US 3573430 A
Description (OCR text may contain errors)
United States Patent I 72] lnventor Paul Eisler London, England  Appl. No. 607,601
 Filed Dec. 30, 1966  Patented Apr. 6, 1971  SURFACE HEATING DEVICE Primary Examiner-J. V. Truhe Assistant ExaminerC. L. Albritton Atlorney-Watson, Cole, Grindle and Watson I ABSTRACT: A dispensable container for a substance to be heated therein incorporates a low voltage surface pattern heating film with externally accessible terminals, the relative disposition of the film container and substance being such that the heat generated by the film does not exceed that dissipated into the substance by more than 4 watts per square inch, means also being provided to ensure that more heat reaches the substance than the external surface of the complete package. I
There may be heat insulation between the container and its surface. The film may be of patterned metallic foil. There may be provision to supply heat from outside by radiation or conduction. There may also be provision for a small body of liquid between the film and substance, the liquid having access to a substantial area of the substance so that the temperature is limited to the boiling point of the liquid.
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SHEET 12 0F 12 y PCZI/ Z 26/" 4% L r SURFACE HEATING DEVICE This application is a continuation-in-part of my Ser. No. 301,488 filed Aug. 12, 1963 for Surface Heating Device (now matured into US. Pat. No. 3,296,4l5) which was itself a continuationin-part of my Ser. No. 749,554 filed Jul. 18, 1958 for Surface Heating Device (now matured into US. Pat. No. 3,100,71 l
The invention relates to the heating of substances contained in packages of relatively small size. Foodstuffs in single or multiportions for immediate consumption are a convenient example illustrative bothof the order of size and the kind of substance but the invention is not restricted to this example and can be applied to many other substances which it may be desirable or necessary to heat in the package, as for example. adhesives, coating materials, synthetic resins and similar thermosetting or thermoplastic materials, greases and chemicals. Hereinafter foodstuffs will usually be referred to for convenience.
The present invention provides for a substance to be heated while contained in a dispensable container included in a package to which end a thin low-voltage heating film is incorporated in the package at least during the heating operation, this film having a surface pattern presenting a resistive electrical path between at least two terminals to which access can be obtained for connection to a supply without removing the substance from the container. Thus by making connection of the terminals to a supply having a voltage appropriate to the resistance of the path heat can be generated in the film by which the substance can be heated. One object of the present invention is to enable such an arrangement to be used to heat the substance rapidly without any risk of hot spots in the conductive pattern which might damage the material, damage the pattern or have other undesirable results.
If it could be ensured that the whole conductive pattern were in intimate contact with the substance so that direct conduction of heat into the substance took place, the temperature gradient would be small, there would be no local hot spots and the permissible rate of heating would be limited essentially only by the heat conductivity of the substance and the time necessary for the substance to reach the required temperature. ln practice however the conductive pattern usually cannot be allowed to come into direct contact with the substance because such contact may be undesirable for electrical reasons or on account of the nature of the substance and material of the pattern, for reasons of packaging, use or processing or storing of the substance, etc. There will usually therefore be at least one thin layer of material between the pattern and the substance to insulate the former and protect the latter; there may be more than one such layer as will appear later. Also it may be necessary for the pattern of the film to extend to parts of the container which are not or may not remain in direct contact on their external surfaces with the substances or even extend outside the container altogether, so that from these parts of the film heat can be dissipated only by radiation or possibly by radiation with some convection. Shortly stated therefore the dissipation of heat from the film in general will not be a simple function only of its area, and there will be a serious risk of local hot spots if a uniformly distributed resistive pattern is uniformly supplied with current without consideration of any differentiation required by the particular conductive heat transfer into the substance.
For reasons of efficiency, and it may be to enable the package to be handled in comfort, it is desirable that as much of the heat as possible should be dissipated with the substance and as little as possible in other directions.
According to the present invention the problems thus presented are solved by dimensioning the pattern so that in operation in addition to the dissipation into the substance no pan of the pattern has to dissipate more than 4 watts per square inch. or in other words when the pattern is connected to a supply to the appropriate predetermined voltage the difference between the heat dissipated into the substance in the container from any area of the surface of the heating film and the wattage supplied to said area is less than 4 watts per square inch of said area, while means are also included in the package ensuring that when the film is energized more heat is dissipated into the substance than reaches the external surface of the complete package. While such a difference may not be critical in any absolute sense, extensive investigations have shown that under such conditions rapid heating by a dispensable heating film without hot spots or damage becomes possible.
Depending on the manner in which the substance and the film are disposed in relation to one another during operation and the disposition in relation to one another during operation of layers which come between the actual conductive pattern and the substance itself it may be possible to use a film the loading of which is uniformly distributed over the whole patterned area, or it may be necessary to vary the loading in different parts of the lilm.
To assist in controlling the relative rate of dissipation of heat into the substance and to the external surface of the package, in some cases the film may be spaced a substantial distance inwardly from the external surface of the package, and the space thus left may be at least partly filled with thermal insulation. The package may include a wall having a flexible, thin, impervious and heat resistant inner layer, eg of metallic foil, and means ensuring intimate contact of the heat ing film with the outside of said layer at least when the film is connected to the supply.
A development of the invention provides for some other substance to be carried on a common supporting means such as a tray, thermal insulating means being provided whereby heat reaching the external surface of the package is hindered from reaching the further substance, thus for example enabling meals to be prepared consisting of both hot and cold foods A further object of the invention is to provide a heater additional to the heating film and so to construct a wall of the package that the heating of the substance can be supplemented by heat radiated by the additional heater.
