JP2000164191A - Separator for alkaline battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for an alkaline battery having an excellent self-discharge control action and capable of easily hydrophilization processed in manufacturing process. SOLUTION: A separator for an alkaline battery includes a gas transparent sheet having hydrophilic portion. The hydrophilic portion includes methacrylic acid or its derivative comonomer and ethylene comonomer and has methacrylic acid/ethylene copolymer component whose crystallinity is not less than 25%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a separator for an alkaline battery.

[0002]

2. Description of the Related Art Conventionally, an electrolyte has been held between these electrodes so that a positive electrode and a negative electrode of an alkaline battery can be separated from each other to prevent a short circuit, and that an electromotive reaction can be carried out smoothly. A possible separator is arranged.

[0003] Since the separator is required not to be attacked by an electrolytic solution such as potassium hydroxide, a separator containing a polyolefin fiber having excellent alkali resistance can be preferably used. However, polyolefin-based fibers have a low affinity for the electrolytic solution, and thus have a drawback of poor retention of the electrolytic solution.

[0004] Therefore, as one of means for imparting affinity to an electrolytic solution to such a separator containing polyolefin fibers, a method of sulfonating a separator containing polyolefin fibers is known. However, since the sulfonation of the separator containing the polyolefin fiber is performed under dangerous conditions such as low reaction efficiency and the use of fuming sulfuric acid, the sulfonation can be performed efficiently and under mild conditions. In addition, a method of sulfonating a fiber sheet containing a fiber having a copolymer of ethylene and acrylic acid on the fiber surface as a polyolefin fiber is known (for example, Japanese Patent Application Laid-Open No. 5-1)
21062, JP-A-5-121063, JP-A-5-21063
307947, JP-A-6-111801, JP-A-6-207321, etc.).

[0005] As described above, the method of sulfonating a fiber sheet containing a fiber having a copolymer of ethylene and acrylic acid on the fiber surface can be efficiently sulfonated. When used as a separator for batteries, self-discharge can hardly be suppressed, and there is a problem that a remarkable decrease in battery capacity is often observed.

[0006]

SUMMARY OF THE INVENTION The present inventors have developed a methacrylic acid containing methacrylic acid or a derivative thereof and ethylene.
It has been found that when the crystallinity of the ethylene copolymer component is 25% or more, the self-discharge suppressing effect is excellent, and that the methacrylic acid / ethylene copolymer component containing methacrylic acid or its derivative and ethylene is easily hydrophilized. Was. The present invention is based on such findings. Accordingly, an object of the present invention is to provide an alkaline battery separator which solves the above-mentioned disadvantages of the prior art and has an excellent self-discharge suppressing action, and which can be easily hydrophilized in a manufacturing process. Is to do.

[0007]

The object of the present invention is to provide an alkaline battery separator including a gas-permeable sheet including a hydrophilic portion according to the present invention, wherein the hydrophilic portion has at least a part of its surface. A separator for an alkaline battery (hereinafter, simply referred to as a “separator”) comprising a methacrylic acid / ethylene copolymer component containing methacrylic acid or a derivative thereof comonomer and an ethylene comonomer and having a crystallinity of 25% or more. Sometimes)
Can be solved by

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The gas permeable sheet in the alkaline battery separator of the present invention can be, for example, a fiber sheet (for example, a nonwoven fabric, a woven fabric, a knitted fabric, or a composite thereof) or a porous film. . The fibrous sheet can include a hydrophilic portion in the form of a hydrophilic fiber having a methacrylic acid / ethylene copolymer component on at least a portion of the surface (ie, the surface of the hydrophilic fiber), , A hydrophilic powder material having a methacrylic acid / ethylene copolymer component in an exposed state on at least a part of the surface of the hydrophilic powder material. Further, the porous film may include a hydrophilic portion in a surface layer of the film. When using such a porous film, it is preferable to have a fibrous sheet on at least one surface.

The hydrophilic fiber or hydrophilic powder material which can be used in the present invention is, in particular, a fiber or powder material having a methacrylic acid / ethylene copolymer component on at least a part of its surface and showing little hydrophilicity. A hydrophilic fiber or a hydrophilized powder material obtained by newly imparting hydrophilicity, or a fiber having a methacrylic acid / ethylene copolymer component on at least a part of its surface and having poor hydrophilicity. A hydrophilic fiber or a hydrophilic powder material obtained by improving the hydrophilicity of the powder material.

[0010] The porous film containing a hydrophilic portion which can be used in the present invention is, in particular, a porous film having a methacrylic acid / ethylene copolymer component on at least a part of its surface and showing almost no hydrophilicity. Is a hydrophilicized porous film obtained by newly imparting hydrophilicity, or a methacrylic acid / ethylene copolymer component on at least a part of the surface, and the porous film having poor hydrophilicity. It is a hydrophilized porous film obtained by improving hydrophilicity.

In one embodiment of the present invention, the separator for an alkaline battery is, for example, a single layer made of a fiber sheet containing the above-mentioned hydrophilic fiber, and in another embodiment, a laminate made of a porous film and a fiber sheet. It is a sheet or a laminated sheet composed of two fiber sheets and a porous film sandwiched therebetween. In the case of a laminated sheet including a porous film, the hydrophilic portion can be included in the porous film and / or the fiber sheet.

