Conductive paste and method for producing the same

Abstract

To provide a conductive paste which can suppress separation of conductive metallic powder and ceramic powder, and a method for producing the same.SOLUTION: A conductive paste contains conductive metallic powder, ceramic powder, a dispersion agent, a binder resin, and an organic solvent. The binder resin is at least one selected from the group consisting of a cellulose resin, an acetal resin and an acrylic resin. The organic solvent contains a first solvent composed of a terpene-based solvent, a second solvent composed of petroleum-based hydrocarbon, and a solvent different from the first solvent and the second solvent. A Huggins coefficient at 25°C of an organic vehicle composed of a binder resin and an organic solvent is 0.80 or more and 1.20 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a conductive paste used as a material for internal electrodes of electronic components, including multilayer ceramic capacitors, and a method for producing the same. [Background technology]

[0002] As electronic devices such as mobile phones and digital devices become smaller and more powerful, there is a demand for smaller, higher-capacity, and higher-performance electronic components that make up these devices. To meet these demands, for example, in multilayer ceramic capacitors (hereinafter referred to as "MLCCs"), which are one type of electronic component, the internal electrode layers and dielectric layers are becoming thinner and more multilayered.

[0003] MLCCs are manufactured, for example, as follows: First, a conductive paste for the internal electrodes is printed (applied) in a predetermined electrode pattern onto 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. This dry film and the dielectric green sheet are alternately stacked and integrated by heat and pressure to form a pressed body. This pressed body is cut to a predetermined size to form green chips, and then subjected to a binder removal process at 500°C or less in an oxidizing or inert atmosphere. Subsequently, to prevent oxidation of the internal electrodes, the green chips are fired at approximately 1300°C in a reducing or inert atmosphere. Then, a conductive paste is applied to both ends of the fired green chips, which are fired to form external electrodes. The surfaces of these external electrodes are then nickel-plated or otherwise processed to complete the MLCC.

[0004] The temperature at which dielectric ceramic powder begins to sinter and shrink (hereinafter referred to as the "sintering start temperature") is approximately 1200°C, which is significantly different from the sintering start temperature of conductive metal powder. For this reason, structural defects such as delamination (interlayer peeling) and cracks are likely to occur in the sintered green chip. In particular, the more internal electrode layers and dielectric layers are multilayered and the thinner the dielectric layers are, in order to accommodate the miniaturization and high performance of electronic devices, the more pronounced the occurrence of the structural defects described above becomes.

[0005] To address this issue, ceramic powder primarily composed of barium titanate or strontium zirconate perovskite oxides, which have a similar composition to the dielectric layers, is typically added to the conductive paste for the internal electrodes. This allows the sintering start temperature of the conductive paste to be delayed to at least the same temperature as the dielectric layers, thereby suppressing the structural defects described above.

[0006] However, if the particle size or specific gravity of the ceramic powder added to delay the sintering start temperature of the conductive paste is significantly different from the particle size or specific gravity of the conductive metal powder, the dispersion stability of the conductive paste may decrease, and the ceramic powder and the conductive metal powder may separate. If such separation occurs, the ceramic powder will be unevenly distributed in the dried film obtained by printing and drying the conductive paste, making it difficult to control the sintering start temperature of the conductive paste.

[0007] JP 2019-179683 A describes a technology for improving the dispersion stability of a conductive paste by adjusting the transmittance change rate, which is defined as the change per unit time in the integrated transmittance calculated based on the transmittance distribution along the centrifugal sedimentation direction, to 0.003 or less when evaluating the centrifugal sedimentation behavior of the conductive powder and dielectric powder when the conductive paste is subjected to centrifugal sedimentation processing, based on the transmittance change rate defined as the change per unit time in the integrated transmittance calculated based on the transmittance distribution along the centrifugal sedimentation direction.

[0008] Japanese Patent Application Laid-Open Publication No. 2012-174797 describes a technology for suppressing separation between conductive powder and dielectric powder in a conductive paste for gravure printing by adding a polycarboxylic acid polymer or a salt of polycarboxylic acid as a separation inhibitor.

[0009] Japanese Patent Application Laid-Open No. 2020-080266 describes a technology for suppressing uneven distribution of fine particles in the formed coating film by using a specific alkylamide-type dispersant as a dispersant. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Patent Publication No. 2019-179683 [Patent Document 2] Patent Publication No. 2012-174797 [Patent Document 3] Patent Publication No. 2020-080266 Summary of the Invention [Problem to be solved by the invention]

[0011] In the above-mentioned prior art, it is possible to suppress separation between the conductive metal powder and the ceramic powder to some extent, but in a situation where the internal electrode layers and the dielectric layers are multi-layered and the dielectric layers are thinned, it is required to further suppress separation between the conductive metal powder and the ceramic powder in the conductive paste. That is, the present invention aims to provide a conductive paste that can be suitably applied to electronic components such as MLCCs even when the internal electrode layers and the dielectric layers are multi-layered and thinned, and that can sufficiently suppress separation between the conductive metal powder and the ceramic powder, and a manufacturing method thereof. [Means for solving the problem]

[0012] The conductive paste of one embodiment of the present invention comprises: The composition includes a conductive metal powder, a ceramic powder, a dispersant, a binder resin, and an organic solvent. the binder resin is at least one selected from the group consisting of a cellulose resin, an acetal resin, and an acrylic resin, and The organic solvent is composed of a mixed solvent containing a first solvent made of a terpene-based solvent, a second solvent made of a petroleum-based hydrocarbon, and a third solvent different from the first and second solvents.

