Resin composition, film, and display device

Abstract

To provide a resin composition for films that is capable of yielding a film with strong resilience.SOLUTION: A resin composition contains a heat-reactive crosslinking agent and one or more resins selected from polyamide-imide resins and polyamide resins.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a resin composition, a film, and a display device.

Background Art

[0002] Foldable devices have recently attracted attention in order to further enhance the portability of portable information terminals such as smartphones and tablets. Conventionally, glass has been used as a member such as a cover window used for a display constituting such a foldable device. However, since glass is a rigid material, films using polymers have been studied in terms of flexibility.

[0003] For example, in Patent Document 1, an aromatic polyamideimide film having a specific structural unit has been proposed. Further, in Patent Document 2, a polyimide film having a specific structural unit has been proposed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] Foldable devices are assumed to repeatedly fold the device or hold it in a folded state for a long time. For the polymer film used for the display, when such use is made, it is required that compression marks and bending marks (hereinafter, "folding marks") are unlikely to occur on the display surface of the device.

[0006] In this regard, the polyamideimide film of Patent Document 1 had room for improvement. On the other hand, the polyimide film of Patent Document 2 aims to improve the resilience against physical deformation caused by external forces, and for this purpose controls the resilience of the film, but it is made of expensive polyimide. Therefore, a film using a resin other than polyimide is required, which has a large resilience to suppress the occurrence of folding marks.

Means for Solving the Problems

[0007] The inventors of the present invention conducted studies on polyamide films and polyamideimide films, and found that by using a thermoreactive crosslinking agent in the formation of these films, it is possible to increase the resilience of the films, and thus completed the present invention.

[0008] The gist configuration of the present invention is as follows. [1] A resin composition containing at least one resin selected from a polyamideimide resin and a polyamide resin and a thermoreactive crosslinking agent. [2] The resin composition of [1], wherein the resin is a polyamideimide resin. [3] The resin composition of [1] or [2], wherein the thermoreactive crosslinking agent has a thermoreactive group selected from a methylol group, an alkoxymethyl group, a maleimide group, an epoxy group, an allyl group, and an alkoxysilyl group. [4] The resin composition according to any one of [1] to [3], wherein the thermoreactive crosslinking agent is 1 to 50 parts by mass with respect to 100 parts by mass of the resin. [5] A film formed using the resin composition according to any one of [1] to [4]. [6] The film of [5], wherein R according to the following formula (1) is 0.91 to 2.00 MPa. R = α·ε / 2 (1) In the formula, α is the yield strength (unit: MPa), and ε is the yield strain. [7] A display device including the film of [5].

Effects of the Invention

[0009] According to the resin composition of the present invention, a film with high resilience is provided, and it is expected that this film is less likely to have folding marks even when repeatedly folded or held in a folded state for a long time.

Brief Description of the Drawings

[0010]

Figure 1

Embodiments for Carrying Out the Invention

[0011] <Resin Composition> The resin composition of the present invention contains at least one resin selected from polyamide resins and polyamide-imide resins and a thermally reactive crosslinking agent.

[0012] [Polyamide-Imide Resin] A polyamide-imide resin can be used in the resin composition of the present invention. The polyamide-imide resin can be obtained by reacting diamine compounds, tetracarboxylic acid compounds, and dicarboxylic acid compounds, which are monomer components. Specifically, a polymer having an imide precursor structure is synthesized by reacting a diamine compound and a tetracarboxylic acid compound, and then a copolymer having an imide precursor structure and an amide structure is synthesized by reacting the polymer with a dicarboxylic acid compound. After that, a product obtained by subjecting the imide precursor structure in the copolymer to a ring-closing reaction (imidation) can be mentioned. Also, a polymer having an imide precursor structure may be synthesized by reacting a diamine compound and a tetracarboxylic acid compound, the imide precursor may be subjected to a ring-closing reaction, and then a copolymer having an imide structure and an amide structure may be synthesized by reacting with a dicarboxylic acid compound.

[0013] That is, the polyamideimide resin in the resin composition of the present invention can have a structure in which a residue obtained by reacting a diamine compound and a tetracarboxylic acid compound is bonded via an imide structure, and a residue obtained by reacting a dicarboxylic acid compound via an amide structure is bonded thereto. Among them, the polyamideimide resin preferably contains at least one structure selected from the group consisting of a structure in which residues obtained by reacting the diamine compound and the tetracarboxylic acid compound are linked by an alkylene group which may be substituted with a fluorine atom, an aliphatic ring, and aromatic rings with a sulfonyl group or a fluorine atom.

[0014] Examples of the diamine compound used for synthesizing the polyamideimide resin in the resin composition of the present invention include aliphatic diamines, aromatic diamines, and mixtures thereof. Here, the "aromatic diamine" represents a diamine in which an amino group is directly bonded to an aromatic ring, and may contain an aliphatic group or other substituents in a part of its structure. This aromatic ring may be a monocyclic ring or a condensed ring, and examples thereof include a benzene ring, a naphthalene ring, an anthracene ring, and a fluorene ring, but are not limited thereto. Among these, a benzene ring is preferable. The "aliphatic diamine" represents a diamine in which an amino group is directly bonded to an aliphatic group, and may contain an aromatic ring or other substituents in a part of its structure. The diamine compound can be used alone or in combination of two or more.

[0015] Specific examples of the aliphatic diamine include acyclic aliphatic diamines such as hexamethylenediamine; and cyclic aliphatic diamines such as 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, norbornanediamine, and 4,4'-diaminodicyclohexylmethane. These can be used alone or in combination of two or more.

