JP7739963B2 - Conductive paste and method for producing the same - Google Patents

Description

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 manufacturing the same.

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 multilayered ceramic capacitors (MLCCs), one type of electronic component, the internal electrode layers and dielectric layers are becoming thinner and more multilayered.

An MLCC is manufactured, for example, as follows: First, a conductive paste for 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 (BaTiO ₃ ) 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, which are then subjected to a binder removal treatment at 500°C or less in an oxidizing or inert atmosphere. Subsequently, the green chips are fired at approximately 1300°C in a reducing or inert atmosphere to prevent oxidation of the internal electrodes. 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.

Incidentally, the temperature at which dielectric ceramic powder begins to sinter and shrink (hereinafter referred to as the "sintering start temperature") is around 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 sintered green chips. 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 above-mentioned structural defects becomes.

To address this issue, the conductive paste for the internal electrodes typically contains a ceramic powder whose main component is a barium titanate or strontium zirconate perovskite-type oxide, which has a similar composition to the dielectric layers. This allows the sintering start temperature of the conductive paste to be delayed to at least close to the sintering start temperature of the dielectric layers, thereby suppressing the structural defects mentioned above.

However, if the particle size and specific gravity of the ceramic powder added to delay the sintering start temperature of the conductive paste differ significantly from those of the conductive metal powder, the dispersion stability of the conductive paste may decrease, and the ceramic powder and conductive metal powder may separate. When this 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.

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 amount of change per unit time in 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 using the transmittance change rate, which is defined as the amount of change per unit time in integrated transmittance calculated based on the transmittance distribution along the centrifugal sedimentation direction.

JP 2012-174797 A 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.

JP 2020-080266 A describes a technology that uses a specific alkylamide-type dispersant as a dispersant to suppress uneven distribution of fine particles in the formed coating film.

Patent Publication No. 2019-179683 Patent Publication No. 2012-174797 Patent Publication No. 2020-080266

While the above-mentioned prior art technologies are able to suppress separation between the conductive metal powder and ceramic powder to some extent, in situations where the internal electrode layers and dielectric layers are multi-layered and the dielectric layers are thin, there is a need to further suppress separation between the conductive metal powder and ceramic powder in the conductive paste. In other words, the present invention aims to provide a conductive paste that can sufficiently suppress separation between the conductive metal powder and ceramic powder, and a method for manufacturing the same, which can be suitably applied to electronic components such as MLCCs, even when the internal electrode layers and dielectric layers are multi-layered and thin.

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.

In particular, in one embodiment of the conductive paste of the present invention, 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, 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.

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.

It is preferable that the Huggins coefficient at 25°C of the organic vehicle composed of the binder resin and the organic solvent is 0.80 or more and 1.20 or less.

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

The average particle size of the conductive metal powder is preferably 0.05 μm or more and 0.5 μm or less.

It is preferable 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.

It is preferable that the content of the binder resin relative to the total amount of the conductive paste be 1% by mass or more and 5% by mass or less.

The ceramic powder preferably contains barium titanate powder.

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

It is preferable that the ceramic powder is contained in an amount of 3 to 25 parts by mass per 100 parts by mass of the conductive metal powder.

The conductive paste preferably has a viscosity of 0.8 Pa·s or less at a shear rate of 100 sec ⁻¹ at 25° C. Also, the conductive paste preferably has a viscosity of 0.18 Pa·s or less at a shear rate of 10,000 sec ⁻¹ at 25° C.

The dry film obtained after printing and drying the conductive paste preferably has a dry film density (DFD) of more than 5.0 g/cm ^3. The arithmetic mean roughness Sa of the dry film is preferably 0.25 μm or less.

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.

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.

One aspect of the present invention provides a conductive paste that can sufficiently suppress separation between 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 in electronic components such as MLCCs.

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

The following describes a conductive paste and its manufacturing method according to one embodiment of the present invention.

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.

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

[Conductive metal powder]
The conductive metal powder is used as an electrode 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. In one example, a metal powder of nickel, copper, gold, silver, or platinum, or an alloy powder 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.

The average particle size of the conductive metal powder is not particularly limited and can be selected appropriately depending on the desired electronic component. For example, when manufacturing a highly laminated 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 impossible to obtain appropriate viscosity characteristics, or the conductive paste may 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.

