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

Abstract

To provide a conductive paste for gravure printing that suppresses separation between a conductive powder and a ceramic powder and exhibits good viscosity stability over time, and provide an electronic component and a multilayer ceramic capacitor.SOLUTION: The present invention provides a conductive paste for gravure printing, the conductive paste containing a conductive powder, a ceramic powder, a dispersant, a binder resin and an organic solvent, wherein the dispersant contains a carboxylic acid-based polymer dispersant that has a weight average molecular weight of 5,000 or more, and the carboxylic acid-based polymer dispersant is contained in an amount of 0.01 mass% or more and less than 2.0 mass% relative to the total amount of the conductive paste.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a conductive paste for gravure printing, electronic components, and multilayer ceramic capacitors. [Background technology]

[0002] With the miniaturization and increased performance of electronic devices such as mobile phones and digital equipment, there is a demand for smaller and higher-capacitance electronic components, including multilayer ceramic capacitors. Multilayer ceramic capacitors have a structure in which multiple dielectric layers and multiple internal electrode layers are alternately stacked, and miniaturization and increased 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 dielectric green sheet containing dielectric powder such as barium titanate (BaTiO3) and a binder resin is printed in a predetermined electrode pattern onto its surface, and this is stacked in multiple layers to obtain a laminate in which the internal electrodes and dielectric green sheet are stacked in multiple layers. Next, this laminate is heated and compressed to integrate it and form a compressed body. This compressed body is cut, subjected to a de-organic binder treatment in an oxidizing or inert atmosphere, and then fired to obtain a fired chip. Subsequently, an external electrode paste is applied to both ends of the fired chip, and after firing, nickel plating or the like is applied to the surface of the external electrodes to obtain a multilayer ceramic capacitor.

[0004] While screen printing has traditionally been the most common printing method used to print conductive paste onto dielectric green sheets, the demands for miniaturization, thinner films, and improved productivity of electronic devices necessitate the printing of finer electrode patterns with higher productivity.

[0005] One proposed printing method for conductive paste is gravure printing, a continuous printing method in which conductive paste is filled into recesses in a printing plate and then pressed onto the surface to be printed, thereby transferring the conductive paste from the 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 to adjust its viscosity and other properties to a range suitable for gravure printing.

[0006] For example, Patent Document 1 describes a conductive paste used for forming an internal conductive film in a multilayer ceramic electronic component comprising a plurality of ceramic layers and an internal conductive film extending along a specific interface between the ceramic layers by gravure printing, comprising 30 to 70% by weight of a solid component containing metal powder, 1 to 10% by weight of an ethylcellulose resin component with an ethoxy group content of 49.6% or more, 0.05 to 5% by weight of a dispersant, and a solvent component as the remainder, with a shear rate of 0.1 (s -1 ) viscosity η 0.1 The pressure is 1 Pa·s or greater, and the shear rate is 0.02 (s) -1 ) viscosity η 0.02 A conductive paste is described that is a thixotropic fluid satisfying the conditions expressed by a specific formula.

[0007] Furthermore, Patent Document 2 describes a conductive paste used for formation by gravure printing, similar to Patent Document 1, comprising 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 a solvent component as the remainder, with a shear rate of 0.1 (s -1 A thixotropic fluid with a viscosity of 1 Pa·s or more at ) and a shear rate of 0.1 (s -1 When the viscosity at ) is used as the reference, the shear rate is 10 (s -1 A conductive paste is described in which the viscosity change rate at ) is 50% or more.

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

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

[0010] [Patent Document 1] Japanese Patent Publication No. 2003-187638 [Patent Document 2] Japanese Patent Publication No. 2003-242835 [Patent Document 3] Japanese Patent Publication No. 2012-174797 [Overview of the Initiative] [Problems that the invention aims to solve]

[0011] Low viscosity is required for conductive pastes used in gravure printing. However, in low-viscosity conductive pastes, compared to high-viscosity conductive pastes used in screen printing, the difference in sedimentation velocity due to the difference in specific gravity between ceramic powders such as barium titanate and conductive powders such as nickel has a more pronounced effect, making the conductive powder and ceramic powder more prone to separation.

[0012] For example, in conductive pastes for gravure printing, a phenomenon called "white floating" (two-layer separation) can occur when the conductive paste is made, in which a white separation layer containing ceramic powder forms on top.

[0013] Furthermore, the inventors' investigations revealed that, compared to conductive pastes used for screen printing, conductive pastes for gravure printing have lower viscosity, which tends to result in a higher viscosity increase over time, calculated as the ratio of viscosity after long-term storage to viscosity immediately after manufacturing. Compared to screen printing, the appropriate viscosity range for gravure printing is narrower, requiring precise viscosity control of the paste used. However, pastes with a high viscosity increase over time pose a problem, as the printing process becomes more complex, requiring viscosity adjustments each time gravure printing is performed.

