Conductive paste, electronic component, and multilayer ceramic capacitor

Abstract

Provided is a conductive paste capable of achieving both viscosity characteristics and dry film characteristics even when conductive powder having a small particle diameter is used.　This conductive paste contains a 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 2.60-2.72 and a weight-average molecular weight of 80,000-200,000, and the dispersant contains a carboxylic-acid-based polymer dispersant having a weight-average molecular weight of 5000 or greater.

Description

Conductive paste, electronic components, and multilayer ceramic capacitors

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

[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] For example, a multilayer ceramic capacitor is manufactured as follows: First, barium titanate (BaTiO ３ A multilayer laminate is obtained by stacking multiple layers of dielectric green sheets containing dielectric powders such as ethylenediaminetetraacetic acid (EPO) and binder resin, on the surfaces of which are printed internal electrode pastes (conductive pastes) containing conductive powders, binder resins, and organic solvents in a predetermined electrode pattern. The laminates are then integrated by heat and pressure to form a pressed body. The pressed body is then cut, subjected to an organic binder removal treatment in an oxidizing or inert atmosphere, and then fired to obtain fired chips. Next, an external electrode paste is applied to both ends of the fired chips, and 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.

[0007] JP 2015-216244 A JP 2023-160730 A

[0008] As described in Patent Documents 1 and 2 above, conventional methods for adjusting the viscosity of a conductive paste 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.

[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] In a first aspect of the present invention, there is provided 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 diameter of 0.05 μm or more and 0.3 μm or less. The conductive paste is preferably sintered at a shear rate of 4 sec. －１ Preferably, the viscosity at 1000 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. Furthermore, 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. Furthermore, the conductive paste may contain ceramic powder. Furthermore, the ceramic powder may contain barium titanate. Furthermore, the ceramic powder may have an average particle size of 0.01 μm or more and 0.5 μm or less. Furthermore, the ceramic powder may be contained in an amount of 1 mass % or more and 20 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 multilayer ceramic capacitor having at least a laminate in which dielectric layers and internal electrode layers are laminated, the internal electrode layers being formed using the conductive paste.

[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.

[0017] 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.

[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. For example, powders of one or more elements selected from Ni, Pd, Pt, Au, Ag, Cu, and alloys thereof can be used. 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 element S to suppress rapid gas generation due to partial thermal decomposition of the binder resin during binder removal treatment.

[0020] The average particle diameter of the conductive powder is, for example, 1.0 μm or less, preferably 0.05 μm or more and 0.3 μm or less. When the average particle diameter of the conductive powder is small, it can be suitably used as a paste for internal electrodes of thin-film multilayer ceramic capacitors (multilayer ceramic components). When the average particle diameter of the conductive powder is small, 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 diameter of the conductive powder is 0.3 μm or less. Furthermore, the average particle diameter of the conductive powder may be 0.05 μm or more and 0.2 μm or less, or 0.06 μm or more and 0.1 μm or less. The average particle diameter is a value determined by observation with a scanning electron microscope (SEM), and is the average (number average particle diameter) obtained by measuring the particle diameter of each of a plurality of particles in an image observed with the 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 electrical 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, a perovskite oxide containing Ba and Ti can be used as the ceramic powder, and preferably barium titanate (BaTiO ３ ) is included.

[0023] The ceramic powder may be a ceramic powder 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 powder include barium titanate (BaTiO ３Examples of suitable perovskite-type oxide ferroelectric ceramic powders include those in which Ba atoms or Ti atoms of the above-mentioned ferroelectric ceramic powders are substituted with other atoms such as Sn, Pb, or Zr.

[0024] The ceramic powder used in the conductive paste for the internal electrodes may be powder of the same composition as the dielectric ceramic powder constituting the green sheets of the multilayer ceramic capacitor (electronic component). This suppresses the occurrence of cracks due to a mismatch in shrinkage at the interface between the dielectric layer and the internal electrode layer during the sintering process. In addition to the perovskite oxides containing Ba and Ti, such ceramic powders may also be, for example, ZnO, ferrite, PZT, BaO, Al ２ O ３ , Bi ２ O ３ , R (rare earth element) ２ O ３ , TiO ２ , Nd ２ O ３ The ceramic powder may be one type or two or more types.

