DISPOSABLE BODY WARMER

Abstract: A disposable body warmer comprises a flat bag and, in a flat form having a thickness of 2 to 5mm, a heat generating agent composed of iron powder as a main ingredient and mixed therewith 9 to 11% by weight of a water-retaining agent, 18 to 22% by weight of water, a heat generation promoter and common salt. The flat bag is provided with one air-permeable surface having air permeability per unit time limited to 5000 to 10000 sec/100cc so as to bring about a reduction in the pressure accompanying oxidative heat generation of the heat generating agent packed in said flat bag, and the other surface of the flat bag is provided with a non­ transferable self-adhesive layer.

Description: The present invention relates to a self-adhesive disposable body warmer, and more particularly to a self-adhesive disposable body warmer comprising iron powder as a main ingredient, which can set up and maintain a stable attachment, can keep a stable heat distribution state and further can be comfortably used in direct contact with or in close proximity to the skin. A disposable body warmer comprises an air-permeable bag and, accommodated therein, a mixture of metal powder such as iron powder available at a relatively low cost with assistants such as water, activated carbon, wood flour and salt and utilizes an exothermic reaction caused by supplying oxygen(air) thereto. It can be easily used by merely opening a wrapped, hermetically sealed bag, and occupies a major proportion of the body warmers in these days. However, the above-described disposable body warmer requires the use of an attaching means in order to attach the body warmer to the human body. More precisely, the disposable body warmer cannot set up a state attached to the human body without being put in receptacle of an attaching band or the like, or placed in a pocket provided in underwear. In other words, although the disposable body warmer per se is inexpensive, the attaching means is considerably expensive and the attachment of the body warmer to the attaching means and removal thereof from this means are complicated. Further, even when the body warmer is put in such an attaching means or a pocket and attached to the human body, the position of attachment is limited, which often makes it impossible to attach the disposable body warmer properly to that part of the body where a thermal effect is most required. As an expedient for eliminating the disadvantage of the conventional ordinary disposable body warmer, a self-adhesive heat generating bag has been proposed in Japanese Utility Model Publication (Y2) No.34735/1981. This bag comprises a heat generating agent capable of generating heat upon being exposed to oxygen and placed in a flat heat generating bag having one surface permeable to oxygen with the other surface being provided with a non-transferable self-adhesive layer all over the surface or in a pattern form. This bag can be substantially properly applied to any site of the human body or the like and can be applied without use any expensive and special attaching means or pocket. Although the non-transferable disposable body warmer may be thought to have above-described advantage, studies on the utility of this warmer conducted by the present inventor have revealed that such a body warmer generally stands substantially perpendicular or slant at least when applied to the human body and that in order to attain substantially uniform heat generation and heat quantity, the heat generating agent placed in the bag should be basically of a flat form and cannot be packed densely like, e.g., a sausage even when the peripheral portion is of a thin layer form. That is, the heat generating agent should be packed in a flat form while leaving a considerable space, which inevitably brings about uneven distribution or agglomeration of this agent in the bag when the body warmer is applied to the human body or the like. The uneven distribution, in turn makes the heat generation of the agent in the bag and the temperature distribution accompanying the heat generation uneven, and the agglomeration gives an unpleasantness to the user and further disturbs the state of heat generation. Specifically, in one part of the heat generating agent, heat generation begins and is completed in an early stage, while in the other part thereof, remarkable heat generation occurs, thus causing burn of the skin or the like. The agglomerated heat generating agent deteriorates the touch, particularly gives an unpleasantness in a state directly applied to the skin or applied to the skin through underwear, and remarkably disturbs the state of heat generation because the amount of supply of oxygen is lowered. US-A-4756299 and US-E-32026 each disclose a flat heating pad in which is disposed a particulate chemical mixture, including iron powder, sodium chloride and carbon, which is exothermic in the presence of air. The pad is contained in an inner envelope having air admission holes therein, and the inner envelope is in