JP6748422B2 - Alkaline battery separator and method of manufacturing the same - Google Patents

Description

The present invention relates to an alkaline battery separator and a method for manufacturing the same. More specifically, alkaline primary batteries such as alkaline manganese battery, mercury battery, silver oxide battery, and air battery, nickel-cadmium battery, silver-zinc battery, silver-cadmium battery, nickel-zinc battery, nickel-hydrogen battery. The present invention relates to a separator that can be used for an alkaline secondary battery such as a rechargeable alkaline manganese battery, and particularly a separator that can be suitably used for a battery that generates oxygen when overcharged such as a nickel-cadmium battery or a nickel-hydrogen battery, and the like. It relates to a manufacturing method.

BACKGROUND ART Conventionally, a separator has been used so as to separate a positive electrode and a negative electrode of an alkaline battery to prevent a short circuit and to hold an electrolytic solution to smoothly perform an electromotive reaction. Since this separator needs to hold an electrolytic solution made of potassium hydroxide or the like, a nonwoven fabric made of a polyolefin-based fiber having excellent alkali resistance has been used. However, since polyolefin fibers have low affinity with the electrolyte and poor electrolyte retention, a nonwoven fabric made of polyolefin fibers is hydrophilized by various methods to impart electrolyte retention. It was

For example, the applicant of the present application has a core-sheath type high-strength polypropylene fiber having a tensile strength of 4.5 cN/dtex or more and having a high-density polyethylene as a sheath component and a polypropylene as a core component. A separator (Patent Document 1), which is made of a non-woven fabric in which high-strength polypropylene fibers are fused and is subjected to a sulfonation treatment, and has an average 5% modulus strength of 50 to 120 N/5 cm width, has been proposed. This separator was excellent in alkali resistance and excellent in retaining electrolyte, but due to oxygen generated during overcharging, the separator deteriorated and a short circuit occurred, or oxygen-deteriorated products affected the electrode plate. Could shorten the life of the battery.

JP, 2004-296355, A

The present invention has been made under such circumstances, and an object of the present invention is to provide a separator excellent in oxidation resistance in addition to alkali resistance and electrolyte retention, and a manufacturing method thereof.

The invention according to claim 1 of the present invention is a non-woven fabric separator comprising a core-sheath type composite fiber having polypropylene as a core component and polyethylene as a sheath component, wherein the polyethylene as the sheath component has a sulfonic acid group. And the polypropylene as the core component has a crystallinity of 46% or more.

The invention according to claim 2 of the present invention relates to "crystals of polypropylene as a core component by sulfonation after forming a nonwoven fabric using a core-sheath type composite fiber having polypropylene as a core component and polyethylene as a sheath component. A method for producing a separator for an alkaline battery, which comprises introducing a sulfonic acid group into polyethylene as the sheath component so that the degree of conversion is 46% or more."

The invention according to claim 1 of the present invention is a separator composed of a core-sheath type composite fiber containing polyethylene as a sheath component, and therefore has excellent alkali resistance. In addition, since polyethylene, which is a sheath component, has a sulfonic acid group, it is also excellent in retaining electrolyte. Furthermore, since the crystallinity of polypropylene, which is the core component, is 46% or more, the oxidation resistance is excellent.

The invention according to claim 2 of the present invention can produce a separator excellent in alkali resistance, electrolyte retention and oxidation resistance according to claim 1.

The alkaline battery separator of the present invention (hereinafter sometimes simply referred to as a “separator”) is made of a core-sheath type composite fiber containing polypropylene as a core component and polyethylene as a sheath component so that it has excellent alkali resistance. Is a non-woven fabric separator.

