JPH09190810A - Alkaline battery separator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a separator having high electrolyte holding capacity and a function to prevent the transfer of an active material, by aligning a continuous fiber in the plane direction, on the surface or inside a random oriented fiber web having a specific fiber diameter. SOLUTION: A nonwoven fablic sheet 6 used for an alkaline battery separator is a compound of a random printed fiber web having the fiber diameter less than 10μm, and a continuous fiber 5. That is, it is compounded by providing numerous reinforcing continuous fibers 5, on the surface or inside a nonwoven web, in the plane direction of the web, and orienting in the same direction each other. The diameter of the continuous fiber 5 is less than about 80% of the thickness of the separator, and it is preferable to have about 5 to 60μm. It is favorable to include the continuous fiber 5 about 3 to 30wt.% to the nonwoven fabric. Consequently, even through the separator is made thin, the necessary tensile strength can be secured in the manufacturing process of the battery.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a battery separator used in alkaline batteries such as nickel-cadmium batteries, nickel-hydrogen batteries and nickel-zinc batteries.

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for alkaline batteries having a high energy density per unit volume or unit weight as batteries used in portable devices such as mobile phones. Therefore, higher capacity of alkaline batteries is being demanded more and more, and as one of the attempts, insulation of the positive electrode and the negative electrode of the battery in the alkaline battery and the powdery active material dropped from the respective electrodes are used. Attempts have been made to reduce the overall battery volume by reducing the thickness of the separator that is responsible for preventing migration and retaining the electrolytic solution that participates in the battery reaction.

Conventionally, dry process short fiber nonwoven fabrics made of nylon fibers, polypropylene fibers and the like have been used as separators for alkaline secondary batteries. As mentioned above, thinning of the separator is required, and in the conventional short-fiber nonwoven fabric by the dry method, simply reducing the thickness of the non-woven fabric will maintain the amount of electrolyte necessary for a smooth battery reaction. The function to do so (this function is sometimes called liquid retention) cannot be maintained. The short fiber non-woven fabric produced by the dry method usually has a fiber diameter of 10 μm or more, and has a large pore diameter between the fibers, which prevents migration of powdered active material constituting the positive and negative electrodes of the battery. Function (this function is sometimes called a filter function)
There is a problem that the thickness is lowered by making the separator thin.

In order to solve this problem of the short fiber non-woven fabric by the dry method, the diameter of the fibers constituting the separator may be reduced, but the short fibers having a fiber diameter of less than 10 μm are bulky and entangled with each other. Since it is strong, it becomes difficult to loosen the fibers and form a web of uniform thickness,
It has the drawback of becoming a high-cost separator.

As a method for solving these problems, a plurality of polymer nozzles are used in a method of extruding a molten polymer into a high-speed air stream, pulling and thinning the molten polymer and collecting it on a moving screen to form a nonwoven fabric. There has been proposed a method of forming a separator by a melt-blown nonwoven fabric using a melt-blowing method in which a pair of gas slit nozzles that form a high-speed air flow are arranged on both sides of a straight line of the polymer nozzles. Since the meltblown nonwoven fabric is composed of ultrafine fibers, it is possible to increase the porosity, so that it is possible to hold a larger amount of electrolytic solution per unit volume, and it is also possible to reduce the pore diameter between fibers,
The function of preventing the migration of the powdery active material can be ensured even if the separator is made thin, which is effective for solving the above problems.

However, the melt-blown non-woven fabric has a small fiber diameter, and because the fiber is not stretched due to the manufacturing method, the strength of the fiber itself is low, and the non-woven fabric also has low mechanical strength because the fiber orientation is random. . In the process of assembling an alkaline battery, there is a process in which a strip-shaped battery separator is sandwiched between a strip-shaped positive electrode plate and a negative electrode plate, and these are wound in a spiral shape. In this process, tension is applied to the separator in the winding direction, and the separator is cut off. Generally, in order to improve the strength of the non-woven fabric, it is sufficient to increase the basis weight (weight per unit area), but when the thickness of the separator is constant, the increase in the basis weight reduces the porosity inside the separator, Liquid retention, which is important for the performance of battery separators, the speed at which the separator, which affects productivity during battery manufacturing, absorbs the electrolyte (absorption speed), and the function that smoothly transfers oxygen gas generated at the positive electrode to the negative electrode during battery charging (This function is sometimes called breathability).

