JP2003036832A - Separator for alkali cell and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for an alkali secondary cell which oxygen gas generated on the overcharge of the cell smoothly passes through, hardly raising the cell inner pressure, and has superior discharge and cycle life performances. SOLUTION: A porous sheet composed of a thermoplastic resin, preferably a polyolefinic resin, is fabricated, hydrophilized and then given unevenness on its surface, whereby the separator hydrophilized and with unevenness thereon for an alkali cell is provided. The use of said separator for a cell provides a cell having superior inner pressure controlling, discharge and cycle life performances.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sealed alkaline battery such as a nickel-hydrogen storage battery or a nickel-cadmium storage battery, and more particularly to a battery separator and a method for producing the same.

[0002]

2. Description of the Related Art A sealed alkaline storage battery has a positive electrode, a negative electrode,
The electrolyte is roughly divided into an electrolyte, a separator, and a container, and the positive electrode and the negative electrode are separated by the separator and are stored in the container in a state of being immersed in the electrolyte solution.

Further, in a sealed alkaline storage battery, a system is adopted in which the negative electrode absorbs oxygen gas generated in the positive electrode during overcharge. Therefore, the internal pressure rise at the time of overcharge is relatively small and the safety is high. Therefore, application to large current applications such as electric vehicles and electric tools is being promoted.
However, during overcharge, if the generation rate of oxygen gas at the positive electrode becomes faster than the absorption rate of oxygen gas at the negative electrode side, the internal pressure of the battery gradually rises, causing damage or shortening of the life of the battery, or the generated gas is a separator. By pushing away the electrolyte solution inside, the effective area of the negative electrode is reduced, the discharge characteristics, especially the discharge characteristics at a high rate are deteriorated, and the resistance inside the battery is caused to shorten the battery life (or cycle life in other words). It also has drawbacks. Therefore, various studies have been made to improve the oxygen absorption rate of the negative electrode. Particularly for separators, studies are underway to smoothly transmit the generated oxygen gas from the positive electrode to the negative electrode.

In order to solve such a problem, for example, in Japanese Unexamined Patent Publication No. 10-106525, a high density layer is provided on the side facing the positive electrode plate, and a low fiber density lower than the high density layer is provided on the side facing the negative electrode plate. Nonwoven fabric having a density layer, JP-A-6-11
1847 discloses a negative-fiber-side fine fiber-containing layer (liquid-retaining layer).
And a thick fiber-containing layer on the positive electrode side.
82115 discloses a nonwoven fabric in which an acrylic acid-containing fiber-containing layer and a polyolefin-based fiber-containing layer are heat-bonded and, if necessary, subjected to a sulfonation treatment, JP-A-8-11573.
Non-woven fabric obtained by graft-polymerizing a hydrophilic monomer to a non-woven fabric in which a thick fiber-containing layer and a fine fiber-containing layer described in JP-A No. 9 are integrated. In JP-A-7-57712, two or more non-woven fabrics are integrated by hot air. Nonwoven Fabric, JP-A-11-54
No. 101 discloses a multilayer non-woven fabric produced by hydroentangling treatment, and JP-A No. 5-89869 discloses a battery in which an electrolytic solution resistant mesh material is installed between a separator and a negative electrode. In the publication, a battery in which a plurality of separators are partially laminated is reported. However, any of the methods is characterized in that a plurality of layers having different characteristics are superposed, and the process becomes complicated. In addition, there is a drawback that the thickness is increased by that amount, which is not suitable for increasing the capacity of the battery. Further, the fibers present in the non-woven fabric are entangled with each other, and there are a large number of spaces (in other words, pores) in which gases and electrolytes of various sizes created by the entanglement of fibers can move. Here, a layer mainly composed of thick fibers, a low-density layer, or a non-woven fabric having a portion with few fibers is particularly large in pore size (hereinafter referred to as pore diameter), and electrode burrs There is also a drawback that the electrode active material particles penetrating through or separated from the electrode are buried in the separator to cause a short circuit.

In addition to the attempts to improve the structure of the separator as described above, attempts have also been made to control the hydrophilicity. For example, Japanese Patent Laid-Open No. 8-255629
In Japanese Patent Laid-Open No. 7-53042 and Japanese Patent Laid-Open No. 7-53042, it is attempted to suppress an increase in internal pressure by mixing a hydrophilic portion and a hydrophobic portion in a separator. In these separators, it was possible to improve the oxygen consumption rate in the hydrophobic portion in contact with the negative electrode, but since there is little space where oxygen gas can exist on the negative electrode side, the oxygen consumption rate improving effect is effectively used. No, I have not completely solved the problem of internal pressure. In addition, since the hydrophobic portion cannot hold the electrolytic solution, dryout is likely to occur, and the battery has a short life.

Generally, when a nonwoven fabric, a porous film or other porous sheet is used as a separator for an alkaline battery, it is necessary to maintain its affinity with an electrolytic solution for a long period of time, and the hydrophobicity such as a polyolefin resin is used. When using a resin, it is necessary to carry out a hydrophilic treatment. Further, as the method of hydrophilization treatment, graft treatment, sulfonation treatment, surfactant attachment treatment, corona treatment, plasma treatment, fluorine gas treatment, resin coating treatment, and the like can be mentioned. Since it can be maintained for a long period of time and has an adsorbing function for impurities (ammonia), which is a problem in nickel-hydrogen batteries, sulfonation treatments such as sulfuric acid treatment, fuming sulfuric acid treatment, and sulfur trioxide gas treatment, Alternatively, it is preferable to carry out at least any one of grafting treatment of a monomer having a hydrophilic functional group represented by acrylic acid. Further, it is also possible to combine the sulfonation treatment or the graft treatment with other hydrophilic treatment formulations.

In the present invention, when the porous sheet on which irregularities are previously formed is hydrophilized by sulfonation or grafting, uneven distribution occurs in the hydrophilic functional group,
It was found that the performance of the battery incorporating the separator is deteriorated. It is estimated that this is because the electrolyte solution was not uniformly distributed.

[0008]

SUMMARY OF THE INVENTION In view of the above problems, the inventors of the present invention allow oxygen gas generated during overcharge of an alkaline secondary battery to pass satisfactorily, and the internal pressure of the battery is less likely to rise.
In addition, for the purpose of easily obtaining a separator having excellent discharge characteristics and cycle life, the inventors have made earnest studies on the raw material and shape of the porous sheet and the hydrophilization treatment method, and have invented a separator satisfying the above objective and a manufacturing method thereof.

[0009]

Means for Solving the Problems That is, the inventors of the present invention prepared a porous sheet made of a thermoplastic resin, particularly a polyolefin resin, and subjected it to a hydrophilic treatment in advance before forming irregularities, and then the porous sheet. The present invention relates to a hydrophilized alkaline battery separator having unevenness on the surface by forming unevenness on a sheet, and when the separator is incorporated into a battery, has an excellent effect of suppressing internal pressure, discharge characteristics, and cycle life. It has been found that a battery having

The depth of the recess of the present invention is 5% or more and 50% or less of the apparent thickness of the separator, and the area of the recess is 5% or more and 50% or less with respect to the total area of the separator. The present invention relates to an alkaline battery separator.

The present invention also relates to an alkaline battery separator in which the thermoplastic resin is a polyolefin resin.

