Planar heating element

Abstract

To provide a planar heating element with high optical transparency capable of making heating area be large area and making a shape of the heating area be an arbitrary shape.SOLUTION: A planar heating element to solving the problem includes a support substrate having optical transparency, a pair of electrodes disposed on the support substrate, and a transparent heating film having optical transparency disposed on the pair of electrodes, where each of the pair of electrodes includes a main electrode and a comb-shaped sub-electrode electrically connected to the main electrode and having optical transparency, and one sub-electrode and the other sub-electrode of the pair of electrodes are alternately disposed.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a sheet heating element. [Background technology]

[0002] Sheet heating elements are used for a variety of purposes, such as heaters for heating, for melting snow or preventing freezing, or as industrial heat sources. Depending on the application, sheet heating elements may be required to be light-transmitting to ensure design and visibility. Sheet heating elements that are visible light-transmitting have been proposed in the past, and in these sheet heating elements, a pair of electrodes are generally placed on both ends of the heating area, and a heating element that is visible light-transmitting is placed to cover them (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-74325 Summary of the Invention [Problem to be solved by the invention]

[0004] However, with such a sheet heating element, the resistance of the heating area becomes very large as the area of ​​the heating area increases. Therefore, it cannot be operated at low voltage, and there are issues such as limitations on the environment in which it can be used. Furthermore, with a sheet heating element of the above structure, if the shape of the heating area is other than rectangular, the distance between the electrodes is not constant. As a result, there is also the issue of temperature differences occurring within the heating area.

[0005] A main object of the present disclosure is to provide a highly light-transmitting sheet heating element that allows the heating area to be large and the shape of the heating area to be arbitrarily chosen. [Means for solving the problem]

[0006] In order to solve the above problems, the present disclosure provides the following sheet heating element. [1] A planar heating element comprising a light-transmitting support substrate, a pair of electrodes arranged on the support substrate, and a light-transmitting heat-generating film arranged on the pair of electrodes, wherein each of the pair of electrodes includes a main electrode and a light-transmitting comb-like sub-electrode electrically connected to the main electrode, and one sub-electrode and the other sub-electrode of the pair of electrodes are arranged alternately. [2] The sheet heating element according to [1], wherein the support substrate, the sub-electrode, and the light-transmitting heat-generating film are transparent to visible light. [3] The sheet heating element according to [1] or [2], wherein the total light transmittance of the auxiliary electrode measured in accordance with JIS K 7361 is 50% or more, and the total light transmittance of the main electrode measured in accordance with JIS K 7361 is 50% or more. [4] The sheet heating element according to [2] or [3], wherein the sub-electrode is made of thin metal wires arranged in a mesh pattern. [5] The sheet heating element according to any one of [2] to [4], wherein the sub-electrode is made of a conductive film that is transparent to visible light. [6] The sheet heating element according to any one of [2] to [5], further comprising a dummy electrode between the one sub-electrode and the other sub-electrode, the dummy electrode being transparent to visible light and not electrically connected to the pair of electrodes. [7] The sheet heating element according to any one of [2] to [6], wherein the light-transmitting heat-generating film is a film having PTC resistance. [8] The sheet heating element according to [7], wherein the PTC-resistant film contains a binder resin and multi-walled carbon nanotubes. [9] The sheet heating element according to [1], wherein the support substrate, the sub-electrode, and the light-transmitting heat-generating film are infrared light transmissive.

[10] The planar heating element according to [9], wherein the light-transmitting heat-generating film is a film in which thin metal wires are arranged in a mesh pattern.

[11] The planar heating element according to

[10] , wherein the auxiliary electrode is a film in which thin metal wires are arranged in a mesh pattern, and the maximum opening diameter of the mesh of the translucent heat-generating film is larger than the maximum opening diameter of the mesh of the auxiliary electrode. [Effects of the Invention]

[0007] According to the present disclosure, a highly light-transmitting planar heating element is provided that allows the heating area to be large and the shape of the heating area to be any desired shape. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1A is a plan view showing the structure of a sheet heating element according to a first embodiment of the present disclosure, and FIG. 1B is a cross-sectional view taken along line AA in FIG. 1A. [Figure 2] FIG. 2A is a plan view showing the structure of a sheet heating element according to a modified example of the first embodiment of the present disclosure, and FIG. 2B is a cross-sectional view taken along line BB in FIG. 2A. [Figure 3] FIG. 3 is a plan view showing the structure of a sheet heating element according to a modified example of the first embodiment of the present disclosure. [Figure 4] FIG. 4A is a plan view showing the structure of a sheet heating element according to a second embodiment of the present disclosure, and FIG. 4B is a partially enlarged cross-sectional view of the dashed line portion in FIG. 4A. DETAILED DESCRIPTION OF THE INVENTION

[0009] In this specification, a numerical range indicated by "to" means a numerical range including the numerical values ​​written before and after "to".

[0010] The sheet heating element of the present disclosure includes a light-transmitting support substrate, a pair of electrodes disposed on the support substrate, and a light-transmitting, translucent heating film disposed on the pair of electrodes. In the sheet heating element, each of the pair of electrodes includes a main electrode and a light-transmitting, comb-like sub-electrode electrically connected to the main electrode, with one sub-electrode and the other sub-electrode of the pair of electrodes arranged alternately. In this specification, light transmittance does not necessarily mean transmittance for visible light, but also refers to transmittance for infrared light. The sheet heating element of the present disclosure may be transmittance for only visible light, only infrared light, or both. The sheet heating element of the present disclosure will be described below using two exemplary embodiments. However, the sheet heating element of the present disclosure is not limited to these.

[0011] 1. First Embodiment (Configuration of sheet heating element) An example of a sheet heating element according to a first embodiment will be described with reference to FIG. 1. The sheet heating element of this embodiment is primarily transparent to visible light. The sheet heating element 10 of this embodiment has a support substrate 11, a pair of electrodes 12 (a first electrode 12a and a second electrode 12b) arranged on the support substrate 11, and a light-transmitting heating film 17 arranged on the electrodes. In the sheet heating element 10 of this embodiment, the region where the light-transmitting heating film 17 is arranged becomes the heating area. Note that the sheet heating element 10 may have further components other than those described above. In this embodiment, the sheet heating element 10 further has a terminal 19 that connects the main electrode 13 to an external power source. Each component constituting the sheet heating element 10 will be described below.

