Self-heating flexible package

Improved heaters and self-heating packages that function without application of external energy. Heat is generated by contact of a heat-producing composition, such as calcium oxide, and an activating solution which is typically water. The heater contains multi-compartments containing heat-producing composition and activating solution. The heater is activated by application of hand pressure to rupture a frangible seal which allows the heater components to mix. The heater compartments are at least in part formed from flexible walls. The self-heating package has one or more products or product containers in thermal contact with one or more heaters. In preferred packaging embodiments, the heating package has one or more product containers or pouches in thermal contact with one or more heaters. In a specific embodiment, the product container is integrally formed with the heater. Preferred self-heating packages are constructed entirely of flexible packaging materials.

BACKGROUND OF TBE INVENTION
 This invention relates to improved flexible self-heating packages that can
 be used to heat or warm liquid, semi-liquid, or solid products, or to
 maintain the temperature of products sold hot, to make them more suitable
 for their intended use. The self-heating device is one in which a solid or
 semi-solid heat-producing composition is reacted with an activating
 liquid, typically water or an aqueous solution, to generate heat. A number
 of self-heating containers have been reported, but all suffer from
 disadvantages that decrease their convenience of use or increase the
 expense for their manufacture.
 U.S. Pat. No. 5,628,304 Freiman et al (1997) reports a recyclable
 self-heating container having two compartments which contain anhydrous
 calcium chloride and water, respectively. The container is provided with a
 cutting device that is used to open the water compartment and allow water
 to contact the anhydrous calcium chloride and release heat.
 U.S. Pat. No. 4,773,389 Hamasaki et al. (1988) reports a self-heating
 foodstuff container having a body with two chambers, a liquid container
 and a support member. One of the chambers of the body is provided to
 receive a foodstuff and the second is provided to receive an exothermic
 reaction agent. The heater is activated by sliding a support member in
 contact with the body to cause the liquid to be discharged into the second
 chamber to initiate exothermic reaction.
 U.S. Pat. No. 4,793,323 Guida et al. (1988) reports a single-use
 self-heating container ith a plastic vessel within and attached to an
 external insulated envelope. Two compartments, an upper and a lower
 compartment, are provided in the vessel separated by a membrane. The upper
 compartment contains a solid reactant and the lower contains an activating
 liquid. The exothermic reaction is initiated by actuating a
 membrane-breaking member in the liquid compartment. The upper compartment
 of the vessel optionally contains a temperature control substance which
 undergoes a phase change between 90.degree. C. and 100.degree. C.
 U.S. Pat. No. 4,809,673 Charvin (1989) reports a device for heating food
 having an upper compartment for receiving food and a lower compartment in
 which two reagents are separated from each other by one or more watertight
 partitions. The device is provided with internal radial blades operated
 from outside of the container by an external control knob to tear the
 watertight partitions and initiate the exothermic reaction.
 U.S. Pat. No. 5,220,909 Pickard et al. (1993) reports a self heating
 individual meal module includes a tub for holding food to be heated. The
 tub is welded to a tray and in contact with a pad of an
 electrolytic-solution-activated exothermic-chemical. The heater also has a
 pouch containing an electrolytic solution. A pull-tab is provided on the
 pouch to release the electrolytic solution to activate the chemical pad to
 generate heat.
 U.S. Pat. No. 5,255,812 Hsu (1993) reports a self-heating tin container
 having a chemical compound for releasing heat upon mixing with a liquid
 catalyzer. The tin has a cap having an internal compartment containing
 liquid catalyzer and a pin on its inside surface which is used to pierce
 the internal compartment and allow liquid catalyzer to contact the
 chemical compound in the tin. Pressing an elastic top edge of the cap when
 in place on the tin, causes the pin to pierce the compartment permitting
 the liquid catalyst to flow into the tin.
 U.S. Pat. No. 4,057,047 of Gossett (1977) reports a thermal pack in which
 heat or cold is generated by contacting water with selected chemicals to
 generate an exothermic or an endothermic reaction. The thermal pack has
 three bags, two of which form the outer surface and inner surface of the
 pack, respectively. The inner of these bags holds the chemicals that will
 react with water. A third smaller bag containing water is inserted into
 the inner bag which contains the chemicals. The inner bag is ruptures by
 hand pressure to release water and activate the chemicals. The smaller
 inner bag is provided with a marginal seal that facilitates rupture on
 application of hand pressure.
 While a number of self-heating devices have been described, there is a
 continuing need in the art for devices that are more convenient to use and
 less expensive to manufacture. Many prior art devices require an
 additional device element, such as a pin or serrated edge, to bring the
 heater components into contact to generate heat. This requirement adds to
 the inconvenience and expense of the device. Other prior art self-heating
 devices are constructed with one or more rigid pieces that again generally
 increase cost and add to the bulk of the device.
 SUMMARY OF THE INVENTION
 The present invention provides heaters and self-heating packages that are
 more convenient to use and less expensive to manufacture than are
 currently available. The self-heating package of this invention contains a
 multi-compartment heater which is activated by application of hand
 pressure to rupture a frangible seal in the heater.
