Polyimide polymer film, substrate for flexible display device using the same, and flexible display device

Abstract

The present disclosure relates to a polyimide polymer film capable of achieving excellent optical characteristics and high heat resistance, a substrate for a flexible display device using the same, and a flexible display device.

Description

Technical Field

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of Korean Patent Application No. 10-2020-0154457 filed on November 18, 2020, in the Korean Intellectual Property Office, and Korean Patent Application No. 10-2021-0106253 filed on August 11, 2021, in the Korean Intellectual Property Office, the disclosures of which are incorporated herein by reference in their entirety.

[0003] The present disclosure relates to a polyimide polymer film capable of achieving excellent optical characteristics and high heat resistance, a substrate for a flexible display device using the same, and a flexible display device. Background Art

[0004] The display device market is rapidly evolving, driven by flat panel displays (FPDs) that are easy to manufacture over large areas and can reduce thickness and weight. These FPDs include liquid crystal displays (LCDs), organic light emitting displays (OLEDs), and electrophoretic displays (EPDs).

[0005] In recent efforts to further expand the applications and uses of flat panel displays, particular attention has been focused on so-called flexible display devices in which flexible substrates are applied to flat panel displays. Applications of such flexible display devices have been particularly evaluated based on mobile devices such as smartphones, and their application fields have gradually expanded.

[0006] Generally, when producing flexible display devices and lighting devices, a multi-layer inorganic film such as a buffer layer, an active layer, and a gate insulator are formed on cured polyimide to produce a TFT device.

[0007] However, flexible displays exhibit problems such as afterimage recovery due to the application of plastic substrates. In addition, the deterioration of heat resistance, thermal conductivity and electrical insulation of plastic material substrates compared to those of glass substrates is problematic.

[0008] However, research is actively being conducted to replace glass substrates and apply plastic substrates having advantages of being lightweight and flexible and capable of being produced by a continuous process to mobile phones, notebook PCs, TVs, and the like.

[0009] Polyimide polymers have the advantages of being easy to synthesize, can be produced as thin films, and can be used in high-temperature processes. In line with the trend toward lighter and more sophisticated electronic devices, polyimide polymers are widely used as integration materials for semiconductor materials. In particular, much research is underway into the application of polyimide polymers in flexible plastic display panels, which require lightweight and flexible properties. Summary of the Invention

[0010] Technical issues

[0011] An object of the present disclosure is to provide a polyimide polymer film capable of achieving excellent optical characteristics and high heat resistance.

[0012] Another object of the present disclosure is to provide a substrate for a flexible display device and a flexible display device using the polyimide polymer film.

[0013] Technical Solution

[0014] To achieve the above object, according to one aspect of the present disclosure, there is provided a polyimide polymer film, comprising: a polyimide polymer comprising repeating units derived from a reaction product between three or more aromatic tetracarboxylic acids or derivatives thereof and an aromatic diamine having different structures, wherein the transmittance at wavelengths of 450 nm and 550 nm is 70% or greater, respectively, the thermal expansion coefficient in a temperature range of 100° C. or greater and 400° C. or less is −10 ppm / ° C. or greater and 30 ppm / ° C. or less, and the glass transition temperature is 400° C. or higher.

[0015] According to another aspect, provided is a substrate for a flexible display device including the polyimide polymer film.

[0016] According to yet another aspect, a flexible display device including the polyimide polymer film is provided.

[0017] Hereinafter, a polyimide polymer film according to a specific embodiment of the present disclosure, a substrate for a flexible display device using the same, and a flexible display device will be described in more detail.

[0018] Throughout this specification, unless otherwise stated, the technical terms used herein are only used to refer to specific embodiments and are not intended to limit the present disclosure.

[0019] As used herein, singular forms include plural references unless the context clearly indicates otherwise.

[0020] As used herein, the terms “include” or “comprising” specify specific features, regions, integers, steps, actions, elements and / or components, but do not preclude the existence or addition of different specific features, regions, integers, steps, actions, elements, components and / or groups.

[0021] Terms including ordinal numbers such as "first," "second," and the like are used only to distinguish one component from another and are not limited by the ordinal numbers. For example, a first component may be referred to as a second component, or similarly, a second component may be referred to as a first component without departing from the scope of the present disclosure.

[0022] In the present disclosure, (co)polymer is meant to include both polymers and copolymers, a polymer means a homopolymer composed of a single repeating unit, and a copolymer means a composite polymer containing two or more repeating units.

[0023] In the present disclosure, examples of the substituent are described below, but are not limited thereto.

[0024] In the present disclosure, the term "substituted" means that other functional groups are bonded to replace hydrogen atoms in the compound, and the position of substitution is not limited as long as the position is a position where the hydrogen atom is substituted (i.e., a position where a substituent can be substituted), and when two or more substituents are substituted, the two or more substituents may be the same as or different from each other.

[0025] In the present disclosure, the term "substituted or unsubstituted" means unsubstituted or substituted with one or more substituents selected from the group consisting of deuterium, a halogen group, a cyano group, a nitro group, a hydroxyl group, a carbonyl group, an ester group, an imide group, an amide group, a primary amino group, a carboxyl group, a sulfonic acid group, a sulfonamide group, a phosphine oxide group, an alkoxy group, an aryloxy group, an alkylthio group, an arylthio group, an alkylsulfonyl group, an arylsulfonyl group, a silyl group, a boron group, an alkyl group, a cycloalkyl group, an alkenyl group, an aryl group, an aralkyl group, an aralkenyl group, an alkylaryl group, an alkoxysilylalkyl group, an arylphosphino group, or a heterocyclic group containing at least one of N, O, and S atoms, or unsubstituted or substituted with a substituent in which two or more substituents are linked together from the substituents exemplified above. For example, a "substituent in which two or more substituents are linked together" may be a biphenyl group. That is, the biphenyl group may be an aryl group, and may also be interpreted as a substituent in which two phenyl groups are linked together.

[0026] In this disclosure, the symbol or It means a bond to another substituent, and a direct bond means a case where no other atom exists in the portion represented by L.

[0027] In this disclosure, aromaticity is the property of satisfying Huckel's Rule, according to which a compound can be defined as aromatic if all of the following three conditions are met.

[0028] 1) There must be 4n+2 electrons that are completely conjugated by empty p orbitals, unsaturated bonds, and lone electron pairs.

[0029] 2) 4n+2 electrons must form a planar isomer and form a ring structure.

[0030] 3) All atoms of the ring must be able to participate in conjugation.

