Polyvinyl Acetal Resin

Abstract

The present invention provides a polyvinyl acetal resin that has exceptional dispersibility and that enables production of a molded body having high mechanical strength. The present invention is a polyvinyl acetal resin having water absorption per unit area ranging from 2 mg / cm2 to 50 mg / cm2 (inclusive) when molded into a 10-μm-thick film.

Description

[Technical field]

[0001] The present invention relates to a polyvinyl acetal resin which has excellent dispersibility and from which molded articles having high mechanical strength can be produced. [Background technology]

[0002] Polyvinyl acetal resins are excellent in toughness, film-forming properties, dispersibility of inorganic powders such as pigments and organic powders, adhesion to coating surfaces, and the like, and therefore are used in applications such as ceramic green sheets constituting multilayer ceramic capacitors, conductive pastes, inks, paints, baking enamels, wash primers, and the like.

[0003] Among them, multilayer ceramic capacitors are generally manufactured through the following steps. First, a ceramic raw material powder is added to a binder resin such as polyvinyl butyral resin, and the mixture is mixed uniformly to obtain a slurry composition. The obtained slurry composition is applied to a support surface that has been subjected to a release treatment. The volatile matter such as the solvent is removed by heating or the like, and then the sheet is peeled off from the support to obtain a ceramic green sheet. Next, a conductive paste containing polyvinyl butyral resin or the like as a binder resin is applied to the obtained ceramic green sheet by screen printing or the like, and multiple sheets are alternately stacked on top of each other and heated and pressed to produce a laminate. Furthermore, after a degreasing treatment, a multilayer ceramic capacitor is obtained by sintering external electrodes on the end faces of the ceramic sintered product obtained by sintering.

[0004] Regarding such binder resins, Patent Document 1 discloses that metal corrosion of peripheral devices can be prevented by using a polyvinyl acetal resin obtained by generating acetic acid from sodium acetate remaining in polyvinyl alcohol and acetalizing the polyvinyl alcohol using the acetic acid thus obtained as a catalyst. Furthermore, Patent Document 2 discloses that the flexibility and heat-sealing properties of the resulting sheet can be improved by using a polyvinyl acetal resin obtained by acetalizing a specific modified polyvinyl alcohol with acetaldehyde and butylaldehyde. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 3043106 [Patent Document 2] Patent No. 3110146 Summary of the Invention [Problem to be solved by the invention]

[0006] However, for example, magnetic powders such as ferrites have poor dispersibility, and when the polyvinyl acetal resins described in Patent Documents 1 and 2 are used as binder resins, there is room for improvement in dispersibility and dispersion stability, such as the magnetic powder not being sufficiently dispersed in the slurry composition, settling over time, etc. In addition, when such a slurry composition is used, the mechanical strength of the obtained sheet is low, and problems may occur when processing the molded sheet.

[0007] An object of the present invention is to provide a polyvinyl acetal resin which has excellent dispersibility and from which a molded article having high mechanical strength can be produced. [Means for solving the problem]

[0008] The present invention has a water absorption per unit area of ​​2 mg / cm when molded into a film with a thickness of 10 μm. 2 More than 50mg / cm 2 The following is a polyvinyl acetal resin. The present invention will be described in detail below.

[0009] As a result of extensive research, the inventors have found that by adjusting the water absorption per unit area under certain conditions, it is possible to improve the dispersibility of poorly dispersible substances such as magnetic powders and to produce a film having high mechanical strength, and have completed the present invention. Furthermore, the present invention can exhibit high adhesion to substrates.

[0010] The polyvinyl acetal resin of the present invention has a water absorption per unit area of ​​2 mg / cm when molded into a film having a thickness of 10 μm. 2 More than 50mg / cm 2 When the water absorption amount per unit area is within the above range, the dispersibility of ferrite is excellent and the strength of the obtained sheet can be improved. The preferable lower limit of the water absorption amount per unit area is 3 mg / cm. 2 , the preferred upper limit is 40 mg / cm 2 and a more preferred upper limit is 30 mg / cm 2 It is.

[0011] The water absorption amount per unit area can be calculated by the method described below. Specifically, the polyvinyl acetal resin of the present invention is molded into a film having a thickness of 10 μm, dried at 70° C. for 3 hours, and then left in an environment with a temperature of 20° C. and a humidity of 55% for 1 hour or more, and the weight A of the film is measured. Next, the main surface of the molded and dried film is exposed to water vapor in hot water at a temperature of 50° C. Thereafter, when water droplets are observed on the surface of the film, the exposure to water vapor is stopped, and the weight B of the molded film is measured. The amount of water absorption is calculated by subtracting weight A from weight B. The amount of water absorption per unit area is calculated by dividing the amount of water absorption by the exposed area. In this specification, the state in which water droplets are observed on the surface of the film is regarded as the amount of saturated water vapor.

