Polyvinyl acetal resin, conductive paste, and multi-layer ceramic capacitor

Abstract

The purpose of the present invention is to provide: a polyvinyl acetal resin which has a high paste viscosity after kneading with a conductive powder and has excellent thixotropy and printability; a conductive paste using said polyvinyl acetal resin; and a multi-layer ceramic capacitor. The present invention is a polyvinyl acetal resin having a structural unit represented by formula (1), wherein R1 in formula (1) is a hydrocarbon group having 4 to 20 carbon atoms, the total acetal group content is 68.5 mol% or more, and the average degree of polymerisation is less than 2,300.

Description

Polyvinyl acetal resin, conductive paste and multilayer ceramic capacitor

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

[0002] Multilayer electronic components such as multilayer circuit boards, multilayer coils, and multilayer ceramic capacitors are widely used. Among these, 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 ester resin, dissolved in an organic solvent, and the resulting mixture is uniformly mixed 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 other methods. The resulting green ceramic sheets are then peeled off from the support to obtain ceramic green sheets. Next, multiple green ceramic sheets are alternately stacked on top of each other, coated with a conductive paste for internal electrodes by screen printing or gravure printing, and then heated and pressed together to form a laminate. Subsequently, the laminate is subjected to a degreasing process, which involves thermally decomposing and removing binder resin components and other components contained in the laminate. External electrodes are then sintered onto the end faces of the resulting sintered ceramic body, resulting in a multilayer ceramic capacitor.

[0003] Conductive pastes for internal electrodes are obtained by kneading conductive powder, an organic solvent, and a binder resin. Examples of the binder resin include ethyl cellulose and polyvinyl acetal resin. However, when polyvinyl acetal resin is used as the binder resin, there is a problem of stringiness 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 conductive powder in order to solve the above problem. Patent Document 2 also discloses a conductive paste containing a polyvinyl acetal resin having an ethylene group in order to solve the above problem.

[0004] JP 2017-228780 A JP 2008-285590 A

[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 resin described in Patent Document 1 or 2 is used as a binder resin for a conductive paste for internal electrodes, the viscosity of the paste after being kneaded with a conductive powder is low, and bleeding of the conductive paste for internal electrodes may occur during screen printing or gravure printing.

[0006] The present invention aims to provide a polyvinyl acetal resin that has a high paste viscosity after being mixed 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. Here, the printability means that both stringiness and bleeding can be prevented during screen printing or gravure printing.

[0007] The present disclosure 1 has a constitutional unit represented by the following formula (1), and R １ is a hydrocarbon group having 4 to 20 carbon atoms, the total amount of acetal groups is 68.5 mol % or more, and the average degree of polymerization is less than 2,300. This disclosure 2 describes a 10 mass% solution of dihydroterpineol acetate (DHTA) dissolved in a solvent, measured at a temperature of 20°C and in a shear region of 100 s －１ The polyvinyl acetal resin according to Disclosure 1 has a viscosity of 1.5 Pa s or more when measured using a rotational rheometer under the conditions of １ is a hydrocarbon group having 6 to 20 carbon atoms and an acetyl group content of 5 mol % or less. １is a linear hydrocarbon group having 6 or 9 carbon atoms. Disclosure 5 is the polyvinyl acetal resin according to any one of Disclosures 1 to 4, wherein the content of the structural unit represented by Formula (1) is 5 mol% or more and 35 mol% or less. Disclosure 6 is the polyvinyl acetal resin according to any one of Disclosures 1 to 5, wherein the content of the structural unit represented by Formula (1) relative to the total amount of acetal groups (content of structural units represented by Formula (1) / total amount of acetal groups) is 0.06 or more and 0.6 or less. Disclosure 7 is the polyvinyl acetal resin according to any one of Disclosures 1 to 6, wherein the amount of hydroxyl groups is 10 mol% or more and 30 mol% or less. Disclosure 8 is the polyvinyl acetal resin according to any one of Disclosures 1 to 7, wherein the average degree of polymerization is 500 or more. Disclosure 9 is a conductive paste containing the polyvinyl acetal resin according to any one of Disclosures 1 to 8, an organic solvent, a conductive powder, and a dispersion improver. Disclosure 10 is a multilayer ceramic capacitor formed using the conductive paste according to Disclosure 9.

[0008] As a result of extensive research, the present inventors have found that a polyvinyl acetal resin containing a specific structural unit and having a total acetal group content within a predetermined range 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 of the present invention has a structural unit represented by the following formula (1), and R １ is a hydrocarbon group having 4 to 20 carbon atoms. By having such a hydrocarbon group, the compound has excellent solubility in a solvent, high paste viscosity, and good thixotropy, and can improve printability.

[0010]

[0011] The above R １ The number of carbon atoms in the hydrocarbon group 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 9. The number of carbon atoms is particularly preferably 6 or 9. １may be a combination of two or more hydrocarbon groups having different numbers of carbon atoms. By having such a number of carbon atoms, the solubility in a solvent can be improved. １ Since the structure of the compound (I) is a straight-chain hydrocarbon group, the paste has high viscosity and good thixotropy, and can provide good printability.

[0012] The above (R １ The hydrocarbon group having from 4 to 20 carbon atoms is preferably an alkyl group having from 4 to 20 carbon atoms. Examples of the alkyl group having from 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.

