JP2020029486A - Polyimide powder, polyimide varnish, polyimide film and polyimide porous membrane - Google Patents

Abstract

To provide polyimide powder and polyimide varnish which give a polyimide membrane excellent in heat resistance, transparency and mechanical properties, and exhibit lower color and have less impurities, and to provide a polyimide film and a polyimide porous membrane obtained by forming films by using the polyimide powder and the polyimide varnish.SOLUTION: The polyimide powder has a structural unit derived from at least one kind of aromatic diamine compound and a structural unit derived from two or more kinds of tetracarboxylic acids, and has an imidization ratio of 90% or more and is soluble in N,N-dimethylacetamide of 5 wt.% or more. A structural unit derived from 2,2'-bis(trifluoromethyl)-4,4'- diaminobiphenyl accounts for 50 mol% or more of the whole structural unit derived from the at least one aromatic diamine compound. A structural unit derived from 4,4'-(1,1,1,3,3,3-hexafluoropropane-2,2-diyl) diphthalic dianhydride accounts for 30 to 70 mol% of the whole structural unit derived from the two or more kinds of tetracarboxylic acids. A structural unit derived from 3,3', 4,4'-biphenyltetracarboxylic dianhydride accounts for 30 to 60 mol% of the whole structural unit derived from the two or more kinds of tetracarboxylic acids.SELECTED DRAWING: None

Description

  The present invention relates to a polyimide powder, a polyimide varnish, a polyimide film and a polyimide porous film, and particularly, a polyimide film having excellent heat resistance, transparency and mechanical properties, which is suitably used for display applications and electronic material applications. Also, the present invention relates to a polyimide powder and a polyimide varnish which provide a polyimide porous film which can be suitably used for a separator of a lithium ion battery or the like which has both good resistance to an electrolyte and heat resistance.

  Polyimide resin is used as a plastic having excellent heat resistance in a wide range of fields requiring heat resistance and high reliability, such as aerospace field, electric insulation field, and electronic field. In recent years, transparent polyimides having both heat resistance and transparency have been proposed. For example, Patent Literature 1 discloses an excellent transparency suitable for an optical waveguide, which is synthesized from a specific monomer containing a fluorine atom. Soluble polyimides have been proposed. Patent Document 2 proposes a transparent polyimide soluble in an organic solvent using a specific alicyclic diamine. However, since the polyimide described in Patent Document 1 is subjected to a heat treatment at a temperature of 300 ° C. or more with respect to the polyimide after film formation, it is difficult to ensure sufficient transparency, and the polyimide described in Patent Document 2 is described. Since polyimide uses an alicyclic diamine as a raw material, there is a problem that heat resistance is poor and the polyimide is colored by heating.

  As a polyimide powder, a method is disclosed in which a poor solvent such as water or methanol is added to a soluble polyimide varnish to precipitate a massive polyimide resin (Patent Document 3).

  Patent Document 4 proposes a powder of an imidized polyamic acid obtained by polymerizing a diamine and an acid dianhydride.

  However, the polyimide powders described in Patent Literature 3 and Patent Literature 4 do not pay attention to the mechanical properties, particularly elastic modulus, of the polyimide film obtained from the polyimide powder, However, when a stress such as bending or pulling is applied, there is a problem that it is easily deformed.

  Patent Document 5 discloses a polyimide film having a relatively low linear expansion coefficient and obtained by removing an imidized polyamic acid obtained by polymerizing diamines and acid dianhydrides. Particularly, in Examples 1 to 3, 2,2'-bis (trifluoromethyl) -4,4'-diaminobiphenyl was used as a diamine, and 2,2-bis (3,4-dicarboxyphenyl) was used as an acid anhydride. A) a polyamic acid obtained by copolymerizing hexafluoropropane dianhydride (6FDA) and biphenyltetracarboxylic dianhydride (BPDA) in a molar ratio of 6FDA: BPDA = 80: 20 to 50:50; After imidation in methanol, the solid content powder of the polyimide obtained by precipitation, filtration and drying in methanol is redissolved in an N, N-dimethylacetamide solvent. As a polyimide solution was film is applied onto a stainless steel plate, a polyimide film obtained finally raised to 300 ° C. is disclosed. However, in the technique disclosed in Patent Document 5, the imidation ratio is suppressed to as low as about 80.5% in order to maintain the solubility of the polyimide powder in a solvent. Heat treatment at the above temperature completes imidization. Thus, when the imidation ratio of the polyimide powder is low, when the polyimide varnish is converted to a polyimide powder, or when stored as a polyimide powder, the molecular weight decreases with time and the mechanical properties decrease accordingly. In addition, the heat treatment at a high temperature in the state of the film causes a problem of discoloration of the film. In addition, since heat treatment at a high temperature is required, when a polyimide film is formed and heat-treated, it is necessary to heat-treat the polyimide alone or use a substrate having high heat resistance. There was a problem that it was difficult to select a base material and a heat treatment method.

JP-A-4-235505 JP 2000-169579 A JP-A-2004-285355 JP-T-2013-523939 JP 2011-208143 A

  An object of the present invention is to provide a polyimide film having excellent heat resistance, transparency and mechanical properties, a polyimide powder having little coloring and impurities, a polyimide varnish and a polyimide film or a polyimide porous film obtained by forming the same. Is to give.

  The present inventors, by increasing the imidation rate of the polyimide powder having a specific structure, while maintaining transparency and solubility in a solvent, mechanical properties, particularly to give a film having a high elastic modulus, Further, they have found that such a powder gives a porous film having excellent heat resistance and electrolytic solution resistance, and completed the present invention.

