Abstract:
The disclosure relates to a method of preparing a web of flexible material for production of receptacles for packaging. The method comprises the steps of feeding a web of flexible material past a succession of stations in which operations are carried out on the web including defining blanks for receptacles having walls and tabs by creating fold lines in the web, and then laminating a film of heat-sealable plastics materials to a face of the web of the flexible material. The film of heat-sealable plastics provides a heat-sealable surface on the web for bonding tabs of each blank together to form seams between adjacent walls whereby the blanks, when severed from the web, can be erected to form receptacles having openings to receive items to be packaged.

Description:
This application is a 371 of PCT International Application No. PCT/GB07/03273, filed Aug. 29, 2007, which claims priority to United Kingdom Application No. 06 16995.7, filed Aug. 29, 2006, the contents of such applications being incorporated by reference herein. 
     FIELD 
     This invention relates to methods of preparing web material for production of receptacles for food or other products and also to receptacles per se. 
     BACKGROUND 
     Our EP-B-1032531 discloses a container for foodstuff formed from a one piece blank of card and having isosceles triangular shaped end walls connected by quadrilateral side walls to form a triangular prism shaped container, one side wall of the container being hinged along the base of one of the end walls to provide a lid for the container, with a window in the lid to permit the contents of the container to be viewed. Blanks for forming the containers are preformed with fold lines and windows. Selected walls of the blanks have tabs which are glued to the inside faces of adjacent walls to form prism shaped containers. Fold lines are formed in the triangular walls of the container and lid to enable the container to be folded flat. 
     Our UK-A-2397573 discloses a carton for a diagonally cut sandwich or like foodstuff formed from a blank of card and having triangular end walls connected by quadrilateral side walls to form a triangular prism-shaped container. One side wall of the container is hinged to one of the end walls of the container to provide an opening for insertion/removal of foodstuff and to form a lid for closing the opening. The edges of the opening have out-turned flanges, and the periphery of the lid overlies the out-turned flanges encircling the opening when the lid is in the closed position whereby the lid can be bonded to the flanges to seal the contents of the carton. 
     SUMMARY 
     It is an object of the invention to provide a method of forming receptacles for food and other products and a receptacle per se which can be produced more efficiently. 
     This invention provides a method of preparing a web of flexible material for production of receptacles for food and the like, the method comprising the steps of feeding a web of flexible material past a succession of stations in which operations are carried out on the web including defining blanks for receptacles having walls and tabs by creating fold lines in the web and then laminating a film of heat-sealable plastics materials to one face of the web of the flexible material to provide a heat-sealable surface for bonding the tabs of each blank together to form seams between adjacent walls whereby the blanks, when severed from the web, can be erected to form receptacles. 
     In one method according to the invention the fold lines may be formed by at least partially cutting through or scoring the web of flexible material. Alternatively the fold lines may be defined by continuous partial cuts in the web or by skip cut or discontinuous cut lines through the web. 
     Preferably the seams formed by the bonded tabs are external to the receptacle. 
     It is a further preferred that a portion of at least one wall of each blank delineated in the web is cut out to form a window for the receptacle to be formed from the blank and over which the heat-sealable plastic extends. 
     In the latter method the blank may include a wall which provides a lid for the receptacle and the window may be formed in the lid. 
     In any of the above methods the laminated web may be formed onto a reel for subsequent processing into containers. 
     In a preferred form of the method each blank delineated on the web has a centre line about which it is symmetrical with respective walls, part walls and tabs disposed on either side of the centre line and the laminated web is folded about the centre line of the blanks to bring the surfaces of the plastic material including the tabs on either side of the centre line together and the tabs are then heat-sealed together to form the seams in the blank which allow the blank to be erected to form a receptacle. 
     In the latter method the folded web may be cut round the folded profile of each blank to separate the blanks in folded form from the web for subsequent erection on traditional or custom built flow wrapping lines. 
     In any of the above methods each blank delineated on the web may have triangular side walls and rectangular end walls to enable a prism shaped receptacle to be erected from the blank. 
     In the latter case one of the end walls may be hinged to another wall to form an openable lid to the receptacle. 
