Polyvinyl acetal resin and method for producing polyvinyl acetal resin solution

Abstract

To provide: a polyvinyl acetal resin which contains little foreign matter and enables the production of a ceramic green sheet having high mechanical strength, and with which it is possible to produce a multilayer ceramic capacitor having excellent reliability; a method for producing a polyvinyl acetal resin solution using the polyvinyl acetal resin; slurry for a ceramic green sheet; a ceramic green sheet; and a multilayer ceramic capacitor.SOLUTION: In the polyvinyl acetal resin, if P(MIX) is the number of particles having a size of 0.5-1.0 μm in a 0.2 mass% ethanol-toluene mixed solution (ethanol:toluene=50:50), and P(EOH) is the number of particles having a size of 0.5-1.0 μm in a 0.2-mass% ethanol solution, then P(MIX) is 1-20,000 particles / 10 ml and P(EOH) / P(MIX) is 1.2-7.0. In addition, in an IR absorption spectrum measured using an infrared spectrophotometer, among wavenumbers exhibiting transmittance a (%) satisfying [100-(100-X) / 2], where X (%) refers to the minimum transmittance of a peak in the wavenumber range of 3050-3750 cm-1, the wavenumber on the lower wavenumber side is represented by A and the wavenumber on the higher wavenumber side is represented by B; and then the hydroxyl-group-content-converted wavenumber width obtained by formula (1) using the wavenumbers A and B and the hydroxyl group content measured by 1H-NMR is 8.31 or more, where formula (1) is defined by [hydroxyl-group-content-converted wavenumber width (cm-1 / mol%)]=[(B-A) / (hydroxyl group content)].SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polyvinyl acetal resin, a method for producing a polyvinyl acetal resin solution, a slurry for a ceramic green sheet, a ceramic green sheet, and a multilayer ceramic capacitor. [Background technology]

[0002] BACKGROUND ART In recent years, electronic components mounted in various electronic devices have become increasingly smaller and more laminated, and 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 plasticizer, dispersant, etc. are added to a solution prepared by dissolving a binder resin such as polyvinyl butyral resin or poly(meth)acrylic ester resin in an organic solvent, followed by the addition of a ceramic raw material powder and uniform mixing using a mixing device such as a bead mill or ball mill to obtain a ceramic slurry composition with a certain viscosity after degassing. This slurry composition is then cast onto a support surface such as a release-treated polyethylene terephthalate film or SUS plate using a doctor blade, reverse roll coater, etc., and the volatile components such as the solvent are removed by heating or other methods, after which the sheet is peeled off from the support to obtain a ceramic green sheet. Next, a conductive paste that will become the internal electrodes is applied to the obtained ceramic green sheets by screen printing, and multiple sheets are stacked alternately and heated and pressed to form a laminate. After that, a process to thermally decompose and remove binder resin components and the like contained in the laminate, known as a degreasing process, is performed, and external electrodes are sintered onto the end faces of the ceramic sintered body obtained by firing, to obtain a multilayer ceramic capacitor.

[0003] For example, Patent Document 1 describes a polyvinyl acetal resin suitable as a ceramic binder, which has a predetermined degree of polymerization, vinyl ester unit content, and degree of acetalization, and in which the molar ratio of the portion acetalized with acetaldehyde to the portion acetalized with butylaldehyde is within a predetermined range. Furthermore, Patent Document 2 describes a polyvinyl acetal resin having a predetermined degree of polymerization, a vinyl ester unit content, a degree of acetalization, and specific structural units. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-236304 [Patent Document 2] International Publication No. 2012 / 023517 Summary of the Invention [Problem to be solved by the invention]

[0005] On the other hand, in recent years, with the trend toward multifunctionality and miniaturization of electronic devices, multilayer ceramic capacitors are being demanded to have larger capacitance and smaller size, and ceramic green sheets are also being demanded to be thinner. However, when conventional polyvinyl acetal resins are used in thin ceramic green sheets, the presence of foreign matter in the resin can cause short circuits in the multilayer ceramic capacitor and degradation of various electrical properties. Another problem is that the strength of the resulting ceramic green sheets is insufficient.

[0006] The present invention aims to provide a polyvinyl acetal resin that can produce ceramic green sheets with little foreign matter in the resin and high mechanical strength, and that can be used to fabricate highly reliable multilayer ceramic capacitors; a method for producing a polyvinyl acetal resin solution using the polyvinyl acetal resin; a slurry for ceramic green sheets; a ceramic green sheet; and a multilayer ceramic capacitor. [Means for solving the problem]

[0007] Disclosure 1 provides a method for producing a 0.2% by mass ethanol-toluene (ethanol:toluene=50:50) mixed solution containing 0.5 to 1.0 μm particles, where P(MIX) is the number of particles having a size of 0.5 to 1.0 μm in the mixed solution, and P(EOH) is the number of particles having a size of 0.5 to 1.0 μm in the 0.2% by mass ethanol solution. The method provides a 0.2% by mass ethanol solution containing 0.5 to 1.0 μm particles, where P(MIX) is 1 to 20,000 particles / 10 ml and P(EOH) / P(MIX) is 1.2 to 7.0, and the IR absorption spectrum measured by an infrared spectrophotometer has a wavenumber of 3050 to 3750 cm -1 When the minimum transmittance of the peak within the range is X (%), among the wave numbers showing transmittance a (%) that satisfies [100-(100-X) / 2], the wave number on the low wave number side is A and the wave number on the high wave number side is B. 1 The polyvinyl acetal resin has a hydroxyl group amount converted wavenumber width of 8.31 or more, calculated by formula (1) using the amount of hydroxyl groups measured by H-NMR. Hydroxyl group amount equivalent wavenumber width (cm -1 / mol%) = [(BA) / hydroxyl group content] (1) Disclosure 2 is the polyvinyl acetal resin according to Disclosure 1, in which P(EOH) is 4,000 to 60,000 particles / 10 ml. Disclosure 3 is the polyvinyl acetal resin according to Disclosure 1 or 2, in which the wavenumber width calculated by formula (1) is 8.45 or more. Disclosure 4 is a polyvinyl acetal resin according to any one of Disclosures 1 to 3, wherein, in GPC measurement using a differential refractive index detector, Mz(THF) / Mz(NMP) is 1.7 to 2.0, where Mz(THF) is the z-average molecular weight obtained using THF as a mobile phase and Mz(NMP) is the z-average molecular weight obtained using NMP as a mobile phase. The present disclosure 5 is a method for producing a polyvinyl acetal resin solution using the polyvinyl acetal resin according to any one of the present disclosures 1 to 4, the method comprising the steps of dissolving the polyvinyl acetal resin in an ethanol / toluene mixed solvent having an ethanol content of 70% by weight or more, removing particles by a filtration step, and then adding toluene. The present disclosure 6 is a slurry for a ceramic green sheet, which contains the polyvinyl acetal resin according to any one of the present disclosures 1 to 4, an organic solvent, and ceramic powder. The seventh aspect of the present disclosure is a ceramic green sheet obtained by using the slurry for the ceramic green sheet according to the sixth aspect of the present disclosure. Disclosure 8 is a multilayer ceramic capacitor obtained using the ceramic green sheet according to Disclosure 7. The present invention will be described in detail below.

[0008] As a result of extensive investigations, the present inventors have found that the number of particles of 0.5 to 1.0 μm size in an ethanol solution relative to the number of particles of 0.5 to 1.0 μm size in an ethanol-toluene mixed solution is within a predetermined range, and that the IR absorption spectrum measured by an infrared spectrophotometer has a peak of 3050 to 3750 cm -1 The present inventors have found that a polyvinyl acetal resin having a peak wavenumber width within a predetermined range has little foreign matter in the resin, can produce a ceramic green sheet with high mechanical strength, and can fabricate a multilayer ceramic capacitor with excellent reliability, and have completed the present invention.

