JP2016044257A - Conductive coating and planar heating element using conductive coating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a conductive coating having STS property with almost no change between an initial current value and an aging current value and extremely low electrification effect by residual solvent, and a planar heating element using the same.SOLUTION: There is provided a conductive coating having STS property by dispersion blending a conductive material, a binder resin and a crystal low molecular organic compound, where the STS property exhibiting solvent is non-aqueous solvent with relative dielectric constant of 6 or less and an SP value of the STS property exhibiting solvent is 17 to 22 (MPa). A planar heating layer which the conductive coating having the STS property is impregnated or laminated into or on a holding material with an electrode is coated with an insulation sheet substrate.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a conductive paint having an STS (Self Temperature Saturation) characteristic that enters a thermal equilibrium (temperature saturation) state when a temperature rise reaches a certain value, and a planar heating element having an STS characteristic.

  Unlike a linear heating element such as a nichrome wire heater, the planar heating element is a heating element that spreads two-dimensionally, so that a large area can be secured. For this reason, the planar heating element is widely used in, for example, heat heating appliances such as mats, floor heating heaters, snow melting heaters, drying appliances, agricultural appliances, and the like.

  One type of such a planar heating element has a PTC (Positive Temperature Coefficient) characteristic (self-temperature controllability: a property in which a resistance value increases as the temperature rises). A planar heating element exhibiting PTC characteristics (hereinafter referred to as a “PTC planar heating element”) has a self-temperature control function because the current value decreases and the resistance value increases rapidly when the load voltage is constant. It becomes possible. As a result, the PTC planar heating element automatically controls overheating due to sunlight and stagnation heat, so that it does not pose a risk of burns and the like to the human body, and can also realize low power consumption. It is widely used.

  The PTC planar heating element is impregnated or coated with a conductive coating having PTC characteristics (hereinafter referred to as “PTC conductive coating”) on a base fabric such as a nonwoven fabric, or is coated or printed on a substrate such as a polymer film. Then, it is manufactured through steps such as baking, drying, and aging. PTC conductive paints are usually paraffin as a PTC imparting agent, carbon black or graphite as a conductivity imparting agent, a resin component such as a thermoplastic resin or a thermosetting resin as a structural material, and an organic solvent component, etc. Containing.

  In Patent Document 1, a part of the longitudinal fiber yarn or the transverse fiber yarn constituting the woven fabric is used as a conductive wire, and a conductive material is applied by applying a carbon-based conductive paint to the woven fabric thus woven. A planar heating element is disclosed in which the upper and lower surfaces of these carbon conductive materials are covered with an electrically insulating coating material, and electrode terminals are attached to the ends of the electrode strips. However, the ratio of the carbon-based conductive coating to the high-molecular thermoplastic resin, which is a carbon-based conductive binder resin, is 10 to 30% by weight, and it can be said that the sheet-like heating element is sufficiently conductive. Absent. Further, STS characteristics are not disclosed.

  In Patent Documents 2 and 3, as a planar heating element having a PTC characteristic in which the resistance value increases as the temperature rises, the room temperature resistance value during non-operation is sufficiently low, and the rate of change between the room temperature resistance value and the resistance value during operation is disclosed. Is a self-control heating element that has a sufficiently large resistance and a small change in resistance value due to repeated operation, and uses a crystalline low-molecular organic compound such as wax (hereinafter referred to as “crystalline low-molecular organic compound”), and a thermoplastic as a binder. A self-control type heating element is disclosed in which a conductive material having a polymer and a thermoplastic polymer (hereinafter referred to as “binder resin”) as a matrix is blended. When a crystalline low molecular weight organic compound is used as an operating substance, since the crystallinity is generally higher than that of a polymer, there is an advantage that the rise when the resistance increases due to temperature rise becomes sharp. In addition, since the polymer tends to take a supercooled state, it usually exhibits hysteresis such that the temperature at which the resistance value decreases at the time of temperature decrease is lower than the temperature at which the resistance value increases at the time of temperature increase. This hysteresis can be suppressed by using a compound. Furthermore, if crystalline low molecular organic compounds having different melting points are used, the temperature at which the resistance increases (operating temperature) can be easily controlled.

  However, a planar heating layer in which a PTC conductive paint in which a crystalline low molecular organic compound is dispersed and blended in a binder resin blended with a conductive material is impregnated or laminated on a holding material provided with an electrode is covered with an insulating sheet substrate. In the heating element (PTC heater), since the conductive material is not sufficiently covered with the crystalline low molecular organic compound, the current value at the start of energization (hereinafter referred to as “initial value”) is caused by contact between the conductive materials that are not sufficiently covered at low temperatures. "Current value") increases. On the other hand, the contact of the conductive material is released by the expansion of the binder resin at a high temperature, and the resistance value increases with time (see FIG. 3). For this reason, it is necessary to increase the electric capacity of the breaker in consideration of the initial current value. Further, in order to connect the PTC heater to the temperature control unit, it is necessary to make it less than the rated current amount of the temperature control unit. To avoid this, a planar heating element (eg, mat, floor heating heater, snow melting heater, etc.) However, there is a problem that the laying area of the PTC heater must be reduced. In addition, since a current value (hereinafter referred to as “time-dependent current value”) due to energization gradually decreases, there is also a problem that the heat generation temperature of the planar heating element cannot be increased beyond a certain value (see the upper part of FIG. 5). Furthermore, after impregnating or applying a PTC conductive paint to a non-woven fabric or other base fabric and laminating the planar heating layer on which a coating film is formed by drying with an insulating sheet substrate, the temperature rises due to the energizing action of the residual solvent. There is also a problem that the increase of the resistance value due to is not sufficient and the PTC characteristic cannot be exhibited.

