Heating implement

Abstract

A heating implement (10) wherein: a heat-generating layer (1) contains a carbon component and water; a water-retaining layer (2) contains one or more layers selected from a dispersion layer comprising a thermoplastic resin in which a water-absorbing polymer is dispersed, and a layer comprising a thermoplastic water-absorbing resin; the water-retaining layer (2) holds water; the heat-generating layer (1) and the water-retaining layer (2) are adjacent to each other and are disposed in a closed space sandwiched between a first sheet (3) and a second sheet (4); the first sheet (3) is air-permeable; and in a plan view, the heat-generating layer (1) and the water-retaining layer (2) have a smaller area than the first sheet (3) and the second sheet (4), and there are flap parts that overlap the first sheet (3) and the second sheet (4) on the outside of the outer peripheral edges of the heat-generating layer (1) and the water-retaining layer (2).

Description

heating equipment

[0001] The present invention relates to a heating device.

[0002] Various proposals have been made for heating devices that utilize the heat of oxidation generated by the oxidation reaction of oxidizable metals. For example, Patent Document 1 describes a sweat-absorbing heating structure in which a heat-generating composition is enclosed in a flat pouch. The support on the back of the flat pouch is made of a laminated film consisting of a synthetic resin film and a porous synthetic resin film with a water-absorbing layer interposed between them, and a pressure-sensitive adhesive layer is partially formed on the exposed surface of the porous synthetic resin film. This support ensures close contact with the skin in the area of ​​the pressure-sensitive adhesive layer, while in areas without the pressure-sensitive adhesive layer, sweat and waste products are absorbed by the water-absorbing layer, resulting in a clean skin surface. Patent Document 2 also describes a heating device in which a steam-generating element consisting of a heat-generating layer and a water-absorbent sheet is housed in a breathable pouch. The heat-generating layer contains a water-absorbent polymer, and the mass ratio of the water-absorbent sheet to the water-absorbent polymer is between 0.9 and 15. This is said to improve temperature rise and appropriately increase the amount of water vapor generated. The document describes that the water-absorbent sheet in this heating implement is made of paper, nonwoven fabric, or a laminate of paper and nonwoven fabric, which are made of fibrous materials.

[0003] JP 3-100090 A JP 2017-23712 A

[0004] The discussion of the background art provided herein is intended to generally indicate the context of the disclosure. To the extent that it is described in this background art section, the work of the presently named inventors, as well as statements that may not be prior art at the time of filing, are not admitted, expressly or impliedly, as prior art against the present invention.

[0005] The present invention provides a heating device having a first sheet, a second sheet, a heat-generating layer, and a water-retaining layer. Preferably, the heat-generating layer contains an oxidizable metal, a carbon component, and water. Preferably, the water-retaining layer contains one or more selected from a dispersion layer, which is a layer of thermoplastic resin in which a water-absorbent polymer is dispersed, and a layer of thermoplastic water-absorbent resin. Preferably, the water-retaining layer retains water. Preferably, the heat-generating layer and the water-retaining layer are adjacent to each other. Preferably, the heat-generating layer and the water-retaining layer are arranged in a closed space sandwiched between the first sheet and the second sheet. Preferably, the first sheet is breathable. Preferably, in a plan view of the heating device, the heat-generating layer and the water-retaining layer have smaller areas than the first sheet and the second sheet. Preferably, there is a flap portion where the first sheet and the second sheet overlap, outside the outer periphery of the heat-generating layer and the water-retaining layer.

[0006] The present invention also provides a method for manufacturing a heating device. Preferably, the manufacturing method includes a step of coating one surface of a first sheet with a paint containing an oxidizable metal, a carbon component, and water. Preferably, the manufacturing method includes a step of coating one surface of a second sheet with a slurry of molten thermoplastic resin containing water-absorbent polymer particles and / or a molten thermoplastic water-absorbent resin. Preferably, the manufacturing method includes a step of laminating the two sheets so that the coated surfaces of the two sheets face each other. Preferably, in the manufacturing method, one or both of the first sheet and the second sheet are breathable sheets.

[0007] The above and other features and advantages of the present invention will become more apparent from the following description, taken in conjunction with the accompanying drawings where appropriate.

[0008] 1 is a cross-sectional view schematically showing a preferred embodiment of the heating implement of the present invention. (A) is a cross-sectional view schematically showing another preferred embodiment of the heating implement of the present invention. (B) is a plan view showing an example in which the water-retaining layer in the embodiment of (A) is divided and arranged. (A) is a cross-sectional view schematically showing an example of a water-retaining layer including a dispersion layer. (B) is a cross-sectional view schematically showing an example of a water-retaining layer including a layer of thermoplastic water-absorbent resin. (A) is a plan view showing an example of five locations to be observed when measuring the mass content ratio of the fiber material in the water-retaining layer. (B) is a plan view showing another example of (A). (A) is a plan view showing an example of locations where a cross-section of the heating implement is prepared when measuring the thickness of the water-retaining layer. (B) is a cross-sectional view showing an example of five locations to be observed in the cross section taken along line 5B-5B shown in (A). 1 is a photograph substituted for a drawing, showing an example of an embodiment including an arrangement in which adjacent water-absorbent polymers are in contact with each other in the dispersion layer included in the water-retaining layer. 8A and 8B are cross-sectional views showing an example of five slice positions to be observed in the cross section of the water-retaining layer when measuring the standard deviation of the area distribution of the water-absorbent polymer in the water-retaining layer. In an embodiment where the water-retaining layer is a dispersion layer containing a layer having a water-soluble resin, (A) cross-sectional views schematically showing a state before the water-retaining layer absorbs water, and (B) a state where the water-retaining layer absorbs water and a thermoplastic resin network is formed and the water-absorbent polymer swells. (A) and (B) are photographs substituted for drawings showing an example of the surface state of the dispersion layer on the heat-generating layer side in the state shown in FIG. 8B. (A) and (B) are photographs substituted for drawings showing an example of a state where the dispersion layer contains cracks on the surface on the heat-generating layer side in an embodiment where the water-retaining layer contains a dispersion layer. An explanatory diagram showing a preferred embodiment of the method for manufacturing a heating implement of the present invention. An explanatory diagram showing another preferred embodiment of the method for manufacturing a heating implement of the present invention. An explanatory diagram showing yet another preferred embodiment of the method for manufacturing a heating implement of the present invention. (A) is a cross-sectional view schematically showing a heating implement sample of Comparative Example 1. 1B is a cross-sectional view schematically showing the heating device samples of Comparative Examples 2 and 3. FIG. Detailed Description of the Invention

[0009] The present invention relates to a heating device that can be thinned and at the same time can increase the maximum temperature during heating. "During heating" as used herein means the entire period during which the heating device generates heat.

[0010] A heating device comprises a heat-generating layer containing an oxidizable metal, a carbon component, and water, and a water-retaining layer that controls the amount of water retained by the heat-generating layer. Specifically, the water-retaining layer controls the amount of water retained by the heat-generating layer by absorbing excess water from the heat-generating layer and supplying moisture while the heat-generating layer is generating heat. A water-retaining layer with such functions is essential for the heat-generating properties of the heating device to be well-developed. Heating devices are used in contact with the skin of the human body, and a good fit to the skin is required for proper heat transfer. From the standpoint of such fit, it is preferable to make the thickness of the heating device as thin as possible. Furthermore, the thinner the heating device, the more flexible it becomes, which, combined with the aforementioned fit, enhances the comfortable feel when used on the skin. However, reducing the thickness of the water-retaining layer to achieve this has traditionally been limited by its adverse effect on the heat-generating properties of the heat-generating layer. In other words, there has traditionally been a trade-off between thinning the water-retaining layer and achieving good heat-generating properties, making it difficult to achieve both.

[0011] In contrast, the heating device of the present invention can be made thinner while simultaneously increasing the maximum temperature during heating. Furthermore, the manufacturing method of the heating device of the present invention allows for successful manufacturing of the heating device of the present invention. These and other objects of the present disclosure have been realized, individually or in combination, by the following discoveries.

[0012] Any numerical limit or range set forth herein includes the recited endpoints of that limit or range. Also, all values ​​and subranges within a numerical limit or range are expressly included as if expressly stated. As used herein, the words "singular," "a," "an," and the like mean "one or more." Obviously, numerous modifications and variations of the present invention are possible in light of the above and following disclosures. Accordingly, it should be understood that the present invention may be practiced in embodiments not expressly set forth herein within the scope of the claims. The entire disclosures of the above and following patent documents and other publications are incorporated herein by reference in their entirety as if fully set forth herein.

