Abstract:
A can, and device and method for producing same, includes two circular end elements forming a base and lid. The can further includes a sleeve which has fold lines forming edges, the can sleeve having a circular cross-sectional area at both ends and a polygonal-sectional area in its central region. The polygonal cross-sectional area in the central region is at most decagonal.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional of U.S. patent application Ser. No. 12/779,273, filed May 13, 2010, which is a continuation of U.S. patent application Ser. No. 10/512,242, filed Oct. 22, 2004, which is a National Phase of International Application Serial No. PCT/EP03/03921, filed Apr. 15, 2003 and also claims the benefit of Switzerland Application No. 0706/02, filed Apr. 24 2002, each of which is incorporated by reference in their entirety. 
    
    
     FIELD OF INVENTION 
     The invention relates to the field of cans with fold lines and devices for their production. 
     BACKGROUND OF THE ART 
     It is known that the transport of empty cans to the place of filling and the stocking of empty cans at the place of filling entail a significant effort. This logistical effort can be dramatically reduced if the can is manufactured at the place of filling. 
     The publication DE-A1-31 10 697 discloses a packaging container in which a three-dimensional sleeve is shaped from a packaging material blank at the filling plant. An accuracy of the butt joint or of the overlap in the region of the two open ends of the sleeve, which accuracy is required for the subsequent tightness of the container, can be achieved only with difficulty; on the other hand, cylindrical cans having a sleeve obtained from a flat cardboard sheet do not have the stable grip required by the user. 
     WO 98/03403 discloses polygonal cans having externally prefabricated can sleeves. However, this can concept which is advantageous in particular for medium-sized and smaller series has not become established in practice. Firstly, polygonal end pieces are expensive to process and to seal. 
     A drum-shaped container having a multiplicity of vertical fold lines in the sleeve is described in U.S. Pat. No. 3,712,530. Although such a container fulfils the desire for a small volume of the collapsed sleeve, it uses very complicated lid constructions to enable the drum to be rolled and does not improve the rigidity compared with a sleeve free of fold lines. 
     A further possibility of a drum-like container having a polygonal cross-section and circular base and lid is described in U.S. Pat. No. 2,989,219, the object of the invention disclosed therein being primarily to provide a safe lid construction suitable for large containers. 
     U.S. Pat. No. 5,778,639 in turn describes a method and a device by means of which a round base can be imposed on packaging having a noncircular cross-section. 
     SUMMARY OF THE INVENTION 
     It is the object of the invention to eliminate the deficiencies of the prior art. Thus, it is intended, inter alia, to propose a can in which the cost for the transport and the storage of the empty cans can be kept low, the use of commercial round lids is permitted and the rigidity or stability of grip of the sleeve of the filled can is improved. This object is achieved for the first time in a surprising manner. 
     Further advantageous and alternative developments of the invention, in particular a method and a device for the production of the can according to the invention, are described herein. 
     When the term circular is used in association with the invention, it is also intended to be understood as meaning shapes deviating slightly from the circular shape, for example ellipses having semiaxes differing only slightly from one another. 
     Cans having circular end pieces have a number of advantages. Firstly, standardized, circular end elements or sealing elements, but especially existing sealing machines, can be used. Secondly, it is known in principle that a circular opening is in principle technically less complicated to seal. 
     When a can is gripped, compressive forces directed substantially perpendicularly to the can axis are exerted on the can sleeve, and the can has to withstand said forces. However, if the can consists of two circular end pieces and a sleeve which is produced from a piece of a flat paper and/or cardboard. 
     In a manner known per se, on perpendicular application of a compressive force, a sheet-like member no longer has dimensional stability above a certain magnitude of the force. Thus, for example, bends or dents occur. In contrast, when a sheet-like member is provided with edges, its dimensional stability improves considerably. Bends and dents occur only at substantially greater compressive forces. 
     It is also known that the bending energy required for bending a sheet-like member produced in particular from a paper and/or cardboard composite is substantially reduced by providing a fold line. The bending of the member therefore preferably takes place at the fold line, with the result that an edge is automatically formed in the region of the fold line. 
     The invention is based on the discovery that a sleeve which is closed all round and which is produced from a paper and/or cardboard composite and connects two circular end elements to one another automatically forms edges if the can sleeve is provided with fold lines perpendicular to the circumferential direction. The individual segments between the fold lines arch inwards owing to the circular cross-sectional area imposed by the end elements at both ends, and the edges formed by the fold lines arch outwards. Consequently, the stability of the can, in particular the region where it is gripped, is decisively improved. 
