JP2009224100A - Separator for battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a separator for a battery, and its manufacturing method, excellent in alkali resistance, separability, and electrolyte-solution absorptivity. <P>SOLUTION: The separator for a battery contains cellulose-system extra-fine fiber with a cellulose overlay with a single-yarn fineness of 0.05 to 0.8 dtex, with the cellulose-system extra-fine fiber having fine pores on its overlay. In the manufacturing method of the separator for a battery, cellulose ester extra-fine fiber made of cellulose acetate propionate and/or cellulose acetate butyrate is put under alkali saponification to be made into nonwoven fabric containing the extra-fine fiber. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a battery separator containing cellulosic ultrafine fibers and a method for producing the same. More specifically, the present invention relates to a battery separator obtained by alkali saponifying cellulose ester ultrafine fibers and then forming a nonwoven fabric containing the ultrafine fibers, and a method for producing the same.

  The battery separator plays an important role of isolating the positive electrode and the negative electrode in the battery and holding the electrolytic solution to ensure ionic conductivity between the positive electrode and the negative electrode. For example, characteristics required for an alkaline battery separator include alkali resistance, separation property, electrolyte solution absorption property, and the like. When the alkali resistance is poor, the battery separator is deteriorated by an alkaline aqueous solution such as an aqueous potassium hydroxide solution used as an electrolytic solution, and thus an internal short circuit occurs in the battery. Also, when the separation property is lacking, since the positive electrode active material, the negative electrode active material, and the needle-like crystals of conductive zinc oxide generated by the battery reaction pass through the pores of the battery separator, an internal short circuit occurs in the battery. It will occur. Furthermore, when the electrolyte solution lacks, the electrolyte solution necessary for the battery reaction cannot be sufficiently contained, so that the electromotive reaction cannot be sufficiently performed, and the battery reaction has a short duration. End up.

  In order to obtain a battery separator having the above characteristics, various studies have been made conventionally. In general, a nonwoven fabric is used for the battery separator, and examples of the fiber material constituting the nonwoven fabric include polyvinyl alcohol fibers, cellulose fibers, polyamide fibers, and polyolefin fibers. Among them, polyvinyl alcohol fibers excellent in alkali resistance, hydrophilicity, mechanical properties, etc., and cellulose fibers excellent in electrolyte solution absorbability in addition to alkali resistance, hydrophilicity, mechanical properties, etc. are suitably used. Has been.

  Battery separator made of non-woven fabric by using polyvinyl alcohol fiber and cellulose fiber alone, or battery separator made of non-woven fabric by mixing them, to improve the separation property and electrolyte absorption by refining the pore size For the purpose of this, ultrafine fiber has been studied. By selecting a spinning method and spinning conditions, the polyvinyl alcohol fiber can be reduced in the single yarn fineness, and an ultrafine fiber having a single yarn fineness of about 0.1 to 1 dtex can be obtained. Patent Documents 1 to 3 propose a battery separator that is excellent in separation properties by mixing polyvinyl alcohol-based ultrafine fibers and cellulose-based fibers to form a nonwoven fabric. However, since the single fiber fineness of the cellulosic fibers is large, the pore size cannot be made sufficiently small, and the separation property is insufficient. Moreover, although the separator for batteries which used the polyvinyl alcohol type | system | group ultrafine fiber independently is excellent in a separator property, since electrolyte solution absorptivity is inferior to a cellulose fiber, electrolyte solution absorptivity was inadequate. Thus, it was not possible to obtain a battery separator that had the alkali resistance, separation property, and electrolyte solution absorbability required for battery separators by simply making the polyvinyl alcohol fiber very fine.

  On the other hand, cellulosic fibers such as rayon and cupra have low spinnability and extremely low single yarn fineness because cellulose is dissolved in a solvent and then spun while removing the solvent in a solution called a coagulation bath. It is difficult to make it smaller. For this reason, fibrillation by beating treatment is generally performed for the purpose of refining cellulosic fibers. Patent Documents 4 to 6 propose battery separators that are made by mixing beating-treated cellulose fibers and polyvinyl alcohol-based ultrafine fibers into a non-woven fabric and are excellent in separation properties and electrolyte solution absorption properties. However, when cellulosic fibers refined by the beating process are used, there arises a problem that a beating defect portion or a foreign material that cannot be removed is mixed into the battery separator. Furthermore, since the fibrillated fine fiber portion deteriorates by being in contact with the positive electrode active material in the battery for a long time and dissolves in the electrolytic solution, the separation property is lowered, and further, an internal short circuit occurs in the battery. was there.

Thus, in the prior art, it was not possible to obtain a battery separator having characteristics such as alkali resistance, separation property, and electrolyte solution absorption.
JP 49-127147 A Japanese Patent Laid-Open No. 62-154559 Japanese Patent Laid-Open No. 1-146249 Japanese Patent Laid-Open No. 2-119049 Japanese Patent Laid-Open No. 10-92411 JP 2006-4844 A

  An object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a battery separator made of cellulosic ultrafine fibers and excellent in alkali resistance, separation property, and electrolyte solution absorption, and a method for producing the same. is there.

  The above-mentioned problems of the present invention can be solved by a battery separator including cellulosic ultrafine fibers having a single yarn fineness of 0.05 to 0.8 dtex, in which the fiber surface layer is cellulose.

  Moreover, it can employ | adopt suitably that a cellulose ultrafine fiber has a micropore in the surface layer of a fiber.

  Furthermore, the problem is solved by a method for producing a battery separator, characterized in that cellulose ester ultrafine fibers composed of cellulose acetate propionate and / or cellulose acetate butyrate are alkali saponified and then made into a nonwoven fabric containing the ultrafine fibers. Can do.

  According to the present invention, by using a cellulosic ultrafine fiber, it is possible to provide a battery separator having alkali resistance, separation property, and electrolyte absorption, and the battery separator can be an alkaline manganese battery, silver oxide, or the like. It can be suitably used for alkaline primary batteries such as batteries, mercury batteries, and zinc-air batteries.

  Hereinafter, the battery separator excellent in alkali resistance, separation property, and electrolyte solution absorbability of the present invention and a method for producing the same will be described in detail.

  The battery separator of the present invention is mainly composed of cellulosic ultrafine fibers whose surface layer is cellulose. This is because cellulose is excellent in alkali resistance, hydrophilicity, mechanical properties, and electrolyte solution absorption. That the surface layer of the fiber is cellulose includes not only fibers in which all the fibers are cellulose, but also composite fibers such that the surface layer portion of the fibers is cellulose and the inner layer portion is cellulose ester. From the viewpoint of alkali resistance, cellulosic ultrafine fibers in which all of the fibers are cellulose are suitably employed in the present invention.

  The cellulosic ultrafine fiber in the present invention preferably has fine pores in the surface layer of the fiber. When the surface layer of the fiber has micropores, the surface area of the fiber is increased, and therefore, a battery separator having excellent electrolyte solution absorbability can be obtained. It is preferable that the micropores exist entirely from the surface layer portion of the fiber to the center portion of the fiber. Further, the shape of the fine holes may be a columnar shape elongated in the fiber axis direction or a bubble shape close to a sphere.

