JP7726075B2 - Conductive paste, electronic components, and multilayer ceramic capacitors - Google Patents

Description

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

As electronic devices such as mobile phones and digital devices become smaller and more powerful, there is a demand for smaller electronic components, including multilayer ceramic capacitors, with higher capacitance. Multilayer ceramic capacitors have a structure in which multiple dielectric layers and multiple internal electrode layers are alternately stacked, and by thinning these dielectric layers and internal electrode layers, it is possible to achieve smaller size and higher capacitance.

Multilayer ceramic capacitors are manufactured, for example, as follows: First, a conductive paste for internal electrodes is printed 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 then dried to form a dry film. Next, the dried film and the green sheet are alternately stacked to obtain a laminate. Next, this laminate is integrated by heat and pressure bonding to form a pressed body. This pressed body is cut, subjected to a binder removal treatment in an oxidizing or inert atmosphere, and then fired to obtain fired chips. Next, a paste for external electrodes is applied to both ends of the fired chips, and after firing, the surfaces of the external electrodes are nickel-plated or the like to obtain a multilayer ceramic capacitor.

Generally, the conductive paste used to form the internal electrode layers contains conductive powder, ceramic powder, binder resin, and organic solvent. The conductive paste may also contain a dispersant to improve the dispersibility of the conductive powder, etc. In recent years, as the internal electrode layers have become thinner, the particle size of the conductive powder has also tended to become smaller. When the particle size of the conductive powder is small, the specific surface area of the particle surface increases, which increases the surface activity of the conductive powder (metal powder), which can result in a decrease in the dispersibility of the conductive powder and a decrease in the viscosity characteristics of the conductive paste.

In response, attempts have been made to improve the viscosity characteristics of conductive pastes over time. For example, Patent Document 1 describes a conductive paste containing at least a metal component, an oxide, a dispersant, and a binder resin, in which the metal component is Ni powder whose surface composition has a specific composition ratio, the dispersant has an acid site number of 500 to 2000 μmol/g, and the binder resin has an acid site number of 15 to 100 μmol/g. According to Patent Document 1, this conductive paste is said to have good dispersibility and viscosity stability.

Furthermore, Patent Document 2 describes a conductive paste for internal electrodes comprising conductive powder, resin, organic solvent, co-materials of ceramic powder mainly composed of _TiBaO3 , and an aggregation inhibitor, wherein the content of the aggregation inhibitor is 0.1% by weight or more and 5% by weight or less, and the aggregation inhibitor is a tertiary amine or secondary amine represented by a specific structural formula. According to Patent Document 2, this conductive paste for internal electrodes inhibits aggregation of the co-material components, has excellent long-term storage properties, and enables the thinning of multilayer ceramic capacitors.

On the other hand, when thinning the internal electrode layer, a high density is required for the dried film obtained by printing a conductive paste for the internal electrodes on the surface of a dielectric green sheet and drying it. For example, Patent Document 3 proposes an ultrafine metal powder slurry containing an organic solvent, a surfactant, and ultrafine metal particles, where the surfactant is oleoyl sarcosine, the ultrafine metal powder is contained in the ultrafine metal powder slurry at 70% by mass or more and 95% by mass or less, and the surfactant is contained in an amount of more than 0.05 parts by mass and less than 2.0 parts by mass per 100 parts by mass of the ultrafine metal powder. Patent Document 3 claims that by preventing aggregation of the ultrafine particles, an ultrafine metal powder slurry can be obtained that is free of aggregated particles and has excellent dispersibility and dry film density.

Japanese Patent Application Laid-Open No. 2015-216244 JP 2013-149457 A Japanese Patent Application Laid-Open No. 2006-063441

However, with the recent trend toward thinner electrode patterns, there is a demand for conductive pastes that use conductive powders with an average particle size of 100 nm or less. Furthermore, these conductive pastes are required to have high smoothness when printed and dried to form electrode patterns, and to maintain their viscosity characteristics over time.

In light of these circumstances, the present invention aims to provide a conductive paste that forms a conductive film with high smoothness after drying and exhibits little change in viscosity over time.

In order to solve the above problems, the conductive paste of the present invention is a conductive paste containing a conductive powder, a ceramic powder, a dispersant, a binder resin, and an organic solvent, and the dispersant is composed of at least two amine-based dispersants, including one or more secondary or tertiary amines represented by the following general formula (1) and one or more alkylamines:

(In formula (1), R ₁ represents a hydrogen atom, an alkyl group having 1 to 7 carbon atoms, an alkenyl group having 2 to 7 carbon atoms, an alkynyl group having 2 to 7 carbon atoms, a hydroxyethyl group, or a hydroxypropyl group; R ₂ represents a hydroxyethyl group, a hydroxypropyl group, an aminoethyl group, or an aminopropyl group; and R ₃ represents a hydrogen atom, an alkyl group having 1 to 7 carbon atoms, an alkenyl group having 2 to 7 carbon atoms, an alkynyl group having 2 to 7 carbon atoms, a hydroxyethyl group, a hydroxypropyl group, an aminoethyl group, or an aminopropyl group.)

The mass ratio of the total amount of the amine-based dispersant to the conductive powder may be 0.01 to 4:100, and the content of the conductive powder relative to the total amount of the conductive paste may be 40% to 65% by mass.

