JP2003026849A - Porous polyimide film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide porous polyimide film that has a uniform pore diameter and distribution. SOLUTION: The porous polyimide film has pores on the both sun faces and satisfies the following conditions: (1) The difference in the average pore sizes on both sun faces is smaller than 200% calculating pore sizes by using the smaller average value between the average pore values on one or the other sun faces; (2) The variation index of the pore diameter is smaller than 70% in individual sun faces; (3) The variation index of the pore distance is smaller than 50% on individual sun faces; (4) The average pore size is 0.05-5 μm on individual sun faces.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyimide porous membrane having uniform pore diameters and uniform pore distances.

[0002]

2. Description of the Related Art As a method for producing a porous polyimide film,
T. Takeichi et. al. High Per
format Polymers, Vol. 11, 1p
(1999), the polyimide porous membrane is made of polyurethane-
Synthesize imide and then add urethane segment to 300
It is disclosed that a polyimide porous film is obtained by decomposition by heat treatment at ˜400 ° C.

Also, Polymer 36, 1325, 1995, and Polymer
37,5229,1996 discloses a method of obtaining a porous polyimide that decomposes by making a segment copolymer other than polyimide an α-methylstyrene segment that is easily decomposed into a block copolymer or a graft copolymer made of polyimide, and subjecting the segment other than the polyimide to heat treatment. Has been done.

Further, the present inventors have disclosed in Japanese Patent Laid-Open No. 11-310.
As the Japanese Patent No. 658, inventing a porous film having through holes in the film cross section and having no dense layer on the surface. This manufacturing method, the polyimide precursor solution is cast on the substrate, by contacting the coagulation solvent through the solvent displacement rate adjusting material, to deposit a porous film of the polyimide precursor having the through holes. There is.

In addition, Japanese Patent Laid-Open No. 2001-1 by the present inventors
Japanese Patent Laid-Open No. 45826 discloses a method for producing a polyimide porous membrane, which comprises using a mixed solution of a good solvent and a non-solvent as a polyimide precursor precursor.

Further, it is desired to obtain a polyimide membrane which is simpler and can be manufactured economically and inexpensively without using a solvent substitution rate adjusting material or the like.
There is also a demand for a method of producing a polyimide porous membrane that is homogeneous in quality. However, it was difficult to obtain a uniform polyimide porous film.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a porous polyimide film having a uniform pore diameter and a distance between pores.

In the present invention, when a liquid film of a polyimide precursor is cast to obtain a solid film, the composition gradient of the dope solution of the polyimide precursor and the coagulation bath is made as slow as possible to generate pores. The present invention has been completed based on the finding that a more uniform porous film can be obtained in terms of quality.

[0009]

The present invention has pores on both sides, and each pore has the following conditions 1) to 4): 1) The difference between the average pore diameters on both sides is the average of the average pore diameters. It is smaller than 200% based on the smaller value. 2) The variation coefficient of the pore diameter on each surface is smaller than 70%. 3) The coefficient of variation of the distance between holes on each surface is smaller than 50%. 4) The average pore size on each surface is 0.05 to 5 μm. The present invention relates to a polyimide porous membrane satisfying the above.

The polyimide porous membrane of the present invention is prepared by casting a polyimide precursor dope solution and immersing it in a coagulating liquid to produce a polyimide precursor porous membrane. The coagulation liquid can be obtained by a method for producing a polyimide porous film whose composition satisfies the conditions. (1) The polyimide precursor dope solution is 99.8 to 70% by weight of a mixed solvent in which the polyimide precursor is 0.2 to 30% by weight and its solvent and a non-solvent are mixed. (2) Of 100 wt% of the mixed solvent of the dope solution, 50-90 wt% of the solvent and 50-10 wt% of the non-solvent thereof
Is. (3) The coagulation liquid is 50 to 90% by weight of the non-solvent of the polyimide precursor and 50 to 10% by weight of the solvent, which is a total of 100% by weight. (4) However, the composition of the solvent of the dope solution is larger than the composition of the solvent of the coagulation liquid.

