Carbon ink, electronic component, and method for producing the same

Abstract

To provide a carbon ink that enables formation of fine conductive wiring having excellent bending durability by screen printing, and to provide an electronic component and a method for producing the electronic component.SOLUTION: A carbon ink contains graphite and carbon black, ethylene glycol, a first polyvinylpyrrolidone, and a second polyvinylpyrrolidone, wherein the first and second polyvinylpyrrolidones differ from each other in molecular structure, the first polyvinylpyrrolidone has, in its molecular structure, only repeating units derived from vinylpyrrolidone, the second polyvinylpyrrolidone has, in its molecular structure, repeating units derived from vinylpyrrolidone and repeating units derived from components other than vinylpyrrolidone, hydrogen atoms possessed by the repeating units derived from vinylpyrrolidone in the molecular structure are not substituted with alkyl groups, and both the first and second polyvinylpyrrolidones are dissolved in the ethylene glycol.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a carbon ink, an electronic component, and a method for manufacturing the same. [Background technology]

[0002] Conventionally, conductive pastes in which conductive particles such as metal or carbon are dispersed in a dispersant have been used in a wide variety of applications, such as the formation of electrodes and electronic circuits, through-hole connections in printed wiring boards, crossovers in printed wiring, mounting of semiconductor elements, and adhesion of heat dissipation members such as heat sinks. For example, wiring and electrodes can be formed by applying or printing the conductive paste onto various substrates to form a conductive coating film, which is then heated, dried, and cured.

[0003] Patent Document 1 discloses a conductive paste containing metal particles, a fatty acid ester as a lubricant, and a thermosetting resin such as an epoxy resin or an acrylic resin. It claims that by pulverizing the metal particles to improve their dispersibility and adding a lubricant to prevent the metal particles from agglomerating, wiring and the like with excellent conductivity can be formed.

[0004] Patent Document 2 discloses a method for forming a conductive circuit using a conductive paste containing coated metal particles, in which the surfaces of metal core particles are coated with carbon, a binder resin, and an organic solvent. Because the metal core particles are coated with carbon, it is said that oxidation of the metal is suppressed and migration of the metal components can be prevented. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-265802 [Patent Document 2] Japanese Patent Application Publication No. 2018-022755 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when metal particles are used as the main conductor as disclosed in Patent Document 1, there are concerns that oxidation of the metal particles may occur, reducing conductivity, or that migration of the metal components may occur, causing short circuits between wirings. Also, there is a concern that coating metal core particles with carbon as disclosed in Patent Document 2 may increase costs and be unacceptable to users.

[0007] Furthermore, sensor modules using conductive pastes often require densely packed, thin wires to be connected to PCBs, and may even be bent when used. These thin wires must be conductive and resistant to bending, and a carbon ink with excellent printability is required to achieve these at a high level.

[0008] The present invention provides a carbon ink that can be used to form thin conductive wiring with excellent bending resistance by screen printing, an electronic component that uses the carbon ink, and a method for manufacturing the electronic component. [Means for solving the problem]

[0009] [1] A carbon ink comprising graphite and carbon black, ethylene glycol, a first polyvinylpyrrolidone, and a second polyvinylpyrrolidone, wherein the first and second polyvinylpyrrolidones have different molecular structures, the first polyvinylpyrrolidone has only repeating units derived from vinylpyrrolidone in its molecular structure, the second polyvinylpyrrolidone has repeating units derived from vinylpyrrolidone and repeating units derived from a compound other than vinylpyrrolidone in its molecular structure, and hydrogen atoms of the repeating units derived from vinylpyrrolidone in its molecular structure are not substituted with alkyl groups, and both the first and second polyvinylpyrrolidones are dissolved in the ethylene glycol. [2] The carbon ink according to [1], wherein the second polyvinylpyrrolidone has a repeating unit derived from vinyl acetate. [3] The carbon ink described in [1], wherein the second polyvinylpyrrolidone is a graft copolymer having repeating units derived from vinyl alcohol, the repeating units derived from vinyl alcohol forming a polyvinyl alcohol chain, the repeating units derived from vinylpyrrolidone forming a polyvinylpyrrolidone chain, and the polyvinylpyrrolidone chain being grafted onto the polyvinyl alcohol chain. [4] The carbon ink according to any one of [1] to [3], further comprising a thermally reactive water-based urethane resin having a blocked isocyanate group and a urethane skeleton. [5] A carbon ink according to any one of [1] to [4], further comprising a third polyvinylpyrrolidone having a molecular structure different from the first and second polyvinylpyrrolidones, the third polyvinylpyrrolidone including a repeating unit derived from vinylpyrrolidone in its molecular structure, and at least a portion of the hydrogen atoms of the repeating unit derived from vinylpyrrolidone being substituted with an alkyl group. [6] The carbon ink according to any one of [1] to [5], wherein the total content of the graphite and the carbon black relative to the total mass of the non-volatile components of the carbon ink is 40 to 80 mass%, the total content of the first polyvinylpyrrolidone, the second polyvinylpyrrolidone, and the third polyvinylpyrrolidone is 30 to 100 mass parts, and the content of the ethylene glycol is 100 to 240 mass parts, relative to 100 mass parts of the total content of the graphite and the carbon black. [7] The carbon ink according to any one of [1] to [6], wherein the content of the second polyvinylpyrrolidone is 1 to 90 parts by mass per 100 parts by mass of the first polyvinylpyrrolidone. [8] The carbon ink according to [5], wherein the content of the third polyvinylpyrrolidone is 30 to 100 parts by mass per 100 parts by mass of the first polyvinylpyrrolidone. [9] A method for manufacturing an electronic component, comprising a step of forming one or more conductive wirings made of a cured product of the carbon ink described in any one of [1] to [8] on a substrate by screen printing, wherein the conductive wirings form a line-and-space conductive pattern arranged parallel to each other on the substrate, and at least one conductive wiring constituting the conductive pattern has a line width of 0.30 mm or less, and at least one space constituting the conductive pattern has a width of 0.30 mm or less.

