Conductive paste and multilayer ceramic capacitors

Abstract

To provide a conductive paste which has high dispersibility and excellent viscosity stability over time.SOLUTION: A conductive paste contains conductive powder, ceramic powder, a binder resin, an organic solvent, and a dispersant, in which the conductive powder has an H2O adsorption amount per unit area at a relative pressure P / P0=0.5 of 0.30 mg / m2 or more and 0.70 mg / m2 or less, and the dispersant has a relative dielectric constant of 10 or more, and contains at least one compound selected from the group consisting of 1) a compound having an acid group, and 2) a compound having an amine group.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to a conductive paste and a multilayer ceramic capacitor. [Background technology]

[0002] With the miniaturization and increased performance of electronic devices such as mobile phones and digital equipment, there is a demand for smaller and higher-capacitance electronic components, including multilayer ceramic capacitors. Multilayer ceramic capacitors have a structure in which multiple dielectric layers and multiple internal electrode layers are alternately stacked, and miniaturization and increased capacitance can be achieved by thinning these dielectric layers and internal electrode layers.

[0003] Multilayer ceramic capacitors are manufactured, for example, as follows: First, a conductive paste for internal electrodes is printed (coated) in a predetermined electrode pattern onto the surface of a dielectric green sheet containing dielectric powder such as barium titanate (BaTiO3) and a binder resin, and then dried to form a dry film. Next, the dry film and the green sheet are stacked alternately to obtain a laminate. Then, this laminate is heated and compressed to form a bonded body. This bonded body is cut, subjected to a de-organic binder treatment in an oxidizing or inert atmosphere, and then fired to obtain a fired chip. Next, paste for external electrodes is applied to both ends of the fired chip, and after firing, nickel plating or the like is applied to the surface of the external electrodes to obtain a multilayer ceramic capacitor.

[0004] The conductive paste used to form the internal electrode layer includes, for example, conductive powder, ceramic powder, binder resin, and organic solvent. The conductive paste may also contain a dispersant to improve the dispersibility of the conductive powder and other components.

[0005] With the recent trend towards thinner internal electrode layers, the conductive powder contained in conductive pastes also tends to become smaller in particle size (micronized). When the particle size of conductive powder decreases, the surface area per unit volume increases, so the properties of the particle surface become dominant. In particular, when the particles constituting the conductive powder are at the submicron level, the particles tend to adhere to each other due to forces such as intermolecular forces and electrostatic forces, forming coarse aggregates. If such aggregates are present in the conductive powder, they may form convex portions on the surface of the internal electrode layer during the manufacturing of multilayer ceramic capacitors, and in some cases, they may penetrate the ceramic dielectric layer and cause a short circuit between the internal electrode layers.

[0006] Conductive pastes are produced, for example, by mixing and dispersing conductive powder and other materials into an organic vehicle, which is made by dissolving a binder resin in an organic solvent. Conventional mixing methods in the manufacturing process of conductive pastes include using equipment such as high-speed shear mixers or planetary mixers with two or more shafts to mix (knead) conductive powder, inorganic powders such as ceramic powder, dispersants, and organic solvents into the organic vehicle.

[0007] However, with conventional mixing methods, as the particle size of conductive powder decreases, problems such as insufficient mixing of the organic vehicle and insufficient wetting of the conductive powder or ceramic powder surfaces may occur. Furthermore, even when dispersion treatment is performed after mixing using a three-roll mill or similar method, problems such as poor dispersion of conductive powder (metal fine powder) and flake formation may occur.

[0008] Furthermore, conductive powder produced by the wet manufacturing method, which is one of the common methods for producing fine metal powders, is prone to aggregation during the drying process of the wet manufacturing method. As a result, many aggregates (secondary particles) are already formed when the conductive powder is mixed with an organic vehicle, making it susceptible to the aforementioned problems.

[0009] In the manufacturing process of a conductive paste containing a dispersant, when focusing on the dispersion process of conductive powder and ceramic powder (hereinafter, both are collectively referred to as "inorganic powder"), the process by which the particles constituting the inorganic powder are dispersed in the paste can be divided into the following steps, for example.

[0010] (1) A process in which the surface of the particles (including secondary particles) constituting the inorganic powder is "wetted". (2) A process in which secondary particles are crushed and the crushed particles are dispersed in the paste. (3) A process to suppress the "re-aggregation" of particles after crushing.

[0011] The wetting process described in (1) above is a process in which an organic vehicle / organic solvent adheres to the surface of the particles constituting the conductive powder and ceramic powder. In conductive pastes containing a dispersant, during this process, the dispersant is adsorbed onto the surface of secondary particles (aggregates), and at the same time, the air present in the voids inside the secondary particles is replaced by the organic solvent containing the dispersant, causing the dispersant to adsorb onto the inner wall of the secondary particles.

[0012] Furthermore, (1) the wetting process specifically refers to the process of kneading and stirring using equipment such as the mixer mentioned above, and is also called the pretreatment process. The degree of "wetting" of the conductive powder and ceramic powder affects the processing time in the subsequent dispersion process.

[0013] The above (2) dispersion process is a process that greatly affects the dispersibility of conductive powder and ceramic powder (inorganic powder) in conductive paste. Specifically, it is a process in which secondary particles (aggregates) of inorganic powder are crushed using a disperser such as a three-roll machine, and the crushed particles (e.g., individual primary particles or secondary particles formed by the aggregation of a small number of primary particles) are dispersed in an organic vehicle. (2) If the dispersibility of the particles after the dispersion process is poor, the variability of various properties of the conductive paste will increase, and the smoothness of the surface of the dried film will deteriorate due to coarse particles caused by insufficiently crushed secondary particles.