[0013] The above (R １ The hydrocarbon group having 4 to 20 carbon atoms (above) may be a linear alkyl group or a branched alkyl group. A linear alkyl group is preferred. 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 these, the R １ is 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.

[0014] Examples of the branched alkyl group include an isobutyl group, an isopentyl group, a neopentyl group, a 1-methylhexyl group, a 1-methylheptyl group, a 1-methyloctyl group, a 1-methylnonyl group, a 1-methyldecyl group, a 1-methylundecyl group, and a 1-methyldodecyl group. Other examples include a 1-methyltridecyl group, a 1-methyltetradecyl group, a 1-methylheptadecyl group, a 1-methylhexadecyl group, a 1-methylpentadecyl group, a 1-methyloctadecyl group, and a 1-methylnonadecyl group. Further examples include alkyl groups in which an alkyl group having two or more carbon atoms is substituted on the first carbon atom (e.g., a 1-ethyldecyl group, a 1-propylnonyl group, a 1-butyloctyl group, a 1-pentylheptyl group, and a 1-octyldecyl group). Furthermore, in a branched alkyl group, the branching position is not limited to the first carbon atom, and may be the second or higher carbon atom. For example, alkyl groups in which a methyl group is substituted on the second or higher carbon atom include a 2-methylpentyl group, a 2-methylundecyl group, a 3-methylundecyl group, and a 4-methylundecyl group. Furthermore, alkyl groups in which an alkyl group having two or more carbon atoms is substituted on the second or higher carbon atom include a 2-ethylhexyl group, a 2-ethylheptyl group, a 2-ethyloctyl group, a 2-ethylundecyl group, a 2-ethyloctadecyl group, a 2-propylundecyl group, a 2-butylundecyl group, and a 2-octylundecyl group. Further examples include a 3-ethylundecyl group, a 4-ethyloctadecyl group, a 4-butyloctadecyl group, and a neodecyl group. The branched alkyl group is preferably a 2-methylpentyl group.

[0015] 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. １ may be an alkyl group based on a bio-derived aldehyde having 4 or more carbon atoms.

[0016] The content of the structural unit represented by the above formula (1) in the polyvinyl acetal resin of the present invention is preferably 5 mol %, more preferably 10 mol %, and more preferably 35 mol %, and even more preferably 33 mol %. 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 Measurement is performed using C-NMR (nuclear magnetic resonance spectrum).

[0017] 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), the polyvinyl acetal resin can have excellent solubility in solvents, high paste viscosity, and good thixotropy, thereby improving printability.

[0018] In formula (2), R ２ represents an alkyl group having 1 to 19 carbon atoms.

[0019] 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. The alkyl group having 1 to 19 carbon atoms may be the same as the alkyl group having 4 to 20 carbon atoms, but is preferably an alkyl group having 1 to 3 carbon atoms. Among these, the R ２ is preferably a linear hydrocarbon group having 1 or 3 carbon atoms, is preferably a methyl group or an n-propyl group, and is more preferably an n-propyl group. By having such a hydrocarbon group, the solubility in a solvent can be improved.

[0020] The content of the acetal unit 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 unit 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 unit represented by the above formula (2) is １ H-NMR and １３ Measurement is performed using C-NMR (nuclear magnetic resonance spectrum).

[0021] When the polyvinyl acetal resin of the present invention contains the acetal units represented by the above formula (1) and the acetal units represented by the above formula (2), the lower limit of their total content is preferably 69 mol%, more preferably 71 mol%, and preferably 90 mol%, more preferably 80 mol%. By setting the total content within the above ranges, excellent solubility in solvents, high paste viscosity, good thixotropy, and good printability can be achieved.

[0022] 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 the two (content of acetal units represented by formula (1) / content of acetal units represented by formula (2)) is preferably 0.06 or more and 1.50 or less. It is more preferably 0.40 or more and 1.40 or less, even more preferably 0.55 or more and 1.20 or less, and particularly preferably 0.60 or more and 0.86 or less. By keeping the ratio within the above range, excellent solubility in solvents, high paste viscosity, good thixotropy, and good printability can be achieved.

[0023] The total acetal group content (total amount of all acetal units) of the polyvinyl acetal resin of the present invention is 68.5 mol% or more, preferably 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 content is 68.5 mol%, preferably 69 mol%, more preferably 71 mol%, and the upper limit is preferably 90 mol%, more preferably 82 mol%, and even more preferably 79 mol%. By setting the total acetal group content to be particularly equal to or less than the upper limit, good solubility in solvents can be achieved. The total acetal group content is １ H-NMR and １３ It is measured using C-NMR (nuclear magnetic resonance spectroscopy). The content of the structural unit represented by formula (1) relative to the total amount of acetal groups (content of structural units represented by formula (1) / total amount of acetal groups) preferably has a lower limit of 0.06 and an upper limit of 0.6. It is more preferably 0.3 or more and 0.55 or less, even more preferably 0.35 or more and 0.53 or less, and particularly preferably 0.38 or more and 0.46 or less. By keeping the ratio within the above range, excellent solubility in solvents, high paste viscosity, and good thixotropy and printability can be achieved.

