Abstract:
The present invention relates to a thermoform packaging machine as well as to a method for producing a skin pack, comprising the steps of preforming a skin film prior to a sealing station and subjecting it to a further forming step in the sealing station, so that the skin film can wrap around a product protruding far beyond a packaging trough.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This Application claims priority to European Patent Application Number 14173592.8 filed Jun. 24, 2014, to Bernhard Grimm et al., currently pending, the entire disclosure of which is incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to a thermoform packaging machine and method of operating a thermoform packaging machine. 
       BACKGROUND OF THE INVENTION 
       [0003]    DE 102 37 933 A1 discloses a tray sealer used for producing skin packs in which the product protrudes beyond a tray edge. To this end, the skin film is clamped in position on the sealing-tool upper part and drawn into a dome prior to moving the sealing-tool lower part, together with the tray and the product, into contact with the sealing-tool upper part. The skin film does not come into contact with the product until the skinning process takes place. 
         [0004]    EP 2 412 643 A1 shows a thermoform packaging machine with a top-film forming station for sealing a product that protrudes vertically beyond a tray edge with a shrink film and a trough, without the product itself deforming the shrink film by an upward movement prior to the sealing process. The top-film forming station, which is located upstream of the sealing station, ensures that the shrink film is pre-deformed. A clamp chain is arranged on both sides for laterally holding and guiding the deformed shrink film while it is being conveyed from the top-film forming station to the sealing station, and for positioning it precisely onto the trough. 
         [0005]    WO 2004/000650 A1 discloses a thermoform packaging machine for producing a shrink pack, where both the bottom film and the top film are shrink films. The thermoform packaging machine comprises a bottom-film and a top-film forming station, in which each film is thermoformed individually prior to the sealing process, so that a product to be packed can be packed in the sealing station. The shrinking effect of the films, through which the films are caused to wrap tightly around the product, is produced in a shrinking apparatus, which is located downstream of the thermoform packaging machine, through introduction of heat, for example, in a hot water bath. A difference between shrink packs and skin packs is to be seen in that in the case of shrink packs the heat for the shrinking process is supplied only after the packaging process, whereas in the case of skin packs the heat is introduced into the skin film already in the sealing station prior to the sealing process. A similar shrink film packaging machine is disclosed in EP 2 412 643 A1. 
         [0006]    EP 0 270 208 A1 discloses a thermoform packaging machine for producing a skin pack. A skin film used as a top film and a trough, which has been formed in a bottom film and into which a product has been placed, are conveyed together into a first forming station and are clamped on all sides thereof between a forming-tool lower part and a forming-tool upper part for drawing the skin film then upwards into a dome by means of a vacuum and for heating it there. This process results in a minor deformation so that, when the forming-tool lower part and the forming-tool upper part have been opened, the skin film, while being conveyed together with the trough and the product into a downstream sealing station, will not apply pressure to the product as long as the product does not protrude too far upwards beyond the trough. Due to the heat input, the skin film already exhibits an elasticity which is suitable for allowing the skin film to be drawn, in the sealing station after the formation of a chamber through a sealing-tool lower part and a sealing-tool upper part, into a dome by means of a vacuum, the dome comprising a much larger (four times larger) hollow than the dome in the forming-tool upper part. Subsequently, the skin film is heated to an elevated temperature in the dome for producing then, by means of a vacuum between the skin film and the trough, a skin pack in the case of which the skin film wraps tightly around the product and the inner surfaces of the trough, thus sealing the product in an air-tight manner. A larger deformation of the skin film in the forming station is not provided. 
         [0007]    Products protruding vertically beyond the trough edge entail the risk of wrinkle formation in the clamping area during closing of the sealing-tool lower part and the sealing-tool upper part, and this may lead to faulty sealing and leakiness later on. In order to reduce or avoid such wrinkle formation, also the lateral distance from the product to the trough edge has hitherto been increased, when there is an increase in product protrusions. The resultant packages thus have a large trough area with an upwardly protruding product. These packages are, on the one hand, not attractive and, on the other hand, they necessitate the use of a larger amount of top film and bottom film, which, in turn, results in an increase in packaging costs and simultaneously in a reduction of the packaging performance of the thermoform packaging machine, since the number of products that can be processed during one work cycle decreases. In thermoform packaging machines with a multi-lane or multi-row format, the risk of wrinkle formation increases still further. 
