Conductive paste and multilayer ceramic capacitor

Abstract

To provide a conductive paste having high dispersibility and excellent in viscosity stability with time.SOLUTION: A conductive paste includes a conductive powder, a ceramic powder, a binder resin, an organic solvent and a dispersant. An H2O adsorption amount of the conductive powder per unit area at a relative pressure P / P0=0.5 is 0.30 mg / m2 to 0.70 mg / m2. The dispersant has a dielectric constant of 10 or more and includes at least one kind of compound selected from a group consisting of 1) a compound having an acid group and 2) a compound having an amine group.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] With the miniaturization and high performance of electronic devices such as mobile phones and digital devices, miniaturization and high capacitance are desired for electronic components including multilayer ceramic capacitors. A multilayer ceramic capacitor has a structure in which a plurality of dielectric layers and a plurality of internal electrode layers are alternately laminated, and by thinning these dielectric layers and internal electrode layers, miniaturization and high capacitance can be achieved.

[0003] A multilayer ceramic capacitor is manufactured, for example, as follows. First, a conductive paste for an internal electrode is printed (applied) in a predetermined electrode pattern on the surface of a dielectric green sheet containing a dielectric powder such as barium titanate (BaTiO3) and a binder resin, and dried to form a dry film. Next, a laminate is obtained by laminating the dry film and the green sheet so as to alternately overlap. Next, this laminate is heat-pressed and integrated to form a pressed body. This pressed body is cut, and after performing a deorganic binder treatment in an oxidizing atmosphere or an inert atmosphere, firing is performed to obtain a fired chip. Next, an external electrode paste is applied to both ends of the fired chip, and after firing, nickel plating or the like is applied to the external electrode surface to obtain a multilayer ceramic capacitor.

[0004] The conductive paste used for forming the internal electrode layer contains, for example, a conductive powder, a ceramic powder, a binder resin, and an organic solvent. Further, the conductive paste may contain a dispersant in order to improve the dispersibility of the conductive powder and the like.

[0005] In recent years, with the thinning of the internal electrode layer, the conductive powder contained in the conductive paste also tends to have a smaller particle size (become fine powder). When the particle size of the conductive powder becomes smaller, 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 reach the sub-micron level, the particles tend to adhere to each other by forces such as intermolecular forces and electrostatic forces, easily forming coarse aggregates. If such aggregates exist in the conductive powder, they may form convex portions on the surface of the internal electrode layer during the manufacture of the multilayer ceramic capacitor, and in some cases, may break through the ceramic dielectric layer, causing a short circuit between the internal electrode layers.

[0006] The conductive paste is produced, for example, by dissolving a binder resin in an organic solvent to form an organic vehicle, and then containing other materials such as conductive powder and kneading and dispersing them. As a kneading method in the conventional manufacturing process of the conductive paste, for example, a method of using devices such as a high-speed shear mixer or a planetary mixer with two or more axes to mix (knead) inorganic powders such as conductive powder and ceramic powder, a dispersant, an organic solvent, etc. in the organic vehicle is used.

[0007] However, in the conventional kneading method, with the reduction of the particle size of the conductive powder, there may be a state where the organic vehicle is not sufficiently mixed, or the surface of the conductive powder or ceramic powder is not sufficiently wetted. Furthermore, when a dispersion treatment is performed with a three-roll mill or the like after kneading, problems such as poor dispersion of the conductive powder (fine metal powder) and flakes may occur.

[0008] In addition, the conductive powder produced by the wet manufacturing method, which is one of the general methods for manufacturing fine metal powder, is prone to promote the aggregation of the conductive powder at the stage of the drying process of the wet manufacturing method, and a large number of aggregates (secondary particles) have already been formed when the conductive powder is kneaded into the organic vehicle, and the above problems are likely to occur.

[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 in which the particles constituting the inorganic powder are dispersed in the paste can be divided into the following steps, for example.

