Polyimide resin, polyimide varnish and polyimide film

Abstract

A polyimide resin having a structural unit A derived from a tetracarboxylic acid dianhydride and a structural unit B derived from a diamine, wherein the structural unit A includes a structural unit (A-1) derived from a compound represented by formula (a-1), and the structural unit B includes a structural unit (B-1) derived from a compound represented by formula (b-1) and a structural unit (B-2) derived from a compound represented by formula (b-2).

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 electric and electronic components, etc. For example, it is desirable to replace 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 being conducted on polyimide films suitable for such plastic substrates. In an image display device, when light emitted from a display element is emitted through a plastic substrate, the plastic substrate is required to be colorless and transparent. However, when light passes through a retardation film or a polarizing plate (for example, a liquid crystal display, a touch panel, etc.), in addition to colorless transparency, the substrate is required to have high optical isotropy (i.e., low Rth).

[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 containing a structure consisting of a combination of 3,3'-diaminodiphenylsulfone and another specific diamine as a diamine component, with the aim of obtaining a polyimide film that contains a polyamide having good solubility in a solvent and excellent processability, is colorless and transparent, and has excellent toughness. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2016 / 158825 Summary of the Invention [Problem to be solved by the invention]

[0005] As described above, polyimide films are required to have good optical properties such as colorless transparency and optical isotropy. Optical isotropy is particularly important for applications such as liquid crystal displays. On the other hand, polyimide has a rigid and strong molecular structure, so breakage has been an issue during film production or when used in products with moving parts. When highly flexible components are introduced into the molecule to prevent breakage or additives are added to the resin, the optical properties generally deteriorate. Thus, there has been a demand for polyimide films that have good optical properties and ductility. Furthermore, chemical resistance is also important. For example, when a varnish for forming a resin layer (e.g., a color filter or resist) is applied to a polyimide film in order to form the resin layer on the polyimide film, the polyimide film is required to have resistance to the solvent contained in the varnish. If the solvent resistance of the polyimide film is insufficient, the film may dissolve or swell, making it useless as a substrate. However, in order to ensure the optical properties as described above, the polyimide film must be in the form of a solution when it is produced, and it has been difficult to achieve both of these properties. Thus, there has been a demand for a polyimide resin capable of giving a polyimide film having flexibility and excellent chemical resistance while maintaining the optical properties, particularly optical isotropy, of the resulting polyimide film. Therefore, an object of the present invention is to provide a polyimide resin, a polyimide varnish, and a polyimide film which are capable of forming a film having excellent optical isotropy, flexibility, and chemical resistance. [Means for solving the problem]

[0006] The present inventors discovered that a polyimide resin containing a combination of structural units derived from a specific tetracarboxylic dianhydride and structural units derived from two specific types of diamines can solve the above-mentioned problems, and thus completed the invention.

[0007] That is, the present invention provides the following <1> ~ <8> Regarding. <1> A polyimide resin having a structural unit A derived from a tetracarboxylic dianhydride and a structural unit B derived from a diamine, wherein the structural unit A includes a structural unit (A-1) derived from a compound represented by the following formula (a-1), and the structural unit B includes a structural unit (B-1) derived from a compound represented by the following formula (b-1), and a structural unit (B-2) derived from a compound represented by the following formula (b-2):

[0008] [ka]

[0009] <2> The ratio of the structural unit (B-1) in the structural unit B is 5 to 80 mol %, and the ratio of the structural unit (B-2) in the structural unit B is 20 to 95 mol %. <1> The polyimide resin according to claim 1. <3> The molar ratio of the structural unit (B-1) to the structural unit (B-2) in the structural unit B [(B-1) / (B-2)] is 5 / 95 to 80 / 20. <1> or <2> The polyimide resin according to claim 1. <4> The structural unit A further contains at least one selected from the group consisting of a structural unit (A-2-1) derived from a compound represented by the following formula (a-2-1) and a structural unit (A-2-2) derived from a compound represented by the following formula (a-2-2): <1> ~ <3> 10. The polyimide resin according to claim 9,

[0010] [ka]

[0011] <5> The structural unit B further comprises at least one selected from the group consisting of a structural unit (B-3-1) derived from a compound represented by the following formula (b-3-1) and a structural unit (B-3-2) derived from a compound represented by the following formula (b-3-2): <1> ~ <4> 10. The polyimide resin according to claim 9,

[0012] [ka] (In formula (b-3-1), Z 1 and Z 2 each independently represents a divalent aliphatic group or a divalent aromatic group which may contain an oxygen atom; R 1 and R 2 each independently represents a monovalent aromatic group or a monovalent aliphatic group; R 3 and R 4 each independently represents a monovalent aliphatic group; R 5 and R 6 each independently represents a monovalent aliphatic group or a monovalent aromatic group, m and n each independently represent an integer of 1 or more, and the sum of m and n represents an integer of 2 to 1000. 1 and R 2 At least one of represents a monovalent aromatic group.

[0013] <6> R in the above formula (b-3-1) 1 and R 2 is a phenyl group. <5> The polyimide resin according to claim 1. <7> the above <1> ~ <6> 2. A polyimide varnish obtained by dissolving the polyimide resin according to any one of 1 to 11 in an organic solvent. <8> the above <1> ~ <6> 13. A polyimide film comprising the polyimide resin according to claim 12. Effect of the Invention

[0014] According to the present invention, it is possible to provide a polyimide resin, a polyimide varnish, and a polyimide film which are capable of forming a film having excellent optical isotropy, flexibility, and chemical resistance. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] [Polyimide resin] The polyimide resin of the present invention is a polyimide resin having a structural unit A derived from a tetracarboxylic dianhydride and a structural unit B derived from a diamine, in which the structural unit A contains a structural unit (A-1) derived from a compound represented by the following formula (a-1), and the structural unit B contains a structural unit (B-1) derived from a compound represented by the following formula (b-1), and a structural unit (B-2) derived from a compound represented by the following formula (b-2). resin.

[0016] [ka]

[0017] Although the reason why the polyimide resin of the present invention has excellent flexibility and chemical resistance while maintaining optical isotropy is unclear, it is believed that the polyimide resin of the present invention has excellent flexibility and chemical resistance while maintaining optical isotropy because it has an alicyclic structure, an ether skeleton, and an aromatic group in an appropriate ratio. In particular, it is believed that the polyimide resin of the present invention has a high imide group concentration because it has a small diamine-derived constitutional unit having an alicyclic structure in its structure, and therefore has excellent chemical resistance while maintaining optical isotropy.

[0018] <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 (A-1) derived from a compound represented by the following formula (a-1).