[0016] Specific examples of the aromatic diamine include aromatic diamines having one aromatic ring, such as p-phenylenediamine, m-phenylenediamine, 2,4-toluenediamine, m-xylylenediamine, p-xylylenediamine, 1,5-diaminonaphthalene, 2,6-diaminonaphthalene; 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 (TFMB), 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)fluorene, 9,9-bis(4-amino-3-fluorophenyl)fluorene, etc., which are aromatic diamines having two or more aromatic rings. These can be used alone or in combination of two or more kinds.

[0017] Among the above diamine compounds, from the viewpoint of improving the colorless transparency and elasticity as a film, one or more selected from the group consisting of aromatic diamines having a biphenyl structure, specifically, one or more selected from the group consisting of 2,2'-dimethylbenzidine, 2,2'-bis(trifluoromethyl)benzidine, 4,4'-bis(4-aminophenoxy)biphenyl, and 4,4'-diaminodiphenyl ether are preferably used. Further, from the viewpoint of easily improving the colorless transparency, a diamine having a biphenyl structure and having a part or all of the hydrogen atoms on the aromatic ring substituted with a substituent selected from a fluoro group, a trifluoromethyl group, or a trifluoromethoxy group, specifically, 2,2'-bis(trifluoromethyl)benzidine is more preferably used.

[0018] Examples of the tetracarboxylic acid compound used for synthesizing the polyamideimide resin in the resin composition of the present invention include tetracarboxylic acids or tetracarboxylic acid derivatives. Tetracarboxylic acid derivatives include anhydrides of tetracarboxylic acids, preferably dianhydrides, acid chlorides, and the like. Examples of the tetracarboxylic acid compound include aromatic tetracarboxylic acids and their anhydrides, preferably aromatic tetracarboxylic acid compounds such as their dianhydrides; aliphatic tetracarboxylic acid compounds and their anhydrides, preferably aliphatic tetracarboxylic acid compounds such as their dianhydrides. These tetracarboxylic acid compounds can be used alone or in combination of two or more.

[0019] Specific examples of the aromatic tetracarboxylic dianhydride include non-condensed polycyclic aromatic tetracarboxylic dianhydrides, monocyclic aromatic tetracarboxylic dianhydrides, and condensed polycyclic aromatic tetracarboxylic dianhydrides. Examples of non-condensed polycyclic aromatic tetracarboxylic dianhydrides include 4,4'-oxydiphthalic dianhydride (sODPA), 3,4-oxydiphthalic dianhydride (aODPA), 4,4'-(4,4'-isopropylidenediphenoxy)diphthalic dianhydride (BPADA), 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 2,2',3,3'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride (sBPDA), 2,2',3,3'-biphenyltetracarboxylic dianhydride (aBPDA), 3,3',4,4'-diphenylsulfone tetracarboxylic 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, 4,4'-(hexafluoroisopropylidene)diphthalic dianhydride (6FDA), 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, bis(3,4-dicarboxyphenyl)methane dianhydride, bis(2,3-dicarboxyphenyl)methane dianhydride, 4,4'-(p-phenylenedioxy)diphthalic dianhydride, 4,4'-(m-phenylenedioxy)diphthalic dianhydride, and 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride (BPAF). Examples of monocyclic aromatic tetracarboxylic dianhydrides include 1,2,4,5-benzenetetracarboxylic dianhydride, and examples of condensed polycyclic aromatic tetracarboxylic dianhydrides include 2,3,6,7-naphthalenetetracarboxylic dianhydride.

[0020] Examples of the aliphatic tetracarboxylic dianhydride include cyclic or acyclic aliphatic tetracarboxylic dianhydrides. The cyclic aliphatic tetracarboxylic dianhydride is a tetracarboxylic dianhydride having an alicyclic hydrocarbon structure. Specific examples thereof include cycloalkane tetracarboxylic dianhydrides such as 1,2,4,5-cyclohexane tetracarboxylic dianhydride (HPMDA), 1,2,3,4-cyclobutane tetracarboxylic dianhydride (CBDA), and 1,2,3,4-cyclopentane tetracarboxylic dianhydride; bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride; dicyclohexyl-3,3’,4,4’-tetracarboxylic 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 dianhydride include 1,2,3,4-butane tetracarboxylic dianhydride and 1,2,3,4-pentane tetracarboxylic dianhydride. 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.

[0021] Among tetracarboxylic acid compounds, from the viewpoint of improving the flexural resistance and optical properties as a film, an aromatic tetracarboxylic dianhydride having a substituent selected from a fluoro group, a trifluoromethyl group, or a trifluoromethoxy group, specifically, 4,4'-(hexafluoroisopropylidene)diphthalic dianhydride (6FDA), and a tetracarboxylic dianhydride having a biphenyl structure, a fluorene structure, or an alicyclic hydrocarbon structure, specifically, 3,3',4,4'-biphenyltetracarboxylic dianhydride (sBPDA), 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride (BPAF), 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA), dicyclohexyl-3,3',4,4'-tetracarboxylic dianhydride (HBPDA) are preferably used in combination as one selected from the group consisting of them, and the composition ratio (any one of 6FDA:sBPDA, BPAF, CBDA, HBPDA) of 4,4'-(hexafluoroisopropylidene)diphthalic dianhydride and one selected from the group consisting of 1,2,3,4-cyclobutanetetracarboxylic dianhydride and dicyclohexyl-3,3',4,4'-tetracarboxylic dianhydride is more preferably 1:2 as a molar ratio.

