Polyimides, molded articles, and films

Abstract

The present invention aims to provide polyimides and molded articles such as films that are environmentally safe, soluble in organic solvents, and have excellent transparency and mechanical properties. [Solution] The above problem can be solved by a polyimide having a tetracarboxylic dianhydride component and a diamine component, wherein the diamine component comprises a fluorine atom-containing diamine having a CF3-O- structure selected from 2,2'-bis(trifluoromethoxy)benzidine, 3,3'-bis(trifluoromethoxy)benzidine, and / or 2,3'-bis(trifluoromethoxy)benzidine, and the tetracarboxylic dianhydride component comprises a tetracarboxylic dianhydride having a fluorene structure and a bis(trimellitic anhydride) ester.

Description

[Technical Field]

[0001] This invention relates to polyimide and molded articles such as films. [Background technology]

[0002] Display devices such as liquid crystal displays, organic EL displays, and electronic paper, as well as electronic devices such as solar cells and touch panels, are required to be thinner, lighter, and more flexible. By replacing the glass materials used in these devices with film materials, flexibility, thinning, and weight reduction can be achieved. Transparent polyimide film has been developed as a glass substitute material and is used in display substrates and cover films, etc.

[0003] As a method for producing highly transparent polyimide films, a method has been proposed using a polyimide resin that is soluble in organic solvents and does not require high-temperature imidation after film formation. Such soluble polyimides use fluorine-containing compounds as the diamine and / or tetracarboxylic dianhydride monomers from the viewpoint of balancing transparency and mechanical properties, and many soluble polyimides using fluoroalkyl-substituted benzidines such as 2,2'-bis(trifluoromethyl)benzidine (TFMB) as the diamine have been proposed (for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] International Publication No. 2020 / 004236 [Overview of the project] [Problems that the invention aims to solve]

[0005] In recent years, the environmental persistence of organofluorine compounds (PFAS) has become a concern. Generally, the carbon-fluorine bonds in organofluorine compounds have high bond energy and are difficult to decompose in the environment. In particular, organofluorine compounds containing structures in which a trifluoromethyl group is bonded to a carbon atom (-C-CF3) or structures in which carbon atoms are bonded to both ends of a difluoromethylene group (-C-CF2-C-) have low decomposability in the environment, and their effects on human health have also been pointed out.

[0006] In view of these issues, the present invention aims to provide polyimides and molded articles such as films that are environmentally safe, soluble in organic solvents, and have excellent transparency and mechanical properties. [Means for solving the problem]

[0007] As a result of diligent research, the inventors have found that the above problem can be solved by the following configuration.

[0008] 1) A polyimide having a tetracarboxylic dianhydride component and a diamine component, The diamine component includes a fluorine atom-containing diamine having a CF3-O- structure selected from 2,2'-bis(trifluoromethoxy)benzidine, 3,3'-bis(trifluoromethoxy)benzidine, and / or 2,3'-bis(trifluoromethoxy)benzidine. A polyimide comprising a tetracarboxylic dianhydride having a fluorene structure and a bis(trimellitic anhydride) ester as tetracarboxylic dianhydride components.

[0009] 2) The polyimide according to 1), wherein the diamine component is 2,2'-bis(trifluoromethoxy)benzidine.

[0010] 3) The polyimide according to 1) or 2), wherein the tetracarboxylic dianhydride having a fluorene structure is 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride.

[0011] 4) A polyimide according to any one of items 1) to 3), wherein the amount of bis(trimellitic anhydride) ester relative to the total amount of tetracarboxylic dianhydride components is 1 to 80 mol%.

[0012] 5) The polyimide according to any one of claims 1) to 4), wherein the bis(trimellitic anhydride) ester is one or more selected from the group consisting of 5,5'-(3,3'-dimethyl[1,1'-biphenyl]-4,4'-diyl)bis(1,3-dihydro-1,3-dioxo-5-isobenzofuran carboxylate), bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylic acid)-biphenyl-4,4'-diyl, bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylic acid)-2,2',3,3',5,5'-hexamethylbiphenyl-4,4'-diyl, p-phenylenebis(trimellitic anhydride), tert-butylhydroquinonebis(trimellitate anhydride), and trimethylhydroquinonebis(trimellitate anhydride).

[0013] 6) The amount of diamine having a structure in which CF3- or -C(CF3)2- is directly bonded to the carbon atom of the aromatic ring, relative to the total amount of diamine components, is less than 0.5 mol%. The polyimide according to any one of items 1) to 5), wherein the amount of tetracarboxylic dianhydride having a structure in which CF3- or -C(CF3)2- is directly bonded to the carbon atom of the aromatic ring is less than 0.5 mol% of the total amount of tetracarboxylic dianhydride components.

[0014] 7) A polyimide according to any one of items 1) to 6), which is soluble in dimethylformamide at 23°C.

[0015] 8) A molded article containing a polyimide as described in any one of items 1) to 7).

[0016] 9) A film containing the polyimide described in any one of items 1) to 7). [Effects of the Invention]

[0017] The polyimide of the present invention contains a specific diamine as a diamine component and contains a tetracarboxylic dianhydride having a fluorene structure and bis(anhydrotrimellitic acid) ester as a tetracarboxylic dianhydride component, and is excellent in solubility in organic solvents, transparency, and mechanical properties. Further, since the specific diamine has lower environmental persistence compared to organic fluorine compounds such as fluoroalkyl-substituted benzidine, the polyimide of the present invention is excellent in environmental safety.

Embodiments for Carrying Out the Invention

[0018] [Polyimide] Polyimide is obtained by dehydrating and cyclizing a polyamic acid obtained by the addition polymerization of a tetracarboxylic dianhydride (hereinafter, may be referred to as "acid dianhydride") and a diamine. That is, polyimide is a polycondensate of a tetracarboxylic dianhydride and a diamine, and has an acid dianhydride-derived structure (acid dianhydride component) and a diamine-derived structure (diamine component).

[0019] The polyimide of the present invention is a polyimide having a tetracarboxylic dianhydride component and a diamine component, and as the diamine component, it contains a fluorine atom-containing diamine having a CF3-O- structure selected from 2,2'-bis(trifluoromethoxy)benzidine, 3,3'-bis(trifluoromethoxy)benzidine, and / or 2,3'-bis(trifluoromethoxy)benzidine, and as the tetracarboxylic dianhydride component, it contains a tetracarboxylic dianhydride having a fluorene structure and bis(anhydrotrimellitic acid) ester.

