Substrate for display device or flexible display device and display device or flexible display device using the same

Abstract

The present disclosure relates to a substrate for a display device or a flexible display device achieving low dielectric characteristics and excellent heat resistance, and a display device or a flexible display device using the same.

Description

Technical Field

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of Korean Patent Application No. 10-2020-0155897 filed in the Korean Intellectual Property Office on November 19, 2020, and Korean Patent Application No. 10-2021-0148107 filed in the Korean Intellectual Property Office on November 1, 2021, the disclosures of which are incorporated herein by reference in their entirety.

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

[0004] The display device market is changing rapidly based on flat panel displays (FPD) that are easy to manufacture in large areas and can reduce thickness and weight. Such flat panel displays include liquid crystal displays (LCD), organic light emitting displays (OLED) or electrophoretic displays (EPD).

[0005] A rigid type display is manufactured using a glass substrate as a substrate, and a flexible type display is manufactured using a plastic substrate as a substrate.

[0006] However, when the plastic substrate is applied to a flexible display, problems such as restoration afterimages occur. In addition, the plastic substrate has problems in that heat resistance, thermal conductivity, and electrical insulation properties are inferior to those of a glass substrate.

[0007] However, research is actively being conducted to apply plastic substrates, which have advantages of being lightweight, flexible, and capable of being manufactured by a continuous process, to mobile phones, notebook computers, TVs, and the like, instead of glass substrates.

[0008] Polyimide resins are easy to synthesize, can be manufactured into thin films, and have the advantage of being applicable to high-temperature processes. In line with the trend toward lightweight and precision-oriented electronic devices, polyimide resins are often applied to semiconductor materials as integrated materials. In particular, much research is being conducted to apply polyimide resins to flexible plastic display panels that require lightweight and flexible properties. Summary of the invention

[0009] Technical issues

[0010] An object of the present disclosure is to provide a substrate for a display device or a flexible display device that achieves excellent heat resistance and high resistance characteristics without causing film deformation even during a high temperature process.

[0011] Another object of the present disclosure is to provide a display device or a flexible display device using the substrate for a display device or a flexible display device.

[0012] Technical Solution

[0013] To achieve the above objectives, according to one aspect of the present disclosure, a substrate for a display device or a flexible display device is provided, comprising: a first polyimide resin layer having a Td 1% of 570°C or higher and a yellowness index of 25 or higher and 60 or lower; a second polyimide resin layer having a yellowness index less than 25; a first inorganic material layer, the first inorganic material layer being positioned between the first polyimide resin layer and the second polyimide resin layer and having a thickness of 100 nm or higher and 700 nm or lower; and a second inorganic material layer, the second inorganic material layer being formed on the second polyimide resin layer and having a thickness of 100 nm or higher and 500 nm or lower, wherein the yellowness index of each of the first polyimide resin layer and the second polyimide resin layer is measured based on a thickness of 10±1 μm.

[0014] According to another aspect, a display device or a flexible display device including the substrate for a display device or a flexible display device is provided.

[0015] Hereinafter, a substrate for a display device or a flexible display device and a display device or a flexible display device according to specific embodiments of the present disclosure will be described in more detail.

[0016] Unless otherwise stated throughout the specification, the technical terms used herein are only used to refer to specific embodiments and are not intended to limit the present disclosure.

[0017] As used herein, the singular forms include plural references unless the context clearly indicates otherwise.

[0018] As used herein, the terms "comprises" or "comprising" specify specific features, regions, integers, steps, actions, elements and / or components, but do not exclude the existence or addition of different specific features, regions, integers, steps, actions, elements, components and / or groups.

[0019] Terms including ordinal numbers such as "first", "second", etc. are only used for the purpose of distinguishing one component from another component and are not limited by the ordinal numbers. For example, without departing from the scope of the present disclosure, a first component may be referred to as a second component, or similarly, a second component may be referred to as a first component.

[0020] In the present disclosure, a (co)polymer is meant to include both a polymer and a copolymer, a polymer means a homopolymer composed of a single repeating unit, and a copolymer means a composite polymer containing two or more repeating units.

[0021] In the present disclosure, examples of the substituent are described below, but are not limited thereto.

[0022] In the present disclosure, the term "substituted" means that other functional groups are bonded to replace the hydrogen atoms in the compound, and the position of substitution is not limited as long as the position is the position where the hydrogen atom is substituted, that is, the position where the substituent can be substituted, and when two or more are substituted, the two or more substituents may be the same as or different from each other.

[0023] In the present disclosure, the term "substituted or unsubstituted" means unsubstituted or substituted with one or more substituents selected from the following: deuterium; halogen group; cyano group; nitro group; hydroxyl group; carbonyl group; ester group; imide group; amide group; primary amino group; carboxyl group; sulfonic acid group; sulfonamide group; phosphine oxide group; alkoxy group; aryloxy group; alkylthio group; arylthio group; alkylsulfonyl group; arylsulfonyl group; silyl group; boron group; alkyl group; cycloalkyl group; alkenyl group; aryl group; aralkyl group; aralkenyl group; alkylaryl group; alkoxysilylalkyl group; arylphosphino group; or a heterocyclic group containing at least one of N, O and S atoms, or unsubstituted or substituted with a substituent in which two or more substituents are connected among the substituents exemplified above. For example, "a substituent in which two or more substituents are connected" can be a biphenyl group. That is, the biphenyl group can also be an aryl group, and can be interpreted as a substituent in which two phenyl groups are connected.

[0024] In this disclosure, the symbol or means a bond to another substituent, and a direct bond means the case where no other atom exists in the portion represented as L.

[0025] In the present disclosure, aromaticity is a property of satisfying Huckel's Rule, and a compound may be defined as aromatic if it satisfies all of the following three conditions according to Huckel's Rule.

[0026] 1) It must have 4n+2 electrons that are completely conjugated by empty p orbitals, unsaturated bonds, lone electron pairs, etc.

[0027] 2) 4n+2 electrons must form a planar isomer and form a ring structure.

[0028] 3) All atoms of the ring must be able to participate in conjugation.

[0029] In the present disclosure, an alkyl group is a monovalent functional group derived from an alkane and may be a straight chain or a branched chain. The number of carbon atoms of the straight chain alkyl group is not particularly limited, but is preferably 1 to 20. In addition, the number of carbon atoms of the branched chain alkyl group is 3 to 20. Specific examples of the alkyl group include methyl, ethyl, propyl, n-propyl, isopropyl, butyl, n-butyl, isobutyl, tert-butyl, sec-butyl, 1-methyl-butyl, 1-ethyl-butyl, pentyl, n-pentyl, isopentyl, neopentyl, tert-pentyl, hexyl, n-hexyl, 1-methylpentyl, 2-methylpentyl, 4-methyl-2-pentyl, 3,3-dimethylbutyl, 2-ethylbutyl, heptyl, n-heptyl, 1-methylhexyl, octyl, n-octyl, tert-octyl, 1-methylheptyl, 2-ethylhexyl, 2-propylpentyl, n-nonyl, 2,2-dimethylheptyl, 1-ethyl-propyl, 1,1-dimethyl-propyl, isohexyl, 2-methylpentyl, 4-methylhexyl, 5-methylhexyl, 2,6-dimethylheptan-4-yl and the like, but are not limited thereto. The alkyl group may be substituted or unsubstituted, and when substituted, examples of the substituent are the same as described above.

[0030] In the present disclosure, haloalkyl means a functional group in which the above alkyl is substituted by a halogen group, and examples of the halogen group are fluorine, chlorine, bromine or iodine. The haloalkyl may be substituted or unsubstituted, and when substituted, examples of the substituent are the same as above.

