JP3421164B2 - Alkaline battery separator - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an alkaline battery separator.

[0002]

2. Description of the Related Art Conventionally, a separator has been used 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 carry out an electromotive reaction.

For example, Japanese Unexamined Patent Publication No. 6-140015 discloses a separator made of fibers having a fiber diameter of 10 μm or less, preferably 2 to 10 μm, and a grafting ratio of 20% or less, preferably 3 to 20%. Has been done. However, as described in the examples of this publication, a separator using fibers having a fiber diameter of about 9 μm does not have sufficient liquid retention,
On the other hand, although a separator using fibers having a fiber diameter of about 2 μm has liquid retention properties, since the fiber diameter is small and it has no rigidity, wrinkles are likely to occur when the battery is manufactured by involving the separator and the electrode, It was a bad thing.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide an alkaline battery with excellent liquid retention and workability in battery production. To provide a separator.

[0005]

The alkaline battery separator of the present invention (hereinafter referred to as "separator") is made of a polyester.
Polyolefin <br/> emissions system dividable composite fibers obtained by combining the styrene and polypropylene (hereinafter referred to as "dividable composite fiber") obtained by dividing a fiber diameter 0.01~6μm polyethylene
Ren ultrafine fibers and polypropylene ultrafine fibers (hereinafter, fiber diameter
Polyolefin-based ultrafine fibers of 0.01 to 6 μm
Containing a called Wei "), yet the vinyl monomer to the ultrafine fibers obtained by graft polymerizing at least one direction of bending resistance consists of hydro-entangled nonwoven fabric is not less than 20Mgf.

[0006]

In the separator of the present invention, the ultrafine fibers constituting the separator have a fiber diameter of 6 μm or less, a microspace is formed by the ultrafine fibers, and a capillary effect is exerted, and a vinyl monomer is grafted to the ultrafine fibers. Since it is polymerized and has an excellent liquid retention property, it can extend the life of the battery. In addition, the ultrafine fibers are intimately entangled by the water flow, and the rigidity is imparted by the graft polymerization of the vinyl monomer. Therefore, the bending resistance is 20 mgf or more in at least one direction, and the battery can be formed without wrinkling. It is a separator that can be manufactured and has excellent workability.

The ultrafine fibers constituting the separator of the present invention are obtained by dividing the splittable conjugate fiber, and are preferably made of a polyolefin resin component having electrolytic solution resistance and oxidation resistance. As the splittable conjugate fiber, it is preferable to use a fiber in which a polyolefin resin such as polyethylene, polypropylene, polymethylpentene, ethylene-propylene copolymer, ethylene-butene-propylene copolymer, or ethylene-vinyl alcohol copolymer is appropriately combined. Among these, the splittable conjugate fiber in which polyethylene and polypropylene are combined is divided into polyethylene ultrafine fibers and polypropylene ultrafine fibers, and a separator containing these ultrafine fibers is a sealed secondary battery, and gas is generated. Even in such a case, the generated gas can be quickly permeated to the other electrode and consumed, and there is no risk of the internal pressure rising and bursting, so that it can be suitably used. This is because the vinyl monomer is relatively easy to be graft-polymerized on the polyethylene ultrafine fiber, whereas the polypropylene monomer is not easily graft-polymerized on the polypropylene ultrafine fiber, so that the electrolytic solution is easily retained around the polyethylene ultrafine fiber. This is because there is a poor electrolyte solution around the ultrafine fibers, and the generated gas has a portion that easily permeates to the other electrode.

Since splittable conjugate fibers obtained by combining polyethylene and polypropylene have high compatibility and are difficult to split, either resin and polystyrene-based, polycarbonate-based, polypropylene, or other resin is used so that splitting is easier. By increasing the rigidity,
It is preferable to make it easy to divide. Among these, it is preferable to mix polypropylene, which is a polyolefin type and has a high fiber-forming ability, with polyethylene.

