JPH11149911A - Battery separator, its manufacture, and battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure improvement in liquid absorbency, liquid storage properties, proper air ventilation, and improvement in battery capacitance by a split conjugate fiber being splitted, a extremely thin fiber being formed, an inter-fiber crossing, part of the fiber being mutually bonded, a fiber existing in a surface of a non-woven cloth having a functional group, and a rate of the functional group or bond to all carbon element being within a specific range, respectively. SOLUTION: A separator is composed of a short fiber at least comprised of 0 to 50 wt.% of a fiber degree greater than that of an extremely thin fiber formed by a split conjugate fiber of 15 to 75 wt.%, a thermally adhesive fiber of 20 to 60 wt.%, and a split conjugate fiber being splitted in which a polyolefin polymer and a polyolefin polymer including an oxygen element are adjacently disposed alternately on a fiber section. A rate of a functional group or bond to all carbon element is aldehyde group or bond of 10 to 40%, a carbonyl group or bond of 3 to 30%, a carboxinyl group or ester bond of 0 to 15%, and remaining carbon element of 15 to 87%.

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, etc., a method of manufacturing the same, and batteries.

[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, since nonwoven fabrics made of polyolefin fibers are hydrophobic and have poor wettability when used in battery separators, various methods for hydrophilizing nonwoven fabrics made of polyolefin fibers have been proposed.
For example, a non-woven fabric obtained by imparting a hydrophilic surfactant to a non-woven fabric is well known. Japanese Patent Publication No. 1-36231 discloses a nonwoven fabric comprising a core / sheath composite fiber of polypropylene / polyethylene grafted with a vinyl monomer, and Japanese Patent Publication No. 5-46056 discloses a method in which a fluorine gas is contacted and reacted with a polypropylene nonwoven fabric. Thing, JP-A-7
JP-A-142047 discloses a mixture obtained by mixing a splittable conjugate fiber composed of a polyolefin / ethylene-vinyl alcohol copolymer and a polyolefin-based fiber, performing a hydroentanglement treatment, and then performing a corona discharge treatment.

[0004]

However, the above-mentioned battery separator has the following problems. For example, a battery separator obtained by imparting a hydrophilic surfactant to a nonwoven fabric to make it hydrophilic.
Although the initial liquid absorption and liquid retention properties are excellent, the surfactant adhering to the surface of the nonwoven fabric is washed away when the battery is repeatedly charged and discharged, and the wettability of the electrolyte is extremely reduced, This may cause the battery life to be shortened.

[0005] In the battery separators disclosed in Japanese Patent Publication No. 1-36231 and Japanese Patent Publication No. 5-46056, a hydrophilic group is imparted by modifying the surface of a nonwoven fabric to improve the durability and hydrophilicity. Due to the special processing method, workability and productivity are poor, cost is high, and it is not practical.

The battery separator disclosed in Japanese Patent Application Laid-Open No. 7-142047 contains 75 to 100% by weight of a splittable conjugate fiber composed of a hydrophobic polyolefin polymer and a hydrophilic ethylene vinyl alcohol copolymer, and is subjected to corona discharge treatment. By applying a hydrophilic group, the hydrophilic group is imparted to improve the durability and hydrophilicity. However, the voids of the nonwoven fabric are too small, the air permeability is low, and the gas permeability required for a sealed battery is not preferable.

In view of these circumstances, the present invention provides a battery separator which has excellent liquid absorption, liquid retention and moderate air permeability, and which can contribute to an improvement in battery capacity without reducing the battery life. The purpose of the present invention is to obtain a battery having battery characteristics.

[0008]

In order to achieve the above object, in the battery separator of the present invention, a polyolefin polymer (component A) and a polyolefin polymer containing oxygen element (component B) are alternately adjacent to each other in a fiber cross section. 15 to 75% by weight of the splittable conjugate fibers, 20 to 60% by weight of the heat-adhesive fibers, and a fineness greater than the fineness of the microfibers formed by splitting the splittable conjugate fibers. That is, short fibers composed of at least 0 to 50% by weight of synthetic fibers (thickness of the fibers is large) are mixed, the splittable conjugate fibers are split to form ultrafine fibers, and the fibers are entangled. A part of the fibers adhere to each other, and the fibers present on the surface of the nonwoven fabric have a functional group, and the ratio of the functional group or the bond to the total carbon element is in the following range, respectively. . (1) Aldehyde group (-CHO) or aldehyde bond (-C ⁺ H-
^{O -): 10~40% (2} ) carbonyl groups or carbonyl bonds (-CO -): 3~3
0% (3) carboxyl groups (-COO ^-) or ester bonds (-COO
-): 0 to 15% (4) Remaining carbon element: 15 to 87%

In the battery separator of the present invention,
The fiber length of the splittable conjugate fiber, the heat-adhesive fiber, and the synthetic fiber is preferably in the range of 3 to 25 mm, and the fineness of the synthetic fiber is preferably equal to or smaller than the fineness of the heat-adhesive fiber.
Further, in the battery separator of the present invention, the air permeability is preferably 5 to 50 ccs.

