Planar heating element

Abstract

To provide a planar heating element with a short heating time, uniform surface heating, and excellent light transmission. [Solution] The heat-generating resistor 2 includes a carbon fiber fabric, wherein the carbon fiber fabric has a diameter of 5 μm or more and 15 μm or less for each single yarn constituting at least one of the interwoven yarns, and the width of at least one of the interwoven yarns is 180 μm or less, the porosity of the carbon fiber fabric is 35% or more and 90% or less, and electrodes 4 having electrical connection terminals are provided on opposite sides of the carbon fiber fabric, and the carbon fiber fabric and electrodes 4 are enclosed in a light-transmitting insulating material 3 with the electrical connection terminals exposed.

Description

Technical Field

[0001] The present invention relates to a planar heating element used for heating, drying, etc. More specifically, the present invention relates to a planar heating element having excellent instant heating property and light transmittance, which uses a carbon fiber fabric coated with a sheet-like resin as a heating element. Here, the instant heating property refers to the property of raising the temperature in a short time.

Background Art

[0002] Generally, unlike a linear heating element such as a nichrome wire heater or a carbon heater, a planar heating element can uniformly heat a wide range. For example, it is used in many applications such as floor heating, vegetable dryers, toilet seats, low-temperature startup of lithium-ion batteries, and signal snow-melting heaters. Planar heating elements with various configurations have been proposed as follows. For example, Patent Document 1 discloses an invention of a planar heating element in which carbon fiber as a resistance heating material is uniformly distributed over the entire surface of a square-shaped Japanese paper to form a heating element sheet (carbon fiber mixed-copied sheet), copper electrodes made of a sprayed film are respectively formed on both side ends of the surface of the carbon fiber mixed-copied sheet, and both surfaces of the heating element sheet are coated with a resin such as FRP. Patent Document 2 discloses a planar heating element in which inorganic particles are included in a continuous carbon fiber sheet and the sheet is sandwiched between matrix resins and compression-molded by heating. Patent Document 3 discloses a planar heating element in which carbon fiber is impregnated in a thermosetting resin. Further, Patent Document 4 discloses a planar heater having light transmittance, in which a transparent conductive film is sandwiched between glass plates.

[0003] However, the carbon fiber-containing papermaking sheet used in Patent Document 1, while providing uniform heat generation across the entire surface, suffers from low mechanical strength due to the random orientation of short fibers. When installed in the outer layer of a structure, it can tear due to external impacts and stresses. Patent Document 2, on the other hand, contains inorganic particles, resulting in a long heating time. Furthermore, the carbon fiber sheet described in Patent Document 3 uses short carbon fibers and natural pulp, which has poor heat transfer properties, bonded together with polyvinyl alcohol, leaving gaps, which also results in a long heating time. In particular, heating toilet seats involves making serpentine contact with heat-resistant resin to evenly heat the contact area when seated. To prevent the heat-resistant resin from melting at the contact point with the heating element, it is necessary to slowly raise the temperature over time. Although the power consumption is low, the heater is used continuously, and its standby power consumption is not insignificant. Therefore, there is a strong demand for a surface heating element that can heat up quickly and does not require power after use. Furthermore, Patent Document 4 proposes a translucent planar heating element, but it involves forming a transparent conductive film such as ITO (Indium Tin Oxide) on a glass plate and using the transparent conductive film as a heat source. This presents challenges in terms of difficulty in scaling up the area and high costs. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 5-258842 [Patent Document 2] Japanese Patent Publication No. 2021-012814 [Patent Document 3] Patent No. 4250866 [Patent Document 4] Japanese Patent Publication No. 2012-74325 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] The present invention was made to solve the above-mentioned problems, and its objective is to provide a heating element with a short heating time, uniform surface heating, and excellent light transmittance. Furthermore, it is applicable to applications such as heating and window materials, signal lights with snow melting functions, and residential building materials, and aims to provide a planar heating element that is light-transmitting despite being a heating element. [Means for solving the problem]

[0006] To achieve the above objective, the planar heating element of the present invention has a heating resistor containing a carbon fiber fabric, The carbon fiber fabric is characterized in that the diameter of the single yarn constituting at least one of the interwoven yarns is 5 μm or more and 15 μm or less, and the width of at least one of the interwoven yarns is 180 μm or less. The porosity of the carbon fiber fabric is 35% or more and 90% or less. The carbon fiber fabric has electrodes with electrical connection terminals on opposite sides, The carbon fiber fabric and the electrode are characterized in that the electrical connection terminals are encased in a light-transmitting insulating material with the terminals extended. Here, the yarn width refers to the average value of the yarn widths of the warp and weft threads at any five locations, measured under a 250x magnification using a transmissive magnifying glass.

