JPH06163021A - Nonwoven fabric separator for alkaline battery and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a battery separator having excellent affinity with electrolyte and liquid preserving characteristics by forming nonwoven fabric of mixed fiber of copolymerization fiber and polyolefine type fiber, carrying out hydrolysis processing, and introducing a carboxyl group. CONSTITUTION:A nonwoven fabric sheet is formed of mixed fiber of copolymerization fiber of acrylonitrile and vinyl chloride and polyolefine type fiber. When hydrolysis processing is carried out on this nonwoven fabric by potassium hydroxide solution, a nitrile group in the copolymerization fiber is converted into a carboxyl group being a hydrophilic group. A battery separator is formed by using the nonwoven fabric in which this carboxyl group is introduced. This separator has excellent hygroscopicity, and affinity with electrolyte and liquid preserving characteristics can be heightened over a long period of time, and the service life of a battery can be lengthened.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-woven fabric separator for an alkaline battery, which is preferably used for a sealed alkaline battery such as a nickel-cadmium battery, a nickel-hydrogen battery and a nickel-zinc battery, and a method for producing the same.

[0002]

2. Description of the Related Art Separator used in alkaline storage batteries is
It is required to hold the alkaline electrolyte for a long period of time against repeated charging / discharging for a long period of time to prevent a short circuit due to contact between electrodes.

At present, polyamide-based fibers, which are widely used as non-woven fabrics for alkaline battery separators, do not have sufficient chemical resistance such as alkali resistance and oxidation resistance during repeated charging / discharging for a long period of time, so that fiber deterioration is caused. However, there is a defect that the battery life progresses and the battery life is shortened due to a short circuit between the electrodes.

On the other hand, a separator using a polyolefin fiber excellent in chemical resistance such as alkali resistance and oxidation resistance has been proposed. However, since the hydrophilicity is poor, the electrolyte retention is extremely poor and the charge and discharge are poor. There was a drawback in that the electrolyte solution was easily dried out due to repetition.

As a method for solving these drawbacks, a method in which a surfactant is added (JP-A-58-175256) and a method in which hydrophilic inorganic powder is added (JP-A-64).
No. 57568), polyethylene fibers or polypropylene fibers are sulfonated to introduce a sulfonic acid group which is a hydrophilic group (Japanese Patent Laid-Open Nos. 1-132043 and 1-132044). ing.

[0006]

The method of applying the above-mentioned surfactant and the method of adding the hydrophilic inorganic powder are such that the surface active agent and the inorganic powder fall off from the fiber surface into the electrolytic solution due to the cell reaction. In many cases, it is difficult to maintain stable hydrophilicity over a long period of time. Further, regarding the above-mentioned sulfonization treatment, α-
Since olefin is subjected to sulfonation treatment with fuming sulfuric acid, it is difficult to control quantitatively to efficiently introduce a predetermined amount of sulfonic acid group, and it is difficult to maintain stable hydrophilicity for a long period of time.

An object of the present invention is to provide a non-woven fabric separator for an alkaline battery, which is capable of sustaining hydrophilicity for a long period of time and is also excellent in chemical stability such as alkali resistance and oxidation resistance, and a method for producing the same. Is.

[0008]

The present invention comprises a mixed fiber of a copolymer fiber having a carboxyl group introduced on a part or the whole of the fiber surface and a polyolefin fiber.

The above-mentioned copolymer fiber is composed of a single fiber composed of a single component of the copolymer resin, or a composite fiber such as a split type or a core-sheath type with another resin, and its shape is not particularly limited.

Examples of the above-mentioned polyolefin fibers include polypropylene fibers and polypropylene-polyethylene composite fibers, but they are not particularly limited as long as they are chemically resistant polyolefin fibers.

The mixing ratio of the above-mentioned mixed fibers can be arbitrarily changed in order to adjust the adhesive strength and hydrophilicity of the nonwoven fabric separator and is not particularly limited.

Further, the present invention is characterized in that the copolymer fiber contains the compound shown in Chemical formula 2.

[0013]

[Chemical 2]

In the present invention, the copolymer fiber is 20 to 80.
It is characterized by containing acrylonitrile in a weight percentage.