Another object is to include means in the heat path between the film and the substance whereby the surface temperature at any point on the substance is prevented from rising above a predetermined maximum value, e.g. a value at which it is damaged or develops some undesirable characteristic such as stickiness. Thus at least during part of the heating period the film may be spaced from the surface of the substance to be heated thereby, and a small body of liquid may be present in the space which has access to the substantial area of the substance so that the temperature of the substance is kept down to boiling point of the liquid. This provision for the presence of liquid between the heating film and the substance is well adapted for use with deep frozen substances. The deep frozen substances may be enclosed within the container at least by a wrapper of metallic foil having perforations distributed thereover, a further substance which boils when heat is supplied also being included in the package and having access to the perforated foil. Such a package may be supplied separately from a heating film so that the two can be put together for use, or the package be heated by some conventional heater such as a gas or electric cooker.
Still another object of the invention is to enable the heat supplied by the film to be supplemented by conducted heat from another source, to which end a heat conductive flexible wall with one surface in contact with the substance, may have in contact with its other surface over a substantial area a plate equipped with means for supplying heat to it under the control of a temperature sensing element within the plate whereby the temperature of the plate is maintained within known limits, so enabling heat to be supplied to the substance at a rapid rate without the risk of local hot spots or temperature rises.
It may here he mentioned that for the purposes of this specification and in the claims dispensable containers means not that the container has to be dispensed with for technical reasons such as destruction being necessary for access to the contents but that it is economically dispensable. Generally speaking food and many other substances are packaged in containers the cost of which in comparison with the cost of their contents makes it economically feasible to dispense with them once opened, a highly desirable possibility from the hygienic point of view at least in the case of food. The films used in the present invention can also be produced sufficiently cheaply to enable them to be dispensed with, and their nature will generally be such that their cost will be lower than the cost of collecting, cleaning and reconditioning (cg. sterilizing) and reassembling with other parts of the package so that there will be no incentive to attempt their recovery which would generally be undesirable at least in the case of food.
As will be shown they may be made of materials such as metallic foils which are commonly used in packaging, sometimes with the addition of such material as carbon e.g. graphite which in the quality and quantity required is also very cheap.
As mentioned above the films are designed to operate on a low voltage which is not dangerous to human contact generally below 50 volts and preferably a good deal below 50 volts. This not only avoids danger, but considerably cheapens the film by avoiding the need for high-class insulation. The low voltage may advantageously be the same as that of the usual motor car battery, namely 12 volts. Voltages ofthis order enable meander patterns of very convenient dimensions to be used in practicing the invention.
Further objects and features of the invention will become apparent from the following description with reference to the accompanying drawings. The drawings are diagrammatic and in particular where the heating film or other material is shown in section in most cases thicknesses are much exaggerated.
FIG. 1 is a perspective view, and
FIG. 2 a cross section of a moulded troughlike dispensable container according to the invention.
FIG. 3 illustrates the heating film used in FIGS. 1 and 2.
FIG. 4 illustrates the production of a heating film for a folded container.
FIG. 5 is a plan of the blank from which such a container can be made.
FIG. 6 is a perspective view of the folded container.
FIG. 7 is a perspective view, and
FIG. 8 a cross section of another folder container.
FIG. 9 is a perspective view, and
FIG. 10 a section of yet another folded container.
FIGS. 11 and 12 illustrate the production of a heating film with two branches.
FIG. 13 is a vertical section of a dispensable container for heating and dispensing a batch of liquid.
FIG. 14 is a circuit diagram of the container of FIG. 13.
FIG. 15 is a perspective view, and
FIG. 16 is a detail section of another dispensable container for heating and dispensing a batch of liquid.
FIG. 17 is a perspective view, and
FIG. 18 a section of a dispensable container in which the heating film also indicates the quantity of substance removed.
FIG. 19 is a section of an embodiment which provides for movement of the heating film in relation to the contents of the container.
FIG. 20 is a perspective view, partly in section of a further development for steaming or similar heating a substance.
FIGS. 21 and 22 are detail sections of FIG. 20.
FIG. 23 is a detail similar to FIG. 21 of an alternative to FIGS. 20 to 22.
FIG. 24 is another detail of this alternative.
FIGS. 25 and 26 show two stages in the use of a dispensable container in which the configuration of the heating film is changed between stages.
FIG. 27 is a perspective view of a container the contents of which are to be heated by radiant heat.
FIG. 28 is a perspective view showing the container of FIG. 27 in position prior to heating.
FIG. 29 is a perspective view and FIGS. 30 and 31 are details of a further development for radiant heating.
FIG. 32 is a section of another container the contents of which are to be heated by a contact heater.
FIG. 33 is a detail ofa modification of FIG. 32.
FIG. 34 is a detail section and FIG. 35 a perspective view of an arrangement for heating a substance while maintaining another substance on the same support cold.
FIG. 36 is a perspective view of a more elaborate arrangement for the same purposes as that of FIGS. 34 and 35.
FIGS. 37 and 38 are details of FIG. 36.
FIGS. 39 and 40 are a plan and cross section of one of the trays used in this arrangement, the former with no food container in place.
FIG. 41 is another detail.
FIG. 42 illustrates a plant which may be used for processing food during packaging in containers according to the inventron.
FIG. 43 is a detail side view, and
FIG. 44 is a plan view ot'clip device making connection to a heating film.
FIG. 45 illustrates the terminals of the film for which the device of FIGS. 43 and 44 is designed.
FIG. 46 is a detail longitudinal section of FIG. 44.
FIG. 47 shows a circuit using the device of FIGS. 43 to 46.
FIG. 48 is a longitudinal section ofa plug, and
FIG. 49 is a longitudinal section of a socket for making connection to a clip device for connection to the heating film.
FIG. 50 shows a form of heating film which can be used in the invention.
FIG. 51 is a sectional plan and FIG. 52 a sectional elevation ofa form of package within the scope of the invention.
FIG. 53 is a cross section of a heating film which can be used in the invention, embodying a carbon film.
FIG. 54 is a plan of the electrodes, and
FIG. 55 a section of another form of heating film embodying a carbon film.
