Resin film and method for manufacturing resin film

Abstract

Provided is a resin film that is excellent in heat resistance, maintains a low linear expansion coefficient in a high temperature region, has a high tensile elastic modulus, and has a small ratio of linear expansion coefficients, a small ratio of tensile elastic moduli, and a good isotropy of physical properties in the MD direction and the TD direction of the resin film. A resin film that satisfies the following (1) and (2). (1) The peak temperature (A) of a temperature dependence curve of tan δ, which is a value obtained by dividing a loss modulus by a storage modulus, is in the range of 250 to 500°C, and the peak temperature (A) of the temperature dependence curve of tan δ and the inflection point temperature (B) of a linear expansion coefficient have the following relationship: (40 + 0.8 × A) ≤ B < A, (2) The weight average molecular weight of a resin that is a raw material of the resin film is in the range of 50,000 to 500,000, and the molecular weight distribution, which is a value obtained by dividing the weight average molecular weight by the number average molecular weight of the resin, is in the range of 1.0 to 5.0.

Description

Technical Field

[0001] This invention relates to a resin film and a method for manufacturing the resin film. More specifically, it relates to a resin film with excellent heat resistance, maintaining a low coefficient of linear expansion even in high-temperature regions, having a high tensile modulus of elasticity, a small ratio of the coefficient of linear expansion in the TD direction to the coefficient of linear expansion in the MD direction, a small ratio of the tensile modulus of elasticity, good isotropic properties, and excellent transparency, as well as a method for manufacturing the resin film. Background Technology

[0002] In recent years, with the development of miniaturization, lightweighting, and convenience of high-functionality mobile phones, digital cameras, display devices, and other electronic components, resin film substrate materials with excellent heat resistance, low coefficient of linear expansion, high tensile modulus, flexibility, impact resistance, and transparency have become increasingly anticipated to replace the hard and impact-resistant glass substrates used in the past.

[0003] Resin films are manufactured industrially by forming organic polymer resin materials into a film shape through a film-forming process. Film-forming methods include melt film-forming, where the organic polymer resin is melted and extruded through a slit-shaped die, and solution film-forming, where an organic polymer resin solution is uniformly coated onto a support and the solvent is allowed to dry and evaporate. Among organic polymer resin materials, polyimide resin and polyamide-imide resin, which have particularly excellent heat resistance, are infusible and only melt at very high temperatures; therefore, they are typically obtained as resin films through solution film-forming.

[0004] In solution film-forming methods such as those that allow the coating solvent to dry and evaporate, uneven thickness and orientation can occur due to coating and drying conditions. For example, Patent Document 1 proposes a method that reduces transverse striation unevenness in the length direction by improving coating conditions such as the rotation speed of the support.

[0005] In addition, a method for suppressing film relaxation deviations was described, which found that relaxation is related to anisotropy index, principal axis orientation coefficient, thermal shrinkage rate, and drying temperature, and suppressed drying temperature unevenness in the width direction and deviations in linear expansion coefficient, i.e., dimensional changes (Patent Document 2).

[0006] Patent document 3 describes a manufacturing method for reducing the anisotropy of the linear expansion coefficients in the MD direction (mechanical direction) and TD direction (width direction) of a polyimide film that will have a significant decrease in elastic modulus above the glass transition temperature. This method involves fixing the two ends of the film without slack in a transmission that corresponds to the width of the film changing due to shrinkage and expansion during the heating process. Existing technical documents Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2013-203838 Patent Document 2: Japanese Patent Application Publication No. 2018-70842 Patent Document 3: Japanese Patent Application Publication No. 2000-290401 Summary of the Invention The problem the invention aims to solve

[0008] To directly form functional components such as electrodes and display elements on surfaces, resin films used as alternatives to glass substrates are required to have high tensile modulus of elasticity, low CTE, as well as heat resistance and chemical resistance. Polyimide, polyamide-imide, and polyamic acid, a precursor to polyimide, which are suitable resins for forming such films, exhibit heat resistance due to their high molecular weight and the presence of numerous rigid molecular chains with low flowability. Furthermore, increasing the molecular weight results in a wider molecular weight distribution.

[0009] When coating and drying such resin solutions, when there are many rigid molecular chains with high molecular weight and wide molecular weight distribution and low fluidity, as the solvent is removed, the orientation direction, orientation degree and entanglement of the first molecules formed are relatively tight, resulting in a higher-order structure that is different from the orientation direction, orientation degree and entanglement of the later molecules formed, thus forming their own domains.

[0010] In the industrial continuous manufacturing of films by coating and drying resin solutions, the film exhibits process / shape anisotropy in both the MD direction (travel direction) and TD direction (width direction) due to the roller-to-roll conveying process into the furnace. This process / shape anisotropy affects the formation of the aforementioned categories with different higher-order structures, causing deviations in the orientation direction, degree of orientation, and entanglement of molecules in either the width or mechanical direction, resulting in dimensional variations and anisotropy in physical properties.

[0011] While the method in Patent Document 1 can reduce transverse striation unevenness in the length direction and suppress anisotropy of physical properties caused by thickness differences, it fails to suppress anisotropy of physical properties caused by deviations in the orientation direction, degree of orientation, and entanglement of molecules within the film. Furthermore, in Patent Document 2, although drying is performed under conditions where the drying temperature in the width direction is not uniformly below 20°C, resulting in thermal shrinkage rates of less than 0.05% in both the length and width directions, the ratio of the maximum thermal shrinkage rate in the width direction to the length direction is at most 0.33 in the embodiment, failing to suppress anisotropy of the thermal shrinkage rate in the MD direction (length direction) and TD direction (width direction).

[0012] The polyimide film manufacturing method in Patent Document 3 involves a process of sequentially passing through a furnace with gradually increasing temperatures. In the first half of the process, the film is intentionally contracted in the width direction, while in the second half of the process, during the relaxation stage of film production, it expands in the width direction. This manufacturing process is carried out without relaxation, which reduces the anisotropy of the film in the width and forward directions. However, in the embodiment, the ratio of the linear expansion coefficients of the polyimide film in the MD (mechanical direction) direction to the TD (width direction) direction is 0.96, which raises the issue of further reducing anisotropy.

[0013] As such, polyimide possesses excellent heat resistance, low coefficient of linear expansion, and high tensile modulus. On the other hand, due to its rigid molecular chains with high molecular weight, wide molecular weight distribution, and low fluidity, as the solvent dries, different categories of higher-order structures are formed based on the orientation direction, degree of orientation, and entanglement of the corresponding molecules. It has become a research topic to obtain resin films that can maintain a low coefficient of linear expansion even in high-temperature regions, have a small ratio of the coefficient of linear expansion in the MD direction to the TD direction, a small ratio of the tensile modulus, and good isotropic physical properties. Technical solutions to the problem

[0014] The inventors conducted in-depth research to solve the aforementioned problems, and as a result, discovered that the problems could be solved, thus realizing the present invention. That is, the present invention has the following structure.

[0015] A resin film that satisfies the following (1) to (2). (1) The peak temperature (A) of the temperature dependence curve of tanδ is in the range of 250 to 500℃, where tanδ is the value obtained by dividing the loss modulus by the storage modulus. The peak temperature (A) of the temperature dependence curve of tanδ and the inflection point temperature (B) of the coefficient of linear expansion have the following relationship. (40 + 0.8 × A) ≤ B < A, (2) The weight-average molecular weight of the resin raw material of the resin membrane is in the range of 50,000 to 500,000, and the molecular weight distribution is in the range of 1.0 to 5.0. The molecular weight distribution is the value obtained by dividing the weight-average molecular weight by the number-average molecular weight of the resin.

[0016] The resin film preferably further satisfies (3) to (4). (3) The linear expansion coefficients measured in both the MD and TD directions within the range of 35–200℃ are in the range of -5ppm / ℃ to +55ppm / ℃, and the ratio of the linear expansion coefficients in the TD direction to the MD direction is in the range of 0.97–1.03. (4) The tensile modulus of elasticity in both the MD and TD directions is in the range of 2 to 20 GPa, and the ratio of the tensile modulus of elasticity in the TD direction to that in the MD direction is in the range of 0.97 to 1.03.

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

[0018] The method for manufacturing the resin film is characterized by comprising step A, which involves coating a resin solution onto a support, drying it, and forming a resin film laminate containing the solvent. Step B involves peeling the support from the laminate to obtain a resin film containing solvent. Step C involves removing the solvent from the solvent-containing resin membrane, or simultaneously removing the solvent while performing a dehydration and ring-closing reaction. At least a portion of step C is performed by microwave heating.

