Conductive paste, electronic component, and laminated ceramic capacitor

Abstract

To provide a conductive paste which can achieve both viscosity characteristic and dry film characteristic, even if conductive powder having a small particle diameter is used.SOLUTION: A conductive paste contains conductive powder, a dispersant, a binder resin, and an organic solvent, wherein the binder resin contains ethyl cellulose, the ethyl cellulose has a degree of substitution of 2.60 or more and 2.72 or less and a weight average molecular weight of 80,000 or more and 200,000 or less, and the dispersant contains a carboxylic acid-based polymer dispersant having a weight average molecular weight of 5,000 or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a conductive paste, an electronic component, and a multilayer ceramic capacitor. [Background technology]

[0002] As electronic devices such as mobile phones and digital devices become smaller and more powerful, there is a demand for smaller electronic components, including multilayer ceramic capacitors, with higher capacitance. Multilayer ceramic capacitors have a structure in which multiple dielectric layers and multiple internal electrode layers are alternately stacked, and by reducing the thickness of these dielectric layers and internal electrode layers, it is possible to achieve smaller size and higher capacitance.

[0003] Multilayer ceramic capacitors are manufactured, for example, as follows. First, a paste for internal electrodes (conductive paste) containing conductive powder, binder resin, and organic solvent is printed in a predetermined electrode pattern on the surface of a dielectric green sheet containing a dielectric powder such as barium titanate (BaTiO) and a binder resin. These sheets are then stacked in multiple layers to obtain a laminate in which the internal electrodes and dielectric green sheets are stacked in multiple layers. Next, this laminate is integrated by heat and pressure bonding to form a pressed body. This pressed body is cut, subjected to an organic binder removal process in an oxidizing or inert atmosphere, and then fired to obtain fired chips. Next, a paste for external electrodes is applied to both ends of the fired chips. After firing, nickel plating or the like is applied to the surfaces of the external electrodes to obtain a multilayer ceramic capacitor.

[0004] To achieve thinner internal electrode layers for smaller and higher capacity multilayer ceramic capacitors, it is necessary to reduce the particle size of the nickel particles contained in the conductive paste. However, reducing the particle size of the nickel particles can increase the specific surface area, which can lead to an increase in the viscosity of the conductive paste. Therefore, it is necessary to adjust the viscosity appropriately to suit the printing method.

[0005] Attempts have been made to improve the viscosity characteristics of conductive pastes. For example, Patent Document 1 describes a conductive paste containing at least a metal component, an oxide, a dispersant, and a binder resin, in which the metal component is Ni powder having a surface composition with a specific composition ratio, the dispersant has an acid site number of 500 to 2000 μmol / g, and the binder resin has an acid site number of 15 to 100 μmol / g. According to Patent Document 1, this conductive paste is said to have good dispersibility and viscosity stability.

[0006] Furthermore, for example, Patent Document 2 describes a conductive paste containing a conductive powder, a ceramic powder, a dispersant, a binder resin, and an organic solvent, wherein the binder resin contains ethyl cellulose having a mass average molecular weight of 30,000 to 150,000 and an ethoxy group content of 45 to 50 mass%, the dispersant contains an amine-based dispersant represented by a specific general formula, and the organic solvent contains dihydroterpineol and a solvent represented by a specific general formula. Patent Document 2 also claims to be able to provide a conductive paste, electronic component, and multilayer ceramic capacitor that have high smoothness as a conductive film after drying and little change in viscosity over time. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-216244 [Patent Document 2] Japanese Patent Application Publication No. 2023-160730 Summary of the Invention [Problem to be solved by the invention]

[0008] As described in Patent Documents 1 and 2 above, conventional methods for adjusting the viscosity of conductive pastes include, for example, adjusting the type, molecular weight, and properties of the binder resin contained in the conductive paste, and adjusting the type and content of the dispersant.

[0009] However, when the type, molecular weight, and content of the binder resin, and the type and content of the dispersant are adjusted in accordance with the reduction in particle size of the conductive powder, various properties other than the viscosity of the conductive paste also change significantly, making it difficult to obtain a conductive paste that achieves both the viscosity characteristics of the conductive paste and various other properties. Therefore, it has been desired to maintain or improve the favorable properties (e.g., dry film properties) obtained in conductive pastes using conductive powders with large particle sizes, even when the particle size of the conductive powder is reduced, and to further improve the viscosity characteristics.

[0010] In view of the above circumstances, an object of the present invention is to provide a conductive paste that achieves both good viscosity characteristics and good dry film characteristics even when the particle size of the conductive powder is reduced, and to provide an electronic component and a multilayer ceramic capacitor that use the same. [Means for solving the problem]

[0011] As a result of investigations, the inventors have found that in a conductive paste containing a specific dispersant and binder resin, by adjusting the degree of substitution of the ethoxy group of the ethyl cellulose contained in the conductive paste within a specific range, it is possible to achieve both favorable dry film properties and favorable viscosity properties of the conductive paste, and have completed the present invention.

