Polyimide resin, polyimide varnish and polyimide film

Abstract

A polyimide resin containing a constituent unit A derived from a tetracarboxylic acid dianhydride and a constituent unit B derived from a diamine, wherein the constituent unit A includes a constituent unit (A1) derived from a tetracarboxylic acid dianhydride having a two-norbornane skeleton in each molecule, and the constituent unit B includes a constituent unit (B1) derived from a compound represented by formula (b1).

Description

[Technical Field]

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

[0002] Various applications of polyimide resins are being considered in the fields of electrical and electronic components, etc. For example, it is desirable to replace the glass substrates used in image display devices such as liquid crystal displays and OLED displays with plastic substrates in order to make the devices lighter and more flexible, and research is underway into polyimide films suitable for such plastic substrates. Films used in image display devices are required to have various optical properties. For example, when light emitted from a display element is emitted through a plastic substrate, the plastic substrate must be transparent.

[0003] In order to satisfy the above-mentioned performance requirements, polyimide resins with various compositions have been developed. For example, Patent Document 1 discloses a polyimide film having a structure formed by combining an acid dianhydride having a norbornane skeleton with 2,2'-bis(trifluoromethyl)benzidine as a diamine component, with the aim of obtaining a polyimide film having excellent transparency and high heat resistance. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6431369 Summary of the Invention [Problem to be solved by the invention]

[0005] Polyimide films are expected to replace glass substrates, and therefore must be transparent. Here, when manufacturing an image display device, for example, a heat treatment is performed on a polyimide film with an inorganic film laminated thereon, and outgassing from the polyimide film accumulates between the polyimide film and the inorganic film, which can cause discoloration such as yellowing of the polyimide film. Therefore, the polyimide film is required to have heat resistance that suppresses discoloration when exposed to high temperatures with an inorganic film laminated thereon. Furthermore, when manufacturing an image display device, the process temperature can exceed 400°C, for example, and therefore the polyimide film used as the substrate is required to have heat resistance capable of withstanding high temperatures of 400°C or higher. Polyimide films have a high glass transition temperature (Tg) and excellent heat resistance, but there is a concern that defects such as cracks may occur in the inorganic film when exposed to high temperatures in a state where an inorganic film is laminated thereon. Therefore, polyimide films are required to have heat resistance that will prevent defects such as cracks from occurring in the inorganic film when exposed to high temperatures in a state where an inorganic film is laminated thereon. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a polyimide resin and polyimide varnish which can provide a polyimide film which has excellent transparency and heat resistance when laminated with an inorganic film, and a polyimide film which has excellent transparency and heat resistance when laminated with an inorganic film. [Means for solving the problem]

[0006] The present inventors discovered that the above-mentioned problems can be solved by 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, and thus completed the present invention.

[0007] That is, the present invention provides the following: <1> ~ <11> Regarding. <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 contains a structural unit (A1) derived from a tetracarboxylic dianhydride having two norbornane skeletons in the molecule, A polyimide resin, wherein the structural unit B comprises a structural unit (B1) derived from a compound represented by the following formula (b1): [ka] <2> 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): <1> The polyimide resin according to claim 1. [ka] <3> 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): <1> or <2> The polyimide resin according to claim 1. [ka] <4> 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): <1> ~ <3> 1. The polyimide resin according to claim 1 . [ka] [ka] [ka] <5> The structural unit (B2) includes a structural unit (B21) derived from a compound represented by the following formula (b21): <4> The polyimide resin according to claim 1. [ka] <6> <1> ~ <5> 1. A polyimide varnish obtained by dissolving the polyimide resin according to any one of 1 to 3 in an organic solvent. <7> <1> ~ <5> A polyimide film comprising the polyimide resin according to any one of the above items. <8> Total light transmittance measured in accordance with JIS K7136:2000 is 80% or more. <7> The polyimide film according to claim 1. <9> Used as a transparent substrate constituting a display device, <7> or <8> The polyimide film according to claim 1. <10> <6> 10. A method for producing a polyimide film, comprising the steps of applying or forming the polyimide varnish according to claim 1 into a film and then removing the organic solvent. <11> <7> ~ <9> 1. An image display device comprising the polyimide film according to any one of the above items as a transparent substrate. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a polyimide resin and polyimide varnish which can provide a polyimide film which has excellent transparency and heat resistance when laminated with an inorganic film, as well as a polyimide film which has excellent transparency and heat resistance when laminated with an inorganic film. DETAILED DESCRIPTION OF THE INVENTION

[0009] A 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 carried out by appropriately modifying it within the scope of its gist. In the present embodiment, the preferred specifications can be adopted arbitrarily, and it can be said that a combination of preferred specifications is more preferred. In the present embodiment, the expression "XX to YY" means "XX or more and YY or less."

[0010] [Polyimide resin] The polyimide resin of the present invention is a polyimide resin comprising a structural unit A derived from a tetracarboxylic dianhydride and a structural unit B derived from a diamine, in which the structural unit A comprises a structural unit (A1) derived from a tetracarboxylic dianhydride having two norbornane skeletons in the molecule, and the structural unit B comprises a structural unit (B1) derived from a compound represented by the following formula (b1):

[0011] [ka]

[0012] The reason why the polyimide resin of the present invention can provide a polyimide film that is excellent in transparency and heat resistance when laminated with an inorganic film is not clear, but it is thought that the polyimide resin of the present invention has a norbornane skeleton and a structural unit (B1) that has a bent structure but is expected to suppress molecular motion due to a trifluoromethyl group with large steric hindrance, and therefore can improve heat resistance while maintaining good transparency, resulting in excellent transparency and heat resistance when laminated with an inorganic film (suppression of coloration and suppression of cracking of the inorganic film).

