JP2005150069A - Ptc sheet heating element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new sheet heating element provided with both a superior PTC characteristic and low initial electric resistance, having an excellent heat generation function without causing a local overheat, excellent flexibility and high shape stability, and thin in thickness. <P>SOLUTION: This PTC sheet heating element is composed by sequentially overlaying a soaking sheet on one surface or both surfaces of a planar heat generation sheet formed by impregnating or applying a PTC conductive composition comprising carbon black or graphite, paraffin and a thermoplastic elastomer into/to a fabric cloth, and an insulating film on its both surfaces, and satisfies following conditions: (1) thickness is 0.6-1.2 mm; (2) D<SB>25</SB>is 250-500 W/m<SP>2</SP>; (3) D<SB>25</SB>/D<SB>45</SB>is below 1.5; and (4) D<SB>45</SB>/D<SB>80</SB>is above 7. D<SB>25</SB>, D<SB>45</SB>and D<SB>80</SB>are power density at 25°C°, 45°C and 80°C, respectively. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

Detailed Description of the Invention

  The present invention relates to a PTC sheet heating element, and more particularly to a PTC sheet heating element suitable for floor heating.

Conventionally, as an electric heating element, resistance heating without self-temperature controllability (PTC characteristic: an abbreviation of a positive temperature coefficient of electric resistance, which increases electric resistance as the temperature rises) in a low temperature range of about 100 ° C. or lower. Body, for example, heating elements using nichrome wire are widely used. However, this fatal defect of the heating element has a risk that the temperature rises to a high level that is not preferable for practical use or safety, and a complicated overheat prevention mechanism is required. Moreover, since it is a linear heating element, in order to use it as a planar heating element, a special arrangement of nichrome wires and a high-performance soaking material are required.
It is also known that a conductive paint having PTC characteristics is formed on, for example, a fiber cloth and used as a planar heating element. Paraffin is known as an imparting agent for imparting PTC characteristics to a conductive paint. In general, paraffin has a low melting point and is usually 60 ° C. or lower. Such a conductive paint using paraffin has a defect that a planar heating element obtained therefrom is softened at a relatively low temperature.

  PTC conductive paint using paraffin used for the planar heating element includes carbon black or graphite as a conductive substance, paraffin as a PTC imparting agent, a resin component such as a thermoplastic resin or a thermosetting resin as a structural material, And those composed of a solvent are generally used. A typical method for obtaining a planar heating element from such a PTC conductive paint is to apply the paint to a fiber fabric or film, etc., and then, in the case of using a thermosetting resin, firing, drying for crosslinking, and It consists of a process of sequentially performing processes such as aging. The conventional planar heating element obtained in this way lacks flexibility and is inferior in bending resistance, and cracking occurs due to repeated bending, and the resistance is changed so that it cannot be ignored. In addition to lack of heat stability due to the low melting point of paraffin, the PTC characteristics are exhibited at a temperature that is too low, so that the heating function is inferior, or if the excellent PTC characteristics are not imparted, the initial electrical resistance is reduced. It is too high, that is, it is difficult to combine excellent PTC characteristics and low initial electrical resistance, and a sheet heating element with a large calorific value cannot be obtained in the end. There are very few that are suitable for a floor heating system, which is a typical use of a planar heating element, having defects such as Further, in a sheet heating element having a high PTC magnification, there is a problem that local overheating sometimes called a hot line or a hot spot occurs.

Problems to be solved by the invention

  Therefore, the object of the present invention is to combine excellent PTC characteristics and low initial electrical resistance, have a high heat generation function that does not cause local overheating, and has excellent flexibility and good shape stability. Another object of the present invention is to provide a novel planar heating element having a small thickness.

Means for solving the problem

  As a result of intensive studies by the inventors, the above object of the present invention has been industrially advantageously achieved by the present invention having the following constitution.