In the battery separator of the present invention, it is preferable that the third liquid absorption height (durable liquid absorption height) is 5 mm or more. Further, in the battery separator of the present invention, it is preferable that the heat-adhesive fiber is a core-sheath composite fiber having polyethylene as a sheath and polypropylene as a core. In the battery separator of the present invention, it is preferable that the nonwoven fabric is a composite nonwoven fabric formed by laminating fiber webs having different fiber lengths. Further, in the battery separator of the present invention, it is preferable that another sheet is laminated on at least a part of the nonwoven fabric. In the battery separator of the present invention, the component B is selected from an ethylene-vinyl alcohol copolymer, an ethylene- (meth) acrylate copolymer, an ethylene- (meth) acrylic acid copolymer, and an ethylene-vinyl acetate copolymer. Preferably, it is at least one polymer.

Next, the method for producing a battery separator according to the present invention comprises the steps of:
And a polyolefin polymer (component B) containing an oxygen element are alternately arranged adjacent to each other. 15 to 75% by weight of a splittable conjugate fiber having a length of 3 to 25 mm and a heat-adhesive fiber having a length of 3 to 25 mm 20 to 60% by weight, 0 to 50% by weight of synthetic fiber having a length of 3 to 25 mm, which is larger than the fineness of the ultrafine fiber formed by splitting the splittable conjugate fiber and is equal to or smaller than the fineness of the heat-adhesive fiber % To form a wet nonwoven fabric by wet papermaking to form a wet nonwoven fabric, and in at least one of the wet papermaking process and the wet nonwoven fabric formation process, splitting the splittable conjugate fiber to form an ultrafine fiber, The nonwoven fabric is entangled, and then subjected to corona discharge treatment on both sides of the nonwoven fabric, followed by heat calendering.

In the above method, the splitting of the splittable conjugate fiber is preferably performed by the impact of stirring in the wet papermaking process. Further, in the method, it is preferable that the splitting of the splittable conjugate fiber is performed by performing a high-pressure water flow treatment. Further, in the above method, it is preferable that the entanglement between the divided ultrafine fibers is performed by performing a high-pressure water flow treatment. Further, in the above method, it is preferable that the division of the splittable conjugate fiber and the entanglement between the ultrafine fibers formed after the division are simultaneously performed by performing a high-pressure water flow treatment. In the above method, in the corona discharge treatment, the total discharge amount for treating both surfaces of the nonwoven fabric is preferably in the range of 0.05 to 5 kW · min / m ² . Further, in the above method, it is preferable that a hydrophilic surfactant is applied to the nonwoven fabric after the corona discharge treatment. In the method of the present invention, the component B is at least one selected from an ethylene-vinyl alcohol copolymer, an ethylene- (meth) acrylate copolymer, an ethylene- (meth) acrylic acid copolymer, and an ethylene-vinyl acetate copolymer. Preferably, it is one polymer. According to the battery separator of the present invention and the method for producing the same, excellent liquid absorption,
It is possible to provide a battery separator having a liquid retaining property and a suitable air permeability and capable of contributing to an improvement in battery capacity without reducing the battery life. Next, a battery of the present invention is characterized by incorporating the battery separator of the present invention.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The splittable conjugate fiber used in the battery separator of the present invention is a conjugate fiber having a polyolefin polymer as an A component and a polyolefin polymer containing an oxygen element as a B component. As the polyolefin polymer of the component A, polypropylene, polyethylene and the like can be preferably used. Examples of the oxygen-containing polyolefin polymer (component B) include ethylene-vinyl alcohol copolymer, ethylene- (meth) acrylate copolymer, ethylene- (meth) acrylic acid copolymer, and ethylene-vinyl acetate copolymer. At least one polymer selected from coalescing is exemplified. Among them, ethylene vinyl alcohol copolymer is excellent in melting point and processability. As the ethylene vinyl alcohol copolymer, those having an ethylene content of 20 to 50 mol% can be preferably used in consideration of spinnability and hydrophilicity.

In the splittable conjugate fiber, the A component and the B component are alternately adjacent to each other in the fiber cross section, the constituent units are continuous in the length direction, and a part of all the constituent units is always exposed to the fiber surface. It has a cross-sectional shape. Specifically, those in which the A and B components are arranged as shown in FIGS. 1 to 3 can be preferably used. 1 to 3, reference numeral 1 denotes an A component, and 2 denotes a B component. The composite ratio of the A and B components is preferably about 30:70 to 70:30 (weight ratio) in terms of the ease of the spinning process and the wettability to the electrolytic solution.

