Ultraviolet curable optical glass fiber coatings from acrylate terminated, end-branched polyurethane polyurea oligomers

DETAILED DESCRIPTION What is claimed is: 1.
A ultraviolet curing liquid coating composition which, when cured with ultraviolet light in the presence of a photoinitiator, either provides a single coating for optical glass fiber having adequate strength at room or expected elevated temperature, and a low tensile modulus which remains low to resist microbending difficulties down to around -40.
degree.
C.
, or which can be used to overcoat softer buffer coatings which remain soft to resist microbending difficulties down to around -60.
degree.
C.
, said coating composition consisting essentially of a linear polyacrylate-terminated polyurethane polyurea oligomer comprising a linear polyurethane terminated with an essentially monohydric adduct of low molecular weight diprimary amine with from about 1 to about 2.
5 moles of monoepoxide per mole of diamine and reacted with acrylate-functional monoisocyanate to leave about 1 hydroxy group per molecule, and an ultraviolet curable liquid acrylate or polyacrylate to provide the liquidity needed for application and to adjust the hardness or softness of the cured coating for the selected single coat or topcoat utility.
2.
A coating composition as recited in claim 1 in which said polyacrylate-terminated oligomer constitutes at least about 30% up to about 80% of the reactive components in the coating.
3.
A coating composition as recited in claim 1 in which said polyacrylate-terminated oligomer constitutes at least about 40% up to about 70% of the reactive comonents in the coating.
4.
A coating composition as recited in claim 1 adapted for topcoat application in which said ultraviolet curable liquid comprises an acrylate-functional monomer whose homopolymer has a glass transition temperature above about 55.
degree.
C.
in the absence of acrylic acid.
5.
A coating composition as recited in claim 1 adapted for topcoat application in which said ultraviolet curable liquid comprises a polyacrylate having a molecular weight below about 600.
6.
A coating composition as recited in claim 1 adapted for single coat application in which said ultraviolet curable liquid comprises an acrylate-functional monomer whose homopolymer has a glass transition temperature less than 0