[0031] In the present disclosure, an alkyl group is a monovalent functional group derived from an alkane and may be linear or branched. The number of carbon atoms in a linear alkyl group is not particularly limited, but is preferably 1 to 20. In addition, the number of carbon atoms in a branched alkyl group is 3 to 20. Specific examples of the alkyl group include methyl, ethyl, propyl, n-propyl, isopropyl, butyl, n-butyl, isobutyl, tert-butyl, sec-butyl, 1-methyl-butyl, 1-ethyl-butyl, pentyl, n-pentyl, isopentyl, neopentyl, tert-pentyl, hexyl, n-hexyl, 1-methylpentyl, 2-methylpentyl, 4-methyl-2-pentyl, 3,3-dimethylbutyl, 2-ethylbutyl, heptyl, n-heptyl, 1-methylhexyl, octyl, n-octyl, tert-octyl, 1-methylheptyl, 2-ethylhexyl, 2-propylpentyl, n-nonyl, 2,2-dimethylheptyl, 1-ethyl-propyl, 1,1-dimethyl-propyl, isohexyl, 2-methylpentyl, 4-methylhexyl, 5-methylhexyl, 2,6-dimethylheptan-4-yl, and the like, but are not limited thereto. The alkyl group may be substituted or unsubstituted, and when substituted, examples of the substituent are the same as described above.

[0032] In the present disclosure, haloalkyl means a functional group in which the above-mentioned alkyl is substituted by a halogen group, examples of which are fluorine, chlorine, bromine or iodine. The haloalkyl may be substituted or unsubstituted, and when substituted, examples of the substituent are the same as described above.

[0033] In the present disclosure, a multivalent functional group is a residue in which a plurality of hydrogen atoms bonded to any compound are removed, for example, it can be a divalent functional group, a trivalent functional group, and a tetravalent functional group. As an example, a tetravalent functional group derived from cyclobutane means a residue in which any four hydrogen atoms bonded to cyclobutane are removed.

[0034] In the present disclosure, the electron withdrawing group may include one or more selected from the group consisting of a haloalkyl group, a halogen group, a cyano group, a nitro group, a sulfonic acid group, a carbonyl group, and a sulfonyl group. Preferably, it may be a haloalkyl group such as a trifluoromethyl group (-CF3).

[0035] In this specification, a direct bond or a single bond means a bond connected to a bonding line without the presence of an atom or an atomic group at the corresponding position. Specifically, it means a case where no other atom exists in the portion represented as L1 or L2 in a chemical formula.

[0036] In this specification, weight average molecular weight means the weight average molecular weight according to polystyrene measured by GPC method. In the process of determining the weight average molecular weight according to polystyrene measured by GPC method, known analytical devices, detectors such as refractive index detectors and analytical columns can be used. The temperature, solvent and flow conditions of common applications can be used. A specific example of measurement conditions is as follows: using a Waters PL-GPC220 instrument and using a Polymer Laboratories PLgel MIX-B300mm length column. The evaluation temperature is 160 ° C, and for the solvent, 1,2,4-trichlorobenzene is used at a flow rate of 1 mL / min. The sample is prepared at a concentration of 10 mg / 10 mL and then supplied in an amount of 200 μL, and the value of Mw can be determined using a calibration curve formed using a polystyrene standard. Nine polystyrene standards with molecular weights of 2,000 / 10,000 / 30,000 / 70,000 / 200,000 / 700,000 / 2,000,000 / 4,000,000 / 10,000,000 were used.

[0037] Hereinafter, the present disclosure will be described in more detail.

[0038] According to one embodiment of the present disclosure, a polyimide polymer film can be provided, comprising: a polyimide polymer comprising repeating units derived from a reaction product between three or more aromatic tetracarboxylic acids or derivatives thereof having different structures and an aromatic diamine, wherein the transmittance at wavelengths of 450 nm and 550 nm is 70% or greater, respectively, the thermal expansion coefficient in a temperature range of 100° C. or greater and 400° C. or less is −10 ppm / ° C. or greater and 30 ppm / ° C. or less, and the glass transition temperature is 400° C. or greater.

[0039] The inventors have experimentally discovered that, as in the polyimide polymer film of one embodiment described above, by satisfying the characteristics of a transmittance of 70% or greater at wavelengths of 450 nm and 550 nm, respectively, a thermal expansion coefficient of -10 ppm / °C or greater and 30 ppm / °C or less in a temperature range of 100°C or greater and 400°C or less, and a glass transition temperature of 400°C or greater, it is possible to achieve excellent optical properties of colorless transparency with low yellowness and excellent transmittance while exhibiting a low thermal expansion coefficient and thus achieving high heat resistance, thereby completing the present disclosure.

[0040] Polyimide polymer means including both polyimide and its precursor polymer (such as polyamic acid or polyamic acid ester).That is, polyimide polymer can include at least one selected from polyamic acid repeating unit, polyamic acid ester repeating unit and polyimide repeating unit.That is, the polymer based on polyimide can include a type of polyamic acid repeating unit, a type of polyamic acid ester repeating unit, a type of polyimide repeating unit or a copolymer of these two or more types of repeating units.

[0041] One or more repeating units selected from the group consisting of a polyamic acid repeating unit, a polyamic acid ester repeating unit, and a polyimide repeating unit may form a main chain of the polyimide polymer.

[0042] The polyimide polymer film may include a cured product of the polyimide polymer. The cured product of the polyimide polymer means a product obtained through a curing process of the polyimide polymer.

[0043] As described above, the polyimide polymer film may include: a repeating unit including at least one selected from the group consisting of a repeating unit represented by the following Chemical Formula 1, a repeating unit represented by the following Chemical Formula 2, and a repeating unit represented by the following Chemical Formula 3; a polyimide repeating unit represented by the following Chemical Formula 4; and a polyimide repeating unit represented by the following Chemical Formula 5.

[0044] [Chemical Formula 1]

[0045]

[0046] [Chemical Formula 2]

[0047]

[0048] [Chemical Formula 3]

[0049]

[0050] wherein, in Chemical Formulas 1 to 3, at least one of R1 and R2 is an alkyl group having 1 to 10 carbon atoms, and the remainder is hydrogen, X1 to X3 are each independently a tetravalent organic group including a tetravalent functional group represented by the following Chemical Formula 6, wherein Y1 to Y3 are each independently a divalent organic group substituted with at least one fluorine-based functional group,

[0051] [Chemical Formula 6]

[0052]

[0053] Wherein, in Chemical Formula 6, Ar is a polycyclic aromatic divalent functional group,

[0054] [Chemical Formula 4]

[0055]

[0056] Wherein, in Chemical Formula 4,

[0057] X1' is an aromatic tetravalent functional group having 8 or fewer carbon atoms,

[0058] Y1' is an aromatic divalent functional group substituted with at least one fluorine-based functional group,

[0059] [Chemical Formula 5]

[0060]

[0061] Wherein, in Chemical Formula 5,

[0062] X1″ is an aromatic tetravalent functional group having 9 or more and 15 or less carbon atoms, and

[0063] Y1″ is an aromatic divalent functional group substituted with at least one fluorine-based functional group.