The cross-sectional shape of this splittable conjugate fiber is a chrysanthemum-shaped one in which one component 1 is arranged between the other components 2 as shown in FIGS. 1 (a) to 1 (d), and FIG. 1 (e). As shown in
When the one component 1 and the other component 2 alternately laminated in layers are used, ultrafine fibers having a non-circular cross section, for example,
In the case of FIG. 1C, it can be divided into two types of ultrafine fibers, that is, a wedge-shaped ultrafine fiber and a circular ultrafine fiber, and a finer void can be formed as compared with an ultrafine fiber having a circular cross section.
Since it has more excellent liquid retention and can prevent short circuit due to dendrite, it can be preferably used. Among these, in the fiber cross section as shown in FIG. 1 (c) or (d), which has a circular resin component at the center, which can be divided into ultrafine fibers of different sizes, Dividable conjugate fibers in which other resin components are divided into wedge shapes by the resin components (in the case of c: wedge shape, in the case of d: substantially elliptical shape) located in the periphery can be most preferably used. Further, the splittable conjugate fiber having a chrysanthemum-like or layered cross-sectional shape can be split into ultrafine fibers at the same time by the action of a water stream, and at the same time, can be entangled with each other, which is also a preferable fiber in manufacturing.

Ultrafine fibers obtained by dividing such splittable conjugate fibers form finer voids as they become finer, and are excellent in liquid retaining property and dendrite prevention property. (Hereinafter the same) is preferably 6 μm or less, and if it is too thin, it is difficult to entangle tightly with a water stream, and even if the vinyl monomer is graft-polymerized, it is difficult to obtain the desired bending resistance, so the fiber diameter is 0. It is preferably 0.01 μm or more, and more preferably, the fiber diameter is 0.04 to 5 μm.

In the present invention, it is preferable to use 60% by weight or more of such a splittable conjugate fiber to form fine voids, and more preferably 75% by weight or more,
Most preferably, 80% by weight or more is used. In addition to this splittable conjugate fiber, a polyolefin-based adhesive fiber consisting of a single component such as polyethylene fiber or polypropylene fiber, or a polyethylene component and a polypropylene component,
A core-sheath type, a side-by-side type, or an eccentric type polyolefin-based composite adhesive fiber may be used to increase the bending resistance. Among these, polyolefin-based composite adhesive fibers whose shape is maintained by a resin component that does not adhere can be preferably used, and as the combination of resin components, from the polyethylene component and the polypropylene component, for the same reason as in the case of the splittable composite fiber. Preferably. As described above, as the resin component constituting the splittable conjugate fiber,
Since a combination of polypropylene and polyethylene is preferable, when bonding with a polyolefin-based adhesive fiber other than the splittable conjugate fiber, even the polyethylene ultrafine fiber obtained by splitting the splittable conjugate fiber is bonded to retain the liquid. It is preferable to use high-density polyethylene as a resin component constituting the splittable conjugate fiber and low-density polyethylene as a polyolefin-based adhesive component other than the splittable conjugate fiber so as not to deteriorate the property. In addition, it is preferable to use a fiber having a fiber diameter of 25 μm or less so that the formation of minute voids is not hindered by using the polyolefin-based adhesive fiber.

The fiber length of the above splittable conjugate fiber or polyolefin-based adhesive fiber is not particularly limited,
Fibers having a fiber length of 5 to 60 mm can be preferably used.

The fiber web is formed from the fibers as described above. Examples of the method for forming the fiber web include a dry method and a wet method such as a card method and an air lay method. In the case of forming a fibrous web by the card method, the orientation direction of the fibers can be easily made into one direction, and the bending resistance in the length direction of the obtained separator can be increased, so that a preferable fibrous web is formed. Is the way.

