Abstract:
The present invention discloses a method and apparatus to permit the ARMACEL process (known per se from WO 95/23682, WO/09166 and WO 00/59709) to be used without entrapping gas or air between a heated plastics sheet ( 26 ) and an impervious core ( 40, 50, 60, 70 ). The core ( 40, 50, 60, 70 ) is inclined relative to the sheet ( 26 ) by either maintaining the sheet ( 26 ) level and inclining the core ( 40, 50, 70 ) or by maintaining the core ( 60 ) level and depressing the sheet ( 26 ) to incline same. Apparatus is also disclosed including and inclined perforated base plate ( 22 ), a contact finger ( 55 ) and a pedestal ( 71 ).

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a method of, and apparatus for, forming an article from at least one shape defining fluid impermeable interior member and at least one external skin. The present invention also relates to an article produced in accordance with the method or by the apparatus.  
       BACKGROUND OF THE INVENTION  
       [0002]     It is known to produce structurally strong articles having load bearing capabilities by encapsulating inherently weak materials, such as expanded polystyrene (EPS), with one or more layers of a thermoplastic sheet material, such as APET (amorphous polyethylene terphalate) using the ARMACEL (Trade Mark) process.  
         [0003]     The process is described in the applicant&#39;s International Patent Application No. PCT/AU95/00100 entitled: “A Method and Apparatus for Forming Structural Articles” (WO 95/23682) and International Patent Application No. PCT/AU96/00541 entitled: “Layered Structural Article” (WO 97/09166) and International Patent Application No. PCT/AU00/00250 entitled “Improved Method of Forming Structural Articles” (WO 00/59709), the relevant disclosure of each being incorporated herein by cross-reference. These documents disclose numerous other material suitable for the core and the thermoplastics sheet.  
         [0004]     The ARMACEL process will now briefly be described with reference to FIGS.  1  to  4 .  FIG. 1  shows a block shaped core  20  of essentially air or fluid permeable material, such as EPS. The core  20  is placed above a base plate  22  which primarily functions to support the core  20  and has a series of small holes  24  therethrough. Overlying the core  20  is a sheet  26  of thermoplastic material such as APET, the periphery of which is clamped by means of a clamp  28 . The clamp  28  extends all the way around the periphery of the core  20  in order to provide an effective seal together with the base plate  22 .  
         [0005]     The sheet  26  is heated by means of a heater (not shown but disclosed in the abovementioned specifications) until it is at least soft or plastically deformable and is then moved relatively towards the core  20  while clamped by clamp  28 . The relative movement is accomplished by either moving the clamp  28  downwardly in the direction of arrow A, or moving the base plate  22  and core  20  upwardly in the direction of arrow B, or both. The air or gas located between the sheet  26  and the base plate  22  is drawn through the core  20  and the sheet  26  is conformed to the shape of the core  20 . As the core  20  is fluid permeable, the air which is located between the sheet  26  and the core  20  is able to pass through the core  20  and out the holes  24  in the base plate  22 , as indicated by arrows  30 .  
         [0006]     The removal of the air or gas can be brought about by applying a reduced pressure or vacuum to the holes  24 , by applying a positive pressure to the upper side of the sheet  26 , or by both methods simultaneously. The pressure difference is applied for a sufficient length of time for the sheet  26  to cool, or be cooled, and thereby adopt a final position which is conformed to the shape of the core  20  and which binds the sheet  26  and the core  20  together by the creation of tensional forces in all directions in the sheet  26 . After the release of the clamp  28 , edges  29  of the sheet  26  can be trimmed adjacent the periphery of the core  20 .  
         [0007]      FIG. 2  shows the product of the above process after trimming and inversion. The sheet  26  effectively renders the core  20  fluid impermeable. The coated side  32  is then punctured so as to form a series of apertures  34  to render it fluid permeable again. The process of  FIG. 1  is then repeated, as shown in  FIG. 3 , and the air between upper sheet  36  and the core  20  passes through the fluid permeable core  20  and thereafter through the apertures  34  in the lower sheet in similar fashion to that previously described.  