[0022] Among tetracarboxylic acid compounds, from the viewpoint of improving transparency and adhesion without impairing various properties such as heat resistance and mechanical strength as a film, 3,4-oxydiphthalic dianhydride (aODPA) and at least one selected from the group consisting of 4,4'-oxydiphthalic dianhydride (sODPA), 2,2',3,3'-biphenyltetracarboxylic dianhydride (aBPDA), 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride (BPAF), and 4,4'-(hexafluoroisopropylidene)diphthalic dianhydride (6FDA) are preferably used in combination.

[0023] As the dicarboxylic acid compound used for synthesizing the polyamideimide resin in the resin composition of the present invention, there are dicarboxylic acids or dicarboxylic acid derivatives. Examples of the dicarboxylic acid derivatives include acid chlorides and ester forms of the dicarboxylic acids. The dicarboxylic acid compound can be used alone or in combination of two or more.

[0024] Specific examples of the dicarboxylic acid compound include, for example, 1,3-cyclobutanedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 4,4'-oxybisbenzoic acid, terephthalic acid, 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 benzoic acids linked by a single bond, -CH 2 -, -C(CH 3 ) 2 -, -C(CF 3 ) 2 -, -SO 2 - or alicyclic dicarboxylic acids or aromatic dicarboxylic acids such as compounds linked by a phenylene group and their derivatives (for example, acid chlorides, acid anhydrides); aliphatic dicarboxylic acids such as dicarboxylic acid compounds of chain hydrocarbons having 8 or less carbon atoms and their derivatives (for example, acid chlorides, ester forms), etc. These dicarboxylic acid compounds can be used alone or in combination of two or more.

[0025] Among these, from the viewpoint of improving the elongation at break and elastic modulus as a film, it is preferable to use terephthalic acid or 4,4'-oxybisbenzoic acid or its derivatives, particularly, terephthalic acid chloride (sometimes denoted as TPC) or 4,4'-oxybis(benzoyl chloride) (4,4'-diphenyl ether dicarboxylic acid chloride, sometimes denoted as DEDC).

[0026] In the synthesis of the polyamide-imide resin of the resin composition of the present invention, with respect to a total of 100 mol% of the tetracarboxylic acid compound and the dicarboxylic acid compound, the dicarboxylic acid compound may be more than 0 mol% and less than 100%, but from the viewpoint of being excellent in the effect of improving the resilience of the film by blending an amide structure and a thermally reactive crosslinking agent, 10 mol% or more is preferable, 20 mol% or more is more preferable, and 40 mol% or more is even more preferable. And the composition ratio of this monomer component is such that in the repeating unit in the polyamide-imide resin, the amide structure is more than 0 mol%, preferably 10 mol% or more, more preferably 20 mol% or more, and even more preferably 40 mol% or more. From the viewpoint of sufficiently obtaining the effect of introducing the imide structure, the amide structure is preferably 90 mol% or less, more preferably 80 mol% or less.

[0027] For example, the composition ratio of the monomer components (diamine compound:tetracarboxylic acid compound:dicarboxylic acid compound) can be 7:0.5 to 4:3 to 6.5 as a molar ratio, preferably 7:1.5 to 3.5:3.5 to 5.5, and more preferably 7:2.5 to 3.5:3.5 to 4.5. And according to the composition ratio of the monomer components described above, the composition ratio (molar ratio) of the imide structure and the amide structure in the structure of the polyamide-imide resin can be 0.5 to 4:3 to 6.5, preferably 1.5 to 3.5:3.5 to 5.5, and more preferably 2.5 to 3.5:3.5 to 4.5. By having the composition ratio of the imide structure and the amide structure be the above-described composition ratio, excellent flexibility and high elasticity can be achieved in good balance.

[0028] For the ring-closing reaction (imidation) of the imide precursor in the synthesis of the polyamide-imide resin, either thermal imidization by adding an azeotropic solvent (for example, toluene, xylene, etc.) that azeotropes with water and heating, or chemical imidization using a condensing agent and a reaction accelerator can be used, but chemical imidization is preferable because colorless transparency is easily maintained.

[0029] Examples of the reaction accelerator used for chemical imidization include triethylamine, diisopropylethylamine, N-methylpiperidine, pyridine, 2-methylpyridine, 3-methylpyridine, 4-methylpyridine, 3-ethylpyridine, 3,5-dimethylpyridine, 3,5-diethylpyridine, isoquinoline, imidazole, 1-methylimidazole, 2-methylimidazole, and 1,2-dimethylimidazole. These reaction accelerators may be used alone or in combination of two or more.

[0030] Examples of the condensing agent used for chemical imidization include acid anhydrides such as acetic anhydride, propionic anhydride, and trifluoroacetic anhydride, phosphite esters, and phosphite esters such as triethyl phosphite, triethyl phosphite, tributyl phosphite, dimethyl phosphite, diethyl phosphite, and triphenyl phosphite. These condensing agents may be used alone or in combination of two or more.

[0031] The organic solvent used for the synthesis of the polyamideimide resin is not particularly limited as long as it is an organic solvent 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, etc. may be mentioned. These organic solvents may be used alone or in combination of two or more.

[0032] The ring-closing reaction conditions for the synthesis of the polyamideimide resin in the resin composition of the present invention can be 1 to 27 hours at 10 to 50°C, and from the viewpoint of maintaining colorless transparency, it is preferably synthesized under a nitrogen atmosphere.

[0033] The weight average molecular weight (Mw) of the polyamideimide resin in the resin composition of the present invention is preferably in the range of 50,000 to 1,000,000, more preferably in the range of 80,000 to 800,000, and even more preferably in the range of 110,000 to 600,000 from the viewpoint of improving the elastic modulus and elongation at break. In this specification, the weight average molecular weight (Mw) is a value measured by GPC (gel permeation chromatography) and calculated in terms of polystyrene, and specifically, it is measured by the method described in the examples.