Then, by hydroentangling the fiber web, the orientation direction of the fibers becomes substantially the thickness direction of the non-woven fabric, so that it is possible to resist the pressure between the electrode plates when assembling the battery. Moreover, like a secondary battery, it can withstand the pressure due to the expansion of the electrode plate due to charging and discharging,
It becomes a separator with excellent liquid retention. Further, the separator of the present invention is not only excellent in bending resistance and strength, but also thin, because the ultrafine fibers obtained by dividing the splittable conjugate fiber are densely entangled, and it can be made thinner. Since a large amount of active material can be filled in the battery, the battery has a feature that the battery capacity can be increased. Furthermore, since the oil agent attached to the fibers can be washed away by the water entanglement, not only the adverse effect of the oil agent on the battery performance can be eliminated, but also the below-described vinyl monomer graft polymerization can be efficiently and stably performed. it can.

The water entanglement is, for example, one row with a nozzle diameter of 0.05 to 0.3 mm, preferably 0.08 to 0.2 mm, a pitch of 0.2 to 3 mm, and preferably 0.4 to 2 mm. Nozzle plate arranged in 2 or more, or a nozzle plate in which nozzles are arranged in two or more rows, water pressure is 10 to 300 kg / cm ² , preferably 5
Treat with a water flow of 0-200 kg / cm ² . Such a hydroentangling treatment does not have to be performed once, and is performed twice or more if necessary. Further, the water flow treated surface is one side or both sides of the fiber web. If the support such as a net or mesh that supports the fibrous web at the time of hydroentangling has large holes, the resulting separator also has large holes, and short circuits easily occur. It is more preferable to use a plain weave net having a fine mesh or more, or a perforated plate having a hole distance of 0.4 mm or less.

The hydroentangled nonwoven fabric thus obtained is composed mainly of fine ultrafine fibers having a fiber diameter of 0.01 to 6 μm, but has a bending resistance of at least one direction of 5
It has more than mgf. When the fiber web contains polyolefin-based adhesive fibers, after the hydroentanglement, only the polyolefin-based adhesive fibers can be bonded by heat treatment to further increase the bending resistance.

Next, by graft-polymerizing a vinyl monomer on this hydroentangled nonwoven fabric, liquid retention is enhanced and at the same time bending resistance is enhanced. As the vinyl monomer, for example, acrylic acid, methacrylic acid, and salts thereof, acrylic acid ester, methacrylic acid ester, polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, vinyl pyridine, vinyl pyrrolidone, or styrene may be used. it can. Among these, acrylic acid can be preferably used because it has excellent affinity with the electrolytic solution. When styrene is graft-polymerized, it is sulfonated in order to have an affinity with the electrolytic solution.

The method for polymerizing these vinyl monomers is, for example, a method in which the hydroentangled nonwoven fabric is immersed in a solution containing the vinyl monomer and a polymerization initiator and heated, or the vinyl monomer is applied to the hydroentangled nonwoven fabric and then irradiated with radiation. There is a method of irradiating the hydroentangled nonwoven fabric with radiation and then contacting it with a vinyl monomer, a method of impregnating the hydroentangled nonwoven fabric with a vinyl monomer solution containing a sensitizer, and then irradiating it with ultraviolet rays. Among these, a method of irradiating with ultraviolet rays after impregnating a hydroentangled nonwoven fabric with a vinyl monomer solution containing a sensitizer is a preferable method because the graft polymerization can be performed without lowering the strength of the fiber. Incidentally, before contacting the vinyl monomer solution and the hydroentangled nonwoven fabric, by treating the surface of the hydroentangled nonwoven fabric with ultraviolet irradiation, corona discharge, plasma discharge, etc., the affinity with the vinyl monomer solution becomes high, and more It has the feature that it can be efficiently graft-polymerized.

Graft polymerization of this vinyl monomer is carried out until the water-entangled nonwoven fabric has a bending resistance of at least one direction of 20 mgf or more, more preferably 25 mgf or more. In the case of a hydroentangled nonwoven fabric having a basis weight of about 45 to 65 g / m ² as in the present invention, if the graft ratio of the vinyl monomer is 8% or more, the bending resistance in at least one direction is 20 mgf or more,
A separator having a uniform liquid retaining property can be obtained.
On the other hand, the graft ratio is preferably 30% or less, more preferably 10 to 20% so that the grafted vinyl monomer is not decomposed by the electrolytic solution and from the viewpoint of cost. The graft ratio is a value obtained by the following formula.

