Polyamide resin, polyamide film and flexible material

Abstract

The objective is to provide a polyamide resin that can produce films with good haze value and elastic modulus using monomers that do not fall under the category of PFAS. [Solution] A polyamide resin having structural units derived from a diamine compound and structural units derived from a dicarboxylic acid compound, wherein the structural units derived from the diamine compound include the structural unit shown in formula (1), and the structural units derived from the dicarboxylic acid compound include the structural unit shown in formula (2).

Description

Technical Field

[0001] The present invention relates to polyamide resins, polyamide films, and flexible displays.

Background Art

[0002] Members for display devices such as liquid crystal display devices and organic EL display devices are widely used in various applications such as mobile phones and tablets. Conventionally, as a material for the front panel of such display devices, glass typified by UTG (Ultra-Thin Glass) has been used. However, although glass has high transparency and can exhibit high hardness depending on the type, it is very rigid and prone to cracking. Therefore, it is difficult to use such glass as a front panel material for flexible displays that can be bent or folded.

[0003] Therefore, as a material to replace glass, films utilizing polymer materials have been studied. Since films containing polymer materials are likely to exhibit flexible characteristics, they are expected to be used in various applications such as flexible displays.

[0004] Conventionally, in flexible displays, when operating by finger touch or a touch pen, or when holding the display in a folded state for a long time, marks such as indentation marks and bending marks may occur on the display surface. Therefore, as such a film for a flexible display, it is required to have excellent mechanical strength (such as elastic modulus and maximum stress). In addition, as such a film for a flexible display, it is also required to have excellent optical properties such as transparency (such as haze value and total light transmittance). In response to these requirements, films containing polyamide resins have been studied and proposed.

[0005] For example, Patent Document 1 discloses an aromatic polyamide film having a predetermined structural unit and predetermined absorbance characteristics, which is a film with excellent transparency and solvent resistance. The predetermined structural unit is, in short, a structural unit derived from 2,2'-bis(trifluoromethyl)benzidine (TFMB). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2019-1853 [Overview of the project] [Problems that the invention aims to solve]

[0007] In Patent Document 1, 2,2'-bis(trifluoromethyl)benzidine (TFMB), used as a diamine monomer, has a trifluoromethyl group in its molecule and is a compound that falls under the category of so-called PFAS (Per- and polyfluoroalkyl substances). Compounds that fall under the category of PFAS are restricted or may be restricted in use by laws and regulations both domestically and internationally due to concerns about their impact on the environment or human health.

[0008] Therefore, there is a need for a polyamide-based resin that can exhibit film properties (transparency, mechanical strength) equivalent to or better than those obtained when TFMB is used as a diamine monomer, while avoiding the use of TFMB, and consequently, compounds that fall under the category of PFAS.

[0009] Therefore, the object of the present invention is to solve the problems of the above-mentioned prior art and to provide a polyamide resin that can produce films with good haze value and elastic modulus using monomers that do not fall under the category of PFAS. Furthermore, the present invention aims to provide a film using such polyamide resin, and a flexible display using the film. [Means for solving the problem]

[0010] The inventors of the present invention conducted diligent studies to solve the above problems and found that the above problems can be solved by a polyamide resin having structural units represented by the following formula (1) and structural units represented by the following formula (2), derived from monomers that do not fall under the category of PFAS, and thus completed the present invention. The gist of the present invention, which solves the above problems, is as follows.

[0011] [1] Having structural units derived from diamine compounds and structural units derived from dicarboxylic acid compounds, The structural unit derived from the diamine compound includes the structural unit represented by the following formula (1), A polyamide resin in which the structural units derived from the dicarboxylic acid compound include the structural units represented by the following formula (2). [ka] [ka]

[0012] [2] The polyamide resin according to [1], which has neither a perfluoroalkyl portion nor a polyfluoroalkyl portion.

[0013] [3] The polyamide resin according to [1] or [2], wherein the structural unit derived from the diamine compound further comprises a structural unit represented by the following formula (3). [ka] In formula (3), R 1 and R 2 Each of these independently represents a hydrogen atom, a halogen atom, a hydroxyl group, or an alkyl group having 1 to 5 carbon atoms.

[0014] [4] The polyamide resin according to any one of [1] to [3], wherein the proportion of the structural unit represented by the formula (1) in the structural unit derived from the diamine compound is 50 mol% or more.

[0015] [5] The polyamide resin according to any one of [1] to [4], wherein the structural unit derived from the dicarboxylic acid compound further contains a structural unit represented by the following formula (4). [Chemical formula]

[0016] [6] The polyamide resin according to any one of [1] to [5], wherein the proportion of the structural unit represented by the formula (2) in the structural unit derived from the dicarboxylic acid compound is 50 mol% or more.

[0017] [7] The polyamide resin according to any one of [1] to [6], wherein the structure connecting the monomer components substantially consists only of an amide structure.

[0018] [8] The polyamide resin according to any one of [1] to [7], having a weight average molecular weight of 120,000 or more and 300,000 or less.

[0019] [9] A polyamide film containing the polyamide resin according to any one of [1] to [8].

[0020]

[10] A flexible display including the polyamide film according to [9]. [Advantages of the Invention]

[0021] According to the present invention, it is possible to provide a polyamide resin that can produce a film having good haze value and modulus of elasticity by using monomers that do not fall under PFAS. Further, the present invention can provide a film using such a polyamide resin and a flexible display using the film. [Embodiments for Carrying Out the Invention]

[0022] The polyamide resin, polyamide film, and flexible display of the present invention will be described in detail below based on their embodiments.