[0012] There are no particular restrictions on the type of support substrate 11, as long as it is insulating and transparent to visible light, does not deform or melt due to heat, and can support the electrodes 12 and the light-transmitting heat-generating film 17. In this specification, having "visible light transparency" means that the total light transmittance measured in accordance with JIS K 7361 (i.e., the transmittance of light with a wavelength of 360 nm or more and 830 nm or less, hereinafter simply referred to as "visible light transmittance") is 50% or more.

[0013] The visible light transmittance of the support substrate 11 may be 50% or more as described above, but is preferably 70% or more, and more preferably 80% or more. If the visible light transmittance of the support substrate 11 is 80% or more, it becomes easier to obtain a planar heating element 10 with particularly high visible light transmittance. The visible light transmittance of the support substrate 11 may be higher than the visible light transmittance of the main electrode 13 and the visible light transmittance of the sub-electrode 15, which will be described later. The visible light transmittance of the support substrate 11 is measured in accordance with JIS K 7361, as described above.

[0014] Support substrate 11 may be composed of one layer or two or more layers. Examples of support substrate 11 include glass substrates, polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), polyolefins such as polyethylene (PE), polypropylene (PP), polystyrene, ethylene vinyl acetate (EVA), cycloolefin polymer (COP), and cycloolefin copolymer (COC), vinyl resins, and resin substrates including polycarbonate (PC), polyamide, polyimide, acrylic resin, triacetyl cellulose (TAC), polyphenylene sulfide (PPS), etc. The type of support substrate 11 is selected appropriately depending on the type of sheet heating element 10.

[0015] The planar shape and thickness of the support substrate 11 are appropriately selected depending on the intended use of the sheet heating element. For example, the planar shape of the substrate can be any shape, such as rectangular, circular, or elliptical.

[0016] The pair of electrodes 12 (first electrode 12a and second electrode 12b) are arranged to face each other, and each includes a main electrode 13 (first main electrode 13a and second main electrode 13b) and a comb-shaped sub-electrode 15 (first sub-electrode 15a and second sub-electrode 15b) electrically connected thereto and transparent to visible light. The main electrode 13 and the sub-electrode 15 may be formed integrally or separately as long as they are electrically conductive, but in this embodiment, the main electrode 13 and the sub-electrode 15 are formed integrally and from the same material.

[0017] The planar shape, width, length, thickness, etc. of the main electrode 13 are appropriately selected depending on the application and shape of the sheet heating element 10. In this embodiment, the first main electrode 13a and the second main electrode 13b are arranged parallel to each other on the outer periphery of the sheet heating element 10. In this specification, "parallel" does not only mean that they are completely parallel, but also means that there is a slight misalignment that does not impair the purpose and effects of the invention. For example, "parallel" also includes a case where an angle between two parallel lines is within 0±5°. In this embodiment, the planar shapes of the first main electrode 13a and the second main electrode 13b are both linear. However, they may also be curved, zigzag, or any other shape. Furthermore, their widths may be constant or different. Furthermore, the planar shapes of the first main electrode 13a and the second main electrode 13b may be identical, symmetric (e.g., line symmetry or point symmetry), or asymmetric.

[0018] In this embodiment, the main electrode 13 is formed of a film having a uniform thickness throughout its entire area. The main electrode 13 may or may not be visible light transmissive. Methods for forming the main electrode 13 to be visible light transmissive include using a material that is visible light transmissive for the main electrode 13 or using a mesh structure (a film in which thin metal wires are arranged in a mesh pattern) made of thin metal wires, as in the sub-electrode 15 described below. When the main electrode 13 is visible light transmissive, its visible light transmittance is preferably 50% or more, and may be 50% or more, preferably 60% or more, and more preferably 80% or more. If the visible light transmittance of the main electrode 13 is 80% or more, the main electrode 13 in particular becomes difficult to see when observing the sheet heating element 20. The visible light transmittance of the main electrode 13 may be lower than that of the sub-electrode 15. However, if the visible light transmittances are approximately the same, the pair of electrodes 12 as a whole becomes difficult to see.

[0019] On the other hand, the sub-electrodes 15 (for example, the first sub-electrode 15a) are electrodes that extend from one main electrode 13 (the first main electrode 13a) to the other main electrode (the second main electrode 13b) when the sheet heating element 10 is viewed in a plane. In this embodiment, a plurality of first sub-electrodes 15a and a plurality of second sub-electrodes 15b are arranged, and these are arranged alternately and in parallel within the heat-generating area (the area where the light-transmitting heat-generating film 17 is arranged). The number of sub-electrodes 15 on each electrode 12 and the spacing between them are appropriately selected depending on the size of the sheet heating element 10, the area of ​​the heat-generating area, etc. Furthermore, the length of each sub-electrode 15 is appropriately selected depending on the area of ​​the heat-generating area, etc. In this embodiment, the shape of each sub-electrode 15 in a plane view is linear, but the shape of the sub-electrode 15 may be curved, zigzag, or other shapes. However, regardless of the shape of the sub-electrode 15, it is preferable that the distance between the first sub-electrode 15a and the second sub-electrode 15b is approximately constant, as this makes it easier to make the temperature inside the translucent heat-generating film 17 uniform.

