Heating element, heater, heater module, and method for manufacturing heating element

Abstract

A heating element (46) constituting a belt-shaped heater line is configured such that short metal fibers are at least partially bound together. The magnitude of the ratio of the resistivity of the heating element (46) as measured along a second direction orthogonal to the longitudinal direction with respect to the resistivity of the heating element (46) as measured along a first direction that is the longitudinal direction of the heating element (46) is of a magnitude within the range of 0.9 to 1.1. The magnitude of the ratio of the resistivity of the heating element (46) as measured along the first direction to the resistivity of the heating element (46) as measured along a third direction that forms an angle of 45° with respect to the first direction at the surface of the heating element (46) is 0.8 to 1.2.

Description

[Technical Field]

[0001] The present invention relates to a heating element that is formed from a belt-shaped heater wire that extends along a plane, a heater, a heater module, and a method for manufacturing the heating element. [Background technology]

[0002] Various types of sheet-shaped heaters have been known for some time. For example, Japanese Patent Publication No. 2015-122180 (JP2015-122180A) discloses a flexible heater that includes a highly heat-conductive flexible sheet made of heat-resistant, highly heat-conductive fibers such as metal fibers, and a heater wire disposed in close proximity to or in contact with one side of the highly heat-conductive sheet, with the other side of the highly heat-conductive sheet facing the object to be heated. This heater can stably heat to a predetermined temperature within a very wide temperature range and can prevent the heater wire from melting or breaking due to excessive heating, making it suitable for use in heating molding dies and extruders. Summary of the Invention

[0003] The above-mentioned conventional heaters are composed of a highly heat-conductive sheet made of metal fibers, etc. However, when such a highly heat-conductive sheet is manufactured using a wet papermaking machine, the longitudinal direction of the metal fibers contained in the highly heat-conductive sheet generally coincides with the conveyor's transport direction (papermaking direction), resulting in the metal fibers becoming oriented. In this case, uneven conductivity occurs in the highly heat-conductive sheet, which causes the problem of uneven heat generation depending on the part of the sheet when an electric current is passed through the highly heat-conductive sheet.

[0004] The present invention has been made in consideration of these points, and aims to provide a heating element, a heater, a heater module, and a method for manufacturing a heating element that can prevent uneven heat generation.

[0005] The heating element of the present invention is A heating element that is a belt-shaped heater wire, The heater wire is configured so that the metal short fibers are at least partially bonded to each other, a ratio of a resistivity of the heating element measured along a second direction perpendicular to the longitudinal direction to a resistivity of the heating element measured along a first direction that is a longitudinal direction of the heating element is in the range of 0.9 to 1.1; The ratio of the resistivity of the heating element measured along the first direction to the resistivity of the heating element measured along the third direction that forms an angle of 45° with the first direction on the surface of the heating element is 0.8 or less or 1.2 or more.

[0006] The heater of the present invention comprises: The heating element described above; an insulator laminated on at least one surface of the heating element; The present invention is characterized by the following.

[0007] A heater module of the present invention is a heater module including the heater described above and a temperature regulator, The heater and the temperature regulator are arranged in series in the direction of flow of the fluid to be heated.

[0008] The method for producing a heating element of the present invention comprises the steps of: A method for manufacturing a heating element that forms a belt-shaped heater wire, comprising: a step of producing a metal fiber sheet by papermaking; cutting the metal fiber sheet produced by papermaking into a quadrangle shape having sides extending in a fourth direction that forms an angle within a range of 30° to 60° with respect to the papermaking direction and sides extending in a fifth direction that forms an angle within a range of 80° to 100° with respect to the fourth direction; The present invention is characterized by the following. [Effects of the Invention]

[0009] According to the heating element, heater, heater module, and method for manufacturing a heating element of the present invention, uneven heat generation can be prevented. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic diagram illustrating the configuration of a heater module according to a first example of an embodiment of the present invention. [Figure 2] FIG. 4 is a schematic diagram illustrating the configuration of a heater module according to a second example of the embodiment of the present invention. [Figure 3] FIG. 10 is a schematic diagram illustrating the configuration of a heater module according to a third example of the embodiment of the present invention. [Figure 4] 1 is a diagram illustrating a configuration of a heater used in a heater module according to an embodiment of the present invention. [Figure 5] FIG. 5 is a schematic diagram showing the configuration of a wet paper-making machine used when manufacturing the heat generating element that constitutes the heater shown in FIG. [Figure 6] 6 is a diagram showing a method for cutting a metal fiber sheet produced by the wet paper-making machine shown in FIG. 5. FIG. [Figure 7] 1A and 1B are diagrams showing a conventional method for cutting a metal fiber sheet. [Figure 8] 10A and 10B are diagrams showing another conventional method for cutting a metal fiber sheet. [Figure 9] 10A and 10B are diagrams showing other configurations of the heating element constituting the heater used in the heater module according to the embodiment of the present invention. [Figure 10] 10A and 10B are diagrams showing still another configuration of a heating element constituting a heater used in a heater module according to an embodiment of the present invention. [Figure 11] 10A and 10B are diagrams showing still another configuration of a heating element constituting a heater used in a heater module according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Figs. 1 to 3 are schematic diagrams showing various exemplary configurations of heater modules according to embodiments of the present invention. Fig. 4 is a diagram showing the configuration of a heater according to this embodiment, and Fig. 5 is a schematic diagram showing the configuration of a wet paper-making machine used in manufacturing the heating element that constitutes the heater shown in Fig. 4. Fig. 6 is a diagram showing a method for cutting a metal fiber sheet produced by the wet paper-making machine shown in Fig. 5. Figs. 7 and 8 are diagrams showing conventional methods for cutting a metal fiber sheet. In Figs. 6 to 8, the short metal fibers contained in the metal fiber sheet are shown with thin lines to help understand the orientation of the short metal fibers.

