Planar heating element

Abstract

To provide a technology that suppresses heat dissipation from the back surface and uniformly and efficiently radiates heat from the front surface by using a thin film heat generating layer patterned into a linear thin film as a planar heating element.SOLUTION: A planar heating element includes a thin-film heating layer 11 forming a pattern with lines 11a, a surface member 12 on the side of the heat radiation surface with the thin-film heating layer 11 interposed therebetween, and a back surface member 13 on the side opposite to the heat radiation surface side with the thin-film heating layer 11 interposed therebetween, and the following formula (1) is established between the thermal resistance R1 of the surface member 12 and the thermal resistance R2 of the back surface member 13. 0.006<R1 / R2<0.7 (1).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a sheet heating element that can be used in a heater device that warms air with radiant heat. [Background technology]

[0002] A planar heating element is used in heater devices and the like that utilize heat dissipation from a flat heating layer, and is a member roughly composed of a heating layer, a surface member that protects and covers the heating layer from the heat radiation surface side, and a back member that protects and covers the heating layer from the side opposite the heat radiation surface.

[0003] For such planar heating elements, a technology is described in Patent Document 1 (JP Patent Publication 2010-091185 A) that uses a material with high thermal conductivity for the surface member and a material with high heat insulation for the back member in order to effectively dissipate heat from the surface. However, when this technology is applied to a linear heating layer, the thermal conductivity of the surface member increases and heat is quickly transferred to the surface, making it easy for high-temperature and low-temperature areas to occur on the surface of the surface member, resulting in poor thermal uniformity.

[0004] Meanwhile, Patent Document 2 (WO2017 / 130541) describes a technology for increasing the thermal resistance of the surface member. This technology reduces the transfer of heat from the heat generating layer to the outside, making it possible to increase the temperature of the planar heating element. However, if the thermal resistance of the surface member is too high, the proportion of heat escaping from the back surface increases relatively, which may reduce the power efficiency of the heat radiated from the surface. In addition, a surface member with low thermal conductivity may suppress thermal conductivity in the surface direction, resulting in poor thermal uniformity. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2010-091185 A [Patent Document 2] WO2017 / 130541 publication Summary of the Invention [Problem to be solved by the invention]

[0006] Although various proposals have been made in the prior art, there are no clear guidelines for efficiently dissipating heat from the surface of a sheet heating element, making it difficult to design an effective sheet heating element. The objective of the present invention is to provide a technology that uses a thin-film heating layer in which the heating layer is patterned into a linear thin film, and that can suppress the dissipation of heat from the back surface of a sheet heating element to radiate heat uniformly and efficiently from the front surface. [Means for solving the problem]

[0007] One aspect of the present invention is a heat generating device having a thin-film heating layer that forms a line pattern, a front surface member that is a heat radiating surface side with the thin-film heating layer sandwiched therebetween, and a rear surface member that is an opposite side to the radiating surface side with the thin-film heating layer sandwiched therebetween, and the heat resistance R1 of the front surface member and the heat resistance R2 of the rear surface member are expressed by the following formula (1): 0.006 < R1 / R2 < 0.7...Equation (1) holds true.

[0008] According to one aspect of the present invention, the thin-film heating layer is configured to form a line pattern, so that current flows uniformly throughout the thin-film heating layer, enabling uniform heat dissipation from the entire thin-film heating layer. In addition, since the thin-film heating layer is sandwiched between a front member that is the heat radiating surface side and a back member that is the opposite side to the radiating surface side, the thin-film heating layer is covered and protected by the front member and back member, and by forming the front member and back member into a desired shape, the sheet heating element can also be formed into a desired shape.

[0009] According to one aspect of the present invention, the thermal resistance R1 of the front surface member and the thermal resistance R2 of the back surface member are expressed by the following formula (1): 0.006 < R1 / R2 < 0.7...Equation (1) holds true. By keeping the thermal resistance ratio between the front surface member and the back surface member within a predetermined range in this manner, efficient and uniform heat radiation from the surface of the planar heating element can be achieved.