The present invention also relates to an alkaline battery using a battery separator in which the surface of the separator having irregularities faces at least the negative electrode.

Further, the present invention relates to an alkaline battery separator containing a high-strength polyolefin synthetic fiber having a tensile strength of 3 cN / dtex or more.

Further, the present invention relates to an alkaline battery separator according to any one of claims 1 to 5, which contains an ultrahigh molecular weight polyolefin-based synthetic resin having an intrinsic viscosity of 6 or more.

Further, the present invention relates to a method for manufacturing an alkaline battery separator, wherein the hydrophilic treatment is at least one of a sulfonation treatment and a graft treatment.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION As a concrete method, first, the alkaline battery separator of the present invention needs to be a porous sheet. The porous sheet here refers to a fibrous sheet such as a non-woven fabric, a woven fabric or a knitted fabric, or a foam type porous body typified by a porous film.

When a porous sheet is used as the alkaline battery separator of the present invention, any known method can be used for its production. For example, in the case of a nonwoven fabric, a long sheet produced by the spunbond method is used. A non-woven fabric made of fibers can be used, a non-woven fabric made by a melt blow method or flash spinning can also be used, and a method called an air-laid method of carrying opened fibers by an air stream can also be used. Further, a chemical bond method of bonding dry non-woven fabric represented by a card system with an adhesive, or a thermal bond method of bonding with a self-adhesive or an adhesive fiber can also be used. Furthermore, as a method of entanglement, there are a spunlace method using a high-pressure water flow, a needle punch method of needling a web with a special needle, a stitch bonding method of knitting with a thread, etc., and fine processing is performed so that pinholes are not generated. Can be used in things. In addition, horizontal fourdrinier system, slanted wire fourdrinier system, circular net system, or fourdrinier,
It is also possible to use a non-woven fabric made of fibers by a wet method such as a cylinder combination method, or a non-woven fabric made by a wet method using the same fiber adhesion and fiber entanglement method as the method shown in the above dry method. is there. In any of the methods, it is preferable to control the orientation state of the fibers so that they are oriented in the longitudinal direction.

On the other hand, in the case of a porous film, a general unstretched film is made into a porous film by stretching, or an unstretched film containing an extractable filler, a plasticizer and, if necessary, an inorganic fine powder. If necessary, a filler, a plasticizer and the like are extracted with a solvent to make it porous, and a film made porous by optionally stretching before or after extraction, or a film made porous by irradiating the film with a laser, For example, by heat-fusing a uniform nonwoven fabric containing ultrafine fibers such as fibrillated fibers or split-type fibers into a film, and heat-sealing a powdered or fibrous resin or a mixture thereof. A porous film or the like formed into a film can be used. It is also possible to mix bubbles or substances that generate bubbles during film formation. Furthermore, these can be combined.

Further, as the resin constituting the battery separator of the present invention, any organic resin material can be used, but it is particularly preferable to use a polyolefin resin from the viewpoint of resistance to an electrolytic solution, oxidation resistance and the like. preferable. Here, the polyolefin-based resin is a resin composed of a polyolefin alone, or a resin composed of a copolymer of an olefin and another monomer, and as the polyolefin,
For example, polyethylene, polypropylene, polymethylpentene, polybutene, polyethylene-propylene, polyethylene-butene-propylene and the like can be mentioned, and other monomers copolymerizable with the olefin include styrene, vinyl butyrate and acetic acid. Examples thereof include vinyl. In addition, a polyvinylidene fluoride-based polymer, a tetrafluoroethylene-based fluorine-based polymer, or a polymer including a part thereof may be used.

In addition to these resins, various additives such as antioxidants, ultraviolet ray inhibitors, antistatic agents, colorants, flame retardants, and metal components may be mixed. The addition amount may be within a range that does not deteriorate the battery performance when finally incorporated into the battery.

The above-mentioned resins may be used alone or in combination of two or more kinds, and are not particularly limited.

For example, when a fibrous component is included in the production of the porous sheet, a core-sheath type composite fiber,
It is preferable to use an eccentric body sheath type composite fiber, a parallel type composite fiber, a sea-island type composite fiber, a split type composite fiber, or the like. Non-woven fabrics made by using core-sheath composite fibers in which polyethylene is arranged on the outside of polypropylene, or by mixing them, and non-woven fabrics in which split type composite fibers capable of forming ultrafine fibers are mixed and then opened by water flow are It can be used effectively.

In particular, when a non-woven fabric made mainly of short fibers is used, its strength is weaker than that of a non-woven fabric composed of long fibers. Therefore, the strength of the non-woven fabric is improved by introducing a fusion process. Is preferred. Therefore, it is more stable to manufacture by mixing a plurality of types of polyolefin resin components having different melting points. Therefore, it is more suitable to mix two or more kinds of polyolefin-based resins together than to produce them by using only a single polyolefin-based resin. At this time, at least the resin having the lowest melting point is used as the adhesive component, and a part of the resin is melted and adhered. Therefore, in the fiber containing the polyolefin resin component having the low melting point, the polyolefin resin component having the low melting point is the fiber. It is better to be exposed on at least a part of the surface, preferably 30% or more, preferably 50% or more, of the fiber surface area. If it is less than 30%, there will be a portion where the adhesiveness is insufficient only by melting the resin having the lowest melting point. On the other hand, there is no problem even if the exposure is 100%. Further, it is preferable that the difference in melting point between the plural kinds of resins mixed in the nonwoven fabric is 10 ° C. or more between the resin component having the lowest melting point and the resin component having the highest melting point. For example, a nonwoven fabric using a core-sheath composite fiber in which polyethylene is arranged on the outside of polypropylene or a fiber in which polypropylenes having different melting points are combined can be effectively used.

Further, in the non-woven fabric produced by using the above-mentioned polyolefin synthetic resin and fiber,
The average fineness is preferably in the range of 0.05 to 3 dtex, and more preferably in the range of 0.1 to 2 dtex. If the average fineness is less than 0.05 dtex, the fiber strength is inherently weak and a short circuit occurs during battery production. On the other hand, when the average fineness exceeds 3 dtex, when the separator is used, the number of places having a wide pore diameter increases, leading to a short circuit.

It is also possible to increase the strength of the non-woven fabric by mixing high-strength fibers. At that time, the tensile strength of the high-strength fiber is preferably 3 cN / dtex or more, more preferably 7 cN / dtex or more, and more preferably 10
It is preferably cN / dtex or more. If the tensile strength of the high-strength fiber is weaker than 3 cN / dtex, the effect of improving the strength decreases. The upper limit of the tensile strength of the high-strength fiber should be 40 cN / dtex or less in consideration of handleability during battery production, and if it is stronger than that, a special device is required.

When high-strength fibers are further mixed, it is preferable to use a polyolefin-based resin as the resin component constituting the high-strength fibers from the viewpoint of resistance to an electrolytic solution, oxidation resistance and the like. More specifically, the polyolefin-based resin is a resin composed of a polyolefin alone, or a resin composed of a copolymer of an olefin and another monomer, and examples of the polyolefin include polyethylene, polypropylene, and polymethylpentene. , Polybutene, polyethylene-propylene, polyethylene-butene-propylene, and the like, and other monomers copolymerizable with the olefin include styrene, vinyl butyrate, vinyl acetate, and the like. . Among these resins, those made of polyethylene resin or polypropylene resin are preferable. In addition, a polyvinylidene fluoride-based polymer, a tetrafluoroethylene-based fluorine-based polymer, or a polymer including a part thereof may be used.