[10] An electronic component comprising a substrate and a conductive layer formed on the substrate, wherein the conductive layer is formed from a cured product of the carbon ink according to any one of [1] to [8]. [Effects of the Invention]

[0010] The carbon ink of the present invention can be used in the same way as conventional conductive pastes, and can form conductive wiring and the like that exhibits good conductivity even without containing metal particles. Furthermore, high-resolution conductive patterns (e.g., L / S patterns) can be formed by screen printing. Furthermore, because carbon particles also have excellent weather resistance and chemical resistance, conductive wiring and the like formed using the carbon ink of the present invention have excellent weather resistance and chemical resistance. Furthermore, conductive wiring and the like formed using the carbon ink of the present invention also have excellent bending resistance. According to the method for producing an electronic component of the present invention, an electronic component having a high-definition L / S pattern with excellent bending resistance can be easily produced by screen-printing a carbon ink onto a substrate.

[0011] This invention is believed to contribute to SDG Goal 12, "Responsible Consumption and Production." [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a photograph showing an example of an L / S pattern printed in an example. DETAILED DESCRIPTION OF THE INVENTION

[0013] Carbon ink A first aspect of the present invention is a carbon ink comprising one or more carbon particles, polyvinylpyrrolidone (PVP), and a solvent. A preferred embodiment is a carbon ink comprising graphite and carbon black, ethylene glycol, a first polyvinylpyrrolidone, and a second polyvinylpyrrolidone.

[0014] [carbon particles] The carbon particles contained in the carbon ink of this embodiment are particles made of a carbon material in which at least the center of the particle is formed by bonding between carbon atoms. Any functional group may be added to the surface or a portion of the carbon particles. Furthermore, any surface or portion of the carbon particles may be treated by any chemical modification. The carbon content relative to the total mass of the carbon particles is preferably 90 to 100 mass%, more preferably 95 to 100 mass%, and even more preferably 99 to 100 mass%. In general, a material made only of carbon (containing substantially no impurities) is called a carbon material. The carbon particles contained in this embodiment are preferably a carbon material.

[0015] Suitable carbon particles in this embodiment include, for example, graphite, carbon black, fullerene, carbon nanotube, graphene, etc. Among these, it is preferable to include at least graphite and carbon black. Graphite and carbon black have stable quality, and particle size, particle aggregation state, surface properties (functional groups), etc. can be relatively easily controlled.

[0016] The graphite may be either artificial graphite or natural graphite. Examples of natural graphite include flake graphite, lump graphite, and amorphous graphite. The particle size of the graphite is, for example, about 1 μm to 900 μm. From the viewpoint of enabling high-resolution printing using the carbon ink of this embodiment, the average particle size of the graphite is preferably 5 to 30 μm, more preferably 6 to 15 μm, and even more preferably 7 to 9 μm. Here, the average particle size of the graphite is the volume-based median diameter (D50) of equivalent-sphere diameters measured by laser diffraction.

[0017] Carbon black is distinguished from graphite in that it does not have the large crystal structure that graphite generally has. Examples of carbon black include furnace black, channel black, acetylene black, thermal black, and hollow-shell ketjenblack. The primary particle diameter of carbon black is, for example, approximately 1 nm to 500 nm. Carbon black particles typically aggregate together. From the viewpoint of enabling high-resolution printing using the carbon ink of this embodiment, the average primary particle diameter of carbon black is preferably 5 to 200 nm, more preferably 10 to 100 nm, and more preferably 20 to 50 nm. Here, the average primary particle diameter of carbon black is determined by observing dried carbon black under an electron microscope, measuring the longest diameter of randomly selected primary particles as the particle diameter, and calculating the arithmetic mean value of the measured values ​​of 100 primary particles.

[0018] In the carbon ink of this embodiment, the content of the solvent relative to 100 parts by mass of the total content of the carbon particles is, for example, preferably 100 to 500 parts by mass, more preferably 125 to 300 parts by mass, and even more preferably 150 to 240 parts by mass. When the amount is equal to or greater than the lower limit of the above range, smearing when printing the carbon ink of this embodiment can be suppressed, and the conductivity of the conductive wiring formed from the carbon ink coating can be increased. When the content is equal to or less than the upper limit of the above range, the carbon ink of this embodiment can be printed with high precision, and a conductive pattern with a narrow line width and a narrow pitch can be easily formed.

