JP2021169559A - Method for producing polyimide film - Google Patents

Abstract

To provide a polyimide film.SOLUTION: A polyimide film containing an organic solvent is brought into contact with a liquid for treatment containing an organic halogen solvent and an alcohol. The organic halogen solvent is, for example, an organic fluorine solvent or an organic chlorine solvent. The alcohol is, for example, methanol, ethanol or isopropyl alcohol. The liquid for treatment may contain two or more organic halogen solvents or may contain two or more alcohols. The polyimide film may have a thickness of 5 μm or more.SELECTED DRAWING: None

Description

The present invention relates to a method for producing a polyimide film.

With the rapid progress of electronic devices such as displays, solar cells, and touch panels, it is required to make the devices thinner, lighter, and more flexible. In response to these demands, replacement of glass materials used for substrates, cover windows, etc. with plastic film materials is being considered. In particular, in applications where high heat resistance, dimensional stability at high temperatures, and high mechanical strength are required, the application of a polyimide film as a glass substitute material is being studied.

General all-aromatic polyimides are colored yellow or brown because they have strong intramolecular and intermolecular charge transfer interactions and the absorption edge wavelength extends to the visible light region. Further, the total aromatic polyimide has poor solubility in an organic solvent due to a rigid molecular structure, π-π stacking between molecules, and the like. Therefore, in general, a polyimide film is a method in which a polyamic acid solution, which is a polyimide precursor, is applied in a film form on a support, the solvent is removed by heating, and the polyamic acid is dehydrated and cyclized to be imidized (thermal imide). Manufactured by Thermal imidization is generally performed at a high temperature of 300 ° C. or higher.

As a method for imparting visible light transparency and solvent solubility to polyimide, introduction of an alicyclic structure, introduction of a bent structure, introduction of a fluorine substituent and the like are known. The soluble polyimide can also be produced as a film by applying a polyimide resin solution on the support and removing the solvent (see, for example, Patent Document 1). Since the method using the polyimide resin solution does not require heating at a high temperature for imidization, there is an advantage that coloring due to heating is unlikely to occur and a highly transparent transparent polyimide film can be easily obtained.

In both the method of performing thermal imidization after film formation and the method of forming a film using a soluble polyimide resin solution, the organic solvent is removed by heating the polyimide film after film formation. Patent Document 1 discloses a method of reducing the residual solvent by immersing the polyimide film after thermal imidization in water. Patent Document 2 discloses a method of reducing the residual solvent by applying a polyimide resin solution on a support, heating and drying, and then immersing in a poor solvent. As a specific example of the poor solvent, water, Alcohol-based solvents, ketone-based solvents and acetate-based solvents are described.

Japanese Unexamined Patent Publication No. 2017-186473 Japanese Unexamined Patent Publication No. 2006-56956

The treatment of immersing the polyimide film containing an organic solvent in a poor solvent is effective in reducing the residual solvent. However, when the poor solvent disclosed in Patent Document 2 is used, a long time is required for the treatment for reducing the residual solvent.

In the present invention, the polyimide film containing the residual organic solvent is brought into contact with a predetermined treatment liquid. The treatment liquid is a liquid containing an organic halogen solvent, and may contain alcohol in addition to the organic halogen solvent.

The organic halogen solvent used as the treatment liquid does not show solubility in the polyimide film, and examples thereof include an organic fluorine-based solvent and an organic chlorine-based solvent. The treatment liquid preferably contains an organic fluorine-based solvent, and among the organic fluorine-based solvents, hydrofluoroether is preferable. Examples of the organic halogen solvent include chlorinated hydrocarbons. The treatment liquid may contain two or more kinds of organic halogen solvents.

Examples of the alcohol used in combination with the organic halogen solvent include lower alcohols such as methanol, ethanol and isopropyl alcohol. The treatment liquid may contain two or more alcohols. The alcohol content of the treatment liquid may be 1-90% by weight.

The polyimide film containing an organic solvent can be obtained, for example, by applying a solution in which a polyimide resin is dissolved in an organic solvent onto a support and removing a part of the organic solvent. After peeling the polyimide film from the support, the polyimide film may be brought into contact with the processing liquid.

The polyimide contains, as a tetracarboxylic acid dianhydride component, 2,2-bis (3,4-dicarboxyphenyl) -1,1,1,3,3,3-hexafluoropropane dianhydride (6FDA) and the like. It may contain a fluorine-containing acid dianhydride, or may contain a fluorine-containing diamine such as 2,2'-bis (trifluoromethyl) benzidine (TFMB) as a diamine component. The thickness of the polyimide film after removing the polyimide film and the residual solvent is generally 5 μm or more.

In the method of the present invention, the polyimide film in which the organic solvent remains is brought into contact with a predetermined poor solvent.

[Polyimide]
Polyimide is generally obtained by polymerizing tetracarboxylic acid dianhydride (hereinafter, may be referred to as "acid dianhydride") with diamine to obtain polyamic acid, and dehydrating and cyclizing the polyamic acid. That is, the polyimide has a tetracarboxylic dianhydride-derived structure and a diamine-derived structure.

