Carboxy group-containing polymer dispersant, conductive paste, electronic component, and multilayer ceramic capacitor

Abstract

To provide a low-viscosity conductive paste capable of suppressing separation of conductive powder and ceramic powder and having good viscosity stability with time, a carboxy group-containing polymer dispersant, an electronic component, and a multilayer ceramic capacitor.SOLUTION: A carboxy group-containing polymer dispersant including a copolymer of at least one of acrylic acid and methacrylic acid and at least one of an acrylic acid ester represented by the following general formula (1) and a specific methacrylic acid ester, in which a mass average molecular weight is 2000 or more and less than 30000, a ratio of a total of the acrylic acid and the methacrylic acid to a total of the acrylic acid ester and the methacrylic acid ester is X: SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a carboxyl group-containing polymer dispersant, a conductive paste, an electronic component, and a multilayer ceramic capacitor. [Background technology]

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

[0003] Multilayer ceramic capacitors are manufactured, for example, as follows. First, a paste for internal electrodes (conductive paste) containing conductive powder, binder resin, and organic solvent is printed in a predetermined electrode pattern on the surface of a dielectric green sheet containing a dielectric powder such as barium titanate (BaTiO) and a binder resin. These sheets are then stacked in multiple layers to obtain a laminate in which the internal electrodes and dielectric green sheets are stacked in multiple layers. Next, this laminate is integrated by heat and pressure bonding to form a pressed body. This pressed body is cut, subjected to an organic binder removal process in an oxidizing or inert atmosphere, and then fired to obtain fired chips. Next, an external electrode paste is applied to both ends of the fired chip. After firing, nickel plating or the like is applied to the surfaces of the external electrodes to obtain a multilayer ceramic capacitor.

[0004] Conventionally, screen printing has been the most commonly used printing method for printing conductive paste onto dielectric green sheets. However, due to demands for smaller, thinner electronic devices and improved productivity, there is a demand for printing finer electrode patterns with high productivity.

[0005] One method of printing conductive paste is gravure printing, a continuous printing method in which the conductive paste is filled into recesses in a printing plate and then pressed against the surface to be printed, transferring the conductive paste from the printing plate. Gravure printing has a high printing speed and excellent productivity. When using gravure printing, it is necessary to appropriately select the binder resin, dispersant, solvent, etc. in the conductive paste to adjust properties such as viscosity to within a range suitable for gravure printing.

[0006] For example, Patent Document 1 discloses a conductive paste used to form, by gravure printing, internal conductor films in a multilayer ceramic electronic component having a plurality of ceramic layers and internal conductor films extending along specific interfaces between the ceramic layers, the conductive paste containing 30 to 70% by weight of a solid component including a metal powder, 1 to 10% by weight of an ethyl cellulose resin component having an ethoxy group content of 49.6% or more, 0.05 to 5% by weight of a dispersant, and the remainder as a solvent component, and the paste is applied at a shear rate of 0.1 (s -1 ) Viscosity η 0.1 is 1 Pa·s or more and the shear rate is 0.02(s -1 ) Viscosity η 0.02 A conductive paste is described which is a thixotropic fluid that satisfies the condition expressed by a specific formula:

[0007] Furthermore, Patent Document 2 discloses a conductive paste used for forming a conductive paste by gravure printing, similar to Patent Document 1, which contains 30 to 70% by weight of a solid component including a metal powder, 1 to 10% by weight of a resin component, 0.05 to 5% by weight of a dispersant, and the remainder as a solvent component, and is capable of being applied at a shear rate of 0.1 (s -1 ) is a thixotropic fluid with a viscosity of 1 Pa·s or more at a shear rate of 0.1 (s -1 ) is used as the viscosity reference, and the shear rate is 10 (s -1 ) is described as a conductive paste having a viscosity change rate of 50% or more.

[0008] According to the above Patent Documents 1 and 2, these conductive pastes have a shear rate of 0.1 (s -1) is a thixotropic fluid with a viscosity of 1 Pa·s or more, which is said to enable stable continuous printing at high speeds in gravure printing and to enable the production of multilayer ceramic electronic components such as multilayer ceramic capacitors with good production efficiency.

[0009] Patent Document 3 also describes a conductive paste for use in internal electrodes of multilayer ceramic capacitors, comprising a conductive powder (A), an organic resin (B), an organic solvent (C), an additive (D), and a dielectric powder (E), where the organic resin (B) is polyvinyl butyral with a degree of polymerization of 10,000 to 50,000 and ethyl cellulose with a weight-average molecular weight of 10,000 to 100,000, the organic solvent (C) is propylene glycol monobutyl ether, a mixed solvent of propylene glycol monobutyl ether and propylene glycol methyl ether acetate, or a mixed solvent of propylene glycol monobutyl ether and mineral spirits, and the additive (D) is a conductive paste for gravure printing comprising a separation inhibitor and a dispersant. According to Patent Document 3, this conductive paste has a viscosity suitable for gravure printing and dries quickly. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-187638 [Patent Document 2] Japanese Patent Application Laid-Open No. 2003-242835 [Patent Document 3] Japanese Patent Application Laid-Open No. 2012-174797 Summary of the Invention [Problem to be solved by the invention]

[0011] As electronic components become smaller, electrodes and wiring formed by printing conductive pastes are becoming thinner. Low viscosity conductive pastes are required to apply them thinly and smoothly. However, when ceramic powders such as barium titanate and conductive powders such as Ni are added to low-viscosity conductive pastes, the difference in sedimentation velocity due to the difference in specific gravity between these powders can cause separation of the conductive powder and the ceramic powder.

[0012] For example, when a low-viscosity conductive paste is prepared, a phenomenon called "white floating" (two-layer separation) may occur, in which a white, separated layer containing ceramic powder appears on top. If the composition within the paste becomes non-uniform in this way, the surface of the dried film after application will not be smooth. For example, if the paste is used for the internal electrodes of a multilayer ceramic capacitor, short circuits may occur between the internal electrodes or the desired capacitance may not be achieved.

[0013] Furthermore, as a result of the inventors' investigations, it was found that low-viscosity conductive pastes tend to thicken after long-term storage, resulting in a high viscosity increase ratio over time, calculated as the ratio of the viscosity after long-term storage to the viscosity immediately after production. To obtain a smooth and uniform thin film, it is necessary to control the viscosity of the paste to be applied within a certain range. However, pastes with a high viscosity increase ratio over time have problems such as not being able to obtain a smooth printed surface during printing after long-term use, or requiring viscosity adjustments each time the paste is used for a certain period of time, which complicates the printing process.

[0014] In view of the above circumstances, the present invention aims to provide a conductive paste that has a low viscosity and can stably maintain that low paste viscosity for a long period of time, and that can suppress separation of the conductive powder and the ceramic powder, and also aims to provide a carboxy group-containing polymer dispersant, an electronic component, and a multilayer ceramic capacitor. [Means for solving the problem]

[0015] In order to solve the above problems, the dispersant of the present invention is a carboxyl group-containing polymer dispersant comprising a copolymer of at least one of acrylic acid or methacrylic acid and at least one of an acrylic acid ester represented by the following general formula (1) or a methacrylic acid ester represented by the following general formula (2), wherein the mass average molecular weight is 2000 or more and less than 30000, and the molar ratio of the total of the acrylic acid and the methacrylic acid to the total of the acrylic acid ester and the methacrylic acid ester is X:1-X, where X is 0.1 or more and less than 0.4, and In the following general formula (2), R1 is a linear or branched alkyl group, the distance (Ra) between the Hansen solubility parameter of the dispersant and the Hansen solubility parameter of the solvent is 5.5 or more and 7.5 or less, and the solvent is a mixed solvent obtained by mixing dihydroterpineol, a hydrocarbon-based solvent having a viscosity of less than 3 mPa·s at 20°C, and an ether-based solvent having a viscosity of less than 5 mPa·s at 20°C and Hansen solubility parameters ΔD of 15-17, ΔP of 4-6, and ΔH of 8-10, in a mass ratio of 40-60:10-30:20-40.

