Conductive paste, electronic components, and multilayer ceramic capacitors

Abstract

The present invention provides conductive pastes, electronic components, and multilayer ceramic capacitors that are less prone to sheet attack and exhibit high smoothness of the printed film after screen printing. [Solution] A conductive paste comprising conductive powder, a dispersant, a binder resin, and an organic solvent, wherein the dispersant comprises at least one of a polyalkylene glycol derivative having a mass average molecular weight of 1000 or less and a polyalkylene glycol having a mass average molecular weight of 1000 or less, the organic solvent comprises dihydroterpineol, a hydrocarbon solvent, and an alkanediol, and the content of the organic solvent is 40% by mass or more and 65% by mass or less.

Description

Technical Field

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

Background Art

[0002] With the miniaturization, thinning, and shorting of electronic devices such as mobile phones and digital devices, miniaturization, high capacitance, and high performance are also desired for multilayer ceramic capacitors (MLCCs), which are chip components. The most effective means to achieve these is to reduce the thickness of the internal electrode layer and the dielectric layer and increase the number of layers.

[0003] An MLCC is generally manufactured as follows. First, to form a dielectric layer, a dielectric ceramic powder such as barium titanate (BaTiO3), which is the main component, and a binder resin made of a butyral resin such as polyvinyl butyral or an acrylic resin are used to form a dielectric green sheet. On the surface of the dielectric green sheet, a conductive paste composition in which conductive powder is dispersed in an organic vehicle containing a binder resin and an organic solvent is printed in a predetermined pattern, and drying for removing the organic solvent is performed to form a dried film that becomes the internal electrode layer. After heating and pressing the dielectric green sheets with the dried films formed thereon in a stacked state to integrate them, they are cut to obtain chips, and the chips are subjected to a debinding treatment at 500°C or lower in an oxidizing atmosphere or an inert atmosphere. Then, in order to prevent the internal electrode layer from oxidizing, the chips after the debinding treatment are heat-fired at about 1300°C in a reducing atmosphere to integrate the internal electrode layer and the dielectric layer, and fired chips are obtained. Finally, an external electrode paste is applied and fired to the fired chips, and then nickel plating or the like is applied to the obtained external electrodes, whereby the MLCC is completed.

[0004] Conductive pastes for internal electrodes can be applied using a variety of printing methods, including gravure printing, offset printing, inkjet printing, and screen printing. Therefore, the paste composition for internal electrodes needs to have rheological properties suitable for each printing method. For example, Patent Documents 1 and 2 examine compositions of conductive pastes suitable for gravure printing, Patent Document 3 examines compositions suitable for inkjet printing, and Patent Document 4 examines compositions suitable for screen printing.

[0005] Conductive paste compositions for internal electrodes are generally obtained by dispersing conductive powder, ceramic powder, and a dispersant in an organic vehicle obtained by dissolving a binder resin in an organic solvent, and adjusting the viscosity with the organic solvent. The binder resin constituting this organic vehicle is generally ethyl cellulose, and terpineol has been used as the organic solvent (see Patent Document 5).

[0006] However, because terpineol has high solubility in butyral resins and acrylic resins, when forming the internal electrode layer by coating with conductive paste, the dielectric green sheet may be eroded by the solvent in the conductive paste, resulting in a non-uniform dielectric layer, a phenomenon known as sheet attack. To prevent sheet attack, solvent compositions containing dihydroterpinyl acetate, which has low solubility in butyral resins and acrylic resins, have been investigated (see Patent Document 6).

[0007] However, solvent compositions containing dihydroterpinyl acetate tend to increase the viscosity of the conductive paste, which can make printing on dielectric green sheets difficult.

[0008] Furthermore, with the recent trend towards thinner electrode patterns, there is a growing demand for conductive pastes that use conductive powders with an average particle size of 100 nm or less. However, pastes containing such small-particle conductive powders tend to have high viscosity. Therefore, when using conductive powders with an average particle size of 100 nm or less, using a solvent composition containing dihydroterpinyl acetate as a measure against sheet attack can further increase the viscosity of the conductive paste, making printing difficult and resulting in low smoothness of the resulting printed film. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] International Publication No. 2014 / 073530 [Patent Document 2] Japanese Patent Publication No. 2018-107089 [Patent Document 3] Japanese Patent Publication No. 2017-084588 [Patent Document 4] International Publication No. 2014 / 104053 [Patent Document 5] Japanese Patent Publication No. 2018-168238 [Patent Document 6] Patent No. 2976268 [Overview of the project] [Problems that the invention aims to solve]

[0010] In view of these circumstances, the present invention aims to provide a conductive paste, an electronic component, and a multilayer ceramic capacitor that are less prone to sheet attack and have high smoothness of the printed film after screen printing. [Means for solving the problem]

[0011] To solve the above problems, the conductive paste of the present invention is a conductive paste comprising a conductive powder, a dispersant, a binder resin, and an organic solvent, wherein the dispersant comprises at least one of a polyalkylene glycol derivative having a mass average molecular weight of 1000 or less and a polyalkylene glycol having a mass average molecular weight of 1000 or less, the organic solvent comprises dihydroterpineol, a hydrocarbon solvent, and an alkanediol, and the content of the organic solvent is 40% by mass or more and 65% by mass or less.

[0012] The conductive paste of the present invention may further contain ceramic powder.

[0013] The conductive powder may be nickel powder.

