Polyimide resin film, display device substrate using same, and optical device

Abstract

The present invention relates to a polyimide resin film containing a polyimide resin containing a polyimide repeating unit represented by Chemical Formula 1 and a polyimide repeating unit represented by Chemical Formula 2, and a display device substrate and an optical device using the same.

Description

[Technical field]

[0001] [CROSS REFERENCE TO RELATED APPLICATIONS] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0174999 filed on December 8, 2021 and Korean Patent Application No. 10-2022-0110024 filed on August 31, 2022, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a polyimide resin film capable of realizing excellent warpage characteristics and low retardation, and to a display device substrate and an optical device using the same. [Background technology]

[0003] The display device market is rapidly shifting to flat panel displays (FPDs) that can be easily made large in area and are thin and lightweight. Such flat panel displays include liquid crystal displays (LCDs), organic light emitting displays (OLEDs), and electrophoretic displays (EPDs).

[0004] In particular, in order to further expand the applications and uses of such flat displays, attention has been focused on so-called flexible display elements in which a flexible substrate is applied to the flat display. Such flexible display elements have been considered for application mainly to mobile devices such as smartphones, and the fields of application thereof are gradually expanding.

[0005] In general, in manufacturing flexible display devices and lighting devices, multi-layer inorganic films such as a buffer layer, an active layer, and a gate insulator are formed on a cured polyimide to manufacture a TFT device.

[0006] However, conventional polyimide resins have a large refractive index in the plane direction, which is significantly different from the refractive index in the thickness direction. As a result, polyimide has anisotropic properties, which causes light distortion and significantly reduces visibility.

[0007] In addition, when the polyimide material contained in the polyimide layer (substrate layer) is cured at high temperatures of 400°C or more, the optical properties decrease due to degradation of the polyimide, and there are limitations in that it is difficult to ensure flatness due to the warping properties that cause the polyimide to bend physically.

[0008] Therefore, there is a demand for the development of a new polyimide that can reduce the difference in refractive index between the surface direction and the thickness direction to improve visibility and also satisfy excellent warpage characteristics. Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention provides a polyimide resin film that can achieve excellent optical properties, anti-warping properties, and a low retardation.

[0010] The present invention also provides a display device substrate and an optical device using the polyimide resin film. [Means for solving the problem]

[0011] In order to achieve the above object, the present invention provides a polyimide-based resin film comprising a polyimide-based resin including a polyimide repeating unit represented by the following Chemical Formula 1 and a polyimide repeating unit represented by the following Chemical Formula 2: [Chemical formula 1] [ka] In the above Chemical Formula 1, X1 is an aromatic tetravalent functional group having a single ring, and Y1 is an aromatic divalent functional group having 6 to 10 carbon atoms. [Chemical formula 2] [ka] In the above Chemical Formula 2, X2 is an aromatic tetravalent functional group containing multiple rings, and Y2 is an aromatic divalent functional group having 6 to 10 carbon atoms.

[0012] The present invention further provides a substrate for a display device, comprising the polyimide-based resin film.

[0013] The present invention further provides an optical device comprising the polyimide resin film.

[0014] Hereinafter, a polyimide-based resin film according to a specific embodiment of the present invention and a display device substrate and an optical device using the same will be described in more detail.

[0015] Unless otherwise expressly stated herein, the terminology used is for the purpose of referring to particular embodiments only and is not intended to be limiting of the invention.

[0016] As used herein, the singular forms include the plural forms unless the context clearly dictates to the contrary.

[0017] As used herein, the meaning of "comprising" is to embody certain features, regions, integers, steps, operations, elements, components and / or components, and does not exclude the presence or addition of other certain features, regions, integers, steps, operations, elements, components and / or groups.

[0018] In this specification, terms including ordinal numbers such as "first" and "second" are used for the purpose of distinguishing one component from another component, and are not limited by said terms. For example, within the scope of the present invention, a first component may be named a second component, and similarly, a second component may be named a first component.

[0019] In this specification, the term "(co)polymer" refers to a polymer or copolymer, where the polymer refers to a homopolymer consisting of a single repeating unit, and the copolymer refers to a composite polymer containing two or more types of repeating units.

[0020] In this specification, examples of the substituents will be described below, but are not limited to these.

[0021] As used herein, the term "substituted" means that another functional group is bonded in place of a hydrogen atom in a compound, and the position of the substitution is not limited as long as it is a position at which a hydrogen atom is substituted, i.e., a position at which a substituent can be substituted, and when two or more substitutions are made, the two or more substituents may be the same or different.

[0022] In the present specification, the term "substituted or unsubstituted" means that the group is substituted or unsubstituted with one or more substituents selected from the group consisting of deuterium, halogen, cyano, nitro, hydroxy, carbonyl, ester, imide, amino, primary amino, carboxy, sulfonic acid, sulfonamide, phosphine oxide, alkoxy, aryloxy, alkylthio, arylthio, alkylsulfoxy, arylsulfoxy, silyl, boron, alkyl, cycloalkyl, alkenyl, aryl, aralkyl, aralkenyl, alkylaryl, alkoxysilylalkyl, arylphosphine, or heterocyclic groups containing one or more of N, O, and S atoms, or that the group is substituted or unsubstituted with two or more of the above-listed substituents. For example, the "substituent with two or more substituents connected" may be a biphenyl group. That is, the biphenyl group may be an aryl group, and may be interpreted as a substituent with two phenyl groups connected.

[0023] In this specification, [ka] means a bond connected to another substituent, and a direct bond means that there is no other atom in the moiety represented by L.

[0024] In this specification, aromaticity refers to a property that satisfies Huckel's rule, and a compound is defined as being aromatic when it satisfies all of the following three conditions according to Huckel's rule:

[0025] 1) There must be 4n+2 electrons present, fully conjugated by vacant p-orbitals, unsaturated bonds, electron pairs, etc. 2) The 4n+2 electrons must form a planar isomer and a ring structure. 3) All atoms of the ring must participate in the conjugation.

[0026] In the present specification, a multivalent functional group is a residue in the form in which multiple hydrogen atoms bonded to any compound are removed, and examples thereof include 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 the form in which any four hydrogen atoms bonded to cyclobutane are removed.

[0027] In this specification, the aryl group is a monovalent functional group derived from arene, and is not particularly limited, but preferably has 6 to 20 carbon atoms, and may be a monocyclic aryl group or a polycyclic aryl group. The monocyclic aryl group may be, but is not limited to, a phenyl group, a biphenyl group, a terphenyl group, etc. The polycyclic aryl group may be, but is not limited to, a naphthyl group, an anthracenyl group, a phenanthryl group, a pyrenyl group, a perylenyl group, a chrysenyl group, a fluorenyl group, etc. The aryl group may be substituted or unsubstituted, and when substituted, examples of the substituent are as described above.

