TW202338017A - Electroconductive paste - Google Patents

Abstract

The present invention addresses the problem of providing an electroconductive paste that can be used to produce detailed electroconductive patterns of exceptional electroconductivity even at low temperatures of 100 DEG C or less. The present invention is an electroconductive paste containing electroconductive particles (a), a resin (b), and an imidazolium salt (c). The melting point of the imidazolium salt (c) is 30 to 100 DEG C, and the imidazolium salt (c) content with respect to 100 parts by mass of the electroconductive particles (a) is 0.05 to 3.0 parts by mass.

Description

conductive paste

The present invention relates to a conductive paste.

In recent years, touch panels have been widely used as input devices. A touch panel is composed of a display unit such as a liquid crystal panel or an organic electroluminescence (EL) panel, a touch sensor that detects information input to a specific position, and the like. Touch panel methods are roughly classified into resistive film methods, electrostatic capacitive methods, optical methods, electromagnetic induction methods, ultrasonic methods, etc., depending on the input position detection method. Among them, electrostatic capacitive touch panels are widely used for reasons such as optical brightness, excellent design, simple structure, and excellent functions.

The electrostatic capacitance type touch sensor has a second electrode orthogonal to the first electrode through an insulating layer. Applying a voltage to the electrode on the touch panel surface changes the electrostatic capacitance when a conductor such as a finger comes into contact. The contact position obtained by the detection is output as a signal. As wiring electrodes used in electrostatic capacitive touch sensors, transparent wiring electrodes such as indium tin oxide are generally used from the viewpoint that the wiring electrodes are not easily visible. However, in recent years, due to the increase in sensitivity or the increase in screen size, , opaque wiring electrodes using metallic materials are expanding. In addition, in order to improve the precision, thinness, and visibility of touch sensors, it is required to directly form opaque wiring electrodes on display portions such as liquid crystal panels and organic EL panels. Therefore, in addition to forming fine patterns, it is also necessary to form conductive patterns at low temperatures. Therefore, as a technology for forming a fine conductive pattern that exhibits conductivity under low-temperature curing conditions, a conductive paste containing a conductive filler, a zwitterionic compound, and a thermosetting compound has been proposed (for example, see Patent Document 1). In addition, a conductive paste containing a conductive filler and a quaternary ammonium salt compound has also been proposed (for example, see Patent Document 2). [Prior art documents] [Patent Document]

Patent Document 1: International Publication No. 2014/208445 Patent Document 2: International Publication No. 2019/073926

[Problem to be solved by the invention] According to the technology of Patent Document 1 and Patent Document 2, conductivity can be expressed at a lower temperature than before. However, in recent years, conductivity at even lower temperatures has been required, and conductivity under low-temperature conditions of 100°C or less has been required. Still not enough.

An object of the present invention is to provide a conductive paste capable of producing a fine conductive pattern having excellent conductivity even at a low temperature of 100° C. or lower. [Means to solve the problem]

The present invention and its preferred modes include the following structures. [1] A conductive paste containing conductive particles (a), resin (b), and imidazolium salt (c). The melting point of the imidazolium salt (c) is 30°C to 100°C, and relative to the conductive particles (a) The content of the imidazolium salt (c) is 0.05 to 3.0 parts by mass based on 100 parts by mass. [2] The conductive paste according to [1], wherein the imidazolium salt (c) has an alkyl chain on the nitrogen atom at position 1 or 3 of the imidazole ring. [3] The conductive paste according to [2], wherein the alkyl chain has a carbon number of 2 to 5. [4] The conductive paste according to any one of [1] to [3], wherein the formula weight of the anion of the imidazolium salt (c) is 80 or less. [5] The conductive paste according to any one of [1] to [4], wherein the resin (b) contains a resin having a carboxyl group, and the conductive paste further contains a photopolymerization initiator (d) . [6] The conductive paste as described in any one of [1] to [5], wherein the resin (b) contains a reactive monomer with an unsaturated double bond, and the conductive paste further contains a photopolymerizable Starter (d). [7] The conductive paste according to any one of [1] to [6], wherein the conductive particles (a) have a volume average particle diameter of 0.1 μm to 2.0 μm. [8] The conductive paste according to any one of [1] to [7], wherein the proportion of the conductive particles (a) in the total solid content is 60 mass% to 85 mass%. [9] The conductive paste according to any one of [1] to [8], wherein the conductive particles (a) are particles of a metal selected from the group consisting of gold, silver, and copper. [Effects of the invention]

According to the present invention, a fine conductive pattern having excellent conductivity at a low temperature of 100° C. or lower can be formed.

The conductive paste of the present invention contains conductive particles (a), resin (b), and imidazolium salt (c).

[Conductive particles (a)] The conductive particles (a) are conductive particles, and examples thereof include particles containing silver, gold, copper, platinum, lead, tin, nickel, aluminum, tungsten, molybdenum, chromium, titanium, indium, or alloys of these metals . Among them, particles of gold, silver or copper with high electrical conductivity are preferred, and particles of silver which are highly stable and advantageous in terms of price are more preferred.

The conductive particles (a) may have a layer structure of two or more layers. For example, a core-shell structure may be provided in which a shell containing silver is provided on the surface of a core containing copper. In addition, the surface of the conductive particle (a) may be coated with an organic component, an inorganic oxide, or the like. The organic component functions as a dispersant or conductive aid for small-diameter conductive particles. Examples of organic components include fatty acids, amines, thiols, cyanogens, and the like.

