JP2023139144A - Resin film and method for manufacturing resin film - Google Patents

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

The present invention relates to a resin film and a method for manufacturing the resin film. More specifically, the resin film has excellent heat resistance, maintains a low coefficient of linear expansion up to high temperature ranges, has a high tensile modulus, and has a small ratio of linear expansion coefficient and tensile modulus in the TD direction to the MD direction of the resin film. The present invention relates to a resin film with good isotropy and excellent transparency, and a method for producing the resin film.

In recent years, as mobile phones, digital cameras, display devices, and various other electronic devices have become more sophisticated, they have become smaller, lighter, and more convenient. Resin film substrate materials are expected to have excellent properties such as low linear expansion coefficient, high tensile modulus, flexibility, impact resistance, and transparency.

Resin films are manufactured industrially by processing organic polymer resin materials into a film form, and film forming methods include melt film forming, in which organic polymer resin is melted and then extruded through a slit-shaped die, and organic polymer resin is extruded through a slit die. There is a solution casting method in which a molecular resin solution is uniformly applied to a support and the solvent is dried and volatilized. Polyimide resins and polyamide-imide resins, which have particularly excellent heat resistance among organic polymer resin materials, are infusible or melt at very high temperatures, and therefore resin films are generally obtained by solution casting.

In such a solution film forming method in which coating is performed and the solvent is dried and volatilized, thickness unevenness and orientation unevenness may occur depending on coating conditions and drying conditions. For example, in Patent Document 1, coating conditions such as support rotation speed etc. There is a proposal to reduce the unevenness of horizontal rows in the longitudinal direction by reviewing the structure.

In addition, in order to suppress variations in film sag, we discovered that there is a correlation between sag, anisotropy index, principal axis orientation coefficient, heat shrinkage rate, and drying temperature. A method for suppressing variation in expansion coefficient, that is, dimensional change, is described (Patent Document 2).

Patent Document 3 discloses that when manufacturing a polyimide film that exhibits a remarkable decrease in elastic modulus at temperatures above the glass transition temperature, both ends of the film are fixed and transported without slack, in accordance with the width of the film that changes due to contraction and expansion during the heating process. A manufacturing method is described in which the anisotropy of the linear expansion coefficient in the MD direction (travel direction) and TD direction (width direction) of the film is reduced by doing so.

JP2013-203838A JP2018-70842A Japanese Patent Application Publication No. 2000-290401

In order to directly form functional elements such as electrodes and display elements on the surface, resin films used as a substitute for glass substrates are required to have high tensile modulus, low CTE, and heat resistance and chemical resistance. Polyimide, polyamideimide, and polyamic acid, which is a precursor of polyimide, are suitable resins for such resin films, and they exhibit heat resistance because they contain many rigid molecular chains with low mobility and have a high molecular weight. Moreover, when the molecular weight is increased, the molecular weight has a wide distribution as a result.

When applying and drying such a resin solution, if it contains many rigid molecular chains with high molecular weight and wide molecular weight distribution and low mobility, as the solvent is removed, the orientation direction and degree of orientation of the molecules formed first will change. A denser higher-order structure that reflects the entanglement and a sparser higher-order structure that reflects the orientation direction, degree of orientation, and entanglement of the molecules formed later are different, and each domain is formed.

When films are industrially manufactured continuously from a resin solution by coating and drying, they are conveyed roll-to-roll to a heating furnace, so the continuously manufactured films have two directions: MD direction (travel direction) and TD direction (width direction). It has process and shape anisotropy. Such process and shape anisotropy affects the formation of domains with different higher-order structures as mentioned above, and changes the orientation direction, degree of orientation, and entanglement of molecules in either the width direction or the traveling direction. is biased, causing variations in dimensional changes and anisotropy in physical properties.

Although the method of Patent Document 1 is able to reduce horizontal step unevenness in the longitudinal direction and suppress anisotropy of physical properties caused by differences in thickness, it is possible to suppress the orientation direction, degree of orientation, and entanglement of molecules inside the film. The anisotropy of physical properties due to this phenomenon has not been suppressed. Furthermore, in Patent Document 2, the heat shrinkage rate in the longitudinal direction and the width direction of the film is set to 0.05% or less by drying under conditions such that the drying temperature unevenness in the width direction is 20° C. or less. In the example, the ratio of the maximum heat shrinkage rate in the width direction to the longitudinal direction is 0.33, and the anisotropy of the heat shrinkage rate in the MD direction (longitudinal direction) and TD direction (width direction) is not suppressed. .

In the polyimide film manufacturing method of Patent Document 3, the film is intentionally shrunk in the width direction in the first half of the process in accordance with the process of sequentially passing through ovens at gradually higher temperatures, and the film becomes slack in the second half of the process. The polyimide film is expanded in the width direction in the step to reduce the anisotropy in the width direction and the traveling direction by manufacturing without slack. The ratio of linear expansion coefficients in the ) direction is 0.96, and further reduction of the anisotropy is an issue.

In this way, polyimide has excellent heat resistance, a low coefficient of linear expansion, and a high tensile modulus, but on the other hand, because it has a high molecular weight, wide molecular weight distribution, and rigid molecular chains with low mobility, the molecules become oriented when dried in a solvent. Because domains with different higher-order structures reflecting the direction, degree of orientation, and entanglement are formed, a low coefficient of linear expansion is maintained even in high-temperature regions, and the ratio of the coefficient of linear expansion and tensile modulus in the MD and TD directions of the resin film is maintained. The challenge was to obtain a resin film with small isotropy and good physical isotropy.

As a result of intensive studies to solve the above-mentioned problems, the present inventors found that the problems could be solved and arrived at the present invention. That is, the present invention has the following configuration.

A resin film that satisfies (1) to (2) below.
(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, peaks is within the range of 250 to 500°C, and the temperature dependence curve of tan δ peaks. The temperature (A) and linear expansion coefficient inflection point temperature (B) have the following relationship (40+0.8×A) ≦ B < A
(2) The weight average molecular weight of the resin that is the raw material for 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 1. Within the range of .0 to 5.0

Preferably, the resin film further satisfies (3) to (4).
(3) The linear expansion coefficient measured in the range of 35 to 200°C in both the MD direction and the TD direction 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 that in the MD direction is (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 0.97. ~1.03 range

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.