In the above method for producing a polyimide porous film, it is preferable that the solvent of the polyimide precursor is a polar organic solvent and the non-solvent is an aliphatic alcohol having 3 to 5 carbon atoms.

In the above method for producing a polyimide porous film, the thickness of the polyimide precursor porous film is 5 to 100 μm.
Is preferred.

In the above-mentioned method for producing a polyimide porous film, it is preferable that the polyimide precursor porous film is made into a polyimide porous film by heating or chemical imidization.

The polyimide porous film of the present invention has pores on both sides, and may be referred to as the atmosphere side surface and the substrate side surface during manufacturing. That is, when the liquid film is cast on the side surface of the substrate, the surface in contact with the side surface of the substrate is called the side surface of the substrate, and the surface opposite to the surface of the substrate, that is, the surface where the liquid film contacts the atmosphere when cast is called the side surface of the atmosphere. When the porous membrane is formed by being immersed in the coagulating liquid due to the difference in environmental conditions in which one of the both surfaces is in direct contact with the coagulating liquid and the other is in direct contact with the coagulating liquid, the pore diameter and the position of the pores on both surfaces are often Is often uneven. When these are used in a battery separator or a precision filter, they may cause a problem in liquid permeability or air permeability.

The present invention can be said to be a uniform porous membrane in which there is no difference in pore size on both sides. That is, 1) The difference between the average pore diameters of the atmosphere side surface and the substrate side surface is 200% based on the smaller average value of the average pore diameters.
It is smaller. Here, the average pore diameter refers to the number average value of the diameters of the pores when viewed from the surfaces of the atmosphere side surface and the substrate side surface, respectively. The difference in hole diameter between the atmosphere side surface and the substrate side surface is that the ratio of the difference between both average hole values is smaller than 200% with reference to the value of the surface having the smaller hole diameter. More preferably, it is less than 150%.
If it is more than 200%, the pore sizes on both sides are different,
When it is used for a battery separator or a filter, it is inconvenient because the difference in pore diameter between both sides is remarkable and the liquid permeation performance or air permeation performance is different.

Further, the porous membrane has uniform pore diameters on each surface. That is, 2) The variation coefficient of the hole diameter is smaller than 70% on each of the atmosphere side surface and the substrate side surface. The coefficient of variation (CV) of the distribution of pore diameters is expressed as the ratio of the standard deviation (σ) of the individual pore diameter values (X _i ) measured in the same manner as in the previous section to the number average value (X _n ). It is a thing (Equation 1). It can be used as a measure of the uniformity of pore size. More preferably, the variation coefficient of pore diameter is 60%. If the coefficient of variation of the pore diameter is larger than 70%, the variation of the pore diameter becomes large, so that when it is used in a filter or the like, the uniformity of the filtration performance is deteriorated, which is not preferable.

CV (%) = (σ / X _n ) × 100 (Equation 1)

Furthermore, the present invention is also a porous membrane in which the distance between the pores on each surface is uniform. 3) The variation coefficient of the distance between the centers of gravity of the holes is smaller than 50% on each of the atmosphere side surface and the substrate side surface.
The distance (l _i ) between the center of gravity of holes is the distance from the center of gravity of one hole to the center of gravity of the adjacent hole. This can be a measure of the location of the holes being uniform. If the coefficient of variation of the distance between the center of gravity of the holes is larger than 50%, the positions of the holes are varied, so that the filter and the separator are separated.
When it is used for a filter, an uneven pressure portion may occur, and the porous membrane may be damaged in some cases, which is not preferable. More preferably, the variation coefficient of the distance between the center of gravity of the holes is less than 45%. This value can be similarly obtained by replacing the hole diameter value with the inter-center-of-gravity distance value in the above Equation 1.

