JP6885107B2 - Porous polyimide film, polyimide precursor solution, and method for producing porous polyimide film - Google Patents

Description

The present invention relates to a porous polyimide film, a polyimide precursor solution, and a method for producing 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, in Patent Document 1, a densely packed deposit of monodisperse spherical inorganic particles is fired to form a sintered body of inorganic particles, the gaps between the inorganic particles of the sintered body are filled with polyamic acid, and then fired. A method for producing a separator for a lithium secondary battery, which dissolves and removes the inorganic particles by immersing the polyimide resin in a solution in which the inorganic particles are dissolved but the resin is not dissolved, is described.
Patent Document 2 describes an organic porous body having pores made of polyimide and an ionic conductor holding an electrolyte material containing a cation component and an anion component in the pores.
Patent Document 3 describes a varnish manufacturing process for producing a varnish by mixing polyamic acid or polyimide, silica particles and a solvent, or polymerizing polyamic acid or polyimide in a solvent in which silica particles are dispersed to produce a varnish. After forming a film of the varnish produced in the manufacturing process on a substrate, imidization is completed to produce a polyimide-silica composite film, and a polyimide-silica composite film produced in the composite film manufacturing process. A method for producing a porous polyimide film having a silica removing step for removing silica is described.
Patent Document 4 describes a porous silica mold obtained in a process of manufacturing a porous silica mold obtained by filling silica particles and then sintering them to obtain a porous silica mold, and a porous silica mold obtained in a step of manufacturing a porous silica mold. Describes a method for producing a porous polyimide, which comprises a polyimide filling step of filling the voids of the above with polyimide and a silica removing step of removing silica from a porous silica mold filled with the polyimide to obtain a porous silica.

In Patent Document 5, a spherical particle dispersion slurry prepared by dispersing spherical particles in a dispersion medium is dried to obtain a spherical particle dispersion film, and then this film is heat-treated to form a spherical particle-resin film. Then, the spherical particles-resin film is brought into contact with an inorganic acid other than phosphoric acid, an organic acid, water, or an alkaline solution to dissolve and remove the spherical particles, or the spherical particles-resin film is heated to remove the spherical particles. However, a method for producing a separator for a secondary battery by forming holes is described.
Patent Document 6 describes a positive electrode, a negative electrode, and a separator layer containing a porous polyimide film having an average pore diameter of 5 μm or less and having a porous polyimide film formed by phase separation after being coated with a solution of polyimide or a polyimide precursor. The non-aqueous electrolyte secondary battery to have is described.

Japanese Patent No. 5331627 Japanese Unexamined Patent Publication No. 2008-034212 Japanese Unexamined Patent Publication No. 2012-107144 Japanese Unexamined Patent Publication No. 2011-11470 International Publication 2014/196656 Japanese Unexamined Patent Publication No. 10-302479

When a porous polyimide film obtained by using a polyimide precursor solution containing resin particles and a polyimide precursor is applied, for example, as a separator for a lithium-ion battery, the battery capacity may be significantly reduced when repeatedly charged and discharged. I understand.

An object of the present invention is a total content of a metal group consisting of an alkali metal excluding Li, an alkaline earth metal, and silicon in a porous polyimide film obtained by using a polyimide precursor solution containing resin particles and a polyimide precursor. By providing a porous polyimide film in which a decrease in battery capacity due to repeated charging and discharging when applied as a separator for a lithium ion battery is suppressed as compared with a case where the amount exceeds 100 ppm with respect to the solid content of the porous polyimide film. is there.

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

< 1 >
A porous polyimide film having a total content of a metal group consisting of an alkali metal excluding Li, an alkaline earth metal, and silicon of 100 ppm or less with respect to the porous polyimide film.

< 2 >
The porous polyimide film according to is 50ppm or less the total amount of pre-Symbol metal group <1>.
< 3 >
The porous polyimide film according to is 20ppm or less the total amount of pre-Symbol metal group <2>.

< 4 >
Maximum diameter of the pores is 0.1μm or more 0.5μm or less <1> porous polyimide film according to any one of to <3>.

< 5 >
Aqueous solvent containing water, the resin particles which do not dissolve in the aqueous solvent, an organic amine compound, and containing a polyimide precursor, alkali metal excluding Li, alkaline earth metals, and the total content of metal group consisting of silicon, A polyimide precursor solution having a concentration of 200 ppm or less with respect to the polyimide precursor solution.

< 6 >
The polyimide precursor solution according to the average particle size before Symbol resin particles is 0.1μm or more 0.5μm or less <5>.
< 7 >
The polyimide precursor solution according to the average particle size before Symbol resin particles is 0.25μm or more 0.5μm or less <6>.

< 8 >
Before SL content of the resin particles with respect to the polyimide precursor solid 100 parts by weight, or less 600 weight parts or more and 20 parts by weight <5> polyimide precursor solution according to any one of to <7>.
< 9 >
Before SL content of the resin particles, polyimide precursor solution according to relative polyimide precursor solid 100 parts by mass, 100 parts by mass or less than 30 parts by weight <8>.

< 10 >
The polyimide precursor solution according to prior Symbol resin particles are soap-free emulsion polymerization particles <5> - any one of <9>.
< 11 >
The polyimide precursor solution according to any one of the previous SL resin particles is washed resin particles <5> to <9>.

< 12 >
Before SL-aqueous solvent, the content of the water in an aqueous solvent the total amount is less than 50 wt% to 100 wt% <5> polyimide precursor solution according to any one of to <11>.
< 13 >
Before SL-aqueous solvents are polyimide precursor solution according to is 100 wt% or less than 80 wt% content of the water in an aqueous solvent total amount <12>.

< 14 >
The polyimide precursor solution according to prior Symbol organic amine compound is a tertiary amine compound <5> - any one of <13>.
< 15 >
Before SL organic amine compound, 2-dimethylaminoethanol, 2-diethylaminoethanol, 2-dimethylamino-propanol, pyridine, triethylamine, picoline, N- methylmorpholine, N- ethylmorpholine, 1,2-dimethylimidazole, 2-ethyl The polyimide precursor solution according to < 14 > , which is at least one selected from the group consisting of -4-methylimidazole, N-methylpiperidine, and N-ethylpiperidine.
< 16 >
The polyimide precursor solution according to prior Symbol organic amine compound, an amine compound having a morpholine skeleton <15>.

< 17 >
After applying the polyimide precursor solution according to any one of <5 > to < 16 > to form a coating film, the coating film is dried to form a coating film containing the polyimide precursor and the resin particles. The first step of forming and
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 resin particles.
A method for producing a porous polyimide film having.

According to the inventions according to < 1 > , < 2 > , and < 3 > , in a porous polyimide film obtained by using a polyimide precursor solution containing resin particles and a polyimide precursor, alkali metals and alkaline earths excluding Li are used. Compared to the case where the total content of the metal group consisting of metal and silicon exceeds 100 ppm with respect to the solid content of the porous polyimide film, the decrease in battery capacity due to repeated charging and discharging when applied as a separator for a lithium ion battery is suppressed. The porous polyimide film to be used is provided.

According to the invention according to < 4 > , the total content of the metal group consisting of alkali metal, alkaline earth metal, and silicon excluding Li is empty as compared with the case where the total content of the metal group exceeds 100 ppm with respect to the solid content of the porous polyimide film. Provided is a porous polyimide film having a maximum hole diameter of 0.1 μm or more and 0.5 μm or less, which suppresses a decrease in battery capacity due to repeated charging and discharging when applied as a separator for a lithium ion battery.

According to the invention according to < 5 > , in a polyimide precursor solution containing an aqueous solvent containing water, resin particles insoluble in the aqueous solvent, an organic amine compound, and a polyimide precursor, alkali metals other than Li and alkaline earth Compared to the case where the total content of the metal group consisting of metal and silicon exceeds 200 ppm with respect to the polyimide precursor solution, the decrease in battery capacity due to repeated charging and discharging when applied as a separator for a lithium ion battery is suppressed. A polyimide precursor solution for obtaining a porous polyimide film is provided.