[0031] In the present disclosure, a multivalent functional group is a residue in which a plurality of hydrogen atoms bonded to any compound are removed, for example, it can be a divalent functional group, a trivalent functional group, and a tetravalent functional group. As an example, a tetravalent functional group derived from cyclobutane means a residue in which any four hydrogen atoms bonded to cyclobutane are removed.

[0032] In the present disclosure, the electron withdrawing group may include one or more selected from a haloalkyl group, a halogen group, a cyano group, a nitro group, a sulfonic acid group, a carbonyl group and a sulfonyl group. Preferably, it may be a haloalkyl group such as a trifluoromethyl group (-CF 3 ).

[0033] In this specification, a direct bond or a single bond means a connection with a bonding line, wherein there is no atom or atom group at the corresponding position. Specifically, it means a direct bond or a single bond represented by L in a chemical formula. 1 or L 2 There are no other atoms in the part.

[0034] Now, the present disclosure will be described in more detail.

[0035] According to one embodiment of the present disclosure, a substrate for a display device or a flexible display device can be provided, comprising: a first polyimide resin layer having a Td 1% of 570°C or higher and a yellowness index of 25 or higher and 60 or lower; a second polyimide resin layer having a yellowness index less than 25; a first inorganic material layer, the first inorganic material layer being positioned between the first polyimide resin layer and the second polyimide resin layer and having a thickness of 100 nm or higher and 700 nm or lower; and a second inorganic material layer, the second inorganic material layer being formed on the second polyimide resin layer and having a thickness of 100 nm or higher and 500 nm or lower.

[0036] The inventors have newly developed a substrate for a display device or a flexible display device, in which a first inorganic material layer having a predetermined thickness is positioned between a colored polyimide resin layer having excellent heat resistance and a transparent polyimide resin layer having excellent high resistance, and a second inorganic material layer to be laminated is positioned on the transparent polyimide resin layer, and experimentally determined that even after such a substrate for a display device or a substrate for a flexible display device undergoes a high temperature process of 430°C or higher, optical properties such as yellowness index or transmittance do not change significantly, the morphology of a single layer or the morphology of a stacked structure is not greatly deformed, and physical properties do not change much, thereby completing the present disclosure.

[0037] In particular, a substrate for a display device or a flexible display device according to one embodiment has a structure in which a first inorganic material layer having a predetermined thickness is interposed between a first polyimide resin layer having the above-mentioned properties and a second polyimide resin layer, so that even during the application of a high temperature of 400°C or higher, especially during the manufacturing process of the display device or the flexible display device, the degradation of the optical properties or the deformation of the morphology is not large, and in addition, the surface resistance is high, which can prevent the occurrence of afterimages and malfunctions of the panel unit on the display panel, thereby being able to provide a high-quality substrate for a display device or a flexible display device.

[0038] Specifically, since the substrate for a display device or a flexible display device includes a first polyimide resin layer having a Td 1% of 570°C or higher and a yellowness index of 25 or higher and 60 or lower, the mechanical properties, dimensional stability and excellent heat resistance at high temperatures can be ensured due to the high packing density of the first polyimide resin, and therefore, deformation and degeneration of the resin layer can be significantly reduced even after a high temperature process of 430°C or higher.

[0039] In particular, the first polyimide resin layer having mechanical properties and excellent heat resistance at high temperatures is subjected to more thermal history, and even if the substrate for a display device or the substrate for a flexible display device having a stacked structure according to one embodiment undergoes a high temperature process of 430° C. or higher, the deformation and degeneration of the substrate for a display device or the substrate for a flexible display device can be significantly reduced.

[0040] When Td 1% of the first polyimide resin layer included in the substrate for a display device or the substrate for a flexible display device is lower than 570° C., heat resistance and mechanical properties of the substrate for a display device or the flexible display device are significantly poor, and thus deformation and degradation of the film at high temperature may be severely manifested.

[0041] In addition, by including a second polyimide resin layer having a yellowness index less than 25, high resistance characteristics are achieved due to the wide polymer chain spacing of the second polyimide resin layer, and electrical influence is reduced, which can be beneficial for improving afterimages when applied to a display device or a flexible display device.

[0042] When the second polyimide resin layer included in the substrate for a display device or a flexible display device has a high yellowness index, transmittance of the substrate for a display device or a flexible display device may decrease or the yellowness index may increase, and high resistance characteristics may be deteriorated.

[0043] Specifically, the first polyimide resin layer having Td 1% of 570° C. or more and a yellowness index of 25 or more and 60 or less is excellent in morphological stability at high temperatures, and the second polyimide resin layer having a yellowness index of less than 25 may be excellent in high resistance characteristics.

[0044] More specifically, a substrate for a display device or a flexible display device includes: a first polyimide resin layer, which is first laminated during a manufacturing process and further undergoes a heat treatment process, wherein the yellowness index of the first polyimide resin layer is 25 or more and 60 or less, and it is excellent in morphological stability; and a second polyimide resin layer, which is a layer closer to a thin film transistor, and the thin film transistor is more electrically affected because the second polyimide resin layer is closer to the thin film transistor, wherein the yellowness index of the second polyimide resin layer is less than 25, and it is excellent in high resistance characteristics, thereby the substrate for a display device or a flexible display device according to one embodiment can achieve excellent morphological stability and, at the same time, achieve excellent high resistance characteristics.

[0045] On the other hand, a substrate for a display device or a flexible display device of one embodiment may include a first inorganic material layer, which is positioned between the first polyimide resin layer and the second polyimide resin layer and has a thickness of 100nm or more and 700nm or less, 200nm or more and 600nm or less, or 300nm or more and 500nm or less.

[0046] The first inorganic material layer is positioned between the first polyimide resin layer and the second polyimide resin layer and blocks air and moisture, thereby enabling excellent device stability. In addition, by minimizing the film effect on the thin film transistor, a high-quality substrate for a display device or a flexible display device can be provided.

[0047] When the first inorganic material layer is not included or its thickness is less than 100 nm, air and moisture cannot be blocked, and thus device stability may be reduced. In addition, the film effect on the thin film transistor becomes large, and thus the quality of the substrate for the display device or the flexible display device may be deteriorated.

[0048] In addition, when the thickness of the first inorganic material layer exceeds 700 nm, not only does the first inorganic material layer become too thick, making it susceptible to external changes and stress, but also the productivity is reduced due to increased process cost and vapor deposition time, which may not be suitable for use as a substrate for a display device or a flexible display device.

[0049] The inorganic material layer includes at least one inorganic material selected from the group consisting of silicon oxide (SiOx), silicon nitride (SiNx), silicon oxynitride (SiON), aluminum oxide (AlO), and aluminum oxynitride (AlON).

[0050] The first inorganic material layer may be formed by applying a conventional inorganic material forming method in the technical field to which the present disclosure pertains, such as a chemical vapor deposition (CVD) method.

[0051] In the substrate for a display device or a flexible display device of one embodiment, Td 1% of the first polyimide resin layer may be 570° C. or more, 570° C. or more and 650° C. or less, or 570° C. or more and 600° C. or less.

[0052] Td 1% may mean a temperature (°C) at which a weight reduction rate is 1% based on the mass of the sample at 100°C. The method of measuring Td 1% is not particularly limited, but as an example, it can be measured using a TGA device. More specifically, it can be measured using a Discovery TGA device (TA Instruments).

[0053] In the substrate for a display device or a flexible display device of one embodiment, since the Td 1% of the first polyimide resin layer is 570° C. or higher, excellent heat resistance is exhibited, and mechanical properties and dimensional stability can be ensured without deformation even at high temperatures. Specifically, even when a high temperature process of 430° C. or higher is experienced during the manufacture of the flexible display, deformation and degeneration of the resin layer can be significantly reduced.

[0054] Furthermore, in the substrate for a display device or a flexible display device of one embodiment, the yellowness index of the first polyimide resin layer may be 25 or more and 60 or less, 25 or more and 50 or less, or 25 or more and 30 or less.

