Polyvinyl acetal resin and electrode composition using said polyvinyl acetal resin

Abstract

The purpose of the present invention is to provide: a polyvinyl acetal resin with which it is possible to prevent swelling due to an electrolyte and to obtain an electrode having a low internal resistance, and thus making it possible to fabricate a high-output storage battery; and an electrode composition, a secondary battery electrode, and a conductive paste using said polyvinyl acetal resin. The present invention is a polyvinyl acetal resin in which the retention time of the peak top of a main peak in HPLC analysis under the following conditions is 26.9 minutes or greater, and the average degree of polymerization is less than 2300. [HPLC Conditions] Apparatus: Prominence (manufactured by Shimadzu Corporation) Column: X-BridgeBEH (3.5 μm, 2.1 mm × 50 mm, manufactured by Waters Corporation) Column temperature: 45°C Injection amount: 20 μL Mobile phase: A mobile phase (Milli-Q water), B mobile phase (a mixture of THF and IPA [THF / IPA = 7 / 3 (volume ratio)]) Concentration gradient of mobile phase: A / B = 90 / 10 (volume ratio) from the start to 10 minutes, and thereafter, the volume ratio is linearly changed over time to be held at A / B = 0 / 100 (volume ratio) in 20 minutes after the start Flow rate: 0.4 mL / min Detector: evaporation light scattering detector (ELSD, 40°C)

Description

Polyvinyl acetal resin and electrode composition using said polyvinyl acetal resin

[0001] The present invention relates to a polyvinyl acetal resin, an electrode composition using the polyvinyl acetal resin, a secondary battery electrode, and a conductive paste.

[0002] Polyvinyl acetal resin is a resin synthesized from polyvinyl alcohol and has acetyl groups, hydroxyl groups, and acetal groups in its side chains. This allows it to exhibit excellent toughness and adhesive properties. Furthermore, changing the ratio of side chain groups allows the resin's physical properties to be altered. Taking advantage of these properties, polyvinyl acetal resin is used in many applications, such as storage battery electrodes, pigment compositions, and ceramic green sheets.

[0003] For example, for use in storage battery electrodes, a composition for electrodes containing a polyvinyl acetal resin having a hydroxyl group content of 40 to 95 mol % and a polymerization degree of 250 to 4000 has been disclosed (Patent Document 1).

[0004] JP 2013-178962 A

[0005] However, when the electrode composition described in Patent Document 1 is used, there are problems in that the polyvinyl acetal resin added as a binder swells in the electrolyte, and there are also problems in that the internal resistance of the resulting electrode increases.

[0006] The polyvinyl acetal resin according to the present invention can prevent swelling due to an electrolyte solution and can provide an electrode with low internal resistance, which makes it possible to produce a high-power storage battery. That is, an object of the present invention is to provide a polyvinyl acetal resin, an electrode composition using the polyvinyl acetal resin, a secondary battery electrode, and a conductive paste, which have the above-mentioned excellent properties.

[0007] The present disclosure (1) is a polyvinyl acetal resin having a main peak whose peak top retention time is 26.9 minutes or longer in HPLC analysis under the following conditions and an average degree of polymerization of less than 2300. In the present invention, the main peak means the peak with the greatest peak intensity among the peaks detected in HPLC analysis. [HPLC conditions] Apparatus: Prominence (Shimadzu Corporation) Column: X-BridgeBEH (3.5 μm, 2.1 mm × 50 mm, Waters) Column temperature: 45 ° C. Injection volume: 20 μL Mobile phase: Mobile phase A (Milli-Q water), mobile phase B (mixture of THF and IPA [THF / IPA = 7 / 3 (volume ratio)]) Mobile phase concentration gradient: A / B = 90 / 10 (volume ratio) from the start to 10 minutes, then the volume ratio is changed linearly with time, and A / B = 0 / 100 (volume ratio) is held 20 minutes after the start Flow rate: 0.4 mL / min Detector: Evaporative light scattering detector (ELSD, 40 ° C.) The present disclosure (2) is the polyvinyl acetal resin according to the present disclosure (1), having a sodium content of 200 ppm by mass or less. The present disclosure (3) is the polyvinyl acetal resin according to the present disclosure (1) or (2), which has a glass transition temperature of 65°C or lower. The present disclosure (4) is the polyvinyl acetal resin according to any one of the present disclosures (1) to (3), which has an organic solvent content of 1% by weight or less. The present disclosure (5) is the polyvinyl acetal resin according to any one of the present disclosures (1) to (4), which has a main peak half-width of 0.450 or less obtained by the HPLC analysis. The present disclosure (6) is the polyvinyl acetal resin having an acetal unit represented by the following formula (1), wherein R in the following formula (1) １ is an alkyl group having 4 or more carbon atoms. The present disclosure (7) is a polyvinyl acetal resin according to any one of the present disclosures (1) to (6), having an average degree of polymerization of less than 2,200. The present disclosure (8) is a polyvinyl acetal resin according to any one of the present disclosures (1) to (7), used in an electrode. The present disclosure (9) is a composition for an electrode, containing the polyvinyl acetal resin according to any one of the present disclosures (1) to (8), a filler, and a solvent. The present disclosure (10) is a secondary battery electrode, containing the polyvinyl acetal resin according to any one of the present disclosures (1) to (8), and an active material. The present disclosure (11) is a conductive paste, containing the polyvinyl acetal resin according to any one of the present disclosures (1) to (8), an organic solvent, and a conductive powder.

[0008] As a result of extensive investigations, the present inventors have found that a polyvinyl acetal resin having a main peak top retention time of 26.9 minutes or more in HPLC analysis under specified conditions can prevent swelling with an electrolyte solution and enables the production of a high-power storage battery, thereby completing the present invention.

[0009] The polyvinyl acetal resin of the present invention has a main peak top retention time of 26.9 minutes or longer in HPLC analysis under the following conditions. A retention time of 26.9 minutes or longer can prevent swelling due to the electrolyte, making it possible to produce a high-power storage battery. Furthermore, the polyvinyl acetal resin of the present invention has high solvent solubility, and when used as a material for conductive (electrode) paste, can suppress printing bleeding.

[0010] [HPLC conditions] Apparatus: Prominence (Shimadzu Corporation) Column: X-BridgeBEH (3.5 μm, 2.1 mm × 50 mm, Waters) Column temperature: 45 ° C. Injection volume: 20 μL Mobile phase: Mobile phase A (Milli-Q water), mobile phase B (mixture of THF and IPA [THF / IPA = 7 / 3 (volume ratio)]) Mobile phase concentration gradient: A / B = 90 / 10 (volume ratio) from the start until 10 minutes, after which the volume ratio was changed linearly with time and maintained at A / B = 0 / 100 (volume ratio) 20 minutes after the start Flow rate: 0.4 mL / min Detector: Evaporative light scattering detector (ELSD, 40 ° C.)

[0011] The lower limit of the retention time is preferably 27.0 minutes, more preferably 27.1 minutes, and even more preferably 27.3 minutes. The upper limit is not particularly limited, but it is preferably 30.0 minutes or less. Note that the retention time is an index representing the polarity of the polyvinyl acetal resin, but is not determined solely by the amount of some of the structural units, such as the amount of acetal groups or the amount of hydroxyl groups, of the polyvinyl acetal resin.

[0012] The retention time of the peak top of the main peak in the HPLC analysis can be adjusted by the method and reaction conditions of the acetalization reaction when preparing the polyvinyl acetal resin, the degree of polymerization of the polyvinyl acetal resin, the amount of hydroxyl groups, the amount of acetal groups, the amount of acetyl groups, the structure of the acetal unit (the number of carbon atoms in the alkyl group), the type and content of the modifying group, etc. For example, with regard to the acetalization reaction, by carrying out the acetalization reaction in the presence of a dispersant and causing precipitation, the particle size becomes small, and as a result, the reaction proceeds uniformly throughout the particle, making it possible to achieve a retention time within the range of the present invention. With regard to the amount of hydroxyl groups, a low amount of hydroxyl groups tends to decrease polarity and increase retention time. With regard to the amount of acetal groups, an increase in the amount of acetal groups tends to decrease polarity and increase retention time. With regard to the structure of the acetal unit, an increase in the number of carbon atoms in the alkyl group in the acetal unit tends to increase retention time. With regard to the modifying group, retention time tends to increase when there are few highly polar modifying groups such as carboxylic acids and amines.

[0013] The polyvinyl acetal resin of the present invention preferably has a half-value width of the main peak obtained by the HPLC analysis of 0.450 or less. By having the half-value width be equal to or less than the upper limit, the composition of the polyvinyl acetal resin becomes uniform, and unevenness can be reduced when coating a composition containing the polyvinyl acetal resin of the present invention. The half-value width has a preferred lower limit of 0.200, a more preferred lower limit of 0.250, and a more preferred upper limit of 0.430. The half-value width refers to the peak width at a height that is 1 / 2 (50%) of the observed peak.

