Heating element, heating device, and method for manufacturing a heating element

Abstract

To provide a heating element that can generate a high amount of heat. [Solution] The heating element 1 includes a graphite sheet 10. The volume resistivity of the graphite sheet 10 is 10 mΩ·mm or more.

Description

Technical Field

[0001] The present disclosure relates to a heating element, a heating appliance, and a method for manufacturing a heating element. More specifically, it relates to a heating element used in heating appliances and the like, a heating appliance including this heating element, and a method for manufacturing this heating element.

Background Art

[0002] As a heat source for heating appliances such as electric heaters, electric stoves, and electric cookers, a heating element that generates Joule heat by electric resistance is used.

[0003] Patent Document 1 discloses a heating element unit. This heating element unit is formed of a graphite film obtained by heat-treating a polymer film or a polymer film added with a filler, and has two-dimensional isotropic thermal conductivity in the plane direction and a temperature characteristic of a positive characteristic in which the resistance value increases as the temperature rises. According to the heating element unit of Patent Document 1, it is said that it is small, highly efficient, has high directivity and uniform heating, and can start up quickly.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Depending on the application such as a heating appliance, the above conventional heating element may have insufficient heat generation, and the heating element is required to obtain a high heat generation amount.

[0006] An object of the present disclosure is to provide a heating element capable of obtaining a high heat generation amount, a heating appliance including this heating element, and a method for manufacturing this heating element.

Means for Solving the Problems

[0007] A heating element according to one aspect of the present disclosure includes a graphite sheet, wherein the volume resistivity of the graphite sheet is 10 mΩ·mm or more.

[0008] A heating device according to one aspect of this disclosure comprises the heating element.

[0009] A method for manufacturing a heating element according to one aspect of the present disclosure comprises a first step of obtaining a graphite substrate by heat-treating a polymer film, and a second step of removing the surface layer portion on at least one side of the graphite substrate. [Effects of the Invention]

[0010] According to this disclosure, it is possible to provide a heating element that can generate a high amount of heat, a heating appliance equipped with this heating element, and a method for manufacturing this heating element. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a schematic cross-sectional view showing the heating element according to this embodiment. [Figure 2] Figure 2 is a schematic cross-sectional view showing a method for manufacturing a heating element according to this embodiment. [Figure 3] Figure 3 is a schematic diagram illustrating the method for measuring the deemed shear strength of a graphite sheet using the SAICAS method. [Modes for carrying out the invention]

[0012] 1. Overview The heating element according to this embodiment will be described below. The following embodiments are only one of many embodiments of this disclosure. The following embodiments can be modified in various ways depending on the design, as long as the objectives of this disclosure are achieved.

[0013] In order to solve the above problems, while the inventors were earnestly studying by focusing on the graphite base material, they found that the calorific value varies depending on a part of the graphite base material, and completed the present disclosure.

[0014] The heating element 1 according to the present embodiment includes a graphite sheet 10. The volume resistivity of the graphite sheet 10 is 10 mΩ·mm or more.

[0015] The heating element 1 according to the present embodiment can obtain a high calorific value. The heating element using the conventional graphite film described above is obtained by heat-treating a polymer film or the like as the graphite film, and uses as it is a graphite film having a dense layer on its surface layer portion. The volume resistivity of this graphite film is usually about 5 mΩ·mm or less. In contrast, the heating element 1 according to the present embodiment uses a specific portion of the graphite film obtained by heat-treating the above-mentioned polymer film or the like as the graphite sheet 10. As a result, the volume resistivity of the graphite sheet 10 can be set to 10 mΩ·mm or more. Therefore, according to the heating element 1 including this graphite sheet 10, a high calorific value can be obtained.

[0016] 2. Details <Heating Element> Hereinafter, the heating element 1 according to the present embodiment will be described with reference to the drawings. Each figure is a schematic diagram, and the ratio of the size and thickness of each component in each figure does not necessarily reflect the actual dimensional ratio.

