Resin composition, film, and display device

Abstract

Provided is a resin composition for films that is capable of providing a film having strong resilience. The resin composition contains a heat-reactive crosslinking agent and one or more resins selected from polyamide-imide resins and polyamide resins.

Description

Resin composition, film and display device

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

[0002] Foldable devices have recently attracted attention as they further enhance the portability of mobile information terminals such as smartphones and tablets. Glass has traditionally been used as a material for the cover window and other components used in the displays that make up such foldable devices. However, glass is a rigid material, and polymer films have been considered for their flexibility.

[0003] For example, Patent Document 1 proposes an aromatic polyamideimide film having a specific structural unit, and Patent Document 2 proposes a polyimide film having a specific structural unit.

[0004] International Publication No. 2022 / 071443 Japanese Patent Application Laid-Open No. 2022-135876

[0005] Foldable devices are expected to be folded repeatedly and kept folded for long periods of time, and polymer films used in displays are required to be resistant to pressure marks and flex marks (hereinafter referred to as "fold marks") on the display surface of the device when used in this manner.

[0006] In this regard, the polyamide-imide film of Patent Document 1 leaves room for improvement. On the other hand, the polyimide film of Patent Document 2 aims to improve the restoring force against physical deformation due to external force and controls the resilience of the film, but is made of expensive polyimide. Therefore, there is a demand for a film that has high resilience and uses a resin other than polyimide so that the formation of folding marks can be suppressed.

[0007] The inventors of the present invention have conducted further research into polyamide films and polyamideimide films and have discovered that the use of a thermally reactive crosslinking agent in the molding of these films makes it possible to increase the resilience of the films, thereby completing the present invention.

[0008] The gist of the present invention is as follows: [1] A resin composition comprising one or more resins selected from polyamideimide resins and polyamide resins, and a thermally reactive 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 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 of any one of [1] to [3], wherein the thermally reactive crosslinking agent is contained in an amount of 1 to 50 parts by mass per 100 parts by mass of the resin. [5] A film obtained using any one of the resin compositions 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) where α is yield strength (unit: MPa) and ε is yield strain. [7] A display device comprising the film of [5].

[0009] The resin composition of the present invention provides a film with high resilience, and it is expected that this film will not easily develop folding marks even when repeatedly folded or kept in a folded state for a long period of time.

[0010] FIG. 1 is an image diagram of a curve showing the relationship between stress applied to a film and the strain of the film in response to this stress.

[0011] <Resin Composition> The resin composition of the present invention contains one or more resins selected from polyamide resins and polyamideimide 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 a diamine compound, a tetracarboxylic acid compound, and a dicarboxylic acid compound, which are monomer components. Specifically, a polyamide-imide resin can be obtained by reacting a diamine compound with a tetracarboxylic acid compound to synthesize a polymer having an imide precursor structure, then reacting the polymer with a dicarboxylic acid compound to synthesize a copolymer having an imide precursor structure and an amide structure, and then subjecting the imide precursor structure in the copolymer to a ring-closing reaction (imidization). Alternatively, a diamine compound can be reacted with a tetracarboxylic acid compound to synthesize a polymer having an imide precursor structure, and the imide precursor can be subjected to a ring-closing reaction, followed by reaction with a dicarboxylic acid compound to synthesize a copolymer having an imide structure and an amide structure.

[0013] That is, the polyamideimide resin in the resin composition of the present invention can have a structure in which a residue resulting from the reaction of a diamine compound with a tetracarboxylic acid compound is bonded via an imide structure to a structural unit in which a residue resulting from the reaction of a diamine compound with a tetracarboxylic acid compound is bonded via an amide structure. In particular, the polyamideimide resin preferably contains, as the residue resulting from the reaction of a diamine compound with a tetracarboxylic acid compound, at least one structure selected from the group consisting of fluorine atoms, aliphatic rings, and aromatic rings linked together by an alkylene group optionally substituted with a sulfonyl group or a fluorine atom.