         [0008]      FIG. 4  diagrammatically illustrates the situation that occurs if the above process is used in conjunction with a fluid impermeable core  38 . In this case, when a sheet  37  and the core  38  are brought together the air between the two is unable to pass through the core  38  as it is fluid impermeable and is trapped to form a bubble like space  39 , preventing the sheet  37  from engaging the major surface  38   a  of the core  38 . The relative movement of the core  38  towards the sheet  37  can also create an air current which partially “balloons” the sheet  37 , which exacerbates the problem. This is a particular problem when the core has a large surface area or when the movement is performed quickly. A similar situation occurs when attempting to coat the second side of a coated fluid permeable core  20 , such as that shown in  FIG. 2 , without the apertures  34 .  
         [0009]     The invention disclosed in WO 00/59709 is an attempt to overcome the problem explained herein in relation to  FIG. 4 . In WO 00/59709 the article to be encapsulated is provided with relatively large grooves or channels which assist in removal of the air or gas between the impermeable body or core  38  and the sheet  37 . Even so, not all of the air or gas is removed as illustrated in FIG. 4 of WO 00/59709. This can have consequence when the entrapped air or gas is heated since the heated air or gas expands and therefore exerts a force on the underlying body.  
         [0010]     Prior art searches conducted since the priority date have disclosed PCT/AU98/00957 McCORMACK entitled “Vacuum Press for Pressing Thermoplastic Membrane onto an Article” and published under WO 99/25515. This specification seeks to overcome the abovementioned problems by evacuating the air or gas lying to both sides of the heated plastics sheet. Then, when the-heated plastics sheet is judged to be sufficiently soft, air at atmospheric pressure is introduced above the sheet to drive the heated sheet into contact with the article to be coated. The disclosure is to maintain both the object  10  to be coated level (by being supported by the flat base of the chamber  7 ) and to maintain sheet  11  level whilst heating (by maintaining the sheet  11  at the height of the emitter  26  and transducer  24 ). Thus there is no disclosure of inclining of the sheet  11  relative to the object  10 .  
       OBJECT OF THE INVENTION  
       [0011]     It is an object of the present invention to substantially overcome, or at least ameliorate, some of the above difficulties with the prior art and, in particular, to provide methods of forming articles having at least one shape defining fluid impervious interior members and at least one external skin.  
       SUMMARY OF THE INVENTION  
       [0012]     Accordingly, in a first aspect, the present invention discloses a method of forming an article having load bearing capabilities from at least one shape defining fluid impermeable interior member and at least one external skin, said method comprising the steps of:— 
         [0000]     (i) heating a thermoformable sheet intended to form the external skin,  
         [0000]     (ii) disposing a major surface of the member(s) at an inclined angle relative to the sheet,  
         [0000]     (iii) moving said heated sheet relative to said member(s) to bring the heated sheet into substantially point or line contact with the surface of the member(s),  
         [0013]     (iv) applying a fluid pressure differential between the side of said sheet remote from the member(s) and the side of the member(s) remote from said sheet and continuing the relative movement between the sheet and the member(s), to progressively move the point or line contact front between the sheet and the member(s) across the surface thereby expelling any gas present between the sheet and the surface of the major surface and conforming the sheet to the shape of the major surface and mutually engaging the sheet and the member(s),and  
         [0000]     (v) maintaining said fluid pressure differential until said thermoformable sheet has cooled, whereupon tensional forces arise in the sheet in all directions  
         [0014]     In an embodiment, the major surface(s) of the member(s) is/are disposed at approximately 90° to the sheet and the contact front moves in a substantially vertical direction along the surface(s). In a variation of this embodiment, when the member(s) has/have a pair of parallel or upwardly converging surfaces, the sheet is applied to both the surfaces simultaneously.  
         [0015]     In another embodiment, the surface is inclined at an angle less than 40°, most preferably about 20°.  