[0013] <Constituent unit A> The structural unit A is a structural unit derived from a tetracarboxylic dianhydride contained in the polyimide resin. The structural unit A includes a structural unit (A1) derived from a tetracarboxylic dianhydride having two norbornane skeletons in the molecule. From the viewpoints of heat resistance, transparency, and optical isotropy, the structural unit (A1) preferably 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). From the viewpoints of making the molecular skeleton more rigid and further improving heat resistance, the structural unit (A11) derived from a compound represented by the following formula (a11) It is more preferable that the structural unit (A11) derived from a compound represented by formula (a12) below, a structural unit (A12) derived from a compound represented by formula (a12) below, and a structural unit (A14) derived from a compound represented by formula (a14) below, it is even more preferable that the structural unit (A11) derived from a compound represented by formula (a11) below, and a structural unit (A14) derived from a compound represented by formula (a14) below, and it is even more preferable that the structural unit (A11) derived from a compound represented by formula (a11) below.

[0014] [ka]

[0015] When the structural unit A contains the structural unit (A1) derived from a tetracarboxylic dianhydride having two norbornane skeletons in the molecule, the heat resistance, transparency, and optical isotropy of the resulting polyimide film can be improved.

[0016] The structural unit A may further include a structural unit (A2) in addition to the structural unit (A1). Examples of the structural unit (A2) include at least one selected from the group consisting of the structural unit (A21) derived from a compound represented by the following formula (a21) and the structural unit (A22) derived from a compound represented by the following formula (a22):

[0017] [ka]

[0018] The compound represented by formula (a21) is biphenyltetracarboxylic dianhydride (BPDA), and specific examples thereof include 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-BPDA) represented by the following formula (a211i). Of these, 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA) represented by the following formula (a211s) is preferred.

[0019] [ka]

[0020] From the viewpoints of heat resistance, transparency, and optical isotropy, the proportion of the structural unit (A1) in the structural unit A is preferably 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 of this proportion is not particularly limited, but is 100 mol% or less. Furthermore, when the structural unit A further comprises the structural unit (A2), from the viewpoints of heat resistance, transparency, and optical isotropy, the proportion of the structural unit (A2) in the structural unit A is preferably 60 mol% or less, more preferably 50 mol% or less, even more preferably 40 mol% or less, even more preferably 20 mol% or less, even more preferably 15 mol% or less, even more preferably 10 mol% or less, even more preferably 5 mol% or less, and even more preferably 1 mol% or less. The lower limit of this proportion is not particularly limited, but is at least 0.01 mol%.

[0021] The structural unit A may contain a structural unit other than the structural unit (A1) and the structural unit (A2). The tetracarboxylic acid dianhydride that provides such a structural unit is not particularly limited, but examples include aromatic tetracarboxylic acid dianhydrides such as 4,4'-oxydiphthalic anhydride, pyromellitic dianhydride, and 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (excluding compounds represented by formula (a21) or (a22)); alicyclic tetracarboxylic acid dianhydrides such as 1,2,4,5-cyclohexanetetracarboxylic acid dianhydride and 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride (excluding compounds represented by any of formulas (a11) to (a14)); and aliphatic tetracarboxylic acid dianhydrides such as 1,2,3,4-butanetetracarboxylic acid dianhydride. In this specification, aromatic tetracarboxylic acid dianhydride means a tetracarboxylic acid dianhydride containing one or more aromatic rings, alicyclic tetracarboxylic acid dianhydride means a tetracarboxylic acid dianhydride containing one or more alicyclic rings but no aromatic rings, and aliphatic tetracarboxylic acid dianhydride means a tetracarboxylic acid dianhydride containing neither an aromatic ring nor an alicyclic ring. The structural unit optionally contained in the structural unit A may be one type, or two or more types.

[0022] <Constituent unit B> The structural unit B is a structural unit derived from a diamine contained in the polyimide resin. The structural unit B includes a structural unit (B1) derived from a compound represented by the following formula (b1).

[0023] [ka]

[0024] The compound represented by formula (b1) is 2,2-bis(4-aminophenyl)hexafluoropropane. When the structural unit B contains the structural unit (B1), it is possible to improve toughness while maintaining heat resistance.

[0025] From the viewpoint of improving heat resistance when an inorganic film is laminated, the ratio of the structural unit (B1) in the structural unit B is preferably 20 mol% or more, more preferably 40 mol% or more, even more preferably 50 mol% or more, even more preferably 55 mol% or more, even more preferably 60 mol% or more, even more preferably 80 mol% or more, and even more preferably 99 mol% or more. The upper limit of this ratio is not particularly limited, but is 100 mol% or less.

[0026] The structural unit B may include a structural unit other than the structural unit (B1). It is preferable that the structural unit B further includes a structural unit (B2) in addition to the structural unit (B1). The structural unit (B2) preferably includes 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). From the viewpoint of making the molecular skeleton more rigid and further improving heat resistance, it is more preferable that the structural unit (B21) derived from a compound represented by the following formula (b21) be included. When the structural unit B includes the structural unit (B2), heat resistance in particular is improved, and optical isotropy is also improved.

