Patent Publication Number: US-2011076506-A1

Title: Laminate structures

Description:
This invention relates to laminate structures and methods of making the same. 
     United States of America Patent Application Publication U.S. 2003/0180489 discloses a non-foil barrier laminate structure. Containers constructed from the barrier laminates disclosed therein can be hot filled or cold filled and can be stored at either ambient conditions or refrigerated conditions. The laminate structures progressing inwardly have a polyamide layer for mechanical strength and thermal resistance; a first EVOH layer as a barrier to oxygen ingress applied in direct contact with the polyamide layer and a second barrier layer of EVOH, nylon or the like positioned closer to the contact surface of the product that may act as a barrier to oxygen, water vapour, flavour/aroma, or a combination, which is not in contact with the first oxygen barrier layer of EVOH, and layers of polyolefin on both the matte side (interior) and the gloss side (exterior) of the laminate for heat sealing. The laminate structures of that Publication are all provided with the polyamide layer applied directly on the paperboard substrate in a coating process. This results in a production line that is relatively inefficient, when changes need to be made to the materials that are being laminated onto the substrate. 
     It is therefore an object of the invention to improve upon the known art. 
     According to a first aspect of the present invention, there is provided a method of producing a laminate structure comprising
         producing a multi-layer barrier film by producing a blown film of n layers, by a blown extrusion process, and collapsing the n-layer blown film to form the multi-layer barrier film, which consists of 2n layers, and which comprises a first polymer layer, a gas barrier layer and a second polymer layer, wherein at least one of the first and second polymer layers comprises a polyamide layer,   providing a substrate, and   laminating the multi-layer barrier film to the substrate.       

     According to a second aspect of the present invention, there is provided a laminate structure comprising, from the outside to the inside,
         a substrate, and   a multi-layer barrier film comprising a 2n-layers film consisting of an n-layer blown film collapsed, the film including a first polymer layer, a gas barrier layer and a second polymer layer, wherein at least one of the first and second polymer layers comprises a polyamide layer.       

     According to a third aspect of the present invention, there is provided a laminate structure comprising, from the outside to the inside,
         a substrate, and   a multi-layer barrier film comprising a first polymer layer, a gas barrier layer and a second polymer layer, wherein at least one of the first and second polymer layers comprises a polypropylene layer.       