A convenient form of container used in a package according to the present invention isa troughlike box made of moulded paper mache or similar material or folded from cardboard, paper or the like, the heating film being made integral with a folded-over unpatterned portion which forms an impervious cover layer which serves to enclose the substance in the container notwithstanding that the other material of the package may be porous, a thin electrically insulating layer coming between the folded'over portion and the pattern. The paper mache or folded cardboard, paper or the like is a relatively stiff fibrous material and it forms a thermally insulating layer, while the thin insulation and plain folded-over portion do not impose any great thermal resistance between the pattern and the packaged substance.
FIG. I is a perspective view and FIG. 2 a cross section of an open troughlike box which may be moulded of such material as paper mache. The heating film itself is made from metallic foil of the general form shown in FIG. 3. It consists of a plain part 81 integral with a patterned part 82. In the FIG. a single meander path is formed by the pattern between the central zone and one margin of the complete piece of foil, but this is only one variety; generally the pattern comprises a number of repeats. The part 81 is of somewhat greater length than the part 82. A thin layer of insulating material for example paper of somewhat less width than the portion 82 but greater length is laid over it as indicated by the dotted line 83 and the portion 81 is then folded-over the insulation on the line 84. This portion is of less width than the insulation 83, and thus after folding its edge is overlapped by the insulation. The margin of the portion 82 extends beyond the edge of the insulation 83. The foil and insulation may be held together by adhesive. The film so made is depressed into the troughlike box and the edges are lapped over the edges of the box as indicated by the cross section FIG. 2, the dimensions of the film being designed so that the fold at 84 reaches just under the edge of the box, the edge of the portion 81 remains wholly on top while the projecting margin of the portion 82 is also lapped over the edge of the box. These two margins thus constitute the terminals of the pattern and connection can be made by means of a clip such as described in my US Pat. No. 3,100,71 l.
The length of the patterned portion 82 may be such that it lies wholly within the box while the length of the portion 81 is such that it extends over the end walls of the box and over the upper edge. There will be some puckering of the portion 81 at the corners but this need not damage it and the foil will form an impervious lining which covers the slots in the pattern and is of good heat conductivity. The folding of this portion to fit the container may be facilitated by crimping the material and such crimping may also extend to the patterned portion 81 or the latter may be plain while only the portion 82 is crimped. After the box has been filled the open top may be closed by a cover held by adhesive and this may be arranged actually to press the packed substance against the heating film. Instead of a simple cover a second similar box can be used and the two be secured together by adhesive at the margins but the terminals of the films'will need to be brought further out to permit connection to be made.
FIGS. 4 to 6 illustrate a somewhat similar container to FIGS. 1 to 3, but produced by shaping, scoring and folding of fiat stiff fibrous thermally insulating material such as cardboard, incorporating the heating film. As before the film itself is made of a doubled-piece of foil comprising a plain part 85, a patterned part 86, and a layer of insulation 87 between the two portions. After the film has been made, it is laid on (and may be laminated to) a sheet 88 of cardboard or similar material which has been slotted as at 89 and creased at the dotted lines 91. Thereafter the assembled material is folded at the crease lines and in the corners in the well-known fashion to produce an open box as in FIG. 6.
The laminated packaging material can be produced in a web and is cut up in pieces for shipping as flat stock to be erected into a box when the box is filled. It can instead be supplied in the web, and the plain parts 85 which are to form the impervious inner layer of the box can be left uncrimped, if desired, although the patterned parts 86 may be crimped.
It will be seen in FIG. 5 that the margin of the patterned part 86 extends furthermost to the right, that the insulating sheet 87 does not extend quite as far while the edge of the plain part 85 of the foil does not reach quite to the edge of the paper sheet 87, but all these margins extend so far that when the folding is completed a projecting margin is formed with foil exposed on both sides. This foil constitutes the terminals and the projecting margin of the part 86 may be folded under so that both terminals are slightly overlapped by the paper 87. As before the patterned part 86 does not extend beyond the-ends of the bottom of the box but the plain part 85 covers the bottom and all four walls of the box. The box may be closed by a plain cover or two boxes may be used together if provision is made for access to the terminals.
If it is necessary or desirable to provide for the substance in the box to be heated from the top as well as the bottom as shown in FIGS. 7 and 8 a folded box may be produced having an integral hinged lid 92, a heating film 93 extending into the lid. The film itself is made on the same lines as in FIGS. 4 to 6 the dimensions being modified and the terminals are brought out exactly as in FIG. 6. The shape, slotting and creasing of the cardboard or similar material and the manner of folding are in themselves well known and need not be described further. With this arrangement connection to the film can be effected without opening the box but if preferred the margin with the terminals can be folded inward so that the box must be partially opened to gain access to the terminals though they may then be folded outward. The package may be sealed with the tenninals folded in and the lid sealed so that the purchaser has to destroy the seal to obtain access to the terminals.
Other schemes for supplementing the heat supplied by the heating film, including supplementary heating from the top are described later.
For packaging and heating a liquid, a box as shown in FIGS. 9 and 10 may be used. Such a box again is of well-known form and can be produced by folding from a blank of suitable shape on very similar lines to FIGS. 4 to 8. A heating film 94 with accessible terminals 95 is incorporated and the patterned area extends up to the level 96 while the liquid level is at 97, so that it wholly covers the area of the film in which heat is developed.
By suitably changing the dimension and proportions of the blank various other folded box-type containers can be produced and similarly moulded containers on the lines of FIGS. I to 3 can be produced with different proportions. A moulded container can be provided with a heated lid by extending the film into a moulded lid.
A particular difference between a moulded container and a folded container is that the latter necessarily has sharp corners at the folds while a moulded container can be produced with rounded corners which may be more desirable in some cases. Where the heating film extends into the lid the pattern may be dimensioned so that the heat developed per unit of area is different in the lid from what it is in the bottom of the container.
