HK1131027B - Heat cells comprising exothermic compositions having absorbent gelling material - Google Patents

Description

Heat cells comprising exothermic compositions comprising absorbent gelling materials

Technical Field

The present invention relates to heat cells suitable for incorporation into disposable heat wraps. In particular, the present invention relates to heat cells that are constructed of exothermic compositions that include absorbent gelling materials that can be used to improve heating.

Background

Disposable thermal wraps have become a popular application for applying heat to relieve temporary or chronic pain and discomfort throughout the body. These disposable heat wraps typically comprise an exothermic composition for generating heat, wherein the exothermic composition typically comprises metal powder, salt, and water, such that the exothermic composition is capable of releasing heat upon oxidation of the metal powder. Thermal therapy provided by disposable thermal wraps has been found to be useful in treating ailments associated with stiff muscles and joints, nerve pain, back pain, rheumatism, and the like.

The disposable heating device can provide sustained heat over a period of about one hour to about twenty-four hours and is described as being more compact and easier to use than other conventional heat sources such as whirlpools, hot towels, hot water sandbags, hot pads and elastic compression bands. Disposable heating devices have also been described as satisfactory devices capable of maintaining a stable and controlled temperature, see for example U.S. patent 5,918,590, which discloses heat cells based on specific iron oxidation chemistries that are adapted to be incorporated into disposable body wraps to provide a sustained temperature to achieve stable, convenient and comfortable heating for the treatment of temporary or chronic ailments.

It has been found, however, that the consistency of the sustained temperature supply can be improved while maintaining the temperature for a period of up to about twenty-four hours. One method of enhancing the exothermic reaction is to incorporate carbon materials, such as activated and non-activated carbon materials. Other methods include the addition of water retention agents or materials. See, for example, the disposable heating devices disclosed in U.S. patents 6,436,126, 6,099,556, and 5,233,981. See also the heating devices disclosed in U.S. published patent applications 2004/0042965 and 2004/0178384.

One specific example of an exothermic composition comprising a water-absorbing polymer is disclosed in U.S. patent application publication 2002/0020406. This publication discloses an integrated exothermic medium in which an exothermic agent is mixed with a water-absorbent polymer, and then the exothermic agent/polymer mixture is pressed together with an alcohol, a crosslinking agent or a plasticizer under a certain pressure to be integrated.

Although these disclosures have been published in the field of disposable heating devices comprising exothermic compositions, there remains a need for specific heating devices comprising exothermic compositions to provide a controlled and sustained temperature throughout the heating period. It is known that the thermal performance of heat cells is highly sensitive to moisture content, and a typical heat cell may contain a moisture concentration of about 27% or more to maintain the heating temperature of the heat cell. However, inclusion of a high moisture concentration of about 27% or more may result in an initial heating temperature that is lower than desired. Thus, the ability to quickly reach the temperature required for a therapeutically beneficial effect and the ability to maintain that temperature is difficult to achieve.

Furthermore, current heating devices contain exothermic compositions that are highly prone to segregation effects. It is believed that particle size differences between the components of the composition may contribute to particle segregation. For example, heating devices comprising exothermic compositions comprising water retaining agents (e.g., vermiculite, wood flour, absorbent gelling materials) in combination with iron powder and carbon have a tendency to segregate. Typically, the particle size of the water retaining agent is quite large when compared to iron and carbon particles. For example, current heating devices may contain exothermic compositions wherein the water retaining agent to iron particles average particle size ratio is typically 10: 1 or higher, resulting in a high degree of particle segregation.

Variations in the composition of the particle mixture due to segregation can result in less than optimal product thermal properties and/or a different design than intended. Thus, current heating devices typically do not achieve maximum reaction efficiency because of the excess exothermic composition required to compensate for particle segregation effects. These heating devices typically contain heat cells having a relatively large volume, which allows them to hold an excess of exothermic composition.

It has been found that heat cells comprising an exothermic composition comprising an absorbent gelling material are particularly effective in rapidly reaching the initial heating temperature, and also effective in maintaining a stable temperature for periods of up to twenty-four hours. When used in selected ratios with other compositional components, it has been found that the absorbent gelling material can provide improved heating in addition to providing resistance to compositional changes, such as segregation, to the exothermic composition. To minimize or eliminate segregation effects, the exothermic compositions of the present invention comprise a selected particle size ratio of absorbent gelling material to iron powder.

The heat cells of the present invention have modifiable physical dimensions that enable the heat cells to be incorporated into disposable heating devices such as back wraps, knee wraps, body wraps, joint wraps, menstrual pads, neck-to-arm wraps, and the like.

Summary of The Invention

The present invention relates to a heat cell comprising a particulate exothermic composition, wherein the particulate exothermic composition comprises (a) about 10% to about 90% by weight of iron powder; (b) from about 1% to about 25% by weight of carbon selected from the group consisting of: activated carbon, non-activated carbon, and mixtures thereof; (c) from about 1% to about 25% by weight of an absorbent gelling material having a median particle size of from about 300 μm to about 800 μm; and (d) from about 1% to about 35% by weight of water; wherein the particles of the particulate exothermic composition are combined into pockets forming a unified structure comprising at least two opposing surfaces, wherein at least one surface is oxygen permeable.

It has been found that the temperature consistency of a disposable heating device can be improved whereby the heating device can provide sustained heat over a period of up to twenty-four hours. The heating device described above comprises a specifically designated heat cell, wherein the heat cell comprises an exothermic composition comprising an absorbent gelling material. The absorbent gelling material is capable of retaining water in the particulate exothermic composition such that the water is released at a controlled rate to cause oxidation of the iron powder, which allows the particulate exothermic composition to provide sustained heat generation while providing an improved sustained temperature.