[0016] [ka]

[0017] [ka]

[0018] The hydrocarbon solvent may include mineral spirits A, and the ether solvent may include one or more solvents selected from the group consisting of propylene glycol monobutyl ether, propylene glycol monomethyl ether acetate, and diethylene glycol monobutyl ether acetate.

[0019] In order to solve the above problems, the conductive paste of the present invention is a conductive paste containing the carboxy group-containing polymer dispersant of the present invention.

[0020] The conductive paste of the present invention may further contain a conductive powder, a ceramic powder, a binder resin, and an organic solvent, and the content of the carboxy group-containing polymer dispersant may be 0.01% by mass or more and less than 2.0% by mass.

[0021] The organic solvent may include one or more solvents selected from the group consisting of terpene-based solvents, glycol ether-based solvents, acetate-based solvents, acetate ester-based solvents, ketone-based solvents, and hydrocarbon solvents.

[0022] The organic solvent may include one or more selected from the group consisting of dihydroterpineol, mineral spirits A, propylene glycol monobutyl ether, propylene glycol monomethyl ether acetate, and diethylene glycol monobutyl ether acetate.

[0023] The conductive paste of the present invention may contain a dispersant other than the carboxy group-containing polymer dispersant, and the content of the carboxy group-containing polymer dispersant relative to the total amount of dispersants in the conductive paste may be 30 mass% or more.

[0024] The conductive paste may contain an acid-based dispersant having a mass average molecular weight of less than 2000 as a dispersant other than the carboxy group-containing polymer dispersant, and the content of the acid-based dispersant relative to the total amount of dispersants in the conductive paste may be more than 0 mass% and not more than 70 mass%.

[0025] The conductive powder may contain one or more metal powders selected from Ni, Pd, Pt, Au, Ag, Cu, and alloys thereof.

[0026] The number average particle size of the conductive powder may be 0.05 μm or more and 1.0 μm or less.

[0027] The ceramic powder may include barium titanate.

[0028] The ceramic powder may have a number average particle size of 0.01 μm or more and 0.5 μm or less.

[0029] The content of the ceramic powder may be 1% by mass or more and 20% by mass or less.

[0030] The binder resin may include a cellulose-based resin.

[0031] The conductive paste of the present invention may be used for internal electrodes of multilayer ceramic components.

[0032] The conductive paste of the present invention is subjected to a shear rate of 100 sec at a temperature of 25°C. -1 The viscosity at 2.5 Pa·S or less may be 2.5 Pa·S or less.

[0033] In order to solve the above-mentioned problems, the electronic component of the present invention is an electronic component formed using the conductive paste of the present invention.

[0034] In order to solve the above-mentioned problems, the multilayer ceramic capacitor of the present invention has at least a laminate in which dielectric layers and internal electrode layers are laminated, and the internal electrode layers are formed using the conductive paste of the present invention. [Effects of the Invention]

[0035] The conductive paste of the present invention, even though it is a low-viscosity paste, can suppress separation of the conductive powder and the ceramic powder, and has a good smoothness of the dried film surface after application. Furthermore, since the viscosity of the paste is stable over a long period of time, viscosity adjustment during printing is not required, which contributes to simplifying the printing process. It is particularly effective when used for gravure printing, which requires high-speed printing at low viscosity. [Brief explanation of the drawings]

[0036] [Figure 1] 1A and 1B are schematic diagrams of a multilayer ceramic capacitor according to an embodiment of the present invention, in which FIG. 1A is a perspective view and FIG. 1B is a cross-sectional view. [Figure 2] FIG. 1 is a diagram showing the evaluation results of Ra and dispersibility of a dispersant. DETAILED DESCRIPTION OF THE INVENTION

[0037] Hereinafter, one embodiment of the carboxy group-containing polymer dispersant, conductive paste, electronic component, and multilayer ceramic capacitor of the present invention will be described.

[0038] [Carboxy group-containing polymer dispersant] The carboxyl group-containing polymeric dispersant of the present invention is a copolymer of at least either acrylic acid or methacrylic acid with at least either an acrylic acid ester represented by the following general formula (1) or a methacrylic acid ester represented by the following general formula (2), the copolymer having a mass average molecular weight of 2,000 or more and less than 30,000, and a molar ratio of the total of the acrylic acid and the methacrylic acid to the total of the acrylic acid ester and the methacrylic acid ester of X:1-X, where X is 0.1 or more and less than 0.4. In the following general formulas (1) and (2), R1 is a linear or branched alkyl group.

[0039] [ka]

[0040] [ka]

[0041] The inventors have found that the low-viscosity conductive paste described below has a stable low viscosity with little change over time, and that separation of the conductive powder and the ceramic powder is suppressed, by including a certain amount of a carboxyl group-containing polymer dispersant having a mass-average molecular weight of 2000 or more, thereby making it possible to obtain a smooth dried film.

[0042] The carboxyl group-containing polymer dispersant has a carboxyl group as an adsorbent to the conductive powder or ceramic powder, and has a copolymer structure of at least one of acrylic acid or methacrylic acid and at least one of acrylic acid ester or methacrylic acid ester, thereby achieving both improved solubility in organic solvents (described below) and improved dispersibility of the conductive powder.

[0043] Examples of the copolymer include a copolymer of acrylic acid and an acrylic acid ester, a copolymer of acrylic acid and a methacrylic acid ester, a copolymer of methacrylic acid and an acrylic acid ester, a copolymer of methacrylic acid and a methacrylic acid ester, a copolymer of acrylic acid, methacrylic acid, and an acrylic acid ester, a copolymer of acrylic acid, methacrylic acid, and a methacrylic acid ester, a copolymer of acrylic acid, an acrylic acid ester, and a methacrylic acid ester, a copolymer of methacrylic acid, an acrylic acid ester, and a methacrylic acid ester, and a copolymer of acrylic acid, methacrylic acid, an acrylic acid ester, and a methacrylic acid ester.

[0044] When acrylic acid and an acrylic acid ester are used in combination, the molar ratio thereof can be appropriately adjusted. When an acrylic acid ester and a methacrylic acid ester are used in combination, the molar ratio thereof can be appropriately adjusted.

[0045] In addition, the solubility in organic solvents and dispersibility of conductive powders can be changed by adjusting the molar ratio of the sum of acrylic acid and methacrylic acid (X) to the sum of acrylic acid ester and methacrylic acid ester (1-X) during copolymerization. If the sum of acrylic acid and methacrylic acid is too low, the amount of carboxyl groups acting as adsorbents for the conductive powder is small, resulting in poor dispersibility. On the other hand, if the sum of acrylic acid and methacrylic acid is too high, the hydrophilicity of the carboxyl group-containing polymer dispersant increases, resulting in poor solubility in organic solvents used in the conductive paste.

