JPH0737571A - Battery separator and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a battery separator suited for a sealed type ion secondary battery. CONSTITUTION:A new battery separator, formed of 0.01 to 0.1mm thick paper- shaped object formed by wet making a mixture of 10 to 40wt.% fibrid of m- alamide and 90 to 60wt.% heat resistant short fiber of flat section of 2.0 to 7.0 sectional flatness having ratio of major diameter D1 to minor diameter D2 of a circular section and/or fiber section, is provided. This separator is suitably manufactured by multistage-heat pressure working wet paper, made by mixing the m-alamide fibrid and the heat resistant short fiber with this proportion, in a specific condition.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a novel battery separator and a method for producing the same. More specifically, it has good heat resistance, has a small thickness and excellent physical properties, and also has good liquid retention and gas permeability, and as a separator for small sealed batteries, especially ion secondary batteries. The present invention relates to a suitable battery separator and a method for industrially producing the same.

[0002]

2. Description of the Related Art Conventionally, several types of products have been developed as sheets used as separators for batteries. Among them, recently, nonwoven fabrics made of only synthetic fibers such as polyamide and polyolefin are new ions. It is often used as a separator for secondary batteries.

Generally, a battery separator is a porous sheet, is not attacked by an electrolytic solution, is easily permeated by gas and ions, and in the case of a sealed battery, absorbs and holds the electrolytic solution. High ability is required. Further, in manufacturing a battery, the thickness of the separator is required to be uniform and as thin as possible. Further, from the viewpoint of workability, it is difficult to process by breaking or stretching when pulled, so that it is desired to have appropriate strength and elongation.

Therefore, in recent years, as a battery separator, a synthetic fiber non-woven fabric which is rich in air permeability and impregnating property and which can obtain necessary mechanical characteristics has been used (for example, Japanese Patent Laid-Open No. 63-108664). JP-A-63-108665
(See Japanese Patent Application Laid-Open No. 4-56062).

Such a non-woven fabric is rich in air permeability and impregnation,
This is because it has the advantage that the material can be selected as needed. Incidentally, this non-woven fabric is usually manufactured by a dry method. This is because when a relatively long fiber is used to obtain a nonwoven fabric having high mechanical properties, it is difficult to make it by the wet method.

However, it is difficult to make the thickness of such a dry nonwoven fabric uniform, and it is very difficult to make the thickness uniform. Further, although the dry type nonwoven fabric is rich in impregnation property, it cannot be said that the liquid retention property is necessarily sufficient. For this reason, it is usual that a plurality of thin non-woven fabrics are laminated and used.

[0007]

By the way, as the technological development of batteries progresses, the demands on battery separators have become strict, and in the case of new type batteries such as sealed ion secondary batteries, they are different from conventional ones. Different characteristics are required.

That is, in order to make the battery smaller and have a larger capacity, the separator is required to have an improved liquid holding property so that it can hold a larger amount of the electrolytic solution, and in the case of the ion secondary battery, the electrolytic solution is required. It is required to reduce the thickness of the separator according to the amount. At the same time, in order to deal with heat generation during use of the battery and heat treatment during processing, it is necessary to have high air permeability that is stable even at higher temperatures without being oxidized and that allows ions and gases to easily pass therethrough.

However, it is difficult to say that the conventional dry non-woven fabric battery separators can meet all of these requirements, and in order to obtain a dry non-woven fabric having a uniform thickness, another step such as lamination is required. There is also a problem that the manufacturing cost becomes very high.

[0010]

Means for Solving the Problems As a result of intensive research to solve the above-mentioned problems, the inventors have carried out wet papermaking by mixing m-aramid fibrids and heat-resistant short fibers at a specific ratio as a battery separator. By using a paper-like material with a specific thickness formed by hot pressing, it has excellent heat resistance and liquid retention, high air permeability, and not only has sufficient mechanical properties, it is also thin and uniform. It was found that such a battery separator can be produced stably and efficiently by subjecting the above mixed papermaking paper to hot pressing under special conditions. Reached

That is, the present invention comprises a paper-like sheet obtained by wet-making a mixture of 10 to 40% by weight of m-aramid fibrids and 90 to 60% by weight of heat-resistant short fibers, and has a thickness of 0. The present invention relates to a battery separator comprising a paper-like material having a size of 0.01 to 0.1 mm, preferably 0.02 to 0.05 mm.