[0015] The splittable conjugate fiber is split by wet papermaking or high-pressure water flow treatment, which will be described later, to form an ultrafine fiber. If the ratio of the ultrafine fibers formed by the splitting of the splittable conjugate fibers to the entire nonwoven fabric is too large, or if the fineness of the ultrafine fibers is too small, the size of the voids formed by the entanglement and adhesion of the constituent fibers in the nonwoven fabric is reduced. The ratio of the splittable conjugate fiber is preferably from 15 to 75% by weight, since the size of the splittable conjugate fiber becomes too small and the air permeability and the liquid retaining property are reduced. More preferably, it is 40 to 60% by weight. Further, it is desirable to use a splittable conjugate fiber in which the fineness of the ultrafine fiber formed after splitting is 0.1 to 0.5 denier. When the proportion of the splittable conjugate fiber is less than 15% by weight, the proportion occupied by the ethylene-vinyl alcohol copolymer is small, so that not only is the hydrophilic property deteriorated, but also the voids are increased and the liquid retaining property and liquid absorbing property are deteriorated. If the content exceeds 75% by weight, not only does the air permeability decrease, but also the resin of the ethylene-vinyl alcohol copolymer adheres to the surface of the dryer and the surface of the blanket when the dryer is dried during wet papermaking, resulting in poor processability. Further, since it depends on the entanglement of the ultrafine fibers, the nonwoven fabric is too soft (the nonwoven fabric has no stiffness), the elongation in the vertical direction of the nonwoven fabric is large, and the winding property at the time of assembling the battery is not preferable. On the other hand, if the fineness of the ultrafine fiber exceeds 0.5 denier, the voids become too large, and the liquid absorbing property and the liquid retaining property are inferior.

The heat-adhesive fiber of the present invention refers to a fiber which is softened and melted by heat and functions to bond the fibers. As such a fiber, for example, it is preferable to use a polyolefin-based thermo-adhesive fiber such as polyethylene or polypropylene.

In particular, in the present invention, in order to improve the strength of the separator, it is preferable to use a core-sheath type composite fiber whose sheath is composed of a low melting point component and whose core is composed of a high melting point component. For example, polypropylene / ethylene-vinyl alcohol copolymer, polypropylene / polyethylene, polypropylene / ethylene-propylene copolymer, polypropylene / ethylene-methyl acrylate copolymer, polypropylene / ethylene-vinyl acetate copolymer, and the like, Among them, the core-in-sheath type composite fiber in which the core component is made of polypropylene and the sheath component is made of polyethylene is excellent in alkali resistance because it is made of a polyolefin-based component, and is a split type made of polypropylene and ethylene-vinyl alcohol copolymer. Since the bondability with the conjugate fiber is good, it can be most preferably used. The preferable ratio of the core component and the sheath component is as follows: core component: sheath component 30:70 to 7
About 0:30 (weight ratio) is desirable. The fineness of the heat-adhesive fiber is preferably 0.5 to 5 denier. If it is less than 0.5 denier, the dispersibility of the fibers in the slurry during wet papermaking is poor, and the fibers are entangled with each other, and the processability is improved.
Inferior in quality, and if it exceeds 5 denier, the size of the gap becomes too large, which causes a short circuit at the time of assembling the battery, which is not preferable.

The proportion of the heat-adhesive fibers is preferably from 20 to 60% by weight. More preferably, 20 to 40% by weight
It is. If the amount is less than 20% by weight, the bonding between the fibers is insufficient, the strength of the nonwoven fabric is weak, and the winding property is inferior. If the amount exceeds 60% by weight, the adhesive area becomes too large, so that the number of voids decreases, It is not preferable because of poor liquid retention.

Further, in the battery separator of the present invention, in order to secure voids formed between the fibers, the fineness of the ultrafine fibers formed by splitting the splittable conjugate fibers is larger than that of the heat-adhesive fibers. Or a small synthetic fiber (hereinafter,
It is preferable to mix 0 to 50% by weight of a synthetic fiber). It is more preferably 0 to 30% by weight, and further preferably 10 to 20% by weight. Its fineness is 0.
5 to 5 denier is preferred. The synthetic fiber is selected from those which do not substantially melt at the temperature at which the heat-adhesive fiber melts, and commonly used synthetic fibers such as polypropylene, polyester, and nylon can be used.
For example, when a fiber having a hydrophilic property or an additional function is used as a synthetic fiber, if it is mixed at 20 to 50% by weight, the improvement of the durable hydrophilic property by the surface modification and the hydrophilicity and the additional function of the synthetic fiber are combined. And excellent battery characteristics. If the amount of the synthetic fiber exceeds 50% by weight, the bonding area becomes too small, and the strength of the nonwoven fabric becomes weak, which is not preferable. Further, when the fineness of the synthetic fiber exceeds 5 denier, a dense void in the nonwoven fabric cannot be secured, and when the fineness is less than 0.5 denier, the fibers are entangled during wet papermaking, which adversely affects processability and quality, which is not preferable. . In particular, a relatively rigid and high-strength polypropylene fiber having a fineness of 0.6 to 1.2 denier is most preferably applied in order to impart alkali resistance to the separator and secure an appropriate gap.

