Polyimide resin, polyimide varnish and polyimide film

Abstract

A polyimide resin comprising a structural unit A derived from tetracarboxylic dianhydride and a structural unit B derived from a diamine, wherein the structural unit A comprises a structural unit (A1) derived from 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), wherein the ratio of the structural unit (B1) in the structural unit B is 35 mol% or more and 95 mol% or less.

Description

Technical Field

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

[0002] Polyimide resins are being researched for various applications in the fields of electrical and electronic components. For example, with the goal of making devices lighter and more flexible, there is a desire to replace the glass substrates used in image display devices such as liquid crystal displays and OLED displays with plastic substrates. Consequently, research is underway into polyimide films suitable as such plastic substrates.

[0003] 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 is required to have transparency.

[0004] To meet the aforementioned performance requirements, polyimide resins with various compositions are being developed. For example, Patent Document 1 discloses a polyimide film comprising a structure formed by combining a dianhydride having a norbornane skeleton and 9,9-bis(4-aminophenyl)fluorene as a diamine component, with the goal of obtaining a polyimide film having excellent transparency and high heat resistance.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2019-059959 Summary of the Invention

[0008] Problems to be solved by the invention

[0009] Polyimide films are required to replace glass substrates and have high transparency.

[0010] When manufacturing image display devices, for example, a polyimide film laminated with an inorganic film is subjected to a heat treatment. Consequently, offgases generated from the polyimide film accumulate between the polyimide film and the inorganic film, sometimes causing the polyimide film to discolor, such as yellowing. Therefore, when polyimide films laminated with an inorganic film are exposed to high temperatures, heat resistance is required to suppress discoloration.

[0011] Furthermore, when manufacturing image display devices, process temperatures can reach, for example, over 400°C. Therefore, polyimide films used as substrates are required to have heat resistance that can withstand temperatures exceeding 400°C. Polyimide films with high glass transition temperatures (Tg) and excellent heat resistance can cause problems such as cracking in the inorganic films when exposed to high temperatures while laminated with them. Therefore, when polyimide films are laminated with inorganic films, they are required to have heat resistance that prevents cracking and other problems in the inorganic films.

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

[0013] Solutions for solving problems

[0014] The present inventors have discovered that a polyimide resin comprising a structural unit derived from tetracarboxylic dianhydride having two norbornane skeletons in the molecule and a structural unit derived from a specific diamine can solve the above-mentioned problems, thereby completing the invention.

[0015] That is, the present invention relates to the following <1> ~ <12> .

[0016] <1> A polyimide resin comprising a structural unit A derived from tetracarboxylic dianhydride and a structural unit B derived from 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] The ratio of the structural unit (B1) in the structural unit B is 35 mol% or more and 95 mol% or less.

[0020]

[0021] <2> according to <1> The polyimide resin, 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).

[0022]

[0023] <3> according to <1> or <2> The polyimide resin, wherein the structural unit A further includes a structural unit (A2), and the structural unit (A2) includes 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).

[0024]

[0025] <4> according to <1> ~ <3> The polyimide resin according to any one of the preceding claims, 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), a structural unit (B23) derived from a compound represented by the following formula (b23), and a structural unit (B24) derived from a compound represented by the following formula (b24).

[0026]

[0027]

[0028] <5> according to <4> The polyimide resin, wherein the structural unit (B2) includes a structural unit (B21) derived from a compound represented by the following formula (b21).

[0029]

[0030] <6> A polyimide varnish, which is <1> ~ <5> The polyimide resin described above is dissolved in an organic solvent.

[0031] <7> A polyimide film comprising <1> ~ <5> The polyimide resin described above.

[0032] <8> according to <7> The polyimide film has a tensile elongation at break of 9.5% or more as measured according to JIS K7127:1999 under the conditions of a chuck distance of 50 mm, a test piece size of 10 mm×70 mm, a tensile speed of 20 mm / min, and a measurement temperature of 23° C.

[0033] <9> according to <7> or <8> The polyimide film has a total light transmittance of 80% or more as measured according to JIS K 7136:2000.

[0034] <10> according to <7> ~ <9> The polyimide film described above is used as a transparent substrate constituting a display device.

[0035] <11> A method for manufacturing a polyimide film, comprising: <6> The process of removing the organic solvent after the polyimide varnish is coated or formed into a film.

[0036] <12> An image display device comprising <7> ~ <10> The polyimide film described above is used as a transparent substrate.

[0037] Effects of the Invention

[0038] The present invention can provide a polyimide film having excellent transparency and heat resistance when laminated with an inorganic film, a polyimide resin and a polyimide varnish, and a polyimide film having excellent transparency and heat resistance when laminated with an inorganic film. DETAILED DESCRIPTION

[0039] The mode for implementing the present invention (hereinafter referred to as "this embodiment") is described in detail. The following embodiment is an example for illustrating the present invention and does not limit the content of the present invention. The present invention can be implemented by appropriate modification within the scope of its main purpose. In this embodiment, any preferred provisions can be adopted, and it can be said that a combination of preferred provisions is more preferred. In this embodiment, the description of "XX to YY" means "greater than XX and less than YY".

[0040] [Polyimide resin]

[0041] The polyimide resin of the present invention is a polyimide resin comprising a structural unit A derived from tetracarboxylic dianhydride and a structural unit B derived from a diamine, wherein the structural unit A comprises a structural unit (A1) derived from 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), wherein the ratio of the structural unit (B1) in the structural unit B is 35 mol% or more and 95 mol% or less.

[0042]

[0043] The reason why the polyimide resin of the present invention can produce a polyimide film having excellent transparency and heat resistance when laminated with an inorganic film is not certain, but it is believed that since it has a norbornane skeleton and a structural unit (B1) that is nonlinear and has a small molecular weight, i.e., a high imide group concentration, it is possible to maintain good transparency and improve toughness and heat resistance, resulting in excellent transparency and heat resistance when laminated with an inorganic film (suppression of coloration, suppression of cracks in the inorganic film).

