Polyvinyl acetal resin for manufacturing multilayer ceramic capacitors, conductive paste, and multilayer ceramic capacitors

Abstract

An object of the present invention is to provide a polyvinyl acetal resin for producing a multilayer ceramic capacitor, which has a high paste viscosity after being kneaded with a conductive powder, good thixotropy, and excellent printability, and to provide a conductive paste and a multilayer ceramic capacitor using the polyvinyl acetal resin for producing a multilayer ceramic capacitor. The polyvinyl acetal resin is used in a conductive paste for manufacturing a multilayer ceramic capacitor, and has a constitutional unit represented by the following formula (1), wherein R 1 is a hydrocarbon group having 4 to 20 carbon atoms. [C1] TIFF0007730962000009.tif31156

Description

[Technical Field]

[0001] The present invention relates to a polyvinyl acetal resin for producing a multilayer ceramic capacitor, a conductive paste, and a multilayer ceramic capacitor. [Background technology]

[0002] Multilayer electronic components such as multilayer circuit boards, multilayer coils, and multilayer ceramic capacitors are widely used, and among them, multilayer ceramic capacitors are generally manufactured through the following process. First, a ceramic raw material powder is added to a solution of a binder resin such as polyvinyl butyral resin or poly(meth)acrylic acid ester resin dissolved in an organic solvent, and the mixture is mixed uniformly to obtain a ceramic slurry composition. This slurry composition is cast onto a support, and volatile components such as the solvent are removed by heating or the like, and then peeled off from the support to obtain a ceramic green sheet. Next, a conductive paste for internal electrodes is applied to the obtained ceramic green sheets by screen printing or gravure printing, and multiple sheets are stacked alternately and heated and pressed to form a laminate. After that, a process to thermally decompose and remove binder resin components and the like contained in the laminate, known as a degreasing process, is performed, and external electrodes are sintered onto the end faces of the ceramic sintered body obtained by firing, to obtain a multilayer ceramic capacitor.

[0003] The conductive paste for the internal electrodes is obtained by kneading a conductive powder, an organic solvent, and a binder resin. As the binder resin, ethyl cellulose or polyvinyl acetal resin is used. However, when a polyvinyl acetal resin is used as the binder resin, there is a problem in that stringiness occurs when the paste is printed by screen printing. Patent Document 1 discloses a conductive paste containing a carboxylic acid-modified polyvinyl acetal resin, an organic solvent, and a conductive powder in order to solve the above problems. Patent Document 2 discloses a conductive paste containing a polyvinyl acetal resin having an ethylene group in order to solve the above problems. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2017-228780 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-285590 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, attention has been focused on miniaturization of multilayer ceramic capacitors, and as a result, more precise printability is required for conductive pastes for internal electrodes. However, when the polyvinyl acetal resins described in Patent Documents 1 and 2 are used as binder resins for conductive pastes for internal electrodes, the viscosity of the paste is low after mixing with conductive powder, and bleeding of the conductive paste for internal electrodes may occur during screen printing or gravure printing.

[0006] The polyvinyl acetal resin for producing a multilayer ceramic capacitor according to the present invention has a high paste viscosity after being kneaded with a conductive powder, good thixotropy, and excellent printability, and an object of the present invention is to provide a conductive paste and a multilayer ceramic capacitor using the polyvinyl acetal resin for producing a multilayer ceramic capacitor. Here, the printability means that both stringiness and bleeding can be prevented during screen printing or gravure printing. [Means for solving the problem]

[0007] Disclosure 1 provides a polyvinyl acetal resin used in a conductive paste for manufacturing a multilayer ceramic capacitor, the polyvinyl acetal resin having a constitutional unit represented by the following formula (1), wherein R 1 is a hydrocarbon group having 4 to 20 carbon atoms. [ka] Disclosure 2 is the polyvinyl acetal resin for producing a multilayer ceramic capacitor according to Disclosure 1, which has an average degree of polymerization of less than 2,300. Disclosure 3 is the polyvinyl acetal resin for producing a multilayer ceramic capacitor according to Disclosure 1 or 2, in which the total amount of acetal groups is 69 mol % or more. This disclosure 4 describes a 10 mass% solution of dihydroterpineol acetate (DHTA) in a solvent, measured at a temperature of 20°C and in a shear region of 100 s -1 The polyvinyl acetal resin for producing a multilayer ceramic capacitor according to any one of Disclosures 1 to 3 of the present invention has a viscosity of 1.5 Pa·s or more when measured using a rotational rheometer under the following conditions: Disclosure 5 relates to R in formula (1). 1 is a hydrocarbon group having 6 to 20 carbon atoms, and the amount of acetyl groups is 5 mol % or less. Disclosure 6 relates to R in formula (1). 1 is a linear hydrocarbon group having 6 or 9 carbon atoms. Disclosure 7 is the polyvinyl acetal resin for producing a multilayer ceramic capacitor according to any one of Disclosures 1 to 6, wherein the content of the constitutional unit represented by formula (1) is 5 mol % or more and 35 mol % or less. The present disclosure 8 is a polyvinyl acetal resin for producing a multilayer ceramic capacitor according to any one of the present disclosures 1 to 7, wherein the content of the structural unit represented by formula (1) relative to the total amount of acetal groups (content of the structural unit represented by formula (1) / total amount of acetal groups) is 0.06 or more and 0.51 or less. Disclosure 9 is the polyvinyl acetal resin for producing a multilayer ceramic capacitor according to any one of Disclosures 1 to 8, wherein the amount of hydroxyl groups is 10 mol % or more and 30 mol % or less. Disclosure 10 is the polyvinyl acetal resin for producing a multilayer ceramic capacitor according to any one of Disclosures 1 to 9, which has an average degree of polymerization of 500 or more. Disclosure 11 is a conductive paste containing the polyvinyl acetal resin for producing a multilayer ceramic capacitor according to any one of Disclosures 1 to 10, an organic solvent, a conductive powder, and a dispersion improver. Disclosure 12 is a multilayer ceramic capacitor formed using the conductive paste according to Disclosure 11.