Further, in the present invention, it is important that the pore diameter is in a fine range on each surface. That is, 3) the average pore diameter is 0.05 to 5 μm on the atmosphere side surface and the substrate side surface. More preferably, 0.08
Is about 3 μm. If the average pore size is smaller than 0.3 μ, for example, the filtration rate will be poor when used in a filter. Further, if it is larger than 5 μm, the collection performance is deteriorated, so the above range is preferable.

A method for manufacturing the polyimide porous film will be described. The polyimide precursor is a polyamic acid obtained by polymerizing a monomer belonging to a tetracarboxylic acid component and a diamine component, preferably an aromatic compound, or a partially imidized polyamic acid thereof, and heat treatment or chemical imidization. By doing so, the ring can be closed to obtain a polyimide resin. A polyimide resin has an imidization ratio of about 50% described later.
The above heat-resistant polymer.

The tetracarboxylic acid component and the diamine component are
A polyimide precursor having a logarithmic viscosity (30 ° C., concentration; 0.5 g / 100 mL NMP) of 0.3 or more, particularly 0.5 to 7 is produced by dissolving and polymerizing in approximately the same molar amount in the above organic solvent. It Also, when the polymerization is carried out at a temperature of about 80 ° C. or higher, a partially ring-closed imidized polyimide precursor is produced.

As the diamine, for example, general formula (1)
Or _{(2) H 2 N-Ar} (R 1) -A-Ar (R 1) -NH 2 (1) or _{H 2 N-Ar (R 2} ) -Ar (R 2) -NH 2 (2) ( However, in the above general formula, R ₁ or R ₂ is a substituent such as hydrogen, lower alkyl, or lower alkoxy, and A is O, S, CO, SO ₂ , SO, CH ₂ , C.
(CH ₃₎ aromatic diamine compounds represented by ₂ is a divalent group such) is preferred.

Specific compounds include 4,4'-diaminodiphenyl ether (hereinafter sometimes abbreviated as DADE), 1,4-phenylenediamine, (hereinafter, P
Abbreviated as PDA), 3,3'-dimethyl-
4,4'-diaminodiphenyl ether, 3,3'-diethoxy-4,4'-diaminodiphenyl ether and the like can be mentioned.

The diamine component represented by the general formula H ₂ N—R—NH ₂ may be diaminopyridine represented by the general formula (3) H ₂ N— (Py) —NH ₂ (3). Well, specifically, 2,6-diaminopyridine, 3,6-diaminopyridine, 2,5-diaminopyridine, 3,4-diaminopyridine and the like can be mentioned.

As the biphenyltetracarboxylic acid component, 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride (hereinafter sometimes abbreviated as s-BPDA), 2,3,3', 4 '-Biphenyltetracarboxylic dianhydride (hereinafter sometimes abbreviated as a-BPDA) is preferable, but 2,3,3', 4'- or 3,
3 ', 4,4'-biphenyltetracarboxylic acid, or a salt of 2,3,3', 4'- or 3,3 ', 4,4'-biphenyltetracarboxylic acid or an esterified derivative thereof. Good. The biphenyltetracarboxylic acid component may be a mixture of the above biphenyltetracarboxylic acids.

In addition to the above-mentioned biphenyltetracarboxylic acids, the above-mentioned biphenyltetracarboxylic acid component is tetracarboxylic acid such as pyromellitic acid, 3,
3 ', 4,4'-benzophenone tetracarboxylic acid,
2,2-bis (3,4-dicarboxyphenyl) propane, bis (3,4-dicarboxyphenyl) sulfone,
Tetracarboxylic acids such as bis (3,4-dicarboxyphenyl) ether, bis (3,4-dicarboxyphenyl) thioether, butanetetracarboxylic acid, or their acid anhydrides, salts or esterified derivatives. Is 10 mol% or less based on the total tetracarboxylic acid component, especially 5
You may contain in the ratio of mol% or less.

The solution of the polyimide precursor of the present invention is a polar organic solvent such as N-methylpyrrolidone (NMP), p-chlorophenol (PCP), pyridine, N, N-dimethylacetamide (DMAc),
Examples thereof include N, N-dimethylformamide (DMF), dimethylsulfoxide (DMSO), tetramethylurea, phenol and cresol. Of which, NM
P, DMAc and DMSO are particularly preferred.