[0019] The resin solution preferably contains at least one resin selected from the group consisting of polyamic acid, polyimide and polyamide-imide, and a solvent capable of dissolving the resin in the range of 3.0 to 6.0D. Invention Effects

[0020] According to the present invention, even when a resin solution composed of polyamic acid containing a large number of rigid molecular chains with high molecular weight and wide molecular weight distribution and low fluidity is coated and dried as a precursor of polyimide, polyamide-imide, or polyimide, a resin film with excellent heat resistance, maintaining a low coefficient of linear expansion in high-temperature regions, having a high tensile modulus, a small ratio of the coefficient of linear expansion in the MD direction to the TD direction and a small ratio of the tensile modulus, good isotropic properties, and excellent transparency can be obtained. Detailed Implementation

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

[0022] (1) The peak temperature (A) of the temperature dependence curve of tanδ is in the range of 250 to 500℃, where tanδ is the value obtained by dividing the loss modulus by the energy storage modulus, and the peak temperature of the temperature dependence curve of tanδ has the following relationship with the inflection point temperature of the linear expansion coefficient (B). (40 + 0.8 × A) ≤ B < A

[0023] The temperature dependence curve of tanδ relative to temperature is an indicator of the change in resin viscoelasticity based on temperature changes. If the temperature exceeds the peak temperature of the tanδ temperature dependence curve, the resin viscosity will increase significantly and the strength will decrease. Therefore, to meet the heat resistance requirements of glass substrates used in mobile phones, digital cameras, display devices, and various other electronic components, the peak temperature of the tanδ temperature dependence curve needs to be in the range of 250–500°C, preferably in the range of 260–480°C, and more preferably in the range of 270–460°C. The method for determining the peak temperature of the tanδ temperature dependence curve of the resin film is based on the method described in the examples.

[0024] Resin films expand and contract due to temperature changes, and the coefficient of linear expansion is an indicator of this change. The coefficient of linear expansion of a resin film is not constant relative to the measured temperature range; rather, it increases at a specific temperature corresponding to the resin film. This specific temperature is called the inflection point temperature of the coefficient of linear expansion.

[0025] The resin film of the present invention is preferably obtained by coating and drying a resin solution. During the coating and drying process, as the solvent is removed, relatively tight higher-order structures corresponding to the orientation direction, degree of orientation, and entanglement of the previously formed molecules are generated, as well as relatively loose higher-order structures corresponding to the orientation direction, degree of orientation, and entanglement of the subsequently formed molecules, thus forming their respective domains. When the resin contains a significant amount of rigid molecular chains with high molecular weight and a wide molecular weight distribution and low fluidity, the density of the higher-order structures within each domain varies considerably.

[0026] Although both the peak temperature of the tanδ temperature dependence curve and the inflection point temperature of the coefficient of linear expansion are inflection points of physical properties, the peak temperature of the tanδ temperature dependence curve reflects the average physical property changes of the higher-order structures with varying density formed during the resin film fabrication stage. In contrast, the coefficient of linear expansion reflects the physical property changes of the looser higher-order structures formed during the resin film fabrication stage. Therefore, the inflection point temperature (B) of the coefficient of linear expansion is always lower than the peak temperature (A) of the tanδ temperature dependence curve (B < A). Furthermore, the difference between the peak temperature of the tanδ temperature dependence curve and the inflection point temperature of the coefficient of linear expansion tends to increase as the peak temperature of the tanδ temperature dependence curve increases. In order to maintain a low coefficient of linear expansion required for replacing the glass substrate and also have a low coefficient of linear expansion at high temperatures during the substrate processing, it is preferable to have a higher inflection point temperature (B). Specifically, it is preferable to satisfy the formula (40 + 0.8 × A) ≤ B relative to the peak temperature (A) of the tanδ temperature dependence curve. The method for determining the inflection point temperature of the coefficient of linear expansion of the resin film is based on the method described in the embodiments.

[0027] (2) The weight-average molecular weight of the resin used as the raw material for the resin membrane is in the range of 50,000 to 500,000, and the molecular weight distribution is in the range of 1.0 to 5.0, wherein the molecular weight distribution is the value obtained by dividing the weight-average molecular weight by the number-average molecular weight of the resin.

[0028] The weight-average molecular weight of the resin in 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, further preferably 100,000 to 300,000, and particularly preferably 120,000 to 200,000. If the weight-average molecular weight is above or below the aforementioned lower limit, it can satisfy the requirements for high tensile modulus of elasticity, flexibility, and impact resistance required to replace glass substrates. Furthermore, if the weight-average molecular weight is below or above the aforementioned upper limit, it becomes easier to satisfy the above formula. Additionally, the weight-average molecular weight of the resin in the resin solution is preferably within the aforementioned range.

[0029] The molecular weight distribution of the resin raw material for the resin membrane of the present invention, obtained by dividing the weight-average molecular weight by the number-average molecular weight, is in the range of 1.0 to 5.0, more preferably 1.5 to 4.5, and even more preferably 2.0 to 4.0. If the molecular weight distribution is above the lower limit mentioned above, the cost of resin refining can be reduced; if the molecular weight distribution is below the upper limit mentioned above, it becomes easier to satisfy the above formula. The method for determining the weight-average molecular weight and molecular weight distribution of the resin raw material for the resin membrane is based on the method described in the embodiments.

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

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

[0032] The average coefficient of linear expansion of the resin film in this invention, measured in both the MD and TD directions within a temperature range of 35–200°C, is preferably -5 ppm / °C to +55 ppm / °C. More preferably, it is -4 ppm / °C to +45 ppm / °C, and even more preferably -3 ppm / °C to +35 ppm / °C. If the coefficient of linear expansion is within the above range, the difference between it and the coefficient of linear expansion of the functional element can be kept small, thus preventing the resin film from peeling off from the functional element even when supplied to a heating process, resulting in excellent processability.

[0033] The ratio of the linear expansion coefficient of the resin film in the TD direction to the MD direction is preferably in the range of 0.97 to 1.03. More preferably, it is 0.975 to 1.025, and even more preferably, it is 0.98 to 1.02. If the ratio of the linear expansion coefficient in the TD direction to the MD direction is within the above range, it is possible to provide the resin film to the processing steps of functional elements without distinguishing between the MD direction and the TD direction, thereby improving operability and yield. The method for measuring the linear expansion coefficient of the resin film is based on the method described in the embodiments.

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

[0035] The tensile modulus of the resin film of the present invention is preferably in the range of 2 to 20 GPa in both the MD and TD directions. More preferably, it is 2.5 to 15 GPa, and even more preferably, it is 3 to 10 GPa. If the tensile modulus is above or below the above lower limit, the delamination between the resin film and the functional element can be avoided, resulting in excellent processability. In addition, if the tensile modulus is below or below the above upper limit, the resin film can be used as a flexible film.

[0036] In this invention, the ratio of the tensile modulus of the resin film in the TD direction to the MD direction is preferably in the range of 0.97 to 1.03. More preferably, it is 0.975 to 1.025, and even more preferably, it is 0.98 to 1.02. If the ratio of the tensile modulus of the resin film in the TD direction to the MD direction is within the above range, the processing steps for functional components can be provided without distinguishing between the MD and TD directions of the resin film, thereby improving operability and yield. The method for determining the tensile modulus of the resin film is based on the method described in the embodiments.

[0037] Since the resin film of the present invention is mainly used in the front panel and electrode peripheral devices of image display devices such as touch panels and displays, the yellowness index (yellow index) is preferably 10 or less, more preferably 7 or less, further preferably 5 or less, and even more preferably 3 or less. There is no particular limitation on the lower limit of the yellowness of the resin film, but for use in flexible electronic components, it is preferably 0.1 or more, more preferably 0.2 or more, and even more preferably 0.3 or more. The method for measuring the yellowness index (yellow index) of the resin film is according to the method described in the embodiments.

[0038] Since the resin film of the present invention is mainly used in the front panel and electrode peripheral devices of image display devices such as touch panels and displays, the transmittance at a wavelength of 400 nm is preferably 70% or more, more preferably 72% or more, further preferably 75% or more, and even more preferably 80% or more. There is no particular upper limit to the transmittance of the resin film at a wavelength of 400 nm, but for use as a flexible electronic component, it is preferably 99% or less, more preferably 98% or less, and even more preferably 97% or less. The method for measuring the transmittance of the resin film at a wavelength of 400 nm is according to the method described in the embodiments.

