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

Abstract

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

Description

[Technical field]

[0001] Cross-references to related applications (etc.) This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0030175 dated March 10, 2022 and Korean Patent Application No. 10-2023-0031292 dated March 9, 2023, 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 bending properties and low retardation, and a display device substrate and an optical device using the same. [Background technology]

[0003] The display device market is rapidly changing with the focus on 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 are being considered for application mainly to mobile devices such as smartphones, and the fields of application thereof are gradually expanding.

[0005] Generally, 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, and as a result, polyimides have anisotropic properties, which causes light distortion and significantly reduces visibility.

[0007] In addition, the polyimide material contained in the polyimide layer (substrate layer) has limitations in that when hardened at high temperatures of 400°C or higher, the optical properties decrease due to degradation of the polyimide, and it is difficult to ensure flatness due to its bending properties that cause it to twist physically.

[0008] Therefore, there is a demand for the development of a new polyimide that can reduce the difference in refractive index between the plane direction and the thickness direction, improve the visibility, and at the same time, can satisfy excellent bending 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 bending 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 solve the above problems, the present specification provides a polyimide-based resin including a polyimide repeating unit represented by the following chemical formula 1 and a polyimide repeating unit represented by the following chemical formula 2, wherein the residual stress with an inorganic material substrate at a thickness of 10 μm is 55 MPa or less, and the retardation in the thickness direction at a thickness of 10 μm is R th A polyimide-based resin film having a value of 100 nm or less is provided. [Chemical formula 1] [ka] In the above Chemical Formula 1, X1 is an aromatic tetravalent functional group, and Y1 is an aromatic divalent functional group having 6 to 10 carbon atoms; [Chemical formula 2] [ka] In the above formula 2, X2 is an aromatic tetravalent functional group, and Y2 is an aromatic divalent functional group containing multiple rings.

[0012] The present specification further relates to a polyimide-based resin including a polyimide repeating unit represented by the following chemical formula 1 and a polyimide repeating unit represented by the following chemical formula 2, and the polyimide-based resin has a bow value of 25 μm or less at a thickness of 5 μm and a retardation R th A polyimide-based resin film having a value of 100 nm or less is provided. [Chemical formula 1] [ka] In the above Chemical Formula 1, X1 is an aromatic tetravalent functional group, and Y1 is an aromatic divalent functional group having 6 to 10 carbon atoms; [Chemical formula 2] [ka] In the above formula 2, X2 is an aromatic tetravalent functional group, and Y2 is an aromatic divalent functional group containing multiple rings.

[0013] The present specification further provides a substrate for a display device, comprising the polyimide-based resin film.

[0014] The present specification further provides an optical device including the polyimide-based resin film.

[0015] 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.

[0016] In this specification, unless expressly stated otherwise, the terminology used is for the purpose of referring to particular embodiments only and is not intended to be limiting of the invention.

[0017] As used herein, the singular forms "a," "an," and "the" include the plural forms unless the context clearly indicates to the contrary.

[0018] As used herein, the meaning of "comprising" is to specify certain properties, regions, integers, steps, operations, elements, and / or components, and does not exclude the presence or addition of other specific properties, regions, integers, steps, operations, elements, components, and / or groups.

[0019] 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.

[0020] In this specification, the term "(co)polymer" refers to both a polymer and a 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.

[0021] In this specification, examples of the substituents are described below, but are not limited thereto.

[0022] 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 from each other.

[0023] 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, 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 that the group is 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. In other words, the biphenyl group may be an aryl group, and may be interpreted as a substituent having two phenyl groups connected.

[0024] In this specification, [ka] ,or [ka] means a bond that is connected to another substituent, and a direct bond means that there is no other atom present in the moiety represented by L.

[0025] In this specification, aromaticity is a property that satisfies the Huckels Rule, and a compound can be defined as being aromatic if 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, lone pairs, etc. 2) 4n + 2 electrons must form a planar isomer and must form a ring structure. 3) All atoms of the ring must be able to participate in conjugation.

[0026] In this specification, a multivalent functional group refers to a residue in which multiple hydrogen atoms bonded to an arbitrary compound are removed, such as a divalent functional group, a trivalent functional group, or a tetravalent functional group. For example, a tetravalent functional group derived from cyclobutane means a residue in which four of the hydrogen atoms bonded to cyclobutane are removed.

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

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

[0029] In this specification, the weight average molecular weight means the weight average molecular weight in terms of polystyrene measured by the GPC method. In the process of measuring the weight average molecular weight in terms of polystyrene measured by the GPC method, a commonly known analyzer, a detector such as a refractive index detector, and an analytical column can be used, and commonly applied temperature conditions, solvents, and flow rates can be applied. Specific examples of the measurement conditions include a Polymer Laboratories PLgel MIX-B 300 mm long column, a Waters PL-GPC220 instrument, an evaluation temperature of 160° C., 1,2,4-trichlorobenzene as a solvent, a flow rate of 1 mL / min, a sample prepared to a concentration of 10 mg / 10 mL, and then supplied in an amount of 200 μL, and a calibration curve formed using a polystyrene standard can be used to determine the Mw value. Nine types of polystyrene standards with molecular weights of 2,000 / 10,000 / 30,000 / 70,000 / 200,000 / 700,000 / 2,000,000 / 4,000,000 / 10,000,000 were used.

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

[0031] 1. Polyimide resin film According to one embodiment of the present invention, the polyimide-based resin includes a polyimide repeating unit represented by the following formula 1 and a polyimide repeating unit represented by the following formula 2, and the residual stress with an inorganic material substrate at a thickness of 10 μm is 55 MPa or less, and the retardation R in the thickness direction at a thickness of 10 μm is th It is possible to provide a polyimide-based resin film having a value of 100 nm or less. [Chemical formula 1] [ka] In the above Chemical Formula 1, X1 is an aromatic tetravalent functional group, and Y1 is an aromatic divalent functional group having 6 to 10 carbon atoms; [Chemical formula 2] [ka] In the above formula 2, X2 is an aromatic tetravalent functional group, and Y2 is an aromatic divalent functional group containing multiple rings.

[0032] The present inventors have confirmed through experiments that, when the polyimide repeating unit represented by Chemical Formula 1 and the polyimide repeating unit represented by Chemical Formula 2 are simultaneously contained as in the polyimide resin film of the embodiment, the polyimide resin film cured at a high temperature of 400° C. or more can minimize bending, have high flatness and dimensional stability, and can solve defects due to peeling during panel processing. In addition, the polyimide resin film has high optical isotropy and low retardation, thereby ensuring the diagonal viewing angle of a display to which the polyimide resin film is applied and preventing deterioration of visibility due to light distortion. Thus, the present invention has been completed.

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

[0034] In addition, the polyimide resin includes a reaction product obtained by imidization of aromatic tetracarboxylic dianhydride and aromatic diamine having 6 to 10 carbon atoms, as represented by Chemical Formula 1, and it is believed that the aromatic diamine having 6 to 10 carbon atoms having a curved asymmetric structure reduces the refractive index difference between the plane direction and the thickness direction, thereby achieving a low retardation.