According to the inventions of < 6 > and < 7 >, when the total content of the metal group consisting of alkali metal, alkaline earth metal, and silicon excluding Li exceeds 200 ppm with respect to the polyimide precursor solution. In comparison, even if the average particle size of the resin particles is in the range of 0.1 μm or more and 0.5 μm or less, and further in the range of 0.25 μm or more and 0.5 μm or less, the battery is repeatedly charged and discharged when applied as a separator for a lithium ion battery. Provided is a polyimide precursor solution capable of obtaining a porous polyimide film in which a decrease in capacity is suppressed.

According to the inventions of < 8 > and < 9 >, when the total content of the metal group consisting of alkali metal, alkaline earth metal, and silicon excluding Li exceeds 200 ppm with respect to the polyimide precursor solution. By comparison, even if the content of the resin particles is in the range of 20 parts by mass or more and 600 parts by mass or less, and further 30 parts by mass or more and 100 parts by mass or less with respect to 100 parts by mass of the solid content of the polyimide precursor, the lithium ion battery Provided is a polyimide precursor solution capable of obtaining a porous polyimide film in which a decrease in battery capacity due to repeated charging and discharging when applied as a separator is suppressed.

According to the inventions of < 10 > and < 11 >, when the total content of the metal group consisting of alkali metal, alkaline earth metal, and silicon excluding Li exceeds 200 ppm with respect to the polyimide precursor solution. In comparison, a polyimide precursor in which the resin particles are soap-free emulsion polymerization resin or cleaning resin particles, and a porous polyimide film can be obtained in which a decrease in battery capacity due to repeated charging and discharging is suppressed when applied as a separator for a lithium ion battery. A solution is provided.

According to the inventions of < 12 > and < 13 >, when the total content of the metal group consisting of alkali metal, alkaline earth metal, and silicon excluding Li exceeds 200 ppm with respect to the polyimide precursor solution. In comparison, even if the water content with respect to the total amount of the aqueous solvent is in the range of 50% by mass or more and 100% by mass or less, and further 80% by mass or more and 100% by mass or less, it is repeatedly charged when applied as a separator for a lithium ion battery. Provided is a polyimide precursor solution capable of obtaining a porous polyimide film in which a decrease in battery capacity due to discharge is suppressed.

According to the inventions of < 14 > , < 15 > , and < 16 > , the total content of the metal group consisting of alkali metal, alkaline earth metal, and silicon excluding Li is 200 ppm with respect to the polyimide precursor solution. Even if the organic amine compound is a tertiary amine compound, a polyimide film can be obtained in which a decrease in battery capacity due to repeated charging and discharging is suppressed when applied as a separator for a lithium ion battery. A precursor solution is provided.

According to the invention according to < 17 > , after applying a polyimide precursor solution containing an aqueous solvent containing water, resin particles insoluble in the aqueous solvent, an organic amine compound, and a polyimide precursor to form a coating film, The first step of drying the coating film to form a film containing the polyimide precursor and the resin particles, and the second step of heating the film to imidize the polyimide precursor to form a polyimide film. In the method for producing a porous polyimide film, which comprises the second step including the treatment for removing the resin particles, the polyimide precursor solution contains an alkali metal other than Li, an alkaline earth metal, and an alkaline earth metal. Compared to the case where the total content of the metal group consisting of silicon exceeds 200 ppm with respect to the polyimide precursor solution, the porosity suppresses the decrease in battery capacity due to repeated charging and discharging when applied as a separator for lithium ion batteries. A method for producing a polyimide film is provided.

It is a schematic diagram which shows the form of the porous polyimide film of this embodiment.

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

The polyimide film according to this embodiment has a total content of a metal group consisting of an alkali metal excluding Li, an alkaline earth metal, and silicon (hereinafter, may be referred to as a “specific metal group”) as a porous polyimide. It is 100 ppm or less with respect to the film. In addition, in this specification, ppm is based on mass.

The porous polyimide film is formed, for example, by using a polyimide precursor solution containing resin particles and a polyimide precursor. In this case, a specific metal group may remain in the porous polyimide film. Then, it has been found that when the porous polyimide film is applied to a separator of a lithium ion battery, the battery capacity (hereinafter, may be referred to as "cycle characteristics") when repeatedly charged and discharged decreases.

When the total content of the specific metal group contained in the porous polyimide film exceeds 100 ppm, the amount of metal contained in the porous polyimide film is too large, and the ion flow is disturbed. It is considered that the cycle characteristics are deteriorated.
On the other hand, in the porous polyimide film according to the present embodiment, the total content of the specific metal group is 100 ppm or less, and the content of the metal species considered to cause turbulence of the ion flow permeating through the porous polyimide film. It is presumed that the decrease in cycle characteristics is suppressed because there is little.

From the above, it is presumed that the porous polyimide film according to the present embodiment suppresses a decrease in battery capacity due to repeated charging and discharging when applied as a separator for a lithium ion battery.

Here, in the conventional porous polyimide film, the reason why the total content of the specific metal group exceeds 100 ppm can be considered as follows, for example.
For example, when a conventional porous polyimide film forms a porous polyimide using a polyimide precursor solution containing resin particles and a polyimide precursor, the resin particles are granulated by, for example, a method such as emulsion polymerization. To. When the resin particles are granulated by emulsion polymerization, a metal of a specific metal group may be contained as a surfactant used in the emulsion polymerization. Then, when the resin particles obtained by using the surfactant containing this metal are dispersed in the polyimide precursor solution, the metal contained in the resin particles is derived in the polyimide precursor solution. Contains metal. When this polyimide precursor solution is applied to the formation of a porous polyimide film, the metal contained in the polyimide precursor solution becomes porous in the process of imidization of the film or the process of removing resin particles. It remains on the polyimide film. As a result, it is considered that the total content of the specific metal group remains in excess of 100 ppm with respect to the porous polyimide film.

On the other hand, in the method for producing a porous polyimide film according to the present embodiment, a water-containing aqueous solvent (hereinafter, may be simply referred to as “aqueous solvent”) and resin particles that are insoluble in water-containing aqueous solvent. (Hereinafter, it may be simply referred to as "resin particles"), an organic amine compound, and a polyimide precursor, and the total content of the specific metal group is 200 ppm or less with respect to the polyimide precursor solution. Use body solution. As a result, it is considered that the total content of the specific metal group in the porous polyimide film obtained by the porous polyimide film according to the present embodiment is 100 ppm or less.

[Porous polyimide film]
The porous polyimide film according to the present embodiment has a total content of the specific metal group of 100 ppm or less with respect to the porous polyimide film. It is preferably 50 ppm or less, and more preferably 20 ppm or less. The total content of the specific metal group with respect to the porous polyimide film is preferably small, and the lower limit is not particularly limited, but is preferably 0 ppm. Note that 0 ppm means below the detection limit.
The total content of the specific metal group contained in the porous polyimide film is measured by measuring the porous polyimide film to be measured with an atomic absorption spectrometer.

The method for adjusting the total content of the specific metal group contained in the porous polyimide film is not particularly limited, but for example, reducing the total content of the specific metal group contained in the resin particles used in the polyimide precursor solution described later. There is a method of adjusting with.

-Characteristics of porous polyimide film-
The porous polyimide film has pores having a shape close to a spherical shape connected to each other. In the present specification, the term "close to spherical" in the shape of the pores includes both spherical and substantially spherical shapes. Specifically, it means that the ratio of pores in which the ratio of major axis to minor axis (major axis / minor axis) is 1 or more and 2 or less exists is 50% or more. The greater the presence ratio of these vacancies, the greater the proportion of spherical vacancies. The pores having a major axis to minor axis ratio (major axis / minor axis) of 1 or more and 2 or less are preferably 50% or more and 100% or less, and more preferably 55% or more and 100% or less. Further, as the ratio of the major axis to the minor axis approaches 1, it becomes closer to a true sphere. Since the holes having a shape close to a sphere are connected, the shape of the connected portion is estimated by extrapolation from the portion forming the wall.
Further, when the porous polyimide film is applied to, for example, a battery separator of a lithium ion battery, the generation of turbulence of the ion flow is suppressed, so that the formation of lithium dendrite is easily suppressed. Further, when used as a filter, the accuracy of filtration (for example, the uniformity of the size of substances contained in the filtrate) is improved.

The porous polyimide film is not particularly limited, but the porosity is preferably 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.

