Abstract:
The invention relates to a method for closing already preformed and separated containers ( 19 ), for example trays, with a lid foil ( 24 ) in a closing station ( 3 ). The invention is characterized in that a deep-drawable foil is used as lid foil ( 24 ), that the lid foil ( 24 ) is deep-drawn in a forming means ( 23 ) of the packaging machine ( 1 ), and that the deep-drawing of the lid foil ( 24 ) is accomplished before the containers ( 19 ) are closed with the lid foil ( 24 ). The invention also relates to a packaging machine ( 1 ) suited for carrying out such a method.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims foreign priority benefits under 35 U.S.C. §119(a)-(d) to German patent application number DE 102009020892.5, filed May 13, 2009, which is hereby incorporated by reference in its entirety. 
       TECHNICAL FIELD 
       [0002]    The present invention relates to a method for closing containers, as well as to a packaging machine for carrying out such a method. 
       BACKGROUND 
       [0003]    Packaging machines for closing already preformed and separated containers are known in the form of so-called tray sealers, for example from DE 10 2006 018 327 A1. Such machines are fed with already preformed and separated trays which are usually stacked and stocked after they have been formed. The containers are individually removed from the stock and placed onto a conveying belt where they are filled with a product from above. In the conventional tray sealer, a sealing foil is subsequently applied onto the trays that are open to the top which closes as well as seals the trays. 
         [0004]    In conventional tray sealers, the sealing foil must not be stretched by the product, as otherwise the sealing foil might tear off. Consequently, the trays must be comparably deep to prevent the products from projecting over the edge of the trays. This excessive height of the trays, however, also involves drawbacks. On the one hand, this leads to an increase in the required amount of material and costs of a package. On the other hand, less preformed or filled trays can be accommodated per volume, so that costs increase for the stock-keeping of the empty trays as well as for the distribution of the filled and closed trays. 
       SUMMARY 
       [0005]    It is an object of the present disclosure to overcome these drawbacks with structural means that are as simple as possible. 
         [0006]    An embodiment of the present disclosure involves using a deep-drawable foil for closing already preformed and separated containers, and the foil is deep-drawn in a forming means or device of a packaging machine before the containers are closed with the lid foil. This deep-drawing offers the advantage that the package can be much better adapted to the respective product than before, although the containers are already preformed. In particular, products projecting over the container edge can also be accommodated in the containers, without the lid foil stretching over the product. Moreover, there are also esthetic advantages as, in contrast to conventional tray sealers, the upper side of each package does no longer have to be flat, but can be structured. 
         [0007]    The lid foil may be heated upstream of and/or in the forming device to permit deep-drawing. The preheating of the lid foil upstream of the forming device can accelerate deep-drawing and reduce superfluous waiting times of other components of the packaging machine. 
         [0008]    It is conceivable to deep-draw the lid foil towards the side of the lid foil facing the container during closing altogether or at least in sections. In this manner, a lid section which projects into the interior of the container is formed in the lid foil. This is in particular suited for products or regions of a product which are situated at a lower level than the edge of the container. 
         [0009]    As an alternative or in addition, it is conceivable to deep-draw the lid foil towards the side of the lid foil facing away from the container during closing altogether or at least in sections. In this manner, a dome shaped lid section is formed which projects upwards over the container edge and permits the accommodation of projecting products without the lid foil stretching over the product. 
         [0010]    By the method according to the present disclosure, in the deep-drawing process, at least one concave and/or one convex section can be formed on the side of the lid foil facing the container during closing. They can facilitate the placement of complementary formed regions of the products against the lid to prevent, for example, shifting of the products in the containers. 
         [0011]    The forming device can be provided separately from the closing station. The complete packaging machine, however, becomes more compact and the method thereby less complex, if deep-drawing is carried out within the closing station itself. 
         [0012]    As lid foil, a flexible foil or a hard foil could be used, if they can be deep-drawn in a suited manner. 
         [0013]    Depending on the product, it can be advantageous to use a multilayer foil as lid foil. For example, a combination of an outer layer impermeable to oxygen and an inner layer permeable to oxygen would be conceivable to permit oxygen to flow around the products. 
         [0014]    In one variant of the invention, the lid foil or the lid section formed in it, respectively, is only placed onto the respective containers by a form fit in the form of a “slip lid”. The lid section can, for example, snap in at an edge of the container to securely connect the lid to the container. 
         [0015]    In addition or as an alternative, it is possible for the lid foil to be sealed onto the containers, in particular if the interior of the container is to be hermetically sealed. 
         [0016]    If the lid foil is sealed to the containers, the transport of the closed containers connected with the lid foil out of the closing station can cause further lid foil to be drawn behind, which is used for closing following containers. In this manner, one could do without a separate conveyor device for the lid foil. 