[0012] As shown in FIGS. 1 to 3, heater modules 1, 2, and 3 according to the present embodiment include a heater 40 and a temperature regulator 50, and the heater 40 and the temperature regulator 50 are arranged in series in the flow direction of the fluid to be heated, such as a liquid or gas (indicated by an arrow in FIGS. 1 to 3). In the heater module 1 according to the first example shown in FIG. 1, the temperature regulator 50 and the heater 40 are arranged in this order from the upstream side in the flow direction of the fluid to be heated. That is, the heater 40 is arranged downstream of the temperature regulator 50 in the flow direction of the fluid to be heated. In addition, in the heater module 2 according to the second example shown in FIG. 2, the heater 40 and the temperature regulator 50 are arranged in this order from the upstream side in the flow direction of the fluid to be heated. That is, the heater 40 is arranged upstream of the temperature regulator 50 in the flow direction of the fluid to be heated. In addition, in the heater module 3 according to the third example shown in FIG. 3, the temperature regulator 50, the heater 40, and the temperature regulator 50 are arranged in this order from the upstream side in the flow direction of the fluid to be heated.

[0013] The temperature regulator 50 adjusts the temperature of the heated fluid to be within a predetermined temperature range by heating or cooling the heated fluid. A known temperature regulator 50 is used as this type of temperature regulator 50. For example, a temperature regulator 50 with a simple known configuration that uses cold water or hot water may be used, or a temperature regulator 50 with a configuration that uses a metal fiber structure to improve heat transfer efficiency may be used.

[0014] Furthermore, a heat storage material may be used in the temperature regulator 50 to adjust the temperature of the fluid to be heated to a predetermined range. The heat storage material may be one that stores heat applied to the heat storage material as latent heat when a solid-liquid phase transition occurs, or one that stores heat as latent heat when a solid-solid phase transition occurs.

[0015] Examples of heat storage materials that utilize the latent heat of solid-liquid phase transition include single-component heat storage materials such as water (ice), paraffin, alkali metal hydroxides, magnesium hydroxide, beryllium hydroxide, alkaline earth metal hydroxides, inorganic salts such as nitrates, and inorganic hydrates such as sodium acetate trihydrate; mixtures of multiple components such as mixtures of inorganic salts or inorganic hydrates such as a mixture of magnesium nitrate hexahydrate and magnesium chloride hexahydrate, mixtures of organic compounds such as a mixture of lauric acid and capric acid, and mixtures of inorganic salts and organic compounds such as a mixture of ammonium nitrate and urea. Paraffin-based materials include n-pentadecane, an n-paraffin-based heat storage material, and materials composed of elastomer and paraffin.

[0016] Heat storage materials that utilize the latent heat of solid-solid phase transition include organic compounds such as polyethylene glycol copolymer cross-linked bonds; LiMnO4, LiVS2, LiVO2, NaNiO2, LiRh2O4, V2O3, V4O7, V6O11, Ti4O7, SmBaFe2O5, EuBaFe2O5, GdBaFe2O5, TbBaFe2O5, DyBaFe2O5, HoBaFe2O5, YBaFe2O5, PrB Examples of suitable vanadium dioxides include transition metal ceramics such as aCo2O5.5, DyBaCo2O5.54, HoBaCo2O5.48, and YBaCo2O5.49; and vanadium dioxide (VO2) in which vanadium is partially substituted with metals such as niobium (Nb), molybdenum (Mo), ruthenium (Ru), tantalum (Ta), tungsten (W), rhenium (Re), osmium (Os), and iridium (Ir). Vanadium dioxide in which vanadium is partially substituted with the above metals can be expressed as V1-xMxO2, where M is the substituted metal and x is the amount of substituted M. Here, x is a decimal number greater than 0 and less than 1.

[0017] The heater 40 uniformly heats the fluid to be heated so that the temperature of the fluid falls within a narrow, predetermined range.

[0018] In the heater module 1 according to the first example shown in FIG. 1, the temperature regulator 50 and the heater 40 are arranged in this order from the upstream side in the flow direction of the fluid to be heated. Therefore, after the temperature regulator 50 adjusts the temperature of the fluid to be heated to be within a predetermined temperature range, the heater 40 can uniformly heat the fluid to be heated to be within a narrow predetermined temperature range.

