Polyimide precursor for display substrates, polyimide film for display substrates, and display substrates.

Abstract

This invention provides a polyimide precursor for display substrates, which has a structural unit represented by the following general formula (1), and includes at least a portion of a group containing an acidic group as the group represented by X1 in the above general formula (1), the group represented by Y1 in the above general formula (1), and a terminal group, wherein the content of the acidic group is 15 × 10⁻³ or more. (In the above general formula (1), X1 is a tetravalent aromatic group or an aliphatic group, Y1 is a divalent aromatic group, and R1 and R2 are independently hydrogen atoms, alkyl groups having 1 to 6 carbon atoms, or alkylsilyl groups having 3 to 9 carbon atoms.)

Description

Technical Field

[0001] This invention relates to a polyimide precursor for a display substrate, a polyimide film for a display substrate obtained using the precursor, and a display substrate. The polyimide precursor for the display substrate has a long charged half-life, and the charge decay rate after 120 seconds obtained by the charged half-life measurement is low, which can help suppress charging and achieve higher adhesion. Prior Technology

[0002] Due to its excellent heat resistance, solvent resistance (chemical resistance), mechanical properties, and electrical properties, polyimide is widely used in flexible wiring boards, TAB (Tape Automated Bonding) tapes, and other electrical / electronic applications. For example, polyimides obtained from aromatic tetracarboxylic dianhydrides and aromatic diamines are suitable, especially those obtained from 3,3',4,4'-biphenyltetracarboxylic dianhydrides and p-phenylenediamine.

[0003] Furthermore, in the field of display devices, research is underway to use polyimide as a substitute for glass substrates. By replacing the display substrate used in various display devices with a plastic substrate containing polyimide, a lightweight and highly flexible display that can be bent or rolled can be provided.

[0004] For example, as a polyimide precursor suitable for use in display substrates, Patent Document 1 proposes a method for using a polyimide precursor containing a specific unit structure. [Previous Technical Documents] [Patent Literature]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2012-41531 Summary of the Invention

[0006] [The problem the invention aims to solve]

[0007] When polyimide films are used in display substrates, they are typically used with an inorganic barrier layer such as SiO₂ formed on their surface to ensure sufficient gas barrier properties. However, when polyimide films are used in display substrates, charge accumulates at the interface between the polyimide film and the inorganic barrier layer, causing charging. This charging results in a small current flowing through switching elements, which can lead to image retention on the display. [Technical means to solve the problem]

[0008] The inventors conducted intensive research on this matter and discovered that by including acidic groups in the polyimide film at a specified ratio, the charged half-life can be extended and the charge decay rate after 120 seconds obtained by the charged half-life measurement can be reduced. This promotes the elimination of charge accumulation at the interface between the polyimide film and the inorganic barrier layer, thereby helping to suppress charging and thus completing the present invention. Furthermore, the inventors conducted intensive research and discovered that by adopting the above-described configuration, a higher degree of contact can be achieved.

[0009] That is, the present invention provides the following [1] to [8]. [1] A polyimide precursor for a display substrate, having a structural unit represented by the following general formula (1), and comprising at least a portion of a group containing an acidic group as the group represented by X1 in the above general formula (1), a group represented by Y1 in the above general formula (1), and a terminal group. The content of the above-mentioned acidic groups is 15×10⁻³ or higher. [Chemistry 1] (In the above general formula (1), X1 is a tetravalent aromatic group or an aliphatic group, Y1 is a divalent aromatic group, and R1 and R2 are hydrogen atoms, alkyl groups with 1 to 6 carbon atoms, or alkyl-silyl groups with 3 to 9 carbon atoms.)

[0010] [2] The polyimide precursor for display substrates as described in [1], wherein the acidic group is selected from at least one of a carboxyl group and a sulfonic acid group.

[0011] [3] The polyimide precursor for display substrates as described in [2], wherein the carboxyl group is derived from 3,5-diaminobenzoic acid or 5,5'-methylenebis(2-aminobenzoic acid). [、] The base of at least one of the compounds selected from benzohexacarboxylic acid, benzohexacarboxylic anhydride, and trimellitic anhydride.

[0012] [4] The polyimide precursor for display substrates as described in [3], wherein the carboxyl group is derived from at least one compound selected from 3,5-diaminobenzoic acid, hexacarboxylic acid and hexacarboxylic anhydride, and trimellitic anhydride.

[0013] [5] The polyimide precursor for display substrates described in any of [2] to [4], wherein the sulfonic acid group is derived from at least one compound selected from 1,4-phenylenediamine-2-sulfonic acid, 1,3-phenylenediamine-4-sulfonic acid, 3,5-diamino-2,4,6-trimethylbenzenesulfonic acid, and 4,4'-diaminostilbene-2,2'-disulfonic acid.

[0014] [6] The polyimide precursor for display substrates as described in [5], wherein the sulfonic acid group is derived from the group of at least one compound selected from 1,4-phenylenediamine-2-sulfonic acid and 1,3-phenylenediamine-4-sulfonic acid.

[0015] [7] A polyimide film for a display substrate, which is obtained by using a polyimide precursor for a display substrate as described in any one of [1] to [6].

[0016] [8] A display substrate having a polyimide film for a display substrate as described in [7]. [Effects of the Invention]

[0017] According to the present invention, a polyimide precursor for display substrates is provided, which has a long charged half-life and a low charge decay rate after 120 seconds as obtained by charge half-life measurement, which can help suppress charging and achieve higher adhesion. Implementation

[0018] Polyimide precursors for display substrates The polyimide precursor for display substrates of the present invention is a polyimide precursor used to form a polyimide film for display substrates, and is a polyimide precursor having structural units represented by the following general formula (1). The polyimide precursor for display substrates comprises at least a portion of a group containing an acidic group as the group represented by X1 in the above general formula (1), a group represented by Y1 in the above general formula (1), and a terminal group. The content of the above-mentioned acidic groups is 15×10⁻³ or higher. [Chemistry 2] (In the above general formula (1), X1 is a tetravalent aromatic group or an aliphatic group, Y1 is a divalent aromatic group, and R1 and R2 are independently hydrogen atoms, alkyl groups with 1 to 6 carbon atoms, or alkyl-silyl groups with 3 to 9 carbon atoms.)

[0019] In the above general formula (1), X1 is a residue obtained by removing 4 COOH groups from a tetracarboxylic acid (i.e., a residue obtained by removing 2 carboxylic anhydride groups (CO)2O) from a tetracarboxylic dianhydride), and Y1 is a residue obtained by removing 2 NH2 groups from a diamine. R1 and R2 are preferably hydrogen atoms, alkyl or silyl groups having 3 to 9 carbon atoms, and more preferably hydrogen atoms.

[0020] As the structural unit represented by the above general formula (1), examples can be given of those obtained by reacting the tetracarboxylic acid component with the diamine component to form an amide bond (-CONH-).

[0021] Examples of tetracarboxylic acid components include aromatic tetracarboxylic dianhydrides and aliphatic tetracarboxylic dianhydrides.

