JP2021169560A - Method for producing polyimide film - Google Patents

Abstract

To provide a polyimide film.SOLUTION: A method for producing a polyimide film includes bringing a polyimide film (3) containing an organic solvent into contact with a liquid (11) for first treatment, and then draining a liquid attached to the surface of the polyimide film. The liquid for first treatment is a poor solvent of the polyimide film, and is an organic solvent or a mixture of an organic solvent containing 80 wt.% or less of water and water, and the drainage treatment is treatment by sponge rolls (41 and 42). The polyimide film may be brought into contact with the liquid for first treatment, and may be brought into contact with the liquid (12) for second treatment.SELECTED DRAWING: Figure 1

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.

Japanese Unexamined Patent Publication No. 2017-186473

The treatment of immersing the polyimide film containing an organic solvent in a poor solvent is effective in reducing the residual solvent. However, in immersion in water, a long time is required for the treatment to reduce the residual solvent. In addition, the film after the immersion treatment may have an appearance defect such as a watermark.

In the present invention, the polyimide film containing the residual organic solvent is brought into contact with the liquid for the first treatment, and then the liquid draining treatment is performed. The liquid for the first treatment is a poor solvent for the polyimide film, may be an organic solvent, or may be a mixture of water and an organic solvent. The amount of water in the first treatment liquid is preferably 80% by weight or less. For the liquid draining treatment, it is preferable to use a sponge roll. For example, the liquid draining is performed by niping the polyimide film with a pair of sponge rolls.

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 liquid for the first treatment.

Examples of the method of bringing the polyimide film into contact with the liquid for the first treatment include dipping, spraying, coating and the like. After the polyimide film is brought into contact with the liquid for the first treatment, it may be further brought into contact with the liquid for the second treatment.

The second treatment liquid is a poor solvent for the polyimide film and has a composition different from that of the first treatment liquid. As the liquid for the second treatment, an alcohol solvent containing 20% by weight or more of alcohol may be used. Examples of the alcohol include methanol, ethanol, isopropyl alcohol and the like. The liquid for the second treatment may contain two or more kinds of alcohols. The liquid for the second treatment may contain water in addition to alcohol.

After the polyimide film is brought into contact with the liquid for the first treatment, the liquid for the first treatment adhering to the surface of the polyimide film may be drained before being brought into contact with the liquid for the second treatment. After the second treatment liquid is brought into contact with the polyimide film, the second treatment liquid adhering to the surface of the polyimide film may be drained.

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.

It is a conceptual diagram which shows the state of performing immersion and liquid draining while transporting a polyimide film.

[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.

<Liquid for first treatment>
The treatment liquid (first treatment liquid) used for removing the organic solvent used for film formation is a poor solvent for the polyimide film, and is an organic solvent or a mixture of an organic solvent containing 80% by weight or less of water and water. be. The content of water in the treatment liquid is preferably 70% by weight or less, more preferably 60% by weight or less. The liquid for treatment may have a flash point of 50 ° C. or higher, or may be a liquid that does not show a flash point. Examples of the treatment liquid include organic halogen-based solvents and glycol ether-based solvents. The treatment liquid may be a non-flammable material.

(Liquid for organic halogen treatment)
Examples of the organic halogen solvent used as the treatment liquid include organic fluorine-based solvents, organic chlorine-based solvents, and organic bromine-based solvents. The organic halogen solvent 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 used as the treatment liquid is preferably 100 ° C. or lower, more preferably 80 ° C. or lower.

The liquid for the first treatment preferably contains an organic fluorine-based solvent because it has a high flash point (or does not show a flash point) and 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 organic halogen-based treatment liquid may contain an organic chlorine-based solvent in addition to the organic fluorine-based 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 organic halogen-based 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. The treatment liquid containing two or more kinds of organic halogen solvents preferably has an azeotropic composition. The liquid for the first treatment may contain a solvent other than the organic fluorine-based solvent such as alcohols. The liquid for the first treatment preferably contains 60% by weight or more of an organic halogen solvent. The content of the organic halogen solvent in the liquid for the first treatment may be 70% by weight or more, 80% by weight or more, 90% by weight or more, or 95% by weight or more.