  The diameter of the micropores is preferably 0.05 μm or more and 0.4 μm or less. If the diameter of the micropores is 0.05 μm or more and 0.4 μm or less, the micropores are not crushed, and furthermore, the shape of the ultrafine fibers can be maintained, which is preferable. The diameter of the micropores is more preferably from 0.1 μm to 0.35 μm, and still more preferably from 0.15 μm to 0.3 μm. Further, although there may be micropores having a diameter smaller than 0.05 μm or micropores larger than 0.4 μm, the diameter of 70% or more of the micropores with respect to the total number of micropores is 0.05 μm or more and 0.00. It is preferable that it is 4 micrometers or less. Furthermore, the diameter of the micropores is preferably 1/3 or less of the fiber diameter.

The fine pore distribution density is preferably such that fine pores having a diameter of 0.05 μm or more and 0.4 μm or less exist on average 15 to 40 pores per 1 μm ^{2 of} the fiber surface layer. The fine pore distribution density is an average value of the number of fine pores having a diameter of 0.05 μm or more and 0.4 μm or less present per 1 μm ² of the fiber surface layer. If the fine pore distribution density is 15 or more on average, it is preferable because a battery separator having a large fiber surface area and excellent electrolyte solution absorbability can be obtained. From the viewpoint of good electrolyte solution absorbability, the higher the fine pore distribution density is, the more preferable, but specifically, it is more preferably an average of 17 or more and 40 or less, and an average of 20 or more and 40 or less. More preferably. The average fine pore distribution density may be less than 15 or more than 40, but the average fine pore distribution density at 20 locations randomly selected on the fiber surface layer is 15 or more and 40 or less. It is preferable that

  The average degree of polymerization of the cellulosic ultrafine fibers of the present invention is preferably 250 to 1250. An average polymerization degree of 250 or more is preferable because a battery separator having high fiber strength and excellent durability can be obtained. From the viewpoint of good strength characteristics, the higher the average degree of polymerization is, the more preferable, but specifically, 300 to 1250 is more preferable, and 400 to 1250 is still more preferable.

  It is important that the single yarn fineness of the cellulosic ultrafine fiber of the present invention is 0.05 dtex to 0.8 dtex. A single yarn fineness of 0.05 dtex or more is preferable because a battery separator having high fiber strength and excellent durability can be obtained. The single yarn fineness is more preferably 0.07 dtex or more, and further preferably 0.1 dtex or more. On the other hand, if the single yarn fineness is 0.8 dtex or less, it is preferable because a fine pore size is obtained, and a battery separator excellent in separation property and electrolyte solution absorption property can be obtained. The single yarn fineness is more preferably 0.75 dtex or less, and further preferably 0.7 dtex or less.

  The fiber length of the cellulosic ultrafine fiber of the present invention is preferably 0.3 mm to 25 mm. A fiber length of 0.3 mm or more is preferable because the fibers can be sufficiently entangled and a battery separator having high strength can be obtained. The fiber length is more preferably 0.5 mm or more, and further preferably 1.0 mm or more. On the other hand, if the fiber length is 25 mm or less, the dispersibility of the fibers when making the nonwoven fabric is good, and a battery separator having a uniform thickness, basis weight, and density can be obtained. The fiber length is more preferably 23 mm or less, and still more preferably 20 mm or less.

  From the viewpoint of the durability of the battery separator, the fiber properties of the cellulosic ultrafine fibers of the present invention are preferably 1.0 cN / dtex to 2.0 cN / dtex and 8 to 30% in elongation. If the strength is 1.0 cN / dtex or more, fibrils are not generated and a battery separator having excellent durability can be obtained. From the viewpoint of good strength characteristics, the higher the strength, the more preferable, but specifically 1.2 cN / dtex to 2.0 cN / dtex, more preferably 1.4 cN / dtex to 2.0 cN / dtex. More preferably. Further, if the elongation is 8% or more, the abrasion resistance is good, the generation of fluff is reduced, and a battery separator having excellent durability can be obtained. The elongation is more preferably 10% or more, and further preferably 15% or more. On the other hand, an elongation of 30% or less is preferable because a battery separator having good dimensional stability can be obtained. The elongation is more preferably 28% or less, and further preferably 25% or less.

  The cellulosic ultrafine fiber of the present invention may have a perfect circular cross section with respect to the cross-sectional shape of the fiber, and may be multilobal, flat, elliptical, W-shaped, S-shaped, X-shaped, H Different cross-section yarns such as a letter shape, a C shape, a paddle shape, a cross girder shape, and a hollow shape may be used.

  Next, the manufacturing method of the cellulose ultrafine fiber of this invention is demonstrated.

  The cellulose ultrafine fiber of the present invention can be obtained by alkali saponifying a cellulose ester ultrafine fiber and hydrolyzing an ester bond. The cellulose ester ultrafine fiber may be obtained by direct spinning, or may be a method of removing at least one component from the ultrafine fiber-generating fiber, or peeling each component. Among these, sea-island type composite fibers can be suitably employed as the ultrafine fiber-generating fiber in the present invention.

  The cellulose ester ultrafine fiber in the present invention is preferably a cellulose ester having at least a part of the acyl group having 3 to 18 carbon atoms. Since the cellulose acetate fiber which consists only of an acetyl group having 2 carbon atoms in the acyl group is rigid, there is a problem that it easily fibrillates. On the other hand, at least a part of the fiber made of cellulose ester having 3 to 18 acyl groups is preferable because it is flexible, so that no fibril is generated and a battery separator having excellent durability can be obtained. . Furthermore, since an acyl group having 3 to 18 carbon atoms is sterically bulkier than an acetyl group having 2 carbon atoms, at least a portion of cellulose having 3 to 18 carbon atoms is present. Since fine pores can be effectively formed in the fiber surface layer and the fiber inner layer when the ester fiber is alkali saponified and the ester bond is hydrolyzed, it can be suitably employed in the present invention.

  Specific examples of the cellulose ester having at least a portion of the acyl group having 3 to 18 carbon atoms include cellulose acetate propionate, cellulose propionate, cellulose acetate butyrate, and cellulose butyrate. From cellulose acetate propionate in which at least a part of cellulose ester having 3 to 18 acyl group carbon atoms is bonded to cellulose an acetyl group having 2 acyl group carbon atoms and a propionyl group having 3 acyl group carbon atoms. And fibers made of cellulose acetate butyrate in which an acetyl group having 2 acyl groups and a butyryl group having 4 acyl groups are bonded to cellulose are particularly preferably used in the present invention.

