JPH02256156A - Manufacture of separator - Google Patents

Abstract

PURPOSE:To extend the life of a battery by having a specific graft film neutralized with alkali hydroxide water solution and cleansed with mixture of water and water soluble organic solvent. CONSTITUTION:A graft film, which is obtained by using a polyethylene film as base material and giving it graft copolymerization of acrylic acid, is neutralized with alkali hydroxide water solution and then cleansed with mixture of water and water soluble organic solvent to manufacture a separator. As a result, the separator can be obtained which prevents the transmission of active anode material such as silver ion and has excellent characteristics. It is thus possible to extend the life of the separator itself and also a battery or others which is mounted with the separator.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for manufacturing a separator, and more specifically, to a method for manufacturing a separator, which has an excellent ability to block the permeation of anode active materials such as silver ions in a battery such as a silver oxide battery. The present invention relates to a method for manufacturing a separator that exhibits the following properties.

[Conventional technology]

Generally speaking, battery separators have low electrical resistance;
It is also required to be uniform.

As a method for manufacturing a battery separator having such properties, for example, JP-A-55-105963 discloses a method in which a polyolefin membrane is graft-polymerized with a hydrophilic monomer such as acrylic acid, and then treated with an aqueous potassium hydroxide solution. However, if a function is added to prevent the permeation of positive electrode active materials such as silver ions, the life of the battery can be further extended.

[Problem of invention]

An object of the present invention is to propose a method for producing a separator that exhibits excellent ability to block the permeation of positive electrode active materials such as silver ions in batteries such as silver oxide batteries.

Another object of the present invention is to propose a method for producing a separator that has good anti-blocking properties and is easy to work with when producing a battery.

[Summary of the invention]

The method for producing a separator according to the present invention uses polyethylene as a base material, graft-polymerizes (meth)acrylic acid onto this base material, neutralizes the obtained graft film with an aqueous alkali hydroxide solution, and then mixes water and water-soluble This is a method for producing a separator characterized by washing with a mixed solution with an organic solvent.

The polyethylene used as the base material in the present invention may be high density, medium density, or low density polyethylene. These polyethylenes may contain an α-olefin having 3 to 20 carbon atoms or a vinyl monomer as a comonomer in a proportion of 0 to 10 mol%. α-olefins include propylene, 1-butene, 1-hexene, 4-
Examples include methyl-1-pentene and 1-decene. Examples of vinyl monomers include acrylic acid, methacrylic acid, and rubinyl acid.

Furthermore, the polyethylene used in the present invention usually has an intrinsic viscosity [η] of 0.5 dQ/
g or more, preferably 1.0 to 5. OdQ/g, particularly preferably 2.0 to 4.0 d12/g, is suitable.

In the present invention, the substrate is used in the form of a film. The polyethylene film used as such a base film preferably has a thickness of about 5 to 100 μm, preferably about 7 to 40 μm, from the viewpoint of battery capacity and moldability.

In order to graft-polymerize (meth)acrylic acid to polyethylene as a base material, 1 to 30 Mrad is added to the polyethylene film.
After being irradiated with an electron beam, the polyethylene film was immersed in a sufficiently degassed 5 to 50% by weight aqueous solution of acrylic acid and/or methacrylic acid at 20 to 50°C for 1 to 60 minutes to initiate graft polymerization. conduct.

Next, graph 1 of the polyethylene obtained in this way
~Perform neutralization treatment by immersing the membrane in an aqueous alkali hydroxide solution. Examples of the alkali hydroxide used in this neutralization treatment include potassium hydroxide and sodium hydroxide, with potassium hydroxide being preferred.

The concentration of the alkaline aqueous solution used for the neutralization treatment is preferably within α±5% by weight, where α% by weight is the concentration of the alkaline hydroxide aqueous solution as the electrolyte of the alkaline battery installed as a separator.

For example, when the concentration of potassium hydroxide as the battery electrolyte to be installed is 40% by weight, it is preferable to use a potassium hydroxide solution of 40±5% by weight. Graph 1-
Neutralization treatment of membrane with alkaline aqueous solution is carried out at room temperature to 70℃.
It is preferable to carry out the reaction at a temperature of 10 to 60 minutes.

First, the graft membrane thus neutralized with an aqueous alkali hydroxide solution is washed with a mixed solution of water and a water-soluble organic solvent. Such water-soluble organic solvents include alcohol-based, ketone-based, and carboxylic acid-based organic solvents, and among these organic solvents, alcohol-based organic solvents such as methanol, ethanol, and ethylene glycol, and acetone are preferred. Ketone organic solvents such as the like are preferred. Such organic solvents may be used alone or in a mixture of two or more, and a mixture of ethylene glycol, methanol, and water is particularly preferred.

The water-soluble organic solvent used in the present invention desirably has a solubility in water at 20° C. of 1% by volume or more, preferably 10% by volume or more, more preferably 20% by volume or more, and especially completely compatible organic solvents. It is desirable that

The mixing ratio of water and water-soluble organic solvent in the mixture of water and water-soluble organic solvent used in the present invention is 5=9 by weight.
5-95:5, preferably 20:80-80:
20, particularly preferably 30:70 to 70:30
It is desirable that

When cleaning the graft membrane with the above-mentioned mixture of water and a water-soluble organic solvent, the cleaning temperature is preferably 5 to 70°C, preferably room temperature or higher and lower than 50°C. Washing time is 1-6
0 minutes, preferably 2 to 5 minutes.