Regarding the high-strength fiber, the high-strength resin may be used alone, or a core-sheath type composite fiber, an eccentric body-sheath type composite fiber, a parallel type composite fiber, a sea-island type composite fiber, a split type composite fiber, etc. You may mix two or more kinds of resin like
It is not particularly limited. For example, a porous sheet prepared by using core-sheath composite fibers in which polyethylene is arranged on the outside of high-strength polypropylene or by mixing them together can be effectively used.

Further, the high-strength fiber must be mixed with a nonwoven fabric made of short fibers, for example, a non-woven fabric made by a wet method, or a non-woven fabric made of long fibers that is not sufficiently stretched, for example, made by a melt blow method. I won't.
Nonwoven fabrics made from short fibers and nonwoven fabrics made from long fibers that have not been sufficiently stretched are inherently weak in strength, so if irregularities are made, short circuits easily occur. At that time, the high-strength fiber is preferably mixed in the range of 5% or more and 40% or less, and more preferably in the range of 10% or more and 30% or less. If the mixed amount is less than 5%, the short circuit probability increases. On the contrary, if it exceeds 40%, the handling property becomes worse,
Special equipment is required. On the other hand, for a nonwoven fabric composed of long fibers prepared by sufficiently performing stretching, which is typified by a nonwoven fabric manufactured by a spun bond method, a separator having very good strength characteristics when high-strength fibers are mixed. However, since the original strength is high, it is not always necessary to mix high-strength fibers. Therefore, the high-strength fiber can be mixed in the range of 40% or less, and even if it is mixed in a small amount, it exhibits very good strength characteristics.

The fiber diameter of the high-strength fiber is preferably in the range of average fineness of 0.1 dtex to 3.0 dtex, and more preferably in the range of 0.2 to 2.0 dtex. If the average fineness is less than 0.1 dtex, the effect of improving strength is insufficient. On the other hand, when the average fineness exceeds 3.0 dtex, the number of wide pores increases when the separator is used,
It leads to a short circuit.

On the other hand, when a porous film is used as the porous sheet, different kinds of resins can be mixed. The resin component to be used may have a low molecular weight to an ultra-high molecular weight, and resins having any molecular weight may be used alone or in combination. When used as a separator for alkaline batteries, the separator needs to have hydrophilicity, for example, as an example of the hydrophilic treatment, hydrophilic by sulfonation treatment using sulfur trioxide gas of the polyolefin-based porous film In consideration of conversion, a film having a low molecular weight component has an advantage that it is easily hydrophilized. On the other hand, the film having an ultrahigh molecular weight component has the advantage that it has a high strength and can reduce the probability of short circuit due to electrode burrs penetrating when thinned. Therefore, it is possible to appropriately mix and use resins having different molecular weights.

When the ultrahigh molecular weight resin is mixed in the porous film, it can be selected from the above-mentioned polyolefin resins, but the intrinsic viscosity is 6 or more, more preferably 8 or more, and further 10 or less. A film having good mechanical strength can be produced by using the above materials. On the other hand, if the intrinsic viscosity exceeds 30, the processability of the produced separator deteriorates, which is not suitable. When determining the intrinsic viscosity, the intrinsic viscosity obtained by simply dissolving the resin in a resin prepared by mixing multiple components is the value obtained by mixing resin components with different properties. Therefore, it may be difficult to determine whether or not the ultra-high molecular weight polyolefin resin is mixed. Therefore, it suffices to separate a plurality of resin components by using, for example, GPC, and the separated resin components contain a resin component having an intrinsic viscosity within the above range. The solvent, column, sample preparation conditions, temperature, etc. when using GPC need to be appropriately adjusted for each film so that the resin component contained in the film can be separated. Therefore, the GPC measurement method described below is an example. Further, as the ultrahigh molecular weight polyolefin resin, ultrahigh molecular weight polyethylene or ultrahigh molecular weight polypropylene is particularly preferable.

When a plurality of resin components having different intrinsic viscosities, that is, different molecular weights are mixed in the porous film, the moldability at the time of melt molding is deteriorated. However, in the separator of the present invention, it is particularly important to have unevenness on the separator surface, and since it includes the step of forming unevenness, it is not necessary to consider the influence of the molecular weight distribution, and even when different resin components are mixed. It is possible to obtain a good film separator. Therefore, if the weight average molecular weight / number average molecular weight of the resin raw material used for the separator of the present invention is 20 or less, a good separator can be produced.

When the above ultrahigh molecular weight polyolefin resin is mixed in the porous film, it is preferably contained in an amount of 1% or more, more preferably 3% or more, and most preferably in the basis weight of the separator. Is 5% or more. If the amount of the ultra high molecular weight polyolefin resin used is less than 1%, the effect of mixing the ultra high molecular weight polyolefin resin cannot be sufficiently obtained. On the other hand, when the amount of the ultra high molecular weight polyolefin resin used exceeds 50%, the tensile strength of the separator becomes too strong, which is not desirable in consideration of workability.

In the separator of the present invention, the porous sheet typified by the above-mentioned nonwoven fabric or porous film is
It must have hydrophilicity. Here, the hydrophilic treatment of the porous sheet needs to be performed before the unevenness forming step. It was found that when the hydrophilization treatment is performed after the unevenness is formed, the distribution of the hydrophilic functional groups becomes uneven as described above, which leads to the deterioration of the performance of the battery incorporating the separator. It is estimated that this is because the electrolyte could not be distributed uniformly.

As the method of hydrophilic treatment, it is preferable to carry out either graft treatment or sulfonation treatment. Further, a surface-active agent impregnation treatment, a corona treatment, a plasma treatment, a fluorine gas treatment, a resin coating treatment and the like may be performed together.

As the sulfonation method, a method of dipping in hot sulfuric acid, a method of dipping in fuming sulfuric acid, a method of dipping in chlorosulfuric acid, a method of contacting with sulfur trioxide gas, dipping in sulfuric acid or fuming sulfuric acid And contacting with sulfur trioxide gas or sulfur dioxide gas repeatedly, method of contacting with sulfur trioxide gas after soaking in hot sulfuric acid, method of contacting with mixed gas of sulfur dioxide and oxygen after performing fluorine treatment Any of these can be suitably used. Further, as the grafting method, any known method such as a method of applying energy such as ultraviolet irradiation treatment, plasma treatment, corona treatment, etc. at the same time when a vinyl monomer or the like is brought into contact with a resin and a method using a catalyst can be used. It is possible.