[0008] As a result of extensive research, the present inventors have found that a polyvinyl acetal resin for producing a multilayer ceramic capacitor containing a specific structural unit has a high paste viscosity after being kneaded with a conductive powder, good thixotropy, and excellent printability, and have thus completed the present invention.

[0009] The polyvinyl acetal resin for producing a multilayer ceramic capacitor of the present invention is used in a conductive paste for producing a multilayer ceramic capacitor. When used as such a conductive paste, the paste has a high viscosity after being kneaded with the conductive powder, and is excellent in printability and thixotropy. The conductive paste is preferably a conductive paste for internal electrodes that is printed on ceramic green sheets.

[0010] The polyvinyl acetal resin for producing a multilayer ceramic capacitor of the present invention has a constitutional unit represented by the following formula (1), and R 1is a hydrocarbon group having 4 to 20 carbon atoms. By having such a hydrocarbon group, the compound has excellent solubility in solvents, high paste viscosity, and good thixotropy, which can improve printability.

[0011] [ka]

[0012] Above R 1 The number of carbon atoms in the above R is preferably 5 or more. The lower limit of the number of carbon atoms is more preferably 6, the upper limit is more preferably 15, and the upper limit is still more preferably 10. 1 may be a combination of two or more hydrocarbon groups having different carbon numbers.

[0013] Above (R 1 The hydrocarbon group having 4 to 20 carbon atoms is preferably an alkyl group having 4 to 20 carbon atoms. Examples of the alkyl group having 4 to 20 carbon atoms include a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, an octadecyl group, a nonadecyl group, and an eicosyl group.

[0014] Above (R 1 The hydrocarbon group having 4 to 20 carbon atoms (c) may be a linear alkyl group or a branched alkyl group. Examples of the linear alkyl group include an n-butyl group, an n-pentyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, an n-nonyl group, an n-decyl group, an n-undecyl group, an n-dodecyl group, an n-tridecyl group, an n-tetradecyl group, an n-hexadecyl group, an n-heptadecyl group, an n-octadecyl group, an n-nonadecyl group, and an n-eicosyl group. Among them, the above R 1is preferably a linear hydrocarbon group having 6 or 9 carbon atoms, and is preferably an n-hexyl group or an n-nonyl group. By having such a hydrocarbon group, the resin has excellent solubility in solvents, high paste viscosity, and good thixotropy, which can improve printability.

[0015] Examples of the branched alkyl group include isobutyl, isopentyl, neopentyl, 1-methylhexyl, 1-methylheptyl, 1-methyloctyl, 1-methylnonyl, 1-methyldecyl, 1-methylundecyl, and 1-methyldodecyl groups. Other examples include 1-methyltridecyl, 1-methyltetradecyl, 1-methylheptadecyl, 1-methylhexadecyl, 1-methylpentadecyl, 1-methyloctadecyl, and 1-methylnonadecyl groups. Further examples include alkyl groups in which an alkyl group having two or more carbon atoms is substituted on the carbon atom at position 1 (for example, 1-ethyldecyl group, 1-propylnonyl group, 1-butyloctyl group, 1-pentylheptyl group, 1-octyldecyl group, etc.). Furthermore, in a branched alkyl group, the branching position is not limited to the first carbon atom, but may be the second or higher carbon atom. Examples of alkyl groups in which a methyl group is substituted on the second or higher carbon atom include 2-methylundecyl, 3-methylundecyl, and 4-methylundecyl groups. Examples of alkyl groups in which an alkyl group having two or more carbon atoms is substituted on the second or higher carbon atom include 2-ethylhexyl, 2-ethylheptyl, 2-ethyloctyl, 2-ethylundecyl, 2-ethyloctadecyl, 2-propylundecyl, 2-butylundecyl, and 2-octylundecyl groups. Further examples include 3-ethylundecyl, 4-ethyloctadecyl, 4-butyloctadecyl, and neodecyl groups.

[0016] In the present invention, the hydrocarbon group having 4 to 20 carbon atoms is preferably a linear alkyl group. The alkyl group having 4 to 20 carbon atoms may be composed of two or more alkyl groups including a linear alkyl group and a branched alkyl group, or may be composed of only a linear alkyl group. In addition, R 1 may be a hydrocarbon group based on a bio-derived aldehyde having from 4 to 20 carbon atoms.

[0017] The content of the structural unit represented by the above formula (1) in the polyvinyl acetal resin for manufacturing a multilayer ceramic capacitor of the present invention is preferably 5 mol % at the lower limit, more preferably 10 mol % at the lower limit, and preferably 35 mol % at the upper limit, more preferably 33 mol % at the upper limit. This allows for excellent solubility in solvents, high paste viscosity, good thixotropy, and good printability. The content of the structural unit represented by the above formula (1) is 1 H-NMR and 13 It is measured using C-NMR (nuclear magnetic resonance spectroscopy).

[0018] The polyvinyl acetal resin for producing a multilayer ceramic capacitor of the present invention preferably further contains an acetal unit represented by the following formula (2), which is different from the constitutional unit represented by the above formula (1). By containing the acetal unit represented by the above formula (2), excellent solubility in solvents, high paste viscosity, good thixotropy, and good printability can be achieved.

[0019] [ka] In formula (2), R 2 represents an alkyl group having 1 to 19 carbon atoms.

[0020] Examples of the alkyl group having 1 to 19 carbon atoms include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, an octadecyl group, and a nonadecyl group. The alkyl group having 1 to 19 carbon atoms may be linear or branched. As for the alkyl group having 1 to 19 carbon atoms, the same ones as in the case of the alkyl group having 4 to 20 carbon atoms can be used. Among them, the above R 2 is preferably a linear hydrocarbon group having 1 or 3 carbon atoms, and is preferably a methyl group or an n-propyl group. By having such a hydrocarbon group, the solubility in a solvent can be improved.

[0021] The content of the acetal units represented by the above formula (2) in the polyvinyl acetal resin of the present invention is preferably 34 mol% at the lower limit, more preferably 36 mol%, and preferably 85 mol% at the upper limit, more preferably 80 mol%. By setting the content of the acetal units represented by the above formula (2) within the above range, excellent solubility in solvents, high paste viscosity, good thixotropy, and good printability can be achieved. The content of the acetal units represented by the above formula (2) is 1 H-NMR and 13 It is measured using C-NMR (nuclear magnetic resonance spectroscopy).

