Polyimide resin, polyimide varnish and polyimide film

Abstract

A polyimide resin comprising a structural unit A derived from a tetracarboxylic dianhydride and a structural unit B derived from a diamine, the structural unit A comprising a structural unit (A1) derived from a tetracarboxylic dianhydride having 2 norbornane skeletons in the molecule, and the structural unit B comprising a structural unit (B1) derived from a compound represented by the following formula (b1).

Description

Technical Field

[0001] The present invention relates to a polyimide resin, a polyimide varnish, and a polyimide film. Background Art

[0002] Various uses of polyimide resins in the fields of electrical and electronic components and the like are being studied. For example, for the purpose of lightening and flexibilizing devices, it is desired to replace the glass substrates used in image display devices such as liquid crystal displays and OLED displays with plastic substrates, and thus research on polyimide films suitable as such plastic substrates is underway.

[0003] In films used for image display device applications, various optical properties are required. For example, when light emitted from a display element passes through a plastic substrate and exits, transparency is required for the plastic substrate.

[0004] In order to satisfy the performance requirements described above, polyimide resins having various compositions are being developed. For example, in Patent Document 1, for the purpose of obtaining a polyimide film excellent in transparency and high heat resistance, a polyimide film is disclosed which contains a structure formed by a combination of a dianhydride having a norbornane skeleton and 2,2'-bis(trifluoromethyl)benzidine as a diamine component.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: Japanese Patent No. 6431369 Summary of the Invention

[0008] Problems to be Solved by the Invention

[0009] A polyimide film is required to replace a glass substrate, and transparency is required.

[0010] Here, when manufacturing an image display device, for example, heat treatment is performed in a state where an inorganic film is laminated on a polyimide film, and thus exhaust gas generated from the polyimide film accumulates between the polyimide film and the inorganic film, and as a result, the polyimide film sometimes undergoes coloring such as yellowing. Therefore, for a polyimide film, heat resistance for suppressing coloring is required when exposed to high temperature in a state where an inorganic film is laminated.

[0011] In addition, when manufacturing an image display device, a process temperature exceeding 400 °C can be achieved, for example. Therefore, for a polyimide film used as a substrate, heat resistance to a temperature of 400 °C or higher is required. When a polyimide film having a high glass transition temperature (Tg) and excellent heat resistance is exposed to a high temperature in a state where an inorganic film is laminated, there may be problems such as cracks in the inorganic film. Therefore, for a polyimide film, when exposed to a high temperature in a state where an inorganic film is laminated, the inorganic film is required to have heat resistance that does not cause problems such as cracks.

[0012] The present invention has been completed in view of such circumstances, and an object of the present invention is to provide: a polyimide resin, a polyimide varnish, and a polyimide film capable of obtaining a polyimide film having excellent transparency and heat resistance when an inorganic film is laminated.

[0013] Solutions for Solving the Problems

[0014] The present inventors have found that a polyimide resin containing a structural unit derived from a tetracarboxylic dianhydride having two norbornane skeletons in the molecule and a structural unit derived from a specific diamine can solve the above problems, and thus completed the invention.

[0015] That is, the present invention relates to the following <1> to <11>.

[0016] <1> A polyimide resin comprising a structural unit A derived from a tetracarboxylic dianhydride and a structural unit B derived from a diamine.

[0017] The structural unit A includes a structural unit (A1) derived from a tetracarboxylic dianhydride having two norbornane skeletons in the molecule.

[0018] The structural unit B includes a structural unit (B1) derived from a compound represented by the following formula (b1).

[0019]

[0020] <2> The polyimide resin according to <1>, wherein the structural unit (A1) includes at least one selected from the group consisting of a structural unit (A11) derived from a compound represented by the following formula (a11), a structural unit (A12) derived from a compound represented by the following formula (a12), a structural unit (A13) derived from a compound represented by the following formula (a13), and a structural unit (A14) derived from a compound represented by the following formula (a14).

[0021]

[0022] <3>The polyimide resin according to <1> or <2>, wherein the structural unit A further comprises a structural unit (A2), and the structural unit (A2) comprises at least one selected from the group consisting of a structural unit (A21) derived from a compound represented by the following formula (a21) and a structural unit (A22) derived from a compound represented by the following formula (a22).

[0023]

[0024] <4>The polyimide resin according to any one of <1> to <3>, wherein the structural unit B further comprises a structural unit (B2), and the structural unit (B2) comprises at least one selected from the group consisting of a structural unit (B21) derived from a compound represented by the following formula (b21), a structural unit (B22) derived from a compound represented by the following formula (b22), and a structural unit (B23) derived from a compound represented by the following formula (b23).

[0025]

[0026] <5>The polyimide resin according to <4>, wherein the structural unit (B2) comprises a structural unit (B21) derived from a compound represented by the following formula (b21).

[0027]

[0028] <6>A polyimide varnish, which is obtained by dissolving the polyimide resin according to any one of <1> to <5> in an organic solvent.

[0029] <7>A polyimide film, which comprises the polyimide resin according to any one of <1> to <5>.

[0030] <8>The polyimide film according to <7>, wherein the total light transmittance measured based on JIS K7136:2000 is 80% or more.

[0031] <9>The polyimide film according to <7> or <8>, which is used as a transparent substrate constituting a display device.

[0032] <10>A method for manufacturing a polyimide film, which comprises a step of coating or molding the polyimide varnish according to <6> into a film shape and then removing the organic solvent.

[0033] <11>An image display device, which comprises the polyimide film according to any one of <7> to <9> as a transparent substrate.

[0034] Effects of the Invention

[0035] According to the present invention, there can be provided: a polyimide resin, a polyimide varnish, and a polyimide film that can obtain a polyimide film excellent in transparency and heat resistance when an inorganic film is laminated, and the polyimide film is excellent in transparency and heat resistance when an inorganic film is laminated. Detailed Embodiments

[0036] The mode for carrying out the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail. The following present embodiment is an example for explaining the present invention and does not limit the content of the present invention. The present invention can be appropriately modified and implemented within the scope of its gist. In the present embodiment, preferred regulations can be arbitrarily adopted, and it can be said that a more preferred combination of each other is more preferred. In the present embodiment, the description of "XX to YY" means "XX or more and YY or less".

[0037] [Polyimide Resin]

[0038] The polyimide resin of the present invention is a polyimide resin containing a structural unit A derived from a tetracarboxylic dianhydride and a structural unit B derived from a diamine. The structural unit A contains a structural unit (A1) derived from a tetracarboxylic dianhydride having 2 norbornane skeletons in the molecule, and the structural unit B contains a structural unit (B1) derived from the compound represented by the following formula (b1).

