JPS60130052A - Separator for alkaline battery - Google Patents

Abstract

PURPOSE:To make a hydrophilic highly-alkali-resistant separator having a small electric resistance by impregnating or coating a base material consisting of a woven or nonwoven fabric with an acrylic emulsion before performing alkali treatment. CONSTITUTION:A vinyl compound having a high alkali resistance is caused to react with a weakly-alkaline vinyl compound in an aqueous water-soluble polyolefin solution by means of a water-soluble polymerization initiator to prepare an acrylic emulsion. A base material is impregnated or coated with the thus prepared acrylic emulsion before alkali treatment is performed, thereby making a highly alkali-resistant separator which has a low electric resistance and has no possibility of undergoing swelling, dimensional change or dissolution; with this separator a notably improved life of a battery can be produced. A minimally alkali-resistant compound is one which at least 90% is hydrolyzed into soda acrylate and alcohol within 1hr when mixed with 4% aqueous sodium-hydroxide solution at ordinary temperature. An alkaline-resistant vinyl compound is one which 10% or less is hydrolyzed within 1hr when mixed with 4% aqueous sodium-hydroxide solution.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the improvement of a separator for alkaline batteries, and particularly to provide a separator for alkaline batteries that is hydrophilic, has low electrical resistance, and has excellent alkali resistance.

Conventionally, polyolefin films and polyvinyl alcohol films have been used as the separator for alkaline batteries.

However, in order to use a polyolefin film as a separator, it must be made porous and hydrophilic, but this operation is difficult, and the process of making it porous is particularly difficult and expensive due to the manufacturing process. become. Furthermore, when a microporous polyolefin film is used in the seno-armor of an alkaline battery with zinc as the negative electrode, a problem arises in that zinc dendrites grow along the micropores, causing a short circuit between the positive and negative interpolators. It was something.

Furthermore, polyvinyl alcohol films are susceptible to alkaline liquids, such as swelling, dimensional changes, and dissolution in alkaline liquids, and cannot be used as they are as separators for alkaline batteries.

Therefore, in order to use this film as a separator, it is necessary to chemically crosslink and strengthen the surface or interior of the film. However, when the film is crosslinked, it not only increases the electrical resistance and reduces the permeability of ions, resulting in a decrease in efficiency as a battery, but also becomes unusable as a separator if this tendency becomes significant.

It is also conceivable to use a water-soluble resin such as a water-soluble acrylic resin for the separator, but since it is water-soluble, it has poor chemical resistance.

Furthermore, ethylamine and lacquer films, which have excellent chemical resistance, have high electrical resistance. In order to lower this electrical resistance, the film is immersed in an alkaline solution, but on the contrary, the film has poor chemical resistance and cannot be used as a separator.

The present invention has been made as a result of extensive research in view of the current situation, and has developed a separator that is hydrophilic, has low electrical resistance, and has excellent alkali resistance. That is, the present invention involves impregnating or coating a base material with an acrylic emulsion obtained by reacting a vinyl compound with good alkali resistance and a weakly alkaline vinyl compound with a water-soluble polymerization initiator in an aqueous solution of a water-soluble polyolefin. It is obtained by treating with alkali.

In the present invention, the base material refers to a non-woven fabric or a woven fabric, and although it depends on the thickness of the separator, it is usually 20 to 30 μm and has a basis weight i of 5 to 1001 i'/m2.

Non-woven fabrics or woven fabrics made of one or more of polypropylene-based, polyethylene-based, polyamide-based, and cellulose-based fibers, which tend to have highly alkaline spots, are desirable.

In the present invention, the water-soluble polyolefin is a resin whose main component is an olefin, which is copolymerized with acrylic acid or its ester, and which is treated with an alkali to make it water-soluble. Examples of the alkali treatment agent include alkali metal t1 types such as ammonia, sodium hydroxide, potassium hydroxide, methylamine, ethylamine, and monoethanolamine, and amines. Examples of copolymers of olefin and acrylic acid include Zaixen A (trade name, manufactured by Seitetsu Kagaku Co., Ltd.), and 0PDJ-9169 (manufactured by Nippon Unica Co., Ltd.) is used as a copolymer of olefin and acrylic acid ethyl ester. . These are treated with sodium hydroxide to make them water-soluble.

