MX2008007615A - Thermal device having a controlled heating profile - Google Patents

Abstract

A thermal device that contains an exothermic composition is provided. The exothermic composition includes a metal that is capable of undergoing an oxidation reaction in the presence of moisture and oxygen to generate heat. Certain aspects of the thermal device may be optimized to supply a controlled amount of moisture and/or oxygen to the exothermic composition during use. Through selective control over the supply of these reactants, a heating profile may be achieved in which an elevated temperature is reached quickly and maintained over an extended period of time.

Description

THERMAL DEVICE WITH CONTROLLED HEATING PROFILE Background of the Invention Certain metal powders (for example, iron dust) are oxidized in the presence of air and moisture. Because the oxidation reaction is exothermic and generates heat, the metal powders have been incorporated into the exothermic compositions to provide heat. For example, conventional exothermic compositions contain a metal powder, activated carbon, and metal halide. The activated carbon acts as a catalyst to facilitate the exothermic reaction, while the metal halide removed from the surface of the oxidized films in the metal powder to allow the reaction to proceed to a sufficient extent. Unfortunately, there are several problems when trying to apply such exothermic compositions to a substrate. Specifically, if the exothermic composition was exposed to moisture during application, the exothermic reaction may occur prematurely. This may ultimately decrease the quality of the exothermic composition and give rise to several other problems, such as an increased difficulty in handling due to coagulation. Several techniques were developed in an attempt to overcome these and other problems. For example, US Pat. No. 6,436,128 issued to Usui discloses an exothermic composition containing an exothermic substance, a water absorbing polymer and / or a glutinizing agent, a carbon and / or metal halide component, and Water. An excessive amount of water is used in the composition to suppress a premature oxidation reaction with air. Once formulated, Usui's exothermic composition is laminated and sealed in a thin bag. The bag absorbs water from the composition so that, when the seal is broken, the exothermic reaction can proceed to exposure with air and moisture. Despite overcoming certain problems of conventional techniques, Usui is still very complex for many consumer applications. Moreover, it is often difficult to control the reaction rate of the exothermic substance in such devices.

As such, there is currently a need for an improved thermal device that is simple, effective, and relatively inexpensive to make, and also easily controllable.

Synthesis of the Invention According to an embodiment of the present invention, a thermal device comprising an exothermic composition formed of a metal that is oxidized is described, wherein the exposure of the exothermic composition with oxygen and moisture activates an exothermic reaction to generate heat. The thermal device also comprises a moisture retaining layer and an aqueous solution applied to the moisture retaining layer that is capable of delivering moisture to the exothermic composition, wherein the aqueous solution comprises one or more solubles.

According to another embodiment of the present invention, a method for generating heat is described. The method comprises exposing a thermal device to oxygen to achieve a controlled heat profile in which one or more surfaces of the thermal device reaches a high temperature of from about 35 ° C to about 55 ° C in 20 minutes or less. The thermal device comprises an exothermic composition formed of a metal that is oxidized and a moisture-retaining layer containing an aqueous solution that evaporates at a rate of from about 0.05% to about 0.5%, determined at an initial relative humidity of around 51% and a temperature of around 22 ° C.

Other features and aspects of the present invention are described in more detail below.

Brief Description of the Drawings A complete and capable description of the present invention, which includes the best mode thereof, addressed to one of ordinary skill in the art, is disclosed more particularly in the remainder of the application, which refers to the figures appended thereto. which: Figure 1 illustrates a cross-sectional view of an embodiment of a thermal device of the present invention; Figure 2 illustrates a cross-sectional view of another embodiment of a thermal device of the present invention; Figure 3 is a thermal response curve showing the temperature (° C) versus the time (minutes) for the samples of Examples 1 to 4; Figure 4 is a thermal response curve showing the temperature (° C) versus the time (minutes) for the samples of Examples 6 to 9; Figure 5 is a thermal response curve showing the temperature (° C) versus the time (minutes) for the samples of Examples 11 to 14; Figure 6 is a thermal response curve showing the temperature (° C) versus the time (minutes) for the samples of Examples 16 to 19; and Figure 7 is a thermal response curve showing the temperature (° C) versus the time (minutes) for the samples of Examples 21 to 24; Y Figure 8 is an evaporation curve showing the loss of liquid weight (%) versus time (minutes) for the moisture retaining layers of Example 27.

Detailed Description of Representative Incorporations Definitions As used herein, the term "non-woven fabric or fabric" means a fabric having a structure of individual threads or fibers or which are interlaced, but not in an identifiable manner as in a knitted fabric. Fabrics are non-woven fabrics that have been formed from many processes such as, for example, meltblowing processes, spinning processes, knitting processes, etc.

As used herein, the term "meltblowing" refers to a process in which the fibers are formed by extruding a molten thermoplastic material through a plurality of capillaries, usually circular like fibers fused into streams (eg, air). ) of converging high velocity gas that attenuate the fibers of molten thermoplastic material to reduce its diameter, which can be a microfiber diameter. Then, the meltblown fibers are transported by the high velocity gas stream and are deposited on a collection surface to form a randomly dispersed meltblown fabric. Such a process is described, for example, in United States of America Patent No. 3,849,241 issued to Butin et al., Which is incorporated herein in its entirety by reference thereto for all purposes. Generally speaking, melt blown fibers are microfibers that can be continuous or discontinuous, are generally smaller than 10 microns in diameter, and are generally sticky when deposited on a collection surface.

As used herein, the term "spunbonded" refers to a process in which small diameter substantially continuous fibers are formed by extruding a molten thermoplastic material from a plurality of usually circular, fine capillary vessels of a spinner member. with the diameter of the extruded fibers then being rapidly reduced as by, for example, the eductive pull and / or other well-known spinning linkage mechanisms. The production of non-woven fabrics linked by spinning is described and illustrated, for example, in US Pat. Nos. 4,340,563 issued to Appel et al .; 3,692,618 granted to Dorschner and others; 3,802,817 granted to Matsuki and others; 3,338,992 granted to Kinney; 3,341,394 granted to Kinney; 3,502,763 awarded to Hartman; 3,502,538 awarded to Levy; 3,542,615 granted to Dobo and others; and the 5,382,400 granted to Pike and others, which are incorporated herein in their entirety by reference to them for all purposes. Spunbonded fibers are generally non-tacky when they are deposited on a collection surface. Spunbonded fibers can sometimes have diameters of less than about 40 microns, and are often between about 5 and about 20 microns.

As used herein, the term "coform" generally refers to composite materials comprising a stabilized blender or binder of thermoplastic fibers and a second non-thermoplastic material. As an example, coform materials can be made by a process in which at least one melt blown die head is arranged near a channel through which other materials are added to the fabric while it is being formed. Such other materials may include, but are not limited to, fibrous organic materials such as non-wood or wood pulp such as cotton, rayon, recycled paper, pulp fluff and also super-absorbent particles. absorbent organic and / or inorganic materials, the basic polymeric fibers treated and so on. Some examples of such coform materials are described in U.S. Patent Nos. 4,100,324 issued to Anderson et al .; 5,284,703 granted to Everhart and others; and 5,350,624 granted to Georger and others; which are incorporated herein in their entirety by reference to the same for all purposes.

As used here, the "water vapor transmission rate" (VTR) generally refers to the rate at which water vapor is penetrated through a material as measured in units of grams per square meter per 24 hours (g / m2 / 24 hrs.). The test used to determine the water vapor transmission rate of a material can vary based on the nature of the material. For example, in some embodiments, the water vapor transmission rate can be determined generally in accordance with ASTM Standard E-96E-80. This test may be particularly appropriate for materials that are believed to have a water vapor transmission rate of up to about 3,000 grams per square meter per 24 hours. Another technique to measure the water vapor transmission rate involves the use of a PERMATRAN-W 100K water vapor penetration analysis system, in which it is commercially available from Modern Controls, Inc. of Mmneapolis, Minnesota. Such a system may be particularly well suited for materials that are believed to have a water vapor transmission rate of greater than about 3,000 grams per square meter per 24 hours. However, as is well known in the art, other systems and techniques can also be used to measure the water vapor transmission rate.

As used herein, the term "breathable" means permeable to water vapor and gases, but impermeable to liquid water. For example, "breathable barriers" and "breathable films" allow water vapor to pass through them, but are substantially impervious to liquid water. "Breathing ability" of a material that is measured in terms of the water vapor transmission rate (VTR), with higher values representing more than one vapor permeable material and internal values that represent a lower vapor permeable material. Breathable materials can, for example, have a water vapor transmission rate (WVTR) of at least about 100 grams per square meter per 24 hours (g / m2 / 24 hrs.), in some incorporations from around 500 to around 20,000 grams per square meter for 24 hours, and in some additions, from around 1,000 to around 15,000 grams per square meter for 24 hours.

Detailed description Reference may now be made in detail to several embodiments of the invention, one or more examples of which are disclosed below. Each example is provided by way of explanation, not limitation of the invention. In fact, it may be apparent to those skilled in the art that various modifications and variations may be made in the present invention without departing from the scope or spirit of the invention. For example, the features illustrated or described as part of an embodiment may be used in another embodiment to still yield a further embodiment. Therefore, it is the intention that the present invention cover such modifications and variations.

Generally speaking, the present invention is directed to a thermal device that contains an exothermic composition. The exothermic composition includes a metal that is capable of undergoing an oxidation reaction in the presence of moisture and oxygen to generate heat. The present inventors have discovered that certain aspects of the thermal device can be optimized to deliver a controlled amount of moisture and / or oxygen to the exothermic composition during use. Through selective control over the supply of these reagents, a heat profile can be achieved in which a high temperature is quickly reached and maintained over an extended period of time. For example, a high temperature of from about 30 ° C to about 60 ° C, in some additions from around 35 ° C to around 55 ° C, and in some additions from around 37 ° C to around 43 ° C ° C, can be achieved in 20 minutes or less, and in some additions, 10 minutes or less. This elevated temperature can be substantially maintained for at least about 1 hour, in some embodiments at least about 2 hours, in some embodiments at least about 4 hours, and in some embodiments, at least about 10 hours ( for example, for use during the night).

The exothermic composition can be formed from a variety of different components, including metals that are oxidized, carbon components, binders, electrolytic salts, and so on. Examples of such metals include, but are not limited to, iron, zinc, aluminum, magnesium, and so on. Although not required, the metal can be initially supplied as a powder to facilitate handling and to reduce costs. Various methods for removing impurities from a crude metal (eg iron) to form a powder include, for example, wet processing techniques, such as solvent extraction, ion exchange, and electrolytic refining for separation of elements. metallic; the processing with hydrogen gas (H2) for the removal of gaseous elements, such as oxygen and nitrogen; The refining method of flotation zone foundry. By using such techniques, the purity of the metal can be at least about 95%, at some incorporations at least about 97%, and at some incorporations, at least about 99%. The size of the metal powder particle can also be at least about 500 micrometers, in some embodiments less than about 100 micrometers, and in some embodiments, less than about 50 micrometers. The use of such small particles can improve the contact surface of the metal with air, thereby improving the possibility and efficiency of the desired exothermic reaction. The concentration of the metal powder employed generally can vary depending on the nature of the metal powder, and the desired extent of the exothermic reaction / oxidation. In most embodiments, the metal powder is present in the exothermic composition in an amount of from about 40% by weight to about 95% by weight, in some embodiments from about 50% by weight to about 90% by weight, and in some embodiments, from about 60% by weight to about 80% by weight.

In addition to a metal that is oxidized, a carbon component can also be used in the exothermic composition of the present invention. Without intending to be limited in theory, it is believed that such a carbon component promotes the oxidation reaction of the metal and acts as a catalyst to generate heat. The carbon component can be activated carbon, carbon black, graphite, and so on. When used, activated carbon can be formed from sawdust, wood, coal, peat, lignite, bituminous coal, coconut shells, etc. Some appropriate forms of activated carbon and the techniques for forming them are described in Patents of the United States of America Nos. 5,693,385 granted to Parkb. ; 5,834,114 granted to Economy and others; 6,517,906 granted to Economy and others; 6,573,212 issued to McCrae et al., as well as in the United States Patent Application Publication Nos. 202/0141961 issued to Falat et al., and 2004/0166248 issued to Hu et al., all of which are incorporated herein in their entirety by reference to them for all purposes.

The exothermic composition may also employ a binder to improve the durability of the exothermic composition when applied to a substrate. The binder can also serve as an adhesive to bond a substrate to another substrate. Generally speaking, any of a variety of binders can be used in the exothermic composition of the present invention. Suitable binders may include, for example, those that become insoluble in water upon interlacing. The interlacing can be achieved in a variety of ways, including by reacting the binder with a polyfunctional interlacing agent. Examples of such entangled agents include, but are not limited to, melamine formaldehyde urea dimethylol, urea formaldehyde, polyamide epichlorohydrin, etc.

