JPS5846826B2 - Manufacturing method of separator for alkaline batteries - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a separator for alkaline batteries, and its purpose is to provide a separator for alkaline batteries that is chemically stable and has excellent properties as a separator.

In alkaline batteries such as mercury and silver batteries, which are generally small high-performance batteries, the cathode mixture and anode mixture are separated by a separator, and only the electrolyte moves between the negative and anode electrodes via the separator to carry out the battery reaction. However, the cellophane membrane that has conventionally been widely used as this separator is susceptible to oxidative deterioration due to the oxidizing properties of the anode active material caused by alkaline electrolytes or under alkaline conditions, and the active materials of the cathode and anode may come into contact with each other during battery storage. This has the disadvantage of causing an internal short circuit and self-discharge, resulting in a shortened battery life.

By the way, the characteristics required for alkaline battery separators include the general characteristics of being thin and having moderate mechanical strength, as well as low electrical resistance, good selective permeability of ions, and chemical properties. It is necessary to have the property of stability, and although cellophane membranes almost satisfy these properties, as mentioned above, they still lack chemical stability.

Therefore, the inventors conducted extensive research into a separator that has excellent chemical stability and also satisfies other characteristics.
Focusing on the fact that a porous coagulated film made of polysulfone is chemically stable in an alkaline electrolyte, a bubble pressure method (this method will be described in Example 1 below) was carried out.

), they found that separators with maximum pores in the range of 0.1 to 5μ are particularly excellent as separators for alkaline batteries, and they also discovered a method to obtain such separators industrially, and finally completed this invention.

That is, this invention involves applying a solution of polysulfone dissolved in an organic solvent to a release material or a porous support such as a nonwoven fabric or woven fabric, and then immersing the solution in a coagulating liquid that is miscible with the solvent but does not dissolve the polysulfone. In order to obtain a porous coagulated film, a modifier consisting of an inorganic salt or an organic compound having a salting-out function or a coagulation promoting function, which is dissolved in the solvent and the coagulation liquid, is added and mixed into the polysulfone solution. and a method for producing a separator for alkaline batteries, characterized in that the maximum pores (hereinafter simply referred to as maximum pores) measured by the Pubble-Puktscher method in the coagulated film are set in the range of 0.1 to 5μ. This is related.

The reason why the maximum pore size of the porous coagulated membrane is limited to a range of 0.1 to 5μ in this invention is determined by taking into consideration the internal resistance and ion selective permeability of the separator when incorporated into an alkaline battery. If the maximum pore size is smaller than 0.1μ, the permselective ability will improve, but this will increase the internal resistance of the battery and lower the electromotive force.On the other hand, if the maximum pore size is larger than 5μ, the internal resistance can be lowered, but the permselectivity will decrease. In any case, such as when the negative and positive active materials mix and short-circuit inside the battery,
; is also unsuitable as a separator for alkaline batteries.

The polysulfone used in this invention is an aliphatic or aromatic polymer having a sulfone group in its main chain, and preferably has a molecular weight of about 15,000 to 50,000 and a heat distortion temperature of about 150 to 250°C.

Typical examples include polyethers obtained by the reaction of dichlorodiphenyl sulfone and bisphenol A, or the reaction of diphenolate sulfone with a dichloro compound. There is -1700.

Next, we will discuss the method for producing a porous coagulated membrane with a maximum pore force in the range of 0.1 to 5 μ from this polysulfone. Polysulfone is dissolved in a solvent containing a specific modifier described below, and this solution is After coating it on a release material such as a glass plate or a release resin film to a thickness of usually about 50 to 300μ, it is immersed in a coagulating liquid that is miscible with the solvent but does not dissolve polysulfone, and then removed from the release material. Obtained by peeling.

Here, the solvents in which polysulfone is dissolved include dimethylformamide (hereinafter referred to as DMF'), dimethylacetamide (hereinafter referred to as DMA), dimethylsulfoxide (hereinafter referred to as DMA), and dimethylformamide (hereinafter referred to as DMA).
(hereinafter referred to as DMSO), N-methyl-2-pyrrolidone (
(hereinafter referred to as NMP), chloroform, toluene, etc. may be used alone or in combination of two or more of them. In the present invention, a modifier consisting of an inorganic salt or an organic compound that is dissolved in this solvent and in the coagulation liquid is particularly used. It is important to add and mix.