[0020] <Diamine> (Specific diamine) The polyimide of the present invention contains a fluorine atom-containing diamine having a CF3-O- structure selected from 2,2'-bis(trifluoromethoxy)benzidine, 3,3'-bis(trifluoromethoxy)benzidine, and 2,3'-bis(trifluoromethoxy)benzidine. Hereinafter, these diamines will be referred to as "specific diamines".

[0021] In certain diamines, the carbon atom of the trifluoromethyl group (-CF3) or the carbon atom of the difluoromethylene group (-CF2-) is bonded to an oxygen atom. Compared to structures where the trifluoromethyl group is bonded to a carbon atom (-C-CF3) or structures where carbon atoms are bonded to both ends of the difluoromethylene group (-C-CF2-C-), these diamines tend to be more biodegradable and have lower environmental persistence. Therefore, polyimides containing certain diamines as the diamine component are more environmentally safe than conventional soluble polyimides containing organofluorine compounds such as fluoroalkyl-substituted benzidines as the diamine component.

[0022] The specific diamine, having a trifluoromethoxy group at the 2nd or 3rd position of the biphenyl, is preferable because, in addition to the decrease in π electron density due to the electron-withdrawing properties of the trifluoromethoxy group, the steric hindrance of the trifluoromethoxy group inhibits π-π stacking between the benzene rings, resulting in a shorter wavelength shift in the absorption edge wavelength, which can reduce the coloration of the polyimide and is expected to improve the solubility of the polyimide. Furthermore, 2,2'-bis(trifluoromethoxy)benzidine is even more preferable because the steric hindrance between the trifluoromethoxy groups at the 2nd and 2' positions of the biphenyl causes the bond between the two benzene rings of the biphenyl to twist, reducing the planarity of the π-conjugation, which can also reduce the coloration of the polyimide and is expected to improve the solubility of the polyimide. Moreover, the specific diamine is preferable from the viewpoint of diamine reactivity because it does not have a fluorine atom directly bonded to the aromatic ring to which the amino group is attached.

[0023] The amount of specific diamine relative to the total amount of diamine components is preferably 10 mol% or more, more preferably 30 mol% or more, even more preferably 50 mol% or more, and may be 60 mol% or more, 70 mol% or more, 80 mol% or more, or 90 mol% or more, or even 100 mol%. In particular, it is preferable that the amount of trifluoromethoxy group-containing diamine be within this range, and especially preferable that the amount of trifluoromethoxy-substituted benzidine be within this range. The higher the ratio of specific diamine, the more the discoloration is suppressed, and the mechanical strength of the film, such as pencil hardness, elastic modulus, breaking strength, and elongation at break, may improve.

[0024] (Diamines other than specified diamines) Polyimides may contain diamines other than specified diamines as diamine components. From the viewpoint of environmental safety of polyimides, those that do not contain -C-CF3 and -C-CF2-C- are preferred, and those that do not contain fluorine atoms are particularly preferred.

[0025] Examples of diamines that do not contain a fluorine atom include 2,2'-dimethylbenzidine, p-phenylenediamine, m-phenylenediamine, o-phenylenediamine, 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl sulfide, 3,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 9,9-bis(4-aminophenyl)fluorene, 9,9-bis[4-(4-aminophenoxy)phenyl]fluorene, 9,9-bis(4-amino-3-methylphenyl)fluorene, 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, 1,1-di(3-aminophenyl)-1-phenylethane, 1,1-di(4-aminophenyl)-1-phenylethane, 1-(3-aminophenyl)-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, 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-aminophenoxy)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, 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-dimethyl [Benzyl]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]diphenylsulfone, 4,4'-bis[4-(4-aminophenoxy)phenoxy]diphenyl Lusulfone, 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'-spirobindan, 6,6'-bis(4-aminophenoxy)-3,3,3',3'-tetramethyl-1,1'-spirobindan, 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-aminomethoxy)ethyl ether, bis[2-(2-aminoethoxy)ethyl] ether, bis[2-(3-aminoprothoxy)ethyl] ether, 1,2-bis(aminomethoxy)ethane, 1,2-bis(2-aminoethoxy)ethane, 1,2-bis[2-(aminomethoxy)ethoxy]ethane, 1,2-bis[2-(2-aminoethoxy)ethoxy]ethane, ethylene glycol bis(3-aminopropyl) 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-diaminocyclohexa Examples include trans-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, isophoronediamine, 2,6-bis(aminomethyl)bicyclo[2.2.1]heptane, 2,5-bis(aminomethyl)bicyclo[2.2.1]heptane, etc.

[0026] In addition to specific diamines, using diaminodiphenylsulfone as the diamine may improve the solubility and transparency of the polyimide resin in the solvent. Among diaminodiphenylsulfones, 3,3'-diaminodiphenylsulfone (3,3'-DDS) and 4,4'-diaminodiphenylsulfone (4,4'-DDS) are preferred, and these may be used in combination.

[0027] When diaminodiphenylsulfone is used in addition to specific diamines, the amount of diaminodiphenylsulfone relative to the total amount of diamine components may be 1 to 40 mol%, 3 to 30 mol%, or 5 to 25 mol%.

[0028] In addition to specific diamines, using diamines having a fluorene structure as the diamine may improve the solubility in solvents, transparency, and mechanical strength of the polyimide resin. Preferred fluorene-containing diamines include 9,9-bis(4-aminophenyl)fluorene, 9,9-bis[4-(4-aminophenoxy)phenyl]fluorene, and 9,9-bis(4-amino-3-methylphenyl)fluorene, and these may be used in combination.

[0029] When using a diamine having a fluorene structure in addition to a specific diamine, the amount of the diamine having a fluorene structure relative to the total amount of the diamine component may be 1 to 80 mol%, 3 to 60 mol%, or 5 to 30 mol%.

[0030] In addition to specific diamines, using alicyclic diamines as diamines can sometimes improve the transparency of polyimides. Among alicyclic diamines, isophorone diamine and 1,4-diaminocyclohexane are preferred, and these may be used in combination.

[0031] When using alicyclic diamines in addition to specific diamines, the amount of alicyclic diamine relative to the total amount of diamine components may be 1-70 mol%, 3-50 mol%, 5-40 mol%, 10-30 mol%, or 12-25 mol%.

[0032] The total amount of specific diamines, diaminodiphenylsulfone, diamines having a fluorene structure, and alicyclic diamines relative to the total amount of diamine components in polyimide is preferably 70 mol% or more, more preferably 80 mol% or more, even more preferably 90 mol% or more, and may also be 95 mol% or more or 99 mol% or more, or even 100 mol%.

