JPH0521049A - Separator for alkaline battery - Google Patents

Abstract

PURPOSE:To provide a separator for an alkaline battery, made of a polyolefinic resin, capable of maintaining a hydrophilic property for a long time, having an electrolyte-resistance property, and excellent in supplying and holding hydrophilic properties. CONSTITUTION:The mixture of a low molecular weight polyethylene and a polyethylene emulsion, containing a polar group, is coated on a base material nonwoven fabric sheet composed of a polyolefinic resin fiber.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to batteries, especially Ni-Cd.
, Ni-Zn, Ni-H, etc. have excellent durability against high-concentration alkaline electrolytes for secondary battery applications, improve affinity with electrolytes, and improve liquid absorption and retention. The present invention relates to an alkaline battery separator.

[0002]

2. Description of the Related Art In general, the properties required for a separator for alkaline batteries are that they have a good affinity with an electrolytic solution, an excellent liquid absorption rate and an excellent liquid retention capacity, and can withstand repeated use of charge and discharge for a long period of time. It is required to have various properties such as excellent chemical stability such as alkalinity and oxidation resistance, small internal resistance, air permeability that does not prevent passage of gas and charged ions generated from the electrode.

Therefore, as a separator for an alkaline battery, a non-woven fabric made of polyamide fiber or polyolefin fiber by heat bonding has been conventionally used.

Since this polyolefin separator has excellent chemical stability such as alkali resistance and oxidation resistance when used in a high temperature range, it is formed by using polyolefin fibers such as polypropylene and polyethylene. Although various non-woven fabrics and separators have been proposed, polyolefin-based fibers are inferior in hydrophilicity, so electrolyte retention is extremely poor,
The electrolyte tends to dry out easily after repeated use over a long period of time, and it cannot be used for rapid charging and high rate discharge.

Further, in order to solve the problems of the polyolefin fiber separator, a method of treating with a surfactant, a method of activating the fiber surface by plasma treatment or the like to improve the affinity with an electrolytic solution, and an electronic method A method of graft-polymerizing a hydrophilic monomer on the fiber surface by a ray irradiation method or the like (JP-A-55-88263), or a method of applying a material obtained by copolymerizing a hydrophilic vinyl alcohol with an olefin (JP-A-63-63). No. 34849), a method of introducing a hydrophilic group by a chemical post-treatment method such as sulfonation treatment (JP-A-57-191956, JP-A-1-132044) and the like have been proposed and studied, but all of them have been proposed. There is a problem in that it is difficult to impart stable hydrophilicity for a long period of time and continuously obtain a stable one.

Further, in recent years, there has been an increasing demand for the development of separators that can improve the performance of batteries such as smaller size, lighter weight, longer life, higher capacity, quick charging, and higher temperature.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has the drawbacks of a polyolefin resin fiber nonwoven fabric separator, that is, low electrolytic solution retention and electrolytic solution during long-term repeated use. Prevent the dryout of
(EN) It is intended to obtain an alkaline battery separator which has good affinity with an electrolytic solution and liquid retention, can be repeatedly charged and discharged for a long time, and can be used for rapid charging and high rate discharging.

[0008]

In order to solve the above problems, the present invention has a low molecular weight polyethylene and a polar group in a base non-woven sheet composed of polyolefin resin fibers having excellent chemical resistance. A mixture with a polyethylene emulsion or a mixture of the mixture and a room temperature crosslinkable resin is coated to form a battery separator, which is intended to solve the problem, and has good affinity with an alkaline electrolyte, It has made it possible to obtain a stable alkaline battery separator that has excellent penetrability, liquid retention, and air permeability and that is repeatedly charged and discharged over a long period of time.

