JP2001143680A - Nonwoven fabric and battery separator formed of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide nonwoven fabric that has electrolyte protection property and acid resistance weakening property existing in a nonwoven fabric consisting of polylefinic fiber and adapted to a battery separator. SOLUTION: The battery separator formed of nonwoven fabric contains at least 20 wt.% of a fiber which exposes notless than 20% of blend polymer formed by melting and mixing 4.5-95 wt.% of polypropylene, 4.5-95 wt.% of ethylene denatured polyvinyl alcohol, and 0.5-30 wt.% of boron acid denatured polypropylene to a surface of the fiber.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nonwoven fabric suitable for a battery separator, and more particularly to a separator suitable for a secondary battery using an alkaline solution.

[0002]

2. Description of the Related Art Conventionally, nonwoven fabrics of polyamide fibers and nonwoven fabrics of polyolefin fibers are known as alkaline battery separators, and are used for each battery by utilizing the characteristics of each fiber. However, polyamide fibers,
In particular, non-woven fabrics made of aliphatic polyamide fibers such as nylon 6 and nylon 66 are excellent in alkali resistance and hydrophilicity.
The secondary battery has the advantage of efficiently absorbing oxygen gas generated from the positive electrode at the time of charging at the negative electrode and enabling rapid charging, but is inferior to oxidation deterioration resistance at high temperatures, so it was used for an alkaline secondary battery. In this case, there is a drawback that not only the separator itself is deteriorated by being oxidized by oxygen gas generated from the positive electrode during charging or an electrochemical reaction of the positive electrode, but also the self-discharge reduces the battery capacity. On the other hand, polyolefin fibers are excellent in alkali resistance and oxidation-deterioration resistance, but are poor in hydrophilicity, so that the liquid retaining property of the electrolyte is low and the electric resistance in the electrolyte is high. In the subsequent battery, oxygen gas generated from the positive electrode at the time of charging cannot be efficiently absorbed by the negative electrode, so that the internal pressure rises and rapid charging cannot be performed. the above,
It has been proposed to mix or compound a polyamide fiber and a polyolefin fiber in order to improve the oxidation resistance of the polyamide fiber (JP-A-55-25921, JP-A-55-66864). However, the mixing ratio of the oxidatively decomposing fibers is merely reduced as a whole, and the deterioration can be reduced, and the fundamental solution has not been reached. In addition, a method for imparting hydrophilicity to polyolefin fibers has been proposed in order to improve the liquid retention of the electrolyte solution of the polyolefin fibers. For example, a method of sulfonating a polyolefin fiber separator by treating it with fuming sulfuric acid or chlorosulfuric acid,
Many methods have been proposed, such as a method of sulfonating by treating in a sulfur trioxide gas and a method of graft polymerization of acrylic acid or methacrylic acid by electron beam irradiation. However, the hydrophilization treatment is expensive and it is difficult to maintain the hydrophilicity for a long time. Further, since the treatment is carried out under severe conditions, there is a problem that the fiber strength is reduced.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a battery separator which has hydrophilicity, that is, a liquid retaining property of an electrolyte, and also possesses the oxidation deterioration resistance of a nonwoven fabric made of polyolefin fibers. To provide.

[0004]

That is, the present invention relates to a polyolefin resin (A) of 4.5 to 95% by mass, a polyvinyl alcohol resin (B) of 4.5 to 95% by mass, A non-woven fabric, characterized in that a blend polymer comprising 0.5 to 30% by mass of a compatibilizing agent (C) and a resin (B) contains 20% by mass or more of a fiber exposed on the fiber surface by 20% or more. And a battery separator comprising the nonwoven fabric, and a battery incorporating the separator.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As the polyolefin resin (A) used in the present invention, known resins can be used, and mainly homopolymers of α-olefins such as high-density or low-density polyethylene, polypropylene and polybutene-1, ethylene And propylene, butene-1, hexene-1, etc., and a copolymer of α-olefins. Further, as a copolymerization component with α-olefin, for example, diolefin, N-vinyl carbazole,
Vinyl chloride, vinylidene chloride, vinyl acetate, styrene,
Acrylonitrile, vinyl compounds such as vinyl ether, unsaturated carboxylic acids such as maleic acid, acrylic acid, methacrylic acid, ethacrylic acid, fumaric acid, itaconic acid,
Ester or anhydride thereof, or those obtained by adding a hydroxyl group or an epoxy group thereto, or the like may be used. Also, two or more kinds may be used in combination. Among them, a polypropylene resin is preferably used.

The proportion of the polyolefin resin (A) must be 4.5 to 95% by mass, preferably 20 to 95% by mass, and more preferably 30 to 90% by mass in the blend polymer constituting the fiber. Is particularly preferred. If the amount is less than 4.5% by mass, the strength of the separator is reduced, or the resistance to oxidation deterioration of the separator is reduced, and in the alkaline secondary battery, the separator is oxidized at the time of charging, the strength is deteriorated, and at the same time, the positive electrode is reduced. This causes problems such as discharge. On the other hand, if the amount exceeds 95% by mass, the effect of the addition will not be exhibited.

