JP2019112710A - Manufacturing method of iron powder for exothermic composition - Google Patents

Abstract

To provide a manufacturing method of an iron powder for exothermic composition capable of manufacturing the iron powder for exothermic composition excellent in exothermic property and handling property at good efficiency.SOLUTION: There is provided a manufacturing method of an iron powder for exothermic composition having bulk density of 0.3 g/cmto 1.5 g/cm, having a reduction process for reducing iron oxide to obtain reduced iron, and a process for pulverizing the reduced iron. The reduction process reduces the iron oxide by changing inside of a heating furnace containing no sulfur gas in ambient air or inert gas atmosphere into reductive gas atmosphere by introducing iron oxide and a solid reductant with volatile component content of 10 mass% or more into the heating furnace, and heat treating the same under a condition that atmosphere temperature in the heating furnace is 900°C to 1000°C.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing iron powder for a heat generating composition.

  Conventionally, a heating tool in which a heating element is enclosed in an air-permeable packaging material is widely used as a disposable body warmer to impart heat to the human body. Such a heating element generates heat using the reaction heat generated by the oxidation reaction of iron powder contained in it, but the maintenance of heat generation temperature and heat generation is not sufficient only with iron powder and atmospheric oxygen alone Thus, in general, the heating element further contains, in addition to iron powder, a reaction aid such as sodium chloride and water, and a water retention agent such as activated carbon and a water absorbing polymer, which further supports these substances. In Patent Document 1, a heat generating element is produced through the step of applying a heat generating composition having such a composition and having been made into an ink-like or cream-like thickening onto a film-like or sheet-like substrate. It is described.

In products using a heating element such as disposable thermal insulation, the temperature rising rate at the beginning of heat generation is high, and it is required to heat up quickly after opening, and after reaching a certain temperature, heat is generated stably for a long time The constant temperature condition is required to be continued. Since the heat generation characteristics of the heating element are largely dependent on the characteristics of the iron powder itself, it is said that high activity iron powder may be used for such a demand. Patent Document 2 describes that, in order to improve the oxidation reaction efficiency of iron powder in a heating element, mixing of an active carbon with an appropriate amount of water is mixed with the iron powder. Further, paragraph [0020] of Patent Document 2 describes that it is preferable to set the apparent density of iron powder in the range of 1.5 to 3.5 Mg / m ³ , and the lower limit value of such a preferable range is 1. The reason why ⁵ Mg / m ^{3 is used is} considered that if the apparent density of the iron powder is lower than this, the bulk increases and the downsizing of the body can not be achieved.

  In Patent Document 3, a low density reduced iron powder having an apparent density of 0.5 to 1.5 g / cc is used as a sintered component for a complex shape requiring high formability, and a friction material which is formed with a low pressure. It is stated that it is useful for molding applications where compressibility and moldability are required, such as for use in sintered parts. Further, in Patent Document 3, this low density reduced iron powder is manufactured through a process of reducing reduced iron ore fine powder in a temperature range of 950 to 1150 ° C. to obtain reduced iron, and crushing the reduced iron. Is described. In addition, what is described in patent document 3 regarding the iron powder is only for a molded article use, and nothing is described for the heat generating composition use.

  In Patent Document 4, iron ore is reduced at a temperature range of 750 to 1200 ° C. as a method of producing iron powder having a fibrous structure and suitable for producing a friction lining such as a brake or a joint used for a power carrier. There is described a method of maintaining the concentration of the gaseous sulfur compound to carbon monoxide in the reducing gas atmosphere in a predetermined range when reducing in a reactive gas atmosphere, and thus, the gaseous sulfur compound As a method for keeping the concentration of H 2 O 3 constant, a method of externally introducing a gaseous sulfur compound and a method of adding a solid sulfur compound to iron oxide to be reduced are described. Patent Document 5 also describes, as another method for producing an iron powder having a fibrous structure as in the iron powder described in Patent Document 4, 800 to 1000 of fine iron oxide particles obtained by spray roasting from pickling waste liquid. In the temperature range of ° C., one is described which has the step of reduction in a carbon monoxide atmosphere which is preferably free of sulfur dioxide.

JP-A-9-75388 JP 2001-254101 A Japanese Patent Application Laid-Open No. 52-24147 Japanese Patent Application Laid-Open No. 52-120261 Japanese Patent Application Laid-Open No. 51-52973

  The iron powder for heat generating composition is also required to be excellent in handleability as well as excellent in heat generating characteristics. When the iron powder for heat generating composition is excellent in handleability, when the activated carbon, water, etc. is added thereto to make a paint having fluidity that can be applied, the storage stability of the paint is excellent, and the heat generating composition Since problems such as sedimentation of iron powder for material use, increase in viscosity of the paint and gelation are unlikely to occur, the heating element can be efficiently produced. However, iron powder and heat generating composition for heat generating composition compatible with high levels of heat generating property and handling property have not been provided yet.

  Therefore, an object of the present invention relates to providing a method for producing an iron powder for a heat generating composition which can efficiently produce an iron powder for a heat generating composition which is excellent in heat generation characteristics and handling properties.

The present invention is a method for producing an iron powder for a heat generating composition having a bulk density of 0.3 g / cm ³ or more and 1.5 g / cm ³ or less, wherein the inside does not contain sulfur gas, and an atmosphere or an inert gas atmosphere Iron oxide and a solid reducing agent having a volatile component content of 10% by mass or more are introduced into the inside of the heating furnace, and heat treatment is performed under the condition that the internal atmosphere temperature becomes 900.degree. C. or more and 1000.degree. The method is a method for producing an iron powder for a heat generating composition, comprising the steps of: reducing the inside of the crucible to a reducing gas atmosphere; reducing the iron oxide to obtain reduced iron; and grinding the reduced iron.

  According to the present invention, it is possible to efficiently produce an iron powder for a heat generating composition which is excellent in heat generating properties and handling properties.

FIG. 1 is a schematic view of an embodiment of a heating tool using the iron powder for a heating composition manufactured by the manufacturing method of the present invention, and FIG. 1 (a) is a plan view of the heating tool; (B) is an I-I line sectional view of Drawing 1 (a), and Drawing 1 (c) is a mimetic diagram of a section which expands and shows a heating element in a heating tool shown in Drawing 1 (b). Fig.2 (a) is an electron micrograph (1000 times) of an example of the iron powder for heat generating compositions manufactured by the manufacturing method of this invention, FIG.2 (b) is an example of the conventional iron powder for heat generating compositions. Electron micrograph (1000 ×) of

The method for producing iron powder for heat generating composition according to the present invention, that is, the method for producing iron powder for heat generating composition having a bulk density of 0.3 g / cm ³ or more and 1.5 g / cm ³ or less Iron oxide (Fe ₂ O ₃ ) and a solid reducing agent are introduced, heat treated under predetermined conditions to make the inside a reducing gas atmosphere, and the iron oxide is reduced to obtain reduced iron (so-called sponge iron) It has a reduction step and a grinding step of grinding the reduced iron.