Hereinafter, the present invention will be described mainly on the basis of an embodiment in which the gas-permeable sheet is a fiber sheet containing hydrophilic fibers having a methacrylic acid / ethylene copolymer component.

The fiber sheet in the alkaline battery separator of the present invention contains hydrophilic fibers. In addition, the hydrophilic fiber has methacrylic acid /
Contains an ethylene copolymer component.

The methacrylic acid contained in the hydrophilic fiber /
The ethylene copolymer component can be prepared from a methacrylic acid comonomer or a methacrylic acid derivative comonomer and an ethylene comonomer. As the methacrylic acid derivative, for example, a methacrylic acid ester with an alcohol (preferably an aliphatic saturated alcohol, for example, an aliphatic saturated alcohol having 1 to 8 carbon atoms) or a salt of methacrylic acid can be used. As the methacrylate, for example, methyl methacrylate, ethyl methacrylate, butyl methacrylate, or 2-ethylhexyl methacrylate can be used. As the methacrylic acid salt, for example, an alkali metal salt, for example, a potassium salt, a sodium salt, or a lithium salt can be used. The comonomer is preferably methacrylic acid or a potassium salt of methacrylic acid.

The ratio of methacrylic acid comonomer or methacrylic acid derivative comonomer to ethylene comonomer is such that the crystallinity of the methacrylic acid / ethylene copolymer component is 25.
%, It is not particularly limited. Also, as long as the degree of crystallinity of the methacrylic acid / ethylene copolymer component is 25% or more, one or more other comonomers copolymerizable with the methacrylic acid comonomer or the methacrylic acid derivative comonomer and the ethylene comonomer (ie, the third component) are used. , Methacrylic acid / ethylene copolymer.

The methacrylic acid / ethylene copolymer may be a mixture of ethylene and methacrylic acid or a derivative thereof alternately (ie, an alternating copolymer) or a mixture of ethylene and methacrylic acid or a derivative thereof (ie, a random copolymer). Polymer), in a block (ie, a block copolymer), or a mixture thereof.

The methacrylic acid / ethylene copolymer component contained in the hydrophilic fiber has a crystallinity of 25% or more;
It is preferably at least 26%, more preferably at least 27%, particularly preferably at least 28%. When the crystallinity of the methacrylic acid / ethylene copolymer component is less than 25%, the effect of suppressing self-discharge becomes very poor, although the hydrophilicity is easily increased. The term “crystallinity” as used herein means the heat of fusion of methacrylic acid / ethylene copolymer (unit = J /
g), the heat of fusion of fully crystalline polyethylene (290.
4J / g). The heat of fusion of the methacrylic acid / ethylene copolymer component was measured by a differential scanning calorimeter (DSC) under a nitrogen gas atmosphere.
It means a value obtained by raising the temperature from room temperature to about 200 ° C. at a rate of 10 ° C./min. In the case where the hydrophilization treatment has been performed, the “crystallinity” is a value based on the measured heat of fusion before the hydrophilization treatment.

The methacrylic acid / ethylene copolymer component can occupy a part of the surface of the hydrophilic fiber or the entire surface of the hydrophilic fiber. Because it has a methacrylic acid / ethylene copolymer component on the surface of the hydrophilic fiber,
Excellent in alkali resistance, oxidation resistance, and fusion resistance. On the hydrophilic fiber surface, the larger the area occupied by the methacrylic acid / ethylene copolymer component, the more easily the above-mentioned effect can be exerted. Therefore, the methacrylic acid / ethylene copolymer component may occupy the entire fiber surface of the hydrophilic fiber. preferable.

The hydrophilic fibers may be composed solely of a methacrylic acid / ethylene copolymer component, or may be composed of a methacrylic acid / ethylene copolymer component and one or more other polymer components other than the methacrylic acid / ethylene copolymer component. (I.e., composite fibers). It is preferable to use at least one resin component having a higher melting point than the methacrylic acid / ethylene copolymer component as another polymer component in the composite fiber. In this case, even when the methacrylic acid / ethylene copolymer component is fused, the fiber shape of the hydrophilic fiber can be maintained by the resin component.

The cross-sectional shape of the conjugate fiber is not particularly limited as long as the methacrylic acid / ethylene copolymer is located on at least a part of the surface. For example, core-sheath type, eccentric type, orange type, multiple bimetal type, side-by-side type, or sea-island type can be mentioned. The bicomponent fibers can be split, for example, by mechanical treatment (eg, treatment with a fluid such as a water stream, or calender treatment) or chemical treatment (eg, treatment for removing a polymer or swelling one or more polymer components). It may be.

The polymer other than the methacrylic acid / ethylene copolymer component in the conjugate fiber is preferably made of a polyolefin resin so as to be excellent in alkali resistance and oxidation resistance. For example, polyethylene (for example,
Low density polyethylene, linear low density polyethylene, high density polyethylene, or ultra-high molecular weight polyethylene),
For example, polypropylene, polymethylpentene, ethylene-propylene copolymer, or ethylene-butene-propylene copolymer can be used.

