Carboxy group-containing polymeric dispersant, conductive paste, electronic component, and laminated ceramic capacitor

Abstract

Provided are: a low-viscosity conductive paste which has favorable viscosity stability over time and with which the separation between conductive powder and ceramic powder can be suppressed; a carboxy group-containing polymeric dispersant; an electronic component; and a laminated ceramic capacitor.　This carboxy group-containing polymeric dispersant comprises a copolymer of at least one of acrylic acid or methacrylic acid and at least one of an acrylic acid ester represented by general formula (1) or a methacrylic acid ester represented by general formula (2), wherein: said dispersant has a mass-average molecular weight of at least 2,000 and less than 30,000; the ratio of the total (X) of the acrylic acid and the methacrylic acid and the total (1-X) of the acrylic acid ester and the methacrylic acid ester, in terms of molar ratio, is X:1-X; and the distance (Ra) between the Hansen solubility parameter of said dispersant and the Hansen solubility parameter of a solvent is 5.5-7.5.

Description

Carboxy group-containing polymer dispersants, conductive pastes, electronic components, and multilayer ceramic capacitors

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

[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] For example, a multilayer ceramic capacitor is manufactured as follows: First, barium titanate (BaTiO ３ A multilayer laminate is obtained by stacking multiple layers of dielectric green sheets containing dielectric powder such as ethylenediaminetetraacetic acid (EPO) and binder resin, on the surface of which is printed an internal electrode paste (conductive paste) containing conductive powder, binder resin, and organic solvent, etc., in a predetermined electrode pattern. The laminate is then integrated by heat and pressure bonding to form a pressed body. The pressed body is then cut, subjected to an organic binder removal treatment 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, and 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 wt % of a solid component including a metal powder, 1 to 10 wt % of an ethyl cellulose resin component having an ethoxy group content of 49.6% or more, 0.05 to 5 wt % of a dispersant, and a solvent component as the balance, 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 a solvent component as the remainder, and which is capable of being applied at a shear rate of 0.1 (s －１ A thixotropic fluid having a viscosity of 1 Pa·s or more at a shear rate of 0.1 (s －１ ) is used as the viscosity reference, －１ ) has a viscosity change rate of 50% or more.

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

[0009] Patent Document 3 (JP-A-2003-102666) 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), in which the organic resin (B) is polyvinyl butyral having a degree of polymerization of 10,000 to 50,000 and ethyl cellulose having 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.

[0010] JP 2003-187638 A JP 2003-242835 A JP 2012-174797 A

[0011] As electronic components become smaller, electrodes, wiring, and the like formed by printing conductive paste are becoming thinner. To apply the conductive paste thinly and smoothly, a low viscosity is required. However, when a ceramic powder such as barium titanate and a conductive powder such as Ni are added to a low-viscosity conductive paste, 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 of the paste becomes non-uniform in this way, the smoothness of the dried film surface after application cannot be obtained. For example, when 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 obtained.

[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.

[0015] In order to solve the above problems, the dispersant of the present invention is a carboxy group-containing polymer dispersant consisting of 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 2,000 or more and less than 30,000, and the molar ratio of the total of the acrylic acid and the methacrylic acid (X) to the total of the acrylic acid ester and the methacrylic acid ester (1-X) is X:1-X, where X is 0.1 or more and less than 0.4, and in the following general formulas (1) and (2), R １is 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 having Hansen solubility parameters of δD of 15 to 17, δP of 4 to 6, and δH of 8 to 10, in a mass ratio of 40-60:10-30:20-40.

[0016]

[0017]

[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 mass % or more and less than 2.0 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-based 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 has 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.

[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.

[0036] 1A is a perspective view showing a multilayer ceramic capacitor according to an embodiment of the present invention, and FIG. 1B is a cross-sectional view showing a multilayer ceramic capacitor according to an embodiment of the present invention. It is a graph showing the effect of the distance Ra of the dispersant on the dispersibility of the conductive powder.