[0013] In particular, in a conductive paste according to one embodiment of the present invention, when the conductive paste is sealed in a colorless, transparent glass container having an inner diameter of 3 cm and allowed to stand at 25°C for 48 hours, the amount of separation S, which is calculated by the formula: S = Lc / (Lc + Lp) × 100, where Lc is the thickness of the separated ceramic powder layer observed from the side of the container and Lp is the thickness of the entire conductive paste, is 4.0% or less.

[0014] The organic solvent preferably contains 40% by mass or more and 60% by mass or less of the first solvent, 10% by mass or more and 40% by mass or less of the second solvent, and more than 0% and 50% by mass or less of the third solvent.

[0015] The organic vehicle composed of the binder resin and the organic solvent preferably has a Huggins coefficient at 25° C. of 0.80 or more and 1.20 or less.

[0016] The conductive metal powder preferably contains at least one selected from the group consisting of nickel, copper, gold, silver, platinum, and palladium.

[0017] The conductive metal powder preferably has an average particle size of 0.05 μm or more and 0.5 μm or less.

[0018] The content of the conductive metal powder relative to the total amount of the conductive paste is preferably 30% by mass or more and 70% by mass or less.

[0019] The content of the binder resin relative to the total amount of the conductive paste is preferably 1% by mass or more and 5% by mass or less.

[0020] The ceramic powder preferably includes barium titanate powder.

[0021] The average particle size of the ceramic powder is preferably 0.01 μm or more and 0.2 μm or less.

[0022] It is preferable that the ceramic powder is contained in an amount of 3 parts by mass or more and 25 parts by mass or less per 100 parts by mass of the conductive metal powder.

[0023] The conductive paste was subjected to a shear rate of 100 sec at 25°C. -1 The conductive paste preferably has a viscosity of 0.8 Pa·s or less at a shear rate of 10,000 sec at 25°C. -1 It is preferable that the viscosity at 0.18 Pa·s or less.

[0024] The dry film density (DFD) of the dried film obtained after printing and drying the conductive paste is 5.0 g / cm 3 It is preferable that the arithmetic mean roughness Sa of the dry film is 0.25 μm or less.

[0025] A method for producing a conductive paste according to one aspect of the present invention is a method for producing a conductive paste including a conductive metal powder, a ceramic powder, a dispersant, a binder resin, and an organic solvent, the method comprising: The binder resin is at least one selected from the group consisting of a cellulose resin, an acetal resin, and an acrylic resin, the organic solvent is a mixed solvent containing a first solvent made of a terpene-based solvent, a second solvent made of a petroleum-based hydrocarbon, and a third solvent different from the first solvent and the second solvent; the type of the third solvent and the blending ratios of the first solvent, the second solvent, and the third solvent are set so that the Huggins coefficient at 25°C of an organic vehicle constituted by the binder resin and the organic solvent is 0.80 or more and 1.20 or less; and The conductive metal powder, the ceramic powder, the dispersant, the binder resin, and the organic solvent are mixed together.

[0026] The organic solvent preferably contains 40% by mass or more and 60% by mass or less of the first solvent, 10% by mass or more and 40% by mass or less of the second solvent, and more than 0% by mass or less and 50% by mass or less of the third solvent. [Effects of the Invention]

[0027] According to one aspect of the present invention, it is possible to provide a conductive paste that can sufficiently suppress separation of conductive metal powder and ceramic powder, and a method for manufacturing the same. Such a conductive paste can contribute to further thinning of internal electrodes of electronic components such as MLCCs. [Brief explanation of the drawings]

[0028] [Figure 1A] FIG. 1A is a perspective view showing the appearance of an MLCC using a conductive paste according to an embodiment of the present invention. [Figure 1B] FIG. 1B is a cross-sectional view of the MLCC shown in FIG. 1A. [Figure 2] FIG. 2 is a graph plotting the results of separation evaluation of conductive pastes of examples of the present invention and comparative examples. DETAILED DESCRIPTION OF THE INVENTION

[0029] A conductive paste according to an embodiment of the present invention and a method for producing the same will be described below.

[0030] 1.Conductive paste The conductive paste of this example contains a conductive metal powder, a ceramic powder, a dispersant, a binder resin, and an organic solvent. The binder resin is at least one selected from the group consisting of cellulose resin, acetal resin, and acrylic resin. The organic solvent is composed of a mixed solvent containing a first solvent made of a terpene-based solvent, a second solvent made of a petroleum hydrocarbon, and a third solvent different from the first and second solvents. The conductive paste of this example is characterized in that when the binder resin and the organic solvent are mixed to form an organic vehicle, the Huggins coefficient of this organic vehicle at 25°C is 0.80 or more and 1.20 or less.

[0031] (1) Components First, the components constituting the conductive paste of this example will be described.

[0032] [Conductive metal powder] Conductive metal powders are used as electrodes for electronic components such as MLCCs. The conductive metal powder is not particularly limited, and for example, at least one selected from the group consisting of nickel, copper, gold, silver, platinum, and palladium can be used. For example, metal powders of nickel, copper, gold, silver, or platinum, or alloy powders containing these metals, can be used. In particular, when manufacturing a high-capacity, highly stacked MLCC using the conductive paste of this example, it is preferable to use relatively low-cost nickel or copper.

[0033] The average particle size of the conductive metal powder is not particularly limited and can be appropriately selected depending on the target electronic component. For example, when manufacturing a highly multilayer MLCC using the conductive paste of this example, the average particle size of the conductive metal powder is preferably 0.05 μm or more and 0.5 μm or less. If the average particle size of the conductive metal powder is less than 0.05 μm, the surface activity of the conductive metal powder may be too high, making it difficult to obtain appropriate viscosity characteristics or causing the conductive paste to deteriorate during long-term storage. On the other hand, if the average particle size of the conductive metal powder exceeds 0.5 μm, it becomes difficult to thin the MLCC.

