Polyvinyl acetal resin, conductive paste, and multilayer ceramic capacitor

Abstract

An object of the present invention is to provide a polyvinyl acetal resin from which a conductive paste having excellent storage stability can be obtained even when used in combination with ethyl cellulose, and a conductive paste and a multilayer ceramic capacitor using the polyvinyl acetal resin.SOLUTION: 1% by weight solutions obtained by dissolving ethyl cellulose (EC) having a weight-average molecular weight of 135000, polyvinyl acetal resins (PVACL), and mixed resins (EC-PVACL) obtained by mixing EC and PVACL at a weight ratio of 50:50 in dihydroterpineol acetates (DHTA) at 90 °C for 3 hours were designated as EC1% by weight DHTA solutions, PVACL1% by weight DHTA solutions, and EC / PVACL1% by weight DHTA solutions, respectively; When the haze value of the EC1 wt% DHTA is X, the haze value of the PVACL1 wt% DHTA is Y, and the haze value of the EC / PVACL1 wt% DHTA is Z, the following equations (a) and (b) are satisfied: X ≥ Y (a) X ≥ Z (b) SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polyvinyl acetal resin, 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, such as ethyl cellulose or polyvinyl acetal resin. 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, there has been a growing focus on miniaturizing multilayer ceramic capacitors, which has led to a demand for high adhesion between the internal electrodes (conductive layers) and the dielectric layers. Generally, ethyl cellulose is used as a binder in conductive paste for internal electrodes, but polyvinyl acetal resin is now also used in the conductive paste to improve adhesion with the polyvinyl acetal resin used in the dielectric layers. However, when a conventional polyvinyl acetal resin is used in combination with ethyl cellulose as a binder resin for a conductive paste, there is a problem that the storage stability is reduced and separation occurs after long-term storage.

[0006] An object of the present invention is to provide a polyvinyl acetal resin that can produce a conductive paste having excellent storage stability even when used in combination with ethyl cellulose, and to provide a conductive paste and a multilayer ceramic capacitor that use the polyvinyl acetal resin. [Means for solving the problem]

[0007] Disclosure 1 provides a polyvinyl acetal resin that satisfies the following formulas (a) and (b): ethyl cellulose (EC) having a weight average molecular weight of 135,000, polyvinyl acetal resin (PVACL), and a mixed resin (EC-PVACL) obtained by mixing EC and PVACL in a weight ratio of 50:50 are dissolved in dihydroterpineol acetate (DHTA) at 90°C for 3 hours to prepare 1 wt% solutions, which are designated as a 1 wt% EC DHTA solution, a 1 wt% PVACL DHTA solution, and a 1 wt% EC-PVACL DHTA solution, respectively; the haze value of the 1 wt% EC DHTA solution is X, the haze value of the 1 wt% PVACL DHTA solution is Y, and the haze value of the 1 wt% EC-PVACL DHTA solution is Z. X≧Y (a) X≧Z (b) Disclosure 2 is the polyvinyl acetal resin according to Disclosure 1, in which X, Y, and Z satisfy the following formula (c): (X+Y) / 2≧Z (c) The present disclosure 3 has a constitutional unit represented by the following formula (1), and R 1 is a hydrocarbon group having 4 or more carbon atoms. [ka] Disclosure 4 is the polyvinyl acetal resin according to any one of Disclosures 1 to 3, in which the content of the constitutional unit represented by formula (1) is 1 mol % or more and 45 mol % or less. Disclosure 5 is a conductive paste containing the polyvinyl acetal resin according to any one of Disclosures 1 to 4, an organic solvent, a conductive powder, and a dispersion improver. The sixth aspect of the present disclosure is a multilayer ceramic capacitor formed using the conductive paste according to the fifth aspect of the present disclosure.

[0008] As a result of extensive research, the present inventors have found that polyvinyl acetal resins in which the haze values ​​of the EC 1 wt % DHTA solution, PVACL 1 wt % DHTA solution, and EC-PVACL 1 wt % DHTA solution satisfy a predetermined relationship can be used to prepare conductive pastes with excellent storage stability, even when used in combination with ethyl cellulose, and have thus completed the present invention.