[0010] According to one embodiment of the present invention, the heat generating portion occupies 50% or more, or 80% or more of the area of ​​the heat generating region formed by the heat generating portion formed by the lines and the non-heat generating portion sandwiched between the lines. By setting the area of ​​the thin-film heating layer in the heat generation region to 50% or more and keeping the thermal resistance ratio of the front member and the back member within a specified range, more efficient and uniform heat radiation from the surface of the planar heating element can be achieved. Alternatively, by setting the area of ​​the thin-film heating layer in the heat generation region to 80% or more and keeping the thermal resistance ratio of the front member and the back member within a specified range, even more efficient and uniform heat radiation from the surface of the planar heating element can be achieved.

[0011] According to one embodiment of the present invention, the overall evaluation index A, defined by the relationship Tu / Te between the temperature rise Tu on the surface of the surface member within a specified time and the temperature difference Te at various points on the surface of the surface member after the temperature rise, is 5 or more when the heat-generating portion occupies 50% or more of the area of ​​the heat-generating region, and is 20.3 or more when the heat-generating portion occupies 80% or more of the area of ​​the heat-generating region.

[0012] According to one aspect of the present invention, the overall evaluation index A, defined as the relationship Tu / Te between the temperature rise Tu on the surface of the surface member within a specified time and the temperature difference Te at various points on the surface of the surface member after the temperature rise, is 5 or more when the heat-generating parts occupy 50% or more of the area of ​​the heat-generating region, and is 20.3 or more when the heat-generating parts occupy 80% or more of the area of ​​the heat-generating region, thereby achieving efficient and uniform heat radiation from the surface of the surface heating element.

[0013] In one aspect of the present invention, the overall evaluation index B, which is defined as the relationship Tu·Rn / Te between the temperature rise Tu on the surface of the surface component within a specified time, the temperature difference Te at various points on the surface of the surface component after the temperature rise, and the proportion Rn of the non-heat-generating areas in the heat-generating area, is 1.7 or more.

[0014] According to one embodiment of the present invention, the overall evaluation index B, which is defined as the relationship Tu·Rn / Te between the temperature rise Tu on the surface of the surface member within a specified time, the temperature difference Te at various points on the surface of the surface member after the temperature rise, and the proportion Rn of the non-heat-generating areas in the heat-generating area, is set to 1.7 or more, thereby achieving efficient and uniform heat radiation from the surface of the planar heating element.

[0015] One aspect of the present invention is a thin-film heating layer that is a cured product of a conductive ink in which conductive particles are dispersed in a polymer matrix. According to one aspect of the present invention, since the thin-film heating layer is a cured product of a conductive ink in which conductive particles are dispersed in a polymer matrix, it is easy to form the thin-film heating layer into a desired shape, and the use of a flexible polymer matrix makes it possible to provide a thin-film heating layer that is less likely to break even if deformation occurs.

[0016] In one aspect of the present invention, the thin-film heating layer has a meandering line pattern. According to this aspect of the present invention, the thin-film heating layer has a meandering line pattern, which allows current to flow uniformly within the pattern and increases the proportion of heat-generating parts within the heat generation region, thereby achieving efficient and uniform heat radiation from the surface of the sheet heating element. Effect of the Invention

[0017] According to the present invention, efficient and uniform heat radiation from the surface of the planar heating element can be achieved. [Brief description of the drawings]

[0018] [Figure 1] FIG. 2 is a schematic plan view of the sheet heating element. [Diagram 2] 2 is a cross-sectional view of the sheet heating element shown in FIG. 1 along line II. [Diagram 3] FIG. 4 is an explanatory diagram illustrating a heat generation region. [Figure 4] FIG. 2 is an explanatory diagram showing one mode of use of the sheet heating element. [Diagram 5] FIG. 11 is a schematic plan view of another sheet heating element. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] The sheet heating element of the present invention will be described in detail based on the following embodiment. Fig. 1 shows a schematic plan view of a sheet heating element 10, and Fig. 2 shows its cross-sectional view. In Fig. 2, the thickness is shown thicker than the width in order to clearly show the layer structure, so the aspect ratio is different from the actual one. As shown in these figures, the sheet heating element 10 has a thin-film heating layer 11 that forms a pattern with lines 11a, a front member 12 that sandwiches the thin-film heating layer 11 and forms the heat radiating surface side, and a back member 13 that sandwiches the thin-film heating layer 11 and forms the opposite side to the radiating surface side.