     With a can according to the invention, the conventional wall thicknesses of a sheet-like paper and/or cardboard composite can be reduced by more than half. A light, environmentally friendly and stable can which involves little energy consumption and can be produced on conventional standardized machines with standardized lids is permitted. The greatly reduced wall thicknesses also have advantages in the case of optional gas-tight joining of the can sleeve to the two end elements. 
     The improved rigidity or stability of grip of the can according to the invention could be confirmed by measurements. It was found that, in the case of a standard can size having a height of 120 mm and a diameter of 73 mm, a maximum increase can be achieved in the case of hexagonal and octagonal can sleeves, while both in the case of can sleeves having only 2 or 4 fold lines and in the case of those having 10 or 12 fold lines and hence edges, the force-displacement curves are already close to the round can. 
     In the method according to the invention, for example, a polygonally prefolded can sleeve closed all round is drawn onto a circular intermediate shaping mandrel. As a result, the shape of a cylindrical sleeve is imposed on the polygonally prefolded can sleeve. The end can be connected to a standardized circular end element without problems on a conventional machine. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is described in more detail below with reference to the figures of the drawing, using a hexagonal can sleeve as an example. Identical parts in different embodiments which perform the same functions are provided below with identical designations and reference numerals. In the drawing: 
         FIG. 1  shows a plan view of the lid placed on the opening of a hexagonal sleeve which has been folded out; 
         FIGS. 2 a  and  b    each show a longitudinal section along the line  1 ′- 1 ″ and F′-F″, respectively, from  FIG. 1 ; 
         FIG. 3  shows a cylindrical intermediate shaping mandrel perpendicularly above an aligned can sleeve having a hexagonal base shape, in oblique view; 
         FIG. 4  shows the can sleeve drawn onto the intermediate shaping mandrel, above a sealing means, in oblique view; 
         FIG. 5  shows a sheet-like sealing element above the can sleeve positioned between two intermediate shaping jaws, in oblique view; 
         FIG. 6  shows a second end element and 
         FIG. 7  shows a can sleeve kept circular by a flange shaping device, in side view; 
         FIGS. 8 to 11  show force-displacement curves for the pressure on can sleeves having a polygonal cross-section. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     According to  FIG. 1 , a commercial, circular end element  4 , e.g. a lid, having the radius R, rests concentrically on an unfolded, hexagonal can sleeve  2 . The edge length K of the sleeve is 2Rπ/6. If the sleeve  2  is made circular at its opening, for example by applying an external circular shape (intermediate shaping jaws  6  in  FIG. 5 ), so that the lid  4  can be inserted and/or, for example, rolled over the sleeve edge ( FIG. 4 , lower part), the edges  1  in the region of the lid  4  are drawn inwards when the can is closed. 
     This inevitably causes the edges  1  to project slightly outwards in the middle of the can height between the two lids  4 ,  5 , i.e. to be dished slightly outwards in their contour, axially relative to the can ( FIG. 2 a   ). In contrast, the six prism surfaces F of the sleeve  2  in the region of the two lids  4 ,  5  are each pressed outwards, which inevitably results in the surfaces F in the middle of the can height between the two lids  4 ,  5  projecting slightly inwards, i.e. arching slightly inwards in their contour, axially relative to the can, and hence being prestressed ( FIG. 2 b   ). Both result in an unexpectedly great increase in the rigidity and stability of grip of the can. 
       FIG. 3  shows an intermediate shaping mandrel  3 , which is positioned perpendicularly above a can sleeve  2 . The prefabricated can sleeve  2  which is closed all round and provided with fold lines is removed from a stack of flattened can sleeves and set up as a hexagonal prism by pushing together two opposite fold edges. In this embodiment, the can sleeve  2  has six fold lines  14  oriented parallel to the longitudinal axis of the can sleeve  2 . When the can sleeve  2  has been set up, the fold lines  14  form edges  1  over their entire length. Two edges of the piece of the paper and/or cardboard composite of which the can sleeve  2  consists are adjoined so as to overlap one another in the overlap region  16 . The overlap region  16  is compressed to give the single layer thickness of the paper and/or cardboard composite. A prefabricated can sleeve could, however, equally well have two abutting edges which are joined to one another in a manner known per se by means of a joining strip. 
     Here, the intermediate shaping mandrel  3  has a cylindrical base shape. That end face of the intermediate shaping mandrel  3  which points towards the can sleeve  2  has a feed bevel  13  for the can sleeve  2 . Here, a shaping means  7 , by means of which a can sleeve  2  can optionally be preshaped for further steps of the method, is arranged at the bottom of the intermediate mandrel  3 . 
