JP2000228181A - Alkaline battery separator - Google Patents

Abstract

(57) [Problem] To provide an alkaline battery separator which is excellent in retention of an electrolytic solution, does not break even when a high tension is applied thereto, and is capable of producing a battery in which a short circuit hardly occurs. SOLUTION: The separator for an alkaline battery of the present invention comprises:
The total thickness of the mixed layer in which short fibers having a fiber length of less than 25 mm and long fibers having a fiber length of 25 mm or more are not less than one-third of the total thickness, and the short fibers and / or As long fibers, an unsaturated carboxylic acid, an unsaturated carboxylic acid derivative, an ethylene copolymer comprising ethylene and at least one selected from unsaturated carboxylic acid anhydrides, and a nonwoven fabric containing an ethylene-based fiber having at least a fiber surface. Become.

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, a separator capable of holding an electrolytic solution has been arranged 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. Have been.

[0003] Since the separator must not be attacked by an electrolytic solution such as potassium hydroxide, a separator made of polyolefin fiber having excellent alkali resistance can be suitably 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, one of the means for solving such a disadvantage is as follows.
For example, the sheath component is composed of an acrylic acid-ethylene copolymer, and the core component contains at least 30% by weight of a core-sheath composite fiber composed of a polyamide polymer, and the core-sheath composite fiber has a sulfonic acid group. An introduced alkaline battery separator has been proposed (Japanese Patent Laid-Open No. 5-110663). However, since the core-sheath type conjugate fiber is difficult to draw sufficiently at the stage of producing the fiber and cannot obtain a strong fiber, the separator is easily broken by the tension at the time of forming the electrode plate group. As a result, it has been difficult to efficiently manufacture batteries. In particular, in the case of manufacturing a small and high-capacity battery that has been demanded in recent years, the separator is wound around the electrode plate with high tension so that the volume occupied by the separator is as small as possible. As a result, the above tendency was remarkable. Further, as described in Examples of the above-mentioned publication, the separator uses a long fiber having a fiber length of 38 mm or more, so that the dispersibility of the fiber is poor and, in addition to the fact that unevenness is likely to occur, Since the unevenness is promoted by the tension at the time of winding on the electrode plate, there is a problem that a short circuit is likely to occur.

[0005]

DISCLOSURE OF THE INVENTION The present invention has been made to solve the above problems, and has excellent electrolyte solution retention properties and does not break even when a high tension is applied.
Moreover, it is an object of the present invention to provide an alkaline battery separator capable of producing a battery in which a short circuit hardly occurs.

[0006]

Means for Solving the Problems A separator for an alkaline battery of the present invention (hereinafter sometimes simply referred to as a "separator") has a short fiber having a fiber length of less than 25 mm and a fiber having a fiber length of 25 mm or less.
The total thickness of the mixed layer in which the long fibers are entangled with each other is 1/3 or more of the total thickness, and the staple fibers and / or the long fibers are unsaturated carboxylic acids and unsaturated carboxylic acids. It is made of a non-woven fabric containing ethylene-based fibers having an ethylene copolymer comprising ethylene and one or more kinds selected from acid derivatives and unsaturated carboxylic anhydrides at least on the fiber surface. Thus, the separator of the present invention is an unsaturated carboxylic acid, an unsaturated carboxylic acid derivative, an ethylene copolymer comprising at least one selected from unsaturated carboxylic acid anhydrides and ethylene, at least on the fiber surface having an ethylene copolymer. Excellent retention of electrolyte solution due to the inclusion of fibers. In addition, since long fibers are used and short fibers and long fibers are entangled with each other, the fibers are not broken even when a high tension is applied. Furthermore, since short fibers are included in addition to long fibers, and the uniformity is high, a battery in which a short circuit does not easily occur can be manufactured.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION In the separator of the present invention, the total thickness of a mixed layer in which short fibers having a fiber length of less than 25 mm and long fibers having a fiber length of 25 mm or more are intertwined with each other is 3 minutes of the total thickness. Of one or more nonwoven fabrics. This mixed layer has a more uniform distribution of the electrolytic solution, a lower internal resistance of the battery, and a battery excellent in discharge characteristics and high capacity as compared with a layer composed of only short fibers or a layer composed of only long fibers. It is preferable that the proportion of the mixed layer in the whole is higher, and the thickness of the mixed layer is 3% of the total thickness.
Preferably, it occupies at least two-fifths, and most preferably, the entire separator comprises a mixed layer. The number of the mixed layers does not need to be one, and two or more may be present. When two or more are present as in the latter case, it is sufficient that the total thickness is one third or more of the total thickness. The presence or absence of a layer other than the mixed layer contained in the separator (for example, a layer made of only short fibers, a layer made of only long fibers, and the like)
The arrangement state of the mixed layer and the layers other than the mixed layer is not particularly limited.