     More specifically each blank may include a first complete triangular side wall having end walls hinged along each edge thereof and triangular half walls hinged to respective end walls with tabs on the respective half walls and adjacent end walls which, when the blank is folded can be heat-sealed together to form seams between the respective end walls of the half walls to form a second complete triangular wall in the erected receptacle. 
     Furthermore said first triangular wall of the blank delineated on the web may be an isosceles triangle having an included angle which is a right angle or thereabouts, the triangle being aligned on the web with a centre line which bisects said right angle extending lengthwise of the web, the base of the triangle having a quadrilateral end wall connected by a fold line thereto through which said centre line passes and further end walls being connected by fold lines to the sides of the triangle, the half walls which make up the second triangular wall be located on the sides of the end walls opposite the first triangular wall and the further end walls and half walls having at their adjacent edges which can be heat-sealed together to form seams which support the walls when the carton is erected from the blanks. 
     In any of the above methods the web of flexible material may be a web of paper, card or carton board. The paper weight may be in the range 20 gsm to 250 gsm and possibly up to 500 gsm. Preferably paper in the range 80 gsm to 200 gsm is used. Most food grade papers can be used including uncoated, single coated, double coated and natural coloured papers. The film of transparent plastics with which the paper is laminated may be any suitable heat sealable film including PP, Polyester, PLA and Polyethylene. 
     The film may have an anti-misting coating to prevent fogging of the window. One particularly suitable material for the receptacle consists of a 170 gsm uncoated or double coated bleached paper and a 20 micron PLA with an anti-misting coating. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following is a description of some specific embodiments of the invention, reference being made to the accompanying drawings in which: 
         FIG. 1  is a perspective view looking at the back of a triangular prism shaped non-hermetically sealed sandwich pack shown with a front lid closed; 
         FIG. 2  is a front view of the pack with the lid open and the sides bowed outwardly to receive a sandwich stack; 
         FIG. 3  is a similar view to  FIG. 2  with the pack sides straight; 
         FIG. 4  shows the blank from which the pack is formed; 
         FIG. 5  is a diagrammatic view of the preparation stages of a web from which blanks for the packs are to be subsequently produced; 
         FIG. 6  is a similar view to  FIG. 4  showing further steps in the preparation of the web and production of blanks from the web for forming into sandwich packs; 
         FIG. 7  is an illustration of a folded blank formed by the process; 
         FIG. 8  is an illustration of a stack of carton blanks formed by the process; 
         FIGS. 9 to 13  are similar views to  FIGS. 1 to 4  of an hermetically sealable sandwich pack; 
         FIGS. 14 to 19  show a number of different blank forms for the pack of  FIGS. 9 to 13 ; 
         FIGS. 20 and 21  show a blank for a four sided container and the completed container; and 
         FIGS. 22 to 24  show blanks for an elongate rectangular cross-section container for a baguette or the like and completed containers. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1 to 3  show a completed pack produced by the method of the invention and will be described firstly followed by a description of the blank produced by the method of the invention and finally the method of producing the blank will be described. 
     Referring therefore to  FIGS. 1 to 3 , there is shown a pack indicated generally at  10  intended for holding a food item or items and in particular for holding a cut sandwich stack for display at a retail outlet. The pack is of prism shaped form having an isosceles triangle shaped cross-section and comprises triangular side walls  11  and  12  which are of isosceles triangular form  13  having equal length and a hypotenuse  14 . The included angle between the equal lengths side walls of each triangular side wall is approximately 90°. 
     The triangular side walls  11  and  12  are connected by generally rectangular bottom and end walls  15 , 16  which at the corner of the pack have out-turned flanges  17  which are bonded together to form a seam at the apex of the pack as described later. The end walls may taper slightly towards the apex if the pack is to be machine filled to enable the pack to be supported in a trough shaped holder and readily removed from the holder. 
