JP3279189B2 - Para-oriented aromatic polyamide porous film, production method thereof and use 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 porous film made of para-oriented aromatic polyamide (hereinafter, sometimes referred to as para-aramid) and a method for producing the same. More specifically, the present invention relates to a porous film having a structure in which fibrils made of para-aramid are arranged in a network or a nonwoven fabric in a planar manner and have a layered structure, and a method for producing the same. The para-aramid porous film of the present invention has excellent heat resistance and rigidity, and can be suitably used as a battery separator.

[0002]

2. Description of the Related Art A porous film made of an aromatic polyamide (hereinafter sometimes referred to as aramid) is disclosed in JP-B-59-14494 and JP-B-59-36939.
The production method is described in Japanese Patent Application Laid-Open Publication No. H11-209,878. In the former, a method has been proposed in which a solution in which aramid is dissolved is cast into a film, and the solvent is extracted and removed while solidifying the solution to produce a porous film. It is described that in this production method, a polymer is not coagulated and precipitated, so that a uniform porous film having a pore size of several A to 100 μm can be produced. In the latter, a method for producing a porous film from a deposit composition obtained by adding a poor solvent to an aramid solution is described. Since the precipitate is a liquid phase rich in colloid and a liquid phase poor in colloid,
It is described that a uniform porous film can be produced without a difference in porosity between the surface and the inside of the film.

[0003] Japanese Patent Application Laid-Open No. 2-222430 discloses a microporous aramid film in which micropores are continuous on the front and back of the film. It is described that the film has better heat resistance than the above-mentioned porous film and has excellent dimensional stability against humidity. According to the manufacturing method,
The feature compared with the 36939 publication is that it has a step of casting an aramid solution on a film, immersing it in water, and then immediately stretching it in a longitudinal direction, that is, a stretching step.

[0004] However, the porous film obtained by the method described in the above-mentioned publications is disclosed in Japanese Patent Application Laid-Open No. 22223/1990.
No. 0, that is, the aramid porous film is a film having a through-hole as described in the description that it has continuous micropores, and the invention of the present application is apparent from a comparative example described later. Does not form mesh or non-woven fibrils.

The above-mentioned Japanese Patent Publication Nos. 59-14494 and 59-36939 describe that the obtained porous film is useful as a battery separator. Furthermore, JP-A-53-58636,
JP-A-5-335005 describes a battery separator made of aramid.

Japanese Patent Application Laid-Open No. 53-58636 discloses that a woven or non-woven fabric made of aramid is used as a separator for a storage battery to reduce deterioration at high temperatures.
It describes that the characteristics of the storage battery can be stabilized and the life can be extended. In JP-A-5-335005, a nonwoven fabric or a porous film made of aramid fiber is used.
More specifically, it describes that nomex paper (metaramid paper) manufactured by du Pont is used as a separator of a lithium secondary battery. However, none of these discloses a battery separator using the porous film of the present invention.

[0007]

Under these circumstances, an object of the present invention is to make use of the properties of para-aramid such as high heat resistance, high rigidity, high strength, and excellent solvent resistance, to achieve uniformity and fine voids that cannot be achieved with a nonwoven fabric. And to provide a method for producing the same. Another object of the present invention is to provide a battery separator using such a para-aramid porous film.

[0008]

[Means for Solving the Problems] In view of such circumstances,
The present inventors have arrived at the present invention as a result of intensive studies. That is, the present invention relates to a porous film made of para-oriented aromatic polyamide, wherein the film is constituted by fibrils having a diameter of 1 μm or less, and the fibrils are arranged in a network or nonwoven fabric on a plane and overlapped in layers. The film has a coefficient of linear thermal expansion at 200 to 300 ° C. within ± 50 × 10 ⁻⁶ / ° C. and a porosity of 30 to 9
It relates to a porous film of 5%.

Further, the present invention relates to a method for producing a para-oriented aromatic polyamide porous film having the following steps (a) to (c). (A) 1 to 10% by weight of a para-oriented aromatic polyamide having an intrinsic viscosity of 1.0 to 2.8 dl / g in a polar amide-based solvent or a polar urea-based solvent, Forming a film from a solution containing 1 to 10% by weight of the substance. (B) maintaining the film at a temperature of 20 ° C. or higher or −5 ° C. or lower to precipitate para-oriented aromatic polyamide. (C) The film obtained in step (b) is immersed in an aqueous solution or an alcoholic solution to elute the solvent and the chloride of the alkali metal or alkaline earth metal, and then dried to dry the para-oriented aromatic polyamide porous material. Obtaining a quality film.

Further, the present invention relates to a method for producing a para-oriented aromatic polyamide porous film having the following steps (d) to (f). (D) In a polar amide-based solvent or a polar urea-based solvent, 1 to 10% by weight of a para-oriented aromatic polyamide having an intrinsic viscosity of 1.0 to 2.8 dl / g, and chloride of an alkali metal or an alkaline earth metal. Forming a film from a solution containing 1 to 10% by weight of the substance. (E) a step of immersing the film in a coagulation liquid containing 0 to 70% by weight of a polar amide solvent or a polar urea solvent to coagulate and precipitate the para-oriented aromatic polyamide. (F) dipping the film-like material obtained in step (e) in an aqueous solution or an alcohol-based solution to elute a solvent and a chloride of an alkali metal or an alkaline earth metal, and then drying and evaporating the para-oriented aromatic polyamide porous material; Obtaining a quality film.

Furthermore, the present invention relates to a para-oriented aromatic polyamide porous film produced by the above method. The present invention also relates to a battery separator using such a para-oriented aromatic polyamide porous film. Hereinafter, the present invention will be described in detail.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a para-oriented aromatic polyamide is defined as an amide bond having a para-position of an aromatic ring or an alignment position equivalent thereto (for example, 4,4′-biphenylene, 1,1,2).
It consists essentially of recurring units linked in opposite coaxial or parallel directions such as 5-naphthalene, 2,6-naphthalene, etc., and has excellent mechanical properties such as high strength and high elastic modulus. It is a high heat-resistant polymer that has no properties, no melting point / glass transition point, and may have a thermal decomposition temperature of 500 ° C. or more.

Specifically, poly (paraphenyleneterephthalamide), poly (parabenzamide, poly (4,
4'-benzanilide terephthalamide), poly (paraphenylene-4,4'-biphenylenedicarboxylic amide), poly (paraphenylene-2,6-naphthalenedicarboxylic amide), poly (2-chloro-paraphenylene terephthalamide) ), Paraphenylenediamine / 2,6
Para-aramid having a para-oriented structure or a structure similar to the para-oriented structure, such as a copolymer of dichloroparaphenylenediamine / terephthalic acid dichloride. As the synthesis method, for example, a method described in Japanese Patent Publication No. 50-8474 is known.