[0033] Polyimides may contain fluorine-containing diamines other than specified diamines as their diamine component. However, from the viewpoint of environmental safety of polyimides, the amount of fluorine-containing diamines other than specified diamines relative to the total amount of diamine components in polyimides is preferably 30 mol% or less, more preferably 20 mol% or less, even more preferably 10 mol% or less, and may be 5 mol% or less, 1 mol% or less, or 0.5 mol% or less. Polyimides may also not contain fluorine-containing diamines other than specified diamines as their diamine component.

[0034] Among fluorine atom-containing diamines, those having a structure in which a trifluoromethyl group is bonded to a carbon atom (-C-CF3) and / or a structure in which carbon atoms are bonded to both ends of a difluoromethylene group (-C-CF2-C-) have low degradability and raise concerns about environmental safety. From the viewpoint of improving the transparency and solubility of polyimides, general soluble polyimides contain diamines as diamine components that have a structure in which CF3- or -C(CF3)2- is directly bonded to the carbon atom of the aromatic ring (for example, trifluoromethoxy-substituted benzidines such as 2,2'-bis(trifluoromethyl)benzidine, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane). However, from the viewpoint of the environmental safety of polyimides, it is preferable that they substantially do not contain these diamines. The amount of diamine in which CF3- or -C(CF3)2- is directly bonded to the carbon atom of the aromatic ring, relative to the total amount of diamine components in the polyimide, is preferably less than 0.5 mol%, and may be 0.3 mol% or less, 0.1 mol% or less, or 0.05 mol% or less, or even 0.

[0035] <Tetracarboxylic acid dianhydride> The polyimide of the present invention contains a tetracarboxylic dianhydride having a fluorene structure and a bis(trimellitic anhydride) ester as acid dianhydride components.

[0036] Examples of tetracarboxylic dianhydrides having a fluorene structure include 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride (BPAF), 9,9-bis[4-(3,4-dicarboxyphenoxy)phenyl]fluorene dianhydride (BPF-PA), N,N'-(9H-fluorene-9-ylidenedi-4,1-phenylene)bis[1,3-dihydro-1,3-dioxo-5-isobenzofrancarboxamide] (FDA-ATA), 5,5'-(9H-fluorene-9-ylidenebis(2-methyl-4,1-phenylene)bis[1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxylate] (TBIS.MPN), and 5,5'-spiro[9H- Examples include fluorene-9,9'-[9H]xanthene]-3',6'-diirbis(1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxylate (TBIS.RXN), spiro[fluorene-9,9'xanthene]-2',3',6',7'-tetracarboxylic dianhydride (SFDA), etc. From the viewpoint of polyimide solubility, BPAF, BPF-PA, or TBIS.MPN are preferred, with BPAF or TBIS.MPN being particularly preferred among these, and BPAF being even more preferred. Although TBIS.RXN and SFDA contain xanthene and fluorene structures, they are classified as acidic dianhydrides having a fluorene structure.

[0037] Bis(trimellitic anhydride) esters are represented by the following general formula (1).

[0038] [ka]

[0039] In general formula (1), X is any divalent organic group, with carboxyl groups bonded to the carbon atoms of X at both ends. The carbon atoms bonded to the carboxyl groups may form a ring structure. Specific examples of divalent organic groups X are listed below (A) to (K).

[0040] [ka]

[0041] R in equation (A) 1 m is an alkyl group having 1 to 20 carbon atoms or a fluorine atom, and m is an integer from 0 to 4. The group represented by formula (A) is a hydroquinone which may have substituents on the benzene ring, with two hydroxyl groups removed. Examples of hydroquinone derivatives having substituents on the benzene ring include tert-butylhydroquinone, 2,5-di-tert-butylhydroquinone, and 2,5-di-tert-amylhydroquinone.

[0042] R in equation (B) 2 n is an alkyl group having 1 to 20 carbon atoms or a fluorine atom, and n is an integer from 0 to 4. The group represented by formula (B) is a biphenol which may have substituents on the benzene ring, with two hydroxyl groups removed. Examples of biphenol derivatives having substituents on the benzene ring include 2,2'-dimethylbiphenyl-4,4'-diol, 3,3'-dimethylbiphenyl-4,4'-diol, 3,3',5,5'-tetramethylbiphenyl-4,4'-diol, and 2,2',3,3',5,5'-hexamethylbiphenyl-4,4'-diol.

[0043] The group represented by formula (C) is the group obtained by removing two hydroxyl groups from 4,4'-isopropylidenediphenol (bisphenol A). The group represented by formula (D) is the group obtained by removing two hydroxyl groups from resorcinol.

[0044] In formula (E), p is an integer between 1 and 10. The group represented by formula (E) is a straight-chain diol with 1 to 10 carbon atoms from which two hydroxyl groups have been removed. Examples of straight-chain diols with 1 to 10 carbon atoms include ethylene glycol and 1,4-butanediol.

[0045] The group represented by formula (F) is the group obtained by removing two hydroxyl groups from 1,4-cyclohexanedimethanol.

[0046] R in equation (G)3 X is a hydrogen atom, a fluorine atom, and an alkyl group having 1 to 20 carbon atoms, and q is an integer from 0 to 4. The group represented by formula (G) is a group obtained by removing two hydroxyl groups from bisphenol fluorene, which may have substituents on a benzene ring having phenolic hydroxyl groups. Examples of bisphenol fluorene derivatives having substituents on a benzene ring having phenolic hydroxyl groups include biscresol fluorene. When X has the structure of formula (G), it falls under both acid dianhydrides having a fluorene structure and bis(trimellitic anhydride) esters, but for the classification of specific acid dianhydrides, it is classified as a bis(trimellitic anhydride) ester. Furthermore, a compound in formula (1) where X has the structure of formula (J) falls under any of acid dianhydrides having a fluorene structure, acid dianhydrides having a xanthene structure, and bis(trimellitic anhydride) esters, but for the classification of specific acid dianhydrides, it is classified as a bis(trimellitic anhydride) ester.

[0047] The bis(trimellitic anhydride) ester is preferably an aromatic ester. Of the above (A) to (K), (A), (B), (C), (D), (G), (H), and (I) are preferred as X. Among these, (A) to (D) are preferred, and the group having a biphenyl skeleton of (B) is particularly preferred. When X is a group represented by general formula (B), from the viewpoint of the solubility of the polyimide resin, X is preferably biphenylene or 2,2',3,3',5,5'-hexamethylbiphenyl-4,4'-diyl represented by the following formula (B1).

