JP2006224098A - Polyimide asymmetric membrane comprising multi-component polyimide, gas separation membrane and gas separation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyimide asymmetric membrane which has a dense layer and a porous layer, comprises a multi-component polyimide including a fluorine atom-containing polyimide and is obtained by controlling the proportion of the fluorine atom-containing polyimide in the dense layer, and to provide a practical high-performance gas separation membrane consisting of the polyimide asymmetric membrane. <P>SOLUTION: The polyimide asymmetric membrane is characterized in that the ratio ψ<SB>S</SB>/f of fluorine atom concentration ψ<SB>S</SB>in the dense layer measured by X-ray photoelectron spectroscopy (XPS) to fluorine atom concentration of the whole membrane is 1.1 to 1.8. The practical high-performance gas separation membrane consists of the polyimide asymmetric membrane. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention is a polyimide asymmetric film having a dense layer and a porous layer, which is made of a multi-component polyimide containing a fluorine atom-containing polyimide, and obtained by controlling the ratio of the fluorine atom-containing polyimide in the dense layer It relates to an asymmetric membrane. The present invention also relates to a practical high performance gas separation membrane comprising the polyimide asymmetric membrane and a gas separation method using the gas separation membrane.

  Gas separation membranes are widely used in industrial gas separation processes. Especially, the gas separation membrane formed with the polyimide with high gas selective permeability (separation degree) is used suitably. In general, polyimide has a high gas selective permeability (separation degree) but a low gas permeability (permeability coefficient). For this reason, the gas separation membrane made of polyimide has an asymmetric structure mainly composed of a porous layer that performs a supporting function and a dense layer that mainly performs a separating function, and the gas permeation rate of the dense layer in which gas permeation resistance is generated. It is used thinly so that it does not become small.

  Practical gas separation membranes require characteristics such as mechanical strength in addition to gas permeation performance such as gas permselectivity and gas permeation speed. In a polyimide (homopolymer) composed of one type of tetracarboxylic acid component and one type of diamine component, their characteristics are determined by the combination of the tetracarboxylic acid component and the diamine component used. In order to obtain a gas separation membrane that satisfies various properties required in practice, a part of the tetracarboxylic acid component and / or diamine component is replaced with another tetracarboxylic acid component and / or other diamine component. A gas separation membrane using a copolymerized polyimide has been studied. The characteristics of such a gas separation membrane made of copolymerized polyimide are determined by the composition of a plurality of types of tetracarboxylic acid components and / or diamine components used therein. In such studies, polyimides containing fluorine atoms in tetracarboxylic acid components and diamine components have been often used to improve gas permeation performance, particularly gas permeation rate.

  However, in general, when an asymmetric membrane is formed using, for example, a fluorine atom-containing polyimide having excellent gas permeation performance, the mechanical strength is not sufficient, and conversely, when an asymmetric membrane is formed using a polyimide having excellent mechanical strength, gas permeation is not achieved. There was a problem that the performance was not sufficient.

Patent Document 1 discloses a composite gas separation in which a porous polyacrylonitrile structure support, a gutter layer containing a crosslinked phenyl-containing polar organopolysiloxane, and an extremely thin selective membrane layer made of a specific fluorine atom-containing polyimide are laminated. A membrane is disclosed.
Patent Document 2 discloses a gas composite separation membrane in which an aliphatic porous polyimide support layer and a thin film made of fluorine atom-containing polyimide are laminated.
However, in such a composite film, it is necessary to laminate a uniform thin film on the porous layer, but it is not easy to form a uniform thin film on the porous layer, and these documents have shown. It was not easy to obtain a high performance gas separation membrane by the method.

  Patent Document 3 discloses a method for producing an asymmetric hollow fiber separation membrane by a phase change method using a polymer mixed solution composed of two kinds of polyimides. However, a mixed solution composed of a combination of polyimide components having a specific degree of polymerization is prepared, and the mixed solution is further subjected to a polymerization imidization reaction to prepare a mixed solution containing a block copolymer. There is no description about producing an asymmetric membrane using a mixed solution containing a copolymer having the following.

JP-A-6-269650 JP-A-8-52332 Japanese Patent Application No. 2003-24755

  An object of the present invention is a polyimide asymmetric film having a dense layer and a porous layer, which is made of a multi-component polyimide containing a fluorine atom-containing polyimide, and is obtained by controlling the ratio of the fluorine atom-containing polyimide in the dense layer. A polyimide asymmetric membrane is provided. Another object of the present invention is to provide a practical high performance gas separation membrane comprising the polyimide asymmetric membrane and a gas separation method using the gas separation membrane.

The present invention is a polyimide asymmetric film having a dense layer and a porous layer, which is formed of a multi-component polyimide containing a fluorine atom-containing polyimide and measured by X-ray photoelectron spectroscopy (XPS). The polyimide asymmetric film is characterized in that the ratio (Φ _S / f) of (Φ _S ) to the average fluorine atom concentration (f) in the whole film is 1.1 to 1.8, particularly the polyimide asymmetric film It relates to a gas separation membrane.

In the present invention, the gas separation membrane is a hollow fiber, and a hydrogen gas permeation rate (P ′ _H2 ) is 4.0 × 10 ⁻⁴ cm ³ (STP) / cm ² · sec · cmHg or more, hydrogen gas permeation rate (P _'H2) and nitrogen gas permeation rate (P' ratio of _{N2) (P 'H2 / P} ' N2) of 20 or more, and the tensile elongation at break of the hollow fiber is 15% or more, The gas separation membrane is a hollow fiber, the helium gas permeation rate (P ′ _He ) is 4.0 × 10 ⁻⁴ cm ³ (STP) / cm ² · sec · cmHg or more, the helium gas permeation rate ( The ratio ( _P'He / _P'N2 ) between the _P'He ) and the nitrogen gas transmission rate ( _P'N2 ) is 20 or more, and the tensile elongation at break as a hollow fiber is 15% or more.

  Furthermore, the present invention is characterized in that a mixed gas is supplied to the supply side of the gas separation membrane of the present invention, and at least one kind of mixed gas is selectively permeated to the permeation side of the gas separation membrane. The present invention relates to a method for selectively separating and recovering at least one gas from a gas. In particular, the present invention includes hydrogen gas, characterized in that a gas mixture containing hydrogen gas is supplied to the gas separation membrane supply side, and hydrogen gas is selectively permeated to the permeation side of the gas separation membrane. A method for selectively separating and recovering hydrogen gas from a mixed gas, and a mixed gas containing helium gas is supplied to the supply side of the gas separation membrane, and the helium gas is selectively permeated to the permeation side of the gas separation membrane. The present invention relates to a method for selectively separating and recovering helium gas from a mixed gas containing helium gas.

  According to the present invention, a polyimide asymmetric membrane having a dense layer and a porous layer, which is composed of a multi-component polyimide containing a fluorine atom-containing polyimide, and the proportion of the fluorine atom-containing polyimide in the dense layer is suitably controlled Can be provided. This polyimide non-target membrane is suitable as a gas separation membrane, separation of hydrogen gas and hydrocarbon gas such as methane gas, separation of hydrogen gas and nitrogen gas, separation of helium gas and nitrogen gas, carbon dioxide gas and methane gas It is a practical high-performance gas separation membrane that can be suitably separated from hydrocarbon gas such as oxygen gas and nitrogen gas.

  The polyimide asymmetric membrane of the present invention will be specifically described below as a high-performance gas separation membrane, but the polyimide asymmetric membrane of the present invention is not limited to gas separation membrane applications.

The polyimide asymmetric membrane of the present invention is a polyimide asymmetric membrane having a dense layer and a porous layer, and is formed of a multicomponent polyimide containing a fluorine atom-containing polyimide. Preferably, the polyimide A that the chemical structure containing a fluorine atom ingredients and / or polymerization and imidation reaction product of the ingredients and the polyimide component A, a number average degree of polymerization of the polyimide component A and N _A, polyimide B the polymerization and imidation reaction product of raw material components and / or the ingredients and polyimide component B, and the number average polymerization degree of the polyimide component B as N _B, can be prepared by the following steps 1 to 3.
(Step 1) A polyimide component A and a polyimide component B are mixed in a combination in which N _A and N _B satisfy the following formula to prepare a mixed solution of multi-component polyimide.

（工程２）前記多成分ポリイミドの混合溶液をさらに重合イミド化反応させる
（工程３）前記多成分ポリイミドの混合溶液を用いて相転換法によって非対称膜を得る

(Step 2) The mixed solution of the multicomponent polyimide is further subjected to a polymerization imidization reaction (Step 3) An asymmetric membrane is obtained by a phase conversion method using the mixed solution of the multicomponent polyimide.

In the present invention, the “polyimide component” includes a raw material component of polyimide (unreacted tetracarboxylic acid component, unreacted diamine component) and / or a polymerization imidization reaction product of the raw material component. Here, the polymerized imidized product does not mean only a polymer having a high degree of polymerization. It includes a monomer generated at the initial stage of the reaction when the raw material component of polyimide is polymerized imidized, an oligomer having a low polymerization degree, and the like. That is, the polymerization imidization reaction product is composed of a monomer (a tetracarboxylic acid component and a diamine component imidized by a total of two molecules each) and / or a polymer (a tetracarboxylic acid component and a diamine component). And imidization reaction of 3 molecules or more).
In the present invention, the polymerization degree of the polymerization imidization reaction product is determined by the number of repeating units of the polyimide contained therein. That is, the degree of polymerization of the monomer is 1, and the degree of polymerization of the polymer is> 1. On the other hand, the degree of polymerization of the raw material component of polyimide is defined as 0.5 because it has no repeating unit. The number average degree of polymerization is calculated from the degree of polymerization defined above.
The polyimide component A is composed of a raw material component of polyimide A (unreacted tetracarboxylic acid component, unreacted diamine component) and / or a polymerization imidization reaction product of the raw material component. And the polyimide component B consists of the raw material component (unreacted tetracarboxylic acid component, unreacted diamine component) of the polyimide B, and / or the polymerization imidation reaction product of the said raw material component.

  When the polyimide component A and the polyimide component B are both mixed in the state of an unreacted tetracarboxylic acid component and a diamine component (the degree of polymerization is 0.5) and subjected to a polymerization imidization reaction, both components are marked. A polyimide having a random copolymer as a main component bonded with randomness is formed. When this polyimide is applied to the phase conversion method, an asymmetric membrane consisting of a dense layer and a porous layer can be formed, but there is no uneven distribution of fluorine atom-containing polyimide in the dense layer. A gas separation membrane having both performance and good mechanical properties cannot be obtained. This is because a polyimide exhibiting high gas permeation performance is inferior in mechanical strength, while a polyimide having good mechanical strength is in conflict with gas permeation performance.

  When polyimide A and polyimide B are separately polymerized and imidized and mixed in a state of polyimide having a high degree of polymerization, it is usually difficult to prepare a uniform mixed solution. Although the mixed solution may be almost uniform for a very short time, it is not easy to stably obtain an asymmetric membrane by the phase change method while maintaining the uniform state for a long time. When a mixed solution composed of a plurality of polyimides having a high degree of polymerization is applied to the phase conversion method, macro phase separation rapidly proceeds due to repulsive interaction between both polyimides due to the difference in chemical properties. Here, the macro phase separation means that different types of polyimide are phase separated to form a macro phase separation structure including different domains having a size of 0.1 μm or more and often 1 μm or more. One example of a transmission electron microscope (hereinafter sometimes referred to as TEM) image of a macrophase separation structure is shown in FIG. 1, and another example is shown in FIG. In the macrophase separation structure, a heterogeneous domain having a clear interface is observed in the TEM image. When macrophase separation occurs, a large disturbance occurs in the dense layer, so that an asymmetric membrane with good separation performance cannot be obtained. The thickness of the dense layer of the asymmetric membrane formed by the dry-wet spinning method is often about 1 to 1000 nm, but when macrophase separation occurs, the dense layer has a domain rich in polyimide A and a domain rich in polyimide B. It is formed. This can be easily understood with reference to FIG. In other words, when viewed along the in-plane direction, a non-uniform dense layer is formed in a macro composed of different domains, so that an asymmetric membrane with good separation performance cannot be obtained.

