CN112189039A - Conductive ink - Google Patents

Abstract

The invention provides a conductive ink capable of efficiently forming a wiring and an electrode with excellent conductivity in a thick film. The conductive ink of the present invention contains the following surface-modified silver nanoparticles (a) and the following solvent (B). Surface-modified silver nanoparticles (a): silver nanoparticles having a constitution in which the surface is coated with a protective agent containing an amine; solvent (B): the solvent contains a terpene solvent (b-1) and a glycol ether solvent and/or a glycol ester solvent (b-2), and the content of the solvent having a vapor pressure of 0.05 to 15mmHg at 30 ℃ is 75 wt% or more of the total amount of the solvents.

Description

Conductive ink

Technical Field

The present invention relates to a conductive ink for use in forming wiring on a printed circuit board or the like. The present application claims priority to japanese patent application No. 2018-099041 filed on the sun at 23.5.2018, the contents of which are incorporated herein.

Background

Silver nanoparticles are capable of being sintered at low temperatures, and therefore, have been used for applications such as forming electrodes and wiring on plastic substrates. Further, it is known that silver nanoparticles are easily aggregated, and therefore, the surface thereof is coated with a protective agent to impart dispersibility. Further, a conductive ink in which silver nanoparticles coated on the surface are dispersed in a solvent may be applied to a substrate to form a coating film in a wiring pattern shape, and the coating film may be dried and sintered to form a conductive wiring.

Therefore, the protective agent for silver nanoparticles is required to be rapidly removed by sintering.

In addition, as a solvent for dispersing the silver nanoparticles coated on the surface, an alcohol solvent such as methanol or butanol has been used, but the alcohol solvent is easily volatilized, and the solvent is volatilized before coating to lower the fluidity, and it is difficult to uniformly coat the silver nanoparticles.

Patent document 1 describes the following: silver nanoparticles coated with an amine-containing protective agent on the surface thereof can be rapidly removed even by low-temperature sintering, and the silver nanoparticles are sintered, thereby obtaining excellent conductivity; if a solvent having low volatility such as butyl carbitol or hexyl carbitol is used as the solvent, volatilization of the solvent before application onto the substrate can be suppressed, clogging of a screen plate used for screen printing can be suppressed, and continuous use can be achieved.

Documents of the prior art

Patent document

Patent document 1: international publication No. 2016/132649

Disclosure of Invention

Problems to be solved by the invention

In recent years, in fields requiring a large current, such as industrial robots, electric vehicles, and hybrid vehicles, it has been required to increase the thickness of wiring to several tens of μm to several mm. As a solution, it is considered to form a thick wiring by laminating a plurality of coating films of conductive ink.

In the case of forming wiring by laminating coating films, it is necessary to repeat the steps of forming a first layer by applying a conductive ink and drying the first layer, and then laminating a second layer of coating film until a desired thickness is reached, but when the conductive ink contains a solvent having very low volatility, there is a problem that it takes time to dry and workability is remarkably lowered. Further, if the drying is insufficient, the first layer coating film may be deformed by laminating the second layer coating film. On the other hand, if the drying is performed too quickly, the surface may be formed into a film in a state where the solvent is contained therein, and it is known that a part of the solvent cannot be removed even by the subsequent sintering, and the sheet resistance of the obtained sintered body increases, thereby lowering the conductivity.

Accordingly, an object of the present invention is to provide a conductive ink which is thick and can efficiently form a wiring or an electrode having excellent conductivity.

Another object of the present invention is to provide a method for manufacturing an electronic device using the conductive ink.

Another object of the present invention is to provide a sintered body of the above conductive ink.

Another object of the present invention is to provide an electronic device comprising the above sintered body of conductive ink.

Means for solving the problems

The present inventors have conducted intensive studies to solve the above problems and, as a result, have found that, in a conductive ink obtained by dispersing silver nanoparticles having a structure in which the surface of the silver nanoparticles is coated with a protective agent containing an amine in a solvent containing a terpene solvent, a glycol ether solvent and/or a glycol ester solvent, and the content of the solvent having a vapor pressure of 0.05 to 15mmHg at 30 ℃ is 75 wt% or more of the total amount of the solvents, since the solvent has appropriate volatility (i.e., property of suppressing thickening before coating and rapidly volatilizing after coating), it can be uniformly coated by an offset printing method or the like, even if the second coating film is continuously formed without drying the obtained coating film (first layer), the shape can be maintained without deformation of the first coating film, and lamination can be continuously performed until a desired thickness is obtained.

Further, it has been found that when a binder resin is added in a specific range, the conductive ink can be thickened appropriately without impairing conductivity and transferability, thereby making it possible to increase the thickness of each coating film and reduce the number of coating films stacked to a desired thickness, thereby further improving workability. The present invention has been completed based on these findings.

That is, the present invention provides a conductive ink containing the following surface-modified silver nanoparticles (a) and the following solvent (B).

Surface-modified silver nanoparticles (a): silver nanoparticles having a structure in which the surface is coated with a protective agent containing an amine

Solvent (B): a solvent containing a terpene solvent (b-1) and a glycol ether solvent and/or a glycol ester solvent (b-2), wherein the content of the solvent having a vapor pressure of 0.05 to 15mmHg at 30 ℃ is 75 wt% or more of the total amount of the solvents

The present invention also provides the above-mentioned conductive ink, wherein the protective agent in the surface-modified silver nanoparticles (a) contains, as amines, aliphatic monoamines (1) having 6 or more total carbon atoms, and aliphatic monoamines (2) having 5 or less total carbon atoms and/or aliphatic diamines (3) having 8 or less total carbon atoms.

The present invention also provides the conductive ink described above, further comprising 0.1 to 3.0 parts by weight of a binder resin (C) per 100 parts by weight of the surface-modified silver nanoparticles (a).

The present invention also provides the conductive ink described above, further comprising 0.1 to 3.0 parts by weight of a siloxane compound (D) per 100 parts by weight of the surface-modified silver nanoparticles (a).

The present invention also provides the above conductive ink, wherein the viscosity at 25 ℃ and a shear rate of 10(1/s) is 30 to 80 pas.

The present invention also provides the above conductive ink, which is a conductive ink for offset printing.

In addition, the present invention provides a method of manufacturing an electronic device, the method including: applying the conductive ink onto a substrate by an offset printing method; and a step of sintering.

Further, the present invention provides a sintered body of the above conductive ink.

Further, the present invention provides an electronic device comprising the above sintered conductive ink on a substrate.

ADVANTAGEOUS EFFECTS OF INVENTION

The conductive ink of the present invention contains a solvent having appropriate volatility, and therefore, has excellent storage stability, and can stably maintain good coatability by suppressing a change in composition before coating. Moreover, the coating film was dried quickly after coating. Therefore, even if the second coating film is continuously laminated on the first coating film, the pattern shape of the coating film is not damaged. After the conductive ink is applied, sintering (even low-temperature sintering) is performed, whereby a sintered body having excellent conductivity can be obtained.

In particular, when the conductive ink of the present invention contains a binder resin in a specific range, the coating film thickness per layer can be increased by providing an appropriate viscosity, and the number of layers of coating films to be stacked until a desired thickness is achieved can be reduced, whereby the workability can be further improved. In addition, a thin line can be drawn with high accuracy by an offset printing method or the like.

Therefore, the conductive ink of the present invention can be suitably used for forming wiring and electrodes of a printed board (particularly, a large-current board).

Detailed Description

[ conductive ink ]

The conductive ink of the present invention contains the following surface-modified silver nanoparticles (a) and the following solvent (B).

Surface-modified silver nanoparticles (a): silver nanoparticles having a structure in which the surface is coated with a protective agent containing an amine

Solvent (B): a solvent containing a terpene solvent (b-1) and a glycol ether solvent and/or a glycol ester solvent (b-2), wherein the content of the solvent having a vapor pressure of 0.05 to 15mmHg at 30 ℃ is 75 wt% or more of the total amount of the solvents

The conductive ink of the present invention contains the solvent (B) having an appropriate volatility, and therefore can exhibit quick drying while suppressing a change in composition before application. Therefore, even if the coating film is continuously laminated, the shape is not damaged.

The conductive ink of the present invention preferably has an appropriate viscosity (at 25 ℃ C., a shear rate of 10 (1/s)) of, for example, about 30 to 80 pas, preferably 30 to 70 pas, and particularly preferably 35 to 70 pas, from the viewpoint of forming a good printed pattern, from the viewpoint of excellent coatability, making it possible to form a thick film for each layer, and from the viewpoint of reducing the number of stacked coating films until a desired thickness is achieved when forming wiring by stacking.

When the conductive ink of the present invention has the above viscosity, it can be applied to a substrate with good precision by an offset printing method or the like. In addition, when the conductive ink of the present invention has the above viscosity by containing a binder resin (C) described later (particularly, a cellulose-based resin), a sintered body having excellent conductivity can be obtained by sintering (even low-temperature sintering).