[0024] The polyvinyl acetal resin of the present invention has a structural unit having a hydroxyl group. The content of the structural unit having a hydroxyl group (amount of hydroxyl groups) in the polyvinyl acetal resin of the present invention is preferably 10 mol% or more and 30 mol% or less. By setting it within the above range, the solubility in solvents can be improved. A more preferred lower limit of the amount of hydroxyl groups is 20 mol%, and a more preferred upper limit is 29 mol%. The amount of hydroxyl groups １ H-NMR and １３The measurement is performed using C-NMR (nuclear magnetic resonance spectroscopy). The acetal unit / hydroxyl group amount represented by the above formula (1) preferably has a lower limit of 0.50 and an upper limit of 2.00. It is more preferably 0.80 or more and 1.40 or less, and even more preferably 0.90 or more and 1.20 or less. By keeping the ratio within the above range, excellent solubility in solvents, high paste viscosity, good thixotropy, and good printability can be achieved.

[0025] The polyvinyl acetal resin of the present invention has a structural unit having an acetyl group. The content of the structural unit having an acetyl group (acetyl group amount) in the polyvinyl acetal resin of the present invention is preferably 0.1 mol% in lower limit and 10 mol% in upper limit. 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. The more preferred lower limit of the acetyl group amount is 0.3 mol%, and the more preferred upper limit is 5 mol%. The acetyl group amount １ H-NMR and １３ Measurement is performed using C-NMR (nuclear magnetic resonance spectrum).

[0026] The polyvinyl acetal resin of the present invention may have a structural unit having a carboxylic acid. The content of the structural unit having a carboxylic acid (amount of carboxylic acid modification) 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 amount of carboxylic acid groups to 0.1 mol% or more, the paste viscosity can be increased, and by setting the amount of carboxylic acid modification to 10 mol% or less, the solubility in solvents can be improved. The lower limit of the amount of acetyl groups is more preferably 0.3 mol%, and the upper limit is more preferably 5 mol%. The amount of carboxylic acid modification is １ H-NMR and １３ Measurement is performed using C-NMR (nuclear magnetic resonance spectrum).

[0027] The polyvinyl acetal resin of the present invention has an average degree of polymerization of less than 2300. This allows for good solubility in solvents and good thixotropy. A preferred lower limit of the average degree of polymerization of the polyvinyl acetal resin of the present invention is 500, preferably less than 2300. An average degree of polymerization of 500 or more facilitates industrial production. An average degree of polymerization of less than 2300 allows for good solubility in solvents and good 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.

[0028] 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.

[0029] The polyvinyl acetal resin of the present invention is prepared by dissolving a 10% by mass solution in a DHTA solvent at a measurement temperature of 20°C and a shear region of 100 s －１It is preferable that the viscosity when measured using a rotational rheometer under the conditions is 1.5 Pa·s or more. By setting the viscosity within this range, a conductive paste with high paste viscosity and excellent printability can be produced. The viscosity is more preferably 10 Pa·s or more, 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. Furthermore, it is preferable to adjust the rotor during viscosity measurement appropriately depending on the viscosity, and measurements can be made using a cone plate (Measuring cone CP50-1, D: 50 mm; Angle 1°).

[0030] 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.

[0031] Examples of methods for producing the polyvinyl acetal resin 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.

[0032] Examples of methods for acetalizing the polyvinyl alcohol using at least one aldehyde having 5 to 21 carbon atoms include a method in which aldehydes with different carbon numbers are prepared and then acetalized to introduce acetal units having multiple alkyl groups with different carbon numbers. When producing the polyvinyl acetal resin, acetalization may be performed in the presence of a dispersant. Acetalization in the presence of a dispersant is preferred. Acetalization in the presence of a dispersant allows the acetalization reaction to proceed uniformly, making it easier to adjust the degree of acetalization within a predetermined range and improving solvent solubility. The type of dispersant is not particularly limited, but a water-soluble dispersant is preferred. More specifically, examples include a method in which polyvinyl alcohol not having an acetal unit represented by formula (1) is acetalized with a predetermined aldehyde to introduce the acetal unit represented by formula (1).

[0033] 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.

[0034] The polyvinyl alcohol preferably has a saponification degree of 85 mol% or more, 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%.

[0035] In the method of reacting polyvinyl alcohol with an aldehyde having from 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 from 5 to 21 carbon atoms. Examples of the aliphatic aldehyde having 5 to 21 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, methylnonylacetaldehyde, etc. These aldehydes may be used alone or in combination of two or more. It is particularly preferable to use a combination of an aldehyde having 5 to 21 carbon atoms and an aldehyde having 4 or less carbon atoms. Of these, acetaldehyde, butylaldehyde, decylaldehyde, and heptaldehyde are preferred as the aldehyde.

[0036] 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, when the amount is preferably 5 mol% to 120 mol%, more preferably 10 mol% to 110 mol%, relative to 100 mol% of polyvinyl alcohol, the acetalization reaction proceeds efficiently and unreacted aldehyde is easily removed. That is, the amount of the aldehyde added is preferably 5 to 120 mol%, more preferably 10 to 110 mol%.

[0037] 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.

[0038] In the acetalization step, when an aldehyde having 5 or more carbon atoms is contained, a dispersant may or may not be used. Furthermore, in the acetalization step, a method in which the polyvinyl acetal resin is precipitated during the acetalization reaction (precipitation method) is preferably used, 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, the precipitation method is preferably used.

[0039] 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.