 In one embodiment, the self-heating package has one or more products or
 product containers in thermal contact with one or more heaters. In
 preferred packaging embodiments, the heating package has one or more
 product containers or pouches in thermal contact with one or more heaters.
 In a specific embodiment, the product container is integrally formed with
 the heater. Preferred self-heating packages are constructed entirely of
 flexible packaging materials.
 The heater of this invention has a multi-compartment structure having at
 least one compartment for holding a heat-producing composition and at
 least one adjacent compartment for holding an activating solution.
 Adjacent compartments containing activating solution and heat-producing
 composition are separated by a frangible seal. The heater compartments are
 formed, at least in part, from a flexible packaging material. Application
 of sufficient pressure, for example, as applied by hand by squeezing or
 twisting, on a compartment or compartments of the heater, for example,
 compression of the activation solution-containing compartment, ruptures
 the frangible seal, allowing the solution and the heat-producing material
 to mix and begin heat production. Heaters include those having two
 adjacent compartments for holding heat-producing composition and
 activating solution, respectively, separated by a frangible seal.
 Once activated the multi-compartment heater pouch can be used to heat a
 product or to maintain the temperature of a hot or warm product. During
 use the heater pouch is placed in close proximity to the product to be
 heated or kept hot. For example, the heater pouch can be placed in direct
 contact with the product or in contact with a heat-conducting package
 containing the product. The heater pouch can be placed within thermally
 insulated packaging that also contains the product. Heaters of this
 invention can be employed, for example, to maintain a desirable
 temperature of various take-out foods, including pizza, hamburgers and the
 like, during transport. The size of the heater is generally adjusted to
 the size of the product to be heated and the amount of heater components
 (heat-producing composition and activating solution) in the heater
 compartments are adjusted to provide the desired temperature for a given
 heating or warming application. The amount of activating solution provided
 in the heater is preferably at least enough to react with the amount of
 heat-producing compound in the heater and optionally is provided in excess
 to limit the maximum temperature achieved.
 An advantage of the heater is that the package can be manufactured from
 inexpensive, flexible packaging materials appropriate for retaining the
 liquid activation agent. The packaging material employed preferably can
 withstand temperatures generated up to about 90.degree. C. in the product
 pouch, and somewhat higher temperature in the heater pouch (e.g., up to
 150.degree. C.). The design is compatible with a variety of heat-producing
 materials, and is particularly suited for use with heat-producing
 materials that do not produce a substantial amount of gas in operation, so
 that the package can remain completely sealed. In this way the user never
 comes in contact with the heat-producing materials. Addition of an excess
 amount of activation solution over the amount needed to substantially
 react with the heat-producing composition can function as a heat sink to
 minimize generation of steam.
 Self-heating packages of this invention have a multi-component heater, as
 described above, held, attached or bonded to and in thermal contact with a
 product to be heated or kept hot or warm. Heaters may be held or attached
 directly in contact with the product or with a thermally conductive
 product container or pouch which contains the product. Heaters may be held
 in contact with the product by application of external packaging, such as
 an overwrapping of thermally insulated flexible packaging material that
 also functions to hold the heater in place or by application of an
 adhesive or other bonding agent between the heater and the product or
 product container. The heater inside the packaging material is activated
 by hand pressure to release heat and transfer heat to the product. The
 external packaging or product container can then be opened to extract the
 heated product.
 In a specific embodiment, a self-heating package has a product container or
 pouch integrally formed with the heater package. For example, the product
 container can be formed by sealing or otherwise bonding the edges of a
 sheet of flexible packaging material to a surface of or at the perimeter
 of the heater. In this package, liquid, semi-liquid or powdered product
 introduced into the product container is in thermal contact with the
 heater. Application of hand pressure to the flexible heater compartment(s)
 ruptures the frangible seal and initiates heat release to heat the product
 within the container. The product container can be opened, for example as
 facilitated by appropriate positioning of a tear notch, to remove heated
 product. The product container may be porous or non-porous.
 In another embodiment of the self-heating package, the heater is attached
 to a porous material, such as a scrim, net or webbing, to form a porous
 product container. The porous container contains a dry material that is
 intended to be dissolved or steeped in warm or hot water. The porous
 material retains the dry material and allows liquid to penetrate into the
 container. In this embodiment, the package including the heater and
 attached porous container, once activated, is inserted into a liquid, such
 as water, to heat the liquid. The product in the porous pouch dissolves or
 steeps in the heated liquid to add a desirable flavor or other attribute
 to the liquid. The porous container can contain, for example, a dry
 beverage (tea or coffee) or flavoring agent that is intended for addition
 to or immersion in hot water for consumption.
 In yet another embodiment of the self-heating package, the heater is
 attached to an absorbent or coated substrate or an encapsulated material
 where the product to be heated is absorbed or coated on the substrate or
 is the encapsulated material. In this embodiment, heating results in
 release of the absorbed or coated product from the substrate or release of
 encapsulated product.
