Heat-generating composition and method for manufacturing a heat-generating element using the same

Abstract

To provide an exothermic composition that enables excellent physical properties required at the time of coating to be retained thereafter for a long time.SOLUTION: An exothermic composition comprises powder of oxidizable metal, powder of carbon material, powder of porous substance excluding the oxidizable metal and the carbon material, a thickener, and water. The content of the porous substance is 0.7 mass% or more and 5.0 mass% or less. The content of the water is 40 mass% or more and 70 mass% or less. The porous substance preferably contains silicon-containing inorganic compound. There is also provided a method for producing an exothermic body including the step for applying a coating of the exothermic composition to a substrate.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a heat-generating composition and a method for producing a heat-generating element using the same. [Background technology]

[0002] Various technologies have been proposed relating to heat-generating compositions and heating elements that utilize the heat generated by the oxidation reaction between oxygen in the air and an oxidizable metal. The present applicant previously proposed a method for producing a heating element in which an oxidizable metal-containing coating solution is prepared by charging and mixing a thickener solution, oxidizable metal particles, and an aqueous dispersion of a carbon component into a blending tank, which is a preparation tank, and the coating solution is supplied to a coating means via a supply tank, which is a relay tank capable of temporarily storing the coating solution (Patent Document 1). The method described in Patent Document 1 makes it possible to efficiently produce an oxidizable metal-containing coating material, which is an intermediate product for producing a heating element.

[0003] Patent Document 2 discloses an aqueous coating composition containing 8 to 30 parts by weight of a porous material and 2 to 4 parts by weight of a synthetic resin per 100 parts by weight of an aqueous solvent, to which 0.002 to 0.05% of the total amount of cellulose nanofibers has been added, with the aim of suppressing sedimentation and aggregation of the porous material. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-100470 [Patent Document 2] Japanese Patent Application Publication No. 2019-167497 Summary of the Invention [Problem to be solved by the invention]

[0005] When preparing a coating material as in the technique described in Patent Document 1, the coating material may be held in a tank for a long period of time before actually applying it to a substrate. During this process, stirring is performed to maintain the dispersion of the materials in the coating material. However, the inventors' investigations have revealed that stirring reduces the viscosity of the coating material over time and irreversibly causes water separation of the solids. Furthermore, the inventors' investigations have also revealed that a coating material that has experienced this phenomenon, even if it is stirred again, will not have properties suitable for coating. A coating material that has experienced a decrease in viscosity or water separation will have solids precipitated, which may cause problems such as clogging during coating or adversely affect the quality of the resulting heating element. In these respects, the technique described in Patent Document 1 leaves room for improvement. Furthermore, the technique described in Patent Document 2 does not address any of these issues.

[0006] Therefore, the present invention relates to a heat-generating composition that can maintain the good physical properties required during coating for a long period of time, and a method for producing a heat-generating element using the same. [Means for solving the problem]

[0007] The present invention relates to an exothermic composition. The heat-generating composition preferably contains a powder of an oxidizable metal, a powder of a carbon material, a powder of a porous substance other than the oxidizable metal and the carbon material, a thickener, and water. The heat-generating composition preferably contains the porous material in an amount of 0.7% by mass or more and 5% by mass or less relative to the total mass of the heat-generating composition. The heat-generating composition preferably contains 40% by mass or more and 70% by mass or less of the water relative to the total mass of the heat-generating composition.

[0008] The present invention also relates to a method for producing a heat generating element, which comprises a step of applying the heat generating composition to a substrate. [Effects of the Invention]

[0009] According to the present invention, there is provided a heat-generating composition that can maintain the good physical properties required during coating for a long period of time. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will be described below based on preferred embodiments thereof. The heat-generating composition is capable of generating heat by utilizing the heat generated by the oxidation reaction between an oxidizable metal and oxygen in the air, and is typically used in combination with an electrolyte as a constituent material of the heat-generating element provided in heating devices such as disposable hand warmers. The heat-generating composition and the heating device comprising a heat-generating element manufactured using the same are applied to various articles, or to objects to be heated such as the human body or clothing, and are suitably used for warming or keeping the objects to be heated warm. When the object to be heated is the human body, examples of the application areas include the shoulders, neck, face, eyes, lower back, elbows, knees, thighs, lower legs, abdomen, lower abdomen, hands, soles of the feet, etc.

[0011] The heat-generating composition of the present invention is suitably used as a coating material for applying to a substrate in the manufacture of a heat-generating element. The heat-generating composition preferably contains the following materials (1) to (5). Heat-generating compositions containing these materials are typically mixtures having paste-like or slurry-like fluidity at 1 atmosphere and 20°C. (1) Oxidizable metal powder (2) Carbon material powder (3) Powders of porous materials excluding oxidizable metals and carbon materials (4) Thickener (5)Water

[0012] One of the features of the exothermic composition of the present invention is that it contains a powder of a porous material. In this specification, the term "porous material" means a porous material excluding oxidizable metals and carbon materials, unless otherwise specified. It has been unexpectedly found that the inclusion of such a porous substance prevents syneresis of water from the solid components of the exothermic composition, even during storage or stirring after preparation, and allows the composition to maintain a uniformly dispersed state for a long period of time. It has also been found that even if the solid components of the exothermic composition settle over time, the uniformly dispersed state of the composition can be easily and reversibly restored by a simple method such as stirring.