Step A of applying a resin solution onto a support and drying it to produce a resin film laminate containing a solvent;
Step B of peeling the support from the laminate to obtain a resin film containing a solvent;
Step C of removing the solvent from the resin film containing the solvent, or performing a dehydration ring closure reaction while removing the solvent,
The method for producing the resin film, characterized in that at least a part of the step C is performed by microwave heating.

The resin solution contains at least one resin selected from the group consisting of polyamic acid, polyimide, and polyamideimide, and a solvent that has a dipole moment in the range of 3.0 to 6.0 D and dissolves the resin. It is preferable.

According to the present invention, heat resistant It maintains a low coefficient of linear expansion even in high temperature ranges, has a high tensile modulus, has a small ratio of the linear expansion coefficient and tensile modulus in the MD and TD directions of the resin film, and has good isotropic physical properties. A resin film with excellent transparency can be obtained.

Hereinafter, a resin film and a method for manufacturing the resin film according to an embodiment of the present invention will be described. The resin film of the present invention is a film that satisfies the following (1) to (2).

(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, peaks is within the range of 250 to 500°C, and the temperature dependence curve of tan δ peaks. The relationship between temperature and linear expansion coefficient inflection point temperature (B) is expressed by the following formula.
(40+0.8×A) ≦ B < A

The temperature dependence curve of tan δ with respect to temperature is an index of changes in the viscoelasticity of the resin due to temperature changes, and when the temperature dependence curve of tan δ exceeds the peak temperature, the viscosity of the resin increases significantly and the strength decreases. Therefore, from the viewpoint of heat resistance required as a substitute for glass substrates used in mobile phones, digital cameras, display devices, and various other electronic devices, the temperature at which the temperature dependence curve of tan δ peaks is within the range of 250 to 500 degrees Celsius. It is preferably within the range of 260 to 480°C, more preferably within the range of 270 to 460°C. The temperature at which the temperature dependence curve of tan δ of the resin film reaches its peak is measured by the method described in Examples.

Resin films expand and contract due to temperature changes, and the linear expansion coefficient is an indicator of this change.The linear expansion coefficient of a resin film is not always constant over the measurement temperature range, but the linear expansion coefficient changes at a specific temperature depending on the resin film. becomes higher. This specific temperature is called the linear expansion coefficient inflection point temperature.

The resin film of the present invention is preferably obtained by applying and drying a resin solution. When a resin solution is applied and dried to obtain a resin film, as the solvent is removed, a denser higher-order structure reflecting the orientation direction, degree of orientation, and entanglement of the molecules that is formed first, and a denser higher-order structure that is formed later. A sparser higher-order structure that reflects the orientation direction, degree of orientation, and entanglement of molecules is generated, and each domain is formed. At this time, when the resin has a higher molecular weight, a wider molecular weight distribution, and more rigid molecular chains with low mobility, the higher-order structure of each domain differs more greatly.

The temperature at which the tan δ temperature dependence curve peaks and the linear expansion coefficient inflection point temperature are both physical property inflection point temperatures, but the temperature at which the tan δ temperature dependence curve peaks was formed at the stage of resin film production. While the coefficient of linear expansion reflects the change in the average physical properties of higher-order structures with different density, the coefficient of linear expansion reflects the change in the physical properties of the loose higher-order structure formed during the resin film creation stage. The linear expansion coefficient inflection point temperature (B) is always lower than the temperature (A) at which the curve peaks (B < A). Further, the value obtained by subtracting the linear expansion coefficient inflection point temperature from the temperature at which the tan δ temperature dependence curve peaks tends to increase as the temperature at which the tan δ temperature dependence curve peaks increases. In order to maintain a low linear expansion coefficient required as a substitute for glass substrates and a low linear expansion coefficient even at high temperatures in the substrate processing process, it is preferable that the linear expansion coefficient inflection point temperature (B) is higher. It is preferable that the expression (40+0.8×A)≦B be satisfied with respect to the temperature (A) at which the temperature dependence curve of is at its peak. The linear expansion coefficient inflection point temperature of the resin film was measured by the method described in Examples.

(2) The weight average molecular weight of the resin that is the raw material for 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 1. It is within the range of 0 to 5.0.

The weight average molecular weight of the resin that is the raw material for the resin film of the present invention is within the range of 50,000 to 500,000, more preferably 80,000 to 400,000, even more preferably 100,000 to 300,000, More preferably, it is between 120,000 and 200,000. If the weight average molecular weight is at least the above lower limit, it can satisfy the high tensile modulus, flexibility, and impact resistance required as a substitute for glass substrates. Moreover, if the weight average molecular weight is below the above upper limit, it becomes easy to satisfy the above formula. Further, it is preferable that the weight average molecular weight of the resin in the resin solution is within the above range.

The molecular weight distribution, which is the value obtained by dividing the weight average molecular weight of the resin that is the raw material for the resin film of the present invention by the number average molecular weight, is within the range of 1.0 to 5.0, more preferably 1.5 to 4.5. , more preferably 2.0 to 4.0. When the molecular weight distribution is at least the above lower limit, the cost of resin purification can be reduced, and when the molecular weight distribution is at or below the above upper limit, it becomes easy to satisfy the above formula. The method for measuring the weight average molecular weight and molecular weight distribution of the resin that is the raw material for the resin film is based on the method described in Examples.

It is preferable that the resin film of the present invention further satisfies the following (3) to (4).

(3) The linear expansion coefficient measured in the range of 35 to 200°C in both the MD direction and the TD direction 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 that in the MD direction is It is in the range of 0.97 to 1.03.

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 direction and the TD direction is preferably -5 ppm/°C to +55 ppm/°C. More preferably -4 ppm/°C to +45 ppm/°C, still more preferably -3 ppm/°C to +35 ppm/°C. When the coefficient of linear expansion is within the above range, the difference in the coefficient of linear expansion between the functional element and the functional element can be kept small, the resin film and the functional element can be prevented from peeling off even when subjected to a process of applying heat, and processability can be improved. Excellent in

The ratio of linear expansion coefficient of the resin film in the TD direction to the MD direction in the present invention is preferably in the range of 0.97 to 1.03. More preferably 0.975 to 1.025, still more preferably 0.98 to 1.02. When the ratio of the coefficient of linear expansion in the TD direction to the MD direction is within the above range, the resin film can be used in the processing process with functional elements without distinguishing between the MD and TD directions, improving workability and yield. It can be improved. The linear expansion coefficient of the resin film was measured by the method described in Examples.