[0023] <Polyamide resin> A polyamide resin according to one embodiment of the present invention (hereinafter sometimes referred to as "the polyamide resin of this embodiment") is It has structural units derived from diamine compounds and structural units derived from dicarboxylic acid compounds. The structural unit derived from the diamine compound includes the structural unit represented by the following formula (1), The polyamide resin is characterized in that the structural units derived from the dicarboxylic acid compound include structural units represented by the following formula (2). [ka] [ka]

[0024] The polyamide resin of this embodiment, by containing the structural unit represented by formula (1) and the structural unit represented by formula (2), can contribute to a good haze value and elastic modulus when used in a film.

[0025] In this specification, "polyamide resin" refers to a resin having structural units derived from a diamine compound and structural units derived from a dicarboxylic acid compound, and having an amide structure formed therein. Such a polyamide resin can be obtained, for example, by reacting a diamine compound and a dicarboxylic acid compound, which are monomer components, to form an amide structure through such reaction. In this embodiment, the polyamide resin is characterized by a structure that substantially does not contain imide structures in the structure that binds the constituent monomer components. That is, the polyamide resin of this embodiment is different from a polyamide-imide resin. Furthermore, it is preferable that the polyamide resin of this embodiment consists substantially only of amide structures in the structure that binds the constituent monomer components. In this embodiment, the structure that binds the constituent monomer components does not include a structure in which the end-capturing agent described later binds to the polyamide resin.

[0026] In the resin film of this embodiment, if the resin has a fluorinated alkyl group, it is preferable that at least one hydrogen atom, chlorine atom, bromine atom, or iodine atom is bonded to the fluorinated carbon atom of the alkyl group. In other words, it is preferable that the polyamide resin of this embodiment does not have perfluoroalkyl and polyfluoroalkyl portions. In this embodiment, the perfluoroalkyl and polyfluoroalkyl portions refer to "portions containing a completely fluorinated methyl group or methylene group (a carbon atom to which fluorine is bonded that does not have H, Cl, Br, or I atoms bonded)." If the polyamide resin of this embodiment has perfluoroalkyl and polyfluoroalkyl portions, the polyamide resin may fall under the category of PFAS and be subject to legal regulations. Specifically, the perfluoroalkyl and polyfluoroalkyl moieties include, for example, trifluoromethyl (-CF3) and perfluoroalkylene (-CF2). n -) (provided that the carbon atom to which fluorine is bonded does not have H, Cl, Br, or I atoms bonded to it), and these may further be bonded to alkyl groups or alkylene groups, specifically, for example, -(CH2) n The group represented by CF3, -(CF2) n Examples include groups represented by CH3.

[0027] (Structural units derived from diamine compounds) The polyamide resin of this embodiment includes a structural unit represented by the above formula (1) as a structural unit derived from a diamine compound.

[0028] The structural unit represented by formula (1) is preferably a structural unit derived from the diamine compound represented by the following formula (1A). The diamine compound represented by the following formula (1A) is 2,2'-dimethylbenzidine (m-tolidine (hereinafter sometimes also referred to as "m-Tolidine")). [ka] The m-tolidine represented by formula (1A), which is a diamine compound that can be used to form the structural unit represented by formula (1) above, is thought to contribute to improving the elastic modulus of the film while maintaining a lower haze value compared to conventional diamine compounds (e.g., 2,2'-bis(trifluoromethyl)benzidine (TFMB), etc.). The reason for this is not clear, but it is presumed that because the substituent bonded to the aromatic ring of the diamine compound represented by formula (1A) is a methyl group, the size of the molecular chain is reduced, allowing the polymer to exist more closely within the film, thus moderately improving the density of the film, and thus improving the elastic modulus of the film while maintaining the haze value.

[0029] The polyamide resin of this embodiment may contain structural units other than the structural unit represented by formula (1) above, as structural units derived from the diamine compound, to the extent that it does not impede the effects of the present invention. In general terms, in the synthesis of the polyamide resin of this embodiment, a diamine compound other than m-tolidine may be used as the diamine compound. Such a diamine compound other than m-tolidine may be an aromatic diamine compound or an aliphatic diamine compound. Furthermore, such a diamine compound other than m-tolidine may be a single compound or a combination of two or more compounds. The diamine compound other than m-tolidine is not particularly limited, and conventionally known diamine compounds can be used.

[0030] In addition to the structural unit represented by formula (1) above, the structural unit represented by formula (3) below may also be included in the structural unit derived from the diamine compound. In other words, the polyamide resin of this embodiment may further include the structural unit represented by formula (3) below in addition to the structural unit derived from the diamine compound. [ka] (In formula (3), R 1 and R 2 Each of these independently represents a hydrogen atom, a halogen atom, a hydroxyl group, or an alkyl group having 1 to 5 carbon atoms. The polyamide resin of this embodiment can be made colorless by including the structural unit represented by formula (3) above. The structural unit represented by formula (3) contains aromatic rings (benzene rings, fluorene skeleton), so it has high rigidity and a large molecular volume. In addition, polymers having the structural unit represented by formula (3) have a bent structure (the aromatic rings are oriented in different directions) due to the inclusion of the fluorene skeleton, etc., so they tend to have low birefringence (the phenomenon in which light is refracted in two different directions when incident on a substance). It is presumed that these factors work together to impart good colorlessness to the film when the structural unit represented by formula (3) is included.

[0031] In formula (3) above, examples of halogen atoms include fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms. In formula (3) above, it is more preferable that the halogen atom is a fluorine atom.

[0032] Furthermore, in formula (3) above, the alkyl group having 1 to 5 carbon atoms is preferably an alkyl group having 1 to 3 carbon atoms, and more preferably an alkyl group having 1 carbon atom, i.e., a methyl group. Examples of alkyl groups having 1 to 5 carbon atoms include methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, n-pentyl group, isopentyl group, tert-pentyl group, neopentyl group, 1,2-dimethylpropyl group, cyclopropyl group, cyclobutyl group, cyclopentyl group, and the like.

