JP2000133237A - Cell separator and cell using same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cell that has a long-term appreciable hydrophilic property, a low internal pressure when incorporated in a battery, and a long cycle life, because of the inclusion of a hydrophilic polyolefin-series fiber consisting of a polyolefin-series resin at least partly mixed with a hydrophilicity agent of a weight-average molecular weight of from 200 to 1000. SOLUTION: A polypropylene resin of a melt flow rate of about 30 g/10 min (230 deg.C) is mixed with such a hydrophilicity agent as sodium alkanesulfonate of a weight-average molecular weight of 314 in an amount of from 0.2 to 10% by weight. The obtained resin is then melted, spun, elongated, and supplied with a hydrophilic fiber-setting agent, prior to cut into elements of 10 mm length and 0.9 dtex. The obtained fiber in an amount of 60% by weight is mixed with such a thermo-adhesive fiber as a sheath-core conjugate fiber in an amount of 40% by weight comprising a polypropylene core and a polyethylene sheath, before subjected to the wet-type sheeting process. This sheet is in turn heat-treated and heat-calendered for thickness control to complete the cell separator.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery separator suitable for alkaline storage batteries such as nickel-cadmium batteries, nickel-zinc batteries, nickel-metal hydride batteries, and the like, and batteries using the same.

[0002]

2. Description of the Related Art Generally, non-woven fabrics made of a nylon or polypropylene fiber manufactured by a dry process (hereinafter referred to as dry non-woven fabric) and non-woven fabrics manufactured by a wet papermaking process (hereinafter referred to as wet non-woven fabric) are used as battery separators. Although nonwoven fabrics made of nylon fibers are inferior in alkali resistance, nonwoven fabrics made of polyolefin fibers such as polypropylene are preferably used.

However, nonwoven fabrics made of polyolefin fibers are hydrophobic and have poor wettability when used for battery separators. A method of performing a hydrophilic treatment is being studied. The former includes a method in which a hydrophilic oil agent is attached to the fiber surface as a fiber treatment agent on the polyolefin fiber, or a method in which a hydrophilic agent is mixed with the fiber. The latter includes a sulfonation treatment, a fluorination treatment, a graft polymerization treatment of a vinyl monomer, a corona discharge, a plasma treatment and the like. However, in the latter case, the sulfonation treatment, the fluorination treatment, and the graft polymerization treatment of a vinyl monomer are not only complicated in processing method and increase the cost, but also tend to be avoided due to environmental problems such as waste liquid. In the case of corona discharge or plasma treatment, the discharge energy is not transmitted to the inside of the nonwoven fabric, the hydrophilicity inside the nonwoven fabric is reduced, and the hydrophilicity at the time of charge / discharge under pressure is insufficient.

On the other hand, the former does not require a complicated process,
It is excellent in that substantially uniform hydrophilicity can be obtained even from the outside to the inside of the nonwoven fabric. As a battery separator using a fiber having a hydrophilic oil agent adhered to the surface as a fiber treating agent, JP-A-7-262979 discloses an alkylbenzenesulfonic acid alkali metal salt, an alkylsulfonic acid alkali metal salt, or an alkylnaphthalene. A battery separator comprising a polyolefin fiber coated with a sulfonic acid anionic surfactant composed of an alkali metal sulfonic acid salt or the like is disclosed. Further, as a battery separator using fibers mixed with a hydrophilizing agent, Japanese Patent Application Laid-Open No.
JP-A-98295 proposes a battery separator using a polyolefin-based fiber in which a thermoplastic nonionic water-absorbing agent is mixed and a heat-fusible core-sheath composite fiber in which the water-absorbing agent is mixed with a sheath component. JP-A-7-105927 discloses a battery separator obtained by laminating a nonwoven fabric mainly composed of a polyolefin-based fiber mixed with a polyalkylene oxide and a nonwoven fabric of an alkali-resistant synthetic fiber,
Further, Japanese Patent Application Laid-Open No. H08-212995 discloses a fiber in which polyethylene oxide is mixed with a polyolefin fiber,
Alternatively, a battery separator containing a composite fiber composed of polyethylene oxide and a polyolefin polymer is disclosed. All of these have been attempted to improve the liquid absorbing property and liquid retaining property of the electrolytic solution.