[0014] The conductive paste of the present invention is effective at a temperature of 25°C and a shear rate of 4 sec. -1 The viscosity in , may be 20 Pa·s or more and less than 80 Pa·s.

[0015] The content of the dispersant may be 0.5% by mass or more and 1.0% by mass or less.

[0016] The mass ratio of the dihydroterpineol, the hydrocarbon solvent, and the alkanediol may be 4 to 6:4.2 to 6:0.4 to 0.8.

[0017] The hydrocarbon solvent may also be a mineral spirit.

[0018] The alkanediol may also be 2-ethyl-1,3-hexanediol.

[0019] The binder resin may also contain ethylcellulose.

[0020] In addition to the ethyl cellulose, the binder resin may further contain at least one resin selected from methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, nitrocellulose, and polyvinyl butyral.

[0021] The mass ratio of the total of the polyalkylene glycol derivative and the polyalkylene glycol to the conductive powder may be 0.01 or more and 4 or less: 100, and the content of the conductive powder may be 35% by mass or more and 65% by mass or less.

[0022] The number average particle diameter of the conductive powder may be 30 nm or more and 100 nm or less.

[0023] Also, an electronic component of the present invention for solving the above problems is an electronic component formed using the conductive paste of the present invention.

[0024] Also, in order to solve the above problems, a multilayer ceramic capacitor of the present invention has at least a laminate in which a dielectric layer and an internal electrode layer are laminated, and the internal electrode layer is a multilayer ceramic capacitor formed using the conductive paste of the present invention.

Advantages of the Invention

[0025] As described above, according to the present invention, it is possible to provide a conductive paste, an electronic component, and a multilayer ceramic capacitor in which sheet attack is unlikely to occur and the smoothness of the printed film after screen printing is high.

Brief Description of the Drawings

[0026] [Figure 1] It is a perspective view and a side cross-sectional view showing a multilayer ceramic capacitor.

Embodiments for Carrying Out the Invention

[0027] Hereinafter, an embodiment of the conductive paste, the electronic component, and the multilayer ceramic capacitor of the present invention will be described.

[0028] [Conductive paste] The conductive paste of this embodiment is a conductive paste comprising conductive powder, a dispersant, a binder resin, and an organic solvent, wherein the binder resin may have a mass-average molecular weight of 30,000 or more and 150,000 or less, and may also contain ethyl cellulose with an ethoxy group content of 45% to 52% by mass, the dispersant may contain at least one of a polyalkylene glycol derivative and a polyalkylene glycol, and the organic solvent may contain dihydroterpineol, a hydrocarbon solvent, and an alkanediol. In addition to the conductive powder, dispersant, binder resin, and organic solvent, the conductive paste may further contain ceramic powder, but the ceramic powder is not an essential component. The conductive powder, ceramic powder, binder resin, organic solvent, and dispersant contained in the conductive paste of this embodiment will be described in detail below.

[0029] (conductive powder) The conductive powder is not particularly limited, and metal powders can be used. For example, one or more metal powders selected from Ni, Pd, Pt, Au, Ag, Cu, and their alloys can be used. Among these, Ni or Ni alloy powders are preferred from the viewpoint of conductivity, corrosion resistance, and cost. As a 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. In addition, the Ni powder may contain several hundred ppm of sulfur to suppress rapid gas generation due to partial thermal decomposition of the binder resin during the debindering process.

[0030] The number-average particle size of the conductive powder is preferably 30 nm to 100 nm, and more preferably 40 nm to 90 nm. When the average particle size of the conductive powder is within the above range, it can be suitably used as a conductive paste for the internal electrodes of thin-film multilayer ceramic capacitors, and the smoothness of the dried film is improved. Here, the number-average particle size is a value obtained from observation using a scanning electron microscope (SEM), and is the average value obtained by measuring the particle size of multiple individual particles from an image observed with an SEM at a magnification of 10,000x.

[0031] The content of the conductive powder relative to the total amount of the conductive paste is preferably 35% by mass or more and 65% by mass or less, and more preferably 35% by mass or more and 60% by mass or less. When the content of the conductive powder is within the above range, the conductivity and dispersibility are excellent.

[0032] (Ceramic powder) The ceramic powder is not particularly limited, and any known ceramic powder can be appropriately selected depending on the type of multilayer ceramic capacitor to be applied. Examples of ceramic powders include perovskite-type oxides containing Ba and Ti, and barium titanate (BaTiO3) is preferred.

[0033] As the ceramic powder, a ceramic powder mainly composed of barium titanate and containing oxides as minor components may be used. Examples of oxides include oxides of Mn, Cr, Si, Ca, Ba, Mg, V, W, Ta, Nb, and one or more rare earth elements. Alternatively, as the ceramic powder, a perovskite-type oxide ferroelectric ceramic powder may be used, in which the Ba or Ti atoms of barium titanate (BaTiO3) are substituted with other atoms, such as Sn, Pb, or Zr.

[0034] Furthermore, a ceramic powder with the same composition as the dielectric ceramic powder constituting the green sheet of the multilayer ceramic capacitor may be used as the ceramic powder. This suppresses crack generation due to a mismatch in shrinkage at the interface between the dielectric layer and the internal electrode layer during the sintering process. Examples of such ceramic powders include oxides of ZnO, ferrite, PZT, BaO, Al2O3, Bi2O3, R(rare earth element)2O3, and TiO2. Note that one type of ceramic powder may be used, or two or more types may be used.