When cellulose acetate propionate and / or cellulose acetate butyrate is used as the cellulose ester, the total substitution degree (acetyl substitution degree + acyl substitution degree) of the cellulose ester preferably satisfies the following formula (I). The acyl substitution degree is the total substitution degree of acyl groups other than an acetyl group having 2 acyl group carbon atoms. If the total substitution degree (acetyl substitution degree + acyl substitution degree) of a cellulose ester is 2.5 or more and 3.0 or less, when it is used as a fiber, it is flexible and can be preferably employed because fibrils are not generated. The total substitution degree of the cellulose ester is more preferably 2.6 or more and 2.9 or less, and further preferably 2.65 or more and 2.85 or less.
(I) 2.5 ≦ acetyl substitution degree + acyl substitution degree ≦ 3.0
The degree of acetyl substitution and the degree of acyl substitution preferably satisfy the following formulas (II) and (III) in order to obtain a cellulose ester ultrafine fiber that is flexible and does not generate fibrils when it is made into a fiber.
(II) 1.5 ≦ acetyl substitution degree ≦ 2.5
(III) 0.5 ≦ acyl substitution degree ≦ 1.5
When a composite fiber with a composite component other than cellulose ester is used as the ultrafine fiber-generating fiber in the present invention, the composite component can be adopted as long as the ultrafine fiber can be generated. Specific examples include polystyrene, polyolefin, polyamide, polyester, polylactic acid, sulfoisophthalic acid copolymerized polyester, polyvinyl alcohol, polyethylene glycol, and copolymers and modified polymers thereof. In particular, when polylactic acid polymer, sulfoisophthalic acid copolyester polymer, or polyvinyl alcohol polymer is used as the composite component, the composite component can be eluted by hot water treatment or alkaline aqueous solution treatment to generate ultrafine fibers. Therefore, it can be preferably adopted.

  The sea / island composite ratio (weight ratio) when the sea-island-type composite fiber with a composite component other than cellulose ester and the island as cellulose ester is adopted as the ultrafine fiber-generating fiber is the stability of the sea-island composite form, From the viewpoint of spinning operability and mechanical properties, 5/95 to 80/20 is preferable. A sea component composite ratio of 5% or more is preferable because composite abnormalities such as union of islands do not occur, stable spinning is possible, and no splitting failure occurs. On the other hand, if the composite ratio of the sea component is 80% or less, stable spinning is possible and the mechanical properties of the resulting composite fiber are good, which is preferable. The sea / island composite ratio is more preferably 10/90 to 75/25, and still more preferably 15/85 to 70/30.

  The number of island components in the single fiber of the sea-island type composite fiber is preferably 200 or less. If the number of island components is 200 or less, the die structure is not complicated, and the spinning operability and the strength and elongation properties are not deteriorated due to complex abnormality or the like, which is preferable. The number of island components is more preferably 180 or less, and still more preferably 160 or less.

  Regarding the cross-sectional shape of the fiber, the sea-island type composite fiber may be a perfect circular cross section, or may be a multi-filament, flat, hollow or other irregular cross-section yarn. Further, the fiber surface may be completely covered with the sea component, or the island component may be partially exposed. Furthermore, the cross-sectional shape of the island component after removing the sea component may be a perfect circular cross-section, or may be a multi-filament, flat, hollow or other irregular cross-section yarn.

  The cellulose ester ultrafine fibers and ultrafine fiber-generating fibers in the present invention may contain various additives, for example, inorganic fine particles such as plasticizers and antioxidants, and organic compounds as necessary. You may contain the agent individually or in mixture.

  The cellulose ester ultrafine fiber of the present invention preferably contains a polyhydric alcohol compound as a plasticizer. Specifically, polyalkylene glycol, glycerin compound, caprolactone compound, etc. that have good compatibility with cellulose ester and have a remarkable thermoplastic effect that can be melt-spun, are polyalkylene glycol. preferable. Specific examples of the polyalkylene glycol include polyethylene glycol, polypropylene glycol, polybutylene glycol and the like having a weight average molecular weight of 200 to 4000, and these can be used alone or in combination.

  The cellulose ester ultrafine fiber of the present invention preferably contains a phosphorus-based antioxidant. When a phosphorus-based antioxidant is contained, the effect of preventing the thermal decomposition of the cellulose ester is very remarkable, which is preferable because the fiber strength becomes good. Specific examples of phosphorus antioxidants include tetrakis (2,4-di-t-butylphenyl) [1,1-biphenyl] -4,4′-diylbisphosphonite, tetrakis (2,6-di-). t-butylphenyl) [1,1-biphenyl] -4,4′-diylbisphosphonite, tetrakis (2,6-di-t-butylphenyl-4-methyl) [1,1-biphenyl] -4, 4′-diylbisphosphonite, bis (2.6-di-tert-butyl-4-methylphenyl) pentaerythritol diphosphite, bis (2-tert-butyl-4-cumylphenyl) pentaerythritol diphosphite, bis (4-tert-butyl-2-cumylphenyl) pentaerythritol diphosphite, bis (2.6-di-tert-butyl-4-ethylphenyl) pentaerythritol diphosphite, bis (2.4- A -t- butyl-6-methylphenyl) pentaerythritol diphosphite, inter alia pentaerythritol systems are preferred.

  In the present invention, cellulose ester ultrafine fibers and ultrafine fiber-generating fibers can be obtained by melt spinning. Unlike wet spinning and dry spinning, melt spinning does not use a solvent, and it is not necessary to remove the solvent from the fiber surface layer and the inside of the fiber, so that an ultrafine fiber can be obtained efficiently and can be preferably used. As a melt spinning method, for example, extrusion using an extruder can be suitably employed.

  As the cellulose ester composition of the present invention used for melt spinning, at least a part of the cellulose ester having 3 to 18 acyl group carbon atoms of 70% by weight to 99% by weight and a plasticizer of 1% by weight to 30% by weight The cellulose ester composition containing is used suitably. It is preferable to dry the cellulose ester composition before melt spinning, so that the moisture content of the composition is 0.3% by weight or less. When the moisture content is 0.3% by weight or less, it is preferable that the spinning can be stably performed without foaming due to moisture during melt spinning, and mechanical properties such as fiber strength are improved. The moisture content is more preferably 0.2% by weight or less, further preferably 0.1% by weight or less, and most preferably 0.08% by weight or less.

  The spinning temperature in melt spinning is preferably in the range of 220 ° C to 280 ° C. If the spinning temperature is 220 ° C or higher, the elongational viscosity of the fiber yarn discharged from the spinneret will be sufficiently reduced, so melt fracture (streamline turbulence will occur if the shear stress of the polymer is high when passing through the spinneret hole) In addition, the phenomenon that the irregular shape of the yarn discharged from the spinneret does not appear, and it is preferable because stable spinning can be performed without occurrence of yarn breakage. The spinning temperature is more preferably 225 ° C. or higher, and further preferably 230 ° C. or higher. On the other hand, a spinning temperature of 280 ° C. or lower is preferable because it can suppress a decrease in molecular weight due to thermal decomposition of the cellulose ester composition, and mechanical properties such as fiber strength and elongation are good. The spinning temperature is more preferably 275 ° C. or less, and further preferably 270 ° C. or less.

