Conductive pastes for gravure printing, electronic components, and multilayer ceramic capacitors

Abstract

This invention provides a conductive paste for gravure printing capable of reducing the surface waviness of a dried film. The conductive paste for gravure printing comprises conductive powder, ceramic powder, dispersant, binder resin, and organic solvent, wherein the organic solvent comprises a first organic solvent, which is at least one selected from the group consisting of isobornyl acetate, methyl isobutyl ketone, and diisobutyl ketone.

Description

[Technical Field]

[0001] This invention relates to conductive paste for gravure printing, electronic components, and multilayer ceramic capacitors. [Previous Technology]

[0002] With the miniaturization and high performance of electronic devices such as mobile phones and digital devices, there is also a desire for miniaturization and high capacitance of electronic components, including multilayer ceramic capacitors. Multilayer ceramic capacitors have a structure formed by alternating layers of multiple dielectric layers and multiple internal electrode layers. Miniaturization and high capacitance can be achieved by thinning these dielectric layers and internal electrode layers.

[0003] Multilayer ceramic capacitors are manufactured, for example, as follows: First, a conductive paste for internal electrodes is printed with a predetermined electrode pattern on the surface of a ceramic green sheet containing dielectric powder such as barium titanate (BaTiO3) and binder resin, and then dried to form a dried film. Next, the dried film and the ceramic green sheet are laminated in an alternating overlapping manner to obtain a multilayer body. Next, the multilayer body is heated and pressed to integrate it to form a press-fit body. The press-fit body is cut, and after being treated to remove the organic binder in an oxidizing gas environment or an inert gas environment, it is fired to obtain a fired wafer. Next, a paste for external electrodes is coated on both ends of the fired wafer, and after firing, nickel plating or the like is performed on the surface of the external electrodes to obtain a multilayer ceramic capacitor.

[0004] As a printing method used to print conductive paste onto dielectric film, screen printing has been generally used in the past. However, based on the requirements of miniaturization, thinning and improved productivity of electronic devices, it is required to print finer electrode patterns with higher productivity.

[0005] As one of the printing methods for conductive pastes, gravure printing, as a continuous printing method, has been proposed. Conductive paste is filled into recesses on a printing plate and pressed onto the printing surface, thereby transferring the conductive paste from the printing plate. Gravure printing offers 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, and adjust its viscosity and other properties to a range suitable for gravure printing.

[0006] For example, Patent Document 1 describes a conductive paste for forming an internal conductor film by gravure printing. The internal conductor film is an internal conductor film in a multilayer ceramic electronic component having a plurality of ceramic layers and an internal conductor film extending along a specific interface between the aforementioned ceramic layers. The conductive paste contains 30 to 70% by weight of a solid component containing metal powder, 1 to 10% by weight of an ethyl cellulose resin component with an ethoxy content of 49.6% or more, 0.05 to 5% by weight of a dispersant, and the balance being a solvent component. It is a thixotropic fluid with a viscosity η0.1 of 1 Pa·s or more at a shear rate of 0.1 (s-1) and a viscosity η0.02 of 0.02 (s-1) satisfying the condition expressed by a specific formula.

[0007] Furthermore, Patent Document 2 describes a conductive paste, which, like Patent Document 1, is a conductive paste used to form an internal conductor film by gravure printing. It contains 30 to 70% by weight of a solid component containing metal powder, 1 to 10% by weight of a resin component, 0.05 to 5% by weight of a dispersant, and the remainder is a solvent component. It is a thixotropic fluid with a viscosity of 1 Pa·s or more at a shear rate of 0.1 (s-1). When the viscosity at a shear rate of 0.1 (s-1) is used as a reference, the viscosity change rate at a shear rate of 10 (s-1) is 50% or more.

[0008] According to the above-mentioned patent documents 1 and 2, such conductive pastes are thixotropic fluids with a viscosity of 1 Pa·s or more at a shear rate of 0.1 (s-1), which can achieve stable continuous printing at high speeds in gravure printing, and can manufacture multilayer ceramic electronic components such as multilayer ceramic capacitors with good production efficiency.

[0009] Furthermore, Patent Document 3 discloses a conductive paste for gravure printing, which is a conductive paste for the internal electrodes of a multilayer ceramic capacitor containing conductive powder (A), organic resin (B), organic solvent (C), additive (D), and dielectric powder (E). The organic resin (B) is composed of polyvinyl butyral with a degree of polymerization of 10,000 or more and 50,000 or less, and ethyl cellulose with a weight-average molecular weight of 10,000 or more and 100,000 or less. The organic solvent (C) is composed of any one of propylene glycol monobutyl ether, or 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 oil. The additive (D) is composed of a separation inhibitor and a dispersant. The separation inhibitor is composed of a composition containing a polycarboxylic acid polymer or a polycarboxylate. According to Patent Document 3, this conductive paste has a viscosity suitable for gravure printing, which can improve the uniformity and stability of the paste, and has good drying properties. [Prior Art Documents] [Patent Documents]

[0010] [Patent Document 1] Japanese Patent Application Publication No. 2003-187638 [Patent Document 2] Japanese Patent Application Publication No. 2003-242835 [Patent Document 3] Japanese Patent Application Publication No. 2012-174797 [Summary of the Invention]

[0011] [The technical problem that the invention aims to solve]

[0012] Low viscosity is required in conductive pastes used for gravure printing. However, compared to high viscosity conductive pastes used for screen printing, low viscosity conductive pastes tend to have greater surface waviness when forming a dried film. When such conductive pastes are used to form the internal electrode layer of a multilayer ceramic capacitor, the resulting internal electrode layer thickness deviates, reducing the reliability of the multilayer ceramic capacitor.

