Resin composition and film obtained using same

Abstract

Provided is a resin composition which can maintain transparency as a film while exhibiting a good elastic modulus (specifically an average elastic modulus in the machine direction and transverse direction of 6.0 GPa or more). The resin composition contains a resin component and a fibrous alumina filler, and is characterized in that the resin component contains at least a resin having an amide structure, and the fibrous alumina filler includes a fibrous alumina filler which is dispersed in the resin composition at an average diameter of 4 nm to 30 nm and an average fiber length of 200 nm to 4000 nm.

Description

Resin composition and film using same

[0001] The present invention relates to a resin composition suitable for use in applications such as foldable devices, and a film using the same.

[0002] Foldable devices have recently attracted attention as they further enhance the portability of mobile information terminals such as smartphones and tablets. Components such as cover windows used in flexible displays that constitute such foldable devices need to be flexible in addition to transparent. Specifically, there is a demand for components with extremely high flexibility that can be folded 180° with a small bending radius of about 2.5 mm.

[0003] In response to this, various materials made of flexible organic polymers have been studied as alternatives to rigid glass. For example, films containing polyimide resins have been studied and proposed as flexible organic polymers from the viewpoints of transparency and heat resistance.

[0004] However, flexible displays using films containing such flexible organic polymers have often suffered from pressure marks or flex marks on the display surface when touched with a finger or a touch pen, or when the display is kept folded for a long period of time. Therefore, films for such flexible displays are required to have not only high flexibility but also a high elastic modulus.

[0005] In response to this, a polyimide resin composition containing a polyimide resin having a specific molecular structure and silica fine particles has been proposed as a film for flexible displays that combines heat resistance, transparency, mechanical strength, surface hardness, and bending resistance (see Patent Document 1).

[0006] International Publication No. 2016 / 060213

[0007] However, in the recent field of foldable devices, with further improvements in functionality and productivity and diversification of designs and applications, a higher elastic modulus (particularly an average elastic modulus in the MD and TD directions of 6.0 GPa or more) is required for the components, and the polyimide resin composition of Patent Document 1 was not sufficient. In addition, films for displays are also required to have excellent transparency, but it has been difficult to improve the elastic modulus while maintaining transparency.

[0008] Therefore, a primary object of the present invention is to provide a resin composition that, as a film, maintains transparency while also having a good elastic modulus (particularly, an average elastic modulus in the MD and TD directions of 6.0 GPa or more). Another object of the present invention is to provide a film made of the resin composition.

[0009] The present inventors have conducted extensive research to achieve the above object, and as a result have found that a resin composition containing at least a resin having an amide structure, in which a fibrous alumina filler is dispersed in a specific fiber dimension state, can provide a resin composition that combines a high elastic modulus with maintaining transparency, something that could not be achieved by conventional techniques, and have thus completed the present invention.

[0010] That is, the resin composition of the present invention is a resin composition containing a resin component and a fibrous alumina filler, wherein the resin component contains at least a resin having an amide structure, and the fibrous alumina filler is dispersed in the resin composition in a state in which the average fiber diameter is 1 to 30 nm and the average fiber length is 100 to 4,000 nm.

[0011] Here, in the present invention, the "alumina" of the fibrous alumina filler in the resin composition includes alumina and alumina hydrate, and examples of alumina hydrate include boehmite, pseudo-boehmite, etc. Furthermore, the "average fiber diameter" and "average fiber length" of the fibrous alumina filler are obtained by observing the fibrous alumina filler in the resin composition using an electron microscope image, and the average measured length of the diameter in the short side direction of 50 arbitrarily selected fibrous alumina fillers is defined as the "average fiber diameter," and the average measured length in the long side direction is defined as the "average fiber length."

[0012] In the resin composition of the present invention, the fibrous alumina filler is preferably a boehmite or pseudo-boehmite alumina filler, and the content of the fibrous alumina filler is preferably 1 to 50 parts by mass per 100 parts by mass of the resin.

[0013] In the resin composition of the present invention, the resin having at least an amide structure preferably includes a polyamideimide resin or a polyamide resin.

[0014] The film of the present invention is characterized by comprising the resin composition. The film of the present invention preferably has a protective layer laminated on at least one side. The resin composition or film of the present invention is preferably used as a display member.

[0015] That is, the gist of the present invention is as follows. [1] A resin composition containing a resin component and a fibrous alumina filler, wherein the resin component contains a resin having at least an amide structure, and the fibrous alumina filler is dispersed in the resin composition in a state where the average fiber diameter is 1 to 30 nm and the average fiber length is 100 to 4,000 nm. [2] The resin composition of [1], wherein the fibrous alumina filler is a boehmite or pseudo-boehmite alumina filler. [3] The resin composition of [1] or [2], wherein the fibrous alumina filler is contained in an amount of 1 to 50 parts by mass per 100 parts by mass of the resin having at least an amide structure. [4] The resin composition of any of [1] to [3], wherein the resin having at least an amide structure contains a polyamideimide resin or a polyamide resin. [5] A film made of any of the resin compositions of [1] to [4]. [6] A film, wherein a protective layer is laminated on one side of the film of [5]. [7] A display member comprising the resin composition of any one of [1] to [4] or the film of [5] or [6].

[0016] According to the present invention, it is possible to provide a resin composition that exhibits effects that could not be achieved by conventional techniques, namely, a film that maintains transparency while also having a good elastic modulus (particularly, an average elastic modulus in the MD and TD directions of 6.0 GPa or more).Furthermore, according to the present invention, it is possible to provide a film that combines the above effects and is made of the resin composition.

