Abstract:
A packaging machine is described. A plurality of working stations is arranged between the input side and output side of the machine. A conveyor moves packages carrying a product along a path from the input side to the output side through the working stations. A device feeds a cover film onto the packages. The cover film has two layers bonded together with a limited bonding strength. A first layer has a portion protruding beyond said second layer. Another device separates the first layer from the second layer in a defined region extending across the cover film transversely to the conveyor path. The separator seals the defined region of the cover film and supplies a pressurized fluid to said defined region. The defined region includes at least part of the protruding portion of the first layer. A method of using the packaging machine to package product also is described along with the package that is made.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to an apparatus and a method for separating the layers of a multi-layered film having at least two laminated layers, a packaging machine comprising this apparatus and a package comprising a cover film consisting of at least two laminated layers. 
     In the field of meat packaging the problem arises that fresh meat in contact with the oxygen of the air exhibits a red color, but changes to a brown or violet color under exclusion of oxygen, thereby having an unappetizing appearance. The conventional skin packages have the meat lying in a tray and covered by an upper or cover film which is sealed to the edge of the tray and coats the meat like a skin. In case that this cover film consists of an oxygen impermeable film, some time after the packaging process the above-mentioned color change of the meat to a brown or violet color will take place. When using an oxygen permeable film for the cover film, the meat will retain the red color or take it on again. 
     In order to solve this problem, U.S. Pat. No. 5,591,468 proposes to use two overlying separate layers as cover film, the lower layer being oxygen-permeable and the upper layer being oxygen-impermeable. The two layers are sealed to the edge of the package at respective two separate sealing seams. The upper layer can be pulled off immediately before offering the packages for sale, whereby the meat takes on a red color and a hermetic seal of the package up to this point in time is ensured, thereby keeping the quality of the meat. However, the known method and package disadvantageously require the use of two separate film rolls for producing the package and the generation of two separate sealing seams. This renders the entire method complicated and the corresponding apparatus expensive. 
     European patent application EP 0 721 899 A1 discloses the use, for skin packages, of a cover film consisting of laminated layers. With this known skin package, however, the problem arises that it is difficult to separate the laminated layers from each other and a separate apparatus is required for providing a point of impact for separating the upper layer from the lower layer. 
     OBJECTS OF THE INVENTION 
     It is an object of the invention to provide an improved apparatus and method for separating the layers of a multi-layered film. It is a further object of the invention to provide an improved packaging machine using such a multi-layered film and a package comprising such a multi-layered film. Specifically, it is an object of the invention to provide a package which ensures that the product therein, in particular meat, is kept fresh and which allows, at a desired moment, oxygen to come into contact with the product in an easy manner. It is a still further object of the invention to provide an apparatus for separating a film consisting of at least two laminated layers, and a corresponding method, providing an easy way of separating one layer from the other, whereby this film can be used as cover film in packages. Finally, it is an object of the invention to provide a packaging machine for producing the above-mentioned packages. 
     SUMMARY OF THE INVENTION 
     In order to achieve the above-mentioned objects, the invention provides an apparatus for separating the layers of a multi-layered film in at least an edge region thereof, the film having a first layer and a second layer bonded to the first layer with a limited bonding strength, the first layer having a portion which projects beyond the second layer, the apparatus comprising means for sealing a defined region of the film from the remaining region thereof, the defined region representing the edge region for separating the layers and including at least part of the projecting portion of the first layer, and means for feeding a pressurized fluid to the defined region. 
     According to a further aspect the invention provides a method of separating the layers of a multi-layered film in an edge region thereof, the film having a first layer and a second layer bonded to the first layer with a limited bonding strength, the method comprising the steps of clamping the film along a border of the edge region and passing a pressurized fluid through the edge region. 
     According to a third aspect the invention provides a packaging machine comprising an input side, an output side, a plurality of working stations arranged between the input side and the output side, conveyor means for conveying packages along a conveyor path from the:input side to the output side through the working stations, the packages having product carrying means with a product thereon, means for feeding a cover film onto the packages, the cover film having a first layer and a second layer bonded to the first layer with a limited bonding strength, the first layer having a portion which projects beyond the second layer, and means for separating the first layer from the second layer in a defined region extending across the cover film transversely to the conveyor path. 