[0013] In view of this situation, the object of the present invention is to provide a conductive paste for gravure printing with low surface waviness of the dried film. [Technical Means]

[0014] In the first embodiment of the present invention, a conductive paste for gravure printing is provided, which contains conductive powder, ceramic powder, dispersant, binder resin and organic solvent, wherein the organic solvent contains at least one selected from the group consisting of isobornyl acetate, methyl isobutyl ketone and diisobutyl ketone.

[0015] Furthermore, ideally, the conductive paste further contains dicarboxylic acid in an amount of 0.05% by mass or more and less than 3.0% by mass relative to the total conductive paste. Furthermore, ideally, it contains organic solvent in an amount of 10% by mass or more and less than 60% by mass relative to the total conductive paste. Furthermore, ideally, it contains dispersant in an amount of 0.01% by mass or more and less than 3.0% by mass relative to the total conductive paste. Furthermore, ideally, the dispersant contains an acid-based dispersant. Furthermore, ideally, the conductive powder contains at least one metal powder selected from the group consisting of Ni, Pd, Pt, Au, Ag, Cu, and alloys thereof. Furthermore, ideally, the average particle size of the conductive powder is 0.05 μm or more and 1.0 μm or less. Furthermore, ideally, the ceramic powder contains barium titanate. Ideally, the average particle size of the ceramic powder is 0.01 μm or more and 0.5 μm or less. Furthermore, ideally, the conductive paste contains ceramic powder at a mass percentage of 1% to 20% (by mass) relative to the total conductive paste. Furthermore, ideally, the binder resin contains a cellulose-based resin. Furthermore, ideally, the viscosity of the conductive paste is 3 Pa·s or less at a shear rate of 100 sec⁻¹ and 1 Pa·s or less at a shear rate of 10000 sec⁻¹. Furthermore, ideally, the average height (Wc) of the waviness profile of the dried film obtained by gravure printing of the conductive paste at a printing speed of 30 m / min and a film thickness of 0.50 μm to 2 μm or less is 0.5 μm or less.

[0016] In a second aspect of the present invention, an electronic component formed using the above-described conductive paste is provided.

[0017] In a third embodiment of the present invention, a multilayer ceramic capacitor is provided, which has at least a multilayer body formed by stacking a dielectric layer and an internal electrode layer, wherein the internal electrode layer is formed using the aforementioned conductive paste for gravure printing. [Effects of the Invention]

[0018] The conductive paste of the present invention can reduce the surface waviness of the dried film even when a dried film is formed by gravure printing. Furthermore, the internal electrode layer formed using the conductive paste of the present invention can produce highly reliable multilayer ceramic capacitors with high productivity, even when forming thin-film electrodes.

Implementation Method

[0020] [Conductive Paste] The conductive paste of this embodiment contains conductive powder, ceramic powder, dispersant, binder resin, and organic solvent. The components are described in detail below.

[0021] (Conductive Powder) There are no particular limitations on the conductive powder; metal powders can be used, such as powders selected from Ni, Pd, Pt, Au, Ag, Cu, and alloys thereof. From the viewpoints of conductivity, corrosion resistance, and cost, Ni powder or its alloys (hereinafter, sometimes referred to as "Ni powder") is ideal. 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, ideally 80% by mass or more. Furthermore, in order to suppress the rapid gas generation caused by partial thermal decomposition of the adhesive resin during the adhesive removal treatment, the Ni powder may contain approximately several hundred ppm of element S.

[0022] The average particle size of the conductive powder is ideally 0.05 μm or more and 1.0 μm or less, and more preferably 0.1 μm or more and 0.5 μm or less. When the average particle size of the conductive powder is within the above range, it is suitable for use as a paste for the internal electrodes of thin-film multilayer ceramic capacitors (multilayer ceramic parts), for example, improving the smoothness and density of the dried film. The average particle size is a value obtained based on observation using a scanning electron microscope (SEM), and is the average value obtained by measuring the particle size of a plurality of particles individually from an image obtained by observing the image at 10,000x magnification using SEM (SEM average particle size).

[0023] Ideally, the content of conductive powder relative to the overall conductive slurry is 30% by mass or more and less than 70% by mass, and more ideally, 40% by mass or more and less than 60% by mass. When the content of conductive powder is within the above range, the conductivity and dispersibility are excellent.

[0024] (Ceramic powder) There are no particular limitations on the ceramic powder. For example, in the case of a paste for the internal electrodes of a multilayer ceramic capacitor, a conventional ceramic powder is appropriately selected depending on the type of multilayer ceramic capacitor being used. For example, a perovskite-type oxide containing Ba and Ti can be used as the ceramic powder, and barium titanate (BaTiO3) is ideally present.

[0025] As a ceramic powder, a ceramic powder containing barium titanate as the main component and oxides as secondary components can also 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. Furthermore, as a ceramic powder, for example, a perovskite-type oxide high-electricity ceramic powder in which the Ba and Ti atoms of barium titanate (BaTiO3) are replaced with other atoms such as Sn, Pb, and Zr can be used.

[0026] When using a conductive paste as an internal electrode, the ceramic powder can be a powder with the same composition as the dielectric ceramic powder constituting the green sheet of the multilayer ceramic capacitor (electronic component). This suppresses the formation of cracks due to shrinkage mismatch at the interface between the dielectric layer and the internal electrode layer during the sintering process. Examples of such ceramic powders, besides those described above, include oxides such as ZnO, ferrite, PZT, BaO, Al2O3, Bi2O3, R (rare earth element)2O3, TiO2, and Nd2O3. Furthermore, one or more types of ceramic powder can be used.