As the non-solvent for the polyimide precursor of the present invention, aliphatic alcohols, ketones, ethers, esters, water and the like can be mentioned, with aliphatic alcohols being particularly preferred. More preferably, it is an aliphatic alcohol having 3 to 8 carbon atoms. These are preferable because they have excellent compatibility with the polar organic solvent of the polyimide precursor. Specifically, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol
And tert-butanol are preferred. When a non-solvent such as an alcohol having a carbon number of 2 or less, for example, methanol or ethanol is used, the polyimide precursor solution is immediately polymerized.
Is deposited, and a uniform film may not be formed, which is inconvenient.

In the present invention, when a polyimide precursor dope solution is cast and immersed in a coagulating liquid to produce a polyimide precursor porous membrane, the following dope solution and coagulating liquid are used as composition conditions. A method for producing a polyimide porous membrane characterized by satisfying is preferable.

The polyimide precursor dope solution of the present invention is
It is preferable that the polyimide precursor is 0.2 to 30% by weight and a mixed solvent of 99.8 to 70% by weight obtained by mixing the solvent and the non-solvent. More preferably, it is 1 to 20% by weight. If the concentration of the polyimide precursor is less than 0.2% by weight, the film strength will be reduced, which is not preferable. If it exceeds 30% by weight, it is difficult to form a uniform polymer solution, which is not suitable.

The dope solution of the present invention comprises a mixed solvent consisting of a solvent for a polyimide precursor and a non-solvent, and the solvent is 50 to 70% of the mixed solvent of 100% by weight.
The weight percent and its non-solvent are 50 to 30 weight percent. The solvent is preferably 50 to 65% by weight. When the solvent content of the mixed solvent is less than 50% by weight, the polyimide precursor tends to precipitate, and when the solvent content is more than 70% by weight, it is difficult to form a uniform porous film.

A non-solvent for the polyimide precursor is added to the polyimide precursor dissolved in a solvent so that the polyimide precursor does not precipitate and the composition is kept in a solution state. The criterion for discrimination is that the solution becomes transparent or translucent to the naked eye. The composition of the dope is that the ratio of solvent to non-solvent is
With the above composition, a long-term storage-stable solution is obtained.

The method of casting the polyimide precursor solution to obtain a cast film is not particularly limited, but the polyimide precursor solution is used as a base material on a substrate such as a glass plate or a metal plate or a movable belt. A method such as a method of casting by a spray method or a doctor blade method and a method of extruding the polyimide precursor solution from a T-type die can be used. Alternatively, coating or spin casting may be used.

The casting dope solution may contain a surfactant, a flame retardant, a coloring agent, or a reinforcing material such as glass fiber, silicon fiber or carbon fiber. These additives and reinforcing materials may be added to the above polyimide precursor polymerization solution, or may be added to the casting dope solution.

Then, the dope solution is immersed in the coagulating liquid.
The coagulating liquid of the present invention is a non-solvent of the polyimide precursor 50 to 90
It is preferable that the total amount is 100% by weight, which is 50% by weight and 50% by weight of the solvent. More preferably, the non-solvent is 55-9
0% by weight and the solvent is 45 to 10% by weight. Non-solvent is 5
When it is less than 0% by weight, it takes a long time to form a solid film. Moreover, only a film having low dimensional stability can be formed. When the proportion of the non-solvent is more than 70% by weight, the film formation is too rapid to form a uniform porous film, and thus the above composition is preferable. Since the coagulation liquid having the above composition has a composition close to that of the polyimide precursor dope, the coagulation reaction is slow and phase separation is performed at a very slow rate. A porous film is formed up to the deep part and finally to the surface of the substrate.

