GB2390519A - Microwavable heat retentive receptacle - Google Patents

Abstract

The present invention concerns a microwaveable heat retentive container (1) for heated foods or beverages, which comprises an outer shell (3), an inner wall (2) within said outer shell, and a material (4) susceptible to heating by microwave radiation, said material having a time/temperature profile such that, when from approximately 50-120 grams of said material is subjected to microwave radiation having a frequency of from approximately 2,300-2,600 MHZ, at a power of from approximately 600-1,000 W, for a period of approximately l -2 minutes, said material is heated to a temperature in a range of approximately 76.7-162.8{C(170-325{F).

Description

MICROWAVEABLE HEAT RETENTIVE RECEPTACLE

BACKGROUND OF THE INVENTION

1. FIELD OF THE INVENT101

This invention relates to microwaveable receptacles, containers, and warming modules. More specifically, this invention relates to containers adapted to maintain their contents at elevated temperatures for extenders periccis o'tirne. C:ortainers of this invention include a rnicrowave ID absorbing composition in heat exchange relationship with the contains! content s ar,d preferably in a space defined by inner and outer walls of the container. Upon exposure to microwave energy, the composition absorbs energy in the form of microwaves, which is retained in the composition in the form of thermal energy.

Tne thermal energy can then be transferred into the contents of the container, such :- as a food or beverage, thereby maintaining the contents at an elevated te.nperature Àcr an extended period of time.

>. BACKGROUND OF THE INVENTION AND RELATED ART

Maintaining the temperature of a food or beverage after cooking or preheating has long been of interest in food and beverage service. In domestic, recreational, 2.O field, and commercial environments (among others), maintenance of temPerar re is

desirable when the food or beverage is served some time after cooking or preheating. For example, in commercial environments, food service pans are often placed over a tray of.boiling water or over some other heatirig means to maintain the temperature of the food after preparation. in the home, it is common for a casserole 2: dish to be placed into a wicker basket or wrapped in a cloth towel to insulate the container and maintain the desired temperature of the contents. For the same purpose, electrically heated trivets, or preheated hot-pads, are sometimes used.

Additionally, it is often desirable to be able to consume a food or beverage, prepared earlier, at some location removed from the home, such as at the workplace.

2!: In these circumstances, it is often desirable to place food into a portable container which can be easily carried to a separate location where the food can later be consumed. In some environments, such as in remote wilderness locations, or at

some sporting events, it can be impossible or impractical to reheat the food or beverage prior to consumption. In these instances, it is both pleasing and convenient to open the container at some later period and find that the food or beverage has been maintained at a desirable temperature.

Portable containers which serve this purpose have been known for years.

Early containers designed for this purpose include bottles or other containers, insulated with a foam insulation such as foamable foam polystyrene, e.g., STYROFOAM, or foam polyurethane. Although these containers extend the time a food or beverage may be maintained at an elevated temperature, they do not provide 10 the level of temperature maintenance desired in many instances.

Foarn insulated beverage containers have been known for years. A recent advance in double walled foam insulated beverage containers is disclosed in U.S. Patent No. 5,515,995, to ALLEN et al. This patent discloses a double walled, foam insulated beverage container having a wide base. This patent, and U.S. Patent No. 15 3,684,123, to BRIDGES, cited therein, are hereby incorporated by reference as though set forth in full herein.

In general, vacuum insulated bottles are far superior to those insulated with foam. U.S. Patent No. 3,331,522, to BRIDGES, which is hereby incorporated by reference as though set forth in full herein, describes a vacuum insulated bottle 20 comprising a metal vacuum bottle enclosed in a plastic jacket.

To enhance the ability of the vacuum bottle itself to insulate, attempts have been made to utilize different materials for the vacuum bottle. Although fragile, glass is superior to metal in its lack of thermal conductivity, and thus glass vacuum containers became popular for use in thermally insulated containers.

75 To further enhance the insulating properties of the glass vacuum container, attempts have been made to line glass vacuum containers with reflective coatings to minimize radiant heat loss. U.S. Patent No. 3,910, 441, to BRAMMING, is illustrative, and discloses a glass vacuum bottle construction in which the interior walls are silver-coated Lo reduce heat loss.

0 With the advent of microwave cooking technology and its rapid acceptance and popularity, the need arose for a thermally insulated bottle which could also be used in a microwave oven. However, because metals absorb significant microwave

energy, they can become dangerously hot in a microwave oven. Additionally, reflective metals and coatings containing such metals, e.g., silver, can damage the microwave oven magnetron tube by reflecting microwave energy back into the wave guide, and by "arcings andlor sparking.

5 A number of attempts have been made at solving the aforementioned problem For example, U.S. Patent No. 4,184,601, to STEWART et al., which is hereby incorporated by reference as though set forth in full herein, relates to a microwave-safe vacuum insulated glass container. Instead of a silver lining to reduce radiant heat loss, the annular space of the glass container is substantially 10 filled with finely divided materials which are neither electrically conductive nor absorbent of electromagnetic energy at microwave frequencies. Examples of such materials include finely divided silica and calcium carbonate.

While the vacuum containers which are known in the art are certainly able to conserve the heat of their contents, a continuing need for improvement remains.

15 Most commercially-available vacuum containers l<nown in the art allow a significant loss of thermal energy at a measurable rate Iheat loss/unit of time, i.e., thermal efficiency). A need therefore exists for improved thermal efficiency in a microwaveable container.

The present invention enhances the ability of the thermally insulated container 9() to maintain contents at elevated temperatures. Conventional vacuum insulated containers are designed to conserve the thermal energy already present in the contents of the container. The present invention, on the other hand, actually transfers thermal energy into the contents, adding to the thermal energy of the contents, and thereby keeping the contents at a higher temperature for extended 75 periods of time.

The concept of a container which can be preheated to add thermal energy to the contents is not new. For example, U.S. Patent No. 4,567,877, to SEPAHPUR, discloses a heat storage food container, adapted to be used in microwave ovens, using wet sand as a thermal storage medium. However, an obvious drawback to the 30 SEPAHPUR container is that water undergoes a phase transition (from liquid to gas vaporization) upon heating in the temperature range necessary for food preparation.

Upon the phase change from liquid to gas, the molecules occupy a significantly

greater volume, and consequently, the heat storage container must be engineered to structurally accommodate such changes.

The vaporization problem is addressed in BA! DWIN, U.S. Patent No. 5,601, 744, which discloses a beverage container comprising an inner vessel with bottom and side walls, an outer wall at least practically surrounding the inner vessel, a chamber defined by the space between the inner vessel and the outer wall, and a microwave receptive material disposed within the chamber. Either or both of the inner vessel or the outer wall are transparent to microwave radiation and has a melting point grease, than a rneltingtemperature, and less than a vaporization 10 temperature, of the ninroav" receptive material. Thus, the container is designed to melt before pressure is allowed to build within the closed space containing the microwave receptive inaterial.