In order to wash the graft membrane with the above mixture of water and a water-soluble organic solvent, there are, for example, a method of immersing the graft membrane in the above mixture, a method of showering the graft membrane with the above mixture, and the like.

The manufacture of the separator is completed by the above washing, and the washed graft membrane is used as a separator. The separator produced according to the present invention is suitable for use as a separator for batteries such as silver oxide batteries that require blocking the permeation of anode active materials such as silver ions, but it is suitable for use as a separator for batteries such as silver oxide batteries that require blocking the permeation of anode active materials such as silver ions. It can also be used as a separator for other purposes.

The separator of the present invention can be used alone or in a stack of a plurality of sheets as a separator for batteries, etc., and since it has excellent blocking resistance, workability during production of batteries, etc. is good.

〔Effect of the invention〕

In the method for producing a separator according to the present invention, a polyethylene film is used as a base material, (meth)acrylic acid is graft-polymerized onto this polyethylene film, the obtained graft film is neutralized with an aqueous alkali hydroxide solution, and then mixed with water and an aqueous solution. Since the separator is manufactured by washing with a mixed solution with a neutral organic solvent, the permeation of anode active materials such as silver ions is blocked, and a separator with excellent properties is obtained.The life of the separator itself is extended, and this separator The lifespan of batteries etc. equipped with this will also be extended.

In addition, the obtained separator has good blocking resistance,
The workability of producing batteries and the like also improves.

〔Example〕

EXAMPLES The present invention will be explained below with reference to Examples, but the present invention is not limited to these Examples.

Example 1 High-density polyethylene film (thickness 20 μm, density 0.
955, [η] 3.2 dQ/g), was irradiated with an electron beam of 10 Mrad using an electron beam irradiation device while cooling under a nitrogen atmosphere. Next, this polyethylene film irradiated with an electron beam was immersed for 10 minutes at 40°C in a 30% by weight acrylic acid aqueous solution that had been sufficiently degassed in advance and to which 0.25% Mohr's salt had been added. Perform graft polymerization,
A graft membrane was obtained. The graph 1~ ratio of the obtained graft membrane was 55%.

Next, the graft membrane (I) obtained by immersing in the acrylic acid aqueous solution was neutralized by immersing it in a 40% by weight potassium hydroxide aqueous solution at 40°C for 10 minutes, and then immersed in ethylene glycol, methanol and water. The separator (1) was obtained by washing at room temperature using an aqueous solution having a mixing ratio of 1:5:4 and then drying.

Next, the separator (1) was immersed in a 30% by weight aqueous potassium hydroxide solution saturated with zinc oxide to obtain a separator (II). Next, one separator (1) and seven separators (■) were stacked so that the separator (1) was on top to obtain a separator laminate.

This separator laminate was installed in a silver permeation test cell as shown in FIG. 1, and the amount of silver ions that passed through each separator was measured. Note that the separator (II) was impregnated as described above in order to match the state of the actual battery.

In the silver permeation test cell shown in FIG. 1, 1 is a glass plate, 2 is a separator laminate, 3 is a wall surface, 4 is a sealing member,
5 is silver oxide, 6 is 30% potassium hydroxide aqueous solution, 7
is an air vent.

After leaving the silver permeation test cell thus formed at 70°C for 24 hours, the separator laminate 2 was taken out and the state of silver permeation in each separator was visually observed.
Silver had penetrated only into the second separator (I), but 2~
No silver was observed in the 8th separator (n).

In addition, when the amount of silver retained in each separator was measured by ICP emission spectrometry, the first sheet was 7205 μg, the second sheet was 35 μg,
5 μg of silver was detected on the third sheet, and no silver was detected after the fourth sheet.

Comparative Example 1 The graft membrane (1) obtained in Example 1 was washed with pure water and then dried to obtain a separator (m). This separator (m) was impregnated with a 30% by weight aqueous potassium hydroxide solution saturated with zinc oxide to obtain a separator (IV). When the same test as in Example 1 was conducted using these, silver was observed up to the 7th sheet.

In addition, when the amount of silver retained in each separator was measured in the same manner as in Example 1, the results were 245 μg for the first sheet, 70 μg for the second sheet, 41 μg for the third sheet, 39 μg for the fourth sheet, 26 μg for the fifth sheet, 20 μg for the sixth sheet, and 7 21 μg of silver was detected in the 8th sheet and 21 μg in the 8th sheet.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a silver permeation test cell used in the silver permeation test in Examples. 1...Glass plate 2...Separator laminate 3
...Wall agent Patent attorney Sei Yanagihara

Claims (1)

[Claims] (1) Using polyethylene as a base material, (meth)acrylic acid is graft-polymerized onto this base material, the resulting graft film is neutralized with an aqueous alkali hydroxide solution, and then treated with a mixture of water and a water-soluble organic solvent. A method for producing a separator, which includes washing.