JPH05325932A - Separator for alkaline secondary battery and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a separator for an alkaline secondary battery, having uniform composition and sufficient rigidity in the roll-up direction, and its manufacturing method. CONSTITUTION:A separator for an alkaline secondary battery is made by using a nonwoven fabric consisting of constitutive fibers of fiber orientation of 1.2 or more by microwave measurement which are composed of fibers materially continued of mean diameter of 15mum or less. The manufacturing method is make up of a process for extending a fiber sheet obtained by the spunbond method in one direction and a process for entangling or bonding the constitutive fibers of the fiber sheet together.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a separator used in alkaline secondary batteries, particularly nickel cadmium secondary batteries.

[0002]

2. Description of the Related Art Conventionally, as a separator for an alkaline secondary battery, a non-woven fabric has been used in which sheets made of fibers such as polyamide such as nylon 6, nylon 66 and polypropylene are bonded by thermocompression bonding or, if necessary, a binder. .. The characteristics required of these alkaline secondary battery separators are that they are highly lyophilic with the electrolyte solution and that they are stable to the strong alkali that is the electrolyte solution.
In addition to having good air permeability, increasing the electrode area, and being thin and highly uniform to prevent local increase in charge and discharge current, especially the direction of entrainment to which strong force is applied during assembly. On the other hand, it has a strength that does not cause damage during assembly.

Among these, as means for preventing breakage of the separator, which is particularly likely to occur at the end of the winding start, during assembly by the winding process, JP-A-50-1115.
Japanese Patent Laid-Open No. 45-45 proposes a method in which one end of the separator is impregnated with a resin and then dried to partially reinforce the separator, and the processing portion is processed as a winding start. However, according to this method, it is inevitable that the air permeability of the resin-impregnated portion of the non-woven fabric is reduced, and there is a problem that the impregnated resin component is eluted into the electrolytic solution.

As another method for preventing breakage of the separator during assembly, Japanese Patent Laid-Open No. 63-81763 discloses a fiber having the same composition ratio as the first web mat layer in which fibers are randomly arranged. There is described a method of imparting strength in the winding direction by heating and fusing a second web mat layer in which the above are arranged in parallel. However, this method also has a problem in uniformity of the obtained sheet and handling property such that unevenness is likely to occur because the basis weight of each web mat layer to be laminated is small and wrinkles are likely to occur during lamination. In addition to the above, there is also a problem that it becomes difficult to continuously perform a series of steps from forming a web to laminating and heat fusing because a new laminating step is required.

[0005]

SUMMARY OF THE INVENTION In view of the above points, the present inventors diligently studied a method for obtaining a uniform alkaline secondary battery separator having sufficient strength in the winding direction. As a result, the present invention has been achieved, and an object of the present invention is to easily and efficiently use an alkaline secondary battery that is uniform and has excellent strength in the rolling direction without reducing the effective area of the separator. It is to provide a separator and a manufacturing method thereof.

[0006]

The present invention has the following configuration.

That is, the alkaline secondary battery separator of the present invention is composed of substantially continuous fibers having an average diameter of 15 μm or less and having a fiber orientation degree of 1.2 or more measured by microwave. It is characterized by using a non-woven fabric.

The method for producing a separator for alkaline secondary batteries of the present invention comprises a step of unidirectionally stretching a fiber sheet obtained by the spunbond method and a step of entangled or bonded the constituent fibers of the fiber sheet. It is characterized by becoming.

[0009]

According to the present invention, the use of a non-woven fabric sheet composed of substantially continuous fibers having an average diameter of 15 μm or less and having a fiber orientation degree of 1.2 or more by microwave measurement makes it possible to obtain a uniform The present invention realizes an alkaline secondary battery separator which is excellent in strength in one direction and is less likely to be broken during the winding process. Hereinafter, the alkaline secondary battery separator of the present invention will be described in more detail.

The alkaline secondary battery separator of the present invention has a strong fiber orientation in one direction, and the orientation of the fibers can withstand the tension during winding and prevent breakage and short circuit. Is.

In order to exert sufficient strength in the winding direction, the fibers constituting the alkaline secondary battery separator are substantially continuous, and the degree of orientation by microwave measurement is 1.2. The above is important, and it is preferable that the degree of orientation measured by microwave is 1.4 or more. Here, the degree of orientation measured by microwaves means that the fiber sheet is irradiated with microwaves that are linearly polarized from a direction perpendicular to the fiber sheet, and when the polarization direction is changed, the intensity of the microwaves that pass through the sheet. Is represented by the ratio of the amount of microwave transmission when it becomes maximum and when it becomes minimum, and the amount of microwave transmission is specifically measured by a MOA-2001A type molecular orientation meter manufactured by KS Systems Co., Ltd. Can be measured.

When the fibers constituting the fiber sheet are not substantially continuous, that is, when a non-woven fiber sheet composed of staples having a fiber length of several centimeters, which is usually used, is used, the fibers easily slip through, In order to prevent breakage and elongation due to slipping of such fibers,
If a large amount of adhesive is used or if the adhesive is used for fusion, it is necessary to increase the adhesion area, which is not preferable because it causes a decrease in the air flow rate.

