Resin composition, molded body, and film

Abstract

To provide a molded body such as a film which is excellent in environmental safety and has high transparency and sufficient mechanical strength, and a resin composition which is used in manufacture of the same.SOLUTION: A resin composition contains a polyimide resin and a polyester resin. The polyimide resin has a diamine-derived structure and a tetracarboxylic acid dianhydride-derived structure. The tetracarboxylic acid dianhydride contains a tetracarboxylic acid dianhydride having both an alicyclic structure and an ester structure. The weight average molecular weight of the polyester resin exceeds 10,000.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a resin composition, a molded article, and a film. [Background technology]

[0002] There is a demand for thinner, lighter, and more flexible electronic devices, including display devices such as liquid crystal displays, organic electroluminescence displays, and electronic paper, as well as solar cells and touch panels. Replacing the glass materials used in these devices with film materials can make them more flexible, thinner, and lighter. Transparent polyimide resin films have been developed as glass replacement materials and are used in display substrates, cover films, and other applications.

[0003] Conventional polyimide resin films are obtained by applying a polyamic acid solution, which is a polyimide resin precursor, to a support in the form of a film, followed by high-temperature treatment to remove the solvent and simultaneously perform thermal imidization. However, the heating temperature for thermal imidization is high (e.g., 300°C or higher), and coloring (increased yellowness) due to heating is likely to occur, making it difficult to apply to applications requiring high transparency, such as display cover films.

[0004] As a method for producing a polyimide resin film having high transparency, a method using a polyimide resin that is soluble in organic solvents and does not require high-temperature imidization after film formation has been proposed. For example, Patent Document 1 describes that a polyimide resin containing a fluoroalkyl-substituted benzidine as a diamine and a bis(trimellitic anhydride) ester as a tetracarboxylic dianhydride has excellent solubility in organic solvents and excellent transparency and mechanical strength. However, its transparency is still inferior to that of glass, and improvements have been required.

[0005] Another known method for improving the transparency of polyimide resins is to alloy them with other resins. Patent Document 2 describes that alloying a polyimide resin containing a diamine having a perfluoroalkyl group as the diamine and an alicyclic tetracarboxylic dianhydride as the tetracarboxylic dianhydride with an acrylic resin results in excellent mechanical strength and transparency.

[0006] On the other hand, the environmental persistence of PFAS (Perfluorooctaphenylalanine Sulfates) has become a problem in recent years. Generally, PFAS are difficult to decompose in the environment due to the high bond energy of the carbon-fluorine bonds contained in the compounds, and they remain in water, etc., and their impact on humans has been pointed out.

[0007] Patent Document 3 exemplifies that a polyimide resin that does not correspond to an organic fluorine compound, which contains diethylmethylbenzenediamine as a diamine and 4,4'-oxydiphthalic anhydride as a tetracarboxylic dianhydride, is compatible with a polyester having a molecular weight of 10,000 or less. However, it also describes that if the amount of polyester added exceeds 40% by mass, the compatibility with the polyimide decreases, resulting in a decrease in transparency. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] WO2020 / 004236 [Patent Document 2] WO2023 / 026982 [Patent Document 3] WO2016 / 190105 Summary of the Invention [Problem to be solved by the invention]

[0009] Although the introduction of a rigid structure into a polyimide resin improves its mechanical strength, it can also cause a decrease in solubility in organic solvents and discoloration, making it difficult to achieve both transparency and high mechanical strength with conventional polyimide resins alone. While the use of a fluorine-containing compound is one way to improve solvent solubility, the use of an organic fluorine compound that remains in the environment raises concerns about environmental safety. In view of these issues, the present invention aims to provide a molded article such as a film that is environmentally safe, highly transparent, and has sufficient mechanical strength, as well as a resin composition used for producing the same. [Means for solving the problem]

[0010] As a result of extensive research, the present inventors have found that the above problems can be solved by the following configuration.

[0011] 1) A resin composition comprising a polyimide resin and a polyester resin, wherein the polyimide resin has a structure derived from a diamine and a structure derived from a tetracarboxylic dianhydride, the tetracarboxylic dianhydride includes a tetracarboxylic dianhydride having both a cardo structure and an ester structure, and the weight average molecular weight of the polyester resin exceeds 10,000.

[0012] 2) The resin composition according to 1), wherein the cardo structure is a structure containing an alicyclic structure.

[0013] 3) The resin composition according to 1) or 2), wherein the polyimide resin and the polyester resin are compatible with each other in a composition ratio range of 2:98 to 98:2.

[0014] 4) Tetracarboxylic dianhydrides having both cardo and ester structures are listed as follows: 5,5'-[9H-fluoren-9-ylidenebis(2-methyl-4,1-phenylene)]bis(1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxylate), 5,5'-spiro[9H-fluorene-9,9'-[9H]xanthene]-3',6'-diylbis(1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxylate), The resin composition according to any one of 1) to 3), characterized in that the carboxylic acid is at least one selected from the group consisting of 5,5'-[cyclohexylylenedi-4,1-phenylene]bis(1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxylate), 5,5'-[cyclohexylylenedi-4,1-phenylene]bis(1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxylate), and 5,5'-[cyclododecylidenebis(2-methyl-4,1-phenylene)]bis(1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxylate).

[0015] 5) The resin composition according to any one of 1) to 4), characterized in that the polyester resin has a structure derived from a dicarboxylic acid and a structure derived from a diol, and the diol has one or more diols selected from diols having an alkylene structure or a cycloalkylene structure having 3 or more carbon atoms, diols having a fluorene structure, and diols having a bisphenol derivative structure.

[0016] 6) The resin composition according to 5), wherein the diol having a bisphenol derivative structure has a structure in which alkylene oxide is added to two phenolic hydroxy groups of bisphenol.

[0017] 7) A molded article comprising the resin composition according to any one of 1) to 6).

[0018] 8) A film comprising the resin composition according to any one of 1) to 6). [Effects of the Invention]

[0019] According to the present invention, it is possible to provide a resin composition that is excellent in environmental safety, has high transparency, and has sufficient mechanical strength, as well as a molded article and a film that include the resin composition. DETAILED DESCRIPTION OF THE INVENTION

[0020] [Resin composition] The resin composition of the present invention is a resin composition containing a polyimide resin and a polyester resin, wherein the polyimide resin has a structure derived from a diamine and a structure derived from a tetracarboxylic dianhydride, the tetracarboxylic dianhydride includes a tetracarboxylic dianhydride having both a cardo structure and an ester structure, and the polyester resin has a weight-average molecular weight of more than 10,000.

[0021] <Polyimide resin> Polyimide resins (hereinafter sometimes simply referred to as "PI") are polymers having structural units represented by general formula (I) and are obtained by cyclodehydration of polyamic acid obtained by addition polymerization of tetracarboxylic dianhydride (hereinafter sometimes simply referred to as "acid dianhydride") and diamine. That is, polyimide resins are polycondensates of tetracarboxylic dianhydride and diamine, and have a structure derived from tetracarboxylic dianhydride (tetracarboxylic dianhydride component) and a structure derived from diamine (diamine component). Polyimide resins can also be synthesized by condensation through decarboxylation of diisocyanate and tetracarboxylic dianhydride.

[0022] [ka]

[0023] In general formula (I), X is a tetravalent organic group, and Y is a divalent organic group. X is a tetracarboxylic dianhydride residue, which is an organic group obtained by removing two carboxy anhydride groups from a tetracarboxylic dianhydride represented by the following general formula (II). Y is a diamine residue, which is an organic group obtained by removing two amino groups from a diamine represented by the following general formula (III). When a polyimide resin is synthesized using a diisocyanate, Y is a diisocyanate residue, which is an organic group obtained by removing two isocyanate groups from a diisocyanate compound.

[0024] [ka]

[0025] In other words, the polyimide resin contains a structural unit represented by the following general formula (IIa) and a structural unit represented by the following general formula (IIIa), and the tetracarboxylic dianhydride-derived structure (IIa) and the diamine-derived structure (IIIa) form an imide bond, thereby having the structural unit represented by general formula (I).

[0026] [ka]

[0027] The polyimide resin may contain, in addition to the imide structural unit represented by general formula (I), an amide structural unit represented by the following general formula (IV) or a structural unit containing an amide structure and an imide structure represented by (V). A polyimide resin containing, in addition to the imide structural unit, an amide structural unit or a structural unit containing an amide structure and an imide structure is also called a polyamideimide resin.

[0028] [ka]

[0029] In general formulas (IV) and (V), Y and Z are divalent organic groups, and W is a trivalent organic group. Y is a diamine residue, as in general formula (I). Z is a dicarboxylic acid residue, which is an organic group obtained by removing two carboxy groups from a dicarboxylic acid represented by the following general formula (VI). W is a tricarboxylic acid anhydride residue, which is an organic group obtained by removing a carboxy anhydride group and a carboxy group from a tricarboxylic acid anhydride represented by the following general formula (VII). In the synthesis of polyamide-imide resins, dicarboxylic acid derivatives such as dicarboxylic acid dichlorides, dicarboxylic acid anhydrides, and dicarboxylic acid esters represented by general formula (VI'), and tricarboxylic acid anhydride derivatives such as tricarboxylic acid anhydride chloride represented by general formula (VII') are preferably used instead of dicarboxylic acids or tricarboxylic acid anhydrides.

[0030] [ka]

[0031] The diamine-derived structure represented by the general formula (IIIa) above and the dicarboxylic acid-derived structure represented by the following general formula (VIa) form an amide bond to form an amide structural unit represented by the general formula (IV), and the diamine-derived structure represented by the general formula (IIIa) and the tricarboxylic acid anhydride-derived structure represented by the following general formula (VIIa) form an imide bond and an amide bond to form a structural unit containing an amide structure and an imide structure represented by the general formula (V). That is, the polyamideimide resin contains one or more structures selected from the dicarboxylic acid-derived structure (VIa) or the tricarboxylic acid anhydride-derived structure (VIIa), a tetracarboxylic acid dianhydride-derived structure (IIa), and a diamine-derived structure (IIIa).

[0032] [ka]

[0033] The polyamide-imide resin contains, for example, a structure of the following general formula (VIII) in which a diamine-derived structure (IIIa) is bonded to both ends of a dicarboxylic acid-derived structure (VIa).