The above-mentioned hydrophilic treatment must be carried out before forming irregularities on the porous sheet. When the hydrophilic treatment is performed after the unevenness is formed, unevenness occurs in the distribution of the hydrophilic functional group,
This is because the performance of the battery incorporating the separator is deteriorated. It is estimated that this is because the electrolyte could not be distributed uniformly. The following two possibilities are considered as the reason why the distribution of the hydrophilic functional group is uneven. One comes from the shape of the porous sheet.Since the density of the resin is different between the part where unevenness is present and the part where unevenness is not created, the impregnation property of the hydrophilicizing reagent is different, The theory that the degree of hydrophilicity is different due to the different retention. The other is that the thermal history is different between the uneven portion and the portion where no unevenness is formed, so the characteristics involved in the susceptibility of the resin to hydrophilicity, as represented by the crystallinity, are different. Therefore, it is the theory that the degree of hydrophilicity is different between the uneven portion and the portion where the unevenness is not formed. It is unclear which one is strongly involved, but as a result of the combination of the two, in the separator produced by hydrophilizing and then forming the unevenness, the hydrophilicity is obtained in the uneven portion and the portion where the unevenness is not formed. Because of the difference, it is considered that the distribution of the hydrophilic functional group is uneven. As a result, the electrolytic solution tends to concentrate at a specific location in the separator, which makes it easier to partially dry out, reducing the contact area between the separator and the electrode, and consequently reducing the battery performance. ing.

By performing the above-mentioned hydrophilic treatment, hydrophilic functional groups such as sulfonic acid groups, sulfonic acid esters, carboxyl groups, carbonyl groups, hydroxyl groups, and fluorine-based functional groups can be provided on the surface of the porous sheet. Further, the amount of the hydrophilic functional group is preferably at least 0.0005 meq / g or more when evaluated from the amount of ion exchange, and if the amount of ion exchange is smaller than that, the affinity with the electrolytic solution is expected to be less. Can not. On the other hand, if it is made too hydrophilic, the strength is lowered in the sulfonation treatment, and in the graft treatment, the life when incorporated in a battery is shortened. Therefore, in the sulfonation treatment, the amount of sulfur examined by emission spectroscopy should be 20000 ppm or less. Further, in the graft treatment, the weight increase due to the graft treatment should be suppressed to 25% by weight or less.

In the separator of the present invention, it is necessary to form unevenness after the hydrophilic treatment. The method for providing the unevenness is not particularly limited, and any known method for forming the unevenness can be used. For example, processing with an embossing roll or gear roll, a method of transferring unevenness by pressurizing and / or heating with a die, a metal mesh, a resin net, etc., a method of cutting with a sharp edged tool, a method of squeezing or chaffing A method of forming a non-woven fabric on a net having irregularities, a method of partially melting and compressing or removing a resin, and the like can be given. Note that a method of transferring irregularities by applying pressure or heating, a method of forming a porous sheet on a net having irregularities, or the like is particularly preferable because it does not specifically create a weak spot.

The sectional shape of the concavities and convexities formed by the concavo-convex processing may be any one of U-shape, V-shape or square as shown in FIG. The shape of the unevenness viewed from the upper surface may be either continuous or discontinuous such as grooves and ridges, and these may be used alone or in combination. Examples of the continuous unevenness include those arranged in one direction as shown in FIG. 2 and those intersecting in a lattice pattern or randomly. Examples of the non-continuous shape include a polygonal shape such as a round shape, a star shape, a triangular shape, a quadrangular shape, and a cross shape as shown in FIG. 3, an irregular shape, and a combination thereof, but are not limited. It is particularly effective to have a continuous groove on the surface. Further, it is preferable that the irregularities are uniformly dispersed.

Due to the unevenness provided by the above method, a minute space can be formed between the negative electrode and the separator when the battery is wound. The oxygen gas generated in the positive electrode passes through the inside of the separator and is temporarily held in this space, and is then consumed on the surface of the negative electrode, so that the increase in the internal pressure of the battery can be suppressed. Therefore, in the present invention, the unevenness needs to be such that a sufficiently small space can be formed between the separator and the electrode surface in the battery. At the same time, since it is possible to suppress an increase in internal pressure, it is possible to prevent the gas from pushing away the electrolytic solution in the separator and reducing the effective area of the negative electrode, and it is possible to improve the discharge characteristics, especially at a high rate. Furthermore, since the separator can hold the electrolytic solution for a long time, the cycle life can be improved.

In the separator obtained by hydrophilizing the uneven nonwoven fabric as described above, the depth of the recess is 5% or more with respect to the apparent thickness of the separator.
% Or less, and more preferably 10% or more and 45% or less. This is because if the depth of the recess is less than 5%, a sufficient space is not formed between the electrode surface and the separator, and the effect of unevenness cannot be obtained. Further, when the depth of the recess is larger than 50%, an extremely thin portion is formed, so that the strength of the portion is reduced and breakage or short circuit during battery winding is likely to occur. If the thickness of the recess is increased to avoid this,
The thickness of the entire separator becomes large.

The area of the recesses with respect to the entire area of the separator is preferably in the range of 5% to 50%, more preferably 10% to 35%. If it is less than 5%, the effect of making unevenness cannot be obtained, and conversely, if it is more than 50%, the adhesion with the electrode becomes poor, and the battery performance deteriorates.

Further, particularly in a nonwoven fabric having continuous unevenness, the average value of the width of the recesses is preferably in the range of 0.2 to 3.0 mm, more preferably 0.4 to 3.0 mm.
It is 2.0 mm. If the width of the recess is smaller than 0.2 mm, the space formed between the separator and the negative electrode is small, so that the effect of suppressing the increase in internal pressure decreases. on the other hand,
If it is larger than 3.0 mm, the adhesion with the electrode is deteriorated and the battery performance is deteriorated.

In the porous sheet having the above range, the air permeability measured by the Frazier method is preferably 40 cm ³ / cm ² / s or less, more preferably 30 cm ³ / c.
It is preferably m ² / s or less, more preferably 25 cm ³ / cm ² / s or less. In a non-woven fabric having an air permeability according to the Frazier method of a value of the above range or more, a portion having a wide pore diameter increases and a short circuit occurs. Furthermore, in order to ensure the permeability of oxygen gas generated at the end of charging, the air permeability by the Frazier method is 2c.
It is preferably m ³ / cm ² / s or more, and more preferably 4 cm ³ / cm ² / s or more. Therefore, it is desirable that the nonwoven fabric used in the present invention has an air permeability of ^{2 to} 40 cm ³ / cm ² / s.

In order to produce a porous sheet having the above range, the weight of the porous sheet is 20 g / m ² or more and 80 g or more.
/ M ² or less, and optimally 25 g /
It is preferably m ² or more and 70 g / m ² or less, and more preferably 30 g / m ² or more and 65 g / m ² or less. When the weight of the porous sheet is more than 80 g / m ² , the nonwoven fabric becomes too clogged and the gas permeability becomes insufficient. On the other hand, when the weight of the porous sheet is less than 20 g / m ² , the strength is inherently weak and the separator is apt to be short-circuited.

The maximum pore size of the separator is 5
0 μm or less is preferable, and more preferably, the maximum pore size is 40 μm.
It is preferably m or less, 30 μm or less, and more preferably 25 μm or less. When the maximum pore size of the separator is larger than 50 μm, short circuit is likely to occur. Also, the pore size distribution is preferably as small as possible within the range where the above-mentioned air permeability is satisfied. For example, in the separator of the present invention, pores having a pore diameter of 30 μm or less account for 95% of all pores.
As described above, it may be 100% or more in some cases. This is because it is possible to deform the fibers and reduce the pore size existing in the separator when forming irregularities on the surface by pressing, for example.

