JP7767765B2 - conductive composition - Google Patents

Description

The present invention relates to a conductive composition.

In recent years, in light of the Sustainable Development Goals (SDGs), there has been a shift in wiring formation methods for electronic components from the conventional wet etching method, which uses large amounts of chemicals, to printing methods using screen printers and the like.

Among these, active development is being conducted on wiring formation technology using screen printing machines, a general-purpose printing method, and progress is being made in developing conductive paste compositions suitable for screen printing as materials.

One of the advantages of forming wiring using screen printing is that it allows for continuous printing on film substrates using the roll-to-roll method. For this reason, the use of screen printing to form wiring is being widely investigated with the aim of improving productivity. However, to ensure stable continuous printing using conductive paste, it is necessary to optimize various properties of the conductive paste, such as its viscosity and drying properties, to suit the screen printing conditions.

A characteristic required of conductive pastes produced using the roll-to-roll method is that the cured film obtained by heating and curing the conductive paste during the roll winding process must be free of cracks and breaks. For example, Patent Document 1 discloses a silver paste composition that can improve the uniformity of printed patterns even when produced at a high viscosity, and can produce a cured film with improved adhesion to the substrate.

Special table number 2013-507750

However, while the silver paste composition disclosed in Patent Document 1 above has excellent initial adhesion to the substrate, it has poor adaptability to deformation of the substrate that occurs when the substrate on which the cured film is formed is stored at low or high temperatures. Therefore, when a laminate of the film and the cured conductive paste film is subjected to a thermal shock test in which the film is repeatedly stored at low and high temperatures, peeling or cracking of the cured film may occur.

The problem to be solved by the present invention is to provide a conductive composition that exhibits good continuous printability in screen printing and good resistance to cold and thermal shocks in the cured film formed on the substrate, and that can be used as a wiring-forming material with excellent conductivity.

After extensive research into how to solve the above problems, the inventors discovered that by blending specific components in addition to conductive particles and a binder resin, they could provide a conductive composition that could solve the above problems, leading to the completion of the present invention.

Specifically, the present invention relates to a conductive composition containing (a) polyethylene glycol having a weight-average molecular weight of 200 to 2,000, (b) at least one compound selected from polyether esters having a weight-average molecular weight of 200 to 1,000 and adipic acid esters having a weight-average molecular weight of 200 to 3,000, (c) conductive particles, and (d) a binder resin, wherein, based on the solid content, the total content of components (a) to (d) is 100% by mass, and the content of component (a) is 0.1 to 5% by mass, the content of component (b) is 0.01 to 5% by mass, the content of component (c) is 60 to 99% by mass, and the content of component (d) is 0.5 to 30% by mass.

The conductive composition of the present invention can be used as a wiring-forming material with excellent continuous printability in screen printing. A cured film formed on a film substrate using this conductive composition has excellent adaptability to deformation of the substrate at low and high temperatures. When subjected to a thermal shock test in which the film is repeatedly stored at low and high temperatures, the cured film is less likely to peel or crack, resulting in an increase in resistance (i.e., the cured film has good thermal shock resistance), and a wiring pattern can be formed that exhibits excellent conductivity.

The following describes an embodiment of the present invention.

In this specification, numerical ranges defined using the symbol "to" are intended to include the numerical values at both ends of the symbol (upper and lower limits). For example, "2 to 5" means a range of 2 or more and 5 or less.

Furthermore, when a concentration or amount is specified, any higher concentration or amount can be associated with any lower concentration or amount. For example, the descriptions "2 to 10% by mass" and "preferably 4 to 8% by mass" also encompass the descriptions "2 to 4% by mass," "2 to 8% by mass," "4 to 10% by mass," and "8 to 10% by mass."

The conductive composition according to an embodiment of the present invention contains (a) polyethylene glycol having a weight-average molecular weight of 200 to 2000, (b) at least one compound selected from polyether esters having a weight-average molecular weight of 200 to 1000 and adipic acid esters having a weight-average molecular weight of 200 to 3000, (c) conductive particles, and (d) a binder resin. Furthermore, based on the solid content, the content of component (a) is 0.1 to 5 mass%, the content of component (b) is 0.01 to 5 mass%, the content of component (c) is 60 to 99 mass%, and the content of component (d) is 0.5 to 30 mass%, relative to a total of 100 mass% of components (a) to (d). Each component is described below.