 The heaters and self-beating packages are designed for use with a
 heat-producing material or materials activated by addition of a liquid,
 preferably water or an aqueous solution, to the heat-producing
 compositions. A variety of heat-producing compositions are useful in this
 invention. In particular, heat-producing compositions described in
 PCT/US97/12846, U.S. Pat. No. 5,935,486 and U.S. patent application Ser.
 No. 09/351,821, filed Jul. 12, 1999, all of which are incorporated by
 reference herein in their entirety to the extent that they are not
 inconsistent with the disclosure herein. The beat-producing material or
 materials may be in the form of a pad, powder, granules, or a combination
 of the above. The heat-producing materials are preferably solid or
 semi-solid. Heat-producing compositions can comprise an active
 heat-producing component in combination with an inert material. The inert
 material does not react with activating solution to generate a substantial
 amount of heat and can serve to moderate or control heat release on
 activation. Heat-producing compositions can include, among others, CaO,
 MgCl.sub.2 and Na.sub.2 SO.sub.4. In one preferred embodiment, the active
 heat-producing components area mixture of an acidic anhydride or an acidic
 salt with a basic anhydride and a basic salt. Acidic anhydrides include
 phosphorous pentoxide. Acidic salts include aluminum chloride and
 magnesium chloride. Basic anhydrides include calcium oxide Preferred
 active heat-producing components are calcium oxide alone, a combination of
 phosphorous pentoxide and calcium oxide or a combination of magnesium
 chloride and calcium oxide. Inert materials which typically represent from
 about 1% to about 30% by weight of the heat-producing composition include
 among others surfactants, oils, waxes, and natural or synthetic polymeric
 solids. Preferred heat-producing compositions produce substantially no
 gases on activation. Preferred heat-producing compositions are water-free.

DETAILED DESCRIPTION OF THE INVENTION
 The invention relates to heaters in which heat is generated by exothermic
 reaction of active ingredients. The heaters generate heat without
 application of external heat energy. Preferred active ingredients are a
 liquid activating solution (preferably water or an aqueous solution) and a
 heat-producing solid. In the sealed heaters of this invention liquid is
 brought into contact with the heat-producing material to generate heat.
 The heaters are formed as multi-compartment elements where the
 compartments are preferably formed from flexible packaging materials.
 Activating solution and heat-producing compositions are held in separate
 compartments in the heater. Compartments are separated by frangible seals
 that can be readily ruptured by application of hand pressure to the
 flexible heater compartments. The heater components generate heat on
 activation. Dependent upon the application of the heater a variable amount
 of heat may be desired. Heaters may be used to heat cold items or maintain
 the temperature of warm or hot items. In the latter application, the
 heater need not provide enough heat to raise the temperature of the
 product heated, but only enough heat to slow cooling of the product. The
 heater is provided in a sealed package to avoid contact of heater
 components with the surroundings and to maintain the activity of the
 heat-producing material. Heaters of this invention can be used alone or in
 a self-heating package.
 Self-heating packages combine a heater with a product or product container.
 The heater is in thermal contact with the product or product container in
 the package. The heater is activated in the package, by application of
 hand pressure to rupture one or more frangible seals that cause activation
 of the heater. The heater components are retained in a compartment
 separate from the product. After the product is heated inside the package
 a portion of the packaging can be opened to remove the product for use.
 The invention is further illustrated by reference to the drawings in which
 the same numbers are used to indicate similar features.
 FIG. 1A illustrates an exemplary two-compartment heater 1 of this invention
 constructed from flexible materials. The heater has compartment 9 which
 contains activating solution (preferably water or an aqueous solution) and
 compartment 11 which contains a heat-producing composition which is
 typically a solid. The two compartments are separated by a frangible seal
 13 that prevents contact of the heat-producing composition and the
 activating solution until pressure is applied to rupture the seal. The
 seal is constructed to be ruptured by application of pressure by hand by
 twisting or squeezing the flexible heater. For example, the seal can be
 ruptured by application of hand pressure to a flexible wall of a heater
 compartment. FIG. 1B illustrates a side view of a heater of FIG. 1A. The
 frangible seal is preferably sufficiently large to allow efficient mixing
 of components.
 Various configurations of a self-heating package which combine one or more
 heaters with one or more product containers are shown in FIGS. 1C-1P (in
 side view). The package may be produced in several configurations that
 facilitate heat transport from the heat-producing material to the product
 to be heated The heater package (FIG. 1B) may be roughly rectangular in
 shape, with a thickness that is less than either the length or the width
 with the two compartments illustrated in FIG. 1A for receiving activating
 solution and heat-producing composition 9 and 1, respectively. The
 material to be heated can be attached to one or both sides of the heater
 package. Attachment can be effected by adhesive or mechanical means, if
 the product to be heated consists of a single piece or multiple large
 pieces. If the product to be heated consists of a liquid, semi-liquid, or
 powder, it may be contained within a pouch 5 formed of a single layer of
 flexible packaging material that is bonded to the heater, as shown in
 FIGS. 1C-F, where the product pouch is sealed to the heater so that a
 surface of the heater forms at least a portion of the product pouch.