[0008] In the present specification, the term "mixed layer" means a layer in which short fibers having a fiber length of less than 25 mm and long fibers having a fiber length of 25 mm or more are intertwined and mixed. Such a mixed layer can be formed by laminating a fiber web composed of short fibers and a fiber web composed of long fibers, and then performing at least one entanglement treatment.
In addition, a layer consisting only of short fibers, a layer consisting only of long fibers,
Alternatively, the mixed layer can be clearly distinguished, for example, by observing the cross section of the separator with a microscope. Further, the “thickness” in the present invention refers to a thickness under no load.

[0009] In the present invention, short fibers having a fiber length of less than 25 mm are used so that the fibers have excellent dispersibility. When the fiber length is 25 mm or more, it is difficult to form the fiber web itself, or the dispersibility of the fiber tends to deteriorate, so the preferable fiber length is 5 to 20 mm, and the more preferable fiber length is 10 to 20 mm.

[0010] In the present invention, in addition to the short fibers described above, long fibers having a fiber length of 25 mm or more are included in order to improve the tensile strength, tear strength, and bending resistance of the separator. If the fiber length is shorter than 25 mm, the tensile strength, tear strength and softness may not be sufficiently improved or may not be sufficiently entangled.
110 mm, more preferable fiber length is 25 to 60 m
m.

[0011] In the present invention, "fiber length" is JIS L
1015 (Chemical fiber staple test method) A length obtained by the method B (corrected staple diagram method).

In the present invention, the short fibers and / or long fibers are ethylene copolymers comprising ethylene and at least one selected from unsaturated carboxylic acids, unsaturated carboxylic acid derivatives, and unsaturated carboxylic anhydrides. At least on the fiber surface. Since the ethylene-based fiber has a carboxyl group, it has an effect of not only having excellent affinity with an electrolytic solution, but also having excellent alkali resistance, oxidation resistance, and fusibility. Hereinafter, when simply expressed as “fiber”, both short fibers and long fibers are included.

[0013] Examples of the copolymerization component with ethylene include unsaturated carboxylic acids such as acrylic acid and methacrylic acid, methyl acrylate, acrylate, butyl acrylate, 2-ethylhexyl acrylate, 2-hydroxy acrylate. Acrylates such as ethyl, methacrylates such as methyl methacrylate, methacrylate, butyl methacrylate and 2-ethylhexyl methacrylate, or unsaturated carboxylic anhydrides such as maleic anhydride and itaconic anhydride can be used. . Among these, acrylic acid and methacrylic acid are preferred,
Methacrylic acid is particularly preferred.

[0014] The ethylene copolymer constituting the ethylene-based fiber of the present invention contains at least one kind of the above-mentioned copolymer component. However, the ethylene copolymer of the present invention contains ethylene and the above-mentioned copolymer component alternately. It may be a material, a random material, a block material, or a mixture thereof. In addition,
The content of the above-described copolymer component is set to 5 mass so that the hydrophilic property is high, the discharge characteristics are good, and the internal pressure of the battery is low.
%, More preferably 5 to 30 m
ass%, more preferably 10 to 20 mass%.
It is. Therefore, the content of methacrylic acid is 5 mass
%, More preferably 5 to 30 mass%, even more preferably 10 to 20 mass%.

[0015] The ethylene-based fiber of the present invention is excellent in affinity with an electrolytic solution, oxidation resistance, alkali resistance, and fusion resistance because the above-described ethylene copolymer exists at least on the fiber surface. It is preferable that the ethylene copolymer occupies 50% or more of the surface of the ethylene-based fiber so that the above effects can be exerted to the maximum.
%, More preferably 100%, and most preferably 100%.

[0016] The ethylene fiber of the present invention may be composed of only an ethylene copolymer, but may contain a polymer other than the ethylene copolymer. As the polymer other than the ethylene copolymer, for example, polyethylene (for example, low-density polyethylene, medium-density polyethylene,
High-density polyethylene, linear low-density polyethylene, etc.), polypropylene, polymethylpentene, ethylene-propylene copolymer, ethylene-butene-propylene copolymer, polyamide (for example, 6 nylon, 66
One or more of nylon and the like and polyester (for example, polyethylene terephthalate, polybutylene terephthalate and the like) can be used. Among these, polyamide has a higher melting point than ethylene copolymer, and can maintain the fiber form of ethylene-based fibers even when fused with ethylene copolymer, and furthermore, polyamide is excellent in hydrophilicity, and the whole ethylene-based fiber is excellent in hydrophilicity. Therefore, it is suitable when the separator of the present invention is used for applications requiring high-rate discharge (for example, a separator of a battery for a power tool).