Further, the vacancies preferably have a shape in which the vacancies are connected to each other and connected (see FIG. 1). 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 pore diameter, 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 maximum value of the pore diameter (maximum diameter of the pore) 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 0.5 μm or less, and is 0. More preferably, it is in the range of .25 μm or more and 0.4 μm or less.

In the porous polyimide film, 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 generation of turbulence of the ion flow is suppressed, so that the formation of lithium dendrite is easily suppressed.
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 value, minimum value, average value of the pore diameter, the average value of the pore diameter of the part where the pores are connected to each other, and the major axis and the minor axis of the pore diameter 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 the minor axis are observed and measured by the VE SEM manufactured by KEYENCE with the standard image processing software, 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.

(Use of porous film)
Examples of applications to which the porous film according to the present embodiment is applied include a battery separator of a lithium battery. In addition to battery separators for lithium batteries, for example, battery separators other than lithium batteries; separators for electrolytic capacitors; electrolyte films for fuel cells and the like; battery electrode materials; gas or liquid separation films; low dielectric constant materials; various Filter; etc.

When the porous film according to the present embodiment is applied to, for example, a battery separator of a lithium battery, the total content of the specific metal group in the porous polyimide film is small, so that the ion flow distribution of lithium ions varies. It is considered that the formation of lithium dendrite is suppressed by the action of suppressing the amount of lithium dendrite. Further, it is presumed that the variation in the shape, pore diameter, and existence distribution of the pores of the porous polyimide film contained in the porous film of the present embodiment is 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 an ionic gel obtained by gelling a so-called ionic liquid and apply it as an electrolyte membrane. It is considered that the method for producing the porous film of the present embodiment simplifies the process, so that a lower cost electrolyte membrane can be obtained.

[Manufacturing method of porous polyimide film]
Specifically, the polyimide contained in the porous polyimide film is polymerized with a tetracarboxylic dianhydride and a diamine compound to produce a polyimide precursor, and a solution of the polyimide precursor is obtained and subjected to an imidization reaction. can get. More specifically, polyimide is obtained by imidizing a polyimide precursor solution in which a polyimide precursor and an organic amine compound are dissolved in an aqueous solvent containing water. For example, a method of polymerizing a tetracarboxylic acid dianhydride and a diamine compound in the presence of an organic amine compound to produce a resin (polyimide precursor) in an aqueous solvent to obtain a polyimide precursor solution can be mentioned.

It was mentioned that a resin (polyimide precursor) was produced by polymerizing a tetracarboxylic acid dianhydride and a diamine compound in the presence of an organic amine compound to obtain a polyimide precursor solution, but the present invention is limited to this example. It's not a thing. For example, a method using a polyimide precursor solution in which an organic amine compound is not dissolved can be mentioned. Specifically, an aqueous mixed solvent selected from a water-soluble ether solvent, a water-soluble ketone solvent, a water-soluble alcohol solvent, and water (for example, a water-soluble ether solvent and water, or a water-soluble ketone solvent and water, etc.) A method of polymerizing a tetracarboxylic acid dianhydride and a diamine compound in a mixed solvent (combination with a water-soluble alcohol solvent, etc.) to produce a polyimide precursor to obtain a polyimide precursor solution can also be mentioned.

Hereinafter, an example of a suitable manufacturing method for the porous polyimide film according to the present embodiment will be described.
The method for producing a porous polyimide film according to this embodiment includes the first step and the second step listed below.

The first step contains an aqueous solvent, resin particles, an organic amine compound, and a polyimide precursor, and the total content of the metal group consisting of alkali metal, alkaline earth metal, and silicon excluding Li is the polyimide precursor. A polyimide precursor solution having a concentration of 200 ppm or less (preferably 150 ppm or less) is applied to the solution to form a coating film, and then the coating film is dried to form a coating film containing the polyimide precursor and the resin particles. This is the process of forming.
The total content of the specific metal group with respect to the polyimide precursor solution is preferably small, and the lower limit is not particularly limited, but is preferably 0 ppm. Note that 0 ppm means below the detection limit.

Here, the total content of the specific metal group with respect to the polyimide precursor solution contained in the polyimide precursor solution is measured by measuring the polyimide precursor solution to be measured by an atomic absorption spectrometer. Specifically, it is measured by an atomic absorption spectrometer as a polyimide precursor solution in a state where water is evaporated.

The second step is a second step of heating the coating film to imidize the polyimide precursor to form a polyimide film, and is a step including a process of removing resin particles.
When the resin particles are removed by an organic solvent that dissolves the resin particles, the resin particles can be removed by heating even when the removability is low because the resin is crosslinked. ..

The method for adjusting the total content of the specific metal group with respect to the polyimide precursor solution is not particularly limited, but for example, it is adjusted by reducing the total content of the specific metal group contained in the resin particles used for the polyimide precursor described later. The method can be mentioned.

-First step-
In the first step, first, a polyimide precursor solution containing an aqueous solvent, resin particles, an organic amine compound, and a polyimide precursor (hereinafter, may be referred to as "resin particle dispersed polyimide precursor solution") is prepared. To do.
As the polyimide precursor solution, first, resin particles and a polyimide precursor solution in which the polyimide precursor is dissolved in an aqueous solvent are prepared. The polyimide precursor solution in which the polyimide precursor is dissolved is a polyimide precursor solution in which the polyimide precursor and the organic amine compound are dissolved.
Then, the resin particles and the polyimide precursor solution in which the polyimide precursor and the organic amine compound are dissolved are mixed to obtain a resin particle-dispersed polyimide precursor solution.
Next, the obtained resin particle-dispersed polyimide precursor solution is applied onto a substrate to form a coating film. This coating film contains a polyimide precursor solution and resin particles. The resin particles in the coating film are distributed in a state where aggregation is suppressed. Then, the coating film formed on the substrate is dried to form a film containing the polyimide precursor and the resin particles.

The substrate on which the film containing the polyimide precursor and the resin particles is formed 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. It is also effective to roughen the surface of the base material to a size of about the particle size of the resin particles to promote the exposure of the resin particles on the base material contact surface.

The method of applying the resin 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.

When the resin particle-dispersed polyimide precursor solution is formed on the substrate, it is preferable to add the resin particles in an amount that exposes the resin particles from the surface of the coating film.

Then, after forming a coating film containing the polyimide precursor solution obtained by the above method and the resin particles, it is dried to form a film containing the polyimide precursor and the resin particles. Specifically, a coating film containing a polyimide precursor solution and resin 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. This film is in a state where the polyimide precursor can be dissolved in water.
Further, after obtaining the coating film, the resin particles may be exposed in the process of drying to form the film to expose the resin particles. By performing the treatment of exposing the resin particles, the aperture ratio of the porous polyimide film is increased.

Specific examples of the treatment for exposing the resin particles include the following methods.

In the process of obtaining a coating film containing the polyimide precursor solution and the resin particles and then drying the coating film to form a film containing the polyimide precursor and the resin particles, as described above, the film film is formed by the polyimide precursor. , It is in a state where it can be dissolved in water. When the coating film is in this state, the resin particles can be exposed by, for example, a treatment of wiping or a treatment of immersing the film in water. Specifically, for example, by performing a treatment of exposing the resin particle layer by wiping with water, the polyimide precursor solution existing on the resin particle layer is removed. Then, the resin particles existing in the upper region of the resin particle layer (that is, the region on the side of the resin particle layer away from the substrate) are exposed from the surface of the coating film.

In the case of forming a film on the substrate using the resin particle-dispersed polyimide precursor solution, the above-mentioned treatment for exposing the resin particles embedded in the film even when the film in which the resin particles are embedded is formed is described above. A process similar to the process for exposing the resin particles of the above can be adopted.

The method for producing the resin particle-dispersed polyimide precursor solution is not limited to the above-mentioned production method. From the viewpoint of simplifying the process, it is also preferable to synthesize the polyimide precursor in an aqueous solvent dispersion in which resin particles that are not dissolved in the polyimide precursor solution are dispersed in the aqueous solvent in advance. For example, specifically, the following method can be mentioned.
A resin particle dispersion liquid in which resin particles are granulated in an aqueous solvent containing water is used. Then, in the resin particle dispersion liquid, the tetracarboxylic acid dianhydride and the diamine compound are polymerized in the presence of the organic amine compound to produce a resin (polyimide precursor), which is used as a polyimide precursor solution.

