WO2022071443A1

WO2022071443A1 - Polyamidimide copolymer and film which uses same

Info

Publication number: WO2022071443A1
Application number: PCT/JP2021/035997
Authority: WO
Inventors: 斉二郎福田; 佳純橋本; 楽渡部; 譲本松
Original assignee: 太陽ホールディングス株式会社
Priority date: 2020-09-30
Filing date: 2021-09-29
Publication date: 2022-04-07
Also published as: CN116134077A; JPWO2022071443A1; KR20230075391A; TW202229414A

Abstract

[Problem] To provide a favorable polyamidimide copolymer which exhibits excellent toughness, such as elasticity, excellent transparency, and favorable wettability when made into a film. [Solution] A polyamidimide copolymer which contains an imide structural unit and an amide structural unit, wherein the imide structural unit includes an imide structural unit I-1 represented by formula (1) and one or more types of imide structural unit I-2 selected from the group consisting of those represented by formulas (2)-(5), and the amide structural unit includes an amide structural unit A-1 which is represented by formula (6).

Description

Polyamide-imide copolymer and film using it

The present invention relates to a polyamide-imide copolymer that can be suitably used for a cover window of a foldable display element such as a foldable device.

Foldable devices have recently been attracting attention in order to further enhance the portability of mobile information terminals such as smartphones and tablets. As a member such as a cover window used for a flexible display constituting such a foldable device, it is necessary to have flexibility in addition to transparency. Specifically, there is a demand for a member having extremely high flexibility that can realize a bending of 180 ° with a small bending radius of about 2.5 mm.

On the other hand, conventionally, as a material to replace rigid glass, various materials made of a flexible organic polymer have been studied. For example, from the viewpoint of transparency and heat resistance, a film containing a polyimide resin has been studied and proposed as a flexible organic polymer.

However, in a flexible display using a film containing an organic polymer having such flexibility, pressure marks and bending are formed on the display surface when the display is operated by a finger touch or a stylus, and when the display is held in a folded state for a long time. Scars could occur. Therefore, the film for such a flexible display is required to have a high elastic modulus in addition to high flexibility. To solve such problems, a fluorine-substituted polyimide film has been attracting attention as a film for a flexible display having heat resistance, transparency, mechanical strength, surface hardness, and bending resistance.

By the way, in the recent foldable device field, with further improvement in functionality and productivity, diversification of designs and applications, as a cover window film for foldable devices, while maintaining transparency, at the time of processing. Proposed polyimide copolymers with further improved solubility in solvents and bending resistance, polyamide-imide copolymers with further improved mechanical strength, and the like have been proposed (Patent Document 1 and the like).

Japanese Patent Publication No. 2014-528490

The polyamideimide copolymer as proposed in Patent Document 1 and the like is 4,4'-(hexafluoroisopropyridene) diphthalic acid dianhydride as a tetracarboxylic acid dianhydride component that contributes to solubility and transparency. A fluorine-substituted acid anhydride such as a substance (6FDA) is used, and 3,3', 4,4'-biphenyltetracarboxylic acid dianhydride (sBPDA) or the like is used as a tetracarboxylic acid dianhydride component that contributes to bending resistance. It has an imide structural unit using the acid anhydride of No. 1 and an amide structural unit using terephthalic acid chloride (TPC) which contributes to mechanical strength as a dicarboxylic acid component.

However, in a copolymer using a fluorine-substituted acid anhydride such as 6FDA, the surface wettability and adhesiveness of the film are inferior, and when the film is laminated with another base material or coating material, it is inferior. Surface treatment was required.

Further, although the toughness such as bending resistance of the copolymer is improved by using an acid anhydride having an intermolecular interaction such as sBPDA, the YI value (yellowish) of the copolymer is due to π-electron conjugation. In order to reduce the YI value, it was necessary to add a brewing agent to the film. Therefore, in applications such as cover window films that require colorless transparency, the light transmittance may be insufficient.

Therefore, an object of the present invention is to provide a polyamide-imide copolymer having excellent toughness such as bending resistance, excellent transparency, and good wettability and adhesion when made into a film.

The present inventors have focused on the imide structural unit of the polyamide-imide copolymer and investigated various tetracarboxylic acid dianhydrides. By combining two specific tetracarboxylic acid dianhydrides, the above-mentioned We obtained the finding that the problem can be solved. The present invention has been completed based on such findings. The gist of the present invention is as follows.

[1] A polyamide-imide copolymer containing an imide structural unit and an amide structural unit.
The imide structural unit is the imide structural unit I-1 represented by the following formula (1):

and,
At least one imide structural unit selected from the group consisting of the following formulas (2) to (5): I-2:

(In the formulas (1) to (5), X ₁ to X ₅ each independently represent a divalent organic group derived from a diamine.)
Including
The amide structural unit is represented by the following formula (6): amide structural unit A:

(In the formula, X ₆ represents a divalent organic group derived from a diamine, and Y represents a divalent organic group derived from a dicarboxylic acid or a dicarboxylic acid derivative.)
A polyamide-imide copolymer comprising.
[2] X ₁ to X ₆ are the following equations (7):

(In the formula, * is a binding group.)
The polyamide-imide copolymer according to [1], which is represented by.
[3] Y is the following equations (8) to (10):

(In the formula, * is a binding group.)
The polyamide-imide copolymer according to [1] or [2], which is at least one selected from.
[4] The polyamide-imide copolymer according to any one of [1] to [3], wherein the imide structural unit I-2 is represented by the above formula (2).
[5] The polyamide-imide copolymer according to any one of [1] to [4], wherein the imide structural unit and the amide structural unit are contained in a molar ratio of 2: 8 to 8: 2.
[6] A film containing the polyamide-imide copolymer according to any one of [1] to [5].
[7] The film according to [6], wherein the contact angle of water on the surface of a film having a thickness of 50 μm measured in accordance with JIS R3257: 1999 is 55 degrees or less.
[8] The film according to [6] or [7], which is used as a cover window of a foldable device.