The bending resistance of the present invention is JIS 1018.
^{-1990 The} value measured according to 6.21.1 (Gurley method). The separator to be measured is 1/2 inch long,
A width of 1 inch was used.

The separator of the present invention preferably has a liquid retention under pressure of 20% or more, which indicates the liquid retention.
The pressurized liquid retention rate is a value obtained as follows. First, the separator is allowed to reach water equilibrium under the conditions of a temperature of 20 ° C. and a relative humidity of 65%, and then the weight (W ₀ ) is measured.
Next, so that the air in the separator is replaced with a potassium hydroxide solution, the separator is immersed in a potassium hydroxide solution having a specific gravity of 1.3 (20 ° C.) for 1 hour to hold the potassium hydroxide solution. Then, this separator is sandwiched between upper and lower three filter papers (diameter 30 mm), and a pressure pump applies a pressure of 58 kg / cm ² for 30 seconds, and then the separator weight (W ₁ ).
The value calculated from the following formula when measuring is referred to as the pressurized liquid retention rate. This measurement is 4 for one separator.
It is repeated, and the average is taken as the pressurized liquid retention rate. Liquid retention under pressure (%) = [(W ₁ −W ₀ ) / W ₀ ] × 100

If the separator has a graft rate of 10 to 30%, it has a liquid absorption rate of 30 mm / 30 minutes or more,
No problem occurs in battery production, but graft ratio is 5 to 1
If it is a separator of about 0%, it may take too much time in the process of injecting the electrolytic solution, resulting in poor efficiency.
After the graft polymerization, it is preferable to perform discharge treatment such as corona discharge or plasma discharge so that the liquid absorption rate becomes 30 mm / 30 minutes or more. This liquid absorption speed is 2 cm for the separator,
Cut it to a length of 180 cm, and immerse one end of this separator in a potassium hydroxide aqueous solution with a specific gravity of 1.3 to 0.5 cm,
It is a value obtained by measuring the height of the liquid after the lapse of minutes.

Further, the unit weight and thickness of the separator of the present invention are not limited, but when used for a small alkaline secondary battery, for example, when the unit weight is too small and too thin, the pore size formed becomes large, Short circuit is likely to occur, and conversely, if the fabric weight is large and the thickness is too thick, it is difficult to obtain a battery having a large battery capacity. Therefore, the fabric weight is 50 to 80 g / m ² , and the thickness is 0.10.
It is preferably about 0.20 mm. Therefore, the thickness may be adjusted with a calendar or the like.

The separator of the present invention obtained as described above is excellent in electrolytic solution resistance and oxidation resistance, so that a short circuit does not occur, and in addition, it is excellent in liquid retention, so that it can be used for a long period of time. It can be used. Therefore, the separator of the present invention, for example, alkaline manganese battery, mercury battery,
It can be suitably used for primary batteries such as silver oxide batteries and air batteries, and for secondary batteries such as nickel-cadmium batteries, silver-zinc batteries, silver-cadmium batteries, nickel-zinc batteries and nickel-hydrogen batteries.

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

[0026]