[0022] When the polyvinyl acetal resin of the present invention contains the acetal units represented by the formula (1) and the acetal units represented by the formula (2), the total content thereof is preferably 69 mol% at the lower limit, more preferably 71 mol% at the lower limit, and preferably 90 mol% at the upper limit, more preferably 80 mol% at the upper limit. By keeping the total content within the above range, excellent solubility in solvents, high paste viscosity, good thixotropy, and good printability can be achieved.

[0023] When the polyvinyl acetal resin of the present invention contains acetal units represented by the above formula (1) and acetal units represented by the above formula (2), the ratio between them (content of acetal units represented by formula (1) / content of acetal units represented by formula (2)) is preferably 0.06 to 1.03. By keeping the ratio within the above range, excellent solubility in solvents, high paste viscosity, good thixotropy, and good printability can be achieved.

[0024] The polyvinyl acetal resin for use in producing a multilayer ceramic capacitor of the present invention preferably has a total acetal group content (total amount of all acetal units) of 69 mol % or more. By setting the total acetal group content within the above range, excellent solubility in solvents, high paste viscosity, good thixotropy, and good printability can be achieved. The lower limit of the total acetal group amount is more preferably 69 mol %, and even more preferably 71 mol %, and the upper limit is preferably 90 mol %, and even more preferably 80 mol %. 1 H-NMR and 13 It is measured using C-NMR (nuclear magnetic resonance spectroscopy). Furthermore, the content of the structural unit represented by the above formula (1) relative to the total amount of acetal groups (content of structural unit represented by formula (1) / total amount of acetal groups) has a preferred lower limit of 0.06 and a preferred upper limit of 0.51.

[0025] The polyvinyl acetal resin for producing a multilayer ceramic capacitor of the present invention has a structural unit having a hydroxyl group. The content of the hydroxyl group-containing structural unit (hydroxyl group amount) in the polyvinyl acetal resin for producing a multilayer ceramic capacitor of the present invention is preferably 10 mol % or more and 30 mol % or less, which can improve the solubility in solvents. The more preferred lower limit of the amount of hydroxyl groups is 20 mol %, and the more preferred upper limit is 29 mol %. 1 H-NMR and 13It is measured using C-NMR (nuclear magnetic resonance spectroscopy).

[0026] The polyvinyl acetal resin for producing a multilayer ceramic capacitor of the present invention has a structural unit having an acetyl group. The content of the acetyl group-containing structural units (acetyl group amount) in the polyvinyl acetal resin for producing a multilayer ceramic capacitor of the present invention preferably has a lower limit of 0.1 mol % and an upper limit of 10 mol %. By setting the acetyl group amount to 0.1 mol % or more, solubility in solvents can be improved, and by setting the acetyl group amount to 10 mol % or less, solubility in solvents can be improved. A more preferred lower limit of the acetyl group amount is 0.3 mol %, and a more preferred upper limit is 5 mol %. The amount of acetyl groups is 1 H-NMR and 13 It is measured using C-NMR (nuclear magnetic resonance spectroscopy).

[0027] The polyvinyl acetal resin for producing a multilayer ceramic capacitor of the present invention may have a structural unit having a carboxylic acid. The content of the carboxylic acid-containing structural unit (carboxylic acid modification amount) in the polyvinyl acetal resin for producing a multilayer ceramic capacitor of the present invention preferably has a lower limit of 0.1 mol% and an upper limit of 10 mol%. By setting the carboxylic acid group amount to 0.1 mol% or more, the paste viscosity can be increased, and by setting the carboxylic acid modification amount to 10 mol% or less, the solubility in solvents can be improved. The more preferred lower limit of the acetyl group amount is 0.3 mol%, and the more preferred upper limit is 5 mol%. The amount of carboxylic acid modification 1 H-NMR and 13 It is measured using C-NMR (nuclear magnetic resonance spectroscopy).

[0028] The polyvinyl acetal resin for producing a multilayer ceramic capacitor of the present invention preferably has an average degree of polymerization of less than 2300. This makes it possible to improve the solubility in solvents and the thixotropy. The polyvinyl acetal resin for use in producing a multilayer ceramic capacitor of the present invention preferably has a lower limit of 500, more preferably less than 2300. Having an average degree of polymerization of 500 or more facilitates industrial production. Having an average degree of polymerization of less than 2300 improves solubility in solvents and thixotropy. A more preferred lower limit of the average degree of polymerization is 800, and a more preferred upper limit is 2000. The average degree of polymerization of the polyvinyl acetal resin can be determined from the polyvinyl alcohol used as a raw material.

[0029] The polyvinyl acetal resin for manufacturing multilayer ceramic capacitors of the present invention may be copolymerized with an ethylenically unsaturated monomer as long as the effects of the present invention are not impaired. Examples of the ethylenically unsaturated monomer include, but are not limited to, acrylic acid, methacrylic acid, phthalic acid (anhydride), maleic acid (anhydride), and itaconic acid (anhydride). Other examples include acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, trimethyl-(3-acrylamido-3-dimethylpropyl)-ammonium chloride, acrylamido-2-methylpropanesulfonic acid, and its sodium salt. Other examples include ethyl vinyl ether, butyl vinyl ether, N-vinylpyrrolidone, vinyl chloride, vinyl bromide, vinyl fluoride, vinylidene chloride, vinylidene fluoride, tetrafluoroethylene, sodium vinyl sulfonate, and sodium allyl sulfonate. Alternatively, a terminal-modified polyvinyl alcohol can be used, which is obtained by copolymerizing a vinyl ester monomer such as vinyl acetate with ethylene in the presence of a thiol compound such as thiolacetic acid or mercaptopropionic acid, and then saponifying the copolymer.

