Abstract:
Apparatus and methods of forming selected portions of integral sheets of material are disclosed. Unformed portions of the sheets may remain undistorted during the forming process, allowing them to contain text, art work, or other desired information without material risk of the information being degraded or becoming unintelligible during the forming process. This result may be accomplished, moreover, with less trim than usually occurs in conventional forming processes.

Description:
REFERENCE TO PROVISIONAL APPLICATION 
       [0001]    This application is based on, claims priority to, and hereby refers to U.S. Provisional Patent Application Ser. No. 61/350,107, filed Jun. 1, 2010, the entire contents of which are incorporated herein by this reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to shaping heated polymeric materials in a mold and more particularly, although not necessarily exclusively, to heating selected areas of the materials to forming temperatures while not forming other areas of the materials. 
       BACKGROUND OF THE INVENTION 
       [0003]    Conventional thermoforming involves heating a polymer sheet to a pliable forming temperature (which depends at least in part on the type of sheet being heated), forming the sheet to a specific shape on a mold, and thereafter trimming unformed portions of the sheet to create a useful product. The sheet, sometimes referred to as “film” when thin gauges or certain types of materials are formed, is typically heated in an oven to the forming temperature so that it may be stretched into or onto a mold and then cooled to retain a finished shape. During the heating process, the entire sheet of material is heated to the forming temperature. Portions of the sheet that are not formed are usually referred to as “trim” and not reused until after further processing. 
         [0004]    U.S. Pat. No. 4,878,826 to Wendt, the entire contents of which are incorporated herein by this reference, is one of many patents disclosing apparatus for thermoforming articles from sheets of plastic material. The apparatus of the Wendt patent may include both male and female molds together with a heating means and evacuation equipment. One such heating means is described as being hot oil circulating through an associated manifold such that it crystallizes a sheet of plastic material. See Wendt, col. 10, 11. 9-12. According to the Wendt patent, the sheet also may be pre-heated to 10-15% crystallization before entering the mold. See id., col. 12, 11. 50-57. Indeed, over-crystallization of the sheet apparently is an issue with the apparatus of the Wendt patent, requiring cold air to be injected into various mold cavities. See id., col. 13, 11. 53-65. 
         [0005]    Thermoforming a plastic sheet necessarily distorts it. However, in some circumstances distortion of certain portions of a sheet is undesirable. As an example, distortion of portions of a sheet containing printing or art work may render them unintelligible or, at minimum, diminish their aesthetic appeal. Consequently, conventional thermoforming requires pre-printing of text and art in a distorted form so that the further distortion caused by the thermoforming can counteract the pre-distortion and, at least theoretically, produce intelligible images. Thus, providing apparatus and methods that would allow thermoforming of selected portions of a plastic sheet while avoiding distortion of other portions of the sheet thus would be a beneficial-albeit difficult-achievement. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention accomplishes this desired result. Notwithstanding its use of an integral sheet of polymeric material, the present invention allows heating and forming of only selected portions of the material. By contrast, unformed portions of the material remain substantially undistorted and thus may contain undistorted printing, art work, or other text, symbols, or information without concern as to whether intelligibility of the information will be degraded during the forming process. Even if information is not present in unformed regions of a sheet, the mere fact that the unformed regions may retain their original shapes (typically but not necessarily flat) and thicknesses permits a broader range of products to be created. Further, apparatus and methods of the present invention admit productive use of the vast majority of each sheet (e.g. 95% in some cases), so that little trim is created when products are formed. 
         [0007]    In at least some embodiments of the invention, energy-absorbing or -reflecting material may be employed to limit heat or other energy transferred to the polymer sheets. Such material may be in the form of metallic or other plates having simple or complex shapes. The plates may include cut-outs so that heat or other energy may be transferred efficiently to areas of a sheet that is to be thermoformed. Various embodiments of the invention also may utilize controllable banks of heaters to allow variable heating of the molds themselves. 
         [0008]    It thus is an optional, non-exclusive object of the present invention to provide apparatus and methods for selectively thermoforming integral polymeric materials. 
         [0009]    It is another optional, non-exclusive object of the present invention to provide apparatus and methods for thermoforming portions of a polymer sheet while not forming, or otherwise materially distorting, other portions of the sheet. 
         [0010]    It is an additional optional, non-exclusive object of the present invention to provide apparatus and methods permitting text, art work, or other information to be printed on to-be-formed material in an undistorted manner yet remain intelligible post-forming. 
         [0011]    It is also an optional, non-exclusive object of the present invention to provide apparatus and methods for selective thermoforming including use of mechanical heat-transfer barriers. 
         [0012]    It is yet another optional, non-exclusive object of the present invention to provide apparatus and methods in which the heat-transfer barriers are in the form of plates having cut-outs through which heat may readily pass. 
