JP7231537B2 - conductive composition - Google Patents

Description

The present invention relates to conductive compositions.

BACKGROUND ART Conventionally, a conductive composition containing conductive particles and an epoxy resin has been proposed as a material for forming electrodes in solar cells and the like (for example, Patent Document 1).

WO2016/017618

The conductive composition is required to have good screen-printability, low resistance in the resulting cured product, excellent adhesiveness to substrates, excellent storage stability, and the like. In particular, for finger electrode applications in solar cells, there is a demand for finer finger lines in screen printing in order to increase the light-receiving area in order to improve power generation efficiency.
Further, when the conductive composition is used, for example, as a busbar electrode of a solar cell, the busbar electrode is connected by a copper ribbon (interconnector) or the like coated with solder on the surface. The busbar electrode used is required to be excellent in solderability (bondability and/or bond strength between the conductive composition and solder).
Under such circumstances, the present inventors prepared a composition with reference to Patent Document 1 and evaluated it. It has become clear that there are cases where the level of adhesiveness or storage stability that is required these days is not met.
Accordingly, an object of the present invention is to provide a conductive composition that is excellent in solderability, screen printability, low resistance, adhesion to substrates, and storage stability.

As a result of intensive research by the present inventors to solve the above problems,
conductive particles;
an epoxy resin A that has an epoxy equivalent of less than 500 g/eq and is liquid at 25°C;
an epoxy resin B that has an epoxy equivalent of 400 g/eq to 5000 g/eq and is solid at 25°C;
a thermoplastic resin C having a weight average molecular weight of 25,000 to 65,000;
a curing agent D;
containing a solvent and
The total amount of the epoxy resin A, the epoxy resin B, the thermoplastic resin C, and the curing agent D is 3 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the conductive particles,
The mass ratio [(A+B)/C] of the total amount of the epoxy resin A and the epoxy resin B to the content of the thermoplastic resin C is 50/50 to 95/5,
The mass ratio [A/(B+C)] of the content of the epoxy resin A to the total amount of the epoxy resin B and the thermoplastic resin C is 15/85 to 85/15,
The mass ratio [D/(A+B)] of the content of the curing agent D to the total amount of the epoxy resin A and the epoxy resin B is 2/98 to 10/90,
The inventors have found that the desired effect can be obtained by substantially not containing a carboxylic acid metal salt, and have arrived at the present invention.
The present invention is based on the above knowledge and the like, and specifically solves the above problems with the following configuration.

1. conductive particles;
an epoxy resin A that has an epoxy equivalent of less than 500 g/eq and is liquid at 25°C;
an epoxy resin B that has an epoxy equivalent of 400 g/eq to 5000 g/eq and is solid at 25°C;
a thermoplastic resin C having a weight average molecular weight of 25,000 to 65,000;
a curing agent D;
containing a solvent and
The total amount of the epoxy resin A, the epoxy resin B, the thermoplastic resin C, and the curing agent D is 3 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the conductive particles,
The mass ratio [(A+B)/C] of the total amount of the epoxy resin A and the epoxy resin B to the content of the thermoplastic resin C is 50/50 to 95/5,
The mass ratio [A/(B+C)] of the content of the epoxy resin A to the total amount of the epoxy resin B and the thermoplastic resin C is 15/85 to 85/15,
The mass ratio [D/(A+B)] of the content of the curing agent D to the total amount of the epoxy resin A and the epoxy resin B is 2/98 to 10/90,
A conductive composition substantially free of metal carboxylate.
2. 2. The conductive composition as described in 1 above, wherein the epoxy resin A has a viscosity at 25° C. of 15 to 60,000 mPa·s.
3. 3. The conductive composition according to 1 or 2 above, wherein the thermoplastic resin C has a glass transition point of 80 to 100°C.
4. 4. The conductive material according to any one of 1 to 3 above, wherein the conductive particles are at least one selected from the group consisting of silver powder, copper powder, and silver-coated conductive powder having a surface at least partially coated with silver. sex composition.
5. 5. The conductive composition according to any one of 1 to 4 above, wherein the epoxy resin A contains an epoxy resin A1 having a cyclic structure and an epoxy resin A2 having a chain structure.
6. 6. The conductive composition according to 5 above, wherein the mass ratio of the content of the epoxy resin A1 to the content of the epoxy resin A2 [epoxy resin A1/epoxy resin A2] is 15/85 to 85/15.
7. 7. The conductive composition according to 5 or 6 above, wherein the epoxy resin A1 contains at least an epoxy resin having one cyclic structure in one molecule.

The conductive composition of the present invention is excellent in solderability, screen printability, low resistance, adhesion to substrates, and storage stability.

The present invention will be described in detail below.
In this specification, a numerical range represented by "-" means a range including the numerical values before and after "-" as lower and upper limits.
In this specification, unless otherwise specified, each component can be used singly or in combination of two or more substances corresponding to the component. When the component contains two or more substances, the content of the component means the total content of the two or more substances.
In the present invention, each component is not particularly limited in its manufacturing method. For example, a conventionally well-known thing is mentioned.
In the present specification, it means that at least one of solderability, screen printability, low resistance, adhesion to a substrate, and storage stability is superior, and that the effect of the present invention is superior. be.

