JP2001110393A - Separator for battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for battery with a high strength, a high stiffness and excellent durability, a nonwoven fabric for it and its production method. SOLUTION: This separator consists of a nonwoven fabric comprising split type composite fibers whose fundamental skeleton is an ethylene-vinyl alcohol copolymer, and using a modified ethylene-vinyl alcohol copolymer in which unit having sulfonic acid group and/or sulfonate group are polymerized at least as a component in its principal chain.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to alkaline primary batteries such as alkaline manganese batteries, mercury batteries, silver oxide batteries, zinc-air batteries, lead batteries, nickel-cadmium batteries, nickel-hydrogen batteries, nickel-iron batteries, nickel-
The present invention relates to a battery separator suitable for a secondary battery such as a zinc battery, a silver oxide-zinc battery, and an aluminum-air battery, a nonwoven fabric for a battery separator, and a method for producing the same.

[0002]

2. Description of the Related Art In general, batteries such as secondary batteries use a separator for separating an anode active material and a cathode active material. This separator can prevent an internal short circuit between the anode material and the cathode material, and has a small internal resistance. It has a high electrolyte absorbing property to generate a sufficient electromotive reaction. Low occupancy when used, and the amount of anode active material, cathode active material, etc. can be increased (battery life can be extended). Excellent in preventing shrinkage and deterioration of electrolytes such as potassium hydroxide and sulfuric acid. Various performances such as high durability are required. In particular, in a secondary battery separator, durability during an oxidation-reduction reaction accompanying charge / discharge is highly required.

[0003] As a battery separator having the above performance, a separator using an olefin fiber having excellent chemical resistance has been studied. For example, a separator having a melt-blown non-woven fabric layer made of an olefin-based fiber (Japanese Unexamined Patent Publication No.
Japanese Patent Application Laid-Open No. 282794, Japanese Patent Application Laid-Open No. 7-280627) and the like have been proposed. However, since the olefin fiber has high hydrophobicity, it is necessary to perform a hydrophilization treatment such as a sulfonation treatment, a plasma discharge treatment, and a corona discharge treatment in order to improve the electrolyte retention of the separator.
Therefore, there is a problem that the process becomes complicated and the cost is increased for commercialization. In order to solve the above problems, use of an ethylene-vinyl alcohol copolymer-containing fiber has been studied. Ethylene-vinyl alcohol copolymers have higher hydrophilicity than polypropylene-based polymers, polyethylene-based polymers, and the like, and therefore have excellent effects in terms of liquid retention and wettability.

For example, Japanese Patent Application Laid-Open No. 3-257755 proposes a method using a splittable conjugate fiber composed of a polyolefin polymer and a specific ethylene-vinyl alcohol copolymer. According to this method, it is not necessary to perform a hydrophilization treatment such as a sulfonation treatment, and since a polyolefin polymer having excellent heat-resistant alkali resistance is used in combination, an excellent effect can be obtained in terms of durability. Furthermore, it is also possible to split the splittable fiber by a water entanglement treatment or the like to obtain a separator having more excellent separating properties.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a battery separator and a method for producing the same, which are more excellent in various properties such as durability and hydrophilicity, and a nonwoven fabric for a battery separator and a method for producing the same. It is in.

[0006]

