Polyimide film and optical device comprising the same

Abstract

A polyimide film and an optical device including the same are disclosed. The polyimide film satisfies a predetermined Formula 1 and has a maximum elongation rate of 50% or more as measured according to ASTM D882.

Description

Technical Field

[0001] It relates to a polyimide film and an optical device including the same. More specifically, it relates to a polyimide film that satisfies physical properties required for a film for an optical device, such as modulus, elongation at break, strength, etc., and an optical device including the same. Background Art

[0002] Flexible displays such as curved, bendable, foldable, rollable, etc. are next-generation displays that have recently attracted attention in both academia and industry. Among various materials constituting flexible displays, functional film / coating materials, as important polymer substrate materials for flexible displays, can be said to be core materials essential for the successful realization and development of flexible displays. As such a material, polyimide has attracted much attention.

[0003] Polyimide is a polymer characterized by having a heteroimide ring in its main chain. In addition to excellent heat resistance, it also has excellent mechanical properties, flame retardancy, chemical resistance, low dielectric constant, etc., and is thus widely used in applications such as coating materials, molding materials, and composite materials.

[0004] The most important physical property required for a polymer substrate for a flexible display is flexibility. In particular, such a polymer substrate should not only not be damaged during the processes of bending, folding, curling, and stretching that repeatedly deform the flexible display, but also not lose various initial physical properties. Summary of the Invention

[0005] Technical Problem

[0006] An object of the present invention is to provide a polyimide film that satisfies physical properties required for a film for an optical device, such as modulus, elongation at break, strength, etc.

[0007] Another object of the present invention is to provide an optical device including the above polyimide film.

[0008] Means for Solving the Problem

[0009] 1. According to one aspect, there is provided a polyimide film. The above polyimide film satisfies the following formula 1, and the maximum elongation at break measured according to ASTM D882 can be 50% or more:

[0010] <Formula 1>

[0011] 45 ≤ (A × B) / 10 ≤ 60

[0012] In Formula 1,

[0013] A is the modulus (unit: GPa) of the polyimide film measured at a tensile speed of 200 mm / min according to ASTM D882,

[0014] B is the tensile strength (unit: MPa) at an elongation of 20% of the polyimide film measured at a tensile speed of 200 mm / min in accordance with ASTM D882.

[0015] In the above first embodiment, the above A may be from 2.5 GPa to 4.5 GPa.

[0016] In the above first or second embodiment, the above B may be 140 MPa or more.

[0017] 4. In any one of the above first to third embodiments, the above polyimide film is derived from the imidization of a polyamic acid formed by the reaction of a dianhydride monomer and a diamine monomer. Among the above dianhydride monomers, based on the total molar amount of the above dianhydride monomers, it may contain 55 mol% to 85 mol% of pyromellitic dianhydride (PMDA) and 15 mol% to 45 mol% of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA). Among the above diamine monomers, based on the total molar amount of the above diamine monomers, it may contain 50 mol% to 80 mol% of 4,4'-oxydianiline (ODA) and 20 mol% to 50 mol% of 4,4'-methylenedianiline (MDA).

[0018] 5. In the above fourth embodiment, the molar ratio of PMDA to MDA (PMDA:MDA) may be from 1.1:1 to 3.25:1.

[0019] 6. In the above fourth or fifth embodiment, the molar ratio of BPDA to MDA (BPDA:MDA) may be from 0.3:1 to 1.75:1.

[0020] 7. According to another aspect, there is provided an optical device. The above optical device may include any one of the polyimide films in the above first to sixth embodiments.

[0021] 8. In the above seventh embodiment, the above optical device is a display device and may include the above polyimide film as a back plate film.

[0022] Advantages of the Invention

[0023] The present invention has the effect of providing a polyimide film that satisfies the physical properties required for a film for an optical device, such as modulus, elongation, strength, etc., and an optical device including the same. Detailed Embodiments

[0024] Best Mode for Carrying Out the Invention

[0025] In this specification, unless otherwise clearly specified in the context, singular expressions include plural expressions.

[0026] In this specification, terms such as "comprising" or "having" mean that there are the features or components described in the specification, and do not preclude the additional possibility of one or more other features or components in advance.

