Abstract:
The disclosure relates to a method for manufacturing a package whereby a packaging tray is formed into a packaging film and filled with a product. The disclosure is distinguished by the fact that at least the inner and/or outer side of the packaging tray is covered with a barrier layer after the forming of the packaging tray. The disclosure also relates to a thermoforming machine for carrying out this method as well as to a package manufactured by means of the method.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims foreign priority benefits under 35 U.S.C. §119(a)-(d) to European patent application number EP 10 008 471.4 filed Aug. 13, 2010, which is incorporated by reference in its entirety. 
       TECHNICAL FIELD 
       [0002]    The disclosure relates to a method for manufacturing a package, a thermoforming machine for forming a package and to a package that can be manufactured by means of the method or with the thermoforming machine. 
       BACKGROUND 
       [0003]    The manufacturing of packages by using thermoforming machines is widespread. Such a thermoforming machine in which packaging trays are thermoformed with a packaging film that is usually made of plastic and filled with a product is described in DE 10 2007 013 698 A1. 
         [0004]    DE 10 2007 013 698 A1 already discloses that the characteristics of the package, particularly the gas permeability of the packaging material, can have a substantial influence on the shelf-life of the perishable goods contained in the package. These goods can be, in particular, foodstuffs. 
         [0005]    EP 0 872 164 B1 and WO 2008/046553 A1 disclose devices for generating microwave plasmas. These two documents suggest that workpieces can be covered by means of a plasma treatment in which they are exposed to the microwave plasma generated by the devices. The two documents do not, however, contain any reference whatsoever to packages or packaging methods. 
       SUMMARY 
       [0006]    An object of the present disclosure is to improve a method for manufacturing a package, a thermoforming machine and a package itself to the effect that a longer shelf-life is achieved for the packaged products by means of the simplest possible design means. 
         [0007]    A method according to the present disclosure is distinguished by the fact that at least the inner and/or the outer side of the packaging tray is covered with a barrier layer after the forming of the packaging tray. This gas barrier layer influences the gas permeability of the packaging film, in particular the permeability for oxygen. By reducing the transfer of oxygen through the packaging film, the barrier layer extends the shelf-life of a packaged product. The application of the barrier layer onto the packaging tray after the forming of the packaging tray has, in comparison to the also theoretically possible use of a packaging film already covered before the forming of the packaging tray, the advantage that excessive stretching and loading of the barrier layer are avoided during the forming of the packaging tray. This makes it possible also to use very thin barrier layers. 
         [0008]    In a variant of the present disclosure, the covering with the gas barrier layer takes place even before the filling of the packaging tray with a product. In this way, the covering can be carried out without the possibly disturbing presence of the product. 
         [0009]    Additionally or alternatively, the covering of the outer side of the package, i.e., the packaging tray and/or a top film that seals the packaging tray, can take place after the manufacture of the entire package, i.e., after the packaging tray has been sealed with the top film. The advantage of this variant is that in this way, even very thin or flexible films can be covered, in particular, skin films. After the application of the skin film used as the top film to the product under a vacuum, the skin film can no longer move. This prevents the gas barrier layer, which is only applied later, from peeling off. 
         [0010]    The barrier layer preferably has an oxygen permeability level of less than 10 cubic centimetres (ccm) per (m 2 ×24 hours×pressure difference [bar]). In other words, in this case an oxygen volume of less than 10 ccm occurs or passes through each square metre (m 2 ) of the packaging film provided with the barrier layer per 1 bar pressure difference between two opposite sides of the packaging film and barrier layer in 24 hours. This very low oxygen permeability rate guarantees a very long shelf-life for the product in the packaging. 
         [0011]    It has proven to be particularly advantageous if the covering of the packaging tray with the barrier layer takes place by means of a plasma covering. This type of packaging makes it possible to apply extremely gas-impermeable barrier layers with a continuously constant thickness even on to packages with complicated shapes. 
         [0012]    The plasma needed for the plasma covering can, for example, be created in a packaging machine used for manufacturing the package. In this way, the plasma covering device is integrated into the packaging machine, and the entire packaging machine is much more compact than if an additional plasma covering system were to be provided. 
         [0013]    The method according to the present disclosure is particularly suitable for the use of a biodegradable packaging film. Very low gas-transfer rates can also be achieved here with conventional multi-layer films, for example, with an EVOH film (ethylene vinyl alcohol film). These have the disadvantage, however, that they have to be comparatively thick and that the gas barrier layer is very sensitive to moisture with the EVOH film. This barrier layer could consequently become more gas-permeable again if, for example, moist foods are contained in the package. This, in turn, reduces the shelf-life. 