The para-oriented aromatic polyamide porous film (hereinafter sometimes referred to as a porous film) according to the present invention is a porous film obtained from the above-mentioned para-oriented aromatic polyamide. It is composed of para-aramid fibrils and has a network-like or non-woven-like form when viewed microscopically. That is, the para-oriented aromatic polyamide porous film referred to in the present invention has a structure in which fibrils having a diameter of 1 μm or less, which are made of para-aramid, are arranged in a network or a non-woven fabric on a plane, and overlap in layers. Here, being arranged on a plane means that the fibrils are arranged in parallel with the film surface. Further, the porous film according to the present invention is composed of fibrils,
It has many voids, and its porosity is 30-95%,
Preferably it is 35-90%. Porosity is 30%
If it is less than 95%, it cannot be said that the film is substantially porous. If it exceeds 95%, the strength of the film becomes low and handling becomes difficult.

Further, the porous film of the present invention has a thickness of 200
± 50 × 10 ^-6 / ° C.
Within, preferably within ± 25 × 10 ⁻⁶ / ° C. The small coefficient of linear thermal expansion indicates good dimensional stability in the planar direction.

The porous film of the present invention is a film in which voids formed by fibrils have a uniform structure in the thickness direction. Further, according to the present invention, it is also possible to provide a film in which the size of the void is relatively small on one side of the porous film and large on the other side, that is, the size of the voids on both sides. The present invention also includes a porous film having a structure in which the size of voids formed by fibrils changes continuously in the thickness direction of the porous film.

The method for producing the porous film made of para-oriented aromatic polyamide used in the present invention is not particularly limited. For example, an aromatic polyamide solution dissolved in an amide solution is cast into a film and then solidified. After that, a method of extracting a solvent to form a porous membrane may be used. As a preferred method for producing a para-oriented aromatic polyamide porous film, a para-oriented aromatic polyamide solution is cast in a film form, and then maintained at a temperature of 20 ° C or higher or -5 ° C or less to precipitate the para-oriented aromatic polyamide. After that, a method of extracting the solvent, or a method of immersing in a coagulation solution immediately after casting in a film form to coagulate the para-oriented aromatic polyamide, and then extracting the solvent.

As a specific example of the former method, there is a method of manufacturing from the following steps (a) to (c). (A) 1 to 10% by weight of a para-oriented aromatic polyamide having an intrinsic viscosity of 1.0 to 2.8 dl / g in a polar amide-based solvent or a polar urea-based solvent, Forming a film from a solution containing 1 to 10% by weight of the substance. (B) maintaining the film at a temperature of 20 ° C. or higher or −5 ° C. or lower to precipitate para-oriented aromatic polyamide. (C) The film obtained in step (b) is immersed in an aqueous solution or an alcoholic solution to elute the solvent and the chloride of the alkali metal or alkaline earth metal, and then dried to dry the para-oriented aromatic polyamide porous material. Obtaining a quality film.

Each step will be described in more detail.
The para-aramid solution used in the step (a) is, for example,
It can be suitably manufactured by the operations described below. That is, the alkali metal or alkaline earth metal chloride is 1 to
In a polar amide-based solvent or a polar urea-based solvent in which 10% by weight is dissolved, with respect to 1.0 mol of a para-oriented aromatic diamine,
Para-oriented aromatic dicarboxylic acid halide 0.94 to 0.9
9 mol is added and condensation polymerization is performed at a temperature of -20 ° C to 50 ° C to produce a para-aramid solution having a para-aramid concentration of 1 to 10% by weight.

The amount of the alkali metal or alkaline earth metal chloride in the para-aramid solution is 1 to 10% by weight, more preferably 2 to 8% by weight. Generally, when the alkali metal or alkaline earth metal chloride is less than 1% by weight,
The solubility of para-aramid is insufficient, and when it exceeds 10% by weight, chlorides of alkali metals or alkaline earth metals do not dissolve in polar amide solvents or polar urea solvents. More precisely, the amount of alkali metal or alkaline earth metal chloride in the para-aramid solution is ranged relative to the amount of para-aramid (amide groups in para-aramid). That is, the amount of the chloride to be added to the polymerization system is preferably in the range of 0.5 to 6.0 mol, more preferably in the range of 1.0 to 4.0 mol, per 1.0 mol of the amide group formed by condensation polymerization. preferable. If the chloride is less than 0.5 mol, the solubility of the produced para-aramid becomes insufficient. When the amount exceeds 6.0 mol, the amount of chloride substantially dissolved in the solvent is not preferable.

The concentration of para-aramid in the para-aramid solution is 1 to 10% by weight, more preferably 2 to 8% by weight.
When the para-aramid concentration is less than 1% by weight, productivity is remarkably reduced, which is industrially disadvantageous. 10% by weight of para-aramid
If the temperature exceeds the above, para-aramid precipitates and does not become a stable para-aramid solution.

The para-aramid in the step (a) is expressed by an intrinsic viscosity (in the present invention, the intrinsic viscosity is defined later), and is 1.0 to 2.8 dl / g, preferably 1.5 to dl / g. Refers to para-aramid exhibiting a value of ~ 2.6 dl / g. If the intrinsic viscosity is less than 1.0 dl / g, sufficient film strength cannot be obtained. When the intrinsic viscosity exceeds 2.8 dl / g, it is difficult to obtain a stable para-aramid solution, and para-aramid precipitates, making it difficult to form a film.

Examples of the para-oriented aromatic diamine used in the condensation polymerization of para-aramid in the step (a) include:
Paraphenylenediamine, 4,4'-diaminobiphenyl, 2-methyl-paraphenylenediamine, 2-chloro-paraphenylenediamine, 2,6-dichloro-paraphenylenediamine, 2,6-naphthalenediamine, 1,
Examples thereof include 5-naphthalenediamine, 4,4'-diaminobenzanilide, and 3,4'-diaminodiphenyl ether. The para-oriented aromatic diamine may be used alone or in combination of two or more for the condensation polymerization.

Examples of the para-oriented aromatic dicarboxylic acid dihalide used in the condensation polymerization of para-aramid in the step (a) include terephthalic acid dichloride, biphenyl-4,4'-dicarboxylic acid chloride, 2-chloroterephthalic acid dichloride, 5-dichloroterephthalic acid dichloride, 2-methylterephthalic acid dichloride,
2,6-naphthalenedicarboxylic acid chloride, 1,5-
Examples include naphthalenedicarboxylic acid chloride. The para-oriented aromatic dicarboxylic dihalide may be used alone or in combination of two or more for the condensation polymerization.

In the step (a), the condensation polymerization of para-aramid is carried out in a polar amide solvent or a polar urea solvent. Examples of these solvents include N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, or N, N, N ′, N′-tetramethylurea, and particularly preferred. Is N-methyl-2-pyrrolidone, but is not limited thereto.

In the step (a), an alkali metal or alkaline earth metal chloride is preferably used for the purpose of improving the solubility of para-aramid in a solvent. Specific examples include lithium chloride or calcium chloride,
It is not limited to these.

In the step (a), when a film is produced, the para-aramid solution is cast onto a substrate such as a glass plate or a polyester film to maintain the shape of the film. be able to.
As the casting method, various methods such as a method of extruding from a bar coater or a T-die onto a substrate can be appropriately employed.

