WO2009135173A2

WO2009135173A2 - Thermal blanket

Info

Publication number: WO2009135173A2
Application number: PCT/US2009/042600
Authority: WO
Inventors: Michael Sheppard Bolmer; Cullen M. Sabin; Zbigniew R. Paul
Original assignee: Tempra Technologies, Inc.
Priority date: 2008-05-02
Filing date: 2009-05-01
Publication date: 2009-11-05
Also published as: WO2009135173A3

Abstract

A thermal blanket is capable of generating heat at a desired rate. The thermal blanket includes a lower thermoplastic film sheet having a top side, a bottom side and edges, an upper thermoplastic film sheet having a top side, a bottom side and edges corresponding to and bonded to the edges of the lower thermoplastic film sheet, and a planar matrix layer between the top side of the lower thermoplastic film sheet and the bottom surface of the upper thermoplastic film sheet between the edges and bonded to at least one of the lower or upper thermoplastic film sheets. The planar matrix layer has randomly distributed voids, at least some of which contain oxygen-activated heating composition. The planar matrix layer has sufficient integrity to prevent substantial lateral migration of the heating composition.

Description

THERMAL BLANKET

FIELD OF THE INVENTION

This invention relates to sheet materials containing single-use chemical heating compositions for use, for example, as thermal body wraps.

BACKGROUND

Thermal heat packs of various types have long been used in the medical field and by athletes for the purpose of applying heat to localized areas of the body to, for example, alleviate stiffness and minimize damage due to freezing of the skin.

Heat packs use electrical, chemical or hot water energy to generate heat. Chemical heat packs may be portable, disposable and may use iron oxidation.

SUMMARY OF THE INVENTION

In one aspect, a thermal blanket is disclosed that is capable of generating heat at a desired rate. The thermal blanket includes a lower thermoplastic film sheet having a top side, a bottom side and edges and an upper thermoplastic film sheet having a top side, a bottom side and edges corresponding to and bonded to the edges of the lower thermoplastic film sheet. A planar matrix layer is between the top side of the lower thermoplastic film sheet and the bottom side of the upper thermoplastic film sheet, between the edges and bonded to at least one of the lower or upper thermoplastic film sheets. The planar matrix layer has a plurality of voids randomly distributed throughout. Particulate or granular oxygen-activated heating composition is distributed throughout the voids in the planar matrix layer. At least one of either the upper or lower thermoplastic film sheets is oxygen permeable. The planar matrix layer has sufficient integrity to prevent substantial lateral migration of the heating composition.

In some implementations, the particulate or granular oxygen-activated heating composition is distributed with substantial uniformity lengthwise and widthwise along the planar matrix layer.

In some implementations the lower and upper thermoplastic film sheets have apertures that together provide sufficient oxygen permeability so that, when exposed to an oxygen- containing atmosphere, the oxygen-activated heating composition can create the desired rate of heat generation. A typical implementation also includes a somewhat thermally insulating fabric top cover outside of the top side of the upper thermoplastic film sheet and a fabric bottom cover that is suitable for placement against a human body outside of the bottom side of the lower thermoplastic film sheet. The fabric top cover may be affixed to the fabric bottom cover at least at the edges thereof. At least one of (or, more typically, both) the top and bottom cover typically is oxygen permeable.

According to some implementations, the planar matrix layer is bonded to the upper and lower thermoplastic film sheets.

In certain embodiments, the thermal blanket has a substantially oxygen-impermeable layer (e.g., a plastic bag) arranged to inhibit oxygen from reaching the oxygen-activated heating composition until the oxygen-impermeable layer is compromised. The oxygen-impermeable layer is a substantially airtight enclosure surrounding the other parts of the blanket.

Typically, the oxygen-activated heating composition is an iron-based heating composition. The planar matrix layer may be a loose non- woven batting material, fabric or porous foam.

In another aspect, a method of using a thermal blanket, as described above, to heat an object (e.g., a mammal or an inanimate object) includes positioning the thermal blanket in thermal contact with the object to be heated and supplying oxygen to the oxygen-activated heating composition. Typically, supplying oxygen to the oxygen-activated heating composition includes compromising the oxygen-impermeable layer that inhibits oxygen flow to the heating compound.