(4) The tensile modulus in both the MD direction and the TD direction 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.

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 direction and the TD direction. More preferably 2.5 to 15 GPa, still more preferably 3 to 10 GPa. If the tensile modulus is equal to or higher than the above lower limit, peeling of the resin film and the functional element can be avoided, resulting in excellent handling properties. Moreover, if the tensile modulus is below the above upper limit, the resin film can be used as a flexible film.

The ratio of the tensile modulus of the resin film in the TD direction to the MD direction in the present invention is preferably in the range of 0.97 to 1.03. More preferably 0.975 to 1.025, still more preferably 0.98 to 1.02. When the ratio of the tensile modulus of elasticity in the TD direction to the MD direction is within the above range, the resin film can be used in the processing process with functional elements without distinguishing between the MD and TD directions, improving workability and yield. You can. The tensile modulus of the resin film was measured by the method described in Examples.

Since the resin film of the present invention is mainly used for the front plate and around the electrodes of image display devices such as touch panels and displays, the yellow index is preferably 10 or less, more preferably 7 or less, and Preferably it is 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 in order to use it as a flexible electronic device, it is preferably 0.1 or more, more preferably 0.2 or more, and still more preferably 0.3 or more. be. The yellow index of the resin film was measured by the method described in Examples.

Since the resin film of the present invention is mainly used for the front plate and electrode periphery 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, More preferably, it is 75% or more, even more preferably 80% or more. The upper limit of the light transmittance of the resin film at a wavelength of 400 nm is not particularly limited, but in order to use it as a flexible electronic device, it is preferably 99% or less, more preferably 98% or less, and still more preferably 97% or less. It is. The light transmittance of the resin film at a wavelength of 400 nm was measured by the method described in Examples.

Since the resin film of the present invention is mainly used for the front plate and around the 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, and even more preferably is 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 in order to use it as a flexible electronic device, it is preferably 99% or less, more preferably 98% or less, and still more preferably 97% or less. . The total light transmittance of the resin film was measured by the method described in Examples.

The resin film of the present invention is preferably obtained by coating and drying a resin solution in order to reach a temperature at which the desired tan δ temperature dependence curve peaks. 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.

A polyamic acid solution can be obtained by stirring and/or mixing diamines and tetracarboxylic acids in a solvent, and increasing the molecular weight while forming amide bonds through a condensation reaction.

The first method is to obtain a polyimide solution by heating, stirring and/or mixing diamines and tetracarboxylic acids in a solvent, and increasing the molecular weight while generating imide bonds in one step through a dehydration ring-closing reaction. I can do it. In the second method, after obtaining the polyamic acid solution described above, an imidization accelerator and an imidization agent are added, and while stirring and/or mixing, an imide bond is generated in two steps by a dehydration ring closure reaction. It can be obtained by increasing the molecular weight.

The polyamide-imide solution can be obtained by heating, stirring and/or mixing diisocyanates and tricarboxylic acids in a solvent, and increasing the molecular weight while generating amide bonds and imide bonds in one step through a decarboxylation reaction.

When increasing the molecular weight of the above-mentioned polyamic acid, polyimide, and polyamide-imide, dicarboxylic acids can be used as a copolymerization component within a range that does not impair the properties of the resin solution and resin film.

The resin solution used in the present invention can be a resin solid obtained by pouring the resin solution obtained above into a poor solvent to precipitate the resin component, washing, filtering, and drying it, or a resin solid obtained by casting and drying the resin solution. It can also be obtained by dissolving the resulting resin solid again in a soluble solvent.

Examples of the tetracarboxylic acids, tricarboxylic acids, and dicarboxylic acids include aromatic tetracarboxylic acids (including their acid anhydrides) and aliphatic tetracarboxylic acids (including their acid anhydrides) commonly used in polyimide synthesis and polyamideimide synthesis. , 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), (including anhydrides), aromatic dicarboxylic acids, aliphatic dicarboxylic acids, alicyclic dicarboxylic acids, and the like. Among these, aromatic tetracarboxylic anhydrides and alicyclic tetracarboxylic anhydrides are preferred, aromatic tetracarboxylic anhydrides are more preferred from the viewpoint of heat resistance, and alicyclic tetracarboxylic anhydrides are more preferred from the viewpoint of light transparency. More preferred are tetracarboxylic acids. When the tetracarboxylic acids are acid anhydrides, the number of anhydride structures in the molecule may be one or two, but preferably those having two anhydride structures (dianhydride ) is better. Tetracarboxylic acids, tricarboxylic acids, and dicarboxylic acids may be used alone or in combination of two or more.

The 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'-benzophenone tetra Carboxylic acid, 4,4'-[(3H-2,1-benzoxathiol-1,1-dioxide-3,3-diyl)bis(toluene-2,5-diyloxy)]dibenzene-1,2-dicarvone 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',3,3'-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, 4,4'-[spiro(xanthene-9,9'- Examples include tetracarboxylic acids such as (fluorene)-3,6-diylbis(oxycarbonyl)]diphthalic acid and acid anhydrides thereof. Among these, dianhydrides having two acid anhydride structures are preferred, particularly 4,4'-(2,2-hexafluoroisopropylidene)diphthalic dianhydride, 4,4'-oxydiphthalic dianhydride, Acid dianhydrides are preferred. Incidentally, the aromatic tetracarboxylic acids may be used alone or in combination of two or more kinds. When heat resistance is important, the aromatic tetracarboxylic acids are preferably 50% by mass or more of the total tetracarboxylic acids, more preferably 60% by mass or more, still more preferably 70% by mass or more, and still more preferably It is 80% by mass or more.

