Abstract: Provided is a radiation curable resin composition suitable for use as a primary coating material for optical fibers, which can form a cured coating with a low modulus of elasticity exhibiting a high breaking strength, and small light transmission loss; the coating composition comprises (A) a polymer containing polymerizable unsaturated groups in an average amount of 1.2 per molecule, a urethane bond in a molecular chain, and having a number average molecular weight from 3,000 to 30,000, (B) a poly-functional monomer having two or more polymerizable unsaturated groups, (C) a monomer having one polymerizable unsaturated group, and (D) a radiation active initiator. The secant modulus of the coating is less than 0.15 kg/mm2, the tensile strength is more than 0.15 kg/mm2.

Abstract: To provide a liquid curable resin composition which can produce transparent cured products with a high refractive index, high hardness, and superior abrasion resistance, and can be suitably used as a coating material.