Polyvinyl acetal resin, conductive paste, and multilayer ceramic capacitors

Abstract

The present invention provides a polyvinyl acetal resin capable of producing a conductive paste with excellent thread breakage during printing and smoothness of the printed surface, and a conductive paste and multilayer ceramic capacitor made using the polyvinyl acetal resin. [Solution] A polyvinyl acetal resin that satisfies the following formulas (1) and (2) when a 10% by mass DHTA solution dissolved in dihydroterpinyl acetate (DHTA) solvent has a solution haze at room temperature (20°C) of A, and a solution haze after being stored at -5°C for one week and then left for 24 hours to return to room temperature (20°C) of B. (1) 0.1 ≤ A ≤ 2.0 (2)|AB|≦1.0

Description

[Technical Field]

[0001] This invention relates to polyvinyl acetal resin, conductive paste, and multilayer ceramic capacitors. [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 slurry composition is obtained by adding ceramic raw material powder to a solution in which a binder resin such as polyvinyl butyral resin or poly(meth)acrylic acid ester resin is dissolved in an organic solvent and mixing it uniformly. This slurry composition is cast onto a support, and after removing volatile components such as solvents by heating, it is peeled off from the support to obtain a ceramic green sheet. Next, multiple sheets of the obtained ceramic green sheet, onto which conductive paste for internal electrodes is applied by screen printing or gravure printing, are stacked alternately and heated and pressed together to create a laminate. Subsequently, a process called degreasing is performed to remove binder resin components and other substances contained in the laminate, and an external electrode is sintered onto the end face of the ceramic sintered body obtained by firing, thereby obtaining a multilayer ceramic capacitor.

[0003] The conductive paste for internal electrodes is obtained by kneading conductive powder, an organic solvent, and a binder resin. Ethyl cellulose and polyvinyl acetal resin are used as the binder resins mentioned above. Patent Document 1 discloses a conductive paste comprising a carboxylic acid-modified polyvinyl acetal resin, an organic solvent, and a conductive powder, from the viewpoint of improving the above-mentioned problems. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-228780

Summary of the Invention

Problems to be Solved by the Invention

[0005] In recent years, the demand for miniaturization and multi-layerization of multilayer ceramic capacitors (MLCCs) has been intensifying, and higher printing accuracy is required for the conductive paste for the internal electrodes of MLCCs. In particular, it is necessary that the amount of the conductive paste scattered outside the printing portion during printing is small. Also, the surface smoothness of the printing surface of the conductive paste is required. On the other hand, when the polyvinyl acetal resin described in the patent document is used for the conductive paste, there is a problem that the conductive paste scatters outside the printing portion because the thread break time is long.

[0006] The present invention provides a polyvinyl acetal resin capable of producing a conductive paste excellent in thread breakability during printing and smoothness of the printing surface, a conductive paste using the polyvinyl acetal resin, and a multilayer ceramic capacitor.

Means for Solving the Problems

[0007] The present disclosure No. 1 is a polyvinyl acetal resin that satisfies the following formulas (1) and (2) when, for a 10 mass% DHTA solution dissolved in a dihydroterpinyl acetate (DHTA) solvent, the solution haze at room temperature (20 ° C) is A, and after storing at -5 ° C for 1 week and then leaving it for 24 hours and returning to room temperature (20 ° C), the solution haze is B. (1) 0.1 ≤ A ≤ 2.0 (2) |A - B| ≤ 1.0 The present disclosure No. 2 is the polyvinyl acetal resin of the present disclosure No. 1 in which, for a 10 mass% DHTA solution, the viscosity ratio A' / B' is 1.1 or less when the viscosity measured by applying a shear rate of 10 s -1 at room temperature (20 ° C) is A', after storing at -5 ° C for 1 week and then leaving it for 24 hours and returning to room temperature (20 ° C), and the viscosity measured by applying a shear rate of 10 s -1 is B'. Disclosure 3 is a polyvinyl acetal resin according to Disclosure 1 or 2, having a weight-average molecular weight (Mw) / number-average molecular weight (Mn) of 3.5 to 5.0. Disclosure 4 is a polyvinyl acetal resin of Disclosure 1, 2, or 3, having a hydroxyl group content of 2 to 25 mol%. Disclosure 5 is a polyvinyl acetal resin of Disclosure 1, 2, 3, or 4, having an acetyl group content of 5 to 30 mol%. Disclosure 6 is a conductive paste comprising the polyvinyl acetal resin, organic solvent, and conductive powder of Disclosure 1, 2, 3, 4, or 5. Disclosure 7 is a multilayer ceramic capacitor made using the conductive paste of Disclosure 6. The present invention will be described in detail below.

[0008] As a result of diligent research, the inventors discovered that by using a polyvinyl acetal resin in which solution haze A and B, measured under predetermined conditions, satisfy a predetermined relationship, it is possible to produce a conductive paste with excellent thread breakability, smooth surface of the printed surface, and superior printability, thus completing the present invention.

[0009] The polyvinyl acetal resin of the present invention satisfies the following formulas (1) and (2) when a 10% by mass DHTA solution dissolved in dihydroterpinyl acetate (DHTA) solvent has a solution haze at room temperature (20°C) of A, and a solution haze after being stored at -5°C for one week and then left for 24 hours to return to room temperature (20°C) of B. (1) 0.1 ≤ A ≤ 2.0 (2)|AB|≦1.0 By using a polyvinyl acetal resin that satisfies the above relationship, it becomes possible to produce a conductive paste with excellent thread breakability, smooth surface of the printed surface, and superior printability. In the present invention, the relationship between the solution hazes A and B serves as an indicator of the ease with which intermolecular networks, such as hydrogen bonds, are formed between polyvinyl acetal resin molecules. When the polyvinyl acetal resin solution is cooled, the intermolecular interactions are fixed, so a larger |AB| indicates stronger intermolecular interactions, and a smaller |AB| indicates weaker intermolecular interactions. By sufficiently reducing the size of the intermolecular network, it is possible to sufficiently lower the viscosity and improve thread breakability. Furthermore, with the above configuration, improved solubility in low-polarity solvents can be achieved, and in addition to improved thread breakability, excellent surface smoothness of the printed surface can also be obtained. The above solution haze A is 0.1 or more and 2.0 or less, preferably 0.2 or more, and preferably 1.5 or less. The above |AB| is 1.0 or less, and preferably 0.85 or less. Furthermore, AB is preferably 0 or greater, more preferably 0.2 or greater, preferably 1.0 or less, and more preferably 0.85 or less. The above-mentioned solution haze A can be measured using a haze meter (such as one manufactured by Nippon Denshoku Industries Co., Ltd.) with a wavelength of 400 nm and a measurement temperature of 20°C, using a 10% by mass DHTA solution obtained by dissolving polyvinyl acetal resin in a dihydroterpinyl acetate (DHTA) solvent. The above-mentioned solution haze B can be measured in the same manner as solution haze A after preparing a 10% by mass DHTA solution, storing it in a -5°C constant temperature bath for one week, then removing it from the constant temperature bath and leaving it at room temperature (20°C) for 24 hours to allow the solution to return to room temperature (20°C).