[0017] The resin composition of the present invention is described in detail below. The resin composition of the present invention is a resin composition containing a resin component and a fibrous alumina filler, wherein the resin component contains at least a resin having an amide structure, and the fibrous alumina filler is dispersed in the resin composition in a state in which the average fiber diameter is 1 to 30 nm and the average fiber length is 100 to 4,000 nm.

[0018] [Resin Component] The resin component constituting the resin composition of the present invention includes a resin having at least an amide structure. Examples of the resin having at least an amide structure include polyamide resins having a structure in which structural units containing an amide structure are polymerized. Furthermore, the resin having at least an amide structure may be a resin having an amide structure and an imide structure, such as a polyamideimide resin having a structure in which structural units containing an imide structure and structural units containing an amide structure are copolymerized. By further dispersing a fibrous alumina filler (described below) in a specific fiber dimension state in a resin composition containing at least a resin component having an amide structure, a film made from such a resin composition can achieve high levels of excellent transparency and high elasticity, two properties that are difficult to achieve together. Furthermore, it can be advantageous in achieving excellent thermal dimensional stability (thermal properties).

[0019] [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.

[0020] 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 structures in which aromatic rings are linked together via an alkylene group which may be substituted with a sulfonyl group or a fluorine atom.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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).

[0030] 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.

[0031] 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.

[0032] 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).

[0033] 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%, preferably 10 mol% or more, more preferably 20 mol% or more, and even more preferably 40 mol% or more, relative to the total 100 mol% of the tetracarboxylic acid compound and the dicarboxylic acid compound. The amide structure is preferably more than 0 mol%, more preferably 10 mol% or more, more preferably 20 mol% or more, and even more preferably 40 mol% or more, in the repeating units of the polyamideimide resin. To fully obtain the effects of introducing the imide structure, the amide structure is preferably 90 mol% or less, more preferably 80 mol% or less.

[0034] For example, in the synthesis of the polyamide-imide resin of the resin composition of the present invention, the molar ratio of the monomer components (diamine compound:tetracarboxylic acid compound:dicarboxylic acid compound) is preferably 7:0.5-4:3-6.5, more preferably 7:1.5-3.5:3.5-5.5, and particularly 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 is preferably 0.5-4:3-6.5, more preferably 1.5-3.5:3.5-5.5, and particularly 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.

[0035] The ring-closing reaction (imidization) of an imide precursor in the synthesis of a 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. However, chemical imidization is preferred because it is easier to maintain colorless transparency.

[0036] 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 may be used alone or in combination of two or more.

[0037] Condensing agents used in chemical imidization include acid anhydrides such as acetic anhydride, propionic anhydride, and trifluoroacetic anhydride, and phosphites such as trimethyl 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.

[0038] The organic solvent used in the synthesis of polyamideimide 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 may be used alone or in combination of two or more.

[0039] 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.

[0040] From the viewpoint of improving the elastic modulus 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. The weight average molecular weight (Mw) is a value measured by GPC (gel permeation chromatography) and calculated in terms of polystyrene, specifically by the method described in the Examples.

[0041] In the present invention, the content of polyamideimide resin in the non-volatile components of the resin composition is preferably in the range of 50 to 96 mass %, more preferably in the range of 59 to 90 mass %, and even more preferably in the range of 67 to 83 mass %, from the viewpoint of maintaining colorless transparency and improving elongation.

[0042] [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, an acid anhydride, etc.).

[0043] 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 and 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 structures other than the amide structure and is composed of an amide structure.

[0044] 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.

[0045] 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 fluoro groups, trifluoromethyl groups, or trifluoromethoxy groups, specifically 2,2'-bis(trifluoromethyl)benzidine.

[0046] 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 OBBC are essentially introduced into the polyamide resin.

[0047] The polyamide resin preferably contains the following structure (1) and / or (2) as repeating units, and more preferably 10 to 100 mol % of all repeating units are the following structure (1) and / or (2). It is particularly preferable that all repeating units are substantially composed of the following structure (1) and / or (2).

[0048] The polyamide resin can be produced by a known method for producing polyamides, such as solution polymerization, interfacial polymerization, melt polymerization, solid-state polymerization, etc. As the method for producing the polyamide resin of the present invention, the solution polymerization and interfacial polymerization are particularly preferably used.

[0049] 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.

[0050] 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 ethylene oxide, propylene oxide, 1,2-butylene oxide, ammonia, or pyridine, is used.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] The reaction conditions for synthesizing the polyamide resin can be 10 to 50° C. for 10 minutes to 27 hours, and the synthesis may be carried out in a nitrogen atmosphere in order to maintain colorless transparency.

[0056] 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.

[0057] 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.

[0058] 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. The number average molecular weight (Mn) and weight average molecular weight (Mw) are values ​​measured by GPC (gel permeation chromatography) and calculated in terms of polystyrene.

[0059] In the present invention, the content of the polyamide resin in the non-volatile components of the resin composition is preferably in the range of 50 to 96 mass%, more preferably in the range of 59 to 90 mass%, and even more preferably in the range of 67 to 83 mass%, from the viewpoint of maintaining colorless transparency and improving elongation.