[0039]

[0040] When the polyimide resin of the present invention is used, the reason for obtaining a polyimide film excellent in transparency and heat resistance when an inorganic film is laminated is not clear, but it is considered that due to having a norbornane skeleton and a structural unit (B1) capable of suppressing molecular motion due to a trifluoromethyl group having a bent structure but a large steric hindrance, transparency can be well maintained, and heat resistance can be improved. Therefore, the transparency and heat resistance (suppression of coloring, suppression of cracks in the inorganic film) when an inorganic film is laminated are excellent.

[0041] [Structural Unit A]

[0042] The structural unit A is a structural unit derived from the tetracarboxylic dianhydride contained in the polyimide resin.

[0043] The structural unit A contains a structural unit (A1) derived from a tetracarboxylic dianhydride having 2 norbornane skeletons in the molecule.

[0044] From the viewpoints of heat resistance, transparency, and optical isotropy, the structural unit (A1) preferably contains at least one selected from the group consisting of a structural unit (A11) derived from a compound represented by the following formula (a11), a structural unit (A12) derived from a compound represented by the following formula (a12), a structural unit (A13) derived from a compound represented by the following formula (a13), and a structural unit (A14) derived from a compound represented by the following formula (a14). From the viewpoint of making the molecular skeleton more rigid and further improving heat resistance, it is more preferably to contain at least one selected from the group consisting of a structural unit (A11) derived from a compound represented by the following formula (a11), a structural unit (A12) derived from a compound represented by the following formula (a12), and a structural unit (A14) derived from a compound represented by the following formula (a14). It is further preferably to contain at least one selected from the group consisting of a structural unit (A11) derived from a compound represented by the following formula (a11) and a structural unit (A14) derived from a compound represented by the following formula (a14). It is further preferably to contain a structural unit (A11) derived from a compound represented by the following formula (a11).

[0045]

[0046] By making the structural unit A contain a structural unit (A1) derived from a tetracarboxylic dianhydride having two norbornane skeletons in the molecule, the heat resistance, transparency, and optical isotropy of the obtained polyimide film can be improved.

[0047] In addition to the structural unit (A1), the structural unit A may further contain a structural unit (A2). As the structural unit (A2), for example, at least one selected from the group consisting of a structural unit (A21) derived from a compound represented by the following formula (a21) and a structural unit (A22) derived from a compound represented by the following formula (a22) can be cited.

[0048]

[0049] The compound represented by the formula (a21) is biphenyltetracarboxylic dianhydride (BPDA). As specific examples thereof, 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA) represented by the following formula (a211s), 2,3,3',4'-biphenyltetracarboxylic dianhydride (a-BPDA) represented by the following formula (a211a), and 2,2',3,3'-biphenyltetracarboxylic dianhydride (i-BBDA) represented by the following formula (a211i) can be cited. Among them, 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA) represented by the following formula (a211s) is preferred.

[0050]

[0051] From the viewpoints of heat resistance, transparency, and optical isotropy, the ratio of the structural unit (A1) in the structural unit A is preferably 40 mol% or more, more preferably 50 mol% or more, still more preferably 60 mol% or more, still more preferably 80 mol% or more, still more preferably 85 mol% or more, still more preferably 90 mol% or more, still more preferably 95 mol% or more, still more preferably 99 mol% or more. The upper limit value of this ratio is not particularly limited, but it is 100 mol% or less.

[0052] In addition, when the structural unit A further contains the structural unit (A2), from the viewpoints of heat resistance, transparency, and optical isotropy, the ratio of the structural unit (A2) in the structural unit A is preferably 60 mol% or less, more preferably 50 mol% or less, still more preferably 40 mol% or less, still more preferably 20 mol% or less, still more preferably 15 mol% or less, still more preferably 10 mol% or less, still more preferably 5 mol% or less, still more preferably 1 mol% or less. The lower limit value of this ratio is not particularly limited and is 0.01 mol% or more.

[0053] The structural unit A may contain a structural unit other than the structural unit (A1) and the structural unit (A2). As the tetracarboxylic dianhydride that provides such a structural unit, there is no particular limitation, and examples thereof include aromatic tetracarboxylic dianhydrides such as 4,4'-oxybisphthalic anhydride, pyromellitic dianhydride, and 4,4'-(hexafluoroisopropyl)diphthalic anhydride (however, compounds represented by the formula (a21) or (a22) are excluded); alicyclic tetracarboxylic dianhydrides such as 1,2,4,5-cyclohexanetetracarboxylic dianhydride and 1,2,3,4-cyclobutanetetracarboxylic dianhydride (however, compounds represented by any of the formulas (a11) to (a14) are excluded); and aliphatic tetracarboxylic dianhydrides such as 1,2,3,4-butane tetracarboxylic dianhydride.

[0054] It should be noted that in this specification, an aromatic tetracarboxylic dianhydride refers to a tetracarboxylic dianhydride containing one or more aromatic rings, an alicyclic tetracarboxylic dianhydride refers to a tetracarboxylic dianhydride containing one or more alicyclic rings and not containing an aromatic ring, and an aliphatic tetracarboxylic dianhydride refers to a tetracarboxylic dianhydride not containing an aromatic ring and an alicyclic ring.

[0055] The structural unit optionally contained in the structural unit A may be one kind or two or more kinds.

[0056] <Structural unit B>

[0057] The structural unit B is a structural unit derived from a diamine in the polyimide resin.

[0058] The structural unit B contains a structural unit (B1) derived from the compound represented by the following formula (b1).

[0059]

[0060] The compound represented by formula (b1) is 2,2-bis(4-aminophenyl)hexafluoropropane. By making structural unit B contain structural unit (B1), the toughness can be improved while maintaining the heat resistance.

[0061] From the viewpoint of improving the heat resistance when laminating the inorganic film, the ratio of structural unit (B1) in structural unit B is preferably 20 mol% or more, more preferably 40 mol% or more, still more preferably 50 mol% or more, still more preferably 55 mol% or more, still more preferably 60 mol% or more, still more preferably 80 mol% or more, still more preferably 99 mol% or more. The upper limit value of this ratio is not particularly limited, but it is 100 mol% or less.

[0062] Structural unit B may contain structural units other than structural unit (B1).

