Patent ID: 8853295

Claim:
A process for preparing a radiation-curable allophanate having a residual monomer content of less than 0.5 weight % and an NCO content of less than 1 weight %, comprising (1) preparing a urethane comprising NCO and radiation-curable groups from A) a compound comprising NCO groups; B) a mixture comprising I) from 30 to 60 mol %, wherein mol % refers to the mol % of OH groups based on the total OH groups in component B), of from 20 to 80 mol % of 2-hydroxyethyl acrylate and from 80 to 20 mol % of 2-hydroxypropyl acrylate, with the proviso that the sum of said 2-hydroxyethyl acrylate and said 2-hydroxypropyl acrylate is 100 mol %; II) from 15 to 35 mol %, wherein mol % refers to the mol % of OH groups based on the total OH groups in component B), of 2-hydroxyethyl acrylate modified with ε-caprolactone; and III) from 15 to 35 mol %, wherein mol % refers to the mol % of OH groups based on the total OH groups in component B), of pentaerythritol triacrylate; with the proviso that the sum of I), II), and III) is 100 mol %; C) optionally a radiation-curable compound different from B) and which comprises NCO-reactive groups; D) optionally a compound comprising NCO-reactive groups and free from radiation-curable groups; and E) optionally in the presence of a catalyst and (2) subsequently or simultaneously and without further addition of a compound comprising NCO groups, reacting said urethane comprising NCO and radiation-curable groups in the presence of F) an allophanatization catalyst; and G) optionally a tertiary amine; to form an end product; wherein the allophanatization catalyst is from 0.05 to 0.5 weight % based on the solids content of the end product, wherein the allophanatization catalyst is selected from the group consisting of zinc octoate, zinc acetylacetonate and zinc 2-ethylcaproate; wherein the ratio of NCO groups of the compound of A) to the OH groups of the compound of B), optionally C), and optionally D) is in the range of from 1.45:1.0 to 1.1:1.0; and wherein the radiation-curable allophanate has a shear viscosity at 23° C. of <30,000 mPas.