Polyvinyl acetal resin and method for producing polyvinyl acetal resin solution

Abstract

The present invention provides: a polyvinyl acetal resin which has little foreign matter in the resin 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; a slurry for a ceramic green sheet; a ceramic green sheet; and a multilayer ceramic capacitor. Provided is a polyvinyl acetal resin wherein: 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, P(MIX) is 1-20,000 particles / 10 ml and P(EOH) / P(MIX) is 1.2-7.0; and if A is the wave number on the lower wave number side and B is the wave number on the higher wave number side among the wave numbers showing a transmittance a (%) that satisfies [100-(100-X) / 2], where X (%) is the minimum transmittance at a peak within the wave number range of 3,050-3,750 cm-1 in the IR absorption spectrum determined with an infrared spectrophotometer, the wave number width in terms of the hydroxyl group amount determined by formula (1) using A, B and the hydroxyl group amount that is measured by 1H-NMR is 8.31 or more. (1): Wave number width in terms of hydroxyl group amount (cm-1 / mol%) = [(B-A) / (hydroxyl group amount)]

Description

Polyvinyl acetal resin and method for producing polyvinyl acetal resin solution

[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.

[0002] In recent years, electronic components mounted in various electronic devices have become increasingly miniaturized and multilayered, resulting in widespread use of multilayer electronic components such as multilayer circuit boards, laminated coils, and multilayer ceramic capacitors. Multilayer ceramic capacitors, among others, are generally manufactured through the following process. First, a plasticizer, dispersant, etc. are added to a solution of a binder resin, such as polyvinyl butyral resin or poly(meth)acrylate resin, dissolved in an organic solvent. Then, ceramic raw material powder is added and uniformly mixed using a mixing device such as a bead mill or ball mill. After degassing, a ceramic slurry composition with a constant viscosity is obtained. This slurry composition is cast onto a support surface, such as a release-treated polyethylene terephthalate film or SUS plate, using a doctor blade or reverse roll coater. The resulting ceramic green sheets are then heated to remove volatiles such as the solvent, and the sheets are peeled off from the support to obtain ceramic green sheets. Next, multiple sheets of the resulting ceramic green sheets, each coated with a conductive paste for internal electrodes by screen printing, are alternately stacked and heated and pressed together to form a laminate. Thereafter, the laminate is subjected to a process of thermally decomposing and removing binder resin components and the like contained in the laminate, a so-called degreasing process, and then 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. Also, Patent Document 2 describes a polyvinyl acetal resin having a predetermined degree of polymerization, vinyl ester unit content, and degree of acetalization, and having specific structural units.

[0004] JP 2011-236304 A International Publication No. 2012 / 023517

[0005] On the other hand, in recent years, with the trend toward multifunctionality and miniaturization of electronic devices, multilayer ceramic capacitors are required to have higher capacitance and be smaller, and ceramic green sheets are also required to be thinner. However, when conventional polyvinyl acetal resins are used in thin-layer 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.

[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, and P(EOH) is the number of particles having a size of 0.5 to 1.0 μm in a 0.2% by mass ethanol solution, and P(EOH) / P(MIX) is 1.2 to 7.0. In an 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 The polyvinyl acetal resin has a hydroxyl group amount equivalent wavenumber width (cm) of 8.31 or more, which is calculated by the formula (1) using the amount of hydroxyl groups measured by H-NMR. －１ / mol%)=[(B−A) / amount of hydroxyl groups] (1) Disclosure 2 is the polyvinyl acetal resin according to Disclosure 1, wherein P(EOH) is 4,000 to 60,000 / 10 ml. Disclosure 3 is the polyvinyl acetal resin according to Disclosure 1 or 2, wherein the wavenumber width calculated by Equation (1) is 8.45 or more. Disclosure 4 is the polyvinyl acetal resin according to any one of Disclosures 1 to 3, wherein Mz(THF) / Mz(NMP) is 1.7 to 2.0, where 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 in GPC measurement using a differential refractive index detector. Disclosure 5 is a method for producing a polyvinyl acetal resin solution using the polyvinyl acetal resin according to any one of Disclosures 1 to 4, the method comprising 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 process, and then adding toluene. Disclosure 6 is a slurry for a ceramic green sheet containing the polyvinyl acetal resin according to any one of Disclosures 1 to 4, an organic solvent, and a ceramic powder. Disclosure 7 is a ceramic green sheet obtained using the slurry for a ceramic green sheet according to Disclosure 6. Disclosure 8 is a multilayer ceramic capacitor obtained using the ceramic green sheet according to Disclosure 7. The present invention is 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] The polyvinyl acetal resin of the present invention has a P(EOH) / P(MIX) ratio of 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 with a size of 0.5 to 1.0 μm is measured using a particle counter after preparing a predetermined solution (0.2 mass% ethanol-toluene mixed solution, 0.2 mass% ethanol solution). A P(EOH) / P(MIX) ratio within the above range improves the uniformity of the slurry, enabling the production of smoother ceramic green sheets and reducing the occurrence of sheet defects such as cracks. This has the advantage of improving the reliability of the resulting multilayer ceramic capacitor. The P(EOH) / P(MIX) ratio is preferably 3.3 or more, more preferably 3.8 or more, and even more preferably 4.3 or more. Furthermore, the P(EOH) / P(MIX) ratio is preferably 6.5 or less, more preferably 6.0 or less, and even more preferably 5.8 or less. In the present invention, P(EOH) / P(MIX) serves as an index of the ease of particle precipitation in ethanol. Polyvinyl acetal resins contain highly polar components such as hydroxyl groups and low-polarity components such as acetal groups, and their solubility varies depending on the polarity of the solvent. Generally, the solubility of polyvinyl acetal resins is related to the amount of highly polar components such as hydroxyl groups in highly polar solvents such as ethanol, while the solubility of low-polarity solvents such as toluene is related to the amount of low-polarity components such as acetal groups, resulting in different particle counts depending on the solvent type. Therefore, the degree of particle precipitation in ethanol can be determined by calculating the particle number ratio of an ethanol solution to an ethanol-toluene mixed solution. The particle counter may be, for example, "KS-42C" manufactured by Rion Co., Ltd. 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 setting 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 particles 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 setting 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 10,000 particles / 10 ml or less, and even more preferably 500 particles / 10 ml or more and 8,000 particles / 10 ml or less.

