D1378 CA RADIATION-CURABLE PRIMARY COATING FOR OPTICAL FIBER

PROBLEM TO BE SOLVED: To provide a radiation-curable coating for use as a primary coating for an optical fiber, an optical fiber coated with the coating, and a method for preparing a coated optical fiber.SOLUTION: There is provided a radiation-curable primary coating composition which comprises: an oligomer; a diluent monomer; a photopolymerization initiator; an antioxidant; and an adhesion promoter, wherein the oligomer is a reaction product of a hydroxyethyl acrylate, an aromatic isocyanate, an aliphatic isocyanate, a polyol, a catalyst and a polymerization inhibitor; the catalyst is an organobismuth catalyst; the oligomer has a number average molecular weight of at least approximately 4,000 g/mol to approximately 15,000 g/mol or less, and a cured film of the radiation-curable coating composition has a peak tan δ Tg at approximately -25°C to approximately -45°C and an elastic modulus of approximately 0.50 MPa to approximately 1.2 MPa.