WO2018216739A1

WO2018216739A1 - Electroconductive composition

Info

Publication number: WO2018216739A1
Application number: PCT/JP2018/019876
Authority: WO
Inventors: 一雄荒川; 丈章齋木; 石川　和憲
Original assignee: 横浜ゴム株式会社
Priority date: 2017-05-25
Filing date: 2018-05-23
Publication date: 2018-11-29
Also published as: JPWO2018216739A1; TW201901699A; JP7231537B2; CN110603293A

Abstract

The purpose of the present invention is to provide an electroconductive film composition which is excellent in terms of solderability, screen printability, low resistance, adhesion to substrates, and storage stability. The electroconductive composition of the present invention comprises electroconductive particles, an epoxy resin A which has an epoxy equivalent less than 500 g/eq and is liquid at 25°C, an epoxy resin B which has an epoxy equivalent of 400-5,000 g/eq and is solid at 25°C, a thermoplastic resin C having a weight-average molecular weight of 25,000-65,000, a hardener D, and a solvent, the total amount of the components A, B, C, and D being 3-10 parts by mass per 100 parts by mass of the electroconductive particles, the mass ratio of the sum of the components A and B to the content of the component C, (A+B)/C, being 50/50 to 95/5, the mass ratio of the content of the component A to the sum of the components B and C, A/(B+C), being 15/85 to 85/15, and the mass ratio of the component D to the sum of the components A and B, D/(A+B), being 2/98 to 10/90. The electroconductive composition contains substantially no metal carboxylate.

Description

Conductive composition

The present invention relates to a conductive composition.

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

International Publication No. 2016/017618

The conductive composition is required to have screen printing properties, a cured product to be obtained with low resistance, excellent adhesion to a substrate, and excellent storage stability. In particular, in finger electrode applications for solar cells, thinning of fingers is required in screen printing in order to increase the light receiving area in order to improve power generation efficiency.
In addition, when the conductive composition is used for, for example, a bus bar electrode of a solar cell, the bus bar electrode is connected with a copper ribbon (interconnector) coated with solder on the surface, and thus formed with the conductive composition. The bus bar electrode to be used is required to have excellent solderability (bondability and / or bonding strength between the conductive composition and the solder).
Under these circumstances, the present inventors prepared a composition with reference to Patent Document 1 and evaluated it. As a result, such a composition was found to be solderable, screen printable, low resistance, It has been found that there are cases where the level required recently for adhesiveness or storage stability is not satisfied.
Then, an object of this invention is to provide the electroconductive composition which is excellent in solderability, screen printing property, low resistance, adhesiveness with a base material, and storage stability.

As a result of earnest research to solve the above problems, the present inventors,
Conductive particles;
Epoxy resin A having an epoxy equivalent of less than 500 g / eq and liquid at 25 ° C .;
An epoxy equivalent of 400 g / eq or more and 5000 g / eq or less, and a solid epoxy resin B at 25 ° C .;
A thermoplastic resin C having a weight average molecular weight of 25,000 to 65,000,
Curing agent D;
A solvent,
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 a desired effect can be obtained by substantially not containing a metal carboxylate, and have reached the present invention.
The present invention is based on the above knowledge and the like, and specifically, solves the above problems by the following configuration.

1. Conductive particles;
Epoxy resin A having an epoxy equivalent of less than 500 g / eq and liquid at 25 ° C .;
An epoxy equivalent of 400 g / eq or more and 5000 g / eq or less, and a solid epoxy resin B at 25 ° C .;
A thermoplastic resin C having a weight average molecular weight of 25,000 to 65,000,
Curing agent D;
A solvent,
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 electrically conductive composition which does not contain a carboxylic acid metal salt substantially.
2. 2. The conductive composition according to 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, wherein the conductive particles are at least one selected from the group consisting of silver powder, copper powder, and silver-coated conductive powder in which at least a part of the surface is coated with silver. Sex composition.
5). 5. The conductive composition according to any one of 1 to 4, 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 a 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 includes 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 a substrate, and storage stability.

The present invention will be described in detail below.
In this specification, a numerical range expressed using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.
In this specification, unless otherwise specified, each component can be used alone or in combination of two or more of the substances corresponding to the component. When a component contains two or more types of substances, the content of the component means the total content of the two or more types of substances.
In the present invention, each component is not particularly limited with respect to its production method. For example, a conventionally well-known thing is mentioned.
In this specification, it is said that the effect of the present invention is more excellent that at least one of solderability, screen printability, low resistance, adhesion to a substrate, and storage stability is more excellent. is there.