[0027] The average particle size of the ceramic powder is, for example, 0.01 μm or more and 0.5 μm or less, ideally in the range of 0.01 μm or more and 0.3 μm or less. By ensuring that the average particle size of the ceramic powder is within the above range, when used as a slurry for internal electrodes, a sufficiently thin and uniform internal electrode can be formed. The average particle size is a value obtained based on observation using a scanning electron microscope (SEM), and is the average value obtained by measuring the particle size of a plurality of particles individually from an image obtained by observing the SEM at a magnification of 50,000x (SEM average particle size).

[0028] Ideally, the content of ceramic powder relative to the overall conductive slurry is 1% by mass or more and 20% by mass or less, more preferably 3% by mass or more and 15% by mass or less. When the content of ceramic powder is within the above range, the dispersibility and sintering properties are excellent.

[0029] Furthermore, based on 100 parts by mass of conductive powder, the content of ceramic powder is ideally more than 1 part by mass and less than 30 parts by mass, and more preferably more than 3 parts by mass and less than 30 parts by mass.

[0030] (Adhesive Resin) There are no particular limitations on the adhesive resin used; conventional resins can be used. Examples of adhesive resins include cellulose-based resins such as methylcellulose, ethylcellulose, ethyl hydroxyethylcellulose, and nitrocellulose, acrylic resins, and butyral-based resins such as polyvinyl butyral. From the viewpoint of solubility in solvents and combustion decomposition properties, it is ideal to contain a cellulose-based resin, and more ideally, it should contain ethylcellulose.

[0031] Furthermore, when used as a paste for internal electrodes, from the viewpoint of improving the adhesion strength with the green sheet, it may contain butyral resin, or butyral resin may be used alone. When the adhesive resin contains butyral resin, the viscosity can be easily adjusted to be suitable for gravure printing, and the adhesion strength with the green sheet can be further improved. For example, the adhesive resin may contain 20% by mass or more of butyral resin relative to the total adhesive resin, or it may contain 30% by mass or more.

[0032] When the adhesive resin contains cellulose resin and butyral resin, relative to the total content (100% by mass) of cellulose resin and butyral resin, it may contain 20% or more and 80% or less of acetal resin, or 30% or more and 80% or less of acetal resin, or 30% or more and 60% or less of acetal resin.

[0033] Furthermore, the degree of polymerization and weight-average molecular weight of the adhesive resin can be appropriately adjusted within the above range according to the required viscosity of the conductive slurry.

[0034] For example, when a cellulose-based resin is used as the adhesive resin, the weight-average molecular weight (Mw) can be 10,000 or more and 300,000 or less, 30,000 or more and 200,000 or less, or 50,000 or more and 150,000 or less. When the Mw of the cellulose-based resin is within the above range, the viscosity of the conductive slurry can be adjusted to an appropriate range, and the surface waviness of the dried film can be reduced.

[0035] Furthermore, the hydroxyl value of the cellulose resin is not particularly limited, but ideally it is 0.1 mg KOH / g or more and 15 mg KOH / g or less, more ideally it is 0.5 mg KOH / g or more and 7 mg KOH / g or less, and even more ideally it is 1.5 mg KOH / g or more and 3 mg KOH / g or less. When the hydroxyl value of the cellulose resin is within the above range, the dispersibility of conductive powders and ceramic powders is excellent, and therefore it is suitable for use as a conductive paste for gravure printing. Also, the hydroxyl value is a value determined according to JIS K 0070, and represents the number of mg of potassium hydroxide equivalent to hydroxyl groups in 1 g of sample.

[0036] In addition, the ethoxy content of the cellulose resin is not particularly limited. For example, it can be 40% or more by mass and 55% or less by mass, or 45% or more by mass and 52% or less by mass, or 48% or more by mass and 50% or less by mass.

[0037] For example, when the butyral resin is used as the adhesive resin, the weight-average molecular weight (Mw) can be 30,000 or more and 300,000 or less, 50,000 or more and 200,000 or less, or 100,000 or more and 150,000 or less. When the Mw of the butyral resin is within the above range, the viscosity of the conductive slurry can be adjusted to a suitable range, and the surface waviness of the dried film can be reduced.

[0038] The binder resin content is ideally 0.5% by mass or more and 10% by mass or less, and more ideally 1% by mass or more and 7% by mass or less, relative to the overall conductive slurry. When the binder resin content is within the above range, the conductivity and dispersibility are excellent.

[0039] Based on 100 parts by weight of conductive powder, the content of adhesive resin is ideally more than 1 part by weight and less than 20 parts by weight, and more preferably more than 1 part by weight and less than 14 parts by weight.

[0040] (Organic Solvent) The conductive paste according to this embodiment contains at least one of the group selected from isobornyl acetate (IBA), methyl isobutyl ketone (MIBK), and diisobutyl ketone (DIBK) (hereinafter referred to as the "first organic solvent") as an organic solvent. Ideally, it contains one or both of isobornyl acetate and diisobutyl ketone, and more preferably, it contains isobornyl acetate. By containing the above-mentioned organic solvent (hereinafter also referred to as the "first organic solvent"), the waviness of the film surface during the formation of the dried film can be reduced. Furthermore, one or more first organic solvents may be used. In addition, when two or more are contained as the first organic solvent, isobornyl acetate and diisobutyl ketone may be contained.