[0005]

However, the battery separator has the following problems. For example, in the battery separator described in Japanese Patent Application Laid-Open No. 7-262979, although the initial liquid retaining property of the electrolytic solution is excellent, the surfactant is easily washed away when charge and discharge are repeated, and the durability is deteriorated. Inferior. Also, JP-A-5-198295,
JP-A-7-105927 and JP-A-8-21
In the battery separator described in Japanese Patent No. 2995, the hydrophilic agent made of thermoplastic polyethylene oxide hardly bleeds out to the fiber surface, is stable for a long time, and cannot maintain a high degree of hydrophilicity.

The present invention has been made in view of the above problems, and is a hydrophilic polyolefin which is excellent in initial hydrophilicity and durable hydrophilicity, is stable for a long time, and can maintain high hydrophilicity. An object of the present invention is to provide a battery separator made of a system fiber and a battery having excellent battery characteristics.

[0007]

In order to achieve the above object, a battery separator according to the present invention comprises a polyolefin resin having at least a part thereof having a weight average molecular weight of 200 to 100.
A hydrophilic polyolefin-based fiber obtained by mixing 0.2 to 10% by weight of a hydrophilizing agent (referred to as a hydrophilizing agent A) of at least 20% by weight. By adopting such a configuration, a high degree of hydrophilicity can be maintained for a long time, and a battery having a low internal pressure and a long cycle life can be obtained even when incorporated into a battery.

The hydrophilic agent A to be mixed with the hydrophilic polyolefin fiber of the battery separator of the present invention is desirably a metal salt of an organic sulfonic acid. The metal salt of an organic sulfonic acid is desirably a metal salt of an alkanesulfonic acid represented by the following formula (Formula 2).

[0009]

Embedded image

In the alkanesulfonic acid metal salt, the total number of carbon atoms of R ¹ and R ^{2 represented by} the above formula (Formula 2) is 9
Alkanesulfonic acid sodium salt having an alkyl group in which both R ¹ and R ² are an integer of 1 or more.

In the hydrophilic polyolefin fiber, a weight average molecular weight of 1,000 to 10,000 is added to at least a part of the polyolefin resin together with the hydrophilicizing agent A.
It is desirable that 0.2 to 10% by weight of a hydrophilizing agent (referred to as a hydrophilizing agent B) is mixed. Such hydrophilizing agent B
By mixing, the durable hydrophilicity is remarkably improved, the speed balance with the bleeding speed of the organic sulfonic acid metal salt is excellent, and the hydrophilicity can be constantly maintained for a long period of time. Also, a battery having a low internal pressure and a long cycle life can be obtained.

The hydrophilizing agent B has 2 to 4 carbon atoms.
The alkylene oxide adduct having an alkylene group is desirably. Further, the alkylene oxide adduct is desirably an ethylene oxide adduct of a polyhydric alcohol fatty acid ester.

The battery separator of the present invention preferably contains at least 20 to 60% by weight of a polyolefin-based heat-adhesive fiber based on 20 to 80% by weight of a hydrophilic polyolefin-based fiber. Further, a battery separator containing 20 to 60% by weight of a hydrophilic polyolefin-based fiber, 20 to 40% by weight of a polyolefin-based thermoadhesive fiber, and 20 to 60% by weight of an ultrafine fiber having a fineness of 0.5 dtex or less is an ultrafine battery. It is excellent in that the electrolyte can be held in the fine voids formed by the fibers.

The battery incorporating the battery separator has excellent battery characteristics such as battery internal pressure and cycle life. Hereinafter, the contents of the present invention will be specifically described.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Polyolefin resins used in the present invention include polypropylene, polyethylene, polybutene-1, polymethylpentene, ethylene-propylene copolymer, ethylene-propylene-butene-1 copolymer, ethylene- One or two or more selected from vinyl alcohol copolymer, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-methyl acrylate copolymer and the like can be used.

The hydrophilizing agent A mixed with at least a part of the polyolefin resin has a weight average molecular weight of 200 to 10
It is preferable that the amount of the hydrophilizing agent A is 0.2 to 10% by weight. More preferably, the weight average molecular weight is from 200 to 50.
0 of the hydrophilizing agent A is 0.5 to 5% by weight. When the weight average molecular weight is 200 to 1,000, it is preferable because the bleeding rate with the hydrophilic agent B having a weight average molecular weight of 1,000 to 100,000 described later is excellent, and more stable hydrophilicity can be maintained. When the weight average molecular weight of the hydrophilizing agent A is less than 200, it easily bleeds to the fiber surface,
The fiber surface has a tacky feel and a weight average molecular weight of 1
If it exceeds 000, the initial hydrophilicity becomes insufficient. Also,
If the content of the hydrophilizing agent A is less than 0.2% by weight, sufficient hydrophilicity cannot be obtained, and if it exceeds 10% by weight, not only poor spinnability at the time of melt spinning but also high cost is required. Become.

