JP5370357B2 - Conductive paste for sheet heating element, printed circuit using the same, sheet heating element - Google Patents

Abstract

Disclosed is a conductive paste for planar heating elements that has excellent solvent solubility even if a polymer with a crystalline melting point is used as the resin therein, that has excellent specific resistance and PTC properties even with repeated heating, and that does not abruptly lose resistance even when heated above its melting point. The conductive paste for planar heating elements comprises a polyurethane resin (I) with a crystalline melting point and conductive particles (II). In this conductive paste for planar heating elements, the crystalline melting point of the polyurethane resin (I) is preferably 20-100ºC, and the polyurethane resin (I) is preferably one in which at least an amorphous constituent and a crystalline constituent were reacted.

Description

  The present invention relates to a conductive paste, and more particularly to forming a circuit or forming a planar heating element by applying, printing, or curing a conductive paste on a film or substrate. It is. More specifically, the present invention relates to a planar heating element having PTC (Positive Temperature Coefficient) characteristics.

  Planar heating elements are used for floor heating, anti-fogging of mirrors in automobiles and bathrooms, and warming pets and foliage plants. Of these, a planar heating element with a self-temperature control function, that is, a PTC characteristic, allows continuous temperature control compared to a heating element without a PTC characteristic, and does not require a thermistor, thereby reducing the number of parts. And is widely used in the above applications. Usually, such a planar heating element is composed of a resin and a conductive material, and as the temperature of the planar heating element rises, the resin undergoes volume expansion, and the conduction between the conductive substances is blocked. It is said that the characteristics are expressed.

  Conventionally, a planar heating element having such PTC characteristics is obtained by kneading a conductive material made of carbon black, graphite, metal powder, or the like into an olefin resin, and dispersing or dissolving the resin and the conductive material in a solvent. The thing etc. which apply | coated and dried what is formed are proposed (for example, patent document 1). In addition, as a method for producing such a planar heating element, the former has been a method by extrusion molding or press molding, and the latter has been a method of applying to a substrate by means such as screen printing. The latter method is often used from the viewpoint that the shape can be freely designed, and the paste type is widely used to enable screen printing.

  In the paste type, a polymer using a polymer resin such as ethylene-vinyl acetate copolymer (EVA) as a base polymer has been proposed (for example, Patent Document 2). This is because the ethylene part in the base polymer exhibits PTC characteristics and the vinyl acetate part exhibits solvent solubility, which is suitable as a conductive paste material for a planar heating element. In this case, in order to achieve both solvent solubility and PTC characteristics, it is necessary to adjust the vinyl acetate content of EVA. However, if the copolymerization ratio of vinyl acetate is increased to improve the solubility, the PTC characteristics are lowered. On the contrary, when the copolymerization ratio of vinyl acetate is decreased, the PTC characteristics are improved, but the solvent solubility is deteriorated.

  Moreover, the electrically conductive paste which improved the PTC characteristic by using resin with a glass transition temperature of 50 degrees C or less is proposed (for example, patent document 3). However, in this case, when a voltage is repeatedly applied, the PTC characteristics tend to deteriorate. This is because, when the base resin is exposed for a long time in the vicinity of 40 ° C. to 70 ° C., which is the use temperature of the planar heating element, a minute fluidized portion is generated in the resin, and the dispersion structure of the conductive fine particles changes. This is considered to be a cause.

  Moreover, the electrically conductive paste which combined crystalline resin is proposed (for example, patent document 4). In this case, the PTC characteristics can be improved by blending a crystalline resin having a large volume change before and after melting. However, an ink-like or paste-like PTC composition is prepared using such a crystalline resin as a base polymer. The biggest challenge in manufacturing is the compatibility between the solvent solubility of the base polymer and the PTC characteristics. That is, in order to obtain an ink-like or paste-like composition, it is indispensable to dissolve the base polymer in an appropriate solvent. However, if the degree of crystallinity of the polymer is high, the PTC characteristics are excellent, but it is difficult to dissolve in the solvent. On the contrary, if the degree of crystallinity of the polymer is low, the solvent is easily dissolved in the solvent but the PTC characteristics are inferior. For this reason, it cannot be said that the conductive paste combined with such a crystalline resin is sufficiently satisfactory in both solvent solubility and PTC characteristics. Moreover, since the solvent which can be used is also very limited, there exists a problem also in terms of versatility.

  Furthermore, when a crystalline resin is used, the resistance value may drop rapidly after reaching the peak temperature beyond the melting point. It is considered that this is because when the temperature is raised above the melting point and the crystalline polymer is melted, the conductive fillers dispersed therein come into contact with each other again and become conductive. When the PTC composition having such properties is heated to a peak temperature or higher for some reason, the self-temperature control function is lost and a large current flows. As a result, the temperature rises and eventually burns down. It can be connected.

  In order to improve the property that the resistance value suddenly decreases again after reaching the peak temperature as described above, in the conventional crystalline olefin resin-based PTC composition, after being pressed into a sheet shape, an electron beam or a γ ray The resin is crosslinked by irradiating with radiation. However, in addition to the expensive equipment used for such irradiation, depending on the conditions, it may leave active radicals in the resin, which may significantly deteriorate the heat resistance and durability. And had a cost problem.

JP-A-1-304704 Japanese Patent Laid-Open No. 10-183039 JP 2000-88672 A JP 2001-76850 A

  An object of the present invention is to improve the problems of these conventional conductive resin compositions and conductive pastes. That is, while using a polymer having a crystalline melting point as the resin, the solvent solubility is good, and even if repeated heating is performed, the specific resistance and PTC characteristics are good, and even if the temperature is raised above the melting point, It is an object of the present invention to provide a conductive paste for a planar heating element that does not cause a rapid decrease in resistance value.

  As a result of diligent studies to solve the above problems, it was surprisingly possible to significantly improve the PTC characteristics and conductivity in a high temperature region by using a polyurethane resin having a crystalline melting point as a binder. The present invention has been reached. That is, the present invention has very good PTC characteristics while maintaining solvent solubility, good return characteristics in which the specific resistance returns to its original value even when repeatedly raised and lowered, and the temperature is raised above the melting point. However, it is possible to provide a conductive paste for a planar heating element that does not have a sudden decrease in resistance value.

  That is, the present invention relates to the following conductive paste, a printed circuit using the same, and a planar heating element.