[1] A sheet heating sheet formed by impregnating or applying a PTC conductive composition composed of carbon black or graphite, paraffin, and thermoplastic elastomer to a fiber fabric, and a soaking sheet is insulated on one or both sides, and insulated on both sides. A PTC sheet heating element which is coated with a film and satisfies the following conditions (1) to (4);
▲ 5 ▼ thickness is in the range of 0.6mm~1.2mm ▲ 6 ▼ that _{D 25} is in the range of ^{250W / m 2 ~500W / m 2} ▲ 7 ▼ D 25 / D 45 is 1 .5 or less (8) D ₄₅ / D ₈₀ is 7 or more, where D ₂₅ , D ₄₅ , and D ₈₀ mean power densities at 25 ° C., 45 ° C., and 80 ° C., respectively.
[2] The PTC planar heating element according to the above [1], wherein D ₂₅ / D ₈₀ is 20 or more.
[3] The PTC planar heating element as described in [1] or [2] above, wherein the soaking sheet is a resin film / aluminum laminate.
(4) The PTC planar heating element according to any one of the above [1] to [3], wherein the insulating film is a polyethylene terephthalate film.
[5] The PTC planar heating element according to any one of the above [1] to [4], wherein the PTC conductive composition further contains a crystalline thermoplastic resin.
[6] The PTC planar heating element according to any one of [1] to [5], wherein the PTC conductive composition further contains a thermosetting resin.
[7] The PTC surface according to any one of [1] to [6] above, wherein the amount of carbon black or graphite in the PTC conductive composition is in the range of 14 wt% to 22 wt%. Heating element.
[8] The PTC planar heating element according to any one of [1] to [7], wherein the paraffin has a melting point in the range of 70 ° C to 85 ° C.
[9] The PTC planar heating element according to any one of [1] to [8], which is for floor heating.

  The greatest feature of the present invention is that it has excellent PTC characteristics and high electrode density at 25 ° C. by adopting a specific PTC conductive composition, specifying power density at a plurality of temperatures, and specifying thickness. Combined with this, a new surface shape with a thin thickness that does not cause local overheating called hotline or hot spot, has an excellent heat generation function, has excellent flexibility and good shape stability. The heating element is provided.

  In the present invention, the PTC conductive composition is composed of a resin component containing graphite or carbon black, paraffin and a thermoplastic elastomer. As a typical method for impregnating or applying such a PTC conductive composition to a fiber fabric, a PTC conductive paint comprising a uniform mixture of this PTC conductive composition and an appropriate amount of solvent is prepared, and this paint is applied to the fiber. The method of apply | coating to a fabric is taken. Graphite or carbon black is a conductivity imparting material, paraffin is a PTC imparting material, and a thermoplastic elastomer is a resin component that functions as a so-called structural material, and these are solid components. In the PTC conductive paint, the ratio of the solid component to the solvent is referred to as a solid solution ratio.

  In the present invention, carbon black or graphite is preferably in the range of 14 to 22% by weight based on the total solid content. When this value is less than 14% by weight, the initial electric resistance becomes too high, and when it exceeds 22% by weight, it becomes difficult to obtain a desired PTC magnification. Any kind of carbon black or graphite can be used. This conductive material is usually used in the form of a fine powder.

In the present invention, the paraffin preferably has a melting point in the range of 70 ° C to 85 ° C. If the melting point is less than 70 ° C, the heat resistance tends to be inferior and softening tends to occur at a low temperature. If the melting point exceeds 85 ° C, the temperature at which the PTC characteristics are sufficiently exhibited becomes too high, and the temperature is separately controlled. Ingenuity is required, which is not preferable as a planar heating element for floor heating. A more preferable range of the melting point of paraffin is in the range of 75 ° C to 85 ° C. There are coal-based and petroleum-based paraffins from the origin, but any of them can be used in the present invention.
The weight ratio of paraffin to carbon black or graphite is preferably in the range of 1.5 to 3.5, and if it is less than 1.5, it becomes difficult to impart desired PTC characteristics, and 3.5 Exceeding this results in a drastic decrease in the concentration of carbon black, and the initial electrical resistance becomes too high.
In the present invention, it is preferable that the paraffin is in the range of 40% by weight to 80% by weight with respect to the total amount of the resin component containing the thermoplastic elastomer and the paraffin. When this value is less than 40% by weight, it becomes difficult to impart desired PTC characteristics, and when it exceeds 80% by weight, the resin component as a structural material becomes too small, and the resulting planar heating element has a mechanical property. The physical properties tend to be impaired.
A more preferred range is 50% by weight to 70% by weight. The paraffin used in the present invention is preferably one having a low isoparaffin content in order to obtain remarkable PTC characteristics. Paraffin is preferably in the form of fine powder.