         [0016]     In a further embodiment, a contact finger is used to deform the heated sheet into a V or cone shape having an apex contacting the major surface(s) of the member(s) thereby dividing the sheet into two regions each disposed at the inclined angle to the surface of the interior member(s), whereby subsequent relative movement between the sheet and the surface progressively moves a contact front for each region of the sheet across the major surface(s).  
         [0017]     In a second aspect, the present invention discloses an apparatus for forming an article having load bearing capabilities from at least one shape defining fluid impermeable interior member and at least one external skin, said apparatus comprising:—
        a sheet holding device to hold a sheet of thermoformable plastics material at least a pair of opposite edges thereof;     inclining means to dispose a major surface of said member(s) at an inclined angle relative to said sheet;     translation means to move the member relative to the sheet holding device to move the sheet and the surface together;     heating means to heat a thermoformable plastic sheet held in said sheet holding device to at last partially soften said sheet;     pressure differential means to create a pressure differential between the sheet and the member(s) to conform the sheet to the member(s), wherein the translation means move the heated sheet into substantially point or line contact the with said major surface of the member(s) and thereafter progressively moves the point or line contact front between the sheet and the member(s) across the major surface thereby expelling any gas present between the sheet and the major surface; and     maintaining said pressure differential until said thermoformable sheet has cooled, whereupon tensional forces arise in the sheet in all directions.        
 
         [0024]     In a third aspect, the present invention discloses an article coated by the above method and/or apparatus. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]     Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which;  
         [0026]      FIG. 1  is a cross-sectional view of a prior art method of forming an article from a fluid permeable member and an external skin;  
         [0027]      FIG. 2  is an inverted cross-sectional side view of the article formed in  FIG. 1 ;  
         [0028]      FIG. 3  is an article shown in  FIG. 2  being coated with a further external skin in accordance with the prior art method of  FIG. 1 ;  
         [0029]      FIG. 4  is a cross-sectional side view of a prior art method of forming an article from a fluid impervious member and an external skin;  
         [0030]      FIG. 5  is a cross-sectional side view of the initial stages of a method of forming an article from a fluid impervious member and an external skin in accordance with a first embodiment of the invention;  
         [0031]      FIG. 6  is a cross-sectional side view of a subsequent stage of the method shown in  FIG. 5 ;  
         [0032]      FIG. 7  is a cross-sectional inverted side view of the article formed in  FIGS. 5 and 6  being coated with a further external coating in accordance with the method of  FIGS. 5 and 6 ;  
         [0033]      FIG. 8  is a cross-sectional side view of the initial stages of a method of forming an article from a fluid impervious member and an external skin in accordance with a second embodiment of the invention;  
         [0034]      FIG. 9  is a cross-sectional side view of the article shown in  FIG. 8  during the coating process;  
         [0035]      FIG. 10  is a cross-sectional side view of the article shown in  FIG. 8  after the coating process;  
         [0036]      FIG. 11  is a cross-sectional side view of the initial stages of a method of forming an article from a fluid member and an external skin in accordance with a third embodiment of the invention;  
         [0037]      FIG. 12  is a cross-sectional side view of the initial stage of a method of forming an article from a fluid impermeable member and an external skin in accordance with a fourth embodiment of the invention.  
         [0038]      FIG. 13  is a view similar to  FIG. 7  but showing the member mounted on a pedestal, and  
         [0039]      FIG. 14  is a perspective view of a core member containing a plurality of shallow incisions. 
     
    
     DETAILED DESCRIPTION  
       [0040]     Referring to FIGS.  5  to  7 , there is shown a method of forming an article having load bearing capabilities according to a first embodiment of the invention.  FIG. 5  shows a core  40  of essentially fluid impermeable material, such as metal, glass or dense wood.  
         [0041]     The core  40  is placed above a base plate  22  which primarily functions to support the core  40  and has a series of small holes  24  therethrough. Overlying the core  40  is a first sheet  26  of APET, the periphery of which is clamped by means of a peripheral clamp  28 .  