Examples of alicyclic tetracarboxylic acids include 1,2,3,4-cyclobutanetetracarboxylic acid, 1,2,3,4-cyclopentanetetracarboxylic acid, 1,2,3,4-cyclohexanetetracarboxylic acid, 1 , 2,4,5-cyclohexanetetracarboxylic acid, 3,3',4,4'-bicyclohexyltetracarboxylic acid, bicyclo[2,2,1]heptane-2,3,5,6-tetracarboxylic acid, Bicyclo[2,2,2]octane-2,3,5,6-tetracarboxylic acid, bicyclo[2,2,2]oct-7-ene-2,3,5,6-tetracarboxylic 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-methano Naphthalene-2,3,6,7-tetracarboxylic acid, norbornane-2-spiro-α-cyclopentanone-α'-spiro-2''-norbornane-5,5'',6,6''-tetra Carboxylic 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-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, norbornane-2-spiro-α-(methylcyclohexanone)-α'-spiro-2''-norbornane Examples include tetracarboxylic acids such as -5,5'',6,6''-tetracarboxylic acid, and acid anhydrides thereof. Among these, dianhydrides having two acid anhydride structures are preferred, particularly 1,2,3,4-cyclobutanetetracarboxylic dianhydride and 1,2,3,4-cyclohexanetetracarboxylic dianhydride. Acid dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride is preferred, and 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride Acid dianhydride is more preferred, and 1,2,3,4-cyclobutanetetracarboxylic dianhydride is even more preferred. Note that these may be used alone or in combination of two or more. When transparency is important, the alicyclic tetracarboxylic acids are preferably 50% by mass or more of the total tetracarboxylic acids, more preferably 60% by mass or more, still more preferably 70% by mass or more, and even more preferably is 80% by mass or more.

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 diphenylsulfone-3,3',4'-tricarboxylic acid. acids, or hydrogenated products of the above aromatic tricarboxylic acids such as hexahydrotrimellitic acid, alkylenes such as ethylene glycol bis trimellitate, propylene glycol bis trimellitate, 1,4-butanediol bis trimellitate, and polyethylene glycol bis trimellitate. Examples include glycol bistrimelitate, 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. Incidentally, these may be used alone or in combination.

Examples of dicarboxylic acids include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid, naphthalene dicarboxylic acid, 4,4'-oxydibenzenecarboxylic acid, or the above-mentioned aromatic dicarboxylic acids such as 1,6-cyclohexanedicarboxylic acid. Hydrogenates of oxalic acid, succinic acid, glutaric acid, adipic acid, heptanedioic acid, octanedioic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, 2-methylsuccinic acid, and acid chlorides thereof Alternatively, examples include esterified products. Among these, aromatic dicarboxylic acids and hydrogenated products thereof are preferred, with terephthalic acid, 1,6-cyclohexanedicarboxylic acid, and 4,4'-oxydibenzenecarboxylic acid being particularly preferred. Note that dicarboxylic acids may be used alone or in combination.

The diamines or diisocyanates used in the present invention to obtain a colorless and highly transparent polyimide are not particularly limited, and include aromatic diamines, aliphatic diamines, and alicyclic diamines commonly used in polyimide synthesis and polyamideimide synthesis. diisocyanates, aromatic diisocyanates, aliphatic diisocyanates, alicyclic diisocyanates, etc. can be used. From the viewpoint of heat resistance, aromatic diamines are preferred, and from the viewpoint of transparency, alicyclic diamines are preferred. Further, when aromatic diamines having a benzoxazole structure are used, it becomes possible to exhibit high elastic modulus, low thermal shrinkage, and low coefficient of linear expansion as well as high heat resistance. Diamines and diisocyanates may be used alone or in combination of two or more.

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, 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' -diaminodiphenylsulfide, 4,4'-diaminodiphenylsulfide, 3,3'-diaminodiphenylsulfoxide, 3,4'-diaminodiphenylsulfoxide, 4,4'-diaminodiphenylsulfoxide, 3,3'-diaminodiphenylsulfone, 3,4'-diaminodiphenylsulfone, 4,4'-diaminodiphenylsulfone, 3,3'-diaminobenzophenone, 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-amino) phenoxy)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-amino) phenoxy)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]diphenylsulfone, 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-trifluoro) methylphenoxy)-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-5'-phenoxybenzophenone, 3,3'-diamino -4,4'-Dibiphenoxybenzophenone, 4,4'-diamino-5,5'-dibiphenoxybenzophenone, 3,4'-diamino-4,5'-dibiphenoxybenzophenone, 3,3'-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- dimethyl (aminophenyl)cyclobutane-1,3-dicarboxylate, and some or all of the hydrogen atoms on the aromatic ring of the aromatic diamine are halogen atoms, alkyl groups or alkoxyl groups having 1 to 3 carbon atoms, cyano groups, Alternatively, examples thereof include aromatic diamines substituted with a halogenated alkyl group or alkoxyl group having 1 to 3 carbon atoms, in which some or all of the hydrogen atoms of the alkyl group or alkoxyl group are substituted with halogen atoms. Further, the aromatic diamines having the benzoxazole structure are not particularly limited, and examples thereof include 5-amino-2-(p-aminophenyl)benzoxazole, 6-amino-2-(p-aminophenyl)benzoxazole, Oxazole, 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'-diamino) diphenyl)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, in particular, 2,2'-ditrifluoromethyl-4,4'-diaminobiphenyl, 4-amino-N-(4-aminophenyl)benzamide, 4,4'-diaminodiphenylsulfone, 3,3 '-Diaminobenzophenone is preferred. Incidentally, the aromatic diamines may be used alone or in combination.

Examples of alicyclic diamines include 1,4-diaminocyclohexane, 1,4-diamino-2-methylcyclohexane, 1,4-diamino-2-ethylcyclohexane, 1,4-diamino-2-n-propyl Cyclohexane, 1,4-diamino-2-isopropylcyclohexane, 1,4-diamino-2-n-butylcyclohexane, 1,4-diamino-2-isobutylcyclohexane, 1,4-diamino-2-sec-butylcyclohexane, Examples include 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. Incidentally, the alicyclic diamines may be used alone or in combination.

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'-diethyldiphenylmethane-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, diphenyl ether-4,4'-diisocyanate, 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'-(2,2bis(4-phenoxyphenyl)propane) diisocyanate, 3, 3'- or 2,2'-dimethylbiphenyl-4,4'-diisocyanate, 3,3'- or 2,2'-diethylbiphenyl-4,4'-diisocyanate, 3,3'-dimethoxybiphenyl-4, Aromatic diisocyanates such as 4'-diisocyanate, 3,3'-diethoxybiphenyl-4,4'-diisocyanate, and diisocyanates obtained by hydrogenating any of these (e.g., isophorone diisocyanate, 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, hexamethylene diisocyanate) and the like. 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. Note that the diisocyanates may be used alone or in combination.