[0013] Although the reason why syneresis of water from the solid content of heat-generating compositions occurs irreversibly in the prior art is not clear, it is thought that the thickening effect of the thickener is not easily exerted when the thickener is adsorbed inside the carbon material, and the viscosity and material dispersibility required for coating the heat-generating composition are not maintained. This is thought to be likely to occur when a polysaccharide such as xanthan gum is used as the thickener and activated carbon is used as the carbon material. On the other hand, it is not clear why the porous material prevents water separation from the solid components, as in the case of the heat-generating composition of the present invention, and why the heat-generating composition can maintain a uniformly dispersed state for a long period of time. However, it is thought that the presence of the porous material can reduce the interaction between the thickener and the carbon material described above, and that, unlike carbon materials, the molecular structure of the thickener can be present on the surface of the porous material in a three-dimensionally entangled state, allowing the thickening effect of the thickener to be exerted, and as a result, a viscosity sufficient to maintain the heat-generating composition in a uniformly dispersed state can be maintained for a long period of time.

[0014] The powder of the porous material that constitutes the heat-generating composition can be one that has the function of retaining moisture within the particles, and is preferably an aggregate of porous inorganic compound particles. Specific examples of the porous material include silicon-containing inorganic compounds such as zeolite, silica, vermiculite, perlite, and calcium silicate, which may be used alone or in combination. The porous material may be anhydrous or hydrated. The pores formed in the porous material may be open-cell, closed-cell, or a combination thereof.

[0015] When calcium silicate is used as the porous material, examples of calcium silicate include gyrolite-based compounds, wollastonite-based compounds, tobermorite-based compounds, and calcium silicate hydrate-based compounds, which can be used alone or in combination of two or more.

[0016] In particular, the gyrolite-based compounds include gyrolite (Ca 16 (SiO 20 )3(OH)8·14H2O), truscotite (Ca 14 (SiO 20 )(Si 16 O 38 )8·2H2O), and Z phase (Ca(Si2O5)·2H2O). Wollastonite-based compounds include necoite (Ca3(SiO 15 )·8H2O), okenite (Ca3(SiO 15 )·6H2O), xonotlite (Ca6(SiO 17 )(OH)2), foshagite (Ca4(Si3O9)(OH)2), and hillebrandite (Ca2(SiO3)(OH)2). Tobermorite-based compounds include 14Å tobermorite (Ca5(SiO 18 H2) 8H2O), 11Å tobermorite (Ca5(SiO 18 H2) 4H2O), and 9Å tobermorite (Ca5(SiO 18 H2)), and quasicrystalline calcium silicate (with a Ca / Si molar ratio of 0.8 to 2.0). Examples of calcium silicate hydrate compounds include tricalcium silicate hydrate (Ca6(Si2O7)(OH)6) and α-dicalcium silicate hydrate (Ca2(SiO4H)(OH)). The calcium silicate may be a commercially available product, such as Fluorite R (registered trademark), which is a gyrolite-based compound.

[0017] From the viewpoint of making it easier to maintain the dispersion state of the composition without inhibiting heat generation when used as a heat generating element and improving handleability, the porous substance preferably contains the silicon-containing inorganic compound described above, and more preferably contains calcium silicate. When the porous material contains a silicon-containing inorganic compound, the content of the silicon-containing inorganic compound in the porous material is preferably 80 mass% or more, more preferably 90 mass% or more, and even more preferably 100 mass%, relative to the mass of the entire heat-generating composition, from the viewpoints of more easily maintaining the dispersion state of the composition, ensuring the fluidity of the heat-generating composition, and improving coatability and handleability.

[0018] The content of the porous material in the heat-generating composition is preferably 0.7% by mass or more, more preferably 0.9% by mass or more, even more preferably 1.1% by mass or more, and is preferably 5% by mass or less, more preferably 4% by mass or less, even more preferably 2.5% by mass or less, based on the mass of the entire heat-generating composition. By keeping the content within such a range, the flowability of the heat-generating composition when applied to an object can be maintained, improving handleability, while maintaining good physical properties required during application, such as uniform dischargeability, uniform application ability, and uniform dispersibility of materials, for a long period of time.

[0019] The pore volume of the porous substance is preferably 1 mL / g or more, more preferably 3 mL / g or more, even more preferably 5 mL / g or more, and preferably 25 mL / g or less, more preferably 20 mL / g or less, even more preferably 10 mL / g or less, in the pore diameter range of 0.001 μm or more and 40 μm or less. Since the pore volume is roughly correlated with the degree of water retention of the porous substance, by having the pore volume in this range, the fluidity of the exothermic composition can be maintained in a state suitable for coating, and good physical properties such as handleability and coatability required during coating can be maintained for a long period of time.