[0044] <Structural Unit A>

[0045] The structural unit A is a structural unit derived from tetracarboxylic dianhydride which occupies the polyimide resin.

[0046] The structural unit A includes a structural unit (A1) derived from tetracarboxylic dianhydride having two norbornane skeletons in the molecule.

[0047] 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 the structural unit (A11) derived from the compound represented by the following formula (a11), the structural unit (A12) derived from the compound represented by the following formula (a12), the structural unit (A13) derived from the compound represented by the following formula (a13) and the structural unit (A14) derived from the compound represented by the following formula (a14). From the viewpoint of making the molecular skeleton more rigid and further improving the heat resistance, it is more preferable to contain at least one selected from the group consisting of the structural unit (A11) derived from the compound represented by the following formula (a11), the structural unit (A12) derived from the compound represented by the following formula (a12) and the structural unit (A14) derived from the compound represented by the following formula. It is further preferable to contain at least one selected from the group consisting of the structural unit (A11) derived from the compound represented by the following formula (a11) and the structural unit (A14) derived from the compound represented by the following formula (a14). It is further preferable to contain the structural unit (A11) derived from the compound represented by the following formula (a11).

[0048]

[0049] When the structural unit A contains the structural unit (A1) derived from tetracarboxylic dianhydride having two norbornane skeletons in the molecule, the heat resistance, transparency, and optical isotropy of the obtained polyimide film can be improved.

[0050] 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 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).

[0051]

[0052] The compound represented by formula (a21) is biphenyltetracarboxylic dianhydride (BPDA). 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-BBDA) represented by the following formula (a211i). Among them, 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA) represented by the following formula (a211s) is preferred.

[0053]

[0054] 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 60 mol% or more, even more preferably 70 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, even more preferably 99 mol% or more. The upper limit of this ratio is not particularly limited, but is 100 mol% or less.

[0055] 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 40 mol% or less, even more preferably 30 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, even more preferably 1 mol% or less. The lower limit of this ratio is not particularly limited, but is 0.01 mol% or more.

[0056] Structural unit A may contain structural units other than structural unit (A1) and structural unit (A2). Tetracarboxylic dianhydrides providing such structural units are not particularly limited, and examples thereof include aromatic tetracarboxylic dianhydrides such as 4,4'-oxydiphthalic anhydride, pyromellitic dianhydride, and 4,4'-(hexafluoroisopropyl)diphthalic anhydride (excluding compounds represented by formula (a21) or (a22)); alicyclic tetracarboxylic dianhydrides such as 1,2,4,5-cyclohexanetetracarboxylic dianhydride and 1,2,3,4-cyclobutanetetracarboxylic dianhydride (excluding compounds represented by any one of formulas (a11) to (a14)); and aliphatic tetracarboxylic dianhydrides such as 1,2,3,4-butanetetracarboxylic dianhydride.

[0057] In this specification, aromatic tetracarboxylic dianhydride refers to a tetracarboxylic dianhydride containing one or more aromatic rings, alicyclic tetracarboxylic dianhydride refers to a tetracarboxylic dianhydride containing one or more alicyclic rings and no aromatic ring, and aliphatic tetracarboxylic dianhydride refers to a tetracarboxylic dianhydride containing neither an aromatic ring nor an alicyclic ring.

[0058] The structural unit arbitrarily contained in the structural unit A may be one type or two or more types.

[0059] <Structural Unit B>

[0060] The structural unit B is a structural unit derived from diamine contained in the polyimide resin.

[0061] The structural unit B includes a structural unit (B1) derived from a compound represented by the following formula (b1).

[0062]

[0063] The compound represented by formula (b1) is 1,3-phenylenediamine. When structural unit B includes structural unit (B1), toughness can be improved while maintaining heat resistance.

[0064] From the viewpoint of improving heat resistance when laminated with an inorganic film, the ratio of the structural unit (B1) in the structural unit B is 35 mol% or more, preferably 40 mol% or more, more preferably 45 mol% or more, even more preferably 50 mol% or more, and even more preferably 60 mol% or more. From the viewpoint of improving polymerizability, solubility, transparency, and optical isotropy, the ratio of the structural unit (B1) in the structural unit B is 95 mol% or less, preferably 90 mol% or less, more preferably 85 mol% or less, even more preferably 80 mol% or less, and even more preferably 75 mol% or less.

[0065] The structural unit B may contain structural units other than the structural unit (B1).

[0066] In addition to the structural unit (B1), the structural unit B also preferably includes a structural unit (B2). The structural unit (B2) is preferably 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), a structural unit (B23) derived from a compound represented by the following formula (b23), and a structural unit (B24) derived from a compound represented by the following formula (b24). From the viewpoint that the molecular skeleton becomes more rigid and the heat resistance is further improved, it is preferred to include at least one selected from the group consisting of a structural unit (B21) derived from a compound represented by the following formula (b21) and a structural unit (B23) derived from a compound represented by the following formula (b23), and further preferably includes a structural unit (B21) derived from a compound represented by the following formula (b21). By making the structural unit B include the structural unit (B2), heat resistance is particularly improved, and optical isotropy is also improved. In addition, by the structural unit (B2), the solubility of the imidized resin is improved, and polymerization can be performed more effectively.

[0067]

[0068] When the structural unit B further contains the structural unit (B2), the ratio of the structural unit (B2) in the structural unit B is preferably 5 mol% or more, more preferably 10 mol% or more, even more preferably 15 mol% or more, even more preferably 20 mol% or more, even more preferably 25 mol% or more. The upper limit of the ratio is 65 mol% or less, preferably 60 mol% or less, more preferably 55 mol% or less, even more preferably 50 mol% or less, even more preferably 40 mol% or less.

