CN116569293A

CN116569293A - Conductive paste and multilayer ceramic capacitor

Info

Publication number: CN116569293A
Application number: CN202180078301.4A
Authority: CN
Inventors: 铃木伸寿
Original assignee: Sumitomo Metal Mining Co Ltd
Current assignee: Sumitomo Metal Mining Co Ltd
Priority date: 2020-11-26
Filing date: 2021-11-26
Publication date: 2023-08-08
Also published as: JP2022084400A; WO2022114121A1; KR20230110244A; TW202234427A

Abstract

The invention provides a conductive paste which has high dispersibility and excellent viscosity stability with time. The conductive paste contains conductive powder, ceramic powder, binder resin, organic solvent and dispersing agent, wherein the conductive powder is at relative pressure P/P ₀ H per unit area when =0.5 ₂ The O adsorption amount is 0.30mg/m ² Above and 0.70mg/m ² Hereinafter, 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.

Description

Conductive paste and multilayer ceramic capacitor

Technical Field

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

Background

With miniaturization and higher performance of electronic devices such as mobile phones and digital devices, miniaturization and higher capacity are also demanded for electronic components including multilayer ceramic capacitors. The 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 the dielectric layers and the internal electrode layers, miniaturization and high capacity can be achieved.

The multilayer ceramic capacitor is manufactured, for example, as follows. First, barium titanate (BaTiO) ₃ ) The dielectric powder and the binder resin are printed (coated) with a conductive paste for internal electrodes in a predetermined electrode pattern on the surface of a dielectric green sheet, and dried to form a dry film. Next, the dried film and the green sheet were stacked alternately to obtain a laminate. Then, the laminate is integrated by thermocompression bonding to form a bonded body. The pressed body is cut, subjected to organic binder removal treatment in an oxidizing atmosphere or an inert atmosphere, and then fired to obtain a fired chip. Next, external electrode paste is applied to both end portions 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.

The conductive paste used for forming the internal electrode layers contains, for example, conductive powder, ceramic powder, binder resin, and organic solvent. In addition, in order to improve dispersibility of the conductive powder or the like, the conductive paste may contain a dispersant.

With the recent thinning of the internal electrode layers, the conductive powder contained in the conductive paste tends to be small in particle size (micronized). When the particle diameter of the conductive powder is reduced, the surface area per unit volume increases, and therefore the properties of the particle surface become dominant. In particular, when the particles constituting the conductive powder reach submicron order, the particles adhere to each other due to intermolecular forces, electrostatic forces, or the like, and coarse aggregates are easily formed. If such aggregates are present in the conductive powder, they form convex portions on the surface of the internal electrode layer in the production of the multilayer ceramic capacitor, and there is a possibility that the ceramic dielectric layer may be pierced to cause a short circuit between the internal electrode layers.

The conductive paste is produced, for example, by mixing and dispersing an organic vehicle in which a binder resin is dissolved in an organic solvent, with other materials such as conductive powder. As a kneading method in a conventional process for producing a conductive paste, for example, the following method is used: an inorganic powder such as a conductive powder and a ceramic powder, a dispersant, an organic solvent, and the like are mixed (kneaded) in an organic vehicle using a high-speed shear mixer, a planetary mixer of twin screw or more, and the like.

However, in the conventional kneading method, with the decrease in particle size of the conductive powder, there are cases where the organic vehicle is not sufficiently mixed, the surfaces of the conductive powder and the ceramic powder are not sufficiently wetted, and the like. Further, when dispersion treatment is performed by a three-roll mill or the like after kneading, problems such as poor dispersion of conductive powder (metal fine powder) and flakes may occur.

In addition, the conductive powder produced by the wet production method, which is one of the general methods for producing metal fine powder, tends to promote aggregation of the conductive powder at the stage of the drying step of the wet production method, and a large amount of aggregates (secondary particles) are already formed at the time point when the conductive powder is kneaded with the organic carrier, which tends to cause the above-described problem.

In the process of producing a conductive paste containing a dispersant, focusing on the dispersion process of a conductive powder and a ceramic powder (hereinafter, both are also collectively referred to as "inorganic powder"), the process of dispersing particles constituting the inorganic powder in the paste is classified into, for example, the following processes.

(1) A step of "wetting" the surfaces of particles (including secondary particles) constituting the inorganic powder

(2) A step of pulverizing the secondary particles and dispersing the pulverized particles in the slurry

(3) Inhibiting "reagglomeration" of the pulverized particles

The wetting process (1) is a step of adhering an organic vehicle/organic solvent to the surfaces of particles constituting the conductive powder and the ceramic powder, and in the conductive paste containing the dispersant, the dispersant is adsorbed to the surfaces of the secondary particles (aggregates) and the air existing in the voids inside the secondary particles is replaced with the organic solvent containing the dispersant, whereby the dispersant is adsorbed to the inner walls of the secondary particles.

Specifically, the wetting step (1) is, for example, a step of kneading and stirring using the above-mentioned mixer or the like, 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 subsequent dispersion process.