The composite fiber containing a methacrylic acid / ethylene copolymer component as a fusion component is preferably combined with a polymer resin having a melting point higher than that of the methacrylic acid / ethylene copolymer component by 10 ° C. or more.
It is more preferable to combine with a polymer resin having a melting point higher than 20 ° C. Specifically, polypropylene,
Mention may be made of high density polyethylene, polymethylpentene, or ethylene-propylene copolymer. In this specification, the “melting point” means a temperature at which an extreme value of a melting absorption curve obtained by raising the temperature from room temperature using a differential scanning calorimeter at a temperature rising rate of 10 ° C./minute is meant.

Examples of the hydrophilization treatment include a sulfonation treatment, a fluorine gas treatment, a graft polymerization treatment, and an electric discharge treatment. By performing one or more of these hydrophilic treatments, the hydrophilicity can be increased. Fibers having no or poor hydrophilicity can be made hydrophilic.

The sulfonation treatment is not particularly limited, but for example, fuming sulfuric acid, sulfuric acid, chlorosulfuric acid,
Or immersion in a solution such as sulfuryl chloride, SO
Examples of the treatment include a treatment in which the gas is brought into contact with _three gases or a treatment in which electric discharge is caused in the presence of SO gas and / or SO ₂ gas. Among these, sulfonation treatment with fuming sulfuric acid is preferable because it has high reactivity and can be sulfonated relatively easily. In this case, a sulfonic acid group is mainly introduced.

The sulfur (S) constituting the sulfonic acid group introduced into the separator by the sulfonation treatment and the carbon (C) constituting the polyolefin polymer (supposed to constitute the fiber sheet) in the separator. The molar ratio (S / C; hereinafter, referred to as “degree of sulfonation”) is 1
It has been confirmed by experiments that the effect of suppressing self-discharge is excellent when it is about × 10 ⁻³ or more (preferably about 2 × 10 ⁻³ or more). Preferably, the degree of sulfonation is from 1 × 10 ⁻³ to 1 from the viewpoint of the self-discharge suppressing effect and the strength deterioration being small.
0 × 10 ⁻³ , more preferably 1 × 10 ^{−3 to} 5 × 1
0 ^-3 , more preferably 1.5 × 10 ^-3 to 4 × 10
It is ^-3 .

In the present specification, the term “degree of sulfonation”
Means a value obtained as follows. First, the area density
A (g / m^Two) 44mm diameter test piece from separator
After sampling, the X-ray intensity is measured with a fluorescent X-ray device.
And the amount of sulfur per unit area M _S(G / m^Two)
You. Next, the sulfur amount M_S(G / m^Two) With the atomic weight of sulfur (3
Divide by 2) to calculate the number of moles of sulfur (S). on the other hand,
The composition of the test piece is considered to consist of polyolefin only,
Area density A (g / m^Two) CH_TwoDivided by the molecular weight of (14)
Thereby, the number of moles of carbon (C) is calculated. In addition, before
The calculation is based on the assumption that the test piece of the fiber sheet is a polyolefin resin.
Based on the assumption that it consists only of Moles of these sulfur
(S) and the number of moles of carbon (C), the degree of sulfonation (S
/ C) is obtained by dividing the number of moles of sulfur (S) by the number of moles of carbon (C).
Can be calculated.

The fluorine gas treatment is not particularly limited. For example, fluorine gas diluted with an inert gas (eg, nitrogen gas or argon gas), oxygen gas, carbon dioxide gas, and sulfur dioxide gas may be used. For example, a treatment with a mixed gas with at least one kind of gas selected from the above. The method in which a sulfur dioxide gas is attached to a fiber sheet in advance and then brought into contact with a fluorine gas is an efficient and permanent hydrophilization treatment method. In this case, a fluorine-containing group can be introduced.

In the graft polymerization treatment, a graft-polymerizable monomer such as a vinyl monomer can be polymerized. As the vinyl monomer, for example,
Acrylic acid, methacrylic acid, acrylates, methacrylates, vinylpyridine, vinylpyrrolidone, styrene and the like can be used. In addition,
When styrene is graft-polymerized, sulfonation is preferably performed in order to impart affinity with the electrolytic solution.
Among these, acrylic acid is preferable because of its excellent affinity with the electrolytic solution.

The method for polymerizing the graft-polymerizable monomer includes, for example, a method in which a fiber sheet is immersed in a solution containing a graft-polymerizable monomer and a polymerization initiator and heated; A method of irradiating the fiber sheet with radiation, applying a radiation to the fiber sheet and then contacting it with a graft-polymerizable monomer, or impregnating the fiber sheet with a graft-polymerizable monomer solution containing a sensitizer and then applying ultraviolet rays to the fiber sheet. There is a method of irradiation. Before the graft polymerizable monomer solution and the fiber sheet are brought into contact with each other, if the surface of the fiber sheet is modified by ultraviolet irradiation, corona discharge, or plasma discharge, the affinity with the graft polymerizable monomer solution becomes higher. Since it is high, graft polymerization can be performed efficiently.

Examples of the discharge treatment include a corona discharge treatment, a plasma treatment, a glow discharge treatment, a creeping discharge treatment, and an electron beam treatment.