[0019] [ka]

[0020] The compound represented by formula (a-1) is 4,4'-oxydiphthalic anhydride. When the structural unit A contains the structural unit (A-1), the chemical resistance and toughness of the film can be improved.

[0021] The ratio of the structural unit (A-1) in the structural unit A is preferably 40 mol% or more, more preferably 50 mol% or more, even more preferably 55 mol% or more, and even more preferably 60 mol% or more. From the viewpoint of the toughness of the film, it is more preferably 70 mol% or more. The upper limit of the ratio of the structural unit (A-1) is not particularly limited, that is, it is 100 mol%. The structural unit A may be composed of only the structural unit (A-1).

[0022] The structural unit A may contain a structural unit other than the structural unit (A-1). In addition to the structural unit (A-1), from the viewpoint of heat resistance, the structural unit A preferably contains at least one structural unit (A-2) selected from the group consisting of a structural unit (A-2-1) derived from a compound represented by the following formula (a-2-1) and a structural unit (A-2-2) derived from a compound represented by the following formula (a-2-2). That is, the structural unit (A-2-1) and the structural unit (A-2-2) are collectively referred to as the structural unit (A-2).

[0023] [ka]

[0024] The compound represented by formula (a-2-1) is 1,2,4,5-cyclohexanetetracarboxylic dianhydride. The compound represented by formula (a-2-2) is norbornane-2-spiro-α-cyclopentanone-α'-spiro-2″-norbornane-5,5″,6,6″-tetracarboxylic acid dianhydride. From the viewpoint of improving heat resistance, chemical resistance, and optical isotropy, the ratio of the structural unit (A-2) in the structural unit A is preferably 10 to 50 mol %, more preferably 15 to 45 mol %, and even more preferably 20 to 40 mol %. When the structural unit A contains the structural unit (A-2), the molar ratio of the structural unit (A-1) to the structural unit (A-2) in the structural unit A [(A-1) / (A-2)] is, from the viewpoint of improving heat resistance, chemical resistance, and optical isotropy, preferably from 50 / 50 to 90 / 10, more preferably from 55 / 45 to 85 / 15, and even more preferably from 60 / 40 to 80 / 20.

[0025] The structural unit A may contain structural units other than the structural unit (A-1) and the structural unit (A-2). The tetracarboxylic dianhydride that gives such a structural unit is not particularly limited, but includes aromatic tetracarboxylic dianhydrides such as pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 9,9'-bis(3,4-dicarboxyphenyl)fluorene dianhydride, and 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (excluding the compound represented by formula (a-1)); alicyclic tetracarboxylic dianhydrides such as 1,2,3,4-cyclobutanetetracarboxylic dianhydride (excluding the compounds represented by formula (a-2-1) and formula (a-2-2)); and aliphatic tetracarboxylic dianhydrides such as 1,2,3,4-butanetetracarboxylic dianhydride. In this specification, the term "aromatic tetracarboxylic acid dianhydride" refers to a tetracarboxylic acid dianhydride containing one or more aromatic rings, the term "alicyclic tetracarboxylic acid dianhydride" refers to a tetracarboxylic acid dianhydride containing one or more alicyclic rings but no aromatic rings, and the term "aliphatic tetracarboxylic acid dianhydride" refers to 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 of one type, or of two or more types.

[0026] <Structural unit B> The structural unit B is a structural unit derived from a diamine contained in the polyimide resin, and includes a structural unit (B-1) derived from a compound represented by the following formula (b-1) and a structural unit (B-2) derived from a compound represented by the following formula (b-2).

[0027] [ka] The compound represented by formula (b-1) is 4,4'-diamino-2,2'-bistrifluoromethyldiphenyl ether. When the structural unit B contains the structural unit (B-1), the optical isotropy and colorless transparency of the film can be improved.

[0028] The compound represented by formula (b-2) is bis(aminomethyl)cyclohexane, and specific examples thereof include 1,3-bis(aminomethyl)cyclohexane represented by the following formula (b-2a) and 1,4-bis(aminomethyl)cyclohexane represented by the following formula (b-2b).

[0029] [ka] The cis:trans ratio of the compound represented by formula (b-2) is preferably 0:100 to 80:20, more preferably 0.1:99.9 to 70:30, even more preferably 0.5:99.5 to 60:40, and even more preferably 1:99 to 20:80, from the viewpoints of organic solvent resistance and heat resistance. When the structural unit B contains the structural unit (B-2), the optical isotropy, flexibility, and chemical resistance of the film can be improved.

[0030] The proportion of the structural unit (B-1) in the structural unit B is preferably from 5 to 80 mol %, more preferably from 10 to 70 mol %, and even more preferably from 30 to 60 mol %. The proportion of the structural unit (B-2) in the structural unit B is preferably from 20 to 95 mol %, more preferably from 30 to 90 mol %, and even more preferably from 40 to 70 mol %. The total ratio of the structural units (B-1) and (B-2) in the structural unit B is preferably 50 mol% or more, more preferably 70 mol% or more, and even more preferably 90 mol% or more. The upper limit of the total ratio of the structural units (B-1) and (B-2) is not particularly limited, that is, it is 100 mol%. The structural unit B may be composed of only the structural unit (B-1) and the structural unit (B-2). From the viewpoint of improving optical isotropy and chemical resistance, the molar ratio of the structural unit (B-1) to the structural unit (B-2) in the structural unit B [(B-1) / (B-2)] is preferably 5 / 95 to 80 / 20, more preferably 10 / 90 to 70 / 30, and even more preferably 30 / 70 to 60 / 40.

[0031] The structural unit B may contain structural units other than the structural units (B-1) and (B-2). In addition to the structural units (B-1) and (B-2), the structural unit B preferably contains at least one structural unit (B-3) selected from the group consisting of the structural unit (B-3-1) derived from a compound represented by the following formula (b-3-1) and the structural unit (B-3-2) derived from a compound represented by the following formula (b-3-2). That is, the structural unit (B-3-1) and the structural unit (B-3-2) are collectively referred to as the structural unit (B-3). In particular, it is preferred that the structural unit B further contains the structural unit (B-3-1) derived from a compound represented by the following formula (b-3-1).

[0032] [ka]

[0033] In formula (b-3-1), Z 1 and Z 2 each independently represents a divalent aliphatic group or a divalent aromatic group which may contain an oxygen atom; R 1 and R 2 each independently represents a monovalent aromatic group or a monovalent aliphatic group; R 3 and R 4 each independently represents a monovalent aliphatic group; R 5 and R6 each independently represents a monovalent aliphatic group or a monovalent aromatic group, m and n each independently represent an integer of 1 or more, and the sum of m and n represents an integer of 2 to 1000. 1 and R 2 At least one of these represents a monovalent aromatic group. In addition, in formula (b-3-1), two or more different repeating units described in [ ] may be repeated in any form and order of random, alternating, or block, regardless of the order of [ ].

