WO2022014210A1 - Resin film and method for manufacturing resin film - Google Patents

Abstract

Provided is a resin film that has excellent heat resistance, has a linear coefficient of expansion that is low up to a high-temperature region, has a high tensile modulus of elasticity, has a low ratio in terms of the linear coefficients of expansion in the MD direction and the TD direction of the resin film and the tensile modulus of elasticity, and has satisfactory isotropy in terms of the properties thereof.　The resin film satisfies items (1)-(2) below.　(1) The temperature (A) at which a temperature dependence curve of tan δ, which is a value where the loss elastic modulus has been divided by the storage modulus of elasticity, reaches a peak is within the range of 250 to 500°C, and the temperature (A) at which the temperature dependence curve of tan δ reaches the peak and the linear coefficient of expansion inflection temperature (B) are related as indicated in the following formula: (40+0.8×A)≤B<A; and (2) the weight average molecular weight of a resin constituting a feedstock of the resin film is within the range of 50,000 to 500,000, and a molecular weight distribution thereof, which is a value where the weight average molecular weight has been divided by the number average molecular weight of the resin, is within the range of 1.0 to 5.0.

Description

Resin film and method for manufacturing resin film

The present invention relates to a resin film and a method for manufacturing a resin film. More specifically, it has excellent heat resistance, maintains a low linear expansion coefficient even in a high temperature region, has a high tensile elastic modulus, has a small ratio of the linear expansion coefficient and the tensile elastic modulus in the TD direction to the MD direction of the resin film, and is a resin. The present invention relates to a resin film having good physical properties and isomorphism of the film and excellent transparency, and a method for producing the resin film.

In recent years, with the progress of miniaturization, weight reduction, and convenience of mobile phones, digital cameras, display devices, and other various electronic devices that have become more sophisticated, heat resistance has been replaced with the hard and impact-sensitive glass substrate that has been used in the past. A resin film substrate material having excellent low linear expansion coefficient, high tensile elastic modulus, flexibility, impact resistance, and transparency is expected.

The resin film is industrially manufactured by forming a film of an organic polymer resin material into a film, and the film forming method is a melt film forming method in which an organic polymer resin is melted and then extruded from a slit-shaped die. There is a solution film forming method in which a molecular resin solution is uniformly applied to a support and the solvent is dried and volatilized. Among the organic polymer resin materials, the polyimide resin and the polyamide-imide resin, which are particularly excellent in heat resistance, are insoluble or melt at a very high temperature, so that a resin film is generally obtained by solution film formation.

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

In addition, in order to suppress the variation in the sagging of the film, we found that there is a correlation between the sagging and the anisotropy index, the spindle alignment coefficient, the coefficient of thermal expansion, and the drying temperature, and suppressed the drying temperature unevenness in the width direction to suppress the line. A method for suppressing variation in expansion coefficient, that is, dimensional change is described (Patent Document 2).

In Patent Document 3, when a polyimide film that causes a remarkable decrease in elastic modulus above the glass transition temperature is manufactured, both ends of the film are fixed and conveyed without slack according to the width of the film that changes due to shrinkage and expansion in the heating step. A manufacturing method for reducing the anisotropy of the linear expansion coefficient in the MD direction (traveling direction) and the TD direction (width direction) of the film is described.

Japanese Unexamined Patent Publication No. 2013-203838 Japanese Unexamined Patent Publication No. 2018-70842 Japanese Unexamined Patent Publication No. 2000-290401

In order to form functional elements such as electrodes and display elements in a straightforward manner on the surface, a resin film used as a substitute for a glass substrate is required to have a high tensile elastic modulus, low CTE, heat resistance and chemical resistance. Polyimide as a resin suitable for such a resin film, polyamide-imide, and polyamic acid as a precursor of polyimide exhibit heat resistance by containing a large amount of rigid molecular chains with low mobility and having a high molecular weight. In addition, it has a wide distribution in molecular weight as a result of increasing the molecular weight.

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

When films are industrially continuously produced from a resin solution by coating and drying, the films that are continuously produced are described in the MD direction (traveling direction) and the TD direction (width direction) in order to be transported to a heating furnace by roll-to-roll. Has process and shape anisotropy. Such process- and morphological anisotropy affects the formation of domains having different higher-order structures as described above, and 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 of physical properties.

The method of Patent Document 1 can reduce the horizontal unevenness in the longitudinal direction and suppress the anisotropy of the physical properties caused by the difference in thickness, but the orientation direction, the degree of orientation and the entanglement of the molecules inside the film are biased. The anisotropy of the physical properties is not suppressed. Further, 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 the condition that the drying temperature unevenness in the width direction is 20 ° C. or less. In the example, the ratio of the maximum value of the heat shrinkage in the width direction to the length is 0.33 at the maximum, and the anisotropy of the heat shrinkage in the MD direction (longitudinal direction) and the TD direction (width direction) is not suppressed. ..

In the method for producing a polyimide film of Patent Document 3, the film is intentionally contracted in the width direction in the first half step in accordance with the step of sequentially passing through a furnace having a gradually higher temperature, and the film is loosened in the second half step. It is expanded in the width direction in stages and manufactured without slack to reduce the anisotropy in the width direction and the traveling direction of the film. However, in the examples, the MD (flow direction) direction and the TD (width direction) of the polyimide film are used. The ratio of the linear expansion coefficient in the) direction is 0.96, and further reduction of anisotropy is an issue.

As described above, polyimide has excellent heat resistance, a low coefficient of linear expansion and a high tensile elastic modulus, but has a rigid molecular chain having a high molecular weight, a wide molecular weight distribution and low mobility. Since domains with different higher-order structures that reflect the direction, degree of orientation, and entanglement are formed, a low coefficient of linear expansion is maintained even in the high temperature region, and the ratio of the coefficient of linear expansion and the coefficient of tensile modulus in the MD and TD directions of the resin film. It was a problem to obtain a resin film having a small size and good physical properties and anisotropy.

As a result of diligent studies to solve the above problems, the present inventors have found that such problems can be solved and arrived at the present invention. That is, the present invention has the following configuration.