[0020] The surface member 12 is a member that covers the thin-film heating layer 11 located on the heat radiation surface side, and when the sheet heating element 10 is used by being incorporated into the interior of a vehicle such as an automobile, it may be a part of the interior material of the automobile, or may be configured as a part provided further inside such an interior material. The surface member 12 can be made of hard resin, flexible film or soft rubber sheet, leather (synthetic leather), foam, fiber, etc., and examples of the material include polyamide, polyethylene terephthalate, polycarbonate, polyimide, synthetic rubber, thermoplastic elastomer, woven fabric, nonwoven fabric, etc. It is preferable to use a material that has flexibility or extensibility that allows the sheet heating element 10 to be attached by following the shape of the vehicle interior part to which it is attached. The surface member 12 made of such a material has a thermal resistance described below.

[0021] The back surface member 13 is a member that covers the thin-film heating layer 11, which is provided on the side opposite the heat radiation surface of the thin-film heating layer 11 described below. The material thereof can be the same as that of the front surface member 12, but it is preferable that the material have a thermal resistance as described below and be a foam or a flexible material.

[0022] The front surface member 12 and the rear surface member 13 each have a predetermined thermal resistance (°C / in 2 W), where R1 is the thermal resistance of the front surface member 12 and R2 is the thermal resistance of the back surface member 13, the relationship between R1 and R2 satisfies the following formula (1).

[0023] 0.006 < R1 / R2 < 0.7 Equation (1)

[0024] This is because if R1 / R2 is smaller than 0.006 or if R1 / R2 is larger than 0.7, efficient heat radiation from the surface of the sheet heating element 10 cannot be achieved.

[0025] The thin-film heating layer 11 is a heat generating source formed of a thin film of metal or conductive resin material, etc., in a linear pattern. More specifically, it is a heating layer in which the thickness is made thinner than the line width to form film-like lines 11a, which are then formed into a desired pattern. The thin-film heating layer 11 thus formed is preferable in that it is possible to make it difficult for air to enter the gaps between the lines 11a when integrated with the front surface member 12 or the back surface member 13, and it is easy to improve the thermal uniformity described below. On the other hand, if a heating layer whose thickness is not thin compared to the line width is provided, when integrated with the front surface member 12 or the back surface member 13, the thickness of the heating layer is large, so that there is a concern that air is likely to enter the step. If air is mixed in, the transfer of heat to the gap is hindered, the temperature difference between the line and the gap becomes large, and the thermal uniformity is deteriorated. An example of a line that is not thin compared to the line width and therefore prone to air being mixed in is a thin metal wire such as a nichrome wire, whose line width and line height are approximately the same length.

[0026] As materials for the thin-film heating layer 11, metals include metals or alloys such as silver, copper, nickel, aluminum, and iron, and conductive resin materials include a layer of a conductive ink in which conductive particles are dispersed in an insulating binder (cured conductive ink), and conductive polymers such as polythiophene conductive polymers (PEDOT / PSS). The polymer matrix constituting the insulating binder may be hard, but flexible crosslinked rubber or thermoplastic elastomer is preferable because it is easy to form the sheet heating element 10 even in shapes having curved surfaces.