[0022] Specific examples of aromatic tetracarboxylic dianhydrides include: 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA), pyromellitic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, 4,4'-oxophthalic dianhydride, diphenyl tan-3,4,3',4'-tetracarboxylic dianhydride, bis(3,4-dicarboxyphenyl)sulfide dianhydride, 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride (also known as: 4,4'-(hexafluoroisopropylidene)diphthalic anhydride), 2,3,3',4'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, 2 2-Bis(3,4-dicarboxyphenyl)propane dianhydride, p-phenylbis(trimethoxymethyl phthalate monoester anhydride), p-biphenylbis(trimethoxymethyl phthalate monoester anhydride), meta-triphenyl-3,4,3',4'-tetracarboxylic acid dianhydride, p-triphenyl-3,4,3',4'-tetracarboxylic acid dianhydride, 1,3-bis(3,4-dicarboxyphenoxy)phenyl dianhydride, 1,4-bis(3,4-dicarboxyphenoxy)phenyl dianhydride, 1,4-bis(3,4-dicarboxyphenoxy)biphenyl dianhydride, 2,2-bis[(3,4-dicarboxyphenoxy)phenyl]propane dianhydride, 2,3,6,7-naphthalenetetracarboxylic acid dianhydride, 1,4,5,8-naphthalenetetracarboxylic acid dianhydride, 4,4'-(2,2-hexafluoroisopropylidene)diphthalic acid dianhydride, etc. These can be used individually or in combination of two or more.

[0023] Alicyclic tetracarboxylic dianhydrides can be suitably used as aliphatic tetracarboxylic dianhydrides. Specific examples of alicyclic tetracarboxylic dianhydrides include: (1S,2R,4S,5R)-cyclohexanetetracarboxylic dianhydride, cis,cis,cis-1,2,4,5-cyclohexanetetracarboxylic dianhydride, (1S,2S,4R,5R)-cyclohexanetetracarboxylic dianhydride, (1R,2S,4S,5R)-cyclohexanetetracarboxylic dianhydride, bicyclo[2.2.2]octane-2,3,5,6-tetracarboxylic dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, 4-(2,5-dioxotetrahydrofuran- 3-yl)-tetrahydronaphthalene-1,2-dicarboxylic anhydride, tetrahydrofuran-2,3,4,5-tetracarboxylic anhydride, bicyclo-3,3',4,4'-tetracarboxylic anhydride, 1,2,3,4-cyclopentanetetracarboxylic anhydride, 1,2,3,4-cyclobutanetetracarboxylic anhydride (hereinafter, sometimes referred to as "CBDA"), 1,3-dimethyl-1,2,3,4-cyclobutanetetracarboxylic anhydride, 1,4-dimethyl-1,2,3,4-cyclobutanetetracarboxylic anhydride, 1,2,3,4-cyclohexanetetracarboxylic anhydride, pentacyclic [8.2.1.1] [4,7.0 2,9.0 3,8]Tetradecane-5,6,11,12-tetracarboxylic dianhydride, 5-(2,5-dioxytetrahydrofuranyl)-3-methyl-3-cyclohexene-1,2-dicarboxylic dianhydride, cyclohexene-1-ene-2,3,5,6-tetracarboxylic dianhydride, bicyclo[2.2.1]heptane-2,3,5,6-tetracarboxylic dianhydride, etc. These can be used alone or in mixtures of two or more.

[0024] Regarding the tetracarboxylic acid compound as a tetracarboxylic acid component, it is preferred to be an acid dianhydride selected from 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA), pyromellitic dianhydride (PMDA), 4,4'-oxophthalic dianhydride (ODPA), 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA), 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride (6FDA), and 3,3',4,4'-diphenyltetracarboxylic dianhydride (DSDA), and more preferably 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA).

[0025] Examples of diamine compounds that are diamine components include: 4,4'-diaminodiphenyl ether, 2,2'-dimethylbenzidine, 4,4'-diaminodiphenylmethane, 4,4'-diamino-1,2-diphenylethane, p-phenylenediamine (PPD), m-phenylenediamine, 2,4-diaminotoluene, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, m-phenylenediamine, p-phenylenediamine, 2,2 -Aromatic diamines containing aromatic groups, such as bis[4-(4-aminophenoxy)phenyl]propane, 4,4'-methylenebis(2,6-dimethylphenylamine), α,α'-bis(4-aminophenyl)-1,4-diisopropylbenzene, 2,2'-dimethyl-4,4'-aminobiphenyl, 3,3'-dimethyl-4,4'-aminobiphenyl, and 2,2'-epenylethyldiphenylamine; 1,4-diaminocyclohexane, 1,4-diamino-2-methylcyclohexane, and 1,4-diamino-2-ethylcyclohexane. 1,4-Diamino-2-n-propylcyclohexane, 1,4-Diamino-2-isopropylcyclohexane, 1,4-Diamino-2-n-butylcyclohexane, 1,4-Diamino-2-isobutylcyclohexane, 1,4-Diamino-2-dibutylcyclohexane, 1,4-Diamino-2-tert-butylcyclohexane, 1,2-Diaminocyclohexane, 1,3-Diaminocyclobutane, 1,4-bis(aminomethyl)cyclohexane, 1,3-bis(aminomethyl)cyclohexane, diaminobicycloheptane, diaminomethyl Alicyclic diamines with alicyclic structures include dicycloheptane, diaminooxydicycloheptane, diaminomethyloxydicycloheptane, isophorone diamine, diaminotricyclodecane, diaminomethyltricyclodecane, bis(aminocyclohexyl)methane, bis(aminocyclohexyl)isopropylidene, 6,6'-bis(3-aminophenoxy)-3,3,3',3'-tetramethyl-1,1'-spirodiindane, and 6,6'-bis(4-aminophenoxy)-3,3,3',3'-tetramethyl-1,1'-spirodiindane.2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 2,2'-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, 2,3,5,6-tetrafluoro-1,4-diaminobenzene, 2,4,5,6-tetrafluoro-1,3-diaminobenzene, 2,3,5,6-tetrafluoro-1,4-benzene (dimethylamine), 2,2'-difluoro-(1,1'-biphenyl)-4,4'-diamine, 2,2',6,6'-tetrafluoro-(1,1'-biphenyl)-4,4'-diamine, 4,4'-diaminooctafluorobiphenyl, 2,2-bis(4-aminophenyl)hexafluoropropane, 4,4'- Fluorinated diamines containing fluorine atoms, such as bis(2,3,5,6-tetrafluoroaniline), 3,3'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 4,4'-diamino-2,2'-bis(trifluoromethyl)diphenyl ether, 1,4-bis[4-amino-2-(trifluoromethyl)phenoxy]benzene, 2,2-bis[4-[4-amino-2-(trifluoromethyl)phenoxy]hexafluoropropane, 3,5-diaminotrifluorobenzene, and 4,4-diamino-2-(trifluoromethyl)diphenyl ether; and diamines containing ester bonds, such as 4-aminophenyl 4-aminobenzoate and bis(4-aminophenyl) terephthalate. These can be used alone or in mixtures of two or more.