The dispersion step (2) is a step of greatly affecting the dispersibility of the conductive powder and the ceramic powder (inorganic powder) in the conductive paste, and specifically, for example, a step of pulverizing secondary particles (aggregates) of the inorganic powder by a dispersing machine such as a three-roll mill and dispersing the pulverized particles (for example, secondary particles obtained by agglomerating single primary particles or a small number of primary particles) in an organic carrier. When the dispersibility of the particles after the dispersion step of (2) is poor, the dispersion of various characteristics of the conductive paste becomes large, or coarse particles due to insufficient pulverization of the secondary particles cause deterioration of the surface smoothness of the dried film.

The step of suppressing reagglomeration in the above (3) is a step of suppressing "reagglomeration" of the particles after pulverization by adsorbing the dispersant on the new surface of the particle surface newly appeared by pulverization. In the dispersing step (2), if the dispersing treatment is not performed for a proper period of time, a portion to which the dispersant is not adsorbed may exist on the fresh surface of the crushed particles, and in the step of suppressing the reagglomeration of the crushed particles, the particles may reagglomerate, and the dispersion stability of the conductive paste may be lowered. The dispersing step (2) and the reagglomeration suppressing step (3) may be performed simultaneously.

As a method for improving the dispersion stability of the conductive paste, for example, patent document 1 discloses a technique of dispersing specific metal fine particles in an organic solvent having a dielectric constant in the range of 4 to 24 as a conductive paste excellent in dispersion stability.

Prior art literature

Patent literature

Patent document 1: japanese patent laid-open No. 2007-095510

Disclosure of Invention

Problems to be solved by the invention

However, in the technique described in patent document 1, although dispersion stability can be improved to some extent, in the dispersing step (2), the effect of improving the grindability of the formed secondary particles is insufficient, coarse particles due to the insufficiently ground secondary particles may be contained, and it is difficult to apply the dispersion to small-sized products that are being thinned.

In view of the above problems, the inventors of the present invention have conducted intensive studies and as a result, found that: by improving the "wettability" with respect to the particle surfaces constituting the inorganic powder, in the dispersion step of (2) above, the pulverization of the secondary particles can be easily performed, and a high dispersibility can be obtained; and (3) the step of suppressing reagglomeration, wherein the dispersant is easily adsorbed on the fresh surface of the pulverized particles, and the particles are prevented from "reagglomerating", so that the dispersion stability of the conductive paste can be maintained even when stored for a long period of time, and the viscosity stability is excellent.

In view of such circumstances, an object of the present invention is to provide a conductive paste, which uses conductive powder or ceramic powder that has been miniaturized for downsizing and thinning of a laminated ceramic electronic component, and which has high dispersibility and excellent viscosity stability.

Means for solving the problems

According to a first aspect of the present invention, there is provided a conductive paste comprising a conductive powder, a ceramic powder, a binder resin, an organic solvent, and a dispersant, wherein the conductive powder is at a relative pressure of P/P ₀ H per unit area when =0.5 ₂ The O adsorption amount is 0.30mg/m ² Above and 0.70mg/m ² The dispersant is 10 or moreAnd 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.

In addition, preferably, (1) the compound having an acid group is a compound containing at least one of a carboxyl group and a phosphate group. In addition, the binder resin preferably contains at least one selected from the group consisting of cellulose-based resins and butyral-based resins. In addition, the content of the binder resin is preferably 0.5 mass% or more and 10 mass% or less with respect to 100 mass% of the conductive paste. Further, the conductive powder preferably contains one or more metal powders selected from the group consisting of Ni, cu, ag, pd, au, pt powder and alloy powder thereof. In addition, preferably, the conductive powder is nickel powder. In addition, in the surface composition of the nickel powder, niO is preferably 20 mol% or more and 90 mol% or less. Further, the content of the conductive powder is preferably 30% by mass or more and 70% by mass or less with respect to 100% by mass of the conductive paste. In addition, preferably, the ceramic powder is at least one selected from the group consisting of barium titanate and strontium zirconate. Further, it is preferable that the change rate of the viscosity of the conductive paste measured with a brookfield viscometer at 25 ℃ and 10rpm after the conductive paste is left standing at 25 ℃ for 30 days after the production is ±10% or less with respect to the viscosity of the conductive paste after 8 hours of the production.

According to a second aspect of the present invention, there is provided a multilayer ceramic capacitor comprising at least a laminate of dielectric layers and internal electrode layers, the internal electrode layers being formed using the above-described conductive paste.

Effects of the invention

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, an electrode which is being thinned, and particularly, an electrode for a laminated ceramic electronic component which is being miniaturized.

Drawings

Fig. 1 is a perspective view and a cross-sectional view showing a multilayer ceramic capacitor according to an embodiment.

Detailed Description

1. Conductive paste

The conductive paste according to the present invention contains a conductive powder, a ceramic powder, a binder resin, an organic solvent, and a dispersant. The components contained in the conductive paste according to the present invention and the characteristics of the conductive paste will be described in detail below.

(1) Conductive powder

The material of the conductive powder is not particularly limited, and a known metal powder or the like may be appropriately selected and used according to the required characteristics. In addition, these conductive powders may be used alone or in combination.

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, and, if comprehensively judged from the viewpoints of conductivity, corrosion resistance, price, and the like, one or more metal powders selected from the group consisting of Ni, cu, and alloys thereof are preferable, and among them, ni metal powder (nickel powder) is more preferable. In addition, the nickel powder may contain sulfur (S) in an amount of about several hundred ppm in order to suppress rapid gas generation due to thermal decomposition of a portion of the binder resin during the binder removal treatment.