[0027] Specific examples of crosslinked rubbers and thermoplastic elastomers include crosslinked rubbers such as silicone rubber, natural rubber, isoprene rubber, butadiene rubber, acrylonitrile butadiene rubber, 1,2-polybutadiene, styrene-butadiene rubber, chloroprene rubber, nitrile rubber, butyl rubber, ethylene-propylene rubber, chlorosulfonated polyethylene rubber, acrylic rubber, epichlorohydrin rubber, fluororubber, and urethane rubber, and thermoplastic elastomers such as styrene-based thermoplastic elastomers, olefin-based thermoplastic elastomers, ester-based thermoplastic elastomers, urethane-based thermoplastic elastomers, amide-based thermoplastic elastomers, vinyl chloride-based thermoplastic elastomers, and fluorine-based thermoplastic elastomers. Among these materials, when extensibility is required, it is preferable to form the thin-film heating layer 11 using silicone rubber. In addition, in order to increase adhesion with the front and back members, it is preferable to use a resin that has good affinity with them. For example, when a urethane foam is used as the back member, it is preferable to use a urethane-based resin as the insulating binder, and it is preferable to use an olefin-based insulating binder for olefin-based members.

[0028] The conductive particles may be conductive powders of carbon, metal, or the like. It is preferable to use metal powders with low resistance, and among metal powders, silver powders having an extremely low resistance value are more preferable.

[0029] The thin-film heating layer 11 having a pattern formed by lines 11a can be a thin-film heating layer 11 having lines 11a wired in a meandering shape, as shown in Fig. 1, for example. Here, forming a pattern by lines 11a means excluding shapes other than lines, such as polygons and circles, because the current flowing through such shapes may be more or less difficult. It is preferable to form a pattern in which the lines 11a, which have a low height relative to the line width, form straight lines and curves on a plane without overlapping each other. Note that the sheet heating element 10a shown in the figure shows an embodiment in which the line width is narrower than that of the sheet heating element 10 shown in Fig. 1, and the intervals between the lines are wider.

[0030] Furthermore, the linear pattern of the thin-film heating layer 11 is formed such that the heating area HA formed by the heating areas H formed by the lines 11a and the non-heating areas A sandwiched between the lines 11a is preferably formed such that the heating areas H occupy 50% or more, more preferably 80% or more of the area. To explain the heating area HA using Figure 3, the lines 11a forming the linear pattern excluding the terminal parts 11b are the heating areas H, and the combined area of ​​the heating areas and the non-heating areas A sandwiched between the heating areas (the area surrounded by the dashed lines in Figure 3) is the heating area HA.

[0031] The reason why the lines which are the heating parts H of the heating region HA should preferably occupy an area of ​​50% or more, and more preferably 80% or more, is that if they occupy less than 50%, it is thought that efficient and uniform heat radiation from the surface of the planar heating element will become difficult and variation will be more likely to occur, and why 80% or more is more preferable, is because a higher thermal efficiency can be obtained than if they occupy less than 80%.

[0032] The thin-film heating layer 11 is laminated with the front surface member 12 and the back surface member 13 by applying a conductive ink to the back surface of the front surface member 12, and then injecting a liquid resin to become the back surface member 13 onto the back surface of the front surface member 12 to which the conductive ink has been applied, and then solidifying the liquid resin, thereby producing the surface heating element 10.

[0033] The shape and thickness of the front surface member 12 and the back surface member 13 can be appropriately formed to a desired shape and thickness. Although it depends on the part and application of the planar heating element 10, it is preferable that the thickness of the front surface member 12 is 0.5 to 2 mm. If it is thinner than 0.5 mm, the heat may be directly transferred to the front surface, resulting in insufficient heat uniformity, and if it is thicker than 2 mm, the heat may not be efficiently transferred to the front surface of the front surface member 12. On the other hand, it is preferable that the thickness of the back surface member 13 is 1 to 10 mm. If it is thinner than 1 mm, the heat dissipation from the back surface side increases, resulting in a large heat loss. Also, if it is thicker than 10 mm, it may not meet the demand for compactness.