In yet another aspect, a method of manufacturing a thermal blanket includes providing a lower thermoplastic film sheet having edges, forming a planar matrix layer of loose non-woven batting material, fabric or porous foam on the lower thermoplastic film sheet, leaving the edges of the lower thermoplastic film sheet exposed. A substantially oxygen-free environment is created, within which an oxygen-activated heating composition is distributed throughout the non- woven batting material, fabric or porous foam with substantial uniformity. An upper thermoplastic film sheet is positioned above the non- woven batting material, fabric or foam. The upper thermoplastic film sheet has edges that correspond to the edges of the lower thermoplastic film sheet. The edges of the upper thermoplastic film sheet are bonded to the corresponding edges of the lower thermoplastic film sheet to enclose the planar matrix layer between the upper and lower thermoplastic film sheets. The planar matrix layer is bonded to at least one of (or both) the upper and lower thermoplastic film sheets. Apertures are formed in at least one of the lower and upper thermoplastic film sheets to accommodate air permeation.

In some implementations, the method also includes forming a user-compromisable, oxygen-impermeable layer (e.g., a plastic bag) to inhibit oxygen from reaching the oxygen- activated, heating composition until the oxygen-impermeable layer is compromised.

In certain embodiments, the planar matrix layer is bonded to both the upper and lower thermoplastic film sheets.

Typically, the method includes forming a fabric top cover outside of the top side of the upper thermoplastic film sheet, said top cover having thermal insulating capability, forming a fabric bottom cover suitable for placement against a human body outside of the bottom side of the lower thermoplastic film sheet and attaching edges of the fabric top cover to corresponding edges of the fabric bottom cover to surround the lower and upper thermoplastic film sheets.

Bonding may be, for example, thermal bonding or adhesive bonding.

A thermal blanket is disclosed having a laminar structure comprised of a plurality of layers. The blanket is intended to cover a human or animal body or other object during use. The terms "lower" and "bottom" are used herein to refer to layers and surfaces toward the body, and "upper" and "top" will be used to refer to layers and surfaces away from the body during use of the blanket. During use, of course, the blanket may be oriented in any way (e.g., laying atop the person or object to be cooled, wrapped around the person or object to be cooled or even underneath the person or object to be cooled). The heating composition is included in the thermal blanket as an inner matrix layer sandwiched between upper and lower thermoplastic film sheets. The inner layer containing the heating composition also includes a matrix having large void spaces. The matrix may be a loose and flexible non-woven fibrous batt or fabric, non- woven fabric or very porous and flexible foam in which the particulate or granular heating composition is embedded. The non- woven or foam prevents lateral migration of the heating composition particles or granules in a direction parallel to the major surfaces of the upper and lower films while having good drape so as to be conformable to the body to which the blanket is applied during use. The films also have good drape, so as not to render the blanket unconformable to a human or animal body. The films are bonded, chemically or thermally, to the inner matrix layer containing the heating composition, which prevents migration of the heating composition particles or granules parallel to the major surfaces of the film sheets out of the non- woven or foam. At least one of the upper and lower film sheets, preferably the upper film sheet, is provided with multiple apertures, such as by needle punching, to impart oxygen (air) permeability while retaining the ability to prevent out migration of the heating composition. The rate of heat generation can be controlled by varying the oxygen permeability by the size and density of the apertures. The films have edges that extend beyond the inner layer and are bonded to one another so as to totally enclose the inner layer.

The thermal blanket preferably further includes two outer layers of fabric. The bottom outer layer is a sheet of fabric that makes the blanket comfortable to the skin, for example, a fleece. It is bonded to the bottom surface of the lower thermoplastic film sheet. The top outer layer is a sheet of fabric that provides a thermal barrier to reduce the amount of generated heat escaping through the top of the blanket. It is bonded to the top surface of the upper thermoplastic film sheet. Any outer fabric layer that is bonded to an apertured film layer has greater oxygen permeability than the apertured film layer and is bonded thereto in a manner that does not interfere with oxygen permeability. Both outer layers have good drape.

An aspect of this invention is a thermal blanket containing a continuous inner layer of iron-base heating composition sandwiched between two thermoplastic films and held in place from migration parallel to the films' surfaces by being imbedded in a loose non- woven batting material or fabric, or foam containing large pores.