The volume average particle diameter of the conductive particles (a) is preferably 0.1 μm to 2.0 μm. By setting the volume average particle diameter of the conductive particles (a) to 0.1 μm or more, more preferably 0.3 μm or more, the contact probability between the conductive particles (a) increases, and the specific resistance value of the formed conductive pattern becomes lower, thereby lowering the specific resistance value. Exposure light during exposure smoothly passes through the coating film of the conductive paste of the present invention, so formation of fine patterns becomes easy. On the other hand, by setting the volume average particle diameter of the conductive particles (a) to 2.0 μm or less, more preferably 1.0 μm or less, the surface smoothness and dimensional accuracy of the formed conductive pattern are improved.

The volume average particle diameter of the conductive particles (a) can be determined by diluting the conductive paste with a solvent in which the resin component is soluble such as tetrahydrofuran (THF) and centrifuging to precipitate the solid components other than the resin component. And recover them, observe the conductive particles (a) with a scanning electron microscope (SEM) or a transmission electron microscope (TEM) on the recovered solid components, and randomly extract 100 conductive particles An image is acquired of the primary particles of particle (a), and the circle-converted diameter is obtained for each primary particle through image analysis, and the average diameter weighted by volume is calculated.

The proportion of the conductive particles (a) in the total solid content is preferably 60 mass% to 85 mass%. By setting the proportion of the conductive particles (a) to 60 mass % or more, more preferably 70 mass % or more, the contact probability between the conductive particles (a) increases, and the specific resistance value of the formed conductive pattern becomes low. On the other hand, by setting the proportion of the conductive particles (a) to 85 mass % or less, more preferably 80 mass % or less, the exposure light during exposure can smoothly pass through the coating film of the conductive paste of the present invention, so that a fine pattern can be obtained Forming becomes easy. The total solid content here refers to all components of the conductive paste excluding the solvent.

The proportion of the conductive particles (a) in the total solid content of the conductive paste of the present invention can be measured as follows. That is, by heating the conductive paste at 60°C to 120°C, the solvent is evaporated and all solid components are recovered. Next, thermogravimetric-differential thermal analysis (TG-DTA) (differential thermal balance) is used to heat all solid components at 400°C to 600°C to burn the resin components, thereby obtaining the total The proportion of inorganic solid components in solid components. Next, the remaining inorganic solid component is dissolved in nitric acid or the like, and inductively coupled plasma (ICP) emission spectrometry is performed to measure the proportion of conductive particles (a) in the inorganic solid component.

[Resin (b)] In the present invention, the resin (b) includes monomers and oligomers in addition to polymers.

Examples of the resin (b) include acrylic resin, polyester resin, phenol resin, epoxy resin, acrylic urethane resin, polyether urethane resin, phenoxy resin, and polycarbonate resin. , polyamide resin, polyamide resin, polyamide imine resin, etc. Two or more types of the above-mentioned resins may be contained.

When the conductive paste of the present invention is a form that further contains the photopolymerization initiator (d), that is, when pattern formation using the conductive paste of the present invention is performed by photolithography, the above-mentioned configuration is preferred. Resin (b) has a carboxyl group. Examples of the carboxyl group-containing resin include acrylic copolymers, carboxylic acid-modified epoxy resins, carboxylic acid-modified phenol resins, polyamic acid, carboxylic acid-modified siloxane polymers, and the like. Two or more types of the above-mentioned resins may be contained. Among these, an acrylic copolymer or a carboxylic acid-modified epoxy resin with high ultraviolet light transmittance is preferred.

As the acrylic copolymer, a copolymer of an acrylic monomer and an unsaturated acid or an acid anhydride thereof is preferred.

Examples of the acrylic monomer include methyl acrylate, ethyl acrylate (hereinafter referred to as "EA"), 2-ethylhexyl acrylate, n-butyl acrylate, isobutyl acrylate, and isoacrylate. Propyl ester, glycidyl acrylate, butoxytriethylene glycol acrylate, dicyclopentyl acrylate, dicyclopentenyl acrylate, 2-hydroxyethyl acrylate, isobornyl acrylate, 2-hydroxypropyl acrylate, Isodecyl acrylate, isooctyl acrylate, lauryl acrylate, 2-methoxyethyl acrylate, methoxyethylene glycol acrylate, methoxydiethylene glycol acrylate, octafluoropentyl acrylate, benzene acrylate Oxyethyl acrylate, stearyl acrylate, trifluoroethyl acrylate, aminoethyl acrylate, phenyl acrylate, phenoxyethyl acrylate, 1-naphthyl acrylate, 2-naphthyl acrylate, thiophenol acrylate, Benzylmercaptan acrylate, allylated cyclohexyl diacrylate, methoxylated cyclohexyl diacrylate, 1,4-butanediol diacrylate, 1,3-butanediol diacrylate, ethyl Glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, polyethylene glycol diacrylate, neopentyl glycol diacrylate, propylene glycol diacrylate, polypropylene glycol diacrylate, triethylene glycol diacrylate, Glyceryl diacrylate, trimethylolpropane triacrylate, di-trimethylolpropane tetraacrylate, dipentaerythritol monohydroxypentacrylate, dipentaerythritol hexaacrylate, acrylamide, N-methoxymethyl Acrylamide, N-ethoxymethacrylamide, N-n-butoxymethacrylamide, N-isobutoxymethacrylamide, methacrylphenol, methacrylamide Aminophen, γ-acryloxypropyltrimethoxysilane, N-(2-hydroxyphenyl)acrylamide, N-(3-hydroxyphenyl)acrylamide, N-(4-hydroxyphenyl) )Acrylamide, o-hydroxyphenyl acrylate, m-hydroxyphenyl acrylate, p-hydroxyphenyl acrylate, 2-(2-hydroxyphenyl)ethyl acrylate, 2-(3-hydroxyphenyl)ethyl acrylate, acrylic acid 2-(4-hydroxyphenyl)ethyl ester, etc., or compounds in which the acrylic acid group is substituted with a methacrylic acid group. Among these, a monomer selected from the group consisting of ethyl acrylate, 2-hydroxyethyl acrylate, and isobornyl acrylate is particularly preferred. Two or more of these may be used.

