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

Abstract

The present invention relates to a polyimide resin film having a thermal hysteresis gap of 100 μm or more and 500 μm or less at a temperature of 50° C. or more and 150° C. or less, 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. 10-2021-0185016 dated December 22, 2021 and Korean Patent Application No. 10-2022-0099145 dated August 9, 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 optical properties 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, polyimide resins are colored brown or yellow due to their high aromatic ring density, and therefore have low transmittance in the visible light region, a yellowish color, low light transmittance, and large birefringence, limiting their use in optical components.

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

[0009] The present invention provides a polyimide resin film that can achieve excellent chemical resistance, optical properties, and 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 resin film having a thermal hysteresis gap of 100 μm or more and 500 μm or less at a temperature of 50° C. or more and 150° C. or less.

[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 the Huckels Rule, and a compound is defined as being aromatic when it satisfies all of the following three conditions according to the Huckels Rule: 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] The present invention will now be described in more detail.

[0030] According to one embodiment of the present invention, it is possible to provide a polyimide resin film having a thermal hysteresis gap of 100 μm or more and 500 μm or less at a temperature of 50° C. or more and 150° C. or less.

[0031] The present inventors have confirmed through experiments that when the thermal hysteresis gap is 100 μm or more and 500 μm or less at a temperature of 50° C. or more and 150° C. or less, as in the polyimide-based resin film of the above embodiment, thermal expansion during high-temperature processing is reduced, and a polyimide-based resin film suitable for display element processing can be provided, and thus the present invention has been completed.

[0032] In addition, as described below, 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 can be effectively increased.

[0033] The polyimide resin film of the embodiment may have a thermal hysteresis gap at a temperature of 50° C. or higher and 150° C. or lower of 100 μm or higher and 500 μm or lower, 150 μm or higher and 500 μm or lower, 200 μm or higher and 500 μm or lower, 250 μm or higher and 500 μm or lower, 100 μm or higher and 400 μm or lower, 150 μm or higher and 400 μm or lower, 200 μm or higher and 400 μm or lower, 250 μm or higher and 400 μm or lower, 100 μm or higher and 300 μm or lower, 150 μm or higher and 300 μm or lower, 200 μm or higher and 300 μm or lower, 250 μm or higher and 300 μm or lower, 100 μm or higher and 260 μm or lower, 150 μm or higher and 260 μm or lower, 200 μm or higher and 260 μm or lower, or 250 μm or higher and 260 μm or lower.

[0034] Specifically, the thermal hysteresis gap refers to a value measured at a temperature of 50°C or more and 150°C or less, 80°C or more and 130°C or less, or 100°C or more.

[0035] It is believed that the thermal hysteresis gap is achieved by using a specific amount of a phosphate-based compound together with m-PDA (m-Phenylenediamine), a diamine having an asymmetric structure, p-PDA (p-Phenylenediamine), a diamine having a symmetric structure, and 4,4'-oxydiphthalic anhydride (ODPA) and 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), which are anhydrides having a bent structure, as monomers used in the manufacture of a polyimide-based resin film, as described below.

[0036] Specifically, the thermal hysteresis gap is determined by using a specific amount of a phosphate-based compound together with m-PDA (m-Phenylenediamine), a diamine having an asymmetric structure, p-PDA (p-Phenylenediamine), a diamine having a symmetric structure, and 4,4'-oxydiphthalic anhydride (ODPA) and 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), which are anhydrides having a bent structure, as monomers used in the production of a polyimide-based resin film, as described below. The polyimide resin contains repeating units derived from linear diamine p-PDA (p-Phenylenediamine) along with repeating units derived from 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (ODPA) and 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), and it is considered that this is achieved by adjusting the hysteresis gap so that the portion of the main chain of the polyimide resin that would normally be stretched by heat has a linear structure that does not stretch by heat.