<Composition of polyamic acid and polyimide>
Examples of acid dianhydrides that can be used as raw materials for polyamic acid and polyimide are ethylenetetracarboxylic dianhydride, butanetetracarboxylic dianhydride, 1,2,3,4-cyclobutanetetracarboxylic dianhydride. , 1,2,3,4-cyclopentanetetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, 1,1'-bicyclohexane-3,3', 4,4 'Tetetracarboxylic dianhydride, 3,3', 4,4'-benzophenonetetracarboxylic dianhydride, 2,2', 3,3'-benzophenonetetracarboxylic dianhydride, 2,2', 3 , 3'-biphenyltetracarboxylic dianhydride, pyromellitic dianhydride, 3,3', 4,4'-biphenyltetracarboxylic dianhydride, 2,2-bis (3,4-dicarboxyphenyl) ) Propane dianhydride, 2,2-bis (2,3-dicarboxyphenyl) propane dianhydride, bis (3,4-dicarboxyphenyl) ether dianhydride, bis (3,4-dicarboxyphenyl) Symphone dianhydride, 1,1-bis (2,3-dicarboxyphenyl) ethane dianhydride, bis (2,3-dicarboxyphenyl) methane dianhydride, bis (3,4-dicarboxyphenyl) methane Dihydride, 2,2-bis (3,4-dicarboxyphenyl) -1,1,1,3,3,3-hexafluoropropane dianhydride, 2,2-bis (2,3-dicarboxyphenyl) Phenyl) -1,1,1,3,3,3-hexafluoropropanedianhydride, 2,2-bis {4- [4- (1,2-dicarboxy) phenoxy] phenyl} -1,1, 1,3,3,3-hexafluoropropane dianhydride, 1,3-bis [(3,4-dicarboxy) benzoyl] benzene dianhydride, 1,4-bis [(3,4-dicarboxy) Benoxyl] benzene dianhydride, 2,2-bis {4- [4- (1,2-dicarboxy) phenoxy] phenyl} propane dianhydride, 2,2-bis {4- [3- (1,2,1,2) -Dicarboxy) phenoxy] phenyl} propane dianhydride, bis {4- [4- (1,2-dicarboxy) phenoxy] phenyl} ketone dianhydride, bis {4- [3- (1,2-di) Carboxy) phenoxy] phenyl} ketone dianhydride, 4,4'-bis [4- (1,2-dicarboxy) phenoxy] biphenyl dianhydride, 4,4'-bis [3- (1,2-di) Carboxi) phenoxy] biphenyl dianhydride, bis {4- [4- ( 1,2-Dicarboxy) phenoxy] phenyl} ketone dianhydride, bis {4- [3- (1,2-dicarboxy) phenoxy] phenyl} ketone dianhydride, bis {4- [4- (1,1,) 2-Dicarboxy) phenoxy] phenyl} sulfone dianhydride, bis {4- [3- (1,2-dicarboxy) phenoxy] phenyl} sulfone dianhydride, bis {4- [4- (1,2-) Dicarboxy) phenoxy] phenyl} sulfide dianhydride, bis {4- [3- (1,2-dicarboxy) phenoxy] phenyl} sulfide dianhydride, 2,2-bis {4- [4- (1,1) 2-Dicarboxy) phenoxy] phenyl} -1,1,1,3,3,3-hexaflupropane dianhydride, 2,2-bis {4- [3- (1,2-dicarboxy) phenoxy] Phenyl} -1,1,1,3,3,3-propane dianhydride, 2,3,6,7-naphthalenetetracarboxylic acid dianhydride, 1,4,5,8-naphthalenetetracarboxylic acid dianhydride , 1,2,5,6-naphthalenetetracarboxylic acid dianhydride, 1,2,3,4-benzenetetracarboxylic acid dianhydride, 3,4,9,10-perylenetetracarboxylic acid dianhydride, 2,3,6,7-anthracene tetracarboxylic acid dianhydride, 1,2,7,8-phenanthrene tetracarboxylic acid dianhydride, bis (1,3-dihydro-1,3-dioxo-5-isobenzofuran) Carboxylic acid) -1,4-phenylene ester, bis (1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxylic acid)-(2,2', 3,3', 5,5'-hexamethyl [1,1'-biphenyl] -4,4'-diyl) ester can be mentioned.

