Eco-friendly polyimide-based film and manufacturing method therefor

Abstract

One embodiment of the present invention relates to an eco-friendly polyimide-based film not containing a perfluoroalkyl group, and provides a polyimide-based film comprising at least one from among an imide repeating unit and an amide repeating unit, wherein the imide repeating unit is formed by a reaction of a diamine compound and a dianhydride compound, the amide repeating unit is formed by a reaction of a diamine compound and a dicarbonyl compound, and the yellowness index after a light resistance test is 10.0 or less.

Description

Eco-friendly polyimide film and method for manufacturing the same

[0001] The present invention relates to an eco-friendly polyimide-based film that does not contain a perfluoroalkyl group and a method for manufacturing the same.

[0002] Polyimide resins possess characteristics such as high heat resistance, oxidation resistance, radiation resistance, low-temperature properties, and chemical resistance, making them widely used in electronic products, optical devices, semiconductors, automobiles, aircraft, and spacecraft. Additionally, polyimide films manufactured in film form are also used as cover windows for display devices.

[0003] Recently, research has been conducted to improve the optical properties of polyimide resins, and polyimide resins with excellent optical properties are being developed without significantly degrading mechanical and thermal properties.

[0004] Polyimide-based films possess excellent mechanical properties, but they exhibit a yellow color due to the charge-transfer complex (CT-Complex) effect. To prevent or minimize the yellowing of polyimide-based films, they are typically manufactured using fluorine-based raw materials.

[0005] Perfluorinated compound groups contained in fluorine-based raw materials, such as -CF2- or -CF3, have strong bonding forces and do not decompose easily, causing environmental pollution problems. Therefore, research is needed on a technology to manufacture polyimide-based films using raw materials that do not contain perfluorinated compound groups in order to prevent environmental pollution.

[0006] One embodiment of the present invention aims to provide a polyimide-based film that does not contain a perfluoroalkyl group.

[0007] One embodiment of the present invention aims to provide a technology for manufacturing a polyimide-based film using a monomer that does not contain a perfluoroalkyl group.

[0008] One embodiment of the present invention aims to provide a polyimide-based film having excellent mechanical properties and excellent optical properties, even when manufactured using a monomer that does not contain a perfluoroalkyl group.

[0009] One embodiment of the present invention aims to provide a polyimide-based film having low yellowness and high light transmittance, even when manufactured using a monomer that does not contain a perfluoroalkyl group.

[0010] To solve the above problem, one embodiment of the present invention provides a polyimide-based film comprising at least one of an imide repeating unit and an amide repeating unit, wherein the imide repeating unit is formed by the reaction of a diamine compound and a dianhydride compound, and the amide repeating unit is formed by the reaction of a diamine compound and a dicarbonyl compound, and the yellowness after a light resistance test is 10.0 or less.

[0011] Here, the lightfastness test is performed by irradiating the polyimide-based film with a Xenon lamp light source at an intensity of 1.1 W / m² for 145.5 hours under conditions of a temperature of 30℃ and a humidity of 55RH%.

[0012] The above diamine compound may include a compound represented by the following chemical formula 1.

[0013] [Chemical Formula 1]

[0014]

[0015] Here, R1 to R8 of the above chemical formula 1 each include at least one of hydrogen (H), a methyl group (-CH3), and an ethyl group (-CH2CH3).

[0016] Each of the above imide repeating unit and amide repeating unit may not include a perfluoroalkyl group.

[0017] At least one of R1 to R8 of the above chemical formula 1 may include a methyl group (-CH3).

[0018] At least one of R1 to R4 of the above chemical formula 1 includes a methyl group (-CH3), and at least one of R5 to R8 of the above chemical formula 1 may include a methyl group (-CH3).

[0019] The compound represented by the above chemical formula 1 may include at least one of the compounds represented by the following chemical formulas 2 to 4.

[0020] [Chemical Formula 2]

[0021]

[0022] [Chemical Formula 3]

[0023]

[0024] [Chemical Formula 4]

[0025]

[0026] The above dicarbonyl compound may include at least one of the compound represented by the following chemical formula 5 and the compound represented by the following chemical formula 6.

[0027] [Chemical Formula 5]

[0028]

[0029] [Chemical Formula 6]

[0030]

[0031] The above dianhydride compound may include a compound represented by the following chemical formula 7.

[0032] [Chemical Formula 7]

[0033]

[0034] Here, R9 to R12 of the above chemical formula 7 each include at least one of hydrogen (H), a methyl group (-CH3), and an ethyl group (-CH2CH3).

[0035] At least one of R9 to R12 of the above chemical formula 7 may include a methyl group (-CH3).

[0036] The compound represented by the above chemical formula 7 may include at least one of the compounds represented by the following chemical formulas 8 to 12.

[0037] [Chemical Formula 8]

[0038]

[0039] [Chemical Formula 9]

[0040]

[0041] [Chemical Formula 10]

[0042]

[0043] [Chemical Formula 11]

[0044]

[0045] [Chemical Formula 12]

[0046]

[0047] Based on the molar amount, the content of the dicarbonyl compound may be 10 mol% or more with respect to the total content of the dicarbonyl compound and the dianhydride compound.

[0048] According to one embodiment of the present invention, the polyimide-based film may include an antioxidant.

[0049] The above antioxidant may include at least one of a phenolic antioxidant, a phosphorus-based antioxidant, and an amine-based antioxidant.

[0050] The above amine-based antioxidant may include Hindered amine light stabilizers (HALS).

[0051] The above antioxidant may include at least one of the compounds represented by the following chemical formulas 13 to 15.

[0052] [Chemical Formula 13]

[0053]

[0054] [Chemical Formula 14]

[0055]

[0056] [Chemical Formula 15]

[0057]

[0058] According to one embodiment of the present invention, a polyimide-based film may include a UV absorber.

[0059] The above ultraviolet absorber may contain at least two nitrogen (N) elements.

[0060] The above ultraviolet absorber may include at least one of a benzylformamidine-based ultraviolet absorber, a triazine-based ultraviolet absorber, a benzotriazine-based ultraviolet absorber, and a triazole-based ultraviolet absorber.

[0061] The above ultraviolet absorber may include a compound represented by any one of the following chemical formulas 16 to 21.

[0062] [Chemical Formula 16]

[0063]

[0064] [Chemical Formula 17]

[0065]

[0066] [Chemical Formula 18]

[0067]

[0068] [Chemical Formula 19]

[0069]

[0070] [Chemical Formula 20]

[0071]

[0072] [Chemical Formula 21]

[0073]

[0074] According to one embodiment of the present invention, a polyimide-based film may have a yellowness of 5.0 or less based on a thickness of 50 μm.

[0075] According to one embodiment of the present invention, a polyimide-based film may have a static folding value of 170° or less based on a thickness of 50 μm.

[0076] Here, the static folding value refers to a value obtained by fitting and fixing the film onto a glass plate with a radius of curvature of 1.5 mm, placing it in a constant temperature and humidity chamber at 60°C and 90% humidity for 24 hours, taking it out, and then measuring the outer edge of the film with the fixed state released using a protractor.

[0077] According to one embodiment of the present invention, a polyimide-based film can be manufactured using a monomer that does not contain a perfluoroalkyl group, so environmental pollution can be prevented.

[0078] According to one embodiment of the present invention, an eco-friendly polyimide-based film that does not contain a perfluoroalkyl group can be manufactured.

[0079] A polyimide-based film according to one embodiment of the present invention does not contain perfluoroalkyl groups, so it has eco-friendly characteristics, while also having excellent mechanical properties and excellent optical properties.

[0080] FIG. 1 is a cross-sectional view schematically illustrating the measurement of static folding values ​​of a polyimide-based film according to one embodiment of the present invention.

[0081] FIG. 2 is a cross-sectional view of a part of a display device according to another embodiment of the present invention.

[0082] Figure 3 is an enlarged cross-sectional view of the "P" portion of Figure 2.

[0083] Embodiments of the present invention are described in detail below. However, the embodiments described below are presented for the purpose of facilitating a clear understanding of the present invention and are merely examples of embodiments of the present invention.