[0034] In formula (b-3-1), Z 1 and Z 2 The divalent aliphatic group or divalent aromatic group in may be substituted with a fluorine atom. Examples of the divalent aliphatic group include a divalent saturated or unsaturated aliphatic group having 1 to 20 carbon atoms and an aliphatic group containing an oxygen atom. The divalent aliphatic group preferably has 3 to 20 carbon atoms. Examples of the divalent saturated aliphatic group include alkylene groups having 1 to 20 carbon atoms, such as a methylene group, an ethylene group, a propylene group, a trimethylene group, a tetramethylene group, a hexamethylene group, an octamethylene group, a decamethylene group, and a dodecamethylene group. The divalent unsaturated aliphatic group may be an alkylene group having 2 to 20 carbon atoms, such as a vinylene group, a propenylene group, or an alkylene group having an unsaturated double bond at a terminal. Examples of the aliphatic group containing an oxygen atom include an alkyleneoxy group and an aliphatic group having an ether bond. Examples of the alkyleneoxy group include a propyleneoxy group and a trimethyleneoxy group. Examples of the divalent aromatic group include an arylene group having 6 to 20 carbon atoms and an aralkylene group having 7 to 20 carbon atoms. 1 and Z 2 Specific examples of the arylene group having 6 to 20 carbon atoms in the formula include an o-phenylene group, an m-phenylene group, a p-phenylene group, a 4,4'-biphenylylene group, and a 2,6-naphthylene group. Z 1 and Z 2As the alkyl group, a trimethylene group or a p-phenylene group is particularly preferable, and a trimethylene group is more preferable.

[0035] In formula (b-3-1), R 1 ~R 6 In the above, examples of the monovalent aliphatic group include monovalent saturated or unsaturated aliphatic groups. Examples of the monovalent saturated aliphatic group include alkyl groups having 1 to 22 carbon atoms, such as methyl, ethyl, and propyl groups. Examples of the monovalent unsaturated aliphatic group include alkenyl groups having 2 to 22 carbon atoms, such as vinyl and propenyl groups. These groups may be substituted with a fluorine atom. R in formula (b-3-1) 1 , R 2 , R 5 and R 6 Examples of the monovalent aromatic group in the formula (I) include an aryl group having 6 to 20 carbon atoms, an aryl group having 7 to 30 carbon atoms and substituted with an alkyl group, and an aralkyl group having 7 to 30 carbon atoms. As the monovalent aromatic group, an aryl group is preferable, and a phenyl group is more preferable. R 1 and R 2 At least one of R represents a monovalent aromatic group. 1 and R 2 are preferably both monovalent aromatic groups, and R 1 and R 2 More preferably, both are phenyl groups. R 3 and R 4 As the alkyl group, an alkyl group having 1 to 6 carbon atoms is preferable, and a methyl group is more preferable. R 5 and R 6 As the group, a monovalent aliphatic group is preferable, and a methyl group is more preferable.

[0036] As described above, among the compounds represented by formula (b-3-1), the compounds represented by the following formula (b-3-11) are preferred.

[0037] [ka] (In formula (b-3-11), m and n have the same meanings as m and n in formula (b-3-1), and the preferred ranges are also the same.)

[0038] In formulas (b-3-1) and (b-3-11), m represents the number of repeating siloxane units to which at least one monovalent aromatic group is bonded, and n in formulas (b-3-1) and (b-3-11) represents the number of repeating siloxane units to which a monovalent aliphatic group is bonded. In formula (b-3-1) and formula (b-3-11), m and n each independently represent an integer of 1 or more, and the sum of m and n (m+n) represents an integer of 2 to 1000. The sum of m and n preferably represents an integer of 3 to 500, more preferably an integer of 3 to 100, and even more preferably an integer of 3 to 50. The ratio of m / n in formula (b-3-1) and formula (b-3-11) is preferably from 5 / 95 to 50 / 50, more preferably from 10 / 90 to 40 / 60, and further preferably from 20 / 80 to 30 / 70.

[0039] The functional group equivalent (amine equivalent) of the compound represented by formula (b-3-1) is preferably 150 to 5,000 g / mol, more preferably 400 to 4,000 g / mol, and even more preferably 500 to 3,000 g / mol. The functional group equivalent means the mass of the compound represented by formula (b-3-1) per mole of the functional group (amino group).

[0040] Among the compounds represented by formula (b-3-1), commercially available products include "X-22-9409", "X-22-1660B", "X-22-161A", and "X-22-161B" manufactured by Shin-Etsu Chemical Co., Ltd.

[0041] When the structural unit B contains the structural unit (B-3-1), the colorless transparency, optical isotropy, and flexibility of the film can be improved.

[0042] The formula (b-3-2) is 4,4'-diaminodiphenylsulfone. When the structural unit B contains the structural unit (B-3-2), the colorless transparency, toughness, and chemical resistance of the film can be improved.

[0043] When the structural unit B contains the structural unit (B-1), the structural unit (B-2), and the structural unit (B-3), the total proportion of the structural units (B-1) and (B-2) in the structural unit B is preferably 70 mol % or more, more preferably 80 mol % or more, and even more preferably 90 mol % or more, and the proportion of the structural unit (B-3) in the structural unit B is preferably 0.1 to 30 mol %, more preferably 1 to 25 mol %, even more preferably 2 to 20 mol %, and still more preferably 3 to 15 mol %. The total ratio of the structural unit (B-1), the structural unit (B-2) and the structural unit (B-3) in the structural unit B is preferably 80 mol% or more, more preferably 90 mol% or more, and particularly preferably 99 mol% or more. The upper limit of the total ratio of the structural unit (B-1), the structural unit (B-2) and the structural unit (B-3) is not particularly limited, that is, it is 100 mol%. The structural unit B may be composed of only the structural unit (B-1), the structural unit (B-2) and the structural unit (B-3).

[0044] When the structural unit B contains the structural unit (B-1), the structural unit (B-2), and the structural unit (B-3-1), the total proportion of the structural units (B-1) and (B-2) in the structural unit B is preferably 70 mol% or more, more preferably 80 mol% or more, and even more preferably 90 mol% or more, and the proportion of the structural unit (B-3-1) in the structural unit B is preferably 0.1 to 30 mol%, more preferably 1 to 25 mol%, even more preferably 2 to 20 mol%, still more preferably 3 to 15 mol%, and even more preferably 3 to 10 mol%. The total ratio of the structural unit (B-1), the structural unit (B-2) and the structural unit (B-3-1) in the structural unit B is preferably 80 mol% or more, more preferably 90 mol% or more, and particularly preferably 99 mol% or more. The upper limit of the total ratio of the structural unit (B-1), the structural unit (B-2) and the structural unit (B-3-1) is not particularly limited, that is, it is 100 mol%. The structural unit B may be composed of only the structural unit (B-1), the structural unit (B-2) and the structural unit (B-3-1).