[0039] Since the resin film of the present invention is mainly used in the front panel and electrode peripheral devices of image display devices such as touch panels and displays, its total light transmittance is preferably 85% or more, more preferably 86% or more, further preferably 87% or more, and even more preferably 88% or more. There is no particular upper limit to the total light transmittance of the resin film, but for use as a flexible electronic component, it is preferably 99% or less, more preferably 98% or less, and even more preferably 97% or less. The method for measuring the total light transmittance of the resin film is based on the method described in the embodiments.

[0040] The resin film of the present invention is preferably obtained by coating and drying a resin solution in order to achieve the desired peak temperature of the temperature dependence curve of tanδ. As the resin solution, a resin solution containing at least one resin selected from the group consisting of polyamic acid, polyimide, and polyamide-imide is preferred. The resin solution can be obtained by any of the following manufacturing methods.

[0041] Polyamic acid solutions can be obtained by stirring and / or mixing diamines and tetracarboxylic acids in a solvent, thereby generating amide bonds through a condensation reaction and simultaneously increasing their molecular weight.

[0042] As a first method, a polyimide solution can be obtained by heating and stirring and / or mixing a diamine and a tetracarboxylic acid in a solvent, generating imide bonds through a first-stage dehydration cyclization reaction while simultaneously increasing its molecular weight. Alternatively, as a second method, after obtaining the above-mentioned polyamic acid solution, an imidization accelerator and an imidizing agent can be added, stirred and / or mixed, and simultaneously generating imide bonds through a second-stage dehydration cyclization reaction while simultaneously increasing its molecular weight.

[0043] Polyamide-imide solutions can be obtained by heating and stirring and / or mixing diisocyanates and tricarboxylic acids in a solvent, generating amide and imide bonds in a first-stage decarboxylation reaction, while simultaneously increasing the molecular weight.

[0044] When increasing the molecular weight of the above-mentioned polyamic acid, polyimide, and polyamide-imide, dicarboxylic acids can be used as copolymerizing components without impairing the properties of the resin solution and resin film.

[0045] The resin solution used in this invention can be obtained by flowing the above-obtained resin solution into a poor solvent, precipitating the resin components and washing / filtering / drying to obtain a resin solid, or by allowing the resin solution to be dried by casting and then dissolving the resin solid in a soluble solvent.

[0046] As the aforementioned tetracarboxylic acids, tricarboxylic acids, and dicarboxylic acids, aromatic tetracarboxylic acids (including their anhydrides), aliphatic tetracarboxylic acids (including their anhydrides), alicyclic tetracarboxylic acids (including their anhydrides), aromatic tricarboxylic acids (including their anhydrides), aliphatic tricarboxylic acids (including their anhydrides), alicyclic tricarboxylic acids (including their anhydrides), aromatic dicarboxylic acids, aliphatic dicarboxylic acids, and alicyclic dicarboxylic acids are commonly used in the synthesis of polyimides and polyamide-imides. Among these, aromatic tetracarboxylic anhydrides and alicyclic tetracarboxylic anhydrides are preferred. From the viewpoint of heat resistance, aromatic tetracarboxylic anhydrides are more preferred, and from the viewpoint of light transmittance, alicyclic tetracarboxylic acids are more preferred. When the tetracarboxylic acid is an anhydride, the anhydride structure within the molecule can be one or two, and it is preferred to have an anhydride (dianhydride) with two anhydride structures. Tetracarboxylic acids, tricarboxylic acids, and dicarboxylic acids can be used alone or in combination of two or more.

[0047] To obtain a colorless and highly transparent polyimide, this invention uses aromatic tetracarboxylic acids, such as 4,4'-(2,2-hexafluoroisopropyl)phthalic acid, 4,4'-oxyphthalic acid, 3,4'-oxyphthalic acid, bis(1,3-dioxane-1,3-dihydro-2-benzofuran-5-carboxylic acid) 1,4-phenylene, bis(1,3-dioxane-1,3-dihydro-2-benzofuran-5-yl)phenyl-1,4-dicarboxylic acid, 4,4'-[4,4'-(3-oxane-1,3-dihydro-2-benzofuran-1,1-diyl)bis(phenyl-1,4-diyloxy)]diphenyl-1,2-dicarboxylic acid, 3,3',4,4'-benzophenone tetracarboxylic acid, 4,4' -[(3-oxoylidene-1,3-dihydro-2-benzofuran-1,1-diyl)bis(toluene-2,5-dioxy)]diphenyl-1,2-dicarboxylic acid, 4,4'-[(3-oxoylidene-1,3-dihydro-2-benzofuran-1,1-diyl)bis(1,4-xylyl-2,5-dioxy)]diphenyl-1,2-dicarboxylic acid, 4,4'-[4,4'-(3-oxoylidene-1,3-dihydro-2-benzofuran-1,1-diyl)bis(4-isopropyl-toluene-2,5-dioxy)]diphenyl-1,2-dicarboxylic acid, 4,4'-[4,4'-(3-oxoylidene-1,3-dihydro-2-benzofuran-1,1-diyl)bis(naphthalene-1,4-dioxy)]diphenyl-1 2-Dicarboxylic acid, 4,4'-[4,4'-(3H-2,1-benzoxathiol)-1,1-dioxide-3,3-diyl)bis(benzyl-1,4-dioxy)]diphenyl-1,2-dicarboxylic acid, 4,4'-benzophenone tetracarboxylic acid, 4,4'-[(3H-2,1-benzoxathiol)-1,1-dioxide-3,3-diyl)bis(toluene-2,5-dioxy)]diphenyl-1,2-dicarboxylic acid, 4,4'-[(3H-2,1-benzoxathiol)-1,1-dioxide-3,3-diyl)bis(1,4-xylene-2,5-dioxy)]diphenyl-1,2-dicarboxylic acid, 4,4'-[4,4'- ... -2,1-Benzothiopyrene-1,1-dioxide-3,3-diyl)bis(4-isopropyl-toluene-2,5-diyloxy)]diphenyl-1,2-dicarboxylic acid, 4,4'-[4,4'-(3H-2,1-benzothiopyrene-1,1-dioxide-3,3-diyl)bis(naphthalene-1,4-diyloxy)]diphenyl-1,2-dicarboxylic acid, 3,3',4,4'-diphenylsulfone tetracarboxylic 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(xanthan-9,9'-fluorene)-2,Tetracarboxylic acids such as 6-dimethylbis(oxycarbonyl)]diphthalic acid, 4,4'-[spiro(xanthon-9,9'-fluorene)-3,6-dimethylbis(oxycarbonyl)]diphthalic acid, and their anhydrides are preferred. Among these, dianhydrides having two anhydride structures are suitable, particularly 4,4'-(2,2-hexafluoroisopropylidene)diphthalic acid dianhydride and 4,4'-oxydiphthalic acid dianhydride are preferred. Furthermore, aromatic tetracarboxylic acids can be used alone or in combination of two or more. Where heat resistance is important, the aromatic tetracarboxylic acids are preferably 50% by mass or more, more preferably 60% by mass or more, further preferably 70% by mass or more, and even more preferably 80% by mass or more.