[0020] Here, when the structure of each sub-electrode 15 (the first sub-electrode 15a and the second sub-electrode 15b) is viewed microscopically, each sub-electrode 15 has a structure in which thin metal wires are arranged in a mesh pattern. Because each sub-electrode 15 has such a structure, the sub-electrode 15 is visible light transmissive. In this specification, the term "visible light transmissive" for the sub-electrodes 15 (the first sub-electrode 15a and the second sub-electrode 15b) refers not only to the case where the material constituting the sub-electrode 15 (e.g., the material constituting the thin metal wires) is visible light transmissive, but also to the case where the entire region of each sub-electrode 15, i.e., the entire region including the mesh-like thin metal wires and the gaps between them, is visible light transmissive. The visible light transmittance of the sub-electrode 15 in which thin metal wires are arranged in a mesh pattern can be measured as follows. First, the sub-electrode 15 is formed on a measurement substrate that is visible light transmissive. Then, the visible light transmittance of the region in which the sub-electrode 15 is formed is measured. Separately, the visible light transmittance of the substrate alone is measured. The visible light transmittance of the measurement substrate is then subtracted as a reference to calculate the visible light transmittance of the sub-electrode 15. The visible light transmittance is measured in accordance with JIS K7361. The visible light transmittance of each sub-electrode 15 should be 50% or higher, preferably 60% or higher, and more preferably 80% or higher. If the visible light transmittance of each sub-electrode 15 is 80% or higher, it will be difficult to see each sub-electrode 15, especially in the heat-generating area (the area where the translucent heat-generating film 17 is arranged).

[0021] The diameter of the thin metal wires constituting each sub-electrode 15 is preferably 20 μm or less, and more preferably 10 μm or less, from the viewpoint of increasing the visible light transmittance of the sub-electrode 15. On the other hand, the lower limit of the diameter may be any diameter that allows good electrical conduction from the end of the sub-electrode 15 on the main electrode 13 side to the opposite end.

[0022] Furthermore, the structure of the mesh is not particularly limited, and the openings may be a lattice pattern with rectangular openings, or may be polygonal, such as triangular or hexagonal. In this embodiment, the openings are approximately square. Here, the mesh opening pitch (in this specification, the maximum diameter of each mesh is treated as the opening pitch) is appropriately selected so as to achieve the desired visible light transmittance. For example, when the mesh openings are square, the mesh opening ratio AR, expressed by the following formula, is proportional to the visible light transmittance. AR={(PW) 2 / P 2}×100(%) (In the above formula, P is the mesh opening pitch, and W is the diameter of the thin metal wire.)

[0023] Therefore, the desired aperture ratio AR and aperture pitch P can be set based on the above formula. As an example, if the diameter W of the thin metal wire is 2 μm and the aperture ratio AR is 96% (visible light transmittance 89%), the aperture pitch P can be set to approximately 100 μm. Alternatively, if the diameter W of the thin metal wire is 4 μm and the aperture ratio AR is 95% (visible light transmittance 86%), the aperture pitch can be set to approximately 150 μm. However, the aperture ratio AR and aperture pitch P of the sub-electrode 15 of this embodiment are not limited to these values, and the numerical values ​​can be set appropriately.

[0024] The width of each sub-electrode 15 is preferably 10 mm or less, more preferably 5 mm or less, and even more preferably 1 mm or less. The lower limit may be set as appropriate as long as good electrical conduction is possible from the end of the sub-electrode 15 on the main electrode 13 side to the opposite end. The thickness of each sub-electrode 15 (the thickness of the region having the thin metal wires) is preferably 50 μm or less, more preferably 20 μm or less, and even more preferably 1 μm or less. When the width and thickness of the sub-electrodes 15 are within these ranges, not only can electrical conduction be more reliably achieved from one longitudinal end of the sub-electrode 15 to the other longitudinal end, but the visible light transmittance of the sheet heating element 10 is also improved.

[0025] The material constituting the main electrode 13 and the sub-electrode 15 may be any conductive material, such as silver, copper, gold, aluminum, or alloys thereof, or transparent metals such as indium tin oxide (ITO).

[0026] The light-transmitting heating film 17 can be a film that is conductive, has a higher resistance than the main electrode 13 and sub-electrode 15, and is visible light transmissive. The light-transmitting heating film 17 is only required to be disposed so as to cover at least the sub-electrode 15, and may also cover the main electrode 13. The visible light transmittance of the light-transmitting heating film 17 should be 50% or more as described above, but is preferably 80% or more. A visible light transmittance of 80% or more from the light-transmitting heating film 17 makes it easier to obtain a planar heating element 10 with higher visible light transmittance. The visible light transmittance of the light-transmitting heating film 17 can be measured in accordance with JIS K7361.

[0027] The thickness of the light-transmitting heat-generating film 17 is selected appropriately depending on the desired heat generation, the use of the planar heating element 10, the material constituting the light-transmitting heat-generating film 17, etc., but is preferably 0.1 mm or less, and more preferably 0.01 mm or less.

[0028] Examples of materials that can be used to form the light-transmitting heating film 17 include transparent metal oxides (e.g., ITO), conductive polymers (e.g., poly-3,4-ethylenedioxythiophene / polystyrene sulfonate (PEDOT / PSS), polyaniline, polyacetylene, polyphenylene vinylene, etc.), carbon nanotubes, silver nanowires, etc. The light-transmitting heating film 17 may contain a binder resin, which will be described later, if necessary.

[0029] The light-transmitting heat-generating film 17 may also be a film having PTC resistance (a PTC resistor film). Such a PTC resistor film may be a film containing conductive particles and a binder resin containing a thermoplastic resin and / or wax.

[0030] Examples of thermoplastic resins include thermoplastic polyurethane resins, polyester resins, polyacrylate resins, polysiloxane resins, vinyl halide resins, vinylidene resins, polyimide resins, phenoxy resins, polyether resins, polyketone resins, polyvinyl butyral resins, polyvinyl pyrrolidone resins, polyacrylate resins, and thermoplastic elastomers.