In some embodiments, a polymer latex can be used as the binder. The polymer suitable for use in latexes typically has a glass transition temperature of about 30 ° C or less so that the flexibility of the resulting substrate is not substantially restricted. Moreover, the polymer typically also has a glass transition temperature of about -25 ° C or more to minimize stickiness of the polymer latex. For example, in some embodiments, the polymer has a glass transition temperature of about -15 ° C to about 15 ° C, and in some embodiments, from about -10 ° C to about 0 ° C. For example, some suitable polymer latexes that can be used in the present invention can be based on polymers such as, but not limited to, styrene-butadiene copolymers, polyvinyl acetate homopolymers, ethylene vinyl copolymers acetate, vinyl acetate-acrylic copolymers, ethylene-vinyl chloride copolymers, ethylene-vinyl chloride-vinyl acetate terpolymers, acrylic polyvinyl chloride copolymers, acrylic polymers, nitrile polymers, and any other suitable anionic polymer latex polymers known in the art. The loading of the polymer latexes described above can be easily varied, as is well known in the art, by using a stabilizing agent having the desired filler during the preparation of the polymer latex. The specific techniques for a carbon / polymer latex system are described in greater detail in US Pat. No. 6,573,212 issued to McCrae et al. The activated carbon / polymer latex systems that can be used in the present invention include the Nuchar® PMA, the DPX-8433-68A, and the DPX-8433-68B, all of which are available from MeadWestvaco Corp. of Stamford , Connecticut.

If desired, the polymer latex can be entangled using any technique known in the art, such as by heating, ionization, etc. Preferably, the polymer latex is self-entangled in which the external entangled agents (e.g. , N-methylol acrylamide) are not required to induce entanglement. Specifically, the interlacing agents can lead to the formation of bonds between the polymer latex and the substrate to which it is applied. Such a union can sometimes interfere with the effectiveness of the substrate in generating heat. Therefore, the polymer latex can be substantially free of interlacing agents. Particularly suitable self-interlacing polymer latexes are the ethylene-vinyl acetate copolymers available from Celanese Corp. of Dallas, Texas under the designation DUR-O-SET® Elite (e.g., PE-25220A).

Alternatively, an inhibitor can simply be employed that reduces the extent of interlacing, such as free radical scavengers, methyl hydroquinone, t-butylcatechol, pH-controlling agents (eg, potassium hydroxide), etc. ..

Although polymer latexes can be effectively used as binders in the present invention, such compounds sometimes result in a reduction in drapery and an increase in residual odor. Therefore, the present inventors have discovered that water-soluble organic polymers can also be used as binders, either alone or in conjunction with polymer latexes, to alleviate such concerns. For example, one class of water-soluble organic polymer that is suitable in the present invention is the polysaccharide and derivatives thereof. Polysaccharides are polymers containing repeated carbohydrate units, which may be cationic, ionic, nonionic, and / or amphoteric. In a particular embodiment, the polysaccharide is a nonionic, cationic, anionic, and / or amphoteric cellulosic ether. The nonionic cellulose ethers can include, but are not limited to alkyl cellulose ethers, such as methyl cellulose and ethyl cellulose; the hydroxyalkyl cellulose ethers, such as hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxybutyl hydroxybutyl cellulose, hydroxyethyl hydroxypropyl cellulose, hydroxybutyl hydroxyethyl cellulose and hydroxybutyl hydroxypropyl hydroxyethyl cellulose; the hydroxyalkyl alkyl cellulose ethers, such as methyl hydroxyethyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl ethyl cellulose, hydroxypropyl ethyl cellulose, methyl ethyl hydroxyethyl cellulose and methyl ethyl hydroxypropyl cellulose; and so on.

Suitable cellulose ethers may include, for example, those available from Akzo Novel of Stamford, Connecticut under the name "BERMOCOLL". Still other suitable cellulosic ethers are those available from Shin-Etsu Chemical Co. , Ltd. of Tokyo, Japan under the name "METOLOSE", which include METOLOSE Type SM (methylcellulose), METOLOSE Type SH (hydroxypropylmethyl cellulose), and METOLOSE Type SE (hydroxyethylmethyl cellulose). A particular example of a suitable non-ionic cellulosic ether is methylcellulose having a degree of methoxy substitution (DS) of 1.8. The degree of methoxyl substitution represents the average number of hydroxyl groups present in each anhydroglucose unit that have been reactivated, which may vary between 0 and 3. One such cellulose ether is METOLOSE SM-100, which is a commercially available methylcellulose from Shin-Etsu Chemical Co. , Ltd .. Other suitable cellulose ethers are also available from Hercules, Inc. of Wilmington, Delaware under the name "CULMINAL".

The concentration of the carbon component and / or binder in the exothermic composition can generally vary based on the desired properties of the substrate. For example, the amount of carbon component is generally custom-made to facilitate the oxidation / exothermic reaction without adversely affecting other properties of the substrate. Typically, the carbon component is present in the exothermic composition in an amount of from about 0.01% by weight to about 20% by weight, in some embodiments from about 0.1% by weight to about 15% by weight, and in some additions, from around 1% by weight to around 12% by weight. Additionally, although relatively higher binder concentrations may provide better physical properties for the exothermic composition, they may likewise have an adverse effect on other properties, such as the absorption capacity of the substrate to which it is applied. Conversely, relatively lower binder concentrations can reduce the ability of the exothermic composition to remain fixed on the substrate. Therefore, in most embodiments, the binder is present in the exothermic composition in an amount of from about 0.01% by weight to about 20% by weight, in some embodiments from about 0.1% by weight to about 10% by weight, and in some incorporations, from around 0.5% by weight to around 8% by weight.

Still other components can also be employed in the exothermic composition of the present invention. For example, as is well known in the art, an electrolytic salt can be used to react with and remove any layer (s) of pacifying oxide (s) that can otherwise prevent the metal from oxidizing. Suitable electrolyte salts may include, but are not limited to, sulfates or alkyl halides, such as sodium chloride, potassium chloride, etc .; sulfates or alkylene halides, such as calcium chloride, magnesium chloride, etc., and so on. When employed, the electrolytic salt is typically present in the exothermic composition in an amount of from about 0.01% by weight to about 10% by weight, in some embodiments from about 0.1% by weight to about 8% by weight, and in some embodiments, from about 1% by weight to about 6% by weight.

Additionally, the particles can also be employed in the exothermic composition which act as moisture retainers. That is, prior to the oxidation / exothermic reaction, these particles can retain moisture. However, after the reaction has proceeded to a certain extent and the moisture concentration is reduced, the particles can release moisture to allow the reaction to continue. In addition to acting as a moisture retainer, the particles may also provide other benefits to the exothermic composition of the present invention. For example, the particles may alter the black color normally associated with the carbon component and / or metal powder. When used, the size of the particles retaining moisture may be less than about 500 micrometers, in some embodiments less than about 100 micrometers, and in some embodiments, less than about 50 micrometers. In the same way, the particles can be porous. Without intending to be limited by theory, it is believed that the porous particles can provide a path for air and / or water vapors to better contact the metal powder. For example, the particles may have pores / channels with a mean diameter of greater than about 5 angstroms, in some incorporations greater than about 20 angstroms, and in some embodiments, greater than about 50 angstroms. The surface area of such films can also be greater than about 15 square meters per gram, in some additions greater than about 25 square meters per gram, and in some additions, greater than about 50 square meters per gram. The surface area can be determined by the physical gas absorption method (BET) of Bruanauer, Emmet, and Teller, Journal of the American Chemical Society, Vol. 60, 1938, p. 309, with nitrogen as the gas of absorption.

In a particular embodiment, porous carbonate particles (eg, calcium carbonate) are used to retain moisture and also to alter the black color normally associated with activated carbon and / or metal powder. Such a color change may be more aesthetically pleasing to a user, particularly when the coating is employed in substrates designed for consumer / personal use. Suitable white calcium carbonate particles are commercially available in both dry forms and aqueous slurry from Omya, Inc. of Proctor, Vermont. Still other suitable inorganic particles that can retain moisture include, but are not limited to, the silicates, such as calcium silicate, alumina silicates (e.g., mica powder, clay, etc.), magnesium silicates ( for example, talcum), quartzite, calcium silicate fluorite, vermiculite, etc .; the alumina; the silica; and so on. The concentration of the particles can generally vary depending on the nature of the particles, and the desired extent of the exothermic reaction and the alteration of color. For example, the particles may be present in the exothermic composition in an amount from about 0.01% by weight to about 30% by weight, in some embodiments from about 0.1% by weight to about 20% by weight, and in some additions, from around 1% by weight to around 15% by weight.

In addition to the aforementioned components, other components, such as surfactants, pH adjusters, dyes / pigments / inks, viscosity modifiers, etc., may also be included in the exothermic coating of the present invention. The viscosity modifiers can be used, for example, to adjust the viscosity of the coating formulation based on the desired coating process and / or the performance of the coated substrate. Suitable viscosity modifiers include gums, such as xanthan gum. Binders, such as cellulose ethers, can also function as appropriate viscosity modifiers. When employed, such additional components typically constitute less than about 5% by weight, in some embodiments less than about 2% by weight, and in some embodiments, from about 0.001% by weight to about 1% of the exothermic coating .

Although not necessarily required, it is usually desired that the exothermic composition be coated to a substrate perform other functions of the thermal device or simply act as a physical carrier for the exothermic composition. Any type of substrate can be applied with the exothermic composition according to the present invention. For example, non-woven fabrics, woven fabrics, knitted fabrics, paper fabrics, films, foams, etc., can be applied with the exothermic composition. When used, non-woven fabrics may include, but are not limited to, spunbond fabrics (perforated or non-perforated), meltblown fabrics, bonded carded fabrics, airlaid fabrics, coform fabrics, weaves and hydraulically entangled, and so on. Typically, the polymers used to form the substrate have a melting or softness temperature that is higher than the temperature necessary to evaporate moisture. One or more components of such polymers can have, for example, a softness temperature of from about 100 ° C to about 400 ° C, in some embodiments from about 110 ° C to about 300 ° C, and in some incorporations, from around 120 ° C to around 250 ° C. Examples of such polymers may include, but are not limited to, synthetic polymers (e.g., polyethylene, polypropylene, polyethylene terephthalate, nylon 6, nylon 66, KEVLAR ™, syndiotactic polystyrene, polyesters crystalline liquids, etc.); cellulosic polymers (soft wood pulp, hardwood pulp, thermomechanical pulp, etc.); the combinations thereof; and so on.

To apply the exothermic composition of the present invention to a substrate, the micially components can be dissolved or dispersed in a solvent. For example, one or more of the aforementioned components can be mixed with a solvent, either sequentially or simultaneously, to form a coating formulation that can be easily applied to a substrate. Any solvent capable of dispersing or dissolving the components is appropriate, for example water; alcohols such as ethanol or methanol; dimethylformamide; dimethyl sulfoxide; hydrocarbons such as pentane, butane, heptane; hexane, toluene and xylene; ethers such as diethyl ether and tetrahydrofuran; ketones and aldehydes such as acetone and methyl ethyl ketone; acids such as acetic acid and formic acid; and halogenated solvents such as dichloromethane and carbon tetrachloride; as well as the mixtures thereof. In a particular embodiment, for example, water is used as the solvent for an aqueous coating formulation to be formed. The concentration of the solvent is generally high enough to inhibit oxidation of the metal before use. Specifically, when it is present in a sufficiently high concentration; The solvent can act as a barrier to prevent air from prematurely contacting the metal that is oxidized. If the amount of solvent is very small, however, the exothermic reaction may occur prematurely. In the same way, if the amount of solvent is very large, the amount of metal deposited on the substrate may be too low to provide the desired exothermic effect. Although the current concentration of solvent (eg, water) employed may generally depend on the type of metal being oxidized and the substrate on which it is applied, it is nevertheless typically present in an amount of from about 10% by weight to about 80% by weight, in some embodiments from about 20% by weight to about 70% by weight, and in some embodiments, from about 25% by weight to about 60% by weight of the coating formulation.