FIGS. I to 10 show the heating pattern consisting only of one meander path. This is done for sake of simplicity of drawing; each pattern can consist of a group of equal or different repeats, i.e. meander paths in parallel. These examples also assume a pattern of a single resistance or resistance grouping between two terminals and thus a single rate of heating and of heat distribution to the contents of the container under a specific supply voltage. A pattern with two branches having its terminals disposed to have connection made to it by a suitable clip (as described with reference to FIGS. l6, l7 and 18 of my US. Pat. No. 3,296,415) may be made as illustrated in FIGS. 11 and 12. A piece of foil (which again may be cut from a continuous length bearing a repeating pattern) has two patterned margins 98' each with a half-length tab 99 at the extreme edge these tabs being relatively longitudinally staggered. The foil is scored and folded at its longitudinal centerline 101 and again at two longitudinal lines 102. Two pieces of sheet insulation e.g. paper are introduced. One piece 103 goes between the two patterns. On one edge it reaches almost to the score lines 102 while on the other edge it reaches just beyond the edges of the tabs 99 so that the latter are effectively insulated from one another. The second sheet of insulation 104 is introduced between the upper surface of one pattern and the undersurface of the doubled center zone of the film. One edge of this insulation reaches the folds 102 while the other leaves the upper tab 99 exposed. The dimensions of the film and position of the score lines 101, 102 are such that the fold at 101 does not reach to the outer edge of the insulation 104 so that the latter effectively insulates the plain part of the foil over the upper pattern. The two tabs 99 constitute terminals while the zone of the plain part of the foil adjacent the fold 101 constitutes a common terminal. It will be clear that a heating film so made can be used for example in boxes such as those described with reference to FIGS. 1 to 10 and that the plain parts of the foil can be made longer to cover the end walls of the box. They can also be used in the heating of liquids at the time of dispensing from a storage vessel as described below.
An arrangement which enables specific quantities of liquid to be drawn out of a storage vessel and then heated before being dispensed comprise a tube having one end portion adapted to be inserted into the vessel, another end portion for discharge and between the end portions an enlargement of such volume as to contain at least one batch of the liquid. Suction is generated at the discharge end of the tube by sucking, by squeezing the flexible tube walls or otherwise and flow control means enable this to be used at choice to draw liquid from the vessel into the enlargement and to draw liquid from the enlargement through the discharge end. The dispensable heating film is in good contact with tube wall at least over the major part of the enlargement and the whole device constitutes a dispensable container. Flow control means may be combined with switching means for the heating film whereby the current can be varied according to whether liquid is being drawn into the enlargement or out of the enlargement, the film then having a pattern with at least two branches as described above.
FIG. 13 shows a device on the above lines. The tube 109 carried for example by a cork or similar stopper 111 and long enough to extend to the bottom of a storage vessel suchas a bottle has a portion 112 of enlarged diameter above the stopper and of a volume to-contain one batch to be dispensed. in good heat conductive contact with the wall of the enlargement 112 is a heating film 113 having two branches the terminals being brought out and connection being made by a clip 114. However there need only be two terminals and two contacts on the clip as the control of the flow through the two branches is not effected through the clip but by means of a drawoff tube 115. The drawotf tube is a sliding fit in the contracted upper end of the enlargement. To draw liquid into the enlargement the tube 115 is brought into its uppermost position shown in FIG. 15, when a fitting 122 ensures a sufficiently airtight closure of the enlargement. Suction on the outer end of the tube 115 will now draw liquid into the enlargement 112 and if the outer end is now closed by the finger the liquid will remain in the enlargement while the tube 115 is depressed until a conical fitting'116 at its lower end seats in the bottom of the enlargement and thus prevents liquid from running back into the bottle. Thereis a hole 117 in the tube 115 which is just above the fitting 116 so that if now suction is applied to the outer end the liquid will be drawn through the hole 117 into the tube 115 and out of its upper end, air entering between the tube 115 and the contracted end of the enlargement, a groove being provided if necessary for the passage of air.
There are two contacts 118 at the lower end of the enlargement which are bridged electrically by the fitting 116 in the lowered position of the tube 115. There are two separate pairs of contacts 119, 121 at the upper end of the enlargement which are separately bridged by the fitting 122 on the tube 115 when this in the position shown in FIG. 13. The circuit is shown in FlG. 14. With the tube 115 in the position of FIG. 13 for drawing liquid into the enlargement there is no bridge across the contacts 118, consequently the supply passes from the lower of the tenninals 123 first to the contacts 119 which are bridged by fitting 122 and thence to a terminal common to the two branches 124 of the heating film and then through the contacts 121 also bridged to the other terminal of the supply. Thus the two branches are in parallel and the maximum rate of heating is achieved. After the liquid has been heated as desired the tube 115 is depressed and in its lowermost position contacts 119 are disconnected, contacts 121 are disconnected, but contacts 118 are bridged. Accordingly the lower terminal of the supply is connected to the upper end of one of the branches 125 and the upper end of the other branch 124 is connected to the other terminal of the supply. The two branches are thus connected in series and the rate of heat development is therefore reduced to a quarter of what it was before, serving to maintain the temperature of the liquid which will slowly rise or fall depending on the conditions of the particular case. Suction can be applied by any means but it is contemplated that this device is generally to be used for a beverage to be consumed by suction applied by the mouth after the fashion of a drinking straw.
The device illustrated in FIGS. and 16 enables suction to be generated by the device itself more conveniently than in the device of FIG. 13.
In this case there is again a tube, marked 125 which reaches to the lower end of the storage vessel 126. It is shown passing through a closure in the top of a bottle but might carry a cork or the like as in FIG. 13. The tube 125 communicates with the upper end of an enlargement 127 which is made of cheap flexible material, e.g. polythene. The enlargement is equipped with a discharge tube 128 which reaches practically to the bottom, but also has an aperture 129 near its upper end, just under the flexible top 131 of the enlargement. Close by is an aperture 132 in the top 131 with a flap 133 which can close it but which tends to spring open.
