Photopolymer composition for the production of three-dimensional objects

A process for forming a three-dimensional object comprises repeatedly imagewise exposing the surface of a reservoir of liquid photohardenable composition, curable by actinic radiation, with actinic radiation to harden the liquid composition near the surface to form a plurality of superimposed layers of hardened composition. In this invention, the liquid photohardenable composition consists essentially of: (a) 25 to 65% of a difunctional acrylated polyurethane oligomer or a mixture of the oligomers; (b) 15 to 65% of a polyglycol ester of the following formula: H2C=CR(CO)-O(CH2-CH2-O)n-(CO)RC=CH2 wherein: R is hydrogen or methyl, and n is an integer from 2 to 5; or a mixture of the polyglycol esters; (c) 0.1 to 10% of a photoinitiator system sensitive to the actinic radiation or a mixture of the photoinitiator systems; and (d) 0 to 30% of a polyfunctional reactive diluent or a mixture of the reactive diluents; wherein the liquid photohardenable composition has a viscosity of 200 to 8000 cP at 25 DEG C.