Conductive paste, electronic components, and multilayer ceramic capacitors

Abstract

To provide a conductive paste having high smoothness as a conductive film after drying and having small viscosity change over time.SOLUTION: A conductive paste contains conductive particles, ceramic particles, a dispersant, a binder resin, and an organic solvent, wherein the dispersant contains at least two or more amine-based dispersants comprising one or more secondary amines or tertiary amines represented by the general formula (1) and one or more alkyl amines, and the organic solvent comprises three or more organic solvents, (in the formula, R1 represents H, a 1-7C alkyl group, a 2-7C alkenyl group, a 2-7C alkynyl group, a hydroxyethyl group or the like, R2 represents a hydroxyethyl group, a hydroxypropyl group, an aminoethyl group or an aminopropyl group, and R3 represents H, a 1-7C alkyl group, a 2-7C alkenyl group, a 2-7C alkynyl group, a hydroxyethyl group, a hydroxypropyl group, an aminoethyl group or the like).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a conductive paste, an electronic component, and a multilayer ceramic capacitor. [Background technology]

[0002] As electronic devices such as mobile phones and digital devices become smaller and more powerful, there is a demand for smaller and higher-capacity electronic components, including multilayer ceramic capacitors. Multilayer ceramic capacitors have a structure in which multiple dielectric layers and multiple internal electrode layers are alternately stacked, and by reducing the thickness of these dielectric layers and internal electrode layers, it is possible to achieve smaller size and higher capacity.

[0003] 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 (BaTiO) and a binder resin, and then dried to form a dry film. Next, the dried film and green sheets 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 process 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.

[0004] Generally, the conductive paste used to form the internal electrode layer contains a conductive powder, a ceramic powder, a binder resin, and an 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 layer has 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 may result in a decrease in the dispersibility of the conductive powder and a decrease in the viscosity characteristics of the conductive paste.

[0005] Therefore, 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.

[0006] Furthermore, Patent Document 2 describes a conductive paste for internal electrodes that is composed of 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.

[0007] 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 electrode 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 at 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. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-216244 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-149457 [Patent Document 3] Japanese Patent Application Laid-Open No. 2006-063441 Summary of the Invention [Problem to be solved by the invention]

[0009] 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 dried after printing to form electrode patterns, and to maintain their viscosity characteristics over time.

[0010] In view of the above circumstances, an object of the present invention is to provide a conductive paste that provides a conductive film with high smoothness after drying and that exhibits little change in viscosity over time. [Means for solving the problem]

[0011] In order to solve the above problems, the conductive paste of the present invention is a conductive paste comprising a conductive powder, a ceramic powder, a dispersant, a binder resin, and an organic solvent, wherein the dispersant comprises at least two or more amine-based dispersants, including one or more secondary amines or tertiary amines represented by the following general formula (1) and one or more alkylamines, and the organic solvent is a conductive paste consisting of three or more organic solvents.

[0012] [ka]

[0013] (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.)

[0014] 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% by mass to 65% by mass.

[0015] The number average particle size of the conductive powder may be 30 nm to 100 nm.

[0016] The content of the organic solvent relative to the total amount of the conductive paste may be 20% by mass to 60% by mass.

[0017] The organic solvent may be any one of dihydroterpineol acetate, isobornyl acetate, isobornyl propionate, isobornyl butyrate, isobornyl isobutyrate, ethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether acetate, dipropylene glycol methyl ether acetate, heptyl acetate, terpineol, dihydroterpineol, tridecane, nonane, cyclohexane, methyl isobutyl ketone, and diisobutyl ketone.

[0018] The organic solvent may be terpineol, diisobutyl ketone, and cyclohexane.

[0019] The mass ratio of the terpineol, the diisobutyl ketone, and the cyclohexane may be terpineol:diisobutyl ketone:cyclohexane=0.1 to 5.0:0.1 to 5.0:23.5 to 43.3.

[0020] In a second aspect of the present invention, there is provided an electronic component formed using the conductive paste of the present invention.

