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

Abstract

The present invention relates to a polyimide resin film having a refractive index difference (Δn) of 0.0068 or less, as calculated by the following mathematical formula 1, and a yellowness index of 5.5 or less at a thickness of 10 μm, 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. 10-2021-0152513 dated November 8, 2021, and all contents disclosed in the documents of that Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a polyimide resin film capable of realizing excellent optical properties and a 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, 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, polyimide resins are colored brown or yellow due to their high aromatic ring density, and have low transmittance in the visible light range, exhibiting a yellow-based color, which reduces light transmittance and has large birefringence, limiting their use as optical components.

[0008] Therefore, there is a demand for the development of new polyimides that can reduce the difference in refractive index between the plane direction and the thickness direction, thereby improving visibility and providing excellent optical properties. Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention relates to a polyimide resin film capable of realizing excellent optical 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 solve the above problems, the present specification provides a polyimide-based resin film having a refractive index difference (Δn) of 0.0068 or less, as calculated by the following mathematical formula 1, and a yellowness index of 5.5 or less at a thickness of 10 μm.

[0012] [Formula 1] Refractive index difference (△n) = n1-n2

[0013] In the above formula 1, n1 is the refractive index value in the plane direction of the polyimide resin film having a thickness of 10 μm, and n2 is the refractive index value in the thickness direction of the polyimide resin film having a thickness of 10 μm.

[0014] The present specification also provides a substrate for a display device, comprising the polyimide-based resin film.

[0015] The present specification also provides an optical device including the polyimide-based resin film.

[0016] 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.

[0017] Unless expressly stated otherwise herein, terminology is for the purpose of referring to particular embodiments only and is not intended to be limiting of the invention.

[0018] As used herein, the singular forms "a," "an," and "the" include the plural forms unless the phrase clearly dictates to the contrary.

[0019] 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 inclusion of other certain features, regions, integers, steps, operations, elements, components and / or groups.

[0020] 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 the ordinal number. For example, within the scope of the present invention, a first component can also be named a second component, and similarly, a second component can be named a first component.

[0021] As used herein, the term "(co)polymer" is intended to include both polymer and copolymer, with the term "polymer" referring to a homopolymer made of a single repeating unit and the term "copolymer" referring to a composite polymer containing two or more types of repeating units.

[0022] In this specification, examples of the substituents are described below, but are not limited thereto.

[0023] 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 substituents are substituted, the two or more substituents may be the same or different from each other.

[0024] The term "substituted or unsubstituted" as used herein means a group substituted or unsubstituted with one or more substituents selected from the group consisting of deuterium, halogen, cyano, nitro, hydroxy, carbonyl, ester, imide, amide, 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 a group substituted or unsubstituted with two or more of the above-listed substituents. For example, the "substituent having 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 having two phenyl groups connected.

[0025] As used herein, [ka] or [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.

[0026] In this specification, aromaticity can be defined as a property that satisfies the Huckels Rule, and a compound can be defined as aromatic if it satisfies all of the following three conditions according to the Huckels Rule:

[0027] 1) There must be 4n+2 electrons present, which are fully conjugated through vacant p-orbitals, unsaturated bonds, unpaired electron pairs, etc.

[0028] 2) The 4n+2 electrons must form a planar isomer and form a ring structure.

[0029] 3) All atoms of the ring must be able to participate in conjugation.

[0030] In the present specification, a multivalent functional group is a residue in which multiple hydrogen atoms bonded to any compound are removed, such as a divalent functional group, a trivalent functional group, or 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.

[0031] In the present 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.

[0032] 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.

[0033] 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. Specific examples of the measurement conditions include using a Polymer Laboratories PLgel MIX-B 300 mm long column and a Waters PL-GPC220 instrument, 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 to 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.

[0034] The present invention will now be described in more detail.

[0035] 1. Polyimide resin film According to one embodiment of the present invention, there is provided a polyimide resin film having a refractive index difference (Δn) of 0.0068 or less, as calculated by the following formula 1, and a yellowness index of 5.5 or less at a thickness of 10 μm.

[0036] [Formula 1] Refractive index difference (△n) = n1-n2

[0037] In the above formula 1, n1 is the refractive index value in the plane direction of a polyimide resin film having a thickness of 10 μm, and n2 is the refractive index value in the thickness direction of a polyimide resin film having a thickness of 10 μm.

[0038] The inventors have confirmed through experiments that, as in the polyimide-based resin film of the embodiment, if the refractive index difference (Δn) obtained by the above formula 1 is 0.0068 or less and the yellowness index at a thickness of 10 μm is 5.5 or less, the low yellowness index improves transparency, thereby increasing light transmittance and having low birefringence, making it suitable for use as an optical member. At the same time, the low refractive index difference (Δn) characteristic improves optical isotropy and realizes low retardation, 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 the distortion of light. Thus, the present invention has been completed.

