JPH05198295A - Separator for alkali battery - Google Patents

Abstract

PURPOSE:To improve water absorbing property by using polyolefin fiber, in which hydrophilic polymer is mixed, as base material fiber and using polyolefin thermal fusion core-sheathed composite fiber, that hydrophilic polymer is mixed in sheath components, as binder fiber to form a separator with such a non- woven cloth. CONSTITUTION:Thermoplastic nonion water absorbing agent is used as hydrophilic polymer, and easy-to-split composite fiber is used as base material fiber from the view of a structure production, a process passing property, etc. Specifically, after 60 part of low density polyethylene and 40 part of thermoplastic nonion water absorbing agent are kneaded at 120-130 deg.C for twenty minutes, these are pelletized to form a master batch, to which low density polyethylene is further added to form sheath components. Binder fiber which is formed of polyethylene and composite fiber spinned therewith are used and heat-pressed with a pair of rollers heated up to 120 deg.C to form a non-woven cloth with weight/unit area of 80g/m<2>.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improved alkaline battery separator.

[0002]

2. Description of the Related Art Nonwoven fabrics made of polyamide fibers have been widely used as separators for sealed alkaline storage batteries such as nickel-cadmium batteries and nickel-hydrogen batteries that use alkali as an electrolyte, but polyamide fibers are generated during charging. There is a problem in that the product is oxidized and deteriorated by oxygen gas, and this oxidation product increases the self-discharge of the battery.

For this reason, attention has been paid to polyolefin fibers excellent in alkali resistance and oxidation resistance. However, since the polyolefin fibers are poor in hydrophilicity and inferior in electrolyte holding ability, discharge characteristics and charge / discharge cycle life characteristics are inferior. There is also a problem that the gas permeability generated during charging is poor and the internal pressure of the sealed battery rises, which shortens the life of the battery.

Further, in the nickel-cadmium battery, there is a problem that metal cadmium as a cathode active material adheres to the inside of the separator during repeated charging and discharging and short-circuits with the cathode, which shortens the life of the battery. It is effective to make the constituent fibers thin to make the voids between the constituent fibers small and uniform. However, when the constituent fibers are hydrophobic fibers such as polyolefin fibers, if the voids between the constituent fibers become smaller, Since the permeability becomes worse, it is necessary to make it hydrophilic.

Conventionally, as a method for making a polyolefin-based nonwoven fabric hydrophilic, a method of attaching a surfactant to the fiber surface (see Japanese Patent Publication No. 57-33828) and a method of grafting a monomer having a hydrophilic group such as acrylic acid ( JP-A-55-88263), a method of introducing sulfone groups to the fiber surface by dipping in concentrated sulfuric acid under appropriate temperature and concentration conditions (see JP-A-1-32042), and fluorine gas. There has been a method of making the fiber surface hydrophilic by using oxygen and sulfur dioxide gas as side reaction gases as the main reaction gas (see JP-A-2-276154).

[0006]

However, all of the above methods have problems such as high cost and generation of substances harmful to the battery due to oxidation.

The present invention solves the above-mentioned conventional problems and provides a separator for an alkaline battery which is low in cost and does not generate harmful substances and is excellent in water absorption.

[0008]

The present invention uses a polyolefin-based heat-fusible core-sheath type in which a hydrophilic polymer-mixed polyolefin fiber is used as a base fiber, and a hydrophilic polymer is mixed in a sheath component as a binder fiber. The gist of the invention is a separator for an alkaline battery, which is composed of a heat-bonded nonwoven fabric using a composite fiber.

As the hydrophilic polymer used in the present invention,
A thermoplastic nonionic water absorbing agent, for example, Aqua Coke [registered trademark of thermoplastic nonionic water absorbing agent manufactured by Sumitomo Seika Co., Ltd.] is preferably used. Further, as the base fiber, it is desirable to use easily splittable conjugate fiber from the viewpoints of fineness and process passability.

[0010]

EXAMPLES The present invention will be described in more detail with reference to the following examples. The water absorption in Examples and Comparative Examples was measured by JI.
S L1096 General fabric test Water absorption test C method (precipitation method).

Example 1 60 parts of low-density polyethylene and 40 parts of Aqua Coke NV-40 [thermoplastic nonionic water-absorbing agent manufactured by Sumitomo Seika Chemicals Co., Ltd.] were kneaded at 120 to 130 ° C. for 20 minutes and pelletized. A masterbatch is made, low-density polyethylene is further added to this masterbatch, and a composite fiber (3 denier x 64 mm) spun with low-density polyethylene containing 10% and 5% aquacoke as a sheath component and polypropylene as a core component is a binder fiber. Polypropylene fiber containing 10% and 5% aqua coke (2
Denier x 64 mm) was used as the base fiber, and was mixed with 30% binder fiber and 70% base fiber, made into a web with a roller card, and then thermocompression bonded by a pair of rollers heated to 120 ° C to give a basis weight of 80 g. / M ² of non-woven fabric was formed. Table 1 shows the results of measuring the water absorption of the obtained nonwoven fabric.

Comparative Example A non-woven fabric was formed under the same conditions as in the examples except that aqua coke was not mixed, and Table 1 also shows the measurement results of the water absorption of the non-woven fabric.

[0013]

[Table 1]

Example 2 A core-sheath type composite fiber (3 denier × 6 mm) having the same composition as that used in Example 1 was used as a binder fiber, and polypropylene and nylon 6 containing 10% and 5% of aqua coke were used. Easily splittable composite fibers (2.5 denier x 6 mm, polypropylene / nylon 6 composite ratio 4: 1, division number 1)
Using a fiber obtained by dividing 2) with a beater as a base fiber, a wet web formed with a mixing ratio of 40% binder fiber and 60% base fiber was dried and thermocompression-bonded by a pair of rollers heated to 120 ° C. A non-woven fabric having a basis weight of 55 g was formed.
Table 2 shows the results of measuring the water absorption of the obtained non-woven fabric.

[0015]

[Table 2]

[0016]

The alkaline battery separator of the present invention constructed as described above has the advantages of excellent water absorption performance, low manufacturing cost, and no generation of harmful substances.

Claims (2)

[Claims] 1. Heat fusion using a polyolefin-based heat-fusible core-sheath type composite fiber in which a hydrophilic polymer is mixed as a base fiber, and a hydrophilic polymer is mixed in a sheath component as a binder fiber. Non-woven fabric alkaline battery separator. 2. The alkaline battery separator according to claim 1, wherein the hydrophilic polymer is a thermoplastic nonionic water absorbing agent.