[0064] Since the polyimide polymer includes the polyimide repeating unit represented by Chemical Formula 4 and the polyimide repeating unit represented by Chemical Formula 5, and a repeating unit including at least one selected from the repeating unit represented by Chemical Formula 1, the repeating unit represented by Chemical Formula 2, and the repeating unit represented by Chemical Formula 3, it can exhibit excellent optical characteristics and simultaneously achieve high heat resistance.

[0065] In Chemical Formulas 1 to 3, X1 to X3 are each independently a tetravalent organic group including a tetravalent functional group represented by Chemical Formula 6, wherein X1 to X3 are functional groups derived from a tetracarboxylic dianhydride compound used to synthesize a polyimide polymer.

[0066] When the tetravalent functional group represented by Chemical Formula 6 is included in X1 to X3, an asymmetric structure with increased steric hindrance due to polycyclic rings is introduced into the polyimide chain structure, thereby reducing the refractive index difference between the plane direction and the thickness direction and achieving a low phase difference.

[0067] In Chemical Formula 6, Ar is a polycyclic aromatic divalent functional group. The polycyclic aromatic divalent functional group is a divalent functional group derived from a polycyclic aromatic hydrocarbon compound or a derivative compound thereof, and may include a fluorenylene group. Derivative compounds include all compounds into which one or more substituents are introduced or carbon atoms are replaced by heteroatoms.

[0068] More specifically, in Ar of Chemical Formula 6, the polycyclic aromatic divalent functional group may include a condensed cyclic divalent functional group including at least two or more aromatic cyclic groups. That is, the polycyclic aromatic divalent functional group may include at least two or more aromatic cyclic groups in the functional group structure, and the functional group may have a condensed ring structure.

[0069] The aromatic cyclic group may include an aromatic hydrocarbon group including one or more benzene rings, or a heteroaromatic hydrocarbon group in which carbon atoms in the aromatic hydrocarbon group are replaced by heteroatoms.

[0070] The polycyclic aromatic divalent functional group may contain at least two or more aromatic cyclic groups, and each of the two or more aromatic cyclic groups may directly form a condensed ring, or may form a condensed ring via another ring structure. As an example, when two benzene rings are each fused with a cycloalkyl ring structure, it can be defined that the two benzene rings form a condensed ring via the cycloalkyl ring.

[0071] The condensed cyclic divalent functional group containing at least two or more aromatic cyclic groups is a divalent functional group derived from a condensed cyclic compound containing at least two or more aromatic cyclic groups or a derivative compound thereof, and the derivative compound includes all compounds into which one or more substituents are introduced or carbon atoms are replaced by heteroatoms.

[0072] In one example, the tetravalent functional group represented by Chemical Formula 6 may include a functional group represented by the following Chemical Formula 6-1.

[0073] [Chemical Formula 6-1]

[0074]

[0075] Meanwhile, in Chemical Formulas 1 to 3, Y1 to Y3 are each independently a divalent organic group substituted with at least one fluorine-based functional group, wherein Y1 to Y3 may be a functional group derived from a diamine compound for synthesizing polyamic acid, polyamic acid ester or polyimide.

[0076] Substitution with highly electronegative fluorine-based functional groups, such as a trifluoromethyl group (-CF3), enhances the ability to suppress the formation of CTCs (charge transfer complexes) of π electrons present in the polyimide polymer chain, thereby ensuring improved transparency. Specifically, the stacking within the polyimide structure or between chains can be reduced, and due to steric hindrance and electrical effects, the electrical interaction between chromophores can be weakened, resulting in high transparency in the visible light region.

[0077] Specifically, the divalent organic group substituted with at least one fluorine-based functional group may include a functional group represented by the following Chemical Formula 7.

[0078] [Chemical Formula 7]

[0079]

[0080] In Chemical Formula 7, p is an integer of 0 or more and 5 or less.

[0081] More specifically, the polyimide polymer has the following characteristics: the terminal anhydride group (-OC-O-CO-) of the tetracarboxylic dianhydride can react with the terminal amino group (-NH2) of the aromatic diamine substituted with at least one fluorine-based functional group, thereby forming a bond between the nitrogen atom of the amino group and the carbon atom of the anhydride group.

[0082] That is, the polyimide polymer may include a combination of tetracarboxylic dianhydride represented by the following Chemical Formula 10′ and an aromatic diamine substituted with at least one fluorine-based functional group.

[0083] [Chemical Formula 10']

[0084]

[0085] In Chemical Formula 10', Ar' is a polycyclic aromatic divalent functional group.

[0086] The polycyclic aromatic divalent functional group is a divalent functional group derived from a polycyclic aromatic hydrocarbon compound, which is a divalent functional group derived from fluorene or its derivative compound, and may include a fluorenylene group. The derivative compound includes all compounds into which one or more substituents are introduced or carbon atoms are replaced by heteroatoms.

[0087] Specific examples of the tetracarboxylic dianhydride represented by Chemical Formula 10′ include 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride (BPAF).

[0088] The aromatic diamine substituted with at least one fluorine-based functional group is a compound in which amino groups (-NH2) are bonded to both ends of an aromatic divalent functional group substituted with at least one fluorine-based functional group. The details of the aromatic divalent functional group substituted with at least one fluorine-based functional group are the same as those described above.

[0089] More specifically, the polyimide polymer has the following characteristics: the terminal anhydride group (-OC-O-CO-) of the tetracarboxylic dianhydride represented by Chemical Formula 10' can react with the terminal amino group (-NH2) of the aromatic diamine substituted with at least one fluorine-based functional group, thereby forming a bond between the nitrogen atom of the amino group and the carbon atom of the anhydride group.

[0090] X1′ may be an aromatic tetravalent functional group having 8 or less carbon atoms, and X1″ may be an aromatic tetravalent functional group having 9 or more and 15 or less carbon atoms.

[0091] For example, the aromatic tetravalent functional group may be one of tetravalent functional groups represented by the following Chemical Formula 13.

[0092] [Chemical Formula 13]

[0093]

[0094] Wherein, in Chemical Formula 13, R1 to R6 are each independently hydrogen or an alkyl group having 1 to 6 carbon atoms, and L3 is any one selected from the following: a single bond, -O-, -CO-, -COO-, -S-, -SO-, -SO2-, -CR7R8-, -(CH2) t -、-O(CH2) t O-, -COO(CH2) t OCO-, -CONH-, phenylene, or a combination thereof, wherein R7 and R8 are each independently one of hydrogen, an alkyl group having 1 to 10 carbon atoms, or a haloalkyl group having 1 to 10 carbon atoms, and t is an integer from 1 to 10.