[0012] The polyvinyl acetal resin of the present invention preferably has a water absorption rate of 0.2 mg / min or more and 4.2 mg / min or less under the above-mentioned conditions for measuring the amount of water absorption per unit area. By having the water absorption rate within the above range, a strong sheet strength can be obtained. The more preferred lower limit of the water absorption rate is 0.3 mg / min, and the more preferred upper limit is 4.0 mg / min. The water absorption rate can be measured in the same manner as the water absorption amount per unit area. Specifically, the time from the start of water vapor exposure to the end of water vapor exposure is measured, and the water absorption rate is calculated by dividing the film weight per unit area by the exposure time.

[0013] In the present invention, by adjusting the saponification degree, average polymerization degree, and half-width of the hydroxyl group of the raw material polyvinyl alcohol, as well as the acetalization conditions, etc., it is possible to produce a polyvinyl acetal resin having a water absorption amount per unit area within a predetermined range when formed into a film having a thickness of 10 μm. In addition, by adjusting the amount of hydroxyl groups in the polyvinyl acetal resin, the half-width of the hydroxyl group quantified by IR measurement, and the half-width of the hydroxyl group converted into mole percent quantified by NMR measurement and IR measurement, it is also possible to produce a polyvinyl acetal resin having a water absorption amount per unit area within a predetermined range when formed into a film having a thickness of 10 μm.

[0014] The polyvinyl acetal resin of the present invention preferably has at least a structural unit having a hydroxyl group represented by the following formula (1), a structural unit having an acetal group represented by the following formula (2), and a structural unit having an acetyl group represented by the following formula (3).

[0015] [ka]

[0016] In the above formula (2), R 1 represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms.

[0017] In the above formula (2), R 1When 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. Among these, a methyl group and an n-propyl group are preferable.

[0018] In the polyvinyl acetal resin of the present invention, the content of the structural unit having a hydroxyl group represented by the above formula (1) (hereinafter also referred to as "hydroxyl group amount") is preferably 35 mol% in lower limit and 85 mol% in upper limit. When the hydroxyl group amount is equal to or more than the above lower limit, the water absorption amount per unit area can be easily adjusted within a predetermined range. As a result, the slurry composition obtained by using the polyvinyl acetal resin of the present invention has excellent dispersibility and dispersion stability. In addition, the mechanical strength and substrate adhesion of the obtained molded body are improved. The amount of hydroxyl groups is, for example, 13 It can be measured by C-NMR.

[0019] The polyvinyl acetal resin of the present invention has a preferred lower limit of the half-value width of the hydroxyl group as determined by IR measurement of 280 cm -1 , and a more preferable lower limit is 290 cm -1 , with a preferred upper limit of 420 cm -1 , and a more preferable upper limit of 400 cm -1 By setting the content within the above range, the water absorption per unit area can be easily adjusted to a predetermined range. As a result, the slurry composition obtained by using the polyvinyl acetal resin of the present invention has excellent dispersibility and dispersion stability. In addition, the mechanical strength and substrate adhesion of the obtained molded body are improved.

[0020] The polyvinyl acetal resin has a half-width of 0.01 mol % / cm of hydroxyl groups as determined by NMR and IR measurements. -1 0.30 mol % / cm or more -1By setting the content within the above range, it is possible to obtain a ceramic green sheet that has high mechanical strength and is less susceptible to poor appearance after cutting and dimensional change after drying. In addition, the half-width of the hydroxyl group in terms of mole percent is preferably 0.05 mole % / cm or less. -1 More than 0.290 mol% / cm -1 It is more preferable that: The IR measurement is a measurement of an absorption spectrum by infrared absorption spectroscopy, and can be performed, for example, by an IR spectrometer. The half-width of the hydroxyl group in terms of mole percent was 3500 cm by IR measurement. -1 The half-width of the hydroxyl group is measured from the peak width at half the height of the peak that appears near the peak, and then the amount of hydroxyl groups is measured by NMR measurement, and the amount of hydroxyl groups is divided by the half-width of the hydroxyl group to calculate the amount of hydroxyl groups.