[0013] The present invention will now be described based on preferred embodiments with reference to the drawings. The heating device 10 preferably comprises a first sheet 3, a second sheet 4, a heat-generating layer 1, and a water-retaining layer 2. The first sheet 3 is typically disposed on the skin side, and the second sheet 4 is typically disposed on the non-skin side. However, the present invention is not limited to this arrangement. For example, the second sheet 4 may be disposed on the skin side. The heat-generating layer 1 preferably contains an oxidizable metal 11, a carbon component 12, and water. The water-retaining layer 2 preferably contains one or more selected from a dispersion layer 22S, which is a layer of thermoplastic resin 22 in which a water-absorbent polymer 21 is dispersed, and a layer 23S, which is a layer of thermoplastic water-absorbent resin 23. The water-retaining layer 2 preferably retains water. The heat-generating layer 1 and the water-retaining layer 2 are preferably adjacent to each other. The heat-generating layer 1 and the water-retaining layer 2 are preferably disposed in a closed space 5 sandwiched between the first sheet 3 and the second sheet 4. The "closed space 5" referred to here refers to a sealed space that prevents the constituent materials of the heat generating layer 1 and water retention layer 2 from leaking outside the heating device 10, and can also be described as a bag-like space with a closed opening. It is preferable that the closed space 5 allows gases such as air and steam to pass in and out. It is preferable that the first sheet 3 is breathable. In a plan view of the heating device 10, the heat generating layer 1 and water retention layer 2 preferably have smaller areas than the first sheet 3 and second sheet 4. In a plan view of the heating device 10, it is preferable that a flap portion 6 where the first sheet 3 and second sheet 4 overlap is located outside the outer periphery of the heat generating layer 1 and water retention layer 2. More specifically, the flap portion 6 is preferably a portion where the first sheet 3 and second sheet 4 extend outside the areas of the heat generating layer 1 and water retention layer 2 in a plan view of the heating device 10, overlapping and joining them in the thickness direction. It is preferable that the heat generating layer 1 and water retention layer 2 are not interposed between the flap portion 6. In a plan view of the heating device 10, it is preferable that the area inside the flap portion 6 forms the closed space 5 sandwiched between the first sheet 3 and the second sheet 4. Examples of such an embodiment are shown in Figures 1, 2, 3(A) and 3(B).

[0014] When the heat generating layer 1 comes into contact with air, it generates heat through an oxidation reaction of the oxidizable metal 11. At that time, the water contained therein promotes the oxidation reaction of the oxidizable metal. The carbon component 12 has at least one of the functions of water retention, oxygen supply, and catalytic activity, and promotes the heat generation. The heating device 10 can apply heat to the skin through the heat generated by the heat generating layer 1. Furthermore, in the heating device 10, the water in the heat generating layer 1 may be heated by the heat generated, and hot steam may be applied to the skin.

[0015] As described above, the water retention layer 2 absorbs excess water contained in the heat generating layer 1 and also supplies moisture to the heat generating layer 1 during heat generation, thereby controlling the amount of water retention so as to optimize the heat generating characteristics of the heat generating layer 1. In the dispersion layer 22S described above, the water retention amount of the heat generating layer 1 is controlled by the water absorption capacity of the water-absorbent polymer 21. Furthermore, in the layer 23S of the thermoplastic water-absorbent resin 23 described above, the thermoplastic water-absorbent resin 23 itself has water absorption capacity and controls the amount of water retention of the heat generating layer 1.

[0016] When the water-retaining layer 2 includes the aforementioned dispersion layer 22S, the dispersion layer 22S is a continuous layer in which the thermoplastic resin 22, containing the water-absorbent polymer 21, fills the interior of the layer. Similarly, when the water-retaining layer 2 includes the aforementioned layer 23S of the thermoplastic water-absorbent resin 23, the layer 23S is a continuous layer in which the thermoplastic water-absorbent resin 23 fills the interior of the layer. A water-retaining layer 2 including such a layer is preferably a sheet. The term "continuous layer" as used herein refers to a layer in which the thermoplastic resin 22 or the thermoplastic water-absorbent resin 23 is filled as a single mass, as opposed to a fiber aggregate consisting of an accumulation of multiple separate fibers. The term "continuous layer" includes not only a completely continuous state, but also a state in which the resin components are packed together to form the entire layer, even if cracks are present. Furthermore, in the dispersion layer 22S, a layer in which the thermoplastic resin 22 is filled so as to fix the arrangement of the water-absorbent polymer 21 is referred to as a "continuous layer." The water-absorbing polymer 21 is a surface-crosslinked polymer material known as SAP (Superabsorbent Polymer).

[0017] As described above, the water retaining layer 2 includes a continuous layer of the thermoplastic resin 22 or the thermoplastic water-absorbent resin 23, and therefore the gaps between the fibers, which are present in conventional fiber aggregates, are reduced, making it possible to significantly reduce the thickness of the water retaining layer 2 compared to a fiber layer, thereby making it possible to make it thinner.

[0018] At the same time, the above-described configuration of the water-retaining layer 2 enables uniform water-absorption capacity. The uniformity of water-absorption capacity here primarily refers to the planar direction. The dispersion and arrangement of the water-absorbent polymer 21 is typically fixed in the dispersion layer 22S. This prevents uneven distribution of the water-absorbent polymer due to movement after manufacturing the heating tool. This minimizes fluctuations in the water-absorption capacity of the water-retaining layer 2 and ensures uniformity. In the manufacturing method described below, the water-retaining layer 2 is preferably formed by dispersing the water-absorbent polymer 21 in a slurry of the thermoplastic resin 22 and applying the dispersion. Forming the water-retaining layer 2 through this process facilitates control of the dispersion and arrangement of the water-absorbent polymer, making it easier to achieve uniform water-absorption capacity in the resulting water-retaining layer 2. Furthermore, in the layer 23S of the thermoplastic water-absorbent resin 23, the thermoplastic water-absorbent resin 23 itself absorbs water, so the entire layer exhibits water-absorption capacity. This minimizes fluctuations in the water-absorption capacity of the water-retaining layer 2 and ensures uniformity, as described above. In this way, the water retention layer 2 exhibits uniform water absorption, making it possible to uniformly control the amount of water retention throughout the adjacent heat generation layer 1. As a result, the heating device 10 has a thinner water retention layer 2, reducing its thickness, while simultaneously achieving stable expression of good heat generation characteristics. The heat generation can reach a maximum temperature of, for example, 45°C or higher when measured in accordance with JIS standard S4100, thanks to the uniform control of the amount of water retention within the heat generation layer 1 by the water retention layer 2.

[0019] As described above, the heating device 10 of this embodiment can be made thinner and at the same time can increase the maximum temperature during heating.

[0020] It is preferable that the dispersion layer 22S and the layer 23S of the thermoplastic water-absorbent resin 23 in the water-retaining layer 2 have elasticity. This allows the heating device 10 to be made thinner, improving flexibility and fit to the skin, while also providing a comfortable feel to the skin with a certain degree of elasticity despite its thinness. Furthermore, the "thermoplasticity" of the thermoplastic resin 22 and thermoplastic water-absorbent resin 23 in the water-retaining layer 2 can soften as the heat generation layer 1 generates heat. This makes the heating device 10 softer during use than before use, and the aforementioned soft feel to the skin increases over time during use.

[0021] In the heating device 10 of this embodiment, the heat-generating layer 1 and the water-retaining layer 2 are preferably laminated in the thickness direction of the heating device 10. The order of lamination can be determined as appropriate. For example, the breathable first sheet 3 and the heat-generating layer 1 may be arranged so that they are in contact with each other. In this case, the water-retaining layer 2 adjacent to the heat-generating layer 1 is typically arranged so that it is in contact with the second sheet 4. When the heating device 10 is used with the first sheet 3 facing the skin, the heat generated by the heat-generating layer 1 is not blocked by the water-retaining layer 2 and can be more effectively transferred to the skin via the first sheet 3. Furthermore, the close distance between the heat-generating layer 1 and the skin facilitates heat transfer to the skin. An example of this embodiment is shown in Figure 1. The water-retaining layer 2 may also be arranged so that it is in contact with the first sheet 3. In this case, it is preferable that the area of ​​the water-retaining layer 2 is smaller than the area of ​​the heat-generating layer 1 when viewed from the first sheet 3 side. When the heating device 10 is used with the first sheet 3 facing the skin, the airflow obstruction caused by the water-retaining layer 2 is reduced, allowing the heat-generating layer 1 to generate heat and provide heat to the skin more effectively. Examples of this embodiment are shown in Figures 2(A) and (B). As shown in Figure 2(A), the width of the water retentive layer 2 may be shorter than the width of the heat generating layer 1. Alternatively, or in addition to this, as shown in Figure 2(B), the water retentive layer 2 may be formed into a plurality of strips and arranged intermittently on the plane of the heat generating layer 1.