  In the present invention, it is preferable to use iron ore containing iron (III) oxide as a raw material of reduced iron. In general, as iron oxide which is a raw material of reduced iron, iron oxide (so-called mill scale) produced on the surface of steel materials when hot working steel materials such as steel plates, steel pipes or mold steels in addition to iron ore Iron oxide powder (so-called spray roasted powder) obtained by spray-drying the pickling waste solution of the pickling line in the above, etc. is used, but iron ore (particles of iron ore) or spray is used as an iron source in the present invention. Roasted flour is preferred. When a fine powdery raw material with low iron (III) purity such as mill scale is used as an iron source, iron powder for heat generating composition having a fibrous structure (see FIG. 2 (a)) described later is stable. There is a possibility that the desired heat generation characteristics can not be obtained.

  The iron ore (iron oxide) used in the present invention is particles or iron ore particles. When iron ore (iron ore particles) is used as the iron source, the average particle diameter is preferably 0.5 mm or more, more preferably 1.0 mm or more from the viewpoint of the workability of the iron ore particles in the reduction step. By setting the lower limit of the average particle size of iron ore particles to the above range, it is possible to reduce scattering of iron ore particles in the rotary furnace, particularly when using a rotary furnace as the heating furnace in the reduction step, In this case, the scattered iron ore particles are heated by heat transfer from the wall surface of the rotary furnace, so that the reduction of the heat transfer from the wall surface to the iron ore particles to be originally heated can be reduced. In particular, when a fixed furnace is used as a heating furnace in the reduction step, mixing of iron ore particles and a solid reducing agent is facilitated, and iron ore particles are filled with a solid reducing agent in a heat resistant container (sag). When the reduction step is performed, the filling efficiency to the heat-resistant container is also enhanced.

  When a spray roasted powder (iron oxide) is used as the iron source, the average particle diameter is preferably 0.01 mm or more, more preferably 0.02 mm or more, from the viewpoint of workability in the reduction step. By setting the lower limit of the average particle size of the spray roasted powder to the above range, it is possible to reduce scattering of the spray roasted powder in the rotary furnace, particularly when using a rotary furnace as the heating furnace in the reduction step. In addition, it is possible to prevent the scattered spray roasted powder from flowing out of the system. In particular, when a fixed furnace is used as a heating furnace in the reduction step, mixing of the spray roasted powder with the solid reducing agent is facilitated, and the spray roasted powder with the solid reducing agent is a heat-resistant container (Zagar) In the case of carrying out the reduction step by filling in, the filling efficiency to the outer heat resistant container is also enhanced.

  Further, from the viewpoint of the reducibility of iron oxide in the reduction step and the promotion of formation of a fibrous structure described later, the average particle diameter of iron oxide (iron ore particles, spray roasted powder) is preferably 30 mm or less Preferably it is 25 mm or less. The reduction reaction of iron oxide in the reduction step proceeds from the outside to the inside of the particles, and by setting the upper limit of the average particle size to the above range, the reduction reaction is facilitated, and the reducibility is good. The fibrous structure can be formed well.

  The "average particle size" referred to in the present specification is 1) a volume-based median diameter measured by a laser diffraction type particle size distribution measuring device, or 2) directly measuring the size of an object to be measured (iron ore particles) It is the arithmetic mean of the measured values obtained. The volume-based median diameter of the above 1) is, for example, LA-950V2 manufactured by HORIBA, Ltd., using a standard wet circulation cell, and making the refractive index a real part 3.5 and an imaginary part 3.8i Water can be used as a medium, the refractive index can be 1.33, the circulation speed can be set to 15, and the stirring can be set to 5, and measurement can be performed according to a conventional method. On the other hand, the arithmetic mean value of the measurement value by the direct measurement of the above 2) is calculated by measuring the length of the long side and the short side of the particle to be measured using a measuring instrument such as a caliper or a micrometer. More specifically, it is calculated as an arithmetic average value obtained by measuring the longest Feret diameter and the shortest Feret diameter defined in JIS-Z8827-1 and measuring at least 20 particles.

  The purity of iron oxide (iron ore particles, spray roasted powder) used in the present invention, that is, the mass content of iron (III) oxide in the iron oxide, is 90% by mass from the viewpoint of reducibility in the reduction step. The content is more preferably 95% by mass or more. By setting the purity of iron oxide in the above range, it is possible to stably produce an iron powder for a heat generating composition having a fibrous structure described later, and to increase the content of metal iron to a desired range. In order to increase the purity of iron oxide, it is necessary to repeat washing with sulfuric acid, and by setting the purity of iron oxide within the above range, the sulfur content remaining at the time of sulfuric acid washing can be reduced to the desired range.

  The upper limit of the purity of iron oxide is not particularly limited, but particularly when using a spray roasted powder as iron oxide, the mass content of iron oxide (III) in the spray roasted powder as iron oxide is sulfur From the viewpoint of the content, it is preferably 99.9% by mass or less, more preferably 99.6% by mass or less.

  In the present invention, a solid reducing agent is used as the reducing agent used in combination with iron oxide. Examples of the solid reducing agent include carbon-based solid reducing agents, plastics, wood and the like, and one of these may be used alone, or two or more may be used in combination.

  In the case of using a carbon-based solid reducing agent as the solid reducing agent, examples thereof include coal, coal char, coke, and biomass charcoal such as sawdust charcoal, coconut husk charcoal, wood charcoal etc., and one of these may be used alone. Or it can use combining 2 or more types. Biomass coal is preferable as the carbon-based solid reducing agent from the viewpoint of producing the iron powder for heat-generating composition (see FIG. 2A) having a fibrous structure described later more stably.

  When a plastic is used as the solid reducing agent, for example, polyolefins such as polyethylene and polypropylene, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyesters such as polylactic acid, and polymers such as polystyrene can be mentioned. These can be used alone or in combination of two or more. In addition, the plastic as the solid reducing agent can contain an inorganic filler such as talc, silica, calcium carbonate, titanium oxide, aluminum hydroxide and the like.

  When wood is used as the solid reducing agent, for example, logs, plate materials, sawdust, pulp, wood pellets, etc. may be mentioned, and one of these may be used alone or in combination of two or more. As a wood as a solid reducing agent, a wood pellet is preferable from a viewpoint of raw material handling property in a reduction process.

  The carbon-based solid reducing agent used in the present invention is preferably a powder, and the average particle diameter thereof is preferably 0.03 mm or more, more preferably from the viewpoint of the workability of the carbon-based solid reducing agent in the reduction step. It is 0.05 mm or more. By setting the lower limit of the average particle size of the carbon-based solid reducing agent to the above range, in particular, when using a rotary furnace as the heating furnace in the reduction step, the carbon-based solid reducing agent is scattered in the rotary furnace. Therefore, the scattered carbon-based solid reducing agent is heated by heat transfer from the wall surface of the rotary furnace, thereby reducing the heat transfer from the wall surface to the carbon-based solid reducing agent to be originally heated. You can reduce things. In particular, when a fixed furnace is used as a heating furnace in the reduction step, mixing of the solid reducing agent with the iron ore particles is facilitated, and the solid reducing agent together with iron oxide (iron ore, spray roasted powder) When the heat-resistant container (sagger) is filled to carry out the reduction step, the filling efficiency to the heat-resistant container is also enhanced.