[0021] In the polyvinyl acetal resin of the present invention, the content of the structural unit having the acetal group represented by the above formula (2) (hereinafter also referred to as the "acetal group amount") is preferably 1 mol % in lower limit and 50 mol % in upper limit. When the amount of acetal groups is within the above range, the toughness of the resin can be increased. The more preferred lower limit of the acetal group amount is 2 mol %, and the more preferred upper limit is 45 mol %. In this specification, the method for calculating the amount of acetal groups is to count the two acetalized hydroxyl groups, since the acetal groups of the polyvinyl acetal resin are obtained by acetalizing two hydroxyl groups. The amount of acetal groups can be measured, for example, by NMR.

[0022] R in the above formula (2) 1 is preferably a methyl group or a propyl group. In the polyvinyl acetal resin of the present invention, R 1 When is a methyl group, the amount of acetal groups (amount of acetoacetal groups) is preferably 1 mol % or more and 50 mol % or less. In the polyvinyl acetal resin of the present invention, R 1 When the propyl group is used, the amount of acetal groups (amount of butyral groups) is preferably 1 mol % or more and 10 mol % or less. By keeping it within the above range, a high water absorption amount can be obtained.

[0023] In the polyvinyl acetal resin of the present invention, the content of the structural unit having an acetyl group represented by the above formula (3) (hereinafter also referred to as "acetyl group amount") is preferably 1 mol % in lower limit and 20 mol % in upper limit. When the amount of acetyl groups is within the above range, the toughness of the resin can be increased. The lower limit of the amount of acetyl groups is more preferably 2 mol %, and the upper limit thereof is more preferably 15 mol %. The amount of acetyl groups can be measured, for example, by NMR.

[0024] The polyvinyl acetal resin of the present invention may have a structural unit having an acid-modifying group. Examples of the acid-modified group include a carboxyl group, a sulfonic acid group, a maleic acid group, a sulfinic acid group, a sulfenic acid group, a phosphoric acid group, a phosphonic acid group, an amino group, and salts thereof. Of these, the carboxyl group is preferred. The modified polyvinyl acetal resin has a structural unit having an acid-modified group, and thus the compatibility with epoxy resins is improved, thereby enabling the realization of high mechanical strength.

[0025] The structural unit having the acid-modified group may have a structure in which the acid-modified group is directly bonded to a carbon constituting the main chain as a side chain, or may have a structure in which the acid-modified group is bonded to a carbon constituting the main chain via an alkylene group.

[0026] The structural unit having the acid-modified group may have a three-dimensional structure in which two acid-modified groups are bonded to the same carbon constituting the main chain, or a three-dimensional structure in which one acid-modified group is bonded to the carbon constituting the main chain. In addition, it may have a three-dimensional structure in which an acid-modified group is bonded to each of the adjacent carbons constituting the main chain, or a three-dimensional structure in which an acid-modified group is bonded to only one of the adjacent carbons constituting the main chain. Among them, it is preferable to have a three-dimensional structure in which two acid-modified groups are bonded to the same carbon constituting the main chain, or a three-dimensional structure in which an acid-modified group is bonded to each of the adjacent carbons constituting the main chain. Furthermore, it is preferable to have a three-dimensional structure in which two acid-modified groups are bonded to the same carbon constituting the main chain, since the steric hindrance can be increased to widen the network structure of the cured product obtained by combining with an epoxy resin, and as a result, the flexibility of the obtained cured product can be improved.

[0027] The structural unit having the acid-modified group may have a stereostructure in which the acid-modified groups are bonded in the same direction to the carbons constituting the main chain, that is, an isotactic configuration, or in which the acid-modified groups are bonded alternately to the carbons constituting the main chain on opposite sides, that is, a syndiotactic configuration.Furthermore, the structural unit may have a stereostructure in which the acid-modified groups are bonded randomly, that is, an atactic configuration.

[0028] When the structural unit having the acid-modified group has a structure in which the acid-modified group is bonded to a carbon constituting the main chain via an alkylene group, the alkylene group is preferably an alkylene group having 1 to 10 carbon atoms, more preferably an alkylene group having 1 to 5 carbon atoms, and even more preferably an alkylene group having 1 to 3 carbon atoms.

[0029] Examples of the alkylene group having 1 to 10 carbon atoms include linear alkylene groups, branched alkylene groups, and cyclic alkylene groups. Examples of the linear alkylene group include a methylene group, a vinylene group, an n-propylene group, a tetramethylene group, a pentamethylene group, a hexamethylene group, an octamethylene group, and a decamethylene group. Examples of the branched alkylene group include a methylmethylene group, a methylethylene group, a 1-methylpentylene group, and a 1,4-dimethylbutylene group. Examples of the cyclic alkylene group include a cyclopropylene group, a cyclobutylene group, and a cyclohexylene group. Of these, linear alkylene groups are preferred, methylene groups, vinylene groups and n-propylene groups are more preferred, and methylene groups and vinylene groups are even more preferred.

