TW201629123A - Porous polyimide film and production method thereof - Google Patents

Abstract

The present invention provides a porous polyimide film having a high porosity and a small average pore diameter, in which no porogen and the like are remaining, and a production method thereof. A porous polyimide film of the present invention is characterized by comprising a polyimide containing an oxyalkylene unit and having a porosity of 45 vol% or more to 95 vol% or less and an average pore diameter of 10 nm or more to 1000 nm or less.

Description

Porous polyimine film and manufacturing method thereof

The present invention relates to a porous polyimine (PI) film and a method for producing the same.

The porous PI film is used for industrial materials such as electronic materials, optical materials, separators for lithium secondary batteries, filters, separation membranes, and wire coatings, and medical materials, because of its excellent heat resistance and high porosity. Materials and other fields. In the method of producing the porous PI thin film, Patent Documents 1 to 3 propose that a PI solution containing a good solvent and a poor solvent for PI (including its precursor) is applied onto a substrate. A method of obtaining a porous PI film by drying (hereinafter, this method is simply referred to as "dry porous process").

The dry-type porous process is different from the wet-type porous process in which the porous film is formed by immersing the coating film formed on the substrate in a coagulating liquid containing a poor solvent, and is not required to be porous. The coagulation bath is used for the quality. Therefore, since the dry porous process does not generate waste liquid from the coagulation bath when the porous PI film is produced, it is an excellent method with good environmental compatibility. However, the porous PI film obtained by the dry porous procedure mostly has an average pore diameter of 1000 nm or more, and it is difficult to make it less than 1000 nm. Obtain a porous PI film with an average pore diameter of less than 1000 nm In the case of the PI film, a thermally decomposable organic compound having a thermal decomposition temperature of 350 ° C or less is used as a pore-forming agent (a pore forming agent) to form pores, and a porous PI film is produced. method. In the method described in Patent Document 4, after the PI film is obtained by blending a pore former in a PI film, the pyrolytic organic compound is subjected to a long-time heat treatment at a temperature of 350 ° C or higher to thermally decompose the above. The organic compound is thermally decomposed to disappear and removed, thereby forming pores. Further, Patent Document 5 proposes a method of producing a porous PI film by using a dispersing compound such as polyethylene glycol monomethacrylate as a pore-forming agent and forming pores. In the method described in Patent Document 5, a pore former is blended into a PI film to obtain a PI film, and then a pore former is removed by supercritical carbon dioxide extraction to form pores.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent No. 4947989

[Patent Document 2] Japanese Patent Laid-Open No. 2015-136633

[Patent Document 3] Japanese Patent Laid-Open Publication No. 2015-52061

[Patent Document 4] Japanese Patent Laid-Open Publication No. 2013-216776

[Patent Document 5] Japanese Patent No. 4557409

However, a conventional method using a pore-forming agent such as a thermally decomposable organic compound or a dispersing compound has a pore-forming agent which is not completely removed and remains in the porous PI film. Among them, there is a problem that the heat resistance and mechanical strength of the porous PI film are impaired.

In view of the above, the present invention has been made to solve the above problems, and an object thereof is to provide a porous PI film having a high porosity and a small average pore diameter without leaving a pore former or the like and a method for producing the same.

The inventors of the present invention have found that the above problems can be solved by setting the chemical structure of PI to a specific composition and the pore structure of the porous film to have a specific structure, and have completed the present invention.

The gist of the present invention is as follows.

<1> A porous polyimide film comprising a polyalkylenimine containing an alkylene oxide unit, having a porosity of 45 vol% or more and 95 vol% or less, and an average pore diameter of 10 nm or more. Below 1000nm.

<2> The above porous polyimine film, wherein an active layer is formed on the surface.

<3> A method for producing a porous polyimine film, which comprises a polyphthalic acid containing an alkylene oxide unit and a mixed solvent containing a good solvent and a poor solvent, and the mixed solvent The solution having a poor solvent ratio of 65 mass% or more and 95 mass% or less is applied to the substrate, and then dried at a temperature of less than 350 °C.