[0063] In addition to structural unit (B1), structural unit B preferably further contains structural unit (B2). Structural unit (B2) preferably contains, for example, at least one selected from the group consisting of structural unit (B21) derived from the compound represented by the following formula (b21), structural unit (B22) derived from the compound represented by the following formula (b22), and structural unit (B23) derived from the compound represented by the following formula (b23). From the viewpoint of making the molecular skeleton more rigid and further improving the heat resistance, it is more preferably to contain structural unit (B21) derived from the compound represented by the following formula (b21). By making structural unit B contain structural unit (B2), in particular, the heat resistance is improved, and furthermore, the optical isotropy is also improved.

[0064]

[0065]

[0066] When structural unit B further contains structural unit (B2), the ratio of structural unit (B2) in structural unit B is preferably 10 mol% or more, more preferably 20 mol% or more, still more preferably 30 mol% or more, and further preferably 70 mol% or less, more preferably 60 mol% or less, still more preferably 50 mol% or less.

[0067] When the structural unit B further contains the structural unit (B2), the total ratio of the structural unit (B1) and the structural unit (B2) in the structural unit B is preferably 50 mol% or more, more preferably 70 mol% or more, still more preferably 90 mol% or more, still more preferably 95 mol% or more, and still more preferably 99 mol% or more. The upper limit value of the total ratio of the structural unit (B1) and the structural unit (B2) in the structural unit B is not particularly limited, and is, for example, 100 mol% or less. The structural unit B may also be composed only of the structural unit (B1) and the structural unit (B2).

[0068] When the structural unit B further contains the structural unit (B2), from the viewpoints of improving transparency, optical isotropy, toughness, and heat resistance, the molar ratio [(B1) / (B2)] of the structural unit (B1) and the structural unit (B2) in the structural unit B is preferably 30 / 70 to 90 / 10, more preferably 40 / 60 to 80 / 20, and still more preferably 50 / 50 to 70 / 30.

[0069] The structural unit B may contain structural units other than the structural unit (B1) and the structural unit (B2). The diamine that provides such a structural unit is not particularly limited, and examples thereof include aromatic diamines such as 1,4-phenylenediamine, p-xylenediamine, 1,5-diaminonaphthalene, 2,2'-dimethylbiphenyl-4,4'-diamine, 4,4'-diaminodiphenyl ether, 4,4'-diamino-2,2'-bis(trifluoromethyl)diphenyl ether, 4,4'-diaminodiphenylmethane, 4,4'-diaminobenzanilide, 1-(4-aminophenyl)-2,3-dihydro-1,3,3-trimethyl-1H-indene-5-amine, α,α'-bis(4-aminophenyl)-1,4-diisopropylbenzene, N,N'-bis(4-aminophenyl)terephthalamide, 4,4'-bis(4-aminophenoxy)biphenyl, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, and 2,2-bis(4-(4-aminophenoxy)phenyl)hexafluoropropane (however, compounds represented by any of formulas (b1), (b21) to (b23) are excluded); alicyclic diamines such as 1,3-bis(aminomethyl)cyclohexane and 1,4-bis(aminomethyl)cyclohexane; and aliphatic diamines such as ethylenediamine and hexamethylenediamine.

[0070] It should be noted that, in this specification, an aromatic diamine refers to a diamine containing one or more aromatic rings, an alicyclic diamine refers to a diamine containing one or more alicyclic rings and no aromatic rings, and an aliphatic diamine refers to a diamine containing no aromatic rings and alicyclic rings.

[0071] The structural unit optionally contained in the structural unit B may be one kind or two or more kinds.

[0072] <Properties of polyimide resin>

[0073] From the viewpoint of the mechanical strength of the obtained polyimide film, the weight average molecular weight of the polyimide resin is preferably 5,000 to 300,000. It should be noted that the weight average molecular weight of the polyimide resin can be obtained, for example, based on the conversion value of standard polymethyl methacrylate (PMMA) measured by gel permeation chromatography.

[0074] The polyimide resin may contain a structure other than the polyimide chain (a structure in which structural unit A and structural unit B are bonded by an imide bond). As a structure other than the polyimide chain that can be contained in the polyimide resin, for example, a structure containing an amide bond can be cited.

[0075] The polyimide resin preferably contains a polyimide chain (a structure in which structural unit A and structural unit B are bonded by an imide bond) as the main structure. Therefore, the ratio of the polyimide chain in the polyimide resin is preferably 50% by mass or more, more preferably 70% by mass or more, still more preferably 90% by mass or more, particularly preferably 99% by mass or more, and further, 100% by mass or less. The polyimide resin may also be composed only of polyimide chains.

[0076] The polyimide resin composition containing the above polyimide resin can form a polyimide film that maintains transparency and optical isotropy and has excellent heat resistance. The suitable physical property values of the polyimide film are as follows.

[0077] For the total light transmittance, when the polyimide resin is made into a film with a thickness of 10 μm, it is preferably 80% or more, more preferably 85% or more, still more preferably 88% or more, still more preferably 88.5% or more, and still more preferably 89% or more.

[0078] For the yellowness index (YI), when the polyimide resin is made into a film with a thickness of 10 μm, it is preferably 5.0 or less, more preferably 3.0 or less, still more preferably 2.5 or less, and even more preferably 2.0 or less.

[0079] For the absolute value of the thickness retardation (Rth), when the polyimide resin is made into a film with a thickness of 10 μm, it is preferably 200 nm or less, more preferably 180 nm or less, and still more preferably 160 nm or less.

[0080] In addition, for the film formed using the above polyimide resin, its heat resistance is also good, and it has the following suitable physical property values.

[0081] The glass transition temperature (Tg) is preferably 380 °C or higher, more preferably 390 °C or higher, and still more preferably 400 °C or higher.

[0082] The temperature at which 5% weight loss occurs (Td5%) is preferably 480 °C or higher, more preferably 490 °C or higher, and even more preferably 495 °C or higher.

[0083] Regarding the heat resistance when laminating an inorganic film, when a SiO2 film with a thickness of 300 nm is formed by sputtering on a polyimide film and an ITO (indium tin oxide) film with a thickness of 1230 nm is formed thereon to make a laminated film, it is preferred that no cracks, yellowing or other defects occur on the laminated film during the "annealing treatment at 400 °C for 1 hour", and more preferably no cracks, yellowing or other defects occur on the laminated film during the "annealing treatment at 420 °C for 1 hour".

[0084] It should be noted that for the above physical property values in the present invention, specifically, they can be measured by the methods described in the examples.

[0085] <Method for manufacturing polyimide resin>

[0086] The polyimide resin of the present invention can be manufactured by reacting a tetracarboxylic acid component containing a compound providing the above structural unit (A1) with a diamine component containing a compound providing the above structural unit (B1).