(1) A conductive paste for a planar heating element comprising a polyurethane resin (I) having a crystalline melting point and conductive particles (II).
(2) The conductive paste for a planar heating element according to (1), wherein the crystalline melting point of the polyurethane resin (I) is 20 to 100 ° C.
(3) The conductive paste for a planar heating element according to (1) or (2), wherein the polyurethane resin (I) is obtained by reacting at least an amorphous component and a crystalline component.
(4) The polyurethane resin (I) is obtained by reacting at least an amorphous polyester polyol, a crystalline polyester polyol having a melting point of 5 to 120 ° C., and a polyisocyanate as main components (1) or ( The conductive paste for planar heating elements as described in 2).
(5) The conductive paste for a planar heating element according to any one of (1) to (4), wherein the polyurethane resin (I) is a crystalline polyurethane urea further containing a urea bond. .
(6) The conductive paste for a planar heating element according to (5), wherein the amount of urea bonds in the crystalline polyurethane urea is in the range of 10 to 1000 eq / ton.
(7) The conductive paste for a planar heating element according to any one of (1) to (6), wherein the polyurethane resin (I) is soluble in a solvent.
(8) The planar heating element according to any one of (4) to (7), wherein the number average molecular weight of the crystalline polyester polyol constituting the polyurethane resin (I) is in the range of 1200 to 20000. Conductive paste.
(9) The crystalline polyester polyol constituting the polyurethane resin (I) is copolymerized in an amount of 85 to 300 parts by weight based on 100 parts by weight of the amorphous polyester polyol (4) to (8) The conductive paste for planar heating elements according to any one of the above.
(10) The surface according to any one of (4) to (9), wherein the polyester resin further contains 50 parts by weight or less of crystalline polyester polyol when the polyurethane resin (I) is 100 parts by weight. Conductive paste for heating element.
(11) The sheet heating element according to any one of (1) to (10), wherein the conductive particles (II) are contained at a ratio of 40 to 400 parts by weight with respect to 100 parts by weight of the polyurethane resin (I). Conductive paste.
(12) The conductive particle (II) is a spherical carbon, and the average particle size thereof is 0.1 to 30 μm. The sheet heating element according to any one of (1) to (11), Conductive paste.
(13) A printed circuit using the conductive paste for a planar heating element according to any one of (1) to (12).
(14) A planar heating element using the conductive paste for planar heating element according to any one of (1) to (12).

  The conductive paste of the present invention has basic physical properties such as good conductivity, PTC characteristics, return characteristics, adhesion, and bending resistance, and is suitable for planar heating element applications.

Hereinafter, embodiments of the conductive paste of the present invention will be described in detail. The conductive paste of the present invention has good storage stability and provides good PTC characteristics. The PTC characteristic means a characteristic that the circuit resistance increases as the temperature rises. In the present invention, as shown in the examples, for example, the ratio of the resistance change at 80 ° C. and 30 ° C. (sheet resistance (80 ° C.)). If the sheet resistance (30 ° C.) is 3 or more, it is defined as “having PTC characteristics”. As the PTC characteristic, the magnification is preferably 5 or more, more preferably 10 or more, and still more preferably 100 or more. Although an upper limit is not specifically limited, Generally it is 50000 or less. On the other hand, when a sheet heating element is produced by a printing method, the dry film thickness is generally limited to 20 μm or less, and therefore a specific resistance much lower than that of an extrusion molding type conductive resin composition is required. The specific resistance of the conductive paste of the present invention is preferably 600 Ω · cm or less, more preferably 450 Ω · cm or less, and still more preferably 400 Ω · cm or less. The lower limit is not particularly limited, but is generally 1 × 10 ⁻² Ω · cm or more.

  The polyurethane resin (I) used in the present invention preferably has a crystalline melting point. The term “having a crystalline melting point” in the present invention indicates that a peak of heat of fusion exists when a differential scanning calorimetry (DSC) measurement is performed by a method described later. When the polyurethane resin has a crystalline melting point, the PTC characteristics are remarkably improved as the polymer volume changes in the vicinity of the crystalline melting point. Although the range of melting | fusing point is not specifically limited, Preferably it is 10-100 degreeC, More preferably, it is 20-80 degreeC. When the temperature is 100 ° C. or higher, the solubility in a solvent is remarkably inferior, so that an operation such as heating and melting is required immediately before the workability during production tends to deteriorate. On the other hand, if the melting point is lower than 20 ° C., the resin expands near room temperature, and the resistance value may become unstable. In the conductive paste of the present invention, as other resins than polyurethane having a crystalline melting point, other urethane resins, polyester resins, epoxy resins, phenol resins, acrylic resins, styrene-acrylic resins, styrene-butadiene copolymers, Polystyrene, polyamide resin, polycarbonate resin, and ethylene-vinyl acetate copolymer resin may be used in combination. When the above resins are used in combination, the type is not limited, but polyester resins and polyurethane resins are preferable from the viewpoints of adhesion to a substrate, flex resistance, and solvent solubility. The above combination resin may or may not have a crystalline melting point.

  The number average molecular weight of the polyurethane resin (I) having a crystalline melting point used in the present invention is preferably 3000 or more, more preferably 8000 or more from the viewpoint of bending resistance. When the number average molecular weight is less than 3000, good flex resistance is difficult to obtain, and the paste viscosity is lowered and printability may be lowered. The upper limit is not particularly limited, but is preferably 100,000 or less from the viewpoint of paste viscosity and solubility.

  The polyurethane resin (I) having a crystalline melting point used in the present invention is preferably one obtained by reacting at least an amorphous component, a crystalline component, and a chain extension component. The term “amorphous component” as used herein means that only the component, and when a differential scanning calorimeter (DSC) is measured by the method described later, there is no peak of heat of fusion. Shows a peak of heat of fusion when measured in the same manner. In view of the variety and reactivity of the compounds, the amorphous component is preferably an amorphous polyol, the crystalline component is a crystalline polyol, and the chain extender is preferably a polyisocyanate.

  Examples of the amorphous polyol include polyether polyol and polyester polyol, and polyester polyol is preferable from the viewpoint of freedom of molecular design. Amorphous polyester polyol is obtained by condensation of dicarboxylic acid and polyol. Examples of the dicarboxylic acid used include terephthalic acid, isophthalic acid, orthophthalic acid, 2,6-naphthalenedicarboxylic acid, succinic acid, glutaric acid, adipic acid, sebacic acid, dodecanedicarboxylic acid, azelaic acid and the like, C12-C28 dibasic acid, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 4-methylhexahydrophthalic anhydride, 3-methylhexahydrophthalic anhydride Acid, 2-methylhexahydrophthalic anhydride, dicarboxy hydrogenated bisphenol A, dicarboxy hydrogenated bisphenol S, dimer acid, hydrogenated dimer acid, hydrogenated naphthalene dicarboxylic acid, tricyclodecane dicarboxylic acid, and other alicyclic dicarboxylic acids Acid, hydroxy-benzo Examples include hydroxycarboxylic acids such as acid and lactic acid. From the viewpoint of strength, heat resistance, durability such as moisture resistance and thermal shock resistance, aromatic dicarboxylic acid is copolymerized in an amount of 40 mol% or more of all acid components. It is preferable that More preferably, it is 50 mol% or more. Further, within the range that does not impair the effects of the invention, polyvalent carboxylic acids such as trimellitic anhydride and pyromellitic anhydride, unsaturated dicarboxylic acids such as fumaric acid, and sulfonic acids such as sodium 5-sulfoisophthalic acid A metal base-containing dicarboxylic acid may be used in combination.