[0027] [ka]

[0028] [ka]

[0029] [ka]

[0030] When the structural unit B further contains the structural unit (B2), the proportion of the structural unit (B2) in the structural unit B is preferably 10 mol% or more, more preferably 20 mol% or more, even more preferably 30 mol% or more, and is preferably 70 mol% or less, more preferably 60 mol% or less, even more preferably 50 mol% or less. When the structural unit B further contains the structural unit (B2), the total proportion 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, even more preferably 90 mol% or more, even more preferably 95 mol% or more, and even more preferably 99 mol% or more. There are no particular upper limits for the total proportion of the structural unit (B1) and the structural unit (B2) in the structural unit B, and it is, for example, 100 mol% or less. The structural unit B may be composed only of the structural unit (B1) and the structural unit (B2). When the structural unit B further contains the structural unit (B2), the molar ratio of the structural unit (B1) to the structural unit (B2) in the structural unit B [(B1) / (B2)] is preferably 30 / 70 to 90 / 10, more preferably 40 / 60 to 80 / 20, and even more preferably 50 / 50 to 70 / 30, from the viewpoint of improving transparency, optical isotropy, toughness, and heat resistance.

[0031] The structural unit B may contain a structural unit other than the structural unit (B1) and the structural unit (B2). Diamines that provide such structural units include, but are not limited to, 1,4-phenylenediamine, p-xylylenediamine, 1,5-diaminonaphthalene, 2,2'-dimethylbiphenyl-4,4'-diamine, 4,4'-diaminodiphenyl ether, 4,4'-diamino-2,2'-bistrifluoromethyldiphenyl ether, 4,4'-diaminodiphenylmethane, 4,4'-diaminobenzanilide, 1-(4-aminophenyl)-2,3-dihydro-1,3,3-trimethyl-1H-inden-5-amine, α,α'-bis(4-aminophenyl)-1,4-diisopropylbenzanilide ... aromatic diamines such as benzene, 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 (excluding compounds represented by any of formulas (b1) and (b21) to (b23)); alicyclic diamines such as 1,3-bis(aminomethyl)cyclohexane and 1,4-bis(aminomethyl)cyclohexane; and aliphatic diamines such as ethylenediamine and hexamethylenediamine. In this specification, aromatic diamine means a diamine containing one or more aromatic rings, alicyclic diamine means a diamine containing one or more alicyclic rings but no aromatic rings, and aliphatic diamine means a diamine containing neither an aromatic ring nor an alicyclic ring. The structural unit optionally contained in the structural unit B may be one type, or two or more types.

[0032] <Characteristics of polyimide resin> From the viewpoint of the mechanical strength of the resulting polyimide film, the weight-average molecular weight of the polyimide resin is preferably 5,000 to 300,000. The weight-average molecular weight of the polyimide resin can be determined, for example, from a standard polymethyl methacrylate (PMMA) equivalent value measured by gel filtration chromatography.

[0033] The polyimide resin may contain a structure other than a polyimide chain (a structure formed by imide bonding between the structural unit A and the structural unit B). Examples of structures other than polyimide chains that can be contained in the polyimide resin include structures containing amide bonds. The polyimide resin preferably contains a polyimide chain (a structure formed by imide bonding of structural unit A and structural unit B) as the main structure. Therefore, the proportion of polyimide chains in the polyimide resin is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, and particularly preferably 99% by mass or more, and 100% by mass or less. The polyimide resin may be composed only of polyimide chains.

[0034] A polyimide resin composition containing the above polyimide resin can form a polyimide film that is excellent in heat resistance while maintaining transparency and optical isotropy, and the preferred physical properties of the polyimide film are as follows:

[0035] When the polyimide resin is formed into a film having a thickness of 10 μm, the total light transmittance is preferably 80% or more, more preferably 85% or more, even more preferably 88% or more, even more preferably 88.5% or more, and even more preferably 89% or more. When the polyimide resin is formed into a film having a thickness of 10 μm, the yellow index (YI) is preferably 5.0 or less, more preferably 3.0 or less, even more preferably 2.5 or less, and still more preferably 2.0 or less. The absolute value of the thickness retardation (Rth) is preferably 200 nm or less, more preferably 180 nm or less, and even more preferably 160 nm or less, when the polyimide resin is made into a film having a thickness of 10 μm.

[0036] Furthermore, films that can be formed using the polyimide resins have good heat resistance and the following preferred physical properties. The glass transition temperature (Tg) is preferably 380°C or higher, more preferably 390°C or higher, and even more preferably 400°C or higher. The 5% weight loss temperature (Td5%) is preferably 480°C or higher, more preferably 490°C or higher, and even more preferably 495°C or higher. Regarding heat resistance when laminating inorganic films, when a 300 nm thick SiO2 film is formed on a polyimide film by sputtering, and then a 1230 nm thick ITO (indium tin oxide) film is formed on top of that to form a laminate film, preferably, defects such as cracking and yellowing do not occur in the laminate film after "annealing treatment at 400°C for 1 hour," and more preferably, defects such as cracking and yellowing do not occur in the laminate film after "annealing treatment at 420°C for 1 hour." The above-mentioned physical property values ​​in the present invention can be specifically measured by the methods described in the examples.

[0037] <Method of manufacturing polyimide resin> The polyimide resin of the present invention can be produced by reacting a tetracarboxylic acid component containing a compound that provides the above-mentioned structural unit (A1) with a diamine component containing a compound that provides the above-mentioned structural unit (B1).