[0037] The method and device for measuring the thermal hysteresis gap are not particularly limited, and various methods conventionally used for measurement can be applied without limitation. For example, the thermal hysteresis gap can be measured by measuring the change in length in the length direction (dimension change gap) at a specific temperature after a heating process and a cooling process using a thermomechanical analyzer such as a TMA. More specifically, a TMA (Q400 manufactured by TA) is used to measure the change in thermal expansion profile by measuring the change in length in the length direction (dimension change gap, y-axis) at 100°C after a heating process to 260°C at a heating rate of 5°C / min and a cooling process to 50°C at a cooling rate of 4°C / min.

[0038] The thermal hysteresis gap 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.

[0039] When the thermal hysteresis gap of the polyimide resin film of the above embodiment is less than 100 μm at a temperature of 50° C. to 150° C., the optical properties are degraded. When the thermal hysteresis gap is more than 500 μm, the thermal expansion is large during high-temperature processing, which is not suitable for display device processing.

[0040] Meanwhile, the polyimide-based resin film may have a yellowness index of 2.5 or less, 2.0 or more, 2.1 or more, 2.0 to 2.5, or 2.1 to 2.5 at a thickness of 10 μm. If the yellowness index of the polyimide-based resin film at a thickness of 10 μm is excessively increased, such as exceeding 2.5, the yellowness of the polyimide-based resin film increases, making it difficult to manufacture a colorless and transparent film.

[0041] It is believed that such a low yellowness index (YI) is achieved by using m-PDA (m-Phenylenediamine), a diamine having an asymmetric structure, as a monomer used in the production of polyimide resin films, and 4,4'-oxydiphthalic anhydride (ODPA), an anhydride having an ether group, which is an electron-withdrawing functional group, and a bent, folded structure, as described below.

[0042] More specifically, in the case of polyimide with a planar linear main chain structure, the polyimide molecules pile up by packing side by side, whereas in the case of polyimide with a bent, folded main chain structure, the molecules do not pack well with each other, so transparency is ensured by suppressing CTC, and the electron-withdrawing effect of the ether group enhances the CTC inhibition effect.

[0043] 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).

[0044] 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.

[0045] Meanwhile, the polyimide-based resin film of the embodiment may have a color coordinate b* of 1.0 to 2.0, or 1.0 to 1.5, or 1.3 to 1.5 at a thickness of 10 μm. 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.

[0046] In the present invention, "color coordinates" refers to coordinates in the CIE Lab color space, which are hue values ​​defined by the CIE (Commission International de l'Eclairage), and any position in the CIE color space is expressed by three coordinate values: L*, a*, and b*.

[0047] 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.

[0048] 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 hue biased toward pure blue, and a positive b* value indicates a hue biased toward pure yellow. Comparing b*=50 and b*=80, this means that b*=80 is closer to pure yellow than b*=50.

[0049] The method and device for measuring the color coordinates are not particularly limited, and various methods used in the past 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 (Color-Eye 7000A manufactured by GRETAGMACBETH).

[0050] 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 increases or decreases by a certain value, the physical properties measured from the polyimide-based resin film can also change by a certain value.

[0051] When the color coordinate b* of the polyimide-based resin film at a thickness of 10 μm is excessively increased to be more than 2.0 or more than 1.5, the color coordinate of the polyimide-based resin film is distorted, causing a color distortion phenomenon, which limits its application as a display.

[0052] In addition, the polyimide-based resin film of the embodiment may have a thickness direction retardation value of 10 nm to 60 nm, or 10 nm to 50 nm, or 20 nm to 50 nm, or 30 nm to 50 nm, or 31 nm to 50 nm at a thickness of 10 μm. th ) provides high optical isotropy, and the polyimide resin film can ensure a sufficient diagonal viewing angle for a display to which the film is applied, thereby achieving excellent visibility.

[0053] It is believed that such 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, and 4,4'-Oxydiphthalic Anhydride (ODPA), an anhydride having a bent structure, as monomers used in the manufacture of polyimide resin films, as described below.

[0054] 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.

[0055] 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 conventionally used for measuring thickness direction retardation can be applied without limitation.

[0056] 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.