[0014] Examples of diamine compounds used in the synthesis of the polyamideimide resin in the resin composition of the present invention include aliphatic diamines, aromatic diamines, and mixtures thereof. Here, "aromatic diamine" refers to a diamine in which an amino group is directly bonded to an aromatic ring, and may contain an aliphatic group or other substituent as part of its structure. This aromatic ring may be a single ring or a condensed ring, and examples 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 preferred. Furthermore, "aliphatic diamine" refers to a diamine in which an amino group is directly bonded to an aliphatic group, and may contain an aromatic ring or other substituent as part of its structure. The diamine compounds 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 aromatic diamines include aromatic diamines having one aromatic ring, such as p-phenylenediamine, m-phenylenediamine, 2,4-toluenediamine, m-xylylenediamine, p-xylylenediamine, 1,5-diaminonaphthalene, and 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, and bis(4-aminophenoxy)benzene. Examples of aromatic diamines include aromatic diamines having two or more aromatic rings, such as 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, and 9,9-bis(4-amino-3-fluorophenyl)fluorene. These may be used alone or in combination of two or more.

[0017] Among the above diamine compounds, from the viewpoint of improving the colorless transparency and elasticity of the film, it is preferable to use 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. Furthermore, from the viewpoint of easily improving the colorless transparency, it is more preferable to use a diamine having a biphenyl structure in which some or all of the hydrogen atoms on the aromatic ring are substituted with substituents selected from a fluoro group, a trifluoromethyl group, or a trifluoromethoxy group, specifically, 2,2'-bis(trifluoromethyl)benzidine.

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

[0019] Specific examples of the aromatic tetracarboxylic acid dianhydride include non-condensed polycyclic aromatic tetracarboxylic acid dianhydrides, monocyclic aromatic tetracarboxylic acid dianhydrides, and condensed polycyclic aromatic tetracarboxylic acid 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'-biphenyl tetracarboxylic dianhydride (sBPDA), 2,2',3,3'-biphenyl tetracarboxylic 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, and 2,2 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). Furthermore, examples of the monocyclic aromatic tetracarboxylic dianhydrides include 1,2,4,5-benzenetetracarboxylic dianhydride, and examples of the condensed polycyclic aromatic tetracarboxylic dianhydride include 2,3,6,7-naphthalenetetracarboxylic dianhydride.

[0020] Examples of the aliphatic tetracarboxylic acid dianhydride include cyclic and acyclic aliphatic tetracarboxylic acid dianhydrides. The cyclic aliphatic tetracarboxylic acid dianhydride is a tetracarboxylic acid dianhydride having an alicyclic hydrocarbon structure, and specific examples thereof include cycloalkane tetracarboxylic acid dianhydrides such as 1,2,4,5-cyclohexane tetracarboxylic acid dianhydride (HPMDA), 1,2,3,4-cyclobutane tetracarboxylic acid dianhydride (CBDA), and 1,2,3,4-cyclopentane tetracarboxylic acid dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic acid dianhydride, dicyclohexyl-3,3',4,4'-tetracarboxylic acid dianhydride (HBPDA), and positional isomers thereof. 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-butanetetracarboxylic dianhydride and 1,2,3,4-pentanetetracarboxylic dianhydride, which can be used alone or in combination of two or more. Also, a cyclic aliphatic tetracarboxylic dianhydride and an acyclic aliphatic tetracarboxylic dianhydride can be used in combination.

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

[0022] Among tetracarboxylic acid compounds, from the viewpoint of improving transparency and adhesion without impairing various properties such as heat resistance and mechanical strength of the film, it is preferable to use a combination of 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).

[0023] The dicarboxylic acid compound used in the synthesis of the polyamide-imide resin in the resin composition of the present invention includes a dicarboxylic acid or a dicarboxylic acid derivative, and examples of the dicarboxylic acid derivative include an acid chloride or an ester of the dicarboxylic acid. The dicarboxylic acid compound can be used alone or in combination of two or more kinds.

[0024] Specific examples of the dicarboxylic acid compound include 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, and compounds in which two cyclohexanecarboxylic acids or two benzoic acids are bonded to a single bond, -CH ２ -, -C(CH ３ ) ２ -, -C(CF ３ ) ２ -, -SO ２ alicyclic dicarboxylic acids or aromatic dicarboxylic acids such as compounds linked by a phenylene group or a phenylene group, and derivatives thereof (e.g., acid chlorides, acid anhydrides); aliphatic dicarboxylic acids such as dicarboxylic acid compounds of chain hydrocarbons having 8 or less carbon atoms, and derivatives thereof (e.g., acid chlorides, esters). 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 the elastic modulus of the film, it is preferable to use terephthalic acid or 4,4'-oxybisbenzoic acid or a derivative thereof, in particular terephthalic acid chloride (sometimes referred to as TPC) or 4,4'-oxybis(benzoyl chloride) (4,4'-diphenyl ether dicarboxylic acid chloride, sometimes referred to as DEDC).

