Polyimide film and optical device including same

Abstract

Disclosed is a polyimide film that satisfies the given formula 1 and has a maximum elongation of 50% or more as measured in accordance with ASTM D882, and an optical device including the same.

Description

[Technical field]

[0001] The present invention relates to a polyimide film and an optical device including the same, and more particularly to 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. [Background technology]

[0002] Flexible displays, such as curved, bendable, foldable, and rollable displays, are next-generation displays that have recently been attracting attention from both academia and industry. Among the various types of materials that make up flexible displays, functional film / coating materials are the important polymer substrate materials that make up flexible displays, and are essential core materials for the successful realization and development of flexible displays. Polyimide is attracting attention as such a material. Polyimides are polymers characterized by having heteroimide rings in their main chains. In addition to excellent heat resistance, they also have excellent mechanical properties, flame retardancy, chemical resistance, and low dielectric constant, and are used in a wide range of applications, such as coating materials, molding materials, and composite materials. The most important physical property required for polymer substrates for flexible displays is flexibility. In particular, such polymer substrates must not only not be damaged but also retain various initial physical properties during the curving, bending, folding, rolling, and stretching processes that repeatedly cause deformations in flexible displays. Summary of the Invention [Problem to be solved by the invention]

[0003] An object of the present invention is to provide a polyimide film which satisfies the physical properties required for a film for an optical device, such as modulus, elongation, strength, etc. Another object of the present invention is to provide an optical device including the polyimide film. [Means for solving the problem]

[0004] 1. According to one aspect, there is provided a polyimide film, which may satisfy the following formula 1 and have a maximum elongation of 50% or more as measured according to ASTM D882: <Expression 1> 45≦(A×B) / 10≦60 In formula 1, A is the modulus of the polyimide film (unit: GPa) measured at a tensile speed of 200 mm / min based on ASTM D882, B is the tensile strength (unit: MPa) of the polyimide film at an elongation of 20% measured at a tensile speed of 200 mm / min based on ASTM D882. 2. In the first embodiment, A may be 2.5 GPa to 4.5 GPa. 3. In the first or second embodiment, the B may be 140 MPa or more. 4. In any one of the first to third embodiments, the polyimide film is derived from imidization of a polyamic acid formed from a reaction of a dianhydride monomer and a diamine monomer, and the dianhydride monomer is, based on the total mole number of the dianhydride monomer, 55 mol % to 85 mol % of pyromellitic dianhydride (PMDA) and 3,3',4,4'-biphenyltetracarboxylic dianhydride. The diamine monomer may include 15 mol% to 45 mol% of 3,3',4,4'-biphenyl tetracarboxylic dianhydride (BPDA), and the diamine monomer may include 50 mol% to 80 mol% of 4,4'-oxydianiline (ODA) and 20 mol% to 50 mol% of 4,4'-methylenedianiline (MDA), based on the total number of moles of the diamine monomer. 5. In the fourth embodiment, the molar ratio of PMDA and MDA (PMDA:MDA) may be 1.1:1 to 3.25:1. 6. In the fourth or fifth embodiment, the molar ratio of BPDA to MDA (BPDA:MDA) may be 0.3:1 to 1.75:1. 7. According to another aspect, there is provided an optical device, which may include the polyimide film according to any one of the first to sixth embodiments. 8. In the seventh embodiment, the optical device is a display device, and may include the polyimide film as a back plate film. Effect of the Invention

[0005] The present invention has an 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 DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0006] In this specification, the singular expression includes the plural expression unless the context clearly indicates otherwise.

[0007] In this specification, the terms including or having mean the presence of the features or components described in the specification, without precluding the possibility that one or more other features or components may be added.

[0008] When interpreting elements, they are interpreted as including error ranges even if there is no explicit statement to the contrary.

[0009] In this specification, the "to" in the expression "a to b" indicating a numerical range is defined as ≧a and ≦b.