[0007] In the planar heating element of the present invention, it is preferable that the insulating material includes at least one selected from thermoplastic resins, thermosetting resins, fluororesins, rubbery viscoelastic materials, and glass. [Effects of the Invention]

[0008] According to the present invention, by creating a planar heating element in which carbon fiber fabric is encapsulated with an insulating material, it is possible to provide a planar heating element that heats up much faster and heats up uniformly on the surface compared to conventional planar heating elements made by wrapping nichrome wire or the like. Furthermore, a planar heating element made of carbon fiber fabric with a large open area ratio and a transparent (light-transmitting) insulating material is useful as a heating material that allows light to pass through, a translucent heater that can be attached to the side windows of electric vehicles, and a signal light with a snow-melting function. [Brief explanation of the drawing]

[0009] [Figure 1] This is a cross-sectional view showing one embodiment of the planar heating element of the present invention. [Figure 2] This figure shows the method for measuring the temperature of a planar heating element according to the present invention. [Figure 3] This figure shows the temperature rise curve after energization of the planar heating element (double-sided glass plate) of Example 1. [Figure 4] This figure shows the temperature rise curve after energization of the planar heating element (double-sided glass plate) of Example 2. [Figure 5] This is a photograph of the planar heating element of the present invention, which has light-transmitting properties. Figure 5(A) is a photograph of the planar heating element placed on top of a display object, and Figure 5(B) is a magnified photograph of the same planar heating element. [Figure 6] This figure shows the temperature rise curve of the planar heating element of Example 3 after energization. [Figure 7] This figure shows the temperature rise curve after energization of the planar heating element (sandwiched between a glass plate and an unsaturated polyester resin) of Example 4. [Figure 8] This figure shows the temperature rise curve after energization of the planar heating element (sandwiched between an acrylic plate and urethane resin) of Example 5. [Figure 9] This figure shows the temperature rise curve after energization of the planar heating element (double-sided polyester film) of Example 6. [Modes for carrying out the invention]

[0010] The planar heating element of the present invention will be described with examples. However, the present invention is not limited to the following examples. Note that the drawings referenced below are schematic, and the ratios of the dimensions of the objects depicted in the drawings may differ from the ratios of the dimensions of actual objects. The ratios of the dimensions of objects may also differ between drawings.

[0011] In order to solve the above problems, the inventor has conducted intensive studies. As a result, as the heating resistor, carbon fiber, which has a resistance value two orders of magnitude larger than that of metal and is lightweight, is preferable. Furthermore, by making the interwoven yarn thinner, the relative resistance value also increases. The inventors focused on the fact that by changing the pitch of the interwoven yarn, the watt density per unit area can be freely designed to meet various applications.

[0012] And by reducing the single fiber diameter and making the interwoven yarn thinner, the contact area with the insulating material also increases, resulting in a structure that facilitates heat transfer. This is considered to reduce the temperature gradient between the central part and the outer peripheral part of the heating resistor, reduce thermal distortion, and improve the repetitive life. Therefore, in order to quickly and uniformly transfer heat from the heating resistor to the insulating material, the heating resistor should be made of a fabric structure composed of thin yarns to obtain good instant heating performance.

[0013] Furthermore, by combining a carbon fiber fabric with thinner interwoven yarns and a large aperture ratio and a transparent (light-transmissive) insulating material, a light-transmissive planar heating element can be obtained.

