Conductive paste, electronic component, and multilayer ceramic capacitor

Abstract

The present invention provides a conductive paste having characteristics suitable for gravure printing, an electronic component using the conductive paste, and a multilayer ceramic capacitor.　A conductive paste according to the present invention comprises conductive powder, ceramic powder, a dispersant, a binder resin, and an organic solvent, wherein: the binder resin contains ethyl cellulose; the ethyl cellulose has a weight-average molecular weight of less than 100,000 and has an ethoxy group content of more than 50.0 mass% but not more than 53.0 mass%; and the dispersant includes a carboxylic acid-based polymeric dispersant having a weight-average molecular weight of not less than 5,000.

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] Conventionally, screen printing has been the most commonly used printing method for printing conductive paste onto dielectric green sheets. However, due to demands for smaller, thinner electronic devices and improved productivity, there is a demand for printing finer electrode patterns with high productivity.

[0005] One method of printing conductive paste is gravure printing, a continuous printing method in which the conductive paste is filled into recesses in a printing plate and then pressed against the surface to be printed, transferring the conductive paste from the plate. Gravure printing has a high printing speed and excellent productivity. When using gravure printing, it is necessary to appropriately select the binder resin, dispersant, solvent, etc. in the conductive paste to adjust its properties, such as viscosity, to a range suitable for gravure printing.

[0006] For example, Patent Document 1 discloses a conductive paste used to form, by gravure printing, internal conductor films in a multilayer ceramic electronic component having a plurality of ceramic layers and internal conductor films extending along specific interfaces between the ceramic layers, the conductive paste containing 30 to 70 wt % of a solid component including a metal powder, 1 to 10 wt % of an ethyl cellulose resin component having an ethoxy group content of 49.6% or more, 0.05 to 5 wt % of a dispersant, and a solvent component as the balance, and the paste is applied at a shear rate of 0.1 (s －１ ) Viscosity η ０．１ is 1 Pa s or more and the shear rate is 0.02 (s －１ ) Viscosity η ０．０２ A conductive paste is described which is a thixotropic fluid that satisfies the condition expressed by a specific formula:

[0007] Furthermore, Patent Document 2 discloses a conductive paste used for forming a conductive paste by gravure printing, similar to Patent Document 1, which contains 30 to 70% by weight of a solid component including a metal powder, 1 to 10% by weight of a resin component, 0.05 to 5% by weight of a dispersant, and a solvent component as the remainder, and which is capable of being applied at a shear rate of 0.1 (s －１ A thixotropic fluid having a viscosity of 1 Pa·s or more at a shear rate of 0.1 (s －１ ) is used as the viscosity reference, －１ ) has a viscosity change rate of 50% or more.

[0008] According to the above-mentioned Patent Documents 1 and 2, these conductive pastes have a shear rate of 0.1 (s －１) is a thixotropic fluid having a viscosity of 1 Pa·s or more, and is said to provide stable continuous printing properties at high speeds in gravure printing and to be capable of producing multilayer ceramic electronic components such as multilayer ceramic capacitors with good production efficiency.

[0009] Patent Document 3 (JP-A-2003-102666) describes a conductive paste for use in internal electrodes of multilayer ceramic capacitors, comprising a conductive powder (A), an organic resin (B), an organic solvent (C), an additive (D), and a dielectric powder (E), in which the organic resin (B) is polyvinyl butyral having a degree of polymerization of 10,000 to 50,000 and ethyl cellulose having a weight-average molecular weight of 10,000 to 100,000; the organic solvent (C) is propylene glycol monobutyl ether, a mixed solvent of propylene glycol monobutyl ether and propylene glycol methyl ether acetate, or a mixed solvent of propylene glycol monobutyl ether and mineral spirits; and the additive (D) is a conductive paste for gravure printing comprising a separation inhibitor and a dispersant. According to Patent Document 3, this conductive paste has a viscosity suitable for gravure printing and dries quickly.