Around the enlargement 127, in good heat-conductive contact with it, is the dispensable heating film 134 provided with a two branch pattern. Connection is made to one branch by a clip 135, the pivot 136 of which is tubular and 16 and this serves to hold the clip and enlargement together by passing the tube through the pivot.
The second branch of the film pattern has a terminal area 137 covered at its end, near the clip attachment, by thin insulation 138 such as paper and over this is a piece 139 of spring foil with which the clip makes contact and which overlaps the paper 138 but normally springs away from the tenninal area 137.
In use, by closing apertures 129 and 132 by finger pressure on the top 131 and flap 133, and applying suction to the end of the discharge tube 128 liquid can be drawn out of the vessel 126 and the enlargement 127. If the flap 133 is now released while the aperture 129 is held closed, continued suction will draw liquid out of the enlargement 127 and the tube 128. Alternatively the enlargement can be squeezed to drive out air, the apertures 129, 132 and the discharge end of the tube 128 be closed and the enlargement then released when its expansion will generate suction which will draw some liquid up into the enlargement and this pumping action can be repeated until the enlargement is full. Then further squeezing with both apertures closed will discharge liquid from the enlargement through the tube 128.
One terminal of the film will be in circuit as long as the supply is connected, while the other can be brought into action by pressing the foil 139 into contact with the terminal area 137. The fact that these foils are bare does not matter with a low supply voltage of say l2 volts. Both branches are brought into operation for rapid heating of the liquid when the enlargement is full, and one branch to maintain the temperature during the discharge of the enlargement. Alternatively the clip and terminal pattern of the film may be as described above with reference to FIGS. 11 and 12 to enable the heat dissipation to be varied.
The devices shown in FIGS. 13 and 16 can readily be produced by moulding such a material as polythene and will be cheap enough to be dispensable. Their shapes may vary considerably from those shown without any change in their operation. They may also be made of other materials and by other methods without any change in their operation, for example of folded paper or the like of a quality which remains impervious for the necessary period of use.
A dispensable container and dispensable heating film ac cording to the invention can also be used in cases in which only part of the contents of a package are to be used at a time, in which case the film can be provided with means visible from the outside indicating the proportion of heat substance removed from the container. For example the film may be wrapped around the substance and have one end held under tension so that when some of the substance has been withdrawn, the film is drawn close to the reduced volume of the substance, a corresponding length of the film being drawn out of the container and serving as a measure of the removed substance.
As shown in FIGS. 17 and 18 a dispensable container 141 of somewhat similar form to that shown in FIGS. 9 and 10 and which could similarly be made of folded paper or cardboard is equipped with a heating folded-over 142 which surrounds a flexible bag 143 containing the substance 144 to be heated but is not stuck to the inside of the container. The container has a narrow aperture 145 of its full width and one edge 146 of the film is secured to the edge of the aperture, while the margin 147 at the other edge incorporates the terminals and passes through the aperture. When the container is full (FIG. 18) this only need emerge enough to permit access to the terminals by a clip 148 through which connection is made. Before use, this margin may be folded-over and covered with a seal of paper or the like. The container also has provision for withdrawing heated substance through the end. For a granular substance it may for example simply be cut open for the purpose or have a scored area which can easily be removed, or if the substance is a liquid or becomes liquid when hot there may be a tube 149.
To heat the substance the'whole is simply suspended from the clip as indicated in FIG. I7, when the weight holds the film in tension. When some of the heated substance is removed, a corresponding length of the film is drawn out and it is calibrated with markings'indicated at 151 showing what proportion has been removed.
The above example has the film movable in relation to the container and its contents. So far as any part is no longer dissipating heat into the substance it is outside the container and accordingly as long as the film has no area dissipating more than 4 W/sq. inch no difficulty should arise even though this part dissipates heat at the same rate so that in contact with the substance. However othercases arise in which relative movement between the film and container is required, effected by means operable without removing the substance from the container for the purpose of changing the heat dissipating relationship of the film to at least part of the substance in the container. It may be necessary for example to change from con- The heating film is designed so that it develops most heat at the bottom of the bag. The lower part of the bag has at least one concertina fold as at 156 and contains the necessary water or other liquid. This liquid can be in the form of an ice cube inserted during packing or liquid can be added by the user when he opens the upper end of the bag to gain access to the terminals 157. In use the bag is suspended by the terminals I57 in a clip connector such as that described in my US. Pat. No. 3,l00,7ll with reference to FIGS. 4 and'S. The bag at first remains folded until defreezing is completed and the liquid is heated up, but when the pressure rises the fold 156 unfolds and room is left at the top for steam. If need be, there can be several folds depending on the proportions, the rate of boiling and such like conditions. Only a smallsteam escape is provided and there will be a constant reflux of condensed steam back into the body of liquid being boiled. Instead of a bag, a box may be used but this must be large enough to provide the necessary steam space.
A further development of the above scheme which permits a high input of heat to the food or other substances without the temperature rising above a value likely to cause difficulties through the development of stickiness and other undesirable phenomena due to surface decomposition is shown in FIGS. 20 to 24. This is particularly applicable to food or other substances which contain a low proportion of liquid but are permeable to vapor. If the food or other substance should be impenetrable to vapor,'e.g. if it is deep frozen, it is made penetrable by holes or channels being provided for in the slab prior to, during, or after freezing and/or vapor paths being arranged along the sides of the slab by pulling the sidewalls of the package a little away from the frozen slab.
The characteristic of this development is that the substance is packed in such a way that there is a small body of liquid in the space between the heating film and the solid part of the substance at least as soon as melting has progressed sufficiently to affect the solid part.
