JP6343903B2 - Conductive paste and printed circuit using the same - Google Patents

Description

  The present invention relates to a conductive paste, and more particularly to a conductive paste for screen printing, and particularly a wiring circuit that requires low cost and high conductivity, adhesion to a substrate, and storage stability. It is related with the electrically conductive paste suitable for formation of.

Touch panels are used in a wide range of applications such as ATMs and car navigation systems. In general, a transparent conductive substrate in which an indium tin oxide (ITO) layer is formed on a substrate such as a glass / PET film and an electrode is formed by etching is used for the touch panel. The conductive paste is applied on a transparent conductive substrate by printing or the like, whereby a wiring is formed.
Examples of the touch panel detection method include a resistance film type and a capacitance type. The resistance film type includes two opposing transparent conductive substrates, and recognizes the location by detecting the voltage at the operated position. While it is possible to perform pen input in addition to a finger, it responds to pressure, so there are problems of unintentional operation and deterioration of the transparent conductive film due to touch.
On the other hand, the electrostatic capacitance type is a method of detecting a position by capturing a change in electrostatic capacitance between the fingertip and the transparent conductive substrate, and can detect multiple points of the fingertip called multi-touch. Furthermore, since no pressure is required, it has attracted attention because it has many advantages such as excellent durability and transparency.

In order to cope with these detection methods, transparent conductive base materials having various characteristics such as transparency and conductivity have been developed.
The conductive paste is required to have high adhesion with respect to various transparent conductive base materials (including etched portions and electrodes) and high reliability for environmental evaluation. Further, in recent years, even with a capacitance type that is more expensive than a resistance film type, the price has been decreasing, and accordingly, cost reduction for each member has been strongly demanded.
In response to these requirements, conductive pastes containing various binder resins and conductive powders have been developed (for example, Patent Document 1).
In patent document 1, the electroconductive paste with favorable adhesiveness with respect to a transparent conductive base material is disclosed by the cohesive force of an acid value containing urethane resin, and a crosslinking agent. However, in order to obtain good conductivity, silver powder is used as the conductive powder. Therefore, silver accounts for a high proportion of the cost, and it is necessary to occupy 85% or more in the nonvolatile component of the conductive paste. Therefore, there was a limit to the cost reduction.
By the way, among the conductive powders used in the conductive paste, gold and silver have good conductivity, but are expensive and inexpensive nickel, aluminum, zinc, and the like cannot obtain good conductivity. For copper, the conductivity is as good as silver and is inexpensive, but it is easily oxidized and may deteriorate the conductivity or lack stability.

In order to solve such problems, various conductive pastes using copper powder whose surface is coated with silver have been developed. However, these conductive pastes have a drawback in that the storage stability as a paste is difficult to ensure due to increase in viscosity or gelation during storage. The reason for the decrease in storage stability is that the copper powder cannot be completely covered with silver in the process of coating silver on the copper powder, or copper is present on the surface layer, or the copper surface due to mechanical load in the paste dispersion process. It is considered that the viscosity is likely to increase during storage due to the catalytic action of the highly active copper surface.
Then, in order to improve storage stability, in patent document 2, the copper surface is made hard to expose by performing the process of coat | covering silver to copper powder twice. However, the copper powder coated with silver by this method requires a crushing step by a ball mill between the two plating steps, which makes the production complicated and reduces the cost merit. Furthermore, due to the characteristics of the plating process, it is difficult to completely cover silver by preventing the generation of very small pores called pinholes. As a result, even if the stability could be secured at room temperature, the viscosity tended to increase at a high temperature such as 40 ° C. assuming summer.

JP 2012-216287 A JP 2011-28985 A

From the above situation, an object of the present invention is to provide a conductive paste suitable for forming a wiring circuit that requires low cost and high conductivity, adhesion to a substrate, and storage stability.