[0060] The resin composition of the present invention can also use a mixture of a polyimide resin composed of structural units containing an imide structure and a polyamide resin composed of structural units containing an amide structure. For example, when synthesizing the above-mentioned polyamideimide, the structural units containing an imide structure and the structural units containing an amide structure may not copolymerize in the polyamideimide resin solution, and a polyimide resin composed only of structural units containing an imide structure and a polyamide resin composed only of structural units containing an amide structure may be by-produced. Mixtures of two or more of such polyamideimide resins, polyimide resins, and polyamide resins can also be preferably used in the present invention. Alternatively, these resins may be synthesized individually and then mixed.

[0061] [Fiberous Alumina Filler] The fibrous alumina filler constituting the resin composition of the present invention is characterized by being dispersed in a resin composition containing the above-described resin components in a state in which the average fiber diameter is 1 to 30 nm and the average fiber length is 100 to 4,000 nm. The fibrous alumina filler in such a dispersed state is thought to impart a significant effect of high elasticity while suppressing a decrease in transparency by arranging the individual fibers in a lattice pattern in the resin composition. Furthermore, the fibrous alumina filler of the present invention can also impart excellent anti-blocking effects without impairing light transmittance, compared to spherical or amorphous fillers. Specifically, when films made of the resin composition of the present invention are stacked or rolled up for storage, the fibrous alumina filler can suppress sticking (blocking) between the films, improving storage stability and workability.

[0062] The fibrous alumina filler in the resin composition of the present invention is dispersed in a state in which the average fiber diameter is 1 to 30 nm and the average fiber length is 100 to 4,000 nm, preferably in a state in which the average fiber diameter is 2 to 25 nm and the average fiber length is 200 to 3,000 nm, and more preferably in a state in which the average fiber diameter is 3 to 20 nm and the average fiber length is 500 to 2,000 nm. If the fibrous alumina filler is dispersed in the resin composition in a state in which the average fiber diameter and average fiber length are in the above-mentioned ranges, a film made from this resin composition can achieve high elasticity while maintaining transparency. The "average fiber diameter" and "average fiber length" of the fibrous alumina filler in the dispersed state in the resin composition of the present invention are measured by diluting the resin composition 10,000 times with the solvent used to prepare the resin composition (e.g., methyl isobutyl ketone (MIBK) or dimethylacetamide (DMAc)), dropping one drop onto a cover glass (Cover Glass Trophy, manufactured by Matsunami Glass Co., Ltd.), drying at 50°C, and then observing the image under an electron microscope (e.g., a 10,000x magnification image using an FE-SEM manufactured by Hitachi High-Tech). The fibrous alumina filler to be measured may be in the form of either a single fiber or a fiber bundle in which multiple single fibers are aggregated, as long as it is visible as a single fiber in the electron microscope image. The average measured length of the diameter in the short side direction of 50 arbitrarily selected fibrous alumina fillers in the electron microscope image is taken as the "average fiber diameter," and the average measured length in the long side direction is taken as the "average fiber length."

[0063] The fibrous alumina filler constituting the resin composition of the present invention is blended with the above-mentioned resin components in the form of a powder or a dispersion (sol) described below, stirred, and kneaded as necessary to adjust the dispersion state in the resin composition, i.e., the "average fiber diameter" and "average fiber length." For example, stirring or kneading can be carried out using a stirrer such as a dissolver or butterfly mixer, or a kneader such as a roll mill or bead mill. The diameter and length can be adjusted by various conditions, such as the rotation speed of the stirrer / kneader, the shape of the stirring blades / kneading device, the stirring / kneading time, the stirring / kneading temperature, the bead filling rate, and the roll spacing.

[0064] The content of the fibrous alumina filler in the resin composition of the present invention is preferably 1 to 50 parts by mass, more preferably 5 to 40 parts by mass, and even more preferably 10 to 30 parts by mass, relative to 100 parts by mass of the resin having at least an amide structure. If the content of the fibrous alumina filler is within the above-mentioned range, the film can be made highly elastic while maintaining its transparency.

[0065] The fibrous alumina filler in the resin composition of the present invention can be surface-treated or used as a dispersion (sol) dispersed in an organic solvent or the like. By surface-treating the fibrous alumina filler or incorporating it as a dispersion, the dispersed state in the resin composition can be stabilized. In particular, by using a dispersion (sol) in which the dispersed state of the fibrous alumina filler is adjusted to be the same as the dispersed state of the fibrous alumina filler in the resin composition of the present invention, i.e., the "average fiber diameter" and "average fiber length", the resin composition of the present invention can be produced with good productivity.

[0066] The method for surface treatment of the fibrous alumina filler or for preparing a dispersion is not particularly limited, and for example, a surface treatment method using a coupling agent such as a silane-based, titanate-based, aluminate-based, or zircoaluminate-based agent, or a method for producing an organic sulfonic acid-treated dispersion disclosed in JP 2008-31010 A can be used.

[0067] The fibrous alumina filler in the resin composition of the present invention is preferably a boehmite or pseudo-boehmite alumina filler. When the resin component contains a polyamide resin, it is preferable to use a fibrous alumina filler that is a boehmite or pseudo-boehmite alumina filler. Examples of the fibrous alumina filler (component (B)) include the Alumina Sol series manufactured by Kawaken Fine Chemicals.