Examples of the unsaturated acid or its anhydride include acrylic acid (hereinafter referred to as "AA"), methacrylic acid, itaconic acid, crotonic acid, maleic acid, fumaric acid, and vinyl acetate. , or these acid anhydrides, etc. Two or more of these may be used. The acid value of the acrylic copolymer can be adjusted by the copolymerization ratio of unsaturated acid.

Examples of other monomers having unsaturated double bonds include o-hydroxystyrene, m-hydroxystyrene, p-hydroxystyrene, and the like. Two or more of these may be used.

As the carboxylic acid modified epoxy resin, a reaction product of an epoxy compound and an unsaturated acid or an unsaturated acid anhydride is preferred. Here, the carboxylic acid-modified epoxy resin refers to one obtained by modifying the epoxy group of the epoxy compound with carboxylic acid or carboxylic anhydride, and does not include the epoxy group.

Examples of epoxy compounds include glycidyl ethers, glycidyl amines, and epoxy resins.

More specifically, examples of glycidyl ethers include methyl glycidyl ether, ethyl glycidyl ether, butyl glycidyl ether, ethylene glycol diglycidyl ether, and diethylene glycol diglycidyl ether. Propylene glycol diglycidyl ether, tripropylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, bisphenol A diglycidyl ether, hydrogenated bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, bisphenol S Diglycidyl ether, bisphenol fluorene diglycidyl ether, biphenol diglycidyl ether, tetramethylbiphenol glycidyl ether, trimethylolpropane triglycidyl ether, 3',4'-epoxycyclohexylmethyl -3,4-epoxycyclohexanecarboxylate, etc.

Examples of glycidylamines include tert-butylglycidylamine and the like.

Examples of the epoxy resin include bisphenol A-type epoxy resin, bisphenol F-type epoxy resin, biphenyl-type epoxy resin, novolak-type epoxy resin, hydrogenated bisphenol A-type epoxy resin, and the like.

Two or more types of these epoxy compounds may be used.

Examples of the unsaturated acid or unsaturated acid anhydride that reacts with the epoxy compound include the same ones as those exemplified previously as raw materials for the acrylic copolymer.

In the case where the conductive paste of the present invention further contains the photopolymerization initiator (d), that is, when pattern formation using the conductive paste of the present invention is performed by photolithography, the resin (b) It is also preferred to have unsaturated double bonds. By having an unsaturated double bond in the resin (b), the cross-linking density of the exposed portion during exposure can be increased, the development margin can be expanded, and a finer pattern can be formed.

The unsaturated double bond can be introduced by reacting a compound having an unsaturated double bond, such as glycidyl (meth)acrylate, with the acrylic copolymer or carboxylic acid-modified epoxy resin.

In the case where the conductive paste of the present invention further contains the photopolymerization initiator (d), that is, when pattern formation using the conductive paste of the present invention is performed by photolithography, the resin (b) It is also preferred to have a reactive monomer having an unsaturated double bond.

Examples of the reactive monomer having an unsaturated double bond include the acrylic monomers exemplified above as raw materials for the acrylic copolymer, styrene "hereinafter referred to as (St)", and the like. Two or more of these may be contained.

The content of the reactive monomer having an unsaturated double bond in the resin (b) is preferably 1 to 50 mass%. By setting the content of the reactive monomer having an unsaturated double bond to 1% by mass or more, a fine pattern can be formed. On the other hand, by making it 50 mass % or less, hardening shrinkage can be moderately suppressed, and electrical conductivity can be further improved.

As the resin (b), a resin having a phenolic hydroxyl group can preferably be used. By providing the resin (b) with phenolic hydroxyl groups, hydrogen bonds can be formed with polar groups such as hydroxyl groups or amine groups on the surface of the base material, thereby improving the adhesion between the pattern and the base material.

The acid value of resin (b) is preferably 50 mgKOH/g to 250 mgKOH/g. If the acid value is 50 mgKOH/g or more, more preferably 60 mgKOH/g or more, the solubility in the developer becomes high and the generation of development residue can be suppressed. On the other hand, if the acid value is 250 mgKOH/g or less, more preferably 200 mgKOH/g or less, excessive dissolution in the developer can be suppressed and the film of the pattern can be suppressed from being reduced. The acid value of the resin (b) can be measured in accordance with Japanese Industrial Standards (JIS) K 0070 (1992).

Assuming that the content of the imidazolium salt (c) described below is a trace amount and considering the content of the conductive particles (a), the content of the resin (b) in the total solid content of the conductive paste is preferably 15 mass %~40% by mass.

[Imidazolium salt (c)] The conductive paste of the present invention contains imidazolium salt (c). By adding imidazolium salt (c), the diffusion of metal atoms from the conductive particles (a) is significantly promoted, whereby the conductive particles (a) are effectively sintered, and conduction can be achieved even under low temperature and short-time thermal curing. .

The melting point of the imidazolium salt (c) must be 30°C or more and 100°C or less. An imidazolium salt with a melting point lower than 30°C accelerates sintering even at room temperature. Therefore, sintering before pattern formation makes pattern processing difficult and the storage stability of the paste is impaired. In addition, by setting the melting point to 100°C or lower, conductivity can be obtained even at a low temperature of 100°C or lower. The melting point of the imidazolium salt (c) can be measured by differential scanning calorimetry (DSC).