[0031] On the other hand, examples of waxes include hydrocarbon waxes such as polyethylene waxes such as low-density polyethylene wax, medium-density polyethylene wax, and high-density polyethylene wax, polypropylene wax, polybutene wax, ethylene-propylene copolymer wax, and ethylene-propylene-butene copolymer wax; plant waxes such as candelilla wax, carnauba wax, rice wax, Japan wax, and hydrogenated jojoba wax; animal waxes such as beeswax and lanolin wax; montan wax; ozokerite; ceresin; paraffin wax; microcrystalline wax; mineral wax; petroleum wax; higher fatty acids such as stearyl stearate and behenyl behenate; Examples of such waxes include ester waxes obtained from higher alcohols; ester waxes obtained from higher fatty acids such as butyl stearate, propyl oleate, glyceride monostearate, glyceride distearate, and pentaerythritol tetrabehenate and monohydric or polyhydric lower alcohols; ester waxes obtained from higher fatty acids such as diethylene glycol monostearate, dipropylene glycol distearate, diglyceryl distearate, and triglyceryl tetrastearate and polyhydric alcohol multimers; sorbitan higher fatty acid ester waxes such as sorbitan monostearate; and cholesterol higher fatty acid ester waxes such as cholesteryl stearate.

[0032] Examples of conductive particles include carbon-based particles such as graphite, carbon black, multi-walled carbon nanotubes, and graphene, and metal-based particles such as nickel powder, copper powder, and silver powder. Among these, multi-walled carbon nanotubes are more preferable because they tend to improve the visible light transmittance of the translucent heat-generating film 17.

[0033] The average diameter of the multi-walled carbon nanotubes is preferably 2 nm to 400 nm, more preferably 5 nm to 200 nm. The average diameter refers to the outer diameter of the outermost carbon nanotubes. The average length of the multi-walled carbon nanotubes is preferably 100 μm or less, more preferably 5 μm or less. The aspect ratio of the multi-walled carbon nanotubes may be greater than 1, preferably 10 or more. The aspect ratio is preferably 3000 or less, more preferably 2000 or less. When the average diameter, average length, and aspect ratio of the multi-walled carbon nanotubes are within the above ranges, better PTC properties are likely to be exhibited. The average diameter and average length of the multi-walled carbon nanotubes can be measured, for example, from an image obtained by observation with a TEM (transmission electron microscope). The average diameter and average length are values ​​calculated by arithmetic averaging the diameters and lengths of any 50 or more multi-walled carbon nanotubes. The aspect ratio is a value calculated from the average diameter and the average length, and specifically, is a value calculated by dividing the average length by the average diameter.

[0034] When the light-transmitting heat generating film 17 is a PTC resistor film, the total amount of binder resin is preferably 60% by mass or more and 90% by mass or less, and more preferably 70% by mass or more and 85% by mass or less, relative to the total amount of the PTC resistor film. When the total amount of binder resin is 60% by mass or more, the conductive particles are well bonded and the visible light transmittance is also likely to be good.

[0035] When the light-transmitting heating film 17 is a PTC resistor film, the content of multi-walled carbon nanotubes is preferably 4% by mass to 35% by mass, more preferably 10% by mass to 30% by mass, based on the total mass of the PTC resistor. When the amount of multi-walled carbon nanotubes is within this range, sufficient visible light transmittance is obtained and good PTC characteristics are likely to be obtained.

[0036] The sheet heating element 10 may further have other configurations as long as they do not impair the object and effect of this embodiment. Examples of other configurations include, for example, attachment means for attaching the sheet heating element 10 to various devices, temperature control means for controlling the temperature of the sheet heating element 10, a protective layer, etc.

[0037] (Operation of the sheet heating element of the first embodiment) The operation of the sheet heating element 10 of the first embodiment will now be described. The sheet heating element 10 is used by connecting the electrodes 12 to an external power source via the terminals 19. When a voltage is applied between the pair of electrodes 12, electricity flows through the translucent heating film 17, causing its temperature to rise. The area containing the translucent heating film 17 can then be used as a heat source of various types. If the translucent heating film 17 is a PTC resistor film, as its temperature rises, the binder resin expands, widening the distance between the conductive particles and increasing the resistance. Therefore, the resistance rises sharply near the softening temperature or melting point of the binder resin, making it difficult for electricity to pass through. In other words, it is possible to control the temperature so that it does not rise above a certain level.

[0038] (Method for manufacturing the sheet heating element of the first embodiment) The method for manufacturing the sheet heating element 10 of the first embodiment is not particularly limited. First, a support substrate 11 is prepared, and the pair of electrodes 12 described above is formed on the support substrate 11. The main electrode 13 and the sub-electrode 15, which has a mesh structure made of thin metal wires, can be formed by known methods. For example, they can be formed by applying a photosensitive material having an emulsion layer containing a photosensitive silver halide salt to the support substrate 11, exposing the applied photosensitive material to the shape of the main electrode 13 or the sub-electrode 15, and then developing the material. Alternatively, they can be formed by forming metal foil on the support substrate 11, printing or entirely coating each metal foil with a resist in a pattern, exposing and developing the resist to form a pattern, and then etching the metal in the openings. Alternatively, they can be formed by placing a mask having openings corresponding to the shapes of the main electrode 13 and the sub-electrode 15 on the support substrate 11 and then forming the electrodes by sputtering or vapor deposition. Alternatively, the main electrode 13 and the sub-electrode 15 can be formed by inkjet printing, screen printing, or a dispenser method using ink containing conductive particles.

[0039] Thereafter, a light-transmitting heat-generating film 17 is formed to cover the electrodes 12, including the main electrode 13 and the sub-electrode 15. The method for forming the light-transmitting heat-generating film 17 is appropriately selected depending on the type of the film. For example, if the material for the light-transmitting heat-generating film 17 is a transparent metal, sputtering or vapor deposition can be used. Alternatively, if the material for the light-transmitting heat-generating film 17 is a conductive polymer or PTC resistor film, the film can be formed by dissolving or dispersing the material in a solvent as needed, applying it by various application methods (roll coating, screen printing, bar coating, spin coating, inkjet printing, application with a dispenser, etc.), and then drying or solidifying it.

[0040] (Variation) A modified version of the sheet heating element of the first embodiment will be described with reference to Figures 2A and 2B. The sheet heating element 20 of this modified version is similar to the above-described sheet heating element 10, except that it has a dummy electrode 29 between the first sub-electrode 15a and the second sub-electrode 15b. Components similar to those of the above-described sheet heating element 10 are given the same reference numerals and will not be described in detail here; only the dummy electrode 29 will be described below.