 Alternatively, the product to be heated may be contained within two or
 more layers of packaging material, preferably flexible packaging material,
 which form a pouch or container 6 separate from the heater pouch. The
 separate pouch 6 may be attached, e.g., adhesively or mechanically to the
 heater (FIGS. 1G-1J). In yet another embodiment, the product to be heated
 may be contained within a flexible container or pouch 8 that completely or
 partially surrounds the heater (FIGS. 1K-1L). This embodiment has the
 particular advantage of enhancing heat transfer because the heater is
 surrounded by product to be heated. Two product pouches may be formed at
 or attached to opposite sides of the heater (FIGS. 1E, 1F, 1I and 1J). Two
 or more heaters can be formed at or attached to or adjacent to the product
 side of the product pouch (FIGS. 1M-1P). Pouch 12 in FIGS. 1M and 1N is
 integrally formed between two heaters. In all configurations illustrated,
 a thermally insulating material may be provided, either as part of the
 packaging material forming the various compartments of the heating package
 or as a separate layer, to retard transfer of heat from any or all parts
 of the total package to the surroundings. Various insulation materials can
 be employed including flexible paper or plastic structures having enclosed
 air pockets to slow heat transfer. Preferably no insulation is positioned
 between the heater and the product pouch. For example, an outside layer
 (overwrap 3) of insulating material may serve to retard heat transfer to
 the surroundings (FIGS. 1D, IF, 1H, 1J, 1L, 1N and 1P).
 More detailed schematic drawings of a self-heating product of this
 invention, of the general design shown as FIG. 1C, where the product is a
 liquid, semi-liquid or powder solid, are shown in FIG. 2 and FIGS. 3A and
 3B. The combined heater/product pouch package of FIG. 210 has a product
 pouch 5 made of a flexible material. The product pouch is bonded to and in
 thermal contact with a multiple compartment heater pouch 7 having at least
 one compartment 9 for holding activating solution, preferably water, and
 at least one pouch 11 containing heat-producing composition. The two
 compartments 9 and 11 of the heater are separated by a frangible seal 13
 which can be readily ruptured on application of hand pressure (i.e., by
 squeezing or twisting). Product can be removed from the pouch 5 via a tear
 notch 15 opening. FIG. 3A gives a front side (product side) view of the
 pouch illustrating the position of tear notch 15 near the top of the
 product package sealed with the heater package by peripheral seal 16. FIG.
 3B gives a back side view of the heater compartment. Heater material is
 contained in the lower pouch 11 and the activating solution is contained
 in the upper pouch 9. The pouch containing activating solution 9 is sealed
 at the top (opposite the frangible seal 13) with a non-frangible seal 17
 that will withstand pressure applied by hand.
 FIGS. 2, 3A and 3B also illustrate another aspect of this invention, the
 arrangement of heater and product such that it is convenient to open the
 product container while leaving the heater container unopened. This is
 accomplished by having the product container extend past the heater
 container in one direction, as illustrated in FIG. 3B, and providing means
 to open the product container, e.g., a tear notch, along a line that does
 not extend into the heater part of the self-heating product.
 The self-heating package illustrated in FIGS. 3A and B can be formed for
 example by heat sealing a front sheet of packaging material to one surface
 of a multi-compartment heater.
 The heaters in FIGS. 1A, 2, 3A and 3B illustrate heaters with two
 compartments: one for activating solution and one for heat-producing
 composition. Heaters of this invention can contain a plurality of
 compartments for either activating solution or heat-producing composition.
 At least one compartment for activating solution is positioned adjacent to
 at least one compartment containing heat-producing solution with the
 adjacent compartments separated by a frangible seal as described above.
 When the seal is ruptured the activating solution and heat-producing
 composition in adjacent compartments come into contact activating the
 heat-producing composition. One compartment containing heat-producing
 composition may be positioned adjacent to more than one compartment
 containing activating solution to facilitate mixing after rupture of the
 frangible seal.
