Co-extruded multilayer structure and method for obtaining thereof

Abstract

The present invention is directed to a novel co-extruded multilayer structure that possess a draw down ratio superior than the critical draw-down ratio of each one of the polymeric layers, extruded individually. The present invention is also directed to a method for obtaining the co-extruded multilayer structure.The co-extruded multilayer structure obtainable by the method described herein allows preparing films, filaments or spun-melt non-wovens of low weight at high speed using conventional extrusion equipments. The co-extruded multilayer structure is especially suitable as diaper back-sheets or flexible packaging coatings.

1 - 15 . (canceled) 
     
     
         16 . A co-extruded multi-layer structure having an improved extrusion critical draw down ratio compared with the critical draw down ratio of each one of the layer's polymers present in the multi-layer structure, the co-extruded multi-layer structure comprising a first composite layer disposed over a second composite layer, and further comprising an inter-layer disposed between the first and the second composite layer,
 wherein
 the first composite layer contains a first polymer, 
 the second composite layer contains a second polymer, and 
 the inter-layer chemically or physically interacts with the first polymer and the second polymer, 
   wherein the first polymer and the second polymer differ from each other in at least its extensional viscosity, one polymer increasing its extensional viscosity at itself critical draw down ratio under tensile stress and the other polymer decreasing its extensional viscosity at itself critical draw down ratio under tensile stress, wherein the extensional viscosity is the ratio between extensional stress and extensional rate in a conventional extrusion technique,   and wherein the inter-layer is obtainable by an extrusion method comprising using a die, wherein the die is one common die, and the method comprising the steps of:
 dispersing an adhesive material in the first polymer and/or in the second polymer of the first composite layer and/or the second composite layer, respectively, 
 feeding the first and the second composite layers to the one common die under temperature in order to co-extrude the molten layers simultaneously, whereby the inter-layer is formed by chemical interaction between the first and the second polymers when they contact in molten state, 
 or alternatively, 
 adding a third adhesive layer between the first and the second composite layers, thereby forming a multi-layer, and 
 feeding the multi-layer to the one common die under temperature in order to co-extrude it, whereby the inter-layer is formed by physical interaction of the molten first and second polymers with the third adhesive layer simultaneously fed between the first and the second composite layers to the one common die, 
   the method further comprising:—
 when the molten co-extruded layers leave the die, stretching the molten co-extruded layers under tensile stress, whereby the resulted co-extruded multi-layer structure has a draw-down ratio which is higher than the critical draw-down ratio of each one of the first and of the second polymers, individually extruded, thereby decreasing the cross-sectional area of the co-extruded multi-layer structure to a lower value, and 
 cooling down the co-extruded multi-layer structure to room temperature. 
   
     
     
         17 . The co-extruded multi-layer structure according to  claim 16 , wherein the adhesive material is present either in a concentration ranging from 0.5-10% by weight when the first and the second polymers have a tendency to homogeneously mix together when contacted in a molten state, or either in a concentration ranging from 10-60% by weight when the first and the second polymers do not homogeneously mix together when contacted in a molten state. 
     
     
         18 . The co-extruded multi-layer structure according to  claim 16 , wherein the adhesive layer is a tie layer which is made of an adhesive material. 
     
     
         19 . The co-extruded multi-layer structure according to  claim 16 , wherein at least one of the first polymer and the second polymer has a water vapor transmission rate equal to or higher than 1 g mm/m 2  day as measured according to ASTM E96B. 
     
     
         20 . The co-extruded multi-layer structure according to  claim 16 , having a water vapor transmission rate ranging from 1,000-20,000 g/m 2  day as measured according to ASTM1249. 
     
     
         21 . The co-extruded multi-layer structure according to  claim 16 , wherein the co-extruded multi-layer structure is a film with a thickness as low as 1 μm. 
     
     
         22 . The co-extruded multi-layer structure according to  claim 16 , wherein the co-extruded multi-layer structure is a filament with a diameter as low as 1 μm. 
     
     
         23 . The co-extruded multi-layer structure according to  claim 16 , wherein the extrusion technique is selected from the group of cast extrusion, blown film extrusion, extrusion-coating, extrusion-lamination, curtain coating extrusion, profile extrusion, filament spinning and spun-melt non-woven extrusion. 
     
     
         24 . The co-extruded multi-layer structure according to  claim 16 , wherein polymers decreasing their extensional viscosity at their own critical draw down ratio under tensile stress are polymers whose structures are substantially linear or contains short branched chains that when they are subjected to tensile stress their molecule chains became more or less oriented in the shear direction, thereafter the molecule chains disentangle to a certain extent, which lowers their flow resistance. 
     
     
         25 . The co-extruded multi-layer structure according to  claim 16 , wherein polymers increasing their extensional viscosity at their own critical draw down ratio under tensile stress are polymers those structure is substantially long branched chain that when they are subjected to tensile stress their molecule chains tangle and prevent relative motion between the molecule chains, which increases their flow resistance. 
     
     
         26 . The co-extruded multi-layer structure of  claim 16 , further comprising isolating the steps of stretching and cooling of the molten co-extruded multiplayer structure from ambient air by using a vacuum box. 
     
     
         27 . A method for obtaining the co-extruded multi-layer structure of  claim 16 , comprising using a die, wherein the die is one common die, and the method comprises the steps of:
 dispersing an adhesive material in the first polymer and/or in the second polymer of the first composite layer and/or the second composite layer, respectively,   feeding the first and the second composite layers to the one common die under temperature in order to co-extrude the molten layers simultaneously, whereby the inter-layer is formed by chemical interaction between the first and the second polymers when they contact in molten state,   or alternatively,   adding a third adhesive layer between the first and the second composite layers, thereby forming a multi-layer, and   feeding the multi-layer to the one common die under temperature in order to co-extrude it, whereby the inter-layer is formed by physical interaction of the molten first and second polymers with the third adhesive layer simultaneously fed between the first and the second composite layers to the one common die,   
       the method further comprising:—
 when the molten co-extruded layers leave the die, stretching the molten co-extruded layers under tensile stress, whereby the resulted co-extruded multi-layer structure has a draw-down ratio which is higher than the critical draw-down ratio of each one of the first and of the second polymers, individually extruded, thereby decreasing the cross-sectional area of the co-extruded multi-layer structure to a lower value, and 
 cooling down the co-extruded multi-layer structure to room temperature. 
 
     
     
         28 . The method according to  claim 27 , wherein the draw-down ratio is 10% superior to the critical draw-down ratio of each one of the first polymers and of the second polymer, extruded individually. 
     
     
         29 . The method according to  claim 27 , further comprising isolating the steps of stretching and cooling of the molten co-extruded multiplayer structure from ambient air by using a vacuum box. 
     
     
         30 . A coated substrate comprising the co-extruded multi-layer structure of  claim 16 . 
     
     
         31 . The coated substrate of  claim 30 , wherein the substrate of the coated substrate is selected from the group consisting of a polymer, paper, textile material, non-woven material or metal film, and wherein the coated substrate is obtained by using a conventional extrusion method selected from the group of extrusion-coating, curtain-coating extrusion, extrusion-lamination, cast extrusion, blown film extrusion, profile extrusion, filament spinning and spun-melt non-woven extrusion. 
     
     
         32 . The coated substrate of  claim 30 , wherein the coated substrate is a diaper back-sheet.