Examples of the hydrophilizing agent A satisfying the weight average molecular weight of 200 to 1000 include alkylene oxide adducts of higher alcohols, alkylene oxide adducts of alkylphenols, alkylene oxide adducts of higher fatty acids, and alkylene oxide additions of higher alkylamines. object,
Alkylene oxide addition type nonionic surfactants such as alkylene oxide adducts of higher fatty acid amides and ethylene oxide adducts of polypropylene oxide, ester type nonionics such as fatty acid esters of glycerol, fatty acid esters of pentaerythritol, and fatty acid esters of sorbitol and sorbitan. Surfactants, anionic surfactants such as fatty acid amides of alkanolamines, alkyl phosphates, sulfates of higher alcohols and sulfates of higher alkyl ethers, or alkyl sulfonates, alkyl benzene sulfonates,
Organic sulfonic acid-based anionic surfactants such as alkyl naphthalene sulfonate, sulfosuccinic acid alkyl ester sodium salt, and alkane sulfonate are exemplified. Among them, a metal salt of an alkane sulfonic acid represented by the above formula (Formula 2), a metal salt of an alkyl sulfonic acid or a metal salt of alkyl allyl sulfonic acid represented by the following formula (Formula 3),

Embedded image R ³ —SO ₃ M (where R ³ represents an alkyl group or an alkyl allyl group having 7 to 29 carbon atoms) or an organic sulfonic acid having a sulfonic acid group such as a metal salt of a sulfosuccinic acid alkyl ester The metal salt is preferably used because it has hydrophilicity, is chemically stable, and has high heat resistance. Among the organic sulfonic acid metal salts, alkyl sulfonic acid metal salt, alkyl allyl sulfonic acid metal salt, and alkane sulfonic acid metal salt have a bleed rate in an electrolyte solution that is a strong alkaline solution such as KOH as compared with water or the like. Since the leaching gradually proceeds slightly later, the durable hydrophilicity is increased, and it is particularly effective for a battery such as a battery that needs to be repeatedly charged and discharged for a long period of time and needs a durable liquid retaining property of the electrolyte.

In particular, R represented by the above formula (Formula 2)
It is preferable that the metal salt of an alkanesulfonic acid having an alkyl group having a total number of carbon atoms of ¹ and R2 of ⁷ to 29 is used. Alkanesulfonic acid metal salts are different from alkylsulfonic acid metal salts or alkylallylsulfonic acid metal salts in that a sulfonic acid group (hydrophilic group) is not present at one end of a hydrophobic group, but is bonded to a part other than the terminal. Therefore, it is preferable because it is rich in permeability and wettability, and particularly excellent in electrolyte retention.

Further, represented by the above formula (Formula 2)
The total number of carbon atoms of R ¹ and R ² is 9 to 23, and R ¹ and R ² are
Alkanesulfonic acid metal salts having an alkyl group in which both carbon atoms of R ² are an integer of 1 or more are particularly preferable in view of the initial liquid retention of the electrolytic solution and its durability.

Examples of the metal salt include alkali metal salts and alkaline earth metal salts, among which lithium salts, sodium salts, potassium salts and the like are preferable. Further, together with the hydrophilizing agent A, at least a part of the polyolefin resin has a weight average molecular weight of 1,000 to 100,000.
May be mixed in an amount of 0.2 to 10% by weight. More preferably, the amount of the hydrophilic agent B having a weight average molecular weight of 1,000 to 10,000 is 0.2 to 10% by weight, and even more preferably, the amount of the hydrophilic agent B having a weight average molecular weight of 1,000 to 10,000 is 0.5 to 5% by weight. is there. When the weight average molecular weight of the hydrophilizing agent B is less than 1,000, the bleeding rate of the metal organic sulfonic acid salt to the fiber surface becomes substantially the same, the durability hydrophilicity becomes insufficient, and when the weight average molecular weight exceeds 100,000, the fiber This is because it is difficult to bleed to the surface, and there is a great difference from the bleeding speed to the fiber surface in the metal salt of organic sulfonic acid, so that it is stable for a long time and high hydrophilicity cannot be maintained. On the other hand, if the content of the hydrophilizing agent B is less than 0.2% by weight, sufficient durable lyophilicity cannot be obtained and 10% by weight
If it exceeds, not only the spinnability at the time of melt spinning is inferior but also the cost becomes high.