[0039] Specifically, the polyimide-based resin film according to the present invention can increase the refractive index, and when used as a substrate layer in a flexible display device, the difference in refractive index between the layers constituting the device can be reduced, thereby reducing the amount of light lost internally and effectively increasing the bottom emission efficiency.

[0040] Specifically, the polyimide resin film of the embodiment may have a refractive index difference (Δn) calculated by the following formula 1 of 0.0068 or less, or 0.0065 or less, or 0.0050 or less, or 0.0010 or more, or 0.0010 to 0.0068, or 0.0010 to 0.0065, or 0.0010 to 0.0050, or 0.0034 to 0.0045, or 0.0044 to 0.0067. In this way, the refractive index difference (Δn) is small, so that the film has a low retardation and excellent luminous effect.

[0041] [Formula 1] Refractive index difference (△n) = n1-n2

[0042] In the above formula 1, n1 is the refractive index value in the plane direction of a polyimide resin film having a thickness of 10 μm, and n2 is the refractive index value in the thickness direction of a polyimide resin film having a thickness of 10 μm.

[0043] More specifically, the in-plane refractive index at a wavelength of 532 nm, which corresponds to n1 in the formula 1, may be 1.70 to 1.71, or 1.7019 to 1.7066, or 1.7039 to 1.7066, or 1.7019 to 1.7042. Also, the thickness direction refractive index at a wavelength of 532 nm, which corresponds to n2 in the formula 1, may be 1.69 to 1.71, or 1.6957 to 1.7029, or 1.7 to 1.7029, or 1.6957 to 1.6993. That is, in the formula 1, n1 and n2 each satisfy the above-mentioned ranges while simultaneously satisfying the refractive index difference (Δn) range of the formula 1.

[0044] It is believed that such a small refractive index difference (△n) is achieved by reducing the refractive index difference between the plane direction and the thickness direction by using m-PDA (m-Phenylenediamine), a diamine with an asymmetric structure, and 4,4'-Oxydiphthalic Anhydride (ODPA), an anhydride with a bent structure, as monomers used in the production of polyimide resin films, as described below.

[0045] The method and equipment for measuring the in-plane and thickness direction refractive indexes are not specifically limited, and various methods that have been used for measuring refractive indexes in the past can be used 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.

[0046] 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 may also change by a certain value.

[0047] If the refractive index difference (Δn) obtained by the above formula 1 is excessively increased to exceed 0.0068, 0.0065, or 0.0050, etc., the phase difference increases, and thus, when a transparent display is realized, a distortion phenomenon occurs when light is transmitted, resulting in a technical limitation with poor visibility.

[0048] Meanwhile, the polyimide resin film may have a yellowness index at a thickness of 10 μm of 5.5 or less, or 4.3 or less, or 1.0 or more, or 1.0 to 5.5, or 1.0 to 4.3, or 1.91 to 5.23, or 3.03 to 4.16. If the yellowness index at a thickness of 10 μm of the polyimide resin film is excessively increased, such as exceeding 5.5 or 4.3, the degree of yellow discoloration of the polyimide resin film increases, making it difficult to manufacture a colorless and transparent film.

[0049] It is believed that such a low yellowness index (YI) is achieved by using m-PDA (m-Phenylenediamine), a diamine having an asymmetric structure, and 4,4'-Oxydiphthalic Anhydride (ODPA), an anhydride having an ether group, which is an electron-withdrawing functional group, and a bent structure, as monomers used in the production of polyimide resin films, as described below.

[0050] More specifically, in the case of polyimide having a planar linear main chain structure, the polyimide molecules are packed side by side and pile up, whereas in the case of polyimide having a bent main chain structure, the molecules are not well packed with each other, so transparency is ensured by CTC inhibition, and the CTC inhibition effect can be strengthened by the electron-withdrawing effect of the ether group.

[0051] The method and equipment for measuring the yellowness index in the embodiment are not particularly limited, and various methods conventionally used for measuring YI can be applied without limitation. For example, the yellowness index can be measured using a color meter (Gretagmacbeth's Color-Eye 7000A).

[0052] The yellowness index may 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 may also change by a certain value.

[0053] Meanwhile, the polyimide-based resin film of the embodiment may have a color coordinate b* at a thickness of 10 μm of 1 to 4, or 1 to 3.3, or 1 to 3.2, or 1 to 3.1, or 1.19 to 3.60, or 1.62 to 2.95. By lowering the color coordinate b* in this manner, the polyimide-based resin film of the embodiment has low yellowing properties and can achieve excellent optical properties.

[0054] In the present invention, the term "color coordinates" refers to coordinates in the CIE Lab color space, which is a color value defined by the CIE (International Commission on Illumination, Commossion International de l'Eclairage), and any position in the CIE color space can be expressed by three coordinate values: L*, a*, and b*.