[0027] When interpreting components, even if there is no separate and clear description, they are interpreted in a way that includes the error range.

[0028] In this specification, "to" in the numerical range "a to b" is defined as ≥a and ≤b.

[0029] The polyimide film of one aspect of the present invention satisfies the following formula 1, and the maximum elongation rate measured according to ASTM D882 can be 50% or more:

[0030] <Formula 1>

[0031] 45 ≤ (A × B) / 10 ≤ 60

[0032] In Formula 1, A is the modulus of the polyimide film (unit: GPa) measured at a tensile speed of 200 mm / min according to ASTM D882, and B is the tensile strength (unit: MPa) at an elongation rate of 20% of the polyimide film measured at a tensile speed of 200 mm / min according to ASTM D882.

[0033] The polyimide film can satisfy the above Formula 1. Thus, it is possible to advantageously provide a polyimide film that satisfies the physical properties required for a film for an optical device, such as modulus, elongation rate, strength, etc. For example, the lower limit of the value of (A × B) / 10 can be any one of 45, 46, 47, 48, 49, and 50, and the upper limit can be any one of 60, 59, 58, 57, 56, 55, 54, 53, 52, and 51. According to one embodiment, the value of (A × B) / 10 can be 45 to 55, but is not limited thereto.

[0034] The maximum elongation rate of the polyimide film measured at a tensile speed of 200 mm / min according to ASTM D882 can be 50% or more (for example, 55% or more, 60% or more, 65% or more, 70% or more, 75% or more, 80% or more, 85% or more, or 90% or more). In the above range, it is possible to advantageously provide a polyimide film that satisfies the physical properties required for a film for an optical device, such as modulus, elongation rate, strength, etc. The maximum elongation rate of the polyimide film can be, for example, 50% to 150%, or for example, 50% to 100%, or for example, 55% to 95%, but is not limited thereto.

[0035] According to one embodiment, in the above formula (1), A can be from 2.5 GPa to 4.5 GPa (for example, 2.5 GPa, 2.6 GPa, 2.7 GPa, 2.8 GPa, 2.9 GPa, 3.0 GPa, 3.1 GPa, 3.2 GPa, 3.3 GPa, 3.4 GPa, 3.5 GPa, 3.6 GPa, 3.7 GPa, 3.8 GPa, 3.9 GPa, 4.0 GPa, 4.1 GPa, 4.2 GPa, 4.3 GPa, 4.4 GPa, or 4.5 GPa). When within the above range, it is possible to advantageously provide a polyimide film that satisfies the physical properties required for a film for an optical device, such as modulus, elongation at break, strength, etc. A can be, for example, from 2.5 GPa to 4 GPa, or for example, from 3 GPa to 4 GPa, or for example, from 3 GPa to 3.5 GPa, but is not limited thereto.

[0036] According to one embodiment, in the above formula (1), B can be 140 MPa or more (for example, 141 MPa or more, 142 MPa or more, 143 MPa or more, 144 MPa or more, or 145 MPa or more). When within the above range, it is possible to advantageously provide a polyimide film that satisfies the physical properties required for a film for an optical device, such as modulus, elongation at break, strength, etc. B can be, for example, from 140 MPa to 300 MPa, or for example, from 140 MPa to 200 MPa, or for example, from 140 MPa to 170 MPa, or for example, from 140 MPa to 160 MPa, but is not limited thereto.

[0037] According to one embodiment, the thickness of the polyimide film can be, for example, from 10 μm to 500 μm, or for example, from 10 μm to 100 μm, or for example, from 30 μm to 50 μm, but is not limited thereto.