[0009] The polyvinyl acetal resin of the present invention is a polyvinyl acetal resin that satisfies the following formulas (a) and (b), where 1 wt % solutions of EC, PVACL, and EC-PVACL, each having a weight-average molecular weight of 135,000, dissolved in DHTA at 90°C for 3 hours are designated as a 1 wt % EC DHTA solution, a 1 wt % PVACL DHTA solution, and a 1 wt % EC-PVACL DHTA solution, respectively, and the haze value of the 1 wt % EC DHTA solution is designated as X, the haze value of the 1 wt % PVACL DHTA solution is designated as Y, and the haze value of the 1 wt % EC-PVACL DHTA solution is designated as Z: X≧Y (a) X≧Z (b) By satisfying the above formulae (a) and (b), a conductive paste having excellent storage stability can be prepared even when used in combination with ethyl cellulose. The above X, Y and Z (haze values) can be measured, for example, using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd.) at a wavelength of 400 nm and a measurement temperature of 25°C. As the ethyl cellulose, ethyl cellulose having an ethoxyl group content of 48 to 50% by weight can be used in particular.

[0010] The above X is preferably 10.0 or less, and more preferably 5.0 or less. There is no particular lower limit for the above X, but the above X is, for example, 0.001 or more. The above Y is preferably 4.0 or less, and more preferably 2.0 or less. There is no particular lower limit for the above Y, but the above Y is, for example, 0.001 or more. The above Z is preferably 5.0 or less, and more preferably 3.0 or less. There is no particular lower limit for the above Z, but the above Z is, for example, 0.001 or more. The difference between X and Y (XY) is preferably 0.01 or more and 1.5 or less. The difference between X and Z (XZ) is preferably 0.01 or more and 1.0 or less.

[0011] It is preferable that the above X, Y, and Z satisfy the following formula (c), which can further improve the compatibility between EC and PVACL. (X+Y) / 2≧Z (c) The difference between [(X+Y) / 2] and Z, [(X+Y) / 2]-Z, is preferably 0.01 or more, and more preferably 0.03 or more.

[0012] The above X, Y, and Z 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, etc.

[0013] The polyvinyl acetal resin of the present invention has a structural unit represented by the following formula (1), and R 1 Preferably, the hydrocarbon group has 4 or more carbon atoms. By having such a hydrocarbon group, it is possible to improve compatibility with EC and storage stability.

[0014] [ka]

[0015] 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 11, and the upper limit is still more preferably 9. 1 may be a combination of two or more hydrocarbon groups having different carbon numbers.

[0016] The hydrocarbon group having 4 or more carbon atoms is preferably an alkyl group having 4 or more carbon atoms. Examples of the alkyl group having 4 or more 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.

[0017] The hydrocarbon group having 4 or more carbon atoms 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.

[0018] 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.

[0019] In the present invention, the hydrocarbon group having 4 or more carbon atoms is preferably a linear alkyl group. The alkyl group having 4 or more 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 an alkyl group based on a bio-derived aldehyde having 4 or more carbon atoms.

[0020] The content of the structural unit represented by the above formula (1) in the polyvinyl acetal resin of the present invention is preferably 1 mol% at the lower limit, more preferably 15 mol%, and more preferably 45 mol% at the upper limit, more preferably 40 mol%. This allows for excellent compatibility with EC and good storage stability. 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).

[0021] The polyvinyl acetal resin of the present invention preferably further contains an acetal unit represented by the following formula (2), which is different from the constituent unit represented by the above formula (1). By containing the acetal unit represented by the following formula (2), excellent compatibility with EC and good storage stability can be achieved.

[0022] [ka] In formula (2), R 2 represents a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms.

[0023] Examples of the hydrocarbon group having 1 to 3 carbon atoms include a methyl group, an ethyl group, and a propyl group. The hydrocarbon having 1 to 3 carbon atoms is preferably an alkyl group, and may be either linear or branched.