[0010] JP 2003-187638 A JP 2003-242835 A JP 2012-174797 A

[0011] Conductive pastes for gravure printing are required to have low viscosity. However, when ceramic powders such as barium titanate and conductive powders such as Ni are added to a low-viscosity conductive paste for gravure printing, the difference in sedimentation velocity due to the difference in specific gravity between these powders has a more significant effect, compared to a high-viscosity conductive paste for screen printing, and the conductive powder and the ceramic powder are more likely to separate. For example, when a conductive paste for gravure printing is prepared, a phenomenon known as "white floating" (two-layer separation) may occur, in which a white separation layer containing the ceramic powder appears on top.

[0012] As a result of the inventor's investigations, it was found that the acid-based low-molecular-weight dispersant and surfactant promote whitening. On the other hand, if these acid-based low-molecular-weight dispersants and surfactants are not included, the viscosity of the paste cannot be sufficiently reduced, and the surface roughness of the dried film tends to be high.

[0013] Furthermore, as the miniaturization of electronic components leads to thinner electrode patterns, the use of conductive powders with smaller particle sizes is required, but conductive pastes using conductive powders with small particle sizes tend to have increased surface energy, which makes it difficult to disperse the conductive powder in the conductive paste.For example, in Patent Documents 1 and 2, the dispersibility of the paste is improved by removing lumps in the conductive paste by filtration, but the need for a step of removing the lumps tends to complicate the manufacturing process.

[0014] In view of the above circumstances, an object of the present invention is to provide a conductive paste having properties suitable for gravure printing, an electronic component using the same, and a multilayer ceramic capacitor.

[0015] In a first aspect of the present invention, there is provided a conductive paste comprising a conductive powder, a ceramic powder, a dispersant, a binder resin, and an organic solvent, wherein the binder resin comprises ethyl cellulose, the ethyl cellulose having a weight-average molecular weight of less than 100,000 and an ethoxy group content of more than 50.0 mass% and not more than 53.0 mass%, and the dispersant comprises a carboxylic acid-based polymer dispersant having a weight-average molecular weight of 5,000 or more.

[0016] Furthermore, the ethoxy group content of the ethyl cellulose is preferably 52.0% by mass 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 the 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 100 sec. －１ Preferably, the viscosity at 1000 kJ / min is 0.65 Pa·S or less. Preferably, the organic solvent contains one or more selected from the group consisting of dihydroterpineol, dihydroterpinyl acetate, and terpineol. Preferably, the binder resin contains 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. Preferably, the ceramic powder contains barium titanate. Preferably, the ceramic powder has an average particle size of 0.01 μm or more and 0.5 μm or less. Preferably, the ceramic powder is contained in an amount of 1 mass % or more and 20 mass % or less with respect to the entire conductive paste.

[0017] In a second aspect of the present invention, there is provided an electronic component formed using the above-described conductive paste.

[0018] 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 above-mentioned conductive paste.

[0019] According to the present invention, it is possible to obtain a conductive paste having properties suitable for gravure printing, and an electronic component and a multilayer ceramic capacitor using the same.

[0020] 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.

[0021] [Conductive Paste] The conductive paste of this embodiment contains a conductive powder, a ceramic powder, an additive, a binder resin, and an organic solvent. Each component will be described in detail below.

[0022] (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.

[0023] 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 paste is small, the conductive powder tends to easily aggregate. However, in the conductive paste according to this embodiment, even if the average particle diameter of the conductive powder is 0.3 μm or less, aggregation of the conductive powder can be sufficiently suppressed without removing aggregates by filtration using a filter, as described in Patent Documents 1 and 2, for example. 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 of the conductive powder 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.

[0024] 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 and dispersibility.

[0025] (Ceramic Powder) The ceramic powder is not particularly limited, and for example, in the case of a paste for an internal electrode of a multilayer ceramic capacitor, a known ceramic powder is appropriately selected depending on the type of multilayer ceramic capacitor to be applied. As the ceramic powder, for example, a perovskite oxide containing Ba and Ti can be used, and preferably barium titanate (BaTiO ３ ) is included.

[0026] 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 and Ti atoms of the above-mentioned ferroelectric ceramic powders are substituted with other atoms such as Sn, Pb, and Zr.

[0027] 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.

[0028] 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.

[0029] The average particle size of the ceramic powder may be 0.2 μm or less, or 0.1 μm or less. The average particle size of the ceramic powder may be smaller than the average particle size of the conductive powder. In the conductive paste of this embodiment, even if the average particle size of the ceramic powder is within the above range, the occurrence of whitish appearance can be sufficiently suppressed.