[0012] The P(EOH) / P(MIX), P(EOH), and P(MIX) 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 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, and has a wave number of 3050 to 3750 cm －１When the minimum transmittance of the peak within this range is X (%), and the wavenumbers exhibiting a transmittance a (%) that satisfies [100-(100-X) / 2] are A and B, respectively, the hydroxyl group amount-equivalent wavenumber width calculated by the above formula (1) is 8.31 or more. By keeping the hydroxyl group amount-equivalent wavenumber width within this range, a ceramic green sheet with even higher mechanical strength can be obtained. The preferred lower limit of the hydroxyl group amount-equivalent wavenumber width is 8.45, more preferably 8.70, and even more preferably 8.84, and the preferred upper limit is 10.00, and even more preferably 9.70. In the present invention, the hydroxyl group amount-equivalent wavenumber width serves as an indicator of the continuity of hydroxyl group positions. The IR absorption spectrum can be measured by a transmission method using a Fourier transform infrared spectrophotometer (such as FT-720 manufactured by HORIBA or FT / IR-4000 manufactured by JASCO) at 20°C.

[0014] The polyvinyl acetal resin of the present invention is １ Using the amounts of hydroxyl groups and acetyl groups measured by H-NMR, the hydroxyl-acetyl group amount-equivalent wavenumber width calculated by the following formula (2) is preferably 6.5 to 18.0: hydroxyl-acetyl group amount-equivalent wavenumber width=[(B-A) / hydroxyl group amount / acetyl group amount] (2) By keeping the value within this range, a ceramic green sheet with high mechanical strength can be obtained. The lower limit of the hydroxyl-acetyl group amount-equivalent wavenumber width is more preferably 10.5, even more preferably 11.0, and the upper limit is more preferably 16.0, even more preferably 14.0.

[0015] In the analysis of the polyvinyl acetal resin using the infrared spectrophotometer, a spectrum derived from the stretching vibration of the C—H bond of the 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 3050 cm －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 lines is connected. －１A 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 by an infrared spectrophotometer at 20°C is shown in Figure 1. In Figure 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%. Furthermore, the transmittance a (%) satisfying [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 In the above case, if the amount of hydroxyl groups is 30 mol%, the wavenumber width converted into the amount of hydroxyl groups [(B−A) / amount of hydroxyl groups] is 8.67 (cm －１ / mol%). The wave number A is 3250 cm －１ More than 3270 cm is preferable. －１ More preferably, 3350 cm －１ Preferably, 3330 cm －１ The wave number B is preferably 3530 cm or less. －１ More than 3550 cm －１ More preferably, the value is 3600 cm or more. －１ Preferably, 3580 cm or less －１ The following is more preferable: 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. The Mz(THF) / Mz(NMP) ratio is preferably 1.7 to 2.0. By maintaining the ratio within this range, ceramic green sheets with high mechanical strength can be obtained. The Mz(THF) / Mz(NMP) ratio is preferably 1.75 or more, more preferably 1.80 or more. Furthermore, the Mz(THF) / Mz(NMP) ratio is preferably 1.95 or less, more preferably 1.90 or less. In the present invention, the Mz(THF) / Mz(NMP) ratio serves as an indicator of the intermolecular interactions 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 a mobile phase and a solvent and a differential refractive index detector as a detector, using THF as a mobile phase, and then measuring Mz(NMP) obtained by GPC measurement using N-methylpyrrolidone as a mobile phase and a solvent and a differential refractive index detector as a detector, and calculating Mz(THF) / Mz(NMP).

[0019] The Mz(THF) is preferably 400,000 or more, more preferably 700,000 or more, and preferably 6,000,000 or less, and more preferably 2,000,000 or less. The Mz(NMP) is preferably 200,000 or more, more preferably 400,000 or more, and preferably 4,200,000 or less, and 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, amount of hydroxyl groups, amount of 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% by 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. From the viewpoint of improving tensile strength, 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 viscosity stability of the ceramic slurry composition, the viscosity is more preferably 400 mPa·s or less, and even more preferably 200 mPa·s or less. As the Brookfield viscometer, for example, a TVB-10 viscometer manufactured by Toki Sangyo Co., Ltd. can be used. Furthermore, the rotor and rotation speed during viscosity measurement are preferably adjusted appropriately depending on the solution viscosity. For example, it is preferable to measure using SPINDLE Nos. 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]