[Conductive composition]
The conductive composition of the present invention (composition of the present invention) is
conductive particles;
an epoxy resin A that has an epoxy equivalent of less than 500 g/eq and is liquid at 25°C;
an epoxy resin B that has an epoxy equivalent of 400 g/eq to 5000 g/eq and is solid at 25°C;
a thermoplastic resin C having a weight average molecular weight of 25,000 to 65,000;
a curing agent D;
containing a solvent and
The total amount of the epoxy resin A, the epoxy resin B, the thermoplastic resin C, and the curing agent D is 3 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the conductive particles,
The mass ratio [(A+B)/C] of the total amount of the epoxy resin A and the epoxy resin B to the content of the thermoplastic resin C is 50/50 to 95/5,
The mass ratio [A/(B+C)] of the content of the epoxy resin A to the total amount of the epoxy resin B and the thermoplastic resin C is 15/85 to 85/15,
The mass ratio [D/(A+B)] of the content of the curing agent D to the total amount of the epoxy resin A and the epoxy resin B is 2/98 to 10/90,
It is a conductive composition that does not substantially contain a metal carboxylate.

Since the composition of the present invention has such a constitution, it is believed that the desired effect can be obtained. Although the reason is not clear, it is presumed to be approximately as follows.
That is, in the present invention, a liquid epoxy resin A having a predetermined range of epoxy equivalents and a solid epoxy resin B having a predetermined range of epoxy equivalents are used in combination, and the content of each component, etc. is set within a predetermined range. , It is thought that disconnection etc. do not occur easily in screen printing, it is possible to increase the density of conductive particles, and the cured product obtained is tough, so it is considered to be excellent in screen printability, low resistance, and adhesion to substrates. be done.
Further, the composition of the present invention contains a thermoplastic resin having a weight-average molecular weight in a predetermined range with respect to the conductive particles and epoxy resin A and epoxy resin B. and can impart toughness to the composition. Due to the above toughness, the composition of the present invention is considered to be excellent in solderability (in particular, bonding strength between the conductive composition and solder).
The composition of the present invention can balance solderability, screen printability, low resistance, and adhesion to a substrate at a high level by containing each component in a predetermined content. Guess you can.
Moreover, the composition of the present invention is excellent in storage stability because it does not substantially contain a metal carboxylate.
Each component contained in the composition of the present invention will be described in detail below.

<<Conductive particles>>
The conductive particles contained in the composition of the present invention are not particularly limited as long as they are particulate substances having conductivity.
Examples of conductive particles include metal materials having an electrical resistivity of 20×10 ⁻⁶ Ω·cm or less.
Specific examples of the metal material include gold (Au), silver (Ag), copper (Cu), aluminum (Al), magnesium (Mg), and nickel (Ni).

Examples of the conductive particles include silver powder, copper powder, and silver-coated conductive powder whose surface is at least partly coated with silver.
From the viewpoint that the effect of the present invention is superior, the conductive particles are at least one selected from the group consisting of silver powder, copper powder, and silver-coated conductive powder having at least part of the surface coated with silver. preferable.
Examples of the core constituting the silver-coated conductive powder include particles of the metal material.

The average particle size of the conductive particles is preferably from 0.5 to 10 μm, more preferably from 1 to 5 μm, from the viewpoint of superior effects of the present invention.
Here, in the present invention, the average particle diameter of the conductive particles is the particle diameter at 50% cumulative (50% volume cumulative diameter) obtained by measuring the volume-based particle size distribution using a laser diffraction particle size distribution analyzer. Also referred to as "average particle size (D50)"). As such a laser diffraction particle size distribution analyzer, for example, an apparatus conforming to LA-500 (trade name) manufactured by Horiba, Ltd. can be mentioned.

The conductive particles preferably contain at least one selected from the group consisting of flaky particles E and spherical particles F from the viewpoint of achieving superior effects of the present invention.
In the present invention, the term "spherical" refers to a shape of particles having a major axis/minor axis ratio of 2 or less, and the term "flaky" refers to a shape having a major axis/minor axis ratio of more than 2. Here, the long diameter and short diameter of particles constituting the conductive particles can be obtained based on an image obtained from a scanning electron microscope (SEM). In addition, the “major axis” refers to the longest line segment passing through the approximate center of gravity of the particle in the particle image obtained by SEM. The “minor diameter” refers to the shortest line segment passing through the approximate center of gravity of the particle in the particle image obtained by SEM.

The flake-like particles E may be either single crystals or polycrystals.
The specific surface area of the flake-shaped particles E is preferably 0.2 to 1.0 m ² /g, more preferably 0.2 to 0.8 m ² /g, from the viewpoint of superior effects of the invention. If it is more than 1.0 m ² /g, the viscosity tends to be increased. In order to obtain a composition with a viscosity range that allows proper printing, it is necessary to add a larger amount of solvent, and because the solid content decreases, there may be a problem that the aspect ratio of the wiring after printing or curing becomes small. . If it is less than 0.2 m ² /g, the viscosity tends to be low. In order to obtain a composition with a viscosity range that allows proper printing, it is necessary to add a smaller amount of solvent, which may cause a problem of difficulty in controlling the viscosity during production.
In the present invention, the specific surface area of the conductive particles refers to a value obtained based on the BET formula from the nitrogen adsorption isotherm at -196°C.
The average particle diameter of the flake-shaped particles E is preferably 1 to 15 μm, more preferably 3 to 10 μm, from the viewpoint of superior effects of the invention. If the thickness is larger than 10 μm, mesh clogging is likely to occur in a wiring process such as screen printing, and in particular, wire breakage is likely to occur during fine line patterning. If it is less than 1 μm, the number of contacts between the conductive particles increases, the contact resistance increases, and the resistance of the obtained wiring may increase. Furthermore, due to the low thixotropy of the resulting composition, there may occur a problem that it is difficult to form wiring having a high aspect ratio in a wiring process such as screen printing.