[Component (a): Polyethylene glycol]
Component (a) is polyethylene glycol, and its weight-average molecular weight is 200 to 2000, and from the viewpoint of maintaining wettability, it is preferably 400 to 1500, more preferably 500 to 800. These may be used alone or in combination of two or more.

The weight-average molecular weight of polyethylene glycol can be measured by a method that calculates the weight-average molecular weight based on the hydroxyl value measured in accordance with JIS K1557.

The content of component (a) is 0.1 to 5 mass%, and preferably 0.2 to 3 mass%, based on the solids content, relative to 100 mass% of the total of components (a) to (d). If the content of component (a) is too low, the film thickness may be more likely to change as the number of successive screen printings increases. Furthermore, if the content of component (a) is too high, the conductivity of the conductive composition may decrease.

[Component (b)]
The content of component (b) is 0.01 to 5 mass% and preferably 0.1 to 3 mass% based on the solid content, relative to 100 mass% of the total of components (a) to (d). If the content of component (b) is too low, when a cured film of the conductive composition is subjected to a thermal shock test, peeling or cracking of the cured film may occur, resulting in an increase in resistance. If the content of component (b) is too high, the conductivity of the conductive composition may decrease.

Component (b) is at least one compound selected from a specified polyether ester and a specified adipic acid ester. The specified polyether ester may be a compound with a weight-average molecular weight of 200 to 1,000, but a compound with a weight-average molecular weight of 400 to 900 is preferred.

The above polyetheresters can be produced according to known methods, but examples of commercially available products include Adekacizer RS-700 (weight average molecular weight 550), Adekacizer RS-735 (weight average molecular weight 850), Adekacizer RS-966 (weight average molecular weight 470), and Adekacizer RS-1000 (weight average molecular weight 550) (all manufactured by ADEKA Corporation).

The specified adipic acid ester may be a compound with a weight-average molecular weight of 200 to 3000, preferably a compound with a weight-average molecular weight of 1000 to 3000, and more preferably a compound with a weight-average molecular weight of 1500 to 2500.

The above adipic acid esters can be produced according to known methods, but are also available as commercially available products. Examples of commercially available products include Adekasizer PN-150 (weight average molecular weight 1000), Adekasizer PN-170 (weight average molecular weight 1100), Adekasizer P-200 (weight average molecular weight 2000), and Adekasizer PN-350 (weight average molecular weight 3000) (all manufactured by ADEKA Corporation), D620 (weight average molecular weight 800), D623 (weight average molecular weight 1800), D643 (weight average molecular weight 1800), D645 (weight average molecular weight 2200), D633 (weight average molecular weight 1800), D620N (weight average molecular weight 800), D623N (weight average molecular weight 1800), D643D (weight average molecular weight 1800), D640A (weight average molecular weight 1200), and D671A (weight average molecular weight 650) (all manufactured by J-Plus Corporation).

[Component (c): conductive particles]
Component (c) is a conductive particle, and inorganic conductive particles such as copper particles can be used. The copper particles may consist of copper alone, or may further contain a metal other than copper, such as silver or platinum, a metal oxide, or a metal sulfide. When the copper particles further contain a metal other than copper, a metal oxide, or a metal sulfide, the mass ratio of copper in the copper particles is preferably 50 mass% or more. Furthermore, the copper particles may have a surface layer or protrusions formed thereon.

Commercially available conductive particles may be used as they are, but it is preferable to use surface-coated conductive particles with a coating to improve oxidation resistance, etc. In particular, it is preferable to use surface-coated conductive particles with a coating of an amine compound, and it is even more preferable to use surface-coated conductive particles with a coating of an amine compound represented by the following formula (1):

(In formula (1), m is an integer between 0 and 3, and n is an integer between 0 and 2. When n = 0, m is any number between 0 and 3. When n = 1 or n = 2, m is any number between 1 and 3.)

