KR20000016831A - Battery separator and method for manufacturing the same, and battery - Google Patents

Abstract

PURPOSE: A battery separator is provided to improve a battery capacity without dropping a battery lifetime. CONSTITUTION: In the battery separator, a division complex fiber 15 to 75 weight%, a temperature adhesive fiber 20 to 60 weight% and a synthesis fiber 0 to 50 weight% are mixed and then is dry-processed. And an ultra-fine fiber is formed by dividing the division complex fiber after processing at a dry nonwaven fabric with a high pressure. After conducting a corona surface discharge process at both planes of the nonwaven fabric, the nonwaven fabric is conducted with a heat calendar process by a heat roller.

Description

BATTERY SEPARATOR AND METHOD FOR MANUFACTURING THE SAME, AND BATTERY}

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-hydrogen batteries, and the like, a method of manufacturing the same, and a battery using the battery separator.

Usually, as a battery separator, the nonwoven fabric which consists of nylon and a polypropylene fiber is used, and the nonwoven fabric manufactured by the dry method is called dry nonwoven fabric, and the nonwoven fabric manufactured by the wet papermaking method is called a wet nonwoven fabric. Since the nonwoven fabric made of nylon fibers is weak in alkali resistance, a nonwoven fabric made of polyolefin-based fibers such as polypropylene is preferably used.

However, since the nonwoven fabric made of polyolefin fibers is hydrophobic and has poor wettability when used as a battery separator, various methods for hydrophilic treatment of nonwoven fabric made of polyolefin fibers have been proposed. have. For example, it is well known to give a non-woven fabric a hydrophilic surfactant and hydrophilize it. Also, Japanese Patent Application Laid-Open No. 1-36231 discloses a graft copolymer of a vinyl monomer on a nonwoven fabric made of a polypropylene / polyethylene sheath-core composite fiber. JP-A-5-46056 discloses contacting and reacting fluorine gas with a polypropylene nonwoven fabric, and Japanese Patent Laid-Open No. 7-142047 discloses a split composite fiber composed of a polyolefin / ethylene vinyl alcohol copolymer and a polyolefin-based fiber to mix high pressure water flow. After the entanglement process using, the corona surface discharge treatment is disclosed.

However, the battery separator has the following problems. For example, a battery separator obtained by applying a hydrophilic surfactant to a nonwoven fabric and making it hydrophilic has excellent initial alkali absorption and alkali retention properties, but if the battery is repeatedly charged and discharged, the surfactant adhering to the surface of the nonwoven fabric flows out. This greatly lowers the solubility of the alkaline electrolyte, which causes a decrease in the life of the battery.

In addition, the battery separators of Japanese Patent Application Laid-Open Nos. 1-36231 and 5-46056 have improved hydrophilicity by providing a hydrophilic group by modifying the surface of the nonwoven fabric, but have a special processing method. Due to the low workability and productivity, the high cost is not practical.

Further, Japanese Patent Laid-Open No. 7-142047 discloses a battery separator containing 75 to 100% by weight of a split composite fiber composed of a hydrophobic polyolefin polymer and a hydrophilic ethylene vinyl alcohol copolymer. This battery separator improves the hydrophilicity of fibers by imparting a hydrophilic group by performing corona discharge treatment, but the voids of the nonwoven fabric become too small to reduce the air permeability, thereby deteriorating the gas permeability required in a sealed battery. Not desirable

Accordingly, the present invention has been made in view of the above circumstances, and provides a battery separator having excellent alkali absorption, alkali retention and moderate breathability, and improving battery capacity without reducing battery life, and a battery having excellent battery characteristics. The purpose is to.

1 is an enlarged cross-sectional view showing an example of a split-type composite fiber that can be applied to the present invention,

Figure 2 is an enlarged cross-sectional view showing another example of the split type composite fiber that can be applied to the present invention,

Figure 3 is an enlarged cross-sectional view showing another example of the split type composite fiber that can be applied to the present invention.

<Explanation of symbols for main parts of drawing>

1: A component 2: B component

In order to achieve the above object, in the battery separator of the present invention, a polyolefin polymer (component A) and a polyolefin polymer (component B) comprising an oxygen atom are arranged in contact with each other in a fiber cross section. With -75% by weight,

20 to 60% by weight of heat-adhesive fiber,

Staple fibers composed of at least 0 to 50% by weight of synthetic fibers having a fineness (that is, a thicker fiber) than the fineness of the fine fibers formed by dividing the divided composite fibers. ) Is a mixture of

The split composite fibers are split to form microfibers, and the fibers are entangled with each other and a part of the fibers are bonded to each other, and fibers present on the surface of the nonwoven fabric have functional groups, and all carbon atoms The ratio of functional groups or bonds to each is characterized by being in the following ranges.

(1) aldehyde groups (aldehyde基) (- CHO) or an aldehyde bond ^{(-C + HO -): 10~40} %

(2) Carbonyl group or carbonyl bond (-CO-): 3-30%

(3) a carboxyl group (carboxyl基) (- COO ^-), or ester (ester) bond (-COO-): 0~15%

(4) Residual Carbon Atom: 15 ~ 87%

In the battery separator of the present invention, the fiber length of the split composite fiber, the heat-adhesive fiber and the synthetic fiber is in the range of 3 to 25 mm, and the fineness of the synthetic fiber is the same as or smaller than the fineness of the heat-adhesive fiber. desirable.