[0057] Specifically, the thickness direction retardation R th can be calculated by the following Equation 2. [Formula 2] R th (nm)=|[(n x +n y ) / 2]-n z |×d

[0058] 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; d is the thickness of the polyimide resin film.

[0059] 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.

[0060] The polyimide resin film can achieve excellent visual sensation when the retardation value in the thickness direction at a thickness of 10 μm satisfies the above range.

[0061] If the retardation value in the thickness direction of the polyimide resin film at a thickness of 10 μm is excessively increased to more than 60 nm or more than 50 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.

[0062] The polyimide resin film may have an average refractive index at a wavelength of 532 nm of 1.651 to 1.700, or 1.6517 to 1.700, or 1.651 to 1.680, or 1.6517 to 1.680, or 1.6517 to 1.675, or 1.6517 to 1.6733. 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 by the following Equation 3. [Formula 3] Average refractive index = (n x +n y +n z ) / 3

[0063] 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 to z is the refractive index in the thickness direction of the polyimide resin film measured with light having a wavelength of 532 nm.

[0064] 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.

[0065] Meanwhile, the polyimide-based resin film may include a polyimide-based resin and a phosphate-based compound.

[0066] The phosphate-based compound includes a compound containing a phosphate functional group, and has a bulky structure that widens the space between polyimide main chains, thereby realizing high transmittance, low yellow index, and low retardation.

[0067] The phosphate-based compound is included in an amount of 1 wt% to 30 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.

[0068] More specifically, the phosphate compound is added to a resin composition containing a polyimide resin for producing the polyimide resin film, and can remain in the polyimide resin film. In the resin composition containing the polyimide resin, the phosphate compound is contained in an amount of 1 wt% to 30 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 solid content.

[0069] If the content of the phosphate-based compound is too low relative to the total weight of the polyimide-based resin film, it is difficult to achieve low retardation and high transparency due to the phosphate-based compound, whereas if the content of the phosphate-based compound is too high relative to the total weight of the polyimide-based resin film, the haze increases and the yellowness index also increases, resulting in poor optical properties and poor heat resistance.

[0070] The phosphate-based compound may include triaryl phosphate, which has a structure in which three aryl groups are bonded to a phosphate functional group, and the specific example of the triaryl phosphate is not particularly limited, but for example, triphenyl phosphate may be used.

[0071] Meanwhile, the polyimide-based resin means that it includes all of polyimide and its precursor polymers, polyamic acid and polyamic acid ester. That is, the polyimide-based polymer may include one or more 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.

[0072] 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.

[0073] 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.

[0074] Specifically, the polyimide resin film may contain a polyimide resin containing an aromatic imide repeat unit.

[0075] The aromatic imide repeating unit can be realized by the fact that, in the tetracarboxylic acid or its anhydride and the diamine compound used as monomers in the synthesis of the polyimide resin, the tetracarboxylic acid or its anhydride contains an aromatic group, the diamine compound contains an aromatic group, or both the tetracarboxylic acid or its anhydride and the diamine compound contain aromatic groups.

[0076] More specifically, the polyimide-based resin film may contain a polyimide resin containing an aromatic imide repeat unit containing an ether group.

[0077] The aromatic imide repeating unit containing an ether group can be realized by the following: in a tetracarboxylic acid or its anhydride and a diamine compound used as monomers in the synthesis of a polyimide resin, the tetracarboxylic acid or its anhydride contains an aromatic group containing an ether group, the diamine compound contains an aromatic group containing an ether group, or both the tetracarboxylic acid or its anhydride and the diamine compound contain aromatic groups containing an ether group.

[0078] 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 an ether group, and Y1 is an aromatic divalent functional group having 6 to 10 carbon atoms.

[0079] In the above Chemical Formula 1, X1 is an aromatic tetravalent functional group containing an ether group, and X1 is a functional group derived from a tetracarboxylic dianhydride compound used in the synthesis of a polyimide-based resin.