[0035] More specifically, in the case of polyimide having a planar linear main chain structure, polyimides are packed side by side and laminated, so that the refractive index in the thickness direction is low. However, since an asymmetric structure is introduced into the polyimide chain structure in a curved form, the arrangement can be maintained in the thickness direction, and a low phase difference can be realized by reducing the refractive index difference between the plane direction and the thickness direction.

[0036] 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 the device can be reduced, and the bottom emission efficiency can be effectively increased.

[0037] Specifically, the polyimide resin film may contain a polyimide resin. The polyimide resin means that it contains both polyimide and its precursor polymers, polyamic acid and polyamic acid ester. In other words, the polyimide polymer may contain one or more selected from the group consisting of a polyamic acid repeating unit, a polyamic acid ester repeating unit, and a polyimide repeating unit. In other words, the polyimide polymer may contain one type of polyamic acid repeating unit, one type of polyamic acid ester repeating unit, one type of polyimide repeating unit, or a copolymer in which two or more of these repeating units are mixed.

[0038] 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.

[0039] 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.

[0040] 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, and Y1 is an aromatic divalent functional group having 6 to 10 carbon atoms.

[0041] In the above Chemical Formula 1, X1 is an aromatic tetravalent functional group, and the above X1 is a functional group derived from a tetracarboxylic dianhydride compound used in the synthesis of a polyimide-based resin.

[0042] The X1 may be one of tetravalent functional groups represented by the following Chemical Formula 5. [Chemical formula 5] [ka]

[0043] In the above Chemical Formula 5, R1 to R6 are each independently hydrogen or an alkyl group having 1 to 6 carbon atoms, and L3 is a single bond, -O-, -CO-, -COO-, -S-, -SO-, -SO2-, -CR7R8-, -(CH2) t -, -O(CH2) t O-, -COO(CH2) t any one selected from the group consisting of OCO-, -CONH-, phenylene, or a combination thereof, wherein R7 and R8 are each independently one of hydrogen, an alkyl group having 1 to 10 carbon atoms, or a haloalkyl group having 1 to 10 carbon atoms, and t is an integer from 1 to 10.

[0044] A specific example of the functional group represented by the above chemical formula 5 is the functional group represented by the following chemical formula 5-1, which is derived from 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA). [Chemical formula 5-1] [ka]

[0045] When the functional group represented by Formula 5-1 is included as the aromatic tetravalent functional group, it has a more linear structure than functional groups derived from other bulky anhydrides (e.g., BPAF, 6FDA), and therefore has a lower coefficient of thermal expansion (CTE) and suppresses bending during high-temperature curing at 400°C or higher, thereby providing a suitable flatness for laminating devices on the film and enabling subsequent processes.

[0046] Meanwhile, in 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 the synthesis of a polyimide.

[0047] 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]

[0048] A specific example of the functional group represented by the following chemical formula 3 is the functional group represented by the following chemical formula 3-1 derived from m-phenylenediamine (1,3-phenylenediamine, m-PDA (registered trademark)). [Chemical formula 3-1] [ka]

[0049] When the functional group represented by Chemical Formula 3-1 is included in Y1, an asymmetric structure is introduced into the polyimide chain structure in a bent form, thereby maintaining an arrangement 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.

[0050] In contrast, when a functional group derived from p-phenylenediamine (1,4-phenylenediamine, p-PDA), which does not have a curved asymmetric structure, is contained in Y1, it is difficult to realize the curved asymmetric structure. Since the polyimide is polymerized in a linear plane direction and the polymer grows only in the in-plane direction, the polymers are well packed together, which reduces the refractive index in the thickness direction and increases the difference in refractive index between the in-plane direction and the thickness direction.

[0051] Meanwhile, the polyimide-based resin may further include a polyimide repeating unit represented by the following Chemical Formula 2 in addition to the polyimide repeating unit represented by Chemical Formula 1. That is, the polyimide-based resin may include a polyimide repeating unit represented by Chemical Formula 1 and a polyimide repeating unit represented by Chemical Formula 2. [Chemical formula 2] [ka] In the above formula 2, X2 is an aromatic tetravalent functional group, and Y2 is an aromatic divalent functional group containing multiple rings. X2 is the same as X1 in Chemical Formula 1. In the above Chemical Formula 2, Y2 is an aromatic divalent functional group containing multiple rings, and Y2 is a functional group derived from a diamine compound used in the synthesis of a polyimide resin.

[0052] More specifically, the divalent functional group of Y2 may include a divalent functional group represented by the following Chemical Formula 4: [Chemical formula 4] [ka]

[0053] In Formula 4, Ar is a polycyclic aromatic divalent functional group. The polycyclic aromatic divalent functional group is a polycyclic aromatic hydrocarbon compound or a divalent functional group derived from a derivative compound thereof, and the derivative compound includes any compound into which one or more substituents have been introduced or a carbon atom has been replaced with a heteroatom.

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

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

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

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

[0058] In the above formula 4, the polycyclic aromatic divalent functional group may include a fluorenylene group. A specific example of the functional group represented by formula 4 is the functional group represented by formula 4-1 below, which is derived from 9,9'-bis(4-aminophenyl)fluorene (FDA). [Chemical formula 4-1] [ka]

[0059] When the aromatic divalent functional group having multiple rings is included in Y2, a symmetric structure having increased replacement hindrance due to the multiple rings is introduced into the polyimide chain structure, thereby alleviating deformation due to heat and improving heat resistance. A bulky structure having increased replacement hindrance in the thickness direction due to the multiple rings is introduced into the polyimide chain structure, thereby increasing the refractive index in the thickness direction and reducing the refractive index difference between the plane direction and the thickness direction, thereby realizing a low retardation, and intermolecular packing is suppressed to realize high transmittance.

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

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

[0062] A specific example of the aromatic tetracarboxylic dianhydride is 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA).

[0063] 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 explanation of the aromatic divalent functional group having 6 to 10 carbon atoms is the same as that described above. A specific example of the aromatic diamine having 6 to 10 carbon atoms is m-phenylenediamine (1,3-phenylenediamine, m-PDA).

[0064] The aromatic diamine containing multiple rings is a compound in which amino groups (-NH2) are introduced at both ends of the above-mentioned aromatic divalent functional group, and the explanation of the aromatic divalent functional group is the same as that described above. A specific example of the aromatic diamine containing multiple rings is 9,9'-bis(4-aminophenyl)fluorene (FDA).

[0065] More specifically, the polyimide resin may be formed by reacting a terminal anhydride group (-OC-O-CO-) of the aromatic tetracarboxylic dianhydride with a terminal amino group (-NH2) of an aromatic diamine having 6 to 10 carbon atoms and an aromatic diamine containing multiple rings, to form a bond between a nitrogen atom of the amino group and a carbon atom of the anhydride group.