[0014] The step of suppressing the above-mentioned (3) reagglomeration is a step of suppressing the "reagglomeration" of the particles after pulverization by adsorbing a dispersant on the newly formed surface of the particle surface newly exposed by pulverization. In the above-mentioned (2) dispersion step, if an appropriate treatment time for the dispersion treatment is not provided, there may be a portion where the dispersant is not adsorbed on the newly formed surface of the particle surface after pulverization. In the (3) step of suppressing reagglomeration, the particles after pulverization may reagglomerate, and the dispersion stability of the conductive paste may decrease. Incidentally, the above-mentioned (2) dispersion step and (3) step of suppressing reagglomeration may proceed simultaneously.

[0015] As a method for improving the dispersion stability of the conductive paste, for example, in Patent Document 1, as a conductive paste having excellent dispersion stability, a technique of dispersing specific metal fine particles in an organic solvent having a dielectric constant in the range of 4 to 24 is disclosed.

Prior Art Documents

Patent Documents

[0016]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0017] However, in the technique described in the above Patent Document 1, although the dispersion stability can be improved to a certain extent, in the above-mentioned (2) dispersion step, the effect of improving the pulverizability of the formed secondary particles is insufficient, and there may be cases where coarse particles caused by insufficiently pulverized secondary particles are included, making it difficult to be suitably used for small-sized products with progressing thinning.

[0018] In view of the above problems, as a result of the intensive research by the present inventor, the present inventor has found that by improving the "wetting" of the surface of the particles constituting the inorganic powder, in the above (2) dispersion step, the secondary particles can be easily crushed, and high dispersibility can be obtained. In addition, in the above (3) step of suppressing re-aggregation, the dispersant is easily adsorbed on the fresh surface of the crushed particle surface, and the "re-aggregation" of the particles can be prevented. Therefore, the dispersion stability of the conductive paste can be maintained even after long-term storage, and the viscosity stability is also excellent.

[0019] In view of such a situation, the present invention aims to provide a conductive paste having high dispersibility and excellent viscosity stability in a conductive paste using fine conductive powder or ceramic powder for miniaturization and thinning of multilayer ceramic electronic components.

Means for Solving the Problems

[0020] According to a first aspect of the present invention, in a conductive paste containing a conductive powder, a ceramic powder, a binder resin, an organic solvent, and a dispersant, the conductive powder has an H2O adsorption amount per unit area at a relative pressure P / P0 = 0.5 of 0.30 mg / m 2 or more and 0.70 mg / m 2 or less, and the dispersant has a relative permittivity of 10 or more and contains at least one compound selected from the group consisting of 1) a compound having an acid group and 2) a compound having an amine group. A conductive paste is provided.

[0021] Furthermore, it is preferable that the compound having an acid group is a compound containing at least one of a carboxyl group and a phosphate group. Furthermore, it is preferable that the binder resin contains one or more selected from the group consisting of cellulose resins and butyral resins. Furthermore, it is preferable that the binder resin content is 0.5% by mass or more and 10% by mass or less based on 100% by mass of the conductive paste. Furthermore, it is preferable that the conductive powder contains one or more metal powders selected from the group consisting of Ni, Cu, Ag, Pd, Au, Pt powders and alloy powders thereof. Furthermore, it is preferable that the conductive powder is nickel powder. Furthermore, it is preferable that the surface composition of the nickel powder contains 20 mol% or more and 90 mol% or less of NiO. Furthermore, it is preferable that the conductive powder content is 30% by mass or more and 70% by mass or less based on 100% by mass of the conductive paste. Furthermore, it is preferable that the ceramic powder is at least one selected from the group consisting of barium titanate and strontium zirconate. Furthermore, it is preferable that the change in viscosity of the conductive paste, after being left to stand at 25°C for 30 days after manufacturing and measured using a Brookfield viscometer at 25°C and 10 rpm, be ±10% or less compared to the viscosity of the conductive paste 8 hours after manufacturing.

[0022] According to a second aspect of the present invention, a multilayer ceramic capacitor is provided which has at least a laminate in which a dielectric layer and an internal electrode layer are stacked, and the internal electrode layer is formed using the conductive paste described above. [Effects of the Invention]

[0023] The conductive paste of the present invention has high dispersibility and excellent viscosity stability over time. Therefore, the conductive paste of the present invention can be suitably used, for example, in electrodes where thinning is progressing, and is particularly suitable for use as electrodes in multilayer ceramic electronic components where miniaturization is progressing. [Brief explanation of the drawing]

[0024] [Figure 1] Figure 1 is a perspective view and a cross-sectional view showing a multilayer ceramic capacitor according to an embodiment. [Modes for carrying out the invention]

[0025] 1. Conductive paste The conductive paste according to the present invention contains conductive powder, ceramic powder, binder resin, organic solvent, and dispersant. The components contained in the conductive paste according to the present invention, as well as the properties of the conductive paste, will be described in detail below.

[0026] (1) Conductive powder The conductive powder is not limited in material, and known metal powders or the like can be appropriately selected and used depending on the required properties. Furthermore, these conductive powders may be used individually or in mixtures.

[0027] As the conductive powder, one or more metal powders selected from the group consisting of nickel (Ni), copper (Cu), silver (Ag), palladium (Pd), gold (Au), platinum (Pt), and alloys thereof can be used. Among these, from the viewpoint of conductivity, corrosion resistance, price, etc., one or more metal powders from Ni, Cu, and their alloys are preferred, and among these, Ni metal powder (nickel powder) is more preferred. Furthermore, the nickel powder may contain several hundred ppm of sulfur (S) to suppress the rapid generation of gas due to the partial thermal decomposition of the binder resin during the debindering process.