[0034] [Polyamide resin] A polyamide resin can be used in the resin composition of the present invention. The polyamide resin in the resin composition of the present invention can be obtained by reacting a diamine compound and a dicarboxylic acid compound which are monomer components. The dicarboxylic acid compound is a dicarboxylic acid and its derivatives (such as acid chloride, ester, etc.).

[0035] That is, the polyamide resin in the resin composition of the present invention can have an amide structure formed by the reaction of a diamine compound and a dicarboxylic acid compound. The repeating unit constituting the polyamide resin is different from the polyamideimide resin in that it does not substantially contain an imide structure. Further, as the structure bonding the monomer components constituting the polyamide resin, it is more preferable that it substantially does not contain a repeating structure other than the amide structure and consists of an amide structure.

[0036] Here, regarding the diamine compound, the description (including examples and preferred examples) regarding the diamine compound described in the section of the above polyimideamide resin is applicable. Regarding the dicarboxylic acid compound, the description (including examples and preferred examples) regarding the dicarboxylic acid compound described in the section of the above polyimideamide resin is applicable.

[0037] Among the above diamine compounds, from the viewpoint of improving the colorless transparency and elasticity as a film, one or more selected from the group consisting of aromatic diamines having a biphenyl structure, specifically, one or more selected from the group consisting of 2,2'-dimethylbenzidine, 2,2'-bis(trifluoromethyl)benzidine, 4,4'-bis(4-aminophenoxy)biphenyl, and 4,4'-diaminodiphenyl ether are preferably used. Further, from the viewpoint of being more likely to improve the colorless transparency, a diamine having a biphenyl structure and having a part or all of the hydrogen atoms on the aromatic ring substituted with a substituent selected from a fluoro group, a trifluoromethyl group, or a trifluoromethoxy group, specifically, 2,2'-bis(trifluoromethyl)benzidine is more preferably used.

[0038] Among the above dicarboxylic acid compounds, from the viewpoint of improving the elongation at break and elastic modulus as a film, terephthalic acid or 4,4'-oxybisbenzoic acid or a derivative thereof, particularly, terephthaloyl chloride (sometimes abbreviated as TPC) or 4,4'-oxybis(benzoyl chloride) (4,4'-diphenyl ether dicarboxylic acid chloride, sometimes abbreviated as DEDC) is preferably used. It is also preferable to use TPC and DEDC in combination. In that case, the molar ratio (the number of moles of TPC: the number of moles of DEDC) can be 1:4 to 4:1, preferably 2:3 to 4:1. With these molar ratios, substantially, the structural unit derived from TPC and the structural unit derived from DEDC will be introduced into the polyamide resin.

[0039] The polyamide resin can be produced by a method known as a method for producing polyamide. For example, a solution polymerization method, an interfacial polymerization method, a melt polymerization method, a solid-phase polymerization method, etc. can be used. In particular, as a method for producing an aromatic polyamide, a solution polymerization method and an interfacial polymerization method can be preferably used.

[0040] Specifically, a polyamide resin can be synthesized from a dicarboxylic acid chloride and a diamine compound by a solution polymerization method. In this case, the reaction can be carried out in an aprotic organic polar solvent.

[0041] In this reaction, hydrogen chloride is by-produced. When neutralizing this, inorganic neutralizing agents such as calcium hydroxide, calcium carbonate, and lithium carbonate, and organic neutralizing agents such as 1,2-butylene oxide, ethylene oxide, propylene oxide, ammonia, and pyridine are used.

[0042] When polymerization is carried out using two or more kinds of diamine compounds, the diamine compounds are added one by one, 10 to 99 mol% of dicarboxylic acid dichloride is added to the diamine compound and reacted, and then another diamine compound is added, and further dicarboxylic acid dichloride is added and reacted in a stepwise reaction method. Also, a method in which all diamine compounds are mixed and added, and then dicarboxylic acid dichloride is added and reacted can be used. Further, when using two or more kinds of dicarboxylic acid dichloride, similarly, a stepwise method, a method of adding simultaneously, etc. can be used. The molar ratio of all diamine compounds to all dicarboxylic acid dichloride (the number of moles of all diamine compounds: the number of moles of all dicarboxylic acid dichloride) can be appropriately adjusted according to the molecular weight of the target polyamide. For example, by setting it to 49:51 to 51:49, a polyamide with a sufficiently large molecular weight and excellent mechanical properties can be obtained.

[0043] When a diamine compound and a dicarboxylic acid dichloride are used as raw materials, it becomes an amine terminal or a carboxylic acid terminal depending on the composition ratio of the raw materials. From the viewpoint of improving the colorless transparency of the film, it is preferable to perform end capping with other amines, carboxylic acid chlorides, and carboxylic acid anhydrides.

[0044] Examples of the compound used for end capping include acetyl chloride, benzoyl chloride, substituted benzoyl chloride, acetic anhydride, 5-norbornene-2,3-dicarboxylic anhydride, 4-ethynylaniline, 4-phenylethynylphthalic anhydride, maleic anhydride, etc. End capping may not be performed, and in this case, the end group can also be used as a crosslinking point or the like.