[0010] (1) The step in which the surface of the particles (including secondary particles) constituting the inorganic powder "gets wet" (2) The step in which the secondary particles are crushed and the crushed particles are dispersed in the paste (3) The step of suppressing the "re-aggregation" of the crushed particles

[0011] The above step (1) of getting wet is a step in which an organic vehicle / organic solvent adheres to the surface of the particles constituting the conductive powder and the ceramic powder. In a conductive paste containing a dispersant, in this step, the dispersant is adsorbed on the surface of the 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, and the dispersant is adsorbed on the inner wall of the secondary particles.

[0012] Also, the step (1) of getting wet is specifically, for example, a step of performing kneading and stirring using a device such as the above-mentioned mixer, and is also called a pretreatment step. The degree of "wetting" of the conductive powder and the ceramic powder affects the processing time in the next dispersion step.

[0013] The above step (2) of dispersion is a step that greatly affects the dispersibility of the conductive powder and the ceramic powder (inorganic powder) in the conductive paste. Specifically, for example, using a dispersing machine such as a three-roll mill to crush the secondary particles (aggregates) of the inorganic powder and disperse the crushed particles (e.g., single primary particles or secondary particles aggregated by a small number of primary particles) in the organic vehicle. If the dispersibility of the particles after the step (2) of dispersion is poor, the variations in various properties of the conductive paste will increase, or the surface smoothness 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 appeared 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. Note that 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 it may contain coarse particles caused by insufficiently pulverized secondary particles, 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 disintegrated, 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 disintegrated 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] Moreover, 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. Further, it is preferable that the binder resin contains one or more selected from the group consisting of cellulose resins and butyral resins. Further, it is preferable that the content of the binder resin is 0.5% by mass or more and 10% by mass or less with respect to 100% by mass of the conductive paste. Further, 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. Further, it is preferable that the conductive powder is nickel powder. Further, in the surface composition of the nickel powder, it is preferable that NiO is 20 mol% or more and 90 mol% or less. Further, it is preferable that the content of the conductive powder is 30% by mass or more and 70% by mass or less with respect to 100% by mass of the conductive paste. Further, it is preferable that the ceramic powder is at least one selected from the group consisting of barium titanate-based and strontium zirconate-based. Further, after the conductive paste is manufactured, it is left standing at 25 ° C for 30 days, and when measured with a Brookfield viscometer under the conditions of 25 ° C and 10 rpm, the change rate of the viscosity of the conductive paste is ± 10% or less with respect to the viscosity of the conductive paste 8 hours after manufacture.

[0022] According to the second aspect of the present invention, there is provided a laminated ceramic capacitor having at least a laminate of a dielectric layer and an internal electrode layer, and the internal electrode layer is formed using the above conductive paste.

Advantages 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, for example, electrodes with thinning, and particularly can be suitably used for electrodes of laminated ceramic electronic components with progressing miniaturization.

Brief Description of the Drawings

[0024]

Figure 1

Mode 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. Hereinafter, each component contained in the conductive paste according to the present invention, and the characteristics of the conductive paste will be described in detail.

[0026] (1) Conductive Powder The material of the conductive powder is not particularly limited, and known metal powders and the like can be appropriately selected and used according to the required characteristics. In addition, these conductive powders may be used alone or in combination.

[0027] As the conductive powder, for example, 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 comprehensive judgment from the viewpoints of conductivity, corrosion resistance, price, etc., one or more metal powders of Ni, Cu, and alloys thereof are preferable, and among them, nickel metal powder (nickel powder) is more preferable. Further, the nickel powder may contain sulfur (S) of about several hundred ppm in order to suppress the sudden gas generation due to the partial thermal decomposition of the binder resin during the debinding treatment.

[0028] The manufacturing method of the conductive powder is not particularly limited. For example, a method of directly depositing chloride vapor from the gas phase in hydrogen gas, an atomization method from molten metal, a spray pyrolysis method using an aqueous solution, a wet method of reducing a metal salt of a raw material in an aqueous solution, etc. can be applied.