[Conductive composition]
The conductive composition of the present invention (the composition of the present invention)
Conductive particles;
Epoxy resin A having an epoxy equivalent of less than 500 g / eq and liquid at 25 ° C .;
An epoxy equivalent of 400 g / eq or more and 5000 g / eq or less, and a solid epoxy resin B at 25 ° C .;
A thermoplastic resin C having a weight average molecular weight of 25,000 to 65,000,
Curing agent D;
A solvent,
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 an electroconductive composition which does not contain a carboxylic acid metal salt substantially.

Since the composition of this invention takes such a structure, it is thought that a desired effect is acquired. The reason is not clear, but it is presumed that it is as follows.
That is, in the present invention, by using together a liquid epoxy resin A having an epoxy equivalent of a predetermined range and a solid epoxy resin B having an epoxy equivalent of a predetermined range, and setting the content of each component within a predetermined range It is thought that screen printing, low resistance, and adhesion to the substrate are excellent because breakage and the like are less likely to occur in screen printing, the conductive particles can be densified, and the resulting cured product is tough. It is done.
Further, the composition of the present invention contains a thermoplastic resin having a weight average molecular weight within a predetermined range with respect to the conductive particles and the epoxy resin A and the epoxy resin B, so that the composition of the present invention is bonded to solder. And toughness can be imparted to the composition. Due to the toughness, the composition of the present invention is considered to be excellent in solderability (particularly the bonding strength between the conductive composition and solder).
And the composition of this invention can balance solderability, screen printing property, low resistance, and adhesiveness with a base material by a high level by containing each component by predetermined content. I guess you can.
Moreover, the composition of this invention is excellent in storage stability by not containing a carboxylic acid metal salt substantially.
Hereinafter, each component contained in the composition of this invention is explained in full detail.

<< Conductive Particles >>
The conductive particles contained in the composition of the present invention are not particularly limited as long as they are granular substances having conductivity.
Examples of the conductive particles include a metal material having an electric 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 in which at least a part of the surface is coated with silver.
The conductive particles may be at least one selected from the group consisting of silver powder, copper powder, and silver-coated conductive powder in which at least a part of the surface is coated with silver, from the viewpoint of being superior due to the effects of the present invention. preferable.
As a core which comprises the said silver coat electrically conductive powder, the particle | grains of the said metal material are mentioned, for example.

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 that the effect of the present invention is excellent.
Here, in the present invention, the average particle diameter of the conductive particles is obtained by measuring the volume-based particle size distribution using a laser diffraction particle size distribution measuring device, and the particle diameter at 50% accumulation (50% volume accumulated diameter. (Also referred to as “average particle diameter (D50)”). As such a laser diffraction type particle size distribution measuring apparatus, for example, an apparatus according to LA-500 (trade name) manufactured by HORIBA, Ltd. may 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 being excellent due to the effects of the present invention.
In the present invention, a spherical shape refers to the shape of a particle having a major axis / minor axis ratio of 2 or less, and a flake shape refers to a shape having a major axis / minor axis ratio of more than 2. Here, the major axis and minor axis of the particles constituting the conductive particles can be determined based on an image obtained from a scanning electron microscope (SEM). The “major axis” refers to the longest distance among the line segments passing through the approximate center of gravity of the particle in the particle image obtained by SEM. The “short diameter” refers to the shortest distance among the line segments passing through the approximate center of gravity of the particle in the particle image obtained by SEM.

The flaky particles E may be either single crystal or polycrystal.
The specific surface area of the flaky 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 that the specific surface area is excellent due to the effects of the invention. When it is more than 1.0 m ² / g, it is easy to increase the viscosity. In order to obtain a composition in a viscosity range capable of proper printing, it is necessary to add a larger amount of solvent, and the solid content is lowered, which may cause a problem that the aspect ratio of the printed or cured wiring becomes small. . When it is less than 0.2 m ² / g, it is easy to lower the viscosity. In order to obtain a composition having a viscosity range in which proper printing is possible, it is necessary to add less solvent, which may cause a problem that it is difficult to control viscosity during production.
In the present invention, the specific surface area of the conductive particles refers to a value obtained from a nitrogen adsorption isotherm at −196 ° C. based on the BET equation.
The average particle diameter of the flaky particles E is preferably 1 to 15 μm, more preferably 3 to 10 μm, from the viewpoint that the effect of the invention is excellent. When the thickness is larger than 10 μm, mesh clogging is likely to occur in a wiring process such as screen printing, and there is a problem that disconnection is likely to occur particularly during fine line patterning. If it is smaller than 1 μm, the number of contacts between the conductive particles increases, and the resistance of the obtained wiring may increase as the contact resistance increases. Furthermore, due to the low thixotropy of the resulting composition, there may be a problem that it is difficult to make a high aspect ratio wiring in a wiring process such as screen printing.