Examples of the imidazolium salt (c) include: 1-butyl-2,3-dimethylimidazolium chloride, 1-(2-hydroxyethyl)-3-methylimidazolium chloride, 1- Methyl-3-propylimidazolium chloride, 1-ethyl-3-methylimidazolium chloride, 1-benzyl-3-methylimidazolium chloride, 1-dodecyl-3-methyl 1H-imidazolium chloride, 1-ethyl-3-methylimidazolium bromide, 1-dodecyl-3-methylimidazolium bromide 1-butyl-2,3- Dimethylimidazolium hexafluorophosphate, 1-butyl-2,3-dimethylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium methane sulfonate, 1-ethyl- 3-methylimidazolium hexafluorophosphate, 1-benzyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium nitrate, 1-ethyl-3-methyl Imidazolium iodide, etc. Two or more of these may be contained.

The imidazolium salt (c) preferably has an alkyl chain at the nitrogen atom at position 1 or 3 of the imidazole ring. By having an alkyl chain on the nitrogen atom at the 1st or 3rd position, it is easy to cause ionization of anions and cations. In addition, since the alkyl chain is less likely to cause steric hindrance, the diffusion of cations in the coating film becomes easier, and metal atoms can be effectively diffused from the conductive particles (a).

The carbon number of the alkyl chain is more preferably 2 to 5. By setting the carbon number of the alkyl chain to 2 to 5, the diffusion of cations in the coating film can be made easier.

The imidazolium salt (c) preferably has an anionic formula weight of 80 or less. By setting the formula amount to 80 or less, more preferably 70 or less, anions can be easily diffused in the coating film.

The content of the imidazolium salt (c) is 0.05 to 3.0 parts by mass relative to 100 parts by mass of the conductive particles (a). When the content of the imidazolium salt (c) is 0.05 parts by mass or more, preferably 0.1 parts by mass or more, the atomic diffusion phenomenon of the conductive particles (a) is easily promoted, and the conductivity can be improved through low temperature and short-time thermal curing. On the other hand, when the content of the imidazolium salt (c) is 3.0 parts by mass or less, sintering before pattern processing can be suppressed, and high-definition wiring can be formed.

[Photopolymerization initiator (d)] When pattern formation using the conductive paste of the present invention is performed by photolithography, the conductive paste of the present invention preferably contains a photopolymerization initiator (d). The photopolymerization initiator absorbs short-wavelength light such as ultraviolet rays and undergoes decomposition or hydrogen abstraction reaction to generate free radicals.

Examples of the photopolymerization initiator include benzophenone derivatives, acetophenone derivatives, thioxanthone derivatives, benzyl derivatives, benzoin derivatives, oxime compounds, α-hydroxyketone compounds, α-aminoalkylphenone compounds, phosphine oxide compounds, anthrone compounds, anthraquinone compounds, etc.

Examples of benzophenone derivatives include benzophenone, methyl o-phenylbenzoate, 4,4'-bis(dimethylamino)benzophenone, 4,4'- Bis(diethylamino)benzophenone, 4,4'-dichlorobenzophenone, fluorenone, 4-benzoyl-4'-methyldiphenylketone, etc.

Examples of acetophenone derivatives include p-tert-butyldichloroacetophenone, 4-azidobenzylideneacetophenone, 2,2'-diethoxyacetophenone, and the like.

Examples of thioxanthone derivatives include thioxanthone, 2-methylthioxanthone, 2-chlorothioxanthone, 2-isopropylthioxanthone, diethylthioxanthone, and the like.

Examples of benzyl derivatives include benzyl, benzyldimethyl ketal, benzyl-β-methoxyethyl acetal, and the like.

Examples of benzoin derivatives include benzoin, benzoin methyl ether, benzoin butyl ether, and the like.

Examples of oxime compounds include: 1,2-octanedione-1-[4-(phenylthio)-2-(O-benzoyloxime)], ethanone-1-[9-ethyl Base-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-1-(O-acetyl oxime), 1-phenyl-1,2-butanedione-2 -(O-Methoxycarbonyl)oxime, 1-phenyl-propanedione-2-(O-ethoxycarbonyl)oxime, 1-phenyl-propanedione-2-(O-benzoyl) ) oxime, 1,3-diphenyl-glycerol-2-(O-ethoxycarbonyl) oxime, 1-phenyl-3-ethoxy-glycerol-2-(O-benzoyl) base) oxime, etc.

Examples of α-hydroxyketone compounds include: 2-hydroxy-2-methyl-1-phenyl-propan-1-one, 1-[4-(2-hydroxyethoxy)-phenyl]- 2-Hydroxy-2-methyl-1-propan-1-one, etc.

Examples of α-aminoalkylphenone compounds include 2-methyl-(4-methylthiophenyl)-2-morpholinylpropan-1-one, 2-benzyl-2-di Methylamino-1-(4-morpholinylphenyl)-butan-1-one, 2-dimethylamino-2-(4-methylbenzyl)-1-(4-morpholine -4-yl-phenyl)butan-1-one, etc.

Examples of the phosphine oxide-based compound include 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide and bis(2,4,6-trimethylbenzoyl)-phenyl. Phosphine oxide, etc.

Examples of the anthrone compound include anthrone, benzanthrone, dibenzanthrone, and methyleneanthrone.

Examples of the anthraquinone compound include anthraquinone, 2-tert-butylanthraquinone, 2-pentylanthraquinone, β-chloroanthraquinone, and the like.

Two or more of these may be contained. Among these, oxime-based compounds with high photosensitivity are preferred.

The content of the photopolymerization initiator (d) is preferably 1 to 30 parts by mass relative to 100 parts by mass of the resin (b). If the content of the photopolymerization initiator is 1 part by mass or more, the hardened density of the exposed part increases, and the residual film rate after development can be increased. On the other hand, if the content of the photopolymerization initiator is 30 parts by mass or less, excess light absorption caused by the photopolymerization initiator in the upper part of the pattern can be suppressed. As a result, the pattern can be easily formed into a tapered shape, and the adhesiveness with the base material can be improved.