     According to a fourth aspect of the present invention, there is provided a method comprising, at a laminating station on a production line for a laminate structure, laminating together (i) a multi-layer barrier film comprising a first polymer layer, a gas barrier layer and a second polymer layer, wherein at least one of the layers comprises a polyamide, and (ii) a substrate, and, subsequently, laminating together at said station a substrate and another multi-layer barrier film differing from the first-mentioned film. 
     Owing to these aspects of the invention, it is possible to provide a low flavour-scalping laminate structure for use in creating a container for liquid food products. The method of producing the structure using a multi-layer barrier film allows shorter runs on a production line without greatly affecting the overall efficiency of the production line, as different barrier films can be used at different times. There is no need to purge extruders, which is a lengthy process, which is required when changing the layers used to produce a laminate in a coating production line. A more flexible production solution is provided as a result. 
     The lamination may take the form of thermal lamination, by heating that surface layer of the multi-layer barrier film which is to contact the substrate, thereby to render that surface layer tacky prior to application thereof to the substrate. Preferably, however the multi-layer barrier film is extrusion laminated to the substrate by way of an adhesive layer. 
     In the event that the substrate is paperboard or another moisture-absorbent material, it preferably has on the outside thereof an outer layer of a substance which is a barrier to moisture. This outer layer may be extrusion-coated onto the substrate or be the innermost layer of a multi-layer barrier film laminated to the substrate either by thermal lamination, or preferably, by extrusion lamination. 
     Preferably, the first polymer layer, the gas barrier layer and the second polymer layer form a first barrier block, and the multi-layer barrier film further comprises a second barrier block, substantially identical to the first barrier block, whereby there can be two barrier blocks in the multi-layer film, one of which will be relatively closer to the liquid food contents in the ultimate container to provide optimal scalping properties, and the other of which will be relatively closer to the substrate (such as paperboard) to provide oxygen barrier properties. The layer distribution of the components of the barrier blocks provides a better barrier structure with greater consistency. 
     Advantageously, the gas barrier layer comprises an EVOH layer, and each of the first and second polymer layers comprises a polyamide layer. The layer which comprises EVOH (ethylene vinyl alcohol), which has excellent gas and odour barrier properties, is provided with improved flex-crack resistance, by the provision of the polyamide (nylon) layer on one or both sides of the EVOH. In the preferred embodiment, the first polymer layer (polyamide) contacts the gas barrier layer (EVOH) and the gas barrier layer (EVOH) contacts the second polymer layer (polyamide). Alternatively, one of the first and second polymer layers can comprise a polypropylene layer. As an alternative to the polyamide on both sides of the gas barrier EVOH, one side of the EVOH can be a layer of polypropylene. 
     The film of n-layers is blow extruded as a single co-extrusion, and then bubble collapsed in on itself while the internal polymer layer is still hot, in order to form the barrier film that is twice the thickness of the original blown film, i.e. 2n-layers, with each layer repeated twice in the final barrier film. The internal layer welds to itself as the bubble collapses, forming a seal. 
     The use of a blown film that is collapsed in on itself to form the barrier film has a number of advantages. Firstly, it provides an efficient solution to the provision of two barrier blocks in the barrier film, as the layers in the blown film are duplicated in one step, when forming the barrier film. Blowing the film provides good mechanical strength for the layers within the film, as the polymers will be bi-axially oriented in each layer, providing a good strength solution for a given weight of a layer. In addition, the blown film process provides good ventilation of the film as it is being manufactured (as air is circulated inside and outside the film prior to collapse, which helps to remove low molecular weight (volatile) components from the film. The removal of these components prevents them from adversely affecting the flavour and odour properties of the ultimate liquid food contents of a container made using the laminate structure that includes the barrier film, as otherwise these components can migrate into the product. Additionally, the production of the blown film can be carried out offline, separately from the main production line that is producing the laminate structure. Different barrier films can be swapped in and out of the production line with very little downtime compared to a normal change in extruders in a coating line. 
     A preferred example of a value of n within the blown film is n=7. In this case, the n-layer blown film comprises, from the outside to the inside, a polymer layer, a tie layer, the first polymer layer which comprises a polyamide layer, the gas barrier layer which comprises an EVOH layer, the second polymer layer which comprises a polyamide layer, a tie layer and a polymer layer. This film is extrusion laminated onto the substrate with an adhesive layer to create the finished laminate structure. 
    
    
     
       Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
         FIG. 1  is a schematic diagram of a production line, 
         FIG. 2  is a partial cross-section of a device for producing a blown film, 
         FIG. 3  is a partial cross-section, on the line III-III of  FIG. 2 , through the blown film produced by the device of  FIG. 2 , 
         FIG. 4  is a schematic diagram of the multi-layer barrier film produced from the blown film of  FIG. 3 , and 
         FIGS. 5 to 12  are schematic diagrams of different embodiments of a laminate structure. 
     
    
    