The fiber length of the above-mentioned splittable conjugate fiber, synthetic fiber, and heat-adhesive fiber is not particularly limited, but the fiber length is preferably 3 to 25 mm. More preferably, it is 5 to 15 mm. If it is less than 3 mm, the fibers are scattered during high-pressure water flow treatment, and the entanglement between the fibers becomes insufficient.
This is because it is not preferable in the process. If the thickness exceeds 25 mm, especially when a nonwoven fabric is produced by a wet papermaking method, the dispersibility of the fibers in the slurry becomes poor and a uniform nonwoven fabric cannot be obtained.

As another form of the nonwoven fabric, a composite nonwoven fabric in which the mixing ratio is appropriately changed within the range of the constituent fibers described above or the fiber webs having different fiber lengths are laminated may be used. For example, in the case of the latter, a fiber web made of staple fibers having a fiber length of 30 mm or more, or a long fiber web is laminated on at least one surface on a fiber web formed by a wet papermaking method comprising the constituent fibers having a fiber length of 3 to 25 mm. be able to. When fiber webs with different fiber lengths are laminated, a fiber web with a short fiber length contributes to the denseness, and a fiber web with a long fiber length contributes to the improvement of the strength of the non-woven fabric, and is excellent in productivity when incorporated in a battery. convenient. These fiber webs are in any form such as an unbonded web such as a card web, a bonded nonwoven fabric in which a part of the constituent fibers are bonded by an adhesive or self-adhesion, or a nonwoven fabric entangled by needle punching or high pressure water flow treatment. There may be. As a lamination method, the fibers may be entangled after laminating the unbonded webs, or the fibers may be entangled after laminating at least one of the fibrous webs previously formed into a nonwoven fabric by the bonding or entanglement method. You may.

Further, another sheet may be laminated on at least a part of the layer of the nonwoven fabric. The other sheet referred to here is a wet nonwoven fabric made of fibers having a fiber length of 3 to 25 mm, a bonded nonwoven fabric obtained by bonding a part of constituent fibers made of fibers having a fiber length of 30 mm or more with an adhesive or self-adhesive, It refers to a nonwoven fabric or a porous film entangled by needle punch or high-pressure water flow treatment. When a wet nonwoven fabric having a fiber length of 3 to 25 mm among the other sheets is used, a nonwoven fabric having a low basis weight and a low rate of occurrence of through holes is obtained, and a short circuit rate in a battery can be reduced. . If a fiber or a porous film having a fiber length of 30 mm or more is used, the strength of the nonwoven fabric can be further improved. The material of the other sheet is not particularly limited, and may be any of a polyolefin resin, a polyamide resin, and a polyester resin. In addition, the lamination method is not particularly limited as long as another sheet is laminated on at least a part of the layers, and another sheet may be laminated on one side or both sides of the nonwoven fabric of the present invention. Another sheet may be inserted in the second sheet. Further, the laminate may be laminated in two or more layers. The method of bonding between the layers in the laminate is not particularly limited. For example, the nonwoven fabric of the present invention is prepared in advance by high-pressure water flow treatment, and after being laminated with another sheet, hot air or a hot roll. The bonding may be performed by heat treatment, or the fiber web constituting the present invention and another sheet may be stacked in advance, and then bonded by a high-pressure water flow treatment.

The splittable conjugate fiber, the synthetic fiber, and the heat-adhesive fiber are mixed, and the splittable conjugate fiber is divided to form an ultrafine fiber. The non-woven fabric is bonded to the non-woven fabric.

Furthermore, in the nonwoven fabric of the present invention, the fibers present on the surface of the nonwoven fabric have a functional group, and the ratio of the functional group or the bond is in the following range, respectively. (1) Aldehyde group (-CHO) or aldehyde bond (-C ⁺ H-
^{O -): 10~40% (2} ) carbonyl groups or carbonyl bonds (-CO -): 3~3
0% (3) carboxyl groups (-COO ^-) or ester bonds (-COO
-): 0 to 15% (4) Remaining carbon element: 15 to 87% The functional group is determined by electron spectroscopy fo
It can be measured by analyzing the surface element composition of the nonwoven fabric using r chemical analysis (hereinafter referred to as ESCA), separating the peaks of the respective functional groups from the total amount of carbon elements on the surface of the nonwoven fabric, and determining the area ratio.

By modifying the surface of the nonwoven fabric with the functional groups of the nonwoven fabric made of the above fibers, -CO- or -COO
-Increase. -CHO or -C ⁺ HO ^- is 10%, - CO- 3%
If it is less than, the durability is poor, and if -CHO or -C ⁺ HO ^- is more than 40%, -CO- is more than 30%, and -COO- or -COO ^- is more than 15%, the durable hydrophilicity is rich. It is not preferable because the strength of the fiber itself is reduced and the strength of the nonwoven fabric is reduced.

The air permeability of the obtained battery separator is preferably 5 to 50 ccs. More preferably 1
0-25 ccs. The air permeability is based on the mixing ratio of splittable composite fiber, synthetic fiber, and heat-adhesive fiber, high-pressure water flow treatment conditions,
It can be adjusted by the heat treatment temperature or the like. When the air permeability is adjusted to 5 to 50 ccs, an appropriate gap is secured in the battery separator, and the electrolytic solution is held inside the battery separator, in combination with the improvement in durability and hydrophilicity by the surface modification,
Excellent liquid retention can be achieved.