[0012] A first aspect of the present invention provides a conductive paste comprising a conductive powder, a dispersant, a binder resin, and an organic solvent, wherein the binder resin comprises ethyl cellulose, the ethyl cellulose having a degree of substitution of 2.60 or more and 2.72 or less and a weight-average molecular weight of 80,000 or more and 200,000 or less, and the dispersant comprises a carboxylic acid-based polymer dispersant having a weight-average molecular weight of 5,000 or more.

[0013] The degree of substitution of ethyl cellulose is preferably 2.63 or more and 2.70 or less. The content of the binder resin is preferably 2% by mass or more and less than 4% by mass with respect to the entire conductive paste. The content of the carboxylic acid-based polymer dispersant is preferably 0.01% by mass or more and less than 2.0% by mass with respect to the entire conductive paste. The mass ratio of ethyl cellulose to the carboxylic acid-based polymer dispersant is preferably 10:20 to 10:0.5. The carboxylic acid-based polymer dispersant is preferably a carboxylic acid-based polymer dispersant with a comb structure. The carboxylic acid-based polymer dispersant preferably has a graft chain containing an alkylene oxide polymer. The conductive powder preferably has an average particle size of 0.05 μm or more and 0.3 μm or less. The conductive paste is preferably subjected to a shear rate of 4 sec -1 Preferably, the viscosity at 2000 kJ / min is 40 Pa·s or less. Preferably, the organic solvent contains one or more selected from the group consisting of dihydroterpineol, dihydroterpinyl acetate, and terpineol. The binder resin may contain an acetal-based resin. Preferably, the conductive powder contains one or more metal powders selected from Ni, Pd, Pt, Au, Ag, Cu, and alloys thereof. The conductive paste may also contain ceramic powder. The ceramic powder may also contain barium titanate. The ceramic powder may have an average particle size of 0.01 μm or more and 0.5 μm or less. The ceramic powder may be contained in an amount of 1% by mass or more and 20% by mass or less with respect to the entire conductive paste.

[0014] In a second aspect of the present invention, there is provided an electronic component formed using the conductive paste.

[0015] In a third aspect of the present invention, there is provided a laminate including at least dielectric layers and internal electrode layers, The internal electrode layers are formed using the conductive paste, thereby providing a multilayer ceramic capacitor. [Effects of the Invention]

[0016] According to the present invention, it is possible to provide a conductive paste that can achieve both good viscosity characteristics and good dry film characteristics even when a conductive powder with a small particle size is used, and an electronic component and a multilayer ceramic capacitor that use the conductive paste. [Brief explanation of the drawings]

[0017] [Figure 1] 1A and 1B are a perspective view (FIG. 1A) and a cross-sectional view (FIG. 1B) showing a multilayer ceramic capacitor according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0018] [Conductive paste] The conductive paste of this embodiment contains a conductive powder, a dispersant, a binder resin, and an organic solvent. The conductive paste of this embodiment may also contain a ceramic powder. Each component will be described in detail below.

[0019] (conductive powder) The conductive powder is not particularly limited, and metal powders can be used, such as powders of one or more elements selected from Ni, Pd, Pt, Au, Ag, Cu, and alloys thereof. Among these, powders of Ni or its alloys (Ni alloys) are preferred from the viewpoints of conductivity, corrosion resistance, and cost. Examples of Ni alloys that can be used include alloys of Ni with at least one element selected from the group consisting of Mn, Cr, Co, Al, Fe, Cu, Zn, Ag, Au, Pt, and Pd. The Ni content in the Ni alloy is, for example, 50% by mass or more, preferably 80% by mass or more. Furthermore, the Ni powder may contain several hundred ppm of the element S to suppress rapid gas generation due to partial thermal decomposition of the binder resin during binder removal.

[0020] The conductive powder has an average particle size of, for example, 1.0 μm or less, preferably 0.05 μm or more and 0.3 μm or less. When the conductive powder has a small average particle size, it can be suitably used as a paste for internal electrodes of thin-film multilayer ceramic capacitors (multilayer ceramic components). When the conductive powder has a small average particle size, the conductive powder tends to easily aggregate. However, in the conductive paste according to this embodiment, aggregation of the conductive powder can be sufficiently suppressed even when the average particle size of the conductive powder is 0.3 μm or less. Furthermore, the average particle size of the conductive powder may be 0.05 μm or more and 0.2 μm or less, or may be 0.06 μm or more and 0.1 μm or less. The average particle size is a value determined by observation with a scanning electron microscope (SEM), and is the average value (number average particle size) obtained by measuring the particle size of each of a plurality of particles in an image observed with an SEM at 10,000x magnification.