  The present invention is an asymmetric membrane obtained by preparing a mixed solution of a multicomponent polyimide containing a predetermined degree of polymerization and a block copolymer, and applying the mixed solution of the multicomponent polyimide to a phase conversion method. When such a mixed solution of multi-component polyimide is applied to the phase conversion method, macrophase separation does not occur in the phase separation process, and phase separation called microphase separation proceeds. A TEM image of an example of this microphase separation structure is shown in FIG. Here, a phase separation structure (macrophase separation) containing heterogeneous domains is not observed. It seems that fine domains of several nm to 0.1 μm are formed, but the boundary of the domain is unclear as a whole, and many kinds of ambiguous regions where different types of polyimide are not completely phase separated are included. A structure is formed. In this phase separation process, when viewed along the in-plane direction of the film (direction parallel to the film surface), the macroscopic disturbance of the polyimide composition does not occur, and the cross-sectional direction of the film (direction perpendicular to the film surface) ), A multi-component polyimide layer containing more polyimide containing fluorine atoms is formed in the dense layer as will be described later. That is, the present invention is composed of a multi-component polyimide, and by controlling the phase separation between different types of polyimides while causing micro phase separation between different types of polyimides and preventing the phase separation from reaching macro phase separation. A polyimide asymmetric membrane obtained by making the chemical and physical properties of the dense layer and the porous layer of the asymmetric membrane different from each other without causing variation or decrease in the separation performance of the membrane with the progress of phase separation. It is.

In the present invention, polyimide A containing a fluorine atom in its chemical structure is one in which at least one of a tetracarboxylic acid component and a diamine component, which are raw material components, contains a fluorine atom.
As a raw material component of the polyimide A, the polyimide A to be obtained preferably has a high gas permeation rate and a high gas selectivity. In particular, when measured with a uniform film, the helium gas permeability coefficient (P _He ) is 5 × 10 ⁻¹⁰ cm ³ (STP) · cm / cm ² · sec · cmHg or more at 80 ° C. and helium gas and nitrogen gas The transmission coefficient ratio (P _He / P _N2 ) is 20 or more, preferably at 80 ° C., P _He is 2.5 × 10 ⁻⁹ cm ³ (STP) · cm / cm ² · sec · cm Hg or more, and P _He / P _N2 Is preferably 20 or more, more preferably 80 ° C. and P _He is 3 × 10 ⁻⁹ cm ³ (STP) · cm / cm ² · sec · cm Hg or more and P _He / PN ₂ is 30 or more. Since this polyimide A contains a fluorine atom, it has higher solubility in various solvents usually used in the phase change method and a lower surface free energy than those not containing a fluorine atom.
If P _He is lower than the above range or P _He / P _N2 is lower than the above range, the gas selective permeability (separation degree) and gas permeation rate of the obtained asymmetric gas separation membrane are not sufficient. The range of is appropriate.

Although it does not specifically limit as a tetracarboxylic acid component containing the fluorine atom which makes polyimide A, 2, 2-bis (3,4- dicarboxyphenyl) hexafluoropropane, 2,2'-bis (tri Fluoromethyl) -4,4 ′, 5,5′-biphenyltetracarboxylic acid, 4,4 ′-(hexafluorotrimethylene) -diphthalic acid, 4,4 ′-(octafluorotetramethylene) -diphthalic acid, and These dianhydrides and their esterified products can be mentioned. In particular, 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane, dianhydride thereof (hereinafter sometimes abbreviated as 6FDA), and esterified products thereof are preferable.
Although it does not specifically limit as a diamine component containing the fluorine atom which makes the polyimide A, 2, 2-bis (4-aminophenyl) hexafluoropropane, 2,2'-bis (trifluoromethyl) -4 , 4′-diaminobiphenyl, 2,2-bis [4- (4-aminophenoxy) phenyl] hexafluoropropane, 2-trifluoromethyl-p-phenylenediamine, and the like.
These raw material components containing fluorine atoms may be used alone, or may be a mixture of two different types, or may be combined with monomer components not containing fluorine atoms. Moreover, it is preferable that the raw material component which comprises the polyimide A makes the main component (50 mol% or more normally 55 mol% or more) the raw material component in which either a tetracarboxylic-acid component or a diamine component contains a fluorine atom.

  As a diamine component to be combined when the main component is a tetracarboxylic acid component containing a fluorine atom that forms polyimide A, p-phenylenediamine, m-phenylenediamine (hereinafter sometimes abbreviated as MPD), 4, 4′-diaminodiphenyl ether (hereinafter sometimes abbreviated as DADE), 4,4′-diaminodiphenylmethane, 3,3′-dimethyl-4,4′-diaminodiphenylmethane, 3,3 ′, 5,5′- Tetramethyl-4,4′-diaminodiphenylmethane, 3,3′-dichloro-4,4′-diaminodiphenylmethane, dimethyl-3,7-diaminodibenzothiophene = 5,5-dioxide (hereinafter also abbreviated as TSN) The usual TSN is 2,8-dimethyl-3,7-diaminodibenzothiophene = 5,5. Isomers 2,6-dimethyl-3,7-diaminodibenzothiophene = 5,5-dioxide, 4,6-dimethyl-3,7-diaminodibenzothiophene = 5 5-dioxide, etc.), 2,2-bis [4- (4-aminophenoxy) phenyl] propane, 3,3′-dihydroxy-4,4′-diaminodiphenyl, 3,3′- Dicarboxy-4,4′-diaminodiphenyl, 3,3′-dicarboxy-4,4′-diaminodiphenylmethane, 3,3 ′, 5,5′-tetrachloro-4,4′-diaminodiphenyl, diaminonaphthalene 2,4-dimethyl-m-phenylenediamine, 3,5-diaminobenzoic acid (hereinafter sometimes abbreviated as DABA), 3,3′-diamino Phenyl sulfone (hereinafter sometimes abbreviated as MASN) include aromatic diamines such as. As the diamine component to be combined when 6FDA and its derivative are the main components as the tetracarboxylic acid component, among these, aromatic diamines in which the amino group is located at the meta position, such as DABA, MASN, MPD and the like are preferable. Used.

  The tetracarboxylic acid component to be combined with the diamine component containing a fluorine atom forming polyimide A is not particularly limited, but pyromellitic acid, benzophenone tetracarboxylic acid, naphthalene tetracarboxylic acid, bis (dicarboxyphenyl) ) Ether, bis (dicarboxyphenyl) sulfone, 2,2-bis (dicarboxyphenyl) propane, 2,3,3 ′, 4′-biphenyltetracarboxylic acid, 2,2′3,3′-biphenyltetracarboxylic Mention may be made of acids, 3,3 ′, 4,4′-biphenyltetracarboxylic acids, their dianhydrides, and their esterified products. In particular, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (hereinafter sometimes abbreviated as s-BPDA) is preferable.

As a raw material component for forming polyimide B, a film having a tensile strength of 100 MPa or more, preferably 150 MPa or more, and a tensile elongation at breakage of 10% or more, preferably 15% or more is suitably used. If the tensile strength is lower than 100 MPa or the tensile elongation at break is lower than 10%, the mechanical strength of the asymmetric membrane obtained by using the tensile strength is insufficient. The above-mentioned range is preferable because it cannot be used in applications using high pressure gas and is not practical.
Polyimide containing a fluorine atom in its chemical structure has a relatively low mechanical strength. Therefore, in the monomer component forming polyimide B, neither the tetracarboxylic acid component nor the diamine component contains a fluorine atom as at least the main component. It is preferable that no fluorine atom is contained.

The tetracarboxylic acid component of polyimide B is not particularly limited, but pyromellitic acid, benzophenonetetracarboxylic acid, naphthalenetetracarboxylic acid, bis (dicarboxyphenyl) ether, bis (dicarboxyphenyl) sulfone, 2, 2-bis (dicarboxyphenyl) propane, 2,3,3 ′, 4′-biphenyltetracarboxylic acid, 2,2′3,3′-biphenyltetracarboxylic acid, 3,3 ′, 4,4′-biphenyl Mention may be made of tetracarboxylic acids, their dianhydrides, and their esterified products. In particular, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride is preferred.
These tetracarboxylic acid components may be used alone or in combination of two or more different types, and the mixture may further contain a small amount of a fluorine atom-containing tetracarboxylic acid component. For example, you may use combining 6FDA below 0.3 mol part with respect to 1 mol part of s-BPDA.
As the diamine component of the polyimide B, the diamine exemplified in the description of the raw material component forming the polyimide A can be suitably used.

A preferred method for producing the polyimide asymmetric membrane of the present invention will be further described.
In step 1, respectively and a number average polymerization degree of N _A and N _B satisfying Equation 1 has, consists polymerization and imidation reaction product of raw material components and / or the ingredients of the polyimide A that the chemical structure containing a fluorine atom polyimide A mixed solution of a multi-component polyimide is prepared by mixing Component A and a raw material component of polyimide B and / or a polyimide component B composed of a polymerization imidization reaction product of the raw material component. The range of the combination of N _A and N _B satisfying Equation 1 is shown as a hatched area in the graph of FIG. Incidentally, (tetracarboxylic acid component unreacted diamine component unreacted) raw material components of the polyimide from the degree of polymerization is defined as 0.5, N _A and N _B are of course less than 0.5.
Next, in step 2, the mixed solution of the multi-component polyimide is further subjected to a polymerization imidization reaction. As a result, the polyimide component A and the polyimide component B are a mixture obtained by further polymerization imidization reaction, and in addition to the polymer composed of at least the polyimide component A and the polymer composed of the polyimide component B, the polyimide component A and the polyimide It is possible to obtain a mixed liquid of a multi-component polyimide containing a di- or multi-block copolymer in which the component B is bonded to each other at an end and having an appropriate degree of polymerization.
Here, the diblock copolymer refers to a copolymer in which each of a block composed of a polyimide component A and a block composed of a polyimide component B is bonded to each other end, and the multiblock copolymer is a diblock copolymer. A copolymer in which one or more of the two types of blocks are further bonded to the end of the copolymer. In the di- or multi-block copolymer, there may be a portion in which blocks composed of the polyimide component A are continuously bonded and a portion in which blocks composed of the polyimide component B are continuously bonded.

This will be described with reference to the graph of FIG.
A mixed solution of multi-component polyimide in step 1 consist of a combination of N _A and N _B of region A of FIG. 4 was prepared, further polymerization and imidation reacted in step 2, when the produced polymer is viewed on average, A block consisting only of the polyimide component A or a block consisting only of the polyimide component B is not formed, and only a copolymer with extremely high randomness obtained by averaging the polyimide component A and the polyimide component B can be obtained.
A mixed solution of multi-component polyimide in step 1 consist of a combination of N _A and N _B of region B of Figure 4 was prepared, further polymerization and imidation reacted in step 2, the mixing of multicomponent polyimide containing a block copolymer Although a liquid may be obtained, since the degree of polymerization increases, repulsive interaction between polyimides is large, and macrophase separation easily occurs. Therefore, it is not possible to obtain an asymmetric membrane of the present invention in combination with N _A and N _B of A region and B region in FIG.

In the combination range of N _A and N _B satisfying Equation 1 (shaded area in the graph of FIG. 4), in addition to the polymer composed of at least polyimide component A and the polymer composed of polyimide component B, polyimide component A and polyimide A mixed liquid of a multi-component polyimide containing a di- or multi-block copolymer having a block in which the component B is bonded to each other at the terminal and having an appropriate degree of polymerization can be obtained. This multi-component polyimide can suppress macro phase separation due to repulsive interaction, and enables controlled phase separation that should be called micro phase separation.