[0014] In this invention, a heat-resistant material containing a carbon fiber fabric is used, and the diameter of the carbon fiber single filaments in the interwoven yarn constituting the carbon fiber fabric is 5 μm to 15 μm, the width of at least one of the yarns is 180 μm or less, and light transmission is achieved by setting the porosity of the carbon fiber fabric to 35% to 90%. The single filament diameter is preferably 5 μm to 8 μm. Furthermore, the yarn width is preferably 50 μm to 150 μm, and more preferably 50 μm to 110 μm. More than 90% of carbon fibers are manufactured by a method in which acrylic fibers, which are the starting material, are flame-retardant fired in yarn form and then carbonized. This flame-retardant process is an exothermic reaction, and the conditions for uniform heat firing to the center of the fiber cross-section are narrow, resulting in low single filament strength. Therefore, it has been necessary to increase the number of single filaments to ensure productivity in the yarn manufacturing process, which has resulted in thicker interwoven yarns. Furthermore, there is data from guinea pig bioassays indicating a risk of carcinogenicity when the single filament diameter is less than 5 μm, making its use undesirable. Due to these circumstances, the inventor established a method for producing ultra-thin carbon fiber fabrics with single filament diameters of 5 μm to 15 μm by first weaving a fabric from starting acrylic spun yarn with a single filament diameter of 7.5 μm to 23 μm, and then flame-retarding and carbonizing it in this state. For carbon fiber fabrics consisting of fine yarns with a single filament diameter of 5 to 15 μm and a yarn width of 180 μm or less, it is desirable to first weave the fine acrylic spun yarn into a white cloth fabric and then flame-retard and carbonize it in the woven state (see Patent 6956352). Even with fine interwoven yarns, because it is a woven fabric, there is no productivity drawback due to strength degradation during the flame-retarding process; in fact, the fine single filament diameter offers the advantage of shorter time for uniform flame-retarding from the outer edge to the center. The resulting ultra-thin carbon fiber fabric has sufficient strength for use as a planar heating element embedded in insulation material, although it is not suitable for mechanical structures requiring high tensile strength.

[0015] Furthermore, while conventional spun yarns are made by twisting together 65 or more single yarns, to further reduce the number of yarns, a core-sheath spinning method was used, where lost fibers were used as the core yarn and acrylic spun yarn as the sheath. By weaving the resulting yarn, a carbon fiber fabric was obtained consisting of an extremely fine blended yarn with only 45 acrylic spun yarns, and this fabric exhibited good light transmission. The aforementioned lost fibers ensure strength during weaving and are lost during the refining process, contributing to the realization of an ultra-thin fabric. By making the fabric refined in this way flame-resistant and carbonizing it in a planar manner, an ultra-thin carbon fiber fabric was obtained, which could be used as a heat-resistant material, a base material for a planar heating element that can be used in a wide range of applications.

[0016] Therefore, the single yarn diameter of the carbon fiber fabric, which is a heating resistor for a planar heating element with good rapid heating and light transmission, is preferably 5 μm to 15 μm, and the porosity of the carbon fiber fabric for a planar heating element with good light transmission is preferably 35% to 90%. A planar heating element was formed by closely attaching highly conductive electrodes to opposite sides of this heating resistor and enclosing both in an insulating material so that the electrical connection terminals are exposed. A carbon fiber fabric with an porosity of 35% to 90% needs to be a fabric with a much larger mesh opening than gauze, but because the binding force of the weave is weak, it is very difficult to make a uniform fabric in each process of weaving, scouring, and flame-retardant treatment. Therefore, by weaving two to seven times more fibers made of thermoplastic resin such as nylon 6 or polyester into the weft yarn, which is acrylic fiber, it is possible to make a fabric that is easy to pass through the processes. These thermoplastic resin fibers retain their shape even at the flame-retardant temperature of acrylic fibers, and disappear at carbonization temperatures exceeding 1200°C, making this a favorable manufacturing method for obtaining carbon fiber fabrics with very large openings. The porosity is more preferably 50% to 90%, and even more preferably 60% to 90%.

[0017] The insulating material preferably includes at least one selected from translucent thermoplastic resins, thermosetting resins, fluororesins, rubbery viscoelastic materials, and glass. Thermoplastic resins include polyvinyl chloride, polypropylene, polyethylene terephthalate, ABS resin, polycarbonate resin, etc. Thermosetting resins include phenolic resin, polyurethane resin, epoxy resin, melamine resin, polyimide resin, etc. Rubbery viscoelastic materials include natural rubber, NBR, silicone rubber, Viton, etc. Examples of fluororesins include FEP resin. The insulating material may be in the form of a sheet or film, or it may be used as a binder.

