Polycarbonate films of low flammability and improved stress crack resistance

Abstract

The present invention relates to polycarbonate films, and in particular extruded films and cast films, but preferably extruded films, which are characterized in that they contain about 0.01% to 2% by weight of a NH 4 salt, alkali metal salt or alkaline earth metal salt of a perhalogenoalkanesulphonic acid, preferably a perfluoroalkanesulphonic acid.

What is claimed is: 
     
       1. .[.Polycarbonate films,.]. .Iadd.A glass fiber-free polycarbonate film having a thickness of about 0.01 mm to 1 mm comprising an aromatic linear.Iaddend.about 0.01% by weight to 2% by weight of a NH 4  salt, alkali metal salt or alkaline earth metal salt of a perhalogenoalkanesulphonic acid. 
     
     
       2. Polycarbonate films according to claim 1, characterized in that they contain between about 0.01% by weight and 2% by weight of a NH 4  salt, alkali metal salt or alkaline earth metal salt of a perfluoroalkanesulphonic acid. 
     
     
       3. Polycarbonate extruded films according to claim 1. 
     
     
       4. Polycarbonate films according to claim 1, characterized in that they contain NH 4  salts, alkali metal salts or alkaline earth metal salts of perhalogenosulphonic acids of the formula I   R--SO.sub.3 --Me                                           (I)     wherein R represents C n  Hal 2n+1  in which   Hal is F or Cl and   n is 1 to 8, and wherein Me is NH 4 , an alkali metal or an alkaline earth metal.     
     
     
       5. Polycarbonate films according to claim 4, characterized in that Me is potassium. 
     
     
       6. Polycarbonate films according to claim 1, characterized in that the films additionally contain up to about 10% by weight of low-molecular weight, halogen-containing aromatic polycarbonates having average molecular weights Mn of about 4,000 to 20,000. 
     
     
       7. Polycarbonate films according to claim 6, characterized in that the low-molecular weight, halogen-containing polycarbonate used is one based on tetrabromobisphenol A. 
     
     
       8. Polycarbonate films according to claim 1, characterized in that the polycarbonates used are high molecular weight, aromatic copolycarbonates of about 99-90 mol % of bisphenol A and about 1-10 mol % of 1,1-bis-(4-hydroxyphenyl)-cyclohexane having average molecular weight M w , of about 30,000 to 120,000. .[.9. Polycarbonate films according to claim 8, characterized in that the high molecular weight polycarbonates are branched with up to about 0.5 mol %, relative to bisphenol A, of 
     
     
        10. Polycarbonate films according to claim 1 characterized in that mixtures of high-molecular weight polycarbonates having weight average 
     
     
        molecular weights, M w , of from about 25,000 to 80,000 are used. 11. A.Iaddend.aromatic polycarbonate having a weight-average molecular weight, M w , of between about 25,000 and 200,000 and about 0.1 to 2% by weight of a perhalogenoalkanesulphonic acid salt selected from the group consisting of a NH 4  salt, an alkali metal salt and an alkaline earth 
     
     
        metal salt. 12. The polycarbonate film of claim 11 wherein the perhalogenoalkanesulphonic acid salt is of the formula   R--SO.sub.2 --Me     wherein R represents C n  Hal 2n+1     wherein   Hal is F or Cl and   n is 1 to 8, and   
     
     
       Me is NH 4 , an alkali metal or an alkaline earth metal. 13. The polycarbonate film of claim 12 wherein the perhalogenoalkanesulphonic acid 
     
     
       .Iaddend.aromatic polycarbonate having a weight-average molecular weight, M w , of between about 25,000 and 200,000 up to about 10% by weight of a low-molecular weight, halogen-containing aromatic polycarbonate having a number-average molecular weight, Mn, of about 4,000 to 20,000 and about 0.1 to 2% by weight of perhalogenoalkanesulphonic acid salt selected from the group consisting of a NH 4  salt, an alkali metal salt and an 
     
     
        alkaline earth metal salt. 15. A glass fiber-free polycarbonate film.Iaddend.aromatic polycarbonate having a weight-average molecular weight, M w , of between about 25,000 and 200,000 and about 0.1 to 2% by weight.Iaddend.perhalogenoalkanesulphonic acid salt selected from the group consisting of a NH 4  salt, an alkali metal salt and an alkaline earth 
     
     
        metal salt. 16. A process for improving the stress crack resistance of a.Iaddend.comprising incorporating from about 0.01 to 2% by weight of.Iaddend.perhalogenoalkanesulphonic acid salt selected from the group.Iaddend.NH 4  salt, an alkali metal salt and an alkaline earth metal 
     
     
        salt into said polycarbonate film. 17. The process of claim 16 wherein the perhalogenoalkanesulphonic acid salt is of the formula   R--SO.sub.3 --Me     wherein R represents C n  Hal 2n+1     wherein   Hal is F or Cl, and,   n is 1 to 8 and,   
     
     
       wherein Me is NH 4 , an alkali metal or an alkaline earth metal. 18. A.Iaddend.aromatic polycarbonate having a weight average molecular weight, M w , of between about 25,000 and 200,000 and about 0.1 to 2% by weight of a perhalogenoalkanesulphonic acid salt selected from the group.Iaddend.NH 4  salt, an alkali metal salt and an alkaline earth metal salt. .Iadd.19. A glass fiber-free polycarbonate film having a thickness of about 0.05 mm to 0.8 mm comprising an aromatic linear polycarbonate resin characterized in that it contains about 0.01 to 2 percent by weight of a NH 4  salt, alkali metal salt or alkaline earth metal salt of a.Iaddend. noalkylsulphonic acid.