Step 1, respectively and a number average polymerization degree of N _A and N _B satisfying the equation 1 has, consists polymerization and imidation reaction product of raw material components and / or the ingredients of the polyimide A including a fluorine atom in its chemical structure This is a step of preparing a mixed solution of a multi-component polyimide by mixing the polyimide component A and the polyimide B as a raw material component of the polyimide B and / or a polymerization imidization reaction product of the raw material component. The specific method of this step is not particularly limited as long as a mixed solution of the multi-component polyimide can be obtained. A raw material component of polyimide A and a raw material component of polyimide B can be independently prepared by a polymerization imidization reaction as necessary, and then mixed uniformly to obtain a mixed solution of multi-component polyimide. . In addition, when the mixed solution of the multi-component polyimide in Step 1 is a raw material component (unreacted tetracarboxylic acid component, unreacted diamine component), the raw material component of one polyimide component is A solution obtained by polymerization imidization reaction so as to have a predetermined number average degree of polymerization may be prepared, and then an unreacted tetracarboxylic acid component and a diamine component which are other polyimide components may be added to the solution. In particular, since higher molecular weight of polyimide B is suitable for improving the mechanical strength of the asymmetric membrane, in Step 1, first, the raw material component forming polyimide B is subjected to polymerization imidization reaction in a polar solvent to obtain an appropriate degree of polymerization. A method of preparing a mixed solution of a multi-component polyimide by adding the raw material component forming the polyimide A to the polyimide B is convenient.

  The polymerization imidation reaction for obtaining polyimide will be described. The polymerization imidation reaction generates a polyamic acid in a polar solvent in a temperature range of 120 ° C. or more, preferably 160 ° C. or more and the boiling point of the solvent to be used, with a predetermined composition ratio of a tetracarboxylic acid component and a diamine component. At the same time, it is preferably carried out by imidizing by carrying out a dehydration ring closure reaction. Lower reaction temperatures may be employed to achieve a predetermined degree of polymerization. If the amidic acid bond remains, the blocking property of the polyimide may be impaired by the exchange reaction. Therefore, in the polymerization imidization reaction, at least the imidization rate is preferably 40% or more, and the imidization can be substantially completed. More preferred.

In the polymerization imidization reaction, a polyimide having a relatively high molecular weight (high number average degree of polymerization) can be synthesized by reacting with the composition ratio of the tetracarboxylic acid component and the diamine component close to each other. When a relatively high molecular weight polyimide is first prepared, the diamine component is 0.95 to 0.995 mol part or 1.005 to 1.05 mol part, particularly 0 to 1 mol part of the tetracarboxylic acid component. It is preferable to react at a composition ratio in the range of .98 to 0.995 mole part or 1.005 to 1.02 mole part to prepare a relatively high molecular weight polyimide component.
For example, when 6FDA is used as the tetracarboxylic acid component and TSN is used as the diamine component, a dehydration ring closure reaction is performed at 190 ° C. for 30 hours with a composition of 1.02 mol part of TSN with respect to 1 mol part of 6FDA. A polyimide having a number average molecular weight of about 15,000 to 25,000 (number average degree of polymerization of about 20 to 40) can be synthesized. In addition, when a dehydration ring-closing reaction is performed at 190 ° C. for 30 hours with a composition of 1.005 mol part of TSN with respect to 1 mol part of 6FDA, the number average molecular weight is about 30,000 to 40,000 (number average degree of polymerization is about 40 to 60). ) Can be synthesized.
For example, when 6FDA was used as the tetracarboxylic acid component and DABA was used as the diamine component, a dehydration ring closure reaction was caused at 190 ° C. for 30 hours with a composition of 1.02 mol parts of DABA relative to 1 mol part of 6FDA. In this case, a polyimide having a number average molecular weight of about 15,000 to 25,000 (number average degree of polymerization of about 25 to 45) can be synthesized. In addition, when a dehydration ring-closing reaction is caused at 190 ° C. for 30 hours with a composition of DABA of 1.005 moles per 1 mole part of 6FDA, the number average molecular weight is about 40,000 to 50,000 (number average degree of polymerization is about 70 to 90). ) Can be synthesized.

  On the other hand, the diamine component reacts at a composition ratio of 0.98 mol part or less or 1.02 mol part or more with respect to 1 mol part of the tetracarboxylic acid component, so that a relatively low molecular weight (number average polymerization degree is small). A polyimide component can also be prepared.

  The mixed solution of the multi-component polyimide obtained in step 1 is a composition ratio of the total number of moles of the diamine component to the total number of moles of the tetracarboxylic acid component ((total number of moles of diamine component) / (total number of moles of tetracarboxylic acid component). )) Within a range of 0.95 to 0.99 or 1.01 to 1.05 mole part, more preferably 0.96 to 0.99 or 1.015 to 1.04 mole part. However, the number average molecular weight and solution viscosity of the mixed solution of the multicomponent polyimide obtained as a result of Step 2 are preferable.

Step 2 is mixed solution of multi-component polyimide comprising a polyimide A component of the combination of N _A and N _B satisfying Equation 1 obtained polyimide B component is further polymerization and imidation reaction in step 1, at least polyimide component In addition to the polymer composed of A and the polymer composed of polyimide component B, it contains a di- or multi-block copolymer in which polyimide component A and polyimide component B are bonded to each other at the ends, and has an appropriate degree of polymerization. This is a step of obtaining a mixed liquid of multicomponent polyimide.

  Step 2 is characterized in that the mixed solution of the multi-component polyimide obtained in Step 1 is further subjected to a polymerization imidization reaction, and the above-described polymerization imidation reaction method can be suitably employed.

In the mixed solution of multi-component polyimides in Step 1 and Step 2, a polar solvent that uniformly dissolves the multi-component polyimide is used. Here, homogeneously dissolved means a state in which there is no turbidity apparent in appearance because there is no macrophase-separated domain having a size enough to scatter visible light inside the solution. Microphase-separated domains of a size that does not scatter visible light may exist, and it is not an essential requirement to be uniform at the molecular chain level.
If a solvent that is apparently turbid in appearance is used after the preparation of the multi-component polyimide, it is not possible to obtain a gas separation membrane having a high gas processing capacity produced by the present invention.
Such polar solvents are not particularly limited, but include phenols such as phenol, cresol, xylenol, etc., catechols having two hydroxyl groups in the benzene ring, 3-chlorophenol, 4-chlorophenol (hereinafter referred to as PCP). A phenol solvent such as halogenated phenols such as 4-bromophenol and 2-chloro-5-hydroxytoluene, or N-methyl-2-pyrrolidone, N, N-dimethylformamide, Amide solvents such as N, N-dimethylacetamide and N, N-diethylacetamide, or mixtures thereof are preferred.

  The polymerization imidation reaction in step 2 is not particularly limited as long as a di- or multi-block copolymer in which polyimide component A and polyimide component B are bonded to each other can be generated. Usually, a di- or multi-block copolymer can be suitably formed by carrying out the polymerization imidation reaction until the number average molecular weight of the multi-component polyimide mixed solution is preferably 2 times or more, more preferably 5 times or more. . The number average degree of polymerization of the mixed solution of the multicomponent polyimide obtained by the polymerization imidation reaction in step 2 is 20 to 1000, preferably 20 to 500, more preferably 30 to 200. If the number average degree of polymerization is too low, the solution viscosity of the mixed solution is too low, making film formation in Step 3 difficult, and the mechanical strength of the resulting asymmetric film is lowered, which is not preferable. If the number average degree of polymerization is too high, macrophase separation is likely to occur, and the solution viscosity becomes too high, making film formation in Step 3 difficult, which is not preferable. The solution viscosity (rotational viscosity) of the mixed solution of multi-component polyimide obtained in step 2 is to make the solution into a predetermined shape (for example, hollow fiber shape) and stabilize the shape when forming an asymmetric membrane in the phase change method. It is a characteristic required to do. In the present invention, the solution viscosity of the mixed solution of the multi-component polyimide is preferably adjusted to 20 to 17000 poise, preferably 100 to 15000 poise, particularly 200 to 10,000 at 100 ° C. With such a solution viscosity polyimide solution, for example, when a polyimide solution is discharged from a nozzle in the spinning process when manufacturing a hollow fiber asymmetric membrane, a shape after discharge such as a hollow fiber shape can be stably obtained. Is preferred. If the solution viscosity is lower than 20 poise or higher than 17000 poise, it becomes difficult to stably obtain a shape after discharge such as a hollow fiber shape.

  The number average degree of polymerization and the preferred solution viscosity of the suitable mixed solution of the multicomponent polyimide are the composition ratio of the total number of moles of the diamine component to the total number of moles of the tetracarboxylic acid component in the mixed solution of the multicomponent polyimide obtained in Step 1. ((Total number of moles of diamine component) / (total number of moles of tetracarboxylic acid component)) is 0.95 to 0.99 or 1.01 to 1.05 mole part, more preferably 0.96 to 0.99. Alternatively, it can be easily obtained by the polymerization imidation reaction in Step 2 within the range of 1.015 to 1.04 mol part.

  In addition, the amount of solvent may be adjusted so that the polymer concentration of the mixed solution of the multi-component polyimide in Step 1 and Step 2 is 5 to 40% by weight, preferably 8 to 25% by weight, particularly 9 to 20% by weight. Is preferred. When the polymer concentration is less than 5% by weight, defects are likely to occur when an asymmetric membrane is produced by the phase conversion method, and gas permeation performance tends to be poor when a gas separation membrane is used. If the polymer concentration exceeds 40% by weight, the dense layer of the obtained asymmetric membrane becomes thick or the porosity of the porous layer becomes low, resulting in a low gas permeation rate. Therefore, at least an asymmetric membrane suitable as a gas separation membrane It becomes difficult to get.

  Step 3 is characterized in that an asymmetric membrane is formed by a phase conversion method using the mixed solution of the multi-component polyimide obtained in Step 2 above. The phase change method is a known method for forming a film while bringing a polymer solution into contact with a coagulation liquid to cause phase change. In the present invention, a so-called dry and wet method is suitably employed. In the dry-wet method, the solvent on the surface of the polymer solution in the form of a film is evaporated to form a thin dense layer, and then immersed in a coagulation liquid (solvent that is compatible with the solvent of the polymer solution and the polymer is insoluble), This is a method of forming a microporous layer by utilizing the phase separation phenomenon that occurs at that time to form a porous layer, and was proposed by Loeb et al. (For example, US Pat. No. 3,133,132). In the present invention, in step 3, the macro phase separation is suppressed, and the phase separation that should be called micro phase separation proceeds, and a polyimide asymmetric membrane in which the proportion of the fluorine atom-containing polyimide in the dense layer is suitably controlled can be produced. .

In the present invention, the hollow fiber membrane can be suitably produced by adopting a dry and wet spinning method in Step 3. The dry-wet spinning method is a method for producing an asymmetric hollow fiber membrane by applying a dry-wet method to a polymer solution that is discharged from a spinning nozzle to have a hollow fiber-shaped target shape. More specifically, the polymer solution is discharged from the nozzle into a hollow fiber-shaped target shape, and after passing through air or nitrogen gas atmosphere immediately after discharge, the polymer component is not substantially dissolved and the solvent of the polymer mixed solution is This is a method for producing a separation membrane by dipping in a compatible coagulating liquid to form an asymmetric structure, then drying, and further heat-treating as necessary.
As described above, the solution viscosity of the mixed solution of the multi-component polyimide discharged from the nozzle is 20 to 17000 poise, preferably 100 to 15000 poise, particularly 200 to 10,000 poise at the discharge temperature (for example, 100 ° C.). Is preferable because a shape after discharge such as a hollow fiber shape can be stably obtained. For immersion in the coagulation liquid, the film is immersed in the primary coagulation liquid and solidified to such an extent that the shape of the membrane such as a hollow fiber can be maintained, wound on a guide roll, and then immersed in the secondary coagulation liquid to fully saturate the entire film. It is preferable to solidify. For drying the coagulated film, a method of drying after replacing the coagulating liquid with a solvent such as hydrocarbon is effective. The heat treatment is preferably carried out at a temperature lower than the softening point or secondary transition point of each component polymer of the multicomponent polyimide used.