[0045] In the production of polyamide resins, examples of the aprotic polar solvents to be used include sulfoxide solvents such as dimethyl sulfoxide and diethyl sulfoxide, formamide solvents such as N,N-dimethylformamide and N,N-diethylformamide, acetamide solvents such as N,N-dimethylacetamide and N,N-diethylacetamide, pyrrolidone solvents such as N-methyl-2-pyrrolidone and N-vinyl-2-pyrrolidone, or hexamethylphosphoramide, γ-butyrolactone, etc. It is desirable to use these alone or as a mixture, but furthermore, the use of aromatic hydrocarbons such as xylene and toluene is also possible. Furthermore, for the purpose of promoting the dissolution of the polymer, salts of alkali metals or alkaline earth metals at 50% by mass or less can be added to the solvent.

[0046] The reaction conditions for the synthesis of the polyamide resin can be 10 to 50°C for 10 minutes to 27 hours, and from the viewpoint of maintaining colorless transparency, it is preferably synthesized under a nitrogen atmosphere.

[0047] From the viewpoint of improving mechanical properties, the polyamide resin of the present invention preferably has a number average molecular weight (Mn) of 5,000 or more and 200,000 or less, and more preferably 10,000 or more and 180,000 or less.

[0048] From the viewpoint of improving mechanical properties, the polyamide resin of the present invention preferably has a weight average molecular weight (Mw) of 10,000 or more and 1,000,000 or less, more preferably 50,000 or more and 500,000 or less, and even more preferably 100,000 or more and 300,000 or less.

[0049] From the viewpoint of improving mechanical properties, the polyamide resin of the present invention preferably has a dispersity (Mw / Mn) of 1.0 or more and 20 or less, more preferably 1.0 or more and 15 or less, and even more preferably 1.0 or more and 4.0 or less.

[0050] The resin in the resin composition of the present invention may be at least one selected from polyamide resins and polyamide-imide resins, and may be only a polyamide resin, only a polyamide-imide resin, or a combination of a polyamide resin and a polyamide-imide resin. The polyamide resin and the polyamide-imide resin can be used alone or in combination of two or more.

[0051] The resin in the resin composition of the present invention preferably has substantially no hydroxyl group and carboxyl group. When the resin has a hydroxyl group or a carboxyl group, the crosslinking density may increase significantly due to the crosslinking of the thermoreactive crosslinking agent described later with the resin, and the flexibility of the resin may decrease significantly. By substantially having no hydroxyl group and carboxyl group in the resin, the resilience can be increased while maintaining the flexibility of the resin.

[0052] [Thermoreactive crosslinking agent] The film composition of the present invention contains a thermoreactive crosslinking agent. The thermoreactive crosslinking agent is not particularly limited as long as it is a compound containing two or more thermoreactive functional groups. The thermoreactive crosslinking agent preferably contains 2 to 10 thermoreactive functional groups, more preferably 2 to 6 thermoreactive functional groups. The two or more thermoreactive functional groups contained in the thermoreactive crosslinking agent may be the same or different, and are preferably the same.

[0053] Examples of the thermoreactive functional group include a methylol group, an alkoxymethyl group, a maleimide group, an epoxy group, an allyl group, an alkoxysilyl group, an isocyanate group, a cyanate group, an alkoxy group, an oxazoline group, an amino group, a benzoxazine group, a carbodiimide group, etc. Among them, a methylol group, an alkoxymethyl group, a maleimide group, an epoxy group, an allyl group, an alkoxysilyl group are preferable. The number of carbon atoms in the alkoxy moiety of the alkoxymethyl group is preferably 1 to 6, and particularly preferably 1 or 2 carbon atoms. The alkoxysilyl group may be any of mono-, di-, and trialkoxysilyl groups. The number of carbon atoms in the alkoxy moiety of the alkoxysilyl group is preferably 1 to 6, and particularly preferably 1 or 2 carbon atoms.

[0054] Examples of the thermosetting crosslinking agent containing a methylol group or an alkoxymethyl group include crosslinking agents having a melamine skeleton, crosslinking agents having a guanamine skeleton, and crosslinking agents having a glycoluril skeleton. These types of crosslinking agents containing two or more methylol groups or methoxymethyl groups are preferred. Specifically, hexamethylol melamine, tetramethylol benzoguanamine, 1,3,4,6-tetramethylol glycoluril, hexamethoxymethyl melamine, tetramethoxymethyl benzoguanamine, 1,3,4,6-tetrakis(methoxymethyl) glycoluril, 1,3,4,6-tetrakis(butoxymethyl) glycoluril, etc. may be mentioned. These may be in the form of oligomers.

[0055] Examples of the thermosetting crosslinking agent containing a maleimide group include, for example, compounds having two or more maleimide groups. Specifically, 4,4'-diphenylmethane bismaleimide, bis-(3-ethyl-5-methyl-4-maleimidophenyl)methane, 2,2-bis-[4-(4-maleimidophenoxy)phenyl]propane, etc. may be mentioned.

[0056] Examples of the thermosetting crosslinking agent containing an epoxy group include, for example, compounds having two or more epoxy groups. Specifically, bisphenol type epoxy resins such as bisphenol A type epoxy resin and bisphenol F type epoxy resin may be mentioned. Modified bisphenol type epoxy resins can also be used. For example, bisphenol type epoxy resins having an ether bond may be mentioned. Specifically, bisphenol type epoxy resins into which a polyoxyalkylene structure has been introduced, etc. may be mentioned. The thermoreactive crosslinking agent containing an epoxy group may be a dicyclopentadiene aralkyl type epoxy resin such as a naphthalene type epoxy resin, a polyfunctional epoxy resin containing a naphthalene skeleton, a polyfunctional epoxy resin containing a dicyclopentadiene skeleton; a biphenyl aralkyl type epoxy resin such as a polyfunctional epoxy resin containing a biphenyl skeleton; a biphenyl aralkyl type epoxy resin such as a polyfunctional epoxy resin containing a biphenyl skeleton; a novolak type epoxy resin such as a phenol novolak type epoxy resin, a cresol novolak type epoxy resin; a glycidyl ether type epoxy resin; a glycidyl amine type epoxy resin; a glycidyl isocyanurate compound such as triglycidyl isocyanurate, diglycidyl monoallyl isocyanurate, etc.