[0014] The half-width of the main peak in the HPLC analysis can be adjusted by the method and reaction conditions of the acetalization reaction when preparing the polyvinyl acetal resin, the degree of polymerization of the polyvinyl acetal resin, the amount of hydroxyl groups, the amount of acetal groups, the amount of acetyl groups, the structure of the acetal unit (the number of carbon atoms in the alkyl group), the type and content of the modifying group, etc. Regarding the acetalization reaction, by carrying out the acetalization reaction in the presence of a dispersant and causing precipitation, the particle size becomes small, and as a result, the reaction proceeds uniformly throughout the particles, making it possible to achieve a half-width within the above-mentioned range. Regarding the degree of polymerization, by increasing the degree of polymerization, the half-width can be narrowed. Regarding the amount of acetal groups, by increasing the amount of acetal groups, polarity decreases, making it possible to achieve a half-width within the above-mentioned range. Regarding the structure of the acetal unit, by increasing the number of carbon atoms in the alkyl group in the acetal unit, it is possible to achieve a half-width within the above-mentioned range. Regarding the modifying group, when there are few highly polar modifying groups such as carboxylic acids and amines, it is possible to achieve a half-width within the above-mentioned range.

[0015] The polyvinyl acetal resin of the present invention preferably has a sodium ion content of 200 ppm by mass or less. This makes it possible to suppress an increase in internal resistance in an electrode containing the polyvinyl acetal resin of the present invention. The upper limit of the sodium content is more preferably 180 ppm by mass, even more preferably 150 ppm by mass, and particularly preferably 100 ppm by mass. The lower limit is preferably 10 ppm by mass. The sodium content can be measured, for example, using an ICP emission spectrometer (Shimadzu Corporation, ICPE-9000) or the like.

[0016] The polyvinyl acetal resin of the present invention preferably has an organic solvent content of 1% by weight or less. This makes it difficult for an electrode containing the polyvinyl acetal resin of the present invention to swell with an electrolyte solution, and also makes it possible to suppress an increase in internal resistance. The upper limit of the organic solvent content is more preferably 0.8% by weight, even more preferably 0.5% by weight, even more preferably 0.3% by weight, and particularly preferably 0.1% by weight. The lower limit is preferably 0.05% by weight. The content of the organic solvent may be, for example, １ It can be measured by H-NMR (nuclear magnetic resonance spectroscopy) or the like.

[0017] The polyvinyl acetal resin of the present invention preferably has a glass transition temperature (Tg) of 65°C or lower. This improves the adhesion between a composition containing the polyvinyl acetal resin and a metal film. The lower limit of the glass transition temperature is preferably 35°C, more preferably 40°C, and the upper limit is preferably 63°C, more preferably 55°C. The glass transition temperature can be measured using, for example, a differential scanning calorimeter (DSC) or the like.

[0018] The sodium content, organic solvent content, and glass transition temperature can be adjusted by the method and reaction conditions of the acetalization reaction when producing the polyvinyl acetal resin, the degree of polymerization of the polyvinyl acetal resin, the amount of hydroxyl groups, the amount of acetal groups, the amount of acetyl groups, the structure of the acetal unit (the number of carbon atoms in the alkyl group), the type and amount of the modifying group, and the like.

[0019] The polyvinyl acetal resin of the present invention has an acetal unit represented by the following formula (1), and R １ is preferably an alkyl group having 4 or more carbon atoms, and more preferably an alkyl group having 5 or more carbon atoms. This allows the compound to be dissolved in a low-polarity solvent. １ When the alkyl group is an alkyl group having 4 or more carbon atoms, the alkyl group may have a single carbon atom or may have multiple carbon atoms.

[0020]

[0021] The above R１ The number of carbon atoms in R is preferably 4 or more. The lower limit of the number of carbon atoms is more preferably 5, the upper limit is more preferably 11, and the upper limit is still more preferably 9. １ may be a combination of two or more alkyl groups having different carbon numbers.

[0022] Examples of the alkyl group having 4 or more carbon atoms include a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, an octadecyl group, an eicosyl group, and a docosyl group.

[0023] The alkyl group having 4 or more carbon atoms may be linear or branched, but is preferably linear. Examples of the linear alkyl group include an n-butyl group, an n-pentyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, an n-nonyl group, an n-decyl group, an n-undecyl group, an n-dodecyl group, an n-tridecyl group, an n-tetradecyl group, an n-hexadecyl group, an n-heptadecyl group, an n-octadecyl group, an n-eicosyl group, and an n-docosyl group.

[0024] Examples of the branched alkyl group include an isobutyl group, an isopentyl group, a neopentyl group, a 1-methylhexyl group, a 1-methylheptyl group, a 1-methyloctyl group, a 1-methylnonyl group, a 1-methyldecyl group, a 1-methylundecyl group, and a 1-methyldodecyl group. Other examples include a 1-methyltridecyl group, a 1-methyltetradecyl group, a 1-methylheptadecyl group, a 1-methylhexadecyl group, a 1-methylpentadecyl group, a 1-methyloctadecyl group, and a 1-methyleicosyl group. Further examples include alkyl groups in which an alkyl group having two or more carbon atoms is substituted at the first carbon atom (e.g., a 1-ethyldecyl group, a 1-propylnonyl group, a 1-butyloctyl group, a 1-pentylheptyl group, and a 1-octyldecyl group). Furthermore, in a branched alkyl group, the branching position is not limited to the first carbon atom, and may be the second or higher carbon atom. For example, alkyl groups in which a methyl group is substituted on the second or higher carbon atom include a 2-methylundecyl group, a 3-methylundecyl group, and a 4-methylundecyl group. Furthermore, alkyl groups in which an alkyl group having two or more carbon atoms is substituted on the second or higher carbon atom include a 2-ethylhexyl group, a 2-ethylheptyl group, a 2-ethyloctyl group, a 2-ethylundecyl group, a 2-ethyloctadecyl group, a 2-propylundecyl group, a 2-butylundecyl group, and a 2-octylundecyl group. Further examples include a 3-ethylundecyl group, a 4-ethyloctadecyl group, a 4-butyloctadecyl group, and a neodecyl group.

[0025] In the present invention, the alkyl group having 4 or more carbon atoms is preferably a linear alkyl group. The alkyl group having 4 or more carbon atoms may be composed of two or more alkyl groups including a linear alkyl group and a branched alkyl group, or may be composed of only a linear alkyl group. １ may be an alkyl group based on a bio-derived aldehyde having 4 or more carbon atoms.

[0026] The polyvinyl acetal resin of the present invention preferably further contains an acetal unit represented by the following formula (2), which is different from the constituent unit represented by the above formula (1). By containing the acetal unit represented by the following formula (2), increases in swelling ratio and internal resistance can be suppressed, and adhesion can be improved.

[0027] In formula (2), R ２ represents an alkyl group having 1 to 3 carbon atoms.

[0028] Examples of the alkyl group having 1 to 3 carbon atoms include a methyl group, an ethyl group, a propyl group, etc. The alkyl group having 1 to 3 carbon atoms may be linear or branched.

[0029] The content of the acetal unit represented by the formula (1) in the polyvinyl acetal resin of the present invention is preferably 15 mol% at its lower limit, more preferably 20 mol%, and more preferably 85 mol%, and even more preferably 65 mol% at its upper limit. By setting the content of the acetal unit represented by the formula (1) within the above range, increases in the swelling ratio and internal resistance can be suppressed. The content of the acetal unit represented by the formula (1) is １ H-NMR and １３ Measurement is performed using C-NMR (nuclear magnetic resonance spectrum).

[0030] The content of the acetal unit represented by the formula (2) in the polyvinyl acetal resin of the present invention is preferably 25 mol %, more preferably 35 mol %, and more preferably 75 mol %, and even more preferably 55 mol %. By setting the content of the acetal unit represented by the formula (2) within the above range, increases in the swelling ratio and internal resistance can be suppressed. The content of the acetal unit represented by the formula (2) is １ H-NMR and １３ Measurement is performed using C-NMR (nuclear magnetic resonance spectrum).

[0031] When the polyvinyl acetal resin of the present invention contains the acetal units represented by the formula (1) and the acetal units represented by the formula (2), the lower limit of the total content thereof is preferably 75 mol%, more preferably 80 mol%, and the upper limit is preferably 90 mol%, more preferably 85 mol%. By keeping the total content within the above ranges, increases in the swelling ratio and internal resistance can be suppressed.

