Abstract:
A device for heat shrinking thin film onto open-topped containers to form spill-resistant covers is shown. A radiant energy source is intermittently energized in association with timers to direct radiant energy towards the thin film. An energy absorbing body is associated with the thin film to absorb energy and create heat adjacent to the film which in turn causes the thin film to shrink. The energy absorbing body can be the adaptation of the thin film to be opaque to the radiant energy by either being coated with an energy absorbing coating such as printing, or being made partially opaque by means of tinting. The container can also be adapted to absorb energy by including a darkened band adjacent the upper edge of the rim. The device can also interpose an energy absorbing body, such as a darkened aluminum screen adjacent to the film to be heated to cause the thin film to shrink. The device shrinks the thin film around the rim first, then shrinks the film across the top of the container to form a spill-resistant cover. In one embodiment, printed patterns on the film can be used to create perforations.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to a device which may be used to seal food into open-topped containers. In particular, this invention relates to a device suitable for heat shrinking film onto such open-topped containers to seal food or drink inside the container.  
         BACKGROUND OF THE INVENTION  
         [0002]    Presently in the fast food drink industry it is typical to serve a drink in a paper, plastic or other disposable cup topped with a preformed plastic lid. The plastic lid fits tightly over the lip formed at the top of, for example, a paper drink cup, and may include apertures to permit straws or openings to be formed in the lid to directly drink the contents of the cup.  
           [0003]    Unfortunately, there are many problems associated with the use of these plastic lids. For example, the lids are generally expensive. Further, the lids are bulky and create problems in storage and in disposal. Further, the seal formed by the lids is dependant upon the lid being placed on properly, and can leak if not properly placed. Finally, the handling of the lid is not completely hygienic.  
           [0004]    In order to overcome these problems, various devices and methods have been proposed in which a cover is placed on an open-topped container and then heated to shrink it into sealing engagement with the top of such a container. Examples of such devices can be found in the following United States patents: U.S. Pat. Nos. 3,260,775; 3,354,604; 3,460,317 3,491,510; 3,494,098; 3,507,093; 3,621,637; 3,877,200; 3,838,550; 3,916,602; 4,035,987; 4,184,310 and 4,562,688. While the solutions proposed by these prior devices and methods are interesting, they fail to provide a sufficiently cost efficient, easy and inexpensive alternative to preformed rigid plastic lids. As a consequence, rigid plastic lids remain in widespread use. Some of the main failings of these prior devices are that they are bulky, noisy, unresponsive, and expensive. Heating systems comprising blowing air over a hot element and then onto a film require large amounts of unnecessary heat, even when in standby mode, which makes temperature control very difficult. Further, continuous elevated temperatures are expensive to maintain and may be deleterious to the immediate environment.  
         SUMMARY OF THE INVENTION  
         [0005]    Aside from the benefits of increased hygiene and reduced waste, the present invention is directed to providing a practical device which has commercial utility. One aspect of the present device is to provide an energy efficient way of sealing open-topped containers which avoids any substantial build-up of heat. An intermittent source of radiant energy is used, and energy is directed onto an energy absorber located at the specific place where heat is required. Thus, heat is originated where it is needed, when it is needed and a cooler, quieter, safer and more efficient device results.  
           [0006]    The present invention provides a device for heat shrinking a cover onto an open-topped container, said device comprising:  
           [0007]    a housing adapted to receive said container; and having a strip of heat shrinkable thin film;  
           [0008]    a cutting means positioned against said thin film for cutting said thin film upon said thin film being urged onto said cutting means by said container;  
           [0009]    a hood for holding a cut piece of said film in place across said open top of said container, wherein said cut piece includes a portion extending from under said hood downwardly around an upper outer rim of said container;  
           [0010]    a first radiant energy source for directing energy toward said downwardly extending portion of said cut piece of film;  
           [0011]    a first means to absorb radiant energy to transfer heat to said downwardly extending portion of said cut piece of film; and  
           [0012]    a switch means for intermittently energizing said first radiant energy source whereby said downwardly extending portion of said cut piece of film is shrunk onto said rim; 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 is a perspective view of a device according to the present invention in use;  
         [0014]    [0014]FIG. 2 is a front sectional view of an open-topped container according to the present invention with a heat shrunk cover in place;  
         [0015]    [0015]FIG. 2 a  is a top view of the container of FIG. 2.  