[0041] Relative to the total amount of conductive paste, the content of the first organic solvent can be 3% by mass or more and 60% by mass or less, or 5% by mass or more and 40% by mass or less, or 10% by mass or more and 30% by mass or less, or 10% by mass or more and 20% by mass or less. Furthermore, even if the content of the first organic solvent is 5% by mass or more and 10% by mass or less, the waviness of the dried film surface can be reduced.

[0042] Furthermore, when the first organic solvent contains isoborneol acetate (IBA), the content of isoborneol acetate relative to the total amount of conductive slurry is ideally 4% by mass or more, more ideally 5% by mass or more, and even more ideally 8% by mass or more. When the content of isoborneol acetate is within the above range, the waviness of the film surface during the formation of the dried film can be further reduced. In addition, the content of isoborneol acetate relative to the total amount of conductive slurry can be 40% by mass or less, or 30% by mass or less, or 20% by mass or less, or 10% by mass or less.

[0043] Furthermore, when the first organic solvent contains diisobutyl ketone (DIBK), the content of diisobutyl ketone is ideally 4% by mass or more, and more ideally 5% by mass or more, relative to the total amount of conductive paste. When the content of diisobutyl ketone is within the above range, the waviness of the film surface during the formation of the dried film can be further reduced, and furthermore, the viscosity can be easily adjusted to be suitable for gravure printing. Furthermore, when diisobutyl ketone (DIBK) is contained, the drying properties are excellent, and the step of coating the conductive paste onto the raw film by gravure printing and drying it (film forming step) can be completed in a short time. In addition, the content of diisobutyl ketone relative to the total amount of conductive paste can be 30% by mass or less, or 20% by mass or less, or 10% by mass or less, or 7% by mass or less.

[0044] Furthermore, the organic solvent may also include organic solvents other than the first organic solvent. There are no particular limitations on the organic solvent other than the first organic solvent (other organic solvents), and conventional organic solvents capable of dissolving the aforementioned adhesive resin may be used. Examples of other organic solvents include glycol ether solvents, acetate solvents, ketone solvents, terpene solvents, and petroleum hydrocarbon solvents containing aliphatic hydrocarbon solvents. Furthermore, one or more other organic solvents may be used.

[0045] As a glycol ether solvent, examples include diethylene glycol mono-2-ethylhexyl ether, ethylene glycol mono-2-ethylhexyl ether, diethylene glycol monohexyl ether, ethylene glycol monohexyl ether, diethylene glycol monomethyl ether, etc. (ii) ethylene glycol ethers, as well as propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether (PNB), etc., etc.

[0046] As an acetate ester solvent, examples include isobornyl propionate, isobornyl butyrate, isobornyl isobutyrate, ethylene glycol monobutyl ether acetate, diethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether acetate, dipropylene glycol methyl ether acetate, 3-methoxy-3-methylbutyl acetate, 1-methoxypropyl-2-acetate and other glycol ether acetates, ethyl acetate, propyl acetate, isobutyl acetate, butyl acetate, etc.

[0047] As a ketone solvent, examples include methyl ethyl ketone, etc.

[0048] As a terpene solvent, examples include terpineol, dihydroterpineol (DHT), and dihydroterpineol acetate.

[0049] Examples of petroleum-based hydrocarbon solvents containing aliphatic hydrocarbon solvents include solvents containing tridecane, nonane, cyclohexane, etc., mineral oil (MA), and cycloalkane solvents. Ideally, they contain mineral oil, or mineral oil may be the main component (the most abundant solvent among petroleum-based hydrocarbon solvents). Furthermore, mineral oil may contain chain saturated hydrocarbons as the main component, or it may contain more than 20% by mass of chain saturated hydrocarbons relative to the total mineral oil content.

[0050] Other organic solvents may include, for example, terpene solvents and aliphatic hydrocarbon solvents, or may contain only terpene solvents or only aliphatic hydrocarbon solvents. Furthermore, when terpene solvents are included, the content of terpene solvents relative to the total amount of conductive slurry may be 5% by mass or more and 40% by mass or less, or 10% by mass or more and 25% by mass or less. Furthermore, when aliphatic hydrocarbon solvents are included, the content of aliphatic hydrocarbon solvents relative to the total amount of conductive slurry may be 5% by mass or more and 25% by mass or less, or 5% by mass or more and 15% by mass or less.

[0051] The content of organic solvent (total) relative to the total amount of conductive slurry is ideally 20% by mass or more and 60% by mass or less, and more ideally 25% by mass or more and 45% by mass or less. When the content of organic solvent is within the above range, the conductivity and dispersibility are excellent.

[0052] Based on 100 parts by weight of conductive powder, the content of organic solvent is ideally 50 parts by weight or more and 130 parts by weight or less, more preferably 60 parts by weight or more and 90 parts by weight or less. When the content of organic solvent is within the above range, the conductivity and dispersibility are excellent.

[0053] (Dispersant) Conventional dispersants can be used as the dispersant. For example, an acid-based dispersant may be included. In addition, as an acid-based dispersant, a carboxyl-containing dispersant other than the dicarboxylic acid described later may also be included. Furthermore, in this specification, as described later, considering the separation suppression effect of the conductive powder and ceramic powder possessed by the dicarboxylic acid, the dicarboxylic acid and the dispersant are specified separately.

[0054] For example, when using comb-type carboxylic acid as a dispersant, the dispersibility of the conductive paste is improved by containing comb-type carboxylic acid. Furthermore, one or more dispersants may be used. The conductive paste according to this embodiment improves dispersibility by containing a dispersant.