According to the present invention, the following polyimide powder, polyimide varnish, polyimide film and polyimide porous film can be obtained.
[1] An imidization having a structural unit derived from at least one kind of aromatic diamine compound and a structural unit derived from two or more kinds of tetracarboxylic acids and being soluble in N, N-dimethylacetamide in an amount of 5% by weight or more. A polyimide powder having a ratio of 90% or more,
The structural unit derived from 2,2′-bis (trifluoromethyl) -4,4′-diaminobiphenyl accounts for 50 mol% or more of the entire structural unit derived from the at least one aromatic diamine compound;
The structural unit derived from 4,4 ′-(1,1,1,3,3,3-hexafluoropropane-2,2-diyl) diphthalic dianhydride is derived from the two or more kinds of tetracarboxylic acids. Accounts for 30-70 mol% of the total structural units,
The structural unit derived from 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride occupies 30 to 60 mol% of the total structural units derived from the two or more kinds of tetracarboxylic acids. Polyimide powder.
[2] The polyimide powder is formed by polymerization of at least one kind of aromatic diamine compound and two or more kinds of tetracarboxylic dianhydride into polyamic acid, a chemical imidization reaction, and precipitation of the resulting polyimide to form a powder. , And manufactured through the process of drying,
2,2′-bis (trifluoromethyl) -4,4′-diaminobiphenyl is used as the aromatic diamine compound in an amount of 50 mol% or more of the entire aromatic diamine compound;
4,4 ′-(1,1,1,3,3,3-hexafluoropropane-2,2-diyl) diphthalic dianhydride is used as the tetracarboxylic dianhydride based on the molar amount of all tetracarboxylic acids. The polyimide powder according to [1], wherein 30 to 70% of 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride is used in the range of 30 to 60%.
[3] The polyimide powder according to [1] or [2], wherein the reduced viscosity is in a range of 2.0 to 3.5 dL / g.
[4] A 50 μm-thick film obtained by forming a polyimide solution obtained by dissolving in N, N-dimethylacetamide has a total light transmittance of 80% or more and a yellowness of 3 or less. The polyimide powder according to any one of [1] to [3].
[5] A 50 μm-thick film obtained by forming a polyimide solution obtained by dissolving in N, N-dimethylacetamide has a tensile modulus of 4.0 GPa or more, [1] to [4]. ] The polyimide powder according to any one of the above.
[6] A polyimide varnish containing the polyimide powder according to any one of [1] to [5] in a solvent at a concentration of 1 to 30% by weight.
[7] The polyimide varnish according to [6], further comprising 10 to 100 parts by weight of inorganic particles based on 100 parts by weight of the polyimide.
[8] A polyimide film having a thickness of 1 to 200 µm, obtained by forming the polyimide varnish of [6] or [7] into a film.
[9] The polyimide film according to [8], wherein the tensile elastic modulus is 4.0 GPa or more.
[10] A polyimide porous membrane having a thickness of 1 to 200 µm, obtained by forming the polyimide varnish of [6] or [7].

  The present invention provides a polyimide film having excellent mechanical properties such as heat resistance, transparency and high elastic modulus, and a polyimide porous film having excellent electrolytic solution resistance and heat resistance. Varnish can be obtained.

  Polyimide powder of the first embodiment of the present invention, from at least one kind of aromatic diamine compound and two or more kinds of tetracarboxylic dianhydrides described below, polymerization to polyamic acid, chemical imidization reaction, It is manufactured through the steps of forming a powder by precipitation of the resulting polyimide and drying.

  The polyimide varnish according to the second embodiment of the present invention can be manufactured by dissolving the polyimide powder in an organic solvent so as to have a concentration of 1 to 30%.

1. Raw materials 1.1. Aromatic diamine compound As the aromatic diamine compound used in the present invention, 2,2′-bis (trifluoromethyl) -4,4′-diaminobiphenyl (hereinafter, also referred to as TFMB) is essential. The amount is at least 50 mol%, preferably at least 70 mol%, more preferably at least 90 mol%, based on the molar amount of the wholly aromatic diamine. Further, only TFMB may be used as the aromatic diamine compound. When the amount of TFMB used is less than 50 mol% of the total aromatic diamine compound, it becomes difficult to obtain transparency and solubility in a solvent of the obtained polyimide powder.

  As the aromatic diamine compound other than TFMB, any aromatic diamine compound can be used as long as it does not exceed 50 mol% of the entire aromatic diamine compound. For example, m-phenylenediamine, p-phenylenediamine, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl sulfide, 3,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl Sulfone, 3,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminobenzophenone, 3,3'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 4,4'-diamino Diphenylmethane, 2,2-bi (4-aminophenyl) propane, 2,2-bis (3-aminophenyl) propane, 2- (3-aminophenyl) -2- (4-aminophenyl) propane, 2,2-bis (4-aminophenyl ) -1,1,1,3,3,3-hexafluoropropane, 2,2-bis (3-aminophenyl) -1,1,1,3,3,3-hexafluoropropane, 2- (3 -Aminophenyl) -2- (4-aminophenyl) -1,1,1,3,3,3-hexafluoropropane, 1,3-bis (3-aminophenoxy) benzene, 1,3-bis (4 -Aminophenoxy) benzene, 1,4-bis (3-aminophenoxy) benzene, 1,4-bis (4-aminophenoxy) benzene, 4,4'-bis (4-aminophenoxy) biphenyl, 3,3 ' -Screw (4 Aminophenoxy) biphenyl, 3,4'-bis (3-aminophenoxy) biphenyl, bis [4- (4-aminophenoxy) phenyl] sulfide, bis [3- (4-aminophenoxy) phenyl] sulfide, bis [4 -(3-aminophenoxy) phenyl] sulfide, bis [3- (4-aminophenoxy) phenyl] sulfide, bis [3- (3-aminophenoxy) phenyl] sulfide, bis [3- (4-aminophenoxy) phenyl ] Sulfone, bis [4- (4-aminophenyl) sulfone, bis [3- (3-aminophenoxy) phenyl] sulfone, bis [4- (3-aminophenyl) sulfone, bis [4- (3-aminophenoxy) ) Phenyl] ether, bis [4- (4-aminophenoxy) phenyl] ether, bis [ 3- (3-aminophenoxy) phenyl] ether, bis [4- (3-aminophenoxy) phenyl] methane, bis [4- (4-aminophenoxy) phenyl] methane, bis [3- (3-aminophenoxy) Phenyl] methane, bis [3- (4-aminophenoxy) phenyl] methane, 2,2-bis [4- (3-aminophenoxy) phenyl] propane, 2,2-bis [4- (4-aminophenoxy) Phenyl] propane, 2,2-bis [3- (3-aminophenoxy) phenyl] propane, 2,2-bis [4- (3-aminophenoxy) phenyl] -1,1,1,3,3,3 -Hexafluoropropane, 2,2-bis [4- (4-aminophenoxy) phenyl] -1,1,1,3,3,3-hexafluoropropane, 2,2-bis [3- ( -Aminophenoxy) phenyl] -1,1,1,3,3,3-hexafluoropropane, 2,2-bis [3- (4-aminophenoxy) phenyl] -1,1,1,3,3 3-hexafluoropropane, 1,3-bis [4- (4-amino-6-trifluoromethylphenoxy) -α, α-dimethylbenzyl] benzene, 1,3-bis [4- (4-amino-6 -Fluoromethylphenoxy) -α, α-dimethylbenzyl] benzene, 2,2′-dimethyl-4,4′-diaminobiphenyl, 3,3′-dimethyl-4,4′-diaminobiphenyl, 3,3′- Aromatic diamine compounds such as bis (trifluoromethyl) -4,4'-diaminobiphenyl can be used. The aromatic diamine compound referred to in the present invention refers to a compound having one or more aromatic rings and two amino groups.