As the polyolefin resin fiber used in the constitution of the present invention, polyethylene or a fiber composed of a single component of polypropylene, a composite fiber composed of polyethylene and polypropylene, and the like, ethylene and vinyl alcohol are copolymerized. Fibers using ethylene-vinyl alcohol resin obtained by the above, fibers using ethylene-propylene copolymer, copolymers composed of ethylene and various unsaturated carboxylic acid derivatives, and the like, such fibers are appropriate A porous nonwoven fabric fiber sheet obtained by mixing can be used as a base nonwoven fabric sheet.

Next, the low molecular weight polyethylene used for coating the base nonwoven fabric sheet of the present invention has a molecular weight of 500-500.
It is an ethylene low polymer of 10,000, and is produced by a production method such as polymerization of ethylene and decomposition of high molecular weight polyethylene.

Some polyethylene emulsions having a polar group are provided with a polar group by copolymerization with a polar monomer, oxidative decomposition, or various chemical modifications, and the polar group has a high hydrophilic effect, that is, a sulfone group. , A functional group such as a carboxylic acid group is used.

Further, low molecular weight polyethylene alone has a problem that it is inferior in hydrophilicity like a polyolefin fiber, and a polyethylene emulsion having a polar group falls off in an electrolytic solution when used in a high temperature range.

Further, there is a drawback that the hydrophilic substance such as PEG which is generally used, or the hydrophilic substance and the like are removed by the combination of the surfactant and the resin. Therefore, in order to solve these problems, it was found that these problems can be solved by mixing a low molecular weight polyethylene and a polyethylene emulsion having a polar group, and further by mixing a room temperature crosslinkable resin. Is.

The ratio of the mixture of low molecular weight polyethylene and polyethylene emulsion having polar groups is 3
It is preferably in the range of 0:70 to 70:30 (solid ratio), and when the compounding ratio of the low molecular weight polyethylene is less than 30 parts, it tends to fall off in the electrolytic solution, and the compounding ratio of the polyethylene having a polar group is low. If it is less than 30 parts, the hydrophilicity becomes poor, which is not preferable.

Further, when the polyethylene having a polar group exceeds 70 parts, the polyethylene tends to be dropped in the electrolytic solution, and when the polyethylene having a low molecular weight exceeds 70 parts, the problems such as poor hydrophilicity remarkably occur, which is not desirable. . Further, it is possible to further improve the durability by using the room temperature crosslinkable resin in combination with a polyethylene emulsion having a polar group at about 100: 10 to 100: 30.

When these resins are applied to and adhered to a substrate non-woven sheet, the low molecular weight polyethylene used is an aqueous dispersion or an emulsion having a small amount of polar groups, and the adhesion method is as follows. The known impregnation method, coating method, etc. are not particularly limited.

[0017]

The battery separator of the present invention is formed by impregnating and adhering a mixture of a low molecular weight polyethylene and a polar group-containing polyethylene emulsion or a room temperature cross-linkable resin on a base nonwoven fabric sheet made of polyolefin resin fibers. As a result, the polyethylene chains are intricately intertwined with each other and are entangled with each other, so that the chemical durability is good, the affinity with the alkaline electrolyte is good, and the excellent permeability, liquid retention, and air permeability are obtained. A separator for an alkaline battery, which is excellent in stability and which does not decompose or fall off even after repeated charging and discharging for a long time, is formed.

[0018]

The present invention will be described in more detail with reference to the following examples.

Example 1 A core-sheath type composite fiber having a core of polypropylene and a sheath of polyethylene 1.5d × 38 mm 30%, and regular polypropylene fiber 0.9d × 38 mm 70% mixed fibers were mixed by a card machine and a cross wrapper. The formed fibrous body composed of the cross web is thermocompression-bonded by a pair of calender rolls heated to 120 ° C. to give a basis weight of 60 g / m ² , thickness.
A 0.18 mm non-woven sheet A was obtained.