The porous PI film of the present invention is excellent in heat resistance, high in porosity, and does not leave a pore forming agent such as a pore former, and is therefore suitably used for, for example, an electronic material such as a low dielectric constant substrate or a lithium secondary battery separator. Industrial materials such as plates, fuel cell solid electrolyte supporting membranes, filters, separation membranes, and wire coatings, materials for medical materials, and optical materials.

Fig. 1 is a SEM image of a cross section of a porous PI film (P-1) obtained in Example 1.

2 is an SEM image of the surface of the porous PI film (P-1) obtained in Example 1.

3 is an SEM image of a cross section of a porous PI film (R-1) obtained in Comparative Example 1.

Hereinafter, the present invention will be described in detail.

The present invention relates to a porous PI film and a method for producing the same.

Here, the PI (polyimine)-based heat-resistant polymer having a quinone bond in the main chain is usually obtained by polycondensation of a diamine component of a monomer component and a tetracarboxylic acid component. The polyimines also include polyamidoximines, polyesterimines, and the like which are polyimine modified bodies.

Preferably, PI is a PI obtained from polyglycine (hereinafter referred to as "PAA") which is a polyimide precursor. In this case, the PI film is applied to the substrate by reacting a PAA solution obtained by reacting a tetracarboxylic dianhydride with a diamine in a solvent to form a PAA film, and then performing PAA thermally or chemically. The imidization can be obtained. The PI system obtained from PAA may be thermoplastic or non-thermoplastic.

The PI system of the present invention contains an alkylene oxide unit. The alkylene oxide unit may specifically be, for example, an oxidized ethyl group unit, an oxidized propyl unit, an oxybutylene unit or the like. The PI containing an alkylene oxide unit is, for example, a tetracarboxylic dianhydride having an oxidized alkyl unit (hereinafter referred to as "TA-1") and/or a diamine having an alkylene oxide unit (hereinafter referred to as " DA-1"), with a tetrahydroxy acid dianhydride (hereinafter referred to as "TA-2") having no alkylene oxide unit and/or a diamine having no alkylene oxide unit (hereinafter referred to as "DA-2") The PAA (hereinafter referred to as "copolymerized PAA") which is subjected to copolymerization can be obtained by performing imidization. By introducing such an alkylene oxide unit into the PI chain (backbone), a porous PI film having fine pores having an average pore diameter of 1000 nm or less can be formed by a dry pore-forming procedure. Specific examples of the above-mentioned monomers, copolymerization ratios, and the like are to be described later.

The porosity of the porous PI film of the present invention is 45 vol% or more and 95 vol% or less, preferably 50 vol% or more and 90 vol% or less, more preferably 55 vol% or more and 85% by volume or less. By setting the porosity to such a range, it is possible to simultaneously ensure good mechanical properties, excellent penetrability, dielectric properties, and the like when the porous film is formed.

The porosity ratio can be a value calculated by the following formula.

[Formula 1] Porosity (% by volume) = 100 - 100 × (W / D) / (S × T)

In the formula, S represents the area of the porous PI film, T represents the thickness, W represents the mass, and D represents the density of the corresponding non-porous PI film.

The porous PI film of the present invention has an average pore diameter of 10 nm or more and 1000 nm or less, preferably 20 nm or more and 800 nm or less, more preferably 20 nm or more and 600 nm or less. By setting the average pore diameter to such a range, it is possible to simultaneously ensure good mechanical properties, excellent penetrability, dielectric properties, and the like when the porous film is used.

The average pore diameter is obtained by SEM (scanning electron microscope) image of the cross section of the porous PI film at a magnification of 5,000 to 20,000 times, and can be confirmed by analysis using an image processing software.

The pore system of the porous PI film of the present invention may be a continuous pore or an independent pore.

The surface of the porous PI film of the present invention may or may not be open.

The opening ratio at the time of opening is preferably 10% or more and 90% or less, more preferably 20% or more and 80% or less. Further, the average opening diameter of the open pores is preferably 10 nm or more and 1000 nm or less.

Thereby, it is possible to ensure good mechanical properties and good surface smoothness of the open porous film at the same time.

The aperture ratio and the average opening diameter were obtained by taking an SEM image of the surface of the porous PI film at a magnification of 5,000 to 20,000 times, and it was confirmed by analysis using an image processing software.