[0019] Furthermore, in the heater module 2 according to the second example shown in FIG. 2, the heater 40 and the temperature regulator 50 are arranged in this order from the upstream side in the flow direction of the heated fluid. Therefore, the heater 40 uniformly heats the heated fluid so that the temperature of the heated fluid falls within a narrow, predetermined temperature range, and then the temperature regulator 50 adjusts the temperature of the heated fluid so that the temperature falls within the predetermined temperature range.

[0020] Furthermore, in the heater module 3 according to the third example shown in FIG. 3, the temperature regulator 50, heater 40, and temperature regulator 50 are arranged in this order from upstream in the flow direction of the heated fluid. Therefore, the temperature regulator 50 adjusts the temperature of the heated fluid to be within a predetermined temperature range, the heater 40 uniformly heats the heated fluid to be within a narrow predetermined temperature range, and then the temperature regulator 50 can further adjust the temperature of the heated fluid to be within the predetermined temperature range.

[0021] Next, the detailed configuration of the heater 40 will be described below. As shown in Fig. 4, the heater 40 includes a pair of insulating nonwoven fabric sheets 42, 44 (insulators), a heating element 46 sandwiched between the pair of nonwoven fabric sheets 42, 44, and lead wires 48 attached to both ends of the heating element 46.

[0022] Each of the nonwoven fabric sheets 42, 44 is made of a material having electrical insulation and thermal conductivity, such as a PET / PE composite nonwoven fabric.

[0023] The heating element 46 is composed of a belt-shaped heater wire. As shown in FIG. 4, the heater wire is spirally wound. The heater wire is configured so that the short metal fibers are at least partially bonded to each other. Examples of the short metal fibers include at least one type of fiber selected from the group consisting of copper fibers, stainless steel fibers, nickel fibers, aluminum fibers, and alloy fibers thereof. Stainless steel fibers are particularly preferred as the short metal fibers. This is because stainless steel fibers offer an excellent balance between rigidity, plastic deformability, heat conductivity, and cost. The length of the short metal fibers is preferably within a range of 2 to 20 mm, more preferably within a range of 5 to 17 mm, and even more preferably within a range of 8 to 14 mm. The length of the short metal fibers can be confirmed by measuring the length of the heating element 46 through photographic observation using an SEM, optical microscope, or the like. A method for manufacturing the heating element 46 composed of such a belt-shaped heater wire will be described later.

[0024] The longitudinal direction of the heating element 46 refers to the direction in which the longer side of the virtual, substantially rectangular shape occupied by the spiral heater wire extends, and the left-right direction in Fig. 4 is the longitudinal direction of the heating element 46. The strip-shaped heater wire in the heating element 46 includes a portion that extends in the longitudinal direction of the heating element 46 and a portion that extends in a direction perpendicular to the longitudinal direction of the heating element 46 (i.e., the up-down direction in Fig. 4).

[0025] A power source such as a battery (not shown) is attached to the lead wire 48, and when a current flows through the lead wire 48 from the power source, the heating element 46 generates heat.

[0026] Next, a method for manufacturing the heat generating element 46 will be described with reference to Fig. 5. Fig. 5 is a schematic diagram showing the configuration of a wet paper-making machine 10 used when manufacturing the heat generating element 46.

[0027] As shown in Figure 5, the wet papermaking machine 10 includes a head box 12, a papermaking section 14, a dewatering section 16, a press section 20, a drying section 24, and a winding section 30. A slurry containing short metal fibers and water is supplied to the head box 12. In the papermaking section 14, the slurry supplied to the head box 12 is made into paper on a conveyor 15. In the papermaking section 14, the slurry flows along the papermaking direction, which is the movement direction of the conveyor 15 (indicated by an arrow in Figure 5), and the short metal fibers are also oriented along the movement direction of the conveyor 15. In this way, in wet papermaking using the wet papermaking machine 10, the short metal fibers are oriented in the metal fiber sheet.

[0028] The dewatering section 16 dehydrates the sheet that has been made on the conveyor 15. Specifically, the dewatering section 16 is provided with a suction box 18, which sucks water from the sheet. The pressing section 20 presses the sheet on the conveyor 15 with nip rollers 22. The drying section 24 is provided with a Yankee dryer roll 26 and an after-dryer roll 28, which dry the sheet on the conveyor 15. The sheet that has been dried in the drying section 24 is taken up by the winding section 30.

[0029] In addition, before or after the sheet is wound by the winding unit 30, the sheet is sintered in a vacuum or a non-oxidizing atmosphere at a temperature below the melting point of the metal fibers. By carrying out such a sintering process, the metal short fibers become bonded and entangled, thereby increasing the strength of the metal fiber structure after sintering.