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

Examples of the solvent used in the resin solution of the present invention include N,N-dimethylformamide (dipole moment: 3.86D), N,N-dimethylacetamide (DMAc) (dipole moment: 3.72D), N- Methyl-2-pyrrolidone (NMP) (dipole moment: 4.09D), N-methyl-ε-caprolactam (dipole moment: 4.23D), dimethylsulfoxide (dipole moment: 3.96D), dimethylsulfone ( dipole moment: 4.47D), sulfolane (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) (dipolar child moment: 4.27D), and 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) can be used to prevent resin solids from precipitating during microwave heating. It may be used to the extent that it does not impair the uniform heating effect. Further, when two or more types of solvents are mixed, the value of the dipole moment is a weighted average value of the respective values.

Fine particles may be added to the resin solution of the present invention within a range that does not impair the properties of the resin film. The fine particles may be inorganic fine particles or organic fine particles. 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 include. 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.

The resin solid content concentration of the resin solution of the present invention is preferably 5 to 40% by mass, more preferably 7 to 35% by mass, and even more preferably 10 to 30% by mass. When the resin solid content concentration is at least the above lower limit, it is preferable from the viewpoint of obtaining the film thickness required for the resin film, and when it is below the above upper limit, the solution flow is sufficient to not impair the physical isotropy of the resin film. It is preferable from the viewpoint of obtaining characteristics.

The resin film in the present invention is preferably a resin film obtained by the method for producing a resin film described below. Specifically, it is a polymer film having an imide bond in its main chain, preferably a polyimide film or a polyamide-imide film, and more preferably a polyimide film.

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 still more preferably 7 μm or more from the viewpoint of the strength and handling properties required for the resin film. From the viewpoint of uniformly removing the solvent, 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.

A preferred method for producing the resin film of the present invention is as follows:
Step A of producing a resin film laminate containing a solvent by coating and drying the resin solution on a support;
Step B of peeling off the support from the solvent-containing resin film laminate to obtain a solvent-containing resin film;
Step C of removing the solvent from the resin film containing the solvent, or performing a dehydration ring closure reaction while removing the solvent,
It is characterized in that at least a part of the step C is performed by microwave heating.

Step A will be explained. Step A is a step of applying a resin solution onto a support and drying it to produce a resin film laminate (hereinafter also simply referred to as a laminate) containing a solvent. The laminate is obtained by laminating the dried resin solution on the support.

Examples of the support used in the present invention include a resin film base, a stainless steel belt base, and a glass base. As the resin film base material, it is preferable to use a resin film base material that does not swell or dissolve in the solvent contained in the resin solution, such as polyethylene terephthalate (PET) film, polyethylene naphthalate (PEN) film, polyolefin (PP) film. , cycloolefin-based (COP) films, and the like. Moreover, in order to peel the resin film containing the solvent from the support, it is preferable to use a support that has easy peelability.

Examples of methods for applying the resin solution onto the support include die coating, comma coating, blade coating, roll coating, knife coating, and bar coating. You may combine the methods. A comma coating method, a die coating method, or a combination thereof is preferable from the viewpoint of productivity.

Methods for drying the resin solution on the support include air blow drying, hot air drying, infrared heat drying, heat transfer drying from the support, etc. Two of these methods may be combined. good. The solvent content of the dried resin film containing the solvent is preferably 3 to 50% by mass, more preferably 5 to 40% by mass, and still more preferably 7 to 30% by mass. When the solvent content is equal to or higher than the above lower limit, there will be little difference in solvent content and polymer higher-order structure between the surface of the resin film in contact with the support and the opposite surface, and the anisotropy of physical properties in the thickness direction of the resin film will decrease. When the amount is less than the above upper limit, deformation of the resin film after being peeled off from the support is suppressed, and handling becomes easy.

Process B will be explained. Step B is a step of peeling the support from the laminate to obtain a resin film containing a solvent.

The method of peeling the resin film containing the solvent from the support is not particularly limited, but includes a method of rolling it up from the end with tweezers, etc., a method of making a cut in the laminate, and pasting an adhesive tape on one side of the cut portion. Examples include a method in which one side of the cut portion of the resin film is vacuum-adsorbed and then the tape is rolled up from that part.

Step C will be explained. Step C is a step of removing the solvent from the resin film containing the solvent, or performing a dehydration ring closure reaction while removing the solvent, and at least a part of Step C is subjected to microwave heating.

Microwave heating used in the step of removing a solvent from a resin film containing a solvent after peeling from a support is based on the heating principle of vibrating the dipoles of molecules contained in the object to be heated using microwaves. Therefore, the absorption efficiency of microwaves depends on the magnitude of the dipole moment and the ease with which molecules move following the period of the microwave. Therefore, in order to efficiently uniformly heat and remove the solvent from the resin film containing the solvent using microwaves, a solvent having the above-mentioned dipole moment value is specified.

As the frequency of the microwave heating device used in the present invention, it is preferable to select a frequency at which the molecules of the solvent having the above-mentioned dipole moment value are likely to move. However, in general, heating devices with a frequency of 2,450 MHz are common due to restrictions imposed by the Radio Law and restrictions on microwave electron tubes. 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 frequencies of 2,450 MHz and 915 MHz due to such circumstances. Further, the intensity of the microwave is appropriately selected in consideration of the state of foaming, citrus skin, waving, etc. on the surface of the resin film.

By using a resin solution containing a solvent with a specified dipole moment value and using microwave heating, the resin film is uniformly heated and dried in the solvent removal process, and the difference in the density of the higher-order structure formed is is reduced, and it becomes easy to achieve the formula (40+0.8×A)≦B<A. Furthermore, it is possible to improve the physical isotropy of the obtained resin film, and to keep the ratio of the linear expansion coefficient of the resin film in the TD direction to the MD direction and the ratio of the tensile modulus of the resin film in the TD direction to the MD direction to be within a preferable range. becomes easier.

In the present invention, methods such as air drying, hot air drying, infrared heat drying, etc. can be used in combination with microwave heating, and two of these methods may be combined.

The temperature increase profile in the solvent removal step using the above heating method is preferably such that the initial temperature is in the range of 50 to 200°C, and if it is above the lower limit of the specified range, it is difficult to suppress temperature variations in the drying oven. If the initial temperature is below the upper limit of the specified range, it will be easy to suppress foaming of the resin film and yuzu skin on the surface caused by rapid heating of the solvent, and it will also prevent the resin film surface and the resin film from forming. The difference between the solvent content and the polymer higher-order structure with respect to the inside becomes smaller, and it becomes easier to achieve the formula (40+0.8×A)≦B<A.