In the plasma treatment, a fiber sheet is disposed between a pair of electrodes each carrying a dielectric under a pressure equal to or higher than the atmospheric pressure in the air so as to be in contact with both of the dielectrics. When a method is used in which an AC voltage is applied between these two electrodes to generate a discharge inside the fiber sheet, not only the outside of the fiber sheet but also the fiber surface inside the fiber sheet can be treated. Therefore, since the electrolyte solution holding property inside the fiber sheet (inside the separator) is excellent, it is possible to produce a separator excellent in oxygen absorption during overcharge and excellent in internal pressure characteristics.

The fiber sheet in the alkaline battery separator of the present invention can be, for example, a nonwoven fabric, a woven fabric, a knitted fabric, or a composite thereof. Among these, it is preferable to include a nonwoven fabric in that the fibers can be arranged three-dimensionally and are excellent in holding the electrolyte. The ratio of the total surface area of the methacrylic acid / ethylene copolymer component supported on the hydrophilic fibers in the fiber sheet to the total surface area of all the constituent fibers contained in the fiber sheet depends on the self-discharge suppressing action, the hydrophilicity, and the electrolytic solution. It is not particularly limited as long as it is excellent in affinity, alkali resistance, oxidation resistance, and fusing property. However, it is preferably at least 10%, more preferably at least 20%.

In a preferred embodiment of the present invention, the separator for an alkaline battery is essentially composed of only a hydrophilic fiber having a methacrylic acid / ethylene copolymer component having a crystallinity of at least 25% on at least a part of its surface. (Preferably a nonwoven fabric). The fiber sheet in the alkaline battery separator of the present invention may include one or more other fibers, for example, ultrafine fibers, high-strength fibers, and / or fusion fibers, in addition to the hydrophilic fibers.

Examples of the ultrafine fibers include ultrafine fibers having a fineness of 0.5 denier or less (preferably, 7 × 10 ⁻⁷ denier to 0.3 denier). By containing such ultrafine fibers, the retention of the electrolyte can be improved, and the anti-dendriding property is also excellent. When the fiber sheet contains hydrophilic fibers containing a methacrylic acid / ethylene copolymer component as a fusion component, the shape of the ultrafine fibers can be maintained.
The ultrafine fibers preferably have a melting point higher by at least 10 ° C. than the melting point of the methacrylic acid / ethylene copolymer, more preferably have a melting point higher by at least 20 ° C.
Most preferably, it has a melting point higher than 30 ° C. This ultrafine fiber is preferably made of a polyolefin-based polymer [for example, polyethylene (for example, low-density polyethylene, linear low-density polyethylene, high-density polyethylene, or ultrahigh-molecular-weight polyethylene), polypropylene, polymethyl) so as to have excellent alkali resistance. Pentene, ethylene-propylene copolymer or ethylene-butene-propylene copolymer]. More specifically, it is preferably made of polyethylene (low-density polyethylene, linear low-density polyethylene, or high-density polyethylene), polypropylene, polymethylpentene, or the like.

Such an ultrafine fiber may be subjected to, for example, a mechanical treatment (for example, a treatment with a fluid such as a water stream, or a calender treatment) or a chemical treatment (for example, a treatment for removing a polymer or a treatment for swelling at least one polymer). )
Thus, the dividable splittable fiber can be split or formed by a melt blow method. Among the above-mentioned methods, it is preferable to divide and form splittable fibers having excellent fiber strength. Examples of the cross-sectional shape of the preferred splittable fiber include, for example, a sea-island shape, an orange shape,
Alternatively, a multi-bimetallic shape or the like can be given. Such splittable fibers can be spun by a conventional composite spinning method.

The fiber sheet constituting the alkaline battery separator of the present invention may contain high-strength fibers having a tensile strength of 5 g / d or more. The high-strength fiber preferably has a tensile strength of 7 g / d or more, more preferably 9 g / d or more, and most preferably 12 g / d or more. In addition, "tensile strength" in this specification means the value measured by the method prescribed | regulated to JISL1015 (chemical fiber staple test method).
When the fiber sheet contains such high-strength fibers, when manufacturing a battery, it is possible to prevent the burr of the electrode plate from penetrating through the separator or being cut by the edge of the electrode plate to cause a short circuit. .

The high-strength fiber is also made of a polyolefin-based polymer such as polyethylene (for example, low-density polyethylene, linear low-density polyethylene, high-density polyethylene, or ultra-high-molecular-weight polyethylene) or polypropylene so as to have excellent alkali resistance. , Polymethylpentene,
It is preferably an ethylene-propylene copolymer or an ethylene-butene-propylene copolymer.
Among them, it is preferable to be made of polypropylene or ultrahigh molecular weight polyethylene (average molecular weight is about 1,000,000 to 5,000,000).

The fiber sheet constituting the separator for an alkaline battery of the present invention may contain fused fibers in addition to hydrophilic fibers. Examples of the fused fibers include fused fibers used in known nonwoven fabrics. When the fiber sheet contains the fused fibers, the tensile strength and the softness of the separator can be improved, so that the battery can be manufactured with a high yield.