[0045] When the structural unit B contains the structural unit (B-1), the structural unit (B-2), and the structural unit (B-3-2), the total ratio of the structural unit (B-1) and the structural unit (B-2) in the structural unit B is preferably 70 mol% or more, more preferably 80 mol% or more, and even more preferably 90 mol% or more. From the viewpoints of the colorless transparency, toughness, and chemical resistance of the film, the ratio of the structural unit (B-3-2) in the structural unit B is preferably 2 to 30 mol%, more preferably 3 to 30 mol%, even more preferably 10 to 30 mol%, still more preferably 15 to 30 mol%, and even more preferably 15 to 25 mol%. The total ratio of the structural unit (B-1), the structural unit (B-2) and the structural unit (B-3-2) in the structural unit B is preferably 80 mol% or more, more preferably 90 mol% or more, and particularly preferably 99 mol% or more. The upper limit of the total ratio of the structural unit (B-1), the structural unit (B-2) and the structural unit (B-3-2) is not particularly limited, that is, it is 100 mol%. The structural unit B may be composed of only the structural unit (B-1), the structural unit (B-2) and the structural unit (B-3-2).

[0046] The structural unit (B-3) may be only the structural unit (B-3-1), or only the structural unit (B-3-2), or a combination of the structural unit (B-3-1) and the structural unit (B-3-2).

[0047] The structural unit B may contain a structural unit other than the structural units (B-1), (B-2) and (B-3). Diamines that provide such structural units are not particularly limited, but include 1,4-phenylenediamine, p-xylylenediamine, 1,5-diaminonaphthalene, 2,2'-dimethylbiphenyl-4,4'-diamine, 4,4'-diaminodiphenylether, 4,4'-diaminodiphenylmethane, 2,2-bis(4-aminophenyl)hexafluoropropane, 4,4'-diaminobenzanilide, 1-(4-aminophenyl)-2,3-dihydro-1,3,3-trimethyl-1H-inden-5-amine, α,α'-bis(4-aminophenyl)-1,4-diisopropylbenzene, N,N'-bis(4- aromatic diamines such as 4,4'-bis(4-aminophenoxy)biphenyl, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis(4-(4-aminophenoxy)phenyl)hexafluoropropane, and 9,9-bis(4-aminophenyl)fluorene (excluding the compounds represented by formula (b-1), (b-3-1), and (b-3-2)); alicyclic diamines (excluding the compounds represented by formula (b-2)); and aliphatic diamines such as ethylenediamine and hexamethylenediamine. In this specification, an aromatic diamine refers to a diamine containing one or more aromatic rings, an alicyclic diamine refers to a diamine containing one or more alicyclic rings but no aromatic rings, and an aliphatic diamine refers to a diamine containing neither an aromatic ring nor an alicyclic ring. The structural units other than the structural units (B-1), (B-2), and (B-3) optionally contained in the structural unit B may be of one type, or of two or more types.

[0048] <Characteristics of polyimide resin> From the viewpoint of the mechanical strength of the resulting polyimide film, the number average molecular weight of the polyimide resin is preferably 5,000 to 300,000. The number 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.

[0049] The polyimide resin may contain a structure other than a polyimide chain (a structure formed by imide bonding between a structural unit A and a structural unit B). Examples of structures other than a polyimide chain that can be contained in a polyimide resin include a structure containing an amide bond. The polyimide resin preferably contains, as a main structure, a polyimide chain (a structure formed by imide bonding between the structural unit A and the structural unit B). Therefore, the ratio of the polyimide chain in the polyimide resin is preferably 50 mass % or more, more preferably 70 mass % or more, even more preferably 90 mass % or more, and particularly preferably 99 mass % or more.

[0050] The polyimide resin composition of the present invention containing the above polyimide resin can be formed into a film that is excellent in colorless transparency, optical isotropy and chemical resistance, and the suitable physical properties of the film are as follows.

[0051] The total light transmittance, when made into a film having a thickness of 10 μm, is preferably 88% or more, more preferably 88.5% or more, and further preferably 89% or more. The yellow index (YI) when made into a film having a thickness of 10 μm is preferably 4.5 or less, more preferably 3.0 or less, even more preferably 2.0 or less, and still more preferably 1.5 or less. The absolute value of the thickness retardation (Rth) is preferably 70 nm or less, more preferably 60 nm or less, and further preferably 50 nm or less, when the film has a thickness of 10 μm.

[0052] Furthermore, a film that can be formed using the polyimide resin has good mechanical properties and heat resistance, and has the following preferable physical properties. A film that can be formed using the polyimide resin of the present invention has good mechanical properties and heat resistance, and has the following preferable physical properties. The tensile strength is preferably 70 MPa or more, more preferably 80 MPa or more, and further preferably 90 MPa or more. The tensile modulus is preferably 2.0 GPa or more, more preferably 2.5 GPa or more, and further preferably 3.0 GPa or more. The breaking elongation is preferably 8% or more, more preferably 10% or more, and further preferably 15% or more. The glass transition temperature (Tg) is preferably 200° C. or higher, more preferably 230° C. or higher, and further preferably 250° C. or higher. The above-mentioned physical properties in the present invention can be specifically measured by the methods described in the Examples.

[0053] <Method of manufacturing polyimide resin> In the present invention, the polyimide resin can be produced by reacting a tetracarboxylic acid component containing a compound that provides the above-mentioned structural unit (A-1) with a diamine component containing a compound that provides the above-mentioned structural unit (B-1) and a compound that provides the above-mentioned structural unit (B-2).

[0054] Compounds that give the structural unit (A-1) include compounds represented by formula (a-1), but are not limited thereto, and may be derivatives thereof as long as they give the same structural unit. Examples of the derivatives include tetracarboxylic acids (i.e., 4,4'-oxydiphthalic acid) corresponding to the tetracarboxylic dianhydride represented by formula (a-1) and alkyl esters of the tetracarboxylic acid. Among these, the tetracarboxylic dianhydride represented by formula (a-1) is preferred.