[0084] In describing the present invention, if it is determined that a detailed description of related known technology may unnecessarily obscure the essence of the present invention, such detailed description may be omitted.

[0085] Where terms such as "includes," "has," or "consists of" are used in this specification, other parts may be added unless the expression "only" is used. Where a component is expressed in the singular, it includes the plural unless specifically stated otherwise. Furthermore, in interpreting a component, it is interpreted to include a margin of error even without separate explicit description.

[0086] In the case of describing a positional relationship, for example, when the positional relationship between two parts is described using expressions such as 'on,' 'upper,' 'lower,' or 'next to,' one or more other parts may be located between the two parts unless expressions such as 'immediately' or 'directly' are used.

[0087] Spatially relative terms such as "below" or "beneath," "lower," "above," and "upper" may be used to facilitate the description of the relationship between one element or component and another, as illustrated in the drawings. Spatially relative terms should be understood as terms that include different orientations of the element during use or operation, in addition to the orientations illustrated in the drawings. For example, if an element illustrated in the drawings is flipped, an element described as "below" or "beneath" of another element may be placed "above" of that other element. Therefore, the exemplary term "below" may include both the lower and upper directions. Similarly, the exemplary terms "above" or "upper" may include both the upper and lower directions.

[0088] In the case of an explanation of a temporal relationship, for example, when the temporal sequence is explained using expressions such as 'after', 'following', 'next', or 'before', it may include cases where the sequence is not continuous unless expressions such as 'immediately' or 'directly' are used.

[0089] Although terms such as "first," "second," etc. are used to describe various components, these components are not limited by these terms. These terms are used merely to distinguish one component from another. Accordingly, the first component mentioned below may be the second component within the technical scope of the present invention.

[0090] The term “at least one” should be understood to include all combinations that can be presented from one or more related items. For example, the meaning of “at least one of the first item, the second item, and the third item” may mean not only the first item, the second item, or the third item individually, but also all combinations of items that can be presented from two or more of the first item, the second item, and the third item.

[0091] The features of each of the various embodiments of the present invention may be combined or combined with one another, either partially or wholly, and may technically enable various interlocking and operation. Each embodiment may be implemented independently of one another or may be implemented together in an associated relationship.

[0092] One embodiment of the present invention provides a polyimide-based film (100) that does not contain a perfluoroalkyl group.

[0093] A polyimide-based film (100) according to one embodiment of the present invention comprises at least one of an imide repeating unit and an amide repeating unit. The imide repeating unit may be formed by the reaction of a diamine compound and a dianhydride compound. The imide repeating unit does not include a perfluoroalkyl group. The amide repeating unit may be formed by the reaction of a diamine compound and a dicarbonyl compound. The amide repeating unit does not include a perfluoroalkyl group.

[0094] For example, a polyimide-based film (100) may be manufactured from monomer components comprising at least one of a diamine compound, a dianhydride compound, and a dicarbonyl compound. "Monomer components" may refer to all of the plurality of monomers used in the manufacture of the polyimide-based film. The monomer components may be in a mixed state of the plurality of monomers. However, the state of the monomer components is not limited to this, and the monomer components may remain in an unmixed state and then be sequentially mixed during the manufacturing process of the polyimide-based film.

[0095] A polyimide-based film (100) according to one embodiment of the present invention may include an imide repeating unit. The polyimide-based film (100) may include an amide repeating unit. The polyimide-based film (100) may include both an amide repeating unit and an imide repeating unit.

[0096] According to one embodiment of the present invention, the imide repeating unit does not contain a perfluoroalkyl group. The imide repeating unit can be formed by the reaction of a diamine compound and a dianhydride compound.

[0097] According to one embodiment of the present invention, the amide repeating unit does not include a perfluoroalkyl group. The amide repeating unit can be formed by the reaction of a diamine compound and a dicarbonyl compound.

[0098] According to one embodiment of the present invention, monomer components may include a diamine compound and a dicarbonyl compound. When monomer components include a diamine compound and a dicarbonyl compound, the polyimide-based film (100) may have a polyamide polymer structure having amide repeating units.

[0099] According to one embodiment of the present invention, the monomer components may further include a dianhydride compound in addition to the diamine compound and the dicarbonyl compound. When the monomer components further include a dianhydride compound in addition to the diamine compound and the dicarbonyl compound, the polyimide-imide film (100) may have a polyamide-imide copolymer structure having both an imide repeating unit and an amide repeating unit.

[0100] According to one embodiment of the present invention, monomer components may include a diamine compound and a dianhydride compound. When monomer components include a diamine compound and a dianhydride compound, the polyimide film (100) may have a polyimide polymer structure having imide repeating units.

[0101] A film containing imide repeating units may be referred to as a polyimide-based film (100). Additionally, a film containing both amide repeating units and imide repeating units may also be referred to as a polyimide-based film (100). Hereinafter, to avoid confusion, a film containing both amide repeating units and imide repeating units is referred to as a polyimide-based film.

[0102] A polyimide-based film (100) according to one embodiment of the present invention may include, for example, both an imide repeating unit and an amide repeating unit. Accordingly, a polyimide-based film (100) according to one embodiment of the present invention may have an amide-imide copolymer structure. The polyimide-based film (100) may be a polyamide film, a polyimide film, or a polyamide-imide film.

[0103] A polyimide-based film (100) according to one embodiment of the present invention does not contain perfluoroalkyl groups.

[0104] Perfluoroalkyl groups do not decompose easily due to their strong bonding force, so they can cause environmental pollution. A polyimide-based film (100) according to one embodiment of the present invention that does not contain perfluoroalkyl groups can be described as an eco-friendly film that can prevent environmental pollution.

[0105] The perfluoroalkyl group may include *-CF3 and *-CF2-*. Here, *- and -* are used to denote a bond or bonding position with another element, respectively.

[0106] A polyimide-based film (100) according to one embodiment of the present invention that does not contain perfluoroalkyl groups does not contain *-CF3 and *-CF2-*.

[0107] According to one embodiment of the present invention, the content of total organic fluorine (TOF) may be 50 ppm or less with respect to the total weight of the polyimide-based film. Here, organic fluorine may be an organic material containing a single bond of fluorine (F). A polyimide-based film (100) according to one embodiment of the present invention may contain 30 ppm or less of organic fluorine with respect to the total weight, may contain 10 ppm or less of organic fluorine, may contain 5 ppm or less of organic fluorine, may contain 1 ppm or less of organic fluorine, may contain 0.5 ppm or less of organic fluorine, and may contain 0.1 ppm or less of organic fluorine.

[0108] Additionally, a polyimide-based film (100) according to one embodiment of the present invention may not contain fluorine (F). Assuming that a trace amount of fluorine (F) may be unexpectedly included during the manufacturing process of the polyimide-based film, the polyimide-based film (100) according to one embodiment of the present invention may have a fluorine concentration of less than 0.01 ppm.

[0109] According to one embodiment of the present invention, an amide repeating unit is formed by the reaction of a diamine compound and a dicarbonyl compound, wherein the diamine compound does not contain a perfluoroalkyl group. Accordingly, the diamine compound used in the preparation of the amide repeating unit does not contain *-CF3 and *-CF2-*.

[0110] According to one embodiment of the present invention, the diamine compound may include a cyclic structure within its chemical formula.

[0111] As a result of the inventors' research, it was confirmed that a polyimide-based film (100) manufactured using a diamine compound having a cyclic or semi-aromatic ring structure among cyclic structures has low heat resistance and relatively weak mechanical properties, making it difficult to use as a window film for a display device. In particular, when a cyclic diamine compound is used, it was confirmed that problems such as the generation of salt or a decrease in the degree of polymerization occur during the polymerization process, making mass production difficult.

[0112] Accordingly, the inventors designed a polyimide-based film (100) with the main chain having a structure that is as flat as possible, taking into account the problems that arise when using alicyclic raw materials.

[0113] Accordingly, a diamine compound according to one embodiment of the present invention may have an aromatic ring. For example, a diamine compound according to one embodiment of the present invention may include a compound represented by the following chemical formula 1.