The specific surface area of spherical particles F, from the viewpoint of obtaining superior effect of the invention is preferably 0.5 ~ 1.6m ² / g, more preferably 0.5 ~ 1.2m ² / g. When it is more than 1.6 m ² / g, it is easy to increase the viscosity. In order to obtain a composition in a viscosity range capable of proper printing, it is necessary to add a larger amount of solvent, and the solid content is lowered, which may cause a problem that the aspect ratio of the printed or cured wiring becomes small. . When it is less than 0.5 m ² / g, it is easy to lower the viscosity. In order to obtain a composition having a viscosity range in which proper printing is possible, it is necessary to add less solvent, which may cause a problem that it is difficult to control 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 excellent effects of the invention and excellent printability and conductivity. When it is larger than 3 μm, the gap between the particles increases, and the conductive particle density in the composition decreases, so that the resistance of the obtained wiring may increase. When the thickness is smaller than 0.5 μm, the number of contacts between the conductive particles increases, and the resistance of the obtained wiring may increase as the contact resistance increases.

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 from the viewpoint of being excellent in the 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 total 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 superior due to the effects of the invention. Therefore, 75/25 to 25/75 is preferable, and 70/30 to 30/70 is more preferable.

The method for producing the conductive particles is not particularly limited. For example, a conventionally well-known thing is mentioned.
The production method of the spherical conductive particles (for example, the 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 suitably used.
The method for producing the flaky conductive particles (for example, the flaky particles E) is not particularly limited, and a conventionally known method 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, a stirring mill, etc. What was manufactured by the method to convert can be used suitably.

<< Epoxy Resin A, Epoxy Resin B >>
The composition of the present invention contains epoxy resin A and epoxy resin B.
In the present invention, the epoxy resin is a compound having two or more oxirane rings (epoxy groups) in one molecule. The oxirane ring can be bonded to an organic group. The organic group is not particularly limited. For example, the hydrocarbon group which may have a hetero atom like an oxygen atom, a nitrogen atom, and a sulfur atom is mentioned. The hydrocarbon group is not particularly limited. For example, aliphatic hydrocarbon groups (linear, branched, cyclic, and combinations thereof), aromatic hydrocarbon groups, and combinations thereof may be mentioned. The hetero atom 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 is an epoxy resin having an epoxy equivalent of less than 500 g / eq and being liquid at 25 ° C.
The epoxy resin A preferably has 2 or 3 oxirane rings in one molecule.

<Epoxy equivalent of epoxy resin A>
In the present invention, the epoxy equivalent of the 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 of being excellent due to the effect of the present invention.

<Liquid>
In the present invention, the 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 that it is excellent due to the effect 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.

(Epoxy resin A structure)
Examples of the epoxy resin A include an epoxy resin A1 having a cyclic structure and an epoxy resin A2 having a chain structure. The epoxy resin A2 does not have a ring structure.
The epoxy resin A preferably contains an epoxy resin A1 having a cyclic structure and an epoxy resin A2 having a chain structure from the viewpoint of being excellent due to the effects of the present invention.

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 a hydrogenated product 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. Moreover, the epoxy resin A1 may not have a urethane bond.

When the epoxy resin A1 further has a urethane bond, toughness (flexibility) can be imparted to the composition, so that it is more excellent in solderability. The urethane bond may be introduced into the organic group to which the 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. An epoxy resin having a cyclic structure and a hydrogenated product thereof; a urethane-modified product (urethane-modified epoxy resin) and a hydrogenated product thereof by the above epoxy resin; an epoxy resin having one cyclic structure in one molecule and a hydrogenated product 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 the hydrogenated product thereof include, for example, an epoxy resin having a benzenediol skeleton and a hydrogenated product thereof; an epoxy resin having a phthalic acid skeleton and a hydrogenated product thereof; Examples thereof include an epoxy resin having a benzenedimethanol skeleton; an epoxy resin having a cyclohexanedimethanol skeleton; an epoxy resin having an aniline skeleton; and an epoxy resin having a toluidine skeleton.