[0055] The tetracarboxylic acid component contains the compound that gives the structural unit (A-1) in an amount of preferably 40 mol% or more, more preferably 50 mol% or more, and even more preferably 70 mol% or more. The upper limit of the content of the compound that gives the structural unit (A-1) is not particularly limited, that is, it is 100 mol%. The tetracarboxylic acid component may be composed of only the compound that gives the structural unit (A-1).

[0056] The tetracarboxylic acid component may contain a compound other than the compound that provides the structural unit (A-1).

[0057] The tetracarboxylic acid component may further contain a compound that provides the structural unit (A-2), in addition to the compound that provides the structural unit (A-1). Compounds that provide the structural unit (A-2) include compounds represented by formula (a-2-1) and formula (a-2-2), but are not limited thereto, and may be derivatives thereof as long as they provide the same structural unit. Examples of the derivatives include tetracarboxylic acids corresponding to the compounds represented by formula (a-2-1) and formula (a-2-2) and alkyl esters of the tetracarboxylic acids. Compounds that provide the structural unit (A-2) are preferably compounds represented by formula (a-2-1) and formula (a-2-2) (i.e., dianhydrides).

[0058] When the tetracarboxylic acid component contains a compound that provides the structural unit (A-2), the tetracarboxylic acid component preferably contains the compound that provides the structural unit (A-2) in an amount of 10 to 50 mol %, more preferably 15 to 45 mol %, and even more preferably 20 to 40 mol %.

[0059] Compounds other than the compound that gives the structural unit (A-1) optionally contained in the tetracarboxylic acid component are not limited to compounds that give the structural unit (A-2). Examples of 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 compounds optionally contained in the tetracarboxylic acid component other than the compound providing the structural unit (A-1) and the compound providing the structural unit (A-2) may be one type or two or more types.

[0060] The compound that gives the structural unit (B-1) may be a compound represented by formula (b-1), but is not limited thereto, and may be a derivative thereof as long as it gives the same structural unit. The derivative may be a diisocyanate corresponding to the compound (diamine) represented by formula (b-1). Among them, the compound (i.e., diamine) represented by formula (b-1) is preferred. Similarly, the compound that gives the structural unit (B-2) may be a compound represented by formula (b-2), but is not limited thereto, and may be a derivative thereof as long as it gives the same structural unit. The derivative may be a diisocyanate corresponding to the compound (diamine) represented by formula (b-2). The compound that gives the structural unit (B-2) is preferably a compound represented by formula (b-2) (i.e., a diamine).

[0061] The diamine component contains the compound that provides the structural unit (B-1) in an amount of preferably 5 to 80 mol %, more preferably 10 to 70 mol %, and even more preferably 30 to 60 mol %. The diamine component contains the compound that provides the structural unit (B-2) in an amount of preferably 20 to 95 mol %, more preferably 30 to 90 mol %, and even more preferably 40 to 70 mol %. The diamine component contains a compound that gives the structural unit (B-1) and a compound that gives the structural unit (B-2) in a total amount of preferably 50 mol% or more, more preferably 70 mol% or more, and more preferably 90 mol% or more. The upper limit of the total content of the compound that gives the structural unit (B-1) and the compound that gives the structural unit (B-2) is not particularly limited, that is, it is 100 mol%. The diamine component may be composed of only the compound that gives the structural unit (B-1) and the compound that gives the structural unit (B-2).

[0062] The diamine component may contain compounds other than the compound that provides the structural unit (B-1) and the compound that provides the structural unit (B-2).

[0063] The diamine component may further contain a compound that provides the structural unit (B-3), in addition to the compound that provides the structural unit (B-1) and the compound that provides the structural unit (B-2). Compounds that give the structural unit (B-3) include compounds represented by formula (b-3-1) and compounds represented by formula (b-3-2), but are not limited thereto, and may be derivatives thereof as long as they give the same structural unit. Examples of the derivatives include diisocyanates corresponding to the diamines represented by formula (b-3-1) and diisocyanates corresponding to the diamines represented by formula (b-3-2). Compounds that give the structural unit (B-3) are preferably compounds represented by formula (b-3-1) and compounds represented by formula (b-3-2) (i.e., diamines).

[0064] The compound that provides the structural unit (B-3) may be only a compound represented by formula (b-3-1), may be only a compound represented by formula (b-3-2), or may be a combination of a compound represented by formula (b-3-1) and a compound represented by formula (b-3-2).

[0065] When the diamine component contains a compound that provides the structural unit (B-3), the diamine component contains the compound that provides the structural unit (B-3) in an amount of preferably 0.1 to 30 mol %, more preferably 1 to 25 mol %, and even more preferably 5 to 25 mol %. When the diamine component contains a compound that gives the structural unit (B-3), the diamine component contains a compound that gives the structural unit (B-1), a compound that gives the structural unit (B-2), and a compound that gives the structural unit (B-3) in total, preferably 80 mol% or more, more preferably 90 mol% or more, and even more preferably 99 mol% or more. The upper limit of the total content of the compound that gives the structural unit (B-1), the compound that gives the structural unit (B-2), and the compound that gives the structural unit (B-3) is not particularly limited, that is, it is 100 mol%. The diamine component may be composed of only the compound that gives the structural unit (B-1), the compound that gives the structural unit (B-2), and the compound that gives the structural unit (B-3).

[0066] Compounds other than the compound that gives the structural unit (B-1) and the compound that gives the structural unit (B-2) that are optionally contained in the diamine component are not limited to compounds that give the structural unit (B-3). Such optional compounds include the above-mentioned aromatic diamines, alicyclic diamines, and aliphatic diamines, and their derivatives (diisocyanates, etc.). The compound optionally contained in the diamine component other than the compound providing the structural unit (B-1) and the compound providing the structural unit (B-2) may be one type or two or more types.

[0067] In the present invention, the ratio of the amounts of the tetracarboxylic acid component and 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.

[0068] In the present invention, in addition to the above-mentioned tetracarboxylic acid component and diamine component, a terminal blocking agent may be used in the production of the polyimide resin. As the terminal blocking agent, monoamines or dicarboxylic acids are preferred. The amount of the terminal blocking agent to be 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 the monoamine terminal blocking agent include methylamine, ethylamine, propylamine, butylamine, benzylamine, 4-methylbenzylamine, 4-ethylbenzylamine, 4-dodecylbenzylamine, 3-methylbenzylamine, 3-ethylbenzylamine, aniline, 3-methylaniline, and 4-methylaniline, and benzylamine and aniline are preferred. As the dicarboxylic acid terminal blocking agent, dicarboxylic acids are preferred, and a part of them 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, and preferably phthalic acid and phthalic anhydride.