[0041] The dummy electrode 29 is a visible light transmissive member and is disposed between the first sub-electrode 15a and the second sub-electrode 15b in a plan view. The dummy electrode 29 is configured to reduce the visibility of the sub-electrodes 15 in the sheet heating element 20. In the sheet heating element 10 described above, the distance between the first sub-electrode 15a and the second sub-electrode 15b is relatively wide. Therefore, depending on the types of the first sub-electrode 15a and the second sub-electrode 15b, differences in visible light transmissivity may occur between the regions where the first sub-electrode 15a and the second sub-electrode 15b are formed and the regions where they are not formed. In contrast, by disposing the dummy electrode 29 as in this embodiment, the visible light transmissivity of the regions where the first sub-electrode 15a and the second sub-electrode 15b are not formed can be made closer to the visible light transmissivity of the regions where the first sub-electrode 15a and the second sub-electrode 15b are formed. Therefore, the visible light transmittance tends to be uniform across the entire heat generating area of ​​the sheet heating element, making it difficult to see the first sub-electrode 15a and the second sub-electrode 15b.

[0042] The dummy electrode 29 may be disposed on the light-transmitting heat-generating film 17. However, in consideration of its formation efficiency, it is preferable to dispose it between the support substrate 11 and the light-transmitting heat-generating film 17, as shown in FIG. 2B . The dummy electrode 29 may be configured so as not to be electrically conductive with either the first electrode 12a or the second electrode 12b, and may be configured, for example, of an insulating material or a conductive material. If the dummy electrode 29 is configured of an insulating material, it can be disposed so as to fill the first sub-electrode 15a and the second sub-electrode 15b. On the other hand, if the dummy electrode 29 is configured of a conductive material, it is disposed with a gap between the first sub-electrode 15a and the second sub-electrode 15b and the first main electrode 13a and the second main electrode 13b.

[0043] From the viewpoint of bringing the visible light transmittance of the dummy electrode 29 closer to that of the sub-electrode 15, the dummy electrode 29 is preferably made of the same material as the sub-electrode 15 and preferably has the same structure (mesh structure made of thin metal wires). When the dummy electrode 29 has a mesh structure made of thin metal wires, the gap between adjacent sub-electrodes 15 and dummy electrodes 29 is preferably 0.01 mm or more, more preferably 1.0 mm or more, from the viewpoint of avoiding electrical conduction. Furthermore, the visible light transmittance of the dummy electrode 29 is preferably in the range of 0.5 to 2.0, more preferably 0.8 to 1.2, where the visible light transmittance of the sub-electrode 15 is taken as 1. The visible light transmittance of the dummy electrode 29 can be measured in the same manner as the visible light transmittance of the sub-electrode described above.

[0044] 2A and 2B, the planar shape of the dummy electrode 29 is a rectangular parallelepiped, but is not limited to this shape. For example, the dummy electrode 29 may have any shape, such as a collection of multiple dots or a collection of polygons. The dummy electrode 29 can be formed by the same method as the above-mentioned electrode 12 (sub-electrode 15).

[0045] Yet another example (modified example) will be described with reference to Fig. 3. The sheet heating element 30 of this modified example is similar to the above-described sheet heating element 10, except for the structure of the sub-electrodes 35 (first sub-electrode 35a and second sub-electrode 35b). Components similar to those of the above-described sheet heating element 10 are given the same reference numerals, and detailed description will be omitted here; only the sub-electrodes 35 will be described below.

[0046] The sub-electrode 35 of this modified example is composed of a conductive film made of a conductor that is transparent to visible light, and the inside of the sub-electrode 35 is composed of a uniform film. In the above-mentioned embodiment, the sub-electrode 15 has a structure in which thin metal wires are arranged in a mesh pattern, thereby ensuring the visible light transmittance of the sub-electrode 15. However, in this modified example, the visible light transmittance is ensured by using a film made of a conductor that is transparent to visible light. The visible light transmittance of the sub-electrode 35 is preferably 50% or more, and more preferably 80% or more. The visible light transmittance of the sub-electrode 35 can be measured in the same way as the visible light transmittance of the sub-electrode 15 of the above-mentioned embodiment.

[0047] The width of the sub-electrode 35 in this modified example is preferably 10 mm or less, more preferably 5 mm or less, and even more preferably 1 mm or less. The lower limit may be set appropriately as long as good electrical conduction is possible from the end of the sub-electrode 15 on the main electrode 13 side to the opposite end. Furthermore, the thickness of the sub-electrode 35 is preferably 10 μm or less, more preferably 1 μm or less, and even more preferably 0.1 μm or less. When the width and thickness of the sub-electrode 35 are within these ranges, the above-mentioned visible light transmittance is more easily achieved.

[0048] Examples of the conductor constituting the sub-electrode 35 include transparent metal oxides (e.g., ITO) and conductive polymers (e.g., poly-3,4-ethylenedioxythiophene / polystyrenesulfonate (PEDOT / PSS), polyaniline, polyacetylene, polyphenylenevinylene, etc.). Furthermore, the sub-electrode 35 may be a layer containing silver nanowires or carbon nanotubes. Furthermore, the sub-electrode 35 may contain a binder resin as needed.

[0049] The sub-electrode 35 of this modified example may be formed integrally with the main electrode 13. That is, the main electrode 13 may be made of a transparent metal or a conductive polymer. Alternatively, the sub-electrode 35 may be formed separately from the main electrode 13. In this case, the main electrode 13 may be made of silver, copper, gold, aluminum, or an alloy thereof.

[0050] The method for forming the sub-electrode 35 of this modified example is selected appropriately depending on the type of sub-electrode 35. For example, if the material of the sub-electrode 35 is a transparent metal, sputtering or vapor deposition can be used. If the material of the sub-electrode 35 is a conductive polymer, the sub-electrode 35 may be dissolved or dispersed in a solvent as needed, applied by various application methods (roll coating, screen printing, bar coating, spin coating, inkjet printing, application by a dispenser, etc.), and then dried or solidified to form the sub-electrode 35.