In order to solve the drawback of insufficient strength of this meltblown nonwoven fabric, Japanese Patent Laid-Open No. 61-281454 discloses
Described is a battery separator in which a melt blown web having a short fiber diameter of 0.1 to 2 μm and a high-strength dry non-woven fabric of fibers having a diameter of 5 μm or more are laminated and integrated by jetting high-pressure water. In this method, the fine fibers of the meltblown web increase the porosity, and aim at the effect of reducing the pore size between the fibers, by the injection of high-pressure water,
The thin fibers of the meltblown web are entwined with the thick fibers of the dry-type non-woven fabric so as to be bonded to each other, so that the strength required for the battery separator is exhibited. In addition to battery separators, high strength non-woven fabrics such as spunbonded non-woven fabrics (fibers are stretched and fiber diameters are large, so fiber itself is large) for the purpose of improving the strength of melt blown webs. Are being pasted together.

[0008]

As described above, the alkaline battery separator requires mechanical strength in the winding direction during the winding process during battery production. However, the method described in JP-A-61-281454 has been described above. Also, in the method of laminating the spunbonded nonwoven fabric and the meltblown web, a dry nonwoven fabric or a spunbonded nonwoven fabric is used as a reinforcing fiber for the purpose of improving the strength. Features such as high porosity and small pore size are lost.

Therefore, the present invention provides an alkaline battery separator which has a high electrolytic solution holding capacity and a function of preventing the migration of the active material, which corresponds to the thinning of the separator, and which maintains the strength required in the battery manufacturing process. The purpose is to do.

[0010]

That is, the present invention provides 10
In an alkaline battery separator comprising a non-woven fabric containing a randomly oriented fiber web having a fiber diameter of less than or equal to μm, continuous fibers are arranged on the surface or inside of the web in a plane direction of the web and in the same direction. It is a featured alkaline battery separator.

The fibers of the randomly oriented fibrous web used in the present invention can secure the amount of the electrolytic solution necessary for the battery reaction even if the separator is made thin, and transfer of the powdery active material constituting the positive and negative electrodes of the battery. In order not to impair the function to prevent
Since it is necessary to increase the porosity in the web and reduce the pore diameter between the fibers, the diameter of the fibers constituting a normal dry nonwoven fabric is 10 or less.
It must be finer than fibers above 10 μm and less than 10 μm in diameter. Depending on the type of alkaline battery in which the separator is used, the liquid retention required for the separator,
Although the characteristics such as insulation performance, air permeability, and mechanical strength are different, the fibers of the randomly oriented fibrous web are usually made of polyamide such as 6 nylon and 6-6 nylon, or only the surface layer of the fiber is sulphone group, carboxyl group, Fibers made of a polyolefin resin such as polypropylene or polyethylene having a hydrophilic group such as a hydroxyl group introduced therein, fibers made of a copolymer of a monomer having a hydrophilic group and an olefin monomer, and having a diameter of 0.5 to 10 μm, more preferably 1 Short fibers having a length of about 0 to 4 μm and a length of about 5 to 50 mm are used.

The randomly oriented fiber web of ultrafine fibers of 10 μm or less used in the present invention is a wet process of fibers such as split fibers and fibrillated fibers obtained by simultaneously extruding a plurality of incompatible polymers from the same nozzle. It can be formed by a method of making paper by the above method, the melt blow method described above, or the like.