[0026] Regarding the diamine compound as a diamine component, 4,4'-diaminodiphenyl ether, 2,2'-dimethylbenzidine, 4,4'-diaminodiphenylmethane, 4,4'-diamino-1,2-diphenylethane, p-phenylenediamine (PPD), and 2,2-bis[4-(4-aminophenoxy)phenyl]propane are preferred, and p-phenylenediamine (PPD) is even more preferred.

[0027] The polyimide precursor of the present invention comprises at least a portion of a group containing an acidic group as represented by X1 in the above general formula (1), a group represented by Y1 in the above general formula (1), and a terminal group, and the acidic group content is 15 × 10⁻³ or more. The acidic group content is preferably 16 × 10⁻³ or more, more preferably 18 × 10⁻³ or more, and even more preferably 20 × 10⁻³ or more. By containing acidic groups at the above-mentioned content, the polyimide film obtained from the polyimide precursor of the present invention contains a specified amount of acidic groups, thereby extending the charged half-life and suppressing the charge decay rate after 120 seconds to a lower level. This helps to suppress charging and thus achieves higher adhesion. Furthermore, the charged half-life and the charge decay rate after 120 seconds can be determined by measuring the charged half-life according to JIS L 1094A.

[0028] The content of acidic groups can be determined by the following formula. The content of acidic groups = {(number of moles of monomers containing acidic groups used for the formation of polyimide precursors) × (number of acidic groups per molecule of monomers containing acidic groups)} ÷ (number of moles of all monomers used to form polyimide precursors) Here, when using multiple monomers containing acidic groups with different numbers of acidic groups per molecule, the acidic group content can be calculated and used according to the above formula based on their equal usage ratio. Furthermore, regarding tetracarboxylic acids, assuming that four of the acidic groups in one molecule react with the diamine during polymerization to form polyimide without remaining as acidic groups, the acidic group number used to calculate the amount of acidic groups is obtained by subtracting 4 from the number of acidic groups (including anhydride groups) in one molecule of tetracarboxylic acid. That is, the acidic group content is calculated based on the number of free carboxyl groups that do not contribute to the formation of propylene oxide bonds. For example, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride has only four carboxyl groups, and all four carboxyl groups contribute to the formation of propylene oxide bonds; therefore, in the above calculation of the acidic group content, the acidic group number is zero. Furthermore, benzohexacarboxylic acid sometimes exists in a mixed state without an anhydride group, or with one anhydride group, or even with two anhydride groups. However, on the other hand, generally speaking, of the six carboxyl groups that constitute benzohexacarboxylic acid, four are used for the formation of amide bonds. After the formation of polyamide precursors or polyamide films, the number of free carboxyl groups becomes two. Therefore, regarding benzohexacarboxylic acid, the acidity of the acid group can be calculated by simply taking the number of carboxyl groups that are acidic as two.

[0029] There are no particular limitations on the acidic group, but examples include carboxyl groups (-COOH), sulfonic acid groups (-SO3H), and phosphonic acid groups (-PO3H2). Among these, carboxyl and sulfonic acid groups are preferred because they can further extend the charged half-life and suppress the charge decay rate after 120 seconds, thereby improving the charging suppression effect. Furthermore, the acidic group can also be one that is generated by hydrolysis without undergoing esterification.

[0030] There is no particular limitation on the method by which the group represented by X1 in the above general formula (1) includes a group containing an acidic group. For example, a method can be exemplified by using a specific tetracarboxylic acid compound as at least a part of the tetracarboxylic acid component. Such a specific tetracarboxylic acid compound can be exemplified by compounds that, in addition to having carboxyl groups constituting -COOR 1, -COOR 2, and two amide bonds (-CONH-) in the above general formula (1), also have acidic groups such as carboxyl groups (hereinafter referred to as tetracarboxylic acid compounds with acidic groups). That is, a tetracarboxylic acid compound with acidic groups is a compound that, in addition to the tetracarboxylic acid structure that facilitates the amide imidization reaction, also contains acidic groups that do not facilitate the amide imidization reaction.

[0031] Specific examples of tetracarboxylic acid compounds having an acidic group include compounds having a carboxyl group as an acidic group, such as: benzoic acid, benzoic anhydride, methyl benzoate, dimethyl benzoate, trimethyl benzoate, ethyl benzoate, diethyl benzoate, triethyl benzoate, propyl benzoate, dipropyl benzoate, tripropyl benzoate, butyl benzoate, dibutyl benzoate, tributyl benzoate, phenyl benzoate, diphenyl benzoate, and triphenyl benzoate. These can be used alone or in mixtures of two or more. Among these, benzoic acid and benzoic anhydride are preferred.

[0032] The amount of the aforementioned tetracarboxylic acid compound with acidic groups used can be appropriately selected according to the amount of acidic groups contained in the polyimide precursor. Of the total amount of tetracarboxylic acid component, 1 mol% or more is preferred, more preferably 2 mol% or more, and preferably 70 mol% or less, more preferably 60 mol% or less, further preferably 50 mol% or less, further preferably 10 mol% or less, and especially preferably 6 mol% or less.

[0033] Furthermore, there is no particular limitation on the method for making the group represented by Y 1 in the above general formula (1) include a group containing an acidic group. For example, a method of using a diamine compound containing an acidic group as at least a part of the diamine component can be cited. As such a diamine compound containing an acidic group, it is only necessary to be a compound that has an acidic group such as a carboxyl group in addition to having a diamine structure. Examples of compounds that have a carboxyl group as an acidic group include: 3,5-diaminobenzoic acid (3,5-DABA), 5,5'-methylenebis(2-aminobenzoic acid), 3,3'-diamino-4,4'-dicarboxylic biphenyl, 4,4'-diamino-3,3'-dicarboxylic diphenylmethane, 3,3'-diamino-4,4'-dicarboxylic diphenylmethane, 2,2-bis[4-(4-amino-3-carboxyphenyl)phenyl]propane, etc. Furthermore, examples of compounds having a sulfonic acid group as an acidic group include: 1,4-phenylenediamine-2-sulfonic acid, 1,3-phenylenediamine-2-sulfonic acid, 3,5-diamino-2,4,6-trimethylbenzenesulfonic acid, 4,4'-diaminostilbene-2,2'-disulfonic acid, and 4,4'-bis(4-aminophenoxy)biphenyl-3,3'-disulfonic acid. These can be used alone or in combination of two or more. Among these, 3,5-diaminobenzoic acid (3,5-DABA) is preferred as a compound having a carboxyl group as an acidic group, and 1,4-phenylenediamine-2-sulfonic acid and 1,3-phenylenediamine-2-sulfonic acid are preferred as compounds having a sulfonic acid group as an acidic group.

[0034] The amount of the aforementioned diamine compound containing acidic groups used can be appropriately selected based on the amount of acidic groups contained in the polyimide precursor. Of the total amount of diamine component in 100 mol%, it is preferably 2 mol% or more, more preferably 3 mol% or more, more preferably 4 mol% or more, and preferably 70 mol% or less, more preferably 60 mol% or less, more preferably 50 mol% or less, more preferably 10 mol% or less, and especially preferably 6 mol% or less.