In order to solve the above-mentioned problems, the present inventors have intensively studied a resin composition suitable for a conductive paste capable of obtaining low cost and high conductivity, adhesion to a substrate and storage stability. It has been found that the problems are solved by the present invention. The present invention has the following configuration.
1. (A) A conductive paste containing a polyester resin and / or polyurethane resin having an acid value of 5 mgKOH / g or less and a glass transition temperature of 50 ° C. or more , (B) a solvent, and (C) conductive powder, (C) The conductive paste comprises (C1) copper powder coated with silver on the surface and (C2) silver powder.
2. A conductive paste further comprising a polyester resin and / or a polyurethane resin having a glass transition temperature of 20 ° C. or lower .
3. The glass transition temperature of 20 ° C. or less of the polyester resin and / or polyurethane resins are polyester resin, conductive paste characterized by containing the aliphatic dicarboxylic acids at least 20 mol% of the total acid components.
4). (C) Conductive powder, (C1) Copper powder which coat | covered silver on the surface whose average particle diameter is 1-9 micrometers, and (C2) Silver powder whose average particle diameter is 1-9 micrometers, The electrically conductive paste characterized by the above-mentioned.
5. (C) Conductive powder contains (C1) copper powder which coat | covered silver on the surface whose average particle diameter is 1-4 micrometers, and (C2) silver powder whose average particle diameter is 1-4 micrometers, The electrically conductive paste characterized by the above-mentioned.
6). (C) Among conductive powders, the total conductive powder and the total weight% of silver occupied by the silver powder / total weight% of copper are within the range of 86/14 to 15/85% by weight. paste.
1. ~ 6. A printed circuit, wherein the conductive paste according to any one of the above is printed on a substrate.

With the conductive paste of the present invention, it is possible to obtain a conductive paste suitable for forming a wiring circuit that requires low cost and high conductivity, adhesion to a substrate, and storage stability.

The resin (A) used in the present invention is a polyester resin and / or a polyurethane resin having an acid value of 5 mgKOH / g or less. When the acid value of the resin exceeds 5 mgKOH / g, the present inventors have found that the viscosity of the conductive paste increases or gels due to the interaction with the copper surface, particularly during high-temperature storage at 40 ° C. or higher. Found. The acid value of the resin (A) is preferably 5 mgKOH / g or less, more preferably 2 mgKOH / g or less.
By using the polyester and / or polyurethane resin, it is possible to achieve a high storage stability that could not be achieved in the past in a conductive paste containing copper powder coated with silver on the surface. Furthermore, since no special process is required, an increase in cost can be avoided.
The number average molecular weight of the polyester resin and / or polyurethane resin is preferably 10,000 or more and 45,000 or less. If the number average molecular weight is less than 10,000, the cohesive force is lowered, the conductivity is lowered, and the paste viscosity is lowered. On the other hand, if the number average molecular weight exceeds 45,000, the solution viscosity of the resin increases and the productivity decreases, which is not preferable.

The glass transition temperature of the polyester resin and / or polyurethane resin is preferably −20 ° C. or higher and 100 ° C. or lower, and more preferably 50 ° C. or higher. If it is less than −20 ° C., when the curing agent is not blended, the resin softens at a high temperature, which may reduce the reliability of the coating film. Furthermore, the pencil hardness of the coating film also tends to decrease. When using a resin having a glass transition temperature of −20 ° C. to 50 ° C., the pencil hardness of the coating film may be lowered. Therefore, a curing agent may be blended, or a resin having a temperature of 50 ° C. or more may be mixed and blended. desirable. Moreover, when it exceeds 100 degreeC, since the adhesiveness to a base material falls, it is unpreferable.
As the polyester resin and / or polyurethane resin, in particular, a polyester resin and / or polyurethane resin having a glass transition temperature of 50 ° C. or higher and a polyester resin and / or polyurethane resin having a glass transition temperature of 20 ° C. or lower may be blended. This is preferable from the viewpoint of adhesion. In this case, the blending ratio is preferably 50 to 90% by weight of a resin having a glass transition temperature of 20 ° C. or lower with respect to a resin having a glass transition temperature of 50 ° C. or higher.
If it is less than 50% by weight, the adhesion of the coating film is lowered, and if it exceeds 90% by weight, the pencil hardness and adhesion of the coating film may be lowered.

