JP2004089211A - Thermosensitive exothermic element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermosensitive exothermic element capable of surely evading the danger of a low-temperautre burn, or the like. <P>SOLUTION: This thermosensitive exothermic element is constituted by using thermosensitive hydrogel composed of water and a hydrogel-forming polymer, whose balanced water absorption magnification lowers with the rise of a temperature. <P>COPYRIGHT: (C)2004,JPO

Description

比較例１
（高吸水性樹脂を使用した発熱体の試験）
実施例２の感温ハイドロゲル形成性高分子に変えて、市販の高吸水性樹脂（三菱化学製、ダイヤウェット）０．１５ｇを用いる以外、実施例２と同様の実験を行ったところ、鉄粉混合後２０分で最高温度６８℃に達し、４０℃以上の発熱持続時間は９０分であった。
【００６８】
比較例２
（高吸水性樹脂と還元剤を使用した発熱体の試験）
比較例１で用いた食塩水（３．０ｇ）中にアスコルビン酸（和光純薬製）０．３ｇを溶解して用いた以外は、比較例１と同様の実験を行った（室温２７℃、湿度７０％）。上記により得られた温度データを下記（表２）に示す。表２に示すように、鉄粉混合後６０分で最高温度（Ｔｍ）６５．５℃になった。また、０（ｔ０）〜１９５分（ｔ１）の平均温度（Ｔａ）は５４．５℃であった。したがって、Ｔｍ／Ｔａの比は、１．２０であった。
【００６９】
【表２】

【００７０】
【発明の効果】
上述したように本発明によれば、少なくとも水と、ハイドロゲル形成性の高分子とからなり、且つ温度の上昇とともにその平衡吸水倍率が低下する感温ハイドロゲルを含む感温性発熱体が提供される。
【００７１】
上記の構成を有する本発明の感温性発熱体は、発熱部材として、温度の上昇とともにその平衡吸水倍率が低下する感温ハイドロゲルを含むことを特徴とし、所定温度より高い温度になると、該感温ハイドロゲルから水が放出され、その気化熱によって発熱体を冷却し、発熱体が過度に加熱することを防止する。一方、所定温度より低い温度に冷却されると、該感温ハイドロゲルは外部の水を吸収するので水の蒸発による冷却が抑制され、温度が過度に低下することを防止する。このように、本発明の感温発熱体は、発熱体自身が温度を感知してより精密に発熱温度を制御するので、低温火傷の危険性等を回避することができる。
【図面の簡単な説明】
【図１】感温ハイドロゲルを用いた発熱体１を、袋状部材２内に配置した本発明の態様の一例を示す模式断面図である。
【符号の説明】
１…感温ハイドロゲルを用いた発熱体、２…袋状部材。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a heating element that can be suitably used for heating or heating a delicate surface with respect to the temperature of a living body or the like, and more specifically, a function of sensing temperature and preventing runaway of an exothermic reaction is referred to as “per se. And a temperature-sensitive heating element. The heating element of the present invention can be particularly suitably used as a heat-sensitive adhesive such as a "disposable body warmer" for use in medicine, medical care, home use, and leisure, a heat-shipping agent, and a heat plaster.
[0002]
[Prior art]
Many of the commercially available so-called "disposable warmers" and "warm heat-shipping agents" currently utilize reaction heat generated during iron air oxidation. The chemical exothermic agent used for these is generally configured to generate heat by combining iron powder, water, salts, activated carbon and the like. Such a chemical exothermic agent is usually enclosed in a storage bag having an air hole and used as the above-mentioned warmer or the like.
[0003]
Conventionally, water retention agents such as wood flour, silica gel, perlite, and vermiculite have been used to retain the water required for the oxidation reaction of iron powder.However, these water retention agents have a small water retention ability and generate heat. Since water evaporates rapidly, there is a drawback in that the duration of heat generation of a warmer or the like becomes short.
[0004]
In order to improve this point, it is common to use a hydrogel such as a crosslinked product of a polyacrylate salt having a high water retention ability, which is recently called a superabsorbent resin, as the water retention agent. In many cases, the control of the heat generation temperature of a heating device such as a warmer is performed by adjusting the components, the composition and the filling amount of the chemical heating agent, or the ventilation holes of the storage bag.
[0005]
[Problems to be solved by the invention]
In recent years, with the aging society progressing, the number of people who complain of symptoms such as back pain, elbow pain, knee pain, shoulder pain and the like tends to increase. For this reason, warm patches by symptomatic treatment are widely used. However, the conventional heating element utilizing the air oxidation of iron as described above performs temperature control only by controlling the ventilation hole of the storage bag mainly to suppress the oxygen supply amount. Poor control resulted in frequent accidents of so-called "cold burns" (eg, when the skin was exposed to a temperature of about 42 ° C for several hours). The problem of the "low-temperature burn", coupled with the enforcement of the PL Law (Product Liability Law), raises a more serious problem for manufacturers.