[0035] Alternatively, there is no particular limitation on the method of including an acidic group in the terminal group. For example, one could replace a portion of the tetracarboxylic acid component with a dicarboxylic acid compound having an acidic group, or a dicarboxylic anhydride compound having an acidic group. A dicarboxylic acid compound having an acidic group is a compound that, in addition to containing a dicarboxylic acid structure that facilitates aceimination, also contains acidic groups other than the carboxyl group constituting the dicarboxylic acid structure that do not facilitate aceimination. Similarly, a dicarboxylic anhydride compound having an acidic group is a compound that, in addition to containing a dicarboxylic anhydride structure that facilitates aceimination, also contains acidic groups other than the carboxyl group constituting the dicarboxylic anhydride structure that do not facilitate aceimination.

[0036] Regarding dicarboxylic acid compounds or dicarboxylic acid anhydrides having acidic groups, examples of compounds having a carboxyl group as an acidic group include trimellitic acid, trimellitic anhydride, 1,2,3-benzenetricaric acid, and 1,2,3-benzenetricaric anhydride. Examples of compounds having a sulfonic acid group as an acidic group include 3-sulfophthalic acid, 4-sulfophthalic acid, 3-sulfophthalic anhydride, and 4-sulfophthalic anhydride. These can be used alone or in mixtures of two or more. Among these, compounds having a carboxyl group as an acidic group are preferred, and trimellitic anhydride is particularly preferred.

[0037] The amount of the aforementioned dicarboxylic acid compound with an acidic group or dicarboxylic acid anhydride compound with an acidic group used can be appropriately selected based on the amount of acidic groups contained in the polyimide precursor. Of the total 100 mol% of the tetracarboxylic acid component, the dicarboxylic acid compound with an acidic group, and the dicarboxylic acid anhydride compound with an acidic group, the amount converted to tetracarboxylic acid is preferably 1 mol% or more, more preferably 1.5 mol% or more, and even more preferably 2 mol% or more. The amount added is preferably 35 mol% or less, more preferably 30 mol% or less, further preferably 25 mol% or less, and especially preferably 5 mol% or less; and, in terms of compound conversion, preferably 2 mol% or more, more preferably 3 mol% or more, further preferably 4 mol% or more, and preferably 70 mol% or less, more preferably 60 mol% or less, further preferably 50 mol% or less, further preferably 10 mol% or less, and especially preferably 6 mol% or less. Furthermore, since dicarboxylic acid compounds and dicarboxylic acid anhydride compounds having acidic groups contain a dicarboxylic acid structure rather than a tetracarboxylic acid structure as a structure that facilitates aceimination reactions, the amount added in terms of tetracarboxylic acid conversion is usually half the amount added in terms of compound conversion.

[0038] Furthermore, the basis represented by Y1 in the above general formula (1) may also include the basis represented by the following general formula (2). [Chemistry 3] (In the above general formula (2), R3, R4, R5, and R6 are hydrogen atoms, alkyl groups with 1 to 12 carbon atoms that may have substituents, or aryl groups with 6 to 12 carbon atoms that may have substituents).

[0039] By incorporating the base represented by the above general formula (2), the half-life of the charge can be further extended, and the charge decay rate after 120 seconds can be suppressed even lower, thereby further improving the suppression effect of charging.

[0040] As a method of containing the base represented by the above general formula (2) as the base represented by Y 1 in the above general formula (1), for example, a method of using a diamine compound containing a tris(t) structure represented by the following general formula (3) as at least a part of the diamine component can be exemplified.

[0041] [Chemistry 4] (In the above general formula (3), R3, R4, R5, and R6 are the same as in the above general formula (2))

[0042] In the above general formulas (2) and (3), R3, R4, and R5 are independently hydrogen atoms, alkyl groups having 1 to 12 carbon atoms that may have substituents, or aryl groups having 6 to 12 carbon atoms that may have substituents, preferably hydrogen atoms, alkyl groups having 1 to 12 carbon atoms that do not have substituents, or aryl groups having 6 to 12 carbon atoms that do not have substituents, more preferably hydrogen atoms, or alkyl groups having 1 to 4 carbon atoms that do not have substituents, and even more preferably hydrogen atoms.

[0043] Furthermore, in the above general formula (2) and general formula (3), R6 is a hydrogen atom, an alkyl group having 1 to 12 carbon atoms that may have substituents, or an aryl group having 6 to 12 carbon atoms that may have substituents, preferably a hydrogen atom, an alkyl group having 1 to 12 carbon atoms that does not have substituents, or an aryl group having 6 to 12 carbon atoms that does not have substituents, more preferably a hydrogen atom, or an aryl group having 6 to 12 carbon atoms that does not have substituents, and even more preferably a phenyl group.

[0044] Specific examples of diamine compounds containing a tris(t) structure represented by the above general formula (3) include: 2,4-bis(3-aminoanilino)-6-anilino-1,3,5-tris(t) (p-ATDA), 2,4-bis(3-aminoanilino)-6-benzylamino-1,3,5-tris(t) (p-ATDA), 2,4-bis(3-aminoanilino)-6-benzylamino-1,3,5-tris(t) (p-ATDA), 2,4-bis(3-aminoanilino)-6-naphth ...benzylamino-1,3,5-tris(t) (p-ATDA), 2,4-bis(3-aminoanilino)-6-naphthylamino-1,3,5-tris(t) (p-ATDA), 2,4-bis(3-amino 5-Tris(2,4-bis(3-aminoanilino)-6-biphenylamino-1,3,5-tris(2,4-bis(3-aminoanilino)-6-diphenylamino-1,3,5-tris(2,4-bis(3-aminoanilino)-6-diphenylamino-1,3,5-tris(2,4-bis(3-aminoanilino)-6-dinaphthylamino-1,3,5- Tris(2,4-bis(3-aminoanilino)-6-N-methylanilino-1,3,5-tris(2,4-bis(3-aminoanilino)-6-N-methylnaphthylamino-1,3,5-tris(2,4-bis(3-aminoanilino)-6-methylnaphthylamino-1,3,5-tris(2,4-bis(3-aminoanilino)-6-methylanilino-1,3,5-tris(2,4-bis(3-aminoanilino)-6-ethylamino ... - Tris(2,4-bis(3-aminoaniline)-6-dimethylamino-1,3,5-tris(2,4-bis(3-aminoaniline)-6-diethylamino-1,3,5-tris(2,4-bis(3-aminoaniline)-6-dibutylamino-1,3,5-tris(2,4-bis(3-aminoaniline)-6- ...diethylamino-1,3,5-tris(2,4-bis(3-aminoaniline)-6-diethylamino-1,3,5-tris(2,4-bis(3-aminoaniline)-6-diethylamino-1,3,5-tris(2 Of these, 2,4-bis(3-aminoanilino)-6-anilino-1,3,5-tris(p-ATDA) is preferred. By using 2,4-bis(3-aminoanilino)-6-anilino-1,3,5-tris(p-ATDA), the group represented by the following formula (4) can be introduced as Y1 in the above general formula (1). [Chemistry 5]

[0045] As for the amount of the diamine compound containing the tris(t) structure represented by the above general formula (3), it is preferably 50 to 100 mol% of the total diamine content of 100 mol%, more preferably 70 to 100 mol%, and even more preferably 90 to 100 mol%. That is, the ratio of structural units containing the base represented by the above general formula (2) in 100 mol% of the base represented by Y1 is preferably 50 to 100 mol%, more preferably 70 to 100 mol%, and even more preferably 90 to 100 mol.

