Most of the polyurethane adhesives currently in the market are solvent-based. It contains a large amount of organic solvents and a certain amount of free isocyanate, which will affect the environment and human health. With the attention of countries to environmental protection, the development of water-based polyurethane adhesives has achieved rapid development. Although the history of waterborne Polyurethane Adhesive is not long, it has developed very rapidly. In 1943, West German P Schlack successfully made waterborne polyurethane adhesive for the first time. In 1967, the U-Liquid emulsion was first industrialized and put on the market in the United States. In 1972, Baye Company took the lead in using polyurethane aqueous emulsion as a waterborne polyurethane adhesive for leather finishing. As an important commodity, in the 1990s, some foreign companies successfully developed a one-component self-crosslinking water-based polyurethane adhesive by introducing reactive groups into the polymer.
Waterborne polyurethane adhesives can be made by the following two methods:
One is to emulsify the original polyurethane adhesive directly into a stable, water-dispersible emulsion by adding an emulsifier. However, the presence of an emulsifier can affect its water resistance and bond strength.
The second is the introduction of hydrophilic ionic groups in the molecular framework of the polyurethane to form self-dispersing and self-emulsifying systems. The advantage of this system is that it does not contain emulsifiers, has good film formation and can be modified with other anionic or cationic polymerization systems to reduce costs.
In recent years, the industry's research on waterborne polyurethane adhesives has focused on increasing the solid content, increasing the drying speed, increasing the bonding strength and water resistance. With the advent of water-dispersible polyisocyanate curing agents, the performance of the two-component polyurethane adhesives has basically reached the performance of solvent-based two-component polyurethane adhesives. At this point, the application field of water-based polyurethane adhesives began to expand to the coating of wood floors, plastics, metals, concrete, etc., and there are a variety of water-based polyurethane adhesives for industrial applications.
Water-based polyurethane adhesives have achieved good results in the composite film industry but there are still some problems in their application.
(1) It is not as good as the organic solvent is volatile, so when drying, the temperature of the drying tunnel should be increased or the drying tunnel should be lengthened, which will cause waste of energy.
(2) The bonding strength of waterborne polyurethane adhesives is still not up to the requirements for use on some high-end packagings.
(3) Due to the limited product variety of waterborne polyurethane adhesives, there are few products specifically designed for the composite film industry.
Although the application of water-based polyurethane adhesives is not yet perfect, but it has a broad space for development, so waterborne polyurethane adhesives are both opportunities and challenges for domestic adhesive manufacturers.
Author: Li Wei, Yao Xiaoning, Zhou Jianmin Source: "China Printing Materials Market"