[0034] The average particle size of the conductive metal powder is a value determined by observation using a scanning electron microscope (FE-SEM), and is, for example, the arithmetic mean value obtained by measuring the maximum diameter of 200 or more randomly selected conductive metal powder particles from an image observed at a magnification of 10,000 times using an FE-SEM.

[0035] The content of the conductive metal powder relative to the total amount of the conductive paste is preferably 30% by mass to 70% by mass, and more preferably 40% by mass to 60% by mass. If the content of the conductive metal powder is less than 30% by mass, the ability to form an electrode film during firing may be low, making it difficult to obtain the desired capacitor capacitance. On the other hand, if the content of the conductive metal powder exceeds 70% by mass, it becomes difficult to thin the electrode film.

[0036] [Ceramic powder] In MLCCs, ceramic powder is used as a sintering inhibitor to delay the sintering start temperature of the conductive paste to the firing start temperature of the dielectric ceramic powder that constitutes the dielectric green sheet. Examples of ceramic powder that can be used include perovskite-type oxide barium titanate (BaTiO3) and ceramic powders containing barium titanate as the main component and oxides as secondary components. Examples of oxides include oxides of Mn, Cr, Si, Ca, Ba, Mg, V, W, Ta, Nb, and one or more rare earth elements. Examples of ceramic powders that can be used include perovskite-type oxide ferroelectric ceramic powders in which the Ba and Ti atoms of barium titanate (BaTiO3) are replaced with other atoms, such as Sn, Pb, or Zr.

[0037] The ceramic powder used preferably has the same composition as or a similar composition to the ceramic powder used as the main component of the dielectric layer green sheet for MLCC.

[0038] The average particle size of the ceramic powder is preferably 0.01 μm or more and 0.2 μm or less. If the average particle size of the ceramic powder is less than 0.01 μm, the sintering retardation effect of the conductive paste cannot be fully obtained, and structural defects such as delamination and cracks may occur. In addition, the dry film density may decrease, and the ceramic powder may be more likely to aggregate, making it difficult to thin the dielectric layer. As a result, the reliability of the MLCC may decrease due to factors such as a decrease in insulation resistance and an increase in the short-circuit rate. On the other hand, if the average particle size of the ceramic powder exceeds 0.2 μm, the ceramic powder may be less likely to penetrate between the contact points of the conductive metal powder, and the dry film density may decrease. In addition, the sintering retardation effect may not be fully obtained.

[0039] The average particle size of the ceramic powder is a value determined by observation using a scanning electron microscope (FE-SEM), and is, for example, the arithmetic mean value obtained by measuring the maximum diameter of 200 or more randomly selected ceramic powder particles from an image observed at a magnification of 10,000 times using an FE-SEM.

[0040] The content of the ceramic powder is preferably 3 parts by mass or more and 25 parts by mass or less relative to 100 parts by mass of the conductive metal powder. If the content of the ceramic powder is less than 3 parts by mass, the sintering retardation effect cannot be sufficiently obtained, and firing cracks are likely to occur. On the other hand, if the content of the ceramic powder exceeds 25 parts by mass, the ceramic powder constituting the conductive paste will diffuse more into the green sheet (dielectric layer), the effect of the ceramic powder in delaying the start of sintering of the conductive powder will decrease, the continuity of the internal electrode layer will decrease, and the ceramic powder contained in the internal electrode layer and the ceramic powder in the dielectric layer will sinter, increasing the thickness of the dielectric layer and causing a discrepancy in the composition of the conductive paste, which may result in a decrease in electrical properties such as dielectric constant.

[0041] The ceramic powder may be produced by various methods such as a solid-phase method, a hydrothermal synthesis method, an alkoxide method, a sol-gel method, etc. The ceramic powder may be mixed with the other components of the conductive paste in powder form, or may be mixed after being made into a slurry by dispersing and pulverizing the powder using a device such as a bead mill or a high-pressure homogenizer.

[0042] [Dispersant] The dispersant is a component added to stably disperse the conductive metal powder or ceramic powder in a finely divided state in the organic vehicle. The dispersant may be, for example, at least one selected from the group consisting of cationic dispersants, anionic dispersants, nonionic dispersants, amphoteric surfactants, and polymer dispersants.

[0043] Among these, it is preferable to use an anionic dispersant. Anionic dispersants have a strong adsorption force to the surface of conductive metal powder and have the effect of improving the dispersibility of conductive metal powder through their surface modification action, thereby improving the smoothness and dry film density of the coating film of the conductive paste. As the anionic dispersant, for example, at least one selected from carboxylic acid dispersants, phosphoric acid dispersants, and phosphate dispersants can be used.

[0044] The average molecular weight of the dispersant is preferably in the range of 200 to 20,000, more preferably in the range of 300 to 10,000. When the average molecular weight of the dispersant is in this range, the dispersant adsorbs to the surface of the conductive metal powder, thereby imparting electrostatic and steric repulsive forces to the conductive metal powder, thereby producing a conductive paste with excellent dispersibility. If the average molecular weight of the dispersant is less than 200, the electrostatic and steric repulsive forces decrease over time, and the conductive metal powder aggregates, which tends to reduce the dispersibility and storage stability of the conductive paste. On the other hand, if the average molecular weight of the dispersant exceeds 20,000, the compatibility between the organic vehicle and the organic solvent decreases, or the conductive metal powder aggregates, which tends to reduce the dispersibility and storage stability of the conductive paste. In addition, the viscosity of the conductive paste may become too high.

[0045] The content of the dispersant is preferably 0.01 to 2.00 parts by mass, and more preferably 0.20 to 1.00 parts by mass, per 100 parts by mass of the conductive metal powder. If the content of the dispersant is less than 0.01 parts by mass, sufficient dispersibility may not be obtained. On the other hand, if the content of the dispersant exceeds 2.00 parts by mass, not only will it take a long time to dry the conductive paste, but the dry film density may also decrease.