[0018] Figure 1 shows a cross-sectional view of one embodiment of the planar heating element of the present invention. The planar heating element 1 of the present invention can be manufactured, for example, as follows: Conductive copper foil adhesive tape, slightly longer than the fabric, is attached to both ends of a rectangular carbon fiber fabric 2, which is a heating resistor, as electrodes 4. Next, the carbon fiber fabric 2 and electrodes 4 are sandwiched together with a heat-resistant insulating material 3 to form a planar heating element, so that they are electrically insulated except for the electrodes 4 which are exposed as electrical terminals. At this time, the carbon fiber fabric 2 and electrodes 4 may be enclosed in the insulating material 3 via a binder 5. Various methods described later can be used for sealing with the insulating material. In addition, the insulating material 3 and the binder 5 may be made of the same material. The carbon fiber fabric 2 may be fixed to the insulating material 3 with adhesive tape 6 such as adhesive paper tape, as described later.

[0019] Here, the carbon fiber fabric can be plain weave, twill weave, double plain weave, etc., and the basis weight is 5g / m². 2 ~50g / m 2 Preferably 8 g / m 2 ~40g / m 2 It is desirable that the warp and weft thread widths be such that at least one is 180 μm or less, and the other is in the range of 40 μm to 260 μm. 0.05 N / cm 2The thickness under pressure should be 0.04 to 0.2 mm, and the electrical resistance should be measured using a HIOKI mΩ high-tester precision resistance meter. A fabric with a resistance value of 2 to 70 Ω in the longitudinal direction of a 10 cm length cloth with an effective measurement width of 1 cm is suitable for use.

[0020] As electrodes, 5mm wide conductive copper foil adhesive tape manufactured by Teraoka Seisakusho is attached to the designated location. Alternatively, a 10mm wide, 0.1mm thick copper plate may be folded in half, sandwiched between carbon fiber fabric, and pressed and fixed. Furthermore, copper wires of the required size may be soldered to the carbon fiber fabric at a predetermined pitch and taken out as electrodes. The copper wires may be fixed by attaching the conductive copper foil adhesive tape. Furthermore, they may be sewn together with sewing thread (for example, polyester 60 count sewing thread).

[0021] Next, as a method of insulating material sealing (A), the carbon fiber fabric and electrodes are wrapped in a 0.1 mm thick polyethylene terephthalate film to which a heat-curing binder has been thinly applied, and the film is bonded together into a sheet using an Iris Ohyama laminator and pressure heating with rollers. It goes without saying that the electrode terminals are outside the heat-sealed film.

[0022] As an alternative method of insulating material sealing (B), the carbon fiber fabric and electrodes are sandwiched between sheets of polyphenylene sulfite, which has excellent heat resistance and self-extinguishing properties, and heated and pressurized in a heated press with shims placed on the outside to maintain a constant gap. After removal, it is immediately cooled by sandwiching it between aluminum plates. At this time, it is desirable to remove the air from the space sandwiched between the polyphenylene sulfite sheets before heating so that the sheets are in close contact. This allows the sheets to fuse together between the weaves, and eliminates the need to apply a heat-curing binder beforehand.

[0023] As an alternative method of insulating material sealing (C), a carbon fiber fabric with electrodes attached is immersed in a solution of resol-type phenolic resin dissolved in water, the excess is squeezed out with a roller and dried, and then it is pressurized and molded at 170°C for 3 minutes to form a planar heating element. The electrode terminals are masked with paper tape.

[0024] Furthermore, as a method of insulating material sealing (D), a carbon fiber fabric and electrodes made of copper tape or the like are placed on a transparent glass plate, and double-sided adhesive is applied to the outer periphery to prevent the carbon fiber fabric from moving. Then, a glass plate is placed on top of them to fix the two glass plates together and complete the planar heating element.

[0025] As another method of insulating material sealing (E), in method (D), before placing the glass plate on top, a thin layer of transparent insulating resin such as unsaturated polyester resin is poured in, scraped with a sharp edge to prevent air bubbles from being trapped, and the glass plate is placed on top while allowing the transparent insulating resin to solidify slowly. The curing time can be adjusted by adjusting the proportion of catalyst contained in the resin. This results in a transparent, impact-resistant planar heating element.

[0026] Another method of insulating material sealing (F) is to sandwich a heating resistor with electrodes in close contact between transparent insulating sheets, pressurize the surrounding area to ensure tight contact, remove the air between the insulating sheets with a vacuum pump, and then pressurize at a temperature above the fusion temperature of the sheets, thereby creating a planar heating element in which the insulating material encases the heating resistor.