[0010] The above-mentioned solutions Haze A and B can be adjusted by the type of raw material polyvinyl alcohol, 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 type and content of modifying groups, etc. For example, regarding the raw material polyvinyl alcohol, using a highly saponified type can increase the amount of acetyl groups in the resulting polyvinyl acetal resin, thereby suppressing the formation of intermolecular networks such as hydrogen bonds. Furthermore, regarding the acetalization reaction, by ensuring sufficient reaction temperature (aging temperature) and reaction time (aging time), the amount of acetal groups can be sufficiently increased, thereby suppressing the formation of intermolecular networks such as hydrogen bonds. Regarding the amount of hydroxyl groups, a lower amount of hydroxyl groups tends to suppress the formation of intermolecular networks. Regarding the amount of acetyl groups, a relatively high amount of acetyl groups tends to suppress the formation of intermolecular networks. Regarding the amount of acetal groups, increasing the amount of acetal groups tends to suppress the formation of intermolecular networks. Regarding modifying groups, when there are few highly polar modifying groups such as carboxylic acids, there is a tendency to suppress the formation of intermolecular networks.

[0011] The polyvinyl acetal resin of the present invention is subjected to a shear rate of 10 s in the above 10% by mass DHTA solution at room temperature (20°C). -1 The viscosity measured by multiplying by A' was stored at -5°C for one week, then left for 24 hours to return to room temperature (20°C), and subjected to a shear rate of 10s. -1 When the viscosity measured by multiplying by is denoted as B', it is preferable that the viscosity ratio A' / B' is 1.1 or less. By using the above configuration, it is possible to produce a conductive paste with superior thread breakability and surface smoothness of the printed surface. The viscosity ratio A' / B' is preferably 0.95 or higher, and more preferably 1.05 or lower. The viscosity A' is preferably 1.3 mPa·s or higher, more preferably 3 mPa·s or higher, preferably 7.0 mPa·s or lower, and more preferably 6.2 mPa·s or lower. The viscosity B' is preferably 1.3 mPa·s or higher, more preferably 3 mPa·s or higher, preferably 7.0 mPa·s or lower, and more preferably 6.2 mPa·s or lower. The viscosity A' mentioned above was measured using a 10% by mass DHTA solution, obtained by dissolving polyvinyl acetal resin in dihydroterpinyl acetate (DHTA) solvent, for example, using a rotary rheometer at a temperature of 20°C and a shear rate of 10 s. -1Measurements can be taken under these conditions. As a rotary rheometer, for example, a modular compact rheometer (MCR702e, manufactured by Anton Paar) can be used, and as a rotor, for example, a cone plate (Measuring cone CP25-2, D:25mm; Angle 2°) can be used.

[0012] The above viscosities A' and B' can be adjusted by the type of raw material polyvinyl alcohol, 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 molecular weight distribution (Mw / Mn), the amount of hydroxyl groups, the amount of acetal groups, the amount of acetyl groups, the amount of acetal groups, the type and content of modifying groups, etc. For example, with regard to the raw material polyvinyl alcohol, using a highly saponified form increases the intermolecular network, which increases viscosity A' and tends to cause the viscosity ratio A' / B' to deviate from 1. Furthermore, regarding the acetalization reaction, increasing the reaction temperature (aging temperature) tends to reduce the intermolecular network, decreasing viscosity A' and bringing the viscosity ratio A' / B' closer to 1. Similarly, increasing the reaction time (aging time) also tends to decrease viscosity A' and bring the viscosity ratio A' / B' closer to 1. Regarding the amount of hydroxyl groups, a lower amount of hydroxyl groups tends to decrease viscosity A', and the viscosity ratio A' / B' tends to approach 1. Regarding the amount of acetyl groups, a relatively high amount of acetyl groups tends to decrease viscosity A', and the viscosity ratio A' / B' tends to approach 1. Regarding the amount of acetal groups, increasing the amount of acetal groups tends to decrease viscosity A', and the viscosity ratio A' / B' tends to approach 1. Regarding modifying groups, when there are few highly polar modifying groups such as carboxylic acids, viscosity A' tends to decrease, and the viscosity ratio A' / B' tends to approach 1.

[0013] The polyvinyl acetal resin of the present invention has acetal units represented by the following formula (3), and R in the following formula (3) 1However, it is preferable that the alkyl group has 2 or more carbon atoms, and more preferably that it has 3 or more carbon atoms. This allows it to be dissolved in low-polarity solvents.

[0014] [ka]

[0015] The above R 1 The number of carbon atoms is preferably 2 or more. A more preferable lower limit for the number of carbon atoms is 3, a preferred upper limit is 11, and a more preferable upper limit is 9. Note that the above R 1 This may also be a combination of two or more alkyl groups with different numbers of carbon atoms.

[0016] Examples of alkyl groups having 2 or more carbon atoms include ethyl group, propyl group, butyl group, pentyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group, undecyl group, dodecyl group, tridecyl group, tetradecyl group, pentadecyl group, hexadecyl group, heptadecyl group, octadecyl group, eicosyl group, docosyl group, and the like.

[0017] The alkyl group having two or more carbon atoms may be linear or branched. Examples of the linear alkyl groups mentioned above include n-propyl group, n-butyl group, n-pentyl group, n-hexyl group, n-heptyl group, n-octyl group, n-nonyl group, n-decyl group, n-undecyl group, n-dodecyl group, n-tridecyl group, n-tetradecyl group, n-hexadecyl group, n-heptadecyl group, n-octadecyl group, n-eicosyl group, and n-docosyl group.