The amount of the other components added to the coating formulation can vary depending on the amount of heat desired, the wet pickup of the application method used, etc. For example, the amount of metal that is oxidized (in powder form) Within the coating formulation it is generally in the range from about 20% by weight to about 80% by weight, in some embodiments from about 30% by weight to about 70% by weight, and in some embodiments, from about 35% by weight up to about 60% by weight. Additionally, the carbon component can constitute from about 0.1% by weight to about 20% by weight, in some embodiments from about 0.1% by weight to about 15% by weight, and in some embodiments, from about 0.2. % by weight to about 10% by weight of the coating formulation. Binders can range from about 0.01% by weight to about 20% by weight, in some embodiments from about 0.1% by weight to about 15% by weight, and in some embodiments, from about 1% by weight to about 10% by weight of the coating formulation. Electrolytic salts can range from about 0.01% by weight to about 10% by weight, in some incorporations from about 0.1% by weight to about 8% by weight, and in some embodiments, from about 1% by weight up to about 5% by weight of the coating formulation. In addition, moisture retaining particles (eg, calcium carbonate) can range from about 2% by weight to about 30% by weight, in some embodiments from about 3% weight to about 25% by weight, and in some embodiments, from about 4% by weight 10% by weight of the coating formulation. Other components, such as surfactants, pH adjusters, viscosity modifiers, etc., can also constitute from about 0.001% by weight to about 5% by weight, in some embodiments from about 0.01% weight to about of 1% by weight, and in some embodiments from about 0.02% by weight to about 0.5% by weight of the coating formulation.

The solids content and / or viscosity of the coating formulation can be varied to achieve the desired amount of heat generation. For example, the coating formulation can have a solids content of from about 30% to about 80%, in some embodiments from about 40% to about 70%, and in some embodiments, from about 50% to around 60%. By varying the solids content of the coating formulation, the presence of metal powder and other components in the exothermic coating can be controlled. For example, to form an exothermic composition with a higher level of metal powder, the coating formulation can be provided with a relatively high solids content so that a greater percentage of the metal powder is incorporated into the exothermic composition during the process of application. Additionally, the viscosity of the coating formulation may also vary depending on the coating method and / or the type of binder used. For example, lower viscosities may be employed for saturation coating techniques (eg, submerged coating), and while higher viscosities may be employed for pour coating techniques. Generally, the viscosity is less than about 2 X 106 centipoise, in some embodiments less than about 2 X 105 centipoise, in some additions less than about 2 X 104 centipoise, and in some additions, less than about 2 X 103 centipoises, as measured with a Brookfield DV-1 viscometer with an LV spindle. If desired, the thickeners or other viscosity modifiers can be employed in the coating formulation to increase or decrease the viscosity.

The coating formulation can be applied to a substrate using any conventional technique, such as bar, roll, knife, curtain, print (e.g., rotogravure), spraying, slot dye, broth coating, or coating techniques. submerged. The materials forming the substrate of (for example, fibers) can be coated, for example before and / or after incorporation into the substrate. The coating can be applied on one or both surfaces of the substrate. For example, the exothermic composition may be present on a surface of the substrate that is opposite that coating of the user or carrier to avoid the possibility of burning. In addition, the coating formulation can cover a complete surface of the substrate, or can only cover a part of the surface. When the exothermic composition is applied to multiple surfaces, each surface can be coated sequentially or simultaneously.

Despite the manner in which the coating is applied, the resulting thermal substrate is typically heated to a certain temperature to remove the solvent and any moisture from the coating. For example, the thermal substrate can be heated to a temperature of at least about 100 ° C, in some additions to at least about 110 ° C, and in some additions, to at least about 120 ° C. In this manner, the resultant dried exothermic composition is anhydrous, for example, generally free of water. By minimizing the amount of moisture, the exothermic composition is less likely to react prematurely and generate heat. That is, the metal that is oxidized usually does not react with oxygen unless something of a minimal amount of water is present. Therefore, the exothermic composition can remain inactive until it is placed in the vicinity of moisture (eg, next to a layer containing moisture) during use. It should be understood, however, that relatively small amounts of water may still be present in the exothermic composition without causing a substantial exothermic reaction. In some embodiments, for example, in the exothermic composition it contains water in an amount less than about 0.5% by weight, in some incorporations less than about 0.1% by weight, and in some embodiments, less than about 0.01% by weight .

The level of aggregate solids of the exothermic composition can also be varied as desired. The "level of aggregate solids" is determined by subtracting the weight of the untreated substrate from the weight of the treated substrate (after drying), dividing this weight calculated by the weight of the untreated substrate, and then multiplying it by 100%. Lower aggregate levels can optimize certain properties (eg, absorbency), while higher aggregate levels can optimize heat generation. In some additions, for example, the aggregate level is from around 100% to around 5000%, in some incorporations from around 200% to around 2400%, and in some incorporations, from around 400% to around 1200%. The thickness of the exothermic composition may also vary. For example, the thickness can be in the range from about 0.01 millimeters to about 5 millimeters, in some additions, from about 0.01 millimeters to about 3 millimeters, and in some additions, from about 0.1 millimeters to about 2 millimeters. millimeters In some cases, a relatively thin coating may be employed (for example, from about 0.01 millimeters to about 0.5 millimeters). Such a thin coating can improve the flexibility of the substrate, while still providing uniform heat.

To maintain absorbency, porosity, flexibility, and / or some other characteristic of the substrate, sometimes it may be desired to apply the exothermic composition to cover less than 100%, in some incorporations from around 10% to around 80%, and in some incorporations, from around 20% to around 60% of the area of one or more surfaces of the substrate. For example, in a particular embodiment, the exothermic composition is applied to the substrate in a previously selected pattern (e.g., reticular pattern, grille in the form of diamonds, dots, and so on). Although not required, such patterned exothermic composition can provide sufficient heating to the substrate without covering a substantial part of the surface area of the substrate. This may be desired to optimize flexibility, absorbency, and other substrate characteristics. It should be understood, however, that the coating can also be uniformly applied to one or more surfaces of the substrate. Additionally, a patterned exothermic composition may also provide different functionality to each zone. For example, in one embodiment, the substrate is treated with two or more patterns of coated regions that may or may not overlap. The regions may be on the same or different surfaces of the substrate. In one embodiment, one region of a substrate is coated with a first exothermic composition, while another region is coated with a second exothermic composition. If desired, one region may provide a different amount of heat than another region.

In addition to having functionality benefits, the substrate can also have several aesthetic benefits as well. For example, although it contains activated carbon, the thermal substrate can be made without the black color commonly associated with activated carbon. In one embodiment, the lightly colored or white particulates (eg, calcium carbonate, titanium dioxide, etc.) are employed in the exothermic composition so that the resulting substrate has a blue or gray color. Additionally, various pigments, dyes, and / or inks can be employed to alter the color of the exothermic composition. The substrate can also be applied with patterned regions of the exothermic composition to form a substrate having differently colored regions.

Other substrates may also be employed to provide the exothermic properties of the thermal substrate. For example, a first thermal substrate can be used in conjunction with a second thermal substrate. The substrates can work together to provide heat to a surface, or each can provide heat to different surfaces. Additionally, the substrates can be employed that are not applied with the exothermic composition of the present invention, but instead are applied with a coating that simply facilitates the reactivity of the exothermic composition. For example, a substrate can be used near or adjacent to the thermal substrate of the present invention that includes a coating of moisture retaining particles. As previously described, particles that retain moisture can retain and release moisture to activate the exothermic reaction.

As previously indicated, moisture and oxygen are supplied to the exothermic composition to activate the exothermic composition. To provide the desired heat profile, the rate at which the moisture is allowed to contact the exothermic composition can be selectively controlled in accordance with the present invention. Mainly, if a lot of moisture is supplied within a given period of time, the exothermic reaction can produce an excessive amount of heat that overheats or burns the user. On the other hand, if very little moisture is supplied within a given period of time, the exothermic reaction may not be sufficiently activated. The desired application rate can of course be achieved by manually applying the desired amount of moisture, for example, by hand or with the aid of external equipment, such as a syringe. Alternatively, the thermal insert itself may contain a mechanism to control the rate of moisture release.

A technique for using the thermal insert as a mechanism to control the rate of application of moisture involves the use of a moisture retaining layer. The moisture retaining layer can be used in the thermal insert to retain moisture and in a controlled manner release it to the exothermic composition over an extended period of time. The moisture retaining layer may include a formed absorbent fabric using any conventional technique or method, such as a dry forming technique, and an air laying technique, a carding technique, a spinning or blowing technique with fusion, a wet forming technique, a foaming technique, etc. In a laying process with air, for example, bunches of small fibers that have typical lengths in the range of about 3 to about 19 millimeters are separated and introduced into an air supply and then deposited on a forming screen, usually with the assistance of a vacuum supply. The randomly deposited fibers are then joined to one another using, for example, hot air or an adhesive.

The moisture retaining layer typically contains cellulosic fibers, such as synthetic and / or natural fluff pulp fibers. Fiber pulp fibers can be kraft pulp, sulfite pulp, thermomechanical pulp, etc. Additionally, the fluff pulp fibers may include pulp of higher average fiber length, pulp of lower average fiber length, or mixtures thereof. An example of appropriate upper average length of fluff pulp fibers include soft wood kraft pulp fibers. Softwood kraft pulp fibers are derived from coniferous trees and include pulp fibers such as, but not limited to, the softwood species of the south, west, and north, which include redwood, red cedar, the fir, the Oregon pine, the real pines, the pine (for example, the southern pines), the red spruce (for example, the black spruce), the combinations thereof, and so on. Northern softwood kraft pulp fibers can be used in the present invention. An example of commercially available south softwood kraft pulp fibers suitable for use in the present invention include those available from Weyerhauser Company with offices in Federal Way, Washington under the trademark designation of "NB-416". Another type of lint pulp that can be used in the present invention is identified with the brand designation CR1654, available from U.S. Alliance of Childersburg, Alabama, and is a highly absorbent, bleached sulphate wood pulp that mainly contains softwood fibers. Yet another suitable fluff pulp for use in the present invention is a bleached, sulfate wood pulp containing mainly softwood fibers that is available from Bowater Corp. with offices in Greenville, South Carolina under the brand name Pulp. CoosAbsorb S .. Fibers of low average length can also be used in the present invention. An example of pulp fibers of low average length are the hardwood kraft pulp fibers. Hardwood kraft pulp fibers are derived from deciduous trees and include pulp fibers such as, but not limited to, eucalyptus, maple, birch, aspen, etc. Eucalyptus kraft pulp fibers they can be particularly desired to increase softness, improve brilliance, increase opacity, and change the pore structure of the sheet to improve its drainage ability.

If desired, the moisture retaining layer may also contain synthetic fibers, such as monocomponent and multi-component fibers (eg, bi-components). Multicomponent fibers, for example, are fibers formed from at l two thermoplastic polymers that are extruded from separate extruders, but bonded together to form a fiber. In a multi-component sheath / core fiber, a first polymer component is surrounded by a second polymer component. The polymers of the multi-component fibers are arranged in distinct zones substantially constantly positioned across the cross section of the fiber and extend continuously along the length of the fibers. Various polymer combinations for the multi-component fiber may be useful in the present invention, but the first polymer component typically melts at a temperature lower than the melting temperature of the second polymer component. Casting the first polymer component allows the fibers to form a sticky skeletal structure, which upon cooling, captures and bonds many of the pulp fibers. Typically, the polymers of the multicomponent fibers are made of many different such as bicomponent fibers of polyolefin / polyester (sheath / core) thermoplastic materials in which the polyolefin (e.g., polyethylene sheath) melts at a lower temperature than the core (for example, polyester). Thermoplastic polymers example include polyolefins (e.g. polyethylene, polypropylene, polybutylene, and copolymers thereof), polytetrafluoroethylene, polyesters (eg polyethylene terephthalate), polyvinyl acetate, acetate polyvinyl chloride, bitiral polyvinyl acrylic resins (e.g. polyacrylate, polymethacrylate, and polymethylmethacrylate), polyamides (eg, nylon), polyvinyl chloride, polyvinylidene chloride, polystyrene, polyvinyl alcohol, the polyurethanes, cellulose resins (for example, cellulose nitrate, cellulose acetate, cellulose acetate butyrate, and cellulose acetate), and copolymers of any of the above materials such as ethylene acetate copolymers vinyl, the ethylene-acrylic acid copolymers, the styrene-butadiene block copolymers, and so forth.

The moisture retaining layer also includes a super absorbent material, such as natural, synthetic and modified natural materials. Super absorbent materials are materials that swell with water or are capable of absorbing at l about 20 times their weight and, in some cases, at l about 30 times their weight in an aqueous solution containing 0.9% by weight of water. sodium chloride. Examples of synthetic superabsorbent polymers include the alkali metal materials and ammonium salts of polyacrylic acid and polymethacrylic acid, poly (acrylamides), polyvinyl ethers, copolymers of maleic anhydride and vinyl ethers and alpha- olefins, polyvinyl pyrrolidone, poly (vinylmorpholinone), polyvinyl alcohol, and mixtures and copolymers thereof. Additional absorbent materials include natural and modified natural such as grafted starch hydrolyzed acrylonitrile grafted starch acrylic acid, methyl cellulose, chitosan, carboxymethyl cellulose, cellulose, hydroxypropyl and natural gums polymers, such as alginates, xanthan gum, locust bean gum and so on. Mixtures of natural and fully or partially synthetic super absorbent polymers may also be useful in the present invention. Other suitable absorbent gelling materials are described in US Pat. Nos. 3,901,236 issued to Assarsson et al .; 4,076,663 granted to Masuda and others; and the 4,286,082 granted to Tsubakimoto and others, which are hereby incorporated in their entirety by reference to them for all purposes.