As the fused fiber, a resin component having a melting point lower than the melting point of all the constituent fibers other than the fused fiber (low melting point) so as not to lower the fiber strength of all the constituent fibers other than the fused fiber. Component) may be present at least on the fiber surface. The low melting point component is preferably lower by 10 ° C. or more, and more preferably 15 ° C. or more, lower than the melting point of any constituent fibers of the fibers other than the fused fibers. In the case where the methacrylic acid / ethylene copolymer constituting the hydrophilic fiber or the hydrophilic conjugate fiber is fused, the melting point of the low melting point component of the fused fiber does not need to be lower than the melting point of the methacrylic acid / ethylene copolymer. .

The fused fibers are also made of a polyolefin-based polymer such as polyethylene (for example, low-density polyethylene, linear low-density polyethylene, high-density polyethylene, or ultra-high-molecular-weight polyethylene) so as to be excellent in alkali resistance. , Polypropylene, polymethylpentene, ethylene-propylene copolymer, or ethylene-butene-propylene copolymer. When the fiber sheet contains ultra-high molecular weight polyethylene fibers as high-strength fibers, the softening temperature of the ultra-high molecular weight polyethylene fibers (for example, 125 ° C.) so as not to lower the strength of the ultra-high molecular weight polyethylene fibers. It is preferable to fuse the fused fibers at the following temperature. Therefore, the fused fiber in this case preferably contains low-density polyethylene as a low-melting point component.

The fused fibers may be composed of a single resin component, or may be composed of two or more resin components. The latter fused fiber is preferable in that the tensile strength of the separator can be further improved. When composed of two or more types of resin components, the fiber cross-sectional shape can be, for example, a core-sheath type, side-by-side type, eccentric type, sea-island type, multiple bimetal type, or orange type.

The ratio of the hydrophilic fiber, the ultrafine fiber, the high-strength fiber, and the fusion fiber contained in the fiber sheet constituting the separator for an alkaline battery of the present invention is not particularly limited. Usually, the fiber sheet is made of hydrophilic fibers 5
100% by weight, 0 to 70% by weight of ultrafine fibers, 0 to 70% by weight of high-strength fibers, and 0 to 95% by weight of fused fibers.

The fiber sheet constituting the separator for an alkaline battery of the present invention can be produced by a conventional method.
The nonwoven fabric suitable as the fiber sheet in the alkaline battery separator of the present invention can be produced, for example, as follows.

That is, a fiber having a methacrylic acid / ethylene copolymer component having a crystallinity of 25% or more;
A fiber web is formed from the splittable fiber, the high-strength fiber, and / or the fusion fiber which can be added as required by a dry method (for example, a card method or an air lay method) or a wet method. In addition, a fiber web can also be directly formed by a spun bond method or a melt blow method. These fiber webs do not need to be one kind, and two or more kinds of fiber webs can be laminated, for example, a fiber web formed by a dry method and a fiber web formed by a wet method are laminated. As described above, when the fiber web formed by the dry method and the fiber web formed by the wet method are laminated, both the tensile strength of the fiber web formed by the dry method and the uniformity of the fiber web formed by the wet method are provided. Nonwoven fabric can be manufactured.

As the fiber having a methacrylic acid / ethylene copolymer component, for example, a hydrophilized fiber which has been subjected to a hydrophilization treatment by the above-mentioned hydrophilization treatment method can be used, or a hydrophilization treatment has been performed. Non-hydrophilized fibers can also be used. Further, as the fiber, a fiber having a methacrylic acid / ethylene copolymer component on at least a part of its surface may be used, or a fiber having a methacrylic acid / ethylene copolymer component on at least a part of its surface by a division treatment. May be used.

The fiber length of each fiber constituting the fiber sheet is as follows:
The length varies depending on the method of forming the fiber web. When the web is formed by the dry method, for example, a length of about 25 to 160 mm is appropriate.
A length of about 25 mm is appropriate. Note that the average fineness is about 0.5 to 6 denier (the fineness before splitting in the case of including splittable fibers) so as to be excellent in the retention of the electrolytic solution or to easily manufacture the nonwoven fabric. Appropriate.

Subsequently, the nonwoven fabric is formed by bonding the fiber webs. Examples of the bonding method include a method of entanglement with a fluid flow such as a water flow or a needle, a method of partially or completely fusing a fiber having a methacrylic acid / ethylene copolymer component on at least a part of its surface, or a method of fusing. In the case of containing the fused fiber, a method of partially or completely fusing the fused fiber may be used alone or in combination. In the case where the fibrous web contains splittable fibers, if the fiber web is entangled by a fluid flow such as a water flow, the splittable fibers can be split (generation of ultrafine fibers) simultaneously with the entanglement.

The entanglement condition (partial division condition in some cases) by the fluid flow is, for example, a nozzle diameter of 0.05 to 0.3 mm.
And a pressure of 1 MPa to 30 M from a nozzle plate in which nozzles are arranged in one or more rows at a pitch of 0.2 to 3 mm.
What is necessary is just to eject the fluid flow of Pa (especially water flow) to the fiber web. Such a fluid stream is ejected at least once onto one or both sides of the fiber web. In addition, when processing with a fluid flow, if the support for supporting the fiber web has large openings, the resulting nonwoven fabric also has large holes, and short circuits are likely to occur. Preferably, the distance between the openings is 0.25 mm or less.