[0029] The average particle size of the conductive powder is not particularly limited and may be selected according to the size of the electronic component to be used, etc. For example, for a multilayer ceramic capacitor with a progressing thinning of the film, the average particle size of the conductive powder is preferably 5 μm or less, and more preferably 3 μm or less. When the average particle size exceeds 5 μm, the unevenness on the surface of the internal electrode becomes severe, which may deteriorate the electrical characteristics of the capacitor, and this is not preferable. Also, the lower limit of the average particle size of the conductive powder is not particularly limited, but for example, it is 0.05 μm or more. When the average particle size is less than 0.05 μm, handling becomes extremely difficult, and the risk of spontaneous ignition, etc. is likely to occur.

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

[0031] Particle size = 6 / (S.A × ρ) ···(1) ρ = 8.9 (g / cm 3 ): True density of nickel powder S.A: Specific surface area of nickel powder

[0032] Also, depending on the strength of hydrophilicity / hydrophobicity on the surface of the conductive powder used, the wettability with the solvent or vehicle changes, and it particularly greatly affects the disintegration and dispersibility of aggregates of fine powder with progressing refinement. The strength of hydrophilicity / hydrophobicity on the surface of the conductive powder can be evaluated by the H2O adsorption amount.

[0033] In the conductive paste according to this embodiment, the conductive powder used 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 it may also be 0.30 mg / m 2 or more and 0.60 mg / m 2 or less. When the H2O adsorption amount is 0.30 mg / m 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 on 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 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 is not sufficiently adsorbed on the surface of the conductive powder, the wettability with the organic solvent or the organic vehicle deteriorates, and the disintegration of the aggregates (secondary particles) of the conductive powder and the suppression of the 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] Incidentally, the ratio of NiO in the surface composition of nickel powder can be measured using X-ray photoelectron spectroscopy (XPS). For example, when analyzing the Ni2p spectrum of the nickel powder surface using XPS and detecting Ni peak, Ni(OH)2 peak, and NiO peak, the ratio (mol%) of NiO can be measured from the area ratio of the NiO peak to the total peak area of these three components.

[0037] Also, the content ratio of the conductive powder is preferably 30% by mass or more and 70% by mass or less with respect to the total mass of the conductive paste. If the ratio of the conductive powder is less than 30% by mass, the electrode thickness after firing may become extremely thin, the resistance value may increase, or the formation of the electrode film may be insufficient and conductivity may be lost, resulting in failure to obtain the target capacitance, which is not preferable. If it exceeds 70% by mass, it becomes difficult to make the electrode film thinner, which is not preferable. More preferably, the ratio of the conductive powder to the whole paste is 40% by mass or more and 60% by mass or less.

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

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

[0040] The ceramic powder may include other powders other than barium titanate-based and strontium zirconate-based oxide powders. For example, ceramic powders such as zinc oxide (ZnO), ferrite, lead titanate zirconate (PZT), barium oxide (BaO), aluminum oxide (Al2O3), bismuth oxide (Bi2O3), rare earth oxides, titanium oxide (TiO2), neodymium oxide (Nd2O3), etc., which are ceramic powders for forming the green sheet of the multilayer ceramic device, can also be contained.

[0041] The average particle size of the ceramic powder may be selected according to the size of the electronic component to be used, etc. For example, for multilayer electronic components with progressing thinning, a range of 0.01 μm or more and 0.5 μm or less is preferable. If it exceeds 0.5 μm, the unevenness of the film surface after coating and drying becomes severe, and if it is less than 0.01 μm, handling becomes extremely difficult and the risk of spontaneous ignition, etc. also easily occurs, so it is not preferable. The average particle size of the ceramic powder is the particle size calculated using the specific surface area based on the BET method, similar to the measurement method of the average particle size of the above conductive powder (for example, in the case of barium titanate, ρ = 6.1 (g / cm 3 ) is used, and the average particle size is calculated from the above formula (1)).

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

[0043] (3) Binder resin When printing the conductive paste, the binder resin exhibits appropriate viscosity and adhesiveness, improves printability, and also has the effect of improving drying characteristics and the like.

[0044] The binder resin is not particularly limited, and known materials can be used according to the required properties. For example, it preferably contains one or more selected from the group consisting of cellulose resins, butyral resins, and acrylic resins, and more preferably contains one or more selected from the group consisting of cellulose resins and butyral resins.