When used, the super absorbent material can constitute about 1% by weight to about 40% by weight, in some embodiments, from about 5% by weight to about 30% by weight, and in some embodiments, from around from 10% by weight to about 25% by weight of the moisture retaining layer (on a dry basis). In the same way, multi-component fibers can constitute from about 1% by weight to about 30% by weight, in some embodiments, from about 2% by weight to about 20% by weight, and in some embodiments , from about 5% by weight to about 15% by weight of the moisture retaining layer (on a dry basis). Cellulosic fibers can also constitute up to 100% by weight, in some incorporations from about 50% by weight to about 95% by weight, and in some embodiments, from about 65% by weight to about 85% by weight. the layer that retains moisture (on a dry basis).

In accordance with the present invention, it has been discovered that the moisture evaporation rate of the moisture retaining layer can be controlled to achieve the desired heat profile. By controlling the rate of evaporation, the amount of moisture can be released to the exothermic composition within a given period of time. For example, it is usually desired that the average moisture "evaporation rate" of the moisture retaining layer is from about 0. 05% up to around 0.5%, in some incorporations from around 0.10% up to around 0.25%, and in some additions, from around 0.15% up to around 0.20% per minute. The "evaporation rate" is determined by measuring the weight of the layer that retains moisture at a certain time, subtracting this measured weight from the initial wet weight of the layer, dividing this value by the initial wet weight, and then multiplying by 100. Evaporation rates are calculated for several different times and then averaged. The evaporation rate is determined in the present invention at a relative humidity of 51% and a temperature of about 22 ° C. It should be understood that this relative humidity and temperature conditions are "initial" conditions in which these may vary during the test due to the increased presence of water vapor in the atmosphere.

In some embodiments, the desired rate of evaporation of moisture is achieved by controlling the nature of the aqueous solution applied to the moisture retaining layer. Primarily, current inventors have discovered that the application of only steam (vapor pressure of 23.7 mm Hg at 25 ° C) to the moisture retaining layer can sometimes result in a very large vaporization rate. Therefore, a soluble can be added to the aqueous solution to reduce its vapor pressure, for example, the tendency of water molecules to evaporate. At 25 ° C, for example, the soluble can be added so that the added aqueous solution moisture retaining layer has an evaporation rate of less than 23.7 mm Hg, in some incorporations less than about 23.2 mm Hg, and in some Incorporations, from around 20.0 mm Hg to around 23.0 mm Hg. A particularly suitable class of solubles include the organic and / or inorganic metal salts. The metal salts may contain monovalent (eg, Na +), divalent (eg Ca2 +), and / or polyvalent cations. Examples of preferred metal cations include cations of sodium, potassium, calcium, aluminum, iron, magnesium, zirconium, zinc, and so on. Examples of preferred anions include halides, chlorohydrates, sulfates, citrates, nitrates, acetates, and so forth. Particular examples of suitable metal salts include sodium chloride, sodium bromide, potassium chloride, potassium bromide, calcium chloride, etc. The current concentration of the soluble in the aqueous solution can vary depending on the nature of the soluble, the particular configuration of the thermal insert, and the desired heat profile. For example, the soluble may be present in the aqueous solution in an amount from about 0.1% to about 25% by weight, in some embodiments from about 1% by weight to about 20% by weight, and in some embodiments , from about 5% by weight to about 15% by weight of the solution.

In addition to controlling the aspects of the aqueous solution, the moisture retaining layer itself can be selectively made to measure to achieve the desired evaporation rate. For example, current inventors have discovered that moisture retaining layers having a relatively lower density and basis weight tend to release much of an amount of moisture compared to those having a higher basis weight and density. Without intending to be limited by the theory, it is believed that such higher basis weight and higher density fabrics may have a lower porosity, making it more difficult for moisture to escape from the layer over an extended period of time . Therefore, in one embodiment of the present invention, the moisture retaining layer (eg, air-laid fabric) can have a density from retainer from 0.01 to about 0.50, in some embodiments from about 0.05 to about 0.25, and in some additions, from around 0.05 to around 0.15 grams per cubic centimeters (g / cm3). The density is based on the oven-dried mass of the sample of the thickness measurement and made at a load of 0.34 kilopascals (kPa) with a circular plate of 7.62 centimeters in diameter with 50% relative humidity and 23 ° C. Additionally, the base weight of the moisture retaining layer can be from about 50 to about 500 grams per square meter ("gsm"), in some incorporations from about 100 to about 300 grams per square meter, and in some incorporations, from around 150 around 300 grams per square meter.

Other techniques can also be employed to achieve the desired rate of evaporation of moisture from the moisture retaining layer. For example, super absorbent materials are capable of swelling in the presence of an aqueous solution. The swelling increases the absorption capacity of the moisture retaining layer, but in the same way reduces the rate of moisture evaporation while the materials that exhibit a greater tendency to "cling" to the water molecules. Therefore, the rate of evaporation can be increased by reducing the degree of inflation. A technique for reducing the degree of swelling of a super absorbent material involves reducing the temperature of the aqueous solution below the temperature of the environment, such as less than about 25 ° C, and in some embodiments, from about 5 ° C. C up to around 20 ° C. The degree of swelling of the super absorbent material can also be reduced by incorporating one or more ionic compounds in the aqueous solution to increase its ionic strength. The ionic compounds can be the same as the solubles described above. The "ionic strength" of a solution can be determined according to the following equation: I 0. 5? Z, 1 mx where, zi the valence factor; and my is concentration. For example, the ionic strength of a solution containing 1 molar calcium chloride and 2 molar sodium chloride is "3" and is determined as follows: 1 = 0. 5 * [(22 * 1) + (12 * 2) J = 3 Without intending to be limited by theory, it is believed that super absorbent materials that have an opposite ion atmosphere surrounds the ionic spine of polymer chains that collapse when their ionic strength is increased. Specifically, the opposite ion atmosphere is made of charged ions opposite the charges along the spine of a super absorbent polymer and are present in the ionic compound (eg, potassium or sodium cations surrounding the carboxylate anions distributed along the backbone of an anionic polyacrylate polymer). As the concentration of ions contacting the super absorbent polymer increases, the ion concentration gradient in the liquid phase from the exterior to the interior of the polymer begins to decrease and the thickness of the opposite ion atmosphere ("Debye thickness") can be reduced. reduce from about 20 nanometers (in pure water) to about 1 nanometer or less. When the opposite ion atmosphere is highly extended, the opposite ions are more osmotically active and therefore promote a high degree of liquid absorbency. On the other hand, when the ion concentration in the absorbed liquid increases, the opposite ion atmosphere collapses and the absorption capacity is decreased. As a result of the reduction in absorption capacity, the super absorbent material exhibits less of a tendency to retain the water molecules, thereby allowing its release to the exothermic composition.

The thermal device can also be used as a breathable layer that is impermeable to liquids, but permeable to gases. This allows the flow of water vapor and air to activate the exothermic reaction, but avoids an excessive amount of liquids to contact the thermal substrate, which can either suppress the reaction or result in an excessive amount of heat that overheats or burn the user. The breathable layer generally can be formed from a variety of materials as are well known in the art. For example, the breathable layer may contain a breathable film, such as a monolithic or microporous film. The film can be formed of a polyolefin polymer, such as a linear low density polyethylene.

(LLDPE) or polypropylene. Examples of predominantly linear polyolefin polymers include, without limitation, polymers produced from the following monomers: ethylene, propylene, 1-butene, 4-methyl-pentene, 1-hexene, 1-octene and higher olefins as well as copolymers and terpolymers of the previous ones. Additionally, copolymers of ethylene and other olefins including butene, 4-methyl-pentene, hexene, heptene, octene, decene, etc., are also examples of predominantly linear polyolefin polymers.

If desired, the breathable film may also contain an elastomeric polymer, such as elastomeric polyesters, elastomeric polyurethanes, elastomeric polyamides, elastomer polyolefins, elastomeric copolymers, and so forth. Examples of elastomeric copolymers include block copolymers having the general formula ABA 'or AB, wherein A and A1 are each a final block of thermoplastic polymer containing a styreonic moiety (eg, poly (vmilo arene)) and wherein B is a middle block of elastomeric polymer, such as a conjugated diene or a lower alkene polymer (e.g., polystyrene-poly (ethylene-polybutylene) -polystyrene block copolymers). Also suitable are polymers composed of a ABAB tetrablock copolymer, such as described in U.S. Patent No. 5,332,613 issued to Taylor et al., Which is incorporated herein by reference in its entirety for all. purposes. An example of such a tetrablock copolymer is a styrene-poly (ethylene-propylene) -styrene-poly (ethylene-propylene) block copolymer ("S-EP-S-EP"). Commercially available copolymers A-B-A 'and A-B-A-B include several different formulations of Kraton Polymers from Houston, Texas under the trademark designation KRATON®. The KRATON® block copolymers are available in several different formulations, a number of which are identified in U.S. Patent Nos. 4,663,220; 4,323,534; 4,834,738; 5,093,422 and 5,304,599, which are hereby incorporated in their entirety by reference thereto for all purposes. Other commercially available block copolymers include the styrene-poly (ethylene-propylene) -styrene elastomeric copolymer or S-EP-S available from Kuraray Company, Ltd. of Okayama, Japan, under the SEPTON® trademark designation.

Examples of elastomeric polyolefins include polyethylene and ultra low density elastomeric polypropylenes, such as those produced by "metallocene" or "single site" catalyst methods. Such elastomeric olefin polymers are commercially available from ExxonMobil Chemical Co. from Houston, Texas under the brand designations ACHIEVE® (polypropylene-base), EXACT® (ethylene-base), and EXCEED® (ethylene-base). The elastomeric olefin polymers are also commercially available from DuPont Dow Elastomers, LLC (a joint venture between DuPont and Dow Chemical Co.) under the trademark designation ENGAGE® (ethylene-base) and AFFINITY® (ethylene-base). Examples of such polymers are also described in US Pat. Nos. 5., 278,272 and 5,272,236 granted to Lai and others, which are hereby incorporated in their entirety by reference thereto for all purposes. Also useful are certain elastomeric polypropylenes, as described in U.S. Patent Nos. 5,538,056 issued to Yang et al. And 5,596,052 issued to Resconi et al., Which are hereby incorporated by reference in their entirety for reference thereto. all purposes If desired, mixtures of two or more polymers can also be used to form the breathable film. For example, the film can be formed from a mixture of a high performance elastomer and a low performance elastomer. A high performance elastomer is generally an elastomer having a lower level of hysteresis, such as less than about 75%, and in some embodiments, less than about 60%. In the same way, a low performance elastomer is generally an elastomer having a higher level of hysteresis, such as greater than about 75%. The hysteresis value can be determined by first lengthening a sample to an ultimate elongation of 50% and then allowing the sample to retract to an amount where the amount of resistance is zero. Particularly suitable high-performance elastomers may include styrene-based block copolymers, as previously described and commercially available from Kraton Polymers of Houston, Texas under the trademark designation KRATON®. In the same way, particularly suitable low-yield elastomers include polyolefins, such as metallocene-catalyzed polyolefins (e.g., single-site linear metallocene-catalyzed low density polyethylene) commercially available from DuPont Dow Elastomers, LLC under the brand name AFFINITY®. In some embodiments, the high-performance elastomer may constitute from about 25% by weight to about 90% by weight of the polymer component of the film, and the low-yield elastomer in the same manner may constitute from about 10%. up to about 75% of the polymer component of the film. Additional examples of such a mixture of high performance / low yield elastomers are described in United States of America Patent No. 6,794,024 issued to Walton et al., Which is hereby incorporated by reference in its entirety for all purposes .