[0030] The preferred lower limit of the average polymerization degree of the polyvinyl acetal resin of the present invention is 200, and the preferred upper limit is 5000. When the average polymerization degree is within the above range, the mechanical strength of the resulting coating film can be sufficiently increased. A more preferred lower limit of the average polymerization degree is 300, and a more preferred upper limit is 4,000.

[0031] Examples of a method for producing the polyvinyl acetal resin of the present invention include a method in which a polyvinyl acetate resin obtained by polymerizing a monomer such as vinyl acetate is saponified by adding an acid or an alkali to the polyvinyl alcohol resin, and then the polyvinyl alcohol resin is acetalized. In the present invention, a polyvinyl alcohol having a saponification degree, an average polymerization degree, and a half-width of a hydroxyl group within a predetermined range is used and acetalized, whereby a polyvinyl acetal resin having a water absorption per unit area within a predetermined range when formed into a film having a thickness of 10 μm can be produced. For example, the half-width of a hydroxyl group of the above polyvinyl alcohol resin is 340 cm. -1 More than 380cm -1 It is preferable that: The polyvinyl alcohol resin preferably has an average degree of polymerization of 200 or more and 5000 or less, and a degree of saponification of 70 mol % or more and 99.9 mol % or less. In particular, the polyvinyl acetal resin of the present invention is preferably an acetalized product of a polyvinyl alcohol resin having a saponification degree of 75 mol % or more. The specific polyvinyl alcohol as described above can be prepared, for example, by a method of selecting a polyvinyl alcohol by measuring the physical properties of multiple types of polyvinyl alcohol, a method of selecting a polyvinyl alcohol by referring to the physical properties of commercially available polyvinyl alcohol, or a method of synthesizing the polyvinyl alcohol by adjusting the physical property values ​​in a specified process.

[0032] The acetalization can be carried out by a known method, and is preferably carried out in an aqueous solvent, in a mixed solvent of water and an organic solvent compatible with water, or in 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 may 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.

[0033] 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 them, hydrochloric acid, nitric acid, and sulfuric acid are preferred, and hydrochloric acid is particularly preferred.

[0034] The aldehyde used in the acetalization reaction may be an aldehyde having a chain aliphatic group, a cyclic aliphatic group, or an aromatic group having 1 to 10 carbon atoms. Any known aldehyde may be used as the aldehyde. The aldehyde used in the acetalization reaction is not particularly limited, and may be, for example, an aliphatic aldehyde, an aromatic aldehyde, or the like. Examples of the aliphatic aldehyde include formaldehyde, acetaldehyde, propionaldehyde, n-butyraldehyde, isobutyraldehyde, n-valeraldehyde, n-hexylaldehyde, 2-ethylbutyraldehyde, 2-ethylhexylaldehyde, n-heptylaldehyde, n-octylaldehyde, octylaldehyde, n-nonylaldehyde, n-decylaldehyde, and amylaldehyde. Examples of the aromatic aldehyde include aromatic aldehydes such as benzaldehyde, cinnamaldehyde, 2-methylbenzaldehyde, 3-methylbenzaldehyde, 4-methylbenzaldehyde, p-hydroxybenzaldehyde, m-hydroxybenzaldehyde, phenylacetaldehyde, and β-phenylpropionaldehyde. In addition, cyclic polymers such as paraldehyde and metaldehyde can also be used. These aldehydes may be used alone or in combination of two or more. Among them, preferred aldehydes are formaldehyde, acetaldehyde, butylaldehyde, 2-ethylhexylaldehyde, n-nonylaldehyde, and paraldehyde, which have excellent acetalization reactivity and can provide sufficient internal plasticizing effect to the resin produced, thereby imparting good flexibility. In addition, more preferred are formaldehyde, acetaldehyde, butylaldehyde, and paraldehyde, which can provide an adhesive composition that is particularly excellent in impact resistance and adhesion to metals.

[0035] The amount of the aldehyde to be added can be appropriately set according to the amount of acetal groups in the target polyvinyl acetal resin. In particular, it is preferable to add 60 to 95 mol%, preferably 65 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.

[0036] A slurry composition can be prepared by mixing the polyvinyl acetal resin of the present invention with a magnetic powder, a solvent, etc. A slurry composition containing the polyvinyl acetal resin of the present invention, a magnetic powder, and a solvent also constitutes the present invention. The content of the polyvinyl acetal resin of the present invention in the slurry composition of the present invention is preferably 20% by weight as a lower limit, more preferably 25% by weight as a lower limit, preferably 65% ​​by weight as an upper limit, more preferably 60% by weight as an upper limit.