  Examples of polyols used include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 3-methyl-1, 5-pentanediol, 2-methyl-1,5-pentanediol, 2,2-diethyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, 1,9-nonanediol 1,10-decanediol, 1,4-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,2-cyclohexanedimethanol, dimer diol and the like. Moreover, you may use together polyhydric polyols, such as a trimethylol ethane, a trimethylol propane, glycerol, a pentaerythritol, a polyglycerol, in the range which does not impair the effect of invention.

  Examples of the crystalline polyol constituting the polyurethane resin (I) having a crystalline melting point used in the present invention include polyether polyols and polyester polyols. Polyester polyols are preferred from the viewpoint of freedom of molecular design. Crystalline polyester polyol is obtained by condensation of dicarboxylic acid and polyol. Examples of the dicarboxylic acid used include terephthalic acid, isophthalic acid, orthophthalic acid, 2,6-naphthalenedicarboxylic acid, succinic acid, glutaric acid, adipic acid, sebacic acid, dodecanedicarboxylic acid, azelaic acid and the like, C12-C28 dibasic acid, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 4-methylhexahydrophthalic anhydride, 3-methylhexahydrophthalic anhydride Acid, 2-methylhexahydrophthalic anhydride, dicarboxy hydrogenated bisphenol A, dicarboxy hydrogenated bisphenol S, dimer acid, hydrogenated dimer acid, hydrogenated naphthalene dicarboxylic acid, tricyclodecane dicarboxylic acid, and other alicyclic dicarboxylic acids Acid, hydroxy-benzo Examples include hydroxycarboxylic acids such as acid and lactic acid. From the viewpoint of strength, heat resistance, durability such as moisture resistance and thermal shock resistance, aromatic dicarboxylic acid is copolymerized in an amount of 40 mol% or more of all acid components. It is preferable that More preferably, it is 50 mol% or more. Furthermore, the aromatic dicarboxylic acid is preferably terephthalic acid. Further, within the range that does not impair the effects of the invention, polyvalent carboxylic acids such as trimellitic anhydride and pyromellitic anhydride, unsaturated dicarboxylic acids such as fumaric acid, and sulfonic acids such as sodium 5-sulfoisophthalic acid A metal base-containing dicarboxylic acid may be used in combination.

  Examples of polyols used include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 3-methyl-1, 5-pentanediol, 2-methyl-1,5-pentanediol, 2,2-diethyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, 1,9-nonanediol 1,10-decanediol, 1,4-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,2-cyclohexanedimethanol, dimer diol and the like. Moreover, you may use together polyhydric polyols, such as a trimethylol ethane, a trimethylol propane, glycerol, a pentaerythritol, a polyglycerol, in the range which does not impair the effect of invention.

  In consideration of versatility and handling properties, for example, Plaxel 230, Plaxel 240, Plaxel CD220, Plaxel H1P (manufactured by Daicel Chemical), which are crystalline polycaprolactone diols, DYNACOLL7330, DYNACOLL7340, DYNACOLL7390 (which are crystalline copolyesters) commercial products such as HT-310, HT-400, HS2H-350S, HS2H-500S, HS2H-1000S (manufactured by Toyokuni Oil Co., Ltd.), which are crystalline copolyesters, may be used. These may be used alone or in combination of two or more in order to adjust the melting point, there is no problem.

  The crystalline diol constituting the polyurethane resin having a crystalline melting point used in the present invention preferably has a melting point in the range of 5 to 120 ° C, more preferably in the range of 20 to 100 ° C. When the melting point is less than 5 ° C., the melting point as polyurethane is lowered, and the resistance value at room temperature may become unstable when used as a planar heating element. On the other hand, when the melting point exceeds 120 ° C., the handling property is not good, the melting point as polyurethane is increased, and the solubility in a solvent may be deteriorated. In the present invention, two or more crystalline diols within the above melting point range may be used in combination, or a crystalline diol within the above melting point range and a crystalline diol outside the above range are used in combination. You can also.

  The crystalline diol constituting the polyurethane resin having a crystalline melting point used in the present invention is preferably in the range of 1000 to 20000 in terms of number average molecular weight, more preferably in the range of 4000 to 10,000. If the number average molecular weight is less than 1000, crystallinity may not be exhibited. On the other hand, when it is 20000 or more, it may remain without being copolymerized, and the crystallinity may be increased, and the solubility in a solvent may be deteriorated. In the present invention, two or more kinds of crystalline diols within the range of the number average molecular weight may be used in combination, or crystalline diols within the range of the number average molecular weight and crystallinity outside the range. A diol can also be used in combination.

  The conductive paste of the present invention can be used by blending the crystalline diol in addition to the polyurethane resin (I) having a crystalline melting point. The crystalline diol may be contained in a range of 50% by weight or less, more preferably 20% by weight or less with respect to 100% by weight of the polyurethane resin having a crystalline melting point. When blended in an amount exceeding 50% by weight, the stability of the solvent is remarkably lowered, and when used as a planar heating element, the resistance value may be remarkably lowered at a temperature exceeding the melting point of the crystalline diol. . For these reasons, in order to improve the PTC characteristics, the crystalline diol itself in an amount of 50% by weight or less can be appropriately blended with the polyurethane resin.

  The crystalline polyester polyol constituting the polyurethane resin (I) having a crystalline melting point used in the present invention is preferably 85 to 300 parts by weight with respect to 100 parts by weight of the amorphous polyester polyol which is another constituent component. More preferably, it is 120-200 weight part with respect to 100 weight part of amorphous polyester polyol. If the crystalline polyester polyol is less than 85 parts by weight with respect to 100 parts by weight of the amorphous polyester polyol, the crystallinity may not be exhibited. On the other hand, when the amount of the crystalline diol is more than 300 parts by weight with respect to 100 parts by weight of the amorphous polyester diol, the crystallinity becomes strong and the solubility in a solvent may be extremely deteriorated.

  Polyisocyanates constituting the polyurethane resin (I) having a crystalline melting point used in the present invention include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, p-phenylene diisocyanate, 4,4′-diphenylmethane diisocyanate, m-phenylene diisocyanate, 3,3′-dimethoxy-4,4′-biphenylene diisocyanate, 2,6-naphthalene diisocyanate, 3,3′-dimethyl-4,4′-biphenylene diisocyanate, 4,4′-diphenylene diisocyanate 4,4'-diisocyanate diphenyl ether, 1,5-naphthalene diisocyanate, m-xylene diisocyanate, isophorone diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate Toluene diisocyanate, and the like.

  It is desirable that a urea bond be introduced into the polyurethane resin having a crystalline melting point used in the present invention. A urea bond is formed, for example, by reacting an isocyanate compound and a diamine compound. Introducing urea bonds increases the number of hydrogen-bonding sites between molecules, resulting in toughness of the coating film, and when used as a planar heating element, when it reaches the peak temperature beyond the melting point, it rapidly resists. It can suppress that a value falls. That is, resistance value stability at high temperatures can be ensured. This is because the hydrogen bonds in the molecule can maintain intermolecular cohesion even after the temperature is raised above the melting point, so that the conductive fillers dispersed in the system come into contact with each other again. It is expected to be no longer conducting.