As mentioned, the film capable of breathing can be microporous. The microporous form what is often referred to as tortuous trajectories throughout the film. The liquid that contacts one side of the film does not have a direct path through the film. Instead, a network of microporous channels in the film prevents liquids from passing, but allows gases and water vapor to pass. The microporous films can be formed of a polymer and a filler (for example, calcium carbonate). The fillers are particles or other forms of material that can be added to the film polymer extrusion mixture and that will not chemically interfere with the extruded film, but which can be uniformly dispersed throughout the film. Generally, at a dry basis weight, based on the total weight of the film, the film includes about 30% up to about 90% by weight of a polymer. In some embodiments, the film includes about 30% up to about 90% by weight of a filler. Examples of such films are described in US Pat. Nos. 5,843,057 issued to McCormack; 5,855,999 awarded to McCormack; 5,932,497 issued to Morman et al .; 5,997,981 awarded to McCormack and others; 6,002,064 granted to Kobylivker and others; 6,015,764 awarded to McCormack and others; 6,037,281 awarded to Mathis and others; 6,111,163 granted to McCormack and others; and 6,461,467 granted to Taylor and others, which are hereby incorporated by reference in their entirety for all purposes.

Films are generally made breathable by stretching the filled films to create microporous paths while the polymer breaks away from the filler (eg, calcium carbonate) during drawing. For example, the breathable material contains a thin stretched film that includes at least two basic components, for example, a polyolefin polymer and filler. These components are mixed together, heated, and then extruded into a film layer using any of a variety of processes to produce films known to those of ordinary skill in the art of processing film. Such processes for making film include, for example, die-casting, cooling and plane casting, and blown film processes.

Another type of film capable of breathing is a monolithic film that is a continuous, non-porous film, which due to its molecular structure, is capable of forming a vapor permeable barrier, impermeable to liquid. Among the various polymeric films that fall into this type include films made from a sufficient amount of poly (vinyl alcohol), polyvinyl acetate, ethylene vinyl alcohol, polyurethane, ethylene methyl acrylate, and ethylene methyl acrylic acid to make them with ability to breathe. Without intending to be maintained to a particular mechanism of operation, it is believed that films made of such polymers solubilize water molecules and allow the transport of those molecules from one surface of the film to the other. Therefore, these films can be sufficiently continuous, for example, non-porous, to make them substantially impervious to liquid, but still allow for vapor permeability.

Breathable films, such as those previously described, may constitute the fully breathable material, or may be part of a multi-layer film. Films with multiple layers can be prepared by coextruding blown or cast film from the layers, by extrusion coating, or by any conventional layering process. In addition, other breathable materials that may be suitable for use in the present invention are described in U.S. Patent Nos. 4,341,216 issued to Obenour; 4,758,239 granted to Yeo and others; 5,628,737 granted to Dobrin and others; 5,836,932 awarded to Buell; 6,114,024 granted to Forte; 6,153,209 granted to Vega and others; 6,198,018 granted to Curro; 6,203,810 granted to Alemany and others; and the 6,245,401 granted to Ying and others, which are hereby incorporated in their entirety by reference to them for all purposes.

If desired, the breathable film can also be attached to a non-woven fabric, a knitted fabric, and / or a woven using well-known techniques. For example, appropriate techniques for joining a film to a non-woven fabric are described in US Pat. Nos. 5,843,057 to McCormack; 5,855,999 awarded to McCormack; 6,002,064 granted to Kobylivker and others; and 6,037,281 granted to Mathis and others; and WO 99/12734, which are incorporated herein in their entirety by reference thereto for all purposes. For example, the breathable / non-woven film material can be formed from a non-woven layer and a breathable film layer. The layers may be arranged so that the breathable film layer is bonded to the non-woven layer. In a particular embodiment, the breathable material is formed of a non-woven fabric (eg, a polypropylene spunbond fabric) laminated to a breathable film.

Although several with figurations of a thermal device have been described above, it should be understood that other configurations are also included within the scope of the present invention. For example, other layers may also be employed to improve the exothermic properties of the thermal device. For example, a substrate can be used near or adjacent to the thermal substrate of the present invention that includes a coating of moisture retaining particles. As previously mentioned, particles that retain moisture can retain and release moisture to activate the exothermic reaction. Additionally, of particular benefit, one or more of the aforementioned layers can achieve multiple functions of the thermal device. For example, in some embodiments, the breathable layer, the moisture retaining layer, etc., may be coated with an exothermic composition and therefore also serves as a thermal substrate. Although it is not expressly disclosed here, it should be understood that numerous other combinations and configurations may be quite well within the ordinary skill of those in the art.

The breathable and / or moisture retaining layers described above can generally be arranged in any desired position relative to the exothermic composition. In this aspect, various configurations of the thermal device of the present invention can now be described in greater detail. It should be understood, however, that the description that follows is purely exemplary, and that other configurations of the thermal device are also contemplated by the current inventors.

Referring to Figure 1 for example, an embodiment of a thermal device 10 that can be formed according to the present invention is shown. As shown, the thermal device 10 defines two outer surfaces 17 and 19, and is in the form of a material that is bent, conformable, and substantially flat. The size and the total shape of the thermal device 10 are not critical. For example, the thermal device 10 may have a shape that is generally triangular, square, rectangular, pentagonal, hexagonal, circular, elliptical, etc. As shown, the thermal device 10 includes a thermal substrate 12 containing one or more compositions Exothermic In this embodiment, the breathable layers 14a and 14b are included within the thermal device 10 which are impervious to liquids, but permeable to gases. It should be understood that although as shown herein they have two breathable layers, any number of breathable layers (if any) can be employed in the present invention. The thermal device 10 also includes a moisture retaining layer 16 that is configured to absorb and retain moisture for an extended period of time. The breathable layers 14a and 14b and the moisture retaining layer 16 can be positioned in various ways relative to the thermal substrate 12. In Figure 1, for example, the breathable layers 14a and 14b are directly placed adjacent to each other. 12. As a result, the breathable layers 14a and 14b can prevent external liquids from contacting the substrate 12 and can also control the amount of air contacting the substrate 12 over a given period of time. The moisture retaining layer 16 may also be placed in several locations, but is generally positioned to assist in facilitating the moisture supply of the thermal substrate 12. It should be understood that, although they are shown here as having a moisture retaining layer, any number of layers (if any) can be employed in the present invention.

Although not specifically illustrated, the thermal device 10 may also include several other layers. For example, the thermal device 10 may employ a thermally conductive layer to help distribute heat towards a user's direction (e.g., the Z direction) and / or along the XY plane of the device 10, thereby improving uniformity of heat application over a selected area. The thermally conductive layer can have a thermal conductivity coefficient of at least about 0.1 Watts per meter Kelvin (W / m-K), and in some embodiments, from about 0.1 to about 10 Watts per meter Kelvin. Although any thermally conductive material can generally be employed, it is often desired that the selected material be formable to improve the comfort and flexibility of the device 10. Suitable conformable materials include, for example, fibrous materials (e.g., non-woven fabrics). ), movies, and so on. Optionally, the thermally conductive layer may be permeable to gas and / or vapor so that the air can contact the thermal substrate 12 when desired to activate the exothermic reaction. One type of conformable, vapor permeable material that can be used in the thermally conductive layer is a nonwoven fabric material. For example, the thermally conductive layer may contain a non-woven laminate, such as a spin-linked / melt-blown / spin-linked ("SMS") laminate. Such spunbonded / meltblown / spunbonded laminates are formed by well-known methods, as described in U.S. Patent No. 5,213,881 issued Timmons et al., Which is incorporated herein in its entirety by reference. to it for all purposes. Another type of conformable material, to the vapor permeable that can be used in the thermally conductive layer is a breathable film. For example, the thermally conductive layer sometimes uses a non-woven / breathable film.

A variety of techniques can be employed to provide conductivity to the thermally conductive layer. For example, a metallic coating can be used to provide conductivity. Suitable metals for such purposes include, but are not limited to, copper, silver, nickel, zinc, tin, palladium, lead, copper, aluminum, molybdenum, titanium, iron and others. Metal coatings can be formed from a material using any of a variety of known techniques such as vacuum evaporation, electrolytic coating, etc. For example, the patents of the United States of America number 5,656,355 granted to Cohen; 5,599,585 granted to Cohen; 5,562,994 issued to Abba and others; and 5,316,837 issued to Cohen, which are hereby incorporated by reference in their entirety for all purposes, describe suitable techniques for depositing a metal coating on a material. In addition to a metal coating, still other techniques can be employed to provide conductivity. For example, an additive can be incorporated into the material (e.g. fibers, films, etc.) to improve conductivity. Examples of such additives include, but are not limited to, coal fillers, such as carbon fibers and powders; metal fibers, such as copper powder, steel, aluminum powder, and aluminum flakes; ceramic fillers, such as boron nitrite, aluminum nitrite and aluminum oxide. Commercially available examples of suitable conductive materials include, for example, technically conductive compounds available from LNP Engineering Plastics, Inc., of Exton, Pennsylvania under the name Konduit® or Cool Polymers of Warwick, Rhode Island under the trade name CoolPoly ®. While several examples of conductive materials have been described above, it should be understood that any thermally conductive material can be generally used in the present invention.

In addition to a thermally conductive layer, still other optional layers can be employed to improve the effectiveness of the thermal device 10. For example, an insulation layer can be used to inhibit the dissipation of heat to the external environment so that the heat is instead focused on the patient or the user. Because the insulation layer increases the overall heat production efficiency of the device 10, the desired temperature increase can be achieved with a lower amount of exothermic coating or other reagent (e.g. moisture or oxygen). The insulation layer can have a thermal conductivity coefficient of less than about 0.1 Watts per meter-Kelvin (W / m-K), and in some additions, from about 0.01 to about 0.05 Watts per meter-Kelvin. Any known insulation material can be employed in the present invention. If desired, the selected insulation material may be fibrous in nature to improve the overall conformation of the thermal device 10. The fibrous material may possess a high foaming to improve the insulating properties. Suitable high foaming materials may include porous woven materials, porous nonwoven materials, etc. Particularly suitable high foaming materials are multi-component (e.g., bicomponent) nonwoven polymeric fabrics. For example, the multi-component polymers of such fabrics can be mechanically or chemically crimped to increase foaming. Examples of suitable high foaming materials are described in greater detail in U.S. Patent Nos. 5,382,400 issued to Pike et al .; 5,418,945 issued to Pike and others; and 5,906,879 granted to Huntoon and others, which are hereby incorporated in their entirety by reference thereto for all purposes. Still other materials suitable for use in an insulation material are described in US Pat. No. 6,197,045 issued to Carson, which is hereby incorporated by reference in its entirety for all purposes.

The thermal device 10 may also include the layers that were optionally the outer surfaces 17 and 19, respectively, of the thermal device 10. These layers may present a docile, soft-feeling and non-irritating surface to the wearer's skin. For example, the layers may be formed of materials that are permeable to liquid and vapor, liquid impervious and vapor permeable ("breathable") and others. For example, the layers may be formed from a meltblown or bonded fabric with polyolefin fiber yarn, as well as a bonded-carded fabric of short fibers and / or hydraulically entangled from natural and / or synthetic fibers. In another embodiment, the layers can be formed from a breathable non-woven laminate (e.g., a breathable / woven-bonded film laminate) as described above. The layers may also include a composition that is configured to be transferred to the wearer's skin to improve skin health. Suitable compositions are described in U.S. Patent No. 6,149,934 issued to Kryzik et al., Which is hereby incorporated by reference in its entirety for all purposes.

The various layers and / or components of the thermal device 10 can be assembled together using any known attachment mechanism, such as adhesive, ultrasonic, thermal bonds, etc. Suitable adhesives may include, for example, hot melt adhesives, pressure sensitive adhesives and others. When used, the adhesive can be applied as a uniform layer, such as a patterned layer, a spray pattern or any of separate lines, swirls or dots. In some embodiments, the exothermic composition can serve the dual purpose of generating heat and also act as the adhesive. For example, the binder of the exothermic composition can join together one or more layers of the thermal device 10.

To further improve the amount of heat generated by the thermal device, multiple thermal substrates can sometimes be employed. The multiple thermal substrates can be placed side by side or spaced apart by one or more layers. For example, referring to Figure 2, an embodiment of a thermal device 100 is shown which contains a first thermal substrate 112a and a second thermal substrate 112b. Although not required, the thermal device 100 also includes a first breathable layer 114a and a second breathable 114b layer. The thermal device 100 also includes a moisture-containing layer 116 to facilitate the supply of moisture to the thermal substrates 112a and 112b. The moisture-containing layer 116 is placed between the thermal substrate 112a / breathable layer 114a and the thermal substrate 112b / breathable layer 114b. In this way, the amount of moisture supplied to each substrate is relatively uniform. It should be understood, however, that any placement, selection and / or number of layers can be employed in the present invention.