[0087] As the compound providing the structural unit (A1), a compound represented by any of the formulas (a11) to (a14) can be cited, but it is not limited thereto, and derivatives thereof can also be used within the range of providing the same structural unit. As such derivatives, tetracarboxylic acids corresponding to the tetracarboxylic dianhydrides represented by any of the formulas (a11) to (a14) and alkyl esters of such tetracarboxylic acids can be cited. Among them, the tetracarboxylic dianhydride represented by the formula (a11) is preferred.

[0088] In addition to the compound providing the structural unit (A1), the tetracarboxylic acid component may further contain a compound providing the structural unit (A2).

[0089] As the compound providing the structural unit (A2), a compound represented by the formula (a21), a compound represented by the formula (a22), etc. can be cited, but it is not limited thereto, and derivatives thereof can also be used within the range of providing the same structural unit.

[0090] For the tetracarboxylic acid component, the compound providing the structural unit (A1) preferably contains 40 mol% or more, more preferably 50 mol% or more, even more preferably 60 mol% or more, even more preferably 80 mol% or more, even more preferably 85 mol% or more, even more preferably 90 mol% or more, even more preferably 95 mol% or more, and even more preferably 99 mol% or more. The upper limit value of this ratio is not particularly limited, but it is 100 mol% or less.

[0091] The tetracarboxylic acid component may contain any compound other than the compound providing the structural unit (A1) and the compound providing the structural unit (A2).

[0092] Examples of such an arbitrary compound include the above-mentioned aromatic tetracarboxylic dianhydrides, alicyclic tetracarboxylic dianhydrides, and aliphatic tetracarboxylic dianhydrides, and their derivatives (tetracarboxylic acids, alkyl esters of tetracarboxylic acids, etc.).

[0093] The compound optionally contained in the tetracarboxylic acid component may be one kind or two or more kinds.

[0094] Examples of the compound providing the structural unit (B1) include the compound represented by the formula (b1), but are not limited thereto, and derivatives thereof may also be used within the range of providing the same structural unit. Examples of such a derivative include the diisocyanate corresponding to the compound represented by the formula (b1). As the compound providing the structural unit (B1), the compound represented by the formula (b1) (i.e., diamine) is preferred.

[0095] In addition to the compound providing the structural unit (B1), the diamine component may further contain a compound providing the structural unit (B2). Examples of the compound providing the structural unit (B2) include the compound represented by the formula (b21), the compound represented by the formula (b22), the compound represented by the formula (b23), etc., but are not limited thereto, and derivatives thereof may also be used within the range of providing the same structural unit. Examples of such a derivative include the diisocyanate corresponding to the compound represented by the formula (b21), the compound represented by the formula (b22), and the compound represented by the formula (b23). As the compound providing the structural unit (B2), the compound represented by the formula (b21), the compound represented by the formula (b22), and the compound represented by the formula (b23) (i.e., diamine) are preferred.

[0096] For the diamine component, the compound providing the structural unit (B1) preferably contains 20 mol% or more, more preferably 40 mol% or more, still more preferably 50 mol% or more, still more preferably 60 mol% or more, still more preferably 80 mol% or more, and particularly preferably 99 mol% or more. The upper limit value of this ratio is not particularly limited, but is 100 mol% or less.

[0097] For the diamine component, when the compound providing the structural unit (B2) is contained, the compound providing the structural unit (B2) preferably contains 10 mol% or more, more preferably 20 mol% or more, still more preferably 30 mol% or more, further preferably 70 mol% or less, more preferably 60 mol% or less, and still more preferably 50 mol% or less.

[0098] For the diamine component, in the case of a compound containing the structural unit (B2), the total of the compound providing the structural unit (B1) and the compound providing the structural unit (B2) preferably contains 50 mol% or more, more preferably 70 mol% or more, still more preferably 90 mol% or more, still more preferably 95 mol% or more, and still more preferably 99 mol% or more. The upper limit is not particularly limited, and for the diamine component, the total of the compound providing the structural unit (B1) and the compound providing the structural unit (B2) contains, for example, 100 mol% or less. The tetracarboxylic acid component may also be composed only of the compound providing the structural unit (B1) and the compound providing the structural unit (B2).

[0099] In the case where the diamine component contains a compound providing the structural unit (B2), from the viewpoints of improving transparency, optical isotropy, toughness, and heat resistance, the molar ratio [(B1) / (B2)] of the compound providing the structural unit (B1) to the compound providing the structural unit (B2) in the diamine component is preferably 30 / 70 to 90 / 10, more preferably 40 / 60 to 80 / 20, and still more preferably 50 / 50 to 70 / 30.

[0100] The diamine component may further contain any compound other than the compound providing the structural unit (B1) and the compound providing the structural unit (B2).

[0101] Examples of such an arbitrary compound include the above-mentioned aromatic diamines, alicyclic diamines, and aliphatic diamines, and their derivatives (diisocyanates, etc.).

[0102] The compound optionally contained in the diamine component may be one kind or two or more kinds.

[0103] In the production of the polyimide resin of the present invention, for the input ratio of the tetracarboxylic acid component to the diamine component used in the production of the polyimide resin, the diamine component is preferably 0.9 to 1.1 moles relative to 1 mole of the tetracarboxylic acid component.

[0104] In addition, in the production of the polyimide resin of the present invention, a capping agent can be used in addition to the above-mentioned tetracarboxylic acid component and diamine component in the production of the polyimide resin. As the capping agent, monoamines or dicarboxylic acids are preferred. As the input amount of the introduced capping agent, it is preferably 0.0001 to 0.1 mol, more preferably 0.001 to 0.06 mol, relative to 1 mol of the tetracarboxylic acid component. As the monoamine capping agent, for example, methylamine, ethylamine, propylamine, butylamine, benzylamine, 4-methylbenzylamine, 4-ethylbenzylamine, 4-dodecylbenzylamine, 3-methylbenzylamine, 3-ethylbenzylamine, aniline, 3-methylaniline, 4-methylaniline, etc. can be cited, and benzylamine and aniline are preferred. As the dicarboxylic acid capping agent, dicarboxylic acids are preferred, and a part of them can also be cyclized. For example, phthalic acid, phthalic anhydride, 4-chlorophthalic acid, tetrafluorophthalic acid, 2,3-benzophenone dicarboxylic acid, 3,4-benzophenone dicarboxylic acid, cyclohexane-1,2-dicarboxylic acid, cyclopentane-1,2-dicarboxylic acid, 4-cyclohexene-1,2-dicarboxylic acid, etc. can be cited, and phthalic acid and phthalic anhydride are preferred.