[0055] As a dispersant, it may contain, for example, an acidic dispersant having a hydrocarbon group. Examples of such acidic dispersants include higher fatty acids, high molecular weight surfactants, and phosphoric acid dispersants. One or more of these dispersants may be used.

[0056] As a higher fatty acid, it can be either an unsaturated carboxylic acid or a saturated carboxylic acid, without particular limitation. Examples include stearic acid, oleic acid, myristic acid, palmitic acid, linoleic acid, lauric acid, linolenic acid, and other higher fatty acids with 11 or more carbon atoms. Among them, oleic acid or stearic acid is ideal.

[0057] Other than this, there are no particular limitations on the acid-based dispersant. For example, alkyl monoamine salts, represented by monoalkylamine salts, can be listed.

[0058] As an alkyl monoamine salt type, ideally it is oleic acid, which is a compound of glycine and oleic acid, or an amide compound in which higher fatty acids such as stearic acid or lauric acid are used instead of oleic acid.

[0059] In addition, the dispersant may also contain dispersants other than acidic dispersants. Examples of dispersants other than acidic dispersants include basic dispersants, nonionic dispersants, and amphoteric dispersants. One or more of these dispersants may be used.

[0060] Examples of alkaline dispersants include aliphatic amines such as laurylamine, rosinamine, cetylamine, myristicamine, and stearylamine. When the conductive paste contains both acidic and alkaline dispersants, the dispersibility is superior, and the viscosity stability over time is also excellent.

[0061] Ideally, the conductive paste contains 3% by mass or less of a dispersant relative to the overall conductive paste. The upper limit of the dispersant content is ideally 2% by mass or less, and more ideally 1% by mass or less. The lower limit of the dispersant content is not particularly limited, but is, for example, 0.01% by mass or more, and ideally 0.05% by mass or more. When the dispersant content is within the above range, the dispersibility of the conductive paste can be improved, and the paste viscosity can be adjusted to an appropriate range. Furthermore, it can prevent deterioration of drying properties after printing, and further suppress sheet erosion and poor peeling of raw sheets.

[0062] Furthermore, based on 100 parts by weight of conductive powder, it is ideal to contain 0.01 parts by weight and 5 parts by weight of dispersant, more ideally 0.05 parts by weight and 3 parts by weight, and even more ideally 0.4 parts by weight and 3 parts by weight. When the content of dispersant is within the above range, the dispersibility of conductive powder and ceramic powder, as well as the smoothness of the dried electrode surface after coating, are superior. Furthermore, the viscosity of the conductive paste can be adjusted to an appropriate range, and deterioration of drying properties after printing can be prevented. Furthermore, sheet erosion and poor peeling of raw sheets can be suppressed. In addition, the dispersant may also contain acid-based and alkali-based dispersants. When both acid-based and alkali-based dispersants are used as dispersants, it is ideal that the content of the acid-based dispersant is greater than the content of the alkali-based dispersant. For example, the content of the alkali-based dispersant may be 0.1 times or more and less than 1 time, or 0.3 times or more and less than 0.8 times, relative to the content of the acid-based dispersant.

[0063] (Dicarboxylic acid) The conductive paste according to this embodiment may contain dicarboxylic acid as an additive. In the conductive paste for gravure printing, by containing a specific amount of dicarboxylic acid, the separation of conductive powder and ceramic powder can be suppressed, and the formation of a white separation layer containing ceramic powder on top during the production of the conductive paste can be suppressed. Furthermore, when forming an internal electrode layer using the conductive paste according to this embodiment, a higher coverage rate can be achieved.

[0064] Dicarboxylic acid is a carboxylic acid additive with two carboxyl groups (COO- group). Examples of dicarboxylic acids include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, and 2,6-naphthalenedicarboxylic acid; aliphatic dicarboxylic acids such as succinic acid, glutaric acid, adipic acid, sebacic acid, dodecanedicarboxylic acid, and azelaic acid; alicyclic dicarboxylic acids such as dicarboxylic acids, hydrogenated dimer acids, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 4-methylhexahydrophthalic anhydride, 3-methylhexahydrophthalic anhydride, 2-methylhexahydrophthalic anhydride, dicarboxylated hydrogenated bisphenol A, dicarboxylated hydrogenated bisphenol S, hydrogenated naphthalenedicarboxylic acid, and tricyclodecanedicarboxylic acid; and their derivatives, among which derivatives of succinic acid are ideal.

[0065] Furthermore, the average molecular weight of the dicarboxylic acid is not particularly limited; for example, it can be less than 1000, less than 500, or less than 400. When the average molecular weight of the dicarboxylic acid is within the above range, a higher separation inhibition effect can be obtained. The average molecular weight of the dicarboxylic acid can, for example, be more than 100 or more, or more than 200.

[0066] Furthermore, in the conductive paste according to this embodiment, the amount of dicarboxylic acid contained in the conductive paste is 0.05% by mass or more and less than 3.0% by mass, ideally 0.1% by mass or more and less than 1.0% by mass. Furthermore, the upper limit of the content of dicarboxylic acid can be 0.5% by mass or less. When the content of dicarboxylic acid is 3.0% by mass or more, the drying process becomes insufficient during printing and drying, the internal electrode layer becomes soft, and sometimes lamination misalignment occurs in subsequent lamination steps, or the residual dicarboxylic acid vaporizes during firing, generating internal stress due to the vaporized gas components, or causing structural damage to the laminate.

[0067] Furthermore, when the conductive slurry contains a dispersant (other than dicarboxylic acid) and dicarboxylic acid, the total content of the dispersant and dicarboxylic acid relative to the conductive slurry as a whole may be 0.05% by mass or more and 3.0% by mass or less, or 0.1% by mass or more and 2.0% by mass or less, or 0.1% by mass or more and 1.0% by mass or less.