Further, the third liquid absorption height (hereinafter referred to as a durable liquid absorption height) of the obtained battery separator is preferably 5 mm or more. It is more preferably at least 15 mm. When the durable liquid absorption height is 5 mm or more, a durable hydrophilicity is large, and a long-life battery can be obtained.

The liquid retention rate of the obtained battery separator is as follows:
300% or more is preferable. More preferably, it is 400% or more. If the liquid retention ratio is less than 300%, repeated charging and discharging when incorporated in a battery is not preferable because the life of the separator is shortened due to the liquid withering of the separator.

The vertical elongation at break of the obtained battery separator is preferably 30% or less. It is more preferably at most 20%. If the elongation at break in the vertical direction exceeds 30%, it is not preferable to wind while applying tension in the vertical direction in the process of assembling the battery, since the width of the separator becomes extremely short with respect to a predetermined length.

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.
To 75% by weight, 20 to 60% by weight of the heat-adhesive fiber, and 0 to 50% by weight of the synthetic fiber to form 0.01 to 0.6%
And disperse it in water so as to obtain a slurry to prepare a slurry. At this time, a small amount of a dispersant may be added. Then, the splittable conjugate fiber may be split in advance at the time of slurry adjustment, or splitting may be suppressed and the splitting conjugate fiber may be split by a high-pressure water flow treatment described later.

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 depending on the amount of the fiber, but is preferably 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 easily occurs between the positive electrode and the negative electrode.
If it exceeds 00 g / m ² , the air permeability and the like will decrease.

Next, the heat-adhesive fibers are melted to lightly bond the fibers. The melting of the heat-adhesive fibers may be carried out simultaneously with the drying in the drying treatment in the papermaking process, or may be carried out by temporarily forming a wet nonwoven fabric and then heating. Then, the fibers are lightly bonded to each other by fusing the heat-adhesive fibers to stabilize the form, and then subjected to a high-pressure water flow treatment to divide the splittable conjugate fibers to form the ultrafine fibers and to separate the fibers. Confound. For high pressure water flow treatment, the orifice with a hole diameter of 0.05 to 0.5 mm is 0.5 to 1.5
25 to 150 kg of water pressure from nozzles provided at intervals of mm
It is preferable that the columnar water flow of / cm ² is jetted at least once on each of the front and back surfaces of the nonwoven fabric.

After that, it is preferable that both surfaces of the nonwoven fabric are subjected to corona discharge treatment to perform surface modification. The corona discharge treatment is preferably performed on both surfaces of the nonwoven fabric 1 to 20 times, respectively, and the total amount of the treated discharge is preferably 0.05 to 5 kW · min / m ² . More preferably, it is 0.1 to 3 kW · min / m ² .
When the total discharge amount is less than 0.05 kW · min / m ^2, not sufficiently durable hydrophilicity is obtained, strongly decrease the fiber itself exceeds 5 kW · min / m ^2, and thus the nonwoven fabric strength is lowered It is not preferable.

Further, after subjecting the nonwoven fabric to corona discharge,
The addition of a hydrophilic surfactant improves the initial hydrophilicity and is effective. As the hydrophilic surfactant, for example, a phosphate-based anionic surfactant such as an alkyl phosphate ester, a soap-based anionic surfactant such as an aliphatic carboxylic acid soap, and a sulfate-based anionic surfactant such as an alkyl sulfate are used. It is uniformly attached by a method, a spray method, a roll touch method, or the like. Thereafter, the nonwoven fabric to which the surfactant has been applied is dried by a known drying means. After that, it is heat calendered and adjusted to a predetermined thickness.
The battery separator of the present invention is obtained.

[0035]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the contents of the present invention will be described with reference to embodiments. The thickness, tensile strength, elongation at break, air permeability, liquid retention, initial liquid absorption height, durable liquid absorption height, and functional groups on the surface of the nonwoven fabric constituting the separator were measured by the following methods. (1) Thickness: Using a thickness measuring machine (trade name: THICKNESS GAUGE model CR-60A, manufactured by Daiei Kagaku Seiki Seisakusho Co., Ltd.)
The measurement was performed with a load of 20 g applied per 1 cm ^{2 of the} sample. (2) Tensile strength, elongation at break: According to JIS L 1096, a sample piece having a width of 5 cm and a length of 15 cm was gripped at an interval of 10 cm, and a tensile speed of 30 cm was measured using a constant-speed extension type tensile tester.
/ Min, and the load value and the elongation at the time of cutting were defined as tensile strength and elongation at break, respectively. (3) Air permeability: JIS L using a Frazier type testing machine
It was measured according to 1096. (4) Liquid retention ratio: The weight (W) of the test piece in the water equilibrium state was 1
Measure to 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 1 hour, withdrawn from the solution and allowed to stand for 10 minutes, the weight of the test piece (W
₁ ) was measured, and the liquid retention was calculated from the following equation.