[0026] In the synthesis of the polyamideimide resin of the resin composition of the present invention, the dicarboxylic acid compound may be more than 0 mol% and less than 100 mol% relative to the total of 100 mol% of the tetracarboxylic acid compound and the dicarboxylic acid compound. From the viewpoint of obtaining the excellent effect of improving the resilience of the film by blending the amide structure and the thermally reactive crosslinking agent, the content is preferably 10 mol% or more, more preferably 20 mol% or more, and even more preferably 40 mol% or more. The constituent ratio of this monomer component is such that, among the repeating units in the polyamideimide 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 fully 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 molar ratio of the monomer components (diamine compound:tetracarboxylic acid compound:dicarboxylic acid compound) can be 7:0.5-4:3-6.5, preferably 7:1.5-3.5:3.5-5.5, and more preferably 7:2.5-3.5:3.5-4.5. According to the above-described ratios of the monomer components, the molar ratio of imide structures to amide structures in the polyamide-imide resin structure can be 0.5-4:3-6.5, preferably 1.5-3.5:3.5-5.5, and more preferably 2.5-3.5:3.5-4.5. By achieving the above-described ratio of imide structures to amide structures, excellent flexibility and high elasticity can be achieved in a well-balanced manner.

[0028] The ring-closing reaction (imidization) of the imide precursor in the synthesis of the polyamide-imide resin can be carried out by either thermal imidization, in which an azeotropic solvent (e.g., toluene, xylene, etc.) that forms an azeotrope with water is added and heated, or chemical imidization, in which a condensing agent and a reaction accelerator are used. Chemical imidization is preferred because it is easier to maintain colorless transparency.

[0029] Examples of reaction accelerators used in 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 can be used alone or in combination of two or more.

[0030] Condensing agents used in chemical imidization include acid anhydrides such as acetic anhydride, propionic anhydride, and trifluoroacetic anhydride, and phosphites such as triethyl phosphite, triethyl phosphite, tributyl phosphite, dimethyl phosphite, diethyl phosphite, and triphenyl phosphite. These condensing agents can be used alone or in combination of two or more.

[0031] The organic solvent used in the synthesis of polyamide-imide resin is not particularly limited as long as it is an organic solvent inert to the reaction. Examples include N,N-dimethylacetamide (DMAc), N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, dimethyl sulfoxide, m-cresol, γ-butyrolactone, cyclopentanone, cyclohexanone, tetrahydrofuran, etc. These organic solvents can be used alone or in combination of two or more.

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

[0033] From the viewpoint of improving the modulus of elasticity and elongation at break, 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. Note that, 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, is measured by the method described in the Examples.

[0034] [Polyamide Resin] The resin composition of the present invention can use a polyamide resin. 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 or a derivative thereof (e.g., an acid chloride, an ester, etc.).

[0035] That is, the polyamide resin in the resin composition of the present invention may have an amide structure formed by the reaction of a diamine compound with a dicarboxylic acid compound. The repeating units constituting the polyamide resin differ from the polyamideimide resin in that they do not substantially contain an imide structure. Furthermore, it is more preferable that the structure connecting the monomer components constituting the polyamide resin is substantially free of repeating structures other than the amide structure and is composed of an amide structure.

[0036] Here, the description of the diamine compound (including examples and preferred examples) described in the section on polyimideamide resins above applies to the diamine compound, and the description of the dicarboxylic acid compound (including examples and preferred examples) described in the section on polyimideamide resins above applies to the dicarboxylic acid compound.

[0037] Among the above diamine compounds, from the viewpoint of improving the colorless transparency and elasticity of the film, it is preferable to use 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. Furthermore, from the viewpoint of easily improving the colorless transparency, it is more preferable to use a diamine having a biphenyl structure in which some or all of the hydrogen atoms on the aromatic ring are substituted with substituents selected from a fluoro group, a trifluoromethyl group, or a trifluoromethoxy group, specifically, 2,2'-bis(trifluoromethyl)benzidine.