[0038] According to one embodiment, the polyimide film can be derived from the imidization of a polyamic acid formed by the reaction of a dianhydride monomer and a diamine monomer. Regarding the types of the dianhydride monomer and the diamine monomer, known dianhydride monomers and diamine monomers can be used without limitation within the scope that does not impede the object of the present invention. For example, the dianhydride monomer can include pyromellitic dianhydride (PMDA) and 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), and the diamine monomer can include 4,4'-oxydianiline (ODA) and 4,4'-methylenedianiline (MDA). In such a case, it is more beneficial to provide a polyimide film that meets the physical properties required for a film for an optical device, such as modulus, elongation at break, strength, etc. According to one embodiment, among the dianhydride monomers, based on the total molar amount of the dianhydride monomers, it can include 55 mol% to 85 mol% of PMDA and 15 mol% to 45 mol% of BPDA. Among the diamine monomers, based on the total molar amount of the diamine monomers, it can include 50 mol% to 80 mol% of ODA and 20 mol% to 50 mol% of MDA. Within the above ranges, it is more beneficial to provide a polyimide film that meets the physical properties required for a film for an optical device, such as modulus, elongation at break, strength, etc. For example, among the dianhydride monomers, based on the total molar amount of the dianhydride monomers, it can include 55 mol%, 56 mol%, 57 mol%, 58 mol%, 59 mol%, 60 mol%, 61 mol%, 62 mol%, 63 mol%, 64 mol%, 65 mol%, 66 mol%, 67 mol%, 68 mol%, 69 mol%, 70 mol%, 71 mol%, 72 mol%, 73 mol%, 74 mol%, 75 mol%, 76 mol%, 77 mol%, 78 mol%, 79 mol%, 80 mol%, 81 mol%, 82 mol%, 83 mol%, 84 mol% or 85 mol% of PMDA, and can include 45 mol%, 44 mol%, 43 mol%, 42 mol%, 41 mol%, 40 mol%, 39 mol%, 38 mol%, 37 mol%, 36 mol%, 35 mol%, 34 mol%, 33 mol%, 32 mol%, 31 mol%, 30 mol%, 29 mol%, 28 mol%, 27 mol%, 26 mol%, 25 mol%, 24 mol%, 23 mol%, 22 mol%, 21 mol%, 20 mol%, 19 mol%, 18 mol%, 17 mol%, 16 mol% or 15 mol% of BPDA.For example, in the diamine monomer, based on the total molar amount of the diamine monomer, it may contain 50 mol%, 51 mol%, 52 mol%, 53 mol%, 54 mol%, 55 mol%, 56 mol%, 57 mol%, 58 mol%, 59 mol%, 60 mol%, 61 mol%, 62 mol%, 63 mol%, 64 mol%, 65 mol%, 66 mol%, 67 mol%, 68 mol%, 69 mol%, 70 mol%, 71 mol%, 72 mol%, 73 mol%, 74 mol%, 75 mol%, 76 mol%, 77 mol%, 78 mol%, 79 mol% or 80 mol% of ODA, and may contain 50 mol%, 49 mol%, 48 mol%, 47 mol%, 46 mol%, 45 mol%, 44 mol%, 43 mol%, 42 mol%, 41 mol%, 40 mol%, 39 mol%, 38 mol%, 37 mol%, 36 mol%, 35 mol%, 34 mol%, 33 mol%, 32 mol%, 31 mol%, 30 mol%, 29 mol%, 28 mol%, 27 mol%, 26 mol%, 25 mol%, 24 mol%, 23 mol%, 22 mol%, 21 mol% or 20 mol% of MDA.

[0039] According to one embodiment, the molar ratio of BPDA to MDA (BPDA:MDA) may be from 0.3:1 to 2.3:1 (for example, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2:1, 2.1:1, 2.2:1 or 2.3:1, and for another example, from 0.3:1 to 1.75:1). In such a case, it is more favorable to provide a polyimide film that meets the physical properties required for the film for optical devices, such as modulus, elongation at break, strength, etc.

[0040] According to one embodiment, the molar ratio of PMDA to MDA (PMDA:MDA) can be from 1.1:1 to 4.3:1 (for example, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1, 2.6:1, 2.7:1, 2.8:1, 2.9:1, 3:1, 3.1:1, 3.2:1, 3.3:1, 3.4:1, 3.5:1, 3.6:1, 3.7:1, 3.8:1, 3.9:1, 4:1, 4.1:1, 4.2:1, or 4.3:1, and again for example from 1.1:1 to 3.25:1). In such a case, it is more conducive to providing a polyimide film that meets the physical properties required for the film for an optical device, such as modulus, elongation at break, strength, etc.

[0041] According to one embodiment, the molar ratio of BPDA to ODA (BPDA:ODA) can be from 0.1:1 to 0.9:1 (for example, 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, or 0.9:1, and again for example from 0.3:1 to 0.9:1). In such a case, it is more conducive to providing a polyimide film that meets the physical properties required for the film for an optical device, such as modulus, elongation at break, strength, etc.

