Abstract:
The invention relates to an apparatus and method for producing articles ( 5 ) from moulded pulp material that are laminated with a plastic film ( 4 ). Thus an environmental friendly and water-resistant package for food products and for other moulded pulp products such as packages for industrial products is provided. The apparatus comprises a moulding line  1  and a laminating line ( 3 ). The moulding line ( 1 ) comprises a suction moulding station ( 20 ) with a pulp vat ( 25 ) and a number of suction moulds ( 22 ), a drying oven ( 28 ) and conveying means ( 26,28 ) for transporting the moulded pulp articles through the moulding line ( 1 ). The articles are transported in line by a conveyor  10  from the moulding line ( 1 ) to the laminating line ( 3 ), the laminating line ( 3 ) comprises a plastic film supply unit ( 47 ), a heating station ( 69 ) a laminating station ( 80 ) and conveying means ( 56 ) for conveying the articles ( 5 ) through the laminating line ( 3 ).

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates to an apparatus for producing moulded pulp articles that have a plastic film laminated thereon of the kind set forth in the preamble of claim 1. The invention also relates to a method of producing moulded pulp articles with a plastic film laminated thereon of the kind set forth in the preamble of claim 16.  
         BACKGROUND ART  
         [0002]    Moulded pulp articles are a desirable form of packaging since it is an environmental friendly non-expensive alternative to plastic and other materials for three dimensionally contoured packages. The use of such moulded pulp articles as food trays and the like has been desired since several decades. Moulded pulp is however not resistant to moist and as such thus not suitable for holding moist food or beverages. Therefore, several techniques have been developed for coating or laminating the moulded pulp packages with a moist resistant and preferably to provide them with a gas barrier. Other types of moulded pulp articles are packages for industrial products such as mobile phones or print cartridges. Dust and scratching from the pulp material can be problematic for certain sensitive industrial products. There exists therefore also a need for a technique to coat or laminate the moulded pulp articles from this perspective. None of the known techniques for this purpose have been able to meet the requirements for a successful commercial application.  
           [0003]    EP-A-0-196 799 discloses an apparatus for laminating plastic film onto moulded pulp articles. Preformed articles are taken from a stack of articles by a destacking apparatus and placed in rows across a conveyor. The articles are fed by the conveyor and lined with a superimposed plastic film at a laminating station where the plastic film is bonded to the interior of the articles. This apparatus for the laminating of films to moulded pulp articles does not operate at desirably high speeds that allow successful commercial application. Further, the off-line mode of operation of the known prior art laminating line creates problems with handling and storing large amounts of articles between the production of the articles and the laminating line.  
         DISCLOSURE OF THE INVENTION  
         [0004]    On this background, it is the object of the present invention to provide an apparatus for producing moulded pulp articles of the kind referred to initially that operates at high rates. It is another object of the present invention to provide a method for producing moulded pulp articles that are laminated laminating a plastic film onto moulded pulp articles of the kind referred to initially that allows operation at high rates. These objects are achieved in accordance with claim 1 and 16 respectively by transporting the moulded pulp articles in line from the moulding section to the laminating section, thus forming one continuous production line where the pulp articles are transported through the various working stations without intermediate storing.  
           [0005]    According to an embodiment of the invention, the moulding line is adapted to produce a plurality of articles that are mutually interconnected through bridges.  
           [0006]    According to another embodiment of the invention wherein the laminating line is located separately from the moulding line in a dean room, the two lines being connected through an intermediate conveyor.  
           [0007]    According to another alternative embodiment of the invention, the laminating line comprises a hot press station before the heating station. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    In the following detailed portion of the present description, the invention will be explained in more detail with reference to the exemplary embodiments shown in the drawings, in which  
         [0009]    [0009]FIG. 1 is a diagrammatical side view of the moulding line,  
         [0010]    [0010]FIG. 2 is a diagrammatical side view of the laminating line according to the invention,  
         [0011]    [0011]FIG. 3 is a layout of the production line according to the invention, and  
         [0012]    [0012]FIG. 4 a  and  4   b  are elevated views on a plurality of interconnected moulded pulp articles and on a disconnected moulded pulp article. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0013]    With reference to the FIGS. 1 and 2, a production line for manufacture of moulded pulp articles  5  laminated by welding of plastic film sheets comprises a moulding line  1  and a laminating line  3 .  