turn disposed in a sealed outer envelope for storage until the pad is required for use. An object of the present invention is to provide a self-adhesive disposable body warmer comprising iron powder as a main ingredient which can set up and maintain a stable attachment, can keep a stable heat distribution state and further can be comfortably used in direct contact with or in close proximity to the skin. According to the present invention there is provided a disposable body warmer comprising a flat bag having an air-permeability first surface and containing a mixture of iron powder as a heat-generating agent, a water-retaining agent, water, an oxidation promoter and sodium chloride, said mixture being packed in flat form in the bag, characterized in that the air permeability is in the range 0.6 to 1.2 cc/cm²/min thereby to reduce the pressure in the bag accompanying oxydative heat generation of said heat-generating agent to maintain the bag substantially flat, in that the mixture contains 18 to 22% by weight of water and 9 to 11% by weight of a water-retaining agent and has a thickness of 2 to 5mm in said bag, and in that a non-transferable self-adhesive layer is provided on the surface of the bag opposite said first surface for attachment of the flat bag to the user. The non-transferable self-adhesive layer attached to the flat bag enables the body warmer to be attached at an arbitrary position on the human body or clothing, particularly underwear, and further, scarcely any of the self-adhesive remains on or stains the body or clothing when the body warmer is peeled off. An intended exothermic reaction can be achieved at a relatively low cost by packing into the above-described flat bag a heat generating agent comprising iron powder as a main ingredient and reaction assistants incorporated therein. The limitation of the air permeability of the air-permeable surface of the flat bag to 0.6 to 1.2 cc/cm²/min causes the oxidative heat generation of the heat generating agent mainly composed of iron powder placed in the bag to reduce the pressure within the bag. That is, the amount of supply of oxygen (amount of air) is limited to a value less than that necessary for oxidation of that agent so that the above-described flat bag can be maintained in a compression-flattened state under atmospheric pressure during the oxidative heat generation. This compression-flattened flat bag prevents the uneven distribution of the heat generating agent within the bag and equalizes the temperature distribution. The incorporation of 9% by weight or more of a water-retaining agent, such as wood flour or vermiculite, in a heat generating agent mainly composed of iron powder prevents occurrence of shrinkage during the oxidative heat generation, which contributes to prevention of caking of this agent attributable to the shrinkage. Further, limitation of the maximum amount of the water-retaining agent to 11% by weight enables the amount of the iron powder as the main ingredient and the amount of incorporation of the heat generation promotor and the salt to be properly adjusted, so that it is possible to attain heat generation of the agent as a whole suitable for a body warmer. Limitation of the amount of water to 18 % by weight or more enables an exothermic reaction utilizing iron powder to properly proceed. On the other hand, limitation of the maximum amount thereof to 22 % by weight enables set up of a proper heat generation state upon opening of the bag for use, i.e., enables excellent initiation of the heat generation. This prevents the heat generating agent from being unevenly distributed by virtue of proper reduction in the pressure within the bag from the initiation of use of the body warmer and brings about a favorable thermal effect. The above-described prevention of shrinkage during the oxidative heat generation and improvement in the initiation of the heat generation enables the body warmer to be comfortably used in direct contact with or in close vicinity to the skin. Limitation of the thickness of the heat generating agent packed in the above-described flat bag to 2 mm or more contributes to the set up of a heat generation state or temperature distrubution favorable for warming the human body or the like, while limitation of the maximum thickness thereof to 5 mm or less restricts the load per unit area of the agent mainly composed of iron powder to thereby aid the prevention of uneven distribution of the agent. The above described characteristic features of the present invention enables the heat generating agent mainly composed of iron powder to be maintained in a flat and homogeneous state and makes the agent less susceptible to the formation of agglomerations, so that it is possible to provide safe useful and stable warming of the human body or other object in a self-adhesive form. The term "salt" used herein means common salt, i.e. sodium chloride, which is inexpensive and generally regarded as being safe. Embodiments of the above described disposable body warmer