However, the solvent composition of the dope solution must be larger than the solvent composition of the coagulating liquid. That is, when the composition of the solvent of the dope solution and the solvent of the coagulating liquid both are 50% by weight, the respective functions are not fulfilled with this composition. If the solvent composition of the coagulating liquid exceeds the solvent composition of the dope solution, the polyimide precursor liquid film will not be deposited as a solid film even when immersed in the coagulating liquid. The difference in the composition of the solvent between the dope solution and the coagulating liquid is preferably at least 10% by weight.

The polyimide precursor porous film obtained is washed with a non-solvent for the purpose of fixing the structure. The portion adhered or swollen on the film is washed with a nonsolvent of the polyimide precursor to fix the formed structure. Examples of the non-solvent used include aliphatic alcohols of the same type as the coagulating liquid component, aliphatic alcohols having 3 or less carbon atoms, aliphatic ketones, water and the like.

The thickness of the polyimide precursor porous film of the present invention is 5 to 100 μm. Preferably 5 to 90 μm
Is. If the thickness is less than 5 μm, the mechanical strength will be poor and it will be difficult to handle in the subsequent steps. Thickness is 100μ
If it is thicker than m, the solvent and the non-solvent may not be sufficiently penetrated to form a solid film, so that the pores may become small or the pores may not be opened, and the pore diameter may not be uniform.

The cleaned polyimide precursor film is attached to a pin tenter or the like. When the polyimide precursor film is heated, the degree of attachment is adjusted so that the polyimide precursor film does not break due to thermal contraction. Immediately dry and imidize. Temperature 50-1
Thermal imidization can be carried out by continuously or discontinuously drying at 00 ° C. in a hot air drier, a hot air oven or the like, and then further raising the temperature. Alternatively, chemical imidization may be used. The thermal imidization is performed by using a fatty acid anhydride or an aromatic acid anhydride as a dehydrating agent and imidizing with a tertiary amine such as triethylamine as a catalyst. As described in JP-A-4-339835, imidazole, benzimidazole or a substituted derivative thereof may be used. The thermal imidization will be described as an example.

The dried polyimide precursor has a temperature of 28.
The temperature is raised to 0 to 500 ° C. to perform thermal imidization. The temperature may be raised stepwise or may be raised to a predetermined temperature in one step. The temperature may be maintained at 280 to 500 ° C. for 5 to 240 minutes in the atmosphere, preferably in an inert atmosphere. Then, the temperature is lowered to room temperature to obtain a polyimide porous film.

The porosity of the polyimide porous film thus obtained varies depending on the manufacturing conditions, but is 20 to 70.
%, And the average pore diameter is 0.2 to 5 μm. In addition, the difference in the average pore diameter between the atmosphere surface and the substrate surface is smaller,
It is smaller than 0%. Further, it is possible to obtain a uniform porous membrane in which the variation coefficient of the pore diameter is less than 70% and the variation coefficient of the distance between the center of gravity of the pores is less than 50% on each surface.

The polyimide porous membrane may be used in one layer or in combination of two or more layers. Depending on the application, by combining two or more layers, or for reinforcement,
It can be used for thick materials. Further, it may be used in combination with other materials, other polymer films, fibers and inorganic substances.

[0043]

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

Porosity The thickness and weight of the porous film cut into a predetermined size were measured, and the porosity was determined from the weight per unit area by the following equation (2). In the formula (1), S means the area of the porous film, d means the film thickness, W means the measured weight, D means the density of the polyimide, and the density of the polyimide was 1.34 g / cm ³ . Porosity (%) = 100-100 × (W / D) / (S × d) (2)

Average Pore Diameter and Coefficient of Variation The pore diameter on the surface of the film was observed with a scanning electron microscope. The major axis and minor axis of the hole were measured, the area thereof was calculated, and the equivalent diameter of the circle was calculated. The number average pore diameter was determined for 100 or more pores.
The coefficient of variation was determined as in (Equation 1). The measurement was performed on each of the atmosphere side surface and the substrate side surface.