The treatment liquid preferably has a flash point of 50 ° C. or higher or does not exhibit a flash point because the equipment for the residual solvent reduction treatment can be simplified. The flash point of the liquid for treatment is preferably 80 ° C. or higher, more preferably 100 ° C. or higher, and may be 150 ° C. or higher, 200 ° C. or higher, or 250 ° C. or higher. It is particularly preferred that the treatment liquid does not exhibit a flash point.

Even when one or more organic halogen solvents have flammability, the flash point can be set to 50 ° C. or higher or non-flammable by mixing with one or more non-flammable solvents. For example, even when the chlorinated hydrocarbon has flammability, the treatment liquid can be made non-flammable by mixing with a non-flammable fluorine-based solvent. As an example of a mixed halogenated organic solvent having a flash point of 50 ° C. or higher or no flash point and an azeotropic composition, it has a chlorinated hydrocarbon and a hydrofluoroether in a ratio of 5 to 70:95 to 30. Can be mentioned.

(Glycol ether-based treatment liquid)
Examples of the glycol ether solvent used as the treatment liquid include glycol ethers, dialkyl glycol ethers, and glycol ether esters.

Specific examples of glycol ethers include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, ethylene glycol monoethylhexyl ether, ethylene glycol monophenyl ether, and ethylene. Glycol monobenzyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, diethylene glycol monoethylhexyl ether, diethylene glycol monophenyl ether, diethylene glycol monobenzyl ether, propylene glycol monomethyl ether, propylene glycol Monoethyl ether, propylene glycol monoisopropyl ether, propylene glycol monobutyl ether, propylene glycol monohexyl ether, propylene glycol monoethylhexyl ether, propylene glycol monophenyl ether, propylene glycol monobenzyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl Ether, dipropylene glycol monoisopropyl ether, dipropylene glycol monobutyl ether, dipropylene glycol monohexyl ether, dipropylene glycol monoethylhexyl ether, dipropylene glycol monophenyl ether, dipropylene glycol monobenzyl ether, triethylene glycol monomethyl ether, tri Examples thereof include ethylene glycol monoethyl ether, triethylene glycol monobutyl ether, and tetraethylene glycol monomethyl ether.

Specific examples of dialkyl glycol ethers include ethylene glycol dimethyl ether, ethylene glycol methyl ethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol ethyl methyl ether, diethylene glycol methyl ethyl ether, diethylene glycol dipropyl ether, diethylene glycol methyl propyl ether, and diethylene glycol ethyl propyl. Examples thereof include ether, diethylene glycol dibutyl ether, diethylene glycol methyl butyl ether, diethylene glycol ethyl butyl ether, diethylene glycol propyl butyl ether, diethylene glycol dipentyl ether, diethylene glycol methyl pentyl ether, diethylene glycol ethyl pentyl ether, diethylene glycol propyl pentyl ether, diethylene glycol butyl pentyl ether and the like.

As the glycol ether ester, acetate of glycol ether (glycol ether acetates) is preferable. Specific examples of glycol ether acetates include ethylene glycol monoethyl ether acetate, ethylene glycol monoisopropyl ether acetate, ethylene glycol monobutyl ether acetate, ethylene glycol monohexyl ether acetate, ethylene glycol monoethylhexyl ether acetate, and ethylene glycol monophenyl ether acetate. , Ethylene glycol monobenzyl ether acetate, diethylene glycol monoethyl ether acetate, propylene glycol methyl ether acetate, propylene glycol ethyl ether acetate, propylene glycol butyl ether acetate, dipropylene glycol methyl ether acetate and other glycol ether acetates.