         [0017]    The present disclosure also relates to a packaging machine for carrying out a method according to the present disclosure. The packaging machine comprises a forming means or device for deep-drawing the deep-drawable lid foil. 
         [0018]    It is appropriate for the forming device to comprise an exchangeable insert which determines the deformation of the lid foil to a lid section. This insert can be replaced if it is worn down, or if a different shape of the lids for the containers is to be produced. 
         [0019]    Mainly in comparably thick hard foils, the pulling force acting on the lid foil only by the movement of the closed containers still connected to the lid foil might not be sufficient. In this case, it is advantageous to provide, in addition to a transport means for the containers, such as a conveyor belt or any other suitable transport device, a separate conveying means for the lid foil, for example a clamp chain arranged on both sides which can also be used to stretch the lid foil laterally, or any other suitable conveyor device. 
         [0020]    The packaging machine according to the present disclosure may have a tool for placing and/or sealing the lid foil onto the containers. In this tool, the actual closing of the containers is thus accomplished. 
         [0021]    The tool itself can comprise a lower tool and an upper tool which can be moved relative to each other. For example, they can open for receiving the unclosed containers and reduce the space between them for closing and possibly evacuating and/or gassing the containers. 
         [0022]    It is appropriate if the lower tool and the upper tool can be spaced apart by the relative movement at least far enough to correspond to the sum of the height of a container and the height of a lid section of the lid foil. In this manner, the closing tool also permits the accommodation of containers in which the product and the lid project over the edge of the container. 
         [0023]    In the following, two advantageous embodiments of the present disclosure are illustrated more in detail with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]      FIG. 1  is a perspective view of a packaging machine according to the present disclosure; 
           [0025]      FIGS. 2 to 8  show schematic vertical sections through a first embodiment of the packaging machine in different steps of a method according to the present disclosure; and 
           [0026]      FIGS. 9 to 15  show a second embodiment of the packaging machine in different steps of the method according to the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    In the Figures, equal and similar components are provided with the same reference numerals. 
         [0028]      FIG. 1  shows a first embodiment of a packaging machine  1  according to the invention in a perspective view. This embodiment is a tray sealer. The packaging machine  1  has a machine frame  2  on which a closing station  3  is arranged for closing as well as possibly evacuating, gassing and/or sealing supplied, tray-shaped containers as well as for cutting a lid foil used for closing. The closing station  3  is located under a cover  4  that can be opened. 
         [0029]    The packaging machine  1  furthermore has a feed belt  5  for feeding the containers, a discharge belt  6  for carrying away the closed containers, a foil feed roller  7  for taking up and feeding a roll of a lid foil, a foil stretching means  8  for stretching the lid foil, as well as a foil residue winder  9  for winding up the foil residues that remain after sealing. A display  10  permits the operator of the packaging machine  1  to check and control the operation of the packaging machine  1 . To this end, operational controls  11  can be provided at the display  10 , for example operator panels or switches to influence the operation of the packaging machine  1 . 
         [0030]      FIG. 2  shows, in a first embodiment of the packaging machine  1  according to the invention, a vertical section through the closing station  3  in a schematic view. The closing station  3  has a tool  12  which in turn comprises an upper tool  13  and a lower tool  14 . The upper tool  13  and the lower tool  14  can be moved in the vertical direction relative to each other. The upper and lower tools  13 ,  14  can form a closed chamber  15  between themselves in a closed state (see  FIG. 3 ). 
         [0031]    A lifting table  16  is provided at the lower tool  14  which can be traveled in the vertical direction via a lifting rod  17  independent of the lower tool  14 . The lifting table  16  forms a recess or cavity  18  for receiving a prefabricated, tray-shaped container  19 . This container  19  can consist, for example, of hard plastics. After preforming, a plurality of containers  19  are stacked and stocked in this manner. They can be individually removed from this stock and placed onto the feed belt  5  of the packaging machine  1  to be filled there. 
         [0032]    One can see in  FIG. 2  that an edge  20  of the container rests on an edge of the lifting table  16  or cavity  18 . One can also see that the container  19  is filled with a product  21  which projects upwards beyond the level formed by the edge  20  of the container  19 . 
         [0033]    In the present embodiment, the upper tool  13  has a more complex design. It has on its part three tool components which can be traveled relatively to each other in the vertical direction within the upper tool  13  independent of each other as well as independent of the outer wall  22  of the upper tool  13 . The innermost tool component is a forming means  23  for forming a lid section in the single- or multilayer lid foil  24  advance by the foil feed roller  7 . In the present embodiment, the forming means  23  may comprise any suitable forming device, such as a forming mold or tool having a concave design on a surface  25  facing the container  19 . The forming means  23  can have vacuum lines (not shown) to create a vacuum between the surface  25  and the lid foil  24 . 