Among these, the epoxy resin A1 is preferably a urethane-modified epoxy resin, an epoxy resin having one cyclic structure in one molecule, from the viewpoint that it is excellent due to the effects (particularly solderability) of the present invention, and is preferably a urethane-modified epoxy resin, benzene. An epoxy resin having a diol skeleton, an epoxy resin having a phthalic acid skeleton, and an epoxy resin having a cyclohexanedimethanol skeleton are more preferable, and a urethane-modified epoxy resin and a resorcinol diglycidyl ether having a resorcin skeleton are more preferable.

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 polyhydric alcohol glycidyl 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 the alkylene polyol may be either linear or branched. The alkylene group may have 2 to 15 carbon atoms, for example.
Examples of the alkylene group include an ethylene group, a propylene group, and a trimethylene group.

The number of repeating units (oxyalkylene groups) of the poly (oxyalkylene) polyol in the poly (oxyalkylene) polyol is preferably 2 to 15 and more preferably 3 to 10 from the viewpoint of being excellent due to the effect of the present invention.

Examples of the polyglycidyl ether of the alkylene polyol include ethylene glycol diglycidyl ether and propylene glycol diglycidyl ether.
Examples of commercially available polyglycidyl ethers of the above alkylene polyols include trade name EX-810 (manufactured by Nagase Chemtech).
Examples of the polyglycidyl ether of the poly (oxyalkylene) polyol include polyethylene glycol diglycidyl ether and polypropylene glycol diglycidyl ether.
Examples of commercially available polyglycidyl ethers of the above poly (oxyalkylene) polyols include trade names EX-830, EX-841, EX-920, 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 the bisphenol skeleton or a hydrogenated product thereof and the polyhydric alcohol glycidyl type epoxy resin,
A combination of a urethane-modified epoxy resin and the above polyhydric alcohol glycidyl type epoxy resin,
An epoxy resin having one cyclic structure in one molecule (for example, an epoxy resin having a benzenediol skeleton) and the polyhydric alcohol-based glycidyl type epoxy resin (for example, having an oxyalkylene group having a repeating unit of more than 10 and 15 or less, And a combination with 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] From the viewpoint of more excellent effects, 15/85 to 85/15 is preferable, and 30/70 to 70/30 is more preferable.

<< Epoxy resin B >>
Epoxy resin B contained in the composition of the present invention is an epoxy resin having an epoxy equivalent of 400 g / eq or more and 5000 g / eq or less and solid at 25 ° C.
The epoxy resin B preferably has 2 or 3 oxirane rings in one molecule.

<Epoxy equivalent of epoxy resin B>
In the present invention, the epoxy equivalent of the 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 of being excellent due to the effect of the present invention.

<Solid>
In the present invention, the epoxy resin B is solid under the condition 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 excellent.
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 bisphenol A type, bisphenol F type, bisphenol E type, brominated bisphenol A type, hydrogenated bisphenol A type, bisphenol S type, and bisphenol AF type epoxy resins. Can be mentioned.
Especially, the viewpoint that the epoxy resin B is excellent by the effect of this invention has at least 1 sort (s) chosen from the group which consists of a bisphenol A type and a bisphenol F type, for example.

<< Thermoplastic resin C >>
The 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 weight average molecular weight of the thermoplastic resin C is 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 viewpoint that the effect of the present invention is excellent.
In the present invention, the weight average molecular weight of the thermoplastic resin C is a standard polystyrene equivalent value based on a measured value 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, and polycarbonate.
Among these, the thermoplastic resin C is preferably a phenoxy resin from the viewpoint that it is superior due to the effects of the present invention.

-Phenoxy resin The phenoxy resin includes 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 as one of preferred embodiments. The phenoxy resin has a hydroxyl group produced by a reaction between bisphenol and epichlorohydrin.
Preferable embodiments of the phenoxy resin include, for example, a phenoxy resin having a plurality of hydroxyl groups by the above reaction, a chain phenoxy resin, and a chain phenoxy resin having a plurality of hydroxyl groups by the above reaction.
In the present invention, the phenoxy resin may not have an epoxy group. The end of the phenoxy resin can be blocked with, for example, monocarboxylic acid from the viewpoint of being excellent in solderability.

