coating processing techniques include dry method, wet method, hot melt method, transfer method, adhesive method, etc. Among them, the dry method is most used. The so-called dry method is to evenly apply the coating slurry on the base fabric with an applicator. , the solvent or water is volatilized by heating (such as drying or baking), and the coating agent forms a thin film on the surface of the fabric. Our factory adopts a dry process. The multifunctional coating machine in our factory is imported from the Austrian J.Zimer Company. This equipment is used for both roller scraper type and garden mesh. The scraper on the roller has an adjustable blade distance. In order to adapt to the scraping products with different requirements, we conducted the following tests on the blade distance.
(1) Hard-angle hard knife method: Choose a hard-angle knife, that is, the distance between the knife edge and the center of the lining roller is zero, that is, hob scraping. The main advantage of applying this knife distance is that the scraping slurry is on the base fabric The film layer on the coating is thick and soft. After two times of scraping, the thickness of the coating film can reach more than 5 wires. Such a thickness is absolutely unreachable on ordinary coating equipment, but after using this scraper, the drying chamber The temperature should not be too high, otherwise the peeling fastness will be reduced. When the temperature is 130℃ and the vehicle speed is 15 meters/minute, a hard-edged knife can solve the problem of high-thickness coating and scraping. (2) Floating knife method: The floating knife means that the distance between the knife edge and the center of the lining roller is adjusted to 20 to 30 degrees. Floating knife scraping is generally suitable for coating and scraping on the base fabric to form a slightly thin film. After two passes of scraping, Afterwards, the thickness is about 3 wires; the main advantage of the floating knife coating is that it can improve the uniformity and covering properties of the slurry. The temperature of the drying room after floating knife coating can be appropriately increased to about 150°C, and the vehicle speed is 20 ~25 m/min, more suitable for large-scale production. It is also more convenient for workers to clean the lining roller. 1.3 Solve the problem of semi-waterproof quality of base fabric. Polyurethane PU coated textiles require high water resistance, which is difficult to achieve by coating processing alone. For this reason, semi-waterproof finishing must be carried out on the base fabric before scraping to achieve the water resistance requirements of the finished product and improve the quality of the finished product. Feel. Our factory currently has two types of equipment that can perform waterproof finishing: needle plate or cloth clip type setting machines. When these two types of equipment perform waterproof finishing, the needle eye spacing and clip heads produced by both sides of the base fabric after passing through the needle clip or cloth clip are Wrinkle marks are easy to produce edge wrinkle marks when scraping, and they are difficult toResearch
The amount of air permeability, in a sense, determines the wearing comfort of the fabric. In order to improve the breathability of fabrics, improvements have been continuously made on the basis of traditional techniques. Recent research results focus on the following aspects.
3.2.1 Amino acid modified polyurethane[15]
Selecting appropriate amino acids and polyol components to mix them, and then randomly or block-additioning the isocyanate components to form an improved coating or film can greatly improve the breathability of the fabric. According to reports, this type of product, such as Mitsubishi Chemical’s Excepor-U, has a maximum moisture permeability of up to 7000g/m2·24h.
3.2.2 Two types of polyurethane composites［15］
Make hydrophilic polyurethane porous, or make the porous structure hydrophilic. The two mechanisms of microporous structure and hydrophilic structure work together to achieve a more satisfactory breathability effect. The Thintech brand produced by the American 3M Company is this way. The Belgian UCB company also adopts the process of coating the microporous membrane formed by Ucecoat2000(s) with UcecoatNPU2307 finishing agent. EntrantGll, recently developed by Japan’s Toray Company, is a composite of two polyurethane materials. The inner polyurethane contains micropores and ultramicropores (<0.5?m=, which uses its "wicking" effect to suck moisture from the skin and diffuse it. to the outer layer and then discharged into the air to improve perspiration.
3.2.3 Polyurethane coating additives[16]
Use the method of adding other substances to the polyurethane coating agent. It can not only improve the breathability of PU film, but also give the fabric insecticidal and sterilizing effects, as well as an excellent hand feel. Chitin is an extract of the scales of shellfish, aquatic organisms and animals. Its chemical structure is as follows:
Chitin is similar to cellulose macromolecules, but the amide group at the 2-position makes it insoluble in most organic bath agents and antimicrobial. Chitin has high hygroscopicity and hygroscopicity, and has certain antimicrobial properties. After a certain amount of chitin is mixed into the coating agent, it will keep sweat and body fluids clean and have certain medical and health care effects. Such as Japan Asahikaseid’s “Biochiton”. In addition, studies on adding wool shavings, silk shavings, scale powder, cellulose powder, etc. to improve the moisture permeability of fabrics have been reported [14]. The temperature of these powders is high when they are added. When cooled and solidified, the volume shrinks and the phase separation occurs. Micro gaps are formed inside the coating film and around the powder chips, which increases the moisture permeability [1].
3.3 Research and development of pollution-free polyurethane
It has always been the wish of scientific and technological workers to develop a PU coating agent that is completely water-dispersed and has no solvent pollution during the synthesis and application process. Current processing techniques, whether wet or dry, use a certain amount of volatile organic solvents during the processing, which causes environmental pollution problems. If PU is made into a water-soluble coating agent and cross-linked to form a film during the drying process, it will not only greatly reduce production costs, but also overcome environmental pollution problems
problem, so research in this area is also very active. Ureatech, newly launched by Polytech in the United States, is said to be focusing on this aspect and is known as a “high-tech product for the new century”. There are also domestic research reports in this area [17].
3.4 Metal and ceramic coatings
Without affecting the original waterproof and moisture permeability, metal powder is mixed into the resin to form a metal layer that reflects the radiant heat of the human body and reduces heat loss. This kind of coating is suitable for use as sportswear bags for mountaineers in winter or alpine areas, such as Entrantthermo from Toray of Japan and Lyonthermo from Asahi Kasei of Japan [15]. When PU is mixed with ceramic powder with high far-infrared emissivity, this coating can absorb the energy of sunlight or human body heat, radiate far-infrared rays to the human body, improve the warmth retention performance of the fabric, and promote the microcirculation of the human body. [19]. Such as Japan’s Toray Corporation’s Megaclon, Japan’s Asahi Kasei’s VeraV, Japan’s Masonic. Some ceramics also have the function of absorbing odors such as ammonia and hydrogen sulfide. After being mixed into the coating, they become deodorizing waterproof and breathable fabrics, such as Permilan and Deodrant from Japan’s Unitika Company.
4Conclusion
Waterproof, breathable and special functional coated fabrics are high-tech, high value-added products. Various processing technologies constitute a family of waterproof, breathable and special functional coated fabrics, while the polyurethane series is a colorful branch with development potential. Western countries and developed countries such as Japan have invested a lot of manpower and financial resources in competing for development and research, but domestic research is still relatively small. In addition, the United States and Japan also regard such products as high-tech products for the new century. As for the development and research of competitive products in the textile market, our country’s scientific and technological workers in this field should seize the opportunity and catch up

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