[0027] As another method of insulating material sealing (G), an organic solvent such as methyl ethyl ketone can be applied to a transparent acrylic sheet, a heating resistor with electrodes in close contact with it can be sandwiched between the sheets, and the sheet can be held under pressure to obtain a transparent planar heating element.

[0028] In all cases, ensuring close contact between the heating resistor and the insulating material to reduce internal air is crucial for improving rapid heating and light transmission, and for minimizing degradation even after repeated expansion and contraction. The acceleration time of heating is determined by the combination of the carbon fiber fabric (heating element) and the insulating and heat-insulating material, but for transparent, planar heating elements, carbon fiber fabric made of fine threads is a suitable material. [Examples]

[0029] The present invention will be described in detail based on examples, but these are presented for illustrative purposes only. In other words, the following examples are not intended to be exhaustive or to limit the present invention to the forms described. Therefore, the present invention is not limited to the following examples, unless it exceeds the spirit of the invention.

[0030] [Example 1] FCC type carbon fiber fabric was used. This carbon fiber fabric has a warp pitch of 258 μm, a warp thread width of 50 μm, a weft pitch of 305 μm, a weft thread width of 50 μm, and an open area ratio of 67%. This was cut to a size of 155 mm x 130 mm, and 5 mm wide conductive adhesive copper tape (manufactured by Teraoka Seisakusho) was attached to the short sides opposite each other to form electrodes. The center distance between the copper tapes was 150 mm. Here, the single yarn diameter of the carbon fibers in the interwoven yarn constituting the carbon fiber fabric is 5.2 μm.

[0031] Next, the carbon fiber fabric was placed in the center of a 200mm x 150mm 1mm thick glass plate (soda glass), and 100μm thick adhesive paper tape was applied to its outer circumference. The adhesive paper tape was applied to the outer circumference of all four sides of the carbon fiber fabric to prevent it from shifting in the planar direction. Then, 5% of a special hardener was mixed with a transparent unsaturated polyester resin (low viscosity FRP polyester resin: water-based FRP / plastic paint manufactured by Sunday Paint Co., Ltd.), thoroughly degassed, and poured onto the carbon fiber fabric. The excess amount exceeding the thickness of the adhesive paper tape was scraped off with a sharp edge. While the unsaturated polyester resin was still fluid, a 1mm thick glass plate (soda glass) was placed on top to prevent any bubbles from remaining inside. Furthermore, a 200mm wide rubber roller with a rubber hardness of 60 degrees was rolled in one direction to push the unsaturated polyester resin between the two glass plates in one direction, and a weight was placed on top to allow the unsaturated polyester resin to harden with its catalyst. In this way, the carbon fiber fabric (heating element) and the unsaturated polyester resin were sandwiched between two glass plates, minimizing the trapping of air. At this time, the ends of the electrodes were left outside the glass surface. In this way, the planar heating element of this embodiment was obtained. The effective area of ​​the obtained planar heating element was 144 mm × 130 mm, the thickness was 2.1 mm, and the resistance between the electrodes was 4.8 Ω.

[0032] This planar heating element was heated by connecting it to a DC current. A DC circuit was constructed by connecting each electrode to a constant voltage DC generator (manufactured by RUZIZAO) using alligator clips. The surface temperature of the planar heating element was measured using the method shown in Figure 2. As shown in the figure, a height-adjusting block 12 was placed on a heat-resistant plate (ceramic plate) 11, the planar heating element 1 was fixed with tape, and a radiation thermometer (Custom IR302) 14 was fixed at a vertical height of 40 cm from the center of the planar heating element, and the change in surface temperature after the start of heating was measured. 15 in the figure is an abnormal temperature detection sensor. Figure 3 shows the relationship between the energizing time and the surface temperature when the input wattage was varied and maintained at a constant voltage (5.0V, 7.0V, 9.0V, 12V). The room temperature at the time of measurement was 23°C.

[0033] When using a surface heating element as a heater for window panes or glass doors, it is practically sufficient for the heater's surface temperature to rise from room temperature to about 50°C in a few minutes. The resulting surface heating element was found to be able to heat up quickly. Furthermore, an adhesive layer (unsaturated polyester resin) is placed between the two glass plates, ensuring bending strength. Incidentally, if the glass plates used are replaced with tempered glass, which has higher heat resistance, the heating temperature can be increased even further.