JP-A-11-040329 JP 2000-200704 A JP-A-9-027383

  The present invention provides a sheet heating element (eg, a mat, a floor heating heater, a snow melting heater, etc.) having the above problems, specifically, a high initial current value, a large change in current value over time, and a rated current amount. It is necessary to reduce the laying area as a heating / heating device, drying device, agricultural device, etc., and the resistance value is suppressed by the energizing action of the residual solvent after the heating layer is laminated with the insulating sheet substrate. In order to solve the problem, when a sheet heating layer is used in a sheet heating element laminated with an insulating sheet substrate, there is almost no change in the initial current value and the current value over time, that is, a low residual solvent, that is, Provided is a conductive paint having STS characteristics in which an STS characteristic expression solvent (hereinafter referred to as "STS characteristic expression solvent") is dispersed and blended, and a sheet heating element having a rated current amount (eg, mat, heater for floor heating) Thermal heating appliances, such as snow melting heater is to provide a drying device, conductive coatings with optimum STS characteristics for applications agricultural instrument and the like).

The problems described above can be solved by the following aspects. In particular,
(Aspect 1) A conductive coating material having STS characteristics in which a conductive material, a binder resin, a crystalline low molecular weight organic compound, and an STS characteristic expression solvent are dispersed and blended, wherein the STS characteristic expression solvent is a dielectric. It is a conductive paint having STS characteristics, which is a nonaqueous solvent having a rate of 6 or less. When a planar heating element in which a sheet heating layer in which a conductive coating material having STS characteristics is impregnated or applied to a holding material provided with an electrode is coated with an insulating sheet substrate by using a solvent having a relative dielectric constant of 6 or less is used. In addition, even if the solvent that exhibits the STS characteristic remains in the planar heating element, it is low polarizability, so it does not contribute to current conduction, and the current amount is less likely to change over time. .

(Aspect 2) The conductive paint having the STS characteristic according to Aspect 1, wherein the SP value of the STS characteristic expression solvent is 17 to 22 (MPa) ^1/2 . By setting the SP value within a range of 17 to 22 (MPa) ^1/2 , the formation of a film of a crystalline low molecular organic compound on the surface of the conductive material is promoted, and the crystallinity is maintained even when the temperature is increased. The low-molecular organic compound does not dissolve in the binder resin, but only swells in a state where it is coated on the surface of the conductive material, and the bonding of the conductive material is maintained, so that the amount of current at the time of temperature rise does not decrease. This is because there is an effect.

  (Aspect 3) The conductive paint having STS characteristics according to any one of Aspects 1 and 2, wherein the STS characteristic expression solvent is a lower chain carbonate. This is because the lower chain carbonic acid ester has a relative dielectric constant of 3 or less, so that even when it becomes a residual solvent, it has a great effect of hardly causing a change in the amount of current over time.

  (Aspect 4) The STST characteristic according to any one of Aspects 1 to 3, wherein a weight ratio of the STS characteristic expression solvent to the crystalline low molecular weight organic compound is 3.8 to 5.8. It is a conductive paint having. This is because, by setting the weight ratio of the STS characteristic expression solvent to the crystalline low molecular organic compound in the range of 3.8 to 5.8, formation of a film on the surface of the conductive material is promoted.

  (Aspect 5) The aspect 1 in which the conductive material is carbon-based conductive particles, and the weight ratio of the carbon-based conductive particles to the binder resin is 0.3 to 0.9. A conductive paint having STS characteristics described in any one of 1 to 4. By setting the weight ratio of the carbon-based conductive particles to the binder resin in the range of 0.3 to 0.9, there is an effect that the conductivity, that is, the resistance value is within a predetermined range.

  (Aspect 6) The conductive paint having STS characteristics according to any one of Aspects 1 to 5, wherein the crystalline low-molecular-weight organic compound is a microcrystalline wax. This is because a microcrystalline wax having a high melting point is appropriate from the relationship with the temperature setting of the planar heating element.

  (Aspect 7) A planar heating element in which a planar heating layer obtained by impregnating or laminating the conductive paint having the STS characteristics described in any of the above aspects 1 to 6 on a holding material provided with an electrode is covered with an insulating sheet substrate. It is.

  The conductive paint having the STS characteristic of the present invention has a change in the initial current value and the time-dependent current value depending on the blending ratio of the conductive material to the binder resin, the SP value, and the selection of the STS characteristic expression solvent having a specific dielectric constant range. There is almost no electricity, and the heating effect by the residual solvent is extremely low, and the heating element has a rated current (eg, mats, heating heaters such as floor heating heaters, snow melting heaters, drying appliances, agricultural appliances, etc.) It is the most suitable conductive paint for applications.

