JPH09274902A - Separator for alkaline battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the stability of separator against alkaline and the stability of the size of pore as well as the sheet strength for use in batteries without mercury by refining the pore size of separator. SOLUTION: This separator is formed by separator forming fibers comprised of cellulose fibers and synthetic fibers, and all or part of the synthetic fibers comprises alamide fibers. Specifically, the weight of alamide fibers is preferably 5 to 60weight% of total weight of fibers, and cellulose fibers is contained preferably in the range of 20 to 60weight%, and more preferably the freeness of the alamide fibers is in the range not more than 400ml.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a separator used for alkaline batteries such as alkaline manganese batteries, mercury batteries, and silver oxide batteries using alkaline electrolytes.

[0002]

2. Description of the Related Art The functions required for a separator used in various alkaline batteries are to separate an anode active material and a cathode active material to prevent an internal short circuit due to contact, an alkaline electrolyte such as potassium hydroxide or a dioxide. It does not deteriorate even if it is in contact with an oxidizing substance such as manganese for a long period of time, it has sufficient durability, and it instantly generates an electromotive force, so it is excellent in absorbing electrolyte and can hold a battery. Since the internal volume of the battery is limited, the battery capacity can be increased by suppressing the thickness of the separator as much as possible while maintaining the above function. As a constituent material of a conventional separator, a mixture of synthetic fibers having chemical resistance and having a function of controlling the pore size of the separator and a liquid absorbing property of an electrolytic solution and a cellulose fiber having an excellent liquid retaining property is used. Is common. Vinylon fibers and olefin fibers are used as the synthetic fibers, and mercerized pulp, rayon fibers and cotton linter fibers are used as the cellulose fibers, and they are formed into a sheet by using a binder such as polyvinyl alcohol fiber.

In alkaline batteries using zinc as a cathode active material, a method of amalgamating the surface of zinc with mercury to smooth discharge has been adopted until recently, but in recent years, due to environmental problems, mercury-free alkaline batteries have been used. Has become commonplace. In mercury-free batteries, zinc oxide needle crystals are likely to occur due to zinc corrosion, and these needle crystals pass through the separator, causing an internal short circuit. Since the conventional separator has a large pore size, it is difficult to prevent an internal short circuit due to passage of these needle-shaped crystals to the counter electrode, and it is necessary to control the pore size to be smaller.

As disclosed in Japanese Patent Publication No. 5-72063, as a separator having a small pore diameter, a patent has been disclosed in which the fiber diameter of vinylon fiber, which is a synthetic fiber, is 0.8 denier or less than the conventional 1 denier. Further, in Japanese Examined Patent Publication No. 7-48375, it is possible to prevent an internal short circuit without increasing the electric resistance by setting the alkali-resistant cellulose fiber to 10 to 50% by weight and setting the freeness value to a range of 500 ml or less by beating. Is described.

[0005]

However, in order to control the pore size to such an extent that an internal short circuit can be prevented by using a synthetic fiber having a fine chemical resistance and having a small fiber diameter, a fine denier synthetic fiber can be used. It is limited to vinylon fibers, and it is necessary to use ultrafine fibers of about 0.3 denier. In this case, although it is effective in preventing internal short circuit due to the passage of zinc oxide, it is difficult to completely suppress swelling between fibers in the electrolytic solution with vinylon fibers alone,
There is a phenomenon that the pore size gradually expands in the electrolyte. Also,
Since the fiber crossing points increase due to the fine denier, the strength decreases due to the decrease in the binder amount at the crossing points, and it is necessary to increase the binder amount. And, if the amount of the binder is increased, the chemical resistance is deteriorated.

On the other hand, in the formation of fine pores by beating cellulose fibers, even if alkali resistant cellulose fibers such as mercerized pulp are used, the alkali resistance is not sufficient. In addition, since cellulosic fibers generally have a large fiber diameter, even if the average pore diameter due to fibrillation is the same as that using fine denier synthetic fibers, the maximum pore diameter tends to increase, and there is a risk of internal short circuit occurring here. . Further, since the cellulose fiber is a liquid absorbing liquid of the electrolytic solution, the pore size is likely to change due to the swelling due to the liquid absorbing, the stability of the pore size in the electrolytic solution is poor, and there is a risk of causing an internal short circuit. Furthermore, as batteries become smaller and smaller, it is necessary to reduce the thickness of separators. However, if the thickness is reduced, there is a problem of breakage during manufacturing, and the strength such as the tensile strength of the sheet is also required.