The polymer other than the above-mentioned ethylene copolymer may be present in any manner. For example, in the cross section of the ethylene-based fiber, as a core-sheath-shaped (including eccentric) core component, as one of the bonded components, as a sea-island-shaped island component, as a multi-bimetal-shaped one component, or It can be present as an orange component. When a polyamide is contained as a polymer other than the ethylene copolymer, the polyamide is slightly inferior in alkali resistance and oxidation resistance, and is not exposed on the surface of the ethylene-based fiber. It is preferably present as a component.

[0018] The fineness of the ethylene fiber is not particularly limited.
It is preferably at most denier, more preferably at most 5 denier. In addition, it is preferable that it is 0.5 denier or more.

[0019] Such an ethylene-based fiber can be produced by spinning and drawing using a conventional composite spinning apparatus and, if necessary, crimping.

The separator of the present invention comprises a nonwoven fabric containing the above-mentioned ethylene-based fibers as short fibers and / or long fibers. Since the ethylene copolymer constituting this ethylene-based fiber has a relatively low melting point, by fusing this ethylene copolymer, the tensile strength and rigidity of the separator can be increased, and the electrode group can be efficiently formed. it can.
In this way, using the ethylene-based fiber as the fusion fiber,
When increasing the tensile strength or rigidity of the separator, it is preferable that the non-woven fabric contains 30 mass% or more of ethylene-based fibers, and 70 mass% or more, regardless of whether the ethylene-based fibers are long fibers or short fibers. More preferably.

[0021] The separator of the present invention contains the above-mentioned ethylene-based fibers as short fibers and / or long fibers, but may contain fibers other than ethylene-based fibers. For example, it is preferable to include split fibers capable of generating ultrafine fibers and high-strength fibers having a tensile strength of 5 g / d or more.

[0022] Since the split fibers can be split into ultrafine fibers, the retention of the electrolyte can be further improved and dendrites can be prevented. The fineness of the ultrafine fibers generated from the split fibers is preferably 0.6 denier or less so as to produce the above-mentioned effect, and is preferably 0.001 denier or more so as to have a certain strength. More preferably, it is from 01 to 0.4 denier. Note that the fineness of the split fiber is not particularly limited as long as it can generate ultrafine fibers having the above fineness.

[0023] The split fibers are formed by a fluid flow such as a water flow, a needle,
Preferably, it can be divided by a physical action such as a calendar. Among these, if it can be divided by fluid flow,
This is suitable because a microstructured fiber is easily entangled to easily produce a separator having a dense structure, and a short circuit hardly occurs.

The split fibers are composed of two or more types of resin components. For example, as shown in FIGS. 1 to 4, the split fibers have an orange cross section, and as shown in FIG. Mold split fibers can be used. Among these, split fibers having an orange fiber cross section that can be easily split even when a physical action is applied from any direction can be suitably used.

As the resin component constituting the split fiber, for example, a polyamide resin (for example, nylon 6, nylon 66, nylon 12, a nylon copolymer such as a copolymer of nylon 6 and nylon 12, etc.), Ethylene resin (eg, low density polyethylene, medium density polyethylene, high density polyethylene, linear low density polyethylene,
Propylene-based resins (eg, polypropylene, copolymers of propylene with one or more other vinyl compounds), butene-based resins (eg, polybutene, butene and other Such as copolymers with one or more vinyl compounds), methylpentene resins (polymethylpentene, copolymers of methylpentene with one or more other vinyl compounds), and the like. It can be composed of two or more resins. Among these, split fibers obtained by combining polyethylene and polypropylene (particularly, high-density polyethylene and polypropylene) are preferable.

[0026] The ultrafine fibers generated from such split fibers are preferably contained in the nonwoven fabric constituting the separator in an amount of 5 mass% or more so as to have excellent retention of the electrolytic solution.
70m from the balance with other fibers such as ethylene fiber
ass% or less, more preferably 50% or less.
mass% or less, more preferably 30 mass%.
It is as follows. The ultrafine fibers generated from the split fibers may be short fibers or long fibers, but are more preferably long fibers having higher entanglement strength.