The reaction implemented in the thermal blanket may be based on the oxidation of a metal powder by air. The basic principle of a metal oxidation heater is the exothermic oxidization of a metal by oxygen in air, which can proceed rapidly when suitably catalyzed. The metal of choice for this application is iron powder. Shipping and handling of these heaters, which receive their oxygen through controlled porosity in the enclosure surfaces, generally involve that diffusion of air into the reactive mixture be prevented until the heating reaction is desired. When it is desired to use the device, a protective package (normally a sealed plastic layer) is removed, air containing oxygen diffuses into the heater through the designed porosity, and the reaction begins. Heating then continues until the reactive mixture is completely exhausted. (In concept, it is possible to shut off the reaction by again placing the thermal blanket into a sealed bag before the ingredients are entirely expended).

A method of construction and manufacturing is disclosed which allows such reactive structures to be assembled in very large sheets. The active heating section consists of a structure in which a thin layer of reactive ingredients is held in place by entrapment in a layer of fiber batting or open cell foam between two layers of sheet film. In some implementations, the thermal blanket structure consists of several layers of plastic film and non- woven fiber structures, each bonded to the adjacent layers with a continuous seal. One layer contains oxidizable metal powder (e.g., iron metal powder) and catalysts, if any. The other layers may provide heat regulation, comfort, and external insulation. Operation of the thermal blanket may depend upon the diffusion of air through controlled porosity layers to regulate the rate at which heat was generated by the reactive materials.

A thermal blanket may be constructed with the oxygen barrier incorporated in the initial assembly, in which case it would be pulled off of the blanket to initiate the reaction, or alternatively, the blanket could be rolled or folded into a pad, and placed in a diffusion-barrier bag as an additional step in the manufacturing process. To initiate the heating process, the oxygen barrier film with which the device is provided is simply removed or compromised, so that air can get into the reactive mixture and the rusting process can begin.

The heating rate of the thermal blanket's oxygen-activated metal oxidation heater system may be controlled by limiting the porosity of one or both faces of the heater. With high porosity, the heating rate will be high, and the device will be hot to the touch. In that situation, the reactive mixture may be expended quickly, and heating lifetime may be short. With lower porosity, the heating rate may be lower, the reactive mixture may last longer, and the perceived temperature may be lower. In a typical implementation, only the heating layer that faces away from the person's body will be porous, so that areas of contact with the person's body will not inhibit diffusion into the reaction mixture, and the heating will be more uniform over the surface.

The skins of living warm-blooded animals, including humans, are reactive systems. Capillary blood carries heat to or from the skin surface, depending upon complex interactions within the living organism. In addition, the properties of materials touching the surface affect the perceived temperature. The thermal blanket surface may be perceived as comfortably warm when the internal reaction products would be uncomfortably hot, because of the interaction between skin and blanket material.

The heating blanket may consist of a lamination of several layers. For comfort, the innermost layer (the layer next to the skin of the patient) typically is a thin layer of soft, fleece- like material. That innermost layer typically is laminated to a non-porous layer, which forms the lower layer of the active ingredient assembly. The next layer is an open matrix of fiber or foam, which holds the granular heating mixture in place. Over this layer is the film material with designed porosity. This is the layer which controls reaction rate and perceived temperature. In order to minimize loss of heat to the surroundings, a thermal insulator of blanket- like material is laminated to the porous layer to form the outermost layer. That insulating layer typically is a low-density open structure, in order that it not inhibit air diffusion into the heater.

In some implementations, one or more of the following advantages are present.

For example, a self-heating thermal blanket may be provided that provides substantially even heating across the entire blanket. The blanket typically resists lateral movement of heating composition within the blanket, but allows for wide distribution of heating composition inside the blanket.

The thermal blanket may produce heat in a short amount of time and may be adapted to maintain at least some degree of heat production for an extended period of time. Its operation is simple and it is easy and intuitive to activate. The thermal blanket typically is stable in storage for long periods of time. The thermal blanket can be disposed of after use, with minimal environmental impact. Moreover, the thermal blanket is safe to users. The thermal blanket also is inexpensive to manufacture.

Other features and advantages will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a perspective view of a person lying down and under one implementation of a thermal blanket.