         [0014]    The articles  5  are typically three dimensionally contoured moulded pulp packages such as food- or meat trays. These articles  5  have a relatively thin wall of fibre material such as paper pulp or wood pulp. The articles  5  are intended to be food trays and must therefore be laminated in a clean (hygienic) area.  
         [0015]    As shown in FIG. 3, the laminating line  3  is located in a clean room separately from the moulding line  1 . The two lines are separated. The laminating line  3  and the moulding line  1  are connected by a conveyor  10  that passes through an air lock into the clean room. The plastic film  4  must be suitable for thermo-forming, preferable gas impermeable or comprise a barrier against certain gases and moisture. Multilayer films  4  with an overall thickness of approximately 50 pm provide sufficient thickness after laminating to comply with the barrier standards.  
         [0016]    [0016]FIG. 1 shows diagrammatically a suction moulding line  1  for moulding articles  5  from pulp material. The line starts with a moulding station  20 . The moulding station  20  comprises a mould carrier  21 , on the outside of which are placed several liquid-permeable suction moulds  22  adapted to be connected with a source of sub-atmospheric and to a source of super-atmospheric pressure (not shown).  
         [0017]    The mould carrier  21  is with a part of its circumferential surface immersed in a pulp vat  25  containing a fibre pulp suspension. This pulp may be made from a fibre-containing raw material, such as waste paper or cardboard. During the immersion in the pulp mass, a layer of fibre material is deposited by suction on the mould surfaces of the suction mould  22 . Subsequently, when the suction moulds  22  are withdrawn from the fibre suspension in the pulp vat  25 , the suction is continued to compact the deposited fibres while exhausting residual liquid therefrom. After withdrawing the mould from the pulp vat  25 , the mould will follow the rotary trajectory of the rotatable mould carrier  21  and thereby suck air through the articles  5  which are thereby partially dewatered, the moulds  2  are further rotated to the position where the articles  5  are blown off from the suction moulds  22  and aspirated onto transfer moulds on the transfer rotor  26 . After a part of a revolution of the transfer rotor  26 , the articles  5  are blown off therefrom onto a carrier system  27  which transports the articles  5  to a drying oven  28  for a drying procedure. In the drying oven  28 , the articles  5  reach their final dry matter weight content of at least 90 weight per cent.  
         [0018]    A group of articles  5  may be moulded in the form of a common continuous body with bridges interconnecting the articles  5 , said bridges for the sake of simplicity being shown in the form of a common bridge sheet in the drawing (cf. FIG. 4 a ). Instead of a common plate, the bridge connection may also be formed by ribs (cf. FIG. 4 b ), and the bridge connection may also comprise a directly abutting connection between the mutually facing sides of two adjacent articles  5 . The articles  5  are provided with lateral tabs or flanges  6  for engagement or gripping by transport means.  
         [0019]    From the drying oven  28 , a conveyor  10  transports the moulded pulp articles  5  through a humidification station  30  to the laminating line  3 . The conveyor  10  comprises a buffer of articles  5  between the moulding line  1  and the laminating line  3  in order to avoid gaps in the supply of moulded pulp articles  5  to the laminating line  3 . The operation speed of the laminating line  3  depends on the number of articles  5  in the buffer, i.e. less articles  5  in the buffer, the lower result in a low operation speed.  
         [0020]    The articles  5  leaving the drying oven  28  are too dry for a hot press operation. Therefore, a controlled humidification takes place in the humidification station  30  to obtain a smooth surface of the product with exact dimensions after the hot pressing in the heated tools which create a steam pressure.  