[0057] Among the thermoreactive crosslinking agents having an epoxy group, a linear difunctional epoxy resin is preferable, and more preferably a bisphenol type epoxy resin and a modified bisphenol type epoxy resin, in view of having a flexible structure and being expected to improve the resilience of the film.

[0058] From the viewpoint of increasing the resilience while maintaining flexibility, the epoxy resin preferably has an epoxy equivalent (the mass of the epoxy resin containing 1 equivalent of epoxy groups) of 120 or more, more preferably 200 or more. Also, it is preferably 1,000 or less, preferably 700 or less, and more preferably 500 or less.

[0059] Examples of the crosslinking agent having an allyl group include diallyl phthalate (DAP), triallyl isocyanurate (TAIC), triallyl cyanurate (TAC), etc.

[0060] Examples of the crosslinking agent having an alkoxysilyl group include various coupling agents. It may have a combination of an alkoxysilyl group and a thermally reactive functional group other than an alkoxysilyl group (such as an epoxy group, an amino group, an allyl group, etc.). Specifically, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidyloxypropyltrimethoxysilane, 3-glycidyloxypropyltriethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, ureidopropyltriethoxysilane, vinyltriethoxysilane, vinyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-isocyanatopropyltriethoxysilane, methyltriethoxysilane, methyltrimethoxysilane, etc.

[0061] Among them, a crosslinking agent having an epoxy group is preferable, a crosslinking agent having two linear epoxy groups is more preferable, and a crosslinking agent having two linear epoxy groups with an epoxy equivalent of 200 or more and 500 or less is even more preferable.

[0062] The thermally reactive crosslinking agent may be used alone or in combination of two or more.

[0063] [Resin Composition] In the resin composition of the present invention, from the viewpoint of improving resilience, the thermally reactive crosslinking agent is preferably 1 part by mass or more, more preferably 3 parts by mass or more, based on 100 parts by mass of one or more resins selected from polyamideimide resins and polyamide resins. Also, from the viewpoint of obtaining a film excellent in flexibility, the thermally reactive crosslinking agent is preferably 50 parts by mass or less, more preferably 30 parts by mass or less.

[0064] In the resin composition of the present invention, one or more selected from polyamide resins and polyamide-imide resins and a thermoreactive crosslinking agent may be included, and arbitrary additives may also be included as long as the effects of the present invention are not impaired. Specifically, fillers (organic fillers, inorganic fillers), leveling agents, dispersants, surfactants, retardation adjusters, antioxidants, ultraviolet absorbers, light stabilizers, plasticizers, waxes, fillers, pigments, dyes, foaming agents, defoaming agents, dehydrating agents, antistatic agents, antibacterial agents, antifungal agents, bluing agents for reducing the yellowness of films, phosphorus compounds, lubricants, pH adjusters, etc. may be mentioned.

[0065] The resin composition of the present invention can be prepared by dissolving one or more selected from polyamide resins and polyamide-imide resins and a thermoreactive crosslinking agent in a solvent to obtain a resin composition (resin varnish). The solvent is not particularly limited as long as it can dissolve the above components, but from the viewpoints of the coatability of the resin varnish and the transparency of the obtained film, etc., a solvent containing one or more selected from the group consisting of an ester group, an ether group, a ketone group, a hydroxyl group, a sulfone group and a sulfinyl group is preferable.

[0066] Examples of the solvent having an ester group include ester solvents such as methyl acetate, ethyl acetate, butyl acetate, dimethyl carbonate, etc. Solvents having a cyclic ester group can also be used, and examples of lactone solvents include γ-butyrolactone (GBL), δ-valerolactone, ε-caprolactone, γ-crotonolactone, γ-hexanolactone, α-methyl-γ-butyrolactone, γ-valerolactone, α-acetyl-γ-butyrolactone, δ-hexanolactone, etc.

[0067] Examples of the solvent having an ether group include tetrahydrofuran, dioxane, dibutyl ether, etc. Examples of the solvent having a ketone group include ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, etc. Examples of the solvent having a hydroxyl group include phenolic solvents such as m-cresol, etc. Examples of the solvent having a sulfone group include methanesulfonic acid, dimethyl sulfone, ethyl phenyl sulfone, diethyl sulfone, diphenyl sulfone, sulfolane, bisphenol S, sorapsone, dapsone, bisphenol A polysulfone, sulfolane, and the like. Examples of the solvent having a sulfinyl group include sulfoxide solvents such as 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), etc. can be used.

[0068] The resin composition of the present invention has a wide range of uses as materials such as films, sheets, pipes, tubes, filaments, fibers, containers, etc. Among these, it is particularly suitable for use as a film material.

[0069] [Film] The film of the present invention is a film made using the resin composition of the present invention. For example, it can be obtained by turning the resin composition of the present invention into a resin varnish, coating it on a support, drying it, and then peeling it off from the support. It is presumed that the crosslinked structure by the thermally reactive crosslinking agent is formed by the heat during film production, improving the resilience of the film.

[0070] Resilience means the energy per unit volume that a substance can absorb without permanent deformation. The resilience of a film is related to the curve (stress-strain diagram) showing the relationship between the stress applied to the film and the strain of the film in the tensile test of the film, and corresponds to the area of the elastic deformation region hatched in the image diagram of FIG. 1. A high resilience means a high elastic recovery force, and it is expected that a film with high resilience can easily recover to its original state even when repeatedly folded or held in a folded state for a long time, and is less likely to have folding marks.

