Eco-friendly polyimide-based film and method for manufacturing same

Abstract

An embodiment of the present invention relates to an eco-friendly polyimide-based film that does not contain a perfluoroalkyl group, and 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 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, the dianhydride compound comprises at least one of a dianhydride compound containing a methyl group and a dianhydride compound that does not contain a methyl group, and the stress relaxation index calculated according to expression 1 is not more than 60% based on the thickness of 50 ㎛.

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, the amide repeating unit is formed by the reaction of a diamine compound and a dicarbonyl compound, and the dianhydride compound comprises a cycloaliphatic dianhydride compound and an aromatic dianhydride compound, and having a stress relaxation index of 60% or less calculated according to Formula 1 below based on a thickness of 50 μm.

[0011] [Equation 1]

[0012] Stress Relaxation Index (%) = [(F0- F final ) / F0] X 100

[0013] In Equation 1 above, F0 represents the initial load, and F final represents the termination load, and

[0014] The above F0 and F final It is measured based on the evaluation of the film's creep deformation.

[0015] The above imide repeating unit and amide repeating unit may each not include a perfluoroalkyl group.

[0016] The above perfluoroalkyl group may include *-CF3 and *-CF2-*. Here, *- and -* each mean bonded with other elements.

[0017] The above diamine compound may include a benzidine-based diamine.

[0018] The above benzidine-based diamine may include a hydrocarbon group as a substituent.

[0019] The above benzidine-based diamine may include at least one of the compounds represented by the following chemical formulas 1 to 3.

[0020] [Chemical Formula 1]

[0021]

[0022] [Chemical Formula 2]

[0023]

[0024] [Chemical Formula 3]

[0025]

[0026] The above-mentioned cycloaliphatic dianhydride compound may include a cycloaliphatic dianhydride compound containing a methyl group, and the above-mentioned aromatic dianhydride compound may include an aromatic dianhydride compound containing a methyl group.

[0027] The above dianhydride compound containing a methyl group may include at least one of the compounds represented by Chemical Formulas 4 to 8.

[0028] [Chemical Formula 4]

[0029]

[0030] [Chemical Formula 5]

[0031]

[0032] [Chemical Formula 6]

[0033]

[0034] [Chemical Formula 7]

[0035]

[0036] [Chemical Formula 8]

[0037]

[0038] The above-mentioned aromatic dianhydride compound containing a methyl group may include a compound represented by Chemical Formula 9.

[0039] [Chemical Formula 9]

[0040]

[0041] The above-mentioned cycloaliphatic dianhydride compound that does not contain a methyl group may include at least one of the compounds represented by the following chemical formulas 10 to 16.

[0042] [Chemical Formula 10]

[0043]

[0044] [Chemical Formula 11]

[0045]

[0046] [Chemical Formula 12]

[0047]

[0048] [Chemical Formula 13]

[0049]

[0050] [Chemical Formula 14]

[0051]

[0052] [Chemical Formula 15]

[0053]

[0054] [Chemical Formula 16]

[0055]

[0056] The above-mentioned aromatic dianhydride compound that does not contain a methyl group may include at least one of the compounds represented by the following chemical formulas 17 to 21.

[0057] [Chemical Formula 17]

[0058]

[0059] [Chemical Formula 18]

[0060]

[0061] [Chemical Formula 19]

[0062]

[0063] [Chemical Formula 20]

[0064]

[0065] [Chemical Formula 21]

[0066]

[0067] The above dicarbonyl compound may not contain a methyl group.

[0068] The above dicarbonyl compound may include at least one of the compounds represented by the following chemical formulas 22 to 27.

[0069] [Chemical Formula 22]

[0070]

[0071] [Chemical Formula 23]

[0072]

[0073] [Chemical Formula 24]

[0074]

[0075] [Chemical Formula 25]

[0076]

[0077] [Chemical Formula 26]

[0078]

[0079] [Chemical Formula 27]

[0080]

[0081] Based on a total content of 100 mol% of the above dianhydride compound and dicarbonyl compound, the sum of the contents of the above methyl group-containing alicyclic dianhydride compound and the above methyl group-containing aromatic dianhydride compound may be 15 mol% or more.

[0082] Based on a total content of 100 mol% of the dianhydride compound and the dicarbonyl compound, the sum of the contents of the alicyclic dianhydride compound containing a methyl group and the aromatic dianhydride compound containing a methyl group is 15 mol% to 100 mol%, and the sum of the contents of the alicyclic dianhydride compound not containing a methyl group, the aromatic dianhydride compound not containing a methyl group, and the dicarbonyl compound may be 0 mol% to 85 mol%.

[0083] The molar ratio of the cycloaliphatic dianhydride compound containing the methyl group and the aromatic dianhydride compound containing the methyl group may be in the range of 1:9 to 9:1.

[0084] The ratio of the sum of the contents of the methyl-free alicyclic dianhydride compound and the methyl-free aromatic dianhydride compound to the contents of the dicarbonyl compound may be in the range of 100:0 to 0:100.

[0085] The above polyimide-based film may have a yellowness of 6.0 or less based on a thickness of 50 μm.

[0086] The above polyimide-based film can have a light transmittance of 88% or more at a wavelength of 380 to 780 nm.

[0087] The above polyimide-based film can have a Vickers hardness of 35 or higher based on a thickness of 50 μm.

[0088] The above polyimide-based film can have a modulus of 3.8 GPa or more based on a thickness of 50 μm.

[0089] The above polyimide-based film can have an elongation at break of 10% or more based on a thickness of 50㎛.

[0090] 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.

[0091] According to one embodiment of the present invention, an eco-friendly polyimide-based film that does not contain a perfluoroalkyl group can be manufactured.

[0092] 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.

[0093] FIG. 1 is a cross-sectional view of a part of a display device according to another embodiment of the present invention.

[0094] Figure 2 is an enlarged cross-sectional view of the "P" portion of Figure 1.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] 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.

[0103] 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.

