JPH08111215A - Battery separator and method for manufacturing the same - Google Patents

Abstract

(57) [Summary] [Object] To provide a battery separator suitable for an alkaline secondary battery, which is excellent in liquid absorption and liquid retention properties and tensile strength, and a method for producing the same. [Composition] A mixing ratio of a polyolefin short fiber (A) containing an ethylene vinyl alcohol copolymer and a polyolefin short fiber (B) having fine pores on the surface is 90: 1.
A battery separator of 0 to 50:50 and a method for producing the same.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a separator for an alkaline secondary battery known as a nickel-cadmium battery or a nickel-hydrogen battery and a method for manufacturing the separator.

[0002]

2. Description of the Related Art Conventionally, as a separator for an alkaline secondary battery, a nonwoven fabric made of a polyamide fiber such as nylon or a polyolefin fiber such as polyethylene and manufactured by a dry method has been used. However, the non-woven fabric made of these fibers is subjected to surface modification treatment to make it hydrophilic for the purpose of improving hydrophilicity. In recent years, fibers having an ethylene vinyl alcohol-based copolymer component have been used in order to improve affinity with electrolytes and liquid retention, and as a typical example, alkali-resistant polyolefin-based fibers are used. Known is a fiber formed by coating the surface of the fiber with an ethylene vinyl alcohol-based copolymer resin by impregnation or the like, and a non-woven fabric made of the ethylene vinyl alcohol-based copolymer fiber (see JP-A-64-81165). Has been.

[0003]

Among the above-mentioned conventional techniques, the separator using polyamide fiber such as nylon has a problem that it is oxidatively deteriorated by oxygen gas generated during charging. 80 due to discharge
Since the temperature rises to around 0 ° C, the separator using polyamide fiber such as nylon is deteriorated, and the strength is remarkably lowered, which is a problem in heat-resistant alkali resistance. On the other hand, a separator using a polyolefin fiber such as polyethylene is excellent in chemical resistance, but its hydrophilicity is low, so that the affinity or liquid retention with the electrolytic solution is poor, and the gas permeation generated during charging is permeated. However, the sealed battery has a problem that the internal pressure of the battery increases during charging and there is a risk of bursting.

In order to improve the drawbacks of the separator using the polyolefin fiber, the fiber surface of the separator using the polyolefin fiber is coated by impregnation with the ethylene vinyl alcohol copolymer, or the ethylene vinyl alcohol copolymer is used. It has been practiced to use a composite fiber having a shell component as a sheath component and a polyolefin as a core component as a separator (JP-A-3-257755). However, such a composite of the ethylene vinyl alcohol copolymer and the polyolefin can improve the affinity with the electrolytic solution to some extent, but the properties such as the liquid absorbing property to the electrolytic solution are sufficiently improved. Therefore, it is necessary to further modify the surface of the sheet to improve these properties. The object of the present invention is to combine a polyolefin short fiber containing an ethylene vinyl alcohol copolymer with a polyolefin short fiber having fine pores on the surface thereof, without surface modification of each fiber or mixed sheet. It is an object of the present invention to provide a battery separator having excellent liquid absorbency and liquid retention, and to provide a method for producing such a battery separator.

[0005]

The present invention has been made to achieve the above object, and the outline thereof is as follows. A mixed paper sheet comprising a polyolefin short fiber (A) containing an ethylene vinyl alcohol copolymer and a polyolefin short fiber (B) having fine pores on its surface, wherein the mixed ratio of (A) to (B) is Is 90: 10-5
The polyolefin used in the polyolefin short fibers (A) and (B) is 0:50, and polyethylene or polypropylene is preferably applied. In addition, the porosity of the polyolefin short fibers (B) having fine pores on the surface is 20 to
70% is more preferable. In addition, as a method for producing the separator, a polyolefin short fiber (A) containing an ethylene vinyl alcohol copolymer and a polyolefin short fiber (B) having fine pores on the surface thereof are used in an amount of 90 to 5
A battery characterized in that it is dispersed in water at a blending ratio of 0% by weight to 10 to 50% by weight to form a slurry, which is formed into a sheet by a wet papermaking method and heat-treated to bond the entangled fibers together. It is a manufacturing method of a separator for automobiles.

Hereinafter, the present invention will be described in detail. The polyolefin short fiber (A) containing the ethylene vinyl alcohol copolymer constituting the battery separator of the present invention is a core-sheath type in which a polyolefin such as polyethylene or polypropylene is used as a core component and the ethylene vinyl alcohol copolymer is used as a sheath component. Fibers, a fiber such as a polymer blend in which an ethylene vinyl alcohol copolymer is dispersed in the polyolefin, or simply the entire surface or a part of the surface of the polyolefin fiber is coated with the ethylene vinyl alcohol copolymer by a method such as impregnation. It does not matter if the fiber has any form such as the formed fiber.