[0071] Resilience is determined as the area in the elastic deformation region as described above. By approximating the stress-strain diagram of the elastic deformation region as a triangle, an approximate value can be evaluated by R in the following formula (1). The R of the film of the present invention is preferably 0.91 MPa or more, and may be 2.00 MPa or less. R = α·ε / 2 (1) In the formula, α is the yield strength (unit: MPa), and ε is the yield strain. The yield strength is the stress at the yield point in the stress-strain diagram, and the yield strain is the strain at the yield point.

[0072] The yield strength and yield strain of the film can be measured by the method of the examples.

[0073] The yield strength of the film of the present invention is preferably 70 to 200 MPa, more preferably 100 to 180 MPa.

[0074] The yield strain of the film of the present invention is preferably 0.1 to 20%, more preferably 0.5 to 10%.

[0075] The film of the present invention preferably has a film thickness of 5 to 100 μm, more preferably 10 to 70 μm. Within this range, excellent flexibility can be easily obtained, and the film can be suitably used as a cover window for a foldable display or a flexible display.

[0076] The film of the present invention can be obtained by drying the coating film of the resin composition of the present invention. For example, the film of the present invention can be obtained by making the resin composition of the present invention into a resin varnish, coating it on a support, drying it, and then peeling it off from the support.

[0077] The coating method is not particularly limited, and known means can be applied. For example, dip coating method, flow coating method, roll coating method, bar coater method, blade coater method, screen printing method, curtain coating method, spray coating method, etc. can be mentioned. The coating thickness can be adjusted according to the film thickness.

[0078] The drying conditions are not particularly limited as long as the temperature allows the solvent to volatilize. However, from the viewpoint of obtaining a film with excellent transparency, it is preferably about 60 to 250 °C for 10 to 60 minutes.

[0079] [Display Device] The film of the present invention can be used as a member of a display device, and the present invention relates to a display device provided with the film of the present invention.

[0080] The film of the present invention can be suitably used as a cover window of a display device. For example, the film can be arranged and used so as to be located on the surface of various display devices. The method of arranging on the surface is not particularly limited, and for example, a method via an adhesive layer can be mentioned. As the material of the adhesive layer, known adhesive materials can be used. The cover window using the film of the present invention may be provided with a protective layer such as a hard coat layer or further an anti-fingerprint adhesion layer on the film surface.

[0081] The display device of the present invention may be of a flexible type or a non-flexible type. The flexible type includes a foldable type that can be folded, a type that can be rolled into a cylindrical shape, a rollable type, etc. Since the film of the present invention has high resilience, it is suitable for a flexible type display device, and particularly suitable for a foldable type display device.

[0082] The type of the display is not particularly limited, and examples thereof include a liquid crystal display device (LCD), an organic EL display, an inorganic EL display, a field emission display (FED), an electrophoretic display, and the like.

[0083] The device provided with the display device of the present invention is not particularly limited, and examples thereof include mobile terminals such as mobile phones, smartphones, and wristwatch-type terminals, personal computers, televisions, large screens, digital signage (electronic billboards and electronic bulletin boards), and the like.

[0084] The film of the present invention can also be applied to a TFT substrate for an organic EL display, a member for a touch panel, a flexible printed circuit board, a member for a solar cell panel such as a surface protection film and a substrate material, a member for an optical waveguide, and other semiconductor-related members.

Example

[0085] Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples. In the following, "parts" and "%" are based on mass unless otherwise specified.

[0086] <Measurement method> The physical properties of the polyamide resin and the polyamide film produced in the examples were measured as follows.

[0087] (1) Film thickness of the film The film thickness of the produced film was measured using a micrometer (manufactured by Mitutoyo Corporation).

[0088] (2) Yield strength and yield strain The fabricated film was cut into a predetermined size, and the yield strength and yield strain (ε) were measured using a small bench-top testing machine (EZ-SX manufactured by Shimadzu Corporation). The strain was determined by the following formula (2), and the elastic modulus was determined from the slope of the obtained stress-strain diagram when the stress was between 5 MPa and 10 MPa. The strain and stress at the 0.2% proof stress point on the stress-strain curve were defined as the yield strain and yield strength, respectively. The measurement was performed with n = 3, and the average value of the obtained measurement results is shown in Table 1. Strain = (L 1 - L 0 ) / L 0 (2) L 0 is the initial length of the film used for the measurement, and L 1 is the length of the film under a certain stress. [Test Conditions] Sample size: 100 mm × 10 mm Distance between grips: 50 mm Speed: 5 mm / min Number of measurements: 3 times

[0089] (3) Evaluation of resilience Resilience was evaluated by R in the following formula (1), R = α·ε / 2 (1) α and ε are the yield strength (unit: MPa) and yield strain obtained from the above measurement.