Average Distance Between Centers of Gravity and Coefficient of Variation The distance between the centers of gravity of the pores on the surface of the film and the nearest pore was read from a scanning electron micrograph at an arbitrary 100 points. The average distance between center of gravity and its coefficient of variation were calculated. The measurement was performed on each of the atmosphere side surface and the substrate side surface.

The puncture strength sample was fixed to a circular hole holder having a diameter of 11.28 mm and an area of 1 cm 2, and the tip shape was 0.5 R and the diameter was 1 mmφ.
The dollar was lowered at a speed of 2 mm / sec and pierced, and the penetration load was measured.

Smoothness The smoothness of the porous film was qualitatively evaluated visually. ◯: The surface was smooth. Δ: The surface was slightly uneven. X: Roughness was observed.

Example 1 PP for s-BPDA using s-BPDA as the tetracarboxylic acid component and DADE as the diamine component
It was dissolved in NMP so that the molar ratio of DA was 0.994 and the total weight of the monomer components was 19% by weight.
Polymerization was performed at 0 ° C. for 6 hours to obtain a polyimide precursor solution. 1-butanol was added to the polyimide precursor solution,
The polyimide precursor is 14% by weight, the mixed solvent is 86% by weight, NMP in the mixed solution is 66.3% by weight (57% by weight in the dope solution), and 1-butanol is 33.7% by weight.
A dope solution (29% by weight in the dope solution) was prepared, and the dope solution was cast on a glass plate so that the thickness was about 150 μm, and subsequently 1-butano- was kept at room temperature. Le 6
A polyimide precursor film was obtained by immersing in a coagulation liquid of 6.7 wt% and NMP 33.3 wt% for 15 minutes. It was washed with methanol and then with water, and dried at a temperature of 100 ° C. to obtain a polyimide precursor film. Immediately, remove the film from the glass plate, put the polyimide precursor film on the pin tenter, and set the temperature to 400
The mixture was placed in a hot air dryer at 0 ° C. and subjected to thermal imidization for 40 minutes. Thus, a polyimide porous film was obtained.

The polyimide porous film obtained had a thickness of 50.
μm, and the porosity was 65%. Observation with a scanning microscope has an average pore size of 0.09 μm and a coefficient of variation of 3 on the atmosphere surface side.
The average pore diameter was 0.18 μm on the side surface of the substrate, and the coefficient of variation was 52.1%. Average distance between centers of gravity of air holes on the atmosphere side is 0.33 μm, coefficient of variation is 36.9%, average distance between centers of gravity of holes on substrate side is 0.36 μm, coefficient of variation is 25.0%
Met. The ratio of the difference between the average hole diameters on the atmosphere side surface and the substrate side surface was 100% based on the value on the atmosphere side surface. Both sides were smooth and exhibited a uniform porous film. Scanning electron micrographs of the air side of the film and the side of the substrate are shown in FIGS. The results are summarized in Tables 1 and 2.

Comparative Example 1 A polyimide porous film was obtained in the same manner as in Example 1 except that the coagulating liquid was 100% by weight of 1-butanol. The film thickness is 51 μm, the porosity is 71%, and the average pore diameter on the atmosphere surface side is 0.0.
The average pore size on the substrate side was 6 μm, and the average pore size was 0.53 μm. The hole diameters on the atmosphere side and substrate side are 7 based on the hole diameter on the atmosphere side.
There was a large difference between the two surfaces, which was 98%. Scanning electron microscope photographs of the air side of the film and the side of the substrate are shown in FIGS. The results are summarized in Tables 1 and 2.

Example 2 Using s-BPDA as the tetracarboxylic acid component and PPDA as the diamine component, PP for s-BPDA was used.
It was dissolved in NMP so that the molar ratio of DA was 0.994 and the total weight of the monomer components was 8% by weight, and the temperature was 40%.
Polymerization was performed at 6 ° C. for 6 hours to obtain a polyimide precursor solution.

The solvent NMP of the polyimide precursor solution is 6
With respect to 1.7% by weight, non-solvent 1-propanol 38.
Add gradually with stirring to reach 3% by weight.
Solution. Dope solution composition is polyimide precursor 4.
It was 9% by weight and the mixed solvent was 95.1% by weight.