[0006]
An object of the present invention is to provide a temperature-sensitive heating element that has solved the above-mentioned disadvantages of the prior art.
[0007]
Another object of the present invention is to provide a temperature-sensitive heating element that can reliably avoid the danger of low-temperature burns and the like.
[0008]
It is still another object of the present invention to provide a temperature-sensitive heating element capable of sensing the temperature itself and controlling the heating temperature more precisely.
[0009]
[Means for Solving the Problems]
As a result of intensive studies, the present inventor has found that, using a thermosensitive hydrogel having a characteristic that the equilibrium water absorption capacity decreases with an increase in temperature, the ingress and egress of water into and out of the hydrogel can be controlled microscopically. However, they have found that they are extremely effective in solving the above-mentioned problems.
[0010]
The temperature-sensitive heating element of the present invention is based on the above findings, and more specifically, a temperature-sensitive heating element comprising at least water and a hydrogel-forming polymer, and whose equilibrium water absorption capacity decreases with increasing temperature. It is characterized by containing a hydrogel.
[0011]
According to the present invention, there is further provided a heating member including a bag-shaped member and a temperature-sensitive heating element disposed inside the bag-shaped member; wherein the temperature-sensitive heating element includes at least water, A heat-generating member is provided, which comprises a thermosensitive hydrogel made of a gel-forming polymer and having a reduced equilibrium water absorption capacity with increasing temperature.
[0012]
In the conventional heating member that controls the heat generation of the heating element by adjusting the air permeability or the ventilation hole of the storage bag of the heating element, it is difficult to precisely adjust the air permeability of the film constituting the storage bag. The exothermicity of the heating element also tended to vary. In particular, when small holes such as pinholes or cracks are present in the storage bag, these small holes and the like are difficult to detect with the naked eye, but the effect is serious. That is, since the heating element itself does not have a function of "temperature control", it is difficult to avoid the danger that the heating element excessively generates heat due to the presence of the micropores or the like, resulting in a serious result (low-temperature burn).
[0013]
On the other hand, in the heating element of the present invention including the temperature-sensitive hydrogel, when the heat generation proceeds and reaches a predetermined temperature, the temperature-sensitive hydrogel is reduced based on a decrease in the equilibrium water absorption capacity of the polymer constituting the gel. , Water is released from the heating element, and the heating element is cooled by the heat of vaporization, thereby preventing excessive heating of the heating element.
[0014]
On the other hand, when the heating element of the present invention is cooled to a temperature lower than the above-mentioned predetermined temperature, the temperature-sensitive hydrogel absorbs external water based on the increase in the equilibrium water absorption of the polymer constituting the gel. The cooling due to the evaporation of water is suppressed, and the temperature is prevented from excessively lowering.
[0015]
As described above, in the temperature-sensitive heating element of the present invention, the heating element itself senses the temperature and controls the heating temperature more precisely, so that the danger of a low-temperature burn or the like can be avoided.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described more specifically with reference to the drawings as necessary. In the following description, “parts” and “%” representing the quantitative ratios are based on weight unless otherwise specified.
[0017]
(Temperature-sensitive heating element)
The temperature-sensitive heating element of the present invention contains at least a temperature-sensitive hydrogel in the heating section, the equilibrium water absorption capacity of which decreases with an increase in temperature. In the present invention, the thermosensitive hydrogel comprises at least water and a hydrogel-forming polymer.
[0018]
The ratio (Tm / Ta) between the maximum temperature (Tm) and the average temperature (Ta) of the thermosensitive heating element of the present invention is preferably 1.15 or less, more preferably 1.10 or less (particularly 1). 0.08 or less). Here, the maximum temperature (Tm) and the average temperature (Ta) of the temperature-sensitive heating element can be suitably measured by the following method.
[0019]
<Method of measuring Tm and Ta>
In a glass beaker (diameter: 3.0 cm, height: 4.4 cm), about 6 g of a heating element (or heating agent) as a sample to be measured is prepared, and the beaker is placed on a styrene foam plate (size: 20 × 30 cm, thickness). : 20 mm). The upper part of the beaker was covered with filter paper (manufactured by Toyo Roshi Kaisha, Ltd., No. 2 filter paper), and the temperature of the bottom of the beaker was adjusted using a bead type probe (2459-manufactured by Yokogawa Electric Corporation) disposed between the bottom and the styrene foam plate. Using a thermocouple thermometer (trade name: 2455, manufactured by Yokogawa Electric Corporation) using a thermocouple thermometer (type: 0455) (the exothermic agent is stirred every 30 minutes). With such a measurement system, immediately after the start of the measurement (t0), even after the exothermic agent is agitated, a remarkable temperature rise (3 ° C. or more) is not observed, and the thermometer indicates 38.5 ° C. (t1). The temperature is continuously measured until).