The conductive ink of the present invention is excellent in dispersion stability, and when the conductive ink having a silver concentration of 65 wt% is stored at 5 ℃, for example, the increase in viscosity can be suppressed for 1 month or more.

The conductive ink of the present invention has the above-described characteristics, and therefore, can be suitably used as a conductive ink for offset printing, and can be suitably used for forming wiring and electrodes of a printed board (particularly, a large-current board) by an offset printing method or the like.

(surface-modified silver nanoparticle (A))

The surface-modified silver nanoparticles of the present invention have a structure in which the surface of the silver nanoparticles is coated with a protective agent containing an amine, and more specifically, have a structure in which an unshared electron pair of the amine is electrically coordinated to the surface of the silver nanoparticles. The surface-modified silver nanoparticles of the present invention having the above-described structure can prevent re-aggregation of the silver nanoparticles, and can stably maintain a highly dispersed state in the conductive ink.

The average primary particle diameter of the silver nanoparticle portion of the surface-modified silver nanoparticles is, for example, 0.5 to 100nm, preferably 0.5 to 80nm, more preferably 1 to 70nm, and further preferably 1 to 60 nm. The particle size can be determined by observation with a Scanning Electron Microscope (SEM).

The content of the surface-modified silver nanoparticles (a) is, for example, 60 to 85 wt% of the total amount of the conductive ink, and the upper limit is preferably 80 wt%, and particularly preferably 75 wt%, in terms of obtaining a sintered body having good conductivity and excellent dispersion stability (that is, high dispersibility can be stably maintained for a long period of time, and increase in viscosity can be suppressed).

(solvent (B))

The solvent (B) in the present invention contains a terpene solvent (B-1) and a glycol ether solvent and/or a glycol ester solvent (B-2). The content of the solvent having a vapor pressure of 0.05 to 15mmHg at 30 ℃ in the total amount of the solvent (B) is 75 wt% or more of the total amount of the solvent.

The terpene-based solvent (b-1) has a vapor pressure at 30 ℃ of, for example, preferably 0.05 to 5.0mmHg, particularly preferably 0.1 to 3.0mmHg, most preferably 0.5 to 3.0mmHg, and particularly preferably 1.0 to 3.0mmHg, from the viewpoint of having an appropriate volatility.

Examples of the terpene solvent (b-1) include: 4- (1 '-acetoxy-1' -methyl ester) -cyclohexanol acetate, 1,2,5, 6-tetrahydrobenzyl alcohol, 1,2,5, 6-tetrahydrobenzyl acetate, cyclohexyl acetate, 2-methylcyclohexyl acetate, 4-tert-butylcyclohexyl acetate, dihydroterpineol, dihydroterpinyl acetate, dihydroterpineoxyethanol, terpinyl methyl ether, dihydroterpinyl methyl ether, and the like. These may be used alone in 1 kind, or may be used in combination of 2 or more kinds. Of these, the type and content thereof are preferably selected as appropriate so as to satisfy the above conditions.

The above glycol ether solvent and/or glycol ester solvent (b-2) has a vapor pressure at 30 ℃ of, for example, preferably 0.05 to 5.0mmHg, particularly preferably 0.1 to 3.0mmHg, most preferably 0.5 to 3.0mmHg, and particularly preferably 1.0 to 3.0mmHg, from the viewpoint of having an appropriate volatility.

Examples of the glycol ether solvent include compounds represented by the following formula (b-2-1).

R¹¹O-(R¹³O)_m-R¹² (b-2-1)

(in the formula, R¹¹Represents a hydrogen atom, an alkyl group or an aryl group, R¹²Represents alkyl or aryl, R¹³Represents an alkylene group. m represents an integer of 1 or more)

As the above-mentioned R¹¹、R¹²Examples of the alkyl group in (1) include: a linear or branched alkyl group having 1 to 10 carbon atoms (preferably 1 to 5 carbon atoms) such as a methyl group, an ethyl group, a propyl group, and an isopropyl group. Examples of the aryl group include: an aryl group having 6 to 10 carbon atoms (e.g., phenyl group).

As the above-mentioned R¹³The alkylene group in (1) includes, for example: methylene, methyl methylene, dimethyl methylene, ethylene, propylene, trimethylene, tetramethylene, pentamethylene, hexamethylene and the like. In the present invention, among them, an alkylene group having 1 to 4 carbon atoms is preferable, an alkylene group having 1 to 3 carbon atoms is particularly preferable, and an alkylene group having 2 to 3 carbon atoms is most preferable.

m is an integer of 1 or more, for example, an integer of 1 to 8, preferably an integer of 1 to 3, and particularly preferably 1.

Examples of the glycol ether solvent include: ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monoisobutyl ether, ethylene glycol monohexyl ether, ethylene glycol monoketone-Ethylene glycol MonoC such as 2-ethylhexyl Ether_1-10An alkyl ether; ethylene glycol Mono C such as ethylene glycol monophenyl Ether and ethylene glycol monobenzyl Ether_6-10Aryl or C_7-16An aralkyl ether; propylene glycol mono C such as propylene glycol monoethyl ether, propylene glycol monopropyl ether, and propylene glycol monobutyl ether_1-10An alkyl ether; ethylene glycol DC such as ethylene glycol methyl n-propyl ether, ethylene glycol methyl n-butyl ether, and ethylene glycol methyl isoamyl ether_1-10An alkyl ether; propylene glycol di-C such as propylene glycol methyl n-propyl ether, propylene glycol methyl n-butyl ether, propylene glycol methyl isoamyl ether, etc_1-10An alkyl ether; diethylene glycol Mono-C such as diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, and diethylene glycol monoisopropyl ether_1-10An alkyl ether; diethylene glycol Mono-C such as diethylene glycol monophenyl Ether and diethylene glycol Mono-benzyl Ether_6-10Aryl or C_7-16An aralkyl ether; diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol ethyl methyl ether, diethylene glycol isopropyl methyl ether, diethylene glycol methyl n-butyl ether, and other diethylene glycol dimethyl ethers, diethylene glycol diethyl ethers, diethylene glycol ethyl methyl ethers, diethylene glycol isopropyl methyl ethers, diethylene glycol methyl n-butyl ethers, and the like_1-10An alkyl ether; dipropylene glycol di-C such as dipropylene glycol monomethyl ether, dipropylene glycol methyl isoamyl ether, dipropylene glycol dimethyl ether, dipropylene glycol methyl-n-propyl ether, dipropylene glycol methyl-n-butyl ether, and dipropylene glycol methyl cyclopentyl ether_1-10An alkyl ether; triethylene glycol Di-C such as triethylene glycol methyl n-butyl ether_1-10An alkyl ether; tripropylene glycol di-C such as tripropylene glycol methyl n-propyl ether and tripropylene glycol dimethyl ether_1-10Alkyl ethers, and the like. These may be used alone in 1 kind, or may be used in combination of 2 or more kinds. Of these, the type and content thereof are preferably selected as appropriate so as to satisfy the above conditions.

Examples of the glycol ester solvents include: a compound represented by the following formula (b-2-2).

R¹⁴O-(R¹⁶O)_m’-R¹⁵ (b-2-2)

(in the formula, R¹⁴Represents a hydrogen atom, an alkyl group, an aryl group or an acyl group, R¹⁵Represents an acyl group, R¹⁶Represents an alkylene group. m' represents an integer of 1 or more. )

That is, the glycol ester solvent in the present invention also contains a glycol ether ester solvent.

As mentioned aboveR¹⁴、R¹⁵Examples of the acyl group (RCO-group) in (A) include acyl groups wherein R is a linear or branched alkyl group having 1 to 10 carbon atoms (preferably 1 to 5 carbon atoms) (for example, acetyl, propionyl, butyryl, isobutyryl, pivaloyl and the like).

As the above-mentioned R¹⁴Examples of the alkyl group in (1) include: a linear or branched alkyl group having 1 to 10 carbon atoms (preferably 1 to 5 carbon atoms) such as a methyl group, an ethyl group, a propyl group, and an isopropyl group. Examples of the aryl group include: an aryl group having 6 to 10 carbon atoms (e.g., phenyl group).

As the above-mentioned R¹⁶The alkylene group in (1) includes, for example: methylene, methyl methylene, dimethyl methylene, ethylene, propylene, trimethylene, tetramethylene, pentamethylene, hexamethylene and the like. In the present invention, among them, an alkylene group having 1 to 4 carbon atoms is preferable, an alkylene group having 1 to 3 carbon atoms is particularly preferable, and an alkylene group having 2 to 3 carbon atoms is most preferable.

m' is an integer of 1 or more, for example, an integer of 1 to 8, preferably an integer of 1 to 3, and particularly preferably 1.