[0009] In the polyvinyl acetal resin of the present invention, P(EOH) / P(MIX) is 1.2 to 7.0, where P(MIX) is the number of particles with a size of 0.5 to 1.0 μm in a 0.2 mass% ethanol-toluene (ethanol:toluene=50:50) mixed solution, and P(EOH) is the number of particles with a size of 0.5 to 1.0 μm in a 0.2 mass% ethanol solution. The number of particles of 0.5 to 1.0 μm size is measured by preparing predetermined solutions (0.2 mass % ethanol-toluene mixed solution, 0.2 mass % ethanol solution) and then measuring the number of particles of 0.5 to 1.0 μm diameter using a particle counter. When the P(EOH) / P(MIX) ratio is within the above range, the uniformity of the slurry is improved, smoother ceramic green sheets can be produced, and sheet defects such as cracks are less likely to occur, which is advantageous in that the reliability of the resulting multilayer ceramic capacitor is improved. The P(EOH) / P(MIX) ratio is preferably 3.3 or more, more preferably 4.3 or more, and is preferably 6.5 or less, more preferably 6.5 or less. In the present invention, P(EOH) / P(MIX) is an index of the ease of particle deposition in ethanol. As the particle counter, for example, "KS-42C" manufactured by Rion Co., Ltd. can be used. For example, particle measurement using the particle counter is preferably carried out in a clean room at 23°C.

[0010] The polyvinyl acetal resin of the present invention preferably has a particle count P(EOH) of 0.5 to 1.0 μm in size in a 0.2 mass% ethanol solution of 4,000 to 60,000 particles / 10 ml, more preferably 5,000 particles / 10 ml or more and 50,000 particles / 10 ml or less. By keeping the P(EOH) within the above range, particles in the resin solution can be efficiently removed. The P(EOH) is more preferably 7,000 particles / 10 ml or more, and even more preferably 40,000 particles / 10 ml or less.

[0011] The polyvinyl acetal resin of the present invention has a particle count P(MIX) of 0.5 to 1.0 μm in size in a 0.2 mass% ethanol-toluene (ethanol:toluene=50:50) mixed solution of 1 to 20,000 particles / 10 ml. Furthermore, the P(MIX) is preferably 10 particles / 10 ml or more and 15,000 particles / 10 ml or less. By keeping the P(MIX) within the above range, particles in the resin solution can be efficiently removed. The P(MIX) is more preferably 100 particles / 10 ml or more, and even more preferably 8,000 particles / 10 ml or less.

[0012] The P(EOH) / P(MIX), P(EOH), and P(MIX) can be adjusted by, for example, changing the average degree of polymerization and degree of saponification of the raw material polyvinyl alcohol resin, and the temperature and time conditions of the acetalization reaction, and by appropriately setting the amount of acetal groups, hydroxyl groups, acetyl groups, and the like of the polyvinyl acetal resin. In particular, the P(EOH) / P(MIX) can be adjusted by changing the hydrolysis temperature, hydrolysis time, aldehyde introduction temperature, temperature rise time, reaction temperature, reaction time, holding (aging) temperature, and holding (aging) time during the acetalization reaction described below, and particularly by changing the hydrolysis temperature, hydrolysis time, holding (aging) temperature, and holding (aging) time.

[0013] The polyvinyl acetal resin of the present invention has an IR absorption spectrum measured by an infrared spectrophotometer, which has a wave number of 3050 to 3750 cm -1When the minimum transmittance of the peak within this range is X (%), and among the wavenumbers exhibiting transmittance a (%) that satisfies [100-(100-X) / 2], the wavenumber on the lower wavenumber side is A and the wavenumber on the higher wavenumber side is B, the hydroxyl group amount equivalent wavenumber width calculated by the above formula (1) is 8.31 or more. By adjusting the thickness within the above range, it is possible to obtain a ceramic green sheet with even higher mechanical strength. The lower limit of the hydroxyl group amount converted wavenumber width is preferably 8.45, more preferably 8.70, and even more preferably 8.84, and the upper limit is preferably 10.00, and more preferably 9.70. In the present invention, the hydroxyl group amount converted wavenumber width serves as an index of whether the positions of hydroxyl groups are continuous. The IR absorption spectrum can be measured by a transmission method using a Fourier transform infrared spectrophotometer (such as HORIBA's "FT-720" or JASCO's "FT / IR-4000") at 20°C.

[0014] The polyvinyl acetal resin of the present invention is 1 The wave number width of the hydroxyl group-acetyl group amount converted by the following formula (2) using the hydroxyl group amount and the acetyl group amount measured by 1 H-NMR is preferably 6.5 to 18.0. Hydroxyl group acetyl group amount converted wavenumber width = [(BA) / hydroxyl group amount / acetyl group amount] (2) By setting the thickness within the above range, a ceramic green sheet having high mechanical strength can be obtained. The lower limit of the hydroxyl group-acetyl group converted wave number width is more preferably 10.5, and even more preferably 11.0, and the upper limit is more preferably 16.0, and even more preferably 14.0.

[0015] In the analysis of polyvinyl acetal resin using the above infrared spectrophotometer, the spectrum originating from the stretching vibration of the CH bond of polyvinyl acetal resin was observed at 2980 cm -1 The above peak analysis firstly revealed that the minimum transmittance of the peak due to the stretching vibration of the C-H bond is around 2500 cm -1 and 3050cm-1 The film thickness of the measurement sample is adjusted so that it is 20 to 25% of the baseline when the line connecting the two is connected. -1 A baseline is drawn for the peaks that appear within this range, and the data is corrected so that the transmittance at both ends of the peak is 100%.

[0016] The hydroxyl group amount converted wavenumber width can be adjusted, for example, by changing the average degree of polymerization and degree of saponification of the raw material polyvinyl alcohol resin, and the temperature and time conditions of the acetalization reaction, and by appropriately setting the amount of acetal groups, amount of hydroxyl groups, amount of acetyl groups, etc. of the polyvinyl acetal resin. In particular, the wavenumber width can be adjusted by changing the hydrolysis temperature, hydrolysis time, aldehyde introduction temperature, temperature rise time, reaction temperature, reaction time, holding (aging) temperature, and holding (aging) time during the acetalization reaction described below, and in particular, by changing the temperature rise rate, holding (aging) temperature, and holding (aging) time.

[0017] An example of the IR absorption spectrum of the polyvinyl acetal resin of the present invention measured with an infrared spectrophotometer at 20° C. is shown in Fig. 1. In Fig. 1, the vertical axis represents transmittance and the horizontal axis represents wavenumber. In the IR absorption spectrum shown in Figure 1, the minimum transmittance X is 65.7%. The transmittance a (%) that satisfies [100-(100-X) / 2] is 82.85%, and the wavenumber A on the low wavenumber side is 3297 cm -1 , the wave number B on the high wave number side is 3557 cm -1 is. In the above case, if the amount of hydroxyl groups is 30 mol%, the hydroxyl group amount converted wavenumber width [(BA) / amount of hydroxyl groups] is 8.67 (cm -1 / mol%). The wave number A is 3250 cm -1 More than 3270cm is preferable. -1 More than 3350cm is more preferable. -1 The following is preferred: 3330cm -1 The following is more preferred: The wave number B is 3530 cm-1 More than 3550cm is preferable. -1 More preferably, 3600 cm -1 The following is preferable: 3580cm -1 The following is more preferred: The transmittance a is preferably 80% or more and 85% or less.

[0018] In the polyvinyl acetal resin of the present invention, when measured by GPC using a differential refractive index detector, Mz(THF) is the z-average molecular weight obtained using THF as the mobile phase, and Mz(NMP) is the z-average molecular weight obtained using NMP as the mobile phase, and the ratio Mz(THF) / Mz(NMP) is preferably 1.7 to 2.0. By keeping the ratio within the above range, a ceramic green sheet with high mechanical strength can be obtained. The ratio Mz(THF) / Mz(NMP) is preferably 1.75 or more, more preferably 1.80 or more, and is preferably 1.95 or less, more preferably 1.90 or less. In the present invention, Mz(THF) / Mz(NMP) is an index of the intermolecular interaction of the polyvinyl acetal resin. The above Mz(THF) / Mz(NMP) can be calculated by measuring Mz(THF) obtained by gel permeation chromatography (GPC) measurement using tetrahydrofuran as the mobile phase and solvent and a refractive index detector as the detector, using THF as the mobile phase, and then measuring Mz(NMP) obtained by GPC measurement using N-methylpyrrolidone as the mobile phase and solvent and a refractive index detector as the detector, and then calculating Mz(THF) / Mz(NMP).

[0019] The above Mz(THF) is preferably 400,000 or more, more preferably 700,000 or more, and is preferably 6,000,000 or less, more preferably 2,000,000 or less. The above Mz(NMP) is preferably 200,000 or more, more preferably 400,000 or more, and is preferably 4,200,000 or less, more preferably 1,200,000 or less.