[0025] The average particle diameter of the ceramic powder is, for example, 0.01 μm or more and 0.5 μm or less, preferably 0.01 μm or more and 0.3 μm or less. When the average particle diameter of the ceramic powder is in the above range, when used as an internal electrode paste, a sufficiently fine, thin, and uniform internal electrode can be formed. 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 a plurality of particles from 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 conductive paste has excellent dispersibility and sinterability. 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. Generally, at least some of the hydroxyl groups (-OH) in the unit structure (glucose skeleton) contained in cellulose are replaced with ethoxy groups (-OC ２ H ５ ) is produced by substituting ethoxy groups with hydroxyl groups in the unit structure. The degree of substitution of hydroxyl groups in the unit structure 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 containing ethyl cellulose having the above-mentioned degree of substitution 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 a tetrahydrofuran (THF) solvent, and then NaH is added to prepare a treatment solution. This process abstracts 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, thereby obtaining a solid precipitate. The obtained 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 gel permeation chromatography (GPC).

[0032] The content of ethyl cellulose is 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. The content of ethyl cellulose may also be 4.0% by mass or less, or 3.0% by mass or less.

[0033] In addition, 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, 60% by mass, or 90% by mass or more 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 in 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 polymer dispersant is a polymer dispersant (surfactant) having a carboxylic acid group as an adsorption group. The carboxylic acid 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 a method 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 chain may be a graft chain.

[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. When the weight-average molecular weight is 5,000 or more, a stable dispersion effect can be achieved and thickening over time can be sufficiently suppressed. The upper limit of the weight-average molecular weight is not particularly limited, but if the weight-average molecular weight is too high, the initial viscosity of the paste itself may become high and the paste may become 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 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. The mass ratio of the ethyl cellulose to the carboxylic acid-based polymer dispersant may be 10:5 to 10:1, 10:3 to 10:1, or 10:2 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, thereby obtaining a high level of smoothness in the coated and dried film.

[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. Note that the dispersant may not include, for example, a base-based dispersant or an amine-based dispersant.

[0045] The total content of the dispersant is, for example, less than 3.0 mass% with respect to the total conductive paste. If the content of the dispersant is 3.0 mass% or more, drying may be insufficient in the printing and drying process, causing the internal electrode layers to become soft, which may result in lamination misalignment in 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. The organic solvent may also contain one or more solvents selected from the group consisting of dihydroterpineol, dihydroterpinyl acetate, and terpineol. One or more organic solvents 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 them, 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. The organic solvent may, for example, not contain propylene glycol monoalkyl ethers or propylene glycol monobutyl ether (PNB).

[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. Among 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 in the above range, the conductive paste has excellent conductivity and dispersibility.

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

[0054] The conductive paste is applied at a shear rate of 4 seconds. －１ The viscosity may be, for example, 50 Pa·s or less, and is preferably 10 Pa·s or more and 40 Pa·s or less. －１ When the viscosity is in the above range, the paste 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 Component] Hereinafter, embodiments of electronic components and the like of the present invention will be described with reference to the drawings. The drawings may be represented schematically or at a different scale as appropriate. Furthermore, 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 and 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 now be described. 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, each having this dry film on its upper surface, are laminated by pressure bonding to obtain a laminate, which 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 produce a multilayer ceramic capacitor 1. This method will now be described in more detail.

[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 the 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 thinning the internal electrode layer 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 be further placed on both sides of the laminate.

[0062] Next, the laminate is cut to a predetermined size to form green chips, and the green chips are subjected to a binder removal treatment and fired in a reducing atmosphere to produce a fired laminated ceramic body (ceramic laminate 10). The atmosphere in the binder removal treatment is air or N ２It is preferable to carry out the debinding treatment in a gas atmosphere. The temperature during the debinding treatment is, for example, 200°C or higher and 400°C or lower. Furthermore, it is preferable to hold the above temperature for 0.5 hours or higher and 24 hours or lower during the debinding treatment. Furthermore, the firing is carried out in a reducing atmosphere to suppress oxidation of the metal used in the internal electrode layers, and the temperature during firing of the laminate is, for example, 1000°C or higher and 1350°C or lower, and the temperature holding time during firing is, for example, 0.5 hours or higher and 8 hours or lower.