[0040] The acetalization reaction is preferably carried out in the presence of an acid catalyst. Examples of the acid catalyst include mineral acids, carboxylic acids, sulfonic acids, etc. Examples of the mineral acids include sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, etc. Examples of the carboxylic acids include formic acid, acetic acid, propionic acid, etc. Examples of the sulfonic acids include paratoluenesulfonic acid, methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, etc. These acid catalysts may be used alone or in combination of two or more. Among these, paratoluenesulfonic acid and hydrochloric acid are preferred.

[0041] The temperature when the aldehyde is added (aldehyde introduction temperature) is preferably 0°C or higher, more preferably 5°C or higher, and preferably 70°C or lower. The temperature when the catalyst is added is preferably 5°C or higher and 50°C or lower. The holding time in the acetalization reaction is preferably 0.5 hours or higher and 5 hours or lower, more preferably 1 hour or higher and 3 hours or lower. The holding temperature in the acetalization reaction is preferably 0°C or higher and 65°C or lower, more preferably 5°C or higher and 60°C or lower.

[0042] Applications of the polyvinyl acetal resin of the present invention include, for example, binders and dispersants for conductive pastes, battery electrodes, secondary battery electrodes, etc., modifiers for adhesives based on epoxy resins, phenolic resins, etc., ceramic green sheets, etc. In particular, when the polyvinyl acetal resin of the present invention is used as a conductive paste, the paste has high viscosity and good thixotropy after being kneaded with a conductive powder, making it possible to obtain a paste with excellent printability.

[0043] 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.

[0044] The organic solvent may be any organic solvent commonly 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. 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.

[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 approximately spherical in shape. When the average particle diameter is 50 nm or more, the specific surface area of ​​the conductive powder is favorable, 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 "approximately spherical" includes not only a perfect spherical shape but also particles with a shape close to a sphere.

[0048] The amount of the conductive powder 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 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 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. A more preferred lower limit of the amount of the conductive powder 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.

[0049] The conductive paste preferably further contains ceramic powder in addition to the conductive powder. The inclusion of ceramic powder facilitates matching the shrinkage behavior of the conductive powder during firing with that of the ceramic green sheet. The ceramic powder is not particularly limited, but barium titanate, which is used in the green sheet, is preferred. The average particle size of the ceramic powder is not particularly limited, but is preferably smaller than that of the conductive powder, specifically, 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 acids are not particularly limited, but examples 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, tallow fatty acid, and hardened castor fatty acid. Among these, lauric acid, stearic acid, and oleic acid are preferred. The aliphatic amines are not particularly limited, but examples include laurylamine, myristylamine, cetylamine, stearylamine, oleylamine, alkyl (coconut) amines, alkyl (hardened tallow) amines, alkyl (tallow) amines, and alkyl (soybean) amines. The alkanolamides are not particularly limited, but examples include coconut fatty acid diethanolamide, 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, 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.

[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 followed by a degreasing process and firing to form a sintered ceramic body. External electrodes are then formed on the end surfaces of the sintered ceramic body, thereby producing a multilayer ceramic capacitor. Examples of printing processes that can be used include screen printing, die coating, and gravure offset. This 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 produced by applying the conductive paste of the present invention to ceramic green sheets, stacking multiple ceramic green sheets and heating and pressing them to form a laminate, degreasing and firing to form a sintered ceramic body, and forming external electrodes on the end surfaces of the sintered ceramic body.

[0055] According to the present invention, there are provided a polyvinyl acetal resin that has a high paste viscosity after being mixed with a conductive powder, good thixotropy, and excellent printability, a conductive paste using the polyvinyl acetal resin, and a multilayer ceramic capacitor. Furthermore, according to the present invention, there are provided a polyvinyl acetal resin that has excellent solvent solubility and adhesion, and a conductive paste using the polyvinyl acetal resin, and a multilayer ceramic capacitor.

[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 having a saponification degree of 99.2 mol% and an average degree of polymerization of 1700, and 13.5 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 1600 g of pure water and dissolved under 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. Thereafter, the solution was cooled to 15°C, and 20 g of hydrochloric acid having a concentration of 35% by mass, diluted with 180 g of pure water, was added. The liquid temperature was maintained at 15°C, and an acetalization reaction was carried out for 1 hour, allowing the reaction product to precipitate. After 1 hour of acetalization, 13.5 g of 20% by mass sodium dodecylbenzenesulfonate (SDBS) dissolved in pure water was added, and the acetalization reaction was continued for another hour. The temperature was then raised to 45°C at a rate of 2-3°C / 5 min, and the liquid temperature was maintained at 45°C for 3 hours to complete the reaction. The reaction 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 resulting polyvinyl acetal resin was dissolved in CDCl ３ Dissolved in (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 spectrum). 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 The acetal unit was determined by C-NMR. １ = (CH ２ ) ８ CH ３ ] and the acetal unit [R ２ = (CH ２ ) ２ CH ３ ] was.

[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 CDCl ３ Dissolved in (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 spectrum). 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 The acetal unit was determined by C-NMR. １ = (CH ２ ) ８ CH ３ ] and the structural unit represented by the above formula (2) [R ２ = (CH ２ ) ２ CH ３ ] was.

