Patent Publication Number: US-2011061344-A1

Title: Packaging machine with several heater elements

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims foreign priority benefits under 35 U.S.C. §119(a)-(d) to German patent application number DE 102009041563.7, filed Sep. 15, 2009, which is incorporated by reference in its entirety. 
     TECHNICAL FIELD 
     The present disclosure relates to a packaging machine and method for heating of a film to be deformed. 
     BACKGROUND 
     From the state of the art, deep-draw packaging machines are known which have a moulding station in which a film is heated by means of a heating plate such that it can then be formed into a cavity in the lower part of the mould tool. The process must take place very quickly, because on one hand due to the generally cooler compressed air, which is initially present over the complete surface of the upper part of the mould tool, the film is cooled, and on the other hand in the upper regions of the side walls and in the region of the bottom of the mould cavity in the lower part of the mould tool the film can become so cold during the moulding process that subsequent deformation of the film leads to an undesirable or too thin wall thickness, or adequate forming in the whole region of the cavity is no longer possible, because the film has cooled below the temperature required for plastic deformation. 
     Above all, with large deep-drawing depths and small radii in the region of the cavity bottom, there is a great risk that the wall thickness of the film after deformation is too different and these cavities must no longer be used for quality reasons and have to be extracted. 
     In order to be able to individually heat the film before the moulding process, zone heaters can be employed in which the heating plate has been manufactured according to the cavity shape so that different regions of the film are heated differently in order to obtain a uniform wall thickness of the film in the subsequent process. This embodiment is constructively very elaborate and extremely inflexible, because it is linked to the package shape. 
     From JP 55095519, U.S. Pat. No. 5,280,434, DE 102006045327 and GB 1405753 heating devices are known with which a heating surface has a large number of heater elements which can be controlled individually to be able to generate different temperatures on the individual heater elements. The known embodiments are not suitable for also fitting to a moulding stamp nor to moulding surfaces of a lower part of a mould tool such as side walls and bottom surface in order to generate different temperatures in these regions and thus to be able to positively influence the moulding process. 
     In the application DE 102009030508.4, which has not yet been published, a further alternative technique is described. Here, in a film to be deformed, a spatially inhomogeneous temperature distribution is produced so that the film is optimally prepared according to the requirements of the moulding process. This is preferably however realised by a simple continuously heated heating plate and special properties of the film. 
     A further disadvantage of the state of the art is a continuously heated heating plate with a simultaneously cooled upper part of the mould tool. In order to be able to apply the required heat energy to the film for moulding the film and simultaneously to be able to maintain the general processing times in the deep-draw packaging machine short for a high machine capacity, the heating plate is continuously at the necessary temperature, which is transferred to the film at the moment of feeding or heating the film for an appropriate time in the moulding station. These high temperatures of over 100° C. require cooling of the upper part of the mould tool above the heating plate to provide protection against injuring the operating personnel through burning by touching the relatively freely accessible upper part of the mould tool. 
     This high energy storage in the heating plate also has disadvantages in the heating up phase, for example after a tool change, and in a waiting period before renewed setting up in the region of the moulding station due to the necessity of the heating plate having to cool down. 
     From DE 102005043026 a reference is known from the field of household appliances to a possible use of a thick-film heater for heating up water. Here, the economical manufacture and the low space requirement should offer advantages. 
     SUMMARY 
     An object of the present disclosure is to provide a device which is suitable for heating a film individually with different temperature levels taking into account in this respect the energy consumption required for the moulding process and eliminating the disadvantages of the state of the art. 
     For the purpose of the disclosure, “thick-film heating” is taken to mean heating in which the heater elements (without substrate or carrier) have a thickness of at least 1 μm. The term “heater element” is used synonymously with “heating circuit”. 
     The embodiment of the heating surface according to this disclosure has the advantage that due to the low proportion of material the thick-film heaters can be heated quickly to the required temperature and are able to cool down to the ambient temperature just as quickly, because there is no accumulation of heat. In conjunction with a controller this facilitates a temporally limited switch-on period of the thick-film heater elements during which the film is to be heated, and thus low energy consumption. 
     Due to a uniform distribution of a plurality of thick-film heaters, a high flexibility with regard to different package shapes is also produced. 
