Multilayer stretch film having cling properties, a method of preparation thereof and its use for stretch wrapping operations

Abstract

A multilayer stretch film comprising at least a first layer (i) with cling properties comprising an olefin (co)polymer composition, a second layer (ii) with slip properties comprising another olefin (co)polymer composition and if desired at least one core layer (iii) comprising an olefin (co)polymer composition between the first layer (i) and the second layer (ii). The outer surface of the first layer (i) with cling properties is provided with a non-stretchable thin film of one or more slip agent(s) covering at least 50% up to 100% of the outer surface of the first layer (i), lowering the cling properties of the unstretched composite film. The thin film of slip agent(s) is provided either by direct application of the slip agent(s) onto the outer surface or by use of slip agent(s) having limited compatibility with the (co)polymer composition as additive in the (co)polymer composition of the first layer (i). The limited compatibility of the slip agent(s) with the (co)polymer composition of the first layer (i) results in migration of the slip agent(s) to the outer surface and formation of a non-stretchable thin film at the outer surface of the first layer (i). The multilayer stretch film is preferably composed substantially entirely of ethylene or propylene (co)polymer compositions or mixtures thereof. The invention includes a method of preparing a multilayer stretch film according to the present invention by extrusion and the use of the multilayer stretch film in a method for stretch wrapping operations of articles or groups of articles.

What is claimed is:  
     
         1 . A multilayer stretch film comprising at least a first layer (i) with cling properties comprising an olefin (co)polymer composition, a second layer (ii) with slip properties comprising another olefin (co)polymer composition, wherein the outer surface of the first layer (i) is provided with a non-stretchable thin film (iv) of one or more slip agent(s) covering at least 50% up to 100% of the outer surface of the first layer (i) lowering the cling properties of the unstretched film.  
     
     
         2 . The multilayer stretch film of  claim 1 , farther comprising at least one core layer (iii) comprising an olefin (co)polymer composition is present between the first layer (i) and the second layer (ii).  
     
     
         3 . The multilayer stretch film of  claim 2 , wherein the multilayer film consists essentially of ethylene or propylene (co)polymer compositions or mixtures thereof.  
     
     
         4 . The multilayer stretch film of  claim 3 , wherein the olefin (co)polymer composition of the first layer (i) is selected from low density polyethylene (LDPE), linear low density polyethylene (LLDPE), ultra low density polyethylene (ULDPE), polypropylene or copolymers of these polyolefins with other C 3 -C 12 -α-olefins or mixtures thereof having a density of from 0.84 to 0.91 g/cm 3 .  
     
     
         5 . The multilayer stretch film of  claim 3 , wherein the olefin (co)polymer composition of the second layer (ii) is selected from polyethylene homo and copolymers having a density of from 0.90 g/cm 3  to 0.95 g/cm 3 , polypropylene homo and copolymers with C 3 -C 12 -α-olefins, having a density of from 0.90 g/cm 3  to 0.95 g/cm 3  or mixtures thereof.  
     
     
         6 . The multilayer stretch film of  claim 3 , wherein the olefin (co)polymer composition of the at least one core layer (iii) is selected from low density polyethylene (LDPE), medium density polyethylene (MDPE), high density polyethylene (HDPE), linear low density polyethylene (LLDPE), ultra low density polyethylene (ULDPE), polypropylene homo- and copolymers with C 3 -C 12 -α-olefins or mixtures thereof having a density which is higher than the density of the olefin (co)polymer composition used for the first layer (i) having a density of from 0.895 to 0.925 g/cm 3 .  
     
     
         7 . The multilayer stretch film of  claim 1 , wherein the thin non-stretchable film (iv) on the surface of the first layer (i) is provided by migration of the one or more slip agent(s) of limited compatibility with the (co)polymer composition from the (co)polymer composition of the first layer to the outer surface of the first layer (i).  
     
     
         8 . The multilayer stretch film of  claim 1 , wherein the thin non-stretchable film (iv) on the surface of the first layer (i) is provided by coating the outer surface of the first layer with one or more slip agent(s).  
     
     
         9 . The multilayer stretch film of  claim 7 , wherein the slip agent(s) present in the polymer composition of the first layer (i) is (are) selected from stearic acid, 12-hydroxystearic acid, icosanoic acid, docosanoic acid, fatty acid amides such as oleic amide, stearic amide, eruca amide, ethylene disteaoryldiamide, polar ethylene wax, montanic acid, montanic acid ester wax, N,N′-bis-stearoyl ethylene diamine, ester of polycarboxylic acids selected from glycerol distearate, glycerol mono-12-hydroxystearate, glycerol tri-12-hydroxystearate, glycerol tribehenate, glycerol trimontanate, ethoxylated fatty acid amines, N,N-bis-(2-hydroxyethylene)amide of long chain fatty acids or mixtures thereof.  
     