[0037] The slurry composition of the present invention contains a magnetic powder. Examples of the magnetic powder include metal particles, metal oxide particles, and metal nitride particles.

[0038] Examples of metal particles used as the magnetic powder include particles made of iron, cobalt, nickel, and alloys containing these metals. Examples of the alloy include Fe-Ni, Fe-Co, Fe-Cr, Fe-Si, Fe-Al, Fe-Cr-Si, Fe-Cr-Al, Fe-Al-Si, and Fe-Pt.

[0039] The metal oxide is preferably ferrite, specifically, for example, MnFe 2 O 4 , CoFe 2 O 4 , NiFe 2 O 4 , CuFe 2 O 4 , ZnFe 2 O 4 , MgFe 2 O 4 , Fe 3 O 4 , MnFe 2 O 4 , Cu-Zn ferrite, Ni-Zn ferrite, Mn-Zn ferrite, Ba ferrite, Ni-Cu-Zn ferrite, etc. can be used.

[0040] The metal nitride may be, for example, Fe. 2 N, Fe 3 N, Fe 4 N, Fe 16 N 2 , Sm 2 Fe 17 N 3 etc.

[0041] Examples of the shape of the magnetic powder include spherical, ellipsoidal, disc, needle-like, rod-like, flat, tetrapod-like, porous, etc. Among these, from the viewpoint of dispersibility, etc., spherical is preferred.

[0042] The magnetic powder may be surface-treated with a silane coupling agent. By surface-treating the magnetic powder with a silane coupling agent, aggregation of the magnetic powder particles can be suppressed even when a large amount of the magnetic powder is mixed.

[0043] Examples of the silane coupling agent include aminosilanes such as N-phenyl-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-(2-aminoethyl)aminopropyltrimethoxysilane, 3-(2-aminoethyl)aminopropylmethyldimethoxysilane, and 3-(2-aminoethyl)aminopropyltriethoxysilane; vinylsilanes such as vinyltrimethoxysilane, vinyltriethoxysilane, and vinyltriacetoxysilane; methacrylsilanes such as 3-methacryloxypropyltrimethoxysilane and 3-methacryloxypropylmethyldimethoxysilane; 3-mercaptopropyltrimethoxysilane, 3-mercaptopropylmethyldimethoxysilane, and 3-mercaptopropylethoxysilane; mercaptosilane, epoxysilanes such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltriethoxysilane, and 3-glycidoxypropylmethyldiethoxysilane; ureidosilanes such as 3-ureidopropyltriethoxysilane; isocyanatesilanes such as 3-isocyanatepropyltrimethoxysilane and 3-isocyanatepropyltriethoxysilane; alkylsilanes such as methyltrimethoxysilane, dimethyldimethoxysilane, trimethylmethoxysilane, ethyltrimethoxysilane, n-propyltrimethoxysilane, isopropyldimethoxysilane, isobutyltrimethoxysilane, and cyclohexylmethyldimethoxysilane; and phenyltrimethoxysilane.

[0044] Examples of the method for surface-treating the magnetic powder with a silane coupling agent include a wet method in which the magnetic powder is treated in a solution in which it is dispersed, a dry method in which the magnetic powder is directly treated as a powder, and an integral blend method in which the magnetic powder is treated in a resin composition in which it is dispersed in a resin, etc. Among these, the wet method is preferred from the viewpoint of suppressing aggregation of the magnetic powder.

[0045] The preferred lower limit of the average particle size of the magnetic powder is 0.1 μm, and the preferred upper limit is 100 μm. When the average particle size of the magnetic powder is within the above range, the adhesion to the substrate can be further improved. The more preferred lower limit of the average particle size of the magnetic powder is 0.5 μm, and the more preferred upper limit is 70 μm. The average particle size can be measured, for example, by a laser diffraction particle size distribution measuring device.

[0046] The content of the magnetic powder in the slurry composition of the present invention is preferably 5% by weight at the lower limit, more preferably 10% by weight at the lower limit, preferably 40% by weight at the upper limit, more preferably 35% by weight at the upper limit.

[0047] As the solvent, water or an organic solvent compatible with water can be used as described above. Examples of the organic solvent that is compatible with water include alcohols.