[0032] When the polyvinyl acetal resin of the present invention contains acetal units represented by the above formula (1) and acetal units represented by the above formula (2), the ratio between them (content of acetal units represented by formula (1) / content of acetal units represented by formula (2)) is preferably 0.2 to 20. By setting the ratio within the above range, increases in the swelling ratio and internal resistance can be suppressed.

[0033] The total acetal group content (total amount of all acetal units) of the polyvinyl acetal resin of the present invention has a lower limit of preferably 75 mol%, a more preferred lower limit of 80 mol%, and an upper limit of preferably 90 mol%, a more preferred upper limit of 85 mol%. By setting the total acetal group content within the above range, increases in the swelling ratio and internal resistance value can be suppressed. １ Measurement is performed using H-NMR (nuclear magnetic resonance spectrum).

[0034] The polyvinyl acetal resin of the present invention has a structural unit having a hydroxyl group. The content of the structural unit having a hydroxyl group (amount of hydroxyl groups) in the polyvinyl acetal resin of the present invention is preferably 10 mol% or more and 30 mol% or less. By setting the content within the above range, when the resin is formed into an electrode, it is possible to impart binding properties and electrolyte resistance. A more preferred lower limit of the amount of hydroxyl groups is 12 mol%, and a more preferred upper limit is 25 mol%. The amount of hydroxyl groups １ Measurement is performed using H-NMR (nuclear magnetic resonance spectrum).

[0035] The polyvinyl acetal resin of the present invention has a structural unit having an acetyl group. The preferred lower limit of the content of the structural unit having an acetyl group (acetyl group amount) in the polyvinyl acetal resin of the present invention is 0.1 mol%, and the preferred upper limit is 20 mol%. By setting the acetyl group amount to 0.1 mol% or more, the flexibility of the resin can be maintained. By setting the acetyl group amount to 20 mol% or less, the resistance to the electrolyte when used in an electrode of a storage battery can be improved, and the battery can be prevented from deteriorating due to the resin leaching into the electrolyte. The more preferred lower limit of the acetyl group amount is 0.3 mol%, and the more preferred upper limit is 10 mol%. The acetyl group amount １ Measurement is performed using H-NMR (nuclear magnetic resonance spectrum).

[0036] The polyvinyl acetal resin of the present invention may have a structural unit having a carboxylic acid. The preferred lower limit of the content of the structural unit having a carboxylic acid (carboxylic acid modification amount) in the polyvinyl acetal resin of the present invention is 0.1 mol%, and the preferred upper limit is 3 mol%. By setting the carboxylic acid group amount to 0.1 mol% or more, the paste viscosity can be increased, and by setting the carboxylic acid modification amount to 3 mol% or less, the solubility in solvents can be improved. The more preferred lower limit of the acetyl group amount is 0.4 mol%, and the more preferred upper limit is 2 mol%. Examples of the structural unit having a carboxylic acid include structural units derived from acrylic acid, methacrylic acid, maleic acid, itaconic acid, etc. The carboxylic acid modification amount is １ H-NMR and １３ Measurement is performed using C-NMR (nuclear magnetic resonance spectrum).

[0037] The polyvinyl acetal resin of the present invention has an average degree of polymerization of less than 2300. By setting the average degree of polymerization within the above range, internal resistance can be reduced. Furthermore, print bleeding can be suppressed. The preferred lower limit of the average degree of polymerization of the polyvinyl acetal resin of the present invention is 200, and preferably less than 2200. An average degree of polymerization of 200 or more facilitates industrial production. An average degree of polymerization of less than 2200 provides an appropriate solution viscosity, enabling industrial production. A more preferred lower limit of the average degree of polymerization is 500, and a more preferred upper limit is 2100. That is, the average degree of polymerization is preferably 200 or more but less than 2200, and more preferably 500 to 2100. The average degree of polymerization of the polyvinyl acetal resin can be determined from the polyvinyl alcohol used as a raw material.

[0038] The polyvinyl acetal resin of the present invention may be copolymerized with an ethylenically unsaturated monomer, provided that the effects of the present invention are not impaired. The ethylenically unsaturated monomer is not particularly limited, and examples thereof include acrylic acid, methacrylic acid, phthalic acid (anhydride), maleic acid (anhydride), and itaconic acid (anhydride). Other examples include acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, trimethyl-(3-acrylamido-3-dimethylpropyl)-ammonium chloride, acrylamido-2-methylpropanesulfonic acid, and its sodium salt. Further examples include ethyl vinyl ether, butyl vinyl ether, N-vinylpyrrolidone, vinyl chloride, vinyl bromide, vinyl fluoride, vinylidene chloride, vinylidene fluoride, tetrafluoroethylene, sodium vinyl sulfonate, and sodium allyl sulfonate. Alternatively, a terminal-modified polyvinyl alcohol can be used, which is obtained by copolymerizing a vinyl ester monomer such as vinyl acetate with ethylene in the presence of a thiol compound such as thiolacetic acid or mercaptopropionic acid, and then saponifying the copolymer.

[0039] Examples of methods for producing the polyvinyl acetal resin include a method of acetalizing polyvinyl alcohol with an aldehyde, and a method of subsequently acetalizing a polyvinyl acetal resin having an acetal unit represented by formula (1) with an aldehyde having one or more carbon atoms. It is particularly preferable to use a method of acetalizing polyvinyl alcohol with at least one aldehyde having five or more carbon atoms. By using such a production method, the retention time, half-width, sodium content, organic solvent content, and glass transition temperature of the polyvinyl acetal resin of the present invention in HPLC analysis can be adjusted.

[0040] The method of acetalizing the polyvinyl alcohol using at least one aldehyde having 5 or more carbon atoms includes, for example, preparing aldehydes having different carbon numbers and then acetalizing them to introduce acetal units having multiple alkyl groups having different carbon numbers. When producing the polyvinyl acetal resin, the acetalization may be carried out in the presence of a dispersant. More specifically, a method of introducing the acetal unit represented by the formula (1) by acetalizing polyvinyl alcohol that does not have the acetal unit represented by the formula (1) with a specific aldehyde is included.

[0041] The polyvinyl alcohol can be obtained, for example, by saponifying a vinyl ester polymer. Examples of the vinyl ester include vinyl formate, vinyl acetate, vinyl propionate, and vinyl pivalate. Among these, vinyl acetate is preferred from the viewpoint of economy.

[0042] The polyvinyl alcohol resin preferably has a saponification degree of 75 mol% or more, more preferably 76 mol% or more and 99.4 mol% or less, and even more preferably 78 mol% or more and 98 mol% or less. That is, the saponification degree is more preferably 76 to 99.4 mol%, and even more preferably 78 to 98 mol%.

[0043] In the method of reacting polyvinyl alcohol with an aliphatic aldehyde having 5 or more carbon atoms, the aldehyde used in the acetalization reaction is not particularly limited, and examples thereof include linear aliphatic aldehydes and branched aliphatic aldehydes having 5 or more carbon atoms. Examples of the aliphatic aldehydes having 5 or more carbon atoms include valeraldehyde, hexyl aldehyde, 2-ethylbutyraldehyde, 2-ethylhexyl aldehyde, heptyl aldehyde, octyl aldehyde, nonyl aldehyde, decyl aldehyde, undecyl aldehyde, dodecyl aldehyde, tridecyl aldehyde, trimethylhexyl aldehyde, methyloctylacetaldehyde, and methylnonylacetaldehyde. These aldehydes may be used alone or in combination of two or more. Among these, decyl aldehyde is preferred as the aliphatic aldehyde having 5 or more carbon atoms.

[0044] The amount of the aldehyde added can be appropriately set depending on the amount of acetal groups in the target polyvinyl acetal resin. In particular, when the amount is preferably 55 mol% to 120 mol%, more preferably 60 mol% to 110 mol%, relative to 100 mol% of polyvinyl alcohol, the acetalization reaction proceeds efficiently and unreacted aldehyde is easily removed. That is, the amount of the aldehyde added is preferably 55 to 120 mol%, more preferably 60 to 110 mol%.

[0045] In the acetalization step, in addition to the aliphatic aldehyde having 5 or more carbon atoms, an aldehyde having 2 to 4 carbon atoms may be used in combination. This makes it possible to introduce acetal units represented by formula (2) above. Examples of the aldehyde having 2 to 4 carbon atoms include acetaldehyde, propionaldehyde, and butyraldehyde. Furthermore, an aldehyde having a cyclic aliphatic group or an aromatic group may be used in combination. Examples of the aldehyde having an aromatic group include benzaldehyde, cinnamaldehyde, 2-methylbenzaldehyde, 3-methylbenzaldehyde, 4-methylbenzaldehyde, p-hydroxybenzaldehyde, m-hydroxybenzaldehyde, phenylacetaldehyde, and β-phenylpropionaldehyde.

