Resin film and method for producing same

Abstract

To provide a resin film which is excellent in heat resistance, keeps a low coefficient of linear expansion up to a high temperature region, has a high tensile elastic modulus, has a small ratio of coefficients of linear expansion in an MD direction and a TD direction of the resin film to the tensile elastic modulus, and has preferable physical property isotropy.SOLUTION: A method for manufacturing a resin film includes a step A of coating and drying a polyamide acid resin solution onto a support, and manufacturing a resin film laminate containing a solvent, a step B of peeling the support from the laminate, and obtaining a resin film containing a solvent, and a step C of performing a dehydration ring closing reaction while removing the solvent from the resin film containing the solvent, wherein the step C raises the temperature by a combination method of either or both of a step of raising a temperature at a temperature rise speed of 5-60°C / min, and a step of raising the temperature in a step manner with two or more steps, at least a part of the step C is performed by microwave heating, and the obtained polyimide resin film satisfies the following (1) to (2). (1) A temperature (A) at which a temperature dependent curve of tanδ that is a value obtained by dividing a loss elastic modulus by a storage elastic modulus becomes a peak is within a range of 250-500°C, and the temperature (A) at which the temperature dependent curve of the tanδ becomes a peak and a linear expansion coefficient inflection point temperature (B) have a relation of the following expression: (40+0.8×A)≤B<A, and (2) weight average molecular weight of the resin that is a raw material of the resin film is within a range of 50,000 to 500,000, and a molecular weight distribution that is a value obtained by dividing the weight average molecular weight by the number average molecular weight of the resin is within a range of 1.0 to 5.0.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a resin film and a method for producing the resin film, more specifically to a resin film having excellent heat resistance, a low coefficient of linear expansion even in a high temperature range, a high tensile modulus, a small ratio of the coefficient of linear expansion and the tensile modulus in the TD direction to the MD direction of the resin film, and excellent transparency with good isotropic physical properties of the resin film, and a method for producing the resin film. [Background technology]

[0002] In recent years, with the progress in miniaturization, weight reduction and convenience of mobile phones, digital cameras, display devices and various other electronic devices that are becoming more functional, there are high expectations for resin film substrate materials that offer excellent heat resistance, low linear expansion coefficient, high tensile modulus, flexibility, impact resistance and transparency to replace the hard, impact-vulnerable glass substrates that have been used traditionally.

[0003] Resin films are industrially produced by processing organic polymer resin materials into a film shape, and the film-forming method includes a melt film-forming method in which an organic polymer resin is melted and then extruded through a slit-shaped die, a solution film-forming method in which an organic polymer resin solution is uniformly applied to a support and the solvent is dried and volatilized, etc. Among organic polymer resin materials, polyimide resins and polyamideimide resins, which have particularly excellent heat resistance, are infusible or melt at very high temperatures, so that resin films are generally obtained by solution film-forming.

[0004] In such a solution casting method in which the coating is performed and the solvent is then dried and evaporated, uneven thickness and orientation can occur depending on the coating and drying conditions. For example, Patent Document 1 proposes reducing lateral unevenness in the longitudinal direction by reviewing coating conditions such as the support rotation speed.

[0005] Furthermore, in order to reduce the variation in film sagging, a method has been described in which it has been found that there is a correlation between sagging and the anisotropy index, the principal axis orientation coefficient, the thermal shrinkage rate, and the drying temperature, and by reducing the variation in the drying temperature in the width direction, the linear expansion coefficient, i.e., the variation in the dimensional change, is suppressed (Patent Document 2).

[0006] Patent Document 3 describes a production method for reducing the anisotropy of the linear expansion coefficient in the MD (travel direction) and TD (width direction) of a film by fixing both ends of the film and transporting it without slack in accordance with the width of the film that changes due to contraction and expansion during the heating process, when producing a polyimide film that experiences a significant decrease in elastic modulus above the glass transition temperature. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2013-203838 A [Patent Document 2] JP 2018-70842 A [Patent Document 3] JP 2000-290401 A Summary of the Invention [Problem to be solved by the invention]

[0008] Resin films used as replacements for glass substrates in order to directly form functional elements such as electrodes and display elements on their surfaces are required to have high tensile modulus, low CTE, and heat and chemical resistance. Polyimide, polyamide-imide, and polyamic acid, which is the precursor of polyimide, are suitable resins for such resin films. They have high molecular weights due to their high content of rigid molecular chains with low mobility, and as a result, they have a wide molecular weight distribution when polymerized.

[0009] When such a resin solution is applied and dried, if it contains a large amount of rigid molecular chains with a high molecular weight, a wide molecular weight distribution, and low mobility, the denser higher-order structure that reflects the orientation direction, degree of orientation, and entanglement of the molecules that is formed first will differ from the sparser higher-order structure that reflects the orientation direction, degree of orientation, and entanglement of the molecules that is formed later as the solvent is removed, and each domain will be formed.

[0010] When a film is continuously manufactured industrially by coating and drying a resin solution, the film is transported to a heating furnace by roll-to-roll, and the film has process and shape anisotropy in the MD (travel direction) and TD (width direction). Such process and shape anisotropy affects the formation of domains with different higher-order structures as mentioned above, and the orientation direction, degree of orientation, and entanglement of molecules are biased in either the width direction or the travel direction, resulting in variation in dimensional change and anisotropy of physical properties.

[0011] The method of Patent Document 1 reduces the unevenness of the lateral stripes in the longitudinal direction and suppresses the anisotropy of physical properties caused by the difference in thickness, but does not suppress the anisotropy of physical properties caused by the bias of the orientation direction, degree of orientation, and entanglement of molecules inside the film. In addition, Patent Document 2 achieves a heat shrinkage rate of 0.05% or less in the longitudinal and transverse directions of the film by performing drying under conditions where the unevenness of the drying temperature in the transverse direction is 20°C or less, but in the examples, the ratio of the maximum heat shrinkage rate in the transverse direction to the longitudinal direction is a maximum of 0.33, and the anisotropy of the heat shrinkage rate in the MD direction (longitudinal direction) and TD direction (transverse direction) is not suppressed.

[0012] In the polyimide film manufacturing method described in Patent Document 3, the film is intentionally shrunk in the width direction in the early steps in accordance with the process of passing the film successively through furnaces of gradually increasing temperature, and in the latter steps, the film is expanded in the width direction at the stage where slack occurs in the film, thereby manufacturing the film without slack and reducing the anisotropy in the width direction and travel direction of the film. However, in the examples, the ratio of the linear expansion coefficient in the MD (machine direction) direction and the TD (transverse direction) direction of the polyimide film is 0.96, and further reduction of anisotropy remains an issue.

[0013] Thus, while polyimide has excellent heat resistance, a low coefficient of linear expansion, and a high tensile modulus, it has a high molecular weight, a wide molecular weight distribution, and rigid molecular chains with low mobility. As a result, domains with different higher-order structures that reflect the orientation direction, degree of orientation, and entanglement of the molecules are formed as the solvent dries. Therefore, it was a challenge to obtain a resin film that maintains a low coefficient of linear expansion up to high temperature ranges, has a small ratio of the coefficient of linear expansion and tensile modulus in the MD and TD directions of the resin film, and has good isotropic physical properties. [Means for solving the problem]

[0014] As a result of extensive investigations aimed at solving the above problems, the present inventors have found that such problems can be solved and have arrived at the present invention. That is, the present invention has the following configuration.

[0015] A resin film that satisfies the following (1) and (2). (1) The temperature (A) at which the temperature-dependent curve of tan δ, which is the value obtained by dividing the loss modulus by the storage modulus, reaches a peak is in the range of 250 to 500°C, and the temperature (A) at which the temperature-dependent curve of tan δ reaches a peak and the inflection point temperature (B) of the linear expansion coefficient are in the following relationship: (40+0.8×A) ≦ B < A (2) The weight average molecular weight of the resin that is the raw material of the resin film is within the range of 50,000 to 500,000, and the molecular weight distribution, which is the value obtained by dividing the weight average molecular weight by the number average molecular weight of the resin, is within the range of 1.0 to 5.0.

[0016] It is preferable that the resin film further satisfies (3) and (4). (3) The linear expansion coefficient measured in the range of 35 to 200°C in both the MD and TD directions is in the range of -5 ppm / °C to +55 ppm / °C, and the ratio of the linear expansion coefficient in the TD direction to the MD direction is in the range of 0.97 to 1.03. (4) The tensile modulus in both the MD and TD directions is in the range of 2 to 20 GPa, and the ratio of the tensile modulus in the TD direction to the tensile modulus in the MD direction is in the range of 0.97 to 1.03.

[0017] The resin film preferably has a yellow index of 10 or less, a light transmittance at a wavelength of 400 nm of 70% or more, and a total light transmittance of 85% or more.

[0018] A process A of applying a resin solution onto a support and drying the same to prepare a resin film laminate containing a solvent; A step B of peeling the support from the laminate to obtain a resin film containing a solvent; A step C of removing the solvent from the resin film containing the solvent, or performing a dehydration ring-closing reaction while removing the solvent, The method for producing the resin film, wherein at least a part of the step C is carried out by microwave heating.