According to the present invention, (1) the basic skeleton is an ethylene-vinyl alcohol copolymer,
For a battery comprising a nonwoven fabric using a splittable conjugate fiber having at least one modified ethylene-vinyl alcohol copolymer in which a unit having a sulfonic acid group and / or a sulfonate group is copolymerized in its main chain. Separator,
(2) Modified ethylene-vinyl alcohol-based copolymer and polypropylene in which the basic skeleton is an ethylene-vinyl alcohol-based copolymer, and a unit having a sulfonic acid group and / or a sulfonate group in its main chain is copolymerized. (3) The battery separator according to (1) or (2), wherein the splittable composite fiber is divided to have a reduced diameter. (4) The modified ethylene-vinyl alcohol-based copolymer is a copolymer obtained by copolymerizing 2-acrylamido-2-methylpropanesulfonic acid or an alkali metal salt thereof (1) to (3). The battery separator according to any one of (5), wherein the basic skeleton is an ethylene-vinyl alcohol-based copolymer, and a sulfonic acid group and / or a sulfone Non-woven fabric for battery separators using splittable conjugate fibers containing at least one modified ethylene-vinyl alcohol copolymer in which a unit having a salt group is copolymerized, (6) ethylene-vinyl alcohol having a basic skeleton of ethylene-vinyl alcohol Use of a splittable conjugate fiber comprising a modified ethylene-vinyl alcohol copolymer having at least one component, which is a copolymer and has a sulfonic acid group and / or a sulfonate group in its main chain. A non-woven sheet for forming a non-woven sheet, and subjecting the non-woven fabric to a hydroentanglement treatment so as to divide the splittable conjugate fiber.

[0007]

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a specific modified ethylene-
It has been found that by using a splittable conjugate fiber containing a vinyl alcohol-based copolymer as at least one component, a battery separator excellent in various performances can be obtained.
A feature of the present invention resides in using an ethylene-vinyl alcohol copolymer in which a unit having a sulfonic acid group and / or a sulfonate group in the main chain is copolymerized. The introduction of a sulfonic acid group and / or a sulfonate group can increase the hydrophilicity of the copolymer, but simply introducing a hydrophilic group does not provide the desired effect. That is, for example, when a sulfonic acid group or a sulfonate group is introduced into the side chain of the copolymer, it is difficult to sufficiently increase the hydrophilicity because the hydroxyl group of the ethylene-vinyl alcohol copolymer to which the copolymer is introduced is lost. If a large amount of a hydrophilic group is introduced to enhance the hydrophilicity, mechanical performance, durability, etc. will be impaired.

However, when a unit having a sulfonic acid group or a sulfonate group in the main chain is copolymerized,
The hydrophilicity is improved without substantially impairing the mechanical performance, durability and the like of the copolymer. Therefore, by using the copolymer, the hydrophilicity, mechanical performance (stiffness), durability and the like can be improved. A separator excellent in various performances can be obtained. When the hydrophilicity of the separator is improved, the wettability and the liquid retention property of the electrolyte are improved, and when the stiffness of the separator is increased, the permeability in the battery assembling process is improved. An excellent effect is obtained in that the generation of an internal short circuit due to deformation is suppressed. Furthermore, since the adhesiveness is less likely to occur during spinning of the conjugate fiber, the splitting property of the fiber is remarkably improved, and the diameter can be easily reduced by performing a hydroentanglement treatment or the like.

The modified ethylene-vinyl alcohol copolymer used in the present invention has a basic skeleton of an ethylene-vinyl alcohol copolymer and has a sulfonic acid group and / or a sulfonate group in the main chain. Are copolymerized. The modified ethylene-vinyl alcohol-based copolymer is more efficient by copolymerizing a unit (monomer) having a sulfonic acid group and / or a sulfonate group when polymerizing the ethylene-vinyl alcohol-based copolymer. Can be manufactured. The total copolymerization amount of the monomer having a sulfonic acid group and / or a sulfonate group is determined based on the total number of moles of ethylene units and vinyl alcohol units constituting the ethylene-vinyl alcohol-based copolymer. And preferably at least 0.1 mol%, and more preferably at most 10 mol%, especially at most 3 mol%, in view of the mechanical performance, chemical resistance, spinning stability and the like of the copolymer. And particularly preferably 1 mol% or less. According to the present invention, by introducing a small amount of a sulfonic acid group / sulfonate group, the hydrophilicity is greatly improved, so that an excellent effect is obtained without substantially impairing the basic performance of the copolymer.

The unit (monomer) having a sulfonic acid group and / or a sulfonate group introduced into the main chain of the ethylene-vinyl alcohol copolymer includes, for example, an acrylamide sulfonate monomer (2-acrylamide- Sodium 2-methylpropanesulfonate), styrene sulfonate monomer (potassium styrenesulfonate), allylic sulfonate monomer (sodium allyl sulfonate), vinyl sulfonate monomer (sodium vinyl sulfonate) And the like.
In addition, these ammonium salt monomers and acid monomers are also preferable examples, and these sulfonic acid esters can also be used by converting the ester into its salt or acid after polymerization. In addition, these monomers can be used alone or in combination.