The bisphenol that forms the phenoxy resin is not particularly limited. For example, bisphenol A, bisphenol F, bisphenol AF, bisphenol AD, bisphenol S, teramethyl bisphenol A, teramethyl bisphenol F, teramethyl bisphenol AD, teramethyl bisphenol S, Examples thereof include bisphenol A, ceramic mouth bisphenol A, and tetrafluo mouth bisphenol A.
Among these, 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 from 80 to 100 ° C., more preferably from 80 to 90 ° C., from the viewpoint that the effect of the present invention is superior.
In the present invention, the glass transition point of the thermoplastic resin C is in accordance with JIS K7121: 2012 (plastic transition temperature measurement method), and the change in the heat flow rate at a temperature rise of 5 ° C./min using a differential thermal analyzer. This 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 an epoxy resin. Among these, a cationic curing agent is preferable. Examples of the cationic curing agent include amine-based, sulfonium-based, ammonium-based, and phosphonium-based curing agents.

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

<< Solvent >>
The composition of the present invention contains a solvent.
The solvent is not particularly limited. For example, butyl carbitol, butyl carbitol acetate, cyclohexanone, methyl ethyl ketone, isophorone, α-terpineol and the like can be mentioned.
A commercial item 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 excellent. 40 to 100 parts by mass is more preferable.

<Total amount of epoxy resin A, epoxy resin B, thermoplastic resin C and curing agent D>
In the present invention, 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 total amount of the epoxy resin A, the epoxy resin B, the thermoplastic resin C, and the 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 being excellent due to the effect of the present invention.

<[(A + B) / C]>
In the present invention, 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.
[(A + B) / C] is preferably 60/40 to 90/10, and preferably 70/30 to 90 / from the viewpoint that the effect of the present invention is excellent and the viscosity of the paste (composition of the present invention) can be reduced. 10 is more preferable.

<[A / (B + C)]>
In the present invention, 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.
[A / (B + C)] is preferably 30/70 to 70/30, more preferably 50/50 to 70/30 from the viewpoint that the effect of the present invention is excellent and the viscosity of the paste (composition of the present invention) can be reduced. 30 is more preferable.

<[D / (A + B)]>
In the present invention, 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.
[D / (A + B)] is preferably 5/95 to 8/92 from the viewpoints of excellent effects of the present invention and excellent curability.

<Substantially free of carboxylic acid metal salt>
The composition of the present invention is substantially free of carboxylic acid metal salts.
In the present invention, the phrase “substantially containing no carboxylic acid metal salt” means that the content of the carboxylic acid metal salt is 0 to 0.5% by mass relative to the total amount of the composition of the present invention.

The 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 constituting 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. As said organic carboxylic acid, a fatty acid is mentioned, for example. The fatty acid may further have a hydroxyl group.
Examples of the carboxylic acid metal salt include a fatty acid metal salt such as 2-hydroxyisobutyric acid silver salt (the fatty acid constituting the fatty acid metal salt may further have a hydroxy group).

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

The composition of the present invention is not particularly required for a glass frit generally used as a high-temperature (700 to 800 ° C.) firing type conductive paste. The composition of the present invention includes, as one of preferred embodiments, substantially free of glass frit (the content of glass frit is 0 to 0.1 parts by mass with respect to 100 parts by mass of the conductive particles). It is done.

(Method for producing conductive composition)
The manufacturing method of the composition of this invention is not specifically limited, For example, the method of mixing each component mentioned above with a roll, a kneader, an extruder, a universal stirrer etc. is mentioned.

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. For example, a silicon substrate, glass, a metal, a resin substrate, a film, etc. are mentioned. The base material may be subjected to TCO (transparent oxide conductive film) treatment such as ITO (indium tin oxide).
The hardened | cured material formed using the composition of this invention can be used as a die bond of the electrode (for example, finger electrode, bus-bar electrode) of a photovoltaic cell, the electrode of a touch panel, and LED.