The battery separator of the present invention is composed of a thin paper-like material obtained by wet-fabricating a fibrid made of m-aramid and heat-resistant short fibers and subjecting it to hot pressing under specific conditions.

The term "fibrite" as used herein means, for example, as described in JP-B-35-11851, synthetic pulp-like particles obtained by coagulating and precipitating a polymer solution in a precipitant which is being stirred at high speed. The "m-aramid" forming the fibrids is a wholly aromatic polyamide containing m-phenylene isophthalamide as a main constituent unit. The wholly aromatic polyamide is not limited to a homopolymer and may be a copolymer in which a part of the constitutional unit is replaced with p-phenylene terephthalamide.

As the material (polymer) of the fibrids, a hydrophilic polymer having an amino group or a hydroxyl group in the polymer chain or at the terminal is preferable, and the battery tends to become high temperature due to rapid charging, large load capacity, etc. It is preferably heat resistant. The heat resistance as a battery separator is stricter than the heat resistance standard of general polymers, and it is also required that oxidative decomposition due to oxygen or the like substantially generated during charging does not occur. The m-aramid represented by poly-m-phenyleneisophthalamide is a preferable material which meets such requirements.

Fibrids generally have a very large specific surface area as compared with fibers, but the m-aramid fibrids constituting the battery separator of the present invention preferably have a specific surface area of 5 to 100 m ² / g. , Especially 10
It is preferably about 80 m ² / g. If the specific surface area is smaller than this, the water retention is poor, and if it is too large, papermaking becomes difficult. The specific surface area mentioned here is based on the value obtained from the average filtration specific resistance.

In addition to the above-mentioned fibrids, synthetic pulp-like particles include "pulp" in which liquid crystalline p-aramid moldings (fibers or the like) are fibrillated by applying mechanical force such as beating. However, such "pulp" is not suitable for use in the present invention.

As the heat-resistant short fibers mixed with m-aramid fibrids, fibers of m-aramid or p-aramid having good heat resistance are most preferable, and poly-m-phenylene isophthalamide and poly-p-phenylene are preferable. Terephthalamide and poly (p-phenylene terephthalamide /
Heat-resistant aramid short fibers such as 3,4'-diphenyl ether terephthalamide) are particularly suitable, but may be made of other heat-resistant materials, for example, polyether ether ketone (PEEK), polyethylene terephthalate, arylate, cotton. Alternatively, fibers such as ceramics may be used. These fibers can be used in combination of two or more, if necessary. However, it is optimal that the fibrids and the short fibers are made of the same kind of polymer.

In the present invention, in any case, an ordinary circular cross-section fiber may be used as the heat-resistant short fiber, but a flat fiber is preferably used to obtain a sheet having a small thickness. Here, the flat fibers are those having a cross-section flatness represented by the ratio (D ₁ / D ₂ ) of the major axis and the minor axis in the fiber cross section of 2.0 to 7.0, preferably 3.0 to 6.0. It is preferably used.

The cross-sectional shape of the flat fiber is elliptical, oval,
The shape is not limited to a rectangle, and may be, for example, a shape in which a plurality of circles as shown in FIG. When there is a concave portion in the fiber cross section as shown in FIG. 1, the minor axis is defined as D ₂ with the diameter of the thinnest portion.

Naturally, these flat fibers have a larger cross-section perimeter than ordinary circular cross-section fibers.
In the present invention, among the above-mentioned flat fibers, those having a sectional peripheral length ratio α defined by the following formula of 1.4 to 2.0 are preferably used.

[0021]

[Equation 1]

The fiber length of the heat-resistant short fibers is preferably 3 to 10 mm, particularly 3 to 6 mm, and the thickness of the short fibers is preferably 0.8 to 5 de in denier. In the present invention, two or more kinds of fibers may be used in combination as the short fibers. For example, fibers made of different polymers may be mixed and used, or fibers having different cross-sectional shapes may be mixed and used. .