Next, a mixed solution of 50 parts of the low molecular weight polyethylene emulsion A liquid and 50 parts of the carboxylic acid group-added polyethylene emulsion B liquid is impregnated, and the squeezing roll is squeezed to obtain a predetermined adhesion amount. After adjustment 120
After drying at 0 ° C., an alkaline battery separator according to the present invention having a basis weight of 63 g / m ² and a thickness of 0.18 mm was obtained.

Example 2 Using the same substrate nonwoven fabric sheet A obtained in Example 1, the mixing ratio of the low molecular weight polyethylene emulsion and the carboxylic acid group-added polyethylene emulsion was 7
It was impregnated with two kinds of mixed solutions of 0 part: 30 parts and 30 parts: 70 parts, respectively, and in the same manner as in Example 1, the basis weight was 63 g / each.
The alkaline battery separators (a) and (b) according to the present invention having m ² and a thickness of 0.18 mm were obtained.

Comparative Example 1 The base nonwoven fabric sheet A obtained in Example 1 was impregnated with only the liquid A (low molecular weight polyethylene) shown in Example 1, and the basis weight was 63 g / m ² as in Example 1. A 0.18 mm-thick alkaline battery separator was obtained.

Comparative Example 2 The base non-woven fabric sheet A obtained in Example 1 was impregnated with the liquid B (carboxylic acid group-added polyethylene emulsion) shown in Example 1 to give a basis weight of 63 g / m ² as in Example 1. ,thickness
A 0.18 mm separator for alkaline batteries was obtained.

Comparative Example 3 The non-woven fabric substrate A obtained in Example 1 was mixed with the low molecular weight polyethylene emulsion and the polyethylene emulsion having a carboxylic acid group in a mixing ratio of 20 parts: 80 parts and 80 parts: 20 parts. Impregnate each with a mixture of two types,
Similar to Example 1, the fabric weight is 63 g / m ² and the thickness is 0.18 mm.
To obtain the alkaline battery separators (a) and (b).

Example 3 The base non-woven fabric sheet A obtained in Example 1 was mixed with 50 parts of solution A and 50 parts of solution B shown in Example 1 and 10 parts of room temperature crosslinkable aqueous acrylic resin (solution C). The solution was impregnated, and a separator for an alkaline battery according to the present invention was obtained in the same manner as in Example 1. Hereinafter, tests for comparing various physical properties of the alkaline battery separators obtained in Examples and Comparative Examples were conducted and shown in Table 1.

[0026]

[Table 1] * Liquid absorption rate in the table: One end of a separator material with a sample width of 25 mm is immersed in a caustic potash solution with a specific gravity of 1.30, and the liquid absorption height after 30 minutes is shown. Liquid retention rate: Solution absorption rate after dipping the separator material in a caustic potash solution with a specific gravity of 1.30, hanging it for 10 minutes, and draining. Alkali resistance: The weight reduction rate after immersion in a caustic potash solution having a specific gravity of 1.30 at 80 ° C. for 30 days. Oxidation resistance: 250 ml of 5% potassium permanganate solution, specific gravity
In a mixed solution with 50 ml of 1.30 caustic potash solution, 50 ℃ 1
Weight reduction rate after soaking for a period of time.

[0027]

As described above, according to the present invention, the affinity with the electrolytic solution is large, the liquid retaining property is enhanced, the battery is durable against repeated charging and discharging for a long time, and the battery life is greatly improved. It is an invention that has an excellent effect such as being possible.

Claims (3)

[Claims] 1. A separator for an alkaline battery, characterized in that a non-woven fabric sheet of a base material composed of polyolefin resin fibers is coated with a mixture of low molecular weight polyethylene and polyethylene emulsion having a polar group. 2. The mixing ratio of the low molecular weight polyethylene and the polar group-containing polyethylene emulsion is 30:70.
The separator for an alkaline battery according to claim 1, wherein the separator is 70 to 30:30. 3. The alkaline battery separator according to claim 1, wherein the polyethylene emulsion having a polar group is crosslinked with a room temperature crosslinkable resin.