JP7371620B2 - Method for manufacturing conductive patterns - Google Patents

Description

The present invention relates to a method for manufacturing a conductive pattern.

In recent years, touch panels have been widely used as input means. A touch panel is composed of a display section such as a liquid crystal panel or an organic EL (electroluminescence) panel, and a touch sensor that detects information input at a specific position. Touch panel methods are broadly classified into resistive film methods, capacitive methods, optical methods, electromagnetic induction methods, ultrasonic methods, etc., depending on the method of detecting the input position. Among these, capacitive touch panels are widely used because they are optically bright, have an excellent design, have a simple structure, and are functionally superior.

A capacitive touch sensor has a second electrode that is orthogonal to the first electrode via an insulating layer, and when a voltage is applied to the electrode on the touch panel surface, the capacitance increases when a conductive object such as a finger touches it. The contact position obtained by detecting the change is output as a signal. Transparent wiring electrodes such as indium tin oxide have generally been used as the wiring electrodes used in capacitive touch sensors in order to make the wiring electrodes difficult to see. As devices become larger, opaque wiring electrodes made of metal materials are becoming more widespread. Furthermore, in order to achieve higher definition, thinner film, and improved visibility of touch sensors, it is required to directly form opaque wiring electrodes on display parts such as liquid crystal panels and organic EL panels. Therefore, in addition to forming a pattern, it is necessary to form a conductive pattern at a low temperature. Therefore, a conductive paste containing a conductive filler, a zwitterion compound, and a thermosetting compound (see, for example, Patent Document 1) has been proposed as a technique for forming a conductive pattern that exhibits conductivity under low-temperature curing conditions. There is. In addition, as a technique for reducing the electrical resistance of the conductive pattern layer, the conductive pattern layer is subjected to a strong acid treatment process in which it is brought into contact with a strong acid aqueous solution at room temperature, and a weak acid treatment process in which it is brought into contact with a weak acid aqueous solution at a temperature higher than room temperature. A method has been proposed in which the surface resistivity of a conductive pattern layer is reduced by forming a chain in which at least some of the metal particles in the layer are fused (for example, see Patent Document 2).

International Publication No. 2014/208445 Japanese Patent Application Publication No. 2012-15143

Although the technologies disclosed in Patent Documents 1 and 2 are capable of exhibiting conductivity at lower temperatures than before, in recent years, conductivity at even lower temperatures has been required, and conductivity is still insufficient at low temperatures of 100°C or lower. There were challenges that were enough.

In view of the above problems, an object of the present invention is to provide a method for manufacturing a conductive pattern that has excellent conductivity even at low temperatures of 100° C. or lower.

The present invention
(1) forming a pattern containing conductive particles (a) and resin (b) on a base material;
(2) The formed pattern contains at least one salt whose acid dissociation constant (pKa) of the conjugate acid of the anion is 1.0 or less at 25°C, and the pH at 25°C is 1.2 to 3.5. This is a method for manufacturing a conductive pattern, which includes a step of contacting with a certain acidic aqueous solution.

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

FIG. 2 is a schematic diagram of a light-transmitting pattern of a photomask used for evaluating conductivity in Examples.

The method for manufacturing a conductive pattern of the present invention includes:
(1) A step of forming a pattern containing conductive particles (a) and resin (b) on a base material (hereinafter sometimes referred to as step (1));
(2) The formed pattern contains at least one salt whose acid dissociation constant (pKa) of the conjugate acid of the anion is 1.0 or less at 25°C, and the pH at 25°C is 1.2 to 3.5. A step (hereinafter sometimes referred to as step (2)) of bringing into contact with a certain acidic aqueous solution is included. The conductive pattern obtained by the manufacturing method of the present invention is a composite of the organic component of the resin (b) and the inorganic component of the conductive particles (a), and the conductive particles (a) are bonded to each other by an atomic diffusion phenomenon. When they come into contact with each other, they exhibit conductivity. The resin (b) acts as a binder to improve the adhesion between the pattern and the base material. Bringing the pattern into contact with an acidic aqueous solution containing at least one salt having an acid dissociation constant (pKa) of the conjugate acid of the anion of 1.0 or less at 25°C and having a pH of 1.2 to 3.5 at 25°C. This promotes the diffusion of atoms from the surface of the conductive particles and improves the conductivity even at a low temperature of 100° C. or lower.

First, step (1) will be explained.

Examples of the base material include polyester films such as polyethylene terephthalate (hereinafter sometimes referred to as "PET") films, polyimide films, aramid films, epoxy resin films, polyetherimide films, polyether ketone films, and polysulfone films. Examples include a film, a glass substrate, a silicon wafer, an alumina substrate, an aluminum nitride substrate, a silicon carbide substrate, a decorative layer-formed substrate, an insulating layer-formed substrate, and the like.

The pattern formed in step (1) contains conductive particles (a). Examples of the conductive particles (a) include particles of silver, gold, copper, platinum, lead, tin, nickel, aluminum, tungsten, molybdenum, chromium, titanium, indium, and alloys of these metals. Two or more types of these may be contained. Among these, metal particles selected from silver, gold and copper are preferred from the viewpoint of electrical conductivity, and silver particles are more preferred from the viewpoints of cost and stability.