[0019] The resin solution preferably contains at least one resin selected from the group consisting of polyamic acid, polyimide, and polyamideimide, and a solvent having a dipole moment in the range of 3.0 to 6.0 D and capable of dissolving the resin. Effect of the Invention

[0020] According to the present invention, even when a resin solution consisting of polyimide, polyamideimide, or polyamic acid, which is a precursor of polyimide and has a high molecular weight, a wide molecular weight distribution, and a large amount of rigid molecular chains with low mobility, is applied and dried, it is possible to obtain a resin film which has excellent heat resistance, maintains a low linear expansion coefficient even in a high temperature range, has a high tensile modulus, a small ratio between the linear expansion coefficient and the tensile modulus in the MD direction and the TD direction of the resin film, and is excellent in isotropy of physical properties and excellent transparency. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] The resin film and the method for producing the resin film according to the embodiment of the present invention will be described below. The resin film of the present invention is a film that satisfies the following (1) and (2).

[0022] (1) The temperature (A) at which the temperature dependence curve of tan δ, which is the value obtained by dividing the loss modulus by the storage modulus, reaches its peak is in the range of 250 to 500°C, and the temperature at which the temperature dependence curve of tan δ reaches its peak and the inflection point temperature (B) of the linear expansion coefficient are related by the following formula: (40+0.8×A) ≦ B < A

[0023] The temperature-dependent curve of tan δ with respect to temperature is an index of the change in viscoelasticity of the resin due to temperature change, and when the temperature at which the temperature-dependent curve of tan δ is at its peak is exceeded, the viscosity of the resin increases significantly and the strength decreases. Therefore, from the viewpoint of heat resistance required for a glass substrate replacement used in mobile phones, digital cameras, display devices, and various other electronic devices, the temperature at which the temperature-dependent curve of tan δ is at its peak must be in the range of 250 to 500°C, preferably in the range of 260 to 480°C, and more preferably in the range of 270 to 460°C. The temperature at which the temperature-dependent curve of tan δ of the resin film is at its peak is measured according to the method described in the Examples.

[0024] Resin films expand and contract with temperature changes, and the linear expansion coefficient is an index of this change. The linear expansion coefficient of a resin film is not always constant over the measurement temperature range, but becomes high at a specific temperature depending on the resin film. This specific temperature is called the linear expansion coefficient inflection point temperature.

[0025] The resin film of the present invention is preferably obtained by applying and drying a resin solution. When applying and drying a resin solution to obtain a resin film, as the solvent is removed, a denser higher-order structure reflecting the orientation direction, orientation degree, and entanglement of the molecules formed first, and a sparser higher-order structure reflecting the orientation direction, orientation degree, and entanglement of the molecules formed later are generated, and each domain is formed. At this time, if the resin has a higher molecular weight, a wider molecular weight distribution, and contains more rigid molecular chains with low mobility, the density of the higher-order structures of each domain will be more significantly different.

[0026] The temperature at which the temperature dependence curve of tan δ peaks and the inflection point temperature of the linear expansion coefficient are both physical property inflection point temperatures, but the temperature at which the temperature dependence curve of tan δ peaks reflects the average physical property change of the high-order structure with different sparseness and density formed at the stage of resin film production, whereas the linear expansion coefficient reflects the physical property change of the sparse high-order structure formed at the stage of resin film production, so the inflection point temperature of the linear expansion coefficient (B) is always lower than the temperature at which the temperature dependence curve of tan δ peaks (B < A). In addition, the value obtained by subtracting the inflection point temperature of the linear expansion coefficient from the temperature at which the temperature dependence curve of tan δ peaks tends to be larger as the temperature at which the temperature dependence curve of tan δ peaks increases. In order to maintain the low linear expansion coefficient required for glass substrate replacement and the low linear expansion coefficient even at high temperatures during the substrate processing process, it is preferable that the inflection point temperature of the linear expansion coefficient (B) is higher, and specifically, it is preferable that the formula (40+0.8×A) ≦ B is satisfied for the temperature at which the temperature dependence curve of tan δ peaks (A). The inflection point temperature of the linear expansion coefficient of the resin film is measured by the method described in the examples.

[0027] (2) The weight average molecular weight of the resin that is the raw material of the resin film is within the range of 50,000 to 500,000, and the molecular weight distribution, which is the value obtained by dividing the weight average molecular weight by the number average molecular weight of the resin, is within the range of 1.0 to 5.0.

[0028] The weight average molecular weight of the resin, which is the raw material of the resin film of the present invention, is in the range of 50,000 to 500,000, more preferably 80,000 to 400,000, even more preferably 100,000 to 300,000, and even more preferably 120,000 to 200,000. If the weight average molecular weight is equal to or higher than the above lower limit, the high tensile modulus, flexibility, and impact resistance required for a glass substrate replacement can be satisfied. If the weight average molecular weight is equal to or lower than the above upper limit, the above formula can be easily satisfied. In addition, it is preferable that the weight average molecular weight of the resin in the resin solution is within the above range.

[0029] The molecular weight distribution, which is the value obtained by dividing the weight average molecular weight by the number average molecular weight of the resin that is the raw material of the resin film of the present invention, is in the range of 1.0 to 5.0, more preferably 1.5 to 4.5, and even more preferably 2.0 to 4.0. If the molecular weight distribution is equal to or higher than the above lower limit, the cost of resin purification can be reduced, and if the molecular weight distribution is equal to or lower than the above upper limit, it is easy to satisfy the above formula. The weight average molecular weight and molecular weight distribution of the resin that is the raw material of the resin film are measured by the method described in the Examples.

[0030] The resin film of the present invention preferably further satisfies the following (3) and (4).

[0031] (3) The linear expansion coefficients measured in the range of 35 to 200°C in both the MD and TD directions are in the range of -5 ppm / °C to +55 ppm / °C, and the ratio of the linear expansion coefficients in the TD direction to the MD direction is in the range of 0.97 to 1.03.

[0032] The average linear expansion coefficient of the resin film in the present invention measured in the range of 35 to 200°C in both the MD and TD directions is preferably -5 ppm / °C to +55 ppm / °C, more preferably -4 ppm / °C to +45 ppm / °C, and even more preferably -3 ppm / °C to +35 ppm / °C. When the linear expansion coefficient is within the above range, the difference in the linear expansion coefficient with the functional element can be kept small, and peeling between the resin film and the functional element can be prevented even when subjected to a process in which heat is applied, resulting in excellent processability.

[0033] The ratio of the linear expansion coefficient of the resin film in the present invention in the TD direction to the MD direction is preferably in the range of 0.97 to 1.03. More preferably, it is 0.975 to 1.025, and even more preferably, it is 0.98 to 1.02. When the ratio of the linear expansion coefficient in the TD direction to the MD direction is within the above range, the resin film can be subjected to a processing process with a functional element without distinguishing between the MD direction and the TD direction, and workability and yield can be improved. The linear expansion coefficient of the resin film is measured by the method described in the Examples.

[0034] (4) The tensile modulus in both the MD and TD directions is in the range of 2 to 20 GPa, and the ratio of the tensile modulus in the TD direction to the tensile modulus in the MD direction is in the range of 0.97 to 1.03.

[0035] The tensile modulus of the resin film of the present invention is preferably in the range of 2 to 20 GPa in both the MD and TD directions. More preferably, it is 2.5 to 15 GPa, and further preferably, it is 3 to 10 GPa. If the tensile modulus is equal to or higher than the lower limit, peeling of the resin film and the functional element can be prevented, and the resin film has excellent handleability. If the tensile modulus is equal to or lower than the upper limit, the resin film can be used as a flexible film.

[0036] The ratio of the tensile modulus of elasticity in the TD direction to that in the MD direction of the resin film in the present invention is preferably in the range of 0.97 to 1.03. More preferably, it is 0.975 to 1.025, and even more preferably, it is 0.98 to 1.02. When the ratio of the tensile modulus of elasticity in the TD direction to that in the MD direction is within the above range, the resin film can be subjected to a processing process with a functional element without distinguishing between the MD direction and the TD direction, and workability and yield can be improved. The tensile modulus of elasticity of the resin film is measured by the method described in the Examples.

[0037] Since the resin film of the present invention is mainly used for the front panel and the periphery of electrodes of image display devices such as touch panels and displays, the yellowness index (yellow index) is preferably 10 or less, more preferably 7 or less, even more preferably 5 or less, and even more preferably 3 or less. The lower limit of the yellowness of the resin film is not particularly limited, but for use as a flexible electronic device, it is preferably 0.1 or more, more preferably 0.2 or more, and even more preferably 0.3 or more. The yellowness index (yellow index) of the resin film is measured according to the method described in the Examples.

[0038] Since the resin film of the present invention is mainly used for the front panel and the periphery of electrodes of image display devices such as touch panels and displays, the light transmittance at a wavelength of 400 nm is preferably 70% or more, more preferably 72% or more, even more preferably 75% or more, and even more preferably 80% or more. The upper limit of the light transmittance at a wavelength of 400 nm of the resin film is not particularly limited, but in order to be used as a flexible electronic device, it is preferably 99% or less, more preferably 98% or less, and even more preferably 97% or less. The method for measuring the light transmittance at a wavelength of 400 nm of the resin film is the method described in the Examples.

[0039] Since the resin film of the present invention is mainly used for the front panel and the periphery of electrodes of image display devices such as touch panels and displays, the total light transmittance is preferably 85% or more, more preferably 86% or more, even more preferably 87% or more, and even more preferably 88% or more. The upper limit of the total light transmittance of the resin film is not particularly limited, but for use as a flexible electronic device, it is preferably 99% or less, more preferably 98% or less, and even more preferably 97% or less. The method for measuring the total light transmittance of the resin film is the method described in the Examples.