[0022] When the water retaining layer 2 is in contact with the first sheet 3, the ratio (M2 / M1) of the area M2 of the water retaining layer 2 to the area M1 of the heat generating layer 1 is preferably 1.2 or less, more preferably 1.1 or less, and even more preferably 1.0 or less, from the viewpoint of more effectively avoiding inhibition of air permeability by the water retaining layer 2. The ratio (M2 / M1) is preferably 0.2 or more, more preferably 0.3 or more, and even more preferably 0.5 or more, from the viewpoint of more effectively controlling the amount of water retained in the heat generating layer 1 by the water retaining layer 2.

[0023] In the heating device 10 of this embodiment, it is preferable to reduce the content of fibrous material in the water retentive layer 2 from the viewpoint of more suitably achieving the aforementioned thinning. From this viewpoint, the planar area of ​​the fibrous material in the water retentive layer 2 is 0% to 10%, preferably 5% or less, and more preferably 3% or less of the planar area of ​​the entire water retentive layer 2. Furthermore, it is preferable that the proportion of the planar area of ​​the fibrous material is 0%.

[0024] (Method for measuring the ratio of the planar area of ​​the fiber material to the planar area of ​​the entire water-retaining layer 2) (i) Pretreatment First, 5 minutes after initiating the heat-generating reaction of the heating device 10 to be measured, such as by opening the packaging bag, cut the first sheet 3 and second sheet 4 extending outward in the planar direction of the heat-generating layer 1 and water-retaining layer 2 without cutting them. Next, remove the sheet covering the outer surface of the heat-generating layer 1 (first sheet 3 in the laminated form shown in Figure 1, or second sheet 4 in the laminated form shown in Figure 2), and then remove the heat-generating layer 1 with a spatula. This operation is carried out in a nitrogen atmosphere with an oxygen concentration of 3% or less from the time the packaging bag is opened until the time the heat-generating layer 1 is removed with the spatula. (ii) Measurement Next, observe and photograph the surface of the water-retaining layer 2 using a microscope (VHX-5000, manufactured by Keyence Corporation). At this time, a 1 mm section of the central part of the water-retaining layer 2 is cut. ２ and 1 mm in the center ２ 1mm apart at 10mm intervals from each of the four sides ２ For example, in the case of a water-retaining layer 2 having a continuous plane as shown in FIG. 4(A), a central portion P1 of the surface area and portions P2 to P5 surrounding it are observed and photographed. In addition, for example, in the case of a water-retaining layer 2 having a plurality of stripes as shown in FIG. 4(B), a 1 mm２ , 1 mm at the corresponding points P2 and P3 of the horizontal stripe on the left and right from P1 ２ , 1 mm at points P4 and P5 spaced 10 mm above and below P1 ２ 4A and 4B show the case of the laminated structure shown in FIG. 1, but in the case of the laminated structure shown in FIG. 2, the sheet below the water-retaining layer 2 is the first sheet 3 in the above measurement. Next, the area ratio of the fiber material to the other materials is calculated using image editing software. The area is the average value of five points. The area is 1 mm ２ The entire surface is measured. ImageJ (open source) is used as the image editing software for this measurement.

[0025] The thickness of the water-retaining layer 2 is preferably 500 μm or less, more preferably 400 μm or less, and even more preferably 300 μm or less, from the viewpoint of further enhancing the comfortable feel of the heating device 10. The water-retaining layer 2 has a continuous layer of thermoplastic resin 22 and / or thermoplastic water-absorbent resin 23, making it possible to achieve a thickness within the above range, which is not possible with conventional fiber assemblies with voids between the fibers. For example, while a conventional polymer sheet in which a water-absorbent polymer is supported on a fiber sheet such as a nonwoven fabric has a thickness of approximately 600 μm, as measured by the following method, the thickness of the water-retaining layer 2 of the present invention can be significantly thinner. Furthermore, from the viewpoint of ensuring water absorption capacity, the thickness of the water-retaining layer 2 is preferably 140 μm or more, more preferably 150 μm or more, and even more preferably 200 μm or more.

[0026] (Method for Measuring the Thickness of the Water Retaining Layer 2) (i) Pretreatment: Five minutes after initiating the exothermic reaction of the heating device 10 to be measured, such as by opening the packaging bag, the center of the heating device is cut with scissors to prepare a cross section. (ii) Measurement: Next, a total of five locations are observed and photographed on the cross section: the center of the width of the water retaining layer 2 and locations 10 mm and 20 mm apart from the center. The thickness of the water retaining layer 2 is measured from the photographed images. The average thickness of the five locations is taken as the thickness. For example, as shown in Figure 5(A), a cross section is prepared at a position that is half the width T1 of the heating section 10 (T1 / 2 = T2). Furthermore, as shown in Figure 5(B), the thicknesses of the cross sections of the center C1 of the width of the water retaining section 2, locations C2 and C3 10 mm apart from the center C1, and locations C4 and C5 20 mm apart from the center are measured as described above. The average thickness is taken as the thickness of the water retaining layer 2. Although FIG. 5B shows the case of the laminated structure shown in FIG. 1, the same measurement can be performed in the case of the laminated structure shown in FIG.

[0027] In the heating device 10 of this embodiment, when the water retaining layer 2 includes the above-mentioned dispersion layer 22S, the following structures (1) to (10) can be mentioned as preferred structures of the dispersion layer 22S. The water retaining layer 2 may include any one of the following structures (1) to (10), or may include a combination of two or more of them.

[0028] (1) The content ratio of the water-absorbent polymer 21 relative to the total mass of the water-retaining layer 2 is preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 45% by mass or more, from the viewpoints of further increasing the absorption capacity of the water-retaining layer 2, more preferably suppressing excess water in the heat-generating layer 1, and better exhibiting the excellent heat-generating properties of the heat-generating layer 1. Furthermore, the content ratio of the water-absorbent polymer 21 relative to the total mass of the water-retaining layer 2 is preferably 65% ​​by mass or less, more preferably 60% by mass or less, and even more preferably 55% by mass or less, from the viewpoints of keeping the water-absorbent capacity of the water-retaining layer 2 within a more appropriate range and more preferably maintaining the water content necessary for heat generation in the heat-generating layer 1, and of maintaining appropriate fluidity of the slurry in the manufacturing method example described below and improving uniform dispersibility of the water-absorbent polymer.

[0029] (2) The content ratio of the thermoplastic resin 22 to the total mass of the water-retaining layer 2 is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more, from the viewpoint of facilitating more uniform distribution of the water-absorbent polymer 21 in the dispersion layer 22S. This improves the coatability (the property of being able to coat smoothly without unevenness or dripping) of the "slurry of molten thermoplastic resin containing a water-absorbent polymer" in the manufacturing method example described below. Furthermore, the content ratio of the thermoplastic resin 22 to the total mass of the water-retaining layer 2 is practically 60% by mass or less.

[0030] (Method for measuring the mass ratio of the water-absorbent polymer 21 and thermoplastic resin 22 to the total mass of the water-retaining layer 2) (i) Pretreatment: The same treatment as (i) Pretreatment in (Method for measuring the ratio of the planar area of ​​the fiber material to the planar area of ​​the total water-retaining layer 2) is performed. (ii) Measurement: Next, the water-retaining layer 2 (dispersion layer 22S) and the sheet covering its outer surface (second sheet 4 in the configuration shown in Figure 1, or first sheet 3 in the laminated configuration shown in Figure 2) are removed, and the mass A is measured. Thereafter, the removed water-retaining layer 2 and the sheet are immersed in deionized water to allow the water-absorbent polymer 21 to absorb sufficient water. When the water-absorbent polymer 21 has sufficiently absorbed water, the thermoplastic resin 22 and the water-absorbent polymer 21 separate. The sheet also separates from the water-retaining layer 2. If the water-absorbent polymer 21 has penetrated into the thermoplastic resin 22, it is necessary to remove the water-absorbent polymer 21. To do this, pressure is applied with the fingers to squeeze out the water-absorbent polymer 21. Whether the water-absorbent polymer 21 has been sufficiently separated can be determined by whether the water-absorbent polymer 21 is present when the thermoplastic resin 22 is removed and immersed in deionized water again. Next, the thermoplastic resin 22 in a state separated from the water-absorbent polymer 21 and the sheet are removed. These are left to dry for 72 hours at a temperature of 25°C, a pressure of 101.3 kPa, and a humidity of 50%, and the mass B of the thermoplastic resin 22 and the mass C of the sheet are measured. Next, the water-absorbent polymer 21 in a water-absorbed state is left to dry for 72 hours at a temperature of 60°C, a pressure of 0.4 MPa, and a humidity of 50%, and the mass D is measured. From the mass ratio, the mass % (B / (A-C) = mass ratio of the thermoplastic resin 22, D / (A-C) = mass ratio of the water-absorbent polymer 21) is calculated.