Among them, the monomers represented by the following formula (I) can be easily introduced without substantially impairing the performance of the ethylene-vinyl alcohol copolymer. Monomers are preferably used.

[0012]

Embedded image

Wherein R ₁ , R ₂ , R _{3 ,} R ₄ and R ₅
Represents a hydrogen atom or an alkyl group, and M represents a hydrogen atom, an alkali metal or NH ₄ . R ₁ is more preferably a hydrogen atom or a lower alkyl group, and is more preferably a hydrogen atom or a methyl group, particularly a hydrogen atom, from the viewpoint of a high polymerization rate in the copolymerization reaction. Also R
₂ , R ₃ , R ₄ and R ₅ are more preferably an alkyl group from the viewpoint of high stability of the amide bond, not breaking the bond in the saponification reaction of the copolymer, and cost.

M is an alkali metal, particularly Li, Na or K, from the viewpoint of suppressing gelation and decomposition of vinyl acetate.
Among them, Na or K is more preferable. An alkali metal salt can be easily obtained by neutralizing the sulfonic acid group with an alkali. Of course, the above effect can be obtained even if some M is hydrogen.

The following are specific examples of the monomer represented by the general formula (I). 2-acrylamide-
2-methylpropanesulfonic acid or its alkali metal salt, 2-acrylamide-1-methylpropanesulfonic acid or its alkali metal salt, 2-methacrylamide-
2-methylpropanesulfonic acid or an alkali metal salt thereof, of which vinyl ester, especially vinyl acetate, has a high copolymerization rate and is capable of synthesizing a copolymer having a high degree of polymerization, and stability of an amide bond. Is particularly high,
Further, mechanical properties of the obtained copolymer, various properties such as hydrophilicity are high, industrial production is relatively inexpensive, etc., so that 2-acrylamido-2-methylpropanesulfonic acid or an alkali metal salt thereof is used. It can be used most preferably.

The proportion of ethylene units in the ethylene-vinyl alcohol copolymer used in the present invention is preferably 70 mol% or less, particularly 55 mol% or less, more preferably 50 mol% or less from the viewpoint of hydrophilicity. From the viewpoint of mechanical performance and durability, it is preferably at least 10 mol%, particularly preferably at least 30 mol%. Further, from the viewpoint of hydrophilicity, the content of the vinyl alcohol unit is preferably at least 30 mol%, more preferably at least 45 mol%, particularly preferably at least 50 mol%. The degree of saponification of the modified ethylene-vinyl alcohol copolymer used in the present invention is preferably at least 95 mol%, particularly preferably at least 97 mol%, in view of mechanical performance, chemical resistance and the like.

Suitable melt index (MI) of the modified ethylene-vinyl alcohol copolymer used in the present invention
Is 0.1 to 200 g / 10 min, and 0.2 to 1
00 g / 10 mi. Especially 0.5 to 8g / 10min
It is preferred that By setting such a melt index, the mechanical performance of the copolymer is increased, and a separator having a strong “stiffness” is obtained. However, an excellent effect of being hardly deformed and suppressing the occurrence of an internal short circuit due to the deformation can be obtained. Spinnability,
It is more preferably at least 1.0 g / 10 min from the viewpoint of workability and the like, and is preferably 7 g / 10 mi from the viewpoint of mechanical performance.
More preferably, it is n or less.

The modified ethylene used in the present invention is described below.
-A method for producing a vinyl alcohol-based copolymer will be specifically described. The polymerization method is not limited to solution polymerization, and may be either a continuous type or a batch type. For example, the polymerization conditions in the case of batch type solution polymerization are as follows. Alcohols are preferable as the solvent, but an organic solvent such as dimethyl sulfoxide can also be used. As alcohols, methyl alcohol is particularly preferred. As the catalyst, an azonitrile initiator such as 2,2'-azobisisobutyronitrile and an organic peroxide initiator such as isobutyryl peroxide may be used. Polymerization temperature is 2
The polymerization is preferably performed at 0 to 90 ° C. for a polymerization time of 2 to 15 hours, and a polymerization rate of 10 to 90% based on the charged vinyl acetate.