[0028] In the present specification, a direct bond or a single bond means that there is no atom or atomic group at the corresponding position and that the bond is made by a bond line. Specifically, it means that there is no additional atom at the portion represented by L1 or L2 in the chemical formula.

[0029] In this specification, the weight average molecular weight means the weight average molecular weight in terms of polystyrene measured by the GPC method. In the process of measuring the weight average molecular weight in terms of polystyrene measured by the GPC method, a commonly known analyzer, a detector such as a refractive index detector, and an analytical column can be used, and commonly applied temperature conditions, solvents, and flow rates can be applied. As a specific example of the measurement conditions, a Polymer Laboratories PLgel MIX-B 300 mm long column is used with a Waters PL-GPC220 device, the evaluation temperature is 160° C., 1,2,4-trichlorobenzene is used as a solvent, the flow rate is 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 Mw value can be obtained using a calibration curve formed using a polystyrene standard. Nine types of 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.

[0030] The present invention will now be described in more detail.

[0031] 1. Polyimide resin film According to one embodiment of the present invention, there can be provided a polyimide-based resin film comprising a polyimide-based resin including a polyimide repeating unit represented by the following Chemical Formula 1 and a polyimide repeating unit represented by the following Chemical Formula 2. [Chemical formula 1] [ka] In the above Chemical Formula 1, X1 is an aromatic tetravalent functional group having a single ring, and Y1 is an aromatic divalent functional group having 6 to 10 carbon atoms. [Chemical formula 2] [ka] In the above Chemical Formula 2, X2 is an aromatic tetravalent functional group containing multiple rings, and Y2 is an aromatic divalent functional group having 6 to 10 carbon atoms.

[0032] The inventors have confirmed through experiments that, when the polyimide repeating unit represented by Chemical Formula 1 and the polyimide repeating unit represented by Chemical Formula 2 are simultaneously contained as in the polyimide-based resin film of the embodiment, the occurrence of warping is minimized in the polyimide resin film cured at a high temperature of 400° C. or more, thereby improving flatness and dimensional stability, and thus eliminating defects due to lifting during panel processing. In addition, the refractive index in the thickness direction is increased, thereby reducing the refractive index difference between the thickness direction and the plane direction, thereby improving optical isotropy, and a low retardation is realized, thereby ensuring the diagonal viewing angle of a display to which the polyimide-based resin film is applied, and preventing a decrease in visibility due to a distortion of light. Thus, the present invention has been completed.

[0033] In particular, the polyimide resin includes a reaction product obtained by imidization reaction of aromatic tetracarboxylic dianhydride having multiple rings and aromatic diamine having 6 to 10 carbon atoms, as shown in the structure of Chemical Formula 2, and is considered to secure high heat resistance due to physical and chemical action due to the structure of aromatic tetracarboxylic dianhydride having multiple rings, and to achieve excellent flatness not only in a film cured by heat treatment at a high temperature of 400° C. or more, but also when the cured film is further heat-treated at a high temperature of 400° C. or more. In addition, an asymmetric structure with increased steric hindrance due to the multiple rings is introduced into the polyimide chain structure, thereby reducing the refractive index difference between the plane direction and the thickness direction, and realizing a low retardation.

[0034] In addition, it is believed that a low retardation can be achieved by reducing the difference in refractive index between the plane direction and the thickness direction using aromatic diamine having 6 to 10 carbon atoms having a curved asymmetric structure.

[0035] In addition, the polyimide resin includes a reaction product obtained by imidization of an aromatic tetracarboxylic dianhydride having a single ring and an aromatic diamine having 6 to 10 carbon atoms, as represented by the structure of Chemical Formula 1, and is considered to achieve the reduction of the refractive index difference between the plane direction and the thickness direction by the aromatic diamine having 6 to 10 carbon atoms having a curved asymmetric structure.

[0036] More specifically, in the case of polyimide having a planar linear main chain structure, polyimides are packed side by side and piled up, so that the refractive index in the thickness direction is low, but on the other hand, an asymmetric structure in a curved form is introduced into the polyimide chain structure, so that the arrangement in the thickness direction can be maintained, and a low retardation can be realized by reducing the difference in the refractive index between the plane direction and the thickness direction.

[0037] The polyimide-based resin film according to the present invention can increase the refractive index and can be used as a substrate layer in a flexible display device, thereby reducing the difference in refractive index between each layer constituting the device. As a result, the amount of light lost inside can be reduced, and the bottom emission efficiency of light can be effectively increased.

[0038] Specifically, the polyimide-based resin film may contain a polyimide-based resin. The polyimide-based resin means that it contains all of polyimide and its precursor polymers, polyamic acid and polyamic acid ester. That is, the polyimide-based polymer may contain one or more selected from the group consisting of a polyamic acid repeating unit, a polyamic acid ester repeating unit, and a polyimide repeating unit. That is, the polyimide-based polymer may contain one type of polyamic acid repeating unit, one type of polyamic acid ester repeating unit, one type of polyimide repeating unit, or a copolymer in which two or more of these repeating units are mixed.

[0039] At least one repeating unit selected from the group consisting of a polyamic acid repeating unit, a polyamic acid ester repeating unit, and a polyimide repeating unit can form the main chain of the polyimide polymer.

[0040] The polyimide-based resin film may include a cured product of a polyimide-based resin. The cured product of a polyimide-based resin refers to a product obtained through a curing process of the polyimide-based resin.

[0041] In particular, the polyimide resin may include a polyimide repeating unit represented by the following Chemical Formula 1: [Chemical formula 1] [ka] In the above Chemical Formula 1, X1 is an aromatic tetravalent functional group containing a single ring, and Y1 is an aromatic divalent functional group having 6 to 10 carbon atoms.

[0042] In the above Chemical Formula 1, X1 is an aromatic tetravalent functional group having a single ring, and X1 is a functional group derived from a tetracarboxylic dianhydride compound used in the synthesis of a polyimide resin.

[0043] The aromatic tetravalent functional group containing a single ring of X1 may include a functional group represented by the following chemical formula 5 derived from pyromellitic dianhydride (PMDA). [Chemical formula 5] [ka] When the functional group represented by Formula 5 is included as the aromatic tetravalent functional group having a single ring, the packing density of the polymer chain can be increased in a flat structure, thereby realizing high heat resistance and high mechanical properties.

[0044] Meanwhile, in the above Chemical Formula 1, Y1 is an aromatic divalent functional group having 6 to 10 carbon atoms, and Y1 may be a functional group derived from a polyamic acid, a polyamic acid ester, or a diamine compound used in synthesizing a polyimide.