[0055] The yellowness index of the first polyimide resin layer is measured for a first polyimide resin layer sample having a thickness of 10±1 μm, and the method for measuring the yellowness index is not particularly limited, and the yellowness index can be measured, for example, using a colorimeter. More specifically, it can be measured using Color-Eye 7000A from GretagMacbeth.

[0056] Specifically, the yellowness index of the first polyimide resin layer may be a value obtained by coating the composition for forming the first polyimide resin layer on a 10 cm×10 cm glass substrate and then measuring the central portion of the coated first polyimide resin layer film having a thickness of 10±1 μm.

[0057] As described above, in a substrate for a display device or a flexible display device, since the yellowness index of the first polyimide resin layer laminated on the substrate is 25 or more and 60 or less, mechanical properties, dimensional stability and excellent heat resistance at high temperatures can be ensured due to the high stacking density, thereby significantly reducing deformation and degeneration of the resin layer even after undergoing a high temperature process of 430°C or more.

[0058] On the other hand, in the substrate for a display device or a flexible display device of one embodiment, the yellowness index of the second polyimide resin layer may be less than 25, 20 or less, 1 or more and 20 or less, 5 or more and 20 or less, or 5 or more and 15 or less.

[0059] The yellowness index of the second polyimide resin layer is measured for a second polyimide resin layer sample having a thickness of 10±1 μm. The method for measuring the yellowness index is not particularly limited, and can be measured, for example, using a colorimeter. More specifically, it can be measured using Color-Eye 7000A of GretagMacbeth.

[0060] Specifically, the yellowness index of the second polyimide resin layer can be a value obtained by coating a composition for forming a first polyimide resin layer on a 10 cm×10 cm glass substrate to form a first polyimide resin layer, forming a first inorganic material layer on the first polyimide resin layer by plasma chemical vapor deposition, forming a second polyimide resin layer on the first inorganic material layer, and measuring the central portion of the second polyimide resin layer film.

[0061] Since the yellowness index of the second polyimide resin layer is less than 25, excellent low dielectric properties and high resistance properties are achieved due to the wide polymer chain spacing of the second polyimide resin layer, and thus, electrical influence is reduced, which can be beneficial to improving afterimages when applied to display devices or flexible display devices.

[0062] On the other hand, in the substrate for a display device or a flexible display device of one embodiment, the difference between the yellowness index of the first polyimide resin layer and the yellowness index of the second polyimide resin layer may be 5 or more, 5 or more and 50 or less, 5 or more and 30 or less, 5 or more and 15 or less, or 5 or more and 10 or less.

[0063] On the other hand, the substrate for a display device or a flexible display device of one embodiment may further include a second inorganic material layer formed on the second polyimide resin layer and having a thickness of 100 nm or more and 500 nm or less, or 200 nm or more and 400 nm or less.

[0064] That is, a substrate for a display device or a substrate for a flexible display device according to one embodiment may have the following structure: a first polyimide resin layer having a Td 1% of 570° C. or higher and a yellowness index of 25 or higher and 60 or lower is laminated on the substrate, a first inorganic material layer having a thickness of 100 nm or higher and 700 nm or lower is laminated on the first polyimide resin layer, a second polyimide resin layer having a yellowness index of less than 25 is laminated on the first inorganic material layer, and a second inorganic material layer having a thickness of 100 nm or higher and 500 nm or lower, or 200 nm or higher and 400 nm or lower is laminated on the second polyimide resin layer having a yellowness index of 20 or lower.

[0065] The second inorganic material layer is positioned on the second polyimide resin layer and can secondarily block air and moisture, thereby achieving excellent device stability, and further, can provide a high-quality substrate for a display device or a flexible display device by minimizing the influence on the thin film transistor.

[0066] When the second inorganic material layer is not included or its thickness is less than 100 nm, air and moisture cannot be blocked and thus device stability may be deteriorated, and furthermore, the film effect on the thin film transistor increases, which may lead to quality degradation of a substrate for a display device or a flexible display device.

[0067] In addition, when the thickness of the second inorganic material layer exceeds 500 nm, not only does the thickness of the second inorganic material layer become too thick, making it susceptible to external changes and stress, but also the productivity is reduced due to increased process cost and deposition time, which may not be suitable for use as a substrate for a display device or a flexible display device.

[0068] The inorganic material layer may include at least one inorganic material selected from the group consisting of silicon oxide (SiOx), silicon nitride (SiNx), silicon oxynitride (SiON), aluminum oxide (AlO), and aluminum oxynitride (AlON).

[0069] The second inorganic material layer may be formed by applying a conventional inorganic material forming method in the technical field to which the present disclosure pertains, such as chemical vapor deposition (CVD).

[0070] On the other hand, in the substrate for a display device or a flexible display device of one embodiment, the yellowness index of the entire substrate for a display device or a flexible display device may be 36 or less, 10 to 36, 20 to 36, 24 to 36, or 24 to 30.

[0071] As described above, by including the first polyimide resin layer having a yellowness index of 25 or more and 60 or less and the second polyimide resin layer having a yellowness index of 20 or less, the yellowness index of the entire substrate for a display device or a flexible display device may satisfy 36 or less.

[0072] When the yellowness index of the entire substrate for a display device or a flexible display device is high, it may not be suitable for use as a substrate for a transparent display with high transmittance. In addition, when the yellowness index of the entire substrate for a display device or a flexible display device is high, the dielectric constant may appear high due to problems caused by the internal laminated structure, and in particular, the dielectric constant appears too high and the afterimage characteristic is deteriorated, and it may not be suitable for use as a substrate for a display device or a flexible display device.

[0073] The method of measuring the yellowness index is not particularly limited, and the yellowness index can be measured, for example, using a colorimeter. More specifically, it can be measured using Color-Eye 7000A from GretagMacbeth.

[0074] The yellowness index may be measured by a substrate sample for a display device or a flexible display device having a thickness of 16±1 μm. When the thickness of the sample increases or decreases by a specific value, the measured physical properties may also change by a certain value.

[0075] Specifically, the yellowness index of the entire substrate for a display device or a flexible display device can be a value obtained by: coating a composition for forming a first polyimide resin layer on a 10 cm×10 cm glass substrate to form a first polyimide resin layer, forming a first inorganic material layer on the first polyimide resin layer by plasma chemical vapor deposition, forming a second polyimide resin layer on the first inorganic material layer, forming a second inorganic material layer on the second polyimide resin layer by plasma chemical vapor deposition, and measuring the central portion of the second inorganic material layer film.

[0076] On the other hand, in the substrate for a display device or a flexible display device of one embodiment, for the entire substrate for a display device or a flexible display device, the yellowness index after a heat treatment step of raising the temperature to 430°C for 2 hours, undergoing an isothermal process at 430°C for 2 hours, and then cooling to 50°C for 2 hours can be 50 or less, 25 or more and 50 or less, 30 or more and 50 or less, 33 or more and 50 or less, or 33 or more and 40 or less.

[0077] The method of measuring the yellowness index is not particularly limited, and can be measured, for example, using a colorimeter. More specifically, it can be measured using Color-Eye 7000A from GretagMacbeth.

[0078] The yellowness index may be measured by a substrate sample for a display device or a flexible display device having a thickness of 16±1 μm. When the thickness of the sample increases or decreases by a specific value, the measured physical properties may also change by a certain value.

[0079] Since the yellowness index of the entire substrate for a display device or a flexible display device is 50 or less even after a heat treatment step of raising the temperature to 430°C for 2 hours, undergoing an isothermal process at 430°C for 2 hours, and then cooling to 50°C for 2 hours, optical properties such as appropriate transmittance and yellowness index can be ensured, which can be suitable for use in a display device or a flexible display device.

