Лако-красочные материалы — производство

In order to meet environmental regulations pertaining to VOCs, high- solid alkyd resins have been developed with about 80 % by weight or more of the vehicle solids at acceptable viscosity. In high-solid resins, low viscosities are typically achieved by decreasing the MW of the polymers. The reduction in MW has a consequence of relatively poor mechanical and chemical resistance of their films. Additional cross­linking and MW buildup during curing is therefore necessary for acceptable performance. For the short oil alkyds that are used in sto — ving finishes, typically with amino resin cross-linkers, this approach is more feasible, as low MW alkyd resin reacts with curing agent to build up the sufficiently high MW needed for good performance.

Another approach for high-solid alkyd resins is to synthesize the resin with a narrower MW distribution. It has been reported that by decreasing the MW distribution, the solids could be 2 to 10 % higher than an alkyd of the same composition prepared by the conventional method (with broader MW distribution).

Selection of solvents is also an important consideration in designing high-solid alkyd resins. Use of stronger solvents results in resin solutions with lower viscosities at lower solvent content. Hydrogen bonding between hydroxyl and ester groups has a significant effect on viscosity via a hydrogen bonded network; therefore, solvents that can block off hydrogen bonding are effective in viscosity reduction. Some examples of such solvents are lower alcohols and ketones.

Use of reactive diluents for viscosity reduction is another practical approach for high-solid alkyds. These are compounds with very low MW and low viscosity, with functional groups capable of reacting with alkyds and thus being incorporated in the cured film. Linseed oil is one such reactive diluent, but various other compounds such as the allyl acetal of pentaerythritol, allyl ether and acrylate ester compounds are currently used.