[0066] Meanwhile, 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 the functional group represented by Chemical Formula 3, and a second repeating unit containing a repeating unit represented by Chemical Formula 2, in which the diamine-derived repeating unit is the functional group represented by Chemical Formula 4. The first repeating unit and the second repeating unit may be randomly arranged in the polyimide-based polymer to form a random copolymer, or may form a block between the first repeating units and a block between the second repeating units to form a block copolymer.

[0067] The polyimide-based polymer including the repeating unit represented by Formula 1 and the repeating unit represented by Formula 2 can be prepared by reacting 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.

[0068] The molar ratio between the polyimide repeating unit represented by Chemical Formula 1 and the polyimide repeating unit represented by Chemical Formula 2 may be from 9:1 to 1:9, or from 9:1 to 2:1, or from 6:1 to 2:1, or from 6:1 to 3.5:1, or from 3.5:1 to 2:1, or from 1:2 to 1:9, or from 1:2 to 1:6, or from 1:3 to 1:5.

[0069] It has excellent bending properties and excellent optical properties such as colorless transparency, and has low retardation R in the thickness direction. th Due to its characteristics, optical isotropy is increased, and the diagonal viewing angle of the display to which the polyimide resin film is applied is secured, thereby preventing deterioration of visibility due to the distortion of light.

[0070] On the other hand, when the polyimide repeating unit represented by Formula 1 is contained in an excessively small amount and the molar ratio between the polyimide repeating unit represented by Formula 1 and the polyimide repeating unit represented by Formula 2 is deviated from 1:9, the polyimide resin film cured at a high temperature of 400° C. or more is bent to a large extent, making it difficult to laminate a device on the film, and thus making subsequent processes impossible.

[0071] In addition, when the polyimide repeating unit represented by the formula 2 is contained in an excessively small amount and the molar ratio between the polyimide repeating unit represented by the formula 1 and the polyimide repeating unit represented by the formula 2 is out of 9:1, the retardation R thWhen the value increases, the visibility decreases due to the distortion of light caused by the increase in the phase difference, and the film haze increases, decreasing the transparency, resulting in poor optical properties.

[0072] Meanwhile, the polyimide-based resin film according to an embodiment may include a cured product of the polyimide-based resin cured at a temperature of 400° C. or more. The cured product means a material obtained by curing a resin composition containing the polyimide-based resin, and the curing process may be performed at a temperature of 400° C. or more, or from 400° C. to 500° C.

[0073] The polyimide repeating unit represented by Chemical Formula 1 and the polyimide repeating unit represented by Chemical Formula 2 account for 70 mol% or more, or 80 mol% or more, or 90 mol% or more, or 91 mol% or more, or 92 mol% or more, or 93 mol% or more, or 94 mol% or more, or 95 mol% or more, or 96 mol% or more, or 97 mol% or more, or 98 mol% or more, or 99 mol% or more, or 100 mol% or less of the total repeating units contained in the polyimide resin. Alternatively, it may be contained at 70 mol% or more and 100 mol% or less, 80 mol% or more and 100 mol% or less, 91 mol% or more and 100 mol% or less, 92 mol% or more and 100 mol% or less, 93 mol% or more and 100 mol% or less, 94 mol% or more and 100 mol% or less, 95 mol% or more and 100 mol% or less, 96 mol% or more and 100 mol% or less, 97 mol% or more and 100 mol% or less, 98 mol% or more and 100 mol% or less, or 99 mol% or more and 100 mol% or less.

[0074] That is, the polyimide-based resin may be composed only of the polyimide repeating unit represented by Chemical Formula 1 and the polyimide repeating unit represented by Chemical Formula 2, or may be composed mostly of the polyimide repeating unit represented by Chemical Formula 1 and the polyimide repeating unit represented by Chemical Formula 2.

[0075] 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.

[0076] 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 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 use as a display cover substrate.

[0077] More specifically, examples of methods for synthesizing the polyimide-based resin film are 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.

[0078] 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 may be, for example, a method such as screen printing, offset printing, flexographic printing, or inkjet printing.

[0079] 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 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 obtain a solution.

[0080] 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, gamma-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.

[0081] The resin composition containing the polyimide 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% by weight to 25% by weight, or 5% by weight to 20% by weight, or 5% by weight to 15% by weight.

[0082] 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 conductivity, or increase the density. Examples of such additives include surfactants, silane compounds, dielectrics, or crosslinking compounds.

[0083] The step 2 is a step of drying a coating film formed by applying the resin composition containing the polyimide resin to a substrate.

[0084] The step of drying the coating film may be carried out by a heating means such as a hot plate, a hot air circulating oven, or an infrared oven, and may be carried out at a temperature of 50°C or more and 150°C or less, or 50°C or more and 100°C or less.

[0085] Step 3 is a step of heat-treating the dried coating film to harden it, which may be performed by a heating means such as a hot plate, a hot air circulating oven, or an infrared oven at a temperature of 200°C or higher, or from 200°C to 300°C, or from 400°C to 500°C.

[0086] 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 increases or decreases by a certain value, the physical properties measured on the polyimide-based resin film may also change by a certain value.

[0087] Meanwhile, the polyimide-based resin film of one embodiment may have a residual stress with an inorganic material substrate at a thickness of 10 μm of 55 MPa or less, or 50 MPa or less, or 48 MPa or less, or 40 MPa or less, or 31 MPa or less, or 1 MPa or more, or 1 MPa to 55 MPa, or 1 MPa to 50 MPa, or 1 MPa to 48 MPa, or 1 MPa to 40 MPa, or 1 MPa to 31 MPa, or 10 MPa to 48 MPa, or 20 MPa to 48 MPa, or 30 MPa to 48 MPa, or 30.4 MPa to 48 MPa, or 30.4 MPa to 40 MPa, or 30.4 MPa to 32 MPa, or 33 MPa to 40 MPa, or 41 MPa to 48 MPa. As a result of the low residual stress with the inorganic material substrate, the polyimide-based resin film of one embodiment may reduce the residual stress, thereby solving defects due to peeling during panel processing.

[0088] The method and equipment for measuring the residual stress are not particularly limited, and various methods used in measuring the residual stress in the past can be applied without limitation. For example, the residual stress of a polyimide resin film can be measured using a residual stress measuring device. In addition, an example of the inorganic material substrate is a wafer substrate.

[0089] The residual stress can be measured from a polyimide-based resin film sample having a thickness of 10±1 μm. When the thickness of the polyimide-based resin film increases or decreases by a certain value, the physical properties measured on the polyimide-based resin film may also change by a certain value.

[0090] If the residual stress between the polyimide resin film and the inorganic material substrate at a thickness of 10 μm is excessively increased to exceed 55 MPa, the polyimide resin film cured at a high temperature of 400° C. or higher may bend, resulting in defects due to peeling during panel processing.

