Radiation-curable water-dilutable urethane resins, preparation process

Abstract

Radiation-curable water-dilutable urethane resins obtainable by reacting cycloaliphatic and/or aromatic diisocyanates with a mixture of a (meth)acryloyl-containing dihydroxy compound in an amount such that the amount of reactive hydroxyl groups present therein is from 0.2 to 0.6 mol, and with a tri or tetrahydric polyol which has been partly esterified with (meth)acrylic acid and has a residual average hydroxyl functionality of from 1.0 to 1.4 in the molecule, in an amount such that the amount of the reactive hydroxyl groups is from 0.4 to 0.8 mol, the sum of the amounts of the reactive hydroxyl groups always being 1.0 mol, and from 40 to 60% of the isocyanate groups being converted into urethane groups, and reacting the resulting intermediate with an aliphatic saturated monocarboxylic acid having at least two hydroxyl groups in an amount such that the amount of the reactive hydroxyl groups is from 0.6 to 1 mol, until the hydroxyl groups have undergone complete reaction and reacting this product, if desired, with further part-esterified polyol in an amount such that the amount of hydroxyl groups in the polyol is from 0 to 0.5 mol until the remaining free isocyanate groups have undergone complete reaction, the molar proportions of the components being chosen so that the ratio of the number of isocyanate groups to the number of hydroxyl groups is from 0.9:1 to 1:1 and the reaction product possesses carboxyl groups in accordance with an acid number of from 20 to 40 mg/g and has a specific double bond content of not more than 3.5 mol/kg.