[0048] Examples of alicyclic tetracarboxylic acids include 1,2,3,4-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-enyl-2,3,5,6-tetracarboxylic acid, tetrahydroanthracene-2,3,6,7-tetracarboxylic acid, tetratetrahydro-1,4:5,8:9,10-trimethanoanthracene-2,3,6,7-tetracarboxylic acid, and decahydronaphthalene-2,3,6,7-tetracarboxylic acid. -Tetracarboxylic acid, decahydro-1,4:5,8-dimethanonaphthalene-2,3,6,7-tetracarboxylic acid, decahydro-1,4-ethionophthalene-2,3,6,7-tetracarboxylic acid, norbornane-2-spiro-α-cyclopentanone-α'-spiro-2"-norbornane-5,5",6,6"-tetracarboxylic acid (also known as "norbornane-2-spiro-2'-cyclopentanone-5'-spiro-2"-norbornane-5,5",6,6"-tetracarboxylic acid"), methylnorbornane-2-spiro-α-cyclopentanone-α'-spiro-2"-(methylnorbornane)-5,5",6,6"-tetracarboxylic acid, norbornane-2- Spiro-α-cyclohexanone-α'-spiro-2"-norbornane-5,5",6,6"-tetracarboxylic acid (also known as "norbornane-2-spiro-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-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-cyclododecanone-α'-spiro-2"-norbornane-5,5",6,6"-tetracarboxylic acid, norbornane-2-spiro-α-cyclotetradecadecanone-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-5,5",6,6"-tetracarboxylic acid, and other tetracarboxylic acids and their anhydrides. Among these, dianhydrides having two anhydride structures are preferred, particularly 1,2,3,4-cyclobutanetetracarboxylic acid dianhydrides, 1,2,3,4-cyclohexanetetracarboxylic acid dianhydrides, and 1,2,4,5-cyclohexanetetracarboxylic acid dianhydrides, more preferably 1,2,3,4-cyclobutanetetracarboxylic acid dianhydrides and 1,2,4,5-cyclohexanetetracarboxylic acid dianhydrides, and even more preferably 1,2,3,4-cyclobutanetetracarboxylic acid dianhydrides. It should be noted that these can be used alone or in combination of two or more. For alicyclic tetracarboxylic acids, where transparency is important, for example, the content of the total tetracarboxylic acids is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, and still even more preferably 80% by mass or more.

[0049] Examples of tricarboxylic acids include aromatic tricarboxylic acids such as trimellitic acid, 1,2,5-naphthalenetricarboxylic acid, diphenyl ether-3,3',4'-tricarboxylic acid, and diphenyl sulfone-3,3',4'-tricarboxylic acid, or hydrides of the aforementioned aromatic tricarboxylic acids such as hexahydrotriphenylcarboxylic acid; alkylene glycol trimellitic acid esters such as ethylene glycol dipreptyl trimellitate, propylene glycol dipreptyl trimellitate, 1,4-butanediol dipreptyl trimellitate, and polyethylene glycol dipreptyl trimellitate; and their monohydric anhydrides and esterifications. Among these, monohydric anhydrides having one anhydride structure are preferred, and in particular, trimellitic acid tricarboxylic anhydride and hexahydrotriphenylcarboxylic anhydride are preferred. Furthermore, these can be used alone or in combination.

[0050] Examples of dicarboxylic acids include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, and 4,4'-oxydibenzoic acid, or hydrides of the aforementioned aromatic dicarboxylic acids such as 1,6-cyclohexanedicarboxylic acid, oxalic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, octanoic acid, azelaic acid, sebacic acid, undecanoic acid, dodecanoic acid, 2-methylsuccinic acid, and their acyl chlorides or esters. Among these, aromatic dicarboxylic acids and their hydrides are preferred, especially terephthalic acid, 1,6-cyclohexanedicarboxylic acid, and 4,4'-oxydibenzoic acid. Furthermore, dicarboxylic acids can be used alone or in combination.

[0051] In this invention, there are no particular limitations on the diamines or diisocyanates used to obtain colorless and highly transparent polyimides. Aromatic diamines, aliphatic diamines, alicyclic diamines, aromatic diisocyanates, aliphatic diisocyanates, and alicyclic diisocyanates commonly used in polyimide synthesis and polyamide-imide synthesis can be used. From the viewpoint of heat resistance, aromatic diamines are preferred, and from the viewpoint of transparency, alicyclic diamines are preferred. Furthermore, if an aromatic diamine with a benzoxazole structure is used, it exhibits high heat resistance, high elastic modulus, low thermal shrinkage, and a low coefficient of linear expansion. Diamines and diisocyanates can be used alone or in combination of two or more.

[0052] Examples of aromatic diamines include 2,2'-dimethyl-4,4'-diaminobiphenyl, 1,4-bis[2-(4-aminophenyl)-2-propyl]benzene, 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 4,4'-bis(4-aminophenoxy)biphenyl, 4,4'-bis(3-aminophenoxy)biphenyl, bis[4-(3-aminophenoxy)phenyl]ketone, bis[4-(3-aminophenoxy)phenyl]sulfide, bis[4-(3-aminophenoxy)phenyl]sulfone, 2,2-bis[4-(3-aminophenoxy)phenyl]propane, 2,2-bis[4-(3-aminophenoxy)phenyl]-1,1, 1,3,3,3-Hexafluoropropane, m-phenylenediamine, o-phenylenediamine, p-phenylenediamine, m-aminobenzylamine, p-aminobenzylamine, 4-amino-N-(4-aminophenyl)benzamide, 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 2,2'-trifluoromethyl-4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl sulfide, 3,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfoxide, 3,4'-diaminodiphenyl sulfoxide, 4,4'-diaminodiphenyl sulfoxide, 3,3'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone Benzene, 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]propane [4-[4-(4-aminophenoxy)phenyl]butane, 1,4-bis[4-(4-aminophenoxy)phenyl]butane, 2,2-bis[4-(4-aminophenoxy)phenyl]butane, 2,3-bis[4-(4-aminophenoxy)phenyl]butane, 2-[4-(4-aminophenoxy)phenyl]-2-[4-(4-aminophenoxy)-3-methylphenyl]propane, 2,2-bis[4-(4-aminophenoxy)-3-methylphenyl]propane, 2-[4-(4-aminophenoxy)phenyl]-2-[4-(4-aminophenoxy)-3,5-dimethylphenyl]propane, 2,2-bis[4-(4-aminophenoxy)-3,5-dimethylphenyl]propane, 2,2-Bis[4-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, 1,4-bis(3-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 4,4'-bis(4-aminophenoxy)biphenyl, bis[4-(4-aminophenoxy)phenyl]ketone, bis[4-(4-aminophenoxy)phenyl]sulfide, bis[4-(4-aminophenoxy)phenyl]sulfoxide, bis[4-(4-aminophenoxy)phenyl]sulfone, bis[4-(3-aminophenoxy)phenyl]ether, bis[4-(4-aminophenoxy)phenyl]ether, 1,3-bis[4-(4-aminophenoxy)benzoyl]benzene, 1,3-bis[4-(3-aminophenoxy)benzoyl]benzene [phenoxy)benzoyl]benzene, 1,4-bis[4-(3-aminophenoxy)benzoyl]benzene, 4,4'-bis[(3-aminophenoxy)benzoyl]benzene, 1,1-bis[4-(3-aminophenoxy)phenyl]propane, 1,3-bis[4-(3-aminophenoxy)phenyl]propane, 3,4'-diaminodiphenyl sulfide, 2,2-bis[3-(3-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, bis[4-(3-aminophenoxy)phenyl]methane, 1,1-bis[4-(3-aminophenoxy)phenyl]ethane, 1,2-bis[4-(3-aminophenoxy)phenyl]ethane, bis[4-(3-aminophenoxy)phenyl]sulfoxide, 4,4'-bis[3-(4- [Aminophenoxy]benzoyl]diphenyl ether, 4,4'-bis[3-(3-aminophenoxy)benzoyl]diphenyl ether, 4,4'-bis[4-(4-amino-α,α-dimethylbenzyl)phenoxy]benzophenone, 4,4'-bis[4-(4-amino-α,α-dimethylbenzyl)phenoxy]diphenyl sulfone, 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-aminophenoxy)phenoxy-α,α-dimethylbenzyl]benzene, 1,3-bis[4-(4-amino-6-trifluoromethylphenoxy) ... [4-(4-amino-6-methylphenoxy)-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'-Diphenyloxybenzophenone, 4,4'-Diamino-5,5'-Diphenyloxybenzophenone, 3,4'-Diamino-4,5'-Diphenyloxybenzophenone, 3,3'-Diamino-4-Biphenyloxybenzophenone, 4,4'-Diamino-5-Biphenyloxybenzophenone, 3,4'-Diamino-4-Biphenyloxybenzophenone, 3,4'-Diamino-5'-Biphenyloxybenzophenone, 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]benzylnitrile, 4,4'-[9H-fluorene-9,9-diyl]bisaniline (also known as 9,9-bis(4-aminophenyl)fluorene), spiro(xanton-9,9'-fluorene)-2,6-diylbis(oxycarbonyl)]bisaniline, 4,4'-[spiro(xanton-9,9'-fluorene)-2,6-diylbis(oxycarbonyl)]bisaniline, 4,4'-[spiro(xanton-9,9'-fluorene)-3,6-diylbis(oxycarbonyl)]bisaniline [[alkylcarbonyl]] Biphenylamine, 9,10-bis(4-aminophenyl)adenine, 2,4-bis(4-aminophenyl)cyclobutane-1,3-dicarboxylic acid dimethyl ester, and aromatic diamines formed by substituting some or all of the hydrogen atoms on the aromatic ring of the above aromatic diamines (substituents are halogen atoms, alkyl or alkoxy groups with 1 to 3 carbon atoms, cyano, or haloalkyl or alkoxy groups with some or all of the hydrogen atoms of the alkyl or alkoxy group being replaced by halogen atoms, etc.). Furthermore, there are no particular limitations on aromatic diamines having the benzoxazole structure, and examples include 5-amino-2-(p-aminophenyl)benzoxazole, 6-amino-2-(p-aminophenyl)benzoxazole, 5-amino-2-(m-aminophenyl)benzoxazole, 6-amino-2-(m-aminophenyl)benzoxazole, 2,2'-p-phenylenebis(5-aminobenzoxazole), 2,2'-p-phenylenebis(6-aminobenzoxazole), and 1-(5-aminobenzoxazole)-4 -(6-aminobenzoxazole)benzene, 2,6-(4,4'-diaminodiphenyl)benzo[1,2-d:5,4-d']bisoxazole, 2,6-(4,4'-diaminodiphenyl)benzo[1,2-d:4,5-d']bisoxazole, 2,6-(3,4'-diaminodiphenyl)benzo[1,2-d:5,4-d']bisoxazole, 2,6-(3,4'-diaminodiphenyl)benzo[1,2-d:4,5-d']bisoxazole, 2,6-(3,Examples of such diamines include 3'-diaminodiphenyl)benzo[1,2-d:5,4-d']bisoxazole and 2,6-(3,3'-diaminodiphenyl)benzo[1,2-d:4,5-d']bisoxazole. Among these, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 4-amino-N-(4-aminophenyl)benzamide, 4,4'-diaminodiphenyl sulfone, and 3,3'-diaminobenzophenone are particularly preferred. Furthermore, aromatic diamines can be used alone or in combination.