The specific surface area of the spherical particles F is preferably 0.5 to 1.6 m ² /g, more preferably 0.5 to 1.2 m ² /g, from the viewpoint of superior effects of the invention. If it is more than 1.6 m ² /g, the viscosity tends to be high. In order to obtain a composition with a viscosity range that allows proper printing, it is necessary to add a larger amount of solvent, and because the solid content decreases, there may be a problem that the aspect ratio of the wiring after printing or curing becomes small. . If it is less than 0.5 m ² /g, the viscosity tends to be low. In order to obtain a composition with a viscosity range that allows proper printing, it is necessary to add a smaller amount of solvent, which may cause a problem of difficulty in controlling the viscosity during production.
The average particle size of the spherical particles F is preferably 0.5 to 3 μm, more preferably 0.8 to 2 μm, from the viewpoints of superior effects of the invention and superior printability and conductivity. If it is larger than 3 μm, the gaps between the particles increase and the density of the conductive particles in the composition decreases, which may increase the resistance of the obtained wiring. If it is smaller than 0.5 μm, the number of contacts between the conductive particles increases, the contact resistance increases, and the resistance of the obtained wiring may increase.

In the present invention, when a plurality of types of conductive particles are used as the conductive particles, the average specific surface area of the conductive particles is preferably 0.5 to 0.8 m ² /g, and 0.5 to 0.8 m 2 /g, from the viewpoint of superior effects of the invention. 5 to 0.7 m ² /g is more preferable.
In the present invention, the average specific surface area of the conductive particles can be obtained by dividing the sum of the products of the specific surface area of each conductive particle and its content by the sum of the content of each conductive particle.

When the flaky particles E and the spherical particles F are contained as the conductive particles, the mass ratio of the spherical particles F to the flaky particles E (spherical particles F/flaky particles E) is from the viewpoint that the effect of the invention is superior. Therefore, 75/25 to 25/75 is preferable, and 70/30 to 30/70 is more preferable.

A method for producing the conductive particles is not particularly limited. For example, a conventionally well-known thing is mentioned.
The method for producing spherical conductive particles (for example, spherical particles F) is not particularly limited, and for example, those produced by a wet reduction method, an electrolytic method, an atomizing method, or the like can be preferably used.
The method for producing flake-shaped conductive particles (for example, flake-shaped particles E) is not particularly limited, and conventionally known methods can be used. For example, the spherical conductive particles produced by the above-described method are used as a base powder, and the base powder is mechanically processed by a ball mill, a bead mill, a vibration mill, an agitating pulverizer, etc., and the base powder is flakes by physical force. It is possible to preferably use those produced by the method of converting.

<<epoxy resin A, epoxy resin B>>
The composition of the present invention contains epoxy resin A and epoxy resin B.
In the present invention, an epoxy resin is a compound having two or more oxirane rings (epoxy groups) in one molecule. The oxirane ring can be attached to an organic group. The organic group is not particularly limited. Examples thereof include hydrocarbon groups which may have a heteroatom such as an oxygen atom, a nitrogen atom and a sulfur atom. Hydrocarbon groups are not particularly limited. Examples include aliphatic hydrocarbon groups (linear, branched, cyclic, and combinations thereof), aromatic hydrocarbon groups, and combinations thereof. The heteroatom may form, for example, an ether bond, a hydroxy group, or a urethane bond.
In the present invention, the hydrogenated epoxy resin may be either partially hydrogenated or fully hydrogenated.

<<epoxy resin A>>
Epoxy resin A contained in the composition of the present invention has an epoxy equivalent of less than 500 g/eq and is liquid at 25°C.
Epoxy resin A preferably has two or three oxirane rings in one molecule.

<Epoxy equivalent of epoxy resin A>
In the present invention, the epoxy equivalent of epoxy resin A is less than 500 g/eq.
The epoxy equivalent of the epoxy resin A is preferably 100 to 300 g/eq from the viewpoint that the effect of the present invention is superior.

<Liquid>
In the present invention, epoxy resin A is liquid at 25°C.

(Viscosity of epoxy resin A)
The viscosity of the epoxy resin A at 25° C. is preferably 15 to 60,000 mPa·s, more preferably 50 to 15,000 mPa·s, from the viewpoint of superior effects of the present invention.
In the present invention, the viscosity of the epoxy resin was measured according to JIS Z 8803 under the condition of 25°C.

(Structure of epoxy resin A)
Examples of the epoxy resin A include an epoxy resin A1 having a cyclic structure and an epoxy resin A2 having a chain structure. Epoxy resin A2 does not have a cyclic structure.
Epoxy resin A preferably contains epoxy resin A1 having a cyclic structure and epoxy resin A2 having a chain structure, from the viewpoint that the effect of the present invention is superior.

Examples of the cyclic structure include a cyclic aliphatic hydrocarbon group such as a cyclohexane skeleton; an aromatic hydrocarbon group such as a benzene ring and hydrogenated products thereof.
Examples of the chain structure include a poly(oxyalkylene) group and an oxyalkylene group.