[0104] One embodiment of the present invention provides a polyimide-based film (100) that does not contain a perfluoroalkyl group.

[0105] 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.

[0106] For example, a polyimide-based film (100) may be manufactured from monomer components including a diamine compound and a dianhydride compound. "Monomer components" may refer to all of the multiple monomers used in the manufacture of the polyimide-based film. The monomer components may be in a mixed state of multiple 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 (100).

[0107] 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 both an imide repeating unit and an amide repeating unit.

[0108] 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.

[0109] 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.

[0110] According to one embodiment of the present invention, the monomer components may further include a dicarbonyl compound in addition to the diamine compound and the dianhydride compound. When the monomer components further include a dicarbonyl compound in addition to the diamine compound and the dianhydride compound, the polyimide-imide film (100) may have a polyamide-imide copolymer structure having both an imide repeating unit and an amide repeating unit.

[0111] A film containing imide repeating units can be referred to as a polyimide-based film. Additionally, a film containing both imide repeating units and amide repeating units may also be referred to as a polyimide-based film. Hereinafter, to avoid confusion, a film containing both imide repeating units and amide repeating units will be referred to as a polyimide-based film.

[0112] A polyimide-based film (100) according to one embodiment of the present invention may have an imide repeating unit and may have an amide-imide copolymer structure. The polyimide-based film may be a polyimide film or a polyamide-imide film.

[0113] A polyimide-based film (100) according to one embodiment of the present invention does not contain perfluoroalkyl groups.

[0114] 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.

[0115] The perfluoroalkyl group may include *-CF3 and *-CF2-*. Here, *- and -* are used to denote a bond or bonding position with another element, respectively.

[0116] 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-*.

[0117] 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.

[0118] 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.

[0119] 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-*.

[0120] According to one embodiment of the present invention, the diamine compound may include a cyclic structure within its chemical formula.

[0121] 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, it was confirmed that when a cyclic diamine compound is used, problems such as the generation of salt during the polymerization process or a decrease in the degree of polymerization occur, making mass production difficult.

[0122] 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.

[0123] Accordingly, a diamine compound according to one embodiment of the present invention may have an aromatic ring. For example, the diamine compound may include a benzidine-based diamine.

[0124] When a benzidine-based diamine is used as the diamine compound, the main chain of the polymer constituting the polyimide film can have a flat structure.

[0125] Meanwhile, when a benzidine-based diamine without functional groups is used, the rate of stacking between molecules is high, resulting in a high probability of charge-transfer complex (CT-Complex) effects, and consequently, it was confirmed that a yellow color is expressed in the film.

[0126] Accordingly, according to one embodiment of the present invention, a benzidine diamine having a substituent may be used as a benzidine diamine. The substituent may include a hydrocarbon group. More specifically, the substituent may include a methyl group. For example, 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 a benzidine diamine.

[0127] According to one embodiment of the present invention, a benzidine-based diamine may include at least one of a compound represented by the following chemical formula 1 (mTD), a compound represented by the following chemical formula 2 (oTD), and a compound represented by the following chemical formula 3 (TMB).

[0128] [Chemical Formula 1]

[0129]

[0130] [Chemical Formula 2]

[0131]

[0132] [Chemical Formula 3]

[0133]

[0134] In addition, benzidine-based diamines may include atoms or atomic groups with high electronegativity as substituents. According to one embodiment of the present invention, the substituents may include atoms or atomic groups 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.

[0135] When a benzidine-based diamine contains an atom or group of atoms with high electronegativity as a substituent, it can lower the electron density of the polymer chains contained in the polyimide-based film (100), thereby suppressing or reducing the charge-transfer complex (CT-Complex) effect. Additionally, since the atom or group of atoms with high electronegativity has a relatively large volume, the interaction decreases as the distance between polymer chains increases, thereby alleviating the packing of the polymer chains and improving transparency.

[0136] According to one embodiment of the present invention, a benzidine-based diamine substituted with chlorine (Cl) or bromine (Br) may be used as the diamine-based compound.

[0137] According to one embodiment of the present invention, the dianhydride compound may include a cycloaliphatic dianhydride compound and an aromatic dianhydride compound.

[0138] In the manufacture of a polyimide film (100), when a benzidine-based diamine is used as the diamine compound, if a cycloaliphatic dianhydride compound not containing substituents is used alone as the reaction pair of the benzidine-based diamine to manufacture the polyimide film (100), processability may be reduced. Specifically, when a benzidine-based diamine and a cycloaliphatic dianhydride compound not containing substituents react to produce a polyamic acid (PAA), which is a precursor of polyimide, and chemical imidization proceeds, the solubility of the reaction solution may be significantly reduced, thereby reducing processability, and the processability of the manufactured polyimide resin may be significantly worsened.

[0139] According to one embodiment of the present invention, a polyimide-based film (100) is designed to form an imide repeating unit using a dianhydride containing a substituent, taking into account the problem of using a dianhydride compound that does not contain a substituent alone.

[0140] Accordingly, a dianhydride compound according to one embodiment of the present invention may include a dianhydride compound having a substituent. The dianhydride compound may include, for example, a methyl group as a substituent.

[0141] When the dianhydride compound contains a substituent, when reacted with a benzidine-based diamine, the solubility in the solvent is improved during the redissolution process after imidization, thereby improving the difficulty of film formation. Additionally, when the dianhydride compound contains a methyl group as a substituent, the polyimide-based film (100) formed using it may have improved folding characteristics.

[0142] According to one embodiment of the present invention, a dianhydride compound containing a methyl group may be a cyclic compound. Specifically, the dianhydride compound may include at least one of an alicyclic dianhydride compound containing a methyl group and an aromatic dianhydride compound containing a methyl group. More specifically, the dianhydride compound may include an alicyclic dianhydride compound containing a methyl group and an aromatic dianhydride compound containing a methyl group.