[0080] When X1 contains an aromatic tetravalent functional group including an ether group, the ether functional group and a structure in which two benzene rings are bent are introduced into the polyimide chain structure, which makes it difficult for molecules to pack together. As a result, the refractive index in the thickness direction increases, and the refractive index difference between the plane direction and the thickness direction is reduced, thereby achieving 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 achieving excellent optical properties.

[0081] More specifically, the tetravalent functional group of X1 may include a tetravalent functional group represented by the following Chemical Formula 2. [Chemical formula 2] [ka]

[0082] A specific example of the functional group represented by the above chemical formula 2 is a functional group represented by the following chemical formula 2-1 derived from 4,4'-oxydiphthalic anhydride (ODPA). [Chemical formula 2-1] [ka]

[0083] 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.

[0084] 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]

[0085] Specific examples of the functional group represented by the following chemical formula 3 include a functional group represented by the following chemical formula 3-1 derived from m-phenylenediamine (1,3-phenylenediamine, m-PDA) and a functional group represented by the following chemical formula 3-2 derived from p-phenylenediamine (1,4-phenylenediamine, p-PDA). [Chemical formula 3-1] [ka] [Chemical formula 3-2] [ka] .

[0086] 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.

[0087] In addition, when the functional group represented by Chemical Formula 3-2 is contained in Y1, a region in which the molecules are arranged linearly is formed, which increases the rigidity of the polyimide resin and increases its thermal stability, thereby realizing a low thermal hysteresis gap of 100 μm to 500 μm at a temperature of 50° C. to 150° C.

[0088] Specifically, the polyimide resin may contain the functional group represented by Chemical Formula 3-2 in an amount of 0.1 to 0.9 moles, 0.2 to 0.9 moles, 0.3 to 0.9 moles, 0.5 to 0.9 moles, 0.6 to 0.9 moles, 0.1 to 0.8 moles, 0.2 to 0.8 moles, 0.3 to 0.8 moles, 0.5 to 0.8 moles, 0.6 to 0.8 moles, 0.1 to 0.7 moles, 0.2 to 0.7 moles, 0.3 to 0.7 moles, 0.5 to 0.7 moles, or 0.6 to 0.7 moles.

[0089] When the functional group represented by the chemical formula 3-2 is contained in an amount of less than 0.1 mol, less than 0.2 mol, less than 0.3 mol, less than 0.5 mol, or less than 0.6 mol per mol of the functional group represented by the chemical formula 3-1, a bulky structure may be arranged between the polymers, resulting in a decrease in rigidity, a decrease in chemical resistance, and a decrease in thermal stability.

[0090] In addition, when the functional group represented by Chemical Formula 3-2 is contained in an amount of more than 0.9 mol, more than 0.8 mol, or more than 0.7 mol per mol of the functional group represented by Chemical Formula 3-1, it is difficult to realize the curved asymmetric structure of the functional group represented by Chemical Formula 3-1 derived from m-phenylenediamine (1,3-phenylenediamine, m-PDA) described above, and the polymer grows only in the in-plane direction while the polyimide is polymerized in a straight line on the plane, so that the polymers are well packed together, the refractive index in the thickness direction is reduced, and the difference in the refractive index between the in-plane direction and the thickness direction is increased.

[0091] In addition, when a functional group derived from 4,4'-oxydianiline (ODA) is contained in Y1, the structure has symmetry, so that the polymers are well packed together, which may cause a problem that the refractive index in the thickness direction is reduced and the difference in the refractive index between the plane direction and the thickness direction is increased.

[0092] The polyimide resin may contain a combination of an aromatic tetracarboxylic acid dianhydride containing an ether group and an aromatic diamine having 6 to 10 carbon atoms.

[0093] The aromatic tetracarboxylic dianhydride containing an ether group is a compound in which an anhydride group (-OC-O-CO-) is introduced at both ends of the aromatic tetravalent functional group containing an ether group, and the description of the aromatic tetravalent functional group containing an ether group is as described above.