The temperature increase profile in the solvent removal step using the above heating method is preferably such that the final temperature is in the range of 300 to 500°C, and if it is above the lower limit of the specified range, the amount of residual solvent in the resin film can be suppressed. When the final temperature is below the upper limit of the specified range, it becomes easy to suppress thermal deterioration of the resin film.

The temperature increase profile in the solvent removal step using the above heating method is either a temperature increase rate of 5 to 60°C/min, a stepwise increase in the number of stages of 2 or more, or both. It is preferable to raise the temperature by a combination of methods. If the heating rate is above the lower limit of the specified range, the working time in the solvent removal process can be shortened, and if it is below the upper limit of the above specified range, foaming of the resin film due to rapid heating of the solvent may occur. It becomes easier to suppress yuzu skin etc. on the surface, and the difference in solvent content and polymer higher order structure between the surface of the resin film and the inside of the resin film is reduced, and the formula (40 + 0.8 × A) ≦ B < A becomes easier to achieve.

When increasing the temperature in steps, the number of steps is preferably 2 to 10, and the rate of temperature increase between each step is preferably 10 to 100° C./min. When the number of steps is at least the lower limit of the specified range, it is easy to suppress foaming of the resin film and yuzu skin on the surface caused by rapid heating of the solvent, and also to prevent the surface of the resin film and the inside of the resin film from forming. Differences in solvent content and polymer higher-order structure are reduced, making it easier to achieve the formula (40+0.8×A)≦B<A. Further, when the number of steps is less than or equal to the upper limit of the designated range, work efficiency is improved.

It is preferable to determine the 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 above the lower limit of the specified range, it will be easier to suppress foaming of the resin film and yuzu skin on the surface due to rapid heating of the solvent, and if it is below the upper limit, productivity will improve. It becomes easy to suppress thermal deterioration of the resin film.

In the solvent removal step in the present invention, the resin film can be further stretched. The stretching ratio in this stretching operation is preferably 1.5 to 4.0 times in the MD (long length) direction and 1.4 to 3.0 times in the TD (short length) direction. It is preferable that the ratio of the stretching ratio in the TD direction (MD/TD) exceeds 1.0. By setting the stretching conditions within the above range, the average linear expansion coefficient 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 can be improved. It becomes easy to keep it within a preferable range.

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, still more preferably 0.03 to 3.0% by mass. It is in the range of 0% by mass. By setting the solvent content at or above the lower limit above, thermal deterioration of the resin film due to excessive high-temperature treatment can be suppressed, and by setting the solvent content at or below the upper limit, it is easy to keep the coefficient of linear expansion and tensile modulus within a preferable range. becomes.

Hereinafter, the present invention will be described in detail using Examples, but the present invention is not limited to the following Examples unless it exceeds the gist thereof.

In addition, each measurement value in Examples and Comparative Examples was measured by the following method unless otherwise specified.

<Temperature dependence curve peak temperature of tan δ of resin film>
The storage modulus (E'), loss modulus (E"), and loss modulus are measured under the following conditions for three samples each in the flow direction (MD direction) and width direction (TD direction) of the resin film. A temperature dependence curve of tan δ (=E"/E'), which is the value divided by
Device name: DMA Q800 manufactured by TA Instruments
Sample length: 15-20mm
Sample width: 4mm
Heating start temperature: 25℃
Heating end temperature: 500℃
Temperature increase rate: 5℃/min
Measurement frequency: 10Hz

<Linear expansion coefficient inflection point temperature of resin film>
Measure the expansion/contraction rate at three samples each in the flow direction (MD direction) and width direction (TD direction) of the resin film under the following conditions, read the temperature at which the expansion/contraction rate inflection point occurs during the second temperature rise, and determine the flow rate. The average values in the direction (MD direction) and width direction (TD direction) were calculated.
Equipment name: Bruker AXS TMA-4000SA
Sample length: 15mm
Sample width: 2mm
Distance between chucks: 10mm
Load: 5gf
First heating start temperature: 25℃
First heating end temperature: 200℃
First heating rate: 20°C/min
Temperature cooling rate: 5℃/min
Second heating start temperature: 30℃
Second heating end temperature: 500℃
Second heating rate: 10°C/min
Atmosphere: Argon

<Weight average molecular weight, number average molecular weight, and molecular weight distribution of resin>
8 mg of the resin sample was weighed, immersed in 8 ml of 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.
Equipment name: Tosoh Corporation HLC-8420GPC
Column: TSKgel SuperAWH-H×2
Solvent: DMAc (30mM lithium bromide added)
Flow rate: 0.3ml/min
Concentration: 0.1%
Injection volume: 10μl
Temperature: 40℃
Detector: RI

<Thickness of resin film>
Measurement was performed using a micrometer (Millitron 1245D, manufactured by Finereuf Co., Ltd.).

<Coefficient of linear expansion (CTE) of resin film>
The expansion and contraction ratio was measured at three samples each in the flow direction (MD direction) and width direction (TD direction) of the resin film under the following conditions, and the expansion and contraction ratio was measured at intervals of 15°C such as 35°C to 50°C and 50°C to 65°C. The expansion/contraction rate/temperature was measured up to 200° C., and the average value of all measured values was calculated as CTE.
Equipment name: TMA4000S manufactured by MAC Science
Sample length: 20mm
Sample width: 2mm
Heating start temperature: 25℃
Heating end temperature: 400℃
Temperature increase rate: 5℃/min
Atmosphere: Argon

<Tensile modulus of resin film>
A test piece was prepared by cutting out a strip of 100 mm x 10 mm in the flow direction (MD direction) and width direction (TD direction) of the resin film. The test piece was cut out from the center portion in the width direction. The tensile modulus was measured for three samples each in the MD direction and the TD direction under the following conditions, and the average value of all measured values was determined.
Equipment name: Shimadzu Autograph (R) AG-5000A
Distance between chucks: 40mm
Temperature: 25℃
Tensile speed: 50mm/min

<Yellowness index (yellow index, YI) of resin film>
Using a color meter (ZE6000, manufactured by Nippon Denshoku Co., Ltd.) and a C2 light source, the tristimulus XYZ values of the resin film were measured according to ASTM D1925, and the yellowness index (YI) was calculated using the following formula. Note that similar measurements were performed three times and the arithmetic mean value was used.
YI=100×(1.28X-1.06Z)/Y

<400nm light transmittance of resin film>
The light transmittance of the resin film at a wavelength of 400 nm was measured using a spectrophotometer (“U-2001” manufactured by Hitachi), and the obtained value was converted to a thickness of 20 μm based on the Beer-Lambert law. The obtained value was taken as the 400 nm light transmittance of the resin film. Note that similar measurements were performed three times and the arithmetic mean value was used.

