The use of solvent-free polyurethane adhesives for composite films began in Germany and Japan in 1974. This technology was introduced from 1977 to 1997. More than 60 production lines in Europe and the United States have already prepared half of their composite film products using solvent-free polyurethane adhesives.
Solvent-free polyurethane adhesives have now been developed to the third generation. The first generation is a polyether- or polyester-type isocyanate-terminated prepolymer, which has the disadvantages of rapid viscosity change, slow cure speed and easy generation of carbon dioxide bubbles: the second generation is a terminal-based prepolymer and an isocyanate-terminated prepolymer. The two-component type coating device has a precise automatic metering and mixing system but has poor adhesion to materials such as EVA aluminum foil; the third generation is a two-component system improved on the second generation basis and can withstand high-temperature cooking , can also be used for bonding aluminum foil.
Because solvent-free polyurethane adhesives do not contain solvents, they are solvent-saving and environmentally friendly. As the country’s environmental protection requirements gradually limit the amount of solvent emissions, the application of solvent-free polyurethane adhesives will rapidly develop.
There are also problems with the use of solvent-free polyurethane adhesives.
(1) Due to the inability to produce sophisticated automatic metering and mixing systems at home, it is necessary to import expensive equipment from abroad.
(2) Solvent-free composite machines have high speeds (generally above 200m/min) and have high requirements for compounding technology.
(3) The main point is that nowadays solvent-free polyurethane adhesives are expensive and most of them need to be imported. Products from only a few domestic companies can meet the requirements. Therefore, there is still a long way to go for the large-scale use of solvent-free polyurethane adhesives in China.
There are many varieties of polyurethane adhesives that can function in multiple areas as the formulation and raw materials change. The development direction of the adhesive is also changed from the common type to the special type to the compatible type (universal type) so as to exert the optimal performance of the adhesive. Over 20 years of reform and opening up, the Polyurethane Adhesive industry has made rapid development. Especially after the accession to the WTO, the products of many foreign manufacturers have flooded into the Chinese market. The prices of domestic products are getting closer and closer, which undoubtedly brings tremendous pressure to domestic manufacturers. Therefore, how to speed up technological progress, seize opportunities and meet challenges, and timely development has become a problem we must face. We should make use of our own advantages and seek breakthroughs on the basis of learning so that our products can reach or even exceed foreign products to revitalize the national industry.
Author: Li Wei, Yao Xiaoning, Zhou Jianmin Source: "China Printing Materials Market"