[0019] The total content of the carbon particles relative to the total mass of the non-volatile components (solid content) of the carbon ink of this embodiment is, for example, preferably 40 to 80 mass %, more preferably 50 to 75 mass %, and even more preferably 60 to 72 mass %. When the amount is equal to or greater than the lower limit of the above range, smearing when printing the carbon ink of this embodiment can be suppressed, and the conductivity of the conductive wiring formed from the carbon ink coating can be increased. When the content is equal to or less than the upper limit of the above range, the carbon ink of this embodiment can be printed with high precision, and a conductive pattern with a narrow line width and a narrow pitch can be easily formed. The solvent such as ethylene glycol is a volatile component.

[0020] In the carbon ink of this embodiment, the graphite content is preferably greater than the carbon black content, and from the viewpoint of easily realizing this relationship, the carbon black is preferably Ketjen black.

[0021] In the carbon ink of this embodiment, the mass content ratio expressed as (graphite content / carbon black content) is preferably 2.0 to 5.0, more preferably 2.5 to 4.0, and even more preferably 3.0 to 3.6. When the amount is equal to or greater than the lower limit of the above range, smearing when printing the carbon ink of this embodiment can be suppressed, and the conductivity of the conductive wiring formed from the carbon ink coating can be increased. When the content is equal to or less than the upper limit of the above range, the carbon ink of this embodiment can be printed with high precision, and a conductive pattern with a narrow line width and a narrow pitch can be easily formed.

[0022] [solvent] The solvent (solvent) used in this embodiment is preferably one that has excellent compatibility with PVP. For example, an organic solvent that can dissolve PVP at a concentration of 10% by mass or more at 20 to 25° C. is preferred. Examples of such organic solvents include methanol, ethanol, propanol, isopropanol, butanol, secondary butanol, amyl alcohol, 2-ethylhexanol, cyclohexanol, phenol, ethylene glycol, 1,3-butanediol, 1,4-butanediol, glycerin, diacetone alcohol, formic acid, acetic acid, propionic acid, glycol ether, diethylene glycol, triethylene glycol, hexamethylene glycol, polyethylene glycol 400, 2,2-thiodiethanol, γ-butyrolactone, and the like. Examples of suitable solvents include methyl cyclohexanone, ethyl lactate, methylcyclohexanone, dichloromethane, dichloroethane, chloroform, 2-pyrrolidone, N-methyl-2-pyrrolidone (NMP), N-vinyl-2-pyrrolidone, butylamine, cyclohexylamine, aniline, ethylenediamine, pyridine, morpholine, 2-aminoethanol, diethanolamine, triethanolamine, aminoethylethanolamine, 2-hydroxyethylmorpholine, 2-amino-2-methyl-1-propanol, nitromethane, nitroethane, and dimethyl sulfoxide. Water may also be contained as a solvent. The solvent used in this embodiment may be a single type or a mixture of two or more types.

[0023] Among the above solvents, ethylene glycol is particularly preferred. Ethylene glycol can dissolve the first PVP and the second PVP well. Furthermore, when mixed with these PVPs, ethylene glycol gels, imparting viscosity to the carbon ink of this embodiment, making it gel-like. As a result, the coating and printing properties of the carbon ink of this embodiment are improved, blurring is suppressed, and a narrow-linewidth, narrow-pitch conductive pattern can be easily formed.

[0024] The content of the solvent relative to the total mass of the carbon ink of this embodiment is, for example, preferably 30 to 70 mass %, more preferably 35 to 60 mass %, and even more preferably 40 to 55 mass %. When the amount is equal to or greater than the lower limit of the above range, smearing when printing the carbon ink of this embodiment can be suppressed, and the conductivity of the conductive wiring formed from the carbon ink coating can be increased. When the content is equal to or less than the upper limit of the above range, the carbon ink of this embodiment can be printed with high precision, and a conductive pattern with a narrow line width and a narrow pitch can be easily formed.

[0025] [PVP] The carbon ink of this aspect contains at least two types of polyvinylpyrrolidone (PVP) having different molecular structures. A first embodiment of this aspect includes a carbon ink containing a first PVP and a second PVP.

[0026] (First PVP) The first PVP is a so-called general PVP having only repeating units derived from vinylpyrrolidone in its molecular structure. The molecular weight of the first PVP is preferably 500,000 to 6,000,000, more preferably 1,000,000 to 5,000,000, further preferably 1,500,000 to 4,500,000, and most preferably 3,000,000 to 4,000,000. Within the above range, the carbon particles can be sufficiently dispersed together with the second PVP, and the fine line printability and bending resistance can be further improved.

[0027] The molecular weight of the first PVP is preferably an absolute molecular weight measured by gel permeation chromatography (GPC) equipped with a multi-angle light scattering detector (MALLS), but may also be a weight-average molecular weight or number-average molecular weight measured by GPC using a calibration curve of standard samples of known molecular weight.