The polypropylene, which is the core component of the core-sheath type composite fiber of the present invention, can be a homopolymer of propylene or a copolymer of propylene and α-olefin (for example, ethylene, butene-1). You can also More specifically, for example, a crystalline isotactic propylene homopolymer, a low ethylene unit content ethylene-propylene random copolymer, a homopolymer consisting of propylene homopolymer and the content of ethylene units A propylene block copolymer composed of a relatively large number of ethylene-propylene copolymers and a copolymerization part, and each homo- or copolymerization part in the propylene block copolymer further contains butene-1 or the like. Examples thereof include a crystalline propylene-ethylene-α-olefin copolymer made of a copolymerized α-olefin. Among these, isotactic polypropylene homopolymers are preferable because they tend to have high crystallinity, and particularly, isotactic pentad fraction (IPF) is 90% or more, and Q value (index of molecular weight distribution) It is preferable that the weight average molecular weight/number average molecular weight=Mw/Mn ratio) is 6 or less, and the melt index MI (temperature 230° C., load 2.16 kg) is 3 to 50 g/10 minutes. Such polypropylene can be obtained by homopolymerizing propylene or copolymerizing propylene with another α-olefin using a Ziegler-Natta type catalyst or a metallocene catalyst.

On the other hand, the sheath component of the core-sheath type composite fiber is not only excellent in alkali resistance, but even if the sheath component is melted and the fibers are fused by solidification, the core component does not melt and the fiber form is changed. The sheath component is made of polyethylene having a melting point lower than that of polypropylene so that the morphological stability of the separator is maintained and excellent. The polyethylene is not particularly limited, and examples thereof include high-density polyethylene, medium-density polyethylene, low-density polyethylene, and linear low-density polyethylene. Of these, high-density polyethylene has a relatively high melting point, and not only is the separator easy to use at high temperatures, but since high-density polyethylene has a certain degree of hardness, it can be a separator with tension and elasticity, It is suitable because it has excellent properties.

In the core-sheath type composite fiber, the polypropylene as the core component may be in an eccentric state, but since the core components are arranged concentrically in the cross section of the fiber, the core components can be evenly fused. It is suitable.

Further, the volume ratio of the core component and the sheath component is not particularly limited, but the volume of the core component and the sheath component should be such that the fibers can be firmly fused and the fiber form can be maintained during fusion. The ratio is preferably 8:2 to 2:8, more preferably 3:7 to 7:3, and further preferably 4:6 to 6:4.

The polyethylene that is the sheath component of the core-sheath type composite fiber of the present invention has a sulfonic acid group. Therefore, it is excellent in the retention of the electrolytic solution. The core-sheath type composite fiber containing polyethylene having a sulfonic acid group as a sheath component can be obtained by performing a sulfonation treatment in a fiber state or a nonwoven fabric state by a conventional method. The polyethylene may have a hydrophilic group other than the sulfonic acid group (for example, a carboxyl group, a carbonyl group, etc.). In addition to the hydrophilic group containing a sulfonic acid group, a surfactant may be further contained so that the electrolyte solution can be injected easily.

Furthermore, since the crystallinity of polypropylene, which is the core component of the core-sheath type composite fiber of the present invention, is 46% or more, it has excellent oxidation resistance. This is because there are few amorphous parts that are easily oxidized by oxygen. Since this polypropylene is the core component, only the both ends of the fiber are exposed on the fiber surface, and although the exposed area is very small, the crystallinity of the polypropylene, which is the core component, is high. It is surprising that it has a great influence on the oxidation resistance when used as a separator. The higher the crystallinity of this polypropylene, the better the oxidation resistance. Therefore, the crystallinity of polypropylene is more preferably 47% or more, further preferably 48% or more, and 49% or more. Is more preferable, and 50% or more is further preferable.

The “crystallinity” in the present invention is the percentage of the heat of fusion of polypropylene (symbol=Hc, unit=J/g) of the core component with respect to the heat of fusion of completely crystalline polypropylene (symbol=Hp, 209 J/g). means. That is, the crystallinity (Cd) is obtained from the following equation.
Cd=(Hc/Hp)×100=0.478×Hc
The heat of fusion of polypropylene, which is the core component, means a value obtained by heating with a differential scanning calorimeter (DSC) from room temperature to about 200° C. at a rate of 10° C./min in a nitrogen gas atmosphere. To do.

Although the fiber diameter of the core-sheath type composite fiber constituting the separator of the present invention is not particularly limited, it is preferably 5 to 32 μm, more preferably 8 to 17 μm. If the fiber diameter of the core-sheath type composite fiber is less than 5 μm, the strength of the nonwoven fabric tends to be insufficient, and if the fiber diameter exceeds 32 μm, it is difficult to uniformly disperse the core-sheath type composite fiber, resulting in uniform electrolysis. This is because it tends to be difficult to retain the liquid.