[0031] (3) A section including a thickness cross section obtained by cutting the water-retaining layer 2 to a width of 1 mm in the planar direction will be described. From the viewpoint of better expressing the heat-generating properties of the heating device 10 through the uniform water-absorption capacity of the water-retaining layer 2, the standard deviation of the area value of the water-absorbent polymer 21 in the thickness cross section of the five sections is preferably 0 to 10, more preferably 5 or less, and even more preferably 3 or less. An example of the arrangement configuration is shown in Figure 6. In the example of the cross section shown in Figure 6, the standard deviation of the area value of the water-absorbent polymer 21 displayed in white is 2.3, which means that the water-absorbent polymer is uniformly arranged in the planar direction.

[0032] (Method for measuring the standard deviation of the area value of the water-absorbent polymer 21 in the water-retaining layer 2) (i) Pretreatment Six hours after the start of the exothermic reaction of the heating device 10 to be measured, such as by opening the packaging bag, a cross section in the thickness direction of the heating device 10 is cut out in the same manner as in (i) pretreatment in (Method for measuring the thickness of the water-retaining layer 2) described above. Note that six hours from the start of the exothermic reaction refers to the time required for water to be released from the water-absorbent polymer 21 of the water-retaining layer 2. Whether water has been sufficiently released from the water-absorbent polymer 21 can be determined by the change in mass of the water-retaining layer. If water has not been sufficiently released after six hours, the mass change is measured six more hours from that point. The mass change is measured by taking the difference between X and Y, where X is the mass at the start of the measurement, i.e., the aforementioned six-hour point, and Y is the mass one hour later. If the difference between X and Y is less than 1%, it is determined that water has been sufficiently released from the water-absorbent polymer 21. The mass change at this time is measured using a mass meter capable of measuring to three decimal points. The above-mentioned six-hour period and the method for determining and treating water release also apply to other measurement methods described herein that require a six-hour exothermic reaction as a pretreatment. (ii) Measurement Next, slices containing a thickness cross section are prepared by cutting 1 mm wide slices in the planar direction of the cross section. Specifically, the slices are prepared at five locations: the center of the width of the water-retaining layer 2, and two locations spaced 10 mm and 20 mm apart from the center. For example, as shown in Figure 7, slices D1 to D5 are prepared at five locations C1 to C5 on the cross section of the heating device 10: the center and two locations on each side of the center. While Figure 7 shows the laminated structure shown in Figure 1, similar measurements can be made for the laminated structure shown in Figure 2. Next, the cross sections of the five slices are observed and photographed using a scanning electron microscope (SEM: JSM-6510, manufactured by JEOL Ltd.). Next, the area ratio of the water-absorbing polymer 21 to the other parts is calculated using image editing software. The area is the average value of five points. The area is measured over a 1 mm full width. The above-mentioned image editing software is also used for this measurement.

[0033] (4) The dispersion layer 22S preferably contains one or more selected from the water-soluble resin 24 and sodium chloride 25. When the water-soluble resin 24 and sodium chloride 25 come into contact with water and dissolve, voids are formed within the dispersion layer 22S of the water-retaining layer 2. The formation of these voids increases the contact opportunity between the water-absorbent polymer 21 and water, further improving the water absorption capacity of the water-retaining layer 2. In the manufacturing method example described below, the one or more selected from the water-soluble resin 24 and sodium chloride 25 are preferably mixed in the same tank as the thermoplastic resin 22 in which the water-absorbent polymer 21 is dispersed. This allows the one or more selected from the water-soluble resin 24 and sodium chloride 25 to be suitably dispersed and disposed in the dispersion layer 22S. From the viewpoint of more effectively exerting the above-mentioned effect, the total content of the water-soluble resin 24 and sodium chloride 25 relative to the total mass of the water-retaining layer 2 is preferably 2% by mass or more and 30% by mass or less, more preferably 25% by mass or less.

[0034] The water-soluble resin 24 is preferably present in a mixed state with the thermoplastic resin 22 prior to contact with the heating layer raw materials during the manufacturing process. This allows the water-soluble resin 24 to dissolve in water and form a network of thermoplastic resin 24 when it comes into contact with water during the subsequent contact with the heating layer raw materials process. That is, the water-soluble resin 24 falls out, and a network of thermoplastic resin 22 forms around it, forming water channels in the voids S. An example of this configuration is shown in Figures 8(A) and 8(B) and 9. In the cross-sectional schematic diagram of Figure 8(A), the thermoplastic resin 22 and the water-soluble resin 24 are mixed to form a dispersion layer 22S, and the water-absorbent polymer 21 is dispersed and fixed within the dispersion layer 22S. In the water-retaining layer 2 adjacent to the heating layer 1, the water-soluble resin 24 dissolves in water, creating voids S in the water-soluble resin 24 area, as shown in Figure 8(B). 9(A) and 9(B), for example, when observing the water retentive layer 2 from the side of the heat generating layer 1, it can be seen that the thermoplastic resin 22 containing the water-absorbing polymer 21 forms a network surrounding the voids S. In this way, the voids S function as water channels within the network of the thermoplastic resin 22, and water from the heat generating layer 1 is more quickly supplied to the water-absorbing polymer 21 through these channels and retained therein.

[0035] It is preferable that sodium chloride 25 exists as particles in the thermoplastic resin layer before it comes into contact with water, i.e., before it comes into contact with the raw materials for the heat generating layer during the manufacturing process. When sodium chloride 25 comes into contact with water during the process of contacting the raw materials for the heat generating layer, the particles of sodium chloride 25 dissolve in water, creating voids equal to the volume of the particles, and forming water channels similar to those described above.

[0036] (5) The dispersion layer 22S preferably contains a surfactant. The surfactant increases the water permeability in the water retention layer 2. This increases the contact opportunity between the water-absorbent polymer and water, further improving the water absorption capacity of the water retention layer 2. From the viewpoint of more effectively exerting the above-mentioned effect, the content of the surfactant relative to the total mass of the water retention layer 2 is preferably 0.1% by mass or more and 3% by mass or less, and more preferably 1% by mass or less.

[0037] (Method for confirming the presence of water-soluble resin 24, sodium chloride 25, and surfactant in water-retaining layer 2) Using the same method as described above (Method for measuring the mass ratio of water-absorbent polymer 21 and thermoplastic resin 22 to the total mass of water-retaining layer 2), the removed water-retaining layer 2 and the sheet covering the outer surface of the water-retaining layer 2 are immersed in deionized water. Next, the thermoplastic resin 22, water-absorbent polymer 21, and the sheet, as well as the aqueous layer in which the water-retaining layer 2 was immersed, are extracted. Next, the extracted thermoplastic resin 22 and the sheet are left to dry for 72 hours at 25°C, 101.3 kPa, and 50% humidity. The extracted aqueous layer is then left to dry for 72 hours at 60°C, 0.4 MPa, and 50% humidity. The precipitate after drying is analyzed. Specifically, a water-soluble resin is determined to be contained if the viscosity increases when the precipitate is immersed in deionized water of an equivalent mass to the precipitate. Sodium chloride is determined to be contained if the electrical conductivity increases when the precipitate is immersed in deionized water of an equivalent mass. Surfactants are determined by measuring the content of surfactants using the method described in "Qualitative Testing Method for Surfactants" by the Japan Spinner Inspection Association (Tadanori Inoko and Takashi Nakabayashi, "Qualitative Testing Method for Surfactants," Textile Product Consumption Science, Japan Textile Product Consumption Science Association, 1978, Vol. 19, No. 3, pp. 96-103). This method can determine whether the water-soluble resin 24, sodium chloride 25, and surfactant are contained within the water-retaining layer. Furthermore, the content ratios of the water-soluble resin 24, sodium chloride 25, and surfactant relative to the total water-retaining layer 2 are calculated by dividing the mass of the precipitated water-soluble resin 24, sodium chloride 25, and surfactant by the total mass of the water-retaining layer 2, which is measured before the immersion. Specifically, the content ratio is calculated based on the calculation formula shown in the above (Method for measuring the content mass ratio of the water-absorbent polymer 21 and the thermoplastic resin 22 to the total mass of the water-retaining layer 2).

[0038] (6) The dispersion layer 22S preferably includes an arrangement in which adjacent water-absorbent polymers 21, 21 are in contact with each other. This facilitates physical movement of water between the water-absorbent polymers 21, 21 within the water-retaining layer 2, further improving the water-absorption capacity of the water-retaining layer 2. An example of this arrangement is shown in Fig. 6. In the cross section shown in Fig. 6, a plurality of arrangements 21J in which particles (white) of the water-absorbent polymer 21 are in contact with each other in the planar direction are arranged in the thickness direction within the water-retaining layer 2.