[0114] [Chemical Formula 1]

[0115]

[0116] Here, R1 to R8 of Chemical Formula 1 may each include any one of hydrogen (H), methyl group (-CH3), ethyl group (-CH2CH3), bromine (Br), and chlorine (Cl).

[0117] The compound represented by Chemical Formula 1 can also be considered a benzidine-based diamine.

[0118] When a compound represented by Chemical Formula 1 is used as a diamine compound, the main chain of the polymer constituting the polyimide film (100) may have a flat structure.

[0119] Meanwhile, it was confirmed that when the diamine compound does not have substituents, the rate of stacking between molecules is high, resulting in a high probability of charge-transfer complex (CT-Complex) effects, and consequently, yellow color is expressed in the film.

[0120] Accordingly, according to one embodiment of the present invention, R1 to R8 included in the compound represented by Formula 1 may each include hydrogen (H), a methyl group (-CH3), and an ethyl group (-CH2CH3). Specifically, at least one of R1 to R4 of Formula 1 may include either a methyl group (-CH3) or an ethyl group (-CH2CH3), and at least one of R5 to R8 of Formula 1 may include either a methyl group (-CH3) or an ethyl group (-CH2CH3). More specifically, at least one of R1 to R4 of Formula 1 may include a methyl group (-CH3), and at least one of R5 to R8 of Formula 1 may include a methyl group (-CH3).

[0121] According to one embodiment of the present invention, the compound represented by Chemical Formula 1 may include at least one of the compound represented by Chemical Formula 2 (mTD), the compound represented by Chemical Formula 3 (oTD), and the compound represented by Chemical Formula 4 (TMB).

[0122] [Chemical Formula 2]

[0123]

[0124] [Chemical Formula 3]

[0125]

[0126] [Chemical Formula 4]

[0127]

[0128] According to one embodiment of the present invention, for example, any one of 2,2'-dimethylbenzidine (2,2'-Dimethylbenzidine, m-Tolidine) (mTD), 3,3'-dimethylbenzidine (3,3'-Dimethylbenzidine, o-Tolidine) (oTD) or 3,3',5,5'-tetramethylbenzidine (3,3',5,5'-Tetramethylbenzidine) (TMB) may be used as the diamine compound.

[0129] In addition, the diamine compound may include an atom or group of atoms with high electronegativity as a substituent. According to one embodiment of the present invention, the substituent may include an atom or group of atoms having an electronegativity of 2.7 or higher. Examples of atoms having an electronegativity of 2.7 or higher include chlorine (Cl), bromine (Br), etc.

[0130] According to one embodiment of the present invention, at least one of R1 to R8 included in the compound represented by Formula 1 may include either bromine (Br) or chlorine (Cl). More specifically, at least one of R1 to R4 of Formula 1 may include either bromine (Br) or chlorine (Cl), and at least one of R5 to R8 of Formula 1 may include either bromine (Br) or chlorine (Cl).

[0131] According to one embodiment of the present invention, the amide repeating unit does not contain a perfluoroalkyl group, and the dicarbonyl compound applied to the amide repeating unit also does not contain a perfluoroalkyl group. The dicarbonyl compound may not contain fluorine.

[0132] The dicarbonyl compound applied for the formation of amide repeating units may contain chlorine (Cl). Dicarbonyl dichloride compounds may be used as dicarbonyl compounds. The dicarbonyl compound may include aromatic dicarbonyl compounds and aliphatic dicarbonyl compounds.

[0133] According to one embodiment of the present invention, the dicarbonyl compound may have an aromatic ring.

[0134] Dicarbonyl dichloride compounds exhibit a high degree of polymerization with diamine compounds containing compounds represented by Chemical Formula 1, for example, benzidine-based diamines, and the polymer may have excellent mechanical properties. Dicarbonyl dichloride compounds may be compounds having a flat structure or compounds having a kink group.

[0135] According to one embodiment of the present invention, for example, 4,4'-Oxybis(benzoyl chloride) (DEDC) or isophthaloyl chloride (IPC) may be used as the dicarbonyl compound.

[0136] More specifically, the dicarbonyl compound may include at least one of the compound represented by the following chemical formula 5 (DEDC) and the compound represented by the following chemical formula 6 (IPC).

[0137] [Chemical Formula 5]

[0138]

[0139] [Chemical Formula 6]

[0140]

[0141] According to one embodiment of the present invention, an imide repeating unit is formed by the reaction of a diamine compound and a dianhydride compound, wherein the diamine compound and the dianhydride compound do not contain perfluoroalkyl groups. Accordingly, the diamine compound and the dianhydride compound used in the preparation of the imide repeating unit do not contain *-CF3 and *-CF2-*, respectively.

[0142] According to one embodiment of the present invention, together with the diamine compound, the dianhydride compound is also designed to have a main chain structure that is as flat as possible.

[0143] According to one embodiment of the present invention, the dianhydride compound may include a compound represented by the following chemical formula 7.

[0144] [Chemical Formula 7]

[0145]

[0146] Here, R9 to R12 of Chemical Formula 7 may each include any one of hydrogen (H), a methyl group (-CH3) and an ethyl group (-CH2CH3).

[0147] According to one embodiment of the present invention, a dianhydride compound may include a cyclic structure within its formula, such as the compound represented by Formula 7. The compound represented by Formula 7 may also be considered a cycloaliphatic dianhydride compound.

[0148] A cycloaliphatic dianhydride compound that does not significantly disturb the flat structure of the polymer main chain can be used. When a dianhydride compound that does not significantly disturb the flat structure of the polymer main chain is used, optical properties can be improved without degrading the mechanical properties of the polyimide film. For example, a polyimide film (100) prepared using a dianhydride compound containing a compound represented by Chemical Formula 7 can have improved light transmittance and improved yellowness.

[0149] According to one embodiment of the present invention, in the manufacture of a polyimide-based film (100), when a diamine compound comprising a compound represented by Formula 1 is used as the diamine compound, a cycloaliphatic dianhydride compound that does not contain substituents, for example, a compound in which R9 to R12 of Formula 5 all contain hydrogen (H), is used as the reaction pair of the diamine compound to manufacture the polyimide film (100), the mechanical properties are improved, but the processability may be somewhat reduced.

[0150] According to one embodiment of the present invention, in the manufacture of a polyimide-based film (100), when a diamine compound comprising a compound represented by Formula 1 is used as the diamine compound, and a cycloaliphatic dianhydride compound comprising a substituent is used as the reaction pair of the diamine compound, for example, a compound in which at least one of R9 to R12 of Formula 5 comprises either a methyl group (-CH3) or an ethyl group (-CH2CH3), the polyimide-based film (100) is manufactured, and the mechanical properties are the same or similar compared to the case where a cycloaliphatic dianhydride compound not comprising a substituent is used, and the processability can be improved.

[0151] According to one embodiment of the present invention, the dianhydride compound may include at least one of the compounds represented by the following chemical formulas 8 to 12.

[0152] [Chemical Formula 8]

[0153]

[0154] [Chemical Formula 9]

[0155]

[0156] [Chemical Formula 10]

[0157]

[0158] [Chemical Formula 11]

[0159]

[0160] [Chemical Formula 12]

[0161]

[0162] According to one embodiment of the present invention, in order for the polyimide-based film (100) to have excellent mechanical properties and processability, a cycloaliphatic dianhydride compound having a substituent as a dianhydride compound and a cycloaliphatic dianhydride compound not having a substituent may be used together.

[0163] According to one embodiment of the present invention, the imide repeating unit does not contain a perfluoroalkyl group, and the dianhydride compound applied to the imide repeating unit also does not contain a perfluoroalkyl group. The dianhydride compound may not contain fluorine.

[0164] According to one embodiment of the present invention, when a polyimide-based film (100) includes an amide repeating unit, the molar ratio of a dicarbonyl compound and a dianhydride compound is adjusted to a predetermined range so that the solubility of the resin does not change significantly even during a chemical imidization process.

[0165] A polyimide-based film (100) according to one embodiment of the present invention may include 10% or more of amide repeating units based on the total number of repeating units.