according to the present invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a partially cutaway plan view of a disposable body warmer according to the present invention; Figure 2 is a partially cutaway bottom plan view of the disposable body warmer shown in Figure 1; Figure 3(a) is a plan view of a disposable body warmer according to the present invention having a slit on a release paper; and Figure 3(b) illustrates the manner of releasing said release paper of Figure 3(a). In a flat bag 1 preferably having one air-permeable surface 1a, the air permeability per unit time of the air-permeable surface is limited to a value less than of oxygen (the amount of oxygen in the air) necessary for oxidation of a heat generating agent 2 packed in the bag 1 in such a manner as will be described later to that the pressure within the bag is reduced by oxidative heat generation of the agent 2, and further a nontransferable self-adhesive layer 3(a) is attached as an adherent to the other surface of the flat bag. Then, the above-described heat generating agent 2 comprising, as is well-known, iron powder and reaction assistants incorporated therein is packed in a substantially uniform flat form having a thickness of 2 to 5 mm within the bag 1, and the periphery of the bag is sealed. In the resulting flat bag 1, for commercialization, release paper 4 is adhered to the self-adhesive layer 3(a) and the bag is put in a known air-impermeable packaging bag 5, whereupon hermetic sealing 6 of periphery of the packaging bag is conducted. The degree of the pressure reduction in the oxidative heat generation of the agent 2 in the bag 1 is properly selected taking into consideration the mass of the packed agent 2. It has been experimentally confirmed that use of the bag 1 having an air permeability of approximately 0.6 to 1.2 cc/cm²/min (5000 to 10000 sec/100 cc) (JIS P8117) enables a proper negative pressure state to be set up. Further, as described above, a lowering in the water content to 22% by weight or less from that of a usual body warmer, i.e. 24 to 25% by weight, enables the bag 1 to be always compression-flattened at atmospheric pressure under conditions of initiation of the heat generation of the agent from an early stage of the heat generation, so that the movement or uneven distribution of the agent 2 in the bag can be effectively prevented. It is apparent that the above-described air permeability is much smaller than that of the bag used in the ordinary body warmer, i.e. 600 to 2000 cc/cm²/min (3 to 10 sec/100 cc). The heat generating agent 2 is a known one comprising iron powder as a main ingredient and, incorporated therein, water, a water-retaining material (charcoal, vermiculite or the like), an oxidation promoter such as activated carbon, and salt. More particularly, the agent 2 comprises about 55 to 65% by weight of iron powder, 18 to 22 % by weight of water, 9 to 11% by weight of a water-retaining agent, 3.5 to 4.5 % by weight of activated carbon, and about 4.5 to 6 % by weight of salt, and the temperature of heat generation accompanying oxidation is adjusted in such a manner that the maximum temperature is 65°C, preferably 62 to 63 °C, and the average temperature is 50 to 55°C. In the above-described mixing, as described above, the amount of water is smaller than that of the ordinary body warmer, while the amount of the water-retaining agent is slightly larger than that of the ordinary body warmer, i.e., 7 to 8 % by weight. Although the flat bag 1 may have any size, it is generally prepared so as to have an area of 10×5 cm or more and 20×15 cm or less taking into consideration the convenience in use. It is preferred that the bag 1 be well compatible with the human body or underwear. Examples of the flat bag include flexible thermoplastic sheets and films of polyurethane, polypropylene and polyethylene, and plastic and rubber materials prepared by modification thereof, and non-woven fabric may also used. The air permeability of the air-permeable surface 1a of the bag 1 is restricted to the above value by a method wherein a sheet or film having interconnected micropores is used as the above-described sheet or film and subjected to a suitable heat fusion treatment for restriction of the permeability. For example, a properly heated hot-fusing agent is homogeneously dispersed in or applied all over the above-described sheet or film having uniform interconnected pores having a diameter of 1 to 50 µm to restrict the air permeability. Alternatively, it is also possible to properly restrict the air permeability and, at the same time, to obtain a flexible air-permeable surface 1a through lamination of a resin film having interconnected micropores on a known non-woven fabric. The surface on which the nontransferable self-adhesive layer 3(a) is provided may be essentially impermeable to air because air permeation is hindered by the layer 3 itself. However, in order to ensure the flexibility, the above-described flexible sheet or nonwoven fabric is used as the material, and