According to the present invention, by forming an imide structural unit in which two kinds of specific tetracarboxylic acid dianhydrides are combined, the toughness such as bending resistance is excellent, the transparency is also excellent, and the film is wet when formed. It is possible to realize a polyamide-imide copolymer having good properties and adhesion.

Aspects for carrying out the invention

[Polyamide-imide copolymer]
The polyamide imide copolymer according to the present invention is a copolymer having an imide structure and an amide structure, and the imide structural unit is the imide structural unit I-1 represented by the following formula (1) and the following formula (2). It is provided with at least one imide structural unit I-2 selected from the group consisting of the group represented by (5), and has the amide structural unit A represented by the following formula (6) as the amide structural unit. be.

In the present invention, as the imide structural unit constituting the polyamide-imide copolymer, the structural unit I-1 represented by the above formula (1) and one or more of the structural units (2) to (5) are used. By combining with I-2, the transparency of the polyamide-imide copolymer, the wettability when formed into a film, and the adhesion to other members can be improved at the same time. When a fluorine-substituted tetracarboxylic acid dianhydride such as 6FDA is used as the tetracarboxylic acid dianhydride component of the imide structural unit as in the conventional polyamide-imide copolymer, the transparency of the obtained polyamide-imide copolymer is obtained. However, the wettability and adhesion of the film were insufficient. In the present invention, as a result of screening various tetracarboxylic acid dianhydrides from the viewpoint of electron affinity, 3,4-oxydiphthalic acid dianhydride (aODPA) and 4,4'-oxydiphthalic acid dianhydride (sODPA) , 2,2', 3,3'-biphenyltetracarboxylic acid dianhydride (aBPDA), 9,9-bis (3,4-dicarboxyphenyl) fluorene, acid anhydride (BPAF) and 4,4'- (Hexafluoroisopropylidene) By combining with at least one selected from the group consisting of diphthalic acid dianhydride (6FDA), conventional properties derived from the imide structure such as heat resistance and mechanical strength are not impaired. Compared with the conventional polyamideimide copolymer in which 6FDA and sBPDA are combined, the transparency of the resin and the wettability and adhesion when formed into a film are improved at the same time.

Among the structural units I-2 of (2) to (5) to be combined with the structural unit I-1 represented by the above formula (1), the structural unit represented by the above formula (2) is preferable. That is, in the present invention, a combination of aODPA and sODPA is preferable as the tetracarboxylic dianhydride constituting the imide structural unit.

The ratio of the polyamide-imide copolymer to I-1 and I-2 constituting the imide structural unit is preferably in the range of 2: 1 to 1: 2 in terms of molar ratio, and is preferably in the range of 3: 2 to 2: 3. It is more preferably in the range.

The polyamide-imide copolymer of the present invention may contain components other than those described above as the imide structural unit as long as the effects of the present invention are not impaired. Examples of the tetracarboxylic acid component constituting the imide structural unit include various tetracarboxylic acids or tetracarboxylic acid derivatives, and examples of the tetracarboxylic acid derivative include tetracarboxylic acid anhydrides, preferably dianhydrides and acid chlorides. Be done. Examples of the tetracarboxylic acid compound include aromatic tetracarboxylic acid and its anhydride, preferably an aromatic tetracarboxylic acid compound such as its dianhydride; an aliphatic tetracarboxylic acid compound and its anhydride, preferably its dianhydride. Examples thereof include aliphatic tetracarboxylic acid compounds such as. These tetracarboxylic acid compounds can be used alone or in combination of two or more.

Specific examples of the aromatic tetracarboxylic acid dianhydride include a non-condensed polycyclic aromatic tetracarboxylic acid dianhydride, a monocyclic aromatic tetracarboxylic acid dianhydride, and a condensed polycyclic aromatic tetra. Examples include carboxylic acid dianhydride. Examples of the non-condensed polycyclic aromatic tetracarboxylic acid dianhydride include 3,3', 4,4'-biphenyltetracarboxylic acid dianhydride (sBPDA), 4,4'-(4,4'-isopropi). Redendiphenoxy) Diphthalate dianhydride (BPADA), 3,3', 4,4'-benzophenone tetracarboxylic acid dianhydride, 2,2', 3,3'-benzophenone tetracarboxylic acid dianhydride, 3 , 3', 4,4'-diphenylsulfone tetracarboxylic acid dianhydride, 2,2-bis (3,4-dicarboxyphenyl) propane dianhydride, 2,2-bis (2,3-dicarboxyphenyl) ) Propane dianhydride, 2,2-bis (3,4-dicarboxyphenoxyphenyl) propane dianhydride, 1,2-bis (2,3-dicarboxyphenyl) ethane dianhydride, 1,1-bis (2,3-dicarboxyphenyl) ethane dianhydride, 1,2-bis (3,4-dicarboxyphenyl) ethane dianhydride, 1,1-bis (3,4-dicarboxyphenyl) ethane dianhydride Things, bis (3,4-dicarboxyphenyl) methane dianhydride, bis (2,3-dicarboxyphenyl) methane dianhydride, 4,4'-(p-phenylenedioxy) diphthalic acid dianhydride and Examples thereof include 4,4'-(m-phenylenedioxy) diphthalic acid dianhydride. Examples of the monocyclic aromatic tetracarboxylic acid dianhydride include 1,2,4,5-benzenetetracarboxylic acid dianhydride, and the condensed polycyclic aromatic tetracarboxylic acid dianhydride. Examples thereof include 2,3,6,7-naphthalenetetracarboxylic acid dianhydride.