 FIG. 4 illustrates another self-heating package of this invention in which
 the combined heater compartments are attached to a porous pouch 20
 containing a dry material 22, such as instant or ground coffee, tea, or a
 beverage flavoring agent. The pouch contents do not require heating, but
 they are used with hot water to prepare edible beverages or soups. The dry
 ingredients are intended to be dissolved in or steeped in hot water. The
 heater is activated by rupture of the frangible seal 13 with hand pressure
 and the entire package is inserted with attached product scrim 20 into a
 vessel containing water. A layer of insulation 23 is optionally positioned
 between the heater and the pouch 20. The heater is used to heat water in
 the vessel. During and after the water is heated the dry product is
 steeped or dissolved in the warm or hot water. The water is heated
 sufficiently for use as a hot or warm beverage. FIG. 4 illustrates a
 porous pouch (made of porous material 27, e.g., paper or plastic, e.g.,
 tea-bag paper or scrim) containing dry material 22 for dissolving or
 steeping in hot or warm water bonded to a two compartment heater pouch 7
 having a compartment 9 for holding activating solution, preferably water,
 and a pouch containing heater material 11. The two compartments 9 and 11
 of the heater are separated by a frangible seal 13 which can be readily
 ruptured on application of hand pressure (e.g., by squeezing and or
 twisting). A layer of insulation 23 is optionally positioned between the
 porous pouch and the heater compartments. In this embodiment, the heater
 compartments are not insulated from the surroundings, since the heater on
 activation is intended to heat water or other liquid into which it is
 inserted. The heater is activated by breaking the frangible seal between
 the two heater compartments and the entire package is inserted into a
 vessel containing water or other liquid. Heat released from the heater
 heats the water and the dry ingredients in the porous pouch interact with
 the heated water to extract or dissolve flavorings into the water. The dry
 ingredients in the porous pouch can include: natural materials, e.g.,
 mixtures of herbs, coffee and teas (dried or instant), flavoring agents,
 concentrated beverages (soup or bouillon), encapsulated beverages or
 flavorings and freeze-dried beverages or flavorings. The dry ingredients
 can also be mixed with sugar, salt, fruit zest or other seasonings. The
 porous pouch 20 can be formed from a variety of materials with various
 pore sizes adapted to the desired application. Porous produced containers
 can be formed from paper, plastic or related materials. Preferred
 materials are those that can be readily sealed or bonded to heaters of
 this invention.
 The heater package of FIG. 4 can also contain dried or powdered medicinals,
 and herbs, leaves, plant oils and the like having medicinal effect. The
 package can be used to provide heated medicinal solutions and suspensions
 for ingestion. Other heating package configurations of this invention,
 e.g., as in FIG. 2, can be used to provide heated salves or creams for
 application to the skin, and for heated solutions for inhalation.
 In general the heater packages of this invention can be applied for
 generation of heated liquids, creams, salves, lotions, solutions, and like
 media that are edible, used in medicinal applications, used in personal
 care products, used for cleaning, such as dry or moist towels, towelettes
 and wipes, and a wide variety of other applications.
 In a particular embodiment, heater packages of this invention include those
 in which towels, towelettes or wipes (the product) is wrapped around a
 heater, as illustrated in FIG. 1K or 1L, and the combination optionally
 encased in an appropriate outer package. Application of hand pressure to
 the enclosed heater releases heat to warm the towel, towelette or wipe.
 The packaging material is an important component of this invention. The
 packaging material may be either transparent or opaque. A lower water
 vapor transmission rate (WVTR) will increase the shelf life of the
 product. The packaging material may be capable of forming a heat seal of
 variable strength, nonfrangible and frangible seals, such that when
 pressure is applied to the liquid compartment, the frangible seal between
 the liquid compartment and the heater material compartment 13 opens to
 admit the liquid to the heater material compartment, but the nonfrangible
 perimeter seal 16 and any nonfrangible top seal 17 do not open. A heat
 seal strength of about 3 pounds per inch is desirable for the frangible
 seal, while a heat seal strength of about 12 to 15 pounds per inch is
 desirable for the perimeter seal and any top seal to avoid perimeter seal
 breakdown when hand pressure is applied. Both the frangible seal 13, the
 top seal 17, and the perimeter seal 16 may be formed in a single operation
 by adjusting the temperature, pressure, and time of application of the
 bars used to form the heat seal. Those skilled in the art will recognize
 that additional means may be employed as necessary to increase the
 strength of the perimeter seal, such as using a serrated, rather than a
 plain seal or a wider seal.
 A preferred flexible multiple layer packaging material for forming the
 heater comprises a water vapor barrier layer and an inner layer that
 functions to form variable strength heat seals. The inner layer may be
 provided only where seals are intended to be formed. The packaging
 material must have sufficient mechanical strength to withstand typical
 manufacturing processes, transport, storage and handling of such items.
 Mechanical strength may be provided by the water vapor barrier layer or by
 addition of a resin layer, e.g., an olefinic resin layer, to provide
 additional mechanical strength. A polyethylene layer is useful for
 providing sufficient mechanical strength. The packaging material can
 further comprise an outer protective resin layer, that preferably is
 compatible for receiving printing and/or graphic images. A polyester resin
 is suitable for this outer layer.
 An exemplary flexible composite packaging material for use with heaters and
 self-heating packages comprises (1) a thin layer of aluminum foil as a
 water vapor transmission barrier (e.g., a 0.0003 inch layer of aluminum
 foil), and (2) a heat sealable inner layer of an ethylene ionomer, such as
 a 3 mil thick layer of SURLYN.TM. (DuPont). This composite packaging
 material can also have an outer layer of 48 gauge polyester which will
 receive graphics and printing. Further, a layer of 0.7 mil polyethylene
 can be provided between the outer layer and the foil to provide for
 sufficient mechanical strength and to protect the foil from damage.
 Several commercial packaging materials can provide the properties useful
 for heaters of this invention and be capable of forming variable strength
 seals. One particularly useful material is available under the trade name
 Vari-seal (Cadillac Products).
 The aluminum foil layer can be replaced, for example, with other materials
 that provide a water vapor transmission barrier, such as ethylene-vinyl
 alcohol copolymer. Alternative heat sealable layers include linear
 low-density polyethylene.