[0034] [ka]

[0035] In general formula (VIII), Y1 and Y2 are diamine residues, and Z1 is a dicarboxylic acid residue. In general formula (IX), Y3 and Y4 are diamine residues, and Z2 is a tricarboxylic acid anhydride residue. When the moiety [-Y1-NH-CO-Z1-CO-NH-Y2-] in general formula (VIII) or the moiety [-Y3-N-(CO)2-Z2-CO-NH-Y4-] in general formula (IX) is considered as a single divalent organic group, this divalent organic group can be considered as a diamine residue Y containing two amide bonds. That is, in general formula (I), a polyimide resin containing an amide bond in the diamine residue Y is a polyamideimide resin, and polyamideimide resins can be considered a type of polyimide resin. Hereinafter, unless otherwise specified, the term "polyimide resin" includes "polyamideimide resin."

[0036] As described above, the polyimide resin contains a diamine-derived structure and a tetracarboxylic dianhydride-derived structure. The polyimide resin used in this embodiment contains a tetracarboxylic dianhydride-derived structure having both a cardo structure and an ester structure in addition to the tetracarboxylic dianhydride-derived structure.

[0037] (Tetracarboxylic acid dianhydride having both a cardo structure and an ester structure) A cardo structure refers to a skeletal structure in which two aromatic rings are bonded to a carbon atom within the ring. Tetracarboxylic acid dianhydrides having both a cardo structure and an ester structure are bis(trimellitic anhydride) esters having a cardo structure, and are represented by the following general formula (1).

[0038] [ka]

[0039] In general formula (1), A is a divalent organic group containing a cardo structure, and carbon atoms at both ends of A are bonded to carboxy groups. Specific examples of the divalent organic group A containing a cardo structure include the following (i) to (vi). (However, R 1a and R 1b are the same or different and represent a substituent; m1 and m2 are the same or different and represent an integer of 0 to 4; R 2 represents a substituent, n represents 0 or an integer of 1 to 8, and R 3 represents a substituent, k represents an integer of 0 to 10, and R 4 represents a substituent, j represents an integer of 0 to 22, and R 5a and R 5b are the same or different and represent a substituent, i1 and i2 are the same or different and represent an integer of 0 to 8, R 6a and R 6b are the same or different and represent a substituent, and h1 and h2 are the same or different and represent an integer of 0 to 3.

[0040] [ka]

[0041] R in general formulas (i), (ii), (iii), and (iv) 1a and R 1b are the same or different and represent a substituent. The substituent is not particularly limited, but from the viewpoint of the solubility of the polyimide resin, R 1a and R 1b is preferably an alkyl group having 1 to 10 carbon atoms, a phenyl group, an alkoxy group, or a halogen.

[0042] R in general formula (i) 2 represents a substituent. The substituent is not particularly limited, but from the viewpoint of the solubility of the polyimide resin, R 2is preferably an alkyl group having 1 to 10 carbon atoms, a phenyl group, an alkoxy group, or a halogen.

[0043] R in general formula (ii) 3 represents a substituent. The substituent is not particularly limited, but from the viewpoint of the mechanical properties of the resin composition, R 3 is preferably an alkyl group having 1 to 10 carbon atoms, a phenyl group, an alkoxy group, or a halogen.

[0044] R in general formula (iii) 4 represents a substituent. The substituent is not particularly limited, but from the viewpoint of the solubility of the polyimide resin, R 4 is preferably an alkyl group having 1 to 10 carbon atoms, a phenyl group, an alkoxy group, or a halogen.

[0045] R in general formulas (iv) and (v) 5a and R 5b are the same or different and represent a substituent. The substituent is not particularly limited, but from the viewpoint of the solubility of the polyimide resin, R 5a and R 5b is preferably an alkyl group having 1 to 10 carbon atoms, a phenyl group, an alkoxy group, or a halogen.

[0046] R in general formula (vi) 6a and R 6b are the same or different and represent a substituent. The substituent is not particularly limited, but from the viewpoint of the solubility of the polyimide resin, R 6a and R 6b is preferably an alkyl group having 1 to 10 carbon atoms, a phenyl group, an alkoxy group, or a halogen.

[0047] In the tetracarboxylic dianhydride having both a cardo structure and an ester structure, from the viewpoint of transparency, it is preferable that the cardo structure contains an alicyclic structure, and among the above (i) to (v), A is preferably (i) to (iii), and among these, (ii) to (iii) are particularly preferable. When A is a group represented by general formula (ii), from the viewpoint of solubility of the polyimide resin, it is preferable that general formula (1) is 5,5'-[cyclohexylylenedi-4,1-phenylene]bis(1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxylate) (BPZ-TME) represented by the following formula (1-1).

[0048] [ka]

[0049] When A in general formula (1) is a group represented by formula (iii), from the viewpoint of the solubility of the polyimide resin, general formula (1) is preferably 5,5'-[cyclododecylidenebis(2-methyl-4,1-phenylene)]bis(1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxylate) (TBIS-DMPN) represented by the following formula (1-2).

[0050] [ka]

[0051] When A in general formula (1) is a group represented by formula (iv), from the viewpoint of the solubility of the polyimide resin, general formula (1) is preferably 5,5'-[9H-fluoren-9-ylidenebis(2-methyl-4,1-phenylene)]bis(1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxylate) (TBIS-MPN) represented by the following formula (1-3).

[0052] [ka]

[0053] When A in general formula (1) is a group represented by formula (v), from the viewpoint of the solubility of the polyimide resin, general formula (1) is preferably 5,5'-spiro[9H-fluorene-9,9'-[9H]xanthene]-3',6'-diylbis(1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxylate) (TBIS-RXN) represented by the following formula (1-4).

[0054] [ka]

[0055] In terms of compatibility with polyester resins, the polyimide resin preferably contains tetracarboxylic dianhydride-derived structures having both a cardo structure and an ester structure in a ratio of 30 mol % or more, more preferably 50 mol % or more, and even more preferably 60 mol % or more, and may contain 70 mol % or more, or even 100 mol %, of the total amount of tetracarboxylic dianhydride-derived structures.

[0056] (Other tetracarboxylic dianhydrides) The polyimide resin may contain a tetracarboxylic dianhydride-derived structure other than a tetracarboxylic dianhydride having both a cardo structure and an ester structure, provided that the compatibility with the polyester resin is not impaired. Examples of such tetracarboxylic dianhydrides include tetracarboxylic dianhydrides having a bisphenol derivative structure, tetracarboxylic dianhydrides having an ester structure, tetracarboxylic dianhydrides having a fluorene structure, alicyclic tetracarboxylic dianhydrides, tetracarboxylic dianhydrides having an ether bond, and aromatic tetracarboxylic dianhydrides. The alicyclic tetracarboxylic dianhydrides may have at least one alicyclic structure and may have both an alicyclic ring and an aromatic ring in one molecule. The alicyclic ring may be polycyclic or may have a spiro structure.

[0057] Tetracarboxylic acid dianhydrides having a bisphenol derivative structure are tetracarboxylic acid dianhydrides obtained by reacting two hydroxy groups of bisphenols with 5-iodoisobenzofuran-1,3-dione or the like, and are represented by the following general formula (2). (In formula (2), p represents 1 or 2, and R 1a and R 1b are the same or different and represent a substituent; m1 and m2 are the same or different and represent an integer of 0 or 1 to 3; R 2a and R 2b are the same or different and represent a substituent, and n1 and n2 are the same or different and represent 0 or an integer of 1 to 4.

[0058] [ka]

[0059] In general formula (2), B is any divalent organic group, and at both ends of B, a phenyl group and a carbon atom of B are bonded. Specific examples of the divalent organic group B include the following (a) to (c). (However, R 3a and R 3b are the same or different and represent hydrogen, an alkyl group, or a phenyl group; R 4 represents an alkyl group, and k represents 0 or an integer of 1 to 10.

[0060] [ka]

[0061] R in general formula (2) 1a and R 1b are the same or different and represent a substituent. The substituent is not particularly limited, but from the viewpoint of the solubility of the polyimide resin, R 1a and R 1b is preferably an alkyl group having 1 to 10 carbon atoms, a phenyl group, an alkoxy group, or a halogen.

[0062] R in general formula (2) 2a and R2b are the same or different and represent a substituent. The substituent is not particularly limited, but from the viewpoint of the solubility of the polyimide resin, R 2a and R 2b is preferably an alkyl group having 1 to 10 carbon atoms, a phenyl group, an alkoxy group, or a halogen.

[0063] From the viewpoint of solubility of polyimide resins, the tetracarboxylic dianhydride having a bisphenol derivative structure is preferably 4,4'-(4,4'-isopropylidenediphenoxy)diphthalic anhydride. By using the tetracarboxylic dianhydride having a bisphenol derivative structure, a molded product having excellent compatibility with polyester resins, elastic modulus, mechanical strength, etc. can be obtained.

[0064] When a tetracarboxylic dianhydride having a bisphenol derivative structure is used, from the viewpoint of the mechanical strength of the polyimide resin, the ratio of the structure derived from the tetracarboxylic dianhydride having a bisphenol derivative structure to the total amount of structures derived from the tetracarboxylic dianhydride is preferably 1 mol% or more, more preferably 3 mol% or more, even more preferably 5 mol% or more, and may be 10 mol% or more, 12 mol% or more, or 15 mol% or more. From the viewpoint of the weather resistance of the polyimide resin, the ratio of the structure derived from the tetracarboxylic dianhydride having a bisphenol derivative structure to the total amount of structures derived from the tetracarboxylic dianhydride is preferably 70 mol% or less, more preferably 60 mol% or less, and may be 50 mol% or less, 30 mol% or less, or may be absent. The amount of tetracarboxylic dianhydride having a bisphenol derivative structure necessary to ensure compatibility with a polyester resin may vary depending on the type of polyester resin and the tetracarboxylic dianhydride having a bisphenol derivative structure.

[0065] Tetracarboxylic acid dianhydrides having an ester structure generally include tetracarboxylic acid dianhydrides having both a cardo structure and an ester structure. However, in the present specification, the term "tetracarboxylic acid dianhydride having an ester structure" refers to tetracarboxylic acid dianhydrides having an ester structure other than tetracarboxylic acid dianhydrides having both a cardo structure and an ester structure.