When the solar battery cell has a bus bar electrode formed by using the composition of the present invention, the solar battery module is formed by connecting the solar battery cells with an interconnector to connect the solar battery cells. Can be manufactured. In this case, the bus bar electrode of one solar cell is fused and joined to the end of the interconnector with solder, and the bus bar electrode of another solar cell and the other end of the interconnector are fused to each other. Can be joined.
The solder used for the joining 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.
The interconnector is not particularly limited. For example, a conventionally well-known thing is mentioned. Specifically, for example, the interconnector includes a copper core material coated with solder.
The joining of the bus bar electrode and the solder can be performed by heating, for example, at 200 to 300 ° C.

(Adhesion between composition of the present invention and substrate)
The composition of this invention can be adhere | attached with a base material by containing the said epoxy resin A and the epoxy resin B. FIG.
In addition, when the composition of the present invention contains a thermoplastic resin having a hydroxy group (for example, phenoxy resin) as the thermoplastic resin C, the hydroxy group can interact with the base material, and adheres to the base material. Can contribute.

(Fusion 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 bonded 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 to solder. Adhesive strength (bonding strength) increases. Further, when soldering, the thermoplastic resin C does not inhibit the contact between the solder and the conductive particles due to the occurrence of plasticization due to heating in the composition of the present invention, and the composition of the present invention is effective with the solder. Can be fused.

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 of the following Table 1 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 evaluation was performed using the composition manufactured as described above. The results are shown in Table 1.

<Volume resistivity (specific resistance)>
Each composition produced as described above was applied on a glass substrate by screen printing to form a test pattern having a solid coating of 2 cm × 2 cm. Then, it dried and hardened for 30 minutes at 200 degreeC in oven, and produced the electroconductive film.
About each produced electroconductive film, the volume resistivity was evaluated by the 4-terminal 4 probe method using the resistivity meter (Lorestar GP, Mitsubishi Chemical Corporation make).
When the volume resistivity was less than 8.0 μΩ · cm, it was judged that the volume resistivity was good.

<Screen printability>
The screen printability was evaluated for 60 μm printability.
In the present invention, according to the following evaluation, when the printability is 60 μm, the screen printability is excellent.
60 μm printability ITO (indium oxide doped with Sn) was formed as a transparent conductive layer on the surface of the silicon substrate.
Using a stainless steel screen mask having a mesh count of 360 mesh, emulsion thickness of 15 μm, wiring opening width of 60 μm, wire diameter of 16 μm, and opening of 55 μm, a screen plate making A having a line opening width of 60 μm was prepared.
Next, each composition produced as described above was screen-printed on the ITO using a screen plate making A at a printing speed of 200 mm / sec to obtain a wiring having a line width of 60 to 80 μm.
As described above, the wiring obtained by screen printing was observed with a laser microscope (300 times magnification), and the quality of the printability (60 μm printability) at a line opening width of 60 μm was determined according to the following criteria.
(Evaluation criteria)
A case where none of disconnection, meandering, bleeding and mesh marks was confirmed was evaluated as “◯” as having a very good 60 μm printability.
Although no disconnection was confirmed, a case where any one of meandering, bleeding and mesh marks was confirmed was evaluated as “Δ” because the 60 μm printability was slightly inferior.
The case where the disconnection was confirmed was evaluated as “x” because the 60 μm printability was extremely poor.

<Adhesiveness>
On the surface of the silicon substrate, ITO (indium oxide doped with Sn) was formed as a transparent conductive layer.
Next, each composition produced as described above was applied on the transparent conductive layer by screen printing at a printing speed of 200 mm / second to form a thin line-shaped test pattern having a width of 60 to 80 μm and a length of 25 mm. The screen printing mask used at this time was 360 mesh, emulsion thickness 15 μm, wiring opening width 60 μm, wire diameter 16 μm, and opening 55 μm.
Thereafter, the test pattern was dried and cured at 200 ° C. for 30 minutes to prepare a test sample having 20 wires on the transparent conductive layer.
Next, a peel test was performed in which one tape was applied in a direction perpendicular to all of the wirings, and the tape was immediately peeled off from the test sample.
(Evaluation criteria)
As a result of the peeling test, when the wiring did not peel at all from the transparent conductive layer, this was evaluated as having excellent adhesiveness and indicated as “◯”.
When one or two of the 20 wires were peeled off, this was evaluated as having poor adhesion, and “X” was displayed.