 Films for use in heaters and packages of this invention should be
 compatible with the heater components (activating solution and
 heat-producing composition) such that the film is not detrimentally
 affected by those components. The flexible film and other packaging
 materials must be compatible for use with food, beverages, pharmaceuticals
 or personal care products. The materials used must be approved, if
 required, by the pertinent regulatory agencies for use in a given
 application. Many flexible materials may be used in this invention.
 Suitable materials can be selected by one of ordinary skill in the art in
 view of the disclosures herein and in view of the type of application with
 the aid of a standard reference, such as "The Wiley Encyclopedia of
 Packaging Technology" (M. Bakker, ed., NY, Wiley, 1986).
 Seals may be made as is known in the art by applying pressure from a heated
 bar, controlling the temperature of the bar, the pressure and the length
 of time that the pressure is applied to form a seal of desired strength.
 Seals of heaters and self-heating packages specifically exemplified herein
 were formed with a Vertrod heat-sealer. A seal strength of about 3
 lbs/inch is desirable for frangible seals and a seal strength of about
 12-15 lbs/inches is desirable for nonfrangible, perimeter seals. Heater
 packages and self-heating packages of this invention can be filled and
 sealed in a single operation using any conventional equipment, including
 vertical and horizontal form/fill/seal machinery.
 Those of ordinary skill in the art will appreciate that other materials
 known in the art are functionally equivalent to and can be used to replace
 packaging materials specifically described herein. Information on polymer
 film with appropriate properties for use in the heaters and self-heating
 packages of this invention may be found in the "Concise Polymeric
 Materials Encyclopedia" (J. C. Salamone, ed.; NY, CRC Press, 1999).
 A variety of heat-producing compositions can be employed in the practice of
 this invention. Preferred heat-producing compositions are those that are
 activated by the addition of a liquid, preferably water or an aqueous
 solution, to the heat-producing compositions. Heat-producing compositions
 can include inexpensive materials such as lime (CaO), sodium sulfate and
 magnesium chloride and mixtures thereof. Particularly useful
 heat-producing compositions are described in PCT/US97/12846, U.S. Pat. No.
 5,935,486 and U.S. patent application Ser. No. 09/351,821, filed Jul. 12,
 1999, all of which are incorporated by reference herein in their entirety
 to the extent that they are not inconsistent with the disclosure herein.
 Heat-producing compositions can comprise an active beat-producing
 component in combination with an inert material. The inert material does
 not react with activating solution to generate a substantial amount of
 heat and can serve to moderate or control heat release on activation. The
 inert material may serve to inhibit access of the activating solution to
 the active heat-producing components. In preferred embodiments, the active
 beat-producing components are a mixture of an acidic anhydride or an
 acidic salt with a basic anhydride and a basic salt. Acidic anhydrides
 include phosphorous pentoxide. Acidic salts include aluminum chloride.
 Basic anhydrides include calcium oxide. Heat-producing compositions
 include a combination of phosphorous pentoxide and calcium oxide and a
 combination of magnesium chloride and calcium oxide. Specific
 heat-producing compositions include: calcium oxide alone, about 10%-90% by
 weight calcium oxide with the balance being phosphorous pentoxide or about
 25%-50% by weight magnesium chloride with the balance being calcium oxide.
 Inert materials can most generally represent from about 1% to about 30% by
 weight of the heat-producing composition. More preferably the inert
 material represents up to about 20 weight % of the heat-producing
 composition. In specific embodiments heat-producing compositions contain
 from about 10 to 20 weight % of inert materials. Inert materials include
 among others surfactants, oils, waxes, natural or synthetic polymeric
 solids and mixtures and mixtures thereof. Inert materials can include
 mixtures of surfactants and oil. Surfactants of particular interest for
 this application include organic phosphate esters, oil-soluble
 surfactants, polyethoxylated alcohol, and polyamide succinimide. Preferred
 surfactants include among others Actrafos 216 (Trademark), stearic acid,
 dicetylphosphate, Paranox 100 and Brij 30 (Trademark). Preferred oils
 include among others aliphatic hydrocarbons, vegetable oils and mineral
 oil.
 Preferred heat-producing compositions contain a mixture of active
 components, such as CaO or combinations of CaO with P.sub.2 O.sub.5 or
 MgCl.sub.2 in combination with inert material that can be a mixture of
 surfactant, oil, and/or wax. Heat-producing compositions can be prepared
 for example, as pads, pellets or powders. In preferred embodiments of this
 invention, the heat-producing composition is formed into pellets,
 preferably ranging in size from about mesh 6 to about mesh 16. The use of
 larger size pellets tends to decrease the rate of heat generation on
 activation. The rate of heat generation in the heaters of this invention
 can be controlled by selection of the type of active ingredients, the
 amount of inert material included and the physical form of the
 composition.
 Preferred heat-producing compositions produce substantially no gases on
 activation. Preferred heat-producing compositions are water-free.
 Preferably heat-producing compositions are selected and the amount used
 adjusted to provide a desired amount of heat transfer in a given
 application dependent upon the product to be heated and the packaging of
 the product.