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

The volume average particle diameter of the conductive particles (a) is preferably 0.1 μm or more from the viewpoint of appropriately suppressing interactions between particles and improving the dispersibility of the conductive particles (a) in the pattern. On the other hand, the volume average particle diameter of the conductive particles (a) is preferably 2.0 μm or less from the viewpoint of improving the surface smoothness and dimensional accuracy of the conductive pattern and forming a fine conductive pattern. Here, the volume average particle diameter of the conductive particles (a) is determined by dissolving the formed pattern using a solvent in which the resin component is soluble, such as THF (tetrahydrofuron), centrifuging it, and removing the resin component. precipitate and collect. Next, the conductive particles (a) of the recovered solid content were observed using a scanning electron microscope (SEM) or a transmission electron microscope (TEM), and 100 primary particles of the conductive particles (a) were randomly selected. This can be determined by acquiring an image, determining the circular diameter of each primary particle by image analysis, and calculating the average diameter weighted by volume.

The content of the conductive particles (a) in the pattern is preferably 65 to 90% by mass. When the content of the conductive particles (a) is 65% by mass or more, the probability of contact between the conductive particles (a) in step (2) described later is improved, and the conductivity can be further improved. On the other hand, when the content of the conductive particles (a) is 90% by weight or less, a fine pattern can be formed by photolithography. Here, the proportion of the conductive particles (a) in the conductive pattern can be determined by scraping off the formed pattern and burning the organic components at 400 to 600°C using a TG-DTA (differential thermal balance). It can be calculated by dissolving the remaining inorganic solid content in nitric acid or the like and measuring the proportion of conductive particles (a) in the inorganic solid content by ICP emission spectrometry.

The pattern formed in step (1) contains resin (b). Examples of the resin include acrylic resin, polyester resin, phenol resin, epoxy resin, acrylic urethane resin, polyether urethane resin, phenoxy resin, polycarbonate resin, polyimide resin, polyamide resin, and polyamideimide resin. Two or more types of these may be contained.

When pattern formation in step (1) is performed by photolithography, it is preferable that the resin (b) has a carboxyl group, and it is preferable to use a photosensitive paste described below.

Examples of resins containing carboxyl groups include acrylic copolymers, carboxylic acid-modified epoxy resins, carboxylic acid-modified phenol resins, polyamic acids, and carboxylic acid-modified siloxane polymers. Two or more types of these may be contained. Among these, acrylic copolymers or carboxylic acid-modified epoxy resins with high ultraviolet light transmittance are preferred.

The acrylic copolymer is preferably a copolymer of an acrylic monomer and an unsaturated acid or an acid anhydride thereof, and may also be a copolymer of another monomer having an unsaturated double bond.

Examples of acrylic monomers include methyl acrylate, ethyl acrylate (hereinafter sometimes referred to as "EA"), 2-ethylhexyl acrylate, n-butyl acrylate (hereinafter sometimes referred to as "BA"), iso-butyl acrylate, iso-propane acrylate, glycidyl acrylate, butoxytriethylene glycol acrylate, dicyclopentanyl acrylate, dicyclopentenyl acrylate, 2-hydroxyethyl acrylate, isobornyl acrylate, 2-hydroxypropyl acrylate, isodexyl Acrylate, isooctyl acrylate, lauryl acrylate, 2-methoxyethyl acrylate, methoxyethylene glycol acrylate, methoxydiethylene glycol acrylate, octafluoropentyl acrylate, phenoxyethyl acrylate, stearyl acrylate, trifluoroethyl acrylate, aminoethyl acrylate, phenyl acrylate, phenoxyethyl Acrylate, 1-naphthyl acrylate, 2-naphthyl acrylate, thiophenol acrylate, benzyl mercaptan acrylate, allylated cyclohexyl diacrylate, methoxylated cyclohexyl diacrylate, 1,4-butanediol diacrylate, 1,3-butylene glycol diacrylate, Ethylene glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, polyethylene glycol diacrylate, neopentyl glycol diacrylate, propylene glycol diacrylate, polypropylene glycol diacrylate, triglycerol diacrylate, trimethylolpropane triacrylate, ditrimethylolpropane Tetraacrylate, dipentaerythritol monohydroxypentaacrylate, dipentaerythritol hexaacrylate, acrylamide, N-methoxymethylacrylamide, N-ethoxymethylacrylamide, Nn-butoxymethylacrylamide, N-isobutoxymethylacrylamide, methacrylphenol, methacryl Amidophenol, γ-acryloxypropyltrimethoxysilane, N-(2-hydroxyphenyl)acrylamide, N-(3-hydroxyphenyl)acrylamide, N-(4-hydroxyphenyl)acrylamide, o-hydroxyphenylacrylate, m- Hydroxyphenylacrylate, p-hydroxyphenyl acrylate, 2-(2-hydroxyphenyl)ethyl acrylate, 2-(3-hydroxyphenyl)ethyl acrylate, 2-(4-hydroxyphenyl)ethyl acrylate, etc., and their acrylic groups. Examples include compounds substituted with methacrylic groups. Among these, monomers selected from ethyl acrylate, 2-hydroxyethyl acrylate and isobornyl acrylate are particularly preferred. Two or more types of these may be used.

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

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

The carboxylic acid-modified epoxy resin is preferably a reaction product of an epoxy compound and an unsaturated acid or an unsaturated acid anhydride. Here, the carboxylic acid-modified epoxy resin is an epoxy compound in which the epoxy group is modified with a carboxylic acid or a carboxylic acid anhydride, and does not contain an epoxy group.

Examples of the epoxy compound include glycidyl ethers, glycidyl amines, and epoxy resins. More specifically, the glycidyl ethers include, for example, methyl glycidyl ether, ethyl glycidyl ether, butyl glycidyl ether, ethylene glycol diglycidyl ether, 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 glycidyl ether, biphenol diglycidyl ether, tetramethylbiphenol glycidyl ether, Examples include trimethylolpropane triglycidyl ether, 3',4'-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, and the like. Examples of glycidylamines include tert-butylglycidylamine. Examples of the epoxy resin include bisphenol A epoxy resin, bisphenol F epoxy resin, biphenyl epoxy resin, novolac epoxy resin, and hydrogenated bisphenol A epoxy resin. Two or more types of these may be used.

