Conductive composition
阅读说明：本技术 导电性组合物 (Conductive composition ) 是由 荒川一雄 斋木丈章 石川和宪 于 2018-05-23 设计创作，主要内容包括：本发明的目的在于提供一种焊接性、丝网印刷性、低电阻性、与基材的粘接性及储藏稳定性优异的导电膜组合物。本发明涉及一种导电性组合物,其含有导电粒子、环氧当量小于500g/eq且在25℃为液状的环氧树脂A、环氧当量为400g/eq以上且5000g/eq以下且在25℃为固体的环氧树脂B、重均分子量为25,000～65,000的热塑性树脂C、固化剂D及溶剂,并且相对于导电粒子100质量份,上述A、上述B、上述C及上述D的总量为3质量份以上且10质量份以下,上述A及上述B的总量相对于上述C的含量的质量比[(A+B)/C]为50/50～95/5,上述A的含量相对于上述B及上述C的总量的质量比[A/(B+C)]为15/85～85/15,上述D相对于上述A与上述B的总量的质量比[D/(A+B)]为2/98～10/90,上述导电性组合物实质上不含羧酸金属盐。(The invention aims to provide a conductive film composition with excellent welding performance, screen printing performance, low resistance, adhesion with a base material and storage stability. The present invention relates to a conductive composition containing conductive particles, an epoxy resin A having an epoxy equivalent of less than 500g/eq and being liquid at 25 ℃, an epoxy resin B having an epoxy equivalent of 400g/eq or more and 5000g/eq or less and being solid at 25 ℃, a thermoplastic resin C having a weight average molecular weight of 25,000 to 65,000, a curing agent D and a solvent, wherein the total amount of the A, the B, the C and the 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 A and the B with respect to the content of the C is 50/50 to 95/5, the mass ratio [ A/(B + C) ] of the content of the A with respect to the total amount of the B and the C is 15/85 to 85/15, and the mass ratio [ D/(A + B) ] of the D with respect to the total amount of the A and the B is 2/98 to 10/90, the conductive composition does not substantially contain a carboxylic acid metal salt.)
1. An electrically conductive composition comprising:
conductive particles;
epoxy resin A, the epoxy equivalent is less than 500g/eq, and the epoxy resin A is liquid at 25 ℃;
an epoxy resin B having an epoxy equivalent of 400g/eq or more and 5000g/eq or less and being a solid at 25 ℃;
a thermoplastic resin C having a weight average molecular weight of 25,000 to 65,000;
a curing agent D; and
a solvent; and is
The total amount of the epoxy resin A, the epoxy resin B, the thermoplastic resin C and the curing agent D is 3 to 10 parts by mass based on 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 50/50-95/5,
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 15/85-85/15,
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 2/98-10/90,
the conductive composition is substantially free of metal carboxylate salts.
2. The conductive composition according to claim 1, wherein the viscosity of the epoxy resin A at 25 ℃ is 15 to 60,000 mPas.
3. The conductive composition as claimed in claim 1 or 2, wherein the glass transition point of the thermoplastic resin C is 80 to 100 ℃.
4. The conductive composition 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.
5. 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 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. The conductive composition according to claim 5 or 6, wherein the epoxy resin A1 contains at least one epoxy resin having 1 cyclic structure in one molecule.
Technical Field
The present invention relates to a conductive composition.
Background
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).
Disclosure of Invention
Problems to be solved by the invention
The following properties are required for the conductive composition: screen printability, adhesiveness to a substrate, and storage stability are excellent, and the obtained cured product has low resistance, and the like. In particular, in the application of finger electrodes (finger electrodes) of solar cells, in order to increase the light receiving area and improve the power generation efficiency, the screen printing is required to make the finger shape thinner.
When the conductive composition is used, for example, in a bus-bar electrode (solar cell), the bus-bar electrode is connected by a copper tape (interconnector) or the like whose surface is covered with solder, and thus the bus-bar electrode formed of the conductive composition is required to have excellent solderability (bonding property and/or bonding strength between the conductive composition and the solder).
Under such circumstances, the present inventors prepared and evaluated a composition in reference to patent document 1, and as a result, it was found that such a composition may not satisfy the level required in the present days in terms of weldability, screen printability, low electric resistance, adhesiveness to a base material, and storage stability.