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 elastic modulus by the storage elastic modulus, peaks is in the range of 250 to 500 ° C., and the temperature-dependent curve of tan δ becomes the peak. The temperature (A) and the linear expansion coefficient variation point temperature (B) are in the relationship of the following equation (40 + 0.8 × A) ≦ B <A
(2) The weight average molecular weight of the resin which 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 1. In the range of 0.0 to 5.0

It is preferable that 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 MD direction to the TD direction is (4) The tensile modulus in both the MD direction and the TD direction is in the range of 2 to 20 GPa in the range of 0.97 to 1.03, and the ratio of the tensile modulus in the TD direction to the MD direction is 0.97. In the range of ~ 1.03

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

Step A to prepare a resin film laminate containing a solvent by applying a resin solution on a support and drying it.
Step B, in which the support is peeled off 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 closure reaction while removing the solvent is included.
A method for producing the resin film, which comprises performing at least a part of the step C by microwave heating.

The resin solution contains at least one resin selected from the group consisting of polyamic acid, polyimide, and polyamide-imide, and a solvent having a dipole moment in the range of 3.0 to 6.0 D and dissolving the resin. Is preferable.

According to the present invention, even when a resin solution consisting of polyimide, polyamideimide, which has a high molecular weight, a wide molecular weight distribution, and a large number of rigid molecular chains with low mobility, and polyamic acid, which is a precursor of the polyimide, is applied and dried, it is heat resistant. It has excellent properties, maintains a low linear expansion coefficient even in the high temperature region, has a high tensile elastic modulus, has a small ratio of the linear expansion coefficient and tensile elastic modulus in the MD direction and the TD direction of the resin film, and has good physical properties and isotropic properties. A resin film having excellent transparency can be obtained.

Hereinafter, the resin film of the embodiment of the present invention and the method for producing the resin film will be described. The resin film of the present invention is a 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 elastic modulus by the storage elastic modulus, peaks is in the range of 250 to 500 ° C., and the temperature-dependent curve of tan δ becomes the peak. The temperature and the linear expansion coefficient variation point temperature (B) have the relationship of the following equation.
(40 + 0.8 × A) ≦ B <A

The temperature-dependent curve of tan δ with respect to temperature is an index of change in the viscoelasticity of the resin due to the temperature change, and when the temperature where the temperature-dependent curve of tan δ exceeds the peak temperature, the viscosity of the resin increases remarkably and the strength decreases. Therefore, the temperature at which the temperature-dependent curve of tan δ peaks is in the range of 250 to 500 ° C. from the viewpoint of heat resistance required for replacing glass substrates used in mobile phones, digital cameras, display devices and other various electronic devices. It is necessary, preferably in the range of 260 to 480 ° C, and more preferably in the range of 270 to 460 ° C. The method for measuring the temperature at which the temperature-dependent curve of tan δ of the resin film peaks is the method described in Examples.

The resin film expands and contracts due to temperature changes, and the coefficient of linear expansion is an index of that change. Will be higher. This specific temperature is called the coefficient of linear expansion inflection temperature.

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

The temperature at which the temperature-dependent curve of tan δ peaks and the temperature at the turning point of the linear expansion coefficient are both the temperature at which the temperature-dependent curve of tan δ peaks, but the temperature at which the temperature-dependent curve of tan δ peaks was formed at the stage of resin film fabrication. While the linear expansion coefficient reflects the average physical property change of the high-order structure with different sparse and dense, the linear expansion coefficient depends on the temperature of tan δ to reflect the physical property change of the sparse high-order structure formed at the stage of resin film production. The linear expansion coefficient variation 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 temperature-dependent curve of tan δ peaks tends to increase as the temperature at which the temperature-dependent curve of tan δ peaks increases. In order to maintain the low coefficient of linear expansion required by replacing the glass substrate and the low coefficient of linear expansion even at high temperatures in the substrate processing process, it is preferable that the linear expansion coefficient inflection temperature (B) is higher, specifically, tan δ. It is preferable to satisfy the formula (40 + 0.8 × A) ≦ B with respect to the temperature (A) at which the temperature-dependent curve of the above peaks. The method for measuring the linear expansion coefficient inflection temperature of the resin film is as described in Examples.

(2) The weight average molecular weight of the resin which 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 1. It is in the range of 0 to 5.0.

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, still more preferably 100,000 to 300,000. More preferably, it is 120,000 to 200,000. If the weight average molecular weight is equal to or higher than the above lower limit, the high tensile elastic modulus, flexibility, and impact resistance required for a glass substrate substitute can be satisfied. Further, if the weight average molecular weight is not more than the above upper limit, the above formula can be easily satisfied. 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 which is the raw material of the resin film of the present invention by the number average molecular weight, is in the range of 1.0 to 5.0, and more preferably 1.5 to 4.5. , More preferably 2.0 to 4.0. If the molecular weight distribution is at least the above lower limit, the cost of resin purification can be reduced, and if the molecular weight distribution is at least the above upper limit, the above formula can be easily satisfied. The method for measuring the weight average molecular weight and the molecular weight distribution of the resin which is the raw material of the resin film is as described in Examples.

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

(3) The coefficient of linear expansion 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 coefficient of linear expansion in the MD direction to the TD direction is It is in the range of 0.97 to 1.03.

The average coefficient of linear expansion measured in the range of 35 to 200 ° C. in both the MD direction and the TD direction of the resin film in the present invention is preferably −5 ppm / ° C. to + 55 ppm / ° C. It is more preferably -4 ppm / ° C to + 45 ppm / ° C, and even 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 from that of the functional element can be kept small, and it is possible to prevent the resin film and the functional element from peeling off even when subjected to a process of applying heat, and workability is achieved. Excellent for.

The ratio of the linear expansion coefficient of the resin film in the present invention to the MD direction in the TD direction is preferably in the range of 0.97 to 1.03. It is more preferably 0.975 to 1.025, and even more preferably 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 used in the processing process with the functional element without distinguishing between the MD direction and the TD direction, and the workability and the yield can be improved. Can be improved. The method for measuring the coefficient of linear expansion of the resin film is as described in Examples.

(4) The tensile elastic 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 elastic modulus in the TD direction to the MD direction is in the range of 0.97 to 1.03.