In the step (b), the para-aramid is formed into a film from the para-aramid solution in the step (a), and the para-aramid is precipitated before coagulation. The method of the present invention has an excellent feature in producing a porous film by forming para-aramid solution into a film and then precipitating para-aramid before coagulation. According to this method, the finally obtained porous film can have a uniform structure in the thickness direction. The method is 2
It is kept at a temperature of 0 ° C. or higher or −5 ° C. or lower for a certain period of time (hereinafter, sometimes referred to as a high-temperature deposition method and a low-temperature deposition method, respectively). Form factors such as the porosity and fibril diameter of the finally obtained porous film can also be controlled by the deposition temperature and the holding time.

First, the high temperature deposition method will be described. In order to produce a porous film by the present high-temperature deposition method, the para-aramid solution is heated to a temperature of 20 ° C. or more, preferably 30 ° C.
The above-mentioned temperature is maintained for a predetermined time to precipitate para-aramid.

The time at which the precipitation of para-aramid starts depends on the composition of the para-aramid solution (chloride content, para-aramid concentration, etc.).
It is not necessarily limited because it depends on the holding temperature. For example, when the para-aramid concentration is 6% by weight and the amount of calcium chloride is equimolar to the amide group, the para-aramid solution is stable at 20 ° C. for one week or more and does not precipitate, but at 60 ° C., the para-aramid is reduced in about 5 minutes. Precipitates. When the para-aramid concentration is 6% by weight and the amount of calcium chloride is 0.7 mol per 1 mol of the amide group,
After about half a day at 20 ° C. and about 1 hour at 30 ° C., para-aramid precipitates. In order to further shorten the deposition time,
It is preferable to control the humidity in addition to the deposition temperature. In this case, a relative humidity of 40 to 100% is particularly preferably used.

As described above, the higher the temperature, the shorter the time required for the precipitation of para-aramid to begin, but the form factors such as the porosity of the porous film and the diameter of the fibrils also depend on the temperature at which they are deposited. The temperature for deposition is determined by comprehensive judgment according to the purpose.

Next, the low-temperature precipitation method will be described. In order to produce a porous film by the present low-temperature deposition method, the para-aramid solution is heated at a temperature of -5 ° C or lower, preferably -10 ° C.
It is kept at a temperature of not more than ℃ for a predetermined time to precipitate para-aramid to form a film.

The time at which the precipitation of para-aramid starts depends on the composition of the para-aramid solution (chloride amount, para-aramid concentration, etc.).
It is not necessarily limited because it depends on the holding temperature. For example, when the para-aramid concentration is 6% by weight and the amount of calcium chloride is equimolar to the amide group, the para-aramid solution is stable at -5 ° C for one week or more and does not precipitate, but at -20 ° C for about 30 minutes. Para-aramid precipitates. When the concentration of para-aramid is 6% by weight and the amount of calcium chloride is 0.7 mol per mol of amide group, para-aramid precipitates after about half a day at −5 ° C. and about 1 hour at −10 ° C.

As described above, the lower the temperature, the shorter the time required for the precipitation of para-aramid to begin, but the morphological factors such as the porosity of the porous film and the diameter of the fibrils also depend on the temperature at which the precipitation occurs. The temperature for deposition is determined by comprehensive judgment according to the purpose.

In the step (c), a solvent and a chloride of an alkali metal or an alkaline earth metal are removed from the film obtained in the step (b). As a removing method, for example, there is a method in which a film-like material is immersed in a solution to elute a solvent and a chloride.
When the solvent is removed from the film by evaporation, a method of immersing again in a solution such as water to elute the chloride may be employed. As a solution for eluting the solvent or the chloride, an aqueous solution or an alcohol-based solution is preferable because both the solvent and the chloride can be dissolved. Water may be used as the aqueous solution. The film from which the solvent and chloride have been removed is then dried to produce the desired porous film. The drying method is not particularly limited, and various known methods can be used. In the present invention, the term “film-like material” refers to an intermediate form before a porous film as a final product is formed.

As another preferred example of the method for producing a para-oriented aromatic polyamide porous film of the present invention, a para-oriented aromatic polyamide solution is cast in a film form, and then immediately immersed in a coagulation liquid to give the para-oriented aromatic polyamide solution. A method of coagulating a group III polyamide and thereafter extracting a solvent (hereinafter, may be referred to as a coagulation liquid immersion method). Specifically, the following (d)
To (f).

(D) In a polar amide solvent or a polar urea solvent, 1 to 10% by weight of a para-oriented aromatic polyamide having an intrinsic viscosity of 1.0 to 2.8 dl / g, and an alkali metal or alkaline earth. A step of forming a film from a solution containing 1 to 10% by weight of a metal chloride. (E) a step of immersing the film in a coagulation liquid containing 0 to 70% by weight of a polar amide solvent or a polar urea solvent to coagulate and precipitate the para-oriented aromatic polyamide. (F) dipping the film-like material obtained in step (e) in an aqueous solution or an alcohol-based solution to elute a solvent and a chloride of an alkali metal or an alkaline earth metal, and then drying and evaporating the para-oriented aromatic polyamide porous material Obtaining a quality film.

The coagulation solution used in the step (e) is a solvent that does not dissolve para-aramid and is compatible with a polar amide solvent or a polar urea solvent. Preferably, it is a solvent which can also dissolve an alkali metal or alkaline earth metal chloride. Specific examples include water and alcohols such as methanol. The type of the polar amide solvent or the polar urea solvent in the aqueous solution or the alcohol solution is not particularly limited, but using the solvent used for the para-aramid solution simplifies the solvent recovery step industrially. It is preferred. The morphological factors such as the porosity and fibril diameter of the finally obtained porous film can also be controlled by the type of coagulation solution used and the concentration of the polar amide solvent or polar urea solvent in the coagulation solution.

As the coagulation liquid used in this step, a coagulation liquid containing 1 to 70% of a polar amide solvent or a polar urea solvent is more preferably used. If the concentration of the polar amide-based solvent or polar urea-based solvent in the coagulation liquid is less than 1%, the load in the solvent recovery step is too large, which is industrially disadvantageous.
The high concentration side is not particularly limited, but if the concentration exceeds 70%, it takes time for coagulation, and it is difficult to maintain the shape of the film until para-aramid precipitates.

The method of the present invention comprises the steps of:
For example, after forming a film on a substrate and obtaining a film, it is immersed in a coagulation solution containing 0 to 70% by weight of a polar amide solvent or a polar urea solvent to coagulate and precipitate para-aramid. It has excellent characteristics in producing a porous film by a simple method. The present method differs from the low-temperature and high-temperature deposition methods in that the coagulation and precipitation of paraamide are performed simultaneously from a paraamide film in a coagulation solution.

The thickness of the obtained porous film is not particularly limited, but is preferably less than 1 mm when applied to a substrate. When the film thickness at the time of coating becomes 1 mm or more, the film surface solidifies, but the unsolidified portion inside easily flows,
It is difficult to obtain a homogeneous porous film. In this case, it is necessary to provide a dam for preventing flow.

When the coagulation liquid is an aqueous solution, the temperature at the time of coagulation tends to increase as the temperature increases, but there is no significant difference in the structure of voids and the form of fibrils in the range of room temperature to 60 ° C. Therefore, the temperature is not particularly limited, but it is more economical to solidify around room temperature industrially.

According to the method of the present invention, the pores formed by the fibrils are relatively small on one side of the porous film and large on the opposite side. Quality film can be obtained. Further, a porous film having a structure in which the size of voids formed by fibrils continuously varies in the thickness direction of the porous film can also be used.