[0069] The method for reacting the tetracarboxylic acid component and the diamine component is not particularly limited, 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 80°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 a tetracarboxylic acid component is charged, and the mixture is stirred at room temperature (0 to 80°C) for 0.5 to 30 hours as necessary, 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.

[0070] 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. Examples of the solvent include aprotic solvents, phenolic solvents, ether solvents, and carbonate solvents.

[0071] Specific examples of aprotic solvents include amide-based solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone (NMP), N-methylcaprolactam, 1,3-dimethylimidazolidinone, and tetramethylurea; lactone-based solvents such as γ-butyrolactone (GBL) and γ-valerolactone; phosphorus-containing amide-based solvents such as hexamethylphosphoric amide and hexamethylphosphine triamide; sulfur-containing solvents such as dimethyl sulfone, dimethyl sulfoxide, and sulfolane; ketone-based solvents such as acetone, cyclohexanone, and methylcyclohexanone; amine-based solvents such as picoline and pyridine; and ester-based solvents such as 2-methoxy-1-methylethyl acetate.

[0072] 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, and amide solvents and lactone solvents are more preferred. The above reaction solvents may be used alone or in combination of two or more.

[0073] In the imidization reaction, it is preferable to carry out the reaction while removing water generated during the production using a Dean-Stark apparatus, etc. By carrying out such an operation, it is possible to further increase the degree of polymerization and the imidization rate.

[0074] In the above 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 kinds. Among the above, from the viewpoint of ease of handling, it is preferable to use a base catalyst, it is more preferable to use an organic base catalyst, and it is even more preferable to use triethylamine.

[0075] The temperature of the imidization reaction is preferably 120 to 250° C., more preferably 160 to 200° C., from the viewpoints of 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.

[0076] [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. However, it is preferable to use the above-mentioned compounds as reaction solvents used in the production of the polyimide resin, either alone or in combination of two or more kinds. 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 diluted with an additional solvent.

[0077] Since the polyimide resin of the present invention has solvent solubility, it 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 10 to 30 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. In addition, the polyimide varnish of the present invention may contain various additives such as inorganic fillers, adhesion promoters, release agents, flame retardants, UV stabilizers, surfactants, leveling agents, defoamers, 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 any known method can be applied.

[0078] [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 optical isotropy, flexibility and chemical resistance. The preferable physical properties of the polyimide film of the present invention are as described above. The method for producing the polyimide film of the present invention is not particularly limited, and a known method 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, or formed into a film, and then organic solvents such as a reaction solvent and a dilution solvent contained in the varnish are removed by heating.

[0079] Examples of the coating method include known coating methods such as spin coating, slit coating, blade coating, etc. Among these, slit coating is preferred from the viewpoints of controlling intermolecular orientation and improving chemical resistance, as well as workability. A method for removing the organic solvent contained in the varnish by heating is preferably to evaporate the organic solvent at a temperature of 150°C or less to make it tack-free, and then to dry it at a temperature equal to or higher than the boiling point of the organic solvent used (not particularly limited, but preferably 200 to 500°C). It is also preferable to dry it in an air atmosphere or a nitrogen atmosphere. The pressure of the drying atmosphere may be reduced pressure, normal pressure, or increased pressure. The method for peeling off the polyimide film formed on the support from the support is not particularly limited, but examples thereof include a laser lift-off method, a method using a sacrificial layer for peeling (a method in which a release agent is applied in advance to the surface of the support), and a method of adding a release agent.

[0080] The polyimide film of the present invention can also be produced by using a polyamic acid varnish prepared by dissolving a 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 polyaddition reaction between a tetracarboxylic acid component containing a compound that gives the above-mentioned structural unit (A-1) and a diamine component containing a compound that gives the above-mentioned structural unit (B-1) and a compound that gives the structural unit (B-2). The polyamic acid is imidized (dehydration ring closure) to obtain the polyimide resin of the present invention, which is the final product. 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 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 an additional solvent.

[0081] The method for producing a polyimide film using the polyamic acid varnish is not particularly limited, and a 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, or formed into a film, and the organic solvent contained in the varnish, such as a reaction solvent or a dilution solvent, is 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 400° C. The imidization method is not limited to thermal imidization, and chemical imidization can also be applied.

[0082] 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. When the thickness is 1 to 250 μm, practical use as a free-standing film becomes possible. The thickness of the polyimide film can be easily controlled by adjusting the solids concentration and viscosity of the polyimide varnish.

[0083] The polyimide film of the present invention is suitably used as a film for various members such as color filters, flexible displays, semiconductor parts, optical members, etc. The polyimide film of the present invention is particularly suitably used as a substrate for image display devices such as liquid crystal displays and OLED displays. EXAMPLES

[0084] The present invention will be described in detail below with reference to examples, although the present invention is not limited to these examples in any way.

[0085] <Film properties and evaluation> The physical properties of the films obtained in the examples and comparative examples were measured by the methods shown below.

[0086] (1) Film thickness The film thickness was measured using a micrometer manufactured by Mitutoyo Corporation.

[0087] (2) Tensile strength, tensile modulus, and tensile elongation at break (tensile elongation at break is an evaluation of flexibility) The tensile strength, tensile modulus and tensile elongation at break were measured in accordance with JIS K7127:1999 using a tensile tester "Strograph VG-1E" manufactured by Toyo Seiki Co., Ltd. The chuck distance was 50 mm, the test piece size was 10 mm × 70 mm, and the test speed was 20 mm / min.

[0088] (3) 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 the residual stress under the following conditions: sample size 2mm x 20mm, load 0.1N, and heating rate 10℃ / min in tensile mode, and then cooled to room temperature. The specimen elongation was then measured under the same conditions as in the treatment for removing the residual stress, and the point at which an inflection point in the elongation was observed was determined as the glass transition temperature.

[0089] (4) Total light transmittance and yellow index (YI) The total light transmittance and YI were measured in accordance with JIS K7136 using a color / turbidity simultaneous measuring instrument "COH7700" manufactured by Nippon Denshoku Industries Co., Ltd.

[0090] (5) Hayes The measurements were performed in accordance with JIS K7361-1 using a color and turbidity simultaneous measuring device "COH7700" manufactured by Nippon Denshoku Industries Co., Ltd.

[0091] (6) 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 the maximum in-plane refractive index of the polyimide film is nx, the minimum is ny, the refractive index in the thickness direction is nz, and the thickness of the film is d. Rth converted to a film thickness of 10 μm was also calculated. Rth = [{(nx + ny) / 2}-nz] × d

[0092] (7) Solvent resistance (evaluation of chemical resistance) The polyimide film formed on the glass plate was immersed in a solvent at room temperature to check whether there was any change in the film surface. The solvent used was propylene glycol monomethyl ether acetate (PGMEA). The evaluation criteria for solvent resistance were as follows. ○: No change was observed on the film surface. △: Slight cracks occurred on the film surface. ×: The film surface was cracked or dissolved.