From the viewpoint of obtaining better oxidation resistance, it is preferable that surface-coated conductive particles whose surfaces are coated with an amine compound such as the amine compound represented by formula (1) above be further coated with an aliphatic monocarboxylic acid.

As a result, the surface of the conductive particle is coated with a first coating layer formed from an amine compound and a second coating layer formed from an aliphatic monocarboxylic acid. Preferably, the first coating layer is formed on the surface of the conductive particle, and the second coating layer is formed on the first coating layer.

The aliphatic monocarboxylic acid that forms the second coating layer is preferably an aliphatic monocarboxylic acid having 8 to 24 carbon atoms. Examples of such aliphatic monocarboxylic acids include linear saturated aliphatic monocarboxylic acids, linear unsaturated aliphatic monocarboxylic acids, branched saturated aliphatic monocarboxylic acids, and branched unsaturated aliphatic monocarboxylic acids.

Examples of linear saturated aliphatic monocarboxylic acids having 8 to 24 carbon atoms include caprylic acid, pelargonic acid, capric acid, undecylic acid, lauric acid, tridecylic acid, myristic acid, pentadecylic acid, palmitic acid, margaric acid, stearic acid, nonadecylic acid, and arachidic acid. Examples of linear unsaturated aliphatic monocarboxylic acids having 8 to 24 carbon atoms include myristoleic acid, palmitoleic acid, petroselinic acid, and oleic acid. Examples of branched saturated aliphatic monocarboxylic acids having 8 to 24 carbon atoms include 2-ethylhexanoic acid.

As the aliphatic monocarboxylic acid, one selected from the above compounds can be used alone, or two or more can be used in combination.

The method for producing surface-coated conductive particles is not particularly limited. Examples of methods for obtaining surface-coated conductive particles coated with an amine compound include washing conductive particles with, for example, an aqueous ammonium chloride solution, and then adding the washed conductive particles to a solution of an amine compound and heating as needed, and adding conductive particles to a solution containing, for example, ammonium chloride and an amine compound and heating as needed.

One example of a method for producing surface-coated conductive particles coated with a first coating layer formed from an amine compound and a second coating layer formed from an aliphatic monocarboxylic acid is to add surface-coated conductive particles coated with an amine compound to a solution of an aliphatic monocarboxylic acid. After adding the particles to the solution of aliphatic monocarboxylic acid, heating may be performed, if necessary.

There are no particular limitations on the average particle size (D50) of the conductive particles, but it is preferable to control the average particle size (D50) of the conductive particles so that the conductive composition containing conductive particles as component (c) can be printed well using various printing methods such as inkjet printing and screen printing. Specifically, the average particle size (D50) of the conductive particles is preferably 5 nm to 20 μm, and more preferably 10 nm to 10 μm.

The average particle size (D50) of the conductive particles can be measured using a laser diffraction/scattering particle size distribution analyzer (Microtrac MT3000II, manufactured by Microtrac Bell Co., Ltd.).

The BET specific surface area of the conductive particles is preferably 0.05 to 400 m ² /g, and more preferably 0.1 to 200 m ² /g.

The BET specific surface area of the conductive particles can be measured by the BET single-point method using a specific surface area measuring device (Monosorb, manufactured by Yuasa Ionics Co., Ltd.).

There are no particular restrictions on the shape or aspect ratio (ratio of the long axis to the short axis) of the conductive particles, and various shapes can be used, including spherical, polyhedral, flat, plate-like, flake-like, thin plate-like, rod-like, dendritic, and fibrous shapes. Conductive particles can be used singly or in combination, selected from those with different constituents, average particle size, shape, aspect ratio, etc.

The content of component (c) is 60 to 99% by mass, based on the solid content, relative to 100% by mass of the total of components (a) to (d). The lower limit of the content of component (c) is preferably 70% by mass, and more preferably 80% by mass.

[Component (d): Binder Resin]
Component (d) is a binder resin, which acts as a binder in the conductive composition.

Component (d) can be a known binder resin used in conductive compositions, etc. Examples include thermosetting resins, photocurable resins that harden when heated or exposed to light, and thermoplastic resins.