The dicarboxylic acid used in the polyester resin and / or polyurethane resin of (A) used in the present invention is an aromatic dicarboxylic acid such as terephthalic acid, isophthalic acid, orthophthalic acid, 2,6-naphthalenedicarboxylic acid, succinic acid, Glutaric acid, adipic acid, sebacic acid, dodecanedicarboxylic acid, azelaic acid and other aliphatic dicarboxylic acids, 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 naphtha Examples thereof include alicyclic dicarboxylic acids such as range carboxylic acid and tricyclodecane dicarboxylic 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.
From the viewpoint of adhesion to the substrate, a polyester resin containing 20 mol% or more of an aliphatic dicarboxylic acid among all acid components is preferable. Of all the acid components used in the polyester, the content of the aliphatic dicarboxylic acid is preferably 60 mol% or less from the viewpoint of heat and moisture resistance. Among these, as the aromatic dicarboxylic acid, terephthalic acid, isophthalic acid, and orthophthalic acid are preferable from the viewpoint of flexibility. As the aliphatic dicarboxylic acid, sebacic acid, azelaic acid, and 1,4-cyclohexanedimethanol are preferable from the viewpoint of moisture resistance.

The glycol used in the polyester resin and / or polyurethane resin (A) 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, 1,9-nonanediol, 1,10-decanediol, 1,4-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,2-cyclohexanedimethanol, dimer diol, etc. Is mentioned. 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.

Examples of the diisocyanate compound used for the urethane resin include tetramethylene diisocyanate, hexamethylene diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, and isophorone diisocyanate.
The polyurethane resin is polymerized by a known method such as a prepolymer method or a one-shot method.
In these reactions, a known polymerization catalyst represented by an appropriate amount of a tertiary amine, a compound such as tin, titanium, or lead may be used as necessary. These reactions may be performed in a solvent used for the paste, or the solvent used for the reaction may be replaced with another solvent.

As the resin used in the present invention, a resin other than the polyester resin and / or the polyurethane resin may be blended within a range not impairing the content of the invention. For example, polyester urethane resin, polyether urethane resin, polycarbonate urethane resin, vinyl chloride / vinyl acetate copolymer, epoxy resin, phenol resin, acetal resin, phenoxy resin, acrylic resin, polyacrylonitrile resin, polybutadiene resin, hydrogenated polybutadiene You may mix | blend a base resin, nitrocellulose, modified celluloses, such as a cellulose acetate butyrate (CAB) and a cellulose acetate propionate (CAP), and a polyamidoimide resin in the range which does not deteriorate a characteristic. Also in this case, the acid value of each resin is preferably 5 KOHmg / g or less from the viewpoint of storage stability.

The conductive powder (C) used in the present invention contains (C1) a copper powder whose surface is coated with silver and (C2) a silver powder. (C1) The copper powder whose surface is coated with silver can be produced using a known method such as electroless plating or electrolytic plating. In particular, electroless plating by substitution plating capable of forming a uniform film thickness is preferable.
As for the average particle diameter of the copper powder which coat | covered silver on the surface used for this invention, 1-9 micrometers is preferable. Here, the average particle diameter was an average value of 50 measured numbers when the coating film was photographed with a scanning electron microscope at a magnification of 5000 or 10000 and the particle diameter of the silver powder was measured. In addition, about the average particle diameter of 5-9 micrometers, the particle size was measured by 5000 time, and about 1-5 micrometers, the particle size was measured by the magnification of 10,000 times.
If the particle size is smaller than 1 μm, increasing the blending amount of the conductive powder and securing the contact between the particles tends to decrease the conductivity, and the specific surface area increases, so the amount of silver to be coated increases. This may lead to an increase in cost. On the other hand, if it is larger than 9 μm, the copper powder tends to be deformed due to the shear stress at the time of kneading the paste in a roll mill, resulting in a problem that the copper surface is exposed.
Furthermore, when applied to applications that perform fine printing of 100 μm or less, which has recently been required for touch panel applications, the average particle size is more preferably 1 to 5 μm.

(C1) The shape of copper powder coated with silver on the surface is known in the form of flakes (flakes), spherical shapes including irregular shapes, plate shapes, dendritic shapes (dendritic shapes), and spherical primary particles are three-dimensional. From the viewpoint of the inner conductivity and uniformity of the silver coating, a flake shape or a spherical shape including an indefinite shape is preferable.
The amount of silver coated on the surface of the copper powder is preferably in the range of 5 to 30% by weight, more preferably in the range of 10 to 25% with respect to the copper powder from the viewpoint of cost and conductivity.
As a powder characteristic of the copper powder coated with silver, the tap density is preferably 2.5 g / cm ³ or more. If it is less than 2.5 g / cm ³ , if the silver coating amount is the same, the coating may be insufficient and the storage stability may deteriorate. The specific surface area is preferably 0.2 to 1.2 m ² / g from the viewpoint of conductivity and storage stability.