More specifically, ethylene, vinyl acetate,
A monomer containing sulfonic acid and a sulfonic acid group (sulfonate group) was polymerized for a predetermined period of time, and after reaching a predetermined polymerization rate, a polymerization inhibitor was added as necessary, and unreacted ethylene gas was removed by evaporation. Thereafter, unreacted vinyl acetate may be driven off. Next, an alkali catalyst may be added to the copolymer solution from which unreacted vinyl acetate has been removed to saponify the vinyl acetate units in the copolymer. Further, in order to remove unreacted monomers, alkali catalysts, by-product salts and other impurities, it is preferable to neutralize and wash as necessary.

The components other than the ethylene-vinyl alcohol copolymer constituting the splittable conjugate fiber are not particularly limited, and for example, melt-spinnable polymers such as polyolefin polymers and polyamide polymers can be suitably used. By using a composite fiber containing such other components, the durability, swelling resistance, mechanical performance, and the like of the separator can be improved, and the fiber can be further divided into ultrafine fibers. It is preferable to use at least a polyolefin polymer having a vinyl alcohol unit content of less than 30 mol% from the viewpoints of spinnability, splitting property, durability and the like of the conjugate fiber, and it is more preferable to use at least a polypropylene polymer. The polypropylene resin used is not particularly limited, but a resin having a weight average molecular weight of 80,000 to 150,000 is more preferable from the viewpoint of spinnability.

The structure of the conjugate fiber is not particularly limited, and it may be composed of three or more components. However, from the viewpoint of spinnability and splitting property, a bicomponent conjugate fiber is preferable. Among them, a conjugate fiber in which at least one component is divided into two or more, particularly four or more regions by another component in the cross section of the conjugate fiber is preferable. From the viewpoint of ease of division, it is preferable that all components constituting the conjugate fiber are divided into two or more regions by other components in the fiber cross section, and the total number of divisions (total number of regions) in the conjugate fiber cross section , The total number of layers) is more preferably 8 to 40. Further, from the viewpoint of ease of division and spinnability, each layer is preferably substantially continuous in the fiber length direction.

From the viewpoints of the liquid absorption properties, liquid retention properties, ease of division, separation properties of the separator, etc., each region (layer) constituting the composite fiber is 0.6 dtex or less, particularly 0.3 dtex or less, particularly The size is preferably equal to or less than 0.1 dtex.
The size is preferably equal to or more than 008 dtex, particularly preferably equal to or more than 0.05 dtex. The composite state is not particularly limited, and a composite fiber of a laminar split type, a radial split type, or the like can be suitably used, and can be produced by performing a composite spinning by a conventionally known method. It is preferable to use a laminar split type or a radial split type in view of ease of division and spinning process. Of course, a plurality of types of composite fibers can be used in combination.

From the viewpoint of liquid retention, liquid absorption rate and ease of splitting, it is preferable to use a conjugate fiber in which a modified ethylene-vinyl alcohol copolymer is present on at least a part of the fiber surface. The amount of the modified ethylene-vinyl alcohol copolymer constituting the conjugate fiber is preferably from 10 to 90% by weight, and from the viewpoint of hydrophilicity, is preferably at least 30% by weight.
In particular, it is preferably at least 40% by weight. Further, from the viewpoints of chemical resistance, ease of division, and the like, the content is preferably 80% by weight or less. Of course, as long as the effects of the present invention are not impaired, additives such as an antioxidant and a process aid may be incorporated. The fineness of the composite fiber may be appropriately selected,
0.5 to 10 dtex, especially 1 to 6 dt, from the viewpoint of the homogeneity of the nonwoven fabric, the separating property of the nonwoven fabric, and the ease of division of the composite fiber.
ex composite fibers are more preferred. The compounding amount of the composite fiber is 5
0% by weight or more / non-woven fabric, especially 70% by weight or more / non-woven fabric,
In particular, it is preferably at least 80% by weight. Further, a fiber other than such a conjugate fiber may be blended as a main fiber. 0.0 in terms of separation, liquid retention, strength, etc.
Fibers of 1 to 3 dtex can be suitably used, and it is preferable to mix polyolefin fibers from the viewpoint of chemical resistance and the like.