Moisture can be applied at any time before or during the use of the thermal device, such as just before use or during manufacture. For example, water may be applied previously to the moisture-containing layer as described above. The moisture is added in an amount effective to activate an exothermic, electrochemical reaction between the electrochemically oxidizable element (eg metal powder) and the electrochemically reduced element (eg oxygen). Although this amount may vary depending on the reaction conditions and the amount of heat desired, moisture is typically added in an amount of from about 20% by weight to about 500% by weight, and in some embodiments, from about 50% to about 200% by weight, of the weight of the amount of metal that can be oxidized present in the coating. Although not necessarily required, it may be desired to seal such thermal devices treated with water within a material essentially impermeable to liquid (vapor permeable or vapor impermeable) which inhibits the exothermic composition of contacting with sufficient oxygen to activate prematurely. the exothermic reaction. To generate heat, the thermal device is simply removed from the package and exposed to air.

The thermal device of the present invention can be employed in a wide range of articles to provide a heating effect. For example, the thermal device can be used as a heating pad, bandage, food warmer, animal warmer, water heater and others. The thermal device can also be used to deliver heat in various other applications, such as covers or blankets for heating patients during surgical or medical procedures.

The present invention can be better understood with reference to the following examples.

EXAMPLE 1 The ability to form a thermal device according to the present invention was demonstrated. Initially, pieces (7 inches by 12.5 inches) of a carded and bound fabric were provided which had a basis weight of 0.9 ounces per square yard. The fabric was formed from a mixture of 75% by weight of bicomponent fibers and 25% by weight of polyester fibers. The bicomponent fibers were obtained from Fibervisions, Inc., of Covington, Georgia under the name "ESC 215", which had a polyethylene sheath and a polypropylene core, a denier of 3.0, and a finish of 0.55% by weight of "HR6". The polyester fibers were obtained from Invista of Wichita, Kansas under the name "T-295", which had a denier of 6.0 and contained 0.5% by weight of a Ll finish.

The coating formulation was prepared as follows. In a pyrex 400 mL beaker, 5.0 grams of METOLOSE SM-100 (Shin-Etsu Chemical Co., Ltd.) and 12.5 grams of sodium chloride (Mallinckrodt) were added to 150.0 grams of distilled water which were stirred and heated at 69 ° C. The mixture was stirred and allowed to cool when added without sequence the following additional ingredients: 17.3 grams of ethylene-vinyl acetate emulsion DUR-O-SET® Elite PE 25-220A (Celanese Emulsions), 39.7 grams of carbonate solution of calcium shows XC4900 # 04.1919704, (Omya), 15.0 grams of Nuchar SA-20 activated carbon (MeadWestvaco), and 170.0 grams of A-131 iron powder (North American Hóganás). After about 30 minutes of agitation of the formulation with all the ingredients, the temperature was reduced with an ice bath of from about 23 ° C to about 18 ° C. A noticeable increase in viscosity occurred when the temperature reached around 20 ° C. The viscosity of the formulation was measured at 2,538 cP (Brookfield viscometer, spindle LV-4 at 100 revolutions per minute). The calculated concentration of each component of the aqueous formulation is stated below in Table 1.

Table 1: Components of the Aqueous Formulation The aqueous formulation was applied to one side of the 0.9 oz. Pieces of fabric per square yard using a Meyer single coil rod # 60. The coated pieces were dried in an oven for about 15 minutes at 110 ° C. The concentration of the components of the exothermic composition was then calculated from the coated and dried cloth pieces (16.4 ± 0.4 grams), the untreated pieces of cloth (1.9 ± 0.1 grams), and the composition of the aqueous formulation. The results are set down in table 2.

Table 2: Components of the Exothermic Composition A seven-layer structure (3.5 inches x 4 inches) was then designed to activate the exothermic reaction. Specifically, the seven-layer structure included three of the coated fabric pieces placed on one side of the moisture-containing layer, and the other three coated fabric pieces placed on the other side of the moisture-containing layer. The uncoated side of the fabric pieces faced the moisture-containing layer. The total weight of the six layers of the coated fabric was 15.4 grams (10.2 grams of iron). The moisture-containing layer was formed of 75% by weight of wood pulp fluff, 15% by super absorbent weight, and 10% by weight of KoSa T255 bicomponent fiber. The moisture-containing layer had a basis weight of 225 grams per square meter and a density of 0.12 grams per cubic centimeter. The pulp of wood pulp was obtained from Weyerhaeuser under the trade name "NB416". The super absorbent was obtained from Degussa AG under the name "SXM 9543".

Before forming the multi-layer structure, each side of the moisture-containing layer (2.2 grams) was wetted by spraying water (6.6 grams in an amount that increased the layer's mass by a factor of 4.0.) This seven-layer structure It was then placed inside a rectangular bag (4 inches x 4.5 inches) made of a laminated microporous film bonded with nylon yarn.The laminate was obtained from Mitsubishi International Corp., and labeled Type TSF EDFH 5035. The transmission rate Water vapor from the laminate was measured at 455 grams per square meter for 24 hours by using a cup method (ASTM standard E-96E-80) .The bag was sealed with a metallized tape obtained from Nashua.

EXAMPLE 2 A thermal device was formed as described in example 1, except that it was heat sealed in a metallized storage bag for 16 hours before the activation of the reaction. The metallized storage bag was KAL-ML5 from Kapak Corporation, a two-layer structure containing a metallized polyester layer that was adhesively laminated to a linear low density polyethylene film. The total weight of the six layers of coated cloth was 14.8 grams (9.8 grams of iron). The layer containing moisture (2.1 grams) was wet on both sides by spraying water (6.2 grams) in an amount that increased the mass of the layer by a factor of 3.9.

EXAMPLE 3 A coating formulation similar to that described in Example 1 was prepared and applied to one side of a carded and bonded fabric of 0.9 ounces per square yard in the same manner as described in Example 1. The calculated concentration of each component of The aqueous formulation is set out below in Table 3.

Table 3: Components of the Aqueous Formulation The concentration of the components of the exothermic composition was calculated from the coated and dried cloth pieces (11.6 ± 0.3 grams), the untreated pieces of cloth (1.6 ± 0.1 grams) and the composition of the aqueous formulation. The results are set down in table 4.

Table 4: Components of the Exothermic Composition A thermal device (3 inches by 8 inches) with a seven-layer structure was then designed to activate the exothermic reaction. The thermal device was sealed with heat in the middle to produce a segmented device with two equal sections (3 inches by 4 inches). The size of the 7-layer components that was placed in each section was 2.5 inches by 3.5 inches. The total weight of the six coated layers was 8.3 grams (5.2 grams of iron) for one section and 8.6 grams (5.4 grams of iron) for the other section. In addition, 3.9 grams of an aqueous salt solution were applied to the moisture containment layer of the first section and 4.0 grams of the solution were applied to the second section. The salt solution contained 9.9% by weight of sodium chloride in water, and the mass of the moisture containing layer of both sections increased by a factor of 4.0. The seven-layer structure was placed in a laminated bag of microporous film bonded with nylon yarn (described in Example 1) (segmented into two equal sections as described above) and the edges of the bag were heat sealed. The resulting thermal device was heat sealed in a metallized storage bag for 44 hours before activation of the reaction.

EXAMPLE 4 A segmented thermal device was formed as described in Example 3, except that the total weight of the six coated layers was 8.2 grams (5.2 grams of iron) for one section and 8.9 grams (5.6 grams of iron) for the other section . In addition, 4.1 grams and 4.0 grams of an aqueous salt solution were applied to the moisture containment layer of the first and second sections respectively.

The salt solution contained 9.9% by weight of sodium chloride in tap water, and the mass of the moisture containment layer of the first and second sections was increased by a factor of 3.9 and 3.8 respectively. The resulting thermal device was heat sealed in a metallized storage bag for 189 hours before activation of the reaction.

EXAMPLE 5 The ability to achieve a controlled heating profile using a thermal device of the present invention was demonstrated. Specifically, the thermal devices of Examples 1-4 were tested. Because Example 1 was not sealed in the metallized storage bag, it was tested immediately after training. For Examples 2-4, the metallized storage bag was opened to initiate the reaction. The test was carried out by attaching the wired thermocouple to a data collection device on one side of the thermal device. For the segmented thermal devices described for examples 3-4, both sections were tested. The temperature was recorded as a function of time (at intervals of 5 seconds) to give the thermal response curves shown in Figure 3. The results are shown for only a segment of the devices described by Examples 3-4. The thermal response curve for the other segment of the device of Example 3 was very similar to the first segment (1-2 ° C warmer), while the other segment of the device of Example 4 was around 6-8 ° C more hot, more likely due to the higher iron content. As illustrated, curves thermal response to the samples of Examples 3-4 (applied with an aqueous salt solution) reached 38 ° C within about 10 minutes after opening the storage bag, and also remained from about 38 to 42 ° C for at least 3 hours.

EXAMPLE 6 The ability to form a thermal device according to the present invention was demonstrated. A coating formulation similar to that described in Example 3 was prepared, but a higher level of sodium chloride was used. The coating formulation was applied to one side of the carded and bonded fabric of 0.9 ounces per square yard in the same manner as described in Example 1. The calculated concentration of each component of the aqueous formulation is set forth below in Table 5.

Table 5: Components of the Aqueous Formulation The concentration of the components of the exothermic composition was calculated from the piece of coated and dried cloth (16.3 grams), the untreated piece of cloth (1.9 grams) and the composition of the aqueous formulation. The results are set down below in table 6.

Table 6: Components of the Exothermic Composition A thermal device (4 inches by 4.5 inches) with a seven-layer structure was then designed to activate the exothermic reaction. The thermal device was formed as described in Example 1, with the size of the seven-layer components also being 3.5 inches by 4 inches. The total weight of the six coated layers was 15.6 grams (9.4 grams of iron). In addition, each side of the moisture containment layer (2.2 grams) was moistened by spraying 6.1 grams of water in an amount that increased the layer's mass by a factor of 3.8. The seven-layer structure was placed in a bag laminated microporous film attached with nylon yarn (described in Example 1) and the edges of the pouch were sealed with metallized tape obtained Nashua. The resulting thermal device was sealed with heat in a metallized storage bag for 20 hours before activation of the reaction.

EXAMPLE 7 A thermal device was formed as described in Example 1, except that a "separation layer" was used to separate the moisture containing layer from the three coated layers on each side. The separation layer was a film / fabric laminate with small perforated holes to allow steam and gas to pass while preventing the passage of the liquid. It was obtained from Tredegar Film Products with the label FM-425 lot number SHBT040060. Each side of the containment layer Moisture (2.2 grams) was wetted by spraying 6.3 grams of water in an amount that increased the layer's mass by a factor of 3.9. Then the separation layer was placed around it with the fabric side of the separation layer in contact with the wet moisture containment layer. The three coated layers were then placed on each side with the uncoated side in contact with the film side of the separation layer. The total weight of the six coated layers was 14.2 grams (9.2 grams of iron). The nine layer structure was then placed inside a laminated bag of microporous film bonded with nylon yarn (described in Example 1) and the edges of the bag were sealed with metallized tape, obtained from Nashua. The resulting thermal device was sealed with heat in a metallized storage bag for 20 hours before activation of the reaction.

EXAMPLE 8 The thermal device was formed as described in Example 7, except that the six coated layers contained a lower level of sodium chloride.

The calculated concentration of each component of the aqueous formulation that was used to coat one side of the carded and bonded fabric of 0.9 ounces per square yard to produce the coated layers is set forth in Table 7.

Table 7: Components of the Aqueous Formulation The concentration of the components of the exothermic composition was calculated from the piece of coated and dried cloth (16.1 grams), the untreated piece of cloth (1.9 grams) and the composition of the aqueous formulation. The results are set down in table 8 below.

Table 8: Components of the Exothermic Composition A nine layer structure (3.5 inches by 4 inches) as described in example 7 was then designed to activate the exothermic reaction. The moisture containment layer (2.1 gram) was wet on both sides by spraying 6.0 grams of water in an amount that increased the mass of the layer by a factor of 3.8. The total weight of the six coated layers was 15.6 grams (10.7 grams of iron). The nine layer structure was placed inside a laminated bag of microporous film bonded with nylon yarn (described in Example 1) and the edges of the bag were sealed with metallized tape obtained from Nashua. The resulting thermal device was sealed with heat in a metallized storage bag for 20 hours before activation of the reaction.

EXAMPLE 9 A thermal device was formed as described in Example 8 except that the moisture containing layer contained an aqueous salt solution instead of water.

In addition, 6.0 grams of the aqueous salt solution were applied to the moisture containment layer (2.2 grams) by spraying both sides, an amount that increased the layer's mass by a factor of 3.7. The salt solution contained 10.0% by weight of sodium chloride in distilled water.

The total weight of the six coated layers was 15.5 grams (10.7 grams of iron). The resulting thermal device was heat sealed in a metallized storage bag for 20 hours before activating the reaction.