[0028] The method for producing conductive powder is not particularly limited, and for example, methods such as directly precipitating chloride vapor from the gas phase in hydrogen gas, atomization from molten metal, spray pyrolysis using an aqueous solution, and a wet method in which raw material metal salts are reduced in an aqueous solution can be applied.

[0029] The average particle size of conductive powder is not particularly limited and should be selected according to the size of the electronic component to be used. For example, for multilayer ceramic capacitors where thin films are becoming increasingly common, the average particle size of conductive powder is preferably 5 μm or less, and more preferably 3 μm or less. If the average particle size exceeds 5 μm, the surface of the internal electrodes becomes very rough, which can degrade the electrical characteristics of the capacitor and is undesirable. Furthermore, the lower limit of the average particle size of conductive powder is not particularly limited, but for example, it is 0.05 μm or more. If the average particle size is smaller than 0.05 μm, handling becomes extremely difficult, and there is a high risk of spontaneous combustion.

[0030] In this specification, unless otherwise specified, the average particle size of conductive powder is the particle size calculated using the specific surface area based on the BET method. For example, the formula for calculating the average particle size of nickel powder is as follows: (1)

[0031] Particle size=6 / (SA×ρ) ···(1) ρ = 8.9 (g / cm³) 3 ): True density of nickel powder SA: Specific surface area of ​​nickel powder

[0032] Furthermore, the strength of the hydrophilicity or hydrophobicity of the conductive powder surface used affects its wettability with solvents and vehicles, significantly impacting the disintegration and dispersibility of aggregates, especially in finely milled powders. The strength of the hydrophilicity or hydrophobicity of the conductive powder surface can be evaluated by the amount of H2O adsorbed.

[0033] In the conductive paste according to this embodiment, the conductive powder used has an H2O adsorption amount of 0.30 mg / m² per unit area at a relative pressure P / P0 = 0.5. 2 More than 0.70mg / m 2 The following is the case: 0.30 mg / m² 2 More than 0.60mg / m 2 The following may also be acceptable: H2O adsorption amount of 0.30 mg / m³ 2If it is less than this value, the hydrophobicity is too strong, and the viscosity stability may deteriorate. This is presumably because a dispersant with a high relative permittivity (high hydrophilicity) does not adsorb to the conductive powder. Also, when the H2O adsorption amount exceeds 0.70 mg / m 2 exceeds this value, the hydrophilicity becomes too strong, and the viscosity stability may deteriorate. This is presumably because the relative permittivity of the conductive powder becomes too high, so the hydrophobic group of the dispersant adsorbed to the conductive powder does not extend, making it difficult to dissolve in the solvent.

[0034] Also, when nickel powder is used as the conductive powder, in terms of its surface composition, the proportion of NiO is preferably 20 mol% or more and 90 mol% or less. If the proportion of NiO is outside the above range, the adsorption state of the dispersant on the surface of the conductive powder may become inappropriate, or a reaction may occur between the conductive powder and the binder resin. When the dispersant does not adsorb sufficiently on the surface of the conductive powder, the wettability with an organic solvent or an organic vehicle deteriorates, and the disintegration of aggregates (secondary particles) of the conductive powder and the suppression of re-aggregation of the particles (primary particles, etc.) after disintegration are insufficient (that is, the dispersion of the conductive powder is insufficient), resulting in a decrease in the viscosity stability of the conductive paste or inferior surface smoothness of the dry film.

[0035] Also, from the perspective of further improving the viscosity stability of the conductive paste and the surface smoothness of the dry film, the proportion of NiO in the surface composition of the nickel powder may be 50 mol% or more, 60 mol% or more, 70 mol% or more, or 80 mol% or more within the above range. The higher the proportion of NiO within the above range, the higher the dispersibility of the conductive paste can be obtained even with a small amount of the dispersant described later.

[0036] The proportion of NiO in the surface composition of nickel powder can be measured using X-ray photoelectron spectroscopy (XPS). For example, if the Ni2p spectrum of the nickel powder surface is analyzed using XPS and Ni peaks, Ni(OH)2 peaks, and NiO peaks are detected, the proportion of NiO (mol%) can be calculated from the ratio of the NiO peak area to the total peak area of ​​these three components.

[0037] Furthermore, the content of conductive powder is preferably 30% by mass or more and 70% by mass or less, relative to the total mass of the conductive paste. If the proportion of conductive powder is less than 30% by mass, the electrode thickness after firing will be significantly thinner, the resistance value will increase, or the electrode film will not be formed sufficiently, resulting in a loss of conductivity and failure to obtain the desired capacitance, which is undesirable. If it exceeds 70% by mass, it will be difficult to thin the electrode film, which is also undesirable. It is more preferable that the proportion of conductive powder relative to the total paste be 40% by mass or more and 60% by mass or less.

[0038] (2) Ceramic powder The ceramic powder is not particularly limited, and for example, in the case of a paste for the internal electrodes of a multilayer ceramic capacitor, a known ceramic powder can be appropriately selected depending on the type of multilayer ceramic capacitor to be used. The ceramic powder preferably contains at least one oxide powder selected from the group consisting of barium titanate-based and strontium zirconate-based powders, and among these, it is preferable to contain barium titanate (BaTiO3, hereinafter sometimes referred to as "BT") powder.

[0039] As barium titanate-based oxide powders, for example, powders containing barium titanate (BT) as the main component and other oxides as minor components can be used. Examples of other oxides as minor components include one or more oxides selected from manganese (Mn), chromium (Cr), silicon (Si), calcium (Ca), barium (Ba), magnesium (Mg), vanadium (V), tungsten (W), tantalum (Ta), niobium (Nb), and rare earth elements. Alternatively, as barium titanate-based oxide powders, perovskite-type oxide ferroelectric powders may be used, such as those in which the Ba atoms and / or Ti atoms of barium titanate (BaTiO3) are substituted with other atoms, such as tin (Sn), lead (Pb), or zirconium (Zr).