[0038] Among the above dicarboxylic acid compounds, from the viewpoint of improving the elongation at break and modulus of elasticity of the film, it is preferable to use terephthalic acid or 4,4'-oxybisbenzoic acid or a derivative thereof, in particular terephthalic acid chloride (sometimes referred to as TPC) or 4,4'-oxybis(benzoyl chloride) (4,4'-diphenyl ether dicarboxylic acid chloride, sometimes referred to as DEDC). It is also preferable to use TPC and DEDC in combination, in which case the molar ratio (moles of TPC:moles of DEDC) can be 1:4 to 4:1, preferably 2:3 to 4:1. At these molar ratios, structural units derived from TPC and structural units derived from DEDC are essentially introduced into the polyamide resin.

[0039] The polyamide resin can be produced by a known method for producing polyamides, such as a solution polymerization method, an interfacial polymerization method, a melt polymerization method, a solid-state polymerization method, etc. In particular, the solution polymerization method and the interfacial polymerization method are preferably used as methods for producing aromatic polyamides.

[0040] Specifically, polyamide resins can be synthesized from dicarboxylic acid chlorides and diamine compounds by solution polymerization, in which the reaction can be carried out in an aprotic organic polar solvent.

[0041] In this reaction, hydrogen chloride is produced as a by-product, and to neutralize this, an inorganic neutralizing agent such as calcium hydroxide, calcium carbonate, or lithium carbonate, or an organic neutralizing agent such as 1,2-butylene oxide, ethylene oxide, propylene oxide, ammonia, or pyridine, is used.

[0042] When two or more diamine compounds are used for polymerization, various methods can be used, such as adding one diamine compound at a time, adding 10 to 99 mol% of a dicarboxylic acid dichloride to the diamine compound, and then reacting the diamine compound with another diamine compound, followed by adding a dicarboxylic acid dichloride, followed by reacting the other diamine compound and the dicarboxylic acid dichloride. Alternatively, all diamine compounds can be mixed and added, followed by adding a dicarboxylic acid dichloride, followed by reacting the other diamine compounds. Similarly, when two or more dicarboxylic acid dichlorides are used, various methods, such as a stepwise method or simultaneous addition, can be used. The molar ratio of all diamine compounds to all dicarboxylic acid dichlorides (moles of all diamine compounds:moles of all dicarboxylic acid dichlorides) can be adjusted appropriately depending on the molecular weight of the desired polyamide. For example, a ratio of 49:51 to 51:49 can be used to obtain a polyamide with a sufficiently high molecular weight and excellent mechanical properties.

[0043] When a diamine compound and a dicarboxylic acid dichloride are used as raw materials, the end terminals are either amine or carboxylic acid 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, or carboxylic acid anhydrides.

[0044] Examples of compounds used for terminal blocking include acetyl chloride, benzoyl chloride, substituted benzoyl chloride, acetic anhydride, 5-norbornene-2,3-dicarboxylic anhydride, 4-ethynylaniline, 4-phenylethynylphthalic anhydride, maleic anhydride, etc. Terminal blocking may not be performed, in which case the terminal group can be used as a crosslinking point, etc.

[0045] Examples of aprotic polar solvents used in the production of polyamide resins 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, and hexamethylphosphoramide and γ-butyrolactone. These are preferably used alone or as a mixture, but aromatic hydrocarbons such as xylene and toluene can also be used. Furthermore, up to 50% by mass of an alkali metal or alkaline earth metal salt can be added to the solvent to promote dissolution of the polymer.

[0046] The reaction conditions for synthesizing the polyamide resin can be 10 to 50° C. and 10 minutes to 27 hours, and it is preferable to synthesize the polyamide resin under a nitrogen atmosphere in order to maintain colorless transparency.

[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] The polyamide resin of the present invention preferably has a polydispersity (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 polyamideimide resins, and may be a polyamide resin alone, a polyamideimide resin alone, or a combination of a polyamide resin and a polyamideimide resin. The polyamide resin and the polyamideimide resin may be used alone or in combination of two or more.

[0051] It is preferable that the resin in the resin composition of the present invention is substantially free of hydroxyl groups and carboxyl groups. If the resin has hydroxyl groups or carboxyl groups, the crosslinking density may increase significantly due to crosslinking between the resin and the thermally reactive crosslinking agent described below, which may significantly reduce the flexibility of the resin. By having the resin be substantially free of hydroxyl groups and carboxyl groups, the resilience of the resin can be increased while maintaining its flexibility.