[0091] Meanwhile, the polyimide-based resin film of the embodiment may have a retardation value in the thickness direction at a thickness of 10 μm of 100 nm or less, or 90 nm or less, or 80 nm or less, or 73 nm or less, or 1 nm or more, or 1 nm to 100 nm, or 1 nm to 90 nm, or 1 nm to 80 nm, or 1 nm to 73 nm, or 73 nm to 89 nm, or 73 nm to 79 nm, or 80 nm to 89 nm, or 80 nm to 85 nm, or 86 nm to 89 nm. th Due to its characteristics, optical isotropy is increased, and the diagonal viewing angle of the display to which the polyimide resin film is applied can be secured, thereby realizing excellent visibility.

[0092] It is believed that such low retardation is achieved by using m-PDA (m-Phenylenediamine), a diamine with an asymmetric structure, as a monomer used in the production of polyimide resin films, as described below, to reduce the difference in refractive index between the plane direction and the thickness direction.

[0093] More specifically, in the case of polyimide having a planar linear main chain structure, the polyimide molecules are packed side by side and laminated, 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 may increase.

[0094] The retardation in the thickness direction may be measured at a wavelength of 532 nm. Examples of a measuring method and an apparatus are not specifically limited, and various methods used in measuring the retardation in the thickness direction may be applied without limitation.

[0095] 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 on the polyimide-based resin film may also change by a certain value.

[0096] Specifically, the retardation R in the thickness direction th can be calculated using the following mathematical formula 1. [Mathematical formula 1] R th (nm)=|[(n x +n y ) / 2]-n z |×d

[0097] In the above mathematical formula 1, n x is the largest in-plane refractive index of the polyimide resin film measured with light having a wavelength of 532 nm; n y is the in-plane refractive index of a polyimide resin film measured with light of 532 nm wavelength. x is the refractive index perpendicular to n z is the refractive index in the thickness direction of the polyimide resin film measured with light having a wavelength of 532 nm; and d is the thickness of the polyimide resin film.

[0098] That is, the retardation R in the thickness direction th is the refractive index in the thickness direction, n z and the average planar refractive index value [(n x +n y ) / 2] multiplied by the film thickness, the refractive index value in the thickness direction, n z and the average planar refractive index value [(n x +n y ) / 2], the lower the value.

[0099] The polyimide-based resin film satisfies a retardation value in the thickness direction of 100 nm or less at a thickness of 10 μm, and thus a refractive index value in the thickness direction n z and the average planar refractive index value [(nx +n y ) / 2] is reduced, making it possible to realize excellent visual sensation.

[0100] If the retardation value in the thickness direction of the polyimide resin film at a thickness of 10 μm is excessively increased, such as exceeding 100 nm, distortion occurs during light transmission in a structure in which polyimide is present on the upper side when implementing a transparent display, and there is a technical limit in that even a compensation film that technically compensates up to 45 nm cannot correct the refraction of transmitted light.

[0101] Meanwhile, the polyimide resin film may have a haze value at a thickness of 10 μm of 10% or less, 1% or less, 0.1% or more, 0.1% to 10%, 0.1% to 1%, 0.26% to 0.57%, 0.26% to 0.4%, 0.41% to 0.54%, or 0.55% to 0.57%. The haze may be measured from a sample of the polyimide resin film having a thickness of 10±1 μm. When the thickness of the polyimide resin film increases or decreases by a certain value, the physical properties measured on the polyimide resin film may also change by a certain value.

[0102] The polyimide resin film may have a bow value at a thickness of 10 μm of 50 μm or less, or 48 μm or less, or 35 μm or less, or 31 μm or less, or 1 μm or more, or 1 μm to 50 μm, or 1 μm to 48 μm, or 1 μm to 35 μm, or 1 μm to 31 μm, or 10 μm to 48 μm, or 20 μm to 48 μm, or 30.11 μm to 47.6 μm, or 30.11 μm to 40 μm, or 30.11 μm to 32 μm, or 33 μm to 40 μm, or 41 μm to 47.6 μm. The bow may be called a bend or bow, and is a type of surface flatness characteristic of a material, and a specific description thereof, for example, a specific measurement method, may be applied to various methods widely known in the field of semiconductor wafer substrate manufacturing without limitation.

[0103] Specifically, the Bow 3 can be defined as the distance on the central axis 4 between the thickness central plane 1 and the reference plane (Best fit plane of thickness central plane) 2, as shown in FIG. 1 below.

[0104] The thickness center plane 1 refers to a plane connecting points that are half the thickness t / 2 of the measurement object, as shown in FIG. 1 below.

[0105] The reference plane 2 means a cross section along a straight line connecting the center points of the thickness of both ends of the measurement object as shown in FIG. 1 below.

[0106] The central axis 4 means a straight line passing through the center of gravity of the object to be measured and perpendicular to the ground plane, as shown in FIG. 1 below.

[0107] As an example of a method for measuring the Bow 3, a laser stress analyzer may be used. The stress analyzer measures the intensity of light reflected from the back surface of the measurement sample and can automatically calculate and obtain the Bow value through a method of mathematically analyzing the measured intensity.

[0108] The bow may be measured on a polyimide-based resin film sample of the embodiment having a thickness of 10±1 μm.

[0109] The polyimide-based resin film sample used in the measurement of the bow may include a pure polyimide-based resin film; or a laminate including a substrate film and a polyimide-based resin film coated on the substrate film; Examples of the substrate film are not particularly limited, and a glass substrate, a wafer substrate, or a mixture thereof may be used without limitation.

[0110] When the polyimide-based resin film sample used for measuring the bow is made of only a pure polyimide-based resin film, the bow can be automatically measured based on the results of analyzing the polyimide-based resin film sample with a laser stress analyzer. For example, in a laminate including the base film and the polyimide-based resin film coated on the base film, a pure polyimide-based resin film can be obtained through a process of peeling off the base film.

[0111] If the bow value of the polyimide resin film at a thickness of 10 μm is excessively increased, such as exceeding 50 μm, the polyimide resin film cured at a high temperature of 400° C. or more may bend, resulting in defects due to peeling during panel processing.

[0112] In addition, the polyimide resin film may have a yellowness index at a thickness of 10 μm of 25 or less, or 22 or less, or 20 or less, or 15 or less, or 0.1 or more, or 0.1 to 25, or 0.1 to 22, or 0.1 to 20, or 0.1 to 15, or 14.3 to 22.4, or 14.3 to 19, or 20 to 22.4, or 20 to 21.5, or 21.6 to 22.4. If the yellowness index at a thickness of 10 μm of the polyimide resin film is excessively increased, such as exceeding 25, there is a limitation in that the degree of yellow discoloration of the polyimide resin film increases, making it difficult to manufacture a colorless and transparent film.

[0113] The method and equipment for measuring the yellowness index of 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 (Gretagmacbeth's Color-Eye 7000A).

[0114] The yellowness index 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 on the polyimide-based resin film may also change by a certain value.