[0046] [Binder resin] The binder resin functions as a dispersion medium for inorganic components such as conductive metal powder and ceramic powder. At least one type of binder resin is used, selected from the group consisting of cellulose resin, acetal resin, and acrylic resin. Examples of cellulose resins include ethyl hydroxyethyl cellulose and ethyl cellulose. Examples of acetal resins include polyvinyl butyral. Examples of acrylic resins include polymethacrylate and polyacrylate. Among these, it is preferable to use ethyl hydroxyethyl cellulose or ethyl cellulose in terms of solubility in solvents and decomposition by combustion.

[0047] The content of the binder resin relative to the total amount of the conductive paste is not particularly limited, but is preferably 1% by mass or more and 5% by mass or less. If the content of the binder resin is less than 1% by mass, the strength of the dried film may decrease, or the adhesion between the internal electrode layer and the dielectric layer may deteriorate, making them more likely to peel off. On the other hand, if the content of the binder resin exceeds 5% by mass, the binder resin content may be too high, which may worsen the binder removal properties. The content of the binder resin is preferably 1 part by mass or more and 10 parts by mass or less, more preferably 1 part by mass or more and 8 parts by mass or less, relative to 100 parts by mass of the conductive powder.

[0048] When an organic vehicle is composed of a binder resin and an organic solvent, the amount of binder resin in the organic vehicle is preferably 1% by mass or more and 30% by mass or less. This allows the preparation of an organic vehicle with appropriate viscosity. The amount of binder resin in the organic vehicle is more preferably 5% by mass or more and 20% by mass or less.

[0049] [Organic solvents] The organic solvent dissolves the resin components of the binder resin and disperses the conductive metal powder and ceramic powder in the conductive paste, adjusting the viscosity to an appropriate range and enabling printing in a predetermined pattern. The organic solvent can be one that can sufficiently dissolve the binder resin and has little change in viscosity over time. The organic solvent dissipates into the atmosphere by the time of firing.

[0050] In the conductive paste of this example, the organic solvent is a mixed solvent containing a first solvent made of a terpene solvent, a second solvent made of a petroleum hydrocarbon, and a third solvent different from the first and second solvents. By blending these solvents in the binder resin at an appropriate blending ratio, the Huggins coefficient at 25°C of the organic vehicle made of the binder resin and the organic solvent made of this mixed solvent can be controlled within a predetermined range, thereby making it possible to sufficiently suppress separation of the conductive metal powder and the ceramic powder in the conductive paste.

[0051] The first solvent is a good solvent for the binder resin, and examples of the terpene solvent include at least one selected from the group consisting of terpineol and dihydroterpineol.

[0052] The second solvent is a poor solvent for the binder resin, and examples thereof include petroleum hydrocarbons. Examples of solvents made of petroleum hydrocarbons include gasoline, kerosene, coal tar naphtha, petroleum ether, petroleum naphtha, petroleum benzine, turpentine, and mineral spirits. Of these, mineral spirits are preferred. Examples of mineral spirits include mineral thinner, petroleum spirits, white spirits, and mineral turpentine. More specifically, there are LAWS (Low Aromatic White Spirit) and HAWS (High Aromatic White Spirit).

[0053] The third solvent is added to adjust the solubility of the binder resin. Examples of the third solvent include methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, n-pentanol, n-hexanol, n-heptanol, n-octanol, decanol, methylene glycol, ethylene glycol, propylene glycol, butylene glycol, pentylene glycol, hexylene glycol, glycerol, acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, methyl acetate, ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, n-hexyl acetate, n-octyl acetate, 2-ethylhexyl acetate, isobornyl acetate, p- Tolyl acetate, linalyl acetate, 2-furfuryl acetate, ethyl lactate, propyl lactate, isopropyl lactate, butyl lactate, isobutyl lactate, hexyl lactate, acetylacetone, ethyl acetoacetate, n-propyl acetoacetate, isopropyl acetoacetate, n-butyl acetoacetate, methyl propionate, ethyl propionate, n-propyl propionate, isopropyl propyl propionate, n-butyl propionate, isobutyl propionate, n-hexyl propionate, γ-butyrolactone, γ-valerolactone, δ-valerolactone, ε-caprolactone, γ-nonalactone, γ-decalactone, ethylene glycol diacetate, propylene glycol diacetate, 1,4-Diacetoxybutane, hexylene glycol diacetate, ethylene glycol monomethyl ether, ethylene glycol monomethyl ether acetate, ethylene glycol dimethyl ether, diethylene glycol monomethyl ether, diethylene glycol monomethyl ether acetate, diethylene glycol dimethyl ether, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, propylene glycol dimethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monomethyl ether acetate, dipropylene glycol dimethyl ether, diethylene glycol monobutyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, Diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, propylene glycol monohexyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, dipropylene glycol monohexyl ether, ethylene glycol monoethyl ether acetate, ethylene glycol monopropyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol monopropyl ether acetate, propylene glycol monoethyl ether acetate, propylene glycol monopropyl ether acetate, dipropylene glycol monoethyl ether acetate, dipropylene glycol monopropyl ether acetate, and the like can be used.

[0054] Among these, from the viewpoint of the solubility of the binder resin, it is preferable to use at least one selected from the group consisting of n-butanol, n-pentanol, n-hexanol, n-octanol, n-hexyl acetate, n-octyl acetate, 2-ethylhexyl acetate, isobornyl acetate, p-tolyl acetate, linalyl acetate, furfuryl acetate, butyl lactate, ethyl acetoacetate, n-propyl acetoacetate, isopropyl acetate, n-butyl propionate, ethylene glycol monomethyl ether, ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether, diethylene glycol monomethyl ether acetate, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, dipropylene glycol monomethyl ether and dipropylene glycol monomethyl ether acetate.