[0080] On the other hand, in one embodiment, based on the initial yellowness index of the entire substrate for a display device or a flexible display device, the percentage of the yellowness index after a heat treatment step of raising the temperature to 430°C for 2 hours, undergoing an isothermal process at 430°C for 2 hours, and then cooling to 50°C for 2 hours can be 130% or less, or 100% or more and 130% or less, or 110% or more and 130% or less.

[0081] Based on the initial yellowness index of the entire substrate for a display device or a flexible display device of one embodiment, since the percentage of the yellowness index after the heat treatment step of increasing the temperature to 430°C for 2 hours, undergoing an isothermal process at 430°C for 2 hours, and then cooling to 50°C for 2 hours is 130% or less, even after undergoing a high temperature process of 430°C or more, a substrate for a display device or a flexible display device having excellent optical characteristics can be provided. Based on the initial yellowness index of the entire substrate for a display device or a flexible display device of one embodiment, since the substrate for a display device or a flexible display device of this embodiment includes the first polyimide resin layer having a Td1% of 570°C or more and a yellowness index of 25 or more and 60 or less and the second polyimide resin layer having a yellowness index of less than 25 as described above, the percentage of the yellowness index after the heat treatment step of increasing the temperature to 430°C for 2 hours, undergoing an isothermal process at 430°C for 2 hours, and then cooling to 50°C for 2 hours can be achieved.

[0082] On the other hand, the thickness of each of the first polyimide resin layer and the second polyimide resin layer can be determined by considering the thickness or physical properties of each or all of the first inorganic material layer, the second inorganic material layer, and the substrate for the display device or the flexible display device. For example, the thickness of each of the first polyimide resin layer and the second polyimide resin layer can be 0.5 μm to 20 μm.

[0083] At this time, the yellowness index of the first polyimide resin layer and the second polyimide resin layer may vary according to thickness, but as described above, the yellowness index of each of the first polyimide resin layer and the second polyimide resin layer is measured and defined based on a thickness of 10±1 μm.

[0084] More specifically, the thickness of the first polyimide resin layer may be 1 μm to 10 μm, 2 μm to 10 μm, or 6 μm to 10 μm, and the thickness of the second polyimide resin layer may be 0.5 μm to 6 μm, 1 μm to 6 μm, or 3 μm to 6 μm.

[0085] Alternatively, the thickness of the first polyimide resin layer may be 1 μm to 6 μm, 1 μm to 5 μm, or 2 μm to 5 μm, and the thickness of the second polyimide resin layer may be 6 μm to 15 μm, 8 μm to 15 μm, or 10 μm to 15 μm.

[0086] On the other hand, Td 1% of the second polyimide resin layer may be 500°C or more and 560°C or less, 500°C or more and 555°C or less, or 520°C or more and 555°C or less, or 545°C or more and 555°C or less.

[0087] As described above, Td 1% may mean a temperature (°C) at which a weight reduction rate is 1% based on the mass of the sample at 100°C. The method for measuring Td 1% is not particularly limited, but as an example, it may be measured using a TGA device. More specifically, it may be measured using a Discovery TGA device (TA Instruments).

[0088] In the substrate for a display device or a flexible display device of one embodiment, since the Td 1% of the second polyimide resin layer is 500° C. or more and 560° C. or less, the high resistance and excellent optical properties of the second polyimide resin layer and the high heat resistance properties of the first polyimide resin layer having Td 1% of 570° C. or more and better heat resistance can be achieved.

[0089] Specifically, the first polyimide resin layer and the second polyimide resin layer each have a transmittance of 50% or more, 50% or more and 100% or less, 65% or more and 95% or less at a wavelength of 470nm, and may exhibit a haze of 1.0% or less, 0.1% or more and 1.0% or less, and 0.3% or more and 0.8% or less.

[0090] The examples of the method and system for measuring the haze according to an embodiment are not particularly limited, and various methods conventionally used for haze measurement can be applied without limitation. In one example, the haze can be measured using a haze meter (model name: NDH7000, Nippon Denshoku) according to the measurement method of ASTM D1003.

[0091] The example of the method and system for measuring the transmittance according to an embodiment is not particularly limited, and various methods conventionally used for transmittance measurement can be applied without limitation. In an example, the transmittance (T) to light with a wavelength of 470 nm can be measured using a UV-vis spectrometer (Agillent, UV 8453).

[0092] In addition, the transmittance and haze may be values ​​measured for the first polyimide resin layer sample and the second polyimide resin layer sample having a thickness of 10 μm. When the thickness of the resin layer increases or decreases by a certain value, the transmittance and haze may also change by a certain value.

[0093] Since the first polyimide resin layer and the second polyimide resin layer each have a transmittance of 50% or more at a wavelength of 470 nm and exhibit a haze of 1.0% or less, a substrate for a display device or a flexible display device suitable for use in a device for a display device or a device for a flexible display device can be provided by ensuring suitable optical properties such as transmittance and yellowness index.

[0094] Polyimide polymer means including both polyimide and its precursor polymer (such as polyamic acid or polyamic acid ester). That is, the polyimide polymer may include at least one selected from polyamic acid repeating unit, polyamic acid ester repeating unit and polyimide repeating unit. That is, the polymer based on polyimide 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 these two or more types of repeating units are mixed.

[0095] One or more repeating units selected from the group consisting of a polyamic acid repeating unit, a polyamic acid ester repeating unit, and a polyimide repeating unit may form a main chain of the polyimide polymer.

[0096] Specifically, the second polyimide resin layer may include a polyimide resin including a repeating unit derived from a diamine substituted with a fluorine-based functional group.

[0097] More specifically, the second polyimide resin layer may include a reaction product between an aromatic tetracarboxylic acid or anhydride thereof and a diamine substituted with a fluorine-based functional group, or a polyimide resin containing a repeating unit derived therefrom.

[0098] Since the second polyimide resin layer includes a reaction product between an aromatic tetracarboxylic acid or its anhydride and a diamine substituted with a fluorine-based functional group, or a polyimide resin containing a repeating unit derived therefrom, the second polyimide resin layer may achieve a yellowness index of less than 25.

[0099] More specifically, the second polyimide resin layer may include a polyimide resin including a repeating unit represented by Chemical Formula 1 below.

[0100] [Chemical formula 1]

[0101]

[0102] Wherein, in chemical formula 1, X 1is an aromatic tetravalent functional group, and Y 1 It is an aromatic divalent functional group substituted with at least one fluorine-based functional group.

[0103] In chemical formula 1, X 1 is a functional group derived from a tetracarboxylic dianhydride compound used for synthesizing a polyimide-based resin.

[0104] In Chemical Formula 1, Y 1 It is an aromatic divalent functional group in which at least one fluorine-based functional group is substituted, and may be a functional group derived from a diamine compound used for synthesizing a polyimide-based resin.

[0105] Due to the substitution with highly electronegative fluorine-based functional groups such as trifluoromethyl (-CF 3 ), thus increasing the effect of suppressing the formation of CTC (charge transfer complex) of π electrons present in the polyimide polymer chain, thereby ensuring improved transparency. That is, the accumulation in the polyimide structure or between chains can be reduced, and due to the steric effect and the electrical effect, the electrical interaction between the chromophores can be weakened and high transparency can be exhibited in the visible light region.

[0106] Specifically, the divalent organic group Y substituted with at least one fluorine-based functional group 1 A functional group represented by the following Chemical Formula 3-1 may be included.

[0107] [Chemical formula 3-1]

[0108]

[0109] Among them, in chemical formula 3-1,

[0110] p is an integer of 0 or more and 5 or less, preferably an integer of 0 or more and 2 or less.