<Total light transmittance (TT) of resin film>
The total light transmittance (TT) of the resin film was measured using HAZEMETER (NDH5000, manufactured by Nippon Denshoku Co., Ltd.). A D65 lamp was used as a light source. Note that similar measurements were performed three times and the arithmetic mean value was used.

[Synthesis Example 1 (Preparation of polyamic acid solution A)]
After purging the inside of a reaction vessel equipped with a nitrogen introduction tube, a thermometer, and a stirring bar with nitrogen, 1470.8 parts by mass of 1,2,3,4-cyclobutanetetracarboxylic dianhydride was added to the reaction vessel under a nitrogen atmosphere. (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), 21795 parts by mass After charging and dissolving 1 part of N,N-dimethylacetamide (DMAc), the solution was stirred at room temperature for 24 hours to obtain a polyamic acid solution A with a solid content of 17.2 parts by mass and a reduced viscosity of 4.5 dl/g. . Table 1 shows 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.

[Synthesis example 2 (preparation of polyimide solution B)]
After purging the inside of the reaction vessel equipped with a nitrogen introduction tube, a thermometer, and a stirring bar with nitrogen, 551 parts by mass of N,N-dimethylacetamide (DMAc) and 64.1 parts by mass of N,N-dimethylacetamide (DMAc) were added to the reaction vessel under a nitrogen atmosphere. 2,2'-ditrifluoromethyl-4,4'-diaminobiphenyl (TFMB) was added 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 were added under a nitrogen stream. Mass parts of biphenyltetracarboxylic dianhydride (BPDA) were added over about 10 minutes, and the temperature was adjusted to a temperature range of 20 to 40°C while stirring was continued for 6 hours to carry out a polymerization reaction. A viscous polyamic acid solution was obtained.
Next, after diluting the obtained polyamic acid solution by adding 410 parts by mass of DMAc, 25.83 parts by mass of isoquinoline was added as an imidization accelerator, and the polyamic acid solution was heated at 30 to 40°C while stirring. While keeping the temperature within the range, 122.5 parts by mass of acetic anhydride was slowly added dropwise as an imidizing agent over about 10 minutes, and then the liquid temperature was further maintained at 30 to 40°C and stirred for 12 hours. Subsequently, a chemical imidization reaction was performed to obtain a polyimide solution.
Next, 1000 parts by mass of the polyimide solution containing the obtained imidization agent and imidization accelerator was transferred to a reaction vessel equipped with a stirring device and stirring blades, and the mixture was heated to 15 to 25° C. while stirring at a speed of 120 rpm. 1500 parts by mass of methanol was added dropwise thereto at a rate of 10 g/min. When approximately 800 parts by mass of methanol was added, turbidity of the polyimide solution was observed, and precipitation of powdery polyimide was observed. Subsequently, 1500 parts by mass of methanol was added to complete the precipitation of polyimide. Subsequently, 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. Thereafter, 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 system, and further dried at 260°C for 2 hours to remove the remaining volatile components. , 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 having a solid content of 20 parts by mass. Table 1 shows 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.

[Synthesis Example 3 (Preparation of polyimide solution C)]
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. This was followed by 248.18 parts by mass of 4,4'-oxydiphthalic anhydride (ODPA), 58.8 parts by mass of biphenyltetracarboxylic dianhydride (BPDA), 335 parts by mass of GBL, and 390 parts by mass. After adding toluene at room temperature, the internal temperature was raised to 160°C, and the mixture was heated under reflux at 160°C for 1 hour to perform imidization. After the imidization was completed, the temperature was raised to 180°C, and the reaction was continued while extracting toluene. After reacting for 12 hours, the oil bath was removed, the temperature was returned to room temperature, and 1149 parts by mass of GBL was added so that the solid content was 20 parts by mass to obtain a polyimide solution C with a reduced viscosity of 0.6 dl/g. Table 1 shows 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.

[Synthesis Example 4 (Preparation of polyimide solution D)]
While introducing nitrogen gas into a reaction vessel equipped with a nitrogen introduction tube, a Dean-Stark apparatus, a reflux tube, a thermometer, and a stirring bar, 384.38 parts by mass of norbornane-2-spiro-α-cyclopentanone-α' was added. -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 then the internal temperature The temperature was raised to 180°C, and heating imidization was performed at 180°C for 3 hours while toluene was distilled off to obtain a polyimide solution.
Next, 2,500 parts by mass of the obtained polyimide solution was transferred to a reaction vessel equipped with a stirring device and stirring blades, kept at a temperature of 15 to 25°C while stirring at a speed of 120 rpm, and 50,000 parts by mass of acetone was added thereto. It was dropped at a rate of 10 g/min. When about 2,500 parts by mass was added, turbidity of the polyimide solution was observed, and precipitation of powdery polyimide was observed. Subsequently, the remaining 2500 parts by mass of acetone was added to complete the precipitation of polyimide. Subsequently, 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. Thereafter, 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 system, and further dried at 260°C for 2 hours to remove the remaining volatile components. , 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. Table 1 shows 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.

[Synthesis Example 5 (Preparation of polyamic acid solution E)]
After purging the inside of a reaction vessel equipped with a nitrogen introduction tube, a thermometer, and a stirring bar with nitrogen, 196.1 parts by mass of 1,2,3,4-cyclobutanetetracarboxylic dianhydride was added to the reaction vessel under a nitrogen atmosphere. After charging and dissolving 227.3 parts by mass of 4-amino-N-(4-aminophenyl)benzamide (DABAN), and 1694 parts by mass of N,N-dimethylacetamide (DMAc). The mixture was stirred at room temperature for 24 hours to obtain a polyamic acid solution E having a solid content of 20 parts by mass and a reduced viscosity of 4.5 dl/g. Table 1 shows 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.