[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 carboxy group-containing polymer dispersant of the present invention is a carboxy group-containing polymer dispersant comprising a copolymer of at least either acrylic acid or methacrylic acid and 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), wherein the mass average molecular weight is 2,000 or more and less than 30,000, and the molar ratio of the total of the acrylic acid and the methacrylic acid (X) to the total of the acrylic acid ester and the methacrylic acid ester (1-X) is X:1-X, where X is 0.1 or more and less than 0.4. Here, in the following general formulas (1) and (2), R １ is a straight or branched alkyl group.

[0039]

[0040]

[0041] The inventors have found that the low-viscosity conductive paste described below has a stable low viscosity with little change in viscosity 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] Furthermore, by adjusting the molar ratio of the total of acrylic acid and methacrylic acid (X) to the total of acrylic acid ester and methacrylic acid ester (1-X) during copolymerization, the solubility in organic solvents and the dispersibility of the conductive powder can be changed. If the total ratio of acrylic acid and methacrylic acid (X) is too low, the amount of carboxyl groups that act as adsorbing groups for the conductive powder is small, resulting in poor dispersibility. On the other hand, if the total ratio of acrylic acid and methacrylic acid (X) is too high, the hydrophilicity of the carboxyl group-containing polymer dispersant increases, resulting in poor solubility in the organic solvent used in the conductive paste.

[0046] Therefore, there is an appropriate molar ratio between the total of acrylic acid and methacrylic acid (X) and the total of acrylic acid ester and methacrylic acid ester (1-X). That is, when the total of acrylic acid and methacrylic acid (X) 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, and 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] In addition, R of the acrylic acid ester and the methacrylic acid ester shown in the general formula (1) and the general formula (2) １ is a linear or branched alkyl group. １ When is a linear alkyl group, the number of carbon chains is preferably 2 or more and 10 or less, and more preferably 2 or more and 4 or less. 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 it is copolymerized and used as a dispersant, the effect of suppressing separation of the conductive paste may not be sufficiently exhibited, which is not preferred. Also, 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 it is copolymerized and used as a dispersant, the effect of suppressing separation of the conductive paste may not be sufficiently exhibited, and the surface roughness and density of the dried film after forming a film from the conductive paste by gravure printing or the like may deteriorate, which is not preferred.

[0048] Also, R １ When R is a branched alkyl group, １ The total number of carbon atoms 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, resulting in the prevention of separation of the conductive powder and the ceramic powder, 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 preventing separation of the conductive paste may not be fully exerted, or the surface roughness and density of the dried film formed from the conductive paste may be deteriorated.

[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 perspective 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 found that the HSP can be used as an index for the dispersibility of a dispersant in a conductive powder, and the dispersant of the present invention was thus conceived.

[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 has a low viscosity and can stably maintain a low paste viscosity for a long period of time, and can suppress separation of the conductive powder and the ceramic powder.

[0052] (Method for Evaluating Dispersibility) The dispersibility of a dispersant in a 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 by ultrasonic treatment to form a slurry, and the average particle size of the conductive powder in the slurry is measured by 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 effect in suppressing separation between the conductive powder and the ceramic powder, or the surface roughness of the film obtained by drying the conductive paste may be large.

[0055] (Solvent) The solvent that can be used to calculate Ra and evaluate the dispersibility of a dispersant can be the same organic solvent as the conductive paste described below, or a mixture of two or more organic solvents at a predetermined mixing ratio can be used. For example, a mixed solvent can be used that is composed of 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 a Hansen solubility parameter δD (dispersion parameter) of 15 to 17, δP (polarity parameter) of 4 to 6, and δH (hydrogen bonding parameter) of 8 to 10, mixed 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 be used.