The number average particle diameter of the conductive powder may be 30 nm to 100 nm.

A second aspect of the present invention provides an electronic component formed using the conductive paste of the present invention.

A third aspect of the present invention provides a multilayer ceramic capacitor having at least a laminate formed by laminating dielectric layers and internal electrodes, the internal electrodes being formed using the conductive paste of the present invention.

As explained above, the present invention can provide a conductive paste that forms a conductive film with high smoothness after drying and has little change in viscosity over time.

1A and 1B are a perspective view and a side cross-sectional view showing a multilayer ceramic capacitor;

One embodiment of the conductive paste of the present invention is described below.

The conductive paste of this embodiment contains a conductive powder, a ceramic powder, a dispersant, a binder resin, and an organic solvent. The dispersant is composed of at least two amine-based dispersants, including one or more secondary or tertiary amines represented by the following general formula (1) and one or more alkylamines. The conductive powder, ceramic powder, dispersant, binder resin, and organic solvent contained in the conductive paste of this embodiment are described in detail below.

(conductive powder)
The conductive powder is not particularly limited, and metal powders can be used. For example, powders of one or more metals selected from Ni, Pd, Pt, Au, Ag, Cu, and alloys thereof can be used. Among these, Ni or Ni alloy powders are preferred from the viewpoints of conductivity, corrosion resistance, and cost. Examples of Ni alloys that can be used include alloys of Ni with at least one element selected from the group consisting of Mn, Cr, Co, Al, Fe, Cu, Zn, Ag, Au, Pt, and Pd (Ni alloys). The Ni content in the Ni alloy is, for example, 50% by mass or more, preferably 80% by mass or more. Furthermore, the Ni powder may contain several hundred ppm of S to suppress rapid gas generation due to partial thermal decomposition of the binder resin during binder removal.

The number-average particle size of the conductive powder is preferably 30 nm or more and 100 nm or less, and more preferably 40 nm or more and 90 nm or less. When the average particle size of the conductive powder is within this range, it can be suitably used as a conductive paste for the internal electrodes of thin-film multilayer ceramic capacitors, and the smoothness of the dried film is improved. Here, the number-average particle size is a value determined by observation with a scanning electron microscope (SEM), and is the average value obtained by measuring the particle size of each of multiple particles in an image observed with an SEM at 10,000x magnification.

The content of the conductive powder relative to the total amount of the conductive paste is preferably 40% to 65% by mass, and more preferably 45% to 60% by mass. When the content of the conductive powder is within the above range, the conductive paste has excellent conductivity and dispersibility.

(ceramic powder)
The ceramic powder is not particularly limited, and for example, in the case of a conductive paste for an internal electrode of a multilayer ceramic capacitor, a known ceramic powder is appropriately selected depending on the type of multilayer ceramic capacitor to be used. Examples of the ceramic powder include perovskite-type oxides containing Ba and Ti, and preferably barium titanate ( _BaTiO3 ).

The ceramic powder may be a ceramic powder containing barium titanate as a main component and an oxide as a secondary component. Examples of the oxide include oxides of Mn, Cr, Si, Ca, Ba, Mg, V, W, Ta, Nb, and one or more rare earth elements. Alternatively, the ceramic powder may be a perovskite-type oxide ferroelectric ceramic powder in which the Ba atoms and Ti atoms of barium titanate ( _BaTiO3 ) are substituted with other atoms, such as Sn, Pb, or Zr.

In the conductive paste for the internal electrodes, a powder having the same composition as the dielectric ceramic powder constituting the green sheets of the multilayer ceramic capacitor may be used as the ceramic powder. This suppresses cracking due to a shrinkage mismatch at the interface between the dielectric layer and the internal electrode layer during the sintering process. Examples of such ceramic powders include oxides such as ZnO, ferrite, PZT, BaO, Al ₂ O ₃ , Bi ₂ O ₃ , R (rare earth element) ₂ O ₃ , and TiO ₂ . One type of ceramic powder may be used, or two or more types may be used.

The number average particle diameter of the ceramic powder is, for example, 10 nm to 100 nm, and preferably in the range of 10 nm to 70 nm. When the ceramic powder has a number average particle diameter in this range, it is possible to form sufficiently fine, thin, and uniform internal electrodes when used as a conductive paste for internal electrodes. The number average particle diameter is a value determined by observation with a scanning electron microscope (SEM), and is the average value obtained by measuring the particle diameter of each of multiple particles in an image observed with an SEM at 50,000x magnification.

The content of ceramic powder is preferably 1 to 30 parts by mass, and more preferably 3 to 30 parts by mass, per 100 parts by mass of conductive powder. When the content of conductive powder is within the above range, excellent conductivity and dispersibility are achieved.

The ceramic powder content is preferably 1% to 20% by mass, and more preferably 3% to 20% by mass, based on the total conductive paste. When the conductive powder content is within this range, excellent conductivity and dispersibility are achieved.

(binder resin)
The binder resin is not particularly limited, and known resins can be used. Examples include cellulose-based resins such as methyl cellulose, ethyl cellulose, ethyl hydroxyethyl cellulose, and nitrocellulose; acrylic resins; and butyral resins such as polyvinyl butyral. Among these, it is preferable to contain ethyl cellulose from the viewpoints of solubility in solvents and combustion decomposition properties. Furthermore, when used as a conductive paste for internal electrodes, a butyral resin may be contained or used alone to improve the adhesive strength with the green sheet. One type of binder resin may be used, or two or more types may be used. For example, a cellulose-based resin and a butyral resin may be used as the binder resin.