[0021] In a third aspect of the present invention, there is provided a multilayer ceramic capacitor having at least a laminate in which dielectric layers and internal electrode layers are laminated, the internal electrodes being formed using the conductive paste of the present invention. [Effects of the Invention]

[0022] As described above, according to the present invention, it is possible to provide a conductive paste that has high smoothness as a conductive film after drying and that exhibits little change in viscosity over time. [Brief explanation of the drawings]

[0023] [Figure 1] 1A and 1B are a perspective view and a side cross-sectional view showing a multilayer ceramic capacitor; DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, one embodiment of the conductive paste of the present invention will be described.

[0025] The conductive paste of this embodiment is a conductive paste containing a conductive powder, a ceramic powder, a dispersant, a binder resin, and an organic solvent, where the dispersant contains 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, and the organic solvent contains three or more organic solvents. The conductive powder, ceramic powder, dispersant, binder resin, and organic solvent contained in the conductive paste of this embodiment will be described in detail below.

[0026] (conductive powder) The conductive powder is not particularly limited, and metal powders can be used, such as powders of one or more metals selected from Ni, Pd, Pt, Au, Ag, Cu, and alloys thereof. 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.

[0027] The number-average particle size of the conductive powder is preferably 30 nm or more and 100 nm or less, more preferably 40 nm or more and 90 nm or less. When the average particle size of the conductive powder is within the above range, it can be suitably used as a conductive paste for 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 the SEM at 10,000x magnification.

[0028] The content of the conductive powder in the total amount of the conductive paste is preferably 40% by mass to 65% by mass, and more preferably 45% by mass to 60% by mass. When the content of the conductive powder is in the above range, the conductive paste has excellent conductivity and dispersibility.

[0029] (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 applied. Examples of the ceramic powder include perovskite-type oxides containing Ba and Ti, and preferably barium titanate (BaTiO).

[0030] 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 and Ti atoms of barium titanate (BaTiO) are replaced with other atoms, such as Sn, Pb, or Zr.

[0031] In the conductive paste for the internal electrodes, powder of 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 the occurrence of cracks due to a shrinkage mismatch at the interface between the dielectric layer and the internal electrode layer during the sintering process. In addition to the above, examples of such ceramic powders include oxides such as ZnO, ferrite, PZT, BaO, Al2O3, Bi2O3, R (rare earth element)2O3, and TiO2. Note that one type of ceramic powder may be used, or two or more types may be used.

[0032] 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 number average particle diameter of the ceramic powder is in the above range, when used as a conductive paste for internal electrodes, it is possible to form sufficiently fine, thin, and uniform 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 the SEM at a magnification of 50,000 times.

[0033] The content of the ceramic powder is preferably 1 to 30 parts by mass, and more preferably 3 to 30 parts by mass, relative to 100 parts by mass of the conductive powder. When the content of the conductive powder is within the above range, the conductivity and dispersibility are excellent.

[0034] The content of the ceramic powder is preferably 1 to 20% by mass, and more preferably 3 to 20% by mass, based on the total amount of the conductive paste. When the content of the conductive powder is within the above range, the conductivity and dispersibility are excellent.

[0035] (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, butyral resin may be contained or butyral resin may be used alone from the viewpoint of improving 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.

[0036] 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 obtain sufficient viscosity for printing. Even in such cases, printability can be ensured by increasing the content of the cellulose-based resin, but this results in increased residual carbon after firing. A more preferable lower limit of the weight-average molecular weight is 30,000. If the lower limit is 30,000 or higher, sufficient printability can be ensured without increasing the residual carbon content. On the other hand, if the weight-average molecular weight exceeds 300,000, the resulting paste for multilayer ceramic capacitor internal electrodes increases in viscosity, resulting in poor printability. If the weight-average molecular weight is 300,000 or less, a paste for multilayer ceramic capacitor internal electrodes with excellent printability can be obtained while ensuring compatibility with the cellulose-based resin. The preferable upper limit, depending on the compounding ratio with the cellulose-based resin, is 300,000 or less, allowing for a higher compounding ratio of the butyral resin and reducing residual carbon after firing.