That is, when a film of the para-aramid solution is formed on a substrate such as a glass plate or a polyester film and immersed in a coagulating liquid which is an aqueous solution, the surface of the film of the para-aramid solution comes into direct contact with the coagulating liquid. A gap of about 0.005 to 0.030 μm is observed on the side to be scanned with a scanning electron microscope. On the other hand, the substrate side has 0.005 to 0.10 μm.
It shows a non-woven form made of fibrils having voids of m, and the diameter of the fibrils is approximately 0.005 to 0.1 μm
Becomes

As the concentration of water in the coagulating liquid is lower, the obtained porous film has a gradient structure with respect to the above-mentioned voids, that is, a difference in voids and morphology in the thickness direction (nonuniformity).
Tends to be smaller. The concentration of water in the coagulation liquid can be increased to increase non-uniformity.

When an acetone-based solution is used instead of an aqueous solution as a coagulating liquid, the diameter of fibrils and the size of voids both increase, but as in the case of an aqueous solution,
Non-uniformity in the thickness direction of the porous film is observed. The size of the void is not particularly limited, but is about 0.005 to 2 μm on the coagulating liquid side and about 0.005 to 2 μm on the substrate side.
20 μm, and the voids are smaller on the coagulation liquid side. Since the nonuniformity in the thickness direction of the porous film may be preferable depending on the use of the porous film, it is technically advantageous that the nonuniformity can be controlled.

Step (d) is the same step as step (a), and step (f) is the same step as step (c), and the same operations are performed.

The porous film made of para-oriented aromatic polyamide obtained by the method of the present invention has a layer structure in which fibrils of 1 μm or less made of para-oriented aromatic polyamide are arranged in a network or nonwoven fabric plane. . As described above, according to the present invention, there is provided a method capable of easily controlling the diameter of fibrils, the size of voids formed from fibrils, the porosity, and the like.

As described above, the porous film of the present invention has a structure in which, in the form of a film, fibrils composed of para-aramid are arranged on a plane in a mesh or non-woven fabric and are layered. .
Since the fibrils are arranged in a plane, they have various excellent physical properties. The first is that para-aramid has rigidity, heat resistance and mechanical strength, which are the intrinsic properties of para-aramid.
In addition, the second is dimensional stability in the planar direction,
The coefficient of linear thermal expansion at 200 to 300 ° C. is ± 50 × 10 ⁻⁶ /
Within ° C. Furthermore, even if the porosity is high, the mechanical strength is maintained to some extent.

The porous film of the present invention can be used for a battery separator, an electric insulating paper, etc. by utilizing the above-mentioned excellent properties. The film of the present invention has electrical insulation properties, is chemically stable with respect to the electrolytic solution, and has good fibril structure and pores made of the same. It is suitably used for a separator for a secondary battery.

[0051]

EXAMPLES The present invention will now be described specifically with reference to examples, but the present invention is not limited to these examples. Test / evaluation methods or criteria in Examples and Comparative Examples are as follows.

(1) Intrinsic Viscosity In the present invention, the intrinsic viscosity is determined by the following measuring method.
That is, for a solution in which 0.5 g of the para-aramid polymer was dissolved in 100 ml of 96-98% sulfuric acid and for a 96-98% sulfuric acid, the flow time was measured at 30 ° C. using a capillary viscometer, and the flow time ratio was determined. The intrinsic viscosity was determined by the following equation. Intrinsic viscosity = ln (T / T ₀ ) / C [unit: dl /
g] Here, T and T ₀ are the flow times of the para-aramid sulfate solution and sulfuric acid, respectively, and C indicates the para-aramid concentration (dl / g) in the para-aramid sulfate solution.

(2) Tensile test A test piece was punched out from the obtained film with a dumbbell cutter manufactured by Dumbbell Co., Ltd., and JIS was performed using an Instron universal tensile tester model 4301 manufactured by Instron Japan.
The tensile strength was determined according to K-7127.

(3) Porosity The film was cut into a square shape (one side length Lcm),
The weight (Wg) and thickness (Dcm) were measured. Assuming that the true specific gravity of para-aramid was 1.45 g / cm ³ , the porosity (% by volume) was determined from the following equation. Porosity = 100−100 × (W / 1.45) / (L ² ×
D)

(4) Coefficient of Thermal Expansion The test piece was heat-treated at 250 ° C. for 10 minutes. This test piece was measured using a thermal analyzer TMA120 manufactured by Seiko Electronics Co., Ltd. in accordance with ASTM-D696, and calculated by the following equation. αl = ΔL / LoΔT αl; coefficient of linear thermal expansion ΔL; change length of test piece Lo; test piece length before test ΔT; temperature difference (T ₂ −T ₁ : ° C.) T ₂ : 300 ° C., T ₁ ; 200 ° C.

Example 1 1. Polymerization of poly (paraphenylene terephthalamide) Using a 5 liter (l) separable flask having a stirring blade, a thermometer, a nitrogen inlet tube and a powder addition port, poly (paraphenylene) was used. Terephthalamide) (hereinafter PPTA
That. ) Was carried out. Dry the flask thoroughly,
-Methyl-2-pyrrolidone (hereinafter referred to as NMP) 4
200 g was charged, and 272.7 g of calcium chloride dried at 200 ° C. for 2 hours was added, and the temperature was raised to 100 ° C. After the calcium chloride was completely dissolved, the temperature was returned to room temperature, and paraphenylenediamine (hereinafter referred to as PPD) 132.9 was used.
g was added and completely dissolved. This solution is kept at 20 ℃ ± 2 ℃
Terephthalic acid chloride (hereinafter TPC)
That. ) 243.3 g were added in 10 portions and added approximately every 5 minutes. Thereafter, the solution was aged for 1 hour while maintaining the solution at 20 ° C. ± 2 ° C., and stirred under reduced pressure for 30 minutes to remove bubbles. The obtained polymerization liquid (polymer dope) showed optical anisotropy.
A part of the polymerization solution was sampled, reprecipitated with water, taken out as a polymer, and the intrinsic viscosity of the obtained PPTA was measured to be 1.97 dl / g.

2. Preparation of PPTA Solution 100 g of the polymerization solution of the above item 1 was weighed into a 500 ml separable flask having a stirring blade, a thermometer, a nitrogen inlet tube and a liquid addition port, and 5.8% by weight of chloride was added. An NMP solution in which calcium was dissolved was gradually added. Finally,
A PPTA solution having a PPTA concentration of 2.8% by weight is prepared,
This was designated as solution A.

3. Preparation of porous film (low-temperature precipitation method) Bar coater (0.60 m thick) manufactured by Tester Sangyo Co., Ltd.
m), the liquid A was formed into a film on a glass plate to form a film. Immediately after being kept in a freezer at −20 ° C. for about 1 hour, PPTA was precipitated to form a cloudy film. In this case, no dew condensation of water was observed on the surface of the film. This film was immersed in ion-exchanged water. After several minutes, the film-like material was peeled off from the glass plate. The membrane was immersed for about one hour while flowing ion-exchanged water, and then taken out on a circular filter paper having a diameter of 11 cm. The film was transferred to a dry filter paper, fixed in a circular frame while sandwiching the filter paper, and dried at 120 ° C. for 2 hours.
The film obtained by drying had a thickness of 84.2 μm and a porosity of 84%. Further, when observed with a scanning electron microscope, the obtained porous film was about 0.1 to 0.1.
It was made of 3 μm fibrillar PPTA fiber, and the diameter of the pores was about 1 μm or less.