[0069] When the structural unit B further contains the structural unit (B2), the ratio of the total 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, further preferably 90 mol% or more, further preferably 95 mol% or more, further preferably 99 mol% or more. The upper limit of the ratio of the total 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).

[0070] 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 35 / 65 to 95 / 5, more preferably 40 / 60 to 90 / 10, further preferably 45 / 55 to 85 / 15, further preferably 50 / 50 to 80 / 20, and further preferably 60 / 40 to 75 / 25, from the viewpoint of improving transparency, optical isotropy, toughness and heat resistance.

[0071] Structural unit B may contain structural units other than structural unit (B1) and structural unit (B2). The diamine providing such structural units is not particularly limited, and examples thereof include 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-diaminodiphenylmethane, 4,4'-diaminobenzanilide, 1-(4-aminophenyl)-2,3-dihydro-1,3,3-trimethyl-1H-inden-5-amine, and α,α'-bis(4-aminophenyl)-1,4-diaminodiphenylmethane. Aromatic diamines such as isopropylbenzene, 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 the formulae (b1) and (b21) to (b24)); alicyclic diamines such as 1,3-bis(aminomethyl)cyclohexane and 1,4-bis(aminomethyl)cyclohexane; and aliphatic diamines such as ethylenediamine and hexamethylenediamine.

[0072] In this specification, aromatic diamine refers to a diamine containing one or more aromatic rings, alicyclic diamine refers to a diamine containing one or more alicyclic rings and no aromatic ring, and aliphatic diamine refers to a diamine containing neither an aromatic ring nor an alicyclic ring.

[0073] The structural unit arbitrarily contained in the structural unit B may be one type or two or more types.

[0074] <Characteristics of Polyimide Resin>

[0075] From the viewpoint of mechanical strength of the obtained polyimide film, the weight average molecular weight of the polyimide resin is preferably 5000 to 300000. The weight average molecular weight of the polyimide resin can be determined, for example, from a standard polymethyl methacrylate (PMMA) conversion value measured by gel filtration chromatography.

[0076] The polyimide resin may contain structures other than the polyimide chain (a structure formed by imide bonding between structural unit A and structural unit B). Examples of structures other than the polyimide chain that may be contained in the polyimide resin include structures containing amide bonds.

[0077] The polyimide resin preferably contains a polyimide chain (a structure formed by imide bonding of structural unit A and structural unit B) as a 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, further preferably 90% by mass or more, particularly preferably 99% by mass or more, and further preferably 100% by mass or less. The polyimide resin can also be composed only of polyimide chains.

[0078] The polyimide resin composition containing the above-mentioned polyimide resin can form a polyimide film having excellent toughness and heat resistance while maintaining transparency and optical isotropy. The preferred physical properties of the polyimide film are as follows.

[0079] When the polyimide resin is made into a film with a thickness of 10 μm, the total light transmittance is preferably 80% or more, more preferably 85% or more, further preferably 88% or more, further preferably 88.5% or more, and further preferably 89% or more.

[0080] When the polyimide resin is formed into a 10 μm thick film, the yellowness index (YI) is preferably 10.0 or less, more preferably 5.0 or less, further preferably 3.0 or less, further preferably 2.5 or less, and further preferably 2.0 or less.

[0081] The absolute value of the thickness retardation (Rth) is preferably 200 nm or less, more preferably 180 nm or less, further preferably 160 nm or less, and even more preferably 140 nm or less when the polyimide resin is made into a 10 μm thick film.

[0082] Furthermore, a film that can be formed using the polyimide resin has excellent mechanical properties and heat resistance and has the following suitable physical property values.

[0083] The tensile strength of the polyimide resin in a film having a thickness of 10 μm is preferably 70 MPa or more, more preferably 80 MPa or more, and even more preferably 90 MPa or more.

[0084] The tensile modulus of the polyimide resin, when formed into a 10 μm-thick film, is preferably 1.0 GPa or more, more preferably 1.5 GPa or more, further preferably 2.0 GPa or more, and even more preferably 2.3 GPa or more.

[0085] When the polyimide resin is formed into a film having a thickness of 10 μm, the tensile elongation at break is preferably 9.5% or greater, more preferably 10.0% or greater, and even more preferably 10.5% or greater. The upper limit of the tensile elongation at break is preferably 20.0% or less, more preferably 15.0% or less, and even more preferably 13.5% or less.

[0086] The glass transition temperature (Tg) is preferably 380°C or higher, more preferably 400°C or higher, and even more preferably 410°C or higher.

[0087] The 5% weight loss temperature (Td5%) is preferably 460°C or higher, more preferably 470°C or higher, and even more preferably 480°C or higher.

[0088] Regarding the heat resistance when an inorganic film is stacked, a SiO2 film with a thickness of 300 nm is formed on a polyimide film by sputtering, and an ITO (indium tin oxide) film with a thickness of 1230 nm is formed thereon to make a stacked film. It is preferred that "annealing treatment at 400°C for 1 hour" does not cause cracks, yellowing and other adverse conditions on the stacked film, and it is more preferred that "annealing treatment at 420°C for 1 hour" does not cause cracks, yellowing and other adverse conditions on the stacked film.

[0089] It should be noted that the above-mentioned physical property values in the present invention can be specifically measured by the methods described in the Examples.

[0090] <Production Method of Polyimide Resin>

[0091] 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 compound that provides the above-mentioned structural unit (B1).

[0092] As the compound providing the structural unit (A1), a compound represented by any one of formulas (a11) to (a14) can be mentioned, but it is not limited thereto and may be a derivative thereof within the scope of providing the same structural unit. As such derivatives, tetracarboxylic acids corresponding to the tetracarboxylic dianhydride represented by any one of formulas (a11) to (a14) and alkyl esters of such tetracarboxylic acids can be mentioned. Among them, tetracarboxylic dianhydride represented by formula (a11) is preferred.

