Patent ID: RE39106

Claim:
In an improved photohardenable composition composed of a cationically polymerizable and free radical polymerizable organic substance, a photo-generated photo- generating acid precursor, a sensitizer for the photo-generated photo- generating acid precursor and a free radical polymerization initiator wherein the improvement comprises: a) a mixture of photopolymerizable resins consisting essentially of at least two epoxy resins one of which polymerizes , said at least two epoxy resins including a first epoxy resin polymerizing at a slower rate and has a having a higher neat viscosity than at least one other epoxy resin present and the , said first epoxy resin s are being present at a concentration in the mixture of from 5 to 25% by weight, and at least one monoacrylic monomer and at least one multi-acrylic monomer wherein the concentration of the monoacrylic monomer is from 0.12 to 0.90 parts by weight that of the multilayer monomer and wherein the ratio of the weight of the epoxy resins to that of the acrylic monomers is between 3 to 10; and b) a combination of a free radical initiator and a photo-generating acid precursor characterized by optical molar extinction coefficient and optimized for use with a multi-wavelength argonion laser operating in the UV and producing two major wavelengths of 351 nm and 364 nm such that a normalized ratio of the extinction coefficients of the precursor and the initiator at one major wavelength is less than 3 times the ratio of extinction coefficient at a second major wavelength.