[0020]
The obtained temperature-time curve (t = t0 to t1) is integrated, and the quotient obtained by dividing the integrated value by the measurement time (t1−t0) is defined as the average temperature Ta. In this temperature-time curve (t0 to t1), the highest temperature is defined as the highest temperature Tm.
[0021]
(Temperature-sensitive hydrogel)
In the present invention, the “hydrogel” refers to a gel containing at least a crosslinked or network structure composed of a polymer and water supported or held (dispersed liquid) in the structure. The “dispersed liquid” held in the crosslinked or network structure is not particularly limited as long as it is a liquid containing water as a main component. More specifically, for example, the dispersion liquid may be water itself, or any aqueous medium such as an aqueous solution and / or a hydrated liquid (for example, a mixed liquid of water and a monohydric or polyhydric alcohol). It may be.
[0022]
The temperature-sensitive hydrogel used in the present invention is composed of a “temperature-sensitive hydrogel-forming polymer” having a property that its equilibrium water absorption capacity decreases with increasing temperature. The thermosensitive hydrogel-forming polymer has a negative temperature coefficient of solubility in water and / or imparts a crosslinked structure to a polymer compound whose aqueous solution has a lower critical solution temperature (Lower Solution, Temperature, LCST). Or can be obtained by introduction. Here, LCST refers to the temperature at which a uniform aqueous polymer solution separates into two phases, an aqueous phase and a polymer phase, due to an increase in temperature (Heskins, M., et al., J. Macromol. Sci. Chem. {A2 (8)}; {1441, {1968).
[0023]
The “temperature-sensitive hydrogel-forming polymer” obtained by crosslinking a polymer compound having an LCST absorbs water in a temperature range lower than the LCST and swells to form a hydrogel. The equilibrium water absorption capacity is reduced, that is, water is discharged to the outside and gradually contracts, and the LCST contracts remarkably discontinuously. This behavior of the thermosensitive hydrogel is observed thermoreversibly, and when the temperature decreases, it absorbs water again and swells. This temperature-dependent driving force of the reversible swelling-shrinking behavior of the hydrogel is attributed mainly to hydrophobic interaction, and is theoretically understood by Tanaka et al. As a volume phase transition phenomenon of the gel (for example, Tanaka, T, et al., Phys. Rev. Lett., 55; 2455, 1985).
[0024]
That is, in the heating element of the present invention including the above-mentioned temperature-sensitive hydrogel as the heating section, when heat generation proceeds and reaches a predetermined temperature, water is released from the temperature-sensitive hydrogel, and the heating element is cooled by the heat of vaporization. This prevents the heating element from being excessively heated. On the other hand, when cooled to a temperature lower than the predetermined temperature, the thermosensitive hydrogel absorbs external water, so that cooling due to evaporation of water is suppressed, and the temperature is prevented from excessively lowering. As described above, the temperature-sensitive heating element of the present invention senses the temperature by itself and controls the heating temperature more precisely, thereby making it possible to avoid the danger of low-temperature burns and the like.
[0025]
(Equilibrium water absorption ratio)
The temperature-sensitive hydrogel used in the present invention is a temperature-sensitive hydrogel having a property that its equilibrium water absorption capacity decreases as the temperature increases.
[0026]
Here, the "equilibrium water absorption capacity" of the thermosensitive hydrogel in a predetermined aqueous medium at a predetermined temperature is measured as follows.
[0027]
An amount (W1 g) of the dried thermosensitive hydrogel-forming polymer is weighed, and an excess amount (for example, 1.5 times or more the expected water absorption of the thermosensitive hydrogel-forming polymer) of the aqueous medium is measured. The thermosensitive hydrogel-forming polymer is allowed to stand in a thermostat at a predetermined temperature for 2 days (48 hours) to swell the thermosensitive hydrogel-forming polymer. After the excess aqueous medium is removed by filtration or centrifugation at the predetermined temperature, the weight (W2 g) of the water-swelled thermosensitive hydrogel is measured, and the equilibrium water absorption capacity in the aqueous medium at the predetermined temperature is determined by the following equation. Ask for.