In addition to the above-mentioned components, the conductive paste of the present invention may also contain additives such as solvents, plasticizers, leveling agents, surfactants, silane coupling agents, defoaming agents, and pigments.

Specific examples of plasticizers include dibutyl phthalate, dioctyl phthalate, polyethylene glycol, glycerin, and the like. Specific examples of the leveling agent include special vinyl polymers, special acrylic polymers, and the like.

Examples of the silane coupling agent include methyltrimethoxysilane, dimethyldiethoxysilane, phenyltriethoxysilane, hexamethyldisilazane, and 3-methacryloxypropyl Trimethoxysilane, 3-glycidoxypropyltrimethoxysilane, vinyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, etc.

Examples of solvents include N,N-dimethylacetamide, N,N-dimethylformamide, N-methyl-2-pyrrolidone, and 2-dimethylaminoethanol. Called (dimethylaminoethanol, DMEA)", dimethylimidazolidinone, dimethyltrisoxide, γ-butyrolactone, ethyl lactate, 1-methoxy-2-propanol, 1-ethoxy-2 -Propanol, ethylene glycol mono-n-propyl ether, diacetone alcohol, tetrahydrofurfuryl alcohol, propylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether acetate, diethylene glycol Monobutyl ether, diethylene glycol, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, etc. Two or more of these may be contained.

The boiling point of the solvent is preferably 150°C or higher. If the boiling point is 150° C. or higher, volatilization of the solvent is suppressed, and thickening of the paste can be suppressed.

[Preparation] The conductive paste of the present invention can be prepared using a disperser or kneader such as a three-roller mill, a ball mill, or a planetary ball mill.

[Formation of conductive pattern] The method of forming a conductive pattern using the conductive paste of the present invention includes, for example: a coating step, which is to apply the conductive paste of the present invention on a substrate to obtain a coating film; and a photolithography step, which is to expose and develop the coating film. Obtaining a pattern; and a curing step, heating the pattern at 60°C to 250°C to obtain a conductive pattern.

The coating step is a step of applying the conductive paste of the present invention on a substrate to obtain a coating film.

Examples of the substrate include polyethylene terephthalate (PET) film, polyimide film, polyester film, aromatic polyamide film, epoxy resin substrate, and polyether amide. Imine resin substrate, polyetherketone resin substrate, polystyrene resin substrate, glass substrate, silicon wafer, alumina substrate, aluminum nitride substrate or silicon carbide substrate.

Examples of the coating method in the coating step include spin coating using a spinner, spray coating, roll coating, screen printing, blade coater, die coater, and calender coating. machine, meniscus coater or rod coater.

When the conductive paste of the present invention contains a solvent, the obtained coating film may be dried to remove the solvent. Examples of methods for drying the coating film include heat drying using an oven, a hot plate, or infrared irradiation, or vacuum drying. The heating and drying temperature is usually 50°C to 80°C, and the heating and drying time is usually 1 minute to several hours.

The film thickness of the coating film obtained in the coating step may be appropriately determined based on the coating method, the total solid content concentration or viscosity of the conductive paste, and is preferably the film thickness of the dried coating film. 0.1 μm～50 μm.

The photolithography step is a step of exposing and developing the coating film obtained in the coating step to obtain a pattern.

As a light source used for exposing the coating film, i-rays (365 nm), h-rays (405 nm) or g-rays (436 nm) of a mercury lamp are preferred.

After exposure, the unexposed parts are removed using a developer to obtain the desired pattern. Examples of the developer when performing alkali development include tetramethylammonium hydroxide, diethanolamine, diethylaminoethanol, sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, and triethylamine. Diethylamine, methylamine, dimethylamine, dimethylaminoethyl acetate, dimethylaminoethanol, dimethylaminoethyl methacrylate, cyclohexylamine, ethylenediamine or hexamethylene Aqueous solution of diamine. N-methyl-2-pyrrolidinone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethylsulfoxide or γ-butylene can also be added to these aqueous solutions. Polar solvents such as lactones, alcohols such as methanol, ethanol or isopropyl alcohol, esters such as ethyl lactate or propylene glycol monomethyl ether acetate, cyclopentanone, cyclohexanone, isobutyl ketone or methyl isobutyl ketone Ketones or surfactants.

Examples of the developer when performing organic development include N-methyl-2-pyrrolidone, N-acetyl-2-pyrrolidone, N,N-dimethylacetamide, N , Polar solvents such as N-dimethylformamide, dimethyltrisoxide or hexamethylphosphonotriamine or the combination of these polar solvents with methanol, ethanol, isopropyl alcohol, xylene, water, methyl carbitol Or a mixed solution of ethyl carbitol.

Examples of the development method include: a method of spraying a developer toward the surface of the coating film while leaving the substrate stationary or rotating; a method of immersing the substrate in the developer; or a method of immersing the substrate in the developer. A method of applying ultrasonic waves to one side.

The pattern obtained in the development step can also be subjected to cleaning treatment using a cleaning solution. Examples of the cleaning liquid include water or an aqueous solution in which alcohols such as ethanol and isopropyl alcohol or esters such as ethyl lactate or propylene glycol monomethyl ether acetate are added to water.

The curing step is a step of heating the pattern obtained in the photolithography step at 60°C to 250°C to obtain a conductive pattern.

Examples of curing methods include heating and drying using an oven, an inert oven, or a hot plate, heating and drying using electromagnetic waves such as an infrared heater, or vacuum drying.