[0068] Furthermore, the conductive paste according to this embodiment may not contain dicarboxylic acid. Even when the conductive paste according to this embodiment does not contain dicarboxylic acid, as described above, the waviness of the dried film surface can be reduced by containing a specific organic solvent.

[0069] (Other Additives) The conductive paste of this embodiment may contain other additives besides the above-mentioned components as needed. Other additives may include, for example, conventional additives such as defoamers, plasticizers, surfactants, and thickeners.

[0070] (Conductive slurry) The manufacturing method of the conductive slurry involved in this embodiment is not particularly limited, and conventional methods can be used. For example, the conductive slurry can be manufactured by stirring and mixing the above-mentioned components using a three-roll mill, ball mill, mixer, etc. Furthermore, regarding dicarboxylic acid (separation inhibitor), it is ideal to weigh and add it during stirring and mixing in a mixer, etc., in the same way as other materials. However, even if it is added as a separation inhibitor to the material after stirring and mixing (dispersion) is completed, the same separation inhibition effect can be obtained.

[0071] Ideally, the viscosity of the conductive paste at a shear rate of 100 sec⁻¹ should be 3 Pa·s or less. When the viscosity at a shear rate of 100 sec⁻¹ is within the above range, it is suitable for use as a conductive paste for gravure printing. If it exceeds the above range, the viscosity is too high and it is unsuitable for gravure printing. The lower limit of the viscosity at a shear rate of 100 sec⁻¹ is not particularly limited, but for example, it is 0.2 Pa·s or more.

[0072] Furthermore, the viscosity of the conductive paste at a shear rate of 10,000 sec⁻¹ is ideally 1 Pa·S or less. When the viscosity at a shear rate of 10,000 sec⁻¹ is within the above-mentioned range, it is suitable for use as a conductive paste for gravure printing. If the viscosity exceeds the above range, it may be too high and unsuitable for gravure printing. The lower limit of the viscosity at a shear rate of 10,000 sec⁻¹ is not particularly limited, but for example, it may be 0.05 Pa·S or more.

[0073] Conductive pastes are suitable for use in electronic components such as multilayer ceramic capacitors. Multilayer ceramic capacitors have a dielectric layer formed using a dielectric green sheet and an internal electrode layer formed using a conductive paste.

[0074] As a dried film obtained by gravure printing of conductive paste at a printing speed of 30 m / min and a film thickness of 0.50 μm or more and 2 μm or less, the average height (Wc) of the waviness curve element under the condition of applying the cutoff value (λc = 0.08 mm) is ideally less than 0.5 μm, more ideally less than 0.47 μm, more ideally less than 0.45 μm, more ideally less than 0.4 μm, and even more ideally less than 0.35 μm.

[0075] Furthermore, the average height (Wc) of the waviness curve element can be measured according to JIS B 0601:2013. The average height (Wc) of the waviness curve element refers to the average height (Zti) of the waviness curve element (profile curve element) under the reference length. The profile curve element is an element that groups adjacent peaks and valleys together, and the height of the profile curve element is equivalent to the height difference between the adjacent peaks and valleys. Furthermore, the peaks (valleys) constituting the profile element have minimum height and minimum length requirements. Peaks (valleys) with a height (depth) of less than 10% of the maximum height or a length of less than 1% of the length of the calculation interval are considered noise and are included as part of consecutive valleys (peaks).

[0076] [Electronic Components] Hereinafter, embodiments of electronic components, etc., of the present invention will be described with reference to the drawings. In the drawings, sometimes the representation is schematic and the scale is changed as appropriate. Furthermore, the position, orientation, etc. of the components will be described with reference to the XYZ orthogonal coordinate system shown in Figure 1, etc. In this XYZ orthogonal coordinate system, the X and Y directions are horizontal, and the Z direction is vertical (up and down).

[0077] Figures A and B in Figure 1 are diagrams showing a multilayer ceramic capacitor 1 as an example of an electronic component involved in the embodiment. The multilayer ceramic capacitor 1 includes a ceramic multilayer body 10 formed by alternating layers of dielectric layer 12 and internal electrode layer 11, and an external electrode 20.

[0078] Hereinafter, a method for manufacturing a multilayer ceramic capacitor using the above-described conductive paste will be described. First, a conductive paste is printed on a ceramic green sheet and dried to form a dry film. Then, a multilayer body is obtained by laminating multiple ceramic green sheets having the dry film on their upper surfaces by pressing. The multilayer body is then fired to integrate them, thereby creating a ceramic multilayer body 10 formed by alternating layers of internal electrode layer 11 and dielectric layer 12. Next, a multilayer ceramic capacitor 1 is manufactured by forming a pair of external electrodes at both ends of the ceramic multilayer body 10. A more detailed explanation will follow.

[0079] First, a ceramic green sheet, which is an unfired ceramic sheet, is prepared. For example, this ceramic green sheet can be formed by coating a dielectric layer slurry 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 onto a support film such as a PET film, forming a sheet, and then drying it to remove the solvent. Furthermore, there is no particular limitation on the thickness of the dielectric layer composed of the ceramic green sheet, but from the viewpoint of miniaturizing multilayer ceramic capacitors, it is ideally 0.05 μm to 3 μm.

[0080] Next, a plurality of sheets are prepared in which the conductive paste described above is coated on one side of the ceramic green sheet by gravure printing and drying, thereby forming a dry film on one side of the ceramic green sheet. Furthermore, from the viewpoint of the requirement for thinning of the internal electrode layer 11, the thickness of the dry film formed by the conductive paste is ideally less than 1 μm after drying.

