JPH11354094A - Manufacture of battery separator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a battery separator having low METSUKE (mass per unit area of fabric) and no defect in relation to a manufacturing method of a battery separator formed from a divided type ultrafine fiber. SOLUTION: This manufacturing method of a battery separator uses a wet- type abstractively produced web manufacture by dividing a division type composite fiber, capable of being divided into at least two or more extrafine fibers into ultrafine fibers by the use of mechanical shearing force. A thermal fusion process or a water stream entangling process may also be applied to the wet- type abstractively produced web. In addition, it is preferable that an electrolytic solution retention property be improved by applying a hydrophilic process, in particular, a graft processing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a battery separator.

[0002]

2. Description of the Related Art A nonwoven fabric made of ultrafine fibers has a large specific surface area of fibers and a small fiber diameter, and therefore has excellent separation properties, liquid holding properties, wiping properties, concealing properties, and flexibility. It is preferably used. In particular, battery miniaturization and capacity increase have recently been promoted, and battery separators have been required to be thinner, so that nonwoven fabric made of ultrafine fibers can be used very advantageously. Methods for obtaining ultrafine fibers are roughly classified into a sea-island method, a straight spinning method, and a division method.

[0003] Non-woven fabrics using sea-island type ultrafine fibers are disclosed in JP-B-45-6297 and JP-B-45-9907.
Non-woven fabrics disclosed in Japanese Patent Publication No. Sho 60-7723 and the like are known, but in order to obtain a non-woven fabric consisting of the sea-island type ultrafine fibers, a solvent for dissolving the sheath component must be used. In addition, equipment for the melting process must be installed.

[0004] In the case of obtaining a non-woven fabric made of a direct spinning type ultrafine fiber, it is difficult to operate stably for a long time.
In order to stably obtain a nonwoven fabric having a uniform basis weight, it is necessary to use a plurality of spinning machines, which has disadvantages that the production equipment becomes large and the cost is high. Further, the spun fiber has a disadvantage that it is difficult to increase the mechanical strength of the nonwoven fabric because the fiber has a small diameter and is not oriented. Therefore, it is difficult to obtain the mechanical strength required for the battery assembling process by using the nonwoven fabric of the straight spinning method.

[0005] Non-woven fabrics made of divided ultrafine fibers are disclosed in JP-A-4-185793 and JP-A-8-26031.
In JP-A No. 6 and the like, there is an example in which a splittable conjugate fiber is divided by a hydroentanglement treatment. In this case, the mechanical strength of the nonwoven fabric can be increased by entanglement of the fibers at the same time as the division, and a nonwoven fabric with an excellent texture can be obtained. Therefore, this method is suitable as a method for obtaining a nonwoven fabric made of ultrafine fibers. However, when manufacturing a battery separator having a low basis weight, there is a problem that the hydroentanglement marks become pinholes and hinder the separability and concealment.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing a separator for a battery made of a split-type ultrafine fiber, and to provide a method for producing a battery separator having a low weight and having no defects.

[0007]

Means for Solving the Problems The present inventors have made intensive studies to solve the above-mentioned problems, and as a result, have found the following invention.

(1) A method for producing a battery separator using a wet papermaking web containing at least one type of splittable conjugate fiber (hereinafter, fiber A) which can be split into at least two or more ultrafine fibers (hereinafter, fiber B). The method for producing a battery separator according to claim 1, wherein at least a part of the fiber A is divided into the fiber B by using a mechanical shearing force, and then a wet papermaking web is produced.

(2) The method for producing a battery separator according to (1), wherein the wet papermaking web is subjected to a heat fusion treatment.

(3) The method for producing a battery separator according to (1) or (2), wherein the wet papermaking web is subjected to a hydroentanglement treatment to split the remaining fibers A to generate fibers B.

(4) The aspect ratio of the fiber B is 800 to 4
The method for producing a battery separator according to any one of claims 1 to 3.

(5) The method for producing a battery separator according to any one of claims 1 to 4, wherein the fineness of the fiber B is 0.5 denier or less.

(6) The method for producing a battery separator according to any one of claims 1 to 5, wherein the wet papermaking web is subjected to a hydrophilic treatment.

(7) The method for producing a battery separator according to claim 6, wherein the hydrophilic treatment is a graft treatment.