[0115] Meanwhile, the polyimide-based resin film of the embodiment may have a thickness retardation value of 100 nm or less, 90 nm or less, 80 nm or less, 70 nm or less, 68 nm or less, 65 nm or less, 1 nm or more, 1 nm to 100 nm, 1 nm to 90 nm, 1 nm to 80 nm, 1 nm to 70 nm, 1 nm to 68 nm, 1 nm to 65 nm, 65 nm to 79 nm, 65 nm to 69 nm, 70 nm to 79 nm, 70 nm to 74 nm, or 75 nm to 79 nm. th The specific details are the same as those described above, except that the polyimide-based resin film sample of the embodiment having a thickness of 5±1 μm was measured.

[0116] In addition, the polyimide-based resin film of the embodiment may have a residual stress with an inorganic material substrate at a thickness of 5 μm of 52 MPa or less, or 50 MPa or less, or 45 MPa or less, or 43 MPa or less, or 42 MPa or less, or 1 MPa or more, or 1 MPa to 52 MPa, or 1 MPa to 50 MPa, or 1 MPa to 45 MPa, or 1 MPa to 43 MPa, or 1 MPa to 42 MPa, or 41.7 MPa to 48.9 MPa, or 41.7 MPa to 44 MPa, or 41.7 MPa to 42 MPa, or 43 MPa to 44 MPa, or 45 MPa to 48.9 MPa. The specific details of the residual stress with an inorganic material substrate are the same as those described above, except that the polyimide-based resin film sample of the embodiment having a thickness of 5±1 μm was measured.

[0117] In addition, the polyimide-based resin film of the embodiment may have a bow value at a thickness of 5 μm of 25 μm or less, or 24.5 μm or less, or 24 μm or less, or 23 μm or less, or 1 μm or more, or 1 μm to 25 μm, or 1 μm to 24.5 μm, or 1 μm to 24 μm, or 1 μm to 23 μm, or 22.49 μm to 24.7 μm, or 22.49 μm to 24.2 μm, or 22.49 μm to 23.2 μm, or 23.3 μm to 24.2 μm, or 24.3 μm to 24.7 μm. The specific details of the bow are the same as those described above, except that the polyimide-based resin film sample of the embodiment having a thickness of 5±1 μm was measured.

[0118] In addition, the polyimide-based resin film may have a yellowness index at a thickness of 5 μm of 15 or less, or 13.9 or less, or 13 or less, or 10 or less, or 9 or less, or 0.1 or more, or 0.1 to 15, or 0.1 to 13.9, or 0.1 to 13, or 0.1 to 10, or 0.1 to 9, or 8.4 to 10.8, or 8.4 to 9, or 9.1 to 10.8, or 9.1 to 10, or 10.1 to 10.8. The specific details of the yellowness index are the same as those described above, except that the yellowness index was measured on a polyimide-based resin film sample of the embodiment having a thickness of 5±1 μm.

[0119] Meanwhile, the polyimide-based resin film may have a bow value at a thickness of 2 μm of less than 12 μm, 11.9 μm or less, 11.6 μm or less, 11.5 μm or less, 11.2 μm or less, 1 μm or more, 1 μm or more and less than 12 μm, 1 μm to 11.9 μm, 1 μm to 11.6 μm, 1 μm to 11.5 μm, 1 μm to 11.2 μm, 11.2 μm to 11.85 μm, 11.2 μm to 11.6 μm, 11.2 μm to 11.3 μm, 11.4 μm to 11.6 μm, or 11.7 μm to 11.85 μm. The specific details of the bow are the same as those described above, except that the polyimide-based resin film sample of the embodiment having a thickness of 2±1 μm was measured.

[0120] In addition, the polyimide-based resin film of the embodiment may have a thickness retardation value of 40 nm or less, 30 nm or less, 28 nm or less, 25 nm or less, 20 nm or less, 1 nm or more, 1 nm to 40 nm, 1 nm to 30 nm, 1 nm to 28 nm, 1 nm to 25 nm, 1 nm to 20 nm, 20 nm to 29 nm, 20 nm to 24 nm, 24 nm to 29 nm, 24 nm to 28 nm, or 28 nm to 29 nm. th The specific details are the same as those described above, except that the polyimide-based resin film sample of the embodiment having a thickness of 2±1 μm was measured.

[0121] In addition, the polyimide-based resin film of the embodiment may have a residual stress with an inorganic material substrate at a thickness of 2 μm of 50 MPa or less, or 45 MPa or less, or 42 MPa or less, or 1 MPa or more, or 1 MPa to 50 MPa, or 1 MPa to 45 MPa, or 1 MPa to 42 MPa, or 41.3 MPa to 48.6 MPa, or 41.3 MPa to 45 MPa, or 41.3 MPa to 43 MPa, or 43 MPa to 45 MPa, or 46 MPa to 48.6 MPa. The specific details of the residual stress with an inorganic material substrate are the same as those described above, except that the measurement was performed on a polyimide-based resin film sample of the embodiment having a thickness of 2±1 μm.

[0122] In addition, the polyimide-based resin film of the embodiment may have a yellowness index at a thickness of 2 μm of 10 or less, or 7 or less, or 6.5 or less, or 5 or less, or 0.1 or more, or 0.1 to 10, or 0.1 to 7, or 0.1 to 6.5, or 0.1 to 5, or 3.3 to 4.48, or 3.3 to 3.9, or 4 to 4.48, or 4 to 4.2, or 4.2 to 4.48. The specific details of the yellowness index are the same as those described above, except that the yellowness index was measured on a polyimide-based resin film sample of the embodiment having a thickness of 2±1 μm.

[0123] Meanwhile, according to another embodiment of the present invention, the present invention provides a polyimide-based resin including a polyimide repeating unit represented by the following formula 1 and a polyimide repeating unit represented by the following formula 2, and the bow value at a thickness of 5 μm is 25 μm or less, and the retardation R in the thickness direction at a thickness of 5 μm is 1. th It is possible to provide a polyimide-based resin film having a value of 100 nm or less. [Chemical formula 1] [ka] In the above Chemical Formula 1, X1 is an aromatic tetravalent functional group, and Y1 is an aromatic divalent functional group having 6 to 10 carbon atoms; [Chemical formula 2] [ka] In the above formula 2, X2 is an aromatic tetravalent functional group, and Y2 is an aromatic divalent functional group containing multiple rings.

[0124] The polyimide repeating unit represented by Formula 1, the polyimide repeating unit represented by Formula 2, and the polyimide-based resin may include any of the contents described above in the embodiment.

[0125] The molar ratio between the polyimide repeating unit represented by Chemical Formula 1 and the polyimide repeating unit represented by Chemical Formula 2 may be from 9:1 to 1:9, or from 9:1 to 2:1, or from 6:1 to 2:1, or from 6:1 to 3.5:1, or from 3.5:1 to 2:1, or from 1:2 to 1:9, or from 1:2 to 1:6, or from 1:3 to 1:5.