The mixed solution of the multi-component polyimide used in Step 3 is obtained by the polymerization imidization reaction in Step 2 in addition to the polymer consisting of at least polyimide component A and the polymer consisting of polyimide component B, as well as polyimide component A and polyimide. This is a mixed solution of a multi-component polyimide containing a di- or multi-block copolymer in which component B is bonded to each other at an end and having an appropriate degree of polymerization.
When this mixed solution undergoes phase separation in the film-forming process by the phase conversion method, the di- or multi-block copolymer in which the polyimide component A and the polyimide component B are bonded to each other end is obtained from the polyimide component A that is incompatible with each other. The interface between the domain composed of the polyimide component A and the domain composed of the polyimide component B, by acting as a kind of surfactant between the polymer composed of the polymer composed of the polyimide component B and the polymer composed of the polyimide component B When the di- or multi-block copolymer is distributed on the surface, repulsive interaction between different domains can be shielded, macro phase separation can be suppressed, and desirable micro phase separation can be caused.

  Since a fluorine atom-containing polyimide is usually more soluble than a polyimide that does not contain a fluorine atom, it is considered difficult to deposit in a dense layer when an asymmetric film is formed by a phase change method. However, since fluorine-containing polyimide has a low surface free energy, it can be thermodynamically distributed more on the film surface, thereby reducing the enthalpy of the film surface. In the phase separation step of Step 3 of the present invention, it can be presumed that the higher proportion of fluorine-containing polyimide is present in the dense layer due to this thermodynamic reason.

  The polyimide asymmetric membrane of the present invention is an asymmetric membrane having a dense layer and a porous layer, comprising a multi-component polyimide containing a fluorine atom-containing polyimide, and having a higher proportion of fluorine-containing polyimide in the dense layer. It is the obtained polyimide asymmetric membrane. That is, a fluorine atom-containing polyimide having a relatively good gas permeation performance is present in a dense layer requiring high gas permeation performance as a gas separation membrane, while the porous layer does not contain fluorine atoms or Since it is an asymmetric membrane in which a polyimide having a small content and relatively high mechanical strength exists, it is extremely suitable as a gas separation membrane. It can be said that it is an asymmetric film having an inclined structure in the sense that the proportion of each polyimide contained varies depending on the portion in the thickness direction.

Such a tilted structure can be obtained using dynamic secondary ion mass spectrometry (hereinafter sometimes abbreviated as dSIMS). In this method, the film surface is irradiated with O ₂ ⁺ ions, the film is sputter-etched, and the secondary ions sputtered at each etching depth are subjected to mass analysis to analyze in the depth direction. It is. A uniform solution obtained by casting and drying a mixed solution of a multi-component polyimide containing a di- or multi-block copolymer produced by the production method of the present invention and having an appropriate degree of polymerization on a glass plate. FIG. 5 shows the results of depth direction analysis of the fluorine concentration from the film surface toward the inside, and the sample surface was irradiated with O ₂ + ions at an irradiation current of 15 nA / μm ² using an atomic dynamic SIMS 4000. The depth profile of the measured fluorine atom distribution, where the horizontal axis in the figure calculates the average etching rate from the time required to sputter-etch the deuterated polystyrene cover layer with a known thickness on the sample surface, The time when the sample was sputter-etched was converted into a depth from the sample surface and displayed. Here, with respect to the fluorine concentration value in the film having a depth of 150 nm or less from the surface, a region having a high fluorine concentration is observed from the surface to a depth of about 50 nm.
On the other hand, the same analysis result about the uniform film obtained by casting the polyimide dope obtained by the normal polymerization method on a glass plate and drying it is shown in FIG. Here, a large gradient structure is not observed in the fluorine concentration distribution near the surface.

The polyimide asymmetric film of the present invention preferably has a ratio φ _S / f of the fluorine atom concentration φ _{S on the} surface of the dense layer measured by X-ray photoelectron spectroscopy and the average fluorine atom concentration f of the multi-component polyimide forming the film. Is a ratio in the range of 1.1 to 1.8.

A random copolymerized polyimide solution is prepared by a normal polymerization imidization method using the same raw material component composition as the entire raw material component composition of a multi-component polyimide containing a fluorine atom-containing polyimide, and a polyimide asymmetric film is obtained from the polyimide solution by a dry-wet method. Is obtained, the fluorine atom concentration ratio φ _S / f is about 1.0. On the other hand, in the polyimide asymmetric membrane of the present invention, more fluorine atom-containing polyimide is present in the dense layer, and the fluorine atom concentration ratio φ _S / f is preferably in the range of 1.1 to 1.8, more preferably 1. Present in a proportion in the range of 2 to 1.7.

  A polyimide asymmetric membrane used as a gas separation membrane has a dense layer and a porous layer. The dense layer has a density that is substantially different in permeation rate depending on the gas type (for example, the permeation rate ratio of helium gas and nitrogen gas is 1.2 times or more at 50 ° C.) and has a separation function depending on the gas type. Have. On the other hand, the porous layer is a layer having porosity to such an extent that it does not have a substantial gas separation function, and the pore diameter is not necessarily constant, and the fine layer is formed sequentially from a large hole to a dense layer. It does not matter. The polyimide asymmetric membrane obtained according to the present invention has no defects in the dense layer and high gas separation performance. There are no particular limitations on the form, thickness, dimensions, etc., for example, it may be a flat membrane or a hollow fiber. However, when the polyimide asymmetric membrane obtained by the present invention is used as a gas separation membrane, the dense layer has a thickness of 1 to 1000 nm, preferably about 20 to 200 nm, and the porous layer has a thickness of 10 to 2000 μm, preferably 10 to 10 μm. About 500 μm is preferable, and the hollow fiber gas separation membrane has an inner diameter of 10 to 3000 μm, preferably about 20 to 900 μm, and an outer diameter of 30 to 7000 μm, preferably about 50 to 1200 μm. A hollow fiber asymmetric membrane having a dense layer is preferred.

Furthermore, the polyimide asymmetric membrane obtained by the present invention preferably has high performance gas separation performance and practical mechanical strength. That is, the hydrogen gas permeation rate (P ′ _H2 ) is 4.0 × 10 ⁻⁴ cm ³ (STP) / cm ² · sec · cmHg or more, more preferably 5.0 × 10 ⁻⁴ cm ³ (STP) / cm. in is a ² · sec · cmHg or more, the ratio of hydrogen gas permeation rate (P _'H2) and nitrogen gas permeation rate (P' and _{N2) (P 'H2 / P} ' N2) of 20 or more, more preferably 45 or more And the tensile elongation at break is 15% or more, particularly the tensile elongation at break as a hollow fiber membrane is 15% or more. Further, the helium gas transmission rate (P ′ _He ) is 4.0 × 10 ⁻⁴ cm ³ (STP) / cm ² · sec · cmHg or more, more preferably 5.0 × 10 ⁻⁴ cm ³ (STP) / cm. in is a ² · sec · cmHg or more, helium gas permeation rate (P _'He) and nitrogen gas permeation rate (P' ratio of _{N2) (P 'He / P} ' N2) of 20 or more, more preferably 45 or more And the tensile elongation at break is 15% or more, particularly the tensile elongation at break as a hollow fiber membrane is 15% or more.
If the tensile elongation at break as a hollow fiber is less than 15%, it is not practical because it cannot be modularized industrially because it is easily broken or damaged when the hollow fiber membrane is processed into a module. If the tensile elongation at break as a hollow fiber is 15% or more, it is practical because it becomes easy to modularize industrially. If the tensile elongation at break as a hollow fiber is less than 15%, the hollow fiber is likely to be cut during use (especially when high-pressure gas is supplied), and the use conditions are limited, which is not practical.

In the gas separation membrane of the present invention, by supplying a mixed gas to the supply side of the gas separation membrane and bringing the mixed gas into contact with the shared surface of the separation membrane, at least the mixed gas is transferred to the permeation side of the gas separation membrane. One kind of gas component is selectively permeated, a mixed gas with a reduced ratio of the selectively permeated gas component is taken out from the supply side of the gas separation membrane, and the permeation side of the gas separation membrane is selectively permeated. The at least one gas component can be selectively separated from the mixed gas by taking out the mixed gas in which the ratio of the gas component is increased.
Further, the gas separation membrane of the present invention can be suitably used after being modularized by an ordinary method. The separation membrane module of the hollow fiber gas separation membrane is, for example, a bundle of about 100 to 200,000 hollow fiber membranes of appropriate length, with both ends of the hollow fiber bundle held in an open state at the ends of the hollow fibers. The hollow fiber membrane element comprising a hollow fiber bundle and a tube sheet, etc., fixed with a tube plate made of a thermosetting resin, etc. is provided with at least a mixed gas inlet, a permeate gas outlet, and a non-permeate gas outlet. It is obtained by storing and attaching in a container so that the space leading to the inside of the hollow fiber membrane and the space leading to the outside of the hollow fiber membrane are isolated. In such a gas separation membrane module, a mixed gas is supplied from a mixed gas inlet to a space in contact with the inside or outside of the hollow fiber membrane, and specific components in the mixed gas are selectively selected while flowing in contact with the hollow fiber membrane. Gas separation is performed by allowing the permeate gas to permeate the membrane and the non-permeate gas that has not permeated the membrane to be discharged from the non-permeate gas exhaust port.

  Further, the gas separation membrane comprising the polyimide asymmetric membrane of the present invention is a practical high performance gas separation membrane having the above high gas permeation performance and excellent mechanical strength. Used for separation of hydrogen gas, separation of hydrogen gas and nitrogen gas, separation of helium gas and nitrogen gas, separation of hydrocarbon gas such as carbon dioxide gas and methane gas, separation of oxygen gas and nitrogen gas be able to. In particular, it can be suitably used for applications such as separation of hydrogen gas and hydrocarbon gas such as methane gas, separation of hydrogen gas and nitrogen gas, separation of oxygen gas and nitrogen gas.

In the present invention, the degree of polymerization is determined by checking the correspondence between the number average degree of polymerization and the solution viscosity in advance by, for example, gel permeation chromatography (GPC) measurement or measurement of imidization rate by infrared spectroscopy. The number average degree of polymerization can be known by measuring the viscosity. In addition, when the thing of 90% or more of imidation rate is object, it calculated | required by the GPC measuring method, and when the imidation rate was less than 90%, it calculated | required from the imidation rate measuring method by infrared spectroscopy.
In the present invention, GPC measurement was performed as follows. Using 800 series HPLC system manufactured by JASCO Corporation, the column is one Shodex KD-806M, the column temperature is 40 ° C, the detector is an intelligent UV-visible spectroscopic detector (absorption wavelength 350nm) for unknown samples, standard A differential refractometer (standard material is polyethylene glycol) was used for the substance. The solvent used was an N-methyl-2-pyrrolidone solution containing 0.05 mol / L of lithium chloride and phosphoric acid, the solvent flow rate was 0.5 mL / min, and the sample concentration was about 0.1%. Data acquisition and data processing were performed using JASCO-JMBS / BORWIN. Data acquisition was performed twice / second to obtain a chromatogram of the sample. On the other hand, polyethylene glycols having molecular weights of 82, 250, 28, 700, 6, 450, and 1,900 are used as standard substances, and peaks are detected from these chromatograms to obtain a calibration curve indicating the relationship between retention time and molecular weight. It was. Molecular weight analysis of an unknown sample, each calculated molecular weight M _i in the retention time from the calibration curve, also determine the fraction W _{i =} h _{i /} Σh _i to the sum of the height h _i of the chromatogram at each holding time, Based on these, the number average molecular weight Mn was obtained from 1 / {Σ (W _i / M _i )} and the weight average molecular weight Mw was obtained from Σ (W _i · M _i ).
The number average degree of polymerization N was determined by dividing the number average molecular weight Mn by the monomer unit molecular weight <m> averaged according to the charge ratio at the time of polymerization.

なお、モノマー単位分子量＜ｍ＞は下記のとおり求めた。すなわち、複数種のテトラカルボン酸成分（分子量ｍ_１，ｉ、仕込みモル比Ｒ_１，ｉ、但し、ΣＲ_１，ｉ＝１、ｉ＝１，２，３，・・・，ｎ_１）、複数種のジアミン成分（分子量ｍ_２，ｊ、仕込みモル比Ｒ_２，ｊ、但し、ΣＲ_２，ｊ＝１、ｊ＝１，２，３，・・・，ｎ_２）を仕込んだ場合のモノマー単位分子量＜ｍ＞は下記の式に従って求めた。

The monomer unit molecular weight <m> was determined as follows. That is, plural types of tetracarboxylic acid components (molecular weight m _{1, i} , charged molar ratio R _{1, i} , where ΣR _{1, i} = 1, i = 1, 2, 3,..., N ₁ ), plural Monomer unit in the case where seed diamine components (molecular weight m _{2, j} , charged molar ratio R _{2, j} , ΣR _{2, j} = 1, j = 1, 2, 3,..., N ₂ ) are charged. The molecular weight <m> was determined according to the following formula.