Examples of the hydrophilizing agent B satisfying the weight average molecular weight of 1,000 to 100,000 include polyoxyalkylene alkyl ethers having an alkyl group having 9 to 50 carbon atoms, polyoxyalkylene alkyl phenyl ethers, polyoxyalkylene alkyl esters, and Glycerin, polyglycerin, trimethylolpropane,
Alkylene oxide addition of alkylene oxide adducts having 2 to 4 carbon atoms of polyhydric alcohols such as pentaerythritol, sorbitol and sorbitan and / or fatty acid esters thereof, or oligomers having an active hydrogen group such as a hydroxyl group, a carboxyl group or an amino group Things.

Among them, an alkylene oxide adduct having an alkylene group having 2 to 4 carbon atoms is preferable, and an ethylene oxide adduct of a polyhydric alcohol fatty acid ester has high heat resistance and good hydrophilicity. It is preferable because the weight average molecular weight can be easily adjusted to a predetermined range.

There are various ethylene oxide adducts of polyhydric alcohol fatty acid esters, from fatty acid monoesters to full esters, but the heat resistance tends to increase as the esterification rate increases. Therefore, when an ethylene oxide adduct of a polyhydric alcohol fatty acid ester having an esterification rate of 80 mol% or more is used,
It is more preferable in that the heat resistance is improved.

Further, the fatty acid of the ethylene oxide adduct of the polyhydric alcohol fatty acid ester is preferably a hydroxy fatty acid. When an ethylene oxide adduct of a polyhydric alcohol fatty acid ester is synthesized under an alkali catalyst, it is generally difficult to directly add ethylene oxide when the fatty acid is not a hydroxy fatty acid.
Therefore, conventionally, a method of adding a polyhydric alcohol such as water or glycerin and saponifying it to form a partial ester and then adding ethylene oxide or a method of adding ethylene oxide to glycerin and subsequently esterifying with glycerol have been attempted. . However, in the former case, it is difficult to maintain the esterification ratio at 80 mol% or more, and in the latter case, the reaction must be carried out in two stages, ie, an ethylene oxide addition reaction and an esterification reaction. The method becomes complicated and costly. In contrast, when the fatty acid is a polyhydric alcohol fatty acid ester composed of a hydroxy fatty acid such as castor oil or hydrogenated castor oil, the desired adduct can be obtained in a one-step reaction, so that the production is easy. This is particularly excellent in that the cost is reduced.

Then, the above-mentioned hydrophilizing agent A is mixed with at least a part of the polyolefin-based resin and fiberized by known melt spinning. The fiber shape of the polyolefin-based fiber is not particularly limited, and the cross section of a single fiber, a sheath-core composite fiber, an eccentric sheath-core composite fiber, a side-by-side composite fiber, a sea-island composite fiber, a split composite fiber, or the like is circular. And irregular shapes. For example, when used as a conjugate fiber, the hydrophilic agent A may be added to at least one component. In particular, the hydrophilic agent A may be formed so as to occupy at least a part of the fiber surface of the conjugate fiber.

As a method for mixing the hydrophilizing agent A with the polyolefin resin, a known mixing device may be used. For example, mixing is performed with a Henschel mixer, a super mixer or the like, and using a known single-screw or twin-screw extruder. It is convenient to melt-mix and make a master batch in advance. At this time, the polyolefin resin is mixed with additives such as an antioxidant, a stabilizer such as an ultraviolet ray inhibitor and titanium oxide, a metal soap, carbon black, a pigment, an antibacterial agent, and a fungicide, as necessary. Is also good.

When the hydrophilizing agent B is used in combination with the hydrophilizing agent B, the hydrophilizing agent A and the hydrophilizing agent B may be mixed with the polyolefin resin at the same time. In, a predetermined amount may be mixed with the resin.

The fineness of the obtained hydrophilic polyolefin fiber is preferably 10 dtex or less. Fineness is 10
If it exceeds dtex, the amount of the hydrophilizing agent that bleeds to the fiber surface decreases, and the hydrophilicity is insufficient.

The hydrophilic polyolefin-based fiber is made of a non-woven fabric mainly composed of a staple fiber, such as a thermal bond non-woven fabric, a chemical bond non-woven fabric, a high pressure water jet treated non-woven fabric, a needle punched non-woven fabric, a spun-bonded non-woven fabric, a melt-blown non-woven fabric and other long fibers. Non-woven fabric,
Wet non-woven fabric by wet papermaking, non-woven fabric consisting of air-laid non-woven fabric and other short fibers, a laminate thereof, or a wet non-woven fabric having at least a part of the non-woven fabric having a fiber length of 30 mm
A bonded nonwoven fabric in which some of the constituent fibers made of the above fibers are bonded with an adhesive or self-adhesion, a nonwoven fabric entangled by needle punch or high-pressure water flow treatment, or a laminate with another sheet such as a porous film Processed into a non-woven fabric.