[0038] Compounds that provide the structural unit (A1) include, but are not limited to, compounds represented by any of formulas (a11) to (a14), and may also be derivatives thereof as long as they provide the same structural unit. Examples of such derivatives include tetracarboxylic acids corresponding to the tetracarboxylic dianhydrides represented by any of formulas (a11) to (a14), and alkyl esters of such tetracarboxylic acids. Of these, the tetracarboxylic dianhydride represented by formula (a11) is preferred.

[0039] The tetracarboxylic acid component may contain, in addition to the compound that provides the structural unit (A1), a compound that provides the structural unit (A2). Compounds that provide the structural unit (A2) include compounds represented by formula (a21) and compounds represented by formula (a22), but are not limited to these, and may also be derivatives thereof as long as they provide the same structural unit.

[0040] The tetracarboxylic acid component contains a compound that provides the structural unit (A1) in an amount of preferably 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 of this ratio is not particularly limited, but is preferably 100 mol% or less.

[0041] The tetracarboxylic acid component may contain any compound other than the compound that provides the structural unit (A1) and the compound that provides the structural unit (A2). Such optional compounds include the above-mentioned aromatic tetracarboxylic acid dianhydrides, alicyclic tetracarboxylic acid dianhydrides, and aliphatic tetracarboxylic acid dianhydrides, as well as derivatives thereof (tetracarboxylic acids, alkyl esters of tetracarboxylic acids, etc.). The compound optionally contained in the tetracarboxylic acid component may be one type or two or more types.

[0042] Compounds that provide the structural unit (B1) include, but are not limited to, compounds represented by formula (b1), and may also be derivatives thereof as long as they provide the same structural unit. Examples of such derivatives include diisocyanates corresponding to the compound represented by formula (b1). Compounds that provide the structural unit (B1) are preferably compounds represented by formula (b1) (i.e., diamines). The diamine component may contain a compound that provides the structural unit (B2) in addition to the compound that provides the structural unit (B1). Examples of compounds that provide the structural unit (B2) include, but are not limited to, compounds represented by formula (b21), (b22), and (b23). Derivatives that provide the same structural unit may also be used. Examples of such derivatives include diisocyanates corresponding to the compounds represented by formula (b21), (b22), and (b23). Preferred compounds that provide the structural unit (B2) are compounds represented by formula (b21), (b22), and (b23) (i.e., diamines).

[0043] The diamine component preferably accounts for 20 mol% or more of the compound that provides the structural unit (B1), more preferably 40 mol% or more, even more preferably 50 mol% or more, even more preferably 60 mol% or more, even more preferably 80 mol% or more, and particularly preferably 99 mol% or more. The upper limit of this ratio is not particularly limited, but is preferably 100 mol% or less. When the diamine component contains a compound that provides the structural unit (B2), it preferably contains 10 mol% or more of the compound that provides the structural unit (B2), more preferably 20 mol% or more, even more preferably 30 mol% or more, and preferably 70 mol% or less, more preferably 60 mol% or less, even more preferably 50 mol% or less. When the diamine component contains a compound that provides the structural unit (B2), it preferably contains at least 50 mol%, more preferably at least 70 mol%, even more preferably at least 90 mol%, even more preferably at least 95 mol%, and even more preferably at least 99 mol% of the compound that provides the structural unit (B1) and the compound that provides the structural unit (B2). There are no particular upper limits, and the diamine component contains at most 100 mol% of the compound that provides the structural unit (B1) and the compound that provides the structural unit (B2). The tetracarboxylic acid component may consist solely of the compound that provides the structural unit (B1) and the compound that provides the structural unit (B2). When the diamine component contains a compound that provides the structural unit (B2), the molar ratio of the compound that provides the structural unit (B1) to the compound that provides the structural unit (B2) in the diamine component [(B1) / (B2)] is preferably 30 / 70 to 90 / 10, more preferably 40 / 60 to 80 / 20, and even more preferably 50 / 50 to 70 / 30, from the viewpoint of improving transparency, optical isotropy, toughness, and heat resistance.

[0044] The diamine component may further contain any compound other than the compound that provides the structural unit (B1) and the compound that provides the structural unit (B2). Such optional compounds include the above-mentioned aromatic diamines, alicyclic diamines, and aliphatic diamines, as well as derivatives thereof (such as diisocyanates). The compound optionally contained in the diamine component may be one type or two or more types.

[0045] In the production of the polyimide resin of the present invention, the ratio of the amount of the tetracarboxylic acid component to the amount of the diamine component used in the production of the polyimide resin is preferably 0.9 to 1.1 moles of the diamine component per mole of the tetracarboxylic acid component.

[0046] In addition, in the production of the polyimide resin of the present invention, a terminal blocking agent may be used in addition to the tetracarboxylic acid component and diamine component described above. Monoamines or dicarboxylic acids are preferred as terminal blocking agents. The amount of terminal blocking agent introduced is preferably 0.0001 to 0.1 mol, more preferably 0.001 to 0.06 mol, per 1 mol of the tetracarboxylic acid component. Examples of monoamine terminal blocking agents include methylamine, ethylamine, propylamine, butylamine, benzylamine, 4-methylbenzylamine, 4-ethylbenzylamine, 4-dodecylbenzylamine, 3-methylbenzylamine, 3-ethylbenzylamine, aniline, 3-methylaniline, and 4-methylaniline, with benzylamine and aniline being preferred. Dicarboxylic acid terminal blocking agents are preferred, and a portion of the dicarboxylic acid may be ring-closed. Examples include phthalic acid, phthalic anhydride, 4-chlorophthalic acid, tetrafluorophthalic acid, 2,3-benzophenonedicarboxylic acid, 3,4-benzophenonedicarboxylic acid, cyclohexane-1,2-dicarboxylic acid, cyclopentane-1,2-dicarboxylic acid, and 4-cyclohexene-1,2-dicarboxylic acid, with phthalic acid and phthalic anhydride being preferred.