[0030] 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.

[0031] The content of the ceramic powder is preferably 1 part by mass or more and 30 parts by mass or less, and more preferably 3 parts by mass or more and 30 parts by mass or less, relative to 100 parts by mass of the conductive powder.

[0032] (Binder Resin) The binder resin contains ethyl cellulose. The ethyl cellulose preferably has an ethoxy group content of more than 50.0 mass% and not more than 53.0 mass%. The present inventors have discovered that by controlling the ethoxy group content of the ethyl cellulose contained in a conductive paste for gravure printing within a specific range, it is possible to obtain a viscosity suitable for gravure printing and good particle dispersibility even when a conductive powder and a ceramic powder having small particle sizes are used, and have completed the present invention.

[0033] 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 hydroxyl groups in the unit structure with ethoxy groups. The degree of substitution of hydroxyl groups in the unit structure with ethoxy groups is expressed as the degree of substitution, and the ethoxy group content (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, and in this case, the ethoxy group content in ethyl cellulose is approximately 55% by mass. The ethoxy group content of commonly used ethyl cellulose is approximately 48.0 to 49.5% by mass (degree of substitution: 2.50 to 2.58).

[0034] The ethoxy group content of the ethyl cellulose is preferably greater than 50.0% by mass and not more than 53.0% by mass, more preferably not more than 52.0% by mass. By incorporating ethyl cellulose having an ethoxy group content within the above range in combination with other components, the conductive paste according to this embodiment has a viscosity suitable for gravure printing, suppresses separation between the conductive powder and the ceramic powder, and further improves the surface roughness of the dried film. The ethoxy group content of the ethyl cellulose can be measured, for example, by reacting the ethoxy groups in the ethyl cellulose with hydroiodic acid and quantifying the amount of ethyl iodide, the resulting reaction product, by gas chromatography.

[0035] The ethoxy group content 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 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.

[0036] The weight-average molecular weight (Mw) of the ethyl cellulose is preferably less than 100,000, and may be 10,000 to 90,000, or 30,000 to 80,000. Furthermore, when the weight-average molecular weight of the ethyl cellulose is within the above range, it is possible to obtain a suitable viscosity as a conductive paste for gravure printing, and to obtain the above-mentioned effects. The average molecular weight can be measured, for example, by gel permeation chromatography (GPC).

[0037] The content of ethyl cellulose may be 0.5% by mass or more and 7% by mass or less, or 3.5% by mass or less, based on the total amount of the conductive paste. Furthermore, in the conductive paste according to this embodiment, the above-described effects can be obtained even if the content of ethyl cellulose is 1% by mass or less, based on the total amount of the conductive paste. Furthermore, the content of ethyl cellulose may be less than 1% by mass or less, or 0.9% by mass or less.

[0038] Furthermore, as the binder resin, an acetal resin containing an acrylic resin or a butyral resin such as polyvinyl butyral may be used in combination with the above-mentioned ethyl cellulose. For example, the binder resin may contain 20% by mass or more, 30% by mass or more, 50% by mass or more, or 60% by mass or more of the acetal resin relative to the total binder resin. Furthermore, even when the conductive paste according to this embodiment contains a larger amount of acetal resin than the ethyl cellulose resin, it has a viscosity suitable for gravure printing, suppresses separation between the conductive powder and the ceramic powder, and further improves the surface roughness of the dried film.

[0039] The degree of polymerization and weight-average molecular weight of the binder resin other than ethyl cellulose can be appropriately adjusted within the above ranges depending on the required viscosity of the conductive paste. For example, when an acetal resin is included as the binder resin, the weight-average molecular weight of the acetal resin may be 10,000 or more and 100,000 or less, or may be 60,000 or less.

[0040] 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.

[0041] The content of the binder resin is preferably 2 parts by mass or more and 15 parts by mass or less, and more preferably 4 parts by mass or more and 10 parts by mass or less, relative to 100 parts by mass of the conductive powder.

[0042] (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.

[0043] 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.