     The plurality of heater elements, preferably distributed on the heating surface uniformly or in matrix form, can heat a film individually through the individual control of the heater elements such that different regions or areas of the film can be heated to various levels. This leads to different temperature levels, which can be produced appropriately to the subsequent moulding process in order to obtain the desired wall thicknesses and deformations of the moulded cavity during or after the moulding process. 
     Above all with moulding processes with large deep-drawing depths, small radii and thin films the packaging machine according to the invention presents a solution, which offers a more favourable solution in terms of energy than the state of the art and which ensures increased process reliability and thus attainment of the quality of the packaging cavity. 
     For the usual necessity of being able to produce different cavity shapes on one and the same deep-draw packaging machine the heating device according to the invention is found to be an economical solution, because no elaborate components have to be made available specially for the moulding process nor set up during a change of product, and because the individually produced temperature levels, which are necessary for the film, can be saved in the controller and recalled. This can lead to the shortest changeover times. Also changes to the different temperature levels are possible via the controller in order to be able to match varying boundary conditions in the moulding process. These boundary conditions may be, for example, shorter operating cycles or varying film thicknesses. 
     The thick-film technology facilitates integration of a plurality of heater elements in a common layer, which can be fitted on a carrier plate and thus be formed as a heating plate. Preferably, a flat arrangement of this nature can be fitted in an upper part of the mould tool or can preheat the films as a preheater above and/or below the film before the moulding station if the time available in the moulding station is not sufficient. 
     It is conceivable to fit the heater elements individually and to realise them individually or collectively connected to the controller. On a display assigned to the controller the temperature levels can be individually entered, saved and/or specified and fed into the packaging machine from outside in dependence of the heater elements present. 
     During the moulding process, with the initial contact of the film with a stamp or the surfaces of the moulding cavity in the lower part of the mould tool, rapid cooling of the film may occur in these partial regions. The consequence of this may be that the film in these partial regions can no longer extend sufficiently and the wall thickness of the film in the remaining regions reduces excessively. This undesired behaviour during the moulding process can be countered with the packaging machine according to the invention, if in addition or alternatively heating surfaces are fitted at least partially on the stamp or on the walls and/or bottom of the moulding cavity. Thus, the film can be maintained deformable also in these partial regions through a specific temperature level for as long as is necessary for the moulding process. 
     The embodiment as a thick-film heater offers the advantage of cooling the heater elements in the shortest time through cooling in the region of the moulding cavity, for example by means of cooling water channels, such that the heater elements assume the temperature of the cooled moulding cavity or of the lower part of the mould tool and thus this hardly delays the cooling process of the deep-drawn film. 
     The use of the packaging machine according to the invention is particularly practicable in an intermittently operating deep-draw packaging machine, because here the time for an operational cycle, also of the sealing station in the manufacture of packaging under a modified atmosphere, is influenced and in this respect an unwanted dwell time of the film in the moulding station and heating device can occur. The described problem can be avoided by the thick-film heaters which are switched off during this period. 
     The packaging machine according to the invention has a further positive effect during the use and processing of plastic films, which are mostly multi-layered and in line with their properties should therefore be heated very individually for the moulding process in order to be able to obtain the desired results. 
     The methodical sequence according to the invention with an intermittently operating deep-draw packaging machine with at least one heating surface, which has a plurality of preferably uniformly distributed thick-film heaters, whereby a controller can individually control these thick-film heaters, primarily has advantages when heating a film to be deformed to different temperature levels. 
     At the start of an operational cycle the moulding station of the deep-draw packaging machine is fed with the film in the form of a strip-shaped material by means of a feed system via gripper chains arranged on both sides. Then the moulding station is closed and a closed chamber is created. The controller can meanwhile, or also only after the closure of the moulding station, control and heat up the heater elements which are realised as thick-film heater elements. This control can be implemented according to a program saved in the memory of the controller or can occur through entries fed into the controller by the operating personnel. 
     In order to introduce the heat energy into the film, the film is preferably drawn onto the heater elements by a negative pressure in the upper part of the mould tool, so that the film is located uniformly on the heater elements. The film heats up accordingly and the desired individual temperature levels arise within the film. 
     The controller switches off the heater elements once the film moulding process starts and the film is deformed into the lower part of the mould tool by means of compressed air in the upper part of the mould tool and/or negative pressure in the lower part of the mould tool. 
     The process is terminated when the film has cooled to a “stable” temperature range in which it is no longer deformable. 