In the present invention, when the flat fibers as described above are used as the short fibers mixed with the m-aramid fibrids, a thin and tough paper-like material suitable as a battery separator can be obtained. That is, the use of flat fibers not only enables thinning of battery separators to the extent conventionally considered difficult, but also the physical properties of battery separators (especially in comparison with those using ordinary circular cross-section fibers). Strength) is also improved.

As described above, the battery separator of the present invention is manufactured by wet-mixing papermaking of m-aramid fibrids and heat-resistant short fibers. According to the research conducted by the present inventors. In order to satisfy desired air permeability, thickness (thinness), liquid retention and strength in a battery separator, the ratio of m-aramid fibrids and heat resistant short fibers is important. It is necessary to select the weight ratio of aramid fibrids / short fibers within the range of 40/60 to 10/90, preferably 35/65 to 15/85.

That is, the electrolyte impregnating ability of the battery separator is almost determined by the gaps existing in the sheets forming the separator, but the liquid retaining ability is not determined only by that. The wet paper-making material containing fibrids and the dry non-woven fabric. And then
Even if the impregnating properties are the same, the liquid retaining properties are usually good in the former and poor in the latter. The main reason for this is that the fibrids have a specific surface area of 5 to 100 m ² / g,
In the case of ordinary fibers, it is 0.1 m ² / g, and even in the case of flat fibers, it is at most 2 to 3 times that. At this time, when a material polymer containing a hydrophilic group such as m-aramid is used, the liquid retention property is further improved.

However, when the m-aramid fibrids alone are subjected to wet papermaking, the fibrids often adhere to each other, resulting in a marked loss of air permeability and impregnability. Therefore, in the present invention, the short fibers are mixed in the above proportion to prevent the fibrids from adhering to each other and improve the mechanical characteristics of the battery separator. By mixing and making such a fibrid and a short fiber at a specific ratio, the paper-like material that becomes the battery separator has a relatively large gap expanded by the presence of the short fiber and a narrow gap formed only by the fibrids continuous with this gap. Since and will be a structure that is appropriately dispersed,
Air permeability higher than 200 seconds / 100ml, preferably 1
A good battery separator having a thickness of 0.01 to 0.1 mm, preferably 0.02 to 0.05 mm, which is higher than 00 seconds / 100 ml and has a suitable impregnation property and liquid retention property. .

However, if the ratio of the short fibers is below the above range, the air permeability is lowered, and if the ratio of the fibrids is below the above range, the liquid retaining property and the mechanical properties are lowered.

The density of the battery separator of the present invention is
0.3-0.7 g / cm ³ , especially 0.35-0.60 g
/ Cm ³ is preferred. If it deviates from this range, it may be difficult to satisfy air permeability, strength, thickness, etc. at the same time.

The battery separator of the present invention as described above can be industrially manufactured by the following method.

That is, m-aramid fibrid 1
Circular cross-section fibers composed of 0 to 40% by weight and a heat-resistant polymer and / or cross-section flatness (D ₁ / D ₂ ) 2.0 to 7.0,
Preferably, a dilute aqueous slurry containing 90 to 60% by weight of flat cross-section fibers of 3.0 to 6.0 is prepared, and wet papermaking is performed using this slurry, and the obtained wet paper (web) is used alone. Alternatively, after stacking a plurality of sheets and drying, 240 to 3
50 ° C., preferably 250-320 ° C., at least 1
It is manufactured by heat-pressing into a paper-like material having a thickness of 0.01 to 0.1 mm, preferably 0.02 to 0.05 mm.

Wet paper (web) obtained by wet papermaking
After being dried, it is hot pressed between calender rolls. Density as a separator is 0.3-0.7 g /
cm ³ It is preferable to adjust to 0.35 to 0.60 g / cm ^3, and in order to actually set such a region, the hot pressing temperature is 240 ° C. to 350 ° C., particularly 260 ° C. as described above.
It is preferably set to 320 ° C. If it deviates from this range, it is difficult to satisfy the requirements of air permeability, strength and thickness at the same time.