The continuous fibers used in the present invention are continuous fibers,
That is, it is a monofilament having a length of about 10 cm or more, preferably a stretched fiber having high mechanical strength. The nonwoven fabric used for the alkaline battery separator of the present invention is a composite of the above randomly oriented fiber web and continuous fibers. The continuous fibers are compounded with the randomly oriented fiber web by arranging a large number of reinforcing continuous fibers on the surface or inside of the web so as to be oriented in the plane direction of the web and in the same direction as each other. A large number of continuous fibers may be kept parallel to each other as they are and may be compounded with the randomly oriented fiber web by arranging them on the surface (one surface or both surfaces) or inside of the randomly oriented fiber web. Or in a state where a plurality of filaments are bundled in parallel (multifilament yarn) with or without a binder, or in a state where a plurality of filaments are bundled in parallel (a yarn) , May be combined. In addition, it is a combination of the above methods, and it is very difficult to handle it alone, and the fiber diameter is small, for example, the diameter is about ten and several μ.
In the case of a continuous fiber of m, dozens to several hundreds of continuous fibers are bundled in parallel, or a plurality of aggregates of continuous fibers obtained by twisting the bundles are parallel to each other. Immediately before being composited with the randomly oriented fiber web in a state of being spaced apart from each other, a large number of continuous fibers can be arranged in parallel with each other by a treatment such as air flow opening to form a composite with the randomly oriented fiber web. This opening prevents the aggregate of continuous fibers from interfering with the absorption of the electrolyte solution because the gap between the closely-closed continuous fibers is narrow and it becomes difficult for the electrolyte solution of the alkaline battery to enter the gap. .

The larger the diameter of the continuous fiber used in the present invention is, the greater the reinforcing effect is. However, if the continuous fiber is too large, the liquid absorption rate in the direction perpendicular to the orientation direction of the continuous fiber is decreased, and thus the thickness of the separator is reduced. It should be 80% or less and preferably has a diameter of 5-60 μm. A more preferable diameter is 10 to 40 μm. If the mixing ratio is too small, the reinforcing effect does not occur. On the contrary, if the mixing ratio is too large, the liquid absorbing speed and the liquid retaining property are deteriorated. A more preferable content is 5 to 20% by weight.

Since the continuous fibers used in the present invention are arranged so as to be oriented in the direction in which tensile strength is required for the separator during battery production, all of the continuous fibers contribute only to the improvement in the strength of the separator nonwoven fabric in that direction, The amount of continuous fibers added as reinforcing fibers can be kept to a minimum, and a highly oriented electrolyte holding function of a randomly oriented web composed of ultrafine fibers having a fiber diameter of 10 μm or less and a positive electrode and a negative electrode of a battery are configured. The function of preventing the migration of the powdery active material is not impaired.

As the material of the continuous fiber used in the present invention, the alkali-resistant organic fiber is suitable as the material of the fiber of the randomly oriented fiber web because the material deterioration in the inside of the battery is small, and it is cheap and easy to process. . For example, 6
Fibers made of polyamides such as nylon and 6-6 nylon, and only the surface layer of the fibers are sulphone groups, carboxyl groups,
Fibers made of a polyolefin resin such as polypropylene or polyethylene having a hydrophilic group such as a hydroxyl group introduced therein, fibers made of a copolymer of a monomer having a hydrophilic group and an olefin monomer, and the like are suitable for the present invention.

The continuous fiber used in the present invention is produced by continuously drawing the above material from the nozzle at the lower end of the melting crucible. Further, for example, in the case of a monofilament yarn or a multifilament yarn of a composite fiber in which the core is polypropylene and the sheath is polyethylene, the polyethylene having a low melting point serves as an adhesive material during the melt heating and bonding described later, which enables more effective bonding.

In the process for producing the alkaline battery separator of the present invention, when the continuous fiber and the randomly oriented fiber web are produced on separate lines, one sheet is used as a method for integrating the continuous fiber and the randomly oriented web. While randomly sandwiching a plurality of continuous fibers arranged at a predetermined interval with a randomly oriented fiber web of a method of impregnating in a binder liquid and drying, or at least one of the randomly oriented web and continuous fibers is a thermoplastic organic fiber. In such a case, a method may be exemplified in which one random orientation web and a plurality of continuous fibers arranged at a predetermined interval are simultaneously sandwiched by a heat roll to carry out partial melt heating and adhesion of the random orientation web and the continuous fibers.