[0040] The ceramic powder may include other powders besides barium titanate and strontium zirconate oxide powders. For example, it may also contain ceramic powders that form the green sheet of multilayer ceramic devices, such as zinc oxide (ZnO), ferrite, lead titanium zirconate (PZT), barium oxide (BaO), aluminum oxide (Al2O3), bismuth oxide (Bi2O3), rare earth oxides, titanium oxide (TiO2), and neodymium oxide (Nd2O3).

[0041] The average particle size of the ceramic powder should be selected according to the size of the electronic component to be used, but for example, for multilayer electronic components where thin films are becoming increasingly common, a range of 0.01 μm to 0.5 μm is preferable. If it exceeds 0.5 μm, the surface of the film after coating and drying becomes very uneven, and if it is smaller than 0.01 μm, handling becomes extremely difficult and there is a higher risk of spontaneous combustion, so it is undesirable. The average particle size of the ceramic powder is calculated using the specific surface area based on the BET method, similar to the measurement method for the average particle size of conductive powder described above (for example, in the case of barium titanate, ρ = 6.1 (g / cm²)). 3 The average particle size is calculated from equation (1) above using the formula ().

[0042] The ceramic powder content is, for example, 1% to 20% by mass, and more preferably 5% to 20% by mass, relative to the total mass of the conductive paste.

[0043] (3) Binder resin The binder resin exhibits appropriate viscosity and tackiness when printing conductive paste, improving printability and also enhancing drying characteristics.

[0044] The binder resin is not particularly limited, and known materials can be used depending on the required properties. However, it is preferable to include one or more selected from the group consisting of cellulose resins, butyral resins, and acrylic resins, and it is more preferable to include one or more selected from the group consisting of cellulose resins and butyral resins.

[0045] Cellulose resins include acetylcellulose, methylcellulose, ethylcellulose, butylcellulose, nitrocellulose, and partially etherified celluloses. Butyral resins include polyvinyl butyral.

[0046] In particular, it is preferable to include ethylcellulose from the viewpoint of solubility in solvents and combustion decomposition. Furthermore, when used for multilayer electronic components, a butyral resin may be included, or a butyral resin may be used alone, from the viewpoint of improving the adhesive strength with the green sheet. One type of binder resin may be used, or two or more types may be used.

[0047] The binder resin content is preferably 0.5% to 10% by mass, and more preferably 1% to 5% by mass, relative to the total mass of the conductive paste, from the viewpoint of film strength, de-binderability, printability, and viscosity.

[0048] If the binder resin content is lower than the above range, the strength of the dried film may decrease, or the adhesion between the electrode pattern portion of the conductive paste and the dielectric sheet may worsen during lamination, making it prone to peeling. On the other hand, if the binder resin content exceeds the above range, the binder resin content becomes too high, which can worsen the debinding properties and cause some of the binder resin to remain.

[0049] (4) Organic solvents The organic solvent is not particularly limited, and any known organic solvent can be used that can dissolve the binder resin, disperse the conductive powder to adjust the viscosity of the conductive paste, and impart appropriate fluidity, printability, drying properties, etc. As the organic solvent, various known organic solvents (non-water soluble solvents) can be used, such as organic solvents with a boiling point of about 150°C to 250°C, terpene solvents, aliphatic hydrocarbon solvents, alcohols, etc.

[0050] Examples of terpene solvents include terpineol, dihydroterpineol, and dihydroterpinyl acetate. Examples of aliphatic hydrocarbon solvents include decane and tridecane. Examples of alcohols include decanol and tridecanol. Examples of other organic solvents with boiling points of approximately 150°C to 250°C include isobornyl acetate, butyl carbitol acetate, diethylene glycol butyl methyl ether, and tripropylene glycol dimethyl ether.

[0051] The content of the organic solvent is preferably 30% to 70% by mass, and more preferably 40% to 60% by mass, relative to the total mass of the conductive paste, from the viewpoint of evaporation rate, viscosity, compatibility with the binder resin, and printability.

[0052] In the manufacturing process of conductive paste, the order in which each material is mixed is not particularly limited, but it is preferable to first dissolve the binder resin in a portion of the organic solvent to prepare an organic vehicle, and then mix this organic vehicle with the other materials and the remaining organic solvent (for viscosity adjustment). The amount of binder resin contained in the organic vehicle is not particularly limited, but from the viewpoint of achieving an appropriate viscosity for conductive paste used in increasingly miniaturized electronic components, it is preferable to have an amount of 1% by mass or more and 30% by mass or less, and more preferably 5% by mass or more and 20% by mass or less, relative to the total mass of the organic vehicle.

[0053] (5) Dispersant The role of dispersants is to adsorb onto the surface of inorganic powders (conductive powders and ceramic powders) to suppress aggregation of inorganic powders, or to improve wettability with organic vehicles and disperse them within conductive pastes. Dispersants (surfactants) are generally classified into cationic dispersants, anionic dispersants, nonionic dispersants, and amphoteric dispersants.

[0054] Anionic dispersants (such as acidic dispersants like carboxylic acid dispersants, phosphoric acid dispersants, and phosphate dispersants) are preferred as dispersants for dispersing inorganic powders. However, with the decreasing particle size of inorganic powders, even when using anionic dispersants, the inorganic powder may not be sufficiently dispersed.

