Radiation-curable optical fiber coatings having reduced yellowing and fast cure speed

Abstract

Radiation-curable inner and outer primary optical fiber coatings are disclosed having both fast cure speed and reduced rates of yellowing. The compositions comprise particular photoinitiators and UV absorbers which are used in amounts to provide the combination of properties. The UV absorber can have ethylenic unsaturation. Outer primary coatings can be formulated to screen inner primary coatings and have fast cure speed.

What is claimed is:  
     
         1 . A radiation-curable composition for an optical fiber coating comprising the combination of pre-mixture ingredients: 
 about 5 wt. % to about 95 wt. % of at least one radiation-curable oligomer,    about 5 wt. % to about 95 wt. % of at least one reactive diluent,    about 0.1 wt. % to about 20 wt. % of at least one photoinitiator, wherein said photoinitiator is selected to provide a fast cure speed,    about 0.1 wt. % to about 20 wt. % of at least one UV absorbing compound which does not substantially impair said fast cure speed.    
     
     
         2 . A radiation-curable composition according to    claim 1   , wherein the amount of said UV absorber is at least 0.1 wt. %.  
     
     
         3 . A radiation-curable composition according to    claim 2   , wherein the amount of said UV absorber is at least 0.3 wt. %.  
     
     
         4 . A radiation-curable composition according to    claim 3   , wherein the amount of said UV absorber is at least 0.5 wt. %.  
     
     
         5 . A radiation-curable composition according to    claim 1   , wherein said oligomer is a urethane acrylate oligomer.  
     
     
         6 . A radiation-curable composition according to    claim 1   , wherein said composition is cured sufficiently to achieve at least 90% of its maximum modulus.  
     
     
         7 . A radiation-curable composition according to    claim 1   , wherein said photoinitiator is a phosphine oxide compound.  
     
     
         8 . A radiation-curable composition according to    claim 1   , wherein said composition is formulated to be an outer primary optical fiber coating.  
     
     
         9 . A radiation-curable composition according to    claim 1   , wherein said composition is formulated to be an inner primary optical fiber coating.  
     
     
         10 . A radiation-curable composition according to    claim 1   , wherein said UV absorber comprises a radiation-curable functional group.  
     
     
         11 . A radiation-curable composition according to    claim 1   , wherein said composition comprises at least two UV absorbing compounds.  
     
     
         12 . A radiation-curable composition for an optical fiber coating comprising the combination of pre-mixture ingredients: 
 about 5 wt. % to about 95 wt. % of at least one radiation-curable urethane acrylate oligomer,    about 5 wt. % to about 95 wt. % of at least two reactive diluents comprising acrylate functionality,    about 0.1 wt. % to about 20 wt. % of at least one phosphine oxide photoinitiator,    about 0.1 wt. % to about 20 wt. % of at least one UV absorbing compound which comprises an acrylate functionality.    
     
     
         13 . A coated optical fiber comprising the combination of: 
 an optical fiber,    a radiation-cured inner primary optical fiber coating, and    a radiation-cured outer primary optical fiber coating, wherein    said outer primary optical fiber coating comprises, before radiation-cure, the combination of pre-mixture ingredients:    about 5 wt. % to about 95 wt. % of at least one radiation-curable oligomer,    about 5 wt. % to about 95 wt. % of at least one reactive diluent,    about 0.1 wt. % to about 20 wt. % of at least one photoinitiator, wherein said photoinitiator is selected to provide a fast cure speed,    about 0.1 wt. % to about 20 wt. % of at least one UV absorbing compound which does not substantially impair the fast cure speed of the inner or outer primary coating.    
     
     
         14 . A method for reducing the rate of color degradation in an inner primary optical fiber coating comprising the combination of steps of: 
 coating an optical fiber with a radiation-curable inner primary coating,    coating said inner primary coating with a radiation-curable outer primary coating which comprises a UV absorber which does not substantially impair the cure speed of the outer primary coating,    radiation-curing said coatings.    
     
     
         15 . A radiation-curable composition according to    claim 1   , wherein said composition has a cure speed of less than 0.6 J/cm 2  measured wherein cure speed is measured with dose-modulus curves and is the dose at which 95% of maximum modulus is achieved.  
     
     
         16 . A coated optical fiber according to claim  13 , wherein said inner primary coating comprises at least one UV-absorbing compound.  
     
     
         17 . A coated optical fiber according to    claim 16   , wherein said inner primary coating comprises at least one urethane acrylate oligomer, at least two monomer diluents, and at least two photoinitiators, wherein at least one of said photoinititiators is a phosphine oxide compound.  
     
     
         18 . A coated fiber according to    claim 13   , wherein said UV-absorber has ethylenic unsaturation.  
     
     
         19 . A coated fiber according to    claim 17   , wherein said inner primary coating UV absorber and said outer primary UV absorber each have ethylenic unsaturation.  
     
     
         20 . A coated fiber according to    claim 19   , wherein the amounts of said UV absorbers are at least about 5 wt. %.