JPH0676807A - Compound film for separator of alkaline battery - Google Patents

Abstract

PURPOSE:To facilitate the gas absorption in a negative electrode at the time of overcharge, and restrict the growth of dendrite crystal to prolong a lifetime of a battery by laminating a nonwoven fabric on a porous film having a non- porous layer between a hydrophilic part and a hydrophobic part. CONSTITUTION:A nonwoven fabric is laminated on a porous film, in which both of a hydrophilic part 1 and a hydrophobic part 2 communicated with each other in the face and the back thereof at the time of moisturizing are formed and a non-porous layer 3 is provided between the hydrophilic part 1 and the hydrophobic part 2. With this structure, in an alkaline battery such as a nickel-zinc battery, the oxygen gas to be generated from a positive electrode at the time of overcharge is easy to arrive the negative electrode through a separator to facilitate the gas absorption in the negative electrode, and furthermore, the generation of dendrite crystal is restricted to prolong the lifetime of a battery. Since the nonwoven fabric is laminated, generation of non-conforming article at the time of assembling a battery is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel alkaline battery separator porous membrane and composite membrane suitable for a separator used in alkaline batteries such as nickel-cadmium, nickel-hydrogen and nickel-zinc batteries.

[0002]

2. Description of the Related Art Conventionally, in an alkaline battery such as a nickel-zinc battery, a separator which is entirely hydrophilic has been used. For example, Japanese Patent Publication Sho 5
A separator having celluloses formed in the micropores of a microporous film as in JP-A-5-83159, or at least one surface of a hydrophobic microporous membrane as in JP-A-57-55064. A separator coated with a polymer selected from the group consisting of cellulose ester and polyvinyl alcohol has been used. In such a film, oxygen gas generated from the positive electrode at the time of overcharging cannot reach the negative electrode through the separator, which makes it difficult to absorb gas in the negative electrode. If the oxygen gas absorption reaction does not proceed smoothly, the oxygen gas is released to the outside of the battery, so that the negative electrode plate is additionally charged by the amount of electricity consumed to generate the oxygen, and finally the negative electrode plate. Hydrogen gas comes to be generated from. When hydrogen gas is generated from the negative electrode plate, oxygen and hydrogen are released to the outside of the battery, which causes a disadvantage that water in the electrolytic solution is lost. In addition, since overcharging the negative electrode plate is considered to be one of the factors that promote the growth of dendrites, an internal short circuit is likely to occur, which has been a cause of prolonging the life of the battery. As a means for solving such a problem, for example, Japanese Patent Laid-Open No. Sho 58-58-
As shown in Japanese Patent Laid-Open No. 4-4557, a separator having a hydrophilic porous membrane having pores as in 18871, and a superabsorbent polymer forming a hydrogel in an organic fiber non-woven fabric as in Japanese Patent Laid-Open No. 4-4557 are held on the separator. There is a separator with a polymer thin film that is poorly soluble in alkali, but the pores provided in such a membrane and the gaps that form the pores are too large, and the precipitate active material generated during repeated charging and discharging has pores. The battery life was short due to internal short circuits.

[0003]

The present inventors have arrived at the present invention as a result of extensive studies on a composite membrane for an alkaline battery separator which does not have the above-mentioned drawbacks.

[0004]

Means for Solving the Problems The present invention comprises a hydrophilic portion and a hydrophobic portion which are communicated with each other at the time of containing water, and a non-porous layer is provided between the hydrophilic portion and the hydrophobic portion. A composite membrane for an alkaline battery separator, characterized in that a nonwoven fabric is laminated on the porous membrane. The hydrophilic part and the hydrophobic part of the porous membrane communicate with each other in the front and back when water is contained, and the hydrophobic part has a pressure of 2 when water is contained.
It means having air permeability at kg / cm ² , preferably at a pressure of 1 kg / cm ² , and the air permeability here means pressure from one side of 2 kg / cm ² , preferably pressure of 1 kg.
That is, when the air is blown at a rate of less than / cm ² , the air comes out from the other surface.

In addition, the fact that the hydrophilic part communicates with the front and back when it contains water means that ions are permeated, and in the electrical resistance measuring method described later, the electrolytic solution (caustic potash aqueous solution (specific gravity 1.31 g / cm ³ )) is used. ) at the time of water, at least electrical resistance 0.3Ω * 100cm ² / sheet or less, it preferably is 0.1 [Omega * 100 cm ² / sheet or less.

