KR20100133407A - Conductive paste for planar heating element, and printed circuit and planar heating element using same - Google Patents

Abstract

[PROBLEMS] The present invention has good solvent solubility while using a polymer having a crystal melting point as a resin, and has good resistivity and PTC characteristics even after repeated heating, and does not suddenly lower the resistance even when the temperature is raised above the melting point. Provided is a conductive paste for a planar heating element.
The present invention is an electrically conductive paste for a planar heating element comprising a polyurethane resin (I) having a crystalline melting point and conductive particles (II), and preferably a crystal melting point of the polyurethane resin (I) is 20 to 100 ° C. Preferably, the polyurethane resin (I) relates to an electrically conductive paste for a planar heating element in which at least an amorphous component and a crystalline component are reacted.

Description

Conductive paste for planar heating element, printed circuit using same, planar heating element {CONDUCTIVE PASTE FOR PLANAR HEATING ELEMENT, AND PRINTED CIRCUIT AND PLANAR HEATING ELEMENT USING SAME}

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

Planar heating elements are used for floor heating, antifogging of automobiles and bathroom mirrors, and thermal insulation for pets and houseplants. Among them, the surface heating element having a self-temperature control function, that is, PTC characteristic, can continuously adjust temperature compared with the heating element without PTC characteristic, and the number of parts is reduced because thermistor or the like is unnecessary. It is widely used for the above uses. Usually, such a planar heating element is composed of a resin and a conductive material. As the temperature of the planar heating element rises, the resin causes volume expansion, thereby blocking the conduction between the conductive materials, thereby exhibiting PTC characteristics.

Conventionally, a planar heating element having such a PTC characteristic is obtained by kneading a conductive material containing carbon black, graphite, metal powder, or the like into an olefinic resin, or by dispersing or dissolving a resin and a conductive material in a solvent. Etc. are proposed (for example, patent document 1). In addition, as the method of manufacturing the planar heating element, the former method by extrusion molding or press molding and the latter method by applying to the substrate by means of screen printing or the like have been used, but the shape of the planar heating element can be freely designed. In view of the latter method, the latter method is often used, and paste type is widely used to enable screen printing.

In paste type, it is proposed to use polymer resin, such as ethylene-vinyl acetate copolymer (EVA), as a base polymer (for example, patent document 2). It is said that the ethylene part in a base polymer shows a PTC characteristic, and the characteristic which shows the solvent solubility of a vinyl acetate part is suitable as an electrically conductive paste material for surface heating elements. In this case, in order to make solvent solubility compatible with PTC characteristics, it is necessary to adjust the vinyl acetate content of EVA. However, when the copolymerization ratio of vinyl acetate is increased to improve solubility, the PTC characteristics are lowered. On the contrary, when the copolymerization ratio of vinyl acetate is reduced, the PTC characteristic becomes good, but there is a problem that the solvent solubility deteriorates.

Moreover, the electrically conductive paste which improved PTC characteristic by using resin whose glass transition temperature is 50 degrees C or less is proposed (for example, patent document 3). However, in this case, when voltage is repeatedly applied, PTC characteristic tends to be reduced. This is considered to be one of the reasons that when the base resin is exposed to 40 ° C. to 70 ° C., which becomes the use temperature of the planar heating element, for a long time, a minute flow part occurs in the resin, and the dispersion structure of the conductive fine particles changes.

Moreover, the electrically conductive paste which combined crystalline resin is proposed (for example, patent document 4). In this case, by blending the crystalline resin having a large volume change before and after melting, the PTC characteristic can be improved, but the greatest difficulty in preparing the ink composition or paste-like PTC composition as the base polymer is, It is compatible with the solvent solubility of the base polymer and the PTC properties. That is, in order to form an ink or paste composition, it is indispensable to dissolve the base polymer in a suitable solvent. However, when the crystallinity of the polymer is high, the PTC property is excellent, but it is difficult to dissolve in the solvent. Likely to be poor, but with poor PTC properties, both solvent solubility and PTC properties are at opposite performances. For this reason, the electrically conductive paste which combined such a crystalline resin cannot necessarily be fully satisfied in any of solvent solubility and a PTC characteristic. In addition, since the solvents that can be used are very limited, there are problems in terms of versatility.

Moreover, when a crystalline resin is used, after reaching a peak temperature beyond melting | fusing point, a resistance value may fall rapidly. This is considered to be caused by the fact that when the crystalline polymer is melted and the temperature rises above the melting point, the conductive fillers dispersed therein are brought into contact with each other again. When the PTC composition having such a property is raised above the peak temperature due to any factor, as a result of the loss of the self-temperature control function and the large current flowing, the temperature gradually increases and eventually leads to burnout. There may be.

In order to improve the property of rapidly lowering the resistance value again after reaching the peak temperature as described above, in the conventional crystalline olefin resin-based PTC composition, after press molding into a sheet form, radiation such as electron beams or γ-rays is applied. It irradiates and crosslinks resin. However, such irradiation of radiation and the like is not only expensive, but also leaves active radicals in the resin depending on the conditions, and may significantly deteriorate heat resistance and durability, requiring careful management of manufacturing conditions and cost problems. I had.

Japanese Patent Laid-Open No. 1-304704 Japanese Patent Publication No. 10-183039 Japanese Patent Laid-Open No. 2000-86872 Japanese Patent Laid-Open No. 2001-76850

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 a resin, the solvent solubility is good, the specific resistance and PTC characteristics are good even when repeated heating is repeated, and even if the temperature rises above the melting point, there is no sudden decrease in the resistance value of the planar heating element conductive paste To provide.

As a result of earnestly examining in order to solve the above problems, the inventors have found that by using a polyurethane resin having a crystal melting point as a binder, the PTC properties and conductivity in the high temperature region can be remarkably improved, and the present invention has been reached. That is, in the present invention, after maintaining the solvent solubility, the PTC characteristic is very good, and the return characteristic of returning the specific resistance to the original value is good even after repeatedly raising and lowering the temperature. The electrically conductive paste for planar heating elements which does not fall can be provided.

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

(1) The electrically conductive paste for planar heating elements containing polyurethane resin (I) and electroconductive particle (II) which have a crystalline melting point.

(2) The conductive paste for a planar heating element according to (1), wherein the crystal 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) reacts at least an amorphous component with a crystalline component.

(4) The above-mentioned (1) or (2), wherein the polyurethane resin (I) reacts 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. A conductive paste for planar heating elements to be used.