[0045] Examples of the cellulose resin include acetyl cellulose, methyl cellulose, ethyl cellulose, butyl cellulose, nitrocellulose, and partially etherified celluloses. Examples of the butyral resin include polyvinyl butyral.

[0046] Among them, it is preferable to contain ethyl cellulose from the viewpoints of solubility in solvents, combustion and decomposition properties, etc. Also, when used for laminated electronic components, a butyral resin may be included from the viewpoint of improving the adhesion strength with the green sheet, or a butyral resin may be used alone. The binder resin may be used singly or in combination of two or more.

[0047] The content of the binder resin is preferably 0.5% by mass or more and 10% by mass or less, more preferably 1% by mass or more and 5% by mass or less, based on the total mass of the conductive paste, from the viewpoints of film strength, debinding property, printability, and viscosity.

[0048] When the content of the binder resin is less than the above range, the strength of the dry film may decrease, or the adhesion between the electrode pattern portion of the conductive paste and the dielectric sheet may deteriorate during lamination, making it easy to peel off. On the other hand, when the content of the binder resin exceeds the above range, since the content of the binder resin becomes too high, the debinding property deteriorates, and a part of the binder resin may remain.

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

[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 organic solvents having a boiling point of about 150°C to 250°C other than the above 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% by mass or more and 70% by mass or less, more preferably 40% by mass or more and 60% by mass or less, from the viewpoints of evaporation amount, viscosity, compatibility with the binder resin, and printability, based on the total mass of the conductive paste.

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

[0053] (5) Dispersant The role of the dispersant is to adsorb on the surface of the inorganic powder (conductive powder and ceramic powder) to suppress the aggregation of the inorganic powder, or to improve the wettability with the organic vehicle and disperse it in the conductive paste. Dispersants (surfactants) are generally classified into cationic dispersants, anionic dispersants, nonionic dispersants, and amphoteric dispersants.

[0054] As the dispersant for dispersing the inorganic powder, anionic dispersants (for example, acid-based dispersants such as carboxylic acid-based dispersants, phosphoric acid-based dispersants, and phosphate-based dispersants) are preferably used. However, with the reduction in the particle size of the inorganic powder, there were cases where the inorganic powder was not sufficiently dispersed even when an anionic dispersant was used.

[0055] Therefore, as a result of the intensive research and development by the present inventor, it has been found that by combining with the conductive powder having the above-described specific range of H2O adsorption amount, the dispersibility can be improved by using a dispersant containing a compound having a relative dielectric constant of 10 or more and having an acid group and / or an amine group. Such a dispersant has a strong adsorption force on the surface of the inorganic powder and improves the wettability between the inorganic powder and the organic vehicle (the step of "wetting" in (1) above). Therefore, it is considered to contribute to improving the dispersibility by promoting the pulverization of the inorganic powder by its surface modification action (the step of "dispersing" in (2) above) and suppressing re-aggregation (the step of suppressing "re-aggregation" in (3) above).

[0056] The relative permittivity of the dispersant may be 10 or more, may be 11 or more, or may be 12 or more. By using a dispersant whose relative permittivity satisfies the above range, the smoothness and dry film density of the coating film (dry film) can be improved. The relative permittivity of the dispersant used in this specification indicates the relative permittivity at 20°C. The relative permittivity can be measured by putting the evaluation sample (the dispersant to be used) into an electrode cell for liquid samples. The upper limit of the relative permittivity of the dispersant is not particularly limited, but is, for example, about 15 or less.

[0057] Further, the dispersant 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. The dispersant may be a compound corresponding to both 1) the compound having an acid group and 2) the compound having an amine group, that is, 3) a compound having an acid group and an amine group in the same molecule, or may be a mixture containing both 1) the compound having an acid group and 2) the compound having an amine group.

[0058] As the compound having an acid group, a compound containing at least one of a carboxyl group and a phosphate group is preferable. The compound having an amine group includes a primary amine, a secondary amine, and a tertiary amine.

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

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

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

[0062] (6) Other additive components In the conductive paste of the present invention, within the range not departing from the gist of the present invention, one or more known additives such as defoamers, plasticizers, thickeners, chelating agents, dispersants other than the above-mentioned dispersants, and thixotropic agents may be added as necessary.