Preferably, the content of the hydrophilic polyolefin-based fiber with respect to the nonwoven fabric is at least 20% by weight. More preferably it is at least 40% by weight. If the content is less than 20% by weight, stable and high hydrophilicity cannot be obtained for a long period of time.

The other material to be mixed besides the hydrophilic polyolefin fiber is not particularly limited, and one or more materials selected from polyamide fibers such as nylon 6, nylon 66, or polyolefin fibers are arbitrarily selected. Can be used. The shape of the fiber is not particularly limited, and the cross-section of a single fiber, a sheath-core composite fiber, an eccentric sheath-core composite fiber, a side-by-side composite fiber, a sea-island composite fiber, a split composite fiber, or the like is circular or irregular. And so on.
In particular, the hydrophilic polyolefin-based fiber is 20 to 80% by weight.
To at least 2 heat-bondable polyolefin fibers.
A battery separator made of a nonwoven fabric containing 0 to 60% by weight is excellent in that it exhibits stable electrolyte solution retention properties for a long period of time and attains the necessary strength as a separator. Above all, a wet nonwoven fabric made of short fibers having a fiber length of 3 to 25 mm is preferable in that it is excellent in uniformity, the voids formed between the fibers are small, and a short circuit is unlikely to occur. Polyolefin-based heat-bondable fibers include polypropylene, polyethylene, polybutene-1,
A single fiber containing a low melting point component such as an ethylene-propylene copolymer, an ethylene-propylene-butene-1 copolymer, an ethylene-vinyl acetate copolymer, a sheath-core composite fiber, an eccentric sheath-core composite fiber, The cross section of the side-by-side conjugate fiber, the sea-island conjugate fiber, the split conjugate fiber, or the like may be circular or irregular. In particular, the melting point of the sheath component is 10% of the melting point of the core component.
The sheath-core type composite fiber having a temperature of at least ° C is excellent in thermal adhesion, which is convenient. For example, polyethylene / polypropylene,
Ethylene-propylene copolymer / polypropylene and the like. Of course, a hydrophilizing agent may be provided to at least a part of the heat-adhesive fibers.

Further, a hydrophilic polyolefin fiber is
0 to 60% by weight of polyolefin-based heat-adhesive fiber
A battery separator comprising a nonwoven fabric containing 20 to 60% by weight of ultrafine fibers having a fineness of 0.5 dtex or less and an electrolyte solution can hold an electrolytic solution in fine voids formed by the ultrafine fibers. Is preferred in that it increases. The non-woven fabric is not particularly limited, but has a fiber length of 3 to 25.
A wet nonwoven fabric made of short fibers of mm is preferred. If the fineness of the ultrafine fibers is larger than 0.5 dtex, fine voids cannot be obtained, and the retention of the electrolyte is poor, which is not preferable. Fineness 0.5
The ultrafine fiber of dtex or less may be a fiber that generates an ultrafine fiber such as a split type composite fiber or a sea-island type composite fiber,
If it is a splittable conjugate fiber, a combination of polyolefin resins such as polyolefin / polyester and polyolefin / polyamide, or a combination of polyolefin resins such as polyethylene / polypropylene, and particularly a combination of polyolefin resins,
Heat resistance and alkali resistance are good and preferable. Of course, a hydrophilizing agent may be imparted to the splittable conjugate fiber or the sea-island conjugate fiber itself.

Next, a method for manufacturing the battery separator of the present invention will be described. As a method for producing the nonwoven fabric serving as the base material of the separator of the present invention, a wet papermaking method is desirable. This is because a uniform nonwoven fabric can be obtained by the wet papermaking method. The wet papermaking may be performed by a usual method. First, a hydrophilic polyolefin fiber is dispersed in water so as to have a concentration of 0.01 to 0.6% by weight to prepare a slurry. The slurry is made using a short net type, a circular net type, or a paper machine combining the both. The basis weight can be adjusted by the amount of fiber,
It is desirable to set it to 30 to 100 g / m ² . If it is less than 30 g / m ² , the strength of the nonwoven fabric is low, so that a short circuit is likely to occur between the positive electrode and the negative electrode, and if it exceeds 100 g / m ² , air permeability and the like are reduced.