     According to a fourth aspect the invention provides a package comprising a product receiving member having an edge, a product on the product receiving member, and a cover film covering said product and sealed to the edge so as to enclose the product between the product receiving member and the cover film, the cover film being a laminated film having at least two layers bonded to each other with a limited bonding strength and separated from each other at a region adjacent to a lateral edge of the cover film, the cover film projecting beyond the edge of the product receiving member at the separated region. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further advantages, features and objects of the invention will be apparent from the description of embodiments with reference to the drawings. In the drawings: 
     FIG. 1 is a side view of a packaging machine; 
     FIG. 2 shows a section of an apparatus for separating two laminated layers of a packaging film, seen in conveying direction; 
     FIG. 3 is a top view of the apparatus of FIG. 1, showing boundary lines of the separating region; 
     FIG. 4 showing a portion of FIG. 2 in an enlarged representation; 
     FIG. 5 is a top view of a further embodiment of an apparatus for separating two laminated layers; 
     FIG. 6 is a top view of a package having the two laminated layers of the cover film separated at one side of the package; 
     FIG. 7 is a side view of the package of FIG. 6; 
     FIG. 8 is a side view of a package according to FIG. 6 with inert protective gas; and 
     FIG. 9 is a top view of a package having the laminated layers of the cover film separated at one corner of the package. 
     FIG. 10 is a side view of a packaging machine illustrating an alternative location for a station. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in FIG. 1 a packaging machine  1 , specifically a tray sealing machine, comprises a machine frame having an input side  2  and an output side  3 . A plurality of tray carriers  4  adapted to receive trays  5  are conveyed along the frame from the input side to the output side through working stations arranged successively in conveyor direction. A conveyor device  6  formed as a conveyor chain is provided for conveying the continuous series of tray carriers  4 . The working stations include a closing or sealing station  7  for sealing an upper film or cover film  11  to the peripheral flange or edge of the trays for sealing the package and a cutting station  8  for cutting the cover film. A separating station  9  for separating the laminated layers of the cover film is arranged at the supply region of the cover film  11 . Furthermore, there is provided a transporting device  10  for feeding and transporting the cover film  11 . 
     The packaging machine further includes a conveyor belt  12  for taking away the finished packages  13  after their passage through the working stations. Moreover, a roll  14  serves for winding up the remainders of the cover film  11  after the cutting operation. 
     A control device  15  controls the operation of the packaging machine in a coordinated manner. 
     As shown in the FIGS. 2 to  9  the cover film  11  is a laminated film having at least two laminated layers, a first layer  20  which is substantially oxygen impermeable and a second layer  21  which is bonded to the first layer and substantially oxygen-permeable. The first layer and the second layer  21  are bonded to each other with a limited bonding or adhesive strength therebetween which means that the layers can be separated from each other without damaging the same. As shown in particular in the FIGS. 2 to  5  the web of the oxygen-impermeable first layer  20  is wider than that of the oxygen-permeable second layer  21  by an amount s and projects on one side beyond the second layer  21  by the amount s in a border region  22  of the web. The oxygen-impermeable first layer is stronger than the oxygen-permeable layer. Since the oxygen-impermeable layer projects beyond the oxygen-permeable layer and forms the stronger one of both layers, the oxygen-impermeable layer can be firmly gripped without risk of damage at the edges of the film for transport thereof. 
     As particularly shown in FIG. 2 the inventive separating station  9  for the cover film  11  comprises a first tool member being a lower tool member  30  and extending across the entire width of the cover film  11  transversely to the conveyor direction, and a second tool member, being an upper tool member  31  and in working cooperation with the lower tool member  30 . The lower tool  30  can be lifted and lowered relative to the upper tool member  31  by means of a lifting device formed as a piston-cylinder-device  32 , as shown in FIG.  2 . The lower tool member  30  and the upper tool member  31  are both formed as bars or beams having respective short sides  34 ,  36  extending parallel to the conveyor direction and long sides  35 ,  37  extending perpendicular or transverse to the conveyor direction. As shown in the FIGS. 2 to  4 , the lower tool member  30  comprises a hollow or trough-shaped recess  33  spaced from the short side  34 . At a position opposite to the recess  33 , in a cooperating state of both tool members, the upper tool member  31  comprises means for feeding compressed air in the form of two bores  38 ,  39  extending vertically through the entire upper tool member  31 . The upper end of the bores facing away from the lower tool member  30  is connected with a compressed-air source  100 . 
     As shown in the FIGS. 2 to  4  the upper tool member  31  further comprises, at its lower side facing the lower tool member  30 , a channel or groove  40  extending, in the first embodiment shown in FIG. 3, substantially parallel to the long side  37  and substantially parallel to one of the short sides  36  and spaced therefrom. An O-ring gasket or toroidal sealing ring  41  is located within the groove  40  for sealing purposes. The groove  40  is not a closed loop; rather, it is open at the other short side of the upper tool member. The gasket  41  in the groove  40  defines, in cooperating state of the tool members, a region  42  between both tool members within the loop formed by the groove which is sealed off from the region  43  between both tool members outside of the groove. The groove  40  is further arranged so as to include, in a cooperating state of both tool members, the recess  33  at the lower tool member  30  in the sealed region  42 .In the embodiment shown in FIG. 3 the sealed region  42  formed in cooperating state of the tool members  30 ,  31  is formed as a straight strip extending across the film web. The fact that the groove  40  is open at one end enables air to flow through the sealed region  42  from the ends of the bores  38 ,  39  facing the compressed-air source to the side of the upper tool member having the open ends of the groove  40 . 