It is explanatory drawing which shows an example of the embodiment of the structure of the planar heating element of this invention. It is explanatory drawing which shows an example of the embodiment of the cross section of the planar heating element of this invention. Schematic diagram showing the principle of PTC heating element Schematic diagram showing the principle of the STS heating element Graph comparing the relationship between energization time of PTC heating element (upper) and STS heating element (lower), heating element current and temperature

(1) STS characteristic The STS characteristic which the conductive paint of this invention has is demonstrated.
The STS characteristic of the conductive paint of the present invention refers to a self temperature relaxation characteristic. Specifically, by covering the surface of the conductive material with a crystalline low molecular weight organic compound layer, the conductive paint is electrically conductive. The property which can suppress heat_generation | fever by making it difficult to produce the thermal vibration of the molecules which comprise a conductive material, ie, relieving the thermal vibration of a conductive molecule. This STS characteristic is expressed by adding an STS characteristic developing solvent to the conductive paint.
The heating element having the STS characteristic suppresses an increase in the amount of heat generated by the heating element during current heating due to melting of the crystalline low molecular weight organic compound covering the surface, and enters a thermal equilibrium (temperature relaxation) state when reaching a predetermined temperature. It is characterized by suppressing thermal vibration of the conductive material itself, and the contact of the conductive material is maintained even by energization heating, so that the amount of current is constant (see FIG. 4). In this respect, the contact with the conductive material is released as the temperature rises and the resistance value increases, which is different from the PTC (positive temperature coefficient of resonant) characteristic in which the amount of current is suppressed.

(2) Conductive paint About the conductive paint containing the conductive material and binder resin used for the conductive paint having the STS characteristic of the present invention, the conductive material, binder resin, paint solvent and the like constituting the conductive paint will be described.

(2-1) Conductive material The conductive material used for the conductive paint of the present invention is not particularly limited as long as it allows the energization function of the planar heat generating layer described later to be exhibited. Spherical, flaky, and fibrous metal particles (eg, nickel, silver-coated nickel), carbon-based conductive particles (eg, carbon black, graphite, carbon nanotubes, carbon fibers, metal-coated carbon black), ceramic-based conductive particles (eg, , Tungsten carbide, titanium nitride, zirconium nitride, titanium carbide), and conductive potassium titanate whiskers. As the conductive material, the initial resistance value can be lowered by increasing the filling amount, and if a sufficient resistance change rate can be obtained by selecting an STS characteristic expression solvent that expresses the STS characteristic described later, the carbon is also low in cost. System conductive particles are preferred.

  In the conductive paint of the present invention, the weight ratio of the carbon-based conductive particles to the binder resin described later is preferably 0.3 to 0.9, more preferably 0.4 to 0.9, and 0.6 to 0.9. Is more preferable. This is because if the weight ratio is less than 0.3, the initial resistance value is high, and if it exceeds 0.9, the thermal energy due to temperature rise is large and the STS characteristics cannot be exhibited.

(2-2) Binder resin As the binder resin used in the conductive paint of the present invention, a thermoplastic resin and a thermosetting resin are used. This is because only the low molecular weight compound and the conductive material cannot maintain the shape of the surface heating layer formed with the coating film because the melt viscosity of the low molecular weight organic compound is low. For this reason, the shape of the surface heating layer formed with the coating film can be maintained by blending a thermoplastic resin having a higher melting point than the low molecular organic compound and an insoluble and infusible thermosetting resin. Therefore, the types and blending ratios of the thermoplastic resin and the thermosetting resin of the binder resin can be appropriately selected from the viewpoints of the dispersibility of the conductive material and the shape maintenance of the surface heating layer formed with the coating film.

  The thermoplastic resin used for the conductive paint of the present invention is not particularly limited as long as it has a melting point higher than that of the low molecular organic compound. Specifically, a copolymer composed of a monomer unit derived from a polyolefin-based polymer (eg, polyethylene, polypropylene), an olefinically unsaturated monomer containing one or more polar groups, (eg, ethylene- Vinyl acetate copolymer, ethylene-acrylic acid copolymer), halogen-based polymer (eg, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl chloride, polyvinylidene chloride), polyamide (eg, 12-nylon), polystyrene, polyacrylonitrile, heat Examples thereof include a plastic elastomer, polyethylene oxide, polypropylene oxide, polyacetal, thermoplastic modified cellulose, polysulfones, polyethyl acrylate, polymethyl (meth) acrylate, and butyral resin. Such a thermoplastic polymer preferably has a weight average molecular weight Mw of about 10,000 to 5,000,000. Acrylic resin is preferably used.

  The thermosetting resin used in the conductive paint of the present invention is not particularly limited as long as it retains the shape of the surface heating layer formed with a coating film. Specifically, epoxy resin, unsaturated polyester resin, polyimide, polyurethane, phenol resin, and silicone resin are used, and epoxy resin is preferably used. The thermosetting resin to be used can be appropriately selected according to the desired performance and application, and among them, it is preferable to use an epoxy resin or an unsaturated polyester resin.