[0047] There are no particular limitations on the method for reacting the tetracarboxylic acid component and the diamine component, and any known method can be used. Specific reaction methods include: (1) a method in which a tetracarboxylic acid component, a diamine component, and a reaction solvent are charged into a reactor, and the mixture is stirred at 0 to 10°C for 0.5 to 30 hours, and then the temperature is raised to carry out the imidization reaction; (2) a method in which a diamine component and a reaction solvent are charged into a reactor and dissolved, and then the tetracarboxylic acid component is charged, and the mixture is stirred at room temperature (0 to 10°C) for 0.5 to 30 hours as needed, and then the temperature is raised to carry out the imidization reaction; and (3) a method in which a tetracarboxylic acid component, a diamine component, and a reaction solvent are charged into a reactor, and the temperature is immediately raised to carry out the imidization reaction.

[0048] The reaction solvent used in the production of the polyimide resin may be any solvent that does not inhibit the imidization reaction and can dissolve the resulting polyimide, such as aprotic solvents, phenolic solvents, ether solvents, and carbonate solvents.

[0049] Specific examples of aprotic solvents include amide solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone (NMP), N-methylcaprolactam, 1,3-dimethylimidazolidinone, and tetramethylurea; lactone solvents such as γ-butyrolactone (GBL) and γ-valerolactone; phosphorus-containing amide solvents such as hexamethylphosphoric amide and hexamethylphosphine triamide; sulfur-containing solvents such as dimethyl sulfone, dimethyl sulfoxide, and sulfolane; ketone solvents such as acetone, cyclohexanone, and methylcyclohexanone; amine solvents such as picoline and pyridine; and ester solvents such as 2-methoxy-1-methylethyl acetate.

[0050] Specific examples of phenol-based solvents include phenol, o-cresol, m-cresol, p-cresol, 2,3-xylenol, 2,4-xylenol, 2,5-xylenol, 2,6-xylenol, 3,4-xylenol, and 3,5-xylenol. 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, and 1,4-dioxane. Specific examples of carbonate solvents include diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, and propylene carbonate. Among the above reaction solvents, aprotic solvents are preferred, amide solvents and lactone solvents are more preferred, and lactone solvents are even more preferred. The above reaction solvents may be used alone or in combination of two or more.

[0051] The imidization reaction is preferably carried out while removing water generated during the production using a Dean-Stark apparatus, etc. By performing such an operation, the degree of polymerization and the imidization rate can be further increased.

[0052] In the imidization reaction, a known imidization catalyst can be used, such as a base catalyst or an acid catalyst. Examples of the base catalyst include organic base catalysts such as pyridine, quinoline, isoquinoline, α-picoline, β-picoline, 2,4-lutidine, 2,6-lutidine, trimethylamine, triethylamine (TEA), tripropylamine, tributylamine, triethylenediamine, imidazole, N,N-dimethylaniline, and N,N-diethylaniline; and inorganic base catalysts such as potassium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate, potassium hydrogencarbonate, and sodium hydrogencarbonate. Examples of the acid catalyst include crotonic acid, acrylic acid, trans-3-hexenoic acid, cinnamic acid, benzoic acid, methylbenzoic acid, oxybenzoic acid, terephthalic acid, benzenesulfonic acid, paratoluenesulfonic acid, naphthalenesulfonic acid, etc. The above imidization catalysts may be used alone or in combination of two or more. Among these, from the viewpoint of ease of handling, it is preferable to use a base catalyst, more preferable to use an organic base catalyst, and even more preferable to use triethylamine or triethylenediamine.

[0053] The temperature of the imidization reaction is preferably 120 to 250° C., more preferably 160 to 200° C., from the viewpoint of the reaction rate and suppression of gelation, etc. The reaction time is preferably 0.5 to 10 hours after the start of distillation of the produced water.

[0054] [Polyimide varnish] 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. The organic solvent is not particularly limited as long as it dissolves the polyimide resin, but it is preferable to use the compounds described above as reaction solvents used in the production of polyimide resins, either alone or in combination of two or more. The polyimide varnish of the present invention may be a polyimide solution itself in which a polyimide resin obtained by polymerization is dissolved in a reaction solvent, or may be a polyimide solution diluted by further adding a solvent.

[0055] The polyimide resin of the present invention is solvent-soluble, and therefore can be made into a highly concentrated varnish that is stable at room temperature. The polyimide varnish of the present invention preferably contains 5 to 40 mass %, more preferably 5 to 20 mass %, of the polyimide resin of the present invention. 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. The polyimide varnish of the present invention may also contain various additives such as inorganic fillers, adhesion promoters, release agents, flame retardants, UV stabilizers, surfactants, leveling agents, antifoaming agents, fluorescent brightening agents, crosslinking agents, polymerization initiators, and photosensitizers, as long as the additives do not impair the required properties of the polyimide film. The method for producing the polyimide varnish of the present invention is not particularly limited, and known methods can be applied.