[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 CDCl ３ Dissolved in (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 spectrum). 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 The acetal unit was determined by C-NMR.１ = (CH ２ ) ８ CH ３ ] and the structural unit represented by the above formula (2) [R ２ = (CH ２ ) ２ CH ３ ] was.

[0060] Example 4 (Preparation of Polyvinyl Acetal Resin) 150 g of polyvinyl alcohol having a saponification degree of 99.1 mol% and an average degree of polymerization of 1700, and 13.5 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 1600 g of pure water and dissolved under stirring at 90°C for 2 hours. This solution was cooled to 65°C, and 87 g of n-butyl aldehyde and 46 g of n-heptaldehyde were added. Thereafter, the solution was cooled to 15°C, and 20 g of hydrochloric acid having a concentration of 35% by mass, diluted with 180 g of pure water, was added. The liquid temperature was maintained at 15°C, and an acetalization reaction was carried out for 1 hour, allowing the reaction product to precipitate. 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 continued for another hour. The temperature was then raised to 60°C at a rate of 2-3°C / 5 min, and the liquid temperature was maintained at 60°C for 3 hours to complete the reaction. After neutralization, water washing, and drying in the usual manner, a powder of polyvinyl acetal resin (long-chain alkyl-modified) was obtained. The resulting polyvinyl acetal resin was dissolved in CDCl ３ Dissolved in (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 spectrum). 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 The acetal unit was determined by C-NMR. １ = (CH ２ ) ５ CH ３ ] and the structural unit represented by the above formula (2) [R ２ = (CH ２) ２ CH ３ ] was.

[0061] Example 5 (Preparation of Polyvinyl Acetal Resin) 190 g of polyvinyl alcohol having a saponification degree of 99.0 mol% and an average degree of polymerization of 1700, and 25 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 2800 g of pure water and dissolved at 90°C with stirring for 2 hours. This solution was cooled to 40°C, 400 g of hydrochloric acid having a concentration of 35% by mass was added, and then cooled to 15°C. 75 g of n-butyl aldehyde and 95 g of n-decyl aldehyde were added to carry out an acetalization reaction, and the reaction product was precipitated. Next, the temperature was raised to 50°C at a rate of 2-3°C / 5 minutes, and the liquid temperature was maintained at 50°C for 5 hours to complete the reaction. After neutralization, washing with water, and drying by conventional methods, a polyvinyl acetal resin powder was obtained. The obtained polyvinyl acetal resin was dissolved in CDCl ３ Dissolved in (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 spectrum). 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 The acetal unit was determined by C-NMR. １ = (CH ２ ) ８ CH ３ ] and the acetal unit [R ２ = (CH ２ ) ２ CH ３ ] was.

[0062] Example 6 (Preparation of Polyvinyl Acetal Resin) 70 g of polyvinyl alcohol having a saponification degree of 99.8 mol% and an average polymerization degree of 1100 was added to 1100 g of pure water instead of 45 g of polyvinyl alcohol having a saponification degree of 99.1 mol% and an average polymerization degree of 1700, and the mixture was dissolved by stirring at 90°C for 2 hours. This solution was cooled to 70°C, and 50 g of hydrochloric acid having a concentration of 35% by mass was added and reacted for 2 hours. The mixture was then cooled to 10°C, and 51 g of n-butylaldehyde and 40 g of methyl valeraldehyde were added to carry out an acetalization reaction, resulting in precipitation of the reaction product. The mixture was then heated to 50°C at a rate of 2-3°C / 5 min, and the liquid temperature was maintained at 50°C for 5 hours to complete the reaction. The mixture was then neutralized, washed with water, and dried by conventional methods to obtain a polyvinyl acetal resin powder. The resulting polyvinyl acetal resin was dissolved in CDCl ３ (chloroform) and 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 spectrum). The total amount of acetal groups (the sum of the contents of each acetal unit) was calculated from the measured values. The content of each acetal unit was calculated as follows: １３ The quantitative analysis was carried out using C-NMR. The results are shown in Table 1. The acetal unit is a structural unit represented by the above formula (1) [R １ =CH(CH ３ ) C ３ H ７ ] and the structural unit represented by the above formula (2) [R ２ = (CH ２ ) ２ CH ３ ] was.

[0063] Example 7 (Preparation of Polyvinyl Acetal Resin) 185 g of polyvinyl alcohol having a saponification degree of 99.1 mol% and an average degree of polymerization of 1700, and 25 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 2750 g of pure water and dissolved at 90°C with stirring for 2 hours. This solution was cooled to 40°C, 410 g of hydrochloric acid having a concentration of 35% by mass was added, and then cooled to 15°C. 45 g of n-butyl aldehyde and 42 g of n-decyl aldehyde were added to carry out an acetalization reaction, and the reaction product was precipitated. Next, the temperature was raised to 40°C at a rate of 2 to 3°C / 5 minutes, and the liquid temperature was maintained at 40°C for 5 hours to complete the reaction. After neutralization, washing with water, and drying by conventional methods, a polyvinyl acetal resin powder was obtained. The obtained polyvinyl acetal resin was dissolved in CDCl ３ Dissolved in (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 spectrum). 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 The acetal unit was determined by C-NMR. １ = (CH ２ ) ８ CH ３ ] and the structural unit represented by the above formula (2) [R ２ = (CH ２ ) ２ CH ３ ] was.