Examples of the aliphatic tetracarboxylic dianhydride include cyclic or acyclic aliphatic tetracarboxylic dianhydride. The cyclic aliphatic tetracarboxylic acid dianhydride is a tetracarboxylic acid dianhydride having an alicyclic hydrocarbon structure, and specific examples thereof include 1,2,4,5-cyclohexanetetracarboxylic acid dianhydride. Cycloalkanthtetracarboxylic acid dianhydrides such as (HPMDA), 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride (CBDA), 1,2,3,4-cyclopentanetetracarboxylic acid dianhydrides, 1,2,3,4-cyclopentanetetracarboxylic acid dianhydrides. , Bicyclo [2.2.2] Oct-7-en-2,3,5,6-tetracarboxylic acid dianhydride, Dicyclohexyl-3,3', 4,4'-tetracarboxylic acid dianhydride (HBPDA) ) And their positional isomers. These can be used alone or in combination of two or more. Specific examples of the acyclic aliphatic tetracarboxylic acid dianhydride include 1,2,3,4-butanetetracarboxylic acid dianhydride, 1,2,3,4-pentanetetracarboxylic acid dianhydride and the like. These can be used alone or in combination of two or more. Further, a cyclic aliphatic tetracarboxylic dianhydride and an acyclic aliphatic tetracarboxylic dianhydride may be used in combination.

As long as the effect of the present invention is not impaired, the imide structural unit may contain the above-mentioned aqueous adduct of tetracarboxylic dianhydride or the structural unit derived from the tricarboxylic acid compound in addition to the above-mentioned structural unit. good. Examples of the tricarboxylic acid compound include aromatic tricarboxylic acids, aliphatic tricarboxylic acids, acid chloride compounds related thereto, acid anhydrides, and the like, and two or more of them may be used in combination. Specific examples include anhydrate of 1,2,4-benzenetricarboxylic acid; 2,3,6-naphthalentricarboxylic acid-2,3-anhydride; a single bond of phthalic anhydride and benzoic acid, -O-. , -CH _2- , -C (CH ₃ ) _2- , -SO _2- or a compound linked with a phenylene group can be mentioned.

The polyamide-imide copolymer according to the present invention contains an amide structural unit A represented by the following formula (6). By using a copolymer having an imide structure having rigid properties and an amide structure having flexible properties, there is a trade-off relationship between excellent flexibility and high elasticity without sacrificing transparency and wettability. A certain mechanical property can be realized at a high level.

(In the formula, X ₆ represents a divalent organic group derived from a diamine, and Y represents a divalent organic group derived from a dicarboxylic acid or a dicarboxylic acid derivative.)

The polyamide imide copolymer containing the above-mentioned amide structural unit A can be obtained by reacting a diamine compound, a tetracarboxylic acid compound and a dicarboxylic acid compound which are monomer components, and specifically, the diamine compound and the tetracarboxylic acid compound. To synthesize a polymer having an imide precursor structure, and then reacting the polymer with a dicarboxylic acid compound to synthesize a copolymer having an imide precursor structure and an amide structure, and then the co-weight. It is obtained by subjecting the imide precursor structure in the coalescence to a ring-closing reaction (imidization).

The polyamide imide copolymer consists of a structural unit in which residues obtained by reacting a diamine compound and a tetracarboxylic acid compound are bonded via an imide structure, and residues reacted by a dicarboxylic acid compound via an amide structure. Has a structure.

In the amide structural unit A represented by the above formula (7), Y is a divalent organic group derived from a dicarboxylic acid or a dicarboxylic acid derivative. Examples of the dicarboxylic acid derivative include an acid chloride of the dicarboxylic acid. Examples include an ester form. Dicarboxylic acids can be used alone or in combination of two or more.

Specific examples of the dicarboxylic acid include, for example, 1,3-cyclobutanedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 4,4'-oxybis benzoic acid, terephthalic acid, and isophthalic acid. 2,6-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 4,4'-biphenyldicarboxylic acid, 3,3'-biphenyldicarboxylic acid, two cyclohexanecarboxylic acids or two An alicyclic dicarboxylic acid or fragrance such as a compound in which the benzoic acid is single-bonded, -CH _2- , -C (CH ₃ ) _2- , -C (CF ₃ ) _2- , -SO _2- or a phenylene group. Group dicarboxylic acids and their derivatives (eg, acid chlorides, acid anhydrides); aliphatic dicarboxylic acids such as dicarboxylic acid compounds of chain hydrocarbons having 8 or less carbon atoms and their derivatives (eg, acid chlorides, esters) and the like. Can be mentioned. These dicarboxylic acid compounds can be used alone or in combination of two or more.

Among these, terephthalic acid, isophthalic acid, 4,4'-biphenyldicarboxylic acid, or 4,4'-oxybis benzoic acid or a derivative thereof, particularly, from the viewpoint of improving the elongation at break point and the elasticity as a film. It is preferable to use terephthalic acid chloride (TPC), isophthalic acid chloride (IPC), 4,4'-biphenyldicarbonyl chloride (BPC), 4,4'-oxybis (benzoyl chloride) (OBBC), specifically. , Y is a divalent organic group derived from TPC, the amide structural unit A-1 represented by the following formula (11), and Y is a divalent organic group derived from IPC, the following formula (12). It is preferable to have the amide structural unit A-2 represented by the above, or the amide structural unit A-3 represented by the following formula (13) in which Y is a divalent organic group derived from BPC, and in particular, the amide structure. It is preferable to have the unit A-1.

(In the formula, X ₆ represents a divalent organic group derived from diamine.)

As the amide structural unit, the above-mentioned amide structural unit A-1 and other amide structural units may be used in combination, and examples of the other amide structural unit include those derived from the above-mentioned various dicarboxylic acids or dicarboxylic acid derivatives. However, the amide structural unit A-2 or A-3 is preferred. When the amide structural unit A-1 and A-2 or A-3 are used in combination as the amide structural unit, the composition ratio thereof is from the viewpoint of the balance between optical properties such as transparency and mechanical properties such as mechanical strength. Is preferably in the range of 10: 1 to 5: 1.

