Patent Publication Number: US-2006003122-A1

Title: Process for manufacturing a packaging material

Description:
The invention relates to a process for manufacturing a packaging material having at least two films or foils bonded together into a multilayer laminate by means of at least one layer of adhesive, whereby the adhesive layer/layers is/are cure-hardened. Also within the scope of the invention is a self-standing pouch made from the laminate.  
      Laminates for manufacturing self-standing pouches for drinks are manufactured today in two steps using solvent-free adhesives and in one step using solvent-based adhesives.  
      The solvent-free process is environmentally friendly, however, requires two production steps. In a first step an aluminium foil is bonded to a printed polyethyleneterephthalate (PET) film which is coated with a solvent-free poly-urethane (PUR) adhesive. After a curing time of several hours this pre-laminate can be bonded to a polyolefin-film using a solvent-based or solvent-free PUR adhesive. The final structure is: RET-film/adhesive layer/aluminium foil/adhesive layer/polyolefin film. After the final curing over a period of several days, the final laminate can be cut to size and dispatched to the customer. The throughput time from receipt of order to dispatch of the finished product depends essentially on the time required for curing the PUR-adhesive  
      The object of the invention is to provide a process of the kind described at the start by means of which the time required for curing the adhesive needed for the laminate—and with that the throughput time can be reduced in comparison with the adhesive curing time in conventional laminate manufacture.  
      That objective is achieved by way of the invention in treat at least one adhesive layer is of an adhesive that can be cured using an electron beam and the laminate is radiated with electrons for the purpose of curing the adhesive.  
      The application of an electron beam curable adhesive results in an increase of the initial adhesion, the so called greentack, which could not be expected at once. Furthermore the application of an electron beam curable adhesive results not only in an excellent adhesion against plastic films but also against aluminium foils. In addition, an aluminium foil forms a functional barrier for electron beam curable adhesives, which is important with packaging for food, in particular beverages.  
      The radiation curing of plastics that can be cured with an electron beam takes place in a fraction of a second on passing through a radiation station, whereby the final bond strength has already been essentially achieved without an additional curing time when the laminate emerges from the radiation station and is coiled.  
      The advantage of manufacturing laminate using adhesives that can be cured by means of electron beam radiation is not only the much reduced throughput time, but also in the reduction of solvent emissions is solvent based adhesives can be replaced by adhesives that can be cured using an electron beam.  
      A preferred laminate exhibits three films or foils and two adhesive layers, whereby one of the adhesive layers or both adhesive layers is/are of the electron beam curing type of adhesive.  
      If only one of the adhesive layers is curable with an electron beam, a solvent based or solvent-free PUR-adhesive is used by way of preference for the second adhesive layer.  
      A preferred laminate exhibits the following structure: PET film/first adhesive layer of electron beam curable adhesive/aluminium foil/second adhesive layer of an electron beam curable adhesive/polyolefin film.  
      If only one of the two adhesive layers is of an electron beam curable adhesive, a further preferred laminate exhibits the following structure: PET film/first adhesive layer of electron beam curable adhesive/aluminium foil/second adhesive layer of a solvent based or solvent-free PUR adhesive/polyolefin film or PET film/first adhesive layer of a solvent based or solvent-free PUR adhesive/aluminium foil/second adhesive layer of an electron beam curable adhesive/polyolefin film  
      Preferred polyolefin films are sealable films of polyethylene (PE) or polypropylene (PP). For applications involving sterilisation or high temperature cooking, PP is preferable because of its ability to withstand high thermal loads.  
      The PET film may exhibit printing on it. The printing is preferably provided as counterprint on the side coated with adhesive.  
      The electron beam curable adhesive is preferably an adhesive on an acrylate basis.  
      The adhesive on an acrylate basis may contain monomers, oligomers or mixtures of monomers and oligimers as the basis. Examples of monomers are mono, di- and multifunctional acrylates such as phosphoric acid ester acrylates, hydroxy-acrylates, carboxy-acrylates, amino-acrylates, acrylic acid and acrylamide. Examples of oligomers are epoxy-acrylates, urethane-acrylates, polyester-acrylates and silicon-acrylates. The monomers and oligomers mentioned are either available commercially or can be manufactured by routine methods. The term “acrylate” (or “acryl”) used here also includes “methacrylate” (or “methacryl”, whereby the acrylates are preferred.  
      The laminate manufactured according to the invention is particularly suitable for manufacturing self-standing pouches, in particular such for drinks. Preferred is at least for the film of the laminate forming the outside of the pouch to be laminated using an adhesive layer that can be cured using an electron beam.  
    
    
      Further advantages, features and details of the invention are revealed in the following description of preferred exemplified embodiments and with the aid of the drawing which shows schematically in  
       FIG. 1  cross-section through a laminated packaging film;  
       FIG. 2  manufacture of a pre-laminated partial film of the packaging film shown in  FIG. 1 ;  
       FIG. 3  manufacture of the packaging film in  FIG. 1  from the pre-laminated partial film in  FIG. 2 ;  
       FIG. 4  manufacture of the packaging film in  FIG. 1  by triple lamination. 
    