If the tensile strength is weak when the separator is assembled into the battery, a short circuit occurs, so that the tensile strength is 50%.
N / 5 cm or more is desirable, and more preferably 75 N / 5 cm or more. Tensile strength is 50N / 5c
If it is less than or equal to m, the probability that a short circuit will occur when it is incorporated into a battery increases. On the other hand, if the tensile strength exceeds 300 N / 5 cm, the handleability of the separator is deteriorated, so it is preferable to avoid it.

When a battery is constructed using the separator according to the present invention, it is necessary to dispose the surface having irregularities so as to face at least the negative electrode. By arranging the unevenness on the negative electrode side, a space is formed between the negative electrode surface and the separator, the oxygen gas generated from the positive electrode can be efficiently moved to the negative electrode side, and the moved oxygen gas is efficiently on the negative electrode surface. It is well absorbed, and as a result the rise in internal pressure of the battery is suppressed. In addition, as described above, this leads to improvement in discharge characteristics and cycle life.

When a sealed battery is produced using the separator of the present invention, (1) pressure and tension applied to the separator when producing a wound body, (2) flatness of the electrode surface, (3) ) Electrode hardness, (4) Amount of electrolytic solution, (5) Method of injecting electrolytic solution, (6) Resistance when removing core from wound body and concentration of stress on uneven portion, (7) Welding tab At this time, it is necessary to consider at least the temperature applied to the separator. If the pressure or tension applied to the separator at the time of producing the wound body is high, the unevenness existing on the surface of the separator is crushed and the effect of suppressing the internal pressure is weakened. Further, in some cases, a short circuit occurs. Further, if the flatness of the electrode surface is poor, it will lead to a short circuit. On the other hand, if the electrode is too soft, the unevenness is filled up and the effect of suppressing the internal pressure is weakened. Further, if the amount of the electrolytic solution used is too large, the internal pressure tends to rise, and if the amount is too small, the internal resistance increases and the life of the battery is shortened. If the method of injecting the electrolytic solution is bad, the productivity of the battery is deteriorated, or the electrolytic solution is not evenly distributed, so that the performance of the battery varies. In addition, if the resistance at the time of removing the winding core from the wound body is large or stress concentration occurs on the uneven portion, the separator is broken and short-circuited. Also, if the separator is heated and melts or shrinks when welding the tabs needed to remove the battery from the electrode, there is a risk of short circuiting.
Therefore, when producing a battery using the separator of the present invention, it is necessary to consider at least the problematic points in producing such a battery, and the battery produced in consideration of these points is also It is included within the scope of the inventive battery. Further, it is preferable to consider the shape of the battery, the ratio of the electrode and the separator, the alloy composition used for the electrode, the winding method, and the like.

Further, in the separator manufactured under the above conditions, when measured by the evaluation method described later, it is 120 to 2
It is possible to have sufficient gas permeability and separator strength with a thickness of 50 μm, and further, even with a thin separator of about 60 to 120 μm in which the fiber density is relatively high to prevent a short circuit, good gas permeability is obtained. As a result, the internal pressure can be prevented from increasing.

Further, since the gas permeability can be maintained even if the fiber density is increased, the separator having a puncture strength of 5 N or more, which is involved in the short-circuit suppressing performance of the battery, and further 8 N
The above or a separator of 10 N or more can be manufactured.

The methods for measuring the physical properties of various separators according to the present invention will be described below. -Weight, apparent thickness, recess depth (1) From the separator, test piece (width 5 cm, length 10 c
m) was sampled, and the value converted into the weight per 1 m ² based on the weight when dried at 60 ° C. ± 2 ° C. for 10 hours,
The weight was [g / m ² ]. The test piece n was calculated as an average of 20 points. (2) The thickness of the central portion of the test piece was measured with a diameter of 31.
5mm Digital Thickness Gauge (Peacock Digital Thickness Gauge)
Was measured using. It was calculated by the average of n = 20 points. (3) The cross-sectional shape of the separator is magnified 300 times with an optical microscope, and the thickness of the recess is measured. The difference between the thickness of the recess and the apparent thickness was defined as the depth of the recess. It was calculated by the average of n = 30 points.

-Air permeability: According to the air permeability measuring method of JIS L1096-1990,
It was measured by a Frazier type tester.

Tensile strength A sample with a width of 5 cm and a length of 15 cm was used to measure the longitudinal (M
The tensile strength in the D direction is JIS L1068
According to (Tensile test method for textiles), the gripping interval is 10
cm, and the pulling speed was 30 cm / min. The test piece n was calculated as an average of 20 points.

Puncture strength The puncture strength is such that the sample has a diameter of 1.13 cm and an area of 1 cm.
^It was fixed to a circular hole holder No. 2 and the maximum load applied to the needle when the needle having a spherical tip of 0.5R and a diameter of 1 mmΦ was lowered at a speed of 2 mm / sec until it penetrated the sample was used. Specifically, Kato Tech KES-G
The measurement was carried out using a 5 handy compression tester. The average of test pieces n = 100 points was obtained.

The melting point of the resin is DSC292 manufactured by TA Instruments.
It was measured by differential scanning calorimetry (DSC) using 0. Specifically, a separator piece in which 10.0 mg was accurately weighed was placed in an aluminum pan, and the lid was tightly covered. Then, the outer peripheral portion of the aluminum pan was bent inward and completely sealed. Then, the temperature was raised from room temperature to 200 ° C. at 10 ° C./min, and the melting point was determined. The melting point was the temperature at the maximum of the peak. The measurement was performed 5 times and the average thereof was used.

• Pore size Coulter Porometer 2 is used to measure "AS
It was measured by the bubble point method according to "TM F 316-86". The test piece was measured at n = 10 points.

A test piece with an ion exchange amount of 0.2 g was completely impregnated with a 1 mol / L HCl aqueous solution, and then transferred into a 1 mol / L HCl aqueous solution and immersed for 1 hour. Then, the pH is 6-with ion-exchanged water.
Washed several times to 7. Then, it was dried for 2 hours by a blast dryer at 60 ° C. and cooled to room temperature. The cooled test piece was immersed in 100 cm ³ of a 0.01 mol / dm ³ KOH aqueous solution and shaken at 45 ° C. for 1 hour, then the test piece was taken out and 25 cm ³ of the solution was collected to obtain 0.01 mol / L of the solution. Neutralization titration with an aqueous HCl solution. The blank solution was also titrated in the same manner, and the potassium ion exchange amount was calculated from Formula 1.

Ion exchange amount (meq / g) = {(V0-V1) × 100 × 0.01 × f} / (25 × 0.2) (Equation 1) where V1: required for titration of sample Amount of HCl aqueous solution (c
m ³⁾ V0: HCl aq amount required for titration of the blank solution (c
m ³ ) f: Factor of aqueous HCl solution

The specific viscosities of various dilute solutions were measured by using an Ubbelohde-type capillary viscous tube with decalin having an intrinsic viscosity of 135 ° C., and extrapolation to the origin of the straight line obtained by the least-squares approximation of the plot for the concentration of the viscosity The intrinsic viscosity was determined from the points. In the measurement, if the raw material polymer is in the form of powder, it remains in that shape, and if it is in the form of lumps, divide it and add 1 wt% of an antioxidant (trade name "Yoshinox BHT" made by Yoshitomi Pharmaceutical Co., Ltd.) to the polymer, The measurement solution was prepared by dissolving with stirring at 135 ° C. for 5 hours.