[0034] The thickness of the thin-film heating layer 11 is preferably 5 to 200 μm when it is a layer of cured conductive ink, and 0.1 to 50 μm when it is a metal or conductive polymer. If it is thinner than the lower limit, it may not be possible to generate heat, the temperature may not be uniform, and there may be a risk of disconnection. If it is thicker than the upper limit, it is difficult to form. The width of the line of the thin-film heating layer 11 is preferably 1 mm to 50 mm. If it is thinner than 1 mm, the length of the line 11a that occupies 80% or more of the area of ​​the heating region HA becomes too long, so the resistance value increases, sufficient heat cannot be generated, and there is a risk of disconnection. If it is thicker than 50 mm, there is a risk of an inconsistent current flow.

[0035] The sheet heating element 10 thus obtained is connected to a control device by connecting the terminals 11b of the thin-film heating layer 11 to wiring (not shown). When heat is dissipated from the thin-film heating layer 11, the heat is not easily transferred to the back surface member 13, but is easily transferred to the front surface member 12 not only in its thickness direction but also in its surface direction, realizing efficient and uniform heat dissipation from the surface of the front surface member 12.

[0036] The sheet heating element 10 has at least the above-mentioned configuration, but in order to improve the adhesion or adhesion of the thin-film heating layer 11 to the front member 12 or back member 13, or to improve the manufacturing method, an intermediate layer 14 may be provided between the thin-film heating layer 11 and the front member 12 or between the thin-film heating layer 11 and the back member 13. For example, the intermediate layer 14 can be provided to prevent the thin-film heating layer 11 from being scratched or coming into contact with moisture, corrosive gases, etc., and for this purpose, the intermediate layer 14 can be formed as a coating from a liquid material such as an acrylic, urethane, or polyester material.

[0037] Alternatively, in cases where the surfaces of the front member 12 and the back member 13 are rough and it is difficult to directly provide the thin-film heating layer 11, an intermediate layer 14 can be provided to smooth the surfaces so that the conductive ink can be easily applied to these surfaces. The intermediate layer 14 can also be an adhesive layer for the front member 12 and the back member 13. The thickness of the intermediate layer 14 can be 1 to 50 μm, which is smaller than the size of the front member 12 and the back member 13, so that its effect on heat transfer can be ignored.

[0038] As shown in FIG. 4, the sheet heating element 10 can be provided on the door side armrest portion 3 and the center console side armrest portion 4 on both sides of the driver's seat 2 of the automobile 1 to efficiently warm the passengers.

[0039] It will be readily apparent to those skilled in the art that many modifications can be made without substantially departing from the novel features and effects of the present invention. Accordingly, all such modifications are included within the scope of the present invention. EXAMPLES

[0040] Next, the present invention will be further described based on examples (comparative examples). Sheet heating elements having the configurations shown in the following tables were fabricated as samples 1 to 32. These samples were subjected to various tests described later.

[0041] <Preparation of Samples 1 to 32>: The front and back members 12 and 13 were made of the resin material sheets shown in each table, specifically, a polyethylene terephthalate resin film (PET) with a thickness of 1 mm, an acrylonitrile-butadiene-styrene copolymer resin film (ABS) with a thickness of 0.5 mm, and a polypropylene foam with closed pores with a thickness of 2 mm. The thermal resistance of each member is also shown in each table. The thin-film heating layer 11 was made of a silver ink with flaky silver filler dispersed in urethane resin for PET and ABS, and a silver ink with flaky silver filler dispersed in polypropylene resin for polypropylene foam. The ink was applied to the back member 13 in the shape shown in FIG. 1 or FIG. 5 so that the layer thickness was 12 μm, the line width was 15 mm for the shape in FIG. 1, and the line width was 8.5 mm for the shape in FIG. 5. The resistance value of pattern A was 4.1 Ω, and the resistance value of pattern B was 11.0 Ω. The front member 12 and the back member 13 were joined with double-sided tape. The thermal conductivity (1·K) of the above materials was 0.25 for PET, 0.16 for ABS, and 0.04 for foam.