Vinyl compounds with weak alkali resistance are those that, when mixed with 4g of sodium hydroxide aqueous solution, hydrolyze 90 or more molecules within 1 hour at room temperature and decompose into sodium acrylate and alcohol, methyl acrylate, and ethyl acrylate. , acrylic esters such as , acrylic acid, itaconic acid, methacrylic acid, etc. that contain caldic acid groups from the beginning.
Indicates maleic acid. Particularly preferred as the monomer with weak alkali resistance is methyl or ethyl acrylate.

In addition, as an alkali-resistant vinyl compound, it can be mixed with 4% sodium hydroxide aqueous solution and converted to 1096 within 1 hour at room temperature.
This refers to those that undergo the following hydrolysis or those that do not undergo hydrolysis at all. That is, (1) methacrylic acid alkyl ester M Examples are methacrylic acid butyl ester, methacrylic acid ethyl ester,
Methacrylic acid butyl ester, methacrylic acid lauryl ester (2) Methacrylic acid cyclohexyl ester (
3) Acrylic acid alkyl ester having 4 or more carbon atoms, such as acrylic acid butyl ester.

Acrylic acid lauryl ester, acrylic acid octyl ester (4) y, fvn a Example,! t Hastyrene, vinyltoluene, α-methylstyrene, and in the present invention, water-soluble polymerization initiators include potassium persulfate, ammonium persulfate, hydrogen peroxide, hydroxides such as t-butyl g-oxide, etc. It is.

Therefore, the blending ratio of the water-soluble polyolefin and vinyl compound is 70 wt% to 15 wt% for the former and 3 wt% for the latter.
It is preferable to set it as 0 wt96-85 wt%. The mixing ratio of the alkaline vinyl compound and the weakly alkaline vinyl compound is 99.5 w for the former.
t Chi ~ 80 wt Chi: the latter 0.5 wt Chi ~ 20 w
It is desirable to set it to t.

In the ratio of these three components, the polyolefin is 30 w
When bound by t%, alkali-resistant vinyl compound 98 w
t%~8Q wt%, weakly alkaline vinyl compound 2
Wt% ~ 20 wt% is good, polyolefin is 70%
When bound by wt%, the alkali-resistant vinyl compound is preferably 9.5 wt% to 99.5 wt%, and the weakly alkaline vinyl compound is preferably 5 wt% to Q, 5 wt%.

In order to improve chemical resistance in the present invention, it is preferable to add polyfunctional vinyl compounds such as evadivinylbenzene, ethylene glycol dimethacrylate, and glycerin diallyl ether to the above three components, and the amount added is based on the total resin amount. 10wt or less is preferable 0.05
Preferably, wt-chi to 5wt-chi.

Furthermore, titanium oxide is contained within the acrylic emulsion.

By blending a filler containing fR zirconium, the strength of the coating film of the resin can be improved.

In order to impregnate or coat the acrylic emulsion, the base material can be impregnated with the acrylic emulsion by dipping it into the acrylic emulsion, or by using a brush.

Per coater, roll coater, gravure coater.

It is applied to the base material using a spray can or the like. The thickness of the acrylic emulsion applied is preferably 5 to 150 .mu.m, preferably 15 to 50 .mu.m.

If the adhesion thickness exceeds 150μ, even if alkali treatment is performed, sufficient hydrophilicity cannot be imparted.
If the thickness is less than 5 μm, the film is too thin to be used as a separator due to its weak strength.

In the present invention, the alkali used in the alkali treatment is an aqueous solution of lithium hydroxide, sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, etc. with a concentration of 5 wt % or more, preferably 2 Owt % or more.