[0030] The polyvinyl acetal resin for manufacturing a multilayer ceramic capacitor of the present invention is prepared by dissolving a 10 mass % solution in a DHTA solvent in a measuring temperature of 20°C and a shear region of 100 s -1 It is preferable that the viscosity is 1.5 Pa·s or more when measured using a rotational rheometer under the conditions of (a) to (c). By setting the viscosity within the above range, it is possible to prepare a conductive paste with high paste viscosity and excellent printability. The viscosity is more preferably 10 Pa·s or more, and is preferably 100 Pa·s or less, and more preferably 50 Pa·s or less. The viscosity can be measured using, for example, a modular compact rheometer (MCR702e) manufactured by Anton Paar. The rotor used in viscosity measurement is preferably adjusted appropriately depending on the viscosity, and a cone plate (Measuring cone CP50-1, D: 50 mm; Angle 1°) can be used for the measurement.

[0031] The viscosity can be adjusted by the method and reaction conditions of the acetalization reaction when producing the polyvinyl acetal resin, the degree of polymerization of the polyvinyl acetal resin, the amount of hydroxyl groups, the amount of acetal groups, the amount of acetyl groups, the structure of the acetal unit (the number of carbon atoms in the alkyl group), the type and content of the modifying group, and the like.

[0032] Examples of methods for producing the polyvinyl acetal resin for use in producing the multilayer ceramic capacitor include a method of acetalizing polyvinyl alcohol with an aldehyde, and a method of acetalizing a polyvinyl acetal resin having an acetal unit represented by the formula (1) with an aldehyde having 5 to 21 carbon atoms. In particular, it is preferable to use a method of acetalizing polyvinyl alcohol with at least one aldehyde having 5 to 21 carbon atoms. By using such a production method, the viscosity can be adjusted.

[0033] In the method of acetalizing the polyvinyl alcohol with at least one aldehyde having from 5 to 21 carbon atoms, aldehydes having different carbon numbers are prepared, and then acetalization is carried out to introduce acetal units having multiple alkyl groups having different carbon numbers. When producing the polyvinyl acetal resin, the acetalization may be carried out in the presence of a dispersant. More specifically, a method of introducing the acetal unit represented by the above formula (1) by acetalizing polyvinyl alcohol that does not have the acetal unit represented by the above formula (1) with a specific aldehyde can be mentioned.

[0034] The polyvinyl alcohol can be obtained, for example, by saponifying a vinyl ester polymer. Examples of the vinyl ester include vinyl formate, vinyl acetate, vinyl propionate, and vinyl pivalate. Among these, vinyl acetate is preferred from the viewpoint of economy.

[0035] The polyvinyl alcohol resin preferably has a degree of saponification of 85 mol % or more. The saponification degree is more preferably 90 mol % or more and 99.9 mol % or less, and even more preferably 95 mol % or more and 99.4 mol % or less. That is, the saponification degree is preferably 90 to 99.9 mol %, and more preferably 95 to 99.4 mol %.

[0036] In the method of reacting polyvinyl alcohol with an aldehyde having 5 to 21 carbon atoms, the aldehyde used in the acetalization reaction is not particularly limited, and examples thereof include linear aliphatic aldehydes and branched aliphatic aldehydes having 5 to 21 carbon atoms. Examples of the aliphatic aldehyde having 5 to 21 carbon atoms include valeraldehyde, hexylaldehyde, 2-ethylbutyraldehyde, 2-ethylhexylaldehyde, heptylaldehyde, octylaldehyde, nonylaldehyde, decylaldehyde, undecylaldehyde, dodecylaldehyde, tridecylaldehyde, tetradecylaldehyde, pentadecylaldehyde, hexadecylaldehyde, heptadecylaldehyde, octadecylaldehyde, eicosylaldehyde, heneicosylaldehyde, trimethylhexylaldehyde, methyloctylacetaldehyde, and methylnonylacetaldehyde. These aldehydes may be used alone or in combination of two or more. It is particularly preferable to use an aldehyde having 5 to 21 carbon atoms in combination with an aldehyde having 4 or less carbon atoms. Among these, acetaldehyde, butylaldehyde, decyl aldehyde, and heptaldehyde are preferred as aldehydes.

[0037] The amount of the aldehyde added can be appropriately set depending on the amount of acetal groups in the target polyvinyl acetal resin. In particular, it is preferable to add the aldehyde in an amount of 5 mol% to 120 mol%, more preferably 10 mol% to 110 mol%, based on 100 mol% of polyvinyl alcohol, because this allows the acetalization reaction to proceed efficiently and makes it easy to remove unreacted aldehyde. That is, the amount of the aldehyde added is preferably 5 to 120 mol%, more preferably 10 to 110 mol%.

[0038] In the acetalization step, an aldehyde having a cyclic aliphatic group or an aromatic group may be used in combination with the aldehyde having from 5 to 21 carbon atoms. Examples of the aldehyde having an aromatic group include benzaldehyde, cinnamaldehyde, 2-methylbenzaldehyde, 3-methylbenzaldehyde, 4-methylbenzaldehyde, p-hydroxybenzaldehyde, m-hydroxybenzaldehyde, phenylacetaldehyde, and β-phenylpropionaldehyde.

[0039] In the above acetalization step, when an aldehyde having 5 or more carbon atoms is contained, a dispersant may or may not be used. In the acetalization step, it is preferable to use a method in which the polyvinyl acetal resin is precipitated during the acetalization reaction (precipitation method), compared to a method in which the acetalization reaction is carried out in a dissolved state (dissolution method).Furthermore, when acetalization is carried out using the dispersant, it is preferable to use the precipitation method.

[0040] Examples of the dispersant include sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, polyvinylpyrrolidone, polyethylene glycol, polyvinyl alcohol, colloidal silica, polyoxyethylene polyoxypropylene cetyl ether, polyoxyethylene polyoxypropylene lauryl ether, etc. These dispersants may be used alone or in combination of two or more. Among them, sodium dodecylbenzenesulfonate and polyoxyethylene polyoxypropylene cetyl ether are preferred.