[0093] <Abbreviations for ingredients, etc.> The tetracarboxylic acid components and diamine components used in the examples and comparative examples, and their abbreviations, are as follows:

[0094] (Tetracarboxylic acid component) ODPA: 4,4'-oxydiphthalic anhydride (manufactured by Manac Corporation; compound represented by formula (a-1)) HPMDA: 1,2,4,5-cyclohexanetetracarboxylic dianhydride (manufactured by Mitsubishi Gas Chemical Company, Inc.; compound represented by formula (a-2-1)) CpODA: norbornane-2-spiro-α-cyclopentanone-α'-spiro-2″-norbornane-5,5″,6,6″-tetracarboxylic dianhydride (manufactured by JXTG Energy Corporation; compound represented by formula (a-2-2)) 6FDA: 4,4'-(hexafluoroisopropylidene)diphthalic anhydride

[0095] (Diamine component) 6FODA: 4,4'-diamino-2,2'-bistrifluoromethyldiphenyl ether (manufactured by ChinaTech Chemical (Tianjin) Co., Ltd.; compound represented by formula (b-1)) 1,3-BAC: 1,3-bis(aminomethyl)cyclohexane (manufactured by Mitsubishi Gas Chemical Company, Inc.; compound represented by formula (b-2a)) 1,4-BAC: 1,4-bis(aminomethyl)cyclohexane (compound represented by formula (b-2b); trans ratio 40%) 1,4-BACT: 1,4-bis(aminomethyl)cyclohexane (manufactured by Mitsubishi Gas Chemical Company, Inc.; compound represented by formula (b-2b); trans ratio 85%) X-22-9409: (manufactured by Shin-Etsu Chemical Co., Ltd.; compound represented by formula (b-3-1) 4,4'-DDS: 4,4'-diaminodiphenyl sulfone (manufactured by Seika Corporation; compound represented by formula (b-3-2)) 3,3'-DDS: 3,3'-diaminodiphenyl sulfone (Seika Corporation) TFMB: 2,2'-bis(trifluoromethyl)benzidine (Seika Corporation)

[0096] <Production of polyimide resin, varnish and polyimide film> Example 1 A 300 mL five-neck round-bottom flask equipped with a stainless steel half-moon stirring blade, a nitrogen inlet tube, a Dean-Stark equipped with a cooling tube, a thermometer, and a glass end cap was charged with 16.812 g (0.0500 mol) of 6FODA, 7.113 g (0.0500 mol) of 1,4-BACT, and 65.935 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation), and the mixture was stirred at 200 rpm under a nitrogen atmosphere at an internal temperature of 70°C to obtain a solution. To this solution, 31.021 g (0.100 mol) of ODPA and 16.484 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation) were added all at once, and then 0.506 g of triethylamine (manufactured by Kanto Chemical Co., Ltd.) was added as an imidization catalyst, and the reaction system was heated with a mantle heater and the temperature in the reaction system was raised to 190° C. over about 20 minutes. The components distilled off were collected, and the temperature in the reaction system was maintained at 190° C. and refluxed for about 5 hours while adjusting the rotation speed according to the increase in viscosity. Thereafter, 208.517 g of 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 which the mixture was further stirred for about 1 hour for homogenization to obtain a polyimide varnish. The resulting polyimide varnish was then applied onto 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 300°C for 30 minutes under a nitrogen atmosphere (heating rate: 5°C / min) to evaporate the solvent and obtain a film.

[0097] Example 2 A polyimide varnish was prepared in the same manner as in Example 1, except that the amount of ODPA was changed from 31.021 g (0.100 mol) to 24.817 g (0.080 mol) and 7.688 g (0.020 mol) of CpODA was added, to obtain a polyimide varnish with a solid content concentration of 15 mass%. A film was obtained in the same manner as in Example 1 using the obtained polyimide varnish.

[0098] Example 3 A polyimide varnish was prepared in the same manner as in Example 2, except that the amount of 6FODA was changed from 16.812 g (0.0500 mol) to 16.429 g (0.04886 mol), the amount of 1,4-BACT was changed from 7.113 g (0.0500 mol) to 6.950 g (0.04886 mol), and 2.941 g (0.00228 mol) of X-22-9409 was added, to obtain a polyimide varnish with a solids concentration of 15 mass%. A film was obtained in the same manner as in Example 1 using the obtained polyimide varnish.

[0099] Example 4 A polyimide varnish was prepared in the same manner as in Example 2, except that the amount of 6FODA was changed from 16.812 g (0.0500 mol) to 16.012 g (0.04762 mol), the amount of 1,4-BACT was changed from 7.113 g (0.0500 mol) to 6.774 g (0.04762 mol), and 6.140 g (0.00476 mol) of X-22-9409 was added, to obtain a polyimide varnish with a solids concentration of 15 mass%. A film was obtained in the same manner as in Example 1 using the obtained polyimide varnish.

[0100] Example 5 The amount of ODPA was changed from 31.021 g (0.100 mol) to 15.511 g (0.050 mol), CpODA was added at 19.219 g (0.050 mol), the amount of 6FODA was changed from 16.812 g (0.0500 mol) to 15.980 g (0.04753 mol), the amount of 1,4-BACT was changed from 7.113 g (0.0500 mol) to 6.760 g (0.04753 mol), and 6.386 g (0.00495 mol) of X-22-9409 was added. Except for this, a polyimide varnish was prepared in the same manner as in Example 1, and a polyimide varnish with a solid content concentration of 15% by mass was obtained. A film was obtained in the same manner as in Example 1 using the obtained polyimide varnish.

[0101] Example 6 A polyimide varnish was prepared in the same manner as in Example 1, except that the amount of ODPA was increased from 31.021 g (0.100 mol) to 15.511 g (0.050 mol) and HPMDA was increased by 11.209 g (0.050 mol), to obtain a polyimide varnish with a solid content concentration of 15 mass %. A film was obtained in the same manner as in Example 1 using the obtained polyimide varnish.

[0102] Example 7 A polyimide varnish having a solid content concentration of 15 mass % was prepared in the same manner as in Example 2, except that 7.688 g (0.020 mol) of CpODA was changed to 4.483 g (0.020 mol) of HPMDA. A film was obtained in the same manner as in Example 1 using the obtained polyimide varnish.