[0021] The content of the conductive powder is preferably 30% by mass or more and less than 70% by mass, more preferably 40% by mass or more and 60% by mass or less, based on the total amount of the conductive paste. When the content of the conductive powder is within the above range, the conductive paste has excellent conductivity.

[0022] (ceramic powder) The conductive paste according to this embodiment may contain ceramic powder. The ceramic powder is not particularly limited, and for example, in the case of a paste for internal electrodes of a multilayer ceramic capacitor, a known ceramic powder is appropriately selected depending on the type of multilayer ceramic capacitor to be used. For example, the ceramic powder may be a perovskite oxide containing Ba and Ti, and preferably contains barium titanate (BaTiO).

[0023] The ceramic powder may be one containing barium titanate as a main component and an oxide as a secondary component. The oxide may be one or more oxides selected from Mn, Cr, Si, Ca, Ba, Mg, V, W, Ta, Nb, and rare earth elements. Examples of such ceramic powders include perovskite-type oxide ferroelectric ceramic powders in which the Ba and Ti atoms of barium titanate (BaTiO) are replaced with other atoms, such as Sn, Pb, or Zr.

[0024] The ceramic powder used in the conductive paste for the internal electrodes may have the same composition as the dielectric ceramic powder constituting the green sheets of the multilayer ceramic capacitor (electronic component). This prevents cracks from occurring at the interface between the dielectric layer and the internal electrode layer during the sintering process due to a mismatch in shrinkage. Examples of such ceramic powders include perovskite oxides containing Ba and Ti, as well as oxides such as ZnO, ferrite, PZT, BaO, Al2O3, Bi2O3, R (rare earth element)2O3, TiO2, and Nd2O3. One type of ceramic powder may be used, or two or more types may be used.

[0025] The average particle diameter of the ceramic powder is, for example, 0.01 μm to 0.5 μm, preferably 0.01 μm to 0.3 μm. When the average particle diameter of the ceramic powder is in the above range, when used as an internal electrode paste, it is possible to form sufficiently fine, thin, and uniform internal electrodes. The average particle diameter is a value determined by observation with a scanning electron microscope (SEM), and is the average value (number average particle diameter) obtained by measuring the particle diameter of each of multiple particles in an image observed with the SEM at a magnification of 50,000 times.

[0026] The content of the ceramic powder is preferably 1% by mass or more and 20% by mass or less, more preferably 3% by mass or more and 15% by mass or less, based on the total mass of the conductive paste. When the content of the ceramic powder is within the above range, the dispersibility and sinterability are excellent. Note that the conductive paste does not necessarily need to contain ceramic powder.

[0027] (binder resin) The binder resin contains ethyl cellulose. The ethyl cellulose preferably has a degree of substitution of 2.60 or more and 2.72 or less. The present inventors discovered that by controlling the degree of substitution of the ethoxy group of the ethyl cellulose contained in the conductive paste within a specific range, it is possible to obtain a viscosity suitable for the printing method and at the same time good particle dispersibility, even when a conductive powder with a small particle size is used, and thus completed the present invention.

[0028] Ethyl cellulose is a type of cellulose derivative. It is generally produced by substituting at least a portion of the hydroxyl groups (-OH) in the unit structure (glucose skeleton) contained in cellulose with ethoxy groups (-OC2H5). The degree to which hydroxyl groups in the unit structure are substituted with ethoxy groups is expressed as the degree of substitution, and the degree of ethoxylation in ethyl cellulose varies depending on the degree of substitution. Since cellulose contains three hydroxyl groups in the unit structure, the maximum degree of substitution of ethoxy groups is 3. The degree of substitution of commonly used ethyl cellulose is approximately 2.50 to 2.58.

[0029] The degree of substitution of ethyl cellulose is preferably 2.60 or more and 2.72 or less, more preferably 2.63 or more and 2.70 or less. By including ethyl cellulose having a degree of substitution in the above range in combination with other components, the conductive paste according to this embodiment has a viscosity suitable for screen printing and can further improve the surface roughness of the dried film. The degree of substitution of ethyl cellulose can be measured, for example, by calculating the number of ethoxy groups in the unit structure of ethyl cellulose through analysis of the peak intensity ratio obtained by nuclear magnetic resonance analysis (NMR).

[0030] The degree of substitution of ethyl cellulose can be adjusted, for example, by the following procedure. First, ethyl cellulose is dissolved in tetrahydrofuran (THF) solvent, and then NaH is added to prepare a treatment solution. This process removes protons from the hydroxyl groups of ethyl cellulose, increasing its reactivity. Next, ethyl iodide is added to the treatment solution, and the solution is maintained at a reaction temperature of 60°C for 6 hours. This process ethoxylates the hydroxyl groups of ethyl cellulose. The degree of substitution can be adjusted by the amount of ethyl iodide added. After ethoxylation, the treatment solution is dropped into pure water to perform a reprecipitation process, yielding a solid precipitate. The resulting solid precipitate is dried to obtain ethyl cellulose.