[0028]
(Equation 1) Equilibrium water absorption ratio = (W2−W1) / W1
The equilibrium water absorption ratio has a substantially constant minimum value at a temperature higher than the LCST, and increases with a decrease in temperature in a temperature range lower than the LCST. In the present invention, it is preferable that the equilibrium water absorption capacity greatly changes in a narrow temperature range. When the equilibrium water absorption capacity at a temperature higher than the LCST (substantially constant minimum value) is set to 1, at a temperature 2 ° C. lower than the LCST. The equilibrium water absorption ratio is preferably 1.2 or more, more preferably 1.5 or more (particularly 2 or more).
[0029]
(Polymer having LCST)
As the “polymer compound having an LCST” in the present invention, for example, a poly N-substituted acrylamide derivative, a poly N-substituted methacrylamide derivative, and a poly N-substituted acrylamide derivative / poly N-substituted methacrylamide copolymer , Polyvinyl methyl ether, polypropylene oxide, polyethylene oxide, etherified methyl cellulose, partially acetylated polyvinyl alcohol, and the like can be suitably used as various copolymers and / or mixtures as necessary.
[0030]
Among these, a poly N-substituted acrylamide derivative or a poly N-substituted methacrylamide derivative, or an N-substituted acrylamide derivative / poly N-substituted methacrylamide copolymer can be particularly preferably used in the present invention.
[0031]
Specific examples of the polymer compound preferably used in the present invention are listed in ascending order of LCST; poly-N-acryloylpiperidine; poly-Nn-propylmethacrylamide; poly-N-isopropylacrylamide; poly-N, N Poly-N-isopropylmethacrylamide; poly-N-cyclopropylacrylamide; poly-N-acryloylpyrrolidine; poly-N, N-ethylmethylacrylamide; poly-N-cyclopropylmethacrylamide; poly-N- Ethyl acrylamide and the like.
[0032]
The above polymer may be a homopolymer (homopolymer), or may be a copolymer of a monomer constituting the polymer and another monomer. As the other monomer constituting such a copolymer, any of a hydrophilic monomer and a hydrophobic monomer can be used.
[0033]
As the hydrophilic monomer, N-vinylpyrrolidone, vinylpyridine, acrylamide, methacrylamide, N-methylacrylamide, hydroxyethyl methacrylate, hydroxyethyl acrylate, hydroxymethyl methacrylate, hydroxymethyl acrylate, having an acidic group Acrylic acid, methacrylic acid and salts thereof, vinyl sulfonic acid, styrene sulfonic acid, etc., and N, N-dimethylaminoethyl methacrylate, N, N-diethylaminoethyl methacrylate, N, N-dimethylaminopropyl having a basic group Examples include, but are not limited to, acrylamide and salts thereof.
[0034]
On the other hand, examples of the hydrophobic monomer include acrylate derivatives and methacrylate derivatives such as ethyl acrylate, methyl methacrylate, butyl methacrylate, and glycyl methacrylate; N-substituted alkyl methacrylamide derivatives such as Nn-butyl methacrylamide; and vinyl chloride. , Acrylonitrile, styrene, vinyl acetate and the like, but are not limited thereto.
[0035]
In general, it is possible to increase the LCST by copolymerizing a hydrophilic monomer with the polymer compound, while lowering the LCST by copolymerizing a hydrophobic monomer. It becomes possible.
[0036]
The above-mentioned LCST can be regarded as one of the factors that determine the temperature dependence of the equilibrium water absorption capacity of the hydrogel-forming polymer of the present invention. That is, the dependence of the LCST or the hydrogel equilibrium water absorption capacity on the temperature can be controlled by selecting the “copolymer component” as described above.
[0037]
The LCST of the polymer compound having an LCST used in the present invention can be appropriately selected depending on the purpose of use of the heating element, but is preferably 30 ° C. or more and 70 ° C. or less in the aqueous medium contained in the temperature-sensitive hydrogel. In particular, when it is used for a thermal patch for preventing low-temperature burns, the temperature is more preferably 35 ° C or more and 50 ° C or less, further preferably 40 ° C or more and 45 ° C or less.
[0038]
If the LCST is too low, the thermosensitive hydrogel releases most of the water in a low-temperature environment (for example, in an environment at a temperature of 30 ° C. or lower), and the tendency to inhibit heat generation increases. On the other hand, when the LCST exceeds 70 ° C., the release of water from the thermosensitive hydrogel in a high-temperature environment (for example, an environment at a temperature of 45 ° C. or higher) decreases, and the heat generation suppressing effect becomes insufficient.
[0039]
(Crosslinking)
As a method for imparting or introducing a cross-linked structure to a polymer compound as described above, a method of introducing a cross-linked structure when polymerizing a monomer to give the polymer compound, and after the polymerization of the monomer Although a method of introducing a crosslinked structure is mentioned, in the present invention, any of these methods can be used.