In the method (1) for producing a battery separator according to the present invention, one or more types of splittable conjugate fibers (hereinafter referred to as fiber A) which can be split into at least two or more ultrafine fibers (hereinafter referred to as fiber B) are contained. In a method for producing a battery separator using a wet papermaking web, a wet papermaking web is produced after at least a part of the fiber A is divided into fibers B using mechanical shearing force. Therefore, there is an advantage that defects such as pinholes are not formed unlike the case where the fiber A is divided by the hydroentanglement treatment. Also, when producing a wet papermaking web, while the fibers are moderately entangled,
Since the water retention is also good, a uniform web can be produced.

In the method (2) for producing a battery separator according to the present invention, the wet-laid web is subjected to a heat-sealing treatment, whereby the mechanical strength required for the battery separator can be obtained. In the case where the hydroentanglement mark is not a problem, for example, when the weight of the battery separator is large, as in the method for producing the battery separator (3) of the present invention, the wet papermaking web is subjected to the hydroentanglement treatment and remains. By dividing the fiber A to generate the fiber B, a battery separator having a higher content of the fiber B can be obtained.

The aspect ratio of the fiber B suitable for the method for producing a battery separator of the present invention is from 800 to 4000,
The fineness of the fiber B is 0.5 denier or less, and the properties of the obtained battery separator, such as separability, concealing property, and electrolyte retaining property, are good.

As in the method (6) for producing a battery separator according to the present invention, by performing a hydrophilization treatment on the wet papermaking web, it is possible to improve the electrolyte-retaining property of the battery separator. As the hydrophilization treatment, a graft treatment is preferable from the viewpoint that the electrolyte retention ability is maintained for a long time.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
The splittable conjugate fiber (hereinafter, fiber A) fiber that can be split into at least two or more ultrafine fibers (hereinafter, fiber B) according to the method for producing a battery separator of the present invention is at least two types having low compatibility with each other. Is a conjugate fiber (for example, JP-B-48-28005) which is easily split by the action of mechanical shearing force to generate a fiber B. As a component constituting the fiber A, an organic component such as polyester, polyolefin, polyacrylonitrile, polyvinyl alcohol, polyamide, and regenerated cellulose is used. These components can be used in combination in consideration of compatibility. In addition, even with the same component, the degree of polymerization can be changed, mixed with other components, or subjected to chemical modification to change the compatibility to form a composite fiber. Examples include a combination of polypropylene and polyethylene.

The cross-sectional shape of the fiber A according to the method for producing a battery separator of the present invention is, for example, as shown in FIGS.
3D, one resin component 1 and another resin component 2 shown in FIG. 3E are alternately laminated in a layer shape. Anything can be used.

The cross-sectional shape of the fiber B is a wedge shape, a substantially elliptical shape, a circular shape, an elliptical shape, a flat shape, or the like. The aspect ratio of the fiber B is 800 to 4000, the fineness thereof is preferably 0.5 denier or less, and the average fiber diameter is, in terms of circular cross section,
0.1 to 6 μm is preferred. If the average fiber diameter is less than 0.1 μm, the mechanical strength of the nonwoven fabric decreases. On the other hand, when the average fiber diameter exceeds 6 μm, the specific surface area decreases, and the feeling becomes poor.

The fineness of the fiber A itself according to the present invention is 0.1.
It is 5 to 8 denier, more preferably 0.5 to 6 denier. When the fiber A having a thickness of more than 8 denier is used, the pressure is difficult to reach the center of the fiber because the fiber is thick in the splitting process, and it is difficult to split the fiber into the fiber B.

In the method for producing a battery separator of the present invention, the method of dividing at least a part of the fiber A into the fiber B by using mechanical shearing force includes dispersing the fiber A in water, using a beater and a refiner. Disintegrate with etc.

In the method for producing a battery separator according to the present invention, the state in which the fiber A is divided includes the state in which the fiber A is completely divided into the fiber B and the generation of the fiber B from the fiber A, the fiber B, and the fiber A. And a state in which the fiber C is being mixed (hereinafter referred to as fiber C). In the state where the fiber B is completely divided,
Since fibers may be entangled during wet papermaking, fiber A,
A state in which the fibers B and C are mixed is more preferable. Fiber C
(A) Separated and separated from the tip like pine needles (b) Separated at the antinode of fiber (c) Separated from fiber A to fiber B in bundles (d) (a) ) To (c) in which fibers are mixed.