Examples of the unsaturated acid or unsaturated acid anhydride include those exemplified above as raw materials for the acrylic copolymer.

An unsaturated double bond can be introduced by reacting the aforementioned acrylic copolymer or carboxylic acid-modified epoxy resin with a compound having an unsaturated double bond such as glycidyl (meth)acrylate. By introducing an unsaturated double bond into the resin (b), it is possible to improve the crosslinking density of the exposed area during exposure, widen the development margin, and form a fine pattern.

As the resin (b), those having a phenolic hydroxyl group can also be preferably used. When the resin (b) has a phenolic hydroxyl group, it can form a hydrogen bond with a polar group such as a hydroxyl group or an amino group on the surface of the base material, thereby improving the adhesion between the pattern and the base material.

The acid value of the resin (b) is preferably 50 to 250 mgKOH/g. If the acid value is 50 mgKOH/g or more, the solubility in the developer will be high, and the generation of development residues can be suppressed. The acid value is more preferably 60 mgKOH/g or more. On the other hand, if the acid value is 250 mgKOH/g or less, excessive dissolution in the developer can be suppressed and pattern film thinning can be suppressed. The acid value is more preferably 200 mgKOH/g or less. Note that the acid value of the resin (b) can be measured in accordance with JIS K 0070 (1992).

As a method for forming a pattern, for example, a paste containing the above-mentioned conductive particles (a), resin (b), and other components as necessary is printed by screen printing, gravure printing, flexo printing, inkjet printing, etc. Examples include a method of forming a pattern, a method of forming a pattern by photolithography including steps of exposure and development, and the like. Methods for forming patterns by photolithography include, for example, methods in which a photosensitive resist is applied on a non-photosensitive paste coating film and a pattern is formed through the steps of exposure, development, etching, and resist removal; and a method of directly forming a pattern through a developing process. Among these, from the viewpoint of thinning the pattern and shortening the number of manufacturing steps, a method of forming a pattern from a photosensitive paste coating film by photolithography, which includes steps of exposure and development, is preferred.

The content of the conductive particles (a) in the paste is preferably 65 to 90% by weight based on the solid content.

The method for forming a conductive pattern of the present invention includes conductive particles (a), a carboxyl group-containing resin (B) (also referred to as a carboxyl group-containing resin (B)), and an unsaturated double bond on a base material. It has a photolithography step of forming a coating film by applying a photosensitive paste containing a reactive monomer (c) and a photopolymerization initiator (d), and forming a pattern by exposing and developing the coating film. It is preferable. By forming a conductive pattern in this manner, a fine pattern can be easily formed using a simple method.

Examples of the carboxyl group-containing resin (B) include the above-mentioned carboxyl group-containing resin (b). Two or more types of these may be contained.

For example, in the case of an acrylic copolymer, the acid value of the carboxyl group-containing resin (B) can be adjusted to a desired range by changing the proportion of unsaturated acids in the constituent components. In the case of a carboxylic acid-modified epoxy resin, it can be adjusted to a desired range by reacting with a polybasic acid anhydride. In the case of a carboxylic acid-modified phenol resin, it can be adjusted to a desired range by adjusting the proportion of polybasic acid anhydride in the constituent components.

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

In addition, when the paste used in step (1) contains an acrylic copolymer and a reactive monomer (c) having an unsaturated double bond, the reactive monomer (c) having an unsaturated double bond in the paste ) is preferably 1 to 100 parts by weight per 100 parts by weight of the acrylic copolymer. By containing 1 part by weight or more of the reactive monomer (c) having an unsaturated double bond, a fine pattern can be formed. On the other hand, by containing 100 parts by weight or less of the reactive monomer (c) having an unsaturated double bond, curing shrinkage can be moderately suppressed and electrical conductivity can be further improved.

The photopolymerization initiator (d) refers to a compound that absorbs short wavelength light such as ultraviolet light and causes decomposition or hydrogen abstraction reaction to generate radicals. Examples of the photopolymerization initiator (d) include benzophenone derivatives, acetophenone derivatives, thioxanthone derivatives, benzyl derivatives, benzoin derivatives, oxime compounds, α-hydroxyketone compounds, α-aminoalkylphenone compounds, and phosphine oxide compounds. , anthrone compounds, anthraquinone compounds, and the like. Examples of benzophenone derivatives include benzophenone, methyl O-benzoylbenzoate, 4,4'-bis(dimethylamino)benzophenone, 4,4'-bis(diethylamino)benzophenone, 4,4'-dichlorobenzophenone, fluorenone, -benzoyl-4'-methyldiphenylketone and the like. Examples of acetophenone derivatives include pt-butyldichloroacetophenone, 4-azidobenzalacetophenone, and 2,2'-diethoxyacetophenone. Examples of thioxanthone derivatives include thioxanthone, 2-methylthioxanthone, 2-chlorothioxanthone, 2-isopropylthioxanthone, and diethylthioxanthone. Examples of benzyl derivatives include benzyl, benzyl dimethyl 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-6-(2-methylbenzoyl) )-9H-carbazol-3-yl]-1-(O-acetyloxime), 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-propanedione-2-(O-ethoxycarbonyl)oxime, 1-phenyl-3-ethoxy- Examples include propanetrione-2-(O-benzoyl)oxime. Examples of α-hydroxyketone compounds include 2-hydroxy-2-methyl-1-phenyl-propan-1-one, 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2- Examples include methyl-1-propan-1-one. Examples of α-aminoalkylphenone compounds include 2-methyl-(4-methylthiophenyl)-2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl) )-butan-1-one, 2-dimethylamino-2-(4-methylbenzyl)-1-(4-morpholin-4-yl-phenyl)butan-1-one, and the like. Examples of the phosphine oxide compounds include 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide. Examples of anthrone compounds include anthrone, benzanthrone, dibenzosuberone, methyleneanthrone, and the like. Examples of anthraquinone compounds include anthraquinone, 2-t-butylanthraquinone, 2-amylanthraquinone, β-chloroanthraquinone, and the like. Two or more types of these may be contained. Among these, oxime compounds with high photosensitivity are preferred.