[0040]
The former (crosslinking at the time of monomer polymerization) method can be generally carried out by copolymerizing a bifunctional monomer (or a monomer having three or more functional groups). For example, bifunctional monomers such as N, N-methylenebisacrylamide, hydroxyethyl dimethacrylate, and divinylbenzene can be suitably used.
The latter method (introduction of cross-linking after completion of monomer polymerization) can be usually carried out by forming cross-links between molecules by irradiation of light, electron beam, γ-ray, or the like.
Further, such a latter method is, for example, a method in which a polyfunctional molecule having a plurality of functional groups (for example, isocyanate groups) capable of binding to a functional group (for example, an amino group) in a polymer compound is used as a crosslinking agent. And can be carried out by crosslinking the polymer compound. The equilibrium water absorption of the hydrogel-forming polymer in the present invention (particularly, the equilibrium water absorption in a low temperature region lower than the LCST) depends on the above-mentioned crosslinked structure, particularly the crosslink density. Tends to be larger. The effect of the crosslink density on the equilibrium water absorption ratio in a high temperature region higher than the LCST tends to be relatively small, so that the lower the crosslink density, the greater the temperature dependence of the equilibrium water absorption ratio.
In the former method, for example, by changing the copolymerization ratio of the bifunctional monomer, such a “crosslink density” is used. In the latter method, for example, the irradiation amount of light, electron beam, γ-ray, etc. Can be arbitrarily controlled to a desired degree.に お い て In the present invention, the crosslink density is preferably in the range of about 0.02 mol% to about 10 mol%, more preferably about 0.05 mol to about 4 mol%, as a molar ratio of branch points to all monomers. When a crosslinked structure is introduced by the former method (crosslinking during polymerization), the copolymerization weight ratio of the bifunctional monomer to all the monomers (including the bifunctional monomer itself) is about 0.03 wt. % To about 3 wt. % (More preferably from about 0.05 wt.% To about 1.5 wt.%).
[0041]
When the crosslink density exceeds about 10 mol% in the present invention, the temperature dependence of the equilibrium water absorption ratio of the hydrogel-forming polymer of the present invention becomes small. The effect of water absorption-water release is reduced. On the other hand, when the crosslink density is less than about 0.02 mol%, the mechanical strength of the hydrogel-forming polymer becomes weak, making it difficult to handle, and at the same time, the mechanical properties during the swelling and shrinking process due to temperature change. The likelihood of damage is increased.
The crosslink density (molar ratio of branch points to all monomers) as described above can be quantified by, for example, 13C-NMR (nuclear magnetic resonance absorption) measurement, IR (infrared absorption spectrum) measurement, or elemental analysis. It is possible.
[0042]
(Hydrogel or polymer shape)
The shape of the thermosensitive hydrogel or the hydrogel-forming polymer used in the present invention is not particularly limited, and can be appropriately selected depending on the type of the heating element, the method of use, and the like. The shape of the hydrogel or polymer can be various shapes such as microbeads, fibers, films, or amorphous shapes.
[0043]
The size of the hydrogel or the polymer in the present invention is determined by increasing the followability of the process of changing the equilibrium water absorption ratio of the hydrogel-forming polymer with respect to temperature change, that is, the swelling and shrinking process, from the viewpoint of increasing the followability to the temperature. It is preferable to increase the surface area per unit volume of the polymer, that is, to decrease the size per hydrogel or one polymer object (for example, one particle). For example, the size of the hydrogel or polymer in the present invention when dried is preferably in the range of about 0.1 μm to 5 mm, more preferably about 1 μm to 1 mm (particularly about 10 μm to 100 μm).
In the present invention, the “size when dried” of the hydrogel or polymer is the average value of the maximum diameter (maximum dimension) of the hydrogel or polymer (the average value of at least 10 or more measured values). Say. More specifically, in the present invention, the following sizes can be used as the “size when dried”, for example, corresponding to the shape of the hydrogel or polymer.
Microbead shape: Particle size (average particle size)
Fibrous: average length of each fibrous piece
Film shape, irregular shape: Average of maximum size of each piece
In the present invention, in place of the above-mentioned “average value of the maximum value”, the diameter of the “sphere” having a volume equal to the average value of the volume of each piece (the average value when at least 10 pieces are measured) is defined as The hydrogel or polymer may be used as the “size when dried”.
[0044]
(Heating part)
As described above, since the temperature control of the temperature-sensitive heating element of the present invention is based on the absorption and release characteristics of water depending on the temperature of the temperature-sensitive hydrogel, there is no restriction on the configuration / type of the heating section. As long as the member or composition has a conventionally known heat-generating property, it can be used in the present invention without any particular limitation. Examples of such a heat-generating member include a heat-generating member using electricity, a heat-generating member using a dry battery or a solar battery, a paper-like battery, and a chemical heating agent. Among them, a chemical exothermic agent is preferably used in terms of good portability, low cost, and the like.