In summary, vinylon fibers do not have perfect alkali resistance, and the thinner fibers reduce the strength. Cellulose fibers have poor alkali resistance, poor uniformity of pore size, and large change in pore size due to alkali. The present invention, in making the pore size of the separator fine so that it can be used in a mercury-free battery, to eliminate the above drawbacks, that is, to further improve the alkali resistance,
At the same time, it is intended to improve the dimensional stability of the pore size and the strength of the sheet.

[0008]

The present invention adopts the following constitution in order to solve the above problems. That is, the first invention of the present invention is "for alkaline batteries, characterized in that the fibers constituting the separator are composed of cellulose fibers and synthetic fibers, and contain aramid fibers as all or part of the synthetic fibers. "Separator". A second invention of the present invention is characterized in that, in the first invention, the aramid fiber is 5 to 60% by weight and the cellulose fiber is 20 to 60% by weight based on the total weight of the fiber. It is a separator for alkaline batteries. A third invention of the present invention is "an alkaline battery separator in which the freeness of aramid fibers in the first or second invention is in a range of 400 ml or less".

In order to solve the above problems, the present inventors have
As a result of intensive studies, it was found that the above problem can be solved by using aramid fiber. Aramid fibers have alkali resistance, and like wood pulp, they become fine fibers when beaten, so it is possible to reduce the pore size of the sheet, and since the beaten pulp-like aramid fibers have a strong binding force, Increases tensile strength.
Therefore, if the pulp-like aramid fiber is blended in a certain amount or more, all the above-mentioned drawbacks can be solved.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The separator for alkaline batteries of the present invention will be described in detail below. The aramid fiber used in the present invention is preferably so-called para-type aramid fiber typified by polyparaphenylene terephthalamide fiber. In the present invention, it is particularly preferable to use pulp-like aramid fiber as the aramid fiber. Pulpy aramid fibers are highly fibrillated aramid staple fibers obtained from filament yarns. The pulp-like aramid fiber can be typically produced by beating with a papermaking refiner, beater or the like. The beaten aramid fibers are composed of a skeleton part having a fiber diameter of about 10 μm and fibrillated and branched fibers of 5 μm to 0.1 μm, and these fine fibers play a role as a small diameter fiber.

In the present invention, the aramid fiber is used as all or a part of the synthetic fiber among the cellulose fiber and the synthetic fiber which are the constituent materials of the separator. In order to exert the effect of reducing the diameter by containing the aramid fiber, it is desirable that the aramid fiber is contained in an amount of 5 to 60% by weight, preferably 5 to 40% by weight, based on the whole fibers. In addition, the freeness of the aramid fiber is set to 400 in order to reproduce the thin diameter effect more efficiently.
It is preferable to set it to not more than ml. The freeness referred to in the present invention is the Canadian standard freeness defined in JIS P8121.

The cellulose fibers used in the present invention are preferably those having excellent chemical resistance, and examples thereof include mercerized pulp, rayon fiber, and cotton linter. Cellulose fiber is necessary to maintain the liquid retaining property of the separator, and it is preferably 20% by weight or more based on the total fiber, and when it exceeds 60% by weight, alkali resistance becomes poor.

As synthetic fibers other than aramid fiber, vinylon fiber, nylon fiber, polyester fiber, polyolefin fiber and the like can be used, and typical examples of polyolefin fiber are polyethylene fiber and polypropylene fiber.

The separator of the present invention is manufactured from an aqueous slurry of raw material fibers by a wet papermaking method, but a binder is required to maintain the strength of the sheet. As the binder, various synthetic resins such as epoxy resin, polyolefin resin and polyvinyl alcohol resin can be used, and the form of the binder may be fibrous, powdery or liquid.
As an example, there is a method in which a binder such as a fibrous or powdered polyvinyl alcohol is mixed with the raw material slurry to make paper. Further, it may be impregnated or sprayed after the sheet is formed.

[0015]

According to the present invention, a separator having a fine pore size which can be used in a mercury-free battery can be obtained, and moreover, the alkali resistance is strong, and at the same time, the dimensional stability of the pore size and the strength of the sheet are improved.