[0060] (Method for calculating Hansen solubility parameters of dispersants) The HSP of a dispersant can be calculated using the following procedure. (1) Check the solubility of the dispersant in solvents (15 to 20 types) whose HSP is known. (2) In Hansen space, find a sphere that contains only the points of the solvents in which the dispersant has been dissolved, among the solvents whose solubility has been checked. (3) Determine the center coordinates of that sphere as the HSP of the dispersant.

[0061] The procedure for calculating the HSP of the dispersant can be performed 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] In the above formula 1, is the energy due to the dispersion forces between solvent molecules, is the energy due to the dispersion force between dispersant molecules, is the energy due to dipole-dipole interactions between solvent molecules, is the energy due to the dipole-dipole interaction between dispersant molecules, is the energy due to hydrogen bonds between solvent molecules, is the energy due to hydrogen bonds between dispersant molecules.

[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. For example, powders of one or more elements selected from Ni, Pd, Pt, Au, Ag, Cu, and alloys thereof can be used. Among these, powders of Ni or its alloys (Ni alloys) are preferred from the viewpoints of conductivity, corrosion resistance, and cost. As the Ni alloy, for example, an alloy 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 can be used. 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 element S to suppress rapid gas generation due to partial thermal decomposition of the binder resin during debinding.

[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 in the above range, it can be suitably used as an internal electrode paste for a thin-film multilayer ceramic capacitor (multilayer ceramic component), 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 a plurality of particles in an image observed with the SEM at a magnification of 10,000 times.

[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 amount of the conductive paste. When the content of the conductive powder is within the above range, the conductive paste has excellent conductivity and dispersibility.

[0068] (Ceramic Powder) The ceramic powder is not particularly limited, and for example, in the case of a paste for an internal electrode of a multilayer ceramic capacitor, a known ceramic powder is appropriately selected depending on the type of multilayer ceramic capacitor to be applied. As the ceramic powder, for example, a perovskite oxide containing Ba and Ti can be used, and preferably barium titanate (BaTiO ３ ) is included.

[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. Examples of such ceramic powder include barium titanate (BaTiO ３ Examples of suitable perovskite-type oxide ferroelectric ceramic powders include those in which Ba atoms and Ti atoms are substituted with other atoms such as Sn, Pb, Zr, etc.

[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 mismatch in shrinkage. Examples of such ceramic powders include, in addition to the perovskite oxides containing Ba and Ti, ZnO, ferrite, PZT, BaO, Al, etc. ２ O ３ , Bi ２ O ３ , R (rare earth element) ２ O ３ , TiO ２ , Nd ２ O ３ The ceramic powder may be one type or two or more types.

[0071] The number average particle diameter of the ceramic powder is, for example, 0.01 μm or more and 0.5 μm or less, preferably 0.01 μm or more and 0.3 μm or less. 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 thin, 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 a plurality of 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 conductive paste has excellent dispersibility and sinterability.

[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 conductive powder has excellent conductivity and dispersibility.

[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, ethyl hydroxyethyl cellulose, and nitrocellulose; acrylic resins; and acetal-based resins containing butyral-based resins such as polyvinyl butyral. Among these, cellulose-based resins are 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, the binder resin may contain a butyral-based resin, or a butyral-based resin may be used alone, from the viewpoint of improving 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 the 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 total binder resin. The binder resin may contain 50% by mass or less of an acetal resin based on the total amount of the 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 or more and 10% by mass or less, more preferably 1% by mass or more and 7% by mass or less, based on the total amount of the conductive paste. When the content of the binder resin is in 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 conductive powder has excellent conductivity and dispersibility.

[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-based 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 a 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-based 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-based 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 conductive powder has excellent conductivity and dispersibility.

[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, relative to the total amount of the conductive paste.