[0040] The resin film of the present invention is preferably obtained by applying and drying a resin solution so as to reach a desired temperature at which the temperature dependence curve of tan δ reaches a peak. As the resin solution, it is preferable to use a resin solution containing at least one resin selected from the group consisting of polyamic acid, polyimide, and polyamideimide. The resin solution can be obtained by any of the following manufacturing methods.

[0041] The polyamic acid solution can be obtained by stirring and / or mixing diamines and tetracarboxylic acids in a solvent and polymerizing the mixture while forming amide bonds through a condensation reaction.

[0042] The first method of obtaining a polyimide solution is to heat, stir, and / or mix diamines and tetracarboxylic acids in a solvent, and increase the molecular weight while forming imide bonds in one step by a dehydration ring-closing reaction.The second method is to add an imidization promoter and an imidization agent to the above-mentioned polyamic acid solution, and increase the molecular weight while stirring and / or mixing, and increase the molecular weight while forming imide bonds in two steps by a dehydration ring-closing reaction.

[0043] A polyamideimide solution can be obtained by heating, stirring and / or mixing diisocyanates and tricarboxylic acids in a solvent, while forming amide bonds and imide bonds in a single step by a decarboxylation reaction, thereby increasing the molecular weight.

[0044] When the above-mentioned polyamic acid, polyimide, and polyamideimide are made to have a high molecular weight, dicarboxylic acids can be used as copolymerization components within the range that does not impair the properties of the resin solution and the resin film.

[0045] The resin solution used in the present invention can also be obtained by pouring the resin solution obtained above into a poor solvent to precipitate the resin, followed by washing, filtering and drying to obtain a resin solid, or by casting and drying the resin solution to obtain a resin solid, and dissolving the resin solid again in a soluble solvent.

[0046] As the tetracarboxylic acids, tricarboxylic acids, and dicarboxylic acids, aromatic tetracarboxylic acids (including their acid anhydrides), aliphatic tetracarboxylic acids (including their acid anhydrides), alicyclic tetracarboxylic acids (including their acid anhydrides), aromatic tricarboxylic acids (including their acid anhydrides), aliphatic tricarboxylic acids (including their acid anhydrides), alicyclic tricarboxylic acids (including their acid anhydrides), aromatic dicarboxylic acids, aliphatic dicarboxylic acids, alicyclic dicarboxylic acids, and the like, which are usually used in polyimide synthesis and polyamideimide synthesis, can be used. Among them, aromatic tetracarboxylic acid anhydrides and alicyclic tetracarboxylic acid anhydrides are preferred, aromatic tetracarboxylic acid anhydrides are more preferred from the viewpoint of heat resistance, and alicyclic tetracarboxylic acids are more preferred from the viewpoint of light transmittance. When the tetracarboxylic acids are acid anhydrides, the anhydride structure may be one or two in the molecule, but preferably has two anhydride structures (dianhydrides). Tetracarboxylic acids, tricarboxylic acids, and dicarboxylic acids may be used alone or in combination of two or more.

[0047] Examples of aromatic tetracarboxylic acids for obtaining a colorless and highly transparent polyimide in the present invention include 4,4'-(2,2-hexafluoroisopropylidene)diphthalic acid, 4,4'-oxydiphthalic acid, 3,4'-oxydiphthalic acid, bis(1,3-dioxo-1,3-dihydro-2-benzofuran-5-carboxylic acid)1,4-phenylene, bis(1,3-dioxo-1,3-dihydro-2-benzofuran-5-yl)benzene-1,4-dicarboxylate, 4,4'-[4,4'-(3-oxo-1,3-dihydro-2-benzofuran-1,1 -diyl)bis(benzene-1,4-diyloxy)]dibenzene-1,2-dicarboxylic acid, 3,3',4,4'-benzophenonetetracarboxylic acid, 4,4'-[(3-oxo-1,3-dihydro-2-benzofuran-1,1-diyl)bis(toluene-2,5-diyloxy)]dibenzene-1,2-dicarboxylic acid, 4,4'-[(3-oxo-1,3-dihydro-2-benzofuran-1,1-diyl)bis(1,4-xylene-2,5-diyloxy)]dibenzene-1,2-dicarboxylic acid, 4,4'-[4,4'-(3-oxo-1, 3-dihydro-2-benzofuran-1,1-diyl)bis(4-isopropyl-toluene-2,5-diyloxy)]dibenzene-1,2-dicarboxylic acid, 4,4'-[4,4'-(3-oxo-1,3-dihydro-2-benzofuran-1,1-diyl)bis(naphthalene-1,4-diyloxy)]dibenzene-1,2-dicarboxylic acid, 4,4'-[4,4'-(3H-2,1-benzoxathiol-1,1-dioxide-3,3-diyl)bis(benzene-1,4-diyloxy)]dibenzene-1,2-dicarboxylic acid, 4,4'-benzo 4,4'-[(3H-2,1-benzoxathiol-1,1-dioxide-3,3-diyl)bis(toluene-2,5-diyloxy)]dibenzene-1,2-dicarboxylic acid, 4,4'-[(3H-2,1-benzoxathiol-1,1-dioxide-3,3-diyl)bis(1,4-xylene-2,5-diyloxy)]dibenzene-1,2-dicarboxylic acid, 4,4'-[4,4'-(3H-2,1-benzoxathiol-1,1-dioxide-3,3-diyl)bis(4-isopropyl-toluene-2,5-diyloxy)]dibenzene-1,2-dicarboxylic acid, 4,4'-[4,4'-(3H-2,1-benzoxathiol-1,1-dioxide-3,3-diyl)bis(naphthalene-1,4-diyloxy)]dibenzene-1,2-dicarboxylic acid, 3,3',4,4'-diphenylsulfonetetracarboxylic acid, 3,3',4,4'-biphenyltetracarboxylic acid, 2,3,3',4'-biphenyltetracarboxylic acid, 2,2',3, Examples of the tetracarboxylic acid include 3'-biphenyltetracarboxylic acid, 2,2'-diphenoxy-4,4',5,5'-biphenyltetracarboxylic acid, pyromellitic acid, 4,4'-[spiro(xanthene-9,9'-fluorene)-2,6-diylbis(oxycarbonyl)]diphthalic acid, and 4,4'-[spiro(xanthene-9,9'-fluorene)-3,6-diylbis(oxycarbonyl)]diphthalic acid, and their acid anhydrides. Among these, dianhydrides having two acid anhydride structures are preferred, and 4,4'-(2,2-hexafluoroisopropylidene)diphthalic dianhydride and 4,4'-oxydiphthalic dianhydride are particularly preferred. The aromatic tetracarboxylic acids may be used alone or in combination of two or more. When heat resistance is important, the aromatic tetracarboxylic acids preferably account for, for example, 50% by mass or more of the total tetracarboxylic acids, more preferably 60% by mass or more, even more preferably 70% by mass or more, and even more preferably 80% by mass or more.

[0048] Examples of alicyclic tetracarboxylic acids include 1,2,3,4-cyclobutane tetracarboxylic acid, 1,2,3,4-cyclopentane tetracarboxylic acid, 1,2,3,4-cyclohexane tetracarboxylic acid, 1,2,4,5-cyclohexane tetracarboxylic acid, 3,3',4,4'-bicyclohexyl tetracarboxylic acid, bicyclo[2,2,1]heptane-2,3,5,6-tetracarboxylic acid, bicyclo[2,2,2]octane-2,3,5,6-tetracarboxylic acid, and bicyclo[2,2,2]oct-7-ene-2,3,5,6-tetracarboxylic acid. carboxylic acid, tetrahydroanthracene-2,3,6,7-tetracarboxylic acid, tetradecahydro-1,4:5,8:9,10-trimethanoanthracene-2,3,6,7-tetracarboxylic acid, decahydronaphthalene-2,3,6,7-tetracarboxylic acid, decahydro-1,4:5,8-dimethanonaphthalene-2,3,6,7-tetracarboxylic acid, decahydro-1,4-ethano-5,8-methanonaphthalene-2,3,6,7-tetracarboxylic acid, norbornane-2-spiro-α-cyclopentanone-α'-spiro-2''-norbornane -5,5'',6,6''-tetracarboxylic acid (also known as "norbornane-2-spiro-2'-cyclopentanone-5'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic acid"), methylnorbornane-2-spiro-α-cyclopentanone-α'-spiro-2''-(methylnorbornane)-5,5'',6,6''-tetracarboxylic acid, norbornane-2-spiro-α-cyclohexanone-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic acid (also known as "norbornane-2-spiro pyro-2'-cyclohexanone-6'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic acid), methylnorbornane-2-spiro-α-cyclohexanone-α'-spiro-2''-(methylnorbornane)-5,5'',6,6''-tetracarboxylic acid, norbornane-2-spiro-α-cyclopropanone-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic acid, norbornane-2-spiro-α-cyclobutanone-α'-spiro-2''-norbornane-5,5'',6,6''-Tetracarboxylic acid, norbornane-2-spiro-α-cycloheptanone-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic acid, norbornane-2-spiro-α-cyclooctanone-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic acid, norbornane-2-spiro-α-cyclononanone-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic acid, norbornane-2-spiro-α-cyclodecanone-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic acid, norbornane-2-spiro-α-cycloundecanone-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic acid, norbornane-2-spiro-α-cyclododecanone-α'-spiro-2''-norbornane-5,5'' ,6,6''-tetracarboxylic acid, norbornane-2-spiro-α-cyclotridecanone-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic acid, norbornane-2-spiro-α-cyclotetradecanone-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic acid, norbornane-2-spiro-α-cyclopentadecanone-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic acid, norbornane-2-spiro-α-(methylcyclopentanone)-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic acid, and norbornane-2-spiro-α-(methylcyclohexanone)-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic acid, and the like tetracarboxylic acids and their acid anhydrides. Among these, dianhydrides having two acid anhydride structures are preferred, and in particular, 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,3,4-cyclohexanetetracarboxylic dianhydride, and 1,2,4,5-cyclohexanetetracarboxylic dianhydride are preferred, and 1,2,3,4-cyclobutanetetracarboxylic dianhydride and 1,2,4,5-cyclohexanetetracarboxylic dianhydride are more preferred, and 1,2,3,4-Cyclobutanetetracarboxylic dianhydride is more preferred. These may be used alone or in combination of two or more. When transparency is important, the alicyclic tetracarboxylic acids preferably account for 50% by mass or more of the total tetracarboxylic acids, more preferably 60% by mass or more, even more preferably 70% by mass or more, and even more preferably 80% by mass or more.