[0014] In view of these circumstances, the present invention aims to provide a conductive paste that has a low paste viscosity suitable for gravure printing and can stably maintain that viscosity over a long period of time, and that can suppress the separation of conductive powder and ceramic powder. [Means for solving the problem]

[0015] In a first aspect of the present invention, a conductive paste for gravure printing is provided, comprising conductive powder, ceramic powder, a dispersant, a binder resin, and an organic solvent, wherein the dispersant comprises a carboxylic acid-based polymer dispersant having a weight-average molecular weight of 5000 or more, and the carboxylic acid-based polymer dispersant is contained in an amount of 0.01% by mass or more and less than 2.0% by mass of the entire conductive paste.

[0016] Further, the acid value of the carboxylic acid-based polymer dispersant is preferably 50 mgKOH / g or more and 250 mgKOH / g or less. Further, it is preferable to contain a polymer dispersant having a comb-shaped structure and / or a block polymer structure as the carboxylic acid-based polymer dispersant. Further, it is preferable that the polymer dispersant having a comb-shaped structure has a graft chain having a structure containing an alkylene oxide polymer.

[0017] Further, it is preferable that the organic solvent contains one or more selected from the group consisting of dihydroterpineol (DHT), dihydroterpinyl acetate (DHTA), terpineol (TPO), propylene glycol monobutyl ether (PNB), diethylene glycol monobutyl ether acetate (BCA), and diisobutyl ketone (DIBK).

[0018] Further, the content of the carboxylic acid-based polymer dispersant may be 60% by mass or more based on the total amount of the dispersant. Further, the dispersant may contain a carboxylic acid-based dispersant having a molecular weight of less than 5000 in an amount of 0% by mass or more and 60% by mass or less based on the total amount of the dispersant.

[0019] Further, the conductive powder preferably contains one or more metal powders selected from Ni, Pd, Pt, Au, Ag, Cu, and alloys thereof. Further, the conductive powder preferably has an average particle size of 0.05 μm or more and 1.0 μm or less. Further, the ceramic powder preferably contains barium titanate. Further, the ceramic powder preferably has an average particle size of 0.01 μm or more and 0.5 μm or less. Further, the ceramic powder is preferably contained in the conductive paste in an amount of 1% by mass or more and 20% by mass or less based on the whole conductive paste. Further, it is preferable that the binder resin contains a cellulose-based resin.

[0020] Further, the conductive paste for gravure printing is preferably for an internal electrode of a multilayer ceramic component. Further, the conductive paste for gravure printing has a viscosity of 1.2 Pa·S or less at a shear rate of 100 sec -1 which is preferable.

[0021] In a second aspect of the present invention, there is provided an electronic component formed using the above-described gravure printing conductive paste.

[0022] In a third aspect of the present invention, there is provided a multilayer ceramic capacitor having at least a laminate in which a dielectric layer and an internal electrode layer are laminated, and the internal electrode layer is formed using the above-described gravure printing conductive paste.

Advantages of the Invention

[0023] The conductive paste of the present invention has characteristics suitable for gravure printing, can suppress the separation of conductive powder and ceramic powder even in a low-viscosity paste, and has good viscosity stability over a long period, so that viscosity adjustment during printing is not required, contributing to the simplification of the printing process.

Brief Description of the Drawings

[0024] [Figure 1] FIG. 1A and FIG. 1B are a perspective view (FIG. 1A) and a cross-sectional view (FIG. 1B) showing a multilayer ceramic capacitor according to an embodiment.

Embodiments for Carrying Out the Invention

[0025] [Conductive Paste] The conductive paste of the present embodiment contains conductive powder, ceramic powder, a dispersant, a binder resin, and an organic solvent. Hereinafter, each component will be described in detail.

[0026] (Conductive Powder) The conductive powder is not particularly limited, and metal powders can be used. For example, one or more powders selected from Ni, Pd, Pt, Au, Ag, Cu, and their alloys can be used. Among these, Ni or its alloy (Ni alloy) powder is 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 element S in order to suppress the rapid generation of gas due to the partial thermal decomposition of the binder resin during the debindering process.

[0027] The average particle size of the conductive powder is preferably 0.05 μm to 1.0 μm, and more preferably 0.1 μm to 0.5 μm. When the average particle size of the conductive powder is within the above range, it can be suitably used as a paste for internal electrodes of thin-film multilayer ceramic capacitors (multilayer ceramic components), and for example, the smoothness and density of the dried film are improved. The 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 (SEM average particle size).

[0028] The conductive powder content is preferably 30% by mass or more and less than 70% by mass, and more preferably 40% by mass or more and 60% by mass or less, relative to the total conductive paste. When the conductive powder content is within the above range, the conductivity and dispersibility are excellent.

[0029] (Ceramic powder) The ceramic powder is not particularly limited, and for example, in the case of a paste for the internal electrodes of a multilayer ceramic capacitor, a known ceramic powder can be appropriately selected depending on the type of multilayer ceramic capacitor to be used. As the ceramic powder, for example, a perovskite-type oxide containing Ba and Ti can be used, and preferably contains barium titanate (BaTiO3).

[0030] 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 one or more oxides selected from Mn, Cr, Si, Ca, Ba, Mg, V, W, Ta, Nb, and rare earth elements. Examples of such ceramic powders include perovskite-type oxide ferroelectric ceramic powders in which the Ba atoms or Ti atoms of barium titanate (BaTiO3) are substituted with other atoms, such as Sn, Pb, or Zr.