[0105] There is no particular limitation on the method of reacting the tetracarboxylic acid component with the diamine component described above, and known methods can be used.

[0106] As specific reaction methods, the following methods can be cited: (1) A method in which the tetracarboxylic acid component, the diamine component, and a reaction solvent are charged into a reactor, stirred at 0 to 10 °C for 0.5 to 30 hours, and then heated to carry out an imidization reaction; (2) A method in which the diamine component and the reaction solvent are charged into a reactor to dissolve them, then the tetracarboxylic acid component is charged and stirred at room temperature of 0 to 10 °C for 0.5 to 30 hours as needed, and then heated to carry out an imidization reaction; (3) A method in which the tetracarboxylic acid component, the diamine component, and the reaction solvent are charged into a reactor and immediately heated to carry out an imidization reaction; etc.

[0107] For the reaction solvent used in the production of the polyimide resin, any solvent that does not hinder the imidization reaction and can dissolve the resulting polyimide can be used. For example, aprotic solvents, phenolic solvents, ether solvents, carbonate solvents, etc. can be cited.

[0108] As specific examples of the aprotic solvent, amide solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone (NMP), N-methylcaprolactam, 1,3-dimethylimidazolidinone, tetramethylurea, etc., lactone solvents such as γ-butyrolactone (GBL), γ-valerolactone, etc., phosphorus-containing amide solvents such as hexamethylphosphoramide, hexamethylphosphorous triamide, etc., sulfur-containing solvents such as dimethyl sulfone, dimethyl sulfoxide, sulfolane, etc., ketone solvents such as acetone, cyclohexanone, methylcyclohexanone, etc., amine solvents such as methylpyridine, pyridine, etc., ester solvents such as acetic acid (2-methoxy-1-methylethyl) ester, etc. can be cited.

[0109] Specific examples of phenolic solvents include phenol, o-cresol, m-cresol, p-cresol, 2,3-xylenol, 2,4-xylenol, 2,5-xylenol, 2,6-xylenol, 3,4-xylenol, 3,5-xylenol, etc.

[0110] Specific examples of ether solvents include 1,2-dimethoxyethane, bis(2-methoxyethyl) ether, 1,2-bis(2-methoxyethoxy)ethane, bis[2-(2-methoxyethoxy)ethyl] ether, tetrahydrofuran, 1,4-dioxane, etc.

[0111] In addition, specific examples of carbonate solvents include diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, etc.

[0112] Among the above reaction solvents, aprotic solvents are preferred, amide solvents and lactone solvents are more preferred, and lactone solvents are further preferred. In addition, the above reaction solvents can be used alone or in combination of two or more.

[0113] In the imidization reaction, it is preferable to use a Dean-Stark water separator device or the like, and the reaction is carried out while removing the water generated during production. By performing such an operation, the degree of polymerization and the imidization rate can be further increased.

[0114] In the above imidization reaction, a known imidization catalyst can be used. Examples of imidization catalysts include base catalysts or acid catalysts.

[0115] Examples of base catalysts include organic base catalysts such as pyridine, quinoline, isoquinoline, α-methylpyridine, β-methylpyridine, 2,4-dimethylpyridine, 2,6-dimethylpyridine, trimethylamine, triethylamine (TEA), tripropylamine, tributylamine, triethylenediamine, imidazole, N,N-dimethylaniline, N,N-diethylaniline, etc.; inorganic base catalysts such as potassium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate, potassium bicarbonate, sodium bicarbonate, etc.

[0116] In addition, examples of acid catalysts include crotonic acid, acrylic acid, trans-3-hexenoic acid, cinnamic acid, benzoic acid, methylbenzoic acid, hydroxybenzoic acid, terephthalic acid, benzenesulfonic acid, p-toluenesulfonic acid, naphthalenesulfonic acid, etc. The above imidization catalysts can be used alone or in combination of two or more.

[0117] Among the above, from the viewpoint of operability, it is preferable to use a base catalyst, more preferably an organic base catalyst, and further preferably triethylamine or triethylenediamine.

[0118] From the viewpoints of reaction rate and inhibition of gelation, etc., the temperature of the imidization reaction is preferably 120 to 250°C, more preferably 160 to 200°C. Further, the reaction time is preferably 0.5 to 10 hours after the start of distillation of the generated water.

[0119] [Polyimide varnish]

[0120] The polyimide varnish of the present invention is obtained by dissolving the polyimide resin of the present invention in an organic solvent. That is, the polyimide varnish of the present invention contains the polyimide resin of the present invention and an organic solvent, and the polyimide resin is dissolved in the organic solvent.

[0121] The organic solvent is not particularly limited as long as it can dissolve the polyimide resin. As the reaction solvent used in the production of the polyimide resin, it is preferable to use the above compounds alone or in combination of two or more.

[0122] The polyimide varnish of the present invention may be the polyimide solution itself in which the polyimide resin obtained by the polymerization method is dissolved in the reaction solvent, or may be a polyimide varnish obtained by further adding a solvent to dilute the polyimide solution.

[0123] Since the polyimide resin of the present invention has solvent solubility, it can be used as a high-concentration varnish stable at room temperature. The polyimide varnish of the present invention preferably contains 5 to 40% by mass of the polyimide resin of the present invention, more preferably 5 to 20% by mass. The viscosity of the polyimide varnish is preferably 1 to 200 Pa·s, more preferably 1 to 100 Pa·s. The viscosity of the polyimide varnish is a value measured at 25°C using an E-type viscometer.

[0124] In addition, the polyimide varnish of the present invention may contain various additives such as inorganic fillers, adhesion promoters, release agents, flame retardants, ultraviolet stabilizers, surfactants, leveling agents, defoaming agents, fluorescent brighteners, crosslinking agents, polymerization initiators, and photosensitizers within a range that does not impair the required properties of the polyimide film.

[0125] The method for producing the polyimide varnish of the present invention is not particularly limited, and known methods can be applied.

[0126] [Polyimide film]

[0127] The polyimide film of the present invention contains the polyimide resin of the present invention. Therefore, the polyimide film of the present invention is excellent in heat resistance, transparency, toughness, optical isotropy, peelability, and chemical resistance. The preferred physical property values of the polyimide film of the present invention are as described above as <characteristics of the polyimide resin>.

[0128] There is no particular limitation on the method for manufacturing the polyimide film of the present invention, and known methods can be used. For example, the following methods can be cited: After the polyimide varnish of the present invention is coated into a film shape on a smooth support such as a glass plate, a metal plate, or plastic, or formed into a film shape, organic solvents such as reaction solvents and diluting solvents contained in the varnish are removed by heating; etc. As the method for manufacturing the polyimide film of the present invention, a method preferably including a step of removing the organic solvent after coating or forming the polyimide varnish into a film shape is preferred.