In the present invention, the non-woven fabric sheet is thin without causing unevenness, particularly a portion having a locally low fiber density,
To obtain a strong non-woven fiber sheet, diameter 15
It is necessary to use fine fibers having a diameter of 12 μm or less, and it is more preferable to use fibers having a diameter of 12 μm or less. The basis weight of the sheet may be appropriately selected together with the fiber diameter so as to satisfy the desired sheet thickness and air permeability, and for example, a fiber having a diameter of 12 μm is used and is 35 to 45 c.
Thickness of about 0.16 with an air flow rate of c / cm ² · min
40 g is preferable for obtaining a sheet of about mm
/ M ^{2 to} 50 g / m ² . Thus, in order to keep the thickness below a certain level, it is necessary to use thin fibers having a diameter of 15 μm or less.

In order for the obtained fiber sheet to be favorably used as a separator for alkaline secondary batteries, the air permeability of the sheet should be 30 cc / cm ² · min or more and the thickness should be 0.2 mm or less. More preferably, the air flow rate is 40 cc / cm ² · min or more, and the thickness is 0.15 mm or less.

In order that the obtained fiber sheet does not cause breakage during rolling and partial reduction in fiber density due to elongation, the fiber sheet preferably has high strength, especially at low elongation. % Stretched strength is 0.7
It is preferably at least kg / cm, and more preferably at least 1 kg / cm.

As a material used for the non-woven fabric sheet constituting the alkaline secondary battery separator of the present invention, a fiber material having excellent alkali resistance such as polyamide such as nylon 6, nylon 66, polypropylene or the like can be used. It can be used alone or mixed with other fiber materials. In particular, mixing and using fibers mainly composed of nylon 6 and nylon 66 not only has excellent alkali resistance and hydrophilicity, but also has a melting point of nylon 6 or more and a melting point of nylon 66 or less after entanglement and stretching. The heat treatment at a temperature is particularly preferable in that strong adhesion and thickness adjustment can be performed at the same time.

As a method for obtaining a sheet composed of substantially continuous fibers constituting the separator for an alkaline secondary battery of the present invention, a spunbond method can be used in terms of strength and uniformity of the obtained fiber sheet. Preferably
The separator for an alkaline secondary battery can be satisfactorily manufactured by subjecting the nonwoven fiber sheet obtained by the spunbond method to a unidirectional stretching step and an entanglement or adhesion step.

More preferably, the fiber sheet obtained by the spunbond method is subjected to preliminary entanglement processing and then stretched in one direction to form the fiber sheet without breaking the fiber sheet. Most of the fibers are oriented in the stretching direction, and then the fibers are entangled or bonded again to fix the orientation of the fibers, thereby making the separator more uniform and excellent in unidirectional strength. Can be obtained.

The entanglement first applied to the fiber sheet obtained by the spunbond method in the present invention is preferably hydroentanglement processing or needle punching processing, but it is difficult to leave punch holes after the entanglement processing and metal The hydroentangling treatment is particularly preferable because contamination of foreign matter is unlikely to occur.
As the strength of the entanglement, when hydroentangling is used as the means of entanglement, the water pressure used is P (kg / cm ² ),
The pitch between nozzles is x (mm), the discharge water amount per nozzle is Q (liter / min.), And the processing speed is v (m).
/ Min. ), Where n is the number of hydroentangling treatments, the strength E of hydroentangling treatment represented by E = PQQn / (vx) is 0.04 to 20.
It is preferably 0, and particularly preferably 0.1 to 10.

When needle punching is used as a means of entanglement, the product of the barb number nb of the needle used and the punch number np per cm ^{2 of} the fiber sheet is 50 to 3
000 is preferable, and further 100 to 100
Particularly preferably 0.

In any case, if the density of the entanglement is lower than the above value, the fibers may easily pass through due to the stretching after the entanglement, which may cause unevenness and breakage of the fiber sheet. It is not preferable because it exists. On the other hand, if the density of the entanglement is higher than the above, the elongation of the sheet decreases, and the orientation of the fibers in the stretching step after the entanglement becomes difficult to occur, which is not preferable.

Prior to being subjected to the entanglement process, the sheet may be optionally subjected to preliminary thermal bonding for the purpose of improving process passability.

The stretching after the pre-entanglement is usually carried out by applying tension in the traveling direction of the fiber sheet to the fiber sheet between rolls nipping the fiber sheet. It can also be performed by applying tension in a direction other than the traveling direction. The draw ratio at this time depends on the strength of the pre-entanglement, but usually 1.1 to 2 times, preferably 1.2 to 1.5 times, a good oriented fiber sheet can be obtained. If the stretching ratio is too small, the orientation of the fibers is not sufficient, and if the stretching ratio is too high, unevenness is increased and the sheet is broken, which is not preferable. When the fiber sheet is stretched, it is possible to take measures to prevent the reduction of the sheet width in the direction perpendicular to the stretching direction.