  Epoxy resin is obtained by curing (crosslinking) an oligomer having a reactive epoxy group at the end (molecular weight of about several hundred to 10,000) with various curing agents. Glycidyl ether type and glycidyl ester type represented by bisphenol A , Glycidylamine type, alicyclic type

  Unsaturated polyester resin is a polyester mainly composed of unsaturated dibasic acid or dibasic acid and polyhydric alcohol (molecular weight of about 1000 to 5000) dissolved in vinyl monomer that acts as a crosslink. It is obtained by curing an organic peroxide such as benzoyl as a polymerization initiator.

  Polyimides are roughly classified into a condensation type and an addition type depending on the production method, and a bismaleimide type polyimide of addition polymerization type polyimide is preferable. The bismaleimide type polyimide can be cured by homopolymerization, reaction with other unsaturated bonds, Michael addition reaction with aromatic amines, Diels-Alder reaction with dienes, or the like.

  Polyurethane is obtained by polyaddition reaction of polyisocyanate and polyol. As the polyisocyanate, there are an aromatic type and an aliphatic type, but an aromatic type is preferable, and 2,4- or 2,6-tolylene diisocyanate, diphenylmethane diisocyanate, naphthalene diisocyanate and the like are preferably used. Polyols include polyether polyols such as polypropylene glycol, polyester polyols, and acrylic polyols, with polypropylene glycol being preferred. The catalyst may be an amine (a tertiary amine such as triethylenediamine and an amine salt), but an organic metal such as dibutyltin dilaurate or stannous octoate is preferably used.

  Phenolic resins are obtained by reacting phenol with aldehydes such as formaldehyde, and are roughly classified into novolak type and resol type depending on the synthesis conditions. The novolak type produced under an acidic catalyst is cured by heating with a crosslinking agent such as hexamethylenetetramine, and the resol type produced under a basic catalyst is cured alone by heating or in the presence of an acid catalyst. In the present invention, either may be used. The synthesis and curing conditions may be determined as appropriate.

(2-3) Paint solvent Any solvent that can dissolve the binder resin component can be used as the solvent used in the conductive paint. For example, alcohol compounds such as methanol, butanol, benzyl alcohol, diacetone alcohol, ketone compounds such as methyl ethyl ketone, cyclohexanone, glycol ester compounds such as propylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, diethylene glycol monoethyl ether acetate, Glycol ether compounds such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, butoxyethanol, diethylene glycol monobutyl ether, amides such as N-methylpyrrolidone, N, N-dimethylformamide and N, N-dimethylacetamide Using one or more selected from compounds Kill. Among these solvents, diethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether, butoxyethanol, and diethylene glycol monobutyl ether are preferable from the viewpoint of the solubility of the resin component and the drying speed when applied. There is no restriction | limiting in particular in the usage-amount of a solvent, It can use suitably in the range which can prepare a uniform composition by mixing and kneading | mixing in consideration of the viscosity of a resin component, the mixing ratio of a resin component and a carbon component, etc. . A specific amount of the solvent is preferably 10 to 1000 parts by mass, more preferably 50 to 500 parts by mass, and still more preferably 100 to 300 parts by mass with respect to 100 parts by mass of the curable resin (B).

(2-4) Other components The coating solvent may include a curing catalyst, a curing agent, a coupling agent, a leveling agent, a dispersant, a rheology control agent, an antifoaming agent, an antioxidant, and a plasticizer as necessary. These various additives may be contained.

(3) Crystalline low molecular weight organic compound and dispersion solvent The crystalline low molecular weight organic compound used in the conductive paint having the STS characteristic of the present invention and the dispersion solvent thereof will be described.

(3-1) Crystalline low molecular weight organic compound The crystalline low molecular weight organic compound used for the conductive paint having the STS characteristic of the present invention has a molecular weight of up to about 2000, preferably up to about 1000, and more preferably from 200 to 800. Although it will not be restrict | limited especially if it is a crystalline substance, what is solid at normal temperature (temperature of about 25 degreeC) is preferable.

  Examples of crystalline low molecular weight organic compounds include waxes (eg, petroleum waxes such as paraffin wax and microcrystalline wax, natural waxes such as plant waxes, animal waxes, and mineral waxes), fats and oils (eg, fat or And so-called solid fat). The components of waxes and fats include hydrocarbons (specifically, alkane linear hydrocarbons having 22 or more carbon atoms), fatty acids (specifically, alkane linear hydrocarbons having 12 or more carbon atoms). Fatty acids), fatty acid esters (specifically, methyl esters of saturated fatty acids obtained from saturated fatty acids having 20 or more carbon atoms and lower alcohols such as methyl alcohol), fatty acid amides (specifically, oleic acid amides, Unsaturated fatty acid amides such as erucic acid amide), aliphatic amines (specifically, aliphatic primary amines having 16 or more carbon atoms), higher alcohols (specifically, n-alkyl alcohols having 16 or more carbon atoms). ), Chloroparaffin, etc., but these can be used alone or in combination as a crystalline low molecular weight organic compound. The crystalline low molecular weight organic compound may be appropriately selected in consideration of the polarity of the polymer matrix in order to improve the dispersion of each component. The crystalline low molecular weight organic compound is preferably a petroleum wax that is inexpensive and stable in quality and supply.