Examples of diamines that can be used as raw materials for polyamic acid and polyimide are 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl sulfide, 3 , 4'-diaminodiphenylsulfide, 4,4'-diaminodiphenylsulfide, 3,3'-diaminodiphenylsulfone, 3,4'-diaminodiphenylsulfone, 4,4'-diaminodiphenylsulfone, bis [4- (3) -Aminophenoxy) phenyl] sulfone, bis [4- (4-aminophenoxy) phenyl] sulfone, 4,4'-bis [4- (4-amino-α, α-dimethylbenzyl) phenoxy] diphenylsulfone, 4, 4'-bis [4- (4-aminophenoxy) phenoxy] diphenylsulfone, 3,3'-diaminobenzophenone, 4,4'-diaminobenzophenone, 3,4'-diaminobenzophenone, 3,3'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 2,2-di (3-aminophenyl) propane, 2,2-di (4-aminophenyl) propane, 2- (3-aminophenyl) -2- (4-aminophenyl) propane, 1,4-diamino-2-fluorobenzene, 1,4-diamino-2,3-difluorobenzene, 1,4-diamino-2,5-difluorobenzene, 1, 4-Diamino-2,6-difluorobenzene, 1,4-diamino-2,3,5-trifluorobenzene, 1,4-diamino-2,3,5,6-tetrafluorobenzene, 1,4-diamino -2- (trifluoromethyl) benzene, 1,4-diamino-2,3-bis (trifluoromethyl) benzene, 1,4-diamino-2,5-bis (trifluoromethyl) benzene, 1,4- Diamino-2,6-bis (trifluoromethyl) benzene, 1,4-diamino-2,3,5-tris (trifluoromethyl) benzene, 1,4-diamino-2,3,5,6-tetrakis ( Trifluoromethyl) benzene, 2-fluorobenzidine, 3-fluorobenzidine, 2,3-difluorobenzidine, 2,5-difluorobenzidine, 2,6-difluorobenzidine, 2,3,5-trifluorobenzidine, 2,3 , 6-Trifluorobenzidine, 2,3,5,6-tetrafluorobenzidine, 2,2'-difluorovezine Ndidin, 3,3'-difluorobenzidine, 2,3'-difluorobenzidine, 2,2', 3-trifluorobenzidine, 2,3,3'-trifluorobenzidine, 2,2', 5-trifluorobenzidine , 2,2', 6-trifluorobenzidine, 2,3', 5-trifluorobenzidine, 2,3', 6,-trifluorobenzidine, 2,2', 3,3'-tetrafluorobenzidine, 2 , 2', 5,5'-tetrafluorobenzidine, 2,2', 6,6'-tetrafluorobenzidine, 2,2', 3,3', 6,6'-hexafluorobenzidine, 2,2' , 3,3', 5,5', 6,6'-octafluorobenzidine, 2- (trifluoromethyl) benzidine, 3- (trifluoromethyl) benzidine, 2,3-bis (trifluoromethyl) benzidine, 2,5-bis (trifluoromethyl) benzidine, 2,6-bis (trifluoromethyl) benzidine, 2,3,5-tris (trifluoromethyl) benzidine, 2,3,6-tris (trifluoromethyl) Benzidine, 2,3,5,6-tetrakis (trifluoromethyl) benzidine, 2,2'-bis (trifluoromethyl) benzidine, 3,3'-bis (trifluoromethyl) benzidine, 2,3'-bis (Trifluoromethyl) benzidine, 2,2', 3-bis (trifluoromethyl) benzidine, 2,3,3'-tris (trifluoromethyl) benzidine, 2,2', 5-tris (trifluoromethyl) Benzidine, 2,2', 6-tris (trifluoromethyl) benzidine, 2,3', 5-tris (trifluoromethyl) benzidine, 2,3', 6,-tris (trifluoromethyl) benzidine, 2, 2', 3,3'-tetrakis (trifluoromethyl) benzidine, 2,2', 5,5'-tetrakis (trifluoromethyl) benzidine, 2,2', 6,6'-tetrakis (trifluoromethyl) Benzidine 2,2-di (3-aminophenyl) -1,1,1,3,3,3-hexafluoropropane, 2,2-di (4-aminophenyl) -1,1,1,3,3 , 3-Hexafluoropropane, 2- (3-aminophenyl) -2- (4-aminophenyl) -1,1,1,3,3,3-hexafluoropropane, 1,1-di (3-amino) Phenyl) -1-phenylethane, 1,1-di (4-aminophenyl) -1-phenylethane, 1- (3-aminopheni) Le) -1- (4-Aminophenyl) -1-phenylethane, 1,3-bis (3-aminophenoxy) benzene, 1,3-bis (4-aminophenoxy) benzene, 1,4-bis (3) -Aminophenoxy) Benzene, 1,4-bis (4-aminophenoxy) benzene, 1,3-bis (3-aminobenzoyl) benzene, 1,3-bis (4-aminobenzoyl) benzene, 1,4-bis (3-Aminobenzoyl) benzene, 1,4-bis (4-aminobenzoyl) benzene, 1,3-bis (3-amino-α, α-dimethylbenzyl) benzene, 1,3-bis (4-amino-) α, α-dimethylbenzyl) benzene, 1,4-bis (3-amino-α, α-dimethylbenzyl) benzene, 1,4-bis (4-amino-α, α-dimethylbenzyl) benzene, 1,3 -Bis (3-amino-α, α-ditrifluoromethylbenzyl) benzene, 1,3-bis (4-amino-α, α-ditrifluoromethylbenzyl) benzene, 1,4-bis (3-amino-α) , Α-Ditrifluoromethylbenzyl) benzene, 1,4-bis (4-amino-α, α-ditrifluoromethylbenzyl) benzene, 2,6-bis (3-aminophenoxy) benzonitrile, 2,6-bis (3-Aminophenoxy) pyridine, 4,4'-bis (3-aminophenoxy) biphenyl, 4,4'-bis (4-aminophenoxy) biphenyl, bis [4- (3-aminophenoxy) phenyl] ketone, Bis [4- (4-aminophenoxy) phenyl] ketone, bis [4- (3-aminophenoxy) phenyl] sulfide, bis [4- (4-aminophenoxy) phenyl] sulfide, bis [4- (3-amino) phenyl] Phenoxy) phenyl] sulfone, bis [4- (4-aminophenoxy) phenyl] sulfone, bis [4- (3-aminophenoxy) phenyl] ether, bis [4- (4-aminophenoxy) phenyl] ether, 2, 2-Bis [4- (3-aminophenoxy) phenyl] propane, 2,2-bis [4- (4-aminophenoxy) phenyl] propane, 2,2-bis [3- (3-aminophenoxy) phenyl] -1,1,1,3,3,3-hexafluoropropane, 2,2-bis [4- (4-aminophenoxy) phenyl] -1,1,1,3,3,3-hexafluoropropane, 1,3-bis [4- (3-aminophenoxy) benzoyl] benzene, 1,3-bis [4- (4-Aminophenoxy) benzoyl] benzene, 1,4-bis [4- (3-aminophenoxy) benzoyl] benzene, 1,4-bis [4- (4-aminophenoxy) benzoyl] benzene, 1 , 3-bis [4- (3-aminophenoxy) -α, α-dimethylbenzyl] benzene, 1,3-bis [4- (4-aminophenoxy) -α, α-dimethylbenzyl] benzene, 1,4 -Bis [4- (3-aminophenoxy) -α, α-dimethylbenzyl] benzene, 1,4-bis [4- (4-aminophenoxy) -α, α-dimethylbenzyl] benzene, 4,4'- Bis [4- (4-aminophenoxy) benzoyl] diphenyl ether, 4,4'-bis [4- (4-amino-α, α-dimethylbenzyl) phenoxy] benzophenone, 4,4'-bis [4- (4) -Amino-α, α-dimethylbenzyl) phenoxy] diphenyl sulfone, 4,4'-bis [4- (4-aminophenoxy) phenoxy] diphenyl sulfone, 3,3'-diamino-4,4'-diphenoxybenzophenone , 3,3'-diamino-4,4'-dibiphenoxybenzophenone, 3,3'-diamino-4-phenoxybenzophenone, 3,3'-diamino-4-biphenoxybenzophenone, 6,6'-bis (3) -Aminophenoxy) -3,3,3', 3'-tetramethyl-1,1'-spirobiindan, 6,6'-bis (4-aminophenoxy) -3,3,3', 3'-tetramethyl -1,1'-spirobiindane, 1,3-bis (3-aminopropyl) tetramethyldisiloxane, 1,3-bis (4-aminobutyl) tetramethyldisiloxane, α, ω-bis (3-aminopropyl) ) Polydimethylsiloxane, α, ω-bis (3-aminobutyl) polydimethylsiloxane, bis (aminomethyl) ether, bis (2-aminoethyl) ether, bis (3-aminopropyl) ether, bis (2-amino) Methoxy) ethyl] ether, bis [2- (2-aminoethoxy) ethyl] ether, bis [2- (3-aminoprotoxy) ethyl] ether, 1,2-bis (aminomethoxy) ethane, 1,2- Bis (2-aminoethoxy) ether, 1,2-bis [2- (aminomethoxy) ethoxy] ethane, 1,2-bis [2- (2-aminoethoxy) ethoxy] ethane, ethylene glycol bis (3-amino) Propyl) ether, diethylene glycol Bis (3-aminopropyl) ether, triethylene glycol bis (3-aminopropyl) ether, ethylenediamine, 1,3-diaminopropane, 1,4-diaminobutane, 1,5-diaminopentane, 1,6-diaminohexane , 1,7-Diaminoheptane, 1,8-diaminooctane, 1,9-diaminononane, 1,10-diaminodecane, 1,11-diaminoundecane, 1,12-diaminododecane, 1,2-diaminocyclohexane, 1, , 3-Diaminocyclohexane, 1,4-diaminocyclohexane, 1,2-di (2-aminoethyl) cyclohexane, 1,3-di (2-aminoethyl) cyclohexane, 1,4-di (2-aminoethyl) Cyclohexane, bis (4-aminocyclohexyl) methane, 2,6-bis (aminomethyl) bicyclo [2.2.1] heptane, 2,5-bis (aminomethyl) bicyclo [2.2.1] heptane Can be mentioned.

In order to obtain a polyimide having high visible light transmittance and being soluble in an organic solvent, an alicyclic such as 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride (CBDA) is used as the acid dianhydride. Fluorine-containing aromatics such as tetracarboxylic acid dianhydride, 2,2-bis (3,4-dicarboxyphenyl) -1,1,1,3,3,3-hexafluoropropane dianhydride (6FDA) Tetracarboxylic hydride; and / or 3,3', 4,4'-biphenyltetracarboxylic hydride (BPDA), p-phenylene bis (trimeritic anhydride) (TMHQ), bis (1, 3-Dioxo-1,3-dihydroisobenzofuran-5-carboxylic acid) -2,2', 3,3', 5,5'-hexamethylbiphenyl-4,4'diyl (also known as 2,2', 3 , 3', 5,5'-Hexamethyl-biphenylenebis (trimeritic acid dianhydride) (TAHMBP), etc. Aromatic tetracarboxylic dianhydride in which two carbonyl groups are bonded to different aromatic rings. Preferably used, as the diamine, fluorine-containing aromatic diamines such as 2,2'-bis (trifluoromethyl) benzidine (TFMB); and / or 3,3'-diaminodiphenylsulfone (especially fluoroalkyl-substituted benzidine); It is preferable to use an aromatic diamine in which an amino group is bonded to each of different aromatic rings such as 3,3'-DDS).