  Further, from the viewpoint of the reducibility of iron oxide in the reduction step, the average particle diameter of the solid reducing agent (carbon-based solid reducing agent, plastic, wood) is preferably 100 mm or less, more preferably 80 mm or less. By setting the upper limit of the average particle size of the solid reducing agent to the above range, the formation of a fibrous structure to be described later in the reduction step can be excellent. The solid reducing agent can also be used by forming a powder by a method such as compression molding.

  When a carbon-based solid reducing agent is used as the solid reducing agent, the carbon content of the carbon-based solid reducing agent is preferably 50% by mass or more, more preferably 60% by mass, relative to the total mass of the solid reducing agent. % Or more. If the carbon content of the carbon-based solid reducing agent is too low, reduction of iron oxide (iron ore, spray roasted powder) may be insufficient. The upper limit of the carbon content of the carbon-based solid reducing agent is preferably 95% by mass or less, more preferably 90% by mass or less, in relation to the volatile component described later. The carbon content of the carbon-based solid reducing agent is measured in accordance with the method of measuring the fixed carbon content of coal and cokes as defined in JIS M8812.

  Further, the volatile component content of the solid reducing agent (carbon-based solid reducing agent, plastic, wood) used in the present invention is 10% by mass or more, preferably 15% by mass or more based on the total mass of the solid reducing agent is there. As used herein, the volatile component content is the total content of components that volatilize from the solid reducing agent when the solid reducing agent is heated. By setting the lower limit of the volatile component content of the solid reducing agent to the above range, reduction of iron oxide (iron ore, spray roasted powder) can be sufficiently performed.

  When a carbon-based solid reducing agent is used as the solid reducing agent, the upper limit of the volatile component content of the carbon-based solid reducing agent is preferably 50% by mass or less, more preferably from the relation with the carbon content described above. It is 40 mass% or less. The volatile component content of the solid reducing agent is measured in accordance with the volatile content determination method of coal and cokes defined in JIS M8812.

  The sulfur content of the solid reducing agent (carbon-based solid reducing agent, plastic, wood) used in the present invention is preferably 500 ppm or less, more preferably 400 ppm or less, based on the total mass of the solid reducing agent. Ideally it is zero. When sulfur is contained in the solid reducing agent, sulfur gas derived from the solid reducing agent is generated inside the heating furnace in the reduction step, which may cause corrosion of manufacturing facilities including the heating furnace. In this respect, if the sulfur content of the solid reducing agent is 500 ppm or less, the inside of the heating furnace is set to an atmosphere substantially free of sulfur gas, so that corrosion of manufacturing facilities including the heating furnace is unlikely to occur.

  In the reduction step, heat treatment is performed with iron oxide (iron ore, spray roasted powder) and a solid reducing agent (carbon-based solid reducing agent, plastic, wood). As the method of this heat treatment, any method commonly used in the production of sponge iron can be appropriately used. Typically, a heat resistant container called sagar is filled with iron oxide and a solid reducing agent, and the heat resistant container is heated in a heating furnace Indirect heating method is adopted.

  In the reduction step, iron oxide (iron ore, spray roasted powder) and a solid reducing agent (carbon-based solid reducing agent, plastic, wood) are each mixed in a powder state, and the mixture is heat-treated, It is preferable for the uniformity of fibrous structure formation mentioned later. Specifically, for example, a mixture of iron oxide and a solid reducing agent mixed in powder form is filled in the hollow portion of a hollow cylindrical heat resistant container (sag), and the heat resistant container is indirectly heated in a heating furnace. Methods are included. The content mass ratio of iron oxide to solid reducing agent in such a mixture is preferably 1 or more, more preferably 1.5 or more, and preferably 18 or less, more preferably 9 or less, as iron oxide / solid reducing agent. It is.

  The reduction step is performed using a heating furnace. As the heating furnace, a heating furnace usually used for the production of sponge iron can be used without particular limitation, and it may be a rotary furnace or a non-rotating fixed furnace. The heating furnace may be an internal combustion type in which the raw material (iron oxide, solid reducing agent) and the heating medium such as the fuel gas are in direct contact, ie, the raw material is directly heated, or the raw material and the heating medium are not in direct contact An external combustion type may be used in which the furnace wall defining the inside of the heating furnace into which the raw material is introduced is heated from the outside with a heating medium, that is, the raw material is indirectly heated by heat transfer via the furnace wall. Specific examples of the rotary furnace include an internal combustion type or an external combustion type rotary kiln. In internal combustion type rotary kilns, for example, there is a type in which the fuel gas fed into the inside of the heating furnace is burned and the raw material is heated by the heat of combustion, and a type in which the raw material is heated by the heating gas blown into the inside of the heating furnace . Generally, in a heating furnace of internal combustion type, since the raw material is in direct contact with the heating medium such as combustion gas and heat gas, dust and the like contained in the heating medium may be mixed in the raw material to reduce the product quality. I am concerned. On the other hand, in the external combustion type heating furnace, since the raw material does not contact the heating medium, the thermal efficiency is lower than that of the internal combustion type, but there is no risk of quality deterioration due to mixing of dust and the like. From the viewpoint of producing the iron powder for heat generating composition (see FIG. 2 (a)) having a fibrous structure described later more stably, it is preferable to carry out heat treatment using an external combustion type fixed furnace or rotary furnace .

  The inside of the heating furnace into which the raw material (iron oxide, solid reducing agent) is introduced needs to be an atmosphere or an inert gas atmosphere which does not contain sulfur gas. The presence of sulfur gas inside the heating furnace may cause corrosion of manufacturing equipment including the heating furnace. Specifically, the term "does not contain sulfur gas" as used herein means that the concentration of sulfur gas inside the heating furnace is preferably 500 ppm or less, more preferably 100 ppm or less, based on the total volume of the inside of the furnace. Means state. Therefore, in the present invention, it is preferable not to introduce sulfur gas into the inside of the heating furnace, and to use a raw material having a sulfur content as small as possible.

  In the reduction step, a raw material (iron oxide, solid reducing agent) is introduced into the inside of the heating furnace in which the inside does not contain sulfur gas and is set to the atmosphere or an inert gas atmosphere, and the atmosphere temperature inside is 900 ° C. Heat treatment is performed under the condition of 1000 ° C. or less to make the inside be a reducing gas atmosphere, and iron oxide is reduced to obtain reduced iron (sponge iron). At the start of heat treatment, the inside of the heating furnace is an air atmosphere or an inert gas atmosphere such as nitrogen, but the solid reducing agent (carbon-based solid reducing agent, plastic, wood) decomposes as the raw material temperature rises. Then, carbon monoxide is generated and diffused into the inside of the heating furnace, whereby the inside becomes a reducing gas atmosphere. The "reducing gas atmosphere" referred to here is an atmosphere containing carbon monoxide, hydrogen, hydrocarbon gas (methane, ethane, propane, etc.) and the like. In this reducing gas atmosphere, carbon monoxide reduces iron oxide (iron ore, spray roasted powder) to produce reduced iron (Fe). At this time, carbon dioxide is simultaneously generated, and the carbon dioxide reacts with the solid reducing agent to form carbon monoxide, and the carbon monoxide diffuses into the inside of the heating furnace to reduce iron oxide.