[0103] Example 8 A polyimide varnish was prepared in the same manner as in Example 6, except that the amount of 6FODA was changed from 16.812 g (0.0500 mol) to 6.725 g (0.020 mol) and the amount of 1,4-BACT was changed from 7.113 g (0.0500 mol) to 11.380 g (0.080 mol), to obtain a polyimide varnish with a solids concentration of 15 mass%. The resulting polyimide varnish was then applied onto a glass plate by spin coating, held on a hot plate at 80°C for 20 minutes, and then heated in an air atmosphere in a hot air dryer at 240°C for 60 minutes to evaporate the solvent and obtain a film.

[0104] Example 9 A polyimide varnish having a solid content concentration of 15 mass % was prepared in the same manner as in Example 1, except that 7.113 g (0.0500 mol) of 1,4-BACT was changed to 7.113 g (0.0500 mol) of 1,3-BAC. A film was obtained in the same manner as in Example 1 using the obtained polyimide varnish.

[0105] Example 10 A polyimide varnish was prepared in the same manner as in Example 6, except that the amount of 6FODA was changed from 16.812 g (0.0500 mol) to 13.450 g (0.0400 mol) and the amount of 1,4-BACT was changed from 7.113 g (0.0500 mol) to 8.535 g (0.0600 mol), to obtain a polyimide varnish with a solids concentration of 15 mass%. The resulting polyimide varnish was then applied onto a glass plate by spin coating, held on a hot plate at 80°C for 20 minutes, and then heated in an air atmosphere in a hot air dryer at 260°C for 30 minutes to evaporate the solvent and obtain a film.

[0106] Example 11 A polyimide varnish having a solid content concentration of 15 mass % was prepared in the same manner as in Example 6, except that 7.113 g (0.0500 mol) of 1,4-BACT was changed to 7.113 g (0.0500 mol) of 1,4-BAC. A film was obtained in the same manner as in Example 10 using the obtained polyimide varnish.

[0107] Example 12 A polyimide varnish was prepared in the same manner as in Example 6, except that the amount of 6FODA was changed from 16.812 g (0.0500 mol) to 10.087 g (0.0300 mol) and 4.966 g (0.0200 mol) of 4,4'-DDS was added, to obtain a polyimide varnish with a solids concentration of 15 mass%. A film was obtained in the same manner as in Example 10 using the obtained polyimide varnish.

[0108] Comparative Example 1 A polyimide varnish with a solid content concentration of 15 mass % was obtained by preparing a polyimide varnish in the same manner as in Example 1, except that 16.812 g (0.0500 mol) of 6FODA was changed to 16.012 g (0.0500 mol) of TFMB. A film was obtained in the same manner as in Example 1 using the obtained polyimide varnish.

[0109] Comparative Example 2 A polyimide varnish was prepared in the same manner as in Example 1, except that the amount of 6FODA was changed from 16.812 g (0.0500 mol) to 33.624 g (0.100 mol) and the amount of 1,4-BACT was changed from 7.113 g (0.0500 mol) to 0 g (0 mol), to obtain a polyimide varnish with a solids concentration of 15 mass%. A film was obtained in the same manner as in Example 1 using the obtained polyimide varnish.

[0110] Comparative Example 3 A polyimide varnish with a solid content concentration of 15 mass % was prepared in the same manner as in Example 9, except that 16.812 g (0.0500 mol) of 6FODA was changed to 12.415 g (0.0500 mol) of 3,3'-DDS. A film was obtained in the same manner as in Example 1 using the obtained polyimide varnish.

[0111] Comparative Example 4 A polyimide varnish having a solid content concentration of 15 mass % was prepared in the same manner as in Example 1, except that 31.021 g (0.100 mol) of ODPA was changed to 44.424 g (0.100 mol) of 6FDA. A film was obtained in the same manner as in Example 1 using the obtained polyimide varnish.

[0112] Comparative Example 5 A polyimide varnish was prepared in the same manner as in Example 1, except that the amount of ODPA was changed from 31.021 g (0.100 mol) to 22.417 g (0.100 mol) of HPMDA, the amount of 6FODA was changed from 16.812 g (0.0500 mol) to 33.624 g (0.100 mol), and the amount of 1,4-BACT was changed from 7.113 g (0.0500 mol) to 0 g (0 mol), and a polyimide varnish with a solid content concentration of 15 mass% was obtained. A film was obtained in the same manner as in Example 10 using the obtained polyimide varnish.

[0113] The polyimide films obtained in the examples and comparative examples were subjected to the above-mentioned physical property measurements and evaluations. The results are shown in Table 1.

[0114] [Table 1]

[0115] As shown in Table 1, the polyimide films of the examples have good optical isotropy, and further have excellent flexibility and chemical resistance.

Claims

1. A polyimide resin having 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 (A-1) derived from a compound represented by the following formula (a-1): The structural unit B includes a structural unit (B-1) derived from a compound represented by the following formula (b-1) and a structural unit (B-2) derived from a compound represented by the following formula (b-2): the total ratio of the structural units (B-1) and (B-2) in the structural unit B is 70 mol % or more, A polyimide resin in which the proportion of the structural unit (B-1) in the structural unit B is 5 to 80 mol %, and the proportion of the structural unit (B-2) in the structural unit B is 20 to 95 mol %. 【Chemistry 1】

2. 2. The polyimide resin according to claim 1, wherein the molar ratio of the structural unit (B-1) to the structural unit (B-2) in the structural unit B, [(B-1) / (B-2)], is 5 / 95 to 80 / 20.

3. The polyimide resin according to claim 1 or 2, wherein the structural unit A further comprises at least one selected from the group consisting of a structural unit (A-2-1) derived from a compound represented by the following formula (a-2-1), and a structural unit (A-2-2) derived from a compound represented by the following formula (a-2-2): 【Chemistry 2】

4. The polyimide resin according to any one of claims 1 to 3, wherein the structural unit B further comprises at least one selected from the group consisting of a structural unit (B-3-1) derived from a compound represented by the following formula (b-3-1), and a structural unit (B-3-2) derived from a compound represented by the following formula (b-3-2): 【Chemistry 3】 (In formula (b-3-1), Z 1 and Z 2 each independently represents a divalent aliphatic group or a divalent aromatic group which may contain an oxygen atom; R 1 and R 2 each independently represents a monovalent aromatic group or a monovalent aliphatic group; R 3 and R 4 each independently represents a monovalent aliphatic group; R 5 and R 6 each independently represents a monovalent aliphatic group or a monovalent aromatic group, m and n each independently represent an integer of 1 or more, and the sum of m and n represents an integer of 2 to 1000. 1 and R 2 At least one of represents a monovalent aromatic group.

5. R in the formula (b-3-1) 1 and R 2 The polyimide resin according to claim 4, wherein is a phenyl group.

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.

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