From the viewpoint of ensuring the transparency, solvent solubility and mechanical strength of the polyimide film, the acid dianhydride component of the polyimide is preferably CBDA, 6FDA, BPDA, TMHQ, TAHMBP and the like, and the diamine component is TFMB, 3, 3 '-DDS or the like is preferable. Of the total 100 mol% of the acid dianhydride component of the polyimide, the content of 6FDA is preferably 20 mol% or more, more preferably 30 mol% or more, 35 mol% or more, 40 mol% or more, 45 mol% or more. Alternatively, it may be 50 mol% or more. The content of 6FDA may be 100 mol% or less, 90 mol% or less, 80 mol% or less, or 70 mol% or less. Of the total 100 mol% of the diamine component of the polyimide, the content of TFMB is preferably 20 mol% or more, more preferably 30 mol% or more, further preferably 40 mol% or more, 50 mol% or more, 60 mol% or more. Alternatively, it may be 70 mol% or more. The content of TFMB may be 100 mol% or less, 95 mol% or less, 90 mol% or less, 85 mol% or less, or 80 mol% or less.

In particular, in order to obtain a polyimide resin having high solubility in an organic solvent, it is preferable to use TFMB or a combination of TFMB and 3,3'-DDS as the diamine. In this case, as the acid dianhydride, a combination of 6FDA and CBDA, a combination of 6FDA and BPDA, a combination of 6FDA and TMHQ, a combination of 6FDA and TMHQ and BPDA, a combination of 6FDA and TAHMBP, and the like are preferable. In addition to the above combinations, other diamines and acid dianhydrides may be included as the diamine and acid dianhydride.

[Preparation of polyimide film]
<Preparation of polyamic acid solution>
Polyimide is obtained by dehydration cyclization of polyamic acid, which is a polyimide precursor. Any known method can be used for producing the polyamic acid, and the method is not particularly limited. For example, acid dianhydride and diamine are dissolved in an organic solvent in approximately equal molar amounts (molar ratio of 95: 100 to 105: 100), and the mixture is stirred until the polymerization of acid dianhydride and diamine is completed. This gives a polyamic acid solution. The concentration of the polyamic acid solution is usually 5 to 35% by weight, preferably 10 to 30% by weight. When the concentration is in this range, a polyamic acid solution having an appropriate molecular weight and viscosity can be obtained. When a plurality of types of diamines and a plurality of types of acid dianhydrides are added, they may be added at once, or the number of additions may be divided into a plurality of times.

The organic solvent used for the polymerization of the polyamic acid is not particularly limited as long as it is a solvent that does not react with the diamine and the acid dianhydride and can dissolve the polyamic acid. Examples of the organic solvent include urea solvents such as methyl urea and N, N-dimethylethyl urea, sulfoxide or sulfone solvents such as dimethyl sulfoxide, diphenyl sulfone and tetramethyl sulfone, and N, N-dimethylacetamide (DMAc), N, Amido solvents such as N-dimethylformamide (DMF), N, N'-diethylacetamide, N-methyl-2-pyrrolidone (NMP), γ-butyrolactone, hexamethylphosphate triamide, alkyl halides such as chloroform and dichloromethane. Examples thereof include based solvents, aromatic hydrocarbon solvents such as benzene and toluene, and ether solvents such as tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, dimethyl ether, diethyl ether and p-cresol methyl ether. Usually, these solvents are used alone or in combination of two or more as needed. From the viewpoint of solubility of polyamic acid and polymerization reactivity, DMAc, DMF, NMP and the like are preferably used.

<Preparation of polyimide resin>
As a method for producing a polyimide film from a polyamic acid solution, (i) a method in which a polyamic acid solution is applied in a film form on a support, the solvent is dried and removed, and the polyamic acid is imidized; and (ii) polyamic acid. Examples thereof include a method in which a polyimide resin is prepared by imidization in a solution state, the polyimide resin solution is applied in a film form on a support, and the solvent is dried and removed. As the polyimide soluble in an organic solvent, any of the above methods (i) and (ii) can be applied. The above method (ii) is preferable because a highly transparent polyimide film can be obtained without requiring heating at a high temperature for imidization.

Examples of a method for preparing a polyimide solution from a polyamic acid solution include a method (chemical imidization) in which a dehydrating agent, an imidization catalyst, or the like is added to the polyamic acid solution to allow imidization to proceed in the solution. The polyamic acid solution may be heated to accelerate the progress of imidization.

The polyimide solution obtained by imidization of the polyamic acid can be used as it is as a film-forming dope, but it is preferable to once precipitate the polyimide resin as a solid substance. By mixing the polyimide solution and the poor solvent, the polyimide resin is precipitated. The poor solvent is a poor solvent of the polyimide resin, preferably miscible with a solvent in which the polyimide resin is dissolved, and examples thereof include water and alcohols. Since a small amount of imidization catalyst, dehydrating agent, etc. may remain in the precipitated polyimide resin, it is preferable to wash with a poor solvent. It is preferable to remove the poor solvent from the polyimide resin after precipitation and washing by vacuum drying, hot air drying, or the like.

By precipitating the polyimide resin as a solid substance, impurities generated during the polymerization of the polyamic acid, residual monomer components, a dehydrating agent, an imidization catalyst, and the like can be washed and removed. Therefore, a polyimide film having excellent transparency and mechanical properties can be obtained. Further, by once precipitating the polyimide resin as a solid substance, a solvent suitable for the film forming conditions can be applied.

<Polyimide solution>
A polyimide solution (also referred to as film-forming dope) is prepared by dissolving the polyimide resin in an organic solvent. The organic solvent is not particularly limited as long as it is soluble and soluble in the polyimide resin. For example, the urea solvent, sulfoxide or sulfone solvent, amide solvent, halogen, which are exemplified above as the organic solvent used for the polymerization of polyamic acid. Examples thereof include alkylation-based solvents, aromatic hydrocarbon-based solvents, ether-based solvents and the like. In addition to these, ketone solvents such as acetone, methyl ethyl ketone, methyl propyl ketone, methyl isopropyl ketone, methyl isobutyl ketone, diethyl ketone, cyclopentanone, cyclohexanone and methyl cyclohexanone are also preferably used as solvents for the polyimide resin.

In order to impart processing characteristics and various functionalities to the polyimide film, an organic or inorganic small molecule or polymer compound may be blended in the film-forming dope. For example, an ultraviolet absorber, a cross-linking agent, a dye, a surfactant, a leveling agent, a plasticizer, fine particles, a sensitizer and the like can be used. The solid content concentration of the film-forming dope is preferably 5 to 30% by weight, and the viscosity of the film-forming dope at 25 ° C. is preferably 0.5 Pa · s to 60 Pa · s. The content of the polyimide resin with respect to 100 parts by weight of the solid content of the film-forming dope is preferably 60 parts by weight or more, more preferably 70 parts by weight or more, still more preferably 80 parts by weight or more.

From the viewpoint of simplifying the equipment for producing the polyimide film by removing the solvent from the polyimide solution, the organic solvent for dissolving the polyimide resin has a flammability of 50 ° C. or higher or does not show a flammable point. preferable. When the organic solvent exhibits a flash point, it is preferable that the flash point of the organic solvent is higher than the heating temperature in the production process of the polyimide film. Considering the drying temperature due to heating, the flash point of the organic solvent is preferably 70 ° C. or higher, more preferably 100 ° C. or higher. The higher the flash point of the organic solvent, the more preferable, and it may be 150 ° C. or higher, 200 ° C. or higher, or 250 ° C. or higher. It is particularly preferable that the organic solvent does not show a flash point. From the viewpoint of facilitating solvent removal at a low temperature, the boiling point of the organic solvent for dissolving the polyimide resin is preferably 80 ° C. or lower, more preferably 60 ° C. or lower, and even more preferably 50 ° C. or lower. Dichloromethane is particularly preferable as the organic solvent because it does not show a flash point and has a low boiling point.