[0028] The K value of the first PVP is preferably 90 or more, more preferably 100 or more, even more preferably 110 or more, and most preferably 120 or more. The upper limit of the K value of the first PVP is preferably 150 or less. Within the above preferred range, even if a relatively small amount is blended, the carbon ink of this embodiment can be printed with high resolution, and a conductive pattern with a narrow line width and a narrow pitch can be easily formed. The K value is generally known as a viscosity characteristic value correlated with molecular weight, and is calculated by applying the relative viscosity value (25°C) to water measured with a capillary viscometer to the Fikentscher formula. The formula and measurement method are specified in ISO 1628-1:1998(E).

[0029] The glass transition point (Tg) of the first PVP is preferably from 160 to 190°C, more preferably from 165 to 185°C, and even more preferably from 170 to 180°C. The Tg of PVP is a value measured by the method of JIS K 7121. Within the above range, the carbon particles can be sufficiently dispersed together with the second PVP, and the fine line printability and bending resistance can be further improved.

[0030] (2nd PVP) The second PVP has, in its molecular structure, repeating units derived from vinylpyrrolidone and repeating units derived from a compound other than vinylpyrrolidone, and the hydrogen atoms of the repeating units derived from vinylpyrrolidone in the molecular structure are not substituted with alkyl groups.

[0031] A preferred example of the second PVP is a copolymer PVP having repeating units derived from vinyl acetate (VA) in addition to vinylpyrrolidone (VP) in its molecular structure, where the molar ratio of VP / VA is preferably from 50 / 50 to 90 / 10, more preferably from 60 / 40 to 80 / 20, and even more preferably from 65 / 35 to 75 / 25. When the amount is equal to or greater than the lower limit of the above range, smearing when printing the carbon ink of this embodiment can be suppressed, and the conductivity of the conductive wiring formed from the carbon ink coating can be increased. When the content is equal to or less than the upper limit of the above range, the carbon ink of this embodiment can be printed with high resolution, and a conductive pattern with high bending resistance and a narrow line width and narrow pitch can be easily formed.

[0032] The preferred molecular weight of the copolymer type PVP is 29,000 to 57,000.

[0033] The copolymer PVP can be obtained by polymerizing a reaction mixture of VP and VA in a predetermined ratio. The mixing ratio of each monomer is reflected in the ratio of repeating units derived from each monomer in the copolymer. Specific examples include commercially available products from Ashland.

[0034] Another preferred example of the second PVP is a graft copolymer having repeating units derived from vinyl alcohol in its molecular structure, the repeating units derived from vinyl alcohol forming polyvinyl alcohol chains, the repeating units derived from vinylpyrrolidone forming polyvinylpyrrolidone chains, and one or more polyvinylpyrrolidone chains grafted onto the polyvinyl alcohol chains.

[0035] In the above graft copolymer, the mass ratio of PVA / PVP is preferably (40 / 60) to (60 / 40). The degree of polymerization of the backbone PVA is preferably 1000 to 2500, more preferably 1300 to 2200, and even more preferably 1500 to 1900. The saponification degree of the backbone PVA is preferably 90 mol% or more, more preferably 95 mol% or more, and even more preferably 98 mol% or more. The number-average molecular weight Mn of the branch PVP is preferably 8,000 to 20,000, more preferably 10,000 to 17,000, and even more preferably 12,000 to 14,000. The weight-average molecular weight Mw of the branch PVP is preferably 50,000 to 120,000, preferably 60,000 to 100,000, and even more preferably 70,000 to 90,000. When the amount is equal to or greater than the lower limit of each of the above ranges, fading when printing the carbon ink of this embodiment can be suppressed, and the conductivity of the conductive wiring formed from the carbon ink coating can be increased. When the content is equal to or less than the upper limit of each of the above ranges, the carbon ink of this embodiment can be printed with high resolution, and a conductive pattern with high bending resistance, narrow line width, and narrow pitch can be easily formed.

[0036] The above graft copolymer can be purchased as a commercially available product, for example, Pitzcol V-7154 manufactured by Daiichi Kogyo Seiyaku Co., Ltd.

[0037] (3rd PVP) The carbon ink of this embodiment may further contain a third polyvinylpyrrolidone having a molecular structure different from the first and second polyvinylpyrrolidones. By including the third PVP, it becomes easier to form finer, higher density conductive wiring.

[0038] A preferred example of the third PVP is one that contains repeating units derived from vinylpyrrolidone in its molecular structure, and at least a portion of the hydrogen atoms of the repeating units derived from vinylpyrrolidone are substituted with alkyl groups (alkylated PVP).