1.2. Tetracarboxylic dianhydride The tetracarboxylic dianhydride used in the present invention includes 4,4 ′-(1,1,1,3,3,3-hexafluoropropane-2,2-diyl) diphthalic acid The dianhydride (hereinafter, also referred to as 6FDA) is 30 to 70 mol% based on the molar amount of the total tetracarboxylic dianhydride, and 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (hereinafter, referred to as 6FDA). BPDA) is used in the range of 30 to 60 mol%. As the tetracarboxylic dianhydride, only two kinds of 6FDA and BPDA may be used, and pyromellitic dianhydride, 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride, 1,4- Other tetracarboxylic dianhydrides such as hydroquinone dibenzoate-3,3 ', 4,4'-tetracarboxylic dianhydride and 3,3', 4,4'-diphenylethertetracarboxylic dianhydride are further added. Copolymerization is also possible.

2. Method for Producing Polyimide Powder Polyimide powder is prepared by using the above aromatic diamine compound and tetracarboxylic dianhydride to polymerize into polyamic acid, a chemical imidization reaction, forming a powder by precipitation of the resulting polyimide, and drying. It is manufactured through the steps of

2.1. Polymerization into polyamic acid Polymerization into polyamic acid can be performed by reacting the above aromatic diamine compound and tetracarboxylic dianhydride under dissolution in a solvent in which the generated polyamic acid is soluble. Solvents used for the polymerization into polyamic acid include N, N-dimethylacetamide, N, N-dimethylformamide, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, dimethylsulfoxide and the like. Can be used.

  The polymerization reaction to the polyamic acid is preferably performed while stirring in a reaction vessel equipped with a stirring device. For example, a method in which a predetermined amount of an aromatic diamine compound is dissolved in the above solvent, a tetracarboxylic dianhydride is charged with stirring, and a reaction is performed to obtain a polyamic acid, and the tetracarboxylic dianhydride is dissolved in the solvent. A method for obtaining a polyamic acid by introducing an aromatic diamine compound while stirring and obtaining a polyamic acid, a method for obtaining a polyamic acid by alternately charging and reacting an aromatic diamine compound and a tetracarboxylic dianhydride, and the like. Can be

  The temperature of the polymerization reaction to the polyamic acid is not particularly limited, but is preferably performed at a temperature of 0 to 70 ° C, more preferably 10 to 60 ° C, and still more preferably 20 to 50 ° C. By performing the polymerization reaction within the above range, it becomes possible to obtain a high-molecular-weight polyamic acid with little coloring and excellent transparency.

  The total amount of the aromatic diamine compound and the total amount of the tetracarboxylic dianhydride used for the polymerization into the polyamic acid are generally used in equimolar amounts. The molar amount of the acid dianhydride / the molar amount of the aromatic diamine compound (molar ratio) can be changed in the range of 0.95 to 1.05. The molar ratio between the tetracarboxylic dianhydride and the aromatic diamine compound is preferably in the range of 1.001 to 1.02, and more preferably 1.001 to 1.01. By slightly increasing the amount of tetracarboxylic dianhydride as described above, the degree of polymerization of the obtained polyamic acid can be stabilized, and the unit derived from tetracarboxylic dianhydride is arranged at the terminal of the polymer. As a result, it is possible to give a polyimide which is less colored and has excellent transparency.

  The concentration of the resulting polyamic acid solution is preferably adjusted to an appropriate concentration (for example, about 10 to 30% by weight) so that the viscosity of the solution is kept appropriate and the handling in the subsequent steps is facilitated.

2.2. Chemical imidization reaction Next, an imidizing agent is added to the obtained polyamic acid solution to perform a chemical imidization reaction. As the imidizing agent, carboxylic anhydrides such as acetic anhydride, propionic anhydride, succinic anhydride, phthalic anhydride, and benzoic anhydride can be used.From the viewpoint of cost and ease of removal after the reaction, anhydrides can be used. Preferably, acetic acid is used. The equivalent of the imidizing agent to be used is not less than the equivalent of the amide bond of the polyamic acid which undergoes the chemical imidization reaction, and is preferably 1.2 to 5 times, preferably 1.5 to 4.5 times the equivalent of the amide bond. Is more preferable, and more preferably 2 to 4 times. By using an excess of the imidizing agent with respect to the amide bond, the imidization reaction can be efficiently performed even at a relatively low temperature, and a polyimide having an imidization ratio of 90% or more can be easily obtained.

  In the chemical imidization reaction, aliphatic, aromatic or heterocyclic tertiary amines such as pyridine, picoline, quinoline, isoquinoline, trimethylamine and triethylamine can be used as an imidization accelerator. By using such amines, an imidization reaction can be efficiently performed at a low temperature, and as a result, coloring during the imidization reaction can be suppressed, and a more transparent polyimide can be obtained.

  Although there is no particular limitation on the temperature of the chemical imidization reaction, the reaction is preferably performed at 10 ° C or higher and lower than 50 ° C, more preferably at 15 ° C or higher and lower than 45 ° C. By performing the chemical imidization reaction at a temperature of 10 ° C. or more and less than 50 ° C., coloring during the imidization reaction is suppressed, and a polyimide having excellent transparency can be obtained.