[Number 1] Hoekiritsu _{(%) = ((W 1} -W) / W) × 100 (5) initial liquid absorption height: three sheets 25 × 250 mm test pieces from a sample width direction was taken, water balance State. Next, the test piece is pinned to a horizontal bar supported at a predetermined height on a water tank containing a potassium hydroxide aqueous solution (hereinafter abbreviated as KOH solution) having a specific gravity of 1.30 and kept at 20 ° C. The lower end of the test piece was aligned, and the horizontal bar was lowered. The test piece was vertically set so that the lower end was immersed in the liquid by 5 mm, and the height at which the KOH solution had risen by capillary action was measured 30 minutes later. (6) Durable liquid absorption height: The sample whose initial liquid absorption height was measured (first liquid absorption height) was washed with water for 5 minutes, dehydrated with blotting paper, and air-dried for about 1 hour. Room temperature 20 ° C, humidity 6
The second liquid absorption height is measured for a sample that has been conditioned under a 5% atmosphere until moisture equilibrium is reached. Then, the same operation was repeated, and the third liquid absorption height (durable liquid absorption height) was measured. (7) Measurement of functional groups on the surface of non-woven fabric fibers constituting the separator The above functional groups are ESCA-33 manufactured by Shimadzu Corporation.
Using No. 00, the surface element composition of the nonwoven fabric was analyzed and measured. As measurement conditions, the source was Mg / Al,
Output 8kW, 30mA, non-woven fabric measuring area 5mm × 10mm,
100 angstroms (10 n
In m), the total carbon element in the olefin main chain and the side chain present on the surface of the nonwoven fabric and the ratio of the functional groups were measured. Note that E
SCA (Electron Spectroscopy for Chemical Analysi)
s) is a measuring means for irradiating a sample with a monochromatic X-ray flux and measuring the emitted photoelectron energy to conduct structural studies or chemical analysis of atoms, molecules or solids. (8) 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. Each of the separators was sandwiched between the above-mentioned negative electrode and positive electrode, inserted into a battery case, and an electrolytic solution was injected to produce a cylindrical sealed nickel-metal hydride battery. (9) Cycle life The Ni-MH battery prepared above was charged at a rate of 0.1 C for 12 hours.
The battery was initialized for 0.5 hours at a discharge rate of 0.1 C at a cutoff voltage of 0.5 V, and was repeatedly charged and discharged for 10 cycles to perform initial battery activation. 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 20 ° C. (10) 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. (11) Short-Circuit Ratio When 100 cylindrical sealed nickel-metal hydride batteries were assembled, the ratio of short-circuits was defined as the short-circuit ratio.

Example 1 A heat-adhesive fiber which is a core-sheath type composite fiber having a fineness of 1.5 denier, a fiber length of 10 mm and a core / sheath component of polypropylene / high-density polyethylene (composite weight ratio of 50/50) was used. 30% by weight, component A is polypropylene, component B is ethylene vinyl alcohol copolymer (ethylene content 38 mol%), has a cross-sectional shape as shown in FIG. 1, and has an area of component A / component B 50/50 ratio
50 denier type conjugate fibers with a denier of 3 denier and a fiber length of 6 mm
% By weight and 20% by weight of a polypropylene fiber having a fineness of 0.7 denier and a fiber length of 10 mm were mixed to prepare a slurry so as to have a concentration of 0.5%.
A wet nonwoven fabric of 5 g / m ² was produced. Next, a high-pressure columnar water stream having a water pressure of 130 kg / cm ² was sprayed on the front and back surfaces of the wet nonwoven fabric to divide the splittable conjugate fiber to a fineness of 0.19.
０．２0.2 denier ultrafine fibers were formed, and the fibers were entangled with each other.
Thereafter, the nonwoven fabric was subjected to corona discharge treatment four times on each side of the nonwoven fabric so that the total discharge amount was 0.462 kW · min / m ^2, and subjected to a heat calendering treatment to obtain a nonwoven fabric for a battery separator.

Example 2 A non-woven fabric for a battery separator was prepared in the same manner as in Example 1 except that 0.2% by weight of an alkyl phosphate ester surfactant was adhered.