The content of the photopolymerization initiator (d) in the photosensitive paste is preferably 1 to 30 parts by weight based on 100 parts by weight of the carboxyl group-containing resin (B). When the content of the photopolymerization initiator (d) is 1 part by weight or more, the cured density of the exposed area increases and the residual film rate after development can be increased. On the other hand, when the content of the photopolymerization initiator (d) is 30 parts by weight or less, excessive light absorption by the photopolymerization initiator (d) in the upper part of the pattern is suppressed. As a result, the pattern can be easily formed into a tapered shape, and the adhesion to the base material can be improved.

In addition to the above, the paste used for pattern formation can also contain additives such as a solvent, a plasticizer, a leveling agent, a surfactant, a silane coupling agent, an antifoaming agent, and a pigment.

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 and special acrylic polymers.

Examples of the silane coupling agent include methyltrimethoxysilane, dimethyldiethoxysilane, phenyltriethoxysilane, hexamethyldisilazane, 3-methacryloxypropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, and vinyltrimethoxysilane. , 3-glycidoxypropylmethyldiethoxysilane and the like.

Examples of the solvent include N,N-dimethylacetamide, N,N-dimethylformamide, N-methyl-2-pyrrolidone, 2-dimethylaminoethanol (hereinafter referred to as (DMEA)), dimethylimidazolidinone, dimethylsulfoxide, 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 monoethyl ether Examples include acetate, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether, diethylene glycol, 2,2,4,-trimethyl-1,3-pentanediol monoisobutyrate, and the like. Two or more types of these may be contained. The boiling point of the solvent is preferably 150°C or higher. When the boiling point is 150° C. or higher, volatilization of the solvent is suppressed, and thickening of the paste can be suppressed.

Step (1) will be explained in more detail by taking as an example a method of forming a pattern from a photosensitive paste coating film by photolithography.

First, a paste is prepared by mixing the conductive particles (a), the resin (b), a solvent, and other components as necessary. Examples of the mixing device include dispersing machines and kneading machines such as a three-roller mill, a ball mill, and a planetary ball mill.

Next, the resulting paste is applied onto a substrate and dried. Examples of the paste application method include spin coating using a spinner, spray coating, roll coating, screen printing, coating using a blade coater, die coater, calendar coater, meniscus coater, or bar coater. Examples of the drying method include heating drying using an oven, hot plate, infrared rays, etc., and vacuum drying. The drying temperature is preferably 50 to 180°C, and the drying time is preferably 1 minute to several hours.

Next, the obtained coating film is exposed to light through an arbitrary pattern-forming mask to form a latent image. As a light source for exposure, I-line (365 nm), H-line (405 nm) or G-line (436 nm) of a mercury lamp is preferably used.

After exposure, the unexposed areas are dissolved and removed by developing with a developer to form a desired pattern. Examples of developing solutions for alkaline development include tetramethylammonium hydroxide, diethanolamine, diethylaminoethanol, sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, triethylamine, diethylamine, methylamine, dimethylamine, and dimethyl acetate. Examples include aqueous solutions of aminoethyl, dimethylaminoethanol, dimethylaminoethyl methacrylate, cyclohexylamine, ethylenediamine, hexamethylenediamine, and the like. Two or more types of these may be used. In some cases, a polar solvent such as N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, or γ-butyrolactone; methanol, ethanol, isopropanol, etc. may be added to these aqueous solutions. Alcohols; esters such as ethyl lactate and propylene glycol monomethyl ether acetate; ketones such as cyclopentanone, cyclohexanone, isobutyl ketone, and methyl isobutyl ketone; and one or more surfactants may be added.

As a developing method, for example, a method of spraying a developer onto the surface of the coated film while the base material having the exposed paste coated film is left standing or rotating, or a method of immersing the base material having the exposed paste coated film in the developer solution. Examples include a method of applying ultrasonic waves while immersing a substrate having an exposed paste coating film in a developer.

After development, rinsing treatment with a rinsing liquid may be performed. Examples of the rinsing liquid include water or an aqueous solution prepared by adding alcohols such as ethanol and isopropyl alcohol, or esters such as ethyl lactate and propylene glycol monomethyl ether acetate to water.

The thickness of the pattern obtained in step (1) is preferably 3 μm or less. By setting the thickness to 3 μm or less, a fine conductive pattern can be formed. In addition, the acidic aqueous solution penetrates easily, and better conductivity can be obtained even in a short time.

Next, step (2) will be explained.

In step (2), the pattern formed in step (1) contains at least one salt having an acid dissociation constant (pKa) of the conjugate acid of the anion of 1.0 or less at 25°C; of 1.2 to 3.5.

