Planar heating element

Abstract

The present invention provides a planar heating element in which a heating area can be increased to a large area, the shape of the heating area can be set to an arbitrary shape, and temperature unevenness is small. This planar heating element for solving the above problem includes: a pair of electrodes arranged on an insulating base material and arranged so as to face each other; and a heating film arranged on the pair of electrodes. Each of the pair of electrodes includes a main electrode, a plurality of first sub-electrodes branched from the main electrode, and second sub-electrodes branched from the first sub-electrodes.

Description

Planar heating element

[0001] The present invention relates to a planar heating element.

[0002] Planar heating elements are used in various applications such as heating, heaters for snow melting or anti-freezing, or industrial heat sources. As the structure of a planar heating element, a structure having an insulating base material 910 shown in FIG. 1, a pair of comb-shaped electrodes 920A and 920B disposed on the insulating base material 910, and a heating film 930 disposed so as to cover the comb-shaped electrodes 920A and 920B is common (for example, Patent Document 1). The comb-shaped electrodes 920A and 920B of the planar heating element 900 each have main electrodes 921a and 921b and sub-electrodes 922a and 922b. In the planar heating element 900, current flows from the sub-electrode 922a of one electrode 920A to the sub-electrode 922b of the other electrode 920B through the heating film 930, and the temperature rises due to the electrical resistance of the heating film 930.

[0003] Japanese Patent Application Laid-Open No. 2007-2143

[0004] However, in the comb-shaped electrodes 920A and 920B of the conventional planar heating element 900, one main electrode 921a or 921b is responsible for supplying current to all the sub-electrodes 922a and 922b connected thereto. Therefore, it is necessary to widen the width of the main electrodes 921a and 921b, and further to lengthen their lengths. On the other hand, there is no electrical conduction between the pair of main electrodes 921a and 921b through the heating film 930. Therefore, when the planar heating element is in use, the temperature near the main electrodes 921a and 921b is lower than the temperature of the sub-electrodes 922a and 922b and the heating film 930. Thus, in the conventional planar heating element 900, there is a problem that the main electrodes 921a and 921b, where it is difficult to increase the temperature, need to occupy a large area of the planar heating element 900, making it difficult to increase the area of the heating area. Furthermore, when the main electrodes 921a and 921b, where it is difficult to increase the temperature, are disposed inside the heating area of the planar heating element 900, temperature unevenness occurs in the heating area. Therefore, the main electrodes 921a and 921b have to be disposed along the outer periphery of the heating area, making it difficult to make the shape of the planar heating element 900 or the heating area an arbitrary shape.

[0005] The main objective of this disclosure is to provide a planar heating element that allows for a large heating area, arbitrary shapes for the heating area, and minimal temperature unevenness.

[0006] To solve the above problems, this disclosure provides the following planar heating elements: [1] A planar heating element having an insulating substrate, a pair of electrodes disposed on the insulating substrate and arranged facing each other, and a heating film disposed on the pair of electrodes, wherein each pair of electrodes includes a main electrode, a plurality of first auxiliary electrodes branched from the main electrode, and a second auxiliary electrode branched from the first auxiliary electrode. [2] The planar heating element according to [1], wherein when the pair of electrodes are viewed from above, the ratio of the area of ​​the main electrode to the total area of ​​the main electrode, the first auxiliary electrode, and the second auxiliary electrode is 30% or less. [3] The planar heating element according to [1] or [2], wherein when the pair of electrodes are viewed from above, at least one of the first auxiliary electrodes and / or at least one of the second auxiliary electrodes extend so as to surround the center of the planar heating element.

[0007] According to this disclosure, it is possible to make the heating area large, or to make the shape of the heating area of ​​the planar heating element an arbitrary shape. Furthermore, according to this disclosure, a planar heating element with less temperature unevenness is provided.

[0008] Figure 1 is a plan view showing the structure of a conventional planar heating element. Figure 2A is a plan view showing the structure of a planar heating element according to one embodiment of the present disclosure, and Figure 2B shows the shape when the heating film is removed from the planar heating element. Figures 3A and 3B are schematic diagrams for explaining the electrode structure of the planar heating element shown in Figures 2A and 2B. Figure 4 is a schematic diagram for explaining potential problems that may arise in a planar heating element. Figure 5A is a plan view showing the structure of a planar heating element according to a modified example of the present disclosure, and Figure 5B shows the shape when the heating film is removed from the planar heating element.