[0020] The above Mz(THF) / Mz(NMP) can be adjusted, for example, by changing the average degree of polymerization and degree of saponification of the raw material polyvinyl alcohol resin, and the temperature and time conditions of the acetalization reaction, and by appropriately setting the amount of acetal groups, hydroxyl groups, acetyl groups, etc. of the polyvinyl acetal resin. In particular, the above Mz(THF) / Mz(NMP) can be adjusted by changing the aldehyde introduction temperature, number of introductions, introduction intervals, temperature rise time, reaction temperature, reaction time, holding (aging) temperature, and holding (aging) time during the acetalization reaction described below, and in particular, it can be adjusted by changing the aldehyde introduction temperature, reaction time, temperature rise rate, holding (aging) temperature, and holding (aging) time.

[0021] The polyvinyl acetal resin of the present invention preferably has a solution viscosity of 30 mPa s or more and 600 mPa s or less when a 5 mass % solution dissolved in a 1:1 mixed solvent of ethanol and toluene is measured using a Brookfield viscometer at a solution temperature of 20°C. The viscosity is more preferably 50 mPa·s or more, and even more preferably 65 mPa·s or more, from the viewpoint of improving the tensile strength. The viscosity is more preferably 400 mPa·s or less, and even more preferably 200 mPa·s or less, from the viewpoint of improving the viscosity stability of the ceramic slurry composition. The B-type viscometer may be, for example, a TVB-10 viscometer manufactured by Toki Sangyo Co., Ltd. The rotor and rotation speed during viscosity measurement are preferably adjusted appropriately depending on the viscosity of the solution, and for example, measurements are preferably performed using spindles No. M1 to M4 at a rotation speed in the range of 0.3 to 100 rpm.

[0022] The viscosity can be adjusted, for example, by changing the average degree of polymerization and degree of saponification of the raw material polyvinyl alcohol resin, and the temperature and time conditions of the acetalization reaction, and by appropriately setting the amount of acetal groups, hydroxyl groups, acetyl groups, etc. of the polyvinyl acetal resin.

[0023] The polyvinyl acetal resin of the present invention preferably has a structural unit having an acetal group represented by the following formula (3), a structural unit having a hydroxyl group represented by the following formula (4), and a structural unit having an acetyl group represented by the following formula (5).

[0024] [ka]

[0025] In the above formula (3), R 1 represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms.

[0026] In the above formula (3), R 1 When is an alkyl group having 1 to 20 carbon atoms, examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a pentyl group, a hexyl group, a heptyl group, a 2-ethylhexyl 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, an octadecyl group, etc. Of these, a methyl group and an n-propyl group are preferred.

[0027] In the polyvinyl acetal resin of the present invention, the content of the structural unit having the acetal group represented by the above formula (3) (hereinafter also referred to as "acetal group amount") is preferably 50 mol % in lower limit and 83 mol % in upper limit. When the amount of acetal groups is 50 mol % or more, the solubility in organic solvents can be improved, and when the amount of acetal groups is 83 mol % or less, the polyvinyl acetal resin can have excellent tensile strength. The acetal group amount has a more preferred lower limit of 55 mol % and a more preferred upper limit of 80 mol %. That is, the acetal group amount is preferably 50 to 83 mol %, and more preferably 55 to 80 mol %. The amount of acetal groups is, for example, 1 It can be measured by H-NMR. Regarding the method for calculating the amount of acetal groups, since the acetal groups of the polyvinyl acetal resin are obtained by acetalizing two hydroxyl groups of polyvinyl alcohol, the method of counting the two acetalized hydroxyl groups is adopted.

[0028] In the polyvinyl acetal resin of the present invention, the content of the structural unit having a hydroxyl group represented by the above general formula (4) (hereinafter also referred to as "hydroxyl group amount") is preferably 18 mol % in lower limit and 40 mol % in upper limit. When the amount of hydroxyl groups is 18 mol % or more, the polyvinyl acetal resin can have high toughness, and when the amount of hydroxyl groups is 40 mol % or less, the solubility in organic solvents can be sufficiently improved. The lower limit of the hydroxyl group amount is more preferably 22 mol % and the upper limit is more preferably 38 mol %. That is, the hydroxyl group amount is preferably 18 to 40 mol %, and more preferably 22 to 38 mol %. By setting the hydroxyl group amount within the above range, the hydroxyl group amount converted wave number width and the hydroxyl group amount converted acetyl group amount converted wave number width can be set within a predetermined range. The amount of hydroxyl groups is, for example, 1 It can be measured by H-NMR.

[0029] In the polyvinyl acetal resin of the present invention, the content of the structural unit having an acetyl group represented by the above general formula (5) (hereinafter also referred to as "acetyl group amount") is preferably 0.1 mol % in lower limit and 22.0 mol % in upper limit. When the acetyl group content is 0.1 mol% or more, the increase in viscosity of the slurry composition for ceramic green sheets due to intramolecular and intermolecular hydrogen bonding of hydroxyl groups in the polyvinyl acetal resin can be suppressed.When the acetyl group content is 22.0 mol% or less, the flexibility of the polyvinyl acetal resin is not excessively increased, and handling properties can be improved. The lower limit of the acetyl group amount is more preferably 0.5 mol % and the upper limit is more preferably 15.0 mol %. That is, the acetyl group amount is preferably 0.1 to 22.0 mol %, and more preferably 0.5 to 15.0 mol %. By setting the acetyl group amount within the above range, the wave number width of the hydroxyl group amount converted into the acetyl group amount can be set within a predetermined range. The amount of acetyl groups is, for example, 1 It can be measured by H-NMR.

[0030] From the viewpoint of maintaining mechanical strength when producing a thin film ceramic green sheet, the polyvinyl acetal resin of the present invention has an average degree of polymerization of preferably 500 or more preferably 600 as a lower limit, and from the viewpoint of solubility in organic solvents and dissolution viscosity, the average degree of polymerization is preferably 10,000 or more preferably 5,000 as an upper limit. That is, the average degree of polymerization is preferably 500 to 10,000 or more preferably 600 to 5,000. The average degree of polymerization of the polyvinyl acetal resin is the same as that of the raw material polyvinyl alcohol, and can be measured in accordance with JIS K 6726.

[0031] The polyvinyl acetal resin of the present invention can usually be produced by acetalizing a polyvinyl alcohol resin.

[0032] As the polyvinyl alcohol resin, for example, a conventionally known polyvinyl alcohol resin such as a resin produced by saponifying a polyvinyl acetate resin with an alkali, an acid, aqueous ammonia, or the like can be used. The polyvinyl alcohol resin may be fully saponified, but does not need to be fully saponified as long as it has at least one unit having two consecutive hydroxyl groups at the meso and racemo positions at at least one location on the main chain, and may be a partially saponified polyvinyl alcohol resin. Furthermore, as the polyvinyl alcohol resin, a copolymer of vinyl alcohol and a monomer copolymerizable with vinyl alcohol, such as an ethylene-vinyl alcohol copolymer resin or a partially saponified ethylene-vinyl alcohol copolymer resin, may also be used. The polyvinyl acetate resin may be, for example, an ethylene-vinyl acetate copolymer.

[0033] The polyvinyl alcohol resin preferably has a degree of saponification of 70 mol % or more. The saponification degree is more preferably 76 mol % or more and 99.4 mol % or less, and even more preferably 78 mol % or more and 99.2 mol % or less. That is, the saponification degree is more preferably 76 to 99.4 mol %, and even more preferably 78 to 99.2 mol %. By using the polyvinyl alcohol resin, the Mz can be set within a predetermined range.