[0048] [ka]

[0049] The dianhydride in general formula (1) where X is biphenylene is bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylic acid)-biphenyl-4,4'diyl (BP-TME). The dianhydride in general formula (1) where X is 3,3'-dimethylbiphenylene is 5,5'-(3,3'-dimethyl[1,1'-biphenyl]-4,4'-diyl)bis(1,3-dihydro-1,3-dioxo-5-isobenzofuran carboxylate) (OCBP-TME). The dianhydride in general formula (1) where X is the group represented by formula (B1) is bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylic acid)-2,2',3,3',5,5'-hexamethylbiphenyl-4,4'diyl (TAHMBP), represented by the following formula (3).

[0050] [ka]

[0051] Preferred bis(trimellitic anhydride) esters in which X in general formula (1) is a structure other than that of formula (B) include p-phenylenebis(trimellitic monoester anhydride) (TMHQ), tert-butylhydroquinonebis(trimellitate anhydride) (TA.BHQ), and trimethylhydroquinonebis(trimellitate anhydride) (TA.TMHQ).

[0052] From the viewpoint of the mechanical properties of the resulting polyimide, it is preferable that the bis(trimellitic anhydride) ester is one or more selected from the group consisting of BP-TME, OCBP-TME, TAHMBP, TMHQ, TA.BHQ, and TA.TMHQ.

[0053] From the viewpoint of polyimide solubility, TMHQ, TAHMBP, and OCBP-TME are particularly preferred as bis(trimellitic anhydride) esters.

[0054] By including bis(trimellitic anhydride) ester in addition to tetracarboxylic dianhydrides having a fluorene structure as an acidic dianhydride component, the solubility of the polyimide in solvents tends to improve, as does its mechanical properties.

[0055] The amount of bis(trimellitic anhydride) ester relative to the total amount of acidic dianhydride components may be 1 mol% or more, 3 mol% or more, 5 mol% or more, 10 mol% or more, 12 mol% or more, or 15 mol% or more. The higher the amount of bis(trimellitic anhydride) ester, the more the solubility in the solvent and mechanical properties tend to improve. On the other hand, if the amount of bis(trimellitic anhydride) ester is too high, the solubility in organic solvents may decrease. From these viewpoints, the amount of bis(trimellitic anhydride) ester relative to the total amount of acidic dianhydride components is preferably 80 mol% or less, more preferably 60 mol% or less, even more preferably 50 mol% or less, and may also be 40 mol% or less, 30 mol% or less, or 20 mol% or less.

[0056] Polyimides containing the aforementioned specific diamine as the diamine component, and containing tetracarboxylic dianhydride having a fluorene structure and bis(trimellitic anhydride) ester as the acid dianhydride component, tend to exhibit solubility in organic solvents, as well as high transparency and mechanical strength.

[0057] From the viewpoint of making the polyimide soluble in organic solvents, the total amount of tetracarboxylic dianhydride having a fluorene structure and bis(trimellitic anhydride) ester relative to the total amount of acid dianhydride components is preferably 15 mol% or more, more preferably 20 mol% or more, even more preferably 25 mol% or more, and may be 30 mol% or more, 35 mol% or more, 40 mol% or more, 45 mol% or more, or 50 mol% or more. The total amount of tetracarboxylic dianhydride having a fluorene structure and bis(trimellitic anhydride) ester relative to the total amount of acid dianhydride components may be 100 mol%, and may be 95 mol% or less, 90 mol% or less, 85 mol% or less, 80 mol% or less, 75 mol% or less, or 70 mol% or less.

[0058] (Dianhydrides other than tetracarboxylic acid dianhydrides and bis(trimellitic anhydride) esters that have a fluorene structure) Polyimides may contain acid dianhydrides other than tetracarboxylic dianhydrides having a fluorene structure and bis(trimellitic anhydride) esters as acid dianhydride components. Examples of such acid dianhydrides include acid dianhydrides having ether bonds, alicyclic tetracarboxylic dianhydrides, and aromatic tetracarboxylic dianhydrides. From the viewpoint of environmental safety of polyimides, those that do not contain -C-CF3 and -C-CF2-C- are preferred, and those that do not contain fluorine atoms are particularly preferred.

[0059] Examples of dianhydrides containing an ether linkage include those in which two phthalic anhydrides are linked via an ether linkage (-O-) or a functional group containing an ether linkage. Examples of dianhydrides in which two phthalic anhydrides are linked via an ether linkage include 3,4'-oxydiphthalic anhydride (a-ODPA) and 4,4'-oxydiphthalic anhydride (s-ODPA).

[0060] Examples of functional groups containing ether bonds include bisphenol derivative structures. Examples of acid dianhydrides in which two phthalic anhydrides are linked via a bisphenol derivative structure include compounds represented by the following general formula (5).

[0061] [ka]

[0062] In general formula (5), A is any divalent organic group, and p is 1 or 2. 1a , R 1b , R 2a and R 2b Each of the substituents is independently an arbitrary substituent, m1 and m2 are independently integers between 0 and 3, and n1 and n2 are independently integers between 0 and 4.

[0063] Examples of the divalent organic group A include the following (a), (b), and (c). R in (a) 3a and R 3b are each independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, or a phenyl group. R in (b) 4 is an alkyl group having 1 to 10 carbon atoms, and k is an integer of 0 to 10. When k is 2 or more, the plurality of R 4 may be the same or different.

[0064]

Chemical formula

[0065] Examples of the substituents R 1a and R 1b and the substituents R 2a and R 2b include an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, a phenyl group, and a halogen.

[0066] From the viewpoint of the solubility of the polyimide resin, the acid dianhydride having an ether bond is preferably represented by the general formula (1), and among them, 4,4'-(4,4'-isopropylidenediphenoxy) diphthalic anhydride (BPADA) is particularly preferred.