         [0016]    [0016]FIG. 3 is a front view of the container of FIG. 2 having a darkened upper band;  
         [0017]    [0017]FIG. 4 is a top view of the device of FIG. 1, with the top wall broken away to show the contents;  
         [0018]    [0018]FIG. 5 is a sectional view taken along lines  5 - 5  of FIG. 4;  
         [0019]    [0019]FIG. 6 is a view similar to FIG. 5 with the container in a raised position;  
         [0020]    [0020]FIG. 7 is a view of a part of the device of FIG. 1; and  
         [0021]    [0021]FIG. 8 is a view along lines  8 - 8  of FIG. 7;  
         [0022]    [0022]FIG. 9 is an alternate configuration for a knife element shown in FIG. 5;  
         [0023]    [0023]FIG. 10 is a view along lines  10 - 10  of FIG.  9 ;  
         [0024]    [0024]FIG. 11 is a schematic sketch of an electronic control circuit for the present invention;  
         [0025]    [0025]FIG. 12 is an alternate embodiment of a micro-switch system according to the present invention;  
         [0026]    [0026]FIG. 13 a  is a view along lines  13 - 13  of FIG. 12 in a first position; and  
         [0027]    [0027]FIG. 13 b  is a view along lines  13 - 13  of FIG. 12 in a second position. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0028]    [0028]FIG. 1 shows a device  10  for heat shrinking a thin film onto an open-topped container  12 . The housing  10  includes an opening  14  of sufficient size to allow placement of the container  12  within the housing  10 . In the embodiment of FIG. 1, placement of the container  12  within the opening  14  is accomplished manually, illustrated by a hand  16 .  
         [0029]    Turning to FIG. 5, there is shown a cross-sectional schematic view of the operational components of the device  10  of FIG. 1. The container  12  is shown in the opening  14 . The opening  14  is defined by side walls  18  and  20  of the device  10 . Shown on the right-hand side is a roll of thin plastic film  22  on an axle  24 . The film  26  passes over a roller  28  across the top of the container  12  across a second roller  30  and onto a take-up axle  32 . Shown at  34  is a rewind motor. It will be appreciated that the rewind motor  34  can rotate the pick-up axle  32  in the direction of arrow  36  which will advance the film  26  across the top of the container  12  and cause the roll of film  22  to rotate in the direction of arrow  38 . Alternatively, the advancing of the film  26  could be accomplished manually by turning a lever or knob mounted on take-up axle  32 .  
         [0030]    The film  26  is preferably a bi-axially oriented shrink film having a preferred thickness of between 60 to 100 gauge. Good results have been achieved with a 75 gauge polyvinyl chloride film purchased from Reynolds Metals Company at Richmond, Va. Other films, such as copolymers, polyolefins and the like may also be appropriate. The film, to be most useful, must be foodgrade contact-approved by the appropriate regulatory authorities. A 7½″ outer diameter roll of 75 gauge shrink film, which includes a 3″ diameter fibre core, will yield approximately 8,000 covers according to the present invention.  
         [0031]    In FIG. 5, the container  12  is located in a locator identified generally at  40 . The locator  40  is shown in more detail in FIGS. 7 and 8. Turning to FIG. 7, there is shown a plate  42  having a pair opposed guides  44  and  46 . The plate  42  also has an opening  48  located between the guides  44 ,  46 . The guides  44  and  46  are substantially identical and therefore the following discussion in respect of guide  44  applies equally to guide  46 .  
         [0032]    The guide  44  comprises a rub rail  50  which contacts an outer edge of a container  12 . Extending from plate  42  are two posts in respect of each guide  44 ,  46 . In respect of guide  44  there is a stop post  52  and a guide post  54 . A slot  56  is formed in the guide  44  and a spring  58  is housed between the guide post  54  and the end of the slot  56 . A pin  59  may be used to secure one end of the spring  58 . A washer  60  is used to retain the other end of the spring  58  within the slot  56 . The washer  60  is placed around the guide post  54 . Between the free end  55  of guide post  54  and the washer  60  is a further spring  61 . The spring  61  allows the guide plate  44  to articulate away from the plate  42  to facilitate removal of the container  12  from the device  10 .  
         [0033]    It will now be appreciated that the guide  44  can move laterally in the direction of double ended arrow  62  guided by means of the stop  52  and the guide post  54  with the slot  56 . It will also be appreciated that the curved portion  64  of the rub rail  50  will provide an indication to anyone inserting a container  12  into the locator that the container is appropriately located. Appropriately in this sense means centered under the plate opening  48 .  