[0042] According to one embodiment, the molar ratio of PMDA to ODA (PMDA:ODA) can be from 0.6:1 to 1.7:1 (for example, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, or 1.7:1, and again for example from 0.8:1 to 1.7:1). In such a case, it is more conducive to providing a polyimide film that meets the physical properties required for the film for an optical device, such as modulus, elongation at break, strength, etc.

[0043] According to one embodiment, the polyamic acid can be formed by further adding the remaining one of BPDA and PMDA and the remaining one of MDA and ODA to a pre-reactant of any one of BPDA and PMDA and any one of MDA and ODA to extend at least a part of the ends of the above pre-reactant. In such a case, it is easy to control the number of bonds of BPDA-MDA, BPDA-ODA, PMDA-MDA, and PMDA-ODA present in the polyimide film. As a result, it is more conducive to providing a polyimide film that meets the physical properties required for the film for an optical device, such as modulus, elongation at break, strength, etc.

[0044] The manufacturing method of the polyimide film is not particularly limited, and a known method can be arbitrarily selected. For example, the polyimide film can be manufactured as follows: reacting a dianhydride monomer and a diamine monomer in a solvent to form a polyamic acid solution; mixing an imidization agent and / or a dehydrating agent in the polyamic acid solution to form a precursor composition for the polyimide film; coating the above precursor composition on a support and drying to form a gel film; and peeling the gel film from the support and performing heat treatment.

[0045] First, a dianhydride monomer and a diamine monomer can be reacted in a solvent to form a polyamic acid solution. The types of the dianhydride monomer and the diamine monomer can refer to the above description.

[0046] As the solvent, there is no particular limitation as long as it can dissolve the polyamic acid. For example, the solvent may include an aprotic polar solvent. Examples of the aprotic polar solvent include amide solvents such as N,N'-dimethylformamide (DMF) and N,N'-dimethylacetamide (DMAc); phenolic solvents such as p-chlorophenol and o-chlorophenol; N-methyl-pyrrolidone (NMP), γ-butyrolactone (GBL), diglyme, etc., which can be used alone or in combination of two or more. Depending on the situation, auxiliary solvents such as toluene, tetrahydrofuran (THF), acetone, methyl ethyl ketone (MEK), methanol, ethanol, water, etc. can also be used to adjust the solubility of the polyamic acid.

[0047] When forming the polyamic acid solution, the diamine monomer and the dianhydride monomer are added to the solvent in a substantially equimolar manner for reaction. Here, the so-called "substantially equimolar" means that based on the total molar number of the diamine monomer, the content of the dianhydride monomer is 99.8 to 100.2 mol%.

[0048] According to one embodiment, based on 100 parts by weight of the polyamic acid solution, the content of the polyamic acid can be 5 parts by weight to 35 parts by weight. In the above range, the polyamic acid solution can have a molecular weight and viscosity suitable for film formation. For example, based on 100 parts by weight of the polyamic acid solution, the content of the polyamic acid can be 5 parts by weight to 30 parts by weight, and for another example, it can be 15 parts by weight to 20 parts by weight, but it is not limited thereto.

[0049] According to one embodiment, the viscosity of the polyamic acid solution at a shear rate of 23°C and 1 s -1 can be 100,000 cP to 500,000 cP. In the above range, the polyamic acid can have a predetermined molecular weight and excellent processability when forming the polyimide film. Here, the "viscosity" can be measured using a HAAKE Mars Rheometer. For example, the viscosity of the polyamic acid solution at 23°C and 1 s-1 The shear rate can be from 100,000 cP to 450,000 cP, for example, it can be from 100,000 cP to 400,000 cP, and for another example, it can be from 100,000 cP to 350,000 cP, but it is not limited thereto.

[0050] According to an embodiment, the weight-average molecular weight of the polyamic acid can be from 100,000 g / mol to 500,000 g / mol. In the above range, it is more beneficial to provide a polyimide film that meets the physical properties required for the film used in optical devices, such as modulus, elongation at break, strength, etc. Here, the "weight-average molecular weight" can be measured by gel permeation chromatography (GPC) using polystyrene as the standard sample. For example, the weight-average molecular weight of the polyamic acid can be from 150,000 g / mol to 500,000 g / mol, and for another example, it can be from 100,000 g / mol to 400,000 g / mol, but it is not limited thereto.

