Method of producing heat-sealable composite films

Abstract

A composite film is provided by providing a polypropylene or other base resin layer, laminating a first covering layer of a resin composition (1) comprising the following components (A), (B), (C) and (D) to one side of the base resin layer and a second covering layer of a resin composition (2) comprising the components (A) and (D) to the other side of the base resin layer, which composite film is optionally stretched. The resin composition (2) may contain component (C). (A) a heat-sealable olefinic polymer (e.g. a propylene series copolymer such as propylene-ethylene copolymer, propylene-butene-1 copolymer or propylene-ethylene-butene-1 copolymer) (B) a diorganopolysiloxane (e.g. dimetylpolysiloxane) (C) a fine-powdered heat-resistant resin (e.g. microspheres of a thermosetting resin) (D) a higher fatty acid amide This composite film is excellent in slidability, antistaticity, releasability and clarity and compatible with a high-speed automatic overwrap packaging machine.

What is claimed is:  
     
         1 . A composite film comprising a base resin layer, a first covering layer of a resin composition (1) comprising the following components (A), (B), (C) and (D) as laminated to one side of said base resin layer and a second covering layer of a resin composition (2) comprising the following components (A) and (D) as laminated to the other side of said base resin layer: 
 (A) a heat-sealable olefinic polymer    (B) a diorganopolysiloxane    (C) a fine-powdered heat-resistant resin    (D) a higher fatty acid amide    
     
     
         2 . A composite film as claimed in  claim 1 , wherein said resin composition (2) further contains said fine-powdered heat-resistant resin (C).  
     
     
         3 . A composite film as claimed in  claim 1 , wherein said base resin layer is formed with a resin composition containing 0.01 to 5 parts by weight of an antistatic agent per 100 parts by weight of a polypropylene with an isotactic index of not less than 92%.  
     
     
         4 . A composite film as claimed in  claim 1 , wherein said heat-sealable olefinic polymer (A) is at least one propylene series copolymer selected from the group consisting of propylene-ethylene copolymer, propylene-butene-1 copolymer, propylene-ethylene-butene-1 copolymer, ethylene-butene-1 copolymer, ethylene-3-methylpentene-1 copolymer, ethylene-propylene-3-methylpentene-1 copolymer, ethylene-4-methylpentene-1 copolymer, ethylene-propylene-4-methylpentene-1 copolymer and ethylene-butene-1-3-methylpentene-1 copolymer.  
     
     
         5 . A composite film as claimed in  claim 1 , wherein said heat-sealable olefinic polymer is at least one propylene series copolymer selected from the group consisting of propylene-ethylene copolymer, propylene-butene-1 copolymer and propylene-ethylene-butene-1 copolymer.  
     
     
         6 . A composite film as claimed in  claim 1 , wherein said diorganopolysiloxane (B) is dimethylpolysiloxane having an average molecular weight of 1×10 4  to 18×10 4  and is contained in said resin composition (1) in a proportion of 0.5 to 3 parts by weight relative to 100 parts by weight of said heat-sealable olefinic polymer (A).  
     
     
         7 . A composite film as claimed in  claim 1 , wherein said fine-powdered heat-resistant resin (C) is microspheres having a mean particle diameter of 1 to 6 μm and is contained in said resin composition (1) in a proportion of 0.1 to 1 part by weight relative to 100 parts by weight of said heat-sealable olefinic polymer (A).  
     
     
         8 . A composite film as claimed in  claim 2 , wherein said fine-powdered heat-resistant resin (C) is microspheres having a mean particle diameter of 1 to 6 μm and is contained in said resin composition (2) in a proportion of 0.1 to 1 part by weight relative to 100 parts by weight of said heat-sealable olefinic polymer (A).  
     
     
         9 . A composite film as claimed in  claim 1 , wherein said fine-powdered heat-resistant resin (C) is microspheres of a thermosetting resin or thermoplastic resin having a thermal deformation temperature higher than the film forming temperature.  
     