[0046] In the acetalization step, when only an aldehyde having 4 or less carbon atoms is used, it is preferable to carry out the acetalization using a dispersant. When an aldehyde having 5 or more carbon atoms is included, a dispersant may or may not be used. Furthermore, in the acetalization step, it is preferable to use a method in which the polyvinyl acetal resin is reacted in a precipitated state during the acetalization reaction (precipitation method), compared to a method in which the acetalization reaction is carried out in a dissolved state (dissolution method). Furthermore, the method of acetalization using a dispersant and the precipitation method may be used in combination.

[0047] Examples of the dispersant include sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, polyvinylpyrrolidone, polyethylene glycol, polyvinyl alcohol, colloidal silica, polyoxyethylene polyoxypropylene cetyl ether, polyoxyethylene polyoxypropylene lauryl ether, etc. These dispersants may be used alone or in combination of two or more. Among them, sodium dodecylbenzenesulfonate and polyoxyethylene polyoxypropylene cetyl ether are preferred.

[0048] Examples of the acid catalyst include mineral acids, carboxylic acids, sulfonic acids, etc. Examples of the mineral acids include sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, etc. Examples of the carboxylic acids include formic acid, acetic acid, propionic acid, etc. Examples of the sulfonic acids include paratoluenesulfonic acid, methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, etc. These acid catalysts may be used alone or in combination of two or more. Of these, paratoluenesulfonic acid and hydrochloric acid are preferred.

[0049] The temperature when the aldehyde is added (aldehyde introduction temperature) is preferably 5°C or higher, more preferably 10°C or higher, and preferably 70°C or lower. The temperature when the catalyst is added is preferably 10°C or higher and 50°C or lower. The holding time in the acetalization reaction is preferably 0.5 hours or higher and 5 hours or lower, more preferably 1 hour or higher and 3 hours or lower. The holding temperature in the acetalization reaction is preferably -5°C or higher and 50°C or lower, and more preferably 5°C or higher and 40°C or lower.

[0050] Applications of the polyvinyl acetal resin of the present invention include, for example, binders and dispersants for battery electrodes, secondary battery electrodes, etc., modifiers for adhesives based on epoxy resins, phenolic resins, etc., ceramic green sheets, conductive pastes, etc. In particular, when the polyvinyl acetal resin of the present invention is used as a binder for secondary battery electrodes, it can prevent deterioration due to electrolytes, making it possible to produce high-power storage batteries. When used as an electrode paste or conductive paste, it can prevent printing bleeding.

[0051] A composition containing the polyvinyl acetal resin of the present invention, a filler, and a solvent can be used as an electrode composition. The electrode composition can be a secondary battery electrode composition. The secondary battery electrode composition can prevent deterioration due to the electrolyte and produce a high-output secondary battery. The composition can also be used as a secondary battery electrode composition containing the polyvinyl acetal resin of the present invention, an active material, and a solvent. Furthermore, a secondary battery electrode containing the polyvinyl acetal resin of the present invention and an active material also constitutes one aspect of the present invention.

[0052] The electrode composition of the present invention contains an active material as a filler. Examples of the active material include a positive electrode active material and a negative electrode active material. Examples of the positive electrode active material include lithium nickel oxide, lithium cobalt oxide, lithium manganese oxide, and lithium nickel manganese cobalt oxide (LiN ｘ M ｙ C ｚ, x+y+z=1), and lithium-containing composite metal phosphate compounds such as lithium iron phosphate and lithium manganese iron phosphate. ２ , LiCoO ２ , LiMn ２ O ４ , LiN １／３ M １／３ C １／３ O ２ , LiN ０．５ M ０．３ C ０．２ O ２ , LiN ０．６ M ０．２ C ０．２ O ２ , LiN ０．８ M ０．１ C ０．１ O ２ , LiN ０．８ C ０．１５ Al ０．０５ O ２ , LiFePO ４ , LiMn ０．７ Fe ０．３ P.O. ４ Examples of the negative electrode active material include materials that have been conventionally used as negative electrode active materials for storage batteries, such as spherical natural graphite, natural graphite, artificial graphite, amorphous carbon, carbon black, and any of these components to which a different element has been added. These may be used alone or in combination of two or more.

[0053] The electrode composition of the present invention contains a solvent. The solvent is preferably an organic solvent. Examples of the solvent include alcohols, polyhydric alcohols, glycol ethers, esters, amide-based solvents, amine-based solvents, and water. Examples of the alcohols include higher alcohols such as ethanol, n-propanol, isopropanol, n-butanol, isobutanol, tert-butyl alcohol, pentanol, hexanol, n-heptanol, 2-heptanol, octanol, 2-ethylhexanol, 3,5,5-trimethylhexanol, nonanol, decanol, and cyclohexanol, as well as benzyl alcohol, terpineol, and dihydroterpineol. Examples of the polyhydric alcohols include ethylene glycol, diethylene glycol, triethylene glycol, and phenyl glycol. Examples of the glycol ethers include propylene glycol monomethyl ether, propylene glycol monobutyl ether, methyl cellosolve, ethyl cellosolve, butyl cellosolve, butyl carbitol, butyl triglycol, and methyl diglycol. Examples of the esters include 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. Also usable are butyl cellosolve acetate, butyl carbitol acetate, terpineol acetate, and dihydroterpineol acetate. 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. Two or more of the above solvents may be mixed and used.

[0054] The electrode composition of the present invention preferably further contains a conductive additive (conductivity-imparting agent). By including the conductive additive, the electrical resistance of the resulting secondary battery electrode composition can be further reduced. Examples of the conductive additive include carbon materials such as graphite, acetylene black, carbon black, ketjen black, vapor-grown carbon fiber, and carbon nanotubes.

[0055] The electrode composition of the present invention preferably further contains a polyvinylidene fluoride resin. By containing both the polyvinyl acetal resin and the polyvinylidene fluoride resin, the composition may exhibit superior binding properties and lower electrical resistance compared to the polyvinyl acetal resin or the polyvinylidene fluoride resin alone. The weight-average molecular weight of the polyvinylidene fluoride resin is preferably 400,000 to 1,200,000, and more preferably 600,000 to 1,000,000. The weight-average molecular weight can be measured by an absolute molecular weight measurement method using gel permeation chromatography (GPC). In addition, in the present invention, the weight ratio of the polyvinyl acetal resin to the polyvinylidene fluoride resin is preferably 0.5:9.5 to 8:2, and more preferably 1:9 to 7:3. By maintaining the weight ratio within the above range, the binding properties can be improved and the electrical resistance can be further reduced. The amount of resin in the present invention (the total weight of the polyvinyl acetal resin and polyvinylidene fluoride resin) is preferably 0.5 to 4 parts by weight, more preferably 0.6 to 3 parts by weight. When the amount of resin is 0.5 part by weight or more, high binding strength can be achieved, and when the amount is 4 parts by weight or less, an electrode with low electrical resistance can be produced.

[0056] In addition to the above-mentioned substances, additives such as a flame retardant aid, a thickener, a defoamer, a leveling agent, and an adhesion promoter may be added to the electrode composition of the present invention, if necessary.

[0057] The present invention also provides a conductive paste containing the polyvinyl acetal resin of the present invention, an organic solvent, and a conductive powder. The organic solvent may be the same as that described above. The conductive powder may be any commonly used powder.

[0058] According to the present invention, a polyvinyl acetal resin can be provided that can prevent swelling due to an electrolytic solution and produce an electrode with low internal resistance, making it possible to fabricate a high-power storage battery. Also, an electrode composition, a secondary battery electrode, and a conductive paste using the polyvinyl acetal resin can be provided. Furthermore, the polyvinyl acetal resin of the present invention has high solvent solubility, and when used as a material for a conductive (electrode) paste, printing bleeding can be suppressed.