    
       FIG. 1  shows a packaging film  10  for manufacturing self-standing pouches for drinks featuring a printed PET film  12  representing the outer side, an aluminium foil  14  as barrier layer and a sealable PE or PP film  16  representing the inner side. The PET film  12  is permanently bonded to the aluminium foil  14  by way of a first adhesive layer  13  and the aluminium foil  14  to the sealing film  16  by way of a second adhesive layer  15 . In a typical packaging film  10  the thickness of the PET film is e.g. 12 μm, the thickness of the aluminium foil 8-10 μm and the thickness of the sealing layer 90-100 μm.  
       FIG. 2  shows the manufacture of a partial film A comprising PET film  12 , adhesive layer  13  and aluminium foil  14 . The printed PET film  12  is uncoiled from a first spool  18  in strip form an continuously coated with adhesive  13 . The aluminium foil  14  is uncoiled in strip form from a second spool  20  and fed to the PET film  12  coated with adhesive  13  and laminated to this to a partial film A. The partial film A is passed through a radiation station  22  in which the adhesive layer  13  is cured by electron beam radiation within a fraction of a second. After leaving the radiation station  22 , the partial film A is coiled onto a third spool  24 .  
      In a further production step, shown in  FIG. 3 , the sealing film  16  is uncoiled from a fourth spool  26  and continuously coated with adhesive  15 . The partial film A is fed from the third spool in strip form and fed to the sealing film  16  coated with adhesive  15  and laminated continuously to this to yield the packaging film  10 . The packaging film passes through a radiation station  28  in which the adhesive layer  15  is cured by electron beam radiation within a fraction of a second. On leaving the radiation station  22  the packaging film  10  is coiled onto a fifth spool  30 .  
      The second adhesive layer  15  does not necessarily have to be an electron beam curing adhesive. Instead, it may e.g. be a conventional PUR adhesive. In that case the curing station  28  is omitted. The longer curing time required for the PUR adhesive has no influence on the process for producing the composite film  10  and simply requires a minimum storage time until it is processed further.  
      Another version of the manufacturing process—not shown in the drawing—is such that first a partial film B comprising sealing film  16 , adhesive layer  15  and aluminium foil  14  is produced. The sealing film  16  is uncoiled from a first spool and Continuously coated with adhesive  15 . The aluminium foil is fed to the sealing film  16  which is coated with adhesive  15  and laminated to this to give a partial film B. The partial film B passes through a radiation station in which the adhesive a layer  15  is cured within a fraction of a second. After leaving the radiation station, the partial film is coiled onto a third spool.  
      In a further step the printed PET film  12  is uncoiled from a fourth spool and coated continuously with adhesive  13 . The partial film B is fed from the third spool to the PET film  12  coated with adhesive  13  and laminated in a continuous manner to yield the packaging film  10 . The packaging film  10  passes through a radiation station in which the adhesive layer  12  is cured by electron beam curing within a fraction of a second. On leaving the radiation station the packaging film  10  is coiled onto a fifth spool.  
      The first adhesive layer  13  does not necessarily have to be an electron beam curing adhesive. Instead, it may e.g. be a conventional PUR adhesive. In that case of course the radiation station is omitted. The longer curing time required by the PUR adhesive has no influence on the process for manufacturing the composite film  10  and requires simply a minimum storage time to be observed until further processing.  
      In a first way of manufacturing the threefold lamination shown in  FIG. 4 , the production of the packaging film  10  takes place by bringing together the PET film  12 , the aluminium foil  14  and the sealing film  16  and adhesively bonding via the two adhesive layers  13 ,  15  in one single pass. The printed PET film  12  is uncoiled from a first spool  32  and coated continuously with adhesive  13 . The aluminium foil  14  is fed in strip form from a second spool  34  to the PET film  12  coated with adhesive  13  and laminated continuously to this to yield partial film A. The sealing film  16  is uncoiled from a third spool  36  and coated continuously with adhesive  15 , fed in strip form to the partial film A and laminated to it in a continuous manner yielding the packaging film  10 . The sealing film  16  is uncoiled from a third spool  36  and coated with (adhesive  15 , fed in strip form to the partial film A and laminated to it in a continuous manner yielding the packaging film  10 . The packaging film  10  passes through a radiation station  38  with adequate capacity enabling both adhesive layers  13 ,  15  to be cured by electron beam radiation within a fraction of a second in one single pass. On leaving the radiation station  38  the packaging film  10  is coiled onto a fourth spool  40 .  
      In a second way of manufacturing the threefold lamination shown in  FIG. 5 , the production of the packaging film  10  takes place the same way as the production shown in  FIG. 4  by bringing together the PET film  12 , the aluminium foil  14  and the sealing film  16  and adhesively bonding via the two adhesive layers  13 , 15  in one single pass. The aluminium foil  14  is uncoiled from a first spool  42  and coated continuously with adhesive  15  at a first adhesive application station  17 . The sealing film  16  is fed in strip form from a second spool  44  to the aluminium foil  14  coated with adhesive  15  and laminated continuously to this to yield partial film B. The partial film B passes through a first radiation station  50  with adequate capacity enabling the adhesive layer  15  to be cured by electron beam radiation within a fraction of a second. The PET film  12  is uncoiled from a third spool  46  and coated continuously with adhesive  13  at a second adhesive application station  19 , fed in strip form to the partial film B on leaving the first radiation station  50  and laminated to it in a continuous manner yielding the packaging film  10 . The packaging film  10  passes through a second radiation station  52  with adequate capacity enabling also the adhesive layer  13  to be cured by electron beam radiation within a fraction of a second. On leaving the radiation station  52  the packaging film  10  is coiled onto a fourth spool  48 .  
      Immediately after coiling onto the spool  40 ,  48  the packaging film  10  with fully cured adhesive layers  13 ,  15  is divided on a slitting line into commercially required breadths ready for dispatch.  
      It is self-evident that, on bonding the films or foils in the above laminating processes, the adhesive may also be deposited on the other films or foils mentioned in the examples.