         [0021]    The laminating line  3  is arranged in a clean room  40  that is separated from the moulding line  1  and the humidification station  30  in order to avoid contamination. In the clean room  40 , an overpressure is maintained in order to avoid unclean air coming in. A wall  42  separating the clean room  40  from the moulding line environment is provided with an opening  43  with a tunnel  45  extending therefrom into the moulding line environment. The tunnel  45  increases the flow restriction for the air flowing out through the opening thereby reducing the amount of lost pressurised air.  
         [0022]    The laminating line  3  comprises a hot press station  50 , a heating station  69 , a laminating station  80 , a crystallisation station  90 , a cutting station  93 , a stacking station  99  and a conveying apparatus  56  which serves to guide and transport the moulded articles  5  and the plastic film  4  through the stations.  
         [0023]    At the start of the laminating line  3 , the moulded pulp articles  5  or the plurality of moulded pulp articles  5  are positioned in the hot press station  50  by means of two transversely spaced sets of actuators  52 , 53  receiving a closed loop control signal from two transversely spaced photo cells  54 , 55  in order to position the front edge of the article or plurality of articles  5  exactly perpendicular to transport direction.  
         [0024]    The hot press  51  comprises an upper  57  and a lower  58  tool complementary shaped in accordance with the article  5  to be laminated. The upper tool  57  and the lower tool  58  both move towards the article  5  when the hot press  51  is closed. Both tools  57 , 58  are heated by conventional means. The hot press action heats the moulded pulp article  5  extremely fast to a temperature of about 50 to 100 degrees Celsius. When the hot press  51  is closed, the lateral tabs or flanges  6  on the articles  5  or plurality of interconnected articles  5  extend out of the tools  57 , 58  so that they can be engaged by the conveyor apparatus  56 .  
         [0025]    A conventional conveying apparatus  56  comprises two transversely spaced rails  59  extending along the longitudinal axis of the laminating line  3 . The distance between the rails  59  can be adjusted in accordance with the width of the articles  5  or the width of the plurality of interconnected articles  5 . Each rail  59  defines two channels, an upper and a lower channel in which a spiked chain is guided (not shown). In the upper channel, the spiked chain moves forward through the laminating line  3  while in the lower channel the spiked chain returns to the start of the laminating line  3 . The upper channel also defines a surface for guiding the tabs or flanges  6  of the articles  5  and is provided with a groove in which the spikes partially extend. Thus, the spikes extend through the tabs or flanges  6  and positively engage the flanges or tabs  6 . The spikes penetrate the tabs or flanges  6  when the article  5  or the plurality of interconnected articles  5  is positively fixed in the closed hot press  51 . When the hot press  51  opens, the chain is driven to transport the articles  5  to the next station.  
         [0026]    Alternatively clamps, belts or other fixating means (not shown) can substitute the spiked chain.  
         [0027]    Directly after the hot press station  50 , the plastic film  4  is fed from a film reel  47  into the rails  59  through a slot in the guiding surface of the upper channels. The spikes of the chain also penetrate the plastic film  4  and the plastic film  4  and the articles  5  are moved in unison by the spiked chain to the heating station  69 .  
         [0028]    The heating station  69  comprises a heating element above  70  and one under  71  the moulded pulp articles  5  and the plastic film  4 . The plastic film  4  only absorbs a part of the radiation from the upper heating element  70  and the rest can be absorbed by the moulded pulp articles  5 . The plastic film  4  is heated to above the glass temperature and the moulded pulp artides  5  have a temperature less than 200 degrees Celsius when they leave the heating station  69 .  
         [0029]    The next station is a conventional laminating  80  station which comprises an upper  81  and a lower table  82 . The upper table  81  is provided with die press tool  83  whereas the lower table  82  is provided with a heated suction mould  84 . Both the upper and lower table move towards the film  4  and the moulded pulp article  5 . A partial vacuum is applied to the suction mould  84 . The film  4  is bonded to the moulded pulp articles  5  by being drawn downwardly by the partial vacuum applied to the suction mould  84  through the moulded pulp article  5  and/or by the press tool  83 . The upper table  81  may also be provided with means (not shown) to apply compressed air to the upper side of the plastic sheet  4 .  
