JPWO2008133073A1 - Conductive paste, printed circuit using the same, and planar heating element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a conductive paste which is excellent in conductivity, adhesion and bending resistance and exhibits excellent PTC characteristics despite low specific resistance. SOLUTION: In a conductive paste containing 40 to 200 parts by mass of spherical carbon particles with respect to 100 parts by mass of a resin containing a polyester resin and / or polyurethane resin, the number of the polyester resin and / or urethane resin The present invention relates to a conductive paste having a mean molecular weight of 3000 or more and a glass transition temperature of −40 to 30 ° C., a printed circuit using the same, and a planar heating element. [Selection figure] None

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 creating 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, the planar heating element with PTC characteristics with a self-temperature control function can control the temperature continuously compared to a heating element without PTC characteristics, and does not require a thermistor. It has features such as reduction, and is widely used in the above applications. Usually, such a planar heating element is composed of a resin and a conductive material, and the resin undergoes volume expansion as the temperature of the planar heating element rises, thereby blocking conduction of the conductive material. It is said that PTC characteristics are expressed.

  Conventionally, a planar heating element having such PTC characteristics is obtained by kneading a conductive material composed of carbon black, graphite, metal powder, etc., with an olefin resin, and dispersing or dissolving the resin and the conductive material in a solvent. The thing etc. which let it be made are proposed (for example, patent document 1). Further, as a method for producing such a planar heating element, the former is a method by extrusion molding or press molding, and the latter is a method of applying to a substrate by means such as screen printing. The latter paste type is widely adopted because of its high degree of freedom in shape.

  In the paste type, a polymer using a polymer 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 characteristic that the vinyl acetate part exhibits solvent solubility 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 limit the vinyl acetate content of EVA. However, in recent years, as the demand for improving the safety of products has increased, it has been limited as described above. Formulation cannot satisfy both PTC required characteristics and solvent solubility. That is, when the copolymerization ratio of vinyl acetate is increased to improve the solubility, the PTC characteristics are lowered. Conversely, when the copolymerization ratio of vinyl acetate is decreased, the PTC characteristics are improved, but the solvent solubility is deteriorated. There's a problem.

  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 was repeatedly applied, the PTC characteristics tended to deteriorate. This is because, when the base resin is exposed to a use temperature of the planar heating element of 40 ° C. to 70 ° C. for a long time, a minute fluidized portion is partially generated in the resin, so that the conductive fine particles are dispersed. The change in the structure is thought to be a factor.

  Furthermore, a conductive paste in which a crystalline resin is combined has been proposed (for example, Patent Document 4). In this case, it is possible to improve the PTC characteristics by blending a crystalline resin having a large volume change. However, even if such a conductive paste is used, the solvent solubility of the resin as the binder component is insufficient. Therefore, there is a problem that the paste thickens under low temperature storage and is inferior in workability.

Japanese Published Patent Publication No. 1-304704 Japanese Published Patent Publication No. 10-183039 Japanese published patent publication 2000-88672 Japanese Patent Publication No. 2001-76850

  The object of the present invention is to improve the problems of these conventional conductive pastes. That is, the present invention provides a conductive paste having good solvent solubility and good specific resistance and PTC characteristics even when repeated heating is performed.

  As a result of diligent studies to solve the above problems, it is surprisingly possible to use a polyester resin or / and polyurethane resin as a binder and further use spherical carbon particles as a conductive filler. The present inventors have found that PTC characteristics and electrical conductivity can be significantly improved. Furthermore, since the return characteristic that the specific resistance returns to the original value is good even when the temperature is repeatedly raised, it is very useful for a planar heating element.

  That is, the present invention provides a conductive paste containing 40 to 200 parts by mass of spherical carbon particles with respect to 100 parts by mass of a resin containing a polyester resin and / or a polyurethane resin, and the polyester resin and / or the urethane resin. The present invention relates to a conductive paste having a number average molecular weight of 3000 or more and a glass transition temperature of −40 to 30 ° C., a printed circuit using the same, and a planar heating element.

  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 a planar heating element.