Further, the fiber length of the core-sheath type composite fiber is preferably 1 to 20 mm, and preferably 2 to 15 mm so that the core-sheath type composite fiber is uniformly dispersed and it is easy to uniformly hold the electrolytic solution. Is more preferable, and 3 to 10 mm is even more preferable.

The separator of the present invention may be composed of one type of core-sheath type composite fiber, or may be a type of polypropylene as a core component, a type of polyethylene as a sheath component, or a fiber cross section of polypropylene as a core component. From two or more types of core-sheath composite fibers that differ in arrangement state, volume ratio of core component to sheath component, amount of sulfonic acid group, crystallinity of polypropylene as the core component, fiber diameter, and/or fiber length It may be configured.

The nonwoven fabric which is the separator of the present invention is composed of the core-sheath type composite fiber as described above, but the nonwoven fabric form is formed by fusion of the sheath component of the core-sheath type composite fiber so that the separator (nonwoven fabric) has excellent morphological stability. Is preferably held. In addition to the fusion of the sheath component of the core-sheath type composite fiber, or in place of the fusion, the shape can be maintained by three-dimensional entanglement that can be formed by hydroentanglement.

The basis weight of the separator of the present invention is not particularly limited, but a high basis weight results in a large amount of fibers, a good texture, and a highly reliable separator. Therefore, it is 40 g/m ² or more. It is preferably 60 g/m ² or more, more preferably 80 g/m ² or more. On the other hand, when the basis weight becomes higher, the separator becomes thicker, since it is difficult to correspond to the high capacity of the battery is preferably at 100 g / ^{m 2} or less, more preferably at 90 g / ^{m 2} or less, 85 g / m It is more preferably ² or less. The "unit weight" in the present invention means the basis weight obtained based on the method specified in JIS P 8124:2011 (Paper and board-Basis weight measuring method).

Further, the thickness of the separator of the present invention can be 0.30 mm or less, and preferably 0.25 mm or less. The “thickness” of the present invention is measured at a load of 5N using an outer micrometer (0 to 25 mm) specified in JIS B 7502:1994 for 10 randomly selected points, and the arithmetic mean thereof is used. Says the value.

The separator of the present invention can be manufactured, for example, by the following method. That is, after forming a non-woven fabric using a core-sheath type composite fiber having polypropylene as a core component and polyethylene as a sheath component, sulfonation treatment is performed so that the crystallinity of polypropylene as the core component is 46% or more. It can be produced by introducing a sulfonic acid group into polyethylene which is the sheath component.

As the core-sheath type composite fiber, the core-sheath type composite fiber as described above can be used, and particularly, it is preferable to use the core-sheath type composite fiber having high-density polyethylene as a sheath component. Further, polypropylene having a crystallinity of 48% or more before the sulfonation treatment is used as a core component so that the crystallinity of the polypropylene, which is the core component of the core-sheath type composite fiber after the sulfonation treatment, is 46% or more. It is preferable to use core-sheath type composite fibers.

Next, a non-woven fabric is formed using the core-sheath type composite fibers. The non-woven fabric can be formed by forming a fiber web using the core-sheath type composite fibers and then bonding the core-sheath type composite fibers together. The method for forming the fiber web may be, for example, a direct method such as a dry method, a wet method, or a melt blow method. However, it is possible to uniformly disperse the core-sheath type composite fibers and hold the electrolyte solution uniformly. In addition, it is preferable to form the fiber web by a wet method. As this preferable wet method, for example, a horizontal Fourdrinier method, a slanted wire type short reticulated method, a cylinder method, or a fourdrinier/cylinder combination method can be mentioned.