[0018] Examples of the branched-chain 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, a 1-methyldodecyl group, etc. Further, 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, a 1-methyleicosyl group, etc. Furthermore, examples include an alkyl group in which an alkyl group having two or more carbon atoms is substituted on the carbon atom at the 1-position (for example, a 1-ethyldecyl group, a 1-propylnonyl group, a 1-butyloctyl group, a 1-pentylheptyl group, a 1-octyldecyl group, etc.). In the branched-chain alkyl group, the branching position is not limited to the carbon atom at the 1-position, and may be a carbon atom at the 2-position or higher. For example, examples of the alkyl group in which a methyl group is substituted on a carbon atom at the 2-position or higher include a 2-methylundecyl group, a 3-methylundecyl group, a 4-methylundecyl group, etc. Further, examples of the alkyl group in which an alkyl group having two or more carbon atoms is substituted on a carbon atom at the 2-position or higher include, for example, 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, a 2-octylundecyl group. Furthermore, examples include a 3-ethylundecyl group, a 4-ethyloctadecyl group, a 4-butyloctadecyl group, a neodecyl group, etc.

[0019] In the present invention, the alkyl group having two or more carbon atoms is preferably a linear alkyl group. Further, the alkyl group having two or more carbon atoms may be composed of two or more types of alkyl groups including a linear alkyl group and a branched-chain alkyl group, or may be composed of only a linear alkyl group. Also, R in the following formula (1) 1 may be an alkyl group based on a bio-derived aldehyde having two or more carbon atoms.

[0020] The polyvinyl acetal resin of the present invention preferably further has acetal units represented by the following formula (4), which are different from the constituent units represented by formula (3) above. Having acetal units represented by formula (4) above can improve the strength of the printed electrode.

[0021] [ka] In formula (4), R 2 represents a hydrogen atom or a methyl group.

[0022] The content of acetal units represented by formula (3) in the polyvinyl acetal resin of the present invention is preferably 35 mol%, more preferably 50 mol%, preferably 90 mol%, and more preferably 85 mol%. By keeping the content of the acetal units represented by formula (3) above within the above range, it can be dissolved in a low-polarity solvent. The content of acetal units represented by the above formula (3) is 1 H-NMR and 13 Measurements are performed using 1C-NMR (nuclear magnetic resonance spectroscopy).

[0023] The content of acetal units represented by formula (4) in the polyvinyl acetal resin of the present invention is preferably 4 mol%, more preferably 8 mol%, preferably 45 mol%, and more preferably 30 mol%. By keeping the content of the acetal units represented by formula (4) above within the above range, it can be dissolved in a low-polarity solvent. The content of acetal units represented by the above formula (4) is 1 H-NMR and 13 Measurements are performed using 1C-NMR (nuclear magnetic resonance spectroscopy).

[0024] The total amount of acetal groups (sum of all acetal units) in the polyvinyl acetal resin of the present invention has a preferred lower limit of 65 mol%, a more preferred lower limit of 70 mol%, a preferred upper limit of 90 mol%, a more preferred upper limit of 85 mol%, and an even more preferred upper limit of 80 mol%. By keeping the total amount of acetal groups within the above range, high thread breakability can be achieved even when using low-polarity solvents, resulting in excellent printability. The total amount of acetal bases mentioned above 1 Measurements are performed using 1H-NMR (nuclear magnetic resonance spectroscopy). Furthermore, the polyvinyl acetal resin of the present invention has a preferred lower limit of 4 mol% for the amount of acetacetal groups (amount of acetacetal units), a more preferred lower limit of 8 mol%, a preferred upper limit of 45 mol%, and a more preferred upper limit of 30 mol%. Furthermore, the polyvinyl acetal resin of the present invention has a preferred lower limit of 35 mol% for the amount of butyral groups (amount of butyral units), a more preferred lower limit of 50 mol%, a preferred upper limit of 90 mol%, and a more preferred upper limit of 85 mol%.

[0025] The polyvinyl acetal resin of the present invention has a constituent unit having a hydroxyl group represented by the following formula (5).

[0026] [ka]

[0027] The content of the above-mentioned hydroxyl group-containing structural units (hydroxyl group amount) in the polyvinyl acetal resin of the present invention is preferably 2 mol% or more and 25 mol% or less. By keeping the material within the above range, excellent thread breakage properties can be achieved even when using low-polarity solvents, resulting in superior printability. The more preferred lower limit for the amount of hydroxyl groups is 10 mol%, the even more preferred lower limit is 16 mol%, the more preferred upper limit is 23 mol%, and the even more preferred upper limit is 20 mol%. 1 Measurements are performed using 1H-NMR (nuclear magnetic resonance spectroscopy).

[0028] The polyvinyl acetal resin of the present invention has a constituent unit having an acetyl group represented by the following formula (6).

[0029] [ka]

[0030] The preferred lower limit for the content (amount of acetyl groups) of the constituent units having the acetyl group in the polyvinyl acetal resin of the present invention is 5 mol%, and the preferred upper limit is 30 mol%. By keeping the range within the above limits, high thread breakability can be achieved even when using low-polarity solvents, resulting in excellent printability. A more preferred lower limit for the amount of acetyl groups is 5 mol%, and a more preferred upper limit is 15 mol%. A more preferable upper limit is 10 mol%. The above acetyl group 1 Measurements are performed using 1H-NMR (nuclear magnetic resonance spectroscopy).

[0031] The polyvinyl acetal resin of the present invention may have constituent units having a carboxylic acid. The preferred lower limit for the content of the carboxylic acid-containing structural units (carboxylic acid modification amount) in the polyvinyl acetal resin of the present invention is 0.02 mol%, and the preferred upper limit is 1.0 mol%. By setting the amount of carboxylic acid groups to 0.02 mol% or more, high thread breakability can be achieved even when using low-polarity solvents, resulting in excellent printability. By setting the amount of carboxylic acid modification to 1.0 mol% or less, good solubility in solvents can be achieved. The more preferred lower limit for the amount of carboxylic acid modification is 0.1 mol%, and the more preferred upper limit is 0.8 mol%. The above amount of carboxylic acid modification 1 H-NMR and 13 It can be measured using 1C-NMR (nuclear magnetic resonance spectroscopy). Note that carboxylic acids include structures to which metal atoms or alkyl groups are bonded.

[0032] Examples of constituent units having the above-mentioned carboxylic acid include the constituent unit represented by the following formula (7-1) and the constituent unit represented by the following formula (7-2).