[0009] In this specification, the numerical range indicated by "~" means the numerical range that includes the numbers written before and after "~".

[0010] A planar heating element according to one embodiment of the present disclosure will be described with reference to Figures 2A and 2B. As shown in Figures 2A and 2B, the planar heating element 100 of this embodiment includes an insulating substrate 110, a pair of electrodes 120A and 120B disposed on the insulating substrate 110, and a heating film 130 disposed to cover the pair of electrodes 120A and 120B. Figure 2A is a plan view of the planar heating element 100 of this embodiment, and Figure 2B is a plan view of the planar heating element 100 with the heating film 130 removed. In the planar heating element 100, the substantially trapezoidal region where the heating film 130 is located becomes the heating area. The various components of the planar heating element 100 of this embodiment will be described below. However, the planar heating element 100 of this embodiment may have other components as needed.

[0011] The insulating substrate 110 is not particularly limited as long as it has insulating properties, can laminate a pair of electrodes 120A and 120B and a heating film 130 onto it, and has heat resistance that can withstand the heat generated when the planar heating element 100 is in use. The shape of the insulating substrate 110 is not particularly limited and can be appropriately selected according to its application. For example, it may be a plate-shaped or film-shaped substrate, or a substrate with any three-dimensional shape.

[0012] The materials constituting the insulating substrate 110 are not particularly limited and may be resins or inorganic materials. Examples of resins include 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 others such as polycarbonate (PC), polyamide, polyimide, acrylic resin, triacetylcellulose (TAC), and polyphenylene sulfide (PPS). Examples of inorganic materials include glass and ceramics.

[0013] Each pair of electrodes 120A and 120B (collectively referred to as "electrode 120") comprises a main electrode 121a and 121b (collectively referred to as "main electrode 121"), a first auxiliary electrode 122a and 122b (collectively referred to as "first auxiliary electrode 122"), and a second auxiliary electrode 123a and 123b (collectively referred to as "second auxiliary electrode 123"). Each electrode 120 also has a terminal 129 for connecting the main electrode 121 to an external power supply.

[0014] To illustrate the shape of each electrode 120 in detail, Figure 3A shows the shape of one electrode 120A, and Figure 3B shows the shape of the other electrode 120B. In Figures 3A and 3B, the main electrode 121, the first auxiliary electrode 122, and the second auxiliary electrode 123 are distinguished from each other by different hatching. However, these are formed as a single unit and are electrically conductive.

[0015] The main electrode 121 of each electrode 120 is an electrode that supplies current supplied from the terminal 129 to the multiple first sub-electrodes 122, or that allows current flowing in from the first sub-electrode 122 to flow to the terminal 129. In this specification, the portion of the electrode 120 that is connected to the terminal 129 and is wider than the portion that branches off from that portion (first sub-electrode 122) is referred to as the main electrode 121. In this specification, the first sub-electrode 122 refers to a region of a certain width that branches off from the main electrode 121. In this specification, a line perpendicular to the sub-electrode 122 is drawn at the end of each sub-electrode 122 on the main electrode 121 side, and this is defined as the boundary between the main electrode 121a and the first sub-electrode 122a.

[0016] The positions of each main electrode 121 when the electrode 120 is viewed from above are not particularly limited, as long as the first and second auxiliary electrodes 122 and 123, described later, can be positioned at desired locations. In this embodiment, the main electrodes 121a and 121b are arranged so as to extend from one corner of the substantially trapezoidal planar heating element 100 toward its center. However, depending on the shape of the first and second auxiliary electrodes 122 and 123, the main electrodes 121a and 121b may be arranged along the outer circumference of the planar heating element 100, or near the center of the planar heating element 100.