[0034] The acetalization is preferably carried out in a water solvent, a mixed solvent of water and an organic solvent compatible with water, or an organic solvent. As the organic solvent compatible with water, for example, an alcohol-based organic solvent can be used. Examples of the organic solvent 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 alcohol-based organic solvent include methanol, ethanol, n-propanol, isopropanol, n-butanol, and tert-butanol. Examples of the aromatic organic solvent include xylene, toluene, ethylbenzene, and methyl benzoate. Examples of the aliphatic ester solvent include methyl acetate, ethyl acetate, butyl acetate, methyl propionate, ethyl propionate, methyl butyrate, ethyl butyrate, methyl acetoacetate, and ethyl acetoacetate. Examples of the ketone solvent include acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, methylcyclohexanone, benzophenone, and acetophenone. Examples of the lower paraffin solvent include hexane, pentane, octane, cyclohexane, and decane. Examples of the ether solvent include diethyl ether, tetrahydrofuran, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, and propylene glycol diethyl ether. Examples of the amide solvent include N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and acetanilide. Examples of the amine solvent include ammonia, trimethylamine, triethylamine, n-butylamine, di-n-butylamine, tri-n-butylamine, aniline, N-methylaniline, N,N-dimethylaniline, and pyridine. These solvents can be used alone or in combination of two or more. Among these, ethanol, n-propanol, isopropanol, and tetrahydrofuran are particularly preferred from the viewpoints of solubility in the resin and ease of purification.

[0035] The acetalization is preferably carried out in the presence of an acid catalyst. The acid catalyst is not particularly limited, and examples thereof include mineral acids such as sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid; carboxylic acids such as formic acid, acetic acid, and propionic acid; and sulfonic acids such as methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, and paratoluenesulfonic acid. These acid catalysts may be used alone or in combination of two or more compounds. Among these, hydrochloric acid, nitric acid, and sulfuric acid are preferred, and hydrochloric acid is particularly preferred.

[0036] The aldehyde used in the acetalization reaction includes aldehydes having a chain aliphatic group, a cyclic aliphatic group, or an aromatic group having 1 to 10 carbon atoms. Any known aldehyde can be used as this aldehyde. The aldehyde used in the acetalization reaction is not particularly limited, and examples thereof include aliphatic aldehydes and aromatic aldehydes. Examples of the aliphatic aldehyde include formaldehyde, acetaldehyde, propionaldehyde, n-butyraldehyde, isobutyraldehyde, n-valeraldehyde, n-hexylaldehyde, 2-ethylbutyraldehyde, 2-ethylhexylaldehyde, n-heptylaldehyde, n-octylaldehyde, n-nonylaldehyde, n-decylaldehyde, and amylaldehyde. Examples of the aromatic aldehyde include benzaldehyde, cinnamaldehyde, 2-methylbenzaldehyde, 3-methylbenzaldehyde, 4-methylbenzaldehyde, p-hydroxybenzaldehyde, m-hydroxybenzaldehyde, phenylacetaldehyde, and β-phenylpropionaldehyde. These aldehydes may be used alone or in combination of two or more. Among them, formaldehyde, acetaldehyde, butylaldehyde, 2-ethylhexylaldehyde, and n-nonylaldehyde are preferred as aldehydes, as they have excellent acetalization reactivity, bring about a sufficient internal plasticizing effect in the resulting resin, and as a result, can impart good flexibility. Furthermore, formaldehyde, acetaldehyde, and butylaldehyde are more preferred, as they can provide an adhesive composition that is particularly excellent in impact resistance and adhesion to metals.

[0037] The amount of the aldehyde to be added can be appropriately determined depending on the amount of acetal groups in the target polyvinyl acetal resin. In particular, it is preferable to add the aldehyde in an amount of 50 mol % to 95 mol % and more preferably 55 mol % to 90 mol % relative to 100 mol % of polyvinyl alcohol, because this allows the acetalization reaction to proceed efficiently and makes it easy to remove unreacted aldehyde.

[0038] In the acetalization reaction, it is preferable to carry out a hydrolysis step using hydrochloric acid or sodium hydroxide before the acetalization reaction, and particularly it is preferable to carry out a hydrolysis step using hydrochloric acid. By carrying out the hydrolysis step using hydrochloric acid, it is possible to adjust P(EOH), P(MIX), and P(EOH) / P(MIX) within a predetermined range. For example, the hydrolysis step using hydrochloric acid is a step in which polyvinyl alcohol is dissolved in water by heating, hydrochloric acid is added, and the mixture is heated and stirred for a certain period of time to hydrolyze the acetyl groups contained in the polyvinyl alcohol to hydroxyl groups. The temperature (hydrolysis temperature), time (hydrolysis time), and amount of hydrochloric acid in the hydrolysis step can be appropriately adjusted depending on the degree of saponification of the starting polyvinyl alcohol and the target degree of saponification after hydrolysis.

[0039] The hydrolysis temperature is preferably 50° C. or higher and 90° C. or lower, more preferably 53° C. or higher and 85° C. or lower, even more preferably 55° C. or higher and 80° C. or lower, and particularly preferably 60° C. or higher and 75° C. or lower. That is, the hydrolysis temperature is preferably 50 to 90° C., more preferably 53 to 85° C., even more preferably 55 to 80° C., and particularly preferably 60 to 75° C. The hydrolysis time is preferably 30 minutes or more and 10 hours or less. More preferably, it is 45 minutes to 8 hours, even more preferably, it is 1 hour to 7 hours, and particularly preferably, it is 2 hours to 6 hours. That is, the hydrolysis time is preferably 30 minutes to 10 hours, more preferably, it is 45 minutes to 8 hours, even more preferably, it is 1 to 7 hours, and particularly preferably, it is 2 to 6 hours. The amount of hydrochloric acid is preferably 10 parts by weight or more and 250 parts by weight or less relative to 100 parts by weight of polyvinyl alcohol. More preferably, it is 15 parts by weight or more and 200 parts by weight or less, and even more preferably, it is 30 parts by weight or more and 120 parts by weight or less. That is, the amount of hydrochloric acid is preferably 10 to 250 parts by weight, more preferably 15 to 200 parts by weight, and even more preferably 30 to 120 parts by weight relative to 100 parts by weight of polyvinyl alcohol.

[0040] In the acetalization, it is preferable to add the aldehyde at a predetermined temperature, carry out a reaction for a predetermined time (reaction step), and then maintain the mixture at a predetermined temperature (aging step). The temperature at which the aldehyde is introduced is preferably 5°C or higher and 35°C or lower, and more preferably 15°C or higher and 25°C or lower. The time from the addition of the aldehyde to the start of temperature increase (temperature increase start time or reaction time) is preferably 150 minutes or more and 420 minutes or less, and more preferably 180 minutes or more and 360 minutes or less. The temperature rise time is preferably 330 minutes or more and 520 minutes or less, and more preferably 400 minutes or more and 510 minutes or less. Furthermore, when the temperature at the time of adding (charging) the aldehyde is less than 35°C, it is preferable to increase the temperature by changing the rate of temperature increase from the temperature at the time of adding the aldehyde to 35°C (temperature increase rate 1) and the rate of temperature increase from 35°C to the holding temperature in the aging step (temperature increase rate 2). The temperature rise rate 1 is preferably 0.02°C / min or more and 0.06°C / min or less. By setting the temperature increase rate 1 within the above range, the viscosity of THF can be set within a predetermined range. The temperature rise rate 2 is preferably 0.10°C / min or more and 0.30°C / min or less. By setting the temperature rise rate 2 within the above range, the hydroxyl group amount equivalent wave number width and the hydroxyl group amount / acetyl group amount equivalent wave number width can be set within a predetermined range.

[0041] The retention time in the aging step is preferably 1 hour or more and 5 hours or less, and more preferably 2.5 hours or more and 3 hours or less. The temperature maintained in the aging step is preferably 50°C or higher and 70°C or lower, and more preferably 55°C or higher and 65°C or lower. By setting the holding time and holding temperature as described above, the hydroxyl group amount equivalent wave number width and the hydroxyl group amount / acetyl group amount equivalent wave number width can be set within a predetermined range.

[0042] The present invention also provides a method for producing a polyvinyl acetal resin solution using the polyvinyl acetal resin of the present invention, the method comprising the steps of dissolving the polyvinyl acetal resin in an ethanol / toluene mixed solvent having an ethanol content of 70% by weight or more, removing particles by a filtration step, and then adding toluene. By using such a production method, it is possible to produce a polyvinyl acetal resin solution containing even fewer particles. The filtration step may be carried out by filtration using a metal mesh, a ceramic filter, a nonwoven fabric, or a resin filter, or by centrifugation.

[0043] By containing the polyvinyl acetal resin of the present invention and a plasticizer, a resin composition for a ceramic green sheet can be obtained. The resin composition for a ceramic green sheet may contain components such as an antioxidant, a surfactant, an ultraviolet absorber, and an antifoaming agent, as long as the effects of the present invention are not impaired.