  The spun fiber may be picked up by using a rotating roller or collected by a net or the like. The spinning speed in the case of taking up using a roller is preferably 500 m / min to 3000 m / min. A spinning speed of 500 m / min or more is preferable because a developed fiber structure can be formed, and a battery separator having high fiber strength and excellent durability can be obtained. The spinning speed is more preferably 750 m / min or more, and further preferably 1000 m / min or more. On the other hand, a spinning speed of 3000 m / min or less is preferred because stable spinning can be performed without occurrence of yarn breakage. The spinning speed is more preferably 2500 m / min or less, and still more preferably 2000 m / min or less. Moreover, the taken-out fiber may be extended | stretched as needed.

  The thickness of the battery separator of the present invention is preferably 10 μm to 200 μm. A thickness of 10 μm or more is preferable because the positive electrode and the negative electrode can be sufficiently separated in the battery and an internal short circuit can be prevented. The thickness is more preferably 15 μm or more, and further preferably 20 μm or more. On the other hand, from the viewpoint of thinning the battery, the thickness is preferably 200 μm or less. The thickness is more preferably 180 μm or less, and further preferably 150 μm or less.

The basis weight of the battery separator of the present invention ^is preferably ^{5g / m 2 ~200g / m 2} . A basis weight of 5 g / m ² or more is preferable because a battery separator having high tensile strength and excellent durability can be obtained. The basis weight is more preferably 10 g / m ² or more, and further preferably 15 g / m ² or more. On the other hand, if the basis weight is 200 g / m ² or less, it is preferable because a battery separator having excellent separation property and electrolyte solution absorption property can be obtained without lowering the porosity between fibers. The basis weight is more preferably 180 g / m ² or less, and further preferably 150 g / m ² or less.

Density of battery separator of the present invention ^is preferably ^{0.30g / cm 3 ~1.0g / cm 3} . A density of 0.30 g / cm ³ or more is preferable because a battery separator having high mechanical strength and excellent durability can be obtained. The density is more preferably 0.35 g / cm ³ or more, and further preferably 0.40 g / cm ³ or more. On the other hand, a density of 1.0 g / cm ³ or less is preferable because a battery separator having excellent separation properties and electrolyte solution absorption properties can be obtained without lowering the porosity between fibers. The density is more preferably 0.95 g / cm ³ or less, and still more preferably 0.90 g / cm ³ or less.

  The weight reduction rate in the alkaline aqueous solution of the battery separator of the present invention is preferably 3% or less. A weight reduction rate of 3% or less is preferable because it is excellent in alkali resistance, so that an internal short circuit is unlikely to occur in the battery, and a battery separator having excellent durability can be obtained. The weight reduction rate is more preferably 2.5% or less, and further preferably 2% or less.

The air permeability of the battery separator of the present invention is preferably 5 cm ³ / (cm ² · s) to 25 cm ³ / (cm ² · s). If the air permeability is 5 cm ³ / (cm ² · s) or more, it is preferable because a battery separator excellent in separation property and electrolyte solution absorption property can be obtained without decreasing the porosity between fibers. The air permeability is more preferably 7 cm ³ / (cm ² · s) or more, and further preferably 10 cm ³ / (cm ² · s) or more. On the other hand, if the air permeability is 25 cm ³ / (cm ² · s) or less, a fine pore size is obtained, and a battery separator having excellent separation properties can be obtained. The air permeability is more preferably 23 cm ³ / (cm ² · s) or less, and further preferably 20 cm ³ / (cm ² · s) or less.

  The water absorption rate of the battery separator of the present invention is preferably 30 mm / 10 min or more. A water absorption speed of 30 mm / 10 min or more is preferable because a battery separator having excellent electrolyte solution absorbability can be obtained. The water absorption rate is more preferably 70 mm / 10 min or more, and further preferably 100 mm / 10 min or more.

  The liquid retention rate of the battery separator of the present invention is preferably 100% or more. A liquid retention rate of 100% or more is preferable because a battery having excellent electrolytic solution holding ability and capable of withstanding long-term use can be obtained. The liquid retention rate is more preferably 200% or more, and further preferably 300% or more.

  Next, the manufacturing method of the battery separator of this invention is demonstrated.

  The battery separator of the present invention can be obtained by alkali saponifying cellulose ester ultrafine fibers composed of cellulose acetate propionate and / or cellulose acetate butyrate and then forming a nonwoven fabric containing the ultrafine fibers.

  As a method for alkali saponification of cellulose ester ultrafine fibers in the present invention, a method using an alkaline aqueous solution containing an alkali compound can be preferably employed. This is because the ester bond of cellulose ester is hydrolyzed by alkali saponification and converted into cellulose excellent in alkali resistance, hydrophilicity, mechanical properties, and electrolyte solution absorption. Furthermore, as the cellulose ester bond is hydrolyzed by the alkali saponification, fine pores are formed in the fiber surface layer and the fiber inner layer, and the fiber surface area is increased.

  Since alkali saponification of cellulose ester ultrafine fibers proceeds from the fiber surface layer, when the cellulose ester ultrafine fibers are alkali saponified, they are converted into core-sheath type composite fibers in which the surface layer portion of the fiber is cellulose and the inner layer portion is cellulose ester. The Moreover, when alkali saponification advances completely, it will convert into a cellulose fiber. In addition, it is possible to confirm that the alkali saponification has progressed by observing the cross section of the cellulose ester ultrafine fiber after the alkali saponification. Moreover, it can be confirmed that the alkali saponification has progressed from the weight loss rate of the cellulose ester ultrafine fiber before and after the alkali saponification.

  Examples of the alkali compound used for alkali saponification in the present invention include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, weak acid salts of alkali metals such as sodium carbonate and potassium carbonate, and the like. You may use.

  The concentration of the alkaline aqueous solution containing the alkaline compound can be arbitrarily determined according to the strength of the alkaline compound and the processing temperature. For example, when an alkali metal hydroxide is used, the concentration of the alkaline aqueous solution is 0.5 wt. % Or more and 10% by weight or less is preferable. It is preferable that the concentration of the alkaline aqueous solution is 0.5% by weight or more because micropores are formed in the fiber surface layer and the fiber inner layer by alkali saponification, and a battery separator having excellent electrolyte solution absorbability can be obtained. The concentration of the alkaline aqueous solution is more preferably 1% by weight or more, and further preferably 1.5% by weight or more. On the other hand, if the concentration of the alkaline aqueous solution is 10% by weight or less, it is preferable because a decrease in the degree of polymerization of cellulose and embrittlement of cellulose fibers can be suppressed. The concentration of the alkaline aqueous solution is more preferably 8% by weight or less, and further preferably 6% by weight or less.