  As a method for introducing a urea bond, in polyurethane polymerization, a method of reacting polyisocyanate and diamine in a lump, a method of adding a polyisocyanate group equivalent to diamine and diamine at the end of the reaction of polyurethane polymerization, Examples include a method in which an isocyanate group is excessively reacted with a diol to prepare a prepolymer, and then an equivalent amount of diamine is introduced with respect to the excess isocyanate group. Any method may be used for producing the polyurethane resin used in the present invention.

  Diamines used for introducing the urea bond include ethylenediamine, metaxylenediamine, 4,4′-diaminodiphenylmethane, 1,6-hexamethylenediamine, 1,8-octanediamine, 1,9-nonanediamine, and 1,10-decanediamine. 1,11-undecanediamine, 1,12-dodecanediamine, 2-methyl-1,5-pentanediamine, 3-methyl-1,5-pentanediamine, 2,2,4-trimethyl-1,6-hexane Diamine, 2,4,4-trimethyl-1,6-hexanediamine, 2-methyl-1,8-octanediamine, 5-methyl-1,9-nonanediamine, 3,4'-diaminodiphenyl ether, 4,4 ' -Diaminodiphenyl ether, 3,4'-diaminodiphenyl sulfone, 3,3'-diamino Phenylsulfone, 4,4′-diaminodiphenylsulfone, 4,4 ′-(p-phenylenediisopropylidene) bisaniline, 4,4 ′-[1,3-phenylenebis (1-methylethylidene)] aniline, 1, 4-bis (4-aminophenoxy) benzene, 1,3-bis (4-aminophenoxy) benzene, 1,3-bis (3-aminophenoxy) benzene, 2,2 ′-[4- (4-aminophenoxy) ) Phenyl] propane, 2,2 ′-[3- (3-aminophenoxy) phenyl] sulfone, 2,2 ′-[4- (4-aminophenoxy) phenyl] sulfone, 2,2′-bis [4- (4-Aminophenoxy)] phenylhexafluoropropane, 2,2-bis (4-aminophenyl) hexafluoropropane, 2- (3-aminophenyl) -2- (4-aminophenyl) propane, 4,4′-bis (4-aminophenoxy) biphenyl, bis [4- (4-aminophenoxy) phenyl] ether, and the like. Used as a mixture.

  The amount of urea bond in the polyurethane resin (I) having a crystalline melting point used in the present invention is preferably in the following range. The urea bond amount in the present invention means a urea group equivalent (eq / ton) per ton of resin, and is a value calculated from the monomer composition ratio of the polyurethane resin. As a preferable urea bond amount, 10-1000 (eq / ton) is preferable, More preferably, it is the range of 50-500 (eq / ton). If it is less than 10 (eq / ton), it does not contribute to the toughness of the coating film, and the PTC characteristics cannot maintain the intermolecular cohesive force after being heated above the melting point. There is a concern that the filler comes into contact again and becomes conductive. On the other hand, when it exceeds 1000 (eq / ton), the varnish stability tends to be remarkably deteriorated.

  The polyurethane resin (I) used in the present invention may be copolymerized, if necessary, with a chain extension component having a molecular weight of less than 5000 and having two or more functional groups that react with isocyanate groups in one molecule. Examples of the compound having a molecular weight of less than 1000 and having two or more functional groups that react with isocyanate groups include hexanediol, 1,2-propylene glycol, 1,3-propanediol, 1,2-butylene glycol, 1, 3-butylene glycol, 2,3-butylene glycol, 2,2-dimethyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 2,2,4-trimethyl-1,3-pentanediol 2-ethyl-1,3-hexanediol, 2,2-dimethyl-3-hydroxypropyl-2 ′, 2′-dimethyl-3-hydroxypropanoate, 2-normalbutyl-2-ethyl-1,3- Propanediol, 3-ethyl-1,5-pentanediol, 3-propyl-1,5-pentanediol, 2,2-diethyl 1,3-propanediol, 3-octyl-1,5-pentanediol, 3-phenyl-1,5-pentanediol, 2,5-dimethyl-3-sodium sulfo-2,5-hexanediol, monoethanolamine Etc. These can be used alone or in combination.

  The conductive paste of the present invention preferably has an F value of 25 to 80%. Preferably it is 35 to 70%, more preferably 40 to 65%. The F value is a numerical value indicating the filler mass part with respect to 100 mass parts of the total solid content contained in the paste, and is represented by F value = (filler mass part / solid mass part) × 100. The solid mass part referred to here includes all carbon particles other than the solvent, other fillers, resins including polyester resins, and other curing agents and additives. When the F value is less than 25%, the specific resistance tends to increase. Moreover, it exists in the tendency for adhesiveness and / or pencil hardness to fall. If it exceeds 80%, the PTC characteristics tend to deteriorate.

  In the conductive paste of the present invention, the conductive fine particles (II) are not particularly limited, but are preferably carbon particles from the viewpoint of specific resistance and PTC characteristics. The carbon particles used in the present invention are preferably spherical, and the shape is particularly preferably spherical in terms of specific resistance, PTC characteristics, and return characteristics. The term “spherical” as used herein means that when the carbon particles are enlarged and observed with an electron microscope, which will be described later, the cross section thereof is almost circular and the ratio of the minor axis to the major axis is 80% or more. More preferably, it is 90% or more.

  The average particle size of the carbon particles used in the present invention is preferably 30 μm or less, more preferably 10 μm or less, and most preferably 7 μm or less. The lower limit is preferably 0.1 μm or more, more preferably 1 μm or more. When the average particle diameter exceeds 30 μm, when screen printing is performed, the screen may be clogged, or the storage stability of the paste may be reduced due to sedimentation of the spherical carbon particles. If the average particle size is less than 0.1 μm, the conductivity may decrease, or the oil absorption may increase and the viscosity of the paste may increase, making it impossible to sufficiently fill the spherical carbon particles. Moreover, there exists a possibility that adhesiveness may fall or printability may deteriorate. As the spherical carbon particles, commercially available ones such as MC0520, MC1020 (manufactured by Nippon Carbon Co., Ltd.), GCP10 (manufactured by Unitika Ltd.) can be used.

  The conductive particles (II) are preferably contained at a ratio of 40 to 400 parts by weight with respect to 100 parts by weight of the polyurethane resin (I). In particular, in the case of carbon particles, the crystalline melting point 40 to 200 parts by mass are preferably included with respect to 100 parts by mass of the polyurethane-based resin (I) having a viscosity of 60 to 180 parts by mass, more preferably 80 to 170 parts from the coating film hardness and adhesion. Most preferably, parts by weight are included. When the amount is less than 40 parts by mass, desired conductivity is difficult to obtain, and the return characteristics tend to deteriorate. When the amount is more than 200 parts by mass, there is a tendency that the PTC characteristic tends to be lowered or dispersion becomes difficult.