       SUMMARY OF THE INVENTION 
       [0008]    It is an object of the present invention to provide a thermoform packaging machine, which reduces film consumption in the production of a skin pack with products exhibiting product protrusions. 
         [0009]    The thermoform packaging machine according to one embodiment the present invention comprises a bottom-film forming station including a number n of mold cavities, n being an integer larger than or equal to 2, for forming n troughs into a bottom film, and a top-film forming station including n evacuable domes, which are each enclosed by a clamping surface and which have a first height between the clamping surface and a hollow (viz. depression), for forming n lids into a top film, which is a skin film The top-film forming station can be arranged upstream of a sealing station in a production direction, the sealing station being configured for sealing the n lids with the n troughs associated therewith, and the sealing station including a sealing-tool upper part comprising n heatable and evacuable domes having a second height. The domes may be configured for allowing the top film to be brought into contact with the respective dome from inside and for heating it to a skin temperature. In one embodiment, the first height amounts to at least 80% of the second height. 
         [0010]    Preforming the skin film in a top-film forming station to a first height amounting to at least 80% of the second height may ensure a pressure-free pulling of the lids over the products, so that the distance between the product placed on the trough and the trough edge can be reduced to, for example, a distance of less than 20 mm, even if products with product protrusions of more than 60 mm are packed with a skin film. By reducing the dimensions of the troughs, the amount of bottom film and top film consumed can be reduced and the efficiency of the machine can be increased, since more packages can be processed during a work cycle in the work stations. In addition, a skin pack with a small distance between the product and the trough edge is more attractive than a skin pack in which the distance is large. Furthermore, the amount of space required for such skin packs on a cooling shelf or in deep freezers can be reduced. 
         [0011]    According to one embodiment, the second height is at least 60 mm, and according to another embodiment at least 80 mm, so that particularly large products and products protruding upwards beyond the trough edge can be packed. 
         [0012]    The skin temperature may be at least 170° C. so as to accomplish air-tight, large-area sealing between the skin film and the trough. 
         [0013]    According to one embodiment, a top-film conveying unit is provided, which is arranged on both sides of the top film, for conveying the lids from the top-film forming station into the sealing station. The lid can thus be transferred synchronously to the trough and the product up to and into the sealing station, and, due to the fact that the skin film is held on both sides until it is clamped in position in the sealing station, transverse stresses in the skin film itself will not result in a formation of wrinkles that may lead to insufficient air tightness. 
         [0014]    The mold cavities have a cavity depth and, in one instance, the second height of the domes in the sealing-tool upper part is at least 5 times, and in another instance, at least 8 times as large as the cavity depth. This allows for the production of an attractive, reduced-volume skin pack with a high product on a kind of plate defined by the trough. 
         [0015]    According to one embodiment, the n mold cavities in the bottom-film forming station each have an opening length in the longitudinal direction of the production direction and an opening width in a direction transverse to the production direction, and the n domes in the top-film forming tool upper part each have a first opening length in the longitudinal direction of the production direction and a first opening width in a direction transverse to the production direction, the first opening length and the first opening width of the domes amounting each to a value between about 80% and about 95% of the opening length and opening width, respectively, of the mold cavity, so that the molded lids will have dimensions that are larger than those of a product to be packed, when they are supplied to the sealing station. The preforming of the lids allows the skin film, due to the small distance at which it is spaced from the inner wall of the domes in the sealing-tool upper part, to be applied rapidly by means of a vacuum and heated, so that the skinning process can be executed subsequently. This reduces the cycle time of the sealing station and increases thus the total packaging output further. 
         [0016]    A method according to one embodiment of the present invention used for operating a thermoform packaging machine for producing a skin pack including a product that protrudes upwards, at least over 50 mm, vertically beyond a trough edge of a trough of a bottom film, the top film being a skin film, comprises the following steps:
       jointly forming a number of n troughs, n being larger than or equal to 2, into a bottom film in a bottom-film forming station during a work cycle,   jointly forming n lids into a top film in a top-film forming station at a first temperature during a work cycle, the lids having then a first height relative to a top-film conveying plane,   jointly supplying the n troughs and the n lids into a sealing station,   bringing the n lids into contact with the inner wall of the domes of the sealing station by means of a vacuum between the n lids and n domes and heating the n lids to a second temperature,   applying the n lids to the respective products and the troughs associated therewith by means of a vacuum generated between the n lids and the n troughs.       
