JP6950307B2 - Particle-dispersed polyimide precursor solution, method for producing porous polyimide film, and porous polyimide film - Google Patents

Description

The present invention relates to a particle-dispersed polyimide precursor solution, a method for producing a porous polyimide film, and a porous polyimide film.

The polyimide resin is a material having excellent mechanical strength, chemical stability, and heat resistance, and a porous polyimide film having these characteristics is attracting attention.

For example, Patent Document 1 describes a porous polyimide film having a specific ratio of repeating units. Examples of the manufacturing method include a wet coagulation method, a dry coagulation method, a stretching method, and the like, and in reality, a porous film is formed by the wet coagulation method.

For example, Patent Document 2 describes a porous resin film using silica particles as a template, having a porosity of 60% or more, having pores having a three-dimensional ordered array structure, and having pores in which the pores are connected to each other. Has been reported to be used as a separator for lithium secondary batteries.

Further, Patent Documents 3 and 4 report that a porous polyimide film is produced using a polyimide precursor solution in which inorganic particles and organic resin particles are dispersed, and used as a separator for a secondary battery. ..

Further, Patent Documents 5 and 6 report a method for producing a porous polyimide film using a polyimide precursor solution in which resin particles are dispersed.

Japanese Unexamined Patent Publication No. 2003-201362 Japanese Patent No. 5331627 Japanese Patent No. 5605566 International Publication 2014/196656 Japanese Unexamined Patent Publication No. 2016-183273 Japanese Unexamined Patent Publication No. 2016-183333

It has been found that when a porous polyimide film is produced using particles, the dispersion stability of the particles may decrease in the polyimide precursor solution used.
For example, a polyimide precursor solution in which particles are dispersed in a polyimide precursor solution containing a polyimide precursor in which tetracarboxylic acid dianhydride and diamine are synthesized using only one type each (particle-dispersed polyimide precursor). In the solution), the interaction between the polyimide precursor and the particles tends to be low, and the particle dispersion stability in the polyimide precursor solution may be lowered.

An object of the present invention is that in a polyimide precursor solution containing particles, the polyimide precursor in the polyimide precursor solution is 3,3,4', 4'-biphenyltetracarboxylic acid dianhydride as a tetracarboxylic acid dianhydride. Polyimide precursor synthesized using only the substance, p-phenylenediamine as the diamine compound, or pyromellitic acid dianhydride as the tetracarboxylic acid dianhydride, 4,4'-diaminodiphenyl ether as the diamine compound. It is an object of the present invention to provide a particle-dispersed polyimide precursor solution in which a decrease in particle dispersion stability in the polyimide precursor solution is suppressed as compared with the case where the polyimide precursor is synthesized using only the polyimide precursor.

The following inventions are provided in order to achieve the above object.

< 1 >
Solvent, particles dispersed polyimide precursor solution containing a polyimide precursor having a repeating unit represented by the following formula (I), and the particles.

In the formula (I), A is a tetravalent organic group and B is a divalent organic group, which satisfies at least one of the following conditions (1) and (2) and also satisfies the following condition (3).
(1): A has a molar ratio (A1 / A2) of a tetravalent organic group A1 having one aromatic ring and a tetravalent organic group A2 having two or more aromatic rings of 5/95 or more and 95/5. It is as follows.
(2): B has a molar ratio (B1 / B2) of a divalent organic group B1 having one aromatic ring and a divalent organic group B2 having two or more aromatic rings of 5/95 or more and 95/5. It is as follows.
(3): Among the raw material monomer components constituting the A1, the A2, the B1, and the B2, the ratio of the component having the lowest content (excluding zero) to the particles is 0.015 mmol / g. As described above, the difference between the ratio of the component having the highest content to the particles and the ratio of the component having the lowest content (excluding zero) to the particles among the raw material monomer components is 9 mmol / g. It is as follows.

< 2 >
A group before Symbol A1 is represented by the following A1-1, particle according to <1> is any one of groups of the A2 is selected from the group shown in the following A2-1 to: A2-5 Dispersed polyimide precursor solution.

< 3 >
There groups before Symbol B1 is represented by the following B1-1 or below B1-2, is any one of groups of the B2 is selected from the group shown in the following B2-1 to: B2-7 <1> Alternatively, the particle-dispersed polyimide precursor solution according to < 2 >.

< 4 >
When meeting the pre Symbol Conditions (1) satisfies one of the conditions represented by the following (I-3) and the following (I-4), when satisfying the condition (2), the following (I-1) and the following The particle-dispersed polyimide precursor solution according to any one of < 1 > to < 3 > , which satisfies any of the conditions shown in (I-2).
(I-1) The A1 / A2 is 60/40 or more and 100/0 or less, and the B1 / B2 is 5/95 or more and 40/60 or less (I-2) The A1 / A2 is 0/100 or more and 40 / 60 or less and the molar ratio of B1 / B2 is 60/40 or more and 95/5 or less (I-3) The A1 / A2 is 5/95 or more and 40/60 or less and the molar ratio of B1 / B2 is 60/40 or more and 100/0 or less (I-4) The A1 / A2 is 60/40 or more and 95/5 or less, and the molar ratio of B1 / B2 is 0/100 or more and 40/60 or less.

< 5 >
Before Symbol conditions shown in (I-1) from to the (I-4) is, particle dispersion according respectively from the following (II-1) shown below (II-4) is a condition indicated by <4> Polyimide precursor solution.
(II-1) The A1 / A2 is 100/0 and the B1 / B2 is 5/95 or more and 30/70 or less (II-2) The A1 / A2 is 0/100 and the B1 / B2 is 70/30 or more and 95/5 or less (II-3) The A1 / A2 is 5/95 or more and 30/70 or less, and the B1 / B2 is 100/0.
(II-4) The A1 / A2 is 70/30 or more and 95/5 or less, and the B1 / B2 is 0/100.

< 6 >
A group before Symbol A1 is represented by A1-1, is a group wherein A2 is represented by A2-1, is a group wherein B1 is represented by B1-1, the B2 is the B2-1 The particle-dispersed polyimide precursor solution according to any one of < 1 > to < 5 > , which is a group represented by.
< 7 >
Prior Symbol polyimide precursor, the A1, the A2, the B1, and of the respective material monomer component constituting the B2, the ratio of the particles of the highest content less components (excluding zero) , 0.03 mmol / g or more. The particle-dispersed polyimide precursor solution according to any one of < 1 > to < 6 >.
< 8 >
Prior Symbol polyimide precursor, the A1, the A2, the B1, and of the respective material monomer component constituting the B2, the ratio between the highest content with respect to the particles of the major components is the largest content The particle-dispersed polyimide precursor solution according to any one of < 1 > to < 7 > , wherein the difference from the ratio of a small amount of components (excluding zero) to the particles is 7 mmol / g or less.

< 9 >
Particles dispersed polyimide precursor solution according to any one of the previous SL particles are resin particles <1> to <8>.

< 10 >
Organic amine compound contains, the proportion of water in the entire solvent is 50 mass% or more <1> particle dispersed polyimide precursor solution according to any one of to <9> to is found.
< 11 >
Particles dispersed polyimide precursor solution according to prior Symbol organic amine compound is a tertiary amine compound <10>.
< 12 >
Et al aprotic polar solvent is, particle dispersion according to contain 3 wt% to 50 wt% of the total amount of particles and the polyimide precursor of the polyimide precursor solution <10> or <11> Polyimide precursor solution.

< 13 >
The volume average particle diameter before Symbol particles is 0.1μm or more 0.5μm or less <1> - particle dispersed polyimide precursor solution according to any one of <12>.
< 14 >
Before SL volume particle size distribution index of the particles of the particle dispersed polyimide precursor solution is 1.30 or less <1> particle dispersed polyimide precursor solution according to any one of - <13>.
< 15 >
The content of the previous SL particles is not more than 30 wt% or more 85 wt% based on the solids content of the particles dispersed polyimide precursor solution <1> - particle dispersed polyimide precursor according to any one of <14> solution.

< 16 >
< 1 > to < 15 > After applying the particle-dispersed polyimide precursor solution according to any one item to form a coating film, the coating film is dried to form a coating film containing the polyimide precursor and the particles. The first step of forming and
The film is provided with spherical pores having a second step of heating the film to imidize the polyimide precursor to form a polyimide film, the second step including a process of removing the particles. A method for producing a porous polyimide film.

< 17 >
The porous polyimide film containing a polyimide having a repeating unit represented by the below following formula (III), and a pore spherical.

In formula (III), A is a tetravalent organic group, B is a divalent organic group, and at least one of the following conditions (1) and (2) is satisfied.
(1): A has a molar ratio (A1 / A2) of a tetravalent organic group A1 having one aromatic ring and a tetravalent organic group A2 having two or more aromatic rings of 5/95 or more and 95/5. It is as follows.
(2): B has a molar ratio (B1 / B2) of a divalent organic group B1 having one aromatic ring and a divalent organic group B2 having two or more aromatic rings of 5/95 or more and 95/5. It is as follows.

< 18 >
A group before Symbol A1 is represented by the following A1-1, holes according to a any one of groups <17> wherein A2 is selected from the group shown in the following A2-1 to: A2-5 Quality polyimide film.

< 19 >
There groups before Symbol B1 is represented by the following B1-1 or below B1-2, is any one of groups of the B2 is selected from the group shown in the following B2-1 to: B2-7 <17> Alternatively, the porous polyimide film according to < 18 >.

< 20 >
When meeting the pre Symbol Conditions (1) satisfies one of the conditions represented by the following (III-3) and the following (III-4), when satisfying the condition (2), the following (III-1) and the following The porous polyimide film according to any one of < 17 > to < 19 > , which satisfies any of the conditions shown in (III-2).
(III-1) The A1 / A2 is 60/40 or more and 100/0 or less, and the B1 / B2 is 5/95 or more and 40/60 or less (III-2) The A1 / A2 is 0/100 or more and 40 / 60 or less and the molar ratio of B1 / B2 is 60/40 or more and 95/5 or less (III-3) The A1 / A2 is 5/95 or more and 40/60 or less and the molar ratio of B1 / B2 is 60/40 or more and 100/0 or less (III-4) The A1 / A2 is 60/40 or more and 95/5 or less, and the molar ratio of B1 / B2 is 0/100 or more and 40/60 or less.

< 21 >
Porous described before Symbol (III-1) from said (III-4) conditions shown in to are each the conditions shown in the following (IV-1) to the following (IV-4) <20> Polyimide film.
(IV-1) The A1 / A2 is 100/0 and the B1 / B2 is 5/95 or more and 30/70 or less (IV-2) The A1 / A2 is 0/100 and the B1 / B2 is 70/30 or more and 95/5 or less (IV-3) The A1 / A2 is 5/95 or more and 30/70 or less, and the B1 / B2 is 100/0.
(IV-4) The A1 / A2 is 70/30 or more and 95/5 or less, and the B1 / B2 is 0/100.

< 22 >
A group before Symbol A1 is represented by A1-1, is a group wherein A2 is represented by A2-1, is a group wherein B1 is represented by B1-1, the B2 is the B2-1 The porous polyimide film according to any one of < 17 > to < 21 > , which is a group represented by.

< 23 >
Et al is a porous polyimide film according resins other than polyimide, the first term or <17> - <22> containing less than 1 wt% 0.005 wt% based on the total porous polyimide film ..

According to the inventions according to < 1 > , < 2 > , < 3 > , < 4 > , < 5 > , and < 6 > , in the polyimide precursor solution containing particles, the polyimide precursor in the polyimide precursor solution is Polyimide precursor or tetracarboxylic acid synthesized using only 3,3,4', 4'-biphenyltetracarboxylic acid dianhydride as a tetracarboxylic acid dianhydride and only p-phenylenediamine as a diamine compound. Compared with the case of a polyimide precursor synthesized using only pyromellitic acid dianhydride as a dianhydride and only 4,4'-diaminodiphenyl ether as a diamine compound, the particle dispersion stability in the polyimide precursor solution is higher. A particle-dispersed polyimide precursor solution in which the decrease is suppressed is provided.
According to the invention according to < 7 > , in the polyimide precursor having the repeating unit represented by the formula (I), the content is the highest among the raw material monomer components constituting A1, A2, B1 and B2. Provided is a particle-dispersed polyimide precursor solution in which a decrease in particle dispersion stability in the polyimide precursor solution is suppressed as compared with the case where the ratio of a small amount of components (excluding zero) to particles is 0.011 mmol / g. ..
According to the invention according to < 8 > , the polyimide precursor having the repeating unit represented by the formula (I) has the highest content among the raw material monomer components constituting A1, A2, B1 and B2. Particles in the polyimide precursor solution compared to the case where the difference between the ratio of the high component (excluding zero) to the particles and the ratio of the lowest content (excluding zero) to the particles is 10.634 mmol / g. Provided is a particle-dispersed polyimide precursor solution in which a decrease in dispersion stability is suppressed.

According to the invention according to < 9 >, there is provided a particle-dispersed polyimide precursor solution in which a decrease in particle dispersion stability in the polyimide precursor solution is suppressed as compared with the case where the particles are silica particles.

According to the inventions of < 10 > , < 11 > , and < 12 > , only 3,3,4', 4'-biphenyltetracarboxylic acid dianhydride as a tetracarboxylic acid dianhydride, p as a diamine compound. A polyimide precursor synthesized using only phenylenediamine, or a polyimide precursor synthesized using only pyromellitic acid dianhydride as a tetracarboxylic acid dianhydride and only 4,4'-diaminodiphenyl ether as a diamine compound. A particle-dispersed polyimide precursor containing an organic amine compound, having a proportion of water in the total solvent of 50% by mass or more, and suppressing a decrease in particle dispersion stability in the polyimide precursor solution, as compared with the case of the body. A body solution is provided.

According to the invention according to < 13 > , the particle dispersion in which the decrease in particle dispersion stability in the polyimide precursor solution is suppressed as compared with the case where the volume average particle size of the particles is less than 0.1 μm or more than 0.5 μm. A polyimide precursor solution is provided.

According to the invention according to < 14 > , the decrease in particle dispersion stability in the polyimide precursor solution is suppressed as compared with the case where the volume particle size distribution index of the particles in the particle-dispersed polyimide precursor solution exceeds 1.30. A particle-dispersed polyimide precursor solution is provided.

According to the invention according to < 15 > , the decrease in particle dispersion stability in the polyimide precursor solution is suppressed as compared with the case where the particle content exceeds 85% by mass with respect to the solid content of the particle-dispersed polyimide precursor solution. A particle-dispersed polyimide precursor solution to be prepared is provided.

According to the invention according to < 16 >, after the particle-dispersed polyimide precursor solution is applied to form a coating film, the coating film is dried to form a coating film containing the polyimide precursor and the particles. A second step of heating the coating film to imidize the polyimide precursor to form a polyimide film, which comprises a second step of removing the particles. In the method for producing a polyimide film, the polyimide precursor uses only 3,3,4', 4'-biphenyltetracarboxylic acid dianhydride as the tetracarboxylic acid dianhydride and only p-phenylenediamine as the diamine compound. Compared with the case of the polyimide precursor synthesized by using only pyromellitic acid dianhydride as the tetracarboxylic acid dianhydride and only 4,4'-diaminodiphenyl ether as the diamine compound. , Provided is a method for producing a porous polyimide film in which breakage when bent is suppressed.

According to the inventions according to < 17 > , < 18 > , < 19 > , < 20 > , < 21 > , and < 22 > , in a porous polyimide film containing a polyimide having a repeating unit represented by the formula (III), Polyimide is a polyimide synthesized by using only 3,3,4', 4'-biphenyltetracarboxylic acid dianhydride as a tetracarboxylic acid dianhydride and only p-phenylenediamine as a diamine compound, or tetracarboxylic. Compared with the case of a polyimide synthesized using only pyromellitic acid dianhydride as the acid dianhydride and only 4,4'-diaminodiphenyl ether as the diamine compound, the porosity is suppressed from being damaged when bent. Polyimide films are provided.

According to the invention according to < 23 > , only 3,3,4', 4'-biphenyltetracarboxylic acid dianhydride is used as the tetracarboxylic acid dianhydride, and only p-phenylenediamine is used as the diamine compound. Compared with the case where the polyimide was synthesized by using only pyromellitic dianhydride as the tetracarboxylic acid dianhydride and only 4,4'-diaminodiphenyl ether as the diamine compound, a resin other than the polyimide was used. Provided is a porous polyimide film containing 0.005% by mass or more and 1% by mass or less with respect to the entire porous polyimide film and suppressing damage due to bending.