[0045] The aromatic divalent functional group having 6 to 10 carbon atoms may include a phenylene group. More specifically, the aromatic divalent functional group having 6 to 10 carbon atoms of Y1 may include a functional group represented by the following chemical formula 3. [Chemical formula 3] [ka]

[0046] A specific example of the functional group represented by the following chemical formula 3 is a functional group represented by the following chemical formula 3-1 derived from m-phenylenediamine (1,3-phenylenediamine, m-PDA). [Chemical formula 3-1] [ka]

[0047] When the functional group represented by Chemical Formula 3-1 is included in Y1, an asymmetric structure in a curved form is introduced into the polyimide chain structure, thereby maintaining alignment in the thickness direction, and reducing the refractive index difference between the plane direction and the thickness direction, thereby achieving a low retardation.

[0048] On the other hand, when Y1 contains a functional group derived from p-phenylenediamine (1,4-phenylenediamine, p-PDA), which does not have a curved asymmetric structure, it is difficult to realize the curved asymmetric structure. Since the polyimide is polymerized in a linear plane direction, the polymer grows only in the in-plane direction. As a result, the polymers are well packed together, reducing the refractive index in the thickness direction, and the refractive index difference between the in-plane direction and the thickness direction increases.

[0049] Meanwhile, the polyimide-based resin may further include a polyimide repeating unit represented by the following Chemical Formula 2 in addition to the polyimide repeating unit represented by Chemical Formula 1. That is, the polyimide-based resin may include a polyimide repeating unit represented by Chemical Formula 1 and a polyimide repeating unit represented by Chemical Formula 2. [Chemical formula 2] [ka] In the above Chemical Formula 4, X2 is an aromatic tetravalent functional group containing multiple rings, and Y2 is an aromatic divalent functional group having 6 to 10 carbon atoms.

[0050] The Y2 is the same as Y1 in Chemical Formula 1.

[0051] In the above formula 2, X2 is an aromatic tetravalent functional group containing multiple rings, and X2 is a functional group derived from a tetracarboxylic dianhydride compound used in the synthesis of polyimide-based resins.

[0052] More specifically, the tetravalent functional group of X2 may include a divalent functional group represented by the following chemical formula 4. [Chemical formula 4] [ka]

[0053] In the formula 4, 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 the derivative compound includes all compounds in which one or more substituents are introduced or a carbon atom is replaced with a heteroatom.

[0054] More specifically, the multi-ring aromatic difunctional group in Ar in Formula 4 may include a fused ring difunctional group containing at least two aromatic ring compounds. That is, the multi-ring aromatic difunctional group includes at least two aromatic ring compounds in the functional group structure, and the functional group has a fused ring structure.

[0055] The aromatic ring compound may include an arene compound containing one or more benzene rings, or a heteroarene compound in which a carbon atom in the arene compound is replaced with a heteroatom.

[0056] The aromatic ring compound is contained in the polycyclic aromatic divalent functional group in at least two or more, and each of the two or more aromatic ring compounds may directly form a condensed ring or may form a condensed ring via another ring structure. For example, when two benzene rings are condensed to a cycloalkyl ring structure, the two benzene rings may be defined as forming a condensed ring via the cycloalkyl ring.

[0057] The fused cyclic divalent functional group containing at least two or more aromatic ring compounds is a divalent functional group derived from a fused ring compound containing at least two or more aromatic ring compounds or a derivative compound thereof, and the derivative compound includes all compounds into which one or more substituents have been introduced or in which a carbon atom has been replaced with a heteroatom.

[0058] The polycyclic aromatic divalent functional group represented by Ar in the above Chemical Formula 4 may include a fluorenylene group. A specific example of the functional group represented by the above Chemical Formula 4 is a functional group represented by the following Chemical Formula 4-1 derived from 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride (BPAF). [Chemical formula 4-1] [ka]

[0059] When the aromatic tetravalent functional group having multiple rings is included in X2, a symmetric structure having increased steric hindrance due to the multiple rings is introduced into the polyimide chain structure, thereby alleviating deformation due to heat and improving heat resistance. A bulky structure having increased steric hindrance in the thickness direction due to the multiple rings is introduced into the polyimide chain structure, thereby increasing the refractive index in the thickness direction and reducing the refractive index difference between the plane direction and the thickness direction, thereby realizing a low retardation, and intermolecular packing is suppressed to realize high transmittance.

[0060] The polyimide resin may include a combination of an aromatic tetracarboxylic dianhydride containing a single ring, an aromatic tetracarboxylic dianhydride containing multiple rings, and an aromatic diamine having 6 to 10 carbon atoms.

[0061] The single ring aromatic tetracarboxylic dianhydride is a compound having an anhydride group (-OC-O-CO-) introduced at both ends of the above-mentioned single ring aromatic tetravalent functional group, and the description of the single ring aromatic tetravalent functional group is as described above.

[0062] A specific example of the aromatic tetracarboxylic dianhydride containing a single ring is pyromellitic dianhydride (PMDA).

[0063] The polycyclic aromatic tetracarboxylic dianhydride is a compound having an anhydride group (-OC-O-CO-) introduced at both ends of the polycyclic aromatic tetravalent functional group, and the polycyclic aromatic tetravalent functional group has been described above.

[0064] A specific example of the aromatic tetracarboxylic dianhydride containing multiple rings is 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride (BPAF).

[0065] The aromatic diamine having 6 to 10 carbon atoms is a compound having amino groups (-NH2) introduced at both ends of the aromatic difunctional group having 6 to 10 carbon atoms, and the aromatic difunctional group having 6 to 10 carbon atoms is as described above. A specific example of the aromatic diamine having 6 to 10 carbon atoms is m-phenylenediamine (1,3-phenylenediamine, m-PDA).

[0066] More specifically, the polyimide resin is formed by reacting a terminal anhydride group (-OC-O-CO-) of the aromatic tetracarboxylic dianhydride or aromatic tetracarboxylic dianhydride containing multiple rings with a terminal amino group (-NH2) of an aromatic diamine having 6 to 10 carbon atoms, so that a bond is formed between a nitrogen atom of the amino group and a carbon atom of the anhydride group.

[0067] Meanwhile, the polyimide-based polymer may include a first repeating unit containing a repeating unit represented by Chemical Formula 1, in which the anhydride-derived repeating unit is a functional group represented by Chemical Formula 5, and a second repeating unit containing a repeating unit represented by Chemical Formula 2, in which the anhydride-derived repeating unit is a functional group represented by Chemical Formula 4. The first repeating unit and the second repeating unit may be randomly arranged in the polyimide-based polymer to form a random copolymer, or may form blocks between the first repeating units and blocks between the second repeating units to form a block copolymer.