[0037] The content of the binder resin is preferably 1 to 10 parts by mass, more preferably 1 to 8 parts by mass, relative to 100 parts by mass of the conductive powder. When the content of the binder resin is within the above range, the conductivity and dispersibility are excellent.

[0038] The content of the binder resin is preferably 0.5% by mass to 10% by mass, and more preferably 1% by mass to 6% by mass, based on the entire conductive paste. When the content of the binder resin is within the above range, the conductive paste has excellent conductivity and dispersibility.

[0039] (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 dihydroterpinyl acetate, isobornyl acetate, isobornyl propionate, isobornyl butyrate, isobornyl isobutyrate, ethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether acetate, dipropylene glycol methyl ether acetate, and heptyl acetate; terpene-based solvents such as terpineol and dihydroterpineol; hydrocarbon-based solvents such as tridecane, nonane, and cyclohexane; and ketone-based solvents such as methyl isobutyl ketone and diisobutyl ketone. Three or more organic solvents are used. Using three or more organic solvents can produce a conductive paste that has high smoothness as a conductive film after drying and little change in viscosity over time, and can maintain a low viscosity as a conductive paste.

[0040] The content of the organic solvent is preferably 40 parts by mass to 100 parts by mass, more preferably 65 parts by mass to 95 parts by mass, relative to 100 parts by mass of the conductive powder. When the content of the organic solvent is within the above range, the conductivity and dispersibility are excellent.

[0041] The content of the organic solvent is preferably 20% by mass to 60% by mass, more preferably 35% by mass to 55% by mass, based on the total amount of the conductive paste. When the content of the organic solvent is within the above range, the conductive paste has excellent conductivity and dispersibility.

[0042] In particular, terpineol, diisobutyl ketone, and cyclohexane can be used as the organic solvent. By using these three types of organic solvents, it is possible to adjust the viscosity.

[0043] When terpineol, diisobutyl ketone, and cyclohexane are used as the organic solvent, the mass ratio thereof can be terpineol:diisobutyl ketone:cyclohexane=0.1-5.0:0.1-5.0:23.5-43.3. By setting this mass ratio, for example, at a shear rate of 4 s -1 This makes it possible to adjust the viscosity to less than 50 Pa·s, making it suitable for use in screen printing of conductive pastes.

[0044] (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 and one or more alkylamines, as described below. 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.

[0045] The amine-based dispersant is preferably not a polymer dispersant, since polymer dispersants are expected to have a high thermal decomposition temperature and therefore produce a large amount of residual carbon after firing.

[0046] One type of amine-based dispersant is a tertiary amine or a secondary amine represented by the following general formula (1).

[0047] [ka]

[0048] (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.)

[0049] The amine dispersant of the above formula (1) comprises a tertiary amine or secondary amine in its molecule, and in addition to the nitrogen atom (i.e., N in the above formula (1)) that constitutes an amino group as a functional group, it may also comprise at least one group selected from the group consisting of an alcohol-based hydroxyl group (hydroxyethyl group, hydroxypropyl group) and another amino group (aminoethyl group, aminopropyl group) as R2 and, optionally, R1 and R3.

[0050] Furthermore, when the amine-based dispersant is a primary amine, even if the molecule contains an alcohol-based hydroxyl group or an amino group constituting another primary amine, this is undesirable because the viscosity of the conductive paste is likely to change over time. Although 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, thereby affecting the stability of the viscosity of the conductive paste over time.

[0051] 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 number of carbon atoms in R1 is within the above range, the powder in the conductive paste has sufficient dispersibility and excellent solubility in the solvent. When R1 is a hydrocarbon, it is preferably a linear hydrocarbon group.