[0111] More specifically, the polyimide-based resin has a feature that a terminal anhydride group (—OC—O—CO—) of a tetracarboxylic dianhydride can react with a terminal amino group (—NH 2 ) reaction, thereby forming a bond between the nitrogen atom of the amino group and the carbon atom of the anhydride group.

[0112] The second polyimide resin layer may be prepared by reacting two or more types of different diamine compounds with a tetracarboxylic dianhydride compound, and the two types of diamine compounds may be added simultaneously to synthesize a random copolymer, or may be added sequentially to synthesize a block copolymer.

[0113] Specifically, the second polyimide resin layer may include a polyimide resin including a repeating unit represented by the following Chemical Formula 1-1 in addition to the repeating unit represented by Chemical Formula 1.

[0114] [Chemical formula 1-1]

[0115]

[0116] Wherein, in chemical formula 1-1, X 2 is an aromatic tetravalent functional group, and Y 2 is the same as Y in chemical formula 1 1 Different aromatic divalent functional groups.

[0117] On the other hand, the first polyimide resin layer may include a polyimide resin including a repeating unit derived from a diamine not substituted with a fluorine-based functional group.

[0118] Specifically, the first polyimide resin layer may include a reaction product between a tetracarboxylic acid or anhydride thereof and a diamine not substituted with a fluorine-based functional group, or a polyimide resin containing a repeating unit derived therefrom.

[0119] Since the first polyimide resin layer includes a reaction product between a tetracarboxylic acid or its anhydride and a diamine not substituted with a fluorine-based functional group, or a polyimide resin containing a repeating unit derived therefrom, the first polyimide resin layer can achieve a Td 1% of 570° C. or higher, and a yellowness index of 25 or more and 60 or less.

[0120] More specifically, the first polyimide resin layer may include a polyimide resin including a repeating unit represented by Chemical Formula 4 below.

[0121] [Chemical formula 4]

[0122]

[0123] Wherein, in chemical formula 4, X 3 is a tetravalent functional group represented by the following Chemical Formula 5, and Y 3 It is an aromatic divalent functional group not substituted with a fluorine-based functional group.

[0124] [Chemical formula 5]

[0125]

[0126] In the chemical formula 5, R 1 To R 6 are each independently hydrogen or an alkyl group having 1 to 6 carbon atoms, L 1 and L 2are the same as or different from each other and each independently represents one of -COO- or -OCO-, L 3 is selected from a single bond, -O-, -CO-, -COO-, -S-, -SO-, -SO 2 -、-CR 7 R 8 -、-(CH 2 ) t -、-O(CH 2 ) t O-, -COO(CH 2 ) t Any one of OCO-, -CONH-, phenylene or a combination thereof, wherein R 7 and R 8 Each is independently one of hydrogen, an alkyl group having 1 to 10 carbon atoms, or a halogenated alkyl group having 1 to 10 carbon atoms, and t is an integer of 1 to 10.

[0127] Specific examples of the functional group represented by Chemical Formula 5 may include a functional group represented by the following Chemical Formula 8-1.

[0128] [Chemical formula 8-1]

[0129]

[0130] In chemical formula 4, X 3 is a functional group derived from a tetracarboxylic dianhydride compound used for synthesizing a polyimide-based resin.

[0131] In chemical formula 4, Y 3 It is an aromatic divalent functional group which is not substituted with a fluorine-based functional group, and may be a functional group derived from a diamine compound used for synthesizing a polyimide-based resin.

[0132] Specifically, the aromatic divalent functional group Y which is not substituted with a fluorine-based functional group 3 A functional group represented by the following Chemical Formula 9-1 may be included.

[0133] [Chemical formula 9-1]

[0134]

[0135] On the other hand, in the substrate for a display device or a flexible display device, each of the first and second polyimide resin layers may have a thermal expansion coefficient of 5 ppm / ° C. or less in a portion at 100° C. or higher and 460° C. or lower.

[0136] The coefficient of thermal expansion is determined by setting the force for pulling the sample to 0.01 N or more and 0.1 N or less, or 0.01 N or more and 0.05 N or less, performing a preliminary temperature rising step at a heating rate of 1°C / min or more and 10°C / min or less, or 4°C / min or more and 6°C / min or less in a temperature range of 100°C or more and 460°C or less, and then cooling the sample at a cooling rate of 1°C / min or more and 10°C / min or less, or 3°C / min or more and 5°C / min or less in a temperature range of 50°C to 100°C, measuring the change in thermal expansion of the polyimide resin layer sample using TMA Q400 (TAInstruments).

[0137] The thermal expansion coefficient can be measured from a polyimide resin layer sample having a thickness of 10±1 μm. When the thickness of the polyimide resin layer increases or decreases by a specific value, the physical properties measured from the polyimide resin layer may also change by a certain value.

[0138] In the substrate for a display device or a flexible display device, since the first polyimide resin layer and the second polyimide resin layer satisfy a thermal expansion coefficient of 5 ppm / °C or less in the portion of 100°C or more and 460°C or less, sufficient heat resistance is ensured even in the substrate for a display device or a flexible display device obtained by high temperature curing. When it is used as a plastic substrate, when a metal layer formed on the plastic substrate is heat-treated, it can prevent the plastic substrate from being damaged by heat, and it can also suppress the occurrence of warping in the metal film formed on the plastic substrate.

[0139] The weight average molecular weight (measured by GPC) of the polyimide resin is not particularly limited, but for example, it may be 1000 g / mol or more and 200000 g / mol or less, or 10000 g / mol or more and 200000 g / mol or less.

[0140] The substrate for a display device or a flexible display device according to the present disclosure can exhibit excellent colorless and transparent properties while maintaining properties such as heat resistance and mechanical strength as is due to the rigid structure, and can therefore be used in various fields, such as substrates for devices, cover substrates for displays, optical films, IC (integrated circuit) packaging, adhesive films, multilayer flexible printed circuits (FRCs), tapes, touch panels, protective films for optical discs, and the like.

[0141] On the other hand, the substrate for a display device or a flexible display device of one embodiment may include a cured product in which the polyimide-based resin is cured at a temperature of 400° C. or higher. The cured product means a material obtained by a curing process of a resin composition including a polyimide-based resin, and the curing process may be performed at a temperature of 400° C. or higher, or 400° C. or higher and 500° C. or lower.

[0142] More specifically, there is no particular limitation on the example of a method for synthesizing a polyimide resin layer for a substrate for a display device or a flexible display device, and for example, a preparation method comprising the following steps can be used: a step of coating a resin composition comprising a polyimide-based resin onto a substrate to form a coating film (step 1); a step of drying the coating film (step 2); and a step of heat-treating and curing the dried coating film (step 3).

[0143] Step 1 is a step of applying a resin composition comprising the above-mentioned polyimide-based resin to a substrate to form a coating film. The method of applying the resin composition comprising the polyimide-based resin to a substrate is not particularly limited, and for example, methods such as screen printing, offset printing, flexographic printing, inkjet printing, etc. can be used.

[0144] In addition, the resin composition containing the polyimide-based resin may be in the form of being dissolved or dispersed in an organic solvent. In the case of having such a form, for example, when the polyimide-based resin is synthesized in an organic solvent, the solution may be the reaction solution itself obtained thereby or may be a solution obtained by diluting the reaction solution with another solvent. In addition, when the polyimide is obtained as a powder, the solution may be a solution obtained by dissolving the powder in an organic solvent.