[0041] The acetalization reaction is preferably carried out in the presence of an acid catalyst. Examples of the acid catalyst include mineral acids, carboxylic acids, and sulfonic acids. Examples of the mineral acid include sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid. Examples of the carboxylic acid include formic acid, acetic acid, and propionic acid. Examples of the sulfonic acid include paratoluenesulfonic acid, methanesulfonic acid, ethanesulfonic acid, and benzenesulfonic acid. These acid catalysts may be used alone or in combination of two or more. Of these, paratoluenesulfonic acid and hydrochloric acid are preferred.

[0042] The temperature at which the aldehyde is added (aldehyde introduction temperature) is preferably 0°C or higher, more preferably 5°C or higher, and is preferably 70°C or lower. The temperature when adding the catalyst is preferably 5°C or higher and 50°C or lower. The retention time for the acetalization reaction is preferably 0.5 hours or more and 5 hours or less, and more preferably 1 hour or more and 3 hours or less. The temperature maintained during the acetalization reaction is preferably 0°C or higher and 65°C or lower, and more preferably 5°C or higher and 60°C or lower.

[0043] The present invention also includes a conductive paste containing the polyvinyl acetal resin for producing a multilayer ceramic capacitor of the present invention, an organic solvent, a conductive powder, and a dispersion improver.

[0044] The organic solvent may be an organic solvent generally used in conductive pastes. Examples of the organic solvent include terpineol derivatives such as dihydroterpineol, terpinyl acetate, isobornyl acetate, dihydroterpinyl acetate, dihydroterpinyl methyl ether, and terpinyl methyl ether; hydrocarbon solvents such as mineral spirits; and ethers and esters such as dipropylene glycol monomethyl ether and dipropylene glycol monomethyl ether acetate. Among these, dihydroterpineol and dihydroterpinyl acetate are preferred. These organic solvents may be used alone or in combination of two or more.

[0045] The amount of the organic solvent is not particularly limited, but a preferred lower limit is 100 parts by weight and a preferred upper limit is 10,000 parts by weight per 100 parts by weight of the polyvinyl acetal resin for producing a multilayer ceramic capacitor. When the amount of the organic solvent is 100 parts by weight or more, the viscosity of the conductive paste can be set within a suitable range, improving printability. When the amount of the organic solvent is 10,000 parts by weight or less, the performance of the polyvinyl acetal resin for producing a multilayer ceramic capacitor can be fully exhibited in the conductive paste. A more preferred lower limit of the amount of the organic solvent is 200 parts by weight and a more preferred upper limit is 5,000 parts by weight per 100 parts by weight of the polyvinyl acetal resin for producing a multilayer ceramic capacitor.

[0046] The conductive powder is not particularly limited, and examples thereof include powders made of nickel, aluminum, silver, copper, and alloys thereof. These conductive powders may be used alone or in combination of two or more. Among these, nickel is preferred because of its excellent conductivity.

[0047] The conductive powder preferably has an average particle diameter of 50 to 300 nm and is substantially spherical in shape. When the average particle diameter is 50 nm or more, the specific surface area of ​​the conductive powder is favorable, thereby improving the dispersibility of the conductive powder. When the average particle diameter is 300 nm or less, the surface smoothness after printing can be improved. Note that substantially spherical includes particles with a shape close to a sphere as well as a perfect sphere.

[0048] The amount of the conductive powder to be added is not particularly limited, but a preferred lower limit is 100 parts by weight and a preferred upper limit is 10,000 parts by weight per 100 parts by weight of the polyvinyl acetal resin for producing the multilayer ceramic capacitor. When the blending amount of the conductive powder is 100 parts by weight or more, the density of the conductive powder in the conductive paste can be kept within a sufficient range, resulting in excellent conductivity.When the blending amount of the conductive powder is 10,000 parts by weight or less, the dispersibility of the conductive powder in the conductive paste can be improved, resulting in excellent printability. The more preferred lower limit of the amount of the conductive powder to be blended is 200 parts by weight, and the more preferred upper limit is 5,000 parts by weight, per 100 parts by weight of the polyvinyl acetal resin for manufacturing a multilayer ceramic capacitor.

[0049] The conductive paste preferably further contains ceramic powder in addition to the conductive powder, which makes it easier to match the shrinkage behavior of the conductive powder during firing with that of the ceramic green sheets. The ceramic powder is not particularly limited, but is preferably barium titanate, which is used in the green sheet. The average particle size of the ceramic powder is not particularly limited, but is preferably smaller than the average particle size of the conductive powder, specifically, preferably 30 nm to 200 nm.

[0050] The dispersion improver is not particularly limited, but examples thereof include fatty acids, aliphatic amines, alkanolamides, and phosphate esters. Silane coupling agents may also be added. The fatty acid is not particularly limited, and examples thereof include saturated fatty acids such as behenic acid, stearic acid, palmitic acid, myristic acid, lauric acid, capric acid, caprylic acid, and coconut fatty acid; and unsaturated fatty acids such as oleic acid, linoleic acid, linolenic acid, sorbic acid, beef tallow fatty acid, and hardened castor fatty acid. Of these, lauric acid, stearic acid, and oleic acid are preferred. The aliphatic amine is not particularly limited, and examples thereof include laurylamine, myristylamine, cetylamine, stearylamine, oleylamine, alkyl(coconut)amine, alkyl(hardened beef tallow)amine, alkyl(beef tallow)amine, and alkyl(soybean)amine. The alkanolamide is not particularly limited, and examples thereof include coconut fatty acid diethanolamide, beef tallow fatty acid diethanolamide, lauric acid diethanolamide, and oleic acid diethanolamide. The phosphate ester is not particularly limited, and examples thereof include polyoxyethylene alkyl ether phosphate ester and polyoxyethylene alkyl allyl ether phosphate ester.

[0051] The conductive paste may contain a plasticizer, a lubricant, an antistatic agent, a surfactant, etc. as appropriate, provided that the effects of the present invention are not impaired.

[0052] Examples of the plasticizer include phthalic acid diesters such as dioctyl phthalate (DOP) and dibutyl phthalate (DBP), adipic acid diesters such as dioctyl adipate, and alkylene glycol diesters such as triethylene glycol-di-2-ethylhexanoate, tetraethylene glycol-di-2-ethylhexanoate, triethylene glycol-di-2-ethylbutyrate, tetraethylene glycol-di-2-ethylbutyrate, tetraethylene glycol-di-heptanoate, and triethylene glycol-di-heptanoate.