[0044] As a method for producing the resin composition for a ceramic green sheet, for example, a plasticizer and other additives that are added as needed can be added to a polyvinyl acetal resin obtained by acetalizing a polyvinyl alcohol resin with an aldehyde, and then mixed to obtain a resin composition for a ceramic green sheet.

[0045] The resin composition for a ceramic green sheet contains a plasticizer, and the addition of the plasticizer can significantly improve the mechanical strength and flexibility of the resulting ceramic green sheet. 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.

[0046] In the resin composition for a ceramic green sheet, the content of the plasticizer relative to 100 parts by weight of the polyvinyl acetal resin is preferably 7 parts by weight at the lower limit, more preferably 8.5 parts by weight at the lower limit, and preferably 18 parts by weight at the upper limit, more preferably 13.5 parts by weight at the upper limit.

[0047] A slurry for ceramic green sheets can be prepared by mixing the polyvinyl acetal resin of the present invention with an organic solvent and ceramic powder.

[0048] The organic solvent is not particularly limited as long as it can dissolve the polyvinyl acetal resin, and examples thereof include ketones such as acetone, methyl ethyl ketone, dipropyl ketone, and diisobutyl ketone. Other examples include alcohols such as methanol, ethanol, isopropanol, and butanol, and aromatic hydrocarbons such as toluene and xylene. Further examples include esters such as methyl propionate, ethyl propionate, butyl propionate, methyl butanoate, ethyl butanoate, butyl butanoate, methyl pentanoate, ethyl pentanoate, butyl pentanoate, methyl hexanoate, ethyl hexanoate, butyl hexanoate, 2-ethylhexyl acetate, and 2-ethylhexyl butyrate. Other examples include methyl cellosolve, ethyl cellosolve, butyl cellosolve, terpineol, dihydroterpineol, butyl cellosolve acetate, butyl carbitol acetate, terpineol acetate, and dihydroterpineol acetate. In particular, alcohols, ketones, aromatic hydrocarbons and mixed solvents thereof are preferred in terms of coating and drying properties, with a mixed solvent of ethanol and toluene and a mixed solvent of methyl ethyl ketone and toluene being more preferred.

[0049] The content of the organic solvent in the ceramic green sheet slurry is determined depending on the type of polyvinyl acetal resin used and is not particularly limited. However, if the content is too low, the solubility required for kneading is difficult to achieve. On the other hand, if the content is too high, the viscosity of the ceramic green sheet slurry composition becomes too low, which can result in poor handling when producing ceramic green sheets. Therefore, the content of the organic solvent is preferably 20% by weight or more and 80% by weight or less.

[0050] The ceramic powders include metal or nonmetal oxide or non-oxide powders used in ceramic production. These powders may be single compositions, compounds, or mixtures. The constituent elements of the metal oxide or non-oxide, both cations and anions, may be single elements or multiple elements, and may further contain additives to improve the properties of the oxide or non-oxide. Specific examples include oxides, carbides, nitrides, borides, and sulfides of elements such as Li, K, Mg, B, Al, Si, Cu, Ca, Sr, Ba, Zn, Cd, Ga, In, Y, lanthanides, actinides, Ti, Zr, Hf, Bi, V, Nb, Ta, W, Mn, Fe, Co, and Ni. Furthermore, when specific oxide powders containing multiple metal elements, commonly called double oxides, are classified based on their crystal structure, those with a perovskite structure include NaNbO3, SrZrO3, PbZrO3, SrTiO3, BaZrO3, PbTiO3, BaTiO3, etc. Those with a spinel structure include MgAl2O4, ZnAl2O4, CoAl2O4, NiAl2O4, MgFe2O4, etc. Those with an ilmenite structure include MgTiO3, MnTiO3, FeTiO3, etc. Those with a garnet structure include GdGa5O 12 , Y6Fe5O 12 Among these, the modified polyvinyl acetal resin of the present invention exhibits excellent properties when mixed with BaTiO3 powder to form a ceramic green sheet.

[0051] The average particle size of the ceramic powder is not particularly limited, but for example, for producing a thin ceramic green sheet (thickness of 5 μm or less), it is preferably 0.5 μm or less.

[0052] The ceramic green sheet slurry may contain other polyvinyl acetal resins other than the polyvinyl acetal resin of the present invention, as well as other resins such as acrylic resins and ethyl cellulose, within the range that does not impair the effects of the present invention. In such cases, the content of the polyvinyl acetal resin of the present invention relative to the total binder resins is preferably 50% by weight or more.

[0053] If necessary, a dispersant, an antioxidant, an ultraviolet absorber, a surfactant, a filler, etc. may be added appropriately to the above-mentioned slurry for the ceramic green sheet, and in some cases, a small amount of other resin such as an acrylic resin or a urethane resin may also be added.

[0054] The method for producing the slurry for the ceramic green sheet is not particularly limited, and examples thereof include a method in which the polyvinyl acetal resin of the present invention, an organic solvent, a ceramic powder, and various additives to be added as needed are mixed using various mixers such as a ball mill, a blender mill, and a three-roll mill.

[0055] After the slurry for the ceramic green sheet is applied, the slurry is heated and dried to obtain a ceramic green sheet. The ceramic green sheets can be used to manufacture ceramic electronic components, for example, by carrying out a step of applying an electrode layer paste to the surfaces of the ceramic green sheets, and a step of stacking the ceramic green sheets on which the electrode layers have been formed, and then heat-pressing and bonding the stacked body, and then degreasing and firing the resulting laminate.

[0056] The method for applying the slurry for the ceramic green sheet is not particularly limited, and examples thereof include methods using a roll coater, a die coater, a curtain coater, etc. As for other specific methods, conventionally known methods can be used.

[0057] The ceramic electronic component is not particularly limited, and examples thereof include a multilayer ceramic capacitor, a multilayer ceramic inductor, a capacitor, a piezoelectric actuator, a multilayer varistor, a multilayer thermistor, an EMI filter, an aluminum nitride multilayer substrate, an alumina multilayer substrate, etc. Such a multilayer ceramic capacitor also constitutes part of the present invention.

[0058] The method for producing a ceramic electronic component includes a step of applying a paste for electrode layers to the surfaces of the ceramic green sheets. The electrode layer paste can be obtained by dissolving, for example, polyvinyl acetal resin, ethyl cellulose, acrylic resin, or the like as a binder resin in an organic solvent and dispersing conductive powder, etc. These resins may be used alone or in combination of two or more. An electrode layer paste containing a polyvinyl acetal resin is preferred because it exhibits excellent adhesion to the ceramic green sheet in the thermocompression bonding process.

[0059] In the method for producing a ceramic electronic component, the ceramic green sheets having electrode layers formed thereon are produced as described above, and then ceramic green sheets having electrode layers formed thereon that are produced in the same manner are stacked and heated and pressed together to obtain a laminate, which is then degreased and fired, thereby obtaining a multilayer ceramic electronic component that solves problems such as sheet attack and cracking. The above-mentioned thermocompression bonding step and the steps of degreasing and firing the laminate are not particularly limited, and conventionally known methods can be used. [Effects of the Invention]

[0060] According to the present invention, it is possible to provide a polyvinyl acetal resin that can produce a ceramic green sheet with little foreign matter in the resin and high mechanical strength, and that can produce a multilayer ceramic capacitor with excellent reliability, as well as a method for producing a polyvinyl acetal resin solution using the polyvinyl acetal resin, a slurry for a ceramic green sheet, a ceramic green sheet, and a multilayer ceramic capacitor. [Brief explanation of the drawings]

[0061] [Figure 1] FIG. 1 is a diagram showing an example of an IR absorption spectrum of a polyvinyl acetal resin of the present invention measured with an infrared spectrophotometer at 20° C. DETAILED DESCRIPTION OF THE INVENTION

[0062] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[0063] Example 1 260 g of polyvinyl alcohol resin (average degree of polymerization: 1700, saponification degree: 88.1 mol%) was added to 3000 g of pure water and stirred at 90°C for approximately 2 hours to dissolve. The solution was cooled to 70°C, and 200 g of 35 wt% hydrochloric acid was added and maintained for 3 hours. The solution was then cooled to 20°C, and 145 g of n-butyl aldehyde was added. After 180 minutes, the temperature was increased to 35°C at a rate of 0.06°C / min [heating rate 1], and then increased from 35°C at a rate of 0.22°C / min [heating rate 2] (heating time: 340 minutes). The temperature was then maintained at 55°C for 2.5 hours to complete the reaction. The mixture was then neutralized, washed with water, and dried in a conventional manner to obtain a white powder of polyvinyl acetal resin. The heating time was the time from the start of heating until the temperature reached the holding temperature.