As the support to which the film-forming dope is applied, a glass substrate, a metal substrate such as SUS, a metal drum, a metal belt, a plastic film, or the like can be used. From the viewpoint of improving productivity, it is preferable to use an endless support such as a metal drum or a metal belt, a long plastic film, or the like as the support, and to manufacture the film by roll-to-roll. When a plastic film is used as a support, a material that does not dissolve in the solvent of the film-forming dope may be appropriately selected, and as the plastic material, polyethylene terephthalate, polycarbonate, polyacrylate, polyethylene naphthalate and the like are used. As a coating method, bar coating, die coating, spin coating and the like can be applied without specific restrictions.

The coating thickness on the support may be set according to the thickness of the target polyimide film. The thickness of the polyimide film is, for example, 5 μm or more. From the viewpoint of achieving both self-supporting property and flexibility and making the film highly transparent, the thickness of the polyimide film is preferably 20 μm to 100 μm, more preferably 30 μm to 90 μm, further preferably 40 μm to 80 μm, and even more preferably 50 μm to 50 μm. 80 μm is particularly preferable. The thickness of the transparent polyimide film used as a cover film for a display is preferably 50 μm or more.

A polyimide film is obtained by applying a polyimide solution on the support and drying and removing the solvent. It is preferable to heat the solvent when it dries. The heating temperature may be as long as the solvent can be removed, for example, 30 ° C. or higher or 50 ° C. or higher. The upper limit of the heating temperature is not particularly limited, but in order to suppress coloring due to heating and obtain a highly transparent polyimide film, 250 ° C. or lower is preferable, and 220 ° C. or lower is more preferable. In order to increase the solvent removal efficiency, the polyimide film may be peeled off from the support and dried after the drying has progressed to some extent. Heating may be carried out under reduced pressure to facilitate solvent removal.

In the above, the example of forming the polyimide film using the polyimide resin solution has been mainly described, but even if the polyamic acid solution is applied in a film form on the support and imidized by heating to form the polyimide film. good. In this case as well, after heating on the support to remove the organic solvent to some extent, the film may be peeled off from the support and heated.

[Residual solvent reduction treatment]
(I) A method in which a polyamic acid solution is applied in a film form on a support to dry and remove the solvent and imidize the polyamic acid; and (ii) a polyimide resin solution is applied in a film form on a support and a solvent is used. In any of the methods for drying and removing the water, it is difficult to completely remove the organic solvent from the polyimide film, and a certain amount of the organic solvent remains in the film. In particular, in the method (ii), since high-temperature heating for imidization is not performed, the organic solvent tends to remain in the polyimide film. Further, in a thick polyimide film (for example, 30 μm or more), when the organic solvent near the surface layer volatilizes, the volatilization of the solvent near the center in the thickness direction is hindered. It may be difficult to make it small enough.

By contacting the polyimide film on which the organic solvent used for film formation (film-forming-doped organic solvent) remains with the treatment liquid, the removal of the organic solvent in the film is promoted and remains at a low temperature in a short time. The amount of solvent can be reduced.

<Processing liquid>
(Organic halogen solvent)
The treatment liquid (treatment liquid) used for removing the organic solvent used for film formation contains an organic halogen solvent. The organic halogen solvent may be any of an organic fluorine-based solvent, an organic chlorine-based solvent, and an organic bromine-based solvent, and may contain a plurality of halogen species. As the organic halogen solvent, a solvent that is liquid at room temperature and does not dissolve the polyimide film can be used without particular limitation. The boiling point of the organic halogen solvent is preferably 100 ° C. or lower, more preferably 80 ° C. or lower.

The treatment liquid preferably contains an organic fluorine-based solvent because it is excellent in removing the organic solvent in the polyimide film. Examples of the organic fluorine-based solvent include perfluorocarbon, hydrofluorocarbon, perfluoroether, hydrofluoroether and the like. Of these, hydrofluoroethers are preferable because they have a small environmental load.

Examples of the hydrofluoroether include 2,2,2-trifluoroethylmethyl ether, 2,2,2-trifluoroethyldifluoromethyl ether, 2,2,3,3,3-pentafluoropropylmethyl ether and 2,2. , 3,3,3-pentafluoropropyldifluoromethyl ether, 2,2,3,3,3-pentafluoropropyl-1,1,2,2-tetrafluoroethyl ether, 1,1,2,2-tetra Fluoroethyl methyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, difluoromethyl ether, 2,2 3,3,3-Pentafluoropropylmethyl ether, 2,2,3,3,3-pentafluoropropyldifluoromethyl ether, 2,2,3,3,3-pentafluoropropyl-1,1,2,2 -Tetrafluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, hexafluoroisopropylmethyl ether, 1,1,3,3,3-pentafluoro- 2-Trifluoromethylpropylmethyl ether, 1,1,2,3,3,3-hexafluoropropylmethyl ether, 1,1,2,3,3,3-hexafluoropropylethyl ether, 2,2,3 , 4,4,4-hexafluorobutyldifluoromethyl ether, 1,1,2,2,3,3,3-heptafluoropropylmethyl ether, (1,1,2,2,3,3,4,4) -Octafluoropentyl) allyl ether, (1,1,2,2-tetrafluoroethyl) allyl ether, heptafluoro-2-propylallyl ether, bis (trifluoroethoxy) ethane, ethoxytrifluoroethoxyethane, methoxytrifluoro Ethoxyethane, 1,1,1,2,2,3,4,5,5-decafluoro-3-methoxy-4-trifluoromethyl-pentane, 1,1,1,2,2,3 4,5,5,5-decafluoro-3-ethoxy-4-trifluoromethyl-pentane, 1,1,1,2,2,3,4,5,5-decafluoro-3-propoxy- 4-Trifluoromethyl-pentane, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 2,2-difluoroethyl-1,1,2,2-tetrafluoro Propyl ether, 2, 2-Difluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1H, 1H, 2'H, 3H-decafluorodipropyl ether, 1,1,1,2,3,3-hexafluoropropyl- 2,2-Difluoroethyl ether, isopropyl 1,1,2,2-tetrafluoroethyl ether, propyl 1,1,2,2-tetrafluoroethyl ether, 1H, 1H, 5H-perfluoropentyl-1,1, 2,2-Tetrafluoroethyl ether, 1H, 1H, 2'H-perfluorodipropyl ether, 1H-perfluorobutyl-1H-perfluoroethyl ether, methyl perfluoropentyl ether, methyl perfluorohexyl ether, methyl 1,1,3,3,3-pentafluoro-2- (trifluoromethyl) propyl ether, 1,1,2,3,3,3-hexafluoropropyl 2,2,2-trifluoroethyl ether, ethyl 1,1,2,3,3,3-hexafluoropropyl ether, 1H, 1H, 5H-octafluoropentyl 1,1,2,2-tetrafluoroethyl ether, 1H, 1H, 2'H-perfluorodi Propyl ether, heptafluoropropyl 1,2,2,2-tetrafluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 2,2,3 Examples thereof include 3,3-pentafluoropropyl-1,1,2,2-tetrafluoroethyl ether, ethyl nonafluorobutyl ether, ethyl nonafluoroisobutyl ether, methyl nonafluorobutyl ether, and methyl nonafluoroisobutyl ether. Among these, 1,1,2,2,3,3,3-heptafluoropropyl methyl ether, 1,1-difluoroethyl-2,2,2-trifluoroethyl ether, methyl nonafluorobutyl ether and ethyl nonafluoro Hydrofluoroethers such as butyl ether, which do not show a flash point, are preferable. Of these, methyl nonafluorobutyl ether and ethyl nonafluorobutyl ether are preferable because they have a small global warming potential and a small environmental load.