[0048] The slurry composition of the present invention may contain resins other than the polyvinyl acetal resin, such as acrylic resins and ethyl cellulose, within the range that does not impair the effects of the present invention. Furthermore, the slurry composition of the present invention may contain additives such as plasticizers, lubricants, and antistatic agents within the range that does not impair the effects of the present invention. Effect of the Invention

[0049] According to the present invention, it is possible to provide a polyvinyl acetal resin which has excellent dispersibility and from which a molded article having high mechanical strength can be produced. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0050] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0051] Example 1 (Preparation of polyvinyl acetal resin) Polyvinyl alcohol resin (saponification degree 88 mol%, average polymerization degree 600, half-value width of hydroxyl group 350 cm -1 500g of acetaldehyde was added to 2500g of pure water and dissolved by stirring at 90°C for about 2 hours. The solution was cooled to 40°C, and 10g of hydrochloric acid with a concentration of 35% by weight was added thereto. The liquid temperature was then lowered to 5°C, and 75g of acetaldehyde was added and the temperature was maintained to carry out an acetalization reaction. The liquid temperature was then maintained at 65°C for 5 hours to complete the reaction, and 40g of an aqueous sodium hydroxide solution was added to carry out a neutralization reaction, yielding a polyvinyl acetal resin. Regarding the obtained polyvinyl acetal resin, 13 The amount of acetal groups (amount of acetoacetal groups, amount of butyral groups), amount of hydroxyl groups, and amount of acetyl groups were measured using C-NMR (nuclear magnetic resonance spectrum). The obtained polyvinyl acetal resin was subjected to IR measurement using a HORIBA FT-720 (manufactured by Horiba, Ltd.) to determine the half-value width of the hydroxyl group. The results are shown in Table 1. Furthermore, after measuring the half-width of the hydroxyl group, 13 The amount of hydroxyl groups measured by C-NMR measurement was divided by the half-width of the hydroxyl groups to calculate the half-width of the hydroxyl groups in terms of mole percent.

[0052] Example 2 Polyvinyl alcohol resin (saponification degree 88 mol%, average polymerization degree 600, half-value width of hydroxyl group 345 cm -1 A polyvinyl acetal resin was obtained in the same manner as in Example 1, except that 1,2-dichlorophenyl ether was used. Measurements were performed in the same manner as in Example 1, and the results were as shown in Table 1 for the amount of acetal groups (amount of acetoacetal groups, amount of butyral groups), amount of hydroxyl groups, amount of acetyl groups, half-width of hydroxyl groups, and half-width of hydroxyl groups converted into mole percent.

[0053] Example 3 Polyvinyl alcohol resin (saponification degree 88 mol%, average polymerization degree 600, half-value width of hydroxyl group 345 cm -1 A polyvinyl acetal resin was obtained in the same manner as in Example 1, except that acetal group amount (acetoacetal group amount, butyral group amount), hydroxyl group amount, acetyl group amount, hydroxyl group half width, and hydroxyl group half width converted to mole % were measured in the same manner as in Example 1, and the results are shown in Table 1.

[0054] Example 4 Polyvinyl alcohol resin (saponification degree 88 mol%, average polymerization degree 600, half-value width of hydroxyl group 380 cm -1 A polyvinyl acetal resin was obtained in the same manner as in Example 1, except that 15.0 g of butyral aldehyde was used instead of acetaldehyde. Measurements were performed in the same manner as in Example 1, and the results were as shown in Table 1 for the amount of acetal groups (amount of acetoacetal groups, amount of butyral groups), amount of hydroxyl groups, amount of acetyl groups, half-width of hydroxyl groups, and half-width of hydroxyl groups converted into mole percent.

[0055] Example 5 Polyvinyl alcohol resin (saponification degree 88 mol%, average polymerization degree 600, half-value width of hydroxyl group 370 cm -1 A polyvinyl acetal resin was obtained in the same manner as in Example 1, except that 100 g of acetaldehyde was used and the amount of acetaldehyde added was changed to 110 g. Measurements were performed in the same manner as in Example 1, and the results were as shown in Table 1 for the amount of acetal groups (amount of acetoacetal groups, amount of butyral groups), amount of hydroxyl groups, amount of acetyl groups, half-width of hydroxyl groups, and half-width of hydroxyl groups converted into mole percent.

[0056] Example 6 Polyvinyl alcohol resin (saponification degree 90 mol%, average polymerization degree 600, half-value width of hydroxyl group 335 cm -1A polyvinyl acetal resin was obtained in the same manner as in Example 1, except that acetal group amount (acetoacetal group amount, butyral group amount), hydroxyl group amount, acetyl group amount, hydroxyl group half width, and hydroxyl group half width converted to mole % were measured in the same manner as in Example 1, and the results are shown in Table 1.