[0007] The battery separator of the present invention must contain the polyvinyl alcohol resin (B) as one component. By blending polyvinyl alcohol, an OH group is provided to the battery separator, the wettability between the separator and the electrolyte is improved, and the liquid retention is also improved. Further, by improving the wettability, oxygen generated at the positive electrode, which is a problem particularly at the time of charging an alkaline secondary battery, is efficiently absorbed by the negative electrode, and rapid charging becomes possible.

The ratio of the polyvinyl alcohol resin (B) is 4.5 to 4.5 in the blend polymer constituting the fiber.
It is necessary to be 95% by mass, preferably 5 to 80% by mass, particularly preferably 10 to 70% by mass. If the amount is less than mass%, the effect of the addition will not be exhibited. On the other hand, when the amount exceeds 95% by mass,
In the alkaline secondary battery, the strength of the separator is reduced, and the resistance to oxidation deterioration of the separator is reduced, so that the separator is oxidized at the time of charging, the strength is deteriorated, and at the same time, the positive electrode is reduced and discharged.

Here, the polyvinyl alcohol resin is
It is a saponified product of a vinyl ester polymer or a copolymer of another vinyl monomer copolymerizable with the vinyl ester. Here, as the vinyl ester, vinyl acetate may be mentioned as a representative example, and in addition, vinyl esters such as vinyl propionate, vinyl pivalate, vinyl valerate, vinyl caprate, and vinyl benzoate may also be mentioned. These vinyl esters may be used alone or in combination of two or more. As the vinyl monomer copolymerizable with the vinyl ester, ethylene, propylene, 1-
Olefin monomers such as butene and isobutene; acrylamide monomers such as acrylamide, N-methylacrylamide, N-ethylacrylamide and N, N-dimethylacrylamide; methacrylamide, N-methylmethacrylamide, N-ethylmethacryl Amide, N, N-
Methacrylamide monomers such as dimethylmethacrylamide; methyl vinyl ether, ethyl vinyl ether, n
Vinyl ether monomers such as -propyl vinyl ether, i-propyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether; allyl alcohol; vinyl trimethoxysilane; N-vinyl-2-pyrrolidone, isopropenyl alcohol, 7-octene-1- All, allyl acetate, isopropenyl acetate and the like can be mentioned.

In particular, α-olefins having 4 or less carbon atoms are
55 mol% copolymerized polyvinyl alcohol is preferably used in view of moldability, and among them, ethylene copolymerized polyvinyl alcohol is particularly preferable. When the copolymerization ratio is 1 mol% or less, the effect of the copolymerization is not remarkable.
If it exceeds mol%, the excellent physical properties of polyvinyl alcohol, that is, the effect of imparting hydrophilicity to the separator will be impaired. The copolymerization ratio is particularly preferably from 3 to 50 mol%. Further, the polyvinyl alcohol-based polymer may be used by mixing polyvinyl alcohol-based polymers different in at least one of the kind and amount of these comonomers, the degree of saponification, and the degree of polymerization.

The polyvinyl alcohol resin used in the present invention preferably has a degree of polymerization of 200 to 2,000.
More preferably, it is 200 to 1,000. When the degree of polymerization is less than 200, the strength of the obtained separator is low. On the other hand, when the degree of polymerization exceeds 2,000, it is difficult to obtain fibers constituting the separator.

The polyvinyl alcohol resin used in the present invention preferably has a saponification degree of 60 to 100 mol%, more preferably 70 to 100 mol%.
It is particularly preferred that it is 80 to 99.99 mol%. If the degree of saponification is less than 60 mol, the polyvinyl alcohol-based resin tends to be thermally degraded when the fibers constituting the separator are obtained by a melt spinning method.

A plasticizer such as glycerin, a derivative thereof, polyethylene glycol, or water may be added to the polyvinyl alcohol resin used in the present invention, if necessary. Further, other additives (a heat stabilizer, an ultraviolet absorber, an antioxidant, a coloring agent, a lubricant, a release agent, a filler, and the like) can be used in the polyvinyl alcohol-based polymer as long as the object of the present invention is not hindered.

The polyvinyl alcohol-based resin (B) used in the present invention preferably contains an alkali metal salt. By blending a specific amount of an alkali metal salt, the polyvinyl alcohol-based resin (B) at the time of hot-melt spinning has good moldability, and deterioration, decomposition, gelation, and coloring of the resin are suppressed, and molding is also performed. It has the effect of reducing the acetic acid odor at the time. The blending amount is polyvinyl alcohol resin (B) 100
The amount is preferably from 0.003 to 1 part by mass, more preferably from 0.007 to 0.6% by mass, based on the mass part.
It is particularly preferred that the content is from 0.01 to 0.5% by mass. If the content of the alkali metal salt is less than 0.003% by mass, gelation of the PVA-based resin becomes remarkable when fibers constituting the separator are obtained by a melt spinning method. On the other hand, if the compounding amount exceeds 1% by mass, decomposition and coloring during melt spinning and furthermore, acetic acid odor becomes intense, which is not preferable. Examples of the alkali metal ion include a potassium ion and a sodium ion. These are mainly salts of lower fatty acids such as acetic acid and propionic acid, or PV.
A exists as a salt of a terminal carboxyl group of A, or a salt of a carboxyl group or a sulfonic acid contained in a comonomer.
The blending amount of the alkali metal is indicated by a value obtained by measuring a sample dissolved in an ash and an acid with an atomic absorption spectrophotometer.