It has been found that particulate exothermic compositions can suffer from segregation effects during processing of the exothermic composition, such that the exothermic composition may not provide a consistent and controllable temperature. To minimize or eliminate segregation effects, the particulate exothermic compositions of the present invention comprise absorbent gelling material to iron powder having a selected median particle size ratio of from about 10: 1 to about 1: 10, preferably from about 7: 1 to about 1: 7, more preferably from about 5: 1 to about 1: 5, and most preferably from about 3: 1 to about 1: 3.

Detailed Description

The heat cells of the present invention comprise a particulate exothermic composition. The particulate exothermic compositions provide improved sustained temperature when heat cells are incorporated into a disposable heating device to relieve temporary or chronic discomfort throughout the body.

The exothermic composition of the present invention is a particulate exothermic composition. As used herein, "particulate" refers to individual particles contained in the composition. In other words, the particulate exothermic compositions defined herein comprise individual particles, wherein each particle has a median particle size in the range of from about 25 μm to about 800 μm.

Varying the particle size of the particulate component in the exothermic compositions as defined herein can cause the particles in the exothermic compositions to separate or segregate. In other words, particle size directly affects the flowability of the particles, and the particulate components defined herein may differ in their flowability, causing the particles to separate or segregate. The exothermic compositions defined herein preferably comprise a particulate component having a defined median particle size range such that the exothermic composition is resistant to particle separation or segregation. It is contemplated, however, that particulate components having a median particle size range above or below the ranges defined herein are also suitable for use in the exothermic compositions defined herein.

As used herein, "sustained temperature" means a temperature in the range of from about 32 ℃ to about 50 ℃, preferably from about 32 ℃ to about 45 ℃, more preferably from about 32 ℃ to about 40, and most preferably from about 32 ℃ to about 37 ℃ over a period of from about twenty seconds to about twenty-four hours, preferably from about twenty minutes to about twenty hours, more preferably from about four hours to about sixteen hours, and most preferably from about eight hours to about twelve hours, wherein the maximum skin temperature and the length of time the skin temperature is maintained at the maximum skin temperature can be suitably selected by the person in need of such treatment to obtain the desired therapeutic benefit without any adverse consequences, such as skin burns that occur as a result of prolonged use of elevated temperatures. It has been shown that maintaining the "sustained temperature" provided by the particulate exothermic compositions of the present invention can provide adequate relief from patients having acute, periodic, and/or chronic pain, including skeletal pain, muscular pain, and/or referred pain, and that even after the disposable heating device containing the particulate exothermic composition is removed from the body pain site, the duration of relief can be extended sufficiently without any adverse consequences.

As used herein, the term "disposable" refers to devices that are intended to be discarded after prolonged use. In other words, "disposable" heating devices as defined herein are those devices that are intended to be placed into an appropriate waste container after the heating device has fully extended release of the heat provided by the heat cells of the present invention. The disposable heating device as defined herein may be stored in a resealable, substantially air-impermeable container for repeated use in alleviating temporary or chronic body aches and pains until the disposable heating device has released heat over its full duration.

The heat cells of the present invention comprise a particulate exothermic composition, wherein the particulate exothermic composition can comprise, consist of, or consist essentially of the elements and limitations of the present invention described herein, as well as any additional or optional ingredients, components, or limitations described herein.

All percentages, parts and ratios are by weight of the particulate exothermic composition, unless otherwise specified. All such weights as they pertain to listed ingredients are based on the particular ingredient level and, therefore, do not include carriers or by-products that may be included in commercially available materials, unless otherwise specified.

All documents cited herein, including relevant portions of the publications, patent applications, and issued patents mentioned herein, are hereby incorporated by reference. The citation of any document is not an admission that it is available as prior art to the present invention.

Heat bag

The present invention relates to heat cells comprising particulate exothermic compositions. The heat cells can be incorporated into disposable heating devices to provide improved sustained temperature, relief from temporary or chronic body aches and pains. The heat cells are preferably incorporated into the disposable heating device in the form of a plurality of heat cells.

The heat cells are in the form of a unitary structure comprising at least two opposing surfaces, preferably film layer substrate surfaces, at least one of which is oxygen permeable and has a fill volume, a void volume, and a cell volume when filled with a particulate exothermic composition. As used herein, "fill volume" refers to the volume of particulate composition in a filled heat cell. As used herein, "void volume" refers to the volume of the cells in the final heat cell that is not filled with the particulate composition, as determined without a pressure differential across the heat cell and without additional stretching or deformation of the base material. As used herein, "cell volume" refers to the sum of the fill volume and the void volume of the heat cell. The ratio of fill volume to bladder volume is from about 0.7 to about 1.0, preferably from about 0.75 to about 1.0, more preferably from about 0.8 to about 1.0, even more preferably from about 0.85 to about 1.0, and most preferably from about 0.9 to about 1.0.

The heat cells may also be measured from their apices. The apices of the heat cells as defined herein have a height of greater than about 0.2cm to about 1.0cm, preferably greater than about 0.3cm to about 0.9cm, more preferably about 0.4cm to about 0.8cm, and most preferably about 0.5cm to about 0.7 cm.

As previously mentioned, the heat cells are in the form of a unitary structure comprising at least two opposing surfaces, preferably film layer substrate surfaces. The film layer substrate is preferably made of a film or a film laminated to a nonwoven fabric. Generally, preferred films are those having heat sealability and being capable of being readily heat fused. If a nonwoven material is used, it may provide support to the film layer substrate and may be integrated into the film layer substrate. Examples of suitable films include polyethylene, polypropylene, nylon, polyester, polyvinyl chloride, polyvinylidene chloride, polyurethane, polystyrene, saponified ethylene-vinyl acetate copolymer, natural rubber, reclaimed rubber, and synthetic rubber. The thin film layer substrate has a thickness in the range of about 1 to about 300 μm and is oxygen permeable or impermeable. For nonwoven fabrics, those having the preferred characteristics of light weight and high tensile strength are suitable, such as nylon, rayon, cellulose esters, polyvinyl derivatives, polyolefins, polyamides or polyesters, cuprammonium cellulose (Bemberg) and other high molecular weight compounds, as well as natural materials such as wool, silk, jute, hemp, cotton, flax, sisal, or ramie. These nonwovens are generally described in Ridel's "Nonwoven Bonding Methods and Materials" (Nonwoven World, 1987), which is incorporated herein by reference in its entirety. Preferred film layer substrates of the present invention are polypropylene nonwoven sheets laminated to poly (ethylene-vinyl acetate) or Low Density Polyethylene (LDPE) films of about 5 to about 100 μm thickness. An example of a commercially available nonwoven sheet is material coded as W502FWH, commercially available from pgi (polymer Group international) located in Waynesboro, VA, u.s.a. An example of a commercially available polypropylene/vinyl acetate (PP/EVA) film is the material encoded as DH245, which is commercially available from Clopay Plastics, located in Cincinnati, OH, u.s.a.