The concentration of the dilute aqueous slurry used for wet papermaking is generally 0.01 to 0.5 (weight)%. The slurry may contain additives, but preferably does not contain an adhesive.

Various well-known papermaking techniques can be used to produce a wet paper web. Two or more wet papers may be laminated if necessary, but if the paper making technology is normal, it is not necessary to laminate a plurality of wet papers to make the thickness uniform, unlike the case of dry non-woven fabric. A sufficiently uniform paper-like sheet is obtained even with layers.

The hot pressing after drying is preferably performed a plurality of times,
First, the temperature is 285 to 320 ° C, the linear pressure is 10 to 200 kg /
at least once in mm ² and then 260 to 3
The paper-like material having a thickness of 0.01 to 0.1 mm, preferably 0.02 to 0.05 mm is obtained by hot-pressing again at a temperature of 00 ° C. and at a temperature and pressure higher than the conditions adopted in the hot-pressing. It is suitable.

Thus, a good battery separator intended for the present invention is manufactured.

According to the present invention as described above, the air permeability is 2
00 sec / 100 ml (preferably 100 sec / 100 m
l) A separator for a battery which is larger than the above-mentioned one and has air permeability, impregnating property and liquid retaining property, and which has a small thickness and is uniform and has good physical properties.

Therefore, this battery separator is
It is suitable for small-sized and large-capacity batteries, and secondary batteries can be rapidly charged. Therefore, it is particularly useful as a separator for new high-performance batteries such as sealed ion secondary batteries.

[0038]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

The flatness and the perimeter ratio of the fiber cross section of the flat fibers in Examples 5 to 7 are measured with 10 samples from the electron micrographs of the fiber cross section.

Further, the air permeability in the present invention is obtained by the following measuring method (Gurley method), and the smaller this value is, the higher the air permeability is. That is, the air permeability is the time (seconds) required for 100 cc of air per sheet of paper to pass using a Gurley type air permeability tester.
It is expressed by measuring

Further, the intrinsic viscosity of each polymer is N
-Methyl-2-pyrrolidone solution is a value measured at room temperature.

[0042]

Example 1 Intrinsic viscosity (IV) obtained by interfacial polymerization method
1.35 of poly-m-phenyleneisophthalamide was described in Japanese Patent Publication No. 52-16262.
The fibrids were manufactured using 50 mm). The freeness of the obtained fibrids is 110m in Canadian freeness.
It was l. This fibrid is disclosed in Japanese Patent Laid-Open No. 63-3587.
Treated according to the method described in Japanese Patent Publication No. 7, a specific surface area of 40 m
² / g.

On the other hand, the same polymer is used in Japanese Examined Patent Publication No. 48-175.
Based on the method described in JP-A-51, spinning, drawing and heat treatment were performed to obtain a normal circular cross-section fiber having a fineness of 2 de. The strength of the fiber was 4.5 g / de and the elongation was 18%. This was cut into a length of 6 mm.

A dilute aqueous slurry was prepared by mixing the above-mentioned m-aramid fibrids and m-aramid short fibers in a weight ratio of 30/70, and using a large tappy paper machine, 200 mm × 250 mm Size of 20g / m ²
It was made into wet paper.

The wet paper was squeezed with water and thoroughly dried. The temperature between these calender rolls is 300 ° C and the linear pressure is 50 kg.
/ Cm heat-press processing, temperature 260 ℃, linear pressure 1
It was heat-pressed at 00 kg / cm. The air permeability of the obtained paper-like sheet is 35 sec / 100 ml (Gurley method),
The thickness was 0.039 mm and the density was 0.4 g / cm ³ .

This sheet was successfully used as a battery separator for sealed secondary batteries.

[0047]

Example 2 Using the fibrids and short fibers used in Example 1, mixing them at a fibrid / short fiber weight ratio of 20/80, and using a large tappy paper machine as in Example 1, 200 mm was used. 25g / m in the size of × 250mm
² was used as the wet paper.