[0064] (Example 8) (Preparation of Polyvinyl Acetal Resin) 150 g of polyvinyl alcohol having a saponification degree of 99.1 mol% and an average degree of polymerization of 1700, and 25 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 1600 g of pure water and stirred at 90 ° C for 2 hours to dissolve. This solution was cooled to 40 ° C, and 410 g of hydrochloric acid having a concentration of 35% by mass was diluted with 330 g of pure water and added, followed by cooling to 15 ° C, and 47 g of n-butyl aldehyde and 130 g of n-decyl aldehyde were added to carry out an acetalization reaction, resulting in precipitation of the reaction product. Next, the temperature was raised to 40 ° C at a heating rate of 2 to 3 ° C / 5 minutes, and the liquid temperature was maintained at 40 ° C for 5 hours to complete the reaction. After neutralization, washing with water, and drying by conventional methods, a polyvinyl acetal resin powder was obtained. The obtained polyvinyl acetal resin was dissolved in CDCl ３ Dissolved in (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 spectrum). 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 The acetal unit was determined by C-NMR. １ = (CH ２ ) ８ CH ３ ] and the structural unit represented by the above formula (2) [R ２ = (CH ２ ) ２ CH ３ ] was.

[0065] Example 9 (Preparation of Polyvinyl Acetal Resin) 112 g of polyvinyl alcohol having a saponification degree of 99.0 mol% and an average degree of polymerization of 1700, and 13.5 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 1600 g of pure water and dissolved under stirring at 90°C for 2 hours. This solution was cooled to 65°C, and 70 g of n-butyl aldehyde and 15 g of n-heptaldehyde were added. Thereafter, the solution was cooled to 15°C, and 20 g of hydrochloric acid having a concentration of 35% by mass, 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, allowing the reaction product to precipitate. 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 continued for another hour. The temperature was then raised to 60°C at a rate of 2-3°C / 5 min, and the liquid temperature was maintained at 60°C for 3 hours to complete the reaction. After neutralization, water washing, and drying in the usual manner, a powder of polyvinyl acetal resin (long-chain alkyl-modified) was obtained. The resulting polyvinyl acetal resin was dissolved in CDCl ３ Dissolved in (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 spectrum). 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 The acetal unit was determined by C-NMR. １ = (CH ２ ) ５ CH ３ ] and the structural unit represented by the above formula (2) [R ２ = (CH ２ ) ２ CH ３ ] was.

[0066] (Example 10) (Preparation of Polyvinyl Acetal Resin) 112 g of polyvinyl alcohol having a saponification degree of 99.0 mol% and an average degree of polymerization of 1700, and 13.5 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 1600 g of pure water and stirred at 90°C for 2 hours to dissolve. This solution was cooled to 65°C, and 85 g of n-heptaldehyde was added. Then, the solution was cooled to 15°C, and 20 g of hydrochloric acid having a concentration of 35% by mass diluted with 180 g of pure water was added. The liquid temperature was maintained at 15°C, and an acetalization reaction was carried out for 1 hour, and the reaction product was precipitated. After 1 hour of the acetalization reaction, 13.5 g of sodium dodecylbenzenesulfonate (SDBS) dissolved in pure water at a concentration of 20% by mass was added, and the acetalization reaction was carried out for another 1 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 a conventional manner to obtain a powder of polyvinyl acetal resin (modified with long-chain alkyl groups). The resulting polyvinyl acetal resin was dissolved in CDCl ３ Dissolved in (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 spectrum). 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 2. The content of each acetal unit was １３ The acetal unit was determined by C-NMR. １ = (CH ２ ) ５ CH ３ ] was.

[0067] Example 11 (Preparation of Polyvinyl Acetal Resin) Instead of 45 g of polyvinyl alcohol having a saponification degree of 99.1 mol% and an average polymerization degree of 1700, 70 g of polyvinyl alcohol having a saponification degree of 99.9 mol% and an average polymerization degree of 840 was added to 1000 g of pure water and stirred at 90°C for 2 hours to dissolve. This solution was cooled to 70°C, and 150 g of hydrochloric acid having a concentration of 35% by mass was diluted with 120 g of pure water and added, followed by a reaction for 2 hours. Thereafter, the solution was cooled to 10°C, and 62 g of n-butyl aldehyde and 40 g of n-dodecyl aldehyde were added to carry out an acetalization reaction, thereby precipitating the reaction product. Next, the temperature was raised to 45°C at a rate of 2 to 3°C per 5 minutes, and the liquid temperature was maintained at 45°C for 5 hours to complete the reaction. After neutralization, water washing, and drying by conventional methods, a polyvinyl acetal resin powder was obtained. The obtained polyvinyl acetal resin was dissolved in CDCl ３ (chloroform) and 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 spectrum). The total amount of acetal groups (the sum of the contents of each acetal unit) was calculated from the measured values. The content of each acetal unit was calculated as follows: １３ The quantitative analysis was carried out using C-NMR. The results are shown in Table 2. The acetal unit is a structural unit represented by the above formula (1) [R １ = (CH ２ ) １０ CH ３ ] and the structural unit represented by the above formula (2) [R ２ = (CH ２ ) ２ CH ３ ] was.