In addition to problems caused by vaporization, problems are also created when microwave susceptible materials undergo phase changes from solid to liquid.

I- In these cases, it is necessary to engineer the container and/or material so as to contain the microwave susceptible material upon melting, ZIELINSKI et al., U.S. Patent No. 5,520,103, discloses a heat retentive server comprising upper and lower shells, which include a thermoplastic material and are joined together to define a cavity therebetween, A heat storage medium comprising a phase-change material :0 substantially fills the cavity and C unrestrained therein. The melting problem is addressed in ZIELINSKI et al. by use of a material which forms a gel at elevated temperatures. Commonly assigned U.S. Patent No. 5,916,470 to 8ESSER et al. discloses microwaveable heat retentive receptacles utilizing microwave absorbing materials.

9: This application is hereby incorporated by reference as though set forth in full herein.

Containers for use in microwave ovens such as that disclosed in U.S. Patent No. 5, 9 16,470 are formed from polymers and are substantially transparent to microwave radiation. By "substantially transparent to microwave radiation" herein is meant that an object formed of such a material and subjected to microwave 9 radiation Qf about 1000 watts for a period of about 2 minutes will exhibit a change in temperature of about 2. 8 C(5 F)or less. Typical materials meeting this definition include polyolefins, e.g., polyethylene and polypropylene.

f) DOBRY, U.S. Paten; No. 4,937,412, discloses a method of heating a load object comprising the steps of using a microwave susceptible material which is fluid at a predetermined elevated operating temperature, enclosing the material in a means of containment, exposing the material to microwave radiation to generate heat and store it in the material and in the means of containment, and placing a load object in proximity to the means of containment. The means of containment may be either closed and flexible, or porous and permeable. If the latter, then the microwave susceptible material is held therein by capillary.. action.

S. Patent No. 5,052,369, to JOHNSON, which is hereby incorpcraT,?1 by 10 reference as though set forth in full herein, also discloses a beat reair,;ng,uu container adapted for microwave use. Unlike SEPAHPUR, the microwave absorbing material of JOHNSON is a mixture of micro crystalline wax which exhibits a fusion remaeracure(melting pointibtween79.9 C(175F) and 149 C(300 F). The melted Aerial is contained by the use of a thin film or a pouch-like enclosure.

j Others have addressed the melt-containment problem by using materials that do no. undergo a solid to liquid transition at higher temperatures. For-example, U.S. Patent No. 4,983,798, to ECKLER et al., discloses the use of materials which undergo a "mesocrystalline" phase change in the solid state prior to melting, such as pentaervthritoi and neopentylglycol. ECKLER et al. is hereby incorporated by JO reference as though set forth in full herein.

BENSON et al., U.S. Patent No. 4,572,864, discloses a cornposie material for storage of heat energy. The material comprises a polyhydric alcohol or derivative which is capable of undergoing a solid-state crystalline phase transformation. Such materials include pentaerylhritol, pentaglycerine, neopentyl glycol, tetramethylol : propane, monoamine penteerythrito!, diamino pentaerythritol, trisThydroxymethyl)acetic acid, and mixtures thereof. The composite material also comprises materials from the group which includes metals, plastics, natural or artificial fibers, and porous rock. Also disclosed is a method of impregnating the phase-change materials into certain solid substances, including porous, fibrous, and of) crone-like materials.

CHAMBERLAIN at al., U.S. Patent No. 5,294,763, discloses a heat suscepror comprising microwaveable heat susceptor particles in a matrix which is substantially

nonreflective (i.e. "capable of transmitting microwave energy") to microwave energy. The particles comprise substrates which, like the matrix, are non-reflective of microwave energy. The particle substrates are coated with a material capable of absorbing microvvave energy and converting it to heat. Materials for the matrix include ceramics and polymers. Materials for the substrate include glass and ceramics. Coating materials include electrically conductive and semi-conductive materials, such as metals and metal-containing compounds.

KREIBICH et al., U.S. Patent No. 4,259,198, discloses a method of using crystalline resins as heat accumulators. The crystalline synthetic crosslinked resins 10 used, which include polyester resins, further include crystallite-forming blocks linked to the resin through ether or ester linkages. The crystallite forming blocks comprise polymethylene chains which alternate with ether or ester linkages, and have at least thirty carbon atoms.

Commercially available standard microwave ovens for domestic use in the 15 home typically are rated as having an "output" of, for example, on the order of from about 600 to about 1,000 watts. Typical commercial "convenience" foods are specifically designed to be heated to or near a desired or serving temperature (e.g., perceived to be desirable by the typical adult) in from about 2 to about t3 minutes.

Consequently, it is believed that typical users of microwave ovens in domestic 20 settings desire or expect to employ a microwave oven to heat the contents of a container to a desired serving temperature in a period of time of from about 2 to about 6 minutes.

SUMMARY OF THE INVENTION

In view of the foregoing, the present invention is directed to providing a 75 microwave treatable component comprising a microwave treatable material which exhibits a desirable response to microwave radiation and which may act as a thermal battery.

The present invention is further directed to providing articles which employ such materials and which can thereby be kept warm by exposure of such materials 30 to microwave radiation.

The present invention is further directed to providing containers which employ such materials and whose contents can thereby be kept warm by exposure of such materials to microwave radiation.

The present invention is also directed to'providing such a container wherein the container can be heated either with or without the contents of food therein and still function as a thermal battery in either case to reduce the net loss of heat from he contents.

it is also within the scope of the present invention to provide a container wherein the container can be heated by microwave energy either with or without the !u contents of food therein during a period of time which is acceptable to, and in fact expected by domestic users, and still function as a thermal battery, to absorb microwave energy, and to reduce the net loss of heat from the contents, while at the same rime avoiding overheating of components of the container, such as by overheating of the microwave susceptible portion of the container.

j - The present invention is still further directed to providing a microwaveable Fontaine! which maintains the temperature of its contents at a higher temperature over time than other commercially available containers.

The present invention is directed to providing a microwaveable container which contains a microwave-absorbing material which, when exposed to microwave SO energy, heats at an optimum rate to an acceptable temperature witlou7 ca'Js.r;, damage to the surrounding container.

The present invention is further directed to providing a microwaveable container which contains a microwave-absorbing material which is solid at room ce-.Derature and remains in a solid phase upon heating to about 149 C(300 E), 95 preferably at least about 204 C(400 F). An advantage of such a material is that cne container itself need not be specially engineered to accommodate a phase cr.a.ge, either to liquid or to gas (from solid, for example).