4. Application to Battery Separator The positive electrode was prepared by applying a paste (NMP solvent) obtained by mixing lithium nickelate powder, carbonaceous conductive material powder, and polyvinylidene fluoride in a weight ratio of 87: 10: 3 to a 20 μm aluminum foil, drying, A sheet having a thickness of 92 μm (packing density: 3.0 g / cc) was prepared and used by pressing. The negative electrode was composed of graphite powder and polyvinylidene fluoride in a weight ratio of 90: 1.
The paste (NMP solvent) mixed at 0 was applied to a 10 μm copper foil, dried and pressed to produce a 110 μm thick sheet, which was used. The electrolyte is prepared by dissolving lithium hexafluorophosphate in a mixed solvent of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate (1 mol / l).
Concentration).

As the separator, the porous film prepared in item 3 was used. The battery has a positive electrode area of 2.34 square cm.
The negative electrode sheet, the separator, and the positive electrode sheet were sequentially stacked in an argon atmosphere box in an argon atmosphere box, and then sufficiently impregnated with an electrolytic solution. The prepared battery was charged at a charge voltage of 4.2 V and a discharge voltage of 2.
When the cycle was repeated at 75 V for 8 cycles, the discharge capacity at the 5th cycle was 6.6 mAH (discharge current: 1.5 mA), and the circuit operated normally without cycle deterioration.

Example 2 A PPTA was experimentally produced in the same manner as in Example 1. PPT obtained
A had an intrinsic viscosity of 2.07 dl / g. This PPT
The polymerization solution A was diluted with an NMP solution in which calcium chloride was dissolved to obtain a solution B. Solution B had a PPTA concentration of 2.0% by weight, and calcium chloride had a ratio of 3 moles to 1 mole of amide groups of PPTA. Liquid B was formed on a glass plate into a film (thickness: 0.35 mm), and a film was prepared according to Example 1. In this case, moisture was condensed on the surface of the film when the film was taken out of the refrigerator. The thickness of the film was 9.2 μm, the porosity was 50%, and the tensile strength was 4.7 kg / mm ² .

Example 3 The PPTA polymerization solution obtained in Example 2 was diluted with NMP,
Solution C was used. Solution C had a PPTA concentration of 2.0% by weight, and calcium chloride had a ratio of 2 moles to 1 mole of amide groups of PPTA. Liquid C was formed in a film shape on a glass plate (film thickness: 0.60 mm), and a film was prepared according to Example 1. Also in this case, when the film was taken out of the refrigerator in the same manner as in Example 2, water condensation was observed on the surface of the film. The thickness of the film is 15.6 μm and the porosity is 43
%, And the tensile strength was 10.9 kg / mm ² . From the above examples, it was found that the porosity can be adjusted by the cooling temperature, humidity, and the like.

Example 4 1. Preparation of porous film (high-temperature deposition method) A bar coater (0.60 m thick) manufactured by Tester Sangyo Co., Ltd.
According to m), the liquid A was formed into a film on a glass plate to form a film. Immediately after being kept in a heating oven at 60 ° C. for about 20 minutes, PPTA was deposited to form a cloudy film.
This film was immersed in ion-exchanged water. After several minutes, the film-like material was peeled off from the glass plate. While flowing deionized water,
After this film was immersed for about 1 hour, it was taken out on a circular filter paper having a diameter of 11 cm. Transfer the film to dry filter paper,
It was fixed to a circular frame while being sandwiched by filter paper, and dried at 120 ° C. for 2 hours. The film obtained by drying has a thickness of 11.4 μm.
And the porosity was 45%. When observed with a scanning electron microscope, the obtained porous film was about 0.1%.
It was a porous film having a large number of voids made of a fibrillar PPTA fiber of μm. The pore diameter was about 1 μm or less. The coefficient of linear thermal expansion measured between 200 and 300 ° C. was −6.3 × 10 ⁻⁶ / ° C.

2. Application to Battery Separator The positive electrode was prepared by applying a paste (NMP solvent) obtained by mixing lithium nickelate powder, carbonaceous conductive material powder, and polyvinylidene fluoride in a weight ratio of 87: 10: 3 to a 20 μm aluminum foil, drying, A sheet having a thickness of 92 μm (packing density: 3.0 g / cc) was prepared and used by pressing. The negative electrode was composed of graphite powder and polyvinylidene fluoride in a weight ratio of 90: 1.
The paste (NMP solvent) mixed at 0 was applied to a 10 μm copper foil, dried and pressed to produce a 110 μm thick sheet, which was used. The electrolyte is prepared by dissolving lithium hexafluorophosphate in a mixed solvent of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate (1 mol / l).
Concentration).

As the separator, the porous film prepared in the item 1 was used. The battery has a positive electrode area of 2.34 square cm.
The negative electrode sheet, the separator, and the positive electrode sheet were sequentially stacked in an argon atmosphere box in an argon atmosphere box, and then sufficiently impregnated with an electrolytic solution. The prepared battery was charged at a charge voltage of 4.2 V and a discharge voltage of 2.
When the cycle was repeated at 75 V for 8 cycles, the discharge capacity at the 8th cycle was 7.3 mAH (discharge current: 1.5 mA), and the circuit operated normally without cycle deterioration.

Examples 5 to 7 PPTA was experimentally produced according to Example 4. PPT obtained
A had an intrinsic viscosity of 2.07 dl / g. This PPT
The polymerization solution A was diluted with NMP in which calcium chloride was dissolved to obtain a solution having the composition shown in Table 1. The solution was formed into a film on a glass plate, and immediately kept in a heating oven at 40 ° C. for about 20 minutes. As a result, PPTA was deposited to form a cloudy film. The film was immersed in ion-exchanged water and dried in the same manner as in Example 4, and the thickness, porosity and tensile strength of the obtained film were measured. The results are shown in Table 1.

[0067]

Table 1 Example 5 Example 6 Example 7 ───────────────────────────── CaCl ₂ / amide group (mol / mol) 4.0 3.0 2.0 Polymer concentration (% By weight) 2.0 2.0 2.0 Film thickness of bar coater (mm) 0.35 0.35 0.35 Film thickness (μm) 9.3 9.2 8.6 Porosity (%) 38 47 51 Tensile strength (kg / mm ² ) 12.8 9.2 10.6 Coefficient of linear thermal expansion (/ ° C) -4.7 × 10 ^-6 -5.4 × 10 ^-6 -5.9 × 10 ^-6 ────── ───────────────────────────

Example 8 1. Polymerization of poly (paraphenylene terephthalamide) PPTA was polymerized using a 5-liter separable flask having a stirring blade, a thermometer, a nitrogen inlet tube and a powder addition port. The flask was sufficiently dried, charged with 4200 g of NMP, and dried at 200 ° C. for 2 hours.
2.7 g was added and the temperature was raised to 100 ° C. After the calcium chloride was completely dissolved, the temperature was returned to room temperature, and PPD132.9 was obtained.
g was added and completely dissolved. This solution is kept at 20 ℃ ± 2 ℃
, While dividing 243.3 g of TPC into 10
Added every minute. Thereafter, the solution was aged for 1 hour while maintaining the solution at 20 ° C. ± 2 ° C., and stirred under reduced pressure for 30 minutes to remove bubbles. The obtained polymerization liquid (polymer dope) showed optical anisotropy. A part of the polymerization solution was sampled, reprecipitated with water, taken out as a polymer, and the intrinsic viscosity of the obtained PPTA was measured to be 1.98 dl / g.