[0166] To this end, the monomer for manufacturing the polyimide-based film (100) can be adjusted so that the content of the dicarbonyl compound is 10 mol% or more with respect to the total content of the dicarbonyl compound and the dianhydride compound on a molar basis.

[0167] More specifically, with respect to the total number of moles of the dicarbonyl compound and the dianhydride compound, the dicarbonyl compound may have a content in the range of 10 mole% to 100 mole%, and the dianhydride compound may have a content in the range of 0 mole% to 90 mole%.

[0168] A polyimide-based film (100) according to one embodiment of the present invention may include an antioxidant.

[0169] Antioxidants include, for example, primary antioxidants and secondary antioxidants. Primary antioxidants stabilize the polymer resin by reacting with radicals generated within the polymer resin, while secondary antioxidants stabilize the polymer resin by removing oxygen atoms from the polymer resin that has already been oxidized.

[0170] Primary antioxidants and secondary antioxidants may be used individually or mixed depending on the required conditions.

[0171] According to one embodiment of the present invention, as a diamine compound and a dianhydride compound containing, for example, a methyl group as a substituent are used in the manufacture of a polyimide-based film (100), oxidation by radicals may occur through the methyl group as a substituent. Therefore, among the primary antioxidant and the secondary antioxidant, using the primary antioxidant may be more effective.

[0172] According to one embodiment of the present invention, the antioxidant may include at least one of a phenolic antioxidant, a phosphorus-based antioxidant, and an amine-based antioxidant.

[0173] According to one embodiment of the present invention, the polyimide-based film (100) may include a phenolic antioxidant. More specifically, the polyimide-based film (100) may include a phenolic primary antioxidant.

[0174] If the polyimide film (100) includes a phenolic primary antioxidant as an antioxidant, the yellowness of the polyimide film (100) can be improved.

[0175] According to one embodiment of the present invention, the polyimide-based film (100) may include a phosphorus-based antioxidant. More specifically, the polyimide-based film (100) may include a phosphorus-based secondary antioxidant.

[0176] If the polyimide-based film (100) includes a phosphorus-based secondary antioxidant as an antioxidant, the thermal stability of the polyimide-based film (100) can be improved.

[0177] According to one embodiment of the present invention, the polyimide-based film (100) may include an amine-based antioxidant. The amine-based antioxidant may include hindered amine light stabilizers (HALS).

[0178] If the polyimide film (100) contains Hals as an antioxidant, the yellowness of the polyimide film (100) can be improved.

[0179] According to one embodiment of the present invention, a polyimide-based film (100) may include at least one of the compounds represented by the following chemical formulas 13 to 15 as an antioxidant.

[0180] [Chemical Formula 13]

[0181]

[0182] [Chemical Formula 14]

[0183]

[0184] [Chemical Formula 15]

[0185]

[0186] A polyimide-based film (100) according to one embodiment of the present invention may contain 0.01 to 1 weight part of an antioxidant with respect to the total amount of polyimide-based resin.

[0187] If the polyimide film (100) contains an excess amount of an antioxidant exceeding 1 weight part relative to the total amount of polyimide resin, light resistance may be reduced and heat resistance may be reduced.

[0188] More specifically, a polyimide-based film (100) according to one embodiment of the present invention may contain 0.01 to 0.5 parts by weight of an antioxidant with respect to the total amount of polyimide-based resin.

[0189] According to one embodiment of the present invention, the polyimide-based film (100) may include a UV absorber.

[0190] As a UV absorber, at least one of a UV A (UVA) absorber that absorbs ultraviolet rays with a wavelength of 320 nm to 400 nm and a UV B (UVB) absorber that absorbs ultraviolet rays with a wavelength of 290 nm to 320 nm may be used.

[0191] According to one embodiment of the present invention, the ultraviolet absorber may include at least two nitrogen (N) elements.

[0192] In one embodiment of the present invention, when a polyimide-based film (100) designed such that the main chain of the polymer resin has a structure that is as flat as possible includes a UV absorber containing at least two nitrogen (N) elements, the compatibility with the polymer resin is excellent, so there may be no or almost no degradation of the optical properties of the film. In addition, the change in yellowness after a light resistance test may be improved, and the folding properties of the film may be improved by preventing moisture penetration into the film.

[0193] According to one embodiment of the present invention, the ultraviolet absorber included in the polyimide-based film (100) may include at least one of a benzylformamidine-based ultraviolet absorber, a triazine-based ultraviolet absorber, a benzotriazine-based ultraviolet absorber, and a triazole-based ultraviolet absorber. More specifically, the ultraviolet absorber included in the polyimide-based film (100) may include a benzotriazine-based ultraviolet absorber.

[0194] According to one embodiment of the present invention, the ultraviolet absorber may include at least one of the compounds represented by the following chemical formulas 16 to 21.

[0195] [Chemical Formula 16]

[0196]

[0197] [Chemical Formula 17]

[0198]

[0199] [Chemical Formula 18]

[0200]

[0201] [Chemical Formula 19]

[0202]

[0203] [Chemical Formula 20]

[0204]

[0205] [Chemical Formula 21]

[0206]

[0207] A polyimide-based film (100) according to one embodiment of the present invention may contain 1 to 10 parts by weight of a UV absorber with respect to the total amount of polyimide-based resin.

[0208] If the polyimide film (100) contains more than 10 parts by weight of an ultraviolet absorber relative to the total amount of polyimide resin, the initial yellowness of the polyimide film (100) may increase, and the brittleness of the film may increase, which may degrade static folding characteristics.

[0209] More specifically, a polyimide-based film (100) according to one embodiment of the present invention may include 2 to 8 parts by weight of a UV absorber with respect to the total amount of polyimide-based resin.

[0210] A polyimide-based film (100) according to one embodiment of the present invention may further include an additive. For example, at least one of microparticles, nanoparticles, a light stabilizer, a polymerization initiator, a leveling agent, and a bluening agent may be used.

[0211] In order to improve the light transmittance or friction coefficient of the polyimide film (100), microparticles having a particle size in the micrometer range or nanoparticles having a particle size in the nanometer range may be used. For example, silicon oxide, metal oxide, etc. may be used as microparticles or nanoparticles.

[0212] A polyimide-based film (100) according to one embodiment of the present invention may include silica particles. For example, silica particles having a particle size in the micrometer range may be used. Alternatively, silica particles having a particle size in the nanometer range may be used.

[0213] More specifically, spherical silica particles with an average particle size of 10 to 15 nm can be used as silica particles.

[0214] According to one embodiment of the present invention, silica particles may have a repeating unit of any one of the following chemical formulas 22 to 27.

[0215] [Chemical Formula 22]

[0216]

[0217] [Chemical Formula 23]

[0218]

[0219] [Chemical Formula 24]

[0220]

[0221] [Chemical Formula 25]

[0222]

[0223] [Chemical Formula 26]

[0224]

[0225] [Chemical Formula 27]

[0226]

[0227] A polyimide-based film (100) according to one embodiment of the present invention containing silica particles may, for example, have excellent light transmittance. The silica particles may, for example, have a content of 1 to 50 parts by weight based on 100 parts by weight of a polymer component applied to the polyimide-based film (100).

[0228] A bluing agent may be used to improve the yellowness of the polyimide-based film (100). The bluing agent may absorb yellow light. A dye-type bluing agent or a pigment-type bluing agent may be used.

[0229] A polyimide-based film (100) according to one embodiment of the present invention may have a yellowness of 10.0 or less after a light resistance test.

[0230] Here, the lightfastness test is performed by irradiating the polyimide-based film with a Xenon lamp light source at an intensity of 1.1 W / m² for 145.5 hours under conditions of a temperature of 30℃ and a humidity of 55RH%.

[0231] A polyimide-based film (100) according to one embodiment of the present invention can have excellent light resistance by using a dianhydride compound containing a compound represented by Chemical Formula 7, thereby suppressing or reducing the occurrence of a charge transfer complex (CT-Complex) effect. In addition, the polyimide-based film (100) according to one embodiment of the present invention can have improved light resistance by being designed to contain a certain amount of a UV absorber. Accordingly, the polyimide-based film (100) according to one embodiment of the present invention can have a yellowness of 10.0 or less even after a light resistance test.