As a method for producing the resin particle-dispersed polyimide precursor solution, for example, a method of mixing the polyimide precursor solution and the dried resin particles, the polyimide precursor solution, and the resin particles are dispersed in an aqueous solvent in advance. Examples thereof include a method of mixing with a dispersion liquid.
As the dispersion liquid in which the resin particles are dispersed in the aqueous solvent in advance, a dispersion liquid in which the resin particles are dispersed in the aqueous solvent in advance may be prepared. A commercially available dispersion in which the resin particles are dispersed in an aqueous solvent in advance may be prepared. When a commercially available dispersion is used, it is preferable that the total content of the metal group contained in the porous polyimide film is 100 ppm or less with respect to the porous polyimide film. When preparing a dispersion liquid of resin particles dispersed in advance, a surfactant containing no metal of the specific metal group may be added in advance to improve the dispersibility of the resin particles.

Then, the resin particle-dispersed polyimide precursor solution obtained as described above is applied onto the substrate by the above-mentioned method to form a coating film. Then, the coating film is dried to form a coating film on the substrate.

-Second step-
The second step is a step of heating the film containing the polyimide precursor and the resin 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 resin particles. A porous polyimide film is obtained through a treatment for removing resin particles.

In the second step, in the step of forming the polyimide film, specifically, the film containing the polyimide precursor and the resin particles obtained in the first step is heated to proceed with 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 the resin particles is performed. The resin 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 process of imidizing the polyimide precursor is to heat the film containing the polyimide precursor and the resin particles obtained in the first step to proceed with the imidization, and the imidization is completed. The process of becoming a state before becoming a polyimide film after being formed is shown.

Specifically, a film in the process of heating the coating film on which the resin particles obtained in the first step are exposed to imidize the polyimide precursor (hereinafter, the film in this state may be referred to as a "polyimide film". Remove the resin particles from (yes). Alternatively, the resin particles may be removed from the polyimide film after the imidization is completed. Then, a porous polyimide film from which the resin particles have been removed can be obtained (see FIG. 1).
In the reference numerals shown in FIG. 1, 3 represents a substrate, 4 represents a release layer, 7 represents pores, and 62 represents a porous polyimide film.

In the process of removing the resin particles, the resin component of the resin particles may be contained in the porous polyimide film as a resin other than the polyimide resin. Although not shown, the porous polyimide film may contain a resin other than the polyimide resin.

The treatment for removing the resin particles may be 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 the removability of the resin particles and the like. preferable. When the imidization ratio is 10% or more, it tends to be difficult to dissolve in an organic solvent and the morphology is easily maintained.

The treatment for removing the resin particles is not particularly limited as long as a porous polyimide film can be obtained. For example, a method of decomposing and 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 decomposing with a laser or the like, and the like can be mentioned.
The removal of the resin particles may be carried out only by decomposition and removal by heat, which also serves as an imidization step, but may be used in combination with decomposition and removal by heating and removal by an organic solvent that dissolves the resin particles. A method including a treatment of removing the resin particles with an organic solvent that dissolves the resin particles is preferable from the viewpoint that the residual stress can be more easily relaxed and the generation of cracks in the porous polyimide film is suppressed. It is presumed that this action is due to the fact that the resin component dissolved in the organic solvent is likely to be transferred to the polyimide resin in the treatment of removing with the organic solvent.

For example, in the method of removing by heating, decomposition gas may be generated by heating depending on the type of resin particles. Then, due to this decomposition gas, the porous polyimide film may be broken or cracked. Therefore, from the viewpoint of suppressing the occurrence of cracks, it is preferable to adopt a method of removing the resin particles with an organic solvent that dissolves them.
It is also effective to increase the removal rate by further heating after removing the resin particles with an organic solvent that dissolves them.

Further, when the resin particles are removed by a method of removing the resin particles with an organic solvent that dissolves the resin particles, the resin component of the resin particles dissolved in the organic solvent may infiltrate into the polyimide film in the process of removing the resin particles. .. Therefore, by adopting this method, a resin other than the polyimide resin can be positively contained in the obtained porous polyimide film. From the viewpoint of containing a resin other than the polyimide resin, it is preferable to adopt a method of removing the resin particles with an organic solvent that dissolves the resin particles. Further, the removal of the resin particles by this method is preferably performed on the film (polyimide film) in the process of imidizing the polyimide precursor in that a resin other than the polyimide resin is contained. In the state of the polyimide film, by dissolving the resin particles with a solvent that dissolves the resin particles, it may be easier to penetrate into the polyimide film.

As a method of removing the resin particles with an organic solvent that dissolves them, for example, a method of contacting the resin particles with an organic solvent that dissolves them (for example, immersing them in a solvent or contacting them with a solvent vapor) to dissolve and remove the resin particles. Can be mentioned. Immersion in a solvent in this state is preferable because 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. Examples thereof include ethers such as tetrahydrofuran and 1,4-dioxane; aromatics such as benzene and toluene; ketones such as acetone; and esters such as ethyl acetate.
Among these, ethers such as tetrahydrofuran and 1,4-dioxane; aromatics such as benzene and toluene are preferable, and tetrahydrofuran and toluene are more preferable.
When the aqueous solvent remains when the resin particles are dissolved, the aqueous solvent is dissolved in the solvent that dissolves the non-crosslinked resin particles, and the polyimide precursor is precipitated, which is similar to the so-called wet phase conversion method. Therefore, it may be difficult to control the pore size. Therefore, the amount of the residual aqueous solvent is reduced to 20% by mass or less, preferably 10% by mass or less with respect to the weight of the polyimide precursor, and then the organic solvent is not used. It is preferable to dissolve and remove the crosslinked resin particles.

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 multiple stages of two or more stages can be mentioned. For example, in the case of heating in two stages, specific examples thereof include the following heating conditions.

The heating condition of the first stage is preferably a temperature at which the shape of the resin 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 400 ° C. or lower (preferably 200 ° C. or higher and 390 ° 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.

When the treatment for exposing the resin particles is not performed in the first step, the resin particles are exposed by performing the treatment for exposing the resin particles in the second step in order to increase the pore size. May be good. In the second step, the treatment for exposing the resin particles is preferably performed in the process of imidizing the polyimide precursor, or after the imidization and before the treatment of removing the resin particles.

The treatment for exposing the resin particles may be performed, for example, when the polyimide film is in the following state.
When the process of exposing the resin 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 water), it is buried in the above-mentioned polyimide film. Examples of the treatment for exposing the resin particles include a treatment of wiping and a treatment of immersing the resin particles in water.

Further, when the imidization rate of the polyimide precursor in the polyimide film is 10% or more (that is, in a state where it is difficult to dissolve in an organic solvent), and when the polyimide film is in a state where imidization is completed, the resin particles. When performing the process of exposing the resin, a method of mechanically cutting with a tool such as a paper scraper to expose the resin particles, a method of etching with an alkaline solution that dissolves the polyimide resin, a method of decomposing the resin with a laser, etc. A method of exposing the particles can be mentioned.
For example, in the case of mechanical cutting, a part of the resin particles existing in the upper region of the resin particle layer embedded in the polyimide film (that is, the region on the side of the resin particle layer away from the substrate) is a resin. It is cut together with the polyimide film existing on the upper part of the particles, and the cut resin particles are exposed from the surface of the polyimide film.

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

When a film is formed on the substrate using the resin particle-dispersed polyimide precursor solution, the resin particle-dispersed polyimide precursor solution is applied onto the substrate to form a coating film in which the resin particles are embedded. In the process of drying the coating film to form a film, if a film containing the polyimide precursor and the resin particles is formed without exposing the resin particles, a film in which the resin particles are embedded may be formed. is there. For example, when the film in which the resin particles are embedded is heated, the film (polyimide film) in the process of imidization is in a state in which the resin particle layer is embedded. As the treatment for exposing the resin particles performed in the second step in order to increase the aperture ratio, the same treatment as the treatment for exposing the resin particles described above can be adopted. Then, it is cut together with the polyimide film existing on the upper part of the resin particles, and the resin particles are exposed from the surface of the polyimide film.