[0059] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[0060] Example 1 (Preparation of Polyvinyl Acetal Resin) 150 g of polyvinyl alcohol having a saponification degree of 99.1 mol% and an average degree of polymerization of 1700, and 13.5 g of Unisafe 10P-8 (polyoxyethylene polyoxypropylene cetyl ether, manufactured by NOF Corporation) diluted with pure water as a dispersant to a concentration of 20% by mass were added to 1600 g of pure water and dissolved under stirring at 90°C for 2 hours. This solution was cooled to 65°C, and 70 g of n-butyl aldehyde and 75 g of n-decyl aldehyde were added. Thereafter, the solution was cooled to 15°C, and 20 g of hydrochloric acid having a concentration of 35% by mass, diluted with 180 g of pure water, was added. The liquid temperature was maintained at 15°C, and an acetalization reaction was carried out for 1 hour, allowing the reaction product to precipitate. After 1 hour of the acetalization reaction, 13.5 g of 20% by mass sodium dodecylbenzenesulfonate (SDBS) dissolved in pure water was added, and the acetalization reaction was continued for another hour. The temperature was then raised to 60°C at a rate of 2-3°C / 5 min, and the liquid temperature was maintained at 60°C for 3 hours to complete the reaction. The mixture was then neutralized, washed with water, and dried in the usual manner to obtain a powder of a long-chain alkyl-modified polyvinyl acetal resin. The resulting polyvinyl acetal resin was dissolved in CDCl ３ Dissolved in (deuterated chloroform) １ H-NMR and１３ The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using C-NMR (nuclear magnetic resonance spectrum). The total amount of acetal groups (the sum of the contents of each acetal unit) was calculated from the measured values. The results are shown in Table 1. The content of each acetal unit was １３ The acetal unit was determined by C-NMR. １ = (CH ２ ) ８ CH ３ ] and the acetal unit [R ２ = (CH ２ ) ２ CH ３ ] was.

[0061] (Example 2) (Preparation of polyvinyl acetal resin) A polyvinyl acetal resin powder was obtained in the same manner as in Example 1, except that 80 g of n-butyl aldehyde and 60 g of n-heptaldehyde were added instead of 70 g of n-butyl aldehyde and 75 g of n-decyl aldehyde. The obtained polyvinyl acetal resin was dissolved in CDCl ３ Dissolved in (deuterated chloroform) １ H-NMR and １３ The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using C-NMR (nuclear magnetic resonance spectrum). The total amount of acetal groups (the sum of the contents of each acetal unit) was calculated from the measured values. The results are shown in Table 1. The content of each acetal unit was １３ The acetal unit was determined by C-NMR. １ = (CH ２ ) ５ CH ３ ] and the acetal unit [R ２ = (CH ２ ) ２ CH ３ ] was.

[0062] Example 3 (Preparation of Polyvinyl Acetal Resin) 150 g of polyvinyl alcohol having a saponification degree of 99.1 mol% and an average degree of polymerization of 1700 was added to 2500 g of pure water and dissolved by stirring at 90°C for 2 hours. This solution was cooled to 40°C, and 20 g of hydrochloric acid with a concentration of 35% by mass was added. The solution was then cooled to 15°C, and 50 g of n-butylaldehyde and 90 g of n-heptaldehyde were added to carry out an acetalization reaction, resulting in precipitation of the reaction product. Furthermore, a hydrochloric acid solution prepared by diluting 100 g of hydrochloric acid with a concentration of 35% by mass with 100 g of pure water was added dropwise over 30 minutes. The temperature was then raised to 40°C at a rate of 2-3 / °C / 5 min, and the liquid temperature was maintained at 40°C to complete the reaction for 6 hours. The solution was then neutralized, washed with water, and dried by conventional methods to obtain a polyvinyl acetal resin powder. The resulting polyvinyl acetal resin was dissolved in CDCl ３ Dissolved in (deuterated chloroform) １ H-NMR and １３ The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using C-NMR (nuclear magnetic resonance spectroscopy). The total amount of acetal groups (the sum of the contents of each acetal unit) was calculated from the measured values. The results are shown in Table 1. The acetal units are the acetal units [R １ = (CH ２ ) ５ CH ３ ] and the acetal unit [R ２ = (CH ２ ) ２ CH ３ ] was.

[0063] (Example 4) (Preparation of Polyvinyl Acetal Resin) 150 g of polyvinyl alcohol with a saponification degree of 99.2 mol% and an average polymerization degree of 1700 was added to 1600 g of pure water and stirred at 90 ° C for 2 hours to dissolve. This solution was cooled to 40 ° C, and 30 g of 35% by weight hydrochloric acid and 30 g of Unisafe 10P-8 (polyoxyethylene polyoxypropylene cetyl ether, manufactured by NOF Corporation) diluted with pure water as a dispersant to a concentration of 20% by weight were added, followed by cooling to 10 ° C, and 55 g of n-butyl aldehyde and 75 g of n-decyl aldehyde were added to carry out an acetalization reaction, resulting in precipitation of the reaction product. Furthermore, a hydrochloric acid solution prepared by diluting 100 g of 35% by weight hydrochloric acid with 100 g of pure water was added dropwise over 30 minutes. The temperature was then raised to 40°C at a rate of 2 to 3°C per 5 minutes, and the liquid temperature was maintained at 40°C for 5 hours to complete the reaction. The mixture was then neutralized, washed with water, and dried in a conventional manner to obtain a polyvinyl acetal resin powder. The resulting polyvinyl acetal resin was dissolved in CDCl ３ Dissolved in (deuterated chloroform) １ H-NMR and １３ The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using C-NMR (nuclear magnetic resonance spectrum). The total amount of acetal groups (the sum of the contents of each acetal unit) was calculated from the measured values. The results are shown in Table 1. The content of each acetal unit was １３ The acetal unit was determined by C-NMR. １ = (CH ２ ) ８ CH ３ ] and the acetal unit [R ２ = (CH ２ ) ２ CH ３ ] was.

[0064] (Example 5) (Preparation of Polyvinyl Acetal Resin) 112 g of polyvinyl alcohol having a saponification degree of 98.5 mol% and an average polymerization degree of 500 was added to 1600 g of pure water and stirred at 90 ° C. for 2 hours to dissolve. This solution was cooled to 40 ° C., and 30 g of hydrochloric acid having a concentration of 35% by mass was added, followed by cooling to 3 ° C., and 55 g of n-butyl aldehyde and 75 g of n-decyl aldehyde were added to carry out an acetalization reaction, and the reaction product was precipitated. Furthermore, 30 g of Unisafe 10P-8 (polyoxyethylene polyoxypropylene cetyl ether, manufactured by NOF Corporation) diluted with pure water to a concentration of 20% by mass as a dispersant was added, and then a hydrochloric acid solution prepared by diluting 100 g of hydrochloric acid having a concentration of 35% by mass with 100 g of pure water was added dropwise over 30 minutes. The temperature was then raised to 40°C at a rate of 2 to 3°C per 5 minutes, and the liquid temperature was maintained at 40°C for 5 hours to complete the reaction. The mixture was then neutralized, washed with water, and dried in a conventional manner to obtain a powder of a long-chain alkyl-modified polyvinyl acetal resin. The obtained polyvinyl acetal resin was treated with CDCl ３ Dissolved in (deuterated chloroform) １ H-NMR and １３ The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using C-NMR (nuclear magnetic resonance spectrum). The total amount of acetal groups (the sum of the contents of each acetal unit) was calculated from the measured values. The results are shown in Table 1. The content of each acetal unit was １３ The acetal unit was determined by C-NMR. １ = (CH ２ ) ８ CH ３ ] and the acetal unit [R ２ = (CH ２ ) ２ CH ３ ] was.

[0065] (Example 6) (Preparation of Polyvinyl Acetal Resin) 112 g of polyvinyl alcohol having a saponification degree of 99.4 mol% and an average polymerization degree of 1700 was added to 1600 g of pure water and stirred at 90 ° C. for 2 hours to dissolve. This solution was cooled to 40 ° C., and 30 g of hydrochloric acid having a concentration of 35% by mass was added, followed by cooling to 10 ° C., and 35 g of n-butyl aldehyde and 100 g of n-decyl aldehyde were added to carry out an acetalization reaction, and the reaction product was precipitated. Furthermore, 30 g of Unisafe 10P-8 (polyoxyethylene polyoxypropylene cetyl ether, manufactured by NOF Corporation) diluted with pure water to a concentration of 20% by mass as a dispersant was added, and then a hydrochloric acid solution prepared by diluting 100 g of hydrochloric acid having a concentration of 35% by mass with 100 g of pure water was added dropwise over 30 minutes. The temperature was then raised to 40°C at a rate of 2 to 3°C per 5 minutes, and the liquid temperature was maintained at 40°C for 5 hours to complete the reaction. The mixture was then neutralized, washed with water, and dried in a conventional manner to obtain a powder of a long-chain alkyl-modified polyvinyl acetal resin. The obtained polyvinyl acetal resin was treated with CDCl ３ Dissolved in (deuterated chloroform) １ H-NMR and １３ The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using C-NMR (nuclear magnetic resonance spectrum). The total amount of acetal groups (the sum of the contents of each acetal unit) was calculated from the measured values. The results are shown in Table 1. The content of each acetal unit was １３ The acetal unit was determined by C-NMR. １ = (CH ２ ) ８ CH ３ ] and the acetal unit [R ２ = (CH ２ ) ２ CH ３ ] was.