As the crystalline low molecular weight organic compound used in the conductive paint of the present invention, it is preferable to use one having a melting point mp of 40 to 100 ° C. As such, paraffin wax (eg, tetracosane C ₂₄ H ₅₀ ; mp 49 to 52 ° C., hexatriacontane C ₃₆ H ₇₄ ; mp 73 ° C., trade name HNP-10 (manufactured by Nippon Seiwa Co., Ltd.); mp 75 ° C., HNP-3 (manufactured by Nippon Seiwa Co., Ltd .; mp 66 ° C.), etc., microcrystalline wax (eg, trade name Hi-Mic-1080 (manufactured by Nippon Seiwa Co., Ltd.); mp 83 ° C., trade name Hi-Mic-1090 (Nippon Seiki) Mp88 ° C, Hi-Mic-1045 (manufactured by Nippon Seiwa); mp70 ° C, Hi-Mic2045 (manufactured by Nippon Seiwa); mp64 ° C, Hi-Mic3090 (manufactured by Nippon Seiwa); mp89 C., Serrata 104 (manufactured by Nippon Oil Refinery); mp 96 ° C., 155 microwax (manufactured by Nippon Oil Refinery); Mp 81 ° C., stearic acid (manufactured by Nippon Seika); mp 72 ° C., palmitic acid (manufactured by Nippon Seika); mp 64 ° C.), fatty acid esters (for example, arachidic acid methyl ester (manufactured by Tokyo Chemical Industry); mp 48 ° C.) ), Etc., and fatty acid amides (eg, oleic acid amide (manufactured by Nippon Seika); mp 76 ° C.), polyethylene wax (eg, trade name Mitsui High Wax 110 (manufactured by Mitsui Petrochemical Co., Ltd.); mp 100 ° C.) and the like. Also, a blended wax obtained by blending a resin with a paraffin wax, or a blended wax obtained by mixing a microcrystalline wax and having a melting point of 40 to 100 ° C. can be preferably used. Furthermore, one type or two or more types can be selected and used depending on the operating temperature.

  As the crystalline low molecular weight organic compound used in the conductive paint of the present invention, those containing at least a microcrystalline wax are preferable. This is because microcrystalline wax has a high component ratio of branched hydrocarbons and saturated cyclic hydrocarbons, and therefore has a relatively high melting point and melt viscosity, and is suitable from the viewpoint of the STS characteristics and the control temperature range for planar heating element applications. .

  The weight of the crystalline low molecular weight organic compound is preferably 0.2 to 4 times, particularly preferably 0.2 to 2.5 times the total weight of the polymer matrix (including a curing agent and the like). When the mixing ratio is reduced and the amount of the low molecular organic compound is reduced, it is difficult to obtain a sufficient resistance change rate. On the contrary, when the mixing ratio is increased and the amount of the low molecular organic compound is increased, the element body is largely deformed when the low molecular compound is melted, and mixing with the conductive material becomes difficult.

(3-2) Dispersion solvent The dispersion solvent of the crystalline low molecular weight organic compound of this invention is a solvent used for viscosity adjustment for mix | blending a crystalline low molecular weight organic compound in an electrically conductive coating material. The crystalline low molecular weight organic compound is dispersed at a temperature equal to or higher than its melting point by adding a dispersion solvent, for example, by a dispersing device such as a three roll mill. Therefore, as the dispersion solvent, a solvent whose boiling point exceeds the melting point of the crystalline low molecular weight organic compound to be blended in the conductive paint and whose solubility parameter (SP value) is close to the crystalline low molecular weight organic compound is appropriately selected. be able to. Specific examples of the dispersion solvent include benzyl alcohol, toluene, xylene, methyl ethyl ketone, acetone, and ethyl acetate.
Note that the crystalline low molecular weight organic compound can be dispersed and blended in the conductive paint without using a dispersion solvent.

(4) STS characteristic expression solvent The STS characteristic expression solvent used for the conductive paint having the STS characteristic of the present invention is (i) forming a coating layer of a crystalline low molecular weight organic compound on a conductive material in order to exhibit the STS characteristic. (Ii) Realizing an appropriate viscosity for applying the coating material on a holding material having an electrode to be described later, (iii) Electromagnetic conductivity even if remaining in a planar heating element to be described later It is a solvent added to the conductive paint for the purpose of not contributing to the above.
In order to achieve this object, the STS characteristic expression solvent of the present invention has a relative dielectric constant of 6 or less. When the relative dielectric constant exceeds 6, when the sheet heating layer using the conductive paint having the STS characteristic of the present invention remains on the sheet heating element laminated with the insulating sheet substrate, it becomes conductive due to the polarization of the solvent. This is because it contributes.
Moreover, it is preferable that the viscosity in 25 degreeC is 0.4-0.9 mPa * s. If the viscosity is less than 0.4 mPa · s, the self-diffusion coefficient (proportional to the reciprocal of the viscosity) is high, the mobility of the remaining solvent is high, and it contributes to electrical conductivity. This is because if it exceeds, the self-diffusion coefficient is low and the compatibility with the conductive material and the like are lacking.
Furthermore, the SP value of the STS characteristic expression solvent is 17 to 22 (MPa) ^1/2 . The STS characteristic expression solvent (SP value: 17 to 22 (MPa) ^1/2 ) acts as a poor solvent for the crystalline low-molecular organic compound (SP value: 14 to 16 (MPa) ^1/2 ), This is because the coating of the crystalline low molecular weight organic compound on the surface of the conductive material is promoted.