         [0013]    It is a further optional, non-exclusive object of the present invention to provide apparatus and methods for selective thermoforming using controllable banks of heaters to allow variable heating of the molds themselves. 
         [0014]    It is, moreover, an optional, non-exclusive object of the present invention to provide apparatus and methods for selective thermoforming while limiting the amount of trim. 
         [0015]    Other objects, features, and advantages of the invention will be apparent to persons skilled in the relevant art with reference to the remaining text and the drawings of this application. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a perspective view of exemplary thermoforming apparatus useful as part of or in connection with the present invention. 
           [0017]      FIG. 2  is a perspective view of a portion of a mold comprising part of the apparatus of  FIG. 1 . 
           [0018]      FIG. 3  is a close-up view of part of the mold portion of  FIG. 2  illustrating especially various plugs protruding upward from its surface onto which a formable sheet may be placed. 
           [0019]      FIG. 4  is a generally elevational view of an exemplary heat-sinking plate that may comprise part of the present invention. 
           [0020]      FIG. 5  is a close-up view illustrating a formed polymer sheet contacting the mold part of  FIG. 3 . 
           [0021]      FIG. 6  is a generally elevational view of an exemplary product thermoformed in the manner of the present invention. 
           [0022]      FIG. 7  is a generally side (edge) view of an exemplary product similar to that shown in  FIG. 6 . 
           [0023]      FIGS. 8A-C  are various views of a plug consistent with  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    Depicted in  FIG. 1  is exemplary thermoforming apparatus  10 . Apparatus  10  may be a conventional thermoforming machine, any number of which are available commercially. Preferably included as part of apparatus  10  are mold  14  (see also  FIGS. 2-3 ) and heater  18 . A computerized controller including actuating means  22  may, if desired, be connected to heater  18  to control aspects of its operation. Actuating means  22  may comprise one or more manual switches as shown in  FIG. 1 . Those skilled in relevant fields will recognize, however, that other manners of actuating heater  18  may be employed instead and that no controller is required. 
         [0025]    Heater  18  preferably is positionable above mold  14  so as to supply heat only to one side of the mold  14 , which itself may be heated.  FIGS. 2-3  show aspects of an exemplary version of mold  14 , which preferably (although not necessarily) is made of aluminum. Alternatively, mold  14  may be of composite type with both male and female components. As illustrated particularly in  FIG. 3 , mold  14  may comprise a generally planar upper surface  26  from which one or more plugs  30  protrude. In use of apparatus  10 , plugs  30  function as three-dimensional objects about which sheets of polymer material are formed. 
         [0026]      FIGS. 8A-C  illustrate aspects of an exemplary plug  30 . Plug  30  may, if desired, be shaped generally as a cylinder and include section  31  comprising upper surface  32  together with side  33 . Formed in side  33  may be one or more notches  35 . At least two, and preferably three (or more) such notches  35  are incorporated into side  33 , with the notches  35  preferably (although not necessarily) being angularly spaced evenly about the circumference of plug  30 . For example, if plug  30  includes three notches  35 , each notch  35  may be spaced one hundred twenty degrees (120°) from adjacent notches  35 . As depicted in the side view of  FIG. 8B , notches  35  need not extend completely to upper surface  32 —although they may do so if desired. 
         [0027]    Also detailed in  FIGS. 2-3  as part of mold  14  are clamps  34  and alignment pins  38 . Clamps  34  surround some or all of perimeter  42  of mold  14  and retain to-be-formed material in place relative to upper surface  26 . Pins  38 , which like plugs  30  extend upward from upper surface  26 , facilitate alignment of the to-be-formed material relative to the plugs  30 . 
         [0028]    An exemplary heat sink  46  appears in  FIG. 4 . Sink  46  may be sized and shaped in any appropriate manner and may of any suitable heat-absorbing (or -reflecting) material. Preferably, however, sink  46  conforms to the shape of the corresponding mold or surface to be heated; as shown in  FIG. 4 , exemplary sink  14  is in the form of a generally rectangular, generally planar aluminum plate. Consistent with the present invention, sink  46  may include one or more cut-outs  50  through its depth, each of which preferably is approximately the size and shape of an associated plug  30 . Sink  46  additionally may include openings  54  for receiving alignment pins  38 . 
         [0029]    Apparatus  10  may be utilized with any thermoformable material. For certain purposes identified herein, however, the material beneficially is polyethylene terephthalate (“PET”), a polymeric plastic resin. Additionally beneficial for various of these purposes is that the PET be transparent. Again, though, the thermoformable material need not necessarily be clear or transparent, nor need it be PET. For ease of handling, the material advantageously may be preformed into a generally planar sheet of predetermined size and shape. 