[0044] 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. Polymeric dispersants having a comb structure are obtained, for example, by polymerizing carboxylic acid-containing monomers, macromonomers, hydrophobic monomers, and the like, and may have graft chains. A polymer having a comb structure refers, for example, to 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.

[0045] The carboxylic acid polymer dispersant preferably contains a carboxylic acid polymer dispersant having a comb structure and / or a block polymer structure, more preferably 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.

[0046] 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. While there is no particular upper limit for the weight-average molecular weight, if the weight-average molecular weight is too high, the initial viscosity of the paste itself may become 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).

[0047] 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.

[0048] The carboxylic acid polymer dispersant is preferably contained in an amount of 0.01% by mass or more and less than 2.0% by mass, more preferably 0.01% by mass or more and 1.0% by mass or less, and even more preferably 0.03% by mass or more and 0.5% by mass or less, based on the entire conductive paste. If the content of the carboxylic acid polymer dispersant is 2.0% 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.

[0049] 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 interaction between particles of the conductive powder and the like caused by the ethyl cellulose is moderately weakened by the carboxylic acid-based polymer dispersant, making it possible to achieve both a reduction in the viscosity of the paste and suppression of white floating at a higher level.

[0050] The conductive paste according to this embodiment may contain only the carboxylic acid-based polymer dispersant as the dispersant, or may contain the carboxylic acid-based polymer dispersant in combination with one or more other known dispersants. The dispersant may, for example, contain an acid-based dispersant with a lower molecular weight than the carboxylic acid-based dispersant (e.g., a molecular weight of 1,000 or less), but it does not have to. The conductive paste according to this embodiment can sufficiently reduce the viscosity of the conductive paste and obtain a dry film with high smoothness, even without containing a low-molecular-weight acid-based dispersant. The dispersant may not contain a base-based dispersant or an amine-based dispersant.

[0051] The total content of the dispersant is, for example, less than 3.0% by mass relative to the total conductive paste. If the dispersant content 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, resulting in lamination misalignment during the subsequent lamination process, or additives remaining during firing may evaporate, causing internal stress due to the evaporated gas components. Furthermore, if the dispersant content is too high, structural destruction of the laminate may occur. The dispersant may contain 50% by mass or more, 70% by mass or more, 90% by mass or more, or 95% by mass or more of the carboxylic acid polymer dispersant relative to the total amount of the dispersant.

[0052] (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 aliphatic 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.

[0053] Examples of terpene solvents include dihydroterpineol acetate (DHTA), terpineol (TPO), and dihydroterpineol (DHT), and among these, dihydroterpineol acetate (DHTA) is preferred.

[0054] Examples of glycol ether 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). Note that the organic solvent may not contain, for example, propylene glycol monoalkyl ethers or propylene glycol monobutyl ether (PNB).

[0055] Examples of acetate solvents include dihydroterpinyl acetate, isobornyl acetate, isobornyl propionate, isobornyl butyrate, isobornyl isobutyrate, and glycol ether acetates such as ethylene glycol monobutyl ether acetate, dipropylene glycol methyl ether acetate, 3-methoxy-3-methylbutyl acetate, and 1-methoxypropyl-2-acetate.

[0056] Examples of acetate solvents include ethyl acetate, propyl acetate, isobutyl acetate, and butyl acetate. Examples of ketone solvents include methyl ethyl ketone and methyl isobutyl ketone. Examples of aliphatic hydrocarbon solvents include tridecane, nonane, and cyclohexane, with mineral spirits (MA) being more preferred.

[0057] The content of the organic solvent is preferably 20% by mass or more and 50% by mass or less, and more preferably 25% by mass or more and 45% 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.

[0058] The content of the organic solvent is preferably 50 parts by mass or more and 130 parts by mass or less, more preferably 60 parts by mass or more and 90 parts by mass or less, relative to 100 parts by mass of the conductive powder. When the content of the organic solvent is within the above range, the conductive powder has excellent conductivity and dispersibility.