In the battery separator of the present invention, the air permeability is preferably in the range of 5 to 50 ccs.

Moreover, in the battery separator of the said invention, it is preferable that the alkali absorption height (durable alkali absorption height) of 3rd time is less than 5 mm.

In the battery separator of the present invention, the heat-adhesive fiber is preferably a sheath-core composite fiber having polyethylene as a sheath and polypropylene as a core.

In the battery separator of the present invention, the nonwoven fabric is preferably a composite nonwoven fabric produced by laminating fiber webs having different fiber lengths.

In the battery separator of the present invention, at least one sheet is preferably laminated on at least one layer of the nonwoven fabric.

In the battery separator of the present invention, the B component is an ethylene vinyl alcohol copolymer, an ethylene- (methyl) acrylate copolymer, an ethylene- (methyl) acrylic acid copolymer, an ethylene- It is preferred that it is at least one polymer selected from vinyl acetate copolymers.

Next, the method of manufacturing the battery separator of the present invention is a split type having a length of 3 to 25 mm in which a polyolefin polymer (component A) and a polyolefin polymer (component B) containing an oxygen atom are arranged in contact with each other when viewed from a fiber cross section. 15 to 75% by weight of the composite fiber, 20 to 60% by weight of the heat-adhesive fiber having a length of 3 to 25 mm, and the fineness of the fine fiber formed by the splitting composite fiber is larger than the fineness of the heat-adhesive fiber. Or mixing 0-50% by weight of synthetic fibers having a small length of 3-25mm and wet papermaking to form a wet nonwoven fabric;

At least one of the steps of the wet papermaking process and the formation of a wet nonwoven fabric, the step of dividing the divided composite fibers to form ultrafine fibers and entangle the fibers; And

It characterized in that it comprises a step of performing a corona surface discharge treatment on both sides of the nonwoven fabric and calendering by a thermal roller.

In the said method, it is preferable to perform division | segmentation of a split type composite fiber by the stirring impact in a wet papermaking process.

Moreover, in the said method, it is preferable to perform division of a split type composite fiber by a high pressure water flow process.

Moreover, in the said method, it is preferable to perform entanglement between the divided microfine fibers by a high pressure water flow process.

Moreover, in the said method, it is preferable to perform division | segmentation of the split type | mold composite fiber, and entanglement between the ultrafine fibers formed after splitting by high pressure water flow treatment.

Moreover, in the said method, it is preferable that the total discharge amount which processes both surfaces of a nonwoven fabric in corona surface discharge treatment exists in the range of 0.05-5 kW * min / m <^2> .

In the above method, it is preferable to impart a hydrophilic surfactant to the nonwoven fabric after the corona discharge treatment.

In the above method, the component B is preferably at least one polymer selected from an ethylene vinyl alcohol copolymer, an ethylene- (methyl) acrylate copolymer, an ethylene- (methyl) acrylic acid copolymer and an ethylene-vinyl acetate copolymer. Do.

According to the above method, there is provided a battery separator having excellent alkali absorption, alkali retention, and moderate air permeability, and improving battery capacity without reducing battery life.

The battery of the present invention is characterized in that the battery separator of the present invention is assembled.

The split composite fiber used in the battery separator of the present invention is a composite fiber composed of a polyolefin polymer (component A) and a polyolefin polymer (component B) containing an oxygen atom. It is preferable to use polypropylene, polyethylene, etc. as a polyolefin polymer (component A). As the polyolefin polymer (component B) containing an oxygen atom, at least one selected from ethylene vinyl alcohol copolymer, ethylene- (methyl) acrylate copolymer, ethylene- (methyl) acrylic acid copolymer, and ethylene-vinyl acetate copolymer It is preferable to use two polymers, among which ethylene vinyl alcohol copolymer is excellent in consideration of melting point and processability. It is preferable to use an ethylene vinyl alcohol copolymer having an ethylene content of 20 to 50 mol% in consideration of spinnabilty and hydrophilicity.

In addition, the split composite fiber has a cross-sectional shape in which the A component and the B component are adjacent to each other, the structural units are continuous in the longitudinal direction, and at least a part of each structural unit is exposed to the fiber surface. . For example, as the fibers having A and B components, it is preferable to use those arranged as shown in Figs. In Fig. 1 to Fig. 3, reference numeral 1 denotes A component and reference numeral 2 denotes B component. The mixing ratio of the A component and the B component is preferably about 30:70 to 70:30 (weight ratio) of the A component: B component in consideration of the ease of the spinning process and the solubility in the electrolyte solution.

