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

Abstract

To provide a carbon ink enabling the formation of fine conductive lines through screen printing, and an electronic component comprising the carbon ink and a production method therefor using the carbon ink.SOLUTION: 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, a first polyvinylpyrrolidone, ethylene glycol, and a second polyvinylpyrrolidone.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 wiring and the like with excellent conductivity can be formed by crushing the metal particles to increase the dispersibility of the metal particles and adding a lubricant to prevent the metal particles from agglomerating together.

[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] JP 2007-265802 A [Patent Document 2] JP 2018-022755 A 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 the metal particles may be oxidized, resulting in a decrease in conductivity, or that migration of metal components may occur, resulting in short circuits between wirings. In addition, there is a concern that coating metal core particles with carbon as disclosed in Patent Document 2 will increase costs and may not be accepted by users.

[0007] On the other hand, the inventors have found that when preparing a carbon ink paint containing carbon particles as a conductor, if the amount of carbon particles contained in the carbon ink is increased in order to improve the conductivity, the particles aggregate, and the required printability cannot be obtained. Therefore, there has been a demand for the development of a carbon ink that has good conductivity (resistance value) and printability even when the carbon particle content is reduced.

[0008] The present invention provides a carbon ink that enables the formation of thin conductive wiring by screen printing, and 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 molecular weight of the first polyvinylpyrrolidone is at least twice as large as the molecular weight of the second polyvinylpyrrolidone, the second polyvinylpyrrolidone may have only repeating units derived from vinylpyrrolidone, or may have repeating units derived from an α-olefin having 3 to 6 carbon atoms in addition to vinylpyrrolidone, and some of the hydrogen atoms of the repeating units derived from vinylpyrrolidone in the second polyvinylpyrrolidone may be substituted by alkyl groups. [2] The carbon ink according to [1], wherein the first polyvinylpyrrolidone contains polyvinylpyrrolidone having a K value of 90 or more. [3] The carbon ink according to [1] or [2], wherein the second polyvinylpyrrolidone contains polyvinylpyrrolidone having a molecular weight of 60,000 or less. [4] The carbon ink described in any one of [1] to [3], wherein the second polyvinylpyrrolidone has, in addition to vinylpyrrolidone, a repeating unit derived from an α-olefin having 3 to 6 carbon atoms, and some of the hydrogen atoms of the repeating unit derived from vinylpyrrolidone are substituted by alkyl groups. [5] The carbon ink according to any one of [1] to [4], wherein the combined content of the graphite and the carbon black is 80 mass % or less relative to the total mass of the non-volatile components of the carbon ink. [6] The carbon ink according to any one of [1] to [5], wherein the content of the second polyvinylpyrrolidone is 50 to 100 parts by mass per 100 parts by mass of the first polyvinylpyrrolidone. [7] The carbon ink described in any of [1] to [6], wherein a total content of the first polyvinylpyrrolidone and the second polyvinylpyrrolidone is 10 to 100 parts by mass per 100 parts by mass of a total content of the graphite and the carbon black. [8] The carbon ink according to any one of [1] to [7], wherein the content of the ethylene glycol is 100 to 240 parts by mass per 100 parts by mass of the combined content of the graphite and the carbon black. [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, at least one conductive wiring constituting the conductive pattern has a line width of 0.05 to 0.20 mm, and at least one space constituting the conductive pattern has a width of 0.05 to 0.20 mm.

[10] 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 described in any one of [1] to [8]. Effect of the Invention

[0010] The carbon ink of the present invention can be used in the same manner as conventional conductive pastes, and can form conductive wiring and the like that exhibits good conductivity even without containing metal particles. In addition, a high-definition conductive pattern (e.g., an L / S pattern) can be formed by screen printing. In addition, since carbon particles have excellent weather resistance and chemical resistance, the conductive wiring and the like formed by the carbon ink of the present invention have excellent weather resistance and chemical resistance. Furthermore, even when the carbon particle content is reduced compared to conventional carbon inks, the above-mentioned good properties can be ensured. According to the method for producing an electronic component of the present invention, electronic components having high-definition L / S patterns can be easily produced by screen-printing carbon ink onto a substrate.