[0068] (Example 12) (Preparation of Polyvinyl Acetal Resin) 185 g of polyvinyl alcohol having a saponification degree of 99.1 mol% and an average degree of polymerization of 1700, and 25 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 2800 g of pure water and stirred at 90 ° C for 2 hours to dissolve. This solution was cooled to 40 ° C, and 410 g of hydrochloric acid having a concentration of 35% by mass was diluted with 330 g of pure water and added, followed by cooling to 15 ° C, and 67 g of n-butyl aldehyde and 95 g of n-decyl aldehyde were added to carry out an acetalization reaction, resulting in precipitation of the reaction product. Next, the temperature was raised to 40 ° C at a heating rate of 2 to 3 ° C / 5 minutes, and the liquid temperature was maintained at 40 ° C for 5 hours to complete the reaction. After neutralization, washing with water, and drying by conventional methods, a polyvinyl acetal resin powder was obtained. The obtained polyvinyl acetal resin was dissolved in CDCl ３ Dissolved in (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 spectrum). 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 2. The content of each acetal unit was １３ The acetal unit was determined by C-NMR. １ = (CH ２ ) ８ CH ３ ] and the structural unit represented by the above formula (2) [R ２ = (CH ２ ) ２ CH ３ ] was.

[0069] (Example 13) (Preparation of polyvinyl acetal resin) Instead of 121 g of polyvinyl alcohol having a saponification degree of 98.4 mol%, an average polymerization degree of 600, 65 g of carboxylic acid-modified polyvinyl alcohol having a saponification degree of 98.6 mol%, an average polymerization degree of 500 (itaconic acid-modified, carboxylic acid modification amount 0.7 mol%), 25 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 was added to 2800 g of pure water, and the mixture was stirred at 90 ° C. for 2 hours to dissolve. This solution was cooled to 40 ° C., and 410 g of hydrochloric acid having a concentration of 35% by mass was diluted with 330 g of pure water and added, followed by cooling to 15 ° C., and 69 g of n-butyl aldehyde and 95 g of n-decyl aldehyde were added to carry out an acetalization reaction, and the reaction product was precipitated. The temperature was then raised to 40°C at a rate of 2 to 3°C per 5 minutes, and the liquid temperature was maintained at 40°C for 5 hours to complete the reaction. The mixture was then neutralized, washed with water, and dried in a conventional manner to obtain a polyvinyl acetal resin powder. The resulting polyvinyl acetal resin was dissolved in CDCl ３ Dissolved in (deuterated chloroform) １ H-NMR and １３ Using C-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. 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 2. The content of each acetal unit was １３ The acetal unit was determined by C-NMR. １ = (CH ２ ) ８ CH ３ ] and the structural unit represented by the above formula (2) [R ２ = (CH ２ ) ２ CH ３ ] was.

[0070] 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 stirred at 90°C for 2 hours to dissolve. 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 9 g of acetaldehyde and 110 g of n-butylaldehyde were added to carry out an acetalization reaction, thereby precipitating the reaction product. The liquid temperature was then maintained at 50°C to complete the reaction for 4 hours. After neutralization, washing with water, and drying by conventional methods, a polyvinyl acetal resin powder was obtained. The obtained polyvinyl acetal resin was dissolved in CDCl ３ (chloroform) and １ 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 using H-NMR (nuclear magnetic resonance spectrum). The total amount of acetal groups (the sum of the contents 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 2. The acetal units were acetoacetal units and butyral units.

[0071] (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. Thereafter, the solution was cooled to 10°C, and 130 g of n-butyl aldehyde was added to carry out an acetalization reaction, thereby precipitating the reaction product. Next, the liquid temperature was maintained at 30°C, and the reaction was completed for 6 hours. After neutralization, washing with water, and drying by conventional methods, a polyvinyl acetal resin powder was obtained. The obtained polyvinyl acetal resin was dissolved in CDCl ３ Dissolved in (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 2. The acetal units were butyral units.

[0072] (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 stirred at 90°C for 2 hours to dissolve. This solution was cooled to 40°C, and 100 g of hydrochloric acid with a concentration of 35% by mass was added. Thereafter, the solution was cooled to 10°C, and 120 g of n-butyl aldehyde was added to carry out an acetalization reaction, thereby precipitating the reaction product. Next, the liquid temperature was maintained at 40°C to complete the reaction for 6 hours, and the reaction was neutralized, washed with water, and dried by a conventional method to obtain a polyvinyl acetal resin powder. The obtained polyvinyl acetal resin was dissolved in CDCl ３ Dissolved in (deuterated chloroform) １ 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 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 2. The acetal units were butyral units.

[0073] (Comparative Example 4) (Preparation of Polyvinyl Acetal Resin) 185 g of polyvinyl alcohol having a saponification degree of 87.0 mol% and an average polymerization degree of 2,300 was added to 2,750 g of pure water and dissolved by stirring at 90°C for 2 hours. This solution was cooled to 40°C, and 410 g of hydrochloric acid with a concentration of 35% by mass was added. After that, the solution was cooled to 10°C, and 45 g of n-butyl aldehyde and 50 g of n-heptaldehyde were added to carry out an acetalization reaction, thereby precipitating the reaction product. Next, the temperature was raised to 40°C at a rate of 2 to 3°C per 5 minutes, and the liquid temperature was maintained at 40°C for 5 hours to complete the reaction. After neutralization, washing with water, and drying by conventional methods, a polyvinyl acetal resin powder was obtained. The obtained polyvinyl acetal resin was dissolved in CDCl ３ Dissolved in (deuterated chloroform) １ H-NMR and １３ Using C-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. 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 2. The content of each acetal unit was１３ The acetal unit was determined by C-NMR. １ = (CH ２ ) ８ CH ３ ] and the structural unit represented by the above formula (2) [R ２ = (CH ２ ) ２ CH ３ ] was.