Hereinafter, embodiments that are an example of the present invention will be described.

<Particle dispersion polyimide precursor solution>
The particle-dispersed polyimide precursor solution according to the present embodiment contains a solvent, a polyimide precursor having a repeating unit represented by the above formula (I) (general formula (I)), and particles.
The solvent is a solvent that dissolves the polyimide precursor and does not dissolve the particles. Further, the particles are in a state of being dispersed in the polyimide precursor solution.

Conventionally, it is known that a porous polyimide film can be obtained by a method of making a porous film by phase separation, for example, as described in Patent Document 1. The pores of this porous polyimide film are non-spherical, and the distribution of pore diameters is wide. Further, as a characteristic of this porous polyimide film, it is possible to obtain a low dielectric constant and a low dielectric loss tangent. Then, this porous polyimide film is made compatible with the film strength due to the porosity by setting it as a repeating unit of a specific ratio. Further, a polyimide circuit board for high frequency such as an electronic device is assumed as an application.

On the other hand, instead of using a porous polyimide film having a non-uniform pore shape and pore diameter distribution, a porous polyimide film having nearly spherical pores and a nearly uniform pore diameter is used using particles. The manufacturing technology is being developed.
Such a porous polyimide film having nearly spherical pores and a nearly uniform pore diameter has advantages in many industrial applications as compared with a non-uniform porous polyimide film produced by the phase separation method. ..

The advantage is that, for example, when applied to a separator of a lithium ion secondary battery, the movement of ions during charging and discharging becomes nearly uniform, and the formation of lithium crystals (dendrites) is suppressed and local fatigue is suppressed. It is said that it has a great effect on improving the stability and life of the battery. Further, for example, when applied to a filter, it is possible to improve the filtration efficiency without lowering the filtration rate.
By the way, it is possible to produce a porous polyimide film by using either particles that are close to spheres or particles that are not spheres.
However, for example, when a porous polyimide film is produced using particles, it has been found that the dispersion stability of the particles may decrease in the polyimide precursor solution used.

Since the polyimide precursor synthesized by using only one type each of the tetracarboxylic acid dianhydride and the diamine compound has high regularity of the repeating unit of the resin, the polyimide precursors in the polyimide precursor solution are mutual to each other. High effect. Therefore, in the particle-dispersed polyimide precursor solution in which the particles are dispersed in the polyimide precursor solution containing the polyimide precursor, the interaction between the polyimide precursor and the particles tends to be low. Immediately after preparing this particle-dispersed polyimide precursor solution, the dispersion of particles is stable, but over time, the dispersion stability of the particles tends to decrease. It is considered that this is because the microscopic aggregation of the polyimide precursors progresses with the passage of time and the particle dispersibility decreases.
As described above, in the particle-dispersed polyimide precursor solution containing the polyimide precursor obtained by synthesizing the tetracarboxylic dianhydride and the diamine compound using only one kind each, the dispersion stability of the particles may be low. It has become clear.

On the other hand, in the particle-dispersed polyimide precursor solution according to the present embodiment, the above configuration suppresses a decrease in particle dispersion stability in the particle-dispersed polyimide precursor solution. The reason for this is not clear, but it is presumed as follows.

In the particle-dispersed polyimide precursor solution according to the present embodiment, a monomer having one aromatic ring and a monomer having two or more aromatic rings are specified in at least one of the tetracarboxylic acid dianhydride and the diamine compound. It has a structure copolymerized at the ratio of. Therefore, it is considered that the polyimide precursor tends to reduce the interaction between the polyimide precursors in the particle-dispersed polyimide precursor solution by reducing the regularity of the repeating unit of the resin. As a result, it is considered that the interaction between the polyimide precursor and the particles in the particle-dispersed polyimide precursor solution is likely to be improved.

For the above reasons, it is presumed that the particle-dispersed polyimide precursor solution according to the present embodiment suppresses the decrease in particle dispersion stability in the particle-dispersed polyimide precursor solution.

The workability is improved by heating the particle-dispersed polyimide precursor solution, for example, when the particle-dispersed polyimide precursor solution has a high viscosity or when the highly viscous particle-dispersed polyimide precursor solution is defoamed. There is. In addition, the particle-dispersed polyimide precursor solution may be stored refrigerated. In a particle-dispersed polyimide precursor solution containing a polyimide precursor in which a tetracarboxylic acid dianhydride and a diamine compound are synthesized using only one type each, the polyimide precursors of the polyimide precursors undergo such thermal history. Particle dispersibility in the coating liquid may decrease due to the progress of microscopic aggregation.
On the other hand, the particle-dispersed polyimide precursor solution according to the present embodiment suppresses the decrease in particle dispersion stability in the particle-dispersed polyimide precursor solution, so that even when the above thermal history is passed. , Particle dispersion It is considered that the decrease in particle dispersion stability in the polyimide precursor solution is likely to be suppressed.

Further, since the decrease in particle dispersion stability in the particle-dispersed polyimide precursor solution is suppressed, even when the particle-dispersed polyimide precursor solution that has undergone the above thermal history is applied, the particle-dispersed polyimide precursor The decrease in particle dispersion stability in the solution is likely to be suppressed. As a result, it is considered that the aggregation of particles is suppressed even in the coating film when the coating film is formed by using the particle-dispersed polyimide precursor solution of the present embodiment.

(Polyimide precursor)
The polyimide precursor is a resin (polyamic acid) having a repeating unit represented by the formula (I), which is obtained by polymerizing a tetracarboxylic dianhydride and a diamine compound.

In the formula (I), A is a tetravalent organic group and B is a divalent organic group, which satisfies at least one of the following conditions (1) and (2) and also satisfies the following condition (3).
(1): A has a molar ratio (A1 / A2) of a tetravalent organic group A1 having one aromatic ring and a tetravalent organic group A2 having two or more aromatic rings of 5/95 or more and 95/5. It is as follows.
(2): B has a molar ratio (B1 / B2) of a divalent organic group B1 having one aromatic ring and a divalent organic group B2 having two or more aromatic rings of 5/95 or more and 95/5. The following (molar ratio).
(3): Among the raw material monomer components constituting the A1, the A2, the B1, and the B2, the ratio of the component having the lowest content (excluding zero) to the particles is 0.015 mmol / g. As described above, the difference between the ratio of the component having the highest content to the particles and the ratio of the component having the lowest content (excluding zero) to the particles among the raw material monomer components is 9 mmol / g. It is as follows.

That is, in the formula (I), A and B may satisfy only the condition (1) above or only the condition (2) above. If the condition (1) is satisfied, B is not particularly limited, and if the condition (2) is satisfied, A is not particularly limited.
Further, as long as the above condition (1) is satisfied, B may contain a divalent organic group B1 having one aromatic ring and a divalent organic group B2 having two or more aromatic rings. Similarly, if the above condition B is satisfied, A may contain a tetravalent organic group A1 having one aromatic ring and a tetravalent organic group A2 having two or more aromatic rings.
Further, A and B may satisfy any of the above-mentioned condition (1) and the above-mentioned condition (2).

Further, among the raw material monomer components constituting A1, A2, B1 and B2, the ratio of the component having the lowest content (excluding zero) to the particles is 0.015 mmol / g or more as described above. Is. This ratio is preferably 0.03 mmol / g or more, more preferably 0.05 mmol / g or more, and most preferably 0.1 mmol / g or more, in that the decrease in particle dispersion stability is more likely to be suppressed. When this value is less than 0.015 mmol / g, the content ratio of these raw material monomers is too low with respect to the content of the particles, and the particle dispersion stability is lowered.
In addition, "excluding zero" means excluding the component not contained from each of the raw material monomer components constituting A1, A2, B1 and B2.
Further, the difference between the ratio of the component having the highest content to the particles and the ratio of the component having the lowest content (excluding zero) to the particles among the above-mentioned raw material monomer components is 9 mmol / g as described above. It is as follows. The difference between the two is preferably 7 mmol / g or less, more preferably 5 mmol / g or less, and most preferably 3 mmol / g or less, in that the decrease in particle dispersion stability is more likely to be suppressed. If this value exceeds 9 mmol / g, the regularity of the repeating unit of the polyimide precursor becomes too large with respect to the amount of particles, and the particle dispersion stability decreases.

Examples of the method for analyzing the above-mentioned A1, A2, B1 and B2 in the polyimide precursor from the particle-dispersed polyimide precursor solution include the following methods.
First, the particles are separated from the particle-dispersed polyimide precursor solution to be measured. Next, methanol is added to the polyimide precursor solution from which the particles have been separated to obtain a reprecipitated product of the polyimide precursor. This reprecipitate is placed in a pressure-resistant container, a 1N aqueous sodium hydroxide solution is added, and the treatment is carried out at 100 ° C. for 2 hours to obtain a hydrolyzate of a polyimide precursor. Next, this hydrolyzate was extracted with chloroform and analyzed from the concentrated solution of the chloroform phase by infrared spectroscopy, nuclear magnetic resonance spectroscopy, and gas chromatography, and the structure of the components derived from the diamine compound and the structure of the components derived from the diamine compound were analyzed. Measure the amount. In addition, the aqueous phase, which is the chloroform-insoluble phase of this hydrolyzate, is neutralized, and after freeze-drying, a dry solid content is obtained. This is extracted with methanol, and the lysate is analyzed by infrared spectroscopy, nuclear magnetic resonance spectroscopy, and gas chromatography to measure the structure and amount of components derived from tetracarboxylic acid dianhydride. ..
For A1, A2, B1, and B2 in the polyimide film, the polyimide film is analyzed by infrared spectroscopy, nuclear magnetic resonance spectroscopy, and gas chromatography.

From this measurement result, the molar ratio (A1 / A2) and the molar ratio (B1 / B2) in the polyimide precursor are calculated.
In addition, the solid content of the particles contained in the particle-dispersed polyimide precursor solution is measured from the separated particles. Then, from the measurement result of the particle content and the measurement result of A1, A2, B1 and B2, among the raw material monomer components of A1, A2, B1 and B2 with respect to the unit particle mass. The ratio of the molar amount with the lowest content excluding 0 (zero) to the molar amount with the highest content among the raw material monomer components of A1, A2, B1 and B2 above per unit particle mass. Is calculated according to the following formula 1 and the following formula 2. Further, the difference between the ratio of the component having the highest content to the particles and the ratio of the component having the lowest content (excluding zero) to the particles is calculated according to the following formula 3.
Formula 1: Mole amount / particle mass of the component having the lowest content excluding 0 among the raw material monomer components Formula 2: Mole amount / particle of the component having the highest content among the raw material monomer components Mass formula 3: (Mole amount / particle mass of the component having the highest content among the above-mentioned raw material monomer components)-(The component having the lowest content except 0 among the above-mentioned raw material monomer components) Amount of mole / mass of particles)

In addition, in this specification, "aromatic ring" represents a monocyclic aromatic ring. "Having two or more aromatic rings" means having two or more monocyclic aromatic rings among divalent organic groups or tetravalent organic groups. That is, "having two or more aromatic rings" does not include those having condensed polycyclic aromatics.
Here, the monocyclic aromatic ring may be an aromatic ring having a hetero atom, but is preferably a benzene ring.

Of A1, the tetravalent organic group having one aromatic ring represents a residue obtained by removing four carboxy groups from the tetracarboxylic acid dianhydride having one aromatic ring in the chemical structure. The tetracarboxylic dianhydride is not particularly limited as long as it has one aromatic ring. The tetracarboxylic acid dianhydride may be an aromatic compound in which the aromatic ring is substituted with four carboxy groups, or may be an aliphatic compound containing no aromatic ring and in which the aromatic ring is not substituted with four carboxy groups. The tetracarboxylic dianhydride is preferably an aromatic compound in which the aromatic ring is substituted with four carboxy groups. That is, A1 is often a residue of the aromatic tetracarboxylic dianhydride having one aromatic ring, excluding the four carboxy groups substituted on the aromatic ring. The compounds shown are preferred.
In the compounds represented by A1-1, A2-1 to A2-5, B1-1, B1-2, and B2-1 to B2-7 below, "*" represents a binding portion.

Of A2, the tetravalent organic group having two or more aromatic rings represents a residue obtained by removing four carboxy groups from the tetracarboxylic dianhydride having two or more aromatic rings in the structure. The tetracarboxylic dianhydride is not particularly limited as long as it has two or more aromatic rings. The tetracarboxylic acid dianhydride may be an aromatic compound in which the aromatic ring is directly substituted with four carboxy groups, or may be an aliphatic compound containing no aromatic ring and in which the aromatic ring is not substituted with four carboxy groups. The tetracarboxylic dianhydride is preferably an aromatic compound in which four carboxy groups are directly substituted on the aromatic ring. That is, A2 is preferably a residue of the aromatic tetracarboxylic dianhydride having two aromatic rings, excluding the four carboxy groups directly substituted with the aromatic rings. Of these, the compounds shown by A2-1 to A2-5 below are preferable, and the compounds shown by A2-1 below are more preferable.

Other examples of the tetracarboxylic dianhydride of the raw material monomer constituting A2 include the compounds shown below.
Examples of the tetracarboxylic acid dianhydride other than the above include, specifically, 3,3', 4,4'-dimethyldiphenylsilane tetracarboxylic acid dianhydride, 3,3', 4,4'-tetra. Phenylsilanetetracarboxylic acid dianhydride, 4,4'-bis (3,4-dicarboxyphenoxy) diphenylsulfide dianhydride, 4,4'-bis (3,4-dicarboxyphenoxy) diphenylsulfone dianhydride , 4,4'-bis (3,4-dicarboxyphenoxy) diphenylpropane dianhydride, 2,3,3', 4'-biphenyltetracarboxylic acid dianhydride, bis (phthalic acid) phenylphosphine oxide dianhydride , P-Phenylene-bis (triphenylphthalic acid) dianhydride, m-phenylene-bis (triphenylphthalic acid) dianhydride, bis (triphenylphthalic acid) -4,4'-diphenyl ether dianhydride, Bis (triphenylphthalic acid) -4,4'-diphenylmethane dianhydride and the like can be mentioned.

Of B1, the divalent organic group having one aromatic ring represents a residue obtained by removing two amino groups from the diamine having one aromatic ring in the chemical structure.
The diamine compound is not particularly limited as long as it has one aromatic ring. The diamine compound may be an aromatic compound in which two amino groups are directly substituted on the aromatic ring, or an aliphatic compound which does not contain the aromatic ring and in which two amino groups are not substituted on the aromatic ring. The diamine compound is preferably an aromatic diamine compound in which two amino groups are directly substituted on the aromatic ring. That is, B1 is preferably a residue of the aromatic diamine compound having one aromatic ring, excluding the two amino groups substituted with the aromatic ring. Of these, the compounds represented by B1-1 and B1-2 below are preferable, and the compounds represented by B1-1 below are more preferable.

Other examples of the diamine compound of the raw material monomer constituting B1 include the following.
Specific examples of the diamine compound other than the above include 4,4'-diaminobenzanilide, 3,5-diamino-3'-trifluoromethylbenzanilide, and 3,5-diamino-4'-trifluoro. Examples thereof include methylbenzanilide and methylylenediamine.

Among B2, the divalent organic group having two or more aromatic rings represents a residue obtained by removing two amino groups from a diamine compound having two or more aromatic rings in the chemical structure. The diamine compound is not particularly limited as long as it has two or more aromatic rings. The diamine compound may be an aromatic diamine compound in which two amino groups are directly substituted in the aromatic ring, or an aliphatic diamine compound which does not contain an aromatic ring and in which two amino groups are not substituted in the aromatic ring. The diamine compound is preferably an aromatic diamine compound in which two amino groups are directly substituted on the aromatic ring. That is, B2 is preferably a residue of the diamine compound having two or more aromatic rings, excluding the two amino groups directly substituted with the aromatic ring. Of these, the compounds shown by B2-1 to B2-7 below are preferable, and the compounds shown by B2-1 below are more preferable.