The opposing surfaces are prepared by bonding the two substrates together around their periphery to form a pouch, envelope or pocket with the film side facing the interior of the pouch, envelope or pocket (the side to be filled) and the nonwoven facing the exterior. Pockets may also be formed in the substrate via thermoforming, mechanical embossing, vacuum embossing, or other acceptable methods. Preferred for use herein is Thermoforming, described in "thermofoming" (The WileyEncyclopedia of Packaging Technology, pp. 668 to 675, 1986) edited by Marilyn Bakker, which is incorporated herein by reference in its entirety.

The resulting heat cell can have any geometric shape, such as a disk, triangle, pyramid, cone, sphere, square, cube, rectangle, cuboid, cylinder, ellipsoid, and the like. Preferred shapes of the present invention include shaped geometries having a capsule diameter of from about 0.2cm to about 5cm, preferably from about 1cm to about 4cm, more preferably from about 2cm to about 3cm, and a disc shape having a height of greater than about 0.2cm to about 1cm, preferably greater than about 0.3cm to about 0.9cm, more preferably from about 0.4cm to about 0.8cm, and most preferably from about 0.5cm to about 0.7cm, resulting in a capsule volume of about 0.0045cm³To about 20cm³Preferably about 0.2cm³To about 11cm³. Alternatively, the heat cells of the present invention may be further elongated in shape in their geometry such that the long axis is parallel to the substrate, the height is from about 0.2cm to about 5cm, preferably greater than about 0.5cm to about 1cm, the width is from about 0.2cm to about 20cm, preferably from about 5cm to about 10cm, and the length is from about 1cm to about 20cm, preferably from about 5cm to about 10cm, the resulting cell volume is about 0.04cm to about 20cm, preferably about 5cm to about 10cm³To about 2000cm³Preferably about 1.25cm³To about 10cm³。

The heat cells of the present invention preferably have about 0.03cm per cell²To about 20cm²More preferably about 0.1cm²To about 15cm²And even more preferably about 1cm²To about10cm²And most preferably about 3cm²To about 7cm²Cross-sectional area of. Heat cells having such cross-sectional areas per cell are readily incorporated into body wraps and the like that provide improved body conformation.

The heat cells of the present invention preferably have a premix weight of from about 0.4 grams of premix per cell to about 2.5 grams of premix per cell, more preferably from about 1.0 gram of premix per cell to about 2.4 grams of premix per cell, and most preferably from about 1.5 grams of premix per cell to about 2.3 grams of premix per cell. Heat cells having such premix weights per cell are also readily incorporated into body wraps and the like which also provide improved body shape consistency and thus provide uniform heat to a target area and improved wearer comfort.

The oxygen permeability of the heat cells of the present invention can be provided by selecting a film layer substrate film or film coating that forms the pouch, envelope, pocket and/or cover layer with a particular desired permeability. The desired permeability may be provided by a microporous film or by a film having pores or holes formed therein. These holes/holes may be formed by die casting/vacuum forming or by hot pin holes. In the present invention, oxygen permeability may also be provided by piercing the vent holes in at least one film layer substrate using, for example, at least one spike, preferably an array of about 20 to about 60 pins, having, for example, a tapered tip, and a diameter of about 0.2mm to about 2mm, preferably about 0.4mm to about 0.9 mm.

Alternatively, after the film layer substrates are bonded together so as to enclose the particulate exothermic composition defined below within the pocket therebetween, the vent holes may be pierced on the heat cell side using, for example, at least one pin, preferably an array of from about 20 to about 60 pins having, for example, tapered tips and diameters of from about 0.2mm to about 2mm, preferably from about 0.4mm to about 0.9 mm. The pins are pressed into the particulate exothermic composition through one side of the heat cell material to a depth of about 2% to about 100%, preferably about 20% to about 100%, and more preferably about 50% to about 100%. This pore configuration allows oxygen to diffuse into the heat cell during oxidation of the particulate exothermic composition,diffusion volume of about 0.01cc O₂Per minute/5 cm²To about 15.0cc O₂Per minute/5 cm²(21 ℃, 0.1MPa (1 ATM)), preferably about 0.9cc O₂Per minute/5 cm²To about 3cc O₂Per minute/5 cm²(21 ℃, 0.1MPa (1 ATM)). Although it is preferred to provide the vent holes in the upper layer of the cover film, vent holes may also be provided in the lower layer of the cover film and/or both.

The heat cells of the present invention may optionally incorporate into the skin a component to be delivered, wherein the optional component includes active aromatic compounds, inactive aromatic compounds, pharmaceutically active substances or other therapeutic agents, and mixtures thereof. The optional components may be incorporated into the heat cells as a separate substrate layer or incorporated into at least one film layer substrate. Such reactive aromatic compounds include, but are not limited to, menthol, camphor, eucalyptus, and mixtures thereof. Such non-reactive aromatic compounds include, but are not limited to, benzaldehyde, citral, decanal, acetaldehyde, and mixtures thereof. The pharmaceutically active/therapeutic agents include, but are not limited to, antibiotics, vitamins, antivirals, analgesics, anti-inflammatories, antipruritics, antipyretics, anesthetics, fungicides, antimicrobials, and mixtures thereof. The heat cells may also comprise a substrate layer alone, or incorporated into at least one film layer substrate, self-adhesive component, and/or sweat-absorbing component.

