Modified polyvinyl acetal resin and composition for storage battery electrode

Abstract

To provide a modified polyvinyl acetal resin which can prevent degradation in an electrolytic solution even when an electrode for a storage battery is used, and can manufacture a battery electrode of a high output, and a composition for a storage battery electrode using the modified polyvinyl acetal resin.SOLUTION: A modified polyvinyl acetal resin contains a structural unit having a fluorine atom.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a modified polyvinyl acetal resin capable of preventing deterioration by an electrolytic solution when used for an electrode of a storage battery and capable of producing a high-output storage battery, and a composition for a storage battery electrode using the modified polyvinyl acetal resin.

Background Art

[0002] Polyvinyl acetal resin is a resin synthesized from polyvinyl alcohol as a raw material and has an acetyl group, a hydroxyl group, and an acetal group in its side chain. Thereby, excellent toughness, adhesiveness, etc. can be exhibited. Further, it is possible to change the resin physical properties by changing the ratio of the side chain groups. Utilizing such characteristics, polyvinyl acetal resin is used in many applications, for example, electrodes of storage batteries, pigment compositions, ceramic green sheets, etc.

[0003] In recent years, with the spread of portable electronic devices such as portable video cameras and portable personal computers, the demand for storage batteries (secondary batteries) as mobile power sources has increased rapidly. Further, the requirements for miniaturization, weight reduction, and high energy density of such secondary batteries are very high. Therefore, as a secondary battery, research and development of a lithium secondary battery using lithium or a lithium alloy for a negative electrode is being actively carried out. This lithium secondary battery has excellent characteristics such as high energy density, little self-discharge, and light weight.

[0004] However, when a conventionally general-purpose resin is used as a binder, while it is possible to produce a flexible thin film, the binding property between the current collector and the active material is inferior, so that part or all of the active material may peel off or fall off from the current collector during the battery manufacturing process. Further, when the battery is charged and discharged, insertion and release of lithium ions are repeated in the active material, and accordingly, there is also a problem that the problem of peeling and falling off of the active material from the current collector may occur.

[0005] In order to solve the above problems, attempts have been made to use new binders. For example, Patent Document 1 describes a binder for non-aqueous secondary batteries composed of a copolymer of an acidic functional group-containing monomer and an amide group-containing monomer. By using such a binder, it is said that good adhesion to the electrode can be achieved and safety during manufacturing can be realized.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, when the binder described in Patent Document 1 is used, the electrolyte resistance is insufficient and the resistance of the electrode is high.

[0008] The modified polyvinyl acetal resin according to the present invention can reduce the electrode resistance and prevent deterioration by the electrolyte when used in the electrodes of storage batteries, making it possible to produce high-output storage batteries. That is, an object of the present invention is to provide a modified polyvinyl acetal resin having the above-described excellent characteristics and a composition for storage battery electrodes using the modified polyvinyl acetal resin.

Means for Solving the Problems

[0009] The present invention is a modified polyvinyl acetal resin containing a structural unit having a fluorine atom. The present invention will be described in detail below.

[0010] As a result of intensive studies, the inventors of the present invention have found that a modified polyvinyl acetal resin containing a structural unit having a fluorine atom can reduce the electrode resistance when used in an electrode of a storage battery, prevent deterioration by an electrolytic solution, and enable the production of a high-output storage battery, thus completing the present invention.

[0011] The following is an explanation of terms used in this specification. The "amount of fluorinated modified unit" means the content of a structural unit having a fluorine atom. The "amount of fluorinated modified acetal bond unit" means the content of a structure (fluorinated modified acetal bond unit) in which a fluorine atom is bonded via an acetal bond. The "degree of non-fluorinated acetalization" means the content of a structural unit having an acetal group excluding the above-mentioned fluorinated modified acetal bond unit. The "degree of acetalization" means the content of a structural unit having an acetal group. That is, it includes the fluorinated modified acetal bond unit.

[0012] The modified polyvinyl acetal resin of the present invention contains a structural unit having a fluorine atom. By containing the structural unit having a fluorine atom, when used in an electrode of a storage battery, the electrode resistance can be reduced, deterioration by an electrolytic solution can be prevented, and it becomes possible to produce a high-output storage battery. In addition, the structural unit having a fluorine atom preferably has one or more fluorine atoms per structural unit, and more preferably has two or more fluorine atoms.

[0013] In the present invention, the structural unit having a fluorine atom is not particularly limited as long as it has a structure having a fluorine atom, but a structure in which a fluorine atom is bonded via an acetal bond, a structure having a fluorine atom or a fluorine atom-containing group in a side chain, etc. are preferable. Note that the structure in which a fluorine atom is bonded via an acetal bond includes a case where it is bonded via a linking group other than an acetal bond.

[0014] When the structural unit having a fluorine atom is a structure in which the fluorine atom is bonded via an acetal bond (hereinafter, such a structural unit is also referred to as a fluorinated modified acetal bond unit), it is preferably a structural unit represented by the following formula (1). By having the structural unit represented by the following formula (1), an appropriate distance can be maintained between the main chain of the modified polyvinyl acetal resin and the fluorine atom. As a result, when the modified polyvinyl acetal resin is used for the electrode of a storage battery, the electrode resistance can be reduced.

[0015]

Chemical formula

[0016] Examples of the fluoroalkyl group include a fluoromethyl group (-CH2F), a fluoroethyl group (-CH2CH2F), a difluoromethyl group, a difluoroethyl group, a fluoropropyl group, a trifluoromethyl group, and the like. In formula (1), R 1 is preferably a fluorine atom, -CH2F, or -CH2CH2F. Further, in the present invention, it is preferable to use a combination in which R 1 is a fluorine atom and R 2 , R 3 are hydrogen atoms.

[0017] Examples of the fluorophenyl group include a 2-fluorophenyl group, a 3-fluorophenyl group, a 4-fluorophenyl group, a 2,4,6-trifluorophenyl group, a perfluorophenyl group, and the like. In addition, examples of the fluoroalkylphenyl group include a 4-trifluoromethylphenyl group, a 3-trifluoromethylphenyl group, a 3,5-ditrifluoromethylphenyl group, a 4-pentafluoroethylphenyl group, a 4-perfluorohexylphenyl group, and the like. Among them, R 1 is preferably a fluorophenyl group or a fluoroalkylphenyl group, and particularly preferably a 4-fluorophenyl group or a 4-trifluoromethylphenyl group.