[0094] A specific example of the aromatic tetracarboxylic acid dianhydride containing an ether group is 4,4'-oxydiphthalic anhydride (ODPA).

[0095] 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 description of the aromatic difunctional group having 6 to 10 carbon atoms is as described above.

[0096] Specific examples of the aromatic diamine having 6 to 10 carbon atoms include m-phenylenediamine (1,3-phenylenediamine, m-PDA) and p-phenylenediamine (1,4-phenylenediamine, p-PDA).

[0097] More specifically, in the polyimide resin, a bond is formed between the nitrogen atom of the amino group and the carbon atom of the anhydride group through a reaction between the terminal anhydride group (-OC-O-CO-) of the aromatic tetracarboxylic dianhydride containing the ether group and the terminal amino group (-NH2) of the aromatic diamine having 6 to 10 carbon atoms.

[0098] 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. [Chemical formula 4] [ka]

[0099] In the above Chemical Formula 4, X2 is an aromatic tetravalent functional group containing a perfluoroalkyl group, and Y2 is an aromatic divalent functional group having 6 to 10 carbon atoms.

[0100] The Y2 is the same as Y1 in Chemical Formula 1.

[0101] The aromatic tetravalent functional group containing a perfluoroalkyl group includes a functional group represented by the following chemical formula 5 derived from 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA). [Chemical formula 5] [ka] .

[0102] When the functional group represented by the formula 5 is included in the Y2, the electron-attracting effect of the perfluoroalkyl group suppresses the formation of a charge transfer complex (CTC) of Pi-electrons present in the imide chain, thereby ensuring transparency and further 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.

[0103] That is, the polyimide-based polymer may include a first repeating unit having a repeating unit represented by chemical formula 1, in which the diamine-derived repeating unit is the functional group represented by chemical formula 3-1 and the anhydride-derived repeating unit is the functional group represented by chemical formula 2; a second repeating unit having a repeating unit represented by chemical formula 3-2, in which the anhydride-derived repeating unit is the functional group represented by chemical formula 2 and the repeating unit represented by chemical formula 1; a third repeating unit having a repeating unit represented by chemical formula 3-1, in which the anhydride-derived repeating unit is the functional group represented by chemical formula 5 and the repeating unit represented by chemical formula 4; and a fourth repeating unit having a repeating unit represented by chemical formula 3-2, in which the anhydride-derived repeating unit is the functional group represented by chemical formula 5 and the repeating unit represented by chemical formula 4. The first to fourth repeating units may be arranged randomly within the polyimide polymer to form a random copolymer, or may form a block copolymer by forming a block between the first repeating units, a block between the second repeating units, a block between the third repeating units, and a block between the fourth repeating units.

[0104] 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 sequentially to synthesize a block copolymer.

[0105] The polyimide resin may contain 50 mol % to 90 mol %, 50 mol % to 80 mol %, or 50 mol % to 70 mol % of the polyimide repeating unit represented by Chemical Formula 1 relative to 100 mol % of all repeating units. The polyimide resin may contain 10 mol % to 60 mol %, 20 mol % to 50 mol %, or 30 mol % to 50 mol % of the polyimide repeating unit represented by Chemical Formula 4. A polyimide resin film synthesized from the polyimide resin within the above-mentioned numerical range may satisfy a thermal hysteresis gap of 100 μm to 500 μm at a temperature of 50° C. to 150° C.

[0106] As a result, a polyimide-based resin film that has little thermal expansion during high-temperature processes and is suitable for display element processes can be provided.

[0107] On the other hand, if the polyimide-based resin contains an excessively small amount of the polyimide repeating unit represented by Chemical Formula 1, the chemical resistance to solutions used in the process is reduced, making additional processes for applying the polyimide-based resin film to a display device difficult.

[0108] In addition, the polyimide-based resin may contain the polyimide repeating unit represented by Chemical Formula 4 in an amount of 0.3 mol or more, 0.4 mol or more, 0.42 mol or more, and 1.0 mol or less, 0.3 mol or more and 1.0 mol or less, 0.4 mol or more and 1.0 mol or less, or 0.42 mol or more and 1.0 mol or less, per 1 mol of the polyimide repeating unit represented by Chemical Formula 1.