【Example】

(Example 1) As a splittable conjugate fiber, a polypropylene component (symbol 2 in the figure, circular polypropylene component: 2.5 μm, wedge-shaped polypropylene component: 4.3 μm) as shown in FIG. 1C was used. A card machine was used to open 100% dividable composite fibers with a chrysanthemum-shaped cross-section, a fine denier of 2 denier and a fiber length of 38 mm, consisting of a high-density polyethylene component (symbols 1, 4.2 μm in the figure, melting point: 138 ° C.) A unidirectional fiber web having a basis weight of 55 g / m ² was obtained. This fiber web is placed on a plain weave net of 80 mesh and the nozzle diameter is
13mm, pitch 0.6mm nozzle plate water pressure 13
After ejecting a water stream of 0 kg / cm ² twice and then reversing it, eject a similar water stream twice to obtain a bending resistance of 13 in the longitudinal direction.
A hydroentangled nonwoven fabric of mgf was obtained. Next, after impregnating this hydro-entangled nonwoven fabric with an aqueous solution of acrylic acid monomer having the following composition, it was placed in a polypropylene bag and sealed under deoxidizing conditions.
2 watts of high pressure mercury lamps are used, 184.9 nm
And low-wavelength ultraviolet light around 253.7 nm were irradiated from a distance of 15 cm for 1 minute to graft-polymerize acrylic acid. The hydroentangled non-woven fabric obtained by the graft polymerization is subjected to linear pressure of 80
Calendered at kg / cm, weight 65g / m ² , thickness 0.1
3 mm, bending resistance in the length direction 27 mgf, liquid retention under pressure of 40%,
A separator having a liquid absorption rate of 150 mm / 30 minutes was obtained. The graft ratio of this separator was 15%. Note (blending of acrylic acid monomer aqueous solution, wt%) Acrylic acid monomer ・ ・ ・ 20.0 Water ・ ・ ・ 76.7 Benzophenone ・ ・ ・ 0.2 Nonionic surfactant ・ ・ ・ 3.0 Ferrous sulfate・ ・ ・ 0.1

(Example 2) Same as in Example 1, 80% by weight of splittable composite fiber having a fineness of 2 denier and a fiber length of 38 mm, polypropylene having a fiber diameter of 17.5 μm and a fiber length of 51 mm (core component) -low density polyethylene (Sheath component, melting point: 120 ° C)
20% by weight of the composite adhesive fiber was mixed, and after hydroentangling, heat treatment was performed at 125 ° C. to fuse only the low-density polyethylene component to obtain a hydroentangled nonwoven fabric having a bending resistance of 16 mgf in the length direction. The same as Example 1 except that the weight was 65 g / m ² , areal weight 0.13 mm, lengthwise bending resistance 35 mgf, pressurized liquid retention 38%, liquid absorption rate 140 mm / 30 min. To obtain a separator. The graft ratio of this separator is 15
%Met.

(Example 3) A splittable conjugate fiber 8 made of the same resin composition as in Example 1 and having a fineness of 2 denier and a fiber length of 5 mm.
Example 2 except that a fiber web was formed by a wet method from 0% by weight and 20% by weight of a composite adhesive fiber having the same resin composition as in Example 2 and having a fiber diameter of 17.5 denier and a fiber length of 10 mm. In exactly the same manner, a basis weight of 65 g / m ² , a thickness of 0.13 mm, a longitudinal bending resistance of 33 mgf, and a liquid retention under pressure of 38.
%, And a liquid absorption speed of 140 mm / 30 minutes was obtained. The graft ratio of this separator was 15%, and the bending resistance in the lengthwise direction of the hydroentangled nonwoven fabric was 16 mgf.

(Comparative Example 1) The irradiation time of low wavelength ultraviolet rays was set to 1
Just as in Example 1, except that the time was 5 seconds, the fabric weight was 65 g / m ² , the thickness was 0.13 mm, and the bending resistance in the longitudinal direction was 13 mg.
f, a pressure-holding liquid retention rate of 18% and a liquid absorption rate of 0 mm / 30 minutes were obtained. The graft ratio of this separator was 3%.