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, the sheet resistance change ratio at 80 ° C. and 30 ° C. (sheet resistance (80 ° C.)). / Sheet resistance (30 ° C.)) is defined as “having PTC characteristics” if it is 3 times or more. The PTC characteristic is preferably 5 times or more, more preferably 10 times or more, and still more preferably 100 times or more. Although an upper limit is not specifically limited, Generally it is 50000 times 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 used in the printing method of the present invention is preferably 100 Ω · cm or less, more preferably 10 Ω · cm or less, and further preferably 1 Ω · cm or less. The lower limit is not particularly limited, but is generally 1 × 10 ⁻² Ω · cm or more.

  The spherical carbon particles used in the present invention are particularly preferably spherical in shape from the viewpoint 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 diameter of the spherical 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 lowered due to sedimentation of the spherical carbon particles. If the average particle size is less than 0.1 μm, the conductivity may be reduced, or the oil absorption may be increased to increase the viscosity of the paste, and the spherical carbon particles may not be sufficiently filled. Moreover, there exists a possibility that adhesiveness may fall or printability may deteriorate. As the spherical carbon particles, commercially available products such as MC1020 (manufactured by Nippon Carbon Co., Ltd.) and GCP10 (manufactured by Unitika Ltd.) can be used.

  In order to exhibit conductivity, the spherical carbon particles are preferably contained in an amount of 40 to 200 parts by mass with respect to a total of 100 parts by mass of a resin including a polyester-based resin and / or a polyurethane-based resin. More preferably, it is contained in an amount of 80 to 170 parts by mass from the viewpoint of coating film hardness and adhesion. 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 addition, non-conductive fillers such as silica powder, fumed silica, colloidal silica, talc, and barium sulfate may be blended in a small amount for the purpose of adjusting paste viscosity and the like without impairing the effects of the invention. In the present invention, other conductive powder 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 or more, more preferably 30% by mass or more of the total conductive powder amount. 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 fillers include graphite powder and conductive carbon black. By using these carbon fillers and the spherical carbon particles of the present invention 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.

  The conductive paste of the present invention preferably has an F value of 30 to 80%. Preferably it is 40 to 70%, more preferably 45 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 as used herein includes all spherical carbon particles other than the solvent, other fillers, resins including polyester resins and / or polyurethane 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 60%, the PTC characteristics tend to deteriorate.

  The conductive paste of the present invention is used in combination with a polyester resin or / and a polyurethane resin and spherical carbon particles.

  The type of polyester-based resin and / or polyurethane-based resin used in the present invention is not limited, but polyester resin, urethane-modified polyester resin, epoxy-modified from the viewpoints of adhesion to a substrate, flex resistance and solvent solubility. Various modified polyester resins such as polyester resins and acrylic modified polyesters, and polyurethane resins such as polyether urethane resins and polycarbonate urethane resins are used.

  In order to improve the PTC characteristics, the glass transition temperature of the polyester-based resin and / or polyurethane-based resin is −40 ° C. to 30 ° C., and preferably −30 to 20 ° C. from the flex resistance and the coating film hardness. When the glass transition temperature is less than −40 ° C., the stability of the PTC characteristics decreases, and when it exceeds 30 ° C., the PTC characteristics decrease. Moreover, the number average molecular weight is 3000 or 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 the printability is lowered. The upper limit is not particularly limited, but is preferably 100,000 or less from the viewpoint of paste viscosity and solubility. In the present invention, the polyester resin obtained by polycondensation by a known method under normal pressure or reduced pressure can be used. Further, after completion of the polycondensation of the polyester resin, an acid anhydride compound such as trimellitic anhydride or phthalic anhydride may be added to the end of the resin to introduce a carboxyl group to the end of the polyester molecule.

  As a polyester resin used for this invention, 40 mol% or more of aromatic dicarboxylic acid is preferable among all the acid components, More preferably, it is 50 mol% or more. If the aromatic dicarboxylic acid content is less than 40 mol%, the strength of the coating film decreases, and durability such as low-temperature flex resistance, heat resistance, moisture resistance, and thermal shock resistance may decrease. The upper limit with preferable aromatic dicarboxylic acid is 100 mol%.