A non-woven fabric may be formed by using such a main fiber, but it is preferable to further blend a binder, particularly a binder fiber, from the viewpoint of enhancing the strength, the “stiffness”, the form stability and the like of the non-woven fabric. By blending the fibrous binder, the above-mentioned effects can be obtained without increasing the internal resistance more than necessary. The fineness of the binder fiber is preferably about 0.5 to 6 dtex from the viewpoint of nonwoven fabric strength, homogeneity, processability, and the like. Note that the fibrous binder does not need to clearly retain the fiber shape after being formed into a nonwoven fabric, and the above effects can be obtained by manufacturing the nonwoven fabric using the fibrous binder. The binder fiber may be composed of a single component, but is preferably composed of two or more components, since it has an adhesive effect and can maintain sufficient strength. Core-sheath type, side-by-side type,
Composite fibers such as a laminar split type and a radial split type, and sea-island fibers can be suitably used. The cross section of the fiber is not particularly limited, such as a round type, a flat type, a cocoon type, a hollow type, and a T type. chemical resistance,
From the viewpoint of adhesiveness to the splittable conjugate fiber and the like, a polyolefin-based binder fiber is preferable, and among these, a binder fiber using at least a polyethylene-based polymer and / or a polypropylene-based polymer is preferable. In particular, sheath-core type composite fibers having a polyethylene resin as a sheath component and a polypropylene resin as a core component can be more preferably used. The blending amount of the binder fiber is preferably 1 to 30% by weight / nonwoven fabric, particularly preferably 3 to 20% by weight / nonwoven fabric, from the viewpoint of nonwoven fabric strength and internal loss.

The method for producing the nonwoven fabric constituting the battery separator of the present invention is not particularly limited, and may be produced by, for example, a dry method (parallel card method, cross layer method, random webber method, etc.) or a wet papermaking method. In the case of manufacturing a nonwoven fabric by a dry method, the fiber length of the compounded fiber is set to 20.
When producing a nonwoven fabric by a wet papermaking method, the fiber length of the compounded fiber is 0.5 to 30 mm, particularly 1 to 200 mm.
The thickness is preferably 20 mm in terms of dispersibility, homogeneity, manufacturing processability, and the like. When a nonwoven fabric is manufactured by a dry method, it is preferable to use crimped fibers.

From the viewpoint of improving the separating property of the separator, and further improving the wettability by increasing the surface area of the fiber, it is preferable to use a nonwoven fabric in which the splittable conjugate fiber is divided and reduced in diameter. A method of dividing the conjugate fiber in advance and then forming a nonwoven fabric, for example, in the case of employing a wet papermaking method, a method in which the fiber is defibrated with a beater, a pulper, or the like at the time of slurry preparation and then divided to form a paper may be adopted. However, it is preferable to split the composite fiber after forming the sheet from the viewpoint of manufacturing processability and obtaining a separator excellent in homogeneity and separation property. As the dividing method, it is preferable to adopt a method of dividing by applying a mechanical shearing force from the viewpoint of production efficiency, and it is preferable to divide by a process such as a needle punching process and a water entanglement process. However, when performing the entanglement process by needle punch, it is necessary to pay attention to the fact that if the diameter of the needle used is large, the pore size becomes large when the separator is used for a battery. From the viewpoint of high productivity and efficient splitting of the conjugate fiber, it is preferable to employ the hydroentanglement treatment.