[0109] When the polyimide repeating unit represented by the formula 4 is contained in an excessively small amount, that is, less than 0.3 mol, less than 0.4 mol, or less than 0.42 mol, relative to 1 mol of the polyimide repeating unit represented by the formula 1, R th It is difficult to lower the YI and b*, the spacing between the polymer molecules becomes closer, and there is a limit to how much the YI and b* can be lowered by increasing the CTC, resulting in poor optical properties.

[0110] In addition, when the polyimide repeating unit represented by Formula 4 is contained in an excessive amount of more than 1.0 mole per mole of the polyimide repeating unit represented by Formula 1, the chemical resistance of the polyimide resin decreases due to an increase in the spacing between the polymer molecules, and cracks occur in processes using solvents such as KOH and PGMEA.

[0111] The polyimide repeating unit represented by Chemical Formula 1 and the polyimide repeating unit represented by Chemical Formula 4 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.

[0112] 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 4, and is mostly composed of the polyimide repeating units represented by Chemical Formula 1 and the polyimide repeating units represented by Chemical Formula 4.

[0113] 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.

[0114] 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.

[0115] 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.

[0116] 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.

[0117] 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.

[0118] 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.

[0119] 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%.

[0120] In addition, the resin composition containing the polyimide resin may further contain other components in addition to the organic solvent. Non-limiting examples include compounds 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 compounds include surfactants, silane compounds, dielectrics, or crosslinking compounds.

[0121] 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.

[0122] 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.

[0123] 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 higher, or 200°C to 300°C.

[0124] 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.

[0125] 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 above embodiment.

[0126] 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.

[0127] 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.

[0128] 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.

[0129] 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.

[0130] 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.

[0131] 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.

[0132] 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.

[0133] Meanwhile, according to yet 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 above embodiment.

[0134] 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.

[0135] 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.

[0136] 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

[0137] According to the present invention, there can be provided a polyimide-based resin film which is suitable for use as an optical member due to its low yellowness index, remarkably improved transparency, enhanced light transmittance, and low birefringence, and which has a low refractive index difference (Δn) characteristic, thereby improving optical isotropy and realizing a low retardation, thereby ensuring the diagonal viewing angle of a display to which the polyimide-based resin film is applied, and which can prevent a decrease in visibility due to the distortion of light, and a display device substrate and an optical device using the same can be provided. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0138] 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.

[0139] <Examples and Comparative Examples: Production of Polyimide Precursor Composition and Polyimide Film>

[0140] Example 1

[0141] (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 p-phenylenediamine (1,4-phenylenediamine, p-PDA) were added and dissolved at the same temperature while maintaining the temperature of the reactor at 25°C. 4,4'-oxydiphthalic anhydride (ODPA) and 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) were added as acid dianhydrides at the same temperature to the solution containing m-phenylenediamine (1,3-phenylenediamine, m-PDA) and p-phenylenediamine (1,4-phenylenediamine, p-PDA), and the mixture was stirred for 24 hours. At this time, the molar ratios of m-PDA, p-PDA, OPDA, and 6FDA are as shown in Table 1 below.

[0142] Thereafter, triphenylphosphate (TPhP) was added in an amount of 15 wt % based on the total solid content, and the mixture was stirred to prepare a polyimide precursor composition.

[0143] (2) Manufacture 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 remove 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).

[0144] Examples 2-3, Comparative Examples 1-5, Reference Examples 1-2 Polyimide precursor compositions and polyimide films were prepared in the same manner as in Example 1, except that the molar ratios of m-PDA, p-PDA, OPDA, and 6FDA, and the content of TPhP were changed as shown in Table 1 below.

[0145] <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.

[0146] 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 (Color-Eye 7000A manufactured by Greta Gmacbeth) according to the measurement method of ASTM D1925. The results are shown in Table 1 below.

[0147] 2. 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 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.)