[0232] If the yellowness of the polyimide-based film (100) exceeds 10.0 after a light resistance test, it may be difficult to apply it as a cover window for a flexible display device.

[0233] A polyimide-based film (100) according to one embodiment of the present invention may have a static folding value of 170° or less based on a thickness of 50 μm.

[0234] Here, the static folding value refers to a value that quantitatively indicates the degree to which the film returns to its original flat state when the fixed state is released after the film has been fixed in a folded state to a predetermined degree and exposed to a high-temperature and high-humidity environment for a long period of time.

[0235] FIG. 1 is a cross-sectional view schematically illustrating the measurement of static folding values ​​of a polyimide-based film (100) according to one embodiment of the present invention.

[0236] According to one embodiment of the present invention, a static folding value is obtained by using a film sample of size 3 cm X 7 cm, fitting it onto a glass plate to have a radius of curvature of 1.5 mm, placing it in a constant temperature and humidity chamber at a temperature of 60°C and a humidity of 90% for 24 hours, and then taking it out. Then, to check the degree of unfolding of the film, the film with the fixed state released is placed on a flat table (310) as shown in FIG. 1, for example, and the outer angle (θ) of the film is measured using a protractor (320).

[0237] According to one embodiment of the present invention, the static folding value measures the outer edge (θ) of the film as shown in FIG. 1, so the smaller the value, the more it means that it has been restored to its original flat state.

[0238] A polyimide-based film (100) according to one embodiment of the present invention can have excellent flexibility and resilience as it is designed so that the main chain has a structure that is as flat as possible. In addition, a polyimide-based film (100) according to one embodiment of the present invention can have excellent heat resistance and environmental resistance as it includes, for example, a phenolic primary antioxidant and a benzotriazine-based ultraviolet absorber. Accordingly, a polyimide-based film (100) according to one embodiment of the present invention can have an excellent static folding value of 170° or less.

[0239] If the static folding value of the polyimide-based film (100) exceeds 170°, it may be difficult to apply it as a cover window of a flexible display device.

[0240] A polyimide-based film (100) according to one embodiment of the present invention may have a yellowness of 5.0 or less based on a thickness of 50 μm.

[0241] According to one embodiment of the present invention, the polyimide-based film (100) includes a diamine compound and a dianhydride compound containing substituents, so that the stacking phenomenon between molecules or polymer chains is less likely to occur and the polymer main chains can have an asymmetric structure, so that it can have a low yellowness even without including perfluoroalkyl groups.

[0242] Accordingly, the polyimide-based film (100) according to one embodiment of the present invention has excellent transparency and can be easily applied as a cover window or protective film of a display device.

[0243] The yellowness of the polyimide film (100) can be measured by a spectrophotometer according to the standard ASTM E313. For example, a KONICA MINOLTA CM-3700D can be used as a spectrophotometer.

[0244] If the yellowness (YI) of the polyimide film (100) exceeds 5.0, the polyimide film (100) may have an excessively yellow tint and may lack visibility, making it difficult to apply to a display device.

[0245] A polyimide-based film (100) according to one embodiment of the present invention may have a light transmittance of 85% or more at a wavelength of 380 to 780 nm.

[0246] The light transmittance of the polyimide-based film (100) can be obtained by measuring the average light transmittance in the wavelength range of 380 to 780 nm using a spectrophotometer according to the standard ASTM E313. For example, the CM-3700D from KONICA MINOLTA can be used as the spectrophotometer.

[0247] If the light transmittance of the polyimide film (100) is less than 85%, it may be difficult to apply it to a display device due to insufficient visibility.

[0248] A polyimide-based film (100) according to one embodiment of the present invention may have a haze of 0.8% or less based on a thickness of 50 μm.

[0249] The haze of the polyimide film (100) can be measured by a haze meter according to the standard ASTM D1003. For example, the HM-150 from MURAKAMI can be used as the haze meter.

[0250] If the haze of the polyimide film (100) exceeds 0.8%, it may be difficult to apply it to a display device due to insufficient visibility.

[0251] A polyimide-based film (100) according to one embodiment of the present invention may have a modulus (Young's modulus) of 4.0 GPa or more based on a thickness of 50 μm.

[0252] The modulus of the polyimide film (100) can be measured using a universal tensile testing machine according to the standard ASTM D885. For example, the MODEL 5967 from Instron can be used as the universal tensile testing machine.

[0253] If the modulus of the polyimide film (100) is less than 4.0 GPa, deformation due to external force may occur.

[0254] A polyimide-based film (100) according to one embodiment of the present invention may have an elongation of 10% or more based on a thickness of 50 μm.

[0255] The elongation at break of the polyimide film (100) can be measured using a universal tensile testing machine according to the standard ASTM D885. For example, the MODEL 5967 from Instron can be used as the universal tensile testing machine.

[0256] If the elongation at break of the polyimide-based film (100) is less than 10%, it may have low folding performance due to low stress absorption ability, making it difficult to apply to a foldable display device.

[0257] A polyimide-based film (100) according to one embodiment of the present invention may have a thickness sufficient to protect a display panel. For example, the polyimide-based film (100) may have a thickness of 10 to 100 μm. More specifically, the polyimide-based film (100) may have a thickness of 30 to 80 μm, a thickness of 40 to 60 μm, or a thickness of 50 μm.

[0258] Hereinafter, with reference to FIGS. 2 and FIGS. 3, a display device (200) using a polyimide-based film (100) according to one embodiment of the present invention will be described.

[0259] FIG. 2 is a cross-sectional view of a part of a display device (200) according to another embodiment of the present invention, and FIG. 3 is an enlarged cross-sectional view of the "P" portion of FIG. 2.

[0260] Referring to FIG. 2, a display device (200) according to another embodiment of the present invention includes a display panel (501) and a polyimide-based film (100) on the display panel (501).

[0261] Referring to FIGS. 2 and 3, a display panel (501) comprises a substrate (510), a thin-film transistor (TFT) on the substrate (510), and an organic light-emitting element (570) connected to the thin-film transistor (TFT). The organic light-emitting element (570) comprises a first electrode (571), an organic light-emitting layer (572) on the first electrode (571), and a second electrode (573) on the organic light-emitting layer (572). The display device (200) disclosed in FIGS. 2 and 3 is an organic light-emitting display device.

[0262] The substrate (510) may be made of glass or plastic. Specifically, the substrate (510) may be made of plastic such as polyimide resin. Although not illustrated, a buffer layer may be placed on the substrate (510).

[0263] A thin-film transistor (TFT) is placed on a substrate (510). The thin-film transistor (TFT) includes a semiconductor layer (520), a gate electrode (530) that is insulated from the semiconductor layer (520) and overlaps with at least a portion of the semiconductor layer (520), a source electrode (541) connected to the semiconductor layer (520), and a drain electrode (542) that is spaced apart from the source electrode (541) and connected to the semiconductor layer (520).

[0264] Referring to FIG. 3, a gate insulating film (535) is disposed between the gate electrode (530) and the semiconductor layer (520). An interlayer insulating film (551) is disposed on the gate electrode (530), and a source electrode (541) and a source electrode (541) can be disposed on the interlayer insulating film (551).

[0265] A flattening film (552) is placed on a thin film transistor (TFT) to flatten the top of the thin film transistor (TFT).

[0266] The first electrode (571) is placed on the planarization film (552). The first electrode (571) is connected to a thin-film transistor (TFT) through a contact hole provided in the planarization film (552).

[0267] The bank layer (580) is disposed on a part of the first electrode (571) and on the planarization film (552) to define a pixel area or a light-emitting area. For example, the bank layer (580) may be disposed in a matrix structure in the boundary area between a plurality of pixels, so that the pixel area can be defined by the bank layer (580).

[0268] The organic light-emitting layer (572) is disposed on the first electrode (571). The organic light-emitting layer (572) may also be disposed on the bank layer (580). The organic light-emitting layer (572) may include a single light-emitting layer or two or more light-emitting layers stacked vertically. Light having any one of red, green, and blue colors may be emitted from the organic light-emitting layer (572), and white light may also be emitted.

[0269] The second electrode (573) is placed on the organic light-emitting layer (572).