The curing temperature is preferably 60°C to 250°C. By setting the curing temperature to 60° C. or higher, more preferably 80° C. or higher, sintering of the metal particles can be sufficiently performed, and the specific resistance value of the obtained conductive pattern can be sufficiently reduced. On the other hand, by setting the curing temperature to 250°C or lower, more preferably 140°C or lower, and even more preferably 100°C or lower, a conductive pattern can be stably formed on a substrate or the like with low heat resistance. [Example]

The present invention will be described in detail below with reference to Examples and Comparative Examples. However, the present invention is not limited only to these examples.

The materials used in each Example and Comparative Example are as follows.

[Conductive particles (a)] Silver particles with volume average particle sizes of 0.5 μm, 0.1 μm, and 2.0 μm.

[Resin (b)] (B-1) Add 150 g of 2-dimethylaminoethanol (DMEA) to the reaction vessel in a nitrogen atmosphere, and use an oil bath to heat it to 80°C. A mixture containing 20 g of ethyl acrylate (EA), 40 g of 2-ethylhexyl methacrylate (2-EHMA), 20 g of styrene (St), and 15 g of acrylic acid ( AA), 0.8 g of 2,2'-azobisisobutyronitrile and 10 g of DMEA. After completion of the dropwise addition, polymerization reaction was further performed for 6 hours. Thereafter, 1 g of hydroquinone monomethyl ether was added to stop the polymerization reaction. Then, a mixture containing 5 g of GMA, 1 g of triethylbenzylammonium chloride and 10 g of DMEA was added dropwise over 0.5 hours. After completion of the dropwise addition, the addition reaction was further performed for 2 hours. The obtained reaction solution was purified with methanol to remove unreacted impurities, and then vacuum dried for 24 hours to obtain an acrylic copolymer in EA/2-EHMA/St/AA (the copolymerization ratio is expressed in parts by mass A carboxyl group-containing acrylic copolymer B-1 to which 5 parts by mass of GMA was added (calculated as 20/40/20/15). The acid value of the obtained B-1 was 103 mgKOH/g.

(B-2) As the reactive monomer having an unsaturated double bond, an acrylic monomer (light acrylate BP-4EA manufactured by Kyeisha Chemical Co., Ltd.) was used. Call it B-2.

[Imidazolium salt (c)] IS-1: 1-methyl-3-propylimidazolium chloride (melting point: 64°C) IS-2: 1-butyl-3-methylimidazolium chloride (melting point: 70°C) IS-3: 1-(2-hydroxyethyl)-3-methylimidazolium chloride (melting point: 83°C) IS-4: 1-benzyl-3-methylimidazolium chloride (melting point: 80°C) IS-5: 1-Dodecyl-3-methyl-1H-imidazole-3-onium chloride (melting point: 48°C) IS-6: 1-ethyl-3-methylimidazolium bromide (melting point: 74°C) IS-7: 1-butyl-2,3-dimethylimidazolium tetrafluoroborate (melting point: 34°C) IS-8: 1-ethyl-3-methylimidazolium hexafluorophosphate (melting point: 61°C) IS-9: 1-butyl-2,3-dimethylimidazolium chloride (melting point: 99°C) IS-10: 1-butyl-3-methylimidazolium trifluoromethanesulfonate (melting point: 16℃) IS-11: 1,3-dimethylimidazolium chloride (melting point: 125℃) IS-12: 1-ethyl-3-methylimidazolium nitrate (melting point: 41°C).

[Substitute for imidazolium salt (c)] AS-1: Tetramethylammonium chloride (melting point: 425℃) AS-2: Tetrabutylammonium chloride (melting point: 70°C).

[Photopolymerization initiator (d)] ·IRGACURE (registered trademark) OXE01 (trade name, manufactured by BASF Japan Co., Ltd., oxime-based compound) (hereinafter referred to as OXE01).

[Solvent] ·DMEA (manufactured by Tokyo Chemical Industry Co., Ltd.).

[Evaluation and Measurement Methods] (1) Pattern Formability The conductive film obtained in each example was coated on a PET film with a thickness of 50 μm by screen printing so that the coating film thickness after drying would be 2.0 μm. paste, and the obtained coating film was dried in a drying oven at 60° C. for 20 minutes. A group of straight lines arranged with a certain line and space (hereinafter referred to as "L/S"), that is, a light-transmitting pattern, is used as a unit to separate three types of photomasks with different values of L/S. After drying, The coating film was exposed and developed to obtain three patterns with different L/S values. Regarding exposure, an exposure device (PEM-6M; manufactured by United Optical Co., Ltd.) was used to perform full-line exposure at an exposure dose of 300 mJ/cm ² (wavelength 365 nm conversion), and the substrate was developed in a 0.20 mass% Na ₂ CO ₃ solution After immersing in the medium for 30 seconds, a cleaning process using ultrapure water was performed.

Thereafter, the obtained patterns were thermally cured at 80° C. and 100° C. for 1 hour, and three conductive patterns with different L/S values were obtained. Furthermore, the L/S values of each unit included in the mask are set to 15/15, 10/10, and 7/7 (respectively representing line width (μm)/space (μm)). The obtained conductive pattern was observed with an optical microscope, and it was confirmed that there was no residue between the patterns and no pattern peeling, and the conductive pattern with the smallest L/S value was judged to be A, 10 when the L/S value was 7/7. The case of /10 was judged as B, the case of 15/15 was judged as C, and the case where the conductive pattern could not be formed at 15/15 was judged as D. In the order of A>B>C>D, the pattern formability is excellent, and it is shown that fine pattern formation is possible. A to C are judged as passed.