       FIG. 1  shows a production line  10  for producing a laminate structure   12 . A roll  14  of paperboard  16  is used to provide a substrate for the laminate structure  12 . A coating station  18  is provided to coat the outside of the substrate  16  with a polymer layer  20  (such as LDPE) from an extruder, and this coated substrate  22  is passed to a station  24  where the coated substrate   22  is extrusion laminated with a multi-layer barrier film  26  fed from a roll  28 . The stations  18  and  24  may include up to nine extruders linked with a feedblock with a corresponding number of dies. In this way, for example, the polymer layer  20  may comprise a plurality of sub-layers forming a more complex laminate structure. For example, a plurality of extruders at the station  18  could be configured to coat a polymer layer structure  20  onto the paperboard  16 , such a polymer layer structure comprising sub-layers and being of the same or similar composition as the multi-layer barrier film  26  (as described below). Alternatively, the coating taking place at the station  18  could be in the form of extrusion laminating involving the coating of the outside of the substrate  16  with, for example, a second multi-layer film, identical or similar to the film  26 . 
     An extruder  30  at the station  24  provides an adhesive layer  32  (such as LDPE) onto the inside of the coated substrate  22  which adheres the film  26  to the coated substrate  22 , as it is passed between a pair of rollers  34 . The final laminate structure  12  is wound onto a roll  36 . At the extrusion lamination station  24 , as shown in  FIG. 1 , the film  26  is laminated to the coated substrate  22  using a single layer  32 , but the extruder  30  could be configured to extrude multiple layers, and thereby provide a more complex laminate structure (see  FIGS. 10 to 12 ). 
     Part of the production of the multi-layer barrier film  26  is shown in  FIG. 2 . In this Figure, a blown film  38  is produced. The device for producing the blown film  38  includes a die  40  which is cylindrical (shown in  FIG. 2  in section) which, in this example of the device includes nine concentric channels  42 . Different dies  40  can be used, depending upon the number of layers that are desired in the blown film  38 . The channels  42  are used to introduce different molten polymer materials  44 , which are used to produce the blown film  38 . The materials  44  flow upwards under pressure, which is normally in the range of 200 to 600 bar. Air is introduced via a central shaft  46  into a chamber (not shown) that contains the blown film  38 , the air being supplied to inside the tubular film  38 . Further channels  48  also introduce air into the chamber but outside the film  38 . 
       FIG. 3  shows a partial cross-section of the blown film  38 . The layers in the blown film  38  are effectively concentric rings corresponding to the materials  44  in the channels  42  of the die  40 . Only three layers are shown (not to scale) for ease of understanding. The outermost layer  50  is cooled by the air introduced by the channels  48 , and is adjacent the wall of the chamber of the blown film apparatus. The innermost layer  52  is cooled by the air from the shaft  46  which is circulated in the bubble formed by the blown film  38 . 
     As discussed above, the step of producing the multi-layer barrier film  26  comprises producing a blown film  38  of n layers, by a blown extrusion process. After the blown film  38  is produced, the process of producing the multi-layer barrier film  26  further comprises collapsing the n-layer blown film  38 , between a pair of rollers (not shown), to form the multi-layer barrier film  26 , the multi-layer barrier film  26  consisting of 2n layers. An example of the finished barrier film  26  is shown in  FIG. 4 , where n=7. This is the preferred embodiment of the invention, in which a seven layer blown film  38  is collapsed into a fourteen layer barrier film  26 . The innermost layer  52  of the original blown film  26  is brought together by the action of the rollers and kept sufficiently hot that the layer  52  welds to itself. The layer  52  comprises a polyolefin plastomer (POP). 
     Other methods of producing the barrier film  26  are possible, such as using a cast co-extrusion process to create the multi-layer barrier film  26 . The layers of the barrier film do not have to be all formed in one process. For example, if a 14 layer film is desired, then a 7 layer film can be produced and this could be extrusion laminated to the coated substrate  22  twice to give the required number of layers. 
     In the preferred embodiment, the n-layer blown film  38  comprises, from the outside to the inside, a polymer layer, a tie layer, the first polymer layer comprising a polyamide (nylon) layer, the gas barrier layer comprising an EVOH layer, the second polymer layer comprising a polyamide layer, a tie layer and a polymer layer. Once this is collapsed to form the barrier film  26  then these layers are repeated. This process provides a multi-layer barrier film   26  which comprises a first polymer layer (polyamide), a gas barrier layer (EVOH) and a second polymer layer (polyamide), wherein both of the first and second polymer layers comprise a polyamide layer. 
     The first polymer layer, the gas barrier layer and the second polymer layer form a first barrier block  54 , and the multi-layer barrier film further comprises a second barrier block  56 , substantially identical to the first barrier block  54 . In the barrier film  26 , the first polymer layer contacts the gas barrier layer and the gas barrier layer contacts the second polymer layer. In the preferred embodiment, the gas barrier layer comprises an EVOH layer. 
     The completed barrier film  26  is extrusion laminated to the substrate  16 , as described above with reference to  FIG. 1 . An example of the finished laminate  12  is shown in  FIG. 5 , which is produced using the barrier film  26  shown in  FIG. 4 . An additional (but optional) product-contacting layer  58  of LDPE is provided on the inside of the laminate structure  12 , which is coated onto the film  26  side of the laminate, in a conventional fashion. The barrier film  26  is shown offset from the other layers of the laminate  12 , purely for illustrative purposes, and in a finished product will be aligned with the other layers that make up the laminate structure  12 . As mentioned above, a second multi-layer barrier film substantially identical to the film  26  and produced in substantially the same way can be extrusion laminated onto the outside of the paperboard substrate  16  in place of the polymer layer  20 . 
     Each of the barrier blocks  54  and  56  in the laminate structure  12  performs a different function. The first barrier block  54  is located relatively closer to the paperboard substrate  16 , and performs an oxygen barrier function in the laminate  12 . The second barrier block  56  is located relatively closer to the ultimate liquid food contents of the eventual container formed from the laminate structure  12 . This second barrier block provides an anti-scalping function in the laminate structure  12 , preventing flavour and odour components from leaching into the laminate structure  12  from the liquid food contents. 
       FIGS. 6 to 9  show further embodiments of the laminate structure  12 . Each layer in the laminate structure  12  in these Figures is provided with a weight in grams per square metre, of the respective layer. The table below shows further details of the weights of the laminate structures  12  in each of  FIGS. 6 to 9 . The top row of weights in the table is the overall gr/m 2  of the respective laminate structures  12 , the second row is the overall weight of the multi-layer barrier film  26  plus the adhesive layer  32 , the third row is the weight of the outer polymer layer  20 , the fourth row is the total weight of all of the polyamide (nylon) layers, and the fifth row is the total weight of all of the gas barrier (EVOH) layers. 
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                 FIG. 6 
                 FIG. 7 
                 FIG. 8 
                 FIG. 9 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 total gr/m 2   
                 504.8 
                 505.6 
                 510.1 
                 510.1 
               