[0126] Meanwhile, the polyimide-based resin film of the other embodiment may have a thickness retardation value of 100 nm or less, 90 nm or less, 80 nm or less, 70 nm or less, 68 nm or less, 65 nm or less, 1 nm or more, 1 nm to 100 nm, 1 nm to 90 nm, 1 nm to 80 nm, 1 nm to 70 nm, 1 nm to 68 nm, 1 nm to 65 nm, 65 nm to 79 nm, 65 nm to 69 nm, 70 nm to 79 nm, 70 nm to 74 nm, or 75 nm to 79 nm. th The specific details are the same as those described above in the first embodiment, except that the polyimide-based resin film sample of the second embodiment having a thickness of 5±1 μm was measured.

[0127] In addition, the polyimide-based resin film of the other embodiment may have a residual stress with an inorganic material substrate at a thickness of 5 μm of 52 MPa or less, or 50 MPa or less, or 45 MPa or less, or 43 MPa or less, or 42 MPa or less, or 1 MPa or more, or 1 MPa to 52 MPa, or 1 MPa to 50 MPa, or 1 MPa to 45 MPa, or 1 MPa to 43 MPa, or 1 MPa to 42 MPa, or 41.7 MPa to 48.9 MPa, or 41.7 MPa to 44 MPa, or 41.7 MPa to 42 MPa, or 43 MPa to 44 MPa, or 45 MPa to 48.9 MPa. The specific details of the residual stress with an inorganic material substrate are the same as those described above in the first embodiment, except that the measurement was performed on a polyimide-based resin film sample of the other embodiment having a thickness of 5±1 μm.

[0128] In addition, the polyimide-based resin film of the other embodiment may have a bow value at a thickness of 5 μm of 25 μm or less, or 24.5 μm or less, or 24 μm or less, or 23 μm or less, or 1 μm or more, or 1 μm to 25 μm, or 1 μm to 24.5 μm, or 1 μm to 24 μm, or 1 μm to 23 μm, or 22.49 μm to 24.7 μm, or 22.49 μm to 24.2 μm, or 22.49 μm to 23.2 μm, or 23.3 μm to 24.2 μm, or 24.3 μm to 24.7 μm. The specific details of the bow are the same as those described above in the first embodiment, except that the polyimide-based resin film sample of the other embodiment having a thickness of 5±1 μm was measured.

[0129] In addition, the polyimide-based resin film of the other embodiment may have a yellowness index at a thickness of 5 μm of 15 or less, or 13.9 or less, or 13 or less, or 10 or less, or 9 or less, or 0.1 or more, or 0.1 to 15, or 0.1 to 13.9, or 0.1 to 13, or 0.1 to 10, or 0.1 to 9, or 8.4 to 10.8, or 8.4 to 9, or 9.1 to 10.8, or 9.1 to 10, or 10.1 to 10.8. The specific details for the yellowness index are the same as those described above in the first embodiment, except that the yellowness index was measured on a polyimide-based resin film sample of the other embodiment having a thickness of 5±1 μm.

[0130] Meanwhile, the polyimide-based resin film of the other embodiment may have a bow value at a thickness of 2 μm of less than 12 μm, 11.9 μm or less, or 11.6 μm or less, or 11.5 μm or less, or 11.2 μm or less, or 1 μm or more, or 1 μm or more and less than 12 μm, or 1 μm to 11.9 μm, or 1 μm to 11.6 μm, or 1 μm to 11.5 μm, or 1 μm to 11.2 μm, or 11.2 μm to 11.85 μm, or 11.2 μm to 11.6 μm, or 11.2 μm to 11.3 μm, or 11.4 μm to 11.6 μm, or 11.7 μm to 11.85 μm. The specific details regarding the bow are the same as those described above in the first embodiment, except that the measurement was performed on a polyimide-based resin film sample of the second embodiment having a thickness of 2±1 μm.

[0131] In addition, the polyimide-based resin film of the other embodiment may have a thickness retardation value of 40 nm or less, 30 nm or less, 28 nm or less, 25 nm or less, 20 nm or less, 1 nm or more, 1 nm to 40 nm, 1 nm to 30 nm, 1 nm to 28 nm, 1 nm to 25 nm, 1 nm to 20 nm, 20 nm to 29 nm, 20 nm to 24 nm, 24 nm to 29 nm, 24 nm to 28 nm, or 28 nm to 29 nm. thThe specific details are the same as those described above in the first embodiment, except that the measurement was performed on a polyimide-based resin film sample of the second embodiment having a thickness of 2±1 μm.

[0132] In addition, the polyimide-based resin film of the other embodiment may have a residual stress with an inorganic material substrate at a thickness of 2 μm of 50 MPa or less, or 45 MPa or less, or 42 MPa or less, or 1 MPa or more, or 1 MPa to 50 MPa, or 1 MPa to 45 MPa, or 1 MPa to 42 MPa, or 41.3 MPa to 48.6 MPa, or 41.3 MPa to 45 MPa, or 41.3 MPa to 43 MPa, or 43 MPa to 45 MPa, or 46 MPa to 48.6 MPa. The specific details of the residual stress with an inorganic material substrate are the same as those described above in the first embodiment, except that the measurement was performed on a polyimide-based resin film sample of the other embodiment having a thickness of 2±1 μm.

[0133] In addition, the polyimide-based resin film of the other embodiment may have a yellowness index at a thickness of 2 μm of 10 or less, or 7 or less, or 6.5 or less, or 5 or less, or 0.1 or more, or 0.1 to 10, or 0.1 to 7, or 0.1 to 6.5, or 0.1 to 5, or 3.3 to 4.48, or 3.3 to 3.9, or 4 to 4.48, or 4 to 4.2, or 4.2 to 4.48. The specific details for the yellowness index are the same as those described above in the first embodiment, except that the yellowness index was measured on a polyimide-based resin film sample of the other embodiment having a thickness of 2±1 μm.

[0134] 2. Display device substrates Meanwhile, according to still another embodiment of the present invention, a substrate for a display device may be provided, the substrate including the polyimide-based resin film of the one embodiment or the other embodiment. The content related to the polyimide-based resin film may include any of the content described above in the one embodiment or the other 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, 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 of the above-mentioned embodiment or the other embodiments may be used in various applications 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.

[0138] 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-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 resin film and the cured layer, which can further improve the solvent resistance or moisture permeability and optical properties, and the silicon oxide layer may be produced by curing polysilazane.

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

[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, an optical device including the polyimide-based resin film of the one embodiment or the other embodiment may be provided. The content related to the polyimide-based resin film may include any of the content described above in the one embodiment or the other embodiment.

[0143] The optical device may include any of various devices that use 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 (LCD), an organic light emitting diode (OLED), a flexible display, a rollable display, or a foldable display.

[0144] 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.

[0145] The polyimide-based resin film of the above embodiment or the other embodiments may be used in various applications 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

[0146] The present invention relates to a polyimide resin film capable of realizing excellent bending properties and low retardation, and a display device substrate and an optical device using the same. [Brief description of the drawings]

[0147] [Figure 1] FIG. 1 shows cross-sectional views for measuring the bow of the polyimide-based resin films obtained in the examples and comparative examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0148] 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 the content of the present invention is not limited to the following examples.