FIG. 2 is a partial cross-sectional view of the thermal blanket of FIG. 1. Like reference characters refer to like elements.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a perspective view of a person 100 lying down under one implementation of a thermal blanket 102. The thermal blanket 102 is capable of generating heat at a desired rate. In a typical implementation, the thermal blanket 102 contains a particulate or granular, oxygen- activated, heating composition that is distributed with substantial uniformity across the length L and width W of the thermal blanket 102. The thermal blanket 102 has one or more small apertures (not visible in FIG. 1) that allow oxygen to reach the oxygen-activated, heating composition. The substantially even distribution of heating composition throughout the thermal blanket 102 helps ensure that, when the thermal blanket 102 is generating heat, the distribution of heat across the length and width of the thermal blanket 102 is substantially uniform.

The thermal blanket 102 has an outer surface 104, an inner surface 106 and four edges 108a-108d. In a typical embodiment, prior to being activated, the thermal blanket 102 may be wrapped in a substantially air-tight enclosure (e.g., a sealed plastic bag). When a person wants to use the thermal blanket 102, he or she opens the air-tight enclosure, thereby exposing the blanket (and the oxygen-activated heating composition therein) to atmospheric-conditions, generally containing oxygen. Upon exposure to an oxygen-containing atmosphere, the thermal blanket 102 begins to generate heat.

Since the illustrated thermal blanket 102 is self-heating and portable, it may be particularly well-suited for use in providing heat in situations where other sources of heat or energy may not be readily available. Hikers who get lost in the cold, for example, risk developing frostbite or hypothermia if exposed to the cold for too long. If such a hiker is rescued, it may be critical to warm up the hiker very quickly. In that situation, the thermal blanket 102 may prove to be quite useful because it generates heat rapidly in a substantially uniform manner and, therefore, should be able to effectively warm every part of the hiker under the thermal blanket 102. The thermal blanket 102 may be particularly well-suited for use in such applications and in various other applications as well.

As illustrated, the thermal blanket 102 may be sized to cover a single adult human. In an exemplary implementation, its length L may be approximately 2 meters and its width W may be approximately 1 meter. The size of the blanket, however, can differ considerably.

FIG. 2 is a partial, cross-sectional view of the thermal blanket 102 of FIG. 1 taken near an edge 108a of the thermal blanket 102.

The illustrated thermal blanket 102 has an inner matrix layer 202 that includes a sheet 204 consisting of a loose non- woven batting material, fabric or foam having voids randomly distributed throughout. At least some of the voids contain particles or granules 203 of iron-based heating composition. In a typical implementation, the size of the particles or granules 203 varies and the size of the voids also varies. Typically, the voids are sufficiently large that they can accommodate or at least partially accommodate some (or all) of the particles or granules 203.

Inner matrix layer 202 is sandwiched between and bonded to an upper thermoplastic film sheet 205 and a lower thermoplastic film sheet 210, which are relatively thin film sheets and substantially flexible. Upper thermoplastic film sheet 205 has multiple needle-punched apertures 206 formed therein. The apertures 206 are large enough to allow oxygen to flow in sufficient quantities into the inner matrix layer 202 to produce a desired heating effect. The apertures 206 are small enough so as to contain the particles or granules 203 of heating composition.

In the illustrated implementation, the apertures 206 are distributed at substantially regular intervals across the upper thermoplastic film sheet 205. Typically, the distribution of apertures 206 forms a matrix pattern. The apertures 206 may be spaced apart from one another a sufficient amount to avoid unduly compromising the structural integrity of the upper thermoplastic film sheet 210, but close enough to one another to ensure sufficient flow of oxygen to the inner matrix layer 202. The apertures 206 can be distributed in any pattern, regular or irregular, across the upper (and/or lower) thermoplastic film sheet. The size, number of and distribution pattern of the apertures 206 can vary considerably and may be tailored to the particular application requirements.

The upper and lower thermoplastic film sheets 205, 210 have edges 207, 211 that extend peripherally beyond an edge 212 of the inner matrix layer 202. The edges 207, 211 are bonded together either thermally or adhesively. The bonded edges 207, 211 extend around the entire periphery of the inner matrix layer 202 and define, in conjunction with the upper and lower thermoplastic film sheets 205, 210, an interior space that contains the inner matrix layer 202. In some implementations, the bonded edges 207, 211 are formed in such a manner that the interior space is just large enough to accommodate the inner matrix layer 202.