[0066] Examples of tetracarboxylic dianhydrides having an ester structure include 1,4-phenylenebis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylate), 2,2',3,3',5,5'-hexamethylbiphenyl-4,4'-diylbis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylate), and tert-butylhydroquinonebis(trimellitic anhydride).

[0067] When a tetracarboxylic dianhydride having an ester structure is used, from the viewpoint of the mechanical strength of the polyimide resin, the ratio of structures derived from the tetracarboxylic dianhydride having an ester structure to the total amount of structures derived from the tetracarboxylic dianhydride is preferably 1 mol% or more, more preferably 3 mol% or more, even more preferably 5 mol% or more, and may be 10 mol% or more, 12 mol% or more, or 15 mol% or more. From the viewpoint of the weather resistance of the polyimide resin, the ratio of structures derived from the tetracarboxylic dianhydride having an ester structure to the total amount of structures derived from the tetracarboxylic dianhydride is preferably 70 mol% or less, more preferably 60 mol% or less, and may be 50 mol% or less, 30 mol% or less, or may be absent. The amount of tetracarboxylic dianhydride having an ester structure necessary to ensure compatibility with a polyester resin may vary depending on the type of polyester resin and the tetracarboxylic dianhydride having an ester structure.

[0068] The tetracarboxylic acid dianhydride having a fluorene structure may have a fluorene structure and two acid anhydride groups. Among them, 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride, 9,9-bis[4-(3,4-dicarboxyphenoxy)phenyl]fluorene dianhydride, spiro[11H-difuro[3,4-b:3',4'-i]xanthene-11,9'-fluorene]-1,3,7,9-tetraone, and N,N'-(9H-fluoren-9-ylidene-4,1-phenylene)bis[1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxamide] are preferred from the viewpoint of solubility and transparency of polyimide resins, and 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride is particularly preferred, because they have a small molecular weight and a relatively high proportion of fluorene skeletons. When a tetracarboxylic dianhydride having a fluorene structure also has an ester structure, it is treated as a tetracarboxylic dianhydride having both a cardo structure and an ester structure.

[0069] When a tetracarboxylic dianhydride having a fluorene structure is used, from the viewpoint of improving compatibility between the polyimide resin and the polyester resin, the ratio of the structure derived from the tetracarboxylic dianhydride having a fluorene structure to the total amount of structures derived from the tetracarboxylic dianhydride is preferably 1 mol% or more, more preferably 3 mol% or more, even more preferably 5 mol% or more, and may be 10 mol% or more, 12 mol% or more, or 15 mol% or more. From the viewpoint of transparency of the polyimide resin, the ratio of the structure derived from the tetracarboxylic dianhydride having a fluorene structure to the total amount of structures derived from the tetracarboxylic dianhydride is preferably 70 mol% or less, more preferably 60 mol% or less, and may be 50 mol% or less, 30 mol% or less, or may be absent. The amount of tetracarboxylic dianhydride having a fluorene structure required to achieve compatibility with the polyester resin may vary depending on the polyester resin and the type of tetracarboxylic dianhydride having a fluorene structure.

[0070] Alicyclic tetracarboxylic dianhydrides include 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, 1,3-dimethylcyclobutane-1,2,3,4-tetracarboxylic dianhydride, 1,2,3,4-tetramethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, 1,1'-bicyclohexane-3,3',4,4'tetracarboxylic-3,4:3',4'-dianhydride, and norbornane-2-spiro-α -Cyclopentanone-α'-spiro-2"-norbornane-5,5",6,6"-tetracarboxylic acid dianhydride, 2,2'-binorbornane-5,5',6,6'tetracarboxylic acid dianhydride, 3-(carboxymethyl)-1,2,4-cyclopentanetricarboxylic acid 1,4:2,3-dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic acid dianhydride, 4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic acid anhydride, cyclohexane-1, 4-Diylbis(methylene)bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylate), 5-(2,5-dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride, bicyclo[2.2.1]heptane-2,3,5,6-tetracarboxylic dianhydride, bicyclo[2.2.2]octane-2,3,5,6-tetracarboxylic dianhydride, 3,5,6-tricarboxynorbornane-2-acetic acid 2,3:5,6-dianhydride, decahydro-1,4,5,8-dimethanonaphthalene -2,3,6,7-tetracarboxylic dianhydride, tricyclo[6.4.0.0(2,7)]dodecane-1,8:2,7-tetracarboxylic dianhydride, octahydro-1H,3H,8H,10H-biphenyleno[4a,4b-c:8a,8b-c']difuran-1,3,8,10-tetrone, 5,5'-(1,2-ethanediyl)bis(octahydro-1,3-dioxo-5-isobenzofurancarboxylate), decahydro[2]benzopyrano[6,5,4,-def][2]benzopyran-1,3,6,8-tetrone, and the like.

[0071] Among the alicyclic tetracarboxylic dianhydrides, from the viewpoint of the transparency and mechanical strength of the polyimide resin, 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, and 1,1'-bicyclohexane-3,3',4,4'tetracarboxylic-3,4:3',4'-dianhydride are preferred, and 1,2,3,4-cyclobutanetetracarboxylic dianhydride is particularly preferred.

[0072] When an alicyclic tetracarboxylic dianhydride is used, from the viewpoints of improving compatibility between the polyimide resin and the polyester resin and transparency, the ratio of structures derived from the alicyclic tetracarboxylic dianhydride to the total amount of structures derived from the tetracarboxylic dianhydride is preferably 1 mol% or more, more preferably 3 mol% or more, even more preferably 5 mol% or more, and may be 10 mol% or more, 12 mol% or more, or 15 mol% or more. From the viewpoint of ensuring solubility of the polyimide resin in organic solvents, the ratio of structures derived from the alicyclic tetracarboxylic dianhydride to the total amount of structures derived from the tetracarboxylic dianhydride is preferably 50 mol% or less, more preferably 40 mol% or less, and may be 30 mol% or less, 20 mol% or less, or may be absent. The amount of alicyclic tetracarboxylic dianhydride required to ensure compatibility with the polyester resin may vary depending on the type of polyester resin and alicyclic tetracarboxylic dianhydride.

[0073] Examples of the tetracarboxylic dianhydride having an ether bond include 3,4'-oxydiphthalic anhydride, 4,4'-oxydiphthalic anhydride, etc. Among the tetracarboxylic dianhydrides having an ether bond, 4,4'-oxydiphthalic anhydride is preferred from the viewpoint of solubility of polyimide resins.

[0074] When a tetracarboxylic dianhydride having an ether bond is used, from the viewpoint of mechanical strength, the content of the tetracarboxylic dianhydride having an ether bond relative to the total amount of structures derived from the tetracarboxylic dianhydride is preferably 1 mol% or more, more preferably 3 mol% or more, even more preferably 5 mol% or more, and may be 10 mol% or more, 12 mol% or more, or 15 mol% or more. From the viewpoint of ensuring solubility of the polyimide resin in organic solvents, the ratio of structures derived from the tetracarboxylic dianhydride having an ether bond relative to the total amount of structures derived from the tetracarboxylic dianhydride is preferably 50 mol% or less, more preferably 40 mol% or less, and may be 30 mol% or less, 20 mol% or less, or may be zero. The amount of tetracarboxylic dianhydride having an ether bond necessary to ensure compatibility with a polyester resin may vary depending on the type of polyester resin and the type of tetracarboxylic dianhydride having an ether bond.

[0075] Examples of aromatic tetracarboxylic dianhydrides include pyromellitic dianhydride, mellophanic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 2,2',3,3'-benzophenonetetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride, 5,5'-dimethylmethylenebis(phthalic anhydride), 2,3,6,7-naphthalenetetracarboxylic dianhydride, carboxylic acid dianhydride, 1,4,5,8-naphthalenetetracarboxylic acid dianhydride, 1,2,5,6-naphthalenetetracarboxylic acid dianhydride, terphenyltetracarboxylic acid dianhydride, 1,4-bis(3,4-dicarboxyphenoxy)benzene dianhydride, 2,2-bis(4-hydroxyphenyl)propanedibenzoate-3,3',4,4'-tetracarboxylic acid dianhydride, 4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic acid dianhydride, and the like.

[0076] Examples of aromatic tetracarboxylic dianhydrides other than those mentioned above include 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 2,2-bis(2,3-dicarboxyphenyl)propane dianhydride, bis(3,4-dicarboxyphenyl)sulfone dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, bis(2,3-dicarboxyphenyl)methane dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, 1,3-bis[(3,4-dicarboxy)benzoyl]benzene dianhydride, 1,4-bis[(3,4-dicarboxy)benzoyl]benzene dianhydride, bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}ketone dianhydride, bis Examples of the dianhydride include {4-[3-(1,2-dicarboxy)phenoxy]phenyl}ketone dianhydride, 4,4'-bis[4-(1,2-dicarboxy)phenoxy]biphenyl dianhydride, 4,4'-bis[3-(1,2-dicarboxy)phenoxy]biphenyl dianhydride, bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}sulfide dianhydride, bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl}sulfide dianhydride, 1,2,3,4-benzenetetracarboxylic dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, 2,3,6,7-anthracenetetracarboxylic dianhydride, and 1,2,7,8-phenanthrenetetracarboxylic dianhydride.

[0077] Among the aromatic tetracarboxylic dianhydrides, pyromellitic dianhydride and mellophanic dianhydride are preferred, with pyromellitic dianhydride being particularly preferred, from the viewpoint of the mechanical strength of the resin composition.

[0078] When an aromatic tetracarboxylic dianhydride is used, from the viewpoint of mechanical strength, the ratio of structures derived from the aromatic tetracarboxylic dianhydride to the total amount of structures derived from the tetracarboxylic dianhydride is preferably 1 mol% or more, more preferably 3 mol% or more, even more preferably 5 mol% or more, and may be 10 mol% or more, 12 mol% or more, or 15 mol% or more. From the viewpoint of transparency of the polyimide resin, the ratio of structures derived from the aromatic tetracarboxylic dianhydride to the total amount of structures derived from the tetracarboxylic dianhydride is preferably 50 mol% or less, more preferably 40 mol% or less, and may be 30 mol% or less, 20 mol% or less, or may be absent. The amount of aromatic tetracarboxylic dianhydride required to ensure compatibility with a polyester resin may vary depending on the type of polyester resin and aromatic tetracarboxylic dianhydride, etc.