[0011] This invention is believed to contribute to SDGs Goal 12, "Responsible Consumption and Production." DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Carbon ink A first aspect of the present invention is a carbon ink that includes 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.

[0013] [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 part of the carbon particles. In addition, any surface or part 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 consisting only of carbon (containing substantially no impurities) is called a carbon material. The carbon particles contained in this embodiment are preferably a carbon material.

[0014] 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 the particle size, the state of aggregation between particles, the surface properties (functional groups), etc. can be relatively easily controlled.

[0015] 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-definition 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 (D 50 ).

[0016] Carbon black is distinguished from graphite in that it does not have the giant crystal structure that graphite generally has. Examples of carbon black include furnace black, channel black, acetylene black, thermal black, and hollow shell-shaped ketjen black. The primary particle diameter of carbon black is, for example, about 1 nm to 500 nm. Usually, carbon black particles aggregate with each other. From the viewpoint of enabling high-definition 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 with an electron microscope, measuring the longest diameter of randomly selected primary particles as the particle diameter, and taking the arithmetic average value of the measured values ​​of 100 primary particles.

[0017] The total content of the carbon particles relative to the total mass of the carbon ink of this embodiment is, for example, preferably from 15 to 50 mass %, more preferably from 20 to 40 mass %, and even more preferably from 30 to 36 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 of 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 a narrow line width and a narrow pitch can be easily formed.

[0018] 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 71 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 of 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 a narrow line width and a narrow pitch can be easily formed. Incidentally, the solvent such as ethylene glycol is a volatile component.

[0019] The graphite content relative to the total mass of the carbon ink of this embodiment is, for example, preferably from 10 to 40 mass %, more preferably from 20 to 35 mass %, and even more preferably from 25 to 30 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 of 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 a narrow line width and a narrow pitch can be easily formed.

[0020] The content of carbon black relative to the total mass of the carbon ink of this embodiment is, for example, preferably from 1 to 20 mass %, more preferably from 3 to 15 mass %, and even more preferably from 5 to 10 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 of 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 a narrow line width and a narrow pitch can be easily formed.

[0021] In the carbon ink of this embodiment, the graphite content is preferably greater than the carbon black content. From the viewpoint of easily realizing this relationship, the carbon black is preferably Ketjen black.

[0022] [PVP] When the carbon ink of this embodiment contains two different polyvinylpyrrolidone (PVP), it may contain a first PVP and a second PVP having a smaller molecular weight than the first PVP. In this case, the molecular weight of the first PVP is preferably at least twice as large as the molecular weight of the second PVP, more preferably at least 10 times as large, particularly preferably at least 50 times as large, and most preferably at least 100 times as large. In addition, the molecular weight of the first PVP is preferably 500 times or less as large as the molecular weight of the second PVP.

[0023] The molecular weight of each PVP is preferably an absolute molecular weight measured by gel permeation chromatography (GPC) equipped with a multi-angle light scattering detector (MALLS), but may be a weight-average molecular weight or number-average molecular weight measured by GPC using a calibration curve of a standard sample with a known molecular weight. Regardless of the molecular weight, as long as the molecular weight of the first PVP is at least twice as large as that of the second PVP, the PVPs can be said to be sufficiently different from each other. In this embodiment, by including two PVPs with significantly different molecular weights, the carbon particles can be sufficiently dispersed, and the fine line printability can be further improved.

[0024] (First PVP) The first PVP is preferably a so-called general PVP having only repeating units derived from vinylpyrrolidone.