GPC Measured by gel permeation chromatography method. The equipment used was manufactured by Waters (150C AL
C / GPC) and column manufactured by Toso Co., Ltd. (GMHXL
It was measured using a series). The molecular weight calibration curve is Po
manufactured by Lymer Laboratories (Polystyren-
High Molecular Weight Calibration Kit). The sample solution used was dissolved in trichlorobenzene or orthodichlorobenzene at 140 ° C. for about 8 hours.

Battery Evaluation Battery evaluation was performed by manufacturing a sealed battery of SC size. First, a paste type nickel hydroxide positive electrode, a paste type hydrogen storage alloy negative electrode, and a separator are spirally wound, inserted into an outer can, and then an aqueous potassium hydroxide solution containing lithium hydroxide is injected as an electrolytic solution to seal the can. A sealed battery (capacity 2500 mAh) was obtained. As the initial activation treatment of the battery, after holding at 45 ° C for 6 hours, charging at 0.2C for 6 hours in an air atmosphere at 20 ° C and discharging 0.2C (discharge end voltage 1.0V) were repeated 10 times. It was
The ratio of the 10th discharge capacity to the theoretical capacity was defined as the discharge capacity ratio of this battery. The 0.2 C discharge is to discharge a densely charged battery over 5 hours, and at this time, the discharge current value is set to an appropriate value.

Discharge capacity ratio As a performance evaluation at the time of high rate discharge test, a battery which had been subjected to the initial activation described above was charged at 0.2 C for 6 hours and then discharged at 4 C to 0.8 V. The ratio of the discharge capacity to the theoretical capacity (discharge capacity ratio) was calculated.

-Battery internal pressure measurement For the battery that has been subjected to the initial activation as described above, 0.5C charging is performed for 3 hours (at a charging depth of 150 at an ambient temperature of 20 ° C).
%) The internal pressure of the battery when measured was measured.

Cycle life A cycle test is conducted on the battery which has completed the initial activation, in which one cycle consists of charging at 0.5C for 2.4 hours (120%) and discharging at 0.5C with an end voltage of 1.0V. did. At this time, it was determined that the life had reached when the discharge capacity reached 80% of the initial value.

Amount of sulfur The amount of sulfur in the present invention was prepared from a standard substance containing sulfur by completely burning a separator test piece at a high temperature of 1400 ° C. in an oxygen stream and measuring its concentration with an infrared detector. The sulfur content was measured according to a calibration curve. In particular,
The measurement was performed using a sulfur analyzer EMIA-120 manufactured by Horiba, Ltd. The basic principle of the burning part of the above measuring method is the same as the flask burning method, and is a method of completely burning sulfur in an oxygen stream and measuring the total amount of sulfur including sulfur in the nonwoven fabric. Flask combustion method, Basic analytical chemistry course, Volume 11, Japan Society for Analytical Chemistry (Kyoritsu Publishing), p.
34-43, September 1965.

[0068]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is by no means limited to these examples.

Example 1 Tensile strength 6 cN / dtex, fineness 2.0 dtex, fiber length 10 m
m polypropylene high strength fiber (melting point 166 ℃) 20wt
%, Fineness 1.1 dtex, fiber length 8 mm polypropylene (melting point 160 ° C.) / Low density polyethylene (melting point 110 ° C.) core-sheath composite fiber (surface coverage of low density polyethylene 1
(00%) 45 wt%, with a substantially triangular shape and a fineness of 0.125
8 dtex polypropylene ultrafine fibers (melting point 160 ° C) and an approximately triangular shape and 8 high density polyethylene components (melting point 130 ° C) with a fineness of 0.125 dtex having an orange cross section, fineness 2 dtex, fiber length 12 mm The slurry obtained by mixing and dispersing 35 wt% of the splittable composite fiber of 3 was paper-made by the inclined wire type fourdrinier system to form a fiber web. In addition,
The fibers were oriented in one direction by adjusting the net for making the fibers and the flow rate of the slurry. Then, this fibrous web was placed on a net having a line length of 0.14 mm, and a water flow having a pressure of 12.3 MPa was jetted twice from both sides alternately from a nozzle plate having a nozzle line of 0.13 mm and a pitch of 0.6 mm,
The entangled porous sheet was manufactured by dividing the divided fibers and entangled the fibers. Next, the entangled porous sheet was dried at a temperature of 124 ° C. and, at the same time, the sheath component of the fusion fiber was fused to produce a fusion-entangled porous sheet. The porous sheet thus prepared was immersed in 18% fuming sulfuric acid at 60 ° C. for 1 minute, further washed with concentrated sulfuric acid, a dilute sulfuric acid aqueous solution and ion-exchanged water, and dried at 65 ° C. A part of the inside was made hydrophilic by forming a hydrophilic functional group such as a sulfonic acid group, a sulfonic acid ester group, a carboxyl group, a carbonyl group, and a hydroxyl group. The amount of ion exchange was 0.012 meq / g. Next, the hydrophilic porous sheet was heated to 100 ° C. and heated and heated by a metal gear roll having a width of the protrusion of 0.5 mm and a convex area of 13% and a stainless steel flat roll heated to 100 ° C. When pressed, the weight is 60 g / m ² , the apparent thickness is 160 μm, the depth of the concave portion is 13 μm, and the specific concave and convex formation state having the concave portion on one side is as follows. A porous sheet that exists uniformly as described above was prepared. The separator thus obtained is referred to as the separator of Example 1. Table 1 shows various physical properties of the separator and performance of the battery using the separator.

Example 2 Tensile strength 8 cN / dtex, fineness 1.5 dtex, fiber length 1
0 mm polypropylene high strength fiber (melting point 165 ° C) 3
0 wt%, fineness 1.1 dtex, fiber length 10 mm polypropylene (melting point 160 ° C) / high density polyethylene (melting point 12
(5 ° C.) core-sheath composite fibers (75% surface coverage of high-density polyethylene) 70 wt% mixed and dispersed slurry is made into paper by the inclined wire type fourdrinier system and dried by exposing to hot air at 130 ° C. Lightly fused at the same time.
Fluorine gas 4 vol
%, Oxygen gas 6 vol%, sulfur dioxide gas 10 vol%, and nitrogen gas 80 vol% in a mixed gas atmosphere, by performing corona discharge, sulfonic acid group, sulfonic acid ester group, carboxyl group to the fiber surface and part of the inside ,
A hydrophilic functional group such as a carbonyl group, a hydroxyl group, and a fluorine-based functional group was formed. Then, after washing with a dilute sulfuric acid aqueous solution and ion-exchanged water, drying was performed at 65 ° C. The amount of ion exchange is 0.043 meq / g and the amount of sulfur is 350
It was 0 ppm. After that, it is sandwiched between a metal gear roll heated to 145 ° C with a width of 0.8 mm and a convex area of 10% and a resilient flat roll made of silicon resin heated to 120 ° C and heated from both sides. By pressurizing, the weight is 50 g / m ² fused by polyethylene, the apparent thickness is 120 μm, and the depth of the recess is 4
8 μm, a concave portion is formed on one side, and a convex portion is formed on the back side of the concave portion. As a specific state of forming irregularities, the irregularity having the second shape from the upper right side of FIG. A porous sheet that was evenly present in was prepared. Thus, the separator of Example 2 was produced. Table 1 shows various physical properties of the separator and performance of the battery using the separator.