[0051] In this modification, a dummy electrode may also be disposed between the first sub-electrode 35a and the second sub-electrode 35b.

[0052] 2. Second embodiment (Configuration of sheet heating element) An example of a sheet heating element according to a second embodiment of the present disclosure will be described with reference to FIG. 4. The sheet heating element of this embodiment is primarily infrared light transmissive. A sheet heating element 40 of this embodiment includes a support substrate 41, a pair of electrodes 42 (a first electrode 42a and a second electrode 42b) arranged on the support substrate 41, and a light-transmitting heating film 47 arranged on the electrodes. In the sheet heating element 40 of this embodiment, the region where the light-transmitting heating film 47 is arranged is the heating area. Note that the sheet heating element 40 may include other components. In this embodiment, the sheet heating element 40 further includes a terminal 19 that connects a main electrode 43 of the pair of electrodes to an external power source. Note that components similar to those of the sheet heating element 10 of the first embodiment (e.g., the terminal 19) are designated by the same reference numerals and will not be described in detail here.

[0053] Although there are no particular restrictions on the wavelength of infrared light primarily transmitted by the sheet heating element 40 of this embodiment, a wavelength of 780 nm to 2500 nm is preferred, and light of 900 nm to 1500 nm is more preferred. If the sheet heating element 40 can transmit such light, it can also transmit millimeter waves used in various automotive radars. Therefore, the sheet heating element 40 can be used in a variety of locations.

[0054] Here, the type of support substrate 41 is not particularly limited as long as it is insulating and infrared light transmissive, does not deform or melt due to heat, and can support the electrodes 42 and the light-transmitting heat-generating film 47. In this specification, having "infrared light transmissive" means that the transmittance of light with a wavelength of 780 nm or more and 2000 nm or less is 50% or more as measured in accordance with JIS B7075:2018.

[0055] The transmittance of the support substrate 41 for light with a wavelength of 780 nm or more and 2000 nm or less (hereinafter also referred to as "infrared light transmittance") may be 50% or more as described above, but is preferably 70% or more, and more preferably 80% or more. If the infrared light transmittance of the support substrate 41 is 80% or more, it becomes easier to obtain a planar heating element 40 with particularly high infrared light transmittance. The infrared light transmittance of the support substrate 41 may be higher than the infrared light transmittance of the electrodes 42 (main electrode 43 and sub-electrode 45). The infrared light transmittance of the support substrate 41 can be measured in accordance with JIS B7075:2018.

[0056] The support substrate 41 may be composed of only one layer, or may be composed of two or more layers. Examples of the support substrate 41 include the above-mentioned substrate similar to the support substrate 11 of the first embodiment, which is transparent to visible light. Among the above-mentioned substrates, a substrate containing polyethylene terephthalate (PET), polycarbonate (PC), polyimide, or cycloolefin polymer (COP) is preferable. Substrates containing these materials are excellent in terms of versatility and infrared light transparency.

[0057] The planar shape and thickness of the support substrate 41 are appropriately selected depending on the intended use of the sheet heating element. For example, the planar shape of the substrate can be any shape, such as rectangular, circular, or elliptical.

[0058] The pair of electrodes 42 (first electrode 42a and second electrode 42b) are arranged to face each other, and each includes a main electrode 43 (first main electrode 43a and second main electrode 43b) and a comb-shaped sub-electrode 45 (first sub-electrode 45a and second sub-electrode 45b) electrically connected thereto and transparent to visible light. The main electrode 43 and the sub-electrode 45 may be formed integrally or separately as long as they are electrically conductive, but in this embodiment, the main electrode 43 and the sub-electrode 45 are formed integrally and from the same material.

[0059] The planar shapes, widths, lengths, thicknesses, etc. of the main electrode 43 and the sub-electrode 45 are appropriately selected according to the application and shape of the sheet heating element 40. In this embodiment, the shapes of the main electrode 43 and the sub-electrode 45 are the same as those of the first embodiment. In this embodiment, the main electrode 43 is configured as a film of uniform thickness across its entire area, but the main electrode 43 may also be a film in which thin metal wires are arranged in a mesh pattern. If the main electrode 43 is infrared-transparent, its infrared transmittance is preferably 50% or more, and may be 50% or more, preferably 60% or more, and more preferably 80% or more. If the infrared transmittance of the main electrode 43 is 80% or more, the sheet heating element 40 can be used for a wider variety of applications.

[0060] On the other hand, in this embodiment, the sub-electrode 45 is infrared-transparent. FIG. 4B shows a partial enlargement of the area surrounded by the dashed line in FIG. 4A. In this embodiment, when the structure of each sub-electrode 45 (the first sub-electrode 45a in FIG. 4B) is viewed microscopically, each sub-electrode 45 has a structure in which a plurality of thin metal wires are arranged in a mesh pattern. By having each sub-electrode 45 have such a structure, it is possible to ensure the infrared-transparent properties of the sub-electrode 45. Note that in this specification, the sub-electrodes 45 (the first sub-electrode 45a and the second sub-electrode 45b) being infrared-transparent refers not only to the case where the material constituting the sub-electrode 45 (e.g., the material constituting the thin metal wires) is infrared-transparent, but also to the case where the entire region of each sub-electrode 45, that is, the entire region including the thin metal wires arranged in a mesh pattern and the gaps between them, is infrared-transparent. The infrared light transmittance of the sub-electrode 45, in which thin metal wires are arranged in a mesh pattern, can be determined using the same method as the visible light transmittance of the first embodiment (however, the infrared light transmittance is measured in accordance with JIS B7075:2018). The infrared light transmittance of each sub-electrode 45 should be 50% or higher, preferably 60% or higher, and more preferably 80% or higher. If the infrared light transmittance of each sub-electrode 45 is 80% or higher, the infrared light transmittance of the heat-generating area (the area where the translucent heat-generating film 47 is arranged) will be good, making it easier to use the planar heating element 40 in a wider variety of applications.