     The triangular side wall  11  of the pack is formed in two parts  11   a ,  11   b  divided at the perpendicular bisector of the triangle  18  to the hypotenuse  14  and which are also of isosceles triangular form. The respective triangular parts have out-turned flanges  19  which are bonded together to form a seam as described later. The other triangular side wall  12  of the pack is formed in one piece and, as best seen in  FIGS. 2 and 3 , has a lid  20  for the pack hinged to the hypotenuse edge  14  of the wall  12 . The lid  20  has a large rectangular window  21  to enable the contents of the pack to be viewed. 
     To avoid the cut edge of the sandwich stack from contacting and possibly smearing the window, the lid, together with the walls  15  and  16  of the stack have pairs of integral in-turned flanges  22   a ,  22   b  which fold inwardly on closing the lid to overlie one another and overlie the end of the stack of sandwiches to be placed in the body of the pack  10  to hold the cut edge of the sandwiches away from the window  21 . 
     The blank for the carton  10  which is illustrated in  FIG. 4  of the drawings will now be described. The triangular side wall  11 , the two parts of the triangular side wall  12 , the bottom wall  15 , back wall  16  and front wall provided by the lid  20  can all be readily seen. Fold lines are formed between the triangular side wall  11  and the bottom and back walls  15  and  16 . Similarly fold lines  24  are formed between the triangular parts  12   a  and the bottom and back walls. 
     Fold lines  25  are formed between the tabs  19  and the bottom and back walls. Fold lines  26  are formed between the tabs  17  and the triangular side wall parts  12   a . Fold lines  26 ,  27  are formed between the tabs  22  and the back/bottom walls and lid  20 . The lid  20  has a fold line  29  between the lid and the hypotenuse  14  of the triangular side wall  11  and the other side of the lid has a fold line  30  between the lid and the tab  23 . 
     The fold lines may be formed by creasing the paper/card from which the blank is formed or by scoring or cutting part way through the blank or by skip or discontinuous cut lines to enable the folds to be readily created when erecting the carton. 
     Reference is now made to  FIG. 5  of the drawings which shows the first stage in the production of the blanks from which the packs are to be formed. A reel of a web of material from which the packs are to be formed is indicated at  30 . The material may be a relatively heavy grade paper or a soft card. For example a paper weight in the range 20 to 25 gsm may be used although 80 to 200 gsm is preferred. Food grade papers can be used including both coated (single or double-sided), uncoated papers and natural papers are suitable as are recycled papers. The reel is mounted on a roller  31  to enable the web to be unrolled and fed to a plurality of stations where different treatments are carried out on the web. 
     Blanks are formed in succession along the length of the web with the line of symmetry of each blank extending lengthwise along the middle of the web. 
     In the first operation the web  32  passes between several (e.g. seven) pairs of upper and lower rollers  33  which apply print colours and varnishes. The upper rollers are print or varnish applying rollers and the lower rollers support the web from below in the region where it is engaged by the upper rollers. Initial upper rollers print text and graphical information on the upper surface of the web and subsequent rollers apply a coating or coatings of varnish to protect the print. The web then passes between upper and lower cutter rollers  34 , 35  on which there are cutting blades designed to form continuous lines of partial sever or discontinuous lines of full sever through the web where the subsequent blank is to be folded between adjacent walls of the blank or between adjacent tabs and walls of the blank. The cutters on the roller  35  also form the window  21  in the lid  20  by forming a rectangular cut fully through the material of the lid and then removing the rectangular piece within the rectangular cut line to form a window. 
     The web then passes to a roller  36  and an A-frame web guide (not shown) which is positioned to turn the web over so that the previously upwardly facing printed surface now faces downwardly. The web then passes between a further pair of drive rollers  37 , 38 . 
     A web of thin plastics transparent film  39  is fed from a roll  40  to the non-printed upper surface of the web  32  to overlie the web. The film is pressed against the upper surface of the web between upper and lower rolls  41  and  42  to laminate the film to the paper web. The rolls are followed by a dryer  43 , 44  after which the laminated web is rolled onto a reel  45 . The transparent film may be polylactic acid (cellulose) or PE (polyethylene—OPP). It will be understood that forming the various lines of cut including those for the window before the laminating of the transparent film to the web avoids the risk of inadvertently slitting the film when cutting the web although it is envisaged that the web could be formed with the cut lines after lamination if accurate cutting can be performed. 