[0068] [(Meth)acrylate Compound or Blocked Isocyanate Compound Having a Molecular Weight of 10,000 or Less] The resin composition of the present invention may contain a (meth)acrylate compound or a blocked isocyanate compound having a molecular weight of 10,000 or less, from the viewpoint of mitigating external stresses such as drying shrinkage, bending, and compression during the film production process. The blend amount of the (meth)acrylate compound or the blocked isocyanate compound having a molecular weight of 10,000 or less is preferably 0.1 to 100 parts by mass, more preferably 1 to 50 parts by mass, and particularly preferably 2 to 20 parts by mass, per 100 parts by mass of the resin having at least an amide structure.

[0069] [(Meth)acrylate Compound Having a Molecular Weight of 10,000 or Less] As the (meth)acrylate compound, a known and commonly used (meth)acrylate oligomer or (meth)acrylate monomer can be used. One (meth)acrylate compound may be used alone, or two or more (meth)acrylate compounds may be used in combination.

[0070] Examples of the (meth)acrylate oligomer include epoxy (meth)acrylates such as phenol novolac epoxy (meth)acrylate, cresol novolac epoxy (meth)acrylate, and bisphenol-type epoxy (meth)acrylate, urethane (meth)acrylate, epoxy urethane (meth)acrylate, polyester (meth)acrylate, polyether (meth)acrylate, and polybutadiene-modified (meth)acrylate.

[0071] Examples of (meth)acrylate monomers include (meth)acrylamides such as acrylamide, methacrylamide, N-hydroxymethylacrylamide, N-hydroxymethylmethacrylamide, N-methoxymethylacrylamide, N-ethoxymethylacrylamide, and N-butoxymethylacrylamide; allyl compounds such as triallyl isocyanurate, diallyl phthalate, and diallyl isophthalate; 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, (meth)acrylic acid esters such as isobornyl (meth)acrylate, phenyl (meth)acrylate, and phenoxyethyl (meth)acrylate; hydroxyalkyl (meth)acrylates such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and pentaerythritol tri(meth)acrylate; alkoxyalkylene glycol mono(meth)acrylates such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate; ethylene glycol di(meth)acrylate, Alkylene polyol poly(meth)acrylates such as tripropylene glycol di(meth)acrylate, butanediol di(meth)acrylates, neopentyl glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, and dipentaerythritol hexa(meth)acrylate; diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, Examples of the poly(meth)acrylate include polyoxyalkylene glycol poly(meth)acrylates such as ethylene glycol di(meth)acrylate, ethoxylated trimethylolpropane triacrylate, trimethylolpropane tri(meth)acrylate, and propoxylated trimethylolpropane tri(meth)acrylate; poly(meth)acrylates such as hydroxypivalic acid neopentyl glycol ester di(meth)acrylate; and isocyanurate-type poly(meth)acrylates such as tris[(meth)acryloxyethyl]isocyanurate.

[0072] [Blocked Isocyanate Compound Having an Isocyanuric Ring] The resin composition of the present invention may contain a blocked isocyanate compound having an isocyanuric ring. The blocked isocyanate group contained in this blocked isocyanate compound having an isocyanuric ring is a group in which the isocyanate group is protected and temporarily inactivated by reaction with a blocking agent. When heated to a predetermined temperature, the blocking agent is cleaved to generate an isocyanate group. Therefore, even after application, the reaction via the isocyanate group of the blocked isocyanate compound having an isocyanuric ring does not proceed until the drying step.

[0073] The blocked isocyanate compound having an isocyanuric ring is an addition reaction product of an isocyanate compound and an isocyanate blocking agent. Examples of the isocyanuric ring-containing isocyanate compound that can react with a blocking agent include 1,3,5-tris[(5-isocyanato-1,3,3-trimethylcyclohexyl)methyl]-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, 2,4,6-trioxohexahydro-1,3,5-triazine-1,3,5-triyltris(6,1-hexanediyl)trisisocyanate, and 1,3,5-tris[3-(isocyanatomethyl)phenyl]-1,3,5-triazine-2,4,6(1H,3H,5H)-trione.

[0074] Examples of the isocyanate blocking agent include phenol-based blocking agents such as phenol, cresol, xylenol, chlorophenol, and ethylphenol; lactam-based blocking agents such as ε-caprolactam, δ-valerolactam, γ-butyrolactam, and β-propiolactam; active methylene-based blocking agents such as ethyl acetoacetate and acetylacetone; alcohol-based blocking agents such as methanol, ethanol, propanol, butanol, amyl alcohol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, propylene glycol monomethyl ether, benzyl ether, methyl glycolate, butyl glycolate, diacetone alcohol, methyl lactate, and ethyl lactate; and formaldehyde. oxime-based blocking agents such as hydroxyl hydroxime, acetaldoxime, acetoxime, methyl ethyl ketoxime, diacetyl monooxime, and cyclohexane oxime; mercaptan-based blocking agents such as butyl mercaptan, hexyl mercaptan, t-butyl mercaptan, thiophenol, methylthiophenol, and ethylthiophenol; acid amide-based blocking agents such as acetic acid amide and benzamide; imide-based blocking agents such as succinimide and maleic acid imide; amine-based blocking agents such as xylidine, aniline, butylamine, and dibutylamine; imidazole-based blocking agents such as imidazole and 2-ethylimidazole; imine-based blocking agents such as methyleneimine and propyleneimine; pyrazole-based blocking agents such as dimethylpyrazole; and maleate ester-based blocking agents such as diethylmaleate.

[0075] The cleavage temperature of the blocked isocyanate compound having an isocyanuric ring is preferably 100° C. or higher. If the temperature is 100° C. or higher, an increase in viscosity is suppressed until the drying step for film formation, and coatability is maintained.