[0049] Examples of tricarboxylic acids include aromatic tricarboxylic acids such as trimellitic acid, 1,2,5-naphthalene tricarboxylic acid, diphenyl ether-3,3',4'-tricarboxylic acid, and diphenyl sulfone-3,3',4'-tricarboxylic acid, or hydrogenated products of the aromatic tricarboxylic acids such as hexahydrotrimellitic acid, alkylene glycol bistrimellitates such as ethylene glycol bistrimellitate, propylene glycol bistrimellitate, 1,4-butanediol bistrimellitate, and polyethylene glycol bistrimellitate, and monoanhydrides and esterified products thereof. Among these, monoanhydrides having one acid anhydride structure are preferred, and trimellitic anhydride and hexahydrotrimellitic anhydride are particularly preferred. These may be used alone or in combination.

[0050] Examples of dicarboxylic acids include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid, and 4,4'-oxydibenzenecarboxylic acid, or hydrogenated products of the aromatic dicarboxylic acids such as 1,6-cyclohexanedicarboxylic acid, oxalic acid, succinic acid, glutaric acid, adipic acid, heptanedioic acid, octanedioic acid, azelaic acid, sebacic acid, undecadioic acid, dodecanedioic acid, 2-methylsuccinic acid, and acid chlorides or esters thereof. Among these, aromatic dicarboxylic acids and hydrogenated products thereof are preferred, and terephthalic acid, 1,6-cyclohexanedicarboxylic acid, and 4,4'-oxydibenzenecarboxylic acid are particularly preferred. The dicarboxylic acids may be used alone or in combination.

[0051] The diamines or diisocyanates for obtaining the colorless and highly transparent polyimide of the present invention are not particularly limited, and aromatic diamines, aliphatic diamines, alicyclic diamines, aromatic diisocyanates, aliphatic diisocyanates, alicyclic diisocyanates, etc., which are usually used in polyimide synthesis and polyamideimide synthesis, can be used. From the viewpoint of heat resistance, aromatic diamines are preferred, and from the viewpoint of transparency, alicyclic diamines are preferred. In addition, when aromatic diamines having a benzoxazole structure are used, it is possible to develop high heat resistance, high elastic modulus, low heat shrinkage, and low linear expansion coefficient. The diamines and diisocyanates may be used alone or in combination of two or more.

[0052] Examples of aromatic diamines include 2,2'-dimethyl-4,4'-diaminobiphenyl, 1,4-bis[2-(4-aminophenyl)-2-propyl]benzene, 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 4,4'-bis(4-aminophenoxy)biphenyl, 4,4'-bis(3-aminophenoxy)biphenyl, bis[4-(3-aminophenoxy)phenyl]ketone, and bis[4-(3-aminophenoxy)phenyl]. Sulfide, bis[4-(3-aminophenoxy)phenyl]sulfone, 2,2-bis[4-(3-aminophenoxy)phenyl]propane, 2,2-bis[4-(3-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, m-phenylenediamine, o-phenylenediamine, p-phenylenediamine, m-aminobenzylamine, p-aminobenzylamine, 4-amino-N-(4-aminophenyl)benzamide, 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4, 4'-Diaminodiphenyl ether, 2,2'-trifluoromethyl-4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl sulfide, 3,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfoxide, 3,4'-diaminodiphenyl sulfoxide, 4,4'-diaminodiphenyl sulfoxide, 3,3'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminobenzo Phenone, 3,4'-diaminobenzophenone, 4,4'-diaminobenzophenone, 3,3'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, bis[4-(4-aminophenoxy)phenyl]methane, 1,1-bis[4-(4-aminophenoxy)phenyl]ethane, 1,2-bis[4-(4-aminophenoxy)phenyl]ethane, 1,1-bis[4-(4-aminophenoxy)phenyl]propane, 1,2-bis[4-(4-aminophenoxy)phenyl]propane, 1,3-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 1,1-bis[4-(4-aminophenoxy)phenyl]butane, 1,3-bis[4-(4-aminophenoxy)phenyl]butane, 1,4-bis[4-(4-aminophenoxy)phenyl]butane, 2,2-bis[4-(4-aminophenoxy)phenyl]butane, 2,3-bis[4-(4-aminophenoxy)phenyl]butane, 2-[4-(4-aminophenoxy)phenyl]-2-[4-(4-aminophenoxy )-3-methylphenyl]propane, 2,2-bis[4-(4-aminophenoxy)-3-methylphenyl]propane, 2-[4-(4-aminophenoxy)phenyl]-2-[4-(4-aminophenoxy)-3,5-dimethylphenyl]propane, 2,2-bis[4-(4-aminophenoxy)-3,5-dimethylphenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, 1,4-bis(3-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 4,4'-bis(4-aminophenoxy)biphenyl, bis[4-(4-aminophenoxy)phenyl]ketone, bis[4-(4-aminophenoxy)phenyl]sulfide, bis[4-(4-aminophenoxy)phenyl]sulfoxide, bis[4-(4-aminophenoxy)phenyl]sulfone, bis[4-(3-aminophenoxy)phenyl]ether, bis[4-(4-aminophenoxy)phenyl]ether, 1,3-bis[4-(4-aminophenoxy)benzoyl]benzene, 1,3-bis [4-(3-aminophenoxy)benzoyl]benzene, 1,4-bis[4-(3-aminophenoxy)benzoyl]benzene, 4,4'-bis[(3-aminophenoxy)benzoyl]benzene, 1,1-bis[4-(3-aminophenoxy)phenyl]propane, 1,3-bis[4-(3-aminophenoxy)phenyl]propane, 3,4'-diaminodiphenyl sulfide, 2,2-bis[3-(3-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, bis[4-(3-aminophenoxy)phenyl]methane, 1,1-bis[4-(3-aminophenoxy)phenyl]ethane, 1,2-bis[4-(3-aminophenoxy)phenyl]ethane, bis[4-(3-aminophenoxy)phenyl]sulfoxide, 4,4'-bis[3-(4-aminophenoxy)benzoyl]diphenyl ether, 4,4'-bis[3-(3-aminophenoxy)benzoyl]diphenyl ether, 4,4'-bis[4-(4-amino-α,α-dimethylbenzyl)phenoxy]benzophenone, 4,4'-bis[4-(4-amino-α,α-dimethylbenzyl)phenoxy]diphenyl Nilsulfone, bis[4-{4-(4-aminophenoxy)phenoxy}phenyl]sulfone, 1,4-bis[4-(4-aminophenoxy)phenoxy-α,α-dimethylbenzyl]benzene, 1,3-bis[4-(4-aminophenoxy)phenoxy-α,α-dimethylbenzyl]benzene, 1,3-bis[4-(4-amino-6-trifluoromethylphenoxy)-α,α-dimethylbenzyl]benzene, 1,3-bis[4-(4-amino-6-fluorophenoxy)-α,α-dimethylbenzyl]benzene, 1,3-bis[4-(4-amino -6-methylphenoxy)-α,α-dimethylbenzyl]benzene, 1,3-bis[4-(4-amino-6-cyanophenoxy)-α,α-dimethylbenzyl]benzene, 3,3'-diamino-4,4'-diphenoxybenzophenone, 4,4'-diamino-5,5'-diphenoxybenzophenone, 3,4'-diamino-4,5'-diphenoxybenzophenone, 3,3'-diamino-4-phenoxybenzophenone, 4,4'-diamino-5-phenoxybenzophenone, 3,4'-diamino-4-phenoxybenzophenone, 3,4'-diamino 3,3'-diamino-4,4'-diamino-5,5'-diamino-4,5'-diamino-4,5'-diamino-4,5'-diamino-5,3'-diamino-4-biphenoxybenzophenone, 4,4'-diamino-5-biphenoxybenzophenone, 3,4'-diamino-4-biphenoxybenzophenone, 3,4'-diamino-5'-biphenoxybenzophenone, 1,3-bis(3-amino-4-phenoxybenzoyl)benzene, 1,4-bis(3-amino-4-phenoxybenzoyl)benzene, 1,3-bis(4-amino-5-phenoxybenzoyl)benzene, 1,4-bis(4-amino-5-phenoxybenzoyl)benzene, 1,3-bis(3-amino-4-biphenoxybenzoyl)benzene, 1,4-bis(3-amino-4-biphenoxybenzoyl)benzene, 1,3-bis(4-amino-5-biphenoxybenzoyl)benzene, 1,4-bis(4-amino-5-biphenoxybenzoyl)benzene, 2,6-bis[4-(4-amino-α,α-dimethylbenzyl)phenoxy]benzonitrile, 4,4'-[9H-fluorene-9,9-diyl]bisaniline (also known as "9,9-bis(4-aminophenyl)fluorene"), spiro(xanthene-9,9'-fluorene)-2,6-diylbis (oxycarbonyl)]bisaniline, 4,4'-[spiro(xanthene-9,9'-fluorene)-2,6-diylbis(oxycarbonyl)]bisaniline, 4,4'-[spiro(xanthene-9,9'-fluorene)-3,6-diylbis(oxycarbonyl)]bisaniline, 9,10-bis(4-aminophenyl)adenine, 2,4-bis(4-aminophenyl)cyclobutane-1,3-dicarboxylate, and aromatic diamines in which some or all of the hydrogen atoms on the aromatic ring of the above-mentioned aromatic diamines are substituted with halogen atoms, alkyl or alkoxy groups having 1 to 3 carbon atoms, cyano groups, or halogenated alkyl or alkoxy groups having 1 to 3 carbon atoms in which some or all of the hydrogen atoms of the alkyl or alkoxy groups are substituted with halogen atoms. The aromatic diamines having a benzoxazole structure are not particularly limited, and examples thereof include 5-amino-2-(p-aminophenyl)benzoxazole, 6-amino-2-(p-aminophenyl)benzoxazole, 5-amino-2-(m-aminophenyl)benzoxazole, 6-amino-2-(m-aminophenyl)benzoxazole, 2,2'-p-phenylenebis(5-aminobenzoxazole), 2,2'-p-phenylenebis(6-aminobenzoxazole), 1-(5-aminobenzoxazolo)-4-(6-aminobenzoxazolo)benzene, 2,6-(4,4'-diaminodiphenyl)benzo[1,2-d:5,4-d']bisoxazole, 2,6-(4,4'-diaminodiphenyl)benzo[1,2-d:4,5-d']bisoxazole, 2,6-(3,4'-diaminodiphenyl)benzo[1,2-d:5,4-d']bisoxazole, 2,6-(3,4'-diaminodiphenyl)benzo[1,2-d:4,5-d']bisoxazole, 2,6-(3,3'-diaminodiphenyl)benzo[1,2-d:5,4-d']bisoxazole, 2,6-(3,3'-diaminodiphenyl)benzo[1,2-d:4,5-d']bisoxazole, and the like. Among these, 2,2'-ditrifluoromethyl-4,4'-diaminobiphenyl, 4-amino-N-(4-aminophenyl)benzamide, 4,4'-diaminodiphenyl sulfone, and 3,3'-diaminobenzophenone are particularly preferred. The aromatic diamines may be used alone or in combination.