If the amount of acrylonitrile is less than 20% by weight,
Even if it is hydrolyzed to be converted into a carboxyl group, the hydrophilic effect is small, and if it exceeds 80% by weight, the surface of the copolymer fiber swells into a gel, which is not preferable.

The present invention is also characterized in that X in the general formula is chlorine (Cl).

In the present invention, the copolymer fiber described in claim 2 is formed into a non-woven fabric and then hydrolyzed.

The above-mentioned hydrolysis treatment is to convert the nitrile group (-CN) in the copolymer fiber into a carboxyl group (-COOH) which is a hydrophilic group by hydrolysis by an alkali treatment or the like. This reaction proceeds in two steps as shown in Chemical Formula 3 below.

[0019]

[Chemical 3]

The above-mentioned hydrolysis treatment is not particularly limited, but it is preferably performed with an alkaline solution such as potassium hydroxide or sodium hydroxide. Alternatively, the copolymer fiber may be previously hydrolyzed and then mixed with the polyolefin fiber to form a non-woven fabric.

[0021]

According to the present invention, the hydrophilicity is improved by the copolymerized fiber into which the carboxyl group which is a hydrophilic group is introduced, and the amount of this carboxyl group is also determined by the mixing ratio with the polyolefin fiber.
It can be easily adjusted by appropriately changing the copolymerization ratio of acrylonitrile in the copolymerized fiber.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below.

Example 1 Copolymerized fiber of acrylonitrile and vinyl chloride (copolymerization ratio 50:50; 2d × 51)
mm) 50% by weight and 50% by weight of a core-sheath type composite fiber (core-sheath weight composite ratio 50:50; 2d × 51 mm) composed of polypropylene resin as a core component and polyethylene resin as a sheath component (card). And a cross web by a known web forming machine such as a cross wrapper, and the web is heated and pressure-bonded (roll wire pressure 10 to 50 kg / m ² ) with a pair of calender rolls heated to 135 ° C.
A non-woven fabric sheet having a g / m ² and a thickness of 0.19 mm was obtained.

Next, this non-woven fabric sheet was hydrolyzed with a potassium hydroxide solution, washed with water and dried to obtain a non-woven fabric separator for alkaline batteries of Example 1.

Example 2 Copolymerized fiber of acrylonitrile and vinyl chloride (copolymerization ratio 30:70; 2d × 51)
mm) 50% by weight and 50% by weight of a core-sheath type composite fiber (core-sheath weight composite ratio 50:50; 2d × 51 mm) composed of a polypropylene resin as a core component and a polyethylene resin as a sheath component. A non-woven fabric sheet was formed by the same method as in Example 1, and then similarly hydrolyzed, to obtain a non-woven fabric separator for alkaline batteries of Example 2.

Example 3 A core-sheath type composite fiber (core-sheath weight composite ratio of 50) in which the sheath component is a copolymer resin of acrylonitrile and vinyl chloride (copolymerization ratio 40:60) and the core component is polypropylene resin. : 50; 2d × 51 mm) is hydrolyzed with a potassium hydroxide solution, washed with water and dried to obtain 50% by weight of the composite fiber, the core component is polypropylene resin, and the sheath component is polyethylene resin. Core-sheath type composite fiber (core-sheath weight composite ratio 50: 5)
(0; 2d × 51 mm) 50% by weight of the mixed fiber was thermocompression bonded in the same manner as in Example 1 to obtain a non-woven fabric separator for alkaline battery of Example 3 having a basis weight of 60 g / m ² and a thickness of 0.19 mm. .

(Comparative Example 1) A core-sheath type composite fiber (core-sheath weight composite ratio of 50: core-sheath composite fiber whose core component is a polypropylene resin is a copolymer fiber of acrylonitrile and vinyl chloride (copolymerization ratio 90:10). : 50; 2d × 51 mm) is hydrolyzed with a potassium hydroxide solution, washed with water and dried to obtain 50% by weight of the composite fiber, the core component is polypropylene resin and the sheath component is polyethylene resin. Core-sheath type composite fiber (core-sheath weight composite ratio 50: 5)
(0; 2d × 51 mm) 50% by weight of the mixed fiber was thermocompression bonded in the same manner as in Example 1 to obtain a non-woven fabric separator for alkaline battery of Comparative Example 1 having a basis weight of 60 g / m ² and a thickness of 0.19 mm. .