[0076] The blocked isocyanuric ring-containing compound of the present invention may be a commercially available product, such as BI7951 or BI7982 manufactured by TRIXENE Corp. Such blocked isocyanuric ring-containing compounds may be used alone or in combination of two or more.

[0077] [Compound containing two or more functional groups selected from methylol groups and alkoxymethyl groups] The resin composition of the present invention can contain a compound containing two or more functional groups selected from methylol groups and alkoxymethyl groups. By containing a compound containing two or more functional groups selected from methylol groups and alkoxymethyl groups, the resilience of a film made from the resin composition of the present invention can be improved, and it is expected that the film will be less likely to develop folding marks even if it is repeatedly folded or kept folded for a long period of time.

[0078] The compound containing two or more functional groups selected from the group consisting of methylol groups and alkoxymethyl groups can be used alone or in combination. ２ It is a group represented by —O—R, where R is an alkyl group. R is preferably an alkyl group having 1 to 6 carbon atoms, more preferably 1 or 2 carbon atoms, and particularly preferably 1 carbon atom.

[0079] The one or more functional groups selected from a methylol group and an alkoxymethyl group are preferably a methylol group or a methoxymethyl group.

[0080] The compound containing two or more functional groups selected from methylol groups and alkoxymethyl groups can be a crosslinking agent having a melamine skeleton, a crosslinking agent having a guanamine skeleton, a crosslinking agent having a glycoluril skeleton, etc. Compounds of this type containing two or more methylol groups or alkoxymethyl groups are preferred. Compounds of this type known as thermally reactive crosslinking agents can also be used.

[0081] The crosslinking agent having a melamine skeleton is a compound having a melamine structure and containing two or more functional groups of one or more types selected from methylol groups and alkoxymethyl groups, and a compound represented by formula (3) can be used. Oligomers of these can also be used. In the formula, R １ is a hydrogen atom or an alkyl group (preferably an alkyl group having 1 to 6 carbon atoms, more preferably a methyl group or an ethyl group, and particularly preferably a methyl group).

[0082] The crosslinking agent having a benzoguanamine skeleton is a compound having a benzoguanamine structure and containing two or more functional groups of one or more types selected from a methylol group and an alkoxymethyl group, and a compound represented by formula (4) can be used. Oligomers of these can also be used. In the formula, R ２ is a hydrogen atom or an alkyl group (preferably an alkyl group having 1 to 6 carbon atoms, more preferably a methyl group or an ethyl group).

[0083] The crosslinking agent having a glycoluril skeleton is a compound having a glycoluril structure containing two or more functional groups of one or more types selected from methylol groups and alkoxymethyl groups, and examples thereof include 1,3,4,6-tetrakis(hydroxymethyl)glycoluril, 1,3,4,6-tetrakis(methoxymethyl)glycoluril, and 1,3,4,6-tetrakis(butoxymethyl)glycoluril.

[0084] Preferred compounds containing two or more functional groups of one or more types selected from methylol groups and alkoxymethyl groups include hexamethylolmelamine, hexamethoxymethylmelamine, tetramethylolbenzoguanamine, tetramethoxymethylbenzoguanamine, and oligomers thereof.

[0085] [Other Components] The resin composition of the present invention may further contain additives and resin components other than the resin having at least an amide structure, within the range that does not impair the effects of the present invention.

[0086] Examples of additives that can be used to modify the fibrous alumina filler and stabilize the solution viscosity of the resin composition include organic carboxylic acid compounds such as acetic acid, benzoic acid, terephthalic acid, citric acid, succinic acid, and lactic acid; organic phosphoric acid compounds such as mono(di)methyl phosphate ester, mono(di)butyl phosphate ester, and phenylphosphonic acid; organic sulfonic acid compounds such as benzenesulfonic acid, p-toluenesulfonic acid, and dodecylbenzenesulfonic acid; and surfactants that improve film-forming properties and defoaming properties.

[0087] Examples of resin components other than resins having at least an amide structure include polyester resins such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), polyimide resins, polyphenylene sulfide resins, polyether ether ketone resins, polyether sulfone resins, polycarbonate resins, polyetherimide resins, epoxy resins, phenolic resins, glass-epoxy resins, polyphenylene ether resins, acrylic resins, polyolefin resins such as polyethylene and polypropylene, and polycycloolefins such as polynorbornene.

[0088] [Film] The film of the present invention is made from the resin composition described above. According to the present invention, the film maintains transparency while exhibiting high elasticity (average modulus of elasticity in the MD and TD directions of 6.0 GPa or more). Furthermore, as described below, the film of the present invention can exhibit anisotropic mechanical properties in the MD and TD directions, for example, a modulus of elasticity in the MD direction of 7.0 GPa or more. Furthermore, the film of the present invention can further improve transparency while maintaining high elasticity; for example, the film's haze value can be set to 1.0% or less, and the YI value can be set to 0 or more and 5.0 or less. The film's modulus of elasticity, YI value, and haze can be measured by the methods described in the Examples. Furthermore, the film of the present invention can be advantageous in terms of excellent thermal dimensional stability (thermal properties), excellent antiblocking properties, and excellent film storage stability and workability.

[0089] The film of the present invention preferably has a thickness of 5 μm or more and 100 μm or less, more preferably 10 μm or more and 70 μm or less. By setting the thickness within the above range, excellent flexibility and excellent transparency can be achieved as a laminate described later.