[0055] Here, the L* value indicates brightness, with L* = 0 indicating black and L* = 100 indicating white. In addition, the a* value indicates whether the color having the corresponding color coordinates is biased toward pure red or pure green, and the b* value indicates whether the color having the corresponding color coordinates is biased toward pure yellow or pure blue.

[0056] Specifically, the a* value ranges from -a to +a. The maximum value of a* (a* max) indicates pure red, and the minimum value of a* (a* min) indicates pure green. The b* value ranges from -b to +b. The maximum value of b* (b* max) indicates pure yellow, and the minimum value of b* (b* min) indicates pure blue. For example, a negative b* value indicates a color biased toward pure blue, and a positive b* value indicates a color biased toward pure yellow. Comparing b*=50 and b*=80, this means that b*=80 is closer to pure yellow than b*=50.

[0057] The method and equipment for measuring the color coordinates are not particularly limited, and various methods conventionally used for measuring color coordinates can be used without limitation. For example, the color coordinate (b*) of a polyimide resin film can be measured using a color meter (Gretagmacbeth's Color-Eye 7000A).

[0058] The color coordinate (b*) 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 is increased or decreased by a certain value, the physical properties measured from the polyimide-based resin film may also change by a certain value.

[0059] If the color coordinate b* of the polyimide resin film at a thickness of 10 μm is excessively increased to more than 4, more than 3.3, more than 3.2, or more than 3.1, the color coordinate of the polyimide resin film is shifted, causing color distortion, which limits its application to displays.

[0060] Meanwhile, the polyimide-based resin film may have a haze value of less than 1.0%, or 0.1% or more and less than 1.0%. The haze may 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 may also change by a certain value.

[0061] In addition, the polyimide-based resin film of the embodiment may have a thickness retardation value of 10 nm to 52 nm, or 10 nm to 50 nm, or 10 nm to 45 nm, or 10 nm to 40 nm, or 10 nm to 35 nm, or 20 nm to 35 nm, or 27 nm to 52 nm at a thickness of 10 μm. th ) characteristic, optical isotropy is improved, and the diagonal viewing angle of the display to which the polyimide resin film is applied can be secured, thereby achieving excellent visibility.

[0062] It is believed that such low retardation is achieved by reducing the difference in refractive index between the plane and thickness directions using m-PDA (m-Phenylenediamine), a diamine with an asymmetric structure, and 4,4'-Oxydiphthalic Anhydride (ODPA), an anhydride with a bent structure, as monomers used in the manufacture of polyimide resin films, as described below.

[0063] 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 well packed together, so the refractive index in the thickness direction can be increased.

[0064] The retardation in the thickness direction may be measured at a wavelength of 532 nm, and examples of a measuring method and equipment are not specifically limited, and various methods conventionally used for measuring retardation in the thickness direction may be applied without limitation.

[0065] The retardation in the thickness direction may 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 may also change by a certain value.

[0066] Specifically, the thickness direction retardation R th can be calculated using the following Equation 2.

[0067] [Formula 2] R th (nm)=|[(n x +n y ) / 2]-n z |×d

[0068] 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 and 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.

[0069] 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.

[0070] The polyimide-based resin film has a thickness direction retardation value of 10 nm to 52 nm, or 10 nm to 50 nm, or 10 nm to 45 nm, or 10 nm to 40 nm, or 10 nm to 35 nm at a thickness of 10 μm, and thereby 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.

[0071] If the retardation value in the thickness direction of the polyimide resin film at a thickness of 10 μm is excessively increased to exceed 52 nm, 50 nm, 45 nm, 40 nm, or 35 nm, distortion 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.

[0072] The polyimide resin film may have an average refractive index at a wavelength of 532 nm of 1.6995 to 1.7060, or 1.6998 to 1.7058, or 1.7028 to 1.7058, or 1.6998 to 1.7026. 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 thickness direction (TM) direction at a wavelength of 532 nm, and the average refractive index is calculated according to the following Equation 3.

[0073] [Formula 3] Average refractive index = (n x +n y +n z ) / 3

[0074] In the above formula 3, 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 toz is the refractive index in the thickness direction of the polyimide resin film measured with light having a wavelength of 532 nm.

[0075] The average refractive index may 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 may also change by a certain value.

[0076] Meanwhile, the polyimide-based resin film may contain a polyimide-based resin. The polyimide-based resin refers to a resin that includes polyimide and its precursor polymers, polyamic acid and polyamic acid ester. That is, the polyimide-based polymer may include one or more repeating units selected from the group consisting of polyamic acid repeating units, polyamic acid ester repeating units, and polyimide repeating units. That is, the polyimide-based polymer may include 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.

[0077] 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.

[0078] 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.

[0079] In particular, the polyimide resin may include a polyimide repeating unit represented by the following Chemical Formula 1.