[0031] The ceramic powder used in the conductive paste for the internal electrodes may have the same composition as the dielectric ceramic powder that constitutes the green sheet of the multilayer ceramic capacitor (electronic component). 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 perovskite-type oxides containing Ba and Ti, as well as oxides such as ZnO, ferrite, PZT, BaO, Al2O3, Bi2O3, R(rare earth element)2O3, TiO2, and Nd2O3. One type of ceramic powder may be used, or two or more types may be used.

[0032] The average particle size of the ceramic powder is, for example, 0.01 μm to 0.5 μm, preferably in the range of 0.01 μm to 0.3 μm. Because the average particle size of the ceramic powder is within this range, when used as a paste for internal electrodes, it is possible to form sufficiently fine, thin, and uniform internal electrodes. The 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 (SEM average particle size).

[0033] The ceramic powder content is preferably 1% to 20% by mass, and more preferably 3% to 15% by mass, relative to the total conductive paste. When the ceramic powder content is within the above range, the dispersibility and sinterability are excellent.

[0034] Furthermore, 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.

[0035] (Binder resin) The binder resin is not particularly limited, and known resins can be used. Examples of binder resins include cellulose-based resins such as methylcellulose, ethylcellulose, ethylhydroxyethylcellulose, and nitrocellulose, acrylic resins, and acetal resins including butyral-based resins such as polyvinyl butyral. Among these, it is preferable to include a cellulose-based resin, and more preferable to include ethylcellulose, from the viewpoint of solubility in solvents and combustion decomposition. Furthermore, when used as a paste for internal electrodes, it may include a butyral-based resin or use a butyral-based resin alone from the viewpoint of improving the adhesive strength with the green sheet. When the binder resin contains an acetal-based resin, the viscosity can be easily adjusted to a level suitable for gravure printing, and the adhesive strength with the green sheet can be further improved. For example, the binder resin may contain 20% by mass or more of acetal-based resin, or 30% by mass or more of acetal-based resin relative to the total binder resin. Alternatively, the binder resin may contain 50% by mass or less of acetal-based resin relative to the total binder resin.

[0036] The degree of polymerization and weight-average molecular weight of the binder resin can be appropriately adjusted within the above range depending on the required viscosity of the conductive paste.

[0037] The binder resin content is preferably 0.5% to 10% by mass, and more preferably 1% to 7% by mass, relative to the total conductive paste. When the binder resin content is within the above range, the conductivity and dispersibility are excellent.

[0038] The binder resin content is preferably 1 to 20 parts by mass, and more preferably 1 to 14 parts by mass, per 100 parts by mass of conductive powder.

[0039] (Organic solvents) The organic solvent is not particularly limited, and any known organic solvent capable of dissolving the binder resin can be used. Examples of organic solvents include terpene solvents, glycol ether solvents, acetate solvents, acetate ester solvents, ketone solvents, and hydrocarbon solvents. One type of organic solvent may be used, or two or more types may be used.

[0040] Examples of terpene solvents include terpineol (TPO), dihydroterpineol (DHT), and dihydroterpinyl acetate (DHTA), with dihydroterpineol (DHT) being preferred.

[0041] Examples of glycol ether solvents include (di)ethylene glycol ethers such as diethylene glycol mono-2-ethylhexyl ether, ethylene glycol mono-2-ethylhexyl ether, diethylene glycol monohexyl ether, and ethylene glycol monohexyl ether, and propylene glycol monoalkyl ethers such as propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, and propylene glycol monobutyl ether (PNB). Among these, propylene glycol monoalkyl ethers are preferred, and propylene glycol monobutyl ether (PNB) is more preferred. When the organic solvent contains a glycol ether solvent, it exhibits excellent compatibility with the binder resin described above, as well as excellent drying properties.

[0042] Examples of acetate-based solvents include glycol ether acetates such as ethylene glycol monobutyl ether acetate, diethylene glycol monobutyl ether acetate (butyl carbitol acetate: BCA), dipropylene glycol methyl ether acetate, 3-methoxy-3-methylbutyl acetate, and 1-methoxypropyl-2-acetate, as well as isobornyl acetate, isobornyl propinate, isobornyl butyrate, and isobornyl isobutyrate.

[0043] Examples of acetate ester solvents include ethyl acetate, propyl acetate, isobutyl acetate, and butyl acetate. Examples of ketone solvents include methyl ethyl ketone, methyl isobutyl ketone, and diisobutyl ketone (DIBK).

[0044] Examples of hydrocarbon solvents include aliphatic hydrocarbon solvents such as tridecane, nonane, cyclohexane, naphthenic solvents, and mineral spirits (MA), and aromatic hydrocarbon solvents such as toluene and xylene. Among these, aliphatic hydrocarbon solvents are preferred, and mineral spirits (MA) are more preferred. Furthermore, mineral spirits (MA) may contain chain-type saturated hydrocarbons as the main component, and may contain chain-type saturated hydrocarbons in an amount of 20% by mass or more relative to the total mineral spirits.