(4-1) Relative permittivity Here, the relative permittivity (εr) will be described. The relative permittivity (dielectric constant) is the ratio of the dielectric constant of the medium to the dielectric constant of the vacuum (ε / ε ₀ = εr), and indicates the ease of dielectric polarization of the medium. The relative dielectric constant is a dimensionless quantity and takes a constant value regardless of the unit system used. The non-aqueous solvent (organic solvent) used as the STS characteristic expression solvent used in the present invention is not particularly limited as long as the relative dielectric constant is 6 or less. Examples of the non-aqueous solvent having a relative dielectric constant of 6 or less include dimethyl carbonate (DMC) having a relative dielectric constant of 2.8, diethyl carbonate (DEC) having a relative dielectric constant of 2.8, and a relative dielectric constant of 2. A chain carbonate such as ethyl methyl carbonate (EMC) which is 9, a cyclic ether such as 1,4-dioxane having a relative dielectric constant of 2.2, diethyl ether having a relative dielectric constant of 4.27, and a relative dielectric constant of 4 0.5 methyl formate, 2-methyltetrahydrofuran having a relative dielectric constant of 5.24, cyclopentyl methyl ether (CPME) having a relative dielectric constant of 4.84, and the like. Such non-aqueous solvents can be used alone or in combination of two or more. Among these, a chain carbonate having a relative dielectric constant of 3 or less is more preferable.

(4-2) SP value Here, the SP value (solubility parameter) will be described. The SP value is called a solubility parameter, and is a numerical value of how easily each other dissolves. The SP value is represented by the attractive force between molecules, that is, the square root of cohesive energy density (CED). The CED is the amount of energy required to evaporate 1 mL. The SP value in the present invention is expressed in SI units (MPa) ^1/2 . The SP value was quoted from a plastic material dictionary or the like, and (cal / cm ³ ) ^1/2 notation data was converted as follows.
SP value (dissolution parameter) = (CED value) ^1/2 = 2.05 × (cal / cm ³ ) ^1/2 = (J / cm ³ ) ^1/2 = (MPa) ^1/2 ... Formula (I )

(4-3) Lower chain carbonate As the STS characteristic expression solvent of the present invention, a lower chain carbonate is preferable. Examples of the lower chain carbonate include dimethyl carbonate (relative dielectric constant: 2.8, viscosity: 0.59 mPa · s, SP value: 20.3 (MPa) ^1/2 , bp: 90.3 ° C.), ethyl methyl Carbonate (dielectric constant; 2.9, viscosity: 0.70 mPa · s, SP value: 19.1 (MPa) ^1/2 , bp; 109 ° C.), diethyl carbonate (dielectric constant; 2.8, viscosity; 0 .75 mPa · s, SP value; 18.0 (MPa) ^1/2 , bp; 127 ° C.).

  In this invention, the weight ratio of the STS characteristic expression solvent with respect to a crystalline low molecular organic compound is 3.8-5.8. When the weight ratio of the STS characteristic expression solvent to the crystalline low molecular organic compound is less than 3.8, the crystalline low molecular organic compound is not sufficiently dispersed in the carbon-based conductive particles and the binder resin. This is because the residual solvent concentration increases when the amount exceeds the above range.

(5) Planar heating element The planar heating element of the present invention is obtained by coating a planar heating layer in which a conductive paint having STS characteristics is impregnated or laminated on a holding material having an electrode with an insulating sheet substrate. (FIG. 2). This will be described below.

(5-1) Holding Material Having Electrode The holding material having the electrode of the present invention is not particularly limited as long as the electrode is provided on a sheet material having certain heat resistance and flexibility. Specifically, a woven fabric (FIG. 1) in which a part of the longitudinal fiber yarn or the lateral fiber yarn constituting the woven fabric is replaced with a conductive wire having the same diameter, and an electrode sheet on the nonwoven fabric made of heat-resistant synthetic fiber. It is printed or bonded.

(5-2) Insulating Sheet Base The insulating sheet base of the present invention is an electrically insulating laminate film that covers a planar heating element. A plastic film has a high volume resistivity (Ω · cm) and is used for an electrically insulating sheet substrate. Specifically, there are a polyethylene film, a polypropylene film, a polyvinyl chloride film, and a polyethylene terephthalate film.

Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples of the present invention (Table 1).