[0046] Therefore, there is an appropriate molar ratio between the total of acrylic acid and methacrylic acid and the total of acrylic acid ester and methacrylic acid ester. That is, when the ratio X of the total of acrylic acid and methacrylic acid is 0.1 or more and less than 0.4, a good balance is achieved between the solubility in organic solvents and the effect of improving the dispersibility of the conductive powder. As a result, separation of the conductive powder and the ceramic powder can be suppressed, and a low-viscosity conductive paste can be provided that has good viscosity stability over time and provides a smooth, dried film surface after application.

[0047] Furthermore, R1 in the acrylic acid ester and methacrylic acid ester shown in general formula (1) and general formula (2) is a linear or branched alkyl group. Here, when R1 is a linear alkyl group, the number of carbon chains is preferably 2 to 10, more preferably 2 to 4. If the number of carbon chains is 1, the carbon chain of the acrylic acid ester or methacrylic acid ester is too short, and when used as a copolymer dispersant, the effect of suppressing separation of the conductive paste may not be sufficiently exhibited, which is undesirable. Furthermore, if the number of carbon chains is 11 or more, the carbon chain of the acrylic acid ester or methacrylic acid ester is too long, and when used as a copolymer dispersant, the effect of suppressing separation of the conductive paste may not be sufficiently exhibited, or the surface roughness and density of the dried film formed by gravure printing or the like from the conductive paste may deteriorate, which is undesirable.

[0048] Furthermore, when R1 is a branched alkyl group, the total carbon number of R1 is preferably 3 to 14, the number of carbon chains in the linear portion is preferably 2 to 10, and the number of carbon atoms in the branched portion is preferably 1 to 4. By satisfying these conditions, a good balance is achieved between solubility in organic solvents and the effect of improving the dispersibility of the conductive powder. As a result, separation of the conductive powder and the ceramic powder can be suppressed, and a low-viscosity conductive paste can be provided that has good viscosity stability over time and provides a smooth, dried film surface after application. On the other hand, if these conditions are not satisfied, when the conductive paste is copolymerized and used as a dispersant, the effect of suppressing separation of the conductive paste may not be fully exerted, or the surface roughness and density of the dried film after formation of the conductive paste may deteriorate.

[0049] The mass-average molecular weight of the carboxyl group-containing polymer dispersant is 2000 or more, and may be 5000 or more, or even 10,000 or more. The mass-average molecular weight of the carboxyl group-containing polymer dispersant affects the initial viscosity, thickening over time, and separation amount of the conductive paste using the same. Therefore, a mass-average molecular weight of 2000 or more can achieve a stable dispersion effect and sufficiently suppress thickening over time and separation. From the viewpoint of suppressing thickening over time, there is no particular upper limit to the mass-average molecular weight. However, if the mass-average molecular weight is too large, the initial viscosity of the conductive paste itself will increase, making it unsuitable for gravure printing. Therefore, the mass-average molecular weight may be 30,000 or less. The mass-average molecular weight of the carboxyl group-containing polymer dispersant can be measured, for example, by gel permeation chromatography (GPC).

[0050] <Hansen Solubility Parameter> The Hansen Solubility Parameter (HSP) is a value used to predict the solubility of a substance. In the present invention, it was discovered that the HSP can be used as an index for the dispersibility of a dispersant in a conductive powder, leading to the invention of the dispersant of the present invention.

[0051] That is, the dispersant of the present invention, which satisfies the condition that the distance (Ra) between the Hansen solubility parameter of the dispersant and the Hansen solubility parameter of the solvent is 5.5 or more and 7.5 or less, can disperse the conductive powder well. By using such a dispersant, it is possible to provide a conductive paste that maintains a low paste viscosity stably over a long period of time even in a low-viscosity conductive paste, and that can suppress separation of the conductive powder and the ceramic powder.

[0052] (Method for evaluating dispersibility) The dispersibility of the dispersant in the conductive powder can be evaluated by dispersing the conductive powder in a solvent with the dispersant to form a slurry, and then measuring the particle size of the conductive powder in the slurry.

[0053] For example, a mixture of conductive powder, dispersant, and solvent in a mass ratio of 0.1:0.1:100 is stirred using ultrasonic treatment to form a slurry, and the average particle size of the conductive powder in the slurry is measured using dynamic light scattering (DLS) to compare and evaluate the average particle size.

[0054] In the evaluation of the dispersibility of the conductive powder described above, when a dispersant with an Ra of less than 5.5 or more than 7.5 is used, the dispersibility of the conductive powder is inferior and the average particle size of the conductive powder remains large compared to when a dispersant with an Ra of 5.5 to 7.5 is used. Therefore, a conductive paste produced using a dispersant with an Ra of less than 5.5 or more than 7.5 may have poor viscosity stability and poor effectiveness in suppressing separation between the conductive powder and the ceramic powder, or the surface roughness of the film produced by drying the conductive paste may be high.

[0055] (solvent) Solvents that can be used to calculate Ra and evaluate the dispersibility of dispersants include the same organic solvents as those used in the conductive paste described below, as well as mixtures of two or more organic solvents in a specific ratio. For example, a mixed solvent can be used that contains dihydroterpineol (DHT), a hydrocarbon solvent with a viscosity of less than 3 mPa·s at 20°C, and an ether solvent with a viscosity of less than 5 mPa·s at 20°C and Hansen solubility parameters δD (dispersion parameter) of 15-17, δP (polarity parameter) of 4-6, and δH (hydrogen bonding parameter) of 8-10, in a mass ratio of 40-60:10-30:20-40.

[0056] The hydrocarbon solvent may include mineral spirits A (MSA).

[0057] The ether solvent may include one or more selected from the group consisting of propylene glycol monobutyl ether (PNB), propylene glycol monomethyl ether acetate (PMA), and diethylene glycol monobutyl ether acetate (BCA).

[0058] Such mixed solvents are typical organic solvents used in conductive pastes, and therefore, by evaluating dispersibility using such mixed solvents, it becomes possible to select a suitable dispersant without producing a conductive paste.

[0059] More specifically, a mixed solvent can be used in which dihydroterpineol (DHT): mineral spirits A (MSA): one or more ether solvents selected from the group consisting of propylene glycol monobutyl ether (PNB), propylene glycol monomethyl ether acetate (PMA), and diethylene glycol monobutyl ether acetate (BCA) are mixed in a mass ratio of 40-60:10-30:20-40, and a mixed solvent in this mass ratio of 46-56:10-30:27-37 can also be used.

[0060] (Calculation method of Hansen solubility parameter of dispersant) The HSP of a dispersant can be calculated by the following procedure. (1) Investigate the solubility of dispersants in solvents (15 to 20 types) with known HSPs. (2) In the Hansen space, find a sphere that contains only the solvent points in which the dispersant is dissolved, among the solvents whose solubility has been investigated. (3) The center coordinates of the sphere are defined as the HSP of the dispersant.

[0061] The procedure for calculating the HSP of the dispersant can be carried out using commercially available software such as HSPIP (Hansen Solubility Parameter in Practice).

[0062] The distance (Ra) between the Hansen solubility parameter of the dispersant and the Hansen solubility parameter of the solvent can be calculated using the formula shown in [Mathematical Expression 1].

[0063]

number

[0064] [Conductive paste] The conductive paste of this embodiment contains the carboxyl group-containing polymer dispersant of the present invention. It may also contain a conductive powder, a ceramic powder, a binder resin, and an organic solvent. Each of these components will be described in detail below.