[0030] Then, as shown in Fig. 6, the produced metal fiber sheet 32 ​​is unwound from the winding section 30 and cut into a rectangular shape (shown by a two-dot chain line in Fig. 6) using a laser or the like. At this time, the first side 34a of the rectangular shape is set at an angle of 30° to 60°, preferably an angle of 40° to 50°, and particularly preferably an angle of approximately 45°, relative to the papermaking direction (shown by the arrow in Fig. 6). The second side 34b of the rectangular shape is set at an angle of 80° to 100°, preferably an angle of 85° to 95°, and particularly preferably an angle of approximately 90°, relative to the first side 34a. That is, the angle 34c in Fig. 6 is set at an angle of 80° to 100°, preferably an angle of 85° to 95°, and particularly preferably an angle of approximately 90°. As a result, in the metal fiber sheet 34 cut into a quadrangle, the short metal fibers are oriented in a direction forming an angle of 30° to 60° with respect to the first side 34a, and also in a direction forming an angle of 30° to 60° with respect to the second side 34b. Cutting the metal fiber sheet 32 ​​into a quadrangle includes cutting the metal fiber sheet 32 ​​into a parallelogram, a rhombus, or a rectangle.

[0031] Then, the metal fiber sheet 34 cut into a rectangular shape is further cut into a spiral shape using a laser or the like to create a belt-shaped heater wire. In this way, a heating element 46 as shown in FIG. 4 is manufactured.

[0032] As described above, the metal fiber sheet 32 ​​unwound from the winding unit 30 is cut into a quadrangle having a first side 34a that forms an angle of 30° to 60° with respect to the paper-making direction and a second side 34b that forms an angle of 80° to 100° with respect to the first side 34a. Therefore, the short metal fibers are also oriented obliquely with respect to the extension direction of the strip-shaped heater wire that constitutes the heating element 46. That is, in the metal fiber sheet 34 cut into a quadrangle, the short metal fibers are oriented in the direction that forms an angle of 30° to 60° with the first side 34a, i.e., the longitudinal direction of the heating element 46, and are also oriented in the direction that forms an angle of 30° to 60° with the second side 34b, i.e., the direction perpendicular to the longitudinal direction of the heating element 46. The belt-shaped heater wire includes a portion extending in the longitudinal direction of the heating element 46 and a portion extending in a direction (i.e., the vertical direction in FIG. 4) perpendicular to the longitudinal direction of the heating element 46. Therefore, the metal short fibers are also oriented obliquely with respect to the extending direction of the belt-shaped heater wire.

[0033] In the heating element 46 formed in this manner, the resistivity of the heating element 46 measured along the longitudinal direction of the heating element 46 is relatively close to the resistivity of the heating element 46 measured along the direction perpendicular to the longitudinal direction of the heating element 46. Specifically, the ratio of the resistivity of the heating element 46 measured along the longitudinal direction of the heating element 46 to the resistivity of the heating element 46 measured along the direction perpendicular to the longitudinal direction of the heating element 46 is within a range of 0.9 to 1.1. This is because the short metal fibers are inclined with respect to both the longitudinal direction of the heating element 46 and the direction perpendicular to the longitudinal direction of the heating element 46.

[0034] On the other hand, the resistivity of the heating element 46 measured along a direction that forms an angle of 45° with respect to the longitudinal direction of the heating element 46 on the surface of the heating element 46 is a different value from the resistivity of the heating element 46 measured along the longitudinal direction of the heating element 46. Specifically, the ratio of the resistivity of the heating element 46 measured along the longitudinal direction of the heating element 46 to the resistivity of the heating element 46 measured along a direction that forms an angle of 45° with respect to the longitudinal direction of the heating element 46 on the surface of the heating element 46 is 0.8 or less or 1.2 or more. This is because the short metal fibers generally extend along a direction that forms an angle within a range of 30° to 60° with respect to the longitudinal direction of the heating element 46.

[0035] Such a heating element 46 prevents the metal fibers from becoming oriented in the longitudinal direction of the heating element 46 or in a direction perpendicular to the longitudinal direction, i.e., in the direction in which the strip-shaped heater wire extends. This prevents uneven conductivity from occurring when current is passed through the heating element 46, and therefore prevents uneven heat generation in different parts of the heating element 46 when current is passed through the lead wires 48 of the heater 40.

[0036] 7 and 8 are diagrams illustrating a conventional method for cutting a metal fiber sheet 32. In the cutting method for a metal fiber sheet 32 ​​shown in FIG. 7, the metal fiber sheet 32 ​​unwound from the winding unit 30 is cut into a rectangular shape including a first side extending along the papermaking direction (indicated by an arrow in FIG. 7) and a second side perpendicular to the first side. The first side of the rectangle is made longer than the second side. In this case, the metal short fibers are oriented in the papermaking direction in the metal fiber sheet 32, and therefore, the metal short fibers are also oriented along the first side in the metal fiber sheet 34p cut into a rectangular shape. Therefore, when the metal fiber sheet 34p is cut into a spiral shape to create a heating element, the metal short fibers are oriented in the longitudinal direction of the heating element. This can cause uneven conductivity when an electric current is passed through the heating element, potentially resulting in uneven heat generation in some parts of the heating element.