In the present invention, the polyolefin resin (A) and the polyalcohol resin (B) are added to the blend polymer.
And a compatibilizer (C). The addition of the compatibilizer not only improves the spinnability when the fibers constituting the separator are melt-spun, but also improves the strength and oxidation resistance of the obtained separator. The proportion of the compatibilizer (C) needs to be 0.5 to 30% by mass in the blend polymer constituting the fiber.
If the compounding amount is less than 0.5% by mass, the resin (A) and the resin (B)
Is not remarkable. On the other hand, when it exceeds 30% by mass, not only the hydrophilicity of the fiber is reduced, but also the separator is easily oxidized and deteriorated.

As the compatibilizer (C) for the polyolefin resin (A) and the polyvinyl alcohol-based resin (B), polyolefin is used as maleic acid, acrylic acid, methacrylic acid,
Or a thermoplastic polymer having at least one functional group selected from boron-containing groups. In particular, a thermoplastic polymer having at least one functional group selected from a boronic acid group, a borinic acid group, and a boron-containing group that can be converted to a boronic acid group or a borinic acid group in the presence of water is added as a compatibilizer. When the resin (A) and the resin (B) are melt-kneaded, the compatibilizer and the resin (B) are chemically bonded to each other, and a resin having high compatibility with the resin (A) is selected as a base polymer of the compatibilizer. As a result, the compatibility and adhesiveness between the resin (A) and the resin (B) can be drastically improved, and as a result, the spinning properties when the fibers constituting the separator are melt-spun are improved. In addition, the strength and the oxidation resistance of the obtained separator are remarkably improved.

The thermoplastic polymer having at least one functional group selected from the group consisting of a boronic acid group, a borinic acid group and a boron-containing group which can be converted into a boronic acid group or a borinic acid group in the presence of water includes: It is preferable that the boron of the functional group is bonded to the main chain, side chain or terminal of the thermoplastic polymer. Of these, a thermoplastic polymer bonded to the side chain or terminal is preferable, and the thermoplastic polymer bonded to the terminal is preferable. Coalescing is optimal. Here, the term "end" means one end or both ends. In the bonding between the functional group and the thermoplastic polymer, the carbon of the boron-carbon bond is derived from a base polymer described later or derived from a boron compound reacted with the base polymer. Preferable examples of the boron-carbon bond include a bond between boron and an alkylene group in a main chain or a terminal or a side chain. In the present invention, the boronic acid group is represented by the following chemical formula 1.

[0018]

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The boron-containing group which can be converted to a boronic acid group in the presence of water (hereinafter simply referred to as boron-containing group) is a boron-containing group which is hydrolyzed in the presence of water, As long as it is a boron-containing group that can be converted to an acid group, any group may be used, and as typical examples, a boronic ester group represented by the following chemical formula 2, a boronic anhydride group represented by the following chemical formula 3, And a boronic acid salt group represented by Chemical Formula 4.

[0020]

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[0021]

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[0022]

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In the formula, X and Y represent a hydrogen atom, an aliphatic hydrocarbon group (such as a linear or branched alkyl group or alkenyl group having 1 to 20 carbon atoms) and an alicyclic hydrocarbon group (cyclo Alkyl group, cycloalkenyl group, etc.) and aromatic hydrocarbon group (phenyl group, biphenyl group, etc.)
X and Y may be the same or different. X and Y may be bonded. However, it is excluded when both X and Y are hydrogen atoms. R ¹ , R ² , and R ³ represent the same hydrogen atom, aliphatic hydrocarbon group, alicyclic hydrocarbon group, and aromatic hydrocarbon group as those of X and Y, and R ¹ , R ² , R ³
May be the same group or different. M represents an alkali metal or an alkaline earth metal. X, Y, R ¹ , R ² and R ³ may have other groups such as a carboxyl group and a halogen atom. ｝

Specific examples of the boronic ester groups represented by Chemical Formulas 2 to 4 include dimethyl boronate, diethyl boronate, dipropyl boronate, diisopropyl boronate, and dibutyl boronate. , Dihexyl boronate, dicyclohexyl boronate, ethylene glycol boronate, propylene glycol boronate (1,2-propanediol boronate, 1,3-propanediol boronate), boron Boronic acid ester groups such as acid trimethylene glycol ester group, boronic acid neopentyl glycol ester group, boronic acid catechol ester group, boronic acid glycerin ester group, boronic acid trimethylolethane ester group, etc .; boronic anhydride group; Alkali metal base phosphate, alkaline earth metal base such as boronic acid.

In the present invention, the borinic acid group is represented by the following formula (5).