 
         [0022]    The lids can be formed in the top-film forming station such that the lids, while being conveyed from the top-film forming station into the sealing station, approach the associated troughs without applying any pressure to the products of the associated troughs. 
         [0023]    According to one embodiment, the top film is conveyed by means of a top-film conveying unit, for example, by means of two clamp chains arranged on both sides of the top film. 
         [0024]    The first temperature to which the skin film is heated may be a temperature between about 100° C. and about 140° C. so as to cause only a permanent deformation of the skin film such that lids are formed. 
         [0025]    The second temperature to which the skin film is heated may be a temperature between about 170° C. and about 220° C. so as to produce the elasticity of the skin film for the subsequent skinning process. 
         [0026]    Other and further objects of the invention, together with the features of novelty appurtenant thereto, will appear in the course of the following description. 
     
    
     
       DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0027]    In the following, an advantageous embodiment of the present invention will be explained in more detail making reference to a drawing. The individual figures show: 
           [0028]      FIG. 1  is a schematic side view of a thermoform packaging machine according to one embodiment of the present invention; 
           [0029]      FIG. 2   a  is a schematic side view of a bottom-film forming station according to one embodiment of the present invention; 
           [0030]      FIG. 2   b  is a top view of a forming-tool lower part according to one embodiment of the present invention; 
           [0031]      FIG. 3  is a schematic side view of a top-film forming station according to one embodiment of the present invention; 
           [0032]      FIG. 3   b  is a top view of a top-film forming tool upper part according to one embodiment of the present invention; 
           [0033]      FIG. 4   a  is a schematic side view of a sealing station at a closed position according to one embodiment of the present invention; 
           [0034]      FIG. 4   b  is a view from below a sealing-tool upper part according to one embodiment of the present invention; 
           [0035]      FIG. 5  is a schematic side view of the sealing station according to  FIG. 4   a  after application of the skin film in the dome; and 
           [0036]      FIG. 6  is a schematic side view of the sealing station according to  FIG. 4   a  after application of the skin film to the product and the trough. 
       
    
    
       [0037]    Like components are provided with like reference numerals throughout the figures. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0038]    The invention will now be described with reference to the drawing figures, in which like reference numerals refer to like parts throughout. For purposes of clarity in illustrating the characteristics of the present invention, proportional relationships of the elements have not necessarily been maintained in the drawing figures. 
         [0039]    The following detailed description of the invention references specific embodiments in which the invention can be practiced. The embodiments are intended to describe aspects of the invention in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments can be utilized and changes can be made without departing from the scope of the present invention. The present invention is defined by the appended claims and the description is, therefore, not to be taken in a limiting sense and shall not limit the scope of equivalents to which such claims are entitled. 
         [0040]      FIG. 1  shows a thermoform packaging machine  1  according to one embodiment of the present invention in a schematic side view, with a production direction R. In the production direction R, a plurality of work stations, such as a bottom-film forming station  2 , a top-film forming station  3 , a sealing station  4 , a cross cutting station  5  and a longitudinal cutting station  6 , can be provided in succession. In the following, the mode of operation of the thermoform packaging machine  1  according to one embodiment of the present invention will be explained in more detail. 
         [0041]    A bottom film/foil  7 , configured, for example, as a hard film made of plastic, can be unwound from a first film roll  8  and grasped on both sides thereof by a clamp chain, which is not shown in detail, and conveyed into the bottom-film forming station  2 . In the bottom-film forming station  2 , the bottom film  7  may be heated and two troughs  9 , which, relative to the drawing plane, are shown as arranged one behind the other and thus in two lanes (i.e., side by side when seen in the production direction R), are formed into the bottom film  7 . Along an infeed line  10 , which is arranged between the bottom-film forming station  2  and the sealing station  4 , products  50  are placed into the troughs  9 , the products  50  having a height of more than 50 mm. 