[0035] The number-average particle size of the ceramic powder is, for example, between 10 nm and 100 nm, preferably between 10 nm and 70 nm. Because the number-average particle size of the ceramic powder is within this range, when used as a conductive paste for internal electrodes, it is possible to form sufficiently fine, thin, and uniform internal electrodes. The number-average particle size is determined from observation using a scanning electron microscope (SEM), and is the average value obtained by measuring the particle size of multiple individual particles from an image observed at a magnification of 50,000x with an SEM.

[0036] The ceramic powder content is preferably 1 to 30 parts by mass, and more preferably 3 to 30 parts by mass, per 100 parts by mass of conductive powder. When the ceramic powder content is within the above range, the conductivity and dispersibility are excellent.

[0037] The ceramic powder content is preferably 1% to 20% by mass, and more preferably 3% to 20% by mass, relative to the total conductive paste. When the ceramic powder content is within the above range, the conductivity and dispersibility are excellent.

[0038] (Binder resin) The binder resin may have a mass-average molecular weight of 30,000 to 150,000 and may contain ethyl cellulose with an ethoxy group content of 45% to 52% by mass. By including such ethyl cellulose, a conductive paste with high smoothness as a conductive film after drying can be obtained. Furthermore, although there is a firing step in the process of processing the conductive paste into internal electrodes, the residual carbon content after firing does not increase excessively, and sufficient printability can be ensured.

[0039] Furthermore, if the mass-average molecular weight of ethylcellulose is less than 30,000, it may be difficult to obtain sufficient viscosity for printing. Also, if the molecular weight is greater than 150,000, the resulting conductive paste may have high viscosity, potentially resulting in poor printability.

[0040] Furthermore, if the ethoxy group content of ethylcellulose is 45% by mass or more and 52% by mass or less, it exhibits excellent compatibility with organic solvents and good solubility, thus enabling the production of a conductive paste with high smoothness as a conductive film after drying. More preferably, the ethoxy group content of ethylcellulose is 47% by mass or more and 52% by mass or less.

[0041] The binder resin may be ethylcellulose alone, or it may further contain resins other than ethylcellulose. For example, the binder resin may further contain, in addition to ethylcellulose, at least one resin selected from methylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, nitrocellulose, and polyvinyl butyral.

[0042] Furthermore, from the viewpoint of improving the adhesive strength with the dielectric green sheet, the binder resin may also contain polyvinyl butyral.

[0043] When the binder resin contains a resin other than ethylcellulose, it is preferable that the mass ratio of ethylcellulose to the other resin be 10 to 90:90 to 10.

[0044] The binder resin content is preferably 1 to 10 parts by mass, and more preferably 1 to 8 parts by mass, per 100 parts by mass of conductive powder. When the binder resin content is within the above range, the conductivity and dispersibility are excellent.

[0045] The binder resin content is preferably 0.5% to 10% by mass, and more preferably 1% to 6% by mass, relative to the total conductive paste. When the binder resin content is within the above range, the conductivity and dispersibility are excellent.

[0046] (Organic solvents) The organic solvents include dihydroterpineol, hydrocarbon solvents, and alkanediol solvents. For example, if the mass ratio of dihydroterpineol, hydrocarbon solvent, and alkanediol is 4 to 6, 4.2 to 6, and 0.4 to 0.8, a conductive paste with no sheet attack and high smoothness after screen printing can be obtained. If the mass ratio does not fall within this range, the conductive paste may have a high viscosity unsuitable for screen printing, resulting in insufficient smoothness as a conductive film after drying.

[0047] Regarding the mass ratio of these materials, for example, a hydrocarbon solvent ratio of 4.2 or higher can suppress sheet attack, while a ratio exceeding 6 can make it difficult to mix with the binder resin, potentially leading to liquid separation. Similarly, an alkanediol ratio of 0.4 or higher provides a viscosity suitable for good printability, but a ratio exceeding 0.8 may cause sheet attack.

[0048] Examples of hydrocarbon solvents include compounds composed solely of carbon and hydrogen. For instance, mixed solvents of tridecane, nonane, naphthenic solvents, petroleum hydrocarbons, xylene solvents, and benzene solvents can be used. Examples include Dry Solvent High Soft, Teclean, Cresol HS, Mineral Spirit, A Solvent, Base Solvent 21, LS Solvent, AF Solvent, No. 0 Solvent, and Isosol. These hydrocarbon solvents are less likely to dissolve the resin contained in the green sheet, thus suppressing sheet attack.

[0049] There are no particular restrictions on the alkanediols used, but 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 2-ethyl-1,3-hexanediol, 2-methyl-2,4-pentanediol, and 3-methyl-1,5-pentanediol are among those that can be used.

[0050] The total content of the organic solvent is preferably 80 parts by mass to 160 parts by mass, and more preferably 100 parts by mass to 140 parts by mass, per 100 parts by mass of conductive powder. When the content of the organic solvent is within the above range, the conductivity and dispersibility are excellent.

[0051] The total content of organic solvents is preferably 40% to 65% by mass, and more preferably 50% to 60% by mass, relative to the entire conductive paste. When the organic solvent content is within the above range, the conductivity and dispersibility are excellent.

[0052] (Dispersant) The dispersant contained in the conductive paste of the present invention is at least one of a polyalkylene glycol derivative having a mass-average molecular weight of 1000 or less, or a polyalkylene glycol having a mass-average molecular weight of 1000 or less. By including such a dispersant, it is possible to obtain a conductive paste that has a viscosity suitable for use in screen printing, and a conductive paste with high smoothness as a conductive film after drying.