     Then the moulding station opens and with the removal of the moulded cavities the next section of the film is introduced into the moulding station. 
     Due to a possible cycle lengthened by the sealing station, there may be waiting periods, for example during cooling of the film in the lower part of the mould tool and/or on opening the moulding station. 
     In the following, an advantageous embodiment of the disclosure is explained in more detail with reference to the below drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic side view of a packaging machine according to the disclosure in the form of a deep-draw packaging machine; 
         FIG. 2  is a schematic vertical section through the moulding station with preheating station of the packaging machine shown in  FIG. 1  in opened position; 
         FIG. 3   a  is a schematic view of the moulding station shown in  FIG. 2  in closed position with the moulding process starting; 
         FIG. 3   b  is a schematic view of the moulding station shown in  FIG. 2  in closed position during the moulding process; 
         FIG. 3   c  is a schematic view of the moulding station shown in  FIG. 2  in closed position with the moulding process finished; 
         FIG. 3   d  is a schematic view of the moulding station shown in  FIG. 2  in open position and with the moulding process finished; 
         FIG. 4   a  is a schematic plan view of the film, the heater elements and the various heating regions; 
         FIG. 4   b  is a graphical representation of the temperature distribution in the film in section IV-IV in  FIG. 4   a;    
         FIG. 5  is a schematic view of the moulding station shown in  FIG. 2  in closed position in a variant with heater elements in the moulding cavity; and 
         FIG. 6  is a schematic view of the moulding station shown in  FIG. 2  in closed position in a variant with heater elements on a stamp. 
     
    
    
     DETAILED DESCRIPTION 
     In the figures identical components are designated with the same reference numerals throughout. 
       FIG. 1  shows a schematic view of a packaging machine  1  according to the disclosure in the form of a deep-draw packaging machine. This deep-draw packaging machine  1  has a moulding station  2 , a sealing station  3 , a transverse cutting device  4  and a longitudinal cutting device  5  which are arranged in this order in the working direction R on a machine frame  6 . At the input end on the machine frame  6  there is a feed roll  7  from which a film  8  is pulled off. In the region of the sealing station  3  a material store  9  is provided from which a lid film  10  is pulled off. At the output end on the packaging machine a removal device  13  in the form of a conveyor belt is provided with which finished, singled-out packages can be taken away. Furthermore, the packaging machine  1  has a feed device, which is not shown and which grips the film  8  to transport it further in the working direction R during each main operating cycle. The feed device can, for example, be realised using transport chains arranged on both sides. 
     In the illustrated embodiment the moulding station  2  is formed as a deep-drawing station with which cavities  14  can be formed in the film  8  by deep drawing. Here, the moulding station  2  can be formed such that several cavities can be formed adjacent to one another in the direction perpendicular to the working direction R. In the working direction R behind the moulding station  2  an insertion section  15  is provided in which the cavities  14  formed in the film  8  are filled with the product  16 . 
     The sealing station  3  has a closable chamber  17  in which the atmosphere in the cavities  14  can be replaced, for example, by gas flushing with a replacement gas or with a gas mixture before sealing. 
     The transverse cutting device  4  is formed as a punch which parts the film  8  and the lid film  10  in a direction transverse to the working direction R between adjacent cavities  14 . Here, the transverse cutting device  4  operates such that the film  8  is not parted over the complete width, but rather is not parted at least in a marginal region. This facilitates controlled further transport by the feed device. 
     In the illustrated embodiment the longitudinal cutting device  5  is formed as a cutter arrangement with which the film  8  and the lid film  10  are parted between adjacent cavities  14  and on the side edge of the film  8  so that singled-out packages are available behind the longitudinal cutting device  5 . 
     The packaging machine  1  also has a controller  18 . It has the task of controlling and monitoring the processes running in the packaging machine  1 . A display device  19  with the operating elements  20  is used for visualising or influencing the process sequences in the packaging machine  1  for, respectively by, an operator. 
     The general principle of operation of the packaging machine  1  is briefly described in the following. 
     The film  8  is pulled off the feed roll  7  and transported through the feed device into the moulding station  2 . In the moulding station  2  cavities  14  are formed in the film  8  by deep drawing. The cavities  14  are transported further together with the surrounding region of the film  8  in a main operating cycle to the insertion section  15  in which they are filled with the product  16 . 