[0033] [ka]

[0034] In the above equation (7-1), R 3 and R 4 Each is independently an alkylene group with 0 to 10 carbon atoms, X 1 and X 2 Each of these independently represents a hydrogen atom, a metal atom, or a methyl group. In formula (7-2) above, R 5 , R 6 and R 7 Each is independently a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, R 8 X is an alkylene group with 0 to 10 carbon atoms. 3 R represents a hydrogen atom, a metal atom, or a methyl group. 3 , R 4 or R 8 The fact that R is an alkylene group with 0 carbon atoms means that 3 , R 4 or R 8 This means that it is a single bond.

[0035] The above R 3 and R 4 These may be the same or different, but it is preferable that they be different. It is also preferable that at least one of them be a single bond.

[0036] Examples of the above-mentioned alkylene groups having 0 to 10 carbon atoms include linear alkylene groups such as single bonds, methylene groups, ethylene groups, trimethylene groups, tetramethylene groups, pentamethylene groups, hexamethylene groups, octamethylene groups, and decamethylene groups; branched alkylene groups such as methylmethylene groups, methylethylene groups, 1-methylpentylene groups, and 1,4-dimethylbutylene groups; and cyclic alkylene groups such as cyclopropylene groups, cyclobutylene groups, and cyclohexylene groups. Among these, linear alkylene groups such as single bonds, methylene groups, ethylene groups, n-propylene groups, and n-butylene groups are preferred, and single bonds, methylene groups, and ethylene groups are more preferred.

[0037] The above X 1 and X 2 If at least one of these is a metal atom, examples of such metal atoms include sodium atoms, lithium atoms, potassium atoms, etc. Among these, sodium atoms are preferred.

[0038] The constituent unit represented by the above formula (7-1) is preferably derived from an α-dicarboxyl monomer. Examples of α-dicarboxyl monomers include dicarboxylic acids having a radically polymerizable unsaturated double bond, such as methylenemalonic acid, itaconic acid, 2-methyleneglutaric acid, 2-methyleneadipic acid, and 2-methylenesebacic acid, as well as their metal salts or methyl esters. Among these, itaconic acid, its metal salts, or its methyl esters are preferably used. In this specification, α-dicarboxyl monomer refers to a monomer having two carboxyl groups at the α-carbon position.

[0039] The above polyvinyl acetal resin preferably has a structural unit represented by the above formula (7-2). When the above polyvinyl acetal resin has a structural unit represented by the above formula (7-2), its solvent solubility can be made better. In the above formula (7-2), R 5 , R 6 and R 7 Each of these independently represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, R 8This represents an alkylene group with 0 to 10 carbon atoms, X 3 This represents a hydrogen atom, a metal atom, or a methyl group.

[0040] In the above equation (7-2), R 5 , R 6 and R 7 When the alkyl group represented by has 1 to 10 carbon atoms, steric hindrance is less likely to occur, allowing the polymerization reaction during raw material synthesis to proceed sufficiently. 5 , R 6 and R 7 The preferred lower limit for the number of carbon atoms in the alkyl group represented is 1, the preferred upper limit is 5, and the more preferred upper limit is 3. R 5 and R 6 These may be the same or different, but it is more preferable that they be the same. Also, R 5 , R 6 and R 7 It is preferable that it is a hydrogen atom.

[0041] Examples of the C1-C10 alkyl groups mentioned above include linear alkyl groups such as methyl, ethyl, propyl, n-butyl, n-pentyl, n-heptyl, n-octyl, n-nonyl, and n-decyl groups; branched alkyl groups such as isopropyl, isobutyl, sec-butyl, tert-butyl, isopentyl, 2,2-dimethylpropyl, 1,1,3,3-tetramethylbutyl, and 2-ethylhexyl groups; and cycloalkyl groups such as cyclopropyl, cyclopropylmethyl, cyclobutyl, cyclopentyl, and cyclohexyl groups. Among these, linear alkyl groups such as methyl, ethyl, propyl, and n-butyl groups are preferred, with methyl and ethyl groups being more preferred.

[0042] In the above equation (7-2), R 8 For example, R in equation (7-1) above 3 and R 4Examples similar to those exemplified above include, among which linear alkylene groups such as single bonds, methylene groups, ethylene groups, trimethylene groups, and tetramethylene groups are preferred, single bonds, methylene groups, and ethylene groups are more preferred, and single bonds are even more preferred.

[0043] The above X 3 If the atom is a metal atom, examples of such metal atoms include sodium atoms, lithium atoms, potassium atoms, etc. Among these, sodium atoms are preferred.

[0044] The preferred lower limit of the average degree of polymerization of the polyvinyl acetal resin of the present invention is 200, and the preferred upper limit is 5000. An average degree of polymerization of 200 or higher facilitates industrial production. An average degree of polymerization of 5000 or lower results in a suitable solution viscosity, enabling industrial manufacturing. The more preferable lower limit for the above average degree of polymerization is 500, the even more preferable lower limit is 600, the more preferable upper limit is 3500, and the even more preferable upper limit is 2000. The average degree of polymerization of the above-mentioned polyvinyl acetal resin can be determined from the polyvinyl alcohol used as a raw material. If there are multiple types of polyvinyl alcohol used as raw materials, the average degree of polymerization is calculated by multiplying the degree of polymerization of each polyvinyl alcohol by its respective addition ratio and summing the results.

[0045] The polyvinyl acetal resin of the present invention preferably has a weight-average molecular weight (Mw) / number-average molecular weight (Mn) of 3.5 or higher, and more preferably 5.0 or lower. By keeping the dimensions within the above range, it is possible to obtain the advantage of excellent thread breakage and printability. The above Mw / Mn ratio is more preferably 3.5 or higher, and more preferably 4.5 or lower. The above Mw and Mn can be measured, for example, by gel permeation chromatography (GPC) using an appropriate standard (e.g., a polystyrene standard). Examples of columns used when measuring Mw and Mn include TSKgel SuperHZM-H.

[0046] The polyvinyl acetal resin of the present invention may be copolymerized with ethylenically unsaturated monomers, to the extent that the effects of the present invention are not impaired. The above ethylenically unsaturated monomers are not particularly limited and include, for example, acrylic acid, methacrylic acid, (anhydride) phthalic acid, (anhydride) maleic acid, (anhydride) itaconic acid, etc. Also, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, trimethyl-(3-acrylamido-3-dimethylpropyl)-ammonium chloride, acrylamide-2-methylpropanesulfonic acid and its sodium salt, etc. Furthermore, ethyl vinyl ether, butyl vinyl ether, N-vinylpyrrolidone, vinyl chloride, vinyl bromide, vinyl fluoride, vinylidene chloride, vinylidene fluoride, tetrafluoroethylene, sodium vinylsulfonate, sodium allylsulfonate, etc. In addition, terminally modified polyvinyl alcohols obtained by copolymerizing vinyl ester monomers such as vinyl acetate with ethylene in the presence of thiol compounds such as thiol acetate and mercaptopropionic acid, and then saponifying the mixture, can also be used.