[0090] When the conductive paste contains hydrocarbon-based solvents, the total content of the hydrocarbon-based solvents may be 1 mass % or more and 20 mass % or less, 3 mass % or more and 15 mass % or less, or 5 mass % or more and 10 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 mass % or more and 20 mass % or less, or may be 3 mass % or more and 15 mass % or less, or may be 3 mass % or more and 10 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 group-containing polymer dispersant represented by the general formula (1) above, or may contain a dispersant other than the carboxyl group-containing polymer dispersant, as described below. When a dispersant other than the carboxyl group-containing polymer dispersant is contained, the content of the carboxyl group-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 group-containing polymer dispersant based on the total amount of the dispersant, the better the effect of suppressing 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 an acid-based dispersant 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 having 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 having 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 having a mass average molecular weight of less than 2000 may be 1000 or less.

[0097] The higher fatty acid may be an unsaturated carboxylic acid or a saturated carboxylic acid, and is not particularly limited, but examples thereof 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] If the content of the acid-based dispersant having 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-based 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 the 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 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, causing the internal electrode layers to become soft, which may result in lamination misalignment during the subsequent lamination process. Furthermore, the dispersant remaining during firing may evaporate, and the evaporated gas components may generate internal stress or cause structural destruction of the laminate.

[0104] (Additives) The conductive paste of the present embodiment may contain additives other than the dispersant as needed. Examples of the additives that can be used include 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 powder and dielectric powder, but in this specification, such separation inhibitors are also included in the acid-based dispersants in a broad sense as agents that improve the dispersibility of inorganic powders.

[0106] (Method for manufacturing conductive paste) The method for manufacturing the conductive paste according to this embodiment is not particularly limited, and a conventionally known method can be used. The conductive paste can be manufactured, for example, by stirring and kneading the above-described components using a triple roll mill, a ball mill, a mixer, or the like. Note that, like the other materials, the dicarboxylic acid (separation inhibitor) is preferably weighed and added when stirring and kneading using a mixer or the like, but the same effect can be obtained by adding it as a separation inhibitor to the materials after stirring and kneading (dispersion) has been completed.

[0107] The conductive paste of the present invention has a shear rate of 100 sec at a temperature of 25°C. －１ The initial viscosity is preferably 2.0 Pa·S or less. －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 and a shear rate of 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 suppressing 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 a screen printing method 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 Component] An example of an electronic component according to this embodiment will be described below with reference to the drawings. The drawings may be represented schematically or at a different scale as appropriate. The positions and directions of components will be described with reference to the XYZ Cartesian coordinate system shown in Figures 1A and 1B as appropriate. In this XYZ Cartesian coordinate system, the X and Y directions are horizontal, and the Z direction is vertical (up-down).

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

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

[0119] Next, the laminate is cut into a predetermined size to form green chips, and the green chips are subjected to a binder removal treatment and fired in a reducing atmosphere to produce a fired laminated ceramic body (ceramic laminate 10). The atmosphere in the binder removal treatment is air or N ２ It is preferable to carry out the debinding treatment in a gas atmosphere. The temperature during the debinding treatment is, for example, 200°C or higher and 400°C or lower. Furthermore, it is preferable to hold the above temperature for 0.5 hours or higher and 24 hours or lower during the debinding treatment. Furthermore, the firing is carried out in a reducing atmosphere to suppress oxidation of the metal used in the internal electrode layers, and the temperature during firing of the laminate is, for example, 1000°C or higher and 1350°C or lower, and the temperature holding time during firing is, for example, 0.5 hours or higher and 8 hours or lower.

[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 the alloy powder mainly composed of nickel is sintered or melted and integrated to form the internal electrodes, thereby forming a multilayer ceramic fired body in which a plurality of dielectric layers 12 and internal electrode layers 11 are alternately stacked. Note that, from the viewpoint of taking oxygen into the dielectric layers to increase reliability and suppressing reoxidation of the internal electrodes, the fired multilayer ceramic fired 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 the multilayer ceramic capacitor 1. For example, the external electrodes 20 include an external electrode layer 21 and a plating layer 22. The external electrode layer 21 is electrically connected to the internal electrode layer 11. Note that, for example, copper, nickel, or an alloy thereof can be suitably used as the material for the external electrodes 20. Note that the electronic component is not limited to a multilayer ceramic capacitor, and electronic components other than a multilayer ceramic capacitor, such as a varistor, can also be used.