[0039] The alkylated PVP is preferably a copolymer-type PVP having repeating units derived from an α-olefin having 3 to 6 carbon atoms. This copolymer-type PVP can be obtained, for example, by polymerizing a reaction solution in which vinylpyrrolidone and an α-olefin are mixed in a predetermined ratio. The mixing ratio of each monomer is reflected in the ratio of repeating units derived from each monomer in the copolymer. The content of repeating units derived from vinylpyrrolidone relative to the total mass of the copolymer-type alkylated PVP is preferably 50 to 99 mass%, more preferably 70 to 98 mass%, and even more preferably 85 to 95 mass%. Here, the remainder other than the repeating units derived from vinylpyrrolidone is the content of structural units derived from the α-olefin.

[0040] In the alkylated PVP as the third PVP, at least a portion of the hydrogen atoms of the repeating units derived from vinylpyrrolidone are substituted with alkyl groups. The alkyl groups are preferably linear or branched alkyl groups having 1 to 6 carbon atoms, more preferably linear alkyl groups having 1 to 3 carbon atoms. The positions of the substituted hydrogen atoms are not particularly limited as long as they are permitted by the chemical configuration, and may be hydrogen atoms bonded to one or more carbon atoms constituting the main chain formed by polymerization of vinyl groups, or hydrogen atoms bonded to one or more carbon atoms (e.g., 2- and 5-positions) constituting a 5-membered cyclic lactam.

[0041] The molecular weight of the third PVP is, for example, preferably 5,000 to 50,000, more preferably 8,000 to 30,000, and even more preferably 10,000 to 25,000.

[0042] The glass transition point (Tg) of the third PVP is preferably from 130 to 170°C, more preferably from 140 to 165°C, and even more preferably from 150 to 160°C.

[0043] (PVP content) The content of the first PVP relative to the total mass of the carbon ink of this embodiment is preferably 3.5 to 8.0 mass %, more preferably 4.0 to 7.5 mass %, and even more preferably 4.5 to 7.0 mass %. The total content of the first and second PVPs and the optional third PVP relative to the total mass of the carbon ink of this embodiment is preferably 4.5 to 20.0 mass%, more preferably 5.0 to 17.0 mass%, and even more preferably 5.5 to 14.0 mass%.

[0044] The content of the second PVP relative to 100 parts by mass of the first PVP contained in the carbon ink of this embodiment is preferably 1.0 to 90.0 parts by mass, more preferably 3.0 to 20.0 parts by mass, and even more preferably 3.5 to 16.0 parts by mass. The content of the third PVP relative to 100 parts by mass of the first PVP contained in the carbon ink of this embodiment is preferably 30.0 to 100.0 parts by mass, more preferably 35.0 to 90.0 parts by mass, and even more preferably 38.0 to 85.0 parts by mass.

[0045] The total content of the first and second PVPs and the optional third PVP relative to 100 parts by mass of the graphite and carbon black contained in the carbon ink of this embodiment is preferably 20.0 to 60.0 parts by mass, more preferably 22.0 to 50.0 parts by mass, and even more preferably 24.0 to 45.0 parts by mass.

[0046] When the PVP content is within the preferred ranges shown above, smearing when printing the carbon ink of this embodiment is suppressed, the conductivity of the conductive wiring formed from the carbon ink coating is increased, and the carbon ink of this embodiment can be printed with high resolution, making it easy to form a conductive pattern with high bending resistance and a narrow line width and narrow pitch.

[0047] [Urethane resin] The carbon ink of this embodiment preferably further contains a thermally reactive waterborne urethane resin having a blocked isocyanate group and a urethane skeleton. The inclusion of a thermally reactive waterborne urethane resin can further improve the bending resistance of the conductive wiring. In particular, when the second PVP contains a PVP containing a repeating unit having a hydroxyl group that may form a salt, the PVP reacts with the unblocked isocyanate group of the urethane resin to form crosslinks, thereby significantly improving the strength of the conductive wiring. As such a PVP, one having a repeating unit derived from the aforementioned vinyl alcohol is preferred.

[0048] The above-mentioned blocked isocyanate group generally refers to an isocyanate group masked with a protecting group or a blocking agent. The mask is dissociated by heating or other predetermined treatment to form the isocyanate group. Thermally reactive water-based urethane resins are commercially available, such as the Elastron (registered trademark) series manufactured by Daiichi Kogyo Seiyaku Co., Ltd. and Takenate (registered trademark) manufactured by Mitsui Chemicals, Inc.

[0049] The content of the thermally reactive water-based urethane resin relative to 100 parts by mass of the second PVP contained in the carbon ink of this embodiment is preferably 200 to 1800 parts by mass, more preferably 400 to 1400 parts by mass, and even more preferably 600 to 1000 parts by mass. When the thickness is equal to or greater than the lower limit of the above range, the bending resistance of the conductive wiring can be further improved, and when the thickness is equal to or less than the upper limit of the above range, the conductive wiring can be formed with higher definition.

[0050] <Electronic component manufacturing method> A second aspect of the present invention is a method for producing an electronic component, comprising a step of forming one or more conductive wirings made of a cured product of the carbon ink of the first aspect on a substrate by screen printing (stencil printing).