[0068] The polyimide-based polymer including the repeating unit represented by Formula 1 and the repeating unit represented by Formula 2 can be prepared by reacting two or more different tetracarboxylic dianhydride compounds with a diamine compound. The two tetracarboxylic dianhydrides can be added simultaneously to synthesize a random copolymer or sequentially to synthesize a block copolymer.

[0069] The molar ratio of the polyimide repeating unit represented by Chemical Formula 1 to the polyimide repeating unit represented by Chemical Formula 2 may be 85:15 to 15:85, or 80:20 to 20:80, or 75:25 to 25:75, or 60:40 to 40:60, or 60:40 to 70:30, or 70:30 to 85:15.

[0070] More specifically, the molar ratio of the polyimide repeating unit represented by Chemical Formula 2 to 1 mole of the polyimide repeating unit represented by Chemical Formula 1 may be 0.17 to 6 moles, or 0.25 to 4 moles, or 0.33 to 3 moles, or 0.6 to 1.5 moles, or 0.4 to 0.7 moles, or 0.17 to 0.5 moles.

[0071] It is possible to realize excellent warpage characteristics and excellent optical characteristics such as colorless transparency, and since the refractive index in the thickness direction is increased, the thickness direction retardation (Rth) characteristics are low, and optical isotropy is improved. In addition, the diagonal viewing angle of the display to which the polyimide-based resin film is applied is secured, thereby preventing deterioration of visibility due to the distortion of light.

[0072] On the other hand, if the polyimide repeating unit represented by Formula 1 is contained in an excessively small amount and the molar ratio of the polyimide repeating unit represented by Formula 1 to the polyimide repeating unit represented by Formula 2 is out of 15:85, the glass transition temperature decreases, thereby reducing heat resistance, and the polyimide resin film cured at a high temperature of 400°C or more is warped to a large extent, making it difficult to laminate a device on the film and making subsequent processes impossible.

[0073] In addition, when the polyimide repeating unit represented by the chemical formula 2 is contained in an excessively small amount and the molar ratio of the polyimide repeating unit represented by the chemical formula 1 to the polyimide repeating unit represented by the chemical formula 2 is out of 85:15, the thickness direction retardation R thAs the value increases, the optical distortion caused by the increase in retardation causes a decrease in visibility, and as the yellowness increases, the transparency decreases, and the refractive index in the thickness direction and the average refractive index decrease, resulting in poor optical properties.

[0074] Meanwhile, the polyimide-based resin film of the embodiment may include a cured product obtained by curing the polyimide-based resin at a temperature of 400° C. or more. The cured product means a material obtained by curing a resin composition containing the polyimide-based resin, and the curing process is performed at a temperature of 400° C. or more, or 400° C. to 500° C.

[0075] The polyimide repeating unit represented by Chemical Formula 1 and the polyimide repeating unit represented by Chemical Formula 2 are contained in an amount of 70 mol% or more, 80 mol% or more, 90 mol% or more, 70 mol% to 100 mol%, 80 mol% to 100 mol%, 70 mol% to 90 mol%, 70 mol% to 99 mol%, 80 mol% to 99 mol%, or 90 mol% to 99 mol% based on the total repeating units contained in the polyimide resin.

[0076] That is, the polyimide resin is composed only of the polyimide repeating units represented by Chemical Formula 1 and the polyimide repeating units represented by Chemical Formula 2, and is mostly composed of the polyimide repeating units represented by Chemical Formula 1 and the polyimide repeating units represented by Chemical Formula 2.

[0077] The weight average molecular weight (measured by GPC) of the polyimide resin is not particularly limited, and may be, for example, from 1,000 g / mol to 200,000 g / mol, or from 10,000 g / mol to 200,000 g / mol.

[0078] The polyimide-based resin according to the present invention can exhibit excellent colorless and transparent properties while maintaining properties such as heat resistance and mechanical strength due to its rigid structure, and is used in various fields such as device substrates, display cover substrates, optical films, IC (integrated circuit) packages, adhesive films, multi-layer FRC (flexible printed circuit), tapes, touch panels, and optical disk protective films, and is particularly suitable for display cover substrates.

[0079] More specifically, the method for synthesizing the polyimide-based resin film is not particularly limited, and for example, a film manufacturing method including a step of applying a resin composition containing the polyimide-based resin to a substrate to form a coating film (step 1), a step of drying the coating film (step 2), and a step of heat-treating the dried coating film to harden it (step 3) can be used.

[0080] The step 1 is a step of forming a coating film by applying the resin composition containing the polyimide resin to a substrate. The method of applying the resin composition containing the polyimide resin to a substrate is not particularly limited, and for example, a method such as screen printing, offset printing, flexographic printing, or inkjet printing may be used.

[0081] The resin composition containing the polyimide resin may be dissolved or dispersed in an organic solvent. In the case of such a form, for example, when the polyimide resin is synthesized in an organic solvent, the solution may be the reaction solution obtained as it is, or may be the reaction solution diluted with another solvent. In addition, when the polyimide resin is obtained as a powder, it may be dissolved in an organic solvent to form a solution.

[0082] Specific examples of the organic solvent include toluene, N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N-methylcaprolactam, 2-pyrrolidone, N-ethylpyrrolidone, N-vinylpyrrolidone, dimethylsulfoxide, tetramethylurea, pyridine, dimethylsulfone, hexamethylsulfoxide, γ-butyrolactone, 3-methoxy-N,N-dimethylpropanamide, 3-ethoxy-N,N-dimethylpropanamide, 3-butoxy-N,N-dimethylpropanamide, 1,3-dimethyl-imidazolidinone, ethyl amyl ketone, methyl nonyl ketone, methyl ethyl ketone, methyl isoamyl ketone, methyl isopropyl alcohol, methyl ethyl ... Examples of the ethylene glycol monoisopropyl ketone, cyclohexanone, ethylene carbonate, propylene carbonate, diglyme, 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.

[0083] The resin composition including the polyimide-based resin may contain a solid content in an amount that provides an appropriate viscosity in consideration of processability such as coatability during a film formation process. For example, the content of the composition may be adjusted so that the total resin content is 5 wt% to 25 wt%, or 5 wt% to 20 wt%, or 5 wt% to 15 wt%.

[0084] In addition, the resin composition containing the polyimide resin may further contain other components in addition to the organic solvent. Non-limiting examples include additives that can improve the uniformity of the film thickness or surface smoothness when the resin composition containing the polyimide resin is applied, improve adhesion to a substrate, change the dielectric constant or conductivity, or increase the density. Examples of such additives include surfactants, silane compounds, dielectrics, or crosslinking compounds.