The split composite fiber is divided by a process described below such as wet papermaking or high pressure water flow treatment to form an ultrafine fiber. If the proportion of the whole nonwoven fabric to the microfine fibers formed by the division of the divided composite fibers is too large or the fineness of the microfine fibers is too small, the size of the voids formed by the entanglement or adhesion of the fibers constituting the nonwoven fabric It becomes too small and air permeability and alkali retention property fall. In order to avoid such a problem, it is preferable that the ratio of split type composite fiber in the whole nonwoven fabric is 15 to 75 weight%, More preferably, it is 40 to 60 weight%. Moreover, it is preferable to use the split type composite fiber in which the fineness of the ultrafine fibers formed after the splitting is 0.1 to 0.5 denier. When the proportion of the split composite fiber is less than 15% by weight, the proportion of the ethylene vinyl alcohol copolymer becomes low, thereby decreasing hydrophilicity and increasing voids, thereby lowering alkali retention and alkali absorption. In addition, when the ratio of the split composite fiber exceeds 75% by weight, not only the breathability is lowered, but also the resin of the ethylene vinyl alcohol copolymer adheres to the dryer side or the blanket side during the drying of the dryer in wet papermaking. Fairness is poor. Moreover, since such properties depend on the intertwining of the fine fibers, the nonwoven becomes too soft (the elasticity becomes non-elastic), or the longitudinal stretch of the nonwoven becomes large, and the winding property during battery assembly is increased. It causes various problems like falling. Moreover, when the fineness of an ultrafine fiber exceeds 0.5 denier, a space | gap becomes large too much, and alkali absorbency and alkali retention property fall, and when less than 0.1 denier, air permeability becomes low and it is unpreferable.

The heat-adhesive fiber of the present invention refers to a fiber that functions to soften and melt with heat to bond between fibers. As such fibers, for example, it is preferable to use polyolefin-based heat-adhesive fibers such as polyethylene and polypropylene.

In particular, in the present invention, in order to improve the strength of the separator, it is preferable to use a sheath-core composite fiber composed of a low melting point component and a high melting point component. Examples of such components include polypropylene / ethylene-vinyl alcohol copolymers, polypropylene / polyethylene, polypropylene / ethylene-propylene copolymers, polypropylene / ethylene-methyl acrylate copolymers, and polypropylene / ethylene-vinyl acetate copolymers. Etc. can be mentioned. Among them, the sheath-core composite fiber in which the core component is made of polypropylene and the polyethylene is made of polyolefin has excellent alkali resistance because it is made of polyolefin-based components, and the split composite made of polypropylene and ethylene vinyl alcohol copolymer. Since adhesiveness with a fiber is also favorable, it can use it most preferably. As for the ratio of a core component and a sheath component, a core component: about 30: 70-70: 30 (weight ratio) grade component is preferable. In addition, the fineness of the heat-adhesive fiber is preferably 0.5 to 5 denier. If the fineness is less than 0.5 denier, the dispersibility of the fibers in the slurry in wet papermaking is deteriorated and the fibers are entangled, resulting in poor processability and quality. On the other hand, if the fineness exceeds 5 denier, the size of the void becomes too large, which is a cause of short circuit during battery assembly, which is not preferable.

It is preferable that the ratio of heat-adhesive fiber in a nonwoven fabric is 20 to 60 polymerization%, More preferably, it is 20 to 40 polymerization%. If the ratio of the heat-adhesive fiber is less than 20% by polymerization, the bonding between the fibers is insufficient, the nonwoven fabric strength becomes weak, and the winding property is inferior. It is not preferable because the number decreases, resulting in poor alkali absorbency and alkali retention.

In addition, in the battery separator of the present invention, in order to secure voids formed between the fibers, a composite having a fineness greater than or equal to the fineness of the heat-adhesive fibers, which is larger than the fineness of the fine fibers formed by the division of the split composite fiber. It is preferable to mix 0-50 polymerization% of fibers. More preferably, it is 0-30 polymerization%, More preferably, it is 10-20 polymerization%. As for the fineness, 0.5-5 denier is preferable. The synthetic fibers are not substantially melted at the temperature at which the heat-adhesive fibers are melted, and may be selected from general-purpose synthetic fibers such as polypropylene, polyester, nylon, and the like. For example, when 20 to 50% of a polymer having hydrophilicity or an additional function as a synthetic fiber is mixed, durability of hydrophilicity due to surface modification, hydrophilicity and an additional function of the synthetic fiber, and excellent battery characteristics are obtained. If the synthetic fiber exceeds 50% by weight, the adhesive area becomes too small, so the nonwoven fabric strength becomes weak, which is not preferable. In addition, if the fineness of the synthetic fiber exceeds 5 denier, the tight voids in the nonwoven fabric can not be secured, and if the fineness of the synthetic fiber is less than 0.5 denier, the fibers are entangled with each other in wet papermaking, which is undesirable because of poor processability and quality. In particular, polypropylene fibers having moderate stiffness of 0.6 to 1.2 denier and high strength are most preferably used to provide alkali resistance to the separator and to secure appropriate voids.

Although the fiber length of said split composite fiber, synthetic fiber, and heat-adhesive fiber is not specifically limited, It is preferable that all the fiber length exists in the range of 3-25 mm, More preferably, it is 5-15 mm. If the fiber length is less than 3 mm, the fiber is scattered during the high-pressure water flow treatment and the entanglement between the fibers is insufficient, which is not preferable in the process. If the fiber length is more than 25 mm, the nonwoven fabric may be manufactured by wet papermaking. In this case, the dispersibility of the fibers in the slurry is deteriorated, so that a uniform nonwoven fabric cannot be obtained.