The weight-average molecular weight of the binder resin is, for example, approximately 20,000 to 300,000. If the weight-average molecular weight is less than 20,000, it becomes difficult to achieve sufficient viscosity for printing. Even in such cases, printability can be ensured by increasing the cellulose-based resin content, but this results in increased residual carbon after firing. A more preferable lower limit for the weight-average molecular weight is 30,000. A lower limit of 30,000 or higher can ensure sufficient printability without increasing residual carbon. On the other hand, if the weight-average molecular weight exceeds 300,000, the resulting multilayer ceramic capacitor internal electrode paste will thicken and its printability will deteriorate. A weight-average molecular weight of 300,000 or less can ensure compatibility with the cellulose-based resin while providing a multilayer ceramic capacitor internal electrode paste with excellent printability. The preferable upper limit depends on the blending ratio with the cellulose-based resin, but by setting it to 300,000 or less, the blending ratio of the butyral resin can be increased, thereby reducing residual carbon after firing.

The binder resin content is preferably 1 to 10 parts by mass, and more preferably 1 to 8 parts by mass, per 100 parts by mass of conductive powder. When the binder resin content is within the above range, excellent conductivity and dispersibility are achieved.

The binder resin content is preferably 0.5% to 10% by mass, and more preferably 1% to 6% by mass, of the entire conductive paste. When the binder resin content is within this range, excellent conductivity and dispersibility are achieved.

(organic solvent)
The organic solvent is not particularly limited, and any known organic solvent capable of dissolving the binder resin can be used. Examples include acetate-based solvents such as dihydroterpineol acetate, isobornyl acetate, isobornyl propionate, isobornyl butyrate, isobornyl isobutyrate, ethylene glycol monobutyl ether acetate, and dipropylene glycol methyl ether acetate; terpene-based solvents such as terpineol and dihydroterpineol; and hydrocarbon-based solvents such as tridecane, nonane, and cyclohexane. One or more organic solvents may be used.

The content of the organic solvent is preferably 40 to 100 parts by mass, and more preferably 65 to 95 parts by mass, per 100 parts by mass of the conductive powder. When the content of the organic solvent is within the above range, excellent conductivity and dispersibility are achieved.

The organic solvent content is preferably 20% to 60% by mass, and more preferably 35% to 55% by mass, of the entire conductive paste. When the organic solvent content is within this range, excellent conductivity and dispersibility are achieved.

(Dispersant)
The dispersant contained in the conductive paste of the present invention is two or more amine-based dispersants, and includes at least two or more amine-based dispersants, including one or more secondary amines or tertiary amines described below and one or more alkylamines. By including such an amine-based dispersant, the dispersed state of the conductive powder in the conductive paste can be maintained, and viscosity change of the conductive paste over time can be reduced. Furthermore, the smoothness of the conductive film after drying can be improved.

It is preferable that the amine-based dispersant is not a polymer dispersant. Polymer dispersants are expected to have a higher thermal decomposition temperature, resulting in a larger amount of residual carbon after firing.

One type of amine-based dispersant is a tertiary amine or secondary amine represented by the following general formula (1):

(In formula (1), _R1 represents a hydrogen atom, an alkyl group having 1 to 7 carbon atoms, an alkenyl group having 2 to 7 carbon atoms, an alkynyl group having 2 to 7 carbon atoms, a hydroxyethyl group, or a hydroxypropyl group; _R2 represents a hydroxyethyl group, a hydroxypropyl group, an aminoethyl group, or an aminopropyl group; and _R3 represents a hydrogen atom, an alkyl group having 1 to 7 carbon atoms, an alkenyl group having 2 to 7 carbon atoms, an alkynyl group having 2 to 7 carbon atoms, a hydroxyethyl group, a hydroxypropyl group, an aminoethyl group, or an aminopropyl group.)

The amine dispersant of the above formula (1) comprises a tertiary amine or a secondary amine in its molecule, and as functional groups, in addition to the nitrogen atom constituting the amino group (i.e., N in the above formula (1)), R ₂ and, optionally, R ₁ and R ₃ may comprise at least one group selected from an alcohol-based hydroxyl group (a hydroxyethyl group, a hydroxypropyl group) and another amino group (an aminoethyl group, an aminopropyl group).

Note that if the amine-based dispersant is a primary amine, even if the molecule contains alcohol-based hydroxyl groups or amino groups that constitute other primary amines, this is undesirable because the viscosity of the conductive paste is likely to change over time. While the details are unclear, it is thought that the steric hindrance caused by the functional groups, alkyl groups, alkenyl groups, and alkynyl groups contained in the amine-based dispersant, which is a secondary amine or tertiary amine as described above, affects adsorption to the metal particles that make up the conductive powder, and as a result, affects the stability of the viscosity of the conductive paste over time.

In the above formula (1), _R1 represents a hydrogen atom, an alkyl group having 1 to 7 carbon atoms, an alkenyl group having 2 to 7 carbon atoms, an alkynyl group having 2 to 7 carbon atoms, a hydroxyethyl group, or a hydroxypropyl group. When the carbon number of _R1 is within the above range, the powder in the conductive paste has sufficient dispersibility and excellent solubility in solvents. When _R1 is a hydrocarbon, it is preferably a linear hydrocarbon group.