[0020] The pore volume of the porous substance can be measured in accordance with the mercury intrusion method described in JIS R1655:2003. Specifically, 0.02 g to 0.1 g of powder of the porous material to be measured was used as a measurement sample, and the measurement cell containing the measurement sample was set in a mercury porosimeter (Autopore IV9500, manufactured by Micromeritics). The mercury injection pressure P was increased within a predetermined range, and the cumulative pore volume V (cm 3 Next, the log differential pore volume (dV / d(log 10 D);cm 3 / g) on the vertical axis to obtain the pore volume distribution. That is, the pore volume distribution is obtained by plotting the converted pore diameter D on the horizontal axis and the pore volume obtained by differentiating the cumulative pore volume V with the logarithm of the converted pore diameter D on the vertical axis. D=4γcosθ / P (A) (γ: surface tension of mercury, θ: contact angle, P: mercury injection pressure)

[0021] The measurement is performed under an environment of 22°C and 65% RH. The surface tension γ of mercury is 480 dyn / cm, the contact angle θ is 140°, and the mercury injection pressure P is in the range of 0 psia (0 MPa) to 60,000 psia (413.685 MPa). Based on the distribution curve of the converted pore diameter D obtained under these measurement conditions, the cumulative total value of the converted pore diameters D in the range of 0.001 μm to 40 μm is defined as the pore volume (mL / g) in the present invention.

[0022] The pore diameter D1 of the pores of the particles constituting the powder of the porous substance is preferably 0.01 μm or more, more preferably 0.05 μm or more, even more preferably 0.15 μm or more, and is preferably 5 μm or less, more preferably 1 μm or less, even more preferably 0.5 μm or less. When the pore diameter D1 of the porous substance is in this range, it is possible to prevent the components of the thickener from being adsorbed inside the porous substance and suppress a decrease in the viscosity of the heat-generating composition, while maintaining the fluidity of the heat-generating composition in a state suitable for coating, and maintaining good physical properties required during coating, such as ease of handling and coatability, for a long period of time. The pore diameter D1 of the porous substance described above can be defined as the median pore diameter D1 (μm) in the distribution curve of the converted pore diameter D obtained by the mercury intrusion method described above.

[0023] The bulk density of the porous substance is preferably 0.05 g / mL or more, more preferably 0.06 g / mL or more, even more preferably 0.07 g / mL or more, and is preferably 0.3 g / L or less, more preferably 0.2 g / mL or less, even more preferably 0.15 g / mL or less. By keeping the bulk density within these ranges, the fluidity of the exothermic composition can be maintained in a state suitable for coating, and good physical properties such as handleability and coatability required during coating can be maintained for a long period of time. The bulk density of the porous material can be measured in accordance with JIS Z2504.

[0024] The particle size of the particles constituting the powder of the porous substance is preferably 1 μm or more, more preferably 10 μm or more, and is preferably 200 μm or less, more preferably 100 μm or less. By keeping the particle size within this range, syneresis of the solid content is prevented, and the heat-generating composition can be easily maintained in a uniformly dispersed state. The particle size described above can be the volume-based median diameter measured by a laser diffraction / scattering method using a laser diffraction / scattering particle size distribution analyzer (manufactured by Horiba, Ltd., model number: LA-950V2). The measurement conditions are as follows: a standard wet circulation cell is used, the refractive index of the iron powder is 3.5 for the real part and 3.8i for the imaginary part, the refractive index of water is 1.33 using the dispersion medium, the circulation speed is 15, and the stirring is 5.

[0025] Other constituent materials of the exothermic composition are described below. The oxidizable metal powder generates heat through an oxidation reaction with oxygen in the air after the heating element is formed, and has the function of being able to impart heat to an object to be heated when used as a heating element. Examples of the oxidizable metal powder constituting the heat-generating composition include aggregates of metal particles such as iron, aluminum, zinc, manganese, magnesium, and calcium. These can be used alone or in combination of two or more. Among these, metallic iron is preferably used from the viewpoints of ease of handling, safety, and production costs, that is, iron powder is preferably used. The iron powder may be, for example, one or more types selected from reduced iron powder and atomized iron powder.

[0026] The content of the oxidizable metal in the heat-generating composition is preferably 20% by mass or more, more preferably 30% by mass or more, even more preferably 35% by mass or more, and is preferably 50% by mass or less, more preferably 40% by mass or less, even more preferably 37% by mass or less, based on the total mass of the heat-generating composition. By keeping the content in this range, the heat generation value of the heat-generating composition can be increased, and the composition can exhibit fluidity and viscosity suitable for coating.