The nonwoven fabric is not limited to the above-described constituent fibers, and may be laminated by appropriately changing the mixing ratio of the fibers within the above-described range, or may be a composite nonwoven fabric obtained by laminating webs having different fiber lengths. For example, in the latter case, a fiber web or filament composed of staple fibers having a fiber length of at least 30 mm on at least one side of the fiber web by the wet papermaking method, which is composed of constituent fibers having a fiber length of 3 to 25 mm. Fiber webs can be laminated. In the case of stacking fiber webs having different fiber lengths, a short fiber length web improves the density of the nonwoven fabric and a long fiber length fiber web improves the nonwoven strength, thereby improving productivity in assembling the battery. These fibrous webs can be either unbonded webs, such as carding webs, bonded nonwoven fabrics in which part of the constituent fibers are bonded by adhesive or self-adhesion, or nonwovens intertwined with each other by needle punching or high pressure water flow treatment. It may be in the form. As the lamination method, the fibers may be entangled with each other after laminating unbonded webs, or the fibers may be entangled after laminating a nonwoven fabric of at least one fiber web by the bonding or entanglement method in advance.

In addition, another sheet may be laminated on at least one layer of the nonwoven fabric. Other sheets referred to herein include wet nonwoven fabrics composed of fibers having a fiber length of 3 to 25 mm, bonded nonwoven fabrics in which a part of the constituent fibers composed of fibers having a fiber length of 30 mm or more by adhesive or self-bonding, needle punching or high pressure water flow treatment. It refers to intertwined nonwoven fabrics, porous films and the like. By using a wet nonwoven fabric composed of fibers having a fiber length of 3 to 25 mm among the other sheets, a non-woven fabric having a low basis weight and a low generation rate of through holes is obtained, thereby reducing the short rate in the battery. You can. In addition, the use of a fiber or porous film having a fiber length of 30 mm or more can further improve nonwoven fabric strength. It does not specifically limit as a raw material of another sheet, Any of polyolefin resin, polyamide resin, or polyester resin may be sufficient. Further, the lamination method is not particularly limited as long as another sheet is laminated on at least one layer, and another sheet may be laminated on one or both sides of the nonwoven fabric of the present invention, or another sheet may be inserted between the nonwoven fabrics.

Moreover, you may laminate | stack two or more layers of the said laminated bodies. In addition, the bonding method between the layers in the laminate is not particularly limited. For example, the nonwoven fabric of the present invention is produced in advance by high pressure water flow treatment, and another sheet is laminated, followed by a hot air or a heat roller. May be bonded by heat treatment, or the fibrous web and other sheets constituting the present invention may be laminated in advance and then bonded by high pressure water flow treatment.

Therefore, the divided composite fibers, the synthetic fibers, and the heat-adhesive fibers are mixed with each other, the fine fibers are formed by the division of the divided composite fibers, and the fibers are entangled with each other to form a nonwoven fabric in which some of the fibers are bonded to each other.

Moreover, the nonwoven fabric of this invention has a functional group in the fiber of a nonwoven fabric surface, and the ratio of a functional group or a bond is in the following range, respectively.

(1) aldehyde groups (-CHO) or aldehyde bond ^{(-C + HO -): 10~40} %

(2) Carbonyl group or carbonyl bond (-CO-): 3-30%

(3) carboxyl groups (-COO ^-) or ester bonds (-COO-): 0~15%

(4) Residual Carbon Atom: 15 ~ 87%

The functional group is subjected to surface elemental composition analysis of the nonwoven fabric by using electron spectroscopy for chemical analysis (hereinafter referred to as ESCA) to separate each functional group at a peak from the total carbon atomic weight of the surface of the nonwoven fabric and determine the area ratio thereof. It can measure by obtaining.

In the functional group of the nonwoven fabric made of the fiber, -CO- or -COO- increases by surface modification of the nonwoven surface. If -CHO or -C ⁺ HO ^- is less than 10% and -CO- is less than 3%, durability hydrophilicity is inferior. On the other hand, if -CHO or -C ⁺ HO ^- is more than 40%, -CO- is 30%, -COO- or -COO ^- is more than 15%, the hydrophilicity is rich, but the strength of the fiber itself is lowered, It is not preferable because the strength of the nonwoven fabric is lowered.

Moreover, it is preferable that the air permeability of the battery separator obtained as mentioned above is 5-50 ccs, More preferably, it is 10-25 ccs. The air permeability can be adjusted by mixing ratio of split composite fiber, synthetic fiber and heat-adhesive fiber, high pressure water flow treatment condition, heat treatment temperature and the like.

When the air permeability is adjusted to 5 to 50 ccs, an air gap appropriate for the battery separator is secured, the hydrophilic durability is improved by the surface modification, and the alkaline electrolyte solution is maintained inside the battery separator, thereby achieving excellent alkali retention.

Moreover, 5 mm or more of the 3rd alkali absorption height (henceforth durable alkali absorption height) of the battery separator obtained as mentioned above is more preferable, More preferably, it is 15 mm or more. If the endurance alkali absorption height is 5 mm or more, the endurance hydrophilicity is increased and a battery having a long life is obtained.