[0026]

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The boron-containing group capable of being converted to a borinic acid group in the presence of water includes a boron-containing group capable of being converted to a borinic acid group represented by the above formula by hydrolysis in the presence of water. Any one may be used as long as it is a representative example, and a borinic acid ester group represented by the following chemical formula 6;
And a borinic acid salt group represented by the following formula (8).

[0028]

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[0029]

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[0030]

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In the formula, X has the same meaning as X in Chemical Formula 2, and Z represents the same aliphatic hydrocarbon group, alicyclic hydrocarbon group, aromatic hydrocarbon group, amino group, Represents an amide group. X and Z may be bonded. R ¹ , R ² ,
R ³ has the same meaning as R ¹ , R ² , and R ^{3 in} Chemical Formula 4 described above. M has the same meaning as M in Chemical Formula 4. ｝

Specific examples of the bolinic acid ester group represented by the formulas (5) to (8) include X, Z, R ¹ , R ² and R ^{3 each} being a methyl group,
Examples thereof include lower hydrocarbon groups such as an ethyl group, a propyl group, a butyl group, a 1-methylpropyl group, a pentyl group, a hexyl group, and a phenyl group. Representative examples include a methyl borinic acid group, a methyl borinic acid methyl ester group, an ethyl borinic acid methyl ester group, a methyl borinic acid ethyl ester group, a butyl borinic acid methyl ester group, and a 3-methyl-2-butyl borinic acid methyl ester group. Among the above functional groups, a boronic acid ester group such as a boronic acid ethylene glycol ester group is particularly preferred from the viewpoint of compatibility with the polyvinyl alcohol-based resin (B). The above-mentioned boron-containing group which can be converted into a boronic acid group or a borinic acid group in the presence of water is defined as a base polymer, water or a liquid mixture of water and an organic solvent (toluene, xylene, acetone, etc.), In a mixture of the aqueous acid solution and the organic solvent, the reaction time is 10 minutes to 2 hours, and the reaction temperature is room temperature to 150 hours.
It means a group that can be converted into a boronic acid group or a borinic acid group when hydrolyzed under the condition of ° C.

The content of the functional group is not particularly limited,
It is preferably 0.0001 to 1 meq / g (milli-equivalent / g), and particularly preferably 0.001 to 0.1 meq / g.
It is surprising that compatibility, transparency, mechanical properties and the like of the resin composition are remarkably improved by the presence of such a small amount of functional groups.

Typical examples of the base polymer include an olefin polymer, a vinyl polymer and a diene polymer which are essentially incompatible with the polyvinyl alcohol resin. Examples of monomers constituting the olefin-based polymer, vinyl-based polymer and diene-based polymer include α-olefins such as ethylene, propylene, 1-butene, isobutene, 3-methylpentene, 1-hexene and 1-octene. Olefinic monomers represented by; vinyl acetate,
Vinyl ester monomers such as vinyl propionate and vinyl pivalate; acrylate monomers such as methyl acrylate, ethyl acrylate, butyl acrylate, hexyl acrylate, octyl acrylate, dodecyl acrylate and 2-ethylhexyl acrylate; methyl methacrylate Methacrylate monomers such as, ethyl methacrylate, butyl methacrylate, octyl methacrylate, dodecyl methacrylate;
Acrylamide monomers such as acrylamide, N-methylacrylamide, N-ethylacrylamide, N, N-dimethylacrylamide; methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide;
Methacrylamide monomers such as N, N-dimethylmethacrylamide; vinyl halide monomers such as vinyl chloride, vinylidene chloride and vinyl fluoride; aromatic vinyl monomers such as styrene and α-methylstyrene Acrylonitrile monomers such as acrylonitrile and methacrylonitrile; and diene monomers such as butadiene and isoprene.

The base polymer is used as a polymer composed of one or more of these monomers. Among these base polymers, in particular, ethylene polymers ｛ultra low density polyethylene, low density polyethylene, medium density polyethylene, high density polyethylene, linear low density polyethylene, ethylene-vinyl acetate copolymer, ethylene-acrylate Copolymer, metal salt of ethylene-acrylic acid copolymer (Na, K, Zn-based ionomer), ethylene-propylene copolymer, etc., propylene-based polymer, aromatic vinyl-based polymer (polystyrene, styrene-acrylonitrile) Copolymer, styrene-butadiene copolymer, styrene-butadiene-acrylonitrile copolymer, styrene-maleic anhydride copolymer), diene-based polymer {aromatic vinyl-based monomer-diene-based monomer-aromatic Block copolymer hydrogenated aromatic vinyl monomer, polyisoprene, polybutadiene , Chloroprene, isoprene - acrylonitrile copolymer (nitrile rubber), isoprene - isobutene copolymer (butyl rubber) and the like} can be mentioned as preferred. Melt index of base polymer (M
I) (value measured at 190 ° C. under a load of 2160 g) is preferably 0.01 to 1000 g / 10 min, and 0.1 to 1 g / min.
00g / 10 minutes is more preferable.

Further, conventionally known additives such as a heat stabilizer, an antioxidant, an ultraviolet absorber, a weathering stabilizer, a plasticizer, a coloring agent, a release agent, and the like can be added to the fiber of the present invention as long as the effect is not hindered. Lubricants, fragrances, fillers and the like can be blended.
Other polymer materials can also be blended. The following are specific examples of the additive.