[0143] According to one embodiment of the present invention, an aromatic dianhydride compound containing a methyl group included in the dianhydride compound may be used, for example, an aromatic dianhydride compound having an ether group (*-O-*) as a linker. In this case, by introducing an ether group (*-O-*) corresponding to a linker into the polymer main chain, the polyimide film (100) formed using this may have excellent elongation at break and folding characteristics. In addition, when an ether group (*-O-*) is introduced into the polymer main chain, the polymer chain may have an asymmetric structure, which can weaken the interaction between polymer chains, and thereby improve the optical properties of the polyimide film (100).

[0144] However, if an aromatic dianhydride compound containing a methyl group, for example, an aromatic dianhydride compound having an ether group (*-O-*) as a linker, is used in an excess amount exceeding a predetermined range, the surface hardness of the polyimide-based film may be lowered.

[0145] Accordingly, in order for the polyimide-based film (100) according to one embodiment of the present invention to simultaneously possess excellent mechanical and optical properties, the dianhydride compound may include a cycloaliphatic dianhydride compound containing a methyl group and an aromatic dianhydride compound containing a methyl group in a molar ratio of 1:9 to 9:1.

[0146] More specifically, the dianhydride compound may contain an alicyclic dianhydride compound containing a methyl group and an aromatic dianhydride compound containing a methyl group and having an ether group (*-O-*) as a linker in a molar ratio of 1:9 to 9:1.

[0147] According to one embodiment of the present invention, a dianhydride compound containing a methyl group is, for example, 1,3-dimethyl-cyclobutane-1,2,3,4-tetracarboxylic dianhydride (DMCBDA), 1,2,3,4-tetramethyl-cyclobutane-1,2,3,4-tetracarboxylic dianhydride, 5-(2,5-dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic dianhydride, 1-methyl-4,9-dioxatricyclo[5.3.0.02,6]decane-3,5,8,10-tetrone, 1,2,6-trimethyl-4,9-dioxatricyclo[5.3.0.02,6]decane-3,5,8,10-tetrone), 3,3′,4,4′-biphenyltetracarboxylic dianhydride, and 2,3,3,4-biphenyltetracarboxylic It may include at least one of dianhydrides (2,3,3,4-biphenyltetracarboxylic dianhydride).

[0148] More specifically, a cycloaliphatic dianhydride compound containing a methyl group may include at least one of the compounds represented by Formulas 4 to 8.

[0149] [Chemical Formula 4]

[0150]

[0151] [Chemical Formula 5]

[0152]

[0153] [Chemical Formula 6]

[0154]

[0155] [Chemical Formula 7]

[0156]

[0157] [Chemical Formula 8]

[0158]

[0159] In addition, aromatic dianhydride compounds containing a methyl group may include compounds represented by Chemical Formula 9.

[0160] [Chemical Formula 9]

[0161]

[0162] According to one embodiment of the present invention, the dianhydride compound may further comprise a dianhydride compound that does not contain a methyl group in addition to a dianhydride compound that contains a methyl group. More specifically, the alicyclic dianhydride compound included in the dianhydride compound may further comprise an alicyclic dianhydride compound that does not contain a methyl group in addition to an alicyclic dianhydride compound that contains a methyl group. Additionally, the aromatic dianhydride compound included in the dianhydride compound may further comprise an aromatic dianhydride compound that does not contain a methyl group in addition to an aromatic dianhydride compound that contains a methyl group.

[0163] For example, dianhydride compounds that do not contain a methyl group may include at least one of alicyclic dianhydride compounds, fluorene dianhydride compounds (cardo-based dianhydride compounds), and aromatic dianhydride compounds.

[0164] According to one embodiment of the present invention, dianhydride compounds not containing a methyl group include cyclobutane-1,2,3,4-tetracarboxylic dianhydride (CBDA), cis-1,2,3,4-cyclopentanetetracarboxylic dianhydride (CPDA), dicyclohexyl-3,4,3',4'-tetracarboxylic dianhydride (HBPDA), and 1,2,4,5-cyclohexanetetracarboxylic dianhydride (CTDA, HPMDA). Hexahydro-4,8-Ethano-1H,3H-benzo[1,2-c:4,5-c']difuran-1,3,5,7-tetrone (BODA), bicyclo[2.2.2]oct-7-en-2,3,5,6-tetracarboxylic dianhydride (Bicyclo[2.2.It may include at least one of 2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride)(BTA), 3-(carboxymethyl)-1,2,4-cyclopentanetricarboxylic acid 1,4:2,3-dianhydride (TCAA), 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride (BPAF), 4,4′-oxydiphthalic anhydride (4,4′-ODPA), and 3,4′-oxydiphthalic anhydride (3,4′-ODPA).

[0165] More specifically, a cycloaliphatic dianhydride compound that does not contain a methyl group may include at least one of the compounds represented by the following chemical formulas 10 to 16.

[0166] [Chemical Formula 10]

[0167]

[0168] [Chemical Formula 11]

[0169]

[0170] [Chemical Formula 12]

[0171]

[0172] [Chemical Formula 13]

[0173]

[0174] [Chemical Formula 14]

[0175]

[0176] [Chemical Formula 15]

[0177]

[0178] [Chemical Formula 16]

[0179]

[0180] In addition, aromatic dianhydride compounds that do not contain a methyl group may include at least one of the compounds represented by the following chemical formulas 17 to 21.

[0181] [Chemical Formula 17]

[0182]

[0183] [Chemical Formula 18]

[0184]

[0185] [Chemical Formula 19]

[0186]

[0187] [Chemical Formula 20]

[0188]

[0189] [Chemical Formula 21]

[0190]

[0191] According to one embodiment of the present invention, by using a dianhydride compound containing a methyl group and a dianhydride compound not containing a methyl group together as dianhydride compounds, a polyimide-based film (100) manufactured using the same can have excellent optical properties and folding properties.

[0192] According to one embodiment of the present invention, in order for the polyimide-based film (100) to have excellent mechanical and optical properties, the dianhydride compound may be designed to contain at least 15 mol% of a dianhydride compound containing a methyl group, based on 100 mol% of the total content of the dianhydride compound.