[0061] The diameter of the thin metal wires constituting each sub-electrode 45 is preferably 20 μm or less, and more preferably 10 μm or less, from the viewpoint of increasing the infrared light transmittance of the sub-electrode 45. On the other hand, the lower limit is usually about 1 μm, as long as good electrical conduction is possible from the end of the sub-electrode 45 on the main electrode 43 side to the opposite end.

[0062] The mesh structure is not particularly limited, and may be a lattice with rectangular openings, or may be a polygonal shape such as a triangle or hexagon. In this embodiment, the openings are substantially square. The opening pitch of the mesh of the sub-electrode 45 (in this specification, the maximum diameter of each mesh is treated as the opening pitch) is appropriately selected so as to achieve the desired infrared light transmittance.

[0063] The width of each sub-electrode 45 is preferably 10 mm or less, more preferably 5 mm or less, and even more preferably 1 mm or less. The lower limit may be set as appropriate as long as good electrical conduction is possible from the end of the sub-electrode 45 on the main electrode 43 side to the opposite end. The thickness of each sub-electrode 45 (the thickness of the region having the thin metal wires) is preferably 50 μm or less, more preferably 20 μm or less, and even more preferably 1 μm or less. When the width and thickness of the sub-electrodes 45 are within these ranges, not only can electrical conduction be more reliably achieved from one longitudinal end of the sub-electrode 45 to the other longitudinal end, but the infrared light transmittance of the sheet heating element 10 is also improved.

[0064] The material constituting the main electrode 43 and the sub-electrode 45 may be any conductive material, such as silver, copper, gold, aluminum, or alloys thereof, or transparent metals such as indium tin oxide (ITO).

[0065] On the other hand, the light-transmitting heating film 47 can be a conductive film with a higher resistance than the main electrode 43 and the sub-electrode 45 and infrared light transparency. In this embodiment, as shown in FIG. 4B, the light-transmitting heating film 47 is composed of a film in which multiple thin metal wires are arranged in a mesh pattern. This structure of the light-transmitting heating film 47 allows infrared light to pass through the mesh openings, ensuring the infrared light transparency of the light-transmitting heating film 47. The infrared light transmittance of the light-transmitting heating film 47 should be 50% or more, but 80% or more is more preferable. An infrared light transmittance of 80% or more for the light-transmitting heating film 47 makes it easier to apply the sheet heating element 40 to a wider variety of applications. The infrared light transmittance of the light-transmitting heating film 47 can be measured in the same way as the infrared light transmittance of the sub-electrode 45.

[0066] The diameter of the thin metal wires that make up the translucent heat-generating film 47 is preferably 20 μm or less, and more preferably 10 μm or less, from the viewpoint of increasing the infrared light transmittance of the translucent heat-generating film 47. On the other hand, the lower limit should be sufficient to conduct electricity within the translucent heat-generating film 47 (thin metal wires) and sufficiently increase the temperature of the planar heating element, and is usually about 1 μm.

[0067] The structure of the mesh made of thin metal wires that constitutes the light-transmitting heat-generating film 47 is not particularly limited. For example, the openings may be a rectangular lattice pattern, or the openings may be polygonal, such as triangular or hexagonal. In this embodiment, the thin metal wires are arranged so that the openings are approximately square. The opening pitch of the mesh of the sub-electrode 45 (in this specification, the maximum diameter of each mesh is treated as the opening pitch) is appropriately selected so as to obtain the desired infrared light transmittance and heat generation properties.

[0068] For example, the maximum opening diameter (d1 in FIG. 4B) of the mesh of the translucent heat generating film 47 is preferably 0.05 mm or more, more preferably 0.1 mm or more, from the viewpoint of increasing infrared light transmittance. On the other hand, from the viewpoint of sufficiently increasing the temperature of the planar heating element 40 by the translucent heat generating film 47, the maximum opening diameter (d1 in FIG. 4B) is preferably 0.8 mm or less, more preferably 0.2 mm or less.

[0069] Furthermore, to sufficiently increase the temperature of the region where the translucent heat-generating film 47 is disposed, the resistance of the translucent heat-generating film 47 must be sufficiently higher than the resistance of the sub-electrode 45. There are several methods for increasing the resistance of the mesh-structured translucent heat-generating film 47 compared to the mesh-structured sub-electrode 45. For example, as shown in FIG. 4B , the maximum mesh opening diameter d1 of the translucent heat-generating film 47 is larger than the maximum mesh opening diameter d2 of the sub-electrode 45. For example, if the thin metal wires constituting the translucent heat-generating film 47 and the sub-electrode 45 are made of the same material and have approximately the same diameter, it is preferable to set d1 to at least 400 times d2. Setting d1 and d2 in this way makes the resistance of the translucent heat-generating film 47 much higher than the resistance of the sub-electrode 45, making the translucent heat-generating film 47 more likely to generate heat. This also significantly increases the infrared light transmittance of the translucent heat-generating film 47.

[0070] Another method is to make the maximum opening diameter d1 of the mesh of the translucent heat generating film 47 and the maximum opening diameter d2 of the mesh of the sub-electrode 45 approximately the same, and to make the resistivity of the material that makes up the translucent heat generating film 47 greater than the resistivity of the material that makes up the sub-electrode 45. In this case, it is preferable to make the resistivity of the material that makes up the translucent heat generating film 47 400 times or more greater than the resistivity of the material that makes up the sub-electrode 45.

[0071] As another method, the diameter of the thin metal wires that make up the light-transmitting heat-generating film 47 may be made smaller than the diameter of the thin metal wires that make up the sub-electrode 45 .

[0072] The material that makes up the thin metal wires of the light-transmitting heat generating film 47 may be any electrically conductive material, such as silver, copper, gold, aluminum, or alloys of these, or transparent metals such as indium tin oxide (ITO).