Examples of the glycol ester solvents include: c such as ethylene glycol monomethyl ether acetate, ethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether acetate, 3-methoxybutyl acetate_2-3Alkylene glycol C_1-10Alkyl ethers C_1-10An alkyl ester; di-C such as diethylene glycol-n-butyl ether acetate, diethylene glycol ethyl ether acetate, diethylene glycol butyl ether acetate, dipropylene glycol methyl ether acetate_2-3Alkylene glycol C_1-10Alkyl ethers C_1-10An alkyl ester; c such as propylene glycol diacetate, 1, 3-butanediol diacetate, 1, 4-butanediol diacetate_2-3Alkylene glycol di C_1-10Alkyl esters, and the like. These may be used alone in 1 kind, or may be used in combination of 2 or more kinds. Of these, the type and content thereof are preferably selected as appropriate so as to satisfy the above conditions.

In the present invention, the solvent (b-2) preferably contains at least a glycol ether solvent, and particularly preferably contains at least a glycol monoether, from the viewpoint of suppressing thickening before coating and rapidly volatilizing after coating.

The glycol monoethers are preferably selected from ethylene glycol mono-C_1-10Alkyl ethers and propylene glycol mono C_1-10At least 1 of the alkyl ethers.

The glycol monoether is preferably ethylene glycol mono-C_1-10Alkyl ethers, propylene glycol mono C_1-10Alkyl ethers, etc.. C_2-3Alkylene glycol mono C_1-10An alkyl ether.

The conductive ink of the present invention may contain 1 or 2 or more other solvents (e.g., ethyl lactate acetate, tetrahydrofurfuryl alcohol, ethylene glycol, etc.) other than the above as the solvent (B), and the content of the other solvents is, for example, preferably 30% by weight or less, more preferably 20% by weight or less, particularly preferably 15% by weight or less, most preferably 10% by weight or less, further preferably 5% by weight or less, and particularly preferably 1% by weight or less of the total amount of the solvents (B) contained in the conductive ink of the present invention. When the content of the other solvent is higher than the above range and a large amount of the solvent having too high volatility is contained, clogging of the coating apparatus tends to easily occur. On the other hand, when a solvent having too low volatility is contained in a large amount, the quick-drying property is impaired, and it is necessary to perform a treatment such as heating for drying after coating, and the workability tends to be lowered.

Therefore, the total content of the terpene-based solvent (B-1), the glycol ether-based solvent and the glycol ester-based solvent (B-2) is, for example, 70 to 100% by weight, and the lower limit is preferably 80% by weight, more preferably 85% by weight, particularly preferably 90% by weight, most preferably 95% by weight, and particularly preferably 99% by weight, based on the total amount of the solvent (B).

A ratio [ (B-1)/(B-2) of the content (total amount in the case of two or more kinds) of the terpene-based solvent (B-1) contained in the solvent (B) to the content (total amount in the case of two or more kinds) of the glycol ether-based solvent and/or the glycol ester-based solvent (B-2); the weight ratio is, for example, 90/10 to 60/40, preferably 85/15 to 65/35, and particularly preferably 80/20 to 70/30.

The content of the terpene-based solvent (B-1) (the total amount thereof in the case of containing two or more kinds) is, for example, 60 to 90% by weight, preferably 65 to 85% by weight, and particularly preferably 70 to 80% by weight of the total amount of the solvent (B).

The content of the terpene solvent (b-1) (the total amount thereof in the case of containing two or more species) is, for example, 5 to 40% by weight, preferably 10 to 35% by weight, and particularly preferably 15 to 30% by weight of the total amount of the conductive ink.

The content of the glycol ether-based solvent and/or the glycol ester-based solvent (B-2) (the total amount thereof in the case of containing two or more types) is, for example, 10 to 40% by weight, preferably 15 to 35% by weight, and particularly preferably 20 to 30% by weight of the total amount of the solvent (B).

The content of the glycol ether solvent and/or the glycol ester solvent (b-2) (the total amount thereof in the case of containing two or more species) is, for example, 0.5 to 20% by weight, preferably 1.0 to 15% by weight, and particularly preferably 3 to 10% by weight of the total amount of the conductive ink.

The content of the solvent (B) is, for example, 30 to 70 parts by weight, preferably 35 to 65 parts by weight, particularly preferably 35 to 60 parts by weight, and most preferably 40 to 55 parts by weight, based on 100 parts by weight of the surface-modified silver nanoparticles (a).

The content of the solvent having a vapor pressure of 0.05 to 15mmHg (preferably 0.1 to 5.0mmHg) at 30 ℃ in the total amount of the solvent (B) is 75 wt% or more, and is preferably 80 wt% or more, more preferably 85 wt% or more, particularly preferably 90 wt% or more, most preferably 95 wt% or more, and particularly preferably substantially only the solvent having a vapor pressure of 0.05 to 15mmHg at 30 ℃ from the viewpoint of achieving both good coatability and quick drying and facilitating management of the time from the end of printing the first layer to the lamination of the second layer.

The content of the solvent having a vapor pressure of 0.05 to 1mmHg (preferably 0.1 to 1mmHg) at 30 ℃ in the total amount of the solvent (B) is, for example, 50 to 80 wt%, preferably 60 to 80 wt%, and particularly preferably 70 to 80 wt%.

The content of the solvent having a vapor pressure at 30 ℃ in the total amount of the solvent (B) in a range of more than 1mmHg and 15mmHg or less (preferably, in a range of more than 1mmHg and 5mmHg or less) is, for example, 20 to 50% by weight, preferably 20 to 40% by weight, and particularly preferably 20 to 30% by weight.

Accordingly, the content of the solvent having a vapor pressure of less than 0.05mmHg (preferably less than 0.1mmHg) at 30 ℃ in the total amount of the solvent (B) is 25 wt% or less, preferably 20 wt% or less, more preferably 10 wt% or less, particularly preferably 5 wt% or less, and most preferably 1 wt% or less. Therefore, the coating film is dried quickly after coating, and the shape of the coating film is not damaged even if the coating film is laminated on the coating film without intervening a drying step.

The content of the solvent having a vapor pressure at 30 ℃ of more than 15mmHg (preferably more than 5mmHg) in the total amount of the solvent (B) is 25 wt% or less, preferably 20 wt% or less, more preferably 10 wt% or less, particularly preferably 5 wt% or less, and most preferably 1 wt% or less. Therefore, the composition change before coating can be suppressed, and the storage stability and coatability are excellent. In addition, the transfer property from the blanket is also excellent.

(other Components)

The conductive ink of the present invention may contain, in addition to the above components, additives such as a binder resin, a surface energy adjuster, a plasticizer, a leveling agent, an antifoaming agent, and an adhesion imparting agent, if necessary.

Among them, the conductive ink of the present invention preferably contains 1 or 2 or more kinds of binder resins (C) from the viewpoint of imparting an appropriate viscosity, making it possible to increase the thickness of each coating film, reducing the number of coating films laminated until a desired thickness is reached in the case of forming wiring by lamination, and improving the handling properties.

Examples of the binder resin (C) include: vinyl chloride-vinyl acetate copolymer resin, polyvinyl butyral resin, polyester resin, acrylic resin, cellulose resin, and the like.

In the present invention, among them, cellulose-based resins are preferably used from the viewpoint that viscosity can be imparted without causing a decrease in conductivity, and commercially available products such as "ETHOCEL std.200" and "ETHOCEL std.300" (manufactured by DOW Chemical) can be used.

The content of the binder resin (C) (e.g., a cellulose-based resin) may be appropriately adjusted so that the viscosity of the conductive ink of the present invention is within the above range, and may be, for example, 0.1 to 3.0 parts by weight based on 100 parts by weight of the surface-modified silver nanoparticles (a).

The content of the binder resin (C) (e.g., a cellulose-based resin) may be appropriately adjusted to be, for example, 0.5 to 5.0 wt% of the total amount of the conductive ink so that the viscosity of the conductive ink of the present invention is within the above range.

In view of good transfer of the conductive ink from the blanket to the substrate in the case of offset printing, it is preferable that the conductive ink of the present invention further contains 1 or 2 or more siloxane compounds (D) as a surface energy adjuster.

Examples of the siloxane compound (D) include compounds represented by the following formula (D).

[ chemical formula 1]

(in the formula, R²¹～R²⁶The same or different represents an optionally substituted alkyl group having 1 to 6 carbon atoms, or an optionally substituted aryl group having 6 to 10 carbon atoms. n represents an integer of 1 or more. In the formula²¹And R²⁴Or may be bonded to each other. )

Examples of the alkyl group having 1 to 6 carbon atoms include a methyl group and the like.

Examples of the aryl group having 6 to 10 carbon atoms include a phenyl group.

Examples of the substituent optionally contained in the alkyl group and the aryl group include: amino groups, epoxy groups, carboxyl groups, polyether groups, and the like.