[0025] The molecular weight of the first PVP is preferably from 100,000 to 6,000,000, more preferably from 500,000 to 5,000,000, further preferably from 1,000,000 to 4,500,000, and most preferably from 3,000,000 to 4,000,000. When the content is within the above range, the carbon particles can be sufficiently dispersed together with the second PVP, and fine line printability can be further improved.

[0026] 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. When the amount is within the above preferred range, the carbon ink of this embodiment can be printed with high resolution even when a relatively small amount is blended, 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 that correlates 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).

[0027] 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. When the content is within the above range, the carbon particles can be sufficiently dispersed together with the second PVP, and fine line printability can be further improved.

[0028] The content of the first PVP relative to the total mass of the carbon ink of this embodiment is, for example, preferably 5 to 12 mass %, more preferably 6 to 11 mass %, further preferably 7 to 10 mass %, and most preferably 8 to 9 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 of 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 a narrow line width and a narrow pitch can be easily formed.

[0029] (Second PVP) The second PVP may be a general PVP having only repeating units derived from vinylpyrrolidone, but is preferably a so-called copolymer-type PVP having repeating units derived from an α-olefin having 3 to 6 carbon atoms in addition to vinylpyrrolidone.

[0030] Copolymer-type PVP is obtained, for example, by polymerizing a reaction solution in which vinylpyrrolidone and α-olefin are mixed in a predetermined ratio. The mixing ratio of each monomer is reflected in the mass ratio of the repeating units derived from each monomer in the copolymer. The content of the repeating units derived from vinylpyrrolidone relative to the total mass of the copolymer-type 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 the constitutional units derived from α-olefin.

[0031] A part of hydrogen atoms of the repeating unit derived from vinylpyrrolidone in the second PVP may be substituted with an alkyl group. In particular, when the second PVP is a copolymer type PVP, a part of hydrogen atoms of the repeating unit derived from vinylpyrrolidone is preferably substituted with an alkyl group. The alkyl group is preferably a linear or branched alkyl group having 1 to 6 carbon atoms, more preferably a linear alkyl group having 1 to 3 carbon atoms. The position of the substituted hydrogen atom is not particularly limited as long as it is permitted by the chemical configuration, and may be a hydrogen atom bonded to one or more carbon atoms constituting the main chain formed by polymerization of vinyl groups, or may be a hydrogen atom bonded to one or more carbon atoms (e.g., 2nd and 5th positions) constituting a 5-membered ring lactam.

[0032] The molecular weight of the second PVP is smaller than the molecular weight of the first PVP and is preferably from 4,000 to 60,000, more preferably from 6,000 to 50,000, further preferably from 7,000 to 40,000, and most preferably from 8,000 to 30,000. When the content is within the above range, the carbon particles can be sufficiently dispersed together with the first PVP, and fine line printability can be further improved.

[0033] The K value of the second PVP is preferably 10-80, more preferably 10-60, further preferably 10-40, and most preferably 10-20. Within the above preferred range, the second PVP becomes more dispersible in ethylene glycol and coats the carbon particles, further enhancing the dispersibility of the carbon particles in ethylene glycol. As a result, the carbon ink of this embodiment can be printed with high resolution to easily form a conductive pattern with a narrow line width and a narrow pitch.

[0034] The glass transition point (Tg) of the second PVP is preferably from 110 to 170°C, more preferably from 120 to 160°C, further preferably from 130 to 150°C, and most preferably from 130 to 140°C. When the content is within the above range, the carbon particles can be sufficiently dispersed together with the first PVP, and fine line printability can be further improved.

[0035] The content of the second PVP relative to the total mass of the carbon ink of this embodiment is, for example, preferably 5 to 12 mass%, more preferably 6 to 11 mass%, further preferably 7 to 10 mass%, and most preferably 6 to 8 mass%. The content of the second PVP is preferably lower than the content of the first PVP. 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 of 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 a narrow line width and a narrow pitch can be easily formed.