     The can sleeve  2  is drawn onto the intermediate shaping mandrel  3  by pressing the latter against the can sleeve  3 . Intermediate shaping jaws  6  shown in  FIG. 5  support the can sleeve  2  laterally in the end region at the other end. 
       FIG. 4  shows the can sleeve from  FIG. 3  drawn onto the intermediate shaping mandrel  3 , above a sealing means  9  equipped with a first end element, e.g. lid,  4 . The can sleeve  2  drawn onto the intermediate shaping mandrel  3  then likewise has a cylindrical shape. The fold lines  14 , too, rest against the intermediate shaping mandrel  3  and no longer form edges. 
     Here, the sealing means  9  is in the form of a conventional rolling means. In addition to a holder not visible in  FIG. 4  and intended for the first end element  4 , the rolling means has two pairs  10  of rollers, of which only the pair of rollers which presses from outside against the end piece  4  is visible. The now cylindrical can sleeve  2  is inserted into the circular gap of the first end element  4 . By turning the intermediate shaping mandrel  3  and the holder relative to the pairs  10  of rollers, the end element  4  is joined to the can sleeve  2  with a tight seal. The can sleeve  2  now joined at one end to the first end element  4  can now be pulled off again from the sealing means  9 . 
       FIG. 5  shows the can sleeve  2  which is joined at one end to the first end element  4  and is positioned at the other end between two intermediate shaping jaws  6 , under an expanding punch  17  known per se. Here, the expanding punch  17  is equipped with a sealing element  11 —for example in the form of an aluminium membrane. 
     After the can has been filled, the can sleeve  2  is converted into an intermediate cylindrical shape at the other end in a region adjacent to the internal opening by moving together the two intermediate shaping jaws  6 . Thereafter, the sealing element  11  is inserted into the region by means of the expanding punch  17  and is heat-sealed tightly to the inner surface  12  of the can sleeve  2 . 
       FIG. 6  shows a second end element  5  in the form of an inserted lid. The inserted lid can be mounted at the other end, for example after the heat-sealing of the sealing element  11  on the can sleeve  2 . The intermediate shaping jaws  6  can optionally have been removed again from the can sleeve  2  since the sealed sealing element  11  is sufficient to produce a circular cross-sectional area of the can sleeve  2 . The imposing of the circular cross-sectional area can be supported by an inserted lid. 
     The can which has now been filled and provided with both end elements  4  and  5  has, with the exception of the two end regions of the can sleeve  2 , one edge each along the six fold lines  14 , the contour of which edge becomes steadily more pronounced towards the central region. Here, the can sleeve has a hexagonal cross-sectional area of the central region. In the central region of the can sleeve  2 —i.e. in the region in which as a rule it is also gripped—the can according to the invention therefore also has the maximum stability of grip. 
       FIG. 7  shows an alternative processing step which is carried out at the other end on the can sleeve  2 . The can sleeve  2  is provided with a circular flange by a flange shaping means  8  which has a shaping punch  18  and two counterparts  19 . The flange shaping means  8  can be heated in a manner known per se. 
       FIGS. 8 to 11  show force-displacement diagrams under external compressive load, perpendicular to the can axis, on cardboard cans of 73 mm diameter and 120 mm height, with a wall thickness of the cardboard sleeve of 0.4 mm and a fold radius of 2 mm. In each case, the force F in Newton is plotted along the ordinate and the indentation depth s in mm is plotted along the abscissa. The curves are denoted in each case by numbers from 2 to 10, indicating the number of fold lines (edges). 
     In  FIGS. 8 and 9 , the curves of the mean values of in each case  8  measurements of the pressure on the can at the height in the middle of the can are plotted, in particular in each case on the edge in  FIG. 8  and in the middle of the respective prism surfaces in  FIG. 9 . Pressure was applied using a punch of 20 mm diameter, starting from an initial pressure of 1 N. It is found that hexagonal and octagonal can sleeves show by far the greatest resistance to deformation; in contrast, decagonal can sleeves on the one hand and biangular or tetragonal can sleeves on the other hand, which in each case already have a greater resemblance to a cylindrical can sleeve, retract to a considerable extent. 
     A similar result is obtained if—as shown in  FIG. 10 —the values of the pressure on the edge are measured at ¼ or at ¾ of the can height or if—as shown in  FIG. 11 —the values of the pressure on the middle of the edges are measured using a punch of 10 mm diameter and have an initial pressure of only 0.1 N. 
     The values are further improved if the can sleeve has an internal circumference which is 0.5 to 1 mm smaller than the lid circumference coming into contact with it, since the can sleeve then has to be expanded slightly at its opening and is prestressed thereby.