In the present invention, commercially available products such as "BYK-302" and "BYK-307" (the above are polyether-modified polydimethylsiloxane, manufactured by BYK Chemie Japan K.K.) can be used.

The content of the siloxane compound (D) may be appropriately adjusted so that the viscosity of the conductive ink of the present invention is within the above range, and may be, for example, 0.1 to 3.0 parts by weight based on 100 parts by weight of the surface-modified silver nanoparticles (a).

The content of the siloxane compound (D) may be appropriately adjusted so that the viscosity of the conductive ink of the present invention is within the above range, and may be, for example, 0.5 to 5.0 wt% based on the total amount of the conductive ink.

(method for producing conductive ink)

The conductive ink of the present invention can be produced, for example, as follows: the ink of the present invention is produced through a step (ink preparation step) of mixing a silver compound and an amine-containing protective agent to produce a complex containing the silver compound and the amine (complex production step), a step (thermal decomposition step) of thermally decomposing the complex, and a step (cleaning step) of cleaning the reaction product as necessary.

(Complex formation step)

As the silver compound, a compound that is easily decomposed by heating to generate metallic silver is preferably used. Examples of such a silver compound include: silver carboxylates such as silver formate, silver acetate, silver oxalate, silver malonate, silver benzoate, and silver phthalate; silver halides such as silver fluoride, silver chloride, silver bromide, and silver iodide; silver sulfate, silver nitrate, silver carbonate, and the like. In the present invention, silver oxalate is preferred among them, because it has a high silver content, can be thermally decomposed without a reducing agent, easily generates metallic silver by decomposition, and is less likely to cause impurities derived from the reducing agent to be mixed into the ink.

The amine is a compound in which at least 1 hydrogen atom of ammonia is substituted with a hydrocarbon group, and includes primary, secondary, and tertiary amines. The amine may be a monoamine or a polyamine such as a diamine. These may be used alone in 1 kind, or may be used in combination of 2 or more kinds.

Among them, the amine preferably contains at least 1 kind selected from the following amines: a monoamine (1) having 6 or more total carbon atoms represented by the following formula (a-1), wherein R is¹、R²、R³Identically or differently hydrogen atoms or 1-valent hydrocarbon radicals (R)¹、R²、R³With the exception of hydrogen atoms); monoamines (2) having 5 or less total carbon atoms, represented by the following formula (a-1), wherein R is¹、R²、R³Identically or differently hydrogen atoms or 1-valent hydrocarbon radicals (R)¹、R²、R³With the exception of hydrogen atoms); and a diamine (3) having 8 or less total carbon atoms, represented by the following formula (a-2), wherein R is⁸Is a 2-valent hydrocarbon radical, R⁴～R⁷The same or different are a hydrogen atom or a 1-valent hydrocarbon group. Particularly preferably, the monoamine (1) and the monoamine (2) and/or the diamine (3) are contained together.

[ chemical formula 2]

The hydrocarbon group includes an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, and an aromatic hydrocarbon group, and among them, an aliphatic hydrocarbon group or an alicyclic hydrocarbon group is preferable, and an aliphatic hydrocarbon group is particularly preferable. Therefore, the monoamine (1), the monoamine (2), and the diamine (3) are preferably an aliphatic monoamine (1), an aliphatic monoamine (2), and an aliphatic diamine (3).

In addition, the 1-valent aliphatic hydrocarbon group includes an alkyl group and an alkenyl group. The 1-valent alicyclic hydrocarbon group includes a cycloalkyl group and a cycloalkenyl group. The 2-valent aliphatic hydrocarbon group includes an alkylene group and an alkenylene group, and the 2-valent alicyclic hydrocarbon group includes a cycloalkylene group and a cycloalkenylene group.

As R¹、R²、R³The 1-valent hydrocarbon group in (1) may be exemplified by: an alkyl group having about 1 to 20 carbon atoms such as a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a pentyl group, a hexyl group, a decyl group, a dodecyl group, a tetradecyl group, an octadecyl group, etc.; alkenyl groups having about 2 to 20 carbon atoms such as vinyl, allyl, methallyl, 1-propenyl, isopropenyl, 1-butenyl, 2-butenyl, 3-butenyl, 1-pentenyl, 2-pentenyl, 3-pentenyl, 4-pentenyl, 5-hexenyl and the like; cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cyclooctylCycloalkyl groups having about 3 to 20 carbon atoms such as a cycloalkyl group; and cycloalkenyl groups having about 3 to 20 carbon atoms such as cyclopentenyl and cyclohexenyl.

As R⁴～R⁷The 1-valent hydrocarbon group in (1) includes the above-exemplified 1-valent hydrocarbon group having 7 or less carbon atoms.

As R⁸The 2-valent hydrocarbon group in (1) includes, for example: alkylene groups having 1 to 8 carbon atoms such as methylene, methylmethylene, dimethylmethylene, ethylene, propylene, trimethylene, tetramethylene, pentamethylene, and heptamethylene; and an alkenylene group having 2 to 8 carbon atoms such as a vinylene group, a propenylene group, a 1-butenylene group, a 2-butenylene group, a butadienylene group, a pentenylene group, a hexenylene group, a heptenylene group, an octenylene group, and the like.

R is as defined above¹～R⁸The hydrocarbon group in (1) may have various substituents [ e.g., halogen atom, oxo group, hydroxy group, substituted oxy group (e.g., C)_1-4Alkoxy radical, C_6-10Aryloxy radical, C_7-16Aralkyloxy radical, C_1-4Acyloxy group, etc.), carboxyl group, substituted oxycarbonyl group (e.g., C)_1-4Alkoxycarbonyl group, C_6-10Aryloxycarbonyl group, C_7-16Aralkoxycarbonyl, etc.), cyano, nitro, sulfo, heterocyclic, etc]. The hydroxyl group and the carboxyl group may be protected with a protecting group commonly used in the field of organic synthesis.

The monoamine (1) is a compound having a function of imparting high dispersibility to the silver nanoparticles, and examples thereof include: primary amines having a linear alkyl group such as hexylamine, heptylamine, octylamine, nonylamine, decylamine, undecylamine, dodecylamine, tridecylamine, tetradecylamine, pentadecylamine, hexadecylamine, heptadecylamine, and octadecylamine; primary amines having a branched alkyl group such as isohexylamine, 2-ethylhexylamine, and tert-octylamine; primary amines having a cycloalkyl group such as cyclohexylamine; primary amines having an alkenyl group such as oleylamine; secondary amines having a linear alkyl group such as N, N-dipropylamine, N-dibutylamine, N-dipentylamine, N-dihexylamine, N-diheptylamine, N-dioctylamine, N-dinonylamine, N-didecylamine, N-diundecamamine, N-didodecylamine, and N-propyl-N-butylamine; secondary amines having a branched alkyl group such as N, N-diisohexylamine and N, N-bis (2-ethylhexyl) amine; tertiary amines having a linear alkyl group such as tributylamine and trihexylamine; tertiary amines having a branched alkyl group such as triisohexylamine and tris (2-ethylhexyl) amine.

Among the monoamines (1), from the viewpoint of ensuring a space from other silver nanoparticles when the amino group is adsorbed on the surface of the silver nanoparticles and thus improving the effect of preventing aggregation of the silver nanoparticles, amines (particularly primary amines) having a linear alkyl group having a total carbon number of 6 or more (from the viewpoint of easy acquisition and easy removal during firing, the upper limit of the total carbon number is preferably about 18, more preferably 16, and particularly preferably 12), and hexylamine, heptylamine, octylamine, nonylamine, decylamine, undecylamine, dodecylamine, and the like are particularly preferable.

In addition, if an amine having a branched alkyl group (particularly, a primary amine) is used among the monoamines (1), it is possible to impart high dispersibility to the silver nanoparticles in a smaller amount due to the steric hindrance of the branched alkyl group than in the case of using an amine having a linear alkyl group having the same total carbon number. Therefore, it is preferable that the amine be removed efficiently during sintering, particularly low-temperature sintering, to obtain a sintered body having more excellent conductivity.

The amine having a branched alkyl group is particularly preferably an amine having a branched alkyl group having 6 to 16 (preferably 6 to 10) total carbon atoms such as isohexylamine and 2-ethylhexylamine, and particularly, an amine having a branched alkyl group having a structure in which the second carbon atom from the nitrogen atom is branched such as 2-ethylhexylamine is effective from the viewpoint of steric hindrance.

The monoamine (2) is considered to have a shorter hydrocarbon chain than the monoamine (1) and thus to have a low function of imparting high dispersibility to the silver nanoparticles, but is considered to have a complex formation accelerating effect because it has a higher polarity than the monoamine (1) and a high coordination ability to silver atoms. Further, since the hydrocarbon chain is short, the silver nanoparticles can be removed from the surface thereof in a short time (for example, 30 minutes or less, preferably 20 minutes or less) even in low-temperature sintering, and a sintered body having excellent conductivity can be obtained.