         [0042]     The sheet  26  is heated by means of a heater (not shown but disclosed in the abovementioned specifications) until it is at least soft or plastically deformable and is then moved relative to the core  40  whilst clamped by the clamp  28 . The relative movement is accomplished by moving the clamp  28  downwardly in the direction of arrow C (as shown in  FIG. 5 ) or moving the base plate  22  and core  40  upwardly in the direction of arrow D, or both.  
         [0043]     As the sheet  26  and base plate  22  are drawn towards each other a pressure differential is created between the sheet  26 , core  40  and base  22  drawing air or gas located from between sheet  26  and core  40  as to form the sheet  26  to the shape of the core  40 .  
         [0044]     As best shown in  FIG. 5 , the side surfaces  41  of the core  40  are disposed at an angle of approximately 90 degrees to the sheet  26  and two line contact fronts, each indicated as X, are formed between the (major) side surfaces  41  of the core  40  and the sheet  26 . As the sheet clamp  28  is moved relative to the core  40 , the fronts XX move in a substantially vertical direction along the side surfaces  41  of the core  40 . The progressive movement of the contact fronts across the side surfaces  41  simultaneously expels any air present between the sheet  26  and the side surfaces  41  of the core  40  and then allows the sheet  26  to conform to the shape of the core  40 . This air removal process advantageously obviates the need for the interior member to be fluid permeable, as air or gas is not required to pass through same.  
         [0045]     After the side surfaces  41  of the core  40  have been fully covered by the sheet  26 , the pressure differential is maintained for a sufficient length of time for the sheet  26  to cool, or be cooled, and thereby adopt a final position which is conformed to the shape of the core  40 . This binds the sheet  26  and the core  40  together and creates tensional forces in all directions of the sheet  26 .  
         [0046]     After the release of the clamp  28 , edges  42  of the sheet  26  are trimmed at the periphery of the core  40 . In this embodiment it will be appreciated that the peripheral clamp  28  extends all the way around the periphery of the core  40  in order to provide an effective seal together with the base plate  22 .  
         [0047]      FIG. 7  shows the product of the above process after trimming and inversion. The process is then repeated, as shown in  FIG. 7 , and the air or gas between second sheet  46  and the core  40  is evacuated in a similar fashion to that previously described.  
         [0048]     The process as shown in  FIG. 7  can also be used with a permeable core, that has been rendered impermeable by coating, without requiring the apertures  34  described with reference to  FIG. 3 . Ass a consequence, a second coat of sheet thermoplastic material can be applied to a core which has previously been fully encapsulated with a prior coat of sheet thermoplastic material.  
         [0049]     The bubble  39  shown in  FIG. 4  is not formed against the (minor) top surface  43  as the sheet  26  effectively makes instantaneous contact with all of the top surface  43 . Preferably the top surface  43  can be tilted slightly so that one edge thereof contacts the sheet  26  before the opposite edge. Further, the small surface area of the top surface  43  does not create the air current described above with reference to  FIG. 4 .  
         [0050]     FIGS.  8  to  10  show a similar process to that shown in FIGS.  5  to  7  except a major surface  51  of a fluid impervious core  50  is inclined at an angle less than 40 degrees to the sheet  26 . As the sheet  26  and base plate  22  are moved toward each other a line contact front, in this case indicated by YY, between the sheet  26  and the core  50  progressively moves down the surface  51  of the core  50 . This progressively expels the air or gas between the sheet  26  and the surface  51  and allows the sheet  26  to conform to the core  50 . After release of the clamp  28 , the edges  53  of the sheet are trimmed at the periphery of the core  50 . The product can then be inverted and the process repeated as previously described.  