[0051] After that, an imidizing agent and / or a dehydrating agent can be mixed in the polyamic acid solution to form a precursor composition for the polyimide film.

[0052] The so-called "dehydrating agent" is a substance that promotes the ring-closing reaction by dehydrating the polyamic acid. Examples of the dehydrating agent include aliphatic acid anhydrides, aromatic acid anhydrides, N,N'-dialkylcarbodiimides, lower aliphatic halides, halogenated lower aliphatic acid anhydrides, diarylphosphonic dihalides, thionyl halides, etc., and they can be used alone or in combination of two or more. Among them, from the viewpoints of availability and cost, aliphatic acid anhydrides such as acetic anhydride, propionic anhydride, and lactic anhydride can be used.

[0053] The so-called "imidizing agent" is a substance that promotes the ring-closing reaction of the polyamic acid. Examples of the imidizing agent include aliphatic tertiary amines, aromatic tertiary amines, heterocyclic tertiary amines, etc. Among them, from the viewpoint of the reactivity as a catalyst, heterocyclic tertiary amines can be used. Examples of the heterocyclic tertiary amines include quinoline, isoquinoline, β-methylpyridine, pyridine, etc., and they can be used alone or in combination of two or more.

[0054] The addition amount of the dehydrating agent and / or the imidizing agent is not particularly limited. Relative to 1 mole of the amic acid group in the polyamic acid, the dehydrating agent can be used at a ratio of 0.5 mole to 5 moles (for example, 1 mole to 4 moles), and relative to 1 mole of the amic acid group in the polyamic acid, the imidizing agent can be used at a ratio of 0.05 mole to 3 moles (for example, 0.2 mole to 2 moles). In the above range, the imidization is sufficient and it is easy to cast into a film.

[0055] Thereafter, the precursor composition can be coated on a support and dried to form a gel film.

[0056] Here, the so-called "gel film" refers to a film that is in an intermediate stage of curing from polyamic acid to polyimide and has self-supporting properties.

[0057] Examples of the support include, but are not limited to, a glass plate, an aluminum foil, an endless stainless steel belt, a stainless steel roller, etc.

[0058] Examples of the coating method include, but are not limited to, a casting method.

[0059] The drying temperature can be, for example, from 40°C to 300°C, or for example, from 80°C to 200°C, but is not limited thereto. The drying time can be, for example, from 3 minutes to 10 minutes, or for example, from 4 minutes to 8 minutes, but is not limited thereto.

[0060] Thereafter, the gel film can be peeled off from the support and heat-treated to produce a polyimide film.

[0061] By the heat treatment of the gel film, it is possible to remove solvents and the like remaining in the gel film and imidize most of the remaining amic acid groups.

[0062] The heat treatment temperature can be, for example, from 50°C to 700°C, or for example, from 150°C to 600°C, or for example, from 200°C to 600°C, but is not limited thereto. The heat treatment time can be, for example, from 5 minutes to 20 minutes, or for example, from 7 minutes to 15 minutes, but is not limited thereto.

[0063] Optionally, before the heat treatment of the gel film, a step of stretching the gel film can be further included to control the thickness, etc. of the finally obtained polyimide film and improve the orientation. The stretching can be performed in either the machine direction (MD) or the transverse direction (TD).

[0064] Optionally, the polyimide film obtained after the heat treatment of the gel film can be heat-finished by heating at 400°C to 650°C for 5 seconds to 400 seconds to further cure the polyimide film. At this time, in order to reduce the internal stress that may remain in the polyimide film, the heat finishing can also be performed under a predetermined tension, but is not limited thereto.

[0065] The above-mentioned polyimide film or the polyimide film manufactured by the above-mentioned manufacturing method can satisfy the physical properties required for the film for optical devices, such as modulus, elongation at break, strength, etc., and thus can be suitably used for optical devices. For example, the above-mentioned optical device can be a display device, and the above-mentioned polyimide film can be used as a backplane film, but it is not limited thereto.