The method for producing the conductive powder is not particularly limited, and for example, a method in which chloride vapor is directly precipitated from a gas phase in hydrogen gas, an atomization method from a molten metal, a spray pyrolysis method using an aqueous solution, a wet method in which a metal salt of a raw material is reduced in an aqueous solution, and the like can be applied.

The average particle diameter of the conductive powder is not particularly limited, and may be selected according to the size of the electronic component to be used, and the like. The average particle diameter of the conductive powder is preferably 5 μm or less, more preferably 3 μm or less, for example, for a laminated ceramic capacitor in which the reduction of the thickness thereof is advanced. When the average particle diameter exceeds 5 μm, irregularities on the surface of the internal electrode become remarkable, and the electrical characteristics of the capacitor may be deteriorated, which is not preferable. The lower limit of the average particle diameter of the conductive powder is not particularly limited, and is, for example, 0.05 μm or more. When the average particle diameter is less than 0.05. Mu.m, handling becomes extremely difficult, and there is a risk of spontaneous combustion or the like.

In the present specification, unless otherwise specified, the average particle diameter of the conductive powder is a particle diameter calculated using a specific surface area by the BET method. For example, the calculation formula for obtaining the average particle diameter of the nickel powder is shown in the following formula (1).

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

In addition, the wettability with a solvent or a carrier varies depending on the strength of hydrophilicity and hydrophobicity of the surface of the conductive powder to be used, and particularly, the pulverization and dispersibility of aggregates of fine powder, which are becoming finer, are greatly affected. The strength of hydrophilicity and hydrophobicity of the surface of the conductive powder can be determined by H ₂ The amount of O adsorbed was evaluated.

In the conductive paste according to the present embodiment, the relative pressure P/P of the conductive powder used is equal to or higher than the relative pressure P/P of the conductive powder ₀ H per unit area when =0.5 ₂ The O adsorption amount is 0.30mg/m ² Above and 0.70mg/m ² Hereinafter, the concentration may be 0.30mg/m ² Above and 0.60mg/m ² The following is given. H ₂ The O adsorption quantity is less than 0.30mg/m ² If the hydrophobicity is too high, the viscosity stability may be deteriorated. It is considered that this is caused by that the dispersant having a relatively high dielectric constant (high hydrophilicity) is not adsorbed to the conductive powder. In addition, at H ₂ The O adsorption quantity exceeds 0.70mg/m ² In the case of (2), hydrophilicity becomes too strong and viscosity stability may be deteriorated. It is considered that this is because the relative dielectric constant of the conductive powder becomes too high, and therefore the hydrophobic group of the dispersant adsorbed to the conductive powder does not extend, and therefore it is difficult to fuse with the solvent.

In the case of using nickel powder as the conductive powder, the proportion of NiO in the surface composition is preferably 20 mol% or more and 90 mol% or less. When the ratio of NiO is outside the above range, the adsorption state of the dispersant on the surface of the conductive powder may become inadequate, or the reaction between the conductive powder and the binder resin may occur. If the dispersant is not sufficiently adsorbed on the surface of the conductive powder, wettability with the organic solvent or the organic carrier is deteriorated, and pulverization of aggregates (secondary particles) of the conductive powder and suppression of reagglomeration of the particles (primary particles or the like) after pulverization become insufficient (that is, dispersion of the conductive powder is insufficient), and there are cases where viscosity stability of the conductive paste is lowered and surface smoothness of the dried film is deteriorated.

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 in the above range from the viewpoint of further improving the viscosity stability of the conductive paste and the surface smoothness of the dried film. The more the proportion of NiO is within the above range, the more the conductive paste having high dispersibility can be obtained even if the amount of the dispersant to be described later is small.

The proportion of NiO in the surface composition of the nickel powder can be measured by X-ray photoelectron spectroscopy (XPS). For example, ni2p spectrum of the nickel powder surface was analyzed by XPS, and Ni peak and Ni (OH) were detected ₂ In the case of the peak and the NiO peak, the proportion (mol%) of NiO can be measured from the area ratio of the NiO peak to the total of the peak areas of the three components.

The content ratio of the conductive powder is preferably 30 mass% or more and 70 mass% or less with respect to the total mass of the conductive paste. If the proportion of the conductive powder is less than 30 mass%, the electrode thickness after firing may be significantly reduced to increase the resistance value, or the electrode film may be insufficiently formed to lose conductivity, and the intended electrostatic capacity may not be obtained, which is not preferable. If the content exceeds 70 mass%, the electrode film becomes difficult to be thinned, which is not preferable. The ratio of the conductive powder to the entire slurry is more preferably 40 mass% or more and 60 mass% or less.

(2) Ceramic powder

The ceramic powder is not particularly limited, and for example, in the case of being a paste for internal electrodes of a multilayer ceramic capacitor, a known ceramic powder may be appropriately selected according to the type of the multilayer ceramic capacitor to be used. The ceramic powder preferably contains, for example, at least one oxide powder selected from the group consisting of barium titanate and strontium zirconate, and among them, barium titanate (BaTiO ₃ Hereinafter sometimes referred to as "BT") powder.