[0067] Alicyclic tetracarboxylic dianhydrides only need to have at least one alicyclic structure, and may have both an alicyclic and an aromatic ring in one molecule. The alicyclic may be polycyclic and may have a spiro structure. Examples of alicyclic tetracarboxylic dianhydrides include 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, 1,3-dimethylcyclobutane-1,2,3,4-tetracarboxylic dianhydride, 1,2,3,4-tetramethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, and 1,1'-bicyclohexane-3,3',4,4'tetracarboxylic acid-3,4:3', 4'-Dianhydride, norbornane-2-spiro-α-cyclopentanone-α'-spiro-2”-norbornane-5,5”,6,6”-tetracarboxylic dianhydride, 2,2'-binorbornane-5,5',6,6'tetracarboxylic dianhydride, 3-(carboxymethyl)-1,2,4-cyclopentanetricarboxylic acid-1,4:2,3-dianhydride, bicyclo[2.2.2]octa-7-en-2,3,5,6-tetracarboxylic dianhydride, 4-(2,5-dioxotetrahydrofuran-3-yl) -1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic acid anhydride, cyclohexane-1,4-diylbis(methylene)bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylate), 5-(2,5-dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic acid anhydride, 5,5'-[cyclohexylidenebis(4,1-phenyleneoxy)]bis-1,3-isobenzofrandione, 5-isobenzofurancarboxylic acid,1, 3-Dihydro-1,3-Dioxo-,5,5'-[1,4-Cyclohexanediylbis(methylene)] ester, Bicyclo[2.2.1]heptane-2,3,5,6-tetracarboxylic dianhydride, Bicyclo[2.2.2]octane-2,3,5,6-tetracarboxylic dianhydride, 3,5,6-Tricarboxynorbornane-2-acetic acid 2,3:5,6-dianhydride, Decahydro-1,4,5,8-Dimethanonaphthalene-2,3,6,7-tetracarboxylic dianhydride, Tricyclo[6.4.0.Examples include 0(2,7) dodecane-1,8:2,7-tetracarboxylic dianhydride, octahydro-1H,3H,8H,10H-biphenyleno[4a,4b-c:8a,8b-c']difuran-1,3,8,10-tetraone, ethylene glycol bis(hydrogenated trimellitic anhydride) ester, decahydro[2]benzopyrano[6,5,4,-def][2]benzopyran-1,3,6,8-tetraone, etc. The inclusion of alicyclic tetracarboxylic dianhydrides tends to improve the solubility and mechanical strength of polyimides in solvents.

[0068] Among alicyclic tetracarboxylic dianhydrides, 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA), 1,2,3,4-cyclopentanetetracarboxylic dianhydride (CPDA), 1,2,4,5-cyclohexanetetracarboxylic dianhydride (H-PMDA), 4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic anhydride (TDA-100), bicyclo[2.2.2]octa-7-ene-2,3,5,6-tetracarboxylic dianhydride (BEDA), bicyclo[2.2.2]octane-2,3,5,6-tetracarboxylic dianhydride (BODA), and 1,1'-bicyclohexane-3,3',4,4'tetracarboxylic dianhydride-3,4:3',4'-dianhydride (H-BPDA) are preferred from the viewpoint of reactivity, transparency of polyimide, and mechanical strength. In particular, from the viewpoint of reactivity and mechanical strength, tetracarboxylic anhydrides in which two acid anhydride groups are bonded to one alicyclic ring are preferred, and CBDA is especially preferred.

[0069] Aromatic tetracarboxylic dianhydrides include pyromellitic dianhydride (PMDA), 1,2,3,4-benzenetetracarboxylic dianhydride (MPDA), 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 2,2',3,3'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA), 2,3,3',4'-biphenyltetracarboxylic dianhydride (a-BPDA), and 2,2',3,3',-biphenyltetracarboxylic dianhydride (i- Examples include BPDA, 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride (DSDA), 5,5'-dimethylmethylenebis(phthalic anhydride), 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, terphenyltetracarboxylic dianhydride, 1,4-bis(3,4-dicarboxyphenoxy)benzene dianhydride, and bis(3,4-dicarboxyphenyl)sulfone dianhydride. Among these aromatic tetracarboxylic dianhydrides, a-BPDA, s-BPDA, i-BPDA, PMDA, and MPDA are preferred from the viewpoint of solubility in solvents and improvement of mechanical strength.

[0070] In addition to tetracarboxylic dianhydrides having a fluorene structure and bis(trimellitic anhydride) esters, when using acid dianhydrides having ether bonds, alicyclic tetracarboxylic dianhydrides, or aromatic tetracarboxylic dianhydrides other than tetracarboxylic dianhydrides having a fluorene structure and bis(trimellitic anhydride) esters, the total amount of acid dianhydrides having ether bonds, alicyclic tetracarboxylic dianhydrides, or aromatic tetracarboxylic dianhydrides relative to the total amount of acid dianhydrides may be 1 mol% or more, 3 mol% or more, 5 mol% or more, 10 mol% or more, 12 mol% or more, or 15 mol% or more. From the viewpoint of ensuring the solubility of polyimide in organic solvents, the total amount of acid dianhydrides having ether bonds, alicyclic tetracarboxylic dianhydrides, or aromatic tetracarboxylic dianhydrides is preferably 80 mol% or less, more preferably 60 mol% or less, even more preferably 50 mol% or less, and may be 40 mol% or less, 30 mol% or less, or 20 mol% or less.

[0071] Polyimide may contain linear aliphatic tetracarboxylic dianhydrides as acid dianhydride components, such as ethylenetetracarboxylic dianhydride, 1,2,3,4-butanetetracarboxylic dianhydride, and meso-butane-1,2,3,4-tetracarboxylic dianhydride.

[0072] The amount of fluorine-containing dianhydride relative to the total amount of dianhydride components in the polyimide is preferably 30 mol% or less, more preferably 20 mol% or less, even more preferably 10 mol% or less, and may also be 5 mol% or less, 1 mol% or less, or 0.5 mol% or less. The polyimide may also not contain fluorine-containing dianhydride as its dianhydride component.

[0073] Among fluorine-containing acid dianhydrides, those having a structure in which a trifluoromethyl group is bonded to a carbon atom (-C-CF3) and / or a structure in which carbon atoms are bonded to both ends of a difluoromethylene group (-C-CF2-C-) have low degradability and raise concerns about environmental safety. In particular, acid dianhydrides having a structure in which CF3- or -C(CF3)2- is directly bonded to a carbon atom of an aromatic ring (e.g., 4,4'-(hexafluoroisopropylidene)diphthalic anhydride, 9,9-bis(trifluoromethyl)xanthenetetracarboxylic dianhydride, 9-trifluoromethylxanthenetetracarboxylic dianhydride) have low environmental degradability, so from the viewpoint of the environmental safety of polyimides, it is preferable that they substantially do not contain these acid dianhydrides. The amount of acid dianhydride in which CF3- or -C(CF3)2- is directly bonded to the carbon atom of the aromatic ring, relative to the total amount of acid dianhydride components of the polyimide, is preferably less than 0.5 mol%, and may be 0.3 mol% or less, 0.1 mol% or less, or 0.05 mol% or less, or even 0.

[0074] <Content of specific fluorine structures in polyimides> As described above, polyimides containing a specific diamine as the diamine component and a tetracarboxylic dianhydride having a fluorene structure and bis(trimellitic anhydride) ester as the acid dianhydride component exhibit solubility in organic solvents without substantially containing structures such as -C-CF3 and -C-CF2-C-.