The treatment liquid may contain an organic chlorine-based solvent in addition to the organic fluorine-based solvent as the organic halogen solvent. Examples of the organochlorine solvent include chlorinated hydrocarbons. Chlorinated hydrocarbons having 1 to 6 carbon atoms are preferable because they have a low boiling point and a high effect of removing the residual solvent of the polyimide film. The carbon number of the chlorinated hydrocarbon is preferably 4 or less, more preferably 2 or less.

Specific examples of chlorinated hydrocarbons include chlorinated methanes (dichloromethane, chloroform and carbon tetrachloride), chlorinated ethanes (1,1-dichloroethane, 1,2-dichloroethane, 1,1,1-trichloroethane, 1). , 1,2-Trichloroethane, 1,1,1,2-tetrachloroethane, 1,1,2,2-tetrachloroethane, etc., pentachloroethane and hexachloroethane), chlorinated ethylenes (1,1-dichloroethylene, cis- 1,2-dichloroethylene, trans-1,2-dichloroethylene, 1,1,2-trichloroethylene and tetrachlorethylene), chlorinated propanes (1,2-dichloropropane, 1,2,3-trichloropropane, etc.), chlorinated Examples thereof include propenes (1,2-dichloropropene, cis-1,3-dichloropropene, trans-1,3-dichloropropene, etc.). Among them, chlorinated ethylenes are preferable, and trans-1,2-dichloroethylene is preferable because the solubility of polyimide is low and the effect of removing residual solvent is high.

The treatment liquid may contain two or more kinds of organic halogen solvents. The two or more kinds of organic halogen solvents may contain an organic fluorine-based solvent and an organic chlorine-based solvent, and may have an azeotropic composition.

(alcohol)
The treatment liquid may contain alcohol in addition to the organic halogen solvent. As the alcohol, a lower alcohol having 1 to 6 carbon atoms is preferable, and among them, an alcohol having 1 to 3 carbon atoms such as methanol, ethanol and isopropyl alcohol is preferable.

The treatment liquid may contain two or more alcohols. The combination of two or more kinds of alcohols may be a combination of an alcohol having 2 or less carbon atoms and an alcohol having 3 or more carbon atoms. Examples of alcohols having 2 or less carbon atoms include methanol and ethanol. Both methanol and ethanol may be contained as the alcohol having 2 or less carbon atoms. Examples of alcohols having 3 or more carbon atoms include n-propanol, isopropyl alcohol, n-butanol and the like. In the combination of the alcohol having 2 or less carbon atoms and the alcohol having 3 or less carbon atoms, the amount (concentration) of the alcohol having 2 or less carbon atoms in the treatment liquid may be 1 to 99% by weight based on the total amount of the alcohol. good.

When a treatment liquid containing alcohol in addition to the organic halogen solvent is used, the organic solvent used for forming the polyimide film can be efficiently removed as in the case where the organic halogen solvent is used alone. Further, by including alcohol in the treatment liquid, it is expected that the removability of the treatment liquid contained in the polyimide film and the treatment liquid adhering to the surface of the polyimide film can be improved.

(Composition of liquid for processing)
The amount of alcohol contained in the treatment liquid is, for example, 1 to 90% by weight. When the amount of alcohol is excessively large, the amount of the organic halogen solvent contained in the treatment liquid tends to be relatively small, and the removability of the organic solvent in the polyimide film tends to decrease. The amount of alcohol in the treatment liquid is 85% by weight or less, 80% by weight or less, 75% by weight or less, 70% by weight or less, 65% by weight or less, 60% by weight or less, 55% by weight or less, or 50% by weight or less. May be. The amount of alcohol in the treatment liquid may be 3% by weight or more, 5% by weight or more, 10% by weight or more, or 15% by weight or more.

The treatment liquid may contain an organic solvent other than the organic halogen solvent and alcohol, or water. From the viewpoint of improving the removability of the organic solvent used for forming the polyimide film, the total content of the organic halogen solvent and the alcohol in the treatment liquid is preferably 60% by weight or more, preferably 70% by weight or more, and 80% by weight or more. , 90% by weight or more, or 95% by weight or more.

The amount of the organic halogen solvent contained in the treatment liquid is preferably 10% by weight or more, 15% by weight or more, 20% by weight or more, 25% by weight or more, 30% by weight or more, 35% by weight or more, 40% by weight or more. It may be 45% by weight or more, or 50% by weight or more.

The liquid for treatment may have a flash point of 50 ° C. or higher, 80 ° C. or higher, 100 ° C. or higher, 150 ° C. or higher, 200 ° C. or higher or 250 ° C. or higher, and may not indicate a flash point. If the flash point of the treatment liquid is high, or if the treatment liquid does not show a flash point, simplification of equipment for residual solvent reduction treatment can be expected. The flash point of the lower alcohol is 50 ° C or lower, but the flash point of the treatment liquid is set to 50 ° C or higher by mixing it with a non-flammable halogen solvent such as hydrofluoroether or an organic solvent having a high flash point. be able to

<Contact between polyimide membrane and processing liquid>
The method of contacting the polyimide film containing the residual solvent with the processing liquid is not particularly limited, and the polyimide film is immersed in the liquid, the liquid is sprayed on the polyimide film, the liquid is applied to the polyimide film, and the processing liquid vapor is used. Alternatively, exposure of the polyimide film to mist and the like can be mentioned.

The contact between the polyimide film and the treatment liquid may be carried out in a state where the polyimide film is laminated on the support, or may be carried out after peeling the polyimide film from the support. From the viewpoint of increasing the efficiency of removing the residual solvent, it is preferable to bring the polyimide film peeled from the support into contact with the treatment liquid. When the treatment liquid is brought into contact with the polyimide film by spraying or coating, the treatment liquid may be brought into contact with only one side of the polyimide film or may be brought into contact with both sides. From the viewpoint of increasing the efficiency of removing the residual solvent, it is preferable to bring the treatment liquid into contact with both sides of the polyimide film. For example, when spraying the treatment liquid, the treatment liquid may be sprayed from both sides of the polyimide membrane. The flow rate (flow velocity) of the liquid from the spray nozzle and the distance between the spray nozzle and the polyimide film may be appropriately adjusted.