[0052] In the above formula (1), R2 represents a hydroxyethyl group (for example, C2H4OH), a hydroxypropyl group, an aminoethyl group, or an aminopropyl group.

[0053] 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.

[0054] In the above formula (1), when any one or more of R1, R2, and R3 is a hydroxyethyl group or a hydroxypropyl group, examples of the hydroxyethyl group include a 1-hydroxyethyl group and a 2-hydroxyethyl group, of which the 2-hydroxyethyl group is preferred, and examples of the hydroxypropyl group include a 1-hydroxypropyl group, a 2-hydroxypropyl group, and a 3-hydroxypropyl group, of which the 3-hydroxypropyl group is preferred. 1、 R 2、 and R3 may be the same group or different groups.

[0055] In the above formula (1), when at least one of R2 and R3 is an aminoethyl group or an aminopropyl group, examples of the aminoethyl group include a 1-aminoethyl group and a 2-aminoethyl group, of which the 2-aminoethyl group is preferred, and examples of the aminopropyl group include a 1-aminopropyl group, a 2-aminopropyl group and a 3-aminopropyl group, of which the 3-aminopropyl group is preferred. 2、 and R3 may be the same group or different groups.

[0056] 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 the stability of the viscosity of the conductive paste over time.

[0057] Furthermore, in the above formula (1), the number of alcohol-based hydroxyl groups or amino groups contained in R1 to R3 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, which in turn leads to the stability of the viscosity of the conductive paste over time.

[0058] In addition, when R1, R2, and R3 in the above formula (1) are atomic groups containing four or more carbon atoms and hydrogen atoms, such as a hydroxybutyl group or an aminobutyl group, and have an alcohol-based hydroxyl group or an amino group, the steric hindrance of the atomic groups 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. 1、 R2 and R3 may be the same or different. For example, when either one of R1 and R3 (R1 or R3) is an alkyl group, the other (R1 or R3) is preferably a hydrogen atom, an alcoholic hydroxyl group (hydroxyethyl group, hydroxypropyl group), or an amino group (aminoethyl group, aminopropyl group), from the viewpoint of further improving the stability of the conductive paste viscosity over time.

[0059] 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 as the amine compound. Specific examples include amine compounds having 20 or less carbon atoms, such as 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.

[0060] When the amine-based dispersant is used in the conductive paste, it is believed that it increases the adsorption of the amine-based dispersant to the metal particles constituting the conductive powder, thereby suppressing the adsorption of the resin component contained in the conductive paste to the metal particles, and as a result, it is believed that the change in viscosity of the conductive paste that increases over time is suppressed.

[0061] The conductive paste may contain the amine-based dispersant in an 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 amine-based dispersant is contained in the above range, viscosity change over time is suppressed, viscosity stability can be improved, and the resulting electrode layer has high smoothness. Note that, when 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.

[0062] The amine-based dispersant may be selected from commercially available products that satisfy the above-mentioned properties. Alternatively, the amine-based dispersant may be produced using a conventionally known production method so as to satisfy the above-mentioned properties.

[0063] The 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 content of the dispersants is within the above range, the viscosity of the conductive paste can be adjusted to an appropriate range, and sheet attack and peeling problems of the green sheet can be suppressed.

[0064] Furthermore, these two or more types of 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, 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, 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, and the smoothness of the electrode layer can be improved.

[0065] The conductive paste may contain a dispersant other than the above-mentioned amine-based dispersant, provided that the effects of the present invention are not impaired. Examples of dispersants other than the above-mentioned dispersants 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.

[0066] (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.

[0067] 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 three-roll mill, a ball mill, a mixer, or the like. In this case, 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 may be dissolved in an organic solvent for the vehicle to produce an organic vehicle, and the conductive powder, ceramic powder, organic vehicle, and dispersant may be added to the organic solvent for the paste, followed by stirring and kneading using a mixer to produce the conductive paste.

[0068] The conductive paste can be suitably used in electronic components such as multilayer ceramic capacitors and varistors. A multilayer ceramic capacitor has dielectric layers formed using dielectric green sheets and internal electrode layers formed using the conductive paste.