[0010] The polyimide film according to one aspect of the present invention may satisfy the following formula 1 and have a maximum elongation of 50% or more as measured according to ASTM D882: <Expression 1> 45≦(A×B) / 10≦60 In Equation 1, A is the modulus (unit: GPa) of the polyimide film measured at a tensile speed of 200 mm / min according to ASTM D882, and 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 according to ASTM D882.

[0011] The polyimide film can satisfy the formula 1. This can advantageously provide a polyimide film that satisfies the physical properties required for a film for an optical device, such as modulus, elongation, and strength. For example, the lower limit of the value of (A×B) / 10 may be any one of 45, 46, 47, 48, 49, and 50, and the upper limit may 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 may be 45 to 55, but is not limited thereto.

[0012] The polyimide film may have a maximum elongation of 50% or more (e.g., 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) measured at a tensile speed of 200 mm / min according to ASTM D882. It may be advantageous to provide a polyimide film in the above range that satisfies the physical properties required for a film for an optical device, such as modulus, elongation, strength, etc. The maximum elongation of the polyimide film may be, for example, 50% to 150%, as another example, 50% to 100%, and as yet another example, 55% to 95%, but is not limited thereto.

[0013] According to one embodiment, in the above formula 1, A may be 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). In the above range, it may be advantageous to provide a polyimide film that satisfies the physical properties required for a film for an optical device, such as modulus, elongation, strength, etc. A may be, for example, 2.5 GPa to 4 GPa, as another example, 3 GPa to 4 GPa, and as yet another example, 3 GPa to 3.5 GPa, but is not limited thereto.

[0014] According to one embodiment, in the above formula 1, B may be 140 MPa or more (e.g., 141 MPa or more, 142 MPa or more, 143 MPa or more, 144 MPa or more, or 145 MPa or more). In this range, it may be advantageous to provide a polyimide film that satisfies the physical properties required for a film for an optical device, such as modulus, elongation, strength, etc. B may be, for example, 140 MPa to 300 MPa, as another example, 140 MPa to 200 MPa, as yet another example, 140 MPa to 170 MPa, and as yet another example, 140 MPa to 160 MPa, but is not limited thereto.

[0015] According to one embodiment, the thickness of the polyimide film may be, for example, 10 μm to 500 μm, as another example, 10 μm to 100 μm, and as yet another example, 30 μm to 50 μm, but is not limited thereto.

[0016] According to one embodiment, the polyimide film is derived from imidization of a polyamic acid formed from the reaction of a dianhydride monomer and a diamine monomer. The types of the dianhydride monomer and the diamine monomer may be any known dianhydride monomer and diamine monomer without limitation within the scope of the present invention. For example, the dianhydride monomer may include pyromellitic dianhydride (PMDA) and 3,3',4,4'-biphenyl tetracarboxylic dianhydride (BPDA), and the diamine monomer may include 4,4'-oxydianiline (ODA) and 4,4'-methylenedianiline (MDA). In this case, it may be more advantageous to provide a polyimide film that satisfies the physical properties required for a film for an optical device, such as modulus, elongation, strength, etc. According to one embodiment, the dianhydride monomer may include 55 mol% to 85 mol% PMDA and 15 mol% to 45 mol% BPDA based on the total number of moles of the dianhydride monomer, and the diamine monomer may include 50 mol% to 80 mol% ODA and 20 mol% to 50 mol% MDA based on the total number of moles of the diamine monomer, and within the above ranges, it may be more advantageous to provide a polyimide film that satisfies the physical properties required for a film for an optical device, such as modulus, elongation, strength, etc. For example, the dianhydride monomer may 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%, 85 mol%, 86 mol%, 87 mol%, 88 mol%, 89 mol%, 90 mol%, 91 mol%, 92 mol%, 93 mol%, 94 mol%, 95 mol%, 96 mol%, 97 mol%, 98 mol%, 99 mol%, 100 mol%, 102 mol%, 104 mol%, 105 mol%, 106 mol%, 107 mol%, 108 mol%, 109 mol%, 110 mol%, 111 and 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% BPDA. For example, the diamine monomer may be, based on the total number of moles of the diamine monomer, ODA may be 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%, The polymer may comprise 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% MDA.