[0095] Specifically, the aromatic tetravalent functional group having 8 or less carbon atoms may include a functional group represented by the following Chemical Formula 10.

[0096] [Chemical Formula 10]

[0097]

[0098] That is, the polyimide polymer may include a polyimide repeating unit including an aromatic tetravalent functional group having 8 or less carbon atoms including the functional group represented by Chemical Formula 10.

[0099] More specifically, the aromatic tetravalent functional group having 9 or more and 15 or less carbon atoms may be a functional group represented by the following Chemical Formula 11.

[0100] [Chemical Formula 11]

[0101]

[0102] Wherein, in Chemical Formula 11, L is any one selected from the following: single bond, -O-, -CO-, -COO-, -S-, -SO-, -SO2-, -CR7R8-, -(CH2) t -、-O(CH2) t O-, -COO(CH2) tOCO-, -CONH-, phenylene, or a combination thereof, and t is an integer from 1 to 10.

[0103] That is, the polyimide polymer may include a polyimide repeating unit including an aromatic tetravalent functional group having 9 or more and 15 or less carbon atoms including the functional group represented by Chemical Formula 11.

[0104] More specifically, the aromatic tetravalent functional group having 9 or more and 15 or less carbon atoms may be a functional group represented by the following Chemical Formula 11-1.

[0105] [Chemical Formula 11-1]

[0106]

[0107] That is, the polyimide polymer includes a functional group derived from a tetracarboxylic dianhydride compound used to synthesize the polyimide polymer, and may include: a repeating unit including a tetravalent functional group represented by Chemical Formula 6, a polyimide repeating unit including an aromatic tetravalent functional group having 8 or less carbon atoms including a functional group represented by Chemical Formula 10, and a polyimide repeating unit including an aromatic tetravalent functional group having 9 or more and 15 or less carbon atoms including a functional group represented by Chemical Formula 11.

[0108] It is a tetracarboxylic dianhydride compound used to synthesize a polyimide polymer during the synthesis of the polyimide polymer, and can be achieved by using a mixture of the following components: a tetracarboxylic dianhydride compound including a tetravalent functional group represented by Chemical Formula 6, a tetracarboxylic dianhydride compound including a functional group represented by Chemical Formula 10, and a tetracarboxylic dianhydride compound including a functional group represented by Chemical Formula 11.

[0109] That is, the polymer may include: a first repeating unit comprising a repeating unit including at least one selected from the group consisting of a repeating unit represented by Chemical Formula 1, a repeating unit represented by Chemical Formula 2, and a repeating unit represented by Chemical Formula 3, wherein the functional group derived from tetracarboxylic dianhydride is a tetravalent functional group represented by Chemical Formula 6; a second repeating unit comprising a polyimide repeating unit represented by Chemical Formula 4, wherein the functional group derived from tetracarboxylic dianhydride is an aromatic tetravalent functional group having 8 or fewer carbon atoms; and a third repeating unit comprising a polyimide repeating unit represented by Chemical Formula 5, wherein the functional group derived from tetracarboxylic dianhydride is an aromatic tetravalent functional group having 9 or more and 15 or fewer carbon atoms. In the polyimide-based polymer, the first to third repeating units may be randomly arranged to form a random copolymer, or may form a block between the first repeating unit, a block between the second repeating unit, and a block between the third repeating unit to produce a block copolymer.

[0110] The polymer comprising the first to third repeating units can be prepared by reacting three or more types of different tetracarboxylic dianhydride compounds with a diamine compound, and the three types of tetracarboxylic dianhydrides can be added simultaneously to synthesize a random copolymer, or the three types of tetracarboxylic dianhydrides can be added sequentially to synthesize a block copolymer.

[0111] Meanwhile, the polyimide polymer may include the polyimide repeating unit represented by Chemical Formula 4 in an amount of 51 mol % or more and 90 mol % or less relative to 100 mol % of the total repeating units.

[0112] When the polymer includes the polyimide repeating unit represented by Chemical Formula 4 in an amount less than 51 mol%, the thermal expansion coefficient is 35 ppm / °C or greater, which may lead to a decrease in heat resistance. When the polyimide repeating unit represented by Chemical Formula 4 is included in an amount greater than 90 mol%, there may be a problem of significant deterioration of optical properties.

[0113] Within the above numerical range, the polyimide polymer film synthesized from the polyimide polymer can simultaneously satisfy the following characteristics: a glass transition temperature of 400°C or higher, a thermal expansion coefficient measured by increasing the temperature within a temperature range of 100°C or higher and 400°C or lower of -10ppm / °C or higher and 30ppm / °C or lower, and a transmittance of 70% or higher and 99% or lower at a wavelength of 450nm at a thickness of 10μm.

[0114] In addition, the polyimide polymer may include a repeating unit including at least one selected from the repeating unit represented by Chemical Formula 1, the repeating unit represented by Chemical Formula 2, and the repeating unit represented by Chemical Formula 3 in an amount of 5 mol% or more and 20 mol% or less, 10 mol% or more and 15 mol% or less, 10 mol% or more and 13 mol% or less, 10 mol% or more and 12.5 mol% or less, or 10 mol% or more and 12 mol% or less, relative to 100 mol% of the total repeating units.

[0115] When the polyimide polymer includes a repeating unit including at least one selected from the repeating unit represented by Chemical Formula 1, the repeating unit represented by Chemical Formula 2, and the repeating unit represented by Chemical Formula 3 in an amount of less than 5 mol%, there may be technical problems in that optical properties such as haze, yellowness, and transmittance are poor, and heat resistance is also deteriorated.

[0116] Within the above numerical range, the polyimide polymer film synthesized from the polyimide polymer can simultaneously satisfy the following characteristics: a glass transition temperature of 400°C or higher, a thermal expansion coefficient measured by increasing the temperature within a temperature range of 100°C or higher and 400°C or lower of -10ppm / °C or higher and 30ppm / °C or lower, and a transmittance of 70% or higher and 99% or lower at a wavelength of 450nm at a thickness of 10μm.

[0117] Meanwhile, the polymer may include the polyimide repeating unit represented by Chemical Formula 5 in an amount of 1 mol % or more and 40 mol % or less, 5 mol % or more and 40 mol % or less, or 5 mol % or more and 35 mol % or less.

[0118] Since the polymer includes the polyimide repeating unit represented by Chemical Formula 5 in an amount of 1 mol % or more and 40 mol % or less, the polymer may exhibit excellent optical characteristics and simultaneously achieve high heat resistance.