Next, the wet papermaking fiber web is subjected to high pressure water flow treatment. High pressure water flow treatment is 0.05 ~ 0.5mm
It is preferable to jet a columnar water stream having a water pressure of 2 to 15 MPa to the front and back of the nonwoven fabric at least once from nozzles provided with orifices at intervals of 0.5 to 1.5 mm.

If necessary, the nonwoven fabric is subjected to corona discharge treatment,
Surface modification by plasma treatment, fluorine gas treatment, ultraviolet irradiation, etc., or phosphate anion activator such as alkyl phosphate ester, soap anion activator such as aliphatic carboxylic acid soap, sulfate anion activator such as alkyl sulfate Agent, alkylene oxide adduct of higher alcohol, alkylene oxide adduct of alkylphenol, alkylene oxide adduct of higher fatty acid,
Alkylene oxide adducts of higher alkylamines, alkylene oxide adducts of higher fatty acid amides, alkylene oxide addition type nonionic surfactants such as ethylene oxide adducts of polypropylene oxide, fatty acid esters of glycerol, fatty acid esters of pentaerythritol, sorbitol and sorbitan The surface treatment may be performed by applying a hydrophilic surfactant such as an ester type nonionic surfactant such as a fatty acid ester to improve the hydrophilicity. Thereafter, the calendering treatment is performed to adjust the thickness to a predetermined value, thereby obtaining the battery separator of the present invention.

[0036]

EXAMPLES Hereinafter, the contents of the present invention will be specifically described with reference to examples. The thickness, tensile strength, liquid retention, durable liquid retention, cycle life, and internal pressure of the obtained nonwoven fabric were measured as follows. (1) Thickness Thickness measuring machine (Product name: THICKNESS GAUGE model CR-60A)
(Manufactured by Daiei Kagaku Seiki Seisaku-Sho, Ltd.) under the condition that a load of 20 g was applied per 1 cm ^{2 of} the sample. (2) Tensile strength According to JIS L 1096, a sample piece having a width of 5 cm and a length of 15 cm is gripped at an interval of 10 cm, and is stretched at a tensile speed of 30 cm / min using a constant-speed stretching type tensile tester. The load value was defined as tensile strength. (3) Liquid retention rate and durable liquid retention rate The weight (W) of the test piece in a water equilibrium state is measured up to 1 mg. Next, the test piece was immersed in a KOH solution having a specific gravity of 1.30, and after absorbing the KOH solution for one hour, withdrawn from the solution and allowed to stand for 10 minutes, the weight (W ₁ ) of the test piece was measured and retained. The liquid retention rate was calculated from the formula of liquid rate (%) = ((W ₁ −W) / W) × 100. After immersing the test piece in a KOH solution for 3 months, the test piece was once dried to a water equilibrium state,
Thereafter, the liquid retention rate was measured in the same manner as described above, and this was taken as the durable liquid retention rate. (4) Cylindrical sealed nickel-metal hydride battery The negative electrode was prepared by adding water to a hydrogen storage alloy, carbonyl nickel, carboxymethylcellulose (CMC), and polytetrafluoroethylene (PTFE) and kneading the mixture to prepare a slurry. This slurry was dip-coated on a nickel-plated punching metal, dried at 80 ° C., and molded under pressure to prepare a hydrogen storage alloy negative electrode. For the positive electrode, a known sintered nickel electrode was used. By inserting each separator between the above-mentioned negative electrode and positive electrode, inserting it into a battery case, and pouring the electrolyte,
A cylindrical sealed nickel-metal hydride battery was manufactured. (5) Cycle life The Ni-MH battery prepared above was charged at a charging rate of 0.1 C for 12 hours.
The battery was initialized for 0.5 hours with a discharge rate of 0.1 C and a final voltage of 1.0 V at a discharge voltage of 10 V, and was repeatedly charged and discharged for 10 cycles. After the initial activation, the number of cycles when the utilization rate with respect to the theoretical capacity becomes 90% or less at a charging rate of 0.1 C for 10 hours, a pause time of 0.5 hours, and a discharging rate of 0.1 C (final voltage of 1.0 V). I asked. Charge and discharge were performed at 25 ° C. (6) Internal pressure Assemble the battery with a hole in the bottom of the battery can and a pressure sensor attached. After initial activation using this battery, charging and discharging were repeated 5 times at a charging rate of 0.1 C for 16 hours, a pause time of 0.5 hours, a discharging rate of 0.1 C, and a final voltage of 1.0 V.
Thereafter, the pressure after charging at a 1.0 C rate for 120 minutes was measured.

