Heat-sealable antistatic polypropylene films

Abstract

An oriented heat-sealable antistatic polypropylene film is manufactured by applying to one or both surfaces of a base polypropylene film, preferably by co-extrusion, a layer of a heat-sealable olefinic polymer (for example, a predominantly linear random copolymer of ethylene with butene-1) containing between 0.2 and 10% by weight of an anionic hydrocarbyl (preferably long chain alkyl) sulphonate. A slip agent, for example oleamide, may also be incorporated in the base polypropylene film. The antistatic film has improved heat-sealing properties which permits it to be run successfully on packaging machinery at high speeds.

We claim: 
     
       1. A method for the manufacture of an oriented heat-sealable antistatic polypropylene film comprising applying to one or both sides of a base polypropylene film .Iadd.which contains from 0.05 to 5.0% weight of a slip agent .Iaddend.a layer of a heat-sealable olefinic polymer capable of forming a heat-seal below 140° C., the olefinic polymer layer containing between 0.2 and 10% by weight of an .[.antistatic agent comprising an.].anionic hydrocarbyl sulphonate, and stretching the combination in one or more directions under stretch orientatable conditions. 
     
     
       2. A method as claimed in claim 1 in which the anionic hydrocarbyl sulphonate is present in the olefinic polymer in an amount in the range between 0.3 and 2.0% by weight.  .[.3. A method as claimed in claim 1 in which the slip agent is incorporated in the base polypropylene film in an 
     
     
        amount in the range between 0.05 and 5.0% by weight..]. 4. A method as claimed in claim 1 in which the base polypropylene film is co-extruded with one or between two layers of the heat-sealable olefinic polymer 
     
     
        through a slot or annular die orifice followed by quenching. 5. A method as claimed in claim 1 in which the hydrocarbyl group in the anionic 
     
     
        hydrocarbyl sulphonate is a long chain alkyl group. 6. A method as claimed in claim 5 wherein the long chain alkyl group contains at least 10 carbon 
     
     
        atoms. 7. A method as claimed in claim 6 wherein the long chain alkyl 
     
     
        group contains from 12 to 18 carbon atoms. 8. A method as claimed in claim 
     
     
        1 in which the olefinic polymer is polyethylene. 9. A method as claimed in claim 1 in which the olefinic polymer is a random copolymer of propylene 
     
     
        with ethylene and/or butene-1 having a major content of propylene. 10. A method as claimed in claim 1 in which the olefinic polymer is a predominantly linear random copolymer of ethylene with propylene and/or butene-1 having a major content of ethylene.  .[.11. A method as claimed in claim 1 in which said antistatic agent consists of said anionic 
     
     
        hydrocarbyl sulphonate..]. 12. An oriented heat-sealable antistatic polypropylene film comprising a base polypropylene film .[.having.]. .Iadd.which contains from 0.05 to 5.0% by weight of a slip agent and which has .Iaddend.on one or both surfaces a layer of an olefinic polymer capable of forming a heat-seal below 140° C., the olefinic polymer layer containing between 0.2 and 10% by weight of an .[.antistatic agent 
     
     
        comprising an.]. anionic hydrocarbyl sulphonate. 13. A polypropylene film as claimed in claim 12 in which the olefinic polymer layer contains 
     
     
        between 0.3 and 2.0% by weight of the anionic hydrocarbyl sulphonate. 14. A polypropylene film as claimed in claim 12 wherein the hydrocarbyl group in the anionic hydrocarbyl sulphonate is a long chain alkyl group. 
     
     
          . A polypropylene film as claimed in claim 14 wherein the long chain alkyl group contains from 12 to 18 carbon atoms.  .[.16. A polypropylene film as claimed in claim 12 in which on manufacture the base polypropylene film contains between 0.05 and 5.0% by weight of a slip agent..]. .[.17. A polypropylene film as claimed in claim 12 in which said antistatic agent consists of said anionic hydrocarbyl sulphonate..].