[0064] (Preparation of ceramic green sheets) [Preparation of resin solution] 8 parts by weight of the obtained polyvinyl acetal resin and 2.1 parts by weight of a plasticizer (G260, manufactured by Sekisui Chemical Co., Ltd.) were added to a mixed solvent of 45 parts by weight of ethanol and 19 parts by weight of toluene, and dissolved with stirring to prepare a solution. Next, the solution was filtered using a ceramic filter with a pore size of 0.5 μm to obtain a filtered solution, and 26 parts by weight of toluene was added to 74.1 parts by weight of the filtered solution and stirred to prepare a resin solution. [Preparation of inorganic powder dispersion] One part by weight of polyvinyl acetal resin (BL-1, manufactured by Sekisui Chemical Co., Ltd.) was added to a mixed solvent of 20 parts by weight of toluene and 20 parts by weight of ethanol and dissolved by stirring. Next, 100 parts by weight of barium titanate powder (BT01, manufactured by Sakai Chemical Industry Co., Ltd.) was added to the resulting solution and stirred for 180 minutes in a bead mill (Ready Mill, manufactured by Imex Co., Ltd.) to prepare an inorganic powder dispersion. [Preparation of slurry for ceramic green sheets] To 141 parts by weight of the obtained inorganic powder dispersion, 100.1 parts by weight of the resin solution was added, and the mixture was stirred for 90 minutes in a bead mill to obtain a slurry for ceramic green sheets. The obtained slurry was applied to a release-treated PET film using a coater so that the thickness after drying would be 20 μm, and then heated and dried to prepare a ceramic green sheet.

[0065] Example 2 260 g of polyvinyl alcohol resin (average degree of polymerization: 1700, saponification degree: 88.1 mol%) was added to 3000 g of pure water and dissolved by stirring at 90°C for approximately 2 hours. The solution was cooled to 70°C, and 200 g of 35 wt% hydrochloric acid was added and maintained for 3 hours. The solution was then cooled to 20°C, and 145 g of n-butyl aldehyde was added. After 180 minutes, the temperature was increased to 35°C at a rate of [temperature increase rate 1] of 0.06°C / min, and then increased from 35°C at a rate of [temperature increase rate 2] of 0.22°C / min (temperature increase time: 340 minutes). The temperature was maintained at 55°C for 3.0 hours to complete the reaction. The solution was then neutralized, washed with water, and dried by conventional methods to obtain a white powder of polyvinyl acetal resin. Furthermore, ceramic green sheets were prepared in the same manner as in Example 1.

[0066] Example 3 260 g of polyvinyl alcohol resin (average degree of polymerization: 1700, saponification degree: 88.1 mol%) was added to 3000 g of pure water and stirred at 90°C for approximately 2 hours to dissolve. The solution was cooled to 70°C, and 200 g of 35 wt% hydrochloric acid was added and maintained for 3 hours. The solution was then cooled to 20°C, and 145 g of n-butyl aldehyde was added. After 180 minutes, the temperature was increased to 35°C at a rate of [temperature increase rate 1] of 0.06°C / min, and then increased from 35°C at a rate of [temperature increase rate 2] of 0.22°C / min (temperature increase time: 363 minutes). The temperature was maintained at 60°C for 3.0 hours to complete the reaction. The mixture was then neutralized, washed with water, and dried in a conventional manner to obtain a white powder of polyvinyl acetal resin. Furthermore, ceramic green sheets were prepared in the same manner as in Example 1.

[0067] Example 4 260 g of polyvinyl alcohol resin (average degree of polymerization: 1700, saponification degree: 88.1 mol%) was added to 3000 g of pure water and stirred at 90°C for approximately 2 hours to dissolve. The solution was cooled to 70°C, and 200 g of 35 wt% hydrochloric acid was added and maintained for 2.5 hours. The solution was then cooled to 20°C, and 145 g of n-butyl aldehyde was added. After 180 minutes, the temperature was increased to 35°C at a rate of [temperature increase rate 1] of 0.06°C / min, and then increased from 35°C at a rate of [temperature increase rate 2] of 0.22°C / min (temperature increase time: 340 minutes). The temperature was maintained at 55°C for 3.0 hours to complete the reaction. The mixture was then neutralized, washed with water, and dried in a conventional manner to obtain a white powder of polyvinyl acetal resin. Furthermore, ceramic green sheets were prepared in the same manner as in Example 1.

[0068] Example 5 260 g of polyvinyl alcohol resin (average degree of polymerization: 1700, saponification degree: 88.1 mol%) was added to 3000 g of pure water and dissolved by stirring at 90°C for approximately 2 hours. The solution was cooled to 60°C, and 200 g of 35 wt% hydrochloric acid was added and maintained for 5.0 hours. The solution was then cooled to 20°C, and 145 g of n-butyl aldehyde was added. After 180 minutes, the temperature was increased to 35°C at a rate of [temperature increase rate 1] of 0.06°C / min, and then increased from 35°C at a rate of [temperature increase rate 2] of 0.22°C / min (temperature increase time: 340 minutes). The temperature was maintained at 55°C for 3.0 hours to complete the reaction. The mixture was then neutralized, washed with water, and dried in a conventional manner to obtain a white powder of polyvinyl acetal resin. Furthermore, ceramic green sheets were prepared in the same manner as in Example 1.

[0069] Example 6 260 g of polyvinyl alcohol resin (average degree of polymerization: 1700, saponification degree: 88.1 mol%) was added to 3000 g of pure water and dissolved by stirring at 90°C for approximately 2 hours. The solution was cooled to 80°C, and 200 g of 35 wt% hydrochloric acid was added and maintained for 1.0 hour. The solution was then cooled to 20°C, and 145 g of n-butyl aldehyde was added. After 180 minutes, the temperature was increased to 35°C at a rate of [temperature increase rate 1] of 0.06°C / min, and then increased from 35°C at a rate of [temperature increase rate 2] of 0.22°C / min (temperature increase time: 340 minutes). The temperature was maintained at 55°C for 3.0 hours to complete the reaction. The mixture was then neutralized, washed with water, and dried in a conventional manner to obtain a white powder of polyvinyl acetal resin. Furthermore, ceramic green sheets were prepared in the same manner as in Example 1.

[0070] Example 7 260 g of polyvinyl alcohol resin (average degree of polymerization: 1700, saponification degree: 88.1 mol%) was added to 3000 g of pure water and dissolved by stirring at 90°C for approximately 2 hours. The solution was cooled to 60°C, and 200 g of 35 wt% hydrochloric acid was added and maintained for 5.0 hours. The solution was then cooled to 20°C, and 145 g of n-butyl aldehyde was added. After 180 minutes, the temperature was increased to 35°C at a rate of [temperature increase rate 1] of 0.06°C / min, and then increased from 35°C at a rate of [temperature increase rate 2] of 0.22°C / min (temperature increase time: 363 minutes). The mixture was maintained at 60°C for 3.5 hours to complete the reaction. The mixture was then neutralized, washed with water, and dried in a conventional manner to obtain a white powder of polyvinyl acetal resin. Furthermore, ceramic green sheets were prepared in the same manner as in Example 1.

[0071] Example 8 260 g of polyvinyl alcohol resin (average degree of polymerization: 1700, saponification degree: 88.1 mol%) was added to 3000 g of pure water and dissolved by stirring at 90°C for approximately 2 hours. The solution was cooled to 70°C, and 200 g of 35 wt% hydrochloric acid was added and maintained for 3.0 hours. The solution was then cooled to 20°C, and 145 g of n-butyl aldehyde was added. After 180 minutes, the temperature was increased to 35°C at a rate of [temperature increase rate 1] of 0.06°C / min, and then increased from 35°C at a rate of [temperature increase rate 2] of 0.22°C / min (temperature increase time: 363 minutes). The temperature was maintained at 60°C for 3.5 hours to complete the reaction. The mixture was then neutralized, washed with water, and dried by conventional methods to obtain a white powder of polyvinyl acetal resin. Furthermore, ceramic green sheets were prepared in the same manner as in Example 1.