The average particle size of the conductive metal powder is a value determined by observation using a scanning electron microscope (FE-SEM). For example, it is 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 10,000x magnification using an FE-SEM.

The content of conductive metal powder relative to the total amount of conductive paste is preferably 30% by mass or more and 70% by mass or less, and more preferably 40% by mass or more and 60% by mass or less. If the content of 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 conductive metal powder exceeds 70% by mass, it becomes difficult to form a thin electrode film.

[Ceramic powder]
In MLCC, 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 constituting the dielectric green sheet. Examples of the ceramic powder include perovskite-type oxide barium titanate ( _BaTiO3 ) and ceramic powders containing barium titanate as a 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 the ceramic powder 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.

It is preferable to use ceramic powder with the same or similar composition as the ceramic powder used as the main component of the dielectric layer green sheets for MLCC.

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 may not be fully achieved, and structural defects such as delamination and cracks may occur. Furthermore, the dry film density may decrease and the ceramic powder may be more likely to agglomerate, making it difficult to thin the dielectric layer. This may result in reduced insulation resistance and an increased short-circuit rate, reducing the reliability of the MLCC. On the other hand, if the average particle size of the ceramic powder exceeds 0.2 μm, the ceramic powder may have difficulty penetrating between the contact points of the conductive metal powder, resulting in a reduced dry film density. Furthermore, the sintering retardation effect may not be fully achieved.

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

The ceramic powder content is preferably 3 to 25 parts by mass per 100 parts by mass of conductive metal powder. If the ceramic powder content is less than 3 parts by mass, the sintering delay effect cannot be fully achieved, and firing cracks are more likely to occur. On the other hand, if the ceramic powder content exceeds 25 parts by mass, the ceramic powder constituting the conductive paste will diffuse more into the green sheet (dielectric layer), reducing the effect of the ceramic powder in delaying the onset of sintering of the conductive powder and reducing the continuity of the internal electrode layer. In addition, sintering of the ceramic powder contained in the internal electrode layer and the ceramic powder in the dielectric layer will increase the thickness of the dielectric layer, causing a discrepancy in the composition of the conductive paste, which may result in a decrease in electrical properties such as dielectric constant.

Ceramic powders produced by various methods, such as the solid-phase method, hydrothermal synthesis, alkoxide method, and sol-gel method, can be used. The ceramic powder can be mixed with the other components of the conductive paste in powder form, or can be dispersed and pulverized using a device such as a bead mill or high-pressure homogenizer to form a slurry, which can then be mixed.

[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. As the dispersant, for example, at least one selected from the group consisting of cationic dispersants, anionic dispersants, nonionic dispersants, amphoteric surfactants, and polymer dispersants can be used.

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 improve the dispersibility of the conductive metal powder through their surface modification action, thereby improving the smoothness and dry film density of the conductive paste coating. As the anionic dispersant, for example, at least one selected from carboxylic acid dispersants, phosphoric acid dispersants, and phosphate dispersants can be used.

The average molecular weight of the dispersant is preferably in the range of 200 to 20,000, and 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, imparting electrostatic and steric repulsive forces to the conductive metal powder, resulting in a conductive paste with excellent dispersibility. If the average molecular weight of the dispersant is less than 200, the electrostatic and steric repulsive forces will decrease over time, and the conductive metal powder will likely aggregate, resulting in a decrease in 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 will decrease, and the conductive metal powder will likely aggregate, resulting in a decrease in the dispersibility and storage stability of the conductive paste. There is also a risk that the viscosity of the conductive paste will become too high.

The content of 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 conductive metal powder. If the content of dispersant is less than 0.01 parts by mass, sufficient dispersibility may not be achieved. On the other hand, if the content of 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.

[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 selected from the group consisting of cellulose resin, acetal resin, and acrylic resin is used as the binder 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, ethyl hydroxyethyl cellulose or ethyl cellulose is preferred from the viewpoints of solubility in solvents and decomposition by combustion.