Exothermic composition

The heat cells of the present invention comprise a particulate exothermic composition. The particulate exothermic compositions can provide improved sustained temperature when the heat cells are incorporated into a disposable heating device, such as a disposable body wrap. The particulate exothermic composition comprises a particulate premix composition and an aqueous salt solution.

The components of the particulate premix composition typically include iron powder, carbon, absorbent gelling material, and water, the components of which are described in more detail below. Likewise, typical brine solution components include a metal salt, water, and optionally a hydrogen gas inhibitor such as sodium thiosulfate. The exothermic compositions defined herein are typically prepared by forming a particulate premix composition and rapidly adding the premix to an aqueous salt solution to cause formation of the heat cells of the present invention. A typical heat cell of the present invention may comprise from about 0.4 grams of the premix per cell to about 2.5 grams of the premix per cell and from about 0.4 grams of the saline solution per cell to about 1.5 grams of the saline solution per cell. Accordingly, the exothermic compositions of the present invention may comprise a total cell weight of from about 0.8 grams to about 4.0 grams, preferably from about 1.5 grams to about 3.5 grams, and more preferably from about 2.5 grams to about 3.0 grams per cell.

The rate, duration, and temperature of the thermooxidative reaction of the particulate exothermic composition can be controlled as desired by varying the area in contact with air, and more specifically by varying the oxygen diffusivity/permeability. Other methods of modifying the exothermic reaction include selecting components in the composition, for example, by selecting particular components, modifying component particle size, and the like, as described below.

By way of illustration, one particular method of modifying the exothermic reaction involves the addition of iron powder having a median particle size of about 200 μm and an absorbent gelling material having a median particle size of about 300 μm, wherein the ratio of the median particle size of the absorbent gelling material to the iron powder is 1.5: 1. It has been found that such selected ratios of absorbent gelling material to iron powder result in exothermic compositions that exhibit rapid initial temperature heating rates and long duration heating performance, which are difficult to achieve with current exothermic compositions. It is believed that current exothermic compositions contain high levels of moisture, which results in the presence of water in the interstitial particle voids, which limits oxygen flow and slows the initial temperature heating rate. It has been found that an exothermic composition comprised of a selected median particle size ratio of absorbent gelling material to iron powder allows excess water to leave the interstitial particle voids for a more rapid initial temperature heating rate.

Iron powder

The particulate exothermic compositions of the present invention comprise one or more iron powder components at a concentration in the range of from about 10% to about 90%, preferably from about 30% to about 88%, more preferably from about 50% to about 87%, by weight of the composition.

It is believed that the particulate exothermic compositions defined herein may release heat upon oxidation of the iron powder. Iron is known to be the anode in the electrochemical reactions associated with the exothermic oxidation of iron. There is no particular limitation in purity, kind, size, etc. of the iron powder as long as it can be used to generate heat together with electrically conductive water and air. For example, iron powders having a median particle size of from about 50 μm to about 400 μm, preferably from about 100 μm to about 400 μm, more preferably from about 150 μm to about 300 μm, have been found suitable for use herein.

The median particle size of the iron powder, as well as any other particulate component defined herein, can be determined using a sieving Method, such as the Method described in "ASTM Method B214". Generally, particles are screened through a series of screens consisting of different sizes, and the weight fraction of particles remaining on each screen is determined. The weight fraction of particles on each screen was then used to construct a cumulative weight distribution curve. The cumulative weight distribution curve was constructed by plotting the particle size versus the weight percent of particles that were cumulatively added to a smaller particle size than the particle size retained by the next larger screen. The median particle size is determined from the cumulative weight distribution curve, wherein the median particle size is defined as the particle size corresponding to 50% cumulative weight. Details of the construction of the cumulative weight distribution curve are described in the 4 th edition of Particle Size Measurement, pages 153 to 156, "Methods of Presenting Size Analysis Data" (Terference Allen, 1990), the description of which is incorporated herein by reference in its entirety. To illustrate the sieving method, about 100g +/-0.1g of the test specimen is placed on the top mesh of a set of U.S. standard screens, each screen having a larger mesh than the underlying screen. The cover is placed on the top screen and then a set of screens is clamped in a mechanically operated shaker screening machine such as a TylerRoTap shaker. The shaker was run for 15 minutes while the machine repeated shaking movements performed during the manual sifting. The screen pack was tapped during the shaking process to help the particles fall through the mesh. After shaking for 15 minutes, the material collected on each screen was weighed to the nearest 0.1 g. The sum of all part weights should be no less than 99.7% of the test specimen weight. The weight of the portion retained on each screen is expressed as a weight percentage of the test specimen to the nearest 0.1%. Any fraction less than or equal to 0.04% by weight of the test specimen should be reported as a "trace amount". Any fraction greater than or equal to 0.05% of the test specimen weight should be reported as 0.1% unless specified to be reported to two decimal places. If the part is not present, it should be reported as 0.0%. The median particle size was then determined.

Preferably, the particulate exothermic compositions are comprised of a selected median particle size ratio of absorbent gelling material, as defined below, to iron powder. Exothermic compositions comprised of components having such selected median particle size ratios have been shown to provide heat cells having improved heat capacity and the ability to resist compositional changes, such as resistance to particle segregation. The median particle size ratio of absorbent gelling material to iron powder is typically in the range of from about 10: 1 to about 1: 10, preferably from about 7: 1 to about 1: 7, more preferably from about 5: 1 to about 1: 5, and most preferably from about 3: 1 to about 1: 3.