Examples of the aromatic dicarboxylic acid copolymerized with the polyester resin include terephthalic acid, isophthalic acid, orthophthalic acid, and 2,6-naphthalenedicarboxylic acid. Of these, terephthalic acid and isophthalic acid are preferably used in combination in view of physical properties and solvent solubility.
Other dicarboxylic acids copolymerized with the polyester include aliphatic dicarboxylic acids such as succinic acid, glutaric acid, adipic acid, sebacic acid, dodecanedicarboxylic acid and azelaic acid, dibasic acids having 12 to 28 carbon atoms, 1,4 -Cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 4-methylhexahydrophthalic anhydride, 3-methylhexahydrophthalic anhydride, 2-methylhexahydrophthalic anhydride, dicarboxy Hydrogenated bisphenol A, dicarboxy hydrogenated bisphenol S, dimer acid, hydrogenated dimer acid, hydrogenated naphthalene dicarboxylic acid, tricyclodecanedicarboxylic acid and other alicyclic dicarboxylic acids, hydroxybenzoic acid, lactic acid and other hydroxycarboxylic acids Although listed Sebacic acid from sexual terms, azelaic acid, 1,4-cyclohexanedicarboxylic acid.

  Further, within the scope of not impairing the contents 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.

  The glycol used for the polyester resin in the present invention is 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, Examples include 1,9-nonanediol, 1,10-decanediol, 1,4-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,2-cyclohexanedimethanol, and dimer diol. 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 content of invention.

The polyester resin used in the present invention is a block copolymer polyester resin comprising a combination of an aliphatic segment and an aromatic polyester segment selected from the group consisting of aliphatic polyester, aliphatic polycarbonate and aliphatic polyether, based on PTC characteristics. It is particularly preferred.
The block copolymerized polyester resin can be obtained by copolymerizing polyethylene glycol, polypropylene glycol, polytetramethylene ether glycol, polypropylene glycol-polyethylene glycol copolymer, aliphatic polycarbonate diol and the like as the polyol component. Further, after polymerization of the polyester resin, it can be blocked by a ring-opening addition reaction of a cyclic ester such as caprolactone at 180 ° C. to 230 ° C. at normal pressure.

  Further, a solvent-soluble crystalline polyester resin or modified polyester resin may be used to enhance the PTC characteristics. When the total amount of dicarboxylic acid is 100 mol%, from the viewpoint of crystallinity, terephthalic acid and / or 2,6-naphthalenedicarboxylic acid is preferably copolymerized at least 20 mol%, more preferably at least 25 mol%. It is. Further, from the viewpoint of PTC characteristics, the terephthalic acid is more preferably 20 mol% or more. From the viewpoint of solvent solubility, these upper limits are preferably 80 mol% or less. When the total glycol component amount is 100 mol%, at least one selected from the group consisting of 1,4-butanediol, 1,6-hexanediol, and 1,4-cyclohexanedimethanol in terms of crystallinity and solvent solubility. The above is preferably copolymerized by 20 mol% or more.

  Moreover, the polyester resin used for the electrically conductive paste of this invention can be modified | denatured and used by well-known methods, such as urethane modification, epoxy modification, (meth) acrylate modification, and (meth) acryl graft modification. Of these, urethane modification is particularly preferred from the viewpoint of bending resistance and adhesion. A urethane-modified resin synthesized by a known method by reacting with an isocyanate compound using a polyester polyol and, if necessary, a chain extender can be used.

  Furthermore, even if a urethane resin is used in the present invention, an excellent effect is exhibited. When the urethane-modified polyester resin is used, the above-described polyester polyol is used as the polyol, but in addition to this, polyether polyol, (meth) acryl polyol, polycarbonate diol, polybutadiene polyol, and the like may be used. As other polyols, polycarbonate diol is particularly preferable in view of adhesiveness, flex resistance, and durability. Examples of the polyol used as a chain extender include known polyols such as neopentyl glycol, 1,6-hexanediol, ethylene glycol, hydroxypivalate ester of neopentyl glycol, trimethylolpropane, and glycerin. Furthermore, carboxyl group-containing polyols such as dimethylolpropionic acid can also be used as chain extenders.

  Examples of the diisocyanate compound used for urethane modification include tetramethylene diisocyanate, hexamethylene diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, and isophorone diisocyanate.