  The thermoplastic elastomer that can be used in the present invention is not particularly limited, and examples thereof include styrene-butadiene-styrene block copolymers, styrene-isoprene-styrene block copolymers, styrene-ethylene / butylene-styrene copolymers, and hydrogenation. Type styrene / butadiene random copolymer, dynamic vulcanization type polyolefin thermoplastic elastomer, polyester thermoplastic elastomer, polyamide thermoplastic elastomer, ethylene-vinyl acetate thermoplastic elastomer, polyvinyl chloride thermoplastic elastomer , Fluoro rubber thermoplastic elastomer, trans-polyisoprene thermoplastic elastomer, chlorinated polyethylene thermoplastic elastomer, and the like.

  In the present invention, a crystalline thermoplastic resin can be used in combination as the resin component. Such a combination is preferable for imparting appropriate flexibility to the planar heating element. In this case, the amount of the crystalline thermoplastic resin used is preferably 35% by weight or less with respect to the thermoplastic elastomer. If it exceeds 35% by weight, the planar heating element becomes too rigid, which is not preferable.

  The crystalline thermoplastic resin that can be used in the present invention is not particularly limited. For example, polyethylene, polypropylene, polyamide, polycarbonate, polyester, polyvinyl chloride, polyvinylidene chloride, polystyrene, polyurethane, polyimide, modified polyphenylene ether, polysulfone, polysulfone Examples include arylate, polyethersulfone, polyetheretherketone, polyetherimide, polyphenylene sulfide, and polyparaxylene.

  In the present invention, the thermoplastic elastomer and the crystalline thermoplastic resin are preferably used in combination of those having the same monomer unit from the viewpoint of good compatibility between them, that is, as the thermoplastic elastomer, styrene-butadiene- When using styrenic thermoplastic elastomers such as styrene block copolymers, styrene-isoprene-styrene block copolymers, styrene-ethylene / butylene-styrene copolymers, hydrogenated styrene / butadiene random copolymers, etc. Preferably, polystyrene is used as the crystalline thermoplastic resin.

  In the present invention, a thermosetting resin can be further used as the resin component. Examples of such thermosetting resins include phenolic resins, epoxy resins, alkyd resins, polyurethane resins, and alkyd / melamine resins that are commonly used for coatings. Of these, alkyd resins and alkyd / melamine resins are preferably used.

  In the present invention, it is necessary to coat a soaking sheet on one or both sides of the sheet heating sheet. As the soaking sheet, a resin film / aluminum laminate is preferably used. As this resin film, a polyester film and a polyolefin film are used, and a polyester film is preferably used. Usually, the heat generating sheet is coated with the pressure-sensitive adhesive or adhesive on the resin film surface of the soaking sheet. After coating the soaking sheet, it is necessary to coat both sides with an insulating film. Examples of the insulating film include a polyester film, a polyamide film, and a polypropylene film. Of these, a polyethylene terephthalate film which is a polyester film is preferably used.

The planar heating element according to the present invention needs to have a thickness in the range of 0.6 mm to 1.2 mm. If it is less than 0.6 mm, it becomes difficult to obtain a desired power density, and if it exceeds 1.2 mm, the application range as a planar heating element is narrowed, which is not preferable. One of the features of the planar heating element of the present invention is that it has high performance despite being extremely thin.
In the present invention, D ₂₅ , D ₄₅ , and D ₈₀ mean power densities at 25 ° C., 45 ° C., and 80 ° C., respectively.
In the present invention, it is necessary to satisfy the following conditions regarding the power density.
Condition _{1: D 25} is in the range of ^{250W / m 2 ~500W / m 2} .
Condition 2: D ₂₅ / D ₄₅ is 1.5 or less.
Condition 3: D ₄₅ / D ₈₀ is 7 or more.
If D ₂₅ is less than 250 W / m ² , the initial heat generation amount is too small, and the speed of heating the object is undesirably slow. If D ₂₅ exceeds 500 W / m ² , the initial heat generation amount is too large. It is difficult to reduce the calorific value at a specific temperature, for example, 80 ° C. in a normal heating system to a desired value, which is not preferable. Especially preferred _{D 25} is in the range of ^{300W / m 2 ~500W / m 2} . On the other hand, if D ₂₅ / D ₄₅ exceeds 1.5, the heat generation capacity of the sheet heating element is undesirably lowered with the passage of time of use. It is more preferable that this value is 1.4 or less. In the present invention, D ₄₅ / D ₈₀ needs to be 7 or more, and if it is less than 7, when the planar heating element is used for heating such as floor heating, the calorific value at high temperature increases. This is not preferable because it is not only uneconomical but also requires a device for controlling the temperature separately. It is more preferable that this value is 13 or more.
In the present invention, it is preferable that the PTC magnification is sufficiently high such that D ₂₅ / D ₈₀ is 20 or more.