The content of binder resin relative to the total amount of conductive paste is not particularly limited, but is preferably 1% by mass or more and 5% by mass or less. If the binder resin content 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 susceptible to peeling. On the other hand, if the binder resin content exceeds 5% by mass, the binder resin content may be too high, which may result in poor debinding properties. The binder resin content is preferably 1 part by mass or more and 10 parts by mass or less, and more preferably 1 part by mass or more and 8 parts by mass or less, per 100 parts by mass of conductive powder.

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 for the production of an organic vehicle with appropriate viscosity. It is more preferable that the amount of binder resin in the organic vehicle be 5% by mass or more and 20% by mass or less.

[Organic solvent]
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.

In the conductive paste of this example, 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. 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, making it possible to sufficiently suppress separation of the conductive metal powder and ceramic powder in the conductive paste.

The first solvent is a good solvent for the binder resin, and examples of such solvents include terpene-based solvents. Examples of terpene-based solvents that can be used include at least one selected from the group consisting of terpineol and dihydroterpineol.

The second solvent is a poor solvent for the binder resin, and examples thereof include petroleum hydrocarbons. Examples of petroleum hydrocarbon solvents 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 specific examples include LAWS (Low Aromatic White Spirit) and HAWS (High Aromatic White Spirit).

A 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, isolactic acid, Propyl, 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 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 Examples of suitable ethylene glycol monoethyl ethers include 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, and dipropylene glycol monopropyl ether acetate.

Among these, from the viewpoint of binder resin solubility, 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.

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% by mass or less and 50% by mass or less for the third solvent. It is more preferable to blend 45% by mass or more and 55% by mass or less for the first solvent, 10% by mass or more and 30% by mass or less for the second solvent, and 5% by mass or more and 30% by mass or less for the third solvent.

The organic solvent content is not particularly limited, but it is preferable to set the content of the conductive metal powder to 30% by mass or more and 70% by mass or less relative to the total amount of the conductive paste. Specifically, the organic solvent content 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 organic solvent content is within this range, a conductive paste with excellent conductivity and dispersibility is obtained. For the same reason, the organic solvent content 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.

[Other additives]
In addition to the additives described above, the conductive paste of this example may also contain known additives for conductive pastes, such as antifoaming agents, plasticizers, thickeners, and chelating agents. Furthermore, depending on the purpose, additional organic solvents and organic binders different from the organic solvents and organic binders described above may also be added. In this case, although various known organic solvents and organic binders can be used as these additional organic solvents and organic binders, it is preferable to use the same organic solvents and organic binders as 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 (particularly 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.

(2) Huggins Coefficient In the conductive paste of this example, the Huggins coefficient of the organic vehicle composed of a binder resin and an organic solvent at 25 ° C. is adjusted to 0.80 or more and 1.20 or less, preferably 0.85 or more and 1.20 or less, more preferably 0.90 or more and 1.10 or less. 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 do not work sufficiently, so separation of 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 that suitable printing characteristics cannot be obtained.

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

η=η _s (1+[η]c+k′[η] ² c ² )...(Formula 1)

In other words, the Huggins coefficient (k') can be calculated from the slope of the approximate line obtained by transforming "Equation 1" into the following "Equation 2" and plotting the concentration c (g/cm ³ ) of the polymer solution on the horizontal axis and (η/η _s −1)/c on the vertical axis.

(η/η _s -1)/c=[η]+k'[η] ² c... (Formula 2)

More specifically, the Huggins coefficient can be measured using the following procedure.

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 molecular entanglement is not expected to occur. Although it depends on the type and molecular weight of the polymer material, it is adjusted to a range of 1×10 ⁻⁴ g/cm ³ or more and 1×10 ⁻¹ g/cm ³ or less, for example.

Next, the viscosity of these solvents and polymer solutions is measured at 25°C. If the concentration of the polymer solution is in the dilute range, it will show a constant viscosity independent of shear rate, so the viscosity value can be read at any shear rate. There are no particular restrictions on the device used to measure viscosity, as long as it is temperature controllable; for example, a viscometer such as a rheometer can be used.

Finally, based on the measurement results, a graph (approximate line) is created by plotting the polymer solution concentration c (g/cm ³ ) on the horizontal axis and (η/η _s −1)/c on the vertical axis. The Huggins coefficient (k') can then be calculated from the slope of this approximate line.