[0034] [Example 2] The same carbon fiber fabric (FCC type) as in Example 1 was cut to a size of 140 mm x 117 mm, and copper tape with conductive adhesive (manufactured by Teraoka Seisakusho) with a width of 5 mm was attached to the short sides opposite each other to form electrodes. The center distance between the copper tapes was 135 mm.

[0035] Next, 130 μm thick double-sided adhesive tape was applied to the surface of a 200 mm x 150 mm, 2 mm thick glass plate (soda glass) at positions corresponding to the outer circumference of the four sides of the carbon fiber fabric, so that the carbon fiber fabric was positioned in the center of the glass plate. After the double-sided adhesive tape prevented the carbon fiber fabric from shifting in the planar direction, another 200 mm x 150 mm, 2 mm thick glass plate (soda glass) was bonded to sandwich the carbon fiber fabric. The effective area of ​​the resulting planar heating element was 130 mm x 117 mm, the thickness was 4.1 mm, and the resistance between electrodes was 4.7 Ω.

[0036] The surface temperature change of the obtained planar heating element was measured in the same manner as in Example 1. Figure 4 shows the relationship between the energizing time and the surface temperature when maintained at a constant voltage (5.0V, 7.0V, 9.0V, 12V). The room temperature at the time of measurement was 23°C. The heating characteristic at that time was 30W, and the temperature rose rapidly from 23°C to 43°C in 2 minutes after energizing.

[0037] Figure 5 shows the obtained planar heating element placed on top of a display object bearing letters and figures. As shown in the figure, this planar heating element was transparent enough that the letters on the back could be clearly read. The planar heating element of this embodiment had sufficient transparency to be used as a rear passenger window glass for an automobile.

[0038] [Example 3] Using the same carbon fiber fabric (FCC type) as in Example 1 and a 3mm thick glass plate (soda glass), a planar heating element with an effective area of ​​65mm x 70mm, a thickness of 6.06mm, and an electrode resistance of 4Ω was fabricated in the same manner as in Example 2. The surface temperature change of the obtained planar heating element was measured in the same manner as in Example 1. Figure 6 shows the relationship between the energizing time and the surface temperature when maintained at a constant voltage (5.0V, 7.0V, 9.0V, 12V). The room temperature during measurement was 23°C. In this example as well, it was confirmed that the heating could be increased in a short time. However, when the heating was continued for more than 120 seconds, lightning-shaped cracks appeared in the upper and lower glass plates at 80°C, rendering the element unusable. This is a similar phenomenon to when hot water is poured into a glass made of thick glass, causing thermal stress on both sides of the glass and resulting in cracking. The carbon fiber fabric used in the planar heating element of the present invention has good rapid heating properties. Therefore, when using a glass plate of a thickness that would cause thermal distortion, it is necessary to reduce the power input to minimize the temperature difference between the inner and outer surfaces of the glass plate. For applications requiring temperatures exceeding 80°C, it is advisable to use thin glass or tempered glass with high heat resistance. Furthermore, for large-area applications such as residential sliding doors, a certain thickness is necessary for strength, in which case the power input will need to be reduced.

[0039] [Example 4] MH4 type carbon fiber fabric was used. This carbon fiber fabric has a warp pitch of 356 μm, a warp thread width of 165 μm, a weft pitch of 573 μm, a weft thread width of 165 μm, and an open area ratio of 38%. The single-fiber diameter of the carbon fibers in the interwoven yarn constituting the carbon fiber fabric is 7.5 μm. Copper tape, the same as in Example 1, was attached to the opposite side to form electrodes, and fixed to a 3 mm thick glass plate (soda glass) with 100 μm thick adhesive paper tape. The same unsaturated polyester resin used in Example 1 was poured on top of this, and the resin was scraped off with a sharp edge so that the thickness of the adhesive paper tape remained on the carbon fiber fabric. After that, it was left to cure so that a smooth free surface remained. In this way, the planar heating element of this embodiment was obtained. The effective area of ​​the obtained planar heating element was 84 mm × 76 mm, the thickness was 3.7 mm, and the resistance between electrodes was 2.9 Ω. The surface temperature change of the obtained planar heating element was measured in the same manner as in Example 1. Figure 7 shows the relationship between the energizing time and the surface temperature when maintained at a constant voltage (5.0V, 7.0V, 9.0V, 12V). When the planar heating element of this example is used for a window, the outer surface is made of glass and the inner surface is made of a resin layer with an ultraviolet blocking effect, thereby cutting ultraviolet rays and preventing condensation on the inner surface.