2.3. Powderization Next, the polyimide in the polyimide solution obtained by imidization is powdered. The powderization of the polyimide can be performed by any method, but a method of adding a poor solvent for the polyimide to precipitate the polyimide to form a powder is simple and preferable. When a polyimide is precipitated and powdered by adding a poor solvent, any poor solvent that can precipitate the polyimide can be used as the poor solvent, and it is desirable that the solvent be miscible with the solvent of the polyimide solution. Specifically, water, methanol, ethanol and the like can be used. Then, it is preferable to use methanol as the poor solvent since a polyimide powder having a stable shape can be obtained with high yield.

  When depositing and pulverizing polyimide with a poor solvent, the amount of the poor solvent to be used needs to be charged in an amount sufficient to perform the deposition and powdering of the polyimide, the structure of the polyimide, the solvent of the polyimide solution, Determined in consideration of the solution concentration of the polyimide, etc., usually at least 0.5 times the weight of the polyimide solution, preferably at least 0.8 times the weight of the polyimide solution, more preferably at least 1 time the weight of the polyimide solution. Use a poor solvent. By using a poor solvent having a weight of 0.5 or more times the weight of the polyimide solution, a polyimide powder having a stable shape can be obtained at a high yield. In addition, usually, a poor solvent having a weight of 10 times or less of the polyimide solution weight, preferably 7 times or less of the polyimide solution weight, more preferably 5 times or less of the polyimide solution weight, and still more preferably 4 times or less of the polyimide solution weight is used. I do.

  When the pulverization of the polyimide is performed by adding the poor solvent to the polyimide solution as described above, it is preferable to perform the method by dropping the poor solvent while stirring the polyimide solution. In order to facilitate the diffusion of the poor solvent, the polyimide solution is preferably adjusted in advance to a concentration of preferably 5 to 30% by weight, more preferably about 10 to 20% by weight. Further, the preferred average particle diameter of the polyimide powder obtained by the present invention is 0.02 to 0.8 mm, but the average particle diameter can be controlled by the addition rate of the poor solvent to the polyimide solution.

  In the present invention, there is no particular limitation on the temperature of powdering the polyimide, but when performing precipitation and powdering by adding a poor solvent, from the viewpoint of suppressing evaporation of the poor solvent and efficiently performing precipitation. It is preferably performed at a temperature of 50 ° C. or lower, more preferably at 40 ° C. or lower.

2.4. Drying Next, the obtained polyimide powder is dried to remove a solvent, an imidizing agent, an imidization accelerator, a poor solvent, and the like. Drying is carried out after removing the polyimide solvent, imidizing agent, and imidization accelerator by removing the polyimide powder by filtering the polyimide powder in advance with a filtration device and further washing as necessary. It is preferable in terms of performance.

  Drying of the polyimide powder can be performed at any temperature as long as residues such as a polyimide solvent, an imidizing agent, an imidization accelerator, and a poor solvent can be removed. Examples of the poor solvent include methanol and ethanol. When a poor solvent having a hydroxy group is used, when drying is performed immediately at a temperature of 100 ° C. or more, the carboxylic acid group or carboxylic anhydride group in the polyimide reacts with the poor solvent to form an ester bond. This may cause problems such as a decrease in heat resistance, coloring, and a decrease in molecular weight. Therefore, it is preferable that the drying step is performed at two or more steps of a temperature of less than 100 ° C and a temperature of 100 to 350 ° C, or by increasing the temperature from a temperature of less than 100 ° C to a temperature of 100 ° C or more and 350 ° C or less. The drying of the polyimide powder may be performed under normal pressure or under reduced pressure.

3. Polyimide Powder The polyimide powder according to the first embodiment of the present invention is soluble in N, N-dimethylacetamide in an amount of 5% by weight or more obtained by the above method, and is obtained by an IR method (ATR method) described later. The polyimide powder has an imidization ratio calculated from an infrared absorption spectrum of 90% or more, preferably 95% or more, more preferably 97% or more, and particularly preferably 99% or more. If the imidation ratio of the polyimide powder is lower than 90%, the polymer may be cleaved in the powder state, and the molecular weight of the polyimide may be reduced, and its properties such as mechanical properties may be reduced. In addition, when a polyimide powder having a low imidization rate is dissolved in a solvent and formed into a polyimide film after being formed into a polyimide varnish, a heat treatment at a high temperature of 300 ° C. or higher is required to promote imidation, The transparency of the polyimide film may be impaired.

  The weight average molecular weight of the polyimide powder of the present invention is preferably from 20,000 to 1,000,000, more preferably from 50,000 to 500,000, even more preferably from 10,000 to 300,000. If the weight average molecular weight is less than the above lower limit, transparency and mechanical properties may be impaired, and if the weight average molecular weight exceeds the above upper limit, the solubility of the polyimide powder in the solvent is deteriorated and the polyimide powder is dissolved. Even if it is possible, the viscosity may be too high and handling may be difficult. The weight average molecular weight of the polyimide can be determined by a size exclusion chromatograph.

  The reduced viscosity is used as an index indicating the degree of polymerization of a polymer such as polyimide. In the polyimide powder of the present invention, the reduced viscosity is preferably in the range of 2.0 to 3.5 dL / g, More preferably, it is in the range of 2.2 to 3.3 dL / g. If the reduced viscosity is less than the above lower limit, transparency and mechanical properties may be impaired. If the reduced viscosity is more than the above upper limit, the viscosity of the polyimide solution may be too high and handling may be difficult.

4. Polyimide varnish The polyimide varnish according to the second embodiment of the present invention is obtained by dissolving the polyimide powder obtained by the above method in any solvent in which polyimide is soluble at a concentration of 1 to 30% by weight. Can be.

  Solvents used for the polyimide varnish of the present invention include N, N-dimethylacetamide, N, N-dimethylformamide, N-methyl-2-pyrrolidone, tetrahydrofuran, 2-butanone, acetone, ethyl acetate, γ-butyrolactone and the like. Any solvent that can dissolve the polyimide powder of one embodiment can be used. In addition, a method of manufacturing a polyimide varnish by dissolving the polyimide powder in a solvent can be any method.Put a predetermined amount of a solvent in a container equipped with a stirring blade, and stir the polyimide powder while stirring. The addition method is preferred because a simple and uniform polyimide varnish can be obtained.