<Example 1>
(1) Preparation of conductive coating containing crystalline low molecular organic compound As binder resin, acrylic resin (manufactured by DIC, ACRICDIC 56-700), epoxy resin (manufactured by Mitsubishi Chemical Corporation, trade name JER828), low molecular organic compound As a conductive particle, carbon black (manufactured by Nippon Seiwa Co., Ltd., trade name HiMic 1080, melting point 83 ° C.) and carbon black (Valcan XC-305, manufactured by Cabot Corporation) were used.
3080 g of acrylic resin, 190 g of epoxy resin, 1500 g of carbon black and paint solvent (acetate-n-butyl 2275 ml, propylene glycol monomethyl ether 9100 ml) were mixed for about 10 minutes with a dissolver, and then passed twice with a three-roll disperser. The mixture was mixed for 10 minutes to obtain a paint-like mixture.
1125 g of microcrystalline wax was added in advance to a mixed solvent of 3600 g of xylene and 900 g of methyl ethyl ketone, and the mixture was added to a solution that had been mixed and dissolved by a dissolver for about 30 minutes to obtain a conductive coating material containing a crystalline low molecular organic compound.

(2) Preparation of conductive paint having STS characteristics 6187 ml of dimethyl carbonate was added to the conductive paint containing a crystalline low molecular organic compound and mixed for 10 minutes with a dissolver to obtain a conductive paint having STS characteristics.

(3) Production of planar heating element Conductivity having STS characteristics prepared in a woven fabric in which electrode terminal portion 2 is attached to electrode 4a made of a copper wire group in which a part of longitudinal fibers shown in FIG. The sheet heating element 1 was obtained by impregnating the paint and drying at a drying temperature of 170 ° C. for 20 minutes. The obtained planar heating element 1 was covered with a polyester laminate film 3 (manufactured by Teijin DuPont Films, trade name GE, film thickness 100 μm) (FIG. 2).

(4) Current value measurement The initial current value and time-dependent current value (after 360 minutes) of the laminated sheet heating element 1 manufactured were measured. The current value was measured using a DIGITAL POWER METER (manufactured by Yokogawa, trade name: WT310).

(5) Surface resistance value measurement The surface resistance value of the laminated sheet heating element 1 thus manufactured was measured using DIGITAL HITESTER (manufactured by HIOKI, trade name: 3238).

(6) STS characteristic evaluation The STS characteristic was determined based on the current value measurement and the surface resistance value measurement. Judgment criteria are as follows.
A: Current value over time / initial current value is 1.0 and surface resistance value is less than 0.3 B: Current value over time / initial current value is 1.0 and surface resistance value is 0.00. 3 to 0.4: Δ: Current value / initial current value is 1.0 and surface resistance value is 0.5 to 0.6 ×: Current value / initial current value is 1.0 Or resistance value exceeds 0.7

<Examples 2 to 7>
The composition ratio (B / A) of the carbon-based conductive particles (B) with respect to the binder resin (A) and the composition ratio (S / C) of the crystalline low-molecular organic compound (C) with respect to the STS expression solvent (S) were changed. Others were the same as in Example 1.

<Example 9>
The same operation as in Example 4 was performed except that paraffin wax (manufactured by Nippon Seiwa Co., Ltd., 115, melting point: 47 ° C.) was used as the crystalline low molecular organic compound.

<Examples 8 and 13>
The STS characteristic expression solvent was changed to methyl ethyl carbonate (EMC) and diethyl carbonate (DEC).

<Examples 10 to 12>
The STS characteristic expression solvent was changed to 1,4-dioxane (1,4-DOx), cyclopentylmethyl ether (CPME), and 2-methyltetrahydrofuran (METHF), and the same procedure as in Example 1 was performed.

<Comparative Example 1>
The procedure was the same as Example 1 except that no STS expression solvent (S) was added.

<Comparative Examples 2 and 3>
The composition ratio (S / C) of the STS expression solvent (S) to the crystalline low molecular weight organic compound (C) was set to 5.9 and 3.6, respectively, and the same as in Example 1.

<Comparative example 4>
The composition ratio (B / A) of the carbon-based conductive particles (B) to the binder resin (A) was set to 0.28, and the same as Example 1.

<Comparative Examples 5-7>
The STS characteristic expression solvent was changed to N, N-dimethylformamide (DMF), γ-butyrolactone (GBL), and methyl ethyl ketone (MEK).

<Summary>
From the results in Table 1,
(1) When a non-aqueous solvent (an STS characteristic expression solvent) having a relative dielectric constant of 6 or less and an SP value of 17 to 20 (MPa) ^1/2 is added to the conductive paint, STS characteristics (current value over time / initial current value, In particular, the lower chain carbonate (DMC, EMC) had a surface resistance of 0.37 kΩ or less (Example 1-13). On the other hand, STS characteristics were not exhibited unless the STS expression solvent was added (Comparative Example 1).
(2) When the composition ratio (S / C) of the STS expression solvent (S) to the crystalline low-molecular-weight organic compound (C) was 5.9 and 3.6, respectively, the expression of STS characteristics was low. (Comparative Examples 2 and 3).
(3) When the composition ratio (B / A) of the carbon-based conductive particles (B) to the binder resin (A) is 0.29, STS characteristics are exhibited, but the surface resistance value exceeds 0.7 kΩ. (Comparative Example 4).
(4) When a nonaqueous solvent having a relative dielectric constant exceeding 6 is added, STS characteristics are not exhibited (Comparative Example 5-7).