[0045] Furthermore, the organic solvent preferably contains one or more selected from the group consisting of dihydroterpineol (DHT), dihydroterpinyl acetate (DHTA), terpineol (TPO), propylene glycol monobutyl ether (PNB), diethylene glycol monobutyl ether acetate (BCA), and diisobutyl ketone (DIBK). By using these solvents, it is possible to achieve both appropriate viscosity and drying speed.

[0046] For example, the organic solvent may include one or more terpene solvents (a) selected from the group consisting of dihydroterpineol (DHT), dihydroterpinyl acetate (DHTA), and terpineol (TPO), one or more solvents (b) selected from the group consisting of propylene glycol monobutyl ether (PNB) and diethylene glycol monobutyl ether acetate (BCA), and a hydrocarbon solvent.

[0047] Furthermore, for example, the organic solvent may include one or more terpene solvents (a) selected from the group consisting of dihydroterpineol (DHT), dihydroterpinyl acetate (DHTA), and terpineol (TPO); one or more solvents (b) selected from the group consisting of propylene glycol monobutyl ether (PNB) and diethylene glycol monobutyl ether acetate (BCA); a hydrocarbon solvent; and diisobutyl ketone (DIBK).

[0048] The content of the organic solvent is preferably 20% to 50% by mass, and more preferably 25% to 45% by mass, relative to the total amount of the conductive paste. When the content of the organic solvent is within the above range, the conductivity and dispersibility are excellent.

[0049] The content of the organic solvent is preferably 50 parts by mass to 130 parts by mass, and more preferably 60 parts by mass to 90 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.

[0050] If the conductive paste contains a terpene-based solvent (a), the amount of the terpene-based solvent may be 5% by mass or more and 40% by mass or less, 10% by mass or more and 30% by mass or less, or 12% by mass or more and 25% by mass or less, based on the total amount of the conductive paste.

[0051] If the conductive paste contains a solvent (b) such as propylene glycol monobutyl ether (PNB), the content of solvent (b) may be 3% by mass or 20% by mass or 5% by mass or more and 20% by mass or less, based on the total amount of the conductive paste.

[0052] If the conductive paste contains a hydrocarbon solvent, the amount of the hydrocarbon solvent may be 1% by mass or more and 20% by mass or less, 3% by mass or more and 15% by mass or less, or 5% by mass or more and 10% by mass or less, based on the total amount of the conductive paste.

[0053] Furthermore, if the conductive paste contains diisobutyl ketone (DIBK), the diisobutyl ketone (DIBK) content is preferably 1% to 20% by mass relative to the total amount of the conductive paste, but may also be 3% to 15% by mass, or 3% to 10% by mass.

[0054] (Dispersant) The conductive paste according to this embodiment contains a carboxylic acid-based polymer dispersant having a molecular weight of 5000 or more. The inventors have found that by including a specific amount of a carboxylic acid-based polymer dispersant having a molecular weight of 5000 or more in a conductive paste for gravure printing, it is possible to stably obtain a viscosity suitable for gravure printing and to suppress the separation of conductive powder and ceramic powder.

[0055] Carboxylic acid-based polymer dispersants are polymer-based dispersants (surfactants) that have a carboxylic acid group as an adsorbent group. Carboxylic acid-based polymer dispersants may be polymers (copolymers) produced by polymerizing two or more monomers, including a carboxylic acid-containing monomer and a hydrophobic monomer. These polymers may also be synthesized by methods such as random polymerization, block polymerization, or graft polymerization.

[0056] Examples of carboxylic acid-based polymeric dispersants include random polymers in which carboxylic acid-containing monomers and hydrophobic monomers are randomly arranged, block polymer structures in which carboxylic acid-containing monomers and hydrophobic monomers are arranged in blocks, and polymeric dispersants having a comb-like structure. Polymeric dispersants having a comb-like structure can be obtained, for example, by polymerizing carboxylic acid-containing monomers, macromonomers, hydrophobic monomers, etc., and may have graft chains.

[0057] The carboxylic acid-based polymer dispersant preferably includes a carboxylic acid-based polymer dispersant having a comb-like structure and / or a block polymer structure, and more preferably includes a carboxylic acid-based polymer dispersant having a comb-like structure. Furthermore, the polymer dispersant having a comb-like structure preferably has graft chains, and it is preferable that the graft chains contain alkylene oxide polymers. Examples of alkylene oxide polymers included in the graft chains include ethylene oxide polymers, propylene oxide polymers, and butylene oxide polymers, and may also include ethylene oxide polymers.

[0058] Furthermore, the average molecular weight of the carboxylic acid-based polymer dispersant is 5000 or more, may be 10000 or more, 20000 or more, or 40000 or more. The average molecular weight of the carboxylic acid-based polymer dispersant affects the initial viscosity of the paste and its viscosity increase over time. When the average molecular weight is 5000 or more, a stable dispersion effect can be achieved, and viscosity increase over time can be sufficiently suppressed. In terms of suppressing viscosity increase over time, there is no particular upper limit to the average molecular weight, but if the average molecular weight is too large, the initial viscosity of the paste itself may become high, making it unsuitable for gravure printing, so the average molecular weight may be 100,000 or less. The average molecular weight is the weight-average molecular weight and can be measured, for example, by GPC (gel permeation chromatography).