[0018] When the modified polyvinyl acetal resin of the present invention has a fluorinated modified acetal bond unit, the fluorinated modified acetal bond unit preferably has an aromatic ring. Thereby, when the obtained modified polyvinyl acetal resin is used for an electrode of a storage battery, the electrode resistance can be reduced. The fluorinated modified acetal bond unit preferably has one or more fluorine atoms per structural unit, and more preferably has two or more fluorine atoms.

[0019] When the structural unit having the fluorine atom has a structure having a fluorine atom or a fluorine atom-containing group in the side chain (hereinafter, such a structural unit is also referred to as a fluorinated modified side chain bond unit), it is preferably a structural unit represented by the following formula (2). By having the structural unit represented by the following formula (2), the modified polyvinyl acetal resin is excellent in adhesiveness and dispersibility, and is further excellent in the stability over time of the obtained composition. In addition, when used for an electrode of a storage battery, the electrode resistance can be reduced.

[0020]

Chemical formula

[0021] The above R 4 As the alkylene group shown in 4 , it is preferably an alkylene group having 1 to 20 carbon atoms. For example, a linear alkylene group, a branched alkylene group, or a cyclic alkylene group is preferable. Examples of the above linear alkylene group include a methylene group, an ethylene group, a trimethylene group, a tetramethylene group, a pentamethylene group, a hexamethylene group, an octamethylene group, and a decamethylene group. Examples of the above branched alkylene group include a methylmethylene group, a methylethylene group, a 1-methylpentylene group, and a 1,4-dimethylbutylene group. Examples of the above cyclic alkylene group include a cyclopropylene group, a cyclobutylene group, and a cyclohexylene group. Among them, linear alkyl groups such as a methylene group, an ethylene group, an n-propylene group, and an n-butylene group are preferable, and a methylene group and an ethylene group are more preferable. The above R 5 As the fluoroalkyl group shown in 5 , the same ones as those of R 1 can be used. In addition, in the present invention, it is preferable to use a combination in which R 4 is a single bond and R 5 is a hydrogen atom.

[0022] The content of the structural unit having a fluorine atom (amount of fluorinated modified unit) in the modified polyvinyl acetal resin of the present invention preferably has a lower limit of 0.1 mol%. By setting the amount of the fluorinated modified unit to 0.1 mol% or more, the electrode resistance of the obtained composition can be reduced. A more preferable lower limit of the amount of the fluorinated modified unit is 1.0 mol%, and a further preferable lower limit is 4.0 mol%. Although not particularly limited, from the viewpoint of handling in production, the upper limit of the amount of the fluorinated modified unit is preferably 30 mol%, and more preferably 25 mol% or less. In addition, when the modified polyvinyl acetal resin of the present invention contains both a fluorinated modified acetal bond unit and a fluorinated modified side chain bond unit, the amount of the fluorinated modified unit means the total of the two. Incidentally, the amount of the fluorinated modification unit can be measured by the method described in the examples below (the method of measuring by proton and fluorine NMR).

[0023] When the modified polyvinyl acetal resin of the present invention contains a structure in which a fluorine atom is bonded via an acetal bond (fluorinated modified acetal bond unit), the more preferable lower limit of the content of the fluorinated modified acetal bond unit is 0.1 mol%. By setting the content of the fluorinated modified acetal bond unit to 0.1 mol% or more, the electrode resistance of the resulting composition can be reduced. The more preferable lower limit of the content of the fluorinated modified acetal bond unit is 1.0 mol%, and the further preferable lower limit is 4.0 mol%. Although not particularly limited, from the viewpoint of handling properties in production, the upper limit of the content of the fluorinated modified acetal bond unit is preferably 30 mol%, and more preferably 25 mol% or less.

[0024] When the modified polyvinyl acetal resin of the present invention contains a structure having a fluorine atom or a fluorine atom-containing group in the side chain (fluorinated modified side chain bond unit), the more preferable lower limit of the content of the fluorinated modified side chain bond unit is 0.1 mol%, and the more preferable upper limit is 15 mol%. Further, the more preferable lower limit is 0.5 mol%, and the more preferable upper limit is 10 mol%. By setting it within the above range, the adhesiveness, dispersibility, and the stability over time of the resulting composition can be improved.

[0025] When the modified polyvinyl acetal resin of the present invention contains both a fluorinated modified acetal bond unit and a fluorinated modified side chain bond unit, the ratio of the two (fluorinated modified acetal bond unit / fluorinated modified side chain bond unit) is preferably 0.5 or more and 3 or less, and more preferably 1 or more and 2 or less.

[0026] The modified polyvinyl acetal resin of the present invention has a structural unit having a hydroxyl group, a structural unit having an acetyl group, and a structural unit having an acetal group.

[0027] The modified polyvinyl acetal resin of the present invention has the structural unit having the above hydroxyl group. In the modified polyvinyl acetal resin of the present invention, the preferable lower limit of the content (amount of hydroxyl groups) of the structural unit having the above hydroxyl groups is 20 mol%, and the preferable upper limit is 70 mol%. By setting the amount of hydroxyl groups to 20 mol% or more, the solubility in an organic solvent is improved, and it can be suitably used as a composition. By setting it to 70 mol% or less, the flexibility of the resin can be maintained. A more preferable lower limit of the amount of hydroxyl groups is 25 mol%, and a more preferable upper limit is 65 mol%.

[0028] The modified polyvinyl acetal resin of the present invention has a structural unit having the above acetyl group. In the modified polyvinyl acetal resin of the present invention, the preferable lower limit of the content (amount of acetyl groups) of the structural unit having the above acetyl groups is 0.1 mol%, and the preferable upper limit is 20 mol%. By setting the amount of acetyl groups to 0.1 mol% or more, the flexibility of the resin can be maintained. By setting the amount of acetyl groups to 20 mol% or less, when used for the electrode of a storage battery, the resistance to the electrolytic solution is improved, and it is possible to prevent the resin from eluting into the electrolytic solution and the battery from deteriorating. A more preferable lower limit of the amount of acetyl groups is 0.3 mol%, and a more preferable upper limit is 10 mol%.

[0029] The modified polyvinyl acetal resin of the present invention has a structural unit having the above acetal group. The content (non-fluorinated acetalization degree) of the structural unit having the above acetal group in the modified polyvinyl acetal resin of the present invention is preferably 20 mol% or more and 75 mol% or less. By setting the non-fluorinated acetalization degree to 20 mol% or more, the solubility in an organic solvent is improved, and it can be suitably used as a composition. By setting the non-fluorinated acetalization degree to 75 mol% or less, adhesiveness and dispersibility can be maintained. More preferably, it is 25 mol% or more and 70 mol% or less.