[0075] To reduce the environmental persistence of fluorine-containing compounds, it is preferable that polyimides use small amounts of diamine components having a specific fluorine structure and acid dianhydride components having a specific fluorine structure. A specific fluorine structure is defined as a structure obtained by excluding those containing only the components of structural formula (i) below from those having a trifluoromethyl group (CF3-), and a structure obtained by excluding those containing only the components of structural formula (ii) below from those having a difluoromethylene group (-CF2-). CF3-X (i) X-CF2-X' (ii)

[0076] In formulas (i) and (ii), X is -OR or -NRR', and in formula (II), X' is one of -H, -CH3, aromatic, -C(O)-, -OR'', -SR'', and NR''R'''. R, R', R'', and R'''' are each independently one of -H, -CH3, -CH2-, aromatic, or -C(O)-.

[0077] From the viewpoint of improving environmental degradability, the amount of fluorine atoms contained in the specific fluorine structure per 1 kg of polyimide is preferably less than 500 mg, more preferably less than 300 mg, even more preferably less than 100 mg, and particularly preferably less than 50 mg.

[0078] <Preparation of polyimides> The reaction of an acidic dianhydride with a diamine yields polyamic acid as a polyimide precursor, and the dehydration and cyclization (imidization) of the polyamic acid yields polyimide. As described above, by adjusting the monomer composition constituting the polyimide, i.e., the type and ratio of acidic dianhydride and diamine, polyimides with solubility in organic solvents and transparency can be obtained.

[0079] The method for preparing polyamic acid is not particularly limited, and any known method can be applied. For example, a polyamic acid solution can be obtained by dissolving an acidic dianhydride and a diamine in approximately equimolar amounts (molar ratio of 90:100 to 110:100) in an organic solvent and stirring. The concentration of the polyamic acid solution is usually 5 to 35% by weight, preferably 10 to 30% by weight. When the concentration is within this range, the polyamic acid obtained by polymerization has an appropriate molecular weight, and the polyamic acid solution has an appropriate viscosity.

[0080] In the polymerization of polyamic acids, it is preferable to add the dianhydride to the diamine to suppress ring-opening of the dianhydride. When adding multiple types of diamines or dianhydrides, they may be added all at once or in multiple steps. The properties of the polyimide can also be controlled by adjusting the order of monomer addition.

[0081] The organic solvent used for polymerization of polyamic acid is not particularly limited, as long as it does not react with diamines and acidic dianhydrides and can dissolve polyamic acid. Examples of organic solvents include urea-based solvents such as methylurea and N,N-dimethylethylurea; sulfoxide or sulfone-based solvents such as dimethyl sulfoxide, diphenyl sulfone, and tetramethylsulfone; amide-based solvents such as N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), N,N'-diethylacetamide, N-methyl-2-pyrrolidone (NMP), γ-butyrolactone, and hexamethylphosphate triamide; alkyl halide-based solvents such as chloroform and methylene chloride; aromatic hydrocarbon-based solvents such as benzene and toluene; and ether-based solvents such as tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, dimethyl ether, diethyl ether, and p-cresol methyl ether. These solvents are usually used individually or in appropriate combinations of two or more as needed. From the viewpoint of polyamic acid solubility and polymerization reactivity, DMAc, DMF, NMP, etc., are preferably used.

[0082] Polyimides can be obtained by the dehydration and cyclization of polyamic acids. One method for preparing polyimides from a polyamic acid solution is to add a dehydrating agent, an imidation catalyst, etc., to the polyamic acid solution and allow imidation to proceed in the solution. The polyamic acid solution may be heated to accelerate the progression of imidation. By mixing the solution containing the polyimide produced by the imidation of polyamic acid with a poor solvent, the polyimide resin precipitates as a solid. By isolating the polyimide resin as a solid, impurities generated during the synthesis of polyamic acid, as well as residual dehydrating agents and imidation catalysts, can be washed and removed with the poor solvent, preventing discoloration and increased yellowness of the polyimide. Furthermore, by isolating the polyimide resin as a solid, solvents suitable for film formation, such as low-boiling point solvents, can be applied when preparing the solution for film production.

[0083] The molecular weight of the polyimide (weight-average molecular weight in terms of polyethylene oxide, measured by gel filtration chromatography (GPC)) is preferably 10,000 to 1,000,000, more preferably 20,000 to 500,000, and even more preferably 40,000 to 300,000. If the molecular weight is too low, the film strength may be insufficient. If the molecular weight is too high, the solubility of the polyimide resin and its compatibility with other resins may be poor.

[0084] Polyimides are preferably soluble in organic solvents. Specifically, polyimides are preferably soluble in dimethylformamide (DMF) at 23°C at a concentration of 1% by weight or more, more preferably at a concentration of 5% by weight or more, and even more preferably at a concentration of 10% by weight or more. In addition to being soluble in amide solvents such as DMF, polyimides are preferably soluble in non-amide solvents. Examples of non-amide solvents include ketone solvents such as acetone and methyl ethyl ketone, alkyl halide solvents such as chloroform and dichloromethane, and ester solvents such as ethyl acetate and γ-butyrolactone. Non-amide solvents have lower boiling points compared to amide solvents, and residual solvents are easily removed during film production; therefore, polyimides soluble in non-amide solvents can be expected to improve film productivity. Polyimides are particularly preferably soluble in methylene chloride.

[0085] From the viewpoint of thermal and photostability of polyimide resins and molded articles such as films, it is preferable that polyimide has low reactivity. The acid value of polyimide is preferably 0.4 mmol / g or less, more preferably 0.3 mmol / g or less, and even more preferably 0.2 mmol / g or less. The acid value of polyimide may also be 0.1 mmol / g or less, 0.05 mmol / g or less, or 0.03 mmol / g or less. From the viewpoint of reducing the acid value, it is preferable that polyimide has a high imidization rate. A low acid value enhances the stability of polyimide.

[0086] [Resin composition] The polyimide of the present invention exhibits solubility in organic solvents by containing a specific diamine as a diamine component and a tetracarboxylic dianhydride having a fluorene structure and a bis(trimellitic anhydride) ester as a tetracarboxylic dianhydride component. Furthermore, the polyimide of the present invention can be made into a resin composition by adding various additives.

[0087] <Preparation of a resin composition containing polyimide> The solvent for a solution containing polyimide is not particularly limited as long as it is soluble in polyimide. Examples of solvents include amide solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone; ether solvents such as tetrahydrofuran and 1,4-dioxane; ketone solvents such as acetone, methyl ethyl ketone, methyl propyl ketone, methyl isopropyl ketone, methyl isobutyl ketone, diethyl ketone, cyclopentanone, cyclohexanone, and methylcyclohexanone; and alkyl halogenated solvents such as chloroform, 1,2-dichloroethane, 1,1,2,2-tetrachloroethane, chlorobenzene, dichlorobenzene, and methylene chloride.