[0027] The particle size of the particles constituting the oxidizable metal powder is preferably 30 μm or more, more preferably 40 μm or more, and preferably 150 μm or less, more preferably 100 μm or less. By keeping the particle size within this range, unintended oxidation of the heat-generating composition can be suppressed, and the heat generation efficiency associated with oxidation of the heat-generating composition when used as a heat generating element can be improved. The particle size of the oxidizable metal can be measured by the same method as used to measure the particle size of the porous material described above.

[0028] The powder of the carbon material has the function of promoting the oxidation reaction after the formation of the heating element, and specifically, the powder can have one or more functions of an oxygen-retaining / supplying material for the oxidizable metal and a catalytic function. Examples of such carbon materials include coconut shell charcoal, charcoal powder, activated carbon such as bicarbonate, peat, and lignite, carbon black, acetylene black, and aggregates of particles of graphite, etc. These may be used alone or in combination of two or more. Among these, activated carbon powder is preferably used as the carbon material powder because it has a good balance between oxygen supply ability and catalytic ability.

[0029] The content of the carbon material in the heat-generating composition is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 4% by mass or more, relative to the mass of the entire heat-generating composition, and is preferably 9% by mass or less, more preferably 7% by mass or less, and even more preferably 5.90% by mass or less. By keeping the content in such a range, the oxidation reaction of the oxidizable metal is promoted to generate heat efficiently, and a sudden decrease in viscosity of the heat-generating composition is suppressed, allowing the composition to exhibit flowability and viscosity suitable for coating.

[0030] The carbonaceous material powder has a particle size of preferably 1 μm or more, more preferably 10 μm or more, and preferably 200 μm or less, more preferably 100 μm or less, in which case the catalytic activity of the oxidation reaction can be fully exerted and the particles can be prevented from settling. The particle size of the carbon material can be measured by the same method as that used to measure the particle size of the porous material described above.

[0031] The pore volume of the carbon material is preferably 0.5 mL / g or more, more preferably 0.7 mL / g or more, even more preferably 1 mL / g or more, and preferably 10 mL / g or less, more preferably 8 mL / g or less, even more preferably 5 mL / g or less, in the pore diameter range of 0.001 μm or more and 40 μm or less. By having the pore volume of the carbon material fall within this range, the oxidation reaction of the oxidizable metal is promoted, thereby efficiently generating heat, and the fluidity and viscosity of the exothermic composition can be maintained in a state suitable for coating, allowing the good physical properties required for coating, such as ease of handling and coatability, to be maintained for a long period of time.

[0032] The pore diameter D2 of the pores of the particles constituting the powder of the carbon material is preferably 0.1 μm or more, more preferably 0.5 μm or more, even more preferably 1 μm or more, and preferably 15 μm or less, more preferably 10 μm or less, even more preferably 5 μm or less. When the pore diameter D2 of the carbon material is in this range, the oxidizability of the oxidizable metal is improved, the temperature of the exothermic composition can be efficiently raised, and the fluidity of the exothermic composition can be maintained in a state suitable for coating, so that good physical properties such as handleability and coatability required during coating can be maintained for a long period of time. The pore volume and pore diameter D2 of the above-mentioned carbon material can be measured by the same methods as those used for the above-mentioned porous substance.

[0033] The exothermic composition contains a thickener to improve its suitability as a coating. Examples of thickeners include substances that increase the consistency in the presence of water or impart thixotropy, thereby maintaining or increasing the dispersibility of solids. Examples of such thickeners include organic acid salts such as stearates and sodium polyacrylates, polysaccharides derived from plants, seaweed or microorganisms, synthetic polymer compounds, inorganic thickeners, and the like.

[0034] Examples of polysaccharides include natural polysaccharides derived from plants, seaweed, or microorganisms, and synthetic polysaccharides. Examples of polysaccharides derived from plants include polysaccharides derived from plant seeds such as locust bean gum and guar gum; polysaccharides derived from tree sap such as gum arabic; polysaccharides derived from fruits such as pectin; and starch-based polysaccharides such as dextrin and starch. Examples of polysaccharides derived from seaweed include acidic polysaccharides such as carrageenan, agar, alginic acid and salts thereof. Examples of polysaccharides derived from microorganisms include acidic polysaccharides such as xanthan gum and gellan gum. Examples of synthetic polysaccharides include carboxymethyl cellulose, ethyl cellulose, hydroxyethyl cellulose, methyl cellulose, and hydroxypropyl cellulose. Examples of synthetic polymer compounds include polyvinyl alcohol, polyvinylpyrrolidone, polyethylene oxide, and polyacrylic acid polymers. Examples of inorganic thickeners include clay minerals such as smectite and bentonite.