[0069] 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. In a multilayer ceramic capacitor manufactured using the conductive paste of this embodiment, sheet attack and peeling failure of the green sheet are suppressed even when the thickness of the dielectric green sheet is, for example, 2 μm or less.

[0070] 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 the range of -5 to +15 Pa·s. The viscosity of the conductive paste is measured, for example, by flow curve measurement using the method described in the Examples (using a rheometer M501 manufactured by Anton Paar) at a rotation speed of 4 sec. -1 ) can be measured under the conditions of ) etc.

[0071] The smoothness of the conductive paste as the electrode layer can be measured by a method in which a dried film of the conductive paste applied to a glass plate is measured with a laser microscope (manufactured by Keyence Corporation).

[0072] [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 as appropriate. In this XYZ Cartesian coordinate system, the X and Y directions are horizontal, and the Z direction is vertical (up-down).

[0073] 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 external electrodes 20.

[0074] A method for manufacturing a multilayer ceramic capacitor 1 using the above-mentioned conductive paste will be described below. First, the conductive paste is printed on a dielectric layer made of a ceramic green sheet and dried to form a dry film. A plurality of dielectric layers having this dry film on their upper surfaces are laminated by pressure bonding to obtain a laminate, and the laminate is then fired and integrated to produce a ceramic laminate 10 in which internal electrode layers 11 and dielectric layers 12 are alternately laminated. A pair of external electrodes 20 is then formed on both ends of the ceramic laminate 10 to manufacture the multilayer ceramic capacitor 1. This method will be described in more detail below.

[0075] First, a ceramic green sheet, which is an unfired ceramic sheet, is prepared. Examples of the ceramic green sheet include a dielectric layer paste obtained by adding an organic binder such as polyvinyl butyral and a solvent such as terpineol to a predetermined ceramic raw material powder such as barium titanate, and then coating the paste on a support film such as a PET film in a sheet form and drying it to remove the solvent. The thickness of the dielectric layer made of the ceramic green sheet is not particularly limited, but is preferably 0.05 μm or more and 3 μm or less in view of the demand for miniaturization of multilayer ceramic capacitors.

[0076] Next, the above-mentioned conductive paste is printed (applied) on one side of this ceramic green sheet by a known method such as screen printing, and then dried to form a dry film, to prepare a plurality of sheets. Note that, from the viewpoint of the requirement for thinning of the internal electrode layer 11, it is preferable that the thickness of the printed conductive paste (dry film) is 1 μm or less after drying.

[0077] Next, the ceramic green sheets are peeled off from the support film, and the dielectric layers made of the ceramic green sheets and the dry film formed on one side thereof are stacked alternately, and then a laminate is obtained by heat and pressure treatment. Note that it is also possible to further place protective ceramic green sheets not coated with the conductive paste on both sides of the laminate.

[0078] Next, the laminate is cut to a predetermined size to form green chips, and the green chips are then 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 during the firing treatment.

[0079] 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 internal electrodes, forming a fired multilayer ceramic body in which multiple dielectric layers 12 and internal electrode layers 11 are alternately stacked. Note that, from the viewpoint of incorporating oxygen into the dielectric layers to increase reliability and suppressing reoxidation of the internal electrodes, the fired multilayer ceramic body may be subjected to an annealing treatment.

[0080] Then, a pair of external electrodes 20 is provided on the produced fired multilayer ceramic body, thereby producing a multilayer ceramic capacitor 1. For example, the external electrodes 20 include an external electrode layer 21 and a plating layer 22. The external electrode layer 21 is electrically connected to the internal electrode layer 11. Note that, for example, copper, nickel, or an alloy thereof can be suitably used as the material for the external electrodes 20. Note that the electronic component is not limited to a multilayer ceramic capacitor, and may be an electronic component other than a multilayer ceramic capacitor. [Example]

[0081] EXAMPLES The present invention will be described in detail below based on examples and comparative examples, but the present invention is not limited to these examples.