In the above formula (1), _R2 represents a hydroxyethyl group ₍ e.g., _C2H4OH ), a hydroxypropyl group, an aminoethyl group, or an aminopropyl group.

In the above formula (1), _R3 represents a hydrogen atom, an alkyl group having 1 to 7 carbon atoms, an alkenyl group having 2 to 7 carbon atoms, an alkynyl group having 2 to 7 carbon atoms, a hydroxyethyl group, a hydroxypropyl group, an aminoethyl group, or an aminopropyl group.

In the above formula (1), when any one or more of R ₁ , R ₂ , and R ₃ is a hydroxyethyl group or a hydroxypropyl group, examples of the hydroxyethyl group include a 1-hydroxyethyl group and a 2-hydroxyethyl group, with the 2-hydroxyethyl group being preferred, and examples of the hydroxypropyl group include a 1-hydroxypropyl group, a 2-hydroxypropyl group, and a 3-hydroxypropyl group, with the 3-hydroxypropyl group being preferred. R _{1 ,} R _{2 ,} and R ₃ may be the same group or different groups.

In the above formula (1), when one or more of R ₂ and R ₃ are aminoethyl groups or aminopropyl groups, examples of the aminoethyl groups include 1-aminoethyl groups and 2-aminoethyl groups, with 2-aminoethyl groups being preferred, and examples of the aminopropyl groups include 1-aminopropyl groups, 2-aminopropyl groups and 3-aminopropyl groups, with 3-aminopropyl groups being preferred. R ₂ and R ₃ may be the same group or different groups.

Furthermore, when _R3 in the above formula (1) is an alkyl group, an alkenyl group, or an alkynyl group, the carbon number is preferably 3 or less. When the carbon number of the alkyl group, alkenyl group, or alkynyl group of _R3 is 3 or less, steric hindrance is less likely to occur, which affects the adsorption of the dispersant to the metal particles, and as a result, leads to stability of the viscosity of the conductive paste over time.

Furthermore, in the above formula (1), the number of alcohol-based hydroxyl groups or amino groups contained in R ₁ to R ₃ can be appropriately selected taking into consideration the oxidation state of the surfaces of the metal particles of the conductive powder, etc. It is believed that the presence of multiple amino groups, or amino groups and alcohol-based hydroxyl groups, in the molecule of the amine-based dispersant affects the adsorption of the dispersant to the metal particles that make up the conductive powder, and as a result, leads to the stability of the viscosity of the conductive paste over time.

In addition, when R ₁ , R ₂ , and R ₃ in the above formula (1) are atomic groups containing four or more carbon atoms and hydrogen atoms and having an alcohol-based hydroxyl group or an amino group, such as a hydroxybutyl group or an aminobutyl group, the steric hindrance caused by the atomic group adversely affects the adsorption of the amine-based dispersant to the metal particles, making it difficult to maintain the stability of the viscosity of the conductive paste over time. R _{1 ,} R ₂ , and R ₃ may be the same or different. For example, when either one of R ₁ and R ₃ (R ₁ or R ₃ ) is an alkyl group, the other (R ₁ or R ₃ ) is preferably a hydrogen atom, an alcohol-based hydroxyl group (hydroxyethyl group, hydroxypropyl group), or an amino group (aminoethyl group, aminopropyl group), from the viewpoint of further improving the stability of the viscosity of the conductive paste over time.

Furthermore, one of the additional amine-based dispersants is preferably an alkylamine having approximately 20 or less carbon atoms. Any conventionally known amine compound can be used without any particular limitation. Specific examples include primary aliphatic amines such as n-butylamine, pentylamine, 2-methoxyethylamine, 2-ethoxyethylamine, 3-methoxypropylamine, 3-ethoxypropylamine, octylamine, hexadecylamine, stearylamine, oleylamine, myristylamine, and laurylamine; secondary aliphatic amines such as dimethylamine, diethylamine, methylbutylamine, ethylpropylamine, ethylisopropylamine, and dioctylamine; and tertiary aliphatic amines such as trimethylamine, dimethylethylamine, diethylmethylamine, and trioctylamine.

When the above-mentioned amine-based dispersant is used in a conductive paste, it is thought that it will be more likely to adsorb to the metal particles that make up the conductive powder, thereby suppressing the adsorption of the resin components contained in the conductive paste to those metal particles. As a result, it is thought that the viscosity of the conductive paste will be less likely to change over time.

The conductive paste may contain 0.01 to 4 parts by mass, preferably 0.02 to 3 parts by mass, of the amine-based dispersant per 100 parts by mass of conductive powder. When the amine-based dispersant is contained within the above range, viscosity changes over time are suppressed, viscosity stability can be improved, and the resulting electrode layer has high smoothness. Note that if the amine-based dispersant content exceeds 4 parts by mass, mesh marks may appear on the printed surface or the viscosity of the paste may decrease significantly when the conductive paste is printed on a green sheet.

Amine-based dispersants that satisfy the above properties can be selected from commercially available products and used. Alternatively, the amine-based dispersants may be manufactured using conventionally known manufacturing methods to satisfy the above properties.