[0046] The polyimide precursor of the present invention can be easily prepared, for example, using previously known methods. The method for preparing the polyimide precursor of the present invention is not particularly limited. For example, approximately equal moles of tetracarboxylic acid and diamine are reacted in a solvent at a relatively low temperature of 100°C or below, preferably 80°C, in a manner that does not involve amide formation or excessive amide formation. This allows the polyimide precursor to be obtained in a solvent-dissolved state, i.e., a polyimide precursor solution. Furthermore, the polyimide precursor solution thus obtained may contain, in addition to polyacrylic acid as a polyimide precursor, partially or completely amide-formed polyimide precursor or polyimide formed by the amide formation reaction.

[0047] The polymerization temperature for obtaining the polyimide precursor of the present invention is preferably 25°C to 100°C, more preferably 40°C to 80°C, and even more preferably 50°C to 80°C. The polymerization time is preferably 0.1 hours to 24 hours, and even more preferably 2 hours to 12 hours. By keeping the polymerization temperature and polymerization time within the above ranges, high molecular weight polyimide precursors can be easily obtained with high production efficiency. Polymerization can also be carried out in an air atmosphere, but it is generally suitable to be carried out in an inert gas atmosphere, preferably a nitrogen atmosphere. The approximately equal moles of tetracarboxylic acid content and diamine content specifically refer to a mole ratio [total tetracarboxylic acid content / total diamine content] of 0.90 to 1.10, preferably 0.95 to 1.05, even more preferably more than 0.98 and less than 1.04, and even more preferably more than 0.98 and less than 1.03. Furthermore, in this specification, "approximately equal moles" means that the above mole ratio is in the range of 0.99 to 1.01, and "equal moles" means a mole ratio of 1.00 significant figures.

[0048] When reacting a tetracarboxylic acid component with a diamine component, the following method can usually be appropriately used: add the diamine component to a polymerization apparatus filled with solvent, and add the tetracarboxylic acid component after confirming that the diamine component has dissolved.

[0049] The solvent used to react the tetracarboxylic acid component with the diamine component can be any solvent, including water and any organic solvent, as long as it can polymerize and dissolve the polyimide precursor. The solvent can be a mixture of two or more solvents, a mixture of two or more organic solvents, or a mixture of water and one or more organic solvents. As an organic solvent, there are no particular limitations. Examples include: N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidineone, N-methylcaprolactam, hexamethylphosphonic triamine, 1,2-dimethoxyethane, bis(2-methoxyethyl) ether, 1,2-bis(2-methoxyethoxy)ethane, tetrahydrofuran, bis[2-(2-methoxyethoxy)ethyl] ether, 1,4-dimethyl ether, dimethyl sulfoxide, dimethyl sulfoxide, diphenyl ether, cyclobutane, diphenyl sulfoxide, tetramethylurea, anisole, m-cresol, phenol, γ-butyrolactone, etc. Furthermore, in this invention, the solvent used to polymerize the polyimide precursor can be directly used as the solvent for the polyimide precursor solution when manufacturing the polyimide film for display substrates.

[0050] There are no particular limitations on the polyimide precursor solution. The concentration of the solids content of the polyimide precursor relative to the total mass of the polyimide precursor and solvent is preferably 5% by mass to 45% by mass, more preferably 5% by mass to 40% by mass, and even more preferably more than 10% by mass and less than 30% by mass. If the solids content concentration is below 5% by mass, achieving a thicker film can sometimes be difficult; if it is above 45% by mass, the solution viscosity can sometimes become too high, sometimes requiring specialized membrane manufacturing equipment.

[0051] Furthermore, the viscosity of the polyimide precursor solution at 30°C is not limited, but in terms of operation, it is preferably 1000 Pa·sec or less, more preferably 0.5 Pa·sec or more and 500 Pa·sec or less, even more preferably 1 Pa·sec or more and 300 Pa·sec or less, and especially preferably 2 Pa·sec or more and 200 Pa·sec or less.

[0052] Known additives, such as amine compounds, dehydrating agents and other additives that promote amide formation, phosphorus-containing organic compounds, the aforementioned fillers, surfactants, silane coupling agents, and leveling agents, may also be added to the polyimide precursor solution as needed.

[0053] Examples of amine compounds include: substituted or unsubstituted nitrogen-containing heterocyclic compounds, N-oxide compounds of such nitrogen-containing heterocyclic compounds, substituted or unsubstituted amino acid compounds, aromatic hydrocarbon compounds with hydroxyl groups, or aromatic heterocyclic compounds. Specific examples of aceiminization catalysts include: imidazole derivatives such as 1,2-dimethylimidazole, N-methylimidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, 5-methylbenzimidazole, and N-benzyl-2-methylimidazole, or substituted pyridine derivatives such as isoquinoline, 3,5-dimethylpyridine, 3,4-dimethylpyridine, 2,5-dimethylpyridine, 2,4-dimethylpyridine, and 4-n-propylpyridine. The amount of amide catalyst used relative to the amide unit of the polyamide precursor is preferably 0.01 equivalents to 2 equivalents, and particularly 0.02 equivalents to 1 equivalent. By using the amide catalyst, the physical properties of the obtained polyamide film, especially the elongation or resistance to breakage, can be improved.

[0054] Other amine compounds include: aliphatic tertiary amines such as trimethylamine and triethyldiamine; aromatic tertiary amines such as dimethylaniline; and heterocyclic tertiary amines such as isoquinoline, pyridine, α-methylpyridine, and β-methylpyridine, which can be added as needed.

[0055] Examples of dehydrating agents include aliphatic carboxylic anhydrides such as acetic anhydride, propionic anhydride, and butyric anhydride; and aromatic carboxylic anhydrides such as benzoic anhydride.

[0056] Examples of phosphorus-containing organic compounds include: monohexyl phosphate, monooctyl phosphate, monolaurate phosphate, monomyristate phosphate, monocetate phosphate, monostearate phosphate, monotearate phosphate, monotearate phosphate of triethylene glycol monotridecyl ether, monotearate phosphate of tetraethylene glycol monolaurate ether, monotearate phosphate of diethylene glycol monostearate ether, dihexyl phosphate, dioctyl phosphate, didecyl phosphate, dilaurate phosphate, dimyristate phosphate, dicetate phosphate, distearate phosphate, diester phosphate of tetraethylene glycol mononepentyl ether, diester phosphate of triethylene glycol monotridecyl ether, diester phosphate of tetraethylene glycol monolaurate ether, diester phosphate of diethylene glycol monostearate ether, and phosphate esters such as diethylene glycol monostearate ether, or amine salts of such phosphate esters. Examples of amines include: ammonia, monomethylamine, monoethylamine, monopropylamine, monobutylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, trimethylamine, triethylamine, tripropylamine, tributylamine, monoethanolamine, diethanolamine, and triethanolamine.