  Further, in the present invention, from the viewpoint of increasing the modulus of elasticity of the finally obtained polyimide film, lowering the thermal expansion and improving the thermal conductivity, based on 100 parts by weight of the polyimide resin dissolved in the varnish, It is possible to add inorganic particles in the range of 10 to 100 parts by weight. As the inorganic particles, particles such as silicon dioxide (silica), talc, alumina, and silicon nitride can be added. Further, in order to express the transparency and good mechanical properties of the finally obtained film, it is preferable to use nanoparticles having a particle diameter in the range of 1 to 100 nm as the inorganic particles to be added. is there. By adding 10 to 100 parts by weight of the nanosilica to 100 parts by weight of the polyimide in the varnish, it is possible to increase the modulus of the polyimide film while maintaining transparency.

5. Polyimide film Next, a polyimide film according to the third embodiment of the present invention is obtained by forming the above-mentioned polyimide varnish into a film. The polyimide film of the present invention may be a polyimide film alone, or may be in the form of a composite film obtained by coating a film on a substrate such as polyethylene terephthalate (PET), acrylic resin, polycarbonate, and cellulose triacetate.

  When manufacturing a polyimide single film, the polyimide varnish of the second embodiment is cast on a coating substrate of a stainless steel drum or a release film, and the polyimide varnish is dried to remove the polyimide from the coating substrate. It can be obtained by peeling, and if necessary, the peeled polyimide can be further dried to remove the residual solvent in the polyimide. When a composite film of polyimide and another substrate is produced, the composite film can be obtained by casting a polyimide varnish on a substrate to be combined with polyimide and drying the solvent.

  The thickness of the polyimide film of the present invention is in the range of 1 to 200 μm, and can be arbitrarily selected according to the application and purpose. Yes, it is more preferably from 10 to 120 μm, even more preferably from 25 to 100 μm.

  Further, the total light transmittance of the polyimide film is preferably 80% or more, more preferably 85% or more, and further preferably 90% or more. Further, the yellowness (yellow index) of the polyimide film is preferably 3.0 or less, more preferably 2.5 or less, and further preferably 2.0 or less. When the total light transmittance of the polyimide film is less than 80% or the yellowness exceeds 3.0, there is a limitation in application to optical applications.

  The tensile modulus of the polyimide film is preferably 4.0 GPa or more, more preferably 4.2 GPa or more. By increasing the tensile modulus of the polyimide to 4.0 GPa or more, even if a stress such as bending or tension is generated in the polyimide film, the polyimide film is not easily deformed, and the effect of improving the elastic modulus by adding an inorganic filler by a method described later is also obtained. There is a feature that it becomes larger.

  In addition, it is also possible to obtain a polyimide porous film according to the fourth embodiment of the present invention by a method such as controlling the solvent drying rate after casting the polyimide varnish on a coating substrate. The polyimide obtained according to the present invention is soluble in a solvent such as N, N-dimethylacetamide, but is insoluble in a solvent such as ethylene carbonate and propylene carbonate generally used for an electrolyte of a lithium ion battery. Therefore, this porous membrane can be suitably used for a separator of a lithium ion battery or the like.

Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited to these Examples.
(Method of measuring reduced viscosity of polyimide)
Polyimide powder was dissolved in N, N-dimethylacetamide (DMAC) at a concentration of 0.5 dL / g to obtain a polyimide solution. Using a Ubbelohde viscometer, the outflow time (T) of the polyimide solution and the outflow time (T0) of the solvent only with DMAC were measured at a temperature of 30 ° C., and the reduced viscosity was determined from the following equation.
Reduced viscosity (dL / g) = (T-T0) /T0/0.5

(Method of measuring total light transmittance and yellowness of polyimide)
(1) Method of preparing film sample for measurement Polyimide powder was dissolved in N, N-dimethylacetamide so as to have the amount specified in the following Examples and Comparative Examples. Next, using an applicator, a film is formed on a smooth glass plate so as to have a thickness of 50 μm after drying, and is kept in a hot air oven at 130 ° C. for 60 minutes, and then 5 ° C. from 130 ° C. to 260 ° C. / Min, dried at 260 ° C. for 10 minutes, and then taken out of the hot air oven, cooled to room temperature, and peeled off from the glass plate to obtain a polyimide film sample for measurement.

(2) Measurement of total light transmittance Using a spectral colorimeter (manufactured by Konica Minolta, Inc., CM-5), based on ASTM E 1164, under the condition of a light source C and a visual field of 2 °, a total of 50 μm in film thickness Light transmittance was determined.

(3) Measurement of Yellowness (YI) Using a spectral colorimeter (manufactured by Konica Minolta, Inc., CM-5), based on ASTM D 1925, with a light source C and a visual field of 2 ° in a wavelength range of 360 to 740 nm. By scanning, the yellowness (YI) at a film thickness of 50 μm was determined.

(Method of measuring imidation ratio)
A film sample having a thickness of 50 μm prepared by the same method as that for measuring the light transmittance of the polyimide was used as a measurement sample, and the film subjected to a heat treatment at 380 ° C. for 30 minutes to complete imidization was used as a comparative sample. Using a Fourier transform infrared spectrophotometer (FT-IR manufactured by Shimadzu Corporation), an infrared absorption spectrum was obtained by the ATR method, and based on the spectrum, the imidation ratio was calculated by the following method.