[0017] According to one embodiment, the molar ratio of BPDA and MDA (BPDA:MDA) may be 0.3:1 to 2.3:1 (e.g., 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, as another example, 0.3:1 to 1.75:1), and in this case, it may be more advantageous to provide a polyimide film that satisfies the physical properties required for a film for an optical device, such as modulus, elongation, strength, etc.

[0018] According to one embodiment, the molar ratio of PMDA and MDA (PMDA:MDA) is from 1.1:1 to 4.3:1 (e.g., 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, as another example, 1.1:1 to 3.25:1), in which case it may be more advantageous to provide a polyimide film that satisfies the physical properties required for a film for an optical device, such as modulus, elongation, strength, etc.

[0019] According to one embodiment, the molar ratio of BPDA to ODA (BPDA:ODA) may be 0.1:1 to 0.9:1 (e.g., 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, as another example, 0.3:1 to 0.9:1), in which case it may be more advantageous to provide a polyimide film that satisfies the physical properties required for a film for an optical device, such as modulus, elongation, strength, etc.

[0020] According to one embodiment, the molar ratio of PMDA to ODA (PMDA:ODA) may be 0.6:1 to 1.7:1 (e.g., 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, as another example, 0.8:1 to 1.7:1), in which case it may be more advantageous to provide a polyimide film that satisfies the physical properties required for a film for an optical device, such as modulus, elongation, strength, etc.

[0021] According to one embodiment, the polyamic acid may be formed by adding the remaining one of BPDA and PMDA and the remaining one of MDA and ODA to a pre-reactant of either BPDA or PMDA and either MDA or ODA, and extending at least a part of the end of the pre-reactant. In this 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, and as a result, it is more advantageous to provide a polyimide film that satisfies the physical properties required for a film for an optical device, such as modulus, elongation, strength, etc.

[0022] The method for producing the polyimide film is not particularly limited, and any known method can be used. For example, a polyamic acid solution is formed by reacting a dianhydride monomer and a diamine monomer in a solvent; an imidizing agent and / or a dehydrating agent are mixed into the polyamic acid solution to form a precursor composition for the polyimide film; the precursor composition is applied onto a support and dried to form a gel film; and the gel film is peeled off from the support and heat-treated to produce a polyimide film.

[0023] First, a dianhydride monomer and a diamine monomer are reacted in a solvent to form a polyamic acid solution. For the types of the dianhydride monomer and the diamine monomer, see above.

[0024] The solvent is not particularly limited as long as it can dissolve the polyamic acid. For example, the solvent can include an aprotic polar solvent. Examples of aprotic polar solvents include amide-based solvents such as N,N'-dimethylformamide (DMF) and N,N'-dimethylacetamide (DMAc), phenol-based solvents such as p-chlorophenol and o-chlorophenol, N-methyl-pyrrolidone (NMP), gamma butyrolactone (GBL), and diglyme, which can be used alone or in combination of two or more. In some cases, the solubility of the polyamic acid may be adjusted using auxiliary solvents such as toluene, tetrahydrofuran (THF), acetone, methyl ethyl ketone (MEK), methanol, ethanol, and water.

[0025] When forming the polyamic acid solution, the diamine monomer and the dianhydride monomer are reacted in a solvent in substantially equimolar amounts. Here, "substantially equimolar" may mean that the dianhydride monomer is contained in an amount of 99.8 to 100.2 mol% based on the total moles of the diamine monomer.

[0026] According to one embodiment, the polyamic acid is included in an amount of 5 to 35 parts by weight based on 100 parts by weight of the polyamic acid solution. In this range, the polyamic acid solution may have a molecular weight and viscosity suitable for forming a film. For example, the polyamic acid is included in an amount of 5 to 30 parts by weight, or in another example, 15 to 20 parts by weight based on 100 parts by weight of the polyamic acid solution, but is not limited thereto.