[0031] The weight-average molecular weight (Mw) of the ethyl cellulose is preferably 80,000 or more and 200,000 or less, and may be 10,000 or more and 190,000 or less. Furthermore, when the weight-average molecular weight of the ethyl cellulose is within the above range, a suitable viscosity can be obtained as a conductive paste for screen printing, and the interaction between nickel particles can be appropriately adjusted, resulting in a smooth dried coating film. The weight-average molecular weight can be measured, for example, by GPC (gel permeation chromatography).

[0032] The content of ethyl cellulose may be preferably 1.0% by mass or more and 10% by mass or less, more preferably 1.0% by mass or more and 5.0% by mass or less, based on the total amount of the conductive paste, and may be 4.0% by mass or less, or 3.0% by mass or less.

[0033] Furthermore, a resin other than the ethyl cellulose may be used in combination as the binder resin. The resin to be used in combination is not particularly limited, and known resins can be used. Examples include cellulose-based resins such as methyl cellulose, ethyl hydroxyethyl cellulose, and nitrocellulose; acrylic resins; and acetal-based resins including butyral-based resins such as polyvinyl butyral. Furthermore, when used as an internal electrode paste, a butyral-based resin may be included to improve the adhesive strength with the green sheet. When the binder resin includes an acetal-based resin, the viscosity can be easily adjusted to a level suitable for gravure printing, and the adhesive strength with the green sheet can be further improved. Alternatively, the binder resin may include only the ethyl cellulose resin. For example, the binder resin may include 20% by mass or more, or 30% by mass or more, of the ethyl cellulose resin relative to the entire binder resin. Furthermore, the binder resin may include 50% by mass or less of the ethyl cellulose resin relative to the entire binder resin.

[0034] The total content of the binder resin is preferably 1% by mass or more and 7% by mass or less, more preferably 2% by mass or more and 4% by mass or less, based on the total amount of the conductive paste. When the content of the binder resin is within the above range, the conductive paste has excellent conductivity and dispersibility.

[0035] (dispersant) The conductive paste according to this embodiment contains a dispersant, which is preferably a carboxylic acid-based polymer dispersant having a weight-average molecular weight of 5,000 or more.

[0036] The carboxylic acid-based polymer dispersant is a polymer dispersant (surfactant) having a carboxylic acid group as an adsorption group. The carboxylic acid-based polymer dispersant may be, for example, a polymer (copolymer) produced by polymerizing two or more types of monomers including a carboxylic acid-containing monomer and a hydrophobic monomer. The polymer may also be synthesized by methods such as random polymerization, block polymerization, or graft polymerization.

[0037] Examples of carboxylic acid-based polymeric dispersants include random polymers in which carboxylic acid-containing monomers and hydrophobic monomers are randomly arranged, block polymer structures in which carboxylic acid group-containing monomers and hydrophobic monomers are arranged in separate blocks, and polymeric dispersants having a comb structure, etc. Polymeric dispersants having a comb structure are obtained, for example, by polymerizing carboxylic acid-containing monomers, macromonomers, hydrophobic monomers, etc., and may have graft chains.

[0038] The carboxylic acid polymer dispersant preferably contains a carboxylic acid polymer dispersant having a comb structure and / or a block polymer structure, and more preferably contains a carboxylic acid polymer dispersant having a comb structure. Furthermore, the polymer dispersant having a comb structure preferably contains a graft chain, and the graft chain preferably contains an alkylene oxide polymer. Examples of the alkylene oxide polymer contained in the graft chain include ethylene oxide polymer, propylene oxide polymer, and butylene oxide polymer, and may contain an ethylene oxide polymer. A polymer having a comb structure refers to, for example, a polymer having a structure in which multiple molecular chains branch out from the main chain of the polymer in a comb-like manner, and the branched chains may be graft chains.

[0039] The weight-average molecular weight (Mw) of the carboxylic acid-based polymer dispersant is 5,000 or more, and may be 8,000 or more, 10,000 or more, 20,000 or more, or 40,000 or more. A weight-average molecular weight of 5,000 or more can provide a stable dispersion effect and sufficiently suppress thickening over time. While there are no particular limitations on the upper limit of the weight-average molecular weight, if the weight-average molecular weight is too high, the initial viscosity of the paste itself may become too high, making it unsuitable for gravure printing. Therefore, for example, the weight-average molecular weight is 100,000 or less. The weight-average molecular weight can be measured, for example, by gel permeation chromatography (GPC).

[0040] The acid value of the carboxylic acid polymer dispersant is preferably 50 mgKOH / g or more and 250 mgKOH / g or less, and may be 50 mgKOH / g or more and 200 mgKOH / g or less. When the acid value is in this range, a sufficient dispersing effect can be obtained. The acid value (mgKOH / g) can be determined, for example, by potentiometric titration in accordance with JIS K0070.