The tensile elastic 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. It is more preferably 2.5 to 15 GPa, still more preferably 3 to 10 GPa. When the tensile elastic modulus is equal to or higher than the above lower limit, it is possible to prevent the resin film and the functional element from peeling off, and the handleability is excellent. Further, if the tensile elastic modulus is not more than the above upper limit, the resin film can be used as a flexible film.

The ratio of the tensile elastic modulus of the resin film in the present invention to the MD direction in the TD direction is preferably in the range of 0.97 to 1.03. It is more preferably 0.975 to 1.025, and even more preferably 0.98 to 1.02. When the ratio of the tensile elastic modulus in the TD direction to the MD direction is within the above range, the resin film can be used in the processing process with the functional element without distinguishing between the MD direction and the TD direction, and workability and yield are improved. Can be done. The method for measuring the tensile elastic modulus of the resin film is as described in Examples.

Since the resin film of the present invention is mainly used for the front plate of an image display device such as a touch panel or a display, and around electrodes, the yellowness index (yellow index) is preferably 10 or less, more preferably 7 or less, and further. It is 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 it is preferably 0.1 or more, more preferably 0.2 or more, still more preferably 0.3 or more for use as a flexible electronic device. be. The method for measuring the yellowness index (yellow index) of the resin film is as described in Examples.

Since the resin film of the present invention is mainly used for the front plate of an image display device such as a touch panel or a display, and around electrodes, the light transmittance at a wavelength of 400 nm is preferably 70% or more, more preferably 72% or more. It is more preferably 75% or more, and 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 is preferably 99% or less, more preferably 98% or less, still more preferably 97% or less for use as a flexible electronic device. Is. The method for measuring the light transmittance of the resin film at a wavelength of 400 nm is the method described in Examples.

Since the resin film of the present invention is mainly used for the front plate of an image display device such as a touch panel or a display, and the periphery of electrodes, the total light transmittance is preferably 85% or more, more preferably 86% or more, and further 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 is preferably 99% or less, more preferably 98% or less, still more preferably 97% or less for use as a flexible electronic device. .. The method for measuring the total light transmittance of the resin film is as described in Examples.

The resin film of the present invention is preferably obtained by applying and drying a resin solution in order to reach a temperature at which the desired temperature-dependent curve of tan δ reaches its 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 polyamide-imide. The resin solution can be obtained by any of the following production methods.

The 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 an amide bond by a condensation reaction.

The polyimide solution is obtained as a first method by heating and stirring and / or mixing diamines and tetracarboxylic acids in a solvent, and increasing the molecular weight while forming an imide bond in one step by a dehydration ring closure reaction. Can be done. In addition, as a second method, after obtaining the above-mentioned polyamic acid solution, an imidization accelerator and an imidizing 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 and stirring and / or mixing diisocyanates and tricarboxylic acids in a solvent, and increasing the molecular weight while forming amide bonds and imide bonds in one step by a decarbonation reaction.

Dicarboxylic acids can be used as the copolymerization component as long as the characteristics of the resin solution and the resin film are not impaired when the above-mentioned polyamic acid, polyimide, and polyamide-imide are made into high molecular weight.

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

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) usually used for polyimide synthesis and polyamideimide synthesis. , Alicyclic tetracarboxylic acids (including its acid anhydrides), aromatic tricarboxylic acids (including its acid anhydrides), aliphatic tricarboxylic acids (including its acid anhydrides), alicyclic tricarboxylic acids (including its acids) (Including anhydrides), aromatic dicarboxylic acids, aliphatic dicarboxylic acids, alicyclic dicarboxylic acids and the like can be used. Among them, aromatic tetracarboxylic acid anhydrides and alicyclic tetracarboxylic acid anhydrides are preferable, aromatic tetracarboxylic acid anhydrides are more preferable from the viewpoint of heat resistance, and alicyclics are more preferable from the viewpoint of light transmission. Formula tetracarboxylic acids are more preferred. When the tetracarboxylic acids are acid anhydrides, the number of anhydride structures in the molecule may be one or two, but those having two anhydride structures (dianhydride) are preferable. ) Is good. Tetracarboxylic acids, tricarboxylic acids, and dicarboxylic acids may be used alone or in combination of two or more.

Examples of the aromatic tetracarboxylic acids for obtaining a highly colorless and transparent polyimide in the present invention include 4,4'-(2,2-hexafluoroisopropyridene) diphthalic acid, 4,4'-oxydiphthalic acid, and 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 (naphthalen-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'-benzophenonetetra Carboxylic acid, 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-Dika Lubonic acid, 4,4'-[4,4'-(3H-2,1-benzoxathiol-1,1-dioxide-3,3-diyl) bis (naphthalen-1,4-diyloxy)] dibenzene- 1,2-Dicarboxylic acid, 3,3', 4,4'-diphenylsulfonetetracarboxylic acid, 3,3', 4,4'-biphenyltetracarboxylic acid, 2,3,3', 4'-biphenyltetra Carvous acid, 2,2', 3,3'-biphenyltetracarboxylic acid, 2,2'-diphenoxy-4,4', 5,5'-biphenyltetracarboxylic acid, pyromellitic acid, 4,4'-[ Spiro (xanthen-9,9'-fluorene) -2,6-diylbis (oxycarbonyl)] diphthalic acid, 4,4'-[spiro (xanthen-9,9'-fluoren) -3,6-diylbis (oxycarbonyl) Carbonyl)] Tetracarboxylic acids such as diphthalic acid and acid anhydrides thereof. Among these, dianhydride having two acid anhydride structures is preferable, and in particular, 4,4'-(2,2-hexafluoroisopropylidene) diphthalic acid dianhydride and 4,4'-oxydiphthal. Acid dianhydride is 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 are preferably, for example, 50% by mass or more, more preferably 60% by mass or more, still more preferably 70% by mass or more, still more preferably 70% by mass or more of all tetracarboxylic acids. It is 80% by mass or more.