Among the above, since the ignition point is high (or the ignition point is not shown) and the residual solvent in the polyimide film is highly removable, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, diethylene glycol monobutyl ether, and triethylene glycol monobutyl ether , Dipropylene glycol monomethyl ether, dipropylene glycol dimethyl ether, diethylene glycol monohexyl ether, and diethylene glycol dibutyl ether are preferable, and among them, diethylene glycol monobutyl ether is particularly preferable because it is excellent in removability of an organic solvent in a polyimide film.

The glycol ether-based treatment liquid preferably contains 60% by weight or more of the glycol ether-based solvent. The content of the glycol ether solvent in the treatment liquid may be 70% by weight or more, 80% by weight or more, 90% by weight or more, or 95% by weight or more.

The treatment liquid may contain an organic solvent other than the glycol ether solvent or water. The glycol ether-based solvent is highly miscible with water, and by mixing the glycol ether-based solvent and water, the flash point can be increased or the flash point can not be exhibited. Further, since the glycol ether and water azeotrope, it is easy to remove the treatment liquid remaining in the polyimide film and the first treatment liquid adhering to the surface of the polyimide film in place of the residual solvent.

When the treatment liquid contains water in addition to the glycol ether solvent, the water content is preferably 2 to 40% by weight, more preferably 3 to 30% by weight. The total content of the glycol ether solvent and water in the treatment liquid is preferably 70% by weight or more, more preferably 80% by weight or more, and may be 85% by weight or more, or 90% by weight or more. The treatment liquid may contain an organic solvent other than the glycol ether solvent and water, and additives such as a surfactant and a defoaming agent.

<Contact between polyimide membrane and processing liquid>
The method of contacting the polyimide film containing the residual solvent with the treatment liquid is not particularly limited, and examples thereof include immersion of the polyimide film in the liquid, spraying of the liquid on the polyimide film, and application of the liquid to the polyimide film.

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. 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. For example, when spraying the treatment liquid, the treatment liquid may be sprayed from one side or 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. Even when heating is performed because the flash point of the treatment liquid is high or the treatment liquid does not show the flash point, it depends on the treatment liquid using general equipment without using special equipment. The residual solvent reduction treatment can be carried out. The contact treatment between the polyimide film and the treatment liquid may be carried out under pressure or reduced pressure.

[Post-processing]
As described above, by bringing the polyimide film into contact with the liquid for the first treatment, the residual amount of the organic solvent used for the film formation can be reduced. 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. As the first treatment liquid, a liquid having high removability of the organic solvent (organic solvent showing solubility in polyimide) used for forming the polyimide film is used, and as the second treatment liquid, it is higher than the first treatment liquid. It is preferable to use one having high volatility. For example, a polyimide is treated by treating with an organic halogen-based first treatment liquid containing an organic fluorine-based solvent such as hydrofluoroether, and then treating with a highly volatile second treatment liquid such as alcohol. The first treatment liquid remaining on the film can be removed, and the treatment liquid can be removed by heating in a short time thereafter.

As the liquid for the second 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.

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. Since the lower alcohol has a small molecule size, it can be easily replaced with the molecule of the liquid for the first treatment 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 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. Examples of alcohols having 3 or more carbon atoms include n-propanol, isopropyl alcohol, n-butanol and the like. Among these, a combination of an alcohol having 2 or less carbon atoms and an isopropyl alcohol is preferable. Both methanol and ethanol may be contained as the alcohol having 2 or less carbon atoms. 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 second treatment liquid is preferably 1 to 99% by weight based on the total amount of the alcohol. ..

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.

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 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 treatment by dipping, spraying, coating or the like can be applied as in the treatment with the liquid for the first treatment. The treatment time and treatment temperature are preferably in the same range as those described above for the treatment with the first treatment liquid.

[Draining process]
After performing the treatment of bringing the polyimide film into contact with the treatment liquid, the liquid draining treatment is performed. When the contact treatment with the first treatment liquid and the contact treatment with the second treatment liquid are carried out, either after the contact with the first treatment liquid or after the contact with the second treatment liquid. The liquid draining treatment may be carried out, or the liquid draining treatment may be carried out after each treatment.