Regarding the infrared absorption spectrum of the comparative sample, absorption near 1,365 cm ⁻¹ (deformation vibration of the CN group of the imide ring), which is one of the characteristic absorptions of the imide, and characteristic absorption of the benzene ring of 1,500 cm ^−1. the absorbance ratio of the a, the infrared absorption spectrum of the measurement sample, a B absorbance ratio of 1,365Cm ^-1 and 1,500Cm ^-1, was determined imidization ratio from the following equation.
Polyimide imidation ratio (%) = (B / A) × 100

(Method of measuring tensile modulus of polyimide film)
By the same method as the method of manufacturing the polyimide film used for the measurement of the total light transmittance and yellowness of the polyimide, be careful not to enter defects such as foreign matter and bubbles in the polyimide film, and a polyimide film having a thickness of 50 μm. Created. Next, the obtained polyimide film is cut into a size of 5 mm × 120 mm using a feather blade (safety razor blade) to form ten test pieces, and then according to the method specified in JIS K7161: 2014. The obtained test piece was subjected to a tensile test using a tensile tester (Autograph AGS-H load cell 50N manufactured by Shimadzu Corporation) at a distance between chucks of 50 mm and a tensile speed of 50 mm / min, and strain ε1 = 0. From the stress σ1 (GPa) at .0005 (0.05%) and the stress σ2 (GPa) at a strain ε2 = 0.0025 (0.25%), each of the test pieces was calculated based on the following equation. The tensile modulus was calculated, and the average value of ten test pieces was defined as the tensile modulus.
Tensile modulus E = (σ2−σ1) / (ε2−ε1)

(Example 1)
In a 2 L separable glass flask equipped with a stirrer and a stirring blade, 424 g of a solvent N, N-dimethylacetamide (DMAC) and 2,2′-bis (trifluoromethyl) -4,4′-diaminobiphenyl ( (TFMB) 64.048 g (0.2000 mol) was added and stirred, and TFMB was dissolved in DMAC. Next, the tetracarboxylic dianhydride 4,4 ′-(1,1,1,3,3,3-hexafluoropropane-2,2-) was stirred under a nitrogen stream while stirring the inside of the separable flask. Diyl) diphthalic dianhydride (6FDA) 53.575 g (0.1206 mol) was added over about 10 minutes, and then 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (BPDA) 23 .655 g (0.0804 mol) was added thereto, and the polymerization reaction was carried out by continuing stirring for 6 hours while adjusting the temperature to a temperature range of 20 to 40 ° C. to obtain a viscous polyamic acid solution. . The molar ratio of 6FDA: BPDA used was 60:40, the molar ratio of tetracarboxylic dianhydride (total of 6FDA and BPDA) / aromatic diamine compound was 1.005, and the concentration of the polyamic acid solution was 25% by weight. Met.

  Next, 377 g of DMAC was added to the obtained polyamic acid solution to dilute the polyamic acid to a concentration of 15% by weight, and then 25.83 g of isoquinoline was added as an imidization accelerator, and the polyamic acid solution was stirred. Maintain the temperature range of 30 to 40 ° C., and slowly add 122.5 g of acetic anhydride as an imidizing agent dropwise over about 10 minutes, and then further maintain the liquid temperature at 30 to 40 ° C. for 12 hours. Stirring was continued to perform a chemical imidization reaction to obtain a polyimide solution.

  Next, 500 g of the obtained polyimide solution containing the imidizing agent and the imidization accelerator was transferred to a 3 L separable flask equipped with a stirrer and stirring blades, and stirred at a speed of 120 rpm at 15 to 25 ° C. The temperature was maintained, and 750 g of methanol was dropped at a rate of 5 g / min. When about 400 g of methanol was charged, turbidity of the polyimide solution was confirmed, and deposition of powdery polyimide was confirmed. Subsequently, 750 g of the entire amount of methanol was added to complete the precipitation of the polyimide.

  Next, the contents of the separable flask were separated by filtration with a suction filtration device, and further washed and filtered with 500 g of methanol.

  Thereafter, 25 g of the polyimide powder containing the residue of the volatile matter separated by filtration was dried at 50 ° C. for 24 hours using a dryer equipped with a local exhaust device, and further dried at 260 ° C. for 2 hours to remove volatile components. Thus, the desired polyimide powder was obtained.

  The reduced viscosity of the obtained polyimide powder was 2.5 dL / g, and the imidation ratio was 99.6%.

  Next, 15 g of the obtained polyimide powder is dissolved in 60 g of DMAC to form a uniform polyimide varnish, and then coated on a glass plate using an applicator, and the DMAC is dried under predetermined conditions. The polyimide film was peeled off from the plate to form a polyimide film having a thickness of 50 μm. The total light transmittance of the obtained polyimide film was as high as 90%, the yellowness was 1.9, no discoloration was visually observed, and the film was extremely excellent in transparency. The tensile modulus was 4.0 GPa.

(Example 2)
The amount of DMAC used for the polyamic acid polymerization reaction was 415 g, and the amounts of tetracarboxylic dianhydride 6FDA and BPDA used were 44.646 g (0.1005 mol) and 29.569 g (0.1005 mol), respectively. In the same manner as in Example 1 except that the amount of the DMAC for dilution before the chemical imidization reaction was 369 g, a polyimide powder having a used 6FDA: BPDA molar ratio of 50:50 was obtained.

  The reduced viscosity of the obtained polyimide powder was 2.9 dL / g, and the imidation ratio was 99.9%.

  Next, 15 g of the obtained polyimide powder is dissolved in 60 g of DMAC to form a uniform polyimide varnish, and then coated on a glass plate using an applicator, and the DMAC is dried under predetermined conditions. To give a polyimide film having a thickness of 50 μm. The total light transmittance of the obtained polyimide film was as high as 90%, the yellowness was 2.3, the discoloration was not observed by visual inspection, and the film was excellent in transparency. The tensile modulus was 4.2 GPa.

(Example 3)
The amount of DMAC used for the polyamic acid polymerization reaction was 406 g, and the amounts of tetracarboxylic dianhydride 6FDA and BPDA used were 35.717 g (0.0804 mol) and 35.483 g (0.1206 mol), respectively. A polyimide powder having a molar ratio of tetracarboxylic dianhydride of 6FDA: BPDA = 40: 60 was prepared in the same manner as in Example 1 except that the amount of DMAC for dilution before the chemical imidization reaction was 361 g. Obtained.

  The reduced viscosity of the obtained polyimide powder was 3.3 dL / g, and the imidation ratio was 99.9%.