(2) Specific resistance value The conductive paste obtained in each example was coated on a PET film with a thickness of 50 μm by screen printing so that the dried coating film thickness became 1.5 μm, and the obtained resultant was dried in a drying oven at 80°C. The coated film was allowed to dry for 15 minutes. A photomask having 100 light-transmitting patterns 100 shown in FIG. 1 was separated, and the dried coating film was exposed and developed to obtain a pattern.

The film thickness was measured using a stylus type step meter ("Surfcom" (registered trademark) 1400 manufactured by Tokyo Seiko Co., Ltd.). More specifically, the film thickness can be calculated by measuring the film thickness at 10 randomly selected positions under the conditions of measurement length: 1 mm and scanning speed: 0.3 mm/sec, and finding the average value of these film thicknesses. .

Thereafter, the obtained pattern was thermally cured at 80° C. and 100° C. for 1 hour to obtain a conductive pattern for specific resistance value measurement. The obtained conductive pattern has a line width of 0.10 mm and a line length of 80 mm. In addition, the conditions of exposure and development were set to be the same as the evaluation method of the pattern formability mentioned above.

In addition, the line width can be calculated by using an optical microscope to observe the line widths of 10 randomly selected positions, analyzing the image data, and obtaining the average value of these line widths.

The respective ends of the obtained conductive patterns for measuring the specific resistance value were connected with a resistance meter (RM3544; manufactured by Hioki) to measure the resistance value, and the specific resistance value was calculated according to the following formula. Specific resistance value = resistance value × film thickness × line width/line length... Formula The smaller the specific resistance value, the better the electrical conductivity.

[Example 1] In a clean bottle with a capacity of 100 mL, add 10.00 g of B-1 and 2.00 g of B-2 as the resin (b), and 0.255 g of IS-1 as the imidazolium salt (c) as a photopolymerization starter. 0.40 g of OXE01 as an agent and 6.00 g of DMEA as a solvent were mixed using a rotation-revolution mixer ("Defoaming Mixer Taro" ARE-310 manufactured by Thinky Co., Ltd.) to obtain 18.66 g of a resin solution. (Total solid content 67.8% by mass).

10.00 g of the resin solution and 27.10 g of Ag particles (volume average particle diameter: 0.5 μm) as conductive particles (a) were mixed, and a three-roller mill (EXAKT M-50 manufactured by EXAKT Corporation) was used. ) and kneaded to obtain 37.10 g of conductive paste 1.

[Example 2 to Example 10] The conductive paste was obtained in the same manner as in Example 1 except that IS-2 to IS-9 and IS-12 were used in each example instead of IS-1 as the imidazolium salt (c) according to the corresponding relationship shown in Table 1. 2~Conductive paste 10.

[Example 11] Except that the addition amount of imidazolium salt (c) IS-1 to the resin solution was set to 0.025 g instead of 0.255 g, and the amount of the resin solution mixed with the conductive particles (a) was set to 10.03 g instead of 10.00 g. The conductive paste 11 was obtained in the same manner as in Example 1.

[Example 12] Except that the addition amount of imidazolium salt (c) IS-1 to the resin solution was set to 0.515 g instead of 0.255 g, and the amount of the resin solution mixed with the conductive particles (a) was set to 9.95 g instead of 10.00 g. The conductive paste 12 was obtained in the same manner as in Example 1.

[Example 13] Except that the addition amount of imidazolium salt (c) IS-1 to the resin solution was set to 1.69 g instead of 0.255 g, and the amount of the resin solution mixed with the conductive particles (a) was set to 9.66 g instead of 10.00 g, the same changes as in the implementation The conductive paste 13 was obtained in the same manner as in Example 1.

[Example 14, Example 15] Conductive pastes 14 and 15 were obtained in the same manner as in Example 1, except that Ag particles with a volume average particle diameter of 0.1 μm and 2.0 μm were used instead of Ag particles with a volume average particle diameter of 0.5 μm as the conductive particles (a).

[Comparative example 1] Except that the addition amount of imidazolium salt (c) IS-1 to the resin solution was set to 0.015 g instead of 0.255 g, and the amount of the resin solution mixed with the conductive particles (a) was set to 10.05 g instead of 10.00 g, the same changes were made as in the implementation The conductive paste 16 was obtained in the same manner as in Example 1.

[Comparative example 2] Except that the addition amount of imidazolium salt (c) IS-1 to the resin solution was set to 2.36 g instead of 0.255 g, and the amount of the resin solution mixed with the conductive particles (a) was set to 9.55 g instead of 10.00 g, the same changes were made as in the implementation The conductive paste 17 was obtained in the same manner as in Example 1.

[Comparative Example 3 to Comparative Example 6] Conductive pastes 18 to 18 were obtained in the same manner as in Example 1, except that AS-1, AS-2, IS-10, and IS-11 were used instead of IS-1 as the imidazolium salt (c) or its substitute. twenty one.

A predetermined pattern was formed using the conductive pastes 18 to 21 obtained in each of the Examples and Comparative Examples, and a conductive pattern was produced by thermal curing, and the pattern formability and the conductivity were evaluated. Among them, Comparative Examples 2 and 5 had poor pattern formability and could not be patterned. The evaluation results are shown in Table 2.