The composition ratio (molar ratio) of the imide structure to the amide structure in the polyamide-imide copolymer of the present invention is preferably 0.5 to 4: 3 to 6.5, more preferably 1.5 to 3.5 :. The ratio is 3.5 to 5.5, particularly preferably 3: 4, and the composition ratio of the imide structure and the amide structure is the above-mentioned composition ratio, so that excellent flexibility and high elasticity can be achieved in a well-balanced manner.

The diamine component (that is, the divalent organic group represented by X ₁ to X ₆ ) constituting the above-mentioned imide structural unit and amide structural unit is not particularly limited, and conventionally known polyimide or polyamide-imide is not particularly limited. The diamine component used in the above can be used, and examples thereof include aliphatic diamines, aromatic diamines and mixtures thereof.
In addition, here, "aromatic diamine" represents a diamine in which an amino group is directly bonded to an aromatic ring, and an aliphatic group or another substituent may be contained in a part of the structure. The aromatic ring may be a monocyclic ring or a condensed ring, and examples thereof include, but are not limited to, a benzene ring, a naphthalene ring, an anthracene ring, and a fluorene ring. Among these, a benzene ring is preferable. Further, the "aliphatic diamine" represents a diamine in which an amino group is directly bonded to an aliphatic group, and an aromatic ring or other substituent may be contained as a part of the structure thereof. Diamine compounds can be used alone or in combination of two or more.

Specific examples of the aliphatic diamine include acyclic aliphatic diamines such as hexamethylenediamine; 1,3-bis (aminomethyl) cyclohexane, 1,4-bis (aminomethyl) cyclohexane, norbornanediamine, 4,4'. -Cycholic aliphatic diamines such as diaminodicyclohexylmethane can be mentioned. These can be used alone or in combination of two or more.

Specific examples of aromatic diamines include p-phenylenediamine, m-phenylenediamine, 2,4-toluenediamine, m-xylylene diamine, p-xylylene diamine, 1,5-diaminonaphthalene, and 2,6-diamino. Aromatic diamines having one aromatic ring, such as naphthalene; 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylpropane, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 3,3 '-Diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 1,4-bis (4-aminophenoxy) benzene, 1,3-bis (4-Aminophenoxy) benzene, bis [4- (4-aminophenoxy) phenyl] sulfone, bis [4- (3-aminophenoxy) phenyl] sulfone, 2,2-bis [4- (4-aminophenoxy) Phenyl] propane, 2,2-bis [4- (3-aminophenoxy) phenyl] propane, 2,2'-dimethylbenzidine, 2,2'-bis (trifluoromethyl) benzidine, 4,4'-bis ( 4-aminophenoxy) biphenyl, 9,9-bis (4-aminophenyl) fluorene, 9,9-bis (4-amino-3-methylphenyl) fluorene, 9,9-bis (4-amino-3-chlorophenyl) ) Fluolene, 9,9-bis (4-amino-3-fluorophenyl) fluorene, 4-aminophenyl-4'-aminozenzoate, (2-phenyl-4-aminophenyl) -4-aminobenzoate, 4 , 4'-Diaminobenzanilide, and the like, and examples thereof include aromatic diamines having two or more aromatic rings. These can be used alone or in combination of two or more.

Among the above diamine compounds, one or more selected from the group consisting of aromatic diamines having a biphenyl structure, specifically 2,2'-dimethylbenzidine, from the viewpoint of improving colorless transparency and elasticity as a film. It is preferable to use one or more selected from the group consisting of 2,2'-bis (trifluoromethyl) benzidine, 4,4'-bis (4-aminophenoxy) biphenyl and 4,4'-diaminodiphenyl ether. A diamine having a biphenyl structure and having a part or all of hydrogen atoms on the aromatic ring substituted with a substituent selected from a fluoro group, a trifluoromethyl group, or a trifluoromethoxy group from the viewpoint of easily improving colorless transparency. Specifically, it is more preferable to use 2,2'-bis (trifluoromethyl) benzidine (TFMB) represented by the following formula.

As the diamine compound, the above-mentioned TFMB may be used alone, or one or more of the above-mentioned various diamine compounds may be used in combination with TFMB. When TFMB and various other diamine compounds are used in combination, the composition ratio is in the range of 10: 1 to 5: 1 from the viewpoint of the balance between optical properties such as transparency and mechanical properties such as mechanical strength. Is preferable.

In the synthesis of the polyamide-imide copolymer, the composition ratio of the monomer components (diamine compound: tetracarboxylic acid compound: dicarboxylic acid compound) may be 7: 0.5 to 4: 3 to 6.5 as a molar ratio. It is more preferably 7: 1.5 to 3.5: 3.5 to 5.5, and particularly preferably 7: 3: 4.

The ring-closing reaction (imidization) of the imide precursor obtained by reacting the above-mentioned diamine compound and the tetracarboxylic acid compound, or the imide precursor by reacting the diamine compound, the tetracarboxylic acid compound and the dicarboxylic acid compound is coexisting with water. Either thermal imidization, in which a boiling co-boiling solvent (eg, toluene, xylene, etc.) is added and heated, or chemical imidization using a condensing agent and a reaction accelerator can be used, but colorless transparency is maintained. Therefore, chemical imidization is preferable.

Reaction accelerators used for chemical imidization include triethylamine, diisopropylethylamine, N-methylpiperidin, pyridine, 2-methylpyridine, 3-methylpyridine, 4-methylpyridine, 3-ethylpyridine, 3,5-dimethylpyridine, and the like. Examples thereof include 3,5-diethylpyridine, isoquinoline, imidazole, 1-methylimidazole, 2-methylimidazole and 1,2-dimethylimidazole. These reaction accelerators may be one kind or a combination of two or more kinds.