The heat cells of the present invention are typically smaller and an excess of exothermic composition cannot be used to compensate for the particle segregation effect as compared to current heat cells. In fact, adding excess exothermic composition can result in significant changes in the thermal performance of the heat cells. It has been found that by using iron powder having a median particle size within the ranges defined herein, especially in combination with a ratio of absorbent gelling material to iron powder, the particle segregation effect is reduced. It is believed that the reaction rate of the exothermic composition is controlled by the porosity of the exothermic composition. In other words, the rate of heat cell exotherm is affected by the particle packing properties (i.e., interstitial particle void volume) and the amount of water contained in the exothermic composition. The iron powder defined herein provides low bulk properties, yet the absorbent gelling material prevents water from entering the voids of the particles, thus allowing the heat cells to exhibit heating properties with a rapid initial temperature heating rate and a long duration to treat temporary or chronic body aches and pains.

Non-limiting examples of suitable iron powder sources for the present invention include cast iron powder, reduced iron powder, electrolytic iron powder, scrap iron powder, sponge iron, pig iron, wrought iron, various steels, iron alloys, treated varieties of these iron sources, and mixtures thereof. Sponge iron is preferred.

Sponge iron is a type of iron powder source that is particularly advantageous due to the high internal surface area of sponge iron. Since the inner surface area is several orders of magnitude larger than the outer surface area, the reactivity may not be controlled by the particle size. Non-limiting examples of commercially available sponge irons include M-100 and F-417, available from Hoeganaes Corporation, New Jersey, U.S. A.

Sponge iron is a material used in the steel industry as a basic source for steel making. Without being limited by any preparation method, hematite (Fe) in powder form can be obtained by subjecting hematite (Fe) to a temperature slightly below blast furnace temperature₂O₃) The iron ore is exposed to a reducing atmosphere to produce sponge iron. Including the preparation of sponge iron, sponge iron is more specifically disclosed in U.S. patents 2,243,110, 2,793,946, 2,807,535, 2,900,247, 2,915,379, 3,128,174, 3,136,623, 3,136,624, 3,136,625, 3,375,098, 3,423,201, 3,684,486, 3,765,872, 3,770,421, 3,779,741, 3,816,102, 3,827,879, 3,890,142, and 3,904,397; the disclosure of which is incorporated herein by reference.

Although oxygen is necessary for the oxidation of iron, no internal oxygen source is required in the heat cells of the present invention. However, oxygen-generating chemicals may be incorporated into the particulate exothermic compositions during their preparation without altering the scope of the present invention. Oxygen sources for the purposes of the present invention include air and artificially produced oxygen of varying purity. Among these oxygen sources, air is preferred because it is most convenient and economical.

Carbon (C)

The particulate exothermic compositions of the present invention comprise one or more carbon components at a concentration in the range of from about 1% to about 25%, preferably from about 1% to about 15%, more preferably from about 1% to about 10%, by weight of the composition.

Non-limiting examples of carbon suitable for use herein include activated carbon, non-activated carbon, and mixtures thereof. The carbon component has a median particle size of from about 25 μm to about 200 μm, preferably from about 50 μm to about 100 μm. Activated carbon is preferred.

Activated carbon can be used as a cathode in electrochemical reactions associated with the exothermic oxidation of iron. However, the cathode capability, i.e., carbon blending, can be extended to reduce costs by additionally using non-activated carbon powder. Therefore, mixtures of the above carbons may also be used in the present invention.

Activated carbon is very porous in internal structure, so that it has excellent oxygen adsorption properties. In fact, when activated carbon is wetted, it has excellent oxygen adsorption capacity, thereby making activated carbon useful as a catalyst in electrochemical reactions.

In addition, activated carbon can adsorb water well and can be used as a water holding material. Also, activated carbon can adsorb odors, such as those resulting from the oxidation of iron powder.

Activated carbon made from coconut shells, wood, charcoal, coal, bone coal, and the like, is suitable for use herein, but those made from other raw materials such as animal products, natural gas, fats, oils, resins, and the like, may also be used in the particulate exothermic compositions of the present invention. There is no limitation on the kind of the activated carbon used, however, the preferred activated carbon has good oxygen adsorption performance. Examples of commercially available activated carbons include activated carbons commercially available from MeadWestvaco located in Covington, virginia (usa).

To provide a rapid heating rate to the exothermic composition while maintaining the duration of heat release, the exothermic composition should have more absorbent gelling material than the activated carbon. It has been shown that if the absorbent gelling material is less than the activated carbon, the exothermic reaction becomes sensitive to water content and rapid heating is not possible. Without being bound by theory, it is believed that this is due to the competition for moisture between the absorbent gelling material and the activated carbon, and that for the exothermic reaction to occur, the activated carbon needs to be sufficiently wetted so that it can act as a catalyst for the adsorption of oxygen.

Further, the amount of carbon in the particulate exothermic compositions defined herein should be minimized to maximize the interstitial particle void volume. Carbon is typically the finest particulate component, and excess carbon will result in carbon filling the interstitial particle void volume. It has been found that the amount of carbon required for the exothermic reaction is significantly lower than the amount of carbon used in current exothermic compositions due to the higher content of absorbent gelling material used. Thus, carbon is primarily used for its catalytic activity, while minimizing the use of its water retention properties.

A small amount of carbon is also highly desirable for the method of making the heat cells of the present invention because it allows the premix to rapidly adsorb the brine solution. This significantly increases the speed of the heat cell preparation process defined herein.

Absorbent gelling material

The particulate exothermic compositions of the present invention comprise one or more absorbent gelling materials at a concentration in the range of from about 1% to about 25%, preferably from about 1% to about 15%, more preferably from about 1% to about 10%, by weight of the composition.

Absorbent gelling materials suitable for use herein are capable of physically or chemically retaining water in the particulate exothermic compositions of the present invention. In particular, the absorbent gelling material serves the function of gradually supplying water to the iron powder component, wherein the water is released at a controlled rate. Without being bound by theory, it is believed that the absorbent gelling material prevents or inhibits water from entering or being retained in interstitial voids of the various particles of the exothermic composition, thereby helping to prevent or inhibit flooding.