         [0014]    Biodegradable films, for example, films made of bioplastics such as PLA (polylactide, polylactic acid) are normally very gas-permeable. The method according to the disclosure now makes it possible to apply a very thin barrier layer to these films in order to reduce their gas permeability without the disadvantage of significantly impairing the biodegradability of these films. 
         [0015]    The barrier layer itself may comprise or consist of, for example, silicon oxide (SiOx) and/or aluminium oxide (AlOx). 
         [0016]    The present disclosure also relates to a thermoforming machine with a forming station for forming packaging trays into a packaging film, as well as with a filling station. The disclosure provides for a covering station to be provided between the forming station and the filling station and/or downstream of a station for sealing the packaging trays with a top film, whereby this covering station is developed such that at least the inner and/or the outer side of the packaging tray is covered with a barrier layer. The advantages described above are achieved in this way. 
         [0017]    The covering station can, for example, be set up for applying a barrier covering with a thickness of less than a micrometre. Even with such a very thin layer, the gas permeability of the packaging material can be greatly limited. 
         [0018]    The present disclosure furthermore relates to a package with a packaging tray formed from a packaging film that can be thermoformed in which the inner and/or outer side of the packaging tray is covered with a barrier layer. 
         [0019]    It has already been explained that the packaging film is preferably biodegradable. 
         [0020]    In order to guarantee a particularly long shelf-life, it is advantageous if the packaging film provided with the barrier layer has an oxygen permeability level of less than 10 ccm per (m 2 ×24 hours×pressure difference [bar]). 
         [0021]    In an advantageous variant of the disclosure, the barrier layer is not sensitive to moisture. As a result, it is particularly suitable for use in a package that is packed with moist foods. 
         [0022]    The barrier layer may comprise SiOx and/or AlOx. 
         [0023]    In the following, an advantageous embodiment of the present disclosure is described in more detail with reference to the below drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]      FIG. 1  is a schematic view of a thermoforming machine according to the present disclosure; and 
           [0025]      FIG. 2  is a schematic cross-sectional view of a package according to the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]      FIG. 1  shows, in a schematic side view, a packaging machine  1  according to the present disclosure in the form of a thermoforming machine. The packaging machine  1  has a forming station  2 . Packaging trays  5  are formed in the forming station  2  into a packaging film  4  drawn from a film roll  3  by means of thermoforming. 
         [0027]    A product  7  is introduced into the packaging trays  5  at a filling station or loading station  6 . This product  7  can be a food, preferably a food  7  with a certain moisture level. 
         [0028]    A sealing station  8  of the packaging machine  1  is used to seal the packaging trays  5  with a top film  9 . The top film  9 , which can, like the packaging film  4 , be a sealable plastic film, is drawn from a further film roll  10 . The top film  9  arrives in the sealing station  8  via a roll guide  11 . 
         [0029]    A hermetically sealed sealing chamber can be formed around the packaging tray  5  in the sealing station  8 . This sealing chamber is evacuated and possibly gassed with a replacement gas before a sealing tool seals the top film  9  to the packaging tray  5 , preferably at the edges of the packaging tray  5 . The part of the top film  9  that juts out beyond the packaging tray  5  can be separated from the now sealed package  13  while the packaging tray  5  is still in the sealing station  8 . The remaining film grid  14  of the top film  9  is fed to a remaining film winder  15  and collected there. 
         [0030]    Downstream of the sealing station  8  in the direction of production P, a cross-wise cutting device  16  and a longitudinal cutting device  17  ensure a separation of the packages  13  that until now have been in an interconnection of the packaging film  4 . A conveyor belt  18  is used to transport the finished and separated packages  13 . 
         [0031]    A covering station  19  is provided, between the forming station  2  and the filling station  6  in the direction of production P. In the embodiment shown, the covering station  19  is a plasma covering station  19 . The covering station  19 , which is integrated into the packaging machine  1 , has a plasma generation device  20 , known, for example, from WO 2008/046553 A1, which is likewise depicted only schematically in  FIG. 1 . The plasma generated by means of the plasma generation device  20  is used in order to cover with a thin barrier layer the inner and/or outer side of the packaging trays  5  in the covering station  19  by means of a plasma covering or by means of plasma-enhanced chemical vapour deposition (PECVD). 