The thermal blanket 102 also has an outer top fabric sheet 208 and outer bottom fabric sheet 209, each of which is bonded to the inner layer 202; that is, outer top fabric sheet 208 is bonded to the upper thermoplastic film sheet 205, and outer bottom fabric sheet 209 is bonded to the lower thermoplastic film sheet 210. Typically, the outer fabric sheets 208 extend to or beyond edges 207, 211 and are bonded to one another so as to peripherally enclose inner layer 202. This bond may be a thermal bond, an adhesive bond or a threaded bond.

Any suitable iron-based heating composition may be used in the thermal blanket 102. Typically, the heating composition includes iron powder, carbon, at least one metal salt, and water, with the iron powder comprising 40-75% by weight, active carbon comprising 8-20% by weight, metal salt(s) comprising 1-5% by weight, and water comprising 10-30% by weight. Exemplary metal salts, that may be used alone or in a mixture, include sodium chloride or cupric chloride. Other metal chlorides, metal sulfates, metal carbonates, metal acetates or metal nitrates also may be used.

The iron-based heating composition also may include one or more additives. Exemplary additives include moisture -retaining materials such as super-absorbent polymers, wood flour and/or vermiculite comprising, generally 1-10% of the composition by weight; agglomeration aids such as gelatin, gums, polysaccharides, PVA and PVP, generally 0.5-5% of the composition by weight; dry binders such as sugars, starches and calcium salts, generally 10-15% of the composition by weight; oxidation enhancers, such as elemental chromium, manganese or copper; hydrogen gas inhibitors, such as hydroxides and carbonates of sodium, potassium and calcium; fillers; thickeners, such as starches; surfactants, typically nonionic surfactants; and extending agents, such as meta silicates. Granulated heating compositions typically include at least an agglomeration aid and a dry binder, such that the composition is suitable for pressing in a tableting machine.

The iron-based heating compound can include iron powder taken from virtually any source (for example, cast iron powder, reduced iron powder, electrolytic iron powder and scrap iron powder). If oxidization and heat generation is slower for a particular iron powder than desired, then it may be helpful to add elements, compounds or mixtures of chromium, manganese and/or copper in very small amounts to the iron powder to increase its oxidation rate. In those instances, small amounts (e.g., 80-500 ppm, calculated as elemental metal based on 100 parts by weight of iron powder) of chromium, manganese, and/or copper may be added either as an element or compound (of which CuCl₂, K₂CrO₄, CuCrO₄ and MnSO₄ are exemplary).

Additionally, in some implementations, 0.5 - 30 parts by weight of iron powder of a sulfate or chloride reaction promoter, such as sodium chloride may be included in the heating composition. Additionally, in some implementations, 2.5-400 parts by weight of active carbon per 100 parts by weight of iron powder may be included in the heating composition. Active carbon particle sizes from small (which can pass through a screen of 104 μ) to considerably larger (up to 300μ) may be included in the heating composition. Use of smaller particle sizes may result in a warmer, softer blanket than larger particle sizes. Use of larger particle sizes may result in the heating composition having a higher bulk. Such heating compositions also may include water, for example 10-250 parts water per 100 parts active carbon. Water and active carbon may be combined preliminarily to blending the entire heating composition. The inclusion of water may affect the heating profile of the blanket over time.

The matrix-forming material of the inner matrix layer may be a loose non- woven batting material, fabric, porous foam or other void-containing materials. It may be air laid, wet laid or meltblown. It may include cotton fibers or continuous staple thermoplastic, for example, polyester, polyethylene, polypropylene or nylon. Preferably, the non-woven material is thermally bondable to the surrounding upper and/or lower thermoplastic film sheets. Alternatively, it may be adhesively bonded. If the matrix-forming material is a porous foam material, then it is preferable that the foam be thermally bondable to the surrounding upper and lower thermoplastic film sheets. Alternatively, it may be adhesively bonded.

Manufacture of a thermal blanket (e.g., thermal blanket 102) may include laying down the planar matrix layer- forming material on an upper surface of the lower thermoplastic film sheet 209, spreading particles or granules 203 of heating composition over an upper surface of the planar matrix layer-forming material, pressing the particles or granules 203 into voids in the planar matrix layer- forming material, adding an upper thermoplastic film sheet 205, and bonding the planar matrix layer-forming material the upper and lower thermoplastic film sheets 205, 210. The edges 207, 211 of the upper and lower thermoplastic film sheets 205, 209 are bonded to one another as well. If adhesive bonding is used, a layer of adhesive can be applied to the bonding surface of each film sheet before it is contacted with the matrix-forming layer.