Non-limiting examples of suitable absorbent gelling materials include those that have fluid absorption properties and can form hydrogels upon contact with water. A specific example of such an absorbent gelling material is a hydrogel-forming absorbent gelling material, which is based on a polybasic acid, such as polyacrylic acid. Such hydrogel-forming polymeric materials are those that absorb the above-mentioned fluids upon contact with a liquid, such as water, and thereby form a hydrogel. These preferred absorbent gelling materials typically comprise a substantially water-insoluble, lightly crosslinked, partially neutralized hydrogel-forming polymeric material prepared from polymerizable, unsaturated, acid-containing monomers. In the above materials, the polymer component formed from the unsaturated acid-containing monomer may comprise the entire gelling agent, or may be grafted onto other types of polymer moieties such as starch or cellulose. Acrylic acid grafted starch materials fall into the latter category. Thus, specific suitable absorbent gelling materials include hydrolyzed acrylonitrile grafted starch, acrylic acid grafted starch, polyacrylates, maleic anhydride-based copolymers, and combinations thereof. Polyacrylate and acrylic acid grafted starch materials are preferred. Non-limiting examples of commercially available polyacrylates include those from Nippon Shokubai, located in Chatanooga, TN (U.S. A.).

The absorbent gelling material has a median particle size of from about 300 μm to about 800 μm, preferably from about 400 μm to about 800 μm, more preferably from about 500 μm to about 800 μm. It has been shown that absorbent gelling materials having a median particle size of 300 μm or more help to minimize or eliminate segregation effects. Reducing segregation effects can provide improved sustained temperatures to achieve the desired therapeutic heating benefits without any adverse consequences, such as skin burns. Reducing segregation effects also allows for the high speed preparation of disposable heating devices containing multiple heat cells that can provide up to twenty-four hours of therapeutic heating.

As noted above, the particulate exothermic compositions defined herein preferably have a selected median particle size ratio of absorbent gelling material to iron powder. It has been shown that exothermic compositions comprised of these components in well-defined selected median particle size ratios exhibit minimal or no segregation effects, which allows the exothermic compositions to conform to the intended thermal performance to achieve the desired therapeutic heating benefits.

In addition to absorbent gelling materials, the particulate exothermic compositions of the present invention may optionally comprise other water-holding materials that have capillary functions and/or hydrophilic properties. These optional water-holding materials may be included in the particulate exothermic compositions at concentrations ranging from about 0.1% to about 25%, preferably from about 0.5% to about 20%, more preferably from about 1% to about 15%, by weight of the composition. Non-limiting examples of such optional water-holding materials include vermiculite, porous silicate, sawdust, wood flour, cotton, paper, plant material, carboxymethyl cellulose salt, inorganic salts, and mixtures thereof. The absorbent gelling materials and optional water-holding materials are further described in U.S. Pat. nos. 5,918,590 and 5,984,995; the description of which is incorporated herein by reference.

Metal salt

The particulate exothermic compositions of the present invention comprise one or more metal salts at a concentration in the range of from about 0.5% to about 10%, preferably from about 0.5% to about 7%, more preferably from about 1% to about 5%, by weight of the composition.

Metal salts suitable for use herein include those metal salts that act as reaction promoters, are used to activate the iron powder surface for an oxidation reaction with air, and can provide electrical conductivity to the exothermic composition to resist corrosion reactions. Generally, there are several suitable alkali, alkaline earth and transition metal salts that may be used alone or in combination to resist the corrosive reaction of iron.

Non-limiting examples of suitable metal salts include sulfates, chlorides, carbonates, acetates, nitrates, nitrites, and mixtures thereof. Specific non-limiting examples of sulfates include ferric sulfate, potassium sulfate, sodium sulfate, manganese sulfate, magnesium sulfate, and mixtures thereof. Specific non-limiting examples of chlorides include cupric chloride, potassium chloride, sodium chloride, calcium chloride, manganese chloride, magnesium chloride, cuprous chloride, and mixtures thereof. Copper chloride, sodium chloride and mixtures thereof are preferred metal salts. One example of commercially available sodium chloride includes sodium chloride from Morton Salt located in Chicago, Illinois (USA).

Water (W)

The particulate exothermic compositions of the present invention comprise water at a concentration in the range of from about 1% to about 35%, preferably from about 5% to about 33%, by weight of the composition. Water suitable for use herein may be from any suitable source. For example, tap, distilled or deionized water, or any mixture thereof, is suitable for use herein.

It is known that the thermal performance of heat cells is highly sensitive to moisture content, and a typical heat cell may contain a moisture concentration at or above about 27% to maintain the heating temperature of the heat cell. However, inclusion of a high moisture concentration of about 27% or more may result in an initial heating temperature that is lower than desired. Thus, the ability to quickly reach the temperature required for a therapeutically beneficial effect and the ability to maintain that temperature is difficult to achieve. It has been found, however, that the particulate exothermic compositions of the present invention not only provide heat cells that are highly effective in maintaining a stable, controlled and consistent temperature, but also provide heat cells that have a rapid initial temperature heating rate such that the heat cells can provide the desired therapeutic heating benefits without any adverse consequences, such as skin burns. This can be accomplished by incorporating a sufficient weight ratio of water to absorbent gelling material such that the particulate exothermic compositions have a high internal water retention and a high interstitial particle void volume. The particulate exothermic compositions of the present invention comprise a weight ratio of water to absorbent gelling material of from about 3: 1 to about 9: 1, preferably from about 4: 1 to about 7: 1, by weight of the exothermic composition.

In addition, current heat cells typically contain high levels of water to increase the heat cell heating temperature retention time. Thus, the exothermic compositions of the present invention may contain high levels of water and occupy lower heat cell weights than current heat cells. Thus, the exothermic compositions of the present invention can use high levels of water more efficiently and require less exothermic composition to reach the desired heating temperature over an extended period of time.