[0081] Next, the ceramic green sheet is peeled off from the support film, and after lamination in a manner in which the ceramic green sheet and a dry film formed on one side of the ceramic green sheet are alternately arranged, a laminate is obtained by heating and pressurizing. Alternatively, the laminate may be configured such that protective ceramic green sheets without conductive paste are further arranged on both sides of the laminate.

[0082] Next, after cutting the laminate to a specified size to form a green wafer, the green wafer is subjected to a binder removal treatment and fired in a reducing gas environment to manufacture a laminated ceramic body (ceramic laminate 10). Ideally, the gas environment for the binder removal treatment is atmospheric or N2 gas. The temperature for the binder removal treatment is, for example, 200°C or higher and 400°C or lower. Furthermore, the holding time at the aforementioned temperature during the binder removal treatment is ideally 0.5 hours or higher and 24 hours or lower. In addition, to suppress oxidation of the metal used in the internal electrode layer, firing is carried out in a reducing gas environment. Furthermore, the firing temperature for the laminate is, for example, 1000°C or higher and 1350°C or lower, and the holding time at the firing temperature is, for example, 0.5 hours or higher and 8 hours or lower.

[0083] By firing the green ceramic wafer, the organic binder in the ceramic green wafer is completely removed, and the ceramic raw material powder is fired to form a ceramic dielectric layer 12. Furthermore, the organic carrier in the dried film is removed, and nickel powder or an alloy powder with nickel as the main component is sintered or melted to form an internal electrode layer 11, thereby forming a laminated ceramic body formed by alternating layers of the dielectric layer 12 and the internal electrode layer 11. Also, from the viewpoint of improving reliability by introducing oxygen into the interior of the dielectric layer and suppressing the re-oxidation of the internal electrode, the fired laminated ceramic body can be annealed.

[0084] Then, a multilayer ceramic capacitor 1 is manufactured by providing a pair of external electrodes 20 to the fabricated multilayer ceramic body. For example, the external electrodes 20 include an external electrode layer 21 and an electroplated layer 22. The external electrode layer 21 is electrically connected to the internal electrode layer 11. Furthermore, copper, nickel, or alloys thereof can ideally be used as the material for the external electrodes 20. Also, electronic components other than multilayer ceramic capacitors can be used. [Example]

[0085] Hereinafter, the present invention will be described in detail based on embodiments and comparative examples, but the present invention is not limited to any of the embodiments.

[0086] [Evaluation Method] (Viscosity of Conductive Paste) The viscosity of the conductive paste after manufacture was measured using a rheometer (manufactured by Anton Paar Japan Co., Ltd.: Rheometer MCR302). The viscosity was measured using a cone plate with a cone angle of 1° and a diameter of 25 mm, under shear rates (shear speeds) of 100 sec⁻¹ and 10000 sec⁻¹.

[0087] (Evaluation of the dried film) Using a small gravure printing press (manufactured by Kurashiki Boshoku Co., Ltd., GP-10TYPEII), conductive paste was printed onto a dielectric sheet at a printing speed of 30 m / min and a conductive powder (Ni powder) concentration of 0.7 mg / cm². The film was then dried in a box dryer at 80°C for 4 minutes to obtain a dried film (2.5 mm wide × 5 mm long) for evaluation. The film thickness was 0.50 μm to 2 μm.

[0088] The waviness of the dried film surface was evaluated using a laser microscope (KEYENCE VK-100, measuring objective × 20, measuring length: 2000 μm) with the waviness curve element having a cutoff value (λc = 0.08 mm) applied. Furthermore, the average height (Wc) of the waviness curve element was the average value obtained from multiple evaluations.

[0089] 〔Materials Used〕 (Conductive Powder) As the conductive powder, Ni powder (SEM average particle size is 0.2μm) is used.

[0090] (Ceramic powder) Barium titanate (BaTiO3; SEM average particle size is 0.10 μm) was used as the ceramic powder.

[0091] (Adhesive resin) Polyvinyl butyral resin and ethyl cellulose are used as adhesive resins.

[0092] (Additive) As an additive, dicarboxylic acid is used.

[0093] (Dispersant) As a dispersant, an acid-based dispersant and a base-based dispersant are used. In addition, as an acid-based dispersant, a comb-type carboxylic acid and a phosphoric acid dispersant are used, and as a base-based dispersant, oleylamine is used.

[0094] (Organic solvent) Isoborneol acetate (IBA), methyl isobutyl ketone (MIBK), diisobutyl ketone (DIBK), dihydroterpineol (DHT), propylene glycol monobutyl ether (PNB), diethylene glycol monobutyl ether acetate (BCA), propylene glycol monomethyl ether acetate (PMA), diethylene glycol monomethyl ether (DEGME), and mineral oil (MA) are used as organic solvents.

[0095] [Example 1] A conductive paste was prepared by mixing 50% by mass of conductive powder, 12.5% ​​by mass of ceramic powder, 0.5% by mass of dispersant (0.3% by mass of acidic dispersant and 0.2% by mass of alkali dispersant), 0.2% by mass of dicarboxylic acid, 2.5% by mass of adhesive resin (polyvinyl butyral resin: ethyl cellulose = 1:2 (mass ratio)), 4.1% by mass of IBA as an organic solvent, 12.0% by mass of MA, and DHT as the balance, with the total amount being 100% by mass. The evaluation results of the content of additives, etc., and the average height of the ripples in the conductive paste are shown in Table 1.