  In the present invention, a method for obtaining a PTC planar heating element satisfying the above conditions (1) to (4) is as follows. Condition (1) that “the thickness is within the range of 0.6 mm to 1.2 mm” is the adjustment of the thickness of the fiber fabric and the adjustment of the amount of impregnation or application of the PTC conductive composition. This can be achieved by adjusting the thickness of the heat sheet and the insulating film.

With meeting the conditions ▲ 1 ▼, "it _{D 25} is in the range of 250W ^{/ m 2} ~500W ^/ m 2" condition ▲ 2 ▼, condition ▲ 3 ▼ _"D 25 _{/ D 45} of 1.5 or less In order to satisfy all the requirements “4” and the condition (4) “D ₄₅ / D ₈₀ is 7 or more”, first of all, PTC conductive material composed of carbon black, graphite, paraffin or thermoplastic elastomer. Suitable combination such as specification of the conductive composition, specification of the fiber fabric, and specification of the impregnation amount or coating amount of the PTC conductive composition on the fiber fabric is necessary. Regarding the specification of the PTC conductive composition, 1) The melting point of paraffin is in the range of 70 ° C. to 85 ° C., 2) the weight ratio of paraffin to carbon black or graphite is in the range of 1.5 to 3.5, and 3) the thermoplasticity of paraffin. Within the range of 40% to 80% by weight with respect to the total amount of the resin component and the paraffin including the elastomer, and (4) within the range of 14% to 22% by weight of the carbon black based on the total solid content. The fiber fabric is preferably a coarse woven fabric made of cotton, and the amount of impregnation or application of the PTC conductive composition is determined by the characteristics relating to the electrical resistance of the PTC conductive composition. In the case of a PTC conductive composition having a low resistance, it is necessary to reduce the impregnation amount or application amount, and in the opposite case, it is necessary to increase the impregnation amount or application amount.

  In the present invention, in order to impregnate or apply the PTC conductive composition to the fiber fabric, a typical example is a method using a PTC conductive coating. The production method of the PTC conductive paint is not particularly limited, but a typical production method is as follows. That is, it is manufactured by the following sequence of steps. (1) An aromatic solvent is put into a heated stirring vessel and heated to a temperature of 40 to 60 ° C. (2) A resin component consisting of a crystalline thermoplastic resin and a thermoplastic elastomer is added, (3) paraffin is added Add and continue stirring until all solids are dissolved or fully dispersed (4) Add conductive black powder of carbon black or graphite, stir until a smooth paste is formed, and (5 ) The paste is kneaded until a substantially uniform dispersion of the conductive fine powder is obtained.

  A typical method for obtaining a planar heating element from this PTC conductive coating is a method of applying and baking the coating to a fiber sheet. The method for applying and firing to the fiber sheet will be described in detail. As the fiber cloth as the fiber sheet, it is preferable to use a fiber cloth containing electrode wires in advance, and as the fiber cloth, cotton, polyester fiber, polyamide-based fiber cloth is preferable. A fiber yarn composed of fiber, acrylic fiber, vinylon fiber, or the like, or a spun yarn containing at least one of them, or a mixed yarn is arranged on the warp and / or the weft, and one of the warp and / or the weft Examples thereof include a textile fabric in which copper wires or good conductive filaments in place of them are arranged at predetermined intervals. As a heating method for firing, for example, far-infrared irradiation, microwave irradiation, dielectric heating and the like can be used. However, the heating method is not limited to these, as long as appropriate temperature management is possible, A method in which the difference in the divergence rate of the solvent of the conductive paint between the surface and the inside of the coating film is not preferable is preferable.

  FIG. 1 shows a typical structure of the planar heating element according to the present invention. In FIG. 1, 1 is a heat generating sheet, 2 is an electrode, 3 is a power line, 4 and 5 are soaking sheets, and 6 and 7 are insulating films. Electrodes are provided at both ends and the center of the 250 mm wide heat generating sheet. Two power lines are connected to the electrodes. Both sides (the back side is not shown) of the heat generating sheet are covered with a soaking sheet and further covered with an insulating film. The length of the heat generating sheet is 600 mm, 1750 mm, and 2650 mm in typical specifications. For example, 10 pieces of 1750 mm length for 6 liters, 10 pieces of 2650 mm for 8 pieces, 15 pieces of 2650 mm pieces for 12 pieces, 3 pieces of 600 mm pieces for kitchen / toilet, Each is connected.