         [0051]      FIG. 11  shows a similar process to that shown in FIGS.  8  to  10  except that the inclination of the sheet relative to the core is created by a contact finger  55  which is used to deform the heated sheet  26  into a V or cone-shape having an apex  57  contacting a major surface  62  of a fluid impervious core  60 . This divides the sheet  26  into two regions each disposed at an inclined angle to the major surface  62  of the core  60 , each having a line contact front indicated by ZZ. The core  60 , as in all of the other embodiments, is placed above a base plate  22  which primarily functions to support the core  60  and has a series of small holes  24  therethrough. Upon the application of a fluid pressure differential between the sheet  26  and the core  60  and relative movement between the sheet  26  and the surface  62 , the contact fronts ZZ for each respective region of the sheet  26  progressively move across the surface  62 . This expels any air or gas present between the sheet  26  and the surface  62  of the core  60  and allows the sheet  26  to conform to the shape of the core  60 . The edges of the sheet (not shown) are then trimmed so as to have the same periphery as the core. Then the core is inverted and the process repeated.  
         [0052]      FIG. 12  shows a method of forming an article having load bearing capabilities according to a further embodiment of the invention. As was described with reference to prior art  FIG. 4 , as the sheet  26  and base plate  22  are moved towards each other, and the pressure differential is applied, the air or gas between the sheet  26  and top surface  61  is trapped between the edges of the core  60 , because it is fluid impermeable, thereby creating a bubble-like space  65 . To expel this air or gas and allow sheet  26  to conform to core  60 , one or more tubes  70  are inserted through one of the holes  24  in base plate  22 . Each tube lies alongside the core  60  allowing fluid communication between the major surfaces  60   a  and  60   b  of the core  60 . A vacuum is then applied to the tube(s)  70  to remove the air or gas present in the space  65  between the sheet  26  and the core  60  which allows the sheet  26  to conform to the core  60 . As with earlier embodiments, the pressure differential is maintained until the sheet  26  has cooled, thereby creating tensional forces in the sheet  26  in all directions. In the trimming process, the tube(s)  70  which are encapsulated below the sheet  26  can be removed by trimming the sheet  26  at the upper edges  63  of the core  60 . Then the core  60  can be inverted and the process of  FIGS. 8-10  used to coat the remaining surfaces of the core  60 . This technique finds particular application in coating a body having one surface which is difficult to coat but having its remaining surfaces easy to coat.  
         [0053]     Turning now to  FIG. 13 , the encapsulation of a two part core  70  having individual core members  70 A and  70 B is illustrated. As in  FIG. 7 , the core  70  has previously been coated on its top and sides by a sheet  26  of thermoplastic material. The sheet  26  is trimmed and the core members  70 A and  70 B inverted and placed on a pedestal  71  which is in turn supported by the base plate  22 .  
         [0054]     Then a second sheet  76  is applied as in  FIG. 7 . However, because of the pedestal  71 , the second sheet  76  is drawn around the lower edges of the core  70  as seen in  FIG. 13 . The sheet  76  is trimmed to allow the release of the pedestal. As the trimmed sheet  76  envelopes the lower edge of the core  70  as seen in  FIG. 13 , this provides an exceptionally strong bond for the sheet  76 .  
         [0055]     Turning now to  FIG. 14 , a still further embodiment is illustrated in which a block shaped core  80  is provided with a series of score lines or incisions  81 . These are illustrated in a greatly magnified form in order to be visible at all in the drawing. The incisions  81  essentially constitute scratches in the surface of the core  80 . These provide channels which allow the air or gas between core  80  and the sheet  26  to escape but are essentially invisible in the finished article. It is not necessary that the incisions  81  be as regularly spaced or as uniformly deep as is illustrated in  FIG. 14 .  
         [0056]     The primary advantage of the invention is it extends the use of the ARMACEL process to relatively high strength, and fluid impervious or substantially impervious, materials such as metal, glass or dense wood.  
         [0057]     The foregoing describes only some embodiments of the present invention and modifications, obvious to those skilled in the art can be made thereto without departing from the scope of the present invention. For example, the core can be fabricated from one, two, or multiple parts.  
         [0058]     The term “comprising” (and its grammatical variations) as used herein is used in the inclusive sense of “having” or “including” and not in the exclusive sense of “consisting only of”.