  In the heat treatment of the reduction step, when the ambient temperature inside the heating furnace is outside the range of 900 ° C. or more and 1000 ° C. or less, production of iron powder for heat generating composition (see FIG. 2A) having a fibrous structure described later It will be difficult. The ambient temperature inside the heating furnace at the time of heat treatment is preferably 910 ° C. or more, more preferably 920 ° C. or more, and preferably 995 ° C. or less, more preferably 990 ° C. or less.

  The heat treatment time in the reduction step (a time during which the ambient temperature of 900 ° C. to 1000 ° C. is maintained) is preferably 0.5 hours or more, more preferably 1 hour or more, and preferably 8 hours or less, more preferably Is less than six hours.

  From the viewpoint of promoting the reduction reaction of iron oxide in the heat treatment of the reduction step, the total content of carbon monoxide and carbon dioxide in the reducing gas atmosphere is preferably as large as possible, preferably 50% by volume or more, more preferably 60 volumes % Or more. The total content of carbon monoxide and carbon dioxide in the reducing gas atmosphere can be adjusted by appropriately adjusting the amount of use of the carbon-based solid reducing agent, the purge gas, and the like.

  In the reduction step, it is preferable to introduce an amount of oxygen corresponding to 1.5% by mass or less of the iron oxide in the inside of the heating furnace during the heat treatment. While the reduction reaction of iron oxide is an endothermic reaction, temperature differences occur inside and outside the heating furnace along with the progress of the reduction reaction especially when the reduction furnace used is a large-sized one, and due to this, the heating furnace There is a concern that the iron oxide introduced into the inside of the iron may not be sufficiently reduced. On the other hand, by introducing oxygen into the inside of the heating furnace, the introduced oxygen burns carbon in the solid reducing agent to generate combustion heat, so the amount of heat lost by the reduction reaction is this combustion Heat compensates and as a result the concern is wiped out. By setting the amount of oxygen introduced into the inside of the heating furnace within the above range, the amount of heat inside the heating furnace can be compensated to sufficiently reduce iron oxide. Moreover, the reoxidation of the reduced iron oxide can be prevented by setting the amount of oxygen introduced into the inside of the heating furnace within the above range so as not to be too small. The reference of the oxygen introduction amount is the content of iron oxide in the iron source (iron ore, spray roasted powder) introduced into the inside of the heating furnace.

  The reduced iron obtained by the reduction step is ground as needed after being subjected to beneficiation treatment (pulverization step). Mineral processing is a process for selecting reduced iron with high purity of metallic iron, and any known method can be used without particular limitation. For example, magnetic metallic iron and non-magnetic component (cangite) can be used as a magnetic force. Methods of separation (magnetic separation method) can be exemplified.

  The method of grinding reduced iron in the grinding step is not particularly limited, and any known method can be adopted. For example, a known grinder such as a rod mill, a roll crusher or a ball mill may be used.

However, from the viewpoint of producing the iron powder for heat generating composition (see FIG. 2 (a)) having the fibrous structure described later more stably, the fibrous structure possessed by reduced iron immediately after reduction is maintained as much as possible. It is preferable to be powdered as it is, and for that purpose, it is preferable to make the degree of grinding of reduced iron weaker than before. For example, in the conventional process of grinding reduced iron, generally, a vibrating rod mill (for example, manufactured by Chuo Kakoki Co., Ltd., trade name "MB-1") is used for 1.0 kg of reduced iron. The milling process is carried out for about 8 to 12 minutes, whereas in the production of the iron powder for the preferred heat-generating composition of the present invention, a vibrating disc mill (eg, a varder) is used for 0.1 kg of reduced iron. -The crushing process is performed for about 5 to 30 seconds at a rotational speed of 700 to 1000 rpm, using Scientific Co., Ltd., trade name "RS200". By applying such relatively weak pulverizing treatment to reduced iron, the bulk density is in the range of 0.3 g / cm ³ or more and 1.5 g / cm ³ or less, and the iron powder having a fibrous structure is more stable. Obtained.

  The iron powder obtained through the grinding step is sieved to a desired particle size, if necessary, and is further subjected to a heat treatment to become an iron powder for heat generating composition.

  The iron powder for a heat generating composition manufactured by the manufacturing method of the present invention described above is used as a material of the heat generating composition. The heat-generating composition generates heat using heat generation associated with the oxidation reaction between iron powder (oxidizable metal) and oxygen in the air, and is typically used as a heating element in a heat-generating tool such as a disposable heat-insulating material. used. The heat generating tool to which the iron powder for a heat generating composition manufactured by the manufacturing method of the present invention can be applied is applied directly to the human body or is applied to clothing and is suitably used for heating the human body. The application site in the human body includes, for example, shoulders, neck, face, eyes, hips, elbows, knees, thighs, lower legs, belly, lower abdomen, hands, soles and the like. In addition to the human body, the heat generating tool to which the iron powder for heat generating composition manufactured by the manufacturing method of the present invention is applicable is applied to various articles and is suitably used for heating and heat retention.

  The heat generating tool 1 which is one Embodiment of the heat generating tool using the iron powder for heat generating compositions manufactured by the manufacturing method of this invention by FIG. 1 is shown. As shown in FIG. 1A, the heating tool 1 is configured to include a heating element 2 and a wrapping material 3 surrounding the heating element 2. The heat generating element 2 is a member that generates heat in the heat generating tool 1 and is configured to include a heat generating composition 20 including the iron powder for a heat generating composition manufactured by the manufacturing method of the present invention. The packaging material 3 is a member that surrounds the entire heating element 2 and forms the outer surface of the heating tool 1, and is partially or entirely breathable. In the heating tool 1, the heating element 2 is in a non-fixed state with respect to the packaging material 3, and hence can be moved independently of the packaging material 3.

  The packaging material 3 includes a first covering sheet 30 and a second covering sheet 31 as shown in FIG. 1 (b). The first covering sheet 30 and the second covering sheet 31 each have an extension area extending outward from the peripheral edge of the heat generating element 2, and the extension areas are joined. The bonding is preferably an annular continuous airtight bonding surrounding the heating element 2. The packaging material 3 formed by joining the two covering sheets 30 and 31 has a space for accommodating the heating element 2 therein, and the heating element 2 is accommodated in the space.

  The heat generating body 2 has a configuration in which a heat generating composition 20 is disposed between two base sheets 21 and 22, as shown in FIG. 1 (c). As the base sheets 21 and 22, the same ones conventionally used in the technical field can be used. For example, the base sheets 21 and 22 may be made of an air-permeable material such as a synthetic resin film, or a fiber sheet such as nonwoven fabric or paper. An air-permeable material or a laminate of the air-permeable material and the fiber sheet may, for example, be mentioned. Moreover, the base sheets 21 and 22 may have high water absorbency, in which case, for example, a fiber sheet containing hydrophilic fibers, particles of a water absorbing polymer, a fiber sheet containing hydrophilic fibers, etc. may be mentioned. . The base sheets 21 and 22 may be the same as or different from each other.