The ethylene vinyl alcohol copolymer used in the present invention preferably has an ethylene content of 20 to 45 mol% and a saponification degree of 98% or more. When the ethylene content is less than 20 mol%, Mechanical properties such as tensile strength in a water-containing state are inferior, and when it exceeds 45 mol%, hydrophilicity is deteriorated and liquid retaining property is impaired. In addition, the polyolefin short fibers (B) having fine pores on the surface which constitute the battery separator of the present invention, foam the fiber surface layer by adding a foaming agent during the spinning of the polyolefin fibers such as polyethylene or polypropylene. It is obtained by spinning a mixture of a polyolefin in a dissolved or molten state and a heterogeneous polymer and phase-separating the surface, that is, the heterogeneous polymer component having a sea-island structure on the surface is removed by solvent extraction or the like. Further, the porosity (according to the following formula) of the fine pores constituting the surface of the polyolefin short fiber (B) in the present invention is preferably 20 to 70%. Porosity = {(A−B) / A} × 100 (%) where A: fineness calculated from diameter (denier) B: weight fineness (denier)

In the above, the sheet made of fibers having a porosity of less than 20% does not exhibit good absorbability and liquid absorption rate, and conversely, when the porosity exceeds 70%, the spinnability of the fibers is deteriorated.
Further, since the short fibers (B) have a large surface area, they are excellent in retaining liquid electrolyte and the like, but it is difficult to make a sheet of these fibers alone. That is, the mixing ratio of the short fiber (B) in the sheet is 10 to 50% by weight,
When the content is more than 50% by weight, the paper-making property is deteriorated, and the resulting mixed-paper sheet has poor formation and mechanical strength, and cannot be used for the intended purpose. Conversely 10
If it is less than 10% by weight, the water absorption is lowered and the function of the separator is lowered, which is not preferable.

As the method for producing the battery separator of the present invention, a wet papermaking method used in ordinary papermaking is used. That is, a specified amount of a polyolefin short fiber (B) having fine pores on the surface which is a raw material fiber and a specified amount of a polyolefin short fiber (A) containing an ethylene vinyl alcohol copolymer are mixed and disaggregated by stirring in water. It is preferable to apply the slurry whose solid content concentration is adjusted to 0.5% or less to a wet paper machine such as a Fourdrinier type or a cylinder type to dehydrate in a continuous wire mesh dewatering part, and then a dryer. It is a method of obtaining a sheet by drying with. At that time, in order to heat-bond the short fibers constituting the sheet obtained by the wet papermaking method to each other to significantly improve the strength of the entire sheet, use of the heating temperature of the dryer of the papermaking apparatus or a thermocompression bonding apparatus such as a heat calender It is necessary to join the entangled fibers with each other. The polyolefin short fiber (A) containing an ethylene vinyl alcohol copolymer shows self-adhesiveness when heated by coexistence of water. Therefore, depending on the blending ratio, the binder may not be added in the separator sheet of the present invention. A handleable sheet can be obtained, but if necessary, polyvinyl alcohol fibers having a binder function, chemical pulp, and polyolefin fibers can be used together as binder fibers. In addition, various paper strength enhancers, dispersants, defoamers, synthetic thickeners, pigment components, and other additives commonly used in papermaking can be added.

The sheet as a separator obtained by the wet papermaking method of the present invention has a more uniform pore size distribution and a thinner sheet than that obtained by the dry method. It has excellent characteristics such as increased capacity.

[0011]

[Examples] Samples of Examples of the present invention and Comparative Examples were prepared, and comparative tests were conducted on liquid absorbency, liquid retention and tensile strength. The wet papermaking method used for preparing the sample is as follows. The blades of a reciprocating agitator were placed in a poly bucket containing 10 liters of water and stirred, and the polyolefin short fibers (A) and (B) prepared in Examples 1-2 and Comparative Examples 1-2 below were stirred therein. The total amount is 50g
And mixed and disaggregated for 10 minutes. Intermediate surfactant (Maruhishi Yuka Kogyo Co., Ltd. product name DPM-20)
Was added to the above fiber raw material, and at the end, a synthetic sticking agent (polyethylene oxide; trade name Alcox manufactured by Iron and Steel Chemical Co., Ltd.) was added to 1% of the raw material to prepare a papermaking raw material. A specified amount of this dispersion was sampled and a wet sheet was prepared using a standard handmade device specified in TAPPI. After that, press dehydration is performed and drying is performed using a Yankee dryer that is heated and adjusted to 125 ° C to obtain a basis weight of 50 g / m ^2.
A test sheet was obtained.

Example 1 Polyolefin short fiber (A) containing ethylene vinyl alcohol copolymer (trade name UBF manufactured by Daiwa Spinning Co .; ethylene content: 30 mol%, 2d × 5 mm) 60% by weight, and polyethylene fine pore short fiber (B) (manufactured by Ube Nitto Kasei Co., Ltd., porosity: 40%, 1d × 5 mm) and 40 wt% were wet-processed under the above conditions to obtain a battery separator of the present invention.