         [0030]    Further, the laminating station  80  comprises a separately movable hot tool  85  for laminating the plastic film  4  to selected (flange) areas of the moulded pulp articles  5  in order to positively weld the film  4  to these areas of the moulded pulp articles  5 .  
         [0031]    The articles  5  with the film  4  laminated thereon are then transported by the conveyor  56  to the crystallisation station  90 . This station comprises an upper heating element  91 . By exposing the plastic film  4  to the heat, a crystallisation from amorphous to crystalline can take place if desired. In the case of food trays, this renders the laminated moulded pulp article  5  resistant to the heat of a domestic oven.  
         [0032]    Next, a conventional cutting station  93  comprising an upper  94  and a lower movable tool  95  for die cuffing separates the plurality of interconnected articles  5  and for removing superfluous flange material such as the tabs or flanges  6  for gripping by the conveyor  56 . Either the upper or the lower tool is provided with a knife  96  to cut of the flange areas. The articles  5  remain connected to the “waste” material by narrow bridges in order to allow further transport to a stacking station  99 .  
         [0033]    After the cuffing station  93 , a conventional stacking station  99  stacks the laminated moulded pulp articles  5  so that they may be removed batch-wise from the laminating line  3 .  
         [0034]    According to a not shown embodiment, a filling and sealing line is arranged in line/off line with the laminating line for filling the trays with food or other products and then sealing the filled tray with a plastic top sheet. Thus, the laminating line does not comprise a stacking station.  
         [0035]    List of Reference Numerals  
         [0036]    [0036] 1  moulding line  
         [0037]    [0037] 3  laminating line  
         [0038]    [0038] 4  plastic film  
         [0039]    [0039] 5  article  
         [0040]    [0040] 6  tab or flange  
         [0041]    [0041] 10  conveyor  
         [0042]    [0042] 20  moulding station  
         [0043]    [0043] 21  mould carrier  
         [0044]    [0044] 22  suction mould  
         [0045]    [0045] 25  pulp vat  
         [0046]    [0046] 26  transfer  
         [0047]    [0047] 27  carrier system  
         [0048]    [0048] 28  drying oven  
         [0049]    [0049] 30  humidification station  
         [0050]    [0050] 40  clean room  
         [0051]    [0051] 42  wall  
         [0052]    [0052] 43  opening  
         [0053]    [0053] 45  tunnel  
         [0054]    [0054] 47  film reel  
         [0055]    [0055] 50  hot press station  
         [0056]    [0056] 51  hot press  
         [0057]    [0057] 52  actuator  
         [0058]    [0058] 53  actuator  
         [0059]    [0059] 54  photocell  
         [0060]    [0060] 55  photo cell  
         [0061]    [0061] 56  conveyor  
         [0062]    [0062] 57  upper tool  
         [0063]    [0063] 58  lower tool  
         [0064]    [0064] 59  rail  
         [0065]    [0065] 69  heating station  
         [0066]    [0066] 70  upper heating element  
         [0067]    [0067] 71  lower heating element  
         [0068]    [0068] 80  laminating station  
         [0069]    [0069] 81  upper table  
         [0070]    [0070] 82  lower table  
         [0071]    [0071] 83  press tool  
         [0072]    [0072] 84  suction mould  
         [0073]    [0073] 85  hot tool  
         [0074]    [0074] 90  crystallisation station  
         [0075]    [0075] 91  upper heating element  
         [0076]    [0076] 93  cutting station  
         [0077]    [0077] 94  uppertool  
         [0078]    [0078] 95  lower tool  
         [0079]    [0079] 96  knife  
         [0080]    [0080] 99  stacking station