[0119] Within the above numerical range, the polyimide polymer film synthesized from the polyimide polymer can simultaneously satisfy the following characteristics: a glass transition temperature of 400°C or higher, a thermal expansion coefficient measured by increasing the temperature within a temperature range of 100°C or higher and 400°C or lower of -10ppm / °C or higher and 30ppm / °C or lower, and a transmittance of 70% or higher and 99% or lower at a wavelength of 450nm at a thickness of 10μm.

[0120] The repeating units including at least one selected from the repeating unit represented by Chemical Formula 1, the repeating unit represented by Chemical Formula 2, and the repeating unit represented by Chemical Formula 3; the polyimide repeating unit represented by Chemical Formula 4; and the polyimide repeating unit represented by Chemical Formula 5 may be included in an amount of 70 mol% or more, or 80 mol% or more, or 90 mol% or more, or 70 mol% or more and 100 mol% or less, 80 mol% or more and 100 mol% or less, 70 mol% or more and 90 mol% or less, 70 mol% or more and 99 mol% or less, 80 mol% or more and 99 mol% or less, or 90 mol% or more and 99 mol% or less.

[0121] That is, the polyimide polymer is composed only of a repeating unit including at least one selected from the repeating unit represented by Chemical Formula 1, the repeating unit represented by Chemical Formula 2, and the repeating unit represented by Chemical Formula 3; the polyimide repeating unit represented by Chemical Formula 4; and the polyimide repeating unit represented by Chemical Formula 5, or most of the polyimide polymer may be composed of a repeating unit including at least one selected from the repeating unit represented by Chemical Formula 1, the repeating unit represented by Chemical Formula 2, and the repeating unit represented by Chemical Formula 3; the polyimide repeating unit represented by Chemical Formula 4; and the polyimide repeating unit represented by Chemical Formula 5.

[0122] More specifically, the polyimide polymer may not be mixed with other diamines except for the diamine capable of generating an aromatic divalent functional group substituted with at least one fluorine-based functional group, or may be mixed in a very small amount of less than 1 mol%.

[0123] Meanwhile, the polyimide polymer film may include a compound represented by the following Chemical Formula 9.

[0124] [Chemical Formula 9]

[0125]

[0126] In Chemical Formula 9, R3 to R5 are each independently hydrogen, hydroxyl, alkyl or aryl.

[0127] Specifically, in Chemical Formula 9, R3 to R5 may each independently be an aryl group.

[0128] For example, the compound represented by Chemical Formula 9 may include a compound represented by the following Chemical Formula 9-1.

[0129] [Chemical Formula 9-1]

[0130]

[0131] Meanwhile, the compound represented by Chemical Formula 9 may be included in an amount of 0.5 wt % or more and 20 wt % or less relative to the total weight of the polymer solid content.

[0132] Within the above numerical range, the polyimide polymer film can simultaneously satisfy the following characteristics: a glass transition temperature of 400°C or higher, a thermal expansion coefficient measured by increasing the temperature within a temperature range of 100°C or higher and 400°C or lower of -10ppm / °C or higher and 30ppm / °C or lower, and a transmittance of 70% or higher and 99% or lower at a wavelength of 450nm at a thickness of 10μm.

[0133] At the same time, the polyimide polymer film can have the following characteristics: a transmittance of 70% or more at wavelengths of 450nm and 550nm, respectively, a thermal expansion coefficient of -10ppm / °C or more and 30ppm / °C or less in a temperature range of 100°C or more and 400°C or less, and a glass transition temperature of 400°C or more.

[0134] An example of a method for measuring the glass transition temperature is not particularly limited, but for example, using a thermomechanical analyzer (TMA Q400 from TA Instruments), the force for stretching the film is set to 0.2 N, a first heating process is performed in a temperature range of 100° C. to 400° C. at a heating rate of 5° C. / min, and then the inflection point appearing in the heating section in the first heating process can be determined as Tg.

[0135] In addition, for the polyimide polymer film, the thermal expansion coefficient measured by increasing the temperature within a temperature range of 100°C or higher and 400°C or lower may be -10ppm / °C or greater, 0ppm / °C or greater, may be 30ppm / °C or less, 25ppm / °C or less, 23ppm / °C or less, may be -10ppm / °C or greater and 30ppm / °C or less, or -10ppm / °C or greater and 25ppm / °C or less, or -10ppm / °C or greater and 23ppm / °C or less, or 0ppm / °C or greater and 23ppm / °C or less.

[0136] The coefficient of thermal expansion is determined by measuring the change in thermal expansion using TMA Q400 (TA Instruments) when the force for stretching the polyimide film sample is set to 0.2 N or less and the temperature is increased at a rate of 1°C / min or more and 10°C / min or less, or 4°C / min or more and 6°C / min or less within a temperature range including a temperature section of 100°C to 400°C.

[0137] As described above, since the polyimide polymer film has a low coefficient of thermal expansion, it can mitigate deformation caused by heat and improve heat resistance. When used as a plastic substrate, it can prevent the plastic substrate from being damaged by heat when a metal layer formed on the plastic substrate is heat-treated, and it can also suppress the occurrence of warping in the metal thin film formed on the plastic substrate.

[0138] The yellowness index YI of the polyimide film at a thickness of 10 μm may be 1.0 or greater and 25.0 or less. When the yellowness index YI of the polyimide polymer film at a thickness of 10 μm excessively increases to greater than 25.0, there is a limitation that the degree of yellowing of the polyimide film increases, making it difficult to produce a colorless and transparent film.

[0139] Examples of the method and apparatus for measuring YI according to one embodiment are not particularly limited, and various methods conventionally used for measuring YI can be applied without limitation. As an example, a colorimeter (Color-Eye 7000A from GRETAGMACBETH) can be used to measure YI.

[0140] In addition, the polyimide polymer film may have transmittances of 70% or more at wavelengths of 450 nm and 550 nm, respectively.

[0141] Specifically, the transmittance of the polyimide film at a wavelength of 450 nm at a thickness of 10 μm may be 70% or more, 71% or more, 99% or less, 95% or less, or 80% or less, or 70% or more and 99% or less, 71% or more and 99% or less, 71% or more and 95% or less, or 71% or more and 80% or less. When the transmittance of the polyimide polymer film at a wavelength of 450 nm at a thickness of 10 μm is less than 70%, the degree of yellowing of the polyimide film increases, making it difficult to produce a colorless and transparent film.

[0142] In addition, the transmittance of the polyimide film at a wavelength of 550 nm at a thickness of 10 μm may be 70% or more, 80% or more, 85% or more, 88% or more, 99% or less, 95% or less, or 90% or less, or 70% or more and 99% or less, 80% or more and 99% or less, 85% or more and 99% or less, 88% or more and 95% or less, or 88% or more and 90% or less. When the transmittance of the polyimide polymer film at a wavelength of 550 nm at a thickness of 10 μm is less than 70%, there is a limitation that the degree of yellowing of the polyimide film increases, making it difficult to produce a colorless and transparent film.