Other examples of the diamine compound as the raw material monomer constituting B2 include the following.
Examples of diamine compounds other than the above include, for example, 4,4'-diaminodiphenylethane, 3,3-dimethyl-4,4'-diaminobiphenyl, 5-amino-1- (4'-aminophenyl). ) -1,3,3-trimethylindan, 6-amino-1- (4'-aminophenyl) -1,3,3-trimethylindan, 4,4'-methylene-bis (2-chloroaniline), 2 , 2', 5,5'-tetrachloro-4,4'-diaminobiphenyl, 2,2'-dichloro-4,4'-diamino-5,5'-dimethoxybiphenyl, 3,3'-dimethoxy-4 , 4'-Diaminobiphenyl, 2,2-bis [4- (4-aminophenoxy) phenyl] propane, 2,2-bis [4- (4-aminophenoxy) phenyl] hexafluoropropane, 1,4-bis (4-Aminophenoxy) benzene, 4,4'-bis (4-aminophenoxy) -biphenyl, 1,3'-bis (4-aminophenoxy) benzene, 4,4'-(p-phenylene isopropylidene) bisaniline , 4,4'-(m-phenylene isopropylidene) bisaniline, 2,2'-bis [4- (4-amino-2-trifluoromethylphenoxy) phenyl] hexafluoropropane, 4,4'-bis [4 -(4-Amino-2-trifluoromethyl) phenoxy] -Diamine compounds such as octafluorobiphenyl and the like can be mentioned.

Next, other raw material monomers that may be used as the tetracarboxylic dianhydride and the diamine compound will be mentioned.

Examples of the tetracarboxylic acid dianhydride include butane tetracarboxylic acid dianhydride, 1,2,3,4-cyclobutane tetracarboxylic acid dianhydride, and 1,3-dimethyl-1,2-2,3,4-cyclobutane. Tetracarboxylic acid dianhydride, 1,2,3,4-cyclopentanetetracarboxylic acid dianhydride, 2,3,5-tricarboxycyclopentylacetic acid dianhydride, 3,5,6-tricarboxynorbonane-2 -Acetic acid dianhydride, 2,3,4,5- tetrahydrofuran tetracarboxylic acid dianhydride, 5- (2,5-dioxotetrahydrofuryl) -3-methyl-3-cyclohexene-1,2-dicarboxylic acid dihydride Examples thereof include anhydrides and tetracarboxylic acid dianhydrides such as bicyclo [2,2,2] -oct-7-ene-2,3,5,6-tetracarboxylic acid dianhydride. In addition, 1,3,3a, 4,5,9b-hexahydro-2,5-dioxo-3-franyl) -naphtho [1,2-c] furan-1,3-dione, 1,3,3a, 4 , 5,9b-Hexahydro-5-Methyl-5- (Tetrahydro-2,5-dioxo-3-furanyl) -naphtho [1,2-c] furan-1,3-dione, 1,3,3a, 4 , 5,9b-Hexahydro-8-methyl-5- (tetrahydro-2,5-dioxo-3-furanyl) -naphtho [1,2-c] furan-1,3-dione and other tetracarboxylic acid dianhydrides And so on.

Examples of the diamine compound include 1,3-propanediamine, tetramethylenediamine, pentamethylenediamine, octamethylenediamine, nonamethylenediamine, 4,4-diaminoheptamethylenediamine, 1,4-diaminocyclohexane, isophoronediamine, and tetrahydrodicyclo. Diamines such as pentadienylenediamine, hexahydro-4,7-methanoin danirenenedimethylenediamine, tricyclo [6,2,1,0 ^2.7 ] -undecylenedimethyldiamine, 4,4'-methylenebis (cyclohexylamine) Examples include compounds. In addition, diamine compounds of 2,7-diaminofluorene and 9,9-bis (4-aminophenyl) fluorene can also be mentioned.

Here, in the particle-dispersed polyimide precursor solution according to the present embodiment, in the polyimide precursor represented by the above formula (I), A and B in the formula (I) are the above-mentioned conditions (1) and (2). ) Satisfy at least one of them. When at least one of A1 / A2 (molar ratio) and B1 / B2 (molar ratio) is out of the range of 5/95 or more and 95/5 or less, the molar ratio of either A1 or A2 or B1 or B2 becomes too little. Therefore, when at least one of A1 / A2 (molar ratio) and B1 / B2 (molar ratio) satisfies the range of 5/95 or more and 95/5 or less, the particle dispersion stability in the particle-dispersed polyimide precursor solution is satisfied. The decrease is suppressed.

When the polyimide precursor represented by the formula (I) satisfies the condition (1), it satisfies any of the following conditions (I-3) and the following (I-4), and the condition (2) When satisfying, any of the following conditions (I-1) and the following (I-2) may be satisfied. When any of the following conditions is satisfied, the characteristics of the porous polyimide film can be more easily improved when the porous polyimide film is obtained by using the particle-dispersed polyimide precursor solution according to the present embodiment.

(I-1) A1 / A2 is 60/40 or more and 100/0 or less, and B1 / B2 is 5/95 or more and 40/60 or less (I-2) A1 / A2 is 0/100 or more and 40/60 or less, And B1 / B2 is 60/40 or more and 95/5 or less (I-3) A1 / A2 is 5/95 or more and 40/60 or less, and B1 / B2 is 60/40 or more and 100/0 or less (I-4) ) A1 / A2 is 60/40 or more and 95/5 or less, and B1 / B2 is 0/100 or more and 40/60 or less.

Further, in the same respect, the polyimide precursor represented by the formula (I) has the conditions represented by the above (I-1) to (I-4), and further, the following (II-1), respectively. It is preferable that the conditions shown in (II-4) to (II-4) are satisfied.

(II-1) A1 / A2 is 100/0 and B1 / B2 is 5/95 or more and 30/70 or less (II-2) A1 / A2 is 0/100 and B1 / B2 is 70/30 or more. 95/5 or less (II-3) A1 / A2 is 5/95 or more and 30/70 or less, and B1 / B2 is 100/0.
(II-4) A1 / A2 is 70/30 or more and 95/5 or less, and B1 / B2 is 0/100.

The number average molecular weight of the polyimide precursor is preferably 1000 or more and 150,000 or less, preferably 5000 or more and 130,000 or less, and more preferably 10,000 or more and 100,000 or less. When the number average molecular weight of the polyimide precursor is in the above range, the decrease in the solubility of the polyimide precursor in the solvent is suppressed, and the film-forming property is easily improved.

The number average molecular weight of the polyimide precursor is measured by a gel permeation chromatography (GPC) method under the following measurement conditions.
-Column: Tosoh TSKgelα-M (7.8 mm ID x 30 cm)
-Eluent: DMF (dimethylformamide) / 30 mM LiBr / 60 mM phosphoric acid-Flow rate: 0.6 mL / min
・ Injection amount: 60 μL
・ Detector: RI (Differential Refractometer)

The content (concentration) of the polyimide precursor is preferably 0.1% by mass or more and 40% by mass or less, preferably 0.5% by mass or more and 25% by mass or less, based on the total amount of the polyimide precursor solution. More preferably, it is 1% by mass or more and 20% by mass or less.

(particle)
The particles are in a state of being dispersed without being dissolved in the particle-dispersed polyimide precursor solution according to the present embodiment, and can be removed by a particle removing step described later when producing a porous polyimide film. If so, the material of the particles is not particularly limited. The particles are roughly classified into resin particles and inorganic particles, which will be described later.

Here, in the present specification, "particles do not dissolve" means that the particles do not dissolve in the target liquid at 25 ° C. and also dissolve in the range of 3% by mass or less. include.

The volume average particle size D50v of the particles is not particularly limited. The volume average particle size D50v of the particles is, for example, preferably 0.1 μm or more and 0.5 μm or less, preferably 0.25 μm or more and 0.5 μm or less, and 0.25 μm or more and 0.48 μm or less. Is preferable, and more preferably 0.25 μm or more and 0.45 μm or less. When the average particle size of the particles is in this range, cohesiveness is likely to be suppressed. Further, when the particles are resin particles, the productivity of the resin particles is likely to be improved.
The volume particle size distribution index (GSDv) of the particles is preferably 1.30 or less, more preferably 1.25 or less, and most preferably 1.20 or less. The particle size distribution index is calculated as ^{(D84v / D16v) 1/2} from the particle size distribution of the particles in the particle-dispersed polyimide precursor solution.

The particle size distribution of the particles in the particle-dispersed polyimide precursor solution according to the present embodiment is measured as follows. The solution to be measured is diluted and the particle size distribution of particles in the solution is measured using a Coulter counter LS13 (manufactured by Beckman Coulter). Based on the particle size distribution to be measured, the particle size distribution is measured by drawing a volume cumulative distribution from the small diameter side with respect to the divided particle size range (channel).
Then, in the volume cumulative distribution drawn from the small diameter side, the particle size having a cumulative 16% is the volume particle size D16v, the particle size having a cumulative 50% is the volume average particle size D50v, and the particle size having a cumulative 84% is the volume grain size. The diameter is D84v.

When the volume particle size distribution of the particles in the particle-dispersed polyimide precursor solution of the present embodiment is difficult to measure by the above method, it is measured by a method such as a dynamic light scattering method.

The shape of the particles is preferably spherical. When a porous polyimide film is produced using spherical particles, a porous polyimide film having spherical pores can be obtained.
In the present specification, the "spherical shape" in a particle includes both a spherical shape and a substantially spherical shape (a shape close to a spherical shape). Specifically, it means that 90% or more of the particles have a major axis to minor axis ratio (major axis / minor axis) of 1 or more and 1.5 or less. The closer the ratio of the major axis to the minor axis is, the closer it becomes to a spherical shape.

As the particles, either resin particles or inorganic particles may be used, but it is preferable to use resin particles.
As will be described later, the resin particles can be easily produced into nearly spherical particles by a known production method such as emulsion polymerization. Further, since the resin particles and the polyimide precursor are organic materials, the particle dispersibility in the coating film and the interfacial adhesion with the polyimide precursor are likely to be improved as compared with the case where the inorganic particles are used. Further, when producing a porous polyimide film, it becomes easy to obtain a porous polyimide film having pores and pore diameters closer to uniform. For these reasons, it is preferable to use resin particles.

Examples of the inorganic particles include silica particles. Silica particles are suitable inorganic particles in that particles that are close to spherical are available. For example, a porous polyimide film having pores in a state close to a spherical shape can be obtained by using a particle-dispersed polyimide precursor solution using silica particles close to a spherical shape. However, when silica particles are used as the particles, it is difficult to absorb the volume shrinkage in the imidization step, so that the polyimide film after imidization tends to have fine cracks. In this respect as well, it is preferable to use resin particles as the particles.

In the particle-dispersed polyimide precursor solution according to the present embodiment, the content of particles is 20% by mass or more and 90% by mass or less (preferably 25% by mass or more and 87% by mass) with respect to 100 parts by mass of the solid content in the solution. Hereinafter, it is more preferably in the range of 30% by mass or more and 85% by mass or less).

Hereinafter, specific materials of the resin particles and the inorganic particles will be described.

-Resin particles-
Specific examples of the resin particles include vinyl polymers typified by polystyrenes, poly (meth) acrylic acids, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl ether, and the like; polyesters, polyurethanes, polyamides, and the like. Examples thereof include resin particles such as a typified condensation polymer; a hydrocarbon polymer typified by polyethylene, polypropylene, polybutadiene, etc.; a fluorinated polymer typified by polytetrafluoroethylene, polyvinyl fluoride, etc.;
Here, "(meth) acrylic" means to include both "acrylic" and "methacryl". Further, the (meth) acrylic acids include (meth) acrylic acid, (meth) acrylic acid ester, and (meth) acrylamide.

The resin particles may or may not be crosslinked. For cross-linking, bifunctional monomers such as divinylbenzene, ethylene glycol dimethacrylate, nonandiacrylate, and decanediol diacrylate, and polyfunctional monomers such as trimethylolpropane triacrylate and trimethylolpropane trimethacrylate are used in combination. You may.

When the resin particles are vinyl resin particles, it is obtained by polymerizing a monomer. Examples of the vinyl resin monomer include the following monomers. For example, styrene, alkyl-substituted styrene (eg, α-methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2-ethylstyrene, 3-ethylstyrene, 4-ethylstyrene, etc.), halogen-substituted styrene. (For example, 2-chlorostyrene, 3-chlorostyrene, 4-chlorostyrene, etc.), styrenes having a styrene skeleton such as vinylnaphthalene; methyl (meth) acrylate, ethyl (meth) acrylate, n (meth) acrylate. (Meta) acrylates such as -propyl, n-butyl (meth) acrylate, lauryl (meth) acrylate, 2-ethylhexyl (meth) acrylate; vinyl nitriles such as acrylonitrile and methacrylonitrile; vinyl methyl Vinyl ethers such as ether and vinyl isobutyl ether; Vinyl ketones such as vinyl methyl ketone, vinyl ethyl ketone and vinyl isopropenyl ketone; Acids such as (meth) acrylic acid, maleic acid, silicic acid, fumaric acid and vinyl styrene acid; Examples thereof include vinyl resin units obtained by polymerizing monomers such as bases such as ethyleneimine, vinylpyridine and vinylamine;
As the other monomer, a monofunctional monomer such as vinyl acetate may be used in combination.
Further, the vinyl resin may be a resin using these monomers alone, or a resin which is a copolymer using two or more kinds of monomers.

The resin particles are preferably polystyrene or poly (meth) acrylic acid particles from the viewpoint of manufacturability and adaptability of the particle removing step described later. Specifically, resin particles of polystyrene, styrene- (meth) acrylic acid copolymers, and poly (meth) acrylic acids are more preferable, and resin particles of polystyrene and poly (meth) acrylic acid esters are most preferable. These resin particles may be used alone or in combination of two or more.

The resin particles are obtained in the process of producing the polyimide precursor solution according to the present embodiment, in the process of applying the polyimide precursor solution when producing the porous polyimide film, and in the process of drying the coating film (before removing the resin particles). It is preferable that the shape of is retained. From this viewpoint, the glass transition temperature of the resin particles is preferably 60 ° C. or higher, preferably 70 ° C. or higher, and more preferably 80 ° C. or higher.

The glass transition temperature is obtained from the DSC curve obtained by differential scanning calorimetry (DSC), and more specifically described in JIS K 7121-1987 "Method for measuring the transition temperature of plastics". It is obtained by the "external glass transition start temperature" of.

-Inorganic particles-
Specific examples of the inorganic particles include silica (silicon dioxide) particles, magnesium oxide particles, alumina particles, zirconia particles, calcium carbonate particles, calcium oxide particles, titanium dioxide particles, zinc oxide particles, and cerium oxide particles. Examples include inorganic particles. The shape of the particles is preferably spherical as described above. From this viewpoint, as the inorganic particles, silica particles, magnesium oxide particles, calcium carbonate particles, magnesium oxide particles, and alumina particles are preferable, and silica particles, titanium oxide particles, and alumina particles are more preferable, and silica particles. Is even more preferable. These inorganic particles may be used alone or in combination of two or more.

If the wettability and dispersibility of the polyimide precursor solution of the inorganic particles in the solvent are insufficient, the surface of the inorganic particles may be modified if necessary. Examples of the surface modification method include a method of treating with an alkoxysilane having an organic group represented by a silane coupling agent; a method of coating with an organic acid such as oxalic acid, citric acid, and lactic acid; and the like.

(solvent)
The solvent is not particularly limited as long as the polyimide precursor is dissolved in the particle-dispersed polyimide precursor solution and the particles are dispersed without being dissolved. The solvent may be either an organic solvent or an aqueous solvent. The solvent may be selected according to the state in which the polyimide precursor is dissolved and the particles are not dissolved but dispersed.

Examples of the solvent include the organic solvents and aqueous solvents shown below. When an aqueous solvent is applied as the solvent, it is preferable to add an organic amine compound described later in order to dissolve the polyimide precursor.

As the solvent, an aqueous solvent is preferable from the viewpoint of environment and cost. In particular, when resin particles are used as the particles, it is preferable to use an aqueous solvent because the resin particles are dissolved in the polyimide precursor and the resin particles are dispersed without being dissolved.

-Organic solvent-
The organic solvent is selected so that the polyimide precursor is dissolved in the particle-dispersed polyimide precursor solution according to the present embodiment, and the particles are not dissolved but dispersed. When selecting an organic solvent, a mixed solvent of a good solvent (S1) for the polyimide precursor and a solvent (S2) other than the good solvent (S1) is preferable.

The good solvent (S1) for the polyimide precursor is used when preparing the polyimide precursor solution. In the present embodiment, the good solvent refers to a solvent in which the solubility of the polyimide precursor is 5% by mass or more. Specifically, N, N-dimethylformamide, N, N-dimethylacetamide, N-methylpyrrolidone, N-ethylpyrrolidone, tetramethylurea, 1,3-dimethyl-2-imidazolidinone, dimethylpropyleneurea, dimethyl Examples thereof include aprotonic polar solvents such as sulfoxide, γ-butyrolactone, β-propiolactone, γ-valerolactone, δ-valerolactone, and γ-caprolactone.
Among these, N, N-dimethylacetamide, N-methylpyrrolidone, tetramethylurea, 1,3-dimethyl-2-imidazolidinone, dimethyl sulfoxide, and γ-butyrolactone are preferable, and N, N-dimethylacetamide and N- Methylpyrrolidone, tetramethylurea, dimethyl sulfoxide and γ-butyrolactone are more preferable, and N, N-dimethylacetamide, N-methylpyrrolidone and γ-butyrolactone are even more preferable.