(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 urea bonding amount of the crystalline polyurethane urea is in a range of 10 to 1000 eq / ton.

(7) The conductive paste for planar heating elements 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) In any one of said (4)-(8), 85-300 weight part of crystalline polyester polyols which comprise a polyurethane resin (I) are copolymerized with respect to 100 weight part of amorphous polyester polyols. A conductive paste for planar heating elements, characterized by the above-mentioned.

(10) When the polyurethane resin (I) is 100 parts by weight, the crystalline polyester polyol is further contained 50 parts by weight or less in any one of the above (4) to (9). Conductive paste for heating element.

(11) The electrically conductive paste for planar heating elements in any one of said (1)-(10) in which electroconductive particle (II) is contained in the ratio of 40-400 weight part with respect to 100 weight part of polyurethane resins (I).

(12) The conductive paste for planar heating elements according to any one of (1) to (11), wherein the conductive particles (II) are spherical carbons, and their average particle diameter is 0.1 to 30 µm.

(13) The printed circuit using the electrically conductive paste for planar heating elements in any one of said (1)-(12).

The planar heating element using the electrically conductive paste for planar heating elements in any one of said (1)-(12).

The electrically conductive paste of this invention has favorable basic physical properties, such as electroconductivity, PTC characteristic, return characteristic, adhesiveness, and bend resistance, and is suitable for a planar heating element use.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of the electrically conductive paste of this invention is described in detail. The electrically conductive paste of this invention is good in storage stability, and provides favorable PTC characteristic. The PTC characteristic means a characteristic in which the circuit resistance increases with an increase in temperature, and in the present invention, as shown in the examples, the magnification of the resistance change at, for example, 80 ° C and 30 ° C (sheet resistance (80 ° C)). / Sheet resistance (30 占 폚) is defined as "has a PTC characteristic". As a PTC characteristic, 5 or more of the said magnifications are preferable, More preferably, it is 10 or more, More preferably, it is 100 or more. The upper limit is not particularly limited, but is generally 50000 or less. On the other hand, when producing a planar heating element by a printing method, since the dry film thickness is usually limited to 20 micrometers or less, the resistivity considerably lower than the electrically conductive resin composition of an extrusion molding system is calculated | required. As a specific resistance of the electrically conductive paste of this invention, 600 ohm * cm or less is preferable, More preferably, it is 450 ohm * cm or less, More preferably, it is 400 ohm * cm or less. The lower limit is not particularly limited, but is generally 1 × 10 ^-2 Ω · cm or more.

It is preferable that the polyurethane resin (I) used by this invention has a crystalline melting point. The term "having a crystal melting point" as used 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 crystal melting point, the PTC characteristic is remarkably improved with the change in the volume of the polymer in the vicinity of the crystal 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. If it is 100 degreeC or more, since the solubility with respect to a solvent will fall remarkably, operation | movement, such as heat-melting immediately before, will be needed, and workability tends to deteriorate at the time of manufacture. On the other hand, when melting | fusing point is lower than 20 degreeC, resin may expand | swell at room temperature vicinity, and resistance value may become unstable. Moreover, in the electrically conductive paste of this invention, as resin other than the polyurethane which has a crystalline melting point, other urethane resin, polyester resin, an epoxy resin, a phenol resin, an acrylic resin, a styrene-acrylic resin, a styrene-butadiene copolymer, Polystyrene, polyamide resin, polycarbonate resin, and ethylene-vinyl acetate copolymer resin can also be used together. Although the kind is not restrict | limited when using said resin together, A polyester resin and a polyurethane resin are preferable from a viewpoint of adhesiveness with respect to a base material, bending resistance, and solvent solubility. The said combined resin may or may not have a crystalline melting point.

As for the number average molecular weight of the polyurethane resin (I) which has the crystal melting point used by this invention, 3000 or more are preferable from a viewpoint of bending resistance, More preferably, it is 8000 or more. If the number average molecular weight is less than 3000, it is difficult to obtain good bend resistance, the paste viscosity may decrease, and printability may decrease. Although an upper limit is not specifically limited, 100,000 or less are preferable from a paste viscosity and solubility viewpoint.

It is preferable that the polyurethane resin (I) which has a crystal melting point used by this invention made the amorphous component, the crystalline component, and the chain extending component react at least. The term "amorphous component" as used herein means that no peak of heat of fusion exists when the differential scanning calorimetry (DSC) is measured by the method described later with only that component. It exists. From the diversity and reactivity of the compound, an amorphous polyol is preferred as the amorphous component, a crystalline polyol as the crystalline component, and polyisocyanate is preferred as the chain extender.

Examples of the amorphous polyol include polyether polyols and polyester polyols, but polyester polyols are preferred from the degrees of freedom of molecular design. Amorphous polyesterpolyols are obtained by condensation of dicarboxylic acids with polyols. Examples of the dicarboxylic acid used include aliphatic compounds such as terephthalic acid, isophthalic acid, orthophthalic acid, 2,6-naphthalenedicarboxylic acid, succinic acid, glutaric acid, adipic acid, sebacic acid, dodecanedicarboxylic acid, and azelaic acid. Dicarboxylic acid, dibasic acid having 12 to 28 carbon atoms, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 4-methylhexa Hydrophthalic anhydride, 3-methylhexahydrophthalic anhydride, 2-methylhexahydrophthalic anhydride, dicarboxy hydrogenated bisphenol A, dicarboxy hydrogenated bisphenol S, dimer acid, hydrogenated dimer acid, hydrogenated naphthalenedicarboxylic acid, Although hydroxycarboxylic acids, such as alicyclic dicarboxylic acid, such as tricyclodecanedicarboxylic acid, hydroxybenzoic acid, and lactic acid, are mentioned, From a viewpoint of strength, heat resistance, durability, such as moisture resistance, thermal shock resistance, etc. , Full acid It is preferable that 40 mol% or more of aromatic dicarboxylic acids are copolymerized in powder. More preferably, it is 50 mol% or more. Moreover, in the range which does not impair the effect of this invention, polyhydric carboxylic acids, such as trimellitic anhydride and a pyromellitic dianhydride, unsaturated dicarboxylic acids, such as a fumaric acid, and 5-sulfoisophthalic acid salt, etc. The sulfonic acid metal base containing dicarboxylic acid can also be used together.