[0088] From the viewpoint of polyimide solubility, amide solvents are preferred. On the other hand, from the viewpoint of solvent removal when producing molded articles such as films, low-boiling non-amide solvents are preferred. Ketone solvents and alkyl halogen solvents are preferred because they have excellent solubility for polyimide and, due to their low boiling point, allow for easy removal of residual solvent during film production.

[0089] The resin composition may contain organic or inorganic low-molecular-weight compounds, high-molecular-weight compounds (e.g., epoxy resins), etc. The resin composition may also contain flame retardants, ultraviolet absorbers, crosslinking agents, dyes, pigments, surfactants, leveling agents, plasticizers, fine particles, sensitizers, etc. The fine particles may include organic fine particles such as polystyrene and polytetrafluoroethylene, and inorganic fine particles such as colloidal silica, carbon, and layered silicates, and may have a porous or hollow structure. The fiber reinforcing material may include carbon fibers, glass fibers, aramid fibers, etc.

[0090] [Molded articles and films] The polyimides and resin compositions containing polyimides described above can be used to form various molded articles. Molding methods include injection molding, transfer molding, press molding, blow molding, inflation molding, calendering, and melt extrusion molding.

[0091] In one embodiment, the molded body is a film. The film may be formed by either a melting method or a solution method, but the solution method is preferred from the viewpoint of producing a film with excellent transparency and uniformity. In the solution method, a film is obtained by coating a solution containing the above-mentioned polyimide onto a support and drying off the solvent.

[0092] As a method for applying the resin solution onto the support, known methods using bar coaters, comma coaters, etc., can be applied. As the support, glass substrates, metal substrates such as SUS, metal drums, metal belts, plastic films, etc., can be used. From the viewpoint of improving productivity, it is preferable to use an endless support such as a metal drum or metal belt, or a long plastic film, as the support and manufacture the film by roll-to-roll. When using a plastic film as the support, a material that does not dissolve in the film-forming doping solvent should be appropriately selected.

[0093] Heating is preferable when drying the solvent. The heating temperature is not particularly limited as long as it can remove the solvent and suppress discoloration of the resulting film, and can be appropriately set between room temperature and approximately 250°C, with 50°C to 220°C being preferred. The heating temperature may be increased in stages. To improve the efficiency of solvent removal, the resin film may be peeled from the support and dried after a certain degree of drying has progressed. Heating may be performed under reduced pressure to promote solvent removal.

[0094] The film may be stretched in one or more directions for purposes such as improving its mechanical strength. When a film is stretched, the polymer chains orient themselves in the direction of stretching, which improves the in-plane strength of the film and tends to suppress the occurrence of cracks and fissures.

[0095] Films used as cover films or substrate materials for foldable displays require high mechanical strength in the direction perpendicular to the bending axis, as they are repeatedly folded along the same point at the same location. Therefore, by arranging the film so that its stretching direction is perpendicular to the bending axis, cracks and breaks are less likely to occur at the folding point even after repeated folding, providing a device with high bending resistance.

[0096] The stretching conditions for the film are not particularly limited. For example, the stretching temperature is approximately ±40°C of the film's glass transition temperature. The stretching temperature for polyimide films may be approximately 120-350°C, 150-300°C, or 180-250°C.

[0097] The stretching ratio is approximately 1-200%, but may also be 5-150%, 10-120%, or 20-100%. The stretching ratio (%) is expressed as 100 × (L1-L0) / L0, where L0 is the length of the film in the stretching direction before stretching (original length), and L1 is the length of the film in the stretching direction after stretching. The larger the stretching ratio, the greater the tensile modulus in the stretching direction tends to be. If the stretching ratio is excessively large, the mechanical strength in the direction perpendicular to the stretching direction tends to decrease, which may reduce the handling properties of the film.

[0098] From the viewpoint of increasing strength in any direction within the plane, the film may be biaxially stretched. Biaxial stretching may be simultaneous biaxial stretching or sequential biaxial stretching. In biaxial stretching, the stretching ratio in one direction and the stretching ratio in the direction perpendicular to it may be the same or different. If there is a difference in the stretching ratio, the mechanical strength tends to be relatively higher in the direction with the larger stretching ratio. When using a biaxially stretched film with anisotropic stretching ratio in a foldable device, it is preferable to position the direction with the larger stretching ratio perpendicular to the folding axis.

[0099] The film thickness is not particularly limited and can be set appropriately depending on the application. For example, the film thickness is 5 to 300 μm. From the viewpoint of achieving both self-supporting properties and flexibility, and a highly transparent film, the film thickness is preferably 20 μm to 200 μm, but may also be 30 μm to 150 μm, 40 μm to 100 μm, or 50 μm to 80 μm. For use as a cover film for displays, the film thickness is preferably 10 μm or more. When stretching the film, it is preferable that the thickness after stretching is within the above range.

[0100] The haze of the film is not particularly limited, but is preferably 10% or less, more preferably 5% or less, even more preferably 4% or less, and may be 3.5% or less, 3% or less, 2% or less, or 1% or less. A lower haze is preferable.

[0101] The total light transmittance of the film is not particularly limited, but is preferably 87% or higher, more preferably 88% or higher, and may be 89% or higher or 90% or higher.

[0102] The yellowness (YI) of the film is not particularly limited, but is preferably 10 or less, more preferably 5.0 or less, and may be 4.0 or less, 3.0 or less, 2.0 or less, 1.5 or less, or 1.0 or less.

[0103] From the viewpoint of strength, the tensile modulus of the film is preferably 3.0 GPa or higher, more preferably 3.5 GPa or higher, and may be 4.0 GPa or higher. The pencil hardness of the film is preferably 4B or higher, more preferably 2B or higher, even more preferably F or higher, and may be H or higher, 2H or higher, or 3H or higher.

[0104] The polyimide-containing film of the present invention is suitable for use as a display material because it has little coloration and high transparency. In particular, films with high mechanical strength can be applied to surface components such as cover windows of displays. Furthermore, because the polyimide substantially does not contain specific fluorine structures, it is highly biodegradable and environmentally safe. For practical use, the film of the present invention may be provided with an antistatic layer, an easy-adhesion layer, a hard coat layer, an anti-reflective layer, etc. on its surface. [Examples]

[0105] The embodiments of the present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the following embodiments.

[0106] [Preparation of polyimide resin] Dimethylformamide (DMF) was placed in a separable flask and stirred under a nitrogen atmosphere. Diamine and tetracarboxylic dianhydride were then added in the ratios (mol%) shown in Tables 1 and 2, and the mixture was stirred under a nitrogen atmosphere for 5 to 48 hours to obtain a polyamic acid solution with a solid content of 18% by weight.