the self-adhesive layer 3(a) is attached thereto. The nontransferable self-adhesive layer 3(a) is one prepared by using am organic solvent type or water-base rubber, acrylic or vinyl acetate self-afhesive and introducing a reactive functional group thereinto to enhance the internal cohesive force. For example, an acrylic monomer having 1 to 10 % by weight of functional monomer introduced thereinto may be used as the nontransferable self-adhesive layer. A compound represented by the following general formula ( I ) is added as the above-described functional monomer in an amount of 1 to 4 % by weight: wherein R₁ is a lower alkyl group having 1 to 4 carbon atoms and R₂ is hydrogen atom or a methylol group. Alternatively, a compound represented by the following general formula (II) may be added in an amount of 6 to 10 % by weight and an acid catalyst may be then added: wherein R₁ is a hydrogen atom or methyl group, R₂ is a hydrogen atom, an alkyl group having 1 to 6 carbon atoms or an alkyl group and R₃ is an alkyl group having 1 to 18 carbon atoms. Further, 1 to 8 % by weight of a functional monomer represented by the following general formula (III) may be added, and 1 to 5 % by weight (in terms of outer percentage) of a water-soluble or dispersive epoxy compound may be then added. All of these nontransferable self-adhesives are known. wherein R₁ is a hydrogen atom or methyl group and R₂ and R₃ are each a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. In the disposable body warmer of the present invention wherein, as described above, the pressure within a flat bag 1 is reduced by oxidative heat generation of a heat generating agent 2, it is preferred that, after opening an air-impermeable packaging bag 5 to take out the flat bag 1 hermetically sealed therein, the flat bag be allowed to stand in the air for a short period of time to initiate the oxidative heat generation before application. As soon as the flat bag is allowed to stand in the air, the oxidative heat generation begins and the pressure wthin the bag 1 is properly reduced from the initiation of the heat generation because, as described above, the water content is small, thereby enabling properly preventing the agent 2 from being moved or unevenly distributed. 15 sec to several min, particularly about 20 sec to 1 min is sufficient as a time for allowing the flat bag to stand in the air. This period of time constitutes no hindrance to the application of the body warmer when a time including one consumed for removing release paper 4 adhered to the self-adhesive layer 3 is taken into consideration. Specific Preparation Examples according to the present invention will now be described. Preparation Example 1 35 g of a heat generating agent 2 comprising a mixture of 60 % by weight of iron powder with 20 % by weight of water, 5.5 % by weight of wood flour, 5 % by weight of vermiculite, 4.5 % by weight of activated carbon and 5 % by weight of salt was packed in a 2 to 5 mm-thick flat from into a flat bag 1 having a size of 13.5 cm x 10 cm. One surface of the bag 1 was used as an air-permeable surface 1a, and 30 to 40g/cm² of a nylon spun bond was hot-fused with a heated roll to a 70 µm-thick polyethylene sheet having interconnected micropores through 30 µm-thick porus polyethelene modified so as to enable low temperature adhesion, thus restricting the air permeability to about .75cc/cm²/min (8000 sec/100 cc). Meanwhile, a nontransferable self-adhesive layer 3(a) comprising a resin emulsion prepared by mixing 98 parts by weight of an acrylic monomer with 2 parts by weight of a functional monomer was formed on the other surface of the bag 1, and release paper 4 was adhered thereto. The resultant body warmer was put in an air-impermeable polyethylene packaging bag 5 having a size of 12.5×17 cm and hermetically sealed, thereby preparing a product. Preparation Example 2 A body warmer was prepared in the same manner as that of Preparation Example 1, except that a resin film having an air permeability restricted to about 1.0 cc/cm²/min (6000 sec/100 cc) under atmospheric pressure was laminated on a nonwoven fabric to form an air-permeable surface of a flat bag for a heat generating agent, and the body warmer thus prepared was put in an air-impermeable packaging bag to prepare a product. Each product prepared in the above Preparation Examples was unsealed, and each body warmer was adhered to underwear worn on the human body to examine the state of heat generation on 10 samples for each product. The results are shown in the following table. Max. temp. Average. temp. Duration Product of Prep. Ex. 1 55 - 58 °C 48 - 52 °C 18 - 20 hr Product of Prep. Ex 2 60 - 63 °C 51 - 53 °C 14 - 16 hr It has been confirmed that all samples exhibit favorable heat generation as a disposable body warmer and can be stably applied without causing uneven distribution of the agent in the bag during use. It is a matter of course that staining of the underwear by the adhesive scarcely occured when each sample was removed from