[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 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 an acetal group represented by formula (3) (hereinafter also referred to as the "acetal group amount") is preferably 50 mol% at the lower limit and 83 mol% at the upper limit. When the acetal group amount is 50 mol% or more, the solubility in organic solvents can be improved. When the acetal group amount is 83 mol% or less, the polyvinyl acetal resin can have excellent tensile strength. The acetal group amount is more preferably 55 mol% at the lower limit, more preferably 81 mol% at the upper limit, even more preferably 58 mol% at the lower limit, even more preferably 80 mol% at the upper limit, even more preferably 61 mol% at the lower limit, even more preferably 77 mol%, particularly preferably 67 mol% at the lower limit, and especially preferably 73 mol% at the upper limit. That is, the amount of acetal groups is preferably 50 to 83 mol%, more preferably 55 to 81 mol%, even more preferably 58 to 80 mol%, even more preferably 61 to 77 mol%, and particularly preferably 67 to 73 mol%. When the polyvinyl acetal resin of the present invention is acetalized using butyraldehyde and acetaldehyde, the amount of butyral groups is preferably 27 to 80 mol%, more preferably 35 to 78 mol%, even more preferably 44 to 72 mol%, and particularly preferably 52 to 65 mol%, and the amount of acetoacetal groups is preferably 1 to 25 mol%, more preferably 2 to 20 mol%, even more preferably 5 to 17 mol%, and particularly preferably 8 to 15 mol%. The amount of acetal groups can be, for example, １ The amount of acetal groups can be measured by H-NMR. Since the acetal groups of the polyvinyl acetal resin are obtained by acetalizing two hydroxyl groups of polyvinyl alcohol, the amount of acetal groups is calculated by counting the two acetalized hydroxyl groups.

[0028] In the polyvinyl acetal resin of the present invention, the content of the hydroxyl group-containing structural unit represented by the general formula (4) (hereinafter also referred to as the "hydroxyl group amount") is preferably 18 mol% at the lower limit and 40 mol% at the upper limit. When the hydroxyl group amount is 18 mol% or more, the polyvinyl acetal resin can have high toughness. When the hydroxyl group amount is 40 mol% or less, the solubility in organic solvents can be sufficiently improved. The hydroxyl group amount is more preferably 22 mol% at the lower limit and 38 mol% at the upper limit, and even more preferably 26 mol% at the lower limit and 32 mol% at the upper limit. That is, the hydroxyl group amount is preferably 18 to 40 mol%, more preferably 22 to 38 mol%, and even more preferably 26 to 32 mol%. By setting the hydroxyl group amount in the above range, the hydroxyl group amount equivalent wavenumber width and the hydroxyl group amount equivalent wavenumber width can be set within a predetermined range. The hydroxyl group amount can be, 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 general formula (5) (hereinafter also referred to as the "acetyl group amount") is preferably 0.1 mol% at the lower limit and 22.0 mol% at the upper limit. When the acetyl group amount is 0.1 mol% or more, it is possible to suppress the increase in viscosity of the slurry composition for a ceramic green sheet due to intramolecular and intermolecular hydrogen bonding of hydroxyl groups in the polyvinyl acetal resin. When the acetyl group amount is 22.0 mol% or less, it is possible to improve the handleability without excessively increasing the flexibility of the polyvinyl acetal resin. The acetyl group amount is more preferably 0.5 mol% at the lower limit and 15.0 mol% at the upper limit. 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 in this range, the hydroxyl group amount-acetyl group amount conversion wavenumber width can be set within a predetermined range. The acetyl group amount can be, for example, １ It can be measured by H-NMR.

[0030] The polyvinyl acetal resin of the present invention has an average degree of polymerization of preferably 500 or more preferably 600, from the viewpoint of maintaining mechanical strength when preparing a thin film ceramic green sheet. Furthermore, 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. That is, the average degree of polymerization is preferably 500 to 10,000, 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. The average degree of polymerization can be measured in accordance with JIS K 6726. When multiple raw material polyvinyl alcohols are used, the average degrees of polymerization of each polyvinyl alcohol resin are multiplied by the proportion of the added amount, and the sum of these values ​​represents the average degree of polymerization of the polyvinyl acetal resin.

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

[0032] The polyvinyl alcohol resin can be, 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. The polyvinyl alcohol resin can be fully saponified, but it 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; it can also be a partially saponified polyvinyl alcohol resin. Furthermore, the polyvinyl alcohol resin can also be 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. Examples of the polyvinyl acetate resin include ethylene-vinyl acetate copolymers.

[0033] The polyvinyl alcohol resin preferably has a degree of saponification of 70 mol% or more. The degree of saponification 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 degree of saponification 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 an aqueous solvent, a mixed solvent of water and a water-compatible organic solvent, or an organic solvent. Examples of the water-compatible organic solvent include alcohol-based organic solvents. 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-based 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 solvents include acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, methylcyclohexanone, benzophenone, and acetophenone. Examples of the lower paraffin solvents include hexane, pentane, octane, cyclohexane, and decane. Examples of the ether solvents include diethyl ether, tetrahydrofuran, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, and propylene glycol diethyl ether. Examples of the amide solvents include N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and acetanilide. Examples of the amine solvents 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] Examples of the aldehyde used in the acetalization include aldehydes having a chain aliphatic group, a cyclic aliphatic group, or an aromatic group having 1 to 10 carbon atoms. Conventionally known aldehydes can be used as these aldehydes. The aldehyde used in the acetalization reaction is not particularly limited, and examples 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 these, preferred aldehydes are formaldehyde, acetaldehyde, butylaldehyde, 2-ethylhexylaldehyde, and n-nonylaldehyde, which have excellent acetalization reactivity and can provide a sufficient internal plasticizing effect to the resulting resin, thereby imparting good flexibility. Furthermore, formaldehyde, acetaldehyde, and butylaldehyde are more preferred because 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 from 50 mol % to 95 mol %, more preferably from 55 mol % to 90 mol %, based on 100 mol % of polyvinyl alcohol, because this allows the acetalization reaction to proceed efficiently and makes it easy to remove unreacted aldehyde.