The porous PI film of the present invention can be produced, for example, by the dry porosification procedure shown below. That is, it will contain a copolymerized PAA, a good solvent and a poor solvent. After the liquid is applied to the substrate, it can be produced by drying.

Here, the "good solvent" means a solvent having a solubility of a solute (polyproline) to a solvent of 25 ° C of 1% by mass or more, and the term "poor solvent" means a solvent having a solubility of less than 1% by mass. The good solvent may be, for example, a guanamine solvent or a urea solvent. These may be used alone or in combination of two or more. Specific examples of the guanamine-based solvent may, for example, be N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide, N,N-dimethylacetamide (DMAc), or the like. . Further, specific examples of the urea solvent include, for example, tetramethylurea, tetraethylurea, dimethylacetamide, dimethylpropionaldehyde, and the like. Among these, NMP and DMAc are preferred.

The poor solvent may be, for example, an ether solvent or an alcohol solvent. These may be used alone or in combination of two or more. Among these, an ether solvent is preferred. The ether solvent may be, for example, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, pentaethylene glycol dimethyl ether, diethylene glycol butyl methyl ether, diethylene glycol. Diethyl ether, dipropylene glycol monomethyl ether, and the like. These may be used alone or in combination of two or more. Among these, triethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether are preferred.

The poor solvent is preferably one having a higher boiling point than the good solvent, and the difference in boiling point is preferably at least 5 ° C, more preferably at least 20 ° C, and particularly preferably at 30 ° C or higher. The amount of the poor solvent blended in the mixed solvent is preferably 65% by mass or more and 95% by mass or less, more preferably 70% by mass or more and 90% by mass or less. Thereby, phase separation can be efficiently initiated in the drying step of the dry porosification process, and a PI film having a high porosity and a small average pore diameter can be obtained. If the solvent is not mixed When the ratio of the good solvent is too small, the porosity of the porous PI film is lowered.

As the above-mentioned copolymerized PAA solution, for example, a solution obtained by subjecting a tetracarboxylic dianhydride belonging to a monomer to a molar ratio of a diamine or a diamine to a polymerization reaction in the above mixed solvent can be used. At this time, since at least one of TA-1 using a tetracarboxylic dianhydride or DA-1 of a diamine is used, a copolymerized PAA having an alkylene oxide unit in the main chain can be obtained, and as a result, a main can be obtained. The chain contains the PI of the oxyalkylene unit.

Specifically, the above-mentioned copolymerized PAA solution may be a tetrahydroxy acid dianhydride (a mixture of TA-1 and TA-2, or only TA-2) and a diamine (DA-1 and DA-) which are monomers. A mixture of 2, or only DA-2) is a solution obtained by subjecting a polymerization reaction at a temperature of 10 to 70 ° C in the above mixed solvent according to about a molar blend. Here, when TA-1 is used, the amount of TA-1 used is preferably from 0.5 to 20 mol%, more preferably from 1 to 10 mol, from the viewpoint of a higher porosity and a smaller average pore diameter. ear%. When DA-1 is used, the amount of DA-1 used is preferably from 0.5 to 20 mol%, more preferably from 1 to 10 mol%, from the same viewpoint. The above "% by mole" means a value calculated according to the following formula.

[Equation 2] "TA-1 usage" (% by mole) = ["TA-1 mole number" / ("TA-1 mole number" + "TA-2 mole number")] × 100 "DA-1 Usage" (Mor%) = ["DA-1 Moir" / ("DA-1 Moir" + "DA-2 Moir")] × 100