As the solvent (S2) other than the good solvent for the polyimide precursor, a solvent having low solubility of the particles to be used is selected. As an example of the solvent selection method, for example, a method of adding particles to a target solvent and selecting a solvent having a dissolution amount of 3% by mass or less can be mentioned.

Examples of the solvent (S2) other than the good solvent for the polyimide precursor include hydrocarbon solvents such as n-decane and toluene; alcohols such as isopropyl alcohol, 1-propanol, 1-butanol, 1-pentanol and phenethyl alcohol. Solvents: Glycol solvents such as ethylene glycol, propylene glycol, ethylene glycol monomethyl ether, 1-methoxy-2-propanol, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether; ethers such as diglime, triglime, tetraglime, methylcellosolve acetate System solvents; phenolic solvents such as phenol and cresol; and the like.

When the above-mentioned resin particles are used as the particles, the solvent (S1) has a very high polarity, so that the solvent (S1) alone may dissolve not only the polyimide precursor but also the resin particles. Therefore, the mixing ratio of the solvent (S1) and the solvent (S2) may be determined so that the polyimide precursor is dissolved and the resin particles are not dissolved. In addition, the boiling point of the solvent (S2) is higher than that of the solvent (S1) in order to prevent the resin particles from melting during the heating process of the coating film of the particle-dispersed polyimide precursor solution and, for example, the shape of the pores being disturbed. It is preferably 10 ° C. or higher, and more preferably 20 ° C. or higher.

-Aqueous solvent-
In the present specification, the aqueous solvent is specifically the aqueous solvent shown below.
The aqueous solvent is an aqueous solvent containing water. Specifically, the aqueous solvent is preferably a solvent containing 50% by mass or more of water with respect to the total aqueous solvent. Examples of water include distilled water, ion-exchanged water, ultra-filtered water, pure water, and the like.

The content of water is preferably 50% by mass or more and 100% by mass or less, more preferably 70% by mass or more and 100% by mass or less, and further preferably 80% by mass or more and 100% by mass or less with respect to the total aqueous solvent.

When the aqueous solvent contains a solvent other than water, examples of the solvent other than water include a water-soluble organic solvent and an aprotic polar solvent. As the solvent other than water, a water-soluble organic solvent is preferable from the viewpoint of mechanical strength of the porous polyimide film and the like. Here, water-soluble means that the target substance dissolves in water in an amount of 1% by mass or more at 25 ° C.

In particular, the aqueous solvent may contain an aprotic polar solvent from the viewpoint of improving various properties (for example, transparency, mechanical strength, heat resistance, electrical properties, solvent resistance, etc.) of the porous polyimide film. In this case, in order to suppress the dissolution and swelling of the particles in the particle-dispersed polyimide precursor solution, the content is preferably 40% by mass or less, preferably 30% by mass or less, based on the total aqueous solvent. Further, in order to suppress the dissolution and swelling of the resin particles when the polyimide precursor solution is dried and formed into a film, the content (solid content) of the particles and the polyimide precursor in the particle-dispersed polyimide precursor solution is 3 It is preferable to use it in a mass% or more and 200% by mass or less, preferably 3% by mass or more and 100% by mass or less, more preferably 3% by mass or more and 50% by mass or less, and further preferably 5% by mass or more and 50% by mass or less. ..

The water-soluble organic solvent may be used alone or in combination of two or more.
When resin particles are used as the particles, the water-soluble organic solvent is preferably one in which the resin particles do not dissolve. The reason for this is that, for example, when an aqueous solvent containing water and a water-soluble organic solvent is used, a coating film of a particle-dispersed polyimide precursor solution can be obtained even if the resin particles are not dissolved in the resin particle dispersion liquid. This is because there is a concern that the resin particles will dissolve in the process.

When resin particles are used as the particles and a water-soluble organic solvent that dissolves the resin particles is used as the aqueous solvent, the amount of the water-soluble organic solvent is used to prevent the particles from dissolving and swelling in the particle-dispersed polyimide precursor solution. Is preferably 40% by mass or less, preferably 30% by mass or less, based on the total aqueous solvent. Further, in order to prevent dissolution and swelling of the resin particles when the coating film of the particle-dispersed polyimide precursor solution is dried and formed into a film, the amount of this water-soluble organic solvent is the same as that of the particles in the particle-dispersed polyimide precursor solution. It is preferable to use 3% by mass or more and 50% by mass or less, preferably 5% by mass or more and 40% by mass or less, and more preferably 5% by mass or more and 35% by mass or less with respect to the total amount of the polyimide precursor.

Examples of the water-soluble organic solvent include the following water-soluble ether-based solvents, water-soluble ketone-based solvents, and water-soluble alcohol-based solvents.

The water-soluble ether solvent is a water-soluble solvent having an ether bond in one molecule. Examples of the water-soluble ether solvent include tetrahydrofuran (THF), dioxane, trioxane, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether and the like. Among these, tetrahydrofuran and dioxane are preferable as the water-soluble ether solvent.

The water-soluble ketone solvent is a water-soluble solvent having a ketone group in one molecule. Examples of the water-soluble ketone solvent include acetone, methyl ethyl ketone, cyclohexanone and the like. Among these, acetone is preferable as the water-soluble ketone solvent.

The water-soluble alcohol-based solvent is a water-soluble solvent having an alcoholic hydroxyl group in one molecule. Water-soluble alcohol solvents include, for example, methanol, ethanol, 1-propanol, 2-propanol, tert-butyl alcohol, ethylene glycol, ethylene glycol monoalkyl ether, propylene glycol, propylene glycol monoalkyl ether, diethylene glycol, and diethylene glycol. Monoalkyl ether, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,5-pentanediol, 2-butene- Examples thereof include 1,4-diol, 2-methyl-2,4-pentanediol, glycerin, 2-ethyl-2-hydroxymethyl-1,3-propanediol, 1,2,6-hexanetriol and the like. Among these, as the water-soluble alcohol solvent, methanol, ethanol, 2-propanol, ethylene glycol, ethylene glycol monoalkyl ether, propylene glycol, propylene glycol monoalkyl ether, diethylene glycol, and diethylene glycol monoalkyl ether are preferable.

When an aprotic polar solvent other than water is contained as the aqueous solvent, the aprotic polar solvent used in combination is a solvent having a boiling point of 150 ° C. or higher and 300 ° C. or lower and a dipole moment of 3.0D or higher and 5.0D or lower. be. Specific examples of the aprotonic polar solvent include N-methyl-2-pyrrolidone (NMP), N, N-dimethylformamide (DMF), N, N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), and the like. Hexamethylphosphoramide (HMPA), N-methylcaprolactam, N-acetyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone (DMI), N, N'-dimethylpropyleneurea, tetramethylurea, Examples thereof include trimethyl phosphate and triethyl phosphate.

When a solvent other than water is contained as the aqueous solvent, the solvent used in combination often has a boiling point of 270 ° C. or lower, preferably 60 ° C. or higher and 250 ° C. or lower, and more preferably 80 ° C. or higher and 230 ° C. or lower. be. When the boiling point of the solvent used in combination is within the above range, it becomes difficult for a solvent other than water to remain in the polyimide molded product, and it becomes easy to obtain a polyimide molded product having high mechanical strength.
Here, when an aqueous solvent is used as the solvent, it is preferable that the aqueous solvent contains an organic amine compound described later and the proportion of water shown in the total solvent is 50% by mass or more. Further, the aqueous solvent may contain an aprotic polar solvent in an amount of 3% by mass or more and 50% by mass or less based on the total amount of the particles and the polyimide precursor.

-Organic amine compound-
When the solvent is an aqueous solvent, an organic amine compound is added to dissolve the polyimide precursor to make it water-soluble. The organic amine compound is a compound that amine-chlorides a polyimide precursor (its carboxy group thereof) to increase its solubility in an aqueous solvent and also functions as an imidization accelerator. Specifically, the organic amine compound is preferably an amine compound having a molecular weight of 170 or less. The organic amine compound is preferably a compound excluding the diamine compound which is a raw material of the polyimide precursor.
The organic amine compound is preferably a water-soluble compound. Water-soluble means that the target substance dissolves in water in an amount of 1% by mass or more at 25 ° C.

Examples of the organic amine compound include a primary amine compound, a secondary amine compound, and a tertiary amine compound.
Among these, as the organic amine compound, at least one selected from a secondary amine compound and a tertiary amine compound (particularly, a tertiary amine compound) is preferable. When a tertiary amine compound or a secondary amine compound is applied as the organic amine compound (particularly, the tertiary amine compound), the solubility of the polyimide precursor in the solution is likely to be increased, the film-forming property is easily improved, and the film-forming property is easily improved. The storage stability of the polyimide precursor solution is likely to be improved.

Moreover, as an organic amine compound, in addition to a monovalent amine compound, a divalent or higher polyvalent amine compound can also be mentioned. When a polyvalent amine compound having a divalent value or higher is applied, a pseudo-crosslinked structure is easily formed between the molecules of the polyimide precursor, and the storage stability of the polyimide precursor solution is easily improved.

Examples of the primary amine compound include methylamine, ethylamine, n-propylamine, isopropylamine, 2-ethanolamine, 2-amino-2-methyl-1-propanol and the like.
Examples of the secondary amine compound include dimethylamine, 2- (methylamino) ethanol, 2- (ethylamino) ethanol, morpholine and the like.
Examples of the tertiary amine compound include 2-dimethylaminoethanol, 2-diethylaminoethanol, 2-dimethylaminopropanol, pyridine, triethylamine, picoline, N-methylmorpholine, N-ethylmorpholine, 1,2-dimethylimidazole, and 2 -Ethyl-4-methylimidazole and the like can be mentioned.

From the viewpoint of pot life of the polyimide precursor solution and film thickness uniformity, a tertiary amine compound is preferable. In this regard, 2-dimethylaminoethanol, 2-diethylaminoethanol, 2-dimethylaminopropanol, pyridine, triethylamine, picoline, N-methylmorpholine, N-ethylmorpholine, 1,2-dimethylimidazole, 2-ethyl-4- More preferably, it is at least one selected from the group consisting of methylimidazole, N-methylpiperidine, and N-ethylpiperidine. In addition, 2-dimethylaminoethanol, 2-diethylaminoethanol, 2-dimethylaminopropanol, triethylamine, N-methylmorpholine, N-ethylmorpholine, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, N-methyl Most preferably, it is at least one selected from the group consisting of piperidine and N-ethylpiperidine.

Here, as the organic amine compound, an amine compound having a heterocyclic structure containing nitrogen (particularly, a tertiary amine compound) is also preferable from the viewpoint of film forming property. Examples of the amine compound having a heterocyclic structure containing nitrogen (hereinafter referred to as “nitrogen-containing heterocyclic amine compound”) include isoquinolins (amine compounds having an isoquinolin skeleton) and pyridines (amine compounds having a pyridine skeleton). ), Pyrimidines (amine compounds with pyrimidine skeleton), pyrazines (amine compounds with pyrazine skeleton), piperazins (amine compounds with piperazin skeleton), triazines (amine compounds with triazine skeleton), imidazoles (imidazole) Examples thereof include amine compounds having a skeleton), morpholins (amine compounds having a morpholin skeleton), polyaniline, polypyridine, and polyamine.

The nitrogen-containing heterocyclic amine compound is preferably at least one selected from the group consisting of morpholins, pyridines, piperidines, and imidazoles from the viewpoint of film-forming property, and morpholins (having a morpholine skeleton). It is more preferably an amine compound). Among these, at least one selected from the group consisting of N-methylmorpholine, N-methylpiperidine, pyridine, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, and picoline is more preferable. More preferably, it is N-methylmorpholine.

Among these, the organic amine compound is preferably a compound having a boiling point of 60 ° C. or higher (preferably 60 ° C. or higher and 200 ° C. or lower, more preferably 70 ° C. or higher and 150 ° C. or lower). When the boiling point of the organic amine compound is 60 ° C. or higher, the organic amine compound is suppressed from volatilizing from the polyimide precursor solution during storage, and the decrease in solubility of the polyimide precursor in the solvent is easily suppressed.

The organic amine compound is preferably contained in an amount of 50 mol% or more and 500 mol% or less, preferably 80 mol% or more and 250 mol% or less, based on the carboxy group (-COOH) of the polyimide precursor in the polyimide precursor solution. , More preferably, it is contained in an amount of 90 mol% or more and 200 mol% or less.
When the content of the organic amine compound is within the above range, the solubility of the polyimide precursor in an aqueous solvent is likely to increase, and the film-forming property is likely to be improved. In addition, the storage stability of the polyimide precursor solution is likely to be improved.

The above-mentioned organic amine compounds may be used alone or in combination of two or more.

-Other additives-
The particle-dispersed polyimide precursor solution according to the present embodiment may contain a catalyst for promoting the imidization reaction, a leveling material for improving the quality of film formation, and the like.
As the catalyst for promoting the imidization reaction, a dehydrating agent such as acid anhydride, an acid catalyst such as a phenol derivative, a sulfonic acid derivative, or a benzoic acid derivative may be used.

Further, for example, a conductive material (for example, a volume resistivity of ^{less than 10 7} Ω · cm) or a semi-conductive material (for example, a volume resistivity of 10 ⁷ Ω · cm or more and 10 ¹³ Ω) added for imparting conductivity. -Cm or less)) may be contained.
Examples of the conductive agent include carbon black (for example, acidic carbon black having a pH of 5.0 or less); metal (for example, aluminum, nickel, etc.); metal oxide (for example, yttrium oxide, tin oxide, etc.); ionic conductive substance (for example, titanium). Potassium acid acid, LiCl, etc.); etc. These conductive materials may be used alone or in combination of two or more.

-Preferable embodiment of the particle-dispersed polyimide precursor solution of the present embodiment-
The following aspects of the particle-dispersed polyimide precursor solution of the present embodiment are preferable in that the decrease in particle dispersion stability in the liquid is easily suppressed.
The particle-dispersed polyimide precursor solution of the present embodiment contains resin particles, a polyimide precursor having a repeating unit represented by the above formula (I), and a solvent. The polyimide precursor has a molar conversion ratio A1 / A2 of a tetravalent organic group A1 having one aromatic ring and a tetravalent organic group A2 having two or more aromatic rings, and 2 having one aromatic ring. The molar conversion ratio B1 / B2 of the valent organic group B1 and the divalent organic group B2 having two or more aromatic rings is any of the conditions shown in the following (I-1) to the following (I-4). It is preferable to satisfy. Further, the particle-dispersed polyimide precursor solution preferably contains an aqueous solvent and a tertiary amine.
(II-1) The molar ratio of A1 / A2 is 100/0 and the molar ratio of B1 / B2 is 5/95 or more and 30/70 or less (II-2) The molar ratio of A1 / A2 is 0/100 and , B1 / B2 molar ratio is 70/30 or more and 95/5 or less (II-3) A1 / A2 molar ratio is 5/95 or more and 30/70 or less, and B1 / B2 molar ratio is 100/0.
(II-4) The molar ratio of A1 / A2 is 70/30 or more and 95/5 or less, and B1 / B2 is 0/100.

Further, the following aspects of the particle-dispersed polyimide precursor solution of the present embodiment are more preferable in that the decrease in particle dispersion stability in the liquid is easily suppressed.
The particles are at least one resin particle selected from the group consisting of polystyrene, poly (meth) acrylic acid ester, and styrene- (meth) acrylic acid ester copolymer.
As the polyimide precursor having the repeating unit represented by the above formula (1), the tetravalent organic group A1 having one aromatic ring is the group represented by A1-1 and the tetravalent having two or more aromatic rings. The organic group A2 is the group represented by A2-1 and the divalent organic group B1 having one aromatic ring is the group represented by B1-1 and the divalent organic group B2 having two or more aromatic rings. Is preferably the group represented by B2-1.
The solvent is preferably an aqueous solvent containing an organic amine compound and having a water content of 50% by mass or more in the total solvent. Further, the aqueous solvent may contain an aprotic polar solvent in an amount of 3% by mass or more and 50% by mass or less with respect to the total amount of the particles and the polyimide precursor. Of these, as the organic amine, a tertiary amine compound is preferable, and 2-dimethylaminoethanol, 2-diethylaminoethanol, 2-dimethylaminopropanol, pyridine, triethylamine, picolin, N-methylmorpholine, N-ethylmorpholine, 1, More preferably, it is at least one selected from the group consisting of 2-dimethylimidazole, 2-ethyl-4-methylimidazole, N-methylpiperidine, and N-ethylpiperidine.