[Table 1] [Table 1] Conductive particles (a) Resin(b) Imidazolium salt (c)/its substitutes Photopolymerization initiator OXE01 Solvent DMEA Volume average particle size (μm) Proportion of total solid content (mass %) Kind Set B-1 to the mass ratio of 100 (parts by mass) Kind Set B-1 to the mass ratio of 100 (parts by mass) Kind The mass ratio (parts by mass) of conductive particles (a) is 100 Melting point (℃) Anionic formula Resin (b) is set to a mass ratio of 100 (parts by mass) Resin (b) is set to a mass ratio of 100 (parts by mass) Example 1 0.5 80 B-1 100 B-2 20 IS-1 0.5 64 35.5 3.33 50 Example 2 0.5 80 B-1 100 B-2 20 IS-2 0.5 70 35.5 3.33 50 Example 3 0.5 80 B-1 100 B-2 20 IS-3 0.5 83 35.5 3.33 50 Example 4 0.5 80 B-1 100 B-2 20 IS-4 0.5 80 35.5 3.33 50 Example 5 0.5 80 B-1 100 B-2 20 IS-5 0.5 48 35.5 3.33 50 Example 6 0.5 80 B-1 100 B-2 20 IS-6 0.5 74 79.9 3.33 50 Example 7 0.5 80 B-1 100 B-2 20 IS-7 0.5 34 86.8 3.33 50 Example 8 0.5 80 B-1 100 B-2 20 IS-8 0.5 61 145.0 3.33 50 Example 9 0.5 80 B-1 100 B-2 20 IS-9 0.5 99 35.5 3.33 50 Example 10 0.5 80 B-1 100 B-2 20 IS-12 0.5 41 62.0 3.33 50 Example 11 0.5 80 B-1 100 B-2 20 IS-1 0.05 64 35.5 3.33 50 Example 12 0.5 80 B-1 100 B-2 20 IS-1 1.0 64 35.5 3.33 50 Example 13 0.5 80 B-1 100 B-2 20 IS-1 3.0 64 35.5 3.33 50 Example 14 0.1 80 B-1 100 B-2 20 IS-1 0.5 64 35.5 3.33 50 Example 15 2.0 80 B-1 100 B-2 20 IS-1 0.5 64 35.5 3.33 50 Comparative example 1 0.5 80 B-1 100 B-2 20 IS-1 0.03 64 35.5 3.33 50 Comparative example 2 0.5 80 B-1 100 B-2 20 IS-1 4.0 64 35.5 3.33 50 Comparative example 3 0.5 80 B-1 100 B-2 20 AS-1 0.5 425 35.5 3.33 50 Comparative example 4 0.5 80 B-1 100 B-2 20 AS-2 0.5 70 35.5 3.33 50 Comparative example 5 0.5 80 B-1 100 B-2 20 IS-10 0.5 16 149.1 3.33 50 Comparative example 6 0.5 80 B-1 100 B-2 20 IS-11 0.5 125 35.5 3.33 50

[Table 2] [Table 2] conductive paste Evaluation of pattern formation Specific resistance value (Ω·cm) Coating film thickness after drying (μm) pattern forming 80℃ 100℃ Example 1 1 2 A 6.5× ^10-5 4.2× ^10-5 Example 2 2 2 A 7.6× ^10-5 5.5× ^10-5 Example 3 3 2 A 1.2× ^10-4 8.5×10 ^-5 Example 4 4 2 A 8.5×10 ^-5 7.5× ^10-5 Example 5 5 2 B 1.1×10 ^-4 7.7× ^10-5 Example 6 6 2 A 9.5× ^10-5 7.8× ^10-5 Example 7 7 2 C 1.7× ^10-4 1.3×10 ^-4 Example 8 8 2 B 3.5× ^10-4 2.7× ^10-4 Example 9 9 2 A 1.5× ^10-4 8.7× ^10-5 Example 10 10 2 B 7.8× ^10-5 6.0× ^10-5 Example 11 11 2 A 6.9×10 ^-4 4.5×10 ^-4 Example 12 12 2 B 5.7× ^10-5 4.1×10 ^-5 Example 13 13 2 C 5.5×10 ^-5 3.9× ^10-5 Example 14 14 0.7 A 9.1× ^10-5 7.0× ^10-5 Example 15 15 5 C 7.5×10 ^-5 5.5× ^10-5 Comparative example 1 16 2 A 1.1× ^10-3 9.2× ^10-4 Comparative example 2 17 2 D Pattern processing is not possible Comparative example 3 18 2 A 7.3× ^10-1 4.6× ^10-3 Comparative example 4 19 2 A 6.6× ^10-1 3.5× ^10-3 Comparative example 5 20 2 D Pattern processing is not possible Comparative example 6 twenty one 2 A 1.7× ^10-3 9.2× ^10-4

100: Translucent pattern

FIG. 1 is a schematic diagram of a light-transmitting pattern of a photomask used for conductivity evaluation in Examples.

Claims (9)

A conductive paste containing conductive particles (a), resin (b), and imidazolium salt (c). The melting point of the imidazolium salt (c) is 30°C to 100°C, and relative to the conductive particles (a) The content of the imidazolium salt (c) is 0.05 to 3.0 parts by mass based on 100 parts by mass. The conductive paste according to claim 1, wherein the imidazolium salt (c) has an alkyl chain on the nitrogen atom at position 1 or 3 of the imidazole ring. The conductive paste according to claim 2, wherein the carbon number of the alkyl chain is 2 to 5. The conductive paste according to claim 1 or claim 2, wherein the formula weight of the anion of the imidazolium salt (c) is 80 or less. The conductive paste according to claim 1 or claim 2, wherein the resin (b) contains a resin having a carboxyl group, and the conductive paste further contains a photopolymerization initiator (d). The conductive paste according to claim 1 or claim 2, wherein the resin (b) contains a reactive monomer having an unsaturated double bond, and the conductive paste further contains a photopolymerization initiator (d). The conductive paste according to claim 1 or claim 2, wherein the conductive particles (a) have a volume average particle diameter of 0.1 μm to 2.0 μm. The conductive paste according to claim 1 or claim 2, wherein the proportion of the conductive particles (a) in the total solid content is 60 mass% to 85 mass%. The conductive paste according to claim 1 or claim 2, wherein the conductive particles (a) are particles of a metal selected from the group consisting of gold, silver and copper.