[0193] More specifically, the dianhydride compound can be designed such that, based on a total dianhydride compound content of 100 mol%, the sum of the contents of a methyl group-containing alicyclic dianhydride compound and an aromatic dianhydride compound containing a methyl group is 15 mol% or more.

[0194] In addition, the molar ratio of the methyl group-containing alicyclic dianhydride compound and the methyl group-containing aromatic dianhydride compound included in the dianhydride compound may be in the range of 1:9 to 9:1.

[0195] According to one embodiment of the present invention, a polyimide-based film (100) may be designed to contain a dianhydride compound containing a methyl group and a dianhydride compound not containing a methyl group in a range of 15:85 to 100:0 with respect to the total content of the dianhydride compound.

[0196] More specifically, the polyimide film (100) can be designed to contain, with respect to the total content of the dianhydride compound, the sum of the alicyclic dianhydride compound containing a methyl group and the aromatic dianhydride compound containing a methyl group and the sum of the alicyclic dianhydride compound not containing a methyl group and the aromatic dianhydride compound not containing a methyl group in the range of 15:85 to 100:0.

[0197] According to one embodiment of the present invention, a polyimide-based film (100) may further include an amide repeating unit in addition to an imide repeating unit. The amide repeating unit is formed by the reaction of a diamine compound and a dicarbonyl compound. 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.

[0198] 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.

[0199] Dicarbonyl dichloride compounds exhibit a high degree of polymerization with benzidine-based diamines used as diamine compounds, and the polymer can have excellent mechanical properties. Dicarbonyl dichloride compounds can be compounds having a flat structure or compounds having a kink group.

[0200] According to one embodiment of the present invention, at least one of 4,4'-Oxybis(benzoyl chloride) (DEDC), isophthaloyl chloride (IPC), phthaloyl chloride, biphenyl-4,4'-dicarboxyl chloride (BPDC), tetraphthaloyl chloride (TPC), and trans-cyclohexane-1,4-(dicarbonyl dichloride) (CHOC) may be used as a dicarbonyl compound.

[0201] More specifically, the dicarbonyl compound may include at least one of the compounds represented by the following chemical formulas 22 to 27.

[0202] [Chemical Formula 22]

[0203]

[0204] [Chemical Formula 23]

[0205]

[0206] [Chemical Formula 24]

[0207]

[0208] [Chemical Formula 25]

[0209]

[0210] [Chemical Formula 26]

[0211]

[0212] [Chemical Formula 27]

[0213]

[0214] According to one embodiment of the present invention, when a polyimide-based film (100) comprises a dianhydride compound and a dicarbonyl compound, the molar ratio of the dicarbonyl compound and the 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.

[0215] According to one embodiment of the present invention, in order for the polyimide-based film (100) to have excellent mechanical and optical properties, the content of the dianhydride compound containing a methyl group can be designed to be 15 mol% or more based on the total content of the dicarbonyl compound and the dianhydride compound, which is 100 mol%.

[0216] More specifically, based on a total content of 100 mol% of dianhydride compounds and dicarbonyl compounds, the sum of the contents of alicyclic dianhydride compounds containing methyl groups and aromatic dianhydride compounds containing methyl groups may be 15 mol% to 100 mol%, and the sum of the contents of alicyclic dianhydride compounds not containing methyl groups, aromatic dianhydride compounds not containing methyl groups, and dicarbonyl compounds may be 0 mol% to 85 mol%.

[0217] In addition, the molar ratio of the methyl group-containing alicyclic dianhydride compound and the methyl group-containing aromatic dianhydride compound included in the dianhydride compound may be in the range of 1:9 to 9:1.

[0218] According to one embodiment of the present invention, the content ratio of a methyl group-free dianhydride compound and a dicarbonyl compound may be in the range of 100:0 to 0:100. More specifically, the content ratio of the sum of the content of a methyl group-free alicyclic dianhydride compound and a methyl group-free aromatic dianhydride compound and the content of a dicarbonyl compound may be in the range of 100:0 to 0:100.

[0219] According to one embodiment of the present invention, when the content ratio of a dianhydride compound not containing a methyl group and a dicarbonyl compound is 100:0, the polyimide-based film (100) does not contain a dicarbonyl compound, so it contains imide repeating units but does not contain amide repeating units. In this case, the polyimide-based film (100) can be regarded as a polyimide film.

[0220] According to one embodiment of the present invention, when the ratio of a dianhydride compound not containing a methyl group to a dicarbonyl compound is less than 100:0, for example, 99:1 to 0:100 based on the dianhydride compound not containing a methyl group, the polyimide-based film (100) contains a dianhydride compound containing a methyl group and a dicarbonyl compound, and thus contains an imide repeating unit and an amide repeating unit. In this case, the polyimide-based film (100) can be viewed as a polyamideimide film.

[0221] According to one embodiment of the present invention, the polyimide-based film (100) may have a ratio of the total number of imide repeating units to the total number of amide repeating units of 15:85 to 100:0 based on the total number of repeating units. The polyimide-based film (100) according to one embodiment of the present invention may further include additives. For example, at least one of an antioxidant, a UV stabilizer, a UV absorber, microparticles, nanoparticles, a light stabilizer, a polymerization initiator, a leveling agent, and a bluening agent may be used.

[0222] 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.

[0223] Primary antioxidants and secondary antioxidants may be used individually or mixed depending on the required conditions.

[0224] According to one embodiment of the present invention, at least one of a phenolic antioxidant, a phosphorus-based antioxidant, and an amine-based antioxidant may be used as an antioxidant.

[0225] For example, phenol-based primary antioxidants and phosphorus-based secondary antioxidants can be used as antioxidants.

[0226] Hindered amine light stabilizers (HALS) can be used as UV stabilizers.

[0227] 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.

[0228] In order to improve the light transmittance or friction coefficient of a polyimide-based 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.

[0229] 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.

[0230] A polyimide-based film (100) according to one embodiment of the present invention may have a stress relaxation index calculated according to the following formula 1, based on a thickness of 50 μm, of 60% or less.