[0017] Furthermore, the two main electrodes 121a and 121b may be arranged facing each other with the first sub-electrode 122 and the second sub-electrode 123 in between, but in this embodiment, the two main electrodes 121a and 121b are arranged adjacent to each other. As in this embodiment, by arranging the main electrodes 121a and 121b adjacent to each other, electrical conductivity occurs between them via the heating film 130. As a result, when the planar heating element 100 is in use, the temperature near the main electrodes 121a and 121b is less likely to be lower than other areas, and the areas near the main electrodes 121a and 121b can also be used as a heating area. However, since the main electrode 121 is wide, the temperature on the inside in the width direction of the main electrode 121 is less likely to be higher than the area on the outside in the width direction. Therefore, it is preferable that the area of ​​the main electrode 121 is small when viewed from above. More specifically, it is preferable that the ratio of the main electrode 121a to the total area of ​​the main electrode 121, the first auxiliary electrode 122, and the second auxiliary electrode 123 is small, and it is preferable that the ratio of the area of ​​the main electrode 121 to the total area of ​​the main electrode 121, the first auxiliary electrode 122, and the second auxiliary electrode 123 is 30% or less, more preferably 20% or less, and even more preferably 15% or less. The area of ​​the main electrode 121 and the areas of the first auxiliary electrode 122 and the second auxiliary electrode when the planar heating element 100 is viewed from above can be determined by analyzing the shape of each electrode using a drafting tool (e.g., CAD). In the electrode 120 shown in Figure 2B, the ratio of the main electrode 121a to the total area of ​​the main electrode 121, the first auxiliary electrode 122, and the second auxiliary electrode 123 is approximately 10%.

[0018] On the other hand, in this specification, the first auxiliary electrode 122 is an electrode having a certain width that branches off from the main electrode 121, as described above, and the second auxiliary electrode 123 is an electrode that further branches off from the first auxiliary electrode 122. As shown in Figure 2B, the first auxiliary electrode 122a and the second auxiliary electrode 123a of one electrode 120A are arranged to face either the first auxiliary electrode 122b or the second auxiliary electrode 123b of the other electrode 120B, respectively. In this embodiment, the first auxiliary electrode 122 functions as an electrode for electrical conduction (heat generation) via the heating film 130, and also functions as an electrode for supplying current to the second auxiliary electrode 123. Therefore, there is no need to increase the length or width of the main electrode 121, and the heating area of ​​the planar heating element can be made into a free shape or its area can be increased.

[0019] The number of first sub-electrodes 122a and 122b on each electrode 120A and 120B is not particularly limited and is set appropriately according to the shape of the planar heating element 100 and the shape of the heating area. Furthermore, all first sub-electrodes 122 may branch to form second sub-electrodes 123, or only some of the first sub-electrodes 122 may branch to form second sub-electrodes 123. In this specification, first sub-electrodes 122a and second sub-electrodes 123a are distinguished as follows. When a first sub-electrode 122 has a branch, the electrode of the route with the longest length after branching is designated as the first sub-electrode 122, and the electrodes branching from it are designated as second sub-electrodes 123. For example, in Figure 3A, the first sub-electrode 122a, which branches off from the main electrode 121a at branch b1, is further branched at branches b2 to b7. In this case, the electrode of the route with the longest length is designated as the first sub-electrode 122a, and the other electrodes are designated as second sub-electrodes 123a.

[0020] On the other hand, the number of second auxiliary electrodes 123a and 123b on each electrode 120A and 120B is not particularly limited and can be set appropriately according to the shape of the planar heating element 100 and the shape of the heating area. The second auxiliary electrode 123 may be further branched as shown in Figure 3B, but in this embodiment, the branched electrodes are also treated as part of the second auxiliary electrode 123. In this embodiment, because such second auxiliary electrodes 123a and 123b are present, the heating area can include corners of the planar heating element and areas with complex shapes, where it was difficult to place auxiliary electrodes in conventional planar heating elements. Furthermore, by having these second auxiliary electrodes 123a and 123b, temperature unevenness within the heating area can be suppressed.