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

[0054] Examples of diisocyanates include, for instance, 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, and 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, diphenyl sulfone-4,4'-diisocyanate, toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, m-xylene diisocyanate, p-xylene 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- Aromatic diisocyanates such as 4,4'-diisocyanate, 3,3'-dimethoxybiphenyl-4,4'-diisocyanate, and 3,3'-diethoxybiphenyl-4,4'-diisocyanate, as well as hydrogenated diisocyanates selected from these (e.g., isophorone diisocyanate, 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, hexamethylene diisocyanate), etc. Among these, considering low hygroscopicity, dimensional stability, price, and polymerizability, diphenylmethane-4,4'-diisocyanate, toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, 3,3'-dimethylbiphenyl-4,4'-diisocyanate, naphthalene-2,6-diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, and 1,4-cyclohexane diisocyanate are preferred. Furthermore, diisocyanates can be used alone or in combination.

[0055] The solvent used in the resin solution of the present invention preferably has a dipole moment in the range of 3.0 to 6.0 D, and is a solvent capable of dissolving at least one resin selected from the group consisting of polyamic acid, polyimide, and polyamide-imide. If the dipole moment is within the above range, the uniform heating effect of microwave heating used in the solvent removal process of the resin film described later is excellent, and it becomes easier to improve the isotropic properties of the obtained resin film.

[0056] Examples of solvents used in the resin solution of this 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), dimethyl sulfoxide (dipole moment: 3.96D), and dimethyl sulfone (dipole moment: 4.47D). D), sulfolane (dipole moment: 4.68D), 1,3-dimethyl-2-imidazolinone (dipole moment: 4.07D), 1,3-dimethyl-2-pyrimidinone (dipole moment: 4.17D), 3-methyl-2-oxazolidinone (dipole moment: 4.10D), hexamethylphosphoramide (dipole moment: 5.54D), γ-butyrolactone (GBL) (dipole moment: 4.27D), etc., can be used alone or in combination of two or more. Additionally, less desirable solvents such as toluene (dipole moment: 0.36D) and xylene (dipole moment: 0.00–0.64D) can be used in combination with these solvents, provided that the resin solids do not precipitate and the uniform heating effect of microwave heating is not compromised. Furthermore, when mixing two or more solvents, the dipole moment value is the weighted average of the individual values.

[0057] To the extent that the properties of the resin film of the present invention are not impaired, particulate matter may be added to the resin solution. The particulate matter may be inorganic or organic. Examples of inorganic particulate matter include silicon nitride, silicon oxide, titanium oxide, aluminum oxide, magnesium oxide, zinc oxide, tin oxide, calcium carbonate, barium sulfate, talc, kaolin, and calcium sulfate. Examples of organic particulate matter include polyamide resins, polyimide resins, benzoguanamine resins, and melamine resins; these particulate matter may be used in combination.

[0058] The resin solids concentration of the resin solution of the present invention is preferably 5 to 40% by mass, more preferably 7 to 35% by mass, and even more preferably 10 to 30% by mass. If the resin solids concentration is above or below the above-mentioned lower limit, it is preferred from the viewpoint of obtaining the film thickness required as a resin film; if it is below or below the above-mentioned upper limit, it is preferred from the viewpoint of obtaining solution fluidity to a degree that does not compromise the isotropic properties of the resin film.

[0059] In this invention, the resin membrane is preferably obtained by the resin membrane manufacturing method described later. Specifically, it is a polymer membrane with imide bonds on the main chain, preferably a polyimide membrane or a polyamide-imide membrane, more preferably a polyimide membrane.

[0060] In this invention, the lower limit of the resin film thickness, from the viewpoint of the required strength and operability of the resin film, is preferably 3 μm or more, more preferably 5 μm or more, and even more preferably 7 μm or more. The upper limit of the resin film thickness, from the viewpoint of uniform solvent removal, is preferably 250 μm or less, more preferably 150 μm or less, and even more preferably 100 μm or less.

[0061] The preferred method for manufacturing the resin film of the present invention is characterized by comprising: Step A, which involves coating the resin solution onto a support and drying it to create a resin film laminate containing the solvent, is described. Step B, which involves peeling the support from the solvent-containing resin film laminate to obtain a solvent-containing resin film, and step C, which involves removing the solvent from the solvent-containing resin film, or performing a dehydration and ring-closing reaction while removing the solvent. At least a portion of step C is performed by microwave heating.

[0062] Step A will be described below. Step A is the process of coating a resin solution onto a support, drying it, and producing a resin film laminate containing the solvent (hereinafter referred to simply as the laminate). The laminate is formed by laminating the dried resin solution onto the support.

[0063] Examples of supports used in this invention include resin film substrates, stainless steel strip substrates, and glass substrates. As the resin film substrate, it is preferable to use a resin film substrate that does not swell or dissolve in the solvent contained in the resin solution; examples include polyethylene terephthalate (PET) film, polyethylene naphthalate (PEN) film, polyolefin (PP) film, and cycloolefin (COP) film. Furthermore, in order to peel the solvent-containing resin film from the support, a support with easy peelability is preferred.

[0064] Methods for applying resin solution to a support include die coating, comma coating, blade coating, roller coating, knife coating, and bar coating, and combinations of these methods are also possible. From a production point of view, comma coating, die coating, or a combination thereof are preferred.

[0065] Methods for drying the resin solution on the support include, for example, drying by forced air, hot air, infrared heating, or heat conduction from the support, and combinations of two of these methods. The solvent content of the dried solvent-containing resin film is preferably 3 to 50% by mass, more preferably 5 to 40% by mass, and even more preferably 7 to 30% by mass. If the solvent content is above the lower limit mentioned above, the difference in solvent content and polymer structure between the resin film surface in contact with the support and the opposite surface is less, reducing the anisotropy of the resin film's properties in the thickness direction and suppressing warping. If it is below the upper limit mentioned above, deformation of the resin film after peeling from the support is suppressed, and operation becomes easier.

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

[0067] There are no particular limitations on the method for peeling the solvent-containing resin film from the support. Examples include using tweezers or similar tools to roll it up from the end, making a cut in the laminate, attaching adhesive tape to one side of the cut portion, and then rolling it up from the tape portion, or vacuum-adhesiveing ​​one side of the cut portion of the resin film and then rolling it up from that portion.

[0068] Step C is described below. Step C is a process of removing solvent from the solvent-containing resin membrane, or performing a dehydration and ring-closing reaction while removing solvent, and at least a portion of Step C is carried out by microwave heating.