In the urethane group concentration of the polyurethane resin, the lower limit is preferably 500 equivalents / 10 ⁶ g or more from the viewpoint of adhesion and flex resistance, and the upper limit is preferably 4000 equivalents / 10 ⁶ g or less from the viewpoint of solubility.

  Furthermore, from the viewpoint of PTC characteristics, a block copolymer polyurethane resin comprising a combination of a polyol selected from the group consisting of an aliphatic polyester polyol, an aliphatic polycarbonate polyol and an aliphatic polyether and an aromatic polyester polyol is particularly preferable.

  The conductive paste of the present invention may contain a curing agent capable of reacting with a resin containing a polyester resin or / and a polyurethane 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, isophorone diisocyanate or trimers of these isocyanate compounds, and excess of these isocyanate compounds High amount of low molecular active hydrogen compounds such as ethylene glycol, propylene glycol, trimethylolpropane, glycerin, sorbitol, ethylenediamine, monoethanolamine, diethanolamine, triethanolamine or various polyester polyols, polyether polyols, polyamides Obtained by reacting with molecularly active hydrogen compounds, etc. Terminal isocyanate group-containing compounds that.

  Examples of the blocking agent for isocyanate groups include phenols such as phenol, thiophenol, methylthiophenol, ethylthiophenol, cresol, xylenol, resorcinol, nitrophenol, 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 restrictions on the type of solvent used in the conductive paste of the present invention, and examples include esters, ketones, ether esters, chlorines, alcohols, ethers, hydrocarbons, etc. The optimum one is selected in consideration of solubility and drying speed. Among these, in the case of screen printing, a high boiling point solvent such as ethyl carbitol acetate, butyl cellosolve acetate, isophorone, cyclohexanone, γ-butyrolactone, benzyl alcohol, N-methyl-2-pyrrolidone, and tetralin is preferable.

  Measured when printing and drying the conductive paste for sheet heating element and then repeatedly raising and lowering the temperature from 30 ° C. to 80 ° C. 5 times and then lowering to 30 ° C. with respect to the sheet resistance value measured at 30 ° C. The change rate (return characteristic) of the sheet resistance value is preferably 80 to 120%. That is, even if the temperature rise and fall is repeated, it becomes an index that exhibits stable PCT characteristics.

  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 chromatograph (GPC) 150c using tetrahydrofuran as an eluent. 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
A 0.2 g 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 an annealed PET film having 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). Resistivity
4). 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). 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)

7). Return characteristics After repeating the temperature increase and decrease in temperature from 30 ° C. to 80 ° C. five times, the sheet resistance was measured by cooling to 30 ° C., and the difference from the initial sheet resistance was evaluated.
3: Almost the same value as the initial resistance (80 to 120%) 2: 2 to 5 times the initial resistance value 1: Remarkably increased

8). 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.
3: almost the same value as the initial viscosity 2: thickening 1.5 to 2 times the initial viscosity 1: remarkably thickened

9. Measuring method of particle diameter by scanning electron microscope (SEM) The particle diameter of the spherical carbon particles was measured by SEM. 0.1 ml of the fine particle suspension was taken, diluted 10 times with acetone, and sonicated for 60 minutes. The surface of a carbon SEM sample stage was mirror-polished, and the suspension was dropped and dried to obtain a sample for SEM observation. Observation and photography were performed with a Hitachi S4500 scanning electron microscope at an acceleration voltage of 15 kV and a magnification of 5,000 times. The particle diameter was measured for 100 particles photographed with SEM, and the average value was expressed.

10. Measurement of sphericity of spherical carbon particles Photographed spherical carbon particles with an electrolytic emission scanning electron microscope (S4500, manufactured by Hitachi, Ltd.) at a magnification of 5000 times or 10,000 times, the short diameter and long diameter of each particle. And the ratio was defined as sphericity. Expressed as an average value of 30 measured samples.