[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 was evaluated by weighing the solvent and dispersant at a weight ratio of 100:1, stirring with a stirrer at room temperature for 30 minutes, and then leaving the solution to stand for 24 hours at room temperature. If the solution was transparent and uniform, the solubility was considered good. If the solution was cloudy or otherwise, the solubility was considered poor.

[0125] (2) In the Hansen space, a sphere was found that contained only the solvent points that successfully dissolved the dispersant among the solvents whose solubility was investigated. (3) The central coordinates of the sphere were determined to be 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 [Equation 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 ... The following mixed solvents were used: 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, dihydroterpineol: isobutanol = 53:47. In Comparative Examples 14 and 15, only dihydroterpineol was used.

[0127]

[0128] (Evaluation of Dispersibility) A mixture of conductive powder, dispersant, and solvent in a mass ratio of 0.1:0.1:100 was stirred by ultrasonic treatment to form a slurry. 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 average particle size measurement results are shown in Table 1. In Table 1, an average particle size of less than 350 nm was evaluated as having good dispersibility, and an average particle size of 350 nm or more was evaluated as not having good dispersibility, and an × was used. Figure 2 shows a graph showing the effect of the distance Ra of the dispersant on the dispersibility of the conductive powder. In Figure 2, the evaluation results of the dispersant are plotted with the distance Ra of the dispersant on the X axis and the average particle size of the conductive powder measured by DLS on the Y axis.

[0129] (Dispersants used in evaluation) A carboxyl group-containing polymeric dispersant, which is a copolymer of acrylic acid and an acrylic acid ester (general formula (1)) having a linear or branched alkyl group and has a mass average molecular weight of 2000 or more, and a commercially available high molecular weight dispersant were used for comparison. Table 2 shows the ratio (X) of acrylic acid 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 acid ester, and the mass average molecular weight.

[0130] As a synthesis example of a carboxy group-containing polymeric dispersant, the synthesis procedure for the carboxy 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] Acrylic acid (12.2 mmol) and an acrylic acid ester (2-ethylhexyl acrylate, 48.8 mmol) were added as main raw material monomers, along with AIBN (0.603 mmol) as a polymerization initiator, dodecanethiol (0.722 mmol) as a chain transfer agent, and 50 mL of 1,4-dioxane as a solvent to a three-neck flask. The solvent was bubbled with nitrogen in an ice bath, and then the mixture was stirred under a nitrogen atmosphere at 65°C for 12 hours. Methanol was then added to cause reprecipitation, and decantation by centrifugation was repeated three times. 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]

[0133]

[0134] 2, the Ni powder was dispersed well in Examples 1 to 3, in which the Ra was 5.5 or more and 7.5 or less. In addition, when the Ra was less than 5.5 or more than 7.5 (Comparative Examples 1 to 5), the average particle size of the Ni powder after dispersion treatment was large, resulting in poorer dispersibility compared to Examples 1 to 3.

[0135] [Preparation of Conductive Paste and Evaluation of Physical Properties] Conductive paste was prepared using the synthetic dispersant whose characteristics are shown in Table 2, and the physical properties of the conductive paste and the electrode film prepared from the conductive paste were evaluated.

[0136] <Preparation of Conductive Paste> 50% by mass of Ni powder (number average particle diameter of 0.2 μm as observed by SEM) was used, 34.7% by mass of a mixed solvent of dihydroterpineol, mineral spirits A, and propylene glycol monobutyl ether (mass ratio: 53:20:27) was used as the solvent, and 0.3% by mass of each of the dispersants shown in Table 2 was used as the dispersant. Furthermore, 0.75% by mass of ethyl cellulose and 1.75% by mass of polyvinyl butyral were used as the binder resin, and 12.5% ​​by mass of barium titanate was used as the ceramic powder. These materials were mixed using a three-roll mill to prepare a conductive paste.