[0036] In the carbon ink of this embodiment, the content of the second PVP relative to 100 parts by mass of the first PVP is preferably 50 to 100 parts by mass, more preferably 60 to 90 parts by mass, and even more preferably 70 to 85 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 of 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 a narrow line width and a narrow pitch can be easily formed.

[0037] In the carbon ink of this embodiment, the total content of the first PVP and the second PVP relative to 100 parts by mass of the total content of carbon particles such as graphite and carbon black is preferably 10 to 100 parts by mass, more preferably 20 to 60 parts by mass, even more preferably 30 to 50 parts by mass, and most preferably 35 to 45 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 of 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 a narrow line width and a narrow pitch can be easily formed.

[0038] [solvent] The solvent contained in this embodiment is preferably one that has excellent compatibility with PVP. For example, an organic solvent capable of dissolving PVP at a concentration of 10% by mass or more at 20 to 25° C. is preferable. Examples of such organic solvents include methanol, ethanol, propanol, isopropanol, butanol, secondary butanol, amyl alcohol, 2-ethyl-hexanol, 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, glycerol ... Examples of suitable solvents include ethyl amine, 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 dimethylsulfoxide. In addition, water may be contained as a solvent. The solvent contained in this embodiment may be one type, or a mixture of two or more types.

[0039] Among the above solvents, ethylene glycol is particularly preferred. Ethylene glycol can dissolve the first PVP and the second PVP well. When mixed with these PVPs, it gels, imparting viscosity to the carbon ink of the present embodiment and making it gel-like. As a result, the coatability and printability of the carbon ink of the present embodiment are improved, blurring is suppressed, and a conductive pattern with a narrow line width and a narrow pitch can be easily formed.

[0040] In the carbon ink of this embodiment, the content of the solvent such as ethylene glycol per 100 parts by mass of the total content of carbon particles such as graphite and carbon black is preferably 100 to 240 parts by mass, more preferably 120 to 230 parts by mass, even more preferably 130 to 220 parts by mass, and most preferably 140 to 200 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 of 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 a narrow line width and a narrow pitch can be easily formed.

[0041] The content of the solvent relative to the total mass of the carbon ink of this embodiment is, for example, preferably from 30 to 70% by mass, more preferably from 40 to 60% by mass, and even more preferably from 50 to 55% 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 of 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 a narrow line width and a narrow pitch can be easily formed.

[0042] <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).

[0043] The substrate used in this embodiment is not particularly limited, and examples thereof include substrates for electronic components, films, etc. Examples of 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 polyvinyl fluoride, and other synthetic resins. Other materials that may be used include paper, cloth, glass, and ceramics.

[0044] The screen printing in this embodiment can be performed by applying a conventional method. For example, a plate is prepared by placing a printing film on a screen with appropriate slits, blocking the slits except for the image lines to be printed, placing carbon ink on the plate, and moving the carbon ink on the plate while applying pressure with a rubber spatula called a squeegee. This allows the carbon ink to pass through the screen in the open parts of the printing film and be pushed out onto the surface of the substrate placed under the plate, making it possible to print using this mechanism.

[0045] The mesh size of the screen used in screen printing is expressed as (mesh pitch)-(line diameter). Generally, a narrower mesh size allows for high-resolution printing, but the requirements for the ink are stricter. The carbon ink used in this embodiment has carbon particles highly dispersed in PVP and a solvent, so a screen with narrow mesh size can be used. The mesh size of the screen printing in this embodiment can be 100 μm or less, and can also be 50 μm or less, and is preferably 20 to 40 μm.

[0046] By the screen printing of this embodiment, a line and space conductive pattern (L / S pattern) in which one or more conductive wires are arranged parallel to each other can be formed on the substrate. In this case, at least one line width of the conductive wire constituting the L / S pattern can be 0.05 to 0.20 mm, and at least one space width of the L / S pattern can be 0.05 to 0.20 mm. More precisely, at least one line width of the conductive wire constituting the L / S pattern can be 0.05 to 0.15 mm, and at least one space width of the L / S pattern can be 0.05 to 0.15 mm.