[0053] Examples of alicyclic diamines include 1,4-diaminocyclohexane, 1,4-diamino-2-methylcyclohexane, 1,4-diamino-2-ethylcyclohexane, 1,4-diamino-2-n-propylcyclohexane, 1,4-diamino-2-isopropylcyclohexane, 1,4-diamino-2-n-butylcyclohexane, 1,4-diamino-2-isobutylcyclohexane, 1,4-diamino-2-sec-butylcyclohexane, 1,4-diamino-2-tert-butylcyclohexane, and 4,4'-methylenebis(2,6-dimethylcyclohexylamine). Among these, 1,4-diaminocyclohexane and 1,4-diamino-2-methylcyclohexane are particularly preferred, and 1,4-diaminocyclohexane is more preferred. The alicyclic diamines may be used alone or in combination.

[0054] Examples of diisocyanates include diphenylmethane-2,4'-diisocyanate, 3,2'- or 3,3'- or 4,2'- or 4,3'- or 5,2'- or 5,3'- or 6,2'- or 6,3'-dimethyldiphenylmethane-2,4'-diisocyanate, 3,2'- or 3,3'- or 4,2'- or 4,3'- or 5,2'- or 5,3'- or 6,2'- or 6,3'-diethyl Diphenylmethane-2,4'-diisocyanate, 3,2'- or 3,3'- or 4,2'- or 4,3'- or 5,2'- or 5,3'- or 6,2'- or 6,3'-dimethoxydiphenylmethane-2,4'-diisocyanate, diphenylmethane-4,4'-diisocyanate, diphenylmethane-3,3'-diisocyanate, diphenylmethane-3,4'-diisocyanate, diphenylether-4,4' -Diisocyanates, benzophenone-4,4'-diisocyanate, diphenylsulfone-4,4'-diisocyanate, tolylene-2,4-diisocyanate, tolylene-2,6-diisocyanate, m-xylylene diisocyanate, p-xylylene diisocyanate, naphthalene-2,6-diisocyanate, 4,4'-(2,2-bis(4-phenoxyphenyl)propane)diisocyanate, 3,3'- or 2,2'-dimethylbiphenyl-4,4'-diisocyanate, 3,3'- or 2,2'-di Examples of the diisocyanates include aromatic diisocyanates such as ethylbiphenyl-4,4'-diisocyanate, 3,3'-dimethoxybiphenyl-4,4'-diisocyanate, and 3,3'-diethoxybiphenyl-4,4'-diisocyanate, and diisocyanates obtained by hydrogenating any of these diisocyanates (for example, isophorone diisocyanate, 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, and hexamethylene diisocyanate).Among these, diphenylmethane-4,4'-diisocyanate, tolylene-2,4-diisocyanate, tolylene-2,6-diisocyanate, 3,3'-dimethylbiphenyl-4,4'-diisocyanate, naphthalene-2,6-diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, and 1,4-cyclohexane diisocyanate are preferred from the viewpoints of low moisture absorption, dimensional stability, cost, and polymerizability. The diisocyanates may be used alone or in combination.

[0055] The solvent used in the resin solution of the present invention is preferably a solvent that has a dipole moment in the range of 3.0 to 6.0 D and dissolves at least one resin selected from the group consisting of polyamic acid, polyimide, and polyamideimide. If the dipole moment is within the above range, the uniform heating effect of microwave heating used in the solvent removal step of the resin film described below is excellent, and it becomes easy to improve the physical property isotropy of the obtained resin film.

[0056] Examples of the solvent used in the resin solution of the present invention include N,N-dimethylformamide (dipole moment: 3.86 D), N,N-dimethylacetamide (DMAc) (dipole moment: 3.72 D), N-methyl-2-pyrrolidone (NMP) (dipole moment: 4.09 D), N-methyl-ε-caprolactam (dipole moment: 4.23 D), dimethyl sulfoxide (dipole moment: 3.96 D), dimethyl sulfone (dipole moment: 4.47 D), sulfuric acid (dipole moment: 4.51 D), and sulfuric acid (dipole moment: 4.51 D). Examples of the solvents include phorane (dipole moment: 4.68D), 1,3-dimethyl-2-imidazolidinone (dipole moment: 4.07D), 1,3-dimethyl-2-pyrimidinone (dipole moment: 4.17D), 3-methyl-2-oxazolidone (dipole moment: 4.10D), hexamethylphosphoramide (dipole moment: 5.54D), γ-butyrolactone (GBL) (dipole moment: 4.27D), etc. These may be used alone or in combination of two or more. In addition to these solvents, poor solvents such as toluene (dipole moment: 0.36D) and xylene (dipole moment: 0.00 to 0.64D) may be used to the extent that the resin solids are not precipitated and the uniform heating effect of microwave heating is not impaired. When two or more types of solvents are mixed, the dipole moment value is the weighted average value of each solvent.

[0057] The resin solution of the present invention may contain fine particles as long as the properties of the resin film are not impaired. The fine particles may be inorganic or organic, and examples of the inorganic fine particles include silicon nitride, silicon oxide, titanium oxide, aluminum oxide, magnesium oxide, zinc oxide, tin oxide, calcium carbonate, barium sulfate, talc, kaolin, and calcium sulfate. Examples of the organic fine particles include polyamide resins, polyimide resins, benzoguanamine resins, and melamine resins, and these fine particles may be used in combination.

[0058] The resin solids concentration of the resin solution of the present invention is preferably 5 to 40% by mass, more preferably 7 to 35% by mass, and further preferably 10 to 30% by mass. The resin solids concentration is preferably equal to or higher than the above lower limit from the viewpoint of obtaining a thickness required for the resin film, and is preferably equal to or lower than the above upper limit from the viewpoint of obtaining a degree of solution fluidity that does not impair the isotropic physical properties of the resin film.

[0059] The resin film in the present invention is preferably a resin film obtained by the resin film manufacturing method described below. Specifically, it is a polymer film having an imide bond in the main chain, preferably a polyimide film or a polyamideimide film, more preferably a polyimide film.

[0060] The lower limit of the thickness of the resin film in the present invention is preferably 3 μm or more, more preferably 5 μm or more, and even more preferably 7 μm or more, from the viewpoint of strength and handleability required for the resin film. The upper limit of the thickness of the resin film is preferably 250 μm or less, more preferably 150 μm or less, and even more preferably 100 μm or less, from the viewpoint of uniformly removing the solvent.

[0061] A preferred method for producing the resin film of the present invention is A step A of applying the resin solution onto a support and drying the same to prepare a resin film laminate containing a solvent; A step B of peeling the support from the solvent-containing resin film laminate to obtain a solvent-containing resin film; A step C of removing the solvent from the resin film containing the solvent, or performing a dehydration ring-closing reaction while removing the solvent, At least a part of the step C is carried out by microwave heating.

[0062] Step A will be described. Step A is a step of preparing a solvent-containing resin film laminate (hereinafter, also simply referred to as a laminate) by applying a resin solution onto a support and drying it. The laminate is a product in which the dried product of the resin solution is laminated onto the support.

