Waterborne polyurethane adhesive still occupies a certain market share in the soft package market. Its performance and operability are completely different from the existing ester soluble polyurethane adhesive. How should we correctly apply the waterborne polyurethane adhesive?
Properties of waterborne polyurethane adhesive
Compared with solvent based polyurethane adhesive, waterborne polyurethane adhesive has the following advantages besides non combustion, solvent-free odor and environmental pollution
1. Solvent based two-component adhesive makes full use of the reaction of NCO groups to enhance the bonding performance in the curing process; because the waterborne polyurethane adhesive does not contain NCO group, the adhesion mainly depends on the cohesion generated by the internal polar groups of polymer. The waterborne polyurethane contains carboxyl group, hydroxyl group and other groups, which can also participate in the reaction under appropriate conditions, so that the adhesive has cross-linking reaction.
2, the important factors affecting the viscosity of waterborne polyurethane are ionic charge, core shell structure and emulsion particle size. The more ions and counter ions of polymer molecules, the greater the viscosity. However, the molecular weight of polyurethane resin, solid content, crosslinking agent and other factors have no obvious influence on the viscosity of waterborne polyurethane, which is conducive to increase the molecular weight of polyurethane and increase the cohesive strength of adhesive. The viscosity of water-borne polyurethane adhesive is smaller than that of solvent-based one with the same solid content.
3. Viscosity is an important index to determine the performance of adhesives. The viscosity of waterborne polyurethane is generally adjusted by water-based thickener or water, while solvent based polyurethane adhesive can be adjusted by increasing solid content, molecular weight or selecting suitable solvent.
4. Because the evaporation rate of water is lower than that of organic solvent, the drying of waterborne polyurethane adhesive is slower. Because of the high surface tension of water, the hydrophobic surface wettability of the substrate is poor. If most of the water has not evaporated from the adhesive to the air, or is still absorbed by the porous substrate, it is difficult to obtain a continuous coating. Because the main solid component of waterborne polyurethane is hydrophilic, if the dried film does not produce a certain degree of crosslinking, the water resistance is poor.
5. Waterborne polyurethane adhesive can be mixed with various waterborne resins to improve performance or reduce cost. At this time, attention should be paid to the pH and other properties of the water-based adhesive, otherwise it may cause condensation.
6. Waterborne polyurethane adhesive has the advantages of small odor, convenient operation and easy cleaning of residual glue. The solvent based polyurethane adhesive needs a lot of solvent in use, and cleaning is not as convenient as water-based adhesive.
Operating conditions
The operation of waterborne polyurethane is similar to that of solvent adhesive, such as hand brush coating, mechanical roller coating and spraying, but some special requirements should be paid attention to, especially wet lamination.
1. Coating amount: the composite strength is related to the coating amount of adhesive, especially the porous substrate. If the amount of glue is too small, most of the glue solution is absorbed by the base material, which will not reach the bonding strength. Therefore, it is suggested that the wet adhesive coating amount should be controlled at about 10-20 grams per square meter, and appropriate adjustments should be made according to different substrates.
2. The temperature of drying channel should be controlled at 70 ℃ - 85 ℃ - 90 ℃, and the air volume should be increased as much as possible. Generally, curing is not required for wet lamination, and water volatilization is very important for waterborne polyurethane adhesive. Therefore, it is necessary to increase the temperature and air volume as much as possible to accelerate the evaporation rate.
3. Coating substrate to ensure that there is no oil and other impurities, so as not to affect the bonding strength.
matters needing attention
1. This product cannot be mixed with other adhesives of different properties.
2. Before compounding, the drying oven temperature must be raised to the set temperature before starting the machine.
3. After gluing, the glue on the cot should be cleaned with tap water and then cleaned with ethyl acetate.
Dongguan Beite packaging materials Co., Ltd. - located in Dongguan City, the world's manufacturing city, is a subsidiary of Beite packaging (China) Co., Ltd., with a plant area of 6000 square meters. It is a flexible packaging enterprise integrating R & D, production and sales. It has a complete set of domestic advanced production equipment, a scientific and humanized management system and a group of experienced technical personnel For backing, to provide customers with quality products and first-class service.
The company produces composite bags, roll film, fruit bags, aluminum foil bags, suction mouth bags, self-supporting bags, zipper bags, anti-static bags, special-shaped bags, etc., which are suitable for the internal and external packaging of food, daily chemicals, electronics, toys, medicine, cosmetics, industrial products and other industries.
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