[0027] According to one embodiment, the polyamic acid solution is heated at 23° C. for 1 s -1The viscosity at a shear rate of 100,000 cP to 500,000 cP may be in the range of 100,000 cP to 500,000 cP. In this range, the polyamic acid can have a predetermined molecular weight while being excellent in processability when forming a polyimide film. Here, the "viscosity" can be measured using a HAAKE Mars Rheometer. For example, the viscosity of a polyamic acid solution is -1 in a shear rate of 100,000 cP to 450,000 cP, in another example 100,000 cP to 400,000 cP, in yet another example 100,000 cP to 350 ,000 cP, but is not limited to this.

[0028] According to one embodiment, the polyamic acid may have a weight average molecular weight of 100,000 g / mol to 500,000 g / mol. In this range, it may be more advantageous to provide a polyimide film that satisfies the physical properties required for a film for an optical device, such as modulus, elongation, strength, etc. Here, the "weight average molecular weight" can be measured using gel chromatography (GPC) and polystyrene as a standard sample. For example, the weight average molecular weight of the polyamic acid may be 150,000 g / mol to 500,000 g / mol, or as another example, 100,000 g / mol to 400,000 g / mol, but is not limited thereto.

[0029] Thereafter, an imidizing agent and / or a dehydrating agent can be mixed with the polyamic acid solution to form a polyimide film precursor composition.

[0030] The "dehydrating agent" is an agent 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, arylphosphonic acid dihalides, and thionyl halides, which can be used alone or in combination of two or more. Among these, from the viewpoints of availability and cost, aliphatic acid anhydrides such as acetic acid anhydride, propionic acid anhydride, and lactic acid anhydride can be used.

[0031] An "imidizing agent" is an agent that promotes a ring-closing reaction with polyamic acid. Examples of imidizing agents include aliphatic tertiary amines, aromatic tertiary amines, and heterocyclic tertiary amines. Among them, heterocyclic tertiary amines can be used from the viewpoint of reactivity as a catalyst. Examples of heterocyclic tertiary amines include quinoline, isoquinoline, β-picoline, and pyridine, which can be used alone or in combination of two or more kinds.

[0032] The amount of the dehydrating agent and / or the imidizing agent to be added is not particularly limited, but the dehydrating agent can be used in a ratio of 0.5 mol to 5 mol (another example is 1 mol to 4 mol) per mol of amic acid group in the polyamic acid, and the imidizing agent can be used in a ratio of 0.05 mol to 3 mol (another example is 0.2 mol to 2 mol) per mol of amic acid group in the polyamic acid. Within the above ranges, imidization is sufficient and casting into a film can be easy.

[0033] The precursor composition can then be coated onto a substrate and dried to form a gel film.

[0034] Here, the term "gel film" can refer to a film that is in an intermediate stage of curing from polyamic acid to polyimide and has self-supporting properties.

[0035] Examples of the support include, but are not limited to, a glass plate, an aluminum foil, an endless stainless steel belt, a stainless steel drum, and the like.

[0036] An example of the application method includes, but is not limited to, a casting method.

[0037] The drying temperature may be, for example but not limited to, 40° C. to 300° C., or in another example, 80° C. to 200° C. The drying time may be, for example but not limited to, 3 minutes to 10 minutes, or in another example, 4 minutes to 8 minutes.

[0038] The gel film can then be peeled off from the support and heat treated to produce a polyimide film.

[0039] By heat treating the gel film, the solvent remaining in the gel film is removed and most of the remaining amic acid groups are imidized.

[0040] The heat treatment temperature may be, for example but not limited to, 50° C. to 700° C., for another example, 150° C. to 600° C., and for yet another example, 200° C. to 600° C. The heat treatment time may be, for example but not limited to, 5 minutes to 20 minutes, and for another example, 7 minutes to 15 minutes.

[0041] Optionally, the method may further include a step of stretching the gel film before the heat treatment of the gel film in order to control the thickness of the final polyimide film and improve the orientation. The stretching is performed in at least one direction of MD (machine direction) and TD (transverse direction).