As the water entanglement treatment, for example, the nozzle diameter is 0.03 mm to 0.3 mm, more preferably 0.09 m
Water pressure of 10 kg / cm ² using a nozzle plate or the like arranged in 1 to 3 rows with a pitch of 0.15 mm to 5 mm, more preferably 0.5 mm to 1.5 mm, and a pitch of 0.15 mm to 5 mm.
A method of treating once or a plurality of times with a water flow of up to 500 kg / cm ² is conceivable. In particular, when a binder fiber is blended, the binder function of the binder fiber is developed after performing the entanglement process, so that the entanglement process and the splitting process can be performed more stably. Also, excellent effects can be obtained from the viewpoint of the splitting property of the composite fiber.

The split state of the splittable conjugate fiber is preferably divided for each region (each layer) constituting the conjugate fiber from the viewpoint of the separating property, but it is not necessary that all the layers are split. Further, one fiber may have a divided portion and a non-divided portion.
For example, each layer may not be completely divided but may be simply divided into branches. The fiber diameter after the division treatment is preferably about 0.6 dtex or less from the point of separation, particularly about 0.3 dtex or less, particularly preferably about 0.2 dtex or less, because the pressure loss is not increased more than necessary. Is preferably about 0.01 dtex or more, particularly about 0.05 dtex or more. By dividing the splittable conjugate fiber and making it extremely fine, the pore size of the nonwoven fabric can be reduced, and the separating property can be improved.

From the viewpoint of maintaining a high degree of separation without unnecessarily increasing the internal loss, the average pore size of the separator is preferably from 5 to 80 μm, particularly preferably from 10 to 50 μm. The maximum pore size is preferably 150 μm or less, particularly preferably 100 μm or less. In addition, the thickness of the nonwoven fabric is set at about 0.1 in terms of enhancing the handleability, increasing the battery life, and further, in terms of mechanical performance.
It is preferably about 0.05 to 0.25 mm, and the basis weight is 2
The density is preferably about 0 to 80 g / m ² and the density is about 0.1 to 0.6 g / cm ³ .

Further, in the present invention, specific ethylene-
Since the splittable conjugate fiber containing the vinyl alcohol copolymer is used, a separator excellent in stiffness and mechanical performance and having a large liquid absorption amount and a liquid absorption speed can be obtained. More specifically, according to the present invention, the breaking length is 4 km or more, especially 5 km or more, more preferably 6 km or more, furthermore, stiffness 0.44 kgf or more, especially 0.48 kgf or more, further 0.50 kgf or more, and even 0 0.6kgf or more non-woven fabric, 0.30g / 2500m
m ² or more, especially 0.35 g / 2500 mm ² or more, further 0.3
A nonwoven fabric having a thickness of 7 g / 2500 mm ² or more and a liquid absorption speed of 200 sec / 25 mm or less, particularly 160 sec / 25 mm or less can be obtained.

The obtained non-woven fabric can be used as it is, or can be processed into a desired shape such as a bag-shaped body or a spiral-shaped body to obtain a battery separator. Of course, a battery separator may be manufactured in combination with a material other than the nonwoven fabric. For example, it can be laminated or spliced with another nonwoven fabric, film, or the like. However, from the viewpoint of efficiently obtaining the effects of the present invention, it is preferable to manufacture the battery separator substantially from only the nonwoven fabric described above. By incorporating the battery separator of the present invention, a battery excellent in various performances can be obtained.

[0032]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples. [Melt index g / 10min] Diameter 2.1m
m, a sample was placed in a cylinder having an orifice having a length of 8 mm, and extruded at 190 ° C. under a load of 2160 g.
The weight of the test material spilled in a minute
The melt index was determined in terms of the outflow weight per minute. However, for samples having a melting point of about 190 ° C. or higher, the outflow amount for 10 minutes at a plurality of temperatures equal to or higher than the melting point under a load of 2160 g is calculated. The value was plotted on the vertical axis (logarithm) and the value extrapolated to 190 ° C. was used as the melt index. [Weight average molecular weight] Measured by GPC method.

[Thickness mm Density g / cm ³ ] JIS
P 8118 "Test methods for thickness and density of paper and paperboard"
It measured according to. [Basic weight g / m ² ] Measured according to JIS P 8124 “Measurement of metric basis weight of paper”. [Tear length km] Measured in accordance with JIS P 8113 "Test method for tensile strength of paper and paperboard".