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

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 containing a polyimide resin and a resin other than the polyimide resin can be obtained. Then, the porous polyimide film may be post-processed depending on the purpose of use.

Here, the imidization ratio 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 (I-1), the following general formula (I-2), and the following general formula (I-3). Precursors can be mentioned.

In the general formula (I-1), the general formula (I-2), and the general formula (I-3), A represents a tetravalent organic group and B represents a divalent organic group. l represents an integer of 1 or more, and m and n independently represent an integer of 0 or 1 or more, respectively.

Note that A and B are synonymous with A and B in the general formula (I) described later.

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 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) A polyimide precursor solution 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 mixed with the solvent component contained in the polyimide precursor solution. Specifically, alcohol solvents such as methanol and ethanol, and ether compounds such as dioxane can be used.
The (iii) coating samples, taken out from in THF, blowing _{N 2} gas into THF adhering to the coating surface of the sample, removed. A polyimide precursor sample is prepared by treating the coating film sample at 5 ° C. or higher and 25 ° C. or lower for 12 hours or longer under a reduced pressure of 10 mmHg or lower to dry the coating film sample.

-Preparation of 100% imidized standard sample (iv) In the same manner as in (i) above, a polyimide precursor solution 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). Aromatic ring-derived absorption peak near 1500 cm ^-1 and 100% imidization standard sample (Ab ratio 'for (1500cm ^-1)), absorption peaks derived from an imide bond in the vicinity of ^{1780cm -1 (Ab' (1780cm -1} )) 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.

Next, each component of the polyimide precursor solution according to this embodiment will be described.

[Polyimide precursor solution]
The polyimide precursor solution contains an aqueous solvent, resin particles, an organic amine compound, and a polyimide precursor.

-Polyimide precursor-
The polyimide precursor is a resin (polyimide precursor) having a repeating unit represented by the general formula (I).

(In the general formula (I), A represents a tetravalent organic group and B represents a divalent organic group.)

Here, in the general formula (I), the tetravalent organic group represented by A is a residue obtained by removing four carboxyl groups from the raw material tetracarboxylic dianhydride.
On the other hand, the divalent organic group represented by B is the residue obtained by removing two amino groups from the diamine compound as a raw material.

That is, the polyimide precursor having a repeating unit represented by the general formula (I) is a polymer of a tetracarboxylic dianhydride and a diamine compound.

Examples of the tetracarboxylic dianhydride include both aromatic and aliphatic compounds, but aromatic compounds are preferable. That is, in the general formula (I), the tetravalent organic group represented by A is preferably an aromatic organic group.

Examples of the aromatic tetracarboxylic acid dianhydride include pyromellitic acid dianhydride, 3,3', 4,4'-benzophenone tetracarboxylic acid dianhydride, 3,3', 4,4'-biphenyl. Sulfontetracarboxylic acid dianhydride, 1,4,5,8-naphthalenetetracarboxylic acid dianhydride, 2,3,6,7-naphthalenetetracarboxylic acid dianhydride, 3,3', 4,4'- Biphenyl ether tetracarboxylic acid dianhydride, 3,3', 4,4'-dimethyldiphenylsilane tetracarboxylic acid dianhydride, 3,3', 4,4'-tetraphenylsilanetetracarboxylic acid dianhydride, 1 , 2,3,4-Frantetracarboxylic 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, 3,3', 4,4'-perfluoroisopropyridene diphthalic acid dianhydride, 3 , 3', 4,4'-biphenyltetracarboxylic acid 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) Acid) -4,4'-diphenylmethane dianhydride and the like.

Examples of the aliphatic tetracarboxylic dianhydride include butanetetracarboxylic dianhydride, 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,3-dimethyl-1,2,3,4. -Cyclobutanetetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, 2,3,5-tricarboxycyclopentylacetic dianhydride, 3,5,6-tricarboxynorbonane -2-Acidylene dianhydride, 2,3,4,5-tetracarboxylic dianhydride, 5- (2,5-dioxotetrahydrofuryl) -3-methyl-3-cyclohexene-1,2-dicarboxylic An aliphatic or alicyclic tetracarboxylic dianhydride such as an acid dianhydride, bicyclo [2,2,2] -oct-7-ene-2,3,5,6-tetracarboxylic dianhydride; 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 or other aliphatic tetracarboxylic acid having an aromatic ring Examples include dianhydride and the like.

Among these, as the tetracarboxylic dianhydride, an aromatic tetracarboxylic dianhydride is preferable, and specifically, for example, pyromellitic dianhydride, 3,3', 4,4'-biphenyl. Tetetracarboxylic dianhydride, 2,3,3', 4'-biphenyltetracarboxylic dianhydride, 3,3', 4,4'-biphenyl ether tetracarboxylic dianhydride, 3,3', 4 , 4'-benzophenonetetracarboxylic dianhydride is preferable, and further, pyromellitic acid dianhydride, 3,3', 4,4'-biphenyltetracarboxylic dianhydride, 3,3', 4,4' -Benzophenonetetracarboxylic dianhydride is preferable, and 3,3', 4,4'-biphenyltetracarboxylic dianhydride is particularly preferable.

The tetracarboxylic dianhydride may be used alone or in combination of two or more.
In addition, when two or more kinds are used in combination, even if aromatic tetracarboxylic dianhydride or aliphatic tetracarboxylic acid is used in combination, aromatic tetracarboxylic dianhydride and aliphatic tetracarboxylic dianhydride are used in combination. It may be combined with an object.

On the other hand, the diamine compound is a diamine compound having two amino groups in its molecular structure. Examples of the diamine compound include both aromatic and aliphatic compounds, but aromatic compounds are preferable. That is, in the general formula (I), the divalent organic group represented by B is preferably an aromatic organic group.

Examples of the diamine compound include p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylethane, 4,4'-diaminodiphenyl ether, and 4,4'-diaminodiphenyl sulfide. , 4,4'-Diaminodiphenylsulfone, 1,5-diaminonaphthalene, 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'-diaminobenzanilide, 3,5-diamino-3'-trifluoromethylbenzanilide , 3,5-Diamino-4'-trifluoromethylbenzanilide, 3,4'-diaminodiphenyl ether, 2,7-diaminofluorene, 2,2-bis (4-aminophenyl) hexafluoropropane, 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, 4,4'-diamino-2,2'-bis (trifluoromethyl) biphenyl, 2,2-bis [4- (4- (4- (4- (4- (4-) 4-) Aminophenoxy) phenyl] propane, 2,2-bis [4- (4-aminophenoxy) phenyl] hexafluoropropane, 1,4-bis (4-aminophenoxy) benzene, 4,4'-bis (4-amino) Phenoxy) -biphenyl, 1,3'-bis (4-aminophenoxy) benzene, 9,9-bis (4-aminophenyl) fluorene, 4,4'-(p-phenylene isopropylidene) bisaniline, 4,4' -(M-Phenylisopropyridene) bisaniline, 2,2'-bis [4- (4-amino-2-trifluoromethylphenoxy) phenyl] hexafluoropropane, 4,4'-bis [4- (4-amino) -2-Trifluoromethyl) phenoxy] -aromatic diamines such as octafluorobiphenyl; aromatics having two amino groups bonded to an aromatic ring such as diaminotetraphenylthiophene and heteroatoms other than the nitrogen atom of the amino group. Group diamines; 1,1-methaxylylene diamine, 1,3-propanediamine, tetramethylenediamine, pentamethylenediamine, octamethylenediamine, nona Methylenediamine, 4,4-diaminoheptamethylenediamine, 1,4-diaminocyclohexane, isophoronediamine, tetrahydrodicyclopentadiene diamine, hexahydro-4,7-methanoin danirange methylenediamine, tricyclo [6,2] , 1,0 ^2.7 ] -Undecylenedimethyldiamine, aliphatic diamines such as 4,4'-methylenebis (cyclohexylamine), alicyclic diamines and the like.

Among these, the diamine compound is preferably an aromatic diamine compound, and specifically, for example, p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl ether, and the like. 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfide, and 4,4'-diaminodiphenyl sulfone are preferable, and 4,4'-diaminodiphenyl ether and p-phenylenediamine are particularly preferable.