[0030] The modified polyvinyl acetal resin of the present invention may or may not have an acetoacetal group acetalized with acetaldehyde. When the acetoacetal group is not present, the electrolyte resistance of the resulting composition is improved. When the acetoacetal group is present, the content (amount of acetoacetal group) of the acetoacetal group is preferably 5 mol% or more and 50 mol% or less, more preferably 10 mol% or more and 30 mol% or less. In addition, the content (butyral group amount) of the butyl acetal group acetalized with butyraldehyde in the modified polyvinyl acetal resin of the present invention is preferably 10 mol% or more and 75 mol% or less. By setting it within the above range, water resistance can be maintained and excellent viscosity characteristics can be obtained. More preferably, it is 20 mol% or more and 70 mol% or less.

[0031] The amounts of the above hydroxyl group, acetyl group, non-fluorinated acetalization degree, acetoacetal group, and butyral group are 1 It can be calculated by H-NMR (nuclear magnetic resonance spectrum).

[0032] When the modified polyvinyl acetal resin of the present invention contains both a fluorinated modified acetal bond unit and a structural unit having other acetal groups, the acetalization degree [non-fluorinated acetalization degree + amount of fluorinated modified acetal bond unit] is preferably 25 mol% or more and 80 mol% or less. By setting it within the above range, while maintaining solubility in an organic solvent, adhesiveness and dispersibility are excellent, and the resulting composition can achieve high stability over time. The acetalization degree is more preferably 30 mol% or more and 75 mol% or less. In addition, the non-fluorinated acetalization degree [non-fluorinated acetalization degree / amount of fluorinated modified acetal bond unit] with respect to the content of the fluorinated modified acetal bond unit is preferably 4 or more and 50 or less. By being within the above range, adhesiveness, dispersibility, and the stability over time of the resulting composition are improved. The non-fluorinated acetalization degree / amount of fluorinated modified acetal bond unit is more preferably 4 or more and 20 or less.

[0033] In the modified polyvinyl acetal resin of the present invention, the total amount of the non-fluorinated acetalization degree and the fluorinated modification unit amount [non-fluorinated acetalization degree + fluorinated modification unit amount] is preferably 25 mol% or more and 80 mol% or less. By being within the above range, the adhesiveness, dispersibility, and the stability over time of the resulting composition are improved. More preferably, the non-fluorinated acetalization degree + fluorinated modification unit amount is 30 mol% or more and 75 mol% or less.

[0034] In the modified polyvinyl acetal resin of the present invention, the ratio of the non-fluorinated acetalization degree to the fluorinated modification unit amount [non-fluorinated acetalization degree / fluorinated modification unit amount] is preferably 1 or more and 50 or less. By being within the above range, the adhesiveness, dispersibility, and the stability over time of the resulting composition are improved. More preferably, the non-fluorinated acetalization degree / fluorinated modification unit amount is 4 or more and 24 or less, and still more preferably 8 or more and 20 or less.

[0035] The preferable lower limit of the degree of polymerization of the modified polyvinyl acetal resin of the present invention is 200, and the preferable upper limit is 4000. When the degree of polymerization is 200 or more, the adhesiveness becomes more excellent. When the degree of polymerization is 4000 or less, the dispersibility becomes more excellent. The more preferable lower limit of the degree of polymerization is 500, and the more preferable upper limit is 2500.

[0036] Examples of the method for producing the modified polyvinyl acetal resin of the present invention include a method of preparing polyvinyl alcohol containing a structural unit having a fluorine atom and then acetalizing it, a method of acetalizing polyvinyl alcohol not containing a structural unit having a fluorine atom and then adding a fluorine atom, and the like. Further, examples include a method of preparing polyvinyl alcohol containing a structural unit having a fluorine atom and polyvinyl alcohol not containing a structural unit having a fluorine atom, and then introducing a structural unit having a fluorine atom by acetalization. More specifically, a method of preparing polyvinyl alcohol having the structural unit represented by the above formula (2) in advance and then acetalizing it, a method of acetalizing polyvinyl alcohol having no structural unit represented by the above formula (2) and then adding a portion corresponding to R 4 , R 5 and the like can be mentioned. Further, a method of preparing polyvinyl alcohol having the structural unit represented by the above formula (2) in advance, preparing polyvinyl alcohol having no structural unit represented by the above formula (2), and then introducing the structural unit represented by the above formula (1) by acetalization and the like can be mentioned.

[0037] As a method for producing polyvinyl alcohol containing the structural unit having the above fluorine atom, for example, a method of copolymerizing heptafluoro-2-propyl allyl ether and vinyl acetate and then adding an acid or an alkali to an alcohol solution of the obtained copolymer to saponify it can be mentioned. Further, polyvinyl alcohol containing the structural unit having the above fluorine atom may be produced by a method of adding a fluorine atom. Further, as a method of adding the above fluorine atom, for example, a method of reacting polyvinyl alcohol with fluorine gas can be mentioned.

[0038] Polyvinyl alcohol not containing the structural unit having the above fluorine atom (hereinafter, also simply referred to as polyvinyl alcohol) can be obtained, for example, by saponifying a copolymer of a vinyl ester and ethylene. Examples of the above vinyl ester include vinyl formate, vinyl acetate, vinyl propionate, vinyl pivalate and the like. Among them, vinyl acetate is preferable from the viewpoint of economy.

[0039] As a method of introducing a structural unit having a fluorine atom by the above acetalization, a method of reacting polyvinyl alcohol with an aldehyde having a fluorine atom or an aldehyde equivalent can be used. When using such a method, it is preferable to react 1 to 20 parts by weight of an aldehyde or aldehyde equivalent having a fluorine atom with respect to 100 parts by weight of polyvinyl alcohol. In particular, by setting it to 20 parts by weight or less, thickening during the reaction can be suppressed, and the modified polyvinyl acetal resin of the present invention can be suitably produced.