Examples of thermosetting resins include epoxy resin, melamine resin, phenolic resin, silicone resin, polyurethane resin, unsaturated polyester resin, vinyl ester resin, polyvinylphenol resin, xylene resin, acrylic resin, oxetane resin, and diallyl phthalate resin. Examples of photocurable resins include acrylic resin, imide resin, urethane resin, and oxetane resin. Examples of thermoplastic resins include polyolefin resins such as polyamide, polyethylene terephthalate, and polyethylene; and acrylonitrile-butadiene-styrene copolymer resin.

As the binder resin of component (d), one selected from these resins can be used alone, or two or more can be used in combination.

In addition, from the viewpoint of curability, it is preferable to use one or more thermosetting resins selected from epoxy resins, phenolic resins, and polyvinylphenol resins, and it is more preferable to use one or two selected from epoxy resins and phenolic resins.

The content of component (d) is 0.5 to 30% by mass, and preferably 1 to 20% by mass, based on the solids content, relative to 100% by mass of the total of components (a) to (d). If the content of component (d) is too low, it may be difficult to achieve sufficient fluidity when printing using the conductive composition. If the content of component (d) is too high, it may be difficult for the conductive particles of component (c) in the conductive composition to come into contact with each other, making it difficult to obtain a cured film that exhibits excellent conductivity.

In addition, the blending ratio of component (d) is preferably adjusted according to the type of component (b) contained in the conductive composition in order to improve adhesion between the cured film obtained from the conductive composition and the substrate.

When a specific polyether ester is used as component (b), the blending ratio of component (d) binder resin is preferably 5 to 30% by mass, and more preferably 5 to 20% by mass, based on the solids content, relative to 100% by mass of the total of components (a) to (d).

When a specific adipic acid ester is used as component (b), the blending ratio of component (d) binder resin is preferably 0.5 to 5% by mass, and more preferably 1 to 5% by mass, based on the solids content, relative to 100% by mass of the total of components (a) to (d).

[Other ingredients]
In addition to the above components (a) to (d), the conductive composition may contain various additives such as solvents, antioxidants, lubricants, leveling agents, dispersants, curing agents, curing accelerators, viscosity modifiers, foaming agents, and antioxidants, as needed, as long as the effects of the present invention are not impaired. The conductive composition may also contain impurities that may be unavoidably mixed in from raw material components and manufacturing equipment. When any of these components is contained, the total amount may be greater than 0 parts by mass and up to 60 parts by mass, preferably up to 30 parts by mass, per 100 parts by mass of the total content of (a) to (d).

(solvent)
The conductive composition may contain a solvent for the purposes of improving the coating properties and adjusting the viscosity.

Examples of solvents include ether alcohols such as ethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether, diethylene glycol monoethyl ether acetate, propylene glycol diacetate, dipropylene glycol monomethyl ether, and ethylene glycol monobutyl ether acetate; non-ether alcohols such as propylene glycol and 1,4-butanediol; esters such as cyclohexanol acetate, methyl methoxypropionate, ethyl ethoxypropionate, and 1,6-hexanediol acetate; ketones such as isophorone and cyclohexanone; terpenes such as terpineol, dihydroterpineol, dihydroterpinyl acetate, and isobornylcyclohexanol; and other hydrocarbons such as octane, decane, dodecane, tetradecane, hexadecane, and propylene carbonate.

Among these solvents, it is preferable to use one or more selected from the above-mentioned ether-based alcohols, esters, and terpenes, and it is even more preferable to use one or more selected from the above-mentioned ether-based alcohols and terpenes.

The type of solvent is not limited to the above, and depending on the application, one solvent selected from a variety of solvents can be used alone, or two or more solvents can be mixed. When two or more solvents are mixed, there are no particular restrictions on the mixing ratio.

When the conductive composition contains a solvent, the content of the solvent is preferably 1 to 30 parts by mass, and more preferably 2 to 20 parts by mass, per 100 parts by mass of the total content of components (a) to (d).