[0037] In the cutting method for the metal fiber sheet 32 ​​shown in FIG. 8, the metal fiber sheet 32 ​​unwound from the winding unit 30 is cut into a rectangular shape including a first side perpendicular to the papermaking direction (indicated by an arrow in FIG. 8) and a second side perpendicular to the first side. In this case, the first side of the rectangle is longer than the second side. In this case, the metal short fibers are also oriented along the second side in the metal fiber sheet 34q cut into a rectangular shape because the metal short fibers are oriented in the papermaking direction in the metal fiber sheet 32. Therefore, when the metal fiber sheet 34p is cut into a spiral to create a heating element, the metal short fibers are oriented in a direction perpendicular to the longitudinal direction of the heating element. This can cause uneven conductivity when a current is passed through the heating element, potentially resulting in uneven heat generation in some parts of the heating element.

[0038] As described above, the heating element 46 of this embodiment is made of a band-shaped heater wire, and the heater wire is configured so that the short metal fibers are at least partially bonded to each other. Furthermore, the ratio of the resistivity of the heating element 46 measured along a second direction (up-down direction in FIG. 4) perpendicular to the longitudinal direction to the resistivity of the heating element 46 measured along a first direction (left-right direction in FIG. 4), which is the longitudinal direction of the heating element 46, to the resistivity of the heating element 46 measured along a third direction (diagonal direction in FIG. 4) that forms an angle of 45° with respect to the first direction on the surface of the heating element 46, to the resistivity of the heating element 46 measured along the first direction is 0.8 or less or 1.2 or more. In such a heating element 46, the metal short fibers are oriented along the third direction and not along the first or second direction, so that uneven conductivity is suppressed when current is passed through the heating element 46, and therefore uneven heat generation in different parts of the heating element 46 can be suppressed when current is passed through the lead wire 48 of the heater 40.

[0039] Furthermore, according to the heater modules 1, 2, and 3 of this embodiment, uneven heat generation in different parts of the heating element 46 can be suppressed when current is passed through the lead wire 48 of the heater 40, so that the heated fluid can be heated uniformly by the heater 40, thereby preventing uneven heating.

[0040] Specifically, in the heater module 1 according to the first example shown in FIG. 1, the temperature of the heated fluid is adjusted by the temperature regulator 50 to be within a predetermined temperature range, and then the heated fluid is heated by the heater 40 to bring the temperature of the heated fluid to a narrow predetermined temperature range. At this time, the heated fluid can be heated uniformly by the heater 40 equipped with the heating element 46 having the above-described characteristics, thereby preventing uneven heating.

[0041] In addition, in the heater module 2 according to the second example shown in FIG. 2, the heater 40 heats the heated fluid so that its temperature falls within a narrow, predetermined range, and then the temperature regulator 50 adjusts the temperature of the heated fluid so that it falls within the predetermined range. At this time, the heater 40, which is equipped with the heating element 46 having the above-described characteristics, can heat the heated fluid uniformly, thereby preventing uneven heating.

[0042] In addition, in the heater module 3 according to the third example shown in FIG. 3, the temperature regulator 50 adjusts the temperature of the heated fluid to be within a predetermined temperature range, and the heater 40 uniformly heats the heated fluid to be within a narrow predetermined temperature range. Thereafter, the temperature regulator 50 further adjusts the temperature of the heated fluid to be within the predetermined temperature range. In this case, the heated fluid can be heated uniformly by the heater 40 equipped with the heating element 46 having the above-described characteristics, thereby preventing uneven heating.

[0043] In this embodiment, the heat generating element and heater are not limited to those having the shape shown in Fig. 4. Heat generating elements and heaters having the configurations shown in Figs. 9 to 11 may also be used.

[0044] A heater 40a according to a modified example shown in FIG. 9 includes a pair of nonwoven fabric sheets 42a and 44a, a heating element 46a sandwiched between the pair of nonwoven fabric sheets 42a and 44a, and lead wires 48a attached to both ends of the heating element 46a. In this heater 40a, the heating element 46a is composed of a strip-shaped heater wire, and the heater wire is configured so that the metal short fibers are at least partially bonded to each other. Furthermore, the ratio of the resistivity of the heating element 46a measured along a second direction perpendicular to the longitudinal direction to the resistivity of the heating element 46a measured along a first direction, which is the longitudinal direction of the heating element 46a, to the resistivity of the heating element 46a measured along the first direction is within a range of 0.9 to 1.1. Furthermore, the ratio of the resistivity of the heating element 46a measured along the first direction to the resistivity of the heating element 46a measured along a third direction at an angle of 45° to the first direction on the surface of the heating element 46a is 0.8 or less or 1.2 or more. 9, the longitudinal direction of the heating element 46a is the left-right direction in Fig. 9, and the direction perpendicular to the longitudinal direction of the heating element 46a is the up-down direction in Fig. 9. The strip-shaped heater wire constituting the heating element 46a extends generally along the direction perpendicular to the longitudinal direction of the heating element 46a (i.e., the up-down direction in Fig. 9).