[0057] Example 7 Polyvinyl alcohol resin (saponification degree 90 mol%, average polymerization degree 4500, half-value width of hydroxyl group 345 cm -1 A polyvinyl acetal resin was obtained in the same manner as in Example 1, except that acetal group amount (acetoacetal group amount, butyral group amount), hydroxyl group amount, acetyl group amount, hydroxyl group half width, and hydroxyl group half width converted to mole % were measured in the same manner as in Example 1, and the results were as shown in Table 1.

[0058] Example 8 Polyvinyl alcohol resin (saponification degree 88 mol%, average polymerization degree 600, half-value width of hydroxyl group 345 cm -1 A polyvinyl acetal resin was obtained in the same manner as in Example 1, except that 1,2-dichlorophenyl ether was used and the amount of acetaldehyde added was changed to 115 g. Measurements were performed in the same manner as in Example 1, and the results were as shown in Table 1 for the amount of acetal groups (amount of acetoacetal groups, amount of butyral groups), amount of hydroxyl groups, amount of acetyl groups, half-width of hydroxyl groups, and half-width of hydroxyl groups converted into mole percent.

[0059] Example 9 Polyvinyl alcohol resin (saponification degree 95 mol%, average polymerization degree 600, half-value width of hydroxyl group 345 cm -1 A polyvinyl acetal resin was obtained in the same manner as in Example 1, except that 100 g of acetaldehyde was used and the amount of acetaldehyde added was changed to 110 g. Measurements were performed in the same manner as in Example 1, and the results were as shown in Table 1 for the amount of acetal groups (amount of acetoacetal groups, amount of butyral groups), amount of hydroxyl groups, amount of acetyl groups, half-width of hydroxyl groups, and half-width of hydroxyl groups converted into mole percent.

[0060] Example 10 Polyvinyl alcohol resin (saponification degree 82 mol%, average polymerization degree 600, half-value width of hydroxyl group 345 cm -1 A polyvinyl acetal resin was obtained in the same manner as in Example 1, except that acetal group amount (acetoacetal group amount, butyral group amount), hydroxyl group amount, acetyl group amount, hydroxyl group half width, and hydroxyl group half width converted to mole % were measured in the same manner as in Example 1, and the results are shown in Table 1.

[0061] Comparative Example 1 Polyvinyl alcohol resin (saponification degree 88 mol%, average polymerization degree 600, half-value width of hydroxyl group 335 cm -1 A polyvinyl acetal resin was obtained in the same manner as in Example 1, except that 1,2-dichlorophenyl ether was used. Measurements were performed in the same manner as in Example 1, and the results were as shown in Table 1 for the amount of acetal groups (amount of acetoacetal groups, amount of butyral groups), amount of hydroxyl groups, amount of acetyl groups, half-width of hydroxyl groups, and half-width of hydroxyl groups converted into mole percent.

[0062] Comparative Example 2 Polyvinyl alcohol resin (saponification degree 88 mol%, average polymerization degree 600, half-value width of hydroxyl group 335 cm -1 A polyvinyl acetal resin was obtained in the same manner as in Example 1, except that 100 g of acetaldehyde was used and the amount of acetaldehyde added was changed to 140 g. Measurements were performed in the same manner as in Example 1, and the results were as shown in Table 1 for the amount of acetal groups (amount of acetoacetal groups, amount of butyral groups), amount of hydroxyl groups, amount of acetyl groups, half-width of hydroxyl groups, and half-width of hydroxyl groups converted into mole percent.

[0063] Comparative Example 3 Polyvinyl alcohol resin (saponification degree 88 mol%, average polymerization degree 600, half-value width of hydroxyl group 335 cm -1 A polyvinyl acetal resin was obtained in the same manner as in Example 1, except that acetal group amount (acetoacetal group amount, butyral group amount), hydroxyl group amount, acetyl group amount, hydroxyl group half width, and hydroxyl group half width converted to mole % were measured in the same manner as in Example 1, and the results are shown in Table 1.

[0064] Comparative Example 4 Polyvinyl alcohol resin (saponification degree 92 mol%, average polymerization degree 600, half-value width of hydroxyl group 345 cm -1 A polyvinyl acetal resin was obtained in the same manner as in Example 1, except that acetal group amount (acetoacetal group amount, butyral group amount), hydroxyl group amount, acetyl group amount, hydroxyl group half width, and hydroxyl group half width converted to mole % were measured in the same manner as in Example 1, and the results were as shown in Table 1.

[0065] Comparative Example 5 Polyvinyl alcohol resin (saponification degree 90 mol%, average polymerization degree 600, half-value width of hydroxyl group 470 cm -1 A polyvinyl acetal resin was obtained in the same manner as in Example 1, except that acetal group amount (acetoacetal group amount, butyral group amount), hydroxyl group amount, acetyl group amount, hydroxyl group half width, and hydroxyl group half width converted to mole % were measured in the same manner as in Example 1, and the results were as shown in Table 1.