[0065] (conductive powder) The conductive powder is not particularly limited, and metal powders can be used, such as powders of one or more elements selected from Ni, Pd, Pt, Au, Ag, Cu, and alloys thereof. Among these, powders of Ni or its alloys (Ni alloys) are preferred from the viewpoints of conductivity, corrosion resistance, and cost. Examples of Ni alloys that can be used include alloys of Ni with at least one element selected from the group consisting of Mn, Cr, Co, Al, Fe, Cu, Zn, Ag, Au, Pt, and Pd. The Ni content in the Ni alloy is, for example, 50% by mass or more, preferably 80% by mass or more. Furthermore, the Ni powder may contain several hundred ppm of the element S to suppress rapid gas generation due to partial thermal decomposition of the binder resin during binder removal.

[0066] The number average particle size of the conductive powder is preferably 0.05 μm or more and 1.0 μm or less, more preferably 0.1 μm or more and 0.5 μm or less. When the number average particle size of the conductive powder is within the above range, it can be suitably used as an internal electrode paste for thin-film multilayer ceramic capacitors (multilayer ceramic components), and for example, the smoothness and density of the dried film are improved. The number average particle size is a value determined by observation with a scanning electron microscope (SEM), and is the average value (SEM average particle size) obtained by measuring the particle size of each of multiple particles in an image observed with the SEM at 10,000x magnification.

[0067] The content of the conductive powder is preferably 30% by mass or more and less than 70% by mass, more preferably 40% by mass or more and 60% by mass or less, based on the total mass of the conductive paste. When the content of the conductive powder is within the above range, the conductivity and dispersibility are excellent.

[0068] (ceramic powder) The ceramic powder is not particularly limited, and for example, in the case of a paste for internal electrodes of a multilayer ceramic capacitor, a known ceramic powder is appropriately selected depending on the type of multilayer ceramic capacitor to be applied. As the ceramic powder, for example, a perovskite oxide containing Ba and Ti can be used, and preferably contains barium titanate (BaTiO).

[0069] The ceramic powder may be a ceramic powder containing barium titanate as a main component and an oxide as a secondary component. The oxide may be one or more oxides selected from Mn, Cr, Si, Ca, Ba, Mg, V, W, Ta, Nb, and rare earth elements. An example of such a ceramic powder is a perovskite-type oxide ferroelectric ceramic powder in which the Ba atoms and Ti atoms of barium titanate (BaTiO3) are substituted with other atoms such as Sn, Pb, or Zr.

[0070] The ceramic powder used in the conductive paste for the internal electrodes may have the same composition as the dielectric ceramic powder constituting the green sheets of the multilayer ceramic capacitor (electronic component). This prevents cracks from occurring at the interface between the dielectric layer and the internal electrode layer during the sintering process due to a shrinkage mismatch. Examples of such ceramic powders include perovskite oxides containing Ba and Ti, as well as oxides such as ZnO, ferrite, PZT, BaO, Al2O3, Bi2O3, R (rare earth element)2O3, TiO2, and Nd2O3. One type of ceramic powder may be used, or two or more types may be used.

[0071] The number average particle diameter of the ceramic powder is, for example, 0.01 μm to 0.5 μm, preferably 0.01 μm to 0.3 μm. When the number average particle diameter of the ceramic powder is in the above range, when the ceramic powder is used as a conductive paste for internal electrodes, it is possible to form sufficiently fine, thin, and uniform internal electrodes. The number average particle diameter is a value determined by observation with a scanning electron microscope (SEM), and is the average value (SEM average particle diameter) obtained by measuring the particle diameter of each of multiple particles in an image observed with the SEM at a magnification of 50,000 times.

[0072] The content of the ceramic powder is preferably 1% by mass or more and 20% by mass or less, more preferably 3% by mass or more and 15% by mass or less, based on the total mass of the conductive paste. When the content of the ceramic powder is within the above range, the dispersibility and sinterability are excellent.

[0073] The content of the ceramic powder is preferably 1 part by mass or more and 30 parts by mass or less, and more preferably 3 parts by mass or more and 30 parts by mass or less, relative to 100 parts by mass of the conductive powder. When the content of the conductive powder is within the above range, the conductivity and dispersibility are excellent.

[0074] (binder resin) The binder resin is not particularly limited, and known resins can be used. Examples of binder resins include cellulose-based resins such as methyl cellulose, ethyl cellulose, ethylhydroxyethyl cellulose, and nitrocellulose; acrylic resins; and acetal-based resins containing butyral-based resins such as polyvinyl butyral. Among these, a cellulose-based resin is preferred, and ethyl cellulose is more preferred, from the viewpoints of solubility in solvents and combustion decomposition. Furthermore, when used as an internal electrode paste, a butyral-based resin may be included or a butyral-based resin may be used alone to improve adhesive strength with the green sheet. When the binder resin contains an acetal-based resin, the viscosity can be easily adjusted to a level suitable for gravure printing, and adhesive strength with the green sheet can be further improved. The binder resin may contain, for example, 20% by mass or more, or 30% by mass or more, of the acetal-based resin relative to the entire binder resin. Furthermore, the binder resin may contain 50% by mass or less of the acetal-based resin relative to the entire binder resin.

[0075] The weight average molecular weight of the binder resin can be adjusted appropriately within the range of 10,000 or more and 200,000 or less depending on the required viscosity of the conductive paste.

[0076] The content of the binder resin is preferably 0.5% by mass to 10% by mass, more preferably 1% by mass to 7% by mass, based on the total amount of the conductive paste. When the content of the binder resin is within the above range, the conductive paste has excellent conductivity and dispersibility.

[0077] The content of the binder resin is preferably 1 part by mass or more and 20 parts by mass or less, more preferably 1 part by mass or more and 14 parts by mass or less, relative to 100 parts by mass of the conductive powder. When the content of the binder resin is within the above range, the conductivity and dispersibility are excellent.

[0078] (organic solvent) The organic solvent is not particularly limited, and any known organic solvent capable of dissolving the binder resin and dispersant can be used. Examples of the organic solvent include terpene-based solvents, glycol ether-based solvents, acetate-based solvents, acetate ester-based solvents, ketone-based solvents, and hydrocarbon solvents. One type of organic solvent may be used, or two or more types may be used.

[0079] Examples of the terpene solvent include terpineol, dihydroterpineol (DHT), dihydroterpinyl acetate, and the like, and among these, dihydroterpineol (DHT) is preferred.

[0080] Examples of glycol ether-based solvents include (di)ethylene glycol ethers such as diethylene glycol mono-2-ethylhexyl ether, ethylene glycol mono-2-ethylhexyl ether, diethylene glycol monohexyl ether, and ethylene glycol monohexyl ether, and propylene glycol monoalkyl ethers such as propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, and propylene glycol monobutyl ether (PNB). Among these, propylene glycol monoalkyl ethers are preferred, and propylene glycol monobutyl ether (PNB) is more preferred. When the organic solvent contains a glycol ether-based solvent, it has excellent compatibility with the binder resin described above and excellent drying properties.

[0081] Examples of acetate solvents include glycol ether acetates such as propylene glycol monomethyl ether acetate (PMA), ethylene glycol monobutyl ether acetate, diethylene glycol monobutyl ether acetate (butyl carbitol acetate) (BCA), dipropylene glycol methyl ether acetate, 3-methoxy-3-methylbutyl acetate, and 1-methoxypropyl-2-acetate, as well as isobornyl acetate, isobornyl propionate, isobornyl butyrate, and isobornyl isobutyrate.