2. Manufacturing Method of Conductive Paste Composition The conductive paste of this example can be manufactured by mixing a binder resin and an organic solvent to form an organic vehicle, determining 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, or mixer. 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.

The binder resin can be dissolved in part of the organic solvent and then added to the remaining organic solvent along with the conductive metal powder, ceramic powder, and dispersant.

3. Characteristics The conductive paste of this example has the following characteristics: Therefore, the conductive paste of this example can be suitably used for electronic components such as MLCCs.

(1) Separation Evaluation In the conductive paste of this example, the separation amount S for evaluating 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.

S=Lc/(Lc+Lp)×100...(Formula 3)

(2) Viscosity The conductive paste of this example has a viscosity of 0.8 Pa·s or less at a shear rate (shear rate) of 100 sec ^-1 at 25°C. The viscosity at a shear rate of 100 sec ^-1 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. When the viscosity at a shear rate of 100 sec ^-1 is 0.8 Pa·s or less, it can be suitably used as a conductive paste for gravure printing. On the other hand, when the viscosity at a shear rate of 100 sec ^-1 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. The lower limit of the viscosity at a shear rate of 100 sec ^-1 is not particularly limited, but a viscosity of about 0.1 Pa·s is sufficient for application to gravure printing.

Furthermore, the conductive paste of this example preferably has a viscosity of 0.18 Pa·s or less at a shear rate of 10,000 sec ^-1 at 25°C, and more preferably less than 0.14 Pa·s. When the viscosity at a shear rate of 10,000 sec ^-1 is within the above range, it can be suitably used as a conductive paste for gravure printing. On the other hand, when the viscosity at a shear rate of 10,000 sec ^-1 exceeds 0.18 Pa·s, the viscosity of the conductive paste becomes too high and may become unsuitable for gravure printing. The lower limit of the viscosity at a shear rate of 10,000 sec ^-1 is not particularly limited, but a viscosity of about 0.05 Pa·s is sufficient for application to gravure printing.

The viscosity of the conductive paste can be measured, for example, using a viscometer such as a rheometer.

(3) Dry Film Density The dry film density (DFD) of the conductive paste of this example obtained after printing and drying is preferably greater than 5.0 g/cm ³ , more preferably greater than 5.2 g/cm ³ , and even more preferably 5.3 g/cm ³ or greater. The upper limit of the dry film density is about 6.5 g/cm ³ , which does not exceed 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 ).

(4) Arithmetic Mean Roughness of Dry Film The conductive paste of this example preferably has an arithmetic mean roughness Sa of the dry 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 dry 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 dry film is not particularly limited, and a smaller value is preferable. The arithmetic mean roughness Sa of the dry film can be calculated by measuring a 20 mm square dry 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.

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 paste. 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.

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 ceramic powder. Therefore, even when the thickness of the dielectric green sheet is, for example, 3 μm or less, it is possible to suppress sheet attack, in which the organic solvent (solvent mixture) in the conductive paste swells or dissolves the binder resin in the dielectric green sheet, and poor peeling of the dielectric green sheet.

An example of an MLCC, an electronic component using the conductive paste of this example, will be described below with reference to the drawings. The drawings may be used in schematic or scaled representations as appropriate. The positions and orientations of components will also 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).

Figures 1A and 1B are diagrams showing an MLCC1 using the conductive paste of this example. Figure 1A is a perspective view showing the appearance of the MLCC1, and Figure 1B is a cross-sectional view of the MLCC1. The MLCC1 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.

This MLCC1 can be manufactured, for example, as follows:

First, multiple dielectric green sheets (ceramic green sheets), which are unsintered ceramic sheets, are prepared. These dielectric green sheets can be prepared, for example, by applying a dielectric layer paste made by mixing a specified 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 PET (polyethylene terephthalate) film, and then drying to remove the solvent. The thickness of the dielectric layer, including the dielectric green sheets, is not particularly limited, but is preferably between 0.05 μm and 3 μm inclusive, in order to reduce the size of the MLCC1.

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 with the desired pattern. In this case, the thickness of the dry film is preferably 1 μm or less, from the perspective of thinning the internal electrode layer 11.