[0024] The content of the acetal unit represented by the above formula (2) in the polyvinyl acetal resin of the present invention is preferably 30 mol% at the lower limit, more preferably 35 mol%, and preferably 75 mol% at the upper limit, more preferably 65 mol%. By setting the content of the acetal unit represented by the above formula (2) within the above range, excellent compatibility with EC and good storage stability can be achieved. The content of the acetal unit represented by the above formula (2) is 1 H-NMR and 13 It is measured using C-NMR (nuclear magnetic resonance spectroscopy).

[0025] 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 0.19 or more and 5.4 or less. By keeping the ratio within the above range, excellent compatibility with EC and good storage stability can be achieved.

[0026] The total acetal group content (total amount of all acetal units) of the polyvinyl acetal resin of the present invention is preferably 70 mol % or more. By setting the total acetal group content within the above range, excellent compatibility with EC and good storage stability can be achieved. The lower limit of the total acetal group content is preferably 73 mol%, more preferably 75 mol%, and the upper limit is preferably 95 mol%, more preferably 90 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 0.07 and a preferred upper limit of 2.0.

[0027] The polyvinyl acetal resin 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 of the present invention is preferably 5 mol % or more and 27 mol % or less. By keeping it within this range, excellent compatibility with EC and good storage stability can be achieved. The more preferred lower limit of the amount of hydroxyl groups is 10 mol %, and the more preferred upper limit is 25 mol %. 1 H-NMR and 13 It is measured using C-NMR (nuclear magnetic resonance spectroscopy).

[0028] The polyvinyl acetal resin 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 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, the solubility in solvents can be improved, and by setting the acetyl group amount to 10 mol% or less, the 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).

[0029] The polyvinyl acetal resin of the present invention may have a structural unit containing a carboxylic acid. The content of the carboxylic acid-containing structural unit (carboxylic acid modification amount) in the polyvinyl acetal resin of the present invention is preferably 0.1 mol% at the lower limit and 10 mol% at the upper limit. 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).

[0030] The preferred lower limit of the average polymerization degree of the polyvinyl acetal resin of the present invention is 800, and the preferred upper limit is 5000. When the average polymerization degree is 800 or more, industrial production becomes easy. When the average polymerization degree is 5000 or less, the solution viscosity becomes appropriate, and industrial production becomes possible. A more preferred lower limit of the average polymerization degree is 1000, and a more preferred upper limit is 3500. The average polymerization degree of the polyvinyl acetal resin can be determined from the polyvinyl alcohol used as a raw material.

[0031] The polyvinyl acetal resin of the present invention may be copolymerized with an ethylenically unsaturated monomer, provided that the effects of the present invention are not impaired. The ethylenically unsaturated monomer is not particularly limited, and examples thereof include 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. Further 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.

[0032] The polyvinyl acetal resin of the present invention is prepared by subjecting a 10 mass% solution dissolved in DHTA solvent to a measurement temperature of 20°C and a shear region of 100 s -1 It is preferable that the viscosity is 6 Pa s or more when measured using a rotational rheometer under the following conditions: By setting the viscosity within this range, the paste has high viscosity and good thixotropy, making it possible to produce a conductive paste with excellent printability. The viscosity is more preferably 15 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.

[0033] The polyvinyl acetal resin of the present invention preferably has a glass transition temperature (Tg) of 60°C or lower. This improves the adhesion between a composition (conductive paste) containing the polyvinyl acetal resin and a ceramic green sheet. The lower limit of the glass transition temperature is preferably 30°C, more preferably 35°C, and the upper limit is preferably 58°C, more preferably 55°C. The glass transition temperature can be measured using, for example, a differential scanning calorimeter (DSC).

[0034] The viscosity and glass transition temperature 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.

[0035] Examples of methods for producing the polyvinyl acetal resin include a method of acetalizing polyvinyl alcohol with an aldehyde. In particular, it is preferable to use a method of acetalizing polyvinyl alcohol with an aldehyde having 4 or less carbon atoms and / or an aldehyde having 5 or more carbon atoms. By using such a production method, the viscosity and glass transition temperature can be adjusted.

[0036] In the method of acetalizing the polyvinyl alcohol with an aldehyde having 4 or less carbon atoms and / or an aldehyde having 5 or more carbon atoms, aldehydes having different numbers of carbon atoms are prepared, and then acetalization is carried out to introduce acetal units having multiple alkyl groups having different numbers of carbon atoms. 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.