-Method of preparing particle-dispersed polyimide precursor solution-
Examples of the method for producing the particle-dispersed polyimide precursor solution according to the present embodiment include the methods according to (i) and (ii) below.
(I) Method of preparing a polyimide precursor solution and then mixing and dispersing with particles (ii) Method of preparing a particle dispersion and synthesizing a polyimide precursor in the dispersion.

(I) Method of mixing and dispersing the polyimide precursor solution with the particles after preparing the polyimide precursor solution First, the polyimide precursor solution before dispersing the particles uses a known method and is a tetracarboxylic acid dianhydride in a solvent. And a diamine compound are polymerized to form a resin (polyimide precursor) to obtain a polyimide precursor solution.
In the case of an aqueous solvent, the above-mentioned aqueous solvent is used and polymerization is carried out in the presence of an organic amine to obtain a polyimide precursor solution. As another example, in an organic solvent such as an aprotonic polar solvent (for example, N-methylpyrrolidone (NMP)), a tetracarboxylic acid dianhydride and a diamine compound are polymerized to form a resin (polymethyl precursor). Is generated, and then put into water or an aqueous solvent such as alcohol to precipitate a resin (polymethyl precursor). Then, a method of dissolving the polyimide precursor and the organic amine compound in an aqueous solvent to obtain a polyimide precursor solution can be mentioned.

Next, the obtained polyimide precursor solution is mixed and dispersed with the particles.
When producing resin particles, for example, when the resin particles are vinyl resin particles, known polymerization methods (emulsion polymerization, soap-free emulsion polymerization, suspension polymerization, miniemulsion polymerization, microemulsion polymerization and other radical polymerization methods) ) Can be produced in an aqueous solvent.

For example, when the emulsion polymerization method is applied to the production of vinyl resin particles, a single amount of styrenes, (meth) acrylic acids, etc. is contained in an aqueous solvent in which a water-soluble polymerization initiator such as potassium persulfate or ammonium persulfate is dissolved. Add body. Then, if necessary, a surfactant such as sodium dodecyl sulfate or diphenyloxide disulfonate is added, and the polymerization is carried out by heating while stirring to obtain vinyl resin particles.

When the particle-dispersed polyimide precursor solution according to the present embodiment is prepared in an aqueous solvent, the aqueous solvent dispersion of the resin particles obtained by the above method and the polyimide precursor solution obtained above are mixed. And by stirring, a particle-dispersed polyimide precursor solution is obtained.

When the particle-dispersed polyimide precursor solution according to the present embodiment is prepared in an organic solvent, the aqueous solvent dispersion of the resin particles is taken out as a powder by a known method such as reprecipitation or freeze-drying. , Mix and stir with the polyimide precursor solution obtained above. Alternatively, the removed resin particle powder may be redispersed in an organic solvent (which may be a single solvent or a mixed solvent) in which the resin particles are not dissolved, and then mixed and stirred with the polyimide precursor solution.
The mixing, stirring, and dispersing methods are not particularly limited. Further, in order to improve the dispersibility of the particles, a known nonionic or ionic surfactant may be added.

When commercially available particles (resin particles or inorganic particles) are used, when the particles are available as powder, the solvent of the particle-dispersed polyimide precursor solution is the desired concentration regardless of whether it is an organic solvent or an aqueous solvent. It is possible to mix and disperse particles. When the particles are available as a dispersion liquid of the particles, the dispersion liquid of the particles and the polyimide precursor solution obtained above are mixed and dispersed in the same manner as in the case of preparing the particles described above to disperse the particles. A polyimide precursor solution is prepared.

(Ii) Method for preparing a particle dispersion and preparing a polyimide precursor in the dispersion When the particle-dispersed polyimide precursor solution according to the present embodiment is prepared with an organic solvent, first, the particles are dissolved. Instead, prepare a solution in which particles are dispersed in an organic solvent that dissolves the polyimide precursor. Next, in the solution, the tetracarboxylic acid dianhydride and the diamine compound are polymerized to form a resin (polyimide precursor) to obtain a particle-dispersed polyimide precursor solution.
When preparing the particle-dispersed polyimide precursor solution according to the present embodiment using an aqueous solvent (aqueous solvent), first, an aqueous solvent dispersion of particles is prepared. Next, in the solution and in the presence of an organic amine, the tetracarboxylic acid dianhydride and the diamine compound are polymerized to form a resin (polyimide precursor) to obtain a particle-dispersed polyimide precursor solution.

When resin particles are used as the particles, the surface of the resin particles may be coated with a resin having a chemical structure different from that of the original resin in order to improve the dispersibility in the particle-dispersed polyimide precursor solution according to the present embodiment. good. The resin to be coated may be changed depending on the solvent used and the chemical structure of the polyimide precursor. Examples of the resin to be coated include a resin having an acidic group or a basic group. As a method of coating the resin on the surface of the resin particles, for example, when vinyl resin particles are produced by emulsion polymerization, after the polymerization of the monomer derived from the original resin particles is completed, methacrylic acid or methacrylic acid is further applied. Examples thereof include a method in which a small amount of a monomer having an acidic group or a basic group such as 2-dimethylaminoethyl is added to continue the polymerization.

Among these, the method (ii) described above is preferable as the method for producing the particle-dispersed polyimide precursor solution according to the present embodiment in that the particle dispersibility can be further improved.

<Particle-containing polyimide film>
The particle-containing polyimide film can be obtained by applying the particle-dispersed polyimide precursor solution according to the present embodiment to form a coating film, and then heating the coating film.
The particle-containing polyimide film includes not only the particle-containing polyimide film that has been imidized, but also the particle-containing polyimide film that has been partially imidized before the imidization is completed.

Specifically, the particle-containing polyimide film according to the present embodiment is, for example, a step of applying a particle-dispersed polyimide precursor solution according to the present embodiment to form a coating film (hereinafter referred to as a “coating film forming step”). A step of heating a coating film to form a polyimide film (hereinafter referred to as a "heating step").

(Coating film forming process)
First, the above-mentioned particle-dispersed polyimide precursor solution is prepared. Next, the particle-dispersed polyimide precursor solution is applied onto the substrate to form a coating film.
Examples of the substrate include a resin substrate; a glass substrate; a ceramic substrate; a metal substrate; and a composite material substrate in which these materials are combined. The substrate may include a peeling layer that has been peeled.
The method for applying the particle-dispersed polyimide precursor solution to the substrate is not particularly limited, and for example, various methods such as spray coating, rotary coating, roll coating, bar coating, slit die coating, and inkjet coating are used. Method can be mentioned.

As the substrate, various substrates can be used depending on the intended use. Examples thereof include various substrates applied to liquid crystal elements; semiconductor substrates on which integrated circuits are formed, wiring boards on which wiring is formed, printed circuit boards on which electronic components and wiring are provided; substrates for wire coating materials; and the like. ..

(Heating process)
Next, the coating film obtained in the above coating film forming step is subjected to a drying treatment. By this drying treatment, a film (a dry film before imidization) is formed.
The heating conditions for the drying treatment are, for example, preferably 10 minutes or more and 60 minutes or less at a temperature of 80 ° C. or higher and 200 ° C. or lower, and the higher the temperature, the shorter the heating time. When heating, it is also effective to blow hot air. Further, the heating may raise the temperature stepwise, or may raise the temperature without changing the heating rate.

Next, the dried film before imidization is heated to perform imidization treatment. As a result, a particle-dispersed polyimide film is formed on the substrate.
As the heating conditions for the imidization treatment, for example, by heating at 150 ° C. or higher and 400 ° C. or lower (preferably 200 ° C. or higher and 300 ° C. or lower) for 20 minutes or longer and 60 minutes or lower, an imidization reaction occurs and a polyimide film is formed. NS. During the heating reaction, the temperature may be gradually increased gradually or at a constant rate before the final temperature of heating is reached.

Through the above steps, a particle-containing polyimide film is formed. Then, if necessary, the particle-containing polyimide film is taken out from the substrate to obtain the particle-containing polyimide film. Further, the particle-containing polyimide film may be post-processed depending on the intended use.

<Manufacturing method of porous polyimide film>
In the method for producing a porous polyimide film according to the present embodiment, the particle-dispersed polyimide precursor solution according to the present embodiment is applied to form a coating film, and then the coating film is dried to form the polyimide precursor and the polyimide precursor. A first step of forming a film containing particles and a second step of heating the film to imidize the polyimide precursor to form a polyimide film, which comprises a process of removing the particles. It has two steps.
Here, according to the method for producing a porous polyimide film according to the present embodiment, a porous polyimide film having spherical pores can be obtained by using spherical particles.

Hereinafter, a method for producing a porous polyimide film according to this embodiment will be described.

(First step)
In the first step, first, the above-mentioned particle-dispersed polyimide precursor solution is prepared. Next, the particle-dispersed polyimide precursor solution is applied onto the substrate to form a coating film containing the polyimide precursor solution and the particles. Then, the coating film formed on the substrate is dried to form a film containing the polyimide precursor and the particles.

The substrate on which the particle-dispersed polyimide precursor solution is applied is not particularly limited. Examples thereof include resin substrates such as polystyrene and polyethylene terephthalate; glass substrates; ceramic substrates; metal substrates such as iron and stainless steel (SUS); composite material substrates in which these materials are combined. Further, if necessary, the substrate may be provided with a release layer by performing a release treatment with, for example, a silicone-based or fluorine-based release agent.

The method of applying the particle-dispersed polyimide precursor solution on the substrate is not particularly limited. For example, various methods such as a spray coating method, a rotary coating method, a roll coating method, a bar coating method, a slit die coating method, and an inkjet coating method can be mentioned.

The coating amount of the polyimide precursor solution and the polyimide precursor solution for obtaining the coating film containing the particles may be set to an amount that can obtain a predetermined film thickness.

After forming a coating film containing a polyimide precursor solution and particles, it is dried to form a coating film containing the polyimide precursor and particles. Specifically, a coating film containing a polyimide precursor solution and particles is dried by a method such as heat drying, natural drying, or vacuum drying to form a film. More specifically, the coating film is formed by drying the coating film so that the solvent remaining in the coating film is 50% or less, preferably 30% or less with respect to the solid content of the coating film.

(Second step)
The second step is a step of heating the film containing the polyimide precursor and particles obtained in the first step to imidize the polyimide precursor to form a polyimide film. The second step includes a process of removing the particles. A porous polyimide film is obtained through a treatment for removing particles.

In the second step, in the step of forming the polyimide film, specifically, the film containing the polyimide precursor and the particles obtained in the first step is heated to promote imidization, and further heated. A polyimide film is formed. As the imidization progresses and the imidization rate increases, it becomes difficult to dissolve in an organic solvent.

Then, in the second step, a process for removing particles is performed. The particles may be removed in the process of heating the coating film to imidize the polyimide precursor, or may be removed from the polyimide film after the imidization is completed (after imidization).
In the present embodiment, the step of imidizing the polyimide precursor is to heat the film containing the polyimide precursor and the particles obtained in the first step to proceed with the imidization, and the imidization is completed. The process of becoming the state before becoming the later polyimide film is shown.

The treatment for removing the particles is preferably performed when the imidization rate of the polyimide precursor in the polyimide film is 10% or more in the process of imidizing the polyimide precursor in terms of particle removability and the like. When the imidization rate is 10% or more, it is easy to maintain the morphology.

Next, the process of removing the particles will be described.
First, a process for removing resin particles will be described.
Examples of the treatment for removing the resin particles include a method of removing the resin particles by heating, a method of removing the resin particles with an organic solvent that dissolves the resin particles, a method of removing the resin particles by decomposition with a laser or the like, and the like. Of these, a method of removing the resin particles by heating and a method of removing the resin particles with an organic solvent that dissolves the resin particles are preferable.

As a method of removing by heating, for example, in the process of imidizing the polyimide precursor, the resin particles may be removed by decomposing the resin particles by heating for advancing the imidization. In this case, there is no operation of removing the resin particles with a solvent, which is advantageous for reducing the number of steps. On the other hand, depending on the type of resin particles, decomposition gas may be generated by heating. Then, due to this decomposition gas, the porous polyimide film may be broken or cracked. Therefore, in this case, it is desirable to adopt a method of removing the resin particles with an organic solvent that dissolves them.

Examples of the method of removing the resin particles with an organic solvent that dissolves the resin particles include a method of contacting (for example, immersing in a solvent) the organic solvent in which the resin particles are dissolved to dissolve and remove the resin particles. Immersion in a solvent in this state is preferable in that the dissolution efficiency of the resin particles is increased.

The organic solvent that dissolves the resin particles for removing the resin particles is particularly limited as long as it does not dissolve the polyimide film and the polyimide film that has been imidized and the resin particles are soluble. is not it. For example, ethers such as tetrahydrofuran (THF); aromatics such as toluene; ketones such as acetone; esters such as ethyl acetate;

When the resin particles are removed by dissolution and removal to make them porous, those dissolved in a general-purpose solvent such as tetrahydrofuran, acetone, toluene, and ethyl acetate are preferable. Water can also be used depending on the resin particles and the polyimide precursor used.
When the resin particles are removed by heating to make them porous, they are not decomposed at the drying temperature after coating, but are thermally decomposed at the temperature at which the film of the polyimide precursor is imidized. From this viewpoint, the thermal decomposition start temperature of the resin particles is preferably 150 ° C. or higher and 320 ° C. or lower, preferably 180 ° C. or higher and 300 ° C. or lower, and more preferably 200 ° C. or higher and 280 ° C. or lower.

Next, the process of removing the inorganic particles will be described.
Examples of the treatment for removing the inorganic particles include a method of removing the inorganic particles using a liquid that dissolves the inorganic particles but does not dissolve the polyimide precursor or the polyimide (hereinafter, may be referred to as “particle removing liquid”). The particle removing liquid is selected depending on the inorganic particles used. For example, aqueous solutions of acids such as hydrofluoric acid, hydrochloric acid, hydrobromic acid, boric acid, perchloric acid, phosphoric acid, sulfuric acid, nitrate, acetic acid, trifluoroacetic acid, citric acid; sodium hydroxide, potassium hydroxide, Examples thereof include aqueous solutions of bases such as tetramethylammonium hydroxide, sodium carbonate, potassium carbonate, ammonia, and the above-mentioned organic amines. Further, depending on the inorganic particles and the polyimide precursor used, water alone can be used.

In the second step, the heating method for heating the film obtained in the first step to promote imidization to obtain a polyimide film is not particularly limited. For example, a method of heating in two steps can be mentioned. When heating in two stages, specific heating conditions include the following.

The heating condition of the first stage is preferably a temperature at which the shape of the particles is maintained. Specifically, for example, the range of 50 ° C. or higher and 150 ° C. or lower is preferable, and the range of 60 ° C. or higher and 140 ° C. or lower is preferable. The heating time is preferably in the range of 10 minutes or more and 60 minutes or less. The higher the heating temperature, the shorter the heating time may be.

Examples of the heating conditions in the second stage include heating at 150 ° C. or higher and 450 ° C. or lower (preferably 200 ° C. or higher and 430 ° C. or lower) for 20 minutes or longer and 120 minutes or lower. By setting the heating conditions in this range, the imidization reaction can proceed further and a polyimide film can be formed. During the heating reaction, the temperature may be gradually increased gradually or at a constant rate before the final temperature of heating is reached.

The heating conditions are not limited to the above two-step heating method, and for example, a one-step heating method may be adopted. In the case of the one-step heating method, for example, the imidization may be completed only by the heating conditions shown in the second step above.

In the second step, from the viewpoint of increasing the pore size, it is preferable to perform a treatment for exposing the particles so that the particles are exposed. In the second step, the treatment for exposing the particles is preferably performed in the process of imidizing the polyimide precursor, or after the imidization and before the treatment of removing the particles.

In this case, for example, when a film is formed on a substrate using a particle-dispersed polyimide precursor solution, the particle-dispersed polyimide precursor solution is applied onto the substrate to form a coating film in which particles are embedded. Next, the coating film is dried to form a film containing a polyimide precursor and particles. The film formed by this method is in a state in which particles are buried. The film is heated to expose the particles from the polyimide film in the process of imidizing the polyimide precursor or after the imidization is completed (after imidization) before the particle removal treatment. May be given.