(antioxidant)
The conductive composition may contain an antioxidant for the purpose of maintaining the performance of each component during storage. Examples of the antioxidant include nitrogen-containing heterocyclic compounds such as 2,2-bipyridyl and 1,10-phenanthroline, Schiff bases such as N,N'-bis(salicylidene)ethylenediamine, N,N'-bis(salicylidene)-1,2-propanediamine, N,N'-bis(salicylidene)-1,3-propanediamine and N,N'-bis(salicylidene)-1,2-phenylenediamine, 1,2-phenylenediamine, and the like. aromatic diamines such as diamine, 1,3-phenylenediamine, 1,4-phenylenediamine, 2,5-dimethyl-1,4-phenylenediamine, 2,3,5,6-tetramethyl-1,4-phenylenediamine, N,N-dimethyl-1,4-phenylenediamine, N,N,N'N'-tetramethyl-1,4-phenylenediamine, and N,N'-diphenyl-1,4-phenylenediamine.

Among these antioxidants, it is preferable to use one or more selected from the nitrogen-containing heterocyclic compounds 2,2-bipyridyl, the Schiff bases N,N'-bis(salicylidene)ethylenediamine and N,N'-bis(salicylidene)-1,2-propanediamine, and the aromatic diamines 1,2-phenylenediamine, 1,3-phenylenediamine, and 1,4-phenylenediamine.

The type of antioxidant is not limited to the above, and depending on the application, one type selected from various solvents can be used alone, or two or more types can be mixed. When two or more types are mixed, there are no particular restrictions on the mixing ratio.

When the conductive composition contains an antioxidant, the content of the antioxidant is preferably 0.01 to 10 parts by mass, and more preferably 0.1 to 5 parts by mass, per 100 parts by mass of the total content of components (a) to (d).

(lubricant)
The conductive composition may contain an appropriate lubricant to adjust the dispersibility of the conductive particles of component (c) in the conductive composition. The type and mixing ratio of the lubricant are not particularly limited, and one type may be used alone or two or more types may be mixed depending on the application.

Examples of types of lubricants include fatty acids such as lauric acid, myristic acid, palmitic acid, stearic acid, and behenic acid; fatty acid metal salts formed from the above fatty acids and metals such as sodium, potassium, barium, magnesium, calcium, aluminum, iron, cobalt, manganese, zinc, and tin; fatty acid amides such as stearic acid amide, oleic acid amide, behenic acid amide, palmitic acid amide, and lauric acid amide; fatty acid esters such as butyl stearate; waxes such as paraffin wax and liquid paraffin; alcohols such as ethylene glycol and stearyl alcohol; polysiloxanes such as silicone oil; and fluorine compounds such as fluorine-based oils.

Among these lubricants, it is preferable to use one or more selected from fatty acids and fatty acid metal salts, and it is even more preferable to use at least one selected from lauric acid and magnesium stearate.

When the conductive composition contains a lubricant, the content of the lubricant is preferably 0.01 to 10 parts by mass, and more preferably 0.1 to 5 parts by mass, per 100 parts by mass of the total content of components (a) to (d).

(Dispersant)
A dispersant may be added to the conductive composition as appropriate to adjust the dispersibility of the conductive particles of component (c) in the conductive composition. The type of dispersant and its mixing ratio are not particularly limited, and one type may be used alone or two or more types may be mixed depending on the application.

Examples of dispersants include sarcosine compounds such as lauroyl sarcosine, myristoyl sarcosine, palmitoyl sarcosine, stearoyl sarcosine, and oleoyl sarcosine; polymeric amine compounds such as Filanol PA-075F, Filanol PA-085C, Filanol PA-107P, Esreem AD-3172M, Esreem AD-374M, and Esreem AD-508E (all manufactured by NOF Corporation; "Esreem" is a registered trademark); and polymeric polycarboxylic acid compounds such as Marialim AKM-0531, Marialim AFB-1521, Marialim AAB-0851, Marialim AWS-0851, Marialim SC-0505K, Marialim SC-1015F, and Marialim SC-0708A (all manufactured by NOF Corporation).

Among these dispersants, it is preferable to use one or more sarcosines, and it is even more preferable to use at least one selected from lauroyl sarcosine and oleoyl sarcosine.