The core-sheath type composite fibers can be bonded to each other by, for example, fusion bonding of polyethylene, which is a sheath component of the core-sheath type composite fibers. As described above, when the polyethylene, which is the sheath component of the core-sheath type composite fiber, is fused, it may be performed under no pressure or under pressure, or after the sheath component is melted under no pressure. You may press. As an apparatus capable of performing such fusion bonding, there are, for example, a thermal calender, a hot air penetration type heat treatment apparatus, and a cylinder contact type heat treatment apparatus. The heating temperature is preferably a temperature within the range from the softening temperature of the sheath component of the core-sheath type composite fiber to the melting point when heating and pressing are performed simultaneously, and when heating and pressing are not performed simultaneously Is preferably performed within a range from the softening temperature of the sheath component of the core-sheath type composite fiber to a temperature 30° C. higher than the melting point. Before fusion of the core-sheath composite fibers by fusion bonding of polyethylene, which is the sheath component of the core-sheath composite fibers, the core-sheath composite fibers are three-dimensionally entangled with each other by a fluid flow such as water flow. May be. Alternatively, the core-sheath type composite fibers are three-dimensionally entangled with each other by a fluid flow such as a water flow without bonding the core-sheath type composite fibers with each other by fusing polyethylene which is a sheath component of the core-sheath type composite fibers. May be.

Then, by the sulfonation treatment, a sulfonic acid group is introduced into the sheath component polyethylene so that the core component polypropylene has a crystallinity of 46% or more, whereby the separator of the present invention can be produced. .. For example, the sulfonation treatment may be performed by immersing in a solution of fuming sulfuric acid, sulfuric acid, chlorosulfuric acid, or sulfuryl chloride, contacting with SO ₃ gas, or discharging in the presence of SO gas and/or SO ₂ gas. However, if the sulfonation conditions are strong, many sulfonic acid groups can be introduced into the polyethylene that is the sheath component, but the polypropylene that is the core component is deteriorated and the crystallinity is high. Since it tends to be low and the oxidation resistance tends to be poor, it is preferable to carry out under relatively mild conditions. For example, when the nonwoven fabric is immersed in a fuming sulfuric acid solution, the temperature of the fuming sulfuric acid solution is lowered to about 60° C. or lower, the concentration of sulfur trioxide in the fuming sulfuric acid solution is lowered to about 15% or lower, and/or It is preferable to introduce a sulfonic acid group so that the crystallinity of polypropylene as a core component is 46% or more by a method such as shortening the immersion time of the nonwoven fabric to about 2 minutes or less.

The above is a method for producing a separator in which a nonwoven fabric is formed using a core-sheath type composite fiber and then a sulfonation treatment is performed to introduce a sulfonic acid group into polyethylene that is a sheath component. The sulfonated core-sheath type composite fiber is obtained by subjecting the sulfonated core-sheath type composite fiber to the sulfonation treatment, and the crystallinity of polypropylene as the core component is 46% or more. However, this non-woven fabric can also be used as a separator.

Since the separator of the present invention is excellent in alkali resistance, electrolyte retention, and oxidation resistance, when the separator of the present invention is used, the electrolyte is less likely to die, short circuit is unlikely to occur, and the alkaline battery has a long life. Can be manufactured. For example, it is possible to manufacture a long-life alkaline battery having a cylindrical shape, a rectangular shape, or a button shape. More specifically, alkaline manganese batteries, mercury batteries, silver oxide batteries, primary batteries such as air batteries, nickel-cadmium batteries, silver-zinc batteries, silver-cadmium batteries, nickel-zinc batteries, nickel-hydrogen batteries. Alternatively, a secondary battery such as a lead storage battery, particularly a nickel-cadmium battery or a nickel-hydrogen battery can be preferably manufactured. The alkaline battery using the separator of the present invention has a long life not only at room temperature but also at a high temperature where oxidation deterioration easily occurs.

Examples of the present invention will be described below, but the present invention is not limited to the following examples.

(Example 1)
A core-sheath type composite fiber (fiber diameter: 11 μm) in which the core component is made of isotactic polypropylene homopolymer (melting point: 168° C., crystallinity: 49%) and the sheath component is made of high-density polyethylene (melting point: 135° C.) , Fiber length: 5 mm, the core components were arranged concentrically in a cross section of the fiber, and the volume ratio of the core to the sheath was 6:4).

Then, only the core-sheath type composite fibers were dispersed to form a slurry, and then a fiber web was formed by a wet method.