This wet paper was squeezed with water and thoroughly dried. This is calendered with a temperature of 300 ° C and a linear pressure of 50 kg / c.
by hot pressing, temperature 260 ℃, linear pressure 100 kg
Hot pressing was performed at / cm. The paper-like sheet obtained had an air permeability of 70 sec / 100 ml (Gurley method) and a thickness of 0.0.
It was 43 mm.

This sheet was successfully used as a battery separator for sealed secondary batteries.

[0050]

Comparative Example 1 The fibrids and short fibers used in Example 1 were mixed at a fibrid / short fiber weight ratio of 60/40, and the same tappy type paper machine was used to obtain 200 m.
A wet paper having a size of m × 250 mm and a weight of 25 g / m ² was prepared.

The wet paper was squeezed with water and thoroughly dried. This product had an air permeability of 540 sec / 100 ml (Gurley method) and a thickness of 0.13 mm.

This sheet had a low air permeability and was unsuitable as a battery separator for secondary batteries.

This sheet is calendered to 300
Heat-pressed at 50 ℃, 50kg / cm, 260 ℃, 10
It was hot pressed at 0 kg / cm. The air permeability of the obtained paper-like sheet is 700 sec / 100 ml (Gurley method) or more,
The thickness was 0.032 mm, but this sheet had a low air permeability and was unsuitable as a battery separator for secondary batteries.

These two examples almost correspond to the current commercial aramid papers, and it is clear from these examples that commercial aramid papers cannot be good separators.

[0055]

Example 3 Using the fibrids and the short fibers used in Example 1, mixing the fibrids / short fibers weight ratio of 30/70, and similarly using a large tappy type paper machine,
A wet paper having a size of 200 mm × 250 mm and a weight of 25 g / m ² was prepared.

This wet paper was squeezed with water and thoroughly dried. The air permeability of the obtained sheet was 180 sec / 100 ml (Gurley method), and the thickness was 0.083 mm. This sheet had a large thickness and was somewhat unsuitable as a battery separator for a secondary battery.

Then, this sheet is rolled with a calendar roll.
It was heated and pressurized at 00 ° C. and 50 kg / cm. The air permeability of the obtained paper-like sheet was 200 sec / 100 ml (Gurley method), and the thickness was 0.039 mm.

This sheet had a slightly small air permeability, and was used as a battery separator for a secondary battery for a battery having a relatively small load.

[0059]

Example 4 A polymer of poly-m-phenylene isophthalamide was produced by an interfacial polymerization method based on the method described in JP-B-47-10863. This polymer has an intrinsic viscosity (IV) of 1.30 measured by dissolving it in N-methyl-2-pyrrolidone and does not contain inorganic salts.

This polymer was obtained by using Japanese Patent Publication No. 52-151621.
A fibrid was prepared using the precipitation device (diameter 150 mm) described in Japanese Patent Publication No. Freeness is Canadian Freeness 97
It was ml. The obtained fibrids are disclosed in JP-A-63-3.
Processed according to the method described in No. 5877.

Also, the same polymer is used in Japanese Examined Patent Publication No. Sho 48-175.
By the method described in JP-A-51, a circular cross-section fiber having a fineness of 2 de was prepared. The strength was 4.5 g / de and the elongation was 18%. This was cut into a length of 6 mm.

The fibers were dispersed as an aqueous slurry having a concentration of 0.1 (wt)%, the fibrids were beaten with a disc refiner to a freeness of 92 ml (Canadian), and mixed at a short fiber / fibrid weight ratio of 75/25. Using a Ford Linear type paper machine with a width of 1000 mm and a basis weight of 2
Paper was made to 0 g / m ² to obtain a wet paper.

After the wet paper was squeezed with water and sufficiently dried, it was hot-pressed with a calendar roll at 300 ° C. and 100 kg / cm, and further hot-pressed at 280 ° C. and 200 kg / cm. The obtained sheet has an air permeability of 35 sec /
The thickness was 100 ml (Gurley method) and 0.035 mm.

This sheet was successfully used as a battery separator for a sealed secondary battery.

[0065]

Example 5 The same poly-m-phenylene isophthalamide fibrid as in Example 1 was prepared.