Preferably the body of liquid is contained in a pervious spacer between the heating film and the substance. Accordingly, as long as any liquid is left, the temperature of the liquid cargtot rise above its boiling point and the vapor thereby producedwhich is at this same temperature, permeates the substance and heats it, mainly by delivering its latent heat to the substance. This causes condensation and the liquid runs back into the bulk container in the spacer. In .the typical case of water the temperature will not rise more than a little above 100 C. because pressure developed will not rise substantially above atmospheric. The rate of heat transferred can be relatively high because with water for example the latent heat amounts to nearly five times the sensible heat at boiling point.
The separator can be of any convenient construction and any convenient material which will withstand the temperature and not give rise to undesirable chemical reactions. Typically it can be of metal, e.g. aluminum or of so-called plastics material, e.g. nylon. In the case of food the liquid and the spacer are desirably edible. Thus the spacer may be a thin slab of ice or edible jelly, or it may be a porous biscuit or wafer or a reticulated structure of jelly, with the spacer filled with water, preferably frozen when assembled.
FIGS. 20 to 24 illustrate two examples. The package itself is similar to that illustrated in the earlier example (FIGS. 1 and 2) and comprises a shallow tray or box 301 of paper mache, or other suitable material, and a heating film 303 lining the bottom of the container. It could equally well be made in accordance with other earlier examples such as those of FIGS. 5 to 10.
The foil pattern 303 is backed by an insulator 302 of paper or the like. If the frozen food pack is heated in a tray or pan the paper mache container is not necessary and the insulator forms the bottom of the frozen food pack. It serves also to insulate the foil pattern 303 from the tray if the latter is a metal tray.
There is also an insulator 305 of paper or the like on the upper surface of the film, but at the two ends the film extends beyond the paper at 304 constituting bus bars or terminals. The upper insulator 305 is covered with an aluminum foil 306 to protect it from the liquid. There is an inner lining 308, the bottom of which is perforated and spaced from the foil 306. This liner 308 receives the substanceto be heated. Its edges are folded-over the insulator 305 (FIGS. 21 and 23) at the ends and closely over the margin of the tray 301 elsewhere (FIG. 22). There is a cover 310 of aluminum foil which is similarly positioned or secured around the edges.
The space between the perforated bottom of the liner 308 and the foil 306 serves to receive a pervious or porous spacer which holds them apart and which holds the liquid. In the first example (FIGS. 20 and 21) this spacer 307 consists of a loosely woven, knitted or simply tangled stranded material which may for instance be of cord, wire or nylon.
In the second example (FIGS. 23 and 24) the spacer is integral with the bottom of the liner 308 which is folded into ribs 309 located between the apertures. It is emphasized that these are only examples of possible materials and constructions of absorbent spacer, and in particular in the case of food the spacer may be of edible material.
Instead of the combined perforated foil 308 and ribs 309 the insulator 305 could be crimped or otherwise folded into ribs (these ribs could be perforated) and form a spacer for either the perforated foil 308 or for the solid food directly, if the solid food parts are large enough to rest on the ribs. In this case a perforated foil 308 is not necessary for preventing direct contact with the heating film.
A similar effect can be obtained by other forms of combined insulating spacer and barrier, such as very porous plastic sheets, nets or sieves used as the insulator without provision of a perforated foil.
While the provision of a foil or film-type spacer barrier is preferred for the purpose of ensuring that there is a body of liquid in the space between the solid food and the heating film, other means to ensure this result are also possible and are within the scope of this invention. The frozen food slab may, for instance, have a slanted bottom like an inverted pyramid or roof the crest resting on the flat tray. The heating film being heavily crimped collects the liquid in the crimps, melts channels for the vapor path and is so lightly fixed to the food that after the ice to which it adhered has melted, it drops away from the bottom of the food to allow more space for the liquid or vapor. In this variety neither a special spacer nor a barrier is required, spacing being effected by the shaping of the frozen food slab.
In another variety of the present invention the perforated foil is used as a wrapping for the frozen food which is supplied packed in this wrapping while the heating film with all or only some of its parts 302, 303, 304, 305 is supplied separately so as to permit a choice for heating the food either by the heating film or in a metal pan on a standard gas or electric cooker.
The rapid heating of the frozen food can be still further accelerated by the tray 30! being vibrated and/or by the heating film being supplied with pulsed current. This shock-heating" by a cyclic succession of heavy current and no or low current periods gives the food a better opportunity to take up the heat of condensation.
For some purposes it may be desirable for the heating film or part of it to occupy a compact configuration before the ultimate removal of the heated substance from the dispensable container, means being provided which are operable without removing the substance from the container for stretching the film or the aforesaid part of it into an extended form and location for transferring heat from it to the substance. To permit heating while the film is in its compact configuration its terminals are made accessible without removing the substance from the container.
An example of food in slices. In FIG. the film is a long web I58 folded concertinawise, the folds holding thin slices 159 of the foodstuff. The whole may be enclosed in a usual wrapping or container not shown. This arrangement permits very quick heating up in view of the large surface area in contact with the food and the thinness of the food sandwiched between the folds of the heating film. Asshown only the odd folds of the web are filled with food slices, the even folds being compressed together; thus the web assumes a comblike configuration. The comb ends may as shown be bent to enclose the slices completely. The heating film may be porous or perforated to permit circulation of liquid or vapor between adjacent slices or the slices may have inner wrappings for easier and cleaner removal. More than one web may be arranged in a food package or container. This application of the heating film is one preferred way for quick defreezing of deep-frozen food, for rendering wafers and biscuits crisp again and for many solid foods which are enclosed in a package of insufficient surface areas to permit a speedy enough penetration of heat from that area to the inside.