[0017] FIG. 1 is a cross-sectional view showing an example of the heating element 1 according to the present embodiment. The heating element 1 includes a graphite sheet 10. The heating element 1 may be composed only of the graphite sheet 10, and may include other parts other than the graphite sheet 10 as long as the effects of the present disclosure are not impaired.

[0018] In the heating element 1 according to the present embodiment, the volume resistivity of the graphite sheet 10 is 10 mΩ·mm (10×10 -3It is important that it is above [[Ω·mm]]. By setting the volume resistivity of the graphite sheet 10 to be above the above value, the heating element 1 can obtain a high calorific value. When the volume resistivity of the graphite sheet is less than the above value, the calorific value of the heating element 1 remains low. The "volume resistivity" of the graphite sheet means the volume resistivity (mΩ·mm) in the plane direction in the graphite sheet 10.

[0019] The volume resistivity of the graphite sheet 10 is preferably 11 mΩ·mm or more, more preferably 12 mΩ·mm or more, and even more preferably 13 mΩ·mm or more. The upper limit of the volume resistivity of the graphite sheet 10 is not particularly limited, but for example, it is 20 mΩ·mm or less.

[0020] The "graphite sheet" means a sheet mainly composed of graphite. The "main component" refers to the component with the largest content rate, for example, a component with a content rate of 50% by mass or more, preferably 80% by mass or more, and more preferably 99% by mass or more. Graphite is a kind of allotrope of carbon, also known as graphite. Graphite has a structure in which layers (graphene layers) arranged in a hexagonal honeycomb lattice by sp 2 bonds are bonded in a plurality of layers in the thickness direction by van der Waals forces. Examples of graphite include those in which a plurality of layers of graphite layers are laminated.

[0021] As shown in FIG. 1, the graphite sheet 10 has a surface layer portion 10a and an inner layer portion 10b. The "surface layer portion" refers to the portion from the surface of the graphite sheet to a depth of 20% of the thickness of the graphite sheet. The "inner layer portion" is the portion other than the surface layer portion in the graphite sheet and is the portion between two surface layer portions.

[0022] Regarding the heating element 1, the configuration and the like of the graphite sheet 10 that can have the above-mentioned volume resistivity will be described below.

[0023] In the heating element 1, it is preferable that the density of the surface layer 10a (hereinafter also referred to as density (a)) is 1.2 times or less the density of the inner layer 10b (hereinafter also referred to as density (b)). In this case, the volume resistivity of the graphite sheet 10 can be increased, and the amount of heat generated by the heating element 1 can be increased.

[0024] The ratio of density (a) to density (b) (density (a) / density (b)) is more preferably 1.1 or less, and even more preferably 1.05 or less.

[0025] Furthermore, density (a) is preferably 0.8 times or more than density (b). In this case, the volume resistivity of the graphite sheet 10 can be further increased, and the heat generation of the heating element 1 can be further increased.

[0026] The density (a) / density (b) is more preferably 0.9 or greater, and even more preferably 0.95 or greater.

[0027] It is particularly preferable that the density (a) / density (b) is approximately 1, that is, that the density (a) of the surface layer 10a and the density (b) of the inner layer 10b are of roughly the same magnitude.

[0028] Densities (a) and (b) are both, for example, 0.1 g / cm³. 3 More than 0.25g / cm 3 The following is the value: 0.12 g / cm³ 3 More than 0.16g / cm 3 The following is preferable:

[0029] The "density" of the entire graphite sheet or each part (surface layer or inner layer) refers to the mass value per unit volume (g / cm³). 3 This refers to the arithmetic mean of the densities measured by cutting out a certain volume from multiple points (for example, any 10 points) in the entire graphite sheet or in each part of it.

[0030] In the heating element 1, it is preferable that the deemed shear strength of the surface layer 10a (hereinafter also referred to as strength (a)) is 1.2 times or less the deemed shear strength of the inner layer 10b (hereinafter also referred to as strength (b)). In this case, the volume resistivity of the graphite sheet 10 can be increased, and the amount of heat generated by the heating element 1 can be increased.

[0031] The ratio of strength (a) to strength (b) (strength (a) / strength (b)) is more preferably 1.1 or less, and even more preferably 1.05 or less.