[0079] Furthermore, as the tetracarboxylic dianhydride, a chain aliphatic tetracarboxylic dianhydride such as ethylene tetracarboxylic dianhydride, 1,2,3,4-butane tetracarboxylic dianhydride, meso-butane-1,2,3,4-tetracarboxylic dianhydride, etc. may be used.

[0080] When a chain aliphatic tetracarboxylic dianhydride is used, from the viewpoint of transparency, the content of the chain aliphatic tetracarboxylic dianhydride relative to the total amount of structures derived from the tetracarboxylic dianhydride is preferably 1 mol% or more, more preferably 3 mol% or more, even more preferably 5 mol% or more, and may be 10 mol% or more, 12 mol% or more, or 15 mol% or more. From the viewpoint of mechanical strength of the polyimide resin, the ratio of structures derived from the chain aliphatic tetracarboxylic dianhydride relative to the total amount of structures derived from the tetracarboxylic dianhydride is preferably 50 mol% or less, more preferably 40 mol% or less, and may be 30 mol% or less, 20 mol% or less, or may be absent. The amount of chain aliphatic tetracarboxylic dianhydride required to ensure compatibility with a polyester resin may vary depending on the type of polyester resin and the chain aliphatic tetracarboxylic dianhydride, etc.

[0081] (diamine) The diamine used in the polyimide resin of the present invention is not particularly limited, and may be an aromatic diamine, a diamine having a fluorene structure, an alicyclic diamine, a diamine having a sulfone group, a chain aliphatic diamine, etc. These diamines may be used alone or in combination.

[0082] Examples of aromatic diamines include p-phenylenediamine, m-phenylenediamine, o-phenylenediamine, p-xylenediamine, m-xylenediamine, o-xylenediamine, 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl sulfide, 3,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfide, and 3,3'-diaminobenzof phenone, 4,4'-diaminobenzophenone, 3,4'-diaminobenzophenone, 3,3'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 2,2-di(3-aminophenyl)propane, 2,2-di(4-aminophenyl)propane, 2-(3-aminophenyl)-2-(4-aminophenyl)propane, 1,1-di(3-aminophenyl)-1-phenylethane, 1,1-di(4-aminophenyl)-1-phenylethane 1-(3-aminophenyl)-1-(4-aminophenyl)-1-phenylethane, 1,3-bis(3-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(3-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminobenzoyl)benzene, 1,3-bis(4-aminobenzoyl)benzene, 1,4-bis(3-aminobenzoyl)benzene, 1,4-bis(4- aminobenzoyl)benzene, 1,3-bis(3-amino-α,α-dimethylbenzyl)benzene, 1,3-bis(4-amino-α,α-dimethylbenzyl)benzene, 1,4-bis(3-amino-α,α-dimethylbenzyl)benzene, 1,4-bis(4-amino-α,α-dimethylbenzyl)benzene, 2,6-bis(3-aminophenoxy)benzonitrile, 2,6-bis(3-aminophenoxy)pyridine, 4,4'-bis(3-aminophenoxy)biphenyl, 4,4'-Bis(4-aminophenoxy)biphenyl, bis[4-(3-aminophenoxy)phenyl]ketone, bis[4-(4-aminophenoxy)phenyl]ketone, bis[4-(3-aminophenoxy)phenyl]sulfide, bis[4-(4-aminophenoxy)phenyl]sulfide, bis[4-(3-aminophenoxy)phenyl]ether, bis[4-(4-aminophenoxy)phenyl]ether, 2,2-bis[4-(3-aminophenoxy)phenyl phenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 1,3-bis[4-(3-aminophenoxy)benzoyl]benzene, 1,3-bis[4-(4-aminophenoxy)benzoyl]benzene, 1,4-bis[4-(3-aminophenoxy)benzoyl]benzene, 1,4-bis[4-(4-aminophenoxy)benzoyl]benzene, 1,3-bis[4-(3-aminophenoxy)-α,α-dimethylbenzyl]benzene, 1,3 -Bis[4-(4-aminophenoxy)-α,α-dimethylbenzyl]benzene, 1,4-bis[4-(3-aminophenoxy)-α,α-dimethylbenzyl]benzene, 1,4-bis[4-(4-aminophenoxy)-α,α-dimethylbenzyl]benzene, 4,4'-bis[4-(4-aminophenoxy)benzoyl]diphenyl ether, 4,4'-bis[4-(4-amino-α,α-dimethylbenzyl)phenoxy]benzophenone, 3,3'-diamino- Examples of aromatic diamines include 4,4'-diphenoxybenzophenone, 3,3'-diamino-4,4'-dibiphenoxybenzophenone, 3,3'-diamino-4-phenoxybenzophenone, 3,3'-diamino-4-biphenoxybenzophenone, 6,6'-bis(3-aminophenoxy)-3,3,3',3'-tetramethyl-1,1'-spirobiindane, and 6,6'-bis(4-aminophenoxy)-3,3,3',3'-tetramethyl-1,1'-spirobiindane. The use of aromatic diamines can sometimes produce molded articles with excellent mechanical strength, such as elastic modulus.

[0083] When an aromatic diamine is used, from the viewpoint of the mechanical strength of the polyimide resin, the ratio of the aromatic diamine-derived structure to the total amount of diamine-derived structures is preferably 5 mol% or more, more preferably 10 mol% or more, and even more preferably 20 mol% or more, and may be 50 mol% or more, 70 mol% or more, 90 mol% or more, or 100 mol%. From the viewpoint of the solubility and transparency of the polyimide resin, the ratio of the aromatic diamine-derived structure to the total amount of diamine-derived structures is preferably 50 mol% or less, more preferably 30 mol% or less, and may be 20 mol% or less, 10 mol% or less, or may be absent. The amount of aromatic diamine required to ensure compatibility with the polyester resin may vary depending on the polyester resin, the type of aromatic diamine, etc.

[0084] The diamine having a fluorene structure may have two amino groups and a fluorene skeleton. Among them, 9,9-bis(4-aminophenyl)fluorene, 9,9-bis(4-amino-3-methylphenyl)fluorene, 9,9-bis(3-amino-4-hydroxyphenyl)fluorene, or 9,9-bis[4-(4-aminophenoxy)phenyl]fluorene is preferred because of its small molecular weight and relatively high proportion of the fluorene skeleton, with 9,9-bis(4-aminophenyl)fluorene being particularly preferred. By using a diamine having a fluorene structure, molded articles with excellent compatibility with polyester resins, elastic modulus, mechanical strength, etc. can be obtained.

[0085] In terms of solubility in solvents and compatibility with polyester resins, the polyimide resin preferably has a ratio of diamine-derived structures having a fluorene structure of 30 mol% or more relative to the total amount of diamine-derived structures, more preferably 50 mol% or more, even more preferably 70 mol% or more, particularly preferably 90 mol% or more, and may even be 100 mol%. From the viewpoint of total light transmittance of the polyimide resin, the ratio of diamine-derived structures having a fluorene structure relative to the total amount of diamine-derived structures is preferably 50 mol% or less, more preferably 30 mol% or less, and may be 20 mol% or less, 10 mol% or less, or may be absent. The amount of diamine having a fluorene structure necessary to ensure compatibility with polyester resins may vary depending on the polyester resin, the type of aromatic diamine, etc.

[0086] Examples of alicyclic diamines include isophorone diamine, 1,2-cyclohexane diamine, 1,3-cyclohexane diamine, 1,4-cyclohexane diamine, 1,2-bis(aminomethyl)cyclohexane, 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, bis(aminomethyl)norbornene, 4,4'-methylenebis(cyclohexylamine), bis(4-aminocyclohexyl)methane, 4,4'-methylenebis(2-methylcyclohexylamine), adamantane-1,3-diamine, 2,6-bis(aminomethyl)bicyclo[2.2.1]heptane, 2,5-bis(aminomethyl)bicyclo[2.2.1]heptane, and 1,1-bis(4-aminophenyl)cyclohexane. The use of alicyclic diamines can sometimes produce molded articles with excellent transparency, such as total light transmittance and yellowness index.

[0087] When an alicyclic diamine is used, from the viewpoint of the solubility and transparency of the polyimide resin, the ratio of the alicyclic diamine-derived structure to the total amount of diamine-derived structures is preferably 1 mol% or more, more preferably 3 mol% or more, even more preferably 5 mol% or more, and may be 10 mol% or more, 12 mol% or more, or 15 mol% or more. From the viewpoint of the mechanical strength of the polyimide resin, the ratio of the alicyclic diamine-derived structure to the total amount of diamine-derived structures is preferably 70 mol% or less, more preferably 50 mol% or less, and may be 30 mol% or less, 20 mol% or less, or may be absent. The amount of alicyclic diamine required to ensure compatibility with the polyester resin may vary depending on the polyester resin, the type of alicyclic diamine, etc.

[0088] Examples of diamines containing sulfone groups include 3,3'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, bis[4-(3-aminophenoxy)phenyl]sulfone, bis[4-(4-aminophenoxy)phenyl]sulfone, 4,4'-bis[4-(4-amino-α,α-dimethylbenzyl)phenoxy]diphenyl sulfone, and 4,4'-bis[4-(4-aminophenoxy)phenoxy]diphenyl sulfone. The use of diamines containing sulfone groups can improve the transparency of polyimide resins and mechanical properties such as elastic modulus and toughness. Among diamines containing sulfone groups, 3,3'-diaminodiphenyl sulfone (3,3'-DDS) and 4,4'-diaminodiphenyl sulfone (4,4'-DDS) are preferred from the perspective of mechanical strength. 3,3'-DDS and 4,4'-DDS may be used in combination.

[0089] When a diamine having a sulfonic acid group is used, from the viewpoint of the transparency and mechanical strength of the polyimide resin, the ratio of the structure derived from the diamine having a sulfonic acid group to the total amount of the structure derived from the diamine is preferably 1 mol% or more, more preferably 3 mol% or more, even more preferably 5 mol% or more, and may be 10 mol% or more, 12 mol% or more, or 15 mol% or more. From the viewpoint of the solubility of the polyimide resin, the ratio of the structure derived from the diamine having a sulfonic acid group to the total amount of the structure derived from the diamine is preferably 50 mol% or less, more preferably 30 mol% or less, and may be 20 mol% or less, 10 mol% or less, or may be absent. The amount of diamine having a sulfonic acid group required to achieve compatibility with a polyester resin may vary depending on the polyester resin, the type of diamine having a sulfonic acid group, etc.

