Composite materials

Abstract

A strip of curable prepreg comprising unidirectional fibres aligned with the length of the strip, the fibres being at least partially impregnated with curable thermosetting resin and comprising a flexible polymeric sheet on an outer face of the strip, wherein the strip has a substantially rectangular cross-section defining a width and a thickness of the strip.

1 . A strip of curable prepreg comprising unidirectional fibres aligned along the length of the strip, the fibres being at least partially impregnated with curable thermosetting resin and comprising a flexible polymeric sheet on an outer face of the strip, Wherein the strip has a substantially rectangular cross-section defining a width and a thickness of the strip, the difference between the maximum width and the minimum width along the length of the strip being less than 0.25 mm. 
     
     
         2 . The strip of  claim 1 , wherein the strip following winding and/or unwinding from a spool or bobbin has a difference between the maximum width and the minimum width along the length of the strip of less than 0.25 mm. 
     
     
         3 . The strip of  claim 1 , wherein the strip has a length of at least 100 m. 
     
     
         4 . The strip of  claim 1 , wherein the strip has a width of from 2.0 to 3000 mm. 
     
     
         5 . The strip of  claim 1 , wherein the flexible polymeric sheet is a polyalphaolefin film or a polyalphaolefin copolymer film. 
     
     
         6 . The strip of  claim 1 , wherein the flexible polymeric sheet is porous. 
     
     
         7 . A process for forming a plurality of strips of prepreg from a sheet of prepreg, wherein the sheet of prepreg comprises unidirectional fibres at least partially impregnated with curable thermosetting resin and comprising a flexible polymeric sheet on an outer face of the sheet of prepreg, the process comprising the step of slitting the prepreg into a plurality of strips, the slits being substantially parallel to the direction of alignment of the fibres. 
     
     
         8 . The process according to  claim 7 , wherein the polymeric sheet is applied under a compressive force before reaching the slitting stage, of at least 0.1 MPa. 
     
     
         9 . The process of  claim 7 , wherein the difference between the maximum width and the minimum width along the length of the strip is less than 0.25 mm. 
     
     
         10 . The process of  claim 7 , wherein the strip following slitting and winding and/or unwinding from a spool or bobbin has a difference between the maximum width and the minimum width along the length of the strip of less than 0.25 mm. 
     
     
         11 . Use of a flexible polymeric sheet on an outer face of a prepreg during slitting of the prepreg into a plurality of strips, said prepreg comprising unidirectional fibres at least partially impregnated with curable thermosetting resin, slitting taking place in a longitudinal direction relative to the unidirectional fibers, the difference between the maximum width and the minimum width along the length of the strip being less than 0.25 mm. 
     
     
         12 . Use of  claim 11 , wherein the strip following slitting and winding and/or unwinding from a spool or bobbin has a difference between the maximum width and the minimum width along the length of the strip of less than 0.25 mm. 
     
     
         13 . Use of  claim 11 , wherein the strip has a length from 10 to 5000 m. 
     
     
         14 . A process of laying down a plurality of strips according to  claim 1 , by means of an automated strip laying apparatus, the apparatus being arranged to lay the strips down parallel to each other and with a gap between the strips of less than 1.00 mm. 
     
     
         15 . A process according to  claim 14 , wherein the strips are laid in contact with one another.