[0055] Therefore, as a result of diligent research and development by the present inventors, it has been found that dispersibility can be improved by using a dispersant containing a compound having a dielectric constant of 10 or more and having an acid group and / or an amine group, in combination with a conductive powder having the above-mentioned specific range of H2O adsorption amount. It is believed that such a dispersant has a large adsorption capacity to the surface of inorganic powder, improving the wettability between the inorganic powder and the organic vehicle (step (1) "wetting"), promoting the disintegration of the inorganic powder through its surface modification effect (step (2) "dispersion"), and suppressing re-aggregation (step (3) "suppressing re-aggregation"), thereby contributing to improved dispersibility.

[0056] The relative permittivity of the dispersant may be 10 or higher, 11 or higher, or 12 or higher. By using a dispersant whose relative permittivity satisfies the above range, the smoothness and dry film density of the coating film (dried film) can be improved. The relative permittivity of the dispersant used in this specification refers to the relative permittivity at 20°C. The relative permittivity can be measured by placing the evaluation sample (dispersant to be used) in an electrode cell for liquid samples. There is no particular upper limit to the relative permittivity of the dispersant, but for example, it is about 15 or less.

[0057] Furthermore, the dispersant contains at least one compound selected from the group consisting of 1) compounds having an acid group and 2) compounds having an amine group. Alternatively, the dispersant may be a compound that falls under both 1) compounds having an acid group and 2) compounds having an amine group, i.e., 3) a compound having both an acid group and an amine group in the same molecule, or a mixture containing both compounds of 1) compounds having an acid group and 2) compounds having an amine group.

[0058] Compounds containing an acidic group are preferred, as are compounds containing at least one of a carboxyl group and a phosphate group. Compounds containing an amine group include primary amines, secondary amines, and tertiary amines.

[0059] Furthermore, it is more preferable that the dispersant contains a dispersant with an amine value of 100 or higher. When a dispersant with an amine value of 100 or higher is used, the dispersibility of the conductive paste is further improved, and the smoothness of the dried film surface after coating can be further improved.

[0060] Furthermore, if the dispersant contains a compound having an acidic group, the acid value of the dispersant having an acidic group may be 30 or more and 300 or less, or 30 or more and 200 or less.

[0061] The dispersant content is preferably 0.1% to 2.0% by mass, and more preferably 0.3% to 1.0% by mass, relative to the total mass of the conductive paste. If the dispersant content is less than 0.1% by mass, the dispersant content may be too low, and the effects of crushing and suppressing re-aggregation may not be obtained. On the other hand, if the dispersant content exceeds 2.0% by mass, the paste properties such as printability may change significantly, which is undesirable.

[0062] (6) Other additives The conductive paste of the present invention may optionally contain one or more known additives, such as defoaming agents, plasticizers, thickeners, chelating agents, dispersants other than the above-mentioned dispersants, and thixotropes, without departing from the spirit of the present invention.

[0063] (7) Method for manufacturing conductive paste and its properties (Manufacturing method) The method for manufacturing the conductive paste according to this embodiment is not particularly limited and can be manufactured using known methods. For example, the conductive paste can be manufactured by kneading and dispersing the above materials using equipment such as a mixer, ball mill, kneader, or roll mill to form a slurry.

[0064] (Viscosity change rate) The conductive paste according to this embodiment was left standing at 25°C for 30 days after manufacturing, and its viscosity (η) was measured using a Brookfield viscometer under the conditions of 25°C and 10 rpm. 30 It is preferable that the rate of change of the viscosity (η0) is ±10% or less relative to the viscosity (η0) 8 hours after manufacturing. When the rate of change of the viscosity of the conductive paste is within the above range, the conductive paste exhibits excellent dispersibility.

[0065] The viscosity change rate of the conductive paste after 30 days of standing can be calculated using the following formula (2).

[0066] Viscosity change rate (%) = (η 30 -η0) / η0×100···(2) η 30 :Viscosity at 10rpm after 30 days η0: Viscosity at 10 rpm 8 hours after manufacturing (initial viscosity)

[0067] (Glossiness) The conductive paste according to this embodiment preferably has a glossiness of 10 or higher, more preferably 15 or higher, and more preferably 20 or higher. A higher glossiness of the dried film indicates less diffuse reflection across the entire surface of the dried film, resulting in a smoother surface.

[0068] The dried film for evaluation can be obtained, for example, by printing a conductive paste onto a PET film over an area of ​​5 × 10 cm to a thickness of 30 μm, and then drying it in air at 120°C for 40 minutes.

[0069] 2. Multilayer ceramic capacitors Hereinafter, embodiments of the multilayer ceramic capacitor according to the present invention will be described with reference to the drawings. In the drawings, schematic representations and changes in scale may be made as appropriate. Furthermore, the position and orientation of the components will be described with reference to the XYZ Cartesian coordinate system shown in Figure 1 and other figures as appropriate. In this XYZ Cartesian coordinate system, the X and Y directions are horizontal directions, and the Z direction is vertical (up and down direction).

[0070] Figures 1A and 1B show a multilayer ceramic capacitor 1, which is an example of an electronic component according to the embodiment. The multilayer ceramic capacitor 1 comprises a ceramic laminate 10 in which dielectric layers 12 and internal electrode layers 11 are alternately stacked, and an external electrode 20.

[0071] The following describes a method for manufacturing a multilayer ceramic capacitor using the conductive paste described above. First, a conductive paste is printed onto a ceramic green sheet and dried to form a dried film. Multiple ceramic green sheets, each having this dried film on its upper surface, are laminated by pressing to obtain a laminate. The laminate is then fired to integrate it, thereby creating a ceramic laminate 10 in which internal electrode layers 11 and dielectric layers 12 are alternately laminated. Subsequently, a pair of external electrodes are formed at both ends of the ceramic laminate 10 to manufacture a multilayer ceramic capacitor 1. A more detailed explanation follows below.