[0045] A heater 40b according to another modification, as shown in FIG. 10, includes a pair of nonwoven fabric sheets 42b, 44b, a heating element 46b sandwiched between the pair of nonwoven fabric sheets 42b, 44b, and lead wires 48b attached to both ends of the heating element 46b. In this heater 40b, the heating element 46b is composed of a strip-shaped heater wire, and the heater wire is configured so that the metal short fibers are at least partially bonded to each other. The ratio of the resistivity of the heating element 46b measured along a second direction perpendicular to the longitudinal direction to the resistivity of the heating element 46b measured along a first direction, which is the longitudinal direction of the heating element 46b, to the resistivity of the heating element 46b measured along the first direction is within a range of 0.9 to 1.1. The ratio of the resistivity of the heating element 46b measured along the first direction to the resistivity of the heating element 46b measured along a third direction at an angle of 45° to the first direction on the surface of the heating element 46b is 0.8 or less or 1.2 or more. 10, the longitudinal direction of the heating element 46b is the left-right direction in Fig. 10, and the direction perpendicular to the longitudinal direction of the heating element 46b is the up-down direction in Fig. 10. The band-shaped heater wire constituting the heating element 46b extends generally along the longitudinal direction of the heating element 46b (i.e., the left-right direction in Fig. 10).

[0046] A heater 40c according to yet another modification, as shown in FIG. 11, includes a pair of nonwoven fabric sheets 42c and 44c, a heating element 46c sandwiched between the pair of nonwoven fabric sheets 42c and 44c, and lead wires 48c attached to both ends of the heating element 46c. In this heater 40c, the heating element 46c is composed of a strip-shaped heater wire, and the heater wire is configured so that the metal short fibers are at least partially bonded to each other. Furthermore, the ratio of the resistivity of the heating element 46c measured along a second direction perpendicular to the longitudinal direction to the resistivity of the heating element 46c measured along a first direction, which is the longitudinal direction of the heating element 46c, to the resistivity of the heating element 46c measured along the first direction is within a range of 0.9 to 1.1. Furthermore, the ratio of the resistivity of the heating element 46c measured along the first direction to the resistivity of the heating element 46c measured along a third direction, which is at an angle of 45° to the first direction, on the surface of the heating element 46c, is 0.8 or less or 1.2 or more. 11, the longitudinal direction of the heating element 46c is the left-right direction in Fig. 11, and the direction perpendicular to the longitudinal direction of the heating element 46c is the up-down direction in Fig. 11. The strip-shaped heater wire constituting the heating element 46c extends generally along the longitudinal direction of the heating element 46c (i.e., the left-right direction in Fig. 11) and the direction perpendicular to the longitudinal direction (i.e., the up-down direction in Fig. 11).

[0047] In the heating elements 46a, 46b, and 46c shown in Figures 9 to 11, as in the heating element 46 shown in Figure 4, the metal short fibers are oriented along the third direction and not along the first or second direction, so that uneven conductivity is suppressed when current is passed through the heating elements 46a, 46b, and 46c, and therefore uneven heat generation in some parts of the heating elements 46a, 46b, and 46c is suppressed when current is passed through the lead wires 48a, 48b, and 48c of the heaters 40a, 40b, and 40c.

[0048] Furthermore, although the above description has been given of a flat heater or heating element, the present embodiment is not limited to this. The heater or heating element according to the present embodiment may be a three-dimensional heater or a curved heater obtained by curving a flat heater or heating element.

[0049] Furthermore, the metal fiber sheet before being cut into a quadrangular shape is not limited to one produced by the wet paper-making machine 10 as shown in Fig. 5. As the metal fiber sheet before being cut into a quadrangular shape, one produced by a paper-making method different from the above-mentioned method may be used as long as it can be produced by paper-making. [Example]

[0050] The present invention will be described in more detail below using examples and comparative examples.

[0051] <First Example> A metal fiber sheet 32 ​​was produced using a wet paper-making machine 10 having the configuration shown in Fig. 5. Specifically, 1.0 m of water was poured into the head box 12. 3 After adding the above, polyethylene fiber having a mass ratio of 45.2% to the water was added to the head box 12, and after addition, the mixture was stirred to confirm the dispersion state. Thereafter, 1.5 kg of stainless steel fiber having a fiber diameter of 8 μm and a fiber length of 3 mm was added to the head box 12, and after addition, the mixture was stirred. Thereafter, 7.54 kg of pulp was added to the head box 12, and after addition, the mixture was stirred. Thereafter, 0.044 kg of polyvinyl alcohol was added to the head box 12, and after addition, the mixture was stirred to confirm the dispersion state. Thereafter, pyracrylamide (Acrypers (registered trademark) 1.0%) having a solid content of 1% was added to the head box 12 as a dispersant, and after addition, the mixture was stirred to confirm the dispersion state. Thereafter, water was added to the head box 12, and the volume of the slurry stored in the head box 12 was increased to 2.0 m 3 It was decided.