[0021] Here, when the pair of electrodes 120A and 120B are viewed from above, it is preferable that at least one first auxiliary electrode 122 and / or at least one second auxiliary electrode 123 extend so as to surround the center of the planar heating element 100. The statement that the first auxiliary electrode 122 or the second auxiliary electrode 123 extends so as to surround the center of the planar heating element 100 includes not only cases where the first auxiliary electrode 122 or the second auxiliary electrode 123 is arranged to surround the center of the planar heating element 100 by 360 degrees or more, but also cases where the first auxiliary electrode 122 or the second auxiliary electrode 123 is arranged to surround the center of the planar heating element 100 by 270 degrees or more. In this embodiment, as shown in Figure 3A, a plurality of first auxiliary electrodes 122a of electrode 120A are arranged to surround the center (not shown) of the planar heating element 100. Furthermore, as shown in Figure 3B, the multiple first auxiliary electrodes 122b of electrode 120B are also arranged to surround the center (not shown) of the planar heating element 100. When the first auxiliary electrodes 122 and the second auxiliary electrodes 123 have this shape, the density of the first auxiliary electrodes 122 and the second auxiliary electrodes 123 within the heating area tends to be uniform, making it less likely for temperature unevenness to occur in the heating area.

[0022] Furthermore, if the first sub-electrode 122 and the second sub-electrode 123 have bent portions that bend at an angle of 90 degrees or less (for example, R1 in Figure 3A and R2 in Figure 3B), it is preferable that the corners of these bent portions are curved. For example, as shown in the schematic diagram of Figure 4, if the corner of the bent portion R is an acute or right angle, the distance between the opposing sub-electrodes 923a and 923b increases in the vicinity of the corner (the area enclosed by the dotted line), making it difficult for electrical conduction through the heating film to occur. As a result, the temperature in this area does not rise easily. Moreover, in this area, the width of the sub-electrodes 923a and 923b increases, and the temperature in the area inside the width direction of the sub-electrodes 923a and 923b also does not rise easily. In contrast, if the corner of the bent portion is curved, the distance between the first sub-electrode 122 and the second sub-electrode 123 tends to remain constant. Furthermore, the widths of the first auxiliary electrode 122 and the second auxiliary electrode 123 are less likely to become excessively wide at these corners. As a result, temperature unevenness is less likely to occur in the heating area.

[0023] Furthermore, as shown in Figure 4, when multiple acute angles are aligned in a straight line, the low-temperature regions (areas enclosed by dotted lines) will be aligned in a straight line, and the effect of temperature unevenness will be greater. Therefore, it is preferable to arrange the first auxiliary electrode 122 and the second auxiliary electrode 123 so that acute angles are not aligned in a straight line within the heating area.

[0024] The pair of electrodes 120A and 120B described above may be made of an electrically conductive material. Each electrode 120 is usually made of metal, and may be made of, for example, aluminum, silver, copper, etc.

[0025] On the other hand, the heating film 130 is a film placed on the pair of electrodes 120A and 120B described above, and can be any film whose temperature rises due to its resistance during electrical conduction. The heating film 130 can be the same as the heating film of a known planar heating element, and can be, for example, a film containing a conductive material such as carbon-based particles or metal particles and a binder resin such as polyester resin. The heating film 130 may also be a PTC-resistant film (PTC resistor film). Such a PTC resistor film can be a film containing a binder resin such as a thermoplastic resin or wax and conductive particles such as carbon-based particles or metal particles.

[0026] (Operation of the Planar Heating Element) The operation of the planar heating element 100 will now be explained. The planar heating element 100 is used in connection with an external power source via the terminals 129 of the electrodes 120. When a voltage is applied between the pair of electrodes 120, electricity conducts through the heating film 130, and its temperature rises. The region having the heating film 130 can then be used as various heat sources. If the heating film 130 is a PTC resistor film, as its temperature rises, the binder resin expands, increasing the distance between conductive particles and raising the resistance. Therefore, the resistance rises sharply near the softening temperature or melting point of the binder resin, making it difficult for electricity to conduct. In other words, it becomes possible to control the temperature so that it does not rise above a certain level.