[0039] (Method for confirming the arrangement in which the water-absorbent polymers are in contact with each other) Six hours after the start of the exothermic reaction of the heating device 10 to be measured, such as by opening the packaging bag, a cross section in the thickness direction of the heating device 10 is cut out in the same manner as in the pretreatment (i) in the above-mentioned (Method for measuring the thickness of the water-retaining layer 2). At this time, slices including a thickness cross section cut out in a 1 mm width in the planar direction are prepared using the same method as in the above-mentioned (Method for measuring the standard deviation of the area value of the water-absorbent polymer 21 in the water-retaining layer 2). Specifically, the slices are prepared at a total of five locations on the cross section: the center of the width of the water-retaining layer 2 and locations spaced 10 mm and 20 mm apart on both sides of the center (for example, slices D1 to D5 in Figure 7). Next, the thickness cross sections of the five slices are confirmed using an SEM. When visually inspecting the observed cut surface, if the water-absorbent polymers (white) are adjacent to each other as shown in Figure 6, it is naturally determined that they are adjacent even when the polymers absorb water and swell, i.e., before the reaction begins.

[0040] (7) In the configuration of (6) above, it is preferable that the water-absorbing polymer 21 includes a polymer that is exposed on the surface of the dispersion layer 22S that faces the heat-generating layer 1. This exposure acts as a driving force, making it easier to absorb water from the heat-generating layer 1.

[0041] (8) It is preferable that the dispersion layer 22S includes cracks K on the surface on the side of the heat generating layer 1. Water can easily penetrate through the cracks K, increasing the chance of contact between the water-absorbent polymer 21 and water, and further improving the water absorption capacity of the water retention layer 2. Examples of the cracks K are shown in the areas indicated by the dashed lines and arrows in Figures 10(A) and (B).

[0042] (Method for checking for exposed water-absorbent polymer and cracks on the surface of the dispersion layer 22S facing the heat-generating layer 1) Six hours after initiating the heat-generating reaction of the heating device 10 to be measured, such as by opening the packaging bag, the heat-generating layer 1 and the sheet covering its outer surface (first sheet 3 in the case of the laminated configuration shown in Figure 1, or second sheet 4 in the case of the laminated configuration shown in Figure 2) are removed using the same method as described above (method for measuring the ratio of the planar area of ​​the fiber material to the planar area of ​​the entire water-retaining layer 2). Next, the surface of the dispersion layer 22S is observed using an SEM. If the water-absorbent polymer 21 or cracks as shown in Figure 10 are confirmed by visual inspection of the observed surface, it is determined that exposed water-absorbent polymer 21 or cracks exist. The presence or absence of cracks remains the same whether immediately after opening or six hours has passed.

[0043] (9) In the water retention layer 2, the water dispersion is preferably uniformly dispersed in the thickness direction and the planar direction. This is inferred from the fact that the water-absorbent polymer 21 is uniformly dispersed in the thickness direction and the planar direction. The supply of water becomes more remarkable by the action of one or more of the above-mentioned configurations (4) to (8).

[0044] (10) From the viewpoint of ease of handling, the average particle size of the water-absorbent polymer in the water-retaining layer is preferably 10 μm or more. Also, from the viewpoint of reducing the thickness of the heating device, the average particle size of the water-absorbent polymer in the water-retaining layer is preferably 320 μm or less, more preferably 180 μm or less, and even more preferably 80 μm or less.

[0045] In reality, the thickness of the heating device 10 of this embodiment is 0.5 mm or more. From the viewpoint of thinning, the thickness of the heating device 10 is preferably 1.2 mm or less, more preferably 1.0 mm or less, and even more preferably 0.8 mm or less. The thickness of the heating device 10 is measured in accordance with JIS K6250 using a constant pressure thickness measuring device PG-20J (manufactured by Teclock Corporation).

[0046] As mentioned above, the heating device 10 of this embodiment can achieve good heat generation characteristics while being thin. From this perspective, the maximum temperature of the heating device 10 when it heats up is preferably 45°C or higher, more preferably 60°C or higher, and even more preferably 65°C or higher. This temperature characteristic allows the user to feel an appropriate warmth. Furthermore, from the perspective of ensuring safety, the maximum temperature of the heating device 10 when it heats up is preferably 75°C or lower, more preferably 73°C or lower, and even more preferably 70°C or lower. Furthermore, from the perspective of speeding up the user's sense of heat generation and further improving the user experience, it is preferable that the time it takes for the heating device 10 to reach 45°C from 35°C is greater than 0 minutes. In practice, this time is preferably 5 minutes or less, more preferably 3 minutes or less, and even more preferably 1 minute or less.

[0047] (Method of measuring the heat generation characteristics of the heating implement 10) Using a measuring device conforming to JIS S4100, the second sheet 4 side of the heating implement 10 is attached to a measurement surface within one minute after opening, and heat generation measurement is carried out.

[0048] In the heating device 10 of this embodiment, the oxidizable metal 11 and carbon component 12 that make up the heat generating layer 1, and the water-absorbing polymer 21, thermoplastic resin 22, thermoplastic water-absorbing resin 23, water-soluble resin 24 and surfactant that make up the water-retaining layer 2 can be made from a variety of materials that can effectively achieve the above-mentioned effects.

[0049] The oxidizable metal 11 may be any of various metals that generate heat of oxidation reaction, such as powders or fibers of one or more metals selected from the group consisting of iron, aluminum, zinc, manganese, magnesium, and calcium. Among these, iron powder is preferred from the viewpoints of ease of handling, safety, production cost, storage stability, and stability. Examples of iron powder include one or more metals selected from the group consisting of reduced iron powder and atomized iron powder.

[0050] The carbon component 12 may be any of a variety of materials having one or more properties selected from the group consisting of water retention, oxygen supply, and catalytic activity. For example, one or more materials selected from activated carbon, acetylene black, and graphite may be used. Of these, activated carbon is preferred from the viewpoints of facilitating oxygen adsorption when wet and maintaining a constant moisture content in the heating layer 1. As the activated carbon, one or more fine powder or granular materials selected from coconut shell charcoal, wood powder charcoal, and peat charcoal are more preferably used. Of these, wood powder charcoal is preferred.

[0051] The water-absorbent polymer 21 in the water-retaining layer 2 typically contains a hydrophilic polymer having a cross-linked structure capable of absorbing and retaining liquid at least 20 times its own weight. The shape of the water-absorbent polymer 21 preferably includes one or more shapes selected from the group consisting of granular, spherical, block, grape-bunch-like, and fibrous shapes.

[0052] The water-absorbent polymer 21 preferably contains one or more selected from the group consisting of starch, cross-linked carboxylmethylated cellulose, a polymer of acrylic acid or an alkali metal salt of acrylic acid, or a copolymer thereof, and polyacrylic acid or a salt thereof, or a polyacrylate graft polymer. Among these, it is preferable to contain one or more selected from a polymer of acrylic acid or an alkali metal salt of acrylic acid, or a copolymer thereof, and polyacrylic acid or a salt thereof, or a polyacrylate graft polymer, since this makes it easier to maintain the amount of water supported by the water-absorbent polymer 21 within a specific range.

[0053] The thermoplastic resin 22 in the water retentive layer 2 is preferably a hot-melt material that has fluidity at room temperature or at high temperatures, from the viewpoint of providing a solid material that maintains the shape of the water retentive layer 2 before, during, and after use, and from the viewpoint of better forming the water retentive layer 2 in the coating method described below. Any common hot-melt material can be used as the material for forming the water retentive layer 2 without any particular restrictions. Specific examples of hot-melt materials include styrene-isobutylene, acrylic, urethane, rubber, silicone, polyisobutylene, styrene-isobutylene-styrene, and polyacrylic acid polymers. Of these, styrene-isobutylene is preferred from the viewpoint of coatability.

[0054] The thermoplastic water-absorbing resin 23 in the water-retaining layer 2 may be a material that has fluidity and water-absorbing ability at room temperature or high temperature, from the viewpoint of providing a solidity that allows the water-retaining layer 2 to maintain its shape before, during, and after use, and from the viewpoint of better forming the water-retaining layer 2 in the coating method described below. Specific examples of the thermoplastic water-absorbing resin 23 include nonionic polyalkylene oxide-based and nylon-based materials.

[0055] The water-soluble resin 24 contained in the water-retaining layer 2 may be a material that has the same characteristics as the thermoplastic resin 22 and is soluble in water. Specific examples of water-soluble resin materials include polyethylene oxide-based and polyethylene glycol-based materials with hydrophilic groups. Among these, polyethylene oxide-based materials are preferred from the viewpoint of coatability.

[0056] As the surfactant contained in the water-retaining layer 2, any general surfactant can be used without particular limitation in order to assist the water absorption of the water-absorbent polymer. Specific examples of the surfactant include nonionic surfactants such as polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, and polyoxyethylene polyoxypropylene glycol. Among these, polyoxyethylene alkyl ether is preferred from the viewpoint of the heat-generating performance of the coating material.