[0040] Examples of the aldehyde having a fluorine atom include fluorine atom-containing aliphatic aldehydes and fluorine atom-containing aromatic aldehydes. Examples of the fluorine atom-containing aliphatic aldehyde include fluoroacetaldehyde, difluoroacetaldehyde, trifluoroacetaldehyde, 2,2,3,3,3-pentafluoropropionaldehyde, 3-fluoropropionaldehyde, 3,3,3-trifluoropropionaldehyde, 4-fluorobutyraldehyde, and the like. Examples of the fluorine atom-containing aromatic aldehyde include fluorobenzaldehyde, fluoromethylbenzaldehyde, difluoromethylbenzaldehyde, trifluoromethylbenzaldehyde, tetrafluorobenzaldehyde, pentafluorobenzaldehyde, 3-(4-fluorophenyl)propionaldehyde, and the like. The aldehyde equivalent is a compound having a protecting group attached to an aldehyde or a compound that can be converted into an aldehyde by a generally used method, and examples thereof include acetal, hemiacetal, aldehyde hydrate, and the like. Among them, an aldehyde equivalent having a fluorine atom is preferable. Examples of the aldehyde equivalent having a fluorine atom include difluoroacetaldehyde ethyl hemiacetal, 2-(perfluorohexyl)acetaldehyde dimethyl acetal, fluoroacetaldehyde dimethyl acetal, fluoroacetaldehyde diethyl acetal, 2-fluoromethyl-1,3-dioxolane, 2-(perfluorohexyl)acetaldehyde dimethyl acetal, difluoroacetaldehyde dimethyl acetal, difluoroacetaldehyde diethyl acetal, trifluoroacetaldehyde dimethyl acetal, trifluoroacetaldehyde diethyl acetal, trifluoroacetaldehyde methyl hemiacetal, trifluoroacetaldehyde ethyl hemiacetal, 2,2,2-trifluoromethyl-1,3-dioxolane, 3-fluoropropionaldehyde dimethyl acetal, 3-fluoropropionaldehyde diethyl acetal, 2-(2-fluoroethyl)-1,3-dioxolane, 4-fluorobutanal dimethyl acetal, 4-fluorobutanal diethyl acetal, 2-(3-fluoropropyl)-1,3-dioxolane, and the like.

[0041] The modified polyvinyl acetal resin of the present invention may be copolymerized with an ethylenically unsaturated monomer as long as 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, (anhydrous) phthalic acid, (anhydrous) maleic acid, (anhydrous) itaconic acid, and the like. Further, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, trimethyl-(3-acrylamido-3-dimethylpropyl)-ammonium chloride, acrylamide-2-methylpropanesulfonic acid and its sodium salt, and the like can be mentioned. Furthermore, ethyl vinyl ether, butyl vinyl ether, N-vinylpyrrolidone, vinyl chloride, vinyl bromide, vinyl fluoride, vinylidene chloride, sodium vinyl sulfonate, sodium allyl sulfonate, and the like can be mentioned. Also, a terminally modified polyvinyl alcohol obtained by copolymerizing a vinyl ester monomer such as vinyl acetate and ethylene in the presence of a thiol compound such as thiol acetic acid or mercaptopropionic acid and saponifying it can also be used.

[0042] Examples of the use of the modified polyvinyl acetal resin of the present invention include binders and dispersants for storage battery electrodes, modifiers for adhesives based on epoxy resins, phenolic resins, etc., ceramic green sheets, conductive pastes, and the like. It can also be used as a binder for ink products such as gel inks, resins for 3D printers, actuators, gas separation membranes, adhesives, raw materials for paints, films, and the like. In particular, when the modified polyvinyl acetal resin of the present invention is used as a binder for a storage battery electrode, it is possible to reduce the electrode resistance and prevent deterioration by the electrolyte, and it becomes possible to produce a high-output storage battery.

[0043] A composition for a storage battery electrode containing the modified polyvinyl acetal resin of the present invention, an organic solvent, and an active material is also one of the present inventions. In such a composition for a battery electrode, the active material has excellent dispersibility and adhesiveness, can reduce the electrical resistance, further prevent deterioration by the electrolyte, and can produce a high-output battery.

[0044] Examples of the above active material include a positive electrode active material and a negative electrode active material. Examples of the above positive electrode active material include lithium-containing composite metal oxides such as lithium nickel oxide, lithium cobalt oxide, and lithium manganese oxide. Specifically, for example, LiNiO2, LiCoO2, LiMn2O4, etc. can be mentioned. In addition, as the above negative electrode active material, for example, materials conventionally used as the negative electrode active material of a battery can be used. For example, spherical natural graphite, natural graphite, artificial graphite, amorphous carbon, carbon black, or those obtained by adding a different element to these components, etc. can be mentioned. These may be used alone or in combination of two or more.

[0045] The composition for a battery electrode according to the present invention preferably further contains a conductive aid. By containing a conductive aid, the electrical resistance of the resulting composition for a battery electrode can be further reduced. Examples of the above conductive aid include carbon materials such as graphite, acetylene black, carbon black, ketjen black, and vapor-grown carbon fibers.

[0046] Examples of the above organic solvent include alcohols, polyhydric alcohols, glycol ethers, esters, etc. Examples of the above alcohols include other 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, cyclohexanol, etc., benzyl alcohol, terpineol, dihydroterpineol, etc. Examples of the above polyhydric alcohols include ethylene glycol, diethylene glycol, triethylene glycol, phenyl glycol, and the like. Examples of the above glycol ethers include propylene glycol monomethyl ether, propylene glycol monobutyl ether, methyl cellosolve, ethyl cellosolve, butyl cellosolve, butyl carbitol, butyl triglycol, methyl diglycol, and the like. Examples of the above esters include methyl propionate, ethyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, butyl butyrate, methyl pentanoate, ethyl pentanoate, butyl pentanoate, methyl hexanoate, ethyl hexanoate, butyl hexanoate, 2-ethylhexyl acetate, 2-ethylhexyl butyrate, and the like. In addition, butyl cellosolve acetate, butyl carbitol acetate, terpineol acetate, dihydroterpineol acetate, and the like can also be used. Also, two or more of the above organic solvents may be mixed and used.

[0047] In the composition for a storage battery electrode of the present invention, in addition to the substances described above, additives such as a flame retardant auxiliary, a thickener, an antifoaming agent, a leveling agent, and an adhesion-imparting agent may be added as necessary.

Effects of the Invention

[0048] According to the present invention, a modified polyvinyl acetal resin excellent in dispersibility, adhesiveness, and the stability over time of the resulting composition can be provided, which can reduce the electrode resistance when used for the electrode of a storage battery, further prevent deterioration by an electrolytic solution, and enable the production of a high-output storage battery. Also, a composition for a storage battery electrode using the modified polyvinyl acetal resin can be provided.

Modes for Carrying Out the Invention

[0049] Examples will be given below to explain the present invention in more detail, but the present invention is not limited only to these examples.

[0050] (Example 1) 120 g of polyvinyl alcohol (a) with a saponification degree of 98.7 mol% and a polymerization degree of 1700 was added to 1400 g of pure water, and stirred at a temperature of 90 °C for about 2 hours to dissolve. This solution was cooled to 40 °C, and 110 g of hydrochloric acid with a concentration of 35% by weight, 62 g of n-butyl aldehyde, and 7 g of 4-trifluoromethylbenzaldehyde were added thereto. Then, the liquid temperature was maintained at 50 °C to carry out an acetalization reaction, and the reaction product was precipitated. Thereafter, the reaction was allowed to proceed for 6 hours while maintaining the liquid temperature at 50 °C. After neutralization, washing with water, and drying by a conventional method, a powder of a fluorinated modified polyvinyl acetal resin containing a structural unit having a fluorine atom was obtained. The obtained fluorinated modified polyvinyl acetal resin was dissolved in DMSO-d6 (dimethyl sulfoxide), 1 1H-NMR and 19 19F-NMR (nuclear magnetic resonance spectrum) were used to measure the amount of hydroxyl groups, the amount of acetyl groups, the amount of butyral groups, and the content of the structural unit having a fluorine atom (amount of fluorinated modified units). The results are shown in Table 1. The structural unit having a fluorine atom was the structural unit represented by the above formula (1) (R 1 = 4-trifluoromethylphenyl group). The amount of fluorinated modified units was measured by the following method. (Measurement of the amount of fluorinated modified units) A sample composed of the obtained fluorinated modified polyvinyl acetal resin was dissolved in deuterated DMSO, and measured at 80 °C using 400 MHz 1 1H and 19 19F-NMR. Also, using hexafluorobenzene as an internal standard sample, the chemical shift reference was set to -162.9 ppm. The calculation method was to calculate the amount of fluorine in the sample from hexafluorobenzene with a known concentration, and then calculate the content of the structural unit having a fluorine atom from that.

[0051] (Example 2) Instead of 62 g of n-butyl aldehyde and 7 g of 4-trifluoromethylbenzaldehyde, 60 g of n-butyl aldehyde and 12 g of 4-trifluoromethylbenzaldehyde were added, and a fluorinated modified polyvinyl acetal resin powder containing a structural unit having a fluorine atom was obtained in the same manner as in Example 1. The obtained fluorinated modified polyvinyl acetal resin was dissolved in DMSO-d6 (dimethyl sulfoxide), 1 1H-NMR and 19 19F-NMR (nuclear magnetic resonance spectrum) were used to measure the amount of hydroxyl groups, the amount of acetyl groups, the amount of butyral groups, and the content of the structural unit having a fluorine atom (amount of fluorinated modified units). The results are shown in Table 1. The structural unit having a fluorine atom was the structural unit represented by the above formula (1) (R 1 = 4-trifluoromethylphenyl group).

[0052] (Example 3) Instead of 62 g of n-butyl aldehyde and 7 g of 4-trifluoromethylbenzaldehyde, 62 g of n-butyl aldehyde and 5 g of 4-trifluoromethylbenzaldehyde were added, and a fluorinated modified polyvinyl acetal resin powder containing a structural unit having a fluorine atom was obtained in the same manner as in Example 1. The obtained fluorinated modified polyvinyl acetal resin was dissolved in DMSO-d6 (dimethyl sulfoxide), 1 1H-NMR and 19 19F-NMR (nuclear magnetic resonance spectrum) were used to measure the amount of hydroxyl groups, the amount of acetyl groups, the amount of butyral groups, and the content of the structural unit having a fluorine atom (amount of fluorinated modified units). The results are shown in Table 1. The structural unit having a fluorine atom was the structural unit represented by the above formula (1) (R 1 = 4-trifluoromethylphenyl group).

[0053] (Example 4) Instead of 62 g of n-butyl aldehyde and 7 g of 4-trifluoromethylbenzaldehyde, 51 g of n-butyl aldehyde and 32 g of 4-trifluoromethylbenzaldehyde were added, and a fluorinated modified polyvinyl acetal resin powder containing a structural unit having a fluorine atom was obtained in the same manner as in Example 1. The obtained fluorinated modified polyvinyl acetal resin was dissolved in DMSO-d6 (dimethyl sulfoxide), 1 1H-NMR and 19 19F-NMR (nuclear magnetic resonance spectrum) were used to measure the amount of hydroxyl groups, the amount of acetyl groups, the amount of butyral groups, and the content of the structural unit having a fluorine atom (fluorinated modified unit amount). The results are shown in Table 1. The structural unit having a fluorine atom was the structural unit represented by the above formula (1) (R 1 = 4-trifluoromethylphenyl group).

[0054] (Example 5) Instead of polyvinyl alcohol (a), polyvinyl alcohol (b) with a saponification degree of 98.7 mol% and a polymerization degree of 300 was used. Also, instead of 62 g of n-butyl aldehyde and 7 g of 4-trifluoromethylbenzaldehyde, 60 g of n-butyl aldehyde and 12 g of 4-trifluoromethylbenzaldehyde were added, and a fluorinated modified polyvinyl acetal resin powder containing a structural unit having a fluorine atom was obtained in the same manner as in Example 1. The obtained fluorinated modified polyvinyl acetal resin was dissolved in DMSO-d6 (dimethyl sulfoxide), 1 1H-NMR and 19 19F-NMR (nuclear magnetic resonance spectrum) were used to measure the amount of hydroxyl groups, the amount of acetyl groups, the amount of butyral groups, and the content of the structural unit having a fluorine atom (fluorinated modified unit amount). The results are shown in Table 1. The structural unit having a fluorine atom was the structural unit represented by the above formula (1) (R 1 = 4-trifluoromethylphenyl group).

[0055] (Example 6) Instead of polyvinyl alcohol (a), polyvinyl alcohol (c) with a saponification degree of 98.7 mol% and a polymerization degree of 500 was used. Also, except that 60 g of n-butyl aldehyde and 12 g of 4-trifluoromethylbenzaldehyde were added instead of 62 g of n-butyl aldehyde and 7 g of 4-trifluoromethylbenzaldehyde, a fluorinated modified polyvinyl acetal resin powder containing a structural unit having a fluorine atom was obtained in the same manner as in Example 1. The obtained fluorinated modified polyvinyl acetal resin was dissolved in DMSO-d6 (dimethyl sulfoxide), 1 1H-NMR and 19 19F-NMR (nuclear magnetic resonance spectrum) were used to measure the amount of hydroxyl groups, the amount of acetyl groups, the amount of butyral groups, and the content of the structural unit having a fluorine atom (fluorinated modified unit amount). The results are shown in Table 1. The structural unit having a fluorine atom was the structural unit represented by the above formula (1) (R 1 = 4-trifluoromethylphenyl group).

[0056] (Example 7) Instead of polyvinyl alcohol (a), polyvinyl alcohol (d) with a saponification degree of 98.7 mol% and a polymerization degree of 4000 was used. Also, except that 60 g of n-butyl aldehyde and 12 g of 4-trifluoromethylbenzaldehyde were added instead of 62 g of n-butyl aldehyde and 7 g of 4-trifluoromethylbenzaldehyde, a fluorinated modified polyvinyl acetal resin powder containing a structural unit having a fluorine atom was obtained in the same manner as in Example 1. The obtained fluorinated modified polyvinyl acetal resin was dissolved in DMSO-d6 (dimethyl sulfoxide), 1 1H-NMR and 19 19F-NMR (nuclear magnetic resonance spectrum) were used to measure the amount of hydroxyl groups, the amount of acetyl groups, the amount of butyral groups, and the amount of fluorinated modified acetal bond units. The results are shown in Table 1. The structural unit having a fluorine atom was the structural unit represented by the above formula (1) (R 1 = 4-trifluoromethylphenyl group).

[0057] (Example 8) Instead of 62 g of n-butyl aldehyde and 7 g of 4-trifluoromethylbenzaldehyde, 54 g of n-butyl aldehyde, 11 g of acetaldehyde and 7 g of 4-trifluoromethylbenzaldehyde were added, and a fluorinated modified polyvinyl acetal resin powder containing a structural unit having a fluorine atom was obtained in the same manner as in Example 1. The obtained fluorinated modified polyvinyl acetal resin was dissolved in DMSO-d6 (dimethyl sulfoxide), 1 1H-NMR and 19 19F-NMR (nuclear magnetic resonance spectrum) were used to measure the amount of hydroxyl groups, the amount of acetyl groups, the amount of butyral groups, the amount of acetal groups and the content of the structural unit having a fluorine atom (fluorinated modified unit amount). The results are shown in Table 1. The structural unit having a fluorine atom was the structural unit represented by the above formula (1) (R 1 = 4-trifluoromethylphenyl group).

[0058] (Example 9) Instead of 62 g of n-butyl aldehyde and 7 g of 4-trifluoromethylbenzaldehyde, 35 g of n-butyl aldehyde and 12 g of 4-trifluoromethylbenzaldehyde were added, and a fluorinated modified polyvinyl acetal resin powder containing a structural unit having a fluorine atom was obtained in the same manner as in Example 1. The obtained fluorinated modified polyvinyl acetal resin was dissolved in DMSO-d6 (dimethyl sulfoxide), 1 1H-NMR and 19 19F-NMR (nuclear magnetic resonance spectrum) were used to measure the amount of hydroxyl groups, the amount of acetyl groups, the amount of butyral groups, and the content of the structural unit having a fluorine atom (fluorinated modified unit amount). The results are shown in Table 1. The structural unit having a fluorine atom was the structural unit represented by the above formula (1) (R 1 = 4-trifluoromethylphenyl group).

[0059] (Example 10) Instead of polyvinyl alcohol (a), polyvinyl alcohol (e) with a saponification degree of 88.2 mol% and a polymerization degree of 1700 was used. Also, except that 60 g of n-butyl aldehyde and 7 g of 4-trifluoromethylbenzaldehyde were added instead of 62 g of n-butyl aldehyde and 7 g of 4-trifluoromethylbenzaldehyde, a fluorinated modified polyvinyl acetal resin powder containing a structural unit having a fluorine atom was obtained in the same manner as in Example 1. The obtained fluorinated modified polyvinyl acetal resin was dissolved in DMSO-d6 (dimethyl sulfoxide), 1 1H-NMR and 19 19F-NMR (nuclear magnetic resonance spectrum) were used to measure the amount of hydroxyl groups, the amount of acetyl groups, the amount of butyral groups, and the content of the structural unit having a fluorine atom (amount of fluorinated modified units). The results are shown in Table 1. The structural unit having a fluorine atom was the structural unit represented by the above formula (1) (R 1 = 4-trifluoromethylphenyl group).

[0060] (Example 11) Except that 5 g of 4-fluorobenzaldehyde was added instead of 7 g of 4-trifluoromethylbenzaldehyde, a fluorinated modified polyvinyl acetal resin powder containing a structural unit having a fluorine atom was obtained in the same manner as in Example 1. The obtained fluorinated modified polyvinyl acetal resin was dissolved in DMSO-d6 (dimethyl sulfoxide), 1 1H-NMR and 19 19F-NMR (nuclear magnetic resonance spectrum) were used to measure the amount of hydroxyl groups, the amount of acetyl groups, the amount of butyral groups, and the content of the structural unit having a fluorine atom (amount of fluorinated modified units). The results are shown in Table 1. The structural unit having a fluorine atom was the structural unit represented by the above formula (1) (R 1 = 4-fluorophenyl group).

[0061] (Example 12) Instead of 7 g of 4-trifluoromethylbenzaldehyde, 4 g of fluoroacetaldehyde and 62 g of n-butylaldehyde were added, and a fluorinated modified polyvinyl acetal resin powder containing a structural unit having a fluorine atom was obtained in the same manner as in Example 1. The obtained fluorinated modified polyvinyl acetal resin was dissolved in DMSO-d6 (dimethyl sulfoxide), 1 1H-NMR and 19 19F-NMR (nuclear magnetic resonance spectrum) were used to measure the amount of hydroxyl groups, the amount of acetyl groups, the amount of butyral groups, and the content of the structural unit having a fluorine atom (amount of fluorinated modified unit). The results are shown in Table 1. The structural unit having a fluorine atom was the structural unit represented by the above formula (1) (R 1 = fluoromethyl group (-CH2F)).

[0062] (Example 13) (Synthesis of modified polyvinyl alcohol (f)) Into a flask equipped with a stirrer, a thermometer, a dropping funnel and a reflux condenser, 1000 parts by weight of vinyl acetate, 90 parts by weight of vinyl fluoride and 300 parts by weight of methanol were added. After replacing the nitrogen in the system, the temperature was raised to 60 °C. 1.1 parts by weight of 2,2-azobisisobutyronitrile was added to this system to initiate polymerization. The polymerization was stopped 5 hours after the start of polymerization. The solid content concentration in the system at the end of polymerization was 53% by weight, and the polymerization yield based on all monomers was 65% by weight. After removing the unreacted monomers under reduced pressure, a 45% by weight methanol solution of the copolymer was obtained. It was confirmed from the quantification of the unreacted monomers that the obtained copolymer contained 90 mol% of vinyl acetate units and 10 mol% of vinyl fluoride units.