[0047] 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.

[0048] Note that multiple conductive wires that make up the 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 prerequisite for an L / S pattern to be of good quality is that there are no faint breaks in the L / S pattern where lines should be connected, and no short-circuits between conductive wires due to line thickening in areas that should be separated as spaces.

[0049] The surface resistivity per unit area of ​​the conductive wiring made of the cured carbon ink of the first embodiment can be, for example, 10 to 100 MΩ, preferably 10 to 25 MΩ, when the line width is 0.90 to 1.10 mm and the thickness is 4 to 10 μm. Similarly, for example, when the line width is 0.10 to 0.15 mm and the thickness is 4 to 10 μm, the surface resistivity can be 50 to 130 MΩ, preferably 50 to 80 MΩ.

[0050] <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 be manufactured by another method. The explanation of the substrate is the same as that of the substrate of the second embodiment, and therefore a duplicate explanation will be omitted. The conductive layer may be formed on the entire surface of any surface of the substrate, or on only a part of the surface. When a conductive layer is formed only on a part 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 the conductive layer may be provided on the same surface and may be roughly divided into an area and an area not provided with the conductive layer. 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.

[0051] 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 adhesion of the conductive layer to the substrate is further improved. The average thickness of the conductive layer is calculated by measuring the thickness at 10 randomly selected locations and averaging the measured values.

[0052] The electronic component of this embodiment can be used to configure a variety of electronic devices, and is suitable for, for example, electrostatic capacitance touch sensors, touch switches, touch pads, pressure-sensitive switches, conductive contacts of push buttons, and the like. EXAMPLES

[0053] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0054] <Preparation of Carbon Ink> [Example 1] The materials (A) to (E) were mixed in the following ratios to obtain a carbon ink. (A) Ethylene glycol 480.0 g (50.7% by mass) (B) First PVP (Ashland, unmodified PVP, model number: K-120, K value of 1% viscosity solution = 114 to 130, absolute molecular weight by GPC / MALS measurement: 3,470,000, Tg: 176°C) 76.2 g (8.1% by mass) (C) Graphite powder (manufactured by Nippon Graphite Co., Ltd., model number: CSP-E, shape: scaly, average particle size 8 μm) 253.0 g (26.7% by mass) (D) Ketjen Black (manufactured by Lion Specialty Chemicals, model number: Carbon ECP, average primary particle size 30 nm) 76.2 g (8.1% by mass) (E) Second PVP (Ashland, unmodified PVP, model number: K-15, K value of 1% viscosity solution = 13 to 19, absolute molecular weight measured by GPC / MALS: 9,700, Tg: 130°C) 60.9 g (6.4% by mass)

[0055] [Example 2] A carbon ink was obtained in the same manner as in Example 1, except that, as the second PVP, the following alkylated PVP (modified PVP) was used instead of K-15 of (E). (E) Second PVP (Ashland Corporation, a copolymer type PVP obtained by copolymerizing vinylpyrrolidone and 1-butene in a mass ratio of 90:10, in which some of the hydrogen atoms of the structural units derived from vinylpyrrolidone are substituted with alkyl groups, model number: P-904LC, weight average molecular weight: 11,000 to 22,000), Tg: 155°C) 60.9 g (6.4 mass%)

[0056] [Comparative Example 1] A carbon ink was obtained in the same manner as in Example 1, except that the second PVP was not added and the proportion of ethylene glycol was increased.