[0045]
(Chemical exothermic agent)
The “chemical exothermic agent” that can be used in the present invention refers to a compound or composition having a property of generating heat using a chemical reaction. As such a chemical exothermic agent, known chemical exothermic agents can be used without particular limitation as long as the function of the above-mentioned thermosensitive hydrogel is not substantially impaired. From the viewpoint of good portability, low cost, and the like, a chemical exothermic agent utilizing heat of oxidation of iron powder can be suitably used.
[0046]
The composition of such a chemical exothermic agent is a substance system that causes an exothermic reaction in the coexistence of air and water, and among them, an iron powder system, water, and a water retention agent (a reaction aid if necessary). Is preferred. More specifically, iron powder, reduced iron powder (iron powder); activated carbon, charcoal, fiber powder, alumina, silica gel, perlite, vermiculite, sodium chloride, potassium chloride, potassium iodide, potassium thiocyanate, calcium hydroxide , Iron chloride, acetic acid, chloroacetic acid (reaction assistant); water; and a composition in which exothermic raw materials such as superabsorbent resin (water retention agent) are appropriately blended and formulated.
[0047]
The temperature-sensitive hydrogel of the present invention also has functions as water and a water retention agent among them. If necessary, the temperature-sensitive hydrogel may be used in combination with a conventionally known water retention agent. The compounding amount of the thermosensitive hydrogel is preferably about 0.1 to 20 wt%, more preferably about 1 to 10 wt% (particularly about 3 to 5 wt%) of the entire chemical exothermic agent as the thermosensitive hydrogel-forming polymer. Preferably, there is.
[0048]
(salts)
As the chemical exothermic agent, various salts are used as a reaction assistant, but the temperature dependency of the thermosensitive hydrogel may change depending on the type and amount of the salt. This is because, as mentioned above, the LCST behavior is based on hydrophobic interactions. That is, when an ion (salt-out salt) which tends to promote structuring of water coexists, the hydrophobic interaction of the polymer tends to be enhanced and the LCST tends to be reduced as the concentration increases. Conversely, when ions (salt-soluble salts) tending to destroy the structure of water coexist, the hydrophobic interaction of the polymer tends to be weakened with an increase in the concentration, and the LCST tends to increase. In the case of salts having these intermediate properties, the LCST does not change regardless of the amount added.
[0049]
Specific examples include sodium chloride as a salting-out salt, potassium thiocyanate as a salt-soluble salt, and potassium iodide as an intermediate salt. Therefore, the temperature dependency of the temperature-sensitive hydrogel can be controlled by the type and amount of the salt used for the chemical exothermic agent.
[0050]
(Reducing agent)
Furthermore, the present inventors have found that the inclusion of a reducing agent in the thermosensitive hydrogel is extremely effective in controlling the temperature of the chemical exothermic agent.
[0051]
In an embodiment in which such a reducing agent is used in combination, when the heat generated by the oxidation reaction of iron progresses and reaches a predetermined temperature, the reducing agent is released together with water from the thermosensitive hydrogel, and the cooling agent is cooled by the heat of vaporization of water. In addition, the oxidation of iron by the reducing agent acts to prevent the heating element from being excessively heated. On the other hand, when cooled to a temperature lower than the predetermined temperature, the thermosensitive hydrogel becomes
Since the reducing agent is absorbed together with the external water, the cooling and the reduction reaction due to the evaporation of the water are suppressed, and the temperature is prevented from excessively lowering.
[0052]
In addition, when the reducing agent is added, the once oxidized iron is reduced, so that the heat generated by the oxidation reaction can be repeated, and the effect of extending the heat generation duration of the heat generating element is also exerted.
[0053]
As the reducing agent that can be used in the present invention, a known reducing agent can be used without any particular limitation as long as it has a function of inhibiting or suppressing the air oxidation reaction of iron. In the present invention, both a water-soluble reducing agent and a fat-soluble reducing agent can be used, but a water-soluble reducing agent is preferably used because it can be used as a uniform aqueous solution.
[0054]
Examples of the water-soluble reducing agent include, but are not limited to, ascorbic acid (salt), dithionous acid (salt), hydrogen sulfite (salt), hydrogen sulfide, thiourea, cysteine, cystamine, glutathione, and the like. Not something.
[0055]
(Bag-like member)
As described above, since the heating element using the temperature-sensitive hydrogel of the present invention has a temperature control function by itself, it is not always necessary to store the heating element in the “bag-shaped member” when the heating function is exhibited. However, from the viewpoint of ease of handling, manufacture and sale, or safety, it is preferable to arrange or house the heating element of the present invention in a “bag-shaped member”.