[0033] The structural unit represented by formula (3) above is preferably a structural unit derived from diamine compounds such as 9,9-bis(4-aminophenyl)fluorene and 9,9-bis(4-amino-3-fluorophenyl)fluorene (FFDA).

[0034] Furthermore, diamine compounds that can be used to form the structural unit represented by formula (3) above (for example, 9,9-bis(4-amino-3-fluorophenyl)fluorene (FFDA)) have the characteristic of being more receptive to various dicarboxylic acid compounds and having better solubility of the resin (polymer) obtained after the reaction compared to conventional diamine compounds (for example, 2'-bis(trifluoromethyl)benzidine (TFMB), etc.). Diamine compounds that can be used to form the structural unit represented by formula (3) above have not only a highly rigid structure but also a moderately bent structure, which allows solvent molecules to easily penetrate the gaps and can weaken intermolecular forces. Therefore, it is presumed that polyamide resins using diamine compounds that can be used to form the structural unit represented by formula (3) above as diamine compounds have lower crystallinity and, as a result, are likely to have better solubility and other properties compared to polyamide resins using conventional diamine compounds such as TFMB.

[0035] In the polyamide resin of this embodiment, it is preferable that the proportion of structural units represented by formula (1) to structural units derived from the diamine compound is 50 mol% or more. In this case, the mechanical strength of the film can be improved. From a similar viewpoint, it is more preferable that the proportion of structural units represented by formula (1) to structural units derived from the diamine compound is 60 mol% or more, even more preferable that it is 75 mol% or more, and even more preferable that it is 85 mol% or more. It is also preferable that the proportion of structural units represented by formula (1) to structural units derived from the diamine compound is 100 mol% (i.e., the structural units derived from the diamine compound consist only of structural units represented by formula (1)). On the other hand, the proportion of structural units represented by formula (1) to structural units derived from the diamine compound may be 95 mol% or less, or 90 mol% or less. The above upper and lower limits can be changed as appropriate.

[0036] Furthermore, in the polyamide resin of this embodiment, if the structural units derived from the diamine compound further include the structural units represented by formula (3), it is preferable that the structural units derived from the diamine compound consist only of the structural units represented by formula (1) and the structural units represented by formula (3). In this case, the molar ratio of the structural units represented by formula (1) to the structural units represented by formula (3) (structural units represented by formula (1):structural units represented by formula (3)) is preferably 90:10 to 25:75, more preferably 90:10 to 50:50, and even more preferably 75:25 to 50:50, from the viewpoint of colorlessness and balance between haze value and elastic modulus.

[0037] (Structural units derived from dicarboxylic acid compounds) The polyamide resin of this embodiment includes a structural unit represented by formula (2) above as a structural unit derived from a dicarboxylic acid compound. It is presumed that by including a structural unit represented by formula (2) above as a structural unit derived from a dicarboxylic acid compound, transparency (low haze value) and other properties can be imparted to the polyamide resin while maintaining a high modulus of elasticity.

[0038] In this specification, "dicarboxylic acid compound" includes dicarboxylic acids and derivatives of dicarboxylic acids. Examples of derivatives of dicarboxylic acids include acid chlorides of dicarboxylic acids and esters of dicarboxylic acids.

[0039] The structural unit represented by formula (2) is preferably a structural unit derived from the dicarboxylic acid dichloride represented by formula (2A) below. The dicarboxylic acid dichloride represented by formula (2A) below is oxybisbenzoyl chloride (DEDC). [ka]

[0040] In the polyamide resin of the present invention, the structural units derived from the dicarboxylic acid compound may include structural units other than the structural unit represented by formula (2) above, as long as they do not hinder the effects of the present invention. The structural units other than the structural unit represented by formula (2) may be a single type or a combination of two or more types.

[0041] Furthermore, the structural units derived from the dicarboxylic acid compound may also include structural units represented by the following formula (4), in addition to the structural units represented by formula (2) above. Including the structural units represented by the following formula (4) improves mechanical strength, such as the modulus of elasticity. [ka]

[0042] The structural unit represented by formula (4) is preferably a structural unit derived from an aromatic dicarboxylic acid dichloride represented by the following formula (4A). The aromatic dicarboxylic acid dichloride represented by the following formula (4A) is terephthalic acid chloride (TPC). [ka]

[0043] Examples of dicarboxylic acid compounds that provide structural units other than those represented by formulas (2) and (4) include aromatic dicarboxylic acid compounds and aliphatic dicarboxylic acid compounds. These dicarboxylic acid compounds may be used individually or in combination of two or more types.

[0044] Examples of aromatic dicarboxylic acid compounds include isophthalic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,4-phenylenedioxydiacetic acid, 1,3-phenylenedioxydiacetic acid, dibenzoic acid, diphenylmethane-4,4'-dicarboxylic acid, diphenylsulfone-4,4'-dicarboxylic acid, 4,4'-biphenyldicarboxylic acid, 3,3'-biphenyldicarboxylic acid, or derivatives thereof. These aromatic dicarboxylic acid compounds may be used individually or in combination of two or more.

[0045] Examples of aliphatic dicarboxylic acid compounds include succinic acid, 1,3-cyclobutanedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 1,10-decanedicarboxylic acid, or derivatives thereof. These aliphatic dicarboxylic acid compounds may be used individually or in combination of two or more.