[0055] In the conductive paste of this example, the blending amount of each organic solvent in the mixed solvent is preferably 40% by mass or more and 60% by mass or less for the first solvent, 10% by mass or more and 40% by mass or less for the second solvent, and more than 0% and 50% by mass or less for the third solvent. It is more preferable that the blending amount of the first solvent is 45% by mass or more and 55% by mass or less for the second solvent, 10% by mass or more and 30% by mass or less for the third solvent, and 5% by mass or more and 30% by mass or less for the third solvent.

[0056] The content of the organic solvent is not particularly limited, but is preferably set so that the content of the conductive metal powder relative to the total amount of the conductive paste is 30% by mass or more and 70% by mass or less. Specifically, the content of the organic solvent is preferably 40 parts by mass or more and 100 parts by mass or less, and more preferably 65 parts by mass or more and 95 parts by mass or less, relative to 100 parts by mass of the conductive powder. When the content of the organic solvent is within this range, a conductive paste with excellent conductivity and dispersibility is obtained. For the same reason, the content of the organic solvent is preferably 20% by mass or more and 60% by mass or less, and more preferably 35% by mass or more and 55% by mass or less, relative to the total amount of the conductive paste.

[0057] [Other additives] In addition to the additives described above, known additives for conductive pastes, such as antifoaming agents, plasticizers, thickeners, and chelating agents, can also be added to the conductive paste of this example. Furthermore, depending on the purpose, additional organic solvents and organic binders different from the organic solvents and organic binders described above can also be added. In this case, various known organic solvents and organic binders can be used as these additional organic solvents and organic binders. However, it is preferable to use the same organic solvents and organic binders as those described above, and they are added within the range of the organic solvent and organic binder blended into the conductive paste described above. However, the above explanation (especially the blending amounts of the resin binder and organic solvent) and the explanation of the Huggins coefficient described below do not apply to these additional organic solvents and organic binders.

[0058] (2) Huggins coefficient In the conductive paste of this example, the Huggins coefficient of the organic vehicle, which is composed of a binder resin and an organic solvent, at 25°C is adjusted to 0.80 to 1.20, preferably 0.85 to 1.20, and more preferably 0.90 to 1.10. If the Huggins coefficient is less than 0.8, the interactions between the conductive metal powders, between the ceramic powders, and between the conductive metal powder and the ceramic powder are insufficient, and separation between the conductive metal powder and the ceramic powder in the conductive paste cannot be sufficiently suppressed. On the other hand, if the Huggins coefficient exceeds 1.20, the interactions between the conductive metal powders, between the ceramic powders, and between the conductive metal powder and the ceramic powder are too strong, resulting in the problem of insufficient printing properties.

[0059] Here, the Huggins coefficient (k´) is the coefficient of the viscosity formula (Huggins' formula) in the dilute region of the polymer solution, and the viscosity of the polymer solution is η (Pa s), and the viscosity of the solvent is η s (Pa s), and intrinsic viscosity [η] (cm 3 / g), and the concentration of the polymer solution is c (g / cm 3) is defined by the following "Formula 1." In this example, the organic vehicle corresponds to the polymer solution, and the solvent corresponds to the organic solvent.

[0060] η=η s (1+[η]c+k´[η] 2 c 2 )...(Formula 1)

[0061] In other words, "Equation 1" is transformed into the following "Equation 2" and the concentration of the polymer solution, c (g / cm 3 ) on the horizontal axis, (η / η s The Huggins coefficient (k') can be calculated from the slope of the approximate line obtained when plotting k with k -1 / c on the vertical axis.

[0062] (η / η s -1) / c=[η]+k´[η] 2 c...(Formula 2)

[0063] More specifically, the Huggins coefficient can be measured by the following procedure.

[0064] First, a polymer solution (organic vehicle) is prepared by dissolving a polymer material (binder resin) in a solvent (organic solvent). Several polymer solutions with different concentrations are prepared. The concentration of each polymer solution is adjusted to a dilute range where entanglement of molecules is not expected to occur. Although it depends on the type and molecular weight of the polymer material, for example, 1 x 10 -4 g / cm 3 More than 1×10 -1 g / cm 3 Adjust to the following range:

[0065] Next, the viscosity of these solvents and polymer solutions is measured at 25°C. In this case, if the concentration of the polymer solution is in the dilute region, it will show a constant viscosity independent of shear rate, so the viscosity value can be read at any shear rate. The device used to measure viscosity is not particularly limited as long as it is temperature controllable, and for example, a viscometer such as a rheometer can be used.

[0066] Finally, based on the measurement results, the concentration of the polymer solution, c (g / cm 3 ) on the horizontal axis, (η / η s -1) / c on the vertical axis to create a graph (approximate line).The Huggins coefficient (k') can then be calculated from the slope of this approximate line.

[0067] 2. Method for producing conductive paste composition The conductive paste of this example can be produced by mixing a binder resin and an organic solvent to form an organic vehicle, setting the type of third solvent and the blending ratios of the first, second, and third solvents so that the Huggins coefficient of this organic vehicle at 25°C is 0.80 or more and 1.20 or less, and then stirring and mixing the above-mentioned components using known means such as a three-roll mill, ball mill, mixer, etc. In this case, if a dispersant is applied to the surface of the conductive metal powder in advance, aggregation of the conductive metal powder is suppressed, making it easier to obtain a uniform conductive paste.

[0068] The binder resin may be dissolved in a portion of the organic solvent and then added to the remaining organic solvent together with the conductive metal powder, ceramic powder, and dispersant.