EXAMPLE 10 The ability to achieve a controlled heating profile using a thermal device of the present invention was demonstrated. Specifically, the thermal devices of Examples 6-9 were tested. The metallized storage bag was opened to initiate the reaction. The test was carried out by attaching a wired thermocouple to a data collection device on one side of the thermal device. The temperature was recorded as a function of time (at intervals of 5 seconds) to give the thermal response curves shown in Figure 4.

As shown in Figure 4, the sample of Example 9 (moisture containing layer containing aqueous salt solution) provided a rapid heating rate (temperature to at least 38 ° C within about 10 minutes) after opening the storage bag. The sample of said example 8 (moisture containing layer containing water) provides a slower heating rate. However, samples of Examples 8 and 9 containing an exothermic composition with less salt, provided higher temperature thermal response curves compared to samples of Examples 6 and 7 which contained higher levels of salt in the exothermic composition of the coated fabrics. Therefore, it appears that the composition of the liquid in the moisture containment layer and the composition of the exothermic coating can be used to control the heating profile of the thermal device. More specifically, the salt content in both compositions can be adjusted to obtain the desired heating profile.

EXAMPLE 11 The ability to form a thermal device according to the present invention was demonstrated. A coating formulation similar to that described in Example 6 was prepared, but sodium chloride was not used. The coating formulation was applied to one side of the carded and bonded fabric of 0.9 ounces per square yard in the same manner as described in Example 1. The calculated concentration of each component of the aqueous formulation is set forth in Table 9 below.

Table 9: Components of the Aqueous Formulation The concentration of the components of the exothermic composition was calculated from the piece of coated and dried cloth (14.9 grams), from the untreated piece of cloth (2.0 grams) and from the composition of the aqueous formulation. The results are set down below in table 10.

Table 10: Components of the Exothermic Composition A thermal device (4.25 inches by 4.5 inches) with a nine-layer structure was then designed to activate the exothermic reaction. The thermal device was formed as described in Example 7 with the size of the nine-layer components being 3.5 inches by 4 inches. The total weight of the six coated layers was 13.9 grams (9.2 grams of iron). In addition, each side of the moisture containment layer (2.4 grams) was wetted by spraying 6.7 grams of water, an amount that increased the layer's mass by a factor of 3.8. The nine layer structure was placed inside a laminated bag of microporous film bonded with nylon yarn (described in Example 1) and the edges of the bag were sealed with metallized tape obtained from Nashua. The resulting thermal device was heat sealed in a metallized storage bag for 19.5 hours before the activation of the reaction.

EXAMPLE 12 A thermal device was formed as described in Example 11, except that the moisture containing layer (2.2 grams) was wet on both sides by the spraying of 6.2 grams of an aqueous salt solution, an amount that increased the mass of the layer by a factor of 3.8. The salt solution contained 10% by weight of sodium chloride in distilled water. The total weight of the six coated layers was 13.7 grams (9.1 grams of iron). The resulting thermal device was heat sealed in a metallized storage bag for 19.5 hours before the activation of the reaction.

EXAMPLE 13 A thermal device was formed as described in Example 7, except that the moisture containing layer (2.2 grams) was wet on both sides by spraying 6.0 grams of an aqueous salt solution, an amount that increased the mass of the layer by a factor of 3.7. The salt solution contained 10% by weight of sodium chloride in distilled water. The thermal device was also slightly larger than that of Example 7 at 4.25 inches by 4.5 inches. The total weight of the six coated layers was 14.6 grams (9.6 grams of iron). The 9-layer structure was then placed inside a laminated bag of microporous film bonded with nylon yarn (described in Example 1) and the edges of the bag were sealed with metallized tape, obtained from Nashua. The resulting thermal device was heat sealed in a metallized storage bag for 18 hours before the activation of the reaction.

EXAMPLE 14 A thermal device was formed as described in example 9. In addition, the moisture containing layer (2.2 grams) was wet on both sides by spraying 6.1 grams of an aqueous salt solution, an amount that increased the mass of the layer by a factor of 3.8. The salt solution contained 10.0% by weight of sodium chloride in distilled water. The total weight of the six coated layers was 16.6 grams (11.4 grams of iron). The resulting thermal device was heat sealed in a metallized storage bag for 18 hours before the activation of the reaction.

EXAMPLE 15 The ability to achieve a controlled heating profile using a thermal device of the present invention was demonstrated. Specifically, the thermal device of Examples 11-14 was tested. The metallized storage bag was opened to initiate the reaction. The test was carried out by attaching the wired thermocouple to a data collection device on one side of the thermal device. The temperature was recorded as a function of time (at intervals of 5 seconds) to give the thermal curves shown in Figure 5.

EXAMPLE 16 The ability to form a thermal device according to the present invention was demonstrated. Initially, a 7-inch-wide roll of a carded and bonded woven fabric was provided which had a basis weight of 1.5 ounces per square yard (50 grams per square meter). The fabric was formed from a mixture of 60% by weight of bicomponent fibers and 40% by weight of polyester fibers. The bicomponent fibers were obtained from FiberVisions, Inc., of Covington, Georgia under the name "ESC 215", which had a polyethylene sheath and a polypropylene core, a 1.5 denier, and 0.55% by weight of a finished " HR6". The polyester fibers were obtained from Invista of Wichita, Kansas, under the name "T-295", which had a denier of 6.0 and contained 0.5% by weight of finished Ll.

The coating formulation was prepared as follows. In a one-gallon metal bucket were stirred 34.5 grams of METOLOSE SM-100 (Shin-Etsu Chemical Co., Ltd.) and 25.0 grams of sodium chloride (Mallinckrodt) were added to 1172.0 of distilled water which were stirred and heated at 68 ° C. The mixture was stirred and allowed to cool when the following additional ingredients were added: 139.6 grams of an emulsion of vinyl acetate-ethylene DUR-O-SET® Elite PE 25-220A (Celanese Emulsions), 330.2 grams of calcium carbonate solution. calcium XP-5200-6 sample # 05.2435503 (Omya), 60.1 grams of Nuchar SA-400 activated carbon (MeadWestvaco), and 1181.1 grams of A-131 iron powder (North American Hoganás). After about 30 minutes of stirring the formulation with all the ingredients, the temperature was reduced with an ice bath at about 10 ° C. A noticeable increase in viscosity occurred when the temperature was reduced. The calculated concentration of each component of the aqueous formulation is stated below in Table 11.

Table 11: Components of the Aqueous Formulation The aqueous formulation was applied to one side of the 1.5 oz. Fabric per square yard in a pilot line process using a knife coater. The separation between the blade and the steel roller that carried the fabric was set to 900 microns. The line speed was 0.25 meters per minute. The pilot line coater contained a 4-foot dryer set at 145 ° C which was used to partially dry the coated fabric. The partially dried coated fabric was cut into 17 inch pieces and placed in a laboratory oven at 110 ° C for about 20 minutes to complete the drying step. The concentration of the components of the exothermic composition was calculated from the coated and dried cloth pieces (56.5 ± 1.5 grams), the piece of untreated cloth (4.3 grams) and the composition of the aqueous formulation. The results are set forth below in table 12 Table 12: Components of the Exothermic Composition A five-layer structure (1.6 inches by 8 inches) was designed to activate the exothermic reaction. Specifically, the five-layer structure included one of the coated fabric pieces placed on one side of the moisture containing layer, and another piece of coated fabric placed on the other side of the moisture containing layer. The uncoated side of the fabric pieces faces the moisture containment layer. The moisture containment layer was formed of 90% by weight of wood pulp fluff (Weyerhaeuser NF401) and 10% by weight of KoSa T255 bicomponent fiber. The humidity containment layer moisture had a basis weight of 175 grams per square meter and a density of 0.8 grams per cubic centimeter. A "separation layer" was used to separate the moisture containing layer from the coated layer on each side. The separation layer was a fabric / film laminate with small perforated holes to allow the passage of vapor and gas while preventing the passage of liquid. This was obtained from Tredegar Film Products with the label FM-425 lot number SHBT040060.

Before forming the multi-layer structure, the moisture containment layer (1.5 grams) was wet on each side with sprayed 4.2 grams of distilled water, an amount that increased the layer's mass by a factor of 3.8. Then the separation layer was placed around it with the fabric side of the separation layer in contact with the wet moisture containment layer. A coated layer was then placed on each side with the uncoated side in contact with the film side of the separation layer. The total weight of the two coated layers was 13.5 grams (9.9 grams of iron). The five-layer structure was then placed inside a bag (3 inches by 9 inches) that was sealed with a heat sealer. The bag was made of a laminate of microporous film bonded with nylon yarn (described in Example 1) which had a short woven fabric layer heat sealed to the side bonded with nylon yarn. The short woven fabric was produced from 20% wood pulp fluff (50% northern softwood kraft fibers / 50% softwood kraft bleached pine from Alabama), 58% polyester fiber from 1.5 denier ( Invista type 103), and 22% bonded with polypropylene yarn (Kimberly-Clark Corp.). The bag also contained two pieces of flat wire, one piece sealed with heat inside each 9-inch bank. The wire measured approximately 8.5 inches in length, 0.1 inches in width, and 0.01 in thickness and was obtained from Noranda Aluminum, Inc., under the designation Alloy 8176 / EEE. The resulting thermal device was sealed with heat in a metallized storage bag for 8 days before activation of the reaction.

EXAMPLE 17 A thermal device was formed as described in Example 16, except that the moisture containing layer contained an aqueous salt solution instead of tap water. In addition, 4.3 grams of the aqueous salt solution was applied to the moisture containment layer (1.5 grams), an amount that increased the layer's mass by a factor of 3.8. The salt solution contained 10.0% by weight of sodium chloride in distilled water. The total weight of the two coated layers was 13.7 grams (10.1 grams of iron). The resulting thermal device was sealed with heat in a metallized storage bag for 8 days before activation of the reaction.

EXAMPLE 18 A thermal device was formed as described in example 16, except that the moisture containing layer was formed of 75% by weight of wood pulp fluff (Weyerhaeuser NB416), 15% by weight of super absorbent (Degussa SXM9543) , and 10% by weight of KoSa T255 bicomponent fiber, and had a basis weight of 225 grams per square meter and a density of 0.12 grams per cubic centimeter. The moisture containment layer also contained an aqueous salt solution instead of tap water; 5.8 grams of the aqueous salt solution were applied to the layer containing moisture (2.2 grams) an amount that increased the mass of the layer by a factor of 3.7. The salt solution contained 10.0% by weight of sodium chloride in distilled water. The total weight of the two coated layers was 14.6 grams (10.7 grams of iron). The resulting thermal device was heat sealed in a metallized storage bag for 66 hours before activating the reaction.

EXAMPLE 19 A thermal device was formed as described in Example 16, except that the moisture-containing layer was formed of the material described in Example 18.

The layer containing moisture also contained an aqueous salt solution instead of tap water; 6.0 grams of the aqueous salt solution were applied to the layer containing moisture (2.1 grams), an amount that increased the layer's mass by a factor of 3.8. The salt solution contained 10.0% by weight of sodium chloride in distilled water. The total weight of the two coated layers was 14.7 grams (10.8 grams of iron). The resulting thermal device was heat sealed in a metallized storage bag for 66 hours before the activation of the reaction.

EXAMPLE 20 The ability to achieve a controlled heating profile using a thermal device of the present invention was demonstrated. Specifically, the thermal devices of examples 16-19 were tested. The metallized storage bag was opened to initiate the reaction. The test was carried out by attaching a wired thermocouple to a data collection device on one side of the thermal device. The temperature was recorded as a function of time (at intervals of 5 seconds) to give the thermal curves shown in Figure 6.

As shown in Figure 6, the thermal response curves for the samples of Examples 17-19 showed a rapid heating rate (temperature of at least 38 ° C within about 10 minutes) and a temperature profile elevated for an extended period of time.

These samples contained salt both in the exothermic composition and in the liquid contained by the moisture containment layer. In addition, a moisture containing layer that did not contain super absorbent was used for the sample of Example 17, and the thermal response curve was similar to the curves for the samples of Examples 18 and 19. Note in Figure 6 that the The thermal response curve for the sample of Example 16 did not show a rapid heating rate and the temperature only reached around 30 ° C. This sample only contained water in the moisture containment layer.

EXAMPLE 21 The ability to form a thermal device according to the present invention was demonstrated. The coated fabric described in Example 16 was used in a five-layer structure (2.5 inches by 7 inches) to activate the exothermic reaction. Specifically, the five-layer structure included one of the coated fabric pieces placed on one side of the moisture containing layer, and another piece of coated fabric placed on the other side of the moisture containing layer. The uncoated side of the fabric pieces faced the moisture containment layer. The moisture containment layer was formed of 75% by weight of wood pulp fluff, 15% by super absorbent weight, and 10% by weight of KoSa T255 bicomponent fiber.