・Epoxy resin A1
The epoxy resin A1 having a cyclic structure may further have a urethane bond in addition to the oxirane ring. Also, the epoxy resin A1 does not have to have a urethane bond.

When the epoxy resin A1 further has a urethane bond, toughness (flexibility) can be imparted to the composition, resulting in better solderability. The urethane bond may be introduced into the organic group to which an oxirane ring can be bonded.

Examples of the epoxy resin A1 having a cyclic structure include bisphenol skeletons such as bisphenol A type, bisphenol F type, bisphenol E type, brominated bisphenol A type, hydrogenated bisphenol A type, bisphenol S type, and bisphenol AF type. and hydrogenated products thereof; urethane-modified products (urethane-modified epoxy resins) and hydrogenated products thereof; epoxy resins having one cyclic structure in one molecule and hydrogenated products thereof.
The urethane-modified epoxy resin has a plurality of cyclic structures in one molecule.

Examples of the epoxy resin having one cyclic structure in one molecule and hydrogenated products thereof include, for example, epoxy resins having a benzenediol skeleton and hydrogenated products thereof; epoxy resins having a phthalic acid skeleton and hydrogenated products thereof; epoxy resins having a benzenedimethanol skeleton; epoxy resins having a cyclohexanedimethanol skeleton; epoxy resins having an aniline skeleton; epoxy resins having a toluidine skeleton;

Among them, the epoxy resin A1 is preferably a urethane-modified epoxy resin, an epoxy resin having one cyclic structure in one molecule, and a urethane-modified epoxy resin, benzene Epoxy resins having a diol skeleton, epoxy resins having a phthalic acid skeleton, and epoxy resins having a cyclohexanedimethanol skeleton are more preferred, and urethane-modified epoxy resins and resorcinol diglycidyl ether having a resorcin skeleton are more preferred.

When the epoxy resin A1 contains an epoxy resin having one cyclic structure in one molecule, the content of the epoxy resin having one cyclic structure in one molecule is 50 to 100 mass with respect to the epoxy resin A1. % is preferred.

・Epoxy resin A2
Examples of the epoxy resin A2 having a chain structure include polyglycidyl ethers of poly(oxyalkylene) polyols and polyglycidyl-type epoxy resins such as polyglycidyl ethers of alkylene polyols.

The poly(oxyalkylene) polyol or alkylene polyol that can constitute the polyhydric alcohol-based glycidyl-type epoxy resin is not particularly limited.
The alkylene group of the poly(oxyalkylene) polyol or alkylene polyol may be linear or branched. The number of carbon atoms in the alkylene group can be, for example, 2 to 15.
Examples of the alkylene group include an ethylene group, a propylene group, and a trimethylene group.

The number of repeating units (oxyalkylene group) of the repeating unit (oxyalkylene group) contained in the poly(oxyalkylene) polyol is preferably 2 to 15, more preferably 3 to 10, from the viewpoint of superior effects of the present invention.

Examples of polyglycidyl ethers of alkylene polyols include ethylene glycol diglycidyl ether and propylene glycol diglycidyl ether.
Examples of commercially available polyglycidyl ethers of alkylene polyols include trade name EX-810 (manufactured by Nagase Chemtech Co., Ltd.).
Polyglycidyl ethers of poly(oxyalkylene) polyols include, for example, polyethylene glycol diglycidyl ether and polypropylene glycol diglycidyl ether.
Examples of commercially available polyglycidyl ethers of poly(oxyalkylene) polyols include trade names EX-830, EX-841, EX-920 and EX-931 (manufactured by Nagase Chemtech).

- Combination of epoxy resin A1 and epoxy resin A2 As a combination of epoxy resin A1 and epoxy resin A2, for example,
a combination of the epoxy resin having a bisphenol skeleton or a hydrogenated product thereof and the polyhydric alcohol-based glycidyl-type epoxy resin;
a combination of a urethane-modified epoxy resin and the polyhydric alcohol-based glycidyl-type epoxy resin;
An epoxy resin having one cyclic structure in one molecule (e.g., an epoxy resin having a benzenediol skeleton) and the polyhydric alcohol-based glycidyl-type epoxy resin (e.g., an oxyalkylene group having repeating units of greater than 10 and 15 or less, and poly(oxyalkylene) diglycidyl ether).

(Epoxy resin A1/epoxy resin A2)
When the epoxy resin A contains the epoxy resin A1 and the epoxy resin A2, the mass ratio of the content of the epoxy resin A1 to the content of the epoxy resin A2 [epoxy resin A1/epoxy resin A2] is the From the viewpoint of superior effects, it is preferably 15/85 to 85/15, more preferably 30/70 to 70/30.

<<epoxy resin B>>
The epoxy resin B contained in the composition of the present invention has an epoxy equivalent of 400 g/eq or more and 5000 g/eq or less and is a solid epoxy resin at 25°C.
Epoxy resin B preferably has two or three oxirane rings in one molecule.

<Epoxy equivalent of epoxy resin B>
In the present invention, the epoxy equivalent of epoxy resin B is 400 g/eq or more and 5000 g/eq or less.
The epoxy equivalent of the epoxy resin B is preferably 1500 to 3500 g/eq from the viewpoint that the effect of the present invention is superior.