[0059] The organic solvent may contain, for example, a terpene solvent as a main solvent and an aliphatic hydrocarbon solvent as a secondary solvent. In this case, the terpene solvent preferably contains either one or both of dihydroterpineol acetate (DHTA) and dihydroterpineol (DHT), and more preferably contains dihydroterpineol acetate (DHTA). The terpene solvent is preferably contained in an amount of 30 to 50 parts by mass, more preferably 40 to 50 parts by mass, per 100 parts by mass of the conductive powder. The aliphatic hydrocarbon solvent is preferably contained in an amount of 10 to 50 parts by mass, more preferably 10 to 30 parts by mass, per 100 parts by mass of the conductive powder.

[0060] (Additives) The conductive paste of the present embodiment may contain additives other than the above components, as needed. Examples of the additives that can be used include conventionally known additives such as antifoaming agents, plasticizers, surfactants, and thickeners.

[0061] (Conductive Paste) The method for producing the conductive paste according to this embodiment is not particularly limited, and a conventionally known method can be used. The conductive paste can be produced, for example, by stirring and kneading the above-mentioned components using a triple-roll mill, a ball mill, a mixer, or the like. Note that in the production process of the conductive paste, it is not necessary to perform filtration using a filter, as described in Patent Documents 1 and 2, for example. The conductive paste according to this embodiment can be produced with high dispersibility and a surface smoothness of the dried film, even without filtration using a filter.

[0062] The conductive paste according to this embodiment is applied at a shear rate of 100 sec. －１ The viscosity of the shear rate is preferably less than 1.20 Pa·s, and more preferably less than 0.66 Pa·s. －１ When the viscosity is within the above range, it can be suitably used as a conductive paste for gravure printing, and a high printing speed can be achieved. When the viscosity is beyond the above range, the viscosity may be too high and the paste may not be suitable for gravure printing. －１ The lower limit of the viscosity is not particularly limited, but is, for example, 0.20 Pa·s or more.

[0063] The conductive paste according to this embodiment is applied at a shear rate of 10,000 sec. －１ The viscosity is preferably 0.25 Pa·s or less, and more preferably 0.20 Pa·s or less. －１ When the viscosity is within the above range, the paste can be suitably used as a conductive paste for gravure printing, and a high printing speed can be achieved. －１ The lower limit of the viscosity is not particularly limited, but is, for example, 0.10 Pa·s or more.

[0064] Furthermore, the thickness of the whitish layer observed one week after preparation of the conductive paste is preferably less than 8%, more preferably less than 6%, and may be 5% or less, 4% or less, or even 3% or less of the total thickness of the conductive paste. The smaller the thickness of the whitish layer, the better the separation suppression effect. The thickness of the whitish layer can be measured by the method described in the Examples below.

[0065] 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 dried according to the method described in the Examples below, the surface roughness Sa is preferably less than 55 nm, more preferably less than 51 nm.

[0066] The conductive paste can be suitably used in electronic components such as multilayer ceramic capacitors. A multilayer ceramic capacitor has dielectric layers formed using dielectric green sheets and internal electrode layers formed using the conductive paste.

[0067] [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).

[0068] 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.

[0069] 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.

[0070] 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.

[0071] Next, the above-mentioned conductive paste is printed and applied to one side of this ceramic green sheet by gravure printing, and then dried to form a dry film, to prepare a plurality of sheets. Note that, from the viewpoint of the requirement for thinning of the internal electrode layer 11, it is preferable that the thickness of the dry film after drying is 1 μm or less.

[0072] 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.

[0073] 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 ２ It 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] [Evaluation Method] (Viscosity of Conductive Paste) The viscosity of the conductive paste after production was measured using a rheometer (Rheometer MCR302 manufactured by Anton Paar Japan Co., Ltd.). The viscosity was measured using a cone plate with a cone angle of 1° and a diameter of 25 mm at a shear rate of 100 sec. －１ , and 10000s －１ The viscosity was measured one week after production.