Polyols used include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, neopentylglycol, 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- cyclohexane dimethanol, 1, 3- cyclohexane dimethanol, 1,2-cyclohexane dimethanol, dimer diol, etc. are mentioned. Moreover, you may use together polyhydric polyols, such as a trimethylol ethane, a trimethylol propane, a glycerin, pentaerythritol, polyglycerol, in the range which does not impair the effect of this invention.

Examples of the crystalline polyol constituting the polyurethane resin (I) having a crystal melting point used in the present invention include polyether polyols, polyester polyols, and the like, but polyester polyols are preferred from the degrees of freedom of molecular design. Crystalline polyester polyol is obtained by condensation of dicarboxylic acid and polyol. Examples of the dicarboxylic acid used include aliphatic compounds such as terephthalic acid, isophthalic acid, orthophthalic acid, 2,6-naphthalenedicarboxylic acid, succinic acid, glutaric acid, adipic acid, sebacic acid, dodecanedicarboxylic acid, and azelaic acid. Dicarboxylic acid, dibasic acid having 12 to 28 carbon atoms, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 4-methylhexa Hydrophthalic anhydride, 3-methylhexahydrophthalic anhydride, 2-methylhexahydrophthalic anhydride, dicarboxy hydrogenated bisphenol A, dicarboxy hydrogenated bisphenol S, dimer acid, hydrogenated dimer acid, hydrogenated naphthalenedicarboxylic acid, Although hydroxycarboxylic acids, such as alicyclic dicarboxylic acid, such as tricyclodecanedicarboxylic acid, hydroxybenzoic acid, and lactic acid, are mentioned, From a viewpoint of strength, heat resistance, durability, such as moisture resistance, thermal shock resistance, etc. , Full acid It is preferable that 40 mol% or more of aromatic dicarboxylic acids are copolymerized in powder. More preferably, it is 50 mol% or more. In addition, it is preferable that aromatic dicarboxylic acid is terephthalic acid. Moreover, in the range which does not impair the effect of this invention, polyhydric carboxylic acids, such as trimellitic anhydride and a pyromellitic dianhydride, unsaturated dicarboxylic acids, such as a fumaric acid, and 5-sulfoisophthalic acid salt, etc. The sulfonic acid metal base containing dicarboxylic acid can also be used together.

Polyols used include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, neopentylglycol, 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- cyclohexane dimethanol, 1, 3- cyclohexane dimethanol, 1,2-cyclohexane dimethanol, dimer diol, etc. are mentioned. Moreover, you may use together polyhydric polyols, such as a trimethylol ethane, a trimethylol propane, a glycerin, pentaerythritol, polyglycerol, in the range which does not impair the effect of this invention.

Moreover, in consideration of versatility and handleability, for example, crystalline polycaprolactone diol, Fraxel 230, Fraxel 240, Fraxel CD220, Fraxel H1P (manufactured by Daicel Chemical Industries, Ltd.), DYNACOLL7330 and DYNACOLL7340, which are crystalline copolyesters, Commercial items, such as DYNACOLL7390 (made by Degussa) and HT-310, HT-400, HS2H-350S, HS2H-500S, and HS2H-1000S (made by Hokoku Seyou Co., Ltd.) which are crystalline copolyesters, can also be used. . These may be used independently and there is no problem even if it uses 2 or more types together in order to adjust melting | fusing point.

As crystalline diol which comprises the polyurethane resin which has a crystalline melting point used by this invention, it is preferable that the melting point is the range of 5-120 degreeC, More preferably, it is the range of 20-100 degreeC. If melting | fusing point is less than 5 degreeC, melting | fusing point as a polyurethane becomes low, and when used as a surface heating element, the resistance value at room temperature may become unstable. On the other hand, when melting | fusing point exceeds 120 degreeC, not only handleability is bad, but melting | fusing point as a polyurethane becomes high, and there exists a possibility that solubility to a solvent may deteriorate. In this invention, 2 or more types of crystalline diol which exists in the range of said melting | fusing point can also be used together, and crystalline diol which exists in the range of said melting | fusing point and crystalline diol outside the range can also be used together.

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 number average molecular weight, and more preferably in the range of 4000 to 10000. If number average molecular weight is less than 1000, crystallinity may not express. On the other hand, when it is 20000 or more, it may not only remain uncopolymerized but it may increase crystallinity and the solubility to a solvent may deteriorate. In this invention, 2 or more types of crystalline diol which exists in the range of the said number average molecular weight can also be used together, and crystalline diol which exists in the range of said number average molecular weight and crystalline diol outside the range can also be used together.

In addition to the polyurethane resin (I) which has a crystalline melting point, the said electrically conductive paste of this invention can mix and use the said crystalline diol. The crystalline diol may be contained in the 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 crystal melting point. When the amount exceeds 50% by weight, not only the solvent stability is significantly lowered, but also when used as a surface heating element, the resistance value may be significantly lowered at a temperature exceeding the melting point of the crystalline diol. For these reasons, in the sense of improving PTC properties, the crystalline diol itself in an amount of 50% by weight or less with respect to the polyurethane resin can be appropriately blended.

It is preferable that the crystalline polyester polyol which comprises the polyurethane resin (I) which has the crystal melting point used by this invention is 85-300 weight part with respect to 100 weight part of amorphous polyester polyol which is another structural component. More preferably, it is 120-200 weight part with respect to 100 weight part of amorphous polyester polyols. If the crystalline polyester polyol is less than 85 parts by weight with respect to 100 parts by weight of the amorphous polyester polyol, crystallinity may not be expressed. On the other hand, when 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 deteriorate very much.

Examples of the polyisocyanate constituting the polyurethane resin (I) having a crystal melting point used in the present invention include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, p-phenylene diisocyanate, and 4,4'-diphenyl Methane diisocyanate, m-phenylenedi isocyanate, 3,3'-dimethoxy-4,4'-biphenylene diisocyanate, 2,6-naphthalenedi isocyanate, 3,3'-dimethyl-4,4'-biphenyl Rendiisocyanate, 4,4'- diphenylene diisocyanate, 4,4'- diisocyanate diphenyl ether, 1, 5- naphthalene diisocyanate, m-xylene diisocyanate, isophorone diisocyanate, tetramethylene diisocyanate, hexamethylene Diisocyanate, toluene diisocyanate, etc. are mentioned.