The alkali retention rate of the battery separator obtained as described above is preferably 300% or more, and more preferably 400% or more. In the case where the alkali retention rate is less than 300%, repeated charge and discharge when the battery is assembled is not preferable because the life is shortened by the dryout of the separator.

The elongation at break in the longitudinal direction of the battery separator obtained as described above is preferably 30% or less, more preferably 20% or less. When the elongation at break in the longitudinal direction exceeds 30%, it is not preferable because the width of the separator becomes extremely short with respect to the predetermined length when the tension is wound while applying the tension in the longitudinal direction in the assembly process to the battery.

Next, the manufacturing method of the battery separator of this invention is demonstrated. As a manufacturing method of the nonwoven fabric used as the base material of the separator of this invention, the wet papermaking method is preferable. This is because the wet papermaking method provides a uniform nonwoven fabric. The wet papermaking may be carried out by a conventional method, and in particular, 15 to 75% by weight of the split type composite fiber, 20 to 60% by weight of the heat-adhesive fiber, and 0 to 50% by weight of the synthetic fiber are mixed at a concentration of 0.01 to 0.6% The slurry is prepared by dispersing with water as much as possible. At this time, a small amount of dispersant may be added. In addition, the split composite fiber may be divided in advance at the time of slurry composition, or may be divided into a high pressure water flow treatment to be described later.

The slurry is papermaking using a short wire former, a cylinder wire former or a combination of both. The basis weight can be controlled by the fiber amount, but is preferably 30 to 100 g / m ² . If the reference weight is less than 30 g / m ^2, since the strength of the nonwoven fabric is lowered, short circuits are likely to occur between the positive electrode and the negative electrode, and if the reference weight exceeds 100 g / m ² , air permeability and the like are not preferable.

The heat-adhesive fibers are then melted to weakly bond between the fibers. Melting of the heat-adhesive fiber may be performed simultaneously with drying at the time of drying treatment in the papermaking process, or may be performed by heat treatment after forming the wet nonwoven fabric once. Then, by melting the heat-adhesive fibers, the fibers are weakly bonded to form a stabilized state, and then the high-pressure water flow treatment is performed to divide the split composite fibers to form ultrafine fibers and to entangle the fibers together. . In the high-pressure water flow treatment, at least one columnar water stream with a water pressure of 25 to 150 kg / cm ² is provided on both sides of the nonwoven fabric from a nozzle having an orifice with a hole diameter of 0.05 to 0.5 mm and a gap of 0.5 to 1.5 mm. Spray it.

Thereafter, corona surface discharge treatment may be performed on both surfaces of the nonwoven fabric to perform surface modification. The corona surface discharge treatment may be performed 1 to 20 times on both sides of the nonwoven fabric, and the total discharge amount treated is preferably 0.05 to 5 kW · min / m ² , and more preferably 0.1 to 3 kW · min ² . . When the total discharge amount is less than 0.05 kW · min / m ² , sufficient hydrophilicity is not obtained. When the total discharge amount is more than 5 kW · min / m ² , the strength of the fiber itself is lowered, and further, the nonwoven fabric strength is preferable. Not.

Moreover, when hydrophilic surfactant is given to a nonwoven fabric after corona surface discharge, initial hydrophilicity improves and it is effective. Hydrophilic surfactants include, for example, phosphate anion activators such as alkylphosphonates, metal salts such as aliphatic carboxylic acid soaps, sulfates such as alkyl sulfates, and the like. A system anionic activator etc. are used, and this activator is uniformly adhered by a deposition method, a spray method, a roll touch method, or the like. The nonwoven fabric imparted with the surfactant is then dried by known drying means. Subsequently, the thermal separator is thermally calendered and adjusted to a predetermined thickness to obtain the battery separator of the present invention.

Hereinafter, the content of the present invention will be described with reference to Examples. Further, various factors of the embodiment (thickness, tensile strength, elongation at break, air permeability, alkali retention rate, initial alkali absorption height, durable alkali absorption height, and functional groups on the surface of the nonwoven fabric constituting the separator) are as follows. Measured by

(1) The thickness was measured using a thickness gauge (trade name: THICKNESS GAUGE model CR-60A manufactured by DAIEI KAGAKUSEIKI SEISAKUSHO LTD) with a load of 20 g and a sample of about 1 cm ² .

(2) Tensile strength and elongation at break are taken at 5cm wide and 15cm long and held at 10cm intervals according to JIS L 1096, and stretched at 30cm / min using a constant-strength tensile tester. The load value and elongation rate were taken as tensile strength and elongation at break, respectively.

(3) The air permeability was measured in accordance with JIS L 1096 using a flaky type tester.

(4) The alkali retention rate is measured by measuring the weight (W) of the water equilibrium state of the sample pieces up to 1 mg, and then immersing the sample pieces in a hydroxide solution (KOH solution) having a specific gravity of 1.30, absorbing the KOH solution for 1 hour, and then removing the sample from the solution. After the piece was taken out and left for 10 minutes, the weight (W ₁ ) of the sample piece was measured, and the alkali retention rate was calculated as follows.