[0053] In the conductive paste, the mass ratio of the total polyalkylene glycol derivative and polyalkylene glycol to the conductive powder is preferably 0.01 to 4:100, and more preferably 0.02 to 3:100. When the polyalkylene glycol derivative and polyalkylene glycol are included within the above range, the viscosity change of the conductive paste over time is suppressed, viscosity stability can be improved, and the resulting electrode layer has high smoothness. Furthermore, sheet attack and peeling defects of the green sheet can be suppressed.

[0054] Furthermore, if the mass ratio of the total amount of polyalkylene glycol derivatives and polyalkylene glycol to the conductive powder is greater than 4:100, when the conductive paste is printed on a green sheet, mesh marks may appear on the printed surface or the viscosity of the paste may decrease significantly. Here, "total amount of polyalkylene glycol derivatives and polyalkylene glycol" includes three cases: "the total amount of polyalkylene glycol derivatives only if the conductive paste contains only polyalkylene glycol derivatives and no polyalkylene glycol," "the total amount of polyalkylene glycol only if the conductive paste contains only polyalkylene glycol and no polyalkylene glycol derivatives," and "the total amount of polyalkylene glycol and polyalkylene glycol derivatives if the conductive paste contains both polyalkylene glycol and polyalkylene glycol derivatives."

[0055] Furthermore, the dispersant content in the conductive paste is preferably 0.5% by mass or more and 1.0% by mass or less, more preferably 0.7% by mass or more and 0.9% by mass or less. By keeping the content within this range, changes in the viscosity of the conductive paste over time are suppressed, viscosity stability is improved, and the resulting electrode layer exhibits high smoothness. Additionally, sheet attack and peeling defects of the green sheet can be suppressed.

[0056] The polyalkylene glycol derivative is acidic and may contain functional groups such as carboxyl groups, phenol groups, sulfo groups, and phosphate groups. The mass-average molecular weight of the polyalkylene glycol derivative and polyalkylene glycol, measured by GPC (Gel Permeation Chromatography), is 1000 or less in terms of polystyrene. If the mass-average molecular weight of the polyalkylene glycol derivative and polyalkylene glycol exceeds 1000, an appropriate viscosity for a conductive paste cannot be obtained. Examples of such dispersants include the Newpol series from Sanyo Chemical Industries, Ltd. and the Unilube series from NOF Corporation, but are not limited to these. Furthermore, polyalkylene glycol and polyalkylene glycol derivatives may be used in combination. In addition, only one type of polyalkylene glycol and polyalkylene glycol derivative may be used as the dispersant, or two or more types may be used.

[0057] The lower limit of the mass-average molecular weight of the polyalkylene glycol derivative and polyalkylene glycol is not particularly limited, and the above-mentioned commercially available products can be used, but for example, 200 can be used as a guideline for the lower limit.

[0058] Furthermore, the conductive paste may contain dispersants other than the polyalkylene glycol derivatives mentioned above, to the extent that they do not impair the effects of the present invention. Other dispersants may include, for example, higher fatty acids, amine-based dispersants and amino acid-based dispersants, cationic dispersants other than acid-based dispersants, nonionic dispersants, amphoteric surfactants and polymer-based dispersants. These dispersants may also be used individually or in combination of two or more.

[0059] (viscosity) The viscosity of the conductive paste was determined at a temperature of 25°C and a shear rate of 4 sec. -1 In this case, the viscosity is preferably between 20 Pa·s and less than 80 Pa·s. Having a viscosity within this range provides rheological properties suitable for screen printing and also improves the smoothness of the printed film after screen printing.

[0060] (Method for manufacturing conductive paste) The method for manufacturing the conductive paste of this embodiment is not particularly limited, and conventionally known methods can be used. The conductive paste can be manufactured, for example, by preparing each of the above components and stirring and kneading them in a three-roll mill, ball mill, mixer, etc. In this case, if a dispersant is applied to the surface of the conductive powder in advance, the conductive powder will not aggregate and will be sufficiently loosened, and the dispersant will spread evenly over the surface, making it easier to obtain a uniform conductive paste. Alternatively, the binder resin may be dissolved in an organic solvent for the vehicle to prepare an organic vehicle, and the conductive powder, ceramic powder, organic vehicle and dispersant may be added to the organic solvent for the paste, and the mixture may be stirred and kneaded in a mixer to prepare the conductive paste.

[0061] Conductive paste can be suitably used in electronic components such as multilayer ceramic capacitors and varistors. A multilayer ceramic capacitor has a dielectric layer formed using a dielectric green sheet and an internal electrode layer formed using the conductive paste.

[0062] In multilayer ceramic capacitors, it is preferable that the dielectric ceramic powder contained in the dielectric green sheet and the ceramic powder contained in the conductive paste have the same composition. In multilayer ceramic capacitors manufactured using the conductive paste of this embodiment, sheet attack and peeling defects of the green sheet are suppressed even when the thickness of the dielectric green sheet is, for example, 2 μm or less.

[0063] [Electronic components] The following describes embodiments of electronic components and the like that can be manufactured using the conductive paste of the present invention, with reference to the drawings. In the drawings, schematic representations and changes in scale may be made as appropriate. The position and orientation of the components will be described with reference to the XYZ Cartesian coordinate system shown in Figure 1, etc., as appropriate. In this XYZ Cartesian coordinate system, the X and Y directions are horizontal directions, and the Z direction is vertical (up and down direction).