[0080] [Chemical formula 1] [ka]

[0081] In the above chemical formula 1, X1 is an aromatic tetravalent functional group containing an ether group, and Y1 is an aromatic divalent functional group having 6 to 10 carbon atoms.

[0082] In the above Chemical Formula 1, X1 is an aromatic tetravalent functional group containing an ether group, and the above X1 is a functional group derived from a tetracarboxylic dianhydride compound used in the synthesis of a polyimide resin.

[0083] When X1 contains the aromatic tetravalent functional group having an ether group, the ether functional group and a structure in which two benzene rings are bent are introduced into the polyimide chain structure, so that the molecules are not well packed with each other, and thus the refractive index in the thickness direction increases, and the refractive index difference between the plane direction and the thickness direction is reduced, thereby realizing a low retardation. In addition, the electron-attracting effect of the ether group suppresses the formation of a charge transfer complex (CTC) of Pi-electrons present in the imide chain, thereby ensuring transparency and realizing excellent optical properties.

[0084] On the other hand, if X1 contains a functional group derived from BPDA (3,3',4,4'-biphenyltetracarboxylic dianhydride) or PMDA (pyromellitic dianhydride) that does not contain an ether group, it may be difficult to realize the transparency and curved structure due to the ether group, and the refractive index difference between the plane direction and the thickness direction may increase, which may cause a problem of increasing the yellowness index.

[0085] More specifically, the X1 tetravalent functional group may include a tetravalent functional group represented by the following Formula 2:

[0086] [Chemical formula 2] [ka]

[0087] A specific example of the functional group represented by Chemical Formula 2 is a functional group represented by Chemical Formula 2-1 below, which is derived from 4,4'-oxydiphthalic anhydride (ODPA).

[0088] [Chemical formula 2-1] [ka]

[0089] 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.

[0090] 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.

[0091] [Chemical formula 3] [ka]

[0092] A specific example of the functional group represented by Chemical Formula 3 is a functional group derived from m-phenylenediamine (1,3-phenylenediamine, m-PDA) represented by the following Chemical Formula 3-1.

[0093] [Chemical formula 3-1] [ka]

[0094] 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, so that the arrangement can be maintained in the thickness direction, and a low retardation can be realized by reducing the refractive index difference between the plane direction and the thickness direction.

[0095] On the other hand, if 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. As 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.

[0096] In addition, if Y1 contains a functional group derived from 4,4'-oxydianiline (ODA), the polymers are well packed together due to the symmetric structure, which may cause a problem of increasing the refractive index difference between the plane and thickness directions.

[0097] The polyimide resin may contain a combination of an aromatic tetracarboxylic dianhydride containing an ether group and an aromatic diamine having 6 to 10 carbon atoms.

[0098] The aromatic tetracarboxylic dianhydride containing an ether group is a compound in which anhydride groups (-O-C-O-CO-) are introduced at both ends of the aromatic tetravalent functional group containing the above-mentioned ether group, and the aromatic tetravalent functional group containing an ether group has been described above.

[0099] A specific example of the aromatic tetracarboxylic dianhydride containing an ether group is 4,4'-oxydiphthalic anhydride (ODPA).

[0100] The aromatic diamine having 6 to 10 carbon atoms is a compound having amino groups (-NH2) introduced at both ends of the aromatic divalent functional group having 6 to 10 carbon atoms, and the description of the aromatic divalent functional group having 6 to 10 carbon atoms is as described above.

[0101] A specific example of the aromatic diamine having 6 to 10 carbon atoms is m-phenylenediamine (1,3-phenylenediamine, m-PDA).

[0102] More specifically, the polyimide resin is formed by reacting a terminal anhydride group (-OC-O-CO-) of the aromatic tetracarboxylic dianhydride containing an ether group with a terminal amino group (-NH2) of an aromatic diamine having 6 to 10 carbon atoms, so that a bond between the nitrogen atom of the amino group and the carbon atom of the anhydride group is formed.

[0103] Meanwhile, the polyimide-based resin may further include a polyimide repeating unit represented by the following Chemical Formula 4 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 4.

[0104] [Chemical formula 4] [ka]

[0105] In the above chemical formula 4, X2 is an aromatic tetravalent functional group containing an ether group, and Y2 is an aromatic divalent functional group having 12 to 17 carbon atoms and containing an ether group.

[0106] X2 is the same as X1 in Chemical Formula 1.

[0107] The aromatic divalent functional group having 12 to 17 carbon atoms and containing an ether group includes a functional group represented by the following chemical formula 5 derived from 4,4'-oxydianiline (ODA).

[0108] [Chemical formula 5] [ka]

[0109] When the functional group represented by the formula 5 is included in the Y2, the electron-attracting effect of the ether group suppresses the formation of a charge transfer complex (CTC) of Pi-electrons present in the imide chain, thereby ensuring transparency and improving optical properties. In addition, since the functional group represented by the formula 5 also has a bent structure, it is possible to maintain a low retardation by suppressing an increase in the refractive index difference between the plane direction and the thickness direction while maintaining a small refractive index in the thickness direction.