[0059] Furthermore, the acid value of the carboxylic acid-based polymer dispersant is preferably 50 mg KOH / g or more and 250 mg KOH / g or less, and may also be 50 mg KOH / g or more and 200 mg KOH / g or less. A sufficient dispersion effect can be obtained with an acid value within this range. The acid value (mg KOH / g) can be determined, for example, by potentiometric titration in accordance with JIS K0070.

[0060] Furthermore, the above-mentioned carboxylic acid-based polymer dispersant is contained in an amount of 0.01% by mass or more and less than 2.0% by mass relative to the entire conductive paste, preferably 0.01% by mass or more and 1.0% by mass or less, and more preferably 0.03% by mass or more and 0.5% by mass or less. When the carboxylic acid-based polymer dispersant is contained within the above range, a viscosity suitable for gravure printing can be stably maintained for a long period of time, and the separation of the conductive powder and the ceramic powder can be suppressed.

[0061] Furthermore, the dispersant may consist solely of a carboxylic acid-based polymer dispersant, but may also contain dispersants other than carboxylic acid-based polymer dispersants, as described later. When a dispersant other than a carboxylic acid-based polymer dispersant is included, the content of the carboxylic acid-based polymer dispersant may be, for example, 40% by mass or more relative to the total amount of dispersant, preferably 60% by mass or more, and more preferably 80% by mass or more. The higher the content of the carboxylic acid-based polymer dispersant relative to the total amount of dispersant, the better the effect of suppressing the separation of conductive powder and ceramic powder.

[0062] Furthermore, the conductive paste of this embodiment may further contain an acidic dispersant other than the carboxylic acid-based polymer dispersant (a dispersant having an acidic adsorption group). Examples of acidic dispersants (excluding the carboxylic acid-based polymer dispersant) include carboxylic acid-based dispersants with an average molecular weight of less than 5000, phosphoric acid-based dispersants, and other acidic polymer surfactants. These acidic dispersants may be used individually or in combination of two or more types.

[0063] Examples of carboxylic acid-based dispersants with an average molecular weight of less than 5000 include higher fatty acids, dicarboxylic acids, polycarboxylic acid-based dispersants, and alkyl monoamine salt-type carboxylic acid-based dispersants. When a conductive paste contains a carboxylic acid-based dispersant with an average molecular weight of less than 5000 along with the above-mentioned carboxylic acid-based polymer dispersant, the dispersibility of ceramic powders such as barium titanate may be further improved. The average molecular weight of the carboxylic acid-based dispersant with an average molecular weight of less than 5000 may be 2000 or less, or 1000 or less.

[0064] The higher fatty acids can be either unsaturated or saturated carboxylic acids, and are not particularly limited, but examples include those with 11 or more carbon atoms, such as stearic acid, oleic acid, myristic acid, palmitic acid, linoleic acid, lauric acid, and linolenic acid. Among these, oleic acid or stearic acid are preferred as higher fatty acids.

[0065] Preferred alkyl monoamine salts include, for example, oleoylsarcosine, a compound of glycine and oleic acid, and stearic acid amide and laurylsarcosine, which are amide compounds using higher fatty acids such as stearic acid or lauric acid instead of oleic acid.

[0066] Furthermore, if the content of carboxylic acid-based dispersants with an average molecular weight of less than 5000 is too high, there is a concern that it may have adverse effects such as inhibiting the adsorption of the carboxylic acid-based polymer dispersant to the metal powder material (filler). Therefore, when using them in combination, it is preferable to adjust the content appropriately.

[0067] For example, the content of a carboxylic acid-based dispersant with an average molecular weight of less than 5000 may be 60% by mass or less of the total amount of dispersant, preferably 40% by mass or less, and more preferably 20% by mass or less. Furthermore, the lower limit of the content of a carboxylic acid-based dispersant with an average molecular weight of less than 5000 is 0% by mass.

[0068] Furthermore, the dispersant may include dispersants other than acidic dispersants. Examples of dispersants other than acidic dispersants include basic dispersants, nonionic dispersants, and amphoteric dispersants. These dispersants may be used individually or in combination of two or more.

[0069] Examples of basic dispersants include aliphatic amines such as laurylamine, rosinamine, cetylamine, myristylamine, stearylamine, and oleylamine.

[0070] Furthermore, the total content of the dispersant is preferably less than 3.0% by mass relative to the total conductive paste. If the content of the carboxylic acid-based polymer dispersant or the total content of the dispersant is too high, drying may be insufficient during the printing and drying processes, resulting in a soft internal electrode layer, which may cause misalignment in the subsequent lamination process. In addition, residual dispersant may vaporize during firing, and the vaporized gas components may cause internal stress or structural failure of the laminate.

[0071] (Additives) The conductive paste of this embodiment may contain other additives besides the dispersant described above, if necessary. Other additives that can be used include, for example, conventionally known additives such as defoamers, plasticizers, surfactants, and thickeners.

[0072] For example, Patent Document 3 describes polycarboxylic acid polymers and salts of polycarboxylic acids as separation inhibitors that suppress the separation of conductive powder and dielectric powder. In this specification, such separation inhibitors are also included in acid-based dispersants in a broad sense as agents that improve the dispersibility of inorganic powders.