[0035] Among these thickeners, it is preferable to use one or more of polysaccharides and synthetic polymer compounds, and it is more preferable to use one or more of natural polysaccharides and synthetic polysaccharides. By using such thickeners, sedimentation of the solid components constituting the heat-generating composition and syneresis are less likely to occur with a small amount of thickener, and the materials of the heat-generating composition can be stably dispersed. In addition, it is possible to develop thixotropy, which is useful as a coating material for manufacturing heat generating elements, by reducing viscosity during application to improve handleability and developing an appropriate viscosity after application to a substrate to improve retention in a predetermined position.

[0036] The content of the thickener in the heat-generating composition is preferably 0.02% by mass or more, more preferably 0.03% by mass or more, even more preferably 0.05% by mass or more, and is preferably 1% by mass or less, more preferably 0.8% by mass or more, even more preferably 0.6% by mass, based on the total mass of the heat-generating composition. By setting the content within such a range, the dispersibility of the materials in the heat-generating composition can be improved without syneresis of water from the solids, and fluidity suitable for coating can be achieved.

[0037] Water serves as a dispersion medium for the heat-generating composition, improving the fluidity and ease of handling when the heat-generating composition is applied to another substrate, and also serves to facilitate interaction between the oxidizable metal powder and the carbon material or the like that acts as a catalyst for the oxidation reaction after the heat-generating element is formed. As the water, any water commonly used in the art can be used without any particular limitations.

[0038] The water content in the heat-generating composition is preferably 40% by mass or more, more preferably 45% by mass or more, even more preferably 50% by mass or more, and is preferably 70% by mass or less, more preferably 65% by mass or less, even more preferably 60% by mass or less, based on the total mass of the heat-generating composition. By keeping the water content in this range, the fluidity of the heat-generating composition can be maintained in a state suitable for coating, syneresis of water from the solids does not occur, and good physical properties such as handleability and coatability of the heat-generating composition can be maintained for a long period of time.

[0039] The exothermic composition may be composed of the above-mentioned oxidizable metal powder, carbon material powder, porous substance powder, thickener, and water, and may be free of other materials. Alternatively, if necessary, it may further contain one or more other materials such as a pH adjuster or an electrolyte. From the viewpoints of improving the dispersibility of the paint components and preventing unintended oxidation of the oxidizable metal during storage of the paint, it is preferable that the exothermic composition of the present invention does not contain an electrolyte.

[0040] Examples of pH adjusters that can be used include weak acid salts and hydroxides of alkali metals or alkaline earth metals, and more preferably strong bases or salts of strong bases and weak acids. More specifically, potassium phosphates, sodium phosphates, etc. can be used. Preferred examples of pH adjusters include potassium hydroxide, potassium monophosphate, potassium diphosphate, potassium tripotassium phosphate, potassium pyrophosphate, potassium tripolyphosphate, potassium metaphosphate, and other potassium phosphate salts. These can be used alone or in combination of two or more. From the viewpoint of stability of the exothermic composition, the pH of the exothermic composition at 25° C. is preferably adjusted to 10.0 or higher, more preferably 10.8 or higher, for example, with the pH adjuster described above.

[0041] When an electrolyte is contained, examples of the electrolyte include one or more of salts of alkali metals or alkaline earth metals with phosphoric acid or sulfuric acid, and chlorides or hydroxides of alkali metals or alkaline earth metals. Of these, from the viewpoint of excellent chemical stability and production costs, it is preferable to use a salt of a strong acid and a strong base as the electrolyte, and it is more preferable to use one or more of sodium chloride and potassium chloride. The electrolyte may be used in the form of a solid such as a powder, or may be used in the form of a liquid dissolved or dispersed in a liquid medium such as water.

[0042] Regardless of whether or not the composition contains other materials, the viscosity of the heat-generating composition of the present invention is preferably 0.5 Pa·s or more, more preferably 1 Pa·s or more, even more preferably 3 Pa·s or more, and preferably 50 Pa·s or less, more preferably 10 Pa·s or less, and even more preferably 8 Pa·s or less. A viscosity within this range improves the dispersibility of materials in the heat-generating composition without syneresis of solids, while providing fluidity suitable for coating. The above-mentioned viscosity can be adjusted appropriately, for example, by adjusting the content of the constituent materials of the heat-generating composition. Viscosity measurements were performed at 20°C and a shear rate of 1.3 s -1 The viscosity can be measured using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd., model number: TVB-10M) under the conditions above.

[0043] The heat-generating composition described above is a dispersion liquid having a slurry or paste-like fluidity, and can be used as a coating material to form a heat-generating element by applying it to a substrate. In other words, the method for producing a heat-generating element of the present invention includes a step of applying the heat-generating composition described above to a substrate (a coating step).

[0044] Specifically, the above-mentioned materials are first mixed together simultaneously or in any order to prepare a heat-generating composition, which is a dispersion. A known mixing device can be used to prepare the heat-generating composition. Next, this heat-generating composition is continuously or intermittently applied directly to one surface of a substrate (first substrate). This allows for the formation of a heat-generating element in which the heat-generating composition is disposed adjacent to one surface of the substrate. Examples of coating devices that can be used include die coaters, roll coaters, bar coaters, and gravure coaters. In addition, if necessary, the above-mentioned electrolyte may be sprayed onto the applied heat-generating composition, and then a second substrate may be further laminated on the heat-generating composition. In this case, the resulting heat-generating element will have the heat-generating composition interposed between the two substrates.