[0027] As another fiber constituting the nonwoven fabric of the separator of the present invention, it is preferable to include a high-strength fiber having a tensile strength of 5 g / d or more. By including such high-strength fibers, it is possible to reliably prevent a short-circuit between the electrode plates due to burrs of the electrode plates penetrating the separator when forming the electrode plate group. More preferably, the tensile strength is 7 g / d
It contains the high-strength fibers described above, and more preferably contains high-strength fibers having a tensile strength of 9 g / d or more. The upper limit of the tensile strength is not particularly limited, but may be 50 g / d.
The degree is appropriate. The tensile strength is JIS L
1015 (chemical fiber staple test method).

This high-strength fiber has the same resin component 1 as the split fiber.
Although it can be composed of more than one kind, it is preferable that at least the fiber surface contains a polyolefin-based resin component (especially polypropylene or ultrahigh molecular weight polyethylene having an average molecular weight of 1,000,000 to 5,000,000) so as to have excellent alkali resistance. preferable. The fineness of the high-strength fiber is preferably 0.5 to 5 denier so that the short-circuit preventing property is excellent and the retention of the electrolytic solution is not deteriorated.

[0029] Such a high-strength fiber is preferably contained in the nonwoven fabric constituting the separator in an amount of 5 mass% or more so as to have excellent short-circuit prevention properties. It is preferably 70 mass% or less, more preferably 40 mass% or less, and even more preferably 30 mass% or less, in view of the balance with other fibers such as ethylene fibers.

[0030] The nonwoven fabric constituting the separator of the present invention preferably contains the above-mentioned ethylene-based fiber, ultrafine fiber and high-strength fiber.
Fused fibers having at least a resin having a melting point similar to or lower than the ethylene copolymer of ethylene-based fibers on the fiber surface, (2) undivided split fibers, (3) fibers having a tensile strength of 5 g / d or less, etc. Can also be included.
Preferably, at least the fiber surface is made of a polyolefin-based resin so that any of these fibers has excellent alkali resistance.

[0031] The separator of the present invention comprises a nonwoven fabric produced from the above-mentioned fibers, and the average fiber diameter of the fibers constituting the nonwoven fabric is preferably 6 to 15 µm. Average fiber diameter is 6
When the thickness is less than μm, the permeability of gas generated from the electrode plate is poor, and it tends to be difficult to use the battery in a sealed battery (especially an alkaline battery such as a power tool requiring high-efficiency discharge). If the average fiber diameter exceeds 15 μm, the retention of the electrolytic solution tends to be reduced and a short circuit tends to occur. Therefore, the more preferable average fiber diameter is 7 to 12 μm.
This average fiber diameter refers to the average value of the fiber diameters of 100 fibers randomly selected from the separator. If the fiber cross-sectional shape is non-circular, the diameter when converted to a circular cross-section is the diameter of the fiber. Regarded as fiber diameter.

In the nonwoven fabric constituting the separator of the present invention, the ratio between the short fibers and the long fibers is such that the fibers are excellent in dispersibility of the fibers by the short fibers, and tensile strength, tear strength or bristles by the long fibers. 20: 80-8
0:20, preferably 30:70 to 70:30
Is more preferable.

[0033] The areal density of the separator of the present invention is 30 to 100 g.
Is preferably from / m ^2, and more preferably 40 and 80 g / m ^2. When the areal density is less than 30 g / m ² ,
This is because the tensile strength may be insufficient, and if it exceeds 100 g / m ² , the battery becomes too thick and it is difficult to increase the capacity of the battery. The thickness is preferably 0.1 to 0.3 mm.

[0034] The tensile strength in the vertical direction (length direction) of the separator of the present invention is preferably 100 N / 50 mm or more, and is preferably 140 N / 50 mm or more so as not to be broken by the tension at the stage of manufacturing the battery. More preferably, there is. The tensile strength is measured by using a 50 mm wide separator with a tensile strength tester (Tensilon UTM-II manufactured by Orientec).
I-100) fixed (distance between chucks 100m)
m), a value measured at a tensile speed of 300 mm / min.

[0035] The separator of the present invention having such a mixed layer in which short fibers and long fibers are entangled can be produced, for example, as follows.