[0148] 3. Haze The haze value of the polyimide film was measured using a Hazemeter (NDH-5000) according to the measurement method of ASTM D1003.

[0149] 4. Glass transition temperature (Tg), CTE and thermal hysteresis gap The polyimide films manufactured in the examples and comparative examples were prepared in a size of 5 x 20 mm, and the samples were loaded using the accessory. The length of the films actually measured was the same at 16 mm. The film was pulled by a force of 0.02 N, and the first heating process was performed at a heating rate of 5 ° C / min to 260 ° C in the temperature range of 50 ~ 430 ° C, and then the first cooling process was performed at a cooling rate of 4 ° C / min to 80 ° C. The thermal expansion change was measured by TMA (TA Q400). At this time, the thermal hysteresis gap, which means the change in length in the length direction (dimension change gap, y axis) at 100 ° C on the graph measured by TMA, was measured.

[0150] After the first cooling, a second heating step was performed again at a heating rate of 5°C / min up to 350°C. When an inflection point was observed in the heating section, this was taken as the glass transition temperature (Tg), and the CTE during each of the first and second heating steps was measured.

[0151] 5. Thickness retardation (Rth) at a wavelength of 550 nm The thickness direction retardation (Rth) was measured by preparing a sample having a length of 20 mm, a width of 20 mm and a thickness of 10 μm from the polyimide film produced in each Example and Comparative Example, inputting the refractive index value of each sample using a measuring device manufactured by AXOMETRICS under the trade name "AxoScan", and measuring the thickness direction retardation using light with a wavelength of 550 nm under the conditions of a temperature of 25°C and a humidity of 40%, and then using the measured value of the thickness direction retardation (measured automatically by the measuring device), the retardation value per 10 μm of the film thickness was calculated.

[0152] The value of "refractive index of the polyimide resin film" used in measuring the thickness direction retardation (Rth) can be determined by forming an unstretched film including the same type of polyimide film as the polyimide film forming the film to be measured for retardation, and then using such an unstretched film as a measurement sample (when the film to be measured is an unstretched film, the film can be used as it is as the measurement sample), using a refractive index measuring device (product name "prism coupler & 3DR measurement / SPA-3DR" of SAIRON THE CHNOLOGY. INC.) as a measuring device, using a 532 nm light source, and measuring the refractive index for 532 nm light in the in-plane direction (direction perpendicular to the thickness direction) of the measurement sample at a temperature condition of 23 ° C.

[0153] [Table 1]

[0154] As shown in Table 1 above, the polyimide films obtained in Examples 1 to 3 (based on a thickness of 10 μm) had a thermal hysteresis gap (Δμm) of 217 μm to 465 μm, a glass transition temperature of 250° C. to 252° C., and a thickness direction retardation R th The value of each of the polyimide films obtained in Examples 1 to 3 was 31 nm to 50 nm, the color coordinate b* was 1.5 or less, YI was 2.5 or less, and the average refractive index at 532 nm was 1.6517 to 1.6733. Therefore, it was confirmed that the polyimide films obtained in Examples 1 to 3 not only had low thermal expansion during high-temperature processes and were therefore suitable for display element processes, but also had excellent chemical resistance and optical properties.

[0155] [Table 2]

[0156] As shown in Table 2 above, the polyimide films (based on a thickness of 10 μm) obtained in Comparative Examples 1 to 3 had a thickness direction retardation R thIt was confirmed that when the value is between 81nm and 109nm, it is difficult to achieve visibility suitable for displays, and when the color coordinate b* is 2.6 or more and the YI is 4.1 or more, color distortion occurs and other optical characteristics are poor.

[0157] In addition, it was confirmed that the polyimide films obtained in Comparative Examples 4 and 5 (based on a thickness of 10 μm) had a thermal hysteresis gap (Δμm) of 754 μm to 1856 μm, which is unsuitable for high-temperature display element processing, and had an average refractive index of 1.70 or more at 532 nm, which is higher than that of the Examples and shows a high retardation.