Synthesis example 1 (polyester resin A)
A four-necked flask equipped with a Gubileu fractionator is charged with 95 parts of dimethyl terephthalic acid, 38 parts of dimethyl isophthalic acid, 93 parts of ethylene glycol, 73 parts of neopentyl glycol and 0.065 part of tetrabutyl titanate, and esterified at 180 ° C. for 3 hours. Exchange was performed. 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 copolymer polyester resin obtained was terephthalic acid / isophthalic acid / sebacic acid / ethylene glycol / neopentyl glycol = 50/20/30/57/43 (molar ratio), reduced viscosity 0.72 dl / g, acid The value was 31 eq / 10 ⁶ g and Tg 10 ° C. The results are shown in Table 1.

Synthesis Examples 2 to 5 (Polyester resins B to E)
Synthesis was performed in the same manner as in Synthesis Example 1. The results are shown in Table 1. The polyester resin B having a low reduced viscosity is a base resin for urethane modification. Polyester resin C is a crystalline polyester having a melting point with good solvent solubility. Polyester resins D and E are block copolymerized polyester resins, and after polymerizing polyester in the same manner as in Synthesis Example 1 using an acid component and a glycol component excluding ε-caprolactone, ε- under normal pressure and nitrogen stream Caprolactone was added and synthesized by reacting at 200 ° C. for 30 minutes.

Synthesis example 6 (polyurethane resin F)
In a reaction vessel equipped with a thermometer, a stirrer, and a condenser, 100 parts of polyester resin B of Synthesis Example 2, 150 parts of ODX-688 (produced by DIC Corporation) as an aliphatic polyester polyol, 1,6 as a chain extender -Hexanediol 5 parts, neopentyl glycol 15 parts, ethyl carbitol acetate / butyl cellosolve acetate = 75/25 (mass ratio) as a solvent, dissolved at 80 ° C., diphenylmethane diisocyanate (MDI) 78 parts and dibutyltin dilaurate 0.07 part was charged and reacted at a solid content concentration of 34% at 80 ° C. for 3 hours or more until there was no residual isocyanate, and then the solid content concentration was ethyl carbitol acetate / butyl cellosolve acetate = 75/25 (mass ratio). The polyurethane resin F was obtained by diluting to 25%. The number average molecular weight was 40000, the acid value was 10 eq / 10 ⁶ g, and Tg-2 ° C. This polyurethane resin is a block copolymer polyurethane resin composed of an aromatic polyester segment and an aliphatic polyester segment.

Synthesis example 7 (polyurethane resin G)
In a reaction vessel equipped with a stirrer, a condenser, and a thermometer, 100 parts of polyester resin B of Synthesis Example 2, 33.3 parts of neopentylglycol hydroxypivalate, Plaxel 220 which is polycaprolactone diol (manufactured by Daicel Chemical Industries, Ltd.) Was added, and 161 parts of ethyl carbitol acetate and 53 parts of butyl cellosolve acetate were added and dissolved at 80 ° C. Next, 5.8 parts of diphenylmethane diisocyanate (MDI) was added and the reaction was continued for 1 hour, and then 0.01 part of dibutyltin dilaurate was added and reacted at 80 ° C. for 4 hours. Thereafter, 321 parts of ethyl carbitol acetate and 107 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 (mass%). The number average molecular weight of the polyurethane resin (G) was 31000, the acid value was 5 eq / 10 ⁶ g, and Tg was 23 ° C.

Synthesis example 8 (polyurethane resin H)
In a reaction vessel equipped with a stirrer, a condenser, and a thermometer, 100 parts of polyester resin B of Synthesis Example 2, 75 of Plaxel 240 (manufactured by Daicel Chemical Industries), polycaprolactone diol, 147 parts of ethyl carbitol acetate, and butyl cellosolve acetate 49 parts were charged and dissolved at 80 ° C. Next, 21 parts of diphenylmethane diisocyanate (MDI) was added and the reaction was continued for 1 hour. Then, 0.02 part of dibutyltin dilaurate was added, and the mixture was further reacted at 80 ° C. for 4 hours. Thereafter, 294 parts of ethyl carbitol acetate and 98 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 (mass%). The number average molecular weight of the polyurethane resin (H) was 40000, an acid value of 10 eq / 10 ⁶ g, and Tg of 16 ° C.