Antioxidants: 2,5-di-tert-butylhydroxine, 2,6-di-tert-butyl-p-cresol, 4,4'-thiobis- (6-tert-butylphenol), 2'-methylene-bis- (4-methyl-6-
t-butylphenol), octadecyl-3- (3 ',
5'-di-t-butyl-4'-hydroxyphenyl) propionate, 4,4'-thiobis- (6-t-butylphenol) and the like.

UV absorber: ethylene-2-cyano-
3,3'-diphenyl acrylate, 2- (2'-hydroxy-5'-methylphenyl) benzotriazole,
2- (2'-hydroxy-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-3'-t-butyl-5 '-Methylphenyl) 5-
Chlorobenzotriazole, 2-hydroxy-4-methoxybenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone, 2-hydroxy-4-oxybenzobenzophenone and the like.

Plasticity: dimethyl phthalate, diethyl phthalate, dioctyl phthalate, wax, liquid paraffin, phosphate ester, polyethylene glycol, glycerin and the like.

Antistatic agents: pentaerythritol monostearate, sorbitan monopalmitate, sulfated polyolefins, polyethylene oxide, carbowax and the like. Lubricants: ethylene bis stearamide, butyl stearate and the like. Colorants: carbon black, phthalocyanine, quinacridone, indoline, azo pigments, red iron, etc. Filler: glass fiber, asbestos, parastonite, calcium silicate, etc.

For melt-mixing the above-mentioned polyolefin resin (A), polyvinyl alcohol resin (B) and compatibilizer (C), a twin screw extruder is usually used. Particularly, as a compatibilizer, a thermoplastic polymer having at least one functional group selected from the boronic acid group, the borinic acid group, and the boron-containing group capable of being converted to a boronic acid group or a borinic acid group in the presence of water, as described above. When using coalescence,
It is preferable that the OH group of (B) and the boron-containing terminal group of the polymer are melt-mixed with a twin-screw extruder so that they are sufficiently chemically bonded. The obtained blended polymer is pelletized and melted by a single screw extruder or a twin screw extruder,
It may be made into fibers, or may be made into fibers as it is when blending. Further, the fiber using the blend polymer may be composed of the blend polymer alone, or may be combined with another polymer to form a composite fiber such as a core-sheath type, a sea-island type, a layered type, a radial type or the like. . Polyolefin resins and polyvinyl alcohol-based resins are used as the polymer to be combined.
Although it is preferable from the viewpoint of resistance to oxidation deterioration, etc., in the present invention, it is necessary to use a fiber in which the blend polymer is exposed on the fiber surface by 20% or more, preferably 50% or more, more preferably 80% or more. The amount of the blend polymer exposed on the fiber surface can be calculated from the structure and cross-sectional shape of the fiber. For example, when the blend polymer is a sheath component in a core-sheath composite fiber, the exposure ratio of the blend polymer is almost 100%, depending on the fiber length. Further, in the case of a side-by-side type conjugate fiber containing 50% by mass of the polymer, the exposed amount of the blended polymer is about 50%. When the exposure of the blend polymer to the fiber surface is less than 20%, the effect of the blend polymer is not obtained, and when the separator obtained from the fiber is used in an alkaline secondary battery, sufficient liquid retention is exhibited. not,
Not only the electric resistance becomes high, but also rapid charging cannot be performed.

The fineness of the fiber is not particularly limited, but is 0.1 to 6 dtex in order to retain the electrolyte, prevent the deposition of the metal constituting the positive electrode and the negative electrode, and prevent a short circuit due to the movement of the electrode active material. Preferably, there is. The fiber cross section may be a circular cross section or an irregular cross section. In the case of an irregular cross section, the value converted into the circular cross section is defined as the fiber diameter. Also, the fiber length is not particularly limited, but can be appropriately set depending on the method of forming the nonwoven fabric. For example, when the nonwoven fabric is formed by a wet method, the thickness is preferably 1 to 30 mm, and when the nonwoven fabric is formed by a dry method such as a card method or an air lay method, the thickness is preferably 10 to 70 mm.

The battery separator of the present invention comprises a non-woven fabric containing at least 20% by mass of a fiber in which the blend polymer occupies 20% or more of the fiber surface,
Preferably, the fiber is 40% by mass or more, more preferably 6% by mass.
It is a nonwoven fabric containing 0% by mass or more. When the fiber content is less than 20% by mass, when the separator is used in an alkaline secondary battery, the separator does not have sufficient liquid retaining properties, so that not only the electrical resistance is increased but also the battery cannot be rapidly charged.

Examples of the fibers that can be mixed with the above-mentioned fibers comprising the blend polymer include general-purpose aliphatic polyamide fibers such as nylon 6 and nylon 66, polyolefin fibers, polyvinyl alcohol fibers, cellulosic fibers, and polyolefin fibers. Arylate fiber, aramid fiber,
Fibers such as PPS fiber and PBO fiber can be given. In addition, the use of fibers having a lower melting point than fibers of the above-mentioned blend polymer, known thermoplastic binder fibers, sizing agents, and the like can improve the form stability of the nonwoven fabric.