[0158] [Table 3]

[0159] As shown in Table 3 above, the polyimide film obtained in Reference Example 1 (based on a thickness of 10 μm) had a color coordinate b* of 4.1 and a YI of 7.6, which confirmed that the optical properties were poor, including the occurrence of color distortion.

[0160] In addition, it was confirmed that the polyimide film (based on a thickness of 10 μm) obtained in Reference Example 2 had a thermal hysteresis gap (Δ μm) of 2900 μm and was unsuitable for high-temperature display element processing.

Claims

1. A thermal hysteresis gap is 100 μm or more and 500 μm or less at a temperature of 50° C. or more and 150° C. or less, The polyimide-based resin film has a thickness direction retardation R th value of 10 nm to 60 nm at a thickness of 10 μm.

2. A thermal hysteresis gap of 100 μm or more and 500 μm or less at a temperature of 50° C. or more and 150° C. or less, The polyimide-based resin film has an average refractive index at a wavelength of 532 nm of 1.651 to 1.

700.

3. A thermal hysteresis gap of 100 μm or more and 500 μm or less at a temperature of 50° C. or more and 150° C. or less, The polyimide-based resin film includes a polyimide-based resin and a phosphate-based compound.

4. The polyimide resin film described in claim 1, wherein the polyimide resin film has a color coordinate b* of 1.0 to 2.0 at a thickness of 10 μm.

5. The polyimide resin film according to claim 3 , wherein the polyimide resin comprises a polyimide resin containing an aromatic imide repeating unit.

6. The polyimide resin film according to claim 3 , wherein the polyimide resin comprises a polyimide resin containing an aromatic imide repeating unit containing an ether group.

7. The polyimide resin film according to claim 3 , wherein the polyimide resin film contains the phosphate compound in an amount of 5% by weight to 30% by weight based on the total weight of solids of the polyimide resin.

8. The polyimide resin is The polyimide-based resin film according to claim 3, comprising a polyimide-based resin containing a polyimide repeating unit represented by the following chemical formula 1: [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 an aromatic divalent functional group having 6 to 10 carbon atoms.

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

10. The Y １ The polyimide resin film according to claim 8, comprising a functional group represented by the following chemical formula 3: [Chemical formula 3] 【Chemistry 3】 。

11. The functional group represented by Chemical Formula 3 includes a functional group represented by Chemical Formula 3-1 and a functional group represented by Chemical Formula 3-2: [Chemical formula 3-1] 【Chemistry 4】 [Chemical formula 3-2] 【Chemistry 5】 。

12. The polyimide resin is The polyimide resin film according to claim 8, comprising 0.1 mol to 0.9 mol of a functional group represented by the following chemical formula 3-2 per 1 mol of a functional group represented by the following chemical formula 3-1: [Chemical formula 3-1] 【Chemistry 6】 [Chemical formula 3-2] 【Chemistry 7】 。

13. 4. The polyimide resin film according to claim 3, wherein the polyimide resin comprises a combination of an aromatic tetracarboxylic acid dianhydride having an ether group and an aromatic diamine having 6 to 10 carbon atoms.

14. The polyimide resin is The polyimide-based resin film according to claim 3, comprising a polyimide repeating unit represented by the following chemical formula 4: [Chemical formula 4] 【Chemistry 8】 In the above Chemical Formula 4, X ２ is an aromatic tetravalent functional group containing a perfluoroalkyl group, Y ２ is an aromatic divalent functional group having 6 to 10 carbon atoms.

15. The Y ２ The polyimide resin film according to claim 14, comprising a functional group represented by the following chemical formula 5: [Chemical formula 5] 【Chemistry 9】 。

16. 9. The polyimide resin film according to claim 8, wherein the polyimide resin contains 50 mol % to 90 mol % of the polyimide repeating unit represented by Chemical Formula 1, based on 100 mol % of all repeating units.

17. The polyimide resin film according to claim 3 , wherein the phosphate compound comprises a triaryl phosphate.

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

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

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