[0110] That is, the polyimide-based polymer may include a first repeating unit containing a repeating unit represented by Chemical Formula 1, in which the diamine-derived repeating unit is a functional group represented by Chemical Formula 3, and a second repeating unit containing a repeating unit represented by Chemical Formula 4, in which the diamine-derived repeating unit is a functional group represented by Chemical Formula 5. The first repeating unit and the second repeating unit may be arranged randomly within the polyimide-based polymer to form a random copolymer, or may form a block copolymer by forming blocks between the first repeating units and blocks between the second repeating units.

[0111] The polyimide-based polymer including the repeating unit represented by Formula 1 and the repeating unit represented by Formula 4 can be prepared by reacting a tetracarboxylic dianhydride compound with two or more different diamine compounds. The two diamine compounds can be added simultaneously to synthesize a random copolymer or added sequentially to synthesize a block copolymer.

[0112] The polyimide resin may contain 20 mol% to 100 mol%, or 30 mol% to 100 mol%, or 50 mol% to 100 mol%, or 70 mol% to 100 mol% of the polyimide repeating unit represented by Chemical Formula 1, based on 100 mol% of the total repeating units. The polyimide resin may contain 0 mol% to 80 mol%, or 0 mol% to 70 mol%, or 0 mol% to 50 mol%, or 0 mol% to 30 mol% of the polyimide repeating unit represented by Chemical Formula 4. Within the above numerical range, a polyimide resin film synthesized from the polyimide resin may simultaneously satisfy the characteristics of a refractive index difference (Δn) of 0.0068 or less obtained by Formula 1 and a yellowness index of 5.5 or less at a thickness of 10 μm.

[0113] As a result, excellent optical properties such as colorless transparency can be achieved through low yellowing, and at the same time, optical isotropy is enhanced through low retardation (Rth) properties in the thickness direction, and the diagonal viewing angle of the display to which the polyimide resin film is applied can be secured, thereby preventing deterioration of visibility due to the distortion of light.

[0114] On the other hand, when the polyimide-based resin contains an excessively small amount of the polyimide repeating unit represented by Chemical Formula 1, the thickness direction retardation R th As the value increases beyond 25 nm, the visibility decreases due to the distortion of light caused by the increase in retardation, and as the color coordinate b* increases beyond 2, the degree of yellow discoloration increases.

[0115] The polyimide repeating units represented by Chemical Formula 1 and the polyimide repeating units represented by Chemical Formula 4 may be contained in an amount of 70 mol% or more, 80 mol% or more, 90 mol% or more, or 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.

[0116] That is, the polyimide-based resin may be composed only of the polyimide repeating unit represented by Formula 1 and the polyimide repeating unit represented by Formula 4, or may be composed mostly of the polyimide repeating unit represented by Formula 1 and the polyimide repeating unit represented by Formula 4.

[0117] 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.

[0118] The polyimide 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 can be 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 protective films for optical disks, and is particularly suitable for display cover substrates.

[0119] More specifically, the method for synthesizing the polyimide-based resin film is not particularly limited, and for example, a film manufacturing method including the steps of applying a resin composition containing the polyimide-based resin to a substrate to form a coating film (Step 1); drying the coating film (Step 2); and heat-treating the dried coating film to harden it (Step 3) may be used.

[0120] 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, methods such as screen printing, offset printing, flexographic printing, and inkjet printing can be used.

[0121] 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 obtained reaction solution itself, or may be a solution obtained by diluting the reaction solution with another solvent. In addition, when the polyimide resin is obtained as a powder, the solution may be a solution obtained by dissolving the powder in an organic solvent.

[0122] 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, dimethyl sulfoxide, tetramethylurea, pyridine, dimethyl sulfone, hexamethyl sulfoxide, 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 Examples of the amines include isopropyl 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, and ethylene glycol monobutyl ether acetate. These may be used alone or in combination.

[0123] The resin composition containing the polyimide resin may contain a solid content in an amount that allows the composition to have an appropriate viscosity in consideration of processability such as coatability during a film formation process, etc. For example, the content of the composition may be adjusted so that the total resin content is 5% by weight to 25% by weight, or 5% by weight to 20% by weight, or 5% by weight to 15% by weight.

[0124] In addition, the resin composition containing the polyimide resin may further contain other components in addition to the organic solvent. As a non-limiting example, when the resin composition containing the polyimide resin is applied, an additive may be further included that can improve the uniformity of the film thickness or the surface smoothness, improve the adhesion to the substrate, change the dielectric constant or the conductivity, or increase the density. Examples of such additives include a surfactant, a silane compound, a dielectric or a crosslinking compound, etc.