In the present invention, the nonwoven fabric used for the battery separator can be obtained by any production method. For example, a fiber web (before entanglement or bonding of a nonwoven fabric) is formed, and the fibers in the web are entangled or bonded to form a nonwoven fabric. The obtained nonwoven fabric may be used as it is, or may be used as a plurality (or a plurality of types) of laminates. Examples of the method of forming the fiber web include a dry method such as a card method and an air lay method, a wet method such as a papermaking method, a spunbond method, and a melt blown method. Among these, the fiber web obtained by the wet method or the melt blown method is used. When used as a battery separator having a dense and uniform surface state, it is possible to effectively prevent metal deposition and migration of an electrode active material. Further, the fiber webs formed by the above respective methods can be used in combination by lamination.

Hereinafter, a method for producing a nonwoven fabric will be specifically described. For forming a fiber web by a dry method, a fiber web can be manufactured using a roller card, a random card, a webber or the like. The webs are classified into parallel webs, cross webs, random webs, and the like according to the directionality of the fibers. Webs in which the orientation directions of the fibers cross each other are preferable because the difference in strength between the vertical and horizontal directions is reduced. As a method of forming a nonwoven fabric from such a fiber web, for example, a method of entanglement of the fiber web by the action of a water stream or a needle, a method of bonding with a binder, a method of tying the web with a sewing thread in a net shape, and the like are described. Yes, these methods can be used alone or in combination.

The formation of a fiber web by the wet method is generally a papermaking method. However, such a method has a higher production speed than other methods, and it is possible to arbitrarily select fibers having different fiber diameters or a plurality of types of fibers using the same apparatus. There is an advantage that it can be mixed in the proportion of That is, the form of the fiber can be selected from a wide variety of staple and pulp shapes, and the fiber diameter to be used can be used from very fine fiber to thick fiber. In this method, first, a fiber obtained by melt spinning is cut and dispersed in water to form a uniform papermaking slurry under gentle stirring, and this papermaking slurry is formed into a wire mesh such as a round net, a long net, and an inclined type. This is a method of making paper using a paper machine having at least one. In addition, the wet paper or the dried paper thus obtained may be entangled with a single sheet or a laminated sheet. The cut fibers may be beaten with a beater or a refiner or the like to form a papermaking slurry, or a viscosity agent or a dispersant may be added during papermaking.

In the case of forming a nonwoven fabric of only a blend polymer comprising the polyolefin resin (A), the polyvinyl alcohol resin (B) and the compatibilizer (C), a high-temperature air stream is blown from the surroundings while melt-spinning. Thinning the fiber,
A melt blow method in which this is collected on a collecting surface is preferable. In addition, while cooling the spun fiber, thinning-drawing-
A spunbond method in which a web forming step is directly connected can also be used. The stretching method may be performed by an air jet or a roller, and the fiber opening may be performed by a triboelectric charging method, a forced charging method, a collision diffusion method, an airflow diffusion method, or the like. The surface of the nonwoven fabric formed by such a method is preferably subjected to a heat calendering treatment for improving the surface smoothness, adjusting the thickness of the nonwoven fabric, heat bonding, strength, and achieving high density.

The battery separator of the present invention may be a primary or secondary battery separator.
It can be used as a separator for secondary batteries. The battery may be open or closed, and may be cylindrical, flat, or square. More specifically, primary batteries such as alkaline manganese batteries, mercury batteries, silver oxide batteries, and air batteries;
It can be suitably used as a secondary battery separator such as a cadmium battery, a silver-zinc battery, a silver-cadmium battery, a nickel-zinc battery, a nickel metal hydride battery, and a lithium ion secondary battery.

Although the present invention is a battery separator, the nonwoven fabric according to the present invention is also useful as an air filter and a liquid filter.

[0051]

Next, the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these examples. In addition, physical properties are shown below in parts, and% means parts by mass and% by mass unless otherwise specified. Each measured value in the examples is a value measured by the following method.

(1) Method of measuring characteristic values of polyvinyl alcohol resin Measured according to JIS-K6726.

(2) Basis Weight (g / m ² ) of Nonwoven Fabric According to JIS P8124, the nonwoven fabric is cut into a 10 cm square, and its mass W is measured by an electronic balance (AE1 manufactured by Mettler Co., Ltd.).
60/60) and a value measured by W / 0.01.

(3) Strength and breaking length (km) of the nonwoven fabric According to JIS P8113, the nonwoven fabric is 15 mm × 25 mm.
Strength using a test piece cut to 0 mm (kg / 15 m
m) was measured, and the breaking length was calculated.