[0064] Figures 1A and 1B are perspective and side cross-sectional views, respectively, of a multilayer ceramic capacitor 1, which is an example of an electronic component according to the embodiment. The multilayer ceramic capacitor 1 comprises a ceramic laminate 10 in which dielectric layers 12 and internal electrode layers 11 are alternately stacked, and an external electrode 20.

[0065] The manufacturing method of the multilayer ceramic capacitor 1 using the conductive paste described above will be explained below. First, a conductive paste is printed onto a dielectric layer made of a ceramic green sheet and dried to form a dried film. Multiple dielectric layers having this dried film on their upper surface are stacked by compression to obtain a laminate, and then the laminate is fired to integrate them, thereby creating a ceramic laminate 10 in which internal electrode layers 11 and dielectric layers 12 are stacked alternately. After that, a pair of external electrodes 20 are formed at both ends of the ceramic laminate 10 to manufacture the multilayer ceramic capacitor 1. A more detailed explanation will be provided below.

[0066] First, an unfired ceramic sheet, known as a ceramic green sheet, is prepared. Examples of this 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, which is then applied in a sheet-like manner to a support film such as a PET film, dried, and the solvent removed. The thickness of the dielectric layer made of the ceramic green sheet is not particularly limited, but from the viewpoint of miniaturizing multilayer ceramic capacitors, a thickness of 0.05 μm to 3 μm is preferred.

[0067] Next, multiple sheets of the ceramic green sheet are prepared by printing (coating) the above-mentioned conductive paste onto one side of the sheet using a known method such as screen printing, drying it, and forming a dried film. It is preferable that the thickness of the conductive paste (dried film) after printing be 1 μm or less after drying, from the viewpoint of thinning the internal electrode layer 11.

[0068] Next, the ceramic green sheet is peeled off the support film, and the dielectric layer made of the ceramic green sheet and the dried film formed on one side thereof are laminated alternately. Then, a laminate is obtained by heating and pressurizing. Alternatively, protective ceramic green sheets without conductive paste can be further arranged on both sides of the laminate.

[0069] Next, the laminate is cut to a predetermined size to form green chips, and then the green chips are subjected to a debinder treatment and fired in a reducing atmosphere to produce the ceramic laminate 10. The atmosphere used for the debinder treatment is preferably air or an N2 gas atmosphere. The temperature used for the debinder treatment is, for example, 200°C to 400°C. Furthermore, the holding time at the above temperature during the debinder treatment is preferably 0.5 hours to 24 hours. The firing is performed in a reducing atmosphere to suppress oxidation of the metal used in the internal electrode layer, and the firing temperature of the laminate is, for example, 1000°C to 1350°C, with a holding time at the temperature of 0.5 hours to 8 hours.

[0070] By firing the green chips, the organic binder in the green sheet is completely removed, and the ceramic raw material powder is fired to form a ceramic dielectric layer 12. In addition, the organic vehicle in the dried film is removed, and nickel powder or nickel-based alloy powder is sintered or melted and integrated to form internal electrodes, thus forming a laminated ceramic fired body in which multiple dielectric layers 12 and internal electrode layers 11 are alternately stacked. Furthermore, from the viewpoint of incorporating oxygen into the dielectric layer to improve reliability and suppressing re-oxidation of the internal electrodes, the laminated ceramic fired body may be subjected to annealing treatment after firing.

[0071] Then, a multilayer ceramic capacitor 1 is manufactured by providing a pair of external electrodes 20 to the fabricated multilayer ceramic firing body. For example, the external electrodes 20 comprise 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, but may be an electronic component other than a multilayer ceramic capacitor, such as a varistor. [Examples]

[0072] The present invention will be described in detail below based on examples and comparative examples, but the present invention is not limited in any way by the examples.

[0073] [Materials used] (conductive powder) As the conductive powder, Ni powder (number-average particle size 60 nm) was prepared and used by the following method.

[0074] <Manufacturing of wet nickel powder> [Preparation of solutions of nickel salts and metal salts of metals nobler than nickel] An aqueous solution of nickel chloride hexahydrate (NiCl2·6H2O, molecular weight: 237.69) was prepared by dissolving 100g of Ni metal in 1L of pure water (referred to as "100g-Ni / L aqueous solution"), and an aqueous solution of palladium(II) ammonium chloride (also known as tetrachloropalladium(II)ate ammonium) ((NH4)2PdCl4, molecular weight: 284.31), a metal salt of a metal nobler than nickel, was prepared by dissolving 1.2g of Pd metal in 1L of pure water (referred to as "1.2g-Pd / L aqueous solution"). Then, 1000 mL of a 100 g-Ni / L aqueous solution, 8.5 mL of a 1.2 g-Pd / L aqueous solution, and 1.27 g of L-methionine (CH3SC2H4CH(NH2)COOH, molecular weight: 149.21), which contains one sulfide group (-S-) in its molecule as a sulfur-containing compound and acts as an aid in inhibiting self-decomposition, were dissolved in 881 mL of pure water to prepare a nickel salt nucleating agent-containing aqueous solution, which contains a nickel salt, a sulfur-containing compound, and a nucleating agent that is a metal salt of a metal nobler than nickel as its main components. In this nickel salt nucleating agent-containing solution, the sulfide compound L-methionine was present in a trace amount of 0.005 (0.5 mol%) molar ratio to nickel, and palladium (Pd) was present in 100 mass ppm (55.16 mol ppm) relative to nickel (Ni).