[0073] The sheet heating element 40 may further have other configurations as long as the purpose and effect of this embodiment are not impaired. Examples of other configurations include, for example, attachment means for attaching the sheet heating element 40 to various devices, temperature control means for controlling the temperature of the sheet heating element 40, a protective layer, etc.

[0074] (Operation of the sheet heating element of the second embodiment) The operation of the sheet heating element 10 of the second embodiment will now be described. The sheet heating element 40 is used by connecting the electrodes 42 to an external power source via the terminals 19. When a voltage is applied between the pair of electrodes 42, electricity is conducted within the light-transmitting heat-generating film 47, causing the temperature to rise. The area having the light-transmitting heat-generating film 47 can then be used as a variety of heat sources.

[0075] (Method for manufacturing the sheet heating element of the second embodiment) There are no particular limitations on the method for manufacturing the sheet heating element 40 of the second embodiment. First, a support substrate 41 is prepared, and the pair of electrodes 42 described above is formed on the support substrate 41. The main electrode 43 and the sub-electrode 45 having a mesh structure made of thin metal wires can be formed by known methods, and can be formed by the methods described in the first embodiment (for example, a patterning method using a resist or a mask, or a printing method such as inkjet printing).

[0076] Thereafter, a transparent heat-generating film 47 made of a mesh of thin metal wires is formed on the electrode 42 including the main electrode 43 and the sub-electrode 45. The method for forming the transparent heat-generating film 47 made of a mesh of thin metal wires can be the same as the method for producing the sub-electrode 45.

[0077] (Variation) In the above description, the light-transmitting heating film 47 is a film in which thin metal wires are arranged in a mesh pattern. However, if a conductive material that is transparent to infrared light is used as the material for the light-transmitting heating film 47, the light-transmitting heating film 47 does not need to be a mesh-like film. In this case, the light-transmitting heating film 47 may be formed uniformly to cover the sub-electrode 45. Examples of such materials include indium tin oxide (ITO) with controlled crystallinity. The light-transmitting heating film 47 may also be a film in which silver nanowires, indium tin oxide (ITO) with controlled crystallinity, or carbon nanotubes that have been subjected to various processes (e.g., oxidation) are dispersed in a binder resin that is transparent to infrared light. Germanium (Ge) or silicon (Si) may also be used in part.

[0078] Furthermore, although it has been described above that the sheet heating element 40 is infrared light transmissive, in the sheet heating element 40 having the light-transmitting heating film 47 in which the thin metal wires are arranged in a mesh pattern, visible light can also pass through between the thin metal wires. Therefore, it is also possible to impart visible light transmissivity to the sheet heating element 40.

[0079] 3. Effects of the present invention In any configuration of the sheet heating element of the present invention, the pair of electrodes includes a main electrode and a sub-electrode. Therefore, even if the heating area of ​​the sheet heating element 10 is large and the first and second main electrodes are far apart, electricity can be conducted within the translucent heating film via the first and second sub-electrodes. Furthermore, even if the heating area of ​​the sheet heating element is not rectangular, electricity can be conducted uniformly within the translucent heating film via the first and second sub-electrodes. Therefore, the heating area can be shaped in a variety of ways, allowing the sheet heating element to be used for a variety of purposes.

[0080] Furthermore, in the sheet heating element of the present invention, the supporting substrate, the sub-electrode, and the light-transmitting heating element are all optically transparent, so the heating area is transparent to visible light, which allows the sheet heating element to be used in a variety of applications, such as windows and various light irradiation devices. [Industrial Applicability]

[0081] The sheet heating element of the present disclosure is optically transparent and can have a large heating area or any shape, making it extremely useful in fields such as automobiles and building materials. [Explanation of symbols]

[0082] 10, 20, 30, 40 sheet heating element 11, 41 Support substrate 12, 42 electrodes 12a, 42a First electrode 12b, 42b Second electrode 13, 43 Main electrode 13a, 43a First main electrode 13b, 43b Second main electrode 15, 35, 45 sub-electrode 15a, 35a, 45a First sub-electrode 15b, 35b, 45b Second sub-electrode 17, 47 Transparent heating film 19 terminals 29 Dummy electrode

Claims

1. a light-transmitting support substrate; A pair of electrodes disposed on the support substrate; a light-transmitting heat-generating film disposed on the pair of electrodes; and each of the pair of electrodes includes a main electrode and a light-transmitting comb-shaped sub-electrode electrically connected to the main electrode; One sub-electrode and the other sub-electrode of the pair of electrodes are alternately arranged. Surface heating element.

2. the supporting substrate, the auxiliary electrode, and the light-transmitting heat-generating film are transparent to visible light; The sheet heating element according to claim 1 .

3. the sub-electrode has a total light transmittance of 50% or more as measured in accordance with JIS K 7361, and the main electrode has a total light transmittance of 50% or more as measured in accordance with JIS K 7361; The sheet heating element according to claim 2 .

4. The sub-electrode is made of thin metal wires arranged in a mesh pattern. The sheet heating element according to claim 2 .

5. the auxiliary electrode is made of a conductive film that is transparent to visible light; The sheet heating element according to claim 2 .

6. a dummy electrode that is transparent to visible light and not electrically connected to the pair of electrodes is further provided between the one sub-electrode and the other sub-electrode; The sheet heating element according to claim 2 .

7. The light-transmitting heat-generating film is a film having PTC resistance. The sheet heating element according to claim 2 .

8. The PTC-resistant film comprises a binder resin, multi-walled carbon nanotubes, Including, The sheet heating element according to claim 7.

9. the support substrate, the auxiliary electrode, and the light-transmitting heat-generating film are infrared light-transmitting; The sheet heating element according to claim 1 .

10. The light-transmitting heat-generating film is a film in which thin metal wires are arranged in a mesh pattern. The sheet heating element according to claim 9.

11. the sub-electrode is a film in which thin metal wires are arranged in a mesh pattern, the maximum opening diameter of the mesh of the translucent heat generating film is larger than the maximum opening diameter of the mesh of the sub-electrode; The sheet heating element according to claim 10.

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