Here, a specific example of TA-1 may be, for example, ethylene glycol bis(trimellitic anhydride) (ethylene) Glycol bis(anhydro-trimellitate), diethylene glycol bis(trimellitic anhydride), triethylene glycol bis(trimellitic anhydride), tetraethylene glycol bis(trimellitic anhydride), polyethylene glycol bis(trimellitic anhydride), ethylene glycol bis(trimellitic anhydride)醯amine, diethylene glycol bis(trimellitic anhydride) decylamine, triethylene glycol bis(trimellitic anhydride) decylamine, tetraethylene glycol bis(trimellitic anhydride) decylamine, polyethylene glycol bis(trimellitic anhydride) decylamine, propylene glycol double (trimellitic anhydride), dipropylene glycol bis(trimellitic anhydride), tripropylene glycol bis(trimellitic anhydride), tetrapropylene glycol bis(trimellitic anhydride), polypropylene glycol bis(trimellitic anhydride), propylene glycol bis(trimellitic anhydride) decylamine, dipropylene glycol bis(trimellitic anhydride) decylamine, three Propylene glycol bis(trimellitic anhydride) decylamine, tetrapropylene glycol bis(trimellitic anhydride) decylamine, polypropylene glycol bis(trimellitic anhydride) decylamine, and the like. These may be used alone or in combination of two or more. Among these, polyethylene glycol bis(trimellitic anhydride) decylamine and polypropylene glycol bis(trimellitic anhydride) decylamine are preferred.

Specific examples of TA-2 can be, for example, pyromellitic dianhydride (PMDA), 3,3',4,4'-biphenyltetrahydroxy dianhydride (BPDA), 2,3,3',4 '-biphenyltetrahydroxy dianhydride, 3,3',4,4'-diphenyl ketone tetrahydroxy dianhydride, 4,4'-oxydicarboxylic anhydride, and 3,3',4, 4'-diphenylfluorene tetrahydroxy acid dianhydride and the like. These may be used alone or in combination of two or more. Among these, PMDA and BPDA are preferred.

Specific examples of DA-1 may be, for example, ethylene glycol bis(2-aminoethyl)ether, diethylene glycol bis(2-aminoethyl)ether, triethylene glycol bis(2-aminoethyl) Ether, tetraethylene glycol bis(2-aminoethyl)ether, polyethylene glycol bis(2-aminoethyl)ether (PEGME), propylene glycol bis(2-aminoethyl)ether, two Propylene glycol bis(2-aminoethyl)ether, tripropylene glycol bis(2-aminoethyl)ether, tetrapropylene glycol bis(2-aminoethyl)ether, polypropylene glycol bis(2-aminoethyl)ether (PPGME), polytetrahydrofuran di-p-aminobenzoate (PTMDA), and the like. These systems can be used separately, Two or more types can be used in combination. Among these, PEGME, PPGME, and PTMDA are preferred. The number average molecular weight of PEGME, PPGM, and PTGMA is preferably from 200 to 5,000, more preferably from 500 to 4,000. By setting the number average molecular weight within such a range, a PI film having a desired average pore diameter can be obtained more easily. Commercially available materials can be used for the DA-1 system. In particular, PEGME, PPGME, and PTMDA can be obtained, for example, Jeffamine D2000 (manufactured by Huntsman Co., Ltd.), Jeffamine D4000 (manufactured by Huntsman Co., Ltd.), and ELASMER-1000 (manufactured by IHARA CHEMICAL Co., Ltd.).

Specific examples of DA-2 may be, for example, 4,4'-diaminodiphenyl ether (DADE), 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP), P-phenylenediamine, m-phenylenediamine, 2,4-diaminotoluene, 4,4'-diaminobiphenyl, 4,4'-diamino-2,2'-bis(trifluoro Methyl)biphenyl, 3,3'-diaminodiphenyl hydrazine, 4,4'-diaminodiphenyl hydrazine, 4,4'-diaminodiphenyl sulfide, 4,4'-diamine Diphenylmethane, 3,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether, 1,4-bis(4-aminophenoxy)benzene, 1,3-double (4-Aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, 4,4'-bis(4-aminophenoxy)biphenyl, bis[4-( 4-aminophenoxy)phenyl]anthracene, bis[4-(3-aminophenoxy)phenyl]anthracene, 2,2-bis[4-(4-aminophenoxy)phenyl Hexafluoropropane, α,ω-diaminopolydimethyloxane, α,ω-bis(3-aminopropyl)polydimethyloxane, 1,3-bis(3-amine Propyl)tetramethyldioxane, 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldioxane, bis(10-amino-based Methyl)tetramethyldioxane, bis(3-aminophenoxymethyl)tetramethyldioxane, α,ω-bis(3-aminopropyl)polymethylphenylhydrazine Alkyl, α, ω- bis (3-aminopropyl) poly (dimethyl siloxane Silicon - Silicon diphenyl siloxane) copolymers. These may be used alone or in combination of two or more. Among these, DADE and BAPP are preferred.