[0041] The carboxylic acid polymer dispersant is preferably contained in an amount of 0.01% by mass or more and less than 4.0% by mass, more preferably 0.01% by mass or more and 3.0% by mass or less, and even more preferably 0.03% by mass or more and 2.0% by mass or less, based on the entire conductive paste. If the content of the carboxylic acid polymer dispersant is 5.0% by mass or more, drying may be insufficient in the printing and drying steps, causing the internal electrode layers to become soft, resulting in lamination misalignment in the subsequent lamination step, or the dicarboxylic acid remaining during firing may evaporate, causing internal stress due to the evaporated gas components, or causing structural destruction of the laminate.

[0042] Furthermore, the mass ratio of the ethyl cellulose to the carboxylic acid-based polymer dispersant is preferably 10:20 to 10:0.5, and more preferably 10:10 to 10:1. When the mass ratio of the ethyl cellulose to the carboxylic acid-based polymer dispersant is within the above range, the dispersibility of the nickel particles is sufficiently ensured, and at the same time, the interaction between the particles of the conductive powder due to the ethyl cellulose is adjusted to a suitable range by the carboxylic acid-based polymer dispersant, so that a highly smooth coated and dried film can be obtained.

[0043] The conductive paste according to this embodiment may contain only the carboxylic acid polymer dispersant as the dispersant, or may contain the carboxylic acid polymer dispersant in combination with another known dispersant. When a dispersant other than the carboxylic acid polymer dispersant is contained, the content of the carboxylic acid polymer dispersant may be, for example, 40% by mass or more, 60% by mass or more, or 80% by mass or more, based on the total amount of the dispersant.

[0044] Other known dispersants may include, for example, acid-based dispersants. Examples of such acid-based dispersants include acid-based dispersants such as higher fatty acids, alkyl monoamine salts, and polymer surfactants, and phosphate-based dispersants. These dispersants may be used alone or in combination of two or more.

[0045] The total content of the dispersant is, for example, less than 3.0% by mass relative to the total conductive paste. If the content of the dispersant is 3.0% by mass or more, drying may be insufficient during the printing and drying process, causing the internal electrode layers to become soft, which may result in misalignment during the subsequent lamination process, or the additives remaining during firing may evaporate, causing internal stress due to the evaporated gas components. Furthermore, if the content of the dispersant is too high, the structure of the laminate may be destroyed.

[0046] (organic solvent) The organic solvent is not particularly limited, and any known organic solvent capable of dissolving the binder resin can be used. Examples of the organic solvent include terpene-based solvents, glycol ether-based solvents, acetate-based solvents, acetate ester-based solvents, ketone-based solvents, and hydrocarbon solvents. One type of organic solvent may be used, or two or more types may be used.

[0047] As the organic solvent, a terpene-based solvent is preferably used. Examples of the terpene-based solvent include terpineol (TPO), dihydroterpineol (DHT), and dihydroterpinyl acetate (DHTA), among which dihydroterpineol (DHT) is preferred. By using these solvents, both appropriate viscosity and drying speed can be achieved.

[0048] Examples of glycol ether-based solvents include (di)ethylene glycol ethers such as diethylene glycol mono-2-ethylhexyl ether, ethylene glycol mono-2-ethylhexyl ether, diethylene glycol monohexyl ether, and ethylene glycol monohexyl ether, and propylene glycol monoalkyl ethers such as propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, and propylene glycol monobutyl ether (PNB). Among these, propylene glycol monoalkyl ethers are preferred, and propylene glycol monobutyl ether (PNB) is more preferred. When the organic solvent contains a glycol ether-based solvent, it has excellent compatibility with the binder resin described above and excellent drying properties.

[0049] Examples of acetate solvents include glycol ether acetates such as ethylene glycol monobutyl ether acetate, diethylene glycol monobutyl ether acetate (butyl carbitol acetate: BCA), dipropylene glycol methyl ether acetate, 3-methoxy-3-methylbutyl acetate, and 1-methoxypropyl-2-acetate, as well as isobornyl acetate, isobornyl propionate, isobornyl butyrate, and isobornyl isobutyrate.

[0050] Examples of acetate solvents include ethyl acetate, propyl acetate, isobutyl acetate, butyl acetate, etc. Examples of ketone solvents include methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone (DIBK), etc.

[0051] Examples of hydrocarbon solvents include aliphatic hydrocarbon solvents such as tridecane, nonane, cyclohexane, naphthenic solvents, and mineral spirits (MA), and aromatic hydrocarbon solvents such as toluene and xylene. Of these, aliphatic hydrocarbon solvents are preferred, and mineral spirits (MA) is more preferred. Furthermore, mineral spirits (MA) may contain chain saturated hydrocarbons as a main component, and may contain chain saturated hydrocarbons in an amount of 20 mass% or more based on the total amount of mineral spirits.