[0107] To 100 g of polyamic acid solution, 5.5 g of pyridine was added as an imidation catalyst and completely dispersed. Then, 8 g of acetic anhydride was added, and the mixture was stirred at 90°C for 3 hours to carry out imidation.

[0108] After cooling the imidized solution to room temperature, 100g of 2-propyl alcohol (hereinafter referred to as IPA) was added at a rate of 2-3 drops / second while stirring to precipitate polyimide. Further 150g of IPA was added, and after stirring for approximately 30 minutes, suction filtration was performed using a Kiriyama funnel. The resulting solid was washed with IPA and then dried in a vacuum oven set to 120°C for 12 hours to obtain polyimide resin.

[0109] [Film fabrication using polyimide film] A polyimide solution with a solid content of 10% by weight was prepared by dissolving the above-mentioned polyimide resin in a solvent. DMF was used as the solvent. Table 1 shows the solubility of the polyimide resin in DMF. The temperature used was 23°C. Solutions that dissolved at a solid content concentration of 5% or higher are marked with ○, while solutions that only dissolved at lower concentrations or were insoluble are marked with ×.

[0110] For polyimides that showed good solubility in DMF, the polyimide solution was applied to an alkali-free glass plate and heated and dried in an air atmosphere at 60°C for 15 minutes, 90°C for 15 minutes, 120°C for 15 minutes, 150°C for 15 minutes, 180°C for 15 minutes, and 200°C for 15 minutes to produce a film with a thickness of approximately 50 μm.

[0111] [Film Evaluation] <Haze and total light transmittance> The film was cut into 3cm squares, and the haze and total light transmittance (TT:%) were measured using a Suga Test Instruments HZ-V3 haze meter in accordance with JIS K7136 and JIS K7361-1.

[0112] <Yellowness> The film was cut into 3cm squares, and the yellowness (YI) was measured according to JIS K7373 using a Suga Test Instruments SC-P spectrophotometer.

[0113] <Tensile modulus> The film was cut into strips 10 mm wide, left to stand at 23°C / 55%RH for one day to adjust humidity, and then the tensile modulus (modulus of elasticity) was measured using Shimadzu Corporation's "AUTOGRAPH AGS-X" under the following conditions. Distance between gripping parts: 100mm Tensile speed: 20.0 mm / min Measurement temperature: 23℃

[0114] [Evaluation Results] The compositions of the polyimides used in the examples and comparative examples, as well as the evaluation results, are shown in Tables 1 and 2.

[0115] In Tables 1 and 2, the composition of the polyimides (amounts of diamine and tetracarboxylic dianhydride) is shown as a molar ratio with the total amount of tetracarboxylic dianhydride set at 100 mole parts, and the compounds are indicated by the following abbreviations. <Diamine> TFMOB: 2,2'-Bis(trifluoromethoxy)benzidine <Acid dianhydride> BPAF: 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride TAHMBP: Bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylic acid)-2,2',3,3',5,5'-hexamethylbiphenyl-4,4'diyl OCBP-TME: 5,5'-(3,3'-dimethyl[1,1'-biphenyl]-4,4'-diyl)bis(1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxylate)

[0116] [Table 1]

[0117] [Table 2]

[0118] The polyimides of Examples 1 and 2, which contained a specific diamine as the diamine component and a tetracarboxylic dianhydride having a fluorene structure and bis(trimellitic anhydride) ester as the tetracarboxylic dianhydride component, were soluble in DMF solvent and allowed for the production of transparent films. On the other hand, Comparative Example 1, which contained a specific diamine and a tetracarboxylic dianhydride having a fluorene structure but did not contain bis(trimellitic anhydride), showed that the polyimide was insoluble in DMF.

[0119] Furthermore, the polyimides of Examples 1 and 2, which contained a specific diamine as the diamine component and a tetracarboxylic dianhydride having a fluorene structure and a bis(trimellitic anhydride) ester as the tetracarboxylic dianhydride component, all exhibited high elastic modulus and excellent optical properties.

[0120] These results indicate that by using a specific diamine that does not contain a specific fluorine structure as the diamine component, and by using a tetracarboxylic dianhydride having a fluorene structure and bis(trimellitic anhydride) ester as the tetracarboxylic dianhydride component, a polyimide with high environmental safety and excellent solubility in organic solvents, transparency, and mechanical properties can be obtained.

Claims

1. A polyimide having a tetracarboxylic dianhydride component and a diamine component, The diamine component is selected from 2,2'-bis(trifluoromethoxy)benzidine, 3,3'-bis(trifluoromethoxy)benzidine, and / or 2,3'-bis(trifluoromethoxy)benzidine. ３ It contains a fluorine atom-containing diamine having an -O- structure, A polyimide comprising a tetracarboxylic dianhydride having a fluorene structure and a bis(trimellitic anhydride) ester as tetracarboxylic dianhydride components.

2. The polyimide according to claim 1, wherein the diamine component is 2,2'-bis(trifluoromethoxy)benzidine.

3. The polyimide according to claim 1, wherein the tetracarboxylic dianhydride having a fluorene structure is 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride.

4. The polyimide according to claim 1, wherein the amount of bis(trimellitic anhydride) ester relative to the total amount of tetracarboxylic dianhydride components is 1 to 80 mol%.

5. The polyimide according to claim 1, wherein the bis(trimellitic anhydride) ester is one or more selected from the group consisting of 5,5'-(3,3'-dimethyl[1,1'-biphenyl]-4,4'-diyl)bis(1,3-dihydro-1,3-dioxo-5-isobenzofuran carboxylate), bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylic acid)-biphenyl-4,4'diyl, bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylic acid)-2,2',3,3',5,5'-hexamethylbiphenyl-4,4'diyl, p-phenylenebis(trimellitic anhydride monoester), tert-butylhydroquinonebis(trimellitate anhydride), and trimethylhydroquinonebis(trimellitate anhydride).

6. CF ３ - or -C (CF ３ ) ２ The amount of diamine having a structure to which a - is directly bonded is less than 0.5 mol%, The total amount of tetracarboxylic dianhydride components is CF at the carbon atoms of the aromatic ring. ３ - or -C (CF ３ ) ２ The polyimide according to claim 1, wherein the amount of tetracarboxylic dianhydride having a structure to which a - is directly bonded is less than 0.5 mol%.

7. The polyimide according to claim 1, which is soluble in dimethylformamide at 23°C.

8. A molded article comprising the polyimide described in any one of claims 1 to 7.

9. A film comprising the polyimide described in any one of claims 1 to 7.

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