Analysis of the green development trend of the hot

2022-09-23
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The development and application of composite adhesives with high solid content and low viscosity

domestic adhesive production enterprises have become mature, and their technological development strength has been greatly enhanced. There have been representative enterprises such as Zhejiang New Oriental, Beijing Chemical Research Institute, Beijing GAOMENG, etc. these enterprises have strong R & D capabilities, and their products are moving towards high solid content Low viscosity and functional development

at present, the use of adhesives with high solid content and low viscosity has become an important development direction of dry composite adhesives. In the past, the solid content of the main agent of two-component polyurethane adhesive was 35% or 50%, but now it has been increased to 75% or 80%. The two-component polyurethane adhesive with 75% solid content accounts for 60% of the market share, and the market of the two-component polyurethane adhesive with 50% solid content is shrinking, and the elongation deformation is also increasing to less than 30% of the market share. Due to the characteristics of high solid content and low viscosity, it is possible to use high working solid content for high-speed composite processing

using high solid content adhesive under the same coating amount can effectively reduce the amount of solvent (2) the hammer body diameter and the inner diameter of the drop hammer tube are about 35mm, and has the following advantages:

(1) reduce solvent consumption

(2) reduce drying load, improve production efficiency and reduce energy consumption

(3) reduce residual solvents

but increasing the solid content (working concentration) also brings some problems:

(1) due to the sharp change of viscosity when the solvent evaporates, it is difficult to uniformly coat the adhesive

(2) due to the short activation period, it is easy to cause blocking, and it is difficult to ensure a uniform coating amount. It is also easy to cause poor appearance

(3) due to the small molecular weight (low viscosity) and cohesion of the adhesive, it is easy to cause processing faults such as tunnel effect. At present, some domestic adhesive manufacturers have produced high solid content and low viscosity products with high initial viscosity through the adjustment of molecular weight and molecular structure

second, the development and application of water-soluble adhesives

the advantages of water-soluble adhesives are that water replaces organic solvents, there is no potential danger of combustion and explosion, there is no pollution to the environment and toxicity to operators, and the cost is low. However, the coating performance of this adhesive is poor, and its wettability to the composite substrate is poor (because the surface tension of water is 72Mn/m, while the surface tension of the substrate is mostly only about 38mn/M), resulting in low adhesion. In addition, the heat capacity of the external water is large, and the drying of the ink will consume more energy, which not only limits the production speed, but also increases the production cost. At the same time, the water vapor also causes certain corrosion to the equipment. These factors limit the wide use of water-based adhesives to a certain extent

III. develop solvent-free composite process

solvent-free adhesive is basically composed of two-component polyurethane adhesive. Its main agent and curing agent have high viscosity at room temperature, but they still have fluidity and are semi-solid substances. When compounding, the main agent and curing agent are mixed in proportion, put into the adhesive tray with heating and insulation function, heat it to reduce the viscosity to an appropriate level, and then apply it to the substrate through the corrugated roller with heating and insulation function. After coating, it can be directly compounded with another substrate without heating and drying. The solvent-free composite process does not have the problem of exhaust gas emission. It does not need a huge and complex heating and ventilation device and exhaust gas exhaust device. The equipment is simple. Therefore, whether the safety belt is qualified or not is 10 points important, and the energy consumption is reduced. The solvent-free compounding process is simple, the equipment covers a small area, which is suitable for reducing costs, saving resources, protecting the environment, and adjusting the horizontal movement of the loading mechanism. Therefore, it will be the main development direction of the compounding process in the future. In recent years, with the strengthening of product quality and environmental protection awareness in China, solvent-free compounding has been increasingly favored by people in the composite film packaging industry in China, and many solvent-free compounding machines have been put into operation in China. At present, most medium and low-grade plastic flexible packaging materials can be produced with solvent-free adhesives, but due to the constraints of composite quality and other factors, it can not completely replace the dry composite process

although the development of adhesives will eventually move towards solventless, because solventless adhesives need special solventless compounding machines, the equipment investment is large, and it will take a long time for large-scale promotion. Therefore, solvent based polyurethane adhesive is still the mainstream product in the market

IV. development and application of alcohol soluble polyurethane adhesives

in the field of plastic flexible packaging, the currently developed non organic solvent adhesives (including solvent-free and waterborne polyurethane adhesives) have not fully reached the level of solvent-based adhesives, so solvent-based polyurethane adhesives will still exist for a long time. Alcohol soluble polyurethane adhesive will gradually occupy a certain market share because it meets the requirements of green environmental protection and has the basic advantages of two-component, solvent based polyurethane adhesive

most polyurethane adhesives use ethyl acetate as diluent, while alcohol soluble polyurethane adhesives can use ethanol as diluent. Compared with ethyl acetate, ethanol has lower toxicity and less solvent residue. At the same time, ethanol is cheap, which can effectively reduce the composite cost. In addition, alcohol soluble polyurethane adhesive, combined with alcohol solvent ink, has good compatibility and bonding performance to alcohol soluble ink, and saves the curing cost because it can be cured at room temperature

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