The diamine compound may be used alone or in combination of two or more. When two or more kinds are used in combination, an aromatic diamine compound or an aliphatic diamine compound may be used in combination, or an aromatic diamine compound and an aliphatic diamine compound may be combined.

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

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 velocity: 0.6 mL / min
・ Injection amount: 60 μL
・ Detector: RI (differential refractive index detector)

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 polyimide precursor solution. It is preferably 1% by mass or more and 20% by mass or less.

[Organic amine compound]
The organic amine compound is a compound that amine-chlorides a polyimide precursor (its carboxyl group) 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 solvent 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, N-methylpiperidine, N-ethylpiperidine 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.

Here, the organic amine compound is referred to as an amine compound having an aliphatic cyclic structure or an aromatic cyclic structure having a heterocyclic structure containing nitrogen (hereinafter, referred to as "nitrogen-containing heterocyclic amine compound") from the viewpoint of film-forming property. ) Is also preferable. The nitrogen-containing heterocyclic amine compound is more preferably a tertiary amine compound.
Examples of the nitrogen-containing heterocyclic amine compound include isoquinolins (amine compounds having an isoquinolin skeleton), pyridines (amine compounds having a pyridine skeleton), pyrimidines (amine compounds having a pyrimidine skeleton), and pyrazines (pyrazin skeleton). Amine compounds with), piperazins (amine compounds with a piperazin skeleton), triazines (amine compounds with a triazine skeleton), imidazoles (amine compounds with an imidazole skeleton), morpholins (amine compounds with a morpholin skeleton), polyaniline , Polypyridine, polyamine and the like.

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 carboxyl 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 the solvent tends to increase, and the film-forming property tends to improve. 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.

[Aqueous solvent containing water]
Specifically, the aqueous solvent containing water 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. As the solvent other than water, a water-soluble organic solvent is preferable from the viewpoint of transparency, mechanical strength and the like of the polyimide molded product. Here, water-soluble means that the target substance dissolves in water in an amount of 1% by mass or more at 25 ° C.

The water-soluble organic solvent may be used alone or in combination of two or more.

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.

Specific examples of the aprotonic polar solvent include N-methyl-2-pyrrolidone (NMP), N, N-dimethylformamide (DMF), N, N-dimethylacetamide (DMAc), N, N-diethyl. Acetamide (DEAc), dimethyl sulfoxide (DMSO), hexamethylenephosphoramide (HMPA), N-methylcaprolactam, N-acetyl-2-pyrrolidone, N, N-dimethylimidazolidinone (DMI), 1,3-dimethyl − Examples include imidazolidone.

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. is there. 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, the range in which the polyimide precursor is dissolved in the solvent is controlled by the content of water, the type and amount of the organic amine compound. In the range where the water content is low, the polyimide precursor is easily dissolved in the region where the content of the organic amine compound is low. On the contrary, in the range where the water content is high, the polyimide precursor is easily dissolved in the region where the content of the organic amine compound is high. Further, when the organic amine compound has high hydrophilicity such as having a hydroxyl group, the polyimide precursor is easily dissolved in the region where the water content is high.

Further, a polyimide precursor synthesized with an organic solvent such as an aprotic polar solvent (for example, N-methylpyrrolidone (NMP)) is added to water or a poor solvent such as alcohol, precipitated, and separated, and the polyimide is separated. It may be a precursor.

[Resin particles]
The resin particles are insoluble in an aqueous solvent containing water. Further, the resin particles are insoluble in the polyimide precursor solution.
The resin particles are not particularly limited, but are resin particles made of a resin other than polyimide. Examples thereof include resin particles obtained by polycondensing polymerizable monomers such as polyester resin and urethane resin, and resin particles obtained by radical polymerization of polymerizable monomers such as vinyl resin and olefin resin. .. Examples of the resin particles obtained by radical polymerization include resin particles of (meth) acrylic resin, (meth) acrylic acid ester resin, styrene / (meth) acrylic resin, polystyrene resin, and polyethylene resin.
The resin particles are preferably resin particles that are soluble in a solvent that does not dissolve the polyimide resin, from the viewpoint of removing the resin particles performed in the second step described above.
Among these, as the resin particles, a resin using a radically polymerizable monomer is preferable from the viewpoint of controlling the particle shape and removability, and (meth) acrylic resin, (meth) acrylic acid ester resin, styrene, and the like. It is preferably at least one selected from the group consisting of (meth) acrylic resin and polystyrene resin.

Here, in the present specification, "insoluble" means that the target substance does not dissolve in the target liquid at 25 ° C. and also dissolves within a range of 3% by mass or less. Also includes.
For example, "insoluble in an aqueous solvent containing water" means that the target resin particles are resin particles that are substantially insoluble in an aqueous solvent containing water at 25 ° C., and the resin particles are water. In addition to being insoluble in an aqueous solvent containing, it also includes being dissolved in the range of 3% by mass or less. Further, "not soluble in the polyimide precursor solution" means that the target resin particles are resin particles that are substantially insoluble in the polyimide precursor solution at 25 ° C., and the resin particles are the polyimide precursor. In addition to not dissolving in the solution, it also includes dissolving in the range of 3% by mass or less.
"Soluble in an organic solvent" means that the target resin particles are dissolved in the target organic solvent by 10% or more on a mass basis at 25 ° C.

In addition, in this specification, "(meth) acrylic" means that both "acrylic" and "methacryl" are included.

For the resin particles, the total content of the specific metal group with respect to the porous polyimide film contained in the porous polyimide film and the total content of the specific metal group with respect to the polyimide precursor solution contained in the polyimide precursor solution are within the above-mentioned ranges. From the point of control, the total content of the specific metal group contained in the resin particles may be reduced to, for example, 200 ppm or less (preferably 150 ppm or less). The total content of the specific metal group contained in the resin particles should be as small as possible, and the lower limit is not particularly limited, but is preferably 0 ppm. Note that 0 ppm means below the detection limit. In addition, the total content of the specific metal group contained in the resin particles is measured by the atomic absorption method.

The method for adjusting the total content of the specific metal group contained in the resin particles within the above range is not particularly limited. When the resin particles are, for example, vinyl resin particles, the synthesis method thereof is not particularly limited, and known polymerization methods (emulsion polymerization, soap-free emulsion polymerization, suspension polymerization, miniemulsion polymerization, microemulsion polymerization, etc.) are not particularly limited. Radical polymerization method) can be applied.

Among them, for example, in terms of adjusting the total content of the specific metal group contained in the resin particles to the above range, a method of emulsion polymerization using a surfactant that does not contain the specific metal group, and no surfactant is used. It is preferable to obtain the resin particles by a method by soap-free emulsion polymerization or a method of washing the resin particles obtained by the emulsion polymerization method.
That is, the resin particles are preferably at least one of surfactant emulsion polymerization particles, soap-free emulsion polymerization particles, and cleaning resin particles that do not contain a specific metal group. These resin particles may be used alone or in combination of two or more.
In the present specification, the cleaning resin particles refer to resin particles obtained by cleaning the resin particles and adjusting the total content of the specific metal group contained in the resin particles within the above range.

For example, when the emulsion polymerization method is applied to the production of vinyl resin particles, monomers such as styrenes and (meth) acrylic acids are mixed in water in which a water-soluble polymerization initiator such as potassium persulfate and ammonium persulfate is dissolved. In addition, by polymerization (soap-free emulsion polymerization) without using a surfactant, vinyl resin particles in which the total content of the specific metal group contained in the resin particles is in the above range can be obtained.
In addition, monomers such as styrenes and (meth) acrylic acids are added to water in which a water-soluble polymerization initiator such as potassium persulfate and ammonium persulfate is dissolved, and if necessary, a specific metal group is contained. By adding a non-surfactant and heating by heating while stirring, vinyl resin particles in which the total content of the specific metal group contained in the resin particles is in the above range can be obtained.
Further, by washing the obtained vinyl resin particles, vinyl resin particles in which the total content of the specific metal group contained in the resin particles is in the above range can be obtained. In particular, when a surfactant containing a specific metal group of metals (for example, anionic surfactant such as sodium lauryl sulfate or sodium dodecyl sulfate) is used as the surfactant, the obtained vinyl resin particles are washed. Then, vinyl resin particles having a total content of the specific metal group in the above range can be obtained.