 The heat-producing compositions may be in the form of a pad, powder,
 pellets, granules, or a combination of the above. The heat-producing
 materials are preferably solid or semi-solid.
 The type and amount of heat-producing composition and activating solution
 in the heater compartments are predetermined to obtain desired heat
 release appropriate for the product to be heated and to minimize the risk
 of rupture of the heater.
 A further aspect of this invention shown in FIG. 5 is a package design that
 enables convenient heating of a liquid product that is volatile or
 contains a volatile component, so as to evaporate or volatilize the
 volatile material into the atmosphere. Examples of such products include
 insect repellent, room deodorizer, or other desirable scents. The volatile
 liquid or mixture containing it may be absorbed onto an absorbent material
 25 such as paper, vermiculite or ground corn cobs. The absorbent material
 is attached to the heater, for example by adhesive or mechanical means and
 may be held within a porous container 20. In particular, if the absorbent
 material is a powder or granular solid, it may be contained and held in
 proximity to the heater by a porous material 27 (such as paper or a
 nonwoven scrim material) having pores chosen so as to retain the absorbent
 and allow the volatile material to pass through. As will be obvious to
 those skilled in the art, a self-heating product of this design may be
 produced with means to prevent the evaporation of the volatile materials
 until desired, either by covering the part of the product containing the
 volatile materials with an additional layer of impermeable flexible
 packaging film, or by containing the entire product 30 in a bag or pouch
 of impermeable flexible packaging film.
 The volatile component may be encapsulated in a material, e.g., a wax, that
 melts on heating. Encapsulated product may be coated or absorbed on to the
 absorbent material. The absorbed material may be treated, for example, by
 soaking in a solution containing the product and removing the solvent.
 The packaging systems and methods of this invention can also be applied to
 packaging of personal care products (e.g., oils and lotions for
 application to the skin or hair). The packaging system of this invention
 is particularly amenable to single-use or single-serving size
 applications.
 The packaging systems and methods of this invention can also be applied to
 packaging of food items which are more palatable when heated and
 particularly to those items that are thick semi-liquid viscous products at
 room temperature, but become less viscous on heating (i.e., sauces for use
 on ice cream, heated salad dressings).
 The performance of two self-heating packages of design illustrated in FIGS.
 2, 3A and 3B is illustrated in the graphs of FIG. 6 and FIG. 7. From these
 data it is clear that a small amount (ca. 5 g) of heater material
 activated with ca. 3-4 g water is sufficient to heat about 20 g of oil or
 fudge sauce. The heater material used in both experiments was the same: a
 mixture of 86.6% by weight of the active ingredient: a 1:1 weight ratio
 mixture of CaO: P.sub.2 O.sub.5 and 13.4% by weight of an inert material:
 a mixture of 74% by weight mineral oil and 26% by weight of the surfactant
 Actrafos 216 (TM), an organic phosphate ester. The packaging for the
 self-heating packages tested comprised an outer layer of 48 gauge
 polyester, a layer of about 0.7 mil polyethylene, an 0.0003 inch layer of
 aluminum foil and a 3 mil layer of an ionomer (Surlyn, Trademark) to form
 the variable strength heat seal. Temperatures ranging from about
 120-180.degree. F. can be attained within about 3 minutes or less. A
 temperature above ambient can be maintained for over 20 minutes.
 Many food and beverage products are sold hot, and are more desirable if
 kept hot until consumed. During the time that passes between purchase and
 consumption, e.g. during transport to another location, the food or
 beverage can cool off and become less desirable. The flexible heater of
 this invention can be inserted into or used in conjunction with various
 hot food or beverage containers to keep these products hot or warm, i.e.,
 to slow the decrease in temperature of the product. In use the package is
 squeezed or twisted to rupture the frangible seal, allowing the heater
 material and water or aqueous solution for activation to mix and begin the
 process that produces heat. The heater is then placed or held in proximity
 to the product to be kept hot, until the product is consumed. It is
 desirable that such a self-heating package reach a temperature hotter than
 the minimum desirable temperature of the product, but less than the
 boiling point of water. In this way heat transfer to keep the product hot
 is feasible, but the self-heating package does not generate any
 significant amount of steam or internal pressure. The self-heating package
 can thereby remain sealed, so that no solid, liquid or vapor from the
 heater comes into contact with the product or the consumer.
 In an exemplary embodiment using the heater in take-out food applications,
 a quarter-pound cheeseburger in a box of thin cardboard, as is commonly
 used in fast food businesses, can be kept hot by using a multi-compartment
 flexible heater. The size of the heater is chosen to fit inside the bottom
 of the food container and preferably to substantially conform in size to
 the dimensions of the container to maximize the contact area available for
 heat transfer from the heater to the product. Various sizes and shapes of
 food and beverage containers are generally employed in food service.
 Heaters of this invention can generally be tailored to fit any of such
 product containers to provide efficient heat-transfer to the product.