The imidation ratio was measured by infrared spectroscopy using Spectrum One manufactured by PerkinElmer Co., Ltd., by total reflection absorption measurement-Fourier transform infrared spectroscopy (ATR-FTIR). Calculation of imidization rate _{p I} is the absorbance _{A I} the internal standard C-N stretching vibration of an imide bond, an aromatic nucleus C = C-plane vibrations of the absorbance A of (wave number approximately 1360 cm ^-1) (a wave number of about 1500 cm ^-1) normalized value (a / a _I) and 5 hours heat-treated samples for the previous and Similarly C-N stretching absorbance a _S arom C = C-plane vibration of the vibration obtained after at 190 ° C. as The absorbance _ASI was divided by a value normalized as an internal standard (A _S / A _SI ).

なお、吸収バンドの吸光度は、吸収バンドの両側の谷を結んだ線をベースラインとしたピーク強度とした。
ここで得られたイミド化率の値から、さらに下記式により数平均重合度Ｎを求めた。

The absorbance of the absorption band was defined as the peak intensity with the line connecting the valleys on both sides of the absorption band as the baseline.
From the value of the imidization ratio obtained here, the number average degree of polymerization N was further determined by the following formula.

ここでｒはポリイミドのテトラカルボン酸成分の総モル数に対するジアミン成分の総モル数の組成比であり、ジアミン成分がテトラカルボン酸成分より多い場合その逆数を取るものとし（即ちどの場合においてもｒは１以下）、ｐ_Ｉはイミド化率である。

Here, r is a composition ratio of the total number of moles of the diamine component to the total number of moles of the tetracarboxylic acid component of the polyimide, and when the diamine component is larger than the tetracarboxylic acid component, the reciprocal is taken (that is, in any case, r Is 1 or less), and p _I is an imidization ratio.

In the present invention, the ratio of fluorine atom-containing polyimide is present in the dense layer, X-rays photoelectron spectroscopy (hereinafter sometimes abbreviated as XPS or ESCA) by knowing by examining the fluorine atom concentration phi _S of the dense layer surface Can do.
Here, the atomic concentration φ _j of the specific element j represents the number of atoms of each element that can be detected in the polyimide (hydrogen atoms and helium atoms cannot be detected) N _i (subscript indicates the type of element) ), And the number of atoms of the specific element j is N _j and is represented by the following mathematical formula.

（ここで、ΣＮ_ｉはポリイミドに含まれる検出可能な全元素の原子数の和を示す。）

(Here, ΣN _i represents the sum of the number of atoms of all detectable elements contained in the polyimide.)

In the XPS measurement, the surface of the dense layer of the polyimide asymmetric film is irradiated with X-rays, the electrons in each orbit of each element contained in the polyimide are emitted into the vacuum, and the kinetic energy of the emitted electrons (photoelectrons) This is done by measuring the photoelectron intensity (photoelectron spectrum). In the present invention, monochromatic AlKα rays from which X-ray components unnecessary for XPS are removed are preferably used as the X-rays to be irradiated in order to suppress damage on the polyimide surface.
Further, the binding energy E _b in the electron substance atom is _obtained from the kinetic energy E _k of the photoelectron by the following mathematical formula.

（ここで、ｈνは照射Ｘ線のエネルギー、Ｗは光電子を検出した分光器の仕事関数である。）
この束縛エネルギーの値は、元素と電子軌道によりほぼ決まった値をとるので、照射Ｘ線のエネルギーを適当に選択すれば、原理的には全元素の検出が可能なはずである。しかしながら、各軌道の電子がＸ線によって励起される確率（光イオン化断面積）が小さい水素とヘリウムに関しては、実際には観測できない。
ポリイミドに含まれる特定の元素ｊのｌ軌道からＸ線照射によって放出された光電子の強度Ｉ_ｊは下記数式で示される。

(Here, hν is the energy of the irradiated X-ray, and W is the work function of the spectrometer that has detected the photoelectrons.)
Since the value of the binding energy is almost determined by the element and the electron orbit, all elements should be detectable in principle if the energy of the irradiated X-ray is appropriately selected. However, in reality, hydrogen and helium, which have a small probability (photoionization cross section) that electrons in each orbit are excited by X-rays, cannot be observed.
The intensity I _j of the photoelectrons emitted by the X-ray irradiation from the l orbital of the specific element j contained in the polyimide is expressed by the following formula.

（ここで、Ｎ_ｊは単位体積当りの元素ｊの原子数、σ_ｊ ^ｌは元素ｊのｌ殻に対する光イオン化断面積、λ_ｊ ^ｌは元素ｊのｌ殻から放出された電子がポリイミド中を走行する際の非弾性散乱平均自由行程、Ａ_ｊ ^ｌは元素ｊのｌ殻から放出された電子に対する装置関数、Ｒはポリイミド非対称膜の表面粗さ係数である。）
光イオン化断面積σ_ｊ ^ｌ、非弾性散乱平均自由行程λ_ｊ ^ｌの値は公知である。Ａ_ｊ ^ｌは装置と測定条件から決まる値である。Ｒの値はサンプルによって異なるが、強度比を取ると消える値であるため、後述する原子濃度の算出には必要ない。

(Where N _j is the number of atoms of element j per unit volume, σ _j ^l is the photoionization cross section for the l shell of element j, and λ _j ^l is the electron emitted from the l shell of element j in the polyimide. Inelastic scattering mean free path when traveling, A _j ^l is a device function for electrons emitted from the l shell of element j, and R is a surface roughness coefficient of the polyimide asymmetric film.)
The values of the photoionization cross section σ _j ^l and the inelastic scattering mean free path λ _j ^l are known. A _j ^l is a value determined from the apparatus and measurement conditions. Although the value of R varies depending on the sample, it is a value that disappears when the intensity ratio is taken.

In the present invention, the atomic concentration φ _j of the specific element j contained in the polyimide was determined by the following formula using the measured photoelectron intensity I _j .

（ここで、Ｓ_ｊ＝σ_ｊ ^ｌλ_ｊ ^ｌＡ_ｊ ^ｌであり、Ｓ_ｊは元素ｉに対する相対的な感度を表しており、Σ（Ｉ_ｉ／Ｓ_ｉ）はポリイミドに含まれる検出できる全ての元素ｉについて光電子の強度を前記の相対感度で除した値の和を表している。）
なお、相対感度Ｓ_ｊは原子濃度が既知である基準物質等を用いて別途決定することができる。相対感度Ｓ_ｊとして、ＸＰＳの装置メーカーなどから提供されている相対感度Ｓ’_ｊを便宜的に用いることがあるが、本発明においては、単一組成からなる、換言すれば１種類のテトラカルボン酸成分と１種類のジアミン成分からなるホモポリイミド（原子濃度が既知）を用いて相対感度を決定した。
すなわち、単一組成のポリイミド（１種類のテトラカルボン酸成分と１種類のジアミン成分からなるホモポリイミド）からなるサンプルについては、表面原子濃度φ_ｓ，ｊの値と該ポリイミドにおける平均の原子濃度の値ｆ_ｊがほぼ一致することが期待されるが、表面原子濃度φ_ｓ，ｊを求める際に用いる相対感度Ｓ_ｊとして、ＸＰＳの装置メーカーなどから提供されている相対感度係数を装置関数で補正した相対感度Ｓ’_ｊをそのまま用いた場合、φ_ｓ，ｊとｆ_ｊの間にしばしばズレが生じる。これは前記相対感度Ｓ’_ｊが、ポリイミド以外の他の標準物質を用いて実験的に決められた値であることによる。このためポリイミド材料の表面原子濃度を求める際の相対感度Ｓ_ｊは、単一組成のホモポリイミドからなるサンプルを用いたときの表面原子濃度φ_ｓ，ｊと平均の原子濃度ｆ_ｊが一致するように、Ｓ’_ｊを補正した値を用いた。すなわち、本発明の相対感度Ｓ_ｊは、下記数式で示される。

(Where S _j = σ _j ^l λ _j ^l A _j ^l , S _j represents the relative sensitivity to element i, and Σ (I _i / S _i ) is all detectable in polyimide Represents the sum of the values obtained by dividing the photoelectron intensity by the above relative sensitivity for element i.)
The relative sensitivity S _j can be separately determined using a reference material having a known atomic concentration. As the relative sensitivity S _j , the relative sensitivity S ′ _j provided by an XPS device manufacturer or the like may be used for convenience. In the present invention, the relative sensitivity S _j consists of a single composition, in other words, one type of tetracarboxylic acid. Relative sensitivity was determined using a homopolyimide (atomic concentration known) consisting of an acid component and one diamine component.
That is, for a sample made of a single composition polyimide (homopolyimide composed of one kind of tetracarboxylic acid component and one kind of diamine component) _, the value of the surface atomic concentration φ _{s, j} and the average atomic concentration of the polyimide Although the values f _j are expected to be substantially the same, the relative sensitivity coefficient provided by an XPS device manufacturer or the like is corrected by a device function as the relative sensitivity S _j used when the surface atomic concentration φ _{s, j} is obtained. When the relative sensitivity S ′ _j is used as it is, a deviation often occurs between φ _{s, j} and f _j . This is because the relative sensitivity S ′ _j is a value experimentally determined using a standard material other than polyimide. For this reason, the relative sensitivity S _j when determining the surface atomic concentration of the polyimide material is such that the surface atomic concentration φ _{s, j} and the average atomic concentration f _j when a sample composed of a homopolyimide having a single composition is matched. A value obtained by correcting S ′ _j was used. That is, the relative sensitivity S _j of the present invention is expressed by the following mathematical formula.

（ここでα_ｊは元素ｊについて、他の標準材料を用いて決定された相対感度Ｓ’_ｊをポリイミド材料に適用するために使用する補正係数である）
本発明においては前記補正係数を元素ごとに測定して求め、その補正係数で補正した相対感度Ｓ_ｊを用いた。
本発明において、光電子の強度Ｉ_ｊは、ＸＰＳ測定の結果得られる光電子スペクトルについて、光電子ピークの面積から求めた。光電子ピークのうち、比較的に光イオン化断面積の大きい遷移に関するものが好適に利用される。通常は光イオン化断面積の値が炭素１ｓ軌道の値の１０％より高い遷移に関する光電子ピークが好適に利用される。本発明では、フッ素に関しては１ｓ軌道からの光電子ピークを好適に利用でき、例えば炭素に関しては１ｓ軌道、窒素に関しては１ｓ軌道、酸素に関しては１ｓ軌道、硫黄に関しては２ｐ軌道から放出された光電子ピークを好適に利用できた。
また、光電子スペクトルは、光電子が試料から真空中へ脱出する過程で非弾性散乱を起こすことにより生じたバックグラウンドを含んでいる。このため、原子濃度の決定に利用する各光電子ピークについて、前記のバックグラウンドを差し引いた後に求めた残りの面積をＩ_ｊとした。

(Where α _j is a correction factor used for applying relative sensitivity S ′ _j , determined using other standard materials, to the polyimide material for element j)
In the present invention, the correction coefficient is measured for each element, and the relative sensitivity S _j corrected with the correction coefficient is used.
In the present invention, the photoelectron intensity I _j was determined from the photoelectron peak area for the photoelectron spectrum obtained as a result of XPS measurement. Of the photoelectron peaks, those relating to transitions having a relatively large photoionization cross section are preferably used. Usually, a photoelectron peak relating to a transition in which the value of the photoionization cross section is higher than 10% of the value of the carbon 1s orbital is preferably used. In the present invention, the photoelectron peak from the 1s orbital can be suitably used for fluorine. For example, the photoelectron peak emitted from the 1s orbital for carbon, the 1s orbital for nitrogen, the 1s orbital for oxygen, and the 2p orbital for sulfur. It was possible to use it suitably.
The photoelectron spectrum includes a background generated by inelastic scattering in the process of photoelectrons escaping from the sample into the vacuum. For this reason, for each photoelectron peak used for determination of the atomic concentration, the remaining area obtained after subtracting the background was defined as I _j .