  When the STS planar heating element exceeds a predetermined temperature, the heating element itself relaxes in temperature, maintains a thermal equilibrium state, does not pose a danger such as a burn to the human body, and can realize low power consumption. For example, the present invention can also be applied to heat heaters such as mats, floor heaters, and snowmelt heaters, drying appliances, and agricultural appliances.

DESCRIPTION OF SYMBOLS 1 Planar heating element 2 Electrode terminal part 3 Laminate film 4 Copper wire 4a Electrode which consists of a copper wire group 5 Fiber yarn 5a Weft 11 Conductive material 12 Binder resin 13 Coating with crystalline low molecular organic compound

The problems described above can be solved by the following aspects. In particular,
And (aspect 1) conductive material, a binder resin, a crystalline low-molecular organic compound and melting point is 40 to 100 ° C. waxes, hydrocarbons, fatty acids, fatty acid esters, fatty acid amides, any or these polyethylene waxes and mixtures, STS property development solvent and to the dielectric constant of 6 or less, and the SP value is, DMC having the characteristics of ^{17~22 (MPa) 1/2, EMC,} DEC, 1,4-DOx, CPME, the METHF A conductive paint having STS characteristics in which any one or a mixture thereof is dispersedly mixed, and the current value of the planar heating element impregnated or laminated with the conductive paint having the STS characteristics is constant over time. This is a conductive paint having STS characteristics. When a planar heating element in which a sheet heating layer in which a conductive coating material having STS characteristics is impregnated or applied to a holding material provided with an electrode is coated with an insulating sheet substrate by using a solvent having a relative dielectric constant of 6 or less is used. In addition, even if the solvent that exhibits the STS characteristic remains in the planar heating element, it is low polarizability, so it does not contribute to current conduction, and the current amount is less likely to change over time. . In addition, by setting the SP value of the STS characteristic expression solvent in the range of 17 to 22 (MPa) ^1/2 , formation of a film of a crystalline low molecular organic compound on the surface of the conductive material is promoted, and Even when the temperature is raised, the crystalline low molecular weight organic compound does not dissolve in the binder resin, but only swells in a state where it is coated on the surface of the conductive material, and the bonding of the conductive material is maintained. This is because the amount of current does not decrease. In particular, lower chain carbonates such as DMC, EMC, and DEC have a relative dielectric constant of 3 or less, and therefore, even when used as a residual solvent, there is a great effect that the amount of current hardly changes over time. . This is because the crystalline low molecular weight organic compound preferably has a melting point of 40 to 100 ° C. in view of the temperature setting of the planar heating element.

(Aspect 2 ) The conductive paint having STST characteristics according to Aspect 1 , wherein a weight ratio of the STS characteristic expression solvent to the crystalline low molecular weight organic compound is 3.8 to 5.8. is there. This is because, by setting the weight ratio of the STS characteristic expression solvent to the crystalline low molecular organic compound in the range of 3.8 to 5.8, formation of a film on the surface of the conductive material is promoted.

(Aspect 3 ) The aspect 1 is characterized in that the conductive material is carbon-based conductive particles, and the weight ratio of the carbon-based conductive particles to the binder resin is 0.3 to 0.9. Or a conductive paint having STS characteristics described in any one of 2 ; By setting the weight ratio of the carbon-based conductive particles to the binder resin in the range of 0.3 to 0.9, there is an effect that the conductivity, that is, the resistance value is within a predetermined range.

(Aspect 4 ) A planar heating element in which a planar heating layer obtained by impregnating or laminating the conductive paint having the STS characteristics described in any of the above aspects 1 to 3 on a holding material including an electrode is covered with an insulating sheet substrate. It is.

Claims (7)

  A conductive paint having an STS characteristic in which a conductive material, a binder resin, a crystalline low molecular weight organic compound, and an STS characteristic expression solvent are dispersed and blended, wherein the STS characteristic expression solvent has a relative dielectric constant of 6 or less. A conductive paint having STS characteristics, which is a non-aqueous solvent. 2. The conductive paint having STS characteristics according to claim 1, wherein an SP value of the STS characteristic expression solvent is 17 to 22 (MPa) ^1/2 .   The conductive paint having an STS characteristic according to claim 1, wherein the STS characteristic expression solvent is a lower chain carbonate.   4. The conductive paint having STST characteristics according to claim 1, wherein a weight ratio of the STS characteristic expression solvent to the crystalline low molecular organic compound is 3.8 to 5.8. 5. .   The conductive material is carbon-based conductive particles, and the weight ratio of the carbon-based conductive particles to the binder resin is 0.3 to 0.9. A conductive paint having the STS characteristics described above.   The conductive paint having an STS characteristic according to any one of claims 1 to 5, wherein the crystalline low molecular weight organic compound is a microcrystalline wax.   A planar heating element in which a planar heating layer obtained by impregnating or laminating the conductive paint having the STS characteristic according to any one of claims 1 to 6 on a holding material provided with an electrode is covered with an insulating sheet substrate.