Coated optical fibre unit and methods of manufacturing coated optical fibre units

Abstract

An optical fibre unit having a sheath and a plurality of optical fibre elements loosely housed in the sheath. The sheath is coated with particles of an adherence reducing substance and has a radial thickness that is not substantially greater than 0.3 mm. The coating of adherence reducing particles is applied as a liquid coating. The liquid coating is a dispersion of the particles and heat is applied to evaporate the liquid content of the liquid coating to produce a dry coating of particles on the sheath.

1 . An optical fibre unit comprising a sheath and a plurality of optical fibre elements loosely housed in said sheath, said sheath having a coating of adherence reducing material particles and a radial thickness not substantially greater than  0 . 3  mm.  
     
     
         2 . The optical fibre unit as claimed in  claim 1 , wherein said sheath has a radial thickness substantially not greater than 0.2 mm.  
     
     
         3 . The optical fibre unit as claimed in  claim 2 , wherein said sheath has a radial thickness substantially in the range of 0.05 to 1.5 mm.  
     
     
         4 . The optical fibre unit as claimed in  claim 1 , wherein said adherence reducing material is graphite.  
     
     
         5 . The optical fibre unit as claimed in  claim 1 , wherein said sheath is made of a low smoke zero halogen material.  
     
     
         6 . The optical fibre unit as claimed in  claim 1 , wherein said particles have a nominal diameter not substantially greater than 8 microns.  
     
     
         7 . The optical fibre unit as claimed in  claim 6 , wherein said particles have a mean nominal diameter not substantially greater than 2 microns.  
     
     
         8 . The optical fibre unit as claimed in  claim 1 , wherein said sheath has twelve optical fibre elements loosely housed therein.  
     
     
         9 . The optical fibre unit as claimed in  claim 1 , wherein said sheath has a nominal outside diameter of 1.3 mm.  
     
     
         10 . The optical fibre element as claimed in  claim 1 , wherein said sheath has a nominal inside diameter of 1.1 mm.  
     
     
         11 . A method of coating an optical fibre unit that comprises a polymeric sheath and a plurality of optical fibre elements loosely housed in said sheath, said method comprising applying a liquid coating comprising a dispersion of adherence reducing material particles to said sheath and applying heat to the optical fibre unit to produce a dry coating of said particles on said sheath.  
     
     
         12 . The method as claimed in  claim 11 , wherein said liquid coating is applied to the polymeric sheath at room temperature.  
     
     
         13 . The method as claimed in  claim 11 , wherein said liquid coating comprises graphite particles and water.  
     
     
         14 . The method as claimed in  claim 13 , wherein said heat applied to said optical fibre unit evaporates the water content of said liquid coating.  
     
     
         15 . The method as claimed in any one of claims  claim 11 , wherein said particles have a nominal diameter not substantially greater than 8 microns.  
     
     
         16 . The method as claimed in  claim 15 , wherein said particles have a mean nominal diameter not substantially greater than 2 microns.  
     
     
         17 . The method as claimed in  claim 11 , wherein said heat is applied such that the temperature of said sheath does not exceed the softening temperature of polymeric material forming the polymeric sheath.  
     
     
         18 . The method as in claimed in  claim 17 , wherein the temperature of said sheath is at least 10° C. lower than the softening temperature of the polymeric material.  
     
     
         19 . The method as claimed in  claim 11 , wherein said heat applying step comprises passing the optical fibre unit through a plurality of drying chambers.  
     
     
         20 . The method as claimed in  claim 19 , wherein as the optical fibre unit passes through each said drying chamber, substantially the same amount of heat is applied to the optical fibre unit.  
     
     
         21 . The method as claimed in  claim 19 , wherein said optical fibre unit passes more than once through at least one of said drying chambers.  
     
     
         22 . The method as claimed in  claim 19 , wherein the direction of movement of the optical fibre unit is different when passing through one of said drying chambers to the direction of movement when passing through one or more of the other drying chambers.  
     
     
         23 . The method as claimed in  claim 19 , wherein said drying chambers each have a length, said length being not substantially greater than 0.35 mm.  
     
     
         24 . The method as claimed in  claim 11 , further comprising applying a surfactant to assist in the application of said liquid coating to said sheath.  
     
     
         25 . The method as claimed in  claim 11 , wherein said liquid coating is applied to said sheath by passing said optical fibre unit through a vessel containing said liquid coating.  
     
     
         26 . The method as claimed in  claim 25 , further comprising applying a surfactant to assist in the application of said liquid coating to said sheath wherein said surfactant is contained in said vessel.  
     
     
         27 . The method as claimed in  claim 11 , wherein said optical fibre unit moves substantially continuously at a speed of approximately 40 m/min during said liquid coating and heat applying steps.  
     
     
         28 . An installation comprising a conduit and at least one optical fibre unit as claimed in  claim 1 , said at least one optical fibre unit being installed in said conduit by blowing the optical fibre unit along said conduit.  
     
     
         29 . An optical fibre unit for blown fibre installation, said optical fibre unit comprising a sheath and a plurality of optical fibre elements loosely housed in said sheath, said sheath having an outer surface coated with adherence reducing material particles and a radial thickness not substantially greater than 0.3 mm.  
     
     
         30 . A method of coating an optical fibre unit for blown fibre installation that comprises a polymeric sheath and a plurality of optical fibre elements loosely housed in said sheath, which sheath has a radial thickness not substantially greater than 0.3 mm, said method comprising applying a liquid coating comprising a dispersion of adherence reducing material particles to an outer surface of said sheath and applying heat to the optical fibre unit to produce a dry coating of said particles on said sheath.  
     
     
         31 . An optical fibre unit for blown fibre installation, said optical fibre unit comprising: 
 a sheath defined by a generally tubular wall, said wall having a radially outermost surface and a radially innermost surface and a radial thickness not substantially greater than 0.3 mm;    a plurality of optical fibres loosely housed in said sheath; and    a coating adhered to said radially outermost surface of said wall, said coating comprising adherence reducing particles.    
     
     
         32 . A method of coating an optical fibre unit for blown fibre installation, said method comprising the steps of: 
 forming a sheath around a plurality of optical fibre elements such that said optical fibre elements are loosely housed by the sheath, said sheath comprising a generally tubular wall having a radially outer surface and a radially inner surface and a radial thickness not substantially greater than 0.3 mm;    applying a liquid coating comprising a dispersion of adherence reducing particles to said radially outer surface; and    passing the optical fibre unit through a heated environment to dry said liquid coating to provide a dry coating of said adherence reducing particles adhering to said radially outer surface.    
     
     
         33 . An installation comprising a conduit and at least one optical fibre unit coated by the method of  claim 11 , said at least one optical fibre being installed in said conduit by blowing the optical fibre unit along said conduit.  
     
     
         34 . The method as claimed in  claim 19 , wherein said drying chambers each have a length, said length being not greater than approximately 0.31 mm.