The copolymerized PAA solution is obtained by, for example, a method of obtaining a solution by carrying out a polymerization reaction in a good solvent, adding a poor solvent thereto, and performing a polymerization reaction in a poor solvent to obtain a suspension, and then adding a good solvent thereto. The method is also available.

In the copolymerized PAA solution, a known additive such as various surfactants and/or a decane coupling agent may be added as needed within the range which does not impair the effects of the present invention. Further, a polymer other than PI may be added to the copolymerized PAA solution as needed within the range which does not impair the effects of the present invention.

The copolymerized PAA solution is applied to the surface of the substrate and dried to form a porous PI film. Then, the porous PI film is peeled off from the substrate to form a porous PI film monomer. Further, the porous PI film formed on the substrate may be used in combination with the substrate without being peeled off from the substrate.

The drying step includes a step 1 of inducing phase separation to form a porous PAA film by volatilizing a solvent contained in the coating film, and a heat-imidization of the porous PAA film to become porous Step 2 of the PI coating. The temperature of the step 1 is preferably about 100 to 200 ° C, and the temperature of the step 2 is less than 350 ° C, for example, preferably 300 ° C. When the temperature at the step 2 is set to 350 ° C or higher, there is a concern that a part of the alkylene oxide unit introduced into the PI is thermally decomposed.

The substrate may be, for example, a metal foil, a metal wire, a glass plate, a plastic film, various woven fabrics, or various nonwoven fabrics, and the metal may be made of gold, silver, copper, platinum, aluminum or the like. These systems may be porous or non-porous. The coating method of the coating liquid can be applied in a continuous or batch manner using a dip coater, a bar coater, a spin coater, a die coater, a spray coater or the like.

The porous PI film of the present invention having continuous pores can form an active layer on its surface (single or double sided). Thereby, the porous PI film of the present invention can be used as a reverse osmosis membrane or a gas separation membrane. Here, the "active layer" means a layer formed of a non-porous film composed of an organic polymer having a separation function and/or an inorganic compound, and by providing such a layer, the porous PI film of the present invention can be used. It is a reverse osmosis membrane or a gas separation membrane. The thickness of the active layer is usually about 0.01 to 500 nm, and by using such an electrode film, good separation performance and penetration performance can be ensured at the same time. Since the average pore diameter of the porous PI film of the present invention is extremely small from 10 to 1000 nm, the above-mentioned electrode film can be uniformly formed.

When the porous PI film of the present invention is used as a reverse osmosis membrane, for example, an active layer composed of linaloamine or the like may be formed on the surface (single or both surfaces) of the porous PI film. In the case of forming such an active layer, a known method disclosed in, for example, Japanese Patent Publication No. Hei 7-90152 and Japanese Patent No. 3181134 can be employed.

In addition, when the porous PI film of the present invention is used as a gas separation membrane (for example, a hydrogen separation membrane), for example, an active layer composed of an epipolar thin film such as palladium, palladium/silver alloy or palladium/copper alloy is formed. The surface of the porous PI film (single or double sided) may be used. In forming such active layers, for example, Journal of Membrane Science Volume 94, Issue 1, 19 September 1994, Pages 299-311, and US patents may be employed. A known method disclosed in No. 4,857,080.

The thickness of the porous PI film of the present invention is usually about 1 to 1000 μm, preferably about 10 to 500 μm.

The porosity and the average pore diameter can be adjusted by selecting the type and/or the amount of the solvent (good solvent and poor solvent) in the copolymerized PAA solution.

As described above, since the pore-forming agent is not used in the production method of the present invention, the porous PI film of the present invention which does not substantially remain as a pore-forming agent can be obtained.

[Examples]

Hereinafter, the present invention will be described in more detail by way of examples. In addition, the invention is not limited by the examples.