     Then the filled cavities  14  are transported into the sealing station  3  by the feed device in the main operating cycle together with the surrounding region of the film  8 . The lid film  10  is transported further with the feeding movement of the film  8  after a process of sealing onto the film  8 . Here the lid film  10  is pulled from the material store  9 . By sealing the lid film  10  onto the cavities  14  closed packages are created which are transported singled-out into the following cutting processes  4  and  5  and transported out of the packaging machine by means of the removal device  13 . 
       FIG. 2  illustrates a moulding station  2  with a preceding preheating station  21  in a variant with a preheater  22  arranged above and also a preheater  23  arranged below. This configuration is practicable primarily with thick films  8 , because the time duration for the heating of the film  8  only in the moulding station  2  is so large that the resulting time of an operational cycle can extend unnecessarily and thus the capacity of the packaging machine  1  can be reduced in terms of the production of packages per minute. 
     The moulding station  2  comprises a lower part of the mould tool  24  with the moulding cavities  25 . The lower part of the mould tool  24  is implemented for movement upwards and downwards via a lifting gear which is not illustrated. Furthermore, the moulding station  2  comprises an upper part of the mould tool  26  in which a heating plate  27  is fitted to the underside. On the heating plate  27  a plurality of uniformly distributed heater elements  28  are arranged, implemented as thick-film heating. The individual heater elements  28  can be controlled via the controller  18 , and the visualisation or the adaptation of the individual temperature levels of the heater elements  28  can be realised via the display device  19 . 
     The heating of the film  8  can occur with the moulding station  2  still open, during the closing process or only when the moulding station  2  is closed. 
     In  FIG. 3   a  the lower part of the mould tool  24  has been moved up and now forms a closed chamber  17  with the upper part of the mould tool  26 . At the same time the film  8  is clamped all around at the edge by means of a seal  11  and by the lower part of the mould tool  24  and the upper part of the mould tool  26  and is tightly closed. Once the film  8  has been heated individually to the desired temperature by means of the individual heater elements  28 , the controller  18  switches the heater elements  28  off and the moulding process starts in the form of deep drawing by overpressure above the film  8  and/or negative pressure below the film  8 . Here, the film  8  initially forms a type of sack due to the pressure difference and the forces acting uniformly on the film  8 . 
     In  FIG. 3   b  the film  8  has reached the bottom  29  of the moulding cavity  25  and also contacts the moulding cavity  25  in the upper region of the side walls  30 . These surfaces have a very much lower temperature than the film  8  so that here the film  8  is cooled. In order that the film  8  does not cool down below the temperature for the plastic deformation in the moulding time remaining, these regions  29  and  30  of the film  8  are heated to a higher temperature level than the other regions. 
     In the further course of the moulding process the film  8  is extended further until the film  8  lies completely in the moulding cavity  25 , as illustrated in  FIG. 3   c . When the film  8  has cooled down so much that the moulded cavity  14  is stable, the moulding station  2  opens with the lower part of the mould tool  24  moving downwards, as illustrated in  FIG. 3   d.    
     In the plan view  FIG. 4   a  shows the heating surface of the heating plate  27  with grid or matrix shaped, closely contacting heater elements  28  and four regions  31  to  34 . The graph in  FIG. 4   b  shows the four different temperature levels  31 ′ to  34 ′ distributed over the heating surface, which arise due to the different temperatures of the heater elements  28  in the regions  31  to  34 . 
     In  FIG. 5  a variant of the packaging machine  1  according to the present disclosure is shown in which, in addition to the heating surface on the upper part of the mould tool  26 , further heating surfaces  35  and  36  are fitted to the walls and bottom of the moulding cavity  25 . 
     As another variant, an embodiment of stamp deformation is illustrated in  FIG. 6 . On the stamp  37  the surfaces which are in contact with the film  8  have heater elements  28  fitted which ensure individual temperature levels in these regions. 
     The heating surfaces of the packaging machine according to the invention are not restricted to the illustrated embodiments, but rather other combinations or regions can be implemented in the moulding station with heater elements. 
     For controlling individual temperature levels it is also conceivable that with many small heater elements  28  they are not all controlled individually, but rather in groups by the controller  18 . 
     The film  8  can comprise a plastic film, another thermoformable material or a combination of materials. 
     The packaging machine  1  according to the invention also comprises a moulding station  2  for a lid film in order to individually heat it and deform it before sealing with the film  8 . 
     While 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.