[0082] [Evaluation method] (Viscosity evaluation of conductive paste) After leaving the conductive paste at room temperature (25°C) for 1 day and after leaving it at room temperature (25°C) for 14 days, the viscosity of each conductive paste was measured by flow curve measurement using a rheometer (Anton Paar MCR501 rheometer) at a rotation speed of 4 seconds. -1 The viscosity after standing for 1 day was used as the reference viscosity, and the viscosity change was calculated by subtracting the reference viscosity from the viscosity after standing for 14 days.

[0083] (Smoothness evaluation 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 using a laser microscope (Keyence VK-X3000) over a measurement area of ​​200 x 250 μm, and measurements were repeated at five random locations. The average of the obtained values ​​was taken as the average roughness of the dried conductive paste film and was used as a measure of smoothness.

[0084] [Materials used] (conductive powder) As the conductive powder, Ni powder (number average particle size 60 nm) was prepared by the following method and used.

[0085] <Wet nickel powder production> [Preparation of solutions of nickel salts and metal salts of metals more noble than nickel] An aqueous solution (referred to as "100g-Ni / L aqueous solution") was prepared by dissolving nickel chloride hexahydrate (NiCl2·6H2O, 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 "2g-Pd / L aqueous solution") was prepared by dissolving ammonium palladium(II) chloride (also known as ammonium tetrachloropalladate(II)) ((NH4)2PdCl4, 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 solution was prepared by dissolving 1000 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-) in the molecule, in 881 mL of purified water. The nickel salt nucleating agent solution contained a trace amount of nickel salt, a sulfide compound, and a nucleating agent, a metal salt of a metal nobler than nickel. The molar ratio of the sulfide compound, L-methionine, to nickel was 0.005 (0.5 mol%), and palladium (Pd) was 100 ppm by mass (55.16 mol ppm) relative to nickel (Ni).

[0086] [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.) was weighed out, which was prepared by diluting hydrazine hydrate (N2H4·H2O, molecular weight: 50.06) 1.67 times with pure water, to prepare a reducing agent solution, which is an aqueous solution containing hydrazine as the main component and does not contain alkali hydroxide.

[0087] [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.

[0088] [Amine compound solution] An amine compound solution was prepared by dissolving 1.02 g of ethylenediamine (abbreviated as EDA) (H2NC2H4NH2, molecular weight: 60.1), an alkyleneamine containing two primary amino groups (-NH2) 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.

[0089] [Crystallization process] The nickel salt nucleating agent 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. Then, a reducing agent solution at a liquid temperature of 27°C was added and mixed over a mixing time of 10 seconds so that the molar ratio of Ni metal to hydrazine hydrate was 1:1.46, to prepare a nickel salt-reducing agent solution. An alkali hydroxide solution at a liquid temperature of 27°C was added and mixed over a mixing time of 120 seconds to this nickel salt-reducing agent solution so that the molar ratio of Ni metal to sodium hydroxide was 1:3.54, to prepare a reaction liquid (nickel chloride + palladium salt + hydrazine + sodium hydroxide) at a liquid temperature of 70°C, and the reduction reaction (crystallization reaction) was initiated (reaction start temperature: 70°C). The amine compound solution was added dropwise to the reaction mixture over a 20-minute period, from 8 to 28 minutes after the start of the reaction, so that the molar ratio of Ni metal to ethylenediamine was 1:0.01 (1.0 mol%). The reduction reaction proceeded while suppressing the autolysis of hydrazine, resulting in the precipitation of nickel crystallized powder in the reaction mixture. The reduction reaction was completed within 60 minutes of the start of the reaction, and the supernatant liquid of the reaction mixture was clear, confirming that all of the nickel components in the reaction mixture had been reduced to metallic nickel and turned into nickel crystallized powder. The reaction mixture containing the nickel crystallized powder was in the form of a slurry. An aqueous solution of mercaptoacetic acid (thioglycolic acid) (HSCH2COOH, molecular weight: 92.12) was added to the nickel crystallized powder-containing slurry to perform a surface treatment (sulfur coating) on ​​the nickel crystallized powder.