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

[0053] Examples of the thermally reactive 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, and a carbodiimide group, and among these, a methylol group, an alkoxymethyl group, a maleimide group, an epoxy group, an allyl group, and an alkoxysilyl group are preferred. The alkoxy moiety in the alkoxymethyl group preferably has 1 to 6 carbon atoms, and particularly preferably has 1 or 2 carbon atoms. The alkoxysilyl group may be a mono-, di-, or trialkoxysilyl group. The alkoxy moiety in the alkoxysilyl group preferably has 1 to 6 carbon atoms, and particularly preferably has 1 or 2 carbon atoms.

[0054] Examples of thermally reactive crosslinking agents 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. Specific examples include hexamethylolmelamine, tetramethylolbenzoguanamine, 1,3,4,6-tetramethylolglycoluril, hexamethoxymethylmelamine, tetramethoxymethylbenzoguanamine, 1,3,4,6-tetrakis(methoxymethyl)glycoluril, and 1,3,4,6-tetrakis(butoxymethyl)glycoluril. These may be in the form of oligomers.

[0055] Examples of thermally reactive crosslinking agents containing maleimide groups include compounds having two or more maleimide groups, such as 4,4'-diphenylmethane bismaleimide, bis-(3-ethyl-5-methyl-4-maleimidophenyl)methane, and 2,2-bis-[4-(4-maleimidophenoxy)phenyl]propane.

[0056] Examples of the thermally reactive crosslinking agent containing an epoxy group include compounds having two or more epoxy groups. Specific examples include bisphenol-type epoxy resins such as bisphenol A-type epoxy resins and bisphenol F-type epoxy resins. Modified bisphenol-type epoxy resins can also be used, such as bisphenol-type epoxy resins having an ether bond, and specific examples include bisphenol-type epoxy resins into which a polyoxyalkylene structure has been introduced. The thermally reactive crosslinking agent containing an epoxy group may be a dicyclopentadiene aralkyl type epoxy resin such as a naphthalene type epoxy resin, a naphthalene skeleton-containing polyfunctional epoxy resin, or a dicyclopentadiene skeleton-containing polyfunctional epoxy resin; a biphenyl aralkyl type epoxy resin such as a biphenyl skeleton-containing polyfunctional epoxy resin; a biphenyl aralkyl type epoxy resin such as a biphenyl skeleton-containing polyfunctional epoxy resin; a novolac type epoxy resin such as a phenol novolac type epoxy resin or a cresol novolac type epoxy resin; a glycidyl ether type epoxy resin; a glycidyl amine type epoxy resin; or a glycidyl isocyanurate compound such as triglycidyl isocyanurate or diglycidyl monoallyl isocyanurate.

[0057] Among the thermally reactive crosslinking agents having an epoxy group, linear bifunctional epoxy resins are preferred, and bisphenol-type epoxy resins and modified bisphenol-type epoxy resins are more preferred, as they have a flexible structure and are expected to improve the resilience of the film.

[0058] In order to increase resilience while maintaining flexibility, the epoxy resin preferably has an epoxy equivalent (mass of the epoxy resin containing one equivalent of epoxy groups) of 120 or more, more preferably 200 or more, and is preferably 1,000 or less, preferably 700 or less, more preferably 500 or less.

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

[0060] Examples of crosslinking agents having an alkoxysilyl group include various coupling agents. They may also 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, or an allyl group). Specific examples include 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, and methyltrimethoxysilane.

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

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

[0063] [Resin Composition] In the resin composition of the present invention, the thermally reactive crosslinking agent is preferably 1 part by mass or more, more preferably 3 parts by mass or more, relative to 100 parts by mass of one or more resins selected from polyamideimide resins and polyamide resins in order to improve resilience. Furthermore, in order to obtain a film with excellent flexibility, the thermally reactive crosslinking agent is preferably 50 parts by mass or less, more preferably 30 parts by mass or less.