[0063] (7) Manufacturing method and characteristics of the conductive paste (Manufacturing method) The manufacturing method of the conductive paste according to the present embodiment is not particularly limited, and it can be manufactured using a known method. For example, the conductive paste is manufactured by kneading and dispersing each of the above materials using a device such as a mixer, ball mill, kneader, or roll mill, and then slurrying.

[0064] (Viscosity change rate) The conductive paste according to the present embodiment is allowed to stand at 25°C for 30 days after manufacturing, and the viscosity (η 30 ) when measured at 25°C and 10 rpm using a Brookfield viscometer preferably has a change rate of ±10% or less with respect to the viscosity (η0) 8 hours after manufacturing. When the change rate of the viscosity of the conductive paste is within the above range, the dispersibility of the conductive paste is excellent.

[0065] Note that the viscosity change rate of the conductive paste after standing for 30 days can be obtained by the following formula (2).

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

[0067] (Gloss) The conductive paste according to this embodiment preferably has a gloss of 10 or more, preferably 15 or more, and more preferably 20 or more for its dry film. The higher the gloss of the dry film, the less diffuse reflection on the entire surface of the dry film, indicating that a smoother surface is obtained.

[0068] Note that the dry film for evaluation can be obtained, for example, by printing the conductive paste on a PET film with an area of 5 × 10 cm to a film thickness of 30 μm and then drying it in air at 120°C for 40 minutes.

[0069] 2. Multilayer ceramic capacitor Hereinafter, embodiments of the multilayer ceramic capacitor according to the present invention will be described with reference to the drawings. In the drawings, it may be schematically represented or the scale may be changed as appropriate. Also, the position, direction, etc. of the members will be described with reference to the XYZ orthogonal coordinate system shown in FIG. 1, etc. as appropriate. In this XYZ orthogonal coordinate system, the X direction and the Y direction are horizontal directions, and the Z direction is the vertical direction (up and down direction).

[0070] FIGS. 1A and B are diagrams showing a multilayer ceramic capacitor 1, which is an example of an electronic component according to the embodiment. The multilayer ceramic capacitor 1 includes a ceramic laminate 10 in which dielectric layers 12 and internal electrode layers 11 are alternately laminated, and external electrodes 20.

[0071] Hereinafter, a method for manufacturing a multilayer ceramic capacitor using the above conductive paste will be described. First, the conductive paste is printed on a ceramic green sheet and dried to form a dried film. After obtaining a laminate by laminating a plurality of ceramic green sheets having this dried film on the upper surface by pressure bonding, the laminate is fired and integrated to produce a ceramic laminate 10 in which internal electrode layers 11 and dielectric layers 12 are alternately laminated. Then, a pair of external electrodes are formed at both ends of the ceramic laminate 10 to manufacture a multilayer ceramic capacitor 1. This will be described in more detail below.

[0072] First, a ceramic green sheet, which is an unfired ceramic 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 raw material powder of a predetermined ceramic such as barium titanate, and applying it in a sheet shape on a support film such as a PET film and drying to remove the solvent. The thickness of the dielectric layer made of the ceramic green sheet is not particularly limited, but from the viewpoint of the demand for miniaturization of the multilayer ceramic capacitor, it is preferably 0.05 μm or more and 3 μm or less.

[0073] Next, using the gravure printing method, the above conductive paste is printed and applied on one side of this ceramic green sheet, dried, and a plurality of ceramic green sheets with a dried film formed on one side are prepared. Note that, from the viewpoint of the demand for thinning of the internal electrode layer 11, the thickness of the dried film formed from the conductive paste is preferably 1 μm or less after drying.

[0074] Next, the ceramic green sheet is peeled from the support film, and after laminating so that the ceramic green sheet and the dried film formed on one side thereof are alternately arranged, a laminate is obtained by heat and pressure treatment. Note that a configuration may also be adopted in which protective ceramic green sheets on which the conductive paste is not applied are further arranged on both sides of the laminate.