[0090] [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 the resulting slurry was subjected to wet crushing to obtain a nickel crystallized powder-containing slurry with a nickel concentration of 25 mass%.

[0091] [Acid washing process] After the wet disintegration step, the nickel crystallized powder-containing slurry was neutralized by adding dropwise 1% by mass of sulfuric acid (H2SO4, molecular weight: 98.08) and maintaining the pH of the nickel crystallized powder-containing slurry at 4 to 5 for 20 minutes. At this time, the nickel concentration of the nickel crystallized powder-containing slurry was 5% by mass. The neutralization reaction formula is Ni(OH)2 + H2SO4 → NiSO4 + 2H2O.

[0092] [Solvent replacement process, solid-liquid separation process] After the acid washing step, filter paper was placed on the Nutsche and the nickel crystallized powder-containing slurry was poured thereon for filtration. Then, pure water with a conductivity of 1 μS / cm was poured onto the nickel crystallized powder on the filter paper, and the filtrate was filtered and washed until the conductivity of the filtrate after filtration reached 30 μS / cm or less. Then, ethanol (boiling point: 78.3°C) with a purity of 99.9% or higher was poured into the Nutsche and passed through, replacing the solvent in the nickel slurry from water to ethanol. The ethanol concentration in the solvent of the nickel slurry after solvent substitution was 92.4% by mass, with the remaining 7.6% by mass being water. The ethanol concentration was determined by collecting the final filtrate (the last 50 mL) from the solid-liquid separation step, measuring the Karl Fischer moisture content (150°C), and calculating "100 - moisture content (%) = solvent concentration (%) in the filtrate." This was used as the solvent concentration in the filtrate. Similar calculations were performed in other examples. After the solvent substitution, filtration was continued to separate the solid content into liquid and solids until the solid content reached 40% by mass or more, thereby obtaining a nickel powder cake.

[0093] [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.

[0094] <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 area of ​​100 to 200 particles whose overall shape could be confirmed. The diameter of each particle was calculated from the measured area by converting it to 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.

[0095] (ceramic powder) Barium titanate (BaTiO3, manufactured by Toda Kogyo Co., Ltd., product name T-BTO-030RF; number average particle size calculated by the above-mentioned SEM observation method is 30 nm) was used as the ceramic powder.

[0096] (binder resin) The binder resins used were a vehicle prepared by dissolving 10% by mass of ethyl cellulose resin (manufactured by Nisshin Seiki Co., Ltd., product name Ethocel STD100) in terpineol, and a vehicle prepared by dissolving 10% by mass of polyvinyl butyral resin (manufactured by Sekisui Chemical Co., Ltd., product name S-LEC BM-1) in diisobutyl ketone, and these were mixed in a mass ratio of 1:1. In other words, the binder resin was prepared by mixing ethyl cellulose resin, polyvinyl butyral resin, terpineol, and diisobutyl ketone in a mass ratio of 5:5:45:45, with the resin dissolved in a solvent.

[0097] (dispersant) As the amine-based dispersant (1), dispersant a represented by R1 = CH3, R2 = C2H4OH, R3 = C2H4OH in the above general formula (1), dispersant b represented by R1 = CH3, R2 = C2H4OH, R3 = H in the above general formula (1), dispersant c represented by R1 = CH3, R2 = C2H4OH, R3 = CH3 in the above general formula (1), dispersant d represented by R1 = C2H4OH, R2 = C2H4OH, R3 = C2H4OH in the above general formula (1), dispersant e represented by R1 = H, R2 = C2H4OH, R3 = C2H4OH in the above general formula (1), and dispersant f represented by R1 = H, R2 = C2H4NH2, R3 = C2H4NH2 in the above general formula (1) were used.