[0069] The microwave heating used in the solvent removal process of the solvent-containing resin film after peeling from the support is based on the principle of causing the dipoles of molecules contained in the heated material to vibrate through microwaves. Therefore, the microwave absorption efficiency depends on the magnitude of the dipole moment and the ease with which molecules follow the microwave cycle. Thus, to effectively and uniformly remove the solvent from the solvent-containing resin film using microwaves, solvents with the aforementioned dipole moment values ​​are specified.

[0070] The frequency of the microwave heating device used in this invention is preferably selected to easily induce molecular motion in solvents having the aforementioned dipole moment values. However, due to limitations imposed by conventional radio wave methods and microwave tubes, a heating device with a frequency of 2,450 MHz is typically used. However, if it would interfere with other communications, 915 MHz can also be used. In this invention, frequencies of 2,450 MHz and 915 MHz are further preferably selected based on the above considerations. Furthermore, the microwave intensity is selected appropriately based on the foaming, orange peel, or undulations on the resin film surface.

[0071] Using a solvent-containing resin solution with a specified dipole moment, the resin film is uniformly heated and dried during the solvent removal process by microwave heating, reducing the density difference of the formed higher-order structure and easily achieving the equation (40 + 0.8 × A) ≤ B < A. Furthermore, the isotropic properties of the resulting resin film can be improved, and the ratio of the linear expansion coefficient (TD direction to MD direction) and the tensile modulus (TD direction to MD direction) of the resin film are more easily controlled within preferred ranges.

[0072] In this invention, methods such as forced-air drying, hot air drying, and infrared heating drying can be used together with microwave heating, or two of these methods can be combined.

[0073] In the solvent removal process using the above heating method, the initial temperature is preferably in the range of 50 to 200°C. If it is above the lower limit of the specified range, it is easy to suppress the temperature deviation in the drying oven. If the initial temperature is below the upper limit of the specified range, it is easy to suppress the foaming of the resin film and the orange peel wrinkles on the surface caused by the rapid heating of the solvent. In addition, it reduces the difference in solvent content and higher molecular structure between the surface of the resin film and the interior of the resin film, making it easier to achieve the formula (40+0.8×A)≤B<A.

[0074] In the solvent removal process using the above heating method, the final temperature is preferably in the range of 300 to 500°C. If it is above the lower limit of the specified range, the amount of residual solvent in the resin film can be easily suppressed. If the final temperature is below the upper limit of the specified range, the thermal degradation of the resin film can be easily suppressed.

[0075] In the solvent removal process using the above heating method, the preferred heating curve is a heating rate of 5–60°C / min, or a stepped heating with two or more stages, or a combination of both. If the heating rate is above the lower limit of the specified range, the working time of the solvent removal process can be shortened. If it is below the upper limit of the specified range, it is easier to suppress foaming of the resin film and orange peel wrinkles on the surface caused by rapid heating of the solvent. Furthermore, it reduces the difference in solvent content and polymer structure between the resin film surface and the interior of the resin film, making it easier to achieve (40 + 0.8 × A) ≤ B < A.

[0076] When using a stepped heating method, the number of stages is preferably 2 to 10, and the heating rate between each stage is preferably 10 to 100 °C / min. If the number of stages is above the lower limit of the specified range, it is easier to suppress foaming of the resin film and orange peel wrinkles on the surface caused by rapid heating of the solvent. Furthermore, it reduces the difference in solvent content and higher molecular structure between the resin film surface and interior, making it easier to achieve the equation (40 + 0.8 × A) ≤ B < A. Conversely, if the number of stages is below the upper limit of the specified range, the working efficiency becomes good.

[0077] In the solvent removal process, the total drying time is preferably determined based on the initial temperature, final temperature, heating rate, and number of stages mentioned above. If the total drying time is above the lower limit of the specified range, it is easy to suppress foaming of the resin film and orange peel wrinkles on the surface caused by the rapid heating of the solvent. If it is below the upper limit, productivity is improved and thermal degradation of the resin film is easily suppressed.

[0078] In the solvent removal process of this invention, the resin film can be further stretched. The stretching ratio in the stretching operation is preferably 1.5 to 4.0 times in the MD (length) direction and 1.4 to 3.0 times in the TD (width) direction, and the ratio of the stretching ratio in the MD direction to the stretching ratio in the TD direction (MD / TD) is preferably greater than 1.0. By keeping the stretching conditions within the above range, it is easy to control the average coefficient of linear expansion of the resin film measured in both the MD and TD directions within the range of 35 to 200°C, as well as the tensile modulus of elasticity in both the MD and TD directions, within the preferred range.

[0079] The solvent content of the resin film after the solvent removal process is preferably 0.01 to 5.0% by mass, more preferably 0.02 to 4.0% by mass, and even more preferably 0.03 to 3.0% by mass. By keeping the solvent content at or above the lower limit, thermal degradation of the resin film due to excessive high-temperature treatment can be suppressed, and by keeping it below the upper limit, the coefficient of linear expansion and tensile modulus of elasticity can be easily controlled within the preferred range. Example

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

[0081] In addition, the measured values ​​in the examples and comparative examples, unless otherwise stated, were measured in accordance with the following methods.

[0082] <Temperature dependence curve peak temperature of tanδ of resin membrane> Three samples were taken from the mechanical direction (MD direction) and the width direction (TD direction) of the resin film, respectively. The temperature dependence curves of the storage modulus (E'), loss modulus (E"), and tanδ (=E" / E') obtained by dividing the loss modulus by the storage modulus were obtained under the following conditions. The peak temperature was obtained, and the average values ​​of the mechanical direction (MD direction) and the width direction (TD direction) were calculated. Device Name: TA Instruments DMA Q800 Sample length: 15-20mm Sample width: 4mm Temperature to start heating: 25℃ End temperature of heating: 500℃ Heating rate: 5℃ / min Measurement frequency: 10Hz

[0083] <Inflection point temperature of linear expansion coefficient of resin film> Three samples were taken from the mechanical direction (MD direction) and the width direction (TD direction) of the resin film. The stretching rate was measured under the following conditions. The temperature of the stretching rate inflection point at the second heating was read, and the average value of the mechanical direction (MD direction) and the width direction (TD direction) was calculated. Equipment Name: Bruker AXS TMA-4000SA Sample length: 15mm Sample width: 2mm Spacing between fixtures: 10mm Load: 5gf First heating start temperature: 25℃ End temperature of the first heating cycle: 200℃ First heating rate: 20℃ / min Cooling rate: 5℃ / min The second heating cycle begins at 30℃. The second heating cycle ended at 500℃. Second heating rate: 10℃ / min Atmosphere: Argon

[0084] <Weight-average molecular weight, number-average molecular weight, and molecular weight distribution of the resin> Weigh 8 mg of resin sample and immerse it in 8 ml of solvent, stirring for 3 hours to obtain a resin solution. Under the following conditions, analyze the resin solution by gel permeation chromatography (GPC), and calculate the weight-average molecular weight, number-average molecular weight, and molecular weight distribution using standard polystyrene. Equipment Name: Tosoh HLC-8420GPC Column: TSKgel SuperAWH-H×2 Solvent: DMAc (with 30mM lithium bromide added) Flow rate: 0.3 ml / min Concentration: 0.1% Injection volume: 10 μl Temperature: 40℃ Detector: RI

[0085] <Resin film thickness> The measurements were performed using a micrometer (FEINPRUF, Millitron 1245D).

[0086] <Coefficient of linear expansion (CTE) of resin film> Three samples were taken from the mechanical direction (MD direction) and the width direction (TD direction) of the resin film. The stretch rate was measured under the following conditions, with the stretch rate / temperature measured at 15°C intervals, such as 35°C to 50°C and 50°C to 65°C. This measurement was carried out until 200°C, and the average value of all measured values ​​was calculated as CTE. Device Name: MAC Science TMA4000S Sample length: 20mm Sample width: 2mm Temperature to start heating: 25℃ End temperature of heating: 400℃ Heating rate: 5℃ / min Atmosphere; Argon

[0087] <Tension elastic modulus of resin film> 100mm × 10mm strips were cut from the resin film along both the mechanical direction (MD direction) and the width direction (TD direction) to serve as test pieces. The test pieces were cut from the central portion along the width direction. Under the following conditions, the tensile modulus of elasticity was measured for three samples each along the MD and TD directions, and the average value of all measured values ​​was obtained. Equipment Name: Shimadzu Autograph® AG-5000A Spacing between fixtures: 40mm Temperature: 25℃ Stretching speed: 50mm / min

[0088] <Yellowness Index (YI) of Resin Film> Using a colorimeter (ZE6000, manufactured by Nippon Denko Co., Ltd.) and a C2 light source, the tristimulus values ​​(XYZ) of the film were measured based on ASTM D1925, and the yellowness index (YI) was calculated according to the following formula. Additionally, three identical measurements were performed, and their arithmetic mean was used. YI = 100 × (1.28X - 1.06Z) / Y

[0089] <400nm transmittance of the resin film> The transmittance of the resin film at a wavelength of 400 nm was measured using a spectrophotometer (Hitachi, U-2001). The obtained value was converted to a thickness of 20 μm according to the Lambert-Beer law, and the value was taken as the transmittance of the resin film at 400 nm. In addition, three identical measurements were performed, and the arithmetic mean was used.