These two or more amine-based dispersants are contained in a total amount of 0.01 to 4 parts by mass, preferably 0.02 to 3 parts by mass, per 100 parts by mass of the conductive powder. When the dispersant content is within the above range, the viscosity of the conductive paste can be adjusted to an appropriate range, and sheet attack and poor peeling of the green sheet can be suppressed.

The two or more amine-based dispersants are preferably contained in a total amount of 3 mass% or less of the entire conductive paste. The upper limit of the dispersant content is preferably 2.5 mass% or less, and more preferably 2 mass% or less. The lower limit of the dispersant content is not particularly limited, but is, for example, 0.01 mass% or more, and preferably 0.05 mass% or more. When the dispersant content is within the above range, the viscosity of the conductive paste can be adjusted to an appropriate range, and sheet attack and poor peeling of the green sheet can be suppressed. By containing the two above amine-based dispersants within the above range, changes in the viscosity of the conductive paste over time can be suppressed, improving the smoothness of the electrode layer.

The conductive paste may contain dispersants other than the above-mentioned amine-based dispersants, provided that the effects of the present invention are not impaired. Examples of dispersants other than the above include acid-based dispersants and amino acid-based dispersants, including higher fatty acids and polymeric surfactants, cationic dispersants other than acid-based dispersants, nonionic dispersants, amphoteric surfactants, and polymeric dispersants. These dispersants may be used alone or in combination of two or more.

(Conductive paste)
The conductive paste according to this embodiment contains the above-mentioned components, thereby maintaining the dispersed state of the conductive powder in the conductive paste and reducing the change in viscosity of the conductive paste over time.

The method for producing the conductive paste of this embodiment is not particularly limited, and conventionally known methods can be used. The conductive paste can be produced, for example, by preparing the above-mentioned components and stirring and kneading them using a triple-roll mill, ball mill, mixer, or the like. In this process, if a dispersant is applied to the surface of the conductive powder in advance, the conductive powder is sufficiently loosened without agglomeration, allowing the dispersant to be distributed evenly across the surface, making it easier to obtain a uniform conductive paste. Alternatively, the binder resin can be dissolved in an organic solvent for the vehicle to produce an organic vehicle, and the conductive powder, ceramic powder, organic vehicle, and dispersant can be added to the organic solvent for the paste, followed by stirring and kneading using a mixer to produce the conductive paste.

The conductive paste can be suitably used in electronic components such as multilayer ceramic capacitors and varistors. Multilayer ceramic capacitors have dielectric layers formed using dielectric green sheets and internal electrode layers formed using the conductive paste.

In a multilayer ceramic capacitor, it is preferable that the dielectric ceramic powder contained in the dielectric green sheet and the ceramic powder contained in the conductive paste are powders of the same composition. Multilayer ceramic capacitors manufactured using the conductive paste of this embodiment suppress sheet attack and green sheet peeling defects even when the thickness of the dielectric green sheet is, for example, 2 μm or less.

When the viscosity of the conductive paste is measured 24 hours after production, the change in viscosity after being left to stand for 13 days (14 days after production) is preferably within -5 to +15 Pa s. The viscosity of the conductive paste can be measured, for example, by the method described in the Examples (a method in which the viscosity is measured using a rheometer M501 manufactured by Anton Paar at a rotation speed of 4 sec ^-1 in a flow curve measurement).

The smoothness of the conductive paste used as an electrode layer can be measured by, for example, measuring a dried film of the conductive paste applied to a glass plate using a laser microscope (manufactured by Keyence Corporation).

[Electronic Components]
Hereinafter, embodiments of electronic components and the like that can be manufactured using the conductive paste of the present invention will be described with reference to the drawings. In the drawings, schematic representations or scale changes may be used as appropriate. Furthermore, the positions and directions of components will be described with reference to the XYZ Cartesian coordinate system shown in FIG. 1 and other figures. In this XYZ Cartesian coordinate system, the X and Y directions are horizontal, and the Z direction is vertical (up-down).

Figures 1A and 1B are a perspective view and a side cross-sectional view showing a multilayer ceramic capacitor 1, which is an example of an electronic component according to an embodiment. The multilayer ceramic capacitor 1 includes a ceramic laminate 10 in which dielectric layers 12 and internal electrode layers 11 are alternately stacked, and an external electrode 20.

The following describes a method for manufacturing a multilayer ceramic capacitor 1 using the above-mentioned conductive paste. First, the conductive paste is printed on a dielectric layer made of a ceramic green sheet and dried to form a dry film. Multiple dielectric layers, each with this dry film on its upper surface, are laminated by pressure bonding to obtain a laminate, which is then fired and integrated to produce a ceramic laminate 10 in which internal electrode layers 11 and dielectric layers 12 are alternately stacked. A pair of external electrodes 20 are then formed on both ends of the ceramic laminate 10 to manufacture the multilayer ceramic capacitor 1. This process is described in more detail below.

First, a ceramic green sheet, which is an unfired ceramic sheet, is prepared. Examples of ceramic green sheets include those made by adding a predetermined ceramic raw material powder, such as barium titanate, an organic binder, such as polyvinyl butyral, and a solvent, such as terpineol, to the dielectric layer paste, which is then applied to a support film, such as a PET film, in the form of a sheet, and then dried to remove the solvent. The thickness of the dielectric layer, made from the ceramic green sheet, is not particularly limited, but is preferably between 0.05 μm and 3 μm inclusive, in light of the need for miniaturization of multilayer ceramic capacitors.