In the method for producing a battery separator of the present invention, a web is produced by a wet papermaking method. In the wet papermaking method, a uniform web can be obtained. First,
Fiber B alone or fiber in which fiber A, fiber B and fiber C are mixed is defibrated and dispersed in water. At this time, a dispersant can be appropriately added. Subsequently, the slurry is gently stirred and uniformly dispersed to prepare a slurry. At this time, it is preferable to add a papermaking adhesive such as a high molecular weight polyethylene oxide or a high molecular weight polyacrylamide aqueous solution. Using the slurry thus prepared, a web is produced by a papermaking method to produce a wet papermaking web. In this case, a binder may be used.

In the method for producing a battery separator according to the present invention, in addition to fiber A, for example, recycled fiber such as rayon, semi-synthetic fiber such as acetate, nylon, vinylon, vinylidene, polyvinyl chloride, polyester, acrylic, Polyolefins such as polyethylene and polypropylene, synthetic fibers such as polyurethane, polyclar, or ethylene-vinyl alcohol copolymer, vegetable fibers such as cotton, and animal fibers such as wool can be mixed. In order to increase the mechanical strength of the non-woven fabric, particularly by a heat fusion treatment, as in the method (2) for producing the battery separator of the present invention, a single resin component or a core-sheath type, a parallel type, or an eccentric type It is preferable to use a heat-fusible fiber composed of a plurality of resin components such as a mold.

In the method for producing the battery separator (3) of the present invention, particularly when a high-weight battery separator is to be obtained, the wet-laid web is subjected to a hydroentanglement treatment so that the remaining fiber A is divided into fibers. B can be generated.
The hydroentanglement treatment is performed by laminating a single layer or a plurality of wet papermaking webs and placing them on a support of about 50 to 200 mesh,
Inject water flow from above.

The diameter of the nozzle for injecting the water stream is 10 to
A range of 500 μm is preferred. Nozzle spacing is 10-1
500 μm is preferred. These nozzles need a range that covers the width of the wet papermaking web in the direction perpendicular to the transport direction, and in the papermaking direction, the fiber A is sufficiently split in consideration of the web type, basis weight, processing speed, and water pressure. The number of nozzle heads can be changed and used within the range. Also,
The number of confounds can also be arbitrarily selected.

The water pressure is preferably in the range of 10 to 250 kg / cm ² . More preferably, 50 to 250
kg / cm ² . If it is less than 10 kg / cm ² , sufficient fiber entanglement cannot be obtained. If it is greater than 250 kg / cm ² , the web breaks due to the fibers falling off from the web. However, the water pressure can be changed depending on the size of the basis weight and the size of the rigidity of the fiber.

The conveying speed of the wet papermaking web is 5 to 200 m.
/ Min range. If the transport speed is low, the web may be damaged by a water stream hitting the web, and this is not preferable in terms of production efficiency. If the transport speed is too high, the energy required for dividing the fiber A cannot be provided.

In the water entanglement process, entanglement can be performed from only one side or both sides. After the confounding, it is also possible to further laminate a web or the like and perform the confounding.

The wet papermaking web that has been subjected to the hydroentanglement treatment is subjected to a method such as suction or wet press for removing excess moisture during or after the entanglement treatment.
Drying can be performed using an air dryer, an air through dryer, a suction drum dryer, or the like.

The hydrophilizing treatment according to the method (6) for producing a battery separator of the present invention includes a grafting treatment, a sulfonation treatment, a surfactant immersion treatment, a corona treatment, a plasma treatment, a fluorine gas treatment, a resin coating treatment and the like. Say. Among these treatments, a graft treatment in which hydrophilicity is maintained semi-permanently is particularly preferable.

Examples of the grafting method according to the method (7) for producing the battery separator of the present invention include a method of immersing a wet papermaking web in a solution containing a monomer and a polymerization initiator and then heating the wet papermaking web, a method of adding a monomer to the wet papermaking web. There is a method of irradiating radiation after application of a varnish, a method of irradiating a wet paper web with a monomer after irradiating it, a method of immersing the wet paper web in a solution containing a sensitizer and a monomer, and then irradiating ultraviolet rays. However, the grafting treatment by ultraviolet rays does not deteriorate the fiber,
Hydrophilic papermaking webs can be imparted with hydrophilicity.