The polyimide precursor dope solution was cast on a glass plate with a doctor blade so that the thickness was 30 μm. Then, 80% by weight of 1-propanol which is a non-solvent of the polyimide precursor and NM which is a solvent.
It was immersed in a coagulation liquid prepared to P20 wt%. Upon immersion, the liquid film became cloudy in 1-2 seconds and a solid film was formed. Other than that was carried out similarly to Example 1, and obtained the polyimide film.

The thickness of the obtained polyimide porous film is 13
μm, the porosity was 51%. Observed with a scanning microscope, the atmospheric surface side has an average pore diameter of 0.48 μm and a coefficient of variation of 3
2.7%, the side surface of the substrate had an average pore diameter of 0.76 μm, and the coefficient of variation was 58.3%. Average distance between centers of gravity of air holes on the atmosphere side is 0.53 μm, coefficient of variation is 24.6%, distance between average centers of gravity of holes on substrate side is 0.90 μm, coefficient of variation is 39.8%.
Met. The ratio of the difference between the average hole diameters on the atmosphere side surface and the substrate side surface was 58% based on the value on the atmosphere side surface. Both sides were smooth and exhibited a uniform porous film. The results are summarized in Tables 1 and 2.

Example 3 DADE was used as the diamine component and 2-propanol was used as the non-solvent, and the concentration of the polyimide precursor in the dope solution was 6.3% by weight, the mixed solvent was 93.7% by weight, and the dope was mixed. The composition of the solvent was 62.5% by weight of the solvent, 37.5% by weight of the non-solvent, and 66.7% by weight of the non-solvent of the coagulating liquid and 33.3% by weight of the solvent were used in the same manner as in Example 2. A polyimide porous film was obtained.

The obtained polyimide porous film has a film thickness of 15
μ, porosity 41%, average pore size on the atmosphere side is 0.73
μm, coefficient of variation 35.3%, average pore size 1.
It was 33 μm and the coefficient of variation was 47.8%. Average distance between centers of gravity of holes on the atmosphere side is 1.94 μm, and coefficient of variation is 38.6.
%, The average distance between the centers of gravity of the holes on the side surface of the substrate was 2.71 μm, and the coefficient of variation was 38.1%. The difference in average pore size between the atmospheric surface and the substrate side surface was 82% based on the value on the atmospheric side surface. Both sides were smooth and exhibited a uniform porous membrane.
The results are summarized in Tables 1 and 2.

Example 4 DADE as the diamine component, DMAc as the solvent, and 2 as the non-solvent.
-Propanol, the concentration of the polyimide precursor in the dope solution is 5.9% by weight, the mixed solvent is 94.1% by weight, the composition of the dope mixed solvent is 58.8% by weight solvent, and 41. Two
A polyimide porous film was obtained in the same manner as in Example 2 except that the non-solvent of the coagulation liquid was 83.3% by weight and the solvent was 16.7% by weight.

The obtained polyimide porous film had a thickness of 14
μ, the porosity is 47%, the average pore size on the atmosphere side is 0.67
μm, the coefficient of variation is 46.4%, and the side surface of the substrate has an average pore diameter of 1.
It was 41 μm and the coefficient of variation was 30.4%. Average distance between centers of gravity of holes on the atmosphere side is 1.13 μm, coefficient of variation is 35.3
%, The average distance between the centers of gravity of the holes on the side surface of the substrate was 3.83 μm, and the coefficient of variation was 31.0%. The difference in average pore size between the atmosphere side surface and the substrate side surface was 110% based on the value on the atmosphere side surface. Both sides were smooth and exhibited a uniform porous film.
The results are summarized in Tables 1 and 2.

Comparative Example 2 The composition of the dope solution was 6.4% by weight of the polyimide precursor,
Dope mixed solvent is 93.6% by weight, mixed solvent is 8
A polyimide porous membrane was obtained in the same manner as in Example 2 except that 0% by weight, 20.0% by weight of nonsolvent, 95% by weight of nonsolvent of the coagulating liquid, and 5% by weight of solvent were used.