[0064] The resin composition of the present invention may contain any additives in addition to one or more selected from polyamide resins and polyamideimide resins and a thermally reactive crosslinking agent, provided that the effects of the present invention are not impaired. Specific examples of such additives include fillers (organic fillers, inorganic fillers), leveling agents, dispersants, surfactants, retardation adjusters, antioxidants, ultraviolet inhibitors, light stabilizers, plasticizers, waxes, bulking agents, pigments, dyes, foaming agents, antifoaming agents, dehydrating agents, antistatic agents, antibacterial agents, antifungal agents, bluing agents for reducing the yellowness of the film, phosphorus compounds, lubricants, and pH adjusters.

[0065] The resin composition of the present invention can be prepared as a resin composition (resin varnish) by dissolving one or more resins selected from polyamide resins and polyamideimide resins and a thermally reactive crosslinking agent in a solvent. 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 resulting film, a solvent containing one or more groups 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 preferred.

[0066] Examples of solvents 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, including lactone solvents such as 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 solvents having an ether group include tetrahydrofuran, dioxane, and dibutyl ether. Examples of solvents having a ketone group include ketone-based solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone. Examples of solvents having a hydroxyl group include phenol-based solvents such as m-cresol. Examples of solvents having a sulfone group include methanesulfonic acid, dimethyl sulfone, ethyl phenyl sulfone, diethyl sulfone, diphenyl sulfone, sulfolane, bisphenol S, sorapsone, dapsone, bisphenol A polysulfone, and sulfolane. Examples of solvents having a sulfinyl group include sulfoxide-based solvents such as dimethyl sulfoxide (DMSO). In addition to the solvents listed above, amide-based solvents such as N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMAc) can also be used.

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

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

[0070] Resilience refers to the amount of energy per unit volume that a material can absorb without permanent deformation. In a tensile test of a film, the resilience of a film corresponds to the area of ​​the hatched elastic deformation region in the image of Figure 1, which is related to the curve (stress-strain diagram) that shows the relationship between the stress applied to the film and the strain of the film in response to this stress. High resilience means high elastic recovery, and a film with high resilience is expected to easily recover to its original state even when folded repeatedly or kept in a folded state for a long time, and to be less likely to leave creases.

[0071] As described above, resilience is determined as the area in the elastic deformation region, but by approximating the stress-strain curve of the elastic deformation region as a triangle, an approximate value can be evaluated using R in the following formula (1). 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 curve, 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 methods described in the Examples.

[0073] The yield strength of the film of the present invention is preferably from 70 to 200 MPa, more preferably from 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 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 a coating film of the resin composition of the present invention. For example, the film of the present invention can be obtained by forming the resin composition of the present invention into a resin varnish, applying it to a support, drying it, and then peeling it off from the support.

[0077] The coating method is not particularly limited, and known methods can be used, such as dip coating, flow coating, roll coating, bar coating, blade coating, screen printing, curtain coating, spray coating, etc. The coating thickness can be adjusted depending on the thickness of the film.

[0078] There are no particular limitations on the drying conditions as long as the temperature is such that the solvent volatilizes, but from the viewpoint of obtaining a film with excellent transparency, drying at 60 to 250° C. for about 10 to 60 minutes is preferred.

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

[0080] The film of the present invention can be suitably used as a cover window for a display device, and can be used, for example, by placing the film on the surface of various display devices. The method for placing the film on the surface is not particularly limited, and examples thereof include a method using an adhesive layer. Known adhesive materials can be used as the material for the adhesive layer. A cover window using the film of the present invention may be provided with a protective layer such as a hard coat layer on the film surface, and may further include a fingerprint prevention layer.

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

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

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

[0084] The film of the present invention can also be applied to TFT substrates for organic EL displays, touch panel members, flexible printed circuit boards, solar cell panel members such as surface protection films and substrate materials, optical waveguide members, and other semiconductor-related members.

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

[0086] <Measurement Methods> The physical properties of the polyamide resins and polyamide films prepared in the examples were measured as follows.