[0053] The method for producing the conductive paste is not particularly limited, and examples thereof include a method in which the polyvinyl acetal resin for producing a multilayer ceramic capacitor, the conductive powder, the organic solvent, and various additives added as needed are mixed using various mixers such as a ball mill, a blender mill, or a three-roll mill.

[0054] The conductive paste is applied to ceramic green sheets by a printing process, and multiple sheets are stacked and heated and pressed to form a laminate. This is then degreased and fired to form a sintered ceramic body, and external electrodes are formed on the end surfaces of the sintered ceramic body to produce a multilayer ceramic capacitor. Examples of the printing process that can be used include screen printing, die coating, and gravure offset. Such a multilayer ceramic capacitor also constitutes one aspect of the present invention. Furthermore, the polyvinyl acetal resin for manufacturing a multilayer ceramic capacitor of the present invention or the conductive paste of the present invention can also be suitably used as a multilayer ceramic capacitor. Furthermore, the multilayer ceramic capacitor of the present invention can be manufactured by carrying out the steps of applying the conductive paste of the present invention onto a ceramic green sheet, stacking a plurality of the ceramic green sheets and heat-pressing them to form a laminate, degreasing and firing the laminate to form a ceramic sintered body, and forming external electrodes on the end faces of the ceramic sintered body. [Effects of the Invention]

[0055] According to the present invention, it is possible to provide a polyvinyl acetal resin for producing a multilayer ceramic capacitor, which has a high paste viscosity after being kneaded with a conductive powder, good thixotropy, and excellent printability, as well as a conductive paste and a multilayer ceramic capacitor using the polyvinyl acetal resin for producing a multilayer ceramic capacitor. Furthermore, the present invention can provide a polyvinyl acetal resin for producing a multilayer ceramic capacitor, which has excellent solvent solubility and adhesion, and a conductive paste and a multilayer ceramic capacitor using the polyvinyl acetal resin for producing a multilayer ceramic capacitor. DETAILED DESCRIPTION OF THE INVENTION

[0056] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[0057] Example 1 (Preparation of polyvinyl acetal resin) 150 g of polyvinyl alcohol with a saponification degree of 99.2 mol% and an average polymerization degree of 1700 and 13.5 g of Unisafe 10P-8 (polyoxyethylene polyoxypropylene cetyl ether, manufactured by NOF Corporation) as a dispersant diluted with pure water to a concentration of 20% by mass were added to 1600 g of pure water and dissolved by stirring at 90°C for 2 hours. This solution was cooled to 65°C, and 70 g of n-butyl aldehyde and 75 g of n-decyl aldehyde were added. The solution was then cooled to 15°C, and 20 g of 35% by mass hydrochloric acid diluted with 180 g of pure water was added. The liquid temperature was maintained at 15°C, and the acetalization reaction was carried out for 1 hour, resulting in precipitation of the reaction product. After 1 hour of the acetalization reaction, 13.5 g of 20% by mass sodium dodecylbenzenesulfonate (SDBS) dissolved in pure water was added, and the acetalization reaction was carried out for another hour. The temperature was then raised to 45°C at a rate of 2–3°C per 5 minutes, and the liquid temperature was maintained at 45°C for 3 hours to complete the reaction. The mixture was then neutralized, washed with water, and dried in the usual manner to obtain a powder of polyvinyl acetal resin (long-chain alkyl-modified). The obtained polyvinyl acetal resin was dissolved in CDCl3 (deuterated chloroform), 1 H-NMR and 13 The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using C-NMR (nuclear magnetic resonance spectroscopy). The total amount of acetal groups (the sum of the contents of each acetal unit) was calculated from the measured values. The results are shown in Table 1. The content of each acetal unit was 13 Quantitative analysis was performed using C-NMR. The acetal unit is a structural unit represented by the above formula (1) [R 1 =(CH2)8CH3] and the acetal unit [R 2=(CH2)2CH3].

[0058] Example 2 (Preparation of polyvinyl acetal resin) A polyvinyl acetal resin powder was obtained in the same manner as in Example 1, except that 90 g of polyvinyl alcohol having a saponification degree of 99.1 mol% and an average polymerization degree of 1700 and 60 g of polyvinyl alcohol having a saponification degree of 98.2 mol% and an average polymerization degree of 800 were used instead of 150 g of polyvinyl alcohol having a saponification degree of 99.2 mol% and an average polymerization degree of 1700. The obtained polyvinyl acetal resin was dissolved in CDCl3 (deuterated chloroform), 1 H-NMR and 13 The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using C-NMR (nuclear magnetic resonance spectroscopy). The total amount of acetal groups (the sum of the contents of each acetal unit) was calculated from the measured values. The results are shown in Table 1. The content of each acetal unit was 13 Quantitative analysis was performed using C-NMR. The acetal unit is a structural unit represented by the above formula (1) [R 1 =(CH2)8CH3] and the structural unit represented by the above formula (2) [R 2 =(CH2)2CH3].

[0059] Example 3 (Preparation of polyvinyl acetal resin) A polyvinyl acetal resin powder was obtained in the same manner as in Example 1, except that 150 g of polyvinyl alcohol having a saponification degree of 98.6 mol% and an average polymerization degree of 800 was used instead of 150 g of polyvinyl alcohol having a saponification degree of 99.2 mol% and an average polymerization degree of 1700. The obtained polyvinyl acetal resin was dissolved in CDCl3 (deuterated chloroform), 1 H-NMR and 13 The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using C-NMR (nuclear magnetic resonance spectroscopy). The total amount of acetal groups (the sum of the contents of each acetal unit) was calculated from the measured values. The results are shown in Table 1. The content of each acetal unit was13 Quantitative analysis was performed using C-NMR. The acetal unit is a structural unit represented by the above formula (1) [R 1 =(CH2)8CH3] and the structural unit represented by the above formula (2) [R 2 =(CH2)2CH3].