[0098] In addition, oleylamine was used as the amine-based dispersant (2).

[0099] (organic solvent) The organic solvents used were solvent (1) terpineol, solvent (2) diisobutyl ketone, and solvent (3) cyclohexane. Note that terpineol and diisobutyl ketone were used to dissolve the resin, and cyclohexane was added when preparing the conductive paste.

[0100] [Example 1] A conductive paste was prepared by mixing 50% Ni powder, 3.8% ceramic powder, 3% binder resin in a vehicle consisting of ethyl cellulose resin and polyvinyl butyral resin (total 3% by mass), 0.5% dispersant a as amine-based dispersant (1), 0.5% oleylamine as amine-based dispersant (2), and the remainder cyclohexane, totaling 100% by mass. The materials were mixed in a three-roll mill to prepare a conductive paste. The mass ratio of the organic solvent in the conductive paste was terpineol:diisobutyl ketone:cyclohexane = 0.15:0.15:42.2.

[0101] The viscosity of the resulting conductive paste after one day was 35 Pa·s, and after 14 days it was 37 Pa·s, a change of -2 Pa·s. The average roughness of the dried film of the conductive paste produced on a glass plate was 0.04 μm. Table 1 shows the dispersant used, the viscosity of the produced conductive paste, and the average roughness of the dried film.

[0102] [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.

[0103] [Comparative Example 1] A conductive paste was prepared in the same manner as in Example 1, except that the amine-based dispersant (2) was not used and all organic solvents, including those in the binder resin, were changed to terpineol. The results of viscosity and average roughness are shown in Table 1.

[0104] [Table 1]

[0105] As can be seen from Table 1, by using amine-based dispersants (1) and (2) in combination with three types of organic solvents, the viscosity of the conductive paste can be stabilized within a viscosity range of 20 Pa·s to 50 Pa·s, which makes it easy to apply the paste, and the smoothness of the dried film obtained from the conductive paste can be improved.

[0106] As described above, the present invention can provide a conductive paste that has high smoothness as a conductive film after drying and that exhibits little change in viscosity over time, and is therefore industrially useful. [Explanation of symbols]

[0107] 1...Multilayer ceramic capacitor 10...Ceramic laminate 11...Internal electrode layer 12...Dielectric layer 20…External electrode 21...External electrode layer 22...plated layer

Claims

1. A conductive paste comprising a conductive powder, a ceramic powder, a dispersant, a binder resin, and an organic solvent, The dispersant contains at least two or more amine-based dispersants, including one or more secondary amines or tertiary amines represented by the following general formula (1) and one or more alkylamines: The conductive paste comprises three or more organic solvents. 【Chemical 1】 (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; 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.

2. 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.

3. 3. The conductive paste according to claim 1, wherein the number average particle diameter of the conductive powder is 30 nm to 100 nm.

4. The conductive paste according to any one of claims 1 to 3, wherein the content of the organic solvent relative to the total amount of the conductive paste is 20 mass % to 60 mass %.

5. The conductive paste according to any one of claims 1 to 4, wherein the organic solvent is any one of dihydroterpineol acetate, isobornyl acetate, isobornyl propionate, isobornyl butyrate, isobornyl isobutyrate, ethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether acetate, dipropylene glycol methyl ether acetate, heptyl acetate, terpineol, dihydroterpineol, tridecane, nonane, cyclohexane, methyl isobutyl ketone, and diisobutyl ketone.

6. The conductive paste according to any one of claims 1 to 5, wherein the organic solvent is terpineol, diisobutyl ketone, and cyclohexane.

7. The conductive paste according to claim 6, wherein the mass ratio of the terpineol, the diisobutyl ketone, and the cyclohexane is terpineol: diisobutyl ketone: cyclohexane = 0.1 to 5.0: 0.1 to 5.0: 23.5 to 43.

3.

8. An electronic component formed using the conductive paste according to any one of claims 1 to 7.

9. 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 7.

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