[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 set P(EOH), P(MIX), and P(EOH) / P(MIX) within predetermined ranges. 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 raw material 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 52°C or higher and 85°C or lower. It is even more preferably 53°C or higher and 80°C or lower, even more preferably 55°C or higher and 75°C or lower, and particularly preferably 60°C or higher and 72°C or lower. That is, the hydrolysis temperature is preferably 50 to 90°C, more preferably 52 to 85°C, even more preferably 53 to 80°C, even more preferably 55 to 75°C, and particularly preferably 60 to 72°C. The hydrolysis time is preferably 30 minutes to 10 hours, more preferably 40 minutes to 8 hours or lower. It is even more preferably 45 minutes to 7 hours, even more preferably 1 hour to 6 hours or lower, and particularly preferably 2 hours to 5 hours or lower. That is, the hydrolysis time is preferably 30 minutes to 10 hours, more preferably 40 minutes to 8 hours, even more preferably 45 minutes to 7 hours, even more preferably 1 hour to 6 hours or lower, and particularly preferably 2 hours to 5 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 15 parts by weight or more and 200 parts by weight or less, and even more preferably 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, react for a predetermined time (reaction step), and then maintain the temperature at the predetermined temperature (aging step). The aldehyde introduction temperature is preferably 5°C or higher and 35°C or lower, more preferably 10°C or higher and 30°C or lower, and even more preferably 15°C or higher and 25°C or lower. The time from the addition of the aldehyde to the start of temperature rise (temperature rise start time or reaction time) is preferably 130 minutes or higher and 500 minutes or lower, more preferably 150 minutes or higher and 420 minutes or lower, and even more preferably 180 minutes or higher and 360 minutes or lower. The temperature rise time is preferably 300 minutes or higher and 550 minutes or lower, more preferably 330 minutes or higher and 520 minutes or lower, and even more preferably 400 minutes or higher and 510 minutes or lower. Furthermore, when the temperature during aldehyde addition (charging) is less than 35°C, it is preferable to change the temperature increase rate (temperature increase rate 1) from the temperature during aldehyde addition to 35°C and the temperature increase rate (temperature increase rate 2) from 35°C to the holding temperature of the aging step. The temperature increase rate 1 is preferably 0.02°C / min or more and 0.08°C / min or less, and more preferably 0.03°C / min or more and 0.06°C / min or less. By setting the temperature increase rate 1 within the above range, the THF viscosity can be set within a predetermined range. The temperature increase rate 2 is preferably 0.10°C / min or more and 0.30°C / min or less, more preferably 0.12°C / min or more and 0.28°C / min or less, and even more preferably 0.15°C / min or more and 0.25°C / min or less. By setting the temperature increase rate 2 within the above range, the hydroxyl group amount equivalent wavenumber width and the hydroxyl group amount / acetyl group amount equivalent wavenumber 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, more preferably 2 hours or more and 4 hours or less, and even more preferably 2.5 hours or more and 3 hours or less. The retention temperature in the aging step is preferably 50° C. or more and 70° C. or less, and more preferably 55° C. or more and 65° C. or less. By setting the retention time and retention temperature as described above, the hydroxyl group amount equivalent wavenumber width and the hydroxyl group amount / acetyl group amount equivalent wavenumber 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, which includes 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, a polyvinyl acetal resin solution with even fewer particles can be produced. Examples of the filtration step include filtration using a metal mesh, ceramic filter, nonwoven fabric, or resin filter, and centrifugation.

[0043] The polyvinyl acetal resin of the present invention and a plasticizer can be used to form a resin composition for a ceramic green sheet. The resin composition for a ceramic green sheet may contain other 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 ceramic green sheets contains a plasticizer. Addition of the plasticizer can significantly improve the mechanical strength and flexibility of the resulting ceramic green sheets. Examples of the plasticizer 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-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 in lower limit, more preferably 8.5 parts by weight in lower limit, and preferably 18 parts by weight in upper limit, more preferably 13.5 parts by weight in 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, but if it is too low, the solubility required for kneading is difficult to exhibit. On the other hand, if it 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] Examples of the ceramic powder include powders of metal or nonmetal oxides or non-oxides used in ceramic production. These powders may be single compositions, compounds, or mixtures. The constituent elements of the metal oxides or non-oxides, both cations and anions, may be single elements or multiple elements, and may further contain additives added to improve the properties of the oxides or non-oxides. Specific examples include oxides, carbides, nitrides, borides, sulfides, etc. of 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, Ni, etc. Specific examples of oxide powders containing multiple metal elements, commonly referred to as double oxides, can be classified based on their crystal structure, such as NaNbO, which has a perovskite structure. ３ , SrZrO ３ , PbZrO ３ , SrTiO ３ , BaZrO ３ , PbTiO ３ , BaTiO ３ Examples of materials that have a spinel structure include MgAl ２ O ４ , ZnAl ２ O ４ , CoAl ２ O ４ , NiAl ２ O4, MgFe ２ O ４ Examples of materials with an ilmenite structure include MgTiO ３ , MnTiO ３ , FeTiO ３ As a material having a garnet structure, GdGa ５ O １２ , Y ６ Fe ５ O １２ Among these, the modified polyvinyl acetal resin of the present invention is BaTiO ３ It exhibits high properties compared to ceramic green sheets mixed with powder.

[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] The ceramic green sheet slurry is applied, followed by heating and drying to obtain a ceramic green sheet. A ceramic electronic component can be manufactured using the ceramic green sheet. For example, a ceramic electronic component can be manufactured by carrying out a step of applying an electrode layer paste to the surface of the ceramic green sheet, and a step of stacking the ceramic green sheets on which the electrode layers have been formed, thermocompression bonding the resulting laminate, 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 one aspect of the present invention.