The monomers that can be used in the grafting process according to the method (7) for producing the battery separator of the present invention include (meth) acrylic acid, crotonic acid, vinyl acetic acid, maleic acid, fumaric acid, itaconic acid and the like. Unsaturated carboxylic acids and their derivatives can be used as monomers.

Examples of sensitizers that can be used in the graft polymerization treatment with ultraviolet light include benzoin butyl ether, benzoin ethyl ether, benzyl dimethyl ketal, diethoxyacetophenone, acyloxime ester, chlorinated acetophenone, hydroxyacetophenone, acylphosphine oxide and the like. Sensitizers having an acetophenone structure, benzophenone, Michler's ketone,
Examples thereof include sensitizers having a thioxanson structure such as dibenzosuberone, 2-ethylanthraquinone, isobutylthioxanson, and benzyl; peroxides such as benzoyl peroxide; and metal ions.

The graft polymerization treatment using ultraviolet rays is preferably performed under deoxygenation. Under deoxygenation, ultraviolet light irradiated with nitrogen is light in the region of 200 to 400 nm, the sensitizer is excited by receiving this light, and hydrogen is extracted from the polyolefin constituting the fibers of the wet papermaking web. Form radicals. The generated radical reacts with the above monomer to initiate polymerization. It is preferable that the monomer not contributing to the graft reaction and the homopolymer not chemically bonded to the fiber be removed through a washing step after polymerization.

As a medium of the solution or dispersion in which the monomer and the sensitizer are dissolved, water can be used advantageously. If the solubility of the monomer or sensitizer in water is low,
Various organic solvents can be added.

[0039]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to embodiments.

Example 1 Production of a wet papermaking web A fineness of 2 denier made of polypropylene and high density polyethylene (melting point 128 ° C.) having a cross-sectional shape as shown in FIG. 1 (d), and 0.1 denier (3 .5μ
m), using a splittable conjugate fiber having a fiber length of 5 mm, the mixture was disintegrated by a Niagara beater for 20 times. Split fiber is 95
It was 0%. A denier of 2.0 denier composed of 65 parts by weight of the splittable conjugate fiber, polypropylene as a core component, and low-density polyethylene as a sheath component (melting point: 110 ° C.);
30 parts by weight of a core-sheath fiber having a fiber length of 10 mm and hot water-soluble polyvinyl alcohol fiber (VPW103; manufactured by Kuraray) 5
And 1 part by weight of a nonionic surfactant in a solution impregnated with water, and the mixture was poured into water, and stirred with a high-speed mixer for 3 minutes to disintegrate the fibers. (Manufactured by Seisakusho Co., Ltd.). Next, a 0.1% by weight aqueous solution of polyacrylamide (viscosity agent) was promptly added, followed by gentle stirring to prepare a uniform slurry. Using this slurry, a wet papermaking web having a width of 50 cm and a basis weight of 35 g / m ² (low basis weight) was produced with a round paper machine.

[0041] The heat-sealing the wet papermaking web through 120 ° C. hot air dryer,
Only the low-density polyethylene component of the core-sheath fiber was fused.
The cross section of the fiber of the web after the heat fusion treatment was observed with a scanning electron microscope, and it was confirmed that the fiber was divided (FIG. 2).

Hydrophilic treatment The above wet papermaking web was treated with polyoxyethylene alkylpropenyl phenyl ether (NE-10: manufactured by Asahi Denka) 1
Parts by weight, acrylic acid 50 parts by weight, benzophenone 0.5
Immersed in a treatment solution consisting of 49 parts by weight of ion-exchanged water and then irradiated with low-wavelength ultraviolet rays for 1 minute using a low-pressure mercury lamp under deoxygenation, followed by washing with ion-exchanged water and graft polymerization. To obtain a nonwoven fabric which has been subjected to a hydrophilic treatment. The nonwoven fabric was used as a battery separator. There was no pinhole visually observed in the battery separator. In addition, nickel-
A hydrogen secondary battery was manufactured. This battery had a high capacity and operated stably for a long time.