Condensing agents used for chemical imidization include acid anhydrides such as acetic acid anhydride, propionic acid anhydride, and trifluoroacetic acid anhydride, phosphorous acid ester, triethyl phosphite, triethyl phosphite, tributyl phosphite, and phosphorous acid. Examples thereof include phosphite esters such as dimethyl, diethyl phosphite, and triphenyl phosphite. These condensing agents may be one kind or a combination of two or more kinds.

The imidization rate is preferably 90% or more, more preferably 93% or more, still more preferably 96% or more. From the viewpoint of easily increasing the optical homogeneity such as transparency, a high imidization ratio is preferable. Further, the upper limit of the imidization rate is 100% or less. The imidization ratio indicates the ratio of the molar amount of imide bond in the imide structural unit to the value of twice the molar amount of the structural unit derived from tetracarboxylic acid dianhydride in the imide structural unit. The imidization rate can be obtained by an IR method, an NMR method, or the like.

The organic solvent used for the synthesis of the polyamide-imide copolymer is not particularly limited as long as it is an organic solvent that is inert to the reaction. For example, N, N-dimethylacetamide (DMAc), N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, dimethyl sulfoxide, m-cresol, γ-butyrolactone, cyclopentanone, cyclohexanone, tetrahydrofuran. And so on. These organic solvents may be used alone or in combination of two or more.

The reaction conditions for the synthesis can be 1 to 27 hours or less at 10 to 50 ° C., and it is preferable to synthesize in a nitrogen atmosphere from the viewpoint of maintaining colorless transparency.

The polyamide-imide copolymer can be isolated (separated and purified) by a conventional method, for example, a separation means such as filtration, concentration, extraction, crystallization, recrystallization, or column chromatography, or a separation means combining these. Often, in a preferred embodiment, a reaction solution containing a transparent polyamide-imide resin can be isolated by adding a large amount of alcohol such as methanol to precipitate the resin, and concentrating, filtering, drying and the like.

The weight average molecular weight (Mw) of the resin having an imide structure obtained as described above is preferably in the range of 50,000 to 1,000,000 from the viewpoint of improving the elastic modulus and the elongation at break point. , 80,000 to 800,000, more preferably 110,000 to 650,000. The weight average molecular weight (Mw) is a value measured by GPC (gel permeation chromatography) and calculated in terms of polystyrene.

<Film>
The polyamide-imide copolymer of the present invention is dissolved in an appropriate solvent to form a resin composition (resin varnish), and the resin composition is applied onto a support to form a coating film, and then the coating film is dried. A film can be obtained by removing the solvent and peeling it from the support. The solvent can be used without particular limitation as long as it can dissolve polyamideimide, but from the viewpoint of the coatability of the resin varnish and the transparency of the obtained film, an ester group, an ether group, a ketone group, etc. can be used. A solvent containing at least one selected from the group consisting of a hydroxyl group, a sulfone group and a sulfinyl group is preferable.

Examples of the solvent having an ester group include ester solvents such as methyl acetate, ethyl acetate, butyl acetate and dimethyl carbonate.
Examples of the solvent having a cyclic ester group include lactone-based solvents such as γ-butyrolactone (GBL), δ-valerolactone, ε-caprolactone, γ-crotonolactone, γ-hexanolactone, and α-methyl-γ-butyrolactone. , Γ-Valerolactone, α-acetyl-γ-butyrolactone, δ-hexanolactone and the like.
Examples of the solvent having an ether group include tetrahydrofuran, dioxane, dibutyl ether and the like.
Examples of the solvent having a ketone group include a ketone solvent, for example, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone and the like.
Examples of the solvent having a hydroxyl group include phenolic solvents such as m-cresol.
Examples of the solvent having a sulfone group include methyl sulfone, ethyl phenyl sulfone, diethyl sulfone, diphenyl sulfone, sulfolane, bisphenol S, sorapson, dapson, bisphenol A polysulfone, sulfolane and the like.
Examples of the solvent having a sulfinyl group include sulfoxide-based solvents such as N, N-dimethyl sulfoxide (DMSO).
In addition to the solvents listed above, amide solvents such as N-methyl-2-pyrrolidone (NMP), N, N-dimethylformamide (DMF), N, N-dimethylacetamide (DMAc) and the like may be used. Can be done.

The resin composition for forming a film may contain any component other than the polyamideimide copolymer, for example, a leveling agent for improving the coatability of a varnish when producing a film. Dispersants, surfactants, retardation modifiers, antioxidants, UV inhibitors, light stabilizers, plasticizers, waxes, fillers, pigments, dyes, foaming agents, defoamers, dehydrating agents, antistatic agents, Examples thereof include antibacterial agents, antifungal agents, and brewing agents for reducing the yellowness of the film.

The content of the polyamide-imide copolymer in the resin composition is preferably in the range of 65 to 100% by mass, more preferably in the range of 80 to 100% by mass, based on the total amount of solids excluding the solvent. , 90-100% by mass, more preferably.

As a means for applying the resin composition containing the polyamide-imide copolymer on the support, conventionally known means can be applied, for example, a dip coating method, a flow coating method, a roll coating method, a bar coater method, and a blade. Examples include a coater method, a screen printing method, a curtain coating method, and a spray coating method.

The drying conditions of the coating film are not particularly limited as long as the temperature at which the solvent volatilizes, but from the viewpoint of obtaining a film having excellent transparency, it is preferably about 10 to 60 minutes at 60 to 250 ° C.

The film thickness of the present invention is preferably 5 μm or more and 100 μm or less, and more preferably 10 μm or more and 50 μm or less. By setting the film thickness within the above range, a film having excellent flexibility can be obtained, so that the film can be suitably used as a cover window of a foldable display or a flexible display. The film thickness can be adjusted by the amount of the resin composition applied.