[0078] 100s －１ The viscosity was evaluated according to the following criteria: 0.20 Pa·s or more and less than 0.66 Pa·s: ◯ 0.66 Pa·s or more and less than 1.20 Pa·s: △ 1.20 Pa·s or more: ×

[0079] 10000s －１ The viscosity was evaluated according to the following criteria: 0.20 Pa·s or less: ◯; More than 0.20 Pa·s and 0.25 Pa·s or less: △; More than 0.25 Pa·s: ×

[0080] (Whitening) 20 g of the conductive paste immediately after preparation was placed in a glass bottle (diameter φ30 mm × height 65 mm). After one week, the appearance of the conductive paste was visually observed, and the percentage of whitening observed was measured. The percentage of whitening (%) was calculated by (thickness of the whitening layer / thickness of the entire paste) * 100. The percentage of whitening (%) was evaluated to evaluate the separation inhibition ability by assigning "Good" to less than 6%, "Average" to 6% or more but less than 8%, and "Poor" to 8% or more.

[0081] (Surface roughness Sa of coated dry 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 dry film sample. Then, three-dimensional data of the coated dry film surface was obtained at a magnification of 3000 times using a laser microscope, and the surface roughness Sa was analyzed. The arithmetic mean roughness Sa is a parameter obtained by expanding the arithmetic mean roughness Ra (arithmetic mean height of the line) to a surface. The surface roughness Sa of the dried film was evaluated by assigning "◯" to less than 51 nm, "△" to 51 nm or more and less than 55 nm, and "×" to 55 nm or more.

[0082] [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)

[0083] (Ceramic Powder) The following ceramic powders were used: Barium titanate (BaTiO ３ , BT1) (average particle size: 0.1 μm) Barium titanate (BaTiO ３ , BT2) (average particle size: 0.01 μm)

[0084] (Binder Resin) The following binder resins were used. Ethyl cellulose (EC1a) (Mw: 44,000, ethoxy group content: 49.0%) Ethyl cellulose (EC1b) (Mw: 44,000, ethoxy group content: 50.1%) Ethyl cellulose (EC1c) (Mw: 44,000, ethoxy group content: 51.1%) Ethyl cellulose (EC1d) (Mw: 44,000, ethoxy group content: 52.0%) Ethyl cellulose (EC1e) (Mw: 44,000, ethoxy group content: 53.0%) Ethyl cellulose (EC1f) (Mw: 44,000, ethoxy group content: 54.0%) Ethyl cellulose (EC2a) (Mw: 77,000, ethoxy group content: 49.0%) Ethyl cellulose (EC2b) (Mw: 77,000, ethoxy group content: 51.1%) Ethyl cellulose (EC3a) (Mw: 135,000, ethoxy group content: 49.0%) Ethyl cellulose (EC3b) (Mw: 135,000, ethoxy group content: 51.1%) Polyvinyl butyral (PVB) (Mw: approximately 30,000)

[0085] The degree of ethoxylation of the ethyl cellulose was adjusted by the following method. First, ethyl cellulose was dissolved in a THF (tetrahydrofuran) solvent, and then NaH was added to abstract protons from the hydroxyl groups in the ethyl cellulose, increasing its reactivity. Ethyl iodide was then added, and the reaction was maintained at a reaction temperature of 60°C for 6 hours, thereby ethoxylating the original hydroxyl groups. The desired degree of substitution can be obtained by adjusting the amount of ethyl iodide added. After ethoxylation, the treatment solution was dropped into pure water to perform a reprecipitation treatment, and the resulting solid precipitate was dried to obtain ethyl cellulose.

[0086] The content of ethoxy groups in the obtained ethyl cellulose was analyzed by gas chromatography. The ethoxy groups in ethyl cellulose react with hydroiodic acid to produce the same molar amount of ethyl iodide per 1 mol of ethoxy groups. The produced ethyl iodide was extracted with o-xylene and quantified by gas chromatography using toluene as an internal standard to analyze the amount of ethoxy groups in the ethyl cellulose, which was then used as the ethoxy group content.

[0087] (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)

[0088] (Organic Solvent) The following organic solvents were used in combination: Dihydroterpineol acetate (DHTA), dihydroterpineol (DHT), hydrocarbon solvent (mineral spirit A: MSA).

[0089] [Example 1] Conductive powder (Ni1) 50% by mass, ceramic powder (BT1) 12.5% ​​by mass, dispersant (D1) 0.3% by mass, binder resin 2.5% by mass (PVB: 1.7% by mass, EC1c: 0.8% by mass), and the remainder organic solvent (solvent 1: remainder, solvent 2: 10.5% by mass, solvent 3: 8.4% by mass) were added to make a total of 100% by mass, and these materials were mixed and dispersed to prepare a conductive paste. Here, solvent 1 was DHTA, solvent 2 was MSA, and solvent 3 was DHT. The test conditions, including details of each material, are shown in Table 1, and the evaluation results are shown in Table 2.