The acidic aqueous solution contains at least one salt whose conjugate acid of the anion has an acid dissociation constant (pKa) of 1.0 or less at 25°C. Here, "salt" refers to a component composed of cations and anions other than protons, and in the present invention, "salt" also includes those that are ionized into cations and anions in an aqueous solution. In addition, a cation may exist as an ion partially bonded to a hydroxyl group, and the aqueous solution in this case becomes acidic. The presence of the anion contained in the salt in the acid aqueous solution promotes the diffusion of atoms from the surface of the conductive particles (a) and improves the conductivity. The presence of cations other than protons contained in the salt in the acid aqueous solution allows the concentration of anions to be increased even if the pH is 1.2 or higher, as described later. As a result, reduction in conductivity due to corrosion of the conductive particles (a) included in the conductive pattern can be suppressed. By controlling the pKa at 25° C. of the conjugate acid of the anion contained in the salt to 1.0 or less, atomic diffusion of the conductive particles is promoted and the conductivity can be improved. The pKa at 25° C. of the conjugate acid of the anion contained in the salt is more preferably −5.0 or less. The pKa at 25° C. of the conjugate acid of the anion contained in the salt can be determined by specifying the anion contained in the salt and then measuring the conjugate acid using an absorption spectrometry method. In addition, if the pKa of the conjugate acid of the anion contained in the salt is -2 or less, literature values etc. can be referred to.

There are no particular restrictions on the salts whose conjugate acid pKa of the anion at 25°C is 1.0 or less as long as they are water-soluble; for example, sodium nitrate, potassium nitrate, sodium chloride, potassium chloride, nickel (II) chloride, iron chloride ( II), iron (III) chloride, tin (II) chloride, copper (II) chloride, sodium bromide, potassium bromide, nickel (II) bromide, iron (II) bromide, iron (III) bromide, Copper (II) bromide, sodium iodide, potassium iodide, nickel (II) iodide, sodium hydrogen sulfate, potassium hydrogen sulfate, sodium benzenesulfonate, potassium benzenesulfonate, sodium trifluoroacetate, potassium trifluoroacetate, etc. can be mentioned. Two or more types of these may be contained.

The concentration of salt is preferably 0.05 mol/L or more. By setting the salt concentration to 0.05 mol/L or more, diffusion of atoms from the surface of the conductive particles (a) can be promoted, and the conductivity can be further improved. Here, "salt concentration" refers to the total concentration of salts when two or more types of salts are contained.

The type and concentration of a salt whose anion has a conjugate acid pKa of 1.0 or less at 25° C. contained in an acidic aqueous solution can be analyzed by ion chromatography, inductively coupled plasma mass spectrometry, or the like.

The pH of the acidic aqueous solution at 25°C is 1.2 to 3.5. By setting the pH to 1.2 or more, it is possible to suppress a decrease in conductivity due to corrosion of the conductive particles (a) included in the conductive pattern. On the other hand, by adjusting the pH to 3.5 or less, diffusion of atoms from the surface of the conductive particles (a) can be promoted and conductivity can be improved. The pH is more preferably 2.5 or less. pH can be measured by the glass electrode method from the potential difference generated between two electrodes, a glass electrode and a reference electrode.

The acidic aqueous solution may contain an acid as a component other than the above salt so as to maintain a predetermined pH range. The acid preferably contains an acid having an acid dissociation constant (pKa) of 2 to 5 at 25°C, that is, a weak acid. When containing a polyhydric acid, it is preferable that the pKa of the first stage that is most easily ionized is 2 to 5, and when two or more types of acids are contained, the pKa of the acid that is most easily ionized is 2 to 5. It is preferable that it is 5. By using a weak acid with a pKa of 2 or more, long-term reliability due to the acid remaining in the conductive pattern can be improved. On the other hand, by setting the pKa to 5 or less, the conductivity can be further improved. The pKa is more preferably 3.5 or less.

Examples of acids having a pKa of 2 to 5 at 25°C include phosphoric acid, citric acid, acetic acid, propionic acid, ascorbic acid, formic acid, and lactic acid. pKa can be measured by analytically identifying an acid and using absorption spectrometry for that acid. Acid HX exists in both ^the HX and ^{X -} states in an aqueous solution, and the concentration of HX and It can be calculated based on 1).

The concentration of the acid having a pKa of 2 to 5 at 25° C. is preferably 0.05 to 1 mol/L. By setting the concentration to 0.05 mol/L, conductivity can be further improved in a short time. On the other hand, by setting the concentration to 1 mol/L or less, acid is less likely to remain in the wiring, and reliability can be improved. Note that the concentration can be adjusted as appropriate depending on the type of acid contained so as to achieve a desired pH.

In step (2), the temperature of the acidic aqueous solution brought into contact with the pattern is preferably 40°C to 90°C. By setting the liquid temperature to 40° C. or higher, conductivity can be improved in a shorter time. The liquid temperature is more preferably 60°C or higher. On the other hand, by controlling the liquid temperature to 90° C. or lower, evaporation of the acidic aqueous solution can be suppressed. Note that the temperature of the acidic aqueous solution can be adjusted as appropriate depending on the type of acid contained.

In step (2), the acidic aqueous solution may be heated in advance and brought into contact with the pattern, or may be heated while the pattern and the acidic aqueous solution are in contact with each other. Examples of the heating method include heating using a hot plate, hot air oven, inert oven, IR oven, microwave, and xenon flash lamp irradiation.

The concentration of the acidic aqueous solution is preferably 0.05 to 1 mol/L. By setting the concentration to 0.05 mol/L, conductivity can be further improved in a short time. On the other hand, by setting the concentration to 1 mol/L or less, acid is less likely to remain in the wiring, and reliability can be improved. Note that the concentration can be adjusted as appropriate depending on the type of acid contained so as to achieve a desired pH.

The conductive pattern obtained in step (2) may be rinsed with a rinsing liquid. Examples of the rinsing liquid include water or an aqueous solution prepared by adding an alcohol such as ethanol or isopropyl alcohol to water, or an ester such as ethyl lactate or propylene glycol monomethyl ether acetate. Rinsing can wash away residual acid and improve the long-term reliability of the wiring.