[0057] Polyimide film for display substrates The polyimide film for display substrates of the present invention is obtained by using the above-mentioned polyimide precursor for display substrates.

[0058] The polyimide film for display substrates of the present invention can be manufactured, for example, using the aforementioned polyimide precursor solution (a solution containing the polyimide precursor for display substrates of the present invention, also referred to as "display substrate forming solution"), by a known method.

[0059] The polyimide film for the display substrate of the present invention can be manufactured, for example, by the following methods: coating a polyimide precursor solution onto a support, drying it to obtain a laminate of the support and the polyimide precursor film, and then chemically imidizing / or thermally imidizing the laminate; coating a polyimide precursor solution onto a support, drying it to obtain a laminate of the support and the polyimide precursor film, chemically imidizing / or thermally imidizing the laminate, and then peeling the polyimide film off the support; or coating a polyimide precursor solution onto a support, drying it, peeling the polyimide precursor film off the support to obtain a self-holding film, fixing the self-holding film, and then chemically imidizing / or thermally imidizing the film.

[0060] The method for coating the polyimide precursor solution onto the support is not particularly limited if it is a method that can form the desired coating film. For example, well-known methods such as spin coating, screen printing, rod coating, electrodeposition, casting, and extrusion can be used appropriately. Considering the subsequent steps such as drying and heating before forming the polyimide film, for example, the thickness of the coating film can be formed to be about 1 μm to 500 μm.

[0061] There are no particular limitations on drying conditions. Drying temperatures can be, for example, between 20°C and 200°C, preferably between room temperature (25°C) and 180°C, and even more preferably between 30°C and 150°C. Drying time varies depending on the heating temperature, for example, between 1 minute and 60 minutes, preferably less than 30 minutes, or less than 20 minutes. Heating methods include hot air, infrared radiation, etc., and there are no particular limitations on the method. The drying process can be repeated multiple times, or the temperature can be increased in stages while heating is being performed. The drying conditions can be selected by considering the characteristics of the polyimide film under conditions such as vacuum, inert gases like nitrogen, or air atmospheres.

[0062] Regarding the support for coating the polyimide precursor solution, there are no particular restrictions as long as the polyimide precursor solution can be coated and it does not affect the subsequent formation of the dried polyimide precursor film, or the heating, chemical chemiimination / or thermoimination reaction. Glass, metal, plastic substrates, etc. are preferred.

[0063] In this invention, chemical amide imidization and / or thermal amide imidization can be performed by heat treatment. Taking thermal amide imidization as an example, the maximum heating temperature during heat treatment is typically above 300°C, preferably above 350°C, more preferably above 450°C, and even more preferably above 470°C. Regarding the upper limit of the heat treatment temperature, it is acceptable as long as it does not degrade the properties of the polyamide film, preferably below 600°C, more preferably below 550°C, and even more preferably below 520°C. Furthermore, the heat treatment can be performed in an air atmosphere, and is generally suitable for an inert gas atmosphere, preferably nitrogen. Chemical amide imidization varies depending on the type of additives such as the chemical amide imidization catalyst, and can be performed under milder heat treatment conditions compared to thermal amide imidization. For example, the heating treatment can be carried out within a temperature range of above 100°C, preferably above 120°C, more preferably above 150°C, and even more preferably above 200°C, and usually below 360°C, preferably below 300°C, more preferably below 250°C, and even more preferably below 220°C.

[0064] The heat treatment for chemical amide imidization / or thermal amide imidization can also be performed in stages. For example, it is preferable to perform a first heat treatment for about 0.5 to 30 minutes at a relatively low temperature of 100°C to 170°C, followed by a second heat treatment for about 0.5 to 30 minutes at a temperature above 170°C but below 220°C, then a third heat treatment for about 0.5 to 30 minutes at a high temperature above 220°C but below 350°C, and finally a fourth high-temperature heat treatment at a temperature above 350°C up to the maximum heating temperature. The heat treatment is preferably performed continuously. For example, it is preferable to perform the heat treatment from a relatively low temperature of 100°C to 170°C up to the maximum heating temperature. There is no particular limitation on the heating rate, but it is preferably 1°C / min to 30°C / min, and particularly preferably 2°C / min to 20°C / min. Within the above range, foaming caused by rapid heating can be suppressed, which is preferable.

[0065] Since the polyimide film for display substrates of the present invention is obtained by using the aforementioned polyimide precursor for display substrates, it has a longer charge half-life. The charge decay rate after 120 seconds obtained by charge half-life measurement is lower, which helps to suppress charging and achieve higher adhesion.

[0066] Specifically, the charged half-life obtained by measurement according to JIS L 1094A is preferably 48 seconds or more, more preferably 50 seconds or more, and even more preferably 52 seconds or more. The charged half-life obtained by measurement is the time from when the polyimide film of the display substrate of the present invention is charged by corona discharge until the charge becomes half.

[0067] The determination of the charged half-life can be performed, for example, as follows. That is, the charged half-life can be determined by subjecting the polyimide film of the display substrate of the present invention to corona discharge according to JIS L 1094A to make it charged.

[0068] Furthermore, the charge decay rate of the polyimide film for the display substrate of the present invention after 120 seconds, obtained by charge half-life measurement according to JIS L 1094A, is preferably 63% or less, more preferably 61% or less. Also, the lower limit of the charge decay rate after 120 seconds is preferably 30% or more. The charge decay rate after 120 seconds obtained by charge half-life measurement is the ratio of the decrease in charge after 120 seconds of corona discharge to charge the polyimide film for the display substrate of the present invention to the charge immediately after charging. That is, it is calculated by charge decay rate (%) after 120 seconds = {(charge immediately after charging - charge after 120 seconds) ÷ charge immediately after charging} × 100.

[0069] The charge decay rate after 120 seconds can be measured, for example, as follows. That is, the polyimide film for the display substrate of the present invention is charged by corona discharge according to JIS L 1094A, and the charge is measured immediately after being charged and after 120 seconds. At this time, the charge half-life can also be measured simultaneously.

[0070] Furthermore, regarding the viewpoint of more appropriately suppressing charging in this invention, when used in display substrate applications, it is preferable that the charged half-life or the charge decay rate after 120 seconds is similar to that of the inorganic material forming the inorganic layer as a barrier layer in the polyimide film for the display substrate. In particular, SiOx is suitable as the inorganic material forming the inorganic layer. Since inorganic materials such as SiOx have a relatively long charged half-life and a relatively small charge decay rate after 120 seconds, as described above, by making the polyimide film for the display substrate have a longer charged half-life and a lower charge decay rate after 120 seconds, it can be made closer to the charged half-life or charge decay rate after 120 seconds of inorganic materials such as SiOx, thereby more appropriately suppressing charging. Furthermore, the charged half-life and the charged decay rate after 120 seconds of the inorganic material forming the inorganic layer are as described above and can be determined by measuring the charged half-life and the charged decay rate after 120 seconds according to JIS L 1094A.