[0093] The tetracarboxylic acid component may contain a compound providing the structural unit (A2) in addition to the compound providing the structural unit (A1).

[0094] Examples of the compound providing the structural unit (A2) include compounds represented by formula (a21) and compounds represented by formula (a22), but are not limited thereto and may be derivatives thereof as long as they provide the same structural unit.

[0095] The tetracarboxylic acid component preferably contains 40 mol% or more of the compound providing the structural unit (A1), more preferably 60 mol% or more, further preferably 70 mol% or more, further preferably 80 mol% or more, further preferably 85 mol% or more, further preferably 90 mol% or more, further preferably 95 mol% or more, further preferably 99 mol% or more. The upper limit of this ratio is not particularly limited, but is 100 mol% or less.

[0096] 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).

[0097] Examples of such an optional compound include the above-mentioned aromatic tetracarboxylic dianhydride, alicyclic tetracarboxylic dianhydride, and aliphatic tetracarboxylic dianhydride, and derivatives thereof (tetracarboxylic acid, alkyl esters of tetracarboxylic acid, and the like).

[0098] The compound arbitrarily contained in the tetracarboxylic acid component may be one kind or two or more kinds.

[0099] As the compound providing the structural unit (B1), the compound represented by formula (b1) can be mentioned, but it is not limited thereto. The derivative thereof can also be mentioned within the scope of providing the same structural unit. As the derivative, the diisocyanate corresponding to the compound represented by formula (b1) can be mentioned. As the compound providing the structural unit (B1), the compound represented by formula (b1) (i.e., diamine) is preferred.

[0100] In addition to the compound providing the structural unit (B1), the diamine component may also include a compound providing the structural unit (B2). As the compound providing the structural unit (B2), the compound shown in formula (b21), the compound shown in formula (b22), the compound shown in formula (b23), the compound shown in formula (b24), etc. can be cited, but it is not limited thereto. Within the scope of providing the same structural unit, it can also be a derivative thereof. As the derivative, the diisocyanate corresponding to the compound shown in formula (b21), the compound shown in formula (b22), the compound shown in formula (b23) and the compound shown in formula (b24) can be cited. As the compound providing the structural unit (B2), the compound shown in formula (b21), the compound shown in formula (b22), the compound shown in formula (b23) and the compound shown in formula (b24) (i.e., diamine) are preferred.

[0101] The diamine component contains 35 mol% or more of the compound providing the structural unit (B1), preferably 40 mol% or more, more preferably 45 mol% or more, further preferably 50 mol% or more, and even more preferably 60 mol% or more. The upper limit of this ratio is 95 mol% or less, preferably 90 mol% or less, more preferably 85 mol% or less, even more preferably 80 mol% or less, and even more preferably 75 mol% or less.

[0102] When the diamine component contains a compound that provides the structural unit (B2), the compound that provides the structural unit (B2) is preferably contained in an amount of 5 mol% or more, more preferably 10 mol% or more, even more preferably 15 mol% or more, even more preferably 20 mol% or more, and even more preferably 25 mol% or more. The upper limit of this ratio is 65 mol% or less, preferably 60 mol% or less, more preferably 55 mol% or less, even more preferably 50 mol% or less, and even more preferably 40 mol% or less.

[0103] In the case of a diamine component containing a compound providing structural units (B2), the total amount of the compound providing structural units (B1) and the compound providing structural units (B2) is preferably 50 mol% or more, more preferably 70 mol% or more, further preferably 90 mol% or more, further preferably 95 mol% or more, and further preferably 99 mol% or more. The upper limit is not particularly limited, but the total amount of the compound providing structural units (B1) and the compound providing structural units (B2) is, for example, 100 mol% or less. The diamine component may also be composed solely of a compound providing structural units (B1) and a compound providing structural units (B2).

[0104] From the viewpoint of improving polymerizability, solubility, transparency, optical isotropy, toughness, and heat resistance, the molar ratio of the compound providing the structural unit (B1) to the compound providing the structural unit (B2) in the diamine component [(B1) / (B2)] is preferably 35 / 65 to 95 / 5, more preferably 40 / 60 to 90 / 10, even more preferably 45 / 55 to 85 / 15, even more preferably 50 / 50 to 80 / 20, and even more preferably 60 / 40 to 75 / 25.

[0105] The diamine component may further contain an arbitrary compound other than the compound providing the structural unit (B1) and the compound providing the structural unit (B2).

[0106] Examples of such optional compounds include the above-mentioned aromatic diamines, alicyclic diamines, and aliphatic diamines, and derivatives thereof (such as diisocyanates).

[0107] The compound arbitrarily contained in the diamine component may be one kind or two or more kinds.

[0108] In the production of the polyimide resin of the present invention, the charging amount ratio of the tetracarboxylic acid component to the diamine component used in the production of the polyimide resin is preferably 0.9 to 1.1 mol of the diamine component per 1 mol of the tetracarboxylic acid component.

[0109] In addition, in the manufacture of the polyimide resin of the present invention, in addition to the above-mentioned tetracarboxylic acid component and diamine component, an end-capping agent can also be used in the manufacture of the polyimide resin. As the end-capping agent, monoamines or dicarboxylic acids are preferred. The amount of the introduced end-capping agent is preferably 0.0001 to 0.1 moles relative to 1 mole of the tetracarboxylic acid component, and more preferably 0.001 to 0.06 moles. As monoamine end-capping agents, 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 mentioned, preferably benzylamine and aniline. As dicarboxylic acid end-capping agents, dicarboxylic acids are preferred, and a portion thereof can also be ring-closed. 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. are mentioned, and phthalic acid and phthalic anhydride are preferable.

[0110] There is no restriction|limiting in particular about the method for making the said tetracarboxylic-acid component and diamine component react, A well-known method can be used.