In some cases where the planar matrix layer- forming material is a non-woven material, it may be possible to premix heating composition particles or granules with the non-woven material and spread them together onto the lower thermoplastic sheet film 210. Similarly, where the planar matrix layer-forming material is foam, it may be possible to premix the foam ingredients and the heating composition prior to foaming. This is not preferred, however, as the particles or granules 203 of heating composition would tend to be surrounded by the planar matrix layer-forming material, thereby reducing oxygen exposure to the heating composition.

If foam is used, it may be thermo-bonded or adhesively bonded to the upper and/or lower thermoplastic film sheets. If adhesive bonding is used, adhesive may be applied to the surfaces of the film sheets or to the upper or lower foam surfaces.

The thickness of the inner matrix layer 202 relates primarily to the amount of heating composition that it is intended to contain. In general, there should be a sufficient amount of matrix-forming material, non-woven material or foam to prevent substantial lateral migration of the heating composition parallel to the major surfaces of the upper and lower thermoplastic film sheets. It is preferred that the amount of matrix-forming material be the minimum required for this purpose, consistent with providing an inner matrix layer that has good drape at room temperature.

The upper and lower thermoplastic film sheets 205, 210 typically are extruded thermoplastic sheets. The sheets are flexible so as to provide good drape at room temperature. Preferably they are as thin as possible and very flexible while maintaining sufficient integrity during manufacture and use to prevent the escape of heating composition. Film thicknesses of less than about 75 μm (3 mils) are generally satisfactory. Preferred film sheets are thermobondable at relatively low temperatures.

The thermoplastic film sheets can be manufactured by extrusion of polymers. In some implementations, for example, two polymers may be co-extruded so as to produce a material having properties of both polymers. If a layer should thermobond at low temperatures, for example, ethylene vinyl acetate may be coextruded with low density polyethylene. Other polymers that may be used alone or in combinations include polypropylene, nylon, polyester, and polyvinyl chloride.

If adhesive bonding is to be used for the film sheet that is apertured for introduction of oxygen to the heating composition, the adhesive should be applied in a manner that does not interfere with oxygen permeability of the apertured sheet. One method that may be useful for applying such adhesive material involves applying a hot melt adhesive, available as 70-4589 from National Starch and Chemical Co., Bridgewater, N. J., via a spiral hot melt system at a rate of about 5 to 10 mg per square inch.

A variety of films may be used as the upper and lower thermoplastic films. The films may be made oxygen-permeable by the inclusion therein of apertures constituting of approximately 0.1-5% of the film's surface area so as to provide effective air permeation, for example, between 0.5 and 400 cc/cm²-min and more preferably between 1 and 150 cc/cm²-min, as measured by the Frazier method. The films can be, for example, polyethylene, polypropylene, nylon, polyvinyl chloride, polyvinylidene chloride, polystyrene, or natural or synthetic rubber. Exemplary polyethylene films can have thicknesses of 25μ, 40μ and lOOμ.

The thermal blanket 102 may be a full body-size structure, for example, one meter by two meters. It may be manufactured as an individual item from appropriately sized layers, with extending edges, as described above. Alternatively, a continuous sandwich of the inner matrix layer, the lower film sheet and the upper film sheet can be prepared and then cut into blanket- sized lengths. In this case, a flexible tape can be bonded, either thermally or adhesively, to the cut edges of the film layers to bond the overhanging edges. Similarly, smaller blankets, suitable for infants or small animals, or suitable for covering only parts of the body, can be manufactured as individual items, or they can be cut from larger blankets or from a continuous sandwich. If cut from a larger item, a flexible tape is bonded to the cut edges as described above.

Various manufacturing processes may be conducted in a manner that minimizes the heating composition's exposure to oxygen during the manufacturing. The heating composition's ingredients may be isolated from air, for example, under a blanket of inert gas. After manufacturing, the thermal blanket typically is enclosed in a substantially oxygen-impermeable storage container (e.g., an airtight bag) until it is ready to be used.