The present invention is still further directed to providing a microwaveable container which contains a microwave-absorbing material which is inherently :0 'raicrovvave active," or "microwave responsive" and does not require the presence OT another material, such as water. An advantage of such a material is that it does not lose moisture and "dry out" with repeated microwaving. Consequently, the

lifetimes of the microwaveable pouch and container are significantly increased.

Moreover, the material can be simply and easily used in the container with reduced manufacturing costs.

The present invention is directed to providing a microwaveable container which radiates thermal energy into its contents, thereby allowing the contents to be maintained at a higher temperature than possible with a comparable vacuum container, yet is thermally insulated on the exterior, preventing outward radiant heat loss. The present invention is further directed to providing a portable thermally 10 insulated bottle which can be heated in a typical microwave oven available to consumers prior to receiving its heated contents, and thereby maintain the heated contents at an acceptable temperature.

The present invention is directed to providing serving containers, such as bowls or serving dishes, for home or commercial use, which can be microwaved 15 prior to receiving their contents, and thereby maintain their contents at a higher temperature, in comparison with other commercially available containers.

The present invention is directed to providing serving containers, such as carafes or pots, for home use, which can be microwaved prior to receiving their contents. and thereby maintain a higher temperature of the contents, in comparison 70 with other commercially available containers.

The present invention is further directed to providing a microwaveable composition which heats easily upon microwave energy absorption, yet does not substantially overheat if overmicrowaved, and yet further, exhibits a thermal capacity sufficient to change the shape of the thermal loss curve compared to 75 containers lacking such compositions, and still further, is nontoxic if exposed to the consumer. The present invention is still further directed to providing a microwaveable heat storage container constructed from durable materials (without the glass vacuum container), which is thereby more useful to the consumer.

30 The present invention is further directed to providing a modular unit comprising a microwaveable composition which can be used instead of, or in addition to, the vacuum insulation in thermally insulated containers

f) The present invention is still further directed to providing a modular unit comprising a microwaveable composition which can be used in medical applications for warming parts of a body.

The present invention is further directed to providing a modular unit comprising a microwaveable composition which can be used in clothing to be worn in cold weather, to aid in warming a body.

These and other objects of the invention are achieved by providing a microwaveable material which exhibits desirable properties in response to microwave radiation.

10 These objects have been achieved by providing articles which employ such materials and which can thereby be kept warm by exposure of such materials to microwave radiation.

These objects have been achieved by providing containers which employ such materials and whose contents can thereby be kept warm by exposure of such l: materials to microwave radiation.

These objects are also achieved by the provision of a microwaveable container including an inner shell adapted to receive a food or beverage product, an outer shell enveloping the inner shell and forming a cavity therebetween, and a microwave absorbing composition contained in the cavity between the inner and outer shell.

SO The microwave absorbing material is preferably disposed within a microwave absorbing material storage volume, which can be of various shapes such as substantially planar, substantially disk-shaped, substantially tubular, annular, or it may be disposed at a bottom portion of the container, and preferably in association with a bottom wall portion of the container. The microwave absorbing material AS storage volume can preferably comprise a pouch.

The microwaveable heat retentive container wall portion can include a cavity and the microwave absorbing material is preferably disposed within the cavity.

In other aspects, a microwaveable heat retentive container for heated foods or beverages, is provided comprising an outer shell, an inner wall positioned within 30 the outer shell, and a material susceptible to heating by microwave radiation, the material having a time/temperature profile such that, when from about 20 to about 150 grams of the material, preferably from about 25 to about 100 grams, more

preferably from about 30 to about 80 grams, and most preferably about 60 grams, is subjected to mic owave radiation, at a frequency of from approximately 2,300-2,600 MHz, more preferably 2,400-2,500 MHz, most preferably 2,450 MHz, at a microwave power from approximately 600 j 1,000 W. more prereraoly 750-1,000 W. the time of heating in the microwa.'e led re_erabl/ being from about 1 to about 3 minutes, more preferably from about 1.25 to about 2.5 minutes, more preferably from about 1.5 to about 2.25 minutes, the material is heated to a temperature of from about 79. C(''75 Fi Lo ecu.:oO C?320), Core preferabi from about 8-!.&C(190 F) to about 135 C O /07_0A), _^,d =.CSt Preferably from abut 93lor(2nQo\ to about 127 C(250 F3.

Pr drably the outer shell is substantially microwave transparent (as defined above) a,.d can comprise polypropylene. As above, the material susceptible to heating --.',nicrowave radiation is preferably contained within a pouch, as described above. Preferably the inner shell is substantially microwave transparent and l: preferably comprises polypropylene.

In the foregoing embodiments, the cavity in the container wall portion further comprise: an insulating means to reduce outward radiant heat loss, which can include, a.- evacuated space, insulating foam material, such as polyurethane foam, polystyrene foam, etc. : In;.,er aspects, these objects are attained by providing a m,cro:'aveable heat retentive container comprising at least one portion for receiving a material, and defining volume; and a mass of microwave absorbing material in heat exchange communication with the at least one portion for receiving a material.

In certain preferred aspects the invention provides a microwaveable heat 9 retentive -ontainer comprising ! at least one portion for receiving a material; and e heat storage mass comprising a microwave absorbing material in heat exchange communication with the at least one portion, the microwave absorbing material comprising at least one polymeric resin having a melting point of at least 205oc(4oooFy, =.c O comprising repeating units having at least one nitrogen, oxygen, or sulfur atom. In such embsiiments, the polymeric resin comprises at least one member selected from

poiyacetals, poiyacerales, cellulosics, nylons, polyamides. polyimines, polyesters, poiyethers, polysulfones, and copolymers thereof.

Preferably, the microwave absorbing material comprises polyester and the polyester preferably comprises a member selected from polyalkyl esters, polyaryl esters, and copolymers thereof.

Suitable polyesters comprise compounds having repeating units having the Allowing formula (or which are derived from compounds having such a formula) I o Rl OOC COORS-

w,.erein and R2, which may be the same or different, are as defined in further detail below.

1: Preferred polyesters comprise a member selected from polyalkylene rerephthala-e, polybutylene terephthalate, polycyclohexamethylene terephthalate, P-'., G. ACTS, PCTA, and copolymers thereof. Of these, PCTG and PETG are especially preferred, with PCTG being especially preferred.

In some embodiments, microwaveable heat retentive containers of the 30 invention include those wherein the container comprises is' an inner shell forming a shape adapted to receive a food or beverage product, and (bl an outer shell associated with the inner shell and forming a cavity therebetween; and wherein a pouch containing a microwaveable material as defined above is disposed ilk the cavity.