As a method for producing a randomly oriented web used in the present invention, a molten polymer typified by a melt-blowing method is extruded into a high-speed air stream to draw and thin the molten polymer, and the thinned fibers are collected on a moving screen. When adopting a method of obtaining a randomly oriented web by
By producing ultrafine fibers having a fiber diameter of 10 μm or less and forming a web at the same time, and by supplying continuous fibers to the portion of the moving screen where the traction finely divided ultrafine fibers are deposited, a randomly oriented web is obtained. Since continuous fibers can be combined at the same time, the alkaline battery separator of the present invention can be manufactured at low cost.

According to the present invention, even if the thickness is reduced, a high electrolytic solution holding function and a function of preventing the migration of the powdery active material forming the positive electrode and the negative electrode of the battery are maintained, and further, It is possible to configure an alkaline battery separator that secures the required tensile strength during the manufacturing process. In particular, the thickness is 50 μm or more and 150 μm or less (more preferably 80 to 12).
0 μm), the weight per unit area is 20 to 50 g / m ² , and the tensile strength is 0.7 kg / mm ² or more, and an alkaline battery separator can be manufactured at low cost, which can greatly contribute to the improvement of the energy density of the alkaline battery.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to examples. Example 1 Melt flow index (load 2.16 kg, measured at 230 ° C.) 1
A band-shaped nonwoven fabric web (randomly oriented fibrous web) having an average fiber diameter of 3.5 μm and a basis weight of 18 g / m ² and a width of 20 cm was produced by a melt-blowing method using polypropylene of 00 g / min. As shown in FIG. 1, these two webs 1 and 2 are superposed on each other, and a pair of calender rolls (surface temperature 125 ° C.)
When heat fusion molding is performed to pass a space between 3 and 4 to a thickness of 100 μm, a filament made of polypropylene having a fiber diameter of 17 μm and having a fiber diameter of 17 μm between the two webs before entering the calender roll ( About 200 loosely twisted multifilament yarns 5 each consisting of 30 continuous fibers were arranged in parallel at about 1 mm in the flow direction of roll molding.
At this time, the compressed air is blown to the yarn in advance, the bundled filaments are disentangled (opened), and the filaments are arranged and heated and pressed to form the fusion-bonded webs 1 and 2 as shown in FIG. A composite non-woven sheet having a thickness of 100 μm was obtained in which yarns were fused and arranged in the plane direction and the length direction of the non-woven fabric in the center of the band-shaped non-woven fabric 6 in which The above-mentioned filaments were arranged at intervals of 2 mm and 5 mm to obtain two kinds of composite non-woven sheet having a thickness of 100 μm in the same manner.

The average basis weights of the sheets with the arrangement intervals of 1 mm, 2 mm and 5 mm are 42.3, 39.8 and 38.1 g / m ² , respectively, and the tensile strengths in the roll forming flow direction are 1.6 and 1.1 per 1 cm of the sample width, respectively. 0.8kg / cm width (tensile strength kg / m
It was 1.6, 1.1, and 0.8 kg / mm ² ) when converted to m ² . And the pore diameters between the fibers are 6.5, 7.4,
It was 7.7 μm. Further, there was almost no difference in breathability, and although there was a difference in the liquid absorption speed from the non-woven fabric containing no yarn, there was no problem.

Example 2 A nonwoven fabric was produced under the same conditions as in Example 1 except that the basis weight was changed to 36 g / m ² . At this time, the same yarn as above is opened on the net that collects the fibers, and it is placed at intervals of 2 mm in parallel with the moving direction of the net, and the fibers are collected on it to open the yarn. To obtain a composite non-woven fabric. This was molded with a calendar roll under the same conditions as above to obtain a composite non-woven sheet having a thickness of 100 μm. The average basis weight at this time increased to 40.5 g / m ² depending on the weight of the added yarn, and the tensile strength in the flow direction was 1.1 kg / cm width per 1 cm width of the sample (converted to tensile strength kg / mm ² 1.1
kg / mm ² ). In addition, there was almost no difference in the pore diameter between the fibers, the air permeability, and the liquid absorption speed, as compared with the non-woven fabric containing no yarn.