the underwear after application. Preparation Example 3 A body warmer was prepared in the same manner as that of Preparation Example 1, except that a heat generating agent 2 comprising a mixture of 58 % by weight of iron powder with 21 % by weight of water, 5 % by weight of vermiculity, 6 % by weight of wood flour, 5 % by weight of activated carbon and 5 % by weight of salt was used, and the body warmer thus prepared was put in on air-impermeable packaging bag to prepare a product. This body warmer is one used in direct contact with the skin of the human body. The state of heat generation was examined for 10 samples of the body warmer. As result, it has been found that the average temperature and the duration were 38 to 41°C and 20 to 24 hr, respectively. Preparation Example 4 A body warmer was prepared in the same manner as that of Preparation Example 1, except that a release paper 4 (4) was separated by a slit at the middle portion, and the adhesive surface 3 was having a non-adhesive portion 3b under said slit which was separating the self-adhesive layer 3a (3a) to easily release the release paper 4. Each product prepared in the above Preparation Example 4 was tested in its adhesion ability through changing area proportion of non-adhesive portion 3b. The results has been that when the area proportion of non-adhesive portion 3b was less than about 30 %, the adhesion ability of the product was sufficient. When the non-adhesive portion 3b was made just the center part of the adhesive surface 3, some of the products having 40 % non-adhesive portion had enough adhesion ability. As is apparent from the foregoing description, the disposable body warmer according to the present invention can be properly applied in a self-adhesive system, hardly causes uneven distribution of the heat generating agent even when it is applied to the human body or underwear in a vertical or inclined state, surely exhibits a thermal effect through stable and substantially even temperature distribution, can be properly attached to any site of the human body or the like without use of any special attaching means, can be used with comfortableness because it can prevent the heat generating agent from being agglomerated and can smoothly achieve useful and simple use as opposed to the conventional disposable body warmer, which renders the present invention very useful from the industrial viewpoint.

Claims: A disposable body warmer comprising a flat bag (1) having an air-permeable first surface and containing a mixture of iron powder as a heat-generating agent (2), a water-retaining agent, water, an oxidation promoter and sodium chloride, said mixture being packed in flat form in the bag, characterized in that the air permeability is in the range 0.6 to 1.2 cc/cm²/min thereby to reduce the pressure in the bag accompanying oxydative heat generation of said heat-generating agent to maintain the bag substantially flat, in that the mixture contains 18 to 22% by weight of water and 9 to 11% by weight of a water-retaining agent and has a thickness of 2 to 5 mm in said bag, and in that a non-transferable self-adhesive layer (3a) is provided on the surface of the bag opposite said first surface for attachment of the flat bag to the user. A disposable body warmer as claimed in claim 1, wherein said self-adhesive layer is covered by a release sheet (4) and wherein the flat bag is contained in a hermetically sealed air-impermeable outer bag (5) for storage purposes until required for use. A disposable body warmer according to claim 1, wherein the air permeability of the air-permeable surface of said flat bag for containing said heat generating agent is restricted by subjecting a sheet having interconnected micropores to a suitable hot-fusion treatment. A disposable body warmer according to claim 3, wherein said sheet having interconnected micropores is a thermoplastic sheet or film of polyurethane, polypropylene or polyethylene, or a plastic or rubber material prepared by the modification thereof. A disposable body warmer according to claim 1, wherein the air permeability of the air-permeable surface of said flat bag for containing said heat generating agent is restricted by laminating a resin film having air-permeable pores on a nonwoven fabric. A disposable body warmer according to any one of the preceding claims, wherein said non-transferable self-adhesive has internal cohesive force enhanced by introducing a reactive functional group into an organic solvent type or water-base rubber, acrylic or vinylacetate self-adhesive. A disposable body warmer according to any one of the preceding claims, wherein said non-transferable self-adhesive layer is interrupted by a non-adhesive portion. A disposable body warmer according to claim 7, wherein said non-adhesive portion occupies less than 30% of the area of said surface opposite the first surface of said flat bag.

Inventors: USUI, AKIO
Applicants: MYCOAL WARMERS COMPANY LIMITED
Application year: 1989
Main classification: A61F7
IPC codes: A61F7, F24J1