[0082] Examples of acetate solvents include ethyl acetate, propyl acetate, isobutyl acetate, butyl acetate, etc. Examples of ketone solvents include methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, etc.

[0083] Examples of hydrocarbon solvents include aliphatic hydrocarbon solvents such as tridecane, nonane, cyclohexane, naphthenic solvents, and mineral spirits, and aromatic hydrocarbon solvents such as toluene and xylene, with aliphatic hydrocarbon solvents being preferred, and mineral spirits A being more preferred. Furthermore, the mineral spirits may contain chain saturated hydrocarbons as the main component, and may contain 20 mass% or more of chain saturated hydrocarbons based on the total amount of the mineral spirits.

[0084] The organic solvent preferably includes one or more selected from the group consisting of dihydroterpineol (DHT), dihydroterpinyl acetate (DHTA), terpineol (TPO), propylene glycol monobutyl ether (PNB), propylene glycol monomethyl ether acetate (PMA), diethylene glycol monobutyl ether acetate (BCA), and diisobutyl ketone (DIBK). By using these solvents, it is possible to achieve both appropriate viscosity and drying speed.

[0085] For example, the organic solvent may include one or more terpene solvents (a) selected from the group consisting of dihydroterpineol (DHT), dihydroterpinyl acetate (DHTA), and terpineol (TPO), one or more solvents (b) selected from the group consisting of propylene glycol monobutyl ether (PNB), propylene glycol monomethyl ether acetate (PMA), and diethylene glycol monobutyl ether acetate (BCA), and a hydrocarbon solvent such as mineral spirits.

[0086] The total content of the organic solvents is preferably 20% by mass or more and 50% by mass or less, and more preferably 25% by mass or more and 45% by mass or less, based on the total amount of the conductive paste. When the content of the organic solvents is within the above range, the conductive paste has excellent conductivity and dispersibility.

[0087] The total content of the organic solvents is preferably 50 parts by mass or more and 130 parts by mass or less, more preferably 60 parts by mass or more and 90 parts by mass or less, relative to 100 parts by mass of the conductive powder. When the content of the organic solvents is within the above range, the conductivity and dispersibility are excellent.

[0088] When the conductive paste contains a terpene-based solvent (a), the total content of the terpene-based solvent (a) may be 5% by mass or more and 40% by mass or less, 10% by mass or more and 30% by mass or less, or 12% by mass or more and 25% by mass or less, relative to the total amount of the conductive paste.

[0089] When the conductive paste contains a solvent (b) such as propylene glycol monobutyl ether (PNB), the total content of the solvent (b) may be 3% by mass or less and 20% by mass or less, or may be 5% by mass or more and 20% by mass or less, based on the total amount of the conductive paste.

[0090] When the conductive paste contains hydrocarbon solvents, the total content of the hydrocarbon solvents may be 1% by mass or more and 20% by mass or less, 3% by mass or more and 15% by mass or less, or 5% by mass or more and 10% by mass or less, relative to the total amount of the conductive paste.

[0091] Furthermore, when the conductive paste contains diisobutyl ketone, the total content of diisobutyl ketone is preferably 1% by mass or more and 20% by mass or less, or may be 3% by mass or more and 15% by mass or less, or may be 3% by mass or more and 10% by mass or less, relative to the total amount of the conductive paste.

[0092] More specifically, a mixed solvent obtained by mixing dihydroterpineol (DHT): mineral spirits A (MSA): one or more ether solvents selected from the group consisting of propylene glycol monobutyl ether (PNB), propylene glycol monomethyl ether acetate (PMA), and diethylene glycol monobutyl ether acetate (BCA) in a mass ratio of 40-60:10-30:20-40 can be used as the organic solvent, and a mixed solvent in this mass ratio of 46-56:10-30:24-37 can be used as the organic solvent.

[0093] (dispersant) The carboxyl group-containing polymer dispersant of the present invention is contained in an amount of 0.01% by mass or more but less than 2.0% by mass, preferably 0.01% by mass or more but less than 1.0% by mass, and more preferably 0.03% by mass or more but less than 0.5% by mass, relative to 100% by mass of the entire conductive paste. When the carboxyl group-containing polymer dispersant is contained in the above range, the conductive paste can stably maintain a low viscosity state for a long period of time and can suppress separation of the conductive powder and the ceramic powder.

[0094] The dispersant may be composed solely of the carboxyl-containing polymer dispersant represented by the general formula (1) above, or may contain a dispersant other than the carboxyl-containing polymer dispersant, as described below. When a dispersant other than the carboxyl-containing polymer dispersant is contained, the content of the carboxyl-containing polymer dispersant may be, for example, 30% by mass or more, preferably 60% by mass or more, and more preferably 80% by mass or more, based on the total amount of the dispersant. The greater the content of the carboxyl-containing polymer dispersant based on the total amount of the dispersant, the more effective it is in preventing separation between the conductive powder and the ceramic powder.

[0095] The conductive paste of this embodiment may further contain an acid-based dispersant (a dispersant having an acidic adsorption group) other than the carboxyl group-containing polymer dispersant. Examples of the acid-based dispersant (other than the carboxylic acid-based polymer dispersant) include acid-based dispersants having a mass average molecular weight of less than 2000. The acid-based dispersants may be used alone or in combination of two or more.

[0096] Examples of acid-based dispersants with a mass average molecular weight of less than 2000 include higher fatty acids, dicarboxylic acids, polycarboxylic acid-based dispersants, and carboxylic acid-based dispersants such as alkyl monoamine salts. When a conductive paste contains an acid-based dispersant with a mass average molecular weight of less than 2000 together with a carboxy group-containing polymer dispersant, the viscosity may be reduced and the dispersibility of ceramic powders such as barium titanate may be improved. Note that the mass average molecular weight of an acid-based dispersant with a mass average molecular weight of less than 2000 may be 1000 or less.

[0097] The higher fatty acid may be either an unsaturated carboxylic acid or a saturated carboxylic acid, and is not particularly limited, but examples include those having 11 or more carbon atoms, such as stearic acid, oleic acid, myristic acid, palmitic acid, linoleic acid, lauric acid, and linolenic acid. Of these, oleic acid or stearic acid is preferred as the higher fatty acid.

[0098] Preferred examples of the alkyl monoamine salt type include oleoyl sarcosine, which is a compound of glycine and oleic acid, and stearic acid amide and lauriloyl sarcosine, which are amide compounds using higher fatty acids such as stearic acid or lauric acid instead of oleic acid.

[0099] In addition, if the content of the acid-based dispersant with an average molecular weight of less than 2000 is too high, there is a concern that it may have adverse effects such as inhibiting the adsorption of the carboxyl group-containing polymer dispersant to the metal powder material (filler). Therefore, when used in combination, it is preferable to adjust the content appropriately.

[0100] For example, the content of the acid dispersant having a mass average molecular weight of less than 2000 may be more than 0 mass% and not more than 70 mass%, preferably not more than 40 mass%, and more preferably not more than 20 mass%, relative to 100 mass% of the total amount of dispersant.

[0101] The dispersant may also contain a dispersant other than an acid-based dispersant. Examples of dispersants other than acid-based dispersants include basic dispersants, nonionic dispersants, and amphoteric dispersants. These dispersants may be used alone or in combination of two or more.

[0102] Examples of basic dispersants include aliphatic amines such as laurylamine, rosinamine, cetylamine, myristylamine, stearylamine, and oleylamine.