[0047] The polyvinyl acetal resin of the present invention may have ethylene units, but it is preferable that it does not. In other words, in the polyvinyl acetal resin of the present invention, it is preferable that the content of ethylene units represented by the following formula (8) (ethylene content) is 0 mol%.

[0048] [ka]

[0049] Methods for producing the above-mentioned polyvinyl acetal resin include methods such as acetalizing polyvinyl alcohol using an aldehyde.

[0050] The above-mentioned polyvinyl alcohol can be obtained, for example, by saponifying a vinyl ester polymer with an alkali, acid, ammonia water, etc. Examples of the vinyl ester include vinyl formate, vinyl acetate, vinyl propionate, and vinyl pivalate. Among these, vinyl acetate is preferred from an economic standpoint.

[0051] The polyvinyl alcohol resin described above preferably has a degree of saponification of 75 mol% or more. The degree of saponification is more preferably 76 mol% to 99.4 mol%, and even more preferably 78 mol% to 98 mol%. Furthermore, it is preferable to use multiple polyvinyl alcohol resins in combination. It is preferable to use multiple polyvinyl alcohol resins in combination, such as a polyvinyl alcohol resin with a degree of saponification of 90 mol% to 99.4 mol% and a polyvinyl alcohol resin with a degree of saponification of 75 mol% to 89.5 mol%.

[0052] The above acetalization is preferably carried out in an aqueous solvent, in a mixed solvent of water and a water-compatible organic solvent, or in an organic solvent. As the above-mentioned organic solvent that is compatible with water, for example, an alcohol-based organic solvent can be used. Examples of the above-mentioned organic solvents include alcohol-based organic solvents, aromatic organic solvents, aliphatic ester-based solvents, ketone-based solvents, lower paraffin-based solvents, ether-based solvents, amide-based solvents, and amine-based solvents. Examples of the above-mentioned alcohol-based organic solvents include methanol, ethanol, n-propanol, isopropanol, n-butanol, and tert-butanol. Examples of the above-mentioned aromatic organic solvents include xylene, toluene, ethylbenzene, and methyl benzoate. Examples of the above-mentioned aliphatic ester solvents include methyl acetate, ethyl acetate, butyl acetate, methyl propionate, ethyl propionate, methyl butyrate, ethyl butyrate, methyl acetoacetate, and ethyl acetoacetate. Examples of the ketone-based solvents mentioned above include acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, methylcyclohexanone, benzophenone, and acetophenone. Examples of the lower paraffinic solvents mentioned above include hexane, pentane, octane, cyclohexane, and decane. Examples of the above-mentioned ether-based solvents include diethyl ether, tetrahydrofuran, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, and propylene glycol diethyl ether. Examples of the above-mentioned amide solvents include N,N-dimethylformamide, N,N-dimethyltesetamide, N-methylpyrrolidone, and acetanilide. Examples of the above-mentioned amine-based solvents include ammonia, trimethylamine, triethylamine, n-butylamine, di-n-butylamine, tri-n-butylamine, aniline, N-methylaniline, N,N-dimethylaniline, and pyridine. These can be used individually or as a mixture of two or more solvents. Among these, ethanol, n-propanol, isopropanol, and tetrahydrofuran are particularly preferred from the viewpoint of solubility in resins and ease of purification.

[0053] In the method of reacting polyvinyl alcohol with an aldehyde as described above, the aldehyde used in the acetalization reaction is not particularly limited, and examples include linear aliphatic aldehydes and branched aliphatic aldehydes. Examples of the above-mentioned aliphatic aldehydes include formaldehyde, acetaldehyde, propylaldehyde, butyraldehyde, varelualdehyde, hexylaldehyde, 2-ethylbutyraldehyde, 2-ethylhexylaldehyde, heptylaldehyde, octylaldehyde, nonylaldehyde, decylaldehyde, undecylaldehyde, dodecylaldehyde, tridecylaldehyde, trimethylhexylaldehyde, methyloctylacetaldehyde, and methylnonylacetaldehyde. These aldehydes may be used individually or in combination of two or more. Among them, acetaldehyde and butyraldehyde are preferred as aldehydes.

[0054] The amount of aldehyde added can be appropriately set according to the amount of acetal groups in the target polyvinyl acetal resin. In particular, a value of 55 mol% to 120 mol%, more preferably 60 mol% to 110 mol%, per 100 mol% of polyvinyl alcohol is preferable because it allows the acetalization reaction to proceed efficiently and makes it easier to remove unreacted aldehydes.

[0055] Furthermore, aldehydes having a cyclic aliphatic group or an aromatic group may be used in combination. Examples of aldehydes having an aromatic group include benzaldehyde, cinnamaldehyde, 2-methylbenzaldehyde, 3-methylbenzaldehyde, 4-methylbenzaldehyde, p-hydroxybenzaldehyde, m-hydroxybenzaldehyde, phenylacetaldehyde, and β-phenylpropionaldehyde.

[0056] In the acetalization process described above, a dispersant may or may not be used. Furthermore, in the acetalization step described above, it is preferable to use a method in which the polyvinyl acetal resin precipitates during the acetalization reaction (precipitation method) compared with a method in which the reaction is carried out with the polyvinyl acetal resin dissolved (dissolution method). Moreover, the method of acetalization using the above dispersant and the above precipitation method may be used in combination.

[0057] Examples of the above-mentioned dispersants include sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, polyvinylpyrrolidone, polyethylene glycol, polyvinyl alcohol, colloidal silica, polyoxyethylene polyoxypropylene cetyl ether, and polyoxyethylene polyoxypropylene lauryl ether. These dispersants may be used individually or in combination of two or more types. Among these, sodium dodecylbenzenesulfonate and polyoxyethylene polyoxypropylene cetyl ether are preferred.