[0090] [Film Manufacturing Method] The film of the present invention can be manufactured by applying a coating solution for film production, prepared by dissolving the resin composition of the present invention in a solvent, onto a support by a known coating means, drying if necessary, and then peeling it off from the support. The coating means is not particularly limited as long as it can be applied to the desired film thickness. It is preferable to appropriately adjust the amount of the coating solution to be applied so that the film thickness after drying falls within a predetermined range.

[0091] When a film is formed using the resin composition of the present invention, the resulting film may have anisotropic mechanical strength depending on the coating method. The reason for this is unclear, but since the fibrous alumina filler described above is dispersed in the resin composition, applying a coating method that applies shear stress is thought to cause the fibrous alumina filler to orient in the direction in which the shear stress acts, resulting in anisotropic mechanical strength in the resulting film. The anisotropy of mechanical strength refers to, for example, when producing a long film, the mechanical properties of the resulting film, such as the tensile modulus, differ between the direction in which the coating film is formed (MD) and the direction perpendicular thereto (TD).

[0092] In the present invention, the anisotropy of the mechanical strength of the resulting film can be suppressed by including 90% by mass or more of an organic solvent having a boiling point of 150°C or higher relative to the total solvent content of the coating solution for film production. The inclusion of a predetermined proportion of a high-boiling organic solvent ensures that the oriented fibrous alumina filler in the coating film can relax when the coating film coated with the resin varnish is dried, and as a result, the fibrous alumina filler can be dispersed in a nearly non-oriented state in the dried coating film (i.e., film). To suppress anisotropy, the organic solvent having a boiling point of 150°C or higher is preferably included in an amount of 92% by mass or more relative to the total solvent content.

[0093] As organic solvents having a boiling point of 150°C or higher that can be used as solvents for coating solutions used in film production, solvents having an ester group, an ether group, a ketone group, a hydroxyl group, a sulfone group or a sulfinyl group, and amide solvents are preferred from the viewpoint of film transparency and the like.

[0094] Examples of solvents having an ester group include γ-butyrolactone (boiling point 204°C), ε-caprolactone (boiling point 230°C), γ-hexanolactone (boiling point 219°C), γ-valerolactone (boiling point 207°C), benzyl benzoate (boiling point 323°C), ethyl benzoate (boiling point 212°C), ethylene glycol monobutyl ether acetate (boiling point 191.5°C), ethylene glycol monoethyl ether acetate (boiling point 156.3°C), butyl lactate (boiling point 188°C), ethyl lactate (boiling point 154°C), and ethyl 3-ethoxypropionate (boiling point 169°C).

[0095] Examples of solvents having an ether group include 2-(2-butoxyethoxy)ethyl acetate (boiling point 245°C), 2-(2-ethoxyethoxy)ethyl acetate (boiling point 217°C), propyl cellosolve (boiling point 150°C), and triethylene glycol dimethyl ether (boiling point 216°C).

[0096] Examples of solvents having a ketone group include cyclohexanone (boiling point 156° C.), 1-phenylethanone (boiling point 202° C.), and benzaldehyde (boiling point 179° C.).

[0097] Examples of solvents having a hydroxyl group include 2-methylphenol (boiling point 190° C.), 3-methylphenol (boiling point 202° C.), and octyl alcohol (boiling point 195° C.).

[0098] Examples of solvents having a sulfonic group include methanesulfonic acid (boiling point 167°C), dimethyl sulfone (boiling point 238°C), diethyl sulfone (boiling point 238°C), sulfolane (boiling point 285°C), and dapsone (boiling point 177°C).

[0099] Examples of the solvent having a sulfinyl group include dimethyl sulfoxide (boiling point: 189° C.).

[0100] Examples of amide solvents that can be used include N-methyl-2-pyrrolidone (boiling point: 202°C), N,N-dimethylformamide (boiling point: 153°C), N,N-dimethylacetamide (boiling point: 165°C), and 3-butoxy-N,N-dimethylpropanamide (boiling point: 252°C).

[0101] Among these solvents, from the viewpoint of reducing the YI value of the film, amide solvents are more preferred, and N,N-dimethylacetamide is particularly preferred.

[0102] The solvent for the coating solution for film production may contain other solvents in addition to the organic solvents having a boiling point exceeding 150° C., as described above. For example, from the viewpoint of drying properties, a solvent having a boiling point lower than 150° C. may be contained. Examples of such solvents include ester solvents such as methyl acetate, ethyl acetate, isopropyl acetate, propyl acetate, butyl acetate, dimethyl carbonate, propylene glycol monomethyl ether acetate, and methyl lactate; ether solvents such as tetrahydrofuran, dioxane, and dibutyl ether; ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclopentanone; amide solvents such as 3-methoxy-N,N-dimethylpropanamide; and aromatic solvents such as toluene.

[0103] From the viewpoint of coatability, the resin composition according to the present invention preferably has a viscosity at 25°C of 10 to 50,000 cP, more preferably 100 to 40,000 cP, and even more preferably 100 to 30,000 cP. Note that by lowering the viscosity of the resin composition, the anisotropy of the mechanical strength when formed into a film can also be reduced. The viscosity of the resin composition can be measured by a standard method using a cone-plate viscometer.