The temperature and time of this treatment cannot be determined depending on the composition of the acrylic emulsion, the film thickness, etc., but it is usually 10°C or higher, preferably 60°C to 10°C.
In the range of 00°C, the treatment time is 1 hour or more, preferably 5
The test is conducted for a period of ~100 hours. In special cases, the temperature may be raised to 150°C and the process may be carried out under pressure.

Next, examples of the present invention will be described.

Example (1) A diacrylic emulsion was prepared according to the composition shown in Table 1.

Table 1 Water-soluble polyolefin 70oz Acrylic butyl Nisdel 150 Methyl methacrylate 15O Acrylic methyl ester 19 Glycerin diallyl ether 2.5 Potassium persulfate 10 Polyoxyethylene octyl ether 5.0 Water 6
40 Note: The water-soluble polyolefin was prepared by bathing EEA, DPDJ-9169 manufactured by Nippon Unicar Co., Ltd. with sodium hydroxide to obtain a 25% water bath solution.

This water, water 1]-soluble polyolefin, and polyoxyethylene octyl ether (emulsifier) are charged into a 2000 ytl four-bottle flask, and the temperature is raised to 60° C. while stirring well. Next, rods of butyl acrylate, methyl methacrylate, methyl acrylate, glycerin triallyl ether, and potassium persulfate (A) were charged to start polymerization, and 60 minutes after the start of polymerization, the remaining monomers and persulfate were added. Potassium sulfate was mixed in, reacted for about 120 minutes, and cooled to below 40°C to obtain an emulsion.

This acrylic emulsion was coated with a gravure coater to form a coating film of about 30 μm on release paper, and after drying, it was heated to 120°C with a hot roll to a thickness of Q, 1Q mm, and a basis weight of 30.
Li! -/m2 of nylon non-woven fabric (2) and rolled up. After immersing this in a 500 t/A KOH aqueous solution (80°C) for 10 hours, washing with water and drying, a separator of the present invention was obtained.

The separator of the present invention obtained by the method was subjected to an alkali resistance test and charged and discharged using it in a nickel-zinc battery. The results are as follows.

In order to compare with the cenocerator of the present invention, a similar test was also conducted on a cenocerator (comparative example product) obtained by forming a polyvinyl alcohol film with a thickness of 30 μm on the above-mentioned nonwoven fabric as in the prior art.

(1) Alkali resistance test A test piece of 5cm in length and 5c1n in width weighed 509g at 80℃.
After being immersed in KOI (aqueous solution (50d)) for 4 hours, it was washed with water and dried, and the weight loss rate was measured.

Inventive product Comparative example product 01 7.5% (2) Charge/discharge test A nickel-zinc battery using 40% caustic potash as the electrolyte was subjected to a charge/discharge test at a discharge rate of 70% at a discharge current density of 20 mA/cm. repeated.

Invention product Comparative example product 200 cycles No abnormality after 35 cycles Unusable Example (2) Using the same acrylic emulsion as in Example (1), polyzolopyrene with a thickness of 0.1 mm and a basis weight of 60 Y-7 Tn Example (1) by treating the nonwoven fabric with fuming sulfuric acid
In the same manner as above, a 30 μm thick layer was transferred, neutralized, washed with water, and dried to obtain a cell/IP plate of the present invention.

When this separator was tested for alkali resistance, the reduction rate was 0.3 inches. Further, a battery was constructed in the same manner as in the example, and a charge/discharge test was conducted.The results showed that no abnormality was observed in the battery after 200 cycles. In addition, the electrical resistance of the nanometer and the rotor at this time is O, 9mΩd.
It was m2.

As detailed above, the separator for alkaline batteries of the present invention has excellent alkali resistance, does not undergo swelling, dimensional changes, or melting, has low electrical resistance, and can significantly improve battery life over a long period of time. It is extremely useful industrially.

Claims (1)

[Claims] A separator for alkaline batteries, which is obtained by impregnating or coating a base material such as woven or nonwoven fabric with an acrylic emulsion, and subjecting it to alkali treatment.