[0090] (4) Weight-average molecular weight (Mw) The weight-average molecular weight (Mw) is the polystyrene-equivalent amount determined by gel permeation chromatography (GPC) measurement. The conditions for GPC measurement are as follows. Apparatus: GL7700 manufactured by GL Sciences Column: TSKgel αM (manufactured by Tosoh Corporation) Column internal temperature: 40 °C Eluent composition: 100 mmol / L of H 3 PO 4 (H 3 PO 4 85% aqueous solution was used as a raw material) and an NMP solution containing 10 mmol / L of LiBr Eluent flow rate: 0.7 mL / min Standard reagent for calibration: Polystyrene Detector wavelength: 260 nm and 300 nm Detector temperature: Room temperature Baseline range during analysis: 15 min to 40 min Molecular weight calculation range during analysis: 20 - 35 min

[0091] <Manufacture of polyamideimide> A 100 mL reactor was filled with 60.0 g of N,N-dimethylacetamide (DMAc), and 4.849 g (15.14 mmol) of 2,2'-bis(trifluoromethyl)benzidine (TFMB) was added. Subsequently, 1.007 g (3.245 mmol) of 3,4-oxydiphthalic dianhydride (aODPA) and 1.4875 g (3.245 mmol) of 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride (BPAF) were added to this solution of TFMB, and the mixture was stirred at 30 °C for 2 hours to react, obtaining a solution containing a polymer having an imide precursor structure. Thereafter, 1.757 g (8.653 mmol) of terephthalic acid chloride (TPC) was added to this solution, and the mixture was stirred at 30 °C for 1.5 hours to react while maintaining the liquid temperature, obtaining a solution containing a copolymer having an imide precursor structure and an amide structure. Thereafter, 2.09 g of pyridine, 2.45 g of acetic anhydride, and 8.53 g of DMAc were added, and the mixture was stirred at 20 - 30 °C for 8 hours to obtain a polyamideimide solution. Further, 99 g of DMAc was added and stirred until homogeneous, then this solution was gradually added to a container containing 4 L of methanol to precipitate, and after the precipitated solid content was filtered and pulverized, it was dried under vacuum at 80 °C for 18 hours to obtain 8.2 g of a solid powder of polyamideimide resin (PAI). The weight average molecular weight in terms of polystyrene by GPC was 597,000.

[0092] <Fabrication of film> The powder of polyamide-imide resin (PAI) and a thermoreactive crosslinking agent were dissolved in a solvent (DMAc) at the compounding amounts (expressed in parts by mass) shown in Table 1, and after adjusting the solid content concentration to 13% by mass, they were dispersed and homogenized to prepare a resin composition for film production. Next, this resin composition was coated on a glass plate using an applicator so that the film thickness of the finally obtained film would be 50 μm using a table coater (AFA-standard manufactured by Coattech Co., Ltd.), and dried in a precision thermostat (Fine Oven DH612 manufactured by Yamato Scientific Co., Ltd.) at 120°C for 20 minutes and then at 220°C for 30 minutes, and the film was formed by peeling it from the glass plate. The evaluation of each obtained film is shown in Table 1.

[0093]

Table 1

[0094] <Thermoreactive crosslinking agent> · Niclac MW-390 manufactured by Sanwa Chemical Co., Ltd. TIFF2025087502000003.tif34154 · BMI-80 manufactured by K.I. Kasei Co., Ltd. TIFF2025087502000004.tif26154 · MA-DGIC manufactured by Shikoku Kasei Kogyo Co., Ltd. TIFF2025087502000005.tif41154 · DA-MGIC manufactured by Shikoku Kasei Kogyo Co., Ltd. TIFF2025087502000006.tif41154 · KBM-403 manufactured by Shin-Etsu Silicone Co., Ltd. TIFF2025087502000007.tif22154 · TEPIC-VL manufactured by Nissan Chemical Industries, Ltd. Epoxy equivalent: 125 - 145 g / eq TIFF2025087502000008.tif56159 · HP-4032D manufactured by DIC Corporation Naphthalene type epoxy equivalent: 136 - 148 g / eq · JER828 manufactured by Mitsubishi Chemical Corporation Bisphenol A type epoxy resin epoxy equivalent: 184 - 194 g / eq · EPICLON 860 manufactured by DIC Bisphenol A type epoxy resin, epoxy equivalent: 235 - 255 g / eq · HP-5000 manufactured by DIC Naphthalene skeleton modified polyfunctional type, epoxy equivalent: 245 - 260 g / eq · HP-7200 manufactured by DIC Dicyclopentadiene type, epoxy equivalent: 254 - 264 g / eq · EXA-4850-150 manufactured by DIC Epoxy equivalent: 410 - 470 g / eq · EXA-4816 manufactured by DIC Epoxy equivalent: 403 g / eq · JER1001 manufactured by Mitsubishi Chemical Corporation Bisphenol A type epoxy resin, epoxy equivalent 474 g / eq

[0095] As shown in Table 1, the films of the examples had greater resilience compared to the films of the comparative examples in which no thermoreactive crosslinking agent was blended.

Industrial Applicability

[0096] According to the resin composition for films of the present invention, a film with high resilience is provided. It is expected that this film is less likely to develop folding marks even when repeatedly folded or held in a folded state for a long time, and thus has high industrial utility.

Claims

1. A resin composition comprising one or more resins selected from a polyamide-imide resin and a polyamide resin and a thermally reactive crosslinking agent.

2. The resin composition according to Claim 1, wherein the resin is a polyamide-imide resin.

3. The resin composition according to Claim 1, wherein the thermally reactive crosslinking agent has a thermally reactive group selected from a methylol group, an alkoxymethyl group, a maleimide group, an epoxy group, an allyl group, and an alkoxysilyl group.

4. The resin composition according to Claim 1, wherein the thermally reactive crosslinking agent is 1 to 50 parts by mass with respect to 100 parts by mass of the resin.

5. A film obtained by using the resin composition according to any one of Claims 1 to 4.

6. The film according to Claim 5, wherein R according to the following formula (1) is 0.91 to 2.00 MPa. R = α·ε / 2 (1) In the formula, α is the yield strength (unit: MPa), and ε is the yield strain.

7. A display device including the film according to Claim 5.

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