[0056] [Polyimide film] 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 properties of the polyimide film of the present invention are as described above under "Properties of polyimide resin." The method for producing the polyimide film of the present invention is not particularly limited, and known methods can be used. For example, the polyimide varnish of the present invention is applied to a smooth support such as a glass plate, a metal plate, or a plastic plate in the form of a film, or formed into a film, and then organic solvents such as reaction solvents and dilution solvents contained in the varnish are removed by heating. As the method for producing the polyimide film of the present invention, a method including a step of applying or forming the polyimide varnish into a film and then removing the organic solvent is preferred.

[0057] Examples of the coating method include known coating methods such as spin coating, slit coating, and blade coating, and spin coating and slit coating are preferred. Among these, slit coating is more preferred from the viewpoint of workability, as it controls intermolecular orientation and improves chemical resistance. A preferred method for removing the organic solvent contained in the varnish by heating is to evaporate the organic solvent at a temperature of 150°C or less to make the varnish tack-free, and then dry it at a temperature equal to or higher than the boiling point of the organic solvent used (preferably 200 to 500°C, although there are no particular limitations). Drying is also preferred in an air or nitrogen atmosphere. The pressure of the drying atmosphere may be reduced, normal, or increased. The method for peeling the polyimide film formed on the support from the support is not particularly limited, but a mechanical peel-off method, a laser lift-off method, or the like can be used.

[0058] The polyimide film of the present invention can also be produced using a polyamic acid varnish prepared by dissolving polyamic acid in an organic solvent. The polyamic acid contained in the polyamic acid varnish is a precursor of the polyimide resin of the present invention, and is a product of a polyaddition reaction between a tetracarboxylic acid component containing a compound that provides the structural unit (A1) and a diamine component containing a compound that provides the structural unit (B1). The polyamic acid is imidized (dehydration ring closure) to obtain the final product, the polyimide resin of the present invention. As the organic solvent contained in the polyamic acid varnish, the organic solvent contained in the polyimide varnish of the present invention can be used. In the production of the polyimide film of the present invention, the polyamic acid varnish may be a polyamic acid solution itself obtained by subjecting a tetracarboxylic acid component and a diamine component to a polyaddition reaction in a reaction solvent, or may be a polyamic acid solution diluted with additional solvent.

[0059] The method for producing a polyimide film using the polyamic acid varnish is not particularly limited, and any known method can be used. For example, the polyamic acid varnish is applied to a smooth support such as a glass plate, a metal plate, or a plastic plate in the form of a film, or formed into a film, and organic solvents such as reaction solvents and dilution solvents contained in the varnish are removed by heating to obtain a polyamic acid film, and the polyamic acid in the polyamic acid film is imidized by heating, thereby producing a polyimide film. The heating temperature when the polyamic acid varnish is dried to obtain a polyamic acid film is preferably 50 to 120° C. The heating temperature when the polyamic acid is imidized by heating is preferably 200 to 450° C. The imidization method is not limited to thermal imidization, and chemical imidization can also be applied.

[0060] The thickness of the polyimide film of the present invention can be appropriately selected depending on the application, etc., but is preferably in the range of 1 to 250 μm, more preferably 5 to 100 μm, even more preferably 8 to 80 μm, and still more preferably 10 to 80 μm. A thickness of 1 to 250 μm enables practical use as a free-standing film. The thickness of the polyimide film can be easily controlled by adjusting the solid content and viscosity of the polyimide varnish.

[0061] In the polyimide film of the present invention, the total light transmittance measured in accordance with JIS K7136:2000 is preferably 80% or more, more preferably 85% or more, even more preferably 88% or more, even more preferably 88.5% or more, and even more preferably 89% or more, from the viewpoint of further improving transparency.

[0062] The polyimide film of the present invention is suitably used as a film for various components such as color filters, flexible displays, semiconductor parts, optical members, 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.

[0063] [Image display device] The image display device of the present invention comprises the polyimide film of the present invention as a transparent substrate. The image display device of the present invention includes, for example, a transparent substrate made of the polyimide film of the present invention, and a display section provided on the transparent substrate. The display unit is not particularly limited, but examples thereof include display elements using TFT elements, organic EL elements, color filters, LEDs, transistors, electron-emitting elements, electronic ink, electrophoretic elements, GLVs (grating light valves), MEMS (microelectromechanical systems), DMDs (digital micromirror devices), DMSs (digital microshutters), IMODs (interferometric modulation) elements, electrowetting elements, piezoelectric ceramic displays, and carbon nanotube-based display elements. Examples of the image display device of the present invention include a liquid crystal display, an OLED display, and a touch panel. The image display device of the present invention can be produced based on known information, except that the polyimide film of the present invention is used as a transparent substrate. The image display device of the present invention uses the polyimide film of the present invention, which has excellent heat resistance when laminated with an inorganic film, as a transparent substrate, and is therefore less likely to cause cracks in the inorganic film or discoloration of the transparent substrate, resulting in excellent reliability. [Example]

[0064] The present invention will be specifically described below with reference to examples, although the present invention is not limited to these examples in any way.

[0065] <Film properties and evaluation> The physical properties of the films obtained in the examples and comparative examples were measured by the following methods.

[0066] (1) Film thickness The film thickness was measured using a micrometer manufactured by Mitutoyo Corporation.

[0067] (2) Glass transition temperature (Tg) Using a thermomechanical analyzer "TMA / SS6100" manufactured by Hitachi High-Tech Science Corporation, the specimen was heated to a temperature sufficient to remove residual stress in tension mode under the following conditions: sample size 3mm x 20mm, load 0.1N, heating rate 10°C / min, and then cooled to room temperature. The specimen elongation was then measured under the same conditions as for the treatment to remove the residual stress, and the inflection point of elongation was extrapolated to determine the glass transition temperature.