It is preferable that the urea bond is introduce | transduced into the polyurethane resin which has the crystal melting point used by this invention. Urea bonds are formed, for example, by reacting an isocyanate compound with a diamine compound. By introducing urea bonds, the sites of intermolecular hydrogen bond formation are increased, the toughness of the coating film is obtained, and when used as a surface heating element, it is possible to suppress the rapid decrease in resistance after reaching the peak temperature beyond the melting point. have. That is, stability of resistance value at high temperature can be ensured. It is expected that this is because the intermolecular cohesion force can be maintained even after the temperature rises above the melting point by having a hydrogen bond in the molecule, so that conductive fillers dispersed in the system do not come into contact with each other again.

As a method for introducing a urea bond, in a polyurethane polymerization, a method of reacting polyisocyanate and diamine in a batch, a method of adding a polyisocyanate group equivalent to diamine and diamine and reacting at the end of the polyurethane polymerization reaction, and also diol After an isocyanate group is made to react too much with respect to, and a prepolymer is produced, the method etc. which introduce | transduce equivalent diamine with respect to an excess isocyanate group are mentioned. At the time of preparation of the polyurethane resin used by this invention, you may use any method.

Examples of the diamine used to introduce the urea bond include ethylenediamine, methaxylenediamine, 4,4'-diaminodiphenylmethane, 1,6-hexamethylenediamine, 1,8-octanediamine, 1,9-nonanediamine, 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-hexanediamine, 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'-diaminodiphenylsulfone, 3,3'-diaminodiphenylsulfone, 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, etc. are mentioned, These are used individually or in mixture of 2 or more types.

It is preferable that the amount of urea bonds in the polyurethane resin (I) which has the crystal melting point used by this invention is the following range. In addition, the urea bond amount in this invention means urea group equivalent (eq / ton) per 1 ton of resin, and is a value computed from the monomer composition ratio of a polyurethane resin. As a preferable amount of urea bond, 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), not only does it contribute to the toughness of the coating film, but also after the temperature rises above the melting point as a PTC characteristic, the intermolecular cohesion force cannot be maintained, so that the conductive filler may be brought into contact again. have. On the other hand, when it exceeds 1000 (eq / ton), the varnish stability tends to be significantly deteriorated.

The polyurethane resin (I) used by this invention may copolymerize the chain extending component of molecular weight less than 5000 which has 2 or more of functional groups which react with an isocyanate group in 1 molecule as needed. Examples of the compound having a molecular weight of less than 1000 having two or more functional groups reacting with an isocyanate group in one molecule include hexanediol, 1,2-propylene glycol, 1,3-propanediol, 1,2-butylene glycol, and 1,3-butyl Ethylene 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-pentane Diol, 3-phenyl-1,5-pentanediol, 2,5-dimethyl-3-sodium sulfo-2,5-hexanediol, monoethanolamine and the like. These can be used individually or in combination.

It is preferable that the F value of the electrically conductive paste of this invention is 25 to 80%. Preferably it is 35 to 70%, More preferably, it is 40 to 65%. F value is a numerical value which shows the filler mass part with respect to 100 mass parts of total solids contained in a paste, and is represented by F value = (filler mass part / solid content mass part) x100. Solid mass part here includes all carbon particles other than a solvent, another filler, resin containing polyester-type resin, and other hardening | curing agents and additives. If the F value is less than 25%, the specific resistance tends to increase. Moreover, there exists a tendency for adhesiveness and / or pencil hardness to fall. When it exceeds 80%, there exists a tendency for a PTC characteristic to fall.

In the electrically conductive paste of this invention, although electroconductive fine particle (II) is not specifically limited, It is preferable that it is carbon particle from a viewpoint of a specific resistance and a PTC characteristic. It is preferable that the carbon particle used by this invention is spherical, and it is especially preferable that the shape is spherical from a viewpoint of a specific resistance, a PTC characteristic, and a return characteristic. The spherical shape here means that when the carbon particle is expanded and observed with the electron microscope mentioned later, the cross section is almost circular and the ratio of the short diameter and long diameter is 80% or more. More preferably, it is 90% or more.

The average particle diameter 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. As for a minimum, 0.1 micrometer or more is preferable, More preferably, it is 1 micrometer or more. When the average particle diameter exceeds 30 µm, when screen printing, clogging may occur on the screen or the storage stability of the paste due to sedimentation of the spherical carbon particles may decrease. If the average particle diameter is less than 0.1 µm, the conductivity may decrease, the oil absorption amount may increase, the viscosity of the paste may increase, and the spherical carbon particles may not be sufficiently filled. Moreover, there exists a possibility that adhesiveness may fall or printability may deteriorate. As spherical carbon particles, those commercially available such as MC0520, MC1020 (manufactured by Nippon Carbon Co., Ltd.), GCP10 (manufactured by Unitica Co., Ltd.) can be used.

It is preferable that electroconductive particle (II) is contained in the ratio of 40-400 weight part with respect to 100 weight part of polyurethane resins (I), In particular, in the case of carbon particle, in order to exhibit electroconductivity, it is a polyurethane-type resin which has a crystalline melting point ( I) It is preferable to contain 40-200 mass parts with respect to 100 mass parts, It is more preferable that 60-180 mass parts is contained from dispersibility, It is most preferable that 80-170 mass parts is contained from coating film hardness and adhesiveness. . When less than 40 mass parts, desired electroconductivity is hard to be obtained and there exists a tendency for a return characteristic to deteriorate. When more than 200 mass parts, there exists a possibility that a PTC characteristic may fall or dispersion becomes difficult.

Electroconductive fine particles other than carbon particle can also be used for the electrically conductive paste of this invention. That is, known flake silver powder, spherical silver powder, silver powder of three-dimensional high order structure, dendritic silver powder, graphite powder, carbon powder, nickel powder, copper powder, gold powder, palladium powder, in the range which does not reduce a characteristic, Although aluminum powder, indium powder, etc. can also be used together, it is preferable to contain the said spherical carbon particle at least 20 mass% or more more preferably 30 mass% or more of the total amount of electroconductive fine particles. As for an upper limit, 60 mass% or less is preferable from a cost point, More preferably, it is 40 mass% or less. Among these, especially preferable other electroconductive fine particles are graphite powder and electroconductive carbon black. By using together these carbon-type filler and spherical carbon particle, a specific resistance and PTC characteristic can be adjusted freely. 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, a known inorganic substance 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, and chromium carbide , Carbides such as 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 (titanium), calcium oxide, magnesium oxide, zinc oxide , Various oxides such as copper oxide, aluminum oxide, silica, colloidal silica, various titanic compounds such as calcium titanate, magnesium titanate and strontium titanate, sulfides such as molybdenum disulfide, various fluorides such as magnesium fluoride and carbon fluoride, aluminum stearate , Various metal soaps such as calcium stearate, zinc stearate, magnesium stearate, talc, Bentonite, talc, calcium carbonate, bentonite, kaolin, glass fibers, mica and the like can be used. Moreover, an antifoamer, a flame retardant, a tackifier, a hydrolysis inhibitor, a leveling agent, a plasticizer, antioxidant, a ultraviolet absorber, a flame retardant, a pigment, and dye can be used. Moreover, carbodiimide, an epoxy, etc. can also be used suitably as a resin decomposition inhibitor. These can be used individually or in combination.