  In the alkali saponification in the present invention, a known alkali weight loss accelerator such as a quaternary ammonium salt may be used in combination in order to advance hydrolysis in a short time. A quaternary ammonium salt is a cation in which a hydrophobic functional group such as an alkyl group, alkenyl group, or allyl group bonded to a nitrogen atom has an affinity for a highly hydrophobic polymer and promotes hydrolysis of an ester bond. It is a sex compound. Specific examples of the alkali weight loss accelerator include octyldimethylammonium chloride, lauryltrimethylammonium chloride, trimethylbenzylammonium chloride, lauryldimethylbenzylammonium chloride, stearyltrimethylammonium chloride, cetyltrimethylammonium chloride, octyltrimethylammonium bromide, lauryldibutylallylammonium Examples thereof include bromide, cetyldimethylcyclohexylammonium bromide, laurylphenyltrimethylammonium methosulphate, stearylethyldihydroxyethylammonium ethosulphate, lauryltrihydroxyethylammonium hydroxide, and the like.

  The content of the quaternary ammonium salt in the alkaline aqueous solution is preferably 0.05% by weight to 3% by weight with respect to the alkaline aqueous solution. A content of 0.05% by weight or more is preferable because the effect as an alkali weight loss promoter can be sufficiently obtained. The content is more preferably 0.1% by weight or more, and further preferably 0.2% by weight or more. On the other hand, if the content is 3% by weight or less, an increase in processing cost can be suppressed, which is preferable. The content is more preferably 2.5% by weight or less, and further preferably 2.0% by weight or less.

  As the fiber shape of the cellulosic ultrafine fiber constituting the nonwoven fabric in the present invention, any fiber such as a tow shape, a staple shape, or a filament shape can be suitably used. In addition, when a nonwoven fabric is produced using fibers capable of generating ultrafine fibers, the composite component may be eluted before or after the nonwoven fabric, but in the present invention, the nonwoven fabric is preferably used after the composite component is eluted. Can be adopted. It is preferable to use an ultrafine fiber from which a composite component is eluted to form a nonwoven fabric because a fine pore size can be obtained and a battery separator having excellent separation properties can be obtained.

  The nonwoven fabric in the present invention may contain other fibers. Other fibers include, for example, polyvinyl alcohol fiber, polyacrylonitrile fiber, polyamide fiber (nylon 6, nylon 66, etc.), polyolefin fiber (polyethylene, polypropylene, etc.), polyvinylidene chloride fiber, polyurethane fiber, composite fiber (polypropylene / polyethylene) , Polypropylene / modified polypropylene, polyamide / modified polyamide, etc.). Among these, polyvinyl alcohol fibers can be suitably used because they are excellent in alkali resistance, hydrophilicity, and mechanical properties.

  The nonwoven fabric in this invention may contain the binder component from viewpoints, such as mechanical performance and dimensional stability. For example, a polyvinyl alcohol binder excellent in alkali resistance and hydrophilicity can be particularly preferably employed. Moreover, although the shape of a binder component may be resinous or fibrous, a fibrous binder can be suitably employed from the viewpoint of suppressing a decrease in the porosity between fibers.

  The manufacturing method of the nonwoven fabric in the present invention can adopt a dry papermaking method, a wet papermaking method, a needle punch method, a spunlace method, a spunbond method, a melt blow method, etc. according to a known method, but the thickness and the uniformity of the texture A wet papermaking method that can obtain a nonwoven fabric excellent in the thickness can be particularly suitably employed.

  A known paper machine or the like may be used as the wet papermaking apparatus used in the wet papermaking method. Specific examples of the paper machine include a circular net type wet paper machine, a short net type wet paper machine, a short net tilt type wet paper machine, and a long net tilt type wet paper machine. Moreover, it is preferable that a hot air type, a contact type or a radiation type dryer is additionally provided in these wet papermaking apparatuses.

  In wet papermaking, the cellulose-based ultrafine fibers according to the present invention and the above-mentioned other fibers and binders are blended as necessary, and further mixed with a dispersion medium such as water, and uniformly dispersed using a pulper or the like. After preparing the slurry, the slurry is subjected to the wet papermaking apparatus as described above. After wet papermaking, the nonwoven fabric is obtained by drying. Moreover, it is also possible to perform a hot press process etc. as needed. In order to increase the strength of the battery separator, the nonwoven fabric may be impregnated or sprayed with an emulsion or solution containing a polyimide precursor, an epoxy resin, etc. In this case, the papermaking section and the drying section of the wet papermaking apparatus An impregnation device, a spray device, or the like may be provided between them.

  The shape of the battery separator of the present invention can be adjusted according to the type and application of the battery. For example, the shape of the battery separator includes a flat paper shape, a cylindrical shape, a bag shape, a spiral shape, and the like, and can be used after being processed into a desired shape. In addition, the battery separator of the present invention and other nonwoven fabrics or films can be laminated or joined together.

  The battery separator of the present invention combines alkali resistance, separation property, and electrolyte solution absorption, and is therefore suitable as a battery separator for alkaline primary batteries such as alkaline manganese batteries, silver oxide batteries, mercury batteries, and zinc-air batteries. Can be adopted. Further, by incorporating the battery separator of the present invention, it is possible to obtain a battery excellent in various performances.

  Hereinafter, the present invention will be described in more detail with reference to examples. Each characteristic value in the examples is obtained by the following method.

A. Average substitution degree of cellulose ester 0.9 g of cellulose ester dried at 80 ° C. for 8 hours was weighed and dissolved by adding 35 ml of acetone and 15 ml of dimethyl sulfoxide, and further 50 ml of acetone was added. While stirring, 30 ml of 0.5N sodium hydroxide aqueous solution was added and saponified for 2 hours. After adding 50 ml of hot water and washing the side of the flask, it was titrated with 0.5N sulfuric acid using phenolphthalein as an indicator. Separately, a blank test was performed in the same manner as the sample. The supernatant of the solution after titration was diluted 100 times, and the composition of the organic acid was measured using an ion chromatograph. From the measurement result and the acid composition analysis result by ion chromatography, the average substitution degree was calculated by the following formula.

TA = (B−A) × F / (1000 × W)
DSace = (162.14 × TA) / [{1− (Mwase− (16.00 + 1.01)) × TA} + {1− (Mwacy− (16.00 + 1.01)) × TA} × (Acy / Ace)]
DSacy = DSace × (Acy / Ace)
TA: Total organic acid amount (ml)
A: Sample titration (ml)
B: Blank test titration (ml)
F: titer of sulfuric acid W: sample weight (g)
DSace: average substitution degree of acetyl group DSacy: average substitution degree of acyl group Mwash: molecular weight of acetic acid Mwacy: molecular weight of other organic acids Acy / Ace: molar ratio of acetic acid (Ace) to other organic acids (Acy) 162 .14: Molecular weight of cellulose repeating unit 16.00: Atomic weight of oxygen 1.01: Atomic weight of hydrogen Weight average molecular weight It was completely dissolved in tetrahydrofuran so that the concentration of the cellulose ester was 0.15% by weight, and used as a sample for GPC measurement. Using this sample, GPC measurement was performed with Waters 2690 under the following conditions, and the weight average molecular weight (Mw) was calculated in terms of polystyrene. In addition, the measurement was performed 3 times per sample, and the average value was defined as the weight average molecular weight (Mw).