[0068] (3) Total light transmittance and yellow index (YI) 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 and turbidity simultaneous measuring instrument "COH7700" manufactured by Nippon Denshoku Industries Co., Ltd.

[0069] (4) 5% weight loss temperature (Td5%) A Hitachi High-Tech Science Corporation NEXTA STA200RV thermogravimetric and differential thermal analyzer was used. The sample was heated from 40 to 150°C at a heating rate of 10°C / min, held at 150°C for 30 minutes to remove moisture, and then heated to 510°C. The temperature at which the weight had 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 weight loss temperature, the better the heat resistance.

[0070] (5) Thickness retardation (Rth) (evaluation of optical isotropy) The thickness retardation (Rth) was measured using an ellipsometer "M-220" manufactured by JASCO Corporation. The thickness retardation value was measured at a measurement wavelength of 590 nm. Rth is expressed by the following formula, where nx is the maximum in-plane refractive index of the polyimide film, ny is the minimum, nz is the refractive index in the thickness direction, and d is the thickness of the film. Rth=[{(nx+ny) / 2}-nz]×d

[0071] (6) Heat resistance evaluation of laminated film A laminated film was produced in accordance with the manufacturing process of an image display device, and the heat resistance of the laminated film was evaluated. The laminated film was produced as follows. Without peeling the polyimide films obtained in the Examples and Comparative Examples from the glass plates, a 300 nm thick SiO2 film was formed on the polyimide film by sputtering, and a 1230 nm thick ITO (indium tin oxide) film was formed on top of that to obtain a laminated film. Next, the resulting laminated film was annealed (heated) at 360° C. for 1 hour or at 400° C. for 1 hour. The laminated film was visually inspected for defects (cracks, yellowing, etc.) before and after annealing, and the heat resistance of the polyimide film (laminate film) laminated with the inorganic film was evaluated according to the following criteria. ◯: No defects such as cracks or yellowing occurred in the laminated film before or after annealing × (cracks or yellowing): Defects such as cracks or yellowing occurred in the laminated film before and after annealing. If there are no defects, polyimide films have excellent heat resistance when laminated with inorganic films.

[0072] <Abbreviations for ingredients, etc.> The tetracarboxylic acid components and diamine components used in the examples and comparative examples, and their abbreviations, are as follows:

[0073] (Tetracarboxylic acid component) CpODA: norbornane-2-spiro-α-cyclopentanone-α'-spiro-2″-norbornane-5,5″,6,6″-tetracarboxylic dianhydride (manufactured by ENEOS Corporation; compound represented by formula (a11)) BNBDA: 5,5'-bis-2-norbornene-5,5',6,6'-tetracarboxylic acid-5,5',6,6'-dianhydride (manufactured by ENEOS Corporation; compound represented by formula (a12)) BPDA: 3,3',4,4'-biphenyltetracarboxylic dianhydride (manufactured by Mitsubishi Chemical Corporation, a compound (s-BPDA) represented by formula (a211s)) BPAF: 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride (manufactured by JFE Chemical Corporation; compound represented by formula (a22))

[0074] (Diamine component) HFDA: 2,2-bis(4-aminophenyl)hexafluoropropane (manufactured by Tokyo Chemical Industry Co., Ltd.; compound represented by formula (b1)) BAFL: 9,9-bis(4-aminophenyl)fluorene (manufactured by JFE Chemical Corporation; compound represented by formula (b21)) TFMB: 2,2'-bis(trifluoromethyl)benzidine (manufactured by Seika Corporation; compound represented by formula (b22)) 6FODA: 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl ether (ChinaTech (Tianjin) Chemical Co., Ltd.)

[0075] <Production of polyimide resin, varnish and polyimide film> Example 1 33.427 g (0.100 mol) of HFDA and 86.238 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation) were placed in a 500 mL five-neck round-bottom flask equipped with a stainless steel half-moon stirring blade, a nitrogen inlet tube, a Dean-Stark system fitted with a condenser, a thermometer, and a glass end cap, and the mixture was stirred at 200 rpm under a nitrogen atmosphere at a system temperature of 70°C to obtain a solution. To this solution, 38.438 g (0.100 mol) of CpODA and 21.560 g of γ-butyrolactone (Mitsubishi Chemical Corporation) were added all at once, followed by the addition of 0.506 g of triethylamine (Kanto Chemical Co., Ltd.) and 0.056 g of triethylenediamine (Tokyo Chemical Industry Co., Ltd.) as imidization catalysts. The mixture was heated with a mantle heater, and the temperature in the reaction system was raised to 190°C over approximately 20 minutes. The components distilled off were collected, and the temperature in the reaction system was maintained at 190°C and refluxed for 5 hours while adjusting the rotation speed according to the increase in viscosity. Thereafter, γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation) was added so that the solid content concentration was 15% by mass, and the temperature inside the reaction system was cooled to 100°C. After that, the mixture was further stirred for about 1 hour to be homogenized, and a polyimide varnish was obtained. The resulting polyimide varnish was then applied to a glass plate by spin coating, held on a hot plate at 80°C for 20 minutes, and then heated in a hot air dryer at 400°C for 30 minutes under a nitrogen atmosphere (heating rate 5°C / min) to evaporate the solvent and obtain a film.

[0076] Example 2 A polyimide varnish with a solid content concentration of 15% by mass was obtained in the same manner as in Example 1, except that 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. A film was obtained in the same manner as in Example 1 using the obtained polyimide varnish.