[0073] (Conductive paste) The method for producing the conductive paste according to this embodiment is not particularly limited, and conventionally known methods can be used. The conductive paste can be produced, for example, by stirring and kneading each of the above components using a three-roll mill, ball mill, mixer, etc. Regarding the dicarboxylic acid (separation inhibitor), it is preferable to weigh and add it when stirring and kneading with a mixer, etc., as with the other materials, but the same effect can be obtained by adding it as a separation inhibitor to the material after stirring and kneading (dispersion) is complete.

[0074] The conductive paste has a shear rate of 100 sec. -1 The viscosity is preferably 1.2 Pa·s or less. Shear rate 100 sec -1When the viscosity is within the above range, it can be suitably used as a conductive paste for gravure printing. If it exceeds the above range, the viscosity may be too high and it may not be suitable for gravure printing. Shear speed 100 sec -1 The lower limit of viscosity is not particularly limited, but for example, it is 0.2 Pa·S or higher.

[0075] Furthermore, the thickness of the white layer observed in the conductive paste from immediately after preparation to one week later is preferably less than 8% of the total thickness of the conductive paste, but may be 5% or less, or 2% or less. The thinner the white layer, the better the effect of suppressing the separation of the conductive powder and the ceramic powder. The thickness of the white layer can be measured by the method described in the examples below.

[0076] Furthermore, the conductive paste of this embodiment can be suitably used in electronic components such as multilayer ceramic capacitors. Multilayer ceramic capacitors have a dielectric layer and an internal electrode layer formed using a dielectric green sheet, and the conductive paste of this embodiment can be suitably used for forming the internal electrode layer.

[0077] [Electronic components] Hereinafter, an example of an electronic component according to this embodiment will be described with reference to the drawings. In the drawings, schematic representations and changes in scale may be used as appropriate. Furthermore, the position and orientation of the components will be described with reference to the XYZ Cartesian coordinate system shown in Figures 1A and 1B as appropriate. In this XYZ Cartesian coordinate system, the X and Y directions are horizontal directions, and the Z direction is vertical (up and down direction).

[0078] Figures 1A and 1B show a multilayer ceramic capacitor 1, which is an example of an electronic component. The multilayer ceramic capacitor 1 comprises a laminate 10 in which dielectric layers 12 and internal electrode layers 11 are alternately stacked, and an external electrode 20.

[0079] The following describes an example of a method for manufacturing a multilayer ceramic capacitor using the conductive paste described above. First, the conductive paste is gravure printed onto a ceramic green sheet (dielectric green sheet) and dried to form a dried film. Multiple ceramic green sheets, each having this dried film on its upper surface, are laminated by compression to obtain a laminate. The laminate is then fired to integrate it, thereby creating a ceramic laminate 10 in which internal electrode layers 11 and dielectric layers 12 are alternately laminated. Subsequently, a pair of external electrodes 20 are formed at both ends of the ceramic laminate 10 to manufacture a multilayer ceramic capacitor 1. A more detailed explanation follows below.

[0080] 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 shape to a support film such as a PET film, dried, and the solvent removed. The thickness 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.

[0081] Next, the conductive paste described above is printed onto one side of the ceramic green sheet using gravure printing, and then dried to form a dried film. Multiple sheets of this dried film are prepared. From the viewpoint of thinning the internal electrode layer 11, the thickness of the dried film is preferably 1 μm or less after drying.

[0082] Next, the ceramic green sheet is peeled off the support film, and the ceramic green sheet and the dried film formed on one side of it are laminated alternately. Then, a laminate is obtained by heating and pressurizing. Alternatively, protective ceramic green sheets without conductive paste can be placed on both sides of the laminate.

[0083] 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 a laminated ceramic fired body (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. 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 temperature used for firing the laminate is, for example, 1000°C to 1350°C, and the holding time at the temperature during firing is, for example, 0.5 hours to 8 hours.

[0084] 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 internal electrode layer 11 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.

[0085] 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. Electronic components other than multilayer ceramic capacitors can also be used. [Examples]

[0086] 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.

[0087] [Evaluation Method] (Viscosity of conductive paste) The viscosity of the conductive paste was measured using a rheometer (Anton Paar Japan Co., Ltd.: Rheometer MCR302). Viscosity was measured using a cone plate with a cone angle of 1° and a diameter of 25 mm, at a shear rate of 100 sec. -1 The values ​​used were those measured under the specified conditions.

[0088] Furthermore, the viscosity of the conductive paste was measured at 1 day and 1 week after manufacturing. The measurement at 1 day was defined as the initial viscosity, and the ratio of the measurement at 1 week to this initial viscosity (measurement at 1 week / measurement at 1 day) was evaluated as the viscosity increase over time ratio. For the initial viscosity, a value of 0.2 Pa·s or higher and less than 1.2 Pa·s was evaluated as "○" and a value of 1.2 Pa·s or higher was evaluated as "×". For the viscosity increase over time ratio, a value of less than 1.3 was evaluated as "○" (sufficient viscosity stability), and a value of 1.3 or higher was evaluated as "×" (insufficient viscosity stability).

