Research on polyurethane PU coating technology
Research on polyurethane PU coating technology
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’s current equipment for waterproof finishing consists of two types of setting machines: needle plate or cloth clip type. Because these two types of equipment are used for waterproof finishing, the distance between the needle holes and the distance between the two sides of the base fabric after passing through the needle clip or cloth clip are generated.Wrinkle marks on the head are easy to produce edge wrinkles during scraping, and are difficult to eliminate and directly affect the scraping. For this reason, we designed and modified a simple semi-waterproof finishing equipment based on the actual situation – a finishing car with rolling grooves. After semi-waterproofing on the equipment, both sides of the base fabric not only do not produce crepe marks, but are also very flat, providing a good quality base fabric for the subsequent coating and scraping process.
2. Conclusion: By solving the conjunctival “hanging skin” of polyurethane PU coating slurry, we improve the fluidity of the slurry, solve the semi-waterproof quality of the base fabric and overcome the problem of high-thickness coating and scratching. The production process of this variety It has been basically perfected. The products developed have successfully completed 300,000 meters. The quality of the finished product is about 95%. Its internal quality is in line with the standards and all indicators have met the requirements of customers. After the products are made into garments, they are exported to the United States and Southeast Asia and other countries, and are well received by customers. Welcome. 3. Conclusion: As a new generation of textiles with high added value, polyurethane PU coated fabrics should have a series of functions such as flame retardancy, heat insulation, reflectiveness, antistatic, etc. These are subject to further research and discussion. We will On the basis of stabilizing the quality of this product, efforts will be made to develop more functional coated textiles, so as to further increase and improve the performance of coated products, further expand the application fields, meet the needs of domestic and foreign textile markets, and enable enterprises to obtain better benefit. LO3qxhB
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