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

[0059] In the method for producing a ceramic electronic component, the ceramic green sheets having electrode layers formed thereon are prepared as described above, and then ceramic green sheets having electrode layers formed thereon that are prepared in the same manner are stacked and thermocompression-bonded 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. Note that the thermocompression-bonding step and the steps of degreasing and firing the laminate are not particularly limited, and conventionally known methods can be used.

[0060] According to the present invention, it is possible to provide a polyvinyl acetal resin that can produce ceramic green sheets with little foreign matter in the resin and high mechanical strength, and can produce highly reliable multilayer ceramic capacitors. It is also possible to provide a method for producing a polyvinyl acetal resin solution using the polyvinyl acetal resin, a ceramic green sheet slurry, a ceramic green sheet, and a multilayer ceramic capacitor. In particular, the present invention can achieve high breaking strain and breaking stress even in thin ceramic green sheets. Furthermore, when producing a slurry for a ceramic green sheet, it is possible to achieve high dispersibility of inorganic fine particles (ceramic powder).

[0061] 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.

[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, degree of saponification 88.1 mol%) was added to 3000 g of pure water and dissolved by stirring at 90°C for approximately 2 hours. This 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 [temperature increase rate 1], and then increased from 35°C at a rate of 0.22°C / min [temperature increase rate 2] (temperature increase time 340 minutes). The temperature was maintained at 55°C for 2.5 hours to complete the reaction. The solution was then neutralized, washed with water, and dried in a conventional manner to obtain a white powder of polyvinyl acetal resin. The temperature increase time was the time from the start of the temperature increase until the temperature reached the maintained 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 the mixture was stirred and dissolved 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. 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] 1 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 the mixture was stirred and dissolved. Next, 100 parts by weight of barium titanate powder (BT01, manufactured by Sakai Chemical Industry Co., Ltd.) was added to the obtained solution, and the mixture was stirred for 180 minutes using a bead mill (Ready Mill, manufactured by Imex Co., Ltd.) to prepare an inorganic powder dispersion. [Preparation of Slurry for Ceramic Green Sheet] 100.1 parts by weight of the resin solution was added to 141 parts by weight of the obtained inorganic powder dispersion liquid, and the mixture was stirred for 90 minutes in a bead mill to obtain a slurry for a ceramic green sheet. 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, degree of saponification: 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 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 [Temperature Increase Rate 1], and then increased from 35°C at a rate of 0.22°C / min [Temperature Increase Rate 2] (340 minutes), and maintained at 55°C for 3.0 hours to complete the reaction. The mixture was then neutralized, washed, and dried in the usual manner to obtain a white powder of polyvinyl acetal resin. A ceramic green sheet was also prepared in the same manner as in Example 1.

[0066] Example 3: 260 g of polyvinyl alcohol resin (average degree of polymerization: 1700, degree of saponification: 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 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 [Temperature Increase Rate 1], and then increased from 35°C at a rate of 0.22°C / min [Temperature Increase Rate 2] (363 minutes), and maintained at 60°C for 3.0 hours to complete the reaction. The mixture was then neutralized, washed, and dried in the usual manner to obtain a white powder of polyvinyl acetal resin. A ceramic green sheet was also prepared in the same manner as in Example 1.

[0067] Example 4: 260 g of polyvinyl alcohol resin (average degree of polymerization: 1700, degree of saponification: 88.1 mol%) was added to 3000 g of pure water and dissolved by stirring at 90°C for approximately 2 hours. This 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 0.06°C / min [Temperature Increase Rate 1], and then increased from 35°C at a rate of 0.22°C / min [Temperature Increase Rate 2] (340 minutes), and maintained at 55°C for 3.0 hours to complete the reaction. The mixture was then neutralized, washed, and dried in the usual manner to obtain a white powder of polyvinyl acetal resin. A ceramic green sheet was also prepared in the same manner as in Example 1.

[0068] Example 5: 260 g of polyvinyl alcohol resin (average degree of polymerization: 1700, degree of saponification: 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 180 minutes, the temperature was increased to 35°C at a rate of 0.06°C / min [Temperature Increase Rate 1], and then increased from 35°C at a rate of 0.22°C / min [Temperature Increase Rate 2] (340 minutes), and maintained at 55°C for 3.0 hours to complete the reaction. The mixture was then neutralized, washed, and dried in the usual manner to obtain a white powder of polyvinyl acetal resin. A ceramic green sheet was also prepared in the same manner as in Example 1.

[0069] Example 6: 260 g of polyvinyl alcohol resin (average degree of polymerization: 1700, degree of saponification: 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 held 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 0.06°C / min [Temperature Increase Rate 1], and then increased from 35°C at a rate of 0.22°C / min [Temperature Increase Rate 2] (340 minutes), and the temperature was maintained at 55°C for 3.0 hours to complete the reaction. The mixture was then neutralized, washed, and dried in the usual manner to obtain a white powder of polyvinyl acetal resin. A ceramic green sheet was also prepared in the same manner as in Example 1.

[0070] Example 7: 260 g of polyvinyl alcohol resin (average degree of polymerization: 1700, degree of saponification: 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 180 minutes, the temperature was increased to 35°C at a rate of 0.06°C / min [Temperature Increase Rate 1], and then increased from 35°C at a rate of 0.22°C / min [Temperature Increase Rate 2] (363 minutes). The reaction was completed by maintaining the temperature at 60°C for 3.5 hours. The mixture was then neutralized, washed, and dried in the usual manner to obtain a white powder of polyvinyl acetal resin. A ceramic green sheet was also prepared in the same manner as in Example 1.