         [0034]    Turning to FIG. 8, the locator  40  of FIG. 7 is shown in cross-sectional view. As can be seen, the guides  44  and  46  are positioned on adjacent side edges of a container  12 . The plate opening  48  is shown together with the plate  42 . The thin film  26  is also shown stretched across the top  13  of the container  12 .  
         [0035]    It can now be appreciated that the container  12  can be moved in the direction of double ended arrow  64  into position beneath plate opening  48 . During this period, the guides  44  and  46  will gradually open and then close about the periphery of the container  12 . Thereafter, as shown in FIG. 8, the container  12  is free to be moved in the direction of double ended arrows  66  as will be discussed below. It will be appreciated that containers  12  of varying diameter can thus be accommodated by the instant invention, since all containers will be centered by the locator beneath the plate opening  48 . This is desirable in a food services environment where cup size selections typically include small, medium and large.  
         [0036]    Turning now to FIG. 5, a container  12  is shown centered in locator  40 . A first radiant energy source  68  and a second radiant heater  70  can now be explained. Located above the centered and located container  12  is a top shrink hood  72 . The second radiant heater  70  is located within the top shrink hood  72 . The top shrink hood  72  includes a glass shield  74  and a heat transfer means  76 . In some circumstances the glass shield  74  may not be required, however, to prevent the possibility of splashes reaching the second radiant energy source  70 , it is preferred. It may not be necessary to use glass. Plastic or other transparent substances may be appropriate. Good results have been achieved when the heat transfer means  76  is made from a screen aluminum material painted a dark colour, such as black. The dark aluminum heats and cools quickly which is desirable in the circumstances.  
         [0037]    A pierce tool  78  is also shown extending outwardly from the heat transfer means  76 . The purpose of the pierce tool  78  is to make a vent opening in the thin film to allow gases such as carbon dioxide from a soft drink to escape the container.  
         [0038]    An alternative to pierce tool  78  is to form small opaque portions  79  in the shrink film. These opaque portions or “dots” will cause a hot point which may perforate the film as more fully explained below. If desired the hot points can be made in a specified pattern to form a sipping opening or the like, as shown in FIG. 2A. Also shown in FIG. 2 is a straw  122  with a pointed end  124  for piercing the film, shown in place as  126 . A fluid, such as a soft drink is shown at  128 .  
         [0039]    Also shown in FIG. 5 is a drive belt  80  which connects a pulley  82  with a motor. Attached to the pulley  82  are a pair of arms  84 . The arms  84  rotate when the pulley  82  is rotated by the belt  80 . Depending from the arms  84  about pivot points  86  are pivot arms  88 . Pivot arms  88  include a roller  90  at one end and the first radiant energy source  68  at the other end. If preferred, a reflector may be provided such as  92  around the first radiant energy source  68 .  
         [0040]    Also show in FIG. 5 is a knife or film cutting blade  94  to which is attached a heating element  96 . The heated blade  94  ensures a quick clean cut of the thin film, upon the thin film contacting the blade  94 . As can be seen from FIG. 5, the blade  94  is below the top hood  72 , so the film will be cut to shape just prior to or about the same time as the container  12  contacts the hood  72 . Good results have been achieved when the blade is made from a two point center face steel cutting rule, and maintained at a temperature of between 275° F. to 400° F. This format appears to limit smoke and fume generation.  
         [0041]    The knife  94  may be circular in shape, or may be as shown in FIGS. 9 and 10. It will be noted that the knife  94  in FIGS. 9 and 10 includes a rounded oblong section  95 . This will result in a similarly shaped section being formed in a cut piece of film, as described below, which can be used as a convenient pull tab for removing a cover which has been shrunk onto a container  12 . In the preferred embodiment the thin film  26  has a width greater than the width of the knife  94  so that a trim  27  (see FIG. 5) is left after the cut is made, and the trim  27  is strong enough to allow the film  26  to be advanced by a tensile force without tearing.  
         [0042]    Turning now to FIG. 6, the operation of an instant device can now be understood. In FIG. 6 the container  12  has been raised in the direction of arrow  100 . This has had the effect of pushing the film  26  upwardly into engagement with the knife heated film cutter blade  94 . This has caused a cut portion of the film shown as  102  to be draped across the top  13  of the container  12 . At this point the hood  72  is holding the cut piece of film  102  generally in place. As the container  12  is raised further, the hood  72  is also raised. Rollers  90  then contact a ledge  104  formed on the outer surface of the hood  72 . Further upward movement causes the movement of the first radiant energy source  68  about the pivot point  86  until the first radiant energy source  68  is closely adjacent to a draped over edge of cut portion  102  shown as  103 . Contact is then made at a limit switch, as explained below in respect of FIG. 11, which energizes a motor  99  (shown in FIG. 4). Upon energization of the motor  99 , the belt  80  revolves causing the rotating arms  84  to revolve rotating the first radiant energy source  68  about the periphery of the top of the container  13 . Simultaneously with the energization of the motor  99  and the rotation of the first radiant energy source  68 , the first radiant energy source  68  is energized to cause radiant energy to be directed towards the dangling edge  103  of the cut portion  102  of the said film  26 .  