By performing the liquid drainage, the carry-in of the treatment liquid to the post-process is reduced, so that the post-process can be simplified and the contamination in the post-process can be suppressed. In addition, poor appearance (watermarks, etc.) on the surface of the polyimide film due to adhesion of droplets can be suppressed.

Examples of the liquid draining method include spraying gas with an air knife or the like, and treatment with a liquid draining roll such as a metal roll, a resin roll, a rubber roll, or a sponge roll. As for the liquid draining roll, it is preferable that a pair of rolls are arranged so as to sandwich the polyimide film. Since the effect of removing the liquid adhering to the surface of the polyimide film is high, it is preferable to use a sponge roll as the liquid draining treatment, and in particular, a method of sandwiching (niping) the polyimide film with a pair of sponge rolls is preferable. ..

Examples of the material of the sponge roll include polyolefin, polyvinyl alcohol, polyurethane and the like, and those which are less likely to be deformed or dissolved by the treatment liquid are preferable. For example, when the treatment liquid is an organic halogen-based solvent or a glycol ester-based solvent, the material of the sponge roll is preferably polyolefin or polyvinyl alcohol.

FIG. 1 is a conceptual diagram showing a state in which a dipping treatment and a liquid draining treatment are performed while transporting the polyimide film 3 by the roll-to-roll method. The treatment tank 1 is bathed with the first treatment liquid 11, and the treatment tank 2 is bathed with the second treatment liquid 12.

The polyimide film 3 that has passed over the transport roll 31 is immersed in the first treatment liquid 11 of the first treatment tank 1 and moves from the transport roll 32 in the treatment tank toward the transport roll 33 to perform the first treatment. Treatment with polyimide is performed. After that, the polyimide film 3 is transported to the outside of the liquid bath of the first treatment liquid 11, and the liquid draining treatment is performed by a pair of sponge rolls 41 and 42.

After the liquid draining treatment with the sponge rolls 41 and 42, the polyimide film 3 passes over the transport rolls 34 and 36 and is immersed in the second treatment liquid 12 of the second treatment tank 2 to be immersed in the second treatment liquid 12 in the treatment tank. By moving from the transport roll 37 toward the transport roll 38, the treatment with the second treatment liquid is performed. Since the first treatment liquid adhering to the surface of the polyimide film is removed before the polyimide film 3 is immersed in the second treatment liquid 12, the amount of the first treatment liquid brought into the second treatment tank is reduced. do. Therefore, the efficiency of treatment with the second treatment liquid can be improved, and the liquid exchange cycle can be lengthened, which can contribute to the improvement of production efficiency.

The polyimide film 3 after the treatment with the second treatment liquid is transported to the outside of the liquid bath of the second treatment liquid 12, and the liquid draining treatment is performed by a pair of sponge rolls 46 and 47. After the liquid draining treatment, the solvent may be further removed by heating, washing with water, or the like.

In FIG. 1, two transfer rolls 32 and 33 are shown in the first processing tank 1, and two transfer rolls 37 and 38 are shown in the second processing tank 2. By arranging a larger number of transport rolls in a staggered pattern, for example, the transport distance of the polyimide film 3 in the liquid bath may be lengthened, and the immersion treatment time may be lengthened.

The sponge rolls do not have to be one pair, and two or more pairs of sponge rolls may be arranged. Further, the treatment with an air knife or the like may be performed before or after the treatment with the sponge roll. As shown in FIG. 1, by arranging the sponge rolls 41 and 42 on the treatment tank 1, the drained treatment liquid falls into the treatment tank 1, so that the decrease of the treatment liquid is suppressed.

[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.
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 (trimellitic acid anhydride)

[Measurement of residual solvent amount]
The amount of residual solvent in the polyimide films of Examples and Comparative Examples 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 9.1% by weight.