[0072] First, an unfired ceramic sheet, known as a ceramic green sheet, is prepared. Examples of this 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, which is then applied in a sheet-like manner to a support film such as a PET film, dried, and the solvent removed. The thickness of the dielectric layer made of the ceramic green sheet is not particularly limited, but from the viewpoint of miniaturizing multilayer ceramic capacitors, a thickness of 0.05 μm to 3 μm is preferred.

[0073] Next, the conductive paste described above is printed and applied to one side of the ceramic green sheet using gravure printing, and then dried to form a dried film on one side of the ceramic green sheet. Multiple such sheets are prepared. The thickness of the dried film formed from the conductive paste is preferably 1 μm or less after drying, from the viewpoint of thinning the internal electrode layer 11.

[0074] Next, the ceramic green sheet is peeled off the support film, and the ceramic green sheet and the dried film formed on one side of it are laminated alternately. Then, a laminate is obtained by heating and pressurizing. Alternatively, protective ceramic green sheets without conductive paste can be placed on both sides of the laminate.

[0075] Next, the laminate is cut to a predetermined size to form green chips, and then the green chips are subjected to a debinder treatment and fired in a reducing atmosphere to produce a laminated ceramic fired body (ceramic laminate 10). The atmosphere used for the debinder treatment is preferably air or an N2 gas atmosphere. The temperature used for the debinder treatment is, for example, 200°C to 400°C. Furthermore, the holding time at the above temperature during the debinder treatment is preferably 0.5 hours to 24 hours. The firing is performed in a reducing atmosphere to suppress oxidation of the metal used in the internal electrode layer, and the firing temperature of the laminate is, for example, 1000°C to 1350°C, with a holding time at the temperature of 0.5 hours to 8 hours.

[0076] By firing the green chips, the organic binder in the ceramic green sheet is completely removed, and the ceramic raw material powder is fired to form a ceramic dielectric layer 12. In addition, the organic vehicle in the dried film is removed, and nickel powder or nickel-based alloy powder is sintered or melted and integrated to form an internal electrode layer 11, and a multilayer ceramic fired body is formed in which multiple dielectric layers 12 and internal electrode layers 11 are alternately stacked. Furthermore, from the viewpoint of incorporating oxygen into the dielectric layer to improve reliability and suppressing re-oxidation of the internal electrode, the multilayer ceramic fired body may be subjected to annealing treatment after firing.

[0077] Then, a multilayer ceramic capacitor 1 is manufactured by providing a pair of external electrodes 20 to the fabricated multilayer ceramic firing body. For example, the external electrodes 20 comprise 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 alloys thereof. Electronic components other than multilayer ceramic capacitors can also be used. [Examples]

[0078] The present invention will be described in detail below based on examples and comparative examples, but the present invention is not limited in any way by the examples.

[0079] [Evaluation items and methods] (1) Rate of change in viscosity of conductive paste over time The rate of change in viscosity over time of conductive paste is calculated as shown in equation (2) below. First, the viscosity of the conductive paste 8 hours after manufacturing is measured as the initial viscosity (η0), and then the viscosity (η) of the conductive paste after standing at room temperature (25°C) for 1 day, 10 days, and 30 days is calculated. x After measuring each viscosity, the change in viscosity after standing for each number of days is expressed as a percentage (%) obtained by dividing the initial viscosity (η0) by the initial viscosity. In addition to the viscosity change rate after 30 days, the viscosity change rates after 1 day and 10 days were also measured to confirm the trend of viscosity change.

[0080] Viscosity change rate (%) = (η x -η0) / η0×100 ···(2) η x :Viscosity at 10 rpm after X days η0: Viscosity at 10 rpm 8 hours after manufacturing (initial viscosity)

[0081] The viscosity of each conductive paste was measured using a Brookfield Type B viscometer at 25°C and 10 rpm (shear rate = 4 sec). -1 The measurement is performed under the following conditions. A smaller change in viscosity over time for the conductive paste is preferable.

[0082] (2) Smoothness (glossiness) of the dried film surface As an indicator of the smoothness of the dried film surface, the following value (glossiness) was measured and evaluated.

[0083] First, conductive paste was printed onto a PET film over an area of ​​5 × 10 cm to a thickness of 30 μm. Then, it was dried in air at 120°C for 40 minutes to obtain a dried film (the conductive paste after drying). The glossiness of the surface of the obtained dried film was measured at an incident angle of 60° using a gloss meter (Gloss Checker; IG-320, Horiba, Ltd.). Higher glossiness indicates less diffuse reflection and a smoother surface.

[0084] (3) Amount of H2O adsorbed The evaluation sample (conductive powder) was degassed under vacuum at 25°C for 8 hours. Then, the H2O adsorption isotherm was measured using a high-precision vapor adsorption measuring device, BELSORP-aqua3 (Microtrac-Bel Co., Ltd.), to determine the amount of H2O adsorbed at a relative pressure P / P0 = 0.5. Furthermore, the specific surface area of ​​the evaluation sample was determined using the BET method based on nitrogen adsorption. The amount of H2O adsorbed per unit area was calculated by dividing the obtained H2O adsorption amount by the specific surface area.

[0085] (4) Percentage of NiO on the nickel powder surface The surface of the Ni powder used as a conductive powder was measured by X-ray photoelectron spectroscopy (XPS), and peaks attributed to nickel hydroxide (Ni(OH)2), nickel oxide (NiO), and metallic nickel were detected. The proportion of NiO (mol%) was calculated from the relative abundances of each peak.

[0086] (5) Relative permittivity of the dispersant The dispersant to be used was placed in an electrode cell for liquid samples, and the relative permittivity was determined using an LCR meter (HP-4278A) under conditions of frequency: 1 MHz and voltage: 1 V.