  The heat generating composition 20 contains an iron powder (iron powder for a heat generating composition manufactured by the manufacturing method of the present invention), a carbon material, a salt of a halide and water. Thus, the heat generating composition 20 in the heat generating element 2 is a water-containing layer containing water, and the halide salt or electrolyte contained in the heat generating composition 20 was dissolved in the water in the heat generating composition 20 It is in the state. The heat-generating composition 20 generates heat using the heat generated by the oxidation reaction between iron powder and oxygen in the air.

The iron powder for a heat generating composition contained in the heat generating composition 20 is characterized in that the bulk density is in the range of 0.3 g / cm ³ or more and 1.5 g / cm ³ or less. The bulk density of the heat-generating composition for iron powder that has been conventionally frequently used, because generally in the range of 1.8~2.5g / cm ³ greater than the 1.5 g / cm ^3, the production method of the present invention It can be said that the iron powder for a heat generating composition manufactured by the method has a bulk density lower than that of the conventional product and is bulky.

  The bulk density of the iron powder (iron powder for heat generating composition) referred to in the present invention is measured using a bulk density measuring instrument (JIS bulk specific gravity measuring instrument JIS Z-2504, manufactured by Tsutsui Rikakai Kikai Co., Ltd.). Metal powder-measured according to the apparent density measurement method.

The iron powder for a heat generating composition manufactured by the manufacturing method of the present invention has a bulk density in a specific range of 0.3 g / cm ³ or more and 1.5 g / cm ³ or less, so that the heat generation of the heat generating composition containing the same. The characteristics can be significantly improved. Specifically, the iron powder for heat generating composition manufactured by the manufacturing method of the present invention is equivalent to the iron powder in comparison with the conventional iron powder for heat generating composition having a bulk density of more than 1.5 g / cm ^3. The amount of heat generation can be achieved for a longer time, and the heat generation amount in the heat generation composition and the reaction rate in the oxidation reaction of iron powder can be dramatically improved. The iron powder for a heat generating composition manufactured by the manufacturing method of the present invention is useful for achieving a thin heat generating composition or a heat generating body using the same, because the reaction rate in the oxidation reaction is thus high. Also, since the control of the heat generation time can be performed relatively easily, the degree of freedom in the design of the heat generating element can be improved. When the bulk density of the iron powder for heat generating composition exceeds 1.5 g / cm ³ , it becomes difficult to obtain such excellent heat generating characteristics. When the bulk density of the iron powder for heat generating composition is less than 0.3 g / cm ³ , handling of the iron powder may be difficult, and thinning of the heat generating composition such as a heat generating element is also difficult. The bulk density of the iron powder for a heat generating composition manufactured by the manufacturing method of the present invention is preferably 0.4 g / cm ³ or more, more preferably 0.5 g / cm ³ or more, and preferably 1.4 g / cm. ^{It is 3} or less, more preferably 1.3 g / cm ³ or less.

  Conventionally, as a method of improving the heat generation characteristics of this type of heat generating element, a method using an iron powder having a relatively small particle size as an iron powder for a heat generation composition is known. However, in general, when the particle size of the iron powder for heat generating composition decreases, the storage stability of the paint (slurry heat generating composition) prepared by adding a carbon material, a salt of a halide, water and the like to this decreases. , Sedimentation of iron powder, increase in viscosity of the paint, gelation and the like easily occur, and the handling property is lowered. It is difficult to apply such low-handling paints to industrial production of heating elements.

  In this point, the iron powder for heat generating composition manufactured by the manufacturing method of the present invention does not cause particle diameter but the bulk density is in the specific range, so that heat generation is not caused due to the decrease in the handling property of the heat generating composition. Properties can be improved. Specifically, when a carbon material, a salt of a halide and water are added to the iron powder for heat generating composition of the present invention to make a paint (slurry heat generating composition), the paint is excellent in storage stability and iron Since powder settling, viscosity increase of the coating, gelation and the like are less likely to occur, the heating element can be efficiently produced.

As described in Patent Document 3, iron powder itself having a bulk density in the range of 1.5 g / cm ³ or less is known. However, what is described in Patent Document 3 is that an iron powder having a low bulk density is used for molding applications, and nothing is described about the heat-generating composition in Patent Document 3 and, naturally, the present invention There is no description or suggestion of the technical idea of the present invention, that is, the improvement of the heat generation characteristics and the handling property of the heat generating composition by using an iron powder having a low bulk density for the heat generating composition. On the other hand, in the technical field of heat generating elements such as disposable body warmers, although the miniaturization of heat generating elements has conventionally been the main issue, as described in paragraph [0020] of Patent Document 2, for heat generating compositions If the bulk density of iron powder is as low as less than 1.5 g / cm ³ , it is technical common knowledge that the bulk of the heat generating element is increased and the miniaturization of the heat generating element is hindered. Iron powder for heat generating composition having a bulk density of 1.5 g / cm ³ or less, such as iron powder for heat generating composition manufactured by the manufacturing method of the present invention, substantially used in heat generating body applications It is not the current situation.

  The average particle diameter of the iron powder for a heat generating composition produced by the production method of the present invention is preferably 30 μm or more, more preferably 40 μm or more, and preferably 150 μm or less, more preferably 100 μm or less. When the average particle diameter of the iron powder for heat generating composition is in such a range, the above-described effects (heat generation characteristics of the heat generating composition or the heat generating member and the effect of improving the handling properties) are more reliably exhibited. The average particle size of the iron powder for heat generating composition can be adjusted by appropriately adjusting the degree of grinding in the above-mentioned grinding step.

  The iron powder for a heat generating composition produced by the production method of the present invention preferably has a content of metal iron of 60% by mass or more, more preferably 70% by mass or more, and preferably 95% by mass or less, more preferably Is 90 mass% or less. When the content of metal iron in the iron powder for heat generating composition is in such a range, the above-described effects (heat generation characteristics of heat generating composition or heat generating member and effect of improving handling property) are more reliably exhibited. Become. The content of metallic iron in iron powder is measured, for example, by a bromine-methanol dissolution method specified in ISO 5416. Adjustment of the content of the metal iron content in the iron powder can be carried out by appropriately adjusting the reduction conditions, the heat treatment conditions after reduction, and the like.

The iron powder for heat generating composition manufactured by the manufacturing method of the present invention contains, for example, about 3% by mass or less of silica (SiO ₂ ) and 15% by mass of carbon (C) as components other than metallic iron. About 3% by mass or less of alumina (Al ₂ O ₃ ) may be contained as follows. Also, since iron powder of this type usually reacts with oxygen in the air at ordinary temperature and is inevitably oxidized to some extent, iron powder for a preferable heat-generating composition of the present invention contains 10 mass of oxygen (O) % Or less. The components other than these metallic iron components are unavoidably mixed mainly in the production process of the iron powder for heat generating composition, and are not particularly important in achieving the above-described predetermined effects of the present invention.