[0052] The content of the organic solvent is preferably 20% by mass or more and 70% by mass or less, and more preferably 25% by mass or more and 65% by mass or less, based on the total amount of the conductive paste. When the content of the organic solvent is within the above range, the conductive paste has excellent conductivity and dispersibility.

[0053] (Conductive paste) The method for producing the microparticle-containing slurry according to the present embodiment is not particularly limited, and any conventionally known method can be used. For example, the slurry can be produced by stirring and kneading the above-mentioned components using a three-roll mill, a ball mill, a mixer, or the like.

[0054] Conductive paste is applied at a shear rate of 4 seconds. -1 The viscosity may be, for example, 50 Pa·s or less, and preferably 10 Pa·s or more and 40 Pa·s or less. Shear rate: 4 sec -1 When the viscosity is within the above range, it can be suitably used as a conductive paste for screen printing. When the viscosity is more than 50 Pa s or less than 10 Pa s, the viscosity may be too high or too low to be suitable for screen printing.

[0055] Furthermore, the lower the film roughness of the dried film obtained by applying and drying the conductive paste, the better. For example, when the conductive paste is applied to a glass substrate using an applicator with a coating thickness of 10 μm and then dried, the surface roughness Sa is preferably 80 nm or less, and more preferably 60 nm or less.

[0056] [Electronic Components] Hereinafter, embodiments of electronic components and the like of the present invention will be described with reference to the drawings. The drawings may be used in schematic form or with a different scale, as appropriate. The positions and directions of components will be described with reference to the XYZ Cartesian coordinate system shown in Figures 1A and 1B, as appropriate. In this XYZ Cartesian coordinate system, the X and Y directions are horizontal, and the Z direction is vertical (up-down).

[0057] 1A and 1B are diagrams showing a multilayer ceramic capacitor 1, which is an example of an electronic component according to an embodiment. The multilayer ceramic capacitor 1 includes a laminate 10 in which dielectric layers 12 and internal electrode layers 11 are alternately stacked, and external electrodes 20.

[0058] A method for manufacturing a multilayer ceramic capacitor using the above-mentioned conductive paste will be described below. First, the conductive paste is printed on a ceramic green sheet (dielectric green sheet) and dried to form a dry film. A plurality of ceramic green sheets having this dry film on their upper surfaces are laminated by pressure bonding to obtain a laminate, and the laminate is then fired and integrated to produce a ceramic laminate 10 in which internal electrode layers 11 and dielectric layers 12 are alternately laminated. A pair of external electrodes is then formed on both ends of the ceramic laminate 10 to manufacture a multilayer ceramic capacitor 1. This method will be described in more detail below.

[0059] First, a ceramic green sheet, which is an unfired ceramic sheet, is prepared. Examples of the ceramic green sheet include a dielectric layer paste obtained by adding an organic binder such as polyvinyl butyral and a solvent such as terpineol to a predetermined ceramic raw material powder such as barium titanate, and then coating the paste on a support film such as a PET film in a sheet form and drying it to remove the solvent. The thickness of the dielectric layer made of the ceramic green sheet is not particularly limited, but is preferably 0.05 μm or more and 3 μm or less in view of the demand for miniaturization of multilayer ceramic capacitors.

[0060] Next, the above-mentioned conductive paste is printed and applied to one side of this ceramic green sheet, and then dried to form a dry film, to prepare a plurality of sheets. The printing method is not particularly limited, but for example, screen printing can be used. Note that, from the viewpoint of the requirement for thin internal electrode layers 11, it is preferable that the thickness of the dry film after drying is 1 μm or less.

[0061] Next, the ceramic green sheets are peeled off from the support film, and the ceramic green sheets and the dried film formed on one side thereof are stacked alternately, followed by a heat and pressure treatment to obtain a laminate. Note that protective ceramic green sheets not coated with the conductive paste may also be placed on both sides of the laminate.

[0062] Next, the laminate is cut to a predetermined size to form green chips, which are then subjected to a binder removal treatment and fired in a reducing atmosphere to produce a fired laminated ceramic body (ceramic laminate 10). The binder removal treatment is preferably performed in air or an N2 gas atmosphere. The temperature during the binder removal treatment is, for example, 200°C or higher and 400°C or lower. The temperature is preferably maintained for 0.5 hours or higher and 24 hours or lower during the binder removal treatment. The firing is performed in a reducing atmosphere to prevent oxidation of the metals used in the internal electrode layers. The temperature during firing of the laminate is, for example, 1000°C or higher and 1350°C or lower, and the temperature is preferably maintained for 0.5 hours or higher and 8 hours or lower during firing.