[0111] Specific reaction methods include the following: (1) a method in which a tetracarboxylic acid component, a diamine component, and a reaction solvent are placed in a reactor, stirred at 0 to 10° C. for 0.5 to 30 hours, and then the temperature is raised to carry out an imidization reaction; (2) a method in which a diamine component and a reaction solvent are placed in a reactor and dissolved, and then a tetracarboxylic acid component is placed in the reactor and stirred at room temperature of 0 to 10° C. for 0.5 to 30 hours as needed, and then the temperature is raised to carry out an imidization reaction; (3) a method in which a tetracarboxylic acid component, a diamine component, and a reaction solvent are placed in a reactor and the temperature is immediately raised to carry out an imidization reaction; and the like.

[0112] 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 produced polyimide, and examples thereof include aprotic solvents, phenolic solvents, ether solvents, and carbonate solvents.

[0113] 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 hexamethylphosphoramide and hexamethylphosphorotriamide; 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.

[0114] Specific examples of the phenolic solvent 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.

[0115] Specific examples of the ether solvent include 1,2-dimethoxyethane, bis(2-methoxyethyl)ether, 1,2-bis(2-methoxyethoxy)ethane, bis[2-(2-methoxyethoxy)ethyl]ether, tetrahydrofuran, and 14-dioxane.

[0116] Specific examples of carbonate-based solvents include diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, and propylene carbonate.

[0117] Among the above reaction solvents, aprotic solvents are preferred, amide solvents and lactone solvents are more preferred, and lactone solvents are further preferred. The above reaction solvents may be used alone or in combination of two or more.

[0118] In the imidization reaction, it is preferred to use a Dean-Stark water trap or the like to carry out the reaction while removing water generated during the production. By performing such an operation, the degree of polymerization and the imidization rate can be further increased.

[0119] In the above-mentioned imidization reaction, a known imidization catalyst can be used. Examples of the imidization catalyst include a base catalyst and an acid catalyst.

[0120] 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 bicarbonate, and sodium bicarbonate.

[0121] Examples of the acid catalyst include crotonic acid, acrylic acid, trans-3-hexenoic acid, cinnamic acid, benzoic acid, methylbenzoic acid, hydroxybenzoic acid, terephthalic acid, benzenesulfonic acid, p-toluenesulfonic acid, and naphthalenesulfonic acid. These imidization catalysts may be used alone or in combination of two or more.

[0122] Among the above, from the viewpoint of operability, it is preferred to use a base catalyst, more preferably an organic base catalyst, and still more preferably triethylamine or triethylenediamine.

[0123] From the viewpoints of reaction rate and gelation suppression, the temperature of the imidization reaction is preferably 120 to 250° C., more preferably 160 to 200° C. The reaction time is preferably 0.5 to 10 hours after the start of distillation of generated water.

[0124] [Polyimide varnish]

[0125] 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.

[0126] The organic solvent is not particularly limited as long as it dissolves the polyimide resin. As the reaction solvent used in the production of the polyimide resin, it is preferred to use the above-mentioned compounds alone or in combination of two or more.

[0127] The polyimide varnish of the present invention may be a polyimide solution itself in which a polyimide resin obtained by a polymerization method is dissolved in a reaction solvent, or may be a polyimide solution obtained by further adding a solvent and diluting the polyimide solution.

[0128] Because the polyimide resin of the present invention is solvent-soluble, it can be used as a high-concentration varnish that is 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, and more preferably contains 5 to 20% by mass. The viscosity of the polyimide varnish is preferably 1 to 200 Pa·s, and 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.

[0129] 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 the range that the required properties of the polyimide film are not impaired.

[0130] The method for producing the polyimide varnish of the present invention is not particularly limited, and a known method can be applied.

[0131] [Polyimide film]

[0132] The polyimide film of the present invention comprises the polyimide resin of the present invention. Therefore, the polyimide film of the present invention exhibits excellent 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 as "Polyimide Resin Characteristics."

[0133] The method for producing the polyimide film of the present invention is not particularly limited, and known methods can be used. For example, methods include applying the polyimide varnish of the present invention to a smooth support such as a glass plate, a metal plate, or a plastic substrate, or forming the polyimide varnish into a film, and then removing organic solvents such as the reaction solvent and the dilution solvent contained in the varnish by heating. The method for producing the polyimide film of the present invention preferably includes the step of removing the organic solvent after applying or forming the polyimide varnish into a film.

[0134] Examples of coating methods include spin coating, slit coating, and blade coating, with spin coating and slit coating being preferred. Slit coating is more preferred from the viewpoint of workability because it controls molecular orientation and improves chemical resistance.

[0135] As a 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 less to render it viscous, followed by drying at a temperature above the boiling point of the organic solvent used (not particularly limited, but preferably 200-500°C). Drying is preferably performed in an air atmosphere or a nitrogen atmosphere. The pressure of the drying atmosphere may be any of reduced pressure, normal pressure, and pressurized pressure.

[0136] The method for peeling the polyimide film formed on the support from the support is not particularly limited, and a mechanical peeling method, a laser peeling method, or the like can be used.

[0137] The polyimide film of the present invention can also be produced using a polyamic acid varnish in which polyamic acid is dissolved in an organic solvent.

[0138] 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 comprising the compound providing the structural unit (A1) and a diamine component comprising the compound providing the structural unit (B1). By imidizing (dehydration ring closure) the polyamic acid, the polyimide resin of the present invention can be obtained as a final product.

[0139] 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.

[0140] In the production of the polyimide film of the present invention, the polyamic acid varnish may be a polyamic acid solution obtained by subjecting a tetracarboxylic acid component and a diamine component to an addition polymerization reaction in a reaction solvent, or may be a polyamic acid solution diluted by further adding a solvent.