[0046] In the polyamide resin of this embodiment, the proportion of structural units represented by formula (2) to structural units derived from the dicarboxylic acid compound is preferably 50 mol% or more. When the proportion of structural units represented by formula (2) is 50 mol% or more, transparency (low haze value) can be maintained while maintaining a high modulus of elasticity. From a similar viewpoint, the proportion of structural units represented by formula (2) to structural units derived from the dicarboxylic acid compound is more preferably 60 mol% or more, even more preferably 75 mol% or more, and still more preferably 85 mol% or more. It is also preferable that the proportion of structural units represented by formula (2) to structural units derived from the dicarboxylic acid compound is 100 mol% (i.e., the structural units derived from the dicarboxylic acid compound consist only of structural units represented by formula (2)). On the other hand, the proportion of structural units represented by formula (2) to structural units derived from the dicarboxylic acid compound may be 95 mol% or less, or 90 mol% or less. The above upper and lower limits can be changed as appropriate.

[0047] Furthermore, in the polyamide resin of this embodiment, if the structural units derived from the dicarboxylic acid compound include the structural units represented by formula (4), it is preferable that the structural units derived from the dicarboxylic acid compound consist only of the structural units represented by formula (2) and the structural units represented by formula (4). In this case, the molar ratio of the structural units represented by formula (2) to the structural units represented by formula (4) (structural units represented by formula (2):structural units represented by formula (4)) is preferably 90:10 to 40:60, and more preferably 90:10 to 60:40, from the viewpoint of balancing transparency and mechanical strength.

[0048] (Various properties of polyamide resins) In this embodiment, the polyamide resin preferably has a number-average molecular weight (Mn) of 5,000 or more and 200,000 or less. When the number-average molecular weight (Mn) of the polyamide resin is 5,000 or more, the colorlessness, transparency, and / or mechanical strength of the film can be further improved, and when it is 200,000 or less, the handling during the synthesis of the polyamide resin and the production of the polyamide film can be further improved. From a similar viewpoint, the number-average molecular weight (Mn) of the polyamide resin in this embodiment is more preferably 10,000 or more, and more preferably 180,000 or less. These upper and lower limits can be appropriately rearranged. The number-average molecular weight (Mn) was measured by GPC (gel permeation chromatography) and calculated on a polystyrene equivalent basis.

[0049] In this embodiment, the polyamide resin preferably has a weight-average molecular weight (Mw) of 120,000 or more and 300,000 or less. When the weight-average molecular weight (Mw) of the polyamide resin is 120,000 or more, the colorlessness, transparency and / or mechanical strength of the film can be further improved, and when it is 300,000 or less, the handling during the synthesis of the polyamide resin and the manufacture of the polyamide film can be further improved. The weight-average molecular weight (Mw) was measured by GPC (gel permeation chromatography) and calculated on a polystyrene basis. Specifically, it can be measured by the method described in the examples.

[0050] The polyamide resin of this embodiment preferably has a dispersion degree (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.

[0051] (Manufacturing of polyamide resin) The polyamide resin of this embodiment is not particularly limited and can be produced (synthesized) by known methods for producing polyamides, such as solution polymerization, interfacial polymerization, melt polymerization, solid-phase polymerization, and precipitation polymerization. In this case, at least 2,2'-dimethylbenzidine (m-tolidine) represented by formula (1A) above can be used as the diamine compound, and oxybisbenzoyl chloride (DEDC) represented by formula (2A) above, which is an acid chloride of a dicarboxylic acid, can be used as the diamine compound.

[0052] The above synthesis can be carried out in an aprotic organic polar solvent. Examples of aprotic organic polar solvents 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; hexamethylphosphoramide; and γ-butyrolactone. These aprotic organic polar solvents may be used individually or in combination of two or more. Aromatic hydrocarbons such as xylene and toluene can also be used as solvents. Furthermore, to promote the dissolution of the resulting polymer, a salt of an alkali metal or alkaline earth metal in an amount of 50% by mass or less may be added to the solvent.

[0053] In the reaction between diamine compounds and dicarboxylic acid dichlorides, hydrogen chloride is produced as a by-product. Therefore, it can be neutralized using a neutralizing agent. Examples of neutralizing agents include inorganic neutralizing agents such as calcium hydroxide, calcium carbonate, and lithium carbonate; and organic neutralizing agents such as 1,2-butylene oxide, ethylene oxide, propylene oxide, ethylene carbonate, glycidylphenyl ether, ammonia, and pyridine.

[0054] When using two or more diamine compounds as monomers, for example, the diamine compounds can be added one by one, reacted with 10 to 99 mol% of dicarboxylic acid dichloride, then the other diamine compounds can be added, followed by further addition of dicarboxylic acid dichloride, allowing for a stepwise reaction. Alternatively, all diamine compounds can be mixed and added, followed by the addition of dicarboxylic acid dichloride, allowing for a single reaction. The same procedure applies when using two or more dicarboxylic acid dichloride monomers.

[0055] The ratio of the diamine compound to the dicarboxylic acid dichloride (moles of diamine compound to moles of dicarboxylic acid dichloride) can be adjusted as appropriate depending on the molecular weight of the target polyamide resin, for example, it can be set to 49:51 to 51:49. In this case, a polyamide resin with a sufficiently large molecular weight and excellent mechanical properties can be obtained.

[0056] To prevent discoloration of the resulting polyamide resin, a yellowing inhibitor may be added to the reaction system described above. Examples of such yellowing inhibitors include phosphorus compounds such as trimethyl phosphate, triethyl phosphate, triphenyl phosphate, and dimethyl phenylphosphonate. The yellowing inhibitor may also be added in the step of preparing the solution containing the polyamide resin in the method for producing the polyamide film described later.