[0071] Example 8: 260 g of polyvinyl alcohol resin (average degree of polymerization: 1700, degree of saponification: 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 70°C, and 200 g of 35 wt% hydrochloric acid was added and held 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 0.06°C / min [Temperature Increase Rate 1], and then increased from 35°C at a rate of 0.22°C / min [Temperature Increase Rate 2] (363 minutes), and the mixture was held at 60°C for 3.5 hours to complete the reaction. The mixture was then neutralized, washed, and dried in the usual manner to obtain a white powder of polyvinyl acetal resin. A ceramic green sheet was also prepared in the same manner as in Example 1.

[0072] Example 9: 260 g of polyvinyl alcohol resin (average degree of polymerization: 1700, degree of saponification: 88.1 mol%) was added to 3000 g of pure water and dissolved by stirring at 90°C for approximately 2 hours. This solution was cooled to 80°C, and 200 g of 35 wt% hydrochloric acid was added and held 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 0.06°C / min [Temperature Increase Rate 1], and then increased from 35°C at a rate of 0.22°C / min [Temperature Increase Rate 2] (363 minutes), and the mixture was held at 60°C for 3.0 hours to complete the reaction. The mixture was then neutralized, washed, and dried in the usual manner to obtain a white powder of polyvinyl acetal resin. A ceramic green sheet was also prepared in the same manner as in Example 1.

[0073] Example 10: 260 g of polyvinyl alcohol resin (average degree of polymerization: 1700, degree of saponification: 88.1 mol%) was added to 3000 g of pure water and dissolved by stirring at 90°C for approximately 2 hours. 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 180 minutes, the temperature was increased to 35°C at a rate of 0.06°C / min [Temperature Increase Rate 1], and then increased from 35°C at a rate of 0.15°C / min [Temperature Increase Rate 2] (420 minutes), and maintained at 60°C for 3.0 hours to complete the reaction. The mixture was then neutralized, washed, and dried in the usual manner to obtain a white powder of polyvinyl acetal resin. A ceramic green sheet was also prepared in the same manner as in Example 1.

[0074] Example 11: 260 g of polyvinyl alcohol resin (average degree of polymerization: 1700, degree of saponification: 88.1 mol%) was added to 3000 g of pure water and dissolved by stirring at 90°C for approximately 2 hours. 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 0.06°C / min [Temperature Increase Rate 1], and then increased from 35°C at a rate of 0.22°C / min [Temperature Increase Rate 2] (340 minutes), and maintained at 55°C for 3.0 hours to complete the reaction. The mixture was then neutralized, washed, and dried in the usual manner to obtain a white powder of polyvinyl acetal resin. A ceramic green sheet was also prepared in the same manner as in Example 1.

[0075] Example 12: 260 g of polyvinyl alcohol resin (average degree of polymerization: 1700, degree of saponification: 88.1 mol%) was added to 3000 g of pure water and dissolved by stirring at 90°C for approximately 2 hours. This solution was cooled to 85°C, and 200 g of 35 wt% hydrochloric acid was added and held 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 0.06°C / min [Temperature Increase Rate 1], and then increased from 35°C at a rate of 0.22°C / min [Temperature Increase Rate 2] (340 minutes). The temperature was then increased to 55°C for 2.5 hours to complete the reaction. The mixture was then neutralized, washed, and dried in the usual manner to obtain a white powder of polyvinyl acetal resin. A ceramic green sheet was also prepared in the same manner as in Example 1.

[0076] Example 13: 260 g of polyvinyl alcohol resin (average degree of polymerization: 3300, degree of saponification: 88.1 mol%) was added to 5000 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 3.5 hours. The solution was then cooled to 15°C, and 18 g of acetaldehyde and 140 g of n-butylaldehyde were added. After 180 minutes, the temperature was increased to 35°C at a rate of 0.06°C / min [Temperature Increase Rate 1], and then increased from 35°C at a rate of 0.22°C / min [Temperature Increase Rate 2] (temperature increase time: 426 minutes). The temperature was then maintained at 55°C for 3 hours to complete the reaction. The mixture was then neutralized, washed, and dried in the usual manner to obtain a white powder of polyvinyl acetal resin. A ceramic green sheet was also prepared in the same manner as in Example 1.

[0077] Example 14 130 g of a first polyvinyl alcohol resin (average degree of polymerization 1000, degree of saponification 88.1 mol%) and 130 g of a second polyvinyl alcohol resin (average degree of polymerization 650, degree of saponification 88.1 mol%) were 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 hydrochloric acid with a concentration of 35 wt% was added and maintained for 0.4 hours. The solution was then cooled to 10°C, and 126 g of n-butyl aldehyde was added thereto. Thereafter, after 180 minutes, the temperature was increased to 35°C at a temperature increase rate [temperature increase rate 1] of 0.06°C / min, and the temperature was increased from 35°C at a temperature increase rate [temperature increase rate 2] of 0.26°C / min (temperature increase time 494 minutes). The reaction was completed by maintaining the temperature at 55°C for 2.5 hours, and the mixture was 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.

[0078] Example 15: 260 g of polyvinyl alcohol resin (average degree of polymerization: 4000, degree of saponification: 88.1 mol%) was added to 7000 g of pure water and dissolved by stirring at 90°C for approximately 2 hours. This solution was cooled to 60°C, and 200 g of 35 wt% hydrochloric acid was added and maintained for 3 hours. The solution was then cooled to 30°C, and 144 g of n-butyl aldehyde was added. After 360 minutes, the temperature was increased to 35°C at a rate of 0.03°C / min [Temperature Increase Rate 1], and then increased from 35°C at a rate of 0.1°C / min [Temperature Increase Rate 2] (367 minutes). The temperature was then maintained at 55°C for 3 hours to complete the reaction. The mixture was then neutralized, washed, and dried in the usual manner to obtain a white powder of polyvinyl acetal resin. A ceramic green sheet was also prepared in the same manner as in Example 1.