[0077] Example 3 A polyimide varnish with a solids concentration of 15% by mass was obtained in the same manner as in Example 1, except that 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), and 13.938 g (0.040 mol) of BAFL was used. A film was obtained in the same manner as in Example 1 using the obtained polyimide varnish.

[0078] Example 4 A polyimide varnish with a solid content concentration of 15% by mass was obtained in the same manner as in Example 2, except that 38.438 g (0.100 mol) of CpODA was changed to 33.034 g (0.100 mol) of BNBDA and the solvent used for the reaction and dilution was changed from GBL to NMP. A film was obtained in the same manner as in Example 1 using the obtained polyimide varnish.

[0079] Comparative Example 1 A polyimide varnish with a solid content concentration of 15% by mass was obtained in the same manner as in Example 1, except that 33.427 g (0.100 mol) of HFDA was changed to 32.024 g (0.100 mol) of TFMB and the solvent used for the reaction and dilution was changed from GBL to NMP. A film was obtained in the same manner as in Example 1 using the obtained polyimide varnish.

[0080] Comparative Example 2 A polyimide varnish having a solid content concentration of 15 mass % was obtained in the same manner as in Example 1, except that 33.427 g (0.100 mol) of HFDA was changed to 33.624 g (0.100 mol) of 6FODA. A film was obtained in the same manner as in Example 1 using the obtained polyimide varnish.

[0081] Comparative Example 3 A polyimide varnish with a solids concentration of 15% by mass was obtained in the same manner as in Example 2, except that 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, and 20.056 g (0.060 mol) of HFDA was changed to 19.214 g (0.060 mol) of TFMB. A film was obtained in the same manner as in Example 1 using the obtained polyimide varnish.

[0082] Comparative Example 4 A polyimide varnish with a solids concentration of 15% by mass was obtained in the same manner as in Example 2, except that the amount of CpODA was changed from 38.438 g (0.100 mol) to 34.594 g (0.090 mol), 4.584 g (0.010 mol) of BPAF was used, HFDA was not used, the amount of BAFL was changed from 13.938 g (0.040 mol) to 15.680 g (0.045 mol), and 17.613 g (0.055 mol) of TFMB was used. A film was obtained in the same manner as in Example 1 using the obtained polyimide varnish.

[0083] Comparative Example 5 33.427 g (0.100 mol) of HFDA and 201.117 g of NMP were placed in a 300 mL five-neck round-bottom flask equipped with a stainless steel half-moon stirring blade, a nitrogen inlet tube, a Dean-Stark condenser, a thermometer, and a glass end cap, and the mixture was stirred at a system temperature of 25°C under a nitrogen atmosphere at a rotation speed of 200 rpm to obtain a solution. To this solution, 29.422 g (0.100 mol) of BPDA and 50.279 g of NMP were added all at once, and the mixture was stirred for 3 hours to obtain a polyamic acid varnish with a solid content of 20.0 mass %. The resulting polyamic acid varnish was then applied to a glass plate by spin coating, held on a hot plate at 80°C for 20 minutes, and then heated in a hot air dryer at 400°C for 60 minutes (heating rate 5°C / min) under a nitrogen atmosphere to evaporate the solvent and obtain a film.

[0084] The polyimide films obtained in the examples and comparative examples were subjected to the above-mentioned property measurements and evaluations. The results are shown in Table 1.

[0085] [Table 1]

[0086] As shown in Table 1, the polyimide films of the Examples were excellent in transparency and heat resistance when laminated with an inorganic film. Furthermore, the polyimide films of the Examples had good optical isotropy. Comparative Examples 1 and 2 were poor in optical isotropy and heat resistance of the laminated film. Comparative Examples 3 and 4 had good Tg, but were poor in optical isotropy and heat resistance of the laminated film. Comparative Example 5 had good optical isotropy, but was poor in Tg, colorless transparency, and heat resistance of the laminated film. Therefore, a polyimide film produced using an acid dianhydride having two norbornane skeletons in the molecule as the tetracarboxylic acid component and HFDA as the diamine component has excellent transparency, optical isotropy, and heat resistance of the laminated film, and can be suitably used as a transparent substrate for display devices such as liquid crystal displays, OLED displays, and touch panels.

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 includes a structural unit (A1) derived from a tetracarboxylic dianhydride having two norbornane skeletons in the molecule, The polyimide resin, wherein the structural unit B comprises a structural unit (B1) derived from a compound represented by the following formula (b1): 【Chemistry 1】

2. 2. The polyimide resin according to claim 1, wherein 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): 【Chemistry 2】

3. 3. 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): 【Transformation 3】

4. The polyimide resin according to any one of claims 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): 【Chemistry 4】 【Transformation 5】 【Transformation 6】

5. The polyimide resin according to claim 4, wherein the structural unit (B2) includes a structural unit (B21) derived from a compound represented by the following formula (b21): 【Transformation 7】

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

7. A polyimide film comprising the polyimide resin according to any one of claims 1 to 5.

8. 8. The polyimide film according to claim 7, which has a total light transmittance of 80% or more as measured in accordance with JIS K7136:2000.

9. 9. The polyimide film according to claim 7, which is used as a transparent substrate for a display device.

10. A method for producing a polyimide film, comprising the steps of applying or forming the polyimide varnish according to claim 6 into a film and then removing the organic solvent.

11. An image display device comprising the polyimide film according to any one of claims 7 to 9 as a transparent substrate.

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