Certain embodiments of thermal blankets include a bottom fabric cover, a top fabric cover, or both. Such fabric covers can be added after construction of sandwich comprising the inner matrix layer, the lower film sheet and the upper film sheet. Alternatively, the fabric covers can be included during construction of that sandwich. Fabric covers may be woven, knitted or non- woven fabrics of natural or synthetic fibers, or mixtures thereof. Exemplary fibers include cotton, polyester, polyethylene, polypropylene, cellulose and rayon. The bottom fabric typically is one that is comfortable against the skin, such as a fleece. The top fabric preferably provides at least some amount of thermal insulation to reduce heat loss to the surroundings.

Preferably, a fabric cover at least covers the entirety of the adjacent film sheet to which it is attached. Its edges may be joined at the same locations as the upper and lower film sheets are joined. If both a bottom cover and a top cover are used, they may extend beyond the edges of the film sheets and be joined to each other outside of the film sheets. Joining may be by thermal bonding, adhesive bonding, sewing, or any other appropriate means.

The outer fabric layers may be adhesively bonded to the interior layers by an adhesive that does not interfere with oxygen permeability of the apertured top thermoplastic sheet. A preferred bottom fabric, attached to the lower plastic sheet, is carded, thermal-bonded polypropylene having a weight of 32 gm/m². The top outer fabric may be the same as the bottom outer fabric, or it may be double the weight. All materials used in the manufacture of thermal blanket 102 should be capable of withstanding the highest temperature to be generated by the heating composition during use, so that functioning of the blanket is not compromised by fusing of the materials.

A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention.

For example, a variety of suitable iron-based heating compositions in particulate or granular form have been described. However, the exact formula for the heating composition is not critical. Any suitable oxygen-activated heating composition may be used.

The order of steps in the various manufacturing processes disclosed herein may be varied considerably. The materials and chemical compositions also can be varied considerably.

Additional layers and other features may be added to the thermal blanket to enhance comfort or to achieve other desired effects.

Other implementations are within the scope of the claims.

Claims

What is claimed is:

1. A thermal blanket capable of generating heat at a desired rate, the thermal blanket comprising: a lower thermoplastic film sheet having a top side, a bottom side and edges; an upper thermoplastic film sheet having a top side, a bottom side and edges corresponding to and bonded to the edges of the lower thermoplastic film sheet; a planar matrix layer between the top side of the lower thermoplastic film sheet and the bottom side of the upper thermoplastic film sheet between the edges and bonded to at least one of the lower or upper thermoplastic film sheets, wherein the planar matrix layer has a plurality of voids randomly distributed throughout; and particulate or granular oxygen-activated heating composition distributed throughout at least some of the voids in the planar matrix layer, wherein at least one of the upper or lower thermoplastic film sheet is oxygen permeable, and wherein the planar matrix layer has sufficient integrity to prevent substantial lateral migration of the heating composition.

2. The thermal blanket of claim 1 wherein the particulate or granular oxygen-activated heating composition is distributed with substantial uniformity lengthwise and widthwise across the planar matrix layer.

3. The thermal blanket of claim 1 wherein at least one of the lower and upper thermoplastic film sheets is sufficiently oxygen permeable that, when exposed to an oxygen-containing atmosphere, a sufficient amount of oxygen can reach the oxygen-activated heating composition to create the desired rate of heat generation.

4. The thermal blanket of claim 1 further comprising: a fabric top cover outside of the top side of the upper thermoplastic film sheet, said top cover having thermal insulating capability; and a fabric bottom cover suitable for placement against a human body outside of the bottom side of the lower thermoplastic film sheet.

5. The thermal blanket of claim 4 wherein the fabric top cover is affixed to the fabric bottom cover at least at the edges thereof.

6. The thermal blanket of claim 4 wherein the oxygen permeability results from apertures formed in at least one of the upper or lower thermoplastic film sheets.

7. The thermal blanket of claim 1 wherein the planar matrix layer is bonded to the upper and lower thermoplastic film sheets.

8. The thermal blanket of claim 1 further comprising: an oxygen-impermeable layer arranged to inhibit oxygen from reaching the oxygen- activated heating composition until the oxygen-impermeable layer is compromised.