(5) The initial alkali absorption height is to take three specimens of 25 × 250 mm in the width direction of the sample and keep the water in equilibrium. Subsequently, a pin is fixed to a horizontal bar supported at a predetermined height on a water bath in which a potassium hydroxide aqueous solution (KOH solution) having a specific gravity of 1.3 is maintained at 20 ° C. The bottom of the sample piece was arranged in a straight line, the horizontal bar was lowered, and the bottom of the sample piece was placed vertically so that only 5 mm was contained in the solution. The height of the KOH solution was measured after 30 minutes by capillary action.

(6) Durable alkali absorption height The sample which measured the initial alkali absorption height (1st alkali absorption height) is wash | cleaned for 5 minutes with water, and it air-dried for about 1 hour after dehydration with a absorber. In addition, moisture is controlled until the sample is in equilibrium with moisture at an ambient temperature of 20 ° C. and a humidity of 65%, and the second alkali absorption height of the sample is measured. And the same operation is repeated and the 3rd alkali absorption height (durable alkali absorption height) with respect to a sample is measured.

(7) The functional group measurement test of the surface of the nonwoven fabric constituting the separator is performed by analyzing the surface atomic composition of the nonwoven fabric using the ESCA-3300 model manufactured by Shimadzu Corporation. As the measurement conditions, the radiation source is Mg / Al, the output is 8kW, 30mA, the nonwoven fabric measuring area is 5mm × 10mm, the depth from the nonwoven surface is 100Å (10nm), and the olefin exists on the nonwoven surface. The proportions of all carbon atoms and functional groups of the main chain and the subchain were measured. In addition, ESCA (Eelectron Spectroscopy for Chemical Analysis) is used as a measurement means for structural studies or academia analysis of atoms, molecules or solids by irradiating a sample with a monochromatic X-ray flux and measuring the emitted photoelectron energy.

(8) A cylindrical sealed nickel hydride battery was prepared as follows. First, the metal hydride cathode is kneaded with water to a hydride metal, carbonyl nickel, carboxy methyl-cellulose (CMC), polytetrafluoro ethylene (PTFE) and kneaded. The slurry was prepared, and the slurry was applied to a nickel-plated punching metal, followed by drying at 80 캜 and press molding. As the positive electrode, a known sintered nickel electrode was used. A cylindrical sealed nickel hydride battery was manufactured by inserting an electrolyte into the battery case and interposing a separator between the negative electrode and the positive electrode.

(9) The cycle life was calculated in the following manner. The Ni-MH electrode prepared above was subjected to battery initial activity by repeating 10 cycles of charging and discharging at 0.1c rate for 12 hours, resting 0.5 hour, and discharging 0.1c rate (final voltage 1.0V). And after performing initial activity, the next cycle was repeated at 20 degreeC until the retention rate with respect to theoretical capacity became 90% or less, and the number of cycles at that time is a cycle life. Here, one cycle consists of 10 hours at 0.1c charge rate, 0.5 hours of rest time, and 0.1c discharge rate (final voltage 1.0V).

(10) Internal pressure was measured in the following manner. Make a hole in the bottom of the battery case and assemble the battery with the pressure sensor. After performing initial activity using this battery, charge and discharge of 5 cycles were repeated. At this time, one cycle consists of 16 hours at 0.1c charge rate, 0.5 hours of rest time, and 0.1c discharge rate (final voltage 1.0V). Then, the pressure after 120 minutes charge at 1.0c rate was measured.

(11) The short rate was calculated as the rate at which short circuit occurred when 100 cylindrical sealed nickel hydride batteries were assembled.

◈ Example 1

30% by weight of heat-adhesive fiber which is a sheath-core type composite fiber having 1.5 denier and 10mm fiber length, 50% by weight of split composite fiber having 3 denier and 6mm fiber length, and 0.7 degree of fineness 0.7 A slurry was prepared to mix 20% by weight of polypropylene fiber having a denier and a fiber length of 10 mm to a concentration of 0.5%, and a wet nonwoven fabric having a reference weight of 55 g / m ² was produced by wet papermaking. Here, the heat-adhesive fiber (cease-core composite fiber) is composed of polypropylene (core component) and high density polyethylene (cease component) in a composite weight ratio of 50/50. In addition, the split composite fiber has a cross section as shown in FIG. 1, and is composed of component A (polypropylene) and component B (ethylene vinyl alcohol copolymer containing 38 mol% of ethylene). The area ratio of B component is 50/50.

Subsequently, by spraying a high pressure columnar water stream of 130 kg / cm ² of water pressure on both sides of the wet nonwoven fabric, the split composite fiber is divided to form ultrafine fibers of 0.19 to 0.2 denier, and the fibers are entangled with each other at 135 ° C. Thermal bonding was carried out simultaneously with drying. Thereafter, the corona surface discharge treatment was carried out so that the total discharge amount was 0.462 kW / m ² for each of the two sides of the nonwoven fabric four times, and thermal calendering treatment was performed to form a nonwoven fabric for battery separator.

◈ Example 2

A nonwoven fabric for battery separator was formed in the same manner as in Example 1 except that 0.2 wt% of the alkyl phosphate ester surfactant was applied.