In the second step, the treatment for exposing the particles may be performed, for example, when the polyimide film is in the following state.
When the treatment for exposing the particles is performed when the imidization rate of the polyimide precursor in the polyimide film is less than 10% (that is, the polyimide film can be dissolved in a solvent), it is buried in the above-mentioned polyimide film. Examples of the treatment for exposing the particles include a treatment for wiping and a treatment for immersing the particles in a solvent. The solvent used at that time may be the same as or different from the solvent used for the particle-dispersed polyimide precursor solution of the present embodiment.

Further, when the imidization rate of the polyimide precursor in the polyimide film is 10% or more (that is, it is difficult to dissolve in water or an organic solvent), or when the polyimide film is in a state where imidization is completed. When performing the process of exposing the particles, a method of mechanically cutting with tools such as paper sand to expose the particles, or when the particles are resin particles, they are decomposed with a laser or the like to expose the resin particles. There is also a method.
For example, in the case of mechanical cutting, a part of the particles existing in the upper region of the particles buried in the polyimide film (that is, the region on the side away from the substrate of the particles) is present on the upper part of the particles. It is cut together with the polyimide film, and the cut particles are exposed from the surface of the polyimide film.

Then, the particles are removed from the exposed polyimide film by the above-mentioned particle removing treatment. Then, a porous polyimide film from which the particles have been removed can be obtained.

In the above, the manufacturing process of the porous polyimide film subjected to the treatment for exposing the particles in the second step has been described, but in terms of increasing the pore size, the treatment for exposing the particles in the first step is performed. May be given. In this case, in the first step, after obtaining the coating film, the particles may be exposed in the process of drying to form the film to expose the particles. By performing the treatment of exposing the particles, the pore size of the porous polyimide film is increased.

For example, in the process of obtaining a coating film containing a polyimide precursor solution and particles and then drying the coating film to form a film containing the polyimide precursor and particles, as described above, the film film is formed by the polyimide precursor. , It is in a state where it can be dissolved in a solvent. When the coating film is in this state, the particles can be exposed by, for example, a wiping treatment or a treatment of immersing in a solvent. Specifically, the polyimide precursor solution existing in the region equal to or larger than the thickness of the particle layer is present in the region equal to or larger than the thickness of the particle layer by performing a treatment for exposing the particle layer by, for example, wiping with a solvent. The polyimide precursor solution is removed. Then, the particles existing in the upper region of the particle layer (that is, the region on the side of the particle layer away from the substrate) are exposed from the surface of the coating film.
It is preferable to have a skin layer having no pores on the surface such as a gas separation membrane, and in this case, it is preferable not to perform a treatment for exposing the particles.

In the second step, the substrate for forming the above-mentioned film used in the first step may be peeled off when it becomes a dry film, and the polyimide precursor in the polyimide film is organic. It may be peeled off when it becomes difficult to dissolve in a solvent, or it may be peeled off when it becomes a film in which imidization is completed.

Through the above steps, a porous polyimide film can be obtained. Then, the porous polyimide film may be post-processed depending on the purpose of use.

Here, the imidization rate of the polyimide precursor will be described.
The partially imidized polyimide precursor has, for example, a structure having a repeating unit represented by the following general formula (V-1), the following general formula (V-2), and the following general formula (V-3). Precursors can be mentioned.

In the general formula (V-1), the general formula (V-2), and the general formula (V-3), A and B are synonymous with A and B in the formula (I). l represents an integer of 1 or more, and m and n independently represent an integer of 0 or 1 or more, respectively.

The imidization ratio of the polyimide precursor is based on the total number of bonded portions (2l + 2m + 2n) of the number of imide-closed bonding portions (2n + m) at the bonding portion of the polyimide precursor (reaction portion between the tetracarboxylic acid dianhydride and the diamine compound). Represents a ratio. That is, the imidization rate of the polyimide precursor is indicated by "(2n + m) / (2l + 2m + 2n)".

The imidization rate of the polyimide precursor (value of "(2n + m) / (2l + 2m + 2n)") is measured by the following method.

-Measurement of imidization rate of polyimide precursor-
-Preparation of polyimide precursor sample (i) The polyimide precursor composition to be measured is applied onto a silicone wafer in a film thickness range of 1 μm or more and 10 μm or less to prepare a coating film sample.
(Ii) The coating film sample is immersed in tetrahydrofuran (THF) for 20 minutes to replace the solvent in the coating film sample with tetrahydrofuran (THF). The solvent to be immersed is not limited to THF, and can be selected from a solvent that does not dissolve the polyimide precursor and can be miscible with the solvent component contained in the polyimide precursor composition. Specifically, alcohol solvents such as methanol and ethanol, and ether compounds such as dioxane can be used.
(Iii) The coating film sample is taken out from the THF, and N2 gas is sprayed onto the THF adhering to the surface of the coating film sample to remove it. A polyimide precursor sample is prepared by treating the coating film sample for 12 hours or more in a range of 5 ° C. or higher and 25 ° C. or lower under a reduced pressure of 10 mmHg or less to dry the coating film sample.

-Preparation of 100% imidized standard sample (iv) In the same manner as in (i) above, the polyimide precursor composition to be measured is applied onto a silicon wafer to prepare a coating film sample.
(V) The coating film sample is heated at 380 ° C. for 60 minutes to carry out an imidization reaction to prepare a 100% imidized standard sample.

-Measurement and analysis (vi) Infrared absorption spectra of 100% imidized standard sample and polyimide precursor sample are measured using a Fourier transform infrared spectrophotometer (FT-730 manufactured by Horiba Seisakusho). Ratio of absorption peaks (Ab'(1780 cm ^-1 )) ^{derived from imide bonds near 1780 cm -1} to aromatic ring-derived absorption peaks (Ab'(1500 cm ^-1 )) near 1500 cm -1 of the 100% imidized standard sample. Find I'(100).
(Vii) In the same manner, was measured on the polyimide precursor sample, relative to the aromatic ring derived absorption peak near ^{1500cm -1 (Ab (1500cm -1)} ), absorption peaks derived from imide bond near 1780 cm ^-1 (Ab ( The ratio I (x) of 1780 cm ^{-1)) is obtained.}

Then, using the measured absorption peaks I'(100) and I (x), the imidization rate of the polyimide precursor is calculated based on the following formula.
Formula: Imidization rate of polyimide precursor = I (x) / I'(100)
-Formula: I'(100) = (Ab'(1780 cm ^-1 )) / (Ab'(1500 cm ^-1 ))
-Formula: I (x) = (Ab (1780 cm ^-1 )) / (Ab (1500 cm ^-1 ))

The measurement of the imidization rate of the polyimide precursor is applied to the measurement of the imidization rate of the aromatic polyimide precursor. When measuring the imidization rate of the aliphatic polyimide precursor, a peak derived from a structure that does not change before and after the imidization reaction is used as an internal standard peak instead of the absorption peak of the aromatic ring.

<Porous polyimide film>
Hereinafter, the porous polyimide film of the present embodiment will be described.

The porous polyimide film according to this embodiment contains a polyimide having a repeating unit represented by the following formula (III). The porous polyimide film according to this embodiment has spherical pores.

In formula (III), A is a tetravalent organic group, B is a divalent organic group, and at least one of the following conditions (1) and (2) is satisfied.
(1): A has a molar ratio (A1 / A2) of a tetravalent organic group A1 having one aromatic ring and a tetravalent organic group A2 having two or more aromatic rings of 5/95 or more and 95/5. It is as follows.
(2): B has a molar ratio (B1 / B2) of a divalent organic group B1 having one aromatic ring and a divalent organic group B2 having two or more aromatic rings of 5/95 or more and 95/5. It is as follows.

A1 is a group represented by A1-1 below, and it is preferable that A2 is any one group selected from the group shown by A2-1 below to A2-5 below.

Further, B1 has a group represented by B1-1 below or B1-2 below, and B2 is preferably any one group selected from the group shown by B2-1 below to B2-7 below. ..

When the porous polyimide film according to the present embodiment satisfies the above condition (1), it satisfies any of the following conditions (III-3) and the following (III-4), and satisfies the above condition (2). When, it is preferable to satisfy any of the conditions shown in the following (III-1) and the following (III-2).

(III-1): A1 / A2 is 60/40 or more and 100/0 or less, and B1 / B2 is 5/95 or more and 40/60 or less (III-2): A1 / A2 is 0/100 or more and 40/60. Below, B1 / B2 is 60/40 or more and 95/5 or less (III-3): The A1 / A2 is 5/95 or more and 40/60 or less, and the B1 / B2 is 60/40 or more and 100/0. The following (III-4): The A1 / A2 is 60/40 or more and 95/5 or less, and the B1 / B2 is 0/100 or more and 40/60 or less.

In the porous polyimide film according to the present embodiment, the conditions shown in (III-1) to (III-4) above are the conditions shown in the following (IV-1) to (IV-4), respectively. Is more preferable.
(IV-1): A1 / A2 is 100/0 and B1 / B2 is 5/95 or more and 30/70 or less (IV-2): A1 / A2 is 0/100 and B1 / B2 is 70 / 30 or more and 95/5 or less (IV-3): A1 / A2 is 5/95 or more and 30/70 or less, and B1 / B2 is 100/0.
(IV-4): A1 / A2 is 70/30 or more and 95/5 or less, and B1 / B2 is 0/100.

In the porous polyimide film according to the present embodiment, A1 is a group represented by A1-1, A2 is a group represented by A2-1, and B1 is a group represented by B1-1. It is preferable that B2 is the group represented by B2-1.

(Characteristics of porous polyimide film)
The porous polyimide film of the present embodiment is not particularly limited, but has a porosity of 30% or more. Further, the porosity is preferably 40% or more, and more preferably 50% or more. The upper limit of the porosity is not particularly limited, but is preferably in the range of 90% or less.

The shape of the holes is spherical. In the present specification, the "spherical shape" in the pores includes both a spherical shape and a substantially spherical shape (a shape close to a spherical shape). Specifically, the spherical shape means that the ratio of particles having a major axis to minor axis ratio (major axis / minor axis) of 1 or more and 1.5 or less is present at 90% or more. The closer the ratio of the major axis to the minor axis is, the closer it becomes to a spherical shape.
Further, it is preferable that the vacancies have a shape in which the vacancies are connected to each other and connected to each other. The pore diameter of the portion where the pores are connected to each other is often, for example, 1/100 or more and 1/2 or less of the maximum diameter of the pores, and preferably 1/50 or more and 1/3 or less. , 1/20 or more and 1/4 or less is more preferable. Specifically, the average value of the pore diameters of the portions where the pores are connected to each other and connected to each other is preferably 5 nm or more and 1500 nm or less.

The average value of the pore diameter is not particularly limited, but is preferably in the range of 0.1 μm or more and 0.5 μm or less, preferably in the range of 0.25 μm or more and 0.48 μm or less, and 0.25 μm or more and 0.45 μm or less. It is more preferable that the range is.

In the porous polyimide film according to the present embodiment, the ratio of the maximum diameter to the minimum diameter of the pores (the ratio of the maximum value to the minimum value of the pore diameter) is 1 or more and 2 or less. It is preferably 1 or more and 1.9 or less, and more preferably 1 or more and 1.8 or less. Within this range, it is more preferable that it is close to 1. Within this range, variation in pore diameter is suppressed. Further, when the porous polyimide film of the present embodiment is applied to, for example, a battery separator of a lithium ion battery, the movement of ions during charging and discharging becomes close to uniform, suppressing the formation of lithium crystals (dendrites) and suppressing the formation of lithium crystals (dendrites). By suppressing local fatigue, it has a great effect on improving battery stability and life. Further, as another example, when applied to a filter, it is possible to improve the filtration efficiency without reducing the filtration rate.
The "ratio of the maximum diameter of the pores to the minimum diameter" is a ratio represented by a value obtained by dividing the maximum diameter of the holes by the minimum diameter (that is, the maximum value / the minimum value of the pore diameter).

The maximum, minimum, and average values of the pore diameters, the average value of the pore diameters where the pores are connected to each other, and the major and minor diameters of the pores are observed with a scanning electron microscope (SEM). And the value to be measured. Specifically, first, a porous polyimide film is cut out and a sample for measurement is prepared. Then, this measurement sample is observed and measured by the VE SEM manufactured by KEYENCE Co., Ltd. with the image processing software provided as standard equipment. Observation and measurement are performed on 100 pieces of each of the pores in the cross section of the sample for measurement, and the average value, the minimum diameter, the maximum diameter, and the arithmetic mean diameter of each are obtained. If the shape of the hole is not circular, the longest part is the diameter. In addition, for each of the above-mentioned pores, the major axis and minor axis are observed and measured with the standard image processing software using VE SEM manufactured by KEYENCE, and the major axis / minor axis ratio is determined. calculate.

The film thickness of the porous polyimide film is not particularly limited, but is preferably 15 μm or more and 500 μm or less.

The porous polyimide film according to the present embodiment may contain a resin other than the polyimide resin. By containing a small amount of a resin other than the polyimide resin, flexibility is easily imparted to the porous polyimide film, and damage to the film due to a physical load (stress) such as bending is easily suppressed.

The content of the resin other than the polyimide resin contained in the porous polyimide film is preferably 0.005% by mass or more and 1% by mass or less, and 0.008% by mass or more 1 with respect to the entire porous polyimide film. More preferably, it is 0.01% by mass or more, and most preferably 0.9% by mass or less.

If the particles used are resin particles, a resin other than the polyimide resin can be contained in the porous polyimide film as a residual component derived from the resin particles without adding a resin other than the polyimide resin. In this case, the amount of the resin other than the polyimide resin contained in the porous polyimide film is, for example, the amount of the resin particles used in the first step of the above-mentioned manufacturing step of the porous polyimide film, and the removal of the resin particles in the second step. It can be controlled by processing conditions and the like.
The presence state of the resin other than the polyimide resin contained in the porous polyimide film is not particularly limited. For example, it may be present inside the porous polyimide film and at least one of the surfaces of the porous polyimide film (including the surface of the pores of the porous polyimide film).

-Method for checking the content of resins other than polyimide resin-
The presence and content of a resin other than polyimide in the porous polyimide film can be measured, for example, by analyzing and quantifying the components detected by thermal decomposition gas chromatograph mass spectrometry (GC-MS). Specifically, the measurement is performed as follows.
The components contained in the porous polyimide film are analyzed by a gas chromatograph mass spectrometer (GCMS QP-2010 manufactured by Shimadzu Corporation) equipped with a drop-type thermal decomposition device (PY-2020D manufactured by Frontier Lab Co., Ltd.).
For the components of the resin other than polyimide, 0.20 mg of the porous polyimide film is accurately weighed and measured at a thermal decomposition temperature of 600 ° C. For resins other than polyimide, the chromatograms at a pyrolysis temperature of 400 ° C. and a pyrolysis temperature of 600 ° C. were compared. It can be confirmed that it is derived from the polymer.
Pyrolysis device: PY-2020D manufactured by Frontier Lab
Gas Chromatograph Mass Spectrometer: Shimadzu, GCMS QP-2010
Pyrolysis temperature: 400 ° C, 600 ° C
Gas chromatography introduction temperature: 280 ° C
Inject method: Split ratio 1:50
Column: Frontier Lab, Ultra ALLOY-5,0.25 μm, 0.25 μm ID, 30 m
Gas chromatograph temperature program: 40 ° C → 20 ° C / min → 280 ° C / 10 min retention Mass range: EI, m / z = 29-600 (content of resin other than polyimide resin)

As another method for quantifying the amount of the resin other than the polyimide resin contained in the porous polyimide film, a resin other than the polyimide resin is subjected to liquid chromatograph (HPLC), nuclear magnetic resonance (NMR), etc. after hydrolyzing the polyimide resin. There is also a method of analyzing the components.

(Use of porous polyimide film)
Applications to which the porous polyimide film of the present embodiment is applied include, for example, a battery separator such as a lithium battery; a separator for an electrolytic condenser; an electrolyte membrane such as a fuel cell; a battery electrode material; a gas or liquid separation membrane; Dielectric constant materials; filter membranes; and the like.