[0066] Example 7 Preparation of Polyvinyl Acetal Resin A polyvinyl acetal resin powder was obtained in the same manner as in Example 1, except that 90 g of n-butyl aldehyde and 30 g of n-heptaldehyde were added instead of 70 g of n-butyl aldehyde and 75 g of n-decyl aldehyde. The obtained polyvinyl acetal resin was dissolved in CDCl３ Dissolved in (deuterated chloroform) １ H-NMR and １３ The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using C-NMR (nuclear magnetic resonance spectrum). The total amount of acetal groups (the sum of the contents of each acetal unit) was calculated from the measured values. The results are shown in Table 1. The content of each acetal unit was １３ The acetal unit was determined by C-NMR. １ = (CH ２ ) ５ CH ３ ] and the acetal unit [R ２ = (CH ２ ) ２ CH ３ ] was.

[0067] (Example 8) (Preparation of polyvinyl acetal resin) A polyvinyl acetal resin powder was obtained in the same manner as in Example 1, except that 135 g of n-heptaldehyde was added instead of 70 g of n-butyl aldehyde and 75 g of n-decyl aldehyde. The obtained polyvinyl acetal resin was dissolved in CDCl ３ Dissolved in (deuterated chloroform) １ H-NMR and １３ The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using C-NMR (nuclear magnetic resonance spectrum). The total amount of acetal groups (the sum of the contents of each acetal unit) was calculated from the measured values. The results are shown in Table 1. The content of each acetal unit was １３ The acetal unit was determined by C-NMR. １ = (CH ２ ) ５ CH ３ ] was.

[0068] Example 9 (Preparation of Polyvinyl Acetal Resin) 25 g of polyvinyl alcohol having a saponification degree of 99.1 mol% and an average degree of polymerization of 1700 was added to a flask containing 170 g of THF, heated to 65°C, and stirred for 1 hour. Thereafter, the mixture was cooled to 55°C, and 2.5 g of 35% by mass hydrochloric acid and 40 g of n-decyl aldehyde were added and reacted at 55°C for 6 hours. The solution was then poured into a water bath to precipitate the resin, and the resin was recovered. This resin was again dissolved in 100 g of THF, and then poured into an aluminum tray with a PET release film placed on it so that the release surface was facing up, and dried in an oven at 80°C for 5 hours or more to obtain a polyvinyl acetal resin film. The obtained polyvinyl acetal resin was dissolved in CDCl ３ Dissolved in (deuterated chloroform) １ H-NMR and １３ The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using C-NMR (nuclear magnetic resonance spectrum). The total amount of acetal groups (the sum of the contents of each acetal unit) was calculated from the measured values. The results are shown in Table 2. The content of each acetal unit was １３ The acetal unit was determined by C-NMR. １ = (CH ２ ) ８ CH ３ ] and the acetal unit [R ２ = (CH ２ ) ２ CH ３ ] was.

[0069] Example 10 (Preparation of Polyvinyl Acetal Resin) 110 g of polyvinyl alcohol having a saponification degree of 99.1 mol% and an average polymerization degree of 1100 was added to 1100 g of pure water and dissolved by stirring at 90°C for 2 hours. This solution was cooled to 70°C, and 45 g of 35% by mass hydrochloric acid was added and the mixture was maintained at 70°C for 2 hours to undergo a saponification reaction. The mixture was cooled to 7°C, and 75 g of n-butyl aldehyde and 50 g of 3-methylbutanal were added to carry out an acetalization reaction, resulting in precipitation of the reaction product. A hydrochloric acid solution prepared by diluting 120 g of 35% by mass hydrochloric acid with 120 g of pure water was added dropwise over 30 minutes. The mixture was then heated to 40°C at a rate of 2-3°C / 5 minutes, and the liquid temperature was maintained at 40°C for 5 hours to complete the reaction. The mixture was then neutralized, washed with water, and dried by conventional methods to obtain a polyvinyl acetal resin powder. The resulting polyvinyl acetal resin was dissolved in CDCl ３ Dissolved in (deuterated chloroform) １ H-NMR and １３ The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using C-NMR (nuclear magnetic resonance spectrum). The total amount of acetal groups (the sum of the contents of each acetal unit) was calculated from the measured values. The results are shown in Table 2. The content of each acetal unit was １３ The acetal unit was determined by C-NMR. １ =CH ２ CH (CH ３ ) ２ ] and the acetal unit [R ２ = (CH ２ ) ２ CH ３ ] was.

[0070] Example 11 (Preparation of Polyvinyl Acetal Resin) 170 g of polyvinyl alcohol having a saponification degree of 99.1 mol% and an average degree of polymerization of 1700 was added to 1700 g of pure water and dissolved by stirring at 90°C for 2 hours. This solution was cooled to 40°C, and 120 g of hydrochloric acid with a concentration of 35% by mass was added. The solution was then cooled to 15°C, and 130 g of n-butyl aldehyde was added. The liquid temperature was then maintained at 45°C to complete the reaction for 6 hours. After neutralization, water washing, and drying by conventional methods, a polyvinyl acetal resin powder was obtained. 25 g of the obtained polyvinyl acetal resin was added to a flask containing 220 g of THF and dissolved with stirring at 65°C. This solution was cooled to 55°C, and 0.5 g of 35 wt% hydrochloric acid and 7.0 g of n-heptaldehyde were added. After reacting at 55°C for 6 hours, the solution was poured into water to precipitate the resin, which was then recovered. This resin was again dissolved in 100 g of THF, poured into an aluminum tray with a PET release film placed on top, and dried in an oven at 80°C for 5 hours or more to obtain a polyvinyl acetal resin film. The resulting polyvinyl acetal resin was dissolved in CDCl ３ Dissolved in (deuterated chloroform) １ H-NMR and １３ The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using C-NMR (nuclear magnetic resonance spectrum). The total amount of acetal groups (the sum of the contents of each acetal unit) was calculated from the measured values. The results are shown in Table 2. The content of each acetal unit was １３ The acetal unit was determined by C-NMR. １ = (CH ２ ) ５ CH ３ ] and the acetal unit [R ２ = (CH ２ ) ２ CH ３ ] was.

[0071] (Example 12) (Preparation of Polyvinyl Acetal Resin) A polyvinyl acetal resin powder was obtained in the same manner as in Example 5, except that a carboxylic acid-modified polyvinyl alcohol (itaconic acid-modified, carboxylic acid modification amount: 0.7 mol%) having a saponification degree of 99.1 mol% and an average polymerization degree of 500 was used instead of the polyvinyl alcohol having a saponification degree of 98.5 mol% and an average polymerization degree of 500. The obtained polyvinyl acetal resin was dissolved in CDCl ３ Dissolved in (deuterated chloroform) １ H-NMR and １３ The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using C-NMR (nuclear magnetic resonance spectrum). The total amount of acetal groups (the sum of the contents of each acetal unit) was calculated from the measured values. The results are shown in Table 2. The content of each acetal unit was １３ The acetal unit was determined by C-NMR. １ = (CH ２ ) ８ CH ３ ] and the acetal unit [R ２ = (CH ２ ) ２ CH ３ ] was.

[0072] Comparative Example 1 Preparation of Polyvinyl Acetal Resin 160 g of carboxylic acid-modified polyvinyl alcohol (itaconic acid-modified, carboxylic acid modification amount: 0.1 mol%) with a saponification degree of 98.1 mol% and an average polymerization degree of 1700 was added to 1700 g of pure water and dissolved by stirring at 90°C for 2 hours. This solution was cooled to 40°C, and 120 g of hydrochloric acid with a concentration of 35% by mass was added. Thereafter, the solution was cooled to 25°C, and 80 g of n-butylaldehyde and 25 g of acetaldehyde were added to carry out an acetalization reaction, thereby precipitating the reaction product. The liquid temperature was then maintained at 50°C to complete the reaction for 6 hours. After neutralization, washing with water, and drying by conventional methods, a polyvinyl acetal resin powder was obtained. The obtained polyvinyl acetal resin was dissolved in CDCl ３ (chloroform) and １The content of each acetal unit, the amount of acetyl groups, the amount of hydroxyl groups, and the amount of carboxylic acid modification were measured using H-NMR (nuclear magnetic resonance spectrum). The total amount of acetal groups (the sum of the contents of each acetal unit) was calculated from the measured values. The content of each acetal unit was calculated as follows: １３ Quantitative analysis was performed using C-NMR, and the results are shown in Table 2. The acetal units were acetoacetal units and butyral units.