◈ Example 3

30% by weight of heat-adhesive fiber with 1.5 denier and 45mm fiber length, 50% by weight of polymer composite fiber with 3 denier and 51mm fiber length, polypropylene with fineness of 1.2 denier and 45mm fiber length 20% by weight of the fibers were mixed and a fibrous web of 20 g / m ² of reference weight was produced using a semi-random carding machine. Here, the heat-adhesive fiber is made of polypropylene as a core component and high density polyethylene as a sheath component, and their composite weight ratio is 50/50. In addition, the split composite fiber has a cross section as shown in FIG. 1, and is composed of component A (polypropylene) and component B (ethylene vinyl alcohol copolymer containing 38 mol% of ethylene). The area ratio of B component is 50/50.

Thereafter, a high pressure columnar water stream of 50 kg / cm ² water pressure was sprayed on both sides of the fiber web to divide the split composite fiber and to entangle the fibers together.

Subsequently, dry adhesion was carried out simultaneously with drying at 135 ° C. to produce a dry nonwoven fabric having a reference weight of 20 g / m ² .

Next, in the wet paper machine, the dry nonwoven fabric was placed on the inlet side of the cylindrical dryer to prepare a slurry having a concentration of 0.5% made of the constituent fibers of Example 1, while the wet papermaking process was carried out so that the reference weight was 30 g / m ² . The dry nonwoven fabric provided in advance was laminated | stacked, heat-processed at 135 degreeC with the cylindrical drier, and the heat-adhesive fiber was adhere | attached on both surfaces of the fiber, and the composite nonwoven fabric was obtained.

In addition, by spraying a high-pressure columnar water stream of 130kg / cm ² water pressure on both sides of the composite nonwoven fabric to separate the split type composite fibers and entangled with each other, and then heat-bonded at 135 ℃ simultaneously. Thereafter, the corona surface discharge treatment was performed so that the total discharge amount was 0.462 kW · min / m ² for each of the two sides of the nonwoven fabric 4 times, and thermal calendered by a thermal roller to form a nonwoven fabric for battery separator.

◈ Comparative Example 1

The same treatment as in Example 1 was conducted except that the corona surface discharge treatment was not performed to form a nonwoven fabric for battery separator.

◈ Comparative Example 2

The same treatment as in Example 2 was carried out except that the corona surface discharge treatment was not performed to form a nonwoven fabric for battery separator.

◈ Comparative Example 3

A nonwoven fabric for a battery separator was formed in the same manner as in Example 1 except that 20 wt% of the heat-adhesive fiber and 80 wt% of the split composite fiber were used.

◈ Comparative Example 4

A nonwoven fabric for battery separator was formed in the same manner as in Example 1 except that 60% by weight of heat-adhesive fiber, 10% by weight of split composite fiber, and 30% by weight of synthetic fiber were used.

Table 1 shows the physical properties of the battery separator using the nonwoven fabric of Examples 1 to 3 and Comparative Examples 1 to 4 described above.

As can be clearly seen from Table 1, in Examples 1 and 2, it was confirmed that the initial and durable liquid absorption height was excellent while securing the tensile strength and air permeability. In Example 3, since the same material as in Example 1 was used for the wet nonwoven fabric and the dry nonwoven fabric, since the dry nonwoven fabric had a reinforcing effect, the tensile strength was significantly improved while maintaining the initial and durable alkali absorption heights. In Comparative Example 2, the initial liquid absorption height was improved by performing a hydrophilic surfactant treatment on the surface of the nonwoven fabric, but no liquid absorption was observed after the second time.

As can be clearly seen from Table 2, in Examples 1 to 3, a predetermined amount of functional group exists. Therefore, even after being assembled into the separator battery, unlike the surfactant treatment, it does not flow out of the fiber surface, but exists semi-permanently on the fiber surface, resulting in a dryout phenomenon (a part of the separator does not penetrate into the electrolyte). Battery cycle life was good. In Comparative Examples 1 and 2, the cycle life of the practical battery is not obtained because it falls from the endurance alkali absorption height, and in Comparative Example 3, the battery internal pressure is increased because the air gap between the fibers of the separator is small and the air permeability is decreased. On the contrary, the short rate was increased because the space between the fibers of the separator was too large.

The battery separator of the invention, fiber is -CHO or -C ⁺ HO present in the non-woven fabric surface while securing the strength of the nonwoven fabric and breathable ^-, -CO-, and -COO ^- since the functional group or bond or -COO- are formed, excellent It exhibits alkali retention, initial alkali absorption and durable alkali absorption, and has excellent wettability with an electrolyte when assembled into a battery, thereby improving battery life. Moreover, initial hydrophilicity and durability hydrophilicity are improved by adhering a hydrophilic surfactant to a nonwoven fabric surface.

In addition, the battery separator of the present invention is advantageous in terms of running cost since sufficient alkali retention and alkali absorption can be obtained even at a small discharge amount at the time of corona surface discharge.

The battery incorporating the battery separator of the present invention has high performance in battery characteristics and is suitable for alkaline storage batteries such as nickel-cadmium batteries, nickel-zinc batteries, nickel-hydrogen batteries and the like.