[0149] <Examples and Comparative Examples: Production of Polyimide Precursor Composition and Polyimide Film> Examples 1-3 (1) Preparation of polyimide precursor composition After filling an organic solvent DEAc in a stirrer with a nitrogen stream, m-phenylenediamine (1,3-phenylenediamine, m-PDA) and 9,9'-bis(4-aminophenyl)fluorene (FDA) were added and dissolved at the same temperature while maintaining the temperature of the reactor at 25°C. 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added as an acid dianhydride to the solution containing m-phenylenediamine (1,3-phenylenediamine, m-PDA) and 9,9'-bis(4-aminophenyl)fluorene (FDA) at the same temperature and stirred for 24 hours to prepare a polyimide precursor composition. The molar ratios of m-PDA, FDA, and BPDA are the same as those shown in Table 1 below.

[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 placed in an oven and heated at a rate of 5°C / min, and cured at 80°C for 30 minutes, 250°C for 30 minutes, and 400°C for 30 minutes. After the curing process was completed, the glass substrate was immersed in water to separate the film formed on the glass substrate, and dried at 100°C in an oven to produce a polyimide film having a thickness of 10 μm (including an error of ±1 μm).

[0151] Comparative Examples 1 to 3 Polyimide precursor compositions and polyimide films were prepared in the same manner as in the above examples, except that the molar ratios of m-PDA, FDA, p-PDA (1,4-phenylenediamine), and BPDA were changed as shown in Table 1 below.

[0152] Comparative Example 4 (1) Preparation of polyimide precursor composition After filling the reactor with the organic solvent DEAc in a stirrer through which a nitrogen stream was flowing, 2,2'-bis(trifluoromethyl)benzidine (TFMB), m-phenylenediamine (m-PDA), and 9,9'-bis(4-aminophenyl)fluorene (FDA) were added and dissolved at 25°C while maintaining the temperature of the reactor at the same temperature. A polyimide precursor composition was prepared by adding 4,4'-(Hexafluoroisopropylidene)diphthalic anhydride (6FDA) as an acid dianhydride to a solution containing 2,2'-bis(trifluoromethyl)benzidine (TFMB), 1,3-phenylenediamine (m-PDA) and 9,9'-bis(4-aminophenyl)fluorene (FDA) at the same temperature and stirring for 24 hours. The molar ratio of 6FDA, TFMB, m-PDA and FDA was 100 / 70 / 20 / 10 (6FDA / TFMB / m-PDA / FDA).

[0153] (2) Production of polyimide film The polyimide precursor composition was spin-coated on a glass substrate. The glass substrate coated with the polyimide precursor composition was placed in an oven and heated at a rate of 5°C / min, and cured at 80°C for 30 minutes, 250°C for 30 minutes, and 400°C for 30 minutes. After the curing process was completed, the glass substrate was immersed in water to separate the film formed on the glass substrate, and dried at 100°C in an oven to produce a polyimide film having a thickness of 10 μm (including an error of ±1 μm).

[0154] Comparative Examples 5 to 6 Polyimide precursor compositions and polyimide films were prepared in the same manner as in the above examples, except that the molar ratios of m-PDA, FDA, and BPDA were changed as shown in Table 1 below.

[0155] <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 Table 1.

[0156] 1. Yellow index (YI) The yellowness index of the polyimide films prepared in the examples and comparative examples was measured using a color meter (Gretagmacbeth's Color-Eye 7000A).

[0157] 2. Haze The haze value of the polyimide film was measured using a Hazemeter (NDH-5000).

[0158] 3. Retardation in the thickness direction (R th ) The measurement device was an AxoScan manufactured by AXOMETRICS, and the refractive index values ​​for 532 nm light of the polyimide films produced in the examples and comparative examples were input. The retardation in the thickness direction and in the plane direction was then measured using light with a wavelength of 532 nm under conditions of temperature: 25°C and humidity: 40%. The retardation value in the thickness direction thus obtained (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.

[0159] Specifically, the retardation R in the thickness direction th was calculated using the following mathematical formula 1. [Mathematical formula 1] R th (nm)=|[(n x +n y ) / 2]-n z|×d (In the above mathematical formula 1, n x is the largest in-plane refractive index of the polyimide resin film measured with light having a wavelength of 532 nm; n y is the in-plane refractive index of a polyimide resin film measured with light of 532 nm wavelength. x is the refractive index perpendicular to n 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 film.

[0160] 4. Residual stress and bow The amount of bending of the wafer was measured in advance using a residual stress meter (FLX2320 by Tencor Corporation) for the polyimide precursor composition prepared in the examples and comparative examples. The composition was applied by a spin coater onto a 6-inch silicon wafer having a thickness of 525 μm (manufactured by Koyo Lindbergh Corporation), and a heat curing treatment was carried out in an oven at 250°C for 30 minutes and 400°C for 30 minutes under a nitrogen atmosphere, to produce a silicon wafer with a resin film attached after curing. The amount of bending of the silicon wafer with the resin film attached was measured by a residual stress meter, and the absolute value of the difference from the amount of bending of the wafer in advance was shown as a real bow value, and the residual stress generated between the silicon wafer and the resin film was measured by the residual stress meter.

[0161] The bow is defined as the distance on the central axis between the thickness central plane of the measurement sample and the reference plane (best fit plane of thickness central plane) as shown in FIG. 1 below, and the bow was measured at room temperature using a stress analyzer (TENCOR FLX-2320) for the sample.

[0162] [Table 1]

[0163] As shown in Table 1, the polyimide films obtained in Examples 1 to 3 had a thickness of 10 μm as a reference and a retardation R th The values ​​were found to be 73 nm to 89 nm, the haze was 0.26% to 0.57%, the YI was 14.3 to 22.4, the residual stress was 30.4 MPa to 48 MPa, and the bow was 30.11 μm to 47.6 μm.

[0164] In contrast, the polyimide film obtained in Comparative Example 1 had a thickness of 10 μm as the standard, and the retardation R th The value was 2222 nm, which was a sharp increase compared to the Examples, and a low retardation could not be realized. The polyimide film obtained in Comparative Example 2 had a thickness of 10 μm as a reference, and the retardation R th It was confirmed that the value was 144 nm, which was higher than that of the Example, and the haze was 15.31%, which was higher than that of the Example, and the transparency characteristics were reduced.

[0165] In addition, the polyimide film (thickness 10 μm) obtained in Comparative Example 3 had a residual stress of 55.7 MPa and a bow of 52.3 μm, which were increased compared to the Examples, and thus there was a problem in that a high level of flatness could not be achieved.

[0166] On the other hand, the polyimide films obtained in Examples 1 to 3 had a thickness of 5 μm as a reference, and the retardation R th The values ​​were found to be 65 nm to 79 nm, YI was 8.4 to 10.8, residual stress was 41.7 MPa to 48.9 MPa, and Bow was 22.49 μm to 24.7 μm.