[0056]
One example of such an embodiment is shown in the schematic cross-sectional view of FIG. In FIG. 1, a heating element 1 using the temperature-sensitive hydrogel of the present invention is arranged or enclosed in a storage bag 2. In FIG. 1, both ends of the storage bag 2 are sealed by a known means such as a heat seal or an adhesive.
[0057]
In a mode in which the heating action of the heating element 1 is adjusted using the inflow of air, the storage bag 2 is preferably a bag-like member capable of restricting the amount of inflow of air. As a material of such a storage bag 2, a conventionally known material, for example, a material obtained by forming a needle hole in a nonwoven fabric in which polyethylene or the like is laminated as a sealant or a porous film can be used without any particular limitation.
[0058]
As described above, since the basic mechanism of the heat generation control by the conventional ventilation rate restriction and the heat generation control using the temperature-sensitive hydrogel are different, when these two are combined, they contribute synergistically, It is possible to provide a heating element with higher safety.
[0059]
Hereinafter, examples showing the effects of the present invention will be illustrated by comparison with comparative examples, but the present invention is not limited to the following examples.
[0060]
【Example】
Example 1
(Synthesis of thermosensitive hydrogel-forming polymer)
20 g (177 mmol) of N-isopropylacrylamide, 5.39 g (75.9 mmol) of acrylamide, and 0.39 g (2.5 mmol) of N, N′-methylenebisacrylamide were dissolved in 374 mL of distilled water in a 500 mL beaker, and nitrogen was dissolved. At room temperature (25 ° C.) under an air stream, 0.26 g of ammonium persulfate and 0.13 mL of N, N, N ′, N′-tetramethylethylenediamine were added to carry out polymerization. It gelled about 10 minutes after the start of the reaction, but was left at room temperature for 4 hours. The gel was transferred to a household mixer, and 400 mL of distilled water was added and pulverized. Next, 350 mL of ethanol was added, the mixture was heated to 60 ° C, and the gel was recovered by centrifugation (1,500 rpm, 5 minutes). After vacuum drying, the mixture was pulverized again by a mixer to obtain 22 g of a thermosensitive hydrogel-forming polymer.
[0061]
0.30 g of the dried thermosensitive hydrogel-forming polymer was immersed in 5 wt% saline at a predetermined temperature (various temperatures as described below) for 48 hours to swell, and then centrifuged at the predetermined temperature to remove excess water. After removal of, the weight of the thermosensitive hydrogel was measured to determine the equilibrium water absorption ratio by (Equation 1). The ratio was 30 times (25 ° C), 22 times (35 ° C), 11 times (40 ° C), 6 times. Double (42 ° C), triple (44 ° C),
It was three times (50 ° C.).
[0062]
Example 2
(Test of heating element)
0.15 g of the dry thermosensitive hydrogel-forming polymer synthesized in Example 1 and 0.30 g of activated carbon (powder, manufactured by Wako Pure Chemical Industries) were placed in a glass beaker (diameter 3.0 cm, height 4.4 cm). Then, 3.0 g of 5 wt% saline was added, and the mixture was stirred well at room temperature. Next, add 3.0 g of iron powder (manufactured by Wako Pure Chemical Industries), stir well with a spoonful of scrubs, place on a styrene foam plate (size: 20 × 30 cm, thickness: 20 mm), cover the top of the beaker with filter paper, and bottom the beaker. Was measured over time using a thermocouple thermometer (trade name: 2455 type, manufactured by Yokogawa Electric Corporation) (the exothermic agent was stirred every 30 minutes). At this time, the bead type probe (type 2459-07, manufactured by Yokogawa Electric Corporation) of the thermocouple thermometer was placed between the bottom surface of the beaker and the styrene foam plate.
[0063]
Twenty minutes after the iron powder was mixed, the maximum temperature was 48 ° C., and the duration of heat generation at 40 ° C. or more was 3 hours.
[0064]
Example 3
(Test of heating element containing reducing agent)
When the same experiment as in Example 2 was performed except that 0.3 g of ascorbic acid (manufactured by Wako Pure Chemical Industries) was dissolved in the saline solution of Example 2, the maximum temperature reached 44 ° C. 10 minutes after mixing the iron powder, The exothermic duration over ℃ was 5 hours or more.