[0270] An organic light-emitting device (570) can be formed by stacking a first electrode (571), an organic light-emitting layer (572), and a second electrode (573).

[0271] Although not illustrated, when the organic light-emitting layer (572) emits white light, individual pixels may include a color filter for filtering the white light emitted from the organic light-emitting layer (572) by wavelength. The color filter is formed on the path of the light.

[0272] A thin film encapsulation layer (590) may be disposed on the second electrode (573). The thin film encapsulation layer (590) may include at least one organic film and at least one inorganic film, and at least one organic film and at least one inorganic film may be disposed alternately.

[0273] A polyimide-based film (100) is placed on a display panel (501) having the laminated structure described above.

[0274] Hereinafter, a method for manufacturing a polyimide-based film (100) according to one embodiment of the present invention will be described in detail.

[0275] A method for manufacturing a polyimide-based film (100) according to one embodiment of the present invention comprises the steps of: preparing a liquid resin composition using monomer components including a diamine compound, a dianhydride compound, and a dicarbonyl compound; molding the liquid resin composition to produce a gel-state film; and drying the gel-state film.

[0276] To manufacture a polyimide-based film (100), first, monomer components including a diamine compound, a dianhydride compound, and a dicarbonyl compound are polymerized.

[0277] A first solvent may be used for the solution polymerization of monomer components. Specifically, monomer components may be reacted in the presence of the first solvent to prepare a first polymer solution. An organic solvent may be used as the first solvent for solution polymerization.

[0278] There are no specific restrictions on the type of the first solvent. As the first solvent, for example, at least one solvent selected from m-cresol, N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), dimethylformamide (DMF), diethylformamide (DEF), dimethylacetamide (DMAc), diethylacetamide (DEAc), acetone, ethyl acetate, propylene glycol monomethyl ether (PGME), and propylene glycol monomethyl ether acetate (PGME). In addition, low-boiling point solvents such as tetrahydrofuran (THF) and chloroform, or low-absorbency solvents such as γ-butyrolactone, may be used as the first solvent. Depending on the purpose, the first solvent may be used alone or as a mixture of two or more types.

[0279] There is no special limitation on the content of the first solvent. The first solvent may have a content of 50 to 95 weight percent relative to the total weight of the first polymer solution. The first solvent may also have a content of 70 to 90 weight percent relative to the total weight of the first polymer solution.

[0280] The first polymer solution may include a polyamic acid solution. In this case, there are no special restrictions on the reaction conditions. The reaction temperature may be adjusted, for example, to a range of -10 to 80°C, and the reaction time may be adjusted to 2 to 48 hours. The step of preparing the first polymer solution may be carried out in an inert gas atmosphere such as argon or nitrogen.

[0281] Next, an imidization process for the first polymer solution may be carried out. At this time, the polyamic acid contained in the first polymer solution may be imidized.

[0282] For imidation, thermal imidation, chemical imidation, or a combination of thermal imidation and chemical imidation may be applied.

[0283] According to one embodiment of the present invention, a chemical imidation method may be applied. The chemical imidation method is a method of applying a dehydrating agent, such as acetic anhydride, and an imidation catalyst, such as isoquinoline, β-picoline, pyridine, or tertiary amine, to a first polymer solution.

[0284] Chemical imidation may be combined with thermal imidation.

[0285] When the thermal imidation method and the chemical imidation method are used in combination, a dehydrating agent and an imidation catalyst are added to the first polymer solution and heated at 20 to 180°C for 1 to 12 hours to proceed with imidation.

[0286] Next, a second solvent is added to the first polymer solution, and the solution is filtered and dried to produce a polymer solid.

[0287] The second solvent is used to obtain a solid component of the polyimide-based resin. Accordingly, a solvent that does not dissolve the polyamic acid contained in the first polymer solution may be used as the second solvent, and a solid component of the polyimide-based polymer may be precipitated due to the difference in solubility. A solvent with lower polarity than the first solvent may be used as the second solvent. As the second solvent, for example, one or more selected from water, alcohols, ethers, and ketones may be used.

[0288] There is no special limitation on the content of the second solvent. A second solvent may be used in an amount of 5 to 20 times the weight of the polyamic acid contained in the first polymer solution.

[0289] The conditions for filtering and drying the obtained polymer solid are determined by considering the boiling points of the second solvent and the first solvent remaining in the polymer solid. For example, the polymer solid can be dried at a temperature of 50 to 150°C for 2 to 24 hours.

[0290] Next, the polymer solid is dissolved in a third solvent to prepare a liquid resin composition. The liquid resin composition may also be referred to as a polyimide-based resin composition.

[0291] According to one embodiment of the present invention, the third solvent may be the same as the first solvent. Accordingly, as the third solvent, for example, at least one selected from m-cresol, N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), dimethylformamide (DMF), diethylformamide (DEF), dimethylacetamide (DMAc), diethylacetamide (DEAc), acetone, ethyl acetate, propylene glycol monomethyl ether (PGME), and propylene glycol monomethyl ether acetate (PGME) may be used.

[0292] The liquid resin composition prepared in this manner may have a viscosity of 100 to 300,000 cPs. If the viscosity of the liquid resin composition is less than 100 cPs, it may be difficult to form the liquid resin composition into a film by casting, and due to the low molecular weight, it may be difficult to peel the film formed by casting from the casting substrate. On the other hand, if the viscosity of the liquid resin composition exceeds 300,000 cPs, the pressure applied during the casting process increases due to the high viscosity, which may be disadvantageous in terms of the process.

[0293] More specifically, the liquid resin composition may have a viscosity of 1,000 to 250,000 cPs. When the liquid resin composition has a viscosity of 1,000 to 250,000 cPs, it is easy to cast the liquid resin composition to form a film, and drying is also easy. For example, when the viscosity of the liquid resin composition is 1,000 cPs or higher, there is no difficulty in casting the liquid resin composition to form a film, and the film formed by casting can be peeled off from the casting substrate without difficulty. In addition, when the viscosity of the liquid resin composition is 250,000 cPs or lower, the casting process can proceed without the pressure for casting the liquid resin composition increasing beyond what is necessary.

[0294] According to one embodiment of the present invention, the liquid resin composition may have a viscosity of 1,000 to 30,000 cPs.

[0295] According to one embodiment of the present invention, the content of solids included in the liquid resin composition can be adjusted to a range of 5 to 30 weight percent with respect to the total weight of the liquid resin composition.

[0296] Next, a gel-state film is prepared using a liquid resin composition. The gel-state film may be referred to as an uncured polyimide-based film. According to one embodiment of the present invention, a gel-state film refers to a film in a state where curing has not been completed. Even if partial curing has occurred, if the curing is not completed, it is referred to as a gel-state film or an uncured polyimide-based film.

[0297] A casting method may be applied to manufacture a gel-state film. Specifically, the step of manufacturing a gel-state film includes the step of casting a liquid resin composition onto a support.

[0298] There are no special restrictions on the casting method, and casting methods known in the art may be applied. A gel-state film is produced by casting.

[0299] Glass plates, aluminum substrates, circulating stainless steel belts, stainless steel drums, or heat-resistant polymer films can be used as supports.

[0300] Next, the gel-state film can be dried and heat-treated to produce a polyimide-based film (100).

[0301] Drying can be performed, for example, in a temperature range of 50 to 150°C. Drying may include primary drying and secondary drying.

[0302] Heat treatment may be performed on the gel-state film after drying. A known thermosetting process may be applied as the heat treatment. For example, the gel-state film may be heat-treated at a temperature of 100 to 500°C for 1 minute to 1 hour. Through this heat treatment, the gel-state film is thermosetting to complete a polyimide-based film. The heat treatment step is also referred to as the thermosetting step.

[0303] The heat treatment step may be performed on a support or on a separate heat treatment support. For example, after drying, the gel-state film may be separated from the support, fixed to a support for heat treatment, and then the heat treatment may proceed.

[0304] According to one embodiment of the present invention, heat treatment may be performed while a constant tension is applied to a polyimide-based film. Residual stress inside the polyimide-based film can be removed by the heat treatment.