[0058] The above acetalization is preferably carried out in the presence of an acid catalyst. Examples of the acid catalysts mentioned above include mineral acids, carboxylic acids, and sulfonic acids. Examples of the above-mentioned mineral acids include sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid. Examples of the carboxylic acids mentioned above include formic acid, acetic acid, and propionic acid. Examples of the above-mentioned sulfonic acids include p-toluenesulfonic acid, methanesulfonic acid, ethanesulfonic acid, and benzenesulfonic acid. These acid catalysts may be used individually or in combination of two or more. Among them, p-toluenesulfonic acid and hydrochloric acid are preferred.

[0059] The temperature at which the above catalyst is added is preferably 20°C or higher, more preferably 30°C or higher, and preferably 50°C or lower. The temperature at which the above-mentioned aldehyde is added (aldehyde addition temperature) is preferably 0°C or higher, more preferably 5°C or higher, and preferably 40°C or lower. The reaction temperature (aging temperature) in the above acetalization reaction is preferably 50°C or higher, more preferably 53°C or higher, preferably 60°C or lower, and more preferably 58°C or lower. The reaction time (maturation time) in the above acetalization reaction is preferably 3 hours or more and 7 hours or less, and more preferably 4 hours or more and 6 hours or less. By setting the conditions described above, the solution hazes A and B in the polyvinyl acetal resin of the present invention can be set to a preferred range, and the printability of the conductive paste made using the polyvinyl acetal resin of the present invention can be improved.

[0060] 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., and ceramic green sheets. In particular, when the polyvinyl acetal resin of the present invention is used in a conductive paste, it is possible to achieve excellent printability and good thread breakage even when using a low-polarity solvent.

[0061] A conductive paste containing the polyvinyl acetal resin, an organic solvent, and a conductive powder is also one of the present inventions.

[0062] The organic solvent mentioned above can be an organic solvent commonly used in conductive pastes. Examples of the above organic solvents include terpineol derivatives such as dihydroterpineol, terpinyl acetate, isovonyl 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 individually or in combination of two or more. In this invention, stringing is less likely to occur, even when using low-polarity solvents such as dihydroterpineol and dihydroterpinyl acetate, making it possible to achieve excellent printability.

[0063] The amount of the above organic solvent is not particularly limited, but a preferred lower limit is 100 parts by mass and a preferred upper limit is 10,000 parts by mass relative to 100 parts by mass of the polyvinyl acetal resin. When the amount of the above organic solvent is 100 parts by mass or more, the viscosity of the conductive paste can be set within a suitable range and the printability can be improved. When the amount of the above organic solvent is 10,000 parts by mass or less, the performance of the above polyvinyl acetal resin can be fully exhibited in the conductive paste. A more preferred lower limit for the amount of the above organic solvent relative to 100 parts by mass of the polyvinyl acetal resin is 200 parts by mass and a more preferred upper limit is 5,000 parts by mass.

[0064] The conductive powders mentioned above are not particularly limited and include, for example, powders made of nickel, aluminum, silver, copper, and alloys thereof. These conductive powders may be used individually or in combination of two or more. Among these, nickel is preferred because of its excellent conductivity.

[0065] The average particle size of the conductive powder is preferably 50 to 300 nm, and its shape is preferably approximately spherical. An average particle size of 50 nm or more allows for a suitable specific surface area of ​​the conductive powder, thereby improving its dispersibility. An average particle size of 300 nm or less improves the surface smoothness after printing. Note that "approximately spherical" includes not only perfectly spherical particles but also particles with a shape close to spherical.

[0066] The amount of conductive powder blended is not particularly limited, but a preferred lower limit is 100 parts by mass and a preferred upper limit is 10,000 parts by mass relative to 100 parts by mass of the polyvinyl acetal resin. If the amount of conductive powder blended is 100 parts by mass or more, the density of the conductive powder in the conductive paste can be kept within a sufficient range, resulting in excellent conductivity. If the amount of conductive powder blended is 10,000 parts by mass or less, the dispersibility of the conductive powder in the conductive paste can be improved, resulting in excellent printability. The amount of conductive powder blended is preferably 200 parts by mass and 5000 parts by mass relative to 100 parts by mass of the polyvinyl acetal resin.

[0067] Preferably, the conductive paste described above further contains ceramic powder in addition to the conductive powder. Including ceramic powder makes it easier to match 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 used in green sheets is preferred. The average particle size of the ceramic powder is not particularly limited, but it is preferably smaller than the average particle size of the conductive powder, and specifically, it is preferably 30 nm to 200 nm.

[0068] The above-mentioned dispersion enhancer is not particularly limited, but for example, fatty acids, aliphatic amines, alkanolamides, and phosphate esters are preferred. Silane coupling agents and the like may also be included. The above fatty acids are not particularly limited and 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 hydrogenated castor fatty acid. Among these, lauric acid, stearic acid, and oleic acid are preferred. The above-mentioned aliphatic amines are not particularly limited and include, for example, laurylamine, myristylamine, cetylamine, stearylamine, oleylamine, alkyl(coconut)amine, alkyl(hydrogenated beef tallow)amine, alkyl(beef tallow)amine, alkyl(soybean)amine, etc. The above-mentioned alkanolamides are not particularly limited and include, for example, coconut fatty acid diethanolamide, beef tallow fatty acid diethanolamide, lauric acid diethanolamide, oleic acid diethanolamide, etc. The above-mentioned phosphate esters are not particularly limited, and examples include polyoxyethylene alkyl ether phosphate esters and polyoxyethylene alkyl allyl ether phosphate esters.

[0069] The conductive paste described above may appropriately contain plasticizers, lubricants, antistatic agents, surfactants, etc., to the extent that it does not impair the effects of the present invention.

[0070] Examples of the above-mentioned plasticizers include phthalate 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-ethyl butyrate, tetraethylene glycol-di-2-ethyl butyrate, tetraethylene glycol-di-heptanoate, and triethylene glycol-di-heptanoate.

[0071] The method for producing the above-mentioned conductive paste is not particularly limited, and examples include mixing the above-mentioned polyvinyl acetal resin, the above-mentioned conductive powder, the above-mentioned organic solvent, and various additives added as needed using various mixers such as a ball mill, a blender mill, or a three-roll mill.

[0072] A multilayer ceramic capacitor can be obtained by applying the above conductive paste onto a ceramic green sheet using a printing process, stacking multiple sheets, heating and pressing them together to create a laminate, then degreasing and firing to form a ceramic sintered body, and finally forming external electrodes on the end faces of the ceramic sintered body. The above printing process can include screen printing, die coating, gravure offset, etc. Furthermore, the polyvinyl acetal resin or conductive paste of the present invention can also be suitably used as a multilayer ceramic capacitor.