<Solid>
In the present invention, epoxy resin B is solid under conditions of 25°C.

(Softening point of epoxy resin B)
The softening point of the epoxy resin B is preferably 50 to 150°C, more preferably 100 to 150°C, from the viewpoint that the effect of the present invention is superior.
In the present invention, the softening point of the epoxy resin was measured according to JIS K-7234.

(Structure of epoxy resin B)
Examples of the epoxy resin B include epoxy resins having a bisphenol skeleton such as bisphenol A type, bisphenol F type, bisphenol E type, brominated bisphenol A type, hydrogenated bisphenol A type, bisphenol S type, and bisphenol AF type. mentioned.
Among them, the epoxy resin B is preferably at least one selected from the group consisting of bisphenol A type and bisphenol F type, for example, from the viewpoint that the effect of the present invention is superior.

<<Thermoplastic resin C>>
Thermoplastic resin C contained in the composition of the present invention is a thermoplastic resin having a weight average molecular weight of 25,000 to 65,000.

<Weight Average Molecular Weight of Thermoplastic Resin C>
In the present invention, the thermoplastic resin C has a weight average molecular weight of 25,000 to 65,000.
The weight-average molecular weight is preferably from 30,000 to 55,000, more preferably from 30,000 to 45,000, from the standpoint of superior effects of the present invention.
In the present invention, the weight-average molecular weight of thermoplastic resin C is a standard polystyrene conversion value based on a measurement by gel permeation chromatography (GPC) using tetrahydrofuran (THF) as a solvent.

(Type of thermoplastic resin C)
Examples of the thermoplastic resin C include phenoxy resin, polyamide, polyester, polycarbonate and the like.
Among them, the thermoplastic resin C is preferably a phenoxy resin from the viewpoint of being superior in the effects of the present invention.

Phenoxy resin One preferred embodiment of the phenoxy resin is a compound formed from bisphenol (a compound having a basic skeleton in which at least two hydroxyphenyl groups are bonded to one carbon atom) and epichlorohydrin. Phenoxy resins have hydroxyl groups produced by the reaction of bisphenol and epichlorohydrin.
Preferred embodiments of the phenoxy resin include, for example, a phenoxy resin having a plurality of hydroxyl groups obtained by the above reaction, a chain phenoxy resin, and a chain phenoxy resin having a plurality of hydroxyl groups obtained by the above reaction.
In the present invention, the phenoxy resin may have no epoxy groups. The ends of the phenoxy resin can be blocked with, for example, monocarboxylic acid from the viewpoint of better solderability.

The bisphenol forming the phenoxy resin is not particularly limited. For example, bisphenol A, bisphenol F, bisphenol AF, bisphenol AD, bisphenol S, tetramethylbisphenol A, tetramethylbisphenol F, tetramethylbisphenol AD, tetramethylbisphenol S, tetramethylbisphenol S, tetramethylbisphenol S, Bisphenol A, tetrafluorobisphenol A and tetrafluorobisphenol A can be mentioned.
Among them, at least one selected from the group consisting of bisphenol A and bisphenol F is preferable.

(Glass transition point of thermoplastic resin C)
The glass transition point (glass transition temperature) of the thermoplastic resin C is preferably 80 to 100° C., more preferably 80 to 90° C., from the viewpoint of superior effects of the present invention.
In the present invention, the glass transition point of the thermoplastic resin C conforms to JIS K7121:2012 (method for measuring the transition temperature of plastics) and is measured using a differential thermal analysis instrument at a temperature elevation of 5°C/min. It is the value obtained by reading the inflection point in the curve obtained when measuring .

<<Curing Agent D>>
The curing agent D contained in the composition of the present invention is not particularly limited as long as it can be used as a curing agent for epoxy resins. Among them, cationic curing agents are preferred. Cationic curing agents include, for example, amine, sulfonium, ammonium, and phosphonium curing agents.

Examples of the curing agent D include boron trifluoride ethylamine, boron trifluoride piperidine, boron trifluoride triethanolamine, boron trifluoride phenol, p-methoxybenzenediazonium hexafluorophosphate, and diphenyliodonium hexafluorophosphate. , tetraphenylsulfonium, tetra-n-butylphosphonium tetraphenylborate, tetra-n-butylphosphonium-o,o-diethylphosphorodithioate and the like.
Among these, boron trifluoride ethylamine, boron trifluoride piperidine, and boron trifluoride triethanolamine, which are complexes of boron trifluoride and an amine compound, can be further reduced in volume resistivity. It is preferred to use at least one complex selected from the group consisting of:

<<Solvent>>
The composition of the invention contains a solvent.
The solvent is not particularly limited. Examples include butyl carbitol, butyl carbitol acetate, cyclohexanone, methyl ethyl ketone, isophorone, α-terpineol and the like.
A commercial product can be used as a solvent.

The content of the solvent is preferably 20 to 200 parts by mass with respect to 100 parts by mass of the total amount of the epoxy resin A, the epoxy resin B, the thermoplastic resin C, and the curing agent D, from the viewpoint that the effect of the present invention is superior. , more preferably 40 to 100 parts by mass.

<Total amount of epoxy resin A, epoxy resin B, thermoplastic resin C and curing agent D>
In the present invention, the total amount of epoxy resin A, epoxy resin B, thermoplastic resin C and curing agent D is 3 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the conductive particles.
The total amount of epoxy resin A, epoxy resin B, thermoplastic resin C, and curing agent D is more preferably 5 to 8 parts by mass with respect to 100 parts by mass of the conductive particles, from the viewpoint of achieving superior effects of the present invention.