First, a fiber web mainly composed of short fibers (hereinafter, referred to as a fiber web)
"Short fiber web") is, for example, 1
More than one sheet is formed. On the other hand, a fiber web mainly composed of long fibers (hereinafter referred to as “long fiber web”) is obtained by a dry method such as a card method, an air lay method, or a spun bond method.
More than one sheet is formed. Ethylene fibers are mixed into at least one of the short fiber web and the long fiber web, preferably both fiber webs. More preferably, split fibers and / or high-strength fibers are also mixed with the short fiber web and / or long fiber web.

Next, one or more short fiber webs and one or more long fiber webs are laminated to form a laminated fiber web. When laminating at least one of the short fiber web and the long fiber web, two or more of the short fiber web and the long fiber web are combined so as to easily form a mixed layer in which the short fibers and the long fibers are entangled. It is preferred to alternately laminate.

Next, a fluid flow such as a water flow is jetted onto the laminated fiber web to perform an entanglement treatment. In this entanglement process, it is necessary to apply a fluid flow having a higher energy than before so that long fibers already entangled to some extent can be entangled with short fibers by changing the arrangement. When split fibers are included as the short fibers and / or long fibers, they can be split simultaneously with the entanglement by the action of the fluid flow. When split fibers are included, a splitting process such as a calendering process or a needle punching process can be performed separately from the entanglement process.

The action of the fluid flow having a higher energy than that of the prior art means that the nozzle diameter is set to R (unit: m
m), when the internal pressure of the nozzle is P (unit: MPa),
(Equation) E value derived from E = R × P ² is 10 or more,
Preferably, 15 or more, more preferably 18 or more, most preferably 20 or more fluid streams are applied at least once. In this equation, since the kinetic energy is proportional to the square of the mass and the velocity, the larger the nozzle diameter, the larger the mass of the fluid that is ejected and acts, and the higher the internal pressure of the nozzle, the greater the ejection. Since the velocity of the fluid is high, the kinetic energy of the fluid flow is represented in a pseudo manner.

The conditions of the fluid flow ejection are as follows. For example, a nozzle plate having a nozzle diameter of 0.05 to 0.3 mm, a pitch of 0.2 to 3 mm and arranged in one or more rows is used.
A fluid of about 0 MPa to 30 MPa can be ejected and entangled. The jet of the fluid stream can be jetted to one side or both sides of the fiber web. The fluid flow is ejected twice or more, and is preferably ejected so that the total of the above-mentioned E values becomes 30 or more, more preferably 40 or more, and more preferably 60 or more. It is more preferable to squirt, and it is most preferable to squirt to be 80 or more. Furthermore, when a coarse support is used as a support for supporting the laminated fiber web when the fluid flow is jetted out, a nonwoven fabric having openings is formed, and the possibility of short-circuiting increases. It is preferable to use a support having a finer texture than that of the support.

[0041] The nonwoven fabric in which the long fiber web and the short fiber web are entangled and integrated as described above does not break even at a high tension. The tensile strength and the like can be further improved.

This fusion may be carried out under no pressure, but it is preferable to carry out pressure application in order to adjust the thickness. This pressurization may be performed simultaneously with heating, or may be performed after heating. The heating temperature in the fusion treatment is preferably within the range from the softening point to the melting point of the ethylene copolymer component when heating and pressurization are performed simultaneously, and when pressurization is performed after heating, It is preferably within the range from the softening point of the ethylene copolymer component to a temperature about 20 ° C. higher than the melting point. Further, the pressurizing condition is preferably a linear pressure of 5 to 30 N / cm in each case. When a fusion fiber other than the ethylene-based fiber is contained, it is preferable that the same relationship as described above is established for the fusion fiber. In the present invention, the “melting point” refers to a temperature at which a maximum value of a melting endothermic curve obtained by raising the temperature from room temperature at a rate of 10 ° C./min using a differential scanning calorimeter is used. It refers to the temperature that gives the starting point of the melting endothermic curve obtained by raising the temperature from room temperature at a rate of 10 ° C./min using a scanning calorimeter.

Since the separator of the present invention contains ethylene-based fibers, it is excellent in the retention of the electrolyte. However, it is preferable to mix polyolefin-based fibers having excellent alkali resistance as fibers other than ethylene-based fibers. Therefore, so as to be more excellent in the retention of the electrolyte, for example, sulfonation treatment, fluorine gas treatment, grafting treatment, surfactant treatment,
It is preferable to perform at least one hydrophilization treatment such as a discharge treatment and a hydrophilic resin adhesion treatment. This hydrophilization treatment may be performed at the fiber stage (that is, at the stage before the formation of the nonwoven fabric), but the hydrophilization treatment after the nonwoven fabric formation is more excellent in workability.