95 Preferably, the cavity further comprises an insulating element, preferably foam, such as polyurethane or polystyrene to reduce outward radiant heat loss. In some such embodiments, the material susceptible to heating by microwave radiation --efe-a has a rimelemperature profile such that, when from approximately 20-150 curares of said material, preferably from about 25 to about 100 grams, and 30 more prs er bly about 30 to about 80 grams, most preferably about 60 grams, is subjected tic microwave radiation having a frequency of from approximately 2,300 2 cOO M.'-;Z, more preferably 2,400-2,500MHZ, more preferably about 2,450MHZ,

fit at a power of from approximately 600-1,000 W. more preferably about 750-1000 W. for a period of approximately 13/-2/' minutes, more preferably approximately 1,/12 i/. said material is heated to a temperature in a range of approximately 79. 4 -160 C (175 -320 F),

In some embodiments, the inner wall of (b) defines a receiving portion having a volume for receiving a material, and wherein the ratio of the mass, in grams, of said material susceptible to microwave radiation, to the volume of the receiving portion, in milliliters, is from about 1:5 to about 1: 12, preferably about 1:5 to about 1:10 and most preferably about 1:B to about 1:8.

IOThe invention also provides a method of providing a heated product to a consumer or user, comprising (a) placing a microwaveable container in a microwave oven, the container comprising a material susceptible to heating by microwave radiation, and having a time/temperature profile as defined above; I-(b) adding heated product to said container, either prior or subsequent to (a); and (c) providing said container with heated product to a consumer or user.

The microwave absorbing materials, container materials and pouch in such methods are all preferably as defined above.

BRIEF DESCRIPTION OF THE DRAWINGS

0The foregoing and other objects, features, and advantages of the invention will be apparent from the following more particular description of the preferred

embodiments, as illustrated in the accompanying drawings, in which reference characters refer to the same, or like, parts throughout the various views, and wherein: 2:Figure 1 is a schematic cross-sectional view of a heat retentive food jar assembled according to the invention.

Figure 2A is a graph of the thermal efficiency of a 0.5 liter heat retentive food jar using a microwave energy absorbing pouch according to the present invention, compared a 0.5 liter food jar insulated by a metallized glass vacuum according to the ()prior art.

1 2

Figure 2B is a graph of the rherrr.al efficiency of a C,.5 liter heat retentive food jar usir:, a microwave energy absorbing pouch according to the present invention, compared a 0.5 liter food jar utilizing glyceryl rnonostearate.

Figure 3 is an enlarged cross-sectional view of the food jar shown in Figure 1, vith a portion broken away.

Figure 4 is a perspective view of a food service tray according to the present invention. Figure 5 is z cross-sectional view of the food service tray of FIG 4, taken aiG.'9 the line A-A.

10 Figure 6 is z perspective view o; a serving container with portion cut away to;hOV! an assembly according to the invention.

Figure 7 is cross-sectional view of a beverage mug according to the invention. iigure 8 is a ross-sec.ional view of a carafe according to the invention.

I j Figure 9 is z cress-sectional view of a wide-bottom mug according to the inveatic.q. Figure 10 is e cross-sectional view of a baby food serving dish according to the invention.

Figure 11 is a cross-sectional view of a microwave heat retentive thermal 9 oortle according to the invention.

Figure 1 Z is a schematic, cross-sectional representation of a microwaveenergy adsorbing pouch according to the invention.

Figure 13 shows an enlarged cross-sectional representation of one way in which the inner liner 2 may be attached to the outer shell 3.

9: Figure 14A is a perspective view of a heat-storing puck according to the present invention.

Figure 148 is a cross-sectional representation of the heat-storing puck of Figu. e 1 AA.

Figure 15 is z perspective view of a heat-storing service tray according to the 0 present invention.

Figure 16 is, cross-sectional view of a tortilla warmer according to the present invention.

DETAILED DESCRIPTION OF PREFERRED

EMBODIMENTS OF THE INVENTION

The microwave absorbing materials of the invention can be employed in any type of article, e.g., receptacle or container The microwave absorbing materials are preferably, although not necessarily, disposed in a pouch. The pouch can then be employed in conjunction with articles, including receptacles or containers to provide various other embodiments of the invention, specific examples of which are lO discussed below.

Figure 1 discloses a microwaveable heat retentive container according to this invention, designated generally as 1. The container preferably has an inner shell, or liner 2, and an outer shell 3. The inner shell or liner 2 and the outer shell 3 may be formed of any suitable material well known to those of ordinary skill in the art such l: as polyethylene, polypropylene, polycarbonate, and acrylonitrile butadiene styrene copolymer. Polyolefins formed from monomers having from 2 carbons to 4 carbons are preferred. Polypropylene is most preferred. As used herein, the terms inner shell and liner can be used interchangeably to refer to the innermost wall of the container, i.e., the wall which actually contacts the contained food. In some embodiments, it 70 is preferable that the inner shell be thermally conductive. In addition, it is preferable that the inner shell consist of materials which are substantially microwave transparent. Thus, the inner shell may be composed of a material which can withstand heating up to approximately 1 50Cc without structural damage. Suitable materials include plastics, such as polymers. Preferably the inner shell is composed 95 of a polypropylene. Preferably the inner shell is composed of a nucleated polypropylene homopolymer. As used herein, the term nucleated polypropylene homopolymer refers to a polypropylene polymer in which agents are added to increase the rate of crystallization of the polymer. A suitable nucleated polypropylene homopolymer is ACCPRO, available from Amoco Plastics.

3U The container of Figure 1 preferably comprises an outer shell, or jacket 3. As used herein, the terms outer shell and jacket are meant to describe the same structural feature in a particular embodiment discussed. In addition, it is preferable that the outer shell consist of materials which are microwave transparent. It is

preferable that the outer snell be composed of a material which will withstand he-:inc -? to acc xima.ely 149 C(30C'F) without structural damage. The outer sire 1 is pre_er=_y fc=ec of a plastic material, more preferably the outer shell is compose- or polypropylene..!ost preferably the outer shell is S Is ose- of c pc2:--ccllene homopoly.er.

The inner and outer shell can be affixed or connected to each other by any me-es v!ell known to those of ordinary skill in the art, such as by a snap fit consTruc.on, or by welding, including solvent welding, spin welrling, sonic elding, etc., and U.S. i'atents Nos. 5,515,935, to ALLEN et al.. 3 684,12S, to BRIDGES, If}]84.71, to STEWART et al. (each incorporated by referei,e ubuve) disclose sui able. orication techniques. The Container of Figure 1 further comprises a pouch 8 csntair,,ng a microwave absorbing material 4. The pouch is preferably composed elf mater als which are microvvave transparent, such as a polyolefin. The pouch in which the microwave absorbing material is placed is preferably formed of l poiythylene, e.g., linear low density polyethylene, polypropylene, nylon, polyester, aor' most preferably polypropylene. In preferred embodiments, the microwave absorbing material substantially fills the pouch.