[0071] Furthermore, the 90-degree peel strength of the polyimide film for display substrates of the present invention is preferably 15 mN / mm or more, and more preferably 20 mN / mm or more. The 90-degree peel strength can be measured by applying the polyimide film for display substrates of the present invention to the surface of glass and then performing a 90-degree peel test on the resulting polyimide film.

[0072] <Display substrate> The polyimide film for display substrates of the present invention is suitable for use in display substrates such as displays and touch panels.

[0073] The display substrate is formed, for example, as follows: First, an inorganic barrier layer is formed on the surface of the polyimide film used in the display substrate of the present invention, using methods such as sputtering, vapor deposition, or gel-sol method, to act as a barrier layer against gases such as water vapor and oxygen. The inorganic barrier layer is formed, for example, from SiO₂. Next, a conductive layer of a conductive material (metal or metal oxide, conductive organic material, conductive carbon, etc.) is formed on the inorganic barrier layer, thereby fabricating the display substrate. The conductive layer is formed into a predetermined circuit pattern using photolithography or various printing methods, inkjet printing, etc. Subsequently, components such as elements or semiconductors for constituting the display can also be added.

[0074] The display substrate of the present invention can also be manufactured through the following steps: an inorganic barrier layer is formed on the surface of a polyimide film obtained using the polyimide precursor for the display substrate of the present invention; a conductive layer is then formed on the polyimide film in a circuit pattern thereon; and the polyimide film with the inorganic barrier layer and the conductive layer formed on its surface is peeled off from the support. The peeling method is not particularly limited; for example, it can be carried out by laser peeling (e.g., irradiating the support side with a laser) or mechanical peeling (e.g., mechanically peeling).

[0075] The display substrate of the present invention thus obtained is formed by forming an inorganic barrier layer on the surface of a polyimide film for a display substrate obtained using the polyimide precursor for a display substrate of the present invention, and then forming a conductive layer thereon in a circuit pattern. Furthermore, the display substrate of the present invention includes a polyimide film for a display substrate obtained using the polyimide precursor for a display substrate of the present invention, and the polyimide film for a display substrate of the present invention has a long charge half-life, thus helping to eliminate charge accumulation at the interface between the polyimide film and the inorganic barrier layer, thereby helping to suppress charging. [Example]

[0076] The present invention will be further described in detail below with reference to examples, comparative examples and reference examples, but the present invention is not limited thereto.

[0077] The measurement methods used in the following examples will be explained.

[0078] [Content of acidic groups] First, the total amount of acidic groups contained in the polyimide film is calculated for each of the raw materials—dianhydride, diamine, tetracarboxylic acid, and capping agent—using the following formula. Regarding tetracarboxylic acid, it is assumed that of the acidic groups in one molecule, four carboxylic acids react with the diamine during polymerization and do not remain as acidic groups during film formation. The acidic group count used in calculating the amount of acidic groups is obtained by subtracting 4 from the number of acidic groups (including anhydride groups) in one molecule of tetracarboxylic acid. The amount of acidic groups in the raw material (mol) = the mass of the raw material (mol) × (the number of acidic groups in one molecule of the raw material). Next, the total mole count of the dianhydride, diamine, tetracarboxylic acid, and capping agent after catalyst removal is set as the total amount of monomer added (mol). The content of acidic groups (-COOH group, -SO 3H group) in the polyimide film is calculated according to the following formula. The content of acidic groups in the membrane = the total amount of acidic groups in the raw materials (mol) / the total amount of monomers added (mol)

[0079] [Charged half-life and charge decay rate after 120 seconds obtained by charging half-life measurement] Polyimide film was cut into 55 mm lengthwise and 55 mm widthwise sections to prepare test pieces. For these test pieces, according to JIS L 1094A, under conditions of 23±2℃ and 50%RH, with an applied voltage of -10 kV for 30 s and a maximum measurement time of 120 s, the charged half-life was measured using a Static Honest meter manufactured by SHISHIDO ELECTROSTATIC Co., Ltd., based on the corona charging method. This determined the charged half-life and the charge decay rate after 120 seconds.

[0080] [90-degree peel strength] The 90-degree peel strength was determined using the following method: A glass plate with a polyimide film was cut into 25 mm wide pieces to obtain test specimens. After attaching a tail joint to the specimen for fixation, the specimen was fixed in a Tensilon RTF-1350 peel test fixture, and a tensile testing machine was used to peel more than 50 mm at a speed of 50 mm / min. The load at this point was measured. The peel load was divided by the peel width (mm) of the specimen, and the resulting value was taken as the 90-degree peel strength.

[0081] The abbreviations of the compounds used in the following examples are as follows. s-BPDA: 3,3',4,4'-Biphenyltetracarboxylic acid dianhydride PPD: p-phenylenediamine 3,5-DABA:3,5-Diaminobenzoic acid MPD: m-phenylenediamine HAB: 3,3'-Dihydroxybenzidine DATP: 4,4''-diamino-p-triphenyl

[0082] [Example 1] 34.4734 g of NMP (N-methylpyrrolidone), 1.4340 g of PPD, and 0.0842 g of 3,5-DABA were added to a reaction vessel equipped with a stirrer and a nitrogen inlet. After stirring for 30 minutes under a nitrogen atmosphere at 50°C, 3.9820 g of s-BPDA was added to continue the reaction, yielding a polyimide precursor solution (polyamide solution). At this point, the molar ratio of s-BPDA:PPD:3,5-DABA was 100:96:4. Next, the polyamide solution prepared in the synthesis example was spin-coated onto an alkali-free glass wafer, and then heated at 120°C, 150°C, 200°C, and 250°C for 10 minutes each, and at 450°C for 5 minutes to remove the solvent and amide imidize, obtaining a polyamide film with a thickness of 10 μm. The evaluation results are shown in Table 1.

[0083] [Example 2] The amounts of diamine and tetracarboxylic acid were set to s-BPDA:trimethylbenzene tricarboxylic anhydride:PPD (molar ratio) = 98:4:100. Otherwise, the procedure was performed in the same manner as in Example 1 to obtain a polyimide precursor solution. Subsequently, a polyimide film was obtained by solvent removal and amide maturation. The evaluation results are shown in Table 1.

[0084] [Example 3] The amounts of diamine and tetracarboxylic acid were set to s-BPDA:benzyl hexacarboxylic acid:PPD (molar ratio) = 98:2:100. Otherwise, the procedure was performed in the same manner as in Example 1 to obtain a polyimide precursor solution. Next, solvent removal and amide formation were performed to obtain a polyimide film. The evaluation results are shown in Table 1. Furthermore, regarding the hexacarboxylic acid used in Example 3, as an acidic group that reacts in the same way as the tetracarboxylic acid component and ultimately remains on the membrane, it is assumed that after removing the four carboxylic acids of the tetracarboxylic acid component from the six carboxylic acids that are the acidic group of hexacarboxylic acid, there are two carboxylic acids. When calculating the content of acidic groups (the number of acidic groups per molecule of raw material), 2 is used for calculation.