Furthermore, in the XPS measurement of the present invention, when the polyimide asymmetric membrane is a hollow fiber, X-rays whose irradiation diameter is narrower than the hollow fiber diameter are used. Since the hollow fiber diameter is 30 μm or more and about 100 μm or more, an irradiation diameter of about 100 μmφ or less is preferably adopted, and further about 20 μmφ is suitably adopted.
Moreover, since the polyimide surface is charged by the emission of photoelectrons, neutralization of the sample surface charge by electron beam irradiation or the like was suitably employed.
In the XPS measurement, the thickness measured by XPS changes according to the photoelectron take-off angle (emission angle) θ measured from the sample surface. 95% of the photoelectrons detected by XPS are emitted from the range of thickness 3λ _j ^l sin θ measured from the sample surface. The value of θ is not particularly limited as long as it can be measured, but 45 ° or the like is preferably used. The thickness to be analyzed is in the range of several nm from the sample surface. For this reason, the atomic concentration measured by XPS is the surface atomic concentration φ _{s, j} in a thickness range of several nm from the surface.

On the other hand, the average atomic concentration f _j for the element j contained in the multi-component polyimide forming the entire film is expressed by the following mathematical formula.

（ここでｎ_ｋはモノマーｋに含まれる元素ｊの原子数であり、モノマーｋがテトラカルボン酸又はその無水物の場合で元素ｊが酸素の場合、ポリイミド重合時に縮合水として脱離する酸素原子の数を除いた数であり、Ｎ_ｋはモノマーｋに含まれるＸ線光電子分光で検出可能な全原子数であり、モノマーｋがテトラカルボン酸又はその無水物の場合、ポリイミド重合時に縮合水として脱離する酸素原子の数を除いた数であり、ｍ_ｋは膜を形成した多成分のポリイミド中におけるモノマーｋのモル分率であり、Σは多成分のポリイミドに含まれる全てのモノマーｋについて和を取ることを示す）
本発明において、膜全体における平均のフッ素原子濃度（ｆ）は、前記数式に基づいて算出されたものである。

(Where n _k is the number of atoms of the element j contained in the monomer k, and when the monomer k is a tetracarboxylic acid or its anhydride and the element j is oxygen, the oxygen atom that is eliminated as condensed water during polyimide polymerization) N _k is the total number of atoms detectable by X-ray photoelectron spectroscopy contained in monomer k, and when monomer k is tetracarboxylic acid or its anhydride, it is used as condensed water during polyimide polymerization. This is the number excluding the number of desorbed oxygen atoms, m _k is the mole fraction of monomer k in the multi-component polyimide that formed the film, and Σ is for all monomers k contained in the multi-component polyimide (Shows the sum)
In the present invention, the average fluorine atom concentration (f) in the entire film is calculated based on the above mathematical formula.

  Hereinafter, the asymmetric film made of the multi-component polyimide of the present invention and its characteristics will be described in detail. In addition, this invention is not limited to a following example.

Various measurement methods in the present invention will be described.
(Preparation of polyimide film)
The polyimide solution was prepared so that the solution viscosity was 50 to 1000 poise at 100 ° C., filtered using a 400 mesh wire net, and then defoamed by standing at 100 ° C. This polyimide solution is cast on a glass plate at 50 ° C. using a 0.5 mm or 0.2 mm doctor knife, heated in an oven at 100 ° C. for 3 hours to evaporate the solvent, and further in an oven at 300 ° C. for 1 hour. Heat treatment was performed to obtain a polyimide film as a measurement sample of the helium gas permeability coefficient.
(Measurement method of helium gas permeability coefficient (P _He ), nitrogen gas permeability coefficient (P _N2 ), and permeability coefficient ratio of helium gas to nitrogen gas (P _He / P _N2 ))
The helium gas permeability coefficient was measured by the high vacuum time lag method. That is, after the polyimide film is mounted on a permeation cell and brought to 80 ° C., a high vacuum of 10 ⁻⁵ torr is applied with a vacuum pump, and then a pressure of 2.5 kgf / cm ² G is applied to the primary side of the film with helium gas. The change with time of the secondary pressure increase due to the permeated gas was obtained, and the helium gas permeability coefficient (P _He ) of the polyimide film was calculated from the film thickness, effective area, secondary volume, primary pressure, etc. . The nitrogen gas permeability coefficient (P _N2 ) was also measured by using the same polyimide film and using nitrogen gas instead of helium gas by the same method. The permeability coefficient ratio (P _He / P _N2 ) between helium gas and nitrogen gas was calculated from the helium gas permeability coefficient (P _He ) and nitrogen gas permeability coefficient (P _N2 ) determined by the above method.

(Measuring method of helium gas and nitrogen gas permeation performance of hollow fiber membrane)
Using 15 hollow fiber membranes, a stainless steel pipe, and an epoxy resin adhesive, an element for evaluating permeation performance having an effective length of 10 cm was prepared and mounted on a stainless steel container to form a pencil module. A permeate flow rate was measured by supplying helium gas at a constant pressure. The permeation rate of helium gas was calculated from the measured amount of permeated helium gas, supply pressure, and effective membrane area. The nitrogen gas permeation rate was also measured in the same manner. These measurements were made at 80 ° C.

(Measurement of tensile strength and breaking elongation of hollow fiber membrane)
Using a tensile tester, measurement was performed at an effective length of 20 mm and a tensile speed of 10 mm / min. The measurement was performed at 23 ° C. The cross-sectional area of the hollow fiber was calculated by observing the cross-section of the hollow fiber with an optical microscope and measuring the dimensions from the optical microscope image.

(Method for measuring rotational viscosity)
The solution viscosity of the polyimide solution was measured at a temperature of 100 ° C. using a rotational viscometer (shear rate of rotor: 1.75 sec ⁻¹ ).

(Measurement of fluorine atom concentration on dense layer surface by X-ray photoelectron spectroscopy)
X-ray photoelectron spectroscopy was performed using a Quantum 2000 scanning X-ray photoelectron spectrometer manufactured by PHI. A monochromatic AlKα ray was used as the irradiation X-ray. X-rays with an irradiation diameter of 20 μmφ were used for the measurement. The emission angle was 45 °, and an electron neutralizing gun was used to suppress charging of the sample surface. For the photoelectron peaks from the carbon 1s orbital, nitrogen 1s orbital, oxygen 1s orbital, fluorine 1s orbital, and sulfur 2p orbital, the peak area was measured after removing the background. In obtaining the atomic concentration from the peak area, PHI Corp. software Multipak version 6.1A (1999) was used for the processing of the photoelectron peak and the calculation of the atomic concentration. Table 1 below shows the values of the relative sensitivity S ′ _j obtained by correcting the relative sensitivity coefficient ASF _j provided by PHI for each photoelectron peak using the device function of the device (transmission function of the spectrometer). In addition, the value of S ′ _{j in} the table is represented by 1 as the value for fluorine 1s.

本発明においては、６ＦＤＡとＴＳＮからなるホモポリイミドのフィルムと６ＦＤＡとＤＡＢＡからなるホモポリイミドのフィルムをサンプルとして用い、ポリイミドに含まれる各元素について前記相対感度Ｓ’_ｊを補正した値Ｓ_ｊ（＝Ｓ’_ｊ×α_ｊ）を用いて原子濃度を算出した。用いた各元素の補正係数（α）を下記表２に示す。

In the present invention, a homopolyimide film composed of 6FDA and TSN and a homopolyimide film composed of 6FDA and DABA are used as samples, and the value S _j (=) obtained by correcting the relative sensitivity S ′ _j for each element contained in the polyimide. The atomic concentration was calculated using S ′ _j × α _j ). The correction coefficient (α) of each element used is shown in Table 2 below.

(Reference Example 1)
12.44 g of 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride (hereinafter sometimes abbreviated as 6FDA), dimethyl-3,7-diaminodibenzothiophene = 5,5- Dioxide (hereinafter sometimes abbreviated as TSN) 4.92 g and 3,5-diaminobenzoic acid (hereinafter also abbreviated as DABA) 1.64 g were mixed with parachlorophenol (hereinafter abbreviated as PCP) as a solvent. In some cases, it was polymerized and imidized in a separable flask at a reaction temperature of 190 ° C. for 31 hours to obtain a polyimide solution having a rotational viscosity of 446 poise and a polymer concentration of 15% by weight.
The permeability coefficient (P _He ) of the helium gas of the polyimide film obtained from this polyimide solution is 1.1 × 10 ⁻⁸ cm ³ (STP) · cm / cm ² · sec · cmHg, and helium gas and nitrogen gas The transmission coefficient ratio (P _He / P _N2 ) was 37.

(Reference Example 2)
In a separable flask, 12.36 g of 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (hereinafter sometimes abbreviated as s-BPDA) and 11.35 g of TSN together with 165 g of PCP as a solvent Polymerization imidization was carried out at a reaction temperature of 190 ° C. for 25 hours to obtain a polyimide solution having a rotational viscosity of 600 poise and a polymer concentration of 11.8% by weight.
The permeability coefficient (P _He ) of the helium gas of the polyimide film obtained from this polyimide solution is 2.2 × 10 ⁻⁹ cm ³ (STP) · cm / cm ² · sec · cmHg. The transmission coefficient ratio (P _He / P _N2 ) was 110. The polyimide film had a tensile strength at break of 260 MPa, Young's modulus of 5925 MPa, and elongation at break of 24%.

(Method for producing an asymmetric hollow fiber membrane)
The method for producing the asymmetric hollow fiber membrane used in the following examples was performed by a dry and wet spinning method. Specifically, after filtering a polyimide solution or a polyimide mixed solution through a 400 mesh wire mesh, a hollow fiber spinning nozzle (circular opening outer diameter 1000 μm, circular opening slit width 200 μm, core opening at a temperature of 71 ° C. It was discharged from an outer diameter of 400 μm, and the discharged hollow fiber-like body was passed through a nitrogen atmosphere, and then immersed in a coagulation liquid composed of a 75 wt% ethanol aqueous solution at 0 ° C. to obtain a wet yarn. This was immersed in ethanol at 50 ° C. for 2 hours to complete the solvent removal treatment, and further washed by immersion in isooctane at 70 ° C. for 3 hours to replace the solvent, followed by drying at 100 ° C. in an absolutely dry state for 30 minutes. Heat treatment was performed at a temperature of 300 ° C. to 320 ° C. for 1 hour. Further, an oiling treatment was performed with silicone oil to prepare a hollow fiber membrane in order to adjust the slip of the surface of the hollow fiber membrane. All of the obtained hollow fiber membranes had an outer diameter of 400 μm, an inner diameter of 200 μm, and a film thickness of 100 μm.

Example 1
Reaction temperature of 12.36 g of s-BPDA and 11.35 g of TSN (0.985 mol part of diamine with respect to 1 mol part of acid dianhydride, B / A = 0.985) together with 165 g of solvent PCP in a separable flask Polymerization imidization was carried out at 190 ° C. for 22 hours to obtain a polyimide B solution having a polymer concentration of 11.8% by weight. The number average degree of polymerization N _B of the polyimide B was measured by the GPC measuring method, it was 74. To this polyimide solution, 12.44 g of 6FDA, 5.21 g of TSN, and 1.73 g of DABA (1.085 mol parts of diamine with respect to 1 mol part of acid dianhydride) were added together with 20 g of PCP as a solvent. This mixed solution of multi-component polyimide was further polymerized and imidized at a reaction temperature of 190 ° C. for 8 hours to obtain a mixed solution of multi-component polyimide having a rotational viscosity of 2046 poise and a polymer concentration of 18% by weight. It was 41 when the number average degree of polymerization of this multicomponent polyimide was measured by the GPC measuring method.
An asymmetric membrane was produced using the mixed solution of the multi-component polyimide, and the characteristics of the obtained asymmetric membrane were measured. The results are shown in Table 3.