When the methacrylic acid / ethylene copolymer component having a degree of crystallinity of 25% or more and / or the fused fiber is fused, the methacrylic acid / ethylene copolymer component and / or the low melting point of the fused fiber are used. It is preferable to carry out the conditions under such conditions that only the components can be fused. More specifically, when heating and pressurization are performed simultaneously, the heating temperature is preferably in the range from the softening temperature to the melting point of the methacrylic acid / ethylene copolymer component or the low melting point component. Further, when the pressure is applied after the heating, the heating temperature is preferably in a range from the softening temperature of the methacrylic acid / ethylene copolymer component or the low melting point component to a temperature 20 ° C. higher than the melting point. In the case where both the methacrylic acid / ethylene copolymer component and the fusion fiber are fused, the softening temperature is set to a lower temperature of the methacrylic acid / ethylene copolymer component and the low melting point component of the fusion fiber. Means, the melting point is
It means the higher temperature of the methacrylic acid / ethylene copolymer component and the low melting point component of the fused fiber. In addition,
In any case, the pressing is preferably performed at a linear pressure of about 5 to 30 N / cm. When ultrahigh molecular weight polyethylene fibers are included as high strength fibers, the softening temperature of ultrahigh molecular weight polyethylene fibers (for example, 1
(25 ° C.) or lower.

The order of the entanglement process and the fusion process is not particularly limited, and the entanglement process may be performed first, and then the fusion process may be performed. Alternatively, the fusion process may be performed. The entanglement process can be performed after the process is performed first. When the fibrous web contains a splittable fiber having a high degree of freedom (particularly, a splittable fiber consisting of only a polyolefin polymer and having a fiber length of about 1 to 20 mm), the splittable fiber is split. Polymer component, hydrophilic fiber (or
After lowering the degree of freedom of the splittable fiber by fusing at least one component of the methacrylic acid / ethylene copolymer component of the fiber before imparting hydrophilicity) or the low melting point component of the fused fiber, a fluid flow, etc. Is preferably acted upon. Note that, when the splittable fiber is split by the action of the fluid flow in this way, the fusion before splitting tends to be destroyed. A methacrylic acid / ethylene copolymer component of a hydrophilic fiber (or a fiber before imparting hydrophilicity),
Alternatively, it is preferable that at least one component of the low melting point component of the fusion fiber is fused to increase the tensile strength and the rigidity.

In the alkaline battery separator of the present invention, the hydrophilic fibers contained in the fiber sheet have a crystallinity of 2 or less.
It has a methacrylic acid / ethylene copolymer component of 5% or more on at least a part of its surface, and has the hydrophilic property imparted by the above-mentioned hydrophilization method. Fiber having a methacrylic acid / ethylene copolymer component on its surface can be easily hydrophilized (especially easily sulfonated), so that it can be efficiently hydrophilized. In addition,
It is preferable that all the constituent fibers constituting the fiber sheet are hydrophilized so as to have more excellent retention of the electrolytic solution. That is, it is preferable that not only fibers having a methacrylic acid / ethylene copolymer component on the surface but also other fibers (for example, ultrafine fibers, high-strength fibers, or fused fibers) have been hydrophilized. The hydrophilization can be performed at the stage of the fiber state (that is, before forming the fiber sheet), or can be performed after the formation of the fiber sheet. In terms of
It is preferable to carry out the latter procedure.

The areal density of the separator of the present invention is 30 to 1
Is preferably ^{00g / m 2, 40~80g / m} 2
Is more preferable. If the areal density is less than 30 g / m ² , the tensile strength may be insufficient, and 100 g / m ²
If it exceeds m ² , it will be too thick and it will be difficult to increase the capacity of the battery.

The separator of the present invention may be, for example, a primary battery (eg, an alkaline manganese battery, a mercury battery, a silver oxide battery, or an air battery) or a secondary battery (eg, a nickel-cadmium battery, a silver-zinc battery, a silver battery). -Cadmium battery, nickel-zinc battery, nickel-hydrogen battery, etc.), and particularly when used as a separator of a nickel-hydrogen battery or a nickel-cadmium battery, it has excellent self-discharge suppressing effect.

[0054]

EXAMPLES The present invention will be described below in more detail with reference to examples, but these examples do not limit the scope of the present invention.

Example 1 Spinning was performed at 260 ° C. using a conventional composite spinning apparatus, and the fiber was drawn three times, and a sheath component composed of an ethylene-methacrylic acid copolymer (melting point = 105 ° C., crystallinity = 28%) and polypropylene ( A core / sheath type ethylene-based fiber (fineness = 2 denier, fiber length = 10 mm, core / sheath ratio = 1: 1) comprising a core component having a melting point of 160 ° C.) was produced.

Next, this core-sheath type ethylene fiber 100
% Was formed into a fiber web by a conventional wet papermaking method. Next, the fiber web was heat-treated with a dryer (under no pressure) set at 115 ° C.
A nonwoven fabric was produced by pressing with a calender having a linear pressure of 9.8 N / cm to fuse the sheath component of the core-sheath type ethylene-based fiber.