[0075] [Preparation of reducing agent solution] As a reducing agent, 207 g of commercially available industrial-grade 60% hydrated hydrazine (manufactured by MGC Otsuka Chemical Co., Ltd.), which was diluted 1.67 times with pure water, was weighed out to prepare a reducing agent solution that was an aqueous solution containing hydrazine as the main component and did not contain alkali hydroxide.

[0076] [Alkali hydroxide solution] As the alkali hydroxide, sodium hydroxide (NaOH, molecular weight: 40.0) was dissolved in pure water to prepare 757 mL of an alkali hydroxide solution containing sodium hydroxide at a concentration of 382 g / L.

[0077] [Amine compound solution] As an amine compound, 1.02 g of ethylenediamine (abbreviated as EDA) (H2NC2H4NH2, molecular weight: 60.1), an alkyleneamine containing two primary amino groups (-NH2) in its molecule, was dissolved in 18 mL of pure water to prepare an amine compound solution containing ethylenediamine. Except for 60% hydrated hydrazine, all reagents used in the nickel salt nucleating agent solution, reducing agent solution, alkali hydroxide solution, and amine compound solution were manufactured by Wako Pure Chemical Industries, Ltd.

[0078] [Crystallization process] A nickel salt nucleating agent-containing solution was placed in a Teflon®-coated stainless steel container equipped with stirring blades and heated while stirring until the liquid temperature reached 85°C. Then, a reducing agent solution at 27°C was added and mixed for 10 seconds to obtain a nickel salt / reducing agent-containing solution, with a molar ratio of Ni metal to hydrazine water encapsulation of 1:1.46. To this nickel salt / reducing agent-containing solution, an alkali hydroxide solution at 27°C was added and mixed for 120 seconds to obtain a molar ratio of Ni metal to sodium hydroxide of 1:3.54. A reaction solution (nickel chloride + palladium salt + hydrazine + sodium hydroxide) at 70°C was prepared, and the reduction reaction (crystallization reaction) was started (reaction start temperature 70°C). From 8 to 28 minutes after the start of the reaction, the above amine compound solution was added dropwise to the reaction solution over a 20-minute period, so that the molar ratio of Ni metal to ethylenediamine was 1:0.01 (1.0 mol%). This allowed the reduction reaction to proceed while suppressing the autodecomposition of hydrazine, causing nickel crystallization powder to precipitate in the reaction solution. The reduction reaction was completed within 60 minutes from the start of the reaction, and the supernatant of the reaction solution was clear, confirming that all nickel components in the reaction solution had been reduced to metallic nickel, resulting in nickel crystallization powder. The reaction solution containing the nickel crystallization powder was in slurry form. An aqueous solution of mercaptoacetic acid (thioglycolic acid) (HSCH2COOH, molecular weight: 92.12) was added to this nickel crystallization powder-containing slurry to perform surface treatment (sulfur coating) on ​​the nickel crystallization powder.

[0079] [Wet crushing process] After surface treatment, the nickel crystallization powder-containing slurry was repeatedly decanted and pure water (conductivity 1 μS / cm) was added until the conductivity of the slurry was 15 μS / cm or less to wash away the nickel crystallization powder. This resulted in a nickel crystallization powder-containing slurry with a nickel concentration of 25% by mass. Using zirconia beads with a diameter of 0.05 mm as a media, wet crushing was performed using a bead mill (HFM02, manufactured by Ashizawa Finetech Co., Ltd.).

[0080] [Acid cleaning process] The nickel crystallization powder-containing slurry after the wet crushing process was neutralized by adding a 1% by mass sulfuric acid aqueous solution (H2SO4, molecular weight: 98.08) dropwise, and the pH of the nickel crystallization powder-containing slurry was maintained at 4-5 for 20 minutes. At this time, the nickel concentration of the nickel crystallization powder-containing slurry was 5% by mass. The reaction equation for neutralization is Ni(OH)2 + H2SO4 → NiSO4 + 2H2O.

[0081] [Solvent replacement process, solid-liquid separation process] After the acid washing step, filter paper was placed on a Nutsche filter, and the nickel crystallization powder-containing slurry was added and filtered. Then, pure water with an conductivity of 1 μS / cm was added to the nickel crystallization powder on the filter paper, and the filtrate was filtered and washed until the conductivity of the filtered filtrate was 30 μS / cm or less. After that, ethanol with a purity of 99.9% or higher (boiling point: 78.3°C) was added to the Nutsche filter and passed through to replace the solvent in the nickel slurry from water to ethanol. The ethanol concentration in the solvent of the nickel slurry after solvent replacement was 92.4% by mass, and the remaining 7.6% by mass was water. Here, the ethanol concentration was determined by collecting the final filtrate (last 50 mL) from the solid-liquid separation step, measuring the Karl Fischer moisture content (150°C), and calculating the solvent concentration in the filtrate using the formula "100 - moisture content (%) = solvent concentration in filtrate (%)". The same calculation was performed in other examples. After solvent replacement, filtration was continued until the solid content concentration reached 40% by mass or more to separate the solids and obtain a nickel powder cake.

[0082] [Drying process] The nickel powder cake was dried in a vacuum dryer set to a temperature of 120°C for 6 hours to obtain wet nickel powder.