(4) Alkali Resistance According to JIS P8113, a nonwoven fabric test piece was
It was immersed in a 10% aqueous sodium hydroxide solution at 60 ° C. for 60 hours. Strength of test piece before and after treatment (kg / 15m
m) was measured and represented by its strength retention. (5) Oxidation-deterioration resistance According to JIS P8113, a test piece of non-woven fabric is made of 5% K.
It was immersed in a mixed solution of MnO ₄ and 30% potassium hydroxide (former / latter = 250/50 cc, 50 ° C.) for 1 hour. The strength (kg / 15 mm) of the test piece before and after the treatment was measured and represented by the strength retention. (6) Liquid Retentivity A test piece obtained by cutting a nonwoven fabric into a square of 5 cm was immersed in a 30% potassium hydroxide solution at 20 ° C. for 30 minutes, and drained in the air by gravity for 30 seconds. The mass of the test piece before treatment was W0 and the mass of the test piece after treatment was W1, and the mass ratio (W1 / W0) was calculated as the total liquid absorption (g / g). In addition, after draining by natural fall, the test piece was
The sample was dehydrated with a centrifugal dehydrator at a centrifugal force of 0 G for 10 minutes, and the mass ratio between the mass of the test piece after centrifugation (W2) and the mass before treatment (W0) was determined as the liquid absorption (g / g) of the fiber. Was.

Synthesis Example 1 (Synthesis of polypropylene having a boronic acid ethylene glycol ester group at the end) In a separable flask equipped with a cooler, a stirrer and a dropping funnel, polypropylene @ MI: 22 g / 10 min (230
° C, load 2160 g), density 0.91, terminal double bond amount 0.020 meq / g｝ 1000 g, decalin 2500
g, and degassing was performed by reducing the pressure at room temperature, followed by purging with nitrogen. Trimethyl borate 78
g, 5.8 g of borane-triethylamine complex,
After reacting at 200 ° C. for 4 hours, a distillation apparatus was attached, and 100 ml of methanol was slowly added dropwise. After completion of the dropwise addition of methanol, low boiling impurities such as methanol, trimethyl borate and triethylamine were distilled off by distillation under reduced pressure. Further, 31 g of ethylene glycol was added, and the mixture was stirred for 10 minutes, reprecipitated in acetone, and dried to give a boronic acid ethylene glycol ester group amount of 0.015 me.
Polypropylene (boronic acid-modified polypropylene, hereinafter abbreviated as B-PP) with q / g and MI of 21 g / 10 min was obtained.

Synthesis Example 2 (Synthesis of Ultra-Low Density Polyethylene Having a Boronic Acid Ethylene Glycol Ester Group) Ultra Low Density Polyethylene M instead of Polypropylene
I: Boronic acid-modified ethylene glycol ester group in the same manner as in Synthesis Example 1 except that 7 g / 10 min (210 ° C., load 2160 g), density 0.89, terminal double bond amount 0.048 meq / g｝ were used. 0.027 meq / g, M
An ultra low density polyethylene (boronic acid-modified polyethylene, hereinafter abbreviated as B-PE) of I5 g / 10 min was obtained.

Examples 1 and 2, Comparative Example 1 70% by mass of polypropylene (MI = 20, hereinafter sometimes abbreviated simply as "PP"), degree of polymerization 330, degree of saponification 97.6 mol%, degree of ethylene modification 30% by mass of 10 mol% of modified polyvinyl alcohol (Table 1: Reference Example 1), and 5 parts by mass of B-PP obtained in Synthesis Example 1 as a compatibilizer based on 100 parts by mass of PP and modified polyvinyl alcohol in total. The mixture was melt-kneaded at a set temperature of 230 ° C. using a twin-screw extruder to obtain a blend polymer pellet. The core-sheath type composite fiber having a core / sheath mass ratio of 1/1 is hot melt-spun at 240 ° C. so that the obtained pellet is a sheath component and PP alone is a core component, stretched, crimped and cut. As a result, raw cotton having a single fiber denier of 2 dtex and a cut length of 51 mm was obtained (proportion of the blended polymer on the fiber surface = 100%). This raw cotton and the core-sheath type binder fiber raw cotton (core PP / sheath PE = 1 /
1, the melting point of PP is 160 ° C. and the melting point of PE is 105 ° C.)
0:30 (Example 1), 50:50 (Example 2), 0:10
0 (Comparative Example 1), and a separator was obtained by carding, hydroentanglement, and calendering (140 ° C). Table 2 shows the evaluation results of the obtained separator.

[0059]

[Table 1]

[0060]

[Table 2]

Examples 3 and 4 The same procedures as in Example 1 were carried out except that the mixing ratio of PP and PVA was 50:50 (Example 3) and 30:70 (Example 4) and pelletized. In the same manner, raw cotton was obtained, and a separator was obtained at a mixing ratio of 70:30 with the raw cotton binder. Table 2 shows the performance of the obtained separator.

Comparative Examples 2 and 3 In place of using the blended polymer as the sheath component, raw cotton was prepared in the same manner as in Example 1 except that PP alone (Comparative Example 2) and PVA alone (Comparative Example 3) were used as the sheath component. A separator was obtained at a mixing ratio of 70:30 with the raw cotton binder. Table 2 shows the performance of the obtained separator.

Example 5, Comparative Examples 4 and 5 In Example 1, the amount of the compatibilizer B-PP was changed to 10 parts by weight (Example 5), 0 parts by weight (Comparative Example 4), and 100 parts by weight (Comparative Example). 5)
Except for the above, raw cotton and a separator were obtained and evaluated in the same manner as in Example 1. Table 2 shows the results.