The electrically conductive paste of this invention can also mix | blend the hardening | curing agent which can react with organic resin. By mix | blending a hardening | curing agent, although PTC characteristic falls, the improvement of coating-film physical property at high temperature beyond melting | fusing point can be expected. Although the kind of hardening | curing agent which can react with these resin is not limited, An isocyanate compound is especially preferable from adhesiveness, bending resistance, curability, etc. Moreover, it is preferable from storage stability to use these isocyanate compounds by blocking. As hardening agents other than an isocyanate compound, well-known compounds, such as amino resin, such as methylated melamine, butylated melamine, benzoguanamine, and urea resin, acid anhydride, imidazole, epoxy resin, and a phenol resin, are mentioned.

As an isocyanate compound, there exist aromatic, aliphatic diisocyanate, and trivalent or more polyisocyanate, and any of a low molecular weight compound and a high molecular compound may be sufficient. 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 excess amounts of these isocyanate compounds and low molecular weight active hydrogens such as ethylene glycol, propylene glycol, trimethylolpropane, glycerin, sorbitol, ethylenediamine, monoethanolamine, diethanolamine, triethanolamine, and the like. And terminal isocyanate group-containing compounds obtained by reacting a compound or various polyester polyols, polyether polyols, and high molecular weight active hydrogen compounds of polyamides.

As a blocking agent of an isocyanate group, For example, phenols, such as phenol, thiophenol, methylthiophenol, ethylthiophenol, cresol, xylenol, resorcinol, nitrophenol, chlorophenol, acetoxime, methyl ethyl ketooxime, Oximes such as cyclohexanone oxime, alcohols such as methanol, ethanol, propanol and butanol, halogen-substituted alcohols such as ethylenechlorohydrin and 1,3-dichloro-2-propanol, t-butanol and t-pentanol And tertiary alcohols such as ε-caprolactam, δ-valerolactam, γ-butyrolactam, and β-propyllactam, and the like. Other examples thereof include aromatic amines, imides, acetylacetone, and acetoacetic acid. Active methylene compounds, such as ester and ethyl malonic acid ester, mercaptans, imines, imidazole, urea, diaryl compounds, sodium bisulfite, etc. are mentioned. Among these, oximes, imidazoles, and amines are especially preferable from curability.

In these crosslinking agents, you may use together the well-known catalyst or promoter chosen according to the kind.

The solvent used for the electrically conductive paste of this invention does not have a restriction | limiting in the kind, For example, aromatic hydrocarbon type, decalin, such as toluene, xylene, tetramethylbenzene, Solvesso 100, Solvesso 150, Solvesso 200, tetralin, Aliphatic hydrocarbons such as hexane, heptane, octane, decane, esters such as methyl acetate, ethyl acetate, isopropyl acetate, butyl acetate, alcohols such as methanol, ethanol, propanol, butanol, 2-ethylhexanol, acetone, Ketones such as methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, (di) ethylene glycol dimethyl ether, diethylene glycol monoethyl ether, dipropylene glycol diethyl ether, dioxane, diethyl ether, tetrahydrofuran, etc. Various solvents of carbitols such as ether-based, cellosolve acetate, ethyl cellosolve, butyl cellosolve, and carbitols such as carbitol and butyl carbitol May have, in consideration of solubility, evaporation rate and the like are used is selected, 1 species, or two or more of them.

As described above, the conductive paste of the present invention has a PTC characteristic when it is three times or more in the magnification (sheet resistance (80 ° C) / sheet resistance (30 ° C)) of resistance change at 80 ° C and 30 ° C, for example. Although defined, there is an important indicator as another performance. It is called "return characteristic", and this return characteristic is a difference (= change rate) between the resistance value when it cools to room temperature (25 degreeC) after heating up at 80 degreeC, and the resistance value of room temperature (25 degreeC) before temperature rising. ) Means. In order for a return characteristic to become favorable, it is preferable that the difference (change rate) of the resistance value at room temperature after cooling after raising temperature with the resistance value of room temperature before temperature rising is within +/- 1 to 100%. That is, it becomes an index which exhibits stable PTC characteristic even if it raises and lowers repeatedly.

In addition to the PTC characteristic and the return characteristic, the stability of the resistance value at high temperature is also important. The stability of the resistance value at high temperature means that there is no remarkable drop in resistance value when the temperature is raised to 80 ° C and further elevated. The good stability of the resistance value at high temperature means that the resistance value after raising the temperature to 120 ° C is reduced by less than 20% from the resistance value of 80 ° C even if the resistance value is equal to or higher than the resistance value of 80 ° C or decreased. . A significant decrease in the resistance value in the high temperature region indicates conduction at high temperature, which is undesirable for safety reasons.

The conductive paste of the present invention is a known method such as screen printing, rotary screen printing, gravure printing, transfer printing, roll coating, commerical coating, flow coating, spray coating, and the like. It can be used for surface heating elements.

<Examples>

EMBODIMENT OF THE INVENTION Hereinafter, although this invention is demonstrated concretely using an Example, this invention is not limited to these Examples. In the examples, those simply negative represent parts by mass. In addition, each measurement item followed the following method.

1. Number average molecular weight

It calculated from the result of having performed GPC measurement by column temperature 30 degreeC and flow volume 1 ml / min using the Waters company gel permeation chromatography (GPC) 150c which made tetrahydrofuran the eluent, and obtained the measured value of polystyrene conversion. For the column, Showa Denko Co., Ltd. shodex KF-802, 804, 806 was used.