[0074] (Comparative Example 5) (Preparation of Polyvinyl Acetal Resin) Instead of 45 g of polyvinyl alcohol having a saponification degree of 99.1 mol% and an average polymerization degree of 1700, 70 g of polyvinyl alcohol having a saponification degree of 98.6 mol% and an average polymerization degree of 1100, 13.5 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 was added to 1600 g of pure water and dissolved at 90 ° C. for 2 hours with stirring. This solution was cooled to 65 ° C., and 67 g of n-butyl aldehyde and 34 g of n-heptaldehyde were added. Thereafter, the solution was cooled to 15 ° C., and 20 g of hydrochloric acid having a concentration of 35% by mass was diluted with 180 g of pure water and added. The liquid temperature was maintained at 15 ° C. and the acetalization reaction was carried out for 1 hour, and the reaction product was precipitated. 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 continued for another hour. The temperature was then raised to 60°C at a rate of 2-3°C / 5 min, and the liquid temperature was maintained at 60°C for 3 hours to complete the reaction. After neutralization, water washing, and drying in the usual manner, a powder of polyvinyl acetal resin (long-chain alkyl-modified) was obtained. The resulting polyvinyl acetal resin was dissolved in CDCl ３ Dissolved in (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 spectrum). 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 2. The content of each acetal unit was １３ The acetal unit was determined by C-NMR. １= (CH ２ ) ５ CH ３ ] and the structural unit represented by the above formula (2) [R ２ = (CH ２ ) ２ CH ３ ] was.

[0075] <Evaluation> The following evaluations were performed on the obtained polyvinyl acetal resin. (1) Measurement of resin viscosity (solution viscosity) 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 The measurement was carried out using a rotor: cone plate (Measuring cone CP50-1, D: 50 mm; Angle 1°) under the conditions of

[0076] (2) Solvent Solubility A polyvinyl acetal resin and dihydroterpinyl acetate were blended 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 7 hours using a hot stirrer so that the temperature of the solution was 90°C, and the state of the solution immediately after mixing was visually confirmed and evaluated according to the following criteria: ◎: Completely dissolved in less than 3 hours; ○: Completely dissolved in 3 to 7 hours; ×: Not completely dissolved even after 7 hours or more.

[0077] (3) Measurement of Paste Viscosity (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.

[0078] (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), and the measurement temperature was 20°C, the shear range was 10 s －１ Measurement was carried out using a rotor: cone plate (Measuring cone CP25-2, D: 25 mm; Angle 2°) under the conditions above, and the results were evaluated according to the following criteria: ⊚: 20.0 Pa·s or more ◯: 12.0 Pa·s or more, less than 20.0 Pa·s ×: less than 12.0 Pa·s

[0079] (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, the shear range was 100 s －１ Measurement was 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 condition of 10 s －１ Viscosity / 100s －１ The viscosity was evaluated according to the following criteria: ⊚: 5.0 or more; ◯: 2.5 or more, less than 5.0; ×: less than 2.5.

[0080]

[0081]

[0082] According to the present invention, it is possible to provide a polyvinyl acetal resin that has a high paste viscosity after being kneaded with a conductive powder, has good thixotropy, and is excellent in printability, as well as a conductive paste and a multilayer ceramic capacitor that use the polyvinyl acetal resin.

Claims

1. A structural unit represented by the following formula (1), wherein R １ is a hydrocarbon group having 4 to 20 carbon atoms, the total amount of acetal groups is 68.5 mol % or more, and the average degree of polymerization is less than 2,300.

2. A 10% by weight solution of dihydroterpineol acetate (DHTA) in a solvent was measured at a temperature of 20°C and a shear region of 100 s. －１ 2. The polyvinyl acetal resin according to claim 1, having a viscosity of 1.5 Pa·s or more when measured using a rotational rheometer under the following conditions:

3. R ​​in the above formula (1) １ The polyvinyl acetal resin according to claim 1 or 2, wherein: is a hydrocarbon group having 6 to 20 carbon atoms, and the amount of acetyl groups is 5 mol % or less.

4. R in the above formula (1) １ is a linear hydrocarbon group having 6 or 9 carbon atoms.

5. A polyvinyl acetal resin according to any one of claims 1 to 4, wherein the content of the structural unit represented by the formula (1) is 5 mol % or more and 35 mol % or less.

6. The polyvinyl acetal resin according to any one of claims 1 to 5, 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 0.6 or less.

7. The polyvinyl acetal resin according to any one of claims 1 to 6, wherein the amount of hydroxyl groups is from 10 mol % to 30 mol %.

8. The polyvinyl acetal resin according to any one of claims 1 to 7, having an average degree of polymerization of 500 or more.

9. A conductive paste comprising the polyvinyl acetal resin according to any one of claims 1 to 8, an organic solvent, a conductive powder, and a dispersion improver.

10. A multilayer ceramic capacitor made using the conductive paste according to claim 9.

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