Inorganic salts include, for example, zinc chloride, ferric chloride, bromolithium, lithium nitrate, aluminum nitrate, copper nitrite, etc., and organic compounds include tartaric acid, acetone, formamide, dioxane, etc.

The modifier is essential to keep the maximum pores of the porous coagulated membrane within the above range, and if this modifier is not used, the maximum pores will be too small, making it difficult to create a porous coagulated membrane suitable for separators for alkaline batteries. can't get it.

Furthermore, the use of a modifier has the advantage that a coagulated film with uniform pores can be obtained, increasing its usefulness when used as a separator for alkaline batteries.

On the other hand, if too much modifier is used, the maximum pore size becomes too large and the ion selective permeability is impaired.

Therefore, the amount of the modifier used must be kept within an optimal range, and this amount varies depending on the type of modifier and the temperature of the coagulating liquid, but is generally 5 to 200 parts by weight per 100 parts by weight of the main component. parts, preferably 20 to 120 parts by weight.

Regarding the function of modifiers, inorganic salts and tartaric acid have a salting-out function when the coated polysulfone solution is immersed in a coagulating liquid and a coagulating film is formed by replacing the coagulating liquid with a solvent. This is thought to be because organic compounds play a coagulation promoting function based on changes in mutual solubility in the formation of similar coagulated films, and when such modifiers are not used, the interaction between the coagulating liquid and the solvent on the surface side of the polysulfone coating layer increases. While preferential substitution causes the maximum pores of the so-called skinned porous membrane to become smaller, the above-mentioned function of the modifier allows it to coagulate uniformly and relatively quickly to the inside of the coating layer. This is thought to be due to the fact that these drawbacks can be avoided to some extent.

The amount of polysulfone to be dissolved in the solvent containing such a modifier is generally such that the resin concentration in the solution is 5 to 25% by weight.

If the resin concentration is too low, the film forming properties will be poor and the pores will tend to become too large, whereas if the resin concentration is too high, the pore diameter will become too small, which is undesirable.

Further, specific examples of coagulating liquids that are miscible with the above solvent and do not dissolve polysulfone include those in which the solvent component is DMF", DMA
, DMSO, NMP, etc., and methanol can be used when the main solvent component is toluene, chloroform, etc.

The temperature at which the polysulfone coating layer is immersed in this coagulation liquid greatly affects the pores of the resulting coagulated film; if the temperature is too low, the pores become small and the maximum pore size does not reach 0.1μ or more. Conversely, if the temperature becomes too high, the pores become too large, with the maximum pore exceeding 5 μm, and this also causes problems in liquid management of the coagulating liquid.

Therefore, usually 35° to 90°C, preferably 40° to
It is preferable to select the optimum temperature within the range of 80°C depending on the coagulating liquid used.

After coagulating in this way, it is dried to volatilize the moisture in the film,
When the film is peeled off from the release material, a porous coagulated film having a maximum pore size of 0.1 to 5 μm is obtained.

Drying is usually carried out by leaving the film at a temperature ranging from room temperature to 80° C. for several minutes, but the pores of the film may become smaller due to vacuum fusion due to volatilization of moisture during this drying.

However, the above-mentioned modifier is added in a specific amount, usually 10% as the main solvent component.
It has been found that when 7 parts by weight or more is used compared to 0 parts by weight, the formation of small pores due to vacuum fusion is suppressed, resulting in a porous coagulated film whose maximum pores are not much different from before drying. The advantages of using this drying process have also been recognized.

On the other hand, since the purpose of this drying is to volatilize moisture, if the workability of battery assembly is ignored, it may be used in an undried state without drying.

In any case, if the porous coagulated membrane obtained by this method is used as a separator for alkaline batteries, the separator will be chemically stable for a long time, have excellent permselective ability, and have low electrical resistance.

In addition, in this manufacturing method, instead of the release material, nonwoven fabrics, cloths, nonwoven fabrics made of synthetic fibers such as polyester, polyethylene, polypropylene, polystyrene, fluororesin, etc., or films made of these synthetic resins with micropores that do not affect electrical resistance are used. By using a porous support such as this and impregnating the voids of this support with a polysulfone solution and immersing it in a coagulation solution, a porous coagulation film in which the support described above is integrally contained inside the membrane can be obtained. It is possible to improve mechanical strength and liquid absorption ability.

Next, embodiments of the present invention will be described, and the present invention will be further explained in detail.

In addition, in the following description, the term "middle part" or "%" means parts by weight or % by weight, respectively.