Examples of the alicyclic tetracarboxylic acids include 1,2,3,4-cyclobutanetetracarboxylic acid, 1,2,3,4-cyclopentanetetracarboxylic acid, 1,2,3,4-cyclohexanetetracarboxylic acid, and 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] octo-7-en-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-Etano-5,8-Metano Naphthalene-2,3,6,7-tetracarboxylic acid, norbornan-2-spiro-α-cyclopentanone-α'-spiro-2''-norbornan-5,5'', 6,6''-tetra Carboxylic acid (also known as "norbornan-2-spiri-2'-cyclopentanone-5'-spiro-2"-norbornan-5,5 ", 6,6" -tetracarboxylic acid "), methylnorbornan- 2-Spiro-α-Cyclopentanone-α'-Spiro-2''-(methylnorbornan) -5,5'', 6,6''-tetracarboxylic acid, norbornan-2-spiro-α-cyclohexanone- α'-Spiro-2''-norbornan-5,5'', 6,6''-tetracarboxylic acid (also known as "norbornan-2-spiriro-2'-cyclohexanone-6'-spiro-2"-norbornan -5,5'', 6,6''-tetracarboxylic acid "), Methylnorbornan-2-spiro-α-cyclohexanone-α'-spiro-2''- (methylnorbornan) -5,5'', 6,6''-tetracarboxylic acid, norbornan-2-spiro-α-cyclopropanol-α'-spiro-2''-norbornan-5,5'', 6,6''-tetracarboxylic acid, norbornan -2-Spiro-α-Cyclobutanone-α'-Spiro-2''-norbornan-5,5'', 6,6''-tetracarboxylic acid, norbornan-2-spiro-α-cycloheptanone-α' -Spiro-2 '' -Norbornan-5,5'', 6,6''-Tetracarboxylic acid, Norbornan-2-spiro-α-cyclooctanone-α'-Spiro-2''-norbornan-5,5'', 6,6''-tetracarboxylic acid, norbornan-2-spiro-α-cyclononanon-α'-spiro-2''-norbornan-5,5'', 6,6''-tetracarboxylic acid, norbornan-2 -Spiro-α-cyclodecanone-α'-spiro-2''-norbornan-5,5'', 6,6''-tetracarboxylic acid, norbornan-2-spiro-α-cycloundecanone-α'-spiro -2''-Norbornan-5,5'', 6,6''-Tetracarboxylic acid, Norbornan-2-spiro-α-cyclododecanone-α'-Spiro-2''-norbornan-5,5' ', 6,6''-tetracarboxylic acid, norbornan-2-spiro-α-cyclotridecanone-α'-spiro-2''-norbornan-5,5'', 6,6''-tetracarboxylic acid , Norbornan-2-spiro-α-cyclotetradecanone-α'-spiro-2''-norbornan-5,5'', 6,6''-tetracarboxylic acid, norbornan-2-spiro-α-cyclo Pentadecanone-α'-spiro-2''-norbornan-5,5'', 6,6''-tetracarboxylic acid, norbornan-2-spiro-α- (methylcyclopentanone) -α'-spiro -2''-Norbornan-5,5'', 6,6''-Tetracarboxylic acid, Norbornan-2-spiro-α- (methylcyclohexanone) -α'-Spiro-2''-norbornan-5,5 '', 6,6''-Tetracarboxylic acids such as tetracarboxylic acids and acid anhydrides thereof. Among these, dianhydride having two acid anhydride structures is preferable, and in particular, 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride and 1,2,3,4-cyclohexanetetracarboxylic are preferable. Acid dianhydride, 1,2,4,5-cyclohexanetetracarboxylic acid dianhydride is preferred, 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride, 1,2,4,5-cyclohexanetetracarboxylic Acid dianhydride is more preferred, and 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride is even more preferred. These may be used alone or in combination of two or more. When transparency is important, the alicyclic tetracarboxylic acids are preferably, for example, 50% by mass or more, more preferably 60% by mass or more, still more preferably 70% by mass or more, still more preferably 70% by mass or more of all tetracarboxylic acids. 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. An acid or an alkylene such as a hydrogenated additive of the above aromatic tricarboxylic acid such as hexahydrotrimellitic acid, ethylene glycol bistrimerite, propylene glycol bistrimerite, 1,4-butanediol bistrimerite, polyethylene glycol bistrimerite. Glycolbitrimeritate and these monoanhydrides and esterified products can be mentioned. Among these, monoanhydride having one acid anhydride structure is preferable, and in particular, trimellitic acid anhydride and hexahydrotrimellitic acid anhydride are preferable. These may be used alone or in combination of two or more.

Examples of the dicarboxylic acids include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid, 4,4'-oxydibenzenecarboxylic acid, and the above aromatic dicarboxylic acid such as 1,6-cyclohexanedicarboxylic acid. Hydrogen additives, oxalic acid, succinic acid, glutaric acid, adipic acid, heptanedioic acid, octanedioic acid, azelaioic acid, sebacic acid, undecadioic acid, dodecanedioic acid, 2-methylsuccinic acid, and acid acidates thereof. Alternatively, an esterified product or the like can be mentioned. Of these, aromatic dicarboxylic acids and hydrogen additives thereof are preferable, and terephthalic acid, 1,6-cyclohexanedicarboxylic acid, and 4,4'-oxydibenzenecarboxylic acid are particularly preferable. The dicarboxylic acids may be used alone or in combination of two or more.