The sulfonation treatment is not particularly limited, but includes, for example, treatment with fuming sulfuric acid, sulfuric acid, sulfur trioxide, chlorosulfuric acid, sulfuryl chloride or the like.
Among these, sulfonation treatment with fuming sulfuric acid is preferred because it has high reactivity and can be relatively easily sulfonated.

The fluorine gas treatment is not particularly limited. For example, an inert gas (for example, nitrogen gas,
The treatment can be performed using a mixture of a fluorine gas diluted with an argon gas, and at least one gas selected from oxygen gas, carbon dioxide gas, sulfur dioxide gas, and the like. In addition, the method of contacting the fluorine gas after the sulfur dioxide gas is attached to the nonwoven fabric in advance,
It is a more efficient and permanent method of hydrophilic treatment.

For the graft polymerization of a vinyl monomer, for example, acrylic acid, methacrylic acid, acrylate, methacrylate, vinylpyridine, vinylpyrrolidone, or styrene can be used as the vinyl monomer. In addition, when styrene is graft-polymerized, it is preferable to sulfonate in order to have an affinity with the electrolytic solution. Among these, acrylic acid can be suitably used because of its excellent affinity with the electrolytic solution.

[0047] Examples of the method for polymerizing these vinyl monomers include (1) a method in which a nonwoven fabric is immersed in a solution containing a vinyl monomer and a polymerization initiator and heated, and (2) a method in which a vinyl monomer is applied to the nonwoven fabric and then irradiated with radiation. Irradiation method, (3)
There are a method in which the nonwoven fabric is irradiated with radiation and then contacted with a vinyl monomer, and a method (4) in which the nonwoven fabric is impregnated with a vinyl monomer solution containing a sensitizer and then irradiated with ultraviolet rays.
If the surface of the nonwoven fabric is treated with ultraviolet irradiation, corona discharge, plasma discharge or the like before the vinyl monomer solution is brought into contact with the nonwoven fabric, graft polymerization can be performed efficiently because of high affinity with the vinyl monomer solution.

As the surfactant treatment, for example, an anionic surfactant (for example, an alkali metal salt of a higher fatty acid, an alkyl sulfonate, or a sulfosuccinate ester salt) or a nonionic surfactant (for example, polyoxy The nonwoven fabric can be immersed in a solution of ethylene alkyl ether or polyoxyethylene alkylphenol ether, or the solution can be applied or sprayed to adhere.

As the discharge treatment, for example, corona discharge treatment,
Examples include plasma treatment, glow discharge treatment, surface discharge treatment, and electron beam treatment. Among these discharge treatments, a nonwoven fabric is arranged between a pair of electrodes each carrying a dielectric under atmospheric pressure in the air so as to contact both of the dielectrics, and an AC voltage is applied between these two electrodes. When the method is applied to generate a discharge inside the nonwoven fabric, not only the outside of the nonwoven fabric but also the fiber surface inside the nonwoven fabric can be treated. Therefore, because of excellent retention of the electrolyte inside the separator, excellent oxygen absorption during overcharge,
A battery having excellent internal pressure characteristics can be manufactured.

As the hydrophilic resin application treatment, for example, a hydrophilic resin such as carboxymethyl cellulose, polyvinyl alcohol, crosslinkable polyvinyl alcohol, or polyacrylic acid can be attached. After dissolving or dispersing these hydrophilic resins in an appropriate solvent, the nonwoven fabric can be immersed in the solvent, or the solvent can be applied or sprayed, and then dried and adhered. The amount of the hydrophilic resin attached is preferably 0.3 to 1 mass% of the whole separator so as not to impair the air permeability.

As the crosslinkable polyvinyl alcohol, for example, there is a polyvinyl alcohol in which a part of a hydroxyl group is substituted with a photosensitive group, and more specifically, a styrylpyridinium-based, styrylquinolinium-based,
There is polyvinyl alcohol substituted with styrylbenzothiazolium. After attaching this crosslinkable polyvinyl alcohol to the nonwoven fabric in the same manner as other hydrophilic resins,
Crosslinking can be performed by light irradiation. Such a polyvinyl alcohol in which a part of the hydroxyl groups is substituted with a photosensitive group has excellent alkali resistance and has a large number of hydroxyl groups capable of forming chelates with ions. This is preferable because a chelate is formed with the ions before the dendritic metal is deposited, so that a short circuit between the electrodes hardly occurs.