Example 1 17 parts of polysulfone (P-1700, already mentioned) was added to NMP
A 17% solution was prepared by dissolving 76 parts of lithium nitrate in a solvent containing a modifier consisting of 7 parts of lithium nitrate. After coating this solution on a glass plate to a coating thickness of 80μ, the solution was heated at 50°C.
The polysulfone was immersed in distilled water for over 1 hour to extract the solvent, and the polysulfone was coagulated to obtain a porous coagulated membrane.

The maximum pores of this porous solidified membrane were measured using the bubble pressure method (
ASTM F 316-7 The roller was 0.45 before drying and 0.40μ after air drying.

In the bubble pressure method, a porous membrane is impregnated with water, and the maximum pore size R (-2,108
/P (μm), (P = kg/crA )).

In addition, the maximum pores of the porous solidified membrane obtained by varying the solidification temperature in the range of 0 to 90°C in Example 1 were measured, and the correlation curve between the solidification temperature and the maximum pores obtained is shown in curve 1 in FIG. Furthermore, this time, the amount of lithium nitrate added to the solvent as a modifier was varied from 0 to
A porous coagulated film was obtained according to the method of Example 1 by varying the amount of lithium nitrate in the range of 15 parts, and the maximum pores were measured.
-ta.

In FIG. 2, curve a is the correlation curve before drying the porous coagulated membrane, and curve a is the correlation curve after drying.

Curve 2 in FIG. 1 shows the case where the method of Example 1 was performed without using any lithium nitrate as a modifier.

Example 2 15 parts of polysulfone (p-1700 supra) was added to DMA79
A 15% solution was prepared by dissolving 6 parts of acetone in a solvent containing 6 parts of acetone, and this solution was applied to a porous support (
The mixture was coated on a polypropylene (nonwoven fabric with fiber lengths of about 5 to 15 and thickness of 50 μm) to a coating thickness of 120 μm, and then treated in the same manner as in Example 1 to obtain a porous coagulated film.

The maximum pore size after air drying was 0.4μ.

Chemical stability and electrical resistance were measured using the various porous coagulated films obtained above.

These results are summarized in the table below.

The porous coagulated membrane obtained in Example 2 was omitted from the table because it had exactly the same characteristics as the porous coagulated membrane obtained in Example 1.

In addition, Comparative Example 1 in the table shows the characteristics using a commercially available cellophane membrane for alkaline battery separators (manufactured by Daicel, thickness 70μ), and Comparative Examples 2 to 5 are the same as in Example 1, with only the solidification temperature being varied. The maximum pore space obtained is o, oiμ, 0
．． The characteristics of porous coagulated membranes of 05μ, 7μ, and 10μ are shown.

The chemical stability is determined by the dimensions and volume when the porous membrane is immersed in a solution of 30% potassium hydroxide solution and 5% potassium permanganate solution mixed at a volume ratio of 4:25 and boiled for several hours. Measure the rate of change and measure the electrical resistance according to JIS C2
313, respectively.

As is clear from the above table, the porous coagulated membrane made of polysulfone according to the present invention is different from the conventional cellophane membrane (Comparative Example 1).
), and has a maximum pore size in the range of 0.1 to 5 μm, so it has excellent electrical resistance, and its selective permeability, which can be estimated from the electrical resistance value, is comparable to that of cello... It can be seen that it has very excellent properties as a separator for alkaline batteries, such as the same level.

[Brief explanation of the drawings] Figure 1 shows the correlation between the maximum pores of the porous coagulated membrane and the coagulation temperature, and Figure 2 shows the relationship between the amount of lithium nitrate blended into the solvent for dissolving polysulfone and the porous coagulated membrane. FIG. 3 is a curve diagram showing the correlation characteristics with the maximum pore space.

Claims (1)

[Claims] 1. A solution of polysulfone dissolved in an organic solvent is applied to a release material or a porous support such as a nonwoven fabric or woven fabric, and then immersed in a coagulation liquid that is miscible with the above solvent but does not dissolve the polysulfone to form a porous coagulation. To obtain the membrane, a modifier consisting of an inorganic salt or an organic compound having a salting out function or a coagulation promoting function, which is dissolved in the solvent and the coagulation liquid, is added and mixed into the polysulfone solution,
A method for producing a separator for an alkaline battery, characterized in that the maximum pore size of the coagulated film measured by a bubble pressure method is set to 0.1 to 5μ.