         [0030]    Among products usefully created using the present inventive techniques are plastic display holders for coins or souvenirs. Collector-quality versions of such holders may, and indeed typically, include color printing, art work, and text in unformed regions. By contrast, formed regions--into which coins are placed-preferably remain clear so as not to impede viewing of the coins. In some cases the holders may be combined back-to-back or placed within clear housings for further protection of the coins. Objects other than coins or souvenirs may be displayed, and products other than display holders may be created, however, as should be apparent to persons skilled in the art. 
         [0031]    According to at least one method of the present invention, mold  14  may be heated to a preset temperature. The temperature may be selected so as to allow thermoformable material to be formed by the mold  14  and so as to be sufficient to remove heat from the material. Preferably, however, the selected temperature is such that warping or chill marks will not be formed on or in the material. 
         [0032]    After mold  14  is heated adequately, a sheet of material containing undistorted color printing, art work, or text (or combinations thereof) may be laid onto upper surface  26  of mold  14 . For at least some display holders, up to six colors may be printed on each side of the sheet, with opaque material (text and art work) then printed over the printed colors. Of course, any or all of the printed matter may be omitted if not needed in the final product. Nevertheless, when present, the printed matter need not be pre-distorted, as it is not subject to material distortion during the forming process. 
         [0033]    Assuming the above-described coin display holders are to be created, the sheet preferably contains openings through its depth for receiving alignment pins  38 , with the openings themselves positioned so that, when pins  38  are received, unprinted (clear) areas of the sheet are positioned on upper surface  26  atop some or all of plugs  30 . Clamps  34  may then be employed to secure the periphery of the sheet against upper surface  26 . Thereafter, sink  46  may be placed atop the sheet, with its openings  54  likewise receiving alignment pins  38  and at least some of its cut-outs  50  aligned with clear areas of the sheet. So placing sink  46  effectively sandwiches the sheet between mold  14  and sink  46 , precluding its longitudinal and lateral movement. 
         [0034]    Following placement of the sheet relative to mold  14 , heater  18  is repositioned closely above sink  46  and activated for a selected period of time. Continuing with the display holder example, heater  18  may be activated for approximately thirty seconds. Heat or other energy from heater  18  transfers to sink  46  and, where cut-outs  50  in sink  46  exist, to (clear) areas of the sheet therewith aligned, where it is absorbed by the polymeric material. 
         [0035]    As the exposed areas of the sheet absorb sufficient heat to reach their forming temperatures, mold  14  is evacuated so as to stretch (form) the material around plugs  30 . Heater  18  then may be repositioned away from mold  14 , the formed sheet of material may be allowed to cool, and sink  46  may be removed so as to expose the sheet of material.  FIG. 5  illustrates material  58  in this exposed state, with the material  58  including (in this example) both unformed portions  62  and formed portions  66 . The sheet of material  58  thereafter may be removed from mold  14  and, if appropriate, divided into display holders, examples of which (designated  70 A and  70 B) are depicted in  FIGS. 6-7 . Moreover, because only the periphery of material  58  was clamped during the forming process and need be trimmed, the vast remaining majority of the material  58  was available to create products. The processes of the invention may be repeated for any number of sheets of material. 
         [0036]    Exemplary holder  70 A includes six formed portions  66 , five generally circular in shape and configured to receive a coin for display (see, e.g.,  FIG. 7 ). In  FIG. 6 , the sixth formed portion ( 66 A) of holder  70 A includes embossed letters “USA.” By contrast, many of unformed portions  62  include color printing, with additional text and art work  74  printed thereon. Distortion-free text spelling “TEST” in printed areas of unformed portions  62  renders apparent the fact that the portions  62  did not distort while portions  66  were forming. Because holder  70 A is merely one of many examples of holders capable of being made by the present invention, in no way is the invention limited to holders having any particular number or type of formed portions  66  or unformed portions  62 . (Further, although not presently preferred, any of portions  66  may include distorted printing that becomes more legible when portions  66  are formed.) 
         [0037]    Because plugs  30  may include notches  35  against which material  58  may be fashioned, formed portions  66  may include a corresponding number of “crush tabs” or “click-in features” protruding inward into the coin-receiving regions. These tabs provide some tolerances for portions  66 . If, for example, a portion  66  is slightly larger in diameter than a to-be-received coin, the coin, when inserted, may (frictionally) bear against the inwardly-protruding tabs to be retained in position. If unneeded, the tabs will be crushed or otherwise deformed upon insertion of the coin so as not to impede its retention. 
         [0038]    The foregoing is provided for purposes of illustrating, explaining, and describing embodiments of the present invention. Modifications and adaptations to these embodiments will be apparent to those skilled in the art and may be made without departing from the scope or spirit of the invention.