[0089] (White cast) 20g of conductive paste immediately after preparation was placed in a glass bottle (diameter φ30 x height 65mm) at room temperature. After one week, the appearance of the conductive paste was visually observed, and the percentage of white floating was measured. The percentage of white floating (%) was calculated as (thickness of the white floating layer / total thickness of the paste) * 100. The percentage of white floating (%) was evaluated as follows: less than 5% as "○" (good separation inhibition effect), 5% to less than 8% as "△" (separation inhibition effect present), and 8% or more as "×" (insufficient separation inhibition effect).

[0090] [Materials used] (conductive powder) Ni powder (SEM average particle size 0.3 μm) was used as the conductive powder.

[0091] (Ceramic powder) Barium titanate (BaTiO3; SEM average particle size 0.10 μm) was used as the ceramic powder.

[0092] (Binder resin) Polyvinyl butyral and ethylcellulose were used as binder resins.

[0093] (Dispersant) Carboxylic acid-based polymer dispersants 1-4 with a molecular weight of 5000 or more, carboxylic acid-based low molecular weight dispersants 1-2, and amine-based polymer dispersant 1 were used. Details of each dispersant are summarized in Table 1. Note that carboxylic acid-based polymer dispersant 4 has a linear block polymer structure (it does not have a comb-like structure).

[0094] [Table 1]

[0095] (Organic solvents) The organic solvents used were propylene glycol monobutyl ether (PNB), butyl carbitol (BCA), mineral spirits (MA), terpineol (TPO), dihydroterpineol (DHT), dihydroterpineol acetate (DHTA), and diisobutyl ketone (DIBK).

[0096] [Example 1] A material was prepared by adding 50% by mass of conductive powder, 12.5% ​​by mass of ceramic powder, 0.05% by mass of dispersant (dispersant type: carboxylic acid polymer dispersant 1), 2.5% by mass of binder resin (1.7% by mass of polyvinyl butyral resin, 0.8% by mass of ethyl cellulose), and an organic solvent as the remainder (solvent 1: remainder, solvent 2: 9.5% by mass, solvent 3: 7% by mass) to a total of 100% by mass. A conductive paste was prepared by mixing and dispersing these materials. Here, solvent 1 is DHT, solvent 2 is PNB, and solvent 3 is MA. The test conditions and evaluation results, including details of the additives, are shown in Table 1.

[0097] [Examples 2-10, Comparative Examples 1-3] A conductive paste was prepared and evaluated in the same manner as in Example 1, except that the type and amount of dispersant and solvents 1-3 were changed as shown in Tables 1 and 2. The mixing ratio due to the difference in the amount of dispersant was adjusted by adjusting the amount of solvent 1 so that the entire conductive paste was 100% by mass. Details of the dispersants are shown in Table 1, and the test conditions and evaluation results are shown in Table 2. [Example 11] The composition of the organic solvents was changed to include four types, with the respective contents being (solvent 1: remainder, solvent 2: 5.3% by mass, solvent 3: 7% by mass, solvent 4: 4.2% by mass). Conductive pastes were prepared and evaluated in the same manner as in Example 2, except that DHT was used as solvent 1, BCA as solvent 2, MSA as solvent 3, and DIBK as solvent 4. Details of the dispersants are shown in Table 1, and the test conditions and evaluation results are shown in Table 2.

[0098] [Table 2]

[0099] (Evaluation results) The conductive paste of the example shows improved viscosity stability over time compared to the conductive pastes of Comparative Examples 1-3, which do not contain carboxylic acid-based polymer dispersants with a molecular weight of 5000 or more. Furthermore, the proportion of white floating that occurs during storage is significantly smaller, indicating an improved separation suppression effect.

[0100] In Comparative Example 1, the conductive paste uses a comb-shaped carboxylic acid-based dispersant, but because its molecular weight is small (approximately 800), the dispersion effect of the fine particles is insufficient, and over time, an unacceptable increase in viscosity occurs for use as a conductive paste for gravure printing. In Comparative Example 2, the conductive paste uses a low molecular weight carboxylic acid-based dispersant, and although the viscosity is sufficiently stable, the proportion of white residue exceeds the acceptable limit. In Comparative Example 3, the conductive paste uses a polymer-based dispersant with a comb-shaped structure, but because the adsorbent group is an amine, the initial viscosity is high and it is not suitable for gravure printing.

[0101] Example 2 is a sample in which the content of the comb-shaped carboxylic acid-based polymer dispersant 1 used in Example 1 was increased, and better results were obtained in initial viscosity, viscosity increase ratio over time, and amount of white floating.

[0102] Examples 3 and 4 are samples using comb-type carboxylic acids (Mw: 10,000-30,000) with a lower average molecular weight than the comb-type carboxylic acid (Mw: 50,000) used in Example 2. In the conductive pastes of Examples 3 and 4, the amount of white residue increased slightly compared to the conductive paste of Example 2, and the viscosity increase over time was also greater in the conductive paste of Example 4.

[0103] Furthermore, the conductive paste of Example 5 uses a block polymerization type carboxylic acid-based polymer dispersant, and by adding a larger amount than in the other examples that use a comb-shaped carboxylic acid-based polymer dispersant, it is possible to achieve the same level of effect as in the other examples.