Example 3 Tensile strength of 12 cN / dtex, fineness of 1.3 dtex, high-strength fiber made of ultra-high molecular weight polyethylene having a fiber length of 12 mm (melting point 150 ° C., trade name: Dyneema manufactured by Toyobo) 25 wt% and fineness 0.9 dtex, Gradient wire-type wire net with a slurry in which 75 wt% of core-sheath composite fibers composed of polypropylene (melting point 162 ° C) / high-density polyethylene (melting point 130 ° C) having a fiber length of 10 mm is mixed and dispersed (55% surface coverage of high-density polyethylene) Papermaking was performed by the method, and the paper was exposed to hot air at 130 ° C. to be dried and at the same time lightly fused. Next, this porous sheet was saturated with nitrogen gas in advance, 20% by weight of acrylic acid, 76.7% of distilled water, and 0.2 of benzophenone.
Wt%, ferrous sulfate 0.1 wt%, nonionic surfactant 3.0 wt% Immerse in a solution for 10 minutes, take out, remove excess liquid, and then remove 180 mW / Ultraviolet rays centered at 365 nm were irradiated from both sides of the porous sheet with an illuminance of cm2 to carry out hydrophilic treatment by graft polymerization (graft ratio 10%), and after repeated washing with water, drying was carried out at 80 ° C. After that, by sandwiching between a metal gear roll having a width of 1.2 mm and a convex area of 30% heated to 150 ° C. and a stainless flat roll heated to 100 ° C., and heating and pressurizing from both sides, Weight fused by polyethylene 44
g / m ² , apparent thickness 105 μm, recess depth 45 μm
As a specific shape of the uneven portion having a concave portion on one surface, a porous sheet having a concave portion in the lower right portion of FIG. 1 uniformly present as in the upper right portion of FIG. 2 was produced. In addition, the thickness of the portion where the unevenness is not formed is 110 μm. Thus, the separator of Example 3 was obtained. Table 1 shows various physical properties of the separator and performance of the battery using the separator.

Example 4 A commercially available polypropylene porous sheet (Nippon Koshigami S.
LF50120, thickness 120 μm, average fineness 1 dtex, weight 50 g / m ² ) was treated with 96% sulfuric acid at 130 ° C. for 2 minutes. Further, after washing with a dilute sulfuric acid aqueous solution and ion-exchanged water, it was dried at 70 ° C. to make it hydrophilic. The amount of ion exchange was 0.003 meq / g. Next, the convex roll heated to 130 ° C has a width of 2.0 mm, the convex roll area ratio is 20%, and the flat roll made of silicon resin at 110 ° C is used to heat and press to have a concave face on one side. As a specific state of forming irregularities having a convex portion, a porous sheet was produced in which the irregularities in the shape at the upper left of FIG. 1 were uniformly present as at the upper right of FIG. The apparent thickness is 130 μm and the depth of the recess is 33 μm. This was used as the separator of Example 4. Table 1 shows various physical properties of the separator and performance of the battery using the separator.

Example 5 20% by weight of finely divided silicic acid and 45% by weight of dioctyl phthalate
Polyethylene resin 2 with an intrinsic viscosity of 3.8
0% by weight and 10% of ultrahigh molecular weight polyethylene resin having an intrinsic viscosity of 11.2 were added and mixed again. The mixture was melt-extruded at 160 ° C. in a film manufacturing apparatus using a twin-screw extruder equipped with a T-die to form a flat film having a thickness of 130 μm. This membrane was immersed in methylene chloride for 15 minutes to extract dioctyl phthalate, dried and further immersed in a 5 mol / l potassium hydroxide aqueous solution at 80 ° C. for 1 hour to extract fine silicic acid. This membrane was stretched again using a biaxial stretching machine to obtain a polyethylene porous film having a thickness of 85 μm. This was exposed to sulfur trioxide gas having a concentration of 30% at room temperature for 1 minute, washed with concentrated sulfuric acid, diluted sulfuric acid, and pure water, and dried at 75% to obtain a hydrophilized film. Then, using a gear roll with a convex area of 40% and continuous grooves with a convex width of 0.25 mm heated to 100 ° C and a flat roll made of stainless steel at 100 ° C, pressure molding is performed, and the depth of the concave portion is formed on only one side. 17 μm
A continuous groove-shaped recess was prepared (as a specific state after the formation of the recess, the groove having the shape in the lower center of FIG. 1 is uniformly present as shown in the upper left of FIG. 2). Thus, the porous film-shaped separator of Example 5 having irregularities on the surface was produced. Table 1 shows various physical properties of the separator and performance of the battery using the separator.

[0074]

Comparative Example A comparative example of the present invention will be shown below. According to the method which is not included in the scope of the present invention, it is impossible to bring out the excellent characteristics as described in the text.

Comparative Example 1 In Example 1, the unevenness was first formed by the gear roll and the flat roll made of stainless steel, and then the fuming sulfuric acid treatment and the washing / drying treatment were performed to produce the separator of Comparative Example 1. The formation state of the unevenness was clearer than that of Example 1, and the one incorporated in the battery was able to effectively suppress the increase in internal pressure. However, the discharge capacity ratio of the battery was somewhat poor and the cycle life was shortened. Since the fuming sulfuric acid treatment was carried out after the unevenness was formed, the hydrophilicity of the separator was uneven due to the difference in the fuming sulfuric acid retention during the fuming sulfuric acid treatment and the difference in the physical properties of the uneven portion and the place where the unevenness was not formed. It is believed that the battery performance was degraded because the liquid was not distributed uniformly. In fact, when disassembling the battery and observing the separator, the electrolytic solution was concentrated on the portion where the unevenness was formed. Considering that the part where the separator and the electrode are in contact is the part where no concavo-convex is formed, that is, the part where there is no electrolytic solution, the decrease in discharge capacity ratio and cycle life is due to the electrolytic contact at the contact between the separator and the electrode. This is probably because the liquid is exhausted. Various physical properties of the separator,
Table 1 shows the performance of the battery using this separator.

Comparative Example 2 The separator of Comparative Example 2 was produced by forming the uneven portion in Example 3 and then performing grafting and washing / drying. As compared with Example 3, the unevenness was formed more clearly and the rise in internal pressure could be effectively suppressed, but the discharge capacity ratio was somewhat poor and the cycle life was short. Similar to Comparative Example 1, the separator has uneven hydrophilicity,
It is thought that this is because the electrolyte solution is not uniformly distributed. Table 1 shows various physical properties of the separator and performance of the battery using the separator.

Comparative Example 3 The separator of Comparative Example 3 was produced by forming the uneven portion in Example 5 and then subjecting it to hydrophilic treatment. As compared with Example 5, the unevenness was formed more clearly and the rise in internal pressure could be effectively suppressed, but the discharge capacity ratio was somewhat poor and the cycle life was short. Comparative Examples 1 and 2
It is considered that this is because the hydrophilicity of the separator has unevenness and the electrolytic solution is not uniformly distributed in the same manner as in. Table 1 shows various physical properties of the separator and performance of the battery using the separator.