The present invention is not limited to the above-described specific embodiments, but can be modified and modified in various ways within the scope not departing from the gist of the present invention. The scope of the present invention is not specified by the above detailed description, but is defined by the appended claims, and all modifications within the meaning and range equivalent to the claims are included in the present invention.

Claims (17)

15 to 75% by weight of the ultrafine fibers formed by dividing in a split composite fiber in which the polyolefin polymer (component A) and the polyolefin polymer (component B) containing oxygen atoms are connected to each other in a cross-sectional view, and heat adhesiveness 20 to 60% by weight of fibers and short fibers composed of 0 to 50% by weight of synthetic fibers having fineness greater than the fineness of the ultrafine fibers are mixed so that the fibers are entangled with each other and some of the fibers are bonded to each other. The fibers present on the surface of the nonwoven fabric have functional groups and the division of functional groups or bonds for all carbon atoms is in the following ranges, respectively. (1) aldehyde groups (-CHO) or aldehyde bond ^{(-C + HO -): 10~40} % (2) Carbonyl group or carbonyl bond (-CO-): 3-30% (3) carboxyl groups (-COO ^-) or ester bonds (-COO-): 0~15% (4) Residual Carbon Atom: 15 ~ 87% A battery separator, characterized in that. The method of claim 1, A fiber separator of split type composite fibers, heat-adhesive fibers and synthetic fibers in the range of 3 to 25 mm, wherein the fineness of the synthetic fibers is equal to or smaller than the fineness of the heat-adhesive fibers. The method of claim 1, A battery separator, wherein the air permeability is in the range of 5 to 50 ccs. The method of claim 1, The alkali absorption height of a 3rd time is at least 5 mm, The battery separator characterized by the above-mentioned. The method of claim 1, And said heat-adhesive fiber is a sheath-core composite fiber having polyethylene as a sheath and polypropylene as a core. The method of claim 1, The nonwoven fabric is a battery separator, characterized in that the composite nonwoven fabric formed by laminating fiber webs having different fiber lengths. The method of claim 1, At least one other sheet is laminated on at least one layer of the nonwoven fabric. The method of claim 1, The component B is at least one polymer selected from an ethylene vinyl alcohol copolymer, an ethylene- (methyl) acrylate copolymer, an ethylene- (methyl) acrylic acid copolymer, and an ethylene-vinyl acetate copolymer. 15 to 75% by weight of a split type composite fiber having a length of 3 to 25 mm and a length of 3 to 25 mm, in which a polyolefin polymer (component A) and a polyolefin polymer (component B) containing an oxygen atom are disposed in contact with each other in a fiber cross section. 20 to 60% by weight of the heat-adhesive fiber of the fiber and 0-50% by weight of the synthetic fiber having a fineness greater than or equal to the fineness of the microfibers formed by the split composite fiber. Mixing and wet papermaking to form a wet nonwoven fabric; A step of dividing the split composite fiber to form an ultrafine fiber and intertwining the fibers in at least one of the wet papermaking process and the wet nonwoven fabric; And A method of manufacturing a battery separator comprising the step of performing a corona surface discharge treatment on both sides of the nonwoven fabric and a thermal calender treatment by a thermal roller. The method of claim 9, The split type composite fiber is a method of manufacturing a battery separator, characterized in that divided by the stirring impact in the wet papermaking process. The method of claim 9, The split composite fiber is a method of manufacturing a battery separator, characterized in that divided by high pressure water flow treatment. The method of claim 9, The divided ultrafine fibers are entangled by high pressure water flow treatment. The method of claim 9, The method of manufacturing a battery separator, characterized in that the splitting of the split composite fiber and the entanglement of the formed ultrafine fibers are carried out simultaneously by a high pressure water flow treatment. The method of claim 9, The total discharge amount which processes both surfaces of a nonwoven fabric by the said corona surface discharge process exists in the range of 0.05-5 kW * min / m <^2> . The method of claim 9, A hydrophilic surfactant is given to a nonwoven fabric after the corona discharge treatment. The method of claim 9, The component B is at least one polymer selected from an ethylene vinyl alcohol copolymer, an ethylene- (methyl) acrylate copolymer, an ethylene- (methyl) acrylic acid copolymer, and an ethylene-vinyl acetate copolymer. Manufacturing method. 15 to 75% by weight of the ultrafine fibers formed by dividing in a split composite fiber in which the polyolefin polymer (component A) and the polyolefin polymer (component B) containing oxygen atoms are connected to each other in a cross-sectional view, and heat adhesiveness 20 to 60% by weight of fibers and short fibers composed of 0 to 50% by weight of synthetic fibers having fineness greater than the fineness of the ultrafine fibers are mixed so that the fibers are entangled with each other and some of the fibers are bonded to each other. In the fibers present on the surface, functional groups exist and the division of functional groups or bonds to all carbon atoms is in the following range (1) aldehyde groups (-CHO) or aldehyde bond ^{(-C + HO -): 10~40} % (2) Carbonyl group or carbonyl bond (-CO-): 3-30% (3) carboxyl groups (-COO ^-) or ester bonds (-COO-): 0~15% (4) Residual Carbon Atom: 15 ~ 87% A battery comprising the battery separator in the assembly.