[0104] The conductive pastes of Examples 6 and 7 combine a carboxylic acid-based comb-type polymer dispersant with a low molecular weight carboxylic acid-based dispersant. Compared to the conductive paste of Example 2, which uses the same type of comb-type carboxylic acid-based polymer dispersant, the conductive pastes of Examples 6 and 7 show a similarly low ratio of thickening over time, but a slight increase in the amount of white residue. Furthermore, compared to the conductive pastes of other examples (e.g., Examples 4 and 5) that use dispersants with a lower average molecular weight than the comb-type carboxylic acid-based polymer dispersant of Example 2, the ratio of thickening over time is lower, but the amount of white residue tends to increase within an acceptable range.

[0105] Examples 8, 9, 10, and 11 are samples in which the solvent type of the conductive paste from Example 2 was changed. Even with the same solvent content, changing the solvent combination slightly alters the viscosity, the ratio of thickening over time, and the amount of white residue, but these do not change significantly. Therefore, it is possible to fine-tune the viscosity by selecting the solvent type according to the usage conditions.

[0106] Furthermore, the technical scope of the present invention is not limited to the embodiments described above. One or more of the requirements described above may be omitted. Also, the requirements described above may be combined as appropriate. In addition, to the extent permitted by law, all disclosures of the documents cited above shall be incorporated as part of the description herein. [Industrial applicability]

[0107] The conductive paste of the present invention maintains a stable viscosity suitable for gravure printing over a long period of time, and exhibits sufficiently low separation between the conductive powder and the ceramic powder. Therefore, the conductive paste of the present invention can be suitably used as a raw material for internal electrodes of multilayer ceramic capacitors, which are chip components of increasingly miniaturized electronic devices such as mobile phones and digital devices, and can be suitably used as a conductive paste for gravure printing. [Explanation of Symbols]

[0108] 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 for gravure printing comprising conductive powder, ceramic powder, dispersant, binder resin and organic solvent, The dispersant comprises a carboxylic acid-based polymer dispersant having a weight-average molecular weight of 5,000 or more and 100,000 or less. The carboxylic acid-based polymer dispersant comprises a polymer-based dispersant having a comb-like structure and / or a block polymer structure. A conductive paste for gravure printing, comprising the carboxylic acid-based polymer dispersant in an amount of 0.01% by mass or more and less than 2.0% by mass relative to the entire conductive paste.

2. The conductive paste for gravure printing according to claim 1, wherein the acid value of the carboxylic acid-based polymer dispersant is 50 mg KOH / g or more and 250 mg KOH / g or less.

3. The conductive paste for gravure printing according to claim 1, wherein the polymeric dispersant having the comb-shaped structure has graft chains containing an alkylene oxide polymer.

4. A conductive paste for gravure printing according to any one of claims 1 to 3, wherein the organic solvent comprises one or more selected from the group consisting of dihydroterpineol (DHT), dihydroterpinyl acetate (DHTA), terpineol (TPO), propylene glycol monobutyl ether (PNB), diethylene glycol monobutyl ether acetate (BCA), and diisobutyl ketone (DIBK).

5. The conductive paste for gravure printing according to any one of claims 1 to 4, wherein the content of the carboxylic acid-based polymer dispersant is 60% by mass or more relative to the total amount of the dispersant.

6. The conductive paste for gravure printing according to any one of claims 1 to 5, wherein the dispersant comprises a carboxylic acid-based dispersant having a molecular weight of less than 5000 in an amount of 0% by mass or more and 60% by mass or less based on the total amount of the dispersant.

7. The conductive paste for gravure printing according to any one of claims 1 to 6, wherein the conductive powder comprises one or more metal powders selected from Ni, Pd, Pt, Au, Ag, Cu, and alloys thereof.

8. The conductive paste for gravure printing according to any one of claims 1 to 7, wherein the conductive powder has an average particle size of 0.05 μm or more and 1.0 μm or less.

9. The conductive paste for gravure printing according to any one of claims 1 to 8, wherein the ceramic powder comprises barium titanate.

10. The conductive paste for gravure printing according to any one of claims 1 to 9, wherein the ceramic powder has an average particle size of 0.01 μm or more and 0.5 μm or less.

11. The conductive paste for gravure printing according to any one of claims 1 to 10, wherein the ceramic powder is contained in an amount of 1% by mass or more and 20% by mass or less of the total conductive paste.

12. The conductive paste for gravure printing according to any one of claims 1 to 11, wherein the binder resin comprises a cellulose-based resin.

13. A conductive paste for gravure printing according to any one of claims 1 to 12, for use as an internal electrode in a multilayer ceramic component.

14. Shear rate 100 sec －１ A conductive paste for gravure printing according to any one of claims 1 to 13, wherein the viscosity at [a certain point] is 0.2 Pa·s or more and 1.2 Pa·s or less.

15. An electronic component formed using a conductive paste for gravure printing as described in any one of claims 1 to 14.

16. The laminate comprises at least a dielectric layer and an internal electrode layer, The internal electrode layer is formed using a conductive paste for gravure printing as described in any one of claims 1 to 14.

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