[0032] Furthermore, it is preferable that strength (a) is 0.8 times or more of strength (b). In this case, the volume resistivity of the graphite sheet 10 can be further increased, and the amount of heat generated by the heating element 1 can be further increased.

[0033] The strength (a) / strength (b) ratio is more preferably 0.9 or higher, and even more preferably 0.95 or higher.

[0034] It is particularly preferable that the strength (a) / strength (b) is approximately 1, that is, that the deemed shear strength (a) of the surface layer 10a and the deemed shear strength (b) of the inner layer 10b are of similar magnitude.

[0035] Strength (a) and strength (b) are both preferably, for example, 0.1 MPa or more and 0.8 MPa or less, and 0.25 MPa or more and 0.4 MPa or less.

[0036] The "deemed shear strength" of the entire graphite sheet or each part (surface or inner layer) refers to the deemed shear strength measured by the SAICAS method, and means the arithmetic mean of the deemed shear strengths measured at multiple points (for example, any 10 points) on the entire graphite sheet or each part, at depths from 0.5 μm to 19 μm from each point.

[0037] The SAICAS method, also known as the Surface and Interfacial Cutting Analysis System, is an evaluation method that involves cutting a material from the surface using a sharp cutting edge at a low speed. Figure 3 is a schematic diagram illustrating the method for measuring the deemed shear strength in the surface portion 11 of a graphite sheet. In Figure 3, the arrow D indicates oblique cutting, and the arrow x indicates displacement. By using the SAICAS method, the horizontal force (Fh) and vertical force (Fw) applied to the cutting edge during cutting of the surface portion 11 of the graphite sheet can be measured, and the deemed shear strength in the surface can be calculated from the horizontal force (Fh) applied to the cutting edge 12, the cutting angle of the cutting edge 12, and the cross-sectional area. Specifically, the surface layer 11 of the graphite sheet is fixed to a SAICAS DN-20 (manufactured by Daipla Wintes Co., Ltd.), and a boron nitride blade with a width of 2 mm, a rake angle of 20°, and a relief angle of 10° is used as the cutting edge 12. The cutting speed is set to a constant speed mode of 0.5 μm / sec horizontally and 0.05 μm / sec vertically. The point at which the horizontal load exceeds 0.002 N is defined as the point at which the cutting edge 12 contacts the surface layer 11 of the graphite sheet, and measurements are taken vertically from there to 19 μm, and the deemed shear strength from 0.5 μm to a depth of 19 μm is calculated. The following formula is used for the calculation.

[0038] t = Fh × (2A × Cot(φ)) (t: deemed shear strength, Fh: horizontal force, A: cross-sectional area of ​​the cutting edge, φ: shear angle)

[0039] The graphite sheet 10 can be manufactured, for example, using a graphite substrate 100 obtained by heat-treating a polymer film. Such a graphite substrate 100 usually contains a dense layer 20, which is formed by further crystallization, mainly in the surface portion, in addition to the main intermediate layer. The dense layer usually has a higher density and a higher apparent shear strength than the intermediate layer. Also, the dense layer has a lower volume resistivity than the intermediate layer.

[0040] Since the graphite substrate 100 has the above-described structure, by reducing the proportion of the dense layer 20 and increasing the proportion of the intermediate layer in the graphite substrate 100, the volume resistivity can be increased, and the above-described volume resistivity can be achieved.

[0041] <Heating equipment> The heating device according to this embodiment (hereinafter also referred to as heating device (H)) comprises a heating element 1.

[0042] Since the heating device (H) is equipped with the heating element 1 described above, it can generate a high amount of heat.

[0043] In addition to the heating element 1, the heating device (H) may also include, for example, an electrical circuit that controls the energization state of the heating element 1 to maintain it at a predetermined temperature.

[0044] Examples of heating appliances (H) include electric heaters and other heating appliances, electric stoves and other heating appliances, electric cooktops and toasters, and other cooking appliances.

[0045] <Method for manufacturing a heating element> The heating element 1 according to the above embodiment can be manufactured simply and reliably by, for example, the following method for manufacturing the heating element 1.

