Лако-красочные материалы — производство

There are two main types of catalyst for the hydroxyl acrylic/isocyanate reaction, namely metallic salts and tertiary amines.

Dibutyl tin dilaurate (DBTDL) is the most commonly used metallic salt, although salts of bismuth, cobalt, zinc, lead and manganese can also be used.

The level of catalyst used can vary from 0.001% — 0.5% in the case of the metallic salts, calculated as metal on solid resin. The function of the catalyst is to accelerate the cure of the coating by increasing the rate of reaction. This also results in a reduction in pot life and, as a result, a reduction in the working time of the lacquer or paint after mixing. High levels of catalyst can also affect the application characteristics due to the rapid increase in viscosity, although this can be overcome by the use of dual feed application equipment. The metallic salts in general are the more efficient catalyst for use with aliphatic isocyanates.

Acetylacetone (2,4 pentanedione) is used to modify the activity of catalyst systems based on metal carboxylates such as DBTDL. It complexes with the metal carboxylate in solution and reduces its activity resulting in longer pot life. When applied as a film, the acetylacetone is rapidly released from the coating due to its high evaporation rate and it than releases the metal carboxylate to catalyse the reaction between the hydroxyl functional acrylic and the isocyanate prepolymer.

Both primary and secondary amines are to be avoided since they will react with the isocyanates. Triethylene diamine and dimethylethanolamine are commonly used tertiary amine catalysts.

Amine accelerators in general have a greater catalytic effect with aromatic isocyanates. Care should be taken in using these catalysts as they can affect water resistance and durability when used in conjunction with aliphatic isocyanates. Highly active amine accelerators have been utilised in the patented vapour injected curing technology of the Sherwin Williams Co. of Cleveland(5). In this system an amine generator is used to supply a fixed quantity of amine catalyst to the coating at the point of atomisation resulting in a rapid increase in cure, without affecting the pot life of the mixed paint or lacquer.