[0066] <Evaluation> The polyvinyl acetal resins obtained in the examples and comparative examples were evaluated as follows, and the results are shown in Table 1.

[0067] (1) Measurement of water absorption amount and water absorption speed per unit area The polyvinyl acetal resins obtained in the Examples and Comparative Examples were formed into films having a thickness of 10 μm using a doctor blade method, dried at 70° C. for 3 hours, and then left to stand in an environment of a temperature of 20° C. and a humidity of 55% for 1 hour or more, and the weight A of the above film was measured. Next, the main surface of the film was exposed to water vapor from hot water at a temperature of 50° C. Thereafter, when water droplets were observed on the surface of the film, the exposure was stopped and the weight B of the film was measured. The amount of water absorption was calculated by subtracting weight A from weight B. The amount of water absorption per unit area was calculated by dividing the amount of water absorption by the exposed area. In the examples and comparative examples of this specification, the exposed area was 40 cm 2 It was decided. Furthermore, the time from the start of water vapor exposure to the point at which water vapor exposure was stopped (exposure time) was measured, and the film weight per unit area was divided by the exposure time to calculate the water absorption rate.

[0068] (2) Dispersibility test (ferrite dispersibility) (Preparation of Slurry Composition) To 50 g of the obtained polyvinyl acetal resin, 21.4 g of ion-exchanged water, 28 g of ferrite as magnetic powder, and 0.6 g of glycerin as a plasticizer were added, and the mixture was stirred at 1200 rpm for 1.5 hours using a Disper manufactured by Primix, and then degassed at 1000 rpm for 30 minutes using a Foam Mixer manufactured by Thinky Corp. to prepare a slurry composition. Ni-Cu-Zn ferrite was used as the ferrite.

[0069] (Particle size distribution measurement) To the obtained slurry composition, 5 g of ethanol and 5 g of toluene were added and stirred to prepare a solution for evaluation. The obtained evaluation solution was subjected to particle size distribution measurement using a laser diffraction particle size distribution analyzer (LA-910, manufactured by Horiba, Ltd.), and the D50 particle size of the magnetic powder was measured. The D50 particle size after being left at 23°C for one week was also measured in the same manner. Furthermore, the rate of change in the D50 particle size was calculated and evaluated according to the following criteria. A: The rate of change was less than 30%. B: The rate of change was 30% or more and less than 60%. C: The rate of change was 60% or more and less than 100%. D: The rate of change was 100% or more.

[0070] (3) Adhesion to substrate (Preparation of resin sheet) The obtained polyvinyl acetal resin was applied onto a release-treated PET film using a coater so that the thickness after drying would be 15 μm, and then the film was dried by heating at 70° C. for 120 minutes to produce a resin sheet.

[0071] The obtained resin sheet was coated onto various substrates (SPCC, PET, PC) so that the film thickness after drying would be 20 μm, and then dried to prepare samples for measuring adhesion. The adhesiveness of the obtained measurement samples was evaluated using the cross-cut adhesion test of JIS K 5400.

[0072] (4) Upper yield stress, breaking strain and breaking stress (Sheet strength) The upper yield stress (MPa), breaking strain (%), and breaking stress (MPa) of the obtained resin sheet were measured at a tensile speed of 20 mm / min using a tensile tester (Shimadzu Corporation, AUTOGRAPH AGS-J) in accordance with JIS K 7113.

[0073] [Table 1] [Industrial Applicability]

[0074] According to the present invention, it is possible to provide a polyvinyl acetal resin which has excellent dispersibility and from which a molded article having high mechanical strength can be produced.

Claims

1. When molded into a 10 μm thick film, the water absorption per unit area is 2 mg / cm ２ 50mg / cm or more ２ The average degree of polymerization is 600 to 4500, the amount of hydroxyl groups is 35 to 85 mol%, the amount of acetyl groups is 5 to 18 mol%, and the half-value width of the hydroxyl groups as determined by IR measurement is 280 to 420 cm －１ Polyvinyl acetal resin.

2. The polyvinyl acetal resin according to claim 1, wherein the amount of acetal groups is 1 to 50 mol %.

3. 3. The polyvinyl acetal resin according to claim 1, which is an acetalized product of a polyvinyl alcohol resin having a saponification degree of 75 mol % or more.

4. A slurry composition comprising the polyvinyl acetal resin according to any one of claims 1 to 3, a magnetic powder, and a solvent.

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