  The PTC planar heating element according to the present invention is used in various applications such as heating floor panels, greenhouse heating equipment, defrosting / water freeze prevention heaters, cookers, snow melting equipment, toilet seat devices, outdoor seats, and plants. It is suitably used for a dryer or the like.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited to this Example.

[Example 1]
3 kg of acetylene black (manufactured by Denki Kagaku): 4 kg of ethylene / propylene / styrene copolymer (manufactured by Shell: Kraton G1701), 1 kg of polystyrene, 7 kg of paraffin having a melting point of 83 ° C., and MEK / xylene = 20/80 mixed solvent Add to 15 kg of solution, stir well, knead with 3 rolls to make uniform paste, then dilute and stir with 1.5 times the amount of xylene to adjust the coating solution containing heating material did.

On the other hand, a copper foil having a width of about 0.3 mm on the surface of a 275 dtex / f polyester filament yarn as a highly conductive filament in a polyester / cotton blend yarn (20/2 meter count) warped at an interval of about 1 mm. Align the five covering yarns wrapped with lacquer, place three electrodes at the center and both ends, and use polyester / cotton blended yarn (20/2 meter count) for wefts and drive them at an interval of about 1 mm. A coarse woven fabric of about 250 mm was formed, and the obtained woven fabric was immersed in the coating solution, squeezed lightly with a roll, and then dried by heating. Thus, a PTC conductive sheet having a length of 600 mm was obtained. Both sides of this heat generating sheet were covered with a sheet of 25 micron polyethylene terephthalate film laminated with 40 micron aluminum foil so that the polyethylene terephthalate film was in contact with the surface of the heat generating sheet, and then both sides were coated with a polyethylene film (50 micron) insulating film. Was coated. The planar heating element was prepared so that the power density at 25 ° C. of the planar heating element generated by adjusting the diaphragm with a roll and preliminary experiments was about 400 W / m ² .
The characteristics of the obtained planar heating element were as follows.
(1) Thickness: 0.7mm
(2) Power density at 25 ° C .: 410 W / m ²
(3) Power density at 45 ° C .: 300 W / m ²
(4) Power density at 80 ° C .: 17 W / m ²
_{Thus, D} 25 _/ D ₄₅ is _{1.37, D} 45 _/ D ₈₀ was 17.6.
This planar heating element was extremely thin and flexible, had excellent heat generation performance, and had extremely high PTC magnification and excellent safety. Further, this planar heating element did not show any local overheating called a hot line or hot spot.

[Example 2]
3.2 kg of acetylene black (manufactured by Denki Kagaku): 3.8 kg of ethylene / propylene / styrene copolymer (manufactured by Shell: Kraton G1701), 1.2 kg of polystyrene, 6.8 kg of paraffin having a melting point of 83 ° C., and MEK / Xylene = 20/80 mixed solution consisting of 15 kg, stirred well, kneaded with 3 rolls to make a uniform paste, then diluted and stirred with 1.5 times the amount of xylene The coating solution containing the heating material was adjusted.

The same fabric as in Example 1 was dipped in the coating solution, squeezed lightly with a roll, and then dried by heating. Thus, a planar heating element having a PTC conductivity length of 600 mm was obtained. Both sides of this heat generating sheet were covered with a sheet of 25 micron polyethylene terephthalate film laminated with 40 micron aluminum foil so that the polyethylene terephthalate film was in contact with the surface of the heat generating sheet, and then both sides were coated with a polyethylene film (50 micron) insulating film. Was coated. The planar heating element was prepared so that the power density at 25 ° C. of the planar heating element generated by adjusting the aperture with a roll and preliminary experiments was about 450 W / m ² .
The characteristics of the obtained planar heating element were as follows.
(1) Thickness: 0.69mm
(2) Power density at 25 ° C .: 460 W / m ²
(3) Power density at 45 ° C .: 340 W / m ²
(4) Power density at 80 ° C .: 22 W / m ²
_{Thus, D} 25 _/ D ₄₅ is _{1.35, D} 45 _/ D ₈₀ was 15.5.
This planar heating element was extremely thin and flexible, had excellent heat generation performance, and had extremely high PTC magnification and excellent safety. Further, this planar heating element did not show any local overheating called a hot line or hot spot.