Synthesis example 9 (polyurethane resin I)
In a reaction vessel equipped with a stirrer, a condenser, and a thermometer, 100 parts of polyester resin B of Synthesis Example 2, 90 parts of Placcel 210 (manufactured by Daicel Chemical Industries), polycaprolactone diol, 168 parts of ethyl carbitol acetate, butyl cellosolve acetate 56 parts were added and dissolved at 80 ° C. Next, 34 parts of diphenylmethane diisocyanate (MDI) was added and the reaction was continued for 1 hour. Then, 0.03 part of dibutyltin dilaurate was added, and the mixture was further reacted at 80 ° C. for 4 hours. Thereafter, 336 parts of ethyl carbitol acetate and 112 parts of butyl cellosolve acetate were added and diluted to obtain polyurethane resin (I). The solid content concentration of the obtained polyurethane resin solution was 25.0 (mass%). The number average molecular weight of the polyurethane resin (I) was 36000, the acid value was 12 eq / 10 ⁶ g, and Tg−5 ° C.

Synthesis example 10 (polyurethane resin J)
To a reaction vessel equipped with a stirrer, a condenser and a thermometer, 100 parts of ODX688 (manufactured by DIC Corporation), 81 parts of ethyl carbitol acetate and 27.2 parts of butyl cellosolve acetate were charged and dissolved at 80 ° C. Thereafter, 8.2 parts of hexamethylene diisocyanate was added and reacted at 80 ° C. for about 1 hour, and then 0.01 part of dibutyltin dilaurate was added and further reacted at 80 ° C. for 4 hours. Thereafter, 162 parts of ethyl carbitol acetate and 54.4 parts of butyl cellosolve acetate were added for dilution to obtain a polyurethane resin (J). The solid content concentration of the obtained polyurethane resin solution was 25.0 (mass%). The number average molecular weight of the polyurethane resin (J) was 28000, an acid value of 8 eq / 10 ⁶ g, and Tg-60 ° C.

Synthesis example 11 (polyurethane resin K)
In a reaction vessel equipped with a stirrer, a condenser and a thermometer, 100 parts of ODX688 (manufactured by DIC Corporation) and 3 parts of dimethylol heptane (DMH) were dissolved in 8 parts of MEK, and then 90 parts of ethyl carbitol acetate and 29 parts of butyl cellosolve acetate were added. .6 parts were charged and dissolved at 80 ° C. Thereafter, 16.6 parts of diphenylmethane diisocyanate was added and reacted at 80 ° C. for about 1 hour, and then 0.02 part of dibutyltin dilaurate was added and further reacted at 80 ° C. for 4 hours. Thereafter, 179.2 parts of ethyl carbitol acetate and 60 parts of butyl cellosolve acetate were added and diluted to obtain a polyurethane resin (K). The solid content concentration of the obtained polyurethane resin solution was 25.0 (mass%). The number average molecular weight of the polyurethane resin (K) was 25000, the acid value was ⁶ eq / 10 ⁶ g, and Tg-35 ° C.

Formulation of spherical carbon particles a NICABEADS MC-0520 (manufactured by Nippon Carbon Co., Ltd.) was used. The average particle diameter was 5 μm, and the sphericity obtained from the short diameter and long diameter was 95.

Blending of spherical carbon particles b NICABEADS MC-1020 (manufactured by Nippon Carbon Co., Ltd.) was used. The average particle diameter was 10 μm, and the sphericity obtained from the short diameter and long diameter was 93.

Formulation of comparative carbon black c Toka Black # 4500 (manufactured by Tokai Carbon Co., Ltd.) was used. The average particle diameter was 0.04 μm, and the sphericity obtained from the short diameter and long diameter was 61.

Formulation of Comparative Carbon Black d Ketjen Black EC (manufactured by Lion Corporation) was used. Since the average particle size was 0.03 μm and the structure was developed, the sphericity could not be measured.

Example 1
23.0 parts of spherical carbon MC0520 (manufactured by Nippon Carbon Co., Ltd.) as conductive fine particles, 68 parts of solid solution of ethyl carbitol acetate / butyl cellosolve acetate = 75/25 (mass ratio) of polyester resin I as organic resin (solid content 25 %), 1.0 part of BYK-354 (Big Chemie Japan Co., Ltd.) as a leveling agent was blended and 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 6.6 Ω · cm, and the PTC characteristics were 3.8 times as good. Moreover, the adhesiveness with respect to PET film was favorable. When a circuit with a line width of 0.4 mm produced with this conductive paste was bent five times by finger folding with the printed surface folded inward, there was almost no increase in resistance value and good bending resistance. When this paste was allowed to stand at 5 ° C. for 7 days, no thickening was observed and good storage stability was exhibited.

