TWI826669B - Method for producing colorless transparent resin film - Google Patents

Abstract

A method for producing a colorless transparent resin film by a solvent casting method in which an organic solvent solution of a resin is flow cast onto a support body and then dried, wherein the organic solvent contains at least one type of organic solvent (S1) with a boiling point of 80° or lower and at least one type of organic solvent (S2) with a boiling point of 130° or higher.

Description

Manufacturing method of colorless transparent resin film

The present invention relates to a method for producing a colorless transparent resin film.

Because polyimide resin has excellent mechanical properties and heat resistance, some people are exploring various uses in fields such as electrical parts and electronic parts. For example, in order to reduce the weight or flexibility of parts, it is expected that glass substrates used in image display devices such as liquid crystal displays and organic EL displays will be replaced by plastic substrates. Polyimide resin is suitable as the plastic material. Research is also ongoing.

Commonly used polyimide films are generally made by casting an organic solvent solution containing polyamide acid onto a belt or drum, and heating the polyamide acid to cause an imidization reaction to proceed.

Commonly used polyimides are known to have high heat resistance. Commonly used polyimides can be obtained from aromatic tetracarboxylic anhydrides and aromatic diamines. Due to the rigidity of the molecules, resonance stabilization, and strong chemical bonding, they have excellent heat resistance, chemical resistance, mechanical properties, and electrical properties. Therefore, it is widely used in the fields of forming materials, composite materials, electrical parts or electronic parts.

However, polyimides synthesized from the above-mentioned aromatic raw materials will be colored yellow or brown after the film is formed due to absorption from intra- or intermolecular electron transfer complexes, so they are not suitable for use in Optical applications such as substrate materials for flat panel displays or mobile phone equipment, optical fibers, optical waveguides, optical sensors, and optical adhesives.

Therefore, in order to take advantage of the high heat resistance of polyimide and improve transparency, fluorinated polyimide has been developed in which perfluoroalkyl groups are introduced into the repeating units, or 1, 2, 4, Alicyclic polyimide made from alicyclic raw materials such as 5-cyclohexanetetracarboxylic anhydride.

Patent Document 1 discloses a method for manufacturing a polyimide-based film, which produces releasability and appearance from a liquid containing a polyimide-based polymer, γ-butyrolactone, and N,N-dimethylacetamide. Excellent polyimide film.

Patent Document 2 shows a method for manufacturing an optical film that reduces scaly unevenness by containing an alcohol-based solvent in a liquid containing a soluble polyimide resin as a main component and methylene chloride as a solvent. [Prior technical literature] [Patent Document]

[Patent Document 1] Japanese Patent Application Publication No. 2017-25204 [Patent Document 2] Japanese Patent Application Publication No. 2017-187617

[Problem to be solved by the invention]

However, in the method of Patent Document 1, when an organic solvent with a high boiling point such as γ-butyrolactone or N,N-dimethylacetamide is used, the temperature in the drying step needs to be high in order to remove the solvent. There is a problem of reduced transparency due to coloring. In addition, in the method of Patent Document 2, in the case of a low-boiling point solvent such as methylene chloride, the solvent may evaporate rapidly and the polyimide aligned by the casting method may be fixed and optical anisotropy may occur. Sexual issues.

The problem to be solved by the present invention is to provide a method for manufacturing a colorless transparent resin film, which can achieve no coloration under high-temperature drying and has good optical isotropy. [Means to solve the problem]

The inventors of the present invention found that when a film is produced by a solution casting method, the organic solvent in the organic solvent solution of the resin contains a low-boiling-point solvent as a main component and a high-boiling-point solvent, thereby solving the above-mentioned problems. invention.

That is, the present invention relates to a method for producing a colorless transparent resin film by a solution casting method including the steps of casting an organic solvent solution of the resin on a support and drying it. The organic solvent contains one or more organic solvents (S1) with a boiling point of 80°C or lower and one or more organic solvents (S2) with a boiling point of 130°C or higher. [Effects of the invention]

According to the method of the present invention, a colorless transparent resin film excellent in transparency and optical isotropy can be produced. The colorless transparent resin film obtained by the method of the present invention has good optical properties such as total light transmittance, yellow index (YI) value, haze, etc., and exhibits low retardation of optical isotropy. Therefore, the colorless transparent resin film obtained by the method of the present invention exhibits good performance when used as a base material for a transparent substrate of a liquid crystal display element, an organic EL display element, or a transparent conductive film of a touch panel.

The method for producing a colorless transparent resin film of the present invention is a method for producing a resin film by a solution casting method including a step of casting an organic solvent solution of the resin on a support and drying it, and the organic solvent contains 1 One or more organic solvents with a boiling point below 80°C (S1) and one or more organic solvents with a boiling point above 130°C (S2). "Colorless and transparent" in the present invention means that when a film with a thickness of 20 to 50 μm is formed, the total light transmittance of the film should be more than 85%, the yellow index (YI) should be less than 5, and the haze should be 2%. The following meanings.

There is no particular requirement for a resin that can be used in this embodiment as long as a resin film can be produced by a solution casting method including a step of casting an organic solvent solution of the resin onto a support and drying it. According to the limitation, the resin of the resin film is preferably polyimide. The organic solvent solution of the resin is preferably an organic solvent solution of polyamide acid or an organic solvent solution of polyimide. Hereinafter, this embodiment will be described in detail using the case where the resin of the resin film is polyimide as a representative example.

Regarding the resin that can be used for the resin film in this embodiment, from the viewpoint of transparency, optical properties, etc., for example, a polyimide containing a repeating unit represented by the following formula [I] is more suitable. [Chemical 1] In the formula, R is a tetravalent alicyclic group with 4 to 39 carbon atoms, and Φ is a divalent aliphatic group with 2 to 39 carbon atoms in total, an alicyclic group, an aromatic group, or a combination thereof. The group, as a bonding group, may also have a group selected from -O-, -SO ₂ -, -CO-, -CH ₂ -, -C(CH ₃ ) ₂ -, -OSi(CH ₃ ) ₂ - At least one of the group consisting of , -C ₂ H ₄ O- and -S-.

The content of the repeating unit of formula [I] in the polyimide is 100 mol% relative to the total repeating units of the polyimide, preferably 10 to 100 mol%, more preferably 50 to 100 mol%. It is further preferably 70 to 100 mol%, and further preferably 90 to 100 mol%. In addition, the number of repeating units of formula [I] in one molecule of polyimide is preferably 10 to 2000, more preferably 20 to 200.

Polyimide is obtained by reacting alicyclic tetracarboxylic acid or a derivative thereof with a diamine or a derivative thereof, using a tetravalent alicyclic tetracarboxylic acid and a divalent diamine as constituent components. Examples of the alicyclic tetracarboxylic acid or its derivatives include alicyclic tetracarboxylic acid, alicyclic tetracarboxylic acid esters, alicyclic tetracarboxylic dianhydride, etc., and alicyclic tetracarboxylic acid is preferred. dianhydride. Examples of diamines and their derivatives include diamines, diisocyanates, diaminodisilanes, and the like, and diamines are preferred.

Examples of the alicyclic tetracarboxylic dianhydride used in the synthesis of polyimide include 1,2,3,4-cyclobutanetetracarboxylic dianhydride and 1,2,4,5-cyclobutanetetracarboxylic dianhydride. Pentane tetracarboxylic dianhydride, 1,2,4,5-cyclohexane tetracarboxylic dianhydride, bicyclo[2,2,2]oct-7-ene-2,3,5,6-tetracarