Binder for power storage device electrode

Abstract

The present invention aims to provide a binder for a power storage device electrode which favorably maintains adhesiveness between active materials in a long-term cycle, and which enables production of a high-capacity storage battery with a small irreversible capacity and low resistance to have excellent output characteristics. The present invention further aims to provide a composition for a power storage device electrode, a power storage device electrode, and a power storage device each prepared using the binder for a power storage device electrode. The present invention relates to a binder for a power storage device electrode used for an electrode of a power storage device, the binder containing a polyvinyl acetal resin, the polyvinyl acetal resin having a hydroxy group-containing structural unit of the formula (1) comprising a hydroxy group-containing structural unit with a sequence length of 1, the hydroxy group-containing structural unit with a sequence length of 1 constituting 25% by weight or less of the whole hydroxy group-containing structural unit in the polyvinyl acetal resin, the polyvinyl acetal resin having a hydroxy group content of 30 to 60 mol %: ##STR00001##

Claims

1. A binder for a power storage device electrode used for an electrode of a power storage device, the binder comprising a polyvinyl acetal resin, wherein the polyvinyl acetal resin has a hydroxy group-containing structural unit of the formula (1) comprising a hydroxy group-containing structural unit with a sequence length of 1, the hydroxy group-containing structural unit with a sequence length of 1 constitutes 25% by weight or less of the whole hydroxy group-containing structural unit in the polyvinyl acetal resin, and the polyvinyl acetal resin has a hydroxy group content of 30 to 60 mol %: ##STR00007## wherein the polyvinyl acetal resin has a structural unit of the formula (3) having an acetyl group, a structural unit of the formula (4) having an acetal group, and a structural unit of the formula (5) having an acetal group including an ionic functional group: ##STR00008## wherein, in the formula (4), R.sup.2 represents a hydrogen atom or a C1-C20 alkyl group, and in the formula (5), R.sup.3 represents a C1-C20 alkylene group or an aromatic ring, and X represents an ionic functional group.

2. The binder for a power storage device electrode according to claim 1, wherein the polyvinyl acetal resin has a structural unit of the formula (2) in an amount of 0.3 mol % or more: ##STR00009## wherein R.sup.1 represents a hydrogen atom or a C1-C20 alkyl group.

3. The binder for a power storage device electrode according to claim 2, wherein the polyvinyl acetal resin has the structural unit of the formula (2) in the amount of 0.3 to 5 mol %.

4. The binder for a power storage device electrode according to claim 1, comprising a dispersion containing the polyvinyl acetal resin dispersed in an aqueous medium, wherein the polyvinyl acetal resin is in the form of fine particles.

5. The binder for a power storage device electrode according to claim 4, wherein the polyvinyl acetal resin has a volume average particle size of 10 to 500 nm.

6. A composition for a power storage device electrode, comprising the binder for a power storage device electrode according to claim 1 and an active material, the composition containing the polyvinyl acetal resin in an amount of 0.1 to 12 parts by weight relative to 100 parts by weight of the active material.

7. A power storage device electrode comprising the composition for a power storage device electrode according to claim 6.

8. A power storage device comprising a power storage device electrode according to claim 7.

9. The binder for a power storage device electrode according to claim 2, comprising a dispersion containing the polyvinyl acetal resin dispersed in an aqueous medium, wherein the polyvinyl acetal resin is in the form of fine particles.

10. The binder for a power storage device electrode according to claim 9, wherein the polyvinyl acetal resin has a volume average particle size of 10 to 500 nm.

11. A composition for a power storage device electrode, comprising the binder for a power storage device electrode according to claim 2 and an active material, the composition containing the polyvinyl acetal resin in an amount of 0.1 to 12 parts by weight relative to 100 parts by weight of the active material.

12. A power storage device electrode comprising the composition for a power storage device electrode according to claim 11.

13. A power storage device comprising a power storage device electrode according to claim 12.

14. The binder for a power storage device electrode according to claim 3, comprising a dispersion containing the polyvinyl acetal resin dispersed in an aqueous medium, wherein the polyvinyl acetal resin is in the form of fine particles.

15. The binder for a power storage device electrode according to claim 14, wherein the polyvinyl acetal resin has a volume average particle size of 10 to 500 nm.

16. A composition for a power storage device electrode, comprising the binder for a power storage device electrode according to claim 3 and an active material, the composition containing the polyvinyl acetal resin in an amount of 0.1 to 12 parts by weight relative to 100 parts by weight of the active material.

17. A power storage device electrode comprising the composition for a power storage device electrode according to claim 16.

18. A power storage device comprising a power storage device electrode according to claim 17.

Description

DESCRIPTION OF EMBODIMENTS

(1) The present invention is more specifically described in the following with reference to, but not limited to, examples.

(2) (Preparation of a Dispersion of Polyvinyl Acetal Resin Fine Particles 1)

(3) In a reaction vessel equipped with a thermometer, a stirrer, and a condenser tube, 20 parts by weight of a polyvinyl acetal resin (degree of polymerization: 1,000, degree of butyralization: 58.6 mol %, hydroxy group content: 40 mol %, acetyl group content: 1.4 mol %) was dissolved in 80 parts by weight of isopropanol. To the obtained solution were added 1 part by weight of sodium 2-formylbenzene sulfonate and 0.05 parts by weight of 12 M concentrated hydrochloric acid to set the acid concentration of the reaction system to 0.12 M. The reaction thereof was carried out at 70 C. for four hours. Then, 1 part by weight of 12 M concentrated hydrochloric acid was added to set the acid concentration of the reaction system to 0.14 M. The reaction thereof was carried out at 81 C. for eight hours, followed by cooling of the reaction solution. Then, a resin was purified by reprecipitation method and finally dried to be collected. The obtained resin was again dissolved in 80 parts by weight of isopropanol, and to the solution was dropwise added 200 parts by weight of water. The solution was stirred under reduced pressure, while the temperature of the solution was maintained at 30 C. The isopropanol and water were thus evaporated. The resulting substance was concentrated to have a solid content of 20% by weight, thereby preparing a dispersion in which polyvinyl acetal resin 1 in the form of fine particles (hereafter, also referred to as polyvinyl acetal resin fine particles 1) was dispersed (amount of polyvinyl acetal resin fine particles 1: 20% by weight).

(4) According to the measurement of the obtained polyvinyl acetal resin by NMR, the degree of butyralization was 58.3 mol %, the hydroxy group content was 37.6 mol %, the acetyl group content was 1.2 mol %, the ionic functional group content of the polyvinyl acetal resin was 0.2 mmol/g, and the amount of the acetal bond (in the formula (5), R.sup.3 is a benzene ring, X is sodium sulfonate) having an ionic functional group was 2.9 mol %. Further, the proportion of the hydroxy group-containing structural unit with a sequence length of 1 was 9.7% relative to the hydroxy group-containing structural unit as a whole in the obtained polyvinyl acetal resin. According to the measurement using a transmission electron microscope, the obtained polyvinyl acetal resin fine particles 1 had a volume average particle size of 100 nm.

(5) (Preparation of a Dispersion of Polyvinyl Acetal Resin Fine Particles 2)

(6) In a reaction vessel equipped with a thermometer, a stirrer, and a condenser tube, 20 parts by weight of a polyvinyl acetal resin (degree of polymerization: 1,000, degree of butyralization: 47.8 mol %, hydroxy group content: 51 mol %, acetyl group content: 1.2 mol %) was dissolved in 80 parts by weight of isopropanol. To the obtained solution were added 1 part by weight of sodium 2-formylbenzene sulfonate and 0.05 parts by weight of 12 M concentrated hydrochloric acid to set the acid concentration of the reaction system to 0.12 M. The reaction thereof was carried out at 70 C. for four hours. Then, 1 part by weight of 12 M concentrated hydrochloric acid was added to set the acid concentration of the reaction system to 0.29 M. The reaction thereof was carried out at 78 C. for six hours, followed by cooling of the reaction solution. Then a resin was purified by reprecipitation method and finally dried to be collected. The obtained resin was again dissolved in 80 parts by weight of isopropanol, and to the solution was dropwise added 200 parts by weight of water. The solution was stirred under reduced pressure, while the temperature of the solution was maintained at 30 C. The isopropanol and water were thus evaporated. The resulting substance was concentrated to have a solid content of 20% by weight, thereby preparing a dispersion in which polyvinyl acetal resin 2 in the form of fine particles (hereafter, also referred to as polyvinyl acetal resin fine particles 2) was dispersed (amount of polyvinyl acetal resin fine particles 2: 20% by weight).

(7) According to the measurement of the obtained polyvinyl acetal resin by NMR, the degree of butyralization was 47.1 mol %, the hydroxy group content was 48.9 mol %, the acetyl group content was 1 mol %, the ionic functional group content of the polyvinyl acetal resin was 0.2 mmol/g, and the amount of the acetal bond (in the formula (5), R.sup.3 is a benzene ring, X is sodium sulfonate) having an ionic functional group was 3 mol %. Further, the proportion of the hydroxy group-containing structural unit with a sequence length of 1 was 10.2% relative to the hydroxy group-containing structural unit as a whole in the obtained polyvinyl acetal resin. According to the measurement using a transmission electron microscope, the obtained polyvinyl acetal resin fine particles 2 had a volume average particle size of 90 nm.

(8) (Preparation of a Dispersion of Polyvinyl Acetal Resin Fine Particles 3)

(9) In a reaction vessel equipped with a thermometer, a stirrer, and a condenser tube, 20 parts by weight of a polyvinyl acetal resin (degree of polymerization: 1,000, degree of butyralization: 63.2 mol %, hydroxy group content: 35 mol %, acetyl group content: 1.8 mol %) was dissolved in 80 parts by weight of isopropanol. To the obtained solution were added 1 part by weight of sodium 2-formylbenzene sulfonate and 0.05 parts by weight of 12 M concentrated hydrochloric acid to set the acid concentration of the reaction system to 0.12 M. The reaction thereof was carried out at 70 C. for four hours. Then, 1 part by weight of 12 M concentrated hydrochloric acid was added to set the acid concentration of the reaction system to 0.29 M. The reaction thereof was carried out at 78 C. for four hours, followed by cooling of the reaction solution. Then, a resin was purified by reprecipitation method and finally dried to be collected. The obtained resin was again dissolved in 80 parts by weight of isopropanol, and to the solution was dropwise added 200 parts by weight of water. The solution was stirred under reduced pressure, while the temperature of the solution was maintained at 30 C. The isopropanol and water were thus evaporated. The resulting substance was concentrated to have a solid content of 20% by weight, thereby preparing a dispersion in which polyvinyl acetal resin 3 in the form of fine particles (hereafter, also referred to as polyvinyl acetal resin fine particles 3) was dispersed (amount of polyvinyl acetal resin fine particles 3: 20% by weight).

(10) According to the measurement of the obtained polyvinyl acetal resin by NMR, the degree of butyralization was 61.6 mol %, the hydroxy group content was 34 mol %, the acetyl group content was 1.4 mol %, the ionic functional group content of the polyvinyl acetal resin was 0.2 mmol/g, and the amount of the acetal bond (in the formula (5), R.sup.3 is a benzene ring, X is sodium sulfonate) having an ionic functional group was 3 mol %. Further, the proportion of the hydroxy group-containing structural unit with a sequence length of 1 was 12.5% relative to the hydroxy group-containing structural unit as a whole in the obtained polyvinyl acetal resin. According to the measurement using a transmission electron microscope, the obtained polyvinyl acetal resin fine particles 3 had a volume average particle size of 110 nm.

(11) (Preparation of a Dispersion of Polyvinyl Acetal Resin Fine Particles 4)

(12) In a reaction vessel equipped with a thermometer, a stirrer, and a condenser tube, 20 parts by weight of a polyvinyl acetal resin (degree of polymerization: 1,000, degree of butyralization: 64.4 mol %, hydroxy group content: 33.8 mol %, acetyl group content: 1.8 mol %) was dissolved in 80 parts by weight of isopropanol. To the obtained solution were added 1 part by weight of sodium 2-formylbenzene sulfonate and 0.05 parts by weight of 12 M concentrated hydrochloric acid to set the acid concentration of the reaction system to 0.12 M. The reaction thereof was carried out at 70 C. for four hours. Then, 0.5 parts by weight of 12 M concentrated hydrochloric acid was added to set the acid concentration of the reaction system to 0.21 M. The reaction thereof was carried out at 75 C. for four hours, followed by cooling of the reaction solution. Then, a resin was purified by reprecipitation method and finally dried to be collected. The obtained resin was again dissolved in 80 parts by weight of isopropanol, and to the solution was dropwise added 200 parts by weight of water. The solution was stirred under reduced pressure, while the temperature of the solution was maintained at 30 C. The isopropanol and water were thus evaporated. The resulting substance was concentrated to have a solid content of 20% by weight, thereby preparing a dispersion in which polyvinyl acetal resin 4 in the form of fine particles (hereafter, also referred to as polyvinyl acetal resin fine particles 4) was dispersed (amount of polyvinyl acetal resin fine particles 4: 20% by weight).

(13) According to the measurement of the obtained polyvinyl acetal resin by NMR, the degree of butyralization was 63.6 mol %, the hydroxy group content was 31.9 mol %, the acetyl group content was 1.5 mol %, the ionic functional group content of the polyvinyl acetal resin was 0.2 mmol/g, and the amount of the acetal bond (in the formula (5), R.sup.3 is a benzene ring, X is sodium sulfonate) having an inonic functional group was 3 mol %. Further, the proportion of the hydroxy group-containing structural unit with a sequence length of 1 was 17.9% relative to the hydroxy group-containing structural unit as a whole in the obtained polyvinyl acetal resin. According to the measurement using a transmission electron microscope, the obtained polyvinyl acetal resin fine particles 4 had a volume average particle size of 110 nm.

(14) (Preparation of a Dispersion of Polyvinyl Acetal Resin Fine Particles 5)

(15) In a reaction vessel equipped with a thermometer, a stirrer, and a condenser tube, 20 parts by weight of a polyvinyl acetal resin (degree of polymerization: 1,000, degree of butyralization: 70 mol %, hydroxy group content: 28.2 mol %, acetyl group content: 1.8 mol %) was dissolved in 80 parts by weight of isopropanol. To the obtained solution were added 1 part by weight of sodium 2-formylbenzene sulfonate and 0.05 parts by weight of 12 M concentrated hydrochloric acid to set the acid concentration of the reaction system to 0.12 M. The reaction thereof was carried out at 70 C. for four hours. Then, 0.1 parts by weight of 12 M concentrated hydrochloric acid was added to set the acid concentration of the reaction system to 0.14 M. The reaction thereof was carried out at 73 C. for one hour, followed by cooling of the reaction solution. Then, a resin was purified by reprecipitation method and finally dried to be collected. The obtained resin was again dissolved in 80 parts by weight of isopropanol, and to the solution was dropwise added 200 parts by weight of water. The solution was stirred under reduced pressure, while the temperature of the solution was maintained at 30 C. The isopropanol and water were thus evaporated. The resulting substance was concentrated to have a solid content of 20% by weight, thereby preparing a dispersion in which polyvinyl acetal resin 5 in the form of fine particles (hereafter, also referred to as polyvinyl acetal resin fine particles 5) was dispersed (amount of polyvinyl acetal resin fine particles 5: 20% by weight).

(16) According to the measurement of the obtained polyvinyl acetal resin by NMR, the degree of butyralization was 69.5 mol %, the hydroxy group content was 26.1 mol %, the acetyl group content was 1.5 mol %, the ionic functional group content of the polyvinyl acetal resin was 0.2 mmol/g, and the amount of the acetal bond (in the formula (5), R.sup.3 is a benzene ring, X is sodium sulfonate) having an ionic functional group was 2.9 mol %. Further, the proportion of the hydroxy group-containing structural unit with a sequence length of 1 was 30.5% relative to the hydroxy group-containing structural unit as a whole in the obtained polyvinyl acetal resin. According to the measurement using a transmission electron microscope, the obtained polyvinyl acetal resin fine particles 5 had a volume average particle size of 140 nm.

(17) (Preparation of a Dispersion of Polyvinyl Acetal Resin Fine Particles 6)

(18) In a reaction vessel equipped with a thermometer, a stirrer, and a condenser tube, 20 parts by weight of a polyvinyl acetal resin (degree of polymerization: 1,000, degree of butyralization: 65 mol %, hydroxy group content: 33.2 mol %, acetyl group content: 1.8 mol %) was dissolved in 80 parts by weight of isopropanol. To the obtained solution were added 1 part by weight of sodium 2-formylbenzene sulfonate and 0.05 parts by weight of 12 M concentrated hydrochloric acid to set the acid concentration of the reaction system to 0.12 M. The reaction thereof was carried out at 70 C. for four hours. Then, 0.3 parts by weight of 12 M concentrated hydrochloric acid was added to set the acid concentration of the reaction system to 0.17 M. The reaction thereof was carried out at 74 C. for three hours, followed by cooling of the reaction solution. Then, a resin was purified by reprecipitation method and finally dried to be collected. The obtained resin was again dissolved in 80 parts by weight of isopropanol, and to the solution was dropwise added 200 parts by weight of water. The solution was stirred under reduced pressure, while the temperature of the solution was maintained at 30 C. The isopropanol and water were thus evaporated. The resulting substance was concentrated to have a solid content of 20% by weight, thereby preparing a dispersion in which polyvinyl acetal resin 6 in the form of fine particles (hereafter, also referred to as polyvinyl acetal resin fine particles 6) was dispersed (amount of polyvinyl acetal resin fine particles 6: 20% by weight).

(19) According to the measurement of the obtained polyvinyl acetal resin by NMR, the degree of butyralization was 64.4 mol %, the hydroxy group content was 31 mol %, the acetyl group content was 1.6 mol %, the ionic functional group content of the polyvinyl acetal resin was 0.2 mmol/g, and the amount of the acetal bond (in the formula (5), R.sup.3 is a benzene ring, X is sodium sulfonate) having an ionic functional group was 3 mol %. Further, the proportion of the hydroxy group-containing structural unit with a sequence length of 1 was 22.7% relative to the hydroxy group-containing structural unit as a whole in the obtained polyvinyl acetal resin. According to the measurement using a transmission electron microscope, the obtained polyvinyl acetal resin fine particles 6 had a volume average particle size of 130 nm.

(20) (Preparation of a Dispersion of Polyvinyl Acetal Resin Fine Particles 7)

(21) In a reaction vessel equipped with a thermometer, a stirrer, and a condenser tube, 20 parts by weight of a polyvinyl acetal resin (degree of polymerization: 1,000, degree of butyralization: 73.4 mol %, hydroxy group content: 24.8 mol %, acetyl group content: 1.8 mol %) was dissolved in 80 parts by weight of isopropanol. To the obtained solution were added 1 part by weight of sodium 2-formylbenzene sulfonate and 0.05 parts by weight of 12 M concentrated hydrochloric acid to set the acid concentration of the reaction system to 0.12 M. The reaction thereof was carried out at 70 C. for four hours. Then, 0.1 parts by weight of 12 M concentrated hydrochloric acid was added to set the acid concentration of the reaction system to 0.14 M. The reaction thereof was carried out at 72 C. for one hour, followed by cooling of the reaction solution. Then, a resin was purified by reprecipitation method and finally dried to be collected. The obtained resin was again dissolved in 80 parts by weight of isopropanol, and to the solution was dropwise added 200 parts by weight of water. The solution was stirred under reduced pressure, while the temperature of the solution was maintained at 30 C. The isopropanol and water were thus evaporated. The resulting substance was concentrated to have a solid content of 20% by weight, thereby preparing a dispersion in which polyvinyl acetal resin 7 in the form of fine particles (hereafter, also referred to as polyvinyl acetal resin fine particles 7) was dispersed (amount of polyvinyl acetal resin fine particles 7: 20% by weight).

(22) According to the measurement of the obtained polyvinyl acetal resin by NMR, the degree of butyralization was 73.1 mol %, the hydroxy group content was 22.4 mol %, the acetyl group content was 1.6 mol %, the ionic functional group content of the polyvinyl acetal resin was 0.2 mmol/g, and the amount of the acetal bond (in the formula (5), R.sup.3 is a benzene ring, X is sodium sulfonate) having an ionic functional group was 2.9 mol %. Further, the proportion of the hydroxy group-containing structural unit with a sequence length of 1 was 33.6% relative to the hydroxy group-containing structural unit as a whole in the obtained polyvinyl acetal resin. According to the measurement using a transmission electron microscope, the obtained polyvinyl acetal resin fine particles 7 had a volume average particle size of 150 nm.

(23) (Preparation of a Dispersion of Polyvinyl Acetal Resin Fine Particles 8)

(24) In a reaction vessel equipped with a thermometer, a stirrer, and a condenser tube, 20 parts by weight of a polyvinyl acetal resin (degree of polymerization: 1,000, degree of butyralization: 47.8 mol %, hydroxy group content: 51 mol %, acetyl group content: 1.2 mol %) was dissolved in 80 parts by weight of isopropanol. To the obtained solution were added 0.3 parts by weight of sodium 2-formylbenzene sulfonate and 0.05 parts by weight of 12 M concentrated hydrochloric acid to set the acid concentration of the reaction system to 0.12 M. The reaction thereof was carried out at 70 C. for four hours. Then, 1 part by weight of 12 M concentrated hydrochloric acid was added to set the acid concentration of the reaction system to 0.29 M. The reaction thereof was carried out at 78 C. for six hours, followed by cooling of the reaction solution. Then, a resin was purified by reprecipitation method and finally dried to be collected. The obtained resin was again dissolved in 80 parts by weight of isopropanol, and to the solution was dropwise added 200 parts by weight of water. The solution was stirred under reduced pressure, while the temperature of the solution was maintained at 30 C. The isopropanol and water were thus evaporated. The resulting substance was concentrated to have a solid content of 20% by weight, thereby preparing a dispersion in which polyvinyl acetal resin 8 in the form of fine particles (hereafter, also referred to as polyvinyl acetal resin fine particles 8) was dispersed (amount of polyvinyl acetal resin fine particles 8: 20% by weight).

(25) According to the measurement of the obtained polyvinyl acetal resin by NMR, the degree of butyralization was 47.4 mol %, the hydroxy group content was 50.7 mol %, the acetyl group content was 1 mol %, the ionic functional group content of the polyvinyl acetal resin was 0.07 mmol/g, and the amount of the acetal bond (in the formula (5), R.sup.3 is a benzene ring, X is sodium sulfonate) having an ionic functional group was 0.9 mol %. Further, the proportion of the hydroxy group-containing structural unit with a sequence length of 1 was 10.4% relative to the hydroxy group-containing structural unit as a whole in the obtained polyvinyl acetal resin. According to the measurement using a transmission electron microscope, the obtained polyvinyl acetal resin fine particles 8 had a volume average particle size of 600 nm.

(26) (Preparation of a Dispersion of Polyvinyl Acetal Resin Fine Particles 9)

(27) In a reaction vessel equipped with a thermometer, a stirrer, and a condenser tube, 20 parts by weight of a polyvinyl acetal resin (degree of polymerization: 1,000, degree of butyralization: 47.8 mol %, hydroxy group content: 51 mol %, acetyl group content: 1.2 mol %) was dissolved in 80 parts by weight of isopropanol. To the obtained solution were added 0.5 parts by weight of sodium 2-folmylbenzene sulfonate and 0.05 parts by weight of 12 M concentrated hydrochloric acid to set the acid concentration of the reaction system to 0.12 M. The reaction thereof was carried out at 70 C. for four hours. Then, 1 part by weight of 12 M concentrated hydrochloric acid was added to set the acid concentration of the reaction system to 0.29 M. The reaction thereof was carried out at 78 C. for six hours, followed by cooling of the reaction solution. Then, a resin was purified by reprecipitation method and finally dried to be collected. The obtained resin was again dissolved in 80 parts by weight of isopropanol, and to the solution was dropwise added 200 parts by weight of water. The solution was stirred under reduced pressure, while the temperature of the solution was maintained at 30 C. The isopropanol and water were thus evaporated. The resulting substance was concentrated to have a solid content of 20% by weight, thereby preparing a dispersion in which polyvinyl acetal resin 9 in the form of fine particles (hereafter, also referred to as polyvinyl acetal resin fine particles 9) was dispersed (amount of polyvinyl acetal resin fine particles 9: 20% by weight).

(28) According to the measurement of the obtained polyvinyl acetal resin by NMR, the degree of butyralization was 47.1 mol %, the hydroxy group content was 50.4 mol %, the acetyl group content was 1 mol %, the ionic functional group content of the polyvinyl acetal resin was 0.1 mmol/g, and the amount of the acetal bond (in the formula (5), R.sup.3 is a benzene ring, X is sodium sulfonate) having an ionic functional group was 1.5 mol %. Further, the proportion of the hydroxy group-containing structural unit with a sequence length of 1 was 10.4% relative to the hydroxy group-containing structural unit as a whole in the obtained polyvinyl acetal resin. According to the measurement using a transmission electron microscope, the obtained polyvinyl acetal resin fine particles 9 had a volume average particle size of 480 nm.

(29) (Preparation of a Dispersion of Polyvinyl Acetal Resin Fine Particles 10)

(30) In a reaction vessel equipped with a thermometer, a stirrer, and a condenser tube, 20 parts by weight of a polyvinyl acetal resin (degree of polymerization: 1,000, degree of butyralization: 47.8 mol %, hydroxy group content: 51 mol %, acetyl group content: 1.2 mol %) was dissolved in 80 parts by weight of isopropanol. To the obtained solution were added 6 parts by weight of disodium 4-formylbenzene-1,3-disulfonate and 0.05 parts by weight of 12 M concentrated hydrochloric acid to set the acid concentration of the reaction system to 0.12 M. The reaction thereof was carried out at 70 C. for four hours. Then, 1 part by weight of 12 M concentrated hydrochloric acid was added to set the acid concentration of the reaction system to 0.29 M. The reaction thereof was carried out at 78 C. for six hours, followed by cooling of the reaction solution. Then, a resin was purified by reprecipitation method and finally dried to be collected. The obtained resin was again dissolved in 80 parts by weight of isopropanol, and to the solution was dropwise added 200 parts by weight of water. The solution was stirred under reduced pressure, while the temperature of the solution was maintained at 30 C. The isopropanol and water were thus evaporated. The resulting substance was concentrated to have a solid content of 20% by weight, thereby preparing a dispersion in which polyvinyl acetal resin 10 in the form of fine particles (hereafter, also referred to as polyvinyl acetal resin fine particles 10) was dispersed (amount of polyvinyl acetal resin fine particles 10: 20% by weight).

(31) According to the measurement of the obtained polyvinyl acetal resin by NMR, the degree of butyralization was 47.1 mol %, the hydroxy group content was 37.9 mol %, the acetyl group content was 1 mol %, the ionic functional group content of the polyvinyl acetal resin was 1.8 mmol/g, and the amount of the acetal bond (in the formula (5), R.sup.3 is a benzene ring, X is sodium sulfonate) having an ionic functional group was 14 mol %. Further, the proportion of the hydroxy group-containing structural unit with a sequence length of 1 was 10.9% relative to the hydroxy group-containing structural unit as a whole in the obtained polyvinyl acetal resin. According to the measurement using a transmission electron microscope, the obtained polyvinyl acetal resin fine particles 10 had a volume average particle size of 9 nm.

(32) (Preparation of a Dispersion of Polyvinyl Acetal Resin Fine Particles 11)

(33) In a reaction vessel equipped with a thermometer, a stirrer, and a condenser tube, 20 parts by weight of a polyvinyl acetal resin (degree of polymerization: 1,000, degree of butyralization: 47.8 mol %, hydroxy group content: 51 mol %, acetyl group content: 1.2 mol %) was dissolved in 80 parts by weight of isopropanol. To the obtained solution were added 0.6 parts by weight of sodium 2-formylbenzene sulfonate and 0.05 parts by weight of 12 M concentrated hydrochloric acid to set the acid concentration of the reaction system to 0.12 M. The reaction thereof was carried out at 70 C. for four hours. Then, 1 part by weight of 12 M concentrated hydrochloric acid was added to set the acid concentration of the reaction system to 0.29 M. The reaction thereof was carried out at 78 C. for six hours, followed by cooling of the reaction solution. Then, a resin was purified by reprecipitation method and finally dried to be collected. The obtained resin was again dissolved in 80 parts by weight of isopropanol, and to the solution was dropwise added 200 parts by weight of water. The solution was stirred under reduced pressure, while the temperature of the solution was maintained at 30 C. The isopropanol and water were thus evaporated. The resulting substance was concentrated to have a solid content of 20% by weight, thereby preparing a dispersion in which polyvinyl acetal resin 11 in the form of fine particles (hereafter, also referred to as polyvinyl acetal resin fine particles 11) was dispersed (amount of polyvinyl acetal resin fine particles 11: 20% by weight).

(34) According to the measurement of the obtained polyvinyl acetal resin by NMR, the degree of butyralization was 47.1 mol %, the hydroxy group content was 50 mol %, the acetyl group content was 1 mol %, the ionic functional group content of the polyvinyl acetal resin was 0.1 mmol/g, and the amount of the acetal bond (in the formula (5), R.sup.3 is a benzene ring, X is sodium sulfonate) having an ionic functional group was 1.9 mol %. Further, the proportion of the hydroxy group-containing structural unit with a sequence length of 1 was 10.4% relative to the hydroxy group-containing structural unit as a whole in the obtained polyvinyl acetal resin. According to the measurement using a transmission electron microscope, the obtained polyvinyl acetal resin fine particles 11 had a volume average particle size of 240 nm.

(35) (Preparation of a Dispersion of Polyvinyl Acetal Resin Fine Particles 12)

(36) In a reaction vessel equipped with a thermometer, a stirrer, and a condenser tube, 20 parts by weight of a polyvinyl acetal resin (degree of polymerization: 1,000, degree of butyralization: 35.5 mol %, hydroxy group content: 63.3 mol %, acetyl group content: 1.2 mol %) was dissolved in 80 parts by weight of isopropanol. To the obtained solution were added 1 part by weight of sodium 2-formylbenzene sulfonate and 0.05 parts by weight of 12 M concentrated hydrochloric acid to set the acid concentration of the reaction system to 0.12 M. The reaction thereof was carried out at 70 C. for four hours. Then, 1 part by weight of 12 M concentrated hydrochloric acid was added to set the acid concentration of the reaction system to 0.29 M. The reaction thereof was carried out at 73 C. for one hour, followed by cooling of the reaction solution. Then, a resin was purified by reprecipitation method and finally dried to be collected. The obtained resin was again dissolved in 80 parts by weight of isopropanol, and to the solution was dropwise added 200 parts by weight of water. The solution was stirred under reduced pressure, while the temperature of the solution was maintained at 30 C. The isopropanol and water were thus evaporated. The resulting substance was concentrated to have a solid content of 20% by weight, thereby preparing a dispersion in which polyvinyl acetal resin 12 in the form of fine particles (hereafter, also referred to as polyvinyl acetal resin fine particles 12) was dispersed (amount of polyvinyl acetal resin fine particles 12: 20% by weight).

(37) According to the measurement of the obtained polyvinyl acetal resin by NMR, the degree of butyralization was 34 mol %, the hydroxy group content was 62 mol %, the acetyl group content was 1 mol %, the ionic functional group content of the polyvinyl acetal resin was 0.2 mmol/g, and the amount of the acetal bond (in the formula (5), R.sup.3 is a benzene ring, X is sodium sulfonate) having an ionic functional group was 3 mol %. Further, the proportion of the hydroxy group-containing structural unit with a sequence length of 1 was 27.3% relative to the hydroxy group-containing structural unit as a whole in the obtained polyvinyl acetal resin. According to the measurement using a transmission electron microscope, the obtained polyvinyl acetal resin fine particles 12 had a volume average particle size of 100 nm.

(38) (Preparation of a Dispersion of Polyvinyl Acetal Resin Fine Particles 13)

(39) In a reaction vessel equipped with a thermometer, a stirrer, and a condenser tube, 20 parts by weight of a polyvinyl acetal resin (degree of polymerization: 1,100, degree of butyralization: 70.2 mol %, hydroxy group content: 27.6 mol %, acetyl group content: 2.2 mol %) was dissolved in 80 parts by weight of isopropanol. To the obtained solution were added 2.3 parts by weight of sodium 2-formylbenzene sulfonate and 0.05 parts by weight of 12 M concentrated hydrochloric acid to set the acid concentration of the reaction system to 0.12 M. The reaction thereof was carried out at 70 C. for four hours. Then, 0.3 parts by weight of 12 M concentrated hydrochloric acid was added to set the acid concentration of the reaction system to 0.14 M. The reaction thereof was carried out at 72 C. for one hour, followed by cooling of the reaction solution. Then, a resin was purified by reprecipitation method and finally dried to be collected. The obtained resin was again dissolved in 80 parts by weight of isopropanol, and to the solution was dropwise added 200 parts by weight of water. The solution was stirred under reduced pressure, while the temperature of the solution was maintained at 30 C. The isopropanol and water were thus evaporated. The resulting substance was concentrated to have a solid content of 20% by weight, thereby preparing a dispersion in which polyvinyl acetal resin 13 in the form of fine particles (hereafter, also referred to as polyvinyl acetal resin fine particles 13) was dispersed (amount of polyvinyl acetal resin fine particles 13: 20% by weight).

(40) According to the measurement of the obtained polyvinyl acetal resin by NMR, the degree of butyralization was 68.8 mol %, the hydroxy group content was 25 mol %, the acetyl group content was 2 mol %, the ionic functional group content of the polyvinyl acetal resin was 0.2 mmol/g, and the amount of the acetal bond (in the formula (5), R.sup.3 is a benzene ring, X is sodium sulfonate) having an ionic functional group was 4.2 mol %. Further, the proportion of the hydroxy group-containing structural unit with a sequence length of 1 was 18.6% relative to the hydroxy group-containing structural unit as a whole in the obtained polyvinyl acetal resin. According to the measurement using a transmission electron microscope, the obtained polyvinyl acetal resin fine particles 13 had a volume average particle size of 90 nm.

(41) (Preparation of a Dispersion of Polyvinyl Acetal Resin Fine Particles 14)

(42) In a reaction vessel equipped with a thermometer, a stirrer, and a condenser tube, 20 parts by weight of a polyvinyl acetal resin (degree of polymerization: 1,100, degree of butyralization: 33.1 mol %, hydroxy group content: 65.6 mol %, acetyl group content: 1.3 mol %) was dissolved in 80 parts by weight of isopropanol. To the obtained solution were added 2 parts by weight of sodium 2-formylbenzene sulfonate and 0.05 parts by weight of 12 M concentrated hydrochloric acid to set the acid concentration of the reaction system to 0.12 M. The reaction thereof was carried out at 70 C. for four hours. Then, 0.6 parts by weight of 12 M concentrated hydrochloric acid were added to set the acid concentration of the reaction system to 0.21 M. The reaction thereof was carried out at 73 C. for 1 hour, followed by cooling of the reaction solution. Then, a resin was purified by reprecipitation method and finally dried to be collected. The obtained resin was again dissolved in 80 parts by weight of isopropanol, and to the solution was dropwise added 200 parts by weight of water. The solution was stirred under reduced pressure, while the temperature of the solution was maintained at 30 C. The isopropanol and water were thus evaporated. The resulting substance was concentrated to have a solid content of 20% by weight, thereby preparing a dispersion in which polyvinyl acetal resin 14 in the form of fine particles (hereafter, also referred to as polyvinyl acetal resin fine particles 14) was dispersed (amount of polyvinyl acetal resin fine particles 14: 20% by weight).

(43) According to the measurement of the obtained polyvinyl acetal resin by NMR, the degree of butyralization was 32.5 mol %, the hydroxy group content was 65 mol %, the acetyl group content was 0.8 mol %, the ionic functional group content of the polyvinyl acetal resin was 0.2 mmol/g, and the amount of the acetal bond (in the formula (5), R.sup.3 is a benzene ring, X is sodium sulfonate) having an ionic functional group was 1.7 mol %. Further, the proportion of the hydroxy group-containing structural unit with a sequence length of 1 was 14.6% relative to the hydroxy group-containing structural unit as a whole in the obtained polyvinyl acetal resin. According to the measurement using a transmission electron microscope, the obtained polyvinyl acetal resin fine particles 14 had a volume average particle size of 90 nm.

(44) (Preparation of a Dispersion of Polyvinyl Acetal Resin Fine Particles 15)

(45) In a reaction vessel equipped with a thermometer, a stirrer, and a condenser tube, 20 parts by weight of a polyvinyl acetal resin (degree of polymerization: 1,100, degree of butyralization: 52 mol %, hydroxy group content: 47.8 mol %, acetyl group content: 0.2 mol %) was dissolved in 80 parts by weight of isopropanol. To the obtained solution were added 1 part by weight of sodium 2-formylbenzene sulfonate and 0.05 parts by weight of 12 M concentrated hydrochloric acid to set the acid concentration of the reaction system to 0.12 M. The reaction thereof was carried out at 70 C. for four hours. Then, 0.2 parts by weight of butyraldehyde and 1 part by weight of 12 M concentrated hydrochloric acid were added to set the acid concentration of the reaction system to 0.15 M. The reaction thereof was carried out at 82 C. for six hours, followed by cooling of the reaction solution. Then, a resin was purified by reprecipitation method and finally dried to be collected. The obtained resin was again dissolved in 80 parts by weight of isopropanol, and to the solution was dropwise added 200 parts by weight of water. The solution was stirred under reduced pressure, while the temperature of the solution was maintained at 30 C. The isopropanol and water were thus evaporated. The resulting substance was concentrated to have a solid content of 20% by weight, thereby preparing a dispersion in which polyvinyl acetal resin 15 in the form of fine particles (hereafter, also referred to as polyvinyl acetal resin fine particles 15) was dispersed (amount of polyvinyl acetal resin fine particles 15: 20% by weight).

(46) According to the measurement of the obtained polyvinyl acetal resin by NMR, the amount of the structural unit of the formula (2) was 0.3 mol %, the degree of butyralization was 51.7 mol %, the hydroxy group content was 45 mol %, the acetyl group content was 0.2 mol %, the ionic functional group content of the polyvinyl acetal resin was 0.2 mmol/g, and the amount of the acetal bond (in the formula (5), R.sup.3 is a benzene ring, X is sodium sulfonate) having an ionic functional group was 2.8 mol %. Further, the proportion of the hydroxy group-containing structural unit with a sequence length of 1 was 9.8% relative to the hydroxy group-containing structural unit as a whole in the obtained polyvinyl acetal resin. According to the measurement using a transmission electron microscope, the obtained polyvinyl acetal resin fine particles 15 had a volume average particle size of 90 nm.

(47) (Preparation of a Dispersion of Polyvinyl Acetal Resin Fine Particles 16)

(48) In a reaction vessel equipped with a thermometer, a stirrer, and a condenser tube, 20 parts by weight of a polyvinyl acetal resin (degree of polymerization: 1,100, degree of butyralization: 45.6 mol %, hydroxy group content: 52.1 mol %, acetyl group content: 2.3 mol %) was dissolved in 80 parts by weight of isopropanol. To the obtained solution were added 0.5 parts by weight of sodium 2-formylbenzene sulfonate and 0.05 parts by weight of 12 M concentrated hydrochloric acid to set the acid concentration of the reaction system to 0.12 M. The reaction thereof was carried out at 70 C. for four hours. Then, 3 parts by weight of butyraldehyde and 0.05 parts by weight of 12 M concentrated hydrochloric acid were added to set the acid concentration of the reaction system to 0.12 M. The reaction thereof was carried out at 70 C. for 0.3 hours, followed by cooling of the reaction solution. Then, a resin was purified by reprecipitation method and finally dried to be collected. The obtained resin was again dissolved in 80 parts by weight of isopropanol, and to the solution was dropwise added 200 parts by weight of water. The solution was stirred under reduced pressure, while the temperature of the solution was maintained at 30 C. The isopropanol and water were thus evaporated. The resulting substance was concentrated to have a solid content of 20% by weight, thereby preparing a dispersion in which polyvinyl acetal resin 16 in the form of fine particles (hereafter, also referred to as polyvinyl acetal resin fine particles 16) was dispersed (amount of polyvinyl acetal resin fine particles 16: 20% by weight).

(49) According to the measurement of the obtained polyvinyl acetal resin by NMR, the amount of the structural unit of the formula (2) was 5 mol %, the degree of butyralization was 46.4 mol %, the hydroxy group content was 45 mol %, the acetyl group content was 2 mol %, the ionic functional group content of the polyvinyl acetal resin was 0.1 mmol/g, the amount of the acetal bond (in the formula (5), R.sup.3 is a benzene ring, X is a sodium sulfonate) was 1.6 mol %. Further, the proportion of the hydroxy group-containing structural unit with a sequence length of 1 was 14.5% relative to the hydroxy group-containing structural unit as a whole in the obtained polyvinyl acetal. According to the measurement using a transmission electron microscope, the obtained polyvinyl acetal resin fine particles 16 had a volume average particle size of 300 nm.

(50) (Preparation of a Dispersion of Polyvinyl Acetal Resin Fine Particles 17)

(51) In a reaction vessel equipped with a thermometer, a stirrer, and a condenser tube, 20 parts by weight of a polyvinyl acetal resin (degree of polymerization: 1,100, degree of butyralization: 46.8 mol %, hydroxy group content: 51.8 mol %, acetyl group content: 1.4 mol %) was dissolved in 80 parts by weight of isopropanol. To the obtained solution were added 2 parts by weight of disodium 4-formylbenzene-1,3-disulfonate and 0.05 parts by weight of 12 M concentrated hydrochloric acid to set the acid concentration of the reaction system to 0.12 M. The reaction thereof was carried out at 70 C. for four hours. Then, 1 part by weight of butyraldehyde and 0.5 parts by weight of 12 M concentrated hydrochloric acid were added to set the acid concentration of the reaction system to 0.21 M. The reaction thereof was carried out at 75 C. for four hours, followed by cooling of the reaction solution. Then, a resin was purified by reprecipitation method and finally dried to be collected. The obtained resin was again dissolved in 80 parts by weight of isopropanol, and to the solution was dropwise added 200 parts by weight of water. The solution was stirred under reduced pressure, while the temperature of the solution was maintained at 30 C. The isopropanol and water were thus evaporated. The resulting substance was concentrated to have a solid content of 20% by weight, thereby preparing a dispersion in which polyvinyl acetal resin 17 in the form of fine particles (hereafter, also referred to as polyvinyl acetal resin fine particles 17) was dispersed (amount of polyvinyl acetal resin fine particles 17: 20% by weight).

(52) According to the measurement of the obtained polyvinyl acetal resin by NMR, the amount of the structural unit of the formula (2) was 2 mol %, the degree of butyralization was 47.4 mol %, the hydroxy group content was 45 mol %, the acetyl group content was 1.1 mol %, the ionic functional group content of the polyvinyl acetal resin was 0.6 mmol/g, and the amount of the acetal bond (in the formula (5), R.sup.3 is a benzene ring and X is sodium sulfonate) having an ionic functional group was 4.5 mol %. Further, the proportion of the hydroxy group-containing structural unit with a sequence length of 1 was 12.4% relative to the hydroxy group-containing structural unit as a whole in the obtained polyvinyl acetal resin. According to the measurement using a transmission electron microscope, the obtained polyvinyl acetal resin fine particles 17 had a volume average particle size of 30 nm.

(53) (Preparation of a Dispersion of Polyvinyl Acetal Resin Fine Particles 18)

(54) In a reaction vessel equipped with a thermometer, a stirrer, and a condenser tube, 20 parts by weight of a polyvinyl acetal resin (degree of polymerization: 800, degree of butyralization: 52 mol %, hydroxy group content: 47.9 mol %, acetyl group content: 0.1 mol %) was dissolved in 80 parts by weight of isopropanol. To the obtained solution were added 2 parts by weight of terephthalaldehydic acid and 0.05 parts by weight of 12 M concentrated hydrochloric acid to set the acid concentration of the reaction system to 0.12 M. The reaction thereof was carried out at 70 C. for four hours. Then, 0.1 parts by weight of butyraldehyde and 1 part by weight of 12 M concentrated hydrochloric acid were added to set the acid concentration of the reaction system to 0.29 M. The reaction thereof was carried out at 82 C. for seven hours, followed by cooling of the reaction solution. Then, a resin was purified by reprecipitation method and finally dried to be collected. The obtained resin was again dissolved in 80 parts by weight of isopropanol, and to the solution was dropwise added 200 parts by weight of water. The solution was stirred under reduced pressure, while the temperature of the solution was maintained at 30 C. The isopropanol and water were thus evaporated. The resulting substance was concentrated to have a solid content of 20% by weight, thereby preparing a dispersion in which polyvinyl acetal resin 18 in the form of fine particles (hereafter, also referred to as polyvinyl acetal resin fine particles 18) was dispersed (amount of polyvinyl acetal resin fine particles 18: 20% by weight).

(55) According to the measurement of the obtained polyvinyl acetal resin by NMR, the amount of the structural unit of the formula (2) was 0.2 mol %, the degree of butyralization was 51.7 mol %, the hydroxy group content was 36 mol %, the acetyl group content was 0.1 mol %, the ionic functional group content of the polyvinyl acetal resin was 1 mmol/g, and the amount of the acetal bond (in the formula (5), R.sup.3 is a benzene ring, X is carboxy group) having an ionic functional group was 12 mol %. Further, the proportion of the hydroxy group-containing structural unit with a sequence length of 1 was 25.4% relative to the hydroxy group-containing structural unit as a whole in the obtained polyvinyl acetal resin. According to the measurement using a transmission electron microscope, the obtained polyvinyl acetal resin fine particles 18 had a volume average particle size of 450 nm.

(56) (Preparation of a Dispersion of Polyvinyl Acetal Resin Fine Particles 19)

(57) In a reaction vessel equipped with a thermometer, a stirrer, and a condenser tube, 20 parts by weight of a polyvinyl acetal resin (degree of polymerization: 1,700, degree of butyralization: 37 mol %, hydroxy group content: 55 mol %, acetyl group content: 8 mol %) was dissolved in 80 parts by weight of isopropanol. To the obtained solution were added 1 part by weight of sodium 2-formylbenzene sulfonate and 0.05 parts by weight of 12 M concentrated hydrochloric acid to set the acid concentration of the reaction system to 0.12 M. The reaction thereof was carried out at 70 C. for four hours. Then, 3.5 parts by weight of butyraldehyde and 0.05 parts by weight of 12 M concentrated hydrochloric acid were added to set the acid concentration of the reaction system to 0.12 M. The reaction thereof was carried out at 70 C. for 0.3 hours, followed by cooling of the reaction solution. Then, a resin was purified by reprecipitation method and finally dried to be collected. The obtained resin was again dissolved in 80 parts by weight of isopropanol, and to the solution was dropwise added 200 parts by weight of water. The solution was stirred under reduced pressure, while the temperature of the solution was maintained at 30 C. The isopropanol and water were thus evaporated. The resulting substance was concentrated to have a solid content of 20% by weight, thereby preparing a dispersion in which polyvinyl acetal resin 19 in the form of fine particles (hereafter, also referred to as polyvinyl acetal resin fine particles 19) was dispersed (amount of polyvinyl acetal resin fine particles 19: 20% by weight).

(58) According to the measurement of the obtained polyvinyl acetal resin by NMR, the amount of the structural unit of the formula (2) was 7 mol %, the degree of butyralization was 38 mol %, the hydroxy group content was 45 mol %, the acetyl group content was 7 mol %, the ionic functional group content of the polyvinyl acetal resin was 0.2 mmol/g, and the amount of the acetal bond (in the formula (5), R.sup.3 is a benzene ring and X is sodium sulfonate) having an ionic functional group was 3 mol %. Further, the proportion of the hydroxy group-containing structural unit with a sequence length of 1 was 19.2% relative to the hydroxy group-containing structural unit as a whole in the obtained polyvinyl acetal resin. According to the measurement using a transmission electron microscope, the obtained polyvinyl acetal resin fine particles 19 had a volume average particle size of 90 nm.

(59) (Preparation of a Dispersion of Polyvinyl Acetal Resin Fine Particles 20)

(60) In a reaction vessel equipped with a thermometer, a stirrer, and a condenser tube, 20 parts by weight of a polyvinyl acetal resin (degree of polymerization: 1,700, degree of butyralization: 66.6 mol %, hydroxy group content: 31 mol %, acetyl group content: 2.4 mol %) was dissolved in 80 parts by weight of isopropanol. To the obtained solution were added 1 part by weight of sodium 2-formylbenzene sulfonate and 0.05 parts by weight of 12 M concentrated hydrochloric acid to set the acid concentration of the reaction system to 0.12 M. The reaction thereof was carried out at 70 C. for four hours. Then, 0.9 parts by weight of butyraldehyde and 0.5 parts by weight of 12 M concentrated hydrochloric acid were added to set the acid concentration of the reaction system to 0.21 M. The reaction thereof was carried out at 75 C. for four hours, followed by cooling of the reaction solution. Then, a resin was purified by reprecipitation method and finally dried to be collected. The obtained resin was again dissolved in 80 parts by weight of isopropanol, and to the solution was dropwise added 200 parts by weight of water. The solution was stirred under reduced pressure, while the temperature of the solution was maintained at 30 C. The isopropanol and water were thus evaporated. The resulting substance was concentrated to have a solid content of 20% by weight, thereby preparing a dispersion in which polyvinyl acetal resin 20 in the form of fine particles (hereafter, also referred to as polyvinyl acetal resin fine particles 20) was dispersed (amount of polyvinyl acetal resin fine particles 20: 20% by weight).

(61) According to the measurement of the obtained polyvinyl acetal resin by NMR, the amount of the structural unit of the formula (2) was 2 mol %, the degree of butyralization was 66.8 mol %, the hydroxy group content was 25 mol %, the acetyl group content was 2 mol %, the ionic functional group content of the polyvinyl acetal resin was 0.3 mmol/g, and the amount of the acetal bond (in the formula (5), R.sup.3 is a benzene ring and X is sodium sulfonate) having an ionic functional group was 4.2 mol %. Further, the proportion of the hydroxy group-containing structural unit with a sequence length of 1 was 19.7% relative to the hydroxy group-containing structural unit as a whole in the obtained polyvinyl acetal resin. According to the measurement using a transmission electron microscope, the obtained polyvinyl acetal resin fine particles 20 had a volume average particle size of 90 nm.

(62) (Preparation of a Dispersion of Polyvinyl Acetal Resin Fine Particles 21)

(63) In a reaction vessel equipped with a thermometer, a stirrer, and a condenser tube, 20 parts by weight of a polyvinyl acetal resin (degree of polymerization: 1,700, degree of butyralization: 30.3 mol %, hydroxy group content: 68.7 mol %, acetyl group content: 1 mol %) was dissolved in 80 parts by weight of isopropanol. To the obtained solution were added 1 part by weight of sodium 2-formylbenzene sulfonate and 0.05 parts by weight of 12 M concentrated hydrochloric acid to set the acid concentration of the reaction system to 0.12 M. The reaction thereof was carried out at 70 C. for four hours. Then, 1.5 parts by weight of butyraldehyde and 0.5 parts by weight of 12 M concentrated hydrochloric acid were added to set the acid concentration of the reaction system to 0.21 M. The reaction thereof was carried out at 75 C. for four hours, followed by cooling of the reaction solution. Then, a resin was purified by reprecipitation method and finally dried to be collected. The obtained resin was again dissolved in 80 parts by weight of isopropanol, and to the solution was dropwise added 200 parts by weight of water. The solution was stirred under reduced pressure, while the temperature of the solution was maintained at 30 C. The isopropanol and water were thus evaporated. The resulting substance was concentrated to have a solid content of 20% by weight, thereby preparing a dispersion in which polyvinyl acetal resin 21 in the form of fine particles (hereafter, also referred to as polyvinyl acetal resin fine particles 21) was dispersed (amount of polyvinyl acetal resin fine particles 21: 20% by weight).

(64) According to the measurement of the obtained polyvinyl acetal resin by NMR, the amount of the structural unit of the formula (2) was 2 mol %, the degree of butyralization was 30.5 mol %, the hydroxy group content was 65 mol %, the acetyl group content was 0.8 mol %, the ionic functional group content of the polyvinyl acetal resin was 0.1 mmol/g, and the amount of the acetal bond (in the formula (5), R.sup.3 is a benzene ring, X is sodium sulfonate) having an ionic functional group was 1.7 mol %. Further, the proportion of the hydroxy group-containing structural unit with a sequence length of 1 was 24.1% relative to the hydroxy group-containing structural unit as a whole in the obtained polyvinyl acetal resin. According to the measurement using a transmission electron microscope, the obtained polyvinyl acetal resin fine particles 21 had a volume average particle size of 90 nm.

(65) (Preparation of a Dispersion of Polyvinyl Acetal Resin Fine Particles 22)

(66) In a reaction vessel equipped with a thermometer, a stirrer, and a condenser tube, 20 parts by weight of a polyvinyl acetal resin (degree of polymerization: 1,700, degree of butyralization: 37.2 mol %, hydroxy group content: 61 mol %, acetyl group content: 1.8 mol %) was dissolved in 80 parts by weight of isopropanol. To the obtained solution were added 6 parts by weight of disodium 4-formylbenzene-1,3-disulfonate and 0.05 parts by weight of 12 M concentrated hydrochloric acid to set the acid concentration of the reaction system to 0.12 M. The reaction thereof was carried out at 70 C. for four hours. Then, 1 part by weight of butyraldehyde and 0.5 parts by weight of 12 M concentrated hydrochloric acid were added to set the acid concentration of the reaction system to 0.21 M. The reaction thereof was carried out at 75 C. for four hours, followed by cooling of the reaction solution. Then, a resin was purified by reprecipitation and finally dried to be collected. The obtained resin was again dissolved in 80 parts by weight of isopropanol, and to the solution was dropwise added 200 parts by weight of water. The solution was stirred under reduced pressure, while the temperature of the solution was maintained at 30 C. The isopropanol and water were thus evaporated. The resulting substance was concentrated to have a solid content of 20% by weight, thereby preparing a dispersion in which polyvinyl acetal resin 22 in the form of fine particles (hereafter, also referred to as polyvinyl acetal resin fine particles 22) was dispersed (amount of polyvinyl acetal resin fine particles 22: 20% by weight).

(67) According to the measurement of the obtained polyvinyl acetal resin by NMR, the amount of the structural unit of the formula (2) was 2 mol %, the degree of butyralization was 37.5 mol %, the hydroxy group content was 45 mol %, the acetyl group content was 1.5 mol %, the ionic functional group content of the polyvinyl acetal resin was 1.8 mmol/g, and the amount of the acetal bond (in the formula (5), R.sup.3 is a benzene ring, X is sodium sulfonate) having an ionic functional group was 14 mol %. Further, the proportion of the hydroxy group-containing structural unit with a sequence length of 1 was 11.9% relative to the hydroxy group-containing structural unit as a whole in the obtained polyvinyl acetal. According to the measurement using a transmission electron microscope, the obtained polyvinyl acetal resin fine particles 22 had a volume average particle size of 9 nm.

(68) (Preparation of a Dispersion of Polyvinyl Acetal Resin Fine Particles 23)

(69) In a reaction vessel equipped with a thermometer, a stirrer, and a condenser tube, 20 parts by weight of a polyvinyl acetal resin (degree of polymerization: 800, degree of butyralization: 50.5 mol %, hydroxy group content: 47.7 mol %, acetyl group content: 1.8 mol %) was dissolved in 80 parts by weight of isopropanol. To the obtained solution were added 0.25 parts by weight of sodium 2-formylbenzene sulfonate and 0.05 parts by weight of 12 M concentrated hydrochloric acid to set the acid concentration of the reaction system to 0.12 M. The reaction thereof was carried out at 70 C. for four hours. Then, 1 part by weight of butyraldehyde and 0.5 parts by weight of 12 M concentrated hydrochloric acid were added to set the acid concentration of the reaction system to 0.21 M. The reaction thereof was carried out at 75 C. for four hours, followed by cooling of the reaction solution. Then, a resin was purified by reprecipitation method and finally dried to be collected. The obtained resin was again dissolved in 80 parts by weight of isopropanol, and to the solution was dropwise added 200 parts by weight of water. The solution was stirred under reduced pressure, while the temperature of the solution was maintained at 30 C. The isopropanol and water were thus evaporated. The resulting substance was concentrated to have a solid content of 20% by weight, thereby preparing a dispersion in which polyvinyl acetal resin 23 in the form of fine particles (hereafter, also referred to as polyvinyl acetal resin fine particles 23) was dispersed (amount of polyvinyl acetal resin fine particles 23: 20% by weight).

(70) According to the measurement of the obtained polyvinyl acetal resin by NMR, the amount of the structural unit of the formula (2) was 2 mol %, the degree of butyralization was 50.8 mol %, the hydroxy group content was 45 mol %, the acetyl group content was 1.5 mol %, the ionic functional group content of the polyvinyl acetal resin was 0.05 mmol/g, and the amount of the acetal bond (in the formula (5), R.sup.3 is a benzene ring, X is sodium sulfonate) having an ionic functional group was 0.7 mol %. Further, the proportion of the hydroxy group-containing structural unit with a sequence length of 1 was 22.9% relative to the hydroxy group-containing structural unit as a whole in the obtained polyvinyl acetal resin. According to the measurement using a transmission electron microscope, the obtained polyvinyl acetal resin fine particles 23 had a volume average particle size of 700 nm.

(71) (Preparation of a Dispersion of Polyvinyl Acetal Resin Fine Particles 24)

(72) In a reaction vessel equipped with a thermometer, a stirrer, and a condenser tube, 20 parts by weight of a polyvinyl acetal resin (degree of polymerization: 1,100, degree of butyralization: 52 mol %, hydroxy group content: 47.8 mol %, acetyl group content: 0.2 mol %) was dissolved in 80 parts by weight of isopropanol. To the obtained solution were added 1 part by weight of sodium 2-formylbenzene sulfonate and 0.05 parts by weight of 12 M concentrated hydrochloric acid to set the acid concentration of the reaction system to 0.12 M. The reaction thereof was carried out at 70 C. for four hours. Then, 1 part by weight of butyraldehyde and 1 part by weight of 12 M concentrated hydrochloric acid were added to set the acid concentration of the reaction system to 0.29 M. The reaction thereof was carried out at 82 C. for six hours, followed by cooling of the reaction solution. Then, a resin was purified by reprecipitation method and finally dried to be collected. The obtained resin was again dissolved in 80 parts by weight of isopropanol, and to the solution was dropwise added 200 parts by weight of water. The solution was stirred under reduced pressure, while the temperature of the solution was maintained at 30 C. The isopropanol and water were thus evaporated. The resulting substance was concentrated to have a solid content of 20% by weight, thereby preparing a dispersion in which polyvinyl acetal resin 24 in the form of fine particles (hereafter, also referred to as polyvinyl acetal resin fine particles 24) was dispersed (amount of polyvinyl acetal resin fine particles 24: 20% by weight).

(73) According to the measurement of the obtained polyvinyl acetal resin by NMR, the amount of the structural unit of the formula (2) was 0.2 mol %, the degree of butyralization was 51.7 mol %, the hydroxy group content was 45 mol %, the acetyl group content was 0.2 mol %, the ionic functional group content of the polyvinyl acetal resin was 0.18 mmol/g, and the amount of the acetal bond (in the formula (5), R.sup.3 is a benzene ring, X is sodium sulfonate) having an ionic functional group was 2.9 mol %. Further, the proportion of the hydroxy group-containing structural unit with a sequence length of 1 was 17.4% relative to the hydroxy group-containing structural unit as a whole in the obtained polyvinyl acetal resin. According to the measurement using a transmission electron microscope, the obtained polyvinyl acetal resin fine particles 24 had a volume average particle size of 200 nm.

(74) (Preparation of Polyvinyl Acetal Resin 25)

(75) In a reaction vessel equipped with a thermometer, a stirrer, and a condenser tube, 20 parts by weight of a polyvinyl acetal resin (degree of polymerization: 1,100, degree of butyralization: 52 mol %, hydroxy group content: 47.8 mol %, acetyl group content: 0.2 mol %) was dissolved in 80 parts by weight of isopropanol. To the obtained solution were added 1 part by weight of sodium 2-formylbenzene sulfonate and 0.05 parts by weight of 12 M concentrated hydrochloric acid to set the acid concentration of the reaction system to 0.12 M. The reaction thereof was carried out at 70 C. for four hours. Then, 0.2 parts by weight of butyraldehyde and 1 part by weight of 12 M concentrated hydrochloric acid were added to set the acid concentration of the reaction system to 0.15 M. The reaction thereof was carried out at 82 C. for six hours, followed by cooling of the reaction solution. Then, a resin was purified by reprecipitation method and finally dried, thereby preparing polyvinyl acetal resin 25.

(76) According to the measurement of the obtained polyvinyl acetal resin by NMR, the amount of the structural unit of the formula (2) was 0.3 mol %, the degree of butyralization was 51.7 mol %, the hydroxy group content was 45 mol %, the acetyl group content was 0.2 mol %, the ionic functional group content of the polyvinyl acetal resin was 0.2 mmol/g, and the amount of the acetal bond (in the formula (5), R.sup.3 is a benzene ring, X is sodium sulfonate) having an ionic functional group was 2.8 mol %. Further, the proportion of the hydroxy group-containing structural unit with a sequence length of 1 was 9.8% relative to the hydroxy group-containing structural unit as a whole in the obtained polyvinyl acetal resin.

(77) (Preparation of Polyvinyl Acetal Resin 26)

(78) In a reaction vessel equipped with a thermometer, a stirrer, and a condenser tube, 20 parts by weight of a polyvinyl acetal resin (degree of polymerization: 1,000, degree of butyralization: 48.1 mol %, hydroxy group content: 50.7 mol %, acetyl group content: 1.2 mol %) was dissolved in 80 parts by weight of isopropanol. To the obtained solution were added 1 part by weight of butylaldehyde and 0.1 parts by weight of 12 M concentrated hydrochloric acid to set the acid concentration of the reaction system to 0.14 M. The reaction thereof was carried out at 73 C. for one hour, followed by cooling of the reaction solution. Then, a resin was purified by reprecipitation method and finally dried, thereby preparing polyvinyl acetal resin 26.

(79) According to the measurement of the obtained polyvinyl acetal resin by NMR, the amount of the structural unit of the formula (2) (in the formula (2), R.sup.1 is a propyl group) was 0.3 mol %, the degree of butyralization was 47.8 mol %, the hydroxy group content was 50.7 mol %, the acetyl group content was 1.2 mol %, the ionic functional group content of the polyvinyl acetal resin was 0 mmol/g, and the amount of the acetal bond having an ionic functional group was 0 mol %. Further, the proportion of the hydroxy group-containing structural unit with a sequence length of 1 was 27.7% relative to the hydroxy group-containing structural unit as a whole in the obtained polyvinyl acetal resin.

(80) TABLE-US-00001 TABLE 1 Polyvinyl acetal resin Proportion of hydroxy group- containing structural unit with a sequence Amount length of 1 of acetal relative to bond Amount the hydroxy De- having of group- gree Degree an structural Ionic containing Volume of of Hydroxy Acetyl ionic unit of Ionic functional structural average poly- buty- group group functional formula func- group unit as a particle meri- ralization content content group (2) tional content whole (% size zation (mol %) (mol %) (mol %) (mol %) (mol %) group (mmol/g) by weight) (nm) Polyvinyl acetal resin fine particles 1 1000 58.3 37.6 1.2 2.9 Sulfonate 0.2 9.7 100 Polyvinyl acetal resin fine particles 2 1000 47.1 48.9 1 3 Sulfonate 0.2 10.2 90 Polyvinyl acetal resin fine particles 3 1000 61.6 34 1.4 3 Sulfonate 0.2 12.5 110 Polyvinyl acetal resin fine particles 4 1000 63.6 31.9 1.5 3 Sulfonate 0.2 17.9 110 Polyvinyl acetal resin fine particles 5 1000 69.5 26.1 1.5 2.9 Sulfonate 0.2 30.5 140 Polyvinyl acetal resin fine particles 6 1000 64.4 31 1.6 3 Sulfonate 0.2 22.7 130 Polyvinyl acetal resin fine particles 7 1000 73.1 22.4 1.6 2.9 Sulfonate 0.2 33.6 150 Polyvinyl acetal resin fine particles 8 1000 47.4 50.7 1 0.9 Sulfonate 0.07 10.4 600 Polyvinyl acetal resin fine particles 9 1000 47.1 50.4 1 1.5 Sulfonate 0.1 10.4 480 Polyvinyl acetal resin fine particles 10 1000 47.1 37.9 1 14 Sulfonate 1.8 10.9 9 Polyvinyl acetal resin fine particles 11 1000 47.1 50 1 1.9 Sulfonate 0.1 10.4 240 Polyvinyl acetal resin fine particles 12 1000 34 62 1 3 Sulfonate 0.2 27.3 100 Polyvinyl acetal resin fine particles 13 1100 68.8 25 2 4.2 Sulfonate 0.2 18.6 90 Polyvinyl acetal resin fine particles 14 1100 32.5 65 0.8 1.7 Sulfonate 0.2 14.6 90 Polyvinyl acetal resin fine particles 15 1100 51.7 45 0.2 2.8 0.3 Sulfonate 0.2 9.8 90 Polyvinyl acetal resin fine particles 16 1100 46.4 45 2 1.6 5 Sulfonate 0.1 14.5 300 Polyvinyl acetal resin fine particles 17 1100 47.4 45 1.1 4.5 2 Sulfonate 0.6 12.4 30 Polyvinyl acetal resin fine particles 18 800 51.7 36 0.1 12 0.2 Carboxylic 1 25.4 450 acid Polyvinyl acetal resin fine particles 19 1700 38 45 7 3 7 Sulfonate 0.2 19.2 90 Polyvinyl acetal resin fine particles 20 1700 66.8 25 2 4.2 2 Sulfonate 0.3 19.7 90 Polyvinyl acetal resin fine particles 21 1700 30.5 65 0.8 1.7 2 Sulfonate 0.1 24.1 90 Polyvinyl acetal resin fine particles 22 1700 37.5 45 1.5 14 2 Sulfonate 1.8 11.9 9 Polyvinyl acetal resin fine particles 23 800 50.8 45 1.5 0.7 2 Sulfonate 0.05 22.9 700 Polyvinyl acetal resin fine particles 24 1100 51.7 45 0.2 2.9 0.2 Sulfonate 0.18 17.4 200 Polyvinyl acetal resin 25 1100 51.7 45 0.2 2.8 0.3 Sulfonate 0.2 9.8 Polyvinyl acetal resin 26 1000 47.8 50.7 1.2 0.3 27.7

Example 1

(81) (Preparation of a Composition for a Lithium Secondary Battery Positive Electrode)

(82) To 10 parts by weight of the dispersion of polyvinyl acetal resin fine particles 1 obtained as a binder was added 90 parts by weight of water to prepare a 2 wt % polyvinyl acetal resin solution. To 100 parts by weight of this solution were added 50 parts by weight of lithium cobaltate (CELLSEED C-5 available from Nippon Chemical Industrial Co., Ltd.) as a positive-electrode active material, 1 part by weight of acetylene black (DENKA BLACK available from Denki Kagaku Kogyo Kabushiki Kaisha) as a conductive aid, and 1 part by weight of carboxymethyl cellulose (available from Aldrich) as a thickener, thereby preparing a composition for a lithium secondary battery positive electrode.

Examples 2 to 19, Comparative Examples 1 to 8

(83) A composition for a lithium secondary battery positive electrode was prepared in the same manner as in Example 1, except that a dispersion of polyvinyl acetal resin fine particles shown in one of Tables 2 to 5 was used and the amount or type of the polyvinyl acetal resin fine particles was changed.

Example 20, Comparative Example 9

(84) A composition for a lithium secondary battery positive electrode was prepared in the same manner as in Example 1, except that a solution prepared by adding 98 parts by weight of N-methylpyrrolidone to 2 parts by weight of a polyvinyl acetal resin shown in one of Tables 2 to 5, instead of the dispersion of polyvinyl acetal resin fine particles, was used.

Example 21

(85) (Preparation of a Composition for a Lithium Secondary Battery Negative Electrode)

(86) To 10 parts by weight of the dispersion of polyvinyl acetal resin fine particles 1 obtained as a binder was added 90 parts by weight of water to prepare a 2 wt % polyvinyl acetal resin solution. To 100 parts by weight of this solution were added 50 parts by weight of spherical natural graphite (CGB-20 available from Nippon Graphite Industries Co., Ltd.) as a negative-electrode active material, 1 part by weight of acetylene black (DENKA BLACK available from Denki Kagaku Kogyo Kabushiki Kaisha) as a conductive aid, and 1 part by weight of carboxymethyl cellulose (available from Aldrich) as a thickener, thereby preparing a composition for a lithium secondary battery negative electrode.

Examples 22 to 39, Comparative Examples 10 to 17

(87) composition for a lithium secondary battery negative electrode was prepared in the same manner as in Example 21, except that a dispersion of the polyvinyl acetal resin fine particles shown in one of Tables 2 to 5 was used and the amount or type of the polyvinyl acetal resin fine particles was changed.

Example 40, Comparative Example 18

(88) A composition for a lithium secondary battery negative electrode was prepared in the same manner as in Example 21, except that a solution prepared by adding 98 parts by weight of N-methylpyrrolidone to 2 parts by weight of a polyvinyl acetal resin shown in one of Tables 2 to 5, instead of the dispersion of polyvinyl acetal resin fine particles, was used.

Example 41

(89) (Preparation of a Composition for a Lithium Secondary Battery Negative Electrode)

(90) To 10 parts by weight of the dispersion of polyvinyl acetal resin fine particles 1 obtained as a binder was added 90 parts by weight of water to prepare a 2 wt % polyvinyl acetal resin solution. To 100 parts by weight of this solution were added 45 parts by weight of spherical natural graphite (CGB-20 available from Nippon Graphite Industries Co., Ltd.) and 5 parts by weight of silicon (SiO, available from Osaka Titanium Technologies) as negative-electrode active materials, 1 part by weight of acetylene black (DENKA BLACK available from Denki Kagaku Kogyo Kabushiki Kaisha) as a conductive aid, and 1 part by weight of carboxymethyl cellulose (available from Aldrich) as a thickener, thereby preparing a composition for a lithium secondary battery negative electrode.

Examples 42 to 59, Comparative Examples 19 to 26

(91) A composition for a lithium secondary battery negative electrode was prepared in the same manner as in Example 41, except that a dispersion of polyvinyl acetal resin fine particles shown in one of Tables 2 to 5 was used and the amount or type of the polyvinyl acetal resin fine particles was changed.

Example 60, Comparative Example 27

(92) A composition for a lithium secondary battery negative electrode was prepared in the same manner as in Example 41, except that a solution prepared by adding 98 parts by weight of N-methylpyrrolidone to 2 parts by weight of a polyvinyl acetal resin shown in one of Tables 2 to 5, instead of the dispersion of polyvinyl acetal resin fine particles, was used.

(93) <Evaluation>

(94) The following evaluations were performed on the compositions for a lithium secondary battery electrode (for a positive electrode, for a negative electrode) obtained in the examples and comparative examples. Tables 2 to 5 show the results.

(95) (1) Adhesiveness

(96) For the compositions for a lithium secondary battery positive electrode obtained in Examples 1 to 20 and Comparative Examples 1 to 9, the adhesiveness to aluminum foil was checked. For the compositions for a lithium secondary battery negative electrode obtained in Examples 21 to 60 and Comparative Examples 10 to 27, the adhesiveness to copper foil was checked.

(97) (1-1) Adhesiveness to Aluminum Foil

(98) The composition for a lithium secondary battery electrode was applied to aluminum foil (thickness of 15 m) to have a dry thickness of 40 m, and dried to prepare a sample in which a sheet-shaped electrode was formed on aluminum foil.

(99) The sample was cut to a size of 10 cm in length and 5 cm in width, and the obtained test piece was attached to an acrylic plate (thickness of 2 mm) with a double-stick tape in such a manner that the aluminum foil side was in contact with the acrylic plate. To the electrode surface of the test piece was placed a tape (product name: Cellotape () No. 252 (available from Sekisui Chemical Co., Ltd.)(JIS Z1522 standard)) with a width of 18 mm, and then peeled in a 90 direction at a speed of 300 mm/min. The peeling force (N) for the peeling was measured with an autograph (AGS-J available from Shimadzu Corporation).

(100) (1-2) Adhesiveness to Copper Foil

(101) The peeling force was measured in the same manner as in the (1-1) Adhesiveness to aluminum foil, except that the aluminum foil was changed to copper foil (thickness of 15 m).

(102) (2) Dispersibility

(103) An amount of 10 parts by weight of the obtained composition for a lithium secondary battery electrode was mixed and diluted with 90 parts by weight of water, and then stirred in an ultrasonic disperser (US-303 available from SND Co., Ltd.) for 10 minutes. The particle size distribution of the dilution was measured with a laser diffraction particle size distribution analyzer (LA-910 available from Horiba Ltd.) to determine the average dispersion size.

(104) (3) Electrolyte Resistance

(105) (Preparation of a Binder Resin Sheet)

(106) To a release-treated polyethylene terephthalate (PET) film was applied each of the polyvinyl acetal resin dispersions or resin solutions used in the examples and comparative examples to a dry thickness of 50 m, and dried to prepare a binder resin sheet.

(107) The obtained binder resin sheet was cut to a size of 3050 mm to prepare a test piece.

(108) The obtained test piece was dried at 110 C. for two hours, and the obtained film was weighed to determine the weight (a) of the film.

(109) Next, a mixed solution (1:1 in volume) of ethylene carbonate and diethyl carbonate was prepared as an electrolyte, and the obtained film was immersed in the electrolyte at 25 C. for three days. The film was taken out and the electrolyte on the surface was immediately wiped off. The weight of the resulting film was weighed to determine the weight (b).

(110) The film was then immersed in 500 g of pure water for two days to completely remove the electrolyte inside thereof, dried at 110 C. for two hours, and weighed to determine the weight (c).

(111) Based on the weights (a), (b), and (c), the dissolution rate and swelling rate of the binder were calculated using the following equations.
Dissolution rate (%)=[(ac)/a]100.
Swelling rate (%)=(b/c)100.

(112) Separately, the conditions for immersion into an electrolyte were changed to 50 C. for one day, and the dissolution rate and swelling rate of the binder were calculated by the similar methods.

(113) A higher dissolution rate indicates that the resin is more likely to be dissolved in the electrolyte, and a higher swelling rate indicates that the resin is more likely to swell with the electrolyte.

(114) (4) Flexibility

(115) For the compositions for a lithium secondary battery positive electrode obtained in Examples 1 to 20 and Comparative Examples 1 to 9, the flexibility of an electrode prepared using aluminum foil was evaluated. For the compositions for a lithium secondary battery negative electrode obtained in Examples 21 to 60 and Comparative Examples 10 to 27, the flexibility of an electrode prepared using copper foil was evaluated.

(116) (4-1) Flexibility in the Case of Using Aluminum Foil

(117) To aluminum foil (thickness of 15 m) was applied the composition for a lithium secondary battery electrode to a dry thickness of 40 m, and dried to prepare a test piece in which a sheet-shaped electrode was formed on aluminum foil.

(118) This sample was cut to a size of 50 cm in length and 2 cm in width, and the obtained test piece was wound around a glass stick with a diameter of 2 mm and left for one day. The sample was released and checked for cracks or fractures in the electrode based on the following criteria. (Excellent): No cracks or fractures were found. (Good): Slight cracks or fractures were found but peeling of the active material was not at all found. (Fair): Cracks or fractures were found and partial peeling of the active material was found. (Poor): Cracks or fractures were found all around the test piece and peeling of the active material was found in most part.
(4-2) Flexibility in the Case of Using Copper Foil

(119) The flexibility was evaluated in the same manner as in (4-1) Flexibility in the case of using aluminum foil, except that the aluminum foil was changed to copper foil (thickness of 15 m).

(120) (5) Evaluation of Battery Performance

(5-1) Examples 1 to 20, Comparative Examples 1 to 9

(121) (a) Preparation of a Secondary Battery

(122) The composition for a lithium secondary battery positive electrode obtained in each of Examples 1 to 20 and Comparative Examples 1 to 9 was uniformly applied to aluminum foil (thickness of 15 m), dried, and cut to a size of 16 mm, thereby preparing a positive electrode. The electrolyte used was a mixed solvent (1:1 in volume) of ethylene carbonate and diethyl carbonate containing LiPF.sub.6(1M).

(123) The positive electrode was set in a bipolar coin cell (product name: HS Flat cell (available from Hohsen Corp.)) in such a manner that the electrode layer surface faces upward. Next, a porous polypropylene separator (thickness of 25 m) punched out to a diameter of 24 mm was placed thereon, and the electrolyte was poured into the cell to avoid entering of air. Then, a lithium metal plate as a counter electrode was further placed thereon, and a top cover was screwed to the cell for sealing, thereby preparing a secondary battery.

(124) (b) Evaluation of Discharge Capacity and Charge-Discharge Cycle

(125) Using a battery test system TOSCAT-3100 available from Toyo System Co., Ltd, the discharge capacity and the charge-discharge cycle of the obtained secondary battery was evaluated.

(126) The evaluation of the discharge capacity and charge-discharge cycle was performed under the conditions of the voltage range of 2.8 to 4.2 V and the temperature of 25 C. The charge-discharge cycle was evaluated based on the calculation of the ratio of the discharge capacity in the 50th cycle to the initial discharge capacity.

(5-2) Examples 21 to 60, Comparative Examples 10 to 27

(127) The composition for a lithium secondary battery negative electrode obtained in each of Examples 21 to 60 and Comparative Examples 10 to 27 was uniformly applied to copper foil (thickness of 15 m), dried, and cut to a size of 16 mm, thereby preparing a negative electrode.

(128) A sealed-type secondary battery was prepared in the same manner as in (5-1), except that the obtained negative electrode was used. Then, the evaluation of the discharge capacity and charge-discharge cycle was performed. The evaluation of the discharge capacity and charge-discharge cycle was performed under the conditions of the voltage range of 0.03 to 3.0 V and the temperature of 25 C. The charge-discharge cycle was evaluated based on the calculation of the ratio of the discharge capacity in the 50th cycle to the initial discharge capacity.

(129) TABLE-US-00002 TABLE 2 Evaluation (2) (3) Electrolyte resistance Con- Polyvinyl (1) Disper- Disso- Swell- Disso- Swell- Active material duc- acetal resin Adhe- sibility lution ing lution ing (5) Battery (parts by weight) tive A- sive- Average rate at rate rate at rate at performance Lith- Spher- aid mount ness dis- 25 C. at 25 50 C. 50 (4) Dis- Charge- ium ical Sili- Acet- (parts Peeling persion in 3 C. in 3 in 1 C. in 1 Flex- charge diccharge cobal- natural con ylene by force size days days day day ibil- capacity cycle tate graphite (SiO) black Type weight) (N) (m) (%) (%) (%) (%) ity (mAh/g) (%) Ex- 50 1 Polyvinyl 2 4.4 7.3 0.4 126 0.9 131 143 96 am- acetal ple 1 resin fine particles 1 Ex- 50 1 Polyvinyl 2 4.3 7.2 0.3 116 0.8 120 156 98 am- acetal ple 2 resin fine particles 2 Ex- 50 1 Polyvinyl 2 4.4 7.3 0.3 139 0.8 152 38 95 am- acetal ple 3 resin fine particles 3 Ex- 50 1 Polyvinyl 2 4.4 7.3 0.4 161 1.2 180 130 93 am- acetal ple 4 resin fine particles 4 Ex- 50 1 Polyvinyl 2 4.5 7 1.2 170 3.1 195 123 90 am- acetal ple 5 resin fine particles 6 Ex- 50 1 Polyvinyl 2 4.6 7.2 0.4 119 0.7 131 127 91 am- acetal ple 6 resin fine particles 8 Ex- 50 1 Polyvinyl 2 4.7 7.2 0.4 117 1 128 140 93 am- acetal ple 7 resin fine particles 9 Ex- 50 1 Polyvinyl 2 4.4 7 0.2 116 0.8 126 124 90 am- acetal ple 8 resin fine particles 10 Ex 50 1 Polyvinyl 2 4.7 7.1 0.3 118 0.8 127 152 98 am- acetal ple 9 resin fine particles 11 Ex- 50 1 Polyvinyl 2 4.3 7.2 0.3 112 0.8 148 151 97 am- acetal ple resin fine 10 particles 15 Ex- 50 1 Polyvinyl 0.3 2.8 7.1 0.3 112 0.8 148 144 96 am- acetal ple resin fine 11 particles 15 Ex- 50 1 Polyvinyl 6 5.9 7.5 0.3 112 0.8 148 135 95 am- acetal ple resin fine 12 particles 15 Ex- 50 1 Polyvinyl 15 8.2 8.1 0.3 112 0.8 148 120 91 am- acetal ple resin fine 13 particles 15 Ex- 50 1 Polyvinyl 2 4.7 7.1 0.5 119 1.3 145 145 96 am- acetal ple resin fine 14 particles 16 Ex- 50 1 Polyvinyl 2 5.1 6.9 0.4 113 1 164 156 99 am- acetal ple resin fine 15 particles 17 Ex- 50 1 Polyvinyl 2 4.1 8 0.9 133 2.1 196 140 95 am- acetal ple resin fine 16 particles 19 Ex- 50 1 Polyvinyl 2 4.6 11 0.3 115 0.8 148 125 90 am- acetal ple resin fine 17 particles 22 Ex- 50 1 Polyvinyl 2 2.1 15 0.6 114 1.5 152 123 89 am- acetal ple resin fine 18 particles 23 Ex- 50 1 Polyvinyl 2 4.1 8 0.8 124 1.6 187 140 95 am- acetal ple resin fine 19 particles 24 Ex- 50 1 Polyvinyl 2 4.5 7.5 0.3 112 0.8 148 120 90 am- acetal ple resin 25 20

(130) TABLE-US-00003 TABLE 3 Evaluation (2) (3) Electrolyte resistance Con- Polyvinyl (1) Disper- Disso- Swell- Disso- Swell- Active material duc- acetal resin Adhe- sibility lution ing lution ing (5) Battery (parts by weight) tive A- sive- Average rate at rate at rate at rate at performance Lith- Spher- aid mount ness dis- 25 C. 25 C. 50 C. 50 C. (4) Dis- Charge- ium ical Sili- Acet- (parts Peeling persion in 3 in 3 in 1 in 1 Flex- charge diccharge cobal- natural con ylene by force size days days day day ibil- capacity cycle tate graphite (SiO) black Type weight) (N) (m) (%) (%) (%) (%) ity (mAh/g) (%) Ex- 50 1 Polyvinyl 2 4 22 0.4 126 0.9 131 330 96 am- acetal ple resin fine 21 particles 1 Ex- 50 1 Polyvinyl 2 4 20 0.3 116 0.8 120 360 98 am- acetal ple resin fine 22 particles 2 Ex- 50 1 Polyvinyl 2 4 22 0.3 139 0.8 145 320 96 am- acetal ple resin fine 23 particles 3 Ex- 50 1 Polyvinyl 2 4.1 24 0.4 161 12 180 298 94 am- acetal ple resin fine 24 particles 4 Ex- 50 1 Polyvinyl 2 4.1 24 1.2 180 3.1 195 280 89 am- acetal ple resin fine 25 particles 6 Ex- 50 1 Polyvinyl 2 4.1 23 0.4 119 0.7 131 290 90 am- acetal ple resin fine 26 particles 8 Ex- 50 1 Polyvinyl 2 4.2 21 0.4 117 1 128 320 92 am- acetal ple resin fine 27 particles 9 Ex- 50 1 Polyvinyl 2 4.6 22 0.2 116 0.8 126 280 90 am- acetal ple resin fine 28 particles 10 Ex- 50 1 Polyvinyl 2 4.3 22 0.3 118 0.8 127 354 98 am- acetal ple resin fine 29 particles 11 Ex- 50 1 Polyvinyl 2 4 21 0.3 112 0.8 148 350 97 am- acetal ple resin fine 30 particles 15 Ex- 50 1 Polyvinyl 0.3 2.4 20 0.3 112 0.8 148 335 96 am- acetal ple resin fine 31 particles 15 Ex- 50 I Polyvinyl 6 5.1 23 0.3 112 0.8 148 315 95 am- acetal ple resin fine 32 particles 15 Ex- 50 1 Polyvinyl 15 7 25 0.3 112 0.8 148 280 92 am- acetal ple resin fine 33 particles 15 Ex- 50 1 Polyvinyl 2 4.2 20 0.5 119 1.3 145 340 96 am- acetal ple resin fine 34 particles 16 Ex- 50 1 Polyvinyl 2 4.7 19 0.4 113 1 164 360 99 am- acetal ple resin fine 35 particles 17 Ex- 50 1 Polyvinyl 2 3.6 23 0.9 133 2.1 196 327 95 am- acetal ple resin fine 36 particles 19 Ex- 50 1 Polyvinyl 2 4 29 0.3 115 0.8 148 290 90 am- acetal ple resin fine 37 particles 22 Ex- 50 1 Polyvinyl 2 1.7 35 0.6 114 1.5 152 285 90 am- acetal ple resin fine 38 particles 23 Ex- 50 1 Polyvinyl 2 3.8 26 0.8 124 1.6 187 334 95 am- acetal ple resin fine 39 particles 24 Ex- 50 1 Polyvinyl 2 4.3 24 0.3 112 0.8 148 280 90 am- acetal ple resin 25 40

(131) TABLE-US-00004 TABLE 4 Evaluation (2) (3) Electrolyte resistance Con- Polyvinyl (1) Disper- Disso- Swell- Disso- Swell- Active material duc- acetal resin Adhe- sibility lution ing lution ing (5) Battery (parts by weight) tive A- sive- Average rate at rate at rate at rate at performance Lith- Spher- aid mount ness dis- 25 C. 25 C. 50 C. 50 C. (4) Dis- Charge- ium ical Sili- Acet- (parts Peeling persion in 3 in 3 in 1 in 1 Flex- charge diccharge cobal- natural con ylene by force size days days day day ibil- capacity cycle tate graphite (SiO) black Type weight) (N) (m) (%) (%) (%) (%) ity (mAh/g) (%) Ex- 45 5 1 Polyvinyl 2 4.2 16.9 0.4 126 0.9 131 530 95 am- acetal ple resin fine 41 particles 1 Ex- 45 5 1 Polyvinyl 2 4.2 15.4 0.3 112 0.8 148 597 98 am- acetal ple resin fine 42 particles 2 Ex- 45 5 1 Polyvinyl 2 4.2 16.9 0.3 130 0.8 175 530 95 am- acetal ple resin fine 43 particles 3 Ex- 45 5 1 Polyvinyl 2 4.3 17.2 0.4 161 1.2 180 491 92 am- acetal ple resin fine 44 particles 4 Ex- 45 5 1 Polyvinyl 2 4.0 18.9 1.2 180 3.1 195 89 82 am- acetal ple resin fine 45 particles 6 Ex- 45 5 1 Polyvinyl 2 4.6 16.4 0.4 119 0.7 131 89 89 am- acetal ple resin fine 46 particles 8 Ex- 45 5 1 Polyvinyl 2 4.4 16.2 0.4 112 1 148 517 95 am- acetal ple resin fine 47 particles 9 Ex- 45 5 1 Polyvinyl 2 4.5 16.6 0.2 116 0.8 126 511 95 am- acetal ple resin fine 48 particles 10 Ex- 45 5 1 Polyvinyl 2 4.5 16.9 0.3 112 0.8 148 588 97 am- acetal ple resin fine 49 particles 11 Ex- 45 5 1 Polyvinyl 2 4.2 16.2 0.3 112 0.8 148 580 97 am- acetal ple resin fine 50 particles 15 Ex- 45 5 1 Polyvinyl 0.3 2.5 15.4 0.3 112 0.8 148 555 96 am- acetal ple resin fine 51 particles 15 Ex- 45 5 1 Polyvinyl 6 5.4 17.7 0.3 112 0.8 148 522 95 am- acetal ple resin fine 52 particles 15 Ex- 45 5 1 Polyvinyl 15 7.4 19.3 0.3 112 0.8 148 464 92 am- acetal ple resin fine 53 particles 15 Ex- 45 5 1 Polyvinyl 2 5.3 18.2 0.5 119 1.3 145 542 97 am- acetal ple resin fine 54 particles 16 Ex- 45 5 1 Polyvinyl 2 4.9 14.6 0.4 113 1 164 597 99 am- acetal ple resin fine 55 particles 17 Ex- 45 5 1 Polyvinyl 2 3.8 17.7 0.9 133 2.1 196 542 95 am- acetal ple resin fine 56 particles 19 Ex- 45 5 1 Polyvinyl 2 4.2 22.3 0.3 115 0.8 148 481 90 am- acetal ple resin fine 57 particles 22 Ex- 45 5 1 Polyvinyl 2 1.8 27.0 0.6 114 1.5 152 472 90 am- acetal ple resin fine 58 particles 23 Ex- 45 5 1 Polyvinyl 2 3.9 17.4 0.8 124 1.6 187 534 94 am- acetal ple resin fine 59 particles 24 Ex- 45 5 1 Polyvinyl 2 4.3 24 0.3 112 0.8 148 468 90 am- acetal ple resin 25 60

(132) TABLE-US-00005 TABLE 5 Evaluation (2) (3) Electrolyte resistance Con- Polyvinyl (1) Disper- Disso- Swell- Disso- Swell- Active material duc- acetal resin Adhe- sibility lution ing lution ing (5) Battery (parts by weight) tive A- sive- Average rate at rate at rate at rate at performance Lith- Spher- aid mount ness dis- 25 C. 25 C. 50 C. 50 C. (4) Dis- Charge- ium ical Sili- Acet- (parts Peeling persion in 3 in 3 in 1 in 1 Flex- charge diccharge cobal- natural con ylene by force size days days day day ibil- capacity cycle tate graphite (SiO) black Type weight) (N) (m) (%) (%) (%) (%) ity (mAh/g) (%) Com- 50 1 Polyvinyl 2 4.3 19 94 350 99 450 Not measurable par- acetal due to ative resi fine binder dissolution Ex- particles am- 5 ple 1 Com- 50 1 Polyvinyl 2 2.1 17.9 93 470 100 550 Not measurable par- acetal due to ative resin fine binder dissolution Ex- particles am- 7 ple 2 Com- 50 1 Polyvinyl 2 3.6 7.8 67 400 71 475 Not measurable par- acetal due to ative resin fine binder dissolution Ex- particles am- 12 ple 3 Com- 50 1 Polyvinyl 2 4 12 76 154 84 368 Not measurable par- acetal due to ative resin fine binder dissolution Ex- particles am- 13 ple 4 Com- 50 1 Polyvinyl 2 4 11.4 61 106 70 342 Not measurable par- acetal due to ative resin fine binder dissolution Ex- particles am- 14 ple 5 Com- 50 1 Polyvinyl 2 3.8 9 3 165 8 248 98 79 par- acetal ative resin fine Ex- particles am- 18 ple 6 Com- 50 1 Polyvinyl 2 3.6 7.8 90 450 98 640 Not measurable par- acetal due to ative resin fine binder dissolution Ex- particles am- 20 ple 7 Com- 50 1 Polyvinyl 2 4.3 19 0.2 107 0.7 149 103 80 par- acetal ative resin fine Ex- particles am- 21 ple 8 Com- 50 1 Polyvinel 2 4 13 1.4 126 3.5 179 96 75 par- acetal ative resin 26 Ex- am- ple 9 Com- 50 1 Polyvinyl 2 3.4 40 94 350 99 450 Not measurable par- acetal due to ative resi fine binder dissolution Ex- particles am- 5 ple 10 Com- 50 1 Polyvinyl 2 1.5 26 93 470 100 550 Not measurable par- acetal due to ative resin fine binder dissolution Ex- particles am- 7 ple 11 Com- 50 1 Polyvinyl 2 3 23 67 470 71 550 Not measurable par- acetal due to ative resin fine binder dissolution Ex- particles am- 12 ple 12 Com- 50 1 Polyvinyl 2 3.2 26.4 76 154 84 368 Not measurable par- acetal due to ative resin fine binder dissolution Ex- particles am- 13 ple 13 Com- 50 1 Polyvinyl 2 3.3 31 61 106 70 342 Not measurable par- acetal due to ative resin fine binder dissolution Ex- particles am- 14 ple 14 Com- 50 1 Polyvinyl 2 3.2 25 3 165 8 248 225 78 par- acetal ative resin fine Ex- particles am- 18 ple 15 Com- 50 1 Polyvinyl 2 3 23 90 450 98 640 Not measurable par- acetal due to ative resin fine binder dissolution Ex- particles am- 20 ple 16 Com- 50 1 Polyvinyl 2 3.4 40 0.2 107 0.7 149 240 78 par- acetal ative resin fine Ex- particles am- 21 ple 17 Com- 50 1 Polyvinel 2 3.9 32 1.4 126 3.5 179 215 73 par- acetal ative resin 26 Ex- am- ple 18 Com- 45 5 1 Polyvinyl 2 3.6 30.8 94 350 99 450 Not measurable par- acetal due to ative resi fine binder dissolution Ex- particles am- 5 ple 19 Com- 45 5 1 Polyvinyl 2 3.5 24.6 93 470 100 550 Not measurable par- acetal due to ative resin fine binder dissolution Ex- particles am- 7 ple 20 Com- 45 5 1 Polyvinyl 2 3.2 17.7 67 400 71 475 Not measurable par- acetal due to ative resin fine binder dissolution Ex- particles am- 12 ple 21 Com- 45 5 1 Polyvinyl 2 3.5 22.2 76 154 84 368 Not measurable par- acetal due to ative resin fine binder dissolution Ex- particles am- 13 ple 22 Com- 45 5 1 Polyvinyl 2 3.3 18.1 61 106 70 342 Not measurable par- acetal due to ative resin fine binder dissolution Ex- particles am- 14 ple 23 Com- 45 5 1 Polyvinyl 2 3.4 19.3 3 165 8 248 370 74 par- acetal ative resin fine Ex- particles am- 18 ple 24 Com- 45 5 1 Polyvinyl 2 3.7 22.4 90 450 98 640 Not measurable par- acetal due to ative resin fine binder dissolution Ex- particles am- 20 ple 25 Com- 45 5 1 Polyvinyl 2 3.3 19.4 0.2 107 0.7 149 389 7 par- acetal ative resin fine Ex- particles am- 21 ple 26 Com- 4.5 5 1 Polyvinel 2 4.1 24.6 1.4 126 3.5 179 358 70 par- acetal ative resin 26 Ex- am- ple 27

INDUSTRIAL APPLICABILITY

(133) The present invention can provide a binder for a power storage device electrode which is excellent in adhesiveness and capable of improving the flexibility of an electrode to be obtained when used as a binder for a power storage device electrode, and which has high resistance against electrolytes. The present invention can also provide a binder for a power storage device electrode which has excellent electrolyte resistance to favorably maintain adhesiveness between active materials in a long-term cycle, and which enables production of a high-capacity storage battery with a small irreversible capacity and low resistance to have excellent output characteristics. The present invention can further provide a composition for a power storage device electrode, a power storage device electrode, and a power storage device each prepared using the binder for a power storage device electrode.