         [0032]    In an embodiment of the method according to the present disclosure or in the event of operation of the packaging machine  1  shown in  FIG. 1 , this packaging machine is operated in cycles. A section of the packaging film  4  is drawn off of the film roll  3  with each work cycle. When the packaging film  4  comes to a standstill, the forming station  2  closes in order to thermoform a packaging tray  5  or a field of packaging trays  5  lying next to one another into the packaging film  4 . 
         [0033]    When the transport continues, the packaging trays  5  arrive in the covering station  9 , in which their inner and/or outer side is given a thin gas barrier layer. 
         [0034]    After the packaging trays  5  have been filled with a product  7  in the filling station  6 , they arrive in the sealing station  8 . There a vacuum is created in the packaging trays  5  and/or a replacement gas (mixture) is fed into the packaging trays  5  before the packaging trays  5  are sealed with the top film  9  in a gas-tight seal. As the now sealed packages  13  are further transported in the direction of production P, the packages  13  are separated by means of the cross-wise and longitudinal cutting devices  16 ,  17 . 
         [0035]      FIG. 2  shows a schematic vertical cut through an embodiment of a package  13  according to the present disclosure, whereby it is possible to manufacture the package  13  with the packaging machine  1 . The package  13  has a packaging tray  5  that is shaped by means of thermoforming into the packaging film  4 . The packaging film  4  in the depicted embodiment is a packaging film made of a biodegradable plastic, also called bioplastic. For example, this could be PLA (polylactide, polylactic acid). 
         [0036]    The packaging tray  5  has an inner side  21  and an outer side  22 . In the depicted embodiment, only the inner side  21  is provided with a gas barrier layer  23  in the plasma covering station  19 . The gas barrier layer  23  has a thickness of less than a micrometre. It is not sensitive to moisture, i.e., it does not change its characteristics under the influence of moisture. The barrier layer  23  can be made of SiOx or of AlOx. The area of the packaging film  4  provided with the barrier layer  23  has a gas permeability level particularly for oxygen of less than 10 ccm per (m 2 ×24 hours×pressure difference [bar]). This guarantees that only a negligibly small amount of oxygen can enter into the package  13 , so that the product  7  contained in the package  13  is given a long shelf-life. 
         [0037]    A top film  9  is sealed on to the edges  24  of the packaging tray  5 , whereby this top film  9  likewise ensures a gas-tight seal of the package  13 . 
         [0038]    Departing from the depicted embodiment, the packaging machine  1  according to the disclosure, the method according to the disclosure and/or the package  13  according to the disclosure can be changed in many respects. In particular, it is conceivable not to apply the barrier layer  23  to the inner side  21  or not only to the inner side  21  of the packaging tray  5 , and instead additionally or alternatively to apply it to the outer side  23  of the packaging tray  5 . By applying the barrier layer  23  to both sides  21 ,  22  of the packaging tray  5 , it is possible to provide a particularly gas-tight package  13 . 
         [0039]    It was already mentioned that in addition to or as an alternative to the covering station shown in  FIG. 1 , a covering station  19  can also be arranged downstream of the sealing station  8 , i.e. consequently in between the sealing station  8  and the separating device  16 . This variant is particularly useful in the event that a very thin film is used as the top film  9 , for example, a skin film that does not have a sufficiently high level of form stability until after it has been applied to the packaging tray  5 . In a covering station  19  downstream of the sealing station  8 , the entire outer side of the package  13  can be given a gas barrier layer  23 , i.e., the outer side  22  of the packaging tray  5  and the outer side of the top film  9 . 
         [0040]    In a further variant, it is conceivable that the outer and/or the inner side of the top film  9 , i.e., the side of the top film  9  facing away from or towards the packaging tray  5 , is covered with a gas barrier layer  23 . For this purpose, a (further) covering station  19  can be provided in the area of the feed of the top film  9  to the sealing station  8 . 
         [0041]    It is furthermore conceivable to provide an aluminium layer as a gas barrier layer  23  that is applied to the packaging tray  5  and/or the top film  9  by means of vaporization. Disadvantageous in the case of an aluminium covering, however, is that the areas of the package  13  covered with it are no longer transparent under some conditions. A covering, for example, with aluminium oxide and/or silicone oxide has the advantage, in contrast, that only a maximum of 20 percent loss of transparency occurs, so that the areas of the package  13  provided with the barrier layer  23  still continue to remain transparent. 
         [0042]    While various embodiments have been illustrated and described above, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.