<[(A+B)/C]>
In the present invention, the mass ratio [(A+B)/C] of the total amount of epoxy resin A and epoxy resin B to the content of thermoplastic resin C is 50/50 to 95/5.
[(A + B) / C] is preferably 60/40 to 90/10, and 70/30 to 90/ 10 is more preferred.

<[A/(B+C)]>
In the present invention, the mass ratio of the content of epoxy resin A to the total amount of epoxy resin B and thermoplastic resin C [A/(B+C)] is 15/85 to 85/15.
[A/(B+C)] is preferably 30/70 to 70/30, and 50/50 to 70/ 30 is more preferred.

<[D/(A+B)]>
In the present invention, the mass ratio of the content of curing agent D to the total amount of epoxy resin A and epoxy resin B [D/(A+B)] is 2/98 to 10/90.
[D/(A+B)] is preferably 5/95 to 8/92 from the viewpoint of excellent curability due to the effects of the present invention.

<Contains substantially no carboxylic acid metal salt>
The compositions of the present invention are substantially free of metal carboxylates.
In the present invention, "substantially free of carboxylic acid metal salt" means that the content of carboxylic acid metal salt is 0 to 0.5% by mass relative to the total amount of the composition of the present invention.

A carboxylic acid metal salt is a metal salt of an organic carboxylic acid. Examples of the carboxylic acid metal salt include fatty acid metal salts.
The metal that constitutes the carboxylic acid metal salt is not particularly limited. Examples of the metal include at least one metal selected from the group consisting of silver, magnesium, nickel, copper, zinc, yttrium, zirconium, tin and lead.
The organic carboxylic acid constituting the carboxylic acid metal salt is not particularly limited as long as it is a hydrocarbon compound having --COOH. The organic carboxylic acid may further have a hydroxyl group. Examples of the organic carboxylic acid include fatty acids. The fatty acid may further have a hydroxyl group.
Carboxylic acid metal salts include, for example, fatty acid metal salts such as 2-hydroxyisobutyric acid silver salt (the fatty acid constituting the fatty acid metal salt may further have a hydroxy group).

(Additive)
If necessary, the composition of the present invention may further contain additives such as epoxy resins other than the epoxy resins A and B, thermoplastic resins other than the thermoplastic resin C, and reducing agents.
Specific examples of the reducing agent include ethylene glycols and the like.

The composition of the present invention does not particularly require a glass frit that is generally used as a high-temperature (700-800° C.) firing type conductive paste. The composition of the present invention contains substantially no glass frit (the content of the glass frit is 0 to 0.1 parts by mass with respect to 100 parts by mass of the conductive particles). be done.

(Method for producing conductive composition)
The method for producing the composition of the present invention is not particularly limited, and examples thereof include a method of mixing each of the above components using a roll, kneader, extruder, universal stirrer, or the like.

For example, the composition of the present invention can be applied to a substrate and heated under conditions of 180 to 230° C. to cure the composition.
The substrate is not particularly limited. Examples include silicon substrates, glass, metals, resin substrates, and films. The substrate may be subjected to a TCO (transparent oxide conductive film) treatment such as ITO (indium tin oxide).
A cured product formed using the composition of the present invention can be used, for example, as electrodes of solar cells (eg, finger electrodes, busbar electrodes), electrodes of touch panels, and die bonds of LEDs.

When a solar cell has a busbar electrode formed using the composition of the present invention, a plurality of solar cells are connected by an interconnector to connect the plurality of solar cells to form a solar cell module. can be manufactured. In this case, the busbar electrode of one solar cell is fused to the end of the interconnector by soldering, and the busbar electrode of another solar cell is fused to the other end of the interconnector by soldering. be joined together.
Solder used for the above bonding is not particularly limited. For example, a conventionally well-known thing is mentioned. Specific examples include alloys such as tin-lead, tin-silver-copper, and tin-bismuth.
Moreover, the interconnector is not particularly limited. For example, a conventionally well-known thing is mentioned. Specifically, for example, the interconnector includes a core material of copper coated with solder.
The bus bar electrode and the solder can be joined by heating at 200 to 300° C., for example.

(Adhesion between the composition of the present invention and a substrate)
By containing the epoxy resin A and the epoxy resin B, the composition of the present invention can adhere to a substrate.
In addition, when the composition of the present invention contains a thermoplastic resin having a hydroxy group as the thermoplastic resin C (for example, a phenoxy resin), the hydroxy group can interact with the substrate, and adhesion with the substrate can contribute to

(Fusing of the composition of the present invention and solder)
Since the composition of the present invention contains conductive particles made of metal, it can be fused and joined to solder by heating.
Since the composition of the present invention contains the thermoplastic resin C, the composition of the present invention is toughened by the thermoplastic resin C, and the composition of the present invention and the solder after the composition of the present invention is joined with the solder. The adhesive strength (bonding strength) with In addition, due to the fact that the composition of the present invention is plasticized by heating during soldering, the thermoplastic resin C does not inhibit the contact between the solder and the conductive particles, and the composition of the present invention is effective with the solder. can be effectively fused.

