Process of radiation and heat treatment of printing medium

In the process of coating a heat resistant substrate selected from glass, metal and ceramic comprising the steps of

• (1) applying a solvent-free printing medium to the heat resistant substrate, wherein the printing medium comprises a ceramic frit and a vehicle therefor;
• (2) curing the printing medium with ultraviolet radiation, pulsed beam ultraviolet radiation or electron beam radiation after it is applied to the substrate;
• and
• (3) thereafter firing the substrate with the applied and cured printing medium at a temperature sufficient to burn off the vehicle and fuse the frit to the substrate;
• the improvement wherein the printing medium is a composition comprised of
• (a) about 2% to 25% by weight of a polymerizable liquid prepolymer comprising hydroxyl terminated polyester, polyether or polyester-polyether backbones containing at least about two ethylenically unsaturated end groups and having a number average molecular weight of from about 15,000 to about 80,000;
• (b) about 2 to 15% by weight of at least one ethylenically unsaturated, polymerizable monomer selected from acrylate and methacrylate containing a polar functional group;
• (c) about 60 to 90% by weight of a ceramic frit;
• and
• (d) about 0.02 to 2% by weight of a polymerization inhibitor.