[0103] Furthermore, the content of the dispersant (total) is preferably less than 2.0% by mass with respect to the entire conductive paste. If the content of the carboxylic acid polymer dispersant or the total dispersant is too high, drying may be insufficient during the conductive paste printing process or drying process, leaving the internal electrode layers in a soft state, which may result in misalignment of the layers during the subsequent lamination process. Furthermore, residual dispersant may evaporate during firing, and the evaporated gas components may generate internal stress or cause structural damage to the laminate.

[0104] (additives) The conductive paste of the present embodiment may contain additives other than the dispersant as needed, such as conventionally known additives such as antifoaming agents, plasticizers, surfactants, and thickeners.

[0105] For example, Patent Document 3 describes polycarboxylic acid polymers and salts of polycarboxylic acids as separation inhibitors that inhibit separation of conductive powders and dielectric powders, but in this specification, such separation inhibitors are also broadly included in the acid-based dispersants as they improve the dispersibility of inorganic powders.

[0106] (Method of manufacturing conductive paste) The method for producing the conductive paste according to this embodiment is not particularly limited, and a conventionally known method can be used. The conductive paste can be produced, for example, by stirring and kneading the above-mentioned components using a three-roll mill, a ball mill, a mixer, or the like. It is preferable to weigh and add the dicarboxylic acid (separation inhibitor) when stirring and kneading the material using a mixer or the like, just like the other materials. However, the same effect can be obtained by adding the dicarboxylic acid as a separation inhibitor to the material after stirring and kneading (dispersion) has been completed.

[0107] The conductive paste of the present invention is subjected to a shear rate of 100 sec at a temperature of 25°C. -1 The initial viscosity is preferably 2.0 Pa·S or less. Shear rate: 100 sec -1 When the viscosity of the conductive paste is within the above range, it is suitable for high-speed and efficient application. If the viscosity exceeds the above range, the viscosity of the conductive paste becomes too high, and the smoothness of the dried film surface after application may be poor. -1 The lower limit of the viscosity is not particularly limited, but is, for example, 0.2 Pa·S or more. -1 A more preferable range of the initial viscosity is 1.2 Pa·S or more and less than 1.8 Pa·S.

[0108] Also, at a temperature of 25°C, the shear rate is 100 sec -1 The viscosity of the ink preferably does not change over time, and is preferably 125% or less, more preferably 120% or less, and even more preferably 110% or less, when the initial viscosity is taken as 100%.

[0109] Therefore, it is preferable that the initial viscosity is 2.0 Pa·S or less, and considering that the change in viscosity over time is preferably 125% or less, it is preferable that the viscosity itself is 125% or less of the initial viscosity of 2.0 Pa·S, that is, at a temperature of 25°C and a shear rate of 100 sec -1 It is preferable that the viscosity at 2.5 Pa·S or less.

[0110] Furthermore, the thickness of the whitish layer observed one week after preparation of the conductive paste is preferably less than 5% of the total thickness of the conductive paste, and may be 3% or less. The smaller the thickness of the whitish layer, the better the effect of inhibiting separation of the conductive powder and the ceramic powder. The thickness of the whitish layer can be measured by the method described in the Examples below.

[0111] Furthermore, the surface roughness (Sa) of the electrode film obtained by forming a conductive film by screen printing using the prepared conductive paste and then drying and sintering is preferably 0.065 μm or less, more preferably 0.060 μm or less, and even more preferably 0.055 μm or less.

[0112] The conductive paste of this embodiment can be suitably used in electronic components such as multilayer ceramic capacitors. Multilayer ceramic capacitors have dielectric layers and internal electrode layers formed using dielectric green sheets, and the conductive paste of this embodiment can be suitably used to form the internal electrode layers.

[0113] [Electronic Components] An example of an electronic component according to this embodiment will be described below with reference to the drawings. The drawings may be used in schematic form or with a different scale, as appropriate. The positions and directions of components will be described with reference to the XYZ Cartesian coordinate system shown in FIGS. 1A and 1B. In this XYZ Cartesian coordinate system, the X and Y directions are horizontal, and the Z direction is vertical (up-down).

[0114] 1A and 1B are a perspective view and a side cross-sectional view showing an example of an electronic component, a multilayer ceramic capacitor 1. The multilayer ceramic capacitor 1 includes a laminate 10 in which dielectric layers 12 and internal electrode layers 11 are alternately stacked, and external electrodes 20.

[0115] An example of a method for manufacturing a multilayer ceramic capacitor 1 using the above-mentioned conductive paste will be described below. First, the conductive paste is gravure-printed on a ceramic green sheet (dielectric green sheet) and dried to form a dry film. A plurality of ceramic green sheets having this dry film on their upper surfaces are laminated by pressure bonding to obtain a laminate, and the laminate is then fired and integrated to produce a ceramic laminate 10 in which internal electrode layers 11 and dielectric layers 12 are alternately laminated. Thereafter, a pair of external electrodes 20 is formed on both ends of the ceramic laminate 10 to manufacture the multilayer ceramic capacitor 1. This will be described in more detail below.

[0116] First, a ceramic green sheet, which is an unfired ceramic sheet, is prepared. Examples of the ceramic green sheet include a dielectric layer paste obtained by adding an organic binder such as polyvinyl butyral and a solvent such as terpineol to a predetermined ceramic raw material powder such as barium titanate, and then coating the paste on a support film such as a PET film in a sheet form and drying it to remove the solvent. The thickness of the ceramic green sheet is not particularly limited, but is preferably 0.05 μm or more and 3 μm or less in view of the demand for miniaturization of multilayer ceramic capacitors.

[0117] Next, the conductive paste is applied by gravure printing to one side of the ceramic green sheet, and then dried to form a dry film, to prepare a plurality of sheets. Note that, from the viewpoint of the requirement for thinning of the internal electrode layer 11, the thickness of the dry film after drying is preferably 1 μm or less.

[0118] Next, the ceramic green sheets are peeled off from the support film, and the ceramic green sheets and the dried film formed on one side thereof are stacked alternately, followed by a heat and pressure treatment to obtain a laminate. Note that protective ceramic green sheets not coated with the conductive paste may also be placed on both sides of the laminate.

[0119] Next, the laminate is cut to a predetermined size to form green chips, which are then subjected to a binder removal treatment and fired in a reducing atmosphere to produce a fired laminated ceramic body (ceramic laminate 10). The binder removal treatment is preferably performed in air or an N2 gas atmosphere. The temperature during the binder removal treatment is, for example, 200°C or higher and 400°C or lower. The temperature is preferably maintained for 0.5 hours or higher and 24 hours or lower during the binder removal treatment. The firing is performed in a reducing atmosphere to prevent oxidation of the metals used in the internal electrode layers. The temperature during firing of the laminate is, for example, 1000°C or higher and 1350°C or lower, and the temperature is preferably maintained for 0.5 hours or higher and 8 hours or lower during firing.

[0120] By firing the green chip, the organic binder in the green sheet is completely removed, and the ceramic raw material powder is fired to form the ceramic dielectric layers 12. Also, the organic vehicle in the internal electrode layers 11 is removed, and the nickel powder or nickel-based alloy powder is sintered or melted and integrated to form the internal electrodes, forming a multilayer ceramic sintered body in which multiple dielectric layers 12 and internal electrode layers 11 are alternately stacked. Note that, from the viewpoint of incorporating oxygen into the dielectric layers to increase reliability and suppressing reoxidation of the internal electrodes, the sintered multilayer ceramic sintered body may be subjected to an annealing treatment.