[0125] The step 2 is a step of coating a substrate with the resin composition containing the polyimide resin and drying the coating film formed.

[0126] The drying step of the coating film can be carried out by a heating means such as a hot plate, a hot air circulating oven, an infrared oven, etc., and can be carried out at a temperature of 50°C to 150°C, or 50°C to 100°C.

[0127] Step 3 is a step of heat-treating the dried coating film to cure it, which 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 higher, or 200°C to 300°C.

[0128] 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 also change by a certain value.

[0129] Meanwhile, the polyimide resin film may include a phosphate-based additive, which includes a compound containing a phosphate functional group and expands the space between polyimide main chains through a bulky structure, thereby realizing high transmittance, low yellow index, and low retardation.

[0130] The phosphate-based additive may be included in an amount of 1 wt% to 50 wt%, or 1 wt% to 40 wt%, or 1 wt% to 30 wt%, or 5 wt% to 50 wt%, or 5 wt% to 40 wt%, or 5 wt% to 30 wt%, or 6 wt% to 30 wt%, or 7 wt% to 30 wt%, or 12 wt% to 30 wt%, or 5 wt% to 25 wt%, or 6 wt% to 25 wt%, or 7 wt% to 25 wt%, or 11 wt% to 25 wt%, or 5 wt% to 18 wt%, or 6 wt% to 18 wt%, or 7 wt% to 18 wt%, or 12 wt% to 18 wt%, based on the total weight of the polyimide-based resin film.

[0131] More specifically, the phosphate additive is added to a resin composition containing a polyimide resin for producing the polyimide resin film, and remains in the polyimide resin film. The phosphate additive may be included in the resin composition containing the polyimide resin in an amount of 1 wt% to 50 wt%, or 1 wt% to 40 wt%, or 1 wt% to 30 wt%, or 5 wt% to 50 wt%, or 5 wt% to 40 wt%, or 5 wt% to 30 wt%, or 6 wt% to 30 wt%, or 7 wt% to 30 wt%, or 12 wt% to 30 wt%, or 5 wt% to 25 wt%, or 6 wt% to 25 wt%, or 7 wt% to 25 wt%, or 11 wt% to 25 wt%, or 5 wt% to 18 wt%, or 6 wt% to 18 wt%, or 7 wt% to 18 wt%, or 12 wt% to 18 wt% based on the total solid content weight.

[0132] If the content of the phosphate-based additive is too low relative to the total weight of the polyimide resin film, it may be difficult to achieve low retardation and high transparency due to the phosphate-based additive, whereas if the content of the phosphate-based additive is too high relative to the total weight of the polyimide resin film, the haze increases and the yellowness index also increases, resulting in poor optical properties and poor heat resistance.

[0133] The phosphate-based additive may include triaryl phosphate, which has a structure in which three aryl groups are bonded to a phosphate functional group, and examples of the triaryl phosphate are not particularly limited, but may include triphenyl phosphate.

[0134] 2. Display device substrates Meanwhile, according to 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 may include all of the content described above in the one embodiment.

[0135] 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.

[0136] The display device may have various structures depending on the application field and specific form, for example, it may have 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.

[0137] The polyimide-based resin film according to the above-mentioned embodiment can 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, can be used as a substrate.

[0138] For example, the substrate for a display device may have a structure in which an element protection layer, a transparent electrode layer, a silicon oxide layer, a polyimide-based resin film, a silicon oxide layer, and a hard coating layer are sequentially laminated.

[0139] 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 formed by curing polysilazane.

[0140] Specifically, the silicon oxide layer may be formed by coating a solution containing polysilazane on at least one surface of the transparent polyimide-based resin film prior to forming a coating layer, drying the solution, and then curing the coated polysilazane.

[0141] 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 bending properties and impact resistance, as well as solvent resistance, optical properties, moisture permeability and scratch resistance.

[0142] 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 may include all of the content described above in the above embodiment.

[0143] The optical device may include any device that uses 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.

[0144] The optical device may have various structures depending on the application field and specific form, for example, it may have 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.

[0145] The polyimide-based resin film according to the above-mentioned embodiment can 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, can be applied to a substrate. Effect of the Invention

[0146] The present invention relates to a polyimide-based resin film that is suitable for use as an optical member by increasing light transmittance through significantly improved transparency due to a low yellowness index and having low birefringence, and at the same time, by increasing optical isotropy through a low refractive index difference (Δn) characteristic and realizing a low retardation, the polyimide-based resin film can ensure the diagonal viewing angle of a display to which the polyimide-based resin film is applied and prevent a decrease in visibility due to the distortion of light, and a display device substrate and an optical device using the same. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0147] The present invention will be described in more detail with reference to the following examples, however, the following examples are merely illustrative of the present invention and are not intended to limit the scope of the present invention. EXAMPLES

[0148] <Examples and Comparative Examples: Production of Polyimide Precursor Composition and Polyimide Film> Example 1 (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. 4,4'-Oxydiphthalic Anhydride (ODPA) was added as an acid dianhydride to the solution containing m-phenylenediamine (1,3-phenylenediamine, m-PDA) at the same temperature and stirred for 24 hours. The molar ratio of m-PDA to OPDA is as shown in Table 1 below.