2. Preparation of PPTA Solution 100 g of the polymerization solution of the above item 1 was weighed into a 500 ml separable flask having a stirring blade, a thermometer, a nitrogen inlet tube and a liquid addition port, and calcium chloride was dissolved therein. NM
The P solution was added slowly. Finally, a PPTA solution having a PPTA concentration of 2.0% by weight and a calcium chloride having a molar concentration of 4 times the amide group of PPTA (calculated from the amount of PPD charged at the time of polymerization) was prepared. did.

3. Preparation of porous film (coagulation liquid immersion method) Tester Sangyo Co., Ltd. bar coater (film thickness 0.35 m)
m), liquid D is formed into a film on a glass plate, and 10%
Was immersed in ion-exchanged water containing NMP. After several minutes, the film-like material was peeled off from the glass plate. This membrane was immersed for about 1 hour while flowing ion-exchanged water. Next, the film was taken out of the water, the free water was wiped off, sandwiched between filter papers, and further sandwiched between glass cloths. The film was sandwiched between filter paper and glass cloth, placed on an aluminum plate, covered with a nylon film, the nylon film and the aluminum plate were sealed with gum, and a conduit for decompression was provided. The whole was put in a hot oven and dried at 120 ° C. while reducing the pressure. The resulting film has a thickness of 15.1 μm,
The porosity was 62.3% and the strength was 6.3 kg / mm ² . Further, when observed with a scanning electron microscope, the glass plate side of the obtained porous film was 0.02 to 0.0
It was composed of fibrils made of 5 μm PPTA and had many voids. The other side is 0.01-0.03 μm
Was formed. The coefficient of thermal expansion is-
7.3 × 10 ⁻⁶ / ° C.

4. Application to Battery Separator The positive electrode was prepared by applying a paste (NMP solvent) obtained by mixing lithium nickelate powder, carbonaceous conductive material powder, and polyvinylidene fluoride in a weight ratio of 87: 10: 3 to a 20 μm aluminum foil, drying, A sheet having a thickness of 92 μm (packing density: 3.0 g / cc) was prepared and used by pressing. The negative electrode was composed of graphite powder and polyvinylidene fluoride in a weight ratio of 90: 1.
The paste (NMP solvent) mixed at 0 was applied to a 10 μm copper foil, dried and pressed to produce a 110 μm thick sheet, which was used. The electrolyte is prepared by dissolving lithium hexafluorophosphate in a mixed solvent of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate (1 mol / l).
Concentration).

As the separator, the porous film prepared in the item 3 was used. The battery has a positive electrode area of 2.34 square cm.
The negative electrode sheet, the separator, and the positive electrode sheet were sequentially stacked in an argon atmosphere box in an argon atmosphere box, and then sufficiently impregnated with an electrolytic solution. The prepared battery was charged at a charge voltage of 4.2 V and a discharge voltage of 2.
When the cycle was repeated at 75 V for 6 cycles, the discharge capacity at the 6th cycle was 6.7 mAH (discharge current: 1.5 mA), and the cycle deterioration was relatively small, and the operation was almost normal.

Examples 9 to 12 According to Example 8, PPTA solutions were prepared. The PPTA polymerization solution of Example 8 was diluted with NMP or NMP in which calcium chloride was dissolved to obtain a solution having the composition shown in Table 2. The solution was formed into a film on a glass plate, and a porous film was produced as a trial according to Example 8. The physical properties of this film are also shown in Table 2.

[0074]

[Table 2] Example 9 Example 10 Example 11 Example 12 ─────────────────────────────────── CaCl ₂ / amide group (mol / mol) 2.0 2 0.0 4.0 4.0 Polymer concentration (% by weight) 2.0 2.0 2.0 2.0 NMP concentration of coagulation liquid (% by weight) 10 30 30 50 Film thickness (μm) 14.7 11.9 12.7 13.6 Porosity (%) 66 63 61 64 Tensile strength (kg / mm ² ) 5.5 5.6 7.0 6.2 ────────────────────

Example 13 1. Polymerization of poly (paraphenylene terephthalamide) PPTA was polymerized using a 500 ml separable flask having a stirring blade, a thermometer, a nitrogen inlet tube and a powder addition port. Dry the flask thoroughly, 420g NMP
And dried at 200 ° C. for 2 hours.
8 g was added and the temperature was raised to 100 ° C. After the calcium chloride was completely dissolved, the temperature was returned to room temperature, and 12.8 g of PPD was added and completely dissolved. While maintaining this solution at 20 ° C. ± 2 ° C., 23.3 g of TPC was added in 10 portions and added about every 5 minutes. Thereafter, the solution was aged for 1 hour while maintaining the solution at 20 ° C. ± 2 ° C., and stirred under reduced pressure for 30 minutes to remove bubbles. The obtained polymerization liquid (polymer dope) showed optical anisotropy. A part of the polymerization solution was sampled, reprecipitated with water and taken out as a polymer, and the intrinsic viscosity of the obtained PPTA was 1.83 dl / g.

2. Preparation of PPTA Solution 100 g of the polymerization solution of the above item 1 was weighed into a 500 ml separable flask having a stirring blade, a thermometer, a nitrogen inlet tube and a liquid addition port, and NMP was gradually added. Finally, a PPTA solution having a PPTA concentration of 2.0% by weight and calcium chloride having a molar concentration twice as large as that of the amide group of PPTA (calculated from the amount of PPD charged during polymerization) was prepared. did.

3. Preparation of Porous Film A bar coater manufactured by Tester Sangyo Co., Ltd. (film thickness 0.35 m)
m) to form a liquid E on the glass plate in the form of a film,
Was immersed in ion-exchanged water containing NMP. After several minutes, the film-like material was peeled off from the glass plate. The film was immersed for about 12 hours while flowing ion-exchanged water. Next, the film was taken out of the water and free water was wiped off. The film was sandwiched between filter papers, further sandwiched between Teflon frames having an outer diameter of 125 mm and an inner diameter of 100 mm, and the frames were fixed with clips. The whole was put in a hot oven and dried at 120 ° C. for 1 hour. The resulting film has a thickness of 9.4 μm and a porosity of 46.4.
%Met. Observation with a scanning electron microscope revealed that the film was a porous film as shown in FIGS. 0.02 to 0.05 μm P on the glass plate side (Fig. 1)
It was composed of fibrils made of PTA and had many voids. The opposite side, ie, the coagulating liquid side (FIG. 2) is 0.01
It was in a form having a void of about 0.03 μm.