[0145] Specific examples of the organic solvent include toluene, N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N-methylcaprolactam, 2-pyrrolidone, N-ethylpyrrolidone, N-vinylpyrrolidone, dimethyl sulfoxide, tetramethylurea, pyridine, dimethyl sulfone, hexamethyl sulfoxide, γ-butyrolactone, 3-methoxy-N,N-dimethylpropionamide, 3-ethoxy-N,N-dimethylpropionamide, 3-butoxy-N,N-dimethylpropionamide, 1,3 -dimethyl-imidazolidinone, ethyl amyl ketone, methyl nonyl ketone, methyl ethyl ketone, methyl isoamyl ketone, methyl isopropyl ketone, cyclohexanone, ethylene carbonate, propylene carbonate, diethylene glycol dimethyl ether, 4-hydroxy-4-methyl-2-pentanone, ethylene glycol monomethyl ether, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether, ethylene glycol monoethyl ether acetate, ethylene glycol monopropyl ether, ethylene glycol monopropyl ether acetate, ethylene glycol monoisopropyl ether, ethylene glycol monoisopropyl ether acetate, ethylene glycol monobutyl ether, ethylene glycol monobutyl ether acetate, etc. These may be used alone or in combination of two or more.

[0146] Considering the processability during the film formation process such as coating characteristics, the resin composition containing the polyimide-based polymer may contain solids in an amount such that the solution has an appropriate viscosity. For example, the content of the composition may be adjusted so that the total content of the resin is 5 wt % or more and 25 wt % or less, or may be adjusted to 5 wt % or more and 20 wt % or less.

[0147] In addition, the resin composition comprising the resin based on polyimide can also include other components in addition to the organic solvent. In a non-limiting example, when coating the resin composition comprising the polyimide polymer, such additives can also be included: it can improve the uniformity and surface smoothness of film thickness, or can improve the adhesion with substrate, or can change dielectric constant and conductivity, or can improve compactness. The examples of these additives include surfactants, silane-based compounds, dielectrics or cross-linked compounds, etc.

[0148] Step 2 is a step of drying a coating film formed by coating a resin composition including a polyimide-based resin on a substrate.

[0149] The step of drying the coating film may be performed by a heating device such as a hot plate, a hot air circulation oven, an infrared oven, etc., and the drying may be performed at a temperature of 50° C. or higher and 150° C. or lower, or 50° C. or higher and 100° C. or lower.

[0150] Step 3 is a step of heat treating and curing the dried coating film. In this case, the heat treatment can be carried out by a heating device such as a hot plate, a hot air circulation oven, an infrared oven, etc., and the heat treatment can be carried out at a temperature of 400° C. or higher, or 400° C. or higher and 500° C. or lower.

[0151] The thickness of the substrate for a display device or a flexible display device is not particularly limited, but, for example, it can be freely adjusted within a range of 0.01 μm or more and 1000 μm or less. If the thickness of the substrate for a display device or a flexible display device increases or decreases by a specific value, the physical properties measured by the substrate for a display device or a flexible display device may also change by a certain value.

[0152] The substrate for a display device or a flexible display device according to the embodiment can further include a silicon oxide layer formed between the polyimide resin layer and the cured layer in order to further improve its solvent resistance, water permeability and optical characteristics, and the silicon oxide layer can be generated by curing polysilazane.

[0153] Specifically, the silicon oxide layer may be formed by curing the applied polysilazane after applying a solution including polysilazane and drying it before the step of forming a coating layer on at least one surface of the polyimide resin layer.

[0154] Meanwhile, according to another embodiment of the present disclosure, a display device or a flexible display device including a substrate for a display device or a flexible display device according to another embodiment may be provided. The details of the substrate for a display device or a flexible display device may include all those described in one embodiment above.

[0155] For the configuration and manufacturing method of the display device or the flexible display device, the technology known in the art may be used, except that the composite substrate for manufacturing the display device or the flexible display device is used for the above-mentioned application.

[0156] The display device or the flexible display device may be used as a touch panel of a mobile communication terminal, a smartphone or a tablet computer, and a cover substrate or an element substrate of various displays in a curved, bendable, flexible, rollable or foldable shape.

[0157] An example of the display device or the flexible display device may be a flexible light emitting element display device.

[0158] For example, in an organic light emitting diode (OLED) display, a cover window of the display device can be positioned outside in the direction of emitting light or an image, and a cathode providing electrons, an electron transport layer, a light emitting layer, a hole transport layer, and an anode providing holes can be sequentially formed.

[0159] In addition, the organic light emitting diode (OLED) display may further include a hole injection layer (HIL) and an electron injection layer (EIL).

[0160] In order for an organic light emitting diode (OLED) display to function and be used as a flexible display, a material having predetermined elasticity may be used in a cathode and an anode and respective constituent components.

[0161] Another example of the display device or the flexible display device may be a rollable display or a foldable display device.

[0162] The rollable display may have various structures according to application fields, specific shapes, etc. For example, the rollable display device may have a structure including a cover plastic window, a touch panel, a polarizing plate, a blocking film, a light emitting element (OLED element, etc.), a transparent substrate, etc.

[0163] Beneficial Effects

[0164] According to the present disclosure, a substrate for a display device or a flexible display device and a display device or a flexible display device using the same can be provided, wherein the substrate for a display device or a flexible display device achieves high resistance and low moisture absorption, does not have film denaturation even during high-temperature heat treatment, and can achieve excellent optical properties. DETAILED DESCRIPTION

[0165] The present disclosure will be described in more detail with reference to the following examples. However, these examples are provided for illustrative purposes only, and the scope of the present invention is not limited thereto.

[0166] Preparation Example 1

[0167] 200g of N-methyl-2-pyrrolidone was charged into a 500mL 4-necked round-bottom flask (reactor) equipped with a stirrer, a nitrogen injection device, a dropping funnel, a temperature controller and a condenser, while slowly passing nitrogen. Then, the temperature of the reactor was adjusted to 60°C, and 133 mmoles of p-phenylenediamine (PDA) were added and completely dissolved.

[0168] While maintaining the temperature of the resulting solution at 60° C., 132 mmol of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) was added to the reactor together with 120 g of N-methyl-2-pyrrolidone, and the mixture was stirred and diluted for 48 hours to obtain a polyimide precursor composition P-1 (solid content: 11 wt %).

[0169] Preparation Example 2

[0170] 100 g of diethylacetamide (DEAC) was charged into a 500 mL 4-necked round-bottom flask (reactor) equipped with a stirrer, a nitrogen injection device, a dropping funnel, a temperature controller and a condenser, while nitrogen was slowly introduced. 33 mmol of p-phenylenediamine (PDA) and 33 mmol of 2,2'-bis(trifluoromethyl)benzidine (TFMB) were added thereto and completely dissolved.

[0171] While the temperature of the obtained solution was maintained at room temperature, 51 mmol of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) and 15 mmol of 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride (BPAF) were added to the reactor together with 100 g of DEAC, and the mixture was stirred and diluted for 48 hours to obtain a polyimide precursor composition P-2 (solid content: 13 wt %).

[0172] Preparation Example 3

[0173] 100 g of diethylacetamide (DEAC) was charged into a 500 mL 4-necked round bottom flask (reactor) equipped with a stirrer, a nitrogen injection device, a dropping funnel, a temperature controller and a condenser, while nitrogen was slowly introduced. 35 mmol of a diamine represented by the following chemical formula A was added thereto and completely dissolved.

[0174] [Chemical formula A]

[0175]

[0176] While maintaining the temperature of the obtained solution at 40° C., 27 mmol of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) and 8 mmol of 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride (BPAF) were added to the reactor together with 60 g of DEAC, and the mixture was stirred and diluted for 48 hours to obtain a polyimide precursor composition P-3 (solid content: 10 wt %).

[0177] Preparation Example 4

[0178] 100 g of diethylacetamide (DEAC) was charged into a 500 mL 4-necked round bottom flask (reactor) equipped with a stirrer, a nitrogen injection device, a dropping funnel, a temperature controller and a condenser, while nitrogen was slowly introduced. 35 mmol of a diamine represented by the following chemical formula B was added thereto and completely dissolved.