[0063] Examples of the support used in the present invention include a resin film substrate, a stainless steel belt substrate, a glass substrate, etc. As the resin film substrate, it is preferable to use a resin film substrate that does not swell or dissolve in the solvent contained in the resin solution, and examples of the resin film substrate include a polyethylene terephthalate (PET) film, a polyethylene naphthalate (PEN) film, a polyolefin-based (PP) film, a cycloolefin-based (COP) film, etc. In addition, it is preferable to use a support having easy peelability in order to peel the resin film containing the solvent from the support.

[0064] Examples of a method for applying a resin solution onto a support include a die coating method, a comma coating method, a blade coating method, a roll coating method, a knife coating method, and a bar coating method, and two of these methods may be combined. The comma coating method, the die coating method, or a combination of these methods is preferred from the viewpoint of productivity.

[0065] Methods for drying the resin solution on the support include air drying, hot air drying, infrared heat drying, and heat drying by heat transfer from the support, and two of these methods may be combined. The solvent content of the resin film containing the solvent after drying is preferably 3 to 50% by mass, more preferably 5 to 40% by mass, and even more preferably 7 to 30% by mass. When the solvent content is equal to or greater than the above lower limit, the difference in the solvent content and polymer high-order structure between the resin film surface in contact with the support and the opposite surface is small, the physical property anisotropy in the thickness direction of the resin film is small, and curling of the resin film is suppressed. When the solvent content is equal to or less than the above upper limit, deformation of the resin film after peeling from the support is suppressed, making handling easy.

[0066] Step B will be described. Step B is a step of peeling the support from the laminate to obtain a resin film containing a solvent.

[0067] The method for peeling off the resin film containing the solvent from the support is not particularly limited, but examples include a method of peeling it off from the edge using tweezers or the like, a method of making a cut in the laminate and attaching adhesive tape to one side of the cut portion and then peeling it off from the tape portion, and a method of vacuum-adsorbing one side of the cut portion of the resin film and then peeling it off from that portion.

[0068] The step C will be described below. The step C is a step of removing the solvent from the resin film containing the solvent, or of carrying out a dehydration ring-closing reaction while removing the solvent, and at least a part of the step C is carried out by microwave heating.

[0069] The microwave heating used in the solvent removal process of the resin film containing a solvent after peeling it off from the support is based on the principle of vibrating the dipoles of the molecules contained in the heated object with microwaves. Therefore, the efficiency of microwave absorption depends on the magnitude of the dipole moment and the ease with which the molecules move in accordance with the microwave period. Therefore, in order to efficiently heat and remove the solvent from the resin film containing a solvent by using microwaves, a solvent having the above-mentioned dipole moment value is specified.

[0070] The frequency of the microwave heating device used in the present invention is preferably selected so that the molecules of the solvent having the above-mentioned dipole moment value can easily move. However, due to the restrictions of the Radio Law and the restrictions of the microwave electron tube, a heating device with a frequency of 2,450 MHz is generally used. However, 915 MHz can also be used as long as it does not interfere with other communications. In the present invention, it is more preferable to select a frequency of 2,450 MHz or 915 MHz for such reasons. In addition, the microwave intensity is appropriately selected taking into consideration the foaming, citron peel, wavy state, etc. of the resin film surface.

[0071] By using a resin solution containing a solvent with a specified dipole moment value and by using microwave heating, the resin film is uniformly heated and dried in the solvent removal process, reducing the difference in density of the formed higher-order structure, making it easy to achieve the formula (40 + 0.8 × A) ≦ B < A. Furthermore, the isotropy of the physical properties of the resulting resin film can be improved, making it easy to keep the ratio of the linear expansion coefficient of the resin film in the MD direction to the TD direction and the ratio of the tensile modulus of elasticity in the MD direction to the TD direction within preferred ranges.

[0072] In the present invention, in addition to microwave heating, methods such as air drying, hot air drying, and infrared heating drying can be used, and two of these methods may be combined.

[0073] The temperature rise profile in the solvent removal process using the above heating method preferably has an initial temperature in the range of 50 to 200°C. If the initial temperature is above the lower limit of the specified range, it is easy to suppress temperature variations in the drying oven, and if the initial temperature is below the upper limit of the specified range, it is easy to suppress foaming of the resin film and citron peel on the surface caused by sudden heating of the solvent, and also the difference in solvent content and polymer higher-order structure between the surface and the interior of the resin film is reduced, making it easy to achieve the formula (40 + 0.8 × A) ≦ B < A.

[0074] The temperature rise profile in the solvent removal process using the above heating method preferably has a final temperature in the range of 300 to 500°C. If the final temperature is above the lower limit of the specified range, it becomes easier to reduce the amount of residual solvent in the resin film, and if the final temperature is below the upper limit of the specified range, it becomes easier to suppress thermal deterioration of the resin film.

[0075] The temperature profile in the solvent removal step using the above heating method is preferably a temperature rise rate of 5 to 60°C / min, a stepwise temperature rise with 2 or more steps, or a combination of both. If the temperature rise rate is equal to or higher than the lower limit of the specified range, the working time in the solvent removal step can be shortened, and if it is equal to or lower than the upper limit of the specified range, it becomes easy to suppress foaming of the resin film and citron peel on the surface caused by sudden heating of the solvent, and the difference in the solvent content and polymer high-order structure between the surface and the inside of the resin film becomes small, making it easy to achieve the formula (40 + 0.8 x A) ≦ B < A.

[0076] When the temperature is raised stepwise, the number of steps is preferably 2 to 10, and the heating rate between each step is preferably 10 to 100°C / min. If the number of steps is equal to or greater than the lower limit of the specified range, it is easy to prevent foaming of the resin film and citron peel on the surface caused by sudden heating of the solvent, and the difference in the solvent content and polymer high-order structure between the surface and the inside of the resin film is small, making it easy to achieve the formula (40+0.8×A)≦B<A. Also, if the number of steps is equal to or less than the upper limit of the specified range, the work efficiency is good.

[0077] It is preferable to determine the above initial temperature, final temperature, heating rate, and number of steps so that the total drying time in the solvent removal step is 5 to 100 minutes. If the total drying time is equal to or greater than the lower limit of the specified range, it becomes easier to prevent foaming of the resin film and citron peel on the surface caused by sudden heating of the solvent, while if it is equal to or less than the upper limit, it becomes easier to improve productivity and prevent thermal deterioration of the resin film.

[0078] In the solvent removal step of the present invention, the resin film can be further stretched. The stretching ratio in such a stretching operation is preferably 1.5 to 4.0 times in the MD (long dimension) direction and 1.4 to 3.0 times in the TD (short dimension) direction, and the ratio of the stretching ratio in the MD direction to the stretching ratio in the TD direction (MD / TD) is preferably more than 1.0. By setting the stretching conditions within the above ranges, it becomes easy to keep the average linear expansion coefficients measured in the range of 35 to 200°C in both the MD and TD directions of the resin film and the tensile modulus in both the MD and TD directions within preferred ranges.

[0079] The solvent content of the resin film after the solvent removal step is preferably 0.01 to 5.0% by mass, more preferably 0.02 to 4.0% by mass, and even more preferably 0.03 to 3.0% by mass. By making the solvent content equal to or greater than the lower limit, thermal deterioration of the resin film due to excessively high-temperature treatment can be suppressed, and by making it equal to or less than the upper limit, it becomes easy to keep the linear expansion coefficient and tensile modulus within the preferred ranges. EXAMPLES

[0080] The present invention will be described in detail below using examples, but the present invention is not limited to the following examples as long as it does not depart from the gist of the present invention.

[0081] In the examples and comparative examples, the respective measured values ​​were measured by the following methods unless otherwise specified.

[0082] <Peak temperature of temperature dependence curve of tan δ of resin film> For three samples in each of the machine direction (MD) and width direction (TD) of the resin film, temperature dependence curves of the storage modulus (E'), loss modulus (E"), and tan δ (=E" / E'), which is the value obtained by dividing the loss modulus by the storage modulus, were obtained under the following conditions to determine the peak temperatures, and the average values ​​in the machine direction (MD) and width direction (TD) were calculated. Device name: TA Instruments DMA Q800 Sample length: 15-20mm Sample width: 4mm Heating start temperature: 25℃ End temperature: 500℃ Heating rate: 5℃ / min Measurement frequency: 10Hz

[0083] <Inflection point temperature of linear expansion coefficient of resin film> The stretch rate was measured under the conditions below for three samples in each of the machine direction (MD) and width direction (TD) of the resin film, and the temperature at which the stretch rate inflection point occurred during the second heating was read, and the average value in the machine direction (MD) and width direction (TD) was calculated. Equipment name: Bruker AXS TMA-4000SA Sample length: 15mm Sample width: 2mm Chuck distance: 10mm Load: 5gf First heating start temperature: 25℃ First heating end temperature: 200℃ First heating rate: 20℃ / min Cooling rate: 5℃ / min Second heating start temperature: 30℃ Second heating end temperature: 500℃ Second heating rate: 10℃ / min Atmosphere: Argon

[0084] <Weight average molecular weight, number average molecular weight and molecular weight distribution of resin> 8 mg of a resin sample was weighed out, immersed in 8 ml of a solvent, and stirred for 3 hours to obtain a resin solution. The resin solution was analyzed by gel permeation chromatography (GPC) under the following conditions, and the weight average molecular weight, number average molecular weight, and molecular weight distribution were calculated in terms of standard polystyrene. Device name: Tosoh HLC-8420GPC Column: TSKgel SuperAWH-H x 2 Solvent: DMAc (with 30 mM lithium bromide) Flow rate: 0.3ml / min Concentration: 0.1% Injection volume: 10μl Temperature: 40℃ Detector: RI

[0085] <Thickness of resin film> The measurement was carried out using a micrometer (Militron 1245D, manufactured by Feinruf Co., Ltd.).

