d1363bt on the radiation-curable optical fiber primary coating

The present invention relates to an optical fiber on D1363BT Radiation-curable primary coating, the coating is such a coating method for preparing such a coated optical fiber and the optical fiber. The radiation curable coating comprising at least one (meth) acrylate functional oligomer and a photoinitiator, wherein the urethane (meth) acrylate oligomer CA / CR comprising (A yl) acrylate groups, at least one polyol backbone and urethane groups, wherein about 15% or more of the urethane groups are derived from 2,4-tolylene diisocyanate and 2, 6- toluene diisocyanate in one or both, wherein at least 15% of the urethane derived from cyclic or branched aliphatic isocyanate, and wherein the (meth) acrylate-functional number-average molecular weight of the oligomer is at least about 4000g / mol, but less than or equal to about 15000g / mol; and wherein a cured film of the radiation curable primary coating composition has a modulus of less than or equal to about 1.2MPa .