(Example 2)
12.36 g of s-BPDA and 11.35 g of TSN were polymerized and imidized in a separable flask together with 169 g of the solvent at a reaction temperature of 190 ° C. for 27 hours to obtain a polyimide B solution having a polymer concentration of 11.6 wt%. The number average degree of polymerization N _B of the polyimide B was measured by the GPC measuring method, it was 75. To this polyimide solution, 12.44 g of 6FDA, 4.17 g of TSN, and 3.77 g of 3,3′-diaminodiphenylsulfone (hereinafter sometimes abbreviated as MASN) were added together with 20 g of PCP as a solvent. This mixed solution of multi-component polyimide was further polymerized and imidized at a reaction temperature of 190 ° C. for 8 hours to obtain a mixed solution of multi-component polyimide having a rotational viscosity of 1693 poise and a polymer concentration of 18% by weight. It was 41 when the number average degree of polymerization of this multicomponent polyimide was measured by the GPC measuring method.
An asymmetric membrane was produced using the mixed solution of the multi-component polyimide, and the characteristics of the obtained asymmetric membrane were measured. The results are shown in Table 3.

(Comparative Example 1)
Polymerization temperature of 12.71 g of s-BPDA, 12.79 g of 6FDA, 16.20 g of TSN and 3.67 g of MASN (1.025 mol part of diamine with respect to 1 mol part of acid dianhydride) together with 195 g of solvent PCP in a separable flask Polymerization imidization was carried out at 190 ° C. for 54 hours to obtain a polyimide solution having a rotational viscosity of 1097 poise and a polymer concentration of 18% by weight. It was 45 when the number average degree of polymerization of this polyimide was measured by the said GPC measuring method.
An asymmetric membrane was produced using this polyimide solution, and the characteristics of the obtained asymmetric membrane were measured. The results are shown in Table 3.
In this example, the raw material composition was almost the same as in Example 2, but Φs / f was 1.02, and the tensile elongation at break was as low as 7%.

(Example 3)
6.36 g of s-BPDA, 12.79 g of 6FDA, 8.10 g of TSN, 3.67 g of MASN, and 1.12 g of DABA were polymerized and imidized at a reaction temperature of 190 ° C. for 27 hours in a separable flask together with 171 g of a solvent, and the polymer concentration was 15.0. A weight% polyimide A solution was obtained. The number average degree of polymerization N _A of the polyimide A was measured by the GPC measuring method, it was 31. To this polyimide solution, 6.36 g of s-BPDA and 6.07 g of TSN were added together with 20 g of PCP as a solvent. This mixed solution of multi-component polyimide was further polymerized and imidized at a reaction temperature of 190 ° C. for 19 hours to obtain a multi-component polyimide solution having a rotational viscosity of 1246 poise and a polymer concentration of 18% by weight. It was 46 when the number average degree of polymerization of this multicomponent polyimide was measured by the said GPC measuring method.
An asymmetric membrane was produced using the mixed solution of the multi-component polyimide, and the characteristics of the obtained asymmetric membrane were measured. The results are shown in Table 3.

Example 4
12.36 g of s-BPDA and 11.35 g of TSN were polymerized and imidized in a separable flask together with 165 g of the solvent PCP at a reaction temperature of 190 ° C. for 27 hours to obtain a polyimide B solution having a polymer concentration of 11.8 wt%. The number average degree of polymerization N _B of the polyimide B was measured by the GPC measuring method, it was 76. To this polyimide solution, 12.44 g of 6FDA, 2.08 g of TSN, 3.77 g of MASN, and 1.16 g of DABA were added together with 20 g of PCP as a solvent. This mixed solution of multicomponent polyimide was further polymerized and imidized at a reaction temperature of 190 ° C. for 30 hours to obtain a mixed solution of multicomponent polyimide having a rotational viscosity of 911 poise and a polymer concentration of 18% by weight. It was 45 when the number average degree of polymerization of this multi-component polyimide was measured by the GPC measurement method.
An asymmetric membrane was produced using the mixed solution of the multi-component polyimide, and the characteristics of the obtained asymmetric membrane were measured. The results are shown in Table 3.

(Example 5)
12.71 g of s-BPDA and 12.15 g of TSN were polymerized and imidized in a separable flask together with 171 g of a solvent at a reaction temperature of 190 ° C. for 27 hours to obtain a polyimide B solution having a polymer concentration of 12.0% by weight. The number average degree of polymerization N _B of the polyimide was measured by the GPC measuring method, it was 79. To this polyimide solution, 12.79 g of 6FDA, 2.02 g of TSN, 3.67 g of MASN, and 1.12 g of DABA were added together with 20 g of PCP as a solvent. This mixed solution of multicomponent polyimide was further polymerized and imidized at a reaction temperature of 190 ° C. for 10 hours to obtain a mixed solution of multicomponent polyimide having a rotational viscosity of 1767 poise and a polymer concentration of 18% by weight. It was 73 when the number average degree of polymerization of this multi-component polyimide was measured by the GPC measurement method.
An asymmetric membrane was produced using the mixed solution of the multi-component polyimide, and the characteristics of the obtained asymmetric membrane were measured. The results are shown in Table 3.

(Example 6)
6.36 g of s-BPDA and 6.07 g of TSN were polymerized and imidized in a separable flask together with 171 g of a solvent at a reaction temperature of 190 ° C. for 27 hours to obtain a polyimide B solution having a polymer concentration of 6.4% by weight. The number average degree of polymerization N _B of the polyimide was measured by the GPC measuring method, it was 57. To this polyimide solution, 6.36 g of s-BPDA, 12.79 g of 6FDA, 8.10 g of TSN, 3.67 g of MASN, and 1.12 g of DABA were added together with 20 g of PCP as a solvent. This mixed solution of multi-component polyimide was further polymerized and imidized at a reaction temperature of 190 ° C. for 19 hours to obtain a mixed solution of multi-component polyimide having a rotational viscosity of 1507 poise and a polymer concentration of 18% by weight. It was 50 when the number average degree of polymerization of this multicomponent polyimide was measured by the GPC measurement method.
An asymmetric membrane was produced using the mixed solution of the multi-component polyimide, and the characteristics of the obtained asymmetric membrane were measured. The results are shown in Table 3.

(Comparative Example 2)
12.71 g of s-BPDA, 12.79 g of 6FDA, 14.17 g of TSN, 3.67 g of MASN, and 1.12 g of DABA were polymerized and imidized in a separable flask with a solvent PCP of 191 g at a reaction temperature of 190 ° C. for 73 hours, and the rotational viscosity was 1190 poise. A polyimide solution having a polymer concentration of 18% by weight was obtained. It was 49 when the number average degree of polymerization of this polyimide was measured by the said GPC measuring method.
An asymmetric membrane was produced using this polyimide solution, and the characteristics of the obtained asymmetric membrane were measured. The results are shown in Table 3.
In this example, the raw material composition was almost the same as in Example 6, but Φs / f was 1.04 and the tensile elongation at break was as low as 7%.

(Example 7)
12.44 g of 6FDA and 4.37 g of DABA were reacted in a separable flask together with 155 g of the solvent PCP at a polymerization temperature of 120 ° C. for 2 hours to obtain a polyimide A solution having a polymer concentration of 9.8 wt%. In order to obtain the number average degree of polymerization of this reaction solution, a part of the reaction solution was cast on a slide glass, immersed and solidified in ethanol, further substituted with a solvent to remove PCP, and vacuum-dried at room temperature for 5 hours. This was used as a sample for FT-IR analysis. The imidation ratio was measured by the above method and was 0.63. Still calculate the number average degree of polymerization N _A from this value was 2.7.
Next, 12.36 g of s-BPDA and 11.81 g of TSN were added to the reaction solution together with 20 g of PCP as a solvent. This mixed solution of multi-component polyimide was further polymerized at a polymerization temperature of 190 ° C. for 30 hours to obtain a multi-component polyimide mixed solution having a rotational viscosity of 1265 poise and a polymer concentration of 18% by weight. It was 72 when the number average degree of polymerization of this multicomponent polyimide was measured by the GPC measurement method.
An asymmetric membrane was produced using the mixed solution of the multi-component polyimide, and the characteristics of the obtained asymmetric membrane were measured. The results are shown in Table 3.

(Example 8)
12.44 g of 6FDA and 4.37 g of DABA were reacted with a solvent PCP of 155 g in a separable flask at a polymerization temperature of 120 ° C. for 1 hour to obtain a polyimide A solution having a polymer concentration of 9.8 wt%. In order to obtain the number average degree of polymerization of this reaction solution, a part of the reaction solution was cast on a slide glass, immersed and solidified in ethanol, further substituted with a solvent to remove PCP, and vacuum-dried at room temperature for 5 hours. This was used as a sample for FT-IR analysis. The imidation ratio was measured by the above method and was 0.52. Still calculate the number average degree of polymerization N _A from this value was 2.1.
Next, 12.36 g of s-BPDA and 11.81 g of TSN were added to the reaction solution together with 20 g of PCP as a solvent. This mixed solution of multi-component polyimide was further polymerized at a polymerization temperature of 190 ° C. for 30 hours to obtain a mixed solution of multi-component polyimide having a rotational viscosity of 1469 poise and a polymer concentration of 18% by weight. It was 78 when the number average degree of polymerization of this multicomponent polyimide was measured by the said GPC measuring method.
An asymmetric membrane was produced using the mixed solution of the multi-component polyimide, and the characteristics of the obtained asymmetric membrane were measured. The results are shown in Table 3.

Example 9
23.10 g of 6FDA, 3.66 g of TSN, 6.62 g of MASN, and 2.03 g of DABA were polymerized and imidized at a reaction temperature of 190 ° C. in a separable flask together with 153 g of PCP as a solvent to obtain a polyimide A solution having a polymer concentration of 18% by weight. . The number average degree of polymerization N _A of the polyimide A was measured by the GPC measuring method, it was 4.9.
21.18 g of s-BPDA and 20.25 g of TSN were polymerized and imidized at a reaction temperature of 190 ° C. for 6 hours in a separable flask together with 177 g of the solvent PCP to obtain a polyimide B solution having a polymer concentration of 18% by weight. The number average degree of polymerization N _B of the polyimide was measured by the GPC measuring method, it was 51.
Next, 88 g of the polyimide A solution and 110 g of the polyimide B solution were weighed and mixed in a separable flask. The mixed solution of the multicomponent polyimide was further polymerized and imidized at a reaction temperature of 190 ° C. for 13 hours to obtain a mixed solution of the multicomponent polyimide having a rotational viscosity of 2232 poise and a polymer concentration of 18% by weight. It was 62 when the number average degree of polymerization of this multi-component polyimide was measured by the GPC measurement method.
An asymmetric membrane was produced using the mixed solution of the multi-component polyimide, and the characteristics of the obtained asymmetric membrane were measured. The results are shown in Table 3.

(Example 10)
21.18 g of s-BPDA and 20.25 g of TSN were polymerized and imidized in a separable flask together with 177 g of a solvent at a reaction temperature of 190 ° C. for 0.5 hours to obtain a polyimide B solution having a polymer concentration of 18% by weight. The number average degree of polymerization N _B of the polyimide was measured by the GPC measuring method, it was 6.0.
Next, 110 g of the polyimide B solution and 88 g of the polyimide A solution having a number average polymerization degree of 4.9 obtained in Example 9 were weighed and mixed in a separable flask. This mixed solution of multicomponent polyimide was further polymerized and imidized at a reaction temperature of 190 ° C. for 19 hours to obtain a mixed solution of multicomponent polyimide having a rotational viscosity of 1376 poise and a polymer concentration of 18% by weight. It was 57 when the number average degree of polymerization of this multi-component polyimide was measured by the GPC measurement method.
An asymmetric membrane was produced using the mixed solution of the multi-component polyimide, and the characteristics of the obtained asymmetric membrane were measured. The results are shown in Table 3.