[0057] In the above reaction, the terminals can be amine-terminated or carboxylic acid-terminated depending on the charging ratio of the monomer raw materials. Therefore, from the viewpoint of further improving the transparency of the produced film, it is preferable to encapsulate the ends of the polyamide resin. Examples of compounds used for encapsulating the ends of the polyamide resin (end encapsulants) include amines other than the monomer used, carboxylic acid chlorides, carboxylic acid anhydrides, etc. More specifically, examples include acetyl chloride (acetyl chloride), benzoyl chloride, substituted benzoyl chloride, acetic anhydride, 5-norbornene-2,3-dicarboxylic acid anhydride, 4-ethynylaniline, 4-phenylethynylphthalic anhydride, maleic anhydride, etc.

[0058] The reaction conditions for the synthesis of polyamide resin can be a temperature of -30 to 50°C and a reaction time of 10 minutes to 27 hours. Furthermore, to maintain colorless transparency, the synthesis may be carried out under a nitrogen atmosphere.

[0059] (Applications of polyamide resin) The polyamide resin of this embodiment is not limited to the films described later, but can be used in a wide range of other applications, including sheets, pipes, tubes, filaments, fibers, containers, and other materials.

[0060] <Polyamide film> A polyamide film according to one embodiment of the present invention (hereinafter sometimes referred to as "the polyamide film of this embodiment") is characterized by containing the polyamide resin of this embodiment described above. Since the polyamide film of this embodiment contains the polyamide resin described above, it has good haze value and elastic modulus. More preferably, the polyamide film of this embodiment can exhibit film properties equivalent to or better than those when TFMB is used as the diamine monomer.

[0061] The thickness of the polyamide film in this embodiment is not particularly limited and can be set appropriately depending on the application. For example, the thickness of the polyamide film can be 10 μm or more, or 30 μm or more, and it can also be 150 μm or less, or 100 μm or less. The thickness of a polyamide film can be measured using a micrometer.

[0062] The polyamide film of this embodiment preferably has a haze value of 10% or less. A haze value of 10% or less in the polyamide film provides excellent transparency, making it suitable as a film for displays and the like. Furthermore, the haze value of the polyamide film is more preferably 5.0% or less, even more preferably 2.0% or less, and particularly preferably 1.0% or less. The haze value can be measured using a haze meter in accordance with ASTM D1003.

[0063] The polyamide film of this embodiment preferably has a total light transmittance of 80% or more, and more preferably 82% or more. Total light transmittance can be measured using a haze meter in accordance with ASTM D1003.

[0064] In this embodiment, the polyamide film preferably has a tensile modulus of 3.0 GPa or higher, more preferably greater than 3.5 GPa, even more preferably greater than 4.0 GPa, and may have a tensile modulus of 6.0 GPa or higher, from the viewpoint of mechanical strength. Furthermore, from the viewpoint of balancing the mechanical strength and flexibility of the film, the tensile modulus may be 10.0 GPa or less, or 8.0 GPa or less. In the case of the polyamide film of this embodiment, if there is anisotropy between the tensile modulus in the MD direction and the tensile modulus in the TD direction, the tensile modulus mentioned above refers to the average value of the tensile modulus in the MD direction and the tensile modulus in the TD direction, unless otherwise specified. The tensile modulus can be measured by the method described in the examples.

[0065] The polyamide film of this embodiment may optionally contain other components in addition to the polyamide resin of this embodiment described above, as long as it does not depart from the objectives of the present invention. Examples of such other components include other resins other than the polyamide resin of this embodiment described above, leveling agents, dispersants, surfactants, retardation modifiers, antioxidants, UV inhibitors, light stabilizers, plasticizers, waxes, fillers, pigments, dyes, foaming agents, defoaming agents, dehydrating agents, antistatic agents, antibacterial agents, antifungal agents, bluing agents to reduce the yellowness of the film, pH adjusters, crosslinking agents, lubricants, and the like.

[0066] The polyamide film of this embodiment is preferably substantially free of compounds having perfluoroalkyl and polyfluoroalkyl moieties, because such compounds may fall under the category of PFAS and be subject to legal regulations.

[0067] Furthermore, from the viewpoint of improving mechanical strength, it is preferable that the other components include a filler. When the polyamide film containing the polyamide resin of this embodiment contains a filler, the polyamide resin of this embodiment has superior dynamic bending durability compared to the polyamide resin using TFMB as the diamine compound. The polyamide resin using TFMB contains fluorine, which results in low compatibility with the filler, and is therefore thought to have low peel strength at the interface with the filler. In contrast, the polyamide resin of this embodiment has high compatibility with the filler, resulting in high peel strength at the interface with the filler, and is therefore presumed to have superior dynamic bending durability compared to the polyamide resin using TFMB as the diamine compound.

[0068] When the polyamide film of this embodiment contains a filler, the material of the filler is not particularly limited, but examples include silica, titanium oxide, alumina (including alumina hydrate), silicon nitride, boron nitride, calcium hydrogen phosphate, calcium phosphate, mica, etc. Examples of alumina hydrate include boehmite type and pseudo-boehmite type. These fillers may be used individually or in combination of two or more. Among these, alumina (including alumina hydrate) is preferred as the material of the filler, boehmite type or pseudo-boehmite type is more preferred, and pseudo-boehmite type is even more preferred. That is, the filler is preferably an alumina filler, more preferably a boehmite type or pseudo-boehmite type alumina filler, and even more preferably a pseudo-boehmite type alumina filler. Furthermore, the filler is preferably fibrous. "Fibrous" refers to a shape with an aspect ratio (filler length / filler diameter) of 5 or more. If the polyamide film of this embodiment contains a filler, it is particularly preferable that the filler is a fibrous alumina filler.