[0042] Alternatively, the polyimide film obtained after the heat treatment of the gel film can be further cured by heat finishing at 400° C. to 650° C. for 5 to 400 seconds. At this time, the heat finishing may be performed under a predetermined tension in order to relieve internal stress that may remain in the polyimide film, but is not limited thereto.

[0043] The polyimide film described above or the polyimide film produced by the above-mentioned production method can satisfy the physical properties required for a film for an optical device, such as modulus, elongation, strength, etc., and therefore can be suitably used in an optical device. For example, the optical device described above is a display device, and the polyimide film described above can be used as a backplate film, but is not limited thereto.

[0044] According to another aspect of the present invention, there is provided an optical device including the above-mentioned polyimide film. The optical device is a display device, and may include the above-mentioned polyimide film as a back plate film. EXAMPLES

[0045] The present invention will be described in more detail below with reference to examples. However, these are presented as preferred examples of the present invention and are not to be construed as limiting the present invention in any sense.

[0046] Working Example Examples 1 to 4 and Comparative Examples 1 to 4 In dimethylformamide (DMF), dianhydride monomers and diamine monomers were mixed as shown in Table 1 and reacted at 30° C. for 2 hours to obtain a viscosity of 150,000 cP (23° C., 1 s -1 A polyamic acid solution having the formula (I) was prepared by controlling the reaction conditions so that the dianhydride monomer and the diamine monomer were substantially equimolar and the reaction between BPDA and MDA was more predominant than the reaction between other monomers. To the polyamic acid solution thus prepared, 3.2 molar ratios of acetic anhydride and 1.0 molar ratios of isoquinoline per mole of amic acid group were added to obtain a precursor composition for a polyimide film. The composition was cast onto a SUS plate (100SA, Sandvik) using a doctor blade and dried at 110° C. for 4 minutes to prepare a gel film. The gel film was separated from the SUS plate and then heat-treated at 380°C for 8 minutes to form a 50μm A polyimide film having a thickness was prepared.

[0047] [Table 1]

[0048] From Table 1, it can be seen that the polyimide films of Examples 1 to 4, in which the (A×B) / 10 value satisfies the range of the present invention and the elongation is 50% or more, exhibit superior physical properties as films for optical devices compared to the polyimide films of Comparative Examples 1 to 4, in which the (A×B) / 10 value satisfies the range of the present invention and the elongation is 50% or more.

[0049] The present invention has been described above with reference to the embodiments. Those skilled in the art will understand that the present invention can be realized in modified forms without departing from the essential characteristics of the present invention. Therefore, the disclosed embodiments should be considered in an illustrative rather than restrictive manner. The scope of the present invention is defined in the claims, not in the above description, and all differences within the scope of the claims should be interpreted as being included in the present invention. [Industrial Applicability]

[0050] The present invention has an 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.

Claims

1. The following formula 1 is satisfied, and the maximum elongation measured based on ASTM D882 is 50% or more, derived from the imidization of a polyamic acid formed from the reaction of a dianhydride monomer and a diamine monomer; The dianhydride monomer includes 55 mol% to 85 mol% of pyromellitic dianhydride (PMDA) and 15 mol% to 45 mol% of 3,3',4,4'-biphenyl tetracarboxylic dianhydride (BPDA) based on the total number of moles of the dianhydride monomer; The diamine monomer includes 50 mol % to 80 mol % of 4,4'-oxydianiline (ODA) and 20 mol % to 50 mol % of 4,4'-methylenedianiline (MDA) based on the total number of moles of the diamine monomer. <Formula 1> 45≦(A×B) / 10≦60 In formula 1, A is the modulus of the polyimide film (unit: GPa) measured at a tensile speed of 200 mm / min based on ASTM D882, B is the tensile strength (unit: MPa) of the polyimide film at an elongation of 20% measured based on ASTM D882, The B is 140 MPa or more.

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

3. The molar ratio of PMDA and MDA (PMDA:MDA) is 1.1:1 to 3.25:

2. The polyimide film according to claim 1, wherein the molecular weight of the polyimide film is 1.

4. 2. 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 comprising 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 and includes the polyimide film as a backplate film.

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