When the film is supplied with current in its folded compact configuration each slice is heated from both sides and this combined with the small external surface ensures rapid heating. When the slices are to be removed, the whole is unfolded into the form shown in FIG. 26. Assuming all the slices I59 remain associated with the corresponding folds of the film 158, when unfolded there will be a single width of film alternating with each slice. Thus if the current supply is maintained a smaller proportion of the total heat will be conducted into the slices so that they will be heated to a lesser extent. The pattern of the film can be designed to proportion the heat which reaches the slices and'that which is simply radiated away as desired, in particular it may be more than 4 watts per square inch in those parts on which the slices rest and less in the other parts.
The heating film can have terminals not shown at the folds or some of them to permit the heating of a single slice or of a group of slices whether in the folded or unfolded configuration.
As above mentioned it may be desirable in some cases to provide for the heat supplied by the heating film to be supplemented by heat from another source. FIGS. 27 to 33 illustrate some possibilities.v
One purpose served by these developments is not only to effect heating quickly and efficiently without the risk of local overheating, but to permit the package itself to determine or directly to control the magnitude and time function of the heating parameters, i.e. temperature, type, direction, and
source of heat energy fed into packaged material; humidity or steam developed and kept in enclosure or released, or material processed dry; pressure in enclosure. 7 y
The example illustrated in FIGS. 27 and 28 is the heating of a deep frozen foodpack but it is to be understood that the scope of the invention is not limited to this example but extends to all materials and services for which this type. of processing can be advantageously employed.
In FIG. 27 a deep frozen foodr ck is illustrated which is on similar lines to those of FIGS. 1 to 8. A heating film suitably of aluminum foil is provided on the inside of a cardboard or paperpulp box forming container 321. The film itself is not shown, but its terminals or bus bars 322 are folded over the edges of the container 321 to enable connection to be made to it as in previous examples. A black-coated aluminum foil 323 covers the top, and the terminals 322 extend sideways. Instead of the dispensable cardboard or paper mache box a tray of heat resistant material (fiberglass moulding, enameled steel tray) can be used into which the frozen food wrapped in heating film is always placed for heating purposes.
The inner layer 324 of the packaging wrap is aluminum foil or a heat stable plastic film. The foil patterned into a heating element is either laminated to this inner layer or is placed inside the foodpack as on immersion type of heater. In the latter case the slots in the foil should, at least to some extent, not be blocked by any supporting film or paper so that there is a free passage for steam or fluid through the foil-heating film. A plastic or woven net, an open mesh textile, fibers stuck on to the foil, perforated paper or plastic film are examples of suitable supporting layers.
A black cover foil 323 is a suitably thin aluminum foil with a matt black epoxide coating on the outside and the natural matt surface inside. Other heat stable coatings of the aluminum foil are also suitable. Foil anodized and dyed black on both sides is preferred where the cost of anodizing is not objectionable. A cheap though less effective alternative is the use of finely embossed foil. The purpose of this surface treatment is to have a cover which is heat stable, and has a high radiant heat absorption factor so that it transmits radiant heat efficiently to the material inside the package. In some cases it may suffice for only the internal surface or external surface of the cover foil to have a high radiant heat absorption factor.
When the heating film is used as immersion film the food is preferably not only covered but fully wrapped in a foil or film which is black on the outside surface. While the wrapping is in contact with the food to which it transmits absorbed heat, mainly by conduction, the cover foil is usually spaced a little from the food. It transmits the absorbed heat to the food therefore mainly by radiation if its inside surface permits efficient emission of radiation. The blackening or matting of its inside as well as outside surface serves this purpose.
FIG. 28 illustrates an enclosure for heating a single foodpack containing for example ten portions. It consists of a base 325 to which a hood 326 is hinged at 327. The base has two contact bars 328 on which the bus bars 322 of the heating film of the foodpack rest. The hood is provided with a preferably black metal sheet 329 of approximately the same size as the cover foil 323 of the foodpack. A flat electric heating element not visible in the drawing, e.g. a heating film, is laminated to the outer surface of the sheet 329, and thermally insulated on its outer side so that the metal sheet 329 can heat up quickly and can radiate almost all the heat generated on to the cover foil 323 of the foodpack when the hood 326 is closed. The closure desirably automatically effects the switching on of the current to both the heating film via the contact bars 328 and to the radiating sheet 329 in the hood. The closed hood also forms a well insulated closed chamber round the foodpack preventing escape of vapor if a hole in its rear wall (not shown) is kept closed.
The food in the pack is heated by both the heating film inside or on the aluminum foil enveloping the food, and by the radiant heat emitted from the hot sheet 329 in the hood. The cover foil 323 absorbs the radiant heat and transmits it to the food by radiation and contact with the vapor to the space between itself and the top surface of the food. If it is desired that this vapor should escape so that the food becomes more concentrated after heating the cover foil 323 is provided with openings and the hole in the rear of the hood is opened. These openings in the cover foil may have been sealed prior to the heating by a film or other sealant of low melting point so that the package is closed all around until it is placed in the enclosure and the heating has progressed to a temperature at which the sealant melts and thereby opens the apertures in the foil.
A slight pressure-cooking effect can be achieved by suitable choice of the sealent'but if a substantial pressure cooking effect is desired the hole in the hood is sealed to the' base by provision of an elastic gasket around its lower edge.
The heating parameters are controlled first of all by the current to the heating film and the current to the radiating sheet which are independently regulated in amperage and according to a time function. The parameters are further controlled by the amount of liquid put into the foodpack, by the provision of a cover foil with or without openings, and by the timed operation of a pressure valve in the hole in the hood.
If the heating film is in the center of, or within the food and used as immersion heater, other permanent heat-radiating sheets similar to the sheet 329 can be arranged on the base 325 or on the sides of the hood in addition to the sheet 329 radiating on to the cover foil 323. These additional heat radiating panels may be controlled in the same way as the top sheet. The food or other packed materials is in this case preferably packed in black, heat absorbent film or foil and/or a black enameled tray is used instead of a cardboard or paper mache box to hold the package during heating and handling afterwards.