[0129] As the coating method, known coating methods such as spin coating, slot coating, and knife coating can be cited, and spin coating and slot coating are preferred. Among them, slot coating controls the intermolecular orientation and improves the chemical resistance, and is more preferred from the viewpoint of operability.

[0130] As the method for removing the organic solvent contained in the varnish by heating, it is preferred to evaporate the organic solvent at a temperature of 150°C or lower until it becomes non-tacky, and then dry at a temperature above the boiling point of the organic solvent used (not particularly limited, preferably 200 - 500°C). In addition, it is preferred to dry in an air atmosphere or a nitrogen atmosphere. The pressure of the drying atmosphere can be any one of reduced pressure, normal pressure, and increased pressure.

[0131] The method for peeling the polyimide film formed on the support from the support is not particularly limited, and mechanical peeling method, laser peeling method, etc. can be used.

[0132] In addition, the polyimide film of the present invention can also be manufactured using a polyamic acid varnish obtained by dissolving polyamic acid in an organic solvent.

[0133] The polyamic acid contained in the aforementioned polyamic acid varnish is a precursor of the polyimide resin of the present invention, and is a product of the addition reaction of the tetracarboxylic acid component of the compound containing the above-provided structural unit (A1) and the diamine component of the compound containing the above-provided structural unit (B1). By imidizing (dehydrating and cyclizing) the polyamic acid, the polyimide resin of the present invention as the final product can be obtained.

[0134] As the organic solvent contained in the above polyamic acid varnish, the organic solvent contained in the polyimide varnish of the present invention can be used.

[0135] In the manufacture of the polyimide film of the present invention, the polyamic acid varnish can be the polyamic acid solution itself obtained by subjecting the tetracarboxylic acid component and the diamine component to an addition reaction in a reaction solvent, or can also be a product obtained by further adding a solvent to dilute the polyamic acid solution.

[0136] There is no particular limitation on the method for manufacturing a polyimide film using a polyamic acid varnish, and known methods can be used. For example, the polyamic acid varnish is coated into a film shape or formed into a film shape on a smooth support such as a glass plate, a metal plate, or plastic, and the organic solvents such as the reaction solvent and the dilution solvent contained in the varnish are removed by heating to obtain a polyamic acid film. The polyamic acid in the polyamic acid film is imidized by heating to manufacture a polyimide film.

[0137] As the heating temperature when drying the polyamic acid varnish to obtain a polyamic acid film, it is preferably 50 to 120°C. The heating temperature when imidizing the polyamic acid by heating is preferably 200 to 450°C.

[0138] It should be noted that the imidization method is not limited to thermal imidization, and chemical imidization can also be applied.

[0139] The thickness of the polyimide film of the present invention can be appropriately selected according to the use and the like, and the range is preferably 1 to 250 μm, more preferably 5 to 100 μm, further preferably 8 to 80 μm, and still further preferably 10 to 80 μm. By making the thickness 1 - 250 μm, it can be practically used as a self-supporting film.

[0140] The thickness of the polyimide film can be easily controlled by adjusting the solid content concentration and viscosity of the polyimide varnish.

[0141] In the polyimide film of the present invention, from the viewpoint of further improving transparency, the total light transmittance measured based on JIS K7136:2000 is preferably 80% or more, more preferably 85% or more, further preferably 88% or more, still further preferably 88.5% or more, and still further preferably 89% or more.

[0142] The polyimide film of the present invention is suitably used as a film for various components such as color filters, flexible displays, semiconductor components, optical components, solar cells, and image display devices, and is particularly suitably used as a transparent substrate constituting these devices. The polyimide film of the present invention is particularly suitably used as a transparent substrate constituting image display devices such as liquid crystal displays, OLED displays, and touch panels.

[0143] [Image display device]

[0144] The image display device of the present invention includes the polyimide film of the present invention as a transparent substrate.

[0145] The image display device of the present invention, for example, has a transparent substrate made of the polyimide film of the present invention and a display portion provided on the above transparent substrate.

[0146] The display unit is not particularly limited. For example, a TFT element, an organic EL element, a color filter, an LED, a transistor, an electron-emitting element, electronic ink, an electrophoretic element, a GLV (grating light valve), a display element using MEMS (microelectromechanical systems), a DMD (digital micromirror device), a DMS (digital microshutter), an IMOD (interferometric modulation) element, an electrowetting element, a piezoelectric ceramic display, a display element using carbon nanotubes, etc. can be cited.

[0147] Examples of the image display device of the present invention include a liquid crystal display, an OLED display, a touch panel, etc.

[0148] The image display device of the present invention can be manufactured based on known information except that the polyimide film of the present invention is used as a transparent substrate.

[0149] The image display device of the present invention uses the polyimide film of the present invention having excellent heat resistance when an inorganic film is laminated as a transparent substrate, so cracks in the inorganic film, coloring of the transparent substrate, etc. are hardly generated, and the reliability is excellent.

[0150] Examples

[0151] Hereinafter, the present invention will be specifically described by way of examples. However, the present invention is not limited by any of these examples.

[0152] <Film Physical Properties and Evaluation>

[0153] The physical properties of the films obtained in the examples and comparative examples were measured by the methods shown below.

[0154] (1) Film Thickness

[0155] The film thickness was measured using a micrometer manufactured by Mitutoyo Corporation.

[0156] (2) Glass Transition Temperature (Tg)

[0157] Using a thermomechanical analysis device “TMA / SS6100” manufactured by Hitachi High-Tech Science Corporation, in the tensile mode, under the conditions of a specimen size of 3 mm × 20 mm, a load of 0.1 N, and a heating rate of 10 °C / min, the temperature was raised to a temperature sufficient to eliminate residual stress to remove the residual stress, and then cooled to room temperature. Thereafter, the elongation of the test piece was measured under the same conditions as the treatment for removing the above residual stress, and the inflection point of the extrapolated elongation was obtained to determine the glass transition temperature.

[0158] (3) Total Light Transmittance and Yellowness Index (YI)

[0159] The total light transmittance was measured in accordance with JIS K7136:2000, and the YI was measured in accordance with ASTM E313-05 (D light source, 65°) using a color / turbidity simultaneous measuring instrument "COH7700" manufactured by Nippon Denshoku Industries Co., Ltd.