  In the conductive paste of the present invention, conductive fine particles other than carbon particles may be further used. In other words, the known flaky silver powder, spherical silver powder, three-dimensional higher order silver powder, dendritic silver powder, graphite powder, carbon powder, nickel powder, copper powder, gold powder, palladium powder, aluminum powder, indium powder as long as the characteristics are not deteriorated However, it is preferable that the spherical carbon particles are contained at least 20% by mass, more preferably 30% by mass or more of the total amount of conductive fine particles. The upper limit is preferably 60% by mass or less, more preferably 40% by mass or less from the viewpoint of cost. Among these, particularly preferable other conductive fine particles include graphite powder and conductive carbon black. By using these carbon fillers and spherical carbon particles in combination, the specific resistance and the PTC characteristics can be freely controlled. In addition, a small amount of non-conductive filler such as silica powder, fumed silica, colloidal silica, talc, and barium sulfate may be blended for the purpose of adjusting paste viscosity.

  In addition to these, known inorganic substances may be added to the conductive paste of the present invention, for example, silicon carbide, boron carbide, titanium carbide, zirconium carbide, hafnium carbide, vanadium carbide, tantalum carbide, niobium carbide, tungsten carbide, Various carbides such as chromium carbide, molybdenum carbide, calcium carbide, diamond carbon lactam, various nitrides such as boron nitride, titanium nitride, zirconium nitride, various borides such as zirconium boride, titanium oxide (titania), calcium oxide, oxidation Various oxides such as magnesium, zinc oxide, copper oxide, aluminum oxide, silica, colloidal silica, various titanate compounds such as calcium titanate, magnesium titanate, strontium titanate, sulfides such as molybdenum disulfide, magnesium fluoride , Fluorocarbon Various metal soaps such as aluminum fluoride, aluminum stearate, calcium stearate, zinc stearate, magnesium stearate, talc, bentonite, talc, calcium carbonate, bentonite, kaolin, glass fiber, mica, etc. can be used. . Moreover, an antifoamer, a flame retardant, a tackifier, a hydrolysis inhibitor, a leveling agent, a plasticizer, an antioxidant, an ultraviolet absorber, a flame retardant, a pigment, and a dye can be used. Furthermore, carbodiimide, epoxy and the like can be used as appropriate as a resin degradation inhibitor. These can be used alone or in combination.

  The conductive paste of the present invention may contain a curing agent that can react with an organic resin. By blending the curing agent, although the PTC characteristics are lowered, it is expected to improve the physical properties of the coating film at a high temperature above the melting point. The curing agent capable of reacting with these resins is not particularly limited, but an isocyanate compound is particularly preferable from the viewpoint of adhesion, flex resistance, curability, and the like. Further, these isocyanate compounds are preferably used after being blocked from the viewpoint of storage stability. Examples of curing agents other than isocyanate compounds include known compounds such as amino resins such as methylated melamine, butylated melamine, benzoguanamine, and urea resin, acid anhydrides, imidazoles, epoxy resins, and phenol resins.

  Examples of the isocyanate compound include aromatic and aliphatic diisocyanates and trivalent or higher polyisocyanates, which may be either low molecular compounds or high molecular compounds. For example, tetramethylene diisocyanate, hexamethylene diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, dimer acid diisocyanate, isophorone diisocyanate or trimers of these isocyanate compounds, And excessive amounts of these isocyanate compounds and low molecular active hydrogen compounds such as ethylene glycol, propylene glycol, trimethylolpropane, glycerin, sorbitol, ethylenediamine, monoethanolamine, diethanolamine, and triethanolamine, or various polyester polyols, polyethers Polymer active water of polyols and polyamides Compounds such as reacted include terminal isocyanate group-containing compounds obtained.

  Examples of the isocyanate group blocking agent include phenols such as phenol, thiophenol, methylthiophenol, ethylthiophenol, cresol, xylenol, resorcinol, nitrophenol, and chlorophenol, oximes such as acetoxime, methyl ethyl ketoxime, and cyclohexanone oxime, Alcohols such as methanol, ethanol, propanol and butanol; halogen-substituted alcohols such as ethylene chlorohydrin and 1,3-dichloro-2-propanol; tertiary alcohols such as t-butanol and t-pentanol; -Lactams such as caprolactam, δ-valerolactam, γ-butyrolactam, β-propylolactam and the like, and other aromatic amines, imides, acetylacetates Emissions, acetoacetic ester, active methylene compounds such as malonic acid ethyl ester, mercaptans, imines, imidazoles, ureas, diaryl compounds, sodium bisulfite, etc. can be mentioned. Of these, oximes, imidazoles, and amines are particularly preferable from the viewpoint of curability.

  These crosslinking agents may be used in combination with known catalysts or accelerators selected according to the type.

  There are no limitations on the type of solvent used in the conductive paste of the present invention. For example, toluene, xylene, tetramethylbenzene, Solvesso 100, Solvesso 150, Solvesso 200, tetralin and other aromatic hydrocarbons, decalin, hexane, heptane Aliphatic hydrocarbons such as octane and decane, esters such as methyl acetate, ethyl acetate, isopropyl acetate and butyl acetate, alcohols such as methanol, ethanol, propanol, butanol and 2-ethylhexanol, acetone, methyl ethyl ketone and methyl Ketones such as isobutyl ketone, cyclohexanone, (di) ethylene glycol dimethyl ether, diethylene glycol monoethyl ether, dipropylene glycol diethyl ether, dioxane, diethyl ether, tetrahydride Various solvents such as ethers such as furan, cellosolves such as cellosolve acetate, ethyl cellosolve and butyl cellosolve, and carbitols such as carbitol and butyl carbitol can be used. Species or two or more are selected and used.

  As described above, the conductive paste of the present invention has PTC characteristics as long as it is at least 3 times the ratio of change in resistance at 80 ° C. and 30 ° C. (sheet resistance (80 ° C.) / Sheet resistance (30 ° C.)). Then, there is another important index for performance. It is called “return characteristics”. The return characteristics are the resistance value when the temperature is raised to 80 ° C. and then cooled to room temperature (25 ° C.), and the resistance value at room temperature (25 ° C.) before the temperature rise. Difference (= rate of change). In order to improve the return characteristics, it is preferable that the difference (rate of change) between the resistance value at room temperature before the temperature rise and the resistance value at room temperature after the temperature rise and after cooling is within ± 1 to 100%. . That is, even if the temperature rise and fall is repeated, it becomes an index that exhibits stable PTC characteristics.

  In addition to the PTC characteristics and return characteristics, the stability of the resistance value at high temperatures is also important. The stability of the resistance value at a high temperature means that there is no significant decrease in the resistance value when the temperature is raised to 80 ° C. and further raised to a higher temperature. The stability of the resistance value at high temperature is good because the resistance value after heating up to 120 ° C. is equal to or higher than the resistance value at 80 ° C. Also means a reduction of less than 20%. A significant decrease in resistance value in a high temperature range is not preferable from a safety standpoint because it conducts at a high temperature.