[0063] By firing the green chip, the organic binder in the green sheet is completely removed, and the ceramic raw material powder is fired to form the ceramic dielectric layers 12. Also, the organic vehicle in the internal electrode layers 11 is removed, and the nickel powder or nickel-based alloy powder is sintered or melted and integrated to form the internal electrodes, forming a multilayer ceramic sintered body in which multiple dielectric layers 12 and internal electrode layers 11 are alternately stacked. Note that, from the viewpoint of incorporating oxygen into the dielectric layers to increase reliability and suppressing reoxidation of the internal electrodes, the sintered multilayer ceramic sintered body may be subjected to an annealing treatment.

[0064] Then, a pair of external electrodes 20 is provided on the produced fired multilayer ceramic body, thereby producing a multilayer ceramic capacitor 1. For example, the external electrodes 20 include an external electrode layer 21 and a plating layer 22. The external electrode layer 21 is electrically connected to the internal electrode layer 11. Note that, for example, copper, nickel, or an alloy thereof can be suitably used as the material for the external electrodes 20. Note that electronic components other than multilayer ceramic capacitors can also be used. [Example]

[0065] EXAMPLES The present invention will be described in detail below based on examples and comparative examples, but the present invention is not limited to these examples.

[0066] [Evaluation method] (Viscosity of conductive paste) The viscosity of the conductive paste after production was measured using a rheometer (Anton Paar Japan: MCR-302e) at a shear rate of 4 sec 1 week after production. -1 (25℃) for 4 seconds. -1 The viscosity at 25°C was evaluated as "Good" for 10 Pa·s or more and 40 Pa·s or less, "Good" for more than 40 Pa·s and 50 Pa·s or less, and "Poor" for less than 10 Pa·s or more than 50 Pa·s.

[0067] (Surface roughness Sa of the applied dry film) Conductive paste was applied to a glass substrate using a bar coater with an applicator to a coating thickness of 10 μm, and then dried at 120°C for 40 minutes to produce a dried coating film sample. Three-dimensional data of the dried coating film surface was then obtained using a laser microscope at a magnification of 3000x, and the surface roughness (arithmetic mean roughness) Sa was analyzed. A roughness of 60 nm or less was evaluated as "Good," a roughness of more than 60 nm and less than 80 nm was evaluated as "Good," and a roughness of more than 80 nm was evaluated as "Poor."

[0068] [Materials used] (conductive powder) The following conductive powders were used: ·Ni powder (Ni1) (average particle size: 0.2μm) ·Ni powder (Ni2) (average particle size: 0.06μm)

[0069] (ceramic powder) The following ceramic powders were used: Barium titanate (BaTiO3, BT1) (average particle size: 0.1 μm)

[0070] (binder resin) The following binder resins were used: Ethyl cellulose (EC1a) (Mw: 105,000, degree of substitution: 2.50) Ethyl cellulose (EC1b) (Mw: 105,000, degree of substitution: 2.63) Ethyl cellulose (EC1c) (Mw: 105,000, degree of substitution: 2.75) Ethyl cellulose (EC2a) (Mw: 180,000, degree of substitution: 2.50) Ethyl cellulose (EC2b) (Mw: 180,000, degree of substitution: 2.60) Ethyl cellulose (EC2c) (Mw: 180,000, degree of substitution: 2.63) Ethyl cellulose (EC2d) (Mw: 180,000, degree of substitution: 2.68) Ethyl cellulose (EC2e) (Mw: 180,000, degree of substitution: 2.72) Ethyl cellulose (EC2f) (Mw: 180,000, degree of substitution: 2.75) Ethyl cellulose (EC3a) (Mw: 44000, degree of substitution: 2.68) Ethyl cellulose (EC4a) (Mw: 77,000, degree of substitution: 2.68)

[0071] (dispersant) The following dispersants were used: Carboxylic acid polymer dispersant (D1) (Mw: 55,000, comb structure, graft chain contains alkylene oxide polymer) Carboxylic acid polymer dispersant (D2) (Mw: 10,000, comb structure, graft chain contains alkylene oxide polymer) Carboxylic acid dispersant (D3) (Mw: 353)

[0072] (organic solvent) The following organic solvents were used: Dihydroterpineol (DHT)

[0073] [Example 1] A material was prepared by blending 50% by mass of conductive powder (Ni1), 0.3% by mass of dispersant (D1), 2.5% by mass of ethyl cellulose (EC2d), and the remainder of the material, an organic solvent (DHT), to a total of 100% by mass. These materials were mixed and dispersed to produce a conductive paste. The blending ratios of each component and the evaluation results are shown in Table 1.

[0074] [Examples 2 to 11, Comparative Examples 1 to 7] Conductive pastes were prepared and evaluated in the same manner as in Example 1, except that the types and contents of the materials used were changed as shown in Table 1. The blending ratios of each component and the evaluation results are shown in Table 1.