[0090] <Total transmittance of resin film (TT)> The total transmittance (TT) of the film was measured using a HAZEMETER (NDH5000, manufactured by Nippon Denshoku Co., Ltd.). A D65 lamp was used as the light source. Three identical measurements were performed, and the arithmetic mean was used.

[0091] [Synthesis Example 1 (Preparation of Polyamic Acid Solution A)] After purging the reaction vessel, which is equipped with a nitrogen inlet pipe, thermometer, and stir bar, with nitrogen, 1470.8 parts by mass of 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA), 775.6 parts by mass of 4,4'-oxyphthalic dianhydride (ODPA), 3202.4 parts by mass of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFMB), and 21795 parts by mass of N,N-dimethylacetamide (DMAc) were added to the reaction vessel under a nitrogen atmosphere and dissolved. The mixture 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 specific viscosity of 4.5 dl / g. The weight-average molecular weight, number-average molecular weight, and molecular weight distribution of the resin in the obtained resin solution are shown in Table 1.

[0092] [Synthesis Example 2 (Preparation of Polyimide Solution B)] After purging the reaction vessel, which is equipped with a nitrogen inlet pipe, thermometer, and stir bar, 551 parts by mass of N,N-dimethylacetamide (DMAc) and 64.1 parts by mass of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFMB) were added to the reaction vessel under a nitrogen atmosphere and stirred to dissolve TFMB in DMAc. Then, while stirring in the reaction vessel under a nitrogen stream, 44.4 parts by mass of 4,4'-(2,2-hexafluoroisopropyl)phthalic anhydride (6FDA) and 29.4 parts by mass of biphenyltetracarboxylic anhydride (BPDA) were added over 10 minutes. The temperature was directly adjusted to the range of 20-40°C while stirring continuously for 6 hours to carry out the polymerization reaction, resulting in a viscous polyamic acid solution. Then, 410 parts by mass of DMAc were added to the obtained polyamic acid solution for dilution, followed by 25.83 parts by mass of isoquinoline as an imidization accelerator. While stirring the polyamic acid solution, the temperature was maintained in the range of 30 to 40°C. Acetic anhydride was slowly added dropwise over about 10 minutes as an imidizing agent. After that, the liquid temperature was maintained at 30 to 40°C while stirring was continued for 12 hours to carry out the chemical imidization reaction, and a polyimide solution was obtained. Then, 1000 parts by weight of the resulting polyimide solution containing the imidizing agent and imidization accelerator were transferred to a reaction vessel equipped with a stirrer and a stir blade. While stirring at 120 rpm and maintaining a temperature of 15–25°C, 1500 parts by weight of methanol were added dropwise at a rate of 10 g / min. Turbidity of the polyimide solution was observed after adding approximately 800 parts by weight of methanol, confirming the precipitation of powdered polyimide. The remaining 1500 parts by weight of methanol were added until complete precipitation of the polyimide. The contents of the reaction vessel were then filtered using a vacuum filter and further washed and filtered with 1000 parts by weight of methanol. Subsequently, 50 parts by weight of the filtered polyimide powder were dried at 50°C for 24 hours using a dryer connected to a local exhaust system, followed by drying at 260°C for 2 hours to remove residual volatile components, yielding polyimide powder. The specific viscosity of the obtained polyimide powder was 2.1 dl / g. Then, 42 parts by mass of the obtained polyimide powder were dissolved in 168 parts by mass of DMAc to obtain a polyimide solution B with 20 parts by mass of solids. The results of the determination of the weight-average molecular weight, number-average molecular weight, and molecular weight distribution of the resin in the obtained resin solution are shown in Table 1.

[0093] [Synthesis Example 3 (Adjustment of C in Polyimide Solution)] In a reaction vessel equipped with a nitrogen inlet tube, a Dean-Stark apparatus, a reflux tube, a thermometer, and a stir bar, nitrogen gas was introduced while 124.15 parts by mass of 4,4'-diaminodiphenyl sulfone (4,4'-DDS), 124.15 parts by mass of 3,3'-diaminodiphenyl sulfone (3,3'-DDS), and 750 parts by mass of γ-butyrolactone (GBL) were added. Then, at room temperature, 248.18 parts by mass of 4,4'-oxyphthalic dianhydride (ODPA), 58.8 parts by mass of biphenyltetracarboxylic dianhydride (BPDA), 335 parts by mass of GBL, and 390 parts by mass of toluene were added. The internal temperature was raised to 160°C, and the reaction was carried out under reflux at 160°C for 1 hour to induce imidization. After imidization, the temperature was raised to 180°C while removing toluene during the reaction. After reacting for 12 hours, the solution was removed from the oil bath and brought back to room temperature. 1149 parts by weight of GBL were added, with a solid content of 20 parts by weight, to obtain a polyimide solution C with a specific viscosity of 0.6 dl / g. The weight-average molecular weight, number-average molecular weight, and molecular weight distribution of the resin in the resulting resin solution are shown in Table 1.

[0094] [Synthesis Example 4 (Adjustment of Polyimide Solution D)] In a reaction vessel equipped with a nitrogen inlet tube, a Dean-Stark apparatus, a reflux tube, a thermometer, and a stir bar, nitrogen gas was introduced while adding 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 γ-butyrolactone (GBL), and 360 parts by mass of toluene. The internal temperature was then raised to 180°C, and toluene was removed by distillation while the mixture was heated at 180°C for 3 hours to induce imidization, yielding a polyimide solution. Then, 2500 parts by weight of the obtained polyimide solution were transferred to a reaction vessel equipped with a stirrer and a stirring blade. While stirring at 120 rpm and maintaining a temperature of 15–25°C, 50,000 parts by weight of acetone were added dropwise at a rate of 10 g / min. After adding approximately 2500 parts by weight, the turbidity of the polyimide solution was confirmed, and the precipitation of powdered polyimide was observed. The remaining 2500 parts by weight of acetone were added until the polyimide was completely precipitated. Subsequently, the contents of the reaction vessel were filtered through a vacuum filter and further washed and filtered with 2000 parts by weight of methanol. Then, 300 parts by weight of the filtered polyimide powder were dried at 50°C for 24 hours using a dryer connected to a local exhaust device, followed by drying at 260°C for 2 hours to remove residual volatile components, yielding polyimide powder. The specific viscosity of the obtained polyimide powder was 0.7 dl / g. Then, 42 parts by mass of the obtained polyimide powder were dissolved in 168 parts by mass of NMP to obtain a polyimide solution D with 20 parts by mass of solids and a specific viscosity of 0.7 dl / g. The weight-average molecular weight, number-average molecular weight, and molecular weight distribution of the resin in the obtained resin solution are shown in Table 1.

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

[0096] [Example 1 of the fabrication of polyimide film (Examples 1-5)] On a mirror-finished stainless steel endless continuous strip (coating width 1240 mm) used as a film-forming support, polyamic acid solution A is coated using a die coater and dried at 90–115°C for 10 minutes. The dried, self-supporting polyamic acid film (containing 9% by mass of residual solvent) is peeled off from the support, and both ends are cut off to obtain the green film. The resulting film was fed into a tenter frame, where both ends of the film were held with a final pin spacing of 1140 mm. It was then inserted into a continuous heating furnace equipped with a microwave heating zone and a hot air circulation device. The film underwent a heat treatment process: a first stage of heating at 170°C for 1 minute, followed by a heating rate of 60°C / min to 230°C; a second stage of heating at 230°C for 1 minute, followed by a heating rate of 60°C / min to 350°C; and a third stage of heating at 350°C for 5 minutes. During this process, a 2450 MHz microwave at 50 kW was introduced into the microwave heating zone. After cooling to room temperature for 2 minutes, the film was slit to remove the portions with poor flatness at both ends and rolled into a roll, yielding resin film 1A as shown in Table 2. Similarly, polyamic acid solution A was replaced with other resin solutions B, C, D, and E, and the coating thickness of the support was varied to obtain resin films 1B, 1C, 1D, and 1E. The performance evaluation results of the obtained resin films are shown in Table 2.