[0083] <Evaluation of conductive powder and its results> (number average particle size) The obtained wet nickel powder was observed using a scanning electron microscope (SEM, JEOL Ltd., JSM-7100F). By processing the SEM images, the area of ​​100 to 200 particles whose overall shape could be confirmed was measured. The diameter of each particle was calculated from the measured area by converting it to a perfect circle, and the average of these calculated diameters was then calculated to determine the number-average particle size. The number-average particle size of the obtained nickel powder was 60 nm.

[0084] (Binder resin) As the binder resin, a vehicle prepared by dissolving ethylcellulose resin (mass-average molecular weight 100,000, ethoxy group content 48.0% to 49.5% by mass) in dihydroterpineol at a concentration of 10.5% by mass was used.

[0085] (Dispersant) As dispersants, polyalkylene glycol derivatives with a mass-average molecular weight of 1000 or less and having acidic functional groups, and polyalkylene glycol derivatives with a mass-average molecular weight of 10000 or more and having acidic functional groups were used.

[0086] [Example 1] Ni powder 44% by mass, ethylcellulose resin (mass-average molecular weight 100x10) 3 A binder resin in a vehicle (with an ethoxy group content of 48.0% to 49.5% by mass), a polyalkylene glycol derivative as a dispersant (a polyalkylene glycol derivative with an average mass molecular weight of 1000 or less and having acidic functional groups), and an organic solvent as listed in the solvent composition column of Table 1 below were prepared. The binder resin was then blended to a total of 3% by mass, the polyalkylene glycol derivative to 0.8% by mass, and the organic solvent to make up the remainder, for a total of 100% by mass. These materials were mixed in a three-roll mill to produce a conductive paste, and its viscosity, print film smoothness, and sheet attack properties were evaluated.

[0087] In Table 1 below, DHTA is dihydroterpinyl acetate, DHT is dihydroterpineol, MSA is mineral spirit A, and EtHexdiol is 2-ethyl-1,3-hexanediol (alkanediol). The numbers such as 70 / 15 / 15 indicate the mass ratio. According to this, for example, in Example 1, where the solvent composition is listed as DHT / MSA / EtHexdiol=50 / 44 / 6, the organic solvents are dihydroterpineol, mineral spirit A, and 2-ethyl-1,3-hexanediol, blended in a mass ratio of 50:44:6.

[0088] [Comparative Examples 1-5] Comparative Examples 1 to 5 were created by changing the composition and formulation of the organic solvent compared to the example. In Comparative Examples 1 to 4, the same polyalkylene glycol derivative dispersant as in Example 1 was used as the dispersant. In Comparative Example 5, a polyalkylene glycol derivative dispersant with a mass-average molecular weight of 10,000 or more and an acidic functional group was used. In each comparative example, the mass% concentration of the dispersant, relative to 100% by mass of the entire conductive paste, was set to one of the following: 0.25% by mass, 0.75% by mass, or 1.00% by mass. The viscosity, print film smoothness, and sheet attack properties of the conductive pastes composed in this way were evaluated in the same manner as in Example 1.

[0089] [Table 1]

[0090] [Evaluation Method] (viscosity) The viscosity of the conductive paste was measured using a rheometer (Anton Paar, Rheometer MCR501) after the conductive paste composition had been left to stand at room temperature (25°C) for one day from the time of manufacture. The viscosity at 25°C and the shear rate (shear rate) were measured for 4 seconds. -1The viscosity was evaluated as follows: ○ (Excellent) if it was 20 Pa·s or more and less than 60 Pa·s, △ (Good) if it was 60 Pa·s or more and less than 80 Pa·s, and × (Unacceptable) if it was 80 Pa·s or more. A ○ (Excellent) or △ (Good) rating indicates a viscosity, i.e., rheological properties, that are particularly suitable for screen printing.

[0091] (Evaluation of smoothness of printed film) A conductive paste was screen-printed onto a 4 μm thick dielectric green sheet and dried in a convection oven at 80°C for 5 minutes. Confocal images were then acquired using a 20x objective laser microscope (Keyence, VK-X1000), and the waviness Wc value (cutoff λc = 0.08 mm) was evaluated. A Wc value of less than 0.45 μm was evaluated as ○ (good), and a Wc value of 0.45 μm or more was evaluated as × (unacceptable).

[0092] (Seat attack evaluation) A conductive paste was applied to a 4μm thick dielectric green sheet in a 0.1mm thickness and 5mm diameter. After drying in a convection oven at 80°C for 20 minutes, the back surface of the dielectric green sheet where the conductive paste was applied was visually inspected for any damage. No damage was rated as ◎ (best), slight damage as ○ (good), partial damage as △ (good), and severe damage where the paste was exposed as × (bad). Additionally, when slight damage was observed on the back surface of the dielectric green sheet where the conductive paste was applied using an optical microscope, it was rated as ○ (good).

[0093] As shown in Example 1 of Table 1, by using a polyalkylene glycol derivative with an acidic functional group and a mass-average molecular weight of 1000 or less as a dispersant, and using dihydroterpineol, mineral spirit A, and 2-ethyl-1,3-hexanediol as organic solvents in a solvent ratio of 50:44:6, and setting the mass% concentration of the dispersant to 0.8 mass%, the viscosity of the conductive paste was stabilized to 20 Pa·s to 60 Pa·s, within a range that facilitates paste application (viscosity judgment: ○). Furthermore, the average roughness of the surface of the dried film obtained from the conductive paste was set to 0.03 μm or less (printed film smoothness judgment: ○), resulting in improved smoothness of the dried film surface. In addition, erosion of the dielectric green sheet by the conductive paste was prevented (sheet attack judgment: ◎).