Since the film of the present invention is formed from a polyamide-imide copolymer containing two specific imide structural units as described above, it has excellent toughness such as bending resistance, excellent transparency, and a surface surface. It also has good wettability and adhesion to other materials. For example, in a single-layer film having a thickness of 50 μm formed from a polyamide-imide copolymer, the YI value can be 2.0 or less. In this specification, the YI value (yellowness) is determined by measuring the transmittance of light of 360 to 780 nm using a spectrocolorimeter in accordance with ASTM E313-73, and the tristimulus values (X, Y). , Z) is obtained, and it is assumed that it means a value calculated based on the formula of YI = 100 × (1-0.847Z) / Y.

Further, the film of the present invention is also excellent in wettability and adhesion. For example, a film formed on a glass substrate so as to have a film thickness of 50 μm and having an arithmetic average surface roughness Ra of the surface of 50 nm or less is used. The contact angle of water is 55 degrees or less. As described above, since the film of the present invention has excellent wettability even if the surface is smooth, for example, when the film is bonded to another base material or laminated with a coating film made of a coloring material for decoration. Unlike the conventional polyimide amide film, there is no need to perform surface treatment on the film. The contact angle of water means the contact angle of water measured in accordance with JIS R3257: 1999, and the arithmetic mean surface roughness Ra was measured by a measuring device in accordance with JIS B0601-1994. Means a value.

[Use]
Display members using the film of the present invention include, for example, thin and bendable foldable organic EL displays, mobile terminals such as smartphones and wristwatch-type terminals, display devices inside automobiles, and flexible wristwatches. Examples include the use of members such as panels. In addition, members for image display devices such as liquid crystal display devices and organic EL display devices, touch panel members, flexible printed substrates, solar cell panel members such as surface protective films and substrate materials, optical waveguide members, and other semiconductor-related members. It can also be applied to such as. Above all, it is suitably used for members such as cover windows and TFT substrates constituting a foldable type organic EL display.

[Display cover window]
As the cover window of the display using the film of the present invention, for example, the film is arranged and used so as to be located on the surface of various displays. The method of arranging on the surface is not particularly limited, and examples thereof include a method via an adhesive layer and the like. As the material of the adhesive layer, a conventionally known adhesive material that can be used for adhering the surface material for a display can be used. The cover window of the display using the film of the present invention may be provided with a protective layer such as a hard coat layer and a fingerprint adhesion prevention layer on the film surface.

[TFT substrate for organic EL display]
The TFT substrate for an organic EL display using the film of the present invention can be obtained, for example, by forming an amorphous silicon TFT (thin film transistor) on the film of the present invention. The TFT includes a gate metal layer, a silicon nitride gate dielectric layer, and an ITI pixel electrode. Further, a structure required for an organic EL display can be formed on this by a known method, and the method for forming a circuit or the like is not particularly limited.

Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to the examples. In the following, "part" and "%" are all based on mass unless otherwise specified.

[Example 1]
<Preparation of polyamide-imide>
A 100 mL reactor was filled with 60.9 g of DMAc and 4.849 g (15.14 mmol) of TFMB was added. Next, 1.007 g (3.245 mmol) of aODPA and 1.4875 g (3.245 mmol) of BPAF are added to this solution of TFMB, and the mixture is stirred and reacted at 30 ° C. for 2 hours to contain a polymer having an imide precursor structure. A solution was obtained. Then, 1.757 g (8.653 mmol) of TPC was added to this solution, and the mixture was stirred and reacted for 1.5 hours while keeping the liquid temperature at 30 ° C. to react with the copolymer having an imide precursor structure and an amide structure. A solution containing the above was obtained.
Then, 2.09 g of pyridine, 2.45 g of acetic anhydride and 8.53 g of DMAc were added and stirred at 20 to 30 ° C. for 8 hours to obtain a polyamide-imide solution. Further, 99 g of DMAc was added and stirred until uniform, and then this solution was gradually added to a container containing 4 L of methanol for precipitation. Then, the precipitated solid content was filtered and pulverized, and then vacuumed at 80 ° C. The mixture was dried for 18 hours to obtain a polyamide-imide copolymer (PAI-1) having a solid content powder of 8.2 g. The polystyrene-equivalent weight average molecular weight by GPC was 597,000.

[Example 2]
A polyamide-imide solution was obtained in the same manner as in Example 1 except that 0.9547 g (3.245 mmol) of aBPDA was added instead of BPAF. The obtained polyamide-imide solution was purified in the same manner as in Example 1 to obtain a polyamide-imide copolymer (PAI-2) of 8.0 g of solid content powder. The polystyrene-equivalent weight average molecular weight by GPC was 201,000.

[Example 3]
A polyamide-imide solution was obtained in the same manner as in Example 1 except that 1.007 g (3.245 mmol) of sODPA was added instead of BPAF. The obtained polyamide-imide solution was purified in the same manner as in Example 1 to obtain a polyamide-imide copolymer (PAI-3) of 7.9 g of solid content powder. The polystyrene-equivalent weight average molecular weight by GPC was 407,000.

[Example 4]
A polyamide-imide solution was obtained in the same manner as in Example 1 except that 1.442 g (3.245 mmol) of 6FDA was added instead of BPAF. The obtained polyamide-imide solution was purified in the same manner as in Example 1 to obtain a polyamide-imide copolymer (PAI-4) of 8.3 g of solid content powder. The polystyrene-equivalent weight average molecular weight by GPC was 311,000.

[Comparative Example 1]
A polyamide-imide solution was obtained in the same manner as in Example 1 except that 0.9547 g (3.245 mmol) of sBPDA was added instead of BPAF. The obtained polyamide-imide solution was purified in the same manner as in Example 1 to obtain a polyamide-imide copolymer (PAI-5) of 8.2 g of solid content powder. The polystyrene-equivalent weight average molecular weight by GPC was 625,000.