[0149] Then, triphenylphosphate (TPhP) was added in an amount of 15 wt % based on the total solid content and stirred to prepare a polyimide precursor composition.

[0150] (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 cured at 80°C for 5 to 30 minutes and at 260°C for 60 minutes. After the curing process was completed, the glass substrate was immersed in water to peel off the film formed on the glass substrate, and the film 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).

[0151] Examples 2-5, Comparative Example 1 Polyimide precursor compositions and polyimide films were prepared in the same manner as in Example 1, except that the molar ratios of m-PDA and OPDA and the content of TPhP were changed as shown in Table 1 below.

[0152] Example 6 (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) and 4,4'-oxydianiline (ODA) were added and dissolved at the same temperature while maintaining the temperature of the reactor at 25°C. 4,4'-oxydiphthalic anhydride (ODPA) was added as an acid dianhydride at the same temperature to the solution containing m-phenylenediamine (1,3-phenylenediamine, m-PDA) and 4,4'-oxydianiline (ODA) and stirred for 24 hours. The molar ratios of m-PDA, ODA, and OPDA are as shown in Table 2 below.

[0153] Then, triphenylphosphate (TPhP) was added in an amount of 10 wt % based on the total solid content and stirred to prepare a polyimide precursor composition.

[0154] (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 cured at 80°C for 5 to 30 minutes and at 260°C for 60 minutes. After the curing process was completed, the glass substrate was immersed in water to peel off the film formed on the glass substrate, and the film 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).

[0155] Examples 7-10, Comparative Example 2 Polyimide precursor compositions and polyimide films were prepared in the same manner as in Example 6, except that the molar ratios of m-PDA, ODA, and OPDA, and the content of TPhP were changed as shown in Table 2 below.

[0156] Comparative Example 3-7 Polyimide precursor compositions and polyimide films were prepared in the same manner as in Example 6, except that the molar ratios of m-PDA, p-PDA (1,4-phenylenediamine), ODA, OPDA, BPDA (3,3',4,4'-biphenyltetracarboxylic dianhydride), and PMDA (pyromellitic dianhydride) and the TPhP content were changed as shown in Table 3 below.

[0157] <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.

[0158] 1. Yellow index (YI), color coordinates (b*) The yellowness index and color coordinate (b*) of the polyimide films prepared in the examples and comparative examples were measured using a color meter (Gretagmacbeth's Color-Eye 7000A) and are shown in Table 1 below.

[0159] 2.Thickness direction retardation (R th ) The measurement device used was an "AxoScan" manufactured by AXOMETRICS. The refractive index of the polyimide films produced in the examples and comparative examples was inputted with respect to light having a wavelength of 532 nm. The retardation in the thickness direction and in the plane direction was then measured using light having 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.

[0160] Specifically, the thickness direction retardation R th was calculated using the following Equation 2.

[0161] [Formula 2] R th (nm)=|[(n x +n y ) / 2]-n z |×d (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 and 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.)

[0162] 3. Refractive Index The refractive indexes in the transverse (TE) and transverse (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 3.

[0163] [Formula 3] Average refractive index = (n x +n y +n z ) / 3 (In the above formula 3, 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 and 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.)

[0164] 4. Haze The haze value of the polyimide film was measured using a Hazemeter (NDH-5000) and evaluated according to the following criteria.

[0165] [Table 1] Experimental Measurement Results of Examples 1-5 and Comparative Example 1 [Table 1]

[0166] As shown in Table 1 above, the polyimide films (based on a thickness of 10 μm) obtained in Examples 1 to 5 had a thickness direction retardation R th The thickness direction retardation R th The value was 60 nm, which was increased compared to Examples 1 to 5, making it difficult to achieve visibility suitable for display, and the color coordinate b* was 6.04 and YI was 9.58, which were high compared to Examples 1 to 5, limiting the occurrence of color distortion. In addition, the refractive index difference (nTE-nTM) at 532 nm was 0.0076, and the average refractive index at 532 nm was 1.708, demonstrating a high retardation compared to Examples 1 to 5.