As the barium titanate-based oxide powder, for example, a powder containing Barium Titanate (BT) as a main component and other oxides as subcomponents can be used. Examples of the other oxide as a subcomponent include oxides of at least one element 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. As the barium titanate-based oxide powder, barium titanate (BaTiO ₃ ) The powder of perovskite oxide ferroelectric material in which Ba atoms and/or Ti atoms are replaced with other atoms such as tin (Sn), lead (Pb), and zirconium (Zr).

The ceramic powder may contain other powders than barium titanate-based and strontium zirconate-based oxide powders, and may contain, for example, zinc oxide (ZnO), ferrite, lead zirconate titanate (PZT), barium oxide (BaO), aluminum oxide (Al ₂ O ₃ ) Bismuth oxide (Bi) ₂ O ₃ ) Rare earth oxide, titanium oxide (TiO) ₂ ) Neodymium oxide (Nd) ₂ O ₃ ) And ceramic powder.

The average particle diameter of the ceramic powder may be selected in accordance with the size of the electronic component to be used, and for example, is preferably in the range of 0.01 μm to 0.5 μm as a laminated electronic component in which thinning is progressing. If the particle size exceeds 0.5. Mu.m, the irregularities on the surface of the film after coating and drying become remarkable, and if the particle size is less than 0.01. Mu.m, handling becomes extremely difficult, and there is a risk of occurrence of spontaneous combustion or the like, which is not preferable. The average particle diameter of the ceramic powder As in the method for measuring the average particle diameter of the conductive powder, the particle diameter calculated using the specific surface area by the BET method (for example, in the case of barium titanate, ρ=6.1 (g/cm ³ ) The average particle diameter was calculated from the above formula (1).

The content of the ceramic powder is, for example, 1% by mass or more and 20% 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 conductive paste.

(3) Adhesive resin

When printing the conductive paste, the binder resin has effects of improving the drying characteristics and the like in addition to proper viscosity and adhesion and improving the printability.

The binder resin is not particularly limited, and a known material may be used depending on the required properties, and for example, it preferably contains one or more selected from the group consisting of cellulose-based resins, butyral-based resins, and acrylic resins, and more preferably contains one or more selected from the group consisting of cellulose-based resins and butyral-based resins.

Examples of the cellulose-based resin include acetyl cellulose, methyl cellulose, ethyl cellulose, butyl cellulose, nitrocellulose, and partially etherified celluloses. The butyral resin is exemplified by polyvinyl butyral.

Among them, ethylcellulose is preferably contained from the viewpoints of solubility in a solvent, combustion degradability, and the like. In addition, in the case of being used for a laminated electronic component, the butyral resin may be contained or used alone from the viewpoint of improving the adhesive strength with the green sheet. One kind of binder resin may be used, or two or more kinds may be used.

From the viewpoints of film strength, binder removal property, printability, and viscosity, the content of the binder resin is preferably 0.5 mass% or more and 10 mass% or less, more preferably 1 mass% or more and 5 mass% or less, relative to the total mass of the conductive paste.

When the content of the binder resin is less than the above range, the strength of the dry film may be reduced, or the adhesion between the electrode pattern portion of the conductive paste and the dielectric sheet may be deteriorated during lamination, and the peeling may be easily performed. On the other hand, when the content of the binder resin exceeds the above range, the content of the binder resin becomes excessive, and thus the binder removal property may be deteriorated, and a part of the binder resin may remain.

(4) Organic solvents

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

Examples of the terpene-based solvent include terpineol, dihydroterpineol, and dihydroterpineol acetate. Examples of the aliphatic hydrocarbon solvent include decane and tridecane. Examples of the alcohols include decanol and tridecanol. Examples of the organic solvent having a boiling point of about 150 to 250 ℃ other than the above include isobornyl acetate, butyl carbitol acetate, diethylene glycol butyl methyl ether, and tripropylene glycol dimethyl ether.

The content of the organic solvent is preferably 30 mass% or more and 70 mass% or less, more preferably 40 mass% or more and 60 mass% or less, relative to the total mass of the conductive paste, from the viewpoints of evaporation amount, viscosity, compatibility with the binder resin, and printability.

In the step of producing the conductive paste, the order of mixing the materials is not particularly limited, and it is preferable that the organic vehicle is prepared by dissolving the binder resin in a part of the organic solvent in advance and then mixing the organic vehicle with the other materials and the remaining organic solvent (for viscosity adjustment). The amount of the binder resin contained in the organic vehicle is not particularly limited, but is preferably 1 mass% or more and 30 mass% or less, more preferably 5 mass% or more and 20 mass% or less, relative to the total mass of the organic vehicle, from the viewpoint of forming the conductive paste for electronic parts, which is being used for miniaturization, into an appropriate viscosity.

(5) Dispersing agent

The dispersant is adsorbed on the surface of the inorganic powder (conductive powder and ceramic powder) to inhibit aggregation of the inorganic powder, or to improve wettability with the organic carrier to disperse the inorganic powder in the conductive paste. Dispersants (surfactants) are generally classified into cationic dispersants, anionic dispersants, nonionic dispersants, and amphoteric dispersants.

As the dispersant for dispersing the inorganic powder, an anionic dispersant (for example, an acid dispersant such as a carboxylic acid dispersant, a phosphoric acid dispersant, or a phosphate dispersant) is preferably used. However, with the decrease in particle size of the inorganic powder, even if an anionic dispersant is used, the inorganic powder may not be sufficiently dispersed.