Accordingly, an object of the present invention is to provide a conductive composition having excellent solderability, screen printability, low resistance, adhesion to a base material, and storage stability.
Means for solving the problems
The present inventors have intensively studied to solve the above problems, and as a result, have found that a desired effect can be obtained by a method comprising:
conductive particles;
epoxy resin A, the epoxy equivalent is less than 500g/eq, and the epoxy resin A is liquid at 25 ℃;
an epoxy resin B having an epoxy equivalent of 400g/eq or more and 5000g/eq or less and being a solid at 25 ℃;
a thermoplastic resin C having a weight average molecular weight of 25,000 to 65,000;
a curing agent D; and
a solvent; and is
The total amount of the epoxy resin A, the epoxy resin B, the thermoplastic resin C and the curing agent D is 3 to 10 parts by mass based on 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 50/50-95/5,
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 15/85-85/15,
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 2/98-10/90,
substantially free of metal carboxylate salts.
The present invention is based on the above findings, and specifically solves the above problems with the following configurations.
1. An electrically conductive composition comprising:
conductive particles;
epoxy resin A, the epoxy equivalent is less than 500g/eq, and the epoxy resin A is liquid at 25 ℃;
an epoxy resin B having an epoxy equivalent of 400g/eq or more and 5000g/eq or less and being a solid at 25 ℃;
a thermoplastic resin C having a weight average molecular weight of 25,000 to 65,000;
a curing agent D; and
a solvent; and is
The total amount of the epoxy resin A, the epoxy resin B, the thermoplastic resin C and the curing agent D is 3 to 10 parts by mass based on 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 50/50-95/5,
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 15/85-85/15,
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 2/98-10/90,
the conductive composition is substantially free of metal carboxylate.
2. The conductive composition as described in claim 1, wherein the viscosity of the epoxy resin A at 25 ℃ is 15 to 60,000 mPas.
3. The conductive composition as described in 1 or 2, wherein the thermoplastic resin C has a glass transition point of 80 to 100 ℃.
4. The conductive composition as described in any one of the above 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 having at least a part of the surface thereof coated with silver.
5. The conductive composition as described in any one of the above 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 as described in the above 5, 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. The conductive composition as described in 5 or 6, wherein the epoxy resin A1 at least contains an epoxy resin having 1 ring structure in one molecule.
ADVANTAGEOUS EFFECTS OF INVENTION
The conductive composition of the present invention is excellent in solderability, screen printability, low resistance, adhesion to a base material, and storage stability.
Detailed Description
The present invention will be described in detail below.
In the present specification, a numerical range expressed by using "to" means a range including numerical values described before and after "to" as a lower limit value and an upper limit value.
In the present specification, unless otherwise specified, two or more of the substances corresponding to each component may be used alone or in combination with each other. When the component contains two or more substances, the content of the component refers to the total content of the two or more substances.
In the present invention, the method for producing each component is not particularly limited. Examples of the production method include the previously known production methods.
In the present specification, it may be said that the effect of the present invention is more excellent when at least one of solderability, screen printability, low resistance, adhesiveness to a base material, and storage stability is more excellent.
[ conductive composition ]
The conductive composition of the present invention (the composition of the present invention) contains:
conductive particles;
epoxy resin A, the epoxy equivalent is less than 500g/eq, and the epoxy resin A is liquid at 25 ℃;
an epoxy resin B having an epoxy equivalent of 400g/eq or more and 5000g/eq or less and being a solid at 25 ℃;
a thermoplastic resin C having a weight average molecular weight of 25,000 to 65,000;
a curing agent D; and
a solvent; and is
The total amount of the epoxy resin A, the epoxy resin B, the thermoplastic resin C and the curing agent D is 3 to 10 parts by mass based on 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 50/50-95/5,
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 15/85-85/15,
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 2/98-10/90,
the conductive composition is substantially free of metal carboxylate.
It is considered that the composition of the present invention can obtain the desired effect by adopting such a constitution. The reason for this is not clear, but is estimated roughly as follows.
That is, in the present invention, it is considered that, by using a liquid epoxy resin a having an epoxy equivalent of a predetermined range in combination with a solid epoxy resin B having an epoxy equivalent of a predetermined range and setting the contents of the respective components and the like to predetermined ranges, disconnection and the like are less likely to occur during screen printing, high density of conductive particles can be realized, and the obtained cured product is tough, and therefore, screen printing properties, low resistance properties, and adhesion properties to a base material are excellent.