When a surfactant is used in the production of vinyl resin particles by the emulsion polymerization method, the surfactant is not particularly limited, but the specific metal group is in that the step of washing the obtained resin particles can be omitted. It is preferable to use a surfactant that does not contain the metal of.
Examples of the surfactant containing no metal in the specific metal group include an anionic surfactant of an ammonium salt such as a sulfonate type; a nonionic surfactant such as an ether type, an ester type, and an ester ether type; Cationic surfactants such as ammonium salt type; amphoteric surfactants such as betaine type; and the like can be mentioned.

Examples of the vinyl resin monomer include styrene and alkyl-substituted styrene (for example, α-methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2-ethylstyrene, 3-ethylstyrene, 4-ethylstyrene, 4). -Styrene having a styrene skeleton such as (ethylstyrene, etc.), halogen-substituted styrene (for example, 2-chlorostyrene, 3-chlorostyrene, 4-chlorostyrene, etc.), vinylnaphthalene, etc .; methyl (meth) acrylate, (meth) acrylic Esters having a vinyl group such as ethyl acid acid, n-propyl (meth) acrylate, n-butyl (meth) acrylate, lauryl (meth) acrylate, 2-ethylhexyl (meth) acrylate; acrylonitrile, methacrylonitrile Vinyl nitriles such as vinyl methyl ether, vinyl ethers such as vinyl isobutyl ether; vinyl ketones such as vinyl methyl ketone, vinyl ethyl ketone, vinyl isopropenyl ketone; (meth) acrylic acid, maleic acid, silicic acid, fumaric acid. , Acids such as vinyl styrene; bases such as ethyleneimine, vinylpyridine, vinylamine; and vinyl resin units obtained by polymerizing monomers such as.
Other monomers include monofunctional monomers such as vinyl acetate, bifunctional monomers such as ethylene glycol dimethacrylate, nonandiacrylate and decanediol diacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate and the like. Polyfunctional monomer of the above 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.

When the monomer used in the resin constituting the vinyl resin particles contains styrene, the ratio of styrene to all the monomer components is preferably 20% by mass or more and 100% by mass or less, and 40% by mass or more and 100% by mass or less. The following is more preferable.

The average particle size of the resin particles is not particularly limited. For example, it is 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 more preferably 0.25 μm or more and 0.4 μm or less. When the average particle size of the resin particles is in this range, the productivity of the resin particles is improved and the cohesiveness is easily suppressed.
The average particle size of the resin particles is divided into particle size ranges (channels) using the particle size distribution obtained by measurement with a laser diffraction type particle size distribution measuring device (for example, Coulter Counter LS13 (manufactured by Beckman Coulter)). On the other hand, the cumulative distribution of the volume is subtracted from the small particle size side, and the particle size that is cumulatively 50% of all particles is measured as the volume average particle size D50v.

As the resin particles of the resin other than the polyimide resin soluble in the solvent that does not dissolve the polyimide resin, for example, uncrosslinked (non-crosslinked) resin particles having a non-crosslinked structure are preferable, but as long as they have the above-mentioned solubility. It may be crosslinked. Specific examples of the resin particles include polymethyl methacrylate (MB-series, manufactured by Sekisui Plastics Co., Ltd.) and (meth) acrylic acid ester / styrene copolymer (FS-series: manufactured by Nippon Paint Co., Ltd.). , Polystyrene and the like. When these resin particles are used, they may be washed and used.

If necessary, acetal resin such as polyvinyl butyral resin; polyamide resin such as nylon; acrylic resin; vinyl resin such as polyvinyl chloride resin and polyvinylidene chloride resin; polyurethane resin; polyvinylpyrrolidone, polyethylene glycol, polyvinyl alcohol, etc. Such as water-soluble ones may be added.

In the resin particle-dispersed polyimide precursor solution, the content of the resin particles is 20% by mass or more and 600% by mass or less (preferably 25% by mass or more) with respect to 100 parts by mass of the polyimide precursor solid content in the polyimide precursor solution. It is preferably in the range of 300% by mass or less, more preferably 30% by mass or more and 100% by mass or less).

[Other additives]
In the method for producing a porous film according to the present embodiment, the polyimide precursor solution 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 an acid anhydride, an acid catalyst such as a phenol derivative, a sulfonic acid derivative, or a benzoic acid derivative may be used.

Further, the polyimide precursor solution, depending on the intended use of the porous polyimide film, for example, conductive materials added to imparting conductivity (conductivity (e.g., a volume resistivity of less than 10 ⁷ Ω · cm) or semiconductive (e.g., less volume resistivity 10 ⁷ Ω · cm or more ^{10 13 Ω} · cm)) may contain.
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.

Further, the polyimide precursor solution may contain inorganic particles added to improve the mechanical strength depending on the purpose of use of the porous polyimide film. Examples of the inorganic particles include particulate materials such as silica powder, alumina powder, barium sulfate powder, titanium oxide powder, mica, and talc. _{Further, LiCoO 2} , LiMn ₂ O and the like used as electrodes of a lithium ion battery may be contained.

-Manufacturing method of polyimide precursor solution-
The method for producing the polyimide precursor solution is not particularly limited, and examples thereof include the following production methods.

One example is a method of polymerizing a tetracarboxylic acid dianhydride and a diamine compound in an aqueous solvent in the presence of an organic amine compound to produce a resin (polyimide precursor) to obtain a polyimide precursor solution. ..
According to this method, since an aqueous solvent is applied, the productivity is high, and the polyimide precursor solution is produced in one step, which is advantageous in terms of simplification of the process.

As another example, a resin (polyimide precursor) is obtained by polymerizing a tetracarboxylic acid dianhydride and a diamine compound in an organic solvent such as an aprotic polar solvent (for example, N-methylpyrrolidone (NMP)). Is generated, and then put into water or an aqueous solvent such as alcohol to precipitate a resin (polyimide 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.

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.

<Method of producing resin particles>
-Resin particles (1-1)-
800 ml of deionized water and 400 ml of methyl methacrylate monomer were placed in a flask, and the temperature was raised to 70 ° C. under a nitrogen atmosphere with stirring at 300 rpm. 0.8 g of the reaction initiator 2,2'-azobis (2-methylpropion amidine) dihydroclide was dissolved in 10 ml of deionized water and added to the flask. The reaction was carried out at 70 ° C. for 6 hours to obtain polymethylmethacrylate resin particles which are soap-free emulsion polymerization particles.

-Resin particles (1-2)-
800 ml of deionized water was placed in a flask, and the temperature was raised to 70 ° C. under a nitrogen atmosphere while stirring at 300 rpm. After adding 100 ml of styrene monomer, when the temperature stabilizes, dissolve 0.35 g of potassium persulfate in 50 ml of deionized water, heat to 70 ° C., add to the flask, and react for 30 hours with soap-free emulsion polymerized particles. Obtained certain styrene resin particles.

-Resin particles (1-3)-
225 g of methyl methacrylate monomer, 5.4 g of Ramtel PD-420 (manufactured by Kao Corporation) as a nonionic surfactant, 0.36 g of potassium persulfate as an initiator, and 112 g of ion-exchanged water were stirred at 600 rpm for 30 minutes. A pre-emulsion was made.
To 160 g of ion-exchanged water, 0.09 g of potassium persulfate, 1.35 g of Ramtel PD-420 (manufactured by Kao Corporation) as a nonionic surfactant, and 17 g of pre-emulsion were added, and the temperature was raised to 80 ° C. by nitrogen substitution. Initial polymerization was carried out for 30 minutes. To this, the pre-emulsion was dropwise-polymerized over 3 hours and further aged for 1 hour to obtain polymethylmethacrylate resin particles which are nonionic surfactant emulsion polymerization particles.

-Resin particles (1-4)-
Cationic surfactant emulsion polymerization particles in the same manner as resin particles (1-3), except that the nonionic surfactant Lamtel PD-420 was replaced with the cationic surfactant Coatamine 24P (manufactured by Kao Co., Ltd.). Polymethylmethacrylate resin particles were obtained.