Example 3
2.7 kg of acetylene black (manufactured by Denki Black: Denka Black), 3.8 kg of ethylene / propylene / styrene copolymer (manufactured by Shell: Kraton G1701), 1.2 kg of polystyrene, 7.3 kg of paraffin having a melting point of 83 ° C., and MEK / Xylene = 20/80 mixed solution consisting of 15 kg, stirred well, kneaded with 3 rolls to make a uniform paste, then diluted and stirred with 1.5 times the amount of xylene The coating solution containing the heating material was adjusted.

The same fabric as in Example 1 was dipped in the coating solution, squeezed lightly with a roll, and then dried by heating. Thus, a planar heating element having a PTC conductivity length of 600 mm was obtained. Both sides of this heat generating sheet were covered with a sheet of 25 micron polyethylene terephthalate film laminated with 40 micron aluminum foil so that the polyethylene terephthalate film was in contact with the surface of the heat generating sheet, and then both sides were coated with a polyethylene film (50 micron) insulating film. Was coated. The planar heating element was prepared so that the power density at 25 ° C. of the planar heating element generated by adjusting the diaphragm with a roll and preliminary experiments was about 370 W / m ² .
The characteristics of the obtained planar heating element were as follows.
(1) Thickness: 0.71mm
(2) Power density at 25 ° C .: 360 W / m ²
(3) Power density at 45 ° C .: 261 W / m ²
(4) Power density at 80 ° C .: 13 W / m ²
_{Thus, D} 25 _/ D ₄₅ is _{1.38, D} 45 _/ D ₈₀ was 20.1.
This planar heating element was extremely thin and flexible, had excellent heat generation performance, and had extremely high PTC magnification and excellent safety. Further, this planar heating element did not show any local overheating called a hot line or hot spot.

The invention's effect

  According to the present invention, it has excellent PTC characteristics and high power density at 25 ° C. by adopting a specific PTC conductive composition, specifying power density at a plurality of temperatures, and specifying thickness. A novel planar heating element that does not cause local overheating, called a hot line or hot spot, has an excellent heat generation function, has excellent flexibility and good shape stability, and is thin. Was provided.

The structure of the PTC planar heating element which concerns on this invention is shown.

Explanation of symbols

1: Heat generating sheet 2: Electrode 3: Power supply lines 4 and 5: Heat equalizing sheets 6 and 7: Insulating film

Claims (9)

A sheet heating sheet made by impregnating or applying a PTC conductive composition made of carbon black or graphite, paraffin, and thermoplastic elastomer to a fiber fabric is coated with a soaking sheet on one or both sides and an insulating film on both sides. And a PTC planar heating element that satisfies the following conditions (1) to (4):
▲ 1 ▼ thickness is in the range of 0.6mm~1.2mm ▲ 2 ▼ that _{D 25} is in the range of ^{250W / m 2 ~500W / m 2} ▲ 3 ▼ D 25 / D 45 is 1 It is .5 or less (4) D ₄₅ / D ₈₀ is 7 or more. However, D ₂₅ , D ₄₅ , and D ₈₀ mean power densities at 25 ° C., 45 ° C., and 80 ° C., respectively. PTC planar heating body according to claim 1, wherein D ₂₅ / _{D 80} is equal to or 20 or more. The PTC sheet heating element according to claim 1 or 2, wherein the soaking sheet is a laminate of resin film / aluminum. The PTC planar heating element according to any one of claims 1 to 3, wherein the insulating film is a polyethylene terephthalate film. The PTC sheet heating element according to any one of claims 1 to 4, wherein the PTC conductive composition further contains a crystalline thermoplastic resin. The PTC sheet heating element according to any one of claims 1 to 5, wherein the PTC conductive composition further contains a thermosetting resin. The PTC planar heating element according to any one of claims 1 to 6, wherein the amount of carbon black or graphite in the PTC conductive composition is in the range of 14 wt% to 22 wt%. The PTC planar heating element according to any one of claims 1 to 7, wherein the melting point of paraffin is in the range of 70C to 85C. It is an object for floor heating, The PTC planar heating element in any one of Claims 1-8.

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