         [0043]    It will be appreciated that the preferred invention causes the first radiant energy source  68  to move into position closely adjacent the downward edge  103  of the cut portion  102 . Such movement is preferred because radiant energy obeys the inverse squared rule in which the amount of energy is proportional to an inverse of the square of the distance from the source. By locating the first radiant energy source  68  close prior to being energized, more energy can be usefully used and focused away, for example, from an operator&#39;s hands. Also, by the pivoting action, the operator&#39;s hands are kept clear of the energy source  68 , until the container  12  is in position.  
         [0044]    After a predetermined length of time, the first radiant energy source  68  is de-energized and the second radiant energy source  70  is energized by a timer  120 . The second radiant energy source  70  energy is directed through the glass shield  74  onto an energy absorbing body  76 . This transfer of heat causes a shrinking of the top portion across container  12  of the cut portion  102 . Thereafter, the sealed container  12  can be lowered and removed from the apparatus.  
         [0045]    A preferred type of energy absorbing body  76  is a darkened aluminum screen. The body  76  is placed very closely adjacent the top portion of the cut section  102  and may be in contact therewith. The darkened screen or body  76  absorbs energy and transfers it onto the top portion. It will be appreciated that aluminum is a suitable material because it will cool rapidly, when the energy source  70  is shut off, thereby preventing premature shrinkage of a top portion on a subsequent container upon being first introduced into the hood  20 .  
         [0046]    It has been found that the preferred radiant energy sources are Tungsten Halogen Lamps. About 70% of the energy produced by these lamps is in the preferred wavelength range of the infrared (750 millimicrons and beyond).  
         [0047]    These lamps are compact, durable, inexpensive and readily available. Lamps in the range of 200 to 300 watts are suitable. It will be appreciated by those skilled in the art that other energy sources which produce sufficient infrared radiant energy may also be used.  
         [0048]    It is also to be noted that the radiant energy emitted by such an energy source can be turned on and off instantaneously and focused and directed to the location it is desired, without stray heat energy being produced, and the energy source does not have to be on continuously, or on standby in readiness for a container, which is the case of prior art hot air systems.  
         [0049]    Turning now to FIG. 4, the belt  80 , pulley  82  and drive motor  99  are all shown. Also are shown two rotating arms  84  and two first radiant heaters  68 . It will be appreciated by those skilled in the art that fewer or more radiant heating elements could be used according to space requirements and preference. However, when the drive motor operates at 100 rpm, two radiant heat means  68  provides good results. By varying the size of the pulley  82 , the speed of revolution of the first radiant energy source  68  can also be varied. Good results have been achieved when the pully  82  is configured to cause the first radiant energy source  68  to rotate at 100 rpm.  
         [0050]    It will also be appreciated that the spinning first radiant energy source  68  could be replaced with a row of fixed position bulbs. However, the process would be slightly more difficult to control, since the total energy output would likely be greater, and more energy expensive. Thus, the moving first energy source  68  is preferred.  
         [0051]    Turning to FIG. 11, a schematic of an electrical system  150  for the instant invention is disclosed, which sets out in more detail the interaction between the container  12  and hood  72  location, and the activation of the various components described above.  
         [0052]    One of the characteristics of the electrical design is that it must compensate for the varying rates that the container  12 , which is moved by a human hand, enters and leaves the device  10 .  
         [0053]    In the preferred embodiment the raising and lowering of hood  72  and the motion of locator  40  will trigger micro-switches which engage timers as described below. Certain events must take place as hood  72  is raised and other events must take place when hood  72  is lowered.  