[0051] The substrate used in this embodiment is not particularly limited, and examples thereof include substrates for electronic components, films, etc. Materials constituting the substrate include polyester resins such as polyethylene terephthalate, polylactic acid, and polyethylene naphthalate, polyolefin resins such as polyethylene, polypropylene, polystyrene, ethylene vinyl acetate, and cyclic olefin copolymers, vinyl resins, polycarbonate, polyamide, polyimide, acrylic resins, cellulose resins, polyurethane, silicone rubber, polyvinyl chloride, and synthetic resins such as polyvinyl fluoride. Other materials that may be used include paper, cloth, glass, and ceramics.

[0052] Conventional methods can be applied to the screen printing performed in this embodiment. For example, a printing plate is prepared by placing a printing film on a screen with appropriate openings, blocking the openings except for the image lines to be printed, placing carbon ink on the plate, and then moving the carbon ink over the plate while applying pressure with a rubber spatula called a squeegee. This allows the carbon ink to pass through the open parts of the screen and be pushed out onto the surface of the substrate placed below the plate, thereby enabling printing.

[0053] The mesh size of a screen used in screen printing is expressed as (mesh pitch) - (wire diameter). Generally, narrower mesh sizes enable higher-resolution printing, but the requirements for the ink become stricter. The carbon ink used in this embodiment uses PVP and a solvent to highly disperse carbon particles, so a screen with narrower mesh sizes can be used. The mesh size for screen printing in this embodiment can be 100 μm or less, and can also be 50 μm or less, with 20 to 40 μm being preferred.

[0054] By screen printing in this embodiment, it is possible to form a line and space conductive pattern (L / S pattern) on a substrate in which one or more conductive wires are arranged parallel to one another. In this case, the line width of at least one location of the conductive wiring constituting the L / S pattern can be 0.30 mm or less, and the space width of at least one location of the L / S pattern can be 0.30 mm or less. Even more precisely, the line width of at least one location of the conductive wiring constituting the L / S pattern can be 0.20 mm or 0.15 mm or less, and the space width of at least one location of the L / S pattern can be 0.20 mm or 0.15 mm or less. Here, the lower limits of the line width and space width are not particularly limited, and a guideline is, for example, 0.05 mm.

[0055] In the L / S pattern, the location where the line width is in the above range and the location where the space width is in the above range may be the same location or different locations. For example, the space width at the location where the first conductive wiring and the second conductive wiring are adjacent to each other may be in the above range, and the line width of at least one of the first conductive wiring and the second conductive wiring at the location where the space width is measured may also be in the above range.

[0056] Note that multiple conductive wires making up an L / S pattern may be connected to a common terminal, or a single conductive wire may be folded back to form an L / S pattern.However, a good product is based on the assumption that the L / S pattern does not have any broken or faint wires where lines should be connected, or that conductive wires where spaces should be separated are not short-circuited due to wire thickening.

[0057] The surface resistivity per unit area of ​​the conductive wiring made of the cured product of the carbon ink of the first embodiment can be, for example, 10 to 100 MΩ when the line width is, for example, 0.90 to 1.10 mm.

[0058] <Electronic Components> A third aspect of the present invention is an electronic component comprising a substrate and a conductive layer formed on the substrate, the conductive layer being formed from a cured product of the carbon ink of the first aspect. The electronic component of the third aspect can be manufactured by the manufacturing method of the second aspect of the present invention, but the electronic component of the third aspect may also be manufactured by another method. The explanation of the substrate is the same as that of the substrate of the second embodiment, so a duplicate explanation will be omitted. The conductive layer may be formed on the entire surface of the substrate or on a part of the surface. When a conductive layer is formed on only a portion of the surface of a substrate, for example, the conductive layer may be a fine conductive pattern including conductive wiring, conductive circuits, electrodes, etc., or may be a roughly divided surface with areas where the conductive layer is provided and areas where it is not provided. The conductive layer may form an L / S pattern on the substrate. The conductive layer may be laminated on any other conductive layer, or may be an independent conductive layer on an insulating substrate without being laminated on another conductive layer.

[0059] The average thickness of the conductive layer is, for example, preferably 10 nm or more and 100 μm or less, more preferably 20 nm or more and 50 μm or less, and even more preferably 30 nm or more and 30 μm or less. When the average thickness of the conductive layer is equal to or greater than the lower limit, high conductivity can be exhibited, and when the average thickness is equal to or less than the upper limit, the adhesiveness of the conductive layer to the substrate is further improved. The average thickness of the conductive layer is determined by measuring the thickness at 10 randomly selected locations and averaging the measured values.

[0060] The electronic component of this embodiment can be used to form a variety of electronic devices, and is suitable for, for example, electrostatic capacitance type touch sensors, touch switches, touch pads, pressure sensitive switches, conductive contacts of push buttons, and the like. [Example]

[0061] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0062] <Preparation of carbon ink> The carbon inks of the respective examples were obtained by mixing the materials according to the formulations shown in Table 1. The numerical values ​​in the table showing the blend amounts are in grams (g).