[0057] [Table 1]

[0058] <Formation of L / S Pattern> A stencil film with an L / S pattern drawn on it was set on a screen with a 35 μm opening, and the carbon ink prepared above was screen-printed onto a PET film (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. Table 2 shows the pitch of the L / S pattern of the stencil film used in Example 1. Here, the pitch is the total value of line width (conductive wiring width): space width = 1:1. That is, a pitch of 2.0 mm indicates printing with a stencil of a line width of 1.0 mm and a space width of 1.0 mm. The line widths (wire widths) of three randomly selected locations from the L / S pattern formed on the substrate in Example 1 were measured with a digital microscope. The average value is shown in Table 1. Furthermore, the length and thickness of the lines were measured, and using a two-terminal method with a resistance meter (manufactured by ADVANTEST, model number: R6551), the electrical resistance (unit: kΩ), volume resistivity (unit: Ω·cm), and surface resistivity per unit area (unit: MΩ) were measured. Note that the unit of the surface resistivity of a predetermined measurement area (square) may be conveniently denoted as Ω / □. The results are shown in Table 2. Subsequently, the measured values of the L / S patterns formed using the carbon inks of Example 2 and Comparative Example 1 are shown in Tables 3 - 4.

[0059]

Table 2

[0060]

Table 3

[0061]

Table 4

[0062] For the results of Examples 1 and 2 and Comparative Example 1, the average values ​​for pitches of 2.0, 1.0, 0.7, and 0.4 mm were calculated and are shown in Table 5. Table 5 also shows the content of carbon material in the solids (non-volatile components) of the carbon inks used in Examples 1 and 2 and Comparative Example 1.

[0063] [Table 5]

[0064] As shown by the above results, although the carbon material (conductive material) contained in the carbon inks of Examples 1 and 2 was less than that of Comparative Example 1, the conductivity of the carbon inks of Examples 1 and 2 was as good as that of Comparative Example 1. On the other hand, when a printing film with a narrow pitch was used, the carbon ink of Comparative Example 1 caused disconnection and had poor fine line printability.

Claims

1. a carbon ink comprising graphite and carbon black, ethylene glycol, a first polyvinylpyrrolidone, and a second polyvinylpyrrolidone; the molecular weight of the first polyvinylpyrrolidone is at least two times greater than the molecular weight of the second polyvinylpyrrolidone; The second polyvinylpyrrolidone may have only a repeating unit derived from vinylpyrrolidone, or may have a repeating unit derived from an α-olefin having 3 to 6 carbon atoms in addition to vinylpyrrolidone, A carbon ink, wherein a part of hydrogen atoms of the repeating units derived from vinylpyrrolidone in the second polyvinylpyrrolidone may be substituted with an alkyl group.

2. The carbon ink according to claim 1 , wherein the first polyvinylpyrrolidone contains polyvinylpyrrolidone having a K value of 90 or more.

3. The carbon ink according to claim 1 , wherein the second polyvinylpyrrolidone comprises polyvinylpyrrolidone having a molecular weight of 60,000 or less.

4. 2. The carbon ink according to claim 1, wherein the second polyvinylpyrrolidone has, in addition to vinylpyrrolidone, a repeating unit derived from an α-olefin having 3 to 6 carbon atoms, and a portion of the hydrogen atoms of the repeating unit derived from vinylpyrrolidone are substituted by alkyl groups.

5. 2. The carbon ink according to claim 1, wherein a combined content of the graphite and the carbon black with respect to a total mass of non-volatile components of the carbon ink is 80 mass % or less.

6. 2. The carbon ink according to claim 1, wherein the content of the second polyvinylpyrrolidone is 50 to 100 parts by mass per 100 parts by mass of the first polyvinylpyrrolidone.

7. 2. The carbon ink according to claim 1, wherein a total content of the first polyvinylpyrrolidone and the second polyvinylpyrrolidone is 10 to 100 parts by mass with respect to 100 parts by mass of a total content of the graphite and the carbon black.

8. 2. The carbon ink according to claim 1, wherein the content of the ethylene glycol is 100 to 240 parts by mass with respect to 100 parts by mass of the total content of the graphite and the carbon black.

9. 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 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 0.05 to 0.20 mm, and at least one space constituting the conductive pattern has a width of 0.05 to 0.20 mm.

10. 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 according to any one of claims 1 to 8.

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