9. The thermal blanket of claim 8 wherein the oxygen-impermeable layer is a substantially airtight enclosure.

10. The thermal blanket of claim 1 wherein the oxygen-activated heating composition is an iron -based heating composition.

11. The thermal blanket of claim 1 wherein the planar matrix layer comprises a loose non- woven batting material.

12. The thermal blanket of claim 1 wherein the planar matrix layer comprises porous foam.

13. The thermal blanket of claim 1 wherein the planar matrix layer comprises a non- woven fabric.

14. A method of using the thermal blanket of claim 1 to heat an object, the method comprising: positioning the thermal blanket in thermal contact with the object to be heated; and supplying oxygen to the oxygen-activated heating composition.

15. The method of claim 14 wherein the thermal blanket comprises : an oxygen-impermeable layer arranged to inhibit oxygen from reaching the oxygen- activated heating composition until the oxygen-impermeable layer is compromised, wherein supplying oxygen to the oxygen-activated heating composition comprises compromising the oxygen-impermeable layer.

16. The method of claim 15 wherein the oxygen-impermeable layer comprises: a substantially airtight enclosure, wherein compromising the oxygen-impermeable layer comprises opening the substantially airtight enclosure, thereby exposing the oxygen-activated heating compound to oxygen.

17. The method of claim 14 wherein positioning the thermal blanket in thermal contact with the object to be heated comprises: wrapping the thermal blanket at least partially around the object to be heated.

18. The method of claim 14 wherein the object to be heated is a mammal or an inanimate object.

19. A method of manufacturing a thermal blanket, the method comprising: providing a lower thermoplastic film sheet having edges; forming a planar matrix layer of loose non- woven batting material, fabric or porous foam on the lower thermoplastic film sheet, leaving the edges of the lower thermoplastic film sheet exposed; creating a substantially oxygen-free environment and within the substantially oxygen-free environment: distributing an oxygen-activated heating composition throughout the non-woven batting material or fabric with substantially lengthwise and widthwise uniformity; positioning an upper thermoplastic film sheet above the non-woven batting material or fabric, wherein the upper thermoplastic film sheet has edges that correspond to the edges of the lower thermoplastic film sheet; and bonding the edges of the upper thermoplastic film sheet to corresponding edges of the lower thermoplastic film sheet to enclose the planar matrix layer between the upper and lower thermoplastic film sheets; and bonding the planar matrix layer to at least one of the upper and lower thermoplastic film sheets; and forming apertures in at least one of the lower and upper thermoplastic film sheets to accommodate air permeation through the apertures.

20. The method of claim 19 further comprising: forming a user-compromisable, oxygen-impermeable layer to inhibit oxygen from reaching the oxygen-activated, heating composition until the oxygen-impermeable layer is compromised.

21. The method of claim 20 wherein forming the user-compromisable, oxygen-impermeable layer comprises forming a substantially airtight enclosure.

22. The method of claim 19 wherein bonding the planar matrix layer to at least one of the upper and lower thermoplastic film sheets comprises bonding the planar matrix layer to both the upper and lower thermoplastic film sheets.

23. The method of claim 19 further comprising: forming a fabric top cover outside of the top side of the upper thermoplastic film sheet, said top cover having thermal insulating capability; forming a fabric bottom cover suitable for placement against a human body outside of the bottom side of the lower thermoplastic film sheet; and attaching edges of the fabric top cover to corresponding edges of the fabric bottom cover to surround the lower and upper thermoplastic film sheets.

24. The method of claim 19 wherein bonding the planar matrix layer to at least one of the upper and lower thermoplastic film sheets comprises thermally or adhesively bonding the planar matrix layer.

25. The method of claim 19 wherein bonding the edges of the upper thermoplastic film sheet to corresponding edges of the lower thermoplastic film sheet comprises thermally or adhesively bonding.

26. The method of claim 19 wherein forming the planar matrix layer comprises air laying, wet laying or melt blowing the planar matrix layer.

27. A thermal blanket comprising: a matrix layer that has voids randomly distributed throughout, wherein the voids contain an oxygen-activated heating composition across substantially an entire width and length of the thermal blanket; and a user-compromisable oxygen-impermeable barrier, compromise of which enables oxygen to reach the heating composition, wherein the matrix layer has sufficient integrity to prevent significant lateral movement of the heating composition through the thermal blanket.