[0063] While stirring 100 parts by weight of the methanol solution of this copolymer at 40 °C, 25 parts by weight of a 3% NaOH methanol solution was added, mixed well, and then left standing. After 30 minutes, the solidified polymer was pulverized with a pulverizer, washed with methanol, and dried to obtain a polymer powder (hereinafter referred to as modified polyvinyl alcohol (f)). The saponification degree of the modified polyvinyl alcohol (f) was 98 mol%, the amount of fluorinated modified side chain bonding units was 10 mol%, and the degree of polymerization was 1700.

[0064] (Synthesis of fluorinated modified polyvinyl acetal resin) Instead of polyvinyl alcohol (a), the obtained polyvinyl alcohol (f) was used. Also, 55 g of n-butyl aldehyde was added instead of 62 g of n-butyl aldehyde and 7 g of 4-trifluoromethylbenzaldehyde. A fluorinated modified polyvinyl acetal resin powder containing a structural unit having a fluorine atom was obtained in the same manner as in Example 1. The obtained fluorinated modified polyvinyl acetal resin was dissolved in DMSO-d6 (dimethyl sulfoxide), 1 1H-NMR and 19 19F-NMR (nuclear magnetic resonance spectrum) were used to measure the amount of hydroxyl groups, the amount of acetyl groups, the amount of butyral groups, and the content of the structural unit having a fluorine atom (fluorinated modified unit amount). The results are shown in Table 1. The structural unit having a fluorine atom was the structural unit represented by the above formula (2) (R 4 = single bond, R 5 = H).

[0065] (Example 14) Instead of 7 g of 4-trifluoromethylbenzaldehyde, 45 g of trifluoroacetaldehyde ethyl hemiacetal and 40 g of n-butyl aldehyde were added. A fluorinated modified polyvinyl acetal resin powder containing a structural unit having a fluorine atom was obtained in the same manner as in Example 1. The obtained fluorinated modified polyvinyl acetal resin was dissolved in DMSO-d6 (dimethyl sulfoxide), 1 1H-NMR and 19 19F-NMR (nuclear magnetic resonance spectrum) were used to measure the amount of hydroxyl groups, the amount of acetyl groups, the amount of butyral groups, and the content of the structural unit having a fluorine atom (fluorinated modified unit amount). The results are shown in Table 1. The structural unit having a fluorine atom was the structural unit represented by the above formula (1) (R 1 = trifluoromethyl group).

[0066] (Example 15) Instead of 7 g of 4-trifluoromethylbenzaldehyde, 10 g of pentafluorobenzaldehyde and 65 g of n-butylaldehyde were added, and a fluorinated modified polyvinyl acetal resin powder containing a structural unit having a fluorine atom was obtained in the same manner as in Example 1. The obtained fluorinated modified polyvinyl acetal resin was dissolved in DMSO-d6 (dimethyl sulfoxide), 1 1H-NMR and 19 19F-NMR (nuclear magnetic resonance spectrum) were used to measure the amount of hydroxyl groups, the amount of acetyl groups, the amount of butyral groups, and the content of the structural unit having a fluorine atom (fluorinated modified unit amount). The results are shown in Table 1. The structural unit having a fluorine atom was the structural unit represented by the above formula (1) (R 1 = perfluorophenyl group).

[0067] (Example 16) Instead of 62 g of n-butylaldehyde and 7 g of 4-trifluoromethylbenzaldehyde, 40 g of n-butylaldehyde and 80 g of 4-trifluoromethylbenzaldehyde were added, and a fluorinated modified polyvinyl acetal resin powder containing a structural unit having a fluorine atom was obtained in the same manner as in Example 1. The obtained fluorinated modified polyvinyl acetal resin was dissolved in DMSO-d6 (dimethyl sulfoxide), 1 1H-NMR and 19 19F-NMR (nuclear magnetic resonance spectrum) were used to measure the amount of hydroxyl groups, the amount of acetyl groups, the amount of butyral groups, and the content of the structural unit having a fluorine atom (fluorinated modified unit amount). The results are shown in Table 1. The structural unit having a fluorine atom was the structural unit represented by the above formula (1) (R 1 = 4-trifluoromethylphenyl group).

[0068] (Comparative Example 1) Instead of 62 g of n-butyl aldehyde and 7 g of 4-trifluoromethylbenzaldehyde, polyvinyl acetal resin powder was obtained in the same manner as in Example 1 except that 65 g of n-butyl aldehyde was added. The obtained polyvinyl acetal resin was dissolved in DMSO-d6 (dimethyl sulfoxide), 1 1H-NMR and 19 19F-NMR (nuclear magnetic resonance spectrum) were used to measure the amount of hydroxyl groups, the amount of acetyl groups, and the amount of butyral groups. The results are shown in Table 1.

[0069] (Comparative Example 2) Instead of 62 g of n-butyl aldehyde and 7 g of 4-trifluoromethylbenzaldehyde, polyvinyl acetal resin powder was obtained in the same manner as in Example 1 except that 76 g of n-butyl aldehyde was added. The obtained polyvinyl acetal resin was dissolved in DMSO-d6 (dimethyl sulfoxide), 1 1H-NMR 19 19F-NMR (nuclear magnetic resonance spectrum) were used to measure the amount of hydroxyl groups, the amount of acetyl groups, and the amount of butyral groups. The results are shown in Table 1.

[0070] (Comparative Example 3) Instead of 62 g of n-butyl aldehyde and 7 g of 4-trifluoromethylbenzaldehyde, polyvinyl acetal resin powder was obtained in the same manner as in Example 1 except that 40 g of n-butyl aldehyde was added. The obtained polyvinyl acetal resin was dissolved in DMSO-d6 (dimethyl sulfoxide), 1 1H-NMR and 19 19F-NMR (nuclear magnetic resonance spectrum) were used to measure the amount of hydroxyl groups, the amount of acetyl groups, and the amount of butyral groups. The results are shown in Table 1.

[0071] (Comparative Example 4) Instead of 62 g of n-butyl aldehyde and 7 g of 4-trifluoromethylbenzaldehyde, polyvinyl acetal resin powder was obtained in the same manner as in Example 1 except that 90 g of n-butyl aldehyde was added. The obtained polyvinyl acetal resin was dissolved in DMSO-d6 (dimethyl sulfoxide), 1 1H-NMR and19 The amounts of hydroxyl groups, acetyl groups, and butyral groups were measured using F-NMR (nuclear magnetic resonance spectrum). The results are shown in Table 1.

[0072] (Comparative Example 5) Polyvinyl alcohol (PVA, manufactured by Nippon Gohsei Kagaku Kogyo Co., Ltd., degree of polymerization 1700, saponification degree 98.7 mol%) was used. Note that the PVA does not contain fluorine atoms.