[0075] Next, after cutting the laminate into a predetermined size to form a green chip, the green chip is subjected to a debinding process and fired in a reducing atmosphere to produce a fired laminated ceramic body (ceramic laminate 10). Note that the atmosphere in the debinding process is preferably an air or N2 gas atmosphere. The temperature during the debinding process is, for example, 200°C or higher and 400°C or lower. Also, the holding time of the above temperature during the debinding process is preferably 0.5 hours or more and 24 hours or less. Further, firing is performed in a reducing atmosphere to suppress oxidation of the metal used in the internal electrode layer, and the temperature during firing of the laminate is, for example, 1000°C or higher and 1350°C or lower, and the holding time of the temperature during firing is, for example, 0.5 hours or more and 8 hours or less.

[0076] By firing the green chip, the organic binder in the ceramic green sheet is completely removed, and the raw material powder of the ceramic is fired to form a ceramic dielectric layer 12. Also, the organic vehicle in the dry film is removed, and the nickel powder or an alloy powder mainly composed of nickel is sintered, melted, and integrated to form an internal electrode layer 11, and a fired laminated ceramic body in which a plurality of dielectric layers 12 and internal electrode layers 11 are alternately laminated is formed. Note that, from the viewpoint of taking in oxygen into the inside of the dielectric layer to improve reliability and suppressing re-oxidation of the internal electrode, an annealing process may be performed on the fired laminated ceramic body.

[0077] Then, a pair of external electrodes 20 are provided on the produced fired laminated ceramic body to manufacture a laminated ceramic capacitor 1. For example, the external electrode 20 includes an external electrode layer 21 and a plating layer 22. The external electrode layer 21 is electrically connected to the internal electrode layer 11. Note that, as the material of the external electrode 20, for example, copper, nickel, or an alloy thereof can be preferably used. Note that electronic components other than laminated ceramic capacitors can also be used as the electronic component.

Example

[0078] Hereinafter, the present invention will be described in detail based on examples and comparative examples, but the present invention is not limited by the examples at all.

[0079] [Evaluation Items and Their Methods] (1) Rate of change in viscosity of the conductive paste over time As shown in the following formula (2), the rate of change in viscosity of the conductive paste over time is first measured with the viscosity of the conductive paste 8 hours after production as the initial viscosity (η0), and then the viscosity (η x ) of the conductive paste after standing at room temperature (25 °C) for 1 day, 10 days, and 30 days is measured respectively. After that, the change amount of viscosity after standing for each number of days is expressed as a percentage (%) obtained by dividing by the initial viscosity (η0). By measuring not only the viscosity change rate after 30 days but also the viscosity change rates after 1 day and 10 days, the tendency of viscosity change was also confirmed.

[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 production (initial viscosity)

[0081] Note that the viscosity of each conductive paste is measured using a Brookfield B-type viscometer under the conditions of 25 °C and 10 rpm (shear rate = 4 sec -1 ). The smaller the rate of change in viscosity of the conductive paste over time, the more preferable.

[0082] (2) Smoothness (glossiness) of the dry film surface As an index of the smoothness of the dry film surface, the value (glossiness) measured by the following method was evaluated.

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

[0084] (3) H2O adsorption amount The sample for evaluation (conductive powder) was vacuum degassed at 25°C for 8 hours, and then the H2O adsorption isotherm was measured using a high-precision vapor adsorption amount measuring device BELSORP-aqua3 (Microtrac BEL Corp.) to obtain the H2O adsorption amount at a relative pressure P / P0 = 0.5. Also, the specific surface area value of the sample for evaluation was determined using the BET method by the nitrogen adsorption method. By dividing the obtained H2O adsorption amount by the specific surface area value, the H2O adsorption amount per unit area was calculated.

[0085] (4) Ratio of NiO on the surface of nickel powder The surface of the Ni powder used as the conductive powder was measured by X-ray photoelectron spectroscopy (XPS) to detect the peaks of nickel attributed to nickel hydroxide (Ni(OH)2), nickel oxide (NiO), and metallic nickel, and the ratio (mol%) of NiO was calculated from their respective abundance ratios.