[0042] <Heat test>: For each sample, the time after electrical conduction to the thin-film heating layer 11 and the state in which the surface member 12 warmed up were investigated. First, the surface temperature of the surface member 12 was measured at position P1, which was the center of one line in the thin-film heating layer 11, and recorded as the initial temperature. Next, a voltage of 12 V was applied to the terminal portion 11b of the thin-film heating layer 11 to allow electricity to flow. The temperature at position P1 was then measured 20 seconds after the application of the voltage, and the difference from the initial temperature was calculated and recorded as "20-second temperature rise (°C)." Similarly, the temperature was measured 80 seconds after the application of the voltage, and the difference from the initial temperature was calculated and recorded as "80-second temperature rise (°C)." In addition, the temperature was measured 80 seconds after the application of the voltage at multiple arbitrary positions P2 in the heat generating region HA, the difference from the initial temperature was calculated, and the value with the largest difference from the initial temperature was recorded as the 80-second temperature rise (°C) at P2. The difference between the 80-second temperature rise (°C) at P1 and the 80-second temperature rise (°C) at P2 was then calculated and recorded as the "80-second thermal uniformity (°C)." These results are shown in each table. A thermograph (manufactured by Nippon Avionics Co., Ltd., model number "InfReC R450PRO") was used to measure the temperature.

[0043] <Sensory test>: For each sample, 80 seconds after electrical conduction to the thin-film heating layer 11, the warmth of the surface of the surface member 12 was evaluated by placing the palm of the hand on it. If the entire surface felt sufficiently warm and evenly heated, it was rated as "A", if the entire surface felt evenly heated, it was rated as "B", if there was some unevenness in the temperature on the surface, it was rated as "C", and if there was obvious unevenness on the surface, it was rated as "D".

[0044] <Indicators for evaluating temperature rise and uniformity>: It is preferable that the heat from the thin-film heating layer 11 is efficiently transferred to the surface of the surface member 12, and this can be evaluated by how quickly the surface of the surface member 12 heats up, so the 80-second temperature rise Tu at P1 was used as one of the evaluation indices. It is also preferable that the heat from the thin-film heating layer 11 spreads all over the surface member 12, and this can be evaluated by how small the surface temperature difference is even if the surface position of the surface member 12 is different, so the 80-second temperature difference Te, which is the temperature difference between P1 and P2 after 80 seconds, was used as one of the evaluation indices. And, with these two indices, when the 80-second temperature rise value is large, the 80-second temperature uniformity value also tends to be large, and when the 80-second temperature rise value is small, the 80-second temperature uniformity value also tends to be small, and the balance between these two indices is important, so the 80-second temperature rise Tu / 80-second temperature uniformity Te, which is an integrated value of these two indices, was derived as one overall index (overall evaluation index A). In addition, because this index varies depending on the proportion of heat-generating (or non-heat-generating) areas in the heat-generating region, in order to suppress the influence of the proportion of heat-generating areas, a different overall index (overall evaluation index B) was obtained by multiplying Tu·Rn / Te by the proportion Rn of non-heat-generating areas in the heat-generating region, and the values ​​of overall evaluation index A and overall evaluation index B were calculated for each sample. The results are shown in each table.

[0045] <Thermal resistance ratio between the front and back materials; R1 / R2>: The thermal resistance of each of the front surface member 12 and the back surface member 13 of each sample was measured, and the thermal resistance ratio R1 / R2 was calculated by dividing the thermal resistance R1 of the front surface member 12 by the thermal resistance R2 of the back surface member 13 and listed in each table.

[0046] [Table 1]

[0047] [Table 2]

[0048] [Table 3]

[0049] [Table 4]

[0050] <Consideration>: (1) Regarding comprehensive evaluation indicators A and B Looking at the results of the sensory test and the values ​​of the overall evaluation index B, samples that received an excellent result of A or B in the sensory test had an overall evaluation index B of 1.7 or more, while samples that received an inferior result of C or D in the sensory test had an overall evaluation index B of less than 1.7, demonstrating that the overall evaluation index B can be used as an appropriate index for evaluating the performance of a sheet heating element. From this, it can be seen that if the temperature rise on the surface of the surface member within a specified time is Tu, the temperature difference after said temperature rise at various points on the surface of the surface member is Te, and the proportion of non-heat-generating areas in the heat-generating area is Rn, then an excellent sheet heating element can be obtained if the overall evaluation index B, defined as the relationship between Tu, Te, and Rn, Tu·Rn / Te, is 1.7 or more.