The iron powder for a heat generating composition manufactured by the manufacturing method of the present invention is characterized not only by the various physical properties described above but also by the appearance thereof. FIG. 2 (a) is an electron micrograph of an example of an iron powder for a heat generating composition manufactured by the manufacturing method of the present invention, and FIG. 2 (b) is a conventional iron powder for a heat generating composition An electron micrograph of iron powder> 1.5 g / cm ³ is shown. In the iron powder for heat generating composition manufactured by the manufacturing method of the present invention, as shown in FIG. 2 (a), the surface layer portion is constituted by arranging a large number of fibrous materials randomly at three dimensions. Is characteristic. In the surface layer portion of the conventional iron powder for heat generating composition shown in FIG. 2 (b), such an aggregate of fibrous materials can hardly be confirmed. The relationship between the appearance characteristics (having a fibrous structure) possessed by the iron powder for a heat generating composition manufactured by the manufacturing method of the present invention and the expression of the above-described effects and effects by the iron powder will be described below. Although it is unclear whether there is any, the fact that the iron powder for a heat generating composition manufactured by the manufacturing method of the present invention is distinctly different from the conventional iron powder for a heat generating composition is observed by such an electron microscope Is also obvious. The fiber diameter of the fibrous material constituting the iron powder for a heat generating composition manufactured by the manufacturing method of the present invention is approximately 10 μm or less. The fiber diameter of the fibrous material is measured, for example, by image analysis of an electron micrograph and measuring the distance between two points.

  As mentioned above, although this invention was demonstrated based on the embodiment, this invention can be suitably changed, without being restrict | limited to the said embodiment. Further, the following appendices will be disclosed regarding the embodiment of the present invention described above.

<1>
A method for producing an iron powder for a heat generating composition having a bulk density of 0.3 g / cm ³ or more and 1.5 g / cm ³ or less,
Iron oxide and a solid reducing agent having a volatile component content of 10% by mass or more are introduced into the inside of the heating furnace in which the inside does not contain sulfur gas and the atmosphere or the inert gas atmosphere is set to A heat treatment is performed under the condition that the atmosphere temperature is 900 ° C. or more and 1000 ° C. or less to make the inside a reducing gas atmosphere, and the iron oxide is reduced to obtain reduced iron;
And c) grinding the reduced iron.
<2>
The method for producing an iron powder for a heat generating composition according to <1>, wherein the iron oxide and the solid reducing agent are mixed in the form of powder, respectively, and the mixture is heat-treated in the reduction step.
<3>
The solid reducing agent is the carbon-based solid reducing agent, the average particle size of the carbon-based solid reducing agent is 0.03 mm or more and 100 mm or less, the carbon content is 50% by mass or more, and the sulfur content is 500 ppm or less The manufacturing method of the iron powder for exothermic composition as described in said <1> or <2> which is it.
<4>
The heat-generating composition according to <3>, wherein the average particle diameter of the carbon-based solid reducing agent is preferably 0.03 mm or more, more preferably 0.05 mm or more, and preferably 100 mm or less, more preferably 80 mm or less Of iron powder for industrial use.
<5>
The solid reducing agent is a carbon-based solid reducing agent, and the carbon content of the carbon-based solid reducing agent is preferably 50% by mass or more, more preferably 60% by mass or more, based on the total mass of the solid reducing agent. And And, Preferably the manufacturing method of the iron powder for exothermic composition of any one of said <1>-<4> which is 95 mass% or less, More preferably, it is 90 mass% or less.
<6>
The solid reducing agent is a carbon-based solid reducing agent, and the sulfur content of the carbon-based solid reducing agent is preferably 500 ppm or less, more preferably 400 ppm or less, based on the total mass of the solid reducing agent. The manufacturing method of the iron powder for heat-generating compositions as described in any one of 1>-<5>.

<7>
The method for producing an iron powder for a heat generating composition according to <1> or <2>, wherein the solid reducing agent is a plastic.
<8>
The method for producing an iron powder for a heat generating composition according to <1> or <2>, wherein the solid reducing agent is wood.
<9>
The iron oxide is iron ore, and the average particle size of the iron ore is preferably 0.5 mm or more, more preferably 1.0 mm or more, and preferably 30 mm or less, more preferably 25 mm or less, specifically The manufacturing method of the iron powder for heat-generating compositions any one of said <1>-<8> which is preferably 0.5 mm or more and 30 mm or less, more preferably 1.0 mm or more and 25 mm or less.
<10>
The iron oxide is a spray roasted powder, and the average particle size of the spray roasted powder is preferably 0.01 mm or more, more preferably 0.02 mm or more, and preferably 30 mm or less, more preferably 25 mm or less. Specifically, the method for producing an iron powder for a heat generating composition according to any one of the above <1> to <8>, which is preferably 0.01 mm to 30 mm, more preferably 0.02 mm to 25 mm. .
<11>
In the reduction step, oxygen is introduced into the heating furnace in an amount corresponding to 1.5 mass% or less of the iron oxide in the inside, according to any one of <1> to <10>. The manufacturing method of the iron powder for exothermic composition.
<12>
The total content of carbon monoxide and carbon dioxide in the reducing gas atmosphere is preferably 50% by volume or more, more preferably 60% by volume or more, according to any one of the above <1> to <11> The manufacturing method of the iron powder for exothermic composition.
<13>
In any one of the above <1> to <12>, the heating furnace is an external combustion type fixed furnace or a rotary furnace, which heats an object to be heat-treated inside the heating furnace by heat transfer via a furnace wall. The manufacturing method of the iron powder for exothermic composition as described.
<14>
The content of metal iron in the iron powder for heat generating composition is preferably 60% by mass or more, more preferably 70% by mass or more, and preferably 95% by mass or less, more preferably 90% by mass or less, specifically Is preferably 60% by mass or more and 95% by mass or less, more preferably 70% by mass or more and 90% by mass or less, the production of the iron powder for heat generating composition according to any one of the above <1> to <13> Method.
<15>
The atmosphere temperature inside the heating furnace at the time of the heat treatment is preferably 910 ° C. or more, more preferably 920 ° C. or more, and preferably 995 ° C. or less, more preferably 990 ° C. or less. The manufacturing method of the iron powder for heat-generating compositions as described in any one of these.
<16>
The heat treatment time of the reduction step, that is, the time during which the ambient temperature of 900 ° C. to 1000 ° C. is maintained, is preferably 0.5 hours or more, more preferably 1 hour or more, and preferably 8 hours or less, more preferably The manufacturing method of the iron powder for heat-generating compositions as described in any one of said <1>-<15> which is 6 hours or less.
<17>
In the step of grinding the reduced iron, the pulverizing treatment is carried out for about 5 to 30 seconds at a rotational speed of 700 to 1000 rpm, using a vibrating disc mill, for 0.1 kg of the reduced iron. The manufacturing method of the iron powder for exothermic composition in any one of 16>.

  Hereinafter, the present invention will be more specifically described by way of examples, but the present invention is not limited to such examples.