Example 1 Melt flow rate (M
FR) is 30 g / 10 min (230 ° C.) polypropylene resin (manufactured by Nippon Polychem Co., Ltd.) with a weight average molecular weight of 31.
The masterbatch A was prepared by mixing 20% by weight of the sodium salt of the alkanesulfonic acid of No.4. MFR is 30g / 10mi
n (230 ° C.) polypropylene resin (manufactured by Nippon Polychem Co., Ltd.) mixed with 2.5% by weight of master batch A, using a spinning temperature of 270 ° C. and a take-up speed of 500 m / mi
The melt spinning was performed at n to obtain a 2.3 dtex spun filament. The spun filament is dried at 130 ° C. for 3 hours.
The fiber was drawn twice, and a hydrophilic fiber treating agent mainly composed of polyoxyethylene lauryl ether was applied in an amount of 1.4% by weight, and cut into 10 mm to finally obtain a 0.9 dtex fiber. The resulting hydrophilic polypropylene fiber contained 0.5% by weight of alkanesulfonic acid sodium salt. The obtained fiber is 60% by weight and a heat-adhesive fiber,
Fineness of polypropylene core and polyethylene sheath 1.
Paper is made by a wet papermaking method using 40% by weight of a sheath-core type composite fiber (manufactured by Daiwa Spinning Co., Ltd .: NBF (H)) having a fiber length of 5 dtex and a fiber length of 10 mm, and is heat-treated at 135 ° C. by a Yankee dryer and thickness by a heat calender After adjustment, a battery separator was obtained.

Example 2 Masterbatch A of Example 1
In addition, ethylene oxide 20 of hydrogenated castor oil having a weight average molecular weight of 9700 was added to a polypropylene resin (manufactured by Nippon Polychem Co., Ltd.) having an MFR of 30 g / 10 min (230 ° C.).
20 wt% of a hydrophilizing agent consisting of 0 mol adduct was mixed, and 2.5 wt% of master batch B obtained in the same manner as above was mixed.
Except for mixing, a battery separator was obtained in the same manner as in Example 1. In the obtained hydrophilic polypropylene fiber,
Alkanesulfonic acid sodium salt is 0.5% by weight, and hydrogenated castor oil ethylene oxide 200 mol adduct is 0.5% by weight.
% By weight.

Example 3 Example 1 was repeated except that a polypropylene resin containing 1.5% by weight of the sodium alkanesulfonic acid salt and 1.5% by weight of the hydrophilizing agent of Example 2 was used.
A battery separator was obtained in the same manner as described above.

Example 4 The hydrophilic polypropylene fiber of Example 1 was 40% by weight, and the sheath-core type composite fiber of Example 1 was 3% by weight.
Fineness 2 in which the fiber cross section composed of 0% by weight and a combination of polypropylene / polyethylene is radially divided into 8
dtex, 30% by weight of split type composite fiber with a fiber length of 6 mm,
Paper was made by a wet papermaking method to obtain a wet nonwoven fabric. A columnar flow is sprayed from the front and back surfaces of the obtained nonwoven fabric at a pressure of 5 MPa to divide the splittable conjugate fiber, and the split conjugate fiber is separated by a suction cylinder.
Heat treatment was performed at 5 ° C., and the thickness was adjusted with a heat calender to obtain a battery separator.

Comparative Example 1 A battery separator was obtained in the same manner as in Example 1, except that sodium alkanesulfonic acid was not contained.

Comparative Example 2 0.5% by weight of the masterbatch A of Example 1 was mixed with the polypropylene resin of Example 1 and finally 0.1% of sodium alkanesulfonic acid salt was added.
Thus, a hydrophilic polypropylene fiber containing about 10% by weight was obtained. The obtained fiber was paper-formed in the same manner as in Example 1 to obtain a battery separator. Table 1 shows the physical properties of Examples 1 to 4 and Comparative Examples 1 and 2.

[0043]

[Table 1]

As is clear from Table 1, the products of Examples of the present invention do not show a decrease in liquid retention even when subjected to excessive pressurization and depressurization due to repeated charging and discharging, and always maintain a sufficient amount of electrolyte. It was confirmed that a rise in internal pressure was suppressed and a battery with a long cycle life was obtained.