Example 6 Instead of "B-PP" as a compatibilizer, polypropylene (MF) having 1.0% by mass of maleic acid modified in a side chain was used.
R = 180) was blended with PP and PVA in an amount of 10 parts by mass and pelletized in the same manner as in Example 1 to obtain and evaluate raw cotton and a separator. Table 2 shows the results.

Examples 7, 8, and 9 Pellets and raw cotton were obtained in the same manner as in Example 1 except that PVA shown in Table 1 (Reference Examples 2, 3, and 4) was used to obtain a separator. Table 2 shows the performance of the obtained separator.

Example 10 Low-density polyethylene (MI = 70, melting point: 105 ° C., hereinafter sometimes abbreviated to PE) was 70% by mass, modified polyvinyl alcohol used in Example 8 was 30% by mass, and a compatibilizing agent was used. 5 parts by mass of B-PE obtained in Synthesis Example 2 with respect to PE and PVA, and a twin-screw extruder was used to set a temperature of 2
The mixture was melt-kneaded at 30 ° C. to obtain a blend polymer pellet. 250 ° C. so that the blend polymer is a layered split conjugate fiber in which the components of the fiber cross section are composed of six layers and the blend polymer used in Example 9 is alternately arranged in the components of five layers.
The fiber is melt-spun, stretched and cut to obtain a single fiber having a fineness of 1.
A split composite cut fiber having 7 dtex and a cut length of 3 mm and divided into 11 layers was obtained (proportion of the blended polymer on the fiber surface = 100%). This cut fiber was dispersed in water, taken out into a 400-mesh wire net, subjected to a water entanglement treatment, and then calendered (130 ° C.) to obtain a separator. Table 2 shows the performance of the obtained separator.

Example 11 The spun yarn of the splittable conjugate fiber obtained in Example 10 was stretched and then crimped and then cut to obtain a single fiber fineness of 3.3 dtex.
A raw cotton with a cut length of 51 mm was obtained. This was made into a nonwoven fabric in the same manner as in Example 1 to obtain a separator. Table 2 shows the performance of the obtained separator.

Example 12 The blended polymer and PP used in Example 1 were melt-kneaded by different extruders, and the blended polymer and PP alone were heated at 240 ° C. at 240 ° C. After melt spinning, stretching, crimping and cutting, a raw cotton having a single fiber denier of 2.2 dtex and a cut length of 51 mm was obtained. This raw cotton and the core-sheath type binder fiber raw cotton used in Example 1 were mixed at a mass ratio of 80:20, carded and calendered (150 ° C.) to obtain a separator. Table 2 shows the evaluation results of the obtained separator.

Example 13 The blend ratio of the blend polymer of Example 12 and PP alone was 6
A separator was obtained in the same manner as in Example 12, except that the ratio was set to 0/40. Table 2 shows the evaluation results of the obtained separator.

Comparative Example 6 A separator was obtained in the same manner as in Example 12, except that the mass ratio of the blend polymer to PP alone was 10/90. Table 2 shows the evaluation results of the obtained separator.

[0071]

According to the present invention, while having a hydrophilic property, that is, a sufficient liquid retaining property for an electrolytic solution, the nonwoven fabric made of polyolefin fibers also has an excellent oxidation-deterioration resistance.
A battery separator can be provided.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hideharu Iwasaki 2045-1, Sazu, Kurashiki-shi, Okayama Prefecture F-term (reference) 4L035 AA05 BB31 DD19 FF01 FF05 GG01 HH05 HH10 LA03 MA05 MA10 4L047 AA14 AA16 AA18 AA27 AA28 AB10 BA04 BA09 BB02 BB09 CB07 CB10 CC12 DA00 EA02 5H021 CC02 EE02 EE04 EE05 EE23 HH01

Claims (6)

[Claims] 1. Polyolefin resin (A) 4.5 to 95
% By mass and polyvinyl alcohol resin (B) 4.5 to 4.5
20% by mass of a fiber in which a blend polymer comprising 95% by mass and 0.5 to 30% by mass of a compatibilizer (C) of the resin (A) and the resin (B) is exposed on the fiber surface by 20% or more. %
A nonwoven fabric comprising the above. 2. The nonwoven fabric according to claim 1, wherein the polyolefin resin (A) is polypropylene. 3. The nonwoven fabric according to claim 1, wherein the polyvinyl alcohol resin (B) is a modified polyvinyl alcohol containing 1 to 55 mol% of ethylene in the main chain. 4. The compatibilizer (C) is at least one functional group selected from the group consisting of a boronic acid group, a borinic acid group, and a boron-containing group capable of being converted to a boronic acid group or a borinic acid group in the presence of water. A polyolefin resin (A) and a polyvinyl alcohol-based resin (B)
The nonwoven fabric according to any one of claims 1 to 3, wherein 1 to 100 parts by mass is blended with respect to 100 parts by mass. 5. A battery separator comprising the nonwoven fabric according to any one of claims 1 to 4. 6. A battery incorporating the battery separator according to claim 5.