Categories and Characteristics of Waterborne Polyurethane Adhesive
With the progress of science and technology and the increasingly strict requirements of environmental protection laws and regulations, the research and development of environmentally friendly adhesives has been paid more and more attention. Mainly includes waterborne polyurethane adhesive and solvent-free adhesive. Solvent-free glue is generally called hot melt glue. It is composed of thermoplastic resin and does not contain any moisture and solvent. It can flow in the molten state and has adhesive properties after cooling. It can be easily automated. The production process provides high productivity without any Environmental pollution, harmless to humans. In addition, there are emulsion/dispersion adhesives, reactive adhesives and natural polymer adhesives.
With the progress of science and technology and the increasingly strict requirements of environmental protection laws and regulations, the research and development of environmentally friendly adhesives has been paid more and more attention. mainly includeswaterborne polyurethane adhesiveand solvent-free adhesives. Solvent-free glue is generally called hot melt glue. It is composed of thermoplastic resin and does not contain any moisture and solvent. It can flow in the molten state and has adhesive properties after cooling. It can be easily automated. The production process provides high productivity without any Environmental pollution, harmless to humans. In addition, there are emulsion/dispersion adhesives, reactive adhesives and natural polymer adhesives.
Environmentally friendly adhesives for shoes not only require the firmness, durability and softness of the bonding shoe material, but also must be environmentally friendly and compatible with different materials to ensure the quality of the shoes.
Environmentally friendly polyurethane adhesive for shoes mainly has no solvent reactive polyurethane hot melt adhesive and waterborne polyurethane adhesive.
a. Solvent-free reactive polyurethane hot melt adhesive
Due to the poor wettability of ordinary contact hot melt adhesives to the surface of the material to be adhered, it has proved that they cannot be widely used in the bonding of large soles. Therefore, reactive hot melt adhesives have been developed. After more than 10 years of efforts, they have now developed products with low viscosity and can be applied under appropriate temperature conditions. Reactive hot melt adhesives are crosslinked with the help of moisture or heat, ultimately achieving better bond strength. The use of solvent-free reactive polyurethane hot melt adhesives requires special gluing equipment and strict operating conditions. Therefore, it is difficult to promote the application. Foreign shoe factory has batch application of polyurethane hot melt adhesive bonding sole. Our country also has the research unit to develop this kind of adhesive. According to reports, the bonding strength is not high enough and is still in the laboratory stage.
B. waterborne polyurethane adhesive
Waterborne polyurethane adhesive does not contain NCO groups, but contains carboxyl, hydroxyl and other groups. Under suitable conditions, for example in the presence of a water-based isocyanate, the molecules of the adhesive can undergo a crosslinking reaction. Most waterborne polyurethane adhesives are cured by polar groups in the molecule to produce cohesion and adhesion. Waterborne polyurethane adhesives have polar groups, such as urethane bonds, urea bonds, ionic bonds, etc., so they have good adhesion to many synthetic materials, especially polar materials and porous materials.
Waterborne polyurethane glue and solvent polyurethane glue, waterborne polyurethane glue no solvent odor, non-toxic, no pollution, convenient operation, easy to clean the residual glue, high solid content, safe and convenient storage, but the water-based glue requires a longer drying time and a higher drying temperature, drying process conditions are strict, to ensure the complete volatilization of water. The wetting ability of water-based glue to the substrate is poor, and the water-soluble polymer thickener in the adhesive will reduce the water resistance. In addition, the water-based surface treatment agent (in the laboratory research stage) has not yet been developed and the solvent-based surface treatment agent is still needed. Therefore, even if the water-based large bottom glue is used, the organic solvent cannot be eradicated at present.
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