[0179] [Chemical formula B]

[0180]

[0181] While maintaining the temperature of the obtained solution at 40° C., 27 mmol of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) and 8 mmol of 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride (BPAF) were added to the reactor together with 60 g of DEAC, and the mixture was stirred and diluted for 48 hours to obtain a polyimide precursor composition P-4 (solid content: 5 wt %).

[0182] <Example>

[0183] Example 1

[0184] The polyimide precursor composition according to Preparation Example 1 was spin-coated onto a glass substrate. The glass substrate coated with the polymer solution was placed in an oven, heated to 470° C. at 3° C. / min, and maintained at 470° C. for 10 minutes to form a first polyimide resin layer (10 μm thick).

[0185] A first inorganic material layer (SiO 2 ,thickness: ).

[0186] The polyimide precursor composition according to Preparation Example 1 was spin-coated on the first inorganic material layer, then placed in an oven, heated to 470° C. at 3° C. / min, and maintained at 470° C. for 10 minutes to form a second polyimide resin layer (6 μm in thickness).

[0187] Subsequently, a second inorganic material layer (SiO 2 ,thickness: ).

[0188] Example 2

[0189] This was prepared in the same manner as in Example 1, except that the polyimide precursor composition according to Preparation Example 2 was used instead of the polyimide precursor composition according to Preparation Example 1 when forming the second polyimide resin layer.

[0190] Example 3

[0191] This was prepared in the same manner as in Example 1, except that the polyimide precursor composition according to Preparation Example 3 was used instead of the polyimide precursor composition according to Preparation Example 1 when forming the second polyimide resin layer.

[0192] Example 4

[0193] This was prepared in the same manner as in Example 1, except that the first polyimide resin layer was formed in a thickness of 2 μm and the second polyimide resin layer was formed in a thickness of 10 μm by using the polyimide precursor composition according to Preparation Example 2 instead of the polyimide precursor composition according to Preparation Example 1.

[0194] Example 5

[0195] This was prepared in the same manner as in Example 1, except that the first polyimide resin layer was formed in a thickness of 5 μm and the second polyimide resin layer was formed in a thickness of 10 μm by using the polyimide precursor composition according to Preparation Example 2 instead of the polyimide precursor composition according to Preparation Example 1.

[0196] <Comparative Example>

[0197] Comparative Example 1

[0198] This was prepared in the same manner as in Example 1, except that the polyimide precursor composition according to Preparation Example 2 was used instead of the polyimide precursor composition according to Preparation Example 1 when forming the first polyimide resin layer.

[0199] Comparative Example 2

[0200] This was prepared in the same manner as in Example 1, except that when forming the first polyimide resin layer, the polyimide precursor composition according to Preparation Example 2 was used instead of the polyimide precursor composition according to Preparation Example 1, and when forming the second polyimide resin layer, the polyimide precursor composition according to Preparation Example 3 was used instead of the polyimide precursor composition according to Preparation Example 1.

[0201] Comparative Example 3

[0202] This was prepared in the same manner as in Example 1, except that when forming the first polyimide resin layer, the polyimide precursor composition according to Preparation Example 3 was used instead of the polyimide precursor composition according to Preparation Example 1, and when forming the second polyimide resin layer, the polyimide precursor composition according to Preparation Example 3 was used instead of the polyimide precursor composition according to Preparation Example 1.

[0203] Reference example 1

[0204] The polyimide precursor composition according to Preparation Example 1 was spin-coated onto a glass substrate. The glass substrate coated with the polymer solution was placed in an oven, heated to 470° C. at 3° C. / min, and maintained at 470° C. for 10 minutes to form a first polyimide resin layer (10 μm thick).

[0205] The polyimide precursor composition according to Preparation Example 2 was spin-coated on the first polyimide resin layer, placed in an oven, heated to 470° C. at 3° C. / min, and maintained at 470° C. for 10 minutes to form a second polyimide resin layer (6 μm in thickness).

[0206] <Experimental example>

[0207] The physical properties of the substrates for a display device or a flexible display device obtained in Examples and Comparative Examples were measured by the following methods, and the results are shown in Table 1 below.

[0208] 1. Coefficient of Thermal Expansion (CTE)

[0209] The polyimide precursor composition according to the preparation example was spin-coated onto a glass substrate. The glass substrate coated with the polymer solution was heated to 470° C. at 3° C. / min and maintained at 470° C. for 10 minutes to form a polyimide resin layer (10 μm in thickness).

[0210] The polyimide resin layer sample was prepared to a size of 5 mm × 20 mm, and then the sample was loaded with an accessory. The actual measured length of the polyimide resin layer was set equal to 16 mm. The force for pulling the sample was set to 0.02 N, and a preliminary heating step was performed at a heating rate of 5 ° C / min in the temperature range of 100 ° C or higher and 460 ° C or lower for Preparation Example 1, and at a temperature range of 100 ° C or higher and 430 ° C or lower for Preparation Examples 2 and 3, and then the sample was cooled at a cooling rate of 4 ° C / min. At this time, the change in thermal expansion was measured using TMA Q400 (TA Instruments).

[0211] 2. Dielectric constant

[0212] The saturated electrostatic voltage of the substrates for display devices or flexible display devices of the embodiments and comparative examples was measured using H-0110 Honestmeter of Shishido Electrostatic according to the standard measuring method of JIS L 1094 at a temperature of 25° C. and a humidity of 40% to 50%.

[0213] The applied voltage is set to 10kV for each manufactured substrate for a display device or a flexible display device. The distance from the tip of the needle-shaped electrode of the applied portion to the surface of the rotating disk is adjusted to 20mm, and the distance from the electrode plate of the power receiving portion to the surface of the rotating disk is adjusted to 15mm. The applied voltage of 10V is started while the rotating disk is rotating, and the application is completed after 100 seconds. While the rotating disk is rotated in this state, the time until the electrostatic voltage decays to half is measured. The half-life is obtained by measuring the time from the time when the application of the high voltage is cut off to the time when the potential value is reduced to 50% of the saturated electrostatic voltage value. The measured saturated electrostatic voltage and its half-life are shown in Table 1 below.

[0214] For reference, corona discharge is a discharge phenomenon that occurs when a high voltage is applied between two electrodes by exciting gas particles on the electrode surface via the high voltage and ionizing them. This phenomenon occurs more frequently as air density increases, as voltage increases, as temperature increases, and as humidity decreases. When corona discharge occurs, the gas is excited and ionized by the electric field near the wire, which causes local insulation breakdown. Thus, current flows and discharges, and the electrons obtained by the electric field collide with gas molecules, and a continuous gas ionization effect of re-emitting the electrons possessed by the gas molecules occurs.

[0215] An arbitrary DC voltage is applied to the sample in the form of corona discharge, the detection value reaches a saturation value, and then the high voltage application is cut off, and the potential on the sample surface is continuously detected through the decay state to determine the electrostatic properties of the material. After the sample is charged in the corona discharge field, the time required for the voltage to decay to half (half-life) is then measured.

[0216] 3. Heat resistance (Td 1%, ℃)

[0217] The temperature (° C.) when the weight reduction rate of the polyimide resin layer sample was 1% was measured using Discovery TGA equipment from TA Instruments under a nitrogen atmosphere.

[0218] Specifically, the temperature was kept isothermally at 50° C. for 5 minutes, and after the temperature was raised to 200° C., the temperature was kept isothermally for 30 minutes. After it was cooled to 50° C. and then stabilized, the temperature was raised to 600° C. at a rate of 10° C. / min. After stabilization, the temperature when the weight reduction rate was 1% was calculated based on the mass at 100° C.

[0219] 4. Haze

[0220] The haze was measured using a haze meter (model name: NDH7000, Nippon Denshoku) according to the measuring method of ASTM D1003.