As the shape of the conductive powder (C2) silver powder used in the present invention, known flaky shape (flaky shape), spherical shape including irregular shape, plate shape, dendritic shape (dendritic shape), spherical primary particles are three-dimensional. From the viewpoint of the inner conductivity and printability, a flake shape or a spherical shape including an indefinite shape is preferable.
As an average particle diameter of silver powder, 1-9 micrometers is preferable. When the particle size is smaller than 1 μm, the conductivity tends to decrease unless the amount of silver powder is increased and the contact between the particles is not secured. On the other hand, if it is larger than 9 μm, the amount of particles larger than the opening of the screen plate increases, which may impair the printability. Furthermore, when applied to applications that perform fine printing of 100 μm or less, which has recently been required for touch panel applications, the average particle diameter is more preferably 1 to 4 μm.
Moreover, it is preferable that a tap density is 1.5-4.5 g / cm < ³ >. If it is less than 1.5 g / cm ³ , the paste viscosity will increase too much, and if it is greater than 4.5 g / cm ³ , the amount of silver powder will increase, leading to an increase in cost.
Furthermore, the specific surface area of the silver powder is preferably 1.0 to 3.5 m ² / g from the viewpoint of storage stability and conductivity.

(C) Of the conductive powder, it is preferable that the silver required for coating and the total weight% of silver occupied by the silver powder / total weight% of copper are 86/14 to 15/85% by weight. If the total weight of silver required for coating and silver occupied by the silver powder exceeds 86% by weight, the cost increases, which is not preferable. On the other hand, if it is less than 15% by weight, the conductivity may not be ensured. In applications where fine printing of 100 μm or less is required, a specific resistance of 2.0 × 10 −4 Ω · cm or less is required, and when the total weight of silver required for coating and silver powder is less than 15% by weight, The specific resistance may not be achieved. From the viewpoint of conductivity and cost, the total weight% of silver and the total weight% of copper occupied by silver and silver powder required for coating is more preferably 76/34 to 37/73 weight%.
As conductive powder (C), in addition to (C1) copper powder coated with silver on the surface and (C2) silver powder, carbon-based fillers such as carbon black and graphite powder, and / or gold, platinum, palladium, Metals such as nickel, aluminum and zinc and alloys selected from these metals can be blended.
Furthermore, silica, talc, mica, inorganic fillers such as barium sulfate, etc. can be mixed and used. However, from the viewpoint of environmental characteristics such as conductivity and moisture resistance and cost, carbon black and silica are contained in the total conductive powder. It is preferable to blend at not more than wt%, more preferably not more than 5 wt% and not less than 0.1 wt%.
The conductive paste of the present invention preferably has an F value of 80 to 95%. More preferably, it is 85 to 92%. The F value is a numerical value indicating the conductive powder part by weight with respect to 100 parts by mass of the total solid content contained in the paste, and is represented by F value = (conductive powder part by weight / solid content part by mass) × 100. The solid mass part referred to here includes all conductive powders other than the solvent, other fillers, resins, other curing agents and additives. If the F value is less than 80%, the conductivity tends to deteriorate. Moreover, adhesiveness and / or pencil hardness may fall. When the F value exceeds 95%, the amount of the binder resin is insufficient, and adhesion and printability may be deteriorated.
When the resin containing (A) contained in the conductive paste of the present invention is 100% by weight, the total of (C1) and (C2) is 400% to 2400% by weight, and (C1) and (C2) When the total is 100% by weight, the conductive powder other than (C1) and (C2) is preferably 0 to 5% by weight.