In addition, the composition of the present invention contains the thermoplastic resin having a weight average molecular weight within a predetermined range with respect to the conductive particles, the epoxy resin a, and the epoxy resin B, whereby the composition of the present invention can be bonded to solder and can impart toughness to the composition. The composition of the present invention is considered to have excellent solderability (particularly, bonding strength between the conductive composition and the solder) due to the toughness.
It is also presumed that the composition of the present invention can balance the solderability, screen printability, low resistance and adhesion to a substrate at a high level by containing the respective components in predetermined amounts.
The composition of the present invention is substantially free of a metal carboxylate, and therefore has excellent storage stability.
The components 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 granular materials having conductivity.
The conductive particles include, for example, those having a resistivity of 20 × 10-6A metal material having a thickness of not more than Ω · cm.
Specific examples of the metal material include: gold (Au), silver (Ag), copper (Cu), aluminum (Al), magnesium (Mg), nickel (Ni), and the like.
Examples of the conductive particles include: silver powder; copper powder; at least a part of the surface is covered with the conductive powder by silver covered silver.
From the viewpoint of further improving the effect of the present invention, the conductive particles are preferably at least one selected from silver powder, copper powder, and silver-coated conductive powder in which at least a part of the surface is coated with silver.
Examples of the core constituting the silver-coated conductive powder include particles of the metal material.
From the viewpoint of further improving the effect of the present invention, the average particle diameter of the conductive particles is preferably 0.5 to 10 μm, and more preferably 1 to 5 μm.
In the present invention, the average particle diameter of the conductive particles is a cumulative 50% point particle diameter (50% volume cumulative diameter, also referred to as "average particle diameter (D50)") obtained by measuring a volume-based particle size distribution using a laser diffraction particle size distribution measuring apparatus. Examples of such a laser diffraction particle size distribution measuring apparatus include an apparatus such as LA-500 (trade name) manufactured by horiba, Inc.
From the viewpoint of further improving the effects of the present invention, the conductive particles preferably contain at least one selected from the group consisting of flake-like particles E and spherical particles F.
In the present invention, spherical means a particle shape having a ratio of major axis/minor axis of 2 or less, and flake means a shape having a ratio of major axis/minor axis of more than 2. Here, the major axis and the minor axis of the particles constituting the conductive particles can be determined based on an image obtained by a Scanning Electron Microscope (SEM). The "major axis" refers to a line segment having the longest distance among line segments passing through the approximate center of gravity of the particle in the particle image obtained by SEM. The "minor axis" refers to a line segment having the shortest distance among 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 crystals or polycrystalline.
From the viewpoint of further improving the effect of the present invention, the specific surface area of the flaky particles E is preferably 0.2 to 1.0m2A more preferable range is 0.2 to 0.8 m/g2(ii) in terms of/g. At more than 1.0m2In the case of/g, the viscosity is easily increased. In order to obtain a composition having a viscosity in a range suitable for printing, it is necessary to add a larger amount of solvent, and the solid content is reduced, so that there is a problem that the aspect ratio of the printed or cured wiring becomes small. At less than 0.2m2In the case of/g, the viscosity is easily lowered. In order to obtain a composition having a viscosity in a range suitable for printing, it is necessary to mix a smaller amount of a solvent, and there is a problem that viscosity control during production becomes difficult.
In the present invention, the specific surface area of the conductive particles is a value determined from the BET formula based on the adsorption isotherm of nitrogen at-196 ℃.
From the viewpoint of further improving the effect of the present invention, the average particle diameter of the flaky particles E is preferably 1 to 15 μm, and more preferably 3 to 10 μm. When the thickness is larger than 10 μm, there is a problem that screen clogging is likely to occur in a wiring step such as screen printing, and particularly, disconnection is likely to occur in fine line patterning. When the thickness is less than 1 μm, the number of contact points between the conductive particles increases, which may increase contact resistance, and the resistance of the resulting wiring may increase. Further, the thixotropic property of the obtained composition may be reduced, which may make it difficult to form a wiring having a high aspect ratio in a wiring step such as screen printing.