[0045] The exothermic composition may be applied to a substrate immediately after it is prepared. Alternatively, depending on the production plan for the heat generating element, the operating status of the production equipment, etc., the process from preparation of the heat generating composition to application to the substrate may include a step (storage step) of storing the prepared heat generating composition in a container for a certain period of time. Storage modes include a mode in which the heat generating composition is stored for a certain period of time while being continuously or intermittently stirred (hereinafter, this is also referred to as the "stirring mode"), and a mode in which the composition is stored for a certain period of time in a static state without intentionally applying external force to the composition, such as without mixing or stirring (hereinafter, this is also referred to as the "static mode"). In either storage mode, non-heating conditions are preferred from the viewpoint of preventing changes in composition due to evaporation of water. In this specification, stirring means stirring the exothermic composition in which the materials are in a dispersed state, and preferably a peripheral speed lower than that employed in the preparation of the exothermic composition is employed.

[0046] When stirring is performed, it is preferable that the total stirring time be within a predetermined range, and then the stirred exothermic composition is applied to a substrate. Specifically, the total stirring time is preferably 5 hours or more, more preferably 6 hours or more, and preferably 24 hours or less, more preferably 20 hours or less. By using such a stirring time, the dispersion state and viscosity of the exothermic composition can be stably maintained without syneresis of water from the solids, and the excellent physical properties of the composition as a coating can be maintained for a long period of time. Furthermore, such an exothermic composition is advantageous in that it has physical properties that allow it to be applied to a substrate immediately after storage. As described above, the exothermic composition may be stirred continuously or intermittently multiple times, as long as the total stirring time is within the above-mentioned range.

[0047] In addition, in the case of a statically standing embodiment, it is preferable that the static standing time is within a predetermined range, and then the statically stood heat-generating composition is stirred, and the stirred heat-generating composition is applied to a substrate. Specifically, the above-mentioned standing time is preferably 5 hours or more, more preferably 6 hours or more, and preferably 48 hours or less, more preferably 24 hours or less. If the standing time is within this range, syneresis of water from the solids does not occur when the composition is stirred again, and the exothermic composition becomes uniformly dispersed, allowing the composition to quickly recover to good physical properties suitable for coating on a substrate.

[0048] The standing time means the continuous time from the preparation of the heat-generating composition until the first stirring is performed. For example, the time between the start of stirring at any time in the above-mentioned intermittent stirring mode and the end of the stirring performed immediately before that is excluded from the standing time in this specification.

[0049] From the same viewpoint, the total stirring time when stirring after standing is preferably 5 hours or more, more preferably 6 hours or more, and preferably 24 hours or less, regardless of whether the stirring is performed continuously or intermittently.

[0050] When the prepared heat-generating composition is stored before coating, the peripheral speed during stirring is preferably 0.1 m / s or more, more preferably 0.3 m / s or more, and preferably 2 m / s or less, more preferably 1.5 m / s or less. By using such stirring conditions, syneresis of water from the solids does not occur, and good physical properties as a coating material can be maintained for a long period of time. The peripheral speed during stirring may be constant throughout the entire stirring period, or may vary within the above-mentioned range.

[0051] When the prepared heat-generating composition is stored before coating, whether it is stirred or left to stand, the viscosity of the heat-generating composition after stirring is preferably in the same range as the above-mentioned range. It is also preferable that the viscosity of the heat-generating composition be satisfied when it is applied to a substrate. Such a viscosity prevents water separation of the solids, thereby exhibiting good physical properties as a coating material, and improving handling when applied to a substrate and coating stability such as uniformity of coating basis weight.

[0052] When the heat-generating composition is stored for a certain period of time after its preparation, the storage time from preparation of the heat-generating composition to application to a substrate, whether by stirring or by leaving to stand, is preferably 5 hours or more, more preferably 6 hours or more, and preferably 48 hours or less, more preferably 24 hours or less. Within this range, water does not synerase from the solids, and the composition can be reversibly restored to good physical properties suitable for application to a substrate.

[0053] In particular, the exothermic composition after stirring and then leaving to stand for a certain period of time preferably has a viscosity of 0.7 Pa s or more, more preferably 0.9 Pa s or more, even more preferably 1.1 Pa s or more, and preferably 5 Pa s or less, more preferably 3 Pa s or less, and even more preferably 2 Pa s or less. By having the viscosity within this range, the dispersibility of the materials in the exothermic composition is improved without syneresis of the solids, and the composition has a fluidity suitable for coating. The viscosity can be measured by the same method as the viscosity measurement method for the heat-generating composition described above.