[0069] 3.Characteristics The conductive paste of this example has the following properties: Therefore, the conductive paste of this example can be suitably used in electronic components such as MLCCs.

[0070] (1) Separation evaluation In the conductive paste of this example, the separation amount S, which is used to evaluate its dispersion stability, is preferably 4.0% or less. The separation amount S is more preferably 3.5% or less, even more preferably 2.6% or less, and particularly preferably 2.0% or less. By setting the separation amount S to 4.0% or less, it is possible to sufficiently suppress separation between the conductive metal powder and the ceramic powder. Here, the separation amount S is a value calculated by the following "Equation 3" when the conductive paste is sealed in a colorless, transparent glass container with an inner diameter of 3 cm and left to stand at 25°C for 48 hours, where Lc is the thickness of the separated ceramic powder layer observed from the side of the container, and Lp is the thickness of the entire conductive paste.

[0071] S = Lc / (Lc + Lp) × 100 (Equation 3)

[0072] (2) Viscosity The conductive paste in this example is subjected to a shear rate of 100 sec at 25°C. -1 The viscosity is 0.8 Pa·s or less at a shear rate of 100 sec -1 The viscosity at a shear rate of 100 sec is preferably 0.5 Pa·s or less, more preferably 0.4 Pa·s or less, and even more preferably 0.3 Pa·s or less. -1 When the viscosity at a shear rate of 100 sec is 0.8 Pa·s or less, it can be suitably used as a conductive paste for gravure printing. -1 If the viscosity exceeds 0.8 Pa·s, the viscosity of the conductive paste becomes too high and may not be suitable as a conductive paste composition for gravure printing. -1 The lower limit of the viscosity is not particularly limited, but a viscosity of about 0.1 Pa·s is sufficient for application to gravure printing.

[0073] The conductive paste of this example was also tested at a shear rate of 10,000 sec at 25°C. -1 The viscosity at a shear rate of 10,000 sec is preferably 0.18 Pa·s or less, and more preferably less than 0.14 Pa·s. -1When the viscosity at a shear rate of 10,000 sec is within the above range, the paste can be suitably used as a conductive paste for gravure printing. -1 If the viscosity exceeds 0.18 Ps·s at a shear rate of 10,000 sec, the viscosity of the conductive paste may become too high and may not be suitable for gravure printing. -1 The lower limit of the viscosity is not particularly limited, but for application to gravure printing, a viscosity of about 0.05 Pa·s is sufficient.

[0074] The viscosity of the conductive paste can be measured, for example, by a viscometer such as a rheometer.

[0075] (3) Dry film density The conductive paste of this example has a dry film density (DFD) of 5.0 g / cm after printing and drying. 3 Preferably, it is greater than 5.2 g / cm 3 More preferably, it is greater than 5.3 g / cm 3 The upper limit of the dry film density is preferably the true density of the conductive metal powder (when nickel powder is used as the conductive metal powder, the true density of nickel is 9.8 g / cm). 3 ) and does not exceed 6.5g / cm 3 That's about it.

[0076] (4) Arithmetic mean roughness of dried film The conductive paste of this example preferably has an arithmetic mean roughness Sa of the dried film of 0.25 μm or less, more preferably 0.2 μm or less, and even more preferably 0.16 μm or less. If the arithmetic mean roughness Sa of the dried film exceeds 0.25 μm, the surface roughness of the internal electrode layer deteriorates, causing short-circuit defects in electronic components such as MLCCs. The lower limit of the arithmetic mean roughness Sa of the dried film is not particularly limited, and a smaller value is preferable. The arithmetic mean roughness Sa of the dried film can be calculated by measuring a 20 mm square dried film with a thickness of 1 μm to 3 μm, which is produced by printing the conductive paste of this example and drying it in air at 120°C for 1 hour, based on the ISO 25178 standard.

[0077] 4.Applications The conductive paste of this example can be suitably used in electronic components such as MLCCs. MLCCs have dielectric layers formed from dielectric green sheets and internal electrode layers formed from conductive pastes. In this MLCC, it is preferable that the dielectric ceramic powder contained in the dielectric green sheets and the ceramic powder contained in the conductive paste are the same powder.

[0078] The multilayer ceramic device manufactured using the conductive paste of this example has improved dispersion stability of the conductive paste and sufficient suppression of separation between the conductive metal powder and the ceramic powder, so that even if the thickness of the dielectric green sheet is, for example, 3 μm or less, sheet attack, in which the organic solvent (mixed solvent) in the conductive paste swells or dissolves the binder resin in the dielectric green sheet, and poor peeling of the dielectric green sheet can be suppressed.

[0079] An example of an MLCC, which is an electronic component using the conductive paste of this example, will be described below with reference to the drawings. The drawings may be depicted schematically or at a different scale as appropriate. The positions and directions of components will be described with reference to the XYZ Cartesian coordinate system shown in Figures 1A and 1B as appropriate. In this XYZ Cartesian coordinate system, the X and Y directions are horizontal, and the Z direction is vertical (up and down).

[0080] 1A and 1B are diagrams showing an MLCC 1 using the conductive paste of this example. FIG. 1A is a perspective view showing the appearance of the MLCC 1, and FIG. 1B is a cross-sectional view of the MLCC 1. The MLCC 1 includes a laminate 10 and an external electrode 20. The laminate 10 has a structure in which internal electrode layers 11 and dielectric layers 12 are alternately stacked. The external electrode 20 includes an external electrode layer 21 electrically connected to the internal electrode layer 11, and a plating layer 22.

[0081] This MLCC 1 can be manufactured, for example, as follows.