A suitable means by which inner liner 2 may be affixed to outer shell 3 by means o, snap fit construction is shown in Figure 13. The snap fit portion of the flu conqruc.T.on is designated generally 94. As shown, the cute, she'd 3 is atta,-,ed co inner liner 2 by means of an intermediate upper collar 10. The inner liner may be Breached to intermediate collar 10 by any means known to one of ordinary skill in the art and preferably by spin welding.

The pouch 8 may be fabricated by any means suitable to those of ordinary skill in tr,e art, such as by heat sealing. As shown in Figure 12, the pouch 8 comprises marginal portions, which are preferably heat sealed by sealing the rr,arginal Dortions or edges 85 with heat and pressure by means well known to those o; ordinary skill in tne art. U.S. Reissue Patent No. RE 34,929, to Tilia, inc., relates | to such systems and is hereby incorporated by reference as though set forth in full 0 herein. Th microwave absorbing composition can be. selected based on its Tme, temaerature profile. Preferred microwave absorbing materials do not depend

on a liquid to solid phase change to maintain thermal efficiency. It is preferable to select a microwave absorbing compound which exhibits a high heat capacity, and is capable of absorbing microwave energy. In this regard, it is a feature of the invention that the microwave absorbing material may be employed in accordance j with the invention without the need to employ adjuvants or additives to alter the response of the microwave absorbing material to microwave energy.

Preferably, the microwave absorbing material contains microwave excitable atoms. While not wishing to be bound by theory, it is believed that these groups are involved in the absorption of microwave energy due their polarity or the net dipole 10 moment of a molecule containing such an atom. Excitable atoms include, but are not limed to, sulfur, nitrogen, oxygen. In preferred embodiments, the microwave absorbing composition contains 1 or more, more preferably 2 or more, even more preferably 3 or more, and most preferably from 2-4 excitable atoms per repeat unit in a microwave absorbable polymer. Materials with 4 or more excitable atoms per 1: repeat unit may also be employed. As used herein, the term repeat unit refers to a single monomeric substituent of a polymer. As used herein, the term "microwave absorbable" or "microwave absorbing" or "microwave susceptible" means capable of absorbing microwave energy, the practical result of which is an increase in temperature. JO The microwave absorbing material preferably comprises a polymer resin.

Polymer resins include, but are not limited to, polymers comprising polyacetals, polyacetates, cellulosics, nylons, polyamides, polyimines, polyimides, polyesters, polyethers, polysulfones, and copolymers thereof. Preferably, the microwave absorbing material comprises polyester, which preferably comprises polyalkyl ester, 75 polyaryl ester, or copolymers thereof. Preferable polyesters include, but are not Indited to polyesters comprising polymers comprising repeating units derived from polyethylene terephthalate and related compounds. Thus preferred polyesters comprise polybutylene terephthalate, polycyclohexamethylene terephthalate, PETG (PET modified with ethylene glycol), PCTG IPET modified with iD polycyclohexamethylene glycol), PCTA (acid modified PET) and copolymers and mixtures comprising these materials.

1 6

Preferred microwave susceptible materials comprising polyester materials include those comprising and/or derived from repeating units having a structure in accordance with the following general formula (Formula l): RiOOC COORS-

(1) 10 wherein R' and R2, which may be the same or different, is each independently selected from a single bond; C6-C'2 cycioalkyl; Cz-C20 alkyl; C2-C20 alkyl containing 15, preferably 1-3 and more preferably 1-2 nitrogen, oxygen or sulfur substituent(s); C2-C20 alkenyl with from 1-5 double bonds (conjugated or unconjugated) and preferably from 1-2 double bonds Iconjugated or unconjugated); or -R3R4R5-, wherein 15 R4 is C6-C,2 cycloalkyl and R3 and Rs are each independently selected from a single bond, C,-C20 alkyl or C2-C20 alkenyl. When R' and R2 are alkyl containing a nitrogen, oxygen or sulfur substituent as defined above, the substituent may be in the carbon chain (for example as a substitute for a C atom, as in -C-O-C-) or as a member of a side chain, or functional group as, for example, in -COOH (carboxylic 70 acid), or -CO- Iketone), for example.

Preferably, R'is a single bond and R2 is preferably selected from C2-C, alkyl, and -R3.R4- R6- wherein R4 is cyclohexyl and R3 and Rs are each CH2-. Most preferably R' is a single bond, and R: is selected trom -CH2-, -CH4- and or -R3R4R5-, wherein R4 is C6-C'2 cycloalkyl and R and Rs is each -CH2 -. Mixtures and/or blends 25 of each of the foregoing can also be employed, and copolymers and multimers derived from mixtures of the foregoing may also be employed. Highly preferred microwave absorbing materials can be structurally represented by the following formulas and/or are derived from materials having the following structural formulas: 1 7

[0- I /CH\;

PET Ipolyethylene terephthalate) t o-c CH CH 2 PBT (polybutylene terephthalate) o O CH2 /CH\ 1 _ - O-it \ l \ 2/ _ CH CH2

PCT (polycyclohexamethylene terephthalate) :0-C< C _o/C\2 0 O CH CHz\ /CH\]; CH O-C C 0 \ // Calm 5/ t O CH, CH \ ITCH O O ARCH \ CH

C C O \ /'CH,\ 7/ 4 c o CH CH 4 CH CH, _: \ /'CH2

1 8

formulas immediately above a suitable number of repeating units can be readily determined by those of ordinary skill in the art. Particularly preferred microwave bearable materials are available from Eastman Performance Plastics, P.O. Box 1969, Kingspor-, TIN 37662, and are sold under the following trade names: EXTAR FB j ACi330 (trade name for PCTA); EKTAR CoioLYESTER PETG ttrade name for PETG); EXTAR F3 CG011 (trade name for PCT); EKTAR FB DG003 (trade name for PCTG).

In preferred embodiments, the mass of the microwave absorbing material is that which, when exposed to microwave radiation in the range of approximately 300 to 2,600 MHZ, at a power of a,rproximately 600 to 1,000 W. for a period of IO pprcximately in to 2H m mutes, heats to a temperature of approximately 79.q co -oroxnarely 1 C(approxlmately 175 F to approximately 320 F).Mcre preferably, the microwave -actuation Is in. the range of approximately 2,400 to 2,500 MHZ, and in the most preferred cccment, the microwave energy is at approximately 2,450 MHZ. The microwave power more preferably falls within the range of approximately 750 to 1,000 W. The time of l hearing at these settings is more preferably approximately 1 I/ to 2/: minutes, and is roost preferably approximately 1/: to 2'/. minutes. Of course, when the microwave absorbing material is exposed to microwave energy at a higher power, line rime c heating will likely be less. Conversely, at a lower power, the heating of the microwave absorbing material could take longer.

LO Microwave absorbing materials of the present.invention preferably comprise oolyreric resin having a melting point of greater than about 177 C(350 F), more prefers greater than about 204C(4O0 F),and most preferably greater than 232C(450 E).