[0054] Preferred examples of the substrates used in the production of heat generating elements include sheet materials, such as fiber sheets containing hydrophilic fibers, such as paper and nonwoven fabric. In this case, the coating process may involve, for example, coating one side of a long, strip-shaped substrate sheet that is transported in one direction with the heat generating composition. This increases the production efficiency of the heat generating element, and allows some of the moisture in the heat generating composition to be absorbed by the substrate sheet, making it easier to adjust the moisture content in the heat generating composition to a level that allows heat generation.

[0055] When a second substrate is used, a fiber sheet containing no water-absorbent polymer is preferably used as the first substrate, and a fiber sheet containing a water-absorbent polymer is preferably used as the second substrate, from the viewpoint of allowing a portion of the moisture in the heat-generating composition to be absorbed by the substrate sheet side, thereby more easily and appropriately adjusting the moisture content in the heat-generating composition. From the viewpoint of improving the production efficiency of the heat-generating element, both substrates are preferably in the form of a long strip.

[0056] The basis weight of the heat generating composition applied to the substrate is preferably 50 g / m 2 More preferably, 100 g / m 2 or more, and preferably 2000 g / m 2 or less, more preferably 1700 g / m 2 The following is the result. When the substrate is in the form of the above-mentioned fiber sheet, the basis weight thereof is preferably 10 g / m 2 More preferably, 20 g / m 2 or more, preferably 200 g / m 2 or less, more preferably 150 g / m 2 The following is the result.

[0057] The heating element thus obtained can be processed to a predetermined size and shape and then subjected to subsequent steps. One embodiment of the steps after the production of the heating element is to place the obtained heating element in a packaging material to produce a heating implement. The packaging material is a bag-shaped member made of two sheets, at least one of which is breathable, allowing oxygen to be smoothly supplied to the heating element, resulting in a heating device that can maintain stable heat generation for a long period of time. Examples of the sheet material that can be used to form the packaging material include a fiber sheet such as paper or nonwoven fabric, a porous resin film having through holes, or a laminate of a fiber sheet and a resin film.

[0058] Although the present invention has been described above based on the preferred embodiments, the present invention is not limited to the above embodiments. [Example]

[0059] The present invention will be described in more detail below with reference to examples, but the scope of the present invention is not limited to these examples.

[0060] [Examples 1 and 2, and Comparative Example 1] The oxidizable metal powder used was iron powder (RKH3, manufactured by DOWA IP Creation Co., Ltd., particle size: 45 μm), the carbon material powder used was activated carbon powder (Carborafine, manufactured by Osaka Gas Chemicals Co., Ltd., particle size: 31 μm, pore diameter D2: 3.3 μm, pore volume: 2.6 mL / g), and the porous material powder used was calcium silicate powder (Floorite R, manufactured by Tomita Pharmaceutical Co., Ltd., particle size: 47 μm, pore diameter D1: 0.18 μm, pore volume: 8.1 mL / g, bulk density: 0.1 g / mL). These materials were mixed with water, a thickener (xanthan gum), and a pH adjuster in the mass proportions shown in Table 1 below to prepare the desired heat-generating paste composition. The mixing conditions during preparation were continuous mixing for 35 minutes at a constant peripheral speed of 4.2 m / s. The theoretical solid content (percentage of solid mass relative to total mass) of the heat-generating compositions based on the mixing ratio of each material, and the viscosity of the heat-generating compositions immediately after preparation, measured by the method described above, are shown in Table 1. The pH of all heat-generating compositions was 10.0 or higher.

[0061] Comparative Examples 2 and 3 The target paste-like heat-generating composition was prepared under the same conditions as in Example 1, except that no porous substance powder was contained and iron powder, activated carbon, water, a thickener, and a pH adjuster were mixed in the mass ratios shown in Table 1 below. The theoretical solid content of the heat-generating compositions and the viscosity of the heat-generating compositions immediately after preparation are shown in the following Table 1. The pH of all the heat-generating compositions was 10.0 or higher.

[0062] [Evaluation of Stability of Heat-Generating Composition] The heat-generating compositions of the Examples and Comparative Examples were evaluated for stability immediately after preparation, and after stirring and storage, as follows. Specifically, the exothermic composition was placed in a container having a predetermined volume, and the actual solid content of the upper part of the container was compared with the theoretical solid content of the exothermic composition to evaluate its stability. The smaller the difference between the actual and theoretical values, the better the stability.

[0063] (1) Measurement of solid content immediately after preparation After preparing the heat-generating compositions of the Examples and Comparative Examples, the upper dispersion liquid was sampled and its solid content was measured. The solid content immediately after preparation can be calculated as the percentage of the mass of the solid content relative to the total mass of the sampled liquid, and the solid content can be obtained by conventional solid-liquid separation.

[0064] (2) Measurement of viscosity immediately after preparation After preparing the heat-generating compositions of the Examples and Comparative Examples, the upper dispersion liquid was sampled and its viscosity was measured by the method described above.