[0090] [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 evaluation results are shown in Table 2.

[0091]

[0092]

[0093] (Evaluation Results) For the conductive paste of the example, －１ , and 10000s －１ The viscosity of the conductive paste of the example was reduced, and the surface roughness of the dried film was small. Furthermore, even though the viscosity of the paste was reduced, the amount of separation layer containing ceramic powder (white floating) was small, and the conductive paste of the example had properties suitable for gravure printing.

[0094] 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 similar 100 s －１ , and 10000s －１ The viscosity of the ink was reduced, the surface roughness of the dried film was small, and the amount of white floating was small, so the ink had properties suitable for gravure printing.

[0095] On the other hand, in the conductive pastes of Comparative Examples 1 to 3 and 5, which used ethyl cellulose with an ethoxy group content of 50.0 mass % or less, the amount of whitening was small, but compared with the Examples, －１The viscosity of the conductive paste was high and the surface roughness of the dried film was greater than in Examples 1 and 2. In Comparative Examples 1 to 3, the smaller the weight average molecular weight (Mw) of ethyl cellulose, the lower the viscosity of the conductive paste. However, in Comparative Example 1 (Mw: 44,000, ethoxy group content: 49.0%), in which only Mw was reduced without adjusting the ethoxy group content, the improvement in the surface roughness of the dried film was insufficient.

[0096] In addition, in the conductive paste of Comparative Example 4, which contains ethyl cellulose having an ethoxy group content of more than 50.0 mass % but an Mw of 100,000 or more, the amount of whitening is small, but the whitening occurs at 100 s. －１ The viscosity was high and the surface roughness of the dried film was also large.

[0097] In addition, in the conductive paste of Comparative Example 6, in which a low molecular weight carboxylic acid-based dispersant was used as the dispersant, －１ , and 10000s －１ The viscosity of the conductive paste of Comparative Example 7, which used ethyl cellulose with an ethoxy group content of more than 53.0% by mass, was reduced and the surface roughness of the dried film was small, but the amount of white floating was large.

[0098] The technical scope of the present invention is not limited to the aspects described in the above-mentioned embodiments, etc. One or more of the requirements described in the above-mentioned embodiments, etc. may be omitted. Furthermore, the requirements described in the above-mentioned embodiments, etc. may be combined as appropriate.

[0099] The conductive paste according to each of the embodiments described above has a viscosity suitable for gravure printing that is stable over a long period of time, and exhibits sufficiently small separation between the conductive powder and the ceramic powder. Therefore, the conductive paste according to each of the embodiments can be suitably used as a raw material for internal electrodes of multilayer ceramic capacitors, which are chip components in electronic devices that are becoming increasingly miniaturized, such as mobile phones and digital devices, and can be suitably used as a conductive paste for gravure printing.

[0100] 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. 2024-089297 are incorporated herein by reference.

[0101] REFERENCE SIGNS LIST 1 Multilayer ceramic capacitor 10 Ceramic laminate 11 Internal electrode layer 12 Dielectric layer 20 External electrode 21 External electrode layer 22 Plated layer

Claims

1. A conductive paste comprising a conductive powder, a ceramic powder, a dispersant, a binder resin, and an organic solvent, wherein the binder resin comprises ethyl cellulose, the ethyl cellulose has a weight-average molecular weight of less than 100,000 and an ethoxy group content of more than 50.0 mass% and not more than 53.0 mass%, 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 ethyl cellulose has an ethoxy group content of 52.0 mass % 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 6, 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 100 sec. －１ 2. The conductive paste according to claim 1, wherein the viscosity at 2000 kJ / min is 0.65 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 ceramic powder comprises barium titanate.

14. The conductive paste according to claim 1, wherein the ceramic powder has an average particle size of 0.01 μm or more and 0.5 μm or less.

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

16. An electronic component formed using the conductive paste according to any one of claims 1 to 15.

17. 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 15.

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