[0305] Drying and heat treatment may be performed simultaneously.

[0306] The present invention will be described in more detail below with reference to specific embodiments. However, the scope of the present invention is not limited by the following embodiments.

[0307] <Example 1>

[0308] 331.101 g of DMAc (N,N-Dimethylacetamide) was filled into a 500 ml reactor equipped with a stirrer, nitrogen injector, dropping funnel, temperature controller, and cooler while passing nitrogen through it. After setting the reactor temperature to 25°C, 14.861 g (0.07 mol) of m-Tolidine was dissolved, and the solution was maintained at 25°C. 6.277 g (0.028 mol) of DMCBDA was added to this solution, and the mixture was stirred for 3 hours to completely dissolve the DMCBDA. After lowering the reactor temperature to below 10°C, 17.352 g of PO (Propylene Oxide) was added. Once it was determined that the solution was evenly stirred, 12.395 g (0.042 mol) of DEDC was added, followed by stirring at a low temperature for about 30 minutes, and then slowly raising the temperature to room temperature. When the temperature of the reactor is adjusted back to 25℃, the reaction is carried out for more than 12 hours to obtain a polymer solution with a solid content concentration of 9 wt%.

[0309] 4.87 g of pyridine and 6.29 g of acetic anhydride are added to the obtained polymer solution and stirred for 30 minutes, after which the temperature of the polymer solution is raised to 80°C. Once the temperature of the polymer solution reaches 80°C, chemical imidation is carried out by stirring at the same temperature for 1 hour, and after completion, the polymer solution is cooled back to room temperature.

[0310] The obtained polymer solution is rapidly stirred while slowly adding approximately 2.2 L of methanol to facilitate the reprecipitation of the solids. The solution after reprecipitation is complete is called the reprecipitate. This reprecipitate is poured into a Buchner funnel-type vacuum system (using filter paper) to begin filtration. As methanol and DMAc are primarily removed from the reprecipitate through the Buchner funnel, only the polymer solids remain; subsequently, approximately 1.4 L of methanol is poured over them to obtain a purer solid through a washing process. To remove as much residual solvent from the obtained solids as possible, they are dried under vacuum at approximately 100°C for at least 6 hours, resulting in a polyimide-based polymer solid suitable for redissolution in an appropriate organic solvent.

[0311] Redissolution using an organic solvent is carried out to form a film of the obtained polymer solid.

[0312] After filling a 500ml reactor with 225g of DMAc and maintaining the reactor temperature at 25℃, 1.5g of Tinosorb S, a UV absorber, is added to the reactor and completely dissolved. Then, 0.025g of Irganox 1010, a phenolic primary antioxidant, is added to the reactor and completely dissolved. Next, the reactor temperature is lowered to 5℃, and 25g of the previously obtained polymer solids is added to the reactor. Afterward, the reactor temperature is raised back to 25℃ and left to stand until completely dissolved.

[0313] Subsequently, the obtained redissolved solution was cast. A casting substrate is used for casting. There are no specific restrictions on the type of casting substrate. Glass substrates, stainless steel (SUS) substrates, Teflon substrates, etc., may be used as casting substrates. According to one embodiment of the present invention, a glass substrate may be used as the casting substrate.

[0314] After casting at room temperature, the film was prepared by placing it in a hot air oven set to a temperature of 80°C and slowly drying it to 120°C at a speed of 3.5°C / min for about 11 to 12 minutes, and the prepared film was peeled off from a glass substrate and fixed to a frame with a pin.

[0315] The frame with the fixed film was placed in a hot air oven and slowly heated from 120°C to 230°C for about 40 minutes, then slowly cooled and separated from the frame to obtain the optical film. The optical film was then heat-treated at 200°C for 1 minute.

[0316] As a result, a polyimide-based film with a thickness of about 50㎛ was completed.

[0317] <Examples 2 and 3>

[0318] Based on the composition and content disclosed in Table 1 below, polyimide-based films according to Examples 2 and 3 were prepared according to the same method as Example 1.

[0319] <Example 4>

[0320] A polyimide-based polymer solid was obtained using the same method as in Example 1 above.

[0321] After filling a 500ml reactor with 225g of DMAc and maintaining the reactor temperature at 25℃, 1.0g of Tinosorb S, a UV absorber, is added to the reactor and completely dissolved. Next, 0.025g of Irganox 1010, a phenolic primary antioxidant, is added to the reactor and completely dissolved. Then, the reactor temperature is lowered to 5℃, and 25g of the previously obtained polymer solids is added to the reactor. Afterward, the reactor temperature is raised back to 25℃ and left to stand until completely dissolved. Once the added polymer solids are completely dissolved, 12.5g of filler dispersion (20wt%) is added to the reactor and stirred until sufficiently dispersed.

[0322] Subsequently, using the obtained redissolved solution, a polyimide-based film with a thickness of about 50 μm was prepared in the same manner as in Example 1.

[0323] <Example 5>

[0324] Based on the composition and content disclosed in Table 1 below, a polyimide-based film according to Example 5 was prepared using the same method as in Example 4, except that the content of the filler dispersion (20 wt%) in Example 4 was 25 g instead of 12.5 g.

[0325] <Comparative Example 1>

[0326] A polyimide-based film according to Comparative Example 1 with a thickness of about 50 μm was prepared using the same method as in Example 1, except that no UV absorber and antioxidant were added in Example 1.

[0327] <Comparative Example 2>

[0328] A polyimide-based film according to Comparative Example 2 with a thickness of about 50 μm was prepared by the same method as Comparative Example 1, except that 1.5 g of Hostabin B Cap, an ultraviolet absorber, was added during the redissolution process for film formation of the obtained polymer solid in Comparative Example 1.

[0329] <Comparative Example 3>

[0330] A polyimide-based polymer solid was obtained using the same method as in Example 1 above.

[0331] After filling a 500ml reactor with 225g of DMAc and maintaining the reactor temperature at 25℃, 0.025g of Irganox 1010, a phenolic primary antioxidant, is added to the reactor and completely dissolved. Then, the reactor temperature is lowered to 5℃, and 25g of the previously obtained polymer solids is added to the reactor. Afterward, the reactor temperature is raised back to 25℃ and left to stand until completely dissolved. Once the added polymer solids are completely dissolved, 25g of filler dispersion (20wt%) is added to the reactor and stirred until sufficiently dispersed.

[0332] Subsequently, using the obtained redissolved solution, a polyimide-based film according to Comparative Example 3 with a thickness of about 50 μm was prepared in the same manner as in Example 1.

[0333] Classification Polymer Solids UV Absorber Antioxidant Filler Dispersion (20 wt%) ABCD Phenol-based Phosphorus-based EF Example 125g 1.5g---0.025g--- Example 225g 1.5g--0.025g--- Example 325g-1.5g-0.025g--- Example 425g 1.5g---0.025g--12.5 Example 525g 1.5g---0.025g--25 Comparative Example 125g--------Comparative Example 225g---1.5g----Comparative Example 325g-----0.05g0.05g25

[0334] UV absorber A: Tinosorb S UV absorber B: Tinuvin 1600

[0335] UV absorber C: Tinuvin 479

[0336] UV absorber D: Hostabin B Cap

[0337] Phenolic antioxidant E: Irganox 1010

[0338] Phenolic antioxidant F: Irganox 1076

[0339] Phosphorus-based antioxidant: Irgafos 168

[0340] Filler dispersion (20 wt%): A filler dispersion in which spherical silica with an average particle size of 12 nm is dispersed in a solvent at a content of 20 wt%.

[0341] Methods for Measuring Physical Properties

[0342] The physical properties of the optical films prepared according to Examples 1 to 5 and Comparative Examples 1 to 3, respectively, were measured by the following method, and the results are disclosed in Table 2.

[0343] (1) Yellow Index (YI)

[0344] The yellowness of the polyimide-based films prepared according to Examples 1 to 5 and Comparative Examples 1 to 3, respectively, was measured using a spectrophotometer (KONICA MINOLTA CM-3700D) in accordance with ASTM E313.