[Liquid absorption g / g] A paper sample of 50 mm × 50 mm was immersed in a 35% KOH solution at a bath ratio of 1/100 for 24 hours.
The sample was immersed for 30 hours and drained naturally for 30 seconds, the weight of the sample was measured, and the amount of liquid absorbed was calculated by dividing the weight of the retained liquid by the weight of the paper. [Liquid Absorption Speed] The end of the sample was immersed in a 35% KOH solution, and the absorption speed was evaluated based on the time required for the 35% KOH solution to suck up to a height of 25 mm.

[Air permeability: cm ³ / cm ² / sec] JIS
L 1096-1996 Measured by a Frazier-type air permeability tester manufactured by Toyo Seiki Seisaku-Sho, Ltd. according to the air permeability measurement method of "General Textile Test Method". [Pore size μm] Measured by colter POROMETER II manufactured by Coulter Electronics Co., Ltd.

[Koshi kgf] A sample of 25 mm × 90 mm was immersed in 35% KOH for 30 minutes, and then wrapped around the center of 20 mm (height) × 7 mmФ in quadruplicate to obtain 20 mm (height).
X 9mmФ (inner diameter), set in a tube, and use “Rheometer RT-2010-CW” manufactured by Leotech Co., Ltd.
A method for measuring compressive strength was used.

[Binder Fiber] A 2.2 dtex core-sheath type composite fiber (“N-740” manufactured by Kuraray Co., Ltd.) having a sheath component of polyethylene and a core component of polypropylene was used. When the sheet is formed by the dry method, the number of crimps is 12 /
In crimp was applied and cut to a length of 51 mm for use. When a sheet was formed by a wet method, the sheet was cut to a length of 5 mm without crimping and used.

Reference Example 1 Methanol as a polymerization solvent
Radical polymerization of ethylene, vinyl acetate and sodium 2-acrylamido-2-methylpropanesulfonate (hereinafter abbreviated as AMPS) under pressure and at 60 ° C. using AIBN (azobisisobutyronitrile) as a polymerization initiator. An AMPS content of 0.2 mol% and an ethylene content of 44
A mole% of AMPS / ethylene / vinyl acetate copolymer was prepared. Next, this AMPS / ethylene / vinyl acetate copolymer was saponified in a methanol solution containing caustic soda, washed and dried to produce a modified ethylene-vinyl alcohol copolymer. The AMPS content of the obtained AMPS / ethylene / vinyl alcohol copolymer was 0.2 mol%, the ethylene content was 44 mol%, the saponification degree was 99.5 mol%, and the melt index was 2 g / 10 min. Composite spinning is carried out at a compounding ratio of 67% by weight of the modified ethylene-vinyl alcohol copolymer obtained and 33% by weight of polypropylene having a weight average molecular weight of 105200 to produce a layered splittable conjugate fiber in which both components are alternately laminated. (3.1 dtex, total number of divisions: 11, division number of ethylene-vinyl alcohol copolymer part: 6, average fineness of each layer: approx.
28 dtex).

REFERENCE EXAMPLE 2 Composite spinning was carried out at a compounding ratio of 67% by weight of the modified ethylene-vinyl alcohol copolymer used in Reference Example 1 and 33% by weight of polypropylene having a weight average molecular weight of 105,200, and both components were alternately laminated. To produce a layered splittable conjugate fiber (3.6 dtex, total split number 32,
Number of divisions of ethylene-vinyl alcohol copolymer part 1
6, average fineness of each layer is about 0.1 dtex).

Reference Example 3 Ethylene content of 44 mol%
Saponification degree 99%, melt index 5.5g / 10m
in ethylene vinyl alcohol copolymer (“E105Y” manufactured by Kuraray Co., Ltd.) 67% by weight, weight average molecular weight 1
33200% by weight of polypropylene of No. 05200 was composite-spun to produce a layered splittable conjugate fiber in which both components were alternately laminated (3.0 dtex, total number of divisions 11, number of divisions of ethylene-vinyl alcohol-based copolymer portion) 6, average fineness of each layer is about 0.27 dtex). Reference Example 4 Polypropylene having a weight average molecular weight of 105,200 was melt-spun to produce a 1.1 dtex fiber.