Next, this fiber web is dried by a hot air circulation type heat treatment machine set to a temperature of 135° C. under no pressure, and at the same time, it is fused with high density polyethylene which is a sheath component of the core-sheath type composite fiber to form a fused nonwoven fabric. did.

Next, the fusion bonded nonwoven fabric is immersed in a fuming sulfuric acid solution (specific gravity 15% SO ₃ solution) at a temperature of 57° C. for 3 minutes, then thoroughly washed with water and dried to obtain a high density which is a sheath component of the core-sheath type composite fiber. A sulfonic acid group was introduced into polyethylene, and the thickness was adjusted with a calendar at room temperature to manufacture a separator having a basis weight of 84 g/m ² and a thickness of 0.22 mm.

(Example 2)
The fused non-woven fabric produced in the same manner as in Example 1 was dipped in a fuming sulfuric acid solution (specific gravity 15% SO ₃ solution) at a temperature of 55° C. for 3 minutes, then thoroughly washed with water and dried to form a core-sheath composite. A sulfonic acid group was introduced into high-density polyethylene, which is the sheath component of the fiber, and the thickness was adjusted with a calendar at room temperature to produce a separator having a basis weight of 84 g/m ² and a thickness of 0.22 mm.

(Example 3)
The fused non-woven fabric manufactured in the same manner as in Example 1 was immersed in a fuming sulfuric acid solution (specific gravity 15% SO ₃ solution) at a temperature of 53° C. for 2 minutes, then thoroughly washed with water and dried to form a core-sheath composite. A sulfonic acid group was introduced into high-density polyethylene, which is the sheath component of the fiber, and the thickness was adjusted with a calendar at room temperature to produce a separator having a basis weight of 84 g/m ² and a thickness of 0.22 mm.

(Comparative example 1)
The fused nonwoven fabric manufactured in the same manner as in Example 1 was immersed in a fuming sulfuric acid solution (specific gravity 15% SO ₃ solution) at a temperature of 60° C. for 3 minutes, then thoroughly washed with water and dried to form a core-sheath composite. A sulfonic acid group was introduced into high-density polyethylene, which is the sheath component of the fiber, and the thickness was adjusted with a calendar at room temperature to produce a separator having a basis weight of 84 g/m ² and a thickness of 0.22 mm.

(Evaluation of the physical properties)
The following procedures evaluated the crystallinity of polypropylene, the liquid retention under pressure, the alkali resistance, and the oxidation resistance (chemical oxygen demand) of each separator. The results are shown in Table 1.

[1] Crystallinity of polypropylene (core component);
The heat of fusion (=Hc) of polypropylene (core component) in each separator was measured using a differential scanning calorimeter (DSC) under the above-mentioned conditions, and the heat of fusion of completely crystalline polypropylene (=Hp, 209 J/g) was obtained. From this, the crystallinity (=Cd) of polypropylene (core component) was calculated from the following formula. This measurement was performed three times for one type of separator, and the average value was taken as the crystallinity.
Cd=(Hc/Hp)×100=0.478×Hc

[2] Pressurized liquid retention rate;
A test piece with a diameter of 30 mm was collected from each separator, and the mass (M ₀ ) was measured after reaching a water equilibrium state at a temperature of 20° C. and a relative humidity of 65%.

Next, in order to replace the air in the separator with the potassium hydroxide solution, it was immersed in a potassium hydroxide solution having a specific gravity of 1.30 (20° C.) for 1 hour or more to hold the potassium hydroxide solution.

Subsequently, each separator was sandwiched between upper and lower three filter papers (40 mm square), a pressure of 5.7 MPa was applied for 30 seconds by a pressure pump, and then the mass (M ₁ ) of the separator was measured.

Then, the pressurized liquid retention rate (=Hp, unit: %) was calculated from the following formula. This measurement was carried out on three test pieces for one type of separator, and the average value thereof was defined as the liquid retention under pressure. The larger the pressurized liquid retention rate, the better the electrolyte retention.
Hp=[(M ₁ −M ₀ )/M ₀ ]×100

[3] Alkali resistance test;
Three 20 cm square test pieces were collected from each separator, and the mass (M) in a state of reaching a water equilibrium state was measured up to 1 mg, and then potassium hydroxide having a specific gravity of 1.3 at a temperature of 20±2° C. Each test piece was boiled with the solution for 1 hour.

