Application of polyurethane dry coating
Application of polyurethane dry coating
Coating finishing is to apply a layer of polymer compounds that can form a thin film on the surface of various fabrics! It is a surface finishing technology that allows the front and back sides of the fabric to produce different functions! Coating can not only improve the appearance and style of the fabric! It can also be customized according to the needs of the fabric. The uses of fabrics are different! Increase the functions of fabrics! Make the fabrics have functions such as waterproof, water pressure resistance, air permeability, flame retardant and antifouling, light-shielding reflection and antistatic, and UV protection! Make the fabric multi-functional and increase its added value! Apply The coating adhesive is a polymer compound for coating finishing! Currently, the coating adhesives mainly use polyacrylates and polyurethanes! Polyurethane coating agents include solvent-based polyurethane and water-dispersed polyurethane! This article mainly discusses solvent-based polyurethane coatings. Discuss the application of agent dry coating! The full name of polyurethane is polyurethane!
A polymer compound with an English name! This unit is formed by the reaction of an isocyanate group and a hydroxyl group! The reaction formula is as follows. The general chemical formula is as a chain extender. The polyurethane coating agent is a flexible segment such as polyester and a rigid segment of isocyanate embedded in it. Segment copolymer! In the molecular chain, the rigid and soft segments are arranged alternately! During the coating process! After the solvent evaporates! Under the action of the cross-linking agent, the polyurethane molecules are cross-linked! Under the action of hydrogen bonding, the rigid segments are close to each other! The formation of knots gives the textile excellent properties! Thus improving water resistance, the soft segments curl softly! Making the fabric feel soft, therefore!, many properties! such as?@% melting point, “modulus”, “elasticity”, “tensile strength”, water absorption Etc.! It can all be achieved by changing the type and molecular weight of the polyester prepolymer! The type of diisocyanate! The ratio of soft and hard segments! The type and amount of chain extender, etc. The advantage of polyurethane coating agents is that the coating is soft The elastic coating has good strength! The coating is porous! It has moisture resistance and ventilation properties! Wear resistance, moisture resistance, dry cleaning resistance, etc. The dry direct coating finishing process is to dissolve the coating agent in water or organic solvents!
Add certain additives to make a coating slurry! Use an applicator to apply it directly and evenly on the fabric! Then heat and dry% to bake! Evaporate the water and solvent! The coating agent passes through its own cohesion or resin on the surface of the fabric. Cross-linking effect! Form a tough film, and dry coating is easy to apply! Suitable for various coating agents. There are many types of coating agents! There are solvent-based, coating glue% water-based, coating glue, solvent-based, It has good strength and water resistance, in terms of components! It can be divided into two-component and single-component categories! The one-component product has a linear structure! It is thermoplastic! And the two-component product has a coating finish When it forms a thermosetting network film, it gives textiles excellent properties! Therefore, in actual production, two-component solvent-based polyurethane coating agents are generally used! We choose resins imported from “%! Comparison of the two coating agents” In view of the two Prices vary!
For products with high water pressure resistance and good hand feel requirements, imported resin is generally used! For products with low water pressure resistance requirements, domestic resin is generally used! Since it is a two-component resin, an external cross-linking agent % polyisocyanine is used. Acids! Cross-linking accelerator% organic amines! Plasticizer! In addition, solvents such as toluene and butanone are used to adjust the viscosity of the coating agent! Floating scraper coating equipment is used! In this equipment, the scraper is placed above the base fabric! There is a support bed under the base cloth! The coating slurry is located between the base cloth and the scraper! Its viscosity is preferably at or above! When coating, the thickness and angle of the scraper are used! And the tension of the base cloth is adjusted by the adjusting roller to control the coating slurry. Coating amount! Since the key operating factor of this equipment is tension! And the tension adjustment fluctuates greatly! Therefore, the coating uniformity is poor! However, if the height, torque and angle of the scraper are controlled well, the coating needs can generally be met! Control the coating amount! The coated fabric requires both moisture permeability and a certain degree of water pressure resistance! A reasonable coating agent must be selected! Proper proportioning! Supplemented by a reasonable coating process! The micro-gap moisture-permeable coating process is A kind of polyurethane resin with special functional groups! A process of direct coating using a dry method! A non-porous and micro-gap coating film is formed on the surface of the fabric to produce a waterproof and moisture-permeable effect! The strong chemical bonds of the polyurethane coating agent and The network structure combined with weak binding force! It will inevitably lead to many tortuous and irregular small gaps between the molecules! The micro gaps are several orders of magnitude smaller than the micropores! Although small water droplets cannot pass through! But single molecules of water vapor molecules can Through! Its moisture permeability is based on the fact that the polymer molecules contain enough polar groups that have weak binding force to water vapor molecules!
Therefore, when the humidity on both sides of the coating film is different and the water vapor flows from the high-humidity side to the low-humidity side, due to the existence of polar groups, a continuous transfer effect can occur, which accelerates the flow rate of water vapor molecules and improves the moisture permeability. !For solvent-based dry coating, use mixed type to delay evaporation! Reduce defects! The drying temperature should not be too high!
Otherwise, the solvent will evaporate too quickly! Micropores will be generated! Under certain temperature conditions! It is better to control the speed of the machine to just dry! The speed of the machine is too slow! The drying time is long! It takes a long time for the coating agent to penetrate into the surface of the fabric! Causes the fabric to deteriorate. The hand feeling becomes worse! The gloss becomes darker! The vehicle speed is too fast! The surface of the fabric is sticky! It affects the quality! For thin fabrics such as taffeta! Generally, the fabric density is high! The surface area is large! The amount of coating per unit area is large! The vehicle speed should be fast! For heavy and heavy fabrics Fabric! The vehicle speed should be slow! The viscosity of the coating slurry is an important parameter that affects the quality! Low viscosity coating slurry! Good penetration into the fabric! Poor film-forming properties on the fabric surface! Low water pressure resistance! Increased viscosity! Water resistance.�Accordingly increase! But it will increase the difficulty of scraping and produce scraper marks!
Generally, it is better to control the viscosity! Mix! Add the components into the barrel in order and “under high-speed stirring of the mixer”, use the high-speed vortex of the material due to the shear force of the impeller to interact with the vortex generated around the barrel to disperse and dissolve. “The heat generated by the mixing of materials spreads to the entire material due to eddy currents. “Avoid local temperature rise.” The mixing time is!” Minutes%8 water pressure resistance 2,,:; and above “Water content is more than 01 minutes%! Factors affecting water pressure resistance” Raised knife edge “Small knife moment” Small tension “High water pressure resistance High viscosity” Small penetration “Thick scraping film” “Thin penetration film” High water pressure resistance Thin fabric “Thin penetration film” Thick coating film “High water pressure resistance %” Double The component coating agent “starts to react after each component is mixed.” Therefore, it is advisable to mix the coating!.21,*+ The knife edge should be cleaned frequently to prevent the cornealization of the knife edge material and affect the quality of the coated product cloth.
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