[0073] (Comparative Example 2) (Preparation of Polyvinyl Acetal Resin) 170 g of polyvinyl alcohol having a saponification degree of 98.0 mol% and an average degree of polymerization of 350 was added to 1700 g of pure water and dissolved by stirring at 90°C for 2 hours. This solution was cooled to 40°C, and 120 g of hydrochloric acid with a concentration of 35% by mass was added. Thereafter, the solution was cooled to 10°C, and 130 g of n-butyl aldehyde was added to carry out an acetalization reaction, thereby precipitating the reaction product. Next, the liquid temperature was maintained at 30°C, and the reaction was completed for 6 hours. After neutralization, washing with water, and drying by conventional methods, a polyvinyl acetal resin powder was obtained. The obtained polyvinyl acetal resin was dissolved in CDCl ３ Dissolved in (deuterated chloroform) １ The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using H-NMR (nuclear magnetic resonance spectroscopy). The total amount of acetal groups (the sum of the contents of each acetal unit) was calculated from the measured values. The results are shown in Table 2. The acetal units were butyral units.

[0074] (Comparative Example 3) (Preparation of Polyvinyl Acetal Resin) 170 g of polyvinyl alcohol with a saponification degree of 98.0 mol% and an average degree of polymerization of 500 was added to 1,700 g of pure water and stirred at 90°C for 2 hours to dissolve. This solution was cooled to 40°C, and 120 g of hydrochloric acid with a concentration of 35% by mass was added. Thereafter, the solution was cooled to 15°C, and 130 g of n-butyl aldehyde was added. Next, the liquid temperature was maintained at 40°C to complete the reaction for 6 hours, and then neutralized, washed with water, and dried by conventional methods to obtain a polyvinyl acetal resin powder. 25 g of the obtained polyvinyl acetal resin was added to a flask containing 220 g of THF and dissolved with stirring at 65°C. This solution was cooled to 55°C, and 0.5 g of hydrochloric acid with a concentration of 35% by weight and 2.1 g of n-butyl aldehyde were added. The reaction was allowed to proceed at 55°C for 5 hours, after which the solution was poured into water to precipitate the resin, which was then recovered. This resin was dissolved again in 100 g of THF, poured into an aluminum tray with a PET release film placed on top, and dried in an oven at 80°C for 5 hours or more to obtain a polyvinyl acetal resin film. ３ Dissolved in (deuterated chloroform) １ The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using H-NMR (nuclear magnetic resonance spectroscopy). The total amount of acetal groups (the sum of the contents of each acetal unit) was calculated from the measured values. The results are shown in Table 2. The acetal units were butyral units.

[0075] Comparative Example 4 Preparation of Polyvinyl Acetal Resin 170 g of polyvinyl alcohol having a saponification degree of 99.1 mol% and an average degree of polymerization of 1700 was added to 1700 g of pure water and dissolved by stirring at 90°C for 2 hours. This solution was cooled to 40°C, and 120 g of hydrochloric acid with a concentration of 35% by mass was added. Thereafter, the solution was cooled to 10°C, and 130 g of n-butyl aldehyde was added. Next, the liquid temperature was maintained at 45°C to complete the reaction for 6 hours, and the reaction was carried out by a conventional method, followed by neutralization, washing with water, and drying to obtain a polyvinyl acetal resin powder. The obtained polyvinyl acetal resin was dissolved in CDCl ３ Dissolved in (deuterated chloroform) １The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using H-NMR (nuclear magnetic resonance spectroscopy). The total amount of acetal groups (the sum of the contents of each acetal unit) was calculated from the measured values. The results are shown in Table 2. The acetal units were butyral units.

[0076] (Comparative Example 5) (Preparation of Polyvinyl Acetal Resin) 160 g of polyvinyl alcohol having a saponification degree of 88.0 mol% and an average degree of polymerization of 2,300 was added to 1,700 g of pure water and stirred at 90°C for 2 hours to dissolve. This solution was cooled to 40°C, and 30 g of hydrochloric acid with a concentration of 35% by mass was added. Thereafter, the solution was cooled to 10°C, and 130 g of n-butyl aldehyde was added to carry out an acetalization reaction, precipitating the reaction product. Furthermore, a hydrochloric acid solution prepared by diluting 180 g of hydrochloric acid with a concentration of 35% by mass with 180 g of pure water was added dropwise over 30 minutes. Next, the temperature was raised to 50°C at a rate of 2 to 3°C per 5 minutes, and the liquid temperature was maintained at 50°C for 3 hours to complete the reaction. After neutralization, washing with water, and drying by conventional methods, a polyvinyl acetal resin powder was obtained. 25 g of the obtained polyvinyl acetal resin was added to a flask containing 220 g of THF and dissolved with stirring at 65°C. This solution was cooled to 55°C, and 0.5 g of 35 wt% hydrochloric acid and 7 g of n-heptaldehyde were added. After reacting at 55°C for 6 hours, the solution was poured into water to precipitate the resin, which was then recovered. This resin was again dissolved in 100 g of THF, poured into an aluminum tray with a PET release film placed on it so that the release surface was facing up, and dried in an oven at 80°C for 5 hours or more to obtain a polyvinyl acetal resin film. The obtained polyvinyl acetal resin was dissolved in CDCl ３ Dissolved in (deuterated chloroform) １ H-NMR and １３ The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using C-NMR (nuclear magnetic resonance spectrum). The total amount of acetal groups (the sum of the contents of each acetal unit) was calculated from the measured values. The results are shown in Table 2. The content of each acetal unit was １３ The acetal unit was determined by C-NMR. １ = (CH ２ )５ CH ３ ] and the acetal unit [R ２ = (CH ２ ) ２ CH ３ ] was.

[0077] <Evaluation> The obtained polyvinyl acetal resins were evaluated as follows. (1) High-Performance Liquid Chromatography [HPLC] Analysis The polyvinyl acetal resins obtained in the Examples and Comparative Examples were adjusted to a concentration of 0.2 mg / mL using a tetrahydrofuran (THF) / isopropanol (IPA) = 7 / 3 [volume ratio] solvent to prepare a measurement sample. The obtained measurement sample was subjected to HPLC analysis under the following HPLC conditions, and the retention time of the peak top of the main peak was measured. The half-width was also calculated from the peak width at 50% of the main peak height.

[0078] [HPLC conditions] Apparatus: Prominence (Shimadzu Corporation) Column: X-BridgeBEH (3.5 μm, 2.1 mm × 50 mm, Waters) Column temperature: 45 ° C. Injection volume: 20 μL Mobile phase: Mobile phase A (Milli-Q water), mobile phase B (mixture of THF and IPA [THF / IPA = 7 / 3 (volume ratio)]) Mobile phase concentration gradient: A / B = 90 / 10 (volume ratio) from the start until 10 minutes, after which the volume ratio was changed linearly with time and maintained at A / B = 0 / 100 (volume ratio) 20 minutes after the start Flow rate: 0.4 mL / min Detector: Evaporative light scattering detector (ELSD, 40 ° C.)

[0079] (2) Measurement of Sodium Content The sodium content of the obtained polyvinyl acetal resin was measured using an ICP emission spectrometer (Shimadzu Corporation, ICPE-9000).

[0080] (3) Measurement of Organic Solvent Content The obtained polyvinyl acetal resin was subjected to measurement of the organic solvent content. ３ Dissolved in (deuterated chloroform) １The content of each acetal unit, the amount of acetyl groups, the amount of hydroxyl groups, and the amount of organic solvents, THF (1.81-1.88 ppm) and methanol (3.15-3.2 ppm), were measured using H-NMR (nuclear magnetic resonance spectroscopy). From the measured values, the content of the organic solvent relative to the polyvinyl acetal resin was calculated.

[0081] (4) Measurement of Glass Transition Temperature The glass transition temperature (Tg) of the obtained polyvinyl acetal resin was measured using a differential scanning calorimeter (DSC).

[0082] (5) Swelling Ratio in Electrolyte Solution (Preparation of Resin Sheet) The polyvinyl acetal resin solutions obtained in the Examples and Comparative Examples were applied to a release-treated polyethylene terephthalate (PET) film so that the film thickness after drying was 30 μm, and then dried to prepare a resin sheet. The resin sheet was then cut into 2 cm squares to prepare a resin sheet test piece.