[0160] (4) 5% weight loss temperature (Td5%)

[0161] Using a differential thermal gravimetric simultaneous measuring device "NEXTA STA200RV" manufactured by Hitachi High-Tech Science Corporation. The sample was heated at a rate of 10 °C / minute to 40 - 150 °C, held at 150 °C for 30 minutes to remove moisture, and then heated to 510 °C. The temperature at which the weight decreased by 5% compared to the weight after holding at 150 °C for 30 minutes was defined as the 5% weight loss temperature. The higher the value of the weight loss temperature, the better the heat resistance.

[0162] (5) Thickness retardation (Rth) (evaluation of optical isotropy)

[0163] The thickness retardation (Rth) was measured using an ellipsometer "M-220" manufactured by JASCO Corporation. The value of the thickness retardation at a measurement wavelength of 590 nm was measured. It should be noted that when the maximum refractive index in the plane of the polyimide film is nx, the minimum is ny, the refractive index in the thickness direction is nz, and the thickness of the film is d, Rth is represented by the following formula.

[0164] Rth = [((nx + ny) / 2) - nz] × d

[0165] (6) Heat resistance evaluation of the laminated film

[0166] Imitating the manufacturing process of an image display device, a laminated film was manufactured and the heat resistance of the laminated film was evaluated. The laminated film was produced as follows.

[0167] Without peeling the polyimide film obtained in the examples and comparative examples from the glass plate, a SiO2 film with a thickness of 300 nm was formed on the polyimide film by sputtering, and an ITO (indium tin oxide) film with a thickness of 1230 nm was formed thereon to obtain a laminated film.

[0168] Next, the obtained laminated film was annealed (heated) at 360 °C for 1 hour or at 400 °C for 1 hour.

[0169] Visually observe whether there are any defects (such as cracks, yellowing, etc.) in the laminated film before and after annealing, and evaluate the heat resistance of the polyimide film (laminated film) with an inorganic film laminated thereon according to the following criteria.

[0170] 〇: No cracks, yellowing or other defects were observed in the laminated film before and after annealing.

[0171] × (Crack or yellowing): Cracks, yellowing or other defects were observed in the laminated film before and after annealing.

[0172] If there are no defects, the heat resistance of the polyimide film laminated with the inorganic film is excellent.

[0173] <Abbreviations of components, etc.>

[0174] The tetracarboxylic acid components, diamine components, and their abbreviations used in the examples and comparative examples are as follows.

[0175] (Tetracarboxylic acid component)

[0176] CpODA: Norbornane-2-spiro-α-cyclopentanone-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic dianhydride (manufactured by ENEOS Corporation; the compound shown in formula (a11))

[0177] BNBDA: 5,5'-Bis-2-norbornane-5,5',6,6'-tetracarboxylic-5,5',6,6'-dianhydride (manufactured by ENEOS Corporation; the compound shown in formula (a12))

[0178] BPDA: 3,3',4,4'-Biphenyltetracarboxylic dianhydride (manufactured by Mitsubishi Chemical Corporation, the compound shown in formula (a211s) (s-BPDA)

[0179] BPAF: 9,9-Bis(3,4-dicarboxyphenyl)fluorene dianhydride (manufactured by JFE Chemical Corporation; the compound shown in formula (a22))

[0180] (Diamine component)

[0181] HFDA: 2,2-Bis(4-aminophenyl)hexafluoropropane (manufactured by Tokyo Chemical Industry Co., Ltd.; the compound shown in formula (b1))

[0182] BAFL: 9,9-Bis(4-aminophenyl)fluorene (manufactured by JFE Chemical Corporation; the compound shown in formula (b21))

[0183] TFMB: 2,2'-Bis(trifluoromethyl)benzidine (manufactured by Seika Corporation; the compound shown in formula (b22))

[0184] 6FODA: 2,2'-Bis(trifluoromethyl)-4,4'-diaminodiphenyl ether (manufactured by ChinaTech (Tianjin) Chemical Co., Ltd.)

[0185] <Manufacture of Polyimide Resin, Varnish and Polyimide Film>

[0186] Example 1

[0187] Into a 500 mL five-necked round-bottom flask equipped with a stainless-steel semi-circular stirring blade, a nitrogen inlet tube, a Dean-Stark water separator device equipped with a condenser, a thermometer, and a glass end cap, 33.427 g (0.100 mol) of HFDA and 86.238 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation) were charged, and the mixture was stirred at a system temperature of 70 °C, under a nitrogen atmosphere, and at a rotation speed of 200 rpm to obtain a solution.

[0188] After adding 38.438 g (0.100 mol) of CpODA and 21.560 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation) to this solution, 0.506 g of triethylamine (manufactured by Kanto Chemical Co., Inc.) and 0.056 g of triethylenediamine (manufactured by Tokyo Chemical Industry Co., Ltd.), which are imidization catalysts, were added, and the mixture was heated in a hooded heater. The temperature inside the reaction system was raised to 190 °C in about 20 minutes. The components removed by distillation were trapped, and while adjusting the rotation speed according to the increase in viscosity, the temperature inside the reaction system was maintained at 190 °C and refluxed for 5 hours.

[0189] After that, γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation) was added so that the solid content concentration was 15% by mass. After cooling the temperature inside the reaction system to 100 °C, the mixture was further stirred for about 1 hour to homogenize it, and a polyimide varnish was obtained.

[0190] Next, the obtained polyimide varnish was spin-coated on a glass plate, held at 80 °C for 20 minutes using a hot plate, and then heated in a hot air dryer at 400 °C for 30 minutes (heating rate: 5 °C / min) under a nitrogen atmosphere to evaporate the solvent and obtain a film.

[0191] Example 2

[0192] The amount of HFDA was changed from 33.427 g (0.100 mol) to 20.056 g (0.060 mol), and 13.938 g (0.040 mol) of BAFL was used. Except for this, a polyimide varnish with a solid content concentration of 15% by mass was obtained by the same method as in Example 1.

[0193] Using the obtained polyimide varnish, a film was obtained by the same method as in Example 1.

[0194] Example 3

[0195] The amount of CpODA was changed from 38.438 g (0.100 mol) to 23.063 g (0.060 mol), 11.769 g (0.040 mol) of BPDA was used, the amount of HFDA was changed from 33.427 g (0.100 mol) to 20.056 g (0.060 mol), 13.938 g (0.040 mol) of BAFL was used. Except for this, a polyimide varnish with a solid component concentration of 15% by mass was obtained by the same method as in Example 1.

[0196] Using the obtained polyimide varnish, a film was obtained by the same method as in Example 1.