[0051] (2) Thermal resistance ratio R1 / R2 between the thermal resistance of the front surface material and the thermal resistance of the back surface material Referring to the results of the sensory test described above, in the samples that achieved excellent results, A or B, in the sensory test, the thermal resistance ratio R1 / R2 of the thin-film heating layer 11 was in the range greater than 0.006 and less than 0.7, while in the samples that achieved poor results, C or D, in the sensory test, the thermal resistance ratio R1 / R2 of the thin-film heating layer 11 was less than 0.006 or greater than 0.7, indicating that the performance of the sheet heating element can be evaluated by the thermal resistance ratio R1 / R2.

[0052] (3) Looking at the overall evaluation index A, which is expressed by 80-second temperature rise Tu / 80-second temperature uniformity Te, for samples with a thermal resistance ratio R1 / R2 in the range of more than 0.006 and less than 0.7, the index was 28.4 to 40.9 for samples with a thin-film heating layer area of ​​94%. The index was 20.3 for samples with a thin-film heating layer area of ​​80%. The index was 5.5 to 6.3 for samples with a thin-film heating layer area of ​​53%. In addition, the index was 1.2 for samples with a nichrome wire heating layer area of ​​2.2%. As a result, it was found that the value of the overall evaluation index A was large when the area was 50% or more. It was also found that the overall evaluation index A was significantly superior when the area of ​​the thin-film heating layer was 80% or more. [Explanation of symbols]

[0053] 10, 10a Planar heating element 11 Thin film heating layer 11a line 11b Terminal section 12 Surface material 13 Back material 14 Middle Class 1. Automobiles 2 Driver's seat 3 Door side armrest 4 Center console armrest HA Heat Generation Area H Fever area A Non-fever area

Claims

1. a thin-film heating layer patterned with lines; a surface member which sandwiches the thin-film heat generating layer and serves as a heat radiating surface; a back surface member on the opposite side to the radiation surface side with the thin-film heat generating layer interposed therebetween, The thermal resistance R1 of the front surface member and the thermal resistance R2 of the back surface member are expressed by the following formula (1): 0.006 < R1 / R2 < 0.7...Formula (1) A sheet heating element in which the following holds true:

2. 2. The sheet heating element according to claim 1, wherein the heated portions occupy 50% or more of an area of ​​a heat generating region formed by the heated portions formed by the wires and non-heat generating portions sandwiched between the wires.

3. Regarding the comprehensive evaluation index A, which is defined by a relationship Tu / Te between a temperature rise Tu on the surface of the surface member within a predetermined time and a temperature difference Te after the temperature rise at each point on the surface of the surface member, 5 or more when the heat generating portion occupies 50% or more of the heat generating region; 3. The sheet heating element according to claim 1, wherein the heat generating portion occupies 80% or more of the area of ​​the heat generating region, and the heat generating portion has a heat generating coefficient of 20.3 or more.

4. A planar heating element as described in any one of claims 1 to 3, wherein a comprehensive evaluation index B defined by the relationship Tu·Rn / Te, where Tu is the temperature rise on the surface of the surface member within a specified time, Te is the temperature difference after the temperature rise at various points on the surface of the surface member, and Rn is the proportion of the non-heat-generating areas in the heat-generating area, is 1.7 or more.

5. 5. The sheet heating element according to claim 1, wherein the thin-film heating layer is a cured product of a conductive ink in which conductive particles are dispersed in a polymer matrix.

6. The sheet heating element according to any one of claims 1 to 5, wherein the pattern is a meandering pattern.

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