[0069] The fibrous alumina filler is preferably dispersed with an average fiber diameter of 1 to 30 nm, preferably 2 to 25 nm, and more preferably 3 to 20 nm. Furthermore, the fibrous alumina filler is preferably dispersed with an average fiber length of 100 to 4,000 nm, preferably 200 to 3,000 nm, and more preferably 500 to 2,000 nm. If the fibrous alumina filler is dispersed in the polyamide film with the above-mentioned average fiber diameter and average fiber length ranges, such a film can achieve high elasticity while maintaining transparency. The average fiber diameter and average fiber length of the fibrous alumina filler in its dispersed state are measured by dissolving and diluting the polyamide film 10,000 times with the solvent used in its preparation (e.g., methyl isobutyl ketone, N,N-dimethylacetamide), dropping one drop onto a cover glass (cover glass trophy, manufactured by Matsunami Glass Co., Ltd.), drying at 50°C, and then observing it with a scanning probe microscope (e.g., topographic observation image using Hitachi High-Tech AFM5000II). Furthermore, the fibrous alumina filler to be measured may be a single fiber or a bundle of multiple single fibers, as long as it is visible as a single fiber in the scanning probe microscope image. The number-average length of the diameter in the short-side direction of 200 arbitrarily selected fibrous alumina fillers in the scanning probe microscope image is defined as the "average fiber diameter," and the number-average length of the diameter in the long-side direction is defined as the "average fiber length."

[0070] The filler content in the polyamide film of this embodiment can be appropriately set depending on the material of the filler, and for example, it can be 1 to 50 parts by mass per 100 parts by mass of polyamide resin. In particular, when the polyamide film of this embodiment contains fibrous alumina filler, the content of fibrous alumina filler 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, per 100 parts by mass of polyamide resin. When the content of fibrous alumina filler is within the above range, the film can be made highly elastic while maintaining transparency. Furthermore, when the content of fibrous alumina filler is within the above range, there is a tendency for an excellent balance between elastic modulus and bending durability.

[0071] Furthermore, when the above-mentioned filler is used, it is preferable to further use a dispersant. That is, when the polyamide film of this embodiment contains a filler, it is preferable to further contain a dispersant. Examples of the above-mentioned dispersant include, from the viewpoint of modifying the above-mentioned filler and stabilizing the viscosity of the solution containing the resin, organic carboxylic acid compounds such as acetic acid, benzoic acid, terephthalic acid, citric acid, succinic acid, and lactic acid; organic phosphoric acid compounds and organic phosphonic acid compounds; organic sulfonic acid compounds such as benzenesulfonic acid (phenylphosphonic acid), p-toluenesulfonic acid, and dodecylbenzenesulfonic acid; and organic bases such as pyridine, tetraethylamine, diisopropylethylamine, 2,6-dimethylpyridine, isoquinoline, and triethylenediamine.

[0072] (Method for manufacturing polyamide film) The method for manufacturing the polyamide film of this embodiment is not particularly limited. For example, the polyamide film of this embodiment can be manufactured by (1) dissolving and dispersing the polyamide resin of this embodiment and any other components in a solvent to prepare a solution containing the polyamide resin, (2) coating the solution onto a substrate to obtain a coating film, (3) drying the coating film, and (4) peeling the dried coating film from the substrate to obtain a film.

[0073] The solvent is not particularly limited as long as it can dissolve the polyamide resin, but from the viewpoint of film transparency and the like, solvents having a functional group selected from the group consisting of ester groups, ether groups, ketone groups, hydroxyl groups, sulfone groups, and sulfinyl groups, as well as amide solvents, are preferred. Such solvents may be used alone or two or more may be used in any ratio.

[0074] Solvents containing 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).

[0075] Examples of solvents containing 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).

[0076] Solvents containing a ketone group include cyclohexanone (boiling point 156°C), 1-phenylethanone (boiling point 202°C), benzaldehyde (boiling point 179°C), and methyl isobutyl ketone.

[0077] Examples of solvents containing hydroxyl groups include 2-methylphenol (boiling point 190°C), 3-methylphenol (boiling point 202°C), and octyl alcohol (boiling point 195°C).

[0078] Examples of solvents containing a sulfone group include methanesulfonic acid (boiling point 167°C), dimethyl sulfone (boiling point 238°C), diethylsulfone (boiling point 238°C), sulfolane (boiling point 285°C), and dapsone (boiling point 177°C).

[0079] Examples of solvents containing a sulfinyl group include dimethyl sulfoxide (boiling point 189°C).

[0080] 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).

[0081] Among these solvents, amide solvents are more preferred from the viewpoint of obtaining a film with excellent colorlessness, and N,N-dimethylacetamide is even more preferred.

[0082] Furthermore, if a solvent is used in the synthesis of polyamide resin, that solvent may be used directly in the preparation of the polyamide film.

[0083] The substrate is not particularly limited and includes glass, ceramics, metals (such as aluminum foil), and resin films (such as polyester films like PET and PEN, polyimide films, polyamide-imide films, polypropylene films, and thermoplastic films like polystyrene films). Circuits may be formed on these substrates using copper or the like.

[0084] Conventional methods can be used to coat the solution onto the substrate, such as dip coating, flow coating, roll coating, bar coating, blade coating, screen printing, curtain coating, and spray coating.

[0085] Methods for drying the coating include, for example, vacuum drying, heat drying, or a combination of both. When drying at atmospheric pressure, drying can be done at 30 to 350°C, and from the viewpoint of obtaining a colorless and highly transparent film, drying at 60 to 250°C for 30 seconds to 180 minutes is preferable. In such drying methods, stepwise drying can be performed by gradually increasing the temperature from a low temperature within the above temperature and time range. Drying may also be performed under a nitrogen atmosphere. After drying, the film may be allowed to cool at room temperature.