The treatment time is, for example, about 30 seconds to 10 hours, and may be appropriately set according to the amount of residual solvent in the polyimide film, the target amount of residual solvent, the type of residual solvent, and the like. From the viewpoint of increasing the production efficiency of the polyimide film, the treatment time is preferably 1 hour or less, more preferably 30 minutes or less, further preferably 10 minutes or less, and may be 5 minutes or less or 3 minutes or less. By using a treatment liquid containing an organic fluorine-based solvent such as hydrofluorocarbon, the amount of residual solvent in the polyimide film can be reduced even in a short treatment time.

The treatment temperature is, for example, 0 to 150 ° C., and the treatment may be performed under heating. The higher the temperature during the treatment, the more the replacement of the residual solvent in the film with the treatment liquid is promoted, and the efficiency of removing the residual solvent tends to be improved. The heating temperature may be between room temperature (for example, 25 ° C.) and the boiling point of the processing liquid to be used. The heating temperature is preferably 30 ° C. or higher, and may be 35 ° C. or higher, 40 ° C. or higher, 45 ° C. or higher, or 50 ° C. or higher. From the viewpoint of suppressing volatilization of the treatment liquid, a boiling point of −10 ° C. or lower is preferable. The contact treatment between the polyimide film and the treatment liquid may be carried out under pressure or reduced pressure.

[Post-processing]
By contacting the polyimide film with the treatment liquid as described above, the residual amount of the organic solvent used for the film formation can be reduced. After the contact treatment between the polyimide and the treatment liquid, the treatment liquid adheres to the surface of the polyimide film, so that the liquid adhering to the surface of the polyimide film may be removed by heating, air blowing, washing with water, or the like. When heating, the heating temperature is preferably room temperature to 200 ° C, more preferably 70 ° C to 180 ° C. The heating time may be appropriately set according to the heating temperature, but is preferably 1 minute to 120 minutes, more preferably 5 minutes to 90 minutes, from the viewpoint of improving productivity and removing the solvent.

In order to remove the treatment liquid (first treatment liquid) used to reduce the residual amount of the organic solvent used for film formation from the polyimide film, the polyimide film is separated into another treatment liquid (for the second treatment). A process of contacting with a liquid) may be performed. As the second treatment liquid, a liquid having a composition different from that of the first treatment liquid is used. For example, after treatment with an organic fluorine-based solvent such as hydrofluoroether and a liquid for first treatment containing alcohol, post-treatment is carried out with a liquid for second treatment that is more volatile than the liquid for first treatment. By doing so, the first treatment liquid remaining on the polyimide film can be removed, and the subsequent treatment liquid can be removed by heating in a short time.

As the liquid for the second treatment used for the post-treatment, a liquid containing 20% by weight or more of alcohol is preferable. From the viewpoint of increasing the cleaning efficiency (solvent removal efficiency), the alcohol content in the second treatment liquid is preferably 30% by weight or more, more preferably 35% by weight or more, still more preferably 40% by weight or more.

The alcohol contained in the second treatment liquid is preferably a lower alcohol having 1 to 6 carbon atoms like the alcohol contained in the first treatment liquid, and among them, methanol, ethanol, isopropyl alcohol and the like having 1 to 3 carbon atoms. Alcohol is preferred. Since the lower alcohol has a small molecular size, it can be easily replaced with an organic halogen solvent adhering to the polyimide film or the surface of the polyimide film, and has a low boiling point and can be easily removed. The liquid for the second treatment may contain two or more kinds of alcohols.

The liquid for the second treatment is preferably a non-combustible material because the equipment for carrying out the treatment with the liquid for the second treatment can be simplified. Specifically, the liquid for the second treatment preferably has an alcohol content of 20% by weight or more and less than 60% by weight. Water is preferable as the solvent other than alcohol. Since the mixture of alcohol and water has an azeotropic composition regardless of the mixing ratio, it is excellent in removing the solvent from the polyimide film. The water content in the alcohol / water mixture is preferably 40 to 80% by weight.

The liquid for the second treatment may contain a liquid component other than alcohol and water. When the liquid for the second treatment is an alcohol / water mixture, the total concentration of alcohol and water is preferably 60% by weight or more, more preferably 70% by weight or more, further preferably 80% by weight or more, and 90% by weight or more. , 95% by weight or more, or 100% by weight.

The liquid for the second treatment may contain an organic halogen solvent, but the amount of the organic halogen solvent contained in the liquid for the second treatment is smaller than the amount of the organic halogen solvent contained in the liquid for the first treatment. Is preferable. The amount of the organic halogen solvent in the liquid for the second treatment is preferably 40% by weight or less, more preferably 30% by weight or less, further preferably 20% by weight or less, 10% by weight or less, 5% by weight or less, or 1% by weight or less. It may be.

Since a large amount of the organic solvent used for forming the polyimide film remains inside the polyimide film in the thickness direction, the liquid for the first treatment is sufficient for the organic solvent remaining inside the polyimide film. It is preferable to have removability. On the other hand, after the treatment with the first treatment liquid, since the first treatment liquid is abundantly present near the surface layer of the polyimide film, it can be easily replaced with the second treatment liquid. Therefore, by using a liquid that is miscible with the first treatment liquid, such as alcohol or an alcohol / water mixed system, as the second treatment liquid, the residual amount of the first treatment liquid can be easily reduced. Further, by using a liquid having a higher volatility than the first treatment liquid as the second treatment liquid, the residual amount of the first treatment liquid can be easily reduced.

The method of bringing the polyimide film into contact with the liquid for the second treatment is not particularly limited, and as in the treatment with the liquid for the first treatment, immersion, spraying, coating, treatment with steam or mist and the like can be applied. The treatment time and treatment temperature are preferably in the same range as those described above for the treatment with the first treatment liquid. After the treatment with the second treatment liquid, the liquid adhering to the surface may be removed by heating, air blowing, washing with water or the like.

[Characteristics and applications of polyimide film]
The polyimide film obtained as described above can be applied to various applications in which a polyimide film is generally used, such as a substrate material such as a flexible printed wiring board and a display, and a cover window for a display. The polyimide film may be transparent in visible light, and may have, for example, a light transmittance of 70% or more or 80% or more at a wavelength of 400 nm.

Hereinafter, the present invention will be described in more detail by showing a comparison between Examples and Comparative Examples, but the present invention is not limited to the following Examples.

Organic solvents and compounds are described by the following abbreviations.
EtOH: Ethanol IPA: Isopropyl alcohol DMF: N, N-dimethylformamide DCM: Dichloromethane TFMB: 2,2'-bis (trifluoromethyl) benzidine 3,3'-DDS: 3,3'-diaminodiphenyl sulfone 6FDA: 2 , 2-Bis (3,4-dicarboxyphenyl) -1,1,1,3,3,3-hexafluoropropane dianhydride TMHQ: p-phenylene bis (trimeritic acid anhydride)

[Measurement of residual solvent amount]
The amount of residual solvent in the polyimide film was measured by the following procedure.
Using about 8.9 g of 1,3-dioxolane as a solvent, about 0.1 g of a polyimide film and about 1 g of DEGBME (diethylene glycol butyl methyl ether) as an internal standard substance were dissolved to prepare a measurement sample. This sample was analyzed using a gas chromatograph (GC) device (manufactured by Shimadzu Corporation), and the amount of residual solvent contained in the polyimide film was determined from the GC peak area and the prepared concentration.