[0090] Diamines include bis(aminomethyl) ether, bis(2-aminoethyl) ether, bis(3-aminopropyl) ether, bis(2-aminomethoxy)ethyl] ether, bis[2-(2-aminoethoxy)ethyl] ether, bis[2-(3-aminoprotoxy)ethyl] ether, 1,2-bis(aminomethoxy)ethane, 1,2-bis(2-aminoethoxy)ethane, 1,2-bis[2-(aminomethoxy)ethoxy]ethane, 1,2-bis[2-(2-aminoethoxy)ethoxy]ethane, ethylene glycol bis(3-aminopropyl) ether, diethylene glycol bis(3-aminopropyl) ether, triethylene glycol bis Chain aliphatic diamines such as bis(3-aminopropyl)ether, ethylenediamine, 1,3-diaminopropane, 1,4-diaminobutane, 1,5-diaminopentane, 1,6-diaminohexane, 1,7-diaminoheptane, 1,8-diaminooctane, 1,9-diaminononane, 1,10-diaminodecane, 1,11-diaminoundecane, 1,12-diaminododecane, 1,3-bis(3-aminopropyl)tetramethyldisiloxane, 1,3-bis(4-aminobutyl)tetramethyldisiloxane, α,ω-bis(3-aminopropyl)polydimethylsiloxane, and α,ω-bis(3-aminobutyl)polydimethylsiloxane can also be used. The use of chain aliphatic diamines can sometimes improve the transparency of the polyimide resin.

[0091] When a chain aliphatic diamine is used, from the viewpoint of transparency of the polyimide resin, the ratio of the chain aliphatic diamine-derived structure to the total amount of diamine-derived structures is preferably 1 mol% or more, more preferably 3 mol% or more, even more preferably 5 mol% or more, and may be 10 mol% or more, 12 mol% or more, or 15 mol% or more. From the viewpoint of mechanical strength of the polyimide resin, the ratio of the chain aliphatic diamine-derived structure to the total amount of diamine-derived structures is preferably 50 mol% or less, more preferably 30 mol% or less, and may be 20 mol% or less, 10 mol% or less, or may be absent. The amount of chain aliphatic diamine required to ensure compatibility with the polyester resin may vary depending on the polyester resin, the type of chain aliphatic diamine, etc.

[0092] (Polyimide resin with excellent environmental safety) To obtain a polyimide resin in which the environmental degradability of fluorine-containing compounds is improved and the environmental persistence of fluorine-containing compounds is significantly reduced, the total content of the structure derived from the tetracarboxylic acid dianhydride having a specific fluorine structure and the structure derived from the diamine having a specific fluorine structure is preferably less than 500 mg, more preferably less than 300 mg, more preferably less than 100 mg, and even more preferably less than 50 mg per kg of polyimide resin. Here, the tetracarboxylic acid dianhydride having a specific fluorine structure and the diamine having a specific fluorine structure refer to tetracarboxylic acid dianhydrides having a fully fluorinated methyl group (CF3-) or methylene group (-CF2-), and diamines having a fully fluorinated methyl group (CF3-) or methylene group (-CF2-), excluding substances containing only the CF3-X or X'-CF2-X structural element. (wherein X is an -OR or -NRR' structure, X' is any one of -H, -CH3, aromatic, -C(=O)-, -OR'', -SR'', NR''R'''', and R, R', R'', R'' are any one of -H, -CH3, -CH2-, aromatic, and -C(=O)-)

[0093] More preferably, the ratio of the tetracarboxylic dianhydride-derived structure having a CF3- group directly bonded to an aromatic ring or a -C(CF3)2- group directly bonded to an aromatic ring to the total amount of tetracarboxylic dianhydride-derived structures is less than 0.5 mol %, and the ratio of the diamine-derived structure having a CF3- group directly bonded to an aromatic ring or a -C(CF3)2- group directly bonded to an aromatic ring to the total amount of diamine-derived structures is less than 0.5 mol %. Examples of tetracarboxylic dianhydrides and diamines having a CF3- group directly bonded to an aromatic ring or a -C(CF3)2- group directly bonded to an aromatic ring include 4,4'-(hexafluoroisopropylidene)diphthalic anhydride, 9,9-bis(trifluoromethyl)xanthenetetracarboxylic dianhydride, 9-trifluoromethylxanthenetetracarboxylic dianhydride, 2,2'-bis(trifluoromethyl)benzidine, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, and 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane.

[0094] In addition, -CF2 (-CF2-) of the polyimide resin composition k the content of a structure derived from a tetracarboxylic dianhydride having -CF2- (k is an integer of 1 or more) is less than 0.5 mol% based on the total amount of structures derived from tetracarboxylic dianhydride, and -CF2 (-CF2-) of the polyimide resin composition m The content of the diamine-derived structure having CF2- (m is an integer of 1 or more) is more preferably less than 0.5 mol % based on the total amount of diamine-derived structures.

[0095] (Preparation of Polyimide Resin) The reaction of tetracarboxylic dianhydride with diamine yields polyamic acid (polyamic acid) as a polyimide resin precursor, and the polyimide resin is obtained by cyclodehydration (imidization) of the polyamic acid. The method for preparing polyamic acid is not particularly limited, and any known method can be used. For example, a polyamic acid solution can be obtained by dissolving tetracarboxylic dianhydride and diamine in approximately equimolar amounts (molar ratio of 90:100 to 110:100) in an organic solvent and stirring the mixture.

[0096] The concentration of the polyamic acid solution is usually 5 to 35% by weight, and preferably 10 to 30% by weight. When the concentration is within this range, the polyamic acid obtained by polymerization has an appropriate molecular weight, and the polyamic acid solution has an appropriate viscosity.

[0097] In the polymerization of polyamic acid, a method of adding tetracarboxylic dianhydride to diamine is preferred to suppress ring-opening of tetracarboxylic dianhydride. When adding multiple types of diamines or multiple types of tetracarboxylic dianhydrides, they may be added all at once or in multiple portions. The physical properties of the polyimide resin can also be controlled by adjusting the order of addition of the monomers.

[0098] The organic solvent used in the polymerization of polyamic acid is not particularly limited as long as it does not react with tetracarboxylic dianhydrides and diamines and can dissolve polyamic acid. Examples of organic solvents include urea-based solvents such as methylurea and N,N-dimethylethylurea; sulfoxide or sulfone-based solvents such as dimethyl sulfoxide, diphenyl sulfone, and tetramethyl sulfone; amide-based solvents such as N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), N,N'-diethylacetamide, N-methyl-2-pyrrolidone (NMP), γ-butyrolactone, and hexamethylphosphoric triamide; alkyl halide solvents such as chloroform and dichloromethane; aromatic hydrocarbon solvents such as benzene, toluene, and cresol; and ether-based solvents such as tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, dimethyl ether, diethyl ether, and p-cresol methyl ether. These solvents are typically used alone or in combination as needed. From the viewpoint of the solubility and polymerization reactivity of the polyamic acid, DMAc, DMF, NMP, etc. are preferably used.

[0099] Polyimide resins are obtained by dehydration cyclization of polyamic acid. One method for preparing polyimide resins from polyamic acid solutions is to add a dehydrating agent, an imidization catalyst, etc. to the polyamic acid solution and allow imidization to proceed in the solution. Heating the polyamic acid solution can be used to accelerate the imidization process. Mixing a solution containing the polyimide resin produced by imidization of polyamic acid with a poor solvent results in the polyimide resin being precipitated as a solid. Isolating the polyimide resin as a solid allows impurities generated during polyamic acid synthesis, as well as residual dehydrating agents and imidization catalysts, to be washed away with a poor solvent, preventing discoloration and increased yellowness of the polyimide resin. Furthermore, isolating the polyimide resin as a solid allows the use of solvents suitable for film formation, such as low-boiling point solvents, when preparing solutions for producing molded products such as films.

[0100] The molecular weight of the polyimide resin (weight average molecular weight in terms of polystyrene measured by gel permeation chromatography (GPC)) is preferably 10,000 to 1,000,000, more preferably 20,000 to 500,000, and even more preferably 40,000 to 300,000. If the molecular weight is too small, the strength of the film may be insufficient. If the molecular weight is too large, the compatibility with polyester resins or film formability may be poor.

[0101] From the viewpoint of the thermal stability and light stability of the resin composition and film, it is preferable that the polyimide resin has low reactivity. The acid value of the polyimide resin is preferably 0.4 mmol / g or less, more preferably 0.3 mmol / g or less, even more preferably 0.2 mmol / g or less, and may be 0.1 mmol / g or less, 0.05 mmol / g or less, or 0.03 mmol / g or less. From the viewpoint of reducing the acid value, it is preferable that the polyimide resin has a high imidization rate. A low acid value tends to increase the stability of the polyimide resin and improve its compatibility with polyester resins.

[0102] The polyimide resin is soluble in a solvent, preferably an amide solvent, a ketone solvent, an alkyl halide solvent, etc. The solubility in the solvent is preferably exhibited at 60° C. or less, more preferably at 40° C. or less, and even more preferably at 23° C. or less. When a polyimide resin is soluble in a solvent, it means that it is soluble at a concentration of 1% by weight or more.

[0103] <Polyester resin> The polyester resin in the present invention is not particularly limited as long as it has a weight-average molecular weight of more than 10,000, but it is preferable that the polyester resin has a structure derived from a dicarboxylic acid and a structure derived from a diol, and that the diol is one or more diols selected from diols having an alkylene structure or a cycloalkylene structure with 3 or more carbon atoms, diols having a fluorene structure, and diols having a bisphenol derivative structure. The diols having an alkylene structure or a cycloalkylene structure with 3 or more carbon atoms, diols having a fluorene structure, and diols having a bisphenol derivative structure may be used alone or in combination.