Next, the above-mentioned conductive paste is printed (applied) onto one side of this ceramic green sheet using a known method such as screen printing, and then dried to form a dry film, to prepare multiple sheets. Note that, in light of the need to thin the internal electrode layer 11, it is preferable that the thickness of the printed conductive paste (dry film) be 1 μm or less after drying.

Next, the ceramic green sheets are peeled off from the support film, and the dielectric layers made from the ceramic green sheets and the dry film formed on one side thereof are stacked alternately, followed by a heat and pressure treatment to obtain a laminate. It is also possible to further place protective ceramic green sheets, which are not coated with conductive paste, on both sides of the laminate.

Next, the laminate is cut to a predetermined size to form green chips, and the green chips are subjected to a binder removal treatment and fired in a reducing atmosphere to produce the ceramic laminate 10. The binder removal treatment is preferably performed in air or an _N2 gas atmosphere. The temperature during the binder removal treatment is, for example, 200°C or higher and 400°C or lower. The temperature is preferably maintained for 0.5 hours or higher and 24 hours or lower during the binder removal treatment. The firing is performed in a reducing atmosphere to suppress oxidation of the metals used in the internal electrode layers. The temperature during firing of the laminate is, for example, 1000°C or higher and 1350°C or lower, and the temperature is preferably maintained for 0.5 hours or higher and 8 hours or lower.

By firing the green chip, the organic binder in the green sheet is completely removed and the ceramic raw material powder is fired to form the ceramic dielectric layer 12. The organic vehicle in the dried film is also removed, and the nickel powder or nickel-based alloy powder is sintered or melted and integrated to form the internal electrodes, resulting in a multilayer ceramic sintered body in which multiple dielectric layers 12 and internal electrode layers 11 are alternately stacked. The sintered multilayer ceramic sintered body may be annealed to incorporate oxygen into the dielectric layers to increase reliability and prevent reoxidation of the internal electrodes.

Then, a pair of external electrodes 20 are provided on the produced sintered laminated ceramic body to produce the multilayer 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. Suitable materials for the external electrode 20 include copper, nickel, or alloys thereof. The electronic component is not limited to a multilayer ceramic capacitor, and may be an electronic component other than a multilayer ceramic capacitor.

The present invention will be described in detail below based on examples and comparative examples, but the present invention is not limited to these examples in any way.

[Evaluation method]
(Viscosity evaluation of conductive paste)
After leaving the conductive pastes at room temperature (25°C) for one day after production, and after leaving them at room temperature (25°C) for 14 days, the viscosity of each conductive paste was measured in a flow curve measurement using a rheometer (Anton Paar MCR501 Rheometer) at a rotation speed of 4 sec ^-1 . The viscosity after leaving them at rest for one day was used as the reference viscosity, and the reference viscosity was subtracted from the viscosity after leaving them at rest for 14 days to calculate the change in viscosity.

(Evaluation of smoothness of dried conductive paste film)
Using an applicator, the conductive paste was applied to a glass plate to a wet film thickness of 10 μm, and the glass plate was then placed in an oven set to 120 ° C. and dried for 20 minutes to obtain a dried film of the conductive paste. The average roughness of the dried film was measured within a measurement range of 200 × 250 μm using a laser microscope (Keyence Corporation, VK-X3000), and measurements were repeated at five random locations. The average value obtained was taken as the average roughness of the dried conductive paste film and was used as a measure of smoothness.

[Materials used]
(conductive powder)
As the conductive powder, Ni powder (number average particle size 60 nm) was prepared by the following method and used.

<Wet nickel powder production>
[Preparation of a solution of nickel salt and metal salt of a metal more noble than nickel]
An aqueous solution (referred to as "100 g-Ni/L aqueous solution") was prepared by dissolving nickel chloride hexahydrate (NiCl ₂ .6H ₂ O, molecular weight: 237.69) in 1 L of pure water so that 100 g of Ni metal was present, and an aqueous solution (referred to as "2 g-Pd/L aqueous solution") was prepared by dissolving ammonium palladium (II) chloride (also known as ammonium tetrachloropalladate (II)) ((NH ₄ ) ₂ PdCl ₄ , molecular weight: 284.31), a metal salt of a metal more noble than nickel, in 1 L of pure water so that 1.2 g of Pd metal was present. A nickel salt nucleating agent-containing solution was prepared by dissolving 1,000 mL of a 100 g Ni/L aqueous solution, 8.5 mL of a 1.2 g Pd/L aqueous solution, and 1.27 g of L-methionine ( _CH3SC2H4CH ( _{NH2 )} COOH, molecular weight: 149.21), a sulfur-containing compound containing one sulfide group ( _-S- ) per molecule as a self-decomposition suppression auxiliary, in 881 mL of purified water. The nickel salt nucleating agent-containing solution contained a nickel salt, a sulfur-containing compound, and a nucleating agent, a metal salt of a metal more noble than nickel, as the main components. The nickel salt nucleating agent-containing solution contained a trace amount of L-methionine, a sulfide compound, at a molar ratio of 0.005 (0.5 mol%) relative to nickel, and palladium (Pd) at 100 ppm by mass (55.16 mol ppm) relative to nickel (Ni).