Comparative Example 4 Commercially available polypropylene porous sheet (Nippon Koshigami S.
LF50120, thickness 120 μm, average fineness 1 dtex, weight 50 g / m ² ) was treated with 96% sulfuric acid at 130 ° C. for 2 minutes. Further, after washing with a dilute sulfuric acid aqueous solution and ion-exchanged water, it was dried at 70 ° C. to make it hydrophilic. The amount of ion exchange was 0.003 meq / g. Then, the width of the convex portion heated to 160 ° C. is 0.8 mm, the area ratio of the convex portion is 53%, and the stainless steel flat roll of 150 ° C.
As a specific state of forming irregularities having a concave portion on one surface by heating and pressurizing, a porous sheet having a concave portion in the lower right portion of FIG. 1 uniformly present as in the upper right portion of FIG. 2 was produced. The apparent thickness is 115 μm and the depth of the recess is 64 μm. This was used as the separator of Comparative Example 4. The strength of the separator was weak and short-circuited during battery production. It is considered that this is because the concave portion has a thin and weak portion specifically. The batteries that could be evaluated were able to suppress the rise in internal pressure, but the discharge capacity ratio and cycle life were poor. It is considered that the internal resistance was increased because the contact area between the separator and the electrode was small. Table 1 shows various physical properties of the separator and performance of the battery using the separator.

Comparative Example 5 Commercially available polypropylene porous sheet (Nippon Koshigami S.
LF50120, thickness 120 μm, average fineness 1 dtex, weight 50 g / m ² ) was treated with 96% sulfuric acid at 130 ° C. for 2 minutes. Further, after washing with a dilute sulfuric acid aqueous solution and ion-exchanged water, it was dried at 70 ° C. to make it hydrophilic. The amount of ion exchange was 0.003 meq / g. Then, the width of the convex portion heated to 90 ° C. is 2.0 mm, and heating is performed using a gear roll having a convex portion area ratio of 2% and a stainless steel flat roll at 90 ° C.
As a concrete state of forming irregularities in which a concave portion is formed on one surface by pressing and a convex portion is formed on the back side of the concave portion, the irregularities having the shape in the lower left of FIG. 1 are uniformly present as in the upper right of FIG. A porous sheet was prepared. The apparent thickness is 120 μm and the depth of the recess is about 4 μm. This was used as a separator of Comparative 5.
The internal pressure of the battery incorporating the separator increased, and the safety valve was activated. It also had a short cycle life. It is considered that the oxygen gas generated during overcharging could not be accumulated on the surface of the negative electrode due to insufficient formation of the unevenness, so that gas absorption by the negative electrode was not performed at a satisfactory rate and the internal pressure of the battery increased. Further, it is considered that the battery life is shortened because the electrolyte solution is pushed out from the separator and dried out when oxygen gas is accumulated in the battery. Table 1 shows various physical properties of the separator and performance of the battery using the separator.

Comparative Example 6 A battery was produced with the surface of the separator of Example 1 having the irregularities facing the positive electrode side. In the manufactured battery, the internal pressure was likely to rise and the safety valve actuated. It also had a short cycle life. It is considered that, because the oxygen gas generated during overcharge could not be accumulated on the surface of the negative electrode, gas absorption by the negative electrode was not performed at a satisfactory rate, and the internal pressure of the battery increased. Further, it is considered that the battery life is shortened because the electrolyte solution is pushed out from the separator and dried out when oxygen gas is accumulated in the battery. Table 1 shows various physical properties of the separator and performance of the battery using the separator.

Comparative Example 7 The separator of Comparative Example 7 was prepared in the same manner as in Example 2 except that 100% of the core / sheath composite fiber made of polypropylene / high-density polyethylene was used without using the polypropylene high-strength fiber. All were prepared by the same method as in Example 2 except that the raw material fiber was changed. The produced separator had low strength and a high short circuit rate. The separator produced by the spunbonding method as in Example 4 had good strength characteristics without the inclusion of high-strength fibers. Indicates that it is necessary to include high strength fibers. Table 1 shows various physical properties of the separator and performance of the battery using the separator.

Comparative Example 8 In Example 5, a separator of Comparative Example 8 was prepared by using 100% of a polyethylene resin having an intrinsic viscosity of 3.8 as a raw material. Other than the raw material resin,
All were manufactured by the same method as in Example 5. The produced separator had low strength and a high short circuit rate. Comparative Example 7
Similarly, it can be seen that a separator made of a porous film which is essentially weak in strength needs to contain a resin having a high intrinsic viscosity. Table 1 shows various physical properties of the separator and performance of the battery using the separator.

[0083]

[Table 1]

As described above, the battery separator and the alkaline battery according to the present invention have been specifically described with reference to the examples. However, the present invention is not limited to the above-mentioned examples and has the above-mentioned meaning. It is also possible to carry out with appropriate modifications within a compatible range, and all of them are included in the technical scope of the present invention.

[0085]

As described above, the battery separator manufactured by the manufacturing method of the present invention can form a minute space between itself and the surface of the negative electrode, and this space is generated in the positive electrode and passes through the separator. Oxygen gas accumulates,
The oxygen gas absorption reaction on the surface of the negative electrode proceeds smoothly, and it is possible to effectively suppress the rise in the battery internal pressure during overcharge. Therefore, the alkaline battery using this separator has excellent safety. At the same time, since it is possible to suppress an increase in internal pressure, it is possible to prevent the gas from pushing away the electrolytic solution in the separator and reducing the effective area of the negative electrode, and it is possible to improve the discharge characteristics, especially at a high rate.
Furthermore, since the separator can hold the electrolytic solution for a long time, the cycle life can be improved.

[Brief description of drawings]

FIG. 1 Example of uneven cross-sectional shape

[Fig.2] Example of concavo-convex part viewed from above (continuous case)

[Fig. 3] Example of seeing uneven parts from above (non-continuous case)

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) // C08L 101: 00 C08L 101: 00 (72) Inventor Naohiko Takimoto 2-1-1 Katata, Otsu City, Shiga Prefecture No. Toyobo Co., Ltd. Research Institute F-term (reference) 4F074 AA16 AA17 AA18 AA20 AA24 CA01 CB01 CB31 CB91 CD01 CD11 CD14 DA03 DA08 DA10 DA23 DA49 5H021 CC01 CC09 EE02 EE04 EE16 EE18 HH00 HH03 HH04 H01 A02 H01 A02

Claims (7)

[Claims] 1. A separator for an alkaline battery, wherein a porous sheet made of a thermoplastic resin is subjected to a hydrophilizing treatment, and then irregularities are formed on at least one surface of the porous sheet. 2. The depth of the recess is 5% or more and 50% or less of the apparent thickness of the separator, and the area of the recess is 5% or more and 50% or less with respect to the total area of the separator. The alkaline battery separator according to claim 1. 3. The alkaline battery separator according to claim 1, wherein the thermoplastic resin is a polyolefin resin. 4. The alkaline battery using the separator for an alkaline battery according to claim 1, wherein the uneven surface of the separator faces at least the negative electrode. 5. The alkaline battery separator according to claim 1, further comprising a high-strength polyolefin-based synthetic fiber having a tensile strength of 3 cN / dtex or more. 6. The alkaline battery separator according to claim 1, further comprising an ultrahigh molecular weight polyolefin synthetic resin having an intrinsic viscosity of 6 or more. 7. The method for producing an alkaline battery separator according to claim 1, wherein the hydrophilization treatment is at least one of a sulfonation treatment and a graft treatment.