[0079] Comparative Example 1: 3100 g of pure water was added to 300 g of polyvinyl alcohol resin (average degree of polymerization: 1700, degree of saponification: 99.2 mol%) and the mixture was stirred at 90°C for approximately 2 hours to dissolve the resin. The solution was cooled to 40°C, and 200 g of hydrochloric acid with a concentration of 35 wt% and 160 g of n-butyl aldehyde were added to the solution. Furthermore, a ceramic green sheet was produced in the same manner as in Example 1.

[0080] Comparative Example 2: 260 g of polyvinyl alcohol resin (average degree of polymerization: 1700, degree of saponification: 99.2 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 20°C, and 200 g of 35 wt% hydrochloric acid and 147 g of n-butyl aldehyde were added to the solution. Thirty minutes after the addition, the temperature was increased at a rate of 0.22°C / min (heating time: 91 minutes), and the mixture was maintained at 40°C for 3 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. A ceramic green sheet was also prepared in the same manner as in Example 1.

[0081] Comparative Example 3: 260 g of polyvinyl alcohol resin (average degree of polymerization: 1700, degree of saponification: 99.1 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 20°C, and 200 g of 35 wt% hydrochloric acid and 147 g of n-butyl aldehyde were added. Sixty minutes after the addition, the temperature was increased at a rate of 0.3°C / min (heating time: 133 minutes). The mixture was maintained at 60°C for 2.2 hours to carry out an acetalization reaction. The mixture was then neutralized, washed, and dried in the usual manner to obtain a white powder of polyvinyl acetal resin. A ceramic green sheet was also prepared in the same manner as in Example 1.

[0082] Comparative Example 4: 3100 g of pure water was added to 300 g of polyvinyl alcohol resin (average degree of polymerization: 1700, degree of saponification: 98.7 mol%) and dissolved by stirring at 90°C for approximately 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-butyl aldehyde were added to the mixture. The mixture was then held at 40°C for 3 hours to carry out an acetalization reaction. The mixture was then neutralized, washed with water, and dried using standard methods to obtain a white powder of polyvinyl acetal resin. A ceramic green sheet was also prepared in the same manner as in Example 1.

[0083] Comparative Example 5: 260 g of polyvinyl alcohol resin (average degree of polymerization: 1700, degree of saponification: 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 88°C, and 200 g of 35 wt% hydrochloric acid was added and maintained for 2 hours. The mixture was then cooled to 20°C, and 145 g of n-butyl aldehyde was added. After 550 minutes, the mixture was heated to 35°C at a rate of 0.3°C / min [heating rate 1], then heated from 35°C at a rate of 0.3°C / min [heating rate 2] (heating time: 133 minutes), and maintained at 60°C for 2.2 hours to complete the reaction. The mixture was then neutralized, washed, and dried in the usual manner to obtain a white powder of polyvinyl acetal resin. Ceramic green sheets were also prepared in the same manner as in Example 1.

[0084] Comparative Example 6: 260 g of polyvinyl alcohol resin (average degree of polymerization: 800, degree of saponification: 93.5 mol%) was added to 3,000 g of pure water and stirred at 90°C for approximately 2 hours to dissolve. This solution was cooled to 45°C, and 200 g of 35 wt% hydrochloric acid was added and held for 0.3 hours. The solution was then cooled to 4°C, and 100 g of n-butyl aldehyde was added. After 120 minutes, the temperature was increased to 36°C at a rate of 0.4°C / min [Temperature Increase Rate 1], and then increased from 35°C at a rate of 0.4°C / min [Temperature Increase Rate 2] (heat increase time: 80 minutes). The temperature was then held at 36°C for 6 hours to complete the reaction. The mixture was then neutralized, washed, and dried in the usual manner to obtain a white powder of polyvinyl acetal resin. Ceramic green sheets were also prepared in the same manner as in Example 1.

[0085] Comparative Example 7: 260 g of polyvinyl alcohol resin (average degree of polymerization: 800, degree of saponification: 98.0 mol%) was added to 3,000 g of pure water and stirred at 90°C for approximately 2 hours to dissolve. This solution was cooled to 20°C, and 200 g of 35 wt% hydrochloric acid and 175 g of n-butyl aldehyde were added. After 60 minutes, the mixture was heated to 72°C at a rate of 0.09°C / min [heating rate 1], then heated from 35°C at a rate of 0.32°C / min [heating rate 2] (heating time: 282 minutes). The mixture was held at 72°C for 1 hour to complete the reaction. The mixture was then neutralized, washed, and dried in the usual manner to obtain a white powder of polyvinyl acetal resin. A ceramic green sheet was also prepared in the same manner as in Example 1.

[0086] Comparative Example 8: 260 g of polyvinyl alcohol resin (average degree of polymerization: 1700, degree of saponification: 77.0 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 30°C, and 200 g of 35 wt% hydrochloric acid was added and maintained for 12 hours. The solution was then cooled to 15°C, and 115 g of n-butyl aldehyde was added. After 60 minutes, the temperature was increased to 45°C at a rate of 0.08°C / min [Temperature Increase Rate 1], and then increased from 35°C at a rate of 0.03°C / min [Temperature Increase Rate 2] (heat increase time: 583 minutes). The mixture was maintained at 45°C for 3 hours to complete the reaction. The mixture was then neutralized, washed, and dried in the usual manner to obtain a white powder of polyvinyl acetal resin. Ceramic green sheets were also prepared in the same manner as in Example 1.

[0087] (Evaluation) The polyvinyl acetal resins and ceramic green sheets obtained in the Examples and Comparative Examples were evaluated as follows. The results are shown in Tables 1 and 2.