[Example 1]
<Immersion treatment 1: Reduction of residual solvent amount>
The above-mentioned polyimide film was immersed in a dipping treatment bath 1 containing a halogen-based mixed solvent 1 at room temperature (25 ° C.) for 5 minutes and then taken out.

<Draining process 1>
The polyimide film taken out from the dipping treatment bath was niped with a sponge roll made of polyolefin (PO) to carry out a liquid draining treatment. The presence or absence of droplets on the surface of the polyimide film after the liquid draining treatment and the appearance of the polyimide film were visually evaluated.

<Immersion treatment 2: Reduction of solvent in immersion treatment 1>
The polyimide film after the liquid draining treatment was immersed in a dipping treatment bath 2 containing a mixed solvent of ethanol / IPA / water (weight ratio 45/5/50) at room temperature for 20 minutes and then taken out.

<Draining process 2>
The polyimide film taken out from the dipping treatment bath 2 was nipped with a sponge roll made of polyvinyl alcohol (PVA) to carry out a liquid draining treatment. The presence or absence of droplets on the surface of the polyimide film after the liquid draining treatment and the appearance of the polyimide film were visually evaluated.

<Heat treatment>
The polyimide film after the liquid draining treatment was heated in an oven at 170 ° C. for 20 minutes, and then the amount of residual solvent was measured.

[Examples 2 to 9]
The liquid, temperature and immersion time of the immersion treatment baths 1 and 2 and the material of the sponge roll were changed as shown in Table 1. Details of the mixed solvent used in Examples and Comparative Examples are as follows.
Halogen-based mixed solvent 1: Methyl nonafluorobutyl ether / trans-1,2-dichloroethylene 50/50 (weight ratio) mixed solution Halogen-based mixed solvent 2: Methyl nonafluorobutyl ether / trans-1,2-dichloroethylene / ethanol 53 / 44/3 (weight ratio) mixed solution Glycol ether-based mixed solvent: 81/5/14 (weight ratio) mixed solution of diethylene glycol monobutyl ether / water / surfactant (polyoxyethylene alkyl ether, etc.)

[Comparative Example 1]
After the dipping treatment 1 and after the dipping treatment 2, the dipping treatment 1, the dipping treatment 2 and the heat treatment were carried out in the same manner as in Example 1 except that the liquid draining treatment with the sponge roll was not performed.

[Comparative Examples 2 and 3]
In Comparative Example 2, the immersion treatment 1 was carried out by putting water in the immersion treatment bath 1. In Comparative Example 3, the dipping treatment 1 was carried out by putting IPA in the dipping treatment bath 1. After the immersion in the immersion treatment bath 1 was carried out under the conditions shown in Table 1, the heat treatment was carried out at 170 ° C. for 20 minutes without performing the liquid draining treatment.

[Evaluation results]
Treatment conditions for polyimide films of Examples and Comparative Examples (conditions for immersion treatment and liquid drainage treatment), appearance after liquid drainage treatment (appearance immediately after immersion treatment when liquid drainage treatment is not performed), and residual after treatment. The amount of solvent is shown in Table 1. The HFE (hydrofluoroether) in Table 1 is a methylnonafluorobutyl ether contained in the halogen-based mixed solvents 1 and 2. As for the appearance of the polyimide film, those without deformation and solvent marks (watermarks) were marked with ◯, and those with deformation or solvent marks were marked with x.

Examples 1 to 5 and Comparative Example 1 in which the immersion treatment 1 was performed with a halogen-based solvent and then the immersion treatment 2 was performed with an alcohol-based solvent, and the immersion treatment 1 was performed with a glycol ether-based solvent and then the immersion treatment was performed with an alcohol-based solvent. In Examples 6 to 9 in which 2 was carried out, the amount of residual DCM was significantly reduced in each case. The removal of DCM was insufficient in Comparative Example 2 which was immersed in water and Comparative Example 3 which was immersed in IPA.