[0085] The step 2 is a step of coating a substrate with the resin composition containing the polyimide resin and drying the coating film formed thereon.

[0086] The coating may be dried by a heating means such as a hot plate, a hot air circulating oven, or an infrared oven at a temperature of 50°C to 150°C, or 50°C to 100°C.

[0087] Step 3 is a step of heat-treating the dried coating film to harden it, where the heat treatment can be performed by a heating means such as a hot plate, a hot air circulating oven, an infrared oven, etc., at a temperature of 200°C or more, or 200°C to 300°C or more, or 400°C or more, or 400°C to 500°C or less.

[0088] The thickness of the polyimide-based resin film is not particularly limited, and can be freely adjusted within a range of, for example, 0.01 μm to 1000 μm. When the thickness of the polyimide-based resin film is increased or decreased by a certain value, the physical properties measured from the polyimide-based resin film may change by a certain value.

[0089] Meanwhile, the polyimide-based resin film of the embodiment may have a residual stress with an inorganic material substrate at a thickness of 10 μm of 46 MPa or less, or 45 MPa or less, or 40 MPa or less, or 35 MPa or less, or 30 MPa or less, or 1 MPa or more, or 1 MPa to 46 MPa, or 10 MPa to 46 MPa, or 20 MPa to 46 MPa, or 1 MPa to 46 MPa, or 1 MPa to 40 MPa, or 1 MPa to 35 MPa, or 1 MPa to 30 MPa, or 10 MPa to 45 MPa, or 20 MPa to 45 MPa, or 28.7 MPa to 45 MPa. In this way, the polyimide-based resin film of the embodiment may have a reduced residual stress with an inorganic material substrate, thereby solving defects due to lifting during panel processing.

[0090] The method and device for measuring the residual stress are not specifically limited, and various methods used for measuring the residual stress can be applied without limitation. For example, the residual stress of a polyimide resin film can be measured using a residual stress measuring device. An example of the inorganic material substrate is a wafer substrate.

[0091] The residual stress can be measured from a polyimide-based resin film sample having a thickness of 10±1 μm. When the thickness of the polyimide-based resin film increases or decreases by a certain value, the physical properties measured from the polyimide-based resin film can change by a certain value.

[0092] If the residual stress between the polyimide resin film and the inorganic material substrate at a thickness of 10 μm is excessively increased to, for example, more than 48 MPa, the polyimide resin film cured at a high temperature of 400° C. or more may warp, causing defects due to lifting during panel processing.

[0093] On the other hand, the polyimide-based resin film of the embodiment may have a thickness direction retardation value at a thickness of 10 μm of 300 nm or less, or 200 nm or less, or 100 nm or less, or 70 nm or less, or 30 nm or less, or 20 nm or less, or 1 nm or more, or 1 nm to 300 nm, or 1 nm to 200 nm, or 1 nm to 100 nm, or 1 nm to 70 nm, or 1 nm to 30 nm, or 1 nm to 20 nm. Thus, the low thickness direction retardation (R th ) provides high optical isotropy, and the polyimide resin film can secure a diagonal viewing angle for a display to which the polyimide resin film is applied, thereby realizing excellent visibility.

[0094] It is believed that such a low retardation is achieved by reducing the difference in refractive index between the plane direction and the thickness direction using m-PDA (m-Phenylenediamine), a diamine having an asymmetric structure, as a monomer used in the production of polyimide resin films, as described below.

[0095] More specifically, in the case of polyimide having a planar linear main chain structure, the polyimide molecules are packed side by side and piled up, so the refractive index in the thickness direction is low, whereas in the case of polyimide having a bent main chain structure, the molecules are not packed well with each other, so the refractive index in the thickness direction increases.

[0096] The thickness direction retardation is measured at a wavelength of 532 nm. Examples of the measurement method and device are not specifically limited, and various methods used in the conventional measurement of thickness direction retardation can be applied without limitation.

[0097] The thickness direction retardation can be measured from the polyimide resin film sample having a thickness of 10±1 μm. When the thickness of the polyimide resin film increases or decreases by a certain value, the physical properties measured from the polyimide resin layer film may change by a certain value.

[0098] Specifically, the thickness direction retardation R thcan be calculated by the following Equation 1. [Formula 1] R th (nm)=|[(n x +n y ) / 2]-n z |×d In the above formula 1, n x is the largest in-plane refractive index of the polyimide resin film measured with light of 532 nm wavelength; n y is the in-plane refractive index of a polyimide resin film measured with light of wavelength 532 nm. x is the refractive index perpendicular to z is the refractive index in the thickness direction of the polyimide resin film measured with light having a wavelength of 532 nm; d is the thickness of the polyimide resin film.

[0099] That is, the thickness direction retardation R th is the refractive index in the thickness direction (n z ) and the average planar refractive index value [(n x +n y ) / 2] is multiplied by the film thickness to obtain the thickness direction refractive index value (n z ) and the average planar refractive index value [(n x +n y The smaller the difference between [(1 / 2) / 2], the lower the value can be indicated.

[0100] The polyimide resin film has a thickness direction retardation value of 100 nm or less at a thickness of 10 μm, and thus has a thickness direction refractive index value (n z ) and the average planar refractive index value [(n x +n y ) / 2] is reduced, thereby achieving excellent visibility.

[0101] If the retardation value in the thickness direction of the polyimide resin film at a thickness of 10 μm is excessively increased to over 100 nm, a distortion phenomenon occurs when light passes through the polyimide structure when a transparent display is realized. Even a compensation film that technically compensates up to 45 nm has a technical limit in that it cannot correct the refraction of the transmitted light.

[0102] The polyimide resin film may have a thickness direction refractive index at a wavelength of 532 nm at a thickness of 10 μm of 1.71 or more, or 1.7103 or more, or 1.7120 or more, or 1.7130 or more, or 1.72 or less, or 1.71 to 1.72, or 1.7103 to 1.72, or 1.7120 to 1.72, or 1.7130 to 1.72, or 1.71 to 1.715, or 1.7102 to 1.7136. The polyimide resin film may have a plane direction refractive index at a wavelength of 532 nm at a thickness of 10 μm of 1.71 to 1.73.

[0103] The method and device for measuring the in-plane and thickness direction refractive indexes are not specifically limited, and various methods used in measuring refractive indexes in the past can be applied without limitation. For example, the in-plane and thickness direction refractive indexes can be measured at a wavelength of 532 nm using a prism coupler.

[0104] The refractive index can be measured from a sample of the polyimide-based resin film having a thickness of 10±1 μm. When the thickness of the polyimide-based resin film increases or decreases by a certain value, the physical properties measured from the polyimide-based resin film can change by a certain value.