[0137] <Evaluation of Physical Properties of Conductive Paste> (Viscosity Evaluation) After leaving the conductive paste at room temperature (25°C) for one day after production and after leaving it at room temperature (25°C) for one month, the viscosity of each conductive paste was measured by flow curve measurement using a rheometer (Anton Paar MCR501 rheometer) at a rotation speed of 100 sec. －１ The viscosity after standing for one day was defined as the initial viscosity, and the viscosity after standing for one month was divided by the initial viscosity and multiplied by 100 to calculate the change in viscosity (%).

[0138] (Evaluation of Whitening) The conductive paste was placed in a glass sample bottle immediately after production and left to stand at room temperature (25°C) for one month, after which the conductive paste was evaluated for the "whitening" state, where a white separation layer appears on the top. Specifically, the ratio (%) of the thickness of the whitening portion to the height of the conductive paste was calculated.

[0139] <Evaluation of Physical Properties of Electrode Film> Using an applicator, the conductive paste was applied to a glass plate so that the wet film thickness was 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 was used as an electrode film. The average roughness of the dried film was measured using a laser microscope (Keyence Corporation, VK-X3000) within a measurement range 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 Sa of the conductive paste dried film, which was used as a measure of smoothness.

[0140] The initial viscosity of the prepared conductive paste, the rate of viscosity change over time, the degree of whitening, and the surface roughness of the electrode film prepared using the conductive paste were evaluated. The evaluation results are shown in Table 3. In the evaluations in Table 3, the initial viscosity was evaluated as ○ if it was 2 Pa·s or less, as × if it exceeded 2 Pa·s, the viscosity change was evaluated as ○ if it was 120% or less, as × if it exceeded 120%, the whitening was evaluated as ○ if it was 5% or less, as × if it exceeded 5%, and the electrode film physical properties were evaluated as ○ if the surface roughness Sa was 0.06 μm or less, as × if it exceeded 0.06 μm. In addition, the overall evaluation was ○ if the initial viscosity, the viscosity change, the whitening, and the electrode film physical properties were all evaluated as ○, and × if any one of these was evaluated as ×.

[0141]

[0142] Table 4 also shows the Hansen solubility parameters δD (dispersion parameter), δP (polar parameter), and δH (hydrogen bond parameter) of the solvents used this time, as well as their viscosities at 20°C. In Table 4, 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.

[0143]

[0144] (Evaluation Results) The conductive pastes of Examples 1 to 9 were all rated as "good" for 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.

[0145] 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.

[0146] REFERENCE SIGNS LIST 1 Multilayer ceramic capacitor 10 Ceramic laminate 11 Internal electrode layer 12 Dielectric layer 20 External electrode 21 External electrode layer 22 Plated layer

Claims

1. A carboxy 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 2,000 or more and less than 30,000, and the molar ratio of the total of the acrylic acid and the methacrylic acid (X) to the total of the acrylic acid ester and the methacrylic acid ester (1-X) is X:1-X, where X is 0.1 or more and less than 0.4, and in the following general formulas (1) and (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, 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 having Hansen solubility parameters of δD of 15 to 17, δP of 4 to 6, and δH of 8 to 10, in a mass ratio of 40-60:10-30:20-40.

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 carboxyl group-containing polymer dispersant according to claim 1.

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

5. The conductive paste according to claim 4, wherein the organic solvent comprises 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-based solvents.

6. 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 according to claim 3, wherein the conductive paste contains a dispersant other than the carboxyl group-containing polymer dispersant, and 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 according to claim 7, wherein the conductive paste contains 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 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. The conductive paste according to claim 4, wherein the number average particle size of the ceramic powder is 0.01 μm or more and 0.5 μm 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. A multilayer ceramic capacitor comprising at least a laminate in which dielectric layers and internal electrode layers are laminated, the internal electrode layers being formed using the conductive paste according to claim 3.

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