The present invention will be described in detail below with reference to Examples and Comparative Examples, but the embodiments of the present invention are not limited thereto.

The materials used in each example and comparative example are as follows.

[Conductive particles (a)]
Silver particles with a volume average particle diameter of 0.3 μm [Reactive monomer (c) having an unsaturated double bond]
Light acrylate BP-4EA (acrylic monomer; manufactured by Kyoeisha Chemical Co., Ltd.).

(Synthesis example 1)
Acrylic copolymer of EA/2-ethylhexyl methacrylate (hereinafter sometimes referred to as "2-EHMA")/styrene/acrylic acid (copolymerization ratio (parts by mass): 20/40/20/15) and 5 parts by mass of glycidyl methacrylate (hereinafter sometimes referred to as "GMA"). 150 g of DMEA (described below) was placed in a reaction vessel in a nitrogen atmosphere, and heated to 80°C using an oil bath. The temperature rose. To this, a mixture consisting of 20 g of EA, 40 g of 2-EHMA, 20 g of St, 15 g of AA, 0.8 g of 2,2'-azobisisobutyronitrile, and 10 g of DMEA was added dropwise over 1 hour. did. After the dropwise addition was completed, the polymerization reaction was further carried out for 6 hours. Thereafter, 1 g of hydroquinone monomethyl ether was added to stop the polymerization reaction. Subsequently, a mixture consisting of 5 g of GMA, 1 g of triethylbenzylammonium chloride and 10 g of DMEA was added dropwise over 0.5 hour. After the addition was completed, the addition reaction was further carried out for 2 hours. The resulting reaction solution was purified with methanol to remove unreacted impurities, and further vacuum-dried for 24 hours to obtain an acrylic copolymer (B-1). The acid value of the obtained acrylic copolymer (B-1) was 103 mgKOH/g.

(Synthesis example 2)
5 parts by mass of GMA was added to an acrylic copolymer of ethylene oxide-modified bisphenol A diacrylate (FA-324A; manufactured by Hitachi Chemical Co., Ltd.)/EA/AA (copolymerization ratio (parts by mass): 50/10/15). Addition reaction 150 g of DMEA was placed in a reaction vessel under nitrogen atmosphere, and the temperature was raised to 80° C. using an oil bath. To this, a mixture consisting of 50 g of ethylene oxide modified bisphenol A diacrylate FA-324A, 20 g of EA, 15 g of AA, 0.8 g of 2,2'-azobisisobutyronitrile and 10 g of DMEA was added for 1 hour. It dripped. After the dropwise addition was completed, the polymerization reaction was further carried out for 6 hours. Thereafter, 1 g of hydroquinone monomethyl ether was added to stop the polymerization reaction. Subsequently, a mixture consisting of 5 g of GMA, 1 g of triethylbenzylammonium chloride and 10 g of DMEA was added dropwise over 0.5 hour. After the addition was completed, the addition reaction was further carried out for 2 hours. The resulting reaction solution was purified with methanol to remove unreacted impurities, and further vacuum-dried for 24 hours to obtain an acrylic copolymer (B-2). The acid value of the obtained acrylic copolymer (B-2) was 96 mgKOH/g.

(Synthesis example 3)
Acrylic copolymer of EA/2-EHMA/BA/N-methylolacrylamide/AA (copolymerization ratio (parts by mass): 20/40/20/5/15)
150 g of DMEA was placed in a reaction vessel under nitrogen atmosphere, and the temperature was raised to 80° C. using an oil bath. To this is added a mixture consisting of 20 g of EA, 40 g of 2-EHMA, 20 g of BA, 5 g of N-methylolacrylamide, 15 g of AA, 0.8 g of 2,2'-azobisisobutyronitrile and 10 g of DMEA. was added dropwise over 1 hour. After the dropwise addition was completed, the polymerization reaction was further carried out for 6 hours. Thereafter, 1 g of hydroquinone monomethyl ether was added to stop the polymerization reaction. The resulting reaction solution was purified with methanol to remove unreacted impurities, and further vacuum-dried for 24 hours to obtain an acrylic copolymer (B-3). The acid value of the obtained acrylic copolymer (B-3) was 103 mgKOH/g.

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

[solvent]
DMEA (manufactured by Tokyo Chemical Industry Co., Ltd.)
Evaluation methods for each example and comparative example are shown below.

<Measurement of pKa>
The pKa of the acid was measured using a pKa analyzer (Sirius-T3; manufactured by Pion) by keeping an acidic aqueous solution containing the acids listed in Table 1 adjusted to 0.01 mol/L at a temperature of 25°C.

The pKa of the conjugate acid of the anion constituting the salt is determined by adjusting the acid consisting of an anion and proton constituting the salt to 0.01 mol/L, keeping the aqueous solution at a liquid temperature of 25°C, and using a pKa analyzer (Sirius-T3). ; manufactured by Pion). If the pKa of the conjugate acid of the anion constituting the salt is -2 or less, refer to "David A. Evans, [online], Internet <URL: http://evans.rc.fas.harvard.edu/pdf/evans_pKa_table. pdf>".

<Measurement of pH>
The pH of the acidic aqueous solution was measured by keeping the acidic aqueous solution listed in Table 1 at a temperature of 25° C. using a pH meter (F-71; manufactured by Horiba, Ltd.).

<Evaluation of patternability>
The patterning evaluation samples obtained in each Example and Comparative Example were observed with an optical microscope, and line and spaces (hereinafter referred to as "L/S") with no residue between patterns and no pattern peeling were observed. ) Check the conductive pattern with the minimum value of L/S, and select A if the L/S value is 7/7, B if it is 10/10, C if it is 15/15. A case where a conductive pattern could not be formed was determined as D. The patterning properties are excellent in the order of A>B>C>D, indicating that fine patterning is possible.