Then, the non-woven fabric was immersed in a fuming sulfuric acid solution (15% SO ₃ solution) at a temperature of 39 ° C. for 10 minutes to perform a sulfonation treatment. Subsequently, the non-woven fabric subjected to the sulfonation treatment is sufficiently washed with water, dried, calendered, and subjected to the separator of the present invention (area density = 60 g / m ² , thickness = 0.15 mm, degree of sulfonation = 4.2 ×). ^10-3 ) was produced.

[0057]

Example 2 A nonwoven fabric produced in the same manner as in Example 1 was immersed in a fuming sulfuric acid solution (15% SO ₃ solution) at a temperature of 50 ° C. for 10 minutes to perform a sulfonation treatment. Next, the non-woven fabric subjected to the sulfonation treatment is sufficiently washed with water, dried, and calendered. The separator of the present invention (area density = 60 g / m ² , thickness = 0.15 mm, degree of sulfonation = 11.0 × ^10-3 ) was produced.

[0058]

Example 3 A nonwoven fabric produced in the same manner as in Example 1 was immersed in a fuming sulfuric acid solution (15% SO ₃ solution) at a temperature of 33 ° C. for 10 minutes to perform a sulfonation treatment. Next, the sulfonated nonwoven fabric is sufficiently washed with water, dried, calendered, and subjected to the separator of the present invention (area density = 60 g / m ² , thickness = 0.15 mm, degree of sulfonation = 2.8 ×). ^10-3 ) was produced.

[0059]

Example 4 A nonwoven fabric manufactured in the same manner as in Example 1 was immersed in a fuming sulfuric acid solution (15% SO ₃ solution) at a temperature of 30 ° C. for 10 minutes to perform a sulfonation treatment. Next, the sulfonated nonwoven fabric is sufficiently washed with water, dried, calendered, and subjected to the separator of the present invention (area density = 60 g / m ² , thickness = 0.15 mm, degree of sulfonation = 2.1 ×). ^10-3 ) was produced.

[0060]

Example 5 The same core-sheath type ethylene-based fiber as in Example 1 (hereinafter referred to as "core-sheath type ethylene-based first fiber") and high-density polyethylene (melting point = 130 ° C., crystallinity = 58)
%) And polypropylene (melting point = 16%).
A core-sheath type ethylene-based second fiber (fineness = 2 denier, fiber length = 10 mm, core-sheath ratio = 1: 1) was prepared.

Next, the core-sheath type ethylene first fiber 3
0 mass% and the core-sheath type ethylene-based second fiber 70 m
A fiber web was formed from the slurry containing ass% by a conventional wet papermaking method. Then, this fiber web was
After heat treatment with a drier (under no pressure) set at 15 ° C., it is pressed by a calender with a linear pressure of 9.8 N / cm to fuse only the sheath component of the core-sheath type ethylene-based first fiber to produce a nonwoven fabric. did. Then, after the non-woven fabric was subjected to sulfonation treatment in exactly the same manner as in Example 2, the non-woven fabric was washed with water, dried,
And a calender treatment, and the separator of the present invention (area density = 60 g / m ² , thickness = 0.15 mm, degree of sulfonation =
4.4 × 10 ⁻³ ) was produced.

[0062]

Example 6 A nonwoven fabric produced in the same manner as in Example 1 was immersed in a fuming sulfuric acid solution (15% SO ₃ solution) at a temperature of 25 ° C. for 10 minutes to perform a sulfonation treatment. Next, the sulfonated nonwoven fabric is sufficiently washed with water, dried, calendered, and subjected to the separator of the present invention (area density = 60 g / m ² , thickness = 0.15 mm, degree of sulfonation = 1.1 ×). ^10-3 ) was produced.

[0063]

Example 7 A nonwoven fabric produced in the same manner as in Example 1 was immersed in a fuming sulfuric acid solution (15% SO ₃ solution) at a temperature of 43 ° C. for 10 minutes to carry out a sulfonation treatment. Next, the non-woven fabric subjected to the sulfonation treatment is sufficiently washed with water, dried, calendered, and subjected to the separator of the present invention (area density = 60 g / m ² , thickness = 0.15 mm, degree of sulfonation = 8.1 ×). ^10-3 ) was produced.

[0064]

Comparative Example 1 Spinning was performed at 260 ° C. using a conventional composite spinning apparatus, and the fiber was stretched three times, and a sheath component composed of an ethylene-methacrylic acid copolymer (melting point = 104 ° C., crystallinity = 24%) and polypropylene ( A core / sheath type ethylene-based fiber (fineness = 2 denier, fiber length = 10 mm, core / sheath ratio = 1: 1) comprising a core component having a melting point of 160 ° C.) was produced.
Next, a nonwoven fabric was manufactured in the same manner as in Example 1.

Then, the nonwoven fabric was immersed in a fuming sulfuric acid solution (15% SO ₃ solution) at a temperature of 30 ° C. for 5 minutes to perform a sulfonation treatment. Next, the non-woven fabric subjected to the sulfonation treatment was sufficiently washed with water, dried, calendered, and used as a separator for comparison (area density = 60 g / m ² , thickness =
0.15 mm, degree of sulfonation = 5.1 × 10 ⁻³ ).