[0086] <Coefficient of linear expansion (CTE) of resin film> The expansion / contraction rate was measured under the following conditions for three samples in each of the machine direction (MD) and width direction (TD) of the resin film. The expansion / contraction rate / temperature was measured at intervals of 15°C, such as 35°C to 50°C and 50°C to 65°C. This measurement was continued up to 200°C, and the average value of all the measured values ​​was calculated as CTE. Device name: MAC Science TMA4000S Sample length: 20mm Sample width: 2mm Heating start temperature: 25℃ End temperature: 400℃ Heating rate: 5℃ / min Atmosphere: Argon

[0087] <Tensile modulus of resin film> The resin film was cut into strips of 100 mm x 10 mm in both the machine direction (MD) and the width direction (TD) to prepare test pieces. The test pieces were cut from the center in the width direction. The tensile modulus was measured for three samples in each of the MD and TD directions under the following conditions, and the average of all measured values ​​was calculated. Device name: Shimadzu Autograph(R)AG-5000A Chuck distance: 40mm Temperature: 25℃ Tensile speed: 50mm / min

[0088] <Yellowness index (YI) of resin film> Using a color meter (ZE6000, manufactured by Nippon Denshoku Industries Co., Ltd.) and a C2 light source, the tristimulus values ​​XYZ of the resin film were measured according to ASTM D1925, and the yellowness index (YI) was calculated according to the following formula. The same measurement was performed three times, and the arithmetic average value was used. YI=100×(1.28X-1.06Z) / Y

[0089] <400 nm light transmittance of resin film> The light transmittance of the resin film at a wavelength of 400 nm was measured using a spectrophotometer (Hitachi U-2001), and the obtained value was converted to a thickness of 20 μm according to the Beer-Lambert law, and the obtained value was used as the 400 nm light transmittance of the resin film. The same measurement was performed three times, and the arithmetic average value was used.

[0090] <Total light transmittance (TT) of resin film> The total light transmittance (TT) of the resin film was measured using a HAZEMETER (NDH5000, manufactured by Nippon Denshoku Co., Ltd.). A D65 lamp was used as the light source. The same measurement was performed three times, and the arithmetic average value was used.

[0091] [Synthesis Example 1 (Preparation of Polyamic Acid Solution A)] After replacing the inside of a reaction vessel equipped with a nitrogen inlet tube, a thermometer, and a stirring rod with nitrogen, 1470.8 parts by mass of 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA), 775.6 parts by mass of 4,4'-oxydiphthalic acid (ODPA), 3202.4 parts by mass of 2,2'-ditrifluoromethyl-4,4'-diaminobiphenyl (TFMB), and 21795 parts by mass of N,N-dimethylacetamide (DMAc) were charged and dissolved in the reaction vessel under a nitrogen atmosphere, and the mixture was stirred at room temperature for 24 hours to obtain a polyamic acid solution A with a reduced viscosity of 4.5 dl / g and a solid content of 17.2 parts by mass. The results of measuring the weight average molecular weight, number average molecular weight, and molecular weight distribution of the resin in the obtained resin solution are shown in Table 1.

[0092] [Synthesis Example 2 (Preparation of Polyimide Solution B)] After replacing the inside of a reaction vessel equipped with a nitrogen inlet tube, a thermometer, and a stirring rod with nitrogen, 551 parts by mass of N,N-dimethylacetamide (DMAc) and 64.1 parts by mass of 2,2'-ditrifluoromethyl-4,4'-diaminobiphenyl (TFMB) were put into the reaction vessel under a nitrogen atmosphere and stirred to dissolve TFMB in DMAc. Next, while stirring the inside of the reaction vessel, 44.4 parts by mass of 4,4'-(2,2-hexafluoroisopropylidene)diphthalic dianhydride (6FDA) and 29.4 parts by mass of biphenyltetracarboxylic dianhydride (BPDA) were put in under a nitrogen stream over about 10 minutes, and the polymerization reaction was carried out by continuing stirring for 6 hours while adjusting the temperature to be in the range of 20 to 40 ° C., to obtain a viscous polyamic acid solution. Next, the obtained polyamic acid solution was diluted with 410 parts by mass of DMAc, and then 25.83 parts by mass of isoquinoline was added as an imidization accelerator. The polyamic acid solution was kept at a temperature range of 30 to 40°C while being stirred, and 122.5 parts by mass of acetic anhydride was slowly added dropwise as an imidization agent over a period of about 10 minutes. Thereafter, the liquid temperature was further kept at 30 to 40°C and stirring was continued for 12 hours to carry out a chemical imidization reaction, thereby obtaining a polyimide solution. Next, 1000 parts by mass of the polyimide solution containing the imidization agent and the imidization accelerator obtained was transferred to a reaction vessel equipped with a stirrer and agitator, and the temperature was kept at 15 to 25 ° C while stirring at a speed of 120 rpm, and 1500 parts by mass of methanol was dropped therein at a rate of 10 g / min. When about 800 parts by mass of methanol was added, the polyimide solution became turbid and precipitation of powder-like polyimide was confirmed. Subsequently, the entire amount of 1500 parts by mass of methanol was added, and the precipitation of polyimide was completed. Next, the contents of the reaction vessel were filtered using a suction filtration device, and further washed and filtered using 1000 parts by mass of methanol. Then, 50 parts by mass of the filtered polyimide powder was dried at 50 ° C for 24 hours using a dryer equipped with a local exhaust device, and further dried at 260 ° C for 2 hours to remove the remaining volatile components, and a polyimide powder was obtained. The reduced viscosity of the obtained polyimide powder was 2.1 dl / g. Next, 42 parts by mass of the obtained polyimide powder was dissolved in 168 parts by mass of DMAc to obtain a polyimide solution B with a solid content of 20 parts by mass. The results of measuring the weight average molecular weight, number average molecular weight and molecular weight distribution of the resin in the obtained resin solution are shown in Table 1.

[0093] [Synthesis Example 3 (Preparation of Polyimide Solution C)] In a reaction vessel equipped with a nitrogen inlet tube, Dean-Stark apparatus, reflux tube, thermometer, and stirrer, 124.15 parts by mass of 4,4'-diaminodiphenylsulfone (4,4'-DDS), 124.15 parts by mass of 3,3'-diaminodiphenylsulfone (3,3'-DDS), and 750 parts by mass of gamma-butyrolactone (GBL) were added while introducing nitrogen gas. Then, 248.18 parts by mass of 4,4'-oxydiphthalic acid dihydrate (ODPA), 58.8 parts by mass of biphenyltetracarboxylic dianhydride (BPDA), 335 parts by mass of GBL, and 390 parts by mass of toluene were added at room temperature, and the internal temperature was raised to 160°C and heated to reflux at 160°C for 1 hour to perform imidization. After completion of imidization, the temperature was raised to 180°C, and the reaction was continued while removing toluene. After reacting for 12 hours, the oil bath was removed, the temperature was returned to room temperature, and 1,149 parts by mass of GBL was added so that the solid content was 20 parts by mass, obtaining a polyimide solution C with a reduced viscosity of 0.6 dl / g. The measurement results of the weight average molecular weight, number average molecular weight and molecular weight distribution of the resin in the obtained resin solution are shown in Table 1.

[0094] [Synthesis Example 4 (Preparation of Polyimide Solution D)] While introducing nitrogen gas into a reaction vessel equipped with a nitrogen inlet tube, a Dean-Stark apparatus, a reflux condenser, a thermometer, and a stirrer, 384.38 parts by mass of norbornane-2-spiro-α-cyclopentanone-α'-spiro-2″-norbornane-5,5″,6,6″-tetracarboxylic dianhydride (CpODA), 348.45 parts by mass of 9,9-bis(4-aminophenyl)fluorene (BAFL), 36.00 parts by mass of triethylamine, 1465 parts by mass of N-methyl-2-pyrrolidone (NMP), 1465 parts by mass of gamma-butyrolactone (GBL), and 360 parts by mass of toluene were added at room temperature, and the internal temperature was raised to 180° C., and imidization was performed by heating at 180° C. for 3 hours while distilling off the toluene, to obtain a polyimide solution. Next, 2500 parts by mass of the obtained polyimide solution was transferred to a reaction vessel equipped with a stirrer and agitator, and the temperature was kept at 15 to 25 ° C while stirring at a speed of 120 rpm, and 50,000 parts by mass of acetone was dropped therein at a rate of 10 g / min. When about 2500 parts by mass were added, the polyimide solution was confirmed to become cloudy, and precipitation of powder-like polyimide was confirmed. Subsequently, the remaining 2500 parts by mass of acetone was added, and the precipitation of polyimide was completed. Next, the contents of the reaction vessel were filtered using a suction filtration device, and further washed and filtered using 2000 parts by mass of methanol. Then, 300 parts by mass of the filtered polyimide powder was dried at 50 ° C for 24 hours using a dryer equipped with a local exhaust device, and further dried at 260 ° C for 2 hours to remove the remaining volatile components, and a polyimide powder was obtained. The reduced viscosity of the obtained polyimide powder was 0.7 dl / g. Next, 42 parts by mass of the obtained polyimide powder was dissolved in 168 parts by mass of NMP to obtain a polyimide solution D having a solid content of 20 parts by mass and a reduced viscosity of 0.7 dl / g. The results of measuring the weight average molecular weight, number average molecular weight and molecular weight distribution of the resin in the obtained resin solution are shown in Table 1.