[0121] Then, a pair of external electrodes 20 is provided on the produced fired multilayer ceramic body, thereby producing a multilayer ceramic capacitor 1. For example, the external electrodes 20 include an external electrode layer 21 and a plating layer 22. The external electrode layer 21 is electrically connected to the internal electrode layer 11. Suitable materials for the external electrodes 20 include, for example, copper, nickel, or alloys thereof. The electronic component is not limited to a multilayer ceramic capacitor, and electronic components other than a multilayer ceramic capacitor, such as a varistor, can also be used. [Example]

[0122] EXAMPLES The present invention will be described in detail below based on examples and comparative examples, but the present invention is not limited to these examples.

[0123] [Calculation of Ra of dispersant and evaluation of dispersibility] Evaluation Method (Calculation of Ra of dispersant) The HSP of the dispersant was calculated by the following steps (1) to (3). Note that HSPIP software was used for steps (2) and (3) and for calculating Ra.

[0124] (1) The solubility of dispersants in solvents with known HSPs was investigated. The solvents used were hexane, diethyl ether, tetrahydrofuran, cyclohexane, toluene, ethyl acetate, benzene, chloroform, dichloromethane, acetone, 2-propanol, acetonitrile, N,N-dimethylformamide (DMF), ethanol, dimethyl sulfoxide (DMSO), methanol, and water. The solubility evaluation procedure was as follows: the solvent and dispersant were weighed out in a weight ratio of 100:1, stirred with a stirrer at room temperature for 30 minutes, and then left to stand at room temperature for a further 24 hours. If the solution was transparent and uniform, the dissolution was considered good; otherwise, such as when cloudy, the dissolution was considered poor.

[0125] (2) In the Hansen space, we sought a sphere that contained only the solvent points that dissolved the dispersant well among the solvents whose solubility was investigated. (3) The center coordinates of the sphere were defined as the HSP of the dispersant.

[0126] The distance (Ra) between the Hansen solubility parameter of the dispersant and the Hansen solubility parameter of the solvent was calculated using the formula shown in [Mathematical Expression 2]. The results are shown in Table 1. The solvents used here were selected in consideration of the solvent composition of the conductive paste, with mass ratios of dihydroterpineol: mineral spirits A: propylene glycol monobutyl ether = 53:20:27, dihydroterpineol: mineral spirits A: propylene glycol monobutyl ether = 46:30:24, dihydroterpineol: mineral spirits A: propylene glycol monobutyl ether = 56:20:24, dihydroterpineol: mineral spirits A: propylene glycol monobutyl ether = 53:10:37 ... Mixtures of dihydroterpineol, mineral spirits A, propylene glycol monobutyl ether = 53:30:17, dihydroterpineol, mineral spirits A, propylene glycol monomethyl ether acetate = 53:20:27, dihydroterpineol, mineral spirits A, diethylene glycol monobutyl ether acetate = 53:20:27, dihydroterpineol, mineral spirits A = 53:47, dihydroterpineol, propylene glycol monobutyl ether = 53:47, and dihydroterpineol, isobutanol = 53:47 were used. In Comparative Examples 14 and 15, only dihydroterpineol was used.

[0127]

number

[0128] (Evaluation of dispersibility) A mixture of conductive powder, dispersant, and solvent in a mass ratio of 0.1:0.1:100 was stirred using ultrasonic treatment to form a slurry, and the average particle size of the conductive powder in the slurry was measured using dynamic light scattering (DLS) to compare and evaluate the average particle size. The results of the average particle size measurements are shown in Table 1. In Table 1, an average particle size of less than 350 nm was evaluated as having good dispersibility and marked with a circle, while an average particle size of 350 nm or greater was evaluated as not having good dispersibility and marked with an ×. Figure 2 also shows the Ra and dispersibility evaluation results for the dispersant.

[0129] (Dispersants used in evaluation) A carboxyl group-containing polymeric dispersant, which is a copolymer of acrylic acid and an acrylic ester (general formula (1)) with a linear or branched alkyl group and has a mass average molecular weight of 2000 or more, was used, along with a commercially available high molecular weight dispersant for comparison. Table 1 shows the ratio of acrylic acid (X) in the molar ratio during copolymerization, the number of carbon atoms in the alkyl group, the structure of the alkyl group, the name of the acrylic ester, and the mass average molecular weight.

[0130] As an example of the synthesis of a carboxyl group-containing polymeric dispersant, the synthesis procedure for the carboxyl group-containing polymeric dispersant of Comparative Example 2 is shown below. Note that Examples 1 to 9 and other Comparative Examples can also be synthesized in the same manner as the synthesis procedure below by changing the molar ratio of acrylic acid to acrylic acid ester so as to change the structure of the alkyl group of the acrylic acid ester or the ratio (X) of acrylic acid, or by adjusting the synthesis temperature, synthesis time, or amount of chain transfer agent added.

[0131] The main raw material monomers, acrylic acid (12.2 mmol) and acrylic acid ester (2-ethylhexyl acrylate, 48.8 mmol), the polymerization initiator AIBN (0.603 mmol), the chain transfer agent dodecanethiol (0.722 mmol), and 50 mL of 1,4-dioxane were added to a three-neck flask. The solvent was bubbled with nitrogen in an ice bath and then stirred under a nitrogen atmosphere at 65 °C for 12 hours. Methanol was then added to reprecipitate the mixture, followed by three rounds of decantation via centrifugation. Finally, the mixture was dissolved in benzene and freeze-dried to obtain a polymeric dispersant. The resulting polymeric dispersant was analyzed by NMR (nuclear magnetic resonance) and SEC (size exclusion chromatography) to determine the acrylic acid ratio (X) and mass-average molecular weight. 2-Mercaptoethanol can also be used as a chain transfer agent.

[0132] [Table 1]

[0133] (Evaluation results) 2, the Ni powder was dispersed well in Examples 1 to 3 where Ra was 5.5 or more and 7.5 or less. When Ra was less than 5.5 or more than 7.5 (Comparative Examples 1 to 4), the average particle size of the Ni powder after dispersion treatment was large, resulting in poorer dispersibility compared to Examples 1 to 3.

[0134] [Preparation of conductive paste and evaluation of its properties] Conductive pastes were prepared using the synthetic dispersants whose characteristics are shown in Table 1, and the physical properties of the conductive pastes and the electrode films prepared from the conductive pastes were evaluated.

[0135] <Preparation of conductive paste> The material used was 50 mass% Ni powder (number average particle diameter 0.2 μm as observed by SEM), 34.7 mass% of a mixed solvent with a mass ratio of dihydroterpineol:mineral spirit A:propylene glycol monobutyl ether = 53:20:27 as the solvent, and 0.3 mass% of each dispersant listed in Table 1. Furthermore, 0.75 mass% of ethyl cellulose and 1.75 mass% of polyvinyl butyral were used as the binder resin, and 12.5 mass% of barium titanate was used as the ceramic powder. These materials were mixed using a three-roll mill to prepare a conductive paste.

[0136] <Evaluation of the physical properties of conductive paste> (Viscosity evaluation) After leaving the conductive paste at room temperature (25°C) for one day and one month, the viscosity of each conductive paste was measured using a rheometer (Anton Paar MCR501 rheometer) at a rotation speed of 100 sec. -1 The viscosity after standing for one day was used as the reference viscosity, and the viscosity after standing for one month was divided by the reference viscosity and multiplied by 100 to calculate the change in viscosity (%).