The polyimide porous film obtained had a film thickness of 24.
μ, porosity 53%, average pore size on the atmosphere side is 0.54
μm, the coefficient of variation is 36.0%, and the side surface of the substrate has an average pore diameter of 0.
It was 47 μm and the coefficient of variation was 98.2%. There was a large variation in the average hole diameter on the side surface of the substrate. Further, the variation coefficient of the distance between the centers of gravity on the side surface of the substrate was 51.2%, which was a large variation. The results are summarized in Tables 1 and 2.

Comparative Example 3 A polyimide film was produced in the same manner as in Example 2 except that the composition of the coagulating liquid was 45% by weight of the non-solvent and 55% by weight of the solvent.
After casting the polyimide precursor, dip it in the coagulation liquid, and then
After 5 minutes, a gel-like solid film was finally deposited.
The gel film was washed with methanol. The formed film was uneven and had no smoothness. There were large variations in the average hole diameter on the side surface of the substrate and the distance between the center of gravity of the holes on both side surfaces. The results of the other properties are shown in Table 2.

Comparative Example 4 The mixed solvent composition of the dope solution was 45% by weight of solvent and 5% of non-solvent.
A polyimide precursor solution was prepared in the same manner as in Example 1 with 5% by weight. However, the polymer was precipitated from the doped solution, so the film production was stopped.

Comparative Example 5 A polyimide film was obtained in the same manner as in Example 1 except that methanol was used as the non-solvent. The obtained polyimide film was a dense film on both sides, and no pores were observed.

[0065]

[Table 1] NMP; N-methylpyrrolidone, DMAc; N, N-dimethylacetamide, 1B; 1-butanol, 1P; 1-
Propanol, 2P; 2-propanol, M; methanol

[0066]

[Table 2]

[0067]

INDUSTRIAL APPLICABILITY The present invention relates to the production of a polyimide porous film having a small difference in pore diameter between the atmosphere surface and the substrate surface, and uniform pore diameter and distance between the centers of gravity of pores. The present invention, a polyimide precursor solution, a dope solution of a specific composition consisting of a solvent and a non-solvent of the polyimide precursor is cast, and immersed in a coagulating liquid of a specific composition consisting of a non-solvent and a solvent. The present invention provides a method for producing a polyimide porous film characterized by the above. The polyimide porous membrane has uniform liquid permeability on both sides, and can be provided for battery separators, fuel cell parts, and the like.

[Brief description of drawings]

FIG. 1 is an electron micrograph showing a surface of an air side surface of a polyimide porous film obtained in Example 1 of the present invention.

FIG. 2 is an electron micrograph showing the surface of the side surface of the substrate of the polyimide porous film obtained in Example 1 of the present invention.

FIG. 3 is an electron micrograph showing a surface of an air side surface of a polyimide porous film obtained in Comparative Example 1 of the present invention.

FIG. 4 is an electron micrograph showing a surface of a side surface of a substrate of a polyimide porous film obtained in Comparative Example 1 of the present invention.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kenji Fukunaga             No. 8 Ube Ko, No. 8 Goi Minami Coast, Ichihara City, Chiba Prefecture             Sanken Co., Ltd. F term (reference) 4F074 AA74 AD04 AD13 AD14 CB34                       CB37 CB43 DA03 DA23

Claims (2)

[Claims] 1. Porosity on both sides, and each pore has the following conditions 1) to 4): 1) The difference between the average pore diameters on both sides is based on the smaller average value of the average pore diameters. Is less than 200%. 2) The variation coefficient of the pore diameter on each surface is smaller than 70%. 3) The coefficient of variation of the distance between holes on each surface is smaller than 50%. 4) The average pore size on each surface is 0.05 to 5 μm. A polyimide porous film that satisfies the requirements. 2. The polyimide porous film according to claim 1, which has a thickness of 5 to 100 μm.