JP3142693B2 - Battery separator and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel battery separator and a method for producing the same. More specifically, a novel battery separator having good air permeability, excellent thermal oxidation resistance, and excellent mechanical properties, and suitable for use in alkaline batteries, particularly, high-speed rechargeable nickel-cadmium batteries, and producing the same. It is about the method.

[0002]

2. Description of the Related Art Generally, a battery separator is a porous sheet, is not eroded by an electrolyte, is easily permeable to gases and ions, and absorbs an electrolyte in a sealed battery. It is required to have a high holding ability. Further, in the production of the battery, the separator is required to be uniform in thickness and as thin as possible. Further, from the viewpoint of workability of the separator, it is desired that the separator has sufficient mechanical properties such as strength and strength.

For this reason, in recent years, a dry nonwoven fabric made of synthetic fibers which is rich in air permeability and impregnation and has the required mechanical properties has been used as a battery separator (for example, Japanese Patent Application Laid-Open No. Sho 52-3120). No., JP-A-63-108
664, JP-A-63-108665 and JP-A-4-56062). However, it is difficult for such a dry nonwoven fabric to have a uniform thickness, and in particular, it is very difficult to reduce the thickness uniformly. Further, the dry nonwoven fabric is rich in impregnation, but it is not always sufficient in liquid retention.

At present, battery separators mainly used are dry nonwoven fabrics made of aliphatic polyamides such as nylon 6 and polyolefins such as polypropylene, but these have poor heat and oxidation resistance. When the temperature becomes high, oxidative decomposition occurs. As a result, a short circuit occurs due to so-called dendride, which causes a problem that the life characteristics of the battery deteriorate.

As a means for solving such a problem found in conventional battery separators, the present inventors have proposed a paper-like sheet prepared by mixing m-aramid fibrid and m-aramid short fiber first. Consisting of 0.01 to 0.
A 1 mm thin battery separator was proposed.

This separator does not have the drawbacks of conventional dry nonwoven fabrics, is excellent in liquid retention, and has good thermal oxidation resistance. However, if the thickness is increased to increase the strength, the air permeability decreases. A material satisfying both thickness, air permeability, and strength (strong) cannot be obtained at the same time, and its use is limited to ion secondary batteries and the like.

[0007]

The functions required for a separator for an alkaline battery, particularly for a nickel-cadmium battery, include a sufficient thickness for electrically isolating the positive electrode and the negative electrode, and oxygen gas generated from the positive electrode during overcharge. The air permeability required for passing through and good thermal oxidation resistance can be given. In addition, mechanical properties such as strength and strength that can withstand the battery assembly process are also required. In particular, considering fast charging,
The thermal oxidation resistance of the separator is required more than ever.

The present invention provides a novel battery separator suitable for alkaline batteries, which simultaneously satisfies the thickness, air permeability, strength, etc., and is excellent in thermal oxidation resistance, liquid retention, impregnation, etc. What you want to do.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, a paper-like sheet obtained by mixing m-aramid fibrids and m-aramid short fibers has been produced. A battery separator having a sufficient thickness and excellent thermal oxidation resistance, air permeability, and mechanical properties by laminating and sandwiching between m-aramid long-fiber nonwoven sheets and hot-pressing this. And reached the present invention.

That is, according to the present invention, the surface layer (A) composed of the non-woven sheet of m-aramid long fiber and the intermediate layer (B) composed of a mixture of m-aramid fibrid and m-aramid short fiber, A battery comprising a laminated structure laminated and integrated such that an intermediate layer portion (B) is present between a surface layer portion (A) and a thickness of 0.1 to 0.3 mm. The present invention relates to a separator for batteries, particularly a battery separator characterized in that the air permeability measured by a Frazier-type air permeability tester is 10 ml / cm ² · sec or more.

Hereinafter, the battery separator of the present invention will be described in detail.