2. Glass transition temperature (Tg) and melting point (Tm)

5 mg of sample was placed in an aluminum sample pan and sealed, and measured using a Seiko Instruments Co., Ltd. differential scanning calorimetry (DSC) DSC-220 at 200 ° C. at a temperature increase rate of 20 ° C./min. The temperature was determined as the crystal melting point. The glass transition temperature was calculated | required by the temperature of the intersection of the extension line of the baseline below glass transition temperature, and the tangent which shows the largest inclination in a transition part.

3. Acid value

0.2 g of the sample was weighed and dissolved in 20 mL of chloroform. Then, it titrated and calculated | required with 0.01 N potassium hydroxide (ethanol solution). As the indicator, a solution of phenolphthalate was used.

4. Adhesiveness

The electrically conductive paste was screen-printed on the 100-micrometer-thick annealed PET film, the pattern of 25x200 mm was printed, it dried at 30 degreeC for 30 minutes, and it was set as the test piece. The dry film thickness was adjusted to be 20-30 micrometers. It evaluated in accordance with JIS K5600 5-6 using this test piece. The cellophane tape CT-12 (Nichiban Co., Ltd. product) was used for the adhesive tape.

5. resistivity

Sheet resistance and film thickness were measured using the test piece produced in 4., and specific resistance was computed. In addition, sheet resistance was measured using the 4-terminal digital multimeter.

6. pencil hardness

The high quality pencil prescribed | regulated to JIS S6006 was used using the test piece produced by 4., and surface hardness was evaluated in accordance with JIS K5400.

7. PTC Characteristics

The sheet resistance was measured at 30 degreeC and 80 degreeC using the test piece produced by 4., and it evaluated by the magnification of the resistance change calculated by following Formula. The larger the number, the better the PTC characteristic.

Magnification of resistance change (times) = sheet resistance (80 ° C) / sheet resistance (30 ° C)

8. Return property

By the method described in 7., the PTC characteristic was repeatedly measured five times (repetition of elevated temperature five times from 30 ° C. to 80 ° C.), and then cooled to room temperature (25 ° C.) to measure sheet resistance, and the initial sheet resistance. It evaluated by difference with.

○: The difference (rate of change) of the initial resistance value is within ± 100%

(Triangle | delta): The change rate with respect to an initial resistance value is +/- 101%-500%

X: The rate of change with respect to the initial resistance is ± 500% or more

9. Stability of resistance value at high temperature

It heated up to 80 degreeC by the method of 6., and further heated up to 120 degreeC, and judged from the comparison with the resistance value at 80 degreeC.

(Double-circle): Resistance value in 120 degreeC is higher than the resistance value of 80 degreeC

(Circle): The resistance value in 120 degreeC is equal to or less than 20% of the resistance value of 80 degreeC.

(Triangle | delta): The resistance value of 120 degreeC reduces 20% or more and less than 40% compared with the resistance value of 80 degreeC.

X: The resistance value of 120 degreeC decreased 40% or more compared with the resistance value of 80 degreeC

10. Storage stability

After the electrically conductive paste was stored at 5 ° C for 1 month, the viscosity was measured at 25 ° C and evaluated by viscosity change.

○: almost the same value as the initial viscosity (less than 1.5 times the initial viscosity)

(Triangle | delta): The thickening of 1.5-2 times of the initial viscosity

X: Significantly thickening (more than twice the initial viscosity)

Production Example of Resin

Synthesis of Polyester Polyol (A)

100 parts of dimethyl terephthalate, 38 parts of dimethyl isophthalate, 93 parts of ethylene glycol, 73 parts of neopentyl glycol, and 0.065 parts of tetrabutyl titanate were added to a reaction vessel equipped with a stirrer, a condenser and a thermometer, and transesterified at 180 ° C. for 3 hours. Was carried out. Subsequently, 61 parts of sebacic acid were thrown in, and also esterification was performed. Subsequently, the mixture was gradually reduced to 1 mmHg or less and polymerized at 240 ° C. for 1.5 hours. The composition of the obtained copolyester is terephthalic acid / isophthalic acid / sebacic acid / ethylene glycol / neopentyl glycol = 50/20/30/57/43 (molar ratio), number average molecular weight 2100, acid value 8eq / ton, Tg 10 degreeC There was no crystal melting point. The results are shown in Table 1 below.

Synthesis of Polyester Polyols (B) to (D)

It synthesize | combined like polyesterpolyol (A). The polyester polyols (B) to (C) had no crystal melting point and were amorphous, while the polyester polyols (D) to (E) had crystal melting points. The results are shown in Table 1.

Synthesis of Polyurethane Resin with Crystal Melting Point

Synthesis of Polyurethane Resin (a)

1000 parts of polyester polyols (A) of the synthesis example were dissolved in 630 parts of ethyl carbitol acetate and 210 parts of butyl cellosolve acetates in 80 degreeC in the reaction container provided with the stirrer, the capacitor, and the thermometer. Subsequently, after adding 250 parts of diphenylmethane diisocyanate, reaction was performed for 2 hours. Thereafter, 2410 parts of cyclohexanone and 2000 parts of Fraxel 240 (manufactured by Daicel Chemical Industries, Melting Point 59 ° C., number average molecular weight 4000) were added thereto, followed by reaction at 80 ° C. for 2 hours, followed by dibutyltin dilaurate as a catalyst. : 0.3 parts was added and reacted at 80 degreeC for 4 hours. Subsequently, the solution was diluted at 990 parts of cyclohexanone and 5510 parts of Solvesso 150, and the polyurethane resin (a) was obtained. Solid content concentration of the obtained polyurethane resin solution was 25.1 (weight%). The number average molecular weight of the polyurethane resin (a) was 38000, an acid value of 8 eq / ton, and a Tm (melting point) of 45 ° C.

Synthesis of Polyurethane Resin (b)

1000 parts of polyester polyols (B) of the synthesis example were dissolved in 630 parts of ethyl carbitol acetate and 210 parts of butyl cellosolve acetates at 80 degreeC in the reaction container provided with the stirrer, the capacitor, and the thermometer. Subsequently, after adding 250 parts of diphenylmethane diisocyanate, reaction was performed for 2 hours. Thereafter, 2910 parts of cyclohexanone and 2500 parts of HS2H-500S (manufactured by Hokoku Seyou Co., Ltd., melting point 70 ° C., number average molecular weight 5000) were added thereto, and the reaction was carried out at 80 ° C. for 2 hours, followed by dibutyltin dilaurate as a catalyst. 0.3 parts were added and reacted at 80 degreeC for 4 hours. Subsequently, the solution was diluted in 990 parts of cyclohexanone and 5510 parts of Solvesso 150, and the polyurethane resin (b) was obtained. Solid content concentration of the obtained polyurethane resin solution was 25.0 (weight%). The number average molecular weight of the polyurethane resin (b) was 40000, the acid value 10 eq / ton, and Tm was 56 ° C.