[0104] (dicarboxylic acid) Examples of aromatic dicarboxylic acids include terephthalic acid, isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid, biphenyldicarboxylic acid, and their anhydrides. Other examples include dicarboxylic acids having a fluorene skeleton, such as 9,9-bis(carboxymethyl)fluorene and 9,9-bis(2-carboxyethyl)fluorene. Among these, terephthalic acid or isophthalic acid is preferred because it enhances the solubility of polyester resins. Terephthalic acid and isophthalic acid may be used alone or in combination. When terephthalic acid and isophthalic acid are used in combination, the molar ratio of terephthalic acid to isophthalic acid is preferably 90:10 to 10:90, more preferably 25:75 to 75:25, and even more preferably 60:40 to 40:60, from the viewpoint of the solubility of polyester resins. In such a case, from the viewpoint of the solubility of the polyester resin, the total content of terephthalic acid and isophthalic acid is preferably 30 mol% or more, more preferably 40 mol% or more, even more preferably 60 mol% or more, and particularly preferably 80 mol% or more, based on the total dicarboxylic acids.

[0105] Examples of aliphatic dicarboxylic acids include oxalic acid, malonic acid, succinic acid, succinic anhydride, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, fumaric acid, maleic acid, maleic anhydride, itaconic acid, citraconic acid, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, tetrahydrophthalic acid, and anhydrides thereof. The inclusion of an aliphatic dicarboxylic acid-derived structure in the dicarboxylic acid-derived structure constituting the polyester resin may improve compatibility with polyimide resins. In such cases, the aliphatic dicarboxylic acid preferably contains an aliphatic dicarboxylic acid having 6 to 12 carbon atoms, particularly 6 to 10 carbon atoms, from the viewpoint of compatibility with polyimide resins. Among the aliphatic dicarboxylic acids having 6 to 12 carbon atoms, particularly 6 to 10 carbon atoms, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid are preferred from the viewpoint of improving the solubility of the polyester resin.

[0106] (Diol having an alkylene structure or cycloalkylene structure with 3 or more carbon atoms) Examples of diols having an alkylene or cycloalkylene structure with 3 or more carbon atoms include propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, diethylene glycol, triethylene glycol, dipropylene glycol, isosorbide, polytetramethylene ether glycol, and 2-butene-1,4-diol. The inclusion of a diol-derived structure having an alkylene or cycloalkylene structure with 3 or more carbon atoms in the diol-derived structure constituting the polyester resin improves the solubility of the polyester resin and also improves compatibility with polyimide resins. Among these, butanediol, neopentyl glycol, and polytetramethylene ether glycol are preferred from the standpoint of compatibility with polyimides. Examples of polyester resins containing a structure derived from a diol having an alkylene structure or a cycloalkylene structure having 3 or more carbon atoms include UE3200G (manufactured by Unitika Ltd., weight average molecular weight 43,000, Tg: 65°C), UE3210 (manufactured by Unitika Ltd., weight average molecular weight 62,000, Tg: 45°C), UE3240 (manufactured by Unitika Ltd., weight average molecular weight 50,000, Tg: 40°C), UE3500 (manufactured by Unitika Ltd., weight average molecular weight 83,000, Tg: 15°C), UE3510 (manufactured by Unitika Ltd., weight average molecular weight 90,000, Tg: 15°C), and UE3240 (manufactured by Unitika Ltd., weight average molecular weight 100,000, Tg: 15°C). Examples of such copolymers include UE9200 (manufactured by Unitika Ltd., weight average molecular weight of 63,000, Tg: -25°C), UE9200 (manufactured by Unitika Ltd., weight average molecular weight of 39,000, Tg: 65°C), UE9800 (manufactured by Unitika Ltd., weight average molecular weight of 40,000, Tg: 85°C), Vylon 200 (manufactured by Toyobo Co., Ltd., weight average molecular weight of 42,000, Tg: 67°C), Vylon 240 (manufactured by Toyobo Co., Ltd., weight average molecular weight of 35,000, Tg: 60°C), and Vylon 600 (manufactured by Toyobo Co., Ltd., weight average molecular weight of 38,000, Tg: 47°C).

[0107] (Diol having a fluorene structure) The diol having a fluorene structure has two hydroxy groups and a fluorene skeleton, and is exemplified by the following general formula (3): (In formula (3), Ar1 and Ar2 represent aromatic hydrocarbon rings, and R 1a and R 1b are the same or different and represent an alkyl group or a phenyl group having 1 to 10 carbon atoms; m1 and m2 are the same or different and represent an integer of 0 or 1 or more; R 2a and R 2b are the same or different and represent an alkyl group or a phenyl group having 1 to 10 carbon atoms; n1 and n2 are the same or different and represent an integer of 0 or 1 to 4; R 3a and R 3b are the same or different and represent an alkylene group; p1 and p2 are the same or different and represent an integer of 0 or 1 or more; and q1 and q2 are the same or different and represent an integer of 1 or more.

[0108] [ka]

[0109] Examples of diols having a fluorene structure represented by formula (3) include 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene, 9,9-bis[4-(2-hydroxypropoxy)phenyl]fluorene, 9,9-bis[4-[2-(2-hydroxyethoxy)ethoxy]phenyl]-9H-fluorene, 2,2'-[(9H-fluorene-9,9-diyl)bis(naphthalene-6,2-diyloxy)]diethanol, 9,9-bis[4-(2-hydroxyethoxy)-3-phenylphenyl]fluorene, 9,9-bis[4-(2-hydroxypropoxy)-3-phenylphenyl]fluorene, and 9,9-bis{4-[2-(2-hydroxyethoxy)ethoxy]-3-phenylphenyl}fluorene. When the diol-derived structure having a fluorene structure is contained in the diol-derived structure constituting the polyester resin, the solubility of the polyester resin is improved, and the compatibility with the polyimide resin is also improved.

[0110] Among these, 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene, 9,9-bis[4-(2-hydroxypropoxy)phenyl]fluorene, and 9,9-bis[4-(2-hydroxyethoxy)-3-phenylphenyl]fluorene are preferred because they improve the heat resistance of the resulting film. Examples of polyester resins containing a structure derived from a diol having a fluorene structure include OKP4HT (manufactured by Osaka Gas Chemicals Co., Ltd., weight-average molecular weight of 38,000, Tg: 142°C) and OKP4 (manufactured by Osaka Gas Chemicals Co., Ltd., weight-average molecular weight of 40,000, Tg: 121°C).

[0111] (Diol with a bisphenol derivative structure) A diol having a bisphenol derivative structure is a diol in which an alkylene oxide such as ethylene oxide or propylene oxide is added to the two phenolic hydroxy groups of a bisphenol.Specifically, these are ethylene oxide or propylene oxide adducts of 2,2-bis(4-hydroxyphenyl)propane (bisphenol A), ethylene oxide or propylene oxide adducts of 1,1-bis(4-hydroxyphenyl)-1-phenylethane (bisphenol AP), ethylene oxide or propylene oxide adducts of 2,2-bis(4-hydroxyphenyl)butane (bisphenol B), and ethylene oxide adducts of bis(4-hydroxyphenyl)diphenylmethane (bisphenol BP). ethylene oxide or propylene oxide adducts of 2,2-bis(3-methyl-4-hydroxyphenyl)propane (bisphenol C), ethylene oxide or propylene oxide adducts of 1,1-bis(4-hydroxyphenyl)ethane (bisphenol E), ethylene oxide or propylene oxide adducts of bis(4-hydroxyphenyl)methane (bisphenol F), 2,2-bis(4-hydroxy-3-isopropylphenyl)propane Ethylene oxide or propylene oxide adducts of bisphenol G (bisphenol G), 1,3-bis(2-(4-hydroxyphenyl)-2-propyl)benzene (bisphenol M), ethylene oxide or propylene oxide adducts of bis(4-hydroxyphenyl)sulfone (bisphenol S), 1,4-bis(2-(4-hydroxyphenyl)-2-propyl)benzene (bisphenol P), Examples include ethylene oxide or propylene oxide adducts of 5,5'-(1-methylethylidene)-bis[1,1'-(bisphenyl)-2-ol]propane (bisphenol PH), ethylene oxide or propylene oxide adducts of 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane (bisphenol TMC), and ethylene oxide or propylene oxide adducts of 1,1-bis(4-hydroxyphenyl)cyclohexane (bisphenol Z).The inclusion of a diol-derived structure having a bisphenol derivative structure in the diol-derived structure constituting the polyester resin improves compatibility with polyimide resins and improves the mechanical properties of the resulting film. Among these, from the viewpoint of solubility of the polyester resin, it is preferable to use an ethylene oxide adduct of bisphenol A, an ethylene oxide adduct of bisphenol S, or an ethylene oxide adduct of bisphenol Z. Examples of polyester resins containing a diol-derived structure having a bisphenol derivative structure include UE3600 (manufactured by Unitika Ltd., weight-average molecular weight of 60,000, Tg: 75°C), UE3690 (manufactured by Unitika Ltd., weight-average molecular weight of 46,000, Tg: 90°C), UE9100 (manufactured by Unitika Ltd., weight-average molecular weight of 77,000, Tg: 19°C), and Vylon 290 (manufactured by Toyobo Co., Ltd., weight-average molecular weight of 61,000, Tg: 72°C).

[0112] (Other diols) In addition to the above diols, for example, ethylene glycol can be mentioned as the diol. When ethylene glycol is used in combination with one or more diols selected from diols having an alkylene structure or a cycloalkylene structure with 3 or more carbon atoms, diols having a fluorene structure, and diols having a bisphenol derivative structure, the molar ratio of the one or more diols selected from diols having an alkylene structure or a cycloalkylene structure with 3 or more carbon atoms, diols having a fluorene structure, and diols having a bisphenol derivative structure to ethylene glycol is preferably 90:10 to 10:90, more preferably 80:20 to 20:80, and even more preferably 60:40 to 40:60, from the viewpoint of compatibility with the polyimide resin.

[0113] (Other ingredients) In addition to diols and dicarboxylic acids, other monomers may be used in the polyester resin as needed, provided that the effects of the present invention are not impaired. Examples of such other monomers include polyols having three or more hydroxy groups (e.g., trimethylolpropane, glycerin), monoalcohols (e.g., octyl alcohol, decyl alcohol, lauryl alcohol, myristyl alcohol, cetyl alcohol, stearyl alcohol, 2-phenoxyethanol), polycarboxylic acids having three or more carboxy groups (e.g., 1,3,4-benzenetricarboxylic acid, 1,2,4,5-benzenetetracarboxylic acid, pyromellitic acid, trimellitic acid, tetrahydrophthalic acid), monocarboxylic acids (e.g., lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, benzoic acid, p-te rt-butylbenzoic acid, cyclohexanoic acid), hydroxycarboxylic acids (e.g., lactic acid, glycolic acid, 2-hydroxybutyric acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 2-hydroxyisobutyric acid, 2-hydroxy-2-methylbutyric acid, 2-hydroxyvaleric acid, 3-hydroxyvaleric acid, 4-hydroxyvaleric acid, 5-hydroxyvaleric acid, 6-hydroxycaproic acid, 10-hydroxystearic acid, 4-hydroxyphenylstearic acid, 4-(β-hydroxy)ethoxybenzoic acid), lactones (e.g., β-propiolactone, β-butyrolactone, γ-butyrolactone, δ-valerolactone, ε-caprolactone), and oxiranes (e.g., ethylene oxide).