[0105] If the refractive index in the thickness direction of the polyimide resin film at a thickness of 10 μm is excessively reduced, for example, to less than 1.71 for a wavelength of 532 nm, the phase difference increases due to an increase in the difference between the refractive index in the plane direction and the refractive index in the thickness direction. As a result, when a transparent display is realized, a distortion phenomenon occurs when light is transmitted, and visibility is poor, resulting in technical limitations.

[0106] The polyimide resin film may have an average refractive index at a wavelength of 532 nm at a thickness of 10 μm of 1.7135 or more, or 1.7140 or more, or 1.7150 or more, or 1.7180 or more, or 1.72 or less, or 1.7135 to 1.72, or 1.7136 to 1.7182, or 1.7140 to 1.72, or 1.7150 to 1.72, or 1.7180 to 1.72. As an example of a method for measuring the average refractive index, a prism coupler is used to measure the refractive index in the transverse (TE) direction and the transverse (TM) direction at a wavelength of 532 nm, and the average refractive index is calculated by the following formula 2. [Formula 2] Average refractive index = (n x +n y +n z ) / 3 In the above formula 2, n x is the largest in-plane refractive index of the polyimide resin film measured with light of 532 nm wavelength; n y is the in-plane refractive index of a polyimide resin film measured with light of wavelength 532 nm. x is the refractive index perpendicular to z is the refractive index in the thickness direction of the polyimide resin film measured with light having a wavelength of 532 nm.

[0107] The average refractive index can be measured from a sample of the polyimide-based resin film having a thickness of 10±1 μm. When the thickness of the polyimide-based resin film increases or decreases by a certain value, the physical properties measured from the polyimide-based resin film can change by a certain value.

[0108] Meanwhile, the polyimide resin film may have a haze value of less than 1.0%, or 0.1% or more and less than 1.0% at a thickness of 10 μm. The haze may be measured from a sample of the polyimide resin film having a thickness of 10±1 μm. When the thickness of the polyimide resin film increases or decreases by a certain value, the physical properties measured from the polyimide resin film may change by a certain value.

[0109] The polyimide resin film may have a bow value at a thickness of 10 μm of 48 μm or less, or 45 μm or less, or 40 μm or less, or 35 μm or less, or 30 μm or less, or 1 μm or more, or 1 μm to 48 μm, or 1 μm to 45 μm, or 1 μm to 40 μm, or 1 μm to 35 μm, or 1 μm to 30 μm, or 10 μm to 48 μm, or 20 μm to 48 μm, or 28.35 μm to 45.62 μm. The bow is called curvature or bow and is a type of surface flatness characteristic of a material, and a specific description thereof, for example, a specific measurement method, may be applied to various methods widely known in the field of semiconductor wafer substrate manufacturing without limitation.

[0110] Specifically, the Bow 3 can be defined as the distance on the central axis 4 between the thickness central plane 1 and the reference plane (Best fit plane of thickness central plane) 2, as shown in FIG.

[0111] The thickness center plane 1, as shown in FIG. 1, refers to a plane connecting points that are half (t / 2) of the thickness (t) from the measurement object.

[0112] The reference plane 2, as shown in FIG. 1, means a cross section defined by a straight line connecting the center points of the thickness of both ends of the measurement object.

[0113] As shown in FIG. 1, the central axis 4 means a straight line that passes through the center of gravity of the object to be measured and is perpendicular to the ground.

[0114] As an example of a method for measuring the Bow 3, a laser stress analyzer can be used. The laser stress analyzer measures the intensity of light reflected from the back surface of a measurement sample and mathematically analyzes the measured intensity to automatically calculate the Bow value.

[0115] The bow may be measured for a polyimide-based resin film sample of the embodiment having a thickness of 10±1 μm.

[0116] The polyimide-based resin film sample used in the bow measurement may include a pure polyimide-based resin film; or a laminate including a substrate film and a polyimide-based resin film coated on the substrate film; Examples of the substrate film are not particularly limited, and a glass substrate, a wafer substrate, or a mixture thereof may be used without limitation.

[0117] When the polyimide-based resin film sample used for the bow measurement is made of only a pure polyimide-based resin film, the bow can be automatically measured based on the results of analyzing the polyimide-based resin film sample with a laser stress analyzer. For example, a pure polyimide-based resin film can be obtained by peeling off the base film from a laminate including the base film and the polyimide-based resin film coated on the base film.

[0118] If the bow value of the polyimide resin film is excessively increased, for example, to more than 48 μm, the polyimide resin film cured at a high temperature of 400° C. or more may warp, resulting in defects due to lifting during panel processing.

[0119] Meanwhile, the polyimide-based resin film may have a yellowness index at a thickness of 10 μm of 25 or less, or 1 or more, or 1 to 25, or 6.27 to 22.8. If the yellowness index at a thickness of 10 μm of the polyimide-based resin film is excessively increased, such as exceeding 25, the yellowness of the polyimide-based resin film increases, making it difficult to manufacture a colorless and transparent film.

[0120] The method and device for measuring the yellowness index in the embodiment are not particularly limited, and various methods used in conventional YI measurement can be applied without limitation. For example, the yellowness index can be measured using a color meter (Color-Eye 7000A manufactured by GRETAGMACBETH).

[0121] The yellowness index can be measured from a sample of the polyimide-based resin film having a thickness of 10±1 μm. When the thickness of the polyimide-based resin film increases or decreases by a certain value, the physical properties measured from the polyimide-based resin film can also change by a certain value.

[0122] 2. Display device substrates Meanwhile, according to yet another embodiment of the present invention, there is provided a substrate for a display device, including the polyimide-based resin film of the other embodiment. The content related to the polyimide-based resin film includes all of the content described above in the one embodiment.

[0123] Display devices including the substrate include, but are not limited to, liquid crystal display devices (LCDs), organic light emitting diodes (OLEDs), flexible displays, rollable displays or foldable displays.

[0124] The display device may have various structures depending on the application field and specific form, for example, a structure including a cover plastic window, a touch panel, a polarizing plate, a barrier film, a light emitting element (such as an OLED element), a transparent substrate, and the like.

[0125] The polyimide-based resin film according to the above-mentioned embodiment may be used for various purposes such as a substrate, an external protective film, or a cover window in such various display devices, and more specifically, may be applied to a substrate.

[0126] For example, the display device substrate may have a structure in which an element protection layer, a transparent electrode layer, a silicon oxide layer, a polyimide resin film, a silicon oxide layer, and a hard coat layer are sequentially laminated.

[0127] The transparent polyimide substrate may include a silicon oxide layer formed between the transparent polyimide-based resin film and the cured layer in order to further improve solvent resistance or moisture permeability and optical properties, and the silicon oxide layer may be produced by curing polysilazane.