         [0034]    Above the forming means  23 , a sealing plate  26  is arranged which has sealing edges  27  projecting downwards. The sealing edges  27  are shaped such that they can contact the edge  20  of the container  19  when the sealing plate  26  is lowered. 
         [0035]    A cutting means  28  is provided above the sealing plate  26 , between the sealing plate  26  and the outer wall  22  of the upper tool  13 . The cutting means  28  may comprise any suitable cutting device, such as a movable cutting tool having cutting edges  29  projecting downwards which are configured for cutting the lid foil  24  in two. The tool  12  can moreover have means for evacuating and/or gassing the chamber  15  formed between the upper and the lower tool  13 ,  14 . For example, the tool  12  may be connected to a vacuum pump, or any other suitable evacuating device, and/or a gas supply system. 
         [0036]    The deep-drawable (e.g., thermoplastic) lid foil  24  passes over a first deflection roller  30  and is there deflected such that it traverses the interior of the tool  12  essentially in parallel to the level formed by the edge  20  of the container  19 . The residual sections of the lid foil  24  remaining after the containers  19  have been closed and the lid sections punched out pass over a second deflection roller  31  to a residual foil winder  9  to be accumulated there. Between the foil feed roller  7  and the tool  12 , a foil stretching means  8 , which is not represented in  FIG. 2  for a better overview, can be moreover provided. The foil stretching means  8  may be any suitable device, such as a movable plate or a system of rotatable drums or cylinders that includes one or more cylinders that are movable toward and away from another cylinder. 
         [0037]    Between the foil feed roller  7  and the first deflection roller  30 , a heating means or a preheating means  32  (if a further heating step is performed), respectively, is moreover provided. The heating means  32  can be a heating plate which is heated, for example, via a thermal fluid or an electric heating medium. The heating means  32  is used to heat a given section  33  of the lid foil  24  to a temperature which permits thermoplastic forming of the lid foil  24  during a deep-drawing operation. 
         [0038]    With reference to  FIGS. 2 to 8 , a method according to the present disclosure and the operating sequence of the packaging machine  1 , respectively, will now be illustrated. 
         [0039]      FIG. 2  shows the tool  12  of the packaging machine  1  in a state in which a tray  19  filled with a product  21  has been inserted into the cavity  18  of the lifting table  16  and guided into the interior of the tool  12 . For this purpose, the upper and the lower tools  13 ,  14  can be removed from each other to such an extent that the distance A between the lower edge of the upper tool  13  and the upper edge of the lower tool  14  is larger than the sum of the height of the container  19  and the projecting part of the product  21 , to permit in this manner the introduction of the filled container  19  into the tool  12 . A certain section  33  of the lid foil  24  is heated under the heating means  32 . 
         [0040]      FIG. 3  shows the tool  12  in a state in which first the lid foil  24  has been conveyed far enough for the heated section  33  to be located underneath the forming means  23 . At this time, the feed of the lid foil  24  is stopped. One can see in  FIG. 3  that the upper tool  13  and the lower tool  14  move towards each other until they clamp the lid foil  24  between their edges and form a closed chamber  15  between themselves. As the feed of the lid foil  24  is stopped, now a further section  33 ′ of the lid foil can be brought to the temperature required for forming under or in the heating means  32 . 
         [0041]    It could already be seen in  FIG. 3  that the forming means  23  contacts the lid foil  24  when the upper tool  13  is lowered. Arrows  34  in  FIG. 4  indicate that now a vacuum is created at the surface  25  of the forming means  23  by suited provisions. In connection with the contact between the forming means  23  and the lid foil  24 , this vacuum takes care that the heated section  33  of the lid foil  24  is pulled against the concave surface  25  of the forming means  23  and in this manner deep-drawn to form a lid section  35 . 
         [0042]    The lid section  35  is represented in  FIG. 5 . It has a shape which is complementary to the edge  20  of the container  19  on the outer surface. On the side facing the product  21 , the lid section  35  is concave. 
         [0043]      FIG. 6  shows the tool  12  in a state in which—starting from the state in FIG.  5 —the lifting table  16  was lifted until the edge  20  of the container  19  came into contact with the lid foil  24 . This movement of the lifting table  16  is indicated by arrow  36 . Simultaneously—as indicated by arrow  37 —the sealing plate  26  was lowered until its sealing edges  27  came into contact with the lid foil  24  from above. In this state, the lid foil  24  is now sealed onto the edge  20  of the container  19 . 
         [0044]    Subsequently or simultaneously with the sealing, the cutting means  28  is lowered—as shown in FIG.  7 —, so that its cutting edges  29  cut out the lid foil  24  all around the closed container  19 . This movement of the cutting means  28  is indicated by arrow  38 . 