After the dry film is formed, the dielectric green sheets are peeled off from the support film and 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 together to form a laminate. Protective dielectric green sheets that do not have any conductive paste printed on them can be placed on the top and bottom surfaces of the laminate.

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

After the binder removal process, the green chip is fired. Firing is carried out in a reducing atmosphere to prevent oxidation of the metal (conductive metal powder) that will become the internal electrode layer 11. The firing temperature is preferably between 1000°C and 1350°C, and the holding time at this temperature is preferably between 0.5 hours and 8 hours.

By debinding and firing, the binder resin in the dielectric green sheets is completely removed, and the ceramic raw material powder is fired to form the dielectric layers 12. The organic vehicle (binder resin and organic solvent) in the dried film is also removed, and the conductive metal powder is sintered or melted to form an integrated internal electrode layer 11. As a result, a multilayer ceramic sintered body (laminate 10) is formed in which multiple dielectric layers 12 and internal electrode layers 11 are alternately stacked. The fired multilayer ceramic sintered body (laminate 10) may be annealed to incorporate oxygen into the dielectric layers 12, thereby improving reliability, and to prevent reoxidation of the internal electrode layers 11.

Finally, a pair of external electrodes 20 are formed on the fired laminated ceramic body (laminate 10). Specifically, external electrode layers 21 are formed on both ends of the laminate 10 so as to electrically connect to the internal electrode layers 11, and a plating layer 22 is formed to cover these external electrode layers 21. Suitable materials for the external electrodes 20 include copper, nickel, or alloys thereof. In this manner, the MLCC 1 can be manufactured.

The present invention will be explained in more detail below using examples and comparative examples, but the present invention is not limited to these examples and comparative examples in any way.

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 prepare 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).

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 viscosities of these organic vehicles A at 25°C were measured using a rheometer. An approximate line was then created by plotting the organic vehicle concentration c (g/cm ³ ) on the horizontal axis and (η/ηs-1)/c on the vertical axis, and the Huggins coefficient (k') was calculated from the slope.

Solvent mixtures B-G and organic vehicles B-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-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-G were also calculated in the same manner. The results are shown in Table 1.

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: nickel powder: 49% by weight, barium titanate powder: 12.25% by weight, oleoyl sarcosine: 0.05% by weight, ethyl cellulose: 2.6% by weight, mixed solvent A: 36.1% by weight). The ethyl cellulose was dissolved in a portion of the dihydroterpineol in mixed solvent A before mixing with the other components.

The conductive paste obtained in this manner was evaluated for separation. 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, if the thickness of the separated ceramic powder layer observed from the side of the container was Lc (mm) and the thickness of the entire conductive paste was Lp (mm), the separation amount S calculated using the above-mentioned "Equation 3" was evaluated as "Good" if it was less than 4.0, and as "Poor" if it was less than 4.0.

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

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. 2.

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. 2.

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 were evaluated. The results are shown in Table 2 and FIG. 2.

(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. 2.

(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. 2.

(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. 2.

1. MLCC
10 laminate 11 internal electrode layer 12 dielectric layer 20 external electrode 21 external electrode layer 22 plating layer

Claims (13)

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. 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. The conductive paste according to claim 1 or 2, wherein the Huggins coefficient at 25°C of the organic vehicle composed of the binder resin and the organic solvent is 0.80 or more and 1.20 or less. The conductive paste according to any one of claims 1 to 3, wherein the conductive metal powder contains at least one metal selected from the group consisting of nickel, copper, gold, silver, platinum, and palladium. The conductive paste according to any one of claims 1 to 4, wherein the conductive metal powder has an average particle size of 0.05 μm or more and 0.5 μm or less. 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% by mass or more and 70% by mass or less. 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% by mass or more and 5% by mass or less. A conductive paste according to any one of claims 1 to 7, wherein the ceramic powder includes barium titanate powder. 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. The conductive paste according to any one of claims 1 to 9, containing 3 to 25 parts by mass of the ceramic powder per 100 parts by mass of the conductive metal powder. The conductive paste according to any one of claims 1 to 10, wherein the viscosity at a shear rate of 100 sec ^-1 at 25°C is 0.8 Pa·s or less, and the viscosity at a shear rate of 10,000 sec ^{-1 at} 25°C is 0.18 Pa·s or less. 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. 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.