[0104] As described above, after the coating solution for film production is applied, the coating is dried as needed to remove the solvent. Examples of drying methods include vacuum drying, heat drying, and a combination of these. When drying at normal pressure, drying is preferably performed at 30 to 350°C, and from the viewpoint of obtaining a highly transparent resin layer, drying at 60 to 250°C for approximately 30 seconds to 180 minutes is preferred. In such a drying method, stepwise drying can also be performed, in which the temperature is gradually increased from a low temperature within the above-mentioned temperature and time ranges. Drying is also preferably performed under a nitrogen atmosphere.

[0105] [Laminated Film] The film of the present invention can be made into a laminated film by forming, on at least one surface of the film, a functional layer such as a hard coat layer that functions as a protective layer to prevent scratches due to scratches, etc. According to the film of the present invention, the above-mentioned film has a high elastic modulus without impairing transparency, and therefore, the occurrence of warping when a protective layer such as a hard coat layer is formed can be suppressed, excellent flatness and high surface hardness can be obtained, and the occurrence of flex marks and compression marks can also be reduced.

[0106] The laminate film using the film of the present invention preferably has a total thickness of 10 to 150 μm, more preferably 25 to 100 μm. If the total thickness of the laminate film is within the above range, a display panel that is flexible and has excellent optical properties can be produced.

[0107] [Hard Coat Layer] For the hard coat layer, a known and commonly used coating solution (hard coat material) for hard coats can be used, and either a photocurable or thermosetting hard coat material can be used. Examples of commercially available products include X-48-500 manufactured by Shin-Etsu Chemical Co., Ltd., which has excellent flexibility, and Luxidia V-6841 manufactured by DIC Corporation.

[0108] The hard coat layer preferably has a YI value of 4 or less at a film thickness of 50 μm, more preferably 1 or less. If the YI value is 4 or less, a laminate film with reduced yellowness (YI value) can be formed.

[0109] The hard coat layer preferably has a pencil hardness (surface hardness) of 2H or more, more preferably 4H or more. A pencil hardness of 2H or more allows for the formation of a laminate film with excellent scratch resistance. The pencil hardness can be measured in accordance with JIS K 5600-5-4.

[0110] Furthermore, the hard coat layer preferably has a thickness of 1 μm or more and 50 μm or less, and more preferably 5 μm or more and 20 μm or less. If the thickness is 50 μm or less, a laminated film having excellent flexibility can be formed.

[0111] [Method for producing laminated film] Examples of a method for producing a laminated film using the film of the present invention include a production method including a step of forming a film by the above-mentioned film production method and a step of forming a protective layer such as a hard coat layer thereon.

[0112] The method for producing the film is as described above, and therefore its description will be omitted here. The process for forming a hard coat layer as a protective layer on a film includes applying a resin solution (hard coat material) for the hard coat layer to one side of the film produced by the film production method described above using a known coating method, followed by drying and curing as necessary. The coating method is not particularly limited as long as it can be applied to the desired film thickness. The amount of resin solution to be applied for the hard coat layer varies depending on the performance required of the resulting laminated film, but it is preferable to appropriately adjust it so that the film thickness after drying is within a predetermined range.

[0113] As described above, the coating film made of the resin solution for the hard coat layer is dried as needed to remove the solvent. Examples of drying methods include drying under reduced pressure, drying by heating, and a combination of these. When drying is performed under normal pressure, it is preferable to dry at 30 to 150°C.

[0114] Furthermore, as a method for curing the hard coat layer, it is preferable to cure the coating film by at least one of light irradiation and heating depending on the components of the resin solution (hard coat material).

[0115] [Display Members] Examples of display members made using the film and laminate film of the present invention include thin, bendable foldable organic EL displays, mobile terminals such as smartphones and wristwatch-type terminals, display devices inside automobiles, flexible panels used in wristwatches, etc. The film and laminate film of the present invention can also be used as members for image display devices such as liquid crystal displays and 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. In particular, the film and laminate film of the present invention are preferably used as members for cover windows and TFT substrates that constitute foldable organic EL displays.

[0116] [Cover window of display] The cover window of a display using the film of the present invention is, for example, arranged so that the above-mentioned laminate film is positioned on the surface of various displays. The method of arrangement on the surface is not particularly limited, and examples thereof include a method via an adhesive layer. As the material for the adhesive layer, conventionally known adhesive materials that can be used for adhering display surface materials can be used. Note that the cover window of a display using the film or laminate film of the present invention may further have a fingerprint-proof layer on the surface on the side of the protective layer such as a hard coat layer.

[0117] [Substrate for TFT of Organic EL Display] A substrate for TFT of an organic EL display using the film of the present invention can be obtained, for example, by forming an amorphous silicon TFT (thin film transistor) on the film of the present invention. The TFT includes a gate metal layer, a silicon nitride gate dielectric layer, and an ITI pixel electrode. Furthermore, structures required for the organic EL display can be formed on this by known methods, and the method for forming circuits, etc. is not particularly limited.

[0118] The present invention will be described in more detail below using examples, but the present invention is not limited to the following examples. In the following, "parts" and "%" are all by mass unless otherwise specified.

[0119] (Synthesis Example of Polyamide PA1) A 100 mL reactor was charged with 60.0 g of N,N-dimethylacetamide (DMAc), and 5.33 g (16.63 mmol) of 2,2'-bis(trifluoromethyl)benzidine (TFMB) and 2.64 g (36.59 mmol) of 1,2-butylene oxide were added. Next, 0.97 g (3.29 mmol) of 4,4'-diphenyl ether dicarboxylic acid chloride (DEDC) and 2.67 g (13.17 mmol) of terephthalic acid chloride (TPC) were added to the TFMB solution, and the mixture was stirred at 30°C for 2 hours to react. Then, 0.026 g (0.33 mmol) of acetyl chloride was added to the solution, and the mixture was stirred at 30°C for 30 minutes to react, yielding a solution containing a polymer (PA1) having an amide structure. The weight average molecular weight (weight average molecular weight) measured by GPC in terms of polystyrene was 184,000.