[0085] [Example 4] The amounts of diamine and tetracarboxylic acid were set to s-BPDA:PPD:1,4-phenylenediamine-2-sulfonic acid (molar ratio) = 100:96:4. Otherwise, the procedure was performed in the same manner as in Example 1 to obtain a polyimide precursor solution. Next, solvent removal and amide oxidation were performed to obtain a polyimide film. The evaluation results are shown in Table 1.

[0086] [Comparative Example 1] The amounts of diamine and tetracarboxylic acid were set to s-BPDA:PPD = 100:100. Otherwise, the procedure was performed in the same manner as in Example 1 to obtain a polyimide precursor solution. Next, solvent removal and amide oxidation were performed to obtain a polyimide film. The evaluation results are shown in Table 1.

[0087] [Comparative Example 2] The amounts of diamine and tetracarboxylic acid were set to s-BPDA:PPD:MPD = 100:96:4. Otherwise, the procedure was performed in the same manner as in Example 1 to obtain a polyimide precursor solution. Next, solvent removal and amide oxidation were performed to obtain a polyimide film. The evaluation results are shown in Table 1.

[0088] [Comparative Example 3] The amounts of diamine and tetracarboxylic acid were set to s-BPDA:PPD:HAB = 100:96:4. Otherwise, the procedure was performed in the same manner as in Example 1 to obtain a polyimide precursor solution. Next, solvent removal and amide maturation were performed to obtain a polyimide film. The evaluation results are shown in Table 1.

[0089] [Comparative Example 4] The amounts of diamine and tetracarboxylic acid were set to s-BPDA:DATP = 100:100. Otherwise, the procedure was performed in the same manner as in Example 1 to obtain a polyimide precursor solution. Next, solvent removal and amide oxidation were performed to obtain a polyimide film. The evaluation results are shown in Table 1.

[0090] [Table 1] Table 1 Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Polyimide composition (Morby) s-BPDA 100 98 98 100 100 100 100 100 Triphenyltricarboxylic anhydride 4 Benzene hexacarboxylic acid 2 PPD 96 100 100 96 100 96 98 3,5-DABA 4 1,4-Phenylenediamine-2-sulfonic acid 4 MPD 4 HAB 2 DATP 100 Evaluation results Acid group content in polyimide (×10⁻³) 20 COOH 20 COOH 20 COOH 20 SO 3H 0 0 0 0 Charged half-life (s) obtained by measuring charged half-life 55.3 68.4 >120 >120 46.7 26.8 30.3 15.6 The decay rate (%) obtained after 120 seconds by measuring the charged half-life 61 58 38 46 64 71 70 77

[0091] As shown in Table 1, by including acidic groups in the polyimide precursor at a specified ratio, a polyimide film with a charged half-life of 48 seconds or more and a charge decay rate of less than 63% after 120 seconds can be obtained. Since the polyimide film obtained in this way has a longer charged half-life and a lower charge decay rate after 120 seconds, it can help suppress charging when used as a polyimide film for display substrates (Examples 1-4). Furthermore, regarding the 90° peel strength, the peel strength in Example 1 was 25 mN / mm, which is higher than the peel strength of 13 mN / mm in Comparative Example 1. In Example 2, it was confirmed that the more difficult the peeling operation of the film performed using the peel strength measuring fixture, the higher the adhesion. [Industrial Applicability]

[0092] The polyimide precursor for display substrates of the present invention is suitable for use in display substrates.

Claims

1. A polyimide precursor for a display substrate, having a structural unit represented by the following general formula (1), and comprising at least a portion of a group containing an acidic group as represented by X1 in the above general formula (1), a group represented by Y1 in the above general formula (1), and a terminal group, wherein the content of the acidic group is 15 × 10⁻³ or more; the polyimide precursor is obtained by reacting a tetracarboxylic acid component, a diamine component, and a suitable dicarboxylic acid compound or a dicarboxylic anhydride compound containing an acidic group; the group containing the acidic group is derived from a tetracarboxylic acid compound containing an acidic group, a diamine compound containing a sulfonic acid group, a dicarboxylic acid compound containing an acidic group, or a dicarboxylic anhydride compound containing an acidic group; the tetracarboxylic acid compound containing the acidic group is a compound containing an acidic group that does not contribute to the acetylation reaction, in addition to a tetracarboxylic acid structure that facilitates the acetylation reaction; The dicarboxylic acid compound having an acidic group is a compound that, in addition to the dicarboxylic acid structure that facilitates the acetilimation reaction, also has an acidic group that does not facilitate the acetilimation reaction; the dicarboxylic acid anhydride compound having an acidic group is a compound that, in addition to the dicarboxylic acid anhydride structure that facilitates the acetilimation reaction, also has an acidic group that does not facilitate the acetilimation reaction; the amount of the diamine compound having a sulfonic acid group is less than 10 mol% of the total diamine content of 100 mol%; the content of the above acidic group is determined by the following formula (5) based on the number of acidic groups that do not facilitate the acetilimation reaction; [Chemical 6] (In the above general formula (1), X1 is a tetravalent aromatic group or an aliphatic group, Y1 is a divalent aromatic group, and R1 and R2 are independently hydrogen atoms, alkyl groups with 1 to 6 carbon atoms, or alkyl-silyl groups with 3 to 9 carbon atoms) The content of acidic groups = {(the number of moles of the monomers containing acidic groups used to form polyimide precursors) × (the number of acidic groups per molecule of the monomers containing acidic groups)} ÷ (the total number of moles of all monomers used to form polyimide precursors) (5).

2. The polyimide precursor for display substrates as claimed in claim 1, wherein the acidic group is selected from at least one of carboxyl groups and sulfonic acid groups.

3. The polyimide precursor for display substrates as claimed in claim 2, wherein the carboxyl group is derived from at least one compound selected from 3,5-diaminobenzoic acid, 5,5'-methylenebis(2-aminobenzoic acid), hexacarboxylic acid and hexacarboxylic anhydride, and trimellitic anhydride.

4. The polyimide precursor for display substrates as claimed in claim 3, wherein the carboxyl group is derived from at least one compound selected from 3,5-diaminobenzoic acid, hexacarboxylic acid and hexacarboxylic anhydride, and trimellitic anhydride.

5. The polyimide precursor for display substrates as claimed in claim 2, wherein the sulfonic acid group is derived from at least one compound selected from 1,4-phenylenediamine-2-sulfonic acid, 1,3-phenylenediamine-4-sulfonic acid, 3,5-diamino-2,4,6-trimethylbenzenesulfonic acid, and 4,4'-diaminostilbene-2,2'-disulfonic acid.

6. The polyimide precursor for display substrates as claimed in claim 5, wherein the sulfonic acid group is derived from a compound selected from at least one compound selected from 1,4-phenylenediamine-2-sulfonic acid and 1,3-phenylenediamine-4-sulfonic acid.

7. A polyimide film for a display substrate, obtained by using a polyimide precursor for a display substrate as claimed in any one of claims 1 to 6.

8. A display substrate having a polyimide film for a display substrate as claimed in claim 7.

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