         [0042]    A top film  11 , configured as a skin film, can be unwound from a second film roll  12  and conveyed by means of a top-film conveying unit  13 , which may be arranged on both sides, into the top-film forming station  3 , where it can be heated to a first temperature of approximately 120° C., for example, so as to form therein two lids  14 , which, relative to the drawing plane, are arranged one behind the other and thus in two lanes. During the conveying movement of the lids  14  by means of the top-film conveying unit  13  towards the sealing station  4 , the lids  14  are moved closer to the troughs  9  and the bottom film  7  and, in the course of this movement, they may be pulled over the products  50  without any pressure being applied to the products  50 , since the lids  14  are formed such that their dimensions are larger than the dimensions of the products  50 . 
         [0043]    The top-film conveying unit  13 , for example, in the form of two clamp chains  13  arranged on both sides of the top film  11 , may fulfill here, on the one hand, the function of precisely positioning the lids  14  above and onto the products  50  and may be moved in synchronism with the clamp chain for the bottom film  7  On the other hand, the top-film conveying unit  13  may fulfill the function of laterally holding the skin film  11  and the lids  14 , respectively, during the conveying movement and in the interior of the sealing tool  4 . A distortion of and wrinkle formation in the skin film  11 , which may be caused by possibly occurring transverse stresses within the skin film  11 , can be prevented in this way. 
         [0044]    In the sealing station  4 , the lids  14  may be formed, after the formation of a chamber  15  through a sealing-tool upper part  16  and a sealing-tool lower part  17 , by means of a vacuum generated between the lids  14  and the domes  18 , which are shown in more detail in  FIG. 3   a , onto the inner wall of the domes  18  in the sealing-tool upper part  16 , and heated to a skin temperature of approximately 180° C., for example, so that they will have an adequate elasticity for the subsequent skinning process. At the same time, a further vacuum is applied in the interior of the package  19 , viz. between the lids  14  and the troughs  9 . Through this vacuum and by venting the sealing-tool upper part  16  to ambient pressure, the elastic lid  14  will fit snugly to the product  50  as well as to the trough  9 , the skin film  11 , i.e., the lids  14 , and the trough  9  establishing a large-area, air-tight sealing during this skinning process. This package  19  can be referred to as skin pack, since the product  50  placed on or rather in the trough  9  is sealed in an air-tight manner onto the bottom film  7  or trough  9  by means of a film  11  which wraps tightly around the product  50 , similar to a second skin. 
         [0045]    While moving on in the production direction R, the packages  19  conveyed side by side on two lanes may be separated from one another by means of the cross cutting station  5  and the longitudinal cutting station  6  and conveyed out of the thermoform packaging machine  1  via a conveyor belt  20 . 
         [0046]    In  FIG. 2   a , the bottom-film forming station  2  is shown in more detail. It can comprise a forming-tool upper part  21  located above the bottom film  7  and may be configured as a heating plate for heating the bottom film  7 , prior to the forming step, to a temperature that is required for such forming. A forming-tool lower part  22  movable in the direction of the arrow and arranged below the bottom film  7  comprises two mold cavities  23  in which the heated bottom film  7  can be formed into troughs  9  by means of a vacuum from below and/or pressurized air from above. The trough  9  and the mold cavity  23  have a trough/cavity depth T oriented perpendicular to the bottom film  7  In addition, the trough  9  itself has, after the forming process, a trough edge  25 . 
         [0047]      FIG. 2   b  shows the forming-tool lower part  22  with the two mold cavities  23  in a top view. The two mold cavities  23  may each have an upwardly directed opening  24 , each of the openings  24  having, in turn, an opening length L extending parallel to the conveying direction R and an opening width B extending transversely thereto. 
         [0048]    Referring to  FIG. 3   a , the top-film forming station  3  will be explained in more detail. The top-film forming station  3  can comprise a top-film forming tool lower part  26  configured as a heating plate and a top-film forming tool upper part  27  movable in the direction of the arrow and comprising two domes  28  and a clamping surface  29  for clamping the skin film  11  between the top-film forming tool lower part  26  and the top-film forming tool upper part  27 . The domes  28  have a first height D 1  defined by the maximum depth of a hollow  35  relative to the plane of the clamping surface  29 . When the top-film forming station  3  is at a closed operating position, the skin film  11  can be clamped between the top-film forming tool lower part  26  and the top-film forming tool upper part  27 , heated by the top-film forming tool lower part  26  and drawn into the domes  28  by means of a vacuum. After opening of the top-film forming station  3 , a lid  14  has been formed in the skin film  11 . 