[0060] Example 4 (Preparation of polyvinyl acetal resin) 150 g of polyvinyl alcohol with a saponification degree of 99.1 mol% and an average polymerization degree of 1700 and 13.5 g of Unisafe 10P-8 (polyoxyethylene polyoxypropylene cetyl ether, manufactured by NOF Corporation) as a dispersant diluted with pure water to a concentration of 20% by mass were added to 1600 g of pure water and dissolved by stirring at 90°C for 2 hours. This solution was cooled to 65°C, and 87 g of n-butylaldehyde and 46 g of n-heptaldehyde were added. The solution was then cooled to 15°C, and 20 g of 35% by mass hydrochloric acid diluted with 180 g of pure water was added. The liquid temperature was maintained at 15°C, and the acetalization reaction was carried out for 1 hour, resulting in precipitation of the reaction product. After 1 hour of the acetalization reaction, 13.5 g of 20% by mass sodium dodecylbenzenesulfonate (SDBS) dissolved in pure water was added, and the acetalization reaction was carried out for another hour. The temperature was then raised to 60°C at a rate of 2 to 3°C per 5 minutes, and the liquid temperature was maintained at 60°C for 3 hours to complete the reaction. The mixture was then neutralized, washed with water, and dried in the usual manner to obtain a powder of polyvinyl acetal resin (long-chain alkyl-modified). The obtained polyvinyl acetal resin was dissolved in CDCl3 (deuterated chloroform), 1 H-NMR and 13 The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using C-NMR (nuclear magnetic resonance spectroscopy). The total amount of acetal groups (the sum of the contents of each acetal unit) was calculated from the measured values. The results are shown in Table 1. The content of each acetal unit was 13 Quantitative analysis was performed using C-NMR. The acetal unit is a structural unit represented by the above formula (1) [R 1 =(CH2)5CH3] and the structural unit represented by the above formula (2) [R2 =(CH2)2CH3].

[0061] (Comparative Example 1) (Preparation of polyvinyl acetal resin) 160 g of carboxylic acid-modified polyvinyl alcohol (itaconic acid-modified, carboxylic acid modification amount 0.5 mol%) with a saponification degree of 98.2 mol% and an average polymerization degree of 800 was added to 1700 g of pure water and dissolved by stirring at 90°C for 2 hours. This solution was cooled to 40°C, and 120 g of hydrochloric acid with a concentration of 35% by mass was added. The solution was then cooled to 15°C, and 9 g of acetaldehyde and 110 g of n-butylaldehyde were added to carry out an acetalization reaction, resulting in the precipitation of a reaction product. The liquid temperature was then maintained at 50°C for 4 hours to complete the reaction, and the resulting mixture was neutralized, washed with water, and dried in the usual manner to obtain a polyvinyl acetal resin powder. The obtained polyvinyl acetal resin was dissolved in CDCl3 (chloroform), 1 Using H-NMR (nuclear magnetic resonance spectroscopy), the content of each acetal unit, the amount of acetyl groups, the amount of hydroxyl groups, and the amount of carboxylic acid modification were measured. In addition, the total amount of acetal groups (the total amount of each acetal unit) was calculated from the measured values. The content of each acetal unit was calculated as follows: 13 Quantitative analysis was performed using C-NMR, and the results are shown in Table 1. The acetal units were acetoacetal units and butyral units.

[0062] (Comparative Example 2) (Preparation of polyvinyl acetal resin) 170 g of polyvinyl alcohol having a saponification degree of 95.0 mol % and an average polymerization degree of 800 was added to 1700 g of pure water and dissolved by stirring at 90° C. for 2 hours. This solution was cooled to 40°C, and 120 g of hydrochloric acid with a concentration of 35% by mass was added. The solution was then cooled to 10°C, and 130 g of n-butyl aldehyde was added to carry out an acetalization reaction, resulting in the precipitation of a reaction product. The liquid temperature was then maintained at 30°C for 6 hours to complete the reaction, and the resulting mixture was neutralized, washed with water, and dried in the usual manner to obtain a polyvinyl acetal resin powder. The obtained polyvinyl acetal resin was dissolved in CDCl3 (deuterated chloroform), 1 The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using H-NMR (nuclear magnetic resonance spectroscopy). The total amount of acetal groups (the sum of the contents of each acetal unit) was calculated from the measured values. The results are shown in Table 1. The acetal unit was a butyral unit.

[0063] (Comparative Example 3) (Preparation of polyvinyl acetal resin) 160 g of carboxylic acid-modified polyvinyl alcohol (itaconic acid-modified, carboxylic acid modification amount 0.2 mol%) with a saponification degree of 98.4 mol% and an average polymerization degree of 1700 was added to 1700 g of pure water and dissolved by stirring at 90°C for 2 hours. This solution was cooled to 40°C, and 100 g of hydrochloric acid with a concentration of 35% by mass was added. The solution was then cooled to 10°C, and 120 g of n-butyl aldehyde was added to carry out an acetalization reaction, resulting in the precipitation of a reaction product. The liquid temperature was then maintained at 40°C for 6 hours to complete the reaction, and the resulting mixture was neutralized, washed with water, and dried in the usual manner to obtain a polyvinyl acetal resin powder. The obtained polyvinyl acetal resin was dissolved in CDCl3 (deuterated chloroform), 1 Using H-NMR (nuclear magnetic resonance spectroscopy), the content of each acetal unit, the amount of acetyl groups, the amount of hydroxyl groups, and the amount of carboxylic acid modification were measured. In addition, the total amount of acetal groups (the sum of the contents of each acetal unit) was calculated from the measured values. The results are shown in Table 1. The acetal unit was a butyral unit.

[0064] <Evaluation> The obtained polyvinyl acetal resin was evaluated as follows. (1) Resin viscosity (solution viscosity) measurement The obtained polyvinyl acetal resin was dissolved in dihydroterpinyl acetate solvent to a concentration of 10% by mass to prepare a sample for viscosity measurement. The viscosity of the obtained sample for viscosity measurement was measured using a rotational rheometer. The rotational rheometer used was a modular compact rheometer (MCR702e) (manufactured by Anton Paar), with a measurement temperature of 20°C and a shear range of 100 s -1 Measurements were carried out using a rotor: cone plate (Measuring cone CP50-1, D: 50 mm; Angle 1°) under the following conditions.