[0065]
Example 4
(Test of heating element)
In a glass beaker (diameter 3.0 cm, height 4.4 cm), 0.50 g of the dry thermosensitive hydrogel-forming polymer synthesized in Example 1, 0.30 g of activated carbon (powder, manufactured by Wako Pure Chemical Industries), and iron A mixture of 3.0 g of powder (manufactured by Wako Pure Chemical Industries) was thoroughly stirred with a spoonful of medicine. Next, 3.0 g of 5 wt% saline was added thereto, and the mixture was further stirred well at room temperature. The beaker was placed on a styrene foam plate (size: 20 × 30 cm, thickness: 20 mm), the upper part of the beaker was covered with filter paper, and the temperature of the bottom of the beaker was measured with a thermocouple thermometer (trade name: 2455 type, manufactured by Yokogawa Electric Corporation). ) Was measured over time. At this time, a bead-type probe (type 2459-07, manufactured by Yokogawa Electric Corporation) of the thermocouple thermometer was placed between the bottom surface of the beaker and the styrene foam plate (room temperature: 27 ° C., humidity: 64%).
[0066]
The temperature data obtained as described above is shown in the following (Table 1). As shown in Table 1, the maximum temperature (Tm) reached 42.8 ° C. 195 minutes after mixing the saline solution. The average temperature (Ta) from 0 (t0) to 330 minutes (t1) was 40.1 ° C. Therefore, the ratio of Tm / Ta was 1.07.
[0067]
[Table 1]

Comparative Example 1
(Test of heating element using super absorbent resin)
When the same experiment as in Example 2 was performed except that 0.15 g of a commercially available superabsorbent resin (manufactured by Mitsubishi Chemical Corporation, Diawet) was used instead of the temperature-sensitive hydrogel-forming polymer of Example 2, iron was obtained. Twenty minutes after the powder was mixed, the maximum temperature reached 68 ° C, and the duration of heat generation at 40 ° C or higher was 90 minutes.
[0068]
Comparative Example 2
(Test of heating element using super absorbent resin and reducing agent)
The same experiment as in Comparative Example 1 was performed except that 0.3 g of ascorbic acid (manufactured by Wako Pure Chemical Industries, Ltd.) was dissolved and used in the saline solution (3.0 g) used in Comparative Example 1 (room temperature: 27 ° C., Humidity 70%). The temperature data obtained as described above is shown in the following (Table 2). As shown in Table 2, the maximum temperature (Tm) reached 65.5 ° C. 60 minutes after mixing the iron powder. The average temperature (Ta) from 0 (t0) to 195 minutes (t1) was 54.5 ° C. Therefore, the ratio of Tm / Ta was 1.20.
[0069]
[Table 2]

[0070]
【The invention's effect】
As described above, according to the present invention, there is provided a temperature-sensitive heating element including a temperature-sensitive hydrogel composed of at least water and a hydrogel-forming polymer, and having a reduced equilibrium water absorption capacity with increasing temperature. Is done.
[0071]
The temperature-sensitive heating element of the present invention having the above-described configuration is characterized in that the heating member includes a temperature-sensitive hydrogel whose equilibrium water absorption capacity decreases as the temperature rises. Water is released from the temperature-sensitive hydrogel, and the heating element is cooled by the heat of vaporization, thereby preventing the heating element from being excessively heated. On the other hand, when cooled to a temperature lower than the predetermined temperature, the thermosensitive hydrogel absorbs external water, so that cooling due to evaporation of water is suppressed, and the temperature is prevented from excessively lowering. As described above, the temperature-sensitive heating element of the present invention senses the temperature itself and controls the heating temperature more precisely, so that the danger of low-temperature burns and the like can be avoided.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view showing an example of an embodiment of the present invention in which a heating element 1 using a temperature-sensitive hydrogel is disposed in a bag-shaped member 2.
[Explanation of symbols]
1. Heating element using thermosensitive hydrogel 2. Bag-shaped member.

Claims (8)

A thermosensitive heating element comprising at least water and a hydrogel-forming polymer, and including a thermosensitive hydrogel whose equilibrium water absorption capacity decreases with increasing temperature. The temperature-sensitive heating element according to claim 1, wherein a ratio (Tm / Ta) between the maximum temperature (Tm) as the heating element and the average temperature (Ta) is 1.15 or less. 3. The heat-sensitive heating element according to claim 1, wherein the heating element generates heat using a chemical reaction. The temperature-sensitive heating element according to claim 3, wherein the temperature-sensitive hydrogel further contains iron powder. The temperature-sensitive heating element according to claim 3, wherein the temperature-sensitive hydrogel further contains a salt. The temperature-sensitive heating element according to any one of claims 3 to 5, wherein the temperature-sensitive hydrogel further contains a reducing agent. A heating member including a bag-shaped member and a temperature-sensitive heating element disposed inside the bag-shaped member;
A heat-generating member, characterized in that the heat-sensitive heating element comprises at least water and a hydrogel-forming polymer, and contains a temperature-sensitive hydrogel whose equilibrium water absorption capacity decreases with increasing temperature. The heating member according to claim 7, wherein the bag-like member is made of an oxygen barrier film.

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