[0040] [Example 5] Using the same carbon fiber fabric (FCC type) as in Example 1, copper tape, also used in Example 1, was attached to the carbon fiber fabric opposite to form electrodes, and this was fixed to a 1 mm thick transparent acrylic plate with 100 μm thick adhesive paper tape. A water-soluble transparent urethane resin (manufactured by Sunday Paint Co., Ltd.) with 5% water added was slowly poured over it, forming a smooth resin film on the carbon fiber fabric in the same manner as in Example 4. It was then left to air dry and harden for 2 hours. This resin passed through the weave of the carbon fiber fabric and reached the acrylic plate, effectively bonding the carbon fiber fabric and the acrylic plate. In this way, the planar heating element of this example was obtained. The effective area of ​​the obtained planar heating element was 44 mm × 33 mm, the thickness was 1.25 mm, and the resistance between electrodes was 8.4 Ω. The surface temperature change of the obtained planar heating element was measured in the same manner as in Example 1. Figure 8 shows the relationship between the energizing time and the surface temperature when a constant voltage (5.0 V) was maintained. This would result in a lightweight, economical, and transparent surface heating element that could be used in traffic signals with snow-melting capabilities.

[0041] [Example 6] In this example, instead of the glass plate used in Example 1, a 50 μm thick transparent polyester film was used to sandwich a carbon fiber fabric (FCC type) and a copper tape. Specifically, an unsaturated polyester resin was poured onto the carbon fiber fabric, and the resin was scraped off with a sharp edge to the thickness of the adhesive paper tape that fixed the carbon fiber fabric. The polyester film was then placed on top to prevent air from entering, and the upper and lower polyester films were bonded together. A weight was then placed on top and it was left to solidify. In this way, the planar heating element of this example was obtained. The effective area of ​​the obtained planar heating element was 52 mm × 45 mm, the thickness was 0.4 mm, and the resistance between electrodes was 5.7 Ω. The surface temperature change of the obtained planar heating element was measured in the same manner as in Example 1. Figure 9 shows the relationship between the energizing time and the surface temperature when a constant voltage (5.0 V, 7.0 V) was maintained. According to this, a transparent heating element that could be freely bent and heated from room temperature to 70°C in 30 seconds with 10 W was obtained. This rapid heating capability is due to the fact that the ability to accelerate heat generation is increased by densely embedding thin carbon fiber threads, which have greater resistance than metal, in a lattice pattern between insulating materials, and that heat transfer is promoted by combining materials with low specific heat.

[0042] Table 1 summarizes the materials and performance of each example. [Table 1]

[0043] These planar heating elements can provide heating and condensation prevention for transparent windows in homes. However, if the glass temperature rises too quickly and the temperature difference between the inner and outer surfaces becomes large, cracks will occur in the glass. Therefore, it is preferable to thin the carbon fibers, widen the thread pitch to increase the resistance, reduce the temperature rise rate, and simultaneously improve transparency. With this method, no cracks occurred in a 3mm thick glass plate even at 80°C in actual measurements. Furthermore, by limiting the input power, it is possible to appropriately select the inherent resistance value of the carbon fiber fabric and design a balanced system to prevent the temperature from rising above a predetermined level. [Explanation of Symbols]

[0044] 1. Planar heating element 2. Heat-generating resistor (carbon fiber fabric) 3. Insulating material 4 electrodes 5. Binding material (insulating material) 6. Adhesive tape 11. Heat-resistant plate (ceramic plate) 12 Raising blocks 14 Radiation thermometer 15. Abnormal temperature detection sensor

Claims

1. It has a heat-resistant element containing carbon fiber fabric, The carbon fiber fabric is characterized in that the diameter of the single yarn constituting at least one of the interwoven yarns is 5 μm or more and 15 μm or less, and the width of at least one of the interwoven yarns is 180 μm or less. The porosity of the carbon fiber fabric is 35% or more and 90% or less. The carbon fiber fabric has electrodes with electrical connection terminals on opposite sides, A planar heating element characterized in that the carbon fiber fabric and the electrodes are enclosed in a light-transmitting insulating material with the electrical connection terminals extended.

2. The planar heating element according to claim 1, wherein the insulating material comprises at least one selected from thermoplastic resin, thermosetting resin, fluororesin, rubbery viscoelastic material, and glass.

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