[0063] [Table 1]

[0064] Details of each material listed in the table are as follows: First PVP: K-120; manufactured by Ashland Corporation, unmodified PVP having only repeating units derived from vinylpyrrolidone, K value of 1% viscosity solution = 114 to 130, absolute molecular weight measured by GPC / MALS: 3,470,000, Tg: 176°C First PVP: K-90; manufactured by Ashland Corporation, unmodified PVP having only repeating units derived from vinylpyrrolidone, K value of 1% viscosity solution = 88 to 100, absolute molecular weight measured by GPC / MALS: 1,570,000, Tg: 174°C Graphite CSP-E: Nippon Graphite Co., Ltd., graphite powder (shape: scaly, average particle size = 8 μm) Carbon ECP: Lion Specialty Chemicals, Ketjen Black, average primary particle size 30 nm · Catalyst DBTDL; Dibutyltin dilaurate · Second PVP: PVP / VA E-735; manufactured by Ashland, vinyl pyrrolidone / vinyl acetate copolymer solution, molar ratio of vinyl pyrrolidone / vinyl acetate = 70 / 30 · Second PVP: Pitts Cole V-7154; manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., water-soluble polymer (PVA-PVP graft copolymer) obtained by grafting polyvinyl pyrrolidone onto polyvinyl alcohol · Urethane resin; Elastron H-15; manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., heat-reactive aqueous urethane resin having a blocked isocyanate group and a urethane skeleton (non-volatile content: 27.0 to 29.0% by mass) · Urethane resin; Takenate WB-3936; manufactured by Mitsui Chemicals, Inc., polyurethane resin having a blocked isocyanate group (non-volatile content: 40% by mass) · Third PVP: P-904LC; manufactured by Ashland, copolymer consisting of 90% repeating units derived from vinyl pyrrolidone and 10% repeating units derived from 1-butene, and at least a part of the hydrogen atoms of the repeating units derived from vinyl pyrrolidone are substituted by an alkyl group, alkylated polyvinyl pyrrolidone, Tg: 155°C, water-soluble

[0065] <Formation of L / S pattern> A plate film with an L / S pattern was set on a screen with a mesh size of 35 μm, and the carbon ink prepared above was screen-printed onto a polyester film (manufactured by Toyobo Co., Ltd., A4360) as a substrate using a screen printing machine. This was dried and cured at 150°C for 30 minutes to form an L / S pattern on the substrate.

[0066] The pitch of the L / S pattern of the printing plate used in Example 1 is shown in Table 2. Here, the pitch is the sum of the line width (conductive wiring width):space width = 1:1. In other words, a pitch of 2.0 mm indicates printing using a printing plate with a line width of 1.0 mm and a space width of 1.0 mm. The printed L / S pattern is connected in one stroke and folded back at a specified length. An example is shown in Figure 1. In the figure, the terminals of a resistance meter (manufactured by ADVANTEST, model number: R6551) were connected to both ends (round terminals) to measure the electrical resistance (unit: kΩ), volume resistivity (unit: Ω·cm), and surface resistivity per unit area (unit: Ω / □) using the two-terminal method. In addition, the line width (line width) of three representative locations on the L / S pattern was measured using a digital microscope. The average values ​​are shown in Table 2.

[0067] [Table 2]

[0068] An L / S pattern was formed using the carbon ink of Example 2 in the same manner as in Example 1, and various measurements were carried out. The results are shown in Table 3.

[0069] [Table 3]

[0070] Using the carbon ink of Example 3, an L / S pattern was formed in the same manner as in Example 1, and various measurements were carried out. The results are shown in Table 4.

[0071] [Table 4]

[0072] An L / S pattern was formed using the carbon ink of Example 4 in the same manner as in Example 1, and various measurements were carried out. The results are shown in Table 5.

[0073] [Table 5]

[0074] An L / S pattern was formed using the carbon ink of Example 5 in the same manner as in Example 1, and various measurements were carried out. The results are shown in Table 6.

[0075] [Table 6]

[0076] Using the carbon ink of Example 6, an L / S pattern was formed in the same manner as in Example 1, and various measurements were carried out. The results are shown in Table 7.

[0077] [Table 7]

[0078] An L / S pattern was formed using the carbon ink of Example 7 in the same manner as in Example 1, and various measurements were carried out. The results are shown in Table 8.

[0079] [Table 8]

[0080] An L / S pattern was formed using the carbon ink of Example 8 in the same manner as in Example 1, and various measurements were carried out. The results are shown in Table 9.

[0081] [Table 9]

[0082] Using the carbon ink of Example 9, an L / S pattern was formed in the same manner as in Example 1, and various measurements were carried out. The results are shown in Table 10.

[0083] [Table 10]

[0084] Using the carbon ink of Example 10, an L / S pattern was formed in the same manner as in Example 1, and various measurements were performed. The results are shown in Table 11.

[0085]

Table 11

[0086] Using the carbon ink of Example 11, an L / S pattern was formed in the same manner as in Example 1, and various measurements were performed. The results are shown in Table 12.

[0087]

Table 12

[0088] Using the carbon ink of Example 12, an L / S pattern was formed in the same manner as in Example 1, and various measurements were performed. The results are shown in Table 13.