[0052] As described above, the separator of the present invention is excellent in electrolyte retention, tensile strength and short-circuit prevention, so that a battery can be stably manufactured. Therefore, the separator of the present invention, for example, alkaline manganese batteries, mercury batteries, silver oxide batteries, primary batteries such as air batteries, nickel-
Cadmium battery, silver-zinc battery, silver-cadmium battery,
It can be suitably used for secondary batteries such as nickel-zinc batteries and nickel-hydrogen batteries.

Hereinafter, embodiments of the separator of the present invention will be described, but the present invention is not limited to these embodiments.

[0054]

(Example) As shown in FIG. 3, a polypropylene component (symbol 12 in the figure, one circular ultrafine polypropylene fiber having a fineness of 0.02 denier (melting point: 160 ° C.) as shown in FIG. Eight polypropylene ultra-fine filaments with a fineness of 0.08 denier (melting point: 160 ° C.) can be generated, and a high-density polyethylene component (symbol 11 in the figure, petal-like ultra-fine long-diameter fiber with a fineness of 0.08 denier) (Melting point: 132 ° C.), having an orange cross section, a fineness of 1.3 denier and a fiber length of 25 mm.
Was prepared.

Further, a core-sheath type ethylene system having a denier of 3 denier and a fiber length of 38 mm, comprising an ethylene-methacrylic acid copolymer (containing 15 mass% of methacrylic acid, melting point: 95 ° C.) as a sheath component and 6 nylon as a core component. Fibers (ethylene-methacrylic acid copolymer occupying 100% of the fiber surface) were prepared. Further, polypropylene high-strength long fibers (melting point: 160 ° C.) having a tensile strength of 9 g / d, a fineness of 2 denier, and a fiber length of 45 mm were prepared.

Next, the above-mentioned split long fiber, core-sheath type ethylene long fiber and polypropylene high-strength long fiber were mixed in a ratio of 40: 3.
After mixing at a mass ratio of 0:30, the mixture was opened by a carding machine to form a unidirectional long fiber web (area density: 20 g / m ² ).

On the other hand, 90 mass% of the core-sheath type ethylene-based short fiber which is exactly the same as the core-sheath type ethylene-based long fiber except that the fiber length is 10 mm, and polypropylene high-strength long fiber except that the fiber length is 10 mm. From a slurry in which exactly the same polypropylene high-strength short fiber of 10 mass% was mixed and dispersed, a short fiber web (area density of 40 g) was obtained by a wet papermaking method.
/ M ² ).

Next, after laminating the above unidirectional long fiber web and short fiber web, the laminated fiber web was placed on a plain woven net having an opening of 0.175 mm, and the nozzle diameter was 0.1 mm.
5mm, 0.8mm pitch arranged in a row, internal pressure 12
A water flow is ejected from the nozzle plate of MPa to the unidirectional long fiber web (E value: 21.6), and the water flow is twice four times, that is, twice on the unidirectional long fiber web side and twice on the short fiber web side. Was spouted (total E value: 86.4) to entangle and split the split fibers at the same time to form an entangled nonwoven fabric.

Next, the entangled nonwoven fabric was heated at 115 ° C. for 10 seconds, and then pressurized with a calender roll having a linear pressure of 9.8 N / cm to obtain a core-sheath type ethylene long fiber and a core-sheath type ethylene short fiber ethylene. Only the copolymer component was fused to form a fused entangled nonwoven fabric.

After that, the fusion entangled nonwoven fabric was subjected to a fluorine gas treatment with a mixed gas of a fluorine gas, an oxygen gas and a sulfur dioxide gas diluted with a nitrogen gas, and a surface density of 60 g /
m ² , 0.15 mm thick separator (average fiber diameter:
7.3 μm). When an electron micrograph was taken of a cross section of the separator to observe the entangled state, a mixed layer in which short fibers and long fibers were entangled was present over the entire thickness of the separator.

(Comparative Example 1) The same split filament 13 ma as in the example
ss%, same core-sheath type ethylene long fiber 70 ma as in the example
After mixing ss% and 17 mass% of the same high-strength polypropylene long fiber as in the example, the mixture was opened by a carding machine to form a unidirectional long fiber web (area density 60 g / m ² ).

Next, the entangled nonwoven fabric is formed by entanglement and splitting of split long fibers on the front and back surfaces of the unidirectional long fiber web under exactly the same conditions as in the example, and then under the same conditions as in the example. Only the ethylene copolymer component of the core-sheath type ethylene-based long fiber is fused to form a fusion-entangled nonwoven fabric, and further, a fluorine gas treatment is performed under exactly the same conditions as in the example, and the areal density is 6
A separator (average fiber diameter: 5.1 μm) having a thickness of 0 g / m ² and a thickness of 0.15 mm was formed.