[0087] [Example 1] As a conductive powder, nickel powder (H2O adsorption capacity 0.31 mg / m³) 2 The mixture consisted of 47% by mass of NiO (surface abundance 34 mol%, particle size 0.4 μm), 4.7% by mass of barium titanate (particle size 0.05 μm) as ceramic powder, 26.67% by mass of an organic vehicle, 0.4% by mass of a dispersant, and 21.23% by mass of the remainder being an organic solvent.

[0088] The organic vehicle used was prepared by mixing 13% by mass of ethylcellulose as a binder resin and 87% by mass of terpineol as an organic solvent, and heating the mixture at 60°C.

[0089] The dispersant used was an amine-based dispersant (a mixture of compounds containing acid groups and compounds containing amine groups) with a dielectric constant of 12.5, an acid value of 58, and an amine value of 110.

[0090] Terpineol was used as the organic solvent.

[0091] These materials were mixed and dispersed in a three-roll mill at 25°C and 55% relative humidity to produce a conductive paste. The initial viscosity and viscosity after a predetermined time were measured, and the viscosity change rate at each time point was calculated. The glossiness of the dried film prepared using the conductive paste was also measured.

[0092] Table 1 shows the types and amounts of each material used, while Table 2 shows the measurement and calculation results.

[0093] [Example 2] As a conductive powder, the H2O adsorption capacity is 0.53 mg / m². 2 A conductive paste was prepared in the same manner as in Example 1, except that Ni powder with a surface NiO content of 26% and a particle size of 0.2 μm was used, the dispersant content was set to 0.6 mass%, and the organic solvent was dihydroterpinyl acetate with a remaining content of 21.03 mass%. The types and contents of each material used are shown in Table 1. Furthermore, the viscosity change rate and gloss of the obtained conductive paste were determined in the same manner as in Example 1. The results are shown in Table 2. [Example 3] As a conductive powder, the H2O adsorption capacity is 0.42 mg / m². 2A conductive paste was prepared in the same manner as in Example 2, except that Ni powder with a surface NiO content of 45% and a particle size of 0.08 μm was used as the ceramic powder, BT with a particle size of 0.02 μm was used, the dispersant content was 1.5 mass%, and the remaining organic solvent content was 20.13 mass%. The types and contents of each material used are shown in Table 1. Furthermore, the viscosity change rate and gloss of the obtained conductive paste were determined in the same manner as in Example 1. The results are shown in Table 2. [Example 4] A conductive paste was prepared in the same manner as in Example 2, except that an acid-based dispersant having a carboxyl group with a dielectric constant of 11.4 and an acid value of 129 was used as the dispersant. The types and contents of each material used are shown in Table 1. In addition, the viscosity change rate and gloss of the obtained conductive paste were determined in the same manner as in Example 1. The results are shown in Table 2. [Example 5] As a conductive powder, the H2O adsorption capacity is 0.53 mg / m². 2 A conductive paste was prepared in the same manner as in Example 4, except that Ni powder with a surface NiO content of 45% and a particle size of 0.08 μm was used as the ceramic powder, BT with a particle size of 0.02 μm was used, the dispersant content was 1.5 mass%, and the remaining organic solvent content was 20.13 mass%. The types and contents of each material used are shown in Table 1. Furthermore, the viscosity change rate and gloss of the obtained conductive paste were determined in the same manner as in Example 1. The results are shown in Table 2. [Example 6] A conductive paste was prepared in the same manner as in Example 2, except that the dispersant content was 1.5 mass% and the remaining organic solvent content was 20.13 mass%. The types and contents of each material used are shown in Table 1. In addition, the viscosity change rate and gloss of the obtained conductive paste were determined in the same manner as in Example 1. The results are shown in Table 2. [Example 7] As a conductive powder, the H2O adsorption capacity is 0.34 mg / m². 2A conductive paste was prepared in the same manner as in Example 6, except that Ni powder with a surface NiO content of 79% and a particle size of 0.2 μm was used. The types and contents of each material used are shown in Table 1. In addition, the viscosity change rate and gloss of the obtained conductive paste were determined in the same manner as in Example 1. The results are shown in Table 2. [Example 8] As a conductive powder, the H2O adsorption capacity is 0.38 mg / m². 2 A conductive paste was prepared in the same manner as in Example 2, except that Ni powder with a surface NiO content of 89% and a particle size of 0.2 μm was used. The types and contents of each material used are shown in Table 1. In addition, the viscosity change rate and gloss of the obtained conductive paste were determined in the same manner as in Example 1. The results are shown in Table 2.

[0094] [Comparative Example 1] A conductive paste was prepared in the same manner as in Example 2, except that an amine-based dispersant with a dielectric constant of 3.0, an acid value of 53, and an amine value of 48 was used as the dispersant. The types and contents of each material used are shown in Table 1. In addition, the viscosity change rate and gloss of the obtained conductive paste were determined in the same manner as in Example 1. The results are shown in Table 2. [Comparative Example 2] A conductive paste was prepared in the same manner as in Example 2, except that an amine-based dispersant having an amine group with a dielectric constant of 8.5, an acid value of 60, and an amine value of 60 was used as the dispersant. The types and contents of each material used are shown in Table 1. In addition, the viscosity change rate and gloss of the obtained conductive paste were determined in the same manner as in Example 1. The results are shown in Table 2. [Comparative Example 3] As a conductive powder, the H2O adsorption capacity is 0.29 mg / m². 2 A conductive paste was prepared in the same manner as in Example 2, except that Ni powder with a surface NiO content of 49% and a particle size of 0.2 μm was used. The types and contents of each material used are shown in Table 1. In addition, the viscosity change rate and gloss of the obtained conductive paste were determined in the same manner as in Example 1. The results are shown in Table 2. [Comparative Example 4] As a conductive powder, the H2O adsorption capacity is 0.29 mg / m². 2A conductive paste was prepared in the same manner as in Example 6, except that Ni powder with a surface NiO content of 49% and a particle size of 0.2 μm was used. The types and contents of each material used are shown in Table 1. In addition, the viscosity change rate and gloss of the obtained conductive paste were determined in the same manner as in Example 1. The results are shown in Table 2. [Comparative Example 5] As a conductive powder, the H2O adsorption capacity is 0.71 mg / m². 2 A conductive paste was prepared in the same manner as in Example 2, except that Ni powder with a surface NiO content of 42% and a particle size of 0.2 μm was used. The types and contents of each material used are shown in Table 1. In addition, the viscosity change rate and gloss of the obtained conductive paste were determined in the same manner as in Example 1. The results are shown in Table 2.