Column: Two Tosoh TSK gel GMHHR-H connected Detector: Waters2410 Differential refractometer RI
Moving bed solvent: Tetrahydrofuran Flow rate: 1.0 ml / min Injection volume: 200 μl
C. Average polymerization degree The average polymerization degree was calculated based on JIS L1015: 1999 (chemical fiber staple test method) 8.30.

D. Fine pore distribution density Deposit a platinum-palladium alloy on the fiber, observe the fiber surface layer with a scanning electron microscope (SEM), and have a diameter of 0.05 μm or more and 0.4 μm or less per 1 μm ^{2 of} the fiber surface layer. The number of micropores was counted. The average value of the number of 20 micropores randomly selected in the fiber surface layer was calculated and used as the micropore distribution density.

SEM apparatus: Hitachi S-4000 type Single yarn fineness The single yarn fineness was calculated based on JIS L1015: 1999 (chemical fiber staple test method) 8.5.1.

F. Fiber length The fiber length was calculated based on JIS L1015: 1999 (chemical fiber staple test method) 8.4.1.

G. Thickness and density The thickness and density of the nonwoven fabric were calculated based on JIS P8118: 1998 (paper and paperboard-thickness and density test method).

H. Basis weight The basis weight of the nonwoven fabric was calculated based on JIS P8124: 1998 (paper and paperboard-basis weight measurement method).

I. Weight reduction rate The weight (W0) after drying about 5 g of nonwoven fabric as a sample at 110 ° C. for 2 hours was measured. This sample was immersed in a 30 wt% potassium hydroxide aqueous solution at 70 ° C. for 8 hours, washed with a large amount of water, dried at 110 ° C. for 6 hours, and the weight (W1) was measured. The weight reduction rate was calculated from the measurement results using the following formula. The measurement was performed three times for each sample, and the average value was defined as the weight reduction rate.

Weight reduction rate (%) = {(W0−W1) / W0} × 100
J. et al. Breathability Breathability was calculated based on JIS L1096: 1999 (General Textile Test Method) 8.27.1.

K. Water absorption rate The water absorption rate was calculated based on JIS L1907: 2004 (Textile water absorption test method) 7.1.2.

L. Liquid retention rate The weight (W0) of a 50 mm × 50 mm non-woven fabric was measured as a sample. This sample was immersed in a 30 wt% aqueous potassium hydroxide solution at 20 ° C. for 1 hour and suspended for 10 minutes with one corner down, and the weight (W1) was measured. The liquid retention rate was calculated from the measurement results using the following formula. In addition, the measurement was performed 3 times per sample, and the average value was defined as the liquid retention rate.

Liquid retention rate (%) = {(W1-W0) / W0} × 100
Synthesis example 1
To 100 parts by weight of cellulose (dissolved pulp manufactured by Nippon Paper Industries Co., Ltd.), 240 parts by weight of acetic acid and 67 parts by weight of propionic acid were added and mixed at 50 ° C. for 30 minutes. After the mixture was cooled to room temperature, 172 parts by weight of acetic anhydride cooled in an ice bath and 168 parts by weight of propionic anhydride were added as an esterifying agent, and 4 parts by weight of sulfuric acid was added as an esterification catalyst, followed by stirring for 150 minutes. An esterification reaction was performed. In the esterification reaction, when it exceeded 40 ° C., it was cooled in a water bath. After the reaction, a mixed solution of 100 parts by weight of acetic acid and 33 parts by weight of water was added as a reaction terminator over 20 minutes to hydrolyze excess anhydride. Thereafter, 333 parts by weight of acetic acid and 100 parts by weight of water were added, and the mixture was heated and stirred at 80 ° C. for 1 hour. After completion of the reaction, an aqueous solution containing 6 parts by weight of sodium carbonate was added, and the precipitated cellulose acetate propionate was filtered off, subsequently washed with water, and dried at 60 ° C. for 4 hours. The cellulose acetate propionate thus obtained had an acetyl substitution degree of 2.0, a propionyl substitution degree of 0.7 (total cellulose ester substitution degree of 2.7), and a weight average molecular weight (Mw) of 178,000. It was.

Synthesis example 2
Cellulose acetate propionate was synthesized in the same manner as in Synthesis Example 1 except that acetic anhydride was changed to 193 parts by weight and propionic anhydride was changed to 111 parts by weight. The obtained cellulose acetate propionate had an acetyl substitution degree of 2.4, a propionyl substitution degree of 0.5 (total cellulose ester substitution degree of 2.9), and a weight average molecular weight (Mw) of 175,000. It was.

Reference example 1
Cellulose acetate propionate prepared in Synthesis Example 1 82.0% by weight, polyethylene glycol (PEG 600) having an average molecular weight of 600 17.9% by weight, and bis (2,6-di-t-butyl- 4-methylphenyl) pentaerythritol diphosphite 0.1% by weight was kneaded at 230 ° C. using a biaxial extruder and cut to about 5 mm to obtain cellulose ester composition pellets (Mw 16,000).

  The cellulose ester composition pellets obtained by the above production method were vacuum-dried at 80 ° C. for 8 hours and introduced into a melt spinning pack having a spinning temperature of 260 ° C. .. 20 mm, hole length 0.40 mm) was spun from a spinneret having 144 holes. This spun yarn is passed through an airflow blocking plate, cooled by cooling air with an air temperature of 25 ° C. and an air speed of 0.2 m / sec, and then concentrated by applying an oil agent with an oil supply device and rotating at 1000 m / min. Take up with a first godet roller and take up with a winder rotating at a speed of winding tension of 0.09 cN / dtex via a second godet roller rotating at the same speed as the first godet roller. A cellulose ester ultrafine fiber (120 dtex-144 fil) was obtained.

  The obtained fiber was cut into 2 mm, and then subjected to alkali saponification treatment with a 3 wt% aqueous sodium hydroxide solution at 95 ° C. for 20 minutes to obtain a cellulosic ultrafine fiber. The fiber characteristics of the obtained fibers are shown in Table 1.

Reference examples 2 and 3
Cellulose ultrafine fibers were prepared in the same manner as in Reference Example 1 except that the cellulose ester ultrafine fibers were cut to 10 mm in Reference Example 2 and 22 mm in Reference Example 3. The fiber characteristics of the obtained fibers are shown in Table 1.

Reference examples 4 and 5
The alkali saponification treatment conditions were as follows: in Reference Example 4, 5% by weight of a 3 wt% sodium hydroxide aqueous solution at 95 ° C., and in Reference Example 5, trimethylbenzylammonium chloride was added at 0.2 wt% as an alkali weight loss accelerator. Cellulose ultrafine fibers were prepared in the same manner as in Reference Example 1 except that the weight% sodium hydroxide aqueous solution was used for 10 minutes. The fiber characteristics of the obtained fibers are shown in Table 1. The fiber obtained in Reference Example 4 was a core-sheath type composite fiber in which the surface layer portion of the fiber was cellulose and the inner layer portion was a cellulose ester from the results of fiber cross-sectional observation.