Examples of the monoamine (2) include: primary amines having 2 to 5 total carbon atoms and having a linear or branched alkyl group, such as ethylamine, n-propylamine, isopropylamine, n-butylamine, isobutylamine, sec-butylamine, tert-butylamine, pentylamine, isopentylamine, and tert-pentylamine; and secondary amines having 2 to 5 carbon atoms in total and having a linear or branched alkyl group, such as N-methyl-N-propylamine, N-ethyl-N-propylamine, N-dimethylamine and N, N-diethylamine.

The monoamine (2) is preferably a primary amine having 2 to 5 (preferably 4 to 5) total carbon atoms and having a linear or branched alkyl group, such as n-butylamine, iso-butylamine, sec-butylamine, tert-butylamine, pentylamine, isopentylamine, and tert-pentylamine, and is particularly preferably a primary amine having 2 to 5 (preferably 4 to 5) total carbon atoms and having a linear alkyl group, such as n-butylamine.

The diamine (3) has 8 or less total carbon atoms (for example, 1 to 8), has higher polarity than the monoamine (1), and has higher coordination ability to silver atoms, and therefore is considered to have a complex formation promoting effect. The diamine (3) has an effect of promoting thermal decomposition at a lower temperature in a short time in the thermal decomposition step of the complex, and if the diamine (3) is used, silver nanoparticles can be produced more efficiently. In addition, the surface-modified silver nanoparticles having a structure coated with a protective agent containing a diamine (3) exhibit excellent dispersion stability in a dispersion medium containing a solvent having high polarity. Further, since the hydrocarbon chain of the diamine (3) is short, the diamine can be removed from the surface of the silver nanoparticles in a short time (for example, 30 minutes or less, preferably 20 minutes or less) even in low-temperature sintering, and a sintered body having excellent conductivity can be obtained.

Examples of the diamine (3) include: ethylenediamine, 1, 3-propylenediamine, 2-dimethyl-1, 3-propylenediamine, 1, 4-butylenediamine, 1, 5-pentylenediamine, 1, 6-hexylenediamine, 1, 7-heptylenediamine, 1, 8-octylenediamine, R in 1, 5-diamino-2-methylpentane equation (a-2)⁴～R⁷Is a hydrogen atom and R⁸A diamine which is a straight-chain or branched alkylene group; n, N ' -dimethylethylenediamine, N ' -diethylethylenediamine, N ' -dimethyl-1, 3-propanediamine, N ' -diethyl-1, 3-propanediamine, N ' -dimethyl-1, 4-butanediamine, N ' -diethyl-1, 4-butanediamine, N ' -dimethylethylenediamine, N ' -butanediamine, N ' -dimethylethylenediamine, N,R in N, N' -dimethyl-1, 6-hexanediamine equation (a-2)⁴、R⁶Are, identically or differently, straight-chain or branched alkyl, and R⁵、R⁷Is a hydrogen atom, R⁸A diamine which is a straight-chain or branched alkylene group; r in the equation (a-2) for N, N-dimethylethylenediamine, N-diethylethylenediamine, N-dimethyl-1, 3-propylenediamine, N-diethyl-1, 3-propylenediamine, N-dimethyl-1, 4-butylenediamine, N-diethyl-1, 4-butylenediamine, N-dimethyl-1, 6-hexanediamine⁴、R⁵Are, identically or differently, straight-chain or branched alkyl, and R⁶、R⁷Is a hydrogen atom, R⁸Diamines which are linear or branched alkylene groups, and the like.

Among these, R in the above formula (a-2) is preferred⁴、R⁵Are, identically or differently, straight-chain or branched alkyl, and R⁶、R⁷Is a hydrogen atom, R⁸Diamine which is a linear or branched alkylene group [ R in the formula (a-2) is particularly preferable⁴、R⁵Is a linear alkyl group, and R⁶、R⁷Is a hydrogen atom, R⁸Diamines being straight-chain alkylene groups]。

R in the formula (a-2)⁴、R⁵The same or different are straight-chain or branched alkyl, R⁶、R⁷In the diamine having a hydrogen atom, that is, a diamine having a primary amino group and a tertiary amino group, the primary amino group has a high coordinating ability to a silver atom, and the tertiary amino group has an insufficient coordinating ability to a silver atom, so that excessive complication of the formed complex can be prevented, and thermal decomposition at a lower temperature in a shorter time can be realized in the thermal decomposition step of the complex. Among these, diamines having 6 or less (for example, 1 to 6) in total carbon atoms are preferable, and diamines having 5 or less (for example, 1 to 5) in total carbon atoms are more preferable, from the viewpoint of being able to remove silver nanoparticles from their surfaces in a short time during low-temperature sintering.

When the amine of the present invention contains both the monoamine (1) and the monoamine (2) and/or the diamine (3), the proportion of the amine used is not particularly limited, and the total amount of the amine [ monoamine (1) + monoamine (2) + diamine (3); 100 mol% ] is preferably in the following range.

Content of monoamine (1): for example, 5 to 65 mol% (the lower limit is preferably 10 mol%, particularly preferably 15 mol%, and the upper limit is preferably 50 mol%, particularly preferably 40 mol%, most preferably 35 mol%)

Total content of monoamine (2) and diamine (3): for example, 35 to 95 mol% (the lower limit is preferably 50 mol%, particularly preferably 60 mol%, most preferably 65 mol%, and the upper limit is preferably 90 mol%, particularly preferably 85 mol%)

Further, in the case of using the monoamine (2) and the diamine (3) at the same time, the total amount of the amines [ monoamine (1) + monoamine (2) + diamine (3); the contents of the monoamine (2) and the diamine (3) are preferably in the following ranges based on 100 mol%.

Monoamine (2): for example, 5 to 70 mol% (the lower limit is preferably 10 mol%, particularly preferably 15 mol%, and the upper limit is preferably 65 mol%, particularly preferably 60 mol%)

Diamine (3): for example, 5 to 50 mol% (the lower limit is preferably 10 mol%, and the upper limit is preferably 45 mol%, and particularly preferably 40 mol%)

By containing the monoamine (1) within the above range, the dispersion stability of the silver nanoparticles can be obtained. When the content of the monoamine (1) is less than the above range, it tends to be difficult to obtain dispersion stability of the silver nanoparticles. On the other hand, when the content of the monoamine (1) is higher than the above range, it tends to be difficult to remove the amine by low-temperature sintering.

By containing the monoamine (2) in the above range, the complex formation promoting effect is easily obtained. Further, the sintering can be performed at a low temperature for a short time, and the diamine (3) can be easily removed from the surface of the silver nanoparticles during the sintering.

By containing the diamine (3) in the above range, the complex formation promoting effect and the thermal decomposition promoting effect of the complex can be easily obtained. In addition, the surface-modified silver nanoparticles having a structure coated with a protective agent containing a diamine (3) exhibit excellent dispersion stability in a dispersion medium containing a solvent having high polarity.

In the present invention, if the monoamine (2) and/or the diamine (3) having a high ability to coordinate to silver atoms is used, the amount of the monoamine (1) can be reduced in accordance with the proportion of the monoamine used, and when sintering is performed at a low temperature in a short time, these amines can be easily removed from the surfaces of silver nanoparticles, and the sintering of the silver nanoparticles can be sufficiently performed.

In the amine used as the protecting agent in the present invention, other amines may be contained in addition to the monoamine (1), the monoamine (2), and the diamine (3), but the total content of the monoamine (1), the monoamine (2), and the diamine (3) is preferably 60 to 100% by weight, for example, and the lower limit is particularly preferably 80% by weight, and most preferably 90% by weight, based on the total amount of all the amines contained in the protecting agent. That is, the content of the other amine is preferably 60% by weight or less, particularly preferably 20% by weight or less, and most preferably 10% by weight or less.

The amount of the amine [ particularly, monoamine (1) + monoamine (2) + diamine (3) ] is not particularly limited, and is preferably about 1 to 50 moles per 1 mole of silver atoms of the silver compound as a raw material, and is preferably 2 to 50 moles, particularly preferably 6 to 50 moles, from the viewpoint of obtaining surface-modified silver nanoparticles in the substantially solvent-free condition. When the amount of the amine is less than the above range, the silver compound which is not converted into a complex tends to remain in the complex formation step, and the uniformity of the silver nanoparticles is impaired in the subsequent thermal decomposition step, resulting in the enlargement of particles, and the silver compound remains without thermal decomposition, which is not preferable.

The reaction of the amine with the silver compound is preferably carried out in the presence of a solvent.