As a result of intensive studies and developments by the present inventors, it was found that H having the above-mentioned specific range ₂ The use of a dispersant containing a compound having a relative dielectric constant of 10 or more and having an acid group and/or an amine group in combination with the conductive powder having an O adsorption amount can improve dispersibility. It is considered that such a dispersant has a large adsorption force on the surface of the inorganic powder, and thus the wettability between the inorganic powder and the organic carrier is improved (the "wetting" step of the above (1)), and therefore the surface modification of the dispersant promotes the pulverization of the inorganic powder (the dispersion step of the above (2)), and the inhibition of the reagglomeration (the step of the above (3)) contributes to the improvement of the dispersibility.

The relative dielectric constant of the dispersant may be 10 or more, 11 or more, or 12 or more. By using a dispersant having a relative dielectric constant satisfying the above range, the smoothness of the coating film (dried film) and the density of the dried film can be improved. The relative permittivity of the dispersant used in the present specification means the relative permittivity at 20 ℃. The relative permittivity can be measured by adding an evaluation sample (dispersant used) to an electrode unit for a liquid sample. The upper limit of the relative dielectric constant of the dispersant is not particularly limited, and is, for example, about 15 or less.

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 the compound (1) having an acid group and the compound (2) having an amine group, that is, may be a compound (3) having an acid group and an amine group in the same molecule, or may be a mixture of compounds including both the compound (1) having an acid group and the compound (2) having an amine group.

As the compound having an acid group, a compound containing at least one of a carboxyl group and a phosphate group is preferable. In addition, the compound having an amine group means a compound containing a primary amine, a secondary amine, and a tertiary amine.

Further, the dispersant more preferably 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 is further improved, and the smoothness of the dried film surface after coating can be further improved.

In the case where the dispersant includes 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 30 or more and 200 or less.

The content of the dispersant is preferably 0.1 mass% or more and 2.0 mass% or less, more preferably 0.3 mass% or more and 1.0 mass% or less, relative to the total mass of the conductive paste. If the content of the dispersant is less than 0.1 mass%, the content of the dispersant may be too small to obtain the effect of suppressing pulverization and recondensing. On the other hand, if the content of the dispersant exceeds 2.0 mass%, the properties of the paste such as printability may be greatly changed, which is not preferable.

(6) Other additive components

To the conductive paste of the present invention, one or more of known additives such as an antifoaming agent, a plasticizer, a thickener, a chelating agent, a dispersing agent other than the above-mentioned dispersing agent, a thixotropic agent, and the like may be added as necessary within the scope not departing from the gist of the present invention.

(7) Method for producing conductive paste and characteristics

(manufacturing method)

The method for producing the conductive paste according to the present embodiment is not particularly limited, and can be produced by a known method. For example, the conductive paste is produced by kneading and dispersing the above materials by a mixer, a ball mill, a kneader, a roll mill, or the like to prepare a paste.

(rate of change of viscosity)

The conductive paste according to the present embodiment was allowed to stand at 25℃for 30 days after production, and then measured in terms of viscosity (. Eta. ₃₀ ) The change rate of (2) is preferably + -10% or less relative to the viscosity (. Eta.0) after 8 hours of production. When the rate of change in the viscosity of the conductive paste is within the above range, the dispersibility of the conductive paste is excellent.

The viscosity change rate of the conductive paste after standing for 30 days can be obtained by the following formula (2).

Viscosity change rate (%) = (η) ₃₀ -η ₀ )/η ₀ ×100…(2)

η ₃₀ : 10rpm viscosity after 30 days

η ₀ : 10rpm viscosity (initial viscosity) after 8 hours of production

(glossiness)

The dry film of the conductive paste according to the present embodiment preferably has a glossiness of 10 or more, more preferably 15 or more, and even more preferably 20 or more. The higher the glossiness of the dried film, the less diffuse reflection of the entire surface of the dried film, and the smoother the surface can be obtained.

The dry film for evaluation can be obtained, for example, as follows: the conductive paste was printed on a PET film so that the film thickness became 30 μm over an area of 5X 10cm, and then dried in air at 120℃for 40 minutes.

2. Multilayer ceramic capacitor

Hereinafter, embodiments of a multilayer ceramic capacitor according to the present invention will be described with reference to the drawings. In the drawings, the drawings may be schematically represented or may be represented by changing the scale. The position, direction, and the like of the member will be described with reference to an XYZ orthogonal coordinate system shown in fig. 1 and the like, as appropriate. In the XYZ orthogonal coordinate system, the X direction and the Y direction are horizontal directions, and the Z direction is vertical direction (vertical direction).

A in fig. 1 and B in fig. 1 are diagrams showing a multilayer ceramic capacitor 1 as 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.

Hereinafter, a method for manufacturing a multilayer ceramic capacitor using the above conductive paste will be described. First, a ceramic laminate 10 is produced by printing a conductive paste on a ceramic green sheet, drying the paste to form a dried film, laminating a plurality of ceramic green sheets having the dried film on the upper surface by pressure bonding to obtain a laminate, and firing the laminate to integrate the laminate, thereby alternately laminating the internal electrode layers 11 and the dielectric layers 12. Thereafter, a pair of external electrodes are formed at both end portions of the ceramic laminate 10 to produce the laminated ceramic capacitor 1. Hereinafter, the present invention will be described in more detail.