[0082] First, a plurality of dielectric green sheets (ceramic green sheets), which are unfired ceramic sheets, are prepared. For example, these dielectric green sheets can be prepared by applying a dielectric layer paste, which is a mixture of a predetermined ceramic raw material powder such as barium titanate, a binder resin such as polyvinyl butyral, and a solvent such as terpineol, onto a support film such as a PET (polyethylene terephthalate) film in the form of a sheet, and then drying the sheet to remove the solvent. The thickness of the dielectric layer, including the dielectric green sheets, is not particularly limited, but is preferably 0.05 μm or more and 3 μm or less from the viewpoint of miniaturization of the MLCC 1.

[0083] Next, the conductive paste of this example is printed on one side of each dielectric green sheet, and the conductive paste is dried to form a dry film having a desired pattern. At this time, the thickness of the dry film is preferably 1 μm or less from the viewpoint of thinning the internal electrode layer 11.

[0084] After the dry film is formed, the dielectric green sheets are peeled from the support film, and the dielectric green sheets are stacked so that the dielectric green sheets and the dry film formed on one side thereof are arranged alternately. The stacked dielectric green sheets are then heated and pressed to form a laminate. Note that protective dielectric green sheets on which no conductive paste is printed can be placed on the top and bottom surfaces of the laminate.

[0085] Next, the laminate is cut to a predetermined size to form green chips, which are then subjected to a binder removal treatment. The binder removal treatment is preferably carried out by heating the green chips in air or a nitrogen gas atmosphere at a temperature (binder removal temperature) of 200°C to 400°C. The holding time at the binder removal temperature is preferably 0.5 hours to 24 hours.

[0086] After the binder removal process, the green chip is fired in a reducing atmosphere to prevent oxidation of the metal (conductive metal powder) that will become the internal electrode layers 11. The firing temperature is preferably 1000°C or higher and 1350°C or lower, and the holding time at this temperature is preferably 0.5 hours or higher and 8 hours or lower.

[0087] By the binder removal treatment and firing, the binder resin in the dielectric green sheet is completely removed, and the ceramic raw material powder is fired to form the dielectric layer 12. In addition, the organic vehicle (binder resin and organic solvent) in the dried film is removed, and the conductive metal powder is integrated by sintering or melting to form the internal electrode layer 11. As a result, a fired multilayer ceramic body (laminate 10) is formed in which a plurality of dielectric layers 12 and internal electrode layers 11 are alternately stacked. Note that, from the viewpoint of incorporating oxygen into the dielectric layer 12 to increase reliability and suppressing reoxidation of the internal electrode layer 11, the fired multilayer ceramic body (laminate 10) may be subjected to an annealing treatment.

[0088] Finally, a pair of external electrodes 20 are formed on the fired multilayer ceramic body (laminate 10). Specifically, external electrode layers 21 are formed on both ends of the laminate 10 so as to be electrically connected to the internal electrode layers 11, and plating layers 22 are formed to cover these external electrode layers 21. Suitable materials for the external electrodes 20 include, for example, copper, nickel, or an alloy thereof. In this manner, the MLCC 1 can be manufactured. [Example]

[0089] EXAMPLES The present invention will be described in more detail below using examples and comparative examples, but the present invention is not limited to these examples and comparative examples.

[0090] First, dihydroterpineol was prepared as the first solvent (X), mineral spirits as the second solvent (Y), and n-pentanol as the third solvent (Z). These solvents were mixed in a mass ratio of X:Y:Z = 53:20:27 to produce mixed solvent A as an organic solvent. The viscosity of this mixed solvent A at 25°C was measured using a rheometer (Anton Paar MCR Rheometer) and was found to be 5.02 (mPa s).

[0091] Next, ethyl cellulose as a resin binder was dissolved in the mixed solvent A to prepare four types of organic vehicles A with different concentrations. The viscosity of these organic vehicles A at 25°C was measured using a rheometer. The concentration c (g / cm 3 ) on the horizontal axis and (η / ηs-1) / c on the vertical axis to create an approximate line, and the Huggins coefficient (k´) was calculated from the slope of the line.

[0092] Solvent mixtures B to G and organic vehicles B to G were prepared under the same conditions except for the type of third solvent and the blending ratio of each solvent in the solvent mixture. The viscosities of solvent mixtures B to G at 25°C were B: 4.84 (mPa·s), C: 3.11 (mPa·s), D: 3.02 (mPa·s), E: 3.45 (mPa·s), F: 4.80 (mPa·s), and G: 4.31 (mPa·s). The Huggins coefficients (k´) of organic vehicles B to G were also calculated in the same manner. The results are shown in Table 1.

[0093] [Table 1]

[0094] Example 1 First, nickel powder with an average particle size of 0.2 μm was prepared as the conductive metal powder, barium titanate powder with an average particle size of 0.05 μm was prepared as the ceramic powder, oleoyl sarcosine was prepared as the anionic dispersant, and ethyl cellulose was prepared as the binder resin. A conductive paste was prepared by mixing 25 parts by weight of barium titanate powder, 0.1 parts by weight of the anionic dispersant, 5.3 parts by weight of ethyl cellulose, and 73.7 parts by weight of mixed solvent A per 100 parts by weight of nickel powder (conductive paste: 49% by weight nickel powder, 12.25% by weight barium titanate powder, 0.05% by weight oleoyl sarcosine, 2.6% by weight ethyl cellulose, and 36.1% by weight mixed solvent A). The ethyl cellulose was dissolved in a portion of the dihydroterpineol in mixed solvent A before mixing with the other components.

[0095] The conductive paste thus obtained was subjected to a separation evaluation. Specifically, the conductive paste was sealed in a colorless, transparent glass container with an inner diameter of 3 cm and left to stand at 25°C for 48 hours. At this time, the thickness of the separated ceramic powder layer observed from the side of the container was defined as Lc (mm), and the thickness of the entire conductive paste was defined as Lp (mm). When the separation amount S calculated by the above-mentioned "Equation 3" was less than 4.0, it was evaluated as "Good", and when it was less than 4.0, it was evaluated as "Poor".