[0072] Example 9 260 g of polyvinyl alcohol resin (average degree of polymerization: 1700, saponification degree: 88.1 mol%) was added to 3000 g of pure water and stirred at 90°C for approximately 2 hours to dissolve. This solution was cooled to 80°C, and 200 g of 35 wt% hydrochloric acid was added and maintained for 1.0 hour. The solution was then cooled to 20°C, and 145 g of n-butyl aldehyde was added. After 180 minutes, the temperature was increased to 35°C at a rate of [temperature increase rate 1] of 0.06°C / min, and then increased from 35°C at a rate of [temperature increase rate 2] of 0.22°C / min (temperature increase time: 363 minutes). The temperature was maintained at 60°C for 3.0 hours to complete the reaction. The mixture was then neutralized, washed with water, and dried in a conventional manner to obtain a white powder of polyvinyl acetal resin. Furthermore, ceramic green sheets were prepared in the same manner as in Example 1.

[0073] Example 10 260 g of polyvinyl alcohol resin (average degree of polymerization: 1700, saponification degree: 88.1 mol%) was added to 3000 g of pure water and dissolved by stirring at 90°C for approximately 2 hours. The solution was cooled to 60°C, and 200 g of 35 wt% hydrochloric acid was added and maintained for 5.0 hours. The solution was then cooled to 20°C, and 145 g of n-butyl aldehyde was added. After 180 minutes, the temperature was increased to 35°C at a rate of [temperature increase rate 1] of 0.06°C / min, and then increased from 35°C at a rate of [temperature increase rate 2] of 0.15°C / min (temperature increase time: 420 minutes). The temperature was maintained at 60°C for 3.0 hours to complete the reaction. The mixture was then neutralized, washed with water, and dried in a conventional manner to obtain a white powder of polyvinyl acetal resin. Furthermore, ceramic green sheets were prepared in the same manner as in Example 1.

[0074] Example 11 260 g of polyvinyl alcohol resin (average degree of polymerization: 1700, saponification degree: 88.1 mol%) was added to 3000 g of pure water and stirred at 90°C for approximately 2 hours to dissolve. This solution was cooled to 60°C, and 200 g of 35 wt% hydrochloric acid was added and maintained for 5.0 hours. The solution was then cooled to 20°C, and 145 g of n-butyl aldehyde was added. After 360 minutes, the temperature was increased to 35°C at a rate of [temperature increase rate 1] of 0.06°C / min, and then increased from 35°C at a rate of [temperature increase rate 2] of 0.22°C / min (temperature increase time: 340 minutes). The temperature was maintained at 55°C for 3.0 hours to complete the reaction. The mixture was then neutralized, washed with water, and dried in a conventional manner to obtain a white powder of polyvinyl acetal resin. Furthermore, ceramic green sheets were prepared in the same manner as in Example 1.

[0075] Example 12 260 g of polyvinyl alcohol resin (average degree of polymerization: 1700, saponification degree: 88.1 mol%) was added to 3000 g of pure water and dissolved by stirring at 90°C for approximately 2 hours. The solution was cooled to 85°C, and 200 g of 35 wt% hydrochloric acid was added and maintained for 0.5 hours. The solution was then cooled to 20°C, and 145 g of n-butyl aldehyde was added. After 360 minutes, the temperature was increased to 35°C at a rate of [temperature increase rate 1] of 0.06°C / min, and then increased from 35°C at a rate of [temperature increase rate 2] of 0.22°C / min (temperature increase time: 340 minutes). The temperature was maintained at 55°C for 2.5 hours to complete the reaction. The mixture was then neutralized, washed with water, and dried by conventional methods to obtain a white powder of polyvinyl acetal resin. Furthermore, ceramic green sheets were prepared in the same manner as in Example 1.

[0076] (Comparative Example 1) 3100 g of pure water was added to 300 g of polyvinyl alcohol resin (average polymerization degree 1700, saponification degree 99.2 mol%) and dissolved by stirring at 90°C for about 2 hours. This solution was cooled to 40°C, and 200 g of hydrochloric acid with a concentration of 35 wt% and 160 g of n-butylaldehyde were added thereto. Furthermore, ceramic green sheets were prepared in the same manner as in Example 1.

[0077] (Comparative Example 2) 3000 g of pure water was added to 260 g of polyvinyl alcohol resin (average degree of polymerization 1700, degree of saponification 99.2 mol%) and dissolved by stirring at 90°C for approximately 2 hours. This solution was cooled to 20°C, and 200 g of hydrochloric acid with a concentration of 35 wt% and 147 g of n-butylaldehyde were added to it. 30 minutes after the addition, the temperature was increased at a rate of 0.22°C / min (heating time: 45 minutes), and the temperature was maintained at 40°C for 3 hours to carry out an acetalization reaction. The mixture was then neutralized, washed with water, and dried by conventional methods to obtain a white powder of polyvinyl acetal resin. Furthermore, ceramic green sheets were prepared in the same manner as in Example 1.

[0078] (Comparative Example 3) 3000 g of pure water was added to 260 g of polyvinyl alcohol resin (average degree of polymerization 1700, degree of saponification 99.1 mol%) and dissolved by stirring at 90°C for approximately 2 hours. This solution was cooled to 20°C, and 200 g of hydrochloric acid with a concentration of 35 wt% and 147 g of n-butylaldehyde were added to it. 60 minutes after the addition, the temperature was increased at a rate of 0.3°C / min (heating time: 150 minutes), and the temperature was maintained at 60°C for 2.2 hours to carry out an acetalization reaction. The mixture was then neutralized, washed with water, and dried in the usual manner to obtain a white powder of polyvinyl acetal resin. Furthermore, ceramic green sheets were prepared in the same manner as in Example 1.

[0079] Comparative Example 4 3100 g of pure water was added to 300 g of polyvinyl alcohol resin (average polymerization degree 1700, saponification degree 98.7 mol%) and dissolved by stirring at 90°C for about 2 hours. This solution was cooled to 40°C, and 200 g of hydrochloric acid with a concentration of 35 wt% and 160 g of n-butylaldehyde were added thereto. Thereafter, the mixture was kept at 40°C for 3 hours to carry out an acetalization reaction, and then neutralized, washed with water and dried in a conventional manner to obtain a white powder of polyvinyl acetal resin. Furthermore, ceramic green sheets were prepared in the same manner as in Example 1.

[0080] (evaluation) The polyvinyl acetal resins and ceramic green sheets obtained in the examples and comparative examples were evaluated as follows, and the results are shown in Table 1.

[0081] (1) Evaluation of polyvinyl acetal resin (1-1) Amount of acetal groups, amount of hydroxyl groups, amount of acetyl groups The obtained polyvinyl acetal resin was analyzed using an AV400 spectrometer (manufactured by Bruker). 1 H-NMR measurement was carried out, and the amounts of acetal groups, hydroxyl groups, and acetyl groups were calculated. The obtained polyvinyl acetal resin was dissolved in DMSO-D6 to a concentration of 1.6% by weight to prepare a measurement solution. 1 H-NMR measurements were carried out at 80°C.

[0082] (1-2) IR absorption spectrum The obtained polyvinyl acetal resin was dissolved in a 1:1 ethanol / toluene mixed solution by weight, and then coated onto a PET film. -1 The film thickness of the measurement sample was adjusted so that the minimum transmittance of the peak appearing around 22% was obtained, and a polyvinyl acetal resin sheet was obtained. The IR absorption spectrum of the obtained polyvinyl acetal resin sheet was measured using an infrared spectrophotometer (HORIBA, FT-720) at 20°C. The measurement results showed that the IR absorption spectrum was measured at wavenumbers of 3050 to 3750 cm. -1 A baseline was drawn for the peaks that appeared within this range, and peak analysis was performed on the data corrected so that the transmittance at both ends of the peak was 100%, and the minimum transmittance X, transmittance a, and peak wavenumbers A and B were measured. 1 Using the amount of hydroxyl groups determined by H-NMR measurement, the hydroxyl group amount converted wavenumber width (cm -1 / mol%) = [(BA) / amount of hydroxyl groups] was calculated. 1 Using the amount of acetyl groups determined by H-NMR measurement, the wave number width of hydroxyl groups converted into the amount of acetyl groups = [(BA) / amount of hydroxyl groups / acetyl groups] was calculated.