<Evaluation of conductivity>
The respective ends of the conductivity evaluation samples obtained in each example and comparative example were connected with a resistance meter (RM3544; manufactured by HIOKI) to measure the resistance value, and the results were compared based on the following formula (2). The resistivity was calculated. The film thickness was measured using a stylus-type step meter such as "Surfcom (registered trademark)" 1400 (manufactured by Tokyo Seimitsu Co., Ltd.). More specifically, the film thickness at 10 randomly selected positions is measured using a stylus stepmeter (length measurement: 1 mm, scanning speed: 0.3 mm/sec), and the average value thereof is determined. It was calculated by The line width was calculated by observing the line widths at 10 randomly selected positions using an optical microscope, analyzing the image data, and calculating the average value thereof.
Specific resistance = resistance value x film thickness x line width/line length... (2)
The smaller the specific resistance, the better the conductivity.

(Example 1)
Put 10.0g of acrylic copolymer (B-1), 2.0g of light acrylate BP-4EA, 0.60g of OXE01, and 9.0g of DMEA into a 100mL clean bottle, and add "Awatori Rentaro". (ARE-310; manufactured by Shinky Co., Ltd.) to obtain 21.6 g of a resin solution (total solid content: 58.3% by mass).

21.6 g of the obtained resin solution and 50.4 g of silver particles were mixed and kneaded using a three-roller mill (EXAKT M-50; manufactured by EXAKT) to obtain 72.0 g of conductive paste 1. .

Conductive paste 1 was applied onto a PET film with a thickness of 50 μm using a screen printing method so that the coating film thickness after drying was 1.5 μm, and the obtained coating film was dried in a drying oven at 80° C. for 15 minutes. . The following patterning properties and conductivity were evaluated.

Patterning properties A group of straight lines arranged at a constant L/S, that is, a transparent pattern, is used as one unit, and the dried coating film is exposed to light through a photomask each having three types of units with different L/S values. The film was developed and three types of patterns having different L/S values were obtained. After that, the three types of patterns obtained were immersed in the acidic aqueous solution listed in Table 1 for a predetermined time, rinsed with ultrapure water to remove the acid, drained with air cut, and dried in a drying oven at 80°C for 3 minutes. Three types of conductive patterns having different L/S values were obtained, and these were used as samples for patterning evaluation. The L/S values of each unit of the photomask were 15/15, 10/10, and 7/7 (each representing line width (μm)/interval (μm)). For exposure, full-line exposure was performed using an exposure device (PEM-6M; manufactured by Union Optical Co., Ltd.) at an exposure dose of 300 mJ/cm ² (converted to a wavelength of 365 nm), and for development, the substrate was placed in a 0.20% by mass Na ₂ CO ₃ solution. After immersing the sample for 30 seconds, the sample was rinsed with ultrapure water. Table 1 shows the evaluation results regarding patternability.

Conductivity The dried coating film was exposed and developed through a photomask having 100 transparent patterns 100 shown in FIG. 1 to obtain a pattern. After that, the obtained pattern was immersed in the acidic aqueous solution listed in Table 1 for the time listed in Table 1, the acid was washed away by rinsing with ultrapure water, the water was removed by air cutting, and the pattern was placed in a drying oven at 80°C for 3 minutes. It was dried to obtain a sample for conductivity evaluation. The line width of the obtained conductive pattern was 0.10 mm, and the line length was 80 mm. The conditions for exposure and development were the same as those described in the preparation of the patterning evaluation sample. Table 1 shows the evaluation results regarding conductivity.

(Examples 2 to 24, 26)
A predetermined pattern was formed using a conductive paste having the composition shown in Table 1, a conductive pattern was manufactured in the same manner as in Example 1 using the acidic aqueous solution shown in Table 1, and the same evaluation as in Example 1 was performed. Table 1 shows the evaluation results regarding patternability and conductivity.

(Example 25)
Put 12.0 g of acrylic copolymer (B-2), 0.60 g of OXE01, and 9.0 g of DMEA into a 100 mL clean bottle, and add "Awatori Rentaro"(ARE-310; manufactured by Shinky Co., Ltd.). 21.6 g of resin solution (total solids content: 58.3% by mass) was obtained.

21.6 g of the obtained resin solution and 50.4 g of silver particles were mixed and kneaded using a three-roller mill (EXAKT M-50; manufactured by EXAKT) to obtain 72.0 g of conductive paste 2. . A predetermined pattern was formed using conductive paste 2, and a conductive pattern was manufactured in the same manner as in Example 1 using the acidic aqueous solution shown in Table 1, and evaluated in the same manner as in Example 1. Table 1 shows the evaluation results regarding patternability and conductivity.

(Example 27)
A predetermined pattern is formed using the conductive paste having the composition shown in Table 1, and the resulting pattern is immersed in the acidic aqueous solution shown in Table 1 for the time shown in Table 1, and then dried in a drying oven at 100°C without washing. Cure for 10 minutes. Thereafter, the acid was washed away by rinsing with ultrapure water, the water was removed by air cutting, and the conductive pattern was dried in a drying oven at 80° C. for 3 minutes to produce a conductive pattern, which was evaluated in the same manner as in Example 1. Table 1 shows the evaluation results regarding patternability and conductivity.

(Example 28)
Put 10.0 g of acrylic copolymer (B-1) and 8.0 g of DMEA into a 100 mL clean bottle, mix with "Awatori Rentaro"(ARE-310; manufactured by Shinky Co., Ltd.), .0 g of resin solution (total solid content 55.6% by mass) was obtained.