[0120] The conditions for the GPC measurement are as follows: Apparatus: GL7700 manufactured by GL Sciences Column: TSKgel αM (manufactured by Tosoh Corporation) Temperature inside column: 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

[0121] (Synthesis Example of Polyamides PA2 to PA5) Solutions containing polymers having an amide structure (PA2 to PA5) were obtained in the same manner as in PA1, except that the amounts (molar ratios) of TFMB, DEDC, and TPC added were set to the values ​​shown in Table 1.

[0122] (Synthesis Example of Polyamideimide PAI) A 100 mL reactor was charged with 60.0 g of DMAc, and 4.849 g (15.14 mmol) of TFMB was added. Next, 1.007 g (3.245 mmol) of 3,4-oxydiphthalic dianhydride (aODPA) and 1.007 g (3.245 mmol) of 4,4'-oxydiphthalic dianhydride (sODPA) 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, 1.37 g (19.03 mmol) of 1,2-butylene oxide and 1.757 g (8.653 mmol) of TPC were 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 then gradually poured into a container containing 4 L of methanol to cause precipitation. The precipitated solid was filtered and pulverized, and then dried in vacuum at 80°C for 18 hours to obtain 8.0 g of a polyamideimide copolymer as a solid powder. The weight average molecular weight in terms of polystyrene measured by GPC was 221,000.

[0123] The composition ratios of the monomer components used in the synthesis of polyamides PA1 to PA5 are shown in Table 1.

[0124]

[0125] (Preparation of Evaluation Sample (Film)) In the blending amounts shown in Table 2, PA1 to 5 or PAI powder, dispersant, and fibrous alumina filler dispersion were blended, and the solids concentration was adjusted to 12.5 wt% using a solvent (DMAc), 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.) using an applicator so that the final film thickness was 50 μm, and then dried in a precision incubator (Fine Oven DH612 manufactured by Yamato Scientific Co., Ltd.) at 120 ° C. for 40 minutes, then at 220 ° C. for 30 minutes, and peeled off from the glass plate to form a film.

[0126] The evaluation samples thus obtained in Examples 1 to 6 and Comparative Example 1 were subjected to the following evaluations. The results are shown in Table 2.

[0127] Film Thickness The film thickness of each evaluation sample was measured using a micrometer (manufactured by Mitutoyo Corporation).

[0128] - Evaluation of Elastic Modulus and Elongation at Break Both the elastic modulus and elongation at break were measured using an EZ-SX manufactured by Shimadzu Corporation under the following conditions. The elastic modulus was determined from the slope of the obtained stress-strain curve at strains of 0.2% to 0.5%. For each evaluation sample, measurements were performed in both the direction parallel to the coating direction of the film (MD) and the direction perpendicular to the coating direction (TD). Note that, for the evaluation samples of Examples 1 to 6, anisotropy in the MD and TD directions was observed for the elastic modulus and elongation at break, so the respective values ​​are listed in Table 2, with the difference between the elastic modulus in the MD direction and the elastic modulus in the TD direction being shown as the elastic modulus anisotropy, and the average value of the elastic modulus in the MD direction and the elastic modulus in the TD direction being shown as the average elastic modulus. [Test conditions] Sample size: 80 mm x 10 mm Distance between grippers: 50 mm Speed: 5 mm / min Number of measurements: 3

[0129] Haze Evaluation Each evaluation sample was cut into a size of 30 mm x 30 mm, and the total light transmittance and haze of each evaluation sample were measured using a haze meter (NDH 7000 II, manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with ASTM D1003. Note that a smaller haze value indicates better transparency.

[0130] Evaluation of YI Value (Yellow Index) Each evaluation sample was cut into a size of 30 mm x 30 mm and measured using a spectrophotometer (CM-5, manufactured by Konica Minolta, Inc.) in accordance with ASTM E313-73. The closer the YI value is to 0, the more excellent the colorlessness is.

[0131]

[0132] The results shown in Table 2 above show that the present invention provides a resin composition that, as a film, maintains transparency while also having a good elastic modulus (particularly, an average elastic modulus in the MD and TD directions of 6.0 GPa or more).

Claims

1. A resin composition comprising a resin component and a fibrous alumina filler, wherein the resin component comprises at least a resin having an amide structure, and the fibrous alumina filler is dispersed in the resin composition in a state in which the average fiber diameter is 1 to 30 nm and the average fiber length is 100 to 4,000 nm.

2. The resin composition according to claim 1, wherein the fibrous alumina filler is a boehmite or pseudo-boehmite alumina filler.

3. The resin composition according to claim 1, wherein the fibrous alumina filler is contained in an amount of 1 to 50 parts by mass per 100 parts by mass of the resin having at least an amide structure.

4. The resin composition according to claim 1, wherein the resin having at least an amide structure includes a polyamideimide resin or a polyamide resin.

5. A film comprising the resin composition according to any one of claims 1 to 4.

6. A film comprising the film according to claim 5, and a protective layer laminated on one side of the film.

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

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