[0089]

Table 13

[0090] Using the carbon ink of Comparative Example 1, an L / S pattern was formed in the same manner as in Example 1, and various measurements were performed. The results are shown in Table 14.

[0091]

Table 14

[0092] Using the carbon ink of Comparative Example 2, an L / S pattern was formed in the same manner as in Example 1, and various measurements were performed. The results are shown in Table 15.

[0093]

Table 15

[0094] <Evaluation of the bending resistance of the L / S pattern> A thin polycarbonate plate was placed on the L / S pattern on the PET film prepared in each example, covering the entire pattern. A metal plate weight weighing approximately 1 kg was placed on the plate and slid across the L / S pattern lines. If, for example, six lines (connected) were crossed in one movement, this was considered to be one bending stress applied to each line. Similarly, the metal plate weight was reciprocated, and after each line had been bent 100 times, the surface resistivity of the continuous L / S pattern was measured, and the increase rate was calculated based on the measurement value before the bending test. The calculated increase rate was the sum of all lines in the L / S pattern. Therefore, if, for example, six lines were included, the increase rate was divided by 6 to determine the increase rate per line (unit: %). The results are shown in Table 16. Note that the measured values ​​are the average of three tests.

[0095] [Table 16]

[0096] The bending resistance test was evaluated on the following three levels. "Excellent": The rate of increase was less than 10% for all pitches from 0.30 to 2.00 mm. "Good": The rate of increase was less than 10% when the pitch was 0.70 to 2.00 mm, and the rate of increase was 10 to 30% when the pitch was 0.30 to 0.40 mm. "X": There were cases where the rate of increase was 10% or more at pitches of 1.00 to 2.00 mm.

[0097] From the above test results, it is clear that Examples 1 to 12 according to the present invention have excellent bending resistance even in an L / S pattern with a pitch of 0.30 mm.

Claims

1. Graphite and carbon black, ethylene glycol, a carbon ink containing a first polyvinylpyrrolidone and a second polyvinylpyrrolidone; the first and second polyvinylpyrrolidones have different molecular structures, the first polyvinylpyrrolidone has only repeating units derived from vinylpyrrolidone in its molecular structure, the second polyvinylpyrrolidone has, in its molecular structure, a repeating unit derived from vinylpyrrolidone and a repeating unit derived from a compound other than vinylpyrrolidone, and a hydrogen atom of the repeating unit derived from vinylpyrrolidone in the molecular structure is not substituted with an alkyl group; The carbon ink, wherein the first and second polyvinylpyrrolidones are both dissolved in the ethylene glycol.

2. The second polyvinylpyrrolidone has a repeating unit derived from vinyl acetate. The carbon ink according to claim 1 .

3. the second polyvinylpyrrolidone has a repeating unit derived from vinyl alcohol, the repeating units derived from vinyl alcohol form a polyvinyl alcohol chain, the repeating units derived from vinylpyrrolidone form a polyvinylpyrrolidone chain, The polyvinylpyrrolidone chain is grafted onto the polyvinyl alcohol chain. is a graft copolymer, The carbon ink according to claim 1 .

4. The carbon ink according to claim 3 , further comprising a thermally reactive water-based urethane resin having a blocked isocyanate group and a urethane skeleton.

5. The composition further comprises a third polyvinylpyrrolidone having a molecular structure different from that of the first and second polyvinylpyrrolidones, the third polyvinylpyrrolidone contains, in its molecular structure, repeating units derived from vinylpyrrolidone, and at least a portion of the hydrogen atoms of the repeating units derived from vinylpyrrolidone are substituted with alkyl groups; The carbon ink according to claim 1 .

6. the total content of the graphite and the carbon black relative to the total mass of the non-volatile components of the carbon ink is 40 to 80 masses, relative to 100 parts by mass of the total content of the graphite and the carbon black, the total content of the first polyvinylpyrrolidone, the second polyvinylpyrrolidone, and the third polyvinylpyrrolidone is 30 to 100 parts by mass, and the content of the ethylene glycol is 100 to 240 parts by mass; The carbon ink according to claim 5 .

7. 2. The carbon ink according to claim 1, wherein the content of the second polyvinylpyrrolidone is 1 to 90 parts by mass per 100 parts by mass of the first polyvinylpyrrolidone.

8. 6. The carbon ink according to claim 5, wherein the content of the third polyvinylpyrrolidone is 30 to 100 parts by mass relative to 100 parts by mass of the first polyvinylpyrrolidone.

9. A method for manufacturing an electronic component, comprising a step of forming one or more conductive wirings made of a cured product of the carbon ink according to any one of claims 1 to 8 on a substrate by screen printing, the conductive wiring forms a line-and-space conductive pattern arranged parallel to one another on the substrate, at least one conductive wiring constituting the conductive pattern has a line width of 0.30 mm or less, and at least one space constituting the conductive pattern has a width of 0.30 mm or less.

10. An electronic component comprising a substrate and a conductive layer formed on the substrate, wherein the conductive layer is formed from a cured product of the carbon ink according to any one of claims 1 to 8.

Images