From the viewpoint of further improving the effect of the present invention, the specific surface area of the spherical particles F is preferably 0.5 to 1.6m2A more preferable range is 0.5 to 1.2 m/g2(ii) in terms of/g. At more than 1.6m2In the case of/g, the viscosity is easily increased. In order to obtain a composition having a viscosity in a range suitable for printing, it is necessary to add a larger amount of solvent, and the solid content is reduced, so that there is a problem that the aspect ratio of the printed or cured wiring becomes small. At less than 0.5m2In the case of/g, the viscosity is easily lowered. In order to obtain a composition having a viscosity in a range suitable for printing, it is necessary to mix a smaller amount of a solvent, and there is a problem that viscosity control during production becomes difficult.
From the viewpoint of further improving the effect of the present invention and providing excellent printability and electrical conductivity, the average particle diameter of the spherical particles F is preferably 0.5 to 3 μm, more preferably 0.8 to 2 μm. When the thickness is more than 3 μm, the number of gaps between particles may increase, and the density of conductive particles in the composition may decrease, thereby increasing the resistance of the resulting wiring. When the thickness is less than 0.5 μm, the number of contact points between the conductive particles increases, which may increase contact resistance, and the resistance of the resulting wiring may increase.
In the present invention, when a plurality of kinds of conductive particles are used as the conductive particles, the average specific surface area of the conductive particles is preferably 0.5 to 0.8m from the viewpoint of further improving the effect of the present invention2A more preferable range is 0.5 to 0.7 m/g2/g。
In the present invention, the average specific surface area of the conductive particles may be obtained by dividing the sum of the products of the specific surface area and the content of each conductive particle by the sum of the contents 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 preferably 75/25 to 25/75, and more preferably 70/30 to 30/70, from the viewpoint of further improving the effect of the invention.
The method for producing the conductive particles is not particularly limited. Examples of the production method include the previously known production methods.
The method for producing spherical conductive particles (for example, the spherical particles F) is not particularly limited, and for example, particles produced by a wet reduction method, an electrolytic method, an atomization method, or the like can be preferably used.
The method for producing the flake-like conductive particles (for example, the flake-like particles E) is not particularly limited, and a conventionally known method can be used. For example, particles produced by the following method can be preferably used: the spherical conductive particles produced by the above method are used as a raw powder, and the raw powder is mechanically treated by a ball mill, a bead mill, a vibration mill, an agitation type pulverizer, or the like, to be flaked by physical force.
< epoxy resin A, epoxy resin B >
The composition of the present invention contains an epoxy resin A and an epoxy resin B.
In the present invention, the epoxy resin is a compound having 2 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. Examples thereof include hydrocarbon groups which may have hetero atoms such as oxygen atom, nitrogen atom and sulfur atom. The hydrocarbon group is not particularly limited. Examples thereof include aliphatic hydrocarbon groups (linear, branched, cyclic, and combinations thereof), aromatic hydrocarbon groups, and combinations thereof. The hetero atom may form an ether bond, a hydroxyl group, or a urethane bond, for example.
In the present invention, the hydride of the epoxy resin may be either partially hydrogenated or fully hydrogenated.
< epoxy resin A >)
The epoxy resin A contained in the composition of the present invention is an epoxy resin having an epoxy equivalent of less than 500g/eq and being in a liquid state at 25 ℃.
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.
From the viewpoint of further improving the effect of the present invention, the epoxy equivalent of the epoxy resin a is preferably 100 to 300 g/eq.
< liquid state >
In the present invention, the epoxy resin A is in a liquid state at 25 ℃.
(viscosity of epoxy resin A)
From the viewpoint of further improving the effect of the present invention, the viscosity of the epoxy resin a at 25 ℃ is preferably 15 to 60,000mPa · s, and more preferably 50 to 15,000mPa · s.
In the present invention, the viscosity of the epoxy resin is measured under the condition of 25 ℃ according to JIS Z8803.
(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. The epoxy resin a2 does not have a cyclic structure.
From the viewpoint of more excellent effects of the present invention, the epoxy resin a preferably contains an epoxy resin a1 having a cyclic structure and an epoxy resin a2 having a chain structure.
Examples of the cyclic structure include: a cyclic aliphatic hydrocarbon group such as a cyclohexane skeleton; aromatic hydrocarbon groups such as benzene rings and hydrogenated products thereof.