[0096] [Examples 2-18] In Examples 2-18, the presence or absence of additives, the type and proportion of organic solvents were changed as shown in Table 1. Otherwise, conductive pastes were prepared and evaluated in the same manner as in Example 1. The evaluation results Wc of the content of additives, etc., and the average height of the waviness of the conductive paste are shown in Table 1.

[0097] [Comparative Examples 1-4] As organic solvents, PNB (Comparative Example 1) was used at 13.7% by mass and the balance as a component; DHT (Comparative Example 2) was used at 13.7% by mass and the balance as a component; MA12% by mass and PMA5.9% by mass and the balance as a component ...

[0098] 〔Table 1〕

[0099] (Evaluation Results) Compared with the conductive pastes of Comparative Examples 1 to 4, which did not use the first organic solvent (IBA, MIBK, DIBK), the conductive pastes of Examples 1 to 18 had a smaller average height (Wc) of the waviness curve element in the dried film.

[0100] Furthermore, in all the conductive pastes of the embodiments and comparative examples shown in Table 1, it was confirmed that the viscosity was 3 Pa·s or less at a shear rate of 100 sec⁻¹ and 1 Pa·s or less at a shear rate of 10000 sec⁻¹, exhibiting a viscosity suitable for gravure printing. [Industrial Applicability]

[0101] When the conductive paste of the present invention is used to form the internal electrodes of a multilayer ceramic capacitor, a multilayer ceramic capacitor with high reliability can be obtained with high productivity. Therefore, the conductive paste of the present invention is particularly suitable as a raw material for the internal electrodes of multilayer ceramic capacitors used as chip parts in increasingly miniaturized electronic devices such as mobile phones and digital devices, and can be suitable as a conductive paste for gravure printing.

[0102] Furthermore, the technical scope of the present invention is not limited to the embodiments described above. Sometimes, one or more elements described in the embodiments above may be omitted. In addition, the elements described in the embodiments above may be appropriately combined. Furthermore, to the extent permitted by law, all disclosures of the documents cited in the embodiments above are incorporated into this specification.

[0103] Sometimes one or more elements described in the above embodiments may be omitted. Furthermore, elements described in the above embodiments may be appropriately combined. Moreover, to the extent permitted by law, all contents of Japanese Patent Application No. 2020-179986, Japanese Patent Application No. 2021-093300, and all documents cited in this specification are incorporated into this specification. [Simplified Explanation of the Diagram]

[0019] [Figure 1] is a perspective view and cross-sectional view of the multilayer ceramic capacitor involved in the embodiment.

Claims

1. A conductive paste for gravure printing, comprising Ni powder, ceramic powder, dispersant, binder resin, and organic solvent, characterized in that: the organic solvent comprises a first organic solvent and an organic solvent other than the first organic solvent; the first organic solvent is at least one selected from the group consisting of isoborneol acetate, methyl isobutyl ketone, and diisobutyl ketone; the organic solvent other than the first organic solvent comprises terpene solvent and aliphatic hydrocarbon solvent; the dispersant comprises an acidic dispersant; the total organic solvent content is 20% by mass or more and 60% by mass or less relative to the total conductive paste content; the first organic solvent content is 3% by mass or more and 10% by mass or less relative to the total conductive paste content; and the dried film obtained by gravure printing of the conductive paste for gravure printing at a printing speed of 30 m / min and a film thickness of 0.50 μm or more and 2 μm or less has an average height (Wc) of the waviness curve element less than 0.5 μm when the application cutoff value (λc = 0.08 mm) is used.

2. The conductive paste for gravure printing as described in claim 1, wherein, It further contains dicarboxylic acid at a concentration of 0.05% by mass or more and less than 3.0% by mass relative to the total conductive slurry.

3. The conductive paste for gravure printing as described in claim 1 or 2, wherein, The organic solvent contains 10% by mass or more and 60% by mass or less relative to the total conductive paste; when the terpene solvent is contained, the content of the terpene solvent is 5% by mass or more and 40% by mass or less; when the aliphatic hydrocarbon solvent is contained, the content of the aliphatic hydrocarbon solvent is 5% by mass or more and 25% by mass or less.

4. The conductive paste for gravure printing as described in claim 1 or 2, wherein, The dispersant contains 0.01% by mass and 3.0% by mass relative to the total conductive slurry.

5. The conductive paste for gravure printing as described in claim 1 or 2, wherein, The average particle size of the Ni powder is greater than 0.05 μm and less than 1.0 μm.

6. The conductive paste for gravure printing as described in claim 1 or 2, wherein, The ceramic powder contains barium titanate.

7. The conductive paste for gravure printing as described in claim 1 or 2, wherein, The ceramic powder has an average particle size of ≥0.01μm and ≤0.5μm.

8. The conductive paste for gravure printing as described in claim 1 or 2, wherein, The ceramic powder contains 1% to 20% by mass relative to the total conductive slurry.

9. The conductive paste for gravure printing as described in claim 1 or 2, wherein, This adhesive resin contains cellulose-based resin.

10. The conductive paste for gravure printing as described in claim 1 or 2, wherein, The viscosity is less than 3 Pa·S at a shear rate of 100 sec⁻¹ and less than 1 Pa·S at a shear rate of 10000 sec⁻¹.

11. An electronic component, characterized in that it is formed using a conductive paste for gravure printing as described in any one of claims 1 to 10.

12. A multilayer ceramic capacitor, characterized in that it has at least a multilayer body formed by multiplying a dielectric layer and an internal electrode layer, wherein the internal electrode layer is formed using a gravure printing conductive paste as described in any one of claims 1 to 10.

Images