[0231] [Equation 1]

[0232] Stress Relaxation Index (%) = [(F0- F final ) / F0] X 100

[0233] In Equation 1 above, F0 represents the initial load, and F final represents the termination load.

[0234] The above F0 and F final It can be measured based on the evaluation of the film's creep deformation.

[0235] Creep deformation evaluation of a film is a method for assessing the deformation behavior of a film under specific conditions, and there are methods for checking the strain rate of the film by applying a fixed load for a certain period of time and methods for checking the load applied to the film by applying a fixed strain rate for a certain period of time.

[0236] Among these, the stress relaxation index of the film can be determined through a creep deformation evaluation method based on verifying the load applied to the film by applying a fixed strain over a certain period. In this case, if the strain is set above the film's yield characteristic, the stress relaxation characteristics in the plastic deformation region can be verified, which is closely related to whether or not crease occurs in the film.

[0237] According to one embodiment of the present invention, the stress relaxation index of the film is determined by performing a creep deformation evaluation of the film, for example, using a universal tensile testing machine under conditions of room temperature and humidity, a strain of 4.5%, a strain rate of 0.9% / sec, and a strain time of 4 hours. Subsequently, the initial load (F0) and final load (F) of the film obtained through the creep deformation evaluation are final The value can be calculated by substituting it into the above Equation 1.

[0238] A polyimide-based film (100) according to one embodiment of the present invention is designed so that the main chain has a structure that is as flat as possible in order to have a modulus of a certain level or higher. However, if the main chain has a structure that is too flat, the surface hardness may increase more than necessary, which may increase the brittleness of the film. Accordingly, in order for the polyimide-based film (100) to maintain a modulus of a certain level or higher while having excellent flexibility, the diamine compound and dianhydride compound used to form the imide repeating unit are designed to include a diamine compound having a methyl group and a cycloaliphatic dianhydride compound having a methyl group, and an aromatic dianhydride compound having a methyl group and an ether group (*-O-*) as a linker. Therefore, the polyimide-based film (100) according to one embodiment of the present invention, having excellent modulus and flexibility, can have a stress relaxation index of 60% or less.

[0239] A polyimide-based film (100) according to one embodiment of the present invention can be used as a cover window of a display device as designed as above. In addition, even if a user uses a display device having the polyimide-based film (100) according to one embodiment of the present invention for a long period of time, or if a repetitive and continuous external force is applied to the film, wrinkles (creases) may not occur.

[0240] A polyimide-based film (100) according to one embodiment of the present invention may have a Vickers hardness (HV) of 35 or higher based on a thickness of 50 μm.

[0241] The Vickers hardness of the polyimide-based film (100) is measured by the surface hardness of an indentation mark formed by pressing the surface of the polyimide-based film (100) with a diamond square pyramid, with a pressing load of C kg and a surface area of ​​D mm. 2 In this case, HV is calculated as C / D. For example, the Vickers hardness of the optical film (100) can be measured using a Vickers hardness measuring device such as Fisher's HM-2000.

[0242] If the Vickers hardness of the polyimide film (100) is less than 42.5, it may be vulnerable to external dents. For example, if an external force is applied to the polyimide film (100), scratches or cracks may easily occur.

[0243] A polyimide-based film (100) according to one embodiment of the present invention may have a yellowness of 6.0 or less based on a thickness of 50 μm.

[0244] 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.

[0245] 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.

[0246] If the yellowness (YI) of the polyimide film (100) exceeds 6.00, the polyimide film (100) may have an excessively yellow tint and may lack visibility, making it difficult to apply to a display device.

[0247] A polyimide-based film (100) according to one embodiment of the present invention may have a light transmittance of 88% or more at a wavelength of 380 to 780 nm.

[0248] The light transmittance of the polyimide-based film (100) can be measured at a wavelength of 550 nm by a spectrophotometer according to the standard ASTM E313. For example, the KONICA MINOLTA CM-3700D can be used as the spectrophotometer.

[0249] If the light transmittance of the polyimide film (100) is less than 88%, it may be difficult to apply it to a display device due to insufficient visibility.

[0250] A polyimide-based film (100) according to one embodiment of the present invention may have a haze of 1.0% or less based on a thickness of 50 μm.

[0251] 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.

[0252] If the haze of the polyimide film (100) is less than 1.0%, it may be difficult to apply it to a display device due to insufficient visibility.

[0253] A polyimide-based film (100) according to one embodiment of the present invention may have a modulus (Young's modulus) of 3.8 GPa or more based on a thickness of 50 μm.

[0254] 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.

[0255] If the modulus of the polyimide film (100) is 3.8 GPa or less, deformation due to external force may occur.

[0256] A polyimide-based film (100) according to one embodiment of the present invention may have an elongation at break of 10% or more based on a thickness of 50 μm.

[0257] According to one embodiment of the present invention, a polyimide-based film (100) may have excellent elongation at break by including an aromatic dianhydride compound having ether groups (*-O-*) as linkers in a predetermined amount or more.

[0258] 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.

[0259] 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.

[0260] 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.

[0261] Hereinafter, with reference to FIGS. 1 and FIGS. 2, a display device (200) using a polyimide-based film (100) according to one embodiment of the present invention will be described.

[0262] FIG. 1 is a cross-sectional view of a part of a display device (200) according to another embodiment of the present invention, and FIG. 2 is an enlarged cross-sectional view of the "P" portion of FIG. 1.

[0263] Referring to FIG. 1, 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).

[0264] Referring to FIGS. 1 and 2, 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. 1 and 2 is an organic light-emitting display device.

[0265] 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).

[0266] 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).

[0267] Referring to FIG. 2, 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).

[0268] A flattening film (552) is placed on a thin film transistor (TFT) to flatten the top of the thin film transistor (TFT).

[0269] 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).

[0270] 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).

[0271] 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.

[0272] The second electrode (573) is placed on the organic light-emitting layer (572).

[0273] 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).

[0274] 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.

[0275] 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.