[Preparation of reducing agent solution]
As a reducing agent, 207 g of commercially available industrial grade 60% hydrazine hydrate (manufactured by Otsuka-MGC Chemical Co., Ltd.), which was prepared by diluting hydrazine hydrate (N ₂ H ₄ ·H ₂ O, molecular weight: 50.06) 1.67 times with pure water, was weighed out to prepare a reducing agent solution, which was an aqueous solution containing hydrazine as the main component and did not contain alkali hydroxide.

[Alkaline hydroxide solution]
As the alkali hydroxide, sodium hydroxide (NaOH, molecular weight: 40.0) was dissolved in pure water to prepare 757 mL of an alkali hydroxide solution containing sodium hydroxide at a concentration of 382 g/L.

[Amine compound solution]
An amine compound solution was prepared as an aqueous solution containing ethylenediamine by dissolving 1.02 g of ethylenediamine (abbreviated as EDA) (H ₂ NC ₂ H ₄ NH ₂ , molecular weight: 60.1), an alkyleneamine containing two primary amino groups (—NH ₂ ) in the molecule, in 18 mL of pure water. All of the materials used in the nickel salt nucleating agent-containing solution, reducing agent solution, alkali hydroxide solution, and amine compound solution, except for 60% hydrazine hydrate, were reagents manufactured by Wako Pure Chemical Industries, Ltd.

[Crystallization process]
The nickel salt nucleating agent-containing solution was placed in a Teflon (registered trademark) coated stainless steel container equipped with a stirring blade and heated with stirring to a liquid temperature of 85°C. After that, a reducing agent solution having a liquid temperature of 27°C was added and mixed for 10 seconds so that the molar ratio of Ni metal to hydrazine hydrate became 1:1.46, to prepare a nickel salt/reducing agent-containing solution. An alkali hydroxide solution having a liquid temperature of 27°C was added and mixed for 120 seconds so that the molar ratio of Ni metal to sodium hydroxide became 1:3.54, to prepare a reaction liquid (nickel chloride + palladium salt + hydrazine + sodium hydroxide) having a liquid temperature of 70°C, and the reduction reaction (crystallization reaction) was initiated (reaction start temperature 70°C). Over a 20-minute period, from 8 to 28 minutes after the start of the reaction, the amine compound solution was added dropwise to the reaction solution so that the molar ratio of Ni metal to ethylenediamine was 1:0.01 (1.0 mol%), and the reduction reaction was allowed to proceed while suppressing the self-decomposition of hydrazine, resulting in the precipitation of nickel crystallized powder in the reaction solution. The reduction reaction was completed within 60 minutes after the start of the reaction, and the supernatant of the reaction solution was transparent, confirming that all of the nickel components in the reaction solution had been reduced to metallic nickel and turned into nickel crystallized powder. The reaction solution containing the nickel crystallized powder was in the form of a slurry, and an aqueous solution of mercaptoacetic acid (thioglycolic acid) (HSCH ₂ COOH, molecular weight: 92.12) was added to this nickel crystallized powder-containing slurry, thereby subjecting the nickel crystallized powder to surface treatment (sulfur coating treatment).

[Wet crushing process]
After the surface treatment, the nickel crystallized powder-containing slurry was washed by repeatedly decanting and adding pure water (electrical conductivity 1 μS/cm) until the electrical conductivity of the slurry became 15 μS/cm or less, and a nickel crystallized powder-containing slurry having a nickel concentration of 25 mass % was obtained, which was then subjected to wet crushing.

[Acid washing process]
The nickel crystallized powder-containing slurry after the wet disintegration step was neutralized by adding dropwise ₁ mass% aqueous sulfuric acid solution ( _H2SO4 , molecular weight: 98.08), and the pH of the nickel crystallized powder-containing slurry was maintained at 4 to ₅ for 20 minutes. The nickel concentration of the nickel crystallized powder-containing slurry at this time was 5 mass%. The neutralization reaction formula was Ni(OH) ₂ + _H2SO4 → _NiSO4 + _2H2O .

[Solvent replacement process, solid-liquid separation process]
After the acid washing process, filter paper was placed on the Nutsche and the nickel crystallized powder-containing slurry was added thereto for filtration. Then, pure water with a conductivity of 1 μS/cm was added to the nickel crystallized powder on the filter paper, and the filtrate was filtered and washed until the conductivity of the filtrate after filtration was 30 μS/cm or less. Then, ethanol (boiling point: 78.3 ° C) with a purity of 99.9% or more was added to the Nutsche and passed through, and the solvent in the nickel slurry was replaced from water to ethanol. The ethanol concentration contained in the solvent of the nickel slurry after solvent replacement was 92.4% by mass, with the remaining 7.6% by mass being water. Here, the ethanol concentration was determined by recovering the final filtrate (the last 50 mL) of the solid-liquid separation process, measuring the Karl Fischer moisture content (150 ° C), and calculating "100 - moisture content (%) = solvent concentration in the filtrate (%)." The ethanol concentration was calculated in the same way in other examples. After the solvent substitution, filtration was continued to separate the solid content into liquid and nickel powder cake until the solid content reached 40% by mass or more.

[Drying process]
The nickel powder cake was dried in a vacuum dryer set at a temperature of 120° C. for 6 hours to obtain wet nickel powder.