In the present invention, a liquid-absorbent polymer is preferably used to form the hydrophilic portion. Examples of the liquid-absorbent polymer include polyvinyl alcohol, polyethylene oxide, polyethylene glycol, polyacrylamide, polyvinylpyrrolidone, polyvinylamine, polyacrylic acid, polymethacrylic acid, polystyrene sulfonic acid, crosslinked polyacrylic acid soda, and crosslinked polyacrylic acid. Hydrogel-forming polymers and starches such as potassium acidate, cross-linked poly ammonium acrylate, cross-linked poly methyl acrylate, cross-linked poly ethyl acrylate, cross-linked poly methyl methacrylate, cross-linked poly ethyl methacrylate, ethyl maleate, etc. Examples thereof include cellulose and cellulose derivatives.

Of these, cellulose and cellulose derivatives are desirable in terms of price and performance. As the cellulose or the cellulose derivative, acetyl cellulose in which a part or all of the hydroxyl groups of the cellulose are esterified,
Cellulose esters such as nitrocellulose, propionic acid, butyric acid, phosphoric acid, sulfuric acid, phthalic acid and mixed esters such as cellulose acetate butyrate cellulose acetate acetate nitrate, and some or all of the hydroxyl groups of cellulose And methyl cellulose, ethyl cellulose, benzyl cellulose, carboxymethyl cellulose and the like.

Even if the arrangement amount of the hydrophilic polymer in the pores of the hydrophobic porous membrane during drying, that is, the content thereof is less than 100% by volume of the pore volume of the porous membrane,
Since the polymer swells when it comes into contact with the electrolytic solution, the inside of the pores is filled with the polymer, and the function as an alkaline battery separator is exerted. Therefore, the amount of the polymer in the pores of the porous film, which is the content of the polymer when dried, is such that the electric resistance is at least 0.3Ω * 100c when the electrolyte solution (caustic potash solution (specific gravity 1.31 g / cm ³ )) contains water.
It is enough if the amount is less than m ² / sheet.

In the present invention, as a method for forming both the hydrophilic portion and the hydrophobic portion on the porous membrane for a separator, a liquid absorbing polymer is formed on the basic hydrophobic porous membrane.
The method of forming a hydrophilic portion by a printing method such as letterpress printing or stencil printing using the organic solvent solution or aqueous solution of, or the hydrophobic porous membrane was protected in advance so as not to be impregnated with the liquid absorbing polymer. After that, after impregnating the organic solvent solution or aqueous solution of the absorbent polymer with an organic solvent solution or aqueous solution of the absorbent polymer by dipping the film, the protection is basically removed. It is possible to form a hydrophilic portion and a hydrophobic portion on the porous film to be formed. From the viewpoint of efficiency, it is desirable to form a hydrophilic portion and a hydrophobic portion by the stencil printing method.

Further, in some cases, a chemical treatment or the like may be performed to enhance hydrophilicity by introducing a hydrophilic group, and a filler having an effect of suppressing the growth of dendrites, for example, Titanium oxide or the like may be added to the organic solvent solution or aqueous solution of the absorbent polymer. The average pore diameter of the porous membrane used in the present invention, which is composed of the hydrophilic portion and the hydrophobic portion, is preferably 5 μm or less in order to suppress the growth of dendrites. When it is larger than 5 μm, resinous crystals are likely to grow through the holes, leading to a decrease in battery life.

Further, the thickness of the porous film used in the present invention is preferably 200 μm or less in view of the requirement for a high density battery. The material of the porous film used in the present invention, for use as an alkaline battery separator, has excellent chemical resistance such as polyethylene-based resins, polyolefin-based resins such as polypropylene-based resins, polyvinylidene fluoride-based, polytetrafluoroethylene-based fluorine, etc. A resin made of a system resin or a system obtained by combining these is preferable as a material, and among them, a polyolefin resin is particularly preferable in terms of cost.

As the material of the non-woven fabric used in the present invention, in addition to the above-mentioned resins, polymers selected from the group consisting of cellulose and cellulose derivatives are preferable as materials, and among them, polyolefin resin, cellulose and Polymers selected from the group consisting of cellulose derivatives are particularly preferred. The porous film used in the present invention, a solvent, a plasticizer, an inorganic fine powder and the like mixed with a thermoplastic resin, after molding, subjected to extraction and drying, a method of performing stretching in some cases, or a solvent to the thermoplastic resin, It can be obtained by means such as mixing and molding a plasticizer and the like, followed by extraction and drying, and optionally stretching.