[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 the alloy powder mainly composed of nickel is sintered or melted and integrated to form the internal electrodes, thereby forming a multilayer ceramic fired body in which a plurality of dielectric layers 12 and internal electrode layers 11 are alternately stacked. Note that, from the viewpoint of taking oxygen into the dielectric layers to increase reliability and suppressing reoxidation of the internal electrodes, the fired multilayer ceramic fired body may be subjected to an annealing treatment.

[0064] A pair of external electrodes 20 is then provided on the produced fired multilayer ceramic body, thereby producing the 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. Suitable materials for the external electrodes 20 include, for example, copper, nickel, or an alloy thereof. Electronic components other than multilayer ceramic capacitors may also be used.

[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 (MCR-302e manufactured by Anton Paar Japan Co., Ltd.) at a shear rate of 4 sec one week after production. －１Measurement was carried out under the condition of 4 seconds (25°C). －１ The viscosity at 25°C was evaluated as "good" if it was 10 Pa·s or more and 40 Pa·s or less, "fair" if it was more than 40 Pa·s and 50 Pa·s or less, and "poor" if it was less than 10 Pa·s or more than 50 Pa·s.

[0067] (Surface roughness Sa of coated and dried film) A conductive paste was applied to a glass substrate using a bar coater with an applicator having a coating thickness of 10 μm, and then dried at 120 ° C. for 40 minutes to prepare a coated and dried film sample. Then, three-dimensional data of the coated and dried film surface was obtained at a magnification of 3000 times using a laser microscope, and the surface roughness (arithmetic mean roughness) Sa was analyzed. 60 nm or less was evaluated as "Good", more than 60 nm and less than 80 nm was evaluated as "Good", and 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: 0.2 μm) Ni powder (Ni2) (average particle size: 0.06 μm)

[0069] (Ceramic Powder) The following ceramic powders were used: Barium titanate (BaTiO ３ , 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: 44,000, degree of substitution: 2.68) Ethyl cellulose (EC4a) (Mw: 77,000, degree of substitution: 2.68)

[0071] (Dispersants) The following dispersants were used: Carboxylic acid polymer dispersant (D1) (Mw: 55,000, comb structure, graft chains containing alkylene oxide polymer) Carboxylic acid polymer dispersant (D2) (Mw: 10,000, comb structure, graft chains containing 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 weight of conductive powder (Ni1), 0.3% by weight of dispersant (D1), 2.5% by weight of ethyl cellulose (EC2d), and the remainder of the material, an organic solvent (DHT), to a total of 100% by weight. These materials were mixed and dispersed to prepare 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]

[0076] (Evaluation Results) For 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 had 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 using ethyl cellulose with a degree of substitution of less than 2.60, －１ In the conductive pastes of Comparative Examples 2 and 4, which used ethyl cellulose with a degree of substitution of more than 2.72, the surface roughness of the dried film was large and the smoothness was insufficient.

[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 the conductive paste of Comparative Example 7 was too low, and the viscosity characteristics were insufficient for the conductive paste for the internal electrodes. Furthermore, the conductive paste of Comparative Example 7, which used a low-molecular-weight carboxylic acid dispersant as the 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.

[0082] Furthermore, to the extent permitted by law, the disclosures of all documents cited in the above embodiments are incorporated herein by reference. Furthermore, to the extent permitted by law, the contents of Japanese Patent Application No. 2024-089298 are incorporated herein by reference.

Claims

1. 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 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 comprises 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 based on the total amount of the conductive paste.

5. The conductive paste according to claim 1, wherein the mass ratio of said ethyl cellulose to said 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 comb-type carboxylic acid-based polymer dispersant.

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 is 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 includes 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. A multilayer ceramic capacitor comprising at least a laminate in which dielectric layers and internal electrode layers are laminated, the internal electrode layers being formed using the conductive paste according to any one of claims 1 to 16.

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