[0143] Examples of the method and instrument for measuring transmittance according to one embodiment are not particularly limited, and various methods conventionally used for measuring transmittance can be applied without limitation. As an example, transmittance (T) can be measured using a UV-vis spectroscopy (model name: HR-100, Murakami Color Research Laboratory) device according to the measurement method of JIS K 7105.

[0144] In addition, the Td 1% of the polyimide polymer film may be 500° C. or higher, or 550° C. or higher, and may be 600° C. or lower, 554° C. or lower, or 500° C. or higher and 600° C. or lower, 550° C. or higher and 600° C. or lower, or 550° C. or higher and 554° C. or lower. Since the polyimide polymer film of the embodiment includes the above-mentioned polyimide polymer, the Td 1% can be achieved.

[0145] Td 1% may mean a temperature when the weight reduction rate of the initial polyimide polymer film is 1%, and is not particularly limited, but for example, it can be measured using Discovery TGA from TA Instruments.

[0146] In addition, the elongation of the polyimide polymer film may be 15% or more, 16% or more, 25% or less, or 24% or less, and may be 15% or more and 25% or less, 15% or more and 24% or less, or 16% or more and 24% or less. Since the polyimide polymer film of the embodiment includes the above-mentioned polyimide polymer, the above elongation can be achieved.

[0147] The elongation is measured by preparing a sample having a size of 5 mm*100 mm and a thickness of 10 μm for the polyimide polymer film of the embodiment, and measuring the distance between the clamps at speeds of 30 mm / min and 10 mm / min using an Instron 3365 instrument.

[0148] In addition, the tensile strength of the polyimide polymer film can be 215 MPa or more, 218 MPa or more, it can also be 350 MPa or less, 330 MPa or less, 320 MPa or less, can be 215 MPa or more and 350 MPa or less, 215 MPa or more and 330 MPa or less, 215 MPa or more and 320 MPa or less, or 218 MPa or more and 320 MPa or less. Since the polyimide polymer film of the embodiment includes the above-mentioned polyimide polymer, the tensile strength can be achieved.

[0149] The tensile strength is measured by preparing a sample having a size of 5 mm*100 mm and a thickness of 10 μm for the polyimide polymer film of the embodiment and measuring the distance between the grips at speeds of 30 mm / min and 10 mm / min using an Instron 3365 instrument.

[0150] In addition, the tensile modulus of the polyimide polymer film may be 5.3 GPa or more, 5.5 GPa or more, 7.0 GPa or less, 6.8 GPa or less, 6.7 GPa or less, 5.3 GPa or more and 7.0 GPa or less, 5.3 GPa or more and 6.8 GPa or less, 5.5 GPa or more and 6.8 GPa or less, or 5.5 GPa or more and 6.7 GPa or less. Since the polyimide polymer film of the embodiment includes the above-mentioned polyimide polymer, the tensile modulus can be achieved.

[0151] The tensile modulus can be measured by preparing a sample having a size of 5 mm*100 mm and a thickness of 10 μm for the polyimide polymer film of the embodiment and measuring the distance between the clamps at speeds of 30 mm / min and 10 mm / min using an Instron 3365 instrument.

[0152] The weight average molecular weight (measured by GPC) of the polyimide polymer is not particularly limited, but for example, it may be 1,000 g / mol or more and 200,000 g / mol or less, or 10,000 g / mol or more and 200,000 g / mol or less.

[0153] The polyimide polymer according to the present disclosure can exhibit excellent colorless and transparent properties while maintaining properties such as heat resistance and mechanical strength as is due to its rigid structure, and thus can be used in various fields, such as substrates for devices, cover substrates for displays, optical films, IC (integrated circuit) packaging, adhesive films, multilayer flexible printed circuits (FRCs), tapes, touch panels, protective films for optical discs, etc.

[0154] More specifically, examples of methods for synthesizing polyimide polymer films are not particularly limited, and for example, a method for producing a film can be used, comprising the steps of applying a resin composition containing a polyimide polymer onto a substrate to form a coating film (step 1); drying the coating film (step 2); and heat-treating and curing the dried coating film (step 3).

[0155] Step 1 is a step of applying a resin composition comprising the above-mentioned polyimide polymer to a substrate to form a coating film. The method of applying the resin composition comprising the polyimide polymer to the substrate is not particularly limited, and for example, methods such as screen printing, offset printing, flexographic printing, inkjet printing, etc. can be used.

[0156] In addition, the resin composition containing the polyimide polymer may be in a form dissolved or dispersed in an organic solvent. In the case of such a form, for example, when the polyimide polymer is synthesized in an organic solvent, the solution may be the reaction solution obtained thereby or may be a solution obtained by diluting the reaction solution with another solvent. In addition, when the polyimide polymer is obtained as a powder, the solution may be a solution obtained by dissolving the powder in an organic solvent.

[0157] Specific examples of the organic solvent include N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N-methylcaprolactam, 2-pyrrolidone, N-ethylpyrrolidone, N-vinylpyrrolidone, dimethyl sulfoxide, tetramethylurea, pyridine, dimethyl sulfone, hexamethyl sulfoxide, γ-butyrolactone, 3-methoxy-N,N-dimethylpropionamide, 3-ethoxy-N,N-dimethylpropionamide, 3-butoxy-N,N-dimethylpropionamide, 1,3- Dimethyl-imidazolidinone, ethyl amyl ketone, methyl nonyl ketone, methyl ethyl ketone, methyl isoamyl ketone, methyl isopropyl ketone, cyclohexanone, ethylene carbonate, propylene carbonate, diethylene glycol dimethyl ether, 4-hydroxy-4-methyl-2-pentanone, ethylene glycol monomethyl ether, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether, ethylene glycol monoethyl ether acetate, ethylene glycol monopropyl ether, ethylene glycol monopropyl ether acetate, ethylene glycol monoisopropyl ether, ethylene glycol monoisopropyl ether acetate, ethylene glycol monobutyl ether, ethylene glycol monobutyl ether acetate, etc. These may be used alone or in combination of two or more.

[0158] Considering the processability during the film forming process, such as coating characteristics, the resin composition containing the polyimide-based polymer may contain solids in an amount such that the solution has an appropriate viscosity. For example, the content of the composition may be adjusted so that the total content of the resin is 5% by weight or more and 25% by weight or less, or may be adjusted to 5% by weight or more and 20% by weight or less, or 5% by weight or more and 15% by weight or less.

[0159] In addition, except organic solvent, the resin combination comprising polyimide polymer can also comprise other components. In a non-limiting example, when coating the resin combination comprising polyimide polymer, the additive that can improve the uniformity and surface smoothness of film thickness or improve the adhesion with substrate or change dielectric constant and specific conductivity or increase compactness can also be comprised.The example of these additives comprises surfactant, compound based on silane, dielectric or cross-linked compound etc.