After that, the product is washed with water until reaching the neutralization point, then dried, and the mass (M ₁ ) in the state of reaching the water equilibrium state again is measured, and the mass reduction rate (=Mr, unit:%) is calculated by the following formula. did. This measurement was performed on three test pieces, and the average value was defined as the mass reduction rate. The smaller the mass reduction rate, the better the alkali resistance.
Mr=(M−M ₁ )/M×100

[4] Measurement of chemical oxygen demand;
The chemical oxygen demand of each separator was measured by the following method.
(1) The separator is cut into a size (5 cm square) that consumes 20 to 40% of potassium permanganate, which will be described later, which acts as an oxidizing agent (area: 0.0025 m ² ), and a water equilibrium state is obtained. The mass (M) in the reached state was measured up to 1 mg.
(2) The above separator was further cut into a size of about 1 to 2 cm square, and then placed in a 300 mL flask.
(3) 100 mL of pure water was injected into the flask with a measuring cylinder.
(4) 10 mL of sulfuric acid water consisting of 2 volumes of distilled water to 1 volume of sulfuric acid was poured into the flask while shaking.
(5) 10 mL of 5 mmol/L (N/40) potassium permanganate solution was poured into a flask with a pipette, shaken and mixed, immediately put in a water bath at 80° C., and reacted for 30 minutes. At this time, the water surface of the hot water bath was set to be higher than the water surface in the flask for sufficient reaction. In addition, it was confirmed that the red color of potassium permanganate remained after the reaction for 30 minutes.
(6) The flask was taken out of the hot water bath, and 10 mL of a 12.5 mmol/L (N/40) sodium oxalate solution was poured into the flask with a pipette, and shaken and mixed to react well. At this time, it was confirmed that the red color of potassium permanganate disappeared and became colorless.
(7) While maintaining the solution in the flask at 60 to 80° C., the solution was titrated with a 5 mmol/L (N/40) potassium permanganate solution. The end point was when maintaining the deep red color for 30 seconds or more. The amount a (mL) of the potassium permanganate solution required at this time was measured.
(8) Separately, 100 mL of pure water was placed in an Erlenmeyer flask and the operations (4) to (7) were performed (blank test). The amount b (mL) of the potassium permanganate solution required at this time was measured.
(9) From the above results, the chemical oxygen demand (=COD, unit: mg-O/g) was calculated by the following formula. This measurement was performed on three test pieces for one type of separator, and the average value thereof was taken as the COD value. The smaller the COD value, the better the oxidation resistance.
COD=(ab)×f×0.2×1/M
Here, a is the amount of potassium permanganate required for the titration (mL), b is the amount of potassium permanganate required for the titration in the blank test (mL), and f is the factor of 5 mmol/L potassium permanganate solution. , M means the weight (g) of the separator, respectively.

From the results shown in Table 1, when the crystallinity of polypropylene, which is the core component of the core-sheath type composite fiber, is 46% or more, alkali resistance, electrolyte retention, and oxidation resistance (chemical oxygen demand) are improved. It was estimated that an excellent alkaline battery with a long life could be manufactured.

The alkaline battery separator of the present invention is particularly suitable for batteries that generate oxygen during overcharge, such as nickel-cadmium batteries and nickel-hydrogen batteries.

Claims (2)

A non-woven fabric separator comprising a core-sheath type composite fiber having polypropylene as a core component and polyethylene as a sheath component, wherein the sheath component polyethylene has a sulfonic acid group, and the core component polypropylene is crystallized. A separator for an alkaline battery (excluding those containing an inorganic substance), which has a degree of 48% or more and 50% or less . After forming a non-woven fabric using a core-sheath type composite fiber containing polypropylene as a core component and polyethylene as a sheath component, the crystallization treatment of the polypropylene as the core component is 48% or more and 50% or less by sulfonation treatment. As described above, a method for producing a separator for an alkaline battery (excluding those in which an inorganic substance is present), which comprises introducing a sulfonic acid group into polyethylene as the sheath component.