[Production example 1 of polyimide film (Examples 1 to 5)]
Polyamic acid solution A was applied using a die coater onto an endless continuous belt made of mirror-finished stainless steel that was a support for film production (coating width 1240 mm), and dried at 90 to 115° C. for 10 minutes. The polyamic acid film (containing 9% by mass of residual solvent), which became 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 processed using a pin tenter until the final pin sheet spacing was 1140 m.
Grip both ends of the film so that the temperature is 60°C/min, insert the film into a continuous heating furnace equipped with a microwave heating zone and a hot air circulation device, heat the film at 170°C for 1 minute in the first stage, and then heat the film at a heating rate of 60°C/min to 230°C. The temperature was raised to 230°C for 1 minute in the second stage, then the temperature was raised to 350°C at a heating rate of 60°C/min, and the heat treatment was performed in the third stage at 350°C for 5 minutes. At this time, 50 kW of 2,450 MHz microwave was introduced into the microwave heating zone. Thereafter, the film was cooled to room temperature for 2 minutes, portions with poor flatness at both ends of the film were cut off using a slitter, and the film was rolled up into a roll to obtain a resin film 1A shown in Table 2. Thereafter, polyamic acid solution A was similarly changed to 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. Table 2 shows the characteristics evaluation results of the obtained resin film.

[Production example 2 of polyimide film (Examples 6 to 10)]
The polyamic acid solution A is used as a film production support, and the area surface roughness (Sa) is 1 nm, the maximum protrusion height (Sp) is 7 nm, and the peak density (Spd) is 20/square μm or less, It was coated on a polyester film without a coating layer on its surface using a comma coater (coating width: 1240 mm) and dried at 90 to 115° C. for 10 minutes. The polyamic acid film (containing 10% by mass of residual solvent) which became 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 with a pin tenter so that the final pin sheet spacing was 1140 mm, and then 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. The temperature was increased at a temperature increase rate of 15° C./min. At this time, 40 kW of 2,450 MHz microwave was introduced into the microwave heating zone. Thereafter, the film was cooled to room temperature for 2 minutes, portions with poor flatness at both ends of the film were cut off using a slitter, and the film was rolled up into a roll to obtain a resin film 2A shown in Table 2. Thereafter, polyamic acid solution A was similarly changed to 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. Table 2 shows the characteristics evaluation results of the obtained resin film.

[Polyimide film production example 3 (comparative examples 1 to 5)]
Polyamic acid solution A was applied using a die coater onto an endless continuous belt made of mirror-finished stainless steel that was a support for film production (coating width 1240 mm), and dried at 90 to 115° C. for 10 minutes. The polyamic acid film (containing 9% by mass of residual solvent), which became 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 with a pin tenter so that the final pin sheet spacing was 1140 mm, and the film was inserted into a continuous heating furnace equipped with a hot air circulation device, and the temperature was raised from 170°C to 350°C at a rate of 15°C. The temperature was increased at a rate of /min. Thereafter, the film was cooled to room temperature for 2 minutes, portions with poor flatness at both ends of the film were cut off using a slitter, and the film was rolled up into a roll to obtain a resin film 3A shown in Table 3. Thereafter, polyamic acid solution A was similarly changed to 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. Table 3 shows the characteristics evaluation results of the obtained resin film.

[Polyimide film production example 4 (comparative examples 6 to 10)]
The polyamic acid solution A is used as a film production support, and the area surface roughness (Sa) is 1 nm, the maximum protrusion height (Sp) is 7 nm, and the peak density (Spd) is 20/square μm or less, It was coated on a polyester film without a coating layer on its surface using a comma coater (coating width: 1240 mm) and dried at 90 to 115° C. for 10 minutes. The polyamic acid film (containing 10% by mass of residual solvent) which became 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 with a pin tenter so that the final pin sheet spacing was 1140 mm, and then 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. The temperature was increased at a temperature increase rate of 70° C./min, and heat treatment was performed at 350° C. for 4 minutes. At this time, 50 kW of 2,450 MHz microwave was introduced into the microwave heating zone. Thereafter, the film was cooled to room temperature for 2 minutes, portions with poor flatness at both ends of the film were cut off using a slitter, and the film was rolled up into a roll to obtain a resin film 4A shown in Table 3. Thereafter, polyamic acid solution A was similarly changed to 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. Table 3 shows the characteristics evaluation results of the obtained resin film.

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 high linear expansion in the MD and TD directions of the resin film. Since the ratio of the modulus and tensile modulus is small and the physical properties are isotropic, it is extremely useful for front plates and electrodes of image display devices such as touch panels and displays.

Claims (6)

Step A of applying a polyamic acid resin solution onto a support and drying it to produce a resin film laminate containing a solvent;
Step B of peeling the support from the laminate to obtain a resin film containing a solvent;
Step C of carrying out a dehydration ring closure reaction while removing the solvent from the resin film containing the solvent,
In the step C, the temperature is raised at a rate of 5 to 60°C/min, the temperature is raised in steps of 2 or more, or a combination of both.
At least a part of the step C is performed by microwave heating,
The obtained polyimide resin film satisfies the following (1) to (2),
Method for manufacturing resin film.
(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, peaks is within the range of 250 to 500°C, and the temperature dependence curve of tan δ peaks. The temperature (A) and linear expansion coefficient inflection point temperature (B) have the following relationship (40+0.8×A) ≦ B < A
(2) The weight average molecular weight of the resin that is the raw material for 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 1. Within the range of .0 to 5.0 The method for producing a resin film according to claim 1, wherein the resin solution contains a solvent that has a dipole moment in the range of 3.0 to 6.0 D and dissolves the resin. The method for producing a resin film according to claim 1 or 2, which further satisfies (3) to (4).
(3) The linear expansion coefficient measured in the range of 35 to 200°C in both the MD direction and the TD direction 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 that in the MD direction is (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 0.97. ~1.03 range The method for producing a resin film according to any one of claims 1 to 3, characterized in that the yellow index is 10 or less, the light transmittance at a wavelength of 400 nm is 70% or more, and the total light transmittance is 85% or more. The method for producing a resin film according to any one of claims 1 to 4, wherein the initial temperature in step C is in the range of 50 to 200°C. The method for producing a resin film according to any one of claims 1 to 5, wherein the final temperature in step C is in the range of 300 to 500°C.