[0095] [Table 1]

[0096] [Table 2]

[0097] (Evaluation results) The conductive paste of the example containing a dispersant with a relative permittivity of 10 or higher exhibits higher gloss and superior smoothness on the dried film surface compared to the conductive paste of the comparative example with a relative permittivity of less than 10. Furthermore, the small viscosity change rate indicates that the improved dispersibility due to the adsorption of the dispersant is maintained over a long period of time.

[0098] Examples 4 and 5, which used a dispersant without an amine value, showed slightly lower gloss compared to the other examples, but still exhibited sufficiently high gloss and a small viscosity change compared to the comparative examples. Therefore, from the viewpoint of improving the overall smoothness of the dried film surface, it is preferable to use a dispersant with an amine value of 100 or higher.

[0099] On the other hand, the conductive paste of the comparative example containing a dispersant with a dielectric constant of less than 10 shows very low gloss on the dried film surface and poor smoothness. This is thought to be because the dispersant does not meet the required properties, resulting in poor wettability to the particle surface and insufficient adsorption of the dispersant to the particle surface. As a result, the disintegration and re-aggregation of particles cannot be sufficiently suppressed, leading to poor dispersibility of the conductive paste, material unevenness, and poor smoothness of the dried film surface. Furthermore, the poor adsorption of the dispersant results in poor dispersion stability, leading to increased aggregation of each material over time, which is thought to cause a larger viscosity change rate over time.

[0100] Furthermore, in Comparative Examples 3 to 5, where the amount of H2O adsorbed per unit area is outside the scope of the invention, although the smoothness is somewhat low, the surface condition of the conductive powder is not appropriate in all cases. As a result, the dispersion stability when pasteurized is poor, aggregation of conductive powders increases over time, and the viscosity change rate also increases over time.

[0101] Furthermore, the technical scope of the present invention is not limited to the embodiments described above. One or more of the requirements described above may be omitted. Also, the requirements described above may be combined as appropriate. In addition, to the extent permitted by law, all disclosures of the documents cited above shall be incorporated as part of the description herein. [Explanation of Symbols]

[0102] 1. Multilayer ceramic capacitor 10 Ceramic Laminate 11 Internal electrode layer 12 Dielectric layer 20 External electrode 21 External electrode layer 22 Plating layer

Claims

1. In a conductive paste containing conductive powder, ceramic powder, binder resin, organic solvent and dispersant, The conductive powder has a relative pressure of P / P ０ = H per unit area at 0.5 ２ O adsorption amount: 0.30 mg / m³ ２ 0.60mg / m or more ２ The following conditions apply, and the average particle size calculated using the specific surface area based on the BET method is 0.05 μm or more and 5 μm or less. The ceramic powder has an average particle size of 0.01 μm or more and 0.5 μm or less, calculated using the specific surface area based on the BET method. The dispersant has a dielectric constant of 10 or more and contains at least one compound selected from the group consisting of 1) compounds having an acid group and 2) compounds having an amine group. Conductive paste.

2. The conductive paste according to claim 1, wherein the compound having the acid group is a compound containing at least one of a carboxyl group and a phosphate group.

3. The conductive paste according to claim 1 or claim 2, wherein the binder resin contains one or more selected from the group consisting of cellulose resins and butyral resins.

4. The conductive paste according to any one of claims 1 to 3, wherein the content of the binder resin is 0.5% by mass or more and 10% by mass or less based on 100% by mass of the conductive paste.

5. The conductive paste according to any one of claims 1 to 4, wherein the conductive powder contains one or more metal powders selected from the group consisting of Ni, Cu, Ag, Pd, Au, Pt powders, and alloy powders thereof.

6. The conductive paste according to any one of claims 1 to 5, wherein the conductive powder is nickel powder.

7. The conductive paste according to claim 6, wherein the surface composition of the nickel powder contains 20 mol% or more and 90 mol% or less of NiO.

8. The conductive paste according to any one of claims 1 to 7, wherein the content of the conductive powder is 30% by mass or more and 70% by mass or less based on 100% by mass of the conductive paste.

9. The conductive paste according to any one of claims 1 to 8, wherein the ceramic powder is at least one selected from the group consisting of barium titanate-based and strontium zirconate-based materials.

10. A conductive paste according to any one of claims 1 to 9, wherein the rate of change in the viscosity of the conductive paste, when left standing at 25°C for 30 days after manufacturing and measured using a Brookfield viscometer under the conditions of 25°C and 10 rpm, is ±10% or less compared to the viscosity of the conductive paste 8 hours after manufacturing.

11. The laminate comprises at least a dielectric layer and an internal electrode layer, A multilayer ceramic capacitor in which the internal electrode layer is formed using the conductive paste described in any one of claims 1 to 10.

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