As the solvent, for example, 1 or 2 or more kinds of alcohol solvents having 3 or more carbon atoms [ for example, n-propanol (boiling point: 97 ℃ C.), isopropanol (boiling point: 82 ℃ C.), n-butanol (boiling point: 117 ℃ C.), isobutanol (boiling point: 107.89 ℃ C.), sec-butanol (boiling point: 99.5 ℃ C.), tert-butanol (boiling point: 82.45 ℃ C.), n-pentanol (boiling point: 136 ℃ C.), n-hexanol (boiling point: 156 ℃ C.), n-octanol (boiling point: 194 ℃ C.), 2-octanol (boiling point: 174 ℃ C.), etc. ], can be used. Among these, alcohol solvents having 4 to 6 carbon atoms are preferable, and n-butanol and n-hexanol are particularly preferable, from the viewpoint of the possibility of setting the temperature of the subsequent thermal decomposition step of the complex to a high level and the convenience of the post-treatment of the obtained surface-modified silver nanoparticles.

The amount of the solvent used is, for example, 120 parts by weight or more, preferably 130 parts by weight or more, and more preferably 150 parts by weight or more, based on 100 parts by weight of the silver compound. The upper limit of the amount of the solvent used is, for example, 1000 parts by weight, preferably 800 parts by weight, and particularly preferably 500 parts by weight.

In the present invention, it is preferable to further use 1 or 2 or more kinds of aliphatic monocarboxylic acids as the protective agent for the purpose of further improving the dispersibility of the silver nanoparticles. By using the aliphatic monocarboxylic acid, the stability of the silver nanoparticles, particularly the stability in a state of being dispersed in the solvent (B), tends to be improved.

Examples of the aliphatic monocarboxylic acid include: saturated aliphatic monocarboxylic acids having 4 or more carbon atoms such as butyric acid, valeric acid, caproic acid, heptanoic acid, caprylic acid, pelargonic acid, capric acid, undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, heptadecanoic acid, octadecanoic acid, nonadecanoic acid, and eicosanoic acid; unsaturated aliphatic monocarboxylic acids having 8 or more carbon atoms such as oleic acid, elaidic acid, linoleic acid, palmitoleic acid, and eicosenoic acid.

Among these, saturated or unsaturated aliphatic monocarboxylic acids having 8 to 18 carbon atoms (in particular, octanoic acid, oleic acid, etc.) are preferred. When the carboxyl group of the aliphatic monocarboxylic acid is adsorbed on the surface of the silver nanoparticles, the saturated or unsaturated aliphatic hydrocarbon chain with 8-18 carbon atoms can become steric hindrance, so that the space between the aliphatic monocarboxylic acid and other silver nanoparticles can be ensured, and the effect of preventing the silver nanoparticles from being condensed with each other is improved. The aliphatic monocarboxylic acid is also preferred in terms of easy acquisition and easy removal during firing.

The amount of the aliphatic monocarboxylic acid to be used is, for example, about 0.05 to 10 mol, preferably about 0.1 to 5 mol, and particularly preferably about 0.5 to 2 mol, based on 1 mol of silver atoms in the silver compound. When the amount of the aliphatic monocarboxylic acid used is less than the above range, the stability-improving effect is hardly obtained. On the other hand, even if the aliphatic monocarboxylic acid is used in an excessive amount, the effect of improving dispersion stability is saturated, and on the other hand, it tends to be difficult to remove the aliphatic monocarboxylic acid by low-temperature sintering.

The reaction of the amine-containing protecting agent with the silver compound is preferably carried out at room temperature (5 to 40 ℃). In the above reaction, the heat generation by the coordination reaction of the amine and the silver compound is accompanied, and therefore, the reaction can be suitably carried out while cooling so that the temperature reaches the above temperature range.

The reaction time of the amine-containing protecting agent and the silver compound is, for example, about 30 minutes to 3 hours. Thereby, a silver-amine complex can be obtained.

(thermal decomposition step)

The thermal decomposition step is a step of thermally decomposing the silver-amine complex obtained through the complex formation step to form surface-modified silver nanoparticles. It is considered that heating the silver-amine complex thermally decomposes the silver compound while maintaining the coordinate bond of the amine to the silver atom to generate a silver atom, and then the silver atom coordinated with the amine is aggregated to form a silver nanoparticle coated with an amine protective film.

The thermal decomposition is preferably carried out in the presence of a solvent, and as the solvent, the above-mentioned alcohol solvent can be suitably used. The thermal decomposition temperature is only required to be a temperature at which the surface-modified silver nanoparticles are generated, and when the silver-amine complex is a silver oxalate-amine complex, the thermal decomposition temperature is, for example, about 80 to 120 ℃, preferably 95 to 115 ℃, and particularly preferably 100 to 110 ℃. From the viewpoint of preventing the surface-modified portion of the surface-modified silver nanoparticles from being detached, it is preferable to perform the surface modification at as low a temperature as possible within the above temperature range. The thermal decomposition time is, for example, about 10 minutes to 5 hours.

The thermal decomposition of the silver-amine complex is preferably performed in an air atmosphere or an inert gas atmosphere such as argon.

(cleaning Process)

When an excessive amount of a protecting agent (for example, amine) is present after the thermal decomposition reaction of the silver-amine complex is completed, it is preferable to perform decantation for removing it. In addition, the surface-modified silver nanoparticles after the decantation is preferably supplied to the ink preparation step described later in a wet state without drying and solidification from the viewpoint that reagglomeration of the silver nanoparticles can be suppressed and high dispersibility of the silver nanoparticles can be maintained.

Without drying/curing of the surface-modified silver nanoparticles, it is inevitable that the washing solvent used in decantation is mixed into the conductive ink of the present invention. Therefore, as the cleaning solvent (the cleaning solvent used last when the cleaning is repeated 2 or more times), a solvent which does not impair the characteristics of the conductive ink of the present invention is preferably used, and the above-mentioned glycol ether-based solvent and/or glycol ester-based solvent (b-2) is particularly preferably used.

The decantation can be performed, for example, by washing the surface-modified silver nanoparticles in a suspended state with a washing solvent, allowing them to settle by centrifugal separation, and removing the supernatant.

The content of the cleaning solvent in the total amount of the wet surface-modified silver nanoparticles obtained by decantation is, for example, about 5 to 15 wt%. Therefore, the proportion of the surface-modified silver nanoparticles in the total amount of the surface-modified silver nanoparticles in a wet state is, for example, about 85 to 95 wt%.

(ink preparation Process)

The ink preparation step is a step of mixing the surface-modified silver nanoparticles (a) (preferably, the surface-modified silver nanoparticles (a) in a wet state with a glycol ether-based solvent and/or a glycol ester-based solvent (B-2)), the solvent (B) containing at least a terpene-based solvent (B-1), and an additive used as needed to obtain the conductive ink of the present invention. The above-mentioned mixing may be carried out, for example: a generally known mixing apparatus such as a rotation and revolution type stirring and defoaming apparatus, a homogenizer, a planetary mixer, a three-roll mill, a bead mill, etc. The components may be mixed simultaneously or may be mixed in a stepwise manner.

[ method for manufacturing electronic device ]

The method for manufacturing an electronic device of the present invention includes: applying the conductive ink onto a substrate by an offset printing method; and a step of sintering.

In the case where the electronic device is an electronic device provided with a large-current substrate, it is necessary to form a thick wiring using a conductive ink, but in this case, a coating film having a wiring pattern shape can be formed into a thick film by laminating the coating film. In the method for manufacturing an electronic device according to the present invention, since the conductive ink having quick-drying properties is used, the solvent can be quickly volatilized and dried without performing a drying treatment on the coating film applied on the substrate. Therefore, even if the second layer is applied without drying after the first layer coating film is formed, the shape of the first layer wiring pattern is not damaged, and a thick wiring can be formed with excellent workability.

When the conductive ink has an appropriate viscosity, a thick coating film (1 layer) can be formed. Therefore, even if the number of stacked coating films is reduced, a thick wiring can be formed, a wiring can be formed with excellent workability, and an electronic device including the wiring can be manufactured.

Since the conductive ink is used in the method for manufacturing an electronic device according to the present invention, the sintering can be performed at a low temperature, for example, 130 ℃ or lower (the lower limit of the sintering temperature is, for example, 60 ℃, and more preferably 100 ℃) and particularly preferably 120 ℃ or lower, from the viewpoint that the sintering can be performed in a short time. The sintering time is, for example, 0.5 to 3 hours, preferably 0.5 to 2 hours, and particularly preferably 0.5 to 1 hour.

When the conductive ink of the present invention is used, sintering of the silver nanoparticles proceeds sufficiently even in low-temperature sintering (particularly, sintering at a low temperature for a short time). As a result, a sintered body having excellent conductivity, that is, volume resistivity of, for example, 15 μ Ω · cm or less, preferably 10 μ Ω · cm or less, particularly preferably 8 μ Ω · cm or less, and most preferably 6 μ Ω · cm or less can be obtained. The volume resistivity of the sintered body can be measured by the method described in examples.