The type of the (B) solvent used in the present invention is not limited, and examples thereof include ester, ketone, ether ester, alcohol, ether, terpene, and hydrocarbon. Among these, high boiling point solvents such as ethyl carbitol acetate, butyl cellosolve acetate, butyl carbitol acetate, DBE, isophorone, benzyl alcohol, terpineol, and γ-butyrolactone suitable for screen printing are preferable. From the viewpoint of resin solubility and printability, ethyl carbitol acetate, butyl cellosolve acetate, butyl carbitol acetate, and DBE are preferred. When A is 100% by weight, C is preferably 50 to 300% by weight. From printability, it is more preferable to set it as 50 to 250 weight%.
When performing fine printing of 100 μm or less using the conductive paste of the present invention, the solvent can be adjusted to a paste viscosity suitable for printability. For example, when the fine printing of 80 μm is performed, the viscosity is 5 × HBDVIII (manufactured by BROOKFIELD), and when measured at 25 ° C. for 3 minutes at 2.5 rpm using the rotor CPE-52, the viscosity is 70 to 150 Pa · s. Is appropriate. From workability, 70-120 Pa.s is more preferable.

You may mix | blend the hardening | curing agent which can react with polyester and / or a polyurethane resin in the electrically conductive paste of this invention. The preferable compounding amount of the curing agent is 1 to 10 parts by weight with respect to 100 parts by weight of the resin. The kind of the curing agent is not particularly limited, but an isocyanate compound is particularly preferable from the viewpoint of curability. These isocyanate compounds are preferably used after being blocked from the viewpoint of storage stability.
Examples of the block isocyanate agent include phenols such as phenol, thiophenol, methylthiophenol, ethylthiophenol, cresol, xylenol, resorcinol, nitrophenol, chlorophenol, oximes such as acetoxime, methyl ethyl ketoxime, cyclohexanone oxime, methanol, Alcohols such as 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, and ε-caprolactam , Δ-valerolactam, γ-butyrolactam, β-propylolactam, and other lactams, and other aromatic amines, imides, acetylacetone 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.
You may add additives, such as a well-known antifoamer, a leveling agent, a dispersing agent, to the electrically conductive paste of this invention.

Hereinafter, the present invention will be described using examples. In the examples, “parts” simply means “parts by weight”. Each measurement item followed the following method.
1. Acid value (mgKOH / g)
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.
2. Glass transition temperature (Tg)
5 mg of sample resin is put in an aluminum sample pan and sealed, and a differential scanning calorimeter (DSC) DSC-220 manufactured by Seiko Instruments Inc. is used to increase the temperature from -50 to 200 ° C. at a rate of temperature increase of 20 ° C./min. And obtained from the temperature at the intersection of the extended line of the base line below the glass transition temperature and the tangent showing the maximum inclination at the transition part.
3. Preparation of test piece Conductive paste on annealed PET film with a thickness of 100μm, 25mm wide and 200mm long pattern (for resistivity, adhesion, pencil hardness measurement) so that the film thickness after drying is 7-12μm Screen printed. What dried this at 130 degreeC on the conditions for 30 minutes using the hot-air circulation type oven was used as the test piece. In addition, the substrate was replaced with a transparent conductive film, and the same pattern was screen-printed for adhesiveness measurement.
4). 2. Specific resistance The sheet resistance and the film thickness were measured using the test piece prepared in step 1 using a film thickness and a 4-terminal resistance measuring instrument, and the specific resistance was calculated from these. The film thickness was measured using a gauge stand ST-022 (manufactured by Ono Sokki Co., Ltd.), and the sheet resistance was measured using MILLIOHMMETER 4338B (manufactured by HEWLETT PACKARD).
5. 2. Adhesion Using the test piece prepared in the above, the adhesion was evaluated by peeling the cross-cut tape. The number of cuts in each direction of the lattice pattern was 11, the cut interval was 1 mm, 100 squares were created, and the cellophane tape CT-12 (manufactured by Nichiban Co., Ltd.) was used as the adhesive tape. After the tape was peeled, the case where 100% coating film in 100 squares remained on the substrate was marked with ◎, the case where 95 to 100% remained was marked with ◯, and the case where it was less than x.
6). 2. Pencil hardness The test piece prepared in (1) was placed on a 2 mm thick SUS304 plate and measured according to JIS K 5600-5-4.
7). Environmental test 3. The test piece prepared on the transparent conductive substrate V150A (manufactured by Nitto Denko Corporation) was subjected to a wet heat resistance test in which heating was performed at 85 ° C. and 85% RH for 240 hours, and adhesion was evaluated.
8). The storage-stable conductive paste was placed in a sealed container and stored at 40 ° C. for 2 weeks. Viscosity before and after storage was 5 × HBDVIII (manufactured by BROOKFIELD), measured at 25 ° C. for 3 minutes at 2.5 rpm using a rotor CPE-52, and the viscosity change after storage was −10 to 10% compared to before storage The inside is ◯, the inside of -30 to 30% is Δ, and the above is ×.
9. Printability Fine printability was evaluated using a print pattern of wiring width / space = 80 μm / 80 μm. The linearity of the straight part is good, the printed film width is 80 μm ± 20 μm, ○, the blur is generated, the wiring width is 80 μm ± 40, the screen plate is clogged, the number of printed sheets The case where chipping occurs at the same location when the two are stacked is designated as x.