[0345] (2) Light transmittance (TT)

[0346] For the polyimide-based films prepared according to Examples 1 to 5 and Comparative Examples 1 to 3, the average light transmittance was measured in the wavelength range of 380 to 780 nm using a spectrophotometer (CM-3700D of KONICA MINOLTA).

[0347] (3) Hayes

[0348] The haze of the polyimide-based films prepared according to Examples 1 to 5 and Comparative Examples 1 to 3, respectively, was measured using a haze meter (HM-150 of MURAKAMI).

[0349] (4) Measurement of modulus and elongation at break

[0350] According to the ASTM D885 method, the modulus (Young's modulus) and elongation at break of the polyimide-based films prepared according to Examples 1 to 5 and Comparative Examples 1 to 3, respectively, were measured using a universal tensile testing machine (Model 5967 of Instron).

[0351] (5) Yellowness measurement after lightfastness test

[0352] A light resistance test was performed by irradiating polyimide-based films prepared according to Examples 1 to 5 and Comparative Examples 1 to 3, respectively, with a Xenon Lamp light source at an intensity of 1.1 W / m² for 145.5 hours using an ATLAS Ci3000+ instrument under conditions of a temperature of 30℃ and a humidity of 55RH%.

[0353] Afterwards, the yellowness of the polyimide-based films prepared according to Examples 1 to 5 and Comparative Examples 1 to 3, respectively, in which a lightfastness test was performed according to ASTM E313, was measured using a spectrophotometer (KONICA MINOLTA CM-3700D).

[0354] (6) Static folding value measurement

[0355] The static folding value was obtained by preparing polyimide-based films prepared according to Examples 1 to 5 and Comparative Examples 1 to 3, respectively, into film samples of size 3 cm X 7 cm, fitting each prepared film sample onto a glass plate to have a radius of curvature of 1.5 mm, placing each sample in a constant temperature and humidity chamber at 60°C and 90% humidity for 24 hours, removing the sample, placing each film sample with the fixed state released onto a flat table as shown in Fig. 1, and measuring the outer angle (θ) of the film using a protractor.

[0356] Classification Y.ITT (%) Haze (%) Modulus (GPa) Elongation at Break (%) Yellowness after Lightfastness Test Static Folding Value (°) Example 1 3.56 88.7 20.5 5.7 35.6 8.56 163 Example 2 4.19 88.68 0.3 5.7 35.69.36 165 Example 3 4.12 88.70 0.4 5.7 35.69.63 168 Example 4 3.28 8.99 0.3 5.9 31.28 1157 Example 5 2.98 89.40.3 6.05 38.27.93 152 Comparative Example 15.48 80.3 5.63 9.8 20.41 80 Comparative Example 28.9787.60.35.639.821.97180 Comparative Example 32.7689.440.35.7240.217.76180

[0357] According to Table 2 above, Examples 1 to 5 have a yellowness value of 5.0 or less and a yellowness value after a lightfastness test of 10 or less, and a static folding value of 170° or less, confirming that they possess excellent optical and mechanical properties. On the other hand, Comparative Examples 1 and 2 have a yellowness value greater than 5.0 and a yellowness value after a lightfastness test greater than 10, and both have a static folding value of 180°, confirming that they lack optical and mechanical properties. Comparative Example 3 has a yellowness value after a lightfastness test greater than 10 and a static folding value of 180°, confirming that it lacks optical and mechanical properties.

[0358] [Explanation of the symbol]

[0359] 100: Polyimide-based film

[0360] 200: Display device

[0361] 501: Display panel

Claims

1. Includes at least one of an imide repeating unit and an amide repeating unit, The above imide repeating unit is formed by the reaction of a diamine compound and a dianhydride compound, and The above amide repeating unit is formed by the reaction of a diamine compound and a dicarbonyl compound, and Polyimide-based film with a yellowness of 10.0 or less after a lightfastness test: Here, the lightfastness test is performed by irradiating the polyimide-based film with a Xenon lamp light source at an intensity of 1.1 W / m² for 145.5 hours under conditions of a temperature of 30℃ and a humidity of 55RH%.

2. In Paragraph 1, The above diamine compound comprises a polyimide-based film comprising a compound represented by the following chemical formula 1: [Chemical Formula 1] Here, R1 to R8 of the above chemical formula 1 each include at least one of hydrogen (H), a methyl group (-CH3), and an ethyl group (-CH2CH3).

3. In Paragraph 2, A polyimide-based film in which each of the above imide repeating unit and amide repeating unit does not contain a perfluoroalkyl group.

4. In Paragraph 2, A polyimide-based film in which at least one of R1 to R8 of the above chemical formula 1 comprises a methyl group (-CH3).

5. In Paragraph 2, At least one of R1 to R4 of the above chemical formula 1 comprises a methyl group (-CH3), and A polyimide-based film in which at least one of R5 to R8 of the above chemical formula 1 comprises a methyl group (-CH3).

6. In Paragraph 2, A polyimide-based film comprising at least one of the compounds represented by the following chemical formulas 2 to 4, wherein the compound represented by the above chemical formula 1. [Chemical Formula 2] [Chemical Formula 3] [Chemical Formula 4] 7. In Paragraph 1, A polyimide-based film comprising at least one of the dicarbonyl compound represented by the following chemical formula 5 and the compound represented by the following chemical formula 6. [Chemical Formula 5] [Chemical Formula 6] 8. In Paragraph 1, The above dianhydride compound comprises a polyimide-based film comprising a compound represented by the following chemical formula 7: [Chemical Formula 7] Here, R9 to R12 of the above chemical formula 7 each include at least one of hydrogen (H), a methyl group (-CH3), and an ethyl group (-CH2CH3).

9. In Paragraph 8, A polyimide-based film in which at least one of R9 to R12 of the above chemical formula 7 comprises a methyl group (-CH3).

10. In Paragraph 8, A polyimide-based film comprising at least one of the compounds represented by the following chemical formulas 8 to 12, wherein the compound represented by the above chemical formula 7. [Chemical Formula 8] [Chemical Formula 9] [Chemical Formula 10] [Chemical Formula 11] [Chemical Formula 12] 11. In Paragraph 1, A polyimide-based film in which, based on the molar amount, the content of the dicarbonyl compound is 10 mol% or more relative to the total content of the dicarbonyl compound and the dianhydride compound.

12. In Paragraph 1, Polyimide-based film containing an antioxidant.

13. In Paragraph 12, The above antioxidant comprises at least one of a phenolic antioxidant, a phosphorus-based antioxidant, and an amine-based antioxidant, in a polyimide film.

14. In Paragraph 12, The above amine-based antioxidant is a polyimide film comprising Hindered amine light stabilizers (HALS).

15. In Paragraph 12, The above antioxidant is a polyimide-based film comprising at least one of the compounds represented by the following chemical formulas 13 to 15. [Chemical Formula 13] [Chemical Formula 14] [Chemical Formula 15] 16. In Paragraph 1, Polyimide-based film containing a UV absorber.

17. In Paragraph 16, The above ultraviolet absorber is a polyimide-based film containing at least two nitrogen (N) elements.

18. In Paragraph 16, The above-mentioned ultraviolet absorber is a polyimide film comprising at least one of a benzylformamidine-based ultraviolet absorber, a triazine-based ultraviolet absorber, a benzotriazine-based ultraviolet absorber, and a triazole-based ultraviolet absorber.

19. In Paragraph 16, The above-mentioned ultraviolet absorber is a polyimide-based film comprising a compound represented by any one of the following chemical formulas 16 to 21. [Chemical Formula 16] [Chemical Formula 17] [Chemical Formula 18] [Chemical Formula 19] [Chemical Formula 20] [Chemical Formula 21] 20. In Paragraph 1, A polyimide-based film having a yellowness of 5.0 or less based on a thickness of 50㎛.

21. In Paragraph 1, Having a static folding value of 170° or less based on a thickness of 50㎛, Polyimide-based film: Here, the static folding value refers to a value obtained by fitting and fixing the film onto a glass plate with a radius of curvature of 1.5 mm, placing it in a constant temperature and humidity chamber at 60°C and 90% humidity for 24 hours, taking it out, and then measuring the outer edge of the film with the fixed state released using a protractor.

Images