  Next, 15 g of the obtained polyimide powder is dissolved in 60 g of DMAC to form a uniform polyimide varnish, and then coated on a glass plate using an applicator, and the DMAC is dried under predetermined conditions. The polyimide film was peeled off from the plate to form a polyimide film having a thickness of 50 μm. The total light transmittance of the obtained polyimide film was as high as 90%, the yellowness was 2.5, the discoloration was not visually observed, and the polyimide film was excellent in transparency. The tensile modulus was 4.5 GPa.

(Example 4)
The amount of DMAC used in the polymerization reaction of the polyamic acid was 407 g, and as a tetracarboxylic dianhydride, 35.717 g (0.0804 mol) of 6FDA, 29.569 g (0.1005 mol) of BPDA, and 3,3 Example 1, except that 6.235 g (0.0201 mol) of ', 4,4'-diphenylethertetracarboxylic dianhydride (ODPA) was used and the amount of DMAC for dilution before the chemical imidization reaction was 362 g. The same operation was performed to obtain a polyimide powder having a molar ratio of tetracarboxylic dianhydride of 6FDA: BPDA: ODPA = 40: 50: 10.

  The reduced viscosity of the obtained polyimide powder was 2.6 dL / g, and the imidation ratio was 99.5%.

  Next, 15 g of the obtained polyimide powder is dissolved in 60 g of DMAC to form a uniform polyimide varnish, and then coated on a glass plate using an applicator, and the DMAC is dried under predetermined conditions. The polyimide film was peeled off from the plate to form a polyimide film having a thickness of 50 μm. The total light transmittance of the obtained polyimide film was as high as 90%, the yellowness was 2.4, no discoloration was observed by visual inspection, and the film was excellent in transparency. The tensile modulus was 4.0 GPa.

(Example 5)
The amount of DMAC used for the polymerization reaction of the polyamic acid was 408 g, and as an aromatic diamine compound, 5.7643 g (0.1800 mol) of TFMB and 4.005 g (0.0200 mol) of 4,4′-diaminodiphenyl ether (DAPE) were used. Polyimide in which the molar ratio of the aromatic diamine compound is TFMB: DAPE = 90: 10, and the molar ratio of the tetracarboxylic dianhydride is 6FDA: BPDA = 50: 50, except that is used. A powder was obtained.

  The reduced viscosity of the obtained polyimide powder was 2.8 dL / g, and the imidation ratio was 99.8%.

  Next, 15 g of the obtained polyimide powder is dissolved in 60 g of DMAC to form a uniform polyimide varnish, and then coated on a glass plate using an applicator, and the DMAC is dried under predetermined conditions. The polyimide film was peeled off from the plate to form a polyimide film having a thickness of 50 μm. The obtained polyimide film had a total light transmittance of 88%, a yellowness of 2.5, and did not show any discoloration visually, and was excellent in transparency. The tensile modulus was 4.1 GPa.

(Example 6)
In a separable flask having a volume of 200 mL, 30 g of dimethylacetamide (DMAc) -dispersed nanosilica having a particle diameter of 10 to 15 nm (manufactured by Nissan Chemical Industries, Ltd., organosilica sol DMAC-ST, silica concentration 20%) was added to 58 g of DMAc. Then, after stirring and dispersing, 12 g of the polyimide powder obtained in Example 2 was added and dissolved by stirring well to prepare 100 g of a polyimide varnish containing 6 g of silica and 12 g of polyimide in solid content. did.

  The obtained nanosilica-dispersed polyimide varnish is applied on a glass plate using an applicator, DMAc is dried under predetermined conditions, and then peeled off from the glass plate to obtain a polyimide containing 50 μm-thick 33.3% nanosilica. A film was made. The total light transmittance of the obtained polyimide film was as high as 90%, the yellowness was as low as 2.5, no discoloration or turbidity was visually observed, and the polyimide film was excellent in transparency. Further, the tensile elastic modulus showed a high value of 5.7 GPa.

(Example 7)
After dissolving 15 g of the polyimide powder obtained in Example 2 in 60 g of DMAC to obtain a polyimide varnish, the polyimide varnish was coated on the smooth surface of the copper foil using the same applicator as used in Example 2. After casting, the DMAC solvent was partially dried at 30 ° C. for 1 hour, immersed in ion-exchanged water at 25 ° C. for 10 minutes to extract DMAC with pure water, and then heated in a hot air oven at 200 ° C. for 10 minutes. After drying, the copper foil was removed by etching using an aqueous ferric chloride solution to obtain a white polyimide porous film. When the polyimide porous film was observed with a scanning electron microscope (SEM), it was confirmed that the polyimide film was a porous film having a large number of pores formed in the polyimide film.

(Comparative Example 1)
The amount of DMAC used for the polymerization reaction of polyamic acid was 460 g, 89.294 g (0.2010 mol) of 6FDA alone was used as the tetracarboxylic dianhydride, and the amount of DMAC for dilution before the chemical imidization reaction was 409 g. Except having performed, it carried out similarly to Example 1 and obtained the polyimide powder.

  The reduced viscosity of the obtained polyimide powder was 2.1 dL / g, and the imidation ratio was 99.9%.

  Next, 15 g of the obtained polyimide powder is dissolved in 60 g of DMAC to form a uniform polyimide varnish, and then coated on a glass plate using an applicator, and the DMAC is dried under predetermined conditions. The polyimide film was peeled off from the plate to form a polyimide film having a thickness of 50 μm. The resulting polyimide film had a total light transmittance of 91%, a yellowness of 1.5, no discoloration visually, and excellent transparency, but a tensile elasticity of 3%. Was as low as 4 GPa.

(Comparative Example 2)
The amount of DMAC used for the polyamic acid polymerization reaction was 437 g, and the amounts of tetracarboxylic dianhydride 6FDA and BPDA used were 66.969 g (0.1508 mol) and 14.785 g (0.0503 mol), respectively. A polyimide powder having a molar ratio of tetracarboxylic dianhydride of 6FDA: BPDA = 75: 25 was prepared in the same manner as in Example 1 except that the amount of DMAC for dilution before the chemical imidization reaction was 389 g. Obtained.

  The reduced viscosity of the obtained polyimide powder was 2.2 dL / g, and the imidation ratio was 99.9%.