 A two-compartment heater was constructed as a composite structure with an
 outer layer of 48 gauge polyester, a 0.0003 inch layer of aluminum foil as
 a water vapor barrier, a layer of about 0.7 mil polyethylene between the
 outer layer and the foil, and an inner 3 mil layer of an ionomer to form a
 variable strength heat seal. One compartment contained 4 g of a
 heat-producing composition that was a mixture of 86.6% by weight of the
 active ingredient: a 1:1 weight ratio mixture of CaO: P.sub.2 O.sub.5 and
 13.4% by weight of an inert material: a mixture of 74% by weight mineral
 oil and 26% by weight of the surfactant Actrafos 216 (TM), an organic
 phosphate ester. The second compartment contains 4 grams of water. This
 self-heating package is 3.5.times.3.5 inches square, divided into two
 compartments by a frangible seal. On activation the mixture in the heater
 package becomes hot, but the package remains sealed. In a comparison test
 in which a heater is placed against the bottom of a cardboard box
 containing a cheeseburger in one case, compared to the same size
 cheeseburger without a heater in the second case, the time-temperature
 profiles shown in FIG. 8 are obtained. In this case the cheeseburger is
 actually heated: its temperature increases from 141.degree. F. to
 152.degree. F. over ten minutes with the heater, where the same size
 cheeseburger without the heater cools from 144 to 125.degree. F. over the
 same time. In practice it is only necessary that use of the self-heating
 package results in the product cooling significantly less than it would
 without the heater, and thereby remaining more attractive to consumers.
 It is an important feature of this invention that the heat producing
 composition (and the residue after activation) can remain sealed before,
 during and after use and does not contact the product. This minimizes any
 negative effect that either part of the heater system may have on the
 heated product. Further, the use of a sealed heater minimizes risk of
 potentially harmful effects of the heater components on users (e.g., toxic
 or allergic reactions). In a specific package design, to ensure that the
 heater package remains sealed, any of the following changes may be made
 singly or in combination: The amount of heat-producing composition may be
 decreased (e.g., by increasing the proportion of inert materials or by
 increasing the particle size of the heater materials, or both), or the
 amount of water or aqueous solution used for activation may be increased
 to provide an additional heat sink.
 As an additional feature of this invention, means may be provided to give
 the user an indication that the heater system has not remained sealed.
 Such means may include a dye added to either the heater material or the
 liquid used to activate the heater, or both. When the integrity of the
 heater system is compromised, the dye will give a visual signal that
 product quality may also be compromised. The heater packaging may be
 transparent or have a transparent window to allow possible undesired
 release of dye to be observed. Alternatively, a substance with a strong,
 objectionable taste or odor may be added to the heater system. When the
 integrity of the heater system is compromised, the objectionable taste or
 odor will signal that product quality may also be compromised and
 discourage inappropriate use.
 The heater or self-heating packages of this invention may also be provided
 with some means to indicate that the heater or the product in the package
 have reached a selected temperature that indicates for example that the
 product is at a temperature suitable for consumption or use. For example,
 liquid crystal materials that change color with increasing temperature can
 be used for such an indicator. Alternatively, dyes that become colorless
 when hot, to reveal a legend or graphic that was previously concealed by
 the dye when colored, can also be used for such an indicator.
 Several heater or heating packages can be combined to conveniently give a
 large quantity of the desired hot product. Combining several smaller
 packages rather than one large package may be advantageous in certain
 applications to provide more efficient and more rapid heat-transfer to
 product.
 The outer packaging of the multi-compartment heaters of this invention are
 intended to remain sealed to prevent release of heater components or
 residues to the surroundings. In the event that excessive pressures occur
 that might rupture the heater package, an optional feature of this
 invention is provision of a vent and means to control the position of
 venting such that any steam or gases vented from the heater are directed
 in a harmless direction, and to insure that the excess pressure does not
 cause the package to rupture. A selective vent can be provided by
 selective placement of a weaker seal region in the perimeter seal of the
 heater. The vent seal would be stronger than the frangible seal so that it
 would not rupture by application of hand pressure, but weaker than the
 perimeter seal.
 Methods for forming frangible seals and nonfrangible perimeter seals are
 well-known in the art and can be readily adapted for use in the
 self-heated products of this invention. U.S. Pat. Nos. 5,699,902 and
 5,873,322 provide details and references to methods for frangible seal
 formation that are applicable to making the packages of this invention.
 All of the heater/product container combinations of FIGS. 1A-1P can be
 readily prepared using methods known in the art in view of the disclosures
 herein. Methods are known in the art for bonding sheets of flexible
 materials, e.g., heat sealing of plastics or related materials, to form
 durable seals needed to form heater compartments and product compartments.
 Similarly, art-known methods can be employed to bond or attach porous
 materials to flexible packaging materials to form porous product
 compartments.
 By using flexible packaging and a frangible seal that is produced as an
 integral part of the packaging and in the same operation as the package is
 formed, self-heating products of this invention may be made at lower cost,
 and are lighter and smaller than comparable products using prior art.
 All of the references cited herein are incorporated by reference herein in
 their entirety to the extent that they are not inconsistent with the
 disclosures herein.