The mass of the microwave absorbing material is preferably chosen based on the volume of the container with which it is associated. Preferably, the ratio of the Jo mass of microwave absorbing material, in grams, to the volume of the container, in milliliters, is from about 1:5 to about 1:12. More preferably, the ratio is from about 1:5 tO abOU1 1:10. In the most preferred embodiment, the ratio is from about 1:6 to about 1:8. For example, for a 500 milliliter container, the mass of the microwave absorbing material is preferably greater than approximately 0 grams, but less than 30 zrproximLely 90 grams. More preferably, the mass of the microwave absorbing material is greater than about 50 grams, and even more preferably, greater than about 60 grams The mass of the microwave absorbing material is preferably less

than about 100 grams, and even more preferably less than about 80 grams. Most preferably, the mass of the microwave absorbing material is about 60 grams. Of course, the highs! the mass of the microwave absorbing material, the longer the time necessary to neat to he desired temperature. However. increasing the mass OT the microwave absorbing mzerlal above approximately 100 grams does nor significantly enhance the heat retentive properties of the container. Therefore, the most preferred err oodimenT, 60 grams, is selected by balancing heating rime with the per,orrnance Of the microwave absorbing material in the finished container.

Preferably, rnicrowavsable heat retentive containers of the,n\/ention can, upon o preheating -he cor,.ainer and placing food or beverage at a tei-c, ,,o,-ature of at least ox Rae & 'cars- -) into the container, maintain the heat of the contents to at least -A -.=,_ly;.4 ct'30 -I, after about six hours in the container, whether the container is heated empty,,.e., without contents therein, or full, i.e., with the contents therein. l: The container of Fieure 1 further comprises insulation 5, preferably foam nsulaticn. 'n preferred embodiments, the foam insulation is a polyurethane foam.

The container of Figure 1 further comprises a two-piece closure assembly, comprising an inner stopper 6, and an outer lid 7. In preferred embodiments, the closure assembly is formed-of plastic materials. More preferably the closure 30 assembl/ is composed of polypropylene. Preferably the closure as:sciniiy is composed of a polypropylene homopolymer.

Portions of fine container shown in Figure 1 are shown in greater:letai! in the cross-sectional viev'of Figure 3. Figure 3 shows the relationship between the pouch 8 containing the n-.icrowave absorbing material 4 and the inner shell 2, the foam : insulation 5, and the outer shell 3. Figure 3 also shows schematically the relationship between the stopper 6, the inner shell 2, the outer shell 3, and the lid 7. Stoppers 6 may be employed to seal the container by any means known to those of ordinary skill in the art, such as threading 9 or friction fit, in conjunction with standard seals. gaskets -and the like.

0 Figures 4 and 5, respectively, show perspective and cross-sectional views of a microwaveable beat retentive rood service tray assembled according to the invention, generally designated 14. The food service tray 14 comprises a tray top

15. The food service tray 14 further comprises an outer shell 3 and an inner shell 2. The outer shell 3 and inner shell 2 can be assembled by any system known to those of ordinary skill in the art such as by way of a snap fit construction and the interior can be filled with foam 5, all of the foregoing being performed as taught in 5 U.S. Patent No. 5,145,090 to Vvyatt, which patent is hereby incorporated by reference as though set forth in full herein. The tray top 15 and the inner shell 2 of the food service tray are formed in a manner to define separate food compartments 16, in a preferred embodiment, those compartments which are intended to contain hot foods, are placed adjacent a pouch containing the microwave absorbing material 10 4. In a preferred embodiment, approximately 40 grams of the material is used, the amount selected based on the volume of the compartment. The tray top 15 and the inner shell 2 can be formed continuously of the same piece of plastic material. In a preferred embodiment, the food service tray 14 further comprises foam insulation 5 which fills the remaining space of the cavity formed by the inner shell 2, tray top 15 15, and outer shell 3. In a preferred embodiment of the invention, those compartments which are intended to hold hot foods are filled with those foods, and the tray 14 is then microwaved for approximately 13/: minutes at approximately 600 to 1,000 watts. After heating in the microwave oven, the tray is removed, and those compartments intended for cold foods are filled. In such an embodiment, the 7() tray keeps the hot foods hot and the cold foods cold.

Figure 6 shows another embodiment of the invention, a microwaveable heat retentive serving container, generally designated 24. The serving container 24 comprises an inner shell 2 which is bowl-shaped. The serving container 24 further comprises an outer shell 3 which is substantially bowl-shaped as well. Because of 95 the size and shape of the serving container, it is preferred to place pouches 8 containing the microwave absorbing material 4 both in the sides 25 of the serving container and in the bottom 26 of the serving container. In addition, the serving container 24 further comprises a foam insulating material 5. in a preferred embodiment, the mass of the microwave absorbing material 4 in the bottom 26 is 3(J preferably 100 grams, and four pouches, each containing 25 grams, are distributed around the sides 25 of the serving container 24. In a preferred embodiment, the serving container 24 is placed in a microwave oven prior to being filled with food.

- r The serving container 24 is heated for approximately 2 minutes at approximately 600 to 1,000 watts. Upon removal from the microwave oven, the container 24 is filled wi.,- rood to be served. In another preferred embodiment, the empty serving container 24 is filled with the food to be served prior to placement in the microwave.

In this embodiment, neither the serving container 24 nor the food is heated prior to placement in the microwave oven. In this embodiment, both the food and serving container 24 are heated simultaneously in the microwave for approximately 4 minutes at approximately 600 to 1,000 watts. The serving container 24 containing the not rood is then removed from the-microwave oven for serving.

1() Figure 7 shows another embodiment of the irvent.on, a microwaveable heat retentive beverage mug, generally designated 34. The mug 34 comprises an inner shell 2, an outer shell 3, a pouch 8 containing a microwave absorbing material 4, and an insulating material 5. The mug 34 also has a handle 35 for ease of use. In 5 c-efe'^- embodiment, the mug 34 has a capacity of 0.35 to 0.59 litrest12 to 20 fluid JO cr-es)a. has a single 50-gram pouch 8 of microwave absorbing material in the base. T^.e mug may be preheated in a microwave oven prior to receiving its contents Aiternativly, the mug may be filled and then heated together with its contents in a microwave oven, Figure 8 shows a microwaveable heat retentive carafe in accordance with the 9() invention, generally designated 44. Preferably, the carafe 44 comprises an inner shell 2, an outer shell 3, a microwave absorbing material 4, and an insulating material 5. The carafe also comprises a handle 45 for ease of use, a stopper 46, and a spout 47 to aid in pouring. In preferred embodiments, the 1.0 liter carafe has a 1 OO-grarr: pouch 8 of microwaveable material in the base 48. Carafes with greater 95.'Clu2s, SC. as 1.42 and 1.89 litres, (48 and 64 fluid ounces) are also contemplated. For :.e larger carafes, it would be preferable to use larger masses of microwaveable materials (such as 1 couch having 120 grams of microwaveable material), and one of ordinary skill in the art would readily recognize how to do so based on the disclosure herein.