  The conductive paste of the present invention is printed on a plastic film such as a PET film (sheet) by a known method such as screen printing, rotary screen printing, gravure printing, transfer printing, roll coating, comma coating, flow coating or spray coating. It can be used for circuits and sheet heating elements.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely using an Example, this invention is not limited to these Examples. In the examples, the term “part” simply means “part by mass”. Each measurement item followed the following method.

1. Number average molecular weight Calculated from the results of GPC measurement at a column temperature of 30 ° C. and a flow rate of 1 ml / min using a water permeation gel permeation chromatography (GPC) 150c using tetrahydrofuran as an eluent, and measured in terms of polystyrene. Got the value. However, Showa Denko Co., Ltd. shodex KF-802, 804, 806 was used for the column.

2. Glass transition temperature (Tg) and melting point (Tm)
5 mg of the sample was put in an aluminum sample pan and sealed, and measured using a differential scanning calorimeter (DSC) DSC-220 manufactured by Seiko Instruments Inc. up to 200 ° C. at a heating rate of 20 ° C./min. The maximum peak temperature of heat of fusion was determined as the crystalline melting point. The glass transition temperature was determined by the temperature at the intersection of the base line extension below the glass transition temperature and the tangent that indicates the maximum slope at the transition.

3. Acid value 0.2 g of a sample was precisely weighed and dissolved in 20 ml of chloroform. Subsequently, it titrated with 0.01N potassium hydroxide (ethanol solution). A phenolphthalein solution was used as an indicator.

4). Adhesion A conductive paste was screen printed on a PET film that had been annealed to a thickness of 100 μm, a 25 × 200 mm pattern was printed, dried and cured at 150 ° C. for 30 minutes, and used as a test piece. The dry film thickness was adjusted to 20 to 30 μm. Evaluation was performed according to JIS K5600 5-6 using this test piece. Cellophane tape CT-12 (manufactured by Nichiban Co., Ltd.) was used as the adhesive tape.

5. Specific resistance The sheet resistance and film thickness were measured using the test piece produced in step 1, and the specific resistance was calculated. The sheet resistance was measured using a 4-terminal digital multimeter.

6). Pencil hardness The surface hardness was evaluated in accordance with JIS K5400 using the high-quality pencil specified in JIS S6006 using the test piece prepared in (1).

7). 3. PTC characteristics The sheet resistance was measured at 30 ° C. and 80 ° C. using the test piece prepared in (1), and evaluated by the resistance change magnification calculated by the following equation. The larger the number, the better the PTC characteristics.
Magnification of resistance change (times) = sheet resistance (80 ° C) / sheet resistance (30 ° C)

8). Return characteristics The PTC characteristics were repeatedly measured 5 times (repeated temperature increase and decrease from 30 ° C. to 80 ° C. 5 times) and then cooled to room temperature (25 ° C.) to measure the sheet resistance. Evaluated by difference.
○: Difference in initial resistance value (rate of change) within ± 100% △: Rate of change with respect to initial resistance value of ± 101 to 500%
×: The rate of change with respect to the initial resistance value is ± 500% or more

9. 5. Resistance value stability at high temperature In this method, the temperature was raised to 80 ° C. and then further compared to the resistance value at 80 ° C. after the temperature was raised to 120 ° C.
A: The resistance value at 120 ° C. is higher than the resistance value at 80 ° C. ○: The resistance value at 120 ° C. is equal to or less than 20% of the resistance value at 80 ° C. Δ: The resistance value at 120 ° C. is 80 ° C. Reduced by 20% or more and less than 40% compared to the resistance value ×: Resistance value at 120 ° C decreased by 40% or more compared with the resistance value at 80 ° C

10. Storage stability After the conductive paste was stored at 5 ° C. for 1 month, the viscosity was measured at 25 ° C. and evaluated by the change in viscosity.
○: almost the same value as the initial viscosity (less than 1.5 times the initial viscosity)
Δ: Thickening 1.5 to 2 times the initial viscosity ×: Remarkably thickening (over 2 times the initial viscosity)

Production Example of Resin Synthesis of Polyester Polyol (A) In a reaction vessel equipped with a stirrer, a condenser, and a thermometer, 100 parts of dimethyl terephthalate, 38 parts of dimethyl isophthalate, 93 parts of ethylene glycol, 73 parts of neopentyl glycol, tetrabutyl titanate 0 0.065 part was charged and transesterification was performed at 180 ° C. for 3 hours. Next, 61 parts of sebacic acid was charged, and an esterification reaction was further performed. Next, the pressure was gradually reduced to 1 mmHg or less, and polymerization was carried out at 240 ° C. for 1.5 hours. The composition of the obtained copolyester was terephthalic acid / isophthalic acid / sebacic acid / ethylene glycol / neopentyl glycol = 50/20/30/57/43 (molar ratio), number average molecular weight 2100, acid value 8 eq / ton. Tg was 10 ° C. and there was no crystalline melting point. The results are shown in Table 1.

Synthesis of polyester polyols (B) to (D) The polyester polyols (A) were synthesized in the same manner. Polyester polyols (B) to (C) had no crystalline melting point and were amorphous, while polyester polyols (D) to (E) had a crystalline melting point. The results are shown in Table 1.

Synthesis of polyurethane resin having crystal melting point Synthesis of polyurethane resin (a) In a reaction vessel equipped with a stirrer, a condenser and a thermometer, 1000 parts of polyester polyol (A) of the synthesis example was added to 630 parts of ethyl carbitol acetate and 210 parts of butyl cellosolve acetate. Dissolved at 80 ° C. Subsequently, after adding 250 parts of diphenylmethane diisocyanate, the reaction was carried out for 2 hours. Thereafter, 2410 parts of cyclohexanone and 2000 parts of Plaxel 240 (manufactured by Daicel Chemical Industries, melting point 59 ° C., number average molecular weight 4000) were added and reacted at 80 ° C. for 2 hours, and then dibutyltin dilaurate: 0.3 part was added as a catalyst. And reacted at 80 ° C. for 4 hours. Subsequently, the solution was diluted with 990 parts of cyclohexanone and 150: 5510 parts of Solvesso to obtain a polyurethane resin (a). The resulting polyurethane resin solution had a solid content concentration of 25.1 (% by weight). The number average molecular weight of the polyurethane resin (a) was 38000, the acid value was 8 eq / ton, and Tm (melting point) was 45 ° C.