-Resin particles (1-5)-
Amphoteric surfactant emulsion polymerized particles in the same manner as resin particles (1-3), except that the nonionic surfactant Ramtel PD-420 was replaced with the amphoteric surfactant Anchtor 20AB (manufactured by Kao Corporation). Polymethylmethacrylate resin particles were obtained.

-Resin particles (1-6)-
The nonionic surfactant Ramtel PD-420 was replaced with the anionic surfactant Ramtel PD-104 (manufactured by Kao Co., Ltd.) having no metal element, in the same manner as the resin particles (1-3). Polymethylmethacrylate resin particles, which are anionic surfactant emulsion polymerization particles having no metal element, were obtained.

-Resin particles (1-7)-
Similar to resin particles (1-3), anionic surfactant having a metal element, except that the nonionic surfactant Lamtel PD-420 was replaced with sodium lauryl sulfate, which is an anionic surfactant having a metal element. Polymethylmethacrylate resin particles, which are emulsion polymerization particles, were obtained.

-Resin particles (1-8)-
The resin particles (1-7) were spray-dried to obtain a polymethylmethacrylate powder. In addition, sodium ion and potassium ion which are metal ions were detected by atomic absorption spectroscopy.

-Resin particles (1-9)-
The resin particles (1-7) were washed with water and then dried by spray drying to obtain polymethylmethacrylate powder which is a washing resin particle. In addition, sodium ion and potassium ion which are metal ions were detected by atomic absorption spectroscopy.

-Resin particles (1-10)-
A commercially available aqueous dispersion of a styrene-acrylic copolymer having an average particle size of 0.1 μm (FS-102E: manufactured by Nippon Paint Co., Ltd., solid content concentration: 21% by mass) was prepared. Sodium ion, which is a metal ion, was detected by atomic absorption spectroscopy.

<Examples 1 to 8, Comparative Examples 1 and 2>
(Preparation of polyimide precursor)
-Polyimide precursor (2-1)-
In 150 parts of the dispersion liquid of the resin particles (1-1), 10 parts of 3,3', 4,4'-biphenyltetracarboxylic dianhydride, 3.5 parts of p-phenylenediamine, and 85 parts of deionized water Was added, the temperature was raised to 50 ° C., and the mixture was stirred. Then, N-methylmorpholine was added dropwise over 1 hour, and the mixture was stirred for 24 hours to dissolve and react to obtain a resin particle-dispersed polyimide precursor solution (2-1).

-Polyimide precursor (2-2)-
The solid content concentration of the dispersion liquid of the resin particles (1-2) was adjusted to be the same as the solid content concentration of the dispersion liquid of the resin particles (1-1). Then, the resin particles were obtained in the same manner as the polyimide precursor (2-1) except that the dispersion liquid of the resin particles (1-1) was replaced with the dispersion liquid of the resin particles (1-2) whose solid content concentration was adjusted. A dispersed polyimide precursor solution (2-2) was obtained.

-Resin particle-dispersed polyimide precursors (2-3) to (2-7)-
The solid content concentration of the dispersion liquid of the resin particles (1-3) to (1-7) was adjusted to be the same as the solid content concentration of the dispersion liquid of the resin particles (1-1). Then, the polyimide precursor (2-1) was replaced with the dispersion of the resin particles (1-3) to (1-7) whose solid content was adjusted, except that the dispersion of the resin particles (1-1) was replaced with the dispersion of the resin particles (1-3) to (1-7). ), The resin particle-dispersed polyimide precursor solutions (2-3) to (2-7) were obtained.

-Resin particle dispersion polyimide precursor (2-8)-
A flask equipped with a stirring rod, a thermometer, and a dropping funnel was filled with 270 parts of deionized water. To this, 3.5 parts of p-phenylenediamine and 10 parts of 3,3', 4,4'-biphenyltetracarboxylic dianhydride were added, and the temperature was raised to 50 ° C. and stirred. Then, 9.5 parts of N-methylmorpholine was added dropwise over 1 hour, and the mixture was stirred for 24 hours to dissolve and react to obtain a polyimide precursor. To this, 21 parts of the powder particles obtained from the resin particles (1-8) were added, and the mixture was stirred and mixed with a dissolver for 3 hours to obtain a resin particle-dispersed polyimide precursor solution (2-8).

-Resin particle dispersed polyimide precursors (2-9), (2-10)-
Same as the resin particle-dispersed polyimide precursor solution (2-8) except that the powder particles obtained from the resin particles (1-8) were replaced with the cleaning resin particles obtained from the resin particles (1-9). To obtain a resin particle-dispersed polyimide precursor solution (2-9).
Further, the resin particles were obtained in the same manner as the resin particle-dispersed polyimide precursor solution (2-8) except that the powder particles obtained from the resin particles (1-8) were replaced with the resin particles (1-10). A dispersed polyimide precursor solution (2-10) was obtained.

(Preparation of porous polyimide film)
-Resin particle dispersed polyimide precursors (3-1) to (3-10)-
Resin particle-dispersed polyimide precursor solutions (2-1) to (2-10) were applied to a glass plate so as to have a thickness of 100 μm, and dried. Then, it was calcined at 320 degreeC for 1 hour, and particles were removed to prepare porous polyimide films (3-1) to (3-10).

<Evaluation>
(Metallicity)
The total content of the specific metal group in the polyimide precursor solution of the resin particle-dispersed polyimide precursor solution obtained in each example and the total content of the specific metal group in the porous polyimide film were measured by the atomic absorption method.

(Cycle electrical characteristics)
Using the porous polyimide film obtained in each example, a lithium ion battery was prepared, and the reduction rate of the battery capacity when repeatedly charged and discharged 500 times (1C charge and 1C discharge at 25 ° C.) was investigated. The smaller the reduction rate, the better the cycle characteristics. Those with a reduction rate of less than 20% were regarded as "good", and those with a reduction rate of 20% or more were regarded as "bad".

In Table 1, among (metal species), K indicates potassium and Na indicates sodium.

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

Claims (11)

The total content of the metal group containing an aqueous solvent containing water, resin particles insoluble in the aqueous solvent, an organic amine compound, and a polyimide precursor, and consisting of an alkali metal excluding Li, an alkaline earth metal, and silicon. the polyimide precursor solution, I der below 200 ppm, the resin particles, polyimide precursor solution is washed resin particles. The polyimide precursor solution according to claim 1 , wherein the average particle size of the resin particles is 0.1 μm or more and 0.5 μm or less. The polyimide precursor solution according to claim 2 , wherein the average particle size of the resin particles is 0.25 μm or more and 0.5 μm or less. The content of the resin particles with respect to the polyimide precursor solid 100 parts by weight, the polyimide precursor solution according to any one of claims 1 to 3 or less 600 parts by mass or more 20 parts by weight. The polyimide precursor solution according to claim 4 , wherein the content of the resin particles is 30 parts by mass or more and 100 parts by mass or less with respect to 100 parts by mass of the solid content of the polyimide precursor. The aqueous solvent, a polyimide precursor solution according to any one of claims 1 to 5 the content of the water in an aqueous solvent total amount of 100 mass% or less than 50 wt%. The polyimide precursor solution according to claim 6 , wherein the aqueous solvent has a water content of 80% by mass or more and 100% by mass or less with respect to the total amount of the aqueous solvent. The organic amine compound, a polyimide precursor solution according to any one of claims 1 to 7 a tertiary amine compound. The organic amine compound is 2-dimethylaminoethanol, 2-diethylaminoethanol, 2-dimethylaminopropanol, pyridine, triethylamine, picoline, N-methylmorpholin, N-ethylmorpholin, 1,2-dimethylimidazole, 2-ethyl-. The polyimide precursor solution according to claim 8 , which is at least one selected from the group consisting of 4-methylimidazole, N-methylpiperidine, and N-ethylpiperidine. The polyimide precursor solution according to claim 9 , wherein the organic amine compound is an amine compound having a morpholine skeleton. After forming a coating film by coating the polyimide precursor solution according to any one of claims 1 to 10, and drying the coating, the coating comprising the polyimide precursor and the resin particles The first step of forming and
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 resin particles.
A method for producing a porous polyimide film having.

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