[0167] [Table 2] Experimental Measurement Results for Examples 6-10 and Comparative Example 2 [Table 2]

[0168] As shown in Table 2 above, the polyimide films (based on a thickness of 10 μm) obtained in Examples 6 to 10 had a thickness direction retardation R thThe thickness direction retardation R th The value was 73 nm, which was increased compared to Examples 6 to 10, making it difficult to achieve visibility suitable for display, and the color coordinate b* was 4.98 and YI was 8.24, which were high compared to Examples 6 to 10, limiting the occurrence of color distortion. In addition, it was confirmed that the refractive index difference (nTE-nTM) at 532 nm was 0.0100 and the average refractive index at 532 nm was 1.7056, which was increased compared to Examples 6 to 10, showing high retardation.

[0169] [Table 3] Experimental results of Comparative Examples 3-7 [Table 3]

[0170] As shown in Table 3 above, the polyimide films (based on a thickness of 10 μm) obtained in Comparative Examples 3 to 5 had a thickness direction retardation R th It was confirmed that the value was 53 nm to 98 nm, the color coordinate b* was 3.32 to 3.83, the YI was 4.37 to 6.46, the refractive index difference (nTE-nTM) at 532 nm was 0.0069 to 0.0121, and the average refractive index at 532 nm was 1.6993 to 1.7024. In addition, the polyimide films (based on a thickness of 10 μm) obtained in Comparative Examples 6 to 7 had a thickness direction retardation R th It was confirmed that the value was 646 nm to 1024 nm, the color coordinate b* was 11.44 to 61.15, the YI was 17.41 to 81, the refractive index difference (nTE-nTM) at 532 nm was 0.0643 to 0.0923, and the average refractive index at 532 nm was 1.7115 to 1.7657. That is, in the cases of Comparative Examples 3 to 7, the thickness direction retardation R thIt was confirmed that the refractive index difference (nTE-nTM) at 532 nm increased compared to Examples 1 to 10, indicating high retardation, and that the value increased compared to Examples 1 to 10, indicating that it was difficult to achieve visibility suitable for displays.

Claims

1. The refractive index difference (Δn) obtained by the following formula 1 is 0.0068 or less, The yellow index at a thickness of 10 μm is 5.5 or less, A polyimide-based resin including a polyimide repeating unit represented by the following chemical formula 1, and a phosphate-based additive, Polyimide resin film: [Chemical formula 1] 【Chemistry 1】 (In the above chemical formula 1, X １ is an aromatic tetravalent functional group containing an ether group, Y １ is a functional group represented by the following chemical formula 3-1) [Chemical formula 3-1] 【Chemistry 13】 [Formula 1] Refractive index difference (Δn) = n1 - n2 In the above formula 1, n1 is the refractive index in the plane direction of the polyimide resin film having a thickness of 10 μm, and n2 is the refractive index in the thickness direction of the polyimide resin film having a thickness of 10 μm.

2. The polyimide resin film according to claim 1, wherein the polyimide resin film has a color coordinate b* of 1 to 4 at a thickness of 10 μm.

3. The polyimide resin film has a thickness difference R ｔｈ 2. The polyimide resin film according to claim 1, wherein the value is 10 nm to 52 nm.

4. 2. The polyimide resin film according to claim 1, wherein the polyimide resin film has an average refractive index at a wavelength of 532 nm of 1.6995 to 1.7060.

5. 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 of 1.70 to 1.

71.

6. 2. The polyimide resin film according to claim 1, wherein the polyimide resin film has a refractive index in the thickness direction at a wavelength of 532 nm of 1.69 to 1.

71.

7. The polyimide resin film according to claim 1 , wherein the polyimide resin film has a haze value of less than 1.0%.

8. The X １ The polyimide-based resin film according to claim 1, wherein the polyimide-based resin film comprises a tetravalent functional group represented by the following chemical formula 2: [Chemical formula 2] 【Chemistry 11】

9. 2. The polyimide resin film according to claim 1, wherein the polyimide resin comprises a combination of an aromatic tetracarboxylic dianhydride having an ether group and an aromatic diamine having 6 to 10 carbon atoms.

10. 2. The polyimide-based resin film according to claim 1, further comprising a polyimide repeating unit represented by the following Chemical Formula 4 in addition to the polyimide repeating unit represented by Chemical Formula 1: [Chemical formula 4] 【Chemistry 14】 In the above chemical formula 4, X ２ is an aromatic tetravalent functional group containing an ether group, Y ２ is an aromatic divalent functional group containing an ether group and having 12 to 17 carbon atoms.

11. The Y ２ The polyimide resin film according to claim 10, comprising a functional group represented by the following chemical formula 5: [Chemical formula 5] 【Chemistry 15】

12. 2. The polyimide resin film according to claim 1, wherein the polyimide resin contains 20 mol % to 100 mol % of the polyimide repeating unit represented by Chemical Formula 1, based on 100 mol % of all repeating units.

13. The polyimide resin film according to claim 1 , wherein the phosphate-based additive comprises a triaryl phosphate.

14. A display device substrate comprising the polyimide resin film of claim 1.

15. An optical device comprising the polyimide resin film of claim 1.

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