Лако-красочные материалы — производство

As discussed in the section on water-reducible alkyd resins (Sec­tion 2.3.8), water-reducible polyesters can also be prepared by the classical approach of formulating an acid-rich resin (acid value 35 to 60 mg KOH/g), which upon neutralization with a tertiary amine, forms an anionic salt. Water is then added to produce reasonably stable dispersions of polyester chains swollen with water and solvent. The method for deriving water-reducible polyesters is very similar to that described for water-reducible alkyds (Section 2.3.8). Hydrolytic stability is a very important concern since ester groups are prone to hydrolysis. Steric shielding of the ester group is one of the approaches to increase hydrolytic stability. In addition, the choice of glycol also affects stability. Polyesters prepared from hydrophobic diols with low water solubility, such as 2-butyl-2-ethyl-1,3-propanediol, have better stability against hydrolysis. In another approach, use of use 2,2-dimethylolpropionic acid (DMPA) as one of the diol components is recommended. The carboxylic acid group of DMPA is located on a tertiary carbon and hence is highly hindered, which makes it possible to esterify the hydroxyl groups while leaving many of the acid groups unreacted and available for neutralization with amine.