[0037] 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.

[0038] 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 %.

[0039] In the method of reacting polyvinyl alcohol with an aldehyde having 5 or more 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 or more carbon atoms. Examples of the aliphatic aldehyde having 5 or more carbon atoms include valeraldehyde, hexyl aldehyde, 2-ethylbutyraldehyde, 2-ethylhexyl aldehyde, heptyl aldehyde, octyl aldehyde, nonyl aldehyde, decyl aldehyde, undecyl aldehyde, dodecyl aldehyde, tridecyl aldehyde, tetradecyl aldehyde, pentadecyl aldehyde, hexadecyl aldehyde, heptadecyl aldehyde, octadecyl aldehyde, eicosyl aldehyde, heneicosyl aldehyde, trimethylhexyl aldehyde, methyloctylacetaldehyde, and methylnonylacetaldehyde. These aldehydes may be used alone or in combination of two or more. Examples of the aliphatic aldehyde having 4 or less carbon atoms include formaldehyde, acetaldehyde, propionaldehyde, and butylaldehyde. It is particularly preferable to use an aldehyde having 5 or more carbon atoms in combination with an aldehyde having 4 or less carbon atoms, and it is even more preferable to use an aldehyde having 5 to 21 carbon atoms in combination with an aldehyde having 4 or less carbon atoms. Of these, acetaldehyde, butylaldehyde, decyl aldehyde, and heptaldehyde are preferred as aldehydes.

[0040] The total amount of the aldehydes added can be appropriately set depending on the amount of acetal groups in the target polyvinyl acetal resin. In particular, a total amount of the aldehydes added is preferably 70 mol% to 120 mol%, more preferably 85 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 aldehydes. That is, the amount of the aldehydes added is preferably 70 to 120 mol%, more preferably 85 to 110 mol%.

[0041] In the acetalization step, in addition to the linear aliphatic aldehydes and branched aliphatic aldehydes, aldehydes having a cyclic aliphatic group or an aromatic group may be used in combination. Examples of the aldehydes having an aromatic group include benzaldehyde, cinnamaldehyde, 2-methylbenzaldehyde, 3-methylbenzaldehyde, 4-methylbenzaldehyde, p-hydroxybenzaldehyde, m-hydroxybenzaldehyde, phenylacetaldehyde, and β-phenylpropionaldehyde.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] The temperature at which the aldehyde is added (aldehyde introduction temperature) is preferably 5°C or higher, more preferably 10°C or higher, and is preferably 70°C or lower. The temperature when adding the catalyst is preferably 10°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.

[0046] Examples of applications of the polyvinyl acetal resin of the present invention include conductive pastes (in which ethyl cellulose is used in combination as a binder), binders and dispersants for battery electrodes, secondary battery electrodes, etc., modifiers for adhesives based on epoxy resins, phenolic resins, etc., and ceramic green sheets. In particular, when the polyvinyl acetal resin of the present invention is used as a conductive paste, the paste has a high viscosity after being kneaded with a conductive powder, and can have excellent printability.

[0047] The present invention also includes a conductive paste containing the polyvinyl acetal resin of the present invention, an organic solvent, a conductive powder, and a dispersion improver.

[0048] 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.

[0049] 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. 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 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.

[0050] 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.

[0051] 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.

[0052] 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. 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.

[0053] 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.

[0054] The conductive paste may contain appropriate additives such as a plasticizer, a lubricant, an antistatic agent, a dispersion improver, and a surfactant, as long as the effects of the present invention are not impaired.

[0055] 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.

[0056] 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.

[0057] The method for producing the conductive paste is not particularly limited, and examples thereof include a method in which the polyvinyl acetal resin, 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, and a three-roll mill.