[0016]

EXAMPLES Examples of the alkaline battery separator of the present invention will be described below. In this example, "part" means "part by weight". <Example 1> 25 parts of mercerized softwood pulp was disintegrated with a pulper (freeness 700 ml), and then 10 parts of 0.7 denier rayon fiber and 1 denier vinylon fiber 4 were used.
Aramid fiber 1 beaten to 0 ml, freeness to 50 ml
It was mixed with 0 part and 15 parts of 1 denier fibrous polyvinyl alcohol was used as a binder to prepare a raw material. This raw material was made into paper by a circular net paper machine, and had a basis weight of 35 g / m ² and a thickness of 1
A 25μ separator was obtained.

<Example 2> Paper was made in the same manner as in Example 1 except that the aramid fiber having a freeness of 400 ml was used in Example 1, and the weight of rice was 35 g / m ² and the thickness was 1
A 30μ separator was obtained.

Example 3 Twenty-five parts of mercerized softwood pulp was disintegrated with a pulper and weakly beaten with a double disc refiner (freeness 550 ml), and then 0.7 denier polyethylene / polypropylene core-sheath fiber 35 was used.
Part, 0.5 denier polynosic rayon fiber 15
Aramid fiber 10 beaten to 50 ml
15 parts of 1-denier fibrous polyvinyl alcohol was used as a binder. This raw material was made into paper with a circular net paper machine, and had a basis weight of 35 g / m ² and a thickness of 13
A 0 μ separator was obtained.

Example 4 25 parts of mercerized softwood pulp was disintegrated with a pulper (freeness 700 m).
l), mixed with 10 parts of 0.7 denier rayon fiber, 45 parts of 0.5 denier vinylon fiber and 5 parts of aramid fiber beaten to a freeness of 50 ml, and using 15 parts of 1 denier fibrous polyvinyl alcohol as a binder And Paper of this raw material is made with a circular net paper machine and weighs 35 g.
A separator having a thickness of 125 μm / m ² was obtained.

<Comparative Example 1> Paper was made in the same manner as in Example 1 except that 50 parts of 0.3 denier vinylon fiber was used in place of 1 denier vinylon fiber and aramid fiber in Example 1 to prepare rice. A separator having a basis weight of 35 g / m ² and a thickness of 125 μ was obtained.

Comparative Example 2 Twenty-five parts of mercerized softwood pulp was added to a freeness of 20 using a double disc refiner.
After beating to 0 ml, 10 parts of 0.5 denier polynosic rayon fiber, 0.5 denier vinylon fiber 50
15 parts of 1-denier fibrous polyvinyl alcohol was used as a binder. This raw material was made into paper by a circular net paper machine, and had a basis weight of 35 g / m ² and a thickness of 12
A 5μ separator was obtained.

Comparative Example 3 Paper was made in the same manner as in Example 1 except that the aramid fiber was not used and 50 parts of 1 denier vinylon fiber was used in Example 1, and the weight of rice was 35 g / m 2.
^2. A separator having a thickness of 135 μ was obtained.

The following tests were conducted on the above Examples and Comparative Examples, and the results are shown in Table 1. (1) Tensile Strength The strength at a width of 15 mm was measured by the method specified in JIS P8113. (2) KOH shrinkage ratio Each separator was cut into 10 cm square and 40% KOH
After immersing in the liquid for 3 days, it was taken out and the contraction rate due to swelling in the thickness direction was measured. (3) Pore size stability Coulter Pore Meter (Coulter Co., Ltd.) shows changes in average and maximum pore sizes before and after immersion in 40% KOH solution for 3 days.
It was measured at. (4) KOH residual rate After each separator was immersed in a 40% KOH solution for 3 days, the weight residual rate was measured.

[0024]

[Table 1]

Claims (3)

[Claims] 1. A separator for an alkaline battery, wherein the fibers constituting the separator are composed of cellulose fibers and synthetic fibers, and contain aramid fibers as all or part of the synthetic fibers. 2. Five to five aramid fibers based on the total weight of the fibers.
60% by weight and 20 to 60% by weight of cellulose fiber
The alkaline battery separator according to claim 1, characterized in that 3. The alkaline battery separator according to claim 1, wherein the freeness of the aramid fiber is in the range of 400 ml or less.