[0221] 5. Transmittance

[0222] The transmittance (T) to light having a wavelength of 470 nm was measured using a UV-vis spectrometer (Agillent, UV 8453).

[0223] [Table 1]

[0224]

[0225] 6. Yellowness Index (YI)

[0226] In Examples and Comparative Examples, the yellowness index after forming each layer was measured using a colorimeter (Color-Eye 7000A by GretagMacbeth), and is shown in Table 2 below.

[0227] Specifically, the yellowness index after forming the first polyimide resin layer on the glass substrate was measured and represented as "first PI resin layer" in Table 2 below.

[0228] The yellowness index after forming the first inorganic material layer on the first polyimide resin layer by the plasma chemical vapor deposition method was measured and represented as "first inorganic material layer" in Table 2 below.

[0229] The yellowness index after forming the second polyimide resin layer on the first inorganic material layer was measured and indicated as "second PI resin layer" in Table 2 below.

[0230] The yellowness index after forming the second inorganic material layer on the second polyimide resin layer by the plasma chemical vapor deposition method was measured and represented as "second inorganic material layer" in Table 2 below.

[0231] The yellowness index after a heat treatment step of increasing the temperature to 430°C for 2 hours, undergoing an isothermal process at 430°C for 2 hours, and then cooling to 50°C for 2 hours was measured and indicated as "post-heat treatment" in Table 2 below.

[0232] The change (%) in YI was calculated according to the following equation and is shown in Table 2 below.

[0233] [Equation]

[0234] Change in YI (%) = Yellowness index after the heat treatment step of increasing the temperature to 430°C for 2 hours, undergoing an isothermal process at 430°C for 2 hours, and then cooling to 50°C for 2 hours / Yellowness index before the heat treatment step of increasing the temperature to 430°C for 2 hours, undergoing an isothermal process at 430°C for 2 hours, and then cooling to 50°C for 2 hours * 100

[0235] 7. Evaluation of membrane separation phenomena

[0236] The substrates for a display device or a flexible display device obtained in Examples and Comparative Examples were heated at a rate of 3° C. / min and subjected to isothermal treatment at 430° C. for 2 hours, and then visually evaluated whether a film separation phenomenon occurred according to the following criteria.

[0237] ○: Membrane separation occurs

[0238] Х: No membrane separation occurred

[0239] [Table 2]

[0240]

[0241] As shown in Tables 1 to 2 above, it was determined that the substrate for a display device or a flexible display device of the embodiment has a long half-life and high resistance characteristics while exhibiting excellent heat resistance and optical characteristics. In particular, it was determined that even after undergoing a high temperature process of 430° C. or higher, optical characteristics such as yellowness index and transmittance did not change significantly, and the morphology of a single layer or the morphology of a laminated structure was not greatly deformed.

[0242] On the other hand, it was determined that the substrate for a display device or a flexible display device of the comparative example was poor in optical properties and heat resistance compared with the embodiment, and in particular, after high-temperature treatment, the yellowness index greatly increased or film separation occurred, which caused defects in the internal laminated structure.

[0243] In addition, it was determined that in the substrate for a display device or a flexible display device of Reference Example 1, since the second polyimide resin layer was directly formed on the first polyimide resin layer without an inorganic material layer, the yellowness index was equivalent to the yellowness index of the embodiment, but the gas barrier properties and moisture permeability properties were low, and air and moisture were not blocked, and the device stability was deteriorated, which was not suitable as a substrate for a display device or a flexible display device.

Claims

1. A substrate for a display device, comprising: a first polyimide resin layer having a Td 1% of 570° C. or more and a yellowness index of 25 or more and 60 or less; A second polyimide resin layer having a yellowness index less than 25; a first inorganic material layer positioned between the first polyimide resin layer and the second polyimide resin layer and having a thickness of 100 nm or more and 700 nm or less; and a second inorganic material layer formed on the second polyimide resin layer and having a thickness of 100 nm or more and 500 nm or less, wherein the yellowness index of each of the first polyimide resin layer and the second polyimide resin layer is measured based on a thickness of 10±1 μm, Wherein, the Td 1% is the temperature when the weight reduction rate of the polyimide resin layer is 1% measured under the following conditions: isothermal maintenance at 50°C for 5 minutes, and after the temperature is increased to 200°C, isothermal maintenance for 30 minutes, after cooling to 50°C and then stabilizing, the temperature is increased to 600°C at a rate of 10°C / min, and after stabilization, the temperature when the weight reduction rate is 1% is calculated based on the mass at 100°C.

2. The substrate for a display device according to claim 1, wherein: The yellowness index of the entire substrate for a display device or a flexible display device is 36 or less.

3. The substrate for a display device according to claim 1, wherein: For the entire substrate for a display device or a flexible display device, the yellowness index after a heat treatment step of raising the temperature to 430° C. for 2 hours, undergoing an isothermal process at 430° C. for 2 hours, and then cooling to 50° C. for 2 hours is 50 or less.

4. The substrate for a display device according to claim 3, wherein: The yellowness index after a heat treatment step of raising the temperature to 430°C for 2 hours, undergoing an isothermal process at 430°C for 2 hours, and then cooling to 50°C for 2 hours is 30 or more and 50 or less.

5. The substrate for a display device according to claim 3, wherein: Based on the initial yellowness index of the entire substrate for a display device or a flexible display device, the percentage of the yellowness index after a heat treatment step of raising the temperature to 430°C for 2 hours, undergoing an isothermal process at 430°C for 2 hours, and then cooling to 50°C for 2 hours is 130% or less.

6. The substrate for a display device according to claim 1, wherein: The thickness of the first polyimide resin layer is 1 μm to 10 μm, and The second polyimide resin layer has a thickness of 0.5 μm to 6 μm.

7. The substrate for a display device according to claim 1, wherein: The thickness of the first polyimide resin layer is 1 μm to 6 μm, and The second polyimide resin layer has a thickness of 6 μm to 15 μm.

8. The substrate for a display device according to claim 1, wherein: The Td 1% of the second polyimide resin layer is 500° C. or higher and 560° C. or lower.

9. The substrate for a display device according to claim 1, wherein: The first polyimide resin layer and the second polyimide resin layer each have: 50% or greater transmittance at a wavelength of 470nm, and 1.0% or less haze.

10. The substrate for a display device according to claim 1, wherein: The second polyimide resin layer includes a polyimide resin including a repeating unit derived from a diamine substituted with a fluorine-based functional group.

11. The substrate for a display device according to claim 1, wherein: The second polyimide resin layer includes a polyimide resin including a repeating unit represented by the following Chemical Formula 1: [Chemical formula 1] Wherein, in Chemical Formula 1, X1 is an aromatic tetravalent functional group, and Y1 is an aromatic divalent functional group in which at least one fluorine-based functional group is substituted.

12. The substrate for a display device according to claim 11, wherein: The second polyimide resin layer includes a polyimide resin further including a repeating unit represented by the following Chemical Formula 1-1: [Chemical formula 1-1] Among them, in chemical formula 1-1, X2 is an aromatic tetravalent functional group, and Y2 is an aromatic divalent functional group different from Y1 of Chemical Formula 1.

13. The substrate for a display device according to claim 11, wherein: The aromatic divalent functional group Y1 substituted with at least one fluorine-based functional group includes a functional group represented by the following Chemical Formula 3-1: [Chemical formula 3-1] Among them, in chemical formula 3-1, p is an integer of 0 or more and 5 or less.

14. The substrate for a display device according to claim 1, wherein: The first polyimide resin layer includes a polyimide resin including a repeating unit derived from a diamine not substituted with a fluorine-based functional group.

15. The substrate for a display device according to any one of claims 1 to 14, wherein: The display device is a flexible display device. 16 . A display device comprising the substrate for a display device according to claim 1 .

17. The display device according to claim 16, wherein: The display device is a flexible display device.

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