               
                 inside coating gr/m 2   
                 68.8 
                 69.6 
                 74.1 
                 74.1 
               
               
                 outside coating gr/m 2   
                 18.0 
                 18.0 
                 18.0 
                 18.0 
               
               
                 nylon total gr/m 2   
                 9.9 
                 9.9 
                 9.9 
                 9.9 
               
               
                 EVOH total gr/m 2   
                 4.9 
                 4.9 
                 4.9 
                 4.9 
               
               
                   
               
            
           
         
       
     
     The  FIG. 6  embodiment, from outside to inside comprises, a layer of LDPE  20 , the paperboard substrate  16 , the adhesive layer of LDPE  32 , and then the fourteen layer barrier film  26 , which is formed by collapsing a seven layer blown film  38 . The layers of the blown film  38 , from the outside to the inside comprise an outer layer  50  of LDPE and polyolefin plastomer (POP), a tie layer of MAH-grafted LLDPE (linear low density polyethylene)  60 , then the barrier block  54  consisting of a layer of aliphatic nylon, a layer of 38 mol% EVOH, and a second layer of nylon, a second tie layer of MAH-grafted LLDPE  62 , and an inner layer  52  of polyolefin plastomer (POP) and LDPE. The remainder of the fourteen layer barrier film  26  is made up of the above seven layers in reverse order. 
     The embodiment of  FIG. 7  differs from the embodiment of  FIG. 6  only in that the outer layer  50  of the barrier film  26  further comprises CaCO 3  (calcium carbonate) which provides good heat resistance during the container forming process, and the nylon within the film  26  is nylon-6. As a result of these differences the weight of this layer is slightly increased, from 8.59 gr/m 2  in  FIGS. 6 , to 9.03 gr/m 2  in  FIG. 7 . 
     The embodiment of  FIG. 8  differs from the embodiment of  FIG. 6  in that one of the first and second polymer layers of the barrier block comprises a polypropylene layer, which replaces the nylon layer. Polypropylene has the advantage that it is even more flex crack resistant than polyamide. The outer layer of the barrier block is MAH-grafted polypropylene and Raco (Random Copolymer) polypropylene. To compensate for the loss of the nylon in this layer, the other nylon layer in the barrier block is enlarged, from 1.47 gr/m 2  in  FIGS. 6 , to 4.97 gr/m 2  in  FIG. 8 , to give the same overall weight of nylon in the laminate structure  12 . The use of a polypropylene layer within the laminate structure further improves the flex-crack resistance of the overall structure, and gives further strength to the gas barrier layer of EVOH, to which the polypropylene is adjacent. 
     The embodiment of  FIG. 9  differs from the embodiment of  FIG. 8  in that the outer layer of the barrier block that is polypropylene in  FIG. 8  is replaced with a tie layer of polyolefin plastomer (POP), which is a high-strength material with a good degree of flexibility, and MAH-grafted LLDPE. 
     The outer layers  50  shown in the embodiments of  FIGS. 6 ,  8  and  9  may have the POP replaced by an anti-blocking agent, for example an inorganic silica additive, which modifies the surface of the LDPE with which it is blended in order to improve the interface characteristics with adjacent layers. 
     The new production line  10  of  FIG. 1  is able to run existing structures but also the new barrier structure  12 . The new line  10  eliminates some of the inefficiencies of the existing lines, and the new line  10  is able to run more productive hours per year, resulting in better yields. The new barrier structure   10 , as well as existing structures, are optimised as to usage of expensive high barrier resins (like EVOH) and co-extrudable adhesives (tie layers) by substantially better profile control allowing down gauging. 