Example 14 PPTA for film production without diluting the polymerization solution of Example 8
Used directly as a solution. A PPTA solution was formed in a film shape on a glass plate using a bar coater (thickness: 0.60 mm) manufactured by Tester Sangyo Co., Ltd., and immersed in an acetone solution containing 1% NMP. After 10 minutes, the film was peeled off from the glass plate. The deposited film was taken out of the acetone solution and immersed in ion-exchanged water for 15 hours. Next, it was taken out of the water, free water was wiped off, and then sandwiched between filter papers, and further sandwiched between glass cloths. The membrane was sandwiched between filter paper and glass cloth, placed on an aluminum plate, covered with a nylon film, the nylon film and the aluminum plate were sealed with a gum, and a conduit for decompression was provided. The whole was put in a hot oven and dried at 120 ° C. while reducing the pressure. The obtained film has a thickness of 264 μm and a porosity of 86.8%.
Met. 3 and 4 show the results of observation with a scanning electron microscope. The glass plate side (FIG. 3) of the obtained porous film had many voids of about 1 to 10 μm. The other side, ie, the coagulating liquid side (FIG. 4) is approximately 0.5 μm
It was a porous film having a fibril diameter of m.
The coefficient of linear thermal expansion was 22 × 10 ⁻⁶ / ° C. between 200 and 300 ° C.

Example 15 According to the method of Example 1, the intrinsic viscosity was 1.74 dl / g.
Of PPTA having a PPTA concentration of 2.0% by weight and calcium chloride having a molar ratio of calcium chloride / PPD of 2.
A NMP solution containing 0 / 2.0 mol / mol was applied on a glass plate with a bar coater (0.80 mm in thickness) manufactured by Tester Sangyo Co., Ltd., and immediately immersed in a 30% NMP aqueous solution to form a film. During this time, PPTA was deposited and the film became cloudy. This film was immersed in ion-exchanged water. After a few minutes, the film was peeled from the glass plate. The membrane was immersed for about one hour while flowing ion-exchanged water, and then taken out on a circular filter paper having a diameter of 11 cm. The film was transferred to dry filter paper and fixed in a circular frame while sandwiching the filter paper.
Dried for 2 hours at ° C. The resulting film has a thickness of 42μ.
m and the porosity was 56%. This film was immersed in water, frozen, solidified, and broken. The folded film was dried and its cross section was observed with a scanning electron microscope. As shown in FIG. 5, it was a porous film having a layer structure in which flakes made of PPTA fibrils were stacked.

Comparative Example 1 (Examination of Example 10 in Japanese Patent Publication No. 59-36939) 50 having a stirring blade, a thermometer, a nitrogen inlet tube and a powder addition port.
PPTA was polymerized using a 0 ml separable flask. 12. Calcium chloride in 400 ml NMP
96 g and PPD 6.28 g (0.05807 mol)
Was dissolved and cooled to 0 ° C. About TPC1 in powder form
2.21 g (0.06014 mol) was added all at once and polymerized. After aging for 30 minutes, 8.5% by weight of water based on NPM was added to the PPTA solution. As a result, white PPTA was precipitated on the surface of the solution, and finally the whole was solidified. This P
A part of the PTA solution was taken, reprecipitated in water, washed and dried, and the intrinsic viscosity was measured to be 1.55 dl / g.

Comparative Example 2 (Japanese Examined Patent Publication No. 59-36939) Additional test of Example 10, except that the molar ratio of PPD / TPC was brought close to 1. A stirring blade, a thermometer, a nitrogen inlet tube and a powder addition port were provided. 50
PPTA was polymerized using a 0 ml separable flask. 12. Calcium chloride in 400 ml NMP
80 g and 6.73 g (0.06223 mol) of PPD
Was dissolved and cooled to 0 ° C. About TPC1 in powder form
2.88 g (0.06344 mol) were added all at once and polymerized. After aging for 60 minutes, the PPTA solution solidified in a jelly state. Take a part of the solidified polymer and reprecipitate in water,
When the intrinsic viscosity was measured after washing and drying, 2.33 dl /
g. As described above, a supplementary test of JP-B-59-36939 was conducted, but the intrinsic viscosity described in Example 10 was 3.81 dl / g, and a polymerization solution in a solution state could not be prepared.

Comparative Example 3 (Examination of Japanese Patent Publication No. 59-14494, Example 3) 50 having a stirring blade, a thermometer, a nitrogen inlet tube and a powder addition port.
PPTA was polymerized using a 0 ml separable flask. 12. Calcium chloride in 400 ml NMP
96 g and PPD 6.28 g (0.05807 mol)
Was dissolved and cooled to 0 ° C. About TPC1 in powder form
2.21 g (0.06014 mol) was added all at once and polymerized. After aging for 30 minutes, the PPTA solution was applied on a glass plate using a bar coater (film thickness: 0.60 mm) manufactured by Tester Sangyo Co., Ltd., immediately maintained at −30 ° C. in a nitrogen atmosphere for 10 minutes, and then −70 ° C. ℃ dry ice-
It was immersed in an acetone solution for 4 hours to obtain a film. This film was washed with water and dried. The resulting film was yellow and transparent. The porosity of this film was 26.4%. FIG. 6 shows a scanning electron micrograph of the obtained film. The photograph shows vapor deposited Au particles and the film surface is smooth, indicating the absence of fibrils.

Comparative Example 4 (Additional Examination of Example 1 in JP-B-59-36939) Polymetaphenylene isophthalate having an intrinsic viscosity of 1.35 dl / g in 18 g of N, N'-dimethylacetamide in which 0.67 g of lithium chloride was dissolved. 4 g of amide was added and dissolved.
Then, 2.17 g of water was added to this solution at room temperature and stirred to obtain a transparent and highly viscous composition solution. This composition solution was applied to a bar coater (film thickness 0.6) manufactured by Tester Sangyo Co., Ltd.
0 mm), stored in a hot air circulating drier set at 140 ° C. for 20 minutes, taken out into water, washed with water and dried. The obtained film was transparent and had a porosity of 15.0%. FIG. 7 shows a scanning electron micrograph of the obtained film. As a result of observation, pores were partially observed, but no fibrils were observed.

Comparative Example 5 8.4 g of polymetaphenylene isophthalamide having an intrinsic viscosity of 1.35 L / g was stirred and dissolved at 90 ° C. in 95.4 g of NMP. The resulting solution was cooled to 10C.
After cooling, the solution was clear. a) The above solution was applied on a glass plate using a bar coater (film thickness: 0.60 mm) manufactured by Tester Sangyo Co., Ltd.
After storing in a hot air circulating drier set at 40 ° C. for 20 minutes, it was taken out into water, washed with water and dried. The obtained film was transparent and had a porosity of 11.2%. (The true specific gravity of polymetaphenylene isophthalamide is 1.38 g /
cm ³ . B) The above solution was applied on a glass plate using a bar coater (film thickness: 0.60 mm) manufactured by Tester Sangyo Co., Ltd., immersed in water, washed with water, and dried. The obtained film had irregularities on the surface and was cloudy. FIG. 8 shows a scanning electron micrograph of the obtained film. As a result of observation, pores were partially observed, but no fibrils were observed. c) The above solution was applied on a glass plate with a bar coater (film thickness 0.60 mm) manufactured by Tester Sangyo Co., Ltd.
After being immersed in a 5% by weight aqueous solution of calcium chloride, washed with water,
Dried. The obtained film had irregularities on the surface and was cloudy. A scanning electron micrograph of the obtained film was observed, but no fibrils were found.