[0073] A multilayer ceramic capacitor using the conductive paste of the present invention is also one of the present inventions.

[0074] Furthermore, the multilayer ceramic capacitor of the present invention can be manufactured by performing the following steps: applying the conductive paste of the present invention onto a ceramic green sheet; stacking multiple ceramic green sheets and heating and pressing them together to create a laminate; degreasing and firing to create a ceramic sintered body; and forming external electrodes on the end faces of the ceramic sintered body. [Effects of the Invention]

[0075] According to the present invention, a polyvinyl acetal resin can be provided that can be used to produce a conductive paste with excellent thread breakage during printing and smoothness of the printed surface. Furthermore, a conductive paste and a multilayer ceramic capacitor can be provided using this polyvinyl acetal resin. [Brief explanation of the drawing]

[0076] [Figure 1] This is a schematic diagram of the printing plate used in the printability evaluation. [Modes for carrying out the invention]

[0077] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0078] (Example 1) (Preparation of polyvinyl acetal resin) 200 g of carboxylic acid-modified polyvinyl alcohol (itaconic acid modified, constituent units represented by the above formula (7-1), carboxylic acid modification amount 0.2 mol%) with a degree of saponification of 92.5 mol% and a degree of polymerization of 800, and Unisafe 10P-8 (polyoxyethylene polyoxypropylene cetyl ether, manufactured by NOF Corporation), diluted with pure water to a concentration of 20% by mass as a dispersant, were added to 1600 g of pure water so that the solid content was 2% by mass relative to the polyvinyl alcohol, and the mixture was stirred at 90°C for 2 hours to dissolve. This solution was cooled to 40°C, 20g of 35% by mass hydrochloric acid was added, and then 160g of n-butyraldehyde and 15g of acetaldehyde were added at a liquid temperature of 10°C. The solution was then maintained at a liquid temperature (aging temperature) of 60°C for 4.5 hours (aging time) to allow the acetalization reaction to proceed. Subsequently, the solution was neutralized by a conventional method, washed with water, and dried to obtain a polyvinyl acetal resin powder.

[0079] (Example 2) (Preparation of polyvinyl acetal resin) Polyvinyl acetal resin powder was obtained in the same manner as in Example 1, except that polyvinyl alcohol with a degree of saponification of 92.1 mol% and a degree of polymerization of 800 (modified with itaconic acid [constituent unit represented by the above formula (7-1)], carboxylic acid modification amount 0.2 mol%) was used, the amount of Unisafe added was as shown in Table 1, and 150 g of n-butyraldehyde and 20 g of acetaldehyde were used.

[0080] (Example 3) A polyvinyl acetal resin powder was obtained in the same manner as in Example 1, except that a carboxylic acid-modified polyvinyl alcohol (itaconic acid modified [constituent unit represented by the above formula (7-1)], carboxylic acid modification amount 0.3 mol%) with a degree of saponification of 93.2 mol% and a degree of polymerization of 800 was used.

[0081] (Example 4) Polyvinyl acetal resin powder was obtained in the same manner as in Example 1, except that a carboxylic acid-modified polyvinyl alcohol (itaconic acid modified [constituent unit represented by the above formula (7-1)], carboxylic acid modification amount 0.2 mol%) with a degree of saponification of 92.7 mol% and a degree of polymerization of 790 was used, and the amount of Unisafe added and the maturation temperature were as shown in Table 1.

[0082] (Example 5) Polyvinyl acetal resin powder was obtained in the same manner as in Example 4, except that a carboxylic acid-modified polyvinyl alcohol (itaconic acid-modified [constituent unit represented by the above formula (7-1)], carboxylic acid modification amount 0.2 mol%) with a degree of saponification of 92.7 mol% and a degree of polymerization of 790 was used, and the maturation time was as shown in Table 1.

[0083] (Example 6) Polyvinyl acetal resin powder was obtained in the same manner as in Example 2, except that a carboxylic acid-modified polyvinyl alcohol (itaconic acid modified [constituent unit represented by the above formula (7-1)], carboxylic acid modification amount 0.2 mol%) with a degree of saponification of 92.1 mol% and a degree of polymerization of 800 was used, and the amount of Unisafe added and the maturation time were as shown in Table 1.

[0084] (Example 7) A polyvinyl acetal resin powder was obtained in the same manner as in Example 6, except that polyvinyl alcohol with a degree of saponification of 92.7 mol% and a degree of polymerization of 800 was used.

[0085] (Example 8) A polyvinyl acetal resin powder was obtained in the same manner as in Example 6, except that a carboxylic acid-modified polyvinyl alcohol (itaconic acid-modified [constituent unit represented by the above formula (7-1)], carboxylic acid modification amount 0.2 mol%) with a degree of saponification of 92.7 mol% and a degree of polymerization of 800 was used, acetaldehyde was not added, and 180 g of n-butyraldehyde was used.

[0086] (Example 9) A polyvinyl acetal resin powder was obtained in the same manner as in Example 1, except that a carboxylic acid-modified polyvinyl alcohol (itaconic acid-modified [constituent unit represented by the above formula (7-1)], carboxylic acid modification amount 0.4 mol%) with a degree of saponification of 92.5 mol% and a degree of polymerization of 800 was used, acetaldehyde was not added, and 180 g of n-butyraldehyde was used.

[0087] (Comparative Example 1) Polyvinyl acetal resin powder was obtained in the same manner as in Example 1, except that a carboxylic acid-modified polyvinyl alcohol (itaconic acid modified [constituent unit represented by the above formula (7-1)], carboxylic acid modification amount 0.5 mol%) with a degree of saponification of 98.3 mol% and a degree of polymerization of 800 was used, Unisafe was not added, and the aging temperature and aging time were as shown in Table 1.

[0088] (Comparative Example 2) Polyvinyl acetal resin powder was obtained in the same manner as in Example 1, except that polyvinyl alcohol with a degree of saponification of 99.0 mol% and a degree of polymerization of 450 was used, Unisafe was not added, 150 g of n-butyraldehyde and 30 g of acetaldehyde were used, and the aging temperature and aging time were as shown in Table 1.

[0089] (Comparative Example 3) Polyvinyl acetal resin powder was obtained in the same manner as in Example 1, except that polyvinyl alcohol with a degree of saponification of 94.4 mol% and a degree of polymerization of 800 was used, Unisafe was not added, acetaldehyde was not added, 180 g of n-butyraldehyde was used, and the aging temperature and aging time were as shown in Table 1.