Examples of the chain structure include a poly (oxyalkylene) group and an oxyalkylene group.
● epoxy A1
The epoxy resin a1 having a cyclic structure may further have a urethane bond in addition to the oxirane ring. In addition, the epoxy resin a1 may not have a urethane bond.
When the epoxy resin a1 further has a urethane bond, the composition can be provided with toughness (flexibility), and therefore the weldability is further excellent. 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: 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, and hydrogenated products thereof; urethane modified products of the above epoxy resins (urethane-modified epoxy resins) and hydrides thereof; epoxy resins having 1 ring structure in one molecule and hydrides thereof.
The urethane-modified epoxy resin has a plurality of cyclic structures in one molecule.
Examples of the epoxy resin having 1 ring structure in one molecule and the hydride thereof include: epoxy resins having a hydroquinone skeleton and hydrides thereof; epoxy resins having a phthalic acid skeleton and hydrides thereof; an epoxy resin having a xylylene glycol skeleton; an epoxy resin having a cyclohexanedimethanol skeleton; an epoxy resin having an aniline skeleton; epoxy resins having a toluidine skeleton, and the like.
Among them, from the viewpoint of more excellent effects (particularly, weldability) of the present invention, the epoxy resin a1 is preferably a urethane-modified epoxy resin or an epoxy resin having 1 cyclic structure in one molecule, more preferably a urethane-modified epoxy resin, an epoxy resin having a benzenediol skeleton, an epoxy resin having a phthalic acid skeleton or an epoxy resin having a cyclohexanedimethanol skeleton, and still more preferably a urethane-modified epoxy resin or a resorcinol diglycidyl ether having a resorcinol skeleton.
When the epoxy resin a1 contains an epoxy resin having 1 cyclic structure in one molecule, the content of the epoxy resin having 1 cyclic structure in one molecule is preferably 50 to 100% by mass based on the epoxy resin a 1.
● epoxy A2
Examples of the epoxy resin a2 having a chain structure include: polyol-based glycidyl epoxy resins such as polyglycidyl ethers of poly (oxyalkylene) polyols and polyglycidyl ethers of alkylene polyols.
The poly (oxyalkylene) polyol or alkylene polyol that can constitute the polyol-based glycidyl epoxy resin is not particularly limited.
The alkylene group of the poly (oxyalkylene) polyol or alkylene polyol may be either linear or branched. The number of carbon atoms of the alkylene group may be, for example, 2 to 15.
Examples of the alkylene group include: ethylene, 1, 2-propylene, trimethylene.
From the viewpoint of further improving the effect of the present invention, the number of repeating units (oxyalkylene groups) of the repeating unit (oxyalkylene group) of the poly (oxyalkylene group) polyol is preferably 2 to 15, more preferably 3 to 10.
Examples of the polyglycidyl ether of the alkylene polyol include ethylene glycol diglycidyl ether and propylene glycol diglycidyl ether.
As a commercially available product of the polyglycidyl ether of alkylene polyol, for example, there can be mentioned trade name EX-810 (manufactured by ナ ガ セ ケ ム テ ッ ク Co.).
Examples of the polyglycidyl ether of the poly (oxyalkylene) polyol include polyethylene glycol diglycidyl ether and polypropylene glycol diglycidyl ether.
Commercially available products of the polyglycidyl ethers of the above poly (oxyalkylene) polyols include, for example: trade names EX-830, EX-841, EX-920, and EX-931 (manufactured by ナ ガ セ ケ ム テ ッ ク Co.).
● combination of epoxy A1 and epoxy A2
Examples of the combination of the epoxy resin a1 and the epoxy resin a2 include:
a combination of the above epoxy resin having a bisphenol skeleton or a hydrogenated product thereof and the above polyol-based glycidyl epoxy resin;
a combination of a urethane-modified epoxy resin and the polyol glycidyl epoxy resin;
a combination of an epoxy resin having 1 cyclic structure in one molecule (for example, an epoxy resin having a hydroquinone skeleton) and the above polyol-based glycidyl epoxy resin (for example, a poly (oxyalkylene) diglycidyl ether having an oxyalkylene repeating unit of more than 10 and 15 or less).
(epoxy A1/epoxy 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 a 1/epoxy resin a2] is preferably 15/85 to 85/15, and more preferably 30/70 to 70/30, from the viewpoint of more excellent effects of the present invention.