EXAMPLES The present invention will be specifically described below with reference to Examples. However, the present invention is not limited to these.
<<Production of composition>>
Each component shown in Table 1 below was used in the composition (parts by mass) shown in the same table, and these were mixed with a stirrer to produce a composition.

<Evaluation>
The following evaluations were performed using the compositions produced as described above. The results are shown in Table 1.

<Volume resistivity (specific resistance)>
Each composition produced as described above was applied to a glass substrate by screen printing to form a solid test pattern of 2 cm×2 cm. After that, it was dried and cured in an oven at 200° C. for 30 minutes to prepare a conductive film.
The volume resistivity of each of the produced conductive films was evaluated by a 4-terminal 4-probe method using a resistivity meter (Loresta GP, manufactured by Mitsubishi Chemical Corporation).
A sample having a volume resistivity of less than 8.0 μΩ·cm was judged to have a good volume resistivity.

<Screen printability>
60 μm printability was evaluated for screen printability.
In the present invention, when the 60 μm printability is ◯ in the following evaluation, the screen printability is considered to be excellent.
· 60 μm printability A film of ITO (indium oxide doped with Sn) was formed as a transparent conductive layer on the surface of a silicon substrate.
Using a stainless steel screen mask with a mesh count of 360 mesh, an emulsion thickness of 15 μm, a wiring opening width of 60 μm, a wire diameter of 16 μm, and an opening of 55 μm, a screen plate A with a line opening width of 60 μm was produced.
Next, each composition prepared as described above was screen-printed on the ITO at a printing speed of 200 mm/sec using screen plate making A to obtain wiring with a line width of 60 to 80 μm.
As described above, the wiring obtained by screen printing was observed with a laser microscope (magnification of 300 times), and the quality of printability at a line opening width of 60 μm (60 μm printability) was determined according to the following criteria.
(Evaluation criteria)
A case in which neither disconnection, meandering, blurring nor mesh mark was observed was evaluated as "Good" as being extremely good in 60 μm printability.
When any one of meandering, blurring, and mesh traces was observed, although no disconnection was observed, the 60 μm printability was evaluated as “Δ” as being slightly inferior.
When disconnection was confirmed, the 60 μm printability was evaluated as “x” as being extremely poor.

<Adhesion>
A film of ITO (Sn-doped indium oxide) was formed as a transparent conductive layer on the surface of the silicon substrate.
Next, each composition produced as described above was applied onto the transparent conductive layer by screen printing at a printing speed of 200 mm/sec to form a fine line test pattern with a width of 60 to 80 μm and a length of 25 mm. The screen printing mask used at this time had a size of 360 mesh, an emulsion thickness of 15 μm, a wiring opening width of 60 μm, a wire diameter of 16 μm, and an opening of 55 μm.
Thereafter, the test pattern was dried and cured at 200° C. for 30 minutes to prepare a test sample having 20 wirings on the transparent conductive layer.
Next, a strip of tape was applied in a direction perpendicular to all of the wirings, and a peeling test was performed by immediately peeling the tape from the test sample.
(Evaluation criteria)
As a result of the peeling test, when the wiring was not peeled from the transparent conductive layer at all, it was evaluated as having excellent adhesiveness and was indicated with "◯".
When 1 or 2 out of 20 wires were peeled off, this was evaluated as poor adhesion and indicated as "x".

<Solderability>
A film of ITO (Sn-doped indium oxide) was formed as a transparent conductive layer on the surface of the silicon substrate.
Next, each composition produced as described above was applied onto the transparent conductive layer by screen printing at a printing speed of 200 mm/sec to form a linear test pattern (busbar electrode) having a width of 1.5 mm and a length of 50 mm. bottom. The screen printing mask used at this time had a line pattern of 250 meshes, an emulsion thickness of 10 μm, and a wiring opening width of 1.5 mm.
Next, a solder ribbon (manufactured by Ulbrich) having a width of 1.5 mm in which Sn/Pb eutectic solder is dipped in a copper core is applied to match the width of the test pattern and the solder ribbon, and the width of the test pattern and the length of 50 mm. was placed on the wiring of the test pattern so as to overlap with the above, and the overlapping portion of the test pattern and the solder ribbon was heated at 250 ° C. and crimped, thereby soldering the wiring and the solder ribbon. .
(Tensile test)
The soldered test piece was cooled to room temperature, and the soldered test piece was subjected to a 180° tensile test under room temperature conditions to measure the solder bond strength.
(Evaluation criteria)
When the solder adhesive strength was 1.0 N/mm or more, the solderability was evaluated as being excellent, and this was indicated by "◯".
When the solder adhesive strength was less than 1.0 N/mm, the solderability was evaluated as poor and indicated as "x".
As for the peel mode (the failure mode of the test piece after the tensile test was visually confirmed), "CF" means cohesive failure, and "AF" means interfacial peel. "CF" is preferred.

<Storage stability>
(Measurement of viscosity)
The viscosity of the composition produced as described above (initial viscosity), and the viscosity of the composition produced as described above after being placed in a refrigerated environment at 5°C for 30 days (viscosity after storage), Each was measured according to JIS K 7117-1:1999. The above measurements were carried out using a cone-plate viscometer (manufactured by Brookfield Co.), rotating a CP52 spindle at 1 rpm, and room temperature.
(Viscosity increase rate)
From the initial viscosity and the viscosity after storage of each composition measured as described above, the viscosity increase rate (%)=(viscosity after storage/initial viscosity)×100 was calculated.
(Evaluation criteria)
When the viscosity increase rate was less than 150%, the storage stability was evaluated as being excellent, and this was indicated as "◯".
When the rate of increase in viscosity was 150% or more, the storage stability was evaluated as poor and indicated as "x".