By the stretching process of the entangled sheet,
Since the fibers are rearranged in the sheet, holes due to the needles formed in the sheet by the entanglement process and striped unevenness caused by the water flow are reduced.

The fibrous sheet in which the fibers have been stretched and oriented has the purpose of stabilizing the oriented structure, or further improving the strength together with stabilizing the oriented structure and adjusting the thickness to a desired value. It is necessary to perform entanglement or adhesion processing again. As the entanglement processing method for this purpose, hydroentanglement processing or needle punching is used, and as the adhesion processing method, a method of passing between heated rolls, application of an adhesive, or the like is usually used for processing a nonwoven fabric. Although various bonding processing methods and the like can be adopted, a method of bonding by passing between heated rolls is preferable because adjustment to a desired thickness can be performed at the same time.

[0026]

【Example】

Example 1 Average fiber diameter 10.3 obtained by spunbond method
A sheet made of nylon 6 fiber having a weight of 45 m / m ² and a basis weight of 45 g / m ² was pre-press-bonded between rolls having a linear pressure of 2 kg / cm at 130 ° C., a water pressure of 40 kg / cm ² , and a pitch between nozzles of 1
0 mm, discharge water amount per nozzle 0.1 (liter / min.), Processing speed 1 m / min. The entangled sheet was obtained by performing the hydroentangling treatment four times under the conditions of. The obtained sheet was stretched 1.3 times, dried, and pressed between rolls heated to 150 ° C. to obtain a sheet having a thickness of 0.16 mm. The degree of orientation of the fibers constituting the obtained sheet by microwave measurement is
It was 1.91. The strength of the obtained sheet at 20% stretching is 8.1 kg / 5 cm, which is excellent in uniformity,
It could be favorably used as a separator for alkaline secondary batteries.

Example 2 Average fiber diameter 12 μm obtained by spunbond method
m, basis weight 50 g / m ² , nylon 6 fiber and nylon 6
A sheet having a mixing ratio of 6 fibers of 30:70 was pre-pressed between rolls having a linear pressure of 2 kg / cm at 130 ° C., and then a water pressure of 50.
kg / cm ² , pitch between nozzles 10 mm, discharge water amount per nozzle 0.11 (liter / min.), processing speed 4 m / min. The entangled sheet was obtained by performing the hydroentangling treatment four times under the conditions of. The obtained sheet was stretched 1.2 times, dried, and pressed between rolls heated to 225 ° C. to give a thickness of 0.17.
A sheet of mm was obtained. The degree of orientation of the fibers constituting the obtained sheet by microwave measurement was 1.46. The strength of the obtained sheet at 20% stretching is 6.5 kg /
cm, excellent in uniformity, and could be favorably used as a separator for alkaline secondary batteries.

Comparative Example 1 A sheet having a thickness of 0.16 mm was obtained by drying an entangled sheet obtained by the same method as in Example 1 above without stretching and pressing between rolls heated to 150 ° C. Got The degree of orientation of the fibers constituting the obtained sheet by microwave measurement was 1.0, and the strength at 20% stretching was as low as 3.1 kg / 5 cm. In addition, striped unevenness (unevenness of thickness) caused by water flow during hydroentangling remained on the obtained sheet, and it was not suitable for use as a separator for alkaline secondary batteries.

[0029]

The separator for an alkaline secondary battery of the present invention is a good one in which the end portion is not damaged at the time of assembly by the winding process and the air permeability is not impaired.

In addition, according to the method for producing a separator for an alkaline secondary battery of the present invention, there is no need to carry out lamination processing, and the effective area as a separator is not reduced by applying an adhesive agent, etc. Alkali 2 with uniform and excellent strength in the winding direction
A secondary battery separator can be manufactured.

Claims (8)

[Claims] 1. An alkali comprising a non-woven fabric composed of constituent fibers having an average diameter of 15 μm or less and being substantially continuous, and having a fiber orientation degree of 1.2 or more measured by microwaves. Secondary battery separator. 2. An average thickness of 0.2 mm or less and an air flow rate of 30.
The alkaline secondary battery separator according to claim 1, which has a cc / cm ² · min or more. 3. The separator for an alkaline secondary battery according to claim 2, which has a strength at 20% stretching of 0.7 kg / cm or more. 4. The separator for an alkaline secondary battery according to claim 1, which contains polyamide as a main component. 5. The separator for an alkaline secondary battery according to claim 1, which is a mixed fiber sheet of a fiber containing nylon-6 as a main component and a fiber containing nylon-66 as a main component. 6. A process for producing a separator for an alkaline secondary battery, which comprises a step of unidirectionally stretching a fiber sheet obtained by a spunbond method and a step of entangled or bonded constituent fibers of the fiber sheet. Method. 7. The method for producing a separator for an alkaline secondary battery according to claim 6, wherein the process of entangling the constituent fibers of the fiber sheet is a hydroentangling process. 8. The method for producing an alkaline secondary battery separator according to claim 5, wherein the process of adhering the constituent fibers of the fiber sheet is a heat-bonding process.