         [0054]    Referring to the wiring system  150 , F 1  is a fuse. When the main switch  170  is turned on, a pilot light R lights up. Then, switches S 1  and S 2  are manually turned on. As shown, S 1  turns on resistance heater  96 , which heat the knife  94 . A thermostatic control is shown at  97 . When S 2  is turned on, it activates motor  99  and also signals timer T 1 . Also shown is a relay TM- 1 . The timer T 1  engages motor  34  and advances the film  26  for a single “space”, which is determined by the time set on timer T 1 . Thus when the machine is activated and ready to operate by turning on switch S 2 , a fresh piece of film  26  is automatically presented. Switch LS 1  is situated on plate  42 , (shown in ghost outline in FIG. 7) so that when guide  46  rotates outwardly on withdrawal of the container, LS 1  also signals timer T 1  which engages motor  34  and advances the film in a like manner.  
         [0055]    Also shown are switches LS 2  and LS 3  which close when hood  72  moves upward. These switches activate a second timer T 2  which activates relay TM- 2  which in turn activates first radiant energy source  68 . On the downward motion switch LS 3  opens and thereby prevents timer T 2  from activating source  68  again.  
         [0056]    On the downward motion of hood  72 , switch LS 4  closes, which activates timer T 3  which through a relay TM- 3 , activates radiant energy source  70  for a predetermined time.  
         [0057]    [0057]FIG. 12 shows in schematic form the microswitch interconnections. On the left hand side of FIG. 12 are the belt  80  around the pulley  82 . A shaft  200  extends upwardly from the top hood  72 . A connecting rod  202  is attached to shaft  200 , and will rise and subside with the hood  72  being raised and lowered. Remote from shaft  200  there is a rack  204  connected to the rod  202  which interacts with a pinion  206 , in a manner shown by double ended arrows  208 . Also shown are a cam shaft  210  attached to eccentric cams  212 .  
         [0058]    Shown in FIGS. 13A and 13B are the means of closing electrical circuits upon rotation of the cam shaft  210  by the pinion  206 . A secondary roller  214  is located on a pivot arm  216 . When cam  212  is rotated in one direction an electrical spring clip  218  is forced into contact with an electrical contact  220  closing a circuit. Upon being rotated in an opposite direction, the cam  212  urges the pivot arm  216  up and out of the way, and does not close the circuit, as shown in FIG. 13B.  
         [0059]    It can now be appreciated that the present invention uses radiant energy from the radiant energy sources to effect shrinkage. Radiant energy is preferred, because it travels relatively unimpeded through transparent mediums such as air or transparent film. The preferred radiant energy source is a Tungsten-Halogen bulb, which is described in more detail above. The present invention has process parameters for heating which depend upon an absorbing means for the radiant energy, and in particular, how close any absorbing means conforms to a theoretically ideal “black body”. An ideal “black body” completely absorbs all radiant energy that strikes it and thus is capable of radiating that same energy outward.  
         [0060]    The way in which the present invention seals heat shrinkable thin film onto a container, is to employ a first means to transfer heat to the downwardly extending portion of the cut piece of thin film. In this sense, the first means can comprise adapting the thin film to absorb energy, interposing an absorbent body adjacent to thin film, or adapting the area of the container just below the rim to become energy absorbing. The thin film can be adapted to absorb energy by being made from a tinted material, or by being coated with an energy absorbent coating, for example, printing. The ability of the opaque or coated film to absorb radiant energy will vary depending upon what type of tinting or coating is used. A darker or more opaque film will absorb more energy.  
         [0061]    An example of a preferred interposed absorbent body is a darkened aluminum screen  112 , which moves closely adjacent the edge  103 . The darkened portion of the screen will absorb energy and then radiate it, giving rise to heat. The heat will be transferred to the air adjacent to the film, then to the film which will shrink the film.  
         [0062]    The container may be adapted to absorb radiant energy, and thus produce heat in a preferred location, by including a darkened band  15  in the area where heat generation is desired, such as just below the rim. For aesthetic reasons, black bands may not be acceptable, but other coloured bands will also work. With a cooler colour, the exposure to the radiant energy source may need to be slightly longer. However, the length of time of exposure to the radiant energy source can be adjusted in the present invention through adjustments made to the timer T 2 . A gap  17  may be incorporated into the band  15  to permit the end user to lift the shrunken cover off the container if so desired.  
         [0063]    In some circumstances, it may be desirable to urge the film onto the cup. Therefore, the present invention also comprehends the use of a spring wire  110 , which trails (or leads) the revolving first radiant heat means  68 , and urges the edge  103  into contact with the container  12  just below the top  13 .  
         [0064]    It will be appreciated by those skilled in the art that the foregoing description relates to a preferred embodiment and that various modifications can be made without departing from the broad scope of the appended claims. Some of these modifications have been discussed above and others will be apparent to those skilled in the art.