< epoxy resin B >)
The epoxy resin B contained in the composition of the present invention is an epoxy resin having an epoxy equivalent of 400g/eq or more and 5000g/eq or less and being solid at 25 ℃.
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 400g/eq or more and 5000g/eq or less.
From the viewpoint of further improving the effect of the present invention, the epoxy equivalent of the epoxy resin B is preferably 1500 to 3500 g/eq.
< solid >
In the present invention, the epoxy resin B is solid at 25 ℃.
(softening Point of epoxy resin B)
From the viewpoint of further improving the effect of the present invention, the softening point of the epoxy resin B is preferably 50 to 150 ℃, more preferably 100 to 150 ℃.
In the present invention, the softening point of the epoxy resin is measured in accordance with 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.
Among them, from the viewpoint of further improving the effect of the present invention, the epoxy resin B is preferably at least one selected from the group consisting of bisphenol a type and 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.
From the viewpoint of further improving the effect of the present invention, the weight average molecular weight is preferably 30,000 to 55,000, and more preferably 30,000 to 45,000.
In the present invention, the weight average molecular weight of the thermoplastic resin C is a standard polystyrene equivalent value based on a measurement value of Gel Permeation Chromatography (GPC) using Tetrahydrofuran (THF) as a solvent.
(kind of thermoplastic resin C)
Examples of the thermoplastic resin C include: phenoxy resins, polyamides, polyesters, polycarbonates, and the like.
Among them, the thermoplastic resin C is preferably a phenoxy resin from the viewpoint of further improving the effect of the present invention.
● phenoxy resin
As the phenoxy resin, 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 is cited as one of preferable embodiments. The phenoxy resin has a hydroxyl group generated by the reaction of bisphenol with epichlorohydrin.
Preferred examples of the phenoxy resin include: a phenoxy resin having a plurality of hydroxyl groups obtained by the above reaction, a chain phenoxy resin, or 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 group. From the viewpoint of better weldability, the terminal of the phenoxy resin can be chain-blocked with, for example, monocarboxylic acid or the like.
The bisphenol forming the phenoxy resin is not particularly limited. Examples thereof include: bisphenol A, bisphenol F, bisphenol AF, bisphenol AD, bisphenol S, tetramethylbisphenol A, tetramethylbisphenol F, tetramethylbisphenol AD, tetramethylbisphenol S, tetrabromobisphenol A, tetrachlorobisphenol A, tetrafluorobisphenol A.
Among them, at least one selected from bisphenol a and bisphenol F is preferable.
(glass transition Point of thermoplastic resin C)
From the viewpoint of further improving the effect of the present invention, the glass transition point (glass transition temperature) of the thermoplastic resin C is preferably 80 to 100 ℃, and more preferably 80 to 90 ℃.
In the present invention, the glass transition point of the thermoplastic resin C is a value obtained by reading an inflection point in a curve obtained when a change in the heat flow rate is measured at a temperature rise temperature of 5 ℃/minute using a differential thermal analyzer in accordance with JIS K7121:2012 (transition temperature measurement method for plastics).
< 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 them, a cationic curing agent is preferable. Examples of the cationic curing agent include: amine, sulfonium, ammonium anda curing agent of (a).
Examples of the curing agent D include: boron trifluoride ethylamine, boron trifluoride piperidine, boron trifluoride triethanolamine, boron trifluoride phenol, p-methoxybenzene diazoHexafluorophosphate and diphenyl iodideHexafluorophosphate, tetraphenylsulfonium, tetra-n-butylTetraphenylborate, tetra-n-butylO, O-diethyldithiophosphate, and the like.
Among these, it is preferable to use at least one complex compound selected from boron trifluoride ethylamine, boron trifluoride piperidine and boron trifluoride triethanolamine as a complex compound of boron trifluoride and an amine compound, from the viewpoint of further reducing the volume resistivity.
< solvent >)
The composition of the present invention contains a solvent.
The solvent is not particularly limited. Examples thereof include: butyl carbitol, butyl carbitol acetate, cyclohexanone, methyl ethyl ketone, isophorone, alpha-terpineol, and the like.
Commercially available products can be used as the solvent.
From the viewpoint of more excellent effects of the present invention, the content of the solvent is preferably 20 to 200 parts by mass, and more preferably 40 to 100 parts by mass, based on 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.