Example 3 A non-woven fabric was produced under the same conditions as in Example 2 and a composite non-woven fabric was obtained by the same method. However, what was put between the non-woven fabrics was a polypropylene monofilament (continuous fiber) having a diameter of 50 μm drawn in place of the yarn, which was placed at 2 mm intervals in the same manner as in Example 2, and a composite of 100 μm thickness was used. A non-woven sheet was obtained.

The average basis weight at this time is 37.8 g / m ² ,
Tensile strength in the flow direction is 0.8 kg per 1 cm of sample width
/ cm width (converted to tensile strength kg / mm ² 0.8kg / mm ² )
Met. The breathability was almost the same as that of the non-woven fabric containing no monofilament. Although the liquid absorption rate was slightly low, there was no problem in practical use.

Comparative Example 1 40 g / m ^{2 under the} same polymer and fiberizing conditions as in Example 1
The non-woven fabric of No. 1 was produced only by the melt blow method, and was formed into a thickness of 100 μm using a calendar roll. The average basis weight at this time was 39.7 g / m ² , and the tensile strength in the flow direction was 0.6 kg / cm width (tensile strength kg / mm ² per 1 cm sample width).
Was 0.6 kg / mm ² ) and the pore diameter between the fibers was 6.2 μm. These results indicate that the pore diameters between the fibers are almost the same as those of the yarn or monofilament mixed product of the example, but the strength is obviously at a low level.

Comparative Example 2 20 g / m under the same polymer and fiberizing conditions as in Example 1.
The non-woven fabric of No. ² is manufactured by the melt blow method, and it is 20 g /
m ² spunbond nonwoven fabric (Mitsui Petrochemical Co., Ltd.,
"Syntex PS-104") and passed between a pair of calender rolls 3 and 4 to have a thickness of 100 μm.
m sheets were heat fusion molded. The tensile strength of this sheet is 1.5 kg / cm width (tensile strength kg /
In in terms of mm ² 1.5kg / mm ^2), pore size between fibers was 20.7Myuemu.

These results show that the strength is as in Example 1.
However, the pore diameter between the fibers was considerably large.

[0029]

EFFECTS OF THE INVENTION The alkaline battery separator of the present invention maintains a high electrolytic solution retaining function and a function of preventing the migration of powdery active materials constituting the positive electrode and the negative electrode of the battery even if the thickness of the separator is reduced. Since the required tensile strength can be secured during the battery manufacturing process, it can contribute to the increase of the energy density of the alkaline battery.

[Brief description of the drawings]

FIG. 1 is a perspective view illustrating production of a separator according to an embodiment of the present invention.

FIG. 2 is a perspective view showing a separator which is an embodiment of the present invention.

[Explanation of symbols]

 1,2--Randomly oriented fiber web 5 ---- Yarn formed by bundling continuous fibers 6 --- Nonwoven fabric sheet

Claims (7)

[Claims] 1. An alkaline battery separator comprising a non-woven fabric containing a randomly oriented fibrous web having a fiber diameter of 10 μm or less, wherein continuous fibers are arranged on the surface or inside of the web in the planar direction of the web and in the same direction. Alkaline battery separator characterized by being made. 2. The alkaline battery separator according to claim 1, wherein the continuous fiber has a fiber diameter of 80% or less of the thickness of the nonwoven fabric. 3. The alkaline battery separator according to claim 2, wherein the continuous fibers have a diameter of 5 to 60 μm. 4. The continuous fibers are 3 to 3 with respect to the nonwoven fabric.
The alkaline battery separator according to claim 1, which contains 30% by weight. 5. The fibrous web obtained by extruding a molten polymer into a high-speed air stream, pulling and finely drawing the molten polymer, and collecting the molten polymer on a moving screen. Alkaline battery separator according to. 6. The non-woven fabric is 10 g / m ² or more, 60 g
/ M ² or less, a thickness of 50 μm or more and 150 μm or less, and a strength of 0.7 kg / mm ² or more in the direction in which the continuous fibers are oriented. Alkaline battery separator. 7. The non-woven fabric has an elongated strip shape, and the continuous fibers are oriented in the longitudinal direction of the non-woven fabric.
~ 6 alkaline battery separator.