Example 3 A heat-adhesive fiber which is a core-sheath type composite fiber having a fineness of 1.5 denier, a fiber length of 45 mm and a core / sheath component of polypropylene / high-density polyethylene (composite weight ratio 50/50) was used. 30% by weight, component A is polypropylene, component B is ethylene vinyl alcohol copolymer (ethylene content 38 mol%), has a cross-sectional shape as shown in FIG. 1, and has an area of component A / component B 50/50 ratio
5 denier split composite fibers with a fiber length of 51 mm
By mixing 0% by weight and 20% by weight of a polypropylene fiber having a fineness of 1.2 denier and a fiber length of 45 mm, a fiber web having a basis weight of 20 g / m ² was prepared using a semi-random card machine. Then, a water pressure of 50 kg / cm ^{2 is applied} to the front and back surfaces of the fiber web.
Was jetted to split the splittable conjugate fibers and entangle the fibers. Then, it was dried and heated at 135 ° C. and bonded to form a dry nonwoven fabric having a basis weight of 20 g / m ² . Next, in a wet paper machine, the dry nonwoven fabric was placed at the entrance side of a cylinder-type dryer, and a 0.5% concentration slurry composed of the constituent fibers of Example 1 was prepared so that the basis weight was 30 g / m ^2. While wet papermaking was performed, a previously set dry nonwoven fabric was laminated, and heat treatment was performed with a cylinder type dryer at 135 ° C. to bond the thermoadhesive fibers of both layers to obtain a composite nonwoven fabric. Further, a high-pressure columnar water stream having a water pressure of 130 kg / cm ² was sprayed on the front and back surfaces of the composite nonwoven fabric to separate and entangle the splittable composite fibers.
At the same time as drying at 5 ° C., heat bonding was performed. After that, both sides of the non-woven fabric were each applied four times, for a total discharge of 0.462 kw · min / m
^The resultant was subjected to corona discharge treatment so as to obtain No. ^2, and subjected to a heat calender treatment to obtain a nonwoven fabric for a battery separator.

Comparative Example 1 The same treatment as in Example 1 was performed except that the corona discharge treatment was not performed, to obtain a nonwoven fabric for a battery separator.

Comparative Example 2 A non-woven fabric for a battery separator was obtained by performing the same treatment as in Example 2 except that the corona discharge treatment was not performed.

Comparative Example 3 The same treatment as in Example 1 was carried out except that the heat-adhesive fiber was 20% by weight and the splittable conjugate fiber was 80% by weight to obtain a non-woven fabric for a battery separator.

Comparative Example 4 A non-woven fabric for a battery separator was obtained by performing the same treatment as in Example 1 except that the heat-adhesive fiber was 60% by weight, the splittable conjugate fiber was 10% by weight, and the synthetic fiber was 30% by weight. did. Tables 1 and 2 show the physical properties of the battery separators of Examples 1 to 3 and Comparative Examples 1 to 4.

[0043]

[Table 1]

As is clear from Table 1, in Examples 1 and 2, it was confirmed that the initial and durable liquid absorption heights were excellent while securing tensile strength and air permeability. Example 3
Since the same material as in Example 1 was used for both the wet nonwoven fabric and the dry nonwoven fabric, the dry nonwoven fabric had a reinforcing effect while maintaining the initial and durable liquid absorption height, and the tensile strength was significantly improved. In Comparative Example 2, the initial liquid-absorbing height was improved by treating the surface of the nonwoven fabric with a hydrophilic surfactant, but no liquid was absorbed after the second time.

[0045]

[Table 2]

As is clear from Table 2, in Examples 1 to 3, the presence of a predetermined amount of the functional group allows the separator to flow off the fiber surface even after the separator is incorporated into the battery as in the case of the surfactant treatment. However, since it exists semi-permanently on the fiber surface, there is no liquid withdrawal phenomenon (dry-out phenomenon) in which a part of the separator is not immersed in the electrolytic solution, and the cycle life of the battery is good. . Comparative Example 1
In Comparative Example 2, the practical battery cycle life was not obtained because of the inferior liquid absorption height, and in Comparative Example 3, the inter-fiber gap of the separator was small and the air permeability was poor, so that the internal pressure of the battery was increased. On the other hand, in Comparative Example 4, the inter-fiber gap of the separator was too large, so that the short-circuit rate was increased.

[0047]

According to the battery separator of the present invention, the fibers present on the surface of the non-woven fabric have an aldehyde group (-CHO) or an aldehyde bond (-C ⁺ H-
O ^- a), a carbonyl group or a carbonyl bond (-CO-) and a carboxyl group (-COO ^- since the functional group or bond) or an ester bond (-COO-) is formed, superior liquid retaining property, initial It exhibits liquid absorption properties and durable liquid absorption properties, and when incorporated into a battery, has excellent wettability with an electrolytic solution, and can improve battery life. Further, by attaching a hydrophilic surfactant to the surface of the nonwoven fabric, the initial hydrophilicity and the durability hydrophilicity are improved.

Further, the battery separator of the present invention can obtain sufficient liquid retention and liquid absorption even with a small discharge amount during corona discharge, and is advantageous in terms of running cost. A battery incorporating the battery separator of the present invention has high performance in all battery characteristics, and is suitable for an alkaline storage battery such as a nickel-cadmium battery, a nickel-zinc battery, and a nickel-hydrogen battery.

[Brief description of the drawings]

FIG. 1 is an enlarged cross-sectional view of an example of a splittable conjugate fiber applicable to the present invention.

FIG. 2 is an enlarged cross-sectional view of an example of a splittable conjugate fiber applicable to the present invention.

FIG. 3 is an enlarged cross-sectional view of an example of a splittable conjugate fiber applicable to the present invention.