< 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.
From the viewpoint of more excellent effects of 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 more preferably 5 to 8 parts by mass with respect to 100 parts by mass of the conductive particles.
<[(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 50/50-95/5.
In view of the excellent effects of the present invention and the low viscosity of the paste (the composition of the present invention), [ (A + B)/C ] is preferably 60/40 to 90/10, more preferably 70/30 to 90/10.
<[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.
From the viewpoint of further improving the effect of the present invention and reducing the viscosity of the paste (the composition of the present invention), [ A/(B + C) ] is preferably 30/70 to 70/30, and more preferably 50/50 to 70/30.
<[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.
From the viewpoint of further improving the effects of the present invention and excellent curability, [ D/(A + B) ] is preferably 5/95 to 8/92.
< substantially no carboxylic acid metal salt >
The composition of the present invention is substantially free of metal carboxylate salts.
In the present invention, the fact that the metal carboxylate is not substantially contained means that the content of the metal carboxylate is 0 to 0.5 mass% with respect to the total amount of the composition of the present invention.
The metal carboxylate is a metal salt of an organic carboxylic acid. Examples of the metal carboxylate salts include metal fatty acid salts.
The metal constituting the metal carboxylate 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.
Examples of the metal carboxylate salt include a fatty acid metal salt such as a silver salt of 2-hydroxyisobutyric acid (the fatty acid constituting the fatty acid metal salt may further have a hydroxyl group).
(additives)
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, as required.
Specific examples of the reducing agent include glycols.
The composition of the present invention does not particularly require a glass frit which is generally used as a conductive paste to be fired at a high temperature (700 to 800 ℃). The composition of the present invention preferably 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).
(method for producing conductive composition)
The method for producing the composition of the present invention is not particularly limited, and examples thereof include: the above-mentioned components are mixed by a method such as a roll, a kneader, an extruder, and a universal mixer.
The composition of the present invention can be applied to, for example, a substrate and heated at 180 to 230 ℃ to cure the composition.
The substrate is not particularly limited. Examples thereof include: silicon substrates, glass, metal, resin substrates, films, and the like. The substrate may be subjected to TCO (transparent oxide conductive film) treatment such as ITO (indium tin oxide).
The cured product formed using the composition of the present invention can be used, for example, as an electrode (e.g., finger electrode or bus bar electrode) of a solar cell, an electrode of a touch panel, or a die bond (LED) of an LED.
When a solar cell has a bus bar electrode formed using the composition of the present invention, a plurality of solar cells are connected to each other by an interconnector, whereby a solar cell module can be manufactured by connecting a plurality of solar cells. In this case, the bus bar electrode of one solar cell and the end of the interconnector may be welded and joined by solder, and the bus bar electrode of the other solar cell and the other end of the interconnector may be welded and joined by solder.
The solder used for the above joining is not particularly limited. For example, a previously known solder can be cited. Specific examples thereof include: tin-lead, tin-silver-copper, tin-bismuth, and the like.
In addition, the above-mentioned interconnector is not particularly limited. For example, previously known interconnectors can be cited. Specifically, for example, an interconnector in which a copper core material is covered with solder is cited as an example of the interconnector.
The bus bar electrode and the solder may be bonded by heating at 200 to 300 ℃.
(bonding of the composition of the present invention to a substrate)
The composition of the present invention can be bonded to a substrate by containing the epoxy resin a and the epoxy resin B.
In addition, in the case where the composition of the present invention contains a thermoplastic resin having a hydroxyl group (for example, phenoxy resin) as the thermoplastic resin C, the hydroxyl group may interact with the substrate and may contribute to adhesiveness with the substrate.
(fusion of the composition of the present invention with solder)
The composition of the present invention contains conductive particles made of metal, and thus can be joined by being fused with solder by heating.
Since the composition of the present invention contains the thermoplastic resin C, toughness is imparted to the composition of the present invention by the thermoplastic resin C, and the adhesion strength (bonding strength) between the composition of the present invention and solder after the composition of the present invention and solder are bonded is improved. In addition, the composition of the present invention is plasticized by heating at the time of soldering, so that the thermoplastic resin C does not interfere with the contact of the solder with the conductive particles, and the composition of the present invention can be effectively fused with the solder.