Optional ingredients

The exothermic compositions of the present invention may further comprise one or more other optional components known or otherwise effective for use in pharmaceutical compositions, provided that the optional components are physically and chemically compatible with the composition components described above, or do not otherwise unduly impair product stability, aesthetics or performance. Other optional components suitable for use herein include, for example, coalescing aids including corn syrup, maltitol syrup, crystalline sorbitol syrup, and amorphous sorbitol syrup; dry binders including microcrystalline cellulose, maltodextrin, lactose spray, co-crystallized sucrose and dextrin, modified dextrose, mannitol, pregelatinized starch, dicalcium phosphate, and calcium carbonate; an oxidation reaction enhancer comprising the elements chromium, manganese, copper, and compounds containing said elements; hydrogen inhibitors, including inorganic and organic basic compounds and salts of basic weak acids, specific non-limiting examples including sodium thiosulfate, sodium sulfite, sodium hydroxide, potassium hydroxide, sodium bicarbonate, sodium carbonate, calcium hydroxide, calcium carbonate, and sodium propionate; fillers, such as natural cellulose segments (including sawdust, cotton linters, and cellulose), synthetic fibers in segment form (including polyester fibers), foamed synthetic resins (such as foamed polystyrene and polyurethane), inorganic compounds (including silica powder, porous silica gel, sodium sulfate, barium sulfate, iron oxide, and aluminum oxide; anti-caking agents, such as tricalcium phosphate and sodium aluminosilicate; and mixtures thereof Amounts range from about 0.01% to about 35%, preferably from about 0.1% to about 30%.

Preparation method

The particulate exothermic compositions of the present invention can be prepared by any known or otherwise effective technique suitable for obtaining an exothermic composition that provides a therapeutic heating benefit. The particulate exothermic compositions of the present invention are preferably prepared using conventional blending techniques. A suitable method for blending the components of the particulate exothermic compositions of the present invention is more fully described in U.S. patent No. 4,649,895 to Yasuki et al, published 3/17 1987, the description of which is incorporated herein by reference.

A typical technique for blending the components of the particulate exothermic composition involves adding carbon to a blender or mixer, followed by a small portion of the total amount of water, and then stirring the carbon/water combination. Water is typically added in sufficient quantity to aid blending while avoiding increased corrosion. The stirring was stopped and absorbent gelling material was added to the carbon/water combination. Stirring was continued until all components were thoroughly mixed, then iron powder was added and stirred. The compositions are then blended until thoroughly mixed to form a particulate premix. Sodium chloride, optionally a hydrogen gas inhibitor such as sodium thiosulfate, and the remaining water are separately mixed to form an aqueous salt solution, which is then added to the iron powder premix to form a particulate exothermic composition, which can be used to construct the heat cells of the present invention. Individual heat cells are typically prepared by adding a fixed amount of the particulate premix composition to a pocket in a film layer substrate sheet, such as a pocket in a polypropylene nonwoven/LDPE film layer substrate sheet. In this process, water or saline is rapidly added on top of the premix composition and the polypropylene nonwoven/poly (ethylene-vinyl acetate) film layer substrate flat sheet is placed over the heat cells with the poly (ethylene-vinyl acetate) film side facing the LDPE film side containing the preformed pocket flat sheet. And (3) bonding the film layers of the two sheets together by using low-temperature heating to form an integrated structure. The resulting heat cell comprises a particulate exothermic composition sealed in a pocket between two film layer substrate sheets.

Alternatively, vacuum forming of the pockets can be used to prepare individual heat cells. In other words, when the particulate premix composition is placed on top of the film layer substrate surface just above the mold, a vacuum is used to pull the film layer substrate surface into the mold. The particulate premix composition falls into a vacuum formed pocket and is held in place at the bottom of the mold by the vacuum applied to the particulate premix composition. Next, a brine solution was quickly added on top of the premix composition. Next, a second film layer substrate surface is placed on the first film layer substrate surface such that the particulate exothermic composition is between the two surfaces. The particulate exothermic composition is then sealed between the first and second film layer substrate surfaces.

The resulting heat cells can be used alone or as a plurality of heat cells, wherein the heat cells can be incorporated into a variety of disposable heating devices, such as disposable body wraps. Typically, the body wrap has means for retaining the wrap around different parts of the body (e.g., knee, neck, back, etc.) and may comprise any number of types and shapes, wherein the retaining means comprises a fastening system, such as a reclosable two-part hook and loop fastening system.

The resulting heat cells are preferably packaged in a secondary air-impermeable package to prevent oxidation until needed, as described in the above-mentioned U.S. patent No. 4,649,895, which is incorporated herein by reference. Alternatively, air impermeable removable adhesive tape may be placed over the heat cell vents. When the tape is removed, air can enter the heat cell, thereby activating the oxidation reaction of the iron powder.

Examples

The following examples further describe and illustrate embodiments within the scope of the present invention. These examples are given solely for the purpose of illustration and are not to be construed as limitations of the present invention, as many variations thereof are possible without departing from the spirit and scope of the invention. All example concentrations are weight-weight percent unless otherwise indicated.

The particulate exothermic compositions exemplified below are prepared by forming the particulate exothermic compositions using conventional blending techniques, wherein the resulting compositions can be used to construct heat cells of the present invention.

The premix is prepared by adding activated carbon and water to a blender or mixer, such as a Littleford DayMixer, and mixing for about ten minutes. An absorbent gelling material such as polyacrylate is then added and the mixture is stirred for about 10 minutes. Next, iron powder, such as sponge iron, is added to the mixer and the resulting premix is stirred for about 5 minutes.

About 2.2 grams of the resulting premix composition was added to a preformed pocket in a sheet of polypropylene nonwoven that had been covered with a LDPE film, which had been thermoformed to form the pocket.