[0086] (Uses of polyamide film) The polyamide film of this embodiment can be used as a glass substitute material for cover films, base films, and the like of various components. Specifically, the polyamide film of this embodiment can be suitably used as a component for displays such as liquid crystal displays and organic EL displays (particularly flexible displays, as described later). In addition to the above, the polyamide film of this embodiment can also be used for touch panel components, flexible printed circuit boards, solar cell panel components, optical waveguide components, and other semiconductor-related components.

[0087] <Flexible Display> A flexible display according to one embodiment of the present invention is characterized by comprising the polyamide film described above. Because such a flexible display uses the polyamide film described above, it has good transparency and mechanical strength.

[0088] For example, the polyamide film of this embodiment can be used as part of the layers of a flexible display, such as a cover window, and bonded to other layers (shatterproof layer, anti-scatter layer, etc.) to create a flexible display. Such a flexible display can be used in flexible devices such as foldable mobile phones or tablets, and deformable solar panels. [Examples]

[0089] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way to the following examples.

[0090] <Measurement method> Various measurements of the polyamide resin and polyamide film prepared in the examples were performed according to the following procedure.

[0091] (1) Number average molecular weight (Mn), weight average molecular weight (Mw) The number-average molecular weight (Mn) and weight-average molecular weight (Mw) of the polyamide resin were measured using the GL7700 from GL Science. Column: TSKgelαM (manufactured by Tosoh Corporation) Column temperature: 40℃ Eluent: NMP solution containing 100 mmol / L H3PO4 (using an 85% aqueous solution of H3PO4 as the raw material) and 10 mmol / L LiBr. Calibration curve: Standard polystyrene Column flow rate: 0.7 mL / min The number-average molecular weight (Mn) and weight-average molecular weight (Mw) are expressed in terms of polystyrene equivalents.

[0092] (2) Total light transmittance, haze value The total light transmittance and haze value of the films were measured in accordance with ASTM D1003. Evaluation samples were prepared by cutting each example film to a size of 30 mm x 30 mm, and each evaluation sample was measured using a haze meter (NDH 7000 II, manufactured by Nippon Denshoku Industries Co., Ltd.). Note that a higher total light transmittance value indicates better transparency, while a lower haze value indicates better transparency.

[0093] (3) Film thickness The film thickness was measured using a micrometer (manufactured by Mitutoyo).

[0094] (4) Elastic modulus, elongation at break, maximum stress The elastic modulus (in GPa), elongation at break, and maximum point stress (in MPa) of the fabricated film were measured using Shimadzu Corporation's "EZ-SX" under the following conditions. The elastic modulus was determined as the slope of the stress in the obtained stress-strain curve from 0.2% to 0.5% strain. [Test conditions] Sample size: 80mm x 10mm Distance between gripping parts: 50mm Speed: 5mm / min Number of measurements: 3 For the filler-added samples, the elastic modulus, elongation at break, and maximum stress were measured in both the direction parallel to (MD) and the direction perpendicular to (TD) the coating direction used during film production. A higher tensile modulus value (or the average of the tensile moduli in the MD and TD directions for filler-added samples) indicates superior mechanical strength.

[0095] (5) Dynamic bending durability The dynamic bending durability of the fabricated film was measured using a benchtop durability tester (DMLHP-CS, manufactured by Yuasa System Equipment Co., Ltd.) under the following conditions. [Test conditions] Sample size: 100mm x 10mm Film thickness: 55-61 μm Direction: TD direction Bending curvature: 2mm between surfaces Folding speed: 40 times / min Maximum number of folds: 500,000 Measurement Method: An image was taken once every 200 folds to measure the maximum number of folds without breakage. For the number of folds, inward folding (indicated as "air-in" in the table) and outward folding (indicated as "air-out" in the table) were performed at the air interface during film formation, and the average value was calculated. Samples that did not break even after 500,000 folds are indicated as ">500" in the table.

[0096] <Monomer raw material: Diamine compound> The diamine compounds used as monomer raw materials in each example are as follows: m-Tolidine:2,2'-dimethylbenzidine FFDA: 9,9-Bis(4-amino-3-fluorophenyl)fluorene TFMB: 2,2'-bis(trifluoromethyl)benzidine

[0097] <Monomer raw material: Dicarboxylic acid compound> The dicarboxylic acid compounds used as monomer raw materials in each example are as follows: DEDC: 4,4'-Oxybisbenzoyl chloride (also known as 4,4'-Oxybis(benzoic acid chloride)) TPC: Terephthalate Chloride

[0098] <Examples 1-1 to 1-7, Comparative Examples 1-1 to 1-2: Polyamide films without fillers> (Synthesis of polyamide resin) In Example 1-1, 166.4 g of N,N-dimethylacetamide (DMAc) and 8.0 g of 1,2-butylene oxide were added to a vial containing a stirring bar, and 10.8 g of the diamine compound shown in Table 1 was dissolved to obtain a solution. Next, 14.7 g of the dicarboxylic acid compound shown in Table 1 was added while stirring, and the mixture was reacted at room temperature (approximately 25°C) for 30 minutes to 1 hour. Then, 0.4 g of an end-capturing agent (acetyl chloride) was added to this solution and stirred for 1 hour to obtain a solution containing the polyamide resin synthesized by the above reaction, with a solid content of 11-13% by mass. Polyamide resins for Examples 1-2 to 1-7 and Comparative Examples 1-1 to 1-2 were synthesized in the same manner as in Example 1-1, except that the molar ratios of each reacted diamine compound and dicarboxylic acid compound were as shown in Table 1.

[0099] The number-average molecular weight (Mn) and weight-average molecular weight (Mw) of the obtained polyamide resins are shown in Table 1.