Synthesis of Polyurethane Resin (b) 1000 parts of the polyester polyol (B) of the synthesis example was dissolved in 630 parts of ethyl carbitol acetate and 210 parts of butyl cellosolve acetate at 80 ° C. in a reaction vessel equipped with a stirrer, a condenser and a thermometer. Subsequently, after adding 250 parts of diphenylmethane diisocyanate, the reaction was carried out for 2 hours. Thereafter, 2910 parts of cyclohexanone and 2500 parts of HS2H-500S (manufactured by Toyokuni Oil Co., Ltd., melting point 70 ° C., number average molecular weight 5000) were added and reacted at 80 ° C. for 2 hours, and then 0.3 parts of dibutyltin dilaurate was added as a catalyst. And reacted at 80 ° C. for 4 hours. Next, the solution was diluted with 990 parts of cyclohexanone and 150: 5510 parts of Solvesso to obtain a polyurethane resin (b). The solid content concentration of the obtained polyurethane resin solution was 25.0 (% by weight). The number average molecular weight of the polyurethane resin (b) was 40000, the acid value was 10 eq / ton, and Tm was 56 ° C.

Synthesis of polyurethane resin (c) In a reaction vessel equipped with a stirrer, a condenser and a thermometer, 1000 parts of polyester polyol (B) of the synthesis example, HS2H-500S (manufactured by Toyokuni Oil Co., Ltd., melting point 70 ° C., number average molecular weight 5000) 500 parts Was dissolved in 1100 parts of cyclohexanone at 80 ° C. Subsequently, 148 parts of diphenylmethane diisocyanate was added and reacted for 2 hours. Thereafter, 0.3 part of dibutyltin dilaurate was added as a catalyst and reacted at 80 ° C. for 4 hours. Subsequently, the solution was diluted with 630 parts, Solvesso 150: 970 parts, ethyl carbitol acetate 1683 parts, and butyl cellosolve acetate 561 parts to obtain a polyurethane resin (c). The solid content concentration of the obtained polyurethane resin solution was 25.0 (% by weight). The number average molecular weight of the polyurethane resin (c) was 41000, the acid value was 11 eq / ton, and Tm was 55 ° C.

Synthesis of Polyurethane Resin (d) 1000 parts of polyester polyol (B) and 1000 parts of polyester polyol (D) of Synthesis Example were dissolved in 1448 parts of cyclohexanone at 80 ° C. in a reaction vessel equipped with a stirrer, a condenser and a thermometer. Next, after adding 172 parts of diphenylmethane diisocyanate, the reaction was carried out for 2 hours. Thereafter, 0.3 part of dibutyltin dilaurate was added as a catalyst and reacted at 80 ° C. for 4 hours. Subsequently, the solution was diluted with 833 parts of cyclohexanone and 150: 4235 parts of Solvesso to obtain a polyurethane resin (d). The solid content concentration of the obtained polyurethane resin solution was 25.0 (% by weight). The number average molecular weight of the polyurethane resin (d) was 44000, the acid value was 21 eq / ton, and Tm was 72 ° C.

Synthesis of polyurethane resin (e) In a reaction vessel equipped with a stirrer, a condenser, and a thermometer, 1000 parts of polyester polyol (B) and 1000 parts of polyester polyol (E) in the synthesis example were added to 1085 parts of ethyl carbitol acetate and 363 parts of butyl cellosolve acetate. Dissolved at 80 ° C. Next, after adding 172 parts of diphenylmethane diisocyanate, the reaction was carried out for 2 hours. Thereafter, 0.3 part of dibutyltin dilaurate was added as a catalyst and reacted at 80 ° C. for 4 hours. Subsequently, the solution was diluted with 2281 parts of cyclohexanone, 2090 parts of ethyl carbitol acetate and 697 parts of butyl cellosolve acetate to obtain a polyurethane resin (e). The solid content concentration of the obtained polyurethane resin solution was 25.0 (% by weight). The number average molecular weight of the polyurethane resin (e) was 45000, the acid value was 19 eq / ton, and Tm was 25 ° C.

Synthesis of Polyurethane Resin (f) 1000 parts of Polyester Polyol (B) of Synthesis Example was dissolved in 630 parts of ethyl carbitol acetate and 210 parts of butyl cellosolve acetate at 80 ° C. in a reaction vessel equipped with a stirrer, a condenser and a thermometer. Subsequently, after adding 250 parts of diphenylmethane diisocyanate, the reaction was carried out for 2 hours. Thereafter, 2010 parts of cyclohexanone and 1600 parts of Plaxel 240 (manufactured by Daicel Chemical Industries, melting point 59 ° C., number average molecular weight 4000) were added and reacted at 80 ° C. for 2 hours, and then 18 parts of diaminodiphenylmethane was added and the reaction was continued. Two hours later, 0.3 part of dibutyltin dilaurate was added as a catalyst, and the mixture was further reacted at 80 ° C. for 4 hours. Subsequently, the solution was diluted with 990 parts of cyclohexanone and 150: 5710 parts of Solvesso to obtain a polyurethane resin (f). The resulting polyurethane resin solution had a solid content concentration of 25.1 (% by weight). The number average molecular weight of the polyurethane resin (f) was 45000, the acid value was 12 eq / ton, the Tm was 46 ° C., and the urea bond amount was 70 eq / ton.

Synthesis of polyurethane resin (g) In a reaction vessel equipped with a stirrer, a condenser and a thermometer, 1000 parts of polyester polyol (B) of synthesis example, ODX688 which is an amorphous copolymerized polyester diol (manufactured by Dainippon Ink Co., Ltd.) 1500 parts, 50 parts of 1,6-hexanediol as a chain extender, 150 parts of neopentyl glycol, 2750 parts of ethyl carbitol acetate and 920 parts of butyl cellosolve acetate as solvents were charged and dissolved at 80 ° C. Subsequently, 760 parts of diphenylmethane diisocyanate (MDI) was added and the reaction was continued for 1 hour. Then, 0.8 part of dibutyltin dilaurate was added and further reacted at 80 ° C. for 4 hours. Thereafter, 5030 parts of ethyl carbitol acetate and 1670 parts of butyl cellosolve acetate were added and diluted to obtain a polyurethane resin (g). The solid content concentration of the obtained polyurethane resin solution was 25.0 (% by weight). The number average molecular weight of the polyurethane resin (g) was 42000, the acid value was 10 eq / ton, and Tg-12 ° C.

Synthesis of polyurethane resin (h) 20 parts of polyester polyol (A) 1000 parts of synthesis example and Plaxel 220 (manufactured by Daicel Chemical Industries, melting point 55 ° C., number average molecular weight 2000) in a reaction vessel equipped with a stirrer, a condenser and a thermometer Then, 570 parts of ethyl carbitol acetate and 190 parts of butyl cellosolve acetate were added and dissolved at 80 ° C. Next, 120 parts of diphenylmethane diisocyanate (MDI) was added and the reaction was continued for 1 hour. Then, 0.2 parts of dibutyltin dilaurate was added and the reaction was further carried out at 80 ° C. for 4 hours. Thereafter, 1196 parts of cyclohexanone, 1096 parts of ethyl carbitol acetate and 365 parts of butyl cellosolve acetate were added and diluted to obtain a polyurethane resin (h). The solid content concentration of the obtained polyurethane resin solution was 25.0 (% by weight). The number average molecular weight of the polyurethane resin (h) was 40000, the acid value was 10 eq / ton, and Tg was 25 ° C.