When the porous polyimide film according to the present embodiment is applied to, for example, a battery separator, the movement of ions during charging / discharging becomes nearly uniform, and the formation of lithium crystals (dendrites) is suppressed or locally. It is considered that the suppression of fatigue contributes to the improvement of battery stability and life.
It is presumed that this is because the shape of the pores and the variation in the pore diameter of the porous polyimide film of the present embodiment are suppressed.
Further, for example, when applied to a battery electrode material, it is considered that the capacity of the battery increases because the chance of contact with the electrolytic solution increases. It is presumed that this is because the amount of the material such as carbon black for the electrode contained in the porous polyimide film exposed on the surface of the pore size of the porous polyimide film and the surface of the film increases.
Further, for example, it is also possible to fill the pores of the porous polyimide film with, for example, an ionic gel obtained by gelling a so-called ionic liquid and apply it as an electrolyte membrane. Since the process is simplified by the manufacturing method of the present embodiment, it is considered that a lower cost electrolyte membrane can be obtained.
Further, as another example, when applied to a filter, it is considered possible to improve the filtration efficiency without lowering the filtration rate.

In the particle-dispersed polyimide precursor solution according to the present embodiment, in producing a porous polyimide film using the particle-dispersed polyimide precursor solution, the polyimide in a state containing particles after the first step described above. Damage when the film or polyimide film is peeled off from the base material and handled is easily suppressed. Further, the obtained porous polyimide film has spherical pores, has high uniformity of gas permeability, has high heat softening resistance, and is easily suppressed from being damaged by bending.

The reason why the porous polyimide film according to the present embodiment can obtain these advantages is not clear, but it is presumed as follows.
When a particle-dispersed polyimide precursor solution using a polyimide precursor synthesized by using only one tetracarboxylic acid dianhydride and one diamine compound is used, aggregation of particles in the film is suppressed and the dry film is peeled off. It has been found that all of the desired properties such as handleability, heat softening resistance of the porous polyimide film, and bending resistance cannot be satisfied.

For example, a polyimide precursor obtained by synthesizing pyromellitic acid dianhydride and 4,4'-diaminodiphenyl ether, and a polyimide obtained by synthesizing biphenyltetracarboxylic acid dianhydride and p-phenylenediamine. In the precursor, only a monomer having one aromatic ring is used for tetracarboxylic acid dianhydride or diamine. Therefore, it is considered that the obtained polyimide precursor is too rigid, so that the interfacial adhesion between the polyimide precursor and the particles tends to decrease. As a result, when the polyimide film or the polyimide film containing particles is peeled off from the base material and handled after the first step described above, it is considered that the film or the film is easily damaged. Further, it is considered that the fine cracks generated at the interface with the particles (or pores) are difficult to be repaired by heating due to the shrinkage during imidization, and the porous polyimide film is damaged when it is bent. On the other hand, heat softening resistance can be easily obtained.

Further, for example, in the polyimide precursor obtained by synthesizing biphenyltetracarboxylic acid dianhydride and 4,4'-diaminodiphenyl ether, both tetracarboxylic acid dianhydride and diamine are single amounts having two or more aromatic rings. I'm using my body. Therefore, it is considered that the rigidity of the polyimide precursor is easily reduced, so that the interfacial adhesion between the polyimide precursor and the particles is easily improved. As a result, when the polyimide film or the polyimide film containing particles is peeled off from the base material and handled after the first step described above, damage to the film or film can be suppressed. In addition, since fine cracks generated at the interface with particles (or pores) due to shrinkage during imidization are repaired by heating, it is considered that breakage when the porous polyimide film is bent is suppressed. .. On the other hand, the heat softening resistance tends to decrease.

On the other hand, in the present embodiment, at least one of the tetracarboxylic acid dianhydride and the diamine compound contains a monomer having one aromatic ring and a monomer having two or more aromatic rings in a specific ratio. A polyimide precursor having a polymerized structure is used. As a result, the monomer having one aromatic ring imparts rigidity to the polyimide precursor, so that the heat softening resistance of the porous polyimide film can be obtained. Further, it is suppressed that the monomer having two or more aromatic rings imparts flexibility to the polyimide precursor and lowers the interfacial adhesion between the polyimide precursor and the particles, and the above-mentioned first step Later, it is considered that the damage caused when the polyimide film or the polyimide film containing particles is peeled off from the base material and handled is suppressed, and further, the breakage due to bending of the porous polyimide film is also suppressed.

Examples will be described below, but the present invention is not limited to these examples. In the following description, unless otherwise specified, "parts" and "%" are all based on mass.

(Evaluation of particle dispersibility in particle-dispersed polyimide precursor solution)
Particle dispersion The particle dispersion of the polyimide precursor solution was evaluated. The specific method is as follows.

[Evaluation over time]
The particle-dispersed polyimide precursor solution was stored in a constant temperature bath at 60 ° C., and the dispersed state of the particles was visually evaluated. When the dispersion of particles deteriorates, layer separation of the solution and sedimentation of the particles are observed.

-Evaluation criteria-
A +: No change in the solution even after the start of storage for more than 2 months A: Layer separation or particle settling is observed within more than 1 month and 2 months after the start of storage B: Layer separation or particles within more than 2 weeks and 1 month after the start of storage C: Layer separation or particle sedimentation is observed within 2 weeks after the start of storage.

[Repeated aging evaluation by heating and refrigerating]
The particle-dispersed polyimide precursor solution was allowed to stand in a constant temperature bath at 60 ° C. for 1 day, and then left in a constant temperature bath at 0 ° C. for 1 day. This storage cycle was set as one cycle, and the storage cycle was repeated to visually evaluate the dispersed state of the particles. When the dispersion of particles deteriorates, layer separation of the solution and sedimentation of the particles are observed.

-Evaluation criteria-
A +: No change in solution even after more than 10 cycles of storage A: Layer separation or particle settling is seen within more than 7 cycles of storage 10 cycles B: Layer separation or particle settling is seen within more than 5 cycles of storage and 7 cycles C : Layer separation or particle settling is observed within 5 storage cycles

(Analysis of the content of resins other than polyimide in the porous polyimide film)
The content of each component was measured using GC-MS by the method described above.

(Particle agglutination of particle-containing polyimide film)
1) Particle-containing polyimide film formed immediately after the particle-containing polyimide precursor solution was prepared, 2) Particle-containing film formed using the particle-containing polyimide precursor solution obtained by repeating the above-mentioned repeated evaluation over time by heating and refrigeration for 5 cycles. Particle aggregation was evaluated for each of the two types of polyimide films. The specific method is as follows.
The area of the particle-containing polyimide film 1 cm ² square was observed with a microscope magnification of 100, and rated the particle agglomeration on the following criteria.

-Evaluation criteria-
A +: Less than 5 agglutinations less than 10 μm A: 5 or more agglutinations less than 10 μm B: Agglutinations of 10 μm or more and less than 50 μm C: Agglutinations of 50 μm or more are seen

(Handability after peeling of particle-containing polyimide film)
A particle-containing polyimide precursor solution was applied to a 5 cm square PET substrate that had been released with a silicone-based mold release agent using an applicator so that the film thickness after firing was 25 μm, and the temperature was 70 ° C. After air-drying for 1 hour, the film was peeled off from the substrate to obtain a self-supporting film of a particle-containing polyimide film having a film thickness of 25 μm. The handleability of this particle-containing polyimide film was evaluated according to the following criteria.

-Evaluation criteria-
A +: Cracking / breaking occurs when the film is rolled along a cylinder with an inner diameter of less than 5 cm A: Cracking / breaking occurs when the film is rolled along a cylinder with an inner diameter of 5 cm or more and less than 10 cm B: For a cylinder with an inner diameter of 10 cm or more If the film is rolled along it, it will crack or break. C: If the film is rolled even a little, it will crack or break.

(Porosity shape and pore distribution of porous polyimide film)
As an index of the hole shape, the ratio of the major axis to the minor axis was calculated, and the ratio of the major axis to the minor axis was calculated to be 1 or more and 1.5 or less. In addition, the ratio of the maximum diameter to the minimum diameter was calculated as an index of the pore distribution. All calculations were performed by the methods described above.

-Evaluation criteria for the ratio of major axis to minor axis-
A +: 95% or more A: 90% or more and less than 95% B: 85% or more and less than 90% C: less than 85%

-Evaluation criteria for the ratio of maximum diameter to minimum diameter-
A +: 1 or more and 1.8 or less A: 1.8 or more and 1.9 or less B: 1.9 or more and 2 or less C: More than 2

(Heat softening resistance of porous polyimide film)
The prepared porous polyimide film was heated on a hot plate at 400 ° C./410 ° C./420 ° C. for 3 hours, respectively, and the pore shape of the heated porous film was observed by the above-mentioned SEM observation. Evaluated in.

-Evaluation criteria-
A +: No change in pore shape and pore diameter even when heated at 420 ° C A: Changes in pore shape are seen when heated at 420 ° C, but the pore diameter is the same B: Changes in pore shape when heated at 410 ° C Seen and the pore diameter changes C: The pore shape changes when heated at 400 ° C, and the pore diameter changes.

(Variation in gas permeability of porous polyimide film)
A porous polyimide film produced cut out in the ^second corner 1cm, and the evaluation sample was 10 sheets collected. Set the sample by sandwiching it between the funnel and the base of the filter holder for vacuum filtration (ADVANTEC, KGS-04), and immerse the filter holder with the sample in the water upside down to determine in advance in the funnel. Filled with water to the desired position. An air pressure of 0.5 atm (0.05 MPas) is applied from the side where the funnel of the base and the base are not in contact, and the time (seconds) for 50 ml of air to pass is measured, and the maximum value of the gas permeation time is measured. The minimum and average values were calculated, and the variation in gas permeability was calculated from the following formula. The smaller this value is, the smaller the variation in gas permeability is, and the better the characteristics are.
(Equation) Variation in gas permeability = (maximum value of gas permeation time-minimum value of gas permeation time) / average value of gas permeation time

-Evaluation criteria-
A +: Variation is less than 0.3 A: Variation is 0.3 or more and less than 0.4 B: Variation is 0.4 or more and less than 0.5 C: Variation is 0.5 or more

(Damage after bending of porous polyimide film)
The prepared porous polyimide film having a size of 5 cm square is folded in half by folding the surface that was in contact with the base material during film formation in a mountain fold, and a load of 500 g is applied from the surface that was in contact with the base material during film formation. It was allowed to stand for 24 hours. After that, the part where the load was released and bent was visually observed and evaluated according to the following criteria.
-Evaluation criteria-
A +: No bending marks and no film damage A: Bending marks but no film damage B: Bending marks and film cracking in part of the bent part Seen C: The film cracks at the bent part

<Synthesis example 1>
(Preparation of PMMA particle dispersion liquid-1)
Mix 670 parts by mass of methyl methacrylate, 25.0 parts by mass of surfactant Dowfax2A1 (47% solution, manufactured by Dow Chemical Co., Ltd.), and 670 parts by mass of ion-exchanged water, and stir with a dissolver at 1,500 rpm for 30 minutes. Emulsification was performed to prepare a monomer emulsified solution. Subsequently, 1.10 parts by mass of Dowfax2A1 (47% solution, manufactured by Dow Chemical Co., Ltd.) and 1500 parts by mass of ion-exchanged water were charged into the reaction vessel. After heating to 75 ° C. under a nitrogen stream, 75 parts by mass of the monomer emulsion was added, and then a polymerization initiator solution in which 15 parts by mass of ammonium persulfate was dissolved in 98 parts by mass of ion-exchanged water was added dropwise over 10 minutes. bottom. After the reaction was carried out for 50 minutes after the dropping, the remaining monomer emulsion was added dropwise over 220 minutes, and after further reacting for 50 minutes, the mixture was cooled to obtain PMMA particle dispersion -1 which is a dispersion of resin particles. .. The solid content concentration was 22.8% by mass. The average particle size of the resin particles was 0.40 μm.

<Synthesis example 2>
(Preparation of PMMA particle dispersion-2)
Mix 670 parts by mass of methyl methacrylate, 31.4 parts by mass of surfactant Dowfax2A1 (47% solution, manufactured by Dow Chemical Co., Ltd.), and 670 parts by mass of ion-exchanged water, and stir with a dissolver at 1,500 rpm for 30 minutes. Emulsification was performed to prepare a monomer emulsified solution. Subsequently, 1.10 parts by mass of Dowfax2A1 (47% solution, manufactured by Dow Chemical Co., Ltd.) and 1500 parts by mass of ion-exchanged water were charged into the reaction vessel. After heating to 75 ° C. under a nitrogen stream, 75 parts by mass of the monomer emulsion was added, and then a polymerization initiator solution in which 15 parts by mass of ammonium persulfate was dissolved in 98 parts by mass of ion-exchanged water was added dropwise over 10 minutes. bottom. After the reaction was carried out for 50 minutes after the dropping, the remaining monomer emulsion was added dropwise over 220 minutes, and after further reacting for 50 minutes, the mixture was cooled to obtain a PMMA particle dispersion 2 which is a dispersion of resin particles. .. The solid content concentration was 23.2% by mass. The average particle size of the resin particles was 0.32 μm.

<Synthesis example 3>
(Synthesis of PSt particle dispersion liquid-1)
Mix 670 parts by mass of styrene, 17.0 parts by mass of surfactant Dowfax2A1 (47% solution, manufactured by Dow Chemical Co., Ltd.), and 670 parts by mass of ion-exchanged water, and stir and emulsify with a dissolver at 1,500 rpm for 30 minutes. This was carried out to prepare a monomer emulsion. Subsequently, 1.10 parts by mass of Dowfax2A1 (47% solution, manufactured by Dow Chemical Co., Ltd.) and 1500 parts by mass of ion-exchanged water were charged into the reaction vessel. After heating to 75 ° C. under a nitrogen stream, 75 parts by mass of the monomer emulsion was added, and then a polymerization initiator solution in which 15 parts by mass of ammonium persulfate was dissolved in 98 parts by mass of ion-exchanged water was added dropwise over 10 minutes. bottom. After the reaction was carried out for 50 minutes after the dropping, the remaining monomer emulsion was added dropwise over 220 minutes, and the reaction was further carried out for 50 minutes and then cooled to obtain a PSt particle dispersion liquid-1. The solid content concentration was 22.8% by mass. The average particle size of the resin particles was 0.42 μm.

<Synthesis example 4>
(Preparation of PSt particle powder-1)
The PSt particle dispersion liquid-1 obtained in Synthesis Example 3: 100 parts by mass of resin particles (containing 338.6 parts by mass of water) in terms of solid content was freeze-dried, and the powder was taken out. After adding 20 parts by mass of deionized water to 100 parts by mass of the obtained powder and stirring, the particles were precipitated by centrifugation and the supernatant was removed. After repeating this operation three times, it was freeze-dried again to take out PSt particle powder-1.

<Example A1>
(Preparation of water-based particle-dispersed polyimide precursor solution (A1) by the above-mentioned preparation method (ii))
PMMA particle dispersion-1: 100 g of resin particles (containing 340.6 g of water) in terms of solid content, ion-exchanged water: 42.74 g, N-methylpyrrolidone: 2.25 g, p-phenylenediamine (molecular weight 108.14) ): 9.38 g (0.086735 mol), 4,4'-diaminodiphenyl ether (molecular weight 200.24): 0.91 g (0.004565 mol), 3,3', 4,4'-biphenyltetracarboxylic acid Dianoxide (molecular weight 294.22): 26.86 g (0.0913 mol) was added, and the mixture was stirred and dispersed at 20 ° C. for 10 minutes. Then, N-methylmorpholine (organic amine compound): 27.7 g (0.2739 mol) was slowly added, and the mixture was dissolved and reacted by stirring for 24 hours while maintaining the reaction temperature at 60 ° C. to carry out the reaction of the aqueous system. A particle-dispersed polyimide precursor solution (A1) was obtained. Particle mass / (mass of total solids) is 0.73, solids concentration: 25% by mass. The obtained particle-dispersed polyimide precursor solution (A1) was diluted with water and the particle size distribution was measured by the method described above. As a result, a single particle size of 0.40 μm was measured as in PMMA particle dispersion liquid-1. It had a peak and was in a good dispersion state. The volume particle size distribution index (GSDv) calculated by the method described above was 1.16.
Under the above conditions, the amount of PMMA particle dispersion-1 added is calculated so that the mass of PMMA particles (solid content) / the mass of the total solid content of the solution is 0.73. It is an amount calculated so that the total amount of tetracarboxylic dianhydride and the total amount of diamine are the same mole. The amount of p-phenylenediamine and 4,4'-diaminodiphenyl ether added is an amount calculated so that the molar ratio of both (p-phenylenediamine / 4,4'-diaminodiphenyl ether) is 95/5. The amount of N-methylpyrrolidone is an amount calculated to be 15% by mass with respect to the solid content of the particle-dispersed polyimide precursor solution. The amount of the added ion-exchanged water is an amount calculated so that the solid content concentration of the particle-dispersed polyimide precursor solution is 25% by mass. The amount of N-methylmorpholine added is calculated to be 150 mol% with respect to the carboxy group of the polyimide precursor (polyamic acid) produced.