[0066] According to another aspect of the present invention, there is provided an optical device including the above-mentioned polyimide film. The above-mentioned optical device is a display device and may include the above-mentioned polyimide film as a backplane film.

[0067] Embodiment

[0068] Hereinafter, examples will be given to explain the present invention in more detail. However, this is provided as a preferred example of the present invention and should not be construed in any sense as limiting the present invention.

[0069] Examples

[0070] Examples 1 to 4 and Comparative Examples 1 to 4

[0071] In dimethylformamide (DMF), the dianhydride monomer and the diamine monomer were mixed as described in Table 1 and reacted at 30 °C for 2 hours to produce a polyamic acid solution having a viscosity of 150,000 cP (23 °C, 1 s -1 ). At this time, the dianhydride monomer and the diamine monomer were made to be substantially equimolar, and the reaction conditions were controlled so that the reaction of BPDA and MDA was prior to the reaction between other monomers.

[0072] Acetic anhydride at a molar ratio of 3.2 and isoquinoline at a molar ratio of 1.0 per 1 mole of amic acid groups were added to the polyamic acid solution thus produced to obtain a precursor composition for a polyimide film.

[0073] The above-mentioned composition was cast on a SUS plate (100SA, Sandvik Co., Ltd.) using a doctor blade and dried at 110 °C for 4 minutes to produce a gel film.

[0074] After separating the above-mentioned gel film from the SUS plate, heat treatment was performed at 380 °C for 8 minutes to produce a polyimide film having a thickness of 50 μm.

[0075] [Table 1]

[0076]

[0077] As can be seen from Table 1 above, the polyimide films of Examples 1 to 4 in which the value of (A×B) / 10 satisfies the scope of the present invention and the elongation at break is 50% or more show excellent physical properties as films for optical devices as compared with the polyimide films of Comparative Examples 1 to 4 which do not satisfy the above conditions.

[0078] So far, the present invention has been understood centering around the embodiments. Those of ordinary skill in the art to which the present invention pertains should be able to implement the present invention in a modified manner without departing from the essential characteristics of the present invention. Therefore, the disclosed embodiments should be considered from an illustrative rather than a limiting perspective. The scope of the present invention is shown in the claims rather than the above description, and all differences within the scope equivalent thereto will be construed as being included in the present invention.

[0079] Industrial Applicability

[0080] The present invention has the effect of providing a polyimide film that satisfies the physical properties required for films for optical devices, such as modulus, elongation at break, strength, etc., and an optical device including the same.

Claims

1. A polyimide film that satisfies the following Formula 1 and has a maximum elongation rate of 50% or more as measured according to ASTM D882: <Formula 1> 45 ≤ (A × B) / 10 ≤ 60 In Formula 1, A is the modulus of the polyimide film measured at a tensile speed of 200 mm / min according to ASTM D882, in GPa, B is the tensile strength at an elongation rate of 20% of the polyimide film measured according to ASTM D882, in MPa, said B is 140 MPa or more, the polyimide film is derived from the imidization of a polyamic acid formed by the reaction of a dianhydride monomer and a diamine monomer, in the dianhydride monomer, based on the total molar amount of the dianhydride monomer, it contains 55 mol% to 85 mol% of pyromellitic dianhydride PMDA and 15 mol% to 45 mol% of 3,3',4,4'-biphenyltetracarboxylic dianhydride BPDA, in the diamine monomer, based on the total molar amount of the diamine monomer, it contains 50 mol% to 80 mol% of 4,4'-diaminodiphenyl ether ODA and 20 mol% to 50 mol% of 4,4'-diaminodiphenylmethane MDA.

2. The polyimide film according to claim 1, wherein A is 2.5 GPa to 4.2 GPa.

3. The polyimide film according to claim 1, wherein the molar ratio of PMDA to MDA, PMDA:MDA, is 1.1:1 to 3.25:

1.

4. The polyimide film according to claim 1, wherein the molar ratio of BPDA to MDA, BPDA:MDA, is 0.3:1 to 1.75:

1.

5. An optical device that includes the polyimide film according to any one of claims 1 to 4.

6. The optical device according to claim 5, wherein the optical device is a display device that includes the polyimide film as a backplane film.

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