[0197] Example 4

[0198] 38.438 g (0.100 mol) of CpODA was changed to 33.034 g (0.100 mol) of BNBDA, the solvent used in the reaction and dilution was changed from GBL to NMP. Except for this, a polyimide varnish with a solid component concentration of 15% by mass was obtained by the same method as in Example 2.

[0199] Using the obtained polyimide varnish, a film was obtained by the same method as in Example 1.

[0200] Comparative Example 1

[0201] 33.427 g (0.100 mol) of HFDA was changed to 32.024 g (0.100 mol) of TFMB, the solvent used in the reaction and dilution was changed from GBL to NMP. Except for this, a polyimide varnish with a solid component concentration of 15% by mass was obtained by the same method as in Example 1.

[0202] Using the obtained polyimide varnish, a film was obtained by the same method as in Example 1.

[0203] Comparative Example 2

[0204] 33.427 g (0.100 mol) of HFDA was changed to 33.624 g (0.100 mol) of 6FODA. Except for this, a polyimide varnish with a solid component concentration of 15% by mass was obtained by the same method as in Example 1.

[0205] Using the obtained polyimide varnish, a film was obtained by the same method as in Example 1.

[0206] Comparative Example 3

[0207] The amount of CpODA was changed from 38.438 g (0.100 mole) to 23.063 g (0.060 mole), 11.769 g (0.040 mole) of BPDA was used, and 20.056 g (0.060 mole) of HFDA was changed to 19.214 g (0.060 mole) of TFMB. Except for this, a polyimide varnish with a solid component concentration of 15% by mass was obtained by the same method as in Example 2.

[0208] Using the obtained polyimide varnish, a film was obtained by the same method as in Example 1.

[0209] Comparative Example 4

[0210] The amount of CpODA was changed from 38.438 g (0.100 mole) to 34.594 g (0.090 mole), 4.584 g (0.010 mole) of BPAF was used, HFDA was not used, the amount of BAFL was changed from 13.938 g (0.040 mole) to 15.680 g (0.045 mole), and 17.613 g (0.055 mole) of TFMB was used. Except for this, a polyimide varnish with a solid component concentration of 15% by mass was obtained by the same method as in Example 2.

[0211] Using the obtained polyimide varnish, a film was obtained by the same method as in Example 1.

[0212] Comparative Example 5

[0213] In a 300 mL five-necked round-bottom flask equipped with a stainless-steel semi-circular stirring blade, a nitrogen inlet tube, a Dean-Stark water separator device equipped with a condenser, a thermometer, and a glass end cap, 33.427 g (0.100 mole) of HFDA and 201.117 g of NMP were charged, and the mixture was stirred at a system temperature of 25 °C, under a nitrogen atmosphere, and at a rotation speed of 200 rpm to obtain a solution.

[0214] To this solution, 29.422 g (0.100 mole) of BPDA and 50.279 g of NMP were simultaneously added and stirred for 3 hours to obtain a polyamic acid varnish with a solid component concentration of 20.0% by mass.

[0215] Next, the obtained polyamic acid varnish was spin-coated on a glass plate, held at 80 °C for 20 minutes using a hot plate, and then heated in a hot air dryer at 400 °C for 60 minutes (heating rate: 5 °C / minute) under a nitrogen atmosphere to evaporate the solvent and obtain a film.

[0216] The above physical property measurements and evaluations were performed on the polyimide films obtained in the examples and comparative examples. The results are shown in Table 1.

[0217] [Table 1]

[0218]

[0219] As shown in Table 1, the polyimide film of the example is excellent in transparency and heat resistance when laminated with an inorganic film. Furthermore, the polyimide film of the example has good optical isotropy. The optical isotropy of Comparative Example 1 and Comparative Example 2 and the heat resistance of the laminated film are poor. The Tg of Comparative Example 3 and Comparative Example 4 is good, but the optical isotropy and the heat resistance of the laminated film are poor. The optical isotropy of Comparative Example 5 is good, but the Tg, colorless transparency, and heat resistance of the laminated film are poor.

[0220] Therefore, for the polyimide film manufactured using an acid dianhydride having two norbornane skeletons in the molecule as the tetracarboxylic acid component and using HFDA as the diamine component, it can be suitably used as a transparent substrate for constituting display devices such as liquid crystal displays, OLED displays, and touch panels as a film excellent in transparency, optical isotropy, and heat resistance of the laminated film.

Claims

1. A polyimide resin comprising a structural unit A derived from a tetracarboxylic dianhydride and a structural unit B derived from a diamine. The structural unit A comprises a structural unit (A1) derived from a tetracarboxylic dianhydride having 2 norbornane skeletons in the molecule, and the structural unit (A1) comprises at least one selected from the group consisting of a structural unit (A11) derived from a compound represented by the following formula (a11), a structural unit (A12) derived from a compound represented by the following formula (a12), a structural unit (A13) derived from a compound represented by the following formula (a13), and a structural unit (A14) derived from a compound represented by the following formula (a14). The structural unit B comprises a structural unit (B1) derived from a compound represented by the following formula (b1). The ratio of the structural unit (A1) in the structural unit A is 40 mol% or more, and the ratio of the structural unit (B1) in the structural unit B is 20 mol% or more.

2. The polyimide resin according to claim 1, wherein The structural unit A further comprises a structural unit (A2), and the structural unit (A2) comprises at least one selected from the group consisting of a structural unit (A21) derived from a compound represented by the following formula (a21) and a structural unit (A22) derived from a compound represented by the following formula (a22).

3. The polyimide resin according to claim 1 or 2, wherein, The structural unit B further comprises a structural unit (B2), and the structural unit (B2) comprises at least one selected from the group consisting of a structural unit (B21) derived from a compound represented by the following formula (b21), a structural unit (B22) derived from a compound represented by the following formula (b22), and a structural unit (B23) derived from a compound represented by the following formula (b23).

4. The polyimide resin according to claim 3, wherein, The structural unit (B2) comprises a structural unit (B21) derived from a compound represented by the following formula (b21).

5. A polyimide varnish obtained by dissolving the polyimide resin according to any one of claims 1 to 4 in an organic solvent.

6. A polyimide film comprising the polyimide resin according to any one of claims 1 to 4.

7. The polyimide film according to claim 6, having a total light transmittance of 80% or more as measured based on JIS K7136:2000.

8. The polyimide film according to claim 6 or 7, used as a transparent substrate constituting a display device.

9. A method for manufacturing a polyimide film, comprising a step of coating or molding the polyimide varnish according to claim 5 into a film shape and then removing the organic solvent.

10. An image display device comprising the polyimide film according to any one of claims 6 to 8 as a transparent substrate.

Images