[Comparative Example 2]
As the tetracarboxylic dianhydride, a polyamide-imide solution was obtained in the same manner as in Example 1 except that 1.488 g (3.245 mmol) of BPAF and 0.9547 g (3.245 mmol) of aBPDA were added instead of aODPA and BPAF. .. The obtained polyamide-imide solution was purified in the same manner as in Example 1 to obtain a polyamide-imide copolymer (PAI-6) of 7.5 g of solid content powder. The polystyrene-equivalent weight average molecular weight by GPC was 114,000.

[Comparative Example 3]
As the tetracarboxylic dianhydride, a polyamide-imide solution was obtained in the same manner as in Example 1 except that 1.488 g (3.245 mmol) of BPAF and 1.007 g (3.245 mmol) of sOPDA were added instead of aODPA and BPAF. .. The obtained polyamide-imide solution was purified in the same manner as in Example 1 to obtain a polyamide-imide copolymer (PAI-7) of 7.3 g of solid content powder. The polystyrene-equivalent weight average molecular weight by GPC was 100,000.

[Comparative Example 4]
As the tetracarboxylic dianhydride, a polyamide-imide solution was obtained in the same manner as in Example 1 except that 0.9547 g (3.245 mmol) of aBPDA and 1.007 g (3.245 mmol) of sODPA were added instead of aODPA and BPAF. .. The obtained polyamide-imide solution was purified in the same manner as in Example 1 to obtain a polyamide-imide copolymer (PAI-8) of 7.0 g of solid content powder. The polystyrene-equivalent weight average molecular weight by GPC was 97,000.

[Comparative Example 5]
As the tetracarboxylic dianhydride, a polyamide-imide solution was obtained in the same manner as in Example 1 except that 1.007 g (3.245 mmol) of sODPA and 1.441 g (3.245 mmol) of 6FDA were added instead of aODPA and BPAF. .. The obtained polyamide-imide solution was purified in the same manner as in Example 1 to obtain a polyamide-imide copolymer (PAI-9) of 8.4 g of solid content powder. The polystyrene-equivalent weight average molecular weight by GPC was 478,000.

[Comparative Example 6]
As the tetracarboxylic dianhydride, a polyamide-imide solution was obtained in the same manner as in Example 1 except that 1.007 g (3.245 mmol) of 6FDA and 0.9547 g (3.245 mmol) of sBPDA were added instead of aODPA and BPAF. .. The obtained polyamide-imide solution was purified in the same manner as in Example 1 to obtain a polyamide-imide copolymer (PAI-10) of 8.0 g of solid content powder. The polystyrene-equivalent weight average molecular weight by GPC was 179,000.

[Comparative Example 7]
As the tetracarboxylic dianhydride, a polyamide-imide solution was obtained in the same manner as in Example 1 except that 1.007 g (3.245 mmol) of sODPA and 0.9547 g (3.245 mmol) of sBPDA were added instead of aODPA and BPAF. .. The obtained polyamide-imide solution was purified in the same manner as in Example 1 to obtain a polyamide-imide copolymer (PAI-11) of 8.3 g of solid content powder. The polystyrene-equivalent weight average molecular weight by GPC was 593,000.

[Comparative Example 8]
As the tetracarboxylic dianhydride, a polyamide-imide solution was obtained in the same manner as in Example 1 except that 0.9547 g (3.245 mmol) of aBPDA and 0.9547 g (3.245 mmol) of sBPDA were added instead of aODPA and BPAF. .. The obtained polyamide-imide solution was purified in the same manner as in Example 1 to obtain a polyamide-imide copolymer (PAI-12) of 7.9 g of solid content powder. The polystyrene-equivalent weight average molecular weight by GPC was 124,000.

[Comparative Example 9]
As the tetracarboxylic dianhydride, a polyamide-imide solution was obtained in the same manner as in Example 1 except that 0.9547 g (3.245 mmol) of aBPDA and 1.441 g (3.245 mmol) of 6FDA were added instead of aODPA and BPAF. .. The obtained polyamide imide solution was purified in the same manner as in Example 1 to obtain 8.1 g of solid content powder polyamide imide copolymer (PAI-13). The polystyrene-equivalent weight average molecular weight by GPC was 77,000.

[Comparative Example 10]
As the tetracarboxylic dianhydride, a polyamide-imide solution was obtained in the same manner as in Example 1 except that 1.488 g (3.245 mmol) of BPAF and 0.9547 g (3.245 mmol) of sBPDA were added instead of aODPA and BPAF. .. The obtained polyamide-imide solution was purified in the same manner as in Example 1 to obtain a polyamide-imide copolymer (PAI-14) of 8.4 g of solid content powder. The polystyrene-equivalent weight average molecular weight by GPC was 391,000.

[Comparative Example 11]
As the tetracarboxylic dianhydride, a polyamide-imide solution was obtained in the same manner as in Example 1 except that 1.488 g (3.245 mmol) of BPAF and 1.441 g (3.245 mmol) of 6FDA were added instead of aODPA and BPAF. .. The obtained polyamide-imide solution was purified in the same manner as in Example 1 to obtain a polyamide-imide copolymer (PAI-15) of 7.8 g of solid content powder. The polystyrene-equivalent weight average molecular weight by GPC was 429,000.

Table 1 shows the molar ratios of the components constituting each polyamide-imide copolymer obtained as described above.

<Making a film>
A resin varnish was prepared by dissolving 5.0 g of each polyamide-imide obtained as described above in 45 g of DMAc. Next, it was applied onto a glass plate using a table coater (AFA-standard manufactured by Cortec), and in an inert gas oven (INL-45N1 manufactured by Yamato Kagaku Co., Ltd.) at 70 ° C. for 1 hour, and then at 250 ° C. for 1 hour. A film was formed by drying and peeling from a glass plate. The film thickness of the obtained film is as shown in Table 1 below.
The following evaluation was performed using each of the obtained films as an evaluation sample.

<Measurement of total light transmittance and haze>
Each film was cut into a size of 30 mm × 30 mm, and the total light transmittance and haze were measured using a haze meter (NDH 7000 II, manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with ASTM D 1003. Each measured value was standardized by the film thickness (50 μm thickness). The measurement results are as shown in Table 1 below.