[0097] [Example 2 of the fabrication of polyimide film (Examples 6-10)] The surface roughness (Sa) of the region serving as the support for membrane fabrication is 1 nm, the maximum protrusion height (Sp) is 7 nm, and the protrusion density (Spd) is 20 / μm. 2 On a polyester film without a coating layer, a polyamic acid solution A (coating width 1240 mm) is coated using a comma coater and dried at 90–115°C for 10 minutes. The dried, self-supporting polyamic acid film (containing 10% by mass residual solvent) is peeled off from the support and both ends are cut off to obtain a green film. The resulting green film is passed through a tenter frame, holding both ends of the film with a final pin spacing of 1140 mm, and inserted into a continuous heating oven equipped with a microwave heating zone and a hot air circulation device. The film is heated from 170°C to 350°C at a heating rate of 15°C / min. At this time, a 2,450 MHz microwave at 40 kW is introduced into the microwave heating zone. Afterward, the film is cooled to room temperature for 2 minutes, and the portions with poor flatness at both ends are cut off using a slitting machine. The film is then rolled into a roll to obtain resin film 2A as shown in Table 2. Similarly, polyamic acid solution A was replaced with other resin solutions B, C, D, and E. Additionally, the coating thickness of the support was varied to obtain resin films 2B, 2C, 2D, and 2E. The performance evaluation results of the obtained resin films are shown in Table 2.

[0098] [Example 3 of the fabrication of polyimide film (Comparative Examples 1-5)] On a mirror-finished stainless steel endless continuous strip used as a support for the film, polyamic acid solution A (coating width 1240 mm) is applied using a die coater and dried at 90–115°C for 10 minutes. The dried, self-supporting polyamic acid film (containing 9% by mass of residual solvent) is peeled off from the support and both ends are cut off to obtain the green film. The resulting film was held at both ends by a tenter frame with a final pin spacing of 1140 mm, and then inserted into a continuous heating furnace equipped with a hot air circulation device. The film was heated from 170°C to 350°C at a heating rate of 15°C / min. Afterward, it was cooled to room temperature for 2 minutes, and the portions with poor flatness at both ends were cut off using a slitting machine. The film was then rolled into a roll to obtain resin film 3A as shown in Table 3. Similarly, polyamic acid solution A was replaced with other resin solutions B, C, D, and E, and the coating thickness of the support was varied to obtain resin films 3B, 3C, 3D, and 3E. The evaluation results of the characteristics of the obtained resin films are shown in Table 3.

[0099] [Example 4 of the fabrication of polyimide film (Comparative Examples 6-10)] The surface roughness (Sa) of the region serving as the support for membrane fabrication is 1 nm, the maximum protrusion height (Sp) is 7 nm, and the protrusion density (Spd) is 20 / μm. 2 On a polyester film without a coating layer, a polyamic acid solution A (coating width 1240 mm) is coated using a comma coater and dried at 90–115°C for 10 minutes. The dried, self-supporting polyamic acid film (containing 10% by mass residual solvent) is peeled off from the support and both ends are cut off to obtain a green film. The obtained green film is passed through a tenter frame, holding both ends of the film with a final pin spacing of 1140 mm, and inserted into a continuous heating oven equipped with a microwave heating zone and a hot air circulation device. The film is heated from 170°C to 350°C at a heating rate of 70°C / min, and heat-treated at 350°C for 4 minutes. At this time, a 2,450 MHz microwave at 50 kW is introduced into the microwave heating zone. Afterward, the film is cooled to room temperature for 2 minutes, and the portions with poor flatness at both ends are cut off using a slitting machine. The film is then rolled into a roll to obtain the resin film 4A shown in Table 3. Similarly, polyamic acid solution A was replaced with other resin solutions B, C, D, and E. Additionally, the coating thickness of the support was varied to obtain resin films 4B, 4C, 4D, and 4E. The performance evaluation results of the obtained resin films are shown in Table 3.

[0100] [Table 1]

[0101] [Table 2]

[0102] [Table 3] Industrial availability

[0103] As described above, the resin film of the present invention has excellent heat resistance and transparency, maintains a low coefficient of linear expansion even in high-temperature regions, has a high tensile modulus of elasticity, and has a small ratio of the coefficient of linear expansion and tensile modulus of elasticity in the MD direction to the TD direction, exhibiting good isotropic properties. Therefore, it is extremely useful for the front panel and electrode peripheral devices of image display devices such as touch panels and displays.

Claims

1. A resin film, wherein, Satisfying the following (1)~(2): (1) The peak temperature (A) of the temperature dependence curve of tanδ is in the range of 250~500℃, where tanδ is the value obtained by dividing the loss modulus by the storage modulus. The peak temperature (A) of the temperature dependence curve of tanδ has the following relationship with the inflection point temperature (B) of the coefficient of linear expansion. (40+0.8×A) ≤ B < A, (2) The weight-average molecular weight of the resin used as the raw material for the resin membrane is in the range of 50,000 to 500,000, and the molecular weight distribution is in the range of 1.0 to 5.

0. The molecular weight distribution is the value obtained by dividing the weight-average molecular weight by the number-average molecular weight of the resin. The resin film is obtained by the following manufacturing method. Step A involves coating a resin solution onto a support, drying it, and then fabricating a resin film laminate containing the solvent. Step B involves peeling the support from the laminate to obtain a resin film containing solvent. Step C involves removing the solvent from the solvent-containing resin membrane, or simultaneously removing the solvent while performing a dehydration and ring-closing reaction. At least a portion of step C is performed by microwave heating. In process C, a temperature rise curve exists. The temperature rise curve uses one or a combination of methods, namely, a temperature rise rate of 5~60℃ / min or a stepped temperature rise with two or more stages. The initial temperature in the temperature rise curve is in the range of 50~200℃, and the final temperature is in the range of 300~500℃. In process A, the solvent content in the solvent-containing resin film after drying the resin solution on the support is 3 to 50% by mass.

2. The resin film according to claim 1, wherein, Further satisfy (3)~(4): (3) The linear expansion coefficients measured in both the MD and TD directions within the range of 35~200℃ are in the range of -5ppm / ℃ to +55ppm / ℃, and the ratio of the linear expansion coefficient in the TD direction to that in the MD direction is in the range of 0.97~1.

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

03.

3. The resin film according to claim 1 or 2, characterized in that, The yellow index is below 10, the transmittance at a wavelength of 400nm is above 70%, and the total transmittance is above 85%.

4. The resin film according to claim 1 or 2, characterized in that, The weight-average molecular weight of the resin used as the raw material for the resin film is in the range of 80,000 to 400,000.

5. The resin film according to claim 1 or 2, characterized in that, The molecular weight distribution of the raw material resin of the resin film, obtained by dividing the weight average molecular weight of the resin by the number average molecular weight of the resin, is in the range of 2.0 to 4.

0.

6. The method for manufacturing the resin film according to any one of claims 1 to 5, characterized in that, Include: Step A involves coating a resin solution onto a support, drying it, and then fabricating a resin film laminate containing the solvent. Step B involves peeling the support from the laminate to obtain a resin film containing solvent. Step C involves removing the solvent from the solvent-containing resin membrane, or simultaneously removing the solvent while performing a dehydration and ring-closing reaction. At least a portion of step C is performed by microwave heating. In process C, a temperature rise curve exists. The temperature rise curve uses one or a combination of methods, namely, a temperature rise rate of 5~60℃ / min or a stepped temperature rise with two or more stages. The initial temperature in the temperature rise curve is in the range of 50~200℃, and the final temperature is in the range of 300~500℃. In process A, the solvent content in the solvent-containing resin film after drying the resin solution on the support is 3 to 50% by mass.

7. The method for manufacturing a resin film according to claim 6, wherein, The resin solution contains: a resin selected from at least one of the group consisting of polyamic acid, polyimide and polyamide-imide, and a solvent capable of dissolving the resin with a dipole moment in the range of 3.0 to 6.0D.

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