[0057] The first sheet 3 can be made of various materials capable of serving as breathable members. Examples include various fiber sheets such as nonwoven fabrics, and porous sheets made of synthetic resins. Specifically, the nonwoven fabric preferably includes one or more types selected from, for example, needle-punched nonwoven fabrics, air-through nonwoven fabrics, and spunbond nonwoven fabrics. The porous synthetic resin sheet preferably includes, for example, a film obtained by stretching polyethylene or polypropylene containing calcium carbonate or the like. When using such a porous sheet, a fiber sheet such as the nonwoven fabric described above may be laminated on the outer surface of the porous sheet to enhance the texture of the first sheet 3. Furthermore, a sheet other than a porous sheet may be used as long as it is impermeable to water but permeable to oxygen and water vapor, and is leak-proof. For example, the first sheet 3 can be made of woven fabric, nonwoven fabric, paper, synthetic paper, etc., which is a mixture of one or more types selected from artificial fibers such as polyamide, vinylon, polyester, rayon, acetate, acrylic resin, polyethylene, polypropylene, and polyvinyl chloride, and natural fibers such as pulp, cotton, hemp, silk, and animal hair.

[0058] From the viewpoint of determining the directionality of heat, the second sheet 4 is preferably one having lower breathability than the first sheet 3. For example, the second sheet 4 may be a synthetic resin film having no holes or having fewer holes than the porous sheet of the first sheet 3. Furthermore, a fiber sheet such as the nonwoven fabric may be laminated on the outer surface of the synthetic resin film to enhance the texture.

[0059] The heating device 10 of this embodiment may contain other agents in addition to the above-mentioned agents, as long as the above-mentioned effects are not impaired. For example, it may contain agents that affect the feeling of use, such as menthol or fragrance.

[0060] Next, a preferred embodiment of the manufacturing method of the heating implement of the present invention will be described below. The manufacturing method of the heating implement of this embodiment (hereinafter also simply referred to as the manufacturing method of this embodiment or the manufacturing method) preferably includes a step S1 in which a paint containing an oxidizable metal 11, a carbon component 12, and water (collectively referred to as the heating layer raw material G1) is applied to one side of a first raw material sheet Q1. By step S1, the heating layer 1 of the heating implement 10 described above can be formed.

[0061] Next, it is preferable to have a step S2 in which a slurry of molten thermoplastic resin 22 containing water-absorbent polymer 21 and / or molten thermoplastic water-absorbent resin 23 (collectively referred to as water-retaining layer raw material G2) is applied to one side of the second raw material sheet Q2. By step S2, the water-retaining layer 2 in the heating device 10 described above can be formed. At this time, since the molten thermoplastic resin 22 containing the water-absorbent polymer 21 is in the form of a slurry, the dispersibility of the water-absorbent polymer 21 can be suitably controlled by stirring or the like. By this control, it is possible to suitably achieve the dispersion and arrangement of the water-absorbent polymer 21 in the water-retaining layer 2 in the heating device 10 described above and the uniformity of the water-absorbent ability of the water-retaining layer 2.

[0062] Furthermore, it is preferable to have a step S3 in which the first raw material sheet Q1 and the second raw material sheet Q2 are bonded together so that their coated surfaces face each other. Step S3 allows for the formation of a laminated structure in the heating device 10, in which the heat-generating layer 1 and the water-retaining layer 2 are disposed in the space between the first sheet 3 and the second sheet 4. It is preferable that one or both of the first raw material sheet Q1 and the second raw material sheet Q2 used in the above-mentioned steps S1, S2, and S3 are breathable sheets. That is, either the first raw material sheet Q1 or the second raw material sheet Q2 becomes the breathable first sheet 3 in the above-mentioned heating device 10. When the first raw material sheet Q1 is the breathable first sheet 3, it is possible to form a heating device 10 with a laminated structure such as that shown in FIG. 1, for example. On the other hand, when the second raw material sheet Q2 is the breathable first sheet 3, it is possible to form a heating device 10 with a laminated structure such as that shown in FIG. 2(A) and / or FIG. 2(B), for example, by reducing the area of ​​the water-retaining layer 2 and the area of ​​the heat-generating layer 1.

[0063] An example of this manufacturing method is shown in FIG. 11. In the example manufacturing method shown in FIG. 11, step S1 is performed continuously in a heat-generating layer coating device 101 and step S2 is performed continuously in a water-retaining layer coating device 102 using long first and second raw material sheets Q1 and Q2. Downstream of steps S1 and S2, step S3 is performed continuously. More specifically, in step S3, downstream of steps S1 and S2, the coated surfaces of the first and second raw material sheets Q1 and Q2 are overlapped facing each other to form a continuous laminate along the machine direction (MD). Further downstream, in a sealing and cutting device 103, the laminate is cut at predetermined length intervals along the cross direction (CD) perpendicular to the machine direction, while simultaneously sealing the four sides of the cut pieces. In this manner, multiple heating devices 10 of this embodiment described above can be manufactured along the MD direction.

[0064] In step S2, it is preferable to manage the water retaining layer raw material G2 to be applied as follows: (S21) Temperature management of melting tank for thermoplastic resin and thermoplastic water absorbent resin It is preferable to manage the melting tank at a temperature higher than the softening points of the thermoplastic resin and thermoplastic water absorbent resin. It is preferable to manage the melting tank at a temperature lower than the carbonization points of the thermoplastic resin and thermoplastic water absorbent resin. (S22) Nozzle lip clearance management It is preferable to manage the nozzle for applying the water retaining layer raw material G2 so that the lip clearance is wider than the maximum particle size of the water absorbent polymer 21.

[0065] In the above-mentioned sealing and cutting device 103, when cutting along the CD direction and sealing the four sides of the cut piece, from the viewpoint of further enhancing the airtightness of the obtained heating device 10 and preventing contamination of the sealing and cutting device 103, it is preferable to carry out steps S1 and S2 as follows. That is, it is preferable to apply the paint and the slurry and / or the molten thermoplastic water-absorbent resin intermittently in the MD direction. Then, it is preferable to seal the first raw material sheet Q1 and the second raw material sheet Q2 outside the coated area in the MD direction. An example of an embodiment of this manufacturing method is shown in Figure 12.

[0066] It is preferable that the coating width (H1, H2) in the CD direction of the paint and the slurry and / or the molten thermoplastic water-absorbent resin is narrower than the width (H3) of the first raw material sheet Q1 and the second raw material sheet Q2. In addition, it is preferable to seal the first raw material sheet Q1 and the second raw material sheet Q2 outside the coated area in the CD direction. Furthermore, from the viewpoint of preventing inhibition of breathability of the heating device 10 to be manufactured, it is preferable that the above-mentioned coating widths (H1, H2) be H1 > H2. Examples of embodiments of these manufacturing methods are shown in Figure 12.

[0067] From the viewpoint of maintaining good breathability of the manufactured heating device 10, it is preferable to apply the paint and the slurry and / or the molten thermoplastic water-absorbent resin intermittently in the CD direction. This is particularly effective when the second raw material sheet Q2 is a breathable sheet and the layered structure of the heating device 10 as shown in Figure 2 is manufactured. An example of an embodiment of this manufacturing method is shown in Figure 13.

[0068] When the step S2 includes a step of coating one surface of the second raw material sheet Q2 with the slurry, the average particle size of the water-absorbent polymer 21 is preferably 1 μm or more, more preferably 10 μm or more, and even more preferably 40 μm or more from the viewpoint of ease of handling. Also, the average particle size of the water-absorbent polymer 21 is preferably 360 μm or less, more preferably 100 μm or less, and even more preferably 80 μm or less from the viewpoint of further improving the dispersibility of the water-absorbent polymer 21 and the coatability of the slurry.

[0069] In step S1, sodium chloride may be contained in the coating material. This makes it possible to omit the step of adding sodium chloride later and efficiently improve the heat generating properties of the heat generating layer 1. From the viewpoint of ensuring coatability, the content of sodium chloride in the coating material is preferably 0% by mass or more and 30% by mass or less, more preferably 17% by mass or less, and even more preferably 10% by mass or less.

[0070] When process S2 includes a step of applying the slurry to one side of the second raw material sheet Q2, in order to improve the application properties, it is preferable that the content ratio of the thermoplastic resin 22 in the slurry is the same as the aforementioned "content ratio of the thermoplastic resin 22 relative to the total mass of the water retention layer 2."