[0141] There is no particular restriction on the method for using polyamic acid varnish to manufacture polyimide film, and known methods can be used. For example, polyamic acid varnish is coated into a film or formed into a film on a smooth support such as a glass plate, a metal plate, or plastics, and then the polyamic acid film is obtained by removing organic solvents such as a reaction solvent and a diluting solvent contained in the varnish by heating. The polyamic acid in the polyamic acid film is imidized by heating to manufacture polyimide film.

[0142] The heating temperature when drying the polyamic acid varnish to obtain a polyamic acid film is preferably 50 to 120° C. The heating temperature when imidizing the polyamic acid by heating is preferably 200 to 450° C.

[0143] It should be noted that the imidization method is not limited to thermal imidization, and chemical imidization may also be applied.

[0144] The thickness of the polyimide film of the present invention can be appropriately selected depending on the application, and is preferably in the range of 1 to 250 μm, more preferably 5 to 100 μm, further preferably 8 to 80 μm, and even more preferably 10 to 80 μm. A thickness of 1 to 250 μm allows practical use as a self-supporting film.

[0145] The thickness of the polyimide film can be easily controlled by adjusting the solid content concentration and viscosity of the polyimide varnish.

[0146] In the polyimide film of the present invention, the tensile elongation at break, as measured in accordance with JIS K7127:1999 under the conditions of a chuck distance of 50 mm, a sample size of 10 mm x 70 mm, a tensile speed of 20 mm / min, and a measurement temperature of 23° C., is preferably 9.5% or greater, more preferably 10.0% or greater, and even more preferably 10.5% or greater, from the perspective of further suppressing cracking of the inorganic film when exposed to high temperatures in a state where the film is laminated with the inorganic film. The upper limit of the tensile elongation at break is preferably 20.0% or less, more preferably 15.0% or less, and even more preferably 13.5% or less.

[0147] 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, further preferably 88% or more, further preferably 88.5% or more, and further preferably 89% or more from the viewpoint of further improving transparency.

[0148] 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.

[0149] [Image Display Device]

[0150] The image display device of the present invention includes the polyimide film of the present invention as a transparent substrate.

[0151] The image display device of the present invention includes, for example, a transparent substrate composed of the polyimide film of the present invention and a display unit provided on the transparent substrate.

[0152] The display portion is not particularly limited, and examples thereof include TFT elements, organic EL elements, color filters, LEDs, transistors, electron emission elements, electronic ink, electrophoretic elements, GLVs (grating light valves), display elements using MEMS (microelectromechanical systems), DMDs (digital micromirror devices), DMSs (digital microshutters), IMODs (interferometry modulation) elements, electrowetting elements, piezoelectric ceramic displays, and display elements using carbon nanotubes.

[0153] Examples of the image display device of the present invention include a liquid crystal display, an OLED display, and a touch panel.

[0154] 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.

[0155] 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. Therefore, cracks in the inorganic film and coloration of the transparent substrate are unlikely to occur, and the device has excellent reliability.

[0156] Example

[0157] Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples.

[0158] <Film Properties and Evaluation>

[0159] The physical properties of the thin films obtained in Examples and Comparative Examples were measured by the methods shown below.

[0160] (1) Film thickness

[0161] The film thickness was measured using a micrometer manufactured by Mitutoyo Corporation.

[0162] (2) Tensile strength, tensile modulus and tensile elongation at break

[0163] Tensile strength, tensile modulus, and tensile elongation at break were measured in accordance with JIS K7127:1999 using a tensile testing machine "Strograph VG-1E" manufactured by Toyo Seiki Co., Ltd. The chuck spacing was 50 mm, the test piece size was 10 mm × 70 mm, the test speed (tensile speed) was 20 mm / min, and the measurement temperature was 23°C.

[0164] (3) Glass transition temperature (Tg)

[0165] Using a Hitachi High-Tech Science Corporation TMA / SS6100 thermomechanical analyzer, the sample was heated to a temperature sufficient to eliminate residual stress in the tensile mode, with a sample size of 3 mm x 20 mm, a load of 0.1 N, and a heating rate of 10°C / min. The sample was then cooled to room temperature, with residual stress removed. The elongation of the test piece was then measured under the same conditions as for the residual stress removal treatment. The inflection point of the elongation was extrapolated to determine the glass transition temperature.

[0166] (4) Total light transmittance and yellowness index (YI)

[0167] The total light transmittance was measured in accordance with JIS K7136:2000, and the YI was measured in accordance with ASTM E313-05 (illuminant D, 65°) using a simultaneous colorimeter and haze analyzer "COH7700" manufactured by Nippon Denshoku Industries, Ltd.

[0168] (5) 5% weight loss temperature (Td5%)

[0169] The NEXTA STA200RV, a simultaneous differential thermal and thermogravimetric measurement system manufactured by Hitachi High-Tech Science Corporation, was used. The sample was heated to 40-150°C at a rate of 10°C / min, held at 150°C for 30 minutes, and then heated to 510°C after removing moisture. 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. A higher value for the weight loss temperature indicates better heat resistance.

[0170] (6) Thickness Retardation (Rth) (Evaluation of Optical Isotropy)

[0171] 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. It should be noted that Rth is expressed by the following formula, where the maximum refractive index in the plane of the polyimide film is set as nx, the minimum is set as ny, the refractive index in the thickness direction is set as nz, and the thickness of the film is set as d.

[0172] Rth=[{(nx+ny) / 2}-nz]×d

[0173] (7) Evaluation of heat resistance of laminated films

[0174] A laminated film was produced by simulating 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.

[0175] Without peeling the polyimide films obtained in the examples and comparative examples from the glass plate, 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 thereon to obtain a laminated film.

[0176] Next, the obtained laminated film was annealed (heated) at 400° C. for 1 hour.

[0177] The laminated film was visually observed before and after annealing to determine if there were any defects (cracks, yellowing, etc.), and the heat resistance of the polyimide film laminated with the inorganic film (laminated film) was evaluated according to the following criteria.