[0066]

[Comparative Example 2] Spinning was performed at 260 ° C using a conventional composite spinning apparatus, and the fiber was drawn three times, and a sheath component composed of an ethylene-acrylic acid copolymer (melting point = 105 ° C, crystallinity = 28%) and polypropylene ( A core / sheath type ethylene-based fiber (fineness = 2 denier, fiber length = 10 mm, core / sheath ratio = 1: 1) comprising a core component having a melting point of 160 ° C.) was produced.
A comparative separator (area density = 60 g / m ² , thickness = 0.15 mm, thickness = 0.15 mm) was obtained by repeating the operation described in Example 1 except that this core-sheath type ethylene-based fiber was used.
Degree of sulfonation = 4.0 × 10 ⁻³ ).

[0067]

[Evaluation of physical properties] (1) Battery capacity test As a current collector of an electrode, a paste-type nickel positive electrode (33 mm width, 182 mm length) using a foamed nickel base material and a paste-type hydrogen storage alloy negative electrode (mesh metal alloy, 3
3 mm width, 247 mm length). Next, after each separator prepared in Examples 1 to 7 and Comparative Examples 1 and 2 was cut into a width of 33 mm and a length of 410 mm, the separator was sandwiched between a positive electrode and a negative electrode, and spirally wound. An electrode group corresponding to the type was created. After storing this electrode group in an outer can, 5N-potassium hydroxide and 1N-lithium hydroxide were injected as electrolytes into the outer can and sealed to form a cylindrical nickel-hydrogen battery.

Next, each cylindrical nickel-metal hydride battery was discharged at 0.1 C, and the initial capacity (A) at a final voltage of 1.0 V was measured. Next, the battery was charged at 0.1 C to 150% of the capacity, and then left in a constant temperature room at a temperature of 65 ° C. for 5 days. Thereafter, the battery was discharged again at 0.1 C, and the capacity (B) at a final voltage of 1.0 V was measured. From these results, the capacity retention ratio (C) was calculated by the following equation: C (%) = (B / A) × 100 The results are shown in Table 1.

(2) Tensile strength test (in the longitudinal direction) Each of the separators prepared in Examples 1 to 7 and Comparative Examples 1 and 2 was cut into a width of 50 mm, and a tensile strength tester (Tensilon UCT-500; According to Orientec Co., Ltd., the tensile strength (N / 50 m) was set on condition that the length between the chucks was 100 mm and the tensile speed was 300 mm / min.
m width) was measured. Table 1 shows the results.

<< Table 1 >> Crystallinity Degree of Sulfonation Degree of Capacity Retention Rate Tensile Strength (%) (× 10 ⁻³ ) (%) (N / 50 mm Width) Example 1 28 4.2 44 147 Example 2 28 11 0.0 52 98 Example 3 28 2.8 43 157 Example 4 28 2.1 30 157 Example 5 28 4.4 51 176 Example 6 28 1.1 31 167 Example 7 28 8.1 51 108 Comparison Example 1 24 5.1 2 127 Comparative Example 2 28 4.0 5 147

As is clear from Table 1, the crystallinity was 25
% Or more, the capacity retention ratio is excellent and practical, and the degree of sulfonation is 1.0 × 10 ⁻³ to 1
When it was about 0 × 10 ⁻³ , it was found that the capacity retention rate and the tensile strength were excellent and practical.

[0072]

As described above, the separator for an alkaline battery of the present invention comprises:
It is excellent in self-discharge suppressing effect, and is easy to hydrophilize in the manufacturing process. In particular, when a sulfonic acid group is introduced by a sulfonation treatment, the above effect is remarkable.

Claims (6)

[Claims] 1. An alkaline battery separator including a gas-permeable sheet including a hydrophilic portion, wherein the hydrophilic portion includes, on at least a part of its surface, methacrylic acid or a derivative comonomer thereof and an ethylene comonomer. A separator for an alkaline battery, comprising a methacrylic acid / ethylene copolymer component having a crystallinity of 25% or more. 2. The gas-permeable sheet is a fiber sheet containing hydrophilic fibers, wherein the hydrophilic fibers have the methacrylic acid / ethylene copolymer component on at least a part of the surface thereof. 4. The separator for an alkaline battery according to item 1. 3. The gas permeable sheet is a fiber sheet containing a hydrophilic resin powder material attached to a surface of a constituent fiber, wherein the hydrophilic resin powder material has at least a part of the surface of the methacrylic resin. The alkaline battery separator according to claim 1, comprising an acid / ethylene copolymer component. 4. The gas-permeable sheet is a porous film including a hydrophilic portion, wherein the hydrophilic portion has the methacrylic acid / ethylene copolymer component on at least a part of its surface. 2. The separator for an alkaline battery according to 1. 5. The alkaline battery separator according to claim 1, wherein the hydrophilicity of the hydrophilic portion is provided by sulfonating the methacrylic acid / ethylene copolymer component. 6. The alkaline battery separator according to claim 5, wherein the degree of sulfonation of the alkaline battery separator is 1 × 10 ⁻³ to 10 × 10 ⁻³ .