[0128] Specifically, the silicon oxide layer may be formed by coating and drying a solution containing polysilazane prior to forming a coating layer on at least one surface of the transparent polyimide-based resin film, and then curing the coated polysilazane.

[0129] The display device substrate according to the present invention includes the above-mentioned element protection layer, and thus provides a transparent polyimide cover substrate having excellent warping properties and impact resistance, as well as solvent resistance, optical properties, moisture permeability and scratch resistance.

[0130] 3.Optical equipment Meanwhile, according to still another embodiment of the present invention, there is provided an optical device including the polyimide-based resin film of the other embodiment. The content related to the polyimide-based resin film includes all of the content described above in the one embodiment.

[0131] The optical device may include all kinds of devices using properties realized by light, such as a display device. Specific examples of the display device include, but are not limited to, a liquid crystal display device (LCD), an organic light emitting diode (OLED), a flexible display, or a rollable display or foldable display.

[0132] The optical device may have various structures depending on the application field and specific form, for example, a structure including a cover plastic window, a touch panel, a polarizing plate, a barrier film, a light emitting element (such as an OLED element), a transparent substrate, and the like.

[0133] The polyimide-based resin film according to the above-mentioned embodiment may be used for various purposes such as a substrate, an external protective film, or a cover window in such various optical devices, and more specifically, may be applied to a substrate. Effect of the Invention

[0134] According to the present invention, it is possible to provide a polyimide resin film capable of realizing excellent optical properties, warpage properties and low retardation, and a display device substrate and an optical device using the polyimide resin film. [Brief description of the drawings]

[0135] [Figure 1] FIG. 2 is a cross-sectional view showing bow measurements of the polyimide resin films obtained in the examples and comparative examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0136] The present invention will be described in more detail with reference to the following examples, however, the following examples are merely illustrative and the content of the present invention is not limited to the following examples.

[0137] <Examples and Comparative Examples: Production of Polyimide Precursor Composition and Polyimide Film>

[0138] Examples 1-4

[0139] (1) Preparation of polyimide precursor composition After filling an organic solvent DMAc in a stirrer with a nitrogen stream, m-phenylenediamine (1,3-phenylenediamine, m-PDA) was added and dissolved at 25°C while maintaining the temperature of the reactor. Pyromellitic dianhydride (PMDA) and 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride (BPAF) were added as acid dianhydrides to the solution containing m-phenylenediamine (1,3-phenylenediamine, m-PDA) at the same temperature and stirred for 24 hours to prepare a polyimide precursor composition. The molar ratios of m-PDA, PMDA, and BPAF are shown in Table 1 below.

[0140] (2) Production of polyimide film 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 cured at 80°C for 30 minutes, 250°C for 30 minutes, and 400°C for 30 minutes. After the curing process was completed, the glass substrate was immersed in water to remove the film formed on the glass substrate, and the substrate was dried in an oven at 100°C to produce a polyimide film having a thickness of 10 μm (including an error of ±1 μm).

[0141] Comparative Examples 1-5 A polyimide precursor composition and a polyimide film were produced in the same manner as in the above Examples, except that the molar ratios of m-PDA, p-PDA (1,4-phenylenediamine), TFMB (2,2'-bis(trifluoromethyl)benzidine), PMDA, and BPAF were changed as shown in Table 2 below.

[0142] Reference example 1-3 Polyimide precursor compositions and polyimide films were prepared in the same manner as in the above examples, except that the molar ratios of m-PDA, PMDA, and BPAF were changed as shown in Table 3 below.

[0143] <Experimental Example: Measurement of physical properties of polyimide precursor compositions and polyimide films obtained in Examples and Comparative Examples> The physical properties of the polyimide precursor compositions and polyimide films obtained in the above Examples and Comparative Examples were measured by the following methods. The results are shown in Tables 1 to 3.

[0144] 1. Yellow index (YI) The yellowness index of the polyimide films prepared in the examples and comparative examples was measured using a color meter (Color-Eye 7000A manufactured by GRETAGMACBETH).

[0145] 2. Haze The haze value of the polyimide film was measured using a Hazemeter (NDH-5000).

[0146] 3.Thickness direction retardation (R th ) The measurement device used was an "AxoScan" manufactured by AXOMETRICS, and the refractive index values ​​for 532 nm light of the polyimide films produced in the examples and comparative examples were input. The retardation in the thickness direction and in the plane direction was then measured using light with a wavelength of 532 nm under conditions of a temperature of 25°C and a humidity of 40%. The measured retardation value in the thickness direction (measured automatically by the measurement device) was then converted into a retardation value per 10 μm of film thickness, as shown in Table 1 below.

[0147] Specifically, the thickness direction retardation R th was calculated according to the following formula 1. [Formula 1] R th (nm)=|[(n x +n y ) / 2]-n z |×d (In the above formula 1, n x is the largest in-plane refractive index of the polyimide resin film measured with light of 532 nm wavelength; n y is the in-plane refractive index of a polyimide resin film measured with light of wavelength 532 nm. x is the refractive index perpendicular to z is the refractive index in the thickness direction of the polyimide resin film measured with light of wavelength 532 nm; d is the thickness of the polyimide film.)

[0148] 4. Residual stress and bow The amount of warpage of the polyimide precursor composition produced in the examples and comparative examples was measured in advance using a residual stress measurement device (FLX2320 manufactured by Tencor Corporation). The composition was applied to a 6-inch silicon wafer with a thickness of 525 um using a spin coater (manufactured by Koyo Lindbergh Corporation), and a heat curing treatment was performed in an oven at 250°C for 30 minutes and at 400°C for 30 minutes under a nitrogen atmosphere. After curing, a silicon wafer with a resin film was produced. The amount of warpage of the silicon wafer with the resin film was measured using a residual stress measurement device, and the absolute value of the difference from the amount of warpage of the wafer in advance was expressed as a real bow value, and the residual stress generated between the silicon wafer and the resin film was measured using the residual stress measurement device.

[0149] The bow is defined as the distance on the central axis between the thickness central plane of the measurement sample and the reference plane (best fit plane of thickness central plane) as shown in FIG. 1, and the bow was measured at room temperature using a stress analyzer (TENCOR FLX-2320) for the sample.

[0150] 5. Refractive Index The refractive indices in the transverse (TE) and thickness direction (TM) directions of the polyimide films prepared in the examples and comparative examples were measured at a wavelength of 532 nm using a prism coupler, and the average refractive index was calculated according to the following Equation 2. [Formula 2] Average refractive index = (n x +n y +n z ) / 3 (In the above formula 2, n x is the largest in-plane refractive index of the polyimide resin film measured with light of 532 nm wavelength; n y is the in-plane refractive index of a polyimide resin film measured with light of wavelength 532 nm. x is the refractive index perpendicular to z is the refractive index in the thickness direction of the polyimide resin film measured with light of wavelength 532 nm.)