First, a ceramic green sheet is prepared as an unfired ceramic sheet. Examples of the ceramic green sheet include a ceramic green sheet formed by applying a slurry for a dielectric layer, which is 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, onto a support film such as a PET film, and drying the support film to remove the solvent. The thickness of the dielectric layer formed of the ceramic green sheet is not particularly limited, but is preferably 0.05 μm or more and 3 μm or less from the viewpoint of the demand for downsizing of the multilayer ceramic capacitor.

Next, a plurality of sheets are prepared, each of which is formed with a dry film on one surface of the ceramic green sheet by printing and applying the conductive paste on one surface of the ceramic green sheet by gravure printing and drying. From the viewpoint of the demand for thinner internal electrode layers 11, the thickness of the dried film formed from the conductive paste is preferably 1 μm or less after drying.

Then, the ceramic green sheet is peeled from the support film, laminated so that the ceramic green sheet and the dry film formed on one surface of the ceramic green sheet are alternately arranged, and then heated and pressed to obtain a laminate. The protective ceramic green sheet to which the conductive paste is not applied may be further disposed on both sides of the laminate.

Next, the laminate was cut into a predetermined size to form green chips, and then the green chips were subjected to binder removal treatment and fired in a reducing atmosphere to produce a laminate ceramic fired body (ceramic laminate 10). The atmosphere in the binder removal treatment is preferably the atmosphere or N ₂ A gas atmosphere. The temperature at which the binder removal treatment is performed is, for example, 200 ℃ to 400 ℃. The holding time at the temperature at the time of the binder removal treatment is preferably 0.5 hours or more and 24 hours or less. In addition, the firing is performed in a reducing atmosphere in order to suppress oxidation of the metal used in the internal electrode layer, and the temperature at which the laminate is fired is, for example, 1000 ℃ to 1350 ℃, and the holding time of the temperature at which the firing is performed is, for example, 0.5 to 8 hours.

The firing of the green chip completely removes the organic binder in the ceramic green sheet, and fires the raw material powder of the ceramic to form the ceramic dielectric layer 12. The internal electrode layers 11 are formed by removing the organic carrier in the dried film and sintering or melting and integrating nickel powder or alloy powder containing nickel as a main component, and a multilayer ceramic fired body is formed by alternately stacking a plurality of dielectric layers 12 and internal electrode layers 11. The laminate ceramic fired body after firing may be subjected to an annealing treatment from the viewpoints of introducing oxygen into the dielectric layer to improve reliability and suppressing reoxidation of the internal electrode.

Then, the laminated ceramic capacitor 1 is manufactured by providing the produced laminated ceramic fired body with a pair of external electrodes 20. 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. As a material of the external electrode 20, copper, nickel, or an alloy thereof, for example, may be preferably used. The electronic component may be an electronic component other than a multilayer ceramic capacitor.

[ example ]

The present invention will be described in detail with reference to examples and comparative examples, but the present invention is not limited to the examples.

[ evaluation item and method thereof ]

(1) Viscosity change rate of conductive paste with time

The viscosity change rate of the conductive paste with time is represented by the following formula (2), and first, the viscosity of the conductive paste after 8 hours of production is measured as the initial viscosity (. Eta. ₀ ) Next, the viscosities (. Eta.) of the conductive pastes after standing at room temperature (25 ℃) for 1 day, 10 days and 30 days were measured, respectively _x ) Then dividing the change in viscosity after each number of days of standing by the initial viscosity (. Eta.) ₀ ) The percentage (%) obtained is shown. The viscosity change tendency was confirmed by measuring not only the viscosity change rate after 30 days but also the viscosity change rate after 1 day and after 10 days.

Viscosity change rate (%) = (η) _x -η ₀ )/η ₀ ×100…(2)

η _x : 10rpm viscosity after X days

η ₀ : 10rpm viscosity (initial viscosity) after 8 hours of production

The viscosity of each conductive paste was measured at 25℃and 10rpm (shear rate=4sec using a B-type viscometer manufactured by Brookfield Co., ltd ^-1 ) Is measured under the condition of (2). The smaller the viscosity change rate of the conductive paste with time is, the more preferable.

(2) Smoothness (gloss) of dried film surface

As an index of smoothness of the surface of the dried film, a value (glossiness) measured by the following method was evaluated.

First, a conductive paste was printed on a PET film so that the thickness of the paste became 30 μm over an area of 5×10cm, and then dried in air at 120 ℃ for 40 minutes to obtain a dried film (dried conductive paste). The surface of the obtained dried film was measured for glossiness at an incident angle of 60 ° using a gloss meter (gloss detector manufactured by horiba, inc. IG-320). The higher the gloss, the less diffuse reflection, resulting in a smoother surface.

(3)H ₂ Adsorption amount of O

After the sample for evaluation (conductive powder) was vacuum-degassed at 25℃for 8 hours, H was measured using a high-precision vapor adsorption measuring device BELSORP-aqua3 (microtracB EL Co.) ₂ O adsorption isotherm is measured to obtain relative pressure P/P ₀ H when=0.5 ₂ O adsorption amount. The specific surface area value of the sample for evaluation was obtained by using the BET method based on the nitrogen adsorption method. The H obtained ₂ Dividing the O adsorption amount by the specific surface area value to calculate H per unit area ₂ O adsorption amount.