[0276] A polyimide-based film (100) is placed on a display panel (501) having the laminated structure described above.

[0277] Hereinafter, a method for manufacturing a polyimide-based film (100) according to one embodiment of the present invention will be described in detail.

[0278] 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 and a dianhydride compound; molding the liquid resin composition to produce a gel-state film; and drying the gel-state film.

[0279] To manufacture a polyimide-based film (100), first, monomer components including a diamine compound and a dianhydride compound are polymerized. The monomer components may further include a diancarbonyl compound.

[0280] When monomer components include a diamine compound, a dianhydride compound, and a dicarbonyl compound, the diamine compound and the dianhydride compound may be polymerized first, and then the diamine compound and the dicarbonyl compound may be polymerized.

[0281] 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.

[0282] 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.

[0283] 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.

[0284] 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.

[0285] 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.

[0286] For imidation, thermal imidation, chemical imidation, or a combination of thermal imidation and chemical imidation may be applied.

[0287] 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.

[0288] Chemical imidation may be combined with thermal imidation.

[0289] 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.

[0290] Next, a second solvent is added to the first polymer solution, and the solution is filtered and dried to produce a polymer solid.

[0291] A second solvent is used to obtain a solid component of the polyimide 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.

[0292] 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.

[0293] 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.

[0294] 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.

[0295] 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.

[0296] 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.

[0297] 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 more than necessary.

[0298] According to one embodiment of the present invention, the liquid resin composition may have a viscosity of 1,000 to 30,000 cPs.

[0299] 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.

[0300] 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.

[0301] 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.

[0302] 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.

[0303] Glass plates, aluminum substrates, circulating stainless steel belts, stainless steel drums, or heat-resistant polymer films can be used as supports.

[0304] Next, the gel-state film can be dried and heat-treated to produce a polyimide-based film (100).

[0305] Drying can be performed, for example, in a temperature range of 50 to 150°C. Drying may include primary drying and secondary drying.

[0306] 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.

[0307] 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.

[0308] 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.

[0309] Drying and heat treatment may be performed simultaneously.

[0310] 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.

[0311] <Example 1>

[0312] 349.874 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, 16.984 g (0.08 mol) of m-Tolidine was dissolved, and the solution was maintained at 25°C. 1.793 g (0.008 mol) of DMCBDA was added to this solution and stirred for 3 hours to completely dissolve the DMCBDA. Then, 4.164 g (0.008 mol) of 4IBA was added and stirred for 3 hours to completely dissolve the 4IBA. Finally, 29.339 g (0.064 mol) of BPAF was added and stirred for 3 hours to completely dissolve the BPAF. Afterward, the reaction is carried out for more than 12 hours to obtain a polymer solution with a solid content concentration of 13% by weight.

[0313] 16.92 g of 1,2-dimethylimidazole and 17.97 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.

[0314] After lowering the temperature to room temperature, approximately 2.4 L of methanol is slowly added while rapidly stirring the polymer solution 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 1.6 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.

[0315] Redissolution using an organic solvent is carried out to form a film of the obtained polymer solid.

[0316] After filling a 500ml reactor with 230g of DMAc and maintaining the reactor temperature at 25℃, 30g of the previously obtained polymer solids is added to the reactor. Then, wait until completely dissolved.

[0317] The obtained redissolved solution was subsequently 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.

[0318] 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.

[0319] 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.

[0320] As a result, an optical film according to Example 1 with a thickness of about 50 μm was manufactured.

[0321] <Example 2>

[0322] 229.187 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, 16.984 g (0.08 mol) of m-Tolidine was dissolved, and the solution was maintained at 25°C. 2.421 g (0.0108 mol) of DMCBDA was added to this solution and stirred for 3 hours to completely dissolve the DMCBDA. Then, 0.625 g (0.0012 mol) of 4IBA was added and stirred for 3 hours to completely dissolve the 4IBA. Afterward, the reactor temperature was lowered to below 10°C, and 17.7724 g of PO (Propylene oxide) was added. Once it is determined that the solution has been thoroughly stirred, 14.217 g (0.068 mol) of CHOC is added, the mixture is stirred at a low temperature for about 30 minutes, and then the temperature is slowly raised 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 13 wt%.

[0323] 2.54 g of 1,2-dimethylimidazole and 2.70 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.

[0324] After lowering the temperature to room temperature, approximately 2.4 L of methanol is slowly added while rapidly stirring the polymer solution 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 1.6 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.

[0325] Redissolution using an organic solvent is carried out to form a film of the obtained polymer solid.

[0326] After filling a 500ml reactor with 230g of DMAc and maintaining the reactor temperature at 25℃, 30g of the previously obtained polymer solids is added to the reactor. Then, wait until completely dissolved.

[0327] The obtained redissolved solution was subsequently 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.

[0328] 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.

[0329] 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.

[0330] As a result, an optical film according to Example 2 with a thickness of about 50 μm was manufactured.

[0331] <Example 3>

[0332] Using the monomer disclosed in Table 1 below, an optical film according to Example 3 was prepared in the same manner as Example 2, according to the composition and content disclosed in Table 1.

[0333] <Examples 4 to 6>

[0334] Optical films according to Examples 4 to 6 were prepared using the monomer disclosed in Table 1 below, according to the composition and content disclosed in Table 1, in the same manner as Example 1.

[0335] The optical films prepared according to Examples 1 to 6 can be described as polyimide-based films.

[0336] <Comparative Example 1>

[0337] Using the monomer disclosed in Table 1 below, an optical film according to Comparative Example 1 was prepared in the same manner as Example 2, according to the composition and content disclosed in Table 1.

[0338] <Comparative Examples 2 and 3>

[0339] Optical films according to Comparative Examples 2 and 3 were each prepared using the monomer disclosed in Table 1 below, according to the composition and content disclosed in Table 1, in the same manner as Example 1.

[0340] The optical films prepared according to Comparative Examples 1 to 3 can be described as polyimide-based films.