[Explanation of symbols]

 1 A component 2 B component

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI H01M 10/24 H01M 10/24 (72) Inventor Shuji Hori 877 Furumiya, Harima-cho, Kako-gun, Hyogo Pref. (72) Inventor Tomofumi Tanaka 877, Komiya, Harima-cho, Kako-gun, Hyogo Prefecture, Japan Inside the Harima Research Institute, Daiwa Boupolitec Co., Ltd.

Claims (17)

[Claims] 1. A polyolefin polymer (component (A)) and a polyolefin polymer (B) containing an oxygen element in a fiber cross section.
Component), 15 to 75% by weight of splittable conjugate fibers alternately arranged adjacent to each other, 20 to 60% by weight of heat-adhesive fibers, and ultrafine fibers formed by splitting the splittable conjugate fibers. Short fibers composed of at least 0 to 50% by weight of synthetic fibers having a fineness larger than the fineness are mixed, and the splittable conjugate fibers are split to form ultrafine fibers;
And the fibers are entangled, some of the fibers adhere to each other, and the fibers present on the surface of the nonwoven fabric have functional groups,
A battery separator, wherein the ratio of the functional group or the bond to the total carbon element is in the following range, respectively. (1) Aldehyde group (-CHO) or aldehyde bond (-C ⁺ H-
^{O -): 10~40% (2} ) carbonyl groups or carbonyl bonds (-CO -): 3~3
0% (3) carboxyl groups (-COO ^-) or ester bonds (-COO
-): 0 to 15% (4) Remaining carbon element: 15 to 87% 2. The splittable conjugate fiber, the heat-adhesive fiber and the synthetic fiber have a fiber length in the range of 3 to 25 mm, and the fineness of the synthetic fiber is equal to or smaller than the fineness of the heat-adhesive fiber. 2. The battery separator according to 1. 3. The battery separator according to claim 1, wherein the battery separator has an air permeability of 5 to 50 ccs. 4. A third liquid absorption height (durable liquid absorption height) of 5
The battery separator according to any one of claims 1 to 3, which is not less than mm. 5. The heat-adhesive fiber is a core-sheath composite fiber having polyethylene as a sheath and polypropylene as a core.
The battery separator according to any one of claims 1 to 4. 6. The battery separator according to claim 1, wherein the nonwoven fabric is a composite nonwoven fabric obtained by laminating fiber webs having different fiber lengths. 7. The battery separator according to claim 1, wherein another sheet is laminated on at least a part of the nonwoven fabric. 8. A polymer wherein the component B is at least one polymer selected from ethylene vinyl alcohol copolymer, ethylene- (meth) acrylate copolymer, ethylene- (meth) acrylic acid copolymer, and ethylene-vinyl acetate copolymer. The battery separator according to claim 1, wherein: 9. A polyolefin polymer (component (A)) and a polyolefin polymer (B) containing an oxygen element in a fiber cross section.
Component 3) and a length of 3 to 25 alternately and adjacently arranged.
15 to 75% by weight of a splittable conjugate fiber having a length of 3 to 25 mm
20 to 60% by weight of the heat-adhesive fiber of 20 mm and larger than the fineness of the microfiber formed by splitting the splittable conjugate fiber,
And a length of 3 which is the same as or smaller than the fineness of the heat-adhesive fiber
２５25 mm of synthetic fibers of 0 to 50% by weight and wet papermaking to form a wet nonwoven fabric, and splitting the splittable conjugate fiber in at least one of the wet papermaking step and the wet nonwoven fabric formation step A method for producing a battery separator, comprising: forming ultrafine fibers, causing the fibers to be entangled, and then subjecting both surfaces of the nonwoven fabric to a corona discharge treatment and a heat calendering treatment. 10. The method for producing a battery separator according to claim 9, wherein the splitting of the splittable conjugate fiber is performed by the impact of stirring in a wet papermaking process. 11. The method for producing a battery separator according to claim 9, wherein the splitting of the splittable conjugate fiber is performed by performing a high-pressure water flow treatment. 12. The method for producing a battery separator according to claim 9, wherein the entanglement between the divided ultrafine fibers is performed by performing a high-pressure water flow treatment. 13. The method for producing a battery separator according to claim 9, wherein the splitting of the splittable conjugate fibers and the entanglement between the ultrafine fibers formed after the splitting are simultaneously performed by performing a high-pressure water flow treatment. 14. The method for producing a battery separator according to claim 9, wherein a total discharge amount for treating both sides of the nonwoven fabric in the corona discharge treatment is in a range of 0.05 to 5 kW · min / m ² . 15. The method for producing a battery separator according to claim 9, wherein a hydrophilic surfactant is applied to the nonwoven fabric after the corona discharge treatment. 16. The polymer according to claim 1, wherein the component B is at least one polymer selected from an ethylene vinyl alcohol copolymer, an ethylene- (meth) acrylate copolymer, an ethylene- (meth) acrylic acid copolymer, and an ethylene-vinyl acetate copolymer. The method for producing a battery separator according to any one of claims 9 to 15, wherein 17. A battery incorporating the battery separator according to claim 1.