[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 the conditions of a frequency of 1 MHz and a voltage of 1 V.

[0087] [Example 1] As the conductive powder, nickel powder (H2O adsorption amount 0.31 mg / m 2 , surface abundance ratio of NiO 34 mol%, particle size 0.4 μm) was 47% by mass, barium titanate (particle size 0.05 μm) as the ceramic powder was 4.7% by mass, the organic vehicle was 26.67% by mass, the dispersant was 0.4% by mass, and the remaining organic solvent was 21.23% by mass, and they were blended.

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

[0089] As the dispersant, an amine-based dispersant (a mixture of a compound having an acid group and a compound having an amine group) with a relative permittivity of 12.5, an acid value of 58, and an amine value of 110 was used.

[0090] Terpineol was used as the organic solvent.

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

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

[0093] [Example 2] As the conductive powder, Ni powder with an H2O adsorption amount of 0.53 mg / m 2 , a surface presence ratio of NiO of 26%, and a particle size of 0.2 μm was used. A conductive paste was prepared in the same manner as in Example 1 except that the content of the dispersant was 0.6 mass% and the organic solvent was dihydroterpinyl acetate with the remaining content being 21.03 mass%. Table 1 shows the types and contents of each material used. Also, regarding the obtained conductive paste, the viscosity change rate and glossiness were determined in the same manner as in Example 1. The results are shown in Table 2. [Example 3] As the conductive powder, H2O adsorption amount 0.42 mg / m 2, A conductive paste was prepared in the same manner as in Example 2, except that Ni powder with a surface occupancy ratio of 45% of NiO and a particle size of 0.08 μm was used, BT with a particle size of 0.02 μm was used as the ceramic powder, the content of the dispersant was 1.5 mass%, and the remaining content of the organic solvent was 20.13 mass%. The types and contents of the respective materials used are shown in Table 1. Also, regarding the obtained conductive paste, the viscosity change rate and glossiness 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 relative dielectric constant of 11.4 and an acid value of 129 was used as the dispersant. The types and contents of the respective materials used are shown in Table 1. Also, regarding the obtained conductive paste, the viscosity change rate and glossiness were determined in the same manner as in Example 1. The results are shown in Table 2. [Example 5] As the conductive powder, with an H2O adsorption amount of 0.53 mg / m 2 , A conductive paste was prepared in the same manner as in Example 4, except that Ni powder with a surface occupancy ratio of 45% of NiO and a particle size of 0.08 μm was used, BT with a particle size of 0.02 μm was used as the ceramic powder, the content of the dispersant was 1.5 mass%, and the remaining content of the organic solvent was 20.13 mass%. The types and contents of the respective materials used are shown in Table 1. Also, regarding the obtained conductive paste, the viscosity change rate and glossiness 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 content of the dispersant was 1.5 mass% and the remaining content of the organic solvent was 20.13 mass%. The types and contents of the respective materials used are shown in Table 1. Also, regarding the obtained conductive paste, the viscosity change rate and glossiness were determined in the same manner as in Example 1. The results are shown in Table 2. [Example 7] As the conductive powder, with an H2O adsorption amount of 0.34 mg / m 2, A conductive paste was prepared in the same manner as in Example 6, except that Ni powder with a surface occupancy ratio of NiO 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. Also, regarding the obtained conductive paste, the viscosity change rate and glossiness were determined in the same manner as in Example 1. The results are shown in Table 2. [Example 8] As the conductive powder, except that Ni powder with an H2O adsorption amount of 0.38 mg / m 2 , A conductive paste was prepared in the same manner as in Example 2, except that Ni powder with a surface occupancy ratio of NiO 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. Also, regarding the obtained conductive paste, the viscosity change rate and glossiness 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 having an amine group with a relative 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. Also, regarding the obtained conductive paste, the viscosity change rate and glossiness 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 relative 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. Also, regarding the obtained conductive paste, the viscosity change rate and glossiness were determined in the same manner as in Example 1. The results are shown in Table 2. [Comparative Example 3] As the conductive powder, except that Ni powder with an H2O adsorption amount of 0.29 mg / m 2 , A conductive paste was prepared in the same manner as in Example 2, except that Ni powder with a surface occupancy ratio of NiO 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. Also, regarding the obtained conductive paste, the viscosity change rate and glossiness were determined in the same manner as in Example 1. The results are shown in Table 2. [Comparative Example 4] As the conductive powder, except that Ni powder with an H2O adsorption amount of 0.29 mg / m 2、Except for using Ni powder with a surface occupancy ratio of NiO of 49% and a particle size of 0.2 μm, a conductive paste was prepared in the same manner as in Example 6. The types and contents of each material used are shown in Table 1. Also, regarding the obtained conductive paste, the viscosity change rate and glossiness were determined in the same manner as in Example 1. The results are shown in Table 2. [Comparative Example 5] As the conductive powder, with a water adsorption amount of 0.71 mg / m 2 、Except for using Ni powder with a surface occupancy ratio of NiO of 42% and a particle size of 0.2 μm, a conductive paste was prepared in the same manner as in Example 2. The types and contents of each material used are shown in Table 1. Also, regarding the obtained conductive paste, the viscosity change rate and glossiness 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) It can be seen that the conductive paste of the example containing a dispersant with a relative permittivity of 10 or more has a higher glossiness on the surface of the dry film and is superior in smoothness compared to the conductive paste of the comparative example with a relative permittivity of less than 10. Also, since the viscosity change rate is small, it can be seen that the improvement in dispersibility due to the adsorption of the dispersant is maintained over a long period.

