Polyurethane adhesive five auxiliaries

solent

In order to adjust the viscosity of polyurethane adhesives and facilitate the process operation, solvents are often used in the preparation process or preparation of polyurethane adhesives. The organic solvent used in polyurethane adhesives must be "ammonia ester grade solvent", which is basically free of active hydrogen compounds such as water and alcohol. "Ammonia ester grade solvent" is the isocyanate equivalent as the main index, that is, the number of grams of solvent required to consume 1mol of NCO base, the value must be greater than 2500, less than 2500 is unqualified. Therefore, the solvent purity of polyurethane adhesives is higher than that of general industrial products.

Solvents used in polyurethane adhesives usually include ketones (milk methyl ethyl ketone, acetone), aromatic hydrocarbons (such as toluene >, dimethylformamide, tetrahydrofuran, etc.). The choice of solvent can be determined according to the dissolution principle of the polyurethane molecule and the solvent, that is, the solubility parameter SP is similar, the polarity is similar, and the volatilization rate of the solvent itself. Mixed solvents can be used to improve the solubility and adjust the volatilization rate to meet the requirements of different bonding processes.

catalyst

There are three main reactions in the preparation of polyurethane resins that require catalysts: NCO/NCO, NCO/OH, and NCO/H2O. The manufacture of polyurethane adhesives mainly requires NCO/OH reaction catalysts and NCO/H2O reaction catalysts.

Organotin catalysts

Organotin catalysts catalyze the NCO/OH reaction better than the NCO/H2O reaction, and most of them are used in the preparation of polyurethane adhesives.

Tertiary amine catalysts

Tertiary amine catalysts are particularly effective in promoting the reaction of isocyanates with water and are generally used in the preparation of polyurethane plastics. Foaming polyurethane adhesives and low temperature curing, moisture curing polyurethane adhesives are also used.

Chain extender and crosslinking agent

Low molecular weight polyfunctional compounds containing hydroxyl or amine groups act as chain extenders and crosslinkers when used together with isocyanates, they affect the relationship between hard and soft segments of polyurethane, and directly affect the adhesive properties of polyurethane. The chain extender can react with excessive isocyanate twice to produce a linking agent.

stabilizer

Polyurethane adhesives also have aging problems, which are mainly thermal oxidation, light curing and hydrolysis. To solve this problem, antioxidant, light stabilizer and hydrolysis stabilizer are added to improve.

Fillers and creep agents

The addition of suitable fillers in the composition of polyurethane adhesives is mainly to improve physical properties, adding fillers can play a reinforcing role, improve the mechanical properties of the adhesive, reduce the shrinkage stress and thermal stress, enhance the stability of thermal damage, reduce the coefficient of expansion, and also improve the viscosity of the adhesive and reduce the cost.

In order to control the fluidity of Polyurethane Adhesive during the cementing process, creep agent was added to the composition of the adhesive. This is especially true for materials with strong absorbency, such as leather, textiles or concrete