[0065] (3) Measurement of solid content and viscosity after stirring and standing After preparing the heat-generating compositions of the Examples and Comparative Examples, they were continuously stirred for 20 hours at a constant peripheral speed of 0.89 m / s. The stirred heat-generating compositions were separated and allowed to stand for 24 hours without stirring. After that, the upper dispersion (supernatant) of the left-standing heat-generating composition was separated, and its solid content and viscosity were measured by the methods described above. The smaller the difference between the results of this evaluation and the solid content immediately after preparation, the more uniformly dispersed the heat-generating composition is even after storage, and the longer it will maintain the good physical properties required for coating. The results are shown in Table 1 below.

[0066] (4) Evaluation of dispersion reversibility The exothermic composition obtained in the above-mentioned step (3) after stirring and standing was stirred again at a constant peripheral speed of 0.89 m / s, and the reversibility of the dispersion was evaluated visually according to the following criteria. The results are shown in Table 1 below.

[0067] <Evaluation criteria for reversibility> ◯: The solid matter that had settled to the bottom of the container was redispersed in the liquid without aggregation, and no settling of the solid matter was observed even over time, so the exothermic composition had reversible dispersion. ×: The sediment in the container remains settled even after re-stirring, or the sediment is stirred in an aggregated state, and the heat-generating composition is irreversibly dispersed.

[0068] As shown in Table 1, the solid content immediately after preparation was equal to the theoretical value for both the Examples and Comparative Examples, but after stirring for a predetermined time, the solid content of the heat-generating composition of the Comparative Example decreased significantly, and the dispersion became irreversible. In particular, the heat-generating composition of the Comparative Example experienced a decrease in solid content, expressed as "([theoretical solid content] - [solid content of the upper part of the heat-generating composition]) / [theoretical solid content] × 100" (%), of more than 70%, indicating significant settling of the solids and irreversible dispersion. Therefore, compared to the comparative examples, the exothermic compositions of the examples have high uniform dispersibility and maintain good physical properties required for coating on substrates, such as uniform dischargeability, uniform application property, and ease of handling, for a long period of time, even when stored after preparation, such as by stirring for a long period of time. Furthermore, even when the exothermic compositions of the examples have been stored for a long period of time, they can be restored to physical properties suitable for coating by re-stirring, without causing syneresis of water from the solids.

[0069] Regarding the above results, it is not clear why the effects of the present invention are achieved when the content of the porous material powder is only slightly increased compared to that of Comparative Example 1, as in Example 2, for example. However, since the volume per unit mass is large due to the relatively small bulk density of the porous material powder, it is thought that the volume proportion of the porous material powder in the heat-generating composition becomes very large, thereby inhibiting the interaction between the carbon material and the thickener.

[0070] [Table 1]

Claims

1. A heat-generating composition comprising a powder of an oxidizable metal, a powder of a carbon material, a powder of a porous substance excluding the oxidizable metal and the carbon material, a thickener, and water, the carbon material comprises activated carbon; the porous material comprises calcium silicate; the thickening agent comprises xanthan gum; The heat-generating composition contains the porous material in an amount of 0.7% by mass or more and 5% by mass or less relative to the total mass of the heat-generating composition, The heat-generating composition contains 40% by mass or more and 70% by mass or less of water relative to the total mass of the heat-generating composition, The heat-generating composition contains the carbon material in an amount of 1% by mass or more and 9% by mass or less relative to the total mass of the heat-generating composition, A heat-generating composition comprising the thickener in an amount of 0.02% by mass or more and 1% by mass or less relative to the total mass of the heat-generating composition.

2. 20°C and shear rate 1.3 s －１ 2. The heat-generating composition according to claim 1, wherein the composition has a viscosity of 0.5 Pa·s or more and 50 Pa·s or less at 1000 kJ / min.

3. 3. The heat-generating composition according to claim 1, wherein the porous material has a pore volume of 1 mL / g or more and 25 mL / g or less.

4. The heat-generating composition according to any one of claims 1 to 3, wherein the porous substance has a bulk density of 0.05 g / mL or more and 0.30 g / mL or less.

5. A method for producing a heat generating element, comprising the step of applying the heat generating composition according to any one of claims 1 to 4 to a substrate.

6. The method according to claim 5, wherein the heat-generating composition is stirred for a total stirring time of 5 hours or more and 24 hours or less, and thereafter the stirred heat-generating composition is applied to the substrate.

7. The heat-generating composition is allowed to stand for 5 hours to 48 hours, and then The exothermic composition is stirred, and then The method according to claim 5 or 6, wherein the heat-generating composition is stirred and applied to the substrate.

8. The exothermic composition was stirred at 20°C and a shear rate of 1.3 s －１ 8. The method according to claim 6, wherein the viscosity of the solvent used is 0.5 Pa·s or more and 50 Pa·s or less.

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