[Example 1]

In a glass reaction vessel, DADE (DA-2) was charged under a nitrogen atmosphere: 0.94 mol, PPGME (DA-1): 0.06 mol (molecular weight: 2000: Jeffamine D2000 manufactured by Huntsman Co., Ltd.), and DMAc and four. A mixed solvent of ethylene glycol dimethyl ether (the ratio of DMAc/tetraethylene glycol dimethyl ether is 25/75 by mass ratio), and the diamine component is stirred and dissolved. This solution was cooled to 30 ° C or less by a jacket, and was slowly introduced into PMDA (TA-2): 1.03 mol, and then subjected to a polymerization reaction at 40 ° C for 5 hours to obtain a copolymerized PAA solution introduced into an oxypropyl unit. The solid concentration of the solution was 21% by mass. Applying the above copolymerized PAA solution to aluminum foil using a doctor blade (thick On a 150 μm basis, it was dried at 130 ° C for 20 minutes to obtain a coating film composed of copolymerized PAA. Subsequently, the temperature was raised to 300 ° C in a nitrogen stream for 120 minutes, and additional drying was carried out at 300 ° C for 60 minutes, and the copolymerized PAA was imidized to obtain a porous PI film having a thickness of about 30 μm on the aluminum foil. -1). The SEM image of the cross section and surface of P-1 is shown in Figures 1 and 2.

The porosity and average pore diameter of the porous PI film (P-1) are shown in Table-1. Further, the aperture ratio and the average opening diameter of the surface were 52% and 650 nm, respectively. In addition, the obtained laminate was heat-treated at 200 ° C and 250 ° C for 1 hour, and the resistance value of the surface of the porous PI film (P-1) was measured. As a result, the resistance value was almost unchanged from that before the treatment, and good heat resistance was confirmed.

[Example 2]

A copolymerized PAA solution was prepared in the same manner as in Example 1 except that the mixing ratio of DMAc/tetraethylene glycol dimethyl ether was changed to 15/85 by mass ratio, and the same procedure as in Example 1 was carried out. A porous PI film (P-2) having a thickness of about 25 μm laminated on the aluminum foil was obtained. The porosity and average pore diameter of P-2 are shown in Table-1.

[Example 3]

A copolymerized PAA was prepared in the same manner as in Example 1 except that DA-1 was used in which PPGME (Jeffamine D4000 manufactured by Huntsman Co., Ltd., molecular weight: 4000) was 0.03 mol, and DA-2 was used as DADE: 0.97 mol. In the same manner as in Example 1, a porous PI film (P-3) having a thickness of about 30 μm laminated on the aluminum foil was obtained in the same manner as in Example 1. The porosity and average pore diameter of the porous PI film (P-3) are shown in Table-1.

[Example 4]

A copolymerized PAA solution was prepared in the same manner as in Example 1 except that DATM was used in the same manner as in Example 1 except that PTMDA: 0.06 mol (molecular weight: ELASMER-1000 manufactured by IHARA CHEMICAL Co., Ltd.) was used. A porous PI film (P-4) having a thickness of about 30 μm was laminated on the aluminum foil. The porosity and average pore diameter of the porous PI film (P-4) are shown in Table-1.

[Example 5]

A porous PI film having a thickness of about 30 μm laminated on an aluminum foil was obtained in the same manner as in Example 1 except that the TA-2 system was used in the same manner as in Example 1 except that BPDA: 1.03 mole was used. P-5). The porosity and average pore diameter of the porous PI film (P-5) are shown in Table-1.

[Example 6]

Copolymerization was carried out in the same manner as in Example 1 except that the TA-2 system used BPDA: 1.03 mol, and the mixing ratio of DMAc/tetraethylene glycol dimethyl ether was 35/65 by mass ratio. As the PAA solution, a porous PI film (P-6) having a thickness of about 35 μm laminated on the aluminum foil was obtained. The porosity and average pore diameter of the porous PI film (P-6) are shown in Table-1.