In Comparative Examples 1 to 3 in which the liquid was not drained by the sponge roll, droplets were attached to the surface of the sample after the immersion treatment, and the appearance was poor such as water marks, whereas the sponge roll was used. In Examples 1 to 9 in which the liquid draining treatment was performed, no droplets were attached and the appearance was good.

1, 2 Treatment tank 3 Polyimide film 11 1st treatment liquid 12 2nd treatment liquid 31-3, 36-39 Conveyance roll 41, 42, 46, 47 Sponge roll

Claims (18)

A method for manufacturing a transparent polyimide film.
It has a step of bringing the polyimide film containing an organic solvent into contact with the liquid for the first treatment; and a step of draining the liquid adhering to the surface of the polyimide film.
The liquid for the first treatment is a poor solvent for the polyimide film, and is an organic solvent or a mixture of an organic solvent containing 80% by weight or less of water and water.
A method for producing a transparent polyimide film. The method for producing a transparent polyimide film according to claim 1, wherein the liquid draining is performed with a sponge roll. A polyimide film containing the organic solvent is prepared by applying a solution in which a polyimide resin is dissolved in the organic solvent on a support and removing a part of the organic solvent.
The method for producing a transparent polyimide film according to claim 1 or 2, wherein the polyimide film containing the organic solvent is brought into contact with the liquid for the first treatment. The method for producing a transparent polyimide film according to claim 3, wherein the polyimide film is peeled off from the support and then the polyimide film is brought into contact with the liquid for the first treatment. The method for producing a transparent polyimide film according to any one of claims 1 to 4, wherein the polyimide film is immersed in the first treatment liquid to bring the polyimide film into contact with the first treatment liquid. .. The method for producing a transparent polyimide film according to any one of claims 1 to 5, wherein the first treatment liquid contains 20% by weight or more of an organic fluorine-based solvent. The method for producing a transparent polyimide film according to claim 6, wherein the organic fluorine-based solvent is hydrofluoroether. The method for producing a transparent polyimide film according to claim 6 or 7, wherein the first treatment liquid further contains an organic chlorine-based solvent that does not show solubility in the polyimide film. The first treatment liquid contains 20% by weight or more of one or more glycol ether-based solvents selected from the group consisting of glycol ethers, dialkyl glycol ethers, and glycol ether acetates, according to claims 1 to 5. The method for producing a transparent polyimide film according to any one of the following items. The method for producing a transparent polyimide film according to claim 9, wherein the first treatment liquid further contains water. The method for producing a transparent polyimide film according to any one of claims 1 to 10, wherein the first treatment liquid is an azeotropic solvent containing two or more kinds of solvents. After the step of bringing the polyimide film into contact with the first treatment liquid, the polyimide film is further made into a second treatment liquid which is a poor solvent for the polyimide film and has a composition different from that of the first treatment liquid. The method for producing a polyimide film according to any one of claims 1 to 11, which comprises a step of contacting the polyimide film. After the step of bringing the polyimide film into contact with the first treatment liquid, before bringing the polyimide film into contact with the second treatment liquid, the first treatment liquid adhering to the surface of the polyimide film is drained. The method for producing a polyimide film according to claim 12. The method for producing a polyimide film according to claim 12 or 13, wherein the liquid for the second treatment has a water content of 80% by weight or less. The method for producing a transparent polyimide film according to claim 12 or 13, wherein the second treatment liquid contains 20% by weight or more and less than 60% by weight of alcohol and 40% by weight or more of water. The transparent polyimide contains 2,2-bis (3,4-dicarboxyphenyl) -1,1,1,3,3,3-hexafluoropropanedi in 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 15, which contains 20 mol% or more of anhydride. The transparent polyimide film according to any one of claims 1 to 16, wherein the transparent polyimide contains 20 mol% or more of 2,2'-bis (trifluoromethyl) benzidine out of a total of 100 mol% of the diamine component. Manufacturing method. The method for producing a transparent polyimide film according to any one of claims 1 to 17, wherein the thickness of the transparent polyimide film is 5 μm or more.

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