The diamines or diisocyanates for obtaining a polyimide having high colorless transparency in the present invention are not particularly limited, and are aromatic diamines, aliphatic diamines, and alicyclic diamines usually used for polyimide synthesis and polyamide-imide synthesis. , Aromatic diamines, aliphatic diamines, alicyclic diamines and the like can be used. From the viewpoint of heat resistance, aromatic diamines are preferable, and from the viewpoint of transparency, alicyclic diamines are preferable. Further, when aromatic diamines having a benzoxazole structure are used, it is possible to exhibit high elastic modulus, low coefficient of thermal expansion, and low linear expansion coefficient 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, and 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'-diaminodiphenylsulfide, 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'-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-aminophenoxy) phenyl] butane, 1,3-bis [4- (4-aminophenoxy) phenyl] ) 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-amino) 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 sulfone, bis [4- {4- (4-aminophenoxy) phenoxy} phenyl] sulfone, 1,4-bis [4- (4- (4- (4- (4-) Aminophenoxy) phenoxy-α, α-dimethylbenzyl] benzene, 1,3-bis [4- (4-aminophenoxy) phenoxy-α, α-dimethylbenzyl] benzene, 1,3-bis [4- (4- (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-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-Bifenoxybenzoyl) 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-fluoren-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 (xanthen-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 dimethyl, and some or all of the hydrogen atoms on the aromatic ring of the aromatic diamine are halogen atoms and have 1 to 3 carbon atoms. Alkyl group or alkoxyl group, cyano group, or aromatic group substituted with a halogenated alkyl group or alkoxyl group having 1 to 3 carbon atoms in which a part or all of the hydrogen atom of the alkyl group or the alkoxyl group is substituted with a halogen atom. Benzene and the like can be mentioned. The aromatic diamine having the benzoxazole structure is not particularly limited, and for example, 5-amino-2- (p-aminophenyl) benzoxazole and 6-amino-2- (p-aminophenyl) benzo. 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-aminobenzoxazole) -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: 5,4-d'] -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'-diaminodiphenyl sulfone, 3,3 '-Diaminobenzophenone is preferred. The aromatic diamines may be used alone or in combination of two or more.

Examples of alicyclic diamines include 1,4-diaminocyclohexane, 1,4-diamino-2-methylcyclohexane, 1,4-diamino-2-ethylcyclohexane, and 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 thereof 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 preferable, and 1,4-diaminocyclohexane is more preferable. The alicyclic diamines may be used alone or in combination of two or more.

Examples of the 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, diphenylether-4,4'-diisocyanate, benzophenone-4,4'-diisocyanate, diphenylsulfon-4,4'-diisocyanate, tolylen-2,4-diisocyanate, Trilen-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'-diethylbiphenyl-4,4'-diisocyanate, 3,3'-dimethoxybiphenyl-4, Aromatic diisocyanates such as 4'-diisocyanate, 3,3'-diethoxybiphenyl-4,4'-diisocyanate, and diisocyanates hydrogenated with any of these (eg, isophorone diisocyanate, 1,4-cyclohexanediisocyanate, etc.). 1,3-Cyclohexanediisocyanate, 4,4'-dicyclohexylmethane diisocyanate, hexamethylene diisocyanate) and the like. Among these, diphenylmethane-4,4'-diisocyanate, tolylen-2,4-diisocyanate, tolylen-2,6-diisocyanate, 3,3'-in terms of low moisture absorption, dimensional stability, price and polymerizable property. Didimethylbiphenyl-4,4'-diisocyanate, naphthalene-2,6-diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, and 1,4-cyclohexanediisocyanate are preferable. The diisocyanates may be used alone or in combination of two or more.

The solvent used in the resin solution of the present invention 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 polyamide-imide. Is preferable. When the dipole moment is within the above range, the uniform heating effect of microwave heating used in the solvent removing step of the resin film described later is excellent, and it becomes easy to improve the physical properties of the obtained resin film.

As the solvent used in the resin solution of the present invention, for example, N, N-dimethylformamide (dipolar moment: 3.86D), N, N-dimethylacetamide (DMAc) (dipolar moment: 3.72D), N- Methyl-2-pyrrolidone (NMP) (dipolar moment: 4.09D), N-methyl-ε-caprolactum (dipolar moment: 4.23D), dimethyl sulfoxide (dipolar moment: 3.96D), dimethylsulfone ( Bipolar moment: 4.47D), Sulfolane (bipolar moment: 4.68D), 1,3-dimethyl-2-imidazolidinone (dipolar moment: 4.07D), 1,3-dimethyl-2-pyrimidinone (Dipolar moment: 4.17D), 3-Methyl-2-oxazolidone (dipolar moment: 4.10D), hexamethylphosphoramide (dipolar moment: 5.54D), γ-butyrolactone (GBL) (bipolar) There are child moments: 4.27D), etc., which 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) are used for microwave heating without precipitation of resin solids. It may be used to the extent that the uniform heating effect is not impaired. Further, the value of the dipole moment when two or more kinds of solvents are mixed is a weighted average value of each value.

Fine particles may be added to the resin solution of the present invention as long as the characteristics of the resin film are not impaired. The fine particles may be inorganic fine particles or organic fine particles, and the inorganic fine particles include, for example, silicon nitride, silicon oxide, titanium oxide, aluminum oxide, magnesium oxide, zinc oxide, tin oxide, calcium carbonate, barium sulfate, talc, kaolin, and calcium sulfate. And so on. Examples of the organic fine particles include polyamide-based resin, polyimide-based resin, benzoguanamine-based resin, and melamine-based resin, 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 further 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 at least the above upper limit, the solution flow is such that the physical properties of the resin film are not impaired. It is preferable from the viewpoint of obtaining sex.

The resin film in the present invention is preferably a resin film obtained by the method for producing a resin film described later. Specifically, it is a polymer film having an imide bond in the 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, still more preferably 7 μm or more, from the viewpoint of the 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 further preferably 100 μm or less from the viewpoint of uniformly removing the solvent.

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

Process A will be explained. Step A is a step of applying a resin solution on a support and drying the resin film laminate (hereinafter, also simply referred to as a laminate) containing a solvent. The laminate is a product in which a dried product of the resin solution is laminated on the support.

Examples of the support used in the present invention include a resin film base material, a stainless steel belt base material, a glass base material, and the like. As the resin film base material, it is preferable to use a resin film base material that does not swell or elute in the solvent contained in the resin solution. For example, polyethylene terephthalate (PET) film, polyethylene naphthalate (PEN) film, polyolefin film (PP) film. , Cycloolefin-based (COP) film and the like. Further, in order to peel off the resin film containing the solvent from the support, it is preferable to use a support having easy peelability.

Examples of the method of applying the resin solution on the support include a die coating method, a comma coating method, a blade coating method, a roll coating method, a knife coating method, a bar coating method, and the like, and two of these methods are used. You may combine the methods. The comma coat method, the die coat method, or a combination thereof is preferable from the viewpoint of productivity.