[0137] (Evaluation of white cast) Immediately after manufacturing the conductive paste, the paste was placed in a glass sample bottle and left to stand at room temperature (25°C) for one month. The conductive paste was then evaluated for the condition of "white floating," where a white separation layer appears on top. Specifically, the ratio (%) of the thickness of the white floating part to the height of the conductive paste was calculated.

[0138] <Evaluation of electrode film properties> Using an applicator, the conductive paste was applied to a glass plate to a wet film thickness of 10 μm. The glass plate was then placed in an oven set at 120°C and dried for 20 minutes to obtain a dried film of the conductive paste. This dried film served as the electrode film. The average roughness of the dried film was measured using a laser microscope (Keyence Corporation, VK-X3000) over a measurement area of ​​200 × 250 μm, and measurements were repeated at five random locations. The average of the obtained values ​​was taken as the arithmetic mean roughness (Ra) of the dried conductive paste film and was used as a measure of smoothness.

[0139] The conductive pastes were evaluated for their initial viscosity, viscosity change rate over time, whitening, and surface roughness of the electrode films fabricated using them. The evaluation results are shown in Table 2. In the evaluations in Table 2, initial viscosity was evaluated as ○ if it was 2 Pa·s or less, and × if it exceeded 2 Pa·s. Viscosity change was evaluated as ○ if it was 120% or less, and × if it exceeded 120%. Whitening was evaluated as ○ if it was 5% or less, and × if it exceeded 5%. Regarding the physical properties of the electrode film, a surface roughness Ra of 0.06 μm or less was evaluated as ○, and × if it exceeded 0.06 μm. The overall evaluation was ○ if the initial viscosity, viscosity change, whitening, and electrode film physical properties were all evaluated as ○, and × if any one of these was evaluated as ×.

[0140] [Table 2]

[0141] Table 3 also shows the Hansen solubility parameters δD (dispersion parameter), δP (polarity parameter), and δH (hydrogen bond parameter) of the solvents used in this study, as well as their viscosities at 20°C. In Table 3, DHT is dihydroterpineol, MSA is mineral spirits A, PNB is propylene glycol monobutyl ether, PMA is propylene glycol monomethyl ether acetate, BCA is diethylene glycol monobutyl ether acetate, and IBA is isobutanol.

[0142] [Table 3]

[0143] (Evaluation results) The conductive pastes of Examples 1 to 9 were rated as good in terms of initial viscosity, viscosity change, whitening, and electrode film properties, and it is clear that they are conductive pastes that can solve the problems of the present invention. [Industrial Applicability]

[0144] The conductive paste of the present invention has a viscosity suitable for gravure printing that is stable over a long period of time, exhibits sufficiently small separation between the conductive powder and the ceramic powder, and produces a dried film with sufficiently low surface roughness after drying. Therefore, the conductive paste of the present invention can be suitably used as a raw material for internal electrodes of multilayer ceramic capacitors, which are chip components in electronic devices that are becoming increasingly miniaturized, such as mobile phones and digital devices, and can be suitably used as a conductive paste for gravure printing. [Explanation of symbols]

[0145] 1. Multilayer ceramic capacitors 10. Ceramic laminate 11 Internal electrode layer 12 Dielectric layer 20 External electrode 21 External electrode layer 22 plating layer

Claims

1. At least one of acrylic acid and methacrylic acid, A carboxyl group-containing polymer dispersant comprising a copolymer with at least one of an acrylic acid ester represented by the following general formula (1) and a methacrylic acid ester represented by the following general formula (2), The mass average molecular weight is 2,000 or more and less than 30,000, a molar ratio of the total of the acrylic acid and the methacrylic acid to the total of the acrylic acid ester and the methacrylic acid ester is X:1-X, where X is 0.1 or more and less than 0.4; In the following general formula (1) and the following general formula (2), R １ is a linear or branched alkyl group, The distance (Ra) between the Hansen solubility parameter of the dispersant and the Hansen solubility parameter of the solvent is 5.5 or more and 7.5 or less; The solvent is a mixed solvent obtained by mixing dihydroterpineol, a hydrocarbon-based solvent having a viscosity of less than 3 mPa·s at 20°C, and an ether-based solvent having a viscosity of less than 5 mPa·s at 20°C and having Hansen solubility parameters δD of 15 to 17, δP of 4 to 6, and δH of 8 to 10, in a mass ratio of 40 to 60:10 to 30:20 to 40. 【Chemistry 1】 【Chemistry 2】

2. 2. The dispersant according to claim 1, wherein the hydrocarbon solvent comprises mineral spirits A, and the ether solvent comprises one or more solvents selected from the group consisting of propylene glycol monobutyl ether, propylene glycol monomethyl ether acetate, and diethylene glycol monobutyl ether acetate.

3. A conductive paste comprising the carboxy group-containing polymer dispersant according to claim 1.

4. Further comprising a conductive powder, a ceramic powder, a binder resin, and an organic solvent; The conductive paste according to claim 3 , wherein the content of the carboxy group-containing polymer dispersant is 0.01% by mass or more and less than 2.0% by mass.

5. 5. The conductive paste according to claim 4, wherein the organic solvent comprises at least one solvent selected from the group consisting of terpene-based solvents, glycol ether-based solvents, acetate-based solvents, acetate ester-based solvents, ketone-based solvents, and hydrocarbon solvents.

6. 5. The conductive paste according to claim 4, wherein the organic solvent comprises one or more selected from the group consisting of dihydroterpineol, mineral spirits A, propylene glycol monobutyl ether, propylene glycol monomethyl ether acetate, and diethylene glycol monobutyl ether acetate.

7. the conductive paste contains a dispersant other than the carboxy group-containing polymer dispersant, The conductive paste according to claim 3 , wherein the content of the carboxyl group-containing polymer dispersant relative to the total amount of dispersants in the conductive paste is 30 mass % or more.

8. the conductive paste contains, as a dispersant other than the carboxy group-containing polymer dispersant, an acid-based dispersant having a mass average molecular weight of less than 2000; The conductive paste according to claim 7 , wherein the content of the acid dispersant relative to the total amount of dispersants in the conductive paste is more than 0 mass % and not more than 70 mass %.

9. The conductive paste according to claim 4 , wherein the conductive powder contains one or more metal powders selected from the group consisting of Ni, Pd, Pt, Au, Ag, Cu, and alloys thereof.

10. The conductive paste according to claim 4 , wherein the number average particle size of the conductive powder is 0.05 μm or more and 1.0 μm or less.

11. The conductive paste of claim 4 , wherein the ceramic powder comprises barium titanate.

12. 5. The conductive paste according to claim 4, wherein the number average particle size of the ceramic powder is 0.01 [mu]m or more and 0.5 [mu]m or less.

13. The conductive paste according to claim 4 , wherein the content of the ceramic powder is 1% by mass or more and 20% by mass or less.

14. The conductive paste according to claim 4 , wherein the binder resin comprises a cellulose-based resin.

15. The conductive paste according to claim 3, which is used for internal electrodes of multilayer ceramic parts.

16. Shear rate 100 sec at 25°C －１ 4. The conductive paste according to claim 3, having a viscosity of 2.5 Pa·S or less at 1000 kJ / min.

17. An electronic component formed using the conductive paste according to claim 3.

18. The laminate has at least a laminate of dielectric layers and internal electrode layers, 4. A multilayer ceramic capacitor, wherein the internal electrode layers are formed using the conductive paste according to claim 3.

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