Synthesis of polyurethane resin (i) In a reaction vessel equipped with a stirrer, a condenser and a thermometer, 1000 parts of polyester polyol (B) of the synthesis example and 900 parts of Plaxel 210 (manufactured by Daicel Chemical Industries, melting point 47 ° C., number average molecular weight 1000) Then, 1680 parts of ethyl carbitol acetate and 560 parts of butyl cellosolve acetate were added and dissolved at 80 ° C. Next, after adding 340 parts of diphenylmethane diisocyanate (MDI) and continuing the reaction for 1 hour, 0.3 part of dibutyltin dilaurate was added and further reacted at 80 ° C. for 4 hours. Thereafter, 2350 parts of cyclohexanone and 150: 2130 parts of Solvesso were added for dilution to obtain a polyurethane resin (i). The solid content concentration of the obtained polyurethane resin solution was 25.0 (% by weight). The number average molecular weight of the polyurethane resin (i) was 36000, the acid value was 12 eq / ton, and Tg-5 ° C.

  Table 2 summarizes the physical properties of the polyurethane resins (a) to (i).

Example 1
150 parts of MC0520 (manufactured by Nippon Carbon Co., Ltd.) as conductive fine particles, polyurethane resin solution (a) synthesized above as a resin (solvent composition (mass) ratio: ethyl carbitol acetate / butyl cellosolve acetate / cyclohexanone / solvesso 150 = 6 / 2/35/57) 400 parts (solid content 25%), 6.0 parts BYK-354 (Big Chemie Japan Co., Ltd.) as a leveling agent were added, and Solvesso 150 was further added, followed by sufficient premixing. Subsequently, it disperse | distributed 3 times with the chilled 3 rolls, and the electrically conductive paste was obtained. The obtained conductive paste was slightly black and had a good viscosity. The specific resistance was 6.6 Ω · cm, the PTC characteristic was 8.5 times as good, and the return characteristic, resistance value stability at high temperature, and storage stability were all good.

Examples 2-9
Evaluation was performed in the same manner as in Example 1. The results are shown in Table 3. All pastes showed good PTC characteristics, return characteristics, resistance value stability at high temperature, and storage stability.

The numbers in Tables 3 and 4 have the following meanings.
1) Organic resin: EVA, commercially available ethylene vinyl acetate having a vinyl acetate content of 30 mol% was used as it was.
2) Carbon a: MC0520 (spherical carbon (average particle diameter 5 μm, sphericity 95)) (manufactured by Nippon Carbon Co., Ltd.)
3) Carbon b: MC1020 (spherical carbon (average particle diameter 10 μm, sphericity 93)) (manufactured by Nippon Carbon Co., Ltd.)
4) Carbon c: # 4500 (conductive carbon (average particle size 0.04 μm)) (manufactured by Tokai Carbon Co., Ltd.)
5) Additive a: LMS100 (particle size 6 μm) (Fujitalc)
6) Additive b: Silo Hovic 603 (particle diameter 6.7 μm) (manufactured by Fuji Silysia)
7) Additive c: Sodium stearate (manufactured by NOF Corporation)
8) Additive d: Plaxel 240 (polycaprolactone diol (number average molecular weight 4000)) (manufactured by Daicel Chemical Industries)
9) Additive e: Carbodilite V-07 (Nisshinbo Co., Ltd.)
10) Leveling agent: BYK-354 (by Big Chemie Japan)
11) ECA: Ethyl carbitol acetate 12) BCA: Butyl cellosolve acetate

Comparative Example 1
150 parts of MC0520 (manufactured by Nippon Carbon Co., Ltd.) as conductive fine particles, 400 parts of the polyurethane resin solution (d) synthesized above as a resin (solvent composition (mass) ratio: ethyl carbitol acetate / butyl cellosolve acetate = 75/25) (Solid content 25%), 6.0 parts of BYK-354 (Big Chemie Japan Co., Ltd.) as a leveling agent were added, 75 parts of ethyl carbitol acetate and 25 parts of butyl cellosolve acetate were added, and the mixture was sufficiently premixed. Subsequently, it disperse | distributed 3 times with the chilled 3 rolls, and the electrically conductive paste was obtained. The obtained conductive paste was slightly black and had a good viscosity. The specific resistance was 4.8 Ω · cm. The PTC characteristic was as bad as 2.7 times.

Comparative Examples 2-7
Evaluation was performed in the same manner as in Comparative Example 1. The results are shown in Table 3. None of the PTC characteristics, return characteristics, storage stability, and the like satisfied the performance superior to the examples.

The conductive paste of the present invention has extremely good PTC characteristics, and further provides a planar heating element having good conductivity, return characteristics, resistance stability at high temperatures, and the like.

Claims (13)

A conductive paste for a planar heating element comprising a polyurethane resin (I) having a crystalline melting point and conductive particles (II) , wherein the polyurethane resin (I) reacts at least an amorphous component and a crystalline component. A conductive paste for a planar heating element, characterized in that   2. The conductive paste for a planar heating element according to claim 1, wherein the polyurethane resin (I) has a crystal melting point of 20 to 100 ° C. 3.   The polyurethane resin (I) is obtained by reacting at least an amorphous polyester polyol, a crystalline polyester polyol having a melting point of 5 to 120 ° C, and a polyisocyanate as main components. Conductive paste for sheet heating element. The conductive paste for a planar heating element according to any one of claims 1 to 3 , wherein the polyurethane resin (I) is a crystalline polyurethane urea further containing a urea bond. The conductive paste for a planar heating element according to claim 4 , wherein the amount of urea bonding of the crystalline polyurethane urea is in the range of 10 to 1000 eq / ton. The conductive paste for a planar heating element according to any one of claims 1 to 5 , wherein the polyurethane resin (I) is soluble in a solvent. The conductive paste for a planar heating element according to any one of claims 3 to 6 , wherein the number average molecular weight of the crystalline polyester polyol constituting the polyurethane resin (I) is in the range of 1200 to 20000. Crystalline polyester polyols constituting the polyurethane resin (I) is, according to any one of claims 3-7, characterized in that it is 85 to 300 parts by weight of copolymer relative to 100 parts by weight of amorphous polyester polyol Conductive paste for sheet heating element. 9. The conductive sheet for a planar heating element according to claim 3 , further comprising 50 parts by weight or less of a crystalline polyester polyol when the polyurethane resin (I) is 100 parts by weight. Sex paste. The conductive paste for planar heating elements according to any one of claims 1 to 9 , wherein the conductive particles (II) are contained at a ratio of 40 to 400 parts by weight with respect to 100 parts by weight of the polyurethane resin (I). The conductive paste for a planar heating element according to any one of claims 1 to 10 , wherein the conductive particles (II) are spherical carbon and have an average particle diameter of 0.1 to 30 µm. Printed circuits using planar heating element conductive paste according to any one of claims 1 to 11. A planar heating element using a planar heating element conductive paste according to any one of claims 1 to 11.