[0114] (Preparation of Polyester Resin) The polymerization method for the polyester resin of the present invention is not particularly limited, and any known production method may be used, such as a transesterification method, a direct esterification method to obtain an oligomer, followed by melt polymerization, or further solid-phase polymerization, but is not limited to the production methods listed here.

[0115] From the viewpoints of solubility in organic solvents, compatibility with the polyimide resin, and strength of molded articles, the weight-average molecular weight (polystyrene equivalent) of the polyester resin should be greater than 10,000. For example, it can be selected from the range of greater than 10,000 to approximately 200,000, preferably 15,000 to 150,000, more preferably 20,000 to 100,000, and even more preferably 30,000 to 80,000. If the weight-average molecular weight of the polyester resin is too low, the durability of the resulting film may be reduced. If the molecular weight of the polyester resin is too high, film formability may be poor. (Here, 15,000 to 150,000 means 15,000 or more and 150,000 or less.)

[0116] From the viewpoint of heat resistance of the resin composition and molded article, the glass transition temperature Tg of the polyester resin may be, for example, -25 to 200°C, preferably 15 to 180°C, more preferably 40 to 150°C, and particularly preferably about 60 to 130°C.

[0117] The polyester resin may be soluble in commonly used organic solvents, but from the viewpoint of the solubility of the polyimide resin and compatibility with the polyimide resin, it is preferable that the polyester resin be soluble in a highly polar solvent such as an amide solvent. Since polyimide resins generally dissolve only in highly polar solvents such as amide solvents, dissolving the polyester resin in a highly polar solvent such as an amide solvent facilitates compatibility with the polyimide resin.

[0118] <Preparation of Resin Composition> The polyimide resin and polyester resin are mixed to prepare a resin composition. While polyimide resins generally exhibit no compatibility with other resins, in this embodiment, as described above, the polyimide resin exhibits compatibility with polyester resins due to the presence of a tetracarboxylic dianhydride-derived structure that includes both a cardo structure and an ester structure. Whether the polyimide resin and polyester resin are compatible with each other is confirmed by preparing a 20 μm-thick film containing the polyimide resin and polyester resin. If the film is transparent and has a haze of 10% or less, the polyimide resin and polyester resin are deemed to be compatible. If the film's haze exceeds 10%, the polyimide resin and polyester resin are deemed to be incompatible.

[0119] The ratio of polyimide resin to polyester resin in the resin composition is not particularly limited. The composition ratio (weight ratio) of polyimide resin to polyester resin may be 2:98 to 98:2, 10:90 to 90:10, 25:75 to 75:25, or 40:60 to 60:40. The higher the ratio of polyimide resin, the higher the mechanical strength of molded articles such as films tends to be. The higher the ratio of polyester resin, the less coloring and the higher the transparency of molded articles such as films tends to be.

[0120] The resin composition may be a simple mixture of a polyimide resin and a polyester resin precipitated as solids, or a kneaded mixture of a polyimide resin and a polyester resin. Furthermore, when a polyimide resin solution is mixed with a poor solvent to precipitate the polyimide resin, a polyester resin may be mixed into the solution, and the resin composition, in which the polyimide resin and the polyester resin are mixed, may be precipitated as a solid (powder).

[0121] The resin composition may be a mixed solution containing a polyimide resin and a polyester resin. The method for mixing the resins is not particularly limited, and the resins may be mixed in a solid state or in a liquid state to form a mixed solution. A polyimide resin solution and a polyester resin solution may be prepared separately, and then the two may be mixed to form a mixed solution of the polyimide resin and the polyester resin.

[0122] The solvent for the solution containing the polyimide resin and the polyester resin may be any solvent that dissolves both the polyimide resin and the polyester resin, and examples thereof include amide solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone; ether solvents such as tetrahydrofuran and 1,4-dioxane; ketone solvents such as acetone, methyl ethyl ketone, methyl propyl ketone, methyl isopropyl ketone, methyl isobutyl ketone, diethyl ketone, cyclopentanone, cyclohexanone, and methylcyclohexanone; and alkyl halide solvents such as chloroform, 1,2-dichloroethane, 1,1,2,2-tetrachloroethane, chlorobenzene, dichlorobenzene, and methylene chloride.

[0123] Generally, polyimide resins have low solubility in solvents and are often soluble only in highly polar solvents. Therefore, amide-based solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone are preferred as solvents. The use of these solvents can improve the compatibility between polyimide resins and polyester resins. Furthermore, from the perspective of solvent removability when producing molded articles such as films, low-boiling non-amide solvents are preferred. Ketone-based solvents and alkyl halide solvents are preferred because they have excellent solubility in both polyimide resins and polyester resins and have low boiling points, making it easy to remove residual solvent during film production. The use of these solvents that readily dissolve polyimide resins reduces the viscosity of the resulting solution, resulting in improved handleability and reduced appearance defects such as unevenness when producing molded articles by film formation, etc.

[0124] Furthermore, a solution of a resin composition containing a polyimide resin and a polyester resin tends to have a lower solution viscosity than a solution of a polyimide resin alone at the same solid content concentration, which is advantageous in terms of ease of handling during transportation and the like, high coatability, and reduction of unevenness in film thickness.

[0125] The resin composition may contain organic or inorganic low molecular weight compounds, polymeric compounds (e.g., epoxy resins), etc. The resin composition may contain flame retardants, ultraviolet absorbers, crosslinking agents, dyes, pigments, surfactants, leveling agents, plasticizers, fine particles, sensitizers, etc. The fine particles include organic fine particles such as polystyrene and polytetrafluoroethylene, and inorganic fine particles such as colloidal silica, carbon, and layered silicates, and may have a porous or hollow structure. The fiber reinforcing material includes carbon fiber, glass fiber, aramid fiber, etc.

[0126] [Molded products and films] The above-mentioned composition can be used to form various molded articles. Molding methods include melt methods such as injection molding, transfer molding, press molding, blow molding, inflation molding, calendar molding, and melt extrusion molding. Resin compositions containing a polyimide resin and a polyester resin tend to have a lower melt viscosity than polyimide resin alone, and are excellent in moldability in injection molding, transfer molding, press molding, melt extrusion molding, and the like.

[0127] In one embodiment, the molded article is a film. The film molding method may be either a melting method or a solution method, but from the viewpoint of producing a film excellent in transparency and uniformity, the solution method in which a resin solution is applied to a support is preferred. In the solution method, a solution containing the above-mentioned polyimide resin and polyester resin is applied to a support, and the solvent is dried and removed to obtain a film.

[0128] The resin solution can be applied to a support by a known method using a bar coater, a comma coater, or the like. Examples of the support that can be used include a glass substrate, a metal substrate such as SUS, a metal drum, a metal belt, and a plastic film. From the viewpoint of improving productivity, it is preferable to use an endless support such as a metal drum or a metal belt, or a long plastic film as the support, and produce the film by a roll-to-roll method. When using a plastic film as the support, it is sufficient to appropriately select a material that is insoluble in the solvent of the resin solution.

[0129] It is preferable to heat the film when drying the solvent. The heating temperature is not particularly limited as long as it can remove the solvent and prevent discoloration of the resulting film, and is appropriately set between room temperature and about 250°C, with 50°C to 220°C being preferred. The heating temperature may be increased in stages. To increase the efficiency of solvent removal, the resin film may be peeled off from the support and dried after drying has progressed to a certain extent. To promote solvent removal, heating may be performed under reduced pressure. Since the polyimide resin and polyester resin are compatible with each other, the glass transition temperature is lower than that of the polyimide resin alone, making it possible to remove the solvent at a lower drying temperature than that of the polyimide resin alone, and as a result, it is possible to reduce discoloration of the film.

[0130] Although polyester resin films may have low mechanical strength, the strength of the film may be improved by adopting a compatible system of polyimide resin and polyester resin. For the purpose of improving the mechanical strength of the film, the film may be stretched in one or more directions. Stretching the film orients the polymer chains in the stretching direction, improving the strength of the film in the in-plane direction and tending to suppress the occurrence of breakage or cracks in the film.

[0131] In particular, in a compatible system of polyimide resin and polyester resin, the tensile modulus in the stretching direction tends to increase, and the flex resistance tends to improve accordingly.

[0132] For example, films used as cover films or substrate materials for foldable displays are repeatedly folded along the folding axis at the same location, and therefore are required to have high mechanical strength in a direction perpendicular to the folding axis. Therefore, by arranging the film so that the stretching direction is perpendicular to the folding axis, the film is less likely to break or crack at the folding location even when repeatedly folded, and a device with high bending resistance can be provided.

[0133] The film stretching method is not particularly limited. Various stretching methods such as free-end stretching, fixed-end stretching, free-end shrinkage, and fixed-end shrinkage are used. Among them, free-end stretching, typified by a method in which a film being transported is stretched in the transport direction by using a difference in peripheral speed between nip rolls before and after the film (so-called longitudinal stretching), or fixed-end stretching, typified by a method in which a film being transported is stretched in a direction perpendicular to the transport direction using a tenter clip device (so-called transverse stretching), is preferred from the viewpoint of unidirectionally orienting the molecules in the film.

[0134] The film stretching conditions (e.g., stretching direction, stretching temperature, stretching ratio) are not particularly limited. Stretching can be performed in various directions, such as the length direction, width direction, thickness direction, and oblique direction. The stretching temperature is not particularly limited, but is about ±40°C of the glass transition temperature of the film, and may be about 120 to 300°C, 150 to 250°C, or 180 to 230°C. The stretching ratio is not particularly limited, but is about 1 to 200%, and may be about 5 to 150%, 10 to 120%, or 20 to 100%. The tensile modulus in the stretching direction tends to increase as the stretching ratio increases. On the other hand, if the stretching ratio is excessively high, the mechanical strength in the direction perpendicular to the stretching direction tends to decrease, which may result in poor handling of the film.