Example 2 Production of wet papermaking web A fineness of 2 denier made of polypropylene and high density polyethylene (melting point 128 ° C.) having a cross-sectional shape as shown in FIG. 1 (d), and 0.1 denier (3 .5μ
m), using a splittable conjugate fiber having a fiber length of 5 mm, the mixture was disintegrated by a Niagara beater for 20 times. Split fiber is 95
It was 0%. A denier of 2.0 denier composed of 65 parts by weight of the splittable conjugate fiber, polypropylene as a core component, and low-density polyethylene as a sheath component (melting point: 110 ° C.);
30 parts by weight of a core-sheath fiber having a fiber length of 10 mm and hot water-soluble polyvinyl alcohol fiber (VPW103; manufactured by Kuraray) 5
And 1 part by weight of a nonionic surfactant was impregnated with water, and the mixture was poured into water and stirred for 3 minutes with a high-speed mixer to disintegrate the fibers. (Manufactured by Seisakusho Co., Ltd.). Next, a 0.1% by weight aqueous solution of polyacrylamide (viscosity agent) was promptly added, followed by gentle stirring to prepare a uniform slurry. Using the slurry, a wet papermaking web having a width of 50 cm and a basis weight of 60 g / m ² (higher basis weight) was produced with a round paper machine.

[0044] The heat-sealing the wet papermaking web through 120 ° C. hot air dryer,
Only the low-density polyethylene component of the core-sheath fiber was fused.
The cross section of the fiber of the web after the heat fusion treatment was observed with a scanning electron microscope, and it was confirmed that the fiber was divided.

Water entanglement treatment The wet papermaking web was laminated on a porous support made of 100-mesh stainless wire, conveyed at a speed of 10 m / min, and entangled with a columnar water flow using the nozzle head shown in Table 1. Was done. Under the same conditions, the hydroentanglement process was performed also from the back surface. The nonwoven fabric after the hydroentanglement treatment was dried at 120 ° C. using a suction through dryer.

[0046]

[Table 1]

Hydrophilic treatment The wet paper web after the hydroentanglement treatment was treated with polyoxyethylene alkylpropenyl phenyl ether (NE-1).
0: manufactured by Asahi Denka) 1 part by weight, 50 parts by weight of acrylic acid, 0.5 parts by weight of benzophenone, and 49 parts by weight of ion-exchanged water. For 1 minute, followed by a washing treatment using ion-exchanged water to obtain a non-woven fabric subjected to a hydrophilic treatment by graft polymerization. The nonwoven fabric was used as a battery separator. In addition, a nickel-hydrogen secondary battery was manufactured using the battery separator. This battery had a high capacity and operated stably for a long time.

[0048]

As described above, according to the method for manufacturing a battery separator of the present invention, a battery separator made of a divided ultrafine fiber can be easily obtained. Especially,
Even with a low basis weight, a battery separator free from defects such as pinholes can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an example of a cross-sectional shape of a splittable conjugate fiber according to the present invention.

FIG. 2 is an electron micrograph showing a cross section of a fiber in a nonwoven fabric after pressure treatment in Example 1.

[Explanation of symbols]

 1 One resin component 2 Other resin components

Claims (7)

[Claims] At least two or more ultrafine fibers (hereinafter referred to as “fine fibers”)
Splittable conjugate fiber that can be split into fibers B) (hereinafter fiber A)
In a method for producing a battery separator using a wet papermaking web containing one or more types, a mechanical shearing force is used,
A method for producing a battery separator, comprising producing a wet papermaking web after at least part of the fibers A is divided into fibers B. 2. The method for producing a battery separator according to claim 1, wherein the wet papermaking web is subjected to a heat fusion treatment. 3. The method for producing a battery separator according to claim 1, wherein the wet papermaking web is subjected to a hydroentanglement treatment to divide the remaining fibers A to generate fibers B. 4. The fiber B has an aspect ratio of 800 to 400.
The method for producing a battery separator according to any one of claims 1 to 3, which is 0. 5. The method for producing a battery separator according to claim 1, wherein the fineness of the fiber B is 0.5 denier or less. 6. The method for producing a battery separator according to claim 1, wherein the wet papermaking web is subjected to a hydrophilic treatment. 7. The method for producing a battery separator according to claim 6, wherein the hydrophilic treatment is a graft treatment.