<YI value (yellow index) evaluation>
Cut each film to a size of 30 mm x 30 mm, obtain the YI value using a spectrocolorimeter (CM-5, manufactured by Konica Minolta Co., Ltd.) in accordance with ASTM E313, and obtain the YI value according to the following evaluation criteria. Was evaluated.
◯: YI value is less than 2 Δ: YI value is 2 or more and less than 3 ×: YI value is 3 or more The evaluation results are as shown in Table 1 below.

<Toughness evaluation>
Each film was cut to a predetermined size, and the elastic modulus, breaking point stress, and breaking point elongation were measured using a small tabletop tester (manufactured by Shimadzu Corporation, EZ-SX). The elastic modulus was obtained from the slope of the obtained stress-strain diagram when the stress was 5 MPa to 10 MPa. In addition, the fracture energy was calculated by obtaining the stress and strain product (that is, the area formed by the stress-strain curve) from the stress-strain curve. The toughness was evaluated according to the following evaluation criteria based on the breaking energy.
◯: Breaking energy is 0.6J or more Δ: Breaking energy is 0.4J or more and less than 0.6J ×: Breaking energy is less than 0.4J The evaluation results are as shown in Table 1 below.

<Film wettability>
The contact angle with water on the surface of each film in contact with the glass plate was measured using a contact angle meter (DM300) manufactured by KYOWA INTERFACE SCIENCE. Based on the measured contact angle, the wettability of the film was evaluated according to the following evaluation criteria.
◯: Water contact angle is 55 degrees or less Δ: Water contact angle is more than 55 degrees, 65 degrees or less ×: Water contact angle is more than 65 degrees The evaluation results are as shown in Table 1 below.

<Film adhesion>
A decorative coloring material is applied to the surface of each film in contact with the glass plate by screen printing so that the film thickness after drying is 2 to 3 μm, and the colored coating film is heated and dried at 80 ° C. for 30 minutes. Was formed, and an adhesion evaluation sample was obtained. The decorative coloring material was prepared as follows.
(Coloring material for decoration)
In a 500 ml separable flask equipped with a nitrogen introduction tube and a stirrer, 4.57 g of (2-phenyl-4-aminophenyl) -4-aminobenzoate (PHBAAB), 4,4'-diamino-3,3'-di 4.29 g of carboxydiphenylmethane (MBAA), 2,2'-bis [4- (3,4-dicarboxyphenoxy) propanoic acid dianhydride] (BPADA) 15.61 g, ethyl benzoate 94.64 g, pyridine 0. 47 g (6 mmol) and 10 g of toluene were added, and the mixture was reacted at 180 ° C. under a nitrogen atmosphere for 4 hours while removing toluene from the system to prepare a polyimide compound solution having a solid content of 20% by mass.
Next, 12.5 g of carbon black and 0.5 g of DBP (a phosphoric acid ester-based adhesion auxiliary agent manufactured by Johoku Chemical Industry Co., Ltd.) were mixed with 50 g of this solution, dispersed until uniform, and used for decoration. A coloring material was produced.

For each sample obtained as described above, the adhesion between the film and the colored coating film was evaluated in accordance with JIS K 5600-5-6 (ISO2409). Specifically, after using a single-edged blade to make 100-square grid-shaped cuts in the colored coating film at 1 mm intervals, affix "cellotape" (registered trademark), and then draw cellophane tape (registered trademark). The state of the peeled and colored coating film was visually confirmed, and evaluation was performed based on the evaluation criteria of JIS K 5600-5-6 (ISO2409) (6 grades of 0 to 5 in descending order of adhesion). The evaluation results are as shown in Table 1 below.

As is clear from the evaluation results in Table 1, a polyamide in which an imide structural unit (unit I-1) derived from aODPA and a specific imide structural unit (unit I-2) are used in combination as a tetracarboxylic acid diacid anhydride component. The imide copolymer (Examples 1 to 4) is derived from a polyamide-imide copolymer (Comparative Example 1) in which an imide structural unit (unit I-1) and another imide structural unit (sBPDA) are used in combination, or aODPA. It can be seen that all of the optical properties, mechanical properties, wettability, and adhesion are excellent with respect to the polyamide-imide copolymers having no structural unit (Comparative Examples 2 to 11).

Claims

A polyamide-imide copolymer containing an imide structural unit and an amide structural unit.
The imide structural unit is the imide structural unit I-1 represented by the following formula (1):

and,
At least one imide structural unit selected from the group consisting of the following formulas (2) to (5): I-2:

(In the formulas (1) to (5), X 1 to X 5 each independently represent a divalent organic group derived from a diamine.)
Including
The amide structural unit is represented by the following formula (6): amide structural unit A:

(In the formula, X 6 represents a divalent organic group derived from a diamine, and Y represents a divalent organic group derived from a dicarboxylic acid or a dicarboxylic acid derivative.)
A polyamide-imide copolymer comprising.
X 1 to X 6 are the following equations (7):

(In the formula, * is a binding group.)
The polyamide-imide copolymer according to claim 1.
Y is the following formula (8) to (10):

(In the formula, * is a binding group.)
The polyamide-imide copolymer according to claim 1 or 2, which is at least one selected from.
The polyamide-imide copolymer according to any one of claims 1 to 3, wherein the imide structural unit I-2 is represented by the formula (2).
The polyamide-imide copolymer according to any one of claims 1 to 4, wherein the imide structural unit and the amide structural unit are contained in a molar ratio of 2: 8 to 8: 2.
A film containing the polyamide-imide copolymer according to any one of claims 1 to 5.
The film according to claim 6, wherein the contact angle of water on the surface of a film having a thickness of 50 μm measured in accordance with JIS R3257: 1999 is 55 degrees or less.
The film according to claim 6 or 7, which is used as a cover window of a foldable device.