[0096] The viscosity of the conductive paste composition was measured using a rheometer (Anton Paar, Rheometer MCR) at 25°C and a shear rate of 100 sec -1 Viscosity at 25°C and shear rate of 10,000 sec -1 The viscosity was measured at 100°C, and the results are shown in Table 2.

[0097] Example 2 A conductive paste was prepared in the same manner as in Example 1 except that mixed solvent B was used as the organic solvent, and the viscosity and separation evaluation were carried out. The results are shown in Table 2 and FIG.

[0098] Example 3 A conductive paste was prepared in the same manner as in Example 1, except that mixed solvent C was used as the organic solvent, and the viscosity and separation evaluation were carried out. The results are shown in Table 2 and FIG.

[0099] Example 4 A conductive paste was prepared in the same manner as in Example 1 except that mixed solvent D was used as the organic solvent, and the viscosity and separation evaluation were carried out. The results are shown in Table 2 and FIG.

[0100] (Comparative Example 1) A conductive paste was prepared in the same manner as in Example 1, except that mixed solvent E was used as the organic solvent, and the viscosity and separation were evaluated. The results are shown in Table 2 and FIG.

[0101] (Comparative Example 2) A conductive paste was prepared in the same manner as in Example 1, except that mixed solvent F was used as the organic solvent, and the viscosity and separation were evaluated. The results are shown in Table 2 and FIG.

[0102] (Comparative Example 3) A conductive paste was prepared in the same manner as in Example 1, except that mixed solvent G was used as the organic solvent, and the viscosity and separation evaluation were carried out. The results are shown in Table 2 and FIG.

[0103] [Table 2] [Explanation of symbols]

[0104] 1 MLCC 10 Laminate 11 Internal electrode layer 12 Dielectric layer 20 External electrode 21 External electrode layer 22 plating layer

Claims

1. The composition includes a conductive metal powder, a ceramic powder, a dispersant, a binder resin, and an organic solvent. the binder resin is at least one selected from a cellulose resin, an acetal resin, and an acrylic resin, and the organic solvent is a mixed solvent containing a first solvent made of a terpene-based solvent, a second solvent made of a petroleum-based hydrocarbon, and a third solvent different from the first solvent and the second solvent; A conductive paste, The conductive paste is sealed in a colorless, transparent glass container having an inner diameter of 3 cm and allowed to stand at 25°C for 48 hours, and the amount of separation S, which is calculated by the formula: S = Lc / (Lc + Lp) x 100, where Lc is the thickness of the separated ceramic powder layer observed from the side of the container and Lp is the thickness of the entire conductive paste, is 4.0% or less. Conductive paste.

2. 2. The conductive paste according to claim 1, wherein the mixed solvent contains 40% by mass or more and 60% by mass or less of the first solvent, 10% by mass or more and 40% by mass or less of the second solvent, and more than 0% and 50% by mass or less of the third solvent.

3. 3. The conductive paste according to claim 1, wherein the organic vehicle composed of the binder resin and the organic solvent has a Huggins coefficient at 25°C of 0.80 or more and 1.20 or less.

4. The conductive paste according to any one of claims 1 to 3, wherein the conductive metal powder contains at least one selected from the group consisting of nickel, copper, gold, silver, platinum, and palladium.

5. 5. The conductive paste according to claim 1, wherein the conductive metal powder has an average particle size of 0.05 μm or more and 0.5 μm or less.

6. The conductive paste according to any one of claims 1 to 5, wherein the content of the conductive metal powder relative to the total amount of the conductive paste is 30 mass % or more and 70 mass % or less.

7. The conductive paste according to any one of claims 1 to 6, wherein the content of the binder resin relative to the total amount of the conductive paste is 1 mass % or more and 5 mass % or less.

8. The conductive paste according to any one of claims 1 to 7, wherein the ceramic powder contains barium titanate powder.

9. The conductive paste according to any one of claims 1 to 8, wherein the ceramic powder has an average particle size of 0.01 µm or more and 0.2 µm or less.

10. The conductive paste according to any one of claims 1 to 9, wherein the ceramic powder is contained in an amount of 3 parts by mass or more and 25 parts by mass or less per 100 parts by mass of the conductive metal powder.

11. Shear rate 100 sec at 25°C －１ The viscosity at 25°C is 0.8 Pa·s or less, and the shear rate is 10,000 sec －１ The conductive paste according to any one of claims 1 to 10, wherein the viscosity at 0.18 Pa·s or less.

12. A method for producing a conductive paste containing a conductive metal powder, a ceramic powder, a dispersant, a binder resin, and an organic solvent, comprising: the binder resin is at least one selected from the group consisting of a cellulose resin, an acetal resin, and an acrylic resin; the organic solvent is a mixed solvent containing a first solvent made of a terpene-based solvent, a second solvent made of a petroleum-based hydrocarbon, and a third solvent different from the first solvent and the second solvent; The type of the third solvent and the blending ratios of the first solvent, the second solvent, and the third solvent are set so that the Huggins coefficient at 25°C of an organic vehicle composed of the binder resin and the organic solvent is 0.80 or more and 1.20 or less, and mixing the conductive metal powder, the ceramic powder, the dispersant, the binder resin, and the organic solvent; The process includes: A method for manufacturing a conductive paste.

13. 13. The method for producing a conductive paste according to claim 12, wherein the organic solvent contains 40% by mass or more and 60% by mass or less of the first solvent, 10% by mass or more and 40% by mass or less of the second solvent, and more than 0% by mass or less and 50% by mass or less of the third solvent.

Images