On the other hand, using the same polymer, Japanese Patent Publication No. 48-1
A flat fiber of 2.18 de was manufactured according to the method described in Japanese Patent No. 7551. The flatness of the cross section represented by the ratio (D ₁ / D ₂ ) of the major axis and the minor axis in the cross section of the flat fiber is 5.
1, and the perimeter ratio represented by the perimeter ratio (α) to the corresponding circular cross-section fiber was 1.50. The strength of this fiber was 5.1 g / de and the elongation at break was 18%. This fiber was cut into a length of 6 mm and used.

From the slurry prepared by mixing the above-mentioned m-aramid fibrid and m-aramid flat fiber at a weight ratio of 30/70 and dispersing them in water at a solid concentration of 0.1 (wt)%, a large tappy type is prepared. 200mm × 25 using a paper machine
A wet paper was prepared by making a paper having a basis weight of 20 g / m ² with a size of 0 mm. The wet paper was squeezed with water and thoroughly dried. Then, this was calendered at a temperature of 300 ° C. and a linear pressure of 50 kg / c.
by hot pressing at a temperature of 260 ° C and a linear pressure of 100 kg
Hot pressing was performed at / cm.

The thickness of the obtained paper-like material is 0.026 mm,
The air permeability (by Gurley method) is 5 seconds / 100 ml, the strength is 3.0 kgf / mm ² , and the elongation is 1.6.
%Met.

Further, as the short fibers, poly-m-phenylene isophthalamide fibers having a circular cross section of 2.2 de (cross sectional plane D ₁ / D ₂ = 1 and peripheral length ratio α = 1) are used.
A paper product was produced in exactly the same manner.

The thickness of the obtained paper-like material was 0.040 mm, the elongation was almost the same as that of Example 1, but the strength was 2.5 kgf / mm ² .

From these results, when flat fibers are used,
It can be seen that the battery separator can be easily thinned and the strength can be improved.

All of these paper-like materials were useful as separators for sealed secondary batteries.

[0073]

Example 6 The same fibrid and flat fiber as in Example 5 were used, and the weight ratio of fibrid / flat fiber was 20/80.
25 g of a 200 mm × 250 mm basis weight using a large tappy paper machine as in Example 1.
/ M ² and made a wet paper. This wet paper is squeezed with water, dried sufficiently, and then calendered at a temperature of 300 ° C.
Thermal pressure processing at linear pressure 50 kg / cm, temperature 260
Hot pressing was performed at a temperature of 100 ° C. and a linear pressure of 100 kg / cm.

The thickness of the obtained paper-like material is 0.030 mm,
The air permeability (by Gurley method) is 70 seconds / 100 ml, the strength is 2.0 kgf / mm ² , and the elongation is 1.3.
%Met.

This paper-like material was successfully used as a separator for a sealed secondary battery.

[0076]

Comparative Example 2 The same fibrids and flat fibers as in Example 5 were used, and the weight ratio of fibrids / flat fibers was 45/5.
5, using a large tappy type paper machine as in Example 1, and weighing 25 g with a size of 200 mm × 250 mm.
/ M ² and made a wet paper. The wet paper was squeezed with water and thoroughly dried. This paper-like material had a thickness of 0.068 mm and an air permeability (by Gurley method) of 540 seconds / 100 ml. This product had a low air permeability and was unsuitable as a separator for secondary batteries.

[0077]

COMPARATIVE EXAMPLE 3 The paper-like material produced in Comparative Example 2 was hot-pressed with a calender roll at a temperature of 300 ° C. and a linear pressure of 50 kg / cm, and further at a temperature of 260 ° C. and a linear pressure of 100 kg / cm. . The thickness of the obtained paper-like material was 0.026 mm, but the air permeability (by Gurley method) was about 7,000 seconds / 100 ml, which was unsuitable as a battery separator.

[0078]

Example 7 Intrinsic viscosity (I.
V. ) Was 1.30 and poly-m-phenylene isophthalamide was produced using the precipitation device (diameter 150 mm) described in JP-B-52-15162.
The freeness was 97 ml in Canadian freeness.
The obtained fibrids were processed according to the method described in JP-A-63-35877.