For example, polyethylene resin, inorganic fine powder,
The mixed composition of the organic liquid is 5 to 70% by volume and 10 respectively.
To 55% by volume, 20 to 75% by volume, and after mixing with an ordinary mixer such as a Henschel mixer, the mixture is kneaded with a melt-kneading device such as an extruder, and the obtained kneaded product is subjected to extrusion molding or the like to give a mixture of 50 to 300 μm. Form to thickness. Furthermore, the organic liquid is extracted from the molded product using a solvent for the organic liquid,
Subsequently, the inorganic fine powder can be extracted with a solvent for extracting the inorganic fine powder to obtain a porous film.

In order to form a non-porous layer in which the pores are completely filled and the electrolyte and air cannot pass between the hydrophilic portion and the hydrophobic portion, the boundary between the hydrophilic portion and the hydrophobic portion is required. The heat-bonding of the hydrophobic part of the, or the photo-curable resin is applied to the hydrophobic part of the boundary between the hydrophilic part and the hydrophobic part by the printing method so that the hydrophobic part remains And the like are used for curing.

If a non-porous layer is not provided between the hydrophilic portion and the hydrophobic portion, when a nickel-zinc secondary battery or the like is assembled, the interface between the hydrophilic portion and the hydrophobic portion will be a zinc branch. Crystals grow and shorten the battery life.
When a nonwoven fabric is laminated on the porous membrane used in the present invention, the lamination may be performed before or after applying the organic solvent solution or aqueous solution of the liquid-absorbent polymer to the porous membrane, but from the viewpoint of handleability, the porous membrane may be formed before application. It is desirable to laminate the membrane and the non-woven fabric. Alternatively, after applying the liquid-absorbent polymer to the laminate of the porous membrane and the nonwoven fabric, the nonwoven fabric may be laminated on the other surface of the porous membrane. In order to stack the layers, it is possible to stack them by a conventionally known method such as stacking, heat fusion or adhesion with an adhesive.

By laminating the non-woven fabrics, when the liquid-absorbent polymer is placed in the pores, the basic porous membrane is prevented from shrinking, and the electrode is provided with slipperiness, which facilitates handling. The occurrence of defects during battery assembly is reduced.
INDUSTRIAL APPLICABILITY The composite film for an alkaline battery separator of the present invention has good wettability with an electrolytic solution and is excellent in a gas venting effect, and is useful for prolonging a battery life.

[0017]

EXAMPLES The present invention will now be described with reference to examples, but the invention is not limited thereto. The test method in the examples is as follows. 1) Film thickness Measured with a dial gauge (minimum scale 1 μm) 2) Average pore size Based on ASTM F-316-80, ethanol was used and evaluated by a half dry method. 3) Electric resistance It was evaluated according to JIS C-2313.

An aqueous solution of caustic potash (specific gravity 1.31 g)
/ Cm ³ ) and preliminarily immersed at room temperature for 1 hour and then taken out, and the Ni plate was used as a current electrode and the Cd plate was used as a voltage electrode to measure the voltage and calculate the electric resistance. 4) Gas Permeability According to ASTM F-316-80, the case where the porous membrane was immersed in distilled water and nitrogen gas was bubbled at 2 kg / cm ² was regarded as good. 5) Battery life A nickel-zinc battery in which positive and negative electrode plates of 1.5 × 4 cm are alternately stacked is manufactured, and the battery is 1/15 C (1/1 of the capacity AH).
(15 current) charge and 1 / 5C discharge, and the deterioration cycle to the initial 80% capacity was 150 times or more was regarded as good. 6) Battery Assembling Property When assembling the nickel-zinc battery in the battery life test, when 20 batteries were manufactured, the occurrence of defective batteries was 2 or more, and 1 or less was good.

[0019]

Reference Example 1 22% by weight of finely divided silicic acid and 44% by weight of dioctyl phthalate were mixed with a Henschel mixer, 34% by weight of a polyethylene resin having a viscosity average molecular weight of 300,000 was added thereto, and the mixture was again mixed with the Henschel mixer. The mixture was formed into a flat film having a thickness of 100 μm by a film manufacturing apparatus in which a T-die having a width of 450 mm was attached to a 30 mmφ twin-screw extruder.

The formed membrane is immersed in 1,1,1-trichloroethane for 10 minutes to extract dioctyl phthalate, which is then dried and further added to 6% in 25% caustic soda at 60 ° C.
It was immersed for 0 minutes to extract finely divided silicic acid, which was then dried and uniaxially stretched 5 times in the machine direction to obtain a porous film having a thickness of 40 μm.