Comparative Example 2 50% by weight of a core-sheath type composite fiber (core-sheath weight composite ratio 50:50; 2d × 51 mm) having a polypropylene resin as a core component and a polyethylene resin as a sheath component, and a regular polypropylene fiber ( 2d x 51
mm) 50% by weight of the mixed fiber was thermocompression bonded in the same manner as in Example 1 to give a basis weight of 60 g / m ² and a thickness of 0.19 mm.
The non-woven fabric separator for alkaline batteries of Comparative Example 2 was prepared.

Table 1 shows the results of a comparative test of various physical properties of the nonwoven fabric separators for alkaline batteries obtained in Examples 1 to 3 and Comparative Examples 1 and 2.

[0030]

[Table 1]

The test methods for the test items in the table are as follows. Moisture content: Moisture content at 20 ° C., RH 65%, after standing for 24 hours. Liquid absorption speed: Liquid absorption height after 30 minutes of immersion of one end of a separator material having a sample width of 25 mm in a caustic potash solution having a specific gravity of 1.30. Liquid retention rate: The solution absorption rate after immersing the separator material in a caustic potash solution having a specific gravity of 1.30, suspending it for 10 minutes, and draining it. Alkali resistance; 80 ℃ in caustic potash solution with specific gravity of 1.30
Weight loss rate after soaking for 30 days. Oxidation resistance: 50% in a mixed solution of 250 ml of a 5% KMnO ₄ solution and 50 ml of a caustic potash solution having a specific gravity of 1.30.
Weight reduction rate after soaking at ℃ for 1 hour.

Further, using the non-woven fabric separators for alkaline batteries obtained in the above Examples and Comparative Examples, the capacity of 1200
FIG. 1 shows the results of testing by incorporating the Ni-Cd battery of mA · hr into the battery. In addition, in FIG. 1, about the change of the discharge capacity maintenance rate of Examples 1-3, the average of each Example is shown.

As shown in FIG. 1, the non-woven separators of Examples 1, 2 and 3 were repeatedly charged and discharged 2000 times (charging condition 400 mA × 4 hr, discharging condition 1 Ω constant resistance discharge × 2 hr). In contrast, the capacity retention rate of 70% was exhibited, whereas in the case of using the non-woven fabric separator of Comparative Example 2, the capacity decreased early after the electrolyte leakage due to the increase in internal pressure which is considered to be caused by the poor hydrophilicity. It was observed. Comparative Example 1
No test was carried out for the above because the swelling was remarkable when immersed in caustic potash.

[0034]

The non-woven fabric separator for alkaline batteries according to the present invention is excellent in hygroscopicity, can maintain the affinity with the electrolytic solution for a long period of time, and can enhance the liquid retaining property. Further, since it has excellent alkali resistance and oxidation resistance, it has durability, and has various effects such as being able to maintain a high capacity during repeated charging and discharging for a long period of time and greatly improving battery life. .

[Brief description of drawings]

FIG. 1 is a curve diagram showing a change in a discharge capacity retention rate with respect to the number of times charging and discharging are repeated.

Claims (5)

[Claims] 1. A non-woven fabric separator for an alkaline battery, comprising a mixed fiber of a copolymer fiber having a carboxyl group introduced on a part or all of the fiber surface and a polyolefin fiber. 2. The non-woven fabric separator for an alkaline battery according to claim 1, wherein the copolymer fiber contains a compound represented by the following general formula. [Chemical 1] 3. The nonwoven fabric separator for an alkaline battery according to claim 2, wherein the copolymer fiber contains 20 to 80% by weight of acrylonitrile. 4. The nonwoven fabric separator for an alkaline battery according to claim 2, wherein X in the general formula is chlorine (Cl). 5. A method for producing a non-woven fabric separator for an alkaline battery, which comprises forming the mixed fiber of the copolymerized fiber according to claim 2 and a polyolefin fiber into a non-woven fabric and then subjecting it to a hydrolysis treatment.