         [0045]    In  FIG. 8 , the tool  12  is opened. This is done by moving the lower tool  14  and the lifting table  16  downwards and the upper tool  13  with the forming means  23 , the sealing plate  26  and the cutting means  28  upwards. The lid section  35  is firmly connected to the rest of the container  19  by the sealing and remains at the container  19 . The filled container  19  can now be removed from the tool  12 . At the same time, the lid foil  24  can be transported forwards, while the rest of the lid foil  24  that remains during cutting is winding up on the foil residue winder  9 . The closing process can now be performed in the same manner for a subsequent container. 
         [0046]      FIG. 9  shows a second embodiment of a packaging machine  1  according to the present disclosure. It differs from the first embodiment in that the forming means  23  for forming the lid sections is now no longer provided in the closing tool  12 , but in the region of the heating means  32 . Apart from that, the upper tool  13  and the lower tool  14  of the closing tool  12  remain unchanged. In particular, the upper tool  13  still comprises a sealing plate  26  and a cutting means  28 , while the lower tool  14  still comprises a lifting table  16 . 
         [0047]    In the second embodiment, the forming means  23  comprises a first forming half  39  and a second forming half  40 . As indicated by the arrows  41 , the two forming halves  39 ,  40  can be moved relative to each other perpendicular to the plane of the lid foil  24 , so that they can close around the lid foil  24  or can release the lid foil  24 , respectively. 
         [0048]    In the first forming half  39 , an exchangeable inset  42  is provided. Its surface  43  facing the lid foil  24  defines the shape of the lid section  35  if the section of the lid foil  24  heated by the heating means  32  in the opposite second forming half  40  is pulled closer by applying a vacuum to the surface  43  of the inset  42  to deep-draw the lid foil  24 . 
         [0049]      FIGS. 9 to 15  show various steps of the method according to the present disclosure during the operation of the packaging machine  1  according to the second embodiment.  FIG. 9  shows the packaging machine  1  in a state in which a fresh section of the lid foil  24  has been brought into the forming means  23 . 
         [0050]    In  FIG. 10 , the two forming halves  39 ,  40  of the forming means  23  have been closed. Arrows  44  indicate that a vacuum is created at the inset  42  of the forming means to place the lid foil  24  in this region against the inset  42  of the first forming half  39  and to form a lid section  35  in this manner. The inset  42  can be exchanged if lid sections  35  having a different shape are to be produced. 
         [0051]      FIG. 11  shows the state of the packaging machine  1  after the lid foil  24  has been deep-drawn in the forming means  23 . The lid foil  24  now has a lid section  35 . 
         [0052]    In  FIG. 12 , the two forming halves  39 ,  40  have been removed from each other. The opening  45  formed between them now must be large enough—at least in the exiting direction out of the forming means  23 —to let the domed lid section  35  pass. 
         [0053]    Between the state in  FIG. 12  and the state in  FIG. 13 , the lid foil  24  has been moved into the conveying direction  45  far enough for the lid section  35  now to be positioned within the closing tool  12  over the container  19  to be closed. The first deflection roller  30  here only lies against an outer edge of the lid foil  24 , so that it does not collide with the lid section  35  in the central region of the lid foil  24 . 
         [0054]      FIG. 14  shows the packaging machine  1  in a state in which the closing tool  12  has been closed by moving the upper tool  13  and the lower tool  14  towards each other. A contact between the sealing edges  27  of the sealing plate  26  and the edge  20  of the container  19 , that is close by due to the lifting of the lifting table  16 , permits to seal the lid foil  24  to the container  19 . Simultaneously or subsequently, the cutting means  28  has been lowered to cut out the closed container. The forming means  23  has simultaneously closed around a new section of the lid foil  24  to form a further lid section  35 . 
         [0055]    In  FIG. 15 , the forming means  23  as well as the closing tool  12  have been opened. The closed container  19  can now be removed from the tool  12 , and the cycle can start anew. 
         [0056]    Starting from the two embodiments described in detail, a method according to the present disclosure and a packaging machine according to the present disclosure can be modified in many ways. It is, for example, conceivable for the lid sections  35  not to be sealed to the edge  20  of the container  19 , but to only be placed onto the container  19  by a form fit in the form of slip lids. It is moreover possible to impart any arbitrary shape to the lid section  35 . In the first embodiment, too, the forming means  23  can have an exchangeable inset  42 . Though it is not shown, several lid sections  35  can be manufactured one after or one next to the other in the forming means  23 , and several containers  19  can be simultaneously closed in the closing station  3 . 
         [0057]    While exemplary embodiments of the invention have been illustrated and described, 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. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.