     A reel of the thus formed laminated web is illustrated at  46  and the laminated and pre-cut web is transported to a further apparatus for completing the blanks. The reel  46  of web is folded along its centre line by an “A” frame (not shown) bringing the faces of the plastics film into contact with one another. The blanks delineated on the web are thus folded about their respective centre lines (see  FIG. 6 ) bringing the tabs  17  on respective triangular walls  12   a  together and the respective tabs  19  on end walls  15  and  16  together. The folded web is then passed between heated rollers  50 , 51  which have shaped dies to engage the tab areas  17  and  19  to heat and press the tab areas together to form a heat seal between the tab areas. 
     The web  32  then passes to a further pair of cutter rollers  55 , 56  having shaped cutters to cut a folded blank from the web to separate the blank which can be erected into a pack form as shown in  FIGS. 2 and 3 . 
     An example of a folded blank produced by the method is shown in  FIG. 7  and a stack of the folded blanks is shown in  FIG. 8 . 
     The folded blanks can readily be unfolded into the condition shown in  FIG. 2  with the triangular side walls splayed outwardly to allow easy insertion or withdrawal of a sandwich stack from the carton. When the lid is closed and the flanges  22  are turned in to overlie the ends of the stack, the stack is kept away from the film forming the window in the lid of the carton. A feature of the carton is that the seams  17  and  19  formed between the back and bottom walls and triangular walls of the side  12  lie on the outer side of the carton to form an externally viewable feature of the design. 
     Suitable heavy grade papers, soft card or carton board materials for forming the receptacles may have weights in the region of 20 to 350 gsm and upwards. 
     The packs described above have integral lids for closing the packs but the packs are not hermetically sealed. Where the packs are to be used for sandwiches or similar food items, the expected shelf life of the pack is two to three hours. Where a longer shelf life of two to three days is required, the pack must be sealed and preferably flushed with a gas such as a nitrogen based gas mixture. The present invention is equally applicable to sealed pack designs which may, for example, be of the form described and illustrated in our British Patent Publication No. 2397573. Various arrangements of such packs will now be described. 
     A carton which can be hermetically sealed is shown in  FIGS. 11 to 13 . Like parts have been allotted the same reference numerals as those used in the previously described embodiments. In this case the opening to the container has out-turned flanges  22   b  along the edges adjacent the lid  20  and out-turned flanges  22   c  along the edge of the opening opposite the lid. The flanges  22   b ,  22   c  are turned outwardly to receive the lid  20  which overlies the flanges to be heat-sealed to the flanges through the plastic laminate coating on the web material which is shown in greyscale. The blank from which the carton is formed is illustrated in  FIGS. 9 and 10 . As can be seen, the blanks has V shaped notches  60  between the adjacent flanges  22   b  and  22   c . These are formed in the blank material at the same time as the fold lines and prior to the laminating phase described above. Similar V shaped notches  61  are formed between the lid  20  and flanges  22   b  and finally the flange  22   c  on one of the part walls  22   a  which makes up one of the triangular side walls of the receptacle is cutaway as indicated at  62  so that when the flanges  22   c  on each of the part walls  12   a  and  12   b  are brought together, the flanges  22   c  form a substantially continuous surface to be sealed to the lid  20 . 
     As indicated above, the notches  60 ,  61  and cutaway  62  are preformed in the web prior to laminating the plastics film. Thus when the film is laminated to the web and the blank cut around the outline of the blank, the film bridges the notches  60  and  61  as indicated at  62  and  63  with a flap  64  being formed where the flange  22   c  is cutaway at  62  to ensure that an hermetic seal is formed between the lid and flanges  22   b ,  22   c  when the carton is closed by heating-sealing the lid to the flanges. 
       FIG. 14  shows a similar blank except that the cutaway on one of the flanges  22   a  is angled as indicated a  62   a  to align with a similarly angled cutaway  62   b  on the other flange  22   c  to form a continuous surface to seal with the lid. 