Examples of the method for drying the resin solution on the support include blower drying, hot air drying, infrared heat drying, heat transfer heat drying from the support, and the like, and even if two of these methods are combined. good. 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 further preferably 7 to 30% by mass. When the solvent content is equal to or higher than the above lower limit, the difference in the solvent content and the polymer higher-order structure between the resin film surface in contact with the support and the opposite surface is small, and the physical property anisotropy in the thickness direction of the resin film becomes small. When the amount is reduced, the curl of the resin film is suppressed, and the value is not more than the above upper limit, the deformation of the resin film after peeling 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 laminated body 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 a method of winding from the end with tweezers or the like, a cut is made in the laminate, and an adhesive tape is attached to one side of the cut portion. After that, a method of winding from the tape portion, a method of vacuum-adsorbing one side of the cut portion of the resin film and then winding from that portion, and the like can be mentioned.

Process 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 the step C is performed by microwave heating.

Microwave heating used in the solvent removal step of the resin film containing the solvent after peeling from the support is based on vibrating the dipoles of the molecules contained in the heated object by microwave as the heating principle. Therefore, the absorption efficiency of microwaves depends on the magnitude of the dipole moment and the ease with which the numerator moves following the period of the microwaves. Therefore, in order to efficiently uniformly heat and remove the solvent from the resin film containing the solvent by 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 molecule of the solvent having the above-mentioned dipole moment value easily moves. However, in general, a heating device having a frequency of 2,450 MHz is common due to the restrictions imposed by the Radio Law and the 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 from such circumstances. Further, the microwave intensity is appropriately selected in consideration of the conditions such as foaming, citron skin, and waviness on the surface of the resin film.

By using a resin solution containing a solvent having a specified dipole moment value and using microwave heating, the resin film is uniformly heated and dried in the solvent removal step, and the difference in sparseness and density of the higher-order structure formed. Is reduced, and it becomes easy to achieve the formula (40 + 0.8 × A) ≤ B <A. Further, the isotropic properties of the obtained resin film can be improved, and 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 elasticity to the MD direction in the TD direction are kept within a preferable range. Becomes easier.

In the present invention, a method by blowing air drying, hot air drying, infrared heating drying, etc. can be used in combination with microwave heating, and two of these methods may be combined.

The temperature rise profile in the solvent removal step using the above heating method preferably has an initial temperature in the range of 50 to 200 ° C., and when it is at least the lower limit of the specified range, temperature variation in the drying furnace can be suppressed. It is easy, and when the initial temperature is not more than the upper limit of the specified range, it becomes easy to suppress the foaming of the resin film and the surface of the resin film due to the rapid heating of the solvent, and the surface of the resin film and the resin film. The difference in solvent content and polymer higher-order structure from the inside is reduced, and it becomes easy to achieve the formula (40 + 0.8 × A) ≤ B <A.

The temperature rise profile in the solvent removing step using the above heating method preferably has a final temperature in the range of 300 to 500 ° C., and when it is at least the lower limit of the specified range, the amount of residual solvent in the resin film is suppressed. When the final temperature is not more than the upper limit of the designated range, it becomes easy to suppress the thermal deterioration of the resin film.

The temperature rise profile in the solvent removal step using the above heating method is to raise the temperature at a temperature rising rate of 5 to 60 ° C./min, or to raise the temperature in steps of 2 or more stages, or both. It is preferable to raise the temperature by a combined method. When the temperature rise rate is at least the lower limit of the specified range, the working time in the solvent removing step can be shortened, and when it is at least the upper limit of the above specified range, the solvent is rapidly heated and the resin film is foamed. It becomes easier to suppress the surface of the resin film, 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. Will be easier to achieve.

When the temperature is raised in steps, the number of steps is preferably 2 to 10 times, and the rate of temperature rise between each step is preferably 10 to 100 ° C./min. When the number of steps is equal to or greater than the lower limit of the specified range, it is easy to suppress foaming of the resin film and the surface of the resin film due to rapid heating of the solvent, and it is easy to suppress the foaming of the resin film and the surface of the resin film. Differences in solvent content and higher-order polymer structure are reduced, and it becomes easier to achieve the formula (40 + 0.8 × A) ≦ B <A. Further, when the number of steps is not more than the upper limit of the designated range, the work efficiency is good.

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 removing step is 5 to 100 minutes. When the total drying time is at least the lower limit of the specified range, it becomes easy to suppress the foaming of the resin film and the surface of the surface of the resin film due to the rapid heating of the solvent, and when it is at least the upper limit, the productivity is improved. It becomes easy to suppress the thermal deterioration of the resin film.

In the solvent removing 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) direction and 1.4 to 3.0 times in the TD (short) direction. The ratio of the draw ratio in the TD direction (MD / TD) is preferably more than 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 direction and the TD direction of the resin film and the tensile elastic modulus in both the MD direction and the TD direction can be obtained. It becomes easy to keep it in 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, and further preferably 0.03 to 3. It is in the range of 0% by mass. By setting the solvent content to the above lower limit value or more, thermal deterioration of the resin film due to excessive high temperature treatment is suppressed, and by setting the solvent content to the upper limit or less, it is easy to keep the linear expansion coefficient and the tensile elastic modulus within a preferable range. It becomes.

Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to the following examples as long as the gist of the present invention is not exceeded.

The measured values in Examples and Comparative Examples were measured by the following methods unless otherwise specified.