(Comparative Example 2) Fiber diameter 9 μm, fiber length 38 mm
80% by weight of polypropylene fiber, fiber diameter 15 μm,
Polypropylene (core component) -low density polyethylene (sheath component, melting point: 120 ° C.) composite adhesive fiber 20 having a fiber length of 38 mm
A unidirectional fiber web opened by a carding machine was used for heat treatment at a temperature of 125 ° C. to obtain a non-woven fabric fused with the low melting point polyethylene component of the composite adhesive fiber. Then
Graft polymerization of an acrylic acid monomer and calendering were carried out in the same manner as in Example 1 to give a weight per unit area of 65 g / m ² , a thickness of 0.13 mm, a bending resistance in the length direction of 52 mgf, and a pressure retention rate of 28.
%, A separator having a liquid absorption rate of 10 mm / 30 minutes was obtained. The graft ratio of this separator was 15%.

(Battery manufacturing test) As a current collector of an electrode, a paste type nickel positive electrode (33
mm width x 182 mm) and paste type hydrogen storage alloy (33 mm
Width x 247 mm) was created. Next, 35 mm width x 41
Each of the separators of Examples 1 to 3 and Comparative Examples 1 and 2 cut to 0 mm was sandwiched between a positive electrode and a negative electrode, and wound by a winder to obtain a SC-type spiral electrode group of 100.
I made it one by one. Then, the resistance between the positive electrode and the negative electrode of this electrode group was measured, and those having a resistance of 500 kΩ or less were determined to be a short circuit defect, and the defect rate of each separator was calculated. The results are shown in Table 1, and the separator of the present invention was excellent with a defective rate of 0%. When the defective electrode groups of Comparative Example 1 and Comparative Example 2 were disassembled and observed, the separator of Comparative Example 1 was laterally displaced and was caught in a wrinkled state to cause a short circuit, and the separator of Comparative Example 2 was formed. It was expected that this was a short circuit due to the large pore size. In addition, Examples 1-3
Table 1 also shows the results of measuring the average pore size of the separators of Comparative Examples 1 and 2 with a pore size distribution measuring device (manufactured by Coulter Electronics Co.).

[0032]

[Table 1]

[0033]

The alkaline battery separator of the present invention comprises:
A fiber diameter of 0.1 was obtained by splitting a polyolefin-based splittable conjugate fiber in which polyethylene and polypropylene were combined .
01-6 μm polyethylene ultrafine fibers and polypropylene
Since it is made of a hydroentangled non-woven fabric containing ultrafine fibers and having a vinyl monomer graft-polymerized to the polyolefin-based ultrafine fibers to have a bending resistance of 20 mgf or more in at least one direction, it has excellent liquid retention and a battery. It is also excellent in manufacturing workability.

[Brief description of drawings]

FIG. 1 (a) is a schematic sectional view of a splittable conjugate fiber of the present invention (b) is a schematic sectional view of another splittable conjugate fiber of the present invention (c) is another splittable conjugate fiber of the present invention (D) A schematic cross-sectional view of another splittable conjugate fiber of the present invention (e) A schematic cross-sectional view of another splittable conjugate fiber of the present invention

[Explanation of symbols]

1 one component 2 Other ingredients

─────────────────────────────────────────────────── --- Continuation of the front page (56) References JP-A-7-29561 (JP, A) JP-A-6-196141 (JP, A) JP-A-4-323286 (JP, A) JP-A-5- 182654 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01M 2/16 D04H 1/42 D04H 1/46

Claims (3)

(57) [Claims] 1. A combination of polyethylene and polypropylene
Obtained by dividing the combined polyolefin dividable composite fibers, polyethylene ultrafine fiber and port fiber diameter 0.01~6μm
A separator for an alkaline battery, which comprises a hydroentangled nonwoven fabric containing re-propylene ultrafine fibers and having a vinyl monomer graft-polymerized to the ultrafine fibers and having a bending resistance of at least 20 mgf in at least one direction. 2. A polyolefin containing adhesive fiber.
High density of polyethylene that composes the splittable bicomponent fiber
Made of polyethylene, the adhesive component of the adhesive fiber is a low-density
2. The resin according to claim 1, which is made of polyethylene.
Lucari battery separator. 3. The alkaline battery separator according to claim 1, wherein the vinyl monomer contains acrylic acid as a main component.