The separator of the present invention is a mixture of m-aramid fibrids and m-aramid short fibers, preferably a paper-like paper mixed and formed by a wet method, in the surface layer (A) comprising a non-woven sheet of m-aramid long fiber. The intermediate layer portion (B) made of a sheet is sandwiched, that is, each layer is (A) / (B)
/ (A), and is constituted by a sandwich-like non-woven fabric laminated structure that is laminated and hot-pressed and integrated.

As the non-woven sheet of m-aramid long fiber constituting the surface layer (A), a spunlace made of continuous long fiber of m-aramid is suitable. In the present invention, "m-aramid" is a general term for poly-m-phenylene isophthalamide or a copolyamide having m-phenylene isophthalamide as a main repeating unit. Also,
The long fiber is a general term for a substantially continuous fiber or a cut fiber having a relatively large fiber length (for example, 10 cm or more). The “spunlace” is a material in which long fibers are entangled with each other using a high-pressure water jet to form a thin nonwoven fabric, and does not substantially include an adhesive.

In the present invention, in addition to the spun lace,
A long-fiber nonwoven sheet or other long-fiber nonwoven sheet obtained by the tow opening method can also be used.

The non-woven sheet constituting the surface layer (A) has a thickness of 0.1 to 0.3 mm before hot pressing and a basis weight of 1
Approximately 100 g / m ² is preferably used.

On the other hand, the paper-like sheet constituting the intermediate layer (B) is composed of a mixture of m-aramid fibrids and m-aramid short fibers. Where "fibrid"
For example, Japanese Patent Publication No. 35-11851, Japanese Patent Publication No.
It is a paper-pullable synthetic pulp particle obtained by supplying a solution of m-aramid into a stirring aqueous coagulation bath and precipitating it by a method described in JP-A-7-5732.
In addition, m-aramid short fiber, stretch heat treatment m
-Aramid fibers cut to a fiber length of about 3 to 10 mm are used. The thickness of the short fiber is 1-10
de is preferred. The cross section of the short fiber may be a normal circular shape or a flat shape.

The mixing ratio of m-aramid fibrids and m-aramid short fibers in the intermediate layer (B) is preferably 5/95 to 40/60 in terms of the fibrid / short fiber weight ratio.

In the intermediate layer (B), the basis weight of m-aramid fibrids is preferably 1.0 to 5.0 g / m ² , and the basis weight of m-aramid short fibers is suitably 5.0 to 30 g / m ^2. It is.

In the battery separator of the present invention, the surface layer (A) and the intermediate layer (B) as described above are formed by (A) / (B) /
By laminating and hot-pressing as in (A), that is, joining and integrating without using an adhesive, the overall thickness is adjusted to 0.1 to 0.3 mm.

This battery separator has an air permeability of 10 ml / cm ² measured by a Frazier-type air permeability tester.
-It is larger than sec and has very good air permeability.

Here, the air permeability was measured using a Frazier-type air permeability tester, and the surface differential pressure of the test piece was 12.7 mmAq.
Of the air per unit area and per unit time.

A battery separator suitable for an alkaline battery, particularly a nickel-cadmium battery, which is an object of the present invention, needs to have a thickness of 0.1 to 0.3 mm, and at the same time, has an air permeability of 10 ml / cm. It is desired to be ² · sec or more, and it is required to have sufficient strength to withstand the assembly of the battery. There was no battery separator. However, in the present invention,
By adopting the sandwich structure of (A) / (B) / (A), for the first time, a heat-resistant and oxidizable battery separator that simultaneously satisfies thickness, air permeability, and strength has been realized.

Next, a method for manufacturing the battery separator as described above will be described in detail.