[0341] Classification Diamine Compounds Dianhydride Compounds Dicarbonyl Compounds mTDoTDTMB44ODADMCBDA4IBACBDABPAFTPCCHOC Example 1 100---1010-80-- Example 2 100---13.51.5---85 Example 3 100---1.513.5--85- Example 4 100---404020-- Example 5 100--404020-- Example 6 100-404020-- Comparative Example 1 100---10----90 Comparative Example 2 100--10-90--- Comparative Example 3 100-1090---

[0342] The content disclosed in Table 1 represents the relative content based on the number of moles, where the total number of moles of the diamine compound is 100.

[0343] [Diamine Compounds]

[0344] mTD: 2,2'-Dimethylbenzidine

[0345] oTD: 3,3'-Dimethylbenzidine

[0346] TMB: 3,3',5,5'-Tetramethylbenzidine

[0347] 44ODA: 4,4′-Oxydianiline

[0348] [Dianhydride compounds]

[0349] DMCBDA: 1,3-Dimethyl-Cyclobutane-1,2,3,4-Tetracarboxylic Dianhydride

[0350] 4IBA: 4,4′-(4,4′-Isopropylidenediphenoxy)bis(phthalic anhydride)

[0351] CBDA: cyclobutane-1,2,3,4-tetracarboxylic dianhydride

[0352] BPAF: 9,9-Bis(3,4-dicarboxyphenyl) fluorene Dianhydride

[0353] [Dicarbonyl Compounds]

[0354] TPC: terephthaloyl chloride

[0355] CHOC: trans-cyclohexane-1,4-dicarbonyl dichloride

[0356] Methods for Measuring Physical Properties

[0357] The physical properties of the optical films prepared according to Examples 1 to 6 and Comparative Examples 1 to 3 were measured by the following method, and the results are disclosed in Table 2.

[0358] (1) Fluorine detection

[0359] The presence of fluorine was confirmed by applying a combustion method.

[0360] Specifically, according to the "BS EN 14582:2016 standard," the optical film specimens were burned and the presence of fluorine was confirmed by the ion chromatography (IC) method. An IC (Ion Chromatography) device was used to confirm the presence of fluorine.

[0361] (2) Yellow Index (YI)

[0362] The yellowness of the polyimide-based films prepared according to Examples 1 to 6 and Comparative Examples 1 to 3 was measured using a spectrophotometer (KONICA MINOLTA CM-3700D) in accordance with ASTM E313.

[0363] (3) Vickers hardness

[0364] For the polyimide-based films prepared according to Examples 1 to 6 and Comparative Examples 1 to 3, the surface area hardness of an indentation formed by pressing with a diamond square pyramid with a diagonal face of 136 degrees was measured according to the ISO 14577-1 method. The pressing load was C kg, and the surface area was D mm. 2 The Vickers hardness of the optical film was calculated using the formula HV = C / D. The measurement was performed using a Fisher HM-2000 Vickers hardness meter.

[0365] - Force: 12mN

[0366] - Running Time: 12s

[0367] - Hold Time: 5s

[0368] (4) Hayes

[0369] The haze of the polyimide-based films prepared according to Examples 1 to 6 and Comparative Examples 1 to 3 was measured using a haze meter (HM-150 of MURAKAMI).

[0370] (5) Measurement of modulus and elongation at break

[0371] 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 6 and Comparative Examples 1 to 3 were measured using a universal tensile testing machine (Model 5967 of Instron).

[0372] (6) Measurement of stress relaxation index

[0373] The stress relaxation index of the polyimide-based films prepared according to Examples 1 to 6 and Comparative Examples 1 to 3 can be obtained by the measurement results according to the following sequence.

[0374] 1) First, a polyimide film sample is prepared using the polyimide films prepared according to Examples 1 to 6 and Comparative Examples 1 to 3, such that the measuring portion is 5 cm (L) x 1 cm (W). Then, a creep deformation evaluation of the polyimide film sample is performed using an Instron universal tensile testing machine (MODEL 5967) according to the following conditions, and the initial load (F0) and the final load (F final ) obtained the value.

[0375] - Temperature and Humidity: Ambient temperature and humid conditions

[0376] - Strain: 4.5%

[0377] - Deformation rate: 0.9% / sec

[0378] - Transformation time: 4 hours

[0379] 2) The initial load (F0) and final load (F) of the film obtained in 1) above final Using the value, the stress relaxation index of the polyimide-based film was calculated and obtained according to Equation 1 below.

[0380] [Equation 1]

[0381] Stress Relaxation Index (%) = [(F0- F final ) / F0] X 100

[0382] (7) Check for the presence of crease

[0383] After performing a dynamic folding test on the polyimide-based films prepared according to Examples 1 to 6 and Comparative Examples 1 to 3 under the following conditions, the presence or absence of crease in the film was visually checked.

[0384] - Sample size: 10cm(L) X 5cm(W)

[0385] - Folding radius: 1.5R

[0386] - Temperature and humidity conditions: Ambient temperature and humidity conditions

[0387] - Number of repetitions: 200,000

[0388] The results of measuring the physical properties of optical films according to the examples and comparative examples are shown in Table 2 below.

[0389] Classification Film Formation Fluorine Detection Stress Relaxation Index (%) Presence or Absence of Crease YI Haze (%) Vickers Hardness Modulus (GPa) Elongation at Break (%) Example 1 OX 57X 2.6 0.2 43 4.613 Example 2 OX 58X 5.9 0.8 49 6.015 Example 3 OX 53X 5.7 0.6 44 5.427 Example 4 OX 48X 3.8 0.3 41 4.465 Example 5 OX 49X 3.9 0.3 39 4.552 Example 6 OX 48X 4.1 0.2 39 4.453 Comparative Example 1 OX 68O 11.3 2.5 45 6.16 Comparative Example 2 OX 72O 2.8 0.4 48 5.96 Comparative Example 3 OX 71O 9.5 0.3 34 4.38

[0390] As disclosed in the measurement results of Table 2, it can be confirmed that the polyimide-based films according to Examples 1 to 6 of the present invention do not have perfluoroalkyl groups and possess excellent mechanical and optical properties. Therefore, the polyimide-based films according to the examples can be used as cover windows for display devices. On the other hand, it can be confirmed that the polyimide-based films according to Comparative Examples 1 to 3 exhibit crease after performing a dynamic folding test and lack mechanical and / or optical properties. Therefore, the polyimide-based films according to the comparative examples may be difficult to use as cover windows for display devices.