<Temperature-dependent curve peak temperature of tan δ of resin film>
The storage elastic modulus (E'), the loss elastic modulus (E "), and the loss elastic modulus are the storage elastic moduli at three points of the sample in the flow direction (MD direction) and the width direction (TD direction) of the resin film, respectively, under the following conditions. The temperature-dependent curve of tan δ (= E ”/ E'), which is the value divided by, was obtained, the peak temperature was obtained, and the average value in the flow direction (MD direction) and the width direction (TD direction) was calculated.
Device name: DMA Q800 manufactured by TA Instruments
Sample length: 15-20 mm
Sample width: 4 mm
Temperature rise start temperature: 25 ° C
Temperature rise end temperature: 500 ° C
Temperature rise rate: 5 ° C / min
Measurement frequency: 10Hz

<Linear expansion coefficient inflection temperature of resin film>
At three sample points in the flow direction (MD direction) and width direction (TD direction) of the resin film, the expansion / contraction rate is measured under the following conditions, and the temperature that becomes the expansion / contraction rate inflection point at the time of the second temperature rise is read and flowed. The average value in the direction (MD direction) and the width direction (TD direction) was calculated.
Device name: Bruker AXS TMA-4000SA
Sample length: 15 mm
Sample width: 2 mm
Distance between chucks: 10 mm
Load: 5gf
First temperature rise start temperature: 25 ° C
First temperature rise end temperature: 200 ° C
First temperature rise rate: 20 ° C / min
Temperature down rate: 5 ° C / min
Second temperature rise start temperature: 30 ° C
Second temperature rise end temperature: 500 ° C
Second temperature rise rate: 10 ° C / min
Atmosphere: Argon

<Weight average molecular weight, number average molecular weight and molecular weight distribution of resin>
A resin sample of 8 mg 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, the number average molecular weight and the molecular weight distribution were calculated in terms of standard polystyrene.
Device name: Tosoh HLC-8420GPC
Column: TSKgel SuperAWH-H x 2
Solvent: DMAc (added 30 mM lithium bromide)
Flow velocity: 0.3 ml / min
Concentration: 0.1%
Injection amount: 10 μl
Temperature: 40 ° C
Detector: RI

<Thickness of resin film>
The measurement was performed using a micrometer (Millitron 1245D manufactured by Fine Wolf Co., Ltd.).

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

<Tension elastic modulus of resin film>
The resin film was cut into strips of 100 mm × 10 mm in the flow direction (MD direction) and the width direction (TD direction), respectively, and used as test pieces. The test piece was cut out from the central portion in the width direction. Under the following conditions, the tensile elastic modulus was measured for each of the three samples in the MD direction and the TD direction, and the average value of all the measured values was obtained.
Device name: Shimadzu Autograph (R) AG-5000A
Distance between chucks: 40 mm
Temperature: 25 ° C
Tensile speed: 50 mm / min

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

<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 (“U-2001” manufactured by Hitachi, Ltd.), and the obtained value was converted to a thickness of 20 μm according to Lambert-Beer's law. The value obtained was taken as the 400 nm light transmittance of the resin film. The same measurement was performed three times, and the arithmetic mean value was adopted.

<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 the light source. The same measurement was performed three times, and the arithmetic mean value was adopted.

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

[Synthesis Example 2 (Preparation of Polyimide Solution B)]
After nitrogen substitution in the reaction vessel equipped with a nitrogen introduction tube, a thermometer, and a stirring rod, 551 parts by mass of N, N-dimethylacetamide (DMAc) and 64.1 parts by mass were placed in the reaction vessel under a nitrogen atmosphere. 2,2'-Ditrifluoromethyl-4,4'-diaminobiphenyl (TFMB) was added and stirred, and TFMB was dissolved in DMAc. Next, 44.4 parts by mass of 4,4'-(2,2-hexafluoroisopropyridene) diphthalic acid dianhydride (6FDA) and 29.4 parts by mass while stirring in the reaction vessel. A mass portion of biphenyltetracarboxylic dianhydride (BPDA) was added over about 10 minutes, and the polymerization reaction was carried out by continuing stirring for 6 hours while adjusting the temperature so that the temperature was in the temperature range of 20 to 40 ° C. A viscous polyamic acid solution was obtained.
Next, 410 parts by mass of DMAc was added to the obtained polyamic acid solution to dilute it, and then 25.83 parts by mass of isoquinoline was added as an imidization accelerator, and the polyamic acid solution was stirred at 30 to 40 ° C. Keep the temperature range, and add 122.5 parts by mass of acetic anhydride as an imidizing agent while slowly dropping it over about 10 minutes, and then keep the solution temperature at 30-40 ° C and stir for 12 hours. The chemical imidization reaction was continuously carried out to obtain a polyimide solution.
Next, 1000 parts by mass of the obtained polyimide solution containing the imidizing agent and the imidization accelerator was transferred to a reaction vessel equipped with a stirring device and a stirring blade, and the temperature was 15 to 25 ° C. while stirring at a speed of 120 rpm. The temperature was maintained at the above, and 1500 parts by mass of methanol was added dropwise at a rate of 10 g / min. When about 800 parts by mass of methanol was added, turbidity of the polyimide solution was confirmed, and precipitation of powdery polyimide was confirmed. Subsequently, 1500 parts by mass of methanol was added to complete the precipitation of polyimide. Subsequently, the contents of the reaction vessel were filtered off by 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. , 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, the number average molecular weight and the molecular weight distribution of the resin in the obtained resin solution.

[Synthesis Example 3 (Preparation of Polyimide Solution C)]
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 stir bar, 124.15 parts by mass of 4,4'-diaminodiphenyl sulfone (4,4') was introduced. -DDS), 124.15 parts by mass of 3,3'-diaminodiphenyl sulfone (3,3'-DDS), and 750 parts by mass of gamma butyrolactone (GBL) were added. Subsequently, 248.18 parts by mass of 4,4'-oxydiphthalic acid hydride (ODPA), 58.8 parts by mass of biphenyltetracarboxylic acid dianhydride (BPDA), 335 parts by mass of GBL, and 390 parts by mass of After adding toluene at room temperature, the temperature was raised to an internal temperature of 160 ° C., and the mixture was heated and refluxed at 160 ° C. for 1 hour to carry out imidization. After the imidization was completed, the temperature was raised to 180 ° C., and the reaction was continued while extracting toluene. After the reaction for 12 hours, the oil bath was removed and 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 having a reduction viscosity of 0.6 dl / g. Table 1 shows the measurement results of the weight average molecular weight, the number average molecular weight and the 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 device, a reflux tube, a thermometer, and a stirring rod, 384.38 parts by mass of norbornane-2-spiro-α-cyclopentanone-α'-Spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic acid 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), 360 parts by mass of toluene, and then the internal temperature. The temperature was raised to 180 ° C., and while toluene was distilled off, heating imidization was performed at 180 ° C. for 3 hours 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 a stirring blade, and the temperature was maintained at 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 2500 parts by mass was added, turbidity of the polyimide solution was confirmed, and precipitation of powdery polyimide was confirmed. Subsequently, the remaining 2500 parts by mass of acetone was added to complete the precipitation of the polyimide. Subsequently, the contents of the reaction vessel were filtered off by 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. , 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 reduced viscosity of 0.7 dl / g having a solid content of 20 parts by mass. Table 1 shows the measurement results of the weight average molecular weight, the number average molecular weight and the molecular weight distribution of the resin in the obtained resin solution.