18.0 g of the obtained resin solution and 90.0 g of silver particles were mixed and kneaded using a three-roller mill (EXAKT M-50; manufactured by EXAKT) to obtain 108.0 g of conductive paste 3. .

Three types of patterns having different L/S values were obtained by gravure printing the conductive paste 3 on a PET film having a thickness of 50 μm. The resulting pattern was dried in a drying oven at 80°C for 15 minutes. After that, the three types of patterns obtained were immersed in the acidic aqueous solution listed in Table 1 for a predetermined time, rinsed with ultrapure water to remove the acid, drained with air cut, and dried in a drying oven at 80°C for 3 minutes. Three types of conductive patterns having different L/S values were obtained, and these were used as samples for patterning evaluation. The L/S values of each unit of the intaglio plate used in gravure printing were 15/15, 10/10, and 7/7 (representing line width (μm)/interval (μm), respectively). Table 1 shows the evaluation results regarding patternability.

A pattern used for evaluating conductivity was obtained by gravure printing the conductive paste 3 on a 50 μm thick PET film. The intaglio plate used in gravure printing has 100 patterns 100 shown in FIG. The resulting pattern was dried in a drying oven at 80°C for 15 minutes. After that, the obtained pattern was immersed in the acidic aqueous solution listed in Table 1 for the time listed in Table 1, the acid was washed away by rinsing with ultrapure water, the water was removed by air cutting, and the pattern was placed in a drying oven at 80°C for 3 minutes. It was dried to obtain a sample for conductivity evaluation. The line width of the obtained conductive pattern was 0.10 mm, and the line length was 80 mm. Table 1 shows the evaluation results regarding conductivity.

(Comparative Examples 1, 2, 6-9)
A predetermined pattern was formed using a conductive paste having the composition shown in Table 2, and a conductive pattern was manufactured in the same manner as in Example 1 using the acidic aqueous solution shown in Table 2, and evaluated in the same manner as in Example 1. Table 2 shows the evaluation results regarding patternability and conductivity.

(Comparative example 3)
A predetermined pattern was formed using a conductive paste having the composition shown in Table 2, and the resulting pattern was immersed for 1 minute in a 0.2 mol/L hydrochloric acid aqueous solution at 25°C, followed by a 0.2 mol/L aqueous solution heated to 70°C. A conductive pattern was produced by immersing it in a citric acid aqueous solution of L for 5 minutes, rinsing with ultrapure water to remove the acid, removing the water with an air cut, and drying it in a drying oven at 80°C for 3 minutes. I gave a similar evaluation. Table 2 shows the evaluation results regarding patternability and conductivity.

(Comparative example 4)
A predetermined pattern was formed using a conductive paste having the composition shown in Table 2, and the resulting pattern was immersed for 1 minute in a 0.2 mol/L hydrochloric acid aqueous solution at 25°C, followed by a 0.2 mol/L aqueous solution heated to 70°C. A conductive pattern was produced by immersing it in a citric acid aqueous solution of L for 10 minutes, rinsing with ultrapure water to remove the acid, removing the water with an air cut, and drying it in a drying oven at 80°C for 3 minutes. I gave a similar evaluation. Table 2 shows the evaluation results regarding patternability and conductivity.

(Comparative example 5)
A predetermined pattern was formed using a conductive paste having the composition shown in Table 2, and the resulting pattern was immersed in a 1 mol/L hydrochloric acid aqueous solution at 25°C for 1 minute, followed by 1 mol/L citric acid heated to 70°C. A conductive pattern was produced by immersing it in an aqueous solution for 10 minutes, rinsing with ultrapure water to remove the acid, removing the water with an air cut, and drying it in a drying oven at 80°C for 3 minutes.The same evaluation as in Example 1 was conducted. did. Table 2 shows the evaluation results regarding patternability and conductivity.

(Comparative example 10)
Example 1 A predetermined pattern was formed using a conductive paste having the composition shown in Table 2, and the resulting pattern was cured in a drying oven at 100° C. for 1 hour without immersion in an acidic aqueous solution to produce a conductive pattern. gave the same evaluation. Table 2 shows the evaluation results regarding patternability and conductivity.

100 Translucent pattern

Claims (7)

(1) forming a pattern containing conductive particles (a) and resin (b) on a base material;
(2) The formed pattern contains at least one salt whose acid dissociation constant (pKa) of the conjugate acid of the anion is 1.0 or less at 25°C, and the pH at 25°C is 1.2 to 3.5. and a step of contacting with a certain acidic aqueous solution ,
The step of forming the pattern in (1) above includes the step of forming a conductive particle (a), a resin containing a carboxyl group (B), a reactive monomer having an unsaturated double bond (c), and photopolymerization on a base material. A method for producing a conductive pattern, which is a photolithography process in which a coating film is formed by applying a photosensitive paste containing an initiator (d), and a pattern is formed by exposing and developing the coating film. The method for manufacturing a conductive pattern according to claim 1, wherein the concentration of the salt contained in the acidic aqueous solution is 0.05 mol/L or more. The method for producing a conductive pattern according to claim 1 or 2, wherein the acidic aqueous solution contains an acid other than the salt, and the acid has a pKa of 2 to 5. The method for manufacturing a conductive pattern according to any one of claims 1 to 3, wherein the acidic aqueous solution has a liquid temperature of 40°C to 90°C. The method for manufacturing a conductive pattern according to any one of claims 1 to 4, wherein heating is performed while the pattern and the acidic aqueous solution are in contact with each other. The method for producing a conductive pattern according to any one of claims 1 to 5 , wherein the conductive particles (a) contain silver particles. The method for manufacturing a conductive pattern according to any one of claims 1 to 6 , wherein the conductive pattern has a thickness of 3 μm or less.

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