[0098] Examples 4 and 5 using a dispersant having no amine value have a slightly lower glossiness compared to other examples, but show a sufficiently high glossiness and a small viscosity change rate compared to the comparative examples. Therefore, from the viewpoint of improving the smoothness of the entire surface of the dry film, it can be seen that it is more preferable to use a dispersant with an amine value of 100 or more.

[0099] On the other hand, it can be seen that the conductive paste of the comparative example containing a dispersant with a relative dielectric constant of less than 10 has a very low gloss on the surface of the dry film and is inferior in smoothness. This is because the dispersant does not satisfy the predetermined characteristics, resulting in poor wettability on the particle surface and insufficient adsorption of the dispersant on the particle surface. As a result, the crushing and re-aggregation of the particles cannot be sufficiently suppressed, leading to poor dispersibility of the conductive paste, material bias, and inferior smoothness of the dry film surface. In addition, due to the poor adsorptivity of the dispersant, the dispersion stability is poor, and the aggregation of each material increases with time. Therefore, it is considered that the viscosity change rate increases with time.

[0100] Moreover, in Comparative Examples 3 to 5 where the H2O adsorption amount per unit area is outside the scope of the invention, although the smoothness is somewhat low, in all cases, the surface state of the conductive powder is inappropriate, resulting in poor dispersion stability during pasting. Aggregation of the conductive powders increases with time, and it is considered that the viscosity change rate also increases with time.

[0101] Note that the technical scope of the present invention is not limited to the aspects described in the above embodiments and the like. One or more of the requirements described in the above embodiments and the like may be omitted. In addition, the requirements described in the above embodiments and the like can be appropriately combined. Also, to the extent permitted by law, the disclosures of all the documents cited in the above embodiments and the like are incorporated by reference and made part of the description herein.

Explanation of Reference Numerals

[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 an H ０ O adsorption amount per unit area at a relative pressure P / P ２ = 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. Conductive paste.

2. The conductive paste according to claim 1, wherein the compound having an 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 2, wherein the binder resin contains one or more selected from the group consisting of cellulose-based resins and butyral-based 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 in the surface composition of the nickel powder, NiO is 20 mol% or more and 90 mol% or less.

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.

10. After production, it is allowed to stand at 25°C for 30 days, and when measured with a Brookfield viscometer under the conditions of 25°C and 10 rpm, the change rate of the viscosity of the conductive paste is ±10% or less with respect to the viscosity of the conductive paste 8 hours after production.

11. It has at least a laminate in which a dielectric layer and an internal electrode layer are laminated, The internal electrode layer is formed using the conductive paste according to any one of claims 1 to 10. Multilayer ceramic capacitor.

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