[0178] ○: No cracks, yellowing, or other defects occurred in the laminated film before and after annealing

[0179] × (cracks or yellowing): cracks, yellowing, and other defects occur in the laminated film before and after annealing

[0180] If there are no problems, the polyimide film laminated with the inorganic film has excellent heat resistance.

[0181] <Abbreviations of ingredients, etc.>

[0182] The tetracarboxylic acid component and the diamine component used in Examples and Comparative Examples, and their abbreviations are as follows.

[0183] (Tetracarboxylic acid component)

[0184] 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))

[0185] BPDA: 3,3',4,4'-biphenyltetracarboxylic dianhydride (manufactured by Mitsubishi Chemical Corporation, compound represented by formula (a211s) (s-BPDA))

[0186] BPAF: 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride (manufactured by JFE Chemical Co., Ltd.; compound represented by formula (a22))

[0187] (Diamine component)

[0188] MPD: 1,3-phenylenediamine (manufactured by Tokyo Chemical Industry Co., Ltd.; compound represented by formula (b1))

[0189] BAFL: 9,9-bis(4-aminophenyl)fluorene (manufactured by JFE Chemical Co., Ltd.; compound represented by formula (b21))

[0190] TFMB: 2,2'-bis(trifluoromethyl)benzidine (manufactured by Seika Corporation; compound represented by formula (b22))

[0191] PPD: 1,4-phenylenediamine (manufactured by Tokyo Chemical Industry Co., Ltd.)

[0192] <Manufacturing of polyimide resin, varnish and polyimide film>

[0193] Example 1

[0194] In a 500 mL five-necked round-bottom flask equipped with a stainless steel half-moon-shaped stirring blade, a nitrogen inlet tube, a Dean-Stark trap equipped with a condenser, a thermometer, and glass end caps, 5.407 g (0.050 mol) of MPD, 17.423 g (0.050 mol) of BAFL, and 73.521 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation) were placed, and the mixture was stirred at a temperature of 70° C., a nitrogen atmosphere, and a rotation speed of 200 rpm to obtain a solution.

[0195] To this solution, 38.438 g (0.100 mol) of CpODA and 18.380 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation) were added simultaneously. Then, 0.506 g of triethylamine (manufactured by Kanto Chemical Co., Ltd.) and 0.056 g of triethylenediamine (manufactured by Tokyo Chemical Industry Co., Ltd.) were added as an imidization catalyst. The mixture was heated in a mantle heater, and the temperature within the reaction system was raised to 190°C over approximately 20 minutes. The components removed by distillation were collected, and the reaction system was refluxed for 3 hours while maintaining the temperature at 190°C, adjusting the rotational speed according to the increase in viscosity.

[0196] Thereafter, γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation) was added to give a solid content concentration of 15% by mass, and the temperature in the reaction system was cooled to 100° C., followed by further stirring for about 1 hour to achieve homogenization, thereby obtaining a polyimide varnish.

[0197] Next, the obtained polyimide varnish was applied to a glass plate by spin coating, maintained at 80°C for 20 minutes on a hot plate, and then heated at 400°C for 30 minutes (heating rate 5°C / min) in a hot air dryer under a nitrogen atmosphere to evaporate the solvent and obtain a thin film.

[0198] Example 2

[0199] A polyimide varnish having a solid content concentration of 15% by mass was obtained by the same method as in Example 1, except that the amount of MPD was changed from 5.407 g (0.050 mol) to 7.570 g (0.070 mol) and the amount of BAFL was changed from 17.423 g (0.050 mol) to 10.454 g (0.030 mol).

[0200] A film was obtained by the same method as in Example 1 using the obtained polyimide varnish.

[0201] Example 3

[0202] A polyimide varnish having a solid content concentration of 15% by mass was obtained by the same method as in Example 1, except that the amount of MPD was changed from 5.407 g (0.050 mol) to 8.651 g (0.080 mol) and the amount of BAFL was changed from 17.423 g (0.050 mol) to 6.969 g (0.020 mol).

[0203] A film was obtained by the same method as in Example 1 using the obtained polyimide varnish.

[0204] Example 4

[0205] A polyimide varnish having a solid content concentration of 15% by mass was obtained by the same method as in Example 1, except that the amount of CpODA was changed from 38.438 g (0.100 mol) to 30.750 g (0.080 mol), 5.885 g (0.020 mol) of BPDA was used, the amount of MPD was changed from 5.407 g (0.050 mol) to 6.488 g (0.060 mol), and the amount of BAFL was changed from 17.423 g (0.050 mol) to 13.938 g (0.040 mol).

[0206] A film was obtained by the same method as in Example 1 using the obtained polyimide varnish.

[0207] Example 5

[0208] A polyimide varnish having a solid content concentration of 15% by mass was obtained by the same method as in Example 1, 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, the amount of MPD was changed from 5.407 g (0.050 mol) to 6.488 g (0.060 mol), and the amount of BAFL was changed from 17.423 g (0.050 mol) to 13.938 g (0.040 mol).

[0209] A film was obtained by the same method as in Example 1 using the obtained polyimide varnish.

[0210] Comparative Example 1

[0211] A polyimide varnish having a solid content concentration of 15% by mass was obtained by the same method as in Example 1 except that MPD was not used and the amount of BAFL was changed from 17.423 g (0.050 mol) to 34.845 g (0.100 mol).

[0212] A film was obtained by the same method as in Example 1 using the obtained polyimide varnish.

[0213] Comparative Example 2

[0214] A polyimide varnish having a solid content concentration of 15% by mass was obtained by the same method 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), BPDA 11.769 g (0.040 mol) was used, MPD was not used, the amount of BAFL was changed from 17.423 g (0.050 mol) to 13.938 g (0.040 mol), and TFMB 19.214 g (0.060 mol) was used.