ne carafe may be preheated in a microwave oven prior to receiving its contents.

so Aiternativ fly, the carafe may be filled and then heated together with its contents in c microwave oven.

if) Figure 9 shows A microwaveable heat retentive wide-bottom mug in accordance with the present invention, generally designated 54. The widebottom mug 54 comprises an inner shell 2, an outer shell 3, a pouch 8 containing a microwave absorbing material 4, and an insulating material 5. In addition, the wide-

bottom mug comprises a handle 55 for ease of use. In a preferred embodiment, the 0.35 to 0.47 litres (12 to 16 fluid ounce) capacity widebotton mug 54 has a s m gle 50-

aram pouch of microwave absorbing material in its base. In one enixxthment, the wide-

coccom mug may be preheated in a microwave oven prior to receiving its contents. In another embodiment, the wido-bottan mug Rena. be filled and then heated together with its IO Contents in a microwave oven.

Figure 10 shows another preferred embodiment, the microwaveable heat retentive baby food dish in accordance with the present invention, generally designated 64. The baby food dish 64 comprises an inner shell 2, an outer shell 3, a pouch 8 containing a microwave absorbing material 4, and an insulating material !; 5. In preferred embodiments, the baby food dish contains a 80-gram pouch in the base of the dish. Upon heating in a 750 watt microwave for approximately 2 I minutes, the microwave absorbing material in the baby food dish heats up to -approximately 110 C(230 E). In preferred embodiments, the baby food dish is preheated in a microwave oven, and then filled with baby food at ambient temperature. In this 0 embodiment, the baby food dish warms the baby food to a temperature that this desirable. and maintains that temperature for a desirable period of time.

Figure 11 discloses an alternative embodiment of a microwaveable heat retentive thermal bottle in accordance with the present invention, generally designated 74. The thermal bottle preferably comprises an inner shell 2, an outer o: shell 3, a pouch 8 containing a microwaveable material 4, a foam insulating material 5, a stopper 6, and a lid 7. Additionally, the thermal bottle comprises a bowl-shaped lid 75, which can be taken off and used as a bowl for.use in eating or drinking.

A, Figure 12 discloses a pouch or envelope 8 containing a microwave absorbing material 4, the whole assembly gene,ally designated 84. The edges 85 can be () sealed with heat and pressure, or by any other means known in the art.

A heat-storing puck, generally designated 105, shown in Figure 14A has a center portion which contains a microwave absorbing material in accordance with

. the present invention. The dotted line in Figure 1 4A roughly indicates the area under which the microwave absorbing rnat-erial is present. Figure 14B shows a cross sectional view of the heat-storing puck of Figure 14A The microwave absorbing material 4 may be held in the center portion of tire hea-storing puck by a stopper piece 107. The puck body 108 may be formed of any material which is suitable for use as a puck and which will withstand microwave heating, and ceramics are especially preferred. The stopper piece 107 may be made of ceramic as well, or may be constructed of a different material. A heat-storing puck in accordance with the present invention may be microwaved prior to supporting a heated dish or food 1() container, or prior to being placed in a food container, such as a food carrying container including insulated plastic food carrying containers, or food carrying containers of other types, such as a pizza delivery box or the like, thereby keeping the temperature of the food in the dish or food container elevated for an extended period of time.

15 A service tray in accordance with the present invention is shown in Figure 15.

The embodiment of Figure 15 includes four separate portions which would contain a treatable member in accordance with the present invention. For example, in one embodiment, the tray may have indentations 116 at the four portions. Into these portions may be inserted the heat-storing pucks of Figure 14A and 14B. For those 70 foods which are to be served hot, the pucks are heated in a microwave prior to placing in the service tray. Alternatively, some of the pucks may be cooled prior to placing in the service tray, thereby enhancing the service of either hot or cold foods.

Of course, the tray may be manufactured with the microwave absorbing material sealed into the tray material, rather than in modular form as described above.

75 The heat-soring puck of Figure 14A and 14B may also be used in a tortilla warmer such as that disclosed in Figure 16. Like in the tray described above, the puck may be heated prior to being placed in the base 127 of the tortilla warmer.

Hot tortillas (or rolls, buns, or any other bread or food desired to be maintained warm, such as pizza, pasta, etc.) is then placed on top of the puck, thereby 30 maintaining the heat of the food for an extended period of time. Heat is contained by the use of a lid 128, which has a handle 129.

The foregoing specific embodiments are illustrative of applications in which the microwave absorbing compositions of the invention can be employed. Those of ordinary skill in the art will readily understand that other applications are suitable for the microwave absorbing material of the invention AS well. Thus, the invention can j be employed to keep the contents of the otherwise conventional coolers, such as picnic coolers, and ice chests, warm, or at elevated temperatures for extended time periods. Additionally, the invention can also be employed to warm mittens or gloves, boots, scarves, etc. In certain applications, the pouch of the present invention can 10 be employed as an insert for clothing, e.g., scarves, jackets, etc. Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The

following preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way

I whatsoever.

? 5

EXAMPLES

Example l

A number of different compounds velure tested for their ability to perform as microwave absorbing heat storage,-naterials within the context of the present j invention. Table l lists those materials which revere tested, whether or not they performed adequately ( + for adecl.'ately, - for inacleq.'ately), as well as comments on their performance (where appropriate).

lo Table 1 - Materials Tested Material Performance Comments Polyesters PET + I- very unevc-n heating - low temperature PET. 15 PETG +

PC Crystalline Resins PE with receptors + very uneven heating ._ PP/CaCO, filled _ PMP (TPX)

tS Acetal + degrades and outgases Nylon 66 + very uneven heating Nylon 6 + melted in spot concentration Nylon 612 + strong odor spotty melting t

Material | Performance Comments Styrenics HIPS I

SAN _ __. __

ABS _.. 1

ASA l l l Ru bbers __ Styrene butadiene TPV _ i Other Resins () PVC

_ _.. _

3 j Ourns eas = PMMA _.. Refractory Materials 1: Ceramic Fiber _ _. = _ Millboard Discs - gonerates steam - Calcium Silicate + generates steam Boa rd .. - Silica-Alumina 70 Board _.. _ Vermiculite Board + burns Organics Olefin Waxes with + uneven heating - separation of added receptors recep tors . _ 5 Glycerine high temperatLre, odor, vapors Monoglycerides + Erucaminde (amide slip agentsl._ -

1 _ Material Performance Comments | Gctadecanoic Acid.