[0090] (Comparative Example 4) Polyvinyl acetal resin powder was obtained in the same manner as in Example 2, except that a carboxylic acid-modified polyvinyl alcohol (itaconic acid-modified [constituent unit represented by the above formula (7-1)], carboxylic acid modification amount 0.2 mol%) with a degree of saponification of 92.7 mol% and a degree of polymerization of 800 was used, and the aging temperature was as shown in Table 1.

[0091] <Rating> The obtained polyvinyl acetal resin was evaluated as follows.

[0092] (1) Amount of acetal groups, hydroxyl groups, acetyl groups, and carboxylic acid modification amount The obtained polyvinyl acetal resin was analyzed using an AV400 spectrometer (manufactured by Bruker). 1 ¹H-NMR measurements were performed to determine the amount of acetal groups, hydroxyl groups, and acetyl groups. The obtained polyvinyl acetal resin was dissolved in DMSO-D6 to a concentration of 1.6% by mass to prepare the measurement solution. 1 1H-NMR measurements were performed at 80°C. Furthermore, the obtained polyvinyl acetal resin was analyzed using an AV600 spectrometer (manufactured by Bruker). 13The amount of carboxylic acid modification in polyvinyl acetal resin was measured by 13C-NMR. The obtained polyvinyl acetal resin was dissolved in DMSO-D6 to a concentration of 12% by mass to prepare the measurement solution. 13 ¹

[0093] (2)Molecular weight 0.04 g of the obtained polyvinyl acetal resin was added to 20 g of tetrahydrofuran, stirred, and dissolved to prepare a resin solution. The weight-average molecular weight (Mw) and number-average molecular weight (Mn) of the above resin solution were measured by gel permeation chromatography using a TSKgelSuperHZM-H column (manufactured by Tosoh Corporation) in terms of polystyrene, and the Mw / Mn ratio was calculated from the obtained Mw and Mn.

[0094] (3) Hayes The obtained polyvinyl acetal resin was dissolved in dihydroterpinyl acetate (DHTA) solvent at 90°C for 3 hours to prepare a 10% by mass DHTA solution. The obtained 10% by mass DHTA solution was measured using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd.) at a wavelength of 400 nm and a measurement temperature of 20°C to determine the solution haze A. Furthermore, the obtained 10% by mass DHTA solution was stored in a -5°C constant temperature bath for one week, then removed from the bath and left for 24 hours to return to room temperature (20°C). The solution haze B was measured in the same manner, and |AB| was calculated.

[0095] (4) Viscosity For a 10% by mass DHTA solution prepared in the same manner as in "(3) Haze," the viscosity A' was measured using a rotary rheometer. For the rotary rheometer, a modular compact rheometer (MCR702e, manufactured by Anton Paar) was used, with a measurement temperature of 20°C and a shear rate of 10s. -1 Measurements were performed using a rotor:cone plate (Measuring cone CP25-2, D:25mm;Angle 2°) under the specified conditions. Furthermore, the obtained 10% by mass DHTA solution was stored in a -5°C constant temperature bath for one week, then removed from the bath and left for 24 hours to return to room temperature (20°C). The viscosity B' was measured in the same manner, and the viscosity ratio A' / B' was calculated.

[0096] (5) Thread breakage (amount of thread scattering during printing) (a) Preparation of conductive paste A resin solution was obtained by dissolving 10 parts by mass of polyvinyl acetal resin obtained in the examples and comparative examples with 90 parts by mass of dihydroterpinyl acetate. After mixing 180 parts by mass of nickel powder as conductive powder, 50 parts by mass of dihydroterpinyl acetate, and 0.1 parts by mass of oleic acid as a dispersion improver, the obtained resin solution was mixed and dispersed using a three-roll machine to obtain a conductive paste. (b) Amount of splatter during printing Using a desktop gravure printing test apparatus (Matsuo Sangyo Co., Ltd., GP-100), the obtained conductive paste was printed onto a PET sheet at a printing speed of 60 m / min on a printing plate with a depth of 60 μm that can print 45 electrodes measuring 1.5 mm × 0.4 mm, as shown in Figure 1. The number of conductive paste spots that adhered to areas other than the electrodes was counted and evaluated according to the following criteria. AA:0 pieces A: 1 or more and 4 or less B: 5 or more and 9 or less C: 10 or more

[0097] (6) Smoothness of the printed surface For the print patterns obtained in the evaluation of "(5) Thread breakage (amount of thread scattering during printing)", the surface roughness Ra was measured using a surface roughness meter (Surfcom, manufactured by Tokyo Seimitsu Co., Ltd.) in accordance with JIS B 0601 (1994) and evaluated according to the following criteria. A: Ra is less than 69.5nm B:Ra is between 69.5nm and less than 89nm C:Ra is 89nm or higher

[0098] [Table 1] [Industrial applicability]

[0099] According to the present invention, a polyvinyl acetal resin can be provided that can be used to produce a conductive paste with excellent thread breakage during printing and smoothness of the printed surface. Furthermore, a conductive paste and a multilayer ceramic capacitor can be provided using this polyvinyl acetal resin.

Claims

1. For a 10% by mass DHTA solution dissolved in dihydroterpinyl acetate (DHTA) solvent, let A be the solution haze at room temperature (20°C), and let B be the solution haze after storing at -5°C for one week and then letting it stand for 24 hours to return to room temperature (20°C). The following equations (1) and (2) are satisfied. A polyvinyl acetal resin having a hydroxyl group content of 2 to 25 mol% and an acetyl group content of 5 to 30 mol%. (1) 0.1 ≤ A ≤ 2.0 (2) |A-B|≦1.0

2. For a 10% by mass DHTA solution, at room temperature (20°C) and a shear rate of 10 s, －１ The viscosity measured by multiplying by A' was stored at -5°C for one week, then left for 24 hours to return to room temperature (20°C), and the shear rate was 10s. －１ The polyvinyl acetal resin according to claim 1, wherein when the viscosity measured by multiplying by is denoted as B', the viscosity ratio A' / B' is 1.1 or less.

3. The polyvinyl acetal resin according to claim 1 or 2, wherein the weight-average molecular weight (Mw) / number-average molecular weight (Mn) is 3.5 to 5.

0.

4. A conductive paste comprising the polyvinyl acetal resin, organic solvent, and conductive powder described in claim 1 or 2.

5. A multilayer ceramic capacitor comprising the conductive paste described in claim 4.

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