     
         10 . The multilayer stretch film of  claim 8 , wherein the slip agent(s) applied onto the surface of the first layer (i) by coating is (are) selected from stearic acid, 12-hydroxystearic acid, icosanoic acid, docosanoic acid, fatty acid amides such as oleic amide, stearic amide, eruca amide, ethylene disteaoryldiamide, polar ethylene wax, montanic acid, montanic acid ester wax, N,N′-bis-stearoyl ethylene diamine, ester of polycarboxylic acids selected from glycerol distearate, glycerol mono-12-hydroxystearate, glycerol tri-12-hydroxystearate, glycerol tribehenate, glycerol trimontanate, ethoxylated fatty acid amines, N,N-bis-(2-hydroxyethylene)amide of long chain fatty acids or mixtures thereof.  
     
     
         11 . The multilayer stretch film of  claim 9 , wherein the slip agent(s) is (are) present in the (co)polymer composition of the first layer (i) in an amount of from 10 to 100.000 ppm based on the weight of the (co)polymer composition.  
     
     
         12 . The multilayer stretch film of  claim 1 , wherein the outer surface of the second layer (ii) is also provided with a thin film of one or more slip agent(s) by migration of the slip agent(s) contained within the polymer composition of the second layer (ii) to the outer surface of the second layer or by coating of the surface with one or more slip agent(s).  
     
     
         13 . A method of preparing a multilayer stretch film comprising at least a first layer (i) with cling properties comprising an olefin (co)polymer composition, a second layer (ii) with slip properties comprising another olefin (co)polymer composition and at the outer surface of the first layer (i) a non-stretchable thin film (iv) of one or more slip agent(s) covering at least 50% up to 100% of the outer surface of the first layer (i) lowering the cling properties of the unstretched film by feeding the (co)polymer compositions for the first layer (i) which comprising one or more slip agent(s) and the second layer (ii), into a coextrusion extruder, melting and mixing each of the (co)polymer compositions itself at melt temperatures above 175° C. and forming at least two molten (co)polymer composition streams, extruding the molten (co)polymer composition streams through a coextrusion feed block to form a multilayer structure of the film tube or a film web, blowing up and cooling said film tube or drawing down and cooling that film web and collecting the unstretched web of the multilayer film.  
     
     
         14 . A method of preparing a multilayer stretch film comprising at least a first layer (i) with cling properties comprising an olefin (co)polymer composition, a second layer (ii) with slip properties comprising another olefin (co)polymer composition and at the outer surface of the first layer (i) a non-stretchable thin film (iv) of one or more slip agent(s) covering at least 50% up to 100% of the outer surface of the first layer (i) lowering the cling properties of the unstretched film by feeding the (co)polymer compositions for the first layer (i) and the second layer (ii), into a coextrusion extruder, melting and mixing each of the (co)polymer compositions itself at melt temperatures above 175° C. and forming at least two molten (co)polymer composition streams, extruding the molten (co)polymer composition streams through a coextrusion feed block to form a multilayer structure of the film tube or a film web, blowing up and cooling said film tube or drawing down and cooling that film web and applying the thin film (iv) of the one or more slip agent(s) onto the outer surface of the first layer (i) and collecting the unstretched web of the multilayer film.  
     
     
         15 . The method of  claim 13 , wherein the molten (co)polymer composition streams are extruded through the coextrusion feed block at temperatures between 160° C. and 300° C.  
     
     
         16 . The method of  claim 14 , wherein the molten (co)polymer composition streams are extruded through the coextrusion feed block at temperatures between 160° C. and 300° C.  
     
     
         17 . The method of  claim 15 , wherein unstretched web of the multilayer film is collected in form of reels having the cling layer either at the inner side or at the outer side of the wound-up web.  
     
     
         18 . The method of  claim 16 , wherein the unstretched web of the multilayer film is collected in form of reels having the cling layer either at the inner side or at the outer side of the wound-up web.  
     
     
         19 . A method of stretch wrapping articles or groups of articles using a multilayer stretch film comprising at least a first layer (i) with cling properties comprising an olefin (co)polymer composition, a second layer (ii) with slip properties comprising another olefin (co)polymer composition, wherein the outer surface of the first layer (i) is provided with a non-stretchable thin film (iv) of one or more slip agent(s) covering at least 50% up to 100% of the outer surface of the first layer (i) lowering the cling properties of the unstretched film.