[0094] Furthermore, as shown in Comparative Examples 1 and 2 of Table 1, when EtHexdiol (2-ethyl-1,3-hexanediol) was not used as the organic solvent, the viscosity was judged as either × (unacceptable) or ○ (excellent). Also, the printability was judged as × (unacceptable). And the sheet attackability was judged as either ○ (excellent) or △ (good). In other words, when EtHexdiol was not used as the organic solvent, excellent or good sheet attackability could be obtained, but it was difficult to obtain a smooth printed film.

[0095] Furthermore, as shown in Comparative Example 3 of Table 1, when a polyalkylene glycol derivative with a mass-average molecular weight of 1000 or less and an acidic functional group was used as a dispersant, and the mass% concentration of the dispersant was 0.25%, the viscosity and print smoothness evaluations were × (unacceptable), while the sheet attack evaluation was ○ (excellent). In other words, when a mass% concentration of a polyalkylene glycol derivative with a mass-average molecular weight of 1000 or less and an acidic functional group is 0.25%, excellent sheet attack properties can be obtained, but it is difficult to obtain a smooth printed film.

[0096] Furthermore, as shown in Comparative Example 4 of Table 1, when a polyalkylene glycol derivative with a mass-average molecular weight of 1000 or less and an acidic functional group was used as a dispersant, and the mass% concentration of the dispersant was 1.00%, the viscosity was judged as ○ (excellent). However, the print film smoothness was judged as × (unacceptable). The sheet attack property was judged as ○ (excellent). In other words, when a polyalkylene glycol derivative with a mass-average molecular weight of 1000 or less and an acidic functional group is used at a mass% concentration of 1.00%, excellent sheet attack property and viscosity can be obtained, but it is difficult to obtain a smooth print film.

[0097] Furthermore, as shown in Comparative Example 5 of Table 1, when a polyalkylene glycol derivative with a mass-average molecular weight of 10,000 or more and an acidic functional group was used as a dispersion, and the mass% concentration of the dispersant was 0.75%, the viscosity and print film smoothness evaluations were × (unacceptable), while the sheet attack performance evaluation was ○ (excellent). In other words, the results showed that while using an acidic polyalkylene glycol derivative with a mass-average molecular weight of 10,000 or more as a dispersion can provide excellent sheet attack performance, it is difficult to obtain a smooth print film.

[0098] Based on the results of Comparative Example 5 and Example 1 described above, it is preferable to set the upper limit of the mass-average molecular weight of the dispersant to 1000. On the other hand, the lower limit of the mass-average molecular weight of the dispersant is not particularly limited, but it may be set to around 200 as a guideline for the polymer.

[0099] Based on the above, the present invention provides a conductive paste that, as a conductive film after drying, is less prone to sheet attack, possesses rheological properties suitable for screen printing, and further exhibits high smoothness of the printed film after screen printing, making it industrially useful. [Explanation of Symbols]

[0100] 1… Multilayer ceramic capacitor 10…Ceramic laminate 11...Internal electrode layer 12…Dielectric layer 20…External electrode 21...External electrode layer 22…Plating layer

Claims

1. A conductive paste comprising conductive powder, a dispersant, a binder resin, and an organic solvent, The dispersant comprises at least one of a polyalkylene glycol derivative having a mass-average molecular weight of 1000 or less and a polyalkylene glycol having a mass-average molecular weight of 1000 or less. The organic solvent comprises dihydroterpineol, a hydrocarbon solvent, and an alkanediol. A conductive paste having an organic solvent content of 40% by mass or more and 65% by mass or less.

2. The conductive paste according to claim 1, further comprising ceramic powder.

3. The conductive paste according to claim 1, wherein the conductive powder is nickel powder.

4. Temperature 25°C and shear rate 4 sec －１ The conductive paste according to claim 1, wherein the viscosity in , is 20 Pa·s or more and less than 80 Pa·s.

5. The conductive paste according to claim 1, wherein the content of the dispersant is 0.5% by mass or more and 1.0% by mass or less.

6. The conductive paste according to claim 1, wherein the mass ratio of the dihydroterpineol, the hydrocarbon solvent, and the alkanediol is 4 or more and 6 or less: 4.2 or more and 6 or less: 0.4 or more and 0.8 or less.

7. The conductive paste according to claim 1, wherein the hydrocarbon solvent is a mineral spirit.

8. The conductive paste according to claim 1, wherein the alkanediol is 2-ethyl-1,3-hexanediol.

9. The conductive paste according to claim 1, wherein the binder resin contains ethylcellulose.

10. The conductive paste according to claim 9, wherein the binder resin further comprises, in addition to the ethylcellulose, at least one resin selected from methylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, nitrocellulose, and polyvinyl butyral.

11. The mass ratio of the polyalkylene glycol derivative and the total polyalkylene glycol to the conductive powder is 0.01 or more and 4 or less:

100. The conductive paste according to claim 1, wherein the content of the conductive powder is 35% by mass or more and 65% by mass or less.

12. The conductive paste according to claim 1, wherein the number-average particle size of the conductive powder is 30 nm or more and 100 nm or less.

13. An electronic component formed using the conductive paste described in claim 1.

14. The laminate comprises at least a dielectric layer and an internal electrode layer, The internal electrode layer is formed using the conductive paste described in claim 1, in a multilayer ceramic capacitor.

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