[0058] 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. The polyvinyl acetal resin 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]

[0059] According to the present invention, it is possible to provide a polyvinyl acetal resin that can produce a conductive paste having excellent storage stability even when used in combination with ethyl cellulose, and a conductive paste and a multilayer ceramic capacitor that use the polyvinyl acetal resin. DETAILED DESCRIPTION OF THE INVENTION

[0060] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[0061] Example 1 (Preparation of polyvinyl acetal resin) 245 g of polyvinyl alcohol with a saponification degree of 99.0 mol% and an average polymerization degree of 1700 and 22.5 g of Unisafe 10P-8 (polyoxyethylene polyoxypropylene cetyl ether, manufactured by NOF Corporation) diluted with pure water as a dispersant to a concentration of 20% by mass were added to 2700 g of pure water and dissolved by stirring at 90°C for 2 hours. This solution was cooled to 65°C, and 145 g of n-butylaldehyde and 77 g of n-heptaldehyde were added. The solution was then cooled to 15°C, and 30 g of 35% by mass hydrochloric acid diluted with 280 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, 22.5 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 2-3°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) [R 2 =(CH2)2CH3].

[0062] Example 2 (Preparation of polyvinyl acetal resin) 15 g of polyvinyl alcohol with a saponification degree of 99.0 mol% and an average polymerization degree of 1700 and 1.35 g of Unisafe 10P-8 (polyoxyethylene polyoxypropylene cetyl ether, manufactured by NOF Corporation) diluted with pure water as a dispersant to a concentration of 20% by mass were added to 170 g of pure water and dissolved by stirring at 90°C for 2 hours. This solution was cooled to 65°C, and 8.1 g of n-butylaldehyde and 6.4 g of n-heptaldehyde were added. The solution was then cooled to 15°C, and 1.9 g of 35% by mass hydrochloric acid diluted with 7.4 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, 1.35 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 2-3°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) [R 2 =(CH2)2CH3].

[0063] Example 3 (Preparation of polyvinyl acetal resin) 15 g of polyvinyl alcohol with a saponification degree of 98.2 mol% and an average polymerization degree of 800 and 1.35 g of Unisafe 10P-8 (polyoxyethylene polyoxypropylene cetyl ether, manufactured by NOF Corporation) diluted with pure water as a dispersant to a concentration of 20% by mass were added to 160 g of pure water and dissolved by stirring at 90°C for 2 hours. This solution was cooled to 65°C, and 6.9 g of n-butyl aldehyde and 7.5 g of n-decyl aldehyde were added. The solution was then cooled to 15°C, and 2.0 g of 35% by mass hydrochloric acid diluted with 18 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].

[0064] Example 4 (Preparation of polyvinyl acetal resin) A polyvinyl acetal resin powder was obtained in the same manner as in Example 2, except that 9.9 g of n-butylaldehyde and 2.8 g of n-heptaldehyde were added instead of 8.1 g of n-butylaldehyde and 6.4 g of n-heptaldehyde. The obtained polyvinyl acetal resin was dissolved in CDCl3 (deuterated chloroform), 1 H-NMR and 13The 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) [R 2 =(CH2)2CH3].

[0065] (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 20 g of acetaldehyde and 100 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.

[0066] (Comparative Example 2) (Preparation of polyvinyl acetal resin) 160 g of polyvinyl alcohol having a saponification degree of 96.0 mol % and an average polymerization degree of 350 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 100 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 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.

[0067] (Comparative Example 3) (Preparation of polyvinyl acetal resin) 160 g of ethylene-modified polyvinyl alcohol (ethylene modification amount: 1.8 mol%) with a saponification degree of 97.7 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 120 g of hydrochloric acid with a concentration of 35% by mass was added. Thereafter, the solution was cooled to 15°C, and 82 g of n-butylaldehyde 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 4 hours to complete the reaction, and the resulting mixture was neutralized, washed with water, and dried in a conventional 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 unit was a butyral unit.

[0068] Comparative Example 4 (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 120 g of hydrochloric acid with a concentration of 35% by mass was added. The solution was then cooled to 25°C, and 80 g of n-butylaldehyde was added to carry out an acetalization reaction, resulting in the precipitation of a reaction product. The liquid temperature was then maintained at 45°C for 3 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, the amount of hydroxyl groups, and the amount of ethylene modification 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.

[0069] (Comparative Example 5) (Preparation of polyvinyl acetal resin) 160 g of polyvinyl alcohol having a saponification degree of 98.0 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 110 g of hydrochloric acid with a concentration of 35% by mass was added. The solution was then cooled to 10°C, and 85 g of n-butylaldehyde 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 3 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), 1The 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.