When the conductive composition contains a dispersant, the content of the dispersant is preferably 0.1 to 10 parts by mass, and more preferably 0.2 to 5 parts by mass, per 100 parts by mass of the total content of components (a) to (d).

The following examples and comparative examples further illustrate embodiments of the present invention.

The components used in the examples and comparative examples are listed below. The physical properties of each component were measured using the methods described herein.

[Component (a): Polyethylene glycol]
PEG200 (polyethylene glycol with a weight average molecular weight of 200)
PEG600 (polyethylene glycol with a weight average molecular weight of 600)
PEG2000 (polyethylene glycol with a weight average molecular weight of 2000)

[Component (a'): Polyethylene glycol having a weight-average molecular weight of more than 2000]
PEG4000 (polyethylene glycol with a weight average molecular weight of 4000)

[Component (a'): Polytetramethylene glycol]
PTMG2000 (polytetramethylene glycol with an average molecular weight of 2000)

[Component (b)]
(b1): Adeka Cizer RS-1000 (polyether ester, weight average molecular weight 550, manufactured by ADEKA Corporation)
(b2): Adeka Cizer P-200 (adipic acid polyester, weight average molecular weight 2000, manufactured by ADEKA Corporation)

[Component (b')]
(b3): bis(2-ethylhexyl) phthalate

[Component (c): conductive particles]
Copper particles (1): spherical copper particles [surface-coated copper particles (1), the production method is shown below.]
Copper particles (2): Plate-like copper particles [surface-coated copper particles (2), the production method is shown below.]

[Component (d): Binder Resin]
Phenolic resin: Resole type phenolic resin [PL-5208, manufactured by Gun-ei Chemical Industry Co., Ltd., solid content 60.0% by mass, solvent: diethylene glycol monoethyl ether]
Epoxy resin: bisphenol F epoxy resin [jER (registered trademark)-806, manufactured by Mitsubishi Chemical Corporation, solid content 100% by mass]

The following materials were used as other ingredients:

(antioxidant)
N,N'-bis(salicylidene)ethylenediamine (lubricant)
・Lauric acid (dispersant)
・Oleoyl sarcosine (solvent)
・Terpineol ・Ethylene glycol monobutyl ether acetate ・Isobornylcyclohexanol

Synthesis Example 1
(Production of Copper Particles (1): Surface-Coated Copper Particles (1))
An aqueous ammonium chloride solution was prepared by dissolving 5 g of ammonium chloride in 100 g of water. 50 g of copper particles a ["1200Y" manufactured by Mitsui Mining & Smelting Co., Ltd.; particle size (D50) 2 μm, BET specific surface area 0.40 m ² /g, shape: spherical] was added to the aqueous ammonium chloride solution and stirred at 30°C for 60 minutes under nitrogen bubbling. Stirring was carried out using a mechanical stirrer at a rotation speed of 150 rpm. Hereafter, stirring was carried out using the same stirring device at the same rotation speed. After stirring was completed, the copper particles were filtered out by vacuum filtration using a Kiriyama funnel with 5C filter paper, and then the copper particles were washed twice with 150 g of water on the Kiriyama funnel.

The washed copper particles were added to 250 g of a 40% by weight aqueous solution of diethylenetriamine, and the mixture was heated and stirred at 60°C for 1 hour while bubbling with nitrogen.

After stopping the stirring and allowing the mixture to stand for 5 minutes, approximately 200 g of the supernatant liquid was removed. Next, 200 g of isopropanol was added to the precipitate as a cleaning solvent, and the mixture was stirred at 30°C for 3 minutes. After stopping the stirring and allowing the mixture to stand for 5 minutes, approximately 200 g of the supernatant liquid was removed. Then, 250 g of a 2% by weight solution of lauric acid in isopropanol was added, and the mixture was stirred at 30°C for 30 minutes.

After stirring was completed, the copper particles were filtered under reduced pressure using a Kiriyama funnel equipped with 5C filter paper. The resulting copper particles were dried under reduced pressure at 25°C for 3 hours to obtain surface-coated copper particles (1) (copper particles (1)).