[Examples 1 to 4 and 7 to 10 and Comparative Examples 1 to 6]
Iron ore (Fe ₂ O ₃ : 96.4% by mass, SiO ₂ : 2.0% by mass, Al ₂ O ₃ : 1.6% by mass, average particle diameter 20 mm) was used as an iron source. 70 g of iron source and 30 g of solid reducing agent are put into a polyethylene bag (Unipack F-8 manufactured by Japan Co., Ltd.) and shaken to obtain a mixture, which is made of SUS303 with an inner diameter of 100 mm and a length of 110 mm. In a heat resistant container. A container filled with the mixture is allowed to stand inside the heating furnace using an external combustion fixed furnace (KDF-900GL manufactured by Denken Co., Ltd.) as the heating furnace, and the container is heat-treated to obtain an iron source A reduction treatment was carried out to obtain reduced iron (reduction step). The heat treatment (reduction treatment) was performed by raising the temperature from a normal temperature to a predetermined temperature at 10 ° C./min in a nitrogen atmosphere, holding the predetermined temperature for 2.5 hours, and gradually cooling to a normal temperature. Further, a predetermined amount of oxygen was introduced into the inside of the heating furnace during the heat treatment. After the heat treatment, the reduced iron is taken out of the container, and coarse iron powder is obtained by crushing for 10 seconds at a rotational speed of 700 rpm using a vibrating disc mill (RS200, standard grinding set made by SUS manufactured by Varda Scientific Co., Ltd.). (Crushing process). The obtained crude iron powder is sifted for 5 minutes using a low tap tester (1038-A manufactured by Yoshida Seisakusho Co., Ltd.) using a 250 μm mesh test sieve (JTS-250-60-37 manufactured by Tokyo Screen Co., Ltd.) The coarse powder was removed to obtain the target iron powder for heat generating composition. The solid reducing agents used were all carbon-based solid reducing agents, the details of which are as described below.

Solid reducing agent A: coconut shell charcoal (average particle size 0.05 mm, carbon content 78 mass%, volatile component content 15 mass%, sulfur content 300 ppm)
Solid reducing agent B: sawdust coal (average particle size 0.15 mm, carbon content 77% by mass, volatile component content 21% by mass, sulfur content 50 ppm)
Solid reducing agent C: wood charcoal (average particle size 0.2 mm, carbon content 74% by mass, volatile component content 25% by mass, sulfur content 40 ppm)
Solid reducing agent D: Char (average particle size 20 mm, carbon content 85 mass%, volatile component content 9 mass%, sulfur content 2500 ppm)
Solid reducing agent E: coke (average particle size 0.05 mm, carbon content 90 mass%, volatile component content 3 mass%, sulfur content 4600 ppm)

[Example 5]
Example except using iron ore (Fe ₂ O ₃ : 96.4 mass%, SiO ₂ : 2.0 mass%, Al ₂ O ₃ : 1.6 mass%, average particle diameter 10 mm) as an iron source In the same manner as in 1, an iron powder for a heat generating composition was obtained.

[Example 6]
Except using iron ore (Fe ₂ O ₃ : 96.4 mass%, SiO ₂ : 2.0 mass%, Al ₂ O ₃ : 1.6 mass%, average particle size 0.5 mm) as an iron source, Conducted in the same manner as in Example 1 to obtain an iron powder for a heat generating composition.

[Example 11]
13.3 kg of iron source, 5.7 kg of solid reducing agent B as solid reducing agent, introduced into batch type rotary furnace (inner diameter 300 mm, heating zone length 1000 mm, made of SUS310S), heat treatment at air flow rate of 1 L / min The temperature was raised from a normal temperature to a predetermined temperature at 10 ° C./min, held at a predetermined temperature for 2.5 hours at an air flow rate of 0 L / min, and gradually cooled to a normal temperature to perform heat treatment (reduction treatment). It carried out like 1 and obtained iron powder for exothermic composition.

[Example 12]
Sprayed roasted flour as iron source (JC-DS, manufactured by JFE Chemical Corporation), plastic as solid reducing agent (solid reducing agent F: polyethylene (Novatec LD, manufactured by Mitsubishi Chemical Corporation, volatile component content 100% by mass)) The temperature is raised from a normal temperature to a predetermined temperature of 25 ° C / min using a heat-resistant container made of SUS303 with an inner diameter of 100 mm and a length of 110 mm, held at 60 ° C for 25 hours, and held for 3.5 hours. Iron powder for a heat generating composition was obtained in the same manner as in Example 1 except that the above was not introduced.

[Example 13]
The same procedure as in Example 12 was carried out except using plastic (solid reducing agent G: polypropylene (MF650Y, manufactured by LyondellBasell, volatile component content 100% by mass)) as the solid reducing agent to obtain an iron powder for heat generating composition. The

Example 14
Iron powder for a heat generating composition was prepared in the same manner as in Example 12 except that 30 g of solid reducing agent F and 10 g of solid reducing agent A were used as solid reducing agents and oxygen was introduced into the heating furnace during heat treatment. Obtained.

[Example 15]
70 g of iron ore as iron source, 60 g of wood as solid reducing agent (solid reducing agent H: wood pellet, easy cat toilet deodorant / antibacterial pine sand, manufactured by Iri Oyama Co., Ltd., volatile component content 86 mass%) An iron powder for a heat generating composition was obtained in the same manner as in Example 12, except that the temperature was maintained at a predetermined temperature for 3.5 hours.

[Example 16]
An iron powder for a heat generating composition was obtained in the same manner as in Example 14 except that 70 g of iron ore as an iron source and 60 g of a plastic (solid reducing agent G) were used as a solid reducing agent.

Comparative Example 7
An iron powder for a heat generating composition was obtained in the same manner as in Example 1 except that the solid reducing agent was not used.

Comparative Example 8
13.3 kg of iron source, 5.7 kg of solid reducing agent D as solid reducing agent, introduced into batch type rotary furnace (inner diameter 300 mm, heating zone length 1000 mm, made of SUS310S), heat treatment at air flow rate of 1 L / min The temperature was raised from a normal temperature to a predetermined temperature at 10 ° C./min, held at a predetermined temperature for 2.5 hours at an air flow rate of 0 L / min, and gradually cooled to a normal temperature to perform heat treatment (reduction treatment). It carried out like 11 and obtained the iron powder for exothermic composition.

〔Evaluation test〕
With respect to the iron powder for heat generating composition obtained in each Example and Comparative Example, the bulk density and the content of metallic iron content were respectively measured, and the fibrous structure as shown in FIG. 2 (a) using an electron microscope. The presence or absence was evaluated. Moreover, the inside of the heating furnace used for manufacture of the iron powder for heat-generating compositions was visually observed, and the presence or absence of corrosion of the furnace material was evaluated.
Moreover, the coating material was prepared by the following method using the iron powder for heat generating composition obtained in each Example and Comparative Example, and the storage stability of the coating material was evaluated by the following method.
Moreover, the heat generating body was manufactured by the following method using the said coating material, and the heat generation characteristic of this heat generating body was evaluated by the following method.
The above results are shown in Tables 1 and 2 below.

(Preparation of paint)
The paint was prepared using the iron powder of each example and comparative example. The composition of the paint was 100 parts by mass of iron powder, 8 parts by mass of carbon material (activated carbon), 0.3 parts by mass of thickener (guar gum), 60 parts by mass of water, and 5 parts by mass of electrolyte (sodium chloride). The paint was prepared by first mixing iron powder and a carbon material, then adding a mixture of water and a thickener to the mixture, and uniformly mixing them.