[0088] (1) Evaluation of Polyvinyl Acetal Resin (1-1) Amount of Acetal Group, Amount of Hydroxyl Group, and Amount of Acetyl Group The obtained polyvinyl acetal resin was measured using an AV400 spectrometer (manufactured by Bruker). １ H-NMR measurement was carried out to calculate the amount of acetal groups, hydroxyl groups, and acetyl groups. ６ The solution was dissolved in water to a concentration of 1.6% by weight to prepare a measurement solution. １ H-NMR measurements were carried out at 80°C.

[0089] (1-2) IR absorption spectrum The obtained polyvinyl acetal resin was dissolved in a mixed solution of ethanol and toluene in a weight ratio of 1:1, and then coated on a PET film. －１ The film thickness of the measurement sample was adjusted so that the minimum transmittance of the peak appearing around 1000 nm was 22%, 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 (FT-720, manufactured by HORIBA Co., Ltd.) 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 data corrected so that the transmittances at both ends of the peak were 100%, to measure the minimum transmittance X, the transmittance a that satisfies [100-(100-X) / 2], and the wavenumbers A and B that indicate the transmittance a (the wavenumber on the low wavenumber side is A, and the wavenumber on the high wavenumber side is B). １ Using the amount of hydroxyl groups determined by H-NMR measurement, the hydroxyl group amount converted wavenumber width (cm －１ / mol%)=[(B−A) / 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=[(B−A) / amount of hydroxyl groups / acetyl groups] was calculated.

[0090] (1-3) Particles The obtained polyvinyl acetal resin was added to an ethanol-toluene (ethanol:toluene = 50:50) mixed solvent so that the solids concentration of the polyvinyl acetal resin was 0.2% by mass, and the mixture was stirred and dissolved at 60 rpm for 24 hours using a mix rotor to prepare an ethanol-toluene mixed solution. For 10 mL of the obtained 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 Corporation, KS-42C, KE-40B1), and the average value was designated as D1. Separately, for the ethanol-toluene (ethanol:toluene = 50:50) mixed solvent used as the solvent for the ethanol-toluene mixed solution, the number of particles was measured three times using a particle counter (manufactured by RION Corporation, KS-42C, KE-40B1), and the average value was designated as C1. From the obtained C1 and D1, P(MIX) was calculated using the following formula. P(MIX)=D1-C1

[0091] Similarly, the obtained polyvinyl acetal resin was added to ethanol so that the solids concentration of the polyvinyl acetal resin was 0.2% by mass, and the mixture was stirred at 60 rpm using a mix rotor for 24 hours to dissolve the resin, 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 Corporation, KS-42C, KE-40B1), and the average value was designated as D2. Separately, the number of particles of the ethanol used as the solvent for the ethanol solution was measured three times using a particle counter (manufactured by RION Corporation, KS-42C, KE-40B1), and the average value was designated as C2. From the obtained C2 and D2, P(EOH) was calculated using the following formula. Furthermore, P(EOH) / P(MIX) was calculated from the obtained P(MIX) and P(EOH). P(EOH) = D2 - C2

[0092] (1-4) Viscosity Measurement The obtained polyvinyl acetal resin was dissolved in a 1:1 weight ratio ethanol / toluene mixed solution to a concentration of 5% by mass to prepare a sample for viscosity measurement. The viscosity of the obtained sample for viscosity measurement was measured using a Brookfield viscometer at a solution temperature of 20°C. The Brookfield viscometer used was a TVB-10 viscometer (manufactured by Toki Sangyo Co., Ltd.), and the rotation speed and rotor were as follows: Examples 1 to 12, Comparative Examples 1 to 4: rotation speed 30 rpm, SPINDLE No. M1

[0093] (1-5) Measurement of z-average molecular weight [Mz(THF), Mz(NMP)] The obtained polyvinyl acetal resin was dissolved in tetrahydrofuran (THF) 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 0.35 mL / min using a GPC apparatus HLC-8420 (manufactured by Tosoh Corporation), THF as the mobile phase, a Bryce-type double-pass refractive index detector (manufactured by Tosoh Corporation) as the detector, and a TSKgel Super HZM-H column (manufactured by Tosoh Corporation). The obtained measurement results were calibrated using a molecular weight calibration curve prepared using monodisperse polystyrene standard samples 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 apparatus GPC-101 (Shodex Corporation), NMP as the mobile phase, a differential refractive index detector RI-715 (Shodex Corporation) as the detector, and an LF-804 (Shodex Corporation) as the column. The obtained measurement results were calibrated using a molecular weight calibration curve prepared with monodisperse polystyrene standard samples 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 above viscosity measurement, "[THF viscosity / Mz(NMP)] x 10,000" was calculated.

[0094] (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

[0095] (2-2) Stress at Break and Strain at Break The obtained ceramic green sheet was cut into a size of 5 cm x 1 cm to prepare a test piece. Using a tensile tester (Shimadzu Corporation, AUTOGRAPH AGS-J), the sheet was pulled at a pulling rate of 500% / min 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 the 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: 34 MPa 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%

[0096]

[0097]

[0098] 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, and 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 The polyvinyl acetal resin has a hydroxyl group amount converted wavenumber width of 8.31 or more, which is calculated by the formula (1) using the amount of hydroxyl groups measured by H-NMR. －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 molecules / 10 ml.

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

4. The polyvinyl acetal resin according to any one of claims 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 the mobile phase and Mz(NMP) is the z-average molecular weight obtained using NMP as the mobile phase.

5. A method for producing a polyvinyl acetal resin solution using the polyvinyl acetal resin according to any one of claims 1 to 4, 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.

6. A slurry for ceramic green sheets, comprising the polyvinyl acetal resin according to any one of claims 1 to 4, 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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