[Example 7]

The same procedure as in Example 1 was carried out except that the ether solvent was a mixed solvent of 50 parts by mass of tetraethylene glycol dimethyl ether and 50 parts by mass of triethylene glycol dimethyl ether. The PAA solution was co-polymerized to obtain a porous PI film (P-7) having a thickness of about 30 μm laminated on the aluminum foil. The porosity and average pore diameter of P-7 are shown in Table-1.

[Example 8]

A copolymerized PAA solution was prepared in the same manner as in Example 1 except that the DA-2 system was a mixture of DADE: 0.8 mol and BAPP: 0.14 mol, and a porous layer having a thickness of about 30 μm on the aluminum foil was obtained. PI film (P-8). The porosity and average pore diameter of P-8 are shown in Table-1.

[Example 9]

The copolymerized PAA solution obtained in Example 1 was applied onto a polyester film (thickness: 200 μm) using a doctor blade, and dried at 130 ° C for 20 minutes to obtain a coating film composed of copolymerized PAA. Next, the coating film was peeled off from the polyester film, and then heated to 250 ° C in a nitrogen stream for 120 minutes, and additionally dried at 250 ° C for 60 minutes, and the copolymerized PAA was imidized to obtain a thickness of about 5%. 50 μm porous PI film (P-9). The porosity and average pore diameter of P-9 are shown in Table-1. P-9 was treated at 200 ° C for 1 hour, and the dimensional change rate was measured, and as a result, it was 1% or less, and good heat resistance was confirmed.

<Comparative Example 1>

A PAA solution was prepared in the same manner as in Example 1 except that DADE (DA-2): 1 mol, PMDA (TA-2): 1.03 mol was used, and the same procedure as in Example 1 was obtained. A porous PI film (R-1) having a thickness of about 30 μm was laminated on the aluminum foil. The SEM image of the cross section of the porous PI film (R-1) is shown in Fig. 3. Porous PI film (R-1) The porosity and average pore size are shown in Table-1.

<Comparative Example 2>

A PAA solution was prepared in the same manner as in Example 1 except that the mixing ratio of DMAc/tetraethylene glycol dimethyl ether was 60/40 by mass ratio, and the same procedure as in Example 1 was obtained. A porous PI film (R-2) having a thickness of about 30 μm was laminated on the aluminum foil. The porosity and average pore diameter of the porous PI film (R-2) are shown in Table-1.

<Comparative Example 3>

A PAA solution was prepared in the same manner as in Example 1 except that the mixing ratio of DMAc/tetraethylene glycol dimethyl ether was 50/50 by mass ratio, and the same procedure as in Example 1 was obtained. A porous PI film (R-3) having a thickness of about 30 μm was laminated on the aluminum foil. The porosity and average pore diameter of the porous PI film (R-3) are shown in Table-1.

As shown in the examples, it was found that the porous PI films P-1 to P-9 of the present invention uniformly formed fine pores having a porosity of 45% by volume or more and an average pore diameter of 1000 nm or less. On the other hand, it was found that the porous PI thin film R-1 of the comparative example did not form fine pores having an average pore diameter of 1000 nm or less. Further, it was found that the porous PI films R-2 and R-3 of the comparative examples were not able to obtain a high porosity.

(industrial availability)

The porous PI film of the present invention in which a large number of fine pores are formed does not have such a residual state because a pore forming agent such as a pore former is not used. Therefore, the heat-resistant porous film can be used for, for example, an electronic material such as a low dielectric constant substrate, a separator for a lithium secondary battery, a solid electrolyte supporting film for a fuel cell, a filter, a separation membrane, and a wire coating. Materials, medical materials, materials for optical materials, etc.

Claims (3)

A porous polyimine film comprising a polyamidene containing an alkylene oxide unit, having a porosity of 45 vol% or more and 95 vol% or less, and an average pore diameter of 10 nm or more and 1000 nm or less. A porous polyimide film according to claim 1, wherein an active layer is formed on the surface. A method for producing a porous polyimine film according to claim 1 or 2, which comprises a polyphthalic acid containing an alkylene oxide unit and a mixed solvent containing a good solvent and a poor solvent, and the above The solution having a poor solvent ratio in the mixed solvent of 65 mass% or more and 95 mass% or less is applied to the substrate, and then dried at a temperature of less than 350 °C.