[0075] [Table 1]

[0076] (Evaluation results) In the conductive paste of the example, 4 seconds -1 The viscosity of the conductive paste was reduced and the surface roughness of the dried film was also small. The details of the reason for this are unknown, but it is thought that the degree of structure formation including fine particles in the conductive paste was adjusted to an appropriate range, which resulted in a viscosity reduction effect and improved leveling properties at the same time.

[0077] In addition, the conductive paste of Example 7, which uses conductive powder with a relatively small particle size (average particle size: 0.06 μm), also showed a 4 sec -1 The viscosity of the coating was sufficiently reduced, and the surface roughness of the dried film was small, similar to that of the other examples.

[0078] On the other hand, in the conductive pastes of Comparative Examples 1 and 3, which used ethyl cellulose with a degree of substitution of less than 2.60, the -1 The viscosity of the conductive pastes was reduced, but the surface roughness of the dried film was large and the smoothness was insufficient. In addition, the conductive pastes of Comparative Examples 2 and 4, which used ethyl cellulose with a degree of substitution of more than 2.72, had a large surface roughness of the dried film and insufficient smoothness.

[0079] In addition, in the conductive pastes of Comparative Examples 5 and 6, in which the weight average molecular weight (Mw) of ethyl cellulose was less than 80,000, -1 The viscosity of Comparative Example 7 was too low, resulting in insufficient viscosity characteristics as a conductive paste for internal electrodes. In addition, the conductive paste of Comparative Example 7, which used a low-molecular-weight carboxylic acid dispersant as a dispersant, had a large surface roughness of the dried film and was not sufficiently smooth.

[0080] The technical scope of the present invention is not limited to the aspects described in the above-mentioned embodiments. One or more of the requirements described in the above-mentioned embodiments may be omitted. The requirements described in the above-mentioned embodiments may be combined as appropriate. Furthermore, to the extent permitted by law, the disclosures of all documents cited in the above-mentioned embodiments are incorporated by reference and are included as part of the description in this document.

[0081] The conductive pastes according to the embodiments described above can achieve both reduced viscosity and good dry film properties, and are expected to become even more useful as conductive particles with smaller particle diameters are used.

Claims

1. A conductive paste containing a conductive powder, a dispersant, a binder resin, and an organic solvent, the binder resin includes ethyl cellulose, The ethyl cellulose has a degree of substitution of 2.60 or more and 2.72 or less and a weight average molecular weight of 80,000 or more and 200,000 or less, The conductive paste, wherein the dispersant contains a carboxylic acid-based polymer dispersant having a weight-average molecular weight of 5,000 or more.

2. The conductive paste according to claim 1 , wherein the degree of substitution of the ethyl cellulose is 2.63 or more and 2.70 or less.

3. The conductive paste according to claim 1 , wherein the content of the binder resin is 2% by mass or more and less than 4% by mass with respect to the entire conductive paste.

4. The conductive paste according to claim 1 , wherein the content of the carboxylic acid-based polymer dispersant is 0.01% by mass or more and less than 2.0% by mass with respect to the entire conductive paste.

5. 2. The conductive paste according to claim 1, wherein the mass ratio of the ethyl cellulose to the carboxylic acid-based polymer dispersant is 10:20 to 10:0.

5.

6. The conductive paste according to claim 1 , wherein the carboxylic acid-based polymer dispersant is a carboxylic acid-based polymer dispersant having a comb structure.

7. The conductive paste according to claim 1 , wherein the carboxylic acid-based polymer dispersant has a graft chain containing an alkylene oxide polymer.

8. The conductive paste according to claim 1 , wherein the conductive powder has an average particle size of 0.05 μm or more and 0.3 μm or less.

9. The conductive paste was applied at a shear rate of 4 sec. －１ 2. The conductive paste according to claim 1, wherein the viscosity at 2000 kJ / min is 40 Pa·s or less.

10. The conductive paste according to claim 1 , wherein the organic solvent comprises at least one selected from the group consisting of dihydroterpineol, dihydroterpinyl acetate, and terpineol.

11. The conductive paste according to claim 1 , wherein the binder resin includes an acetal-based resin.

12. The conductive paste according to claim 1 , wherein the conductive powder contains one or more metal powders selected from the group consisting of Ni, Pd, Pt, Au, Ag, Cu, and alloys thereof.

13. The conductive paste of claim 1 , wherein the conductive paste comprises a ceramic powder.

14. The conductive paste of claim 13 , wherein the ceramic powder comprises barium titanate.

15. The conductive paste according to claim 13, wherein the ceramic powder has an average particle size of 0.01 μm or more and 0.5 μm or less.

16. The conductive paste according to claim 13 , wherein the ceramic powder is contained in an amount of 1% by mass to 20% by mass based on the entire conductive paste.

17. An electronic component formed using the conductive paste according to any one of claims 1 to 16.

18. The laminate has at least a laminate of dielectric layers and internal electrode layers, A multilayer ceramic capacitor, wherein the internal electrode layers are formed using the conductive paste according to any one of claims 1 to 16.

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