The moisture containment layer had a basis weight of 225 grams per square meter and a density of 0.12 grams per cubic centimeter. The pulp of wood pulp was obtained from Weyerhaeuser under the name "NB416". The super absorbent was obtained from Degussa AG under the name "SXM 9543". A "separation layer" was used to separate the moisture containing layer from the coated layer on each side. The separation layer was a fabric / film laminate with small perforated holes to allow the passage of water vapor while preventing the passage of the liquid. This was obtained from Tredegar Film Products with the label FM-425 lot number SHBT040060.

Before forming the multi-layer structure, the moisture containment layer (2.7 grams) was wet on each side by spraying 7.6 grams of an aqueous salt solution, an amount that increased the layer's mass by a factor of 3.8. The salt solution contained 3.0% by weight of sodium chloride in distilled water. Then the separation layer was placed around it with the fabric side of the separation layer in contact with the wet moisture containment layer. A coated layer was then placed on each side with the uncoated side in contact with the film side of the separation layer. The total weight of the two layers was 18.1 grams (13.3 grams of iron). The five-layer structure was then placed inside a bag (3.2 inches by 8 inches) that was sealed with a heat sealer. The bag was made of a laminate of microporous film bonded with nylon yarn (described in example 1) which had a layer of short weave fabric sealed with heat on the side bonded with nylon spinning. The short-woven fabric was produced from 20% wood pulp fluff (50% northern softwood kraft fibers / 50% softwood kraft bleached pinewood fibers from Alabama), 58% from 1.5 denier fiber of polyester (Invista type 103), and 22% bonded with polypropylene yarn (Kimberly-Clark Corporation). The resulting thermal device was sealed with heat in a metallized storage bag for 64 hours before activating the reaction.

EXAMPLE 22 A thermal device was formed as described in Example 21. The moisture containment layer (2.7 grams) contained 7.2 grams of an aqueous salt solution, an amount that increased the mass of the layer by a factor of 3.7. The salt solution contained 3.0% by weight of sodium chloride in distilled water. The total weight of the two coated layers was 17.1 grams (12.5 grams of iron). The resulting thermal device was sealed with heat in a metallized storage bag for 64 hours before activating the reaction.

EXAMPLE 23 A thermal device was formed as described in Example 21. The moisture containment layer (2.7 grams) contained 7.6 grams of an aqueous salt solution, an amount that increased the mass of the layer by a factor of 3.8. The salt solution contained 3.0% by weight of sodium chloride in distilled water. The total weight of the two coated layers was 17.3 grams (12.6 grams of iron). The resulting thermal device was sealed with heat in a metallized storage bag for 64 hours before activating the reaction.

EXAMPLE 2 A thermal device was formed as described in Example 21. The moisture containment layer (2.7 grams) contained 7.2 grams of an aqueous salt solution, an amount that increased the mass of the layer by a factor of 3.7. The salt solution contained 3.0% by weight of sodium chloride in distilled water. The total weight of the two coated layers was 18.0 grams (13.2 grams of iron). The resulting thermal device was sealed with heat in a metallized storage bag for 64 hours before activating the reaction.

EXAMPLE 25 The ability to achieve a controlled heating profile was demonstrated using a thermal device of the present invention. Specifically, the thermal devices of examples 21-24 were tested. The metallized storage bag was opened to initiate the reaction. The test was carried out by attaching a wired thermocouple to a data collection device on one side of the thermal device. The temperature was recorded as a function of time (at intervals of 5 seconds) to give the thermal curves shown in Figure 7. Note that the thermal response curves for the samples of examples 21-24 are lower in temperature but more prolonged than those for the samples of examples 18 and 19 (figure 6). Therefore, the amount of salt in the liquid maintained by the moisture containment layer can be used to control the thermal response curve.

EXAMPLE 26 The breathing capacity of the bag was measured for examples 6-9 and 11-14 to verify that the large difference in the thermal response curves (Figures 4 and 5) was not due to the variability in the ability to breathe of the bag. The bag for these examples was a laminate of microporous film bonded with nylon yarn obtained from Mitsubishi International Corp., and labeled TSF type EDFH 5035. The water vapor transmission rate of laminate was measured at 455 ± 14 grams per square meter for 24 hours (10 samples) using the cup method (ASTM standard E-96E-80). The same method was used to measure the water vapor transmission rate of the bags of Examples 6-9 and 11-14 after the exothermic reaction was completed. The results are shown in table 13.

Table 13: Ability to Breathe (Water Vapor Transmission Rate) for Bags of Examples 6-9 and 11-14 The data shown in Table 13 verify that the bags used for the thermal devices of Examples 6-9 and 11-14 were consistent in the ability to breathe. Therefore, the large differences in the thermal response curves for these thermal devices can be attributed to the liquid applied to the moisture containment layer (water or 10% sodium chloride in water) and / or the composition of the exothermic coating (for example amount of salt).

EXAMPLE 27 The ability to control the delivery of moisture by a moisture containing layer for use in the thermal device of the present invention was demonstrated. Four different samples were tested. Samples A and B were formed from an air-laid fabric that contained 75% by weight of wood pulp fluff (Weyerhaeuser NB416), 15% by super absorbent weight, and 10% by weight of bicomponent fibers "T255" PE / PP (KoSa). The fabric placed by air had a basis weight of 225 grams per square meter and a density of 0.12 grams per cubic centimeter. Samples C and D were formed from an air-laid fabric that contained 90% by weight of wood pulp fluff (Weyerhaeuser NF405) and 10.0% by weight of bicomponent fibers "T255" PE / PP (KaSo). The fabric placed by air obtained a basis weight of 175 grams per square meter and a density of 0.08 grams per cubic centimeter. The super absorbent was obtained from Degussa AG under the name "SXM 9543".

Each substrate placed by air was cut to a size of 3.5 inches by 4.0 inches and was sprayed on each side with an aqueous solution so that the wet weight was about 3.7 to 4.0 times higher than the dry weight. For samples A and C, the aqueous solution contained only distilled water. For samples B and D, the aqueous solution contained 10% by weight of sodium chloride in distilled water. The wet substrates were placed on the scales located inside an environmental chamber. The humidity and temperature inside the chamber were then recorded as a function of time. In addition, the weight of each wet substrate was also recorded to obtain the "percentage of moisture loss" as a function of time. The "moisture loss percentage" was calculated by subtracting the wet weight measured from the original wet weight, dividing this value by the original wet weight, and then multiplying by 100. The resulting evaporation curves are shown in Figure 8. Note that sample B (SAP / salt water) delivered more moisture as a function of time (for example higher evaporation rate) compared to sample A (SAP / water). Also, sample D (without SAP / salt water) had a moisture delivery rate slightly higher than that of sample B, but much less than sample C (without SAP / water).

Although the invention has been described in detail with respect to the specific embodiments thereof, it will be appreciated by those skilled in the art, upon achieving an understanding of the foregoing, that alterations, variations and equivalents of these embodiments can be easily conceived. Therefore, the scope of the present invention should be evaluated as that of the appended claims and any equivalents thereof.

Claims (26)

R E I V I N D I C A C I O N S

1. A thermal device comprising: an exothermic composition formed of a metal that can be oxidized, wherein the exposure of the exothermic composition to oxygen and moisture activates an exothermic reaction to generate heat; a layer of moisture containment; Y an aqueous solution applied to the moisture containing layer that is capable of supplying moisture to the exothermic composition, wherein the aqueous solution comprises one or more solutions.

2. The thermal device as claimed in clause 1, characterized in that the moisture containing layer contains cellulosic fibers

3. The thermal device as claimed in clauses 1 or 2, characterized in that the moisture containing layer contains a super absorbent material.

4. The thermal device as claimed in any one of the preceding clauses, characterized in that the moisture containing layer contains a fibrous fabric having a basis weight of from about 50 to about 500 grams per square meter and a density of from about 0.05 to about 0.25 grams per cubic centimeter.

5. The thermal device as claimed in any one of the preceding clauses, characterized in that the solutions include a metal salt.

6. The thermal device as claimed in clause 5, characterized in that the metal salt is sodium chloride.

7. The thermal device as claimed in any one of the preceding clauses, characterized in that the solution constitutes from about 1 to about 20% by weight of the aqueous solution, and preferably from about 5 to about 15% by weight of the aqueous solution.

8. The thermal device as claimed in any one of the preceding clauses, characterized in that the vapor pressure of the aqueous solution is less than about 27.2 millimeters Hg at 25 ° C, and preferably from about 20.0 millimeters Hg to about of 23.0 mm Hg at 25 ° C.

9. The thermal device as claimed in any one of the preceding clauses, characterized in that the aqueous solution is present in an amount of from about 20% by weight to about 500% by weight of the weight of the oxidizable metal.

10. The thermal device as claimed in any one of the preceding clauses, characterized in that the thermal device further comprises a breathable layer that is capable of regulating the amount of moisture and oxygen that makes contact with the exothermic composition.

11. The thermal device as claimed in any one of the preceding clauses, characterized in that the metal is iron, zinc, aluminum, magnesium or combinations thereof.

12. The thermal device as claimed in any one of the preceding clauses, characterized in that the exothermic composition further comprises a carbon component, binder and an electrolytic salt.

13. The thermal device as claimed in any one of the preceding clauses, characterized in that the exothermic composition is coated on a first thermal substrate.

14. The thermal device as claimed in clause 13, characterized in that the thermal device comprises a second thermal substrate coated with an exothermic composition.

15. The thermal device as claimed in clause 14, characterized in that the moisture containing layer is placed between the first and second thermal substrates.

16. The thermal device as claimed in clause 15, characterized in that it also comprises a first and a second layer capable of breathing, wherein the thermal substrates and the moisture containing layer are placed within the layers capable of breathing .

17. The thermal device as claimed in any one of the preceding clauses, characterized in that the moisture containing layer contains an aqueous solution that releases moisture to the exothermic composition at an evaporation rate of from about 0.05% to about 0.5%, and preferably from about 0.1% to about 0.25%, determined at an initial relative humidity of about 51% and a temperature of about 22 ° C.

18. A method for generating heat, the method comprises exposing a thermal device to oxygen to achieve a controlled heating profile in which one or more surfaces of the thermal device reaches a high temperature of from about 35 ° C to about 55 ° C in 20 minutes or less, wherein the thermal device comprises an exothermic composition formed of a metal that can be oxidized and a moisture containing layer containing an aqueous solution that evaporates at a rate of from about 0.05% to about 0.5% , determined at an initial relative humidity of around 51% and at a temperature of around 22 ° C.

19. The method as claimed in clause 18, characterized in that the aqueous solution is evaporated at a rate of from about 0.1% to about 0.25%, determined at an initial relative humidity of about 51% and at a temperature of about of 22 ° C.

20. The method as claimed in clauses 18 or 19, characterized in that the controlled heating profile is activated in which one or more surfaces of the thermal device reach a high temperature of from about 37 ° C to about 43 ° C in 20 minutes or less.

21. The method as claimed in any one of clauses 18 to 20, characterized in that the elevated temperature is maintained for at least about 1 hour, preferably at least for about 2 hours and more preferably at least about 4 hours

22. The method as claimed in any one of clauses 18 to 21, characterized in that it also comprises: sealing the thermal device within an enclosure that inhibits the passage of oxygen to the exothermic composition; Y open the enclosure to expose the exothermic composition to oxygen.

23. The method as claimed in any one of clauses 18 to 22, characterized in that the aqueous solution comprises one or more solutions.

24. The method as claimed in clause 23, characterized in that the solutions constitute from about 1 to about 20% of the aqueous solution, and preferably from about 5 to about 15% by weight of the aqueous solution .

25. The method as claimed in any one of clauses 18 to 24, characterized in that the vapor pressure of the aqueous solution is less than about 27.2 millimeters Hg at 25 ° C, and preferably from about 20.0 millimeters Hg. to around 23.0 mm Hg at 25 ° C.

26. The method as claimed in any one of clauses 18 to 25, characterized in that the exothermic composition is coated on a thermal substrate. SUMMARY A thermal device containing an exothermic composition is provided. The exothermic composition includes a metal that is capable of undergoing an oxidation reaction in the presence of moisture and oxygen to generate heat. Certain aspects of the thermal device can be optimized to deliver a controlled amount of moisture and / or oxygen to the exothermic composition during use. Through selective control over the supply of these reagents, a heating profile can be achieved in which a high temperature is quickly reached and maintained over an extended period of time.