[0065] (2) Solvent solubility Polyvinyl acetal resin and dihydroterpinyl acetate were mixed in a sealed glass container so that the polyvinyl acetal resin was 10% by mass, to prepare 30 g of a solution. The solution was mixed for 5 hours using a hot stirrer to keep the temperature at 60°C, and the state of the solution immediately after mixing was visually inspected and evaluated according to the following criteria. ◎: Completely dissolved 〇: Partially dissolved ×: Insoluble

[0066] (3) Paste viscosity measurement (a) Preparation of conductive paste A resin solution was prepared by dissolving 10 parts by weight of the polyvinyl acetal resin obtained in each of the examples and comparative examples in 90 parts by weight of dihydroterpinyl acetate. 180 parts by weight of nickel powder as the conductive powder, 50 parts by weight of dihydroterpinyl acetate, and 0.1 parts by weight of oleic acid as a dispersion improver were mixed, and the resulting resin solution was mixed and dispersed using a triple roll mill to prepare a conductive paste.

[0067] (b) Viscosity measurement The viscosity of the obtained conductive paste was measured using a rotational rheometer. The rotational rheometer used was a modular compact rheometer (MCR702e) (manufactured by Anton Paar), with a measurement temperature of 20°C and a shear range of 10 s -1 Measurements were carried out under the conditions above using a rotor: cone plate (Measuring cone CP25-2, D: 25 mm; Angle 2°), and the results were evaluated according to the following criteria. ◎: 20.0 Pa·s or more ○: 14.0 Pa·s or more, less than 20.0 Pa·s ×: Less than 14.0 Pa·s

[0068] (c) Thixotropy The viscosity of the obtained conductive paste was measured using a rotational rheometer. The rotational rheometer used was a modular compact rheometer (MCR702e) (manufactured by Anton Paar), and the measurement temperature was 20°C and the shear range was 100 s -1 Measurements were carried out using a rotor: cone plate (Measuring cone CP25-2, D: 25 mm; Angle 2°) under the condition of 10 s. -1 The thixotropy was also measured under the conditions of 10s -1 Viscosity / 100s -1 The viscosity was evaluated according to the following criteria. ◎: 4.0 or higher 〇: 2.5 or more, less than 4.0 ×: Less than 2.5

[0069] [Table 1] [Industrial Applicability]

[0070] According to the present invention, it is possible to provide a polyvinyl acetal resin for producing a multilayer ceramic capacitor, which has a high paste viscosity after being kneaded with a conductive powder, good thixotropy, and excellent printability, as well as a conductive paste and a multilayer ceramic capacitor using the polyvinyl acetal resin for producing a multilayer ceramic capacitor.

Claims

1. A polyvinyl acetal resin used in a conductive paste for manufacturing a multilayer ceramic capacitor, the polyvinyl acetal resin having a constitutional unit represented by the following formula (1) and an acetal unit represented by the following formula (2) which is different from the constitutional unit represented by the following formula (1), wherein R １ is a hydrocarbon group having 6 to 9 carbon atoms, and R ２ is a propyl group, and the total amount of acetal groups is 69 mol % or more. 【Chemical 1】 【Chemistry 2】

2. A polyvinyl acetal resin used in a conductive paste for manufacturing multilayer ceramic capacitors, the polyvinyl acetal resin having a constituent unit represented by the following formula (1) and an acetal unit represented by the following formula (2) which is different from the constituent unit represented by the following formula (1), wherein R 1 in the following formula (1) is a hydrocarbon group having 6 to 9 carbon atoms, and R 2 in the following formula (2) is a propyl group, the amount of acetyl groups is 5 mol% or less, and the amount of hydroxyl groups is 10 mol% or more and 30 mol% or less. 【Chemistry 3】 【Chemistry 4】

3. 3. The polyvinyl acetal resin for producing a multilayer ceramic capacitor according to claim 1, wherein the polyvinyl acetal resin has an average degree of polymerization of less than 2,300.

4. 3. The polyvinyl acetal resin for producing a multilayer ceramic capacitor according to claim 2, wherein the total amount of acetal groups is 69 mol % or more.

5. A 10 mass% solution of dihydroterpineol acetate (DHTA) dissolved in a solvent was measured at a temperature of 20°C and in a shear region of 100 s －１ 3. The polyvinyl acetal resin for use in producing a multilayer ceramic capacitor according to claim 1, wherein the viscosity of the polyvinyl acetal resin is 1.5 Pa·s or more when measured using a rotational rheometer under the following conditions:

6. 2. The polyvinyl acetal resin for producing a multilayer ceramic capacitor according to claim 1, wherein the amount of acetyl groups is 5 mol % or less.

7. R in the formula (1) １ 3. The polyvinyl acetal resin for producing a multilayer ceramic capacitor according to claim 1, wherein is a linear hydrocarbon group having 6 or 9 carbon atoms.

8. 3. The polyvinyl acetal resin for producing a multilayer ceramic capacitor according to claim 1, wherein the content of the structural unit represented by formula (1) is 5 mol % or more and 35 mol % or less.

9. 3. The polyvinyl acetal resin for producing a multilayer ceramic capacitor according to claim 1, wherein the content of the structural unit represented by formula (1) relative to the total amount of acetal groups (content of the structural unit represented by formula (1) / total amount of acetal groups) is 0.06 or more and 0.51 or less.

10. 2. The polyvinyl acetal resin for producing a multilayer ceramic capacitor according to claim 1, wherein the amount of hydroxyl groups is from 10 mol % to 30 mol %.

11. 3. The polyvinyl acetal resin for producing a multilayer ceramic capacitor according to claim 1, having an average degree of polymerization of 500 or more.

12. 3. A conductive paste comprising the polyvinyl acetal resin for producing a multilayer ceramic capacitor according to claim 1, an organic solvent, a conductive powder, and a dispersion improver.

13. A multilayer ceramic capacitor formed using the conductive paste according to claim 12.

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