     The separating station  9  is disposed in, the packaging machine in such a manner that, in cooperating state of the tool members, the projecting region  22  of the first layer  20  of the cover film  11  overlaps the trough-shaped recess. The diameter of the trough-shaped recess  33  is slightly greater than the projecting amount s of the first layer  20  beyond the second layer  21 , whereby the second layer  21  projects into the trough-shaped recess  33  to some extent in cooperating state of the tool members. 
     In operation of the packaging machine the transporting device  10  firmly grips the cover film  11  on both sides of the film web and passes it through the working stations closely above the trays  5 . In cases in which the product is within the trays, the trays are sealed in the sealing station  7  in conventional manner. However, the same machine is also suitable to seal packages wherein the product projects beyond the upper edge of the trays, since the cover film is held in stretched condition and urges the product into the tray, whereafter the sealing operation is carried out. The cover film  11  connecting the individual packages is cut in the cutting station  8 . The remainders of the cover film are wound up onto the roll  14 . 
     The separating station  9  is operated in every working cycle of the packaging machine. The lifting device  32  moves the lower tool member  30  towards the upper tool member  31  and effects a predetermined contact pressure of the lower tool member  30  against the upper tool member  31 , whereby the cover film  11  is clamped between the lower tool member  30  and the upper tool member  31 . As a result of the positioning of the separating station  9  relative to the film web of the cover film  11  the region  22  of the first layer  20  projecting beyond the second layer  21  is placed above the recess  33  and the gasket  41  is inside of the outer edge of the projecting region  22  of the first layer  20 . 
     In this working cycle pressurized air is subsequently fed into the sealed region  42  through the compressed-air bores  38 ,  39  in the upper tool member  31 . The pressurized air generates a force acting onto the projecting region  22  of the first layer so as to urge this projecting region into the recess  33 . The resulting stress between the first layer  20  and the second layer  21  causes a detachment or separation of the second layer from the first layer first in the region of the recess  33 . Since the sealed region  42  is open at one side of the tool members, the pressurized air may enter or penetrate between the layers, and the separation of the second layer  21  from the first layer  20  continues, starting from the recess  33 , across the entire width of the cover film  11  so as to form, in the cover film, a separated region of both laminated layers  20  and  21 , the separated region forming a straight strip extending transversely across the film web. 
     After passing the cutting station the finished package  13  is formed as shown in FIG.  6 . The tray  5  contains a product  50  and is sealed with the cover film in the region of the peripheral rim or edge  51  of the tray. The packages are severed in the cutting station  8  in such a manner that the separated region of the laminated layers  20 ,  21  of the cover film  11  forms a tab  52  projecting beyond the rim  51  of the tray  5 . Since the tray carriers are adapted to carry the trays  5  having their narrow side extending transversely to the conveyor direction, the tab region  52  is formed at the narrow side of the package  13 . FIG. 7 shows an example of a package  13  wherein the product projects above the upper side  51  of the tray, and FIG. 8 shows an example of a package  13 ′ having the product within the tray and being entirely below the upper rim  51  of the tray, for example, in the case of a package with protective inert gas. The cover film is arranged so that the oxygen-permeable layer  21  is at the side of the cover film facing the product and the oxygen-impermeable layer  20  is on the opposite side of the cover film facing away from the product. 
     Before displaying the packages for sale the first layer  20  of the cover film, i.e., the upper layer, is grasped in that region where it is separated from the lower layer  21 , and pulled off from the layer  21 . 
     In the further embodiment of a separating station  109  shown in FIG. 5 the groove  40  with the gasket  41  therein is specifically shaped for producing the region  60  defining the package  131  shown in FIG. 9, the region  60  defining the separation of the laminated layer  20 ,  21  being produced, in this case, at a corner of a package. To this end the groove  40  runs along a long side of the upper tool member  31  so as to form a number of indentations or bays  61  corresponding to the number of packages arranged side by side and having a contour of a lying divided U, whereby the rounded base  62  of the U corresponds to the curvature of one corner of the tray edge. The bays  61  of the groove  40  define corner regions  63  of the sealed region  42  so that, after cutting the cover film in the cutting station, the region  60  of the cover film shown in FIG.  9  and defining the separated region of the laminated layers is formed at one corner of the package. 
     In a further embodiment shown schematically in FIG. 1 a separating station  9 ′ for separating the laminated layers of the cover film, as described above, is arranged behind the sealing station  7  rather than before the sealing station as in the case of the separation station  9 . The position behind the sealing station is advantageous in that the positions of the separated regions need not be taken into account in the sealing station, because these regions are produced after the sealing operation. 
     While the invention has been described in preferred form, it is not limited to the precise nature shown as various modifications may be made without departing from the scope and spirit of the appended claims.