  Next, 15 g of the obtained polyimide powder is dissolved in 60 g of DMAC to form a uniform polyimide varnish, and then coated on a glass plate using an applicator, and the DMAC is dried under predetermined conditions. The polyimide film was peeled off from the plate to form a polyimide film having a thickness of 50 μm. The total light transmittance of the obtained polyimide film was as high as 90%, the yellowness was 1.7, no discoloration was observed visually, and the transparency was excellent, but the tensile modulus was 3%. It was as low as 0.5 GPa.

(Comparative Example 3)
In a 2 L separable glass flask equipped with a stirrer and stirring blades, 397 g of a solvent N, N-dimethylacetamide (DMAC) and 2,2′-bis (trifluoromethyl) -4,4′-diaminobiphenyl ( (TFMB) 64.048 g (0.2000 mol) was added and stirred, and TFMB was dissolved in DMAC. Next, the tetracarboxylic dianhydride 4,4 ′-(1,1,1,3,3,3-hexafluoropropane-2,2-) was stirred under a nitrogen stream while stirring the inside of the separable flask. Diyl) diphthalic dianhydride (6FDA) (26.788 g, 0.0603 mol) was added over about 10 minutes, and then 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (BPDA) 41 .397 g (0.1407 mol) was added, and the polymerization reaction was carried out by continuously stirring for 6 hours while adjusting the temperature to a temperature range of 20 to 40 ° C. to obtain a viscous polyamic acid solution. . The molar ratio of 6FDA: BPDA used was 30:70, the molar ratio of tetracarboxylic dianhydride (total of 6FDA and BPDA) / aromatic diamine compound was 1.005, and the concentration of the polyamic acid solution was 25% by weight. Met.

  Next, 353 g of DMAC was added to the obtained polyamic acid solution to dilute the polyamic acid so that the concentration of polyamic acid became 15% by weight. Then, 25.83 g of isoquinoline was added as an imidization accelerator, and the polyamic acid solution was stirred. When the temperature was kept at 30 to 40 ° C. and 122.5 g of acetic anhydride was slowly added dropwise as an imidizing agent over about 10 minutes, the polyamic acid varnish solidified in a gel state after the addition and continued stirring. This made it difficult to obtain a polyimide powder.

(Comparative Example 4)
The same procedure as in Example 2 was carried out except that the amount of acetic anhydride used as an imidizing agent in the chemical imidization reaction was changed to 40.84 g instead of 122.5 g, and the molar ratio of the tetracarboxylic dianhydride was changed. A polyimide powder having 6FDA: BPDA = 50: 50 was obtained.

  The reduced viscosity of the obtained polyimide powder was 1.9 dL / g, and the imidation ratio was 85.0%.

  Next, 15 g of the obtained polyimide powder is dissolved in 60 g of DMAC to form a uniform polyimide solution, and then coated on a glass plate using an applicator. The polyimide film was peeled off from the plate to form a polyimide film having a thickness of 50 μm. The resulting polyimide film had a total light transmittance of 83%, a yellowness of 3.8, and was visually confirmed to be slightly yellow. Further, the tensile modulus was 3.8 GPa.

  Table 1 shows the above results.

  If the polyimide powder or the polyimide varnish according to the present invention is used, it has extremely excellent heat resistance, transparency and elastic modulus, and is particularly suitable for a display film or an electronic material application. It is possible to produce a porous membrane having excellent resistance to the electrolyte solution of the battery, and the industrial value is extremely high.

Claims (10)

It has a structural unit derived from at least one kind of aromatic diamine compound and a structural unit derived from two or more kinds of tetracarboxylic acids, and has an imidization ratio of 90% or more soluble in N, N-dimethylacetamide of 90% or more. % Or more of polyimide powder,
The structural unit derived from 2,2′-bis (trifluoromethyl) -4,4′-diaminobiphenyl accounts for 50 mol% or more of the entire structural unit derived from the at least one aromatic diamine compound;
The structural unit derived from 4,4 ′-(1,1,1,3,3,3-hexafluoropropane-2,2-diyl) diphthalic dianhydride is derived from the two or more kinds of tetracarboxylic acids. Accounts for 30-70 mol% of the total structural units,
The structural unit derived from 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride occupies 30 to 60 mol% of the total structural units derived from the two or more kinds of tetracarboxylic acids. Polyimide powder. The polyimide powder is obtained by polymerizing at least one kind of aromatic diamine compound and two or more kinds of tetracarboxylic dianhydride into polyamic acid, a chemical imidization reaction, and forming a powder by precipitation of the resulting polyimide, and drying. Manufactured through the process of
2,2′-bis (trifluoromethyl) -4,4′-diaminobiphenyl is used as the aromatic diamine compound in an amount of 50 mol% or more of the entire aromatic diamine compound;
4,4 ′-(1,1,1,3,3,3-hexafluoropropane-2,2-diyl) diphthalic dianhydride is used as the tetracarboxylic dianhydride based on the molar amount of all tetracarboxylic acids. The polyimide powder according to claim 1, wherein 30 to 70% by weight of 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride is used in a range of 30 to 60%.   The polyimide powder according to claim 1 or 2, wherein the reduced viscosity is in a range of 2.0 to 3.5 dL / g.   The film having a thickness of 50 μm obtained by forming a polyimide solution obtained by dissolving in N, N-dimethylacetamide has a total light transmittance of 80% or more and a yellowness of 3 or less. Item 4. The polyimide powder according to any one of Items 1 to 3.   5. A film having a thickness of 50 [mu] m obtained by forming a polyimide solution obtained by dissolving in N, N-dimethylacetamide and having a tensile modulus of 4.0 GPa or more. Item 12. The polyimide powder according to Item.   A polyimide varnish containing the polyimide powder according to any one of claims 1 to 5 at a concentration of 1 to 30% by weight in a solvent.   The polyimide varnish according to claim 6, further comprising 10 to 100 parts by weight of inorganic particles with respect to 100 parts by weight of the polyimide.   A polyimide film having a thickness of 1 to 200 μm, obtained by forming the polyimide varnish of claim 6 or 7 into a film.   The polyimide film according to claim 8, wherein the tensile modulus is 4.0 GPa or more.   A polyimide porous film having a thickness of 1 to 200 µm, obtained by forming the polyimide varnish of claim 6 or 7 into a film.