(Manufacturing of heating element)
Using the paint prepared using the iron powder of each example and comparative example, a heating element having the same configuration as the heating element 2 shown in FIG. 1 (c) was manufactured. A paper made of wood pulp fibers having a basis weight of 70 g / m ^{2 and} a size of 5 cm × 5 cm was used as the base sheet 21, and the following highly absorbent sheet having a basis weight 80 g / m ² of 5 cm × 5 cm was used as the base sheet 22. A paint is uniformly applied on one side of the base sheet 21 to form a coating layer, and a powder of halide salt (sodium chloride) is uniformly added to the entire coating layer, and then a base sheet The heating element having the same configuration as the heating element 2 was manufactured by overlapping 22. The content of the halide salt in the heat-generating composition was 5 parts by mass with respect to 100 parts by mass of the iron powder in the heat-generating composition. The basis weight of the heat generating composition in the heat generating element was 587 g / m ² .

(Preparation of super absorbent sheet)
The superabsorbent sheet used as the base sheet 22 was manufactured according to the method described in the specification of Japanese Patent No. 5894747. In the super absorbent sheet, particles of a sodium polyacrylate based super absorbent polymer are mainly present in a substantially central region in the thickness direction of the sheet, and the particles are substantially present on the surface of the sheet. It is a single sheet having a structure that is not made. The superabsorbent sheet has a layer of hydrophilic cross-linked bulky cellulose fibers on the front and back sides of the superabsorbent polymer particles. The cross-linked bulky cellulose fiber had a fiber roughness of 0.22 mg / m and an average fiber length of 2.5 mm. The layer of cross-linked bulky cellulose fibers further contained softwood bleached kraft pulp, a paper strength agent (polyvinyl alcohol). The particles of the superabsorbent polymer used had an average particle diameter of 340 μm. The basis weight of the superabsorbent polymer particles was 30 g / m ² , and the basis weight of the superabsorbent sheet or base sheet 22 was 80 g / m ² .

<Method of evaluating storage stability of paint>
The storage stability of the paint was evaluated by comparing the solid content immediately after preparation of the paint and the solid content after standing for 24 hours immediately after preparation of the paint. The solid content of the paint was evaluated by removing the moisture of the paint by heating and measuring the mass of the remaining portion. For example, 1 g of the paint was dried at 120 ° C. for 30 minutes using a moisture meter HR83 manufactured by METTLER TOLEDO, and the mass of the remaining content was measured. With respect to the solid content immediately after preparation, the solid content after standing for 24 hours does not change is regarded as Good (highest evaluation), and the solid content changes by 2% or more after 24 hours is regarded as NG. The storage stability of the paint is closely related to the handling property, and the paint having high storage stability can be evaluated as excellent in handling property and easy in handling and coating suitability.

<Method of evaluating heat generation characteristics of heating element>
The heat generating tool having the same configuration as the heat generating tool 1 shown in FIG. 1 was manufactured using the heat generating body manufactured in each of the examples and the comparative examples. The covering sheet disposed on one side of the heat generating body as a packaging material for surrounding the heat generating body is a 6.3 cm × 6.3 cm air permeable sheet having an air permeability of 3500 seconds / 100 mL, and the other of the heat generating body The covering sheet disposed on the surface side used a packaging material consisting of a non-air-permeable sheet of 6.3 cm × 6.3 cm. Inside the packaging material (between the two coated sheets), the heat generating body to be evaluated is housed so that the permeable sheet of the packaging material and the highly absorbent sheet of the heating material are in contact, and the peripheral edges of both coated sheets are sealed. Then, a heating tool containing the heating element was produced.
The evaluation of the heat generation characteristics of the heat-generating tool using the heat-generating element of each of the examples and the comparative examples thus produced was performed according to the method of JIS S 4100: 2007. In detail, the heat generating tool to be evaluated was housed in a bag made of a needle punched non-woven fabric having a basis weight of 100 g / m ² , and the bag was placed directly on the upper surface of a 40 ° C. thermostat to evaluate heat generation characteristics. This bag is formed in a bag shape by sealing three sides of a needle punched non-woven fabric having a square shape in plan view. The thermometer used for temperature measurement was disposed between the heating tool and the upper surface of the thermostatic chamber, ie, the mounting surface of the heating tool, and the substrate sheet 21 was disposed so as to face the thermometer. The temperature characteristics of the heating element are expressed by plotting the change in temperature with respect to time, integrating over time the region where the temperature exceeds 45 ° C. and comparing with the area (K · min), and those exceeding 300 K · min Good (highest rating) and less than that was NG.

DESCRIPTION OF SYMBOLS 1 heat generating tool 2 heat generating body 20 heat generating composition 21, 22 base material sheet 3 packing material 30, 31 coating sheet

Claims (10)

A method for producing an iron powder for a heat generating composition having a bulk density of 0.3 g / cm ³ or more and 1.5 g / cm ³ or less,
Iron oxide and a solid reducing agent having a volatile component content of 10% by mass or more are introduced into the inside of the heating furnace in which the inside does not contain sulfur gas and the atmosphere or the inert gas atmosphere is set to A heat treatment is performed under the condition that the atmosphere temperature is 900 ° C. or more and 1000 ° C. or less to make the inside be a reducing gas atmosphere, and the iron oxide is reduced to obtain reduced iron;
And c) grinding the reduced iron.   The method for producing an iron powder for a heat generating composition according to claim 1, wherein the iron oxide and the solid reducing agent are mixed in the form of powder, respectively, and the mixture is heat-treated in the reduction step.   The solid reducing agent is the carbon-based solid reducing agent, the average particle size of the carbon-based solid reducing agent is 0.03 mm or more and 100 mm or less, the carbon content is 50% by mass or more, and the sulfur content is 500 ppm or less The method for producing an iron powder for a heat generating composition according to claim 1 or 2,   The method according to claim 1 or 2, wherein the solid reducing agent is a plastic.   The method for producing an iron powder for a heat generating composition according to claim 1, wherein the solid reducing agent is wood.   The method for producing an iron powder for a heat generating composition according to any one of claims 1 to 5, wherein the iron oxide is iron ore, and the average particle diameter of the iron ore is 0.5 mm or more and 30 mm or less.   The heat generating composition according to any one of claims 1 to 6, wherein in the reduction step, an amount of oxygen corresponding to 1.5 mass% or less of the iron oxide in the inside is introduced into the inside of the heating furnace. Method for producing iron powder.   The method according to any one of claims 1 to 7, wherein the total content of carbon monoxide and carbon dioxide in the reducing gas atmosphere is 50% by volume or more.   The heat generation according to any one of claims 1 to 8, wherein the heating furnace is an external combustion fixed furnace or a rotary furnace which heats an object to be heat-treated inside the heating furnace by heat transfer via a furnace wall. The manufacturing method of the iron powder for compositions.   The method for producing an iron powder for a heat generating composition according to any one of claims 1 to 9, wherein a content of metal iron in the iron powder for a heat generating composition is 60% by mass or more and 95% by mass or less.