[Preparation of polyimide film]
DMF was charged into the reaction vessel and stirred under a nitrogen atmosphere. TFMB: 17 parts by weight, 3,3'-DDS: 6 parts by weight, BPDA: 6 parts by weight, TMHQ: 9 parts by weight, and 6FDA: 17 parts by weight were sequentially added thereto for 5 hours in a nitrogen atmosphere. The mixture was stirred to obtain a polyamic acid solution having a solid content concentration of 18%. Pyridine was added to the polyamic acid solution as an imidization catalyst to completely disperse the mixture, acetic anhydride was added, the mixture was stirred at 120 ° C. for 2 hours, and then cooled to room temperature. IPA was added while stirring the solution to precipitate the polyimide. Then, suction filtration was performed, the washing operation by IPA was repeated 4 times, and then dried in a vacuum oven set at 120 ° C. for 12 hours to obtain a polyimide resin.

The above-mentioned polyimide resin was dissolved in DCM to prepare a polyimide resin solution having a solid content concentration of 18% by weight. A polyimide resin solution is applied onto a non-alkali glass plate using a comma coater, dried at 40 ° C. for 30 minutes and 70 ° C. for 60 minutes, and then peeled off from the non-alkali glass plate to form a polyimide film having a thickness of about 70 μm. Obtained. The amount of residual solvent (DCM) in this polyimide film was measured and found to be 8% by weight.

[Reference example 1]
A polyimide film is ^{cut into a size of about 12 cm 2} and immersed in a halogen-based mixed solvent in which methyl nonafluorobutyl ether and trans-1,2-dichloroethylene are mixed at a weight ratio of 50:50 at room temperature (25 ° C.) for 5 minutes. It was taken out and the solvent adhering to the surface was wiped off.

[Reference example 2]
A halogen-based mixed solvent was applied to both sides of the polyimide film using a bar coater, and after 20 minutes, the solvent adhering to the surface was wiped off.

[Reference example 3]
A halogen-based mixed solvent 1 having a temperature of 25 ° C. was sprayed from a spray nozzle on both sides of the polyimide film at a flow rate of 5.9 mL / sec for 5 minutes, and then the liquid adhering to the surface was wiped off.

[Example 1]
The polyimide film ^{was cut into a size of about 12 cm 2} in area, and the halogen-based mixed solvent used in Reference Example 1 and a mixed alcohol (95/5 (weight ratio) mixed solution of EtOH / IPA) were mixed at a weight ratio of 85:15. After immersing in the solvent at room temperature (25 ° C.) for 5 minutes, the mixture was taken out and the solvent adhering to the surface was wiped off.

[Examples 2 and 3]
The immersion treatment was carried out in the same manner as in Example 1 except that the mixing ratio of the halogen-based mixed solvent and the alcohol mixed solvent was changed as shown in Table 1, and the liquid adhering to the surface was wiped off.

[Comparative Example 1]
Water was used instead of the halogen-based mixed solvent, and the immersion time was changed to 20 minutes. Other than that, the liquid adhering to the surface was wiped off after the immersion treatment was performed in the same manner as in Reference Example 1.

[Comparative Example 2]
Water at a temperature of 25 ° C. was sprayed from a spray nozzle on both sides of the polyimide film at a flow rate of 16.7 mL / sec for 5 minutes, and then the liquid adhering to the surface was wiped off.

[Comparative Example 3]
IPA at a temperature of 25 ° C. was sprayed from a spray nozzle on both sides of the polyimide film at a flow rate of 16.7 mL / sec for 5 minutes, and then the liquid adhering to the surface was wiped off.

[Evaluation results]
Table 1 shows the types of treatment liquids of Reference Examples, Examples and Comparative Examples, the contact method between the treatment liquid and the polyimide film, the treatment time, and the amount of residual solvent.

In Comparative Example 1 in which the immersion treatment was carried out in water, the amount of residual solvent was hardly reduced as compared with that before the treatment (8%), and in Comparative Example 2 sprayed with water and Comparative Example 3 sprayed with IPA. It was similar.

In Reference Example 1 in which the immersion treatment was carried out in the halogen-based mixed solvent, the residual solvent was significantly reduced in the treatment for 5 minutes, and Reference Example 2 in which the halogen-based mixed solvent was applied and the halogen-based mixed solvent were sprayed. The same was true for Reference Example 3. In Examples 1 to 3 in which the halogen-based mixed solvent and the mixed alcohol were immersed in the mixed solution, the amount of residual solvent was significantly reduced as in Reference Examples 1 to 3.

From the above results, it is possible to efficiently reduce the residual solvent of the polyimide film by bringing the halogen solvent containing hydrofluoroether into contact with the polyimide film containing the residual solvent, and alcohol is added to the halogen solvent. It can be seen that the same effect is obtained even when the solvent is used.

Claims (12)

It has a step of bringing a polyimide film containing an organic solvent into contact with a processing liquid.
A method for producing a polyimide film, wherein the treatment liquid contains an organic fluorine-based solvent and alcohol. The production of the polyimide film according to claim 1, wherein a polyimide film containing the organic solvent is produced by applying a solution in which a polyimide resin is dissolved in an organic solvent onto a support and removing a part of the organic solvent. Method. The method for producing a polyimide film according to claim 2, wherein the polyimide film is peeled off from the support and then the polyimide film is brought into contact with the processing liquid. The method for producing a polyimide film according to any one of claims 1 to 3, wherein the alcohol is one or more selected from the group consisting of methanol, ethanol and isopropyl alcohol. The method for producing a polyimide film according to any one of claims 1 to 4, wherein the alcohol is a mixed alcohol containing two or more kinds of alcohols. The method for producing a polyimide film according to any one of claims 1 to 5, wherein the treatment liquid contains 1 to 90% by weight of alcohol. The method for producing a polyimide film according to any one of claims 1 to 6, wherein the organic fluorine-based solvent is a hydrofluoro ether. The method for producing a polyimide film according to any one of claims 1 to 7, wherein the treatment liquid further contains an organochlorine solvent that does not show solubility in the polyimide film. The method for producing a polyimide film according to claim 8, wherein the organic chlorine-based solvent is a chlorinated hydrocarbon. Polyimide is 2,2-bis (3,4-dicarboxyphenyl) -1,1,1,3,3,3-hexafluoropropane dianhydride out of a total of 100 mol% of the tetracarboxylic dianhydride component. The method for producing a transparent polyimide film according to any one of claims 1 to 9, which contains 20 mol% or more of the substance. The transparent polyimide film according to any one of claims 1 to 10, wherein the polyimide contains 20 mol% or more of 2,2'-bis (trifluoromethyl) benzidine out of a total of 100 mol% of the diamine component. Production method. The method for producing a polyimide film according to any one of claims 1 to 11, wherein the thickness of the polyimide film is 5 μm or more.