Amine Powd' rs/Pellets Melamine + strong odor, burns SiO2. . ; CaSiO2 +/marginal temperature rise - steam I _ generated CaSO4 | NaOH _ ignited, burns | I Molecular Sieve + steam generation | ! (NaAlO2sio2-H2o) _ Recyclospheres (coal combustion by-product) !: Example 2

Materials were tested for their performance with regard to melting point, molecular weight of the individual repeating units in the chain, and number of excitable groups in the individual repeating units. 100 Grams of each material was subjected to microwave radiation having a frequency of 2450 MHZ and a power of 9: 70 watts, with results reported in Table 2, below: Table 2

POLYMER MELTING REPEATING CHAIN NO. OF EXCITABLE Min. Micw.

POINT MOLECULAR WT. GROUPS IN 100 G. Wt REPEAT CHAIN

- PET 252 C(485.F) 1 94 _ 2. 50 Ct122 F) PBT 25ooc(4a2oF) 222 46. 1 ct115 F' . | PE G 260 C(500 F) 470 e2.2OclaooF, PCTG 2asoc(s4soF) 470 4 7i.loCtl6o.F)

(I Table 2, continued PCTA 1 293.C(560.F) 552 71..CtI60@F) Glass Filled j302.C(575.F' 470 1 79.4.C(175 F) These data demonstrate that, in general, as the number of excitable groups ir, the repeat chain increases, the material in question translates more microwave energy into heat energy under the same conditions [time/power/mass of material, I(J etc.). ExarnDIe 3 The materials of the present invention were evaluated by following the procedures set forth in commonly assigned U.S. Patent No. 5, 916,470, incorporated l by reference above using PCTG and a glass vacuum liner. The thermal efficiency of each of the containers was measured according to the following procedure. 89 to ilanl'3tod ounces)o. water was placed inch the microwave container. The container was heated in a 750 watt microwave oven at full power for approximately 4 minutes.

The container was removed from the oven and the emptied. The container was then 90 filled to capacity with hot water at 85 C, and stoppered. The temperature was recorded at 30 minutes, 60 minutes, and every hour thereafter, until six hours had elapsed from the heating time. The results were compared with those using a vacuum insulated container, described above, which can be considered to be substantially identical to the invention in all respects except that container utilizes 75 a glass vacuum liner for thermal insulation. The results of this test are disclosed in Figures 2a and 2b. As shown in Figures 2a and 2b, the PCTG employed exhibits a tinne/temperature profile which compares favorably with the vacuum insulated container tested and the container employing glycerol monostearate.

Alternatively, the performance of the microwave container can be tested by À at) filling the container to capacity with water at ambient temperature. The container is then placed in a 750 watt microwave oven and heated at full power for 4 to 6 - minutes. The stopper is affixed, and the temperature is then recorded each hour for a total of six hours.

The preceding examples can be repeated with similar success by substituting the generically and specifically described constituents and/or operating conditions of this invention for those used in the preceding examples. From the foregoing descriptions, one skilled in the art can easily ascertain the essential characteristics

of this invention, and without departing from Lyle spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions. In this regard, suitable methods in accordance with the invention as set forth above and in the appended claims may he readily practiced by those of ordinary skill in the art based on the teachings of the present specification. Thus, in view of

10 the teachings above, it will be apparent that one of ordinary skill in the art can employ the microwaveable containers of the invention to practice various methods of heating food and/or maintaining food warm. For example, a cold (refrigerated) or room-temperature food could he warmed by heating a microwaveable container of the invention such as a serving container, and then placing the food in the container 15 or in heat exchange relationship with the heat storage mass therein to be warmed thereby. Such methods have particular utility in warming and serving foods to sensitive individuals, such as, for example serving baby foods to infants or similar individuals, such as patients in nursing homes, hospitals or other institutional settings. 90 Additionally, containers nil the invention inciucling plate-shaped containers (such as heat storage "pellets") and/or trays could be used in food service methods in institutional settings such as those methods disclosed in U.S. Patent No. 5,603,858 to WYATT et al., which patent is hereby incorporated by reference for such teachings as though set forth in full herein. Such methods could also be 95 practiced and applied in food delivery, such as in home delivery of restaurant food, including pizza, Chinese food, etc.

Claims (12)

- 31 CLAIMS

1. A microwaveable heat retentive container for heated foods or beverages comprising 5 (a) an outer shell, (b) an inner wall within said outer shell, and (c) a material susceptible to heating by microwave radiation, said material having a time/temperature profile such that, when from approximately 50-120 grams of said 10 material is subjected to microwave radiation having a frequency of from approximately 2,300-2,600 MHZ, at a power of from approximately 600-1,000 W. for a period of approximately 12 minutes, said material is heated to a temperature in a range of approximately 76.7-162.8 C(170 15 325 ).

2. A microwaveable heat retentive container according to claim 1 wherein said inner wall of (b) defines a receiving portion having a volume for receiving a material, and wherein 20 the ratio of the mass, in grams, of said material susceptible to microwave radiation, to the volume of the receiving portion, in milliliters, is from about 1:5 to about 1:12.

3. A microwaveable heat retentive container according to 25 claim 2 wherein the ratio is from about 1:5 to about 1:10.

4. A microwaveable heat retentive container according to claim 1 or 2 wherein the ratio is from about 1:6 to about 1:.

30

5. A microwaveable heat retentive container according to any preceding claim wherein the outer shell is substantially microwave transparent.

- 32

6. A microwaveable heat retentive container according to any preceding claim wherein the outer shell comprises polypropylene. 5

7. A microwaveable heat retentive container according to any preceding claim wherein said material susceptible to heating by microwave radiation is contained within a pouch.

8. A microwaveable heat retentive container according to any 10 preceding claim wherein the inner shell is substantially microwave transparent.

9. A microwaveable heat retentive container according to any preceding claim wherein the inner shell comprises 1 15 polyproylene.

10. A method of providing a heated product to a consumer or user comprising (a) placing a microwaveable container in a microwave 20 oven, said container comprising a material susceptible to heating by microwave radiation, said material having a time/temperature profile such that, when from approximately 20-120 grams of said material is subjected to microwave radiation having a frequency of from approximately 2,300-2,600 25 MHZ, at a power of from approximately 600-1,000 W. for a period of approximately 1-2 minutes, is heated to a temperature in the range of approximately 79.5-152.8 C (175 F 325 F);

(b) adding heated product to said container, either 30 prior or subsequent to (all and (c) providing said container with heated product to a consumer or user.

- 33

11. A microwaveable heat retentive container for heated foods or beverages substantially as hereinbefore described with reference to the accompanying drawings.

5

12. A method of providing a heated product to a consumer or user substantially as hereinoefore described with reference to the accompanying drawings, .'