[0052] The slurry was then supplied from the head box 12 onto the conveyor 15, and papermaking was carried out in the papermaking section 14. The papermaking speed (i.e., the movement speed of the conveyor 15) was 2 m / min, and the flow rate of the slurry supplied from the head box 12 onto the conveyor 15 was 69.3 L / min. The sheet made on the conveyor 15 was then dehydrated in the dewatering section 16. Specifically, water was sucked from the sheet using a suction box 18. The sheet on the conveyor 15 was then pressed using nip rollers 22 in the press section 20. The sheet on the conveyor 15 was then dried in the drying section 24 using a Yankee dryer roll 26 and an after-dryer roll 28 at 120°C. The sheet dried in the drying section 24 was then wound up by the winding section 30. In addition, before the sheet was wound by the winding section 30 or after the sheet was wound by the winding section 30, the sheet was sintered at 1120° C. in a vacuum or in a non-oxidizing atmosphere.

[0053] Thereafter, the metal fiber sheet 32 ​​was unwound from the winding section 30, and the unwound metal fiber sheet 32 ​​was cut into a rectangular shape. At this time, the first side of the rectangle was set to form an angle of 45° with the paper-making direction, and the second side, which was shorter than the first side, was set to form an angle of 90° with the first side. In other words, the second side was also set to form an angle of 45° with the paper-making direction. The metal fiber sheet 34 cut into a rectangular shape in this way was further cut into a spiral shape, as shown in FIG. 4 A heating element with the same configuration as heating element 46 shown in Figure 1 was created. A heater was manufactured by sandwiching such a heating element between insulating and thermally conductive nonwoven fabric sheets. This heater was placed upstream of a temperature regulator in the flow direction of water, the fluid to be heated, to create a heater module.

[0054] The resistivity of the heating element of this heater was measured in accordance with JIS C 2525 in the longitudinal direction (first direction), the direction perpendicular to the longitudinal direction (second direction), and the direction at a 45° angle to the longitudinal direction (third direction). Specifically, the resistivity of a material is a value specific to that material, but it can be determined by passing a current through the material and measuring the potential difference between electrodes separated by a specified distance. Specifically, a Loresta manufactured by Nitto Seiko Analytech Co., Ltd. was used to measure the resistance (Ω) by pressing two short-needle probes against any location on the heating element along the longitudinal direction and the direction perpendicular to the longitudinal direction. The resistivity (Ω / mm) was determined by dividing the measured resistance (Ω) by the distance between the probes.

[0055] In addition, the in-plane temperature difference was measured when an electric current was passed through the heating element in a room temperature environment. A temperature difference of 5°C or less was evaluated as "good," and a temperature difference of more than 5°C was evaluated as "uneven heating."

[0056] <Second to Tenth Examples> The method for producing the metal fiber sheet 32 ​​is the same as in the first embodiment, except that the metal fiber sheet 32 ​​is unwound from the winding section 30 and cut into rectangular shapes such that the first sides of the rectangles form angles of 50°, 52°, 54°, 56°, 58°, 40°, 38°, 36°, and 34° with respect to the papermaking direction, and the second sides, which are shorter than the first sides, form an angle of 90° with respect to the first sides. In other words, the second sides form angles of 40°, 38°, 36°, 34°, 32°, 50°, 52°, 54°, and 56° with respect to the papermaking direction. The metal fiber sheet 34 cut into rectangular shapes is then further cut into spiral shapes, as shown in FIG. 4 A heating element having the same configuration as heating element 46 shown in FIG. 1 was fabricated. The resistivity of such a heating element in the first direction, second direction, and third direction was measured using the same method as in Example 1. In addition, the in-plane temperature difference was measured when a current was passed through the heating element when the ambient environment was at room temperature, and whether heat generation was uniform was evaluated.

[0057] <First Comparative Example> The method for producing the metal fiber sheet 32 ​​was the same as in the first embodiment. However, when the metal fiber sheet 32 ​​was unwound from the winding section 30 and cut into a rectangular shape, the metal fiber sheet 32 ​​was cut into a rectangular shape including a first side perpendicular to the papermaking direction and a second side perpendicular to the first side, as shown in FIG. 8 . In this case, the first side of the rectangle was longer than the second side. That is, when the unwound metal fiber sheet 32 ​​was cut into a rectangular shape, the first side of the rectangle was set to form an angle of 90° with respect to the papermaking direction, and the second side was set to form an angle of 0° with respect to the papermaking direction. The resistivity of this heating element was measured in the longitudinal direction and in the direction perpendicular to the longitudinal direction using the same method as in the first embodiment. Furthermore, the in-plane temperature difference was measured when an electric current was passed through the heating element at room temperature to evaluate whether heat generation was uniform.

[0058] <Second Comparative Example> The method for producing the metal fiber sheet 32 ​​was the same as in the first embodiment, except that the metal fiber sheet 32 ​​was unwound from the winding section 30 and cut into a rectangular shape, as shown in FIG. 7 . The metal fiber sheet 32 ​​unwound from the winding section 30 was cut into a rectangular shape including a first side extending along the papermaking direction and a second side perpendicular to the first side. The first side of the rectangle was longer than the second side. That is, when the unwound metal fiber sheet 32 ​​was cut into a rectangular shape, the first side of the rectangle was set at an angle of 0° with respect to the papermaking direction, and the second side was set at an angle of 90° with respect to the papermaking direction. The resistivity of this heating element was measured in the longitudinal direction and in the direction perpendicular to the longitudinal direction using the same method as in the first embodiment. Furthermore, the in-plane temperature difference was measured when an electric current was passed through the heating element at room temperature to evaluate whether heat generation was uniform.