Comparative Example 6 (Examination of Example 7 in JP-B-59-36939) 5 g of polymetaphenylene isophthalamide having an intrinsic viscosity of 1.35 dl / g was stirred and dissolved in 20 g of NMP at 90 ° C. When the obtained solution was cooled to 10 ° C., the solution was thickened and devitrified. a) The above solution was applied to a glass plate with a thickness of 0.60 mm by a bar coater manufactured by Tester Sangyo Co., Ltd. This was stored in a hot air circulating drier set at 140 ° C. for 20 minutes, washed with water and dried. The resulting film was translucent. As a result of observation with an electron microscope, no pores or fibrils were observed. b) The above solution was applied on a glass plate with a thickness of 0.60 mm using a bar coater manufactured by Tester Sangyo Co., Ltd.
After being immersed in a weight% aqueous solution of calcium chloride, it was washed with water and dried. The obtained film had irregularities on the surface and was cloudy. As a result of observation with an electron microscope, no fibrils were observed.

[0086]

The porous film of para-oriented aromatic polyamide produced by the method of the present invention is excellent in heat resistance, rigidity and strength, and cannot be achieved with a conventional nonwoven fabric, and has a fibril diameter of about 1 μm or less. Fibrils are arranged on a plane in a mesh or non-woven shape, and have a structure overlapping in layers. The coefficient of linear thermal expansion of the film at 200 to 300 ° C. is as small as ± 50 × 10 ^-6 and the porosity of the film is small. It has a property of 30 to 95% which is not available in the conventional aramid film. In particular, the film obtained by the coagulation liquid immersion method has a relatively small void size on one side of the film and a large size on the opposite side, which cannot be achieved with a conventional nonwoven fabric, and the fibril diameter also varies in the thickness direction. Have different structures. Utilizing these properties, the porous film of the present invention is suitable for a battery separator.

[Brief description of the drawings]

FIG. 1 shows the structure of the surface of the porous film obtained in Example 6 on the glass plate side. Photo (magnification 500)
Scanning electron micrograph at × 00).

FIG. 2 shows the structure of the surface on the coagulation liquid side of the porous film obtained in Example 6. A photo (magnification 5000)
Scanning electron micrograph at 0x).

FIG. 3 shows the structure of the surface of the porous film obtained in Example 7 on the glass plate side. Photo (100x magnification)
Scanning electron micrograph at 0x).

FIG. 4 shows the structure of the surface of the porous film obtained in Example 7 on the coagulating liquid side. A photo (magnification 5000)
Magnification scanning electron micrograph).

FIG. 5 shows a cross-sectional structure of the porous film obtained in Example 15. A photograph instead of a drawing (a scanning electron micrograph at a magnification of 5,000).

FIG. 6 shows the structure of the surface of the film obtained in Comparative Example 3 on the coagulation liquid side. A photograph (scanning electron micrograph at 100,000 magnification) replacing the drawing.

FIG. 7 shows the structure of the surface on the coagulation liquid side of the porous film obtained in Comparative Example 4. Photo (100x magnification)
Scanning electron micrograph at × 00).

FIG. 8 shows the structure of the surface of the porous film obtained in Comparative Example 5 on the glass plate side. Photo (magnification 500)
Magnification scanning electron micrograph).

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-56-8441 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C08J 9/26 101

Claims (10)

(57) [Claims] 1. A porous film comprising a para-oriented aromatic polyamide, wherein the film is composed of fibrils having a diameter of 1 μm or less, and the fibrils are arranged in a network or a nonwoven fabric on a plane and overlap in layers. A para-oriented aromatic polyamide having a structure, a coefficient of linear thermal expansion of the film at 200 to 300 ° C. within ± 50 × 10 ⁻⁶ / ° C., and a porosity of 30 to 95%. Porous film. 2. The size of a void formed by fibrils is as follows:
2. The para-oriented aromatic polyamide porous film according to claim 1, wherein one side of the porous film is relatively small and the other side is large. 3. The size of a void formed by fibrils is as follows:
3. The para-oriented aromatic polyamide porous film according to claim 2, wherein the porous film has a continuously different structure in the thickness direction of the porous film. 4. The para-oriented aromatic polyamide is poly (paraphenylene terephthalamide), poly (parabenzamide), poly (4,4'-benzanilide terephthalamide), poly (paraphenylene-4,4'-biphenylene). Dicarboxylic acid amide), poly (paraphenylene-2,6)
-Naphthalenedicarboxylic acid amide), poly (2-chloro-paraphenyleneterephthalamide), or a copolymer consisting of paraphenylenediamine / 2,6-dichloroparaphenylenediamine / terephthalic dichloride. 4. The para-oriented aromatic polyamide porous film according to any one of 1 to 3. 5. A method for producing a para-oriented aromatic polyamide porous film, comprising the following steps (a) to (c). (A) 1 to 10% by weight of a para-oriented aromatic polyamide having an intrinsic viscosity of 1.0 to 2.8 dl / g in a polar amide-based solvent or a polar urea-based solvent, Forming a film from a solution containing 1 to 10% by weight of the substance. (B) maintaining the film at a temperature of 20 ° C. or higher or −5 ° C. or lower to precipitate para-oriented aromatic polyamide. (C) The film obtained in step (b) is immersed in an aqueous solution or an alcoholic solution to elute the solvent and the chloride of the alkali metal or alkaline earth metal, and then dried to dry the para-oriented aromatic polyamide porous material. Obtaining a quality film. 6. A method for producing a para-oriented aromatic polyamide porous film, comprising the following steps (d) to (f). (D) In a polar amide-based solvent or a polar urea-based solvent, 1 to 10% by weight of a para-oriented aromatic polyamide having an intrinsic viscosity of 1.0 to 2.8 dl / g, and chloride of an alkali metal or an alkaline earth metal. Forming a film from a solution containing 1 to 10% by weight of the substance. (E) a step of immersing the film in a coagulation liquid containing 0 to 70% by weight of a polar amide solvent or a polar urea solvent to coagulate and precipitate the para-oriented aromatic polyamide. (F) dipping the film-like material obtained in step (e) in an aqueous solution or an alcohol-based solution to elute a solvent and a chloride of an alkali metal or an alkaline earth metal, and then drying and evaporating the para-oriented aromatic polyamide porous material; Obtaining a quality film. 7. The method according to claim 1, wherein the polar amide solvent or the polar urea solvent is N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone or tetramethylurea. 7. The method for producing a para-oriented aromatic polyamide porous film according to 5 or 6. 8. The method for producing a para-oriented aromatic polyamide porous film according to claim 5, wherein the chloride of the alkali metal or alkaline earth metal is lithium chloride or calcium chloride. 9. A para-oriented aromatic polyamide porous film produced by the method according to claim 5. Description: 10. A battery separator comprising the aromatic polyamide porous film according to any one of claims 1 to 4.