FIGS. 29, and 31 show trolleys 331 which can belinked into a train to run from a control point to outlying wards of a hospital, or stand behind a serving counter in a canteen, each comprising a chest of drawers 332 each serving as a compartment for one pack such as that of FIG. 27, and a panel 333 with separate controls for each drawer. The lower part of the trolley includes a cubicle 334 for a transformer and electrical accessories common to all drawers. There is also a cupboard 335 for plates, cutlery or other utensils.
FIG. 30 shows a section through one drawer compartment while closed for heating a package and FIG. 31 shows the drawer sprung open for the hot foodpack to be taken out or a cold one just put in. Each drawer is an enclosure very similar to that shown in FIG, 28 above described. There are certain differences: the drawer is wedge shaped so that locking and switching-on devices indicated at 336 also ensure contact pressure on the bus bars and a good seal to the fixed upper pan 337 of the compartment in which the radiant panel 329a and an opening 338 leading to a pressure valve is located in the small space 339 above the cover foil 323a of the foodpack when the latter is in the locked drawer.
The space 339 may be illuminated by a light source not shown and provision can be made for it to be inspected from the outside when the drawer is in the locked position, as by making parts of the front and rear walls of the fixed upper part 337 of clear glass'and/or providing the drawer with a glass front or glass covered opening.
The pressure in the space 339 may be controlled by a solenoid operated pressure valve not shown housed in the panel 333 on the right side of the drawer compartment and to which the opening 338 leads. It permits the vapor or steam developing during the heating to escape fully or to a desired degree only, and it can give to the compartment fully efficient time controlled pressure cooker functions whereby the pressure can be programmed both in magnitude and time.
If air, or steam pressure, or a special gas or vacuum line is available and is carried to the panel, the pressure valve can connect the compartment to such gas, vacuum, air or steam pressure line and achieve the processing of the material under the time controlled influence of the chosen atmosphere. For heating of prepared food this special atmosphere is usually not necessary except when the compartment is required to exercise the function of an autoclave and the food is heated in the pack for sterilization and storage purposes rather than direct consumption. For some other materials, however, this processing control of heating in a special atmosphere of a selected gas or vapor under a desired pressure according to a desired timing is of more general use.
The pressure cooking of food for which a drawer compartment as shown in FIGS. 29 to 31 is suitable is generally cooking under the pressure of the steam developed from the liquid in the food package. Only light pressures would be permissible unless the compartment were very strongly built and sealed. For higher strength the preferred shape of the compartment would be cylindrical or even spherical with bulkhead types of doors instead of rectangular drawers.
FIG. 29 shows a pushbutton switch 341, a pilot light 342, and a slot 343 for a panel of plastics material next to each compartment on the panel 333 at the right-hand side of the drawer compartments which are all at a height off the floor convenient for servicing without bending down. A panel is issued with each foodpack and carries the programme of the processing of this pack in a relief configuration and/or specific perforation. The panels as well as the foodpacks may be color coded and may carry also other symbols to ensure that the panel belonging to a particular foodpack is readily identified.
The heating process starts when the foodpack is placed into the drawer, the drawer is locked, the panel belonging to the particular pack is inserted and the switch 341 pressed. The programme carried by the panel is thereby set in operation which generally means that the radiating panel 329a, the heating film and the pressure valve are energized according to the specific magnitude/time function desired for the particular foodpack. Temperature, humidity and pressure-sensing elements fixed in the compartments may be used to control the execution of the programme.
The electric circuit and the circuit components associated with a particular compartment including fuses, contactors, timers, relays, solenoid operated pressure valve, the circuitry of the sensing elements and the panel sensing circuit and mechanism, are mounted on a separate rack or chassis next to the particular compartment behind the right-hand panel 333 while the transformer in the cubicle 334 of the trolley supplies all the packs, four in this example, with the power required at the preferred low voltages earlier specified herein.
In the foregoing description of FIGS. 27 to 31 it has been shown by way of example how this development of the invention is applied for use in canteens, hospitals or other commu nal food serving establishments when a good many parameters of processing are to be controlled. If the foodpack is smaller, say a single portion pack, and fewer or only one of the parameters needs controlling, the arrangement can, of course, be simplified. In a vending machine, for instance, the insertion of a coin may be used just to set the heaters in operation for a preset cycle and instead of the trolley with its various controls a design on the lines of well known vending machines may be used with much simpler electric circuitry and settings not accessible to the public.
A further development of or alternative to that described with reference to FIGS. 27 to 31 will now be described with reference to FIGS. 32 and 33.
The main feature of this development is a thick plate 351 of material of good thermal conductivity, usually but not neces sarily of metal such as aluminum or copper, which fits easily with plenty of play into a vessel 352 holding the food 353 or other substance to be heated. The food or other substance may be deep frozen. The vessel 352 may itself be a box or the like as described above with reference to FIGS. 1 to 6 and equipped with a heating film, or it could be as described with reference to FIGS. 20 to 24; any cover would be removed before the plate 351 is put into it. When in place the plate 351 rests on the food 353 either directly or with an interposed layer or layers to be described. An electric heater 354 is electrically insulated by insulation indicated at 355 from, but in good thermally conductive contact with, the plate 351. A foil heating film, referred to above, or described in any of US. Pat. Nos. 3,283,284, or 3,033,970, or 3,020,378 or 3,149,406 is a preferred heating element for this application particularly if it is run at a low voltage, not dangerous to touch, i. e. below approximately 50 volts.
A temperature sensing element 356, such as a thermostat of the capillary tube type, is embedded in a hole drilled in the plate 351 and leads to a switch, contactor or other control device 357 which regulates the energy supplied to the heater 354 so that the plate 351 is held at a desired temperature