[0151] [Table 1]

[0152] As shown in Table 1 above, the polyimide films (based on a thickness of 10 μm) obtained in Examples 1 to 4 had a thickness direction retardation R th It was confirmed that the value was 13 nm to 100 nm, the haze was 0.36% to 0.84%, the YI was 6.27 to 22.8, the residual stress was 28.7 MPa to 45 MPa, the bow was 28.35 μm to 45.62 μm, the in-plane refractive index (nTE) at 532 nm was 1.7141 to 1.7222, the thickness direction refractive index (nTM) was 1.7102 to 1.7136, and the average refractive index at 532 nm was 1.7136 to 1.7182.

[0153] [Table 2]

[0154] As shown in Table 2 above, the polyimide films (based on a thickness of 10 μm) obtained in Comparative Examples 1 to 5 had a thickness direction refractive index (nTM) of 1.5773 to 1.7030 at 532 nm and an average refractive index of 1.6114 to 1.7130 at 532 nm, which were smaller than those in the Examples. In particular, the polyimide films (based on a thickness of 10 μm) obtained in Comparative Examples 1 to 3 had a residual stress of 49.1 MPa to 54.5 MPa, which was increased compared to those in the Examples, and there was a problem that flatness could not be achieved.

[0155] In addition, the polyimide film obtained in Comparative Example 4 (thickness: 10 μm) had a thickness direction retardation R th It was confirmed that the value was 319 nm, which increased sharply compared to the examples, making it impossible to realize a low retardation, and that the YI increased to 27.42, resulting in a decrease in the transparency characteristics.

[0156] In addition, the polyimide film (thickness: 10 μm) obtained in Comparative Example 5 had a thickness direction retardation R thIt was confirmed that the value was 508 nm, which increased sharply compared to the examples, making it impossible to realize a low retardation.

[0157] [Table 3]

[0158] As shown in Table 3, the polyimide film obtained in Reference Example 1 (based on a thickness of 10 μm) had a thickness direction refractive index (nTM) of 1.6903 at 532 nm and an average refractive index of 1.7100 at 532 nm, which were smaller than those of the Examples. In addition, the polyimide film obtained in Reference Example 1 (based on a thickness of 10 μm) had a thickness direction retardation R th It was confirmed that the value was 307 nm, which increased sharply compared to the examples, making it impossible to realize a low retardation, and that the YI increased to 28.90, resulting in a decrease in the transparency characteristics.

[0159] On the other hand, the polyimide films (based on a thickness of 10 μm) obtained in Reference Examples 2 and 3 had a residual stress of 48 MPa to 48.5 MPa and a bow of 48.9 μm to 49.5 μm, which were increased compared to the Examples and posed a problem in that a high level of flatness could not be achieved.

Claims

1. A polyimide-based resin film comprising a polyimide-based resin including a polyimide repeating unit represented by the following chemical formula 1 and a polyimide repeating unit represented by the following chemical formula 2: [Chemical formula 1] 【Chemistry 1】 In the above Chemical Formula 1, X １ is an aromatic tetravalent functional group containing a single ring, Y １ is a functional group represented by the following chemical formula 3-1, [Chemical formula 2] 【Chemistry 2】 In the above Chemical Formula 2, X ２ is an aromatic tetravalent functional group containing multiple rings, Y ２ is a functional group represented by the following chemical formula 3-1: [Chemical formula 3-1] 【Chemistry 4】 。

2. 2. The polyimide resin film according to claim 1, wherein the polyimide resin film has a residual stress of 46 MPa or less when combined with an inorganic material substrate at a thickness of 10 μm.

3. The polyimide resin film has a thickness direction retardation R ｔｈ 2. The polyimide resin film according to claim 1, wherein the value is 300 nm or less.

4. 2. The polyimide resin film according to claim 1, wherein the polyimide resin film has a thickness direction refractive index of 1.71 or more at a wavelength of 532 nm when the polyimide resin film has a thickness of 10 μm.

5. The polyimide resin film according to claim 1 , wherein the polyimide resin film has a haze value of less than 1.0% at a thickness of 10 μm.

6. The polyimide resin film according to claim 1 , wherein the polyimide resin film has a Bow value of 48 μm or less at a thickness of 10 μm.

7. The polyimide resin film according to claim 1 , wherein the polyimide resin film has a yellowness index of 25 or less at a thickness of 10 μm.

8. 2. The polyimide resin film according to claim 1, wherein the polyimide resin film has an average refractive index of 1.7135 or more at a wavelength of 532 nm when the film has a thickness of 10 μm.

9. 2. The polyimide resin film according to claim 1, wherein the polyimide resin film has a refractive index in an in-plane direction at a wavelength of 532 nm at a thickness of 10 μm of 1.71 to 1.

73.

10. The X ２ The polyimide resin film according to claim 1, wherein the aromatic tetravalent functional group having a multiple ring includes a tetravalent functional group represented by the following chemical formula 4: [Chemical formula 4] 【Chemistry 5】 In the above formula 4, Ar is a polycyclic aromatic divalent functional group.

11. In the formula 4, Ar represents a polycyclic aromatic divalent functional group. The polyimide resin film according to claim 10, comprising a condensed cyclic difunctional group containing at least two aromatic ring compounds.

12. The polyimide resin film according to claim 10 , wherein the multi-ring aromatic divalent functional group in Ar in the formula 4 includes a fluorenylene group.

13. The polyimide-based resin film according to claim 10, wherein the tetravalent functional group represented by Chemical Formula 4 includes a functional group represented by Chemical Formula 4-1 below: [Chemical formula 4-1] 【Chemistry 6】 。

14. The X １ The polyimide resin film according to claim 1, wherein the aromatic tetravalent functional group having a single ring includes a functional group represented by the following chemical formula 5: [Chemical formula 5] 【Chemistry 7】 。

15. 2. The polyimide-based resin film according to claim 1, wherein the polyimide-based resin comprises a combination of an aromatic tetracarboxylic dianhydride having a single ring, an aromatic tetracarboxylic dianhydride having multiple rings, and an aromatic diamine having 6 to 10 carbon atoms.

16. 2. The polyimide resin film according to claim 1, wherein a molar ratio of the polyimide repeating unit represented by Chemical Formula 1 to the polyimide repeating unit represented by Chemical Formula 2 is 85:15 to 15:

85.

17. A substrate for a display device, comprising the polyimide-based resin film according to claim 1 .

18. An optical device comprising the polyimide resin film according to claim 1 .

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