[0046] The method for manufacturing the heating element 1 according to this embodiment comprises a first step and a second step.

[0047] [1st step] In this process, a graphite substrate 100 is obtained by heat-treating a polymer film.

[0048] In other words, in this process, a carbonized film is obtained by thermally decomposing a polymer film, and then this carbonized film is further fired at approximately 2600°C to graphiteize it, thereby producing a sheet-like graphite substrate 100.

[0049] As the polymer film, for example, a polyimide film can be used. A polymer film containing a filler may also be used.

[0050] The average thickness of the resulting graphite substrate 100 is, for example, 100 μm or more and 1000 μm or less, and preferably 200 μm or more and 800 μm or less. "Average thickness" refers to the arithmetic mean of each thickness measured at multiple points (for example, any 10 points).

[0051] As shown in Figure 2, the graphite substrate 100 produced by heat treatment of the polymer film typically has a dense layer 20 on both surface portions.

[0052] [Second process] In this process, the surface layer of at least one side of the graphite substrate 100 is removed.

[0053] In other words, in this step, the surface portion including the dense layer 20 on one or both sides of the graphite substrate 100 obtained in the first step is removed. In this step, only the surface portion on one side may be removed, but from the viewpoint of increasing the volume resistivity, it is preferable to remove the surface portions on both sides. This results in a graphite sheet 10 with a small proportion of dense layer 20.

[0054] In this process, the removal of the surface layer is usually performed by cutting away the portion containing the dense layer 20 along a direction parallel to the surface of the graphite substrate 100, as shown in Figure 2. This removal is preferably performed using a slicer. A "slicer" refers to a device that can remove a thin layer of the surface layer of the graphite substrate in the planar direction using a blade or the like. In this case, the graphite sheet 10 can be manufactured more simply and reliably.

[0055] The thickness of the surface layer removed in this process can be appropriately set depending on the distribution of the dense layer 20 in the graphite substrate 100, for example, it may be 20 μm or more, 50 μm or more, 80 μm or more, or 100 μm or more. Alternatively, this thickness may be 200 μm or less, 180 μm or less, or 160 μm or less. By doing so, the volume resistivity of the resulting graphite sheet 10 can be increased.

[0056] The average thickness of the resulting graphite sheet 10 is, for example, 50 μm or more and 500 μm or less, and preferably 100 μm or more and 300 μm or less.

[0057] In this way, a heating element 1 with a high heat output can be manufactured.

[0058] 3. Appearance As is clear from the embodiments described above, this disclosure includes the following aspects. In the following, reference numerals are enclosed in parentheses solely to indicate their correspondence with the embodiments.

[0059] The heating element (1) of the first embodiment includes a graphite sheet 10. The volume resistivity of the graphite sheet 10 is 10 mΩ·mm or more.

[0060] According to the first embodiment, the heating element (1) can obtain a high amount of heat.

[0061] In the second embodiment of the heating element (1), the graphite sheet (10) has a surface layer (10a) and an inner layer (10b). The density of the surface layer (10a) is 1.2 times or less the density of the inner layer (10b).

[0062] According to the second embodiment, the heating element (1) can increase the volume resistivity of the graphite sheet (10), thereby enabling a higher heat generation.

[0063] In the third embodiment of the heating element (1), the graphite sheet (10) has a surface layer (10a) and an inner layer (10b) as in the first or second embodiment. The deemed shear strength of the surface layer (10a) is 1.2 times or less the deemed shear strength of the inner layer (10b).

[0064] According to the third embodiment, the heating element (1) can increase the volume resistivity of the graphite sheet (10), thereby enabling a higher heat generation.

[0065] The heating appliance of the fourth embodiment comprises a heating element (1) according to any one of the first to third embodiments.

[0066] According to the fourth embodiment, the heating device is equipped with the above-mentioned heating element (1), so a high amount of heat can be obtained.

[0067] A method for manufacturing a heating element (1) according to a fifth embodiment comprises a first step and a second step. In the first step, a graphite substrate (100) is obtained by heat-treating a polymer film. In the second step, the surface layer portion of at least one side of the graphite substrate (100) is removed.