Since the conductive ink of the present invention can be sintered at a low temperature as described above, general-purpose plastic substrates having low heat resistance, such as a polyethylene terephthalate (PET) film, a polyester film such as a polyethylene naphthalate (PEN) film, and a polyolefin film such as polypropylene, can be suitably used as the substrate in addition to a glass substrate and a heat-resistant plastic substrate such as a polyimide film.

The electronic device obtained by the method for manufacturing an electronic device of the present invention includes, for example: a liquid crystal display, an organic EL display, a Field Emission Display (FED), an IC card, an IC tag, a solar cell, an LED element, an organic transistor, a capacitor (capacitor), electronic paper, a flexible battery, a flexible sensor, a membrane switch, a touch panel, an EMI shield, an industrial robot, an electric vehicle, a hybrid vehicle, or the like.

[ sintered body ]

The sintered body of the present invention is a sintered body of the above conductive ink. The sintered body of the present invention has excellent conductivity and a volume resistivity of, for example, 15 μ Ω · cm or less, preferably 10 μ Ω · cm or less, particularly preferably 8 μ Ω · cm or less, and most preferably 6 μ Ω · cm or less.

As described above, the sintered body of the present invention has excellent electrical conductivity. Therefore, a printed circuit board (particularly, a large current circuit board) including a wiring and an electrode formed by the sintered body of the present invention and an electronic device including the printed circuit board have excellent electrical characteristics.

Examples

The present invention will be described more specifically with reference to the following examples, but the present invention is not limited to these examples.

Preparation example 1 (preparation of surface-modified silver nanoparticles)

Silver oxalate (molecular weight: 303.78) was obtained from silver nitrate (manufactured by Wako pure chemical industries, Ltd.) and oxalic acid dihydrate (manufactured by Wako pure chemical industries, Ltd.).

In a 500mL flask, 40.0g (0.1317 moles) of the above silver oxalate was charged, and 60g of n-butanol was added thereto to prepare a slurry of silver oxalate in n-butanol.

To the resulting slurry, an amine mixture of 115.58g (1.5802 mol) of n-butylamine (molecular weight: 73.14, a reagent manufactured by Tokyo chemical Co., Ltd.), 51.06g (0.3950 mol) of 2-ethylhexylamine (molecular weight: 129.25, a reagent manufactured by Wako pure chemical industries, Ltd.) and 17.02g (0.1317 mol) of n-octylamine (molecular weight: 129.25, a reagent manufactured by Tokyo chemical industries, Ltd.) was added dropwise at 30 ℃.

After the dropwise addition, the mixture was stirred at 30 ℃ for 1 hour to allow the complex formation reaction of silver oxalate with amine to proceed.

After the formation of the silver oxalate-amine complex, the silver oxalate-amine complex was thermally decomposed by heating at 110 ℃ for 1 hour to obtain a dark blue suspension containing surface-modified silver nanoparticles.

The obtained suspension was cooled, and 120g of methanol (Wako pure chemical industries, Ltd., Special grade) was added thereto and stirred, and then, the surface-modified silver nanoparticles were precipitated by centrifugal separation to remove the supernatant. Next, 120g of propylene glycol monobutyl ether was added and stirred, and then, the surface-modified silver nanoparticles were settled by centrifugal separation, and the supernatant was removed. Thus, surface-modified silver nanoparticles in a wet state containing propylene glycol monobutyl ether were obtained. According to the measurement result using a thermobalance of TG/DTA6300 manufactured by SII corporation, the content of the surface-modified silver nanoparticles was 90 wt% in the total amount (100 wt%) of the surface-modified silver nanoparticles in a wet state. That is, the surface-modified silver nanoparticles in a wet state contained 10% by weight of propylene glycol monobutyl ether.

The surface-modified silver nanoparticles in a wet state were observed using a scanning electron microscope (JSM-6700F, manufactured by Nippon electronics Co., Ltd.), and the particle diameters of 10 silver nanoparticles arbitrarily selected in the SEM photograph were determined, and the average particle diameter thereof was defined as the average particle diameter. The average particle diameter (primary particle diameter) of the silver nanoparticle portion in the surface-modified silver nanoparticles was 50 nm.

Example 1 (preparation of silver ink)

Dihydroterpineol (16.62g), EC300(0.86g), and BYK302(0.78g) were added thereto, stirred in an oil bath for 3 hours (100 rpm. times.3 hrs), and then kneaded by a revolution and rotation kneader (Mazerustar KKK2508, manufactured by Bingy textile Co., Ltd.) for 2 minutes. times.3 times to prepare a solution A.

To 30g of the wet surface-modified silver nanoparticles (containing 10 wt% of propylene glycol monobutyl ether) obtained in preparation example 1, 11.54g of liquid a was added, and the mixture was stirred (2 minutes × 3 times) with a rotary and rotary kneader (Mazerustar KKK2508, manufactured by house and textile industries), to obtain a gray black silver ink.

Examples 2 to 3 and comparative examples 1 to 2

Silver inks were obtained in the same manner as in example 1, except that the formulation was changed as shown in table 1 below (unit: part by weight).

The printability (transferability to a base material, and continuous printability) of the silver inks obtained in examples and comparative examples and the conductivity of the sintered body were evaluated by the following methods.

(evaluation of transferability to a substrate)

The silver inks obtained in examples and comparative examples were printed on a PET film in 1 layer at 25 ℃ using a gravure offset printing small-sized printing apparatus (trade name "K PRINTING pro fer", manufactured by songwood industries co., ltd.) equipped with a silicone blanket, and evaluated according to the following criteria.

O: the printing precision is good

X: poor printing precision (caused by transfer failure from a blanket, etc.)

(evaluation of continuous printability)

The silver inks obtained in examples and comparative examples were laminated and printed on a PET film at 25 ℃ for 3 layers using a gravure offset printing small size printer (trade name "K PRINTING pro fer", manufactured by songwood industries co., ltd.) equipped with a silicone blanket, and evaluated according to the following criteria.

O: the printing precision is good

X: poor printing accuracy (due to destruction of the lower layer caused by lamination of the second or more layers)

(evaluation of conductivity of sintered body)

The silver inks obtained in examples and comparative examples were applied to a soda glass plate to form a coating film.

The obtained coating film was rapidly sintered at 120 ℃ for 30 minutes using a blast drying furnace to obtain a silver sintered film having a thickness of 5 μm. The volume resistivity of the obtained silver sintered film was measured by a four-terminal method (Loresta GP MCP-T610).

[ Table 1]

The components in the table are explained below.

Surface modification of silver nanoparticles: the surface-modified silver nanoparticles obtained in the preparation example were used.

Fine silver particles: an average particle diameter (laser analysis) of 1.5 to 3.0 μm, and a trade name of "Siltest TC-505C", manufactured by German laboratories K.K.)

Dihydroterpineol: vapor pressure at 30 ℃ of 0.43mmHg, manufactured by Nippon terpene chemical Co., Ltd

1, 6-HDDA: 1, 6-hexanediol diacetate, vapor pressure at 30 ℃ 0.0004mmHg

Hexyl carbitol: vapor pressure at 30 ℃ of 0.003mmHg

Terpineol C: vapor pressure at 30 ℃ of 0.018mmHg

Butyl carbitol: vapor pressure at 30 ℃ of 0.034mmHg

Propylene glycol monobutyl ether: vapor pressure at 30 ℃ of 1.476mmHg

Ethylene glycol monobutyl ether acetate: vapor pressure at 30 ℃ of 1.222mmHg

Butanol: vapor pressure at 30 ℃ of 9.58mmHg

SOLBIN AL: vinyl chloride/vinyl acetate/vinyl alcohol (93/2/5 wt.%) copolymer resin, manufactured by Nissan chemical industries, Ltd

EC 300: ethyl cellulose resin having a trade name of "ETHOCEL std.300" manufactured by DOW Chemical Co., Ltd

BYK 302: polyether-modified polydimethylsiloxane BYK Chemie Japan K.K

As a summary of the above, the configuration of the present invention and its modifications are described below.

[1] A conductive ink comprising the following surface-modified silver nanoparticles (A) and the following solvent (B),

surface-modified silver nanoparticles (a): silver nanoparticles having a constitution in which the surface is coated with a protective agent containing an amine;

solvent (B): the solvent contains a terpene solvent (b-1) and a glycol ether solvent and/or a glycol ester solvent (b-2), and the content of the solvent having a vapor pressure of 0.05 to 15mmHg at 30 ℃ is 75 wt% or more of the total amount of the solvents.

[2] The conductive ink according to [1], wherein the protective agent in the surface-modified silver nanoparticles (A) contains, as amines, aliphatic monoamines (1) having 6 or more total carbon atoms, and aliphatic monoamines (2) having 5 or less total carbon atoms and/or aliphatic diamines (3) having 8 or less total carbon atoms.

[3] The conductive ink according to [1] or [2], wherein the average primary particle diameter of the silver nanoparticle portion in the surface-modified silver nanoparticles (A) is 0.5 to 100 nm.