Next, a brine solution is prepared by adding water, a metal salt such as sodium chloride, and optionally sodium thiosulfate to a stirrer and stirring for about fifteen minutes. The resulting brine solution is then rapidly added to the premix composition to obtain one or more heat cell constructions of the present invention.

A flat sheet of polypropylene nonwoven material covered with poly (ethylene-vinyl acetate) was then placed over the heat cells and heat bonded to the backsheet. The mass around the heat cell was trimmed to provide a 2.5cm excess mass around the perimeter of the heat cell. One hundred needles of about 0.5mm diameter were pressed simultaneously into one face of the heat cell until they penetrated about 100% into the exothermic composition, but not through the bottom sheet. This perforation method can achieve about 1 cc/min/5 cm²O (at 21 ℃ C. under 0.1MPa (1 ATM))₂And (3) diffusion permeability. Shortly after the saline is added to the granular composition, the heat cells begin to heat up, thus bonding the top and bottom sheets, and the final heat cells are quickly packaged into an air-tight secondary package for future use.

The resulting heat cells can be incorporated into disposable heating devices, including disposable body wraps, such as back wraps, knee wraps, joint wraps, menstrual pads, neck to arm wraps, and the like.

Particulate exothermic compositions

Components	Example 1 (Wt.%)	Example 2 (Wt.%)	Example 3 (Wt.%)
				Iron powder	60.40	56.75	58.70

Activated carbon	4.05	3.81	3.94
				Absorbent gelling material	5.09	4.78	4.94
Sodium chloride	3.02	3.47	1.38
				Sodium thiosulfate	0.38	0.43	---
Water (W)	27.06	30.76	31.04

While particular embodiments of the particulate exothermic compositions suitable for use in the present invention have been described, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. It is intended in the appended claims to cover all such modifications that are within the scope of this invention.

Claims (28)

1. A heat cell comprising a particulate exothermic composition, wherein the particulate exothermic composition comprises:

(a) from 10% to 90% by weight of an iron powder having a median particle size of from 50 μ ι η to 400 μ ι η;

(b) 1% to 25% by weight of carbon selected from the group consisting of: activated carbon, non-activated carbon, and mixtures thereof;

(c) from 1% to 25% by weight of an absorbent gelling material having a median particle size of from 300 μ ι η to 800 μ ι η; and

(d) 1 to 35% by weight of water;

wherein the particulate exothermic composition comprises an absorbent gelling material and iron powder having a median particle size ratio of from 3: 1 to 1: 3; wherein the particles of particulate exothermic composition are combined into pockets forming a unified structure comprising at least two opposing surfaces, wherein at least one surface is oxygen permeable; wherein the particulate exothermic composition in the pocket has interstitial particulate voids.

2. The heat cell of claim 1 wherein the particulate exothermic composition comprises 50% to 87% by weight of iron powder.

3. The heat cell of claim 1, wherein the iron powder has a median particle size of from 150 μ ι η to 300 μ ι η.

4. The heat cell of claim 3, wherein the iron powder is scrap iron powder.

5. The heat cell of claim 4, wherein the scrap iron powder is pig iron.

6. The heat cell of claim 4, wherein the scrap iron powder is sponge iron.

7. The heat cell of claim 4, wherein the scrap iron powder is wrought iron.

8. The heat cell of claim 4, wherein the scrap iron powder is steel.

9. The heat cell of claim 4, wherein the scrap iron powder is an iron alloy.

10. The heat cell of claim 4, wherein the scrap iron powder is cast iron powder.

11. The heat cell of claim 4, wherein the iron dust is reduced iron powder.

12. The heat cell of claim 4, wherein the scrap iron powder is electrolytic iron powder.

13. The heat cell of claim 4, wherein the iron powder is sponge iron.

14. The heat cell of claim 1 wherein the particulate exothermic composition comprises from 1% to 10% by weight of carbon selected from the group consisting of: activated carbon, non-activated carbon, and mixtures thereof.

15. The heat cell of claim 14, wherein the activated carbon is made of: coconut shell, wood, charcoal, coal, animal products, natural gas, fats, oils, or resins.

16. The heat cell of claim 15, wherein the coal is bone coal.

17. The heat cell of claim 1 wherein the particulate exothermic composition comprises from 1% to 15% by weight absorbent gelling material.

18. The heat cell of claim 17, wherein the absorbent gelling material is a hydrogel-forming polymeric material.

19. The heat cell of claim 18, wherein the hydrogel-forming polymeric material is selected from the group consisting of: hydrolyzed acrylonitrile grafted starch, acrylic acid grafted starch, polyacrylates, maleic anhydride-based copolymers, and mixtures thereof.

20. The heat cell of claim 1 wherein the particulate exothermic composition further comprises from 0.5% to 10% by weight of a metal salt.

21. The heat cell of claim 20, wherein the metal salt is selected from the group consisting of: alkali metal salts, alkaline earth metal salts, transition metal salts, and mixtures thereof.

22. The heat cell of claim 21, wherein the metal salt is selected from the group consisting of: sodium chloride, copper chloride, and mixtures thereof.

23. The heat cell of claim 1, wherein the heat cell has a width of 2cm²To 10cm²Cross-sectional area of.

24. The heat cell of claim 23, wherein the heat cell is shaped to: pyramids, cones, spheres, cubes, cuboids, cylinders, or ellipsoids.

25. The heat cell of claim 1, wherein the heat cell has a total cell weight of 0.8 grams to 4.0 grams.

26. The heat cell of claim 25, wherein the heat cell is incorporated into a disposable heating article selected from the group consisting of: back wrap, neck wrap, menstrual pads, joint wraps, and wraps from neck to arm.

27. The heat cell of claim 26, wherein the joint wrap is a knee wrap.

28. The method of claim 23The heat cell of (1), wherein the heat cell has 1.25 to 10cm³The volume of the capsule.