         [0049]      FIG. 3   b  shows, from below, a sectional view of the clamping surface  29  of the top-film forming tool upper part  27 . The two domes  28  can each be provided with an opening  28   a  having, in turn, an opening length L 1  extending parallel to the conveying direction R 1  of the skin film and an opening width B 1  extending transversely thereto. These dimensions correspond to a very large extent to the complementary dimensions of the lids  14 , since shrinking effects may occur. The skin film  11  is conveyed via a top-film conveying unit  13  shown in  FIG. 3   a  in the form of clamp chains  13  arranged on both sides. 
         [0050]      FIG. 4  shows the sealing station  4  in a condition in which the sealing-tool upper part  16  and the sealing-tool lower part  17  are closed, the products  50  being enclosed by the lids  14  and the troughs  9  and the lids  14  as well as the troughs  9  being circumferentially clamped in position between the sealing-tool upper part  16  and the sealing-tool lower part  17 . In the defined chamber  15  the lids  14  may be sucked onto the inner wall  32  of the dome  18  of the sealing-tool upper part  16  through a vacuum V applied to the sealing-tool upper part  16 , and fit then to the inner wall  32 . The sealing-tool upper part  16  can comprise a heating  33  by means of which the lids  14  are heated to the skin temperature. 
         [0051]    Analogously to  FIG. 3   b , the sealing-tool upper part  16  may comprise, like the top-film forming tool upper part  27 , two domes  18  having an opening length L 2  extending parallel to the production direction R and an opening width B 2  extending transversely thereto as well as a second height D 2 . This can be seen in  FIG. 4   b , in which the domes  18  are shown from below. Reference numeral  31  stands here for the opening  18  of each dome  18 . Each of the three dimensions L 2 , B 2  and D 2  of the domes  18  of the sealing-tool upper part  16  exceeds the dimensions L 1 , B 1  and D 1  of the domes  28  of the top-film forming tool upper part  27  by approximately 5% to 20% in size. One of the reasons for this is that it can be advantageous to provide a distance A between two lids  14  following one another in the conveying direction R, so that the sealing-tool upper part  16  can be moved to its closed position, as shown in  FIG. 4 , without a lid  14  located directly upstream of the sealing station  4  being excessively negatively influenced by radiation heat of the sealing-tool upper part  16 , even though, at this position, the lid  14  has already been pulled over the product  50  to a very large extent. 
         [0052]      FIG. 5  shows the phase in which the lids  14  contact the domes  18  from inside and are heated by means of the heating  33  to a second temperature, i.e., the so-called skin temperature, whereas the space between the troughs  9  and the lids  14  is evacuated by means of a vacuum V. 
         [0053]      FIG. 6  shows the situation after venting of the sealing-tool upper part  16  and after the lids  14 , i.e., the skin film  11 , have/has been applied to the product  50  and to the trough  9 . 
         [0054]    From the foregoing, it will be seen that this invention is one well adapted to attain all the ends and objects hereinabove set forth together with other advantages which are obvious and which are inherent to the structure. It will be understood that certain features and sub combinations are of utility and may be employed without reference to other features and sub combinations. This is contemplated by and is within the scope of the claims. Since many possible embodiments of the invention may be made without departing from the scope thereof, it is also to be understood that all matters herein set forth or shown in the accompanying drawings are to be interpreted as illustrative and not limiting. 
         [0055]    The constructions and methods described above and illustrated in the drawings are presented by way of example only and are not intended to limit the concepts and principles of the present invention. Thus, there has been shown and described several embodiments of a novel invention. As is evident from the foregoing description, certain aspects of the present invention are not limited by the particular details of the examples illustrated herein, and it is therefore contemplated that other modifications and applications, or equivalents thereof, will occur to those skilled in the art. The terms “having” and “including” and similar terms as used in the foregoing specification are used in the sense of “optional” or “may include” and not as “required”. Many changes, modifications, variations and other uses and applications of the present construction will, however, become apparent to those skilled in the art after considering the specification and the accompanying drawings. All such changes, modifications, variations and other uses and applications which do not depart from the spirit and scope of the invention are deemed to be covered by the invention which is limited only by the claims which follow.