[0071] When step S2 includes a step of applying the slurry to one surface of the second raw material sheet Q2, it is preferable that the slurry contains one or more selected from the water-soluble resin 24 and sodium chloride 25. As a result, in the water-retaining layer 2 (dispersion layer 22S) of the obtained heating device 10, as described above, the water-soluble resin 24 and sodium chloride 25 dissolve in water to form water channels, and water in the heat-generating layer 1 is more quickly supplied to and retained by the water-absorbent polymer 21. In this regard, it is preferable to perform a process of mixing one or two selected from the water-soluble resin 24 and sodium chloride 25 in a tank containing the thermoplastic resin 22 having the water-absorbent polymer 21 dispersed therein, prior to step S2 and / or in step S2. This improves the dispersion state of the water-soluble resin 24 and sodium chloride 25 in the slurry, allowing the water channels to be formed more uniformly and with less bias within the water-retaining layer 2 (dispersion layer 22S). In order to more effectively exert the above-mentioned effect, it is preferable that the total content ratio of the water-soluble resin 24 and sodium chloride 25 relative to the total mass of the slurry is the same as the above-mentioned "total content ratio of the water-soluble resin 24 and sodium chloride 25 relative to the total mass of the water-retaining layer 2."

[0072] From the same viewpoint as above, it is preferable to add a surfactant to the slurry, and more preferably, this treatment is carried out in a tank containing the thermoplastic resin 22 having the water-absorbing polymer 21 dispersed therein. The content ratio of the surfactant to the total mass of the slurry is preferably the same as the "content ratio of the surfactant to the total mass of the water-retaining layer 2" described above.

[0073] When step S2 includes a step of applying the slurry to one surface of the second raw material sheet Q2, it is preferable to include a step of pressing the applied slurry with a roll. This allows for more effective formation of the cracks in the water retaining layer 2. In particular, applying and pressing the slurry containing one or more selected from the water-soluble resin 24 and sodium chloride 25 is preferable, as this facilitates more clear formation of cracks originating from the water-soluble resin 24 and sodium chloride 25. The pressing force is preferably 0.2 kN or more, more preferably 5 kN or more, and even more preferably 30 kN or more, from the viewpoint of more clearly forming cracks in the water retaining layer 2. The pressing force is preferably 94 kN or less, from the viewpoint of ensuring water absorption performance.

[0074] When step S2 includes a step of applying the slurry to one surface of the second raw material sheet Q2, from the viewpoint of improving the coatability, the ratio of the mass proportion of the thermoplastic resin 22 to the total mass proportion of the water-absorbent polymer 21, sodium chloride 25, and water-soluble resin 24 in the total mass of the slurry (mass proportion of thermoplastic resin / (mass proportion of water-absorbent polymer + mass proportion of sodium chloride + mass proportion of water-soluble resin)) is preferably 0.5 or more, more preferably 0.8 or more, and even more preferably 1.3 or more. From the viewpoint of improving the water absorbency, the ratio of the mass proportion of the thermoplastic resin 22 to the total mass proportion of the water-absorbent polymer 21, sodium chloride 25, and water-soluble resin 24 in the total mass of the slurry (mass proportion of thermoplastic resin / (mass proportion of water-absorbent polymer + mass proportion of sodium chloride + mass proportion of water-soluble resin)) is preferably 5 or less, more preferably 3 or less, and even more preferably 2 or less.

[0075] The present invention will be described in more detail below based on examples, but the present invention should not be construed as being limited thereto. In these examples, "parts" and "%" are all based on mass unless otherwise specified. In Table 1 below, "-" means that the item does not have a corresponding value, etc.

[0076] (Example 1) A sample of the heating device of Example 1 shown in Figure 1 was produced by the manufacturing method shown in Figure 11. The first sheet 3 was a breathable sheet having an air permeability of 1500 seconds / 100 mL and a size of 63 mm x 63 mm. The second sheet 4 was a sheet having a basis weight of 32 g / m². ２ The heat generating layer 1 and the water retaining layer 2 were laminated paper with a size of 63 mm x 63 mm and made of a laminate of paper and a film. The heat generating layer 1 and the water retaining layer 2 were 49 mm x 49 mm and had the compositions shown in Table 1. The area M1 of the heat generating layer / the area M2 of the water retaining layer was 1.0. Specifically, the water retaining layer 2 was formed by heating and mixing 50% by mass of powder of the water-absorbing polymer "Sunfresh YH-2" (trade name, Sanyo Chemical Industries, Ltd., average particle diameter 65 mm) and 50% by mass of solid thermoplastic resin "H2052U" (trade name, manufactured by Bostik-Nitta Corporation), to form a layer (dispersion layer) of thermoplastic resin in which the water-absorbing polymer was dispersed (see FIG. 3(A)).

[0077] (Examples 2 and 3) Heating device samples of Examples 2 and 3 were prepared in the same manner as Example 1, except that the heat generating layer 1 and the water retaining layer 2 had the compositions shown in Table 1. More specifically, the water retaining layer 2 was made by adding sodium chloride particles to the same water-absorbent polymer and thermoplastic resin as in Example 1, as shown in Figure 3(A).

[0078] (Examples 4 and 5) Heating device samples of Examples 4 and 5 were prepared in the same manner as Example 1, except that the water retentive layer 2 had the composition shown in Table 1. The water retentive layer 2 in Example 4 was made of a thermoplastic resin "ME-716" (trade name, manufactured by Henkel Japan Co., Ltd.). The water retentive layer 2 in Example 5 was made of a layer of 100% by mass of a thermoplastic water-absorbent resin "Aquacork TW" (trade name, manufactured by Sumitomo Seika Chemicals Co., Ltd.) (see Figure 3(B)).

[0079] (Examples 6 to 10) Heating device samples of Examples 6 to 10 were prepared in the same manner as Example 1, except that the water-retaining layer 2 had the composition shown in Table 1. The water-retaining layer 2 of Examples 6 and 7 was prepared by adding a powder of water-soluble resin "ALCOX L-11" (trade name, manufactured by Meisei Chemical Industry Co., Ltd.) to the water-absorbent polymer powder and thermoplastic resin solid of Example 1, and mixing them under heat to obtain the composition shown in Table 1. The water-retaining layer 2 of Examples 8 and 9 was prepared by adding a surfactant "1150S-60" (trade name, manufactured by Kao Corporation) to the water-soluble resin of Example 7 without the water-soluble resin, and had the composition shown in Table 1. The water-retaining layer 2 of Example 10 was prepared by removing the water-soluble resin from the water-retaining layer of Example 6 and having the composition shown in Table 1. The water-retaining layer 2 of Example 10 was arranged in the stripe form shown in Figure 4(B), and the "area of ​​heat-generating layer / area of ​​water-retaining layer" was set to "2".

[0080] (Comparative Example 1) A heating device sample of Comparative Example 1 was prepared in the same manner as in Example 1, as shown in Table 1, except that the water-retaining layer 2 was replaced with a polymer sheet "PS-120PHC" (trade name, manufactured by Ino Paper Co., Ltd.) in which a water-absorbent polymer 21 was sandwiched between pulp 26, as the water-retaining layer 291 (FIG. 14(A)).

[0081] (Comparative Example 2) The same amount of water-absorbing polymer (powder) as used in Example 1 was placed between the heat generating layer 1 and the first sheet 3, and the second sheet 4 was placed in contact with the heat generating layer 1 with an area (49 mm × 49 mm) equal to the area of ​​the heat generating layer 1 in a plan view. Furthermore, the outside of the second sheet 4 was covered with a covering sheet 9 (made of the same material as the second sheet 4, with a basis weight of 71 g / m ２ A heating device sample of Comparative Example 2 was prepared in the same manner as in Example 1, except that it was covered with a layer of water-absorbent polymer (size: 63 mm x 63 mm), as shown in Table 1 (Fig. 14(B)). The powdered water-absorbent polymer was scattered over the uneven surface 1 of the heat-generating layer 1, forming a water-retaining layer 292 that conformed to the uneven surface of the heat-generating layer 1, as shown in Fig. 14(B). For this reason, the water-absorbent polymer could not be removed to measure the layer thickness, and the item "Thickness of water-retaining layer" in Table 1 is displayed as "-".

[0082] (Comparative Example 3) A heating device sample of Comparative Example 3 was prepared in the same manner as in Comparative Example 2, except that the absorbent polymer "Sunfresh ST-D500" (trade name, Sanyo Chemical Industries, Ltd., average particle diameter 380 mm) (powder) shown in Table 1 was used in the same amount as in Example 1.

[0083] In each of the above examples and comparative examples, various items related to the water-retaining layer were measured. In doing so, the above-mentioned measuring methods were used as necessary. Similarly, the thickness of the heating device was measured using the above-mentioned measuring methods.

[0084] Next, the maximum temperature, rise time (time required to reach 45°C from 35°C), and duration of fever (time required to reach 45°C or higher) generated by the heating device sample were measured using the following method. In the fever measurement, the horizontal axis was used to plot time and the vertical axis to indicate temperature in 10-second intervals. From the plotted results, the maximum temperature (°C), rise time (min), and duration (min) were calculated. Specifically, the maximum temperature (°C) was the highest temperature (°C) between the start and end of the measurement, the rise time (min) was the time (min) required to reach 45°C from 35°C after the start of the measurement, and the duration (min) was the time (min) required to reach 45°C or higher between the start and end of the measurement.