[0391] [Explanation of the symbol]

[0392] 100: Polyimide-based film

[0393] 200: Display device

[0394] 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 The above dianhydride compound includes a cycloaliphatic dianhydride compound and an aromatic dianhydride compound, and Polyimide-based film having a stress relaxation index of 60% or less calculated according to Formula 1 below, based on a thickness of 50㎛: [Equation 1] Stress Relaxation Index (%) = [(F0- F final ) / F0] X 100 In Equation 1 above, F0 represents the initial load, and F final represents the termination load, and The above F0 and F final It is measured based on the evaluation of the film's creep deformation.

2. In Paragraph 1, The above imide repeating unit and amide repeating unit each do not contain a perfluoroalkyl group, in a polyimide-based film.

3. In Paragraph 2, The above perfluoroalkyl group comprises *-CF3 and *-CF2-, in a polyimide-based film: Here, *- and -* each mean combining with other elements.

4. In Paragraph 1, The above diamine compound is a polyimide film comprising a benzidine-based diamine.

5. In Paragraph 4, The above benzidine-based diamine is a polyimide-based film comprising a hydrocarbon group as a substituent.

6. In Paragraph 4, The above benzidine-based diamine is a polyimide-based film comprising at least one of the compounds represented by the following chemical formulas 1 to 3. [Chemical Formula 1] [Chemical Formula 2] [Chemical Formula 3] 7. In Paragraph 1, The above-mentioned cycloaliphatic dianhydride compound includes a cycloaliphatic dianhydride compound containing a methyl group, and A polyimide-based film comprising an aromatic dianhydride compound having a methyl group and an aromatic dianhydride compound having an ether group (*-O-*) in the main chain.

8. In Paragraph 7, The above-mentioned cycloaliphatic dianhydride compound further comprises a cycloaliphatic dianhydride compound that does not contain a methyl group, and A polyimide-based film comprising an aromatic dianhydride compound that does not contain a methyl group.

9. In Paragraph 7, A polyimide-based film comprising at least one of the compounds represented by Formulas 4 to 8, wherein the methyl group-containing cycloaliphatic dianhydride compound comprises the above-mentioned compound. [Chemical Formula 4] [Chemical Formula 5] [Chemical Formula 6] [Chemical Formula 7] [Chemical Formula 8] 10. In Paragraph 7, The above-mentioned aromatic dianhydride compound containing a methyl group is a polyimide-based film comprising a compound represented by Chemical Formula 9. [Chemical Formula 9] 11. In Paragraph 8, A polyimide-based film comprising at least one of the compounds represented by the following chemical formulas 10 to 16, wherein the above-mentioned cycloaliphatic dianhydride compound not containing a methyl group comprises the above-mentioned compound. [Chemical Formula 10] [Chemical Formula 11] [Chemical Formula 12] [Chemical Formula 13] [Chemical Formula 14] [Chemical Formula 15] [Chemical Formula 16] 12. In Paragraph 8, A polyimide-based film comprising at least one of the compounds represented by the following chemical formulas 17 to 21, wherein the aromatic dianhydride compound not containing a methyl group is a polyimide-based film. [Chemical Formula 17] [Chemical Formula 18] [Chemical Formula 19] [Chemical Formula 20] [Chemical Formula 21] 13. In Paragraph 1, The above dicarbonyl compound is a polyimide-based film that does not contain a methyl group.

14. In Paragraph 1, A polyimide-based film comprising at least one of the compounds represented by the following chemical formulas 22 to 27, wherein the dicarbonyl compound is a polyimide-based film. [Chemical Formula 22] [Chemical Formula 23] [Chemical Formula 24] [Chemical Formula 25] [Chemical Formula 26] [Chemical Formula 27] 15. In Paragraph 8, A polyimide-based film, wherein, based on a total content of 100 mol% of the dianhydride compound and the dicarbonyl compound, the sum of the contents of the methyl group-containing alicyclic dianhydride compound and the methyl group-containing aromatic dianhydride compound is 15 mol% or more.

16. In Paragraph 8, Based on a total content of 100 mol% of the above dianhydride compound and dicarbonyl compound, The sum of the contents of the above-mentioned cycloaliphatic dianhydride compound containing a methyl group and the above-mentioned aromatic dianhydride compound containing a methyl group is 15 mol% to 100 mol%, and A polyimide-based film in which the sum of the contents of the methyl-free alicyclic dianhydride compound, the methyl-free aromatic dianhydride compound, and the dicarbonyl compound is 0 mol% to 85 mol%.

17. In Paragraph 16, A polyimide-based film in which the molar ratio of the methyl group-containing cycloaliphatic dianhydride compound and the methyl group-containing aromatic dianhydride compound is in the range of 1:9 to 9:

1.

18. In Paragraph 8, A polyimide-based film in which the ratio of the sum of the contents of the methyl-free alicyclic dianhydride compound and the methyl-free aromatic dianhydride compound to the content of the dicarbonyl compound is in the range of 100:0 to 0:

100.

19. In Paragraph 1, A polyimide-based film having a yellowness of 6.0 or less based on a thickness of 50㎛.

20. In Paragraph 1, A polyimide-based film having a Vickers hardness of 35 or higher based on a thickness of 50㎛.

21. In Paragraph 1, A polyimide-based film having a haze of 1.0 or less based on a thickness of 50㎛.

22. In Paragraph 1, A polyimide-based film having a modulus of 3.8 GPa or more based on a thickness of 50 µm.

23. In Paragraph 1, A polyimide-based film having an elongation at break of 10% or more based on a thickness of 50㎛.

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