[0083] (Swelling ratio evaluation) After accurately weighing the obtained test piece, the test piece was immersed in an electrolyte solution of 1 mol / L LiPF ６ The test piece was immersed in a mixed solution of EC:DEC:EMC=3:4:3 containing the compounds, and left at 45° C. for 24 hours. After leaving, the test piece was taken out and weighed, and the swelling ratio of the resin sheet was calculated using the following formula (3), and evaluated according to the following criteria: Swelling ratio=resin weight after impregnation / resin weight before impregnation×100 (3) ○: swelling ratio less than 180% △: swelling ratio 180% or more but less than 300% ×: swelling ratio 300% or more

[0084] (6) Battery Performance Evaluation (a) Secondary Battery Fabrication The polyvinyl acetal resins obtained in the Examples and Comparative Examples were dissolved in N-methylpyrrolidone (hereinafter referred to as NMP) to obtain an 8 wt % resin solution. To the resin solution, acetylene black (Li-100, manufactured by Denki Kagaku Kogyo Co., Ltd.) was added as a conductivity imparting agent, lithium iron phosphate (manufactured by Dynanonic Corporation) as an active material, and NMP. The mixture was then kneaded using a Thinky Awatori Rentaro to obtain a secondary battery electrode composition. The weight ratios of the active material, acetylene black, and polyvinyl acetal resin in the composition were 95.5, 2.0, and 2.5. The obtained secondary battery electrode composition was uniformly applied to a 20 μm thick aluminum foil sheet, which was then dried in a hot air dryer at 100 °C to obtain a secondary battery electrode. This sheet was pressed using a roll press at 150 °C and punched out to a diameter of 11 mm to obtain a positive electrode. The capacity of the obtained positive electrode was calculated from the mass of the positive electrode active material per unit area and the theoretical capacity of the positive electrode active material (170 mAh / g). As a result, the capacity of the positive electrode was 3.0 mAh / cm ２ A sheet of copper foil coated with natural graphite (HS-LIB-N-Gr-002, manufactured by Hosen Co., Ltd.) was punched out to a diameter of 14 mm to obtain a negative electrode. ６ A mixed solvent of EC:DEC:EMC (3:4:3 (volume ratio), manufactured by Toyama Pharmaceutical Co., Ltd.) containing (1M) was used. The positive electrode was placed in the bottom can of a 2032 coin cell with the electrode layer surface facing upward. Next, a 16 μm thick porous polypropylene separator punched to a diameter of 16 mm was placed, and the electrolyte was poured in so as to prevent air from entering. The negative electrode was then placed with the surface coated with natural graphite facing downward. A 15 mm diameter and 1 mm thick SUS spacer and spring were further placed on top of the negative electrode, and the top lid was crimped and sealed using a dedicated jig to obtain a secondary battery.

[0085] (b) Measurement of Internal Resistance The obtained secondary battery was connected to a charge / discharge tester (TOSCAT3100, manufactured by Toyo Systems Co., Ltd.) and left in a thermostatic chamber at 25 ° C. for 12 hours without current flow. Next, constant current / constant voltage (CCCV) charging at a current of 0.2 C (charge end voltage: 4.0 V, CV STOP: 5 hours, or current value reached 0.02 C, rest time after charging: 10 minutes), and constant current (CC) discharging at a current of 0.2 C (discharge end voltage: 2.8 V, rest time after discharging: 10 minutes) were repeated five times to confirm whether the battery functioned. Subsequently, DC resistance evaluation was performed in an environment of 25 ° C. DC resistance evaluation was performed by CCCV charging at a current of 0.2 C, followed by CC discharging at a current of 0.2 C for 2.5 hours to a 50% discharge state. Subsequently, the battery was discharged at a current of 1 C for 10 seconds, and the resistance when a current of 1 C was applied was calculated using the following formula (4): Absolute value of (battery voltage before discharge - battery voltage after discharge) / discharge current = resistance (4) Next, the discharge current was changed to 2 C and 4 C in the same manner, and the resistance at a 2 C discharge current and a 4 C discharge current were calculated. The average value of the resistances obtained at currents of 1 C, 2 C, and 4 C was taken as the DC resistance (internal resistance), and evaluated according to the following criteria: ○: Internal resistance less than 150 Ω △: Internal resistance 150 Ω or more but less than 300 Ω ×: If the internal resistance was 300 Ω or more, or if the swelling ratio exceeded 300% in the above swelling ratio evaluation, the internal resistance was also rated as ×.

[0086] (7) Solvent Solubility 19.4 ml of dihydroterpinyl acetate (DHTA) was added to a 50 ml container, and 0.6 g of the polyvinyl acetal resin obtained in the Examples and Comparative Examples was added while stirring. The mixture was stirred at room temperature for 30 minutes, then transferred to a 90°C water bath and stirred for 7 hours to dissolve. The resulting solution was evaluated according to the following criteria: ◯: The solution was colorless and transparent (completely dissolved); △: Some residue remained, but the resin dissolved to the point where it no longer retained its original shape; ×: Swelled and insoluble (remained in its original shape).

[0087] (8) Print bleeding 5 g of the solution obtained in "(7) Solvent solubility" was placed in a 50 ml centrifuge tube and heated in an 80°C water bath for 30 minutes, after which 0.5 g of Ni powder was added and dispersed using a vortex mixer. Centrifugation was then performed to recover the supernatant solution. 1.2 g of the recovered supernatant solution was diluted with 13.66 ml of DHTA, and the (total light) transmittance was measured using a spectroscopic haze meter (SH7000, manufactured by Nippon Denshoku Co., Ltd.) and evaluated according to the following criteria. The better the dispersibility of Ni, the less Ni sinks and remains in the supernatant solution, resulting in lower transmittance and suppressing bleeding during printing. ◯: Transmittance less than 60% △: Transmittance 60% or more but less than 80% ×: Transmittance 80% or more

[0088] (9) Adhesion A 1:1 mixed solvent of toluene and ethanol was placed in a 50 ml container, and the polyvinyl acetal resin obtained in the Examples and Comparative Examples was added and dissolved to prepare a 5-15 wt % resin solution. The resin solution was applied to a release-treated PET film to a thickness of 10 mil using a coater, and then heated and dried to prepare a resin sheet. The tack strength of the obtained resin sheet was measured using a tack tester (TAC1000, manufactured by Rhesca Co., Ltd.) under the following conditions: load 300 N, pressing time 30 seconds, lifting speed 1 mm / s, plate temperature 65°C, probe temperature 60°C. Five measurements were taken for each resin sheet, and the average values ​​were evaluated according to the following criteria: ◯: 150 gf or more △: 80 gf or more but less than 150 gf ×: Less than 80 gf

[0089]

[0090]

[0091] According to the present invention, a polyvinyl acetal resin can be provided that can prevent swelling due to an electrolytic solution and produce an electrode with low internal resistance, making it possible to fabricate a high-power storage battery. Also, an electrode composition, a secondary battery electrode, and a conductive paste using the polyvinyl acetal resin can be provided.

Claims

1. A polyvinyl acetal resin having a main peak top retention time of 26.9 minutes or longer and an average degree of polymerization of less than 2,300 in HPLC analysis under the following conditions: [HPLC conditions] Apparatus: Prominence (Shimadzu Corporation) Column: X-BridgeBEH (3.5 μm, 2.1 mm × 50 mm, Waters Corporation) Column temperature: 45 ° C. Injection volume: 20 μL Mobile phase: Mobile phase A (Milli-Q water), mobile phase B (mixture of THF and IPA [THF / IPA = 7 / 3 (volume ratio)]) Mobile phase concentration gradient: A / B = 90 / 10 (volume ratio) from the start to 10 minutes, and then the volume ratio is changed linearly with time and held at A / B = 0 / 100 (volume ratio) 20 minutes after the start Flow rate: 0.4 mL / min Detector: Evaporative light scattering detector (ELSD, 40 ° C.) 2. The polyvinyl acetal resin according to claim 1, having a sodium content of 200 ppm by mass or less.

3. The polyvinyl acetal resin according to claim 1 or 2, having a glass transition temperature of 65°C or lower.

4. The polyvinyl acetal resin according to any one of claims 1 to 3, wherein the content of the organic solvent is 1% by weight or less.

5. The polyvinyl acetal resin according to any one of claims 1 to 4, wherein the half-value width of the main peak obtained in the HPLC analysis is 0.450 or less.

6. Having an acetal unit represented by the following formula (1), wherein R １ The polyvinyl acetal resin according to any one of claims 1 to 5, wherein is an alkyl group having 4 or more carbon atoms.

7. The polyvinyl acetal resin according to any one of claims 1 to 6, having an average degree of polymerization of less than 2,200.

8. The polyvinyl acetal resin according to any one of claims 1 to 7, which is used for an electrode.

9. A composition for electrodes, comprising the polyvinyl acetal resin according to any one of claims 1 to 8, a filler, and a solvent.

10. A secondary battery electrode comprising the polyvinyl acetal resin according to any one of claims 1 to 8 and an active material.

11. A conductive paste containing the polyvinyl acetal resin according to any one of claims 1 to 8, an organic solvent, and a conductive powder.

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