Details of each component shown in Table 1 are as follows.

The silver flakes in Tables 1 and 2 correspond to the flake-like particles E of the conductive particles in the present invention.
Moreover, spherical silver corresponds to the spherical particles F of the conductive particles in the present invention.
In Table 2, "bis F" means bisphenol F type epoxy resin. "Bis A" means a bisphenol A type epoxy resin. "Biphenyl-type" means a biphenyl-type epoxy resin.

(Preparation of silver 2-hydroxyisobutyrate)
50 g of silver oxide (manufactured by Toyo Kagaku Kogyo Co., Ltd.), 45 g of 2-hydroxyisobutyric acid (manufactured by Tokyo Kasei Kogyo Co., Ltd.), and 300 g of methyl ethyl ketone (MEK) were put into a ball mill and reacted by stirring at room temperature for 24 hours. .
Silver 2-hydroxyisobutyrate was then prepared by removing MEK by suction filtration and drying the resulting powder.

As is clear from the results shown in Table 1, a comparative example containing epoxy resin B-1 or B-7 (solid at 25° C. but epoxy equivalent less than 400 g/eq) instead of predetermined epoxy resin B 1 and 3 had poor solderability.
Comparative Example 2 containing epoxy resin B-6 (epoxy equivalent exceeding 5,000 g/eq) instead of the predetermined epoxy resin B had poor screen printability and solderability.
Comparative Example 4 [(A+B)/C] outside the predetermined range [(A+B) is small and C is large] had poor screen printability.
Comparative Example 5 [(A+B)/C] outside the predetermined range [(A+B) is large and C is small] had poor solderability.
Comparative Example 6 [A is small and (B+C) is large], in which [A/(B+C)] is outside the predetermined range, had poor screen printability.
Comparative Example 7, in which [A/(B+C)] was out of the predetermined range [more A and less (B+C)] had poor solderability.
Comparative Example 8, in which [D/(A+B)] is out of the predetermined range [D is small and (A+B) is large], had poor adhesiveness and solderability.
Comparative Example 9, in which [D/(A+B)] is out of the predetermined range [D is large and (A+B) is small], had poor solderability.
Comparative Example 10, in which the total amount of epoxy resin A, epoxy resin B, thermoplastic resin C and curing agent D was less than the predetermined range, had poor adhesion and solderability.
Comparative Example 11, in which the total amount of epoxy resin A, epoxy resin B, thermoplastic resin C, and curing agent D was more than the predetermined range, exhibited low resistance, poor screen printability, and poor solderability.
Comparative Example 12 containing a metal carboxylate had poor storage stability.
Comparative Example 13, which did not contain the predetermined thermoplastic resin C, had poor solderability.

In contrast, the composition of the present invention was excellent in solderability, screen printability, low resistance, adhesion to substrates, and storage stability.

Claims (4)

conductive particles;
an epoxy resin A that has an epoxy equivalent of less than 500 g/eq and is liquid at 25°C;
an epoxy resin B having a bisphenol skeleton, which has an epoxy equivalent of 400 g/eq or more and 5000 g/eq or less and is solid at 25°C;
a thermoplastic resin C having a weight average molecular weight of 25,000 to 65,000;
a curing agent D;
containing a solvent and
The conductive particles include flaky silver particles E having a specific surface area of 0.2 to 1.0 m ² /g and spherical silver particles F having a specific surface area of 0.5 to 1.6 m ² /g. the mass ratio of the spherical silver particles F to the particles E (spherical silver particles F/flaky silver particles E) is 75/25 to 25/75;
The epoxy resin A contains an epoxy resin A1 having a cyclic structure and an epoxy resin A2 having a chain structure,
The epoxy resin A1 contains at least resorcinol diglycidyl ether having one resorcinol skeleton in one molecule ,
The epoxy resin A2 is a polyhydric alcohol-based glycidyl-type epoxy resin,
The thermoplastic resin C is a phenoxy resin,
The total amount of the epoxy resin A, the epoxy resin B, the thermoplastic resin C, and the curing agent D is 3 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the conductive particles,
The mass ratio [(A+B)/C] of the total amount of the epoxy resin A and the epoxy resin B to the content of the thermoplastic resin C is 50/50 to 95/5,
The mass ratio [A/(B+C)] of the content of the epoxy resin A to the total amount of the epoxy resin B and the thermoplastic resin C is 15/85 to 85/15,
The mass ratio [D/(A+B)] of the content of the curing agent D to the total amount of the epoxy resin A and the epoxy resin B is 2/98 to 10/90,
A conductive composition containing no metal carboxylate. The conductive composition according to claim 1, wherein the epoxy resin A has a viscosity of 15 to 60,000 mPa·s at 25°C. 3. The conductive composition according to claim 1, wherein the thermoplastic resin C has a glass transition point of 80 to 100.degree. 4. Any one of claims 1 to 3, wherein the mass ratio of the content of the epoxy resin A1 to the content of the epoxy resin A2 [epoxy resin A1/epoxy resin A2] is 15/85 to 85/15. The conductive composition according to .