<Evaluation and results>
(number average particle size)
The obtained wet nickel powder was observed with a scanning electron microscope (SEM, manufactured by JEOL Ltd., JSM-7100F), and the SEM images were processed to measure the areas of 100 to 200 particles whose overall shapes could be confirmed. The diameter of each particle was calculated from the measured area by converting it into a perfect circle, and the average of the calculated diameters was calculated and used as the number average particle size. The number average particle size of the obtained nickel powder was 60 nm.

(ceramic powder)
As the ceramic powder, barium titanate (Toda Kogyo Co., Ltd. BaTiO ₃ , trade name T-BTO-030RF; number average particle size calculated by the above-mentioned SEM observation method is 30 nm) was used.

(binder resin)
As the binder resin, ethyl cellulose resin (manufactured by Nisshin Seiki Co., Ltd., trade name Ethocel STD100) and polyvinyl butyral resin (manufactured by Sekisui Chemical Co., Ltd., trade name S-LEC BM-1) were used. These resins were dissolved in terpineol at 10% by mass, and the resulting mixture was mixed at a mass ratio of 1:1 to prepare the binder resin.

(Dispersant)
Examples of the amine dispersant (1) include dispersant a represented by R ₁ =CH ₃ , R ₂ =C ₂ H ₄ OH, R ₃ =C ₂ H ₄ OH in the above general formula (1), dispersant b represented by R ₁ =CH ₃ , R ₂ =C ₂ H ₄ OH, R ₃ =H in the above general formula (1), dispersant c represented by R ₁ =CH ₃ , R ₂ =C ₂ H ₄ OH, R ₃ =CH ₃ in the above general formula (1), dispersant d represented by _{R 1} =C _{2 H 4} OH, R ₂ =C ₂ H ₄ OH, R ₃ =C ₂ H _{4 OH} in the above general formula ( ₁ ), _and Dispersant e represented by the formula: R ₁ =H, R ₂ =C ₂ H ₄ NH 2 , and dispersant f represented by the formula (1) above, where R 1 =H, R 2 =C ₂ H ₄ NH ₂ , and R ₃ =C ₂ H ₄ NH _2, were used.

Oleylamine was used as the amine-based dispersant (2).

(organic solvent)
Terpineol was used as the organic solvent.

[Example 1]
50% by mass of Ni powder, 3.8% by mass of ceramic powder, a total of 3% by mass of binder resin in a vehicle consisting of ethyl cellulose resin and polyvinyl butyral resin, 0.5% by mass of dispersant a as an amine-based dispersant (1), 0.5% by mass of oleylamine as an amine-based dispersant (2), and the remainder being terpineol were blended to a total of 100% by mass, and these materials were mixed in a three-roll mill to prepare a conductive paste.

The viscosity of the resulting conductive paste after one day was 81 Pa·s, and after 14 days it was 77 Pa·s, a change of -4 Pa·s. The average roughness of the dried film of the conductive paste produced on the glass plate was 0.04 mm. The dispersant used, the viscosity of the produced conductive paste, and the average roughness of the dried film are shown in Table 1.

[Examples 2 to 6]
Conductive pastes were prepared in the same manner as in Example 1, except that the amine-based dispersant (1) was changed to an amine-based dispersant shown in Table 1, and the viscosity and average roughness were evaluated. The results are shown in Table 1.

[Comparative Example 1]
Except for not using the amine-based dispersant (2), a conductive paste was prepared in the same manner as in Example 1. The results of viscosity and average roughness are shown in Table 1.

Table 1 shows that the combined use of amine-based dispersants (1) and (2) stabilizes the viscosity of the conductive paste and also improves the smoothness of the dried film obtained from the conductive paste.

As described above, the present invention can provide a conductive paste that has high smoothness as a conductive film after drying and little change in viscosity over time, making it industrially useful.

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 (5)

A conductive paste comprising a conductive powder, a ceramic powder, a dispersant, a binder resin, and an organic solvent,
The conductive paste comprises at least two amine-based dispersants, including one or more secondary amines or tertiary amines represented by the following general formula (1) and one or more alkylamines:
(In formula (1), R ₁ represents a hydrogen atom, an alkyl group having 1 to 7 carbon atoms, an alkenyl group having 2 to 7 carbon atoms, an alkynyl group having 2 to 7 carbon atoms, a hydroxyethyl group, or a hydroxypropyl group; R ₂ represents a hydroxyethyl group, a hydroxypropyl group, an aminoethyl group, or an aminopropyl group; and R ₃ represents a hydrogen atom, an alkyl group having 1 to 7 carbon atoms, an alkenyl group having 2 to 7 carbon atoms, an alkynyl group having 2 to 7 carbon atoms, a hydroxyethyl group, a hydroxypropyl group, an aminoethyl group, or an aminopropyl group.) the mass ratio of the total amount of the amine-based dispersant to the conductive powder is 0.01 to 4:100;
The conductive paste according to claim 1, wherein the content of the conductive powder relative to the total amount of the conductive paste is 40% by mass to 65% by mass. The conductive paste according to claim 1 or 2, wherein the number average particle diameter of the conductive powder is 30 nm to 100 nm. An electronic component formed using the conductive paste described in any one of claims 1 to 3. The laminate has at least a laminate of dielectric layers and internal electrode layers,
A multilayer ceramic capacitor, wherein the internal electrode layers are formed using the conductive paste according to any one of claims 1 to 3.