     Instead of using a complicated line equipped with several multi-layer coating stations, the production line  10  is better through being a relatively simple (cheaper) high speed line that is able to run the normal standard LDPE-based coating structures but is also able to extrusion laminate the off-line made barrier film  26  in the coating structure. 
     The line  10  can be a simple two-station, high-speed state of the art coating line with gravimetric blending and throughput control with investment in a 2.4 metre wide, 7-layer state of the art high output blown co-extrusion line to be able to manufacture the 20 to 35 microns high-barrier, very cost efficient, lamination film  38 , which excels in very low thickness variation, optimal usage of different state of art barrier resins, very high mechanical strength and very high flex-crack resistance (avoiding micro pinholes). 
     The line  10  provides uninterrupted running of the main coating procedures with no down time because of purge procedures for changing on-and back to barrier resin co-extrusion in the coating stations. The line  10  provides a major improvement in net usable production hours. The fact that the extrusion coating line  10  can be running at the same location as the blown line, provides increased efficiency and avoids highly inefficient transportation of mother rolls of blown co-extruded barrier lamination film. 
     The laminate structure in the preferred embodiment provides a significantly improved EVOH-based barrier board  12 , with the ability to use the blown film  38  as a mechanical support in the board structure because the choice of resins in blown film co-extrusion is at least 10 times higher than in extrusion coating, so that mechanically supportive resins can be used more readily. The result is thickness- and cost-reduction without loss of chemical and physical properties. 
     The production line  10  provides the ability to run newly available barrier resins like PGA (polyglycol alcohol) without additional purging. The production line  10  can be the platform for development of, for example, board versions that are based on non-oil based renewable polymers like PLA (polyalactic acid) and PGA (polyglycol alcohol) as well as extrusion lamination of state-of- the-art, high-barrier, coated oriented films; all of this development can be provided without significantly interfering with the day-to-day production of the coating line  10 . 
       FIGS. 10 to 12  show further embodiments of the laminate structure  12 . These Figures show different embodiments for the layer  32  provided by the extruder  30  of  FIG. 1 . These embodiments add temperature and abuse resistance properties to the layer  32 . In older filling machines gas burners are used to heat the polymers prior to sealing of the container formed from the blank. The problem with such gas burner systems is that they overheat the barrier structure and can create pin holes in the outer layers of the structure. The improved layers  32  of these Figures protect the board and the external layer or layers  20  of the structure from the excess heat. 
       FIG. 10  shows the layer  32  being comprised of a blend of a polyolefin (LDPE), nylon (PA) and a compatibiliser (C). The nylon within the blend provides heat resistant properties to the layer  32 . An alternative polyolefin to be used in the blend instead of the LDPE is polypropylene. The compatibiliser is a polymer which has affinity to both the nylon and the polyolefin and assists the formation of the blend between the other two polymers. Alternatively, the layer  32  could be in the form of a polyamide/polyolefin alloy, instead of a simple blended product. A further embodiment is shown in  FIG. 11 , in which the layer  32  is comprised of a blend of high density polyethylene and calcium carbonate.  FIG. 12  shows a yet further embodiment, where the layer  32  is comprised of three sub-layers  70 ,  72  and  74 . The board-facing layer  70  is comprised of nylon, the second sub-layer  72  is a tie layer comprised of a suitable polymer, and the third sub-layer  74  is a polyolefin. These three sub-layers  70 ,  72  and  74  are co-extrusion laminated when the film  26  is laminated to the board  16  at station  24  of  FIG. 1 .