Synthesis example. 1 (Polyester resin 1)
A four-necked flask equipped with a stirrer, a Liebig condenser, and a temperature controller was charged with 101 parts of dimethyl terephthalic acid, 35 parts of dimethyl isophthalic acid, 93 parts of ethylene glycol, 73 parts of neopentyl glycol, 0.068 parts of tetrabutyl titanate, The transesterification was performed at 180 ° C. for 3 hours. Subsequently, 61 parts of sebacic acid was added and esterification was further performed. Next, the pressure was gradually reduced to 1 mmHg or less, and polymerization was performed at 240 ° C. for 1 hour. The composition of the obtained copolyester was terephthalic acid / isophthalic acid / sebacic acid // ethylene glycol / neopentyl glycol = 52/18/30 // 55/45 (molar ratio), number average molecular weight 22,000, acid The value was 1.5 mgKOH / g and Tg was 7 ° C. The results are shown in Table 1.
Synthesis example. 2-6 (Polyester resin 2-7)
Synthesis example. 1 was synthesized in the same manner. The results are shown in Table 1. In addition, about the polyester resins 4 and 5, it is a synthesis example. After the polymerization of 1, the reaction mixture was cooled to 220 ° C. under a nitrogen stream, a predetermined amount of trimellitic anhydride was added, and the reaction was performed for 30 minutes. Moreover, the following were used for the raw material shown in Table 1.
BPE20: New Pole BPE20 (Bisphenol A ethylene oxide adduct) manufactured by Sanyo Chemical Industries
BPE40: New Pole BPE40 (Bisphenol A ethylene oxide adduct) manufactured by Sanyo Chemical Industries
Synthesis example. 7 (Polyurethane resin 1)
In a reaction vessel equipped with a thermometer, a stirrer, and a condenser, 100 parts of polyester resin 6 of the synthesis example, 2 parts of 1,6-hexanediol as a chain extender, 6 parts of neopentyl glycol, and ethyl carbitol acetate as a solvent After dissolving at 80 ° C., charged with 28 parts of diphenylmethane diisocyanate (MDI) and 0.08 part of dibutyltin dilaurate and allowed to react at 35% solid content at 80 ° C. for 3 hours or more until there is no residual isocyanate. The resulting solution was diluted with ethyl carbitol acetate to a solid content concentration of 35% to obtain urethane-modified polyester resin 1. The number average molecular weight was 40,000, the acid value was 0.6 mgKOH / g, and Tg was 83 ° C. The results are shown in Table 2.
Synthesis example. 8-9 (Polyurethane resin 2)
Synthesis example. Synthesized as in 6. The results are shown in Table 2.