[0070] <Evaluation> The obtained polyvinyl acetal resin was evaluated as follows. (1) Haze value measurement Ethyl cellulose (EC, STD45) with a weight-average molecular weight of 135,000 and an ethoxyl group content of 48 to 50 wt%, the resulting polyvinyl acetal resin (PVACL), and a mixed resin (EC-PVACL) made by mixing EC and PVACL in a weight ratio of 50:50 were dissolved in dihydroterpineol acetate (DHTA) at 90°C for 3 hours to form a 1 wt% solution, thereby preparing a 1 wt% EC DHTA solution, a 1 wt% PVACL DHTA solution, and a 1 wt% EC-PVACL DHTA solution. The haze values ​​of the obtained EC 1 wt % DHTA solution, PVACL 1 wt % DHTA solution, and EC-PVACL 1 wt % DHTA solution were measured using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd.) at a wavelength of 400 nm and a measurement temperature of 25°C. The haze value of a 1 wt% EC solution in DHTA was defined as X, the haze value of a 1 wt% PVACL solution in DHTA as Y, and the haze value of a 1 wt% EC-PVACL solution in DHTA as Z, and "(X+Y) / 2" was calculated. For X, Y, and Z, cases where they were not soluble in DHTA and a 1 wt% solution could not be prepared were defined as "unmeasurable." The obtained "X", "Y", "Z", and "(X+Y) / 2" were judged as "Good" if they satisfied the above formulas (a), (b), and (c), and as "Poor" if they did not.

[0071] (2) Storage stability 2.5 g of the obtained polyvinyl acetal resin, 2.5 g of ethyl cellulose (EC, STD45) with a weight-average molecular weight of 135,000 and an ethoxyl group content of 48 to 50 wt%, and 100 g of Ni powder were added to 62 g of organic solvent (DHTA), and the mixture was dispersed using a triple roll to obtain a conductive paste. The prepared conductive paste was left to stand for two weeks, and the change in appearance was visually checked and evaluated according to the following criteria. ◎: No change ○: Some organic solvent was separated, but no separation of Ni powder was observed ×: Ni powder settled and separated from the organic solvent

[0072] [Table 1] [Industrial Applicability]

[0073] According to the present invention, it is possible to provide a polyvinyl acetal resin that can produce a conductive paste having excellent storage stability even when used in combination with ethyl cellulose, and a conductive paste and a multilayer ceramic capacitor that use the polyvinyl acetal resin.

Claims

1. Ethyl cellulose (EC) having a weight average molecular weight of 135,000, polyvinyl acetal resin (PVACL), and a mixed resin (EC-PVACL) obtained by mixing EC and PVACL in a weight ratio of 50:50 were dissolved in dihydroterpineol acetate (DHTA) at 90°C for 3 hours to prepare 1 wt% solutions, which were named EC 1 wt% DHTA solution, PVACL 1 wt% DHTA solution, and EC-PVACL 1 wt% DHTA solution, respectively. A polyvinyl acetal resin that satisfies the following formulas (a) and (b), where the haze value of the EC 1 wt % DHTA solution is X, the haze value of the PVACL 1 wt % DHTA solution is Y, and the haze value of the EC-PVACL 1 wt % DHTA solution is Z: X ≧ Y (a) X≧Z (b)

2. The polyvinyl acetal resin according to claim 1, wherein X, Y, and Z satisfy the following formula (c): (X+Y) / 2≧Z (c)

3. It has a constitutional unit represented by the following formula (1), and R in the following formula (1) １ The polyvinyl acetal resin according to claim 1 or 2, wherein is a hydrocarbon group having 4 or more carbon atoms. 【Chemistry 1】

4. The polyvinyl acetal resin according to claim 1 or 2, wherein the content of the structural unit represented by formula (1) is 1 mol % or more and 45 mol % or less.

5. A conductive paste comprising the polyvinyl acetal resin according to claim 1 or 2, an organic solvent, a conductive powder, and a dispersion improver.

6. A multilayer ceramic capacitor formed using the conductive paste according to claim 5.

Images