[0073] <Evaluation> (1) Evaluation of Resins The following evaluations were performed on the (modified) polyvinyl acetal resins and PVA obtained in the examples and comparative examples. The results are shown in Table 1.

[0074] (1-1) Moisture Resistance The weight of a vacuum-dried aluminum cup was accurately measured, and exactly 5 g of the resins of the examples and comparative examples dried in a vacuum dryer at 60°C for 7 hours or more were accurately weighed and added to the aluminum cup, and the total weight was accurately measured. Next, the aluminum cup containing the sample was left in a thermo-hygrostat (manufactured by ESPEC) at 20°C and 90% RH for 6 hours, and then the weight was measured. The moisture absorption rate was measured from the weight change before and after the test. ○: The weight change rate is 100% or more and 150% or less △: The weight change rate exceeds 150% and is less than 200% ×: The weight change rate is 200% or more

[0075] (2) Evaluation of the Composition for Battery Electrodes To 20 parts by weight of a resin solution containing the obtained resin (resin: 3 parts by weight), 55 parts by weight of lithium cobaltate (manufactured by Nippon Chemical Industry Co., Ltd., Celseed C-5H) as an active material, 5 parts by weight of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd., Denka Black) as a conductivity-imparting agent, and 25 parts by weight of N-methylpyrrolidone were added. Then, it was mixed with a mixer manufactured by Shinky Co., Ltd. to obtain a composition for battery electrodes.

[0076] (2-1) Adhesion (Peeling Force) The adhesion of the obtained composition for battery electrodes to an aluminum foil was evaluated. On an aluminum foil (thickness: 20 μm), an electrode composition was applied and dried so that the film thickness after drying would be 20 μm, and a test piece with an electrode formed in a sheet shape on the aluminum foil was obtained. This sample was cut into a size of 1 cm in length and 2 cm in width. Using an AUTOGRAPH (manufactured by Shimadzu Corporation, "AGS-J"), while fixing the test piece, the electrode sheet was pulled up, and the peeling force (N) required until the electrode sheet was completely peeled off from the aluminum foil was measured, and then judged according to the following criteria. ○: The peeling force is 8.0 N or more △: The peeling force is less than 8.0 N and more than 6.0 N ×: The peeling force is 6.0 N or less

[0077] (2-2) Dispersibility (surface roughness) Regarding the test piece obtained in the above "(2-1) Adhesiveness", the surface roughness Ra was measured based on JIS B 0601 (1994), and the surface roughness of the electrode was evaluated according to the following criteria. Generally, it is said that the higher the dispersibility of the active material, the smaller the surface roughness. ○: Ra is less than 3.0 μm △: Ra is 3.0 μm or more and less than 4.0 μm ×: Ra is 4.0 μm or more

[0078] (2-3) Electrolyte resistance (solvent solubility) (Fabrication of electrode sheet) On a release-treated polyalkylene terephthalate (PET) film, the battery electrode compositions obtained in the examples and comparative examples were applied and dried so that the film thickness after drying would be 20 μm to fabricate an electrode sheet. The electrode sheet was cut into a 2 cm square to fabricate an electrode sheet test piece.

[0079] (Elution evaluation) The weight of the obtained test piece was accurately measured, and the weight of the resin contained in the test piece was calculated from the weight ratio of the components contained in the sheet. Then, the test piece was put into a bag-shaped mesh, and the total weight of the mesh bag and the test piece was accurately measured. Next, the mesh bag containing the test piece was immersed in a mixed solvent of diethyl carbonate: alkylene carbonate = 1:1, which is an electrolytic solution solvent, and left at 60 °C for 5 hours. After leaving it, the mesh bag was taken out and dried under the conditions of 150 °C for 8 hours to completely dry the solvent. After taking it out from the dryer, it was left at room temperature for 1 hour and weighed. The elution amount of the resin was calculated from the weight change before and after the test, and the elution rate of the resin was calculated from the ratio of the elution amount to the weight of the resin calculated in advance, and evaluated according to the following criteria. ○: Elution rate is less than 1.0% △: Elution rate is 1.0% or more and less than 2.0% ×: Elution rate is 2.0% or more

[0080] (2-4) Measurement of electrode resistance value Regarding the test piece obtained in the above "(2-1) Adhesiveness", the electrode resistance value was measured using an electrode resistance measuring instrument (manufactured by Hioki Electric Co., Ltd.) and evaluated according to the following criteria. ◎: Electrode resistance value is less than 400 Ω / sq ○: Electrode resistance value is 400 Ω / sq or more and less than 700 Ω / sq △: Electrode resistance value is 700 Ω / sq or more and less than 1000 Ω / sq ×: Electrode resistance value is 1000 Ω / sq or more

[0081] (2-5) Alkali resistance (solvent solubility) To 10 g of the obtained composition for a battery electrode, about 2 to 3 ml of an aqueous lithium hydroxide solution was dropped with a dropper, and after leaving it for 1 day, its fluidity was confirmed. 〇: Maintaining fluidity △: Slightly losing fluidity ×: Not flowing at all

[0082]

Table 1

Industrial applicability

[0083] According to the present invention, there is provided a modified polyvinyl acetal resin capable of preventing deterioration by an electrolytic solution when used for an electrode of a storage battery and capable of producing a high-output storage battery, and a composition for a storage battery electrode using the modified polyvinyl acetal resin.

Claims

1. A modified polyvinyl acetal resin containing a structural unit having a fluorine atom, wherein the structural unit having a fluorine atom has the structure of the following formula (1) and the degree of non-fluorinated acetalization is 20 mol% or more and 75 mol% or less. 【Chemical 1】 In formula (1), R1 represents a fluorine atom, a fluoroalkyl group, a fluorophenyl group or a fluoroalkylphenyl group.

2. The modified polyvinyl acetal resin according to claim 1, containing 0.1 mol% or more of a structural unit having a fluorine atom.

3. Said R １ The modified polyvinyl acetal resin according to claim 1, wherein R is a fluorophenyl group or a fluoroalkylphenyl group.

4. The modified polyvinyl acetal resin according to any one of claims 1 to 3, wherein the structural unit having a fluorine atom has two or more fluorine atoms per structural unit.

5. The modified polyvinyl acetal resin according to any one of claims 1 to 4, having a degree of polymerization of 200 or more and 4000 or less.

6. The modified polyvinyl acetal resin according to any one of claims 1 to 5, having a hydroxyl group content of 20 mol% or more and 70 mol% or less.

7. A composition for a battery electrode, containing the modified polyvinyl acetal resin according to any one of claims 1 to 6, an organic solvent, and an active material.

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