[0167] In contrast, the polyimide film obtained in Comparative Example 1 had a thickness of 5 μm as the standard, and the retardation R th The value is 1200 nm, which is a sharp increase compared to the Examples. The polyimide film obtained in Comparative Example 2 has a thickness direction retardation R thThe value was 110 nm, which was higher than that of the Examples, and thus low retardation could not be realized. In addition, the polyimide film obtained in Comparative Example 2 had a bow of 26.8 μm based on a thickness of 5 μm, which was higher than that of the Examples, and thus high level flatness could not be realized.

[0168] In addition, the polyimide film (thickness 5 μm) obtained in Comparative Example 3 had a residual stress of 52.8 MPa and a bow of 32.41 μm, which were increased compared to the Examples, and thus there was a problem in that a high level of flatness could not be achieved.

[0169] On the other hand, the polyimide films obtained in Examples 1 to 3 had a thickness of 2 μm as the standard, and the retardation R th The values ​​were found to be 20 nm to 29 nm, YI was 3.3 to 4.48, residual stress was 41.3 MPa to 48.6 MPa, and bow was 11.2 μm to 11.85 μm.

[0170] In contrast, the polyimide film obtained in Comparative Example 1 had a thickness of 2 μm as the standard, and the retardation R th The value was 542 nm, which was a sharp increase compared to the Examples, and a low retardation could not be realized. The polyimide film obtained in Comparative Example 2 had a thickness of 2 μm as a reference, and the retardation in the thickness direction R th The value was 53 nm, which was higher than that of the embodiment, and the bow was 12.2 μm, which was higher than that of the embodiment, so that a high level of flatness could not be achieved.

[0171] In addition, the polyimide film (thickness 2 μm) obtained in Comparative Example 3 had a residual stress of 53.6 MPa and a bow of 14.99 μm, which were increased compared to the Examples, and thus there was a problem in that a high level of flatness could not be achieved.

[0172] In addition, the polyimide film obtained in Comparative Example 4 had a thickness of 10 μm as the standard, and the retardation R thThe value increased compared to the embodiment, so low phase difference could not be realized, and the residual stress and bow increased based on the thickness of 10 μm, 5 μm, and 2 μm compared to the embodiment, so high level of flatness could not be realized.

[0173] On the other hand, the polyimide film obtained in Comparative Example 5 had a retardation R in the thickness direction at a thickness of 10 μm, a thickness of 5 μm as a reference, and a thickness of 2 μm as a reference, similarly to Comparative Example 1. th The polyimide film obtained in Comparative Example 6 had problems in that the residual stress and bow increased compared to the Examples at thicknesses of 10 μm, 5 μm, and 2 μm, similar to Comparative Example 3, and thus a high level of flatness could not be achieved.

Claims

1. The polyimide-based resin includes a polyimide repeating unit represented by the following Chemical Formula 1 and a polyimide repeating unit represented by the following Chemical Formula 2: The residual stress with the inorganic material substrate at a thickness of 10 μm is 55 MPa or less, Phase difference R in the thickness direction at a thickness of 10 μm ｔｈ A polyimide-based resin film having a thickness of 100 nm or less. [Chemical formula 1] 【Chemistry 19】 In the above Chemical Formula 1, X １ is an aromatic tetravalent functional group, Y １ is an aromatic divalent functional group having 6 to 10 carbon atoms, [Chemical formula 2] 【Chemistry 20】 In the above Chemical Formula 2, X ２ is an aromatic tetravalent functional group, Y ２ is an aromatic divalent functional group containing multiple rings, The Y 1 includes a functional group represented by the following Formula 3. [Chemical formula 3] 【Chemistry 23】

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

3. The polyimide resin film according to claim 1 , wherein the polyimide resin film has a Bow value of 50 μm or less at a thickness of 10 μm.

4. The polyimide resin film according to claim 1 , wherein the polyimide resin film has a Bow value of 25 μm or less at a thickness of 5 μm.

5. The polyimide resin film has a thickness direction retardation R ｔｈ 2. The polyimide resin film according to claim 1, wherein the value is 100 nm or less.

6. 2. The polyimide resin film according to claim 1, wherein the polyimide resin film has a residual stress of 52 MPa or less when combined with an inorganic material substrate at a thickness of 5 μm.

7. The polyimide resin film according to claim 1 , wherein the polyimide resin film has a Bow value of less than 12 μm at a thickness of 2 μm.

8. 2. The polyimide resin film according to claim 1, wherein the polyimide resin film has a residual stress of 50 MPa or less when combined with an inorganic material substrate at a thickness of 2 μm.

9. The polyimide resin film has a thickness direction retardation R ｔｈ 2. The polyimide resin film according to claim 1, wherein the value is 40 nm or less.

10. The polyimide-based resin includes a polyimide repeating unit represented by the following Chemical Formula 1 and a polyimide repeating unit represented by the following Chemical Formula 2: The Bow value at a thickness of 5 μm is 25 μm or less, Retardation R in the thickness direction at a thickness of 5 μm ｔｈ A polyimide-based resin film having a thickness of 100 nm or less. [Chemical formula 1] 【Chemistry 21】 In the above Chemical Formula 1, X １ is an aromatic tetravalent functional group, Y １ is an aromatic divalent functional group having 6 to 10 carbon atoms, [Chemical formula 2] 【Chemical 22】 In the above Chemical Formula 2, X ２ is an aromatic tetravalent functional group, Y ２ is an aromatic divalent functional group containing multiple rings, The Y 1 includes a functional group represented by the following Formula 3. [Chemical formula 3] 【Chemistry 23】

11. The polyimide resin film according to claim 10, wherein the polyimide resin film has a residual stress of 52 MPa or less when combined with an inorganic material substrate at a thickness of 5 μm.

12. The polyimide resin film according to claim 10, wherein the polyimide resin film has a Bow value of less than 12 μm at a thickness of 2 μm.

13. The polyimide resin film according to claim 10, wherein the polyimide resin film has a residual stress of 50 MPa or less when combined with an inorganic material substrate at a thickness of 2 μm.

14. The polyimide resin film has a thickness direction retardation R ｔｈ The polyimide resin film according to claim 10, wherein the value is 40 nm or less.

15. The polyimide resin film according to any one of claims 1 to 14, wherein the functional group represented by Chemical Formula 3 includes a functional group represented by Chemical Formula 3-1 below. [Chemical formula 3-1] 【Chemistry 24】 。

16. The Y ２ The polyimide resin film according to claim 1 , wherein the polyimide resin film comprises a divalent functional group represented by the following chemical formula 4: [Chemical formula 4] 【Chemistry 25】 In Formula 4, Ar is a polycyclic aromatic divalent functional group.

17. The polyimide resin film according to claim 16, wherein the divalent functional group represented by the chemical formula 4 includes a functional group represented by the following chemical formula 4-1: [Chemical formula 4-1] 【Chemistry 26】 。

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

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

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