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

[0088] (2) Yield Strength and Yield Strain The prepared film was cut to a predetermined size, and the yield strength and yield strain (ε) were measured using a small tabletop testing machine (Shimadzu Corporation, EZ-SX). The strain was calculated using the following formula (2), and the modulus of elasticity was calculated from the slope of the obtained stress-strain curve where the stress was from 5 MPa to 10 MPa. The strain and stress at the 0.2% proof stress point in the stress-strain curve were taken as the yield strain and yield strength, respectively. Measurements were carried out with n=3, and the average values ​​of the measurement results are shown in Table 1. Strain = (L １ -L ０ ) / L ０ (2) L ０ is the initial length of the film used in the measurement, L１ is the length of the film for a certain stress. [Test conditions] Sample size: 100 mm x 10 mm Distance between grippers: 50 mm Speed: 5 mm / min Number of measurements: 3

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

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

[0091] <Production of Polyamideimide> A 100 mL reactor was charged 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. Next, 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 the TFMB solution, and the mixture was stirred at 30°C for 2 hours to react, yielding a solution containing a polymer having an imide precursor structure. Thereafter, 1.757 g (8.653 mmol) of terephthaloyl chloride (TPC) was added to the solution, and the mixture was stirred and reacted for 1.5 hours while maintaining the liquid temperature at 30°C, yielding a solution containing a copolymer having an imide precursor structure and an amide structure. Subsequently, 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 polyamideimide solution. Further, 99 g of DMAc was added and stirred until homogenous, and the solution was gradually poured into a container containing 4 L of methanol to cause precipitation. The precipitated solids were filtered and pulverized, and then dried in a vacuum at 80°C for 18 hours to obtain 8.2 g of polyamideimide resin (PAI) as a solid powder. The weight average molecular weight (Mw) of the polystyrene equivalent measured by GPC was 597,000.

[0092] <Film Production> In the blending amounts (parts by weight) shown in Table 1, polyamideimide resin (PAI) powder and a thermally reactive crosslinking agent were dissolved in a solvent (DMAc) to adjust the solids concentration to 13% by weight, and then dispersed and homogenized to prepare a resin composition for film production. Next, this resin composition was applied to a glass plate using a table coater (AFA-standard, manufactured by Cortec Co., Ltd.) with an applicator so that the final film thickness was 50 μm. The film was then dried in a precision incubator (Fine Oven DH612, manufactured by Yamato Scientific Co., Ltd.) at 120 ° C. for 20 minutes, followed by 220 ° C. for 30 minutes, and then peeled off from the glass plate to form a film. The evaluation of each obtained film is shown in Table 1.

[0093]

[0094] <Thermal reactive crosslinking agent> ・Nicalac MW-390 manufactured by Sanwa Chemical Co., Ltd. ・K.I. Chemicals BMI-80 ・MA-DGIC manufactured by Shikoku Chemicals Corporation ・DA-MGIC manufactured by Shikoku Chemicals Corporation ・Shinetsetsu Silicone KBM-403 Nissan Chemical Co., Ltd. TEPIC-VL epoxy equivalent 125-145g / eq ・DIC Corporation HP-4032D Naphthalene type Epoxy equivalent: 136-148g / eq ・Mitsubishi Chemical Corporation JER828 Bisphenol A type epoxy resin Epoxy equivalent: 184-194g / eq ・DIC Corporation EPICLON 860 Bisphenol A type epoxy resin Epoxy equivalent: 235-255g / eq ・DIC Corporation HP-5000 Naphthalene skeleton modified multifunctional type Epoxy equivalent: 245-260g / eq ・DIC Corporation HP-7200 Dicyclopentadiene type Epoxy equivalent: 254-264g / eq ・DIC Corporation EXA-4850-150 Epoxy equivalent: 410-470g / eq ・DIC Corporation EXA-4816 Epoxy equivalent: 403 g / eq. Mitsubishi Chemical Corporation JER1001 bisphenol A type epoxy resin, epoxy equivalent: 474 g / eq.

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

[0096] According to the resin composition for films of the present invention, a film with high resilience is provided, and this film is expected to be less likely to develop folding marks even when repeatedly folded or kept in a folded state for a long period of time, and is therefore highly useful in industry.

Claims

1. A resin composition comprising one or more resins selected from polyamideimide resins and polyamide resins, and a heat-reactive crosslinking agent.

2. The resin composition according to claim 1, wherein the resin is a polyamideimide resin.

3. The resin composition according to claim 1, wherein the heat-reactive crosslinking agent has a heat-reactive group selected from the group consisting of 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 heat-reactive crosslinking agent is present in an amount of 1 to 50 parts by mass per 100 parts by mass of the resin.

5. A film made 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) where α is the yield strength (unit: MPa) and ε is the yield strain.

7. A display device comprising the film according to claim 5.

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