According to the production method of the present invention, an m-aramid long-fiber nonwoven sheet such as spunlace is set on a papermaking wire mesh of a paper machine, and m-aramid fibrid and m-aramid are placed thereon. A diluted slurry in which short fibers are dispersed in water is supplied, and a basis weight of about 1 to 3 is applied to the surface of the long fiber nonwoven sheet.
A 5 g / m ² paper-like sheet was formed, and further covered with a m-aramid long fiber sheet to form a wet paper having a sandwich structure, which was dried to remove moisture, and then calender rolled. By hot pressing, the layers are joined together and the total thickness is 0.1 to 0.3 mm
Adjust to

In this case, m-aramid fibrids and m-aramid fibrids in the aqueous slurry supplied onto the long-fiber nonwoven sheet
The mixing ratio of the aramid short fibers is preferably from 9/95 to 40/60 (weight ratio), and the concentration of m-aramid fibrids in the slurry is preferably from 0.01 to 0.1 (weight)%.

The above-mentioned example is a method in which an aqueous slurry containing m-aramid fibrids and m-aramid short fibers is supplied onto a non-woven sheet of m-aramid long fiber to form a paper-like sheet. Instead of wet papermaking, the above aqueous slurry is sprayed on a long-fiber non-woven sheet, and m-
A mixed layer of aramid fibrid and m-aramid short fiber may be formed.

The hot pressing is performed by passing the laminate between one or a plurality of pairs of calender rolls, under the conditions that the roll surface temperature is 200 to 320 ° C. and the linear pressure is 50 to 400 k.
g / cm is appropriate. At this time, if necessary, a plasticizer (for example, an amide-based solvent or an aqueous solution thereof) may be applied to the laminate by spraying, spraying, or the like before the hot pressing. When the conditions of the hot pressing are out of the above range, it is difficult to achieve both the strength and the air permeability of the separator.

[0028]

According to the present invention as described above, the air permeability is 10 ml / cm ² · sec with a Frazier-type air permeability tester.
Provided is a battery separator which is larger, extremely good, and has excellent thermal oxidation resistance, liquid retention and mechanical properties.

Therefore, this battery separator is particularly useful as a battery separator for an alkaline battery, particularly a nickel-cadmium battery for quick charging.

[0030]

The present invention will be described in more detail with reference to the following examples, which should not be construed as limiting the present invention.

The strength was measured at a width of 15 mm, a chuck interval of 50 mm, and a tensile speed of 50 mm / min.

[0032]

Example 1 Poly-m-phenylene isophthalamide having an intrinsic viscosity of 1.35 obtained by an interfacial polymerization method was prepared by using JP-B-52-15
Fibrid was manufactured using the precipitation apparatus described in JP-A-162, and the freeness of the fibrid was adjusted to 200 ml in Canadian freeness. This fibrid is disclosed in
The treatment was carried out according to the method described in JP-A-35877.

On the other hand, using the same polymer,
Polyde-m-phenylene isophthalamide fiber of 2.0 de was produced according to the method described in JP-A-7551. The fiber had a strength of 5.1 g / de and an elongation at break of 18%. This fiber was used after being cut into short fibers having a length of 6 mm.

On the other hand, poly-m prepared from the same polymer
A spunlace (having a basis weight of 27 g / m ² , a thickness of 0.173 mm, and a gas permeability of 350 ml / m ² ) made of phenylene isophthalamide long fiber was prepared.

The above fibrid and short fiber are mixed in a weight ratio of 1
/ 15 at a concentration of 0.03 (weight)% in water
To make a slurry, and using a tappy type paper machine in which the above-mentioned spunlace is set at the bottom in advance, 250
It was a wet paper having a size of mm × 250 mm. Further, the same kind of spunlace was overlapped on the wet paper, squeezed, and dried sufficiently. Next, this was hot-pressed at a temperature of 300 ° C. and a linear pressure of 200 kg / cm using a calender roll to obtain a laminate having a three-layer structure.

The basis weight of the obtained laminate is 79 g / m^Two, Thickness
Only 0.18mm, air permeability 40ml / cm^Two・ Sec
The strength is 7 kgf / 15 mm and the strength is 2 kgf /
mm ^TwoMet.

This laminate was useful as a separator for an alkaline battery.