[0100] (Preparation of polyamide film) Next, the solution containing the obtained polyamide resin (coating liquid) was coated onto a glass substrate using a bar coater to a target thickness of 55 μm after drying. Then, primary drying was performed in a hot air circulating dryer (DH612, manufactured by Yamato Scientific) at 120°C for 20 minutes, followed by secondary drying at 220°C for 20 minutes. After drying, the film was allowed to cool at room temperature (approximately 25°C) and peeled off the glass substrate to obtain a polyamide film.

[0101] The measurement results for the obtained polyamide film are shown in Table 1.

[0102] [Table 1]

[0103] Table 1 shows that the polyamide film of the example has a haze value and elastic modulus that are equivalent to or better than the polyamide film of the comparative example that uses TFMB as the diamine compound.

[0104] <Examples 2-1 to 2-12 and Comparative Examples 2-1 to 2-4: Polyamide films with fillers> (Synthesis of polyamide resins in Examples 2-4) In Example 2-4, 66.0 g of N,N-dimethylacetamide (DMAc) and 3.2 g of 1,2-butylene oxide were added to a vial containing a stirring bar, and 4.3 g of the diamine compound shown in Table 1 was dissolved to obtain a solution. Next, 6.0 g of the carboxylic acid compound was added while stirring, and the mixture was reacted at room temperature (approximately 25°C) for 30 minutes to 1 hour. Then, 0.2 g of the end-capturing agent (acetyl chloride) was added to this solution and stirred for 1 hour to obtain a solution containing the polyamide resin of Example 2-4 synthesized by the above reaction, with a solid content of 11-13% by mass. (Synthesis of polyamide resins in Comparative Examples 2-1 to 2-4) The polyamide resins used in Comparative Examples 2-1 to 2-4 were synthesized in the same manner as in Example 1-1, except that the molar ratios of each reacted diamine compound and dicarboxylic acid compound were as shown in Table 3.

[0105] (Preparation of varnish with alumina filler) In Example 2-1, to the solution containing the polyamide resin of Example 1-1, 3.75 parts by mass of phenylphosphonic acid per 100 parts by mass of polyamide resin, 200 parts by mass of alumina slurry (manufactured by Kawaken Fine Chemicals, alumina filler (pseudoboehmite filler), fiber diameter 5 nm, fiber length 800 nm, N,N-dimethylacetamide (DMAc) dispersion, solid content concentration 10 parts by mass, equivalent to 20 parts by mass of alumina filler per 100 parts by mass of polyamide resin), and 10 parts by mass of DMAc per 100 parts by mass of alumina filler were added and stirred in a rotation-and-revolution type stirring defoamer (manufactured by Shashin Kagaku Co., Ltd., SK-300SII) to prepare the alumina filler-added varnish of Example 2-1. Examples 2-2 to 2-12 and Comparative Examples 2-1 to 2-4, which contain alumina filler, were prepared in the same manner as in Example 2-1, except that the proportions of polyamide resin and filler used were as shown in Table 1. For Example 2-4, the polyamide resin specified in Example 2-4 was used, while the other examples used the polyamide resins synthesized in Examples 1-1 to 1-7, corresponding to the molar ratios shown in Table 2 or Table 3.

[0106] (Preparation of polyamide film) Next, the obtained alumina filler-added varnish was coated onto a glass substrate using a bar coater to a target thickness of 55 μm after drying. Then, primary drying was performed in a hot air circulating dryer (DH612, Yamato Scientific) at 120°C for 20 minutes, followed by secondary drying at 220°C for 20 minutes. After drying, the film was allowed to cool at room temperature (approximately 25°C) and peeled off the glass substrate to obtain a polyamide film with filler.

[0107] The measurement results for the obtained polyamide films are shown in Tables 2 and 3.

[0108] [Table 2]

[0109] [Table 3]

[0110] Table 2 shows that even when fillers are included, the haze value and elastic modulus remain good.

[0111] Table 3 shows that, when containing fillers, the polyamide film of the example exhibits superior bending resistance compared to the polyamide film of the comparative example using TFMB. [Industrial applicability]

[0112] According to the present invention, it is possible to provide a polyamide resin that can produce films with good haze value and elastic modulus using monomers that do not fall under the category of PFAS. Furthermore, the present invention can provide a film using such polyamide resin, and a flexible display using the film.

Claims

1. It has structural units derived from diamine compounds and structural units derived from dicarboxylic acid compounds. The structural unit derived from the diamine compound includes the structural unit represented by the following formula (1): A polyamide resin in which the structural units derived from the dicarboxylic acid compound include the structural units represented by the following formula (2). 【Chemistry 1】 【Chemistry 2】

2. The polyamide resin according to claim 1, which does not have a perfluoroalkyl portion or a polyfluoroalkyl portion.

3. The polyamide resin according to claim 1, wherein the structural unit derived from the diamine compound further includes a structural unit represented by the following formula (3). 【Transformation 3】 In formula (3), R １ and R ２ Each of these independently represents a hydrogen atom, a halogen atom, a hydroxyl group, or an alkyl group having 1 to 5 carbon atoms.

4. The polyamide resin according to claim 1, wherein the proportion of the structural unit represented by formula (1) to the structural units derived from the diamine compound is 50 mol% or more.

5. The polyamide resin according to claim 1, wherein the structural unit derived from the dicarboxylic acid compound further includes a structural unit represented by the following formula (4). 【Chemistry 4】

6. The polyamide resin according to claim 1, wherein the proportion of the structural unit represented by formula (2) to the structural units derived from the dicarboxylic acid compound is 50 mol% or more.

7. The polyamide resin according to claim 1, wherein the structure that binds the constituent monomer components consists substantially only of amide structures.

8. The polyamide resin according to claim 1, wherein the weight-average molecular weight is 120,000 or more and 300,000 or less.

9. A polyamide film comprising the polyamide resin described in any one of claims 1 to 8.

10. A flexible display comprising the polyamide film described in claim 9.

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