On the other hand, the same polymer is used in Japanese Examined Patent Publication No. 48-175.
A flat fiber of 2.18 de was manufactured according to the method described in JP-A-51. The cross-sectional flatness represented by the ratio (D ₁ / D ₂ ) of the major axis to the minor axis in the cross section of this flat fiber is 5.1, and is represented by the ratio (α) of the peripheral length to the corresponding circular cross section fiber. The circumference ratio was 1.50. The strength of this fiber is 5.
The elongation at break was 1 g / de and was 18%. This fiber was cut into a length of 6 mm and used.

The flat fiber was dispersed in water to give a concentration of 0.1.
(Weight)% slurry, while fibrid was beaten with a disc refiner to a freeness of 92 ml (Canadian freeness). Then, the fibrid / flat fibers were mixed at a weight ratio of 25/75, and the mixture was made into a wet paper by using a Ford Linear paper machine to have a width of 1000 mm and a basis weight of 20 g / m ² . The wet paper was squeezed with water and thoroughly dried.
Next, this was heat-pressed with a calender roll at a temperature of 300 ° C. and a linear pressure of 100 kg / cm, and further at a temperature of 280 ° C.,
It was hot pressed at a linear pressure of 200 kg / cm.

The thickness of the obtained paper-like material is 0.026 mm,
Air permeability (by Gurley method) is 35 seconds / 100 ml, strength is 3.5 kgf / mm ² , elongation is 3.6%.
Met.

This paper-like material was successfully used as a separator of a sealed secondary battery.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of a cross-sectional shape of a flat fiber that can be used in the present invention.

[Explanation of symbols]

D ₁ Fiber cross section major axis D ₂ Fiber cross section minimum minor axis

Claims (8)

[Claims] 1. An m-aramid fibrid 10 to 40.
And a heat-resistant short fiber of 90 to 60% by weight.
A battery separator having a thickness of 1 to 0.1 mm. 2. The air permeability of the paper-like sheet is 200 sec / 1.
The battery separator according to claim 1, wherein the separator is higher than 00 ml. 3. The specific surface area of m-aramid fibrids is 5
The separator for a battery according to claim 1 or 2, which has a content of -100 m ² / g. 4. The heat-resistant short fiber is an aramid fiber having a fiber length of 3 to 10 mm.
The battery separator described. 5. The heat-resistant short fiber has a circular cross-section fiber and / or a cross-section flatness of 3.0 to 6.0 and a cross-section perimeter ratio of 1.4.
1. The flat fibers having a size of .about.2.0.
4. The battery separator according to any one of 4 above. 6. When manufacturing the battery separator according to claim 1, 10 to 40% by weight of m-aramid fibrids and 90 to 6 heat-resistant short fibers.
A dilute aqueous slurry containing 0% by weight was formed into a paper, and the wet paper obtained was dried and then hot-pressed at least once at 240 to 350 ° C. to form a paper having a thickness of 0.01 to 0.1 mm. A method for producing a battery separator, which is characterized in that 7. When manufacturing the battery separator according to claim 1, 10 to 40% by weight of m-aramid fibrids and 90 to 6 heat-resistant short fibers.
After diluting a dilute aqueous slurry containing 0% by weight and drying the obtained wet paper, it is hot pressed at 285 to 320 ° C. at least once and then at 260 to 300 ° C. and hot pressed. A method for producing a battery separator, which comprises subjecting to a paper-like material having a thickness of 0.01 to 0.1 mm by hot-pressing again at a temperature lower than the adopted temperature and a high pressure. 8. The wet paper made into paper is heated at a temperature of 285 to 320.
Heat-pressed under conditions of ℃ and linear pressure of 10-200 kg / cm,
Continuously, the temperature is lower than the temperature used in the previous processing and 2
The method for producing a battery separator according to claim 7, wherein the hot pressing is performed at a temperature of 60 to 300 ° C. and a linear pressure of 100 to 400 kg / cm, which is higher than the linear pressure adopted in the previous processing.