[0215] A film was obtained by the same method as in Example 1 using the obtained polyimide varnish.

[0216] Comparative Example 3

[0217] The amount of CpODA was changed from 38.438 g (0.100 mol) to 34.594 g (0.090 mol), BPAF 4.584 g (0.010 mol) was used, MPD was not used, the amount of BAFL was changed from 17.423 g (0.050 mol) to 15.680 g (0.045 mol), TFMB 17.613 g (0.055 mol) was used, and except that, a polyimide varnish having a solid content concentration of 15% by mass was obtained by the same method as in Example 1.

[0218] A film was obtained by the same method as in Example 1 using the obtained polyimide varnish.

[0219] Comparative Example 4

[0220] Synthesis was attempted by the same method as in Example 2 except that 7.570 g (0.070 mol) of MPD was replaced with 7.570 g (0.070 mol) of PPD. However, after adding the imidization catalyst, solids precipitated during imidization during heating to 190° C., and no polyimide varnish could be obtained.

[0221] Comparative Example 5

[0222] Into a 300 mL five-necked round-bottom flask equipped with a stainless steel half-moon-shaped stirring blade, a nitrogen inlet tube, a Dean-Stark trap equipped with a condenser, a thermometer, and glass end caps, 10.814 g (0.100 mol) of MPD and 182.403 g of NMP were placed, and the mixture was stirred at 200 rpm under a nitrogen atmosphere at an internal temperature of 25° C. to obtain a solution.

[0223] 29.422 g (0.100 mol) of BPDA and 45.601 g of NMP were simultaneously added to this solution, and the mixture was stirred for 3 hours to obtain a polyamic acid varnish having a solid content concentration of 15.0% by mass.

[0224] Next, the obtained polyamic acid varnish was applied on a glass plate by spin coating, maintained at 80°C for 20 minutes on a hot plate, and then heated at 430°C for 60 minutes (heating rate 5°C / min) in a hot air dryer under a nitrogen atmosphere to evaporate the solvent and obtain a thin film.

[0225] Comparative Example 6

[0226] A polyimide varnish having a solid content concentration of 15% by mass was obtained by the same method as in Example 1 except that 16.012 g (0.050 mol) of TFMB was used as the diamine instead of MPD.

[0227] A film was obtained by the same method as in Example 1 using the obtained polyimide varnish.

[0228] Comparative Example 7

[0229] A synthesis was attempted by the same method as in Example 1, except that the amount of MPD was changed from 5.407 g (0.050 mol) to 10.814 g (0.100 mol) and BAFL was not used. However, after the imidization catalyst was added, solids precipitated during imidization during the process of heating to 190° C., and a polyimide varnish could not be obtained.

[0230] The polyimide films obtained in the Examples and Comparative Examples were subjected to the above-mentioned physical property measurements and evaluations. The obtained results are shown in Table 1.

[0231] [Table 1]

[0232]

[0233] As shown in Table 1, the polyimide films of the examples are excellent in transparency and heat resistance when laminated with an inorganic film. Furthermore, it can be seen that the polyimide films of the examples are good in optical isotropy. Comparative Examples 1 and 6 are excellent in optical isotropy, but the heat resistance of the laminated films is poor. Comparative Example 2 is poor in optical isotropy and heat resistance of the laminated film. Comparative Example 3 is poor in heat resistance of the laminated film. Comparative Examples 4 and 7 precipitate due to the poor solubility of the imidized resin, so polymerization is not performed thereafter, and a polyimide varnish cannot be obtained. Comparative Example 5 is poor in transparency, optical isotropy, and heat resistance of the laminated film.

[0234] Therefore, a polyimide film produced using an acid dianhydride having two norbornane skeletons in the molecule as the tetracarboxylic acid component and MPD as the diamine component has excellent transparency, optical isotropy, and heat resistance as a laminated film and can be suitably used as a transparent substrate constituting display devices such as liquid crystal displays, OLED displays, and touch panels.

Claims

1. A polyimide resin comprising a structural unit A derived from tetracarboxylic dianhydride and a structural unit B derived from a diamine, The structural unit A comprises a structural unit (A1) derived from tetracarboxylic dianhydride having two norbornane skeletons in the molecule, in, 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 ratio of the structural unit (A1) in the structural unit A is 80 mol% or more, 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 (B1) in the structural unit B is 35 mol% or more and 95 mol% or less, The structural unit B further includes a structural unit (B2), wherein the structural unit (B2) 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), a structural unit (B23) derived from a compound represented by the following formula (b23), and a structural unit (B24) derived from a compound represented by the following formula (b24). The molar ratio of the structural unit (B1) to the structural unit (B2) in the structural unit B, i.e., (B1) / (B2), is 35 / 65 to 95 / 5.

2. The polyimide resin according to claim 1, wherein The structural unit A further includes a structural unit (A2), wherein the structural unit (A2) includes 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 (B2) includes a structural unit (B21) derived from a compound represented by the following formula (b21), A polyimide varnish comprising the polyimide resin according to any one of claims 1 to 3 dissolved in an organic solvent. A polyimide film comprising the polyimide resin according to any one of claims 1 to 3.

6. The polyimide film according to claim 5, wherein the tensile elongation at break measured under the conditions of chuck distance: 50 mm, sample size: 10 mm x 70 mm, tensile speed: 20 mm / min, and measurement temperature: 23°C in accordance with JIS K7127:1999 is 9.5% or more. The polyimide film according to claim 5 or 6, which has a total light transmittance of 80% or more as measured in accordance with JIS K7136:2000.

8. The polyimide film according to claim 5 or 6, which is used as a transparent substrate constituting a display device.

9. A method for producing a polyimide film, comprising the steps of applying or molding the polyimide varnish according to claim 4 into a film and then removing the organic solvent. 10 . An image display device comprising the polyimide film according to claim 5 as a transparent substrate.

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