Synthesis Example 2
(Copper particles (2): Production of surface-coated copper particles (2))
Surface-coated copper particles (2) (copper particles (2)) were obtained in the same manner as in Synthesis Example 1, except that copper particles a were replaced with copper particles b ["1400YP" manufactured by Mitsui Mining & Smelting Co., Ltd.; particle size (D50) 6 μm, BET specific surface area 0.60 m ² /g, shape: plate-like].

Example 1
(Production of conductive composition)

0.5 g of PEG200 was used as component (a), 0.5 g of (b1) Adeka Cizer RS-1000 was used as component (b), 65 g of surface-coated copper particles (copper particles (1)) and 28.0 g of surface-coated copper particles (copper particles (2)) were used as component (c), and 10.0 g (6.0 g as solids) of resol-type phenolic resin [PL-5208, manufactured by Gun-ei Chemical Industry Co., Ltd., solids content 60% by mass, solvent: diethylene glycol monoethyl ether] was used as component (d), 0.5 g of N,N'-bis(salicylidene)ethylenediamine (Salen), and 2.0 g of lauric acid were mixed. Next, primary mixing was performed using a planetary mixer [ARV-310, manufactured by Thinky Corporation] at room temperature for 60 seconds at 1500 rpm.

Next, a three-roll mill [EXAKT-M80S, manufactured by Nagase Screen Printing Laboratory Co., Ltd.] was used to perform secondary mixing by passing the mixture five times at room temperature with a roll distance of 5 μm. 4.0 g of terpineol (Ter) was added to the mixture obtained in the secondary mixing, and the mixture was then stirred and degassed using a planetary mixer at 1000 rpm for 90 seconds under vacuum conditions at room temperature to produce a conductive composition. The blending ratios of each component of the conductive composition are shown in Table 1.

<Conductivity evaluation>
(Formation of cured film)
The obtained conductive composition was applied to a polyimide film using a metal mask to form a pattern having a width x length x thickness of 1.0 mm x 30 mm x 50 μm. The polyimide film to which the conductive composition was applied was heated in a convection oven at 170° C. for 30 minutes to produce a cured film.

(Method for evaluating resistance value)
The electrical conductivity of the cured film obtained by the above method was evaluated by measuring the resistance value as follows: A measuring probe was pressed against both ends of the formed pattern, and the resistance value of the cured film was measured using a digital multimeter [PC7000, manufactured by Sanwa Electric Meter Co., Ltd.], and the electrical conductivity was evaluated according to the following criteria.

The lower the resistance value of the cured film, the easier it is for current to flow, indicating superior conductivity.
⊚: The resistance value is less than 1.0 Ω.
○: The resistance value is 1.0Ω or more and less than 10.0Ω.
△: The resistance value is 10.0Ω or more and less than 50.0Ω.
×: The resistance value is 50.0Ω or more.

<Evaluation of continuous printing>
(Method for evaluating the rate of change in film thickness before and after continuous printing)
The obtained conductive composition was printed continuously onto 50 polyethylene terephthalate (PET) films using a screen printing machine [MT-320T, manufactured by Micro-Tec Co., Ltd.].

The resulting prints were heated in a convection oven at 120°C for 30 minutes to produce cured films. The film thickness of the cured films on the first and 50th sheets was measured using a stylus film thickness measuring device (DEKTAK XT, manufactured by Bruker). The film thickness change rate was calculated using the following formula (I) and evaluated according to the following criteria.

In this test, the closer the film thickness change rate is to 100%, the longer the wettability of the conductive composition is maintained during continuous printing, indicating that wiring patterns can be printed stably.

⊚: The rate of change in film thickness is 90% or more and 100% or less.
◯: The rate of change in film thickness is 70% or more and less than 90%.
△: The rate of change in film thickness is 50% or more and less than 70%.
×: The rate of change in film thickness is less than 50%.

<Evaluation of thermal shock resistance>
(Method for evaluating thermal shock resistance)
A cured film obtained in the same manner as the cured film used in the evaluation of electrical conductivity above was used as a measurement sample for a thermal shock test. The measurement sample was placed in a small thermal shock apparatus (TSE-11, manufactured by Espec Corporation) and subjected to a total of 1,000 cycles, each cycle consisting of holding at -40°C for 1 minute, then raising the temperature to 100°C and holding for 2 minutes.