[4] The conductive ink according to any one of [1] to [3], wherein the content of the surface-modified silver nanoparticles (A) is 60 to 85 wt% of the total amount of the conductive ink.

[5] The conductive ink according to any one of [1] to [4], wherein the terpene solvent (b-1) has a vapor pressure of 0.05 to 5.0mmHg at 30 ℃.

[6] The conductive ink according to any one of [1] to [5], wherein the terpene-based solvent (b-1) is at least 1 solvent selected from 4- (1 '-acetoxy-1' -methyl ester) -cyclohexanol acetate, 1,2,5, 6-tetrahydrobenzyl alcohol, 1,2,5, 6-tetrahydrobenzyl acetate, cyclohexyl acetate, 2-methylcyclohexyl acetate, 4-tert-butylcyclohexyl acetate, dihydroterpineol acetate, dihydroterpineoxy ethanol, terpineol methyl ether, and dihydroterpinemethyl ether.

[7] The conductive ink according to any one of [1] to [6], wherein the vapor pressure of the glycol ether solvent and/or the glycol ester solvent (b-2) at 30 ℃ is 0.05 to 5.0 mmHg.

[8] The conductive ink according to any one of [1] to [7], wherein the glycol ether solvent and/or the glycol ester solvent (b-2) contains at least a glycol ether solvent.

[9] The conductive ink according to any one of [1] to [7], wherein the glycol ether solvent and/or the glycol ester solvent (b-2) contains at least a compound represented by the following formula (b-2-1),

R¹¹O-(R¹³O)_m-R¹²(b-2-1)

(in the formula, R¹¹Represents a hydrogen atom or C_1-5Alkyl radical, R¹²Is represented by C_1-5Alkyl radical, R¹³Is represented by C_2-3An alkylene group, and m represents an integer of 1 to 3. )

[10]According to [1]～[7]The conductive ink according to any one of the above, wherein the glycol ether solvent and/or the glycol ester solvent (b-2) is selected from the group consisting of ethylene glycol mono-C_1-10Alkyl ethers and propylene glycol mono C_1-10At least 1 of the alkyl ethers.

[11]According to [1]～[7]The conductive ink according to any one of the above, wherein the glycol ether solvent and/or the glycol ester solvent (b-2) is C_2-3Alkylene glycol mono C_1-10An alkyl ether.

[12] The conductive ink according to any one of [1] to [11], wherein the contents (total amount in the case of containing two or more species) of ethyl lactate acetate, tetrahydrofurfuryl alcohol, and ethylene glycol are 30 wt% or less of the total amount of the solvent (B).

[13] The conductive ink according to any one of [1] to [12], wherein the total content of the terpene-based solvent (B-1), the glycol ether-based solvent, and the glycol ester-based solvent (B-2) accounts for 70 wt% or more of the total amount of the solvent (B).

[14] The conductive ink according to any one of [1] to [13], wherein the ratio of the content of the terpene-based solvent (b-1) to the content of the glycol ether-based solvent and/or the glycol ester-based solvent (b-2) is 90/10 to 60/40.

[15] The conductive ink according to any one of [1] to [14], wherein the content of the terpene-based solvent (B-1) is 60 to 90% by weight of the total amount of the solvent (B).

[16] The conductive ink according to any one of [1] to [15], wherein the content of the terpene solvent (b-1) is 5 to 40% by weight of the total amount of the conductive ink.

[17] The conductive ink according to any one of [1] to [16], wherein the content of the glycol ether-based solvent and/or the glycol ester-based solvent (B-2) is 10 to 40 wt% of the total amount of the solvent (B).

[18] The conductive ink according to any one of [1] to [17], wherein the content of the glycol ether-based solvent and/or the glycol ester-based solvent (b-2) is 0.5 to 20% by weight based on the total amount of the conductive ink.

[19] The conductive ink according to any one of [1] to [18], wherein the content of the solvent (B) is 30 to 70 parts by weight with respect to 100 parts by weight of the surface-modified silver nanoparticles (A).

[20] The conductive ink according to any one of [1] to [19], wherein the content of the solvent having a vapor pressure of 0.1 to 1mmHg at 30 ℃ in the total amount of the solvent (B) is 50 to 80 wt%.

[21] The conductive ink according to any one of [1] to [20], wherein the content of the solvent having a vapor pressure at 30 ℃ in a range of more than 1mmHg and 5mmHg or less in the total amount of the solvent (B) is 20 to 50 wt%.

[22] The conductive ink according to any one of [1] to [21], wherein a content of the solvent having a vapor pressure of less than 0.1mmHg at 30 ℃ in the total amount of the solvent (B) is 25% by weight or less.

[23] The conductive ink according to any one of [1] to [22], wherein a content of the solvent having a vapor pressure of more than 5mmHg at 30 ℃ in the total amount of the solvent (B) is 25% by weight or less.

[24] The conductive ink according to any one of [1] to [23], further comprising 0.1 to 3.0 parts by weight of a binder resin (C) per 100 parts by weight of the surface-modified silver nanoparticles (A).

[25] The conductive ink according to any one of [1] to [23], further comprising a binder resin (C) in an amount of 0.5 to 5.0 wt% based on the total amount of the conductive ink.

[26] The conductive ink according to [24] or [25], wherein the binder resin (C) is a cellulose-based resin.

[27] The conductive ink according to any one of [1] to [26], further comprising 0.1 to 3.0 parts by weight of a siloxane compound (D) per 100 parts by weight of the surface-modified silver nanoparticles (A).

[28] The conductive ink according to any one of [1] to [26], further comprising a siloxane compound (D) in an amount of 0.5 to 5.0 wt% based on the total amount of the conductive ink.

[29] The conductive ink according to [27] or [28], wherein the siloxane compound (D) is a compound represented by the formula (D).

[30] The conductive ink according to any one of [1] to [29], which has a viscosity of 30 to 80 Pa-s at 25 ℃ and a shear rate of 10 (1/s).

[31] The conductive ink according to any one of [1] to [30], wherein the volume resistivity of the sintered body is 15 [ mu ] Ω & cm or less.

[32] The conductive ink according to any one of [1] to [30], wherein a sintered body having a volume resistivity of 15 [ mu ] Ω & cm or less is obtained by heating the conductive ink at a temperature of 120 ℃ or less for 0.5 to 1 hour.

[33] The conductive ink according to any one of [1] to [32], which is a conductive ink for offset printing.

[34] Use of the conductive ink according to any one of the above [1] to [33] as a conductive ink for offset printing.

[35] A method of manufacturing an electronic device, the method comprising: applying the conductive ink according to any one of [1] to [33] onto a substrate by an offset printing method; and a step of sintering.

[36] A sintered body of the conductive ink according to any one of [1] to [33 ].

[37] The sintered body of conductive ink according to [36], wherein the volume resistivity is 15 [ mu ] Ω & cm or less.

[37] An electronic device comprising a sintered body of the conductive ink according to any one of [1] to [33] on a substrate.

Industrial applicability

The conductive ink of the present invention can be suitably used for forming wiring and electrodes of a printed board.

Claims (9)

1. A conductive ink comprising the following surface-modified silver nanoparticles (A) and the following solvent (B),

surface-modified silver nanoparticles (a): silver nanoparticles having a constitution in which the surface is coated with a protective agent containing an amine;

solvent (B): the solvent contains a terpene solvent (b-1) and a glycol ether solvent and/or a glycol ester solvent (b-2), and the content of the solvent having a vapor pressure of 0.05 to 15mmHg at 30 ℃ is 75 wt% or more of the total amount of the solvents.

2. The conductive ink according to claim 1,

the protective agent in the surface-modified silver nanoparticles (a) contains, as amines, aliphatic monoamines (1) having 6 or more total carbon atoms, and aliphatic monoamines (2) having 5 or less total carbon atoms and/or aliphatic diamines (3) having 8 or less total carbon atoms.

3. The conductive ink according to claim 1 or 2,

and a binder resin (C) in an amount of 0.1 to 3.0 parts by weight per 100 parts by weight of the surface-modified silver nanoparticles (A).

4. The conductive ink according to any one of claims 1 to 3,

and a siloxane compound (D) in an amount of 0.1 to 3.0 parts by weight per 100 parts by weight of the surface-modified silver nanoparticles (A).

5. The conductive ink according to any one of claims 1 to 4, having a viscosity of 30 to 80 Pa-s at 25 ℃ and a shear rate of 10 (1/s).

6. The conductive ink according to any one of claims 1 to 5, which is a conductive ink for offset printing.

7. A method of manufacturing an electronic device, the method comprising:

applying the conductive ink according to any one of claims 1 to 6 to a substrate by an offset printing method; and

and (5) sintering.

8. A sintered body of the conductive ink according to any one of claims 1 to 6.

9. An electronic device comprising a sintered body of the conductive ink according to any one of claims 1 to 6 on a substrate.