Synthesis of Polyurethane Resin (c)

1000 parts of polyester polyols (B) of a synthesis example, and 500 parts of HS2H-500S (made by Hokoku Seiyu, melting | fusing point 70 degreeC, number average molecular weight 5000) in the reaction container provided with a stirrer, a capacitor | condenser, and a thermometer 80 to 1100 parts of cyclohexanone 80 It was dissolved at ℃. Subsequently, after adding 148 parts of diphenylmethane diisocyanate, reaction was performed for 2 hours. Then, 0.3 part of dibutyltin dilaurate was added as a catalyst, and it reacted at 80 degreeC for 4 hours. Subsequently, the solution was diluted with 630 parts, Solvesso 150: 970 parts, ethylcarbitol acetate 1683 parts, and 561 parts of butyl cellosolve acetate, and the polyurethane resin (c) was obtained. Solid content concentration of the obtained polyurethane resin solution was 25.0 (weight%). The number average molecular weight of the polyurethane resin (c) was 41000, the acid value 11 eq / ton, and Tm was 55 degreeC.

Synthesis of Polyurethane Resin (d)

1000 parts of polyester polyols (B) and 1000 parts of polyester polyols (D) of a synthesis example were dissolved in 1448 parts of cyclohexanone at 80 degreeC in the reaction container provided with the stirrer, the capacitor, and the thermometer. Subsequently, after adding 172 parts of diphenylmethane diisocyanate, reaction was performed for 2 hours. Then, 0.3 part of dibutyltin dilaurate was added as a catalyst, and it reacted at 80 degreeC for 4 hours. Subsequently, the solution was diluted in 833 parts of cyclohexanone and 4235 parts of Solvesso 150, and the polyurethane resin (d) was obtained. Solid content concentration of the obtained polyurethane resin solution was 25.0 (weight%). The number average molecular weight of the polyurethane resin (d) was 44000, an acid value 21 eq / ton, and Tm was 72 degreeC.

Synthesis of Polyurethane Resin (e)

1000 parts of polyester polyols (B) and 1000 parts of polyester polyols (E) of Synthesis Example were dissolved in a reaction vessel equipped with a stirrer, a condenser and a thermometer at 80 ° C in 1085 parts of ethylcarbitol acetate and 363 parts of butyl cellosolve acetate. . Subsequently, after adding 172 parts of diphenylmethane diisocyanate, reaction was performed for 2 hours. Then, 0.3 part of dibutyltin dilaurate was added as a catalyst, and it reacted at 80 degreeC 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, and the polyurethane resin (e) was obtained. Solid content concentration of the obtained polyurethane resin solution was 25.0 (weight%). The number average molecular weight of the polyurethane resin (e) was 45000, the acid value 19 eq / ton, and Tm was 25 degreeC.

Synthesis of Polyurethane Resin (f)

1000 parts of polyester polyols (B) of a synthesis example were dissolved in 630 parts of ethyl carbitol acetate and 210 parts of butyl cellosolve acetates in 80 degreeC in the reaction container provided with the stirrer, the capacitor, and the thermometer. Subsequently, after adding 250 parts of diphenylmethane diisocyanate, reaction was performed for 2 hours. Thereafter, 2010 parts of cyclohexanone and 1600 parts of Fraxel 240 (manufactured by Daicel Chemical Co., Ltd., melting point: 59 ° C., number average molecular weight 4000) were added thereto, followed by reaction at 80 ° C. for 2 hours, followed by 18 parts of diaminodiphenylmethane. Was added and the reaction continued. After 2 hours, 0.3 part of dibutyltin dilaurate was added as a catalyst, and further reacted at 80 degreeC for 4 hours. Subsequently, the solution was diluted in 990 parts of cyclohexanone and 5710 parts of Solvesso 150, and the polyurethane resin (f) was obtained. Solid content concentration of the obtained polyurethane resin solution was 25.1 (weight%). The number average molecular weight of the polyurethane resin (f) was 45000, the acid value 12 eq / ton, Tm was 46 degreeC, and the amount of urea bonds was 70 eq / ton.

Synthesis of Polyurethane Resin (g)

1000 parts of polyester polyols (B) of the synthesis example, 1500 parts of ODX688 (made by Dainippon Ink Co., Ltd.) which are amorphous co-polyester diols, and 1, 6-chain extenders in the reaction container provided with a stirrer, a capacitor, and a thermometer. 50 parts of hexanediol, 150 parts of neopentyl glycol, 2750 parts of ethyl carbitol acetate and 920 parts of butyl cellosolve acetate were added as a solvent, and it melt | dissolved at 80 degreeC. Subsequently, 760 parts of diphenylmethane diisocyanate (MDI) were added, and the reaction was continued for 1 hour, 0.8 parts of dibutyltin dilaurate was added and 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). Solid content concentration of the obtained polyurethane resin solution was 25.0 (weight%). The polyurethane resin (g) number average molecular weight was 42000, an acid value 10 eq / ton, and Tg-12 degreeC.

Synthesis of Polyurethane Resin (h)

In a reaction vessel equipped with a stirrer, a condenser and a thermometer, 20 parts of 1000 parts of polyester polyols (A) of Synthesis Example, Fraxel 220 (manufactured by Daicel Chemical Co., Ltd., melting point 55 ° C., number average molecular weight 2000) and ethyl carbitol acetate 570 190 parts of butyl cellosolve acetate were added and it melt | dissolved at 80 degreeC. Subsequently, 120 parts of diphenylmethane diisocyanate (MDI) were added, and the reaction was continued for 1 hour, and then 0.2 part of dibutyltin dilaurate was added and reacted at 80 ° C. for 4 hours. Then, 1196 parts of cyclohexanone, 1096 parts of ethyl carbitol acetate, and 365 parts of butyl cellosolve acetate were added and diluted, and the polyurethane resin (h) was obtained. Solid content concentration of the obtained polyurethane resin solution was 25.0 (weight%). The number average molecular weight of the polyurethane resin (h) was 40000, acid value 10 eq / ton, Tg 25 degreeC.