[0059] <Evaluation> The following table shows the resistivities of the heating elements according to Examples 1 to 10 and Comparative Examples 1 to 2 in the longitudinal direction (first direction), the direction perpendicular to the longitudinal direction (second direction), and the direction forming a 45° angle with the longitudinal direction (third direction). The following table also shows the ratio of the resistivity of the heating element measured along the second direction to the resistivity of the heating element measured along the first direction (first ratio), and the ratio of the resistivity of the heating element measured along the first direction to the resistivity of the heating element measured along the third direction (second ratio). The following table also shows an evaluation of whether the heating elements according to Examples 1 to 10 and Comparative Examples 1 to 2 generated heat uniformly when a current was passed through them.

[0060] [Table 1]

[0061] [Table 2]

[0062] As shown in Tables 1 and 2, in the heating elements according to Examples 1 to 10, the first ratio was within a range of 0.9 to 1.1, while the second ratio was 0.8 or less or 1.2 or more. Furthermore, when current was passed through the heating element in a room temperature environment, the in-plane temperature difference was 5°C or less. Meanwhile, in the heating elements according to Comparative Examples 1 to 2, the first ratio was 0.9 or less or 1.1 or more, or the second ratio was within a range of 0.8 to 1.2. Furthermore, when current was passed through the heating element in a room temperature environment, the in-plane temperature difference exceeded 5°C.

Claims

1. A heating element that is a belt-shaped heater wire, The heater wire is configured so that short metal fibers, which are stainless steel fibers having a length within a range of 2 to 20 mm, are at least partially bonded to each other, a ratio of a resistivity of the heating element measured along a second direction perpendicular to the longitudinal direction to a resistivity of the heating element measured along a first direction that is a longitudinal direction of the heating element is in a range of 0.9 to 1.1; a ratio of the resistivity of the heating element measured along the first direction to the resistivity of the heating element measured along a third direction that forms an angle of 45° with respect to the first direction on the surface of the heating element is 0.8 or less or 1.2 or more; A heating element, wherein the metal short fibers extend along a direction that forms an angle within a range of 30° to 60° with respect to the first direction.

2. The heating element according to claim 1 , wherein the heater wire includes at least one of a portion extending in a longitudinal direction of the heating element and a portion perpendicular to the longitudinal direction of the heating element.

3. 3. The heating element according to claim 1, wherein the heater wire is spirally wound.

4. The heating element according to any one of claims 1 to 3; an insulator laminated on at least one surface of the heating element; A heater equipped with

5. A heater module comprising the heater according to claim 4 and a temperature regulator, The heater module is configured such that the heater and the temperature regulator are arranged in series in the flow direction of the fluid to be heated.

6. 6. The heater module according to claim 5, wherein the heater is disposed downstream of the temperature regulator in the flow direction of the fluid to be heated.

7. 6. The heater module according to claim 5, wherein the heater is disposed upstream of the temperature regulator in the flow direction of the fluid to be heated.

8. 6. The heater module according to claim 5, wherein the temperature regulator, the heater, and the temperature regulator are arranged in this order from the upstream side in the flow direction of the fluid to be heated.

9. 9. The heater module according to claim 5, wherein the heating element is manufactured by forming a metal fiber sheet by papermaking, and cutting the formed metal fiber sheet into a quadrangular shape having sides extending in a fourth direction that forms an angle within a range of 30° to 60° with respect to the papermaking direction, and sides extending in a fifth direction that forms an angle within a range of 80° to 100° with respect to the fourth direction.

10. 10. The heater module according to claim 9, wherein the heating element is manufactured by cutting the rectangular metal fiber sheet obtained by the cutting step to create a strip-shaped heater wire, and the heater wire includes at least one of a portion extending in the longitudinal direction of the rectangular metal fiber sheet and a portion perpendicular to the longitudinal direction of the metal fiber sheet.

11. A method for manufacturing a heating element that forms a belt-shaped heater wire, comprising: a step of producing a metal fiber sheet by papermaking using metal short fibers that are stainless steel fibers having a length in the range of 2 to 20 mm; cutting the metal fiber sheet produced by papermaking into a quadrangle shape having sides extending in a fourth direction that forms an angle within a range of 30° to 60° with respect to the papermaking direction and sides extending in a fifth direction that forms an angle within a range of 80° to 100° with respect to the fourth direction; A method for manufacturing a heating element, comprising:

12. a step of cutting the rectangular metal fiber sheet obtained in the cutting step to create a belt-shaped heater wire, The method for manufacturing a heating element according to claim 11 , wherein the heater wire includes at least one of a portion extending in the longitudinal direction of the rectangular metal fiber sheet and a portion perpendicular to the longitudinal direction of the metal fiber sheet.

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