After the test, the resistance was measured by pressing the measuring probes of a digital multimeter [PC7000, manufactured by Sanwa Electric Instruments Co., Ltd.] against both ends of the cured film, and the rate of change in resistance was calculated using the following formula (II) and evaluated according to the following criteria.

In this test, the closer the resistance change rate is to 100%, the better the thermal shock resistance of the cured film.

Resistance change rate (%) = (resistance after test) / (resistance before test) x 100 (II)

⊚: The rate of change in resistance value is less than 110%.
◯: The rate of change in resistance value is 110% or more and less than 150%.
Δ: The rate of change in resistance value is 150% or more and less than 200%.
×: The rate of change in resistance value is 200% or more.

The above evaluation results are shown in Table 1.

[Examples 2 to 8, Comparative Examples 1 to 5]
Conductive compositions were produced and cured films were formed in the same manner as in Example 1, except that the blending ratios of the components were as shown in Table 1. Regarding the formation of the cured films, heating was performed in the air atmosphere in Examples 2 to 4 and Comparative Examples 1 and 5, while heating was performed in a nitrogen atmosphere in Examples 5 to 8 and Comparative Examples 2 to 4.

Furthermore, the electrical conductivity, continuous printability, and thermal shock resistance of each cured film were evaluated in the same manner as in Example 1. The results are shown in Tables 1 and 2. Note that the phenolic resin content in Tables 1 and 2 is calculated as the solid content.

The following can be seen from Tables 1 and 2.
In Examples 1 to 8, the resistance of the cured film was less than 10.0 Ω, the rate of change in resistance before and after thermal shock testing was less than 150%, and the rate of change in film thickness before and after continuous printing was 70% or more. In contrast, in Comparative Example 1, in which a conductive composition was prepared without blending component (a), the rate of change in resistance before and after thermal shock testing was less than 150%, but the resistance of the cured film was high at 10.0 Ω or more, and the rate of change in film thickness before and after continuous printing was low at less than 50%. Furthermore, in Comparative Example 2, in which a conductive composition was prepared without blending component (b), the resistance of the cured film was less than 1.0 Ω, the rate of change in film thickness before and after continuous printing was less than 90%, but the rate of change in resistance before and after thermal shock testing was high at 200% or more. In Comparative Example 3, in which a conductive composition was prepared using PEG 4000 instead of component (a), the rate of change in resistance before and after the thermal shock test was less than 150%, but the resistance of the cured film was high at 10.0 Ω or more, and the rate of change in film thickness before and after continuous printing was low at less than 70%. Furthermore, in Comparative Example 4, in which a conductive composition was prepared using PTMG 2000 instead of component (a), the rate of change in resistance before and after the thermal shock test was less than 150%, but the resistance of the cured film was high at 50.0 Ω or more, and the rate of change in film thickness before and after continuous printing was low at less than 50%. In Comparative Example 5, in which a conductive composition was prepared using (b3) bis(2-ethylhexyl) phthalate instead of component (b), the resistance of the cured film was less than 10.0 Ω, and the rate of change in film thickness before and after continuous printing was less than 90%, but the rate of change in resistance before and after the thermal shock test was high at 150% or more.

As described above, a conductive composition containing the predetermined components (a) to (d) in the predetermined ratio has good continuous printability, and when formed into a cured film, it also has good resistance to cold and heat shock, and is therefore suitable as a wiring-forming material with excellent conductivity.

Claims (1)

(a) polyethylene glycol having a weight average molecular weight of 200 to 2000;
(b) at least one compound selected from polyether esters having a weight-average molecular weight of 200 to 1,000 and adipic acid esters having a weight-average molecular weight of 200 to 3,000;
(c) conductive particles; and (d) a binder resin;
A conductive composition, in which, based on the solid content, the content of component (a) is 0.1 to 5 mass%, the content of component (b) is 0.01 to 5 mass%, the content of component (c) is 60 to 99 mass%, and the content of component (d) is 0.5 to 30 mass%, relative to 100 mass% of the total of components (a) to (d).