[0085] Furthermore, the "coatability" during the manufacturing process of each heating device was evaluated using the following method. Five judges familiar with sheet processing visually judged the coatability of the water-retaining layer, and a sensory evaluation was conducted based on the average of the five judges' judgments. 20 g of the sample was heated to 180°C and evaluated 20 minutes later. Sample 1 (only thermoplastic resin "H2052U") was given a score of 100, indicating the best coatability, and Sample 2 (Example 3) was given a score of 0, and each Example was assigned a score.

[0086] The results of the above evaluation measurements are shown in Table 5.

[0087]

[0088] As shown in Table 1, the heating device samples of each Example were able to achieve both a thinner thickness and a higher maximum temperature during heating compared to the heating device samples of each Comparative Example. This compatibility was also achieved in Example 10, even when the "heat-generating layer area / water-retaining layer area" ratio was increased. Furthermore, despite being thinner than the heating device samples of each Comparative Example, the heating device samples of each Example exhibited excellent heat-generating characteristics equivalent to those of the heating device samples of each Comparative Example in terms of rise time and heat generation duration. Additionally, Examples 1, 4, and 8-10 showed good results with regard to the coatability of the water-retaining layer during the manufacturing process of the heating device samples of each Example. This is due to the large value of the ratio of the mass fraction of the thermoplastic resin to (mass fraction of the water-absorbent polymer + mass fraction of sodium chloride + mass fraction of the water-soluble resin).

[0089] Although the present invention has been described in conjunction with its embodiments and examples, we do not intend to limit our invention to any of the details of the description unless otherwise specified, and believe that the claims should be broadly construed without departing from the spirit and scope of the invention as set forth in the appended claims.

[0090] REFERENCE SIGNS LIST 1 heat-generating layer 11 oxidizable metal 12 carbon component 2 water-retaining layer 21 water-absorbent polymer 22 thermoplastic resin 22S dispersion layer 23 thermoplastic water-absorbent resin 23S layer of thermoplastic water-absorbent resin 24 water-soluble resin 3 first sheet 4 second sheet 5 closed space 6 flap portion 10 heating device

Claims

1. A warming device having a first sheet, a second sheet, a heat generating layer and a water retention layer, wherein the heat generating layer contains an oxidizable metal, a carbon component and water, the water retention layer includes one or more selected from a dispersion layer which is a layer of a thermoplastic resin in which a water-absorbing polymer is dispersed and a layer of a thermoplastic water-absorbing resin, the water retention layer retains water, the heat generating layer and the water retention layer are adjacent to each other and are disposed in a closed space sandwiched between the first sheet and the second sheet, the first sheet is breathable, in a plan view, the heat generating layer and the water retention layer are smaller in area than the first sheet and the second sheet, and there is a flap portion where the first sheet and the second sheet overlap outside the outer peripheral edges of the heat generating layer and the water retention layer.

2. The warming device according to claim 1, wherein the heat generating layer is in contact with the first sheet.

3. The warming device according to claim 1, wherein the water retention layer is in contact with the first sheet, and in a plan view from the first sheet side, the area of the water retention layer is smaller than the area of the heat generating layer.

4. The warming device according to any one of claims 1 to 3, wherein the plan view area of the fiber material in the water retention layer is 0% or more and 10% or less, preferably 5% or less, more preferably 3% or less of the total plan view area of the water retention layer.

5. The warming device according to any one of claims 1 to 4, wherein the thickness of the water retention layer is 140 μm or more and 500 μm or less, preferably 150 μm or more and 400 μm or less, more preferably 200 μm or more and 300 μm or less.

6. The warming device according to any one of claims 1 to 5, wherein the water retention layer includes the dispersion layer, and the content ratio of the thermoplastic resin with respect to the total mass of the water retention layer is 20% by mass or more and 60% by mass or less, preferably 30% by mass or more, more preferably 40% by mass or more.

7. The warming device according to any one of claims 1 to 6, wherein the water retention layer includes the dispersion layer, and for a section including a thickness cross-section obtained by cutting out a 1 mm width of the water retention layer in a planar direction, the standard deviation of the area value of the water-absorbing polymer in the thickness cut surfaces of 5 such sections is 0 or more and 10 or less, preferably 5 or less, more preferably 3 or less.

8. The warming device according to any one of claims 1 to 7, wherein the water retention layer includes the dispersion layer, and the dispersion layer includes one or more selected from a water-soluble resin and sodium chloride.

9. The total content ratio of the water-soluble resin and the sodium chloride with respect to the mass of the entire water retention layer is 2% by mass or more and 30% by mass or less, preferably 25% by mass or less. The heating device according to claim 8.

10. The water retention layer includes the dispersion layer, and the dispersion layer contains a surfactant. The heating device according to any one of claims 1 to 9.

11. The content ratio of the surfactant with respect to the mass of the entire water retention layer is 0.1% by mass or more and 3% by mass or less, preferably 1% by mass or less. The heating device according to claim 10.

12. The water retention layer includes the dispersion layer, and the dispersion layer includes an arrangement configuration in which adjacent water-absorbing polymers are in contact with each other. The heating device according to any one of claims 1 to 11.

13. The water-absorbing polymer includes those exposed on the surface of the dispersion layer on the side of the heat-generating layer. The heating device according to claim 12.

14. The water retention layer includes the dispersion layer, and the dispersion layer includes a crack portion on the surface on the side of the heat-generating layer. The heating device according to any one of claims 1 to 13.

15. The thickness of the heating device is 0.5 mm or more and 1.2 mm or less, preferably 1.0 mm or less, more preferably 0.8 mm or less. The heating device according to any one of claims 1 to 14.

16. The maximum temperature during heat generation of the heating device is 45°C or more and 75°C or less, preferably 60°C or more and 73°C or less, more preferably 65°C or more and 70°C or less. The heating device according to any one of claims 1 to 15.

17. The time taken for the heating device to reach from 35°C to 45°C is more than 0 minutes and 5 minutes or less, preferably 3 minutes or less, more preferably 1 minute or less. The heating device according to any one of claims 1 to 16.

18. A step of applying a paint containing an oxidizable metal, a carbon component, and water to one surface of a first raw material sheet; a step of applying a slurry of a molten thermoplastic resin containing a water-absorbing polymer and / or a molten thermoplastic water-absorbing resin to one surface of a second raw material sheet; a step of bonding the coated surfaces of the first raw material sheet and the second raw material sheet so as to face each other; and one or both of the first raw material sheet and the second raw material sheet being a breathable sheet. A method for manufacturing a heating device.

19. The method for manufacturing a warming device according to claim 18, wherein the paint, the slurry, and / or the molten thermoplastic water-absorbing resin are intermittently applied in the machine flow direction, and the first raw material sheet and the second raw material sheet outside the applied portion in the machine flow direction are sealed.

20. The method for manufacturing a warming device according to claim 18 or 19, wherein the application width in the width direction orthogonal to the machine flow direction of the paint, the slurry, and / or the molten thermoplastic water-absorbing resin is made narrower than the widths of the first raw material sheet and the second raw material sheet, and the first raw material sheet and the second raw material sheet outside the applied portion in the width direction are sealed.

21. The method for manufacturing a warming device according to any one of claims 18 to 20, wherein the paint, the slurry, and / or the molten thermoplastic water-absorbing resin are intermittently applied in the width direction intersecting the machine flow direction.

22. The method for manufacturing a warming device according to any one of claims 18 to 21, which includes a step of applying the slurry on one surface of the second raw material sheet, and the average particle diameter of the water-absorbing polymer is 1 μm or more and 360 μm or less, preferably 10 μm or more and 100 μm or less, more preferably 40 μm or more and 80 μm or less.

23. The method for manufacturing a warming device according to any one of claims 18 to 22, wherein the content ratio of sodium chloride in the paint is 0% by mass or more and 30% by mass or less, preferably 17% by mass or less, more preferably 10% by mass or less.

24. The method for manufacturing a warming device according to any one of claims 18 to 23, which includes a step of applying the slurry on one surface of the second raw material sheet, and the slurry contains one or more selected from a water-soluble resin and sodium chloride.

25. The method for manufacturing a warming device according to any one of claims 18 to 24, which includes a step of applying the slurry on one surface of the second raw material sheet and a step of pressing the applied slurry with a roll.

26. A method for manufacturing a heating device according to any one of claims 18 to 25, the method having a step of applying the slurry to one surface of the second raw material sheet, and the ratio of the mass ratio of the thermoplastic resin to the mass ratios of the water-absorbing polymer, sodium chloride, and water-soluble resin in the total mass of the slurry (mass ratio of thermoplastic resin / (mass ratio of water-absorbing polymer + mass ratio of sodium chloride + mass ratio of water-soluble resin)) being 0.5 or more and 5 or less, preferably 0.8 or more and 3 or less, and more preferably 1.3 or more and 2 or less.

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