Example 1
Silver powder 1 531 parts, copper powder 1 531 parts coated with 12% by weight of silver, conductive carbon black 8 parts, polyester resin 1 100 solid parts, leveling agent MK Conch (manufactured by Kyoeisha Chemical Co., Ltd.) 6 parts, dispersant 5 parts of Disperbyk 130 (manufactured by Big Chemie Japan Co., Ltd.) and 158 parts of ethyl carbitol acetate as a solvent were blended and sufficiently premixed, and then dispersed three times with a chilled three-roll mill. 4. Obtain the obtained conductive paste. It was printed, dried and evaluated by the method described in 1. The physical properties of the obtained coating film, the specific resistance 1.7 × 10- ⁴ Ω · cm, good adhesion was good with a pencil hardness H. As the transparent conductive substrate, V150 (manufactured by Nitto Denko Corporation) was used. In addition, environmental tests, printability and storage stability were evaluated. The results are shown in Table 3.
Examples 2-6
Evaluation was performed in the same manner as in Example 1. The results are shown in Table 3.
In all the examples, the physical properties of the coating film and the environmental test were good. Further, good results were obtained with respect to storage stability and printability.
The conductive powders, additives and solvents shown in Table 3 were as follows.
Silver powder 1: manufactured by AMES Goldsmith (average particle size 1.5 μm, tap density 4.0 g / cm ³ , specific surface area 1.3 m ² / g)
Silver powder 2: manufactured by AMES Goldsmith (average particle size 8.5 μm, tap density 1.7 g / cm ³ , specific surface area 1.7 m ² / g)
Copper powder coated with silver 1: manufactured by Ferro Japan Co., Ltd. (average particle size 2.5 μm, tap density 4.5 g / cm ³ , specific surface area 0.4 m ² / g, surface coated with 12 wt% silver) )
Copper powder 2 coated with silver: manufactured by AMES Goldsmith (average particle size 5.5 μm, tap density 2.8 g / cm ³ , specific surface area 1.0 m ² / g, surface coated with 10 wt% silver)
Conductive carbon black: Toka Black # 4500 manufactured by Tokai Carbon Co., Ltd.
Leveling agent: MK Conch dispersant manufactured by Kyoeisha Chemical Co., Ltd .: Disperbyk130 manufactured by Big Chemie Japan Co., Ltd.
Solvent: Ethyl carbitol acetate manufactured by Daicel Corporation

Comparative Examples 1-4
Evaluation was performed in the same manner as in Example 1. The results are shown in Table 4.
The conductive powders, additives and solvents shown in Table 4 were as follows. About what was not described, the same thing as the Example was used.
10% by weight of silver-coated copper powder 3: manufactured by Mitsui Kinzoku Co., Ltd. (average particle size 6.3 μm, tap density 0.9 g / cm ³ , specific surface area 1.0 m ² / g)
10% by weight of silver-coated copper powder 4: manufactured by Mitsui Kinzoku Co., Ltd. (average particle size 2.2 μm, tap density 2.7 g / cm ³ , specific surface area 1.8 m ² / g)
In Comparative Example 1, when a polyester resin having a high acid value was used, the storage stability was poor and the paste was gelled. In Comparative Example 2, when a polyurethane resin having a high acid value was used, the paste gelled.
In Comparative Example 3, when silver-coated copper powder having a low tap density was used, storage stability could not be ensured.
In Comparative Example 4, when flaky copper powder coated with silver having a high specific surface area was used, the conductivity was insufficient.

  The conductive paste of the present invention has low cost and high conductivity, adhesion to a substrate, and good storage stability, and is suitable for forming a wiring circuit for a touch panel.

Claims (7)

(A) A conductive paste containing a polyester resin and / or polyurethane resin having an acid value of 5 mgKOH / g or less and a glass transition temperature of 50 ° C. or more , (B) a solvent, and (C) conductive powder, (C) The conductive paste comprises (C1) copper powder coated with silver on the surface and (C2) silver powder. The conductive paste according to claim 1 having a glass transition temperature, characterized in that it comprises in the et to 20 ° C. or less of the polyester resin and / or polyurethane resins. The conductive resin according to claim 2 , wherein the polyester resin and / or polyurethane resin having a glass transition temperature of 20 ° C or lower is a polyester resin, and contains 20 mol% or more of an aliphatic dicarboxylic acid among all acid components. Sex paste.   The conductive powder (C) contains (C1) copper powder having an average particle diameter of 1 to 9 μm coated with silver and (C2) silver powder having an average particle diameter of 1 to 9 μm. 4. The conductive paste according to any one of 3.   The conductive powder (C) contains (C1) copper powder having an average particle diameter of 1 to 4 μm coated with silver and (C2) silver powder having an average particle diameter of 1 to 4 μm. 4. The conductive paste according to any one of 4 above.   (C) Among the conductive powders, the total weight% of silver required for coating and the total weight% of silver occupied by the silver powder / total weight% of copper are within the range of 86/14 to 15/85% by weight. The electrically conductive paste in any one of 1-5 The printed circuit formed by printing the electrically conductive paste in any one of Claims 1-6 on a base material.