       FIG. 15  shows a further variation in which the cutaway in one of the flanges  22   c  has a stepped form as indicated at  66  to align with a similarly stepped form  67  on the other of the flanges  22   c . A further difference in the blank of  FIG. 15  is that the V shaped notches  60 ,  61  of the blank of  FIGS. 9 and 10  are replaced by simple straight cut lines  70 ,  71 . 
       FIG. 16  shows a further variant in the blank form in which the tab  17  on one wall part  12   a  is not cutaway between the flange portions  52   c  but has a projecting element  66  shaped to align with the cutaway end  66  on the adjacent flange  22   c.    
       FIG. 17  shows a variant of the arrangement shown in  FIG. 16  in which the tabs  17  taper outwardly from the apex of the container to the opening to provide a greater overlap of material where the wall portions  12   a  and  12   b  are joined together to increase the stiffness of the wall. 
       FIG. 18  shows a further variant of the arrangement in which corner tabs  70  are formed on the lid with corresponding corner tabs  71  at the junctions of tabs  22   b  and  22   c  and a peelable transparent heat-sealable plastics material is laminated to the blank. The tabs  70 ,  71  provide a convenient grip for the lid and container to enable the lid to be peeled open. 
       FIG. 19  shows a blank in which the out-turned flanges  22   b  and  22   c  have parallel lines of “Concora” indicated engraved in the surface of the web before the plastics sheet is laminated to the web to enable the lid to be torn open by tearing the lid between the “Concora” lines. The “Concora” arrangement is described and illustrated in greater detail in our British Patent Application No. 2397573. 
       FIGS. 20 and 21  illustrate a four sided receptable formed from a blank in a similar manner to that described above and erected using a tray former. 
       FIGS. 22 and 24  illustrate an elongate rectangular cross-section container for a baguette or similar elongate food item and the blank from which the container is formed. 
     The web from which the pack is formed is created as described above by printing any matter required on the web and then creating fold lines by scoring or skip cutting the web and cutting fully through the web to form the window. The web is subsequently laminated to a sheet of plastics film so that wide areas of the web can be heat-sealed together and so that the window through the web is covered by the film. 
     Referring now to  FIGS. 22 and 23  of the drawings, the web of paper/soft card is formed with a pair of parallel lines  80 ,  81  to define the top surface  82  for the container, with parallel fold lines  83 ,  84  to define side walls  85  and  86  for the container and with parallel cut lines  87  and  88  to define the bottom wall of the container  89 ,  90  with out-turned tabs  91 ,  92  which are heat-sealed together as described below to create the container a food item. 
     The end regions of the side walls  85  and  86  of the container have Y shaped lines of cut indicated at  93  which enable the ends to fold in to form gussets adjacent the ends of the pack and to allow the top and bottom walls  82  and  89 / 90  to be brought together to be heat-sealed together to close the ends of the pack. 
     The web of laminated material is fed to a wrapping/filling machine in which a former is used to create the rectangular cross-section of the web around the baguette or other elongate food item to be packaged. The flanges  91 ,  92  on the underside of the container are heat-sealed together, and tooling presses the regions of the side walls  85 ,  86  inwardly to form the gussets indicated at  94  in  FIG. 24  in the end portions of the containers. 
     It will be appreciated that many modifications may be made to the above described embodiments without departing from the scope of the invention. The method of forming the laminate web from which the packs are treated is applicable to many other shapes, styles and forms of pack. By forming the fold lines and any required lines of cut in the web of paper/card prior to laminating to the film, the cutting operation is greatly simplified since there is no risk of severing the film. By applying the film to the whole of the surface of the web, an impervious barrier is created on the inside of the pack which also enables areas of the blank to be heat-sealed together to form the pack. The arrangement therefore lends itself to automated production of a wide variety of packs for food items and other products. 
     As indicated above, the material for the film to be laminated to the paper/card may comprise a number of substances such as polylactic acid (PLA), cellulose, polypropylene, polyethylene and polyethylene terephthalate (PET). These materials may optionally be provided with any of the following: anti-mist coatings, gas and/or moisture barriers such as ethylene vinyl alcohol (EVOH), polyvinylidene dichlorisel (PVdC), nylon peelable coatings.