(4) NiO ratio at Nickel powder surface

The surface of nickel powder used as the conductive powder was measured by X-ray photoelectron spectroscopy (XPS), and nickel hydroxide (Ni (OH) was detected as a property ₂ ) The nickel of nickel oxide (NiO) and the peak of metallic nickel, and the proportion (mol%) of NiO was calculated from the respective existing proportions.

(5) Relative dielectric constant of dispersant

The dispersant used was placed in an electrode unit for a liquid sample at the frequency: 1MHz, voltage: the relative dielectric constant was determined using an LCR meter (HP-4278A) at 1V.

Example 1

47 mass% of nickel powder (H ₂ The O adsorption quantity is 0.31mg/m ² The surface presence ratio of NiO was 34 mol%, and the particle size was 0.4. Mu.m), 4.7 mass% of barium titanate (particle diameter of 0.05 μm) as ceramic powder, 26.67 mass% of organic carrier, 0.4 mass% of dispersant, 21.23 mass% of organic solvent as the balance.

As the organic vehicle, an organic vehicle was used which was prepared by mixing 13 mass% of ethyl cellulose as a binder resin and 87 mass% of terpineol as an organic solvent and heating and mixing at 60 ℃.

An amine dispersant (a mixture of a compound having an acid group and a compound having an amine group) having a relative dielectric constant of 12.5, an acid value of 58, and an amine value of 110 was used as the dispersant.

Terpineol was used as the organic solvent.

These materials were kneaded and dispersed in a three-roll mill at 25℃under a relative humidity of 55%, to prepare a conductive paste. The initial viscosity and the viscosity after a predetermined time are measured for the prepared conductive paste, and the viscosity change rate after each time is calculated. Further, the glossiness of the dried film produced using the produced conductive paste was measured.

The types, contents, and the like of the materials used are shown in table 1, and the measurement results and calculation results are shown in table 2.

Example 2

As the conductive powder, H was used ₂ The O adsorption quantity is 0.53mg/m ² A conductive paste was produced in the same manner as in example 1, except that the surface of NiO was present in a proportion of 26 mol% and the particle diameter was 0.2 μm, the content of the dispersant was 0.6 mass%, the organic solvent was dihydroterpineol acetate, and the balance was 21.03 mass%. The types, contents, etc. of the materials used are shown in table 1. The viscosity change rate and the glossiness of the obtained conductive paste were obtained in the same manner as in example 1. The results are shown in Table 2.

Example 3

As the conductive powder, H was used ₂ The O adsorption quantity is 0.42mg/m ² The NiO had a surface-to-surface ratio of 45 mol% and a particle diameterA conductive paste was produced in the same manner as in example 2, except that 0.08 μm of nickel powder was used as the ceramic powder, BT having a particle diameter of 0.02 μm was used, the content of the dispersant was 1.5 mass%, and the remaining content of the organic solvent was 20.13 mass%. The types, contents, etc. of the materials used are shown in table 1. The viscosity change rate and the glossiness of the obtained conductive paste were obtained 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 relative dielectric constant of 11.4 and an acid value of 129 was used as the dispersant. The types, contents, etc. of the materials used are shown in table 1. The viscosity change rate and the glossiness of the obtained conductive paste were obtained in the same manner as in example 1. The results are shown in Table 2.

Example 5

As the conductive powder, H was used ₂ The O adsorption quantity is 0.42mg/m ² A conductive paste was produced in the same manner as in example 4, except that a nickel powder having a surface of NiO of 45 mol% and a particle diameter of 0.08 μm was used as a ceramic powder, BT having a particle diameter of 0.02 μm was used, the content of the dispersant was 1.5 mass%, and the remaining content of the organic solvent was 20.13 mass%. The types, contents, etc. of the materials used are shown in table 1. The viscosity change rate and the glossiness of the obtained conductive paste were obtained in the same manner as in example 1. The results are shown in Table 2.

Example 6

A conductive paste was produced 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, contents, etc. of the materials used are shown in table 1. The viscosity change rate and the glossiness of the obtained conductive paste were obtained in the same manner as in example 1. The results are shown in Table 2.

Example 7

As the conductive powder, H was used ₂ The O adsorption quantity is 0.34mg/m ² A conductive paste was produced in the same manner as in example 6, except that nickel powder having a particle diameter of 0.2 μm was present in an amount of 79 mol% on the surface of NiO. The types, contents, etc. of the materials used are shown in table 1. The viscosity change rate and the glossiness of the obtained conductive paste were obtained in the same manner as in example 1. The results are shown in Table 2.

Example 8

As the conductive powder, H was used ₂ The O adsorption quantity is 0.38mg/m ² A conductive paste was produced in the same manner as in example 2, except that the surface of NiO was present in a proportion of 89 mol% and the particle diameter was 0.2 μm. The types, contents, etc. of the materials used are shown in table 1. The viscosity change rate and the glossiness of the obtained conductive paste were obtained in the same manner as in example 1. The results are shown in Table 2.

Comparative example 1

A conductive paste was produced in the same manner as in example 2, except that a dispersant having an amine group (a mixture of a compound having an acid group and a compound having an amine group) and having 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, contents, etc. of the materials used are shown in table 1. The viscosity change rate and the glossiness of the obtained conductive paste were obtained in the same manner as in example 1. The results are shown in Table 2.