[0095] [Synthesis Example 5 (Preparation of Polyamic Acid Solution E)] After replacing the atmosphere in a reaction vessel equipped with a nitrogen inlet tube, a thermometer, and a stirring rod with nitrogen, 196.1 parts by mass of 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA), 227.3 parts by mass of 4-amino-N-(4-aminophenyl)benzamide (DABAN), and 1694 parts by mass of N,N-dimethylacetamide (DMAc) were charged and dissolved in the reaction vessel under a nitrogen atmosphere, and the mixture was stirred at room temperature for 24 hours to obtain a polyamic acid solution E with a solid content of 20 parts by mass and a reduced viscosity of 4.5 dl / g. The results of measuring the weight average molecular weight, number average molecular weight, and molecular weight distribution of the resin in the obtained resin solution are shown in Table 1.

[0096] [Polyimide Film Preparation Example 1 (Examples 1 to 5)] The polyamic acid solution A was applied onto a mirror-finished endless continuous belt made of stainless steel, which was a support for film production, using a die coater (coating width: 1240 mm), and dried for 10 minutes at 90 to 115° C. The polyamic acid film (containing 9% by mass of residual solvent) that had become self-supporting after drying was peeled off from the support, and both ends were cut to obtain a green film. The resulting green film was pin tentered to a final pin sheet interval of 1140 mm. The film was held at both ends so that the film was 1.0 m long, inserted into a continuous heating furnace equipped with a microwave heating zone and a hot air circulation device, heated at 170 ° C for 1 minute in the first stage, then heated to 230 ° C at a heating rate of 60 ° C / min, heated at 230 ° C for 1 minute in the second stage, then heated to 350 ° C at a heating rate of 60 ° C / min, and heated at 350 ° C for 5 minutes in the third stage. At this time, 50 kW microwaves of 2,450 MHz were introduced into the microwave heating zone. After that, the film was cooled to room temperature in 2 minutes, and the parts with poor flatness at both ends of the film were cut off with a slitter and wound up into a roll to obtain resin film 1A shown in Table 2. Similarly, polyamic acid solution A was replaced with other resin solutions B, C, D, and E, and the coating thickness on the support was changed to obtain resin films 1B, 1C, 1D, and 1E. The results of the evaluation of the properties of the obtained resin films are shown in Table 2.

[0097] [Polyimide Film Preparation Example 2 (Examples 6 to 10)] The polyamic acid solution A was applied to a polyester film having a surface roughness (Sa) of 1 nm, a maximum peak height (Sp) of 7 nm, and a peak density (Spd) of 20 / μm2 or less, which was a support for film production, and had no coating layer on the surface, using a comma coater (coating width 1240 mm), and dried at 90 to 115 ° C for 10 minutes. After drying, the polyamic acid film (containing 10% by mass of residual solvent) which became self-supporting was peeled off from the support and both ends were cut to obtain a green film. The obtained green film was held at both ends by a pin tenter so that the final pin sheet interval was 1140 mm, and inserted into a continuous heating furnace equipped with a microwave heating zone and a hot air circulation device, and heated from 170 ° C to 350 ° C at a heating rate of 15 ° C / min. At this time, 40 kW of microwaves of 2,450 MHz were introduced into the microwave heating zone. The film was then cooled to room temperature over 2 minutes, and both ends of the film with poor flatness were cut off with a slitter, and the film was wound into a roll to obtain resin film 2A shown in Table 2. Similarly, polyamic acid solution A was replaced with other resin solutions B, C, D, and E, and the coating thickness on the support was changed to obtain resin films 2B, 2C, 2D, and 2E. The property evaluation results of the obtained resin films are shown in Table 2.

[0098] [Polyimide Film Preparation Example 3 (Comparative Examples 1 to 5)] The polyamic acid solution A was applied onto a mirror-finished endless continuous belt made of stainless steel, which was a support for film production, using a die coater (coating width: 1240 mm), and dried for 10 minutes at 90 to 115° C. The polyamic acid film (containing 9% by mass of residual solvent) that had become self-supporting after drying was peeled off from the support, and both ends were cut to obtain a green film. The obtained green film was held at both ends by a pin tenter so that the final pin sheet interval was 1140 mm, and inserted into a continuous heating furnace equipped with a hot air circulation device, and heated from 170 ° C to 350 ° C at a heating rate of 15 ° C / min. Then, it was cooled to room temperature in 2 minutes, and the parts with poor flatness at both ends of the film were cut off with a slitter, and rolled up into a roll to obtain resin film 3A shown in Table 3. Similarly, polyamic acid solution A was replaced with other resin solutions B, C, D, and E, and the coating thickness on the support was changed to obtain resin films 3B, 3C, 3D, and 3E. The property evaluation results of the obtained resin films are shown in Table 3.

[0099] [Polyimide Film Preparation Example 4 (Comparative Examples 6 to 10)] The polyamic acid solution A was applied to a polyester film having a surface roughness (Sa) of 1 nm, a maximum peak height (Sp) of 7 nm, and a peak density (Spd) of 20 / μm2 or less, which was a support for film production, and had no coating layer on the surface, using a comma coater (coating width 1240 mm), and dried at 90 to 115 ° C for 10 minutes. After drying, the polyamic acid film (containing 10% by mass of residual solvent) which became self-supporting was peeled off from the support and both ends were cut to obtain a green film. The obtained green film was held at both ends by a pin tenter so that the final pin sheet interval was 1140 mm, and inserted into a continuous heating furnace equipped with a microwave heating zone and a hot air circulation device, heated from 170 ° C to 350 ° C at a heating rate of 70 ° C / min, and heat-treated at 350 ° C for 4 minutes. At this time, 50 kW of microwaves of 2,450 MHz were introduced into the microwave heating zone. The film was then cooled to room temperature over 2 minutes, and both ends of the film with poor flatness were cut off with a slitter, and the film was wound up into a roll to obtain resin film 4A shown in Table 3. Similarly, polyamic acid solution A was replaced with other resin solutions B, C, D, and E, and the coating thickness on the support was changed to obtain resin films 4B, 4C, 4D, and 4E. The property evaluation results of the obtained resin films are shown in Table 3.

[0100] [Table 1]

[0101] [Table 2]

[0102] [Table 3] [Industrial Applicability]

[0103] As described above, the resin film of the present invention has excellent heat resistance and transparency, maintains a low coefficient of linear expansion even in high temperature ranges, has a high tensile modulus, and has a small ratio of the coefficient of linear expansion and the tensile modulus in the MD and TD directions of the resin film, resulting in good isotropy of physical properties. Therefore, the resin film of the present invention is extremely useful for the front panels and periphery of electrodes of image display devices such as touch panels and displays.

Claims

1. A step A of applying a polyamic acid resin solution onto a support and drying the same to prepare a solvent-containing resin film laminate; A step B of peeling the support from the laminate to obtain a resin film containing a solvent; A step C of carrying out a dehydration ring-closing reaction while removing the solvent from the resin film containing the solvent, The step C is performed by either or a combination of heating at a heating rate of 5 to 60° C. / min or heating in two or more steps, The initial temperature of step C is in the range of 50 to 200° C. The final temperature of step C is in the range of 300 to 500° C. At least a part of the step C is carried out by microwave heating, The obtained polyimide resin film satisfies the following (1) and (2): A method for producing a resin film. (1) The temperature (A) at which the temperature-dependent curve of tan δ, which is the value obtained by dividing the loss modulus by the storage modulus, reaches a peak is in the range of 250 to 500° C., and the temperature (A) at which the temperature-dependent curve of tan δ reaches a peak and the inflection point temperature (B) of the linear expansion coefficient are related by the following formula: (40+0.8×A) ≦ B < A (2) The weight average molecular weight of the resin that is the raw material of the resin film is in the range of 50,000 to 500,000, and the molecular weight distribution, which is the value obtained by dividing the weight average molecular weight by the number average molecular weight of the resin, is in the range of 1.0 to 5.

0.

2. The method for producing a resin film according to claim 1, wherein the resin solution contains a solvent having a dipole moment in the range of 3.0 to 6.0 D and capable of dissolving the resin.

3. The method for producing a resin film according to claim 1 or 2, further satisfying (3) to (4). (3) The linear expansion coefficient measured in the range of 35 to 200°C in both the MD and TD directions is in the range of -5 ppm / °C to +55 ppm / °C, and the ratio of the linear expansion coefficient in the TD direction to the MD direction is in the range of 0.97 to 1.

03. (4) The tensile modulus in both the MD and TD directions is in the range of 2 to 20 GPa, and the ratio of the tensile modulus in the TD direction to the MD direction is in the range of 0.97 to 1.

03.

4. 4. The method for producing a resin film according to claim 1, wherein the resin film has a yellow index of 10 or less, a light transmittance at a wavelength of 400 nm of 70% or more, and a total light transmittance of 85% or more.

5. A method for producing a resin film described in any one of claims 1 to 4, wherein the tetracarboxylic acids constituting the polyamic acid include alicyclic tetracarboxylic acids and / or their acid anhydrides.

6. A method for producing a resin film described in any one of claims 1 to 4, wherein the tetracarboxylic acids constituting the polyamic acid include 1,2,3,4-cyclobutanetetracarboxylic acid and / or its acid anhydride, and the diamines include 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl or 4-amino-N-(4-aminophenyl)benzamide.

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