Synthesis of Polyurethane Resin (i)

In a reaction vessel equipped with a stirrer, a condenser, and a thermometer, 900 parts of polyester polyol (B) of Synthesis Example, Fraxel 210 (manufactured by Daicel Chemical Industries, Melting Point 47 ° C, number average molecular weight 1000) and ethylcarbitol acetate 1680 560 parts of butyl cellosolve acetate were added and dissolved at 80 ° C. Subsequently, 340 parts of diphenylmethane diisocyanate (MDI) were added, and the reaction was continued for 1 hour, and then 0.3 part of dibutyltin dilaurate was added and reacted at 80 ° C. for 4 hours. Then, 2350 parts of cyclohexanone and 2130 parts of Solvesso 150 were added and diluted, and polyurethane resin (i) was obtained. Solid content concentration of the obtained polyurethane resin solution was 25.0 (weight%). The number average molecular weight of the polyurethane resin (i) was 36000, an acid value 12 eq / ton, and Tg-5 degreeC.

Integrating the physical properties of the polyurethane resins (a) to (i) is shown in Table 2 below.

Example 1

Polyurethane resin solution (a) (solvent composition (mass) ratio synthesize | combined above as MC0520 (made by Nippon Carbon Co., Ltd.)) as resin, electroconductive fine particles (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 of BYK-354 (Bikkemi Japan Co., Ltd.) was added as a leveling agent, and Solvesso 150 was further added and premixed sufficiently. . Subsequently, it disperse | distributed 3 times with the frozen triaxial roll and obtained the electrically conductive paste. The obtained electrically conductive paste was slightly black and was viscous. The specific resistance was 6.6 Ω · cm, the PTC characteristic was 8.5 times good, and the return characteristics, resistance stability at high temperatures, and storage stability were all good.

Examples 2-9

It evaluated similarly to Example 1. The results are shown in Table 3 below. Both pastes showed good PTC characteristics, return characteristics, resistance stability at high temperatures, and storage stability.

The numbers in Table 3 and the following Table 4 mean the following.

1) Organic resin: EVA and commercially available ethylene vinyl acetate having 30 mol% of vinyl acetate content were used as it is.

2) Carbon a: MC0520 (Spherical carbon (average particle diameter 5 micrometers, sphericity 95)) (made by Nippon Carbon Corporation)

3) Carbon b: MC1020 (spherical carbon (average particle diameter 10 micrometers, sphericity 93)) (made by Nippon Carbon Co., Ltd.)

4) Carbon c: # 4500 (Conductive carbon (average particle diameter 0.04 µm)) (Tokai Carbon Co., Ltd.)

5) Additive a: LMS100 (particle size 6 micrometers) (made by Fuji Talc)

6) Additive b: Silopobic 603 (particle diameter 6.7 micrometers) (made by Fuji Silysia)

7) Additive c: Sodium stearate (made by Nippon Yushi)

8) Additive d: Fraxel 240 (polycaprolactone diol (number average molecular weight 4000)) (made by Daicel Chemical Industries, Ltd.)

9) Additive e: carbodilite V-07 (made by Nisshinbo Corporation)

10) Leveling agent: BYK-354 (manufactured by Big Chemi Japan Co., Ltd.)

11) ECA: Ethyl Carbitol Acetate

12) BCA: Butyl Cellosolve Acetate

Comparative Example 1

Polyurethane resin solution (d) (solvent composition (mass) ratio synthesize | combined above as 150 parts of MC0520 (made by Nippon Carbon Co., Ltd.) as electroconductive fine particles) (solvent composition (mass) ratio: ethyl carbitol acetate / butyl cellosolve acetate = 75/25) ) 400 parts (solid content 25%) and 6.0 parts of BYK-354 (Bikkemi 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 frozen triaxial roll and obtained the electrically conductive paste. The obtained electrically conductive paste was slightly black and was viscous. The specific resistance was 4.8 Ωcm. The PTC characteristic was defective at 2.7 times.

Comparative Examples 2 to 7

It evaluated similarly to the comparative example 1. The results are shown in Table 3. It did not satisfy the performance superior to the Example, such as a PTC characteristic, a return characteristic, and storage stability.

Industrial availability

The electrically conductive paste of this invention provides the planar heat generating body which has very favorable PTC characteristic, and is excellent in electroconductivity, a return characteristic, resistance stability at high temperature, etc.

Claims (14)

The electrically conductive paste for planar heating elements containing polyurethane resin (I) and electroconductive particle (II) which have a crystalline melting point. The conductive paste for planar heating elements according to claim 1, wherein the melting point of the polyurethane resin (I) is 20 to 100 ° C. The conductive paste for planar heating elements according to claim 1 or 2, wherein the polyurethane resin (I) reacts at least an amorphous component with a crystalline component. The planar heating element according to claim 1 or 2, wherein the polyurethane resin (I) reacts 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. The conductive paste for planar heating elements according to any one of claims 1 to 4, 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 5, wherein the urea bonding amount of the crystalline polyurethane urea is in a range of 10 to 1000 eq / ton. The conductive paste for planar heating elements according to any one of claims 1 to 6, wherein the polyurethane resin (I) is soluble in a solvent. The number average molecular weight of the crystalline polyester polyol which comprises a polyurethane resin (I) exists in the range of 1200-20000, The electrically conductive paste for planar heating elements in any one of Claims 4-7 characterized by the above-mentioned. The crystalline polyester polyol constituting the polyurethane resin (I) is copolymerized with 85 to 300 parts by weight based on 100 parts by weight of the amorphous polyester polyol according to any one of claims 4 to 8. A conductive paste for planar heating elements to be used. The conductive material for planar heating element according to any one of claims 4 to 9, wherein when the polyurethane resin (I) is 100 parts by weight, 50 parts by weight or less of the crystalline polyester polyol is further contained. Paste. The electrically conductive paste for planar heating elements in any one of Claims 1-10 with which electroconductive particle (II) is contained in the ratio of 40-400 weight part with respect to 100 weight part of polyurethane resins (I). Electroconductive particle (II) is spherical carbon, and the average particle diameter is 0.1-30 micrometers, The electrically conductive paste for planar heating elements in any one of Claims 1-11 characterized by the above-mentioned. The printed circuit using the electrically conductive paste for planar heating elements in any one of Claims 1-12. The planar heating element using the electrically conductive paste for planar heating elements in any one of Claims 1-12.