[0045]

According to the battery separator of the present invention, the weight average molecular weight of 20
A hydrophilic polyolefin-based fiber containing 0.2 to 10% by weight of a hydrophilic agent
When the content is contained in the battery by weight, even if the battery is subjected to excessive pressurization and decompression due to repetition of charge and discharge, no deterioration in liquid retention is observed, and a sufficient amount of electrolyte can be always maintained. Therefore, in a battery using this, an increase in internal pressure is suppressed, and a battery with a long cycle life can be obtained.
Further, when the hydrophilizing agent A is a metal salt of an organic sulfonic acid,
It is chemically stable and has high heat resistance. In particular, alkanesulfonic acid metal salts have excellent durability and liquid retention properties with respect to electrolytes which are strong alkaline solutions such as KOH.

Further, a weight-average molecular weight of at least 10
0.2 to 10% by weight of a hydrophilizing agent B of 100 to 100,000
By using a mixed hydrophilic polyolefin-based fiber, the durable hydrophilicity is remarkably improved, the speed balance with the bleeding speed of the organic sulfonic acid metal salt is excellent, and the stable hydrophilicity can be constantly maintained for a long time, Even when incorporated in a battery, an increase in internal pressure is suppressed, and a battery with a longer cycle life can be obtained.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Yasunobu Takahashi 48-2 Kashiyama, Hashikino-shi, Osaka (72) Inventor Hiroyuki Yamamoto 877 Komiya, Harima-cho, Kako-gun, Hyogo Daiwa Boupolitec Co., Ltd. Person Toyohiko Sano 877 Komiya, Harima-cho, Kako-gun, Hyogo Pref. In Harima Research Laboratory, Daiwa Bopolitec Co., Ltd. (72) Inventor Shuji Hori 877, Komiya, Harima-cho, Harima-cho, Kako-gun, Hyogo Pref. Tomobun 877 Harima-cho, Harima-cho, Kako-gun, Hyogo Prefecture Daiwa Bopolitec Co., Ltd. Harima Research Institute (72) Inventor Tatsunobu Kida 877, Harima-cho, Harima-cho Kako-gun Hyogo Prefecture Harima Research Laboratory F-term (reference) 5H021 CC01 EE04 EE18 EE23 EE32 EE34 HH01 HH03 HH07 5H028 AA05 EE02 EE06 EE08 EE09 HH00 HH01 HH05

Claims (10)

[Claims] 1. A hydrophilic polyolefin fiber in which a hydrophilic agent having a weight average molecular weight of 200 to 1000 (hereinafter referred to as a hydrophilic agent A) is mixed in at least a part of the polyolefin resin at 0.2 to 10% by weight. , At least 20% by weight. 2. The battery separator according to claim 1, wherein the hydrophilizing agent A is a metal salt of an organic sulfonic acid. 3. The metal salt of an organic sulfonic acid is a metal salt of an alkanesulfonic acid represented by the following formula (1).
4. The battery separator according to item 1. Embedded image 4. The total number of carbon atoms of R ¹ and R ^{2 represented by} the above formula (Formula 1) is 9 to 23, and both carbon atoms of R ¹ and R ² are integers of 1 or more. The battery separator according to claim 3, which is an alkanesulfonic acid sodium salt having an alkyl group. 5. In a hydrophilic polyolefin-based fiber,
At least a part of the polyolefin-based resin contains a hydrophilizing agent A
The battery separator according to claim 1, wherein a hydrophilizing agent having a weight average molecular weight of 1,000 to 100,000 (hereinafter, referred to as a hydrophilizing agent B) is mixed in an amount of 0.2 to 10% by weight. 6. The hydrophilizing agent B is an alkylene oxide adduct having an alkylene group having 2 to 4 carbon atoms.
4. The battery separator according to item 1. 7. The battery separator according to claim 6, wherein the alkylene oxide adduct is an ethylene oxide adduct of a polyhydric alcohol fatty acid ester. 8. The method according to claim 1, wherein the hydrophilic polyolefin fiber is 20 to 8 or more.
The battery separator according to any one of claims 1 to 7, comprising at least 20 to 60% by weight of the polyolefin-based heat-adhesive fiber based on 0% by weight. 9. The method according to claim 9, wherein the hydrophilic polyolefin fiber is 20 to 6 hours.
0% by weight, 20-40 polyolefin-based heat-adhesive fibers
20% by weight and ultrafine fibers with a fineness of 0.5 dtex or less
The battery separator according to any one of claims 1 to 8, which contains 60% by weight. 10. A battery incorporating the battery separator according to claim 1.