[Example 1] The splittable conjugate fiber 9 of Reference Example 1
0 parts by weight, 10 parts by weight of the above binder fiber are mixed,
A web having a basis weight of 60 g / m ² was produced using a roller card. Next, nozzle diameter 0.1mm, pitch 0.6m
m, using one row of nozzle plates, water pressure 20kg / c
m ² -80 kg / cm ² -60 kg / cm ² -40 kg /
After performing the water entanglement process once each on the front and back with a water flow of 1 cm ² ,
A hot press treatment was performed at 32 ° C. to obtain a nonwoven fabric having a thickness of 20 μm. The obtained nonwoven fabric had high hydrophilicity and was excellent in wettability and liquid absorbability, was excellent in stiffness and mechanical performance, and had excellent performance as a separator. Moreover, since the splittable conjugate fiber was substantially divided into each region (layer) by the hydroentanglement treatment, it had a high degree of separation characteristics. Table 1 shows the results.

Example 2 A nonwoven fabric was produced in the same manner as in Example 1 except that the splittable conjugate fiber of Reference Example 2 was used. The obtained nonwoven fabric had high hydrophilicity, excellent wettability, and excellent liquid absorbency, excellent stiffness and mechanical performance, and had excellent performance as a separator. Moreover, since the splittable conjugate fiber was substantially divided into each region (layer) by the hydroentanglement treatment, it had a high degree of separation characteristics. Table 1 shows the results.

Comparative Example 1 The unmodified ethylene-
A nonwoven fabric was produced in the same manner as in Example 1 except that a fiber containing a vinyl alcohol-based copolymer was used. The obtained nonwoven fabric had excellent performance as a separator, but was inferior in liquid retaining property and wettability as compared with the examples. Table 1 shows the results.

Comparative Example 2 A nonwoven fabric was produced in the same manner as in Example 1 except that the polypropylene fiber of Reference Example 4 was used instead of the splittable conjugate fiber. The obtained nonwoven fabric was inferior in liquid absorption performance and was unsuitable as a battery separator.

[0045]

[Table 1]

Claims (6)

[Claims] The basic skeleton is an ethylene-vinyl alcohol copolymer, and a sulfonic acid group and / or
Alternatively, a battery separator made of a nonwoven fabric using splittable conjugate fibers containing at least one modified ethylene-vinyl alcohol copolymer obtained by copolymerizing a unit having a sulfonate group. 2. The basic skeleton is an ethylene-vinyl alcohol copolymer, and a sulfonic acid group and / or
Alternatively, a battery separator made of a nonwoven fabric using splittable composite fibers made of a modified ethylene-vinyl alcohol-based copolymer and a polypropylene-based polymer in which a unit having a sulfonate group is copolymerized. 3. The battery separator according to claim 1, wherein the splittable conjugate fiber is split to have a reduced diameter. 4. The modified ethylene-vinyl alcohol-based copolymer according to claim 1, wherein the copolymer is obtained by copolymerizing 2-acrylamido-2-methylpropanesulfonic acid or an alkali metal salt thereof. The battery separator according to any one of the above. 5. The basic skeleton is an ethylene-vinyl alcohol copolymer, and a sulfonic acid group and / or
Alternatively, a non-woven fabric for a battery separator using a splittable conjugate fiber containing at least one component of a modified ethylene-vinyl alcohol copolymer in which a unit having a sulfonate group is copolymerized. 6. The basic skeleton is an ethylene-vinyl alcohol copolymer, and a sulfonic acid group and / or
Or forming a nonwoven sheet using a splittable conjugate fiber having a modified ethylene-vinyl alcohol-based copolymer in which a unit having a sulfonate group is copolymerized as at least one component,
A method for producing a nonwoven fabric for a battery separator, wherein the splittable conjugate fiber is split by subjecting the nonwoven fabric to a hydroentanglement treatment.