[0160] Step 2 is a step of drying a coating film formed by coating a resin composition containing a polyimide polymer on a substrate.

[0161] The step of drying the coating film can be performed by a heating device such as a hot plate, a hot air circulation oven, an infrared oven, etc., and the drying can be performed at a temperature of 50°C or higher and 150°C or lower, or 50°C or higher and 100°C or lower.

[0162] Step 3 is a step of heat-treating and curing the dried coating film. In this case, the heat treatment can be carried out by a heating device such as a hot plate, a hot air circulation oven, an infrared oven, etc., and the heat treatment can be carried out at a temperature of 200° C. or higher, or 200° C. or higher and 300° C. or lower.

[0163] The thickness of the polyimide polymer film is not particularly limited, but for example, it can be freely adjusted within a range of 0.01 μm or more and 1000 μm or less. If the thickness of the polyimide polymer film increases or decreases by a specific value, the physical properties measured in the polyimide polymer film may also change by a certain value.

[0164] Meanwhile, according to another embodiment of the present disclosure, a substrate for a display device including the polyimide-based polymer film of another embodiment may be provided. Details of the polyimide polymer film may include all of the contents described above in one embodiment.

[0165] The display device including the substrate may include a liquid crystal display (LCD), an organic light emitting diode (OLED), a flexible display, a rollable display, a foldable display, etc., but is not limited thereto.

[0166] The display device may have various structures depending on application fields and specific shapes, and may include, for example, a cover plastic window, a touch panel, a polarizing plate, a blocking film, a light emitting device (eg, an OLED device), a transparent substrate, and the like.

[0167] The polyimide polymer film of another embodiment described above may be used in various applications, such as a substrate, an outer protective film, or a cover window in such various display devices, and more particularly, may be applied to a substrate.

[0168] For example, the display device substrate may have a structure in which a device protection layer, a transparent electrode layer, a silicon oxide layer, a polyimide polymer film, a silicon oxide layer, and a hard coating layer are sequentially stacked.

[0169] The transparent polyimide substrate may further include a silicon oxide layer formed between the transparent polyimide polymer film and the cured layer to further improve its solvent resistance, water permeability, and optical properties. The silicon oxide layer may be produced by curing polysilazane.

[0170] Specifically, before the step of forming the coating layer on at least one surface of the transparent polyimide polymer film, the silicon oxide layer may be formed by curing the coated polysilazane after coating and drying a solution containing polysilazane.

[0171] The substrate for a display device according to the present disclosure includes the above-mentioned device protection layer, thereby providing a transparent polyimide cover substrate having solvent resistance, optical properties, water permeability, and scratch resistance while having excellent warpage properties and heat resistance.

[0172] Meanwhile, according to another embodiment of the present disclosure, a flexible display device including the polyimide polymer film of another embodiment may be provided. Details of the polyimide polymer film may include all those described above in one embodiment.

[0173] Flexible display devices may include any type of device that utilizes properties achieved by light, and may be, for example, a display device. Specific examples of display devices include, but are not limited to, liquid crystal display devices (LCDs), organic light-emitting diodes (OLEDs), flexible display devices, rollable display devices, or foldable display devices.

[0174] Depending on the application field and specific shape, the flexible display device can have various structures. For example, it can have a structure including a cover plastic window, a touch panel, a polarizing plate, a barrier film, a light-emitting device (such as an OLED device), a transparent substrate, etc.

[0175] The polyimide polymer film of another embodiment described above may be used in various applications such as a substrate, an outer protective film, or a cover window in various display devices, and more particularly, may be applied to a substrate.

[0176] Beneficial effects

[0177] According to the present disclosure, a polyimide polymer film capable of achieving excellent optical characteristics and high heat resistance, a substrate for a flexible display device using the same, and a flexible display device may be provided. DETAILED DESCRIPTION

[0178] Hereinafter, the embodiments of the present disclosure will be described in more detail by way of examples. However, these examples are provided for illustrative purposes only and are not intended to limit the scope of the present disclosure.

[0179] <Examples and Comparative Examples: Preparation of Polyimide Precursor Compositions and Polyimide Films>

[0180] Example 1

[0181] (1) Preparation of polyimide precursor composition

[0182] The organic solvent, DEAc, was placed in a reactor under a nitrogen stream. 2,2'-bis(trifluoromethyl)benzidine (TFMB) was then added and dissolved at 25°C. Pyromellitic dianhydride (PMDA), 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride (BPAF), and 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) were also added at the same temperature and stirred for 48 hours to produce a polyimide precursor composition. The molar ratios of the monomers added are shown in Table 1 below.

[0183] [Chemical formula a]

[0184]

[0185] (2) Preparation of polyimide film

[0186] The polyimide precursor composition was spin-coated on a glass substrate. The glass substrate coated with the polyimide precursor composition was placed in an oven and heated at a rate of 5°C / min, and a curing process was performed by maintaining at 80°C for 5 to 30 minutes, maintaining at 250°C for 30 minutes, and maintaining at 400°C for 30 to 40 minutes.

[0187] After completing the process, the glass substrate was immersed in water to remove the film formed on the glass substrate and dried in an oven at 100° C. to produce a polyimide film having a thickness of 10 μm.

[0188] Examples 2 to 5 and Comparative Examples 1 to 2

[0189] A polyimide precursor composition and a polyimide film were produced in the same manner as in Example 1, except that the molar ratio of each monomer was changed as shown in Table 1 below.

[0190] Examples 6 to 10 and Comparative Examples 3 to 4

[0191] A polyimide precursor composition and a polyimide film were produced in the same manner as in Example 1, except that the molar ratio of each monomer was changed as shown in Table 1 below, and triphenylphosphine oxide (TPPO) was added to the produced polyimide precursor composition in an amount of 2 wt % relative to the total solid content.

[0192] [Table 1]

[0193]

[0194] *PMDA: Pyromellitic Dianhydride *BPDA: 3,3',4,4'-Biphenyltetracarboxylic Dianhydride

[0195] *BPAF: 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride

[0196] *TFMB: 2,2'-bis(trifluoromethyl)benzidine

[0197] *TPPO: triphenylphosphine oxide

[0198] <Experimental Example: Measurement of Physical Properties of Polyimide Precursor Compositions and Polyimide Films Obtained in Examples and Comparative Examples>

[0199] Physical properties of the polyimide precursor compositions and polyimide films obtained in Examples and Comparative Examples were measured by the following methods, and the results are shown in Table 2 below.