<Solderability>
On the surface of the silicon substrate, ITO (indium oxide doped with Sn) was formed as a transparent conductive layer.
Next, each composition produced as described above is applied on the transparent conductive layer by screen printing at a printing speed of 200 mm / second to form a linear test pattern (bus bar electrode) having a width of 1.5 mm and a length of 50 mm. did. The screen printing mask used at this time was a line pattern of 250 mesh, emulsion thickness 10 μm, and wiring opening width 1.5 mm.
Next, a 1.5 mm wide solder ribbon (manufactured by Ulbrich) having a copper core dipped with Sn / Pb eutectic solder is matched to the width of the test pattern and the solder ribbon, and the test pattern is 50 mm in length. The test pattern and the solder ribbon were placed on the wiring so as to overlap with each other, and the portion where the test pattern and the solder ribbon overlapped was heated at 250 ° C. and bonded to thereby solder the wiring and the solder ribbon. .
(Tensile test)
The soldered test piece was cooled to room temperature, a 180 ° tensile test was performed at room temperature using the soldered test piece, and the solder adhesive strength was measured.
(Evaluation criteria)
When the solder adhesive strength was 1.0 N / mm or more, it was evaluated that the solderability was excellent, and this was indicated as “◯”.
When the solder adhesive strength was less than 1.0 N / mm, it was evaluated that the solderability was poor, and this was indicated as “x”.
Note that “CF” means cohesive failure and “AF” means interfacial peeling for the peeling mode (the fracture mode in the test piece after the tensile test was visually confirmed). “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 after storage for 30 days in a refrigerated environment at 5 ° C. (viscosity after storage) Measurements were made according to JIS K 7117-1: 1999, respectively. The measurement was performed using a cone plate viscometer (manufactured by Brookfield) using a CP52 spindle and rotating at 1 rpm at room temperature.
(Viscosity increase rate)
From the initial viscosity of each composition measured as described above and the viscosity after storage, the rate of increase in viscosity (%) = (viscosity after storage / initial viscosity) × 100 was calculated.
(Evaluation criteria)
When the rate of increase in viscosity was less than 150%, it was evaluated that the storage stability was excellent, and this was indicated as “◯”.
When the viscosity increase rate was 150% or more, it was evaluated that the storage stability was poor, and this was indicated as “x”.

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

The flake silver in Tables 1 and 2 corresponds to the flaky particles E of the conductive particles in the present invention.
Moreover, spherical silver corresponds to the spherical particle F of the electrically-conductive particle in this invention.
In Table 2, “Bis F” means a 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)
Silver oxide (manufactured by Toyo Kagaku Kogyo Co., Ltd.) 50 g, 2-hydroxyisobutyric acid (manufactured by Tokyo Chemical Industry Co., Ltd.) 45 g, and methyl ethyl ketone (MEK) 300 g were charged into a ball mill and reacted by stirring at room temperature for 24 hours. .
Subsequently, MEK was removed by suction filtration, and the obtained powder was dried to prepare silver 2-hydroxyisobutyrate.

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

On the other hand, the composition of the present invention was excellent in solderability, screen printability, low resistance, adhesion to a substrate, and storage stability.

Claims

Conductive particles;
Epoxy resin A having an epoxy equivalent of less than 500 g / eq and liquid at 25 ° C .;
An epoxy equivalent of 400 g / eq or more and 5000 g / eq or less, and a solid epoxy resin B at 25 ° C .;
A thermoplastic resin C having a weight average molecular weight of 25,000 to 65,000,
Curing agent D;
A solvent,
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 electrically conductive composition which does not contain a carboxylic acid metal salt substantially.
The conductive composition according to claim 1, wherein the epoxy resin A has a viscosity at 25 ° C of 15 to 60,000 mPa · s.
The conductive composition according to claim 1 or 2, wherein the glass transition point of the thermoplastic resin C is 80 to 100 ° C.
The conductive particles according to any one of claims 1 to 3, wherein the conductive particles are at least one selected from the group consisting of silver powder, copper powder, and silver-coated conductive powder in which at least a part of the surface is coated with silver. The electroconductive composition as described.
The conductive composition according to any one of claims 1 to 4, wherein the epoxy resin A contains an epoxy resin A1 having a cyclic structure and an epoxy resin A2 having a chain structure.
6. The conductive composition according to claim 5, wherein a 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 claim 5 or 6, wherein the epoxy resin A1 includes at least an epoxy resin having one cyclic structure in one molecule.