[0021]

[Reference Example 2] Polyethylene resin 34% by weight having a viscosity average molecular weight of 300,000 and liquid paraffin 66% by weight are 30 mmφ
A flat film having a thickness of 100 μm was formed by a film manufacturing apparatus in which a T-die having a width of 450 mm was attached to a twin-screw extruder. The formed film is immersed in 1,1,1-trichloroethane for 10 minutes to extract liquid paraffin and then dried.
The film was uniaxially stretched at 0 ° C. and stretched 5 times to obtain a porous film having a thickness of 40 μm.

[0022]

Example 1 The thickness of the porous membrane obtained in Reference Example 1 was 6 on one surface.
A 0 μm core / sheath type polyethylene / polypropylene non-woven fabric was spot-fused and laminated by heat to obtain a composite film. Next, a solution in which 7 wt% of acetylcellulose (manufactured by Hanai Task) was dissolved in ethyl lactate was applied to the composite film in a pattern by suction using a stencil printing method, and the acetylcellulose / ethyl lactate solution was applied to the composite film. Soaked in. In order to provide a non-porous layer, UV curable resin is applied to the hydrophobic part of the boundary between the hydrophilic part and the hydrophobic part by the stencil printing method so that the hydrophobic part remains, and UV light is applied. After curing, the mixture was saponified with caustic soda and air-dried for about 1 day to obtain a composite membrane for alkaline battery separator. Table 1 shows the physical properties of the obtained film.

[0023]

Example 2 The thickness of the porous film obtained in Reference Example 1 was 6 on one surface.
A 0 μm polypropylene nonwoven fabric was laminated with a polyamide adhesive, and then a composite membrane for an alkaline battery separator was obtained in the same manner as in Example 1. Table 1 shows the physical properties of the obtained film.
Shown in.

[0024]

Example 3 A composite film for an alkaline battery separator was obtained in the same manner as in Example 2 except that a nonwoven fabric made of cellulose having a thickness of 60 μm was used. Table 1 shows the physical properties of the obtained film.

[0025]

Example 4 A composite film for an alkaline battery separator was obtained in the same manner as in Example 1 except that the porous film obtained in Reference Example 2 was used. Table 1 shows the physical properties of the obtained film.

[0026]

Comparative Example 1 A composite membrane for an alkaline battery separator was obtained by laminating a nonwoven fabric on a hydrophobic porous membrane in the same manner as in Example 1 without impregnating the acetyl cellulose / ethyl lactate solution. Table 1 shows the physical properties of the obtained film.

[0027]

Comparative Example 2 Instead of applying the acetyl cellulose / ethyl lactate solution in a grid pattern while applying suction by the stencil printing method in Example 1, 0 of a fluorosurfactant (F-120 manufactured by Dainippon Ink and Chemicals, Inc.) was used. Immersing the composite membrane in a 5 wt% aqueous solution,
A composite film for an alkaline battery separator was obtained. Table 1 shows the physical properties of the obtained film.

[0028]

[Comparative Example 3] A porous film was obtained in the same manner as in Example 1 except that the nonwoven fabric was not laminated. Table 1 shows the physical properties of the obtained film.

[0029]

Comparative Example 4 A composite film for an alkaline battery separator was obtained in the same manner as in Example 1 except that the non-porous layer was not provided. Table 1 shows the physical properties of the obtained film.

[0030]

[Table 1]

[0031]

EFFECT OF THE INVENTION The composite membrane for alkaline battery separator of the present invention has at least one hydrophilic portion and one or more hydrophobic portion, and a non-porous layer between the hydrophilic portion and the hydrophobic portion. Therefore, in an alkaline battery such as a nickel-zinc battery, oxygen gas generated from the positive electrode during overcharge easily reaches the negative electrode through the separator, which facilitates gas absorption in the negative electrode and further promotes the growth of dendrites. It can be suppressed and the life of the battery can be extended. In addition, since the nonwoven fabrics are laminated, the number of defective products during battery assembly is reduced.

[Brief description of drawings]

FIG. 1 is a plan view showing an example of a laminate of a porous membrane and a nonwoven fabric, which is an example of a composite membrane of the present invention, viewed from the porous membrane side.

[Explanation of symbols]

 1 Hydrophilic part 2 Hydrophobic part 3 Non-porous layer

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[Procedure amendment]

[Submission date] July 12, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0030

[Correction method] Change

[Correction content]

[0030]

[Table 1]

Claims (1)

[Claims] 1. A non-woven fabric is laminated on a porous membrane which is composed of a hydrophilic portion and a hydrophobic portion which communicate with each other when water is contained and which has a non-porous layer between the hydrophilic portion and the hydrophobic portion. A composite film for an alkaline battery separator, which is characterized in that