(Example 11)
23.10 g of 6FDA, 3.66 g of TSN, 6.62 g of MASN, and 2.03 g of DABA were polymerized and imidized at a reaction temperature of 190 ° C. in a separable flask together with 153 g of PCP as a solvent to obtain a polyimide A solution having a polymer concentration of 18% by weight. . The number average degree of polymerization N _A of the polyimide A was measured by the GPC measuring method, it was 22.
21.18 g of s-BPDA and 20.25 g of TSN were polymerized and imidized at a reaction temperature of 190 ° C. for 0.25 hours in a separable flask together with 177 g of the solvent PCP to obtain a polyimide B solution having a polymer concentration of 18% by weight. The number average degree of polymerization N _B of the polyimide B was measured by the GPC measuring method, it was 4.5.
Next, 88 g of the polyimide solution A and 110 g of the polyimide solution B were weighed and mixed in a separable flask. This mixed solution of multicomponent polyimide was further polymerized and imidized at a reaction temperature of 190 ° C. for 29 hours to obtain a mixed solution of multicomponent polyimide having a rotational viscosity of 1172 poise and a polymer concentration of 18% by weight. It was 45 when the number average degree of polymerization of this multi-component polyimide was measured by the GPC measurement method.
An asymmetric membrane was produced using the mixed solution of the multi-component polyimide, and the characteristics of the obtained asymmetric membrane were measured. The results are shown in Table 3.

(Example 12)
23.10 g of 6FDA, 3.66 g of TSN, 6.62 g of MASN and 2.03 g of DABA were polymerized and imidized with a solvent of PCP153 in a separable flask at a reaction temperature of 190 ° C. for 0.5 hours, and a polyimide A solution having a polymer concentration of 18% by weight was obtained. Obtained. The number average degree of polymerization _{N A} of the polyimide A was measured by the GPC measuring method, was 2.76.
21.18 g of s-BPDA and 20.25 g of TSN were polymerized and imidized at a reaction temperature of 190 ° C. for 0.2 hours in a separable flask together with 177 g of the solvent PCP to obtain a polyimide B solution having a polymer concentration of 18% by weight. The number average degree of polymerization N _B of the polyimide B was measured by the GPC measuring method, it was 3.1.
Next, 88 g of the polyimide solution A and 110 g of the polyimide solution B were weighed and mixed in a separable flask. This mixed solution of multi-component polyimide was further polymerized and imidized at a reaction temperature of 190 ° C. for 19 hours to obtain a mixed solution of multi-component polyimide having a rotational viscosity of 1618 poise and a polymer concentration of 18% by weight. It was 78 when the number average degree of polymerization of this multicomponent polyimide was measured by the said GPC measuring method.
An asymmetric membrane was produced using the mixed solution of the multi-component polyimide, and the characteristics of the obtained asymmetric membrane were measured. The results are shown in Table 3.

(Comparative Example 3)
6.36 g of s-BPDA and 6.07 g of TSN were polymerized and imidized at a reaction temperature of 190 ° C. for 5 hours in a separable flask together with 171 g of the solvent PCP to obtain a polyimide B solution having a polymer concentration of 6.4% by weight. The number average degree of polymerization N _B of the polyimide B was measured by the GPC measuring method, it was 7.4. To this polyimide solution, 6.36 g of s-BPDA, 12.79 g of 6FDA, 8.10 g of TSN, 3.67 g of MASN, and 1.12 g of DABA were added together with 20 g of PCP as a solvent. This mixed solution of multi-component polyimide was further polymerized and imidized at a reaction temperature of 190 ° C. for 23 hours to obtain a mixed solution of multi-component polyimide having a rotational viscosity of 1079 poise and a polymer concentration of 18% by weight. It was 49 when the number average degree of polymerization of this multi-component polyimide was measured by the GPC measurement method.
An asymmetric membrane was produced using the mixed solution of the multi-component polyimide, and the characteristics of the obtained asymmetric membrane were measured. The results are shown in Table 3.
This example is intended to have _{N A} and _{N B} is outside the combination range of _{N A} and _{N B} satisfying Equation 1 (A area in Figure 4), .PHI.s / f is 1.07, the tensile elongation at break 8 %.

(Example 13)
12.36 g of s-BPDA and 11.35 g of TSN were polymerized and imidized at a reaction temperature of 190 ° C. for 30 hours in a separable flask together with 158 g of the solvent PCP to obtain a polyimide B solution having a polymer concentration of 11.8 wt%. The number average degree of polymerization N _B of the polyimide was measured by the GPC measuring method, it was 75. To this polyimide solution, 12.44 g of 6FDA, 3.77 g of MASN, and 1.64 g of MPD were added together with 20 g of PCP as a solvent. The mixed solution of the multicomponent polyimide was further polymerized and imidized at a reaction temperature of 190 ° C. for 6 hours to obtain a mixed solution of the multicomponent polyimide having a rotational viscosity of 1432 poise and a polymer concentration of 18% by weight. It was 101 when the number average degree of polymerization of this multi-component polyimide was measured by the GPC measurement method.
An asymmetric membrane was produced using the mixed solution of the multi-component polyimide, and the characteristics of the obtained asymmetric membrane were measured. The results are shown in Table 3.

(Comparative Example 4)
21.32 g of 6FDA, 8.44 g of TSN and 2.81 g of DABA were polymerized and imidized together with 129 g of PCP as a solvent in a separable flask at a reaction temperature of 190 ° C. for 40 hours to obtain a polyimide A solution having a polymer concentration of 19.3% by weight. The number average degree of polymerization N _A of the polyimide A was measured by the GPC measuring method, it was 26.
s-BPDA (27.41 g), TSN (22.22 g) and DADE (1.80 g) were polymerized and imidized in a separable flask with a solvent PCP (210 g) at a reaction temperature of 190 ° C. for 40 hours to obtain a polyimide B solution having a polymer concentration of 18.7 wt%. It was. The number average degree of polymerization N _B of the polyimide B was measured by the GPC measuring method, it was 47.
Next, 90 g of the polyimide A solution and 100 g of the polyimide B solution were weighed and mixed in a separable flask. This mixed solution of multi-component polyimide was further polymerized and imidized at a reaction temperature of 190 ° C. for 3 hours to obtain a mixed solution of multi-component polyimide having a rotational viscosity of 1711 poise and a polymer concentration of 19% by weight. It was 52 when the number average degree of polymerization of this multicomponent polyimide was measured by the GPC measurement method.
An asymmetric membrane was produced using the mixed solution of the multi-component polyimide, and the characteristics of the obtained asymmetric membrane were measured. The results are shown in Table 3.
In this example, N _A and N _B are outside the combination range of N _A and N _B satisfying Equation 1 (B region in FIG. 4), Φs / f is 1.82, and hydrogen gas permeation rate ( P _'H2) and nitrogen gas permeation rate (P' _N2) ratio of _{(P 'H2 / P' N2} ) was 11.

(Comparative Example 5)
26.65 g of 6FDA, 10.49 g of TSN and 3.49 g of DABA were polymerized and imidized in a separable flask together with 161 g of the solvent PCP at a reaction temperature of 190 ° C. for 40 hours to obtain a polyimide A solution having a polymer concentration of 19.3% by weight. The number average degree of polymerization N _A of the polyimide A was measured by the GPC measuring method, it was 44.
52.66 g of s-BPDA, 46.00 g of TSN and 3.73 g of DADE were polymerized and imidized in a separable flask together with 419 g of PCP at a reaction temperature of 190 ° C. for 25 hours to obtain a polyimide B solution having a polymer concentration of 18.7% by weight. It was. The number average degree of polymerization N _B of the polyimide B was measured by the GPC measuring method, it was 66.
Next, 90 g of the polyimide A solution and 100 g of the polyimide B solution were weighed and mixed in a separable flask. This mixed solution of multicomponent polyimide was further stirred and mixed at a temperature of 130 ° C. for 3 hours to obtain a mixed solution of multicomponent polyimide having a rotational viscosity of 2753 poise and a polymer concentration of 19% by weight. It was 56 when the number average degree of polymerization of this multicomponent polyimide was measured by the GPC measurement method.
An asymmetric membrane was produced using the mixed solution of the multi-component polyimide, and the characteristics of the obtained asymmetric membrane were measured. The results are shown in Table 3.
In this example, N _A and N _B are outside the combination range of N _A and N _B satisfying Formula 1 (B region in FIG. 4), and the two polyimide solutions are simply mixed, and the polymerization imidation reaction is substantially It was not done. .Phi.s / f is 2.06, the ratio of hydrogen gas permeation rate (P _'H2) and nitrogen gas permeation rate _{(P' N2) (P '} H2 / P' N2) is 3.

According to the present invention, a polyimide asymmetric film having a dense layer and a porous layer, comprising a multi-component polyimide containing a fluorine atom-containing polyimide, wherein the proportion of the fluorine atom-containing polyimide in the dense layer is suitably controlled Can be provided.
Such a polyimide asymmetric membrane is separated from hydrogen gas and hydrocarbon gas such as methane gas, hydrogen gas and nitrogen gas, helium gas and nitrogen gas, carbon dioxide gas and methane gas such as methane gas. It is suitable as a practical high-performance gas separation membrane capable of suitably performing separation, separation of oxygen gas and nitrogen gas, and the like.

: Is an example of a TEM image of a film cross section in which macro phase separation occurred. This film was obtained by casting a mixed solution of two high molecular weight polyimides (Comparative Example 5) on a glass plate and drying. : An example of a TEM image of a film cross section in which no macrophase separation occurs. This film was obtained by casting and drying a mixed solution of the multi-component polyimide of the present invention (Example 4) on a glass plate. : It is another example of the TEM image of the film cross section which produced the macro phase separation. This film was obtained by casting and drying a mixed solution of two kinds of high molecular weight polyimides on a glass plate. From this TEM image, the macrophase separation near the film surface can be well understood. : Is a graph illustrating the combined range of N _A and N _B of the present invention. : It is the result of having analyzed the fluorine atom of the depth direction of the film obtained by casting and drying the mixed solution (Example 4) of the multicomponent polyimide of this invention on a glass plate by dSIMS. : It is the result of having analyzed the fluorine atom of the depth direction of the film obtained by casting and drying the polyimide solution (comparative example 2) obtained by the normal polymerization method on a glass plate by dSIMS.

Claims (7)

A polyimide asymmetric film having a dense layer and a porous layer, which is formed of a multi-component polyimide containing a fluorine atom-containing polyimide, and has a fluorine atom concentration (Φ _S ) of the dense layer measured by X-ray photoelectron spectroscopy (XPS) And a mean fluorine atom concentration (f) (Φ _S / f) in the whole film is 1.1 to 1.8.   A gas separation membrane comprising the polyimide asymmetric membrane according to claim 1. Hollow fiber with hydrogen gas permeation rate (P ′ _H2 ) of 4.0 × 10 ⁻⁴ cm ³ (STP) / cm ² · sec · cm Hg or more, hydrogen gas permeation rate (P ′ _H2 ) and nitrogen gas permeation The gas separation membrane according to claim 2, wherein the ratio ( _P'H2 / _P'N2 ) to the speed ( _P'N2 ) is 20 or more, and the tensile elongation at break as a hollow fiber is 15% or more. A hollow fiber with a helium gas permeation rate (P ′ _He ) of 4.0 × 10 ⁻⁴ cm ³ (STP) / cm ² · sec · cm Hg or more, a helium gas permeation rate (P ′ _He ) and nitrogen gas permeation The gas separation membrane according to claim 2, wherein the ratio ( _P'He / _P'N2 ) to the speed ( _P'N2 ) is 20 or more, and the tensile elongation at break as a hollow fiber is 15% or more.   The mixed gas is supplied to the supply side of the gas separation membrane according to claim 2, and at least one kind of mixed gas is selectively permeated to the permeation side of the gas separation membrane. A method for selectively separating and collecting at least one gas.   A gas mixture containing hydrogen gas is supplied to a supply side of the gas separation membrane according to claim 2, and hydrogen gas is selectively permeated to a permeation side of the gas separation membrane. A method for selectively separating and recovering hydrogen gas from a mixed gas. A gas mixture containing helium gas is supplied to the supply side of the gas separation membrane according to claim 2, and helium gas is selectively transmitted to the permeation side of the gas separation membrane. A method for selectively separating and recovering hydrogen gas from a mixed gas.

Images