[0083] (1-3) Particles The obtained polyvinyl acetal resin was added to an ethanol-toluene (ethanol:toluene = 50:50) mixed solvent so that the solid content concentration of the polyvinyl acetal resin was 0.2 mass%, and the mixture was stirred at 60 rpm using a mix rotor for 24 hours to dissolve the resin, thereby preparing an ethanol-toluene mixed solution. For 10 mL of the resulting ethanol-toluene mixed solution, the number of particles of 0.5 to 1.0 μm size was measured three times using a particle counter (manufactured by RION, KS-42C, KE-40B1), and the average value was taken as D1. Separately, the number of particles in the ethanol-toluene (ethanol:toluene = 50:50) mixed solvent used as the solvent for the ethanol-toluene mixed solution was measured three times using a particle counter (manufactured by RION, KS-42C, KE-40B1), and the average value was taken as C1. From the obtained C1 and D1, P(MIX) was calculated using the following formula. P(MIX)=D1-C1

[0084] Similarly, the obtained polyvinyl acetal resin was added to ethanol so that the solid content concentration of the polyvinyl acetal resin was 0.2 mass%, and the mixture was stirred at 60 rpm using a mix rotor for 24 hours to dissolve, thereby preparing an ethanol solution. For 10 mL of the obtained ethanol solution, the number of particles of 0.5 to 1.0 μm size was measured three times using a particle counter (manufactured by RION, KS-42C, KE-40B1), and the average value was taken as D2. Separately, the number of particles in the ethanol used as the solvent for the ethanol solution was measured three times using a particle counter (manufactured by RION, KS-42C, KE-40B1), and the average value was taken as C2. From the obtained C2 and D2, P(EOH) was calculated using the following formula. In addition, P(EOH) / P(MIX) was calculated from the obtained P(MIX) and P(EOH). P(EOH)=D2-C2

[0085] (1-4) Viscosity measurement The obtained polyvinyl acetal resin was dissolved in a 1:1 ethanol / toluene mixed solution to a concentration of 5% by mass to prepare a viscosity measurement sample. The viscosity of the obtained viscosity measurement sample was measured using a B-type viscometer at a solution temperature of 20°C. The B-type viscometer used was a TVB-10 viscometer (manufactured by Toki Sangyo Co., Ltd.), and measurements were carried out with the following rotation speeds and rotors: Examples 1 to 12 and Comparative Examples 1 to 4: Rotation speed 30 rpm, SPINDLE No. M1

[0086] (1-5)z average molecular weight [Mz(THF), Mz(NMP)] measurement The resulting polyvinyl acetal resin was dissolved in tetrahydrofuran (THF) at a concentration of 0.2 wt% and passed through a 0.45 μm PTFE filter. The gel was analyzed using a GPC system (HLC-8420, Tosoh Corporation) with a THF mobile phase, a Bryce-type double-pass refractive index detector (Tosoh Corporation), and a TSKgel Super HZM-H column (Tosoh Corporation) at a flow rate of 0.35 mL / min. The results were calibrated using a molecular weight calibration curve prepared using monodisperse polystyrene standards to obtain the z-average molecular weight, Mz (THF). Similarly, the obtained polyvinyl acetal resin was dissolved in N-methylpyrrolidone (NMP) at a concentration of 0.2 wt%, passed through a PTFE filter with a pore size of 0.45 μm, and measured at a flow rate of 0.5 mL / min using a GPC-101 (Shodex) GPC apparatus, NMP as the mobile phase, a differential refractive index detector RI-715 (Shodex) as the detector, and an LF-804 (Shodex) column. The measurement results were calibrated using a molecular weight calibration curve prepared using monodisperse polystyrene standards to obtain the z-average molecular weight Mz (NMP). From the obtained Mz(THF) and Mz(NMP), "Mz(THF) / Mz(NMP)" was calculated. Then, using the THF viscosity obtained from the viscosity measurement, "[THF viscosity / Mz(NMP)] × 10000" was calculated.

[0087] (2) Evaluation of ceramic green sheets (2-1) Surface roughness The ten-point average roughness (Rz) of the obtained ceramic green sheets was measured in accordance with JIS B 0601 (1994) and evaluated according to the following criteria. AA: Rz is 0.25 μm or less A: Rz is more than 0.25 μm and less than 0.30 μm, B: Rz is 0.30 μm or more and less than 0.40 μm C: Rz is 0.40 μm or more

[0088] (2-2) Breaking stress and breaking strain The obtained ceramic green sheet was cut into a size of 5 cm x 1 cm to prepare a test piece. The test piece was pulled at a tension speed of 500% / min using a tensile tester (Shimadzu Corporation, AUTOGRAPH AGS-J) at a measurement temperature of 20°C, and the breaking tensile strength (kg / cm 2 ) was measured. A stress σ (MPa)-strain ε (%) curve was calculated from the obtained values. Note that 500% / min means a speed at which the test piece is moved a distance five times the distance between the chucks in one minute. The stress at break and strain at break were calculated from the obtained stress-strain curve and evaluated according to the following evaluation criteria. (stress at break) AA:34MPa or more A: 33 MPa or more, less than 34 MPa B: 30 MPa or more, less than 33 MPa C: Less than 30 MPa (strain at break) AA: 22% or more A: 21% or more, less than 22% B: 17% or more, less than 21% C: Less than 17%

[0089] [Table 1] [Industrial Applicability]

[0090] According to the present invention, it is possible to provide a polyvinyl acetal resin that can produce a ceramic green sheet with little foreign matter in the resin and high mechanical strength, and that can produce a multilayer ceramic capacitor with excellent reliability, as well as a method for producing a polyvinyl acetal resin solution using the polyvinyl acetal resin, a slurry for a ceramic green sheet, a ceramic green sheet, and a multilayer ceramic capacitor.

Claims

1. When the number of particles of 0.5 to 1.0 μm size in a 0.2 mass% ethanol-toluene (ethanol:toluene=50:50) mixed solution is defined as P(MIX) and the number of particles of 0.5 to 1.0 μm size in a 0.2 mass% ethanol solution is defined as P(EOH), P(MIX) is 1 to 20,000 particles / 10 ml and P(EOH) / P(MIX) is 1.2 to 7.0, In the IR absorption spectrum measured by an infrared spectrophotometer, the wave number is 3050 to 3750 cm －１ When the minimum transmittance of the peak within the range is X (%), among the wave numbers showing transmittance a (%) that satisfies [100-(100-X) / 2], the wave number on the low wave number side is A and the wave number on the high wave number side is B. １ A polyvinyl acetal resin having a hydroxyl group amount converted wavenumber width of 8.31 or more, calculated by formula (1) using the amount of hydroxyl groups measured by H-NMR. Hydroxyl group amount equivalent wavenumber width (cm －１ / mol%) = [(B - A) / amount of hydroxyl groups] (1)

2. The polyvinyl acetal resin according to claim 1, wherein P(EOH) is 4,000 to 60,000 particles / 10 ml.

3. The polyvinyl acetal resin according to claim 1 or 2, wherein the wavenumber width calculated by the formula (1) is 8.45 or more.

4. 3. The polyvinyl acetal resin according to claim 1, wherein Mz(THF) / Mz(NMP) is 1.7 to 2.0, where Mz(THF) is the z-average molecular weight obtained using THF as a mobile phase and Mz(NMP) is the z-average molecular weight obtained using NMP as a mobile phase in GPC measurement using a differential refractive index detector.

5. A method for producing a polyvinyl acetal resin solution using the polyvinyl acetal resin according to claim 1 or 2, comprising: a step of dissolving the polyvinyl acetal resin in an ethanol / toluene mixed solvent having an ethanol content of 70% by weight or more, a step of removing particles by a filtration step, and then a step of adding toluene.

6. A slurry for a ceramic green sheet, comprising the polyvinyl acetal resin according to claim 1 or 2, an organic solvent, and ceramic powder.

7. A ceramic green sheet obtained by using the slurry for ceramic green sheet according to claim 6.

8. A multilayer ceramic capacitor obtained by using the ceramic green sheet according to claim 7.

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