[0027] (Method for manufacturing a planar heating element) The method for manufacturing the planar heating element 100 is not particularly limited. First, an insulating substrate 110 is prepared, and the pair of electrodes 120 described above are formed on the insulating substrate 110. The method for forming the main electrode 121, the first auxiliary electrode 122, and the second auxiliary electrode 123 is not particularly limited and can be formed by known methods. For example, a photosensitive material having an emulsion layer containing a photosensitive silver halide salt may be applied to the insulating substrate 110, and the applied photosensitive material may be exposed to light in the shape of the main electrode 121, the first auxiliary electrode 122, and the second auxiliary electrode 123, and then developed to form the electrodes 120. Alternatively, a metal foil may be formed on the insulating substrate 110, a resist may be printed in a pattern or applied to the entire surface of each metal foil, the resist may be exposed to light and developed to form a pattern, and the electrodes 120 may be formed by etching the metal at the openings. Furthermore, a mask having openings in the shape of the main electrode 121, the first auxiliary electrode 122, and the second auxiliary electrode 123 may be placed on the insulating substrate 110, and the electrodes 120 may be formed by sputtering or vapor deposition. Alternatively, the main electrode 121, the first auxiliary electrode 122, and the second auxiliary electrode 123 may be formed by using an ink containing conductive fine particles, by an inkjet method, screen printing method, or a method using a dispenser, thereby forming the electrodes.

[0028] Subsequently, a heating film 130 is formed to cover the electrode 120, including the main electrode 121, the first auxiliary electrode 122, and the second auxiliary electrode 123. The method for forming the heating film 130 is appropriately selected depending on the type of heating film 130. For example, if the material of the heating film 130 is a conductive material and a binder resin, these can be dissolved or dispersed in a solvent as needed, and then applied by various coating methods (roll coating, screen printing, bar coating, spin coating, inkjet printing, application by dispenser, etc.), and then dried or solidified to form the heating film.

[0029] (Modified Version) Figures 5A and 5B illustrate a modified planar heating element 200 according to the above-described modification. Figure 5A is a plan view of the planar heating element 200, and Figure 5B is a plan view of the planar heating element 200 with the heating film 130 removed. The planar heating element 200 also has an insulating substrate 110, a pair of electrodes 120A and 120B arranged on the insulating substrate 110, and a heating film 130 arranged to cover the pair of electrodes 120A and 120B. The pair of electrodes 120A and 120B each have a main electrode 121a and 121b, a first sub-electrode 122a and 122b, and a second sub-electrode 123a and 123b, respectively. The modified planar heating element 200 is the same as the planar heating element 100 described above, except that the shape of the insulating substrate 110, the shape of the pair of electrodes 120A and 120B, and the shape of the heating film 130 are different. In Figures 5A and 5B, the same components as described above are denoted by the same reference numerals. In the electrode 120 shown in Figure 5B, the ratio of the main electrode 121a to the total area of ​​the main electrode 121, the first auxiliary electrode 122, and the second auxiliary electrode 123 is approximately 10%.

[0030] This application claims priority under Japanese Patent Application No. 2024-226132, filed on 23 December 2024. All contents described in the specification and drawings of said application are incorporated herein by reference.

[0031] The planar heating element of this disclosure allows for a large heating area and the heating area to be shaped in any desired way. Furthermore, the planar heating element of this disclosure exhibits minimal temperature unevenness in the heating area. Therefore, this planar heating element is extremely useful in fields such as automobiles and building materials.

[0032] 100, 200, 900 Planar heating element 110, 910 Insulating substrate 120, 120A, 120B Electrode 121, 121a, 121b Main electrode 122, 122a, 122b First sub-electrode 123, 123a, 123b Second sub-electrode 129 Terminal 130, 930 Heating film 921 Comb-shaped electrode 923a, 923b Sub-electrode

Claims

1. A planar heating element comprising: an insulating substrate; a pair of electrodes disposed on the insulating substrate and arranged facing each other; and a heating film disposed on the pair of electrodes, wherein each pair of electrodes includes a main electrode, a plurality of first auxiliary electrodes branched from the main electrode, and a second auxiliary electrode branched from the first auxiliary electrodes.

2. The planar heating element according to claim 1, wherein, when the pair of electrodes are viewed from above, the ratio of the area of ​​the main electrode to the total area of ​​the main electrode, the first auxiliary electrode, and the second auxiliary electrode is 30% or less.

3. The planar heating element according to claim 1, wherein, when the pair of electrodes are viewed from above, at least one of the first auxiliary electrodes and / or at least one of the second auxiliary electrodes extend so as to surround the center of the planar heating element.

Images