(Comparative Example 2) The same split short fiber 13 ma as in the example
ss%, same core-sheath type ethylene-based short fiber as in Example 70ma
A short fiber web (area density 60 g / m ² ) was formed from a slurry comprising ss% and 17 mass% of the same polypropylene high-strength short fibers as in the examples by a wet papermaking method.

Next, the front and back surfaces of the short fiber web were entangled and split into split short fibers under exactly the same conditions as in the example to form an entangled nonwoven fabric. Only the ethylene copolymer component of the type ethylene short fiber is fused to form a fusion-entangled nonwoven fabric, and further, a fluorine gas treatment is performed under exactly the same conditions as in the example, and the areal density is 60 g /
m ² , 0.15 mm thick separator (average fiber diameter:
6.0 μm).

(Tensile strength in vertical direction) Each separator was fixed to a tensile strength tester (Tensilon UCT-500, manufactured by Orientec) (distance between chucks 100 m).
m), tension was applied at a speed of 300 mm / min, and the tensile strength in the vertical direction was measured. The width of the separator is 50 m
m. The results are shown in Table 1.

[0066]

【table 1】

(Pressure retention rate) Each of the pieces cut to a diameter of 30 mm
Separate the separator at a temperature of 20 ° C and a relative humidity of 65%, respectively.
After reaching water equilibrium under the condition, the mass (M₀) Measure
did. Next, the air in the separator is
Potassium hydroxide having a specific gravity of 1.3 (20 ° C.)
Immersion for 1 hour in potassium solution to keep potassium hydroxide solution
I let it. Next, this separator is placed on the filter paper
(Diameter 30mm), and pressurized with 5.7M
After applying a pressure of Pa for 30 seconds, the mass of the separator
(M ₁) Was measured. Then, by the following formula,
The rate was determined. In addition, this measurement is performed for one separator.
4 times, and the average was taken as the pressure retention rate. As a result
Are also shown in Table 1. Pressure retention rate (%) = [(M₁-M₀) / M₀] X 100

(Short ratio) Using each separator,
When a battery was actually manufactured, short-circuiting was caused by a short-circuit caused by burrs on the electrodes, and the battery could not be manufactured. The results are also shown in Table 1.

As is clear from Table 1, it was found that the separator of the present invention was excellent in electrolyte solution retention and tensile strength, and was hardly short-circuited.

[0070]

The nonwoven fabric constituting the separator for an alkaline battery of the present invention comprises an ethylene copolymer comprising ethylene and at least one selected from unsaturated carboxylic acids, unsaturated carboxylic acid derivatives and unsaturated carboxylic anhydrides. In addition, since it contains at least the ethylene-based fiber on the fiber surface, it has excellent electrolyte solution retention. In addition, since long fibers are used, and short fibers and long fibers are intertwined,
It does not break even when high tension is applied. Furthermore,
Because it contains short fibers in addition to long fibers and has high uniformity,
A battery that does not easily cause a short circuit can be manufactured.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a split fiber that can be used in the present invention.

FIG. 2 is a schematic cross-sectional view of another split fiber that can be used in the present invention.

FIG. 3 is a schematic sectional view of still another split fiber that can be used in the present invention.

FIG. 4 is a schematic sectional view of still another split fiber usable in the present invention.

FIG. 5 is a schematic sectional view of still another split fiber usable in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Split fiber 11 1st component 12 2nd component

 ──────────────────────────────────────────────────の Continued on the front page F-term (reference)

Claims (4)

[Claims] The total thickness of a mixed layer in which short fibers having a fiber length of less than 25 mm and long fibers having a fiber length of 25 mm or more are 絡 or more of the total thickness, and An ethylene-based polymer having at least a fiber copolymer comprising at least one ethylene copolymer composed of ethylene and at least one selected from unsaturated carboxylic acids, unsaturated carboxylic acid derivatives and unsaturated carboxylic anhydrides as short fibers and / or long fibers. A separator for an alkaline battery, comprising a nonwoven fabric containing fibers. 2. The method of claim 1, wherein the ethylene copolymer comprises methacrylic acid-ethylene copolymer.
The separator for an alkaline battery according to the above. 3. The separator for an alkaline battery according to claim 1, wherein the ethylene-based fiber contains a polyamide. 4. The alkaline battery separator according to claim 1, wherein the average fiber diameter is 6 to 15 μm.