[0200] 1. Coefficient of thermal expansion (CTE) and glass transition temperature (Tg)

[0201] The polyimide films obtained in the Examples and Comparative Examples were prepared into 5 mm x 20 mm sizes, and then loaded with the sample fittings. The actual measured length of the film was set to 16 mm. The linear thermal expansion coefficient of the polyimide-based film was measured as the average value of the growth of the test sample over the range of 100°C to 400°C under a load of 0.2 N / 10 μm of film thickness and a heating rate of 5°C / min. The inflection point occurring in the heating stage of the first heating process was determined as the Tg.

[0202] 2. Transparency

[0203] For the polyimide films produced in Examples and Comparative Examples, the transmittance (T) at wavelengths of 450 nm and 550 nm was measured using a UV-vis spectrometer (model name: HR-100, Murakami Color Research Laboratory) instrument according to the measurement method of JIS K 7105, and the results are shown in Table 2 below.

[0204] 3. Thermal decomposition temperature (Td 1%)

[0205] For the polyimide films produced in Examples and Comparative Examples, the temperature when the weight reduction rate of the initial polyimide film was 1% was measured in a nitrogen atmosphere using Discovery TGA manufactured by TA Instruments, and the results are shown in Table 2 below.

[0206] 4. Elongation, tensile strength and tensile modulus

[0207] For the polyimide films produced in Examples and Comparative Examples, samples having a size of 5 mm*100 mm and a thickness of 10 μm were prepared using an Instron 3365 instrument, and the elongation (%), tensile strength (MPa) and tensile modulus (GPa) were measured by setting the distance between the clamps to 30 mm and the speed of each resin film to 10 mm / min. The results are shown in Table 2 below.

[0208] [Table 2] Experimental measurement results of Examples and Comparative Examples

[0209]

[0210] As shown in Table 2, it was determined that the polyimide films obtained in Examples exhibited excellent optical properties and a small thermal expansion coefficient, suppressed shrinkage and expansion at high temperatures, and were also excellent in mechanical physical properties such as mechanical strength and tensile modulus and heat resistance.

[0211] In contrast, it can be determined that the polyimide film of the comparative example is poor in optical properties and heat resistance compared with the embodiment, and in particular, has a large thermal expansion coefficient, and is therefore significantly poor not only in heat resistance (such as shrinkage and expansion at high temperatures) but also in mechanical properties (such as tensile strength and tensile modulus).

Claims

1. A polyimide polymer film comprising: a polyimide polymer comprising repeating units derived from a reaction product between three or more aromatic tetracarboxylic acids or derivatives thereof having different structures and an aromatic diamine, wherein the transmittance at wavelengths of 450nm and 550nm is 70% or greater, respectively, a thermal expansion coefficient of -10 ppm / °C or more and 30 ppm / °C or less in a temperature range of 100°C or more and 400°C or less, and The glass transition temperature is 400℃ or higher, in: The polyimide polymer comprises: a repeating unit comprising at least one selected from the group consisting of a repeating unit represented by the following Chemical Formula 1, a repeating unit represented by the following Chemical Formula 2, and a repeating unit represented by the following Chemical Formula 3; a polyimide repeating unit represented by the following Chemical Formula 4; and A polyimide repeating unit represented by the following Chemical Formula 5, wherein the polyimide polymer comprises 51 mol% or more and 90 mol% or less of the polyimide repeating unit represented by Chemical Formula 4 relative to 100 mol% of the total repeating units, wherein the polyimide polymer includes at least one selected from the repeating unit represented by Chemical Formula 1, the repeating unit represented by Chemical Formula 2, and the repeating unit represented by Chemical Formula 3 in an amount of 5 mol% or more and 20 mol% or less relative to 100 mol% of the total repeating units, and wherein the polyimide polymer includes the polyimide repeating unit represented by Chemical Formula 5 in an amount of 1 mol% or more and 40 mol% or less relative to 100 mol% of the total repeating units: [Chemical Formula 1] [Chemical Formula 2] [Chemical Formula 3] Wherein, in Chemical Formulas 1 to 3, At least one of R1 and R2 is an alkyl group having 1 to 10 carbon atoms, and the rest are hydrogen, X1 to X3 are each independently a tetravalent organic group including a tetravalent functional group represented by the following Chemical Formula 6, wherein Y1 to Y3 are each independently a divalent organic group substituted with at least one fluorine-based functional group, [Chemical Formula 6] Wherein, in Chemical Formula 6, Ar is a polycyclic aromatic divalent functional group, [Chemical Formula 4] Wherein, in Chemical Formula 4, X1' is an aromatic tetravalent functional group having 8 or fewer carbon atoms, Y1' is an aromatic divalent functional group substituted with at least one fluorine-based functional group, [Chemical Formula 5] Wherein, in Chemical Formula 5, X1″ is an aromatic tetravalent functional group having 9 or more and 15 or less carbon atoms, and Y1″ is an aromatic divalent functional group substituted with at least one fluorine-based functional group.

2. The polyimide polymer film according to claim 1, wherein: In Ar of Chemical Formula 6, The polycyclic aromatic divalent functional group includes a condensed cyclic divalent functional group including at least two or more aromatic ring groups.

3. The polyimide polymer film according to claim 1, wherein: In Ar of Chemical Formula 6, The polycyclic aromatic divalent functional group includes a fluorenylene group.

4. The polyimide polymer film according to claim 1, wherein: The tetravalent functional group represented by Chemical Formula 6 includes a functional group represented by the following Chemical Formula 6-1: [Chemical Formula 6-1] 5. The polyimide polymer film according to claim 1, wherein: The aromatic tetravalent functional group having 8 or less carbon atoms includes a functional group represented by the following Chemical Formula 10: [Chemical Formula 10] 6. The polyimide polymer film according to claim 1, wherein: The aromatic divalent functional group substituted with at least one fluorine-based functional group includes a functional group represented by the following Chemical Formula 7: [Chemical Formula 7] In Chemical Formula 7, p is an integer of 0 or more and 5 or less.

7. The polyimide polymer film according to claim 1, wherein: The polyimide polymer film includes a compound represented by the following Chemical Formula 9: [Chemical Formula 9] In Chemical Formula 9, R3 to R5 are each independently hydrogen, hydroxy, alkyl or aryl.

8. The polyimide polymer film according to claim 7, wherein: The compound represented by Chemical Formula 9 includes a compound represented by the following Chemical Formula 9-1: [Chemical Formula 9-1] 9. The polyimide polymer film according to claim 7, wherein: The compound represented by Chemical Formula 9 is included in an amount of 0.5 wt % or more and 20 wt % or less relative to the total weight of the polymer solid content. 10 . A substrate for a flexible display device, comprising the polyimide polymer film according to claim 1 . 11 . A flexible display device comprising the polyimide polymer film according to claim 1 .

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