[Synthesis Example 5 (Preparation of Polyamic Acid Solution E)]
After nitrogen substitution in the reaction vessel equipped with a nitrogen introduction tube, a thermometer, and a stirring rod, 196.1 parts by mass of 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride was placed in 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). , Stirred at room temperature for 24 hours to obtain a polyamic acid solution E having a reduction viscosity of 4.5 dl / g having a solid content of 20 parts by mass. Table 1 shows the measurement results of the weight average molecular weight, the number average molecular weight and the molecular weight distribution of the resin in the obtained resin solution.

[Polyimide film production example 1 (Examples 1 to 5)]
The polyamic acid solution A was applied to a mirror-finished endless continuous belt made of stainless steel, which was a film-making support, using a die coater (coating width 1240 mm), and dried at 90 to 115 ° C. for 10 minutes. A polyamic acid film (containing 9% by mass of residual solvent) that became self-supporting after drying was peeled off from the support and both ends were cut to obtain a green film.
The final pin sheet spacing of the obtained green film is 1140 m by pin tenter.
Both ends of the film are grasped so as to be m, 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, and then 230 at a heating rate of 60 ° C./min. The temperature was raised to ° C. in the second stage at 230 ° C. for 1 minute, 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, a microwave of 50 kW of 2,450 MHz was guided to the microwave heating zone. Then, the film was cooled to room temperature in 2 minutes, and the portions of both ends of the film having poor flatness were cut off with a slitter and wound into a roll to obtain the resin film 1A shown in Table 2. Similarly, the polyamic acid solution A was 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 characteristic evaluation results of the obtained resin film.

[Producing Example 2 of Polyimide Film (Examples 6 to 10)]
The polyamic acid solution A, which is a film-making support, has a region surface roughness (Sa) of 1 nm, a maximum protrusion height (Sp) of 7 nm, and a peak density (Spd) of 20 / square μm or less. A polyester film having no coat layer on the surface was coated with a comma coater (coating width 1240 mm) and dried at 90 to 115 ° C. for 10 minutes. A polyamic acid film (containing 10% by mass of residual solvent) that 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 is gripped at both ends of the film by a pin tenter so that the final pin sheet spacing is 1140 mm, inserted into a continuous heating furnace equipped with a microwave heating zone and a hot air circulation device, and from 170 ° C to 350 ° C. The temperature was raised by heating at a heating rate of 15 ° C./min. At this time, a microwave of 40 kW of 2,450 MHz was guided to the microwave heating zone. Then, the film was cooled to room temperature in 2 minutes, and the portions of both ends of the film having poor flatness were cut off with a slitter and wound into a roll to obtain the resin film 2A shown in Table 2. Similarly, the polyamic acid solution A was 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 characteristic evaluation results of the obtained resin film.

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

[Polyimide film production example 4 (Comparative Examples 6 to 10)]
The polyamic acid solution A, which is a film-making support, has a region surface roughness (Sa) of 1 nm, a maximum protrusion height (Sp) of 7 nm, and a peak density (Spd) of 20 / square μm or less. A polyester film having no coat layer on the surface was coated with a comma coater (coating width 1240 mm) and dried at 90 to 115 ° C. for 10 minutes. A polyamic acid film (containing 10% by mass of residual solvent) that 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 is gripped at both ends of the film by a pin tenter so that the final pin sheet spacing is 1140 mm, inserted into a continuous heating furnace equipped with a microwave heating zone and a hot air circulation device, and from 170 ° C to 350 ° C. The temperature was raised by heating at a heating rate of 70 ° C./min, and heat treatment was performed at 350 ° C. for 4 minutes. At this time, a microwave of 50 kW of 2,450 MHz was guided to the microwave heating zone. Then, the film was cooled to room temperature in 2 minutes, and the portions of both ends of the film having poor flatness were cut off with a slitter and wound into a roll to obtain the resin film 4A shown in Table 3. Similarly, the polyamic acid solution A was 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 characteristic 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 a high temperature region, has a high coefficient of tensile elasticity, and linear expansion of the resin film in the MD direction and the TD direction. Since the ratio of coefficient and tensile modulus is small and the physical properties are good in isotropic properties, it is extremely useful for the front plate of image display devices such as touch panels and displays, and around electrodes.

Claims (5)

1. 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 elastic modulus by the storage elastic modulus, peaks is in the range of 250 to 500 ° C., and the temperature-dependent curve of tan δ becomes the peak. The temperature (A) and the linear expansion coefficient variation point temperature (B) are in the relationship of the following equation (40 + 0.8 × A) ≦ B <A
   (2) The weight average molecular weight of the resin which 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 1. In the range of 0.0 to 5.0
2. The resin film according to claim 1, further satisfying (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 MD direction to the TD direction is (4) The tensile modulus in both the MD direction and the TD direction is in the range of 2 to 20 GPa in the range of 0.97 to 1.03, and the ratio of the tensile modulus in the TD direction to the MD direction is 0.97. In the range of ~ 1.03
3. The resin film according to claim 1 or 2, wherein 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.
4. Step A to prepare a resin film laminate containing a solvent by applying a resin solution on a support and drying it.
   Step B, in which the support is peeled off 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 closure reaction while removing the solvent is included.
   The method for producing a resin film according to any one of claims 1 to 3, wherein at least a part of the step C is performed by microwave heating.
5. The resin solution contains at least one resin selected from the group consisting of polyamic acid, polyimide, and polyamide-imide, and a solvent having a dipole moment in the range of 3.0 to 6.0 D and dissolving the resin. , The method for producing a resin film according to claim 4.