<Examples A2 to A24, A26 to A30, A32 to A34, Comparative Examples A1 to A8>
An aqueous polyimide precursor solution was prepared and film formation was evaluated in the same manner as in Example A1 except that the materials used and various ratios were changed to the values shown in Tables 1 to 3.

<Synthesis example 5>
(Synthesis of water-based polyimide precursor solution-1)
Ion-exchanged water: 35.12 parts by mass, p-phenylenediamine (molecular weight 108.14): 6.49 parts by mass, 4,4'-diaminodiphenyl ether (molecular weight 200.24): 3.00 parts by mass, 3,3 ', 4,4'-Biphenyltetracarboxylic acid dianhydride (molecular weight 294.22): 21.18 parts by mass was added, and the mixture was stirred at 20 ° C. for 10 minutes to disperse. Then, 21.85 parts by mass of N-methylmorpholine (organic amine compound) was slowly added, and the mixture was dissolved and reacted by stirring for 24 hours while maintaining the reaction temperature at 60 ° C. to carry out an aqueous polyimide precursor solution. I got -1.
Under the above conditions, the molar ratio of the total amount of tetracarboxylic dianhydride to the total amount of diamine is 0.96 / 1. The amount of p-phenylenediamine and 4,4'-diaminodiphenyl ether added is an amount calculated so that the molar ratio of both (p-phenylenediamine / 4,4'-diaminodiphenyl ether) is 80/20. The amount of the added ion-exchanged water is an amount calculated so that the solid content concentration (excluding the organic amine compound) of the obtained polyimide precursor solution is 35% by mass. The amount of N-methylmorpholine added is calculated to be 150 mol% with respect to the carboxy group of the polyimide precursor (polyamic acid) produced.

<Example A31>
(Preparation of water-based particle-dispersed polyimide precursor solution (A31) by the above-mentioned preparation method (i))
Ion-exchanged water: 1.16 g and N-methylpyrrolidone: 3.85 g were added to the aqueous polyimide precursor solution-1: 7.00 g (20 g as a solution) obtained in Synthesis Example 5 above. , Mixing while heating to 60 ° C. Then, PMMA particle dispersion-1: 18.93 g of resin particles (containing 77.2 g of water) in terms of solid content was added, and after heating to 60 ° C., a stirrer "Awatori Rentaro" (manufactured by Shinky) The mixture was mixed and stirred at 2000 rpm for 2 minutes and at 2200 rpm for 2 minutes. Then, the mixture was heated to 60 ° C. again, and the mixture was further mixed and stirred at 2000 rpm for 2 minutes and 2200 rpm for 2 minutes to obtain an aqueous particle-dispersed polyimide precursor solution (A31). The mass of the particles / (mass of the total solid content of the solution) was 0.73, and the solid content concentration was 24% by mass. The obtained particle-dispersed polyimide precursor solution (A31) was diluted with water, and the particle size distribution was measured by the method described above. As a result, a single particle size of 0.40 μm was measured as in PMMA particle dispersion liquid-1. It had a peak and was in a good dispersion state. The volume particle size distribution index (GSDv) calculated by the method described above was 1.16.
Under the above conditions, the amount of PMMA particle dispersion-1 added is calculated so that the mass of PMMA particles (solid content) / the mass of the total solid content of the solution is 0.73. The amount of N-methylpyrrolidone is an amount calculated to be 15% by mass with respect to the solid content of the particle-dispersed polyimide precursor solution. The amount of the added ion-exchanged water is an amount calculated so that the solid content concentration of the particle-dispersed polyimide precursor solution is 24% by mass.

<Example A25>
An aqueous polyimide precursor solution was prepared and film formation was evaluated in the same manner as in Example A31, except that the materials used and various ratios were changed to the values shown in Table 3.

<Example B1>
(Preparation of particle-dispersed polyimide precursor solution (B1) in an organic solvent)
N, N-Dimethylacetamide: 144.33 parts by mass, p-phenylenediamine (molecular weight 108.14): 9.38 parts by mass, 4,4'-diaminodiphenyl ether (molecular weight 200.24): 0.91 parts by mass It was added and stirred at 50 ° C. for 10 minutes to disperse. Then, 3,3', 4,4'-biphenyltetracarboxylic acid dianhydride (molecular weight 294.22): 25.79 parts by mass was added, and the mixture was dissolved by stirring for 15 hours while maintaining the reaction temperature at 50 ° C. , The reaction was carried out to obtain a polyimide precursor solution in an organic solvent having a solid content concentration of 20% by mass.
Under the above conditions, the molar ratio of the total amount of tetracarboxylic dianhydride to the total amount of diamine is 0.96 / 1. The amount of p-phenylenediamine and 4,4'-diaminodiphenyl ether added is an amount calculated so that the molar ratio of both (p-phenylenediamine / 4,4'-diaminodiphenyl ether) is 95/5. The amount of N, N-dimethylacetamide added is an amount calculated so that the solid content concentration of the obtained polyimide precursor solution is 20% by mass.

Next, the polyimide precursor solution in the obtained organic solvent: 100 parts by mass (N, N-dimethylacetamide: 80 parts by mass), N, N-dimethylacetamide: 6.42 parts by mass, triglime: 86. .42 parts by mass was added, and the mixture was mixed and stirred at 2000 rpm for 3 minutes and 2200 rpm for 3 minutes with a stirrer "Awatori Rentaro" (manufactured by Shinky). Then, PSt particle powder-1: 54.08 parts by mass and polyoxyethylene dodecyl ether: 0.54 parts by mass obtained in Synthesis Example 4 were added, and the mixture was further mixed and stirred at 2000 rpm for 5 minutes and 2200 rpm for 5 minutes. , A child-dispersed polyimide precursor solution (B1) in an organic solvent was obtained. The mass of the particles / (mass of the total solid content of the solution) is 0.73, and the solid content concentration is 30% by mass.
The obtained particle-dispersed polyimide precursor solution (B1) was diluted with an organic solvent having the same composition, and the particle size distribution was measured by the method described above. As a result, the average particle size was 0. It had a single peak of 42 μm and was in a good dispersion state. The volume particle size distribution index (GSDv) calculated by the method described above was 1.15.
Under the above conditions, the amount of PSt particle powder-1 added is an amount calculated so that the mass of PMMA particles (solid content) / the mass of the total solid content of the solution is 0.73. The amount of N, N-dimethylacetamide and triglime added is calculated so that the solid content concentration is 30% by mass and the mass ratio of N, N-dimethylacetamide / triglime is 50/50.

<Examples B2 to B11, Comparative Examples B1 to B3>
A polyimide precursor solution in an organic solvent was prepared and film formation was evaluated in the same manner as in Example B1 except that the materials used and various ratios were changed to the values shown in Table 4.

<Manufacturing of porous polyimide film>
(When removing particles by thermal decomposition)
The particle-containing polyimide precursor solution obtained above was applied to a glass substrate having a size of 76 mm × 52 mm using an applicator so that the film thickness after firing was 25 μm, and air-dried at 70 ° C. for 1 hour. After that, the temperature was raised from 70 ° C. to the temperature shown in each table at a heating rate of 5 ° C./min, and the temperature was further maintained at that temperature for 30 minutes. Then, it was allowed to cool to room temperature and immersed in water to obtain a porous polyimide film.

(When removing particles by dissolution)
The particle-containing polyimide precursor solution obtained above was applied to a glass substrate having a size of 76 mm × 52 mm using an applicator so that the film thickness after firing was 25 μm, and air-dried at 70 ° C. for 1 hour. After that, it was immersed in the solvent shown in each table for 2 hours. After air-drying the membrane, the temperature was raised from 70 ° C. to the temperature shown in Table 1 at a heating rate of 5 ° C./min, and the temperature was further maintained at that temperature for 30 minutes. Then, it was allowed to cool to room temperature and immersed in water to obtain a porous polyimide film.

<Reference example B1>
(Preparation of porous polyimide film with non-spherical pores)
N, N-dimethylacetamide: 72.38 parts by mass, p-phenylenediamine (molecular weight 108.14): 6.08 parts by mass, 4,4'-diaminodiphenyl ether (molecular weight 200.24): 3.75 parts by mass Was added and stirred at 50 ° C. for 10 minutes to disperse. Then, 3,3', 4,4'-biphenyltetracarboxylic acid dianhydride (molecular weight 294.22): 21.18 parts by mass was added, and the mixture was dissolved by stirring for 15 hours while maintaining the reaction temperature at 50 ° C. , The reaction was carried out to obtain a polyimide precursor solution in an organic solvent having a solid content concentration of 30% by mass.
Under the above conditions, the molar ratio of the total amount of tetracarboxylic dianhydride to the total amount of diamine is 0.96 / 1. The amount of p-phenylenediamine and 4,4'-diaminodiphenyl ether added is an amount calculated so that the molar ratio of both is 75/25. The amount of N, N-dimethylacetamide added is an amount calculated so that the solid content concentration of the obtained polyimide precursor solution is 30% by mass.

The obtained polyimide precursor solution was applied to a glass substrate having a size of 76 mm × 52 mm using an applicator so that the film thickness after firing was 25 μm, and the mixture was air-dried at 70 ° C. for 1 hour. , Soaked in water for 30 minutes. After draining the water from the membrane, the temperature was raised from 70 ° C. to the temperature shown in Table 1 at a heating rate of 5 ° C./min, and the temperature was further maintained for 30 minutes. Then, it was allowed to cool to room temperature and immersed in water to obtain a porous polyimide film having non-spherical pores.

From the above results, it can be seen that in this example, the evaluation result of particle dispersibility is better than that in the comparative example.

The abbreviations in Tables 1 to 4 are as follows.
-"PI": Polyimide-Tetracarboxylic dianhydride-
・ "PMDA": pyromellitic acid dianhydride ・ "BPDA": 3,3', 4,4'-biphenyl tetracarboxylic acid dianhydride ・ "Acid anhydride 1": 3,3', 4,4' -Benzophenone tetracarboxylic acid dianhydride- "Acid anhydride 2": 3,3', 4,4'-biphenyl ether tetracarboxylic acid dianhydride-diamine compound-
・ "PDA": p-phenylenediamine ・ "ODA": 4,4'-diaminodiphenyl ether ・ "Diamine 1": 4,4'-diaminodiphenyl sulfone ・ "Diamine 2": 4,4'-diaminodiphenylmethane-organic Amine compound-
-"MMO": N-methylmorpholine- "DMAet": dimethylaminoethanol- "DMIz": 1,2-dimethylimidazole- "2E4Miz": 2-ethyl-4-methylimidazole-particles-
"PMMA-1": PMMA particle dispersion obtained in Synthesis Example 1-1
"PMMA-2": PMMA particle dispersion obtained in Synthesis Example 2-2
"PSt-1": PSt particle dispersion obtained in Synthesis Example 3-1
"PSt": PSt particle powder-1 obtained in Synthesis Example 4
-"Silica-1": Seahoster KE-P30 manufactured by Nippon Shokubai (spherical, average particle size 0.3 μm)
− Solvent −
-"NMP": N-methylpyrrolidone- "DMAc": N, N-dimethylacetamide- "EG": ethylene glycol-dispersant-
-"Dowfax": Dowfax2A1
"C12EO": Polyoxyethylene dodecyl ether-solvent for particle removal-
-"THF" tetrahydrofuran- "10% HF": 10% by mass concentration tetrahydrofuran- "THF / trol": tetrahydrofuran / toluene = 50/50 (mass ratio) mixed solvent

Claims (13)

A particle-dispersed polyimide precursor solution containing a solvent, a polyimide precursor having a repeating unit represented by the following formula (I), and particles, wherein the particles are resin particles.

In formula (I), A is selected from a tetravalent organic group having one aromatic ring and a tetravalent organic group having two aromatic rings, and B is a divalent organic group having one aromatic ring. It is selected from a divalent organic group having two aromatic rings, satisfies at least one of the following conditions (1) and (2), and satisfies the following condition (3).
When the condition (1) is satisfied, any of the conditions shown in the following (II-3) and the following (II-4) is satisfied, and when the condition (2) is satisfied, the following (II-1) and the following (II-1) are satisfied. Any of the conditions shown in II-2) is satisfied.
(1): A has a molar ratio (A1 / A2) of a tetravalent organic group A1 having one aromatic ring and a tetravalent organic group A2 having two aromatic rings of 5/95 or more and 95/5 or less. Is.
(2): B has a molar ratio (B1 / B2) of a divalent organic group B1 having one aromatic ring and a divalent organic group B2 having two aromatic rings of 5/95 or more and 95/5 or less. Is.
(3): Among the raw material monomer components constituting the A1, the A2, the B1, and the B2, the ratio of the component having the lowest content (excluding zero) to the particles is 0.015 mmol / g. As described above, the difference between the ratio of the component having the highest content to the particles and the ratio of the component having the lowest content (excluding zero) to the particles among the raw material monomer components is 9 mmol / g. It is as follows.
(II-1) The A1 / A2 is 100/0 and the B1 / B2 is 5/95 or more and 45/55 or less (II-2) The A1 / A2 is 0/100 and the B1 / B2 is 50/50 or more and 95/5 or less (II-3) The A1 / A2 is 5/95 or more and 30/70 or less, and the B1 / B2 is 70/30 or more and 100/0 or less (II-4) The A1 / A2 is 50/50 or more and 95/5 or less, and B1 / B2 is 0/100) The particle dispersion according to claim 1, wherein A1 is a group represented by A1-1 below, and A2 is any one group selected from the groups shown in A2-1 to A2-5 below. Polyimide precursor solution.

Claim 1 or claim 1, wherein the B1 is a group represented by the following B1-1 or the following B1-2, and the B2 is any one group selected from the group shown in the following B2-1 to the following B2-7. The particle-dispersed polyimide precursor solution according to claim 2.

Is a group wherein A1 is represented by the following Symbol A1-1, is a group wherein A2 is represented by the following Symbol A2-1, is a group wherein B1 is represented by the following Symbol B1-1, wherein B2 is lower Stories The particle-dispersed polyimide precursor solution according to claim 1, which is the group represented by B2-1.

In the polyimide precursor, the ratio of the component having the lowest content (excluding zero) to the particles among the raw material monomer components constituting the A1, the A2, the B1, and the B2 is determined. The particle-dispersed polyimide precursor solution according to any one of claims 1 to 4, which is 0.03 mmol / g or more. In the polyimide precursor, among the raw material monomer components constituting the A1, the A2, the B1, and the B2, the ratio of the component having the highest content to the particles and the content having the lowest content are the lowest. The particle-dispersed polyimide precursor solution according to any one of claims 1 to 5, wherein the difference from the ratio of the component (excluding zero) to the particles is 7 mmol / g or less. The particle-dispersed polyimide precursor solution according to any one of claims 1 to 6, further containing an organic amine compound and occupying 50% by mass or more of water in the total solvent. The particle-dispersed polyimide precursor solution according to claim 7, wherein the organic amine compound is a tertiary amine compound. The particle-dispersed polyimide precursor according to claim 7 or 8, further containing an aprotonic polar solvent in an amount of 3% by mass or more and 50% by mass or less based on the total amount of the particles and the polyimide precursor in the polyimide precursor solution. Body solution. The particle-dispersed polyimide precursor solution according to any one of claims 1 to 9, wherein the volume average particle diameter of the particles is 0.1 μm or more and 0.5 μm or less. The particle-dispersed polyimide precursor solution according to any one of claims 1 to 10, wherein the volume particle size distribution index of the particles in the particle-dispersed polyimide precursor solution is 1.30 or less. The particle-dispersed polyimide precursor solution according to any one of claims 1 to 11, wherein the content of the particles is 30% by mass or more and 85% by mass or less with respect to the solid content of the particle-dispersed polyimide precursor solution. .. After applying the particle-dispersed polyimide precursor solution according to any one of claims 1 to 12 to form a coating film, the coating film is dried to form a coating film containing the polyimide precursor and the particles. The first step of forming and
The film is provided with spherical pores having a second step of heating the film to imidize the polyimide precursor to form a polyimide film, the second step including a process of removing the particles. A method for producing a porous polyimide film.