[0068] According to the fifth embodiment, a heating element (1) capable of generating a high amount of heat can be manufactured simply and reliably.

[0069] In the manufacturing method of the heating element (1) according to the sixth embodiment, the removal in the second step is performed using a slicer, as in the fifth embodiment.

[0070] According to the sixth embodiment, a heating element (1) capable of generating a high amount of heat can be manufactured more simply and reliably. [Examples]

[0071] The present disclosure will be described in more detail below with reference to examples, but the present disclosure is not limited to these examples.

[0072] <Manufacturing of heating elements> The heating elements of the examples and comparative examples were manufactured as follows. [Manufacturing of graphite substrates] A carbonized film was obtained by thermally decomposing a polyimide film with a thickness of approximately 100 μm. This carbonized film was then calcined at approximately 2600°C to convert it into graphite, thereby obtaining a graphite substrate with a thickness of 576 μm. [Manufacturing of heating elements] (Example 1) The surface layers on both sides of the graphite substrate obtained above were removed to a thickness of 152 μm using a slicer to obtain the heating element of Example 1, which is composed of a graphite sheet with a thickness of 108 μm. [Example 2] Except for setting the thickness of the surface layer to be removed on both sides of the graphite substrate to 154 μm, the heating element of Example 2 was obtained in the same manner as in Example 1, consisting of a graphite sheet with a thickness of 226 μm. [Comparative Example 1] The graphite substrate obtained above was used as is to create the heating element of Comparative Example 1.

[0073] <Measurement> For each of the heating elements obtained above, the density, assumed shear strength, and volume resistivity of the graphite sheet were measured using the method described below. The measurement results are shown in Table 1. (density) For each of the 10 arbitrary points on the graphite sheet of the heating element, a portion of a certain volume was cut out and its density measured. The arithmetic mean of these measurements was then defined as the density. (Deemed shear strength) For 10 arbitrary points on the graphite sheet of the heating element, measurements were taken using the SAICAS method at depths ranging from 0.5 μm to 19 μm from each point, and the arithmetic mean of these measurements was defined as the deemed shear strength. (Volume resistivity) Using a graphite sheet cut into a 50mm square from the heat-generating element obtained above as a test piece, the resistance value (mΩ) of the graphite sheet was measured in accordance with JIS K 7194-1994 (Test method for resistivity of conductive plastics using the 4-probe method) under the conditions of a measurement current of 100mA and a measurement time of 10 seconds in an atmosphere of 23°C and 50% relative humidity. From this resistance value, the surface resistance (Ω / □) was calculated, and the volume resistivity in the planar direction of the graphite sheet (unit: mΩ·mm) was obtained using the formula: Volume resistivity = Surface resistance × Thickness.

[0074] [Table 1]

[0075] Based on the results in Table 1, it is considered that the heating elements of Examples 1 and 2, in which the volume resistivity of the graphite sheet is above a specified value, can produce a high amount of heat. On the other hand, the heating element of Comparative Example 1, in which the volume resistivity is below a specified value, is expected to produce only a low amount of heat. [Explanation of symbols]

[0076] 1. Heating element 10 Graphite Sheets 10a Surface layer 10b Inner layer 20 compact layer

Claims

1. A heating element comprising a graphite sheet, wherein the volume resistivity of the graphite sheet is 10 mΩ·mm or more.

2. The graphite sheet has a surface layer and an inner layer, The density of the surface layer is 1.2 times or less the density of the inner layer. The heating element according to claim 1.

3. The graphite sheet has a surface layer and an inner layer, The deemed shear strength of the surface layer is 1.2 times or less than the deemed shear strength of the inner layer. The heating element according to claim 1.

4. A heating appliance comprising a heating element according to any one of claims 1 to 3.

5. The first step involves obtaining a graphite substrate by heat-treating a polymer film, A second step of removing the surface layer portion on at least one side of the graphite substrate. A method for manufacturing a heating element equipped with the necessary components.

6. The removal in the second step is performed using a slicer. A method for manufacturing a heating element according to claim 5.

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