Example 2 Polyolefin short fibers (A) containing ethylene vinyl alcohol copolymer (UBF manufactured by Daiwa Spinning Co., Ltd., trade name: UBF ethylene content: 30 mol%, 2d × 5 mm) 60% by weight, and polypropylene fine pore short fibers (B) (Made by Ube Nitto Kasei Co., Ltd.
Wet papermaking with a porosity of 20%, 1.5d × 5 mm) and 40% by weight was carried out under the above conditions to obtain a battery separator of the present invention.

Comparative Example 1 Polyolefin short fiber (A) containing ethylene vinyl alcohol copolymer (trade name UBF manufactured by Daiwa Spinning Co., Ltd .; ethylene content; 30 mol%, 2d × 5 mm) 30% by weight, and polyethylene fine pore short fiber 70% by weight of (B) (manufactured by Ube Nitto Kasei Co., Ltd .; porosity: 20%, 1.5d × 5 mm) was wet-processed under the above conditions to obtain a battery separator for comparison.

Comparative Example 2 Polyolefin short fiber (A) containing ethylene vinyl alcohol copolymer (trade name UBF manufactured by Daiwa Spinning Co .; ethylene content: 30 mol%, 2d × 5 mm) 60% by weight, and polyethylene fine pore short fiber (B) (manufactured by Ube Nitto Kasei Co., Ltd. porosity: 20%, 1.5d × 5 mm) 5% by weight,
35% by weight of polypropylene short fibers (PZ manufactured by Daiwa Spinning Co., Ltd .; 2d × 5 mm) without fine pores were wet-fabricated under the above conditions to obtain a battery separator for comparison.

A comparative test was conducted on the three criteria of liquid absorption, liquid retention and tensile strength.
Do the points. The test conditions are as follows. 1) Liquid absorbing property: A sample piece in a water equilibrium state of 15 mm × 200 mm was held vertically and brought into contact with a 30 wt% potassium hydroxide aqueous solution, and the central position of the width of the test piece was increased for 10, 60, and 180 seconds. Read the height up to mm. 2) Liquid retention rate: 30 test pieces (mass W ₀ ) in water equilibrium state
It is immersed in an aqueous solution of potassium hydroxide of wt% at room temperature to absorb the alkaline aqueous solution sufficiently, and then pulled up from the solution to 10
The mass after the minute (W ₁ ) is measured and calculated by the following formula. Liquid retention rate (%) = {(W ₁ −W ₀ ) / W ₀ } × 100 3) Tensile strength: According to JIS P 8113. In the above, a liquid absorption property (180 seconds) of 30 mm or more, a liquid retention rate of 300% or more, and a tensile strength of 2.0 kg or more were evaluated as practically acceptable levels. Table 1 shows Example 1,
2 shows the test results of the liquid absorptivity, the liquid retention and the tensile strength of the battery separators obtained in No. 2 and Comparative Examples 1 and 2. As is clear from Table 1, the battery separators of Examples 1 and 2 showed well-balanced characteristic values in all of the liquid absorption property, the liquid retention property, and the tensile strength, while the battery of Comparative Example 1 The separator for batteries was inferior in tensile strength, and the separator for batteries in Comparative Example 2 was inferior in liquid absorbability and liquid retention.

[0017]

[Table 1]

[0018]

EFFECTS OF THE INVENTION The battery separator of the present invention is excellent in liquid absorption, liquid retention and tensile strength due to proper selection of materials used and proper ratio of short fiber (A) component (B) component. Another object of the present invention is to provide a battery separator, and more particularly, to provide a method for easily manufacturing a battery separator that is excellent in liquid absorbency and liquid retention even without hydrophilization treatment such as surface treatment.

Claims (4)

[Claims] 1. A mixed paper sheet of a polyolefin short fiber (A) containing an ethylene vinyl alcohol copolymer and a polyolefin short fiber (B) having fine pores on the surface, wherein the (A) pair (B) ) Is 90:10 to 5
A battery separator, which is 0:50. 2. An ethylene vinyl alcohol copolymer,
The battery separator according to claim 1, which has an ethylene content of 20 to 45 mol% and a saponification degree of 98% or more. 3. A polyolefin short fiber (B) having fine pores on its surface has a porosity of 20 to 70%.
The battery separator described. 4. A polyolefin short fiber (A) containing an ethylene vinyl alcohol copolymer and a polyolefin short fiber (B) having fine pores on the surface are mixed in an amount of 90 to 50% by weight to 10 to 50% by weight. A method for producing a battery separator, characterized in that the slurry is dispersed in water at a ratio to form a slurry, which is formed into a sheet by a wet papermaking method, and heat-treated to bond the entangled fibers together.