     
         10 . A composite film as claimed in  claim 1 , wherein said higher fatty acid amide (D) is a C 16-24  monocarboxylic acid amide and is contained in said resin composition (1) and resin composition (2) in a proportion of 0.01 to 1.0 part by weight relative to 100 parts by weight of said heat-sealable olefinic polymer (A).  
     
     
         11 . A composite film as claimed in  claim 1 , wherein the thickness of said first covering layer is not greater than 1 μm.  
     
     
         12 . A composite film as claimed in  claim 1 , wherein said second covering layer has a surface tension of not less than 38 dyne/cm.  
     
     
         13 . A composite film as claimed in  claim 1 , which is a oriented film stretched in at least one direction at a stretching ratio of not less than 2.  
     
     
         14 . A composite film comprising a base resin layer of a polypropylene having an isotactic index of not less than 94%, a first covering layer of a resin composition (1) comprising the following components (A), (B), (C) and (D) as laminated to one surface of said base resin layer and a second covering layer formed from a resin composition (2) comprising the following components (A), (C) and (D) as laminated to the other surface of said base resin layer, wherein said composite film is a biaxially oriented film: 
 (A) a heat-sealable polymer having a propylene content of 68 to 99% by weight    (B) dimethylpolysiloxane    (C) microspheres of a heat-resistant resin having a mean diameter of 1.5 to 5 μm    (D) a C 16-24  monocarboxamide    
     
     
         15 . A composite film as claimed in  claim 12 , which comprises a base resin layer, a first covering layer formed of a resin composition comprising the following components (A), (B), (C) and (D) as laminated to one side of said base resin layer and a second covering layer of a resin composition (2) comprising the following components (A), (C) and (D) as laminated to the other side of said base resin layer: 
 (A) a propylene series copolymer having a propylene content of 70 to 96.5% by weight as selected from the group consisting of propylene-ethylene copolymer, propylene-butene-1 copolymer and propylene-ethylene-butene-1 copolymer    (B) dimethylpolysiloxane in a proportion of 0.7 to 1.2 parts by weight based on 100 parts by weight of the propylene series copolymer (A)    (C) microspheres of a thermosetting resin in a proportion of 0.2 to 0.7 part by weight based on 100 parts by weight of propylene series copolymer (A)    (D) a monocarboxamide in a proportion of 0.1 to 0.8 part by weight based on 100 parts by weight of propylene series copolymer (A)    
     
     
         16 . A composite film as claimed in  claim 14 , wherein said base resin layer is formed with a resin composition containing 1 to 30 parts by weight of a hydrocarbon series polymer relative to 100 parts by weight of a polypropylene having an isotactic index of not less than 94%.  
     
     
         17 . A composite film as claimed in  claim 14 , wherein said base resin layer is formed with a resin composition containing 0.1 to 2.5 parts by weight of an antistatic agent and 5 to 15 parts by weight of a hydrocarbon series polymer relative to 100 parts by weight of a polypropylene having an isotactic index of not less than 94%.  
     
     
         18 . A composite film as claimed in  claim 14 , wherein said first covering layer has a thickness of 0.1 to 0.7 μm and said second covering layer has a surface tension of not less than 38 dyne/cm and a thickness of 0.1 to 5 μm.  
     
     
         19 . A method of producing a composite film which comprises laminating a first covering layer of a resin composition (1) comprising the following components (A), (B), (C) and (D) to one side of a base resin layer and a second covering layer of a resin composition (2) comprising the following components (A) and (D) to the other side of said base resin layer; 
 (A) a heat-sealable olefinic polymer    (B) a diorganopolysiloxane    (C) a fine-powdered heat-resistant resin    (D) a higher fatty acid amide    
     
     
         20 . A method of producing a composite film as claimed in  claim 19 , wherein said second covering layer is formed from said resin composition (2) which further contains said fine-powdered heat-resistant resin (C).  
     
     
         21 . A method of producing a composite film as claimed in  claim 19 , which comprises co-extruding a resin composition for the base resin layer, the first resin composition (1) and the second resin composition (2), stretching the extrusion-molded composite film with a stretching ratio of 5 to 10 in the machine direction and the transverse direction and surface-treating the second covering layer of the oriented film.