[0038]

Example 2 The same fibrid and short fiber as in Example 1 were used, and the weight ratio of fibrid / short fiber was set to 1/15.
A wet paper having a size of 250 mm × 250 mm was obtained. Spunlace was further superimposed on the wet paper, squeezed, and dried sufficiently. Next, N-methyl-2 as a plasticizer
-After spraying an aqueous solution of pyrrolidone (hereinafter abbreviated as NMP solution), calender rolls are used at 300 ° C and a linear pressure of 100
A hot / press working at kg / cm was performed to obtain a laminate having a three-layer structure.

The basis weight of the obtained laminate was 77 g / m ² , the thickness was 0.17 mm, and the air permeability was 15 ml / cm ² · sec.
The strength is 10kgf / 15mm and the strength is 4kgf
/ Mm ² .

This laminate was useful as a separator for an alkaline battery.

[0041]

COMPARATIVE EXAMPLE 1 The same fibrid and short fiber as in Example 1 were used, and the weight ratio of fibrid / short fiber was reduced to 1/15 without using spunlace, and the paper was formed into a sheet of 250 mm × 250 mm.
A wet paper having a size of mm was obtained. The wet paper was squeezed and dried sufficiently, and then hot-pressed with a calender roll at 300 ° C. and a linear pressure of 200 kg / cm. However, the strength was remarkably low, and only an unsuitable battery separator was obtained. Did not.

[0042]

Comparative Example 2 Using only the same fibrid as in Example 1,
The same amount of fibrid as in Example 1 was weighed, and the fibrid was formed on a spunlace in the same manner as in Example 1 to obtain a wet paper. This was sufficiently dried and subjected to the same heat and pressure processing as in Example 1 to obtain a laminate. This has a breathability of 1ml
/ Cm ² · sec or less, which was unsuitable as a battery separator.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-53-58636 (JP, A) JP-A-58-144796 (JP, A) JP-A-53-74571 (JP, A) JP-A-2- 181363 (JP, A) JP-A-52-3120 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 2/14-2/18 H01M 10/24-10/34

Claims (7)

(57) [Claims] 1. A surface layer (A) composed of a nonwoven sheet of m-aramid long fiber and an intermediate layer (B) composed of a mixture of m-aramid fibrid and m-aramid short fiber are composed of a surface layer (A). ), The laminated structure is laminated and integrated such that the intermediate layer portion (B) exists between the laminated structures, and the thickness thereof is 0.1.
A battery separator having a thickness of about 0.3 mm. 2. The battery separator according to claim 1, wherein the air permeability measured by a Frazier-type air permeability tester is 10 ml / cm ² · sec or more. 3. The blend ratio of m-aramid fibrids and m-aramid short fibers in the mixture constituting the intermediate layer portion (B) is from 5/95 to 40/60 (weight ratio). The battery separator according to claim 1. 4. On a m-aramid long fiber nonwoven sheet,
A slurry containing m-aramid fibrids and m-aramid short fibers is supplied to supply m-aramid fibrids and m-aramid fibrids.
A layer consisting of a mixture with aramid short fibers was formed, and a non-woven sheet of m-aramid long fibers was further laminated thereon. After drying, the layers were integrated by hot-pressing, and the air permeability was 10 ml. A method for producing a battery separator, comprising obtaining a laminated structure having a thickness of 0.1 to 0.3 mm larger than / cm ² · sec. 5. The basis weight of m-aramid fibrids in the mixture layer formed on the m-aramid long fiber nonwoven sheet is 1.0 to 5.0 g / m ² , and the basis weight of m-aramid short fibers is 5 method for producing a battery separator according to claim 4, characterized in that the .0~30g / m ^2. 6. A paper-like sheet layer comprising a mixture of m-aramid fibrids and m-aramid short fibers is formed on a non-woven sheet of m-aramid long fiber by a wet papermaking method. Or the manufacturing method of the battery separator of Claim 5. 7. The method for producing a battery separator according to claim 4, wherein the hot pressing is performed at a temperature of 200 to 320 ° C. and a linear pressure of 50 to 400 kg / cm. .