Reference Example 6
78.0% by weight of cellulose acetate propionate prepared in Synthesis Example 2, 21.9% by weight of polyethylene glycol (PEG 600) having an average molecular weight of 600, and bis (2,6-di-t-butyl-) as a phosphorus-based antioxidant 4-methylphenyl) pentaerythritol diphosphite 0.1% by weight was kneaded at 230 ° C. using a biaxial extruder, and cut to about 5 mm to obtain cellulose ester composition pellets (Mw 164,000).

  Cellulose ultrafine fibers were prepared in the same manner as in Example 1 except that the cellulose ester composition pellets obtained by the above-described production method were used. The fiber characteristics of the obtained fibers are shown in Table 1.

Reference Example 7
The cellulose ester composition pellet produced in Example 1 was used as an island component, ethylene glycol as a glycol component, and terephthalic acid / isophthalic acid / 5-sodium sulfoisophthalic acid (61.5 / 26.0 / 12.5 as an acid component). Mol%) are copolymerized polyester (softening point 155 ° C., IV = 0.59) as a sea component and melted separately using a compound spinning machine (sea: 265 ° C., island: 260 ° C.). It was discharged from a sea-island type composite base having 16 island components and 12 holes (discharge hole diameter 0.5 mmφ) at 20 ° C. (sea / island composite ratio 20/80 wt%). After passing this spun yarn through a heating cylinder, it is cooled by cooling air with an air temperature of 20 ° C. and an air speed of 0.5 m / sec. It is taken up by a first godet roller rotating at 2300 m / min, wound up by a winder through a second godet roller rotating at the same speed as the first godet roller, and sea island type cellulose ester composite fiber (56 dtex- 12 fil).

  After cutting the obtained fiber to 7 mm, alkali saponification is carried out for 20 minutes with 95 ° C. 4% by weight aqueous sodium hydroxide solution, and the ester bond of cellulose ester is hydrolyzed together with leaching of sea components to obtain cellulose-based ultrafine fibers. It was. The fiber characteristics of the obtained fibers are shown in Table 1.

Reference Example 8
92.0% by weight of cellulose acetate propionate (CAP 482-20) manufactured by Eastman Chemical Co. having an acetyl substitution degree of 0.2 and a propionyl substitution degree of 2.5 (total substitution degree of cellulose ester 2.7), average Biaxially, 7.9% by weight of polyethylene glycol (PEG 600) having a molecular weight of 600 and 0.1% by weight of bis (2,6-di-t-butyl-4-methylphenyl) pentaerythritol diphosphite as a phosphorus-based antioxidant It knead | mixed at 230 degreeC using the extruder, and it cut to about 5 mm, and obtained the cellulose-ester composition pellet (Mw161,000).

  Using the cellulose ester composition pellets obtained by the above process as an island component, poly L-lactic acid (optical purity 98% L-lactic acid, Mw 152,000, residual lactide amount 0.1% by weight) as a sea component, composite spinning Melted separately (sea: 230 ° C., island: 235 ° C.), and discharged from a sea-island type composite die (16 mm diameter hole diameter: 12 mm) with a spinning temperature of 235 ° C. (Sea / island composite ratio 30/70 wt%). This spun yarn is passed through a heat insulating cylinder installed below the spinneret surface, and then cooled by cooling air with an air temperature of 20 ° C. and an air speed of 0.5 m / sec. Taken by a first godet roller rotating at 2300 m / min, wound by a winder through a second godet roller rotating at the same speed as the first godet roller, and sea island type cellulose ester composite fiber (56 dtex -12 fil).

  The obtained fiber was cut to 3 mm, and then subjected to alkali saponification with a 4 wt% sodium hydroxide aqueous solution at 95 ° C. for 20 minutes to hydrolyze the ester bond of the cellulose ester together with the leaching of the sea component to obtain a cellulose-based ultrafine fiber. It was. The fiber characteristics of the obtained fibers are shown in Table 1.

Reference Example 9
Cellulose acetate butyrate (CAB381-20) manufactured by Eastman Chemical Co., which has an acetyl substitution degree of 1.0 and a butyryl substitution degree of 1.7 (cellulose ester total substitution degree of 2.7), an average molecular weight of 600 A biaxial extruder containing 14.9% by weight of polyethylene glycol (PEG 600) and 0.1% by weight of bis (2,6-di-t-butyl-4-methylphenyl) pentaerythritol diphosphite as a phosphorus-based antioxidant Was kneaded at 230 ° C. and cut to about 5 mm to obtain cellulose ester composition pellets (Mw 18.1 million).

  Using the cellulose ester composition pellets obtained by the above process as an island component, poly L-lactic acid (optical purity 98% L-lactic acid, Mw 152,000, residual lactide amount 0.1% by weight) as a sea component, composite spinning Separately using a machine (sea: 230 ° C., island: 235 ° C.), using a sea-island composite die (discharge hole diameter: 0.5 mmφ) with a spinning temperature of 235 ° C. and 32 island components and 12 holes. Discharged (sea / island composite ratio 20/80 wt%). This spun yarn is passed through a heat insulating cylinder installed below the spinneret surface, and then cooled by cooling air with an air temperature of 20 ° C. and an air speed of 0.5 m / sec. Taken by a first godet roller rotating at 2300 m / min, wound by a winder through a second godet roller rotating at the same speed as the first godet roller, and sea island type cellulose ester composite fiber (80 dtex -12 fil).

  After cutting the obtained fiber to 5 mm, alkali saponification is carried out for 20 minutes with a 4% by weight sodium hydroxide aqueous solution at 95 ° C., and the ester bond of the cellulose ester is hydrolyzed together with the leaching of the sea component to obtain a cellulose-based ultrafine fiber. It was. The fiber characteristics of the obtained fibers are shown in Table 1.

Reference Example 10
Cellulose ultrafine fibers were prepared in the same manner as in Reference Example 1 except that the discharge rate was 30 g / min. The fiber characteristics of the obtained fibers are shown in Table 1.

Reference Example 11
The cellulose ester ultrafine fiber (120 dtex-144 fil) obtained in Reference Example 1 was cut into 2 mm. The fiber characteristics of the obtained fibers are shown in Table 1. Since the obtained fiber was not subjected to alkali saponification, it was composed of cellulose ester, and no micropores were observed in the fiber surface layer.

Example 1
The cellulosic ultrafine fibers obtained in Reference Example 1 are dispersed in water at a temperature of 20 ° C., wet-made using a circular mesh wet paper machine, dried with a cylinder dryer at 110 ° C., and the thickness shown in Table 2 Thus, a battery separator having a basis weight and a density was obtained. Table 2 shows physical property values of the obtained battery separator.