[0135] The film may be biaxially stretched to increase the strength in any in-plane direction. The biaxial stretching may be simultaneous biaxial stretching or sequential biaxial stretching. In biaxial stretching, the stretching ratio in one direction and the stretching ratio in the perpendicular direction may be the same or different. When a difference in stretching ratio is made, the mechanical strength in the direction with the larger stretching ratio tends to be relatively larger. When a biaxially stretched film with anisotropic stretching ratio is used in a foldable device, it is preferable to arrange it so that the direction with the larger stretching ratio is perpendicular to the folding axis.

[0136] The thickness of the film is not particularly limited and may be appropriately set depending on the application. The thickness of the film is, for example, 5 to 300 μm. From the viewpoint of obtaining a film that is both self-supporting and flexible and has high transparency, the thickness of the film is preferably 10 μm to 200 μm, and may be 30 μm to 150 μm, 40 μm to 100 μm, or 50 μm to 80 μm. The thickness of the film used as a cover film for a display is preferably 20 μm or more. When the film is stretched, the thickness after stretching is preferably within the above range.

[0137] The haze of the film is preferably 10% or less, more preferably 5% or less, even more preferably 4% or less, and may be 3.5% or less, 3% or less, 2% or less, or 1% or less. The lower the film haze, the better. The lower the film haze, the less the image resolution is impaired when the film is used as a display film, which is preferable. In the present invention, since the polyimide resin and polyester resin are compatible, a film with low haze and high transparency can be obtained. It is preferable that the resin composition obtained by mixing the polyimide resin and polyester resin has a haze of 10% or less when a film with a thickness of 20 μm is produced.

[0138] The total light transmittance of the film is preferably 85% or more, more preferably 86% or more, even more preferably 87% or more, particularly preferably 88% or more, and may be 89% or more, or even 90% or more. A high total light transmittance of the film is preferable because it increases the brightness of the display when used as a display film. The resin composition obtained by mixing a polyimide resin and a polyester resin preferably has a total light transmittance of 85% or more when a film having a thickness of 20 μm is produced.

[0139] The yellowness index (YI) of the film is not particularly limited, but is preferably 20.0 or less, more preferably 10.0 or less, and even more preferably 5.0 or less, and may be 4.0 or less, 3.0 or less, 2.0 or less, 1.0 or less, or 0.0 or less. If the yellowness index (YI) is greater than 20.0, when the film is used as a display film, the display will take on a yellowish tinge, and the color reproducibility of the display will be reduced. It is preferable that the resin composition obtained by mixing a polyimide resin and a polyester resin has a yellowness index of 20.0 or less when a film having a thickness of 20 μm is produced. As described above, by mixing a polyimide and a polyester resin, a film with less coloration and a small YI can be obtained compared to when a polyimide resin is used alone.

[0140] The tensile modulus of the film is not particularly limited. From the viewpoint of strength, the tensile modulus of the film at room temperature is preferably 2.0 GPa or more, more preferably 3.0 GPa or more. The tensile modulus may be anisotropic, and the tensile modulus in at least one direction may be 3.0 GPa or more, 4.0 GPa or more, 5.0 GPa or more, 6.0 GPa or more, 6.5 GPa or more, or 7.0 GPa or more. The pencil hardness of the film is preferably 6B or more, more preferably 4B or more, and may be 2B or more, F or more, or 2H or more. In a compatible system of polyimide resin and polyester resin, the pencil hardness is unlikely to decrease even if the proportion of polyester resin is increased. Therefore, a film with little coloration and excellent transparency can be provided without significantly reducing the excellent mechanical strength unique to polyimide resin.

[0141] Films formed from resin compositions containing polyimide resins and polyester resins are suitable for use as display materials because they have little coloring and high transparency. In particular, films with high mechanical strength can be applied to surface components such as display cover windows. When used in practice, the film of the present invention may be provided with an antistatic layer, an easy-adhesion layer, a hard coat layer, an antireflection layer, or the like on its surface. [Example]

[0142] The following examples will be used to further explain the present invention, but the present invention is not limited to these examples.

[0143] [Preparation of polyimide resin] Dimethylformamide (DMF) was added to a separable flask and stirred under a nitrogen atmosphere. Diamine and tetracarboxylic dianhydride were added in the molar ratios shown in Table 2, followed by acetic acid. The mixture was stirred for 5 to 10 hours under a nitrogen atmosphere to allow the reaction to proceed. A polyamic acid solution with a solids concentration of 13% by weight was obtained. 5.5 g of pyridine was added to 100 g of the resulting polyamic acid solution, and after complete dispersion, 8.0 g of acetic anhydride was added and stirred at 90°C for 3 hours. After cooling to room temperature, 2-propyl alcohol (IPA) was added dropwise while stirring the solution to precipitate a polyimide resin. Further IPA was added, and the mixture was stirred for approximately 30 minutes. The mixture was then subjected to suction filtration using a Kiriyama funnel. The resulting solid was washed with IPA and then dried for 12 hours in a vacuum oven set at 120°C to obtain a polyimide resin.

[0144] [Preparation of Resin Composition (Solution) and Film Fabrication] <Polyimide and polyester resin composition> The polyimide resin polymerized above and a commercially available polyester resin were added in the solvents and weight ratios shown in Table 2 to prepare a resin solution with a solid content of 10% by weight. The commercially available polyester resins are as follows:

[0145] PEs1: OKP4HT (Osaka Gas Chemicals Co., Ltd., weight average molecular weight 38,000, Tg: 142°C) PEs2: Elitel UE3600 (manufactured by Unitika Ltd., weight average molecular weight 60,000, Tg: 75°C) PEs3: Elitel UE9200 (manufactured by Unitika Ltd., weight average molecular weight 39,000, Tg: 65°C)

[0146] The resin solution was applied to a non-alkali glass plate and dried by heating in air at 40°C, 60°C, 90°C, 120°C, and 150°C in that order for 15 minutes each to produce a film with a thickness of 32 μm to 77 μm.

[0147] [evaluation] <Haze, total light transmittance> The haze and total light transmittance (TT) of the films obtained in the above Preparation Examples were measured using a haze meter "HZ-V3" manufactured by Suga Test Instruments in accordance with JIS K7136 and JIS K7361-1.

[0148] <Weight average molecular weight> The polyester resin was dissolved in the eluent shown in Table 1 so that the concentration of the resin was 0.15 wt % relative to the solution, and then the weight average molecular weight was measured under the following conditions.

[0149] [Table 1]

[0150] In Table 2, the compounds are described by the following abbreviations. <Diamine> BAFL: 9,9-bis(4-aminophenyl)fluorene 4,4'-ODA: 4,4'-diaminodiphenyl ether

[0151] <Tetracarboxylic acid dianhydride> TBIS-DMPN: 5,5'-[cyclododecylidenebis(2-methyl-4,1-phenylene)]bis(1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxylate) BPZ-TME: 5,5'-[cyclohexylylenedi-4,1-phenylene]bis(1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxylate) TBIS‐MPN: 5,5′-[9H-fluoren-9-ylidenebis(2-methyl-4,1-phenylene)]bis(1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxylate) TBIS‐RXN: 5,5′-spiro[9H-fluorene-9,9′-[9H]xanthene]-3′,6′-diylbis(1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxylate) CBDA: 1,2,3,4-cyclobutanetetracarboxylic dianhydride BPAF: 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride TAHMBP: 2,2',3,3',5,5'-hexamethylbiphenyl-4,4'-diylbis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylate)

[0152] [Table 2]

[0153] The films containing polyimide resin and polyester resin shown in Examples 1 to 19 exhibited a haze of 10% or less and a total light transmittance (TT) of 85% or more. On the other hand, in Comparative Examples 1 to 6, in which BPAF, a tetracarboxylic dianhydride having a fluorene structure (an example of a cardo structure) but not an ester structure, was used, the polyimide resin did not exhibit compatibility with the polyester resin. Furthermore, in Comparative Examples 7 and 8, in which TAHMBP, a tetracarboxylic dianhydride having an ester structure but not a cardo structure, was used, the solubility of the polyimide resin itself was low and it was insoluble in the solvent.

Claims

1. A resin composition containing a polyimide resin and a polyester resin, the polyimide resin has a structure derived from a diamine and a structure derived from a tetracarboxylic dianhydride, the tetracarboxylic dianhydride includes a tetracarboxylic dianhydride having both a cardo structure and an ester structure, A resin composition characterized in that the weight average molecular weight of the polyester resin exceeds 10,000.

2. The resin composition according to claim 1 , wherein the cardo structure is a structure containing an alicyclic structure.

3. 2. The resin composition according to claim 1, wherein the polyimide resin and the polyester resin are compatible with each other in a composition ratio range of 2:98 to 98:

2.

4. Tetracarboxylic dianhydrides having both cardo and ester structures include 5,5'-[9H-fluoren-9-ylidenebis(2-methyl-4,1-phenylene)]bis(1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxylate), 5,5'-spiro[9H-fluorene-9,9'-[9H]xanthene]-3',6'-diylbis(1,3-dihydro-1,3-dioxo-5-isobenzofuran), 2. The resin composition according to claim 1, wherein the carboxylic acid ester is one or more selected from the group consisting of 5,5'-[cyclohexylylenedi-4,1-phenylene]bis(1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxylate), ... and 5,5'-[cyclododecylidenebis(2-methyl-4,1-phenylene)]bis(1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxylate).

5. 2. The resin composition according to claim 1, wherein the polyester resin has a structure derived from a dicarboxylic acid and a structure derived from a diol, and the diol has one or more diols selected from the group consisting of a diol having an alkylene structure or a cycloalkylene structure having 3 or more carbon atoms, a diol having a fluorene structure, and a diol having a bisphenol derivative structure.

6. 6. The resin composition according to claim 5, wherein the diol having a bisphenol derivative structure has a structure in which an alkylene oxide is added to two phenolic hydroxy groups of a bisphenol.

7. A molded article comprising the resin composition according to any one of claims 1 to 6.

8. A film comprising the resin composition according to any one of claims 1 to 6.

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