Examples 2-13
Evaluation was performed in the same manner as in Example 1. The results are shown in Tables 3, 4, and 5. All the pastes showed good PTC characteristics, adhesion, and storage stability. In Example 2, PTC characteristics were better than using a crystalline polyester resin having a melting point. Moreover, the storage stability was also good. In Example 3, since a block-type polyester resin was used, the PTC characteristics were good and the return characteristics were even better. In Example 4, since a block type polyester resin having a low glass transition temperature was used, the PTC characteristics were good and the solvent solubility was good. In Examples 5 and 6, a block-type urethane-modified polyester resin having a low glass transition temperature was used, so that the PTC characteristics were even better. In Examples 7 and 8, MC1020 having a large particle diameter was used in place of the spherical carbon MC0520, but the specific resistance, return characteristics, and PTC characteristics were also good.
In Examples 9 to 11, PTC characteristics were further improved by using a polyurethane resin having a crystal component, and in Examples 12 and 13 using a polyurethane resin having a low glass transition temperature.

Comparative Examples 1-7
Prepared in the same manner as in Example 1. The results are shown in Tables 6 and 7. In Comparative Example 1, since a polyester resin having a low molecular weight and a high glass transition temperature was used, the PTC characteristics and the bending resistance were not satisfied. Comparative Example 2 is an example using an ethylene-vinyl acetate copolymer resin (EVA), but the PTC characteristics were relatively good, but the storage stability was poor and the viscosity increased at low temperature (5 ° C.) storage. . In Comparative Examples 3, 4, and 5, investigations were made using carbon black and ketjen black without using spherical carbon particles, but both the return characteristics and the PTC characteristics were poor. In Comparative Example 6, a polyester resin and spherical carbon particles were used, but the compounding amount of the carbon particles was small and the PTC characteristics increased, but the return characteristics were poor. In Comparative Example 7, polyester resin and spherical carbon particles were used, but the amount of carbon particles was large and the PTC characteristics were poor.

  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 a planar heating element.

Claims (9)

  In a conductive paste containing 40 to 200 parts by mass of spherical carbon particles with respect to 100 parts by mass of a resin containing a polyester resin and / or a polyurethane resin, the number average molecular weight of the polyester resin and / or urethane resin is 3000. It is the above, The electrically conductive paste characterized by the glass transition temperature being -40-30 degreeC.   The polyester-based resin is a block copolymerized polyester resin formed by a combination of an aliphatic segment and an aromatic polyester segment selected from the group consisting of aliphatic polyester, aliphatic polycarbonate, and aliphatic polyether. The conductive paste according to 1.   The polyurethane-based resin is a block copolymer polyurethane resin formed by a combination of a polyol selected from the group consisting of an aliphatic polyester polyol, an aliphatic polycarbonate polyol and an aliphatic polyether and an aromatic polyester polyol. The conductive paste according to 1.   The conductive paste according to any one of claims 1 to 3, wherein the spherical carbon particles have a sphericity of 80% or more.   The conductive paste according to any one of claims 1 to 4, wherein the spherical carbon particles have an average particle size of 0.1 µm or more and 30 µm or less.   6. The value obtained by dividing the sheet resistance value measured at 80 ° C. by the sheet resistance value measured at 30 ° C. after printing and drying the conductive paste is 3 or more. The conductive paste described in 1.   After the conductive paste was printed and dried, the sheet resistance value measured at 30 ° C was repeatedly increased and decreased from 30 ° C to 80 ° C five times, and then the sheet resistance value measured when the temperature was further decreased to 30 ° C. Change rate is 80 to 120%, The electrically conductive paste in any one of Claims 1-6 characterized by the above-mentioned.   The printed circuit manufactured by printing the electrically conductive paste in any one of Claims 1-7 on a base material.   A planar heating element produced by printing the conductive paste according to claim 1 on a substrate.