Examples 2-12
Using the cellulosic ultrafine fibers obtained in Reference Examples 2 to 9, battery separators were produced in the same manner as in Example 1. Table 2 shows physical property values of the obtained battery separator.

Examples 13-15
Cellulose ultrafine fiber obtained in Reference Example 1, commercially available polyvinyl alcohol fiber (single yarn fineness 0.50 dtex, fiber length 2.0 mm, dissolution temperature in water of 100 ° C. or higher), commercially available polyvinyl alcohol fiber binder (single The yarn fineness of 1.0 dtex, the fiber length of 3.0 mm, and the dissolution temperature in water of 70 ° C.) were dispersed in water at a temperature of 20 ° C. at the blending ratio shown in Table 3, and uniformly mixed and stirred. A battery separator was produced. Table 3 shows the physical property values of the obtained battery separator.

Comparative Examples 1-4
Using the cellulose-based ultrafine fibers obtained in Reference Examples 7 and 10 and the cellulose ester ultrafine fiber obtained in Reference Example 11, a battery separator was produced in the same manner as in Example 1. Table 3 shows the physical property values of the obtained battery separator.

Comparative Example 5
Cellulose triacetate (acetyl substitution degree 2.9, polymerization degree 280) was dry-spun by a conventional method to obtain triacetate fibers (100 dtex-36 fil). The obtained fiber was cut into 2 mm, and then subjected to alkali saponification with a 3 wt% sodium hydroxide aqueous solution at 95 ° C. for 20 minutes to obtain a cellulosic fiber. The fiber characteristics of the obtained fiber are shown in Table 3.

  Using the obtained fiber, a battery separator was prepared in the same manner as in Example 1. Table 3 shows the physical property values of the obtained battery separator.

Comparative Example 6
Commercially available rayon fiber (single yarn fineness 1.70 dtex, fiber length 2.0 mm, polymerization degree 520) was beaten by a conventional method to obtain fibrillated cellulosic ultrafine fibers. The fiber characteristics of the obtained fiber are shown in Table 3.

  Using the obtained fiber, a battery separator was prepared in the same manner as in Example 1. Table 3 shows the physical property values of the obtained battery separator.

Comparative Examples 7-9
Commercially available rayon fiber (single yarn fineness 1.70 dtex, fiber length 2.0 mm, polymerization degree 520), commercially available polyvinyl alcohol fiber (single yarn fineness 0.50 dtex, fiber length 2.0 mm, dissolution temperature in water of 100 ° C. or higher) A commercially available polyvinyl alcohol-based fibrous binder (single yarn fineness 1.0 dtex, fiber length 3.0 mm, water dissolution temperature 70 ° C.) is dispersed in water at a temperature of 20 ° C. at a mixing ratio shown in Table 3 and uniformly After mixing and stirring, a battery separator was prepared in the same manner as in Example 1. Table 3 shows the physical property values of the obtained battery separator.

  The battery separators obtained in Examples 1 to 12 all had alkali resistance, separation properties, and electrolyte solution absorption properties.

  From Examples 13 to 15, all of the battery separators containing the polyvinyl alcohol fiber and / or the binder fiber had alkali resistance, separation property, and electrolyte solution absorption property.

  The battery separator of Comparative Example 1 had extremely high air permeability and poor separation properties. This is because the battery separator was too thin, so there was very little overlap between the fibers and there were very many voids between the fibers.

  The battery separator of Comparative Example 2 had extremely low air permeability and poor separation properties. This is because the battery separator was too thick, so that there was very much overlap between the fibers and there were very few voids between the fibers.

  The battery separator of Comparative Example 3 had high air permeability and poor separation properties. This is because the pore size of the battery separator could not be reduced because the single-fiber fineness of the cellulosic fiber was too large.

  The battery separator of Comparative Example 4 had a very large weight reduction rate in an alkaline aqueous solution and was inferior in alkali resistance. This is because hydrolysis of the ester bond of the cellulose ester ultrafine fiber has progressed in the alkaline aqueous solution. In addition, since the cellulose ester has lower hydrophilicity than cellulose, both the water absorption rate and the liquid retention rate are low, and the electrolyte solution absorbability is poor.

  The battery separator of Comparative Example 5 had extremely high air permeability and poor separation properties. This is because the single yarn fineness of the triacetate fiber was too large, so that the single yarn fineness of the cellulosic fiber obtained by alkali saponification could not be reduced, and the pore size of the battery separator could not be reduced. . In addition, since the cellulose ester used as the raw material for the triacetate fiber consists only of acetyl groups having 2 acyl group carbon atoms, the fine pore distribution density after alkali saponification is small. As a result, both the water absorption rate and the liquid retention rate are low. Low and slightly inferior in electrolyte absorption.

The battery separator of Comparative Example 6 had extremely low air permeability and poor separation properties. This is because rayon fiber was beaten and the fibrillated cellulosic fiber was too fine.
This is because there are extremely few voids between the fibers.

  The battery separator of Comparative Example 7 had extremely high air permeability and poor separation properties. This is because the pore size of the battery separator could not be reduced because the single yarn fineness of the rayon fiber was too large. In addition, since rayon fibers do not have fine pores on the fiber surface, both the water absorption rate and the liquid retention rate are low, and the electrolyte solution absorbability is somewhat inferior.

  The battery separator of Comparative Example 8 had extremely high air permeability and poor separation properties. This is because the pore size of the battery separator could not be reduced because the single yarn fineness of the rayon fiber, which is the main component of the battery separator, was too large. Further, the polyvinyl alcohol-based ultrafine fiber and the polyvinyl alcohol-based fibrous binder constituting the battery separator have low electrolyte solution absorbability, so both the water absorption rate and the liquid retention rate are low, and the electrolyte solution absorbability is slightly inferior.

  The battery separator of Comparative Example 9 had a low water absorption rate and a low liquid retention rate, and was inferior in the electrolyte solution absorbability. This is because the electrolyte solution absorbability of the polyvinyl alcohol-based ultrafine fiber and the polyvinyl alcohol-based fibrous binder constituting the battery separator is low.

  The battery separator of the present invention has excellent alkali resistance, separation property, and electrolyte solution absorption. Therefore, it can be suitably employed for alkaline primary batteries such as alkaline manganese batteries, silver oxide batteries, mercury batteries, and zinc-air batteries.

Claims (3)

  A battery separator comprising cellulosic ultrafine fibers having a single yarn fineness of 0.05 to 0.8 dtex, wherein the fiber surface layer is cellulose.   The battery separator according to claim 1, wherein the surface layer of the cellulosic ultrafine fibers has micropores.   3. The method for producing a battery separator according to claim 1 or 2, wherein the cellulose ester ultrafine fiber comprising cellulose acetate propionate and / or cellulose acetate butyrate is alkali saponified, and then made into a nonwoven fabric containing the ultrafine fiber. .