Comparative example 2

A conductive paste was produced in the same manner as in example 2, except that a dispersant having an amine group (a mixture of a compound having an acid group and a compound having an amine group) and having 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, contents, etc. of the materials used are shown in table 1. The viscosity change rate and the glossiness of the obtained conductive paste were obtained in the same manner as in example 1. The results are shown in Table 2.

Comparative example 3

As the conductive powder, H was used ₂ The O adsorption quantity is 0.29mg/m ² A conductive paste was produced in the same manner as in example 2, except that the surface of NiO was present in a proportion of 49 mol% and the particle diameter was 0.2 μm. The types, contents, etc. of the materials used are shown in table 1. The viscosity change rate and the glossiness of the obtained conductive paste were obtained in the same manner as in example 1. The results are shown in Table 2.

Comparative example 4

As the conductive powder, H was used ₂ The O adsorption quantity is 0.29mg/m ² A conductive paste was produced in the same manner as in example 6, except that the surface of NiO was present in a proportion of 49 mol% and the particle diameter was 0.2 μm. The types, contents, etc. of the materials used are shown in table 1. The viscosity change rate and the glossiness of the obtained conductive paste were obtained in the same manner as in example 1. The results are shown in Table 2.

Comparative example 5

As the conductive powder, H was used ₂ The O adsorption amount is 0.71mg/m ² A conductive paste was produced in the same manner as in example 2, except that the surface of NiO was present in a proportion of 42 mol% and the particle diameter was 0.2 μm. The types, contents, etc. of the materials used are shown in table 1. The viscosity change rate and the glossiness of the obtained conductive paste were obtained in the same manner as in example 1. The results are shown in Table 2.

TABLE 2

(evaluation results)

The conductive paste of the example containing the dispersant having a relative dielectric constant of 10 or more was found to have higher glossiness and excellent smoothness on the dried film surface than the conductive paste of the comparative example having a relative dielectric constant of less than 10. In addition, since the viscosity change rate is also small, the effect of improving the dispersibility by adsorption of the dispersant can be maintained for a long period of time.

Examples 4 and 5 using the dispersant having no amine value (amine group) but only an acid value (acid group) showed slightly lower gloss than other examples, but showed sufficiently high gloss and smaller viscosity change rate than comparative examples. Therefore, it is known that a dispersant having an amine value of 100 or more is preferably used from the viewpoint of improving the smoothness of the whole surface of the dried film.

On the other hand, it was found that the dry film surfaces of the conductive pastes of comparative examples 1 and 2 containing the dispersant having a relative dielectric constant of less than 10 had very low gloss and poor smoothness. This is considered to be because the dispersant does not satisfy the predetermined characteristics, and therefore wettability to the particle surface is poor, and the dispersant cannot be sufficiently adsorbed to the particle surface, and therefore pulverization and suppression of recondensing of the particles cannot be sufficiently achieved, and therefore dispersibility of the conductive paste is poor, material deviation occurs, and smoothness of the dried film surface is poor. In addition, it is considered that the dispersion stability is poor because the adsorptivity of the dispersant is poor, and the aggregation or the like of each material increases with time, so that the rate of change of viscosity increases with time.

In addition, regarding H per unit area ₂ In comparative examples 3 to 5 in which the O adsorption amount was outside the range of the present invention, it is considered that the smoothness was somewhat low and the surface state of the conductive powder was not appropriate, so that the dispersion stability at the time of slurrying was poor, the aggregation of conductive powders and the like increased with time, and the rate of change in viscosity also increased with time.

The technical scope of the present invention is not limited to the embodiments described in the above embodiments and the like. One or more elements described in the above embodiments and the like may be omitted. The elements described in the above embodiments and the like may be appropriately combined. The disclosures of all documents cited in japanese patent application 2020-196256, the above-described embodiments, and the like are incorporated by reference as part of the description herein, as long as they are within the limits allowed by law.

Description of the reference numerals

1: a laminated ceramic capacitor;

10: a ceramic laminate;

11: an internal electrode layer;

12: a dielectric layer;

20: an external electrode;

21: an external electrode layer;

22: plating layers.

Claims

1. A conductive paste containing a conductive powder, a ceramic powder, a binder resin, an organic solvent and a dispersant, characterized in that,

The conductive powder is under relative pressure P/P ₀ H per unit area when =0.5 ₂ The O adsorption amount is 0.30mg/m ² Above and 0.70mg/m ² In the following the procedure is described,

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.

2. The conductive paste according to claim 1, wherein the (1) 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 mass% or more and 10 mass% or less with respect to 100 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 powder and an alloy powder 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 NiO is 20 mol% or more and 90 mol% or less in the surface composition of the nickel powder.

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

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

10. The conductive paste according to any one of claims 1 to 9, wherein a rate of change in viscosity of the conductive paste measured with a brookfield viscometer at 25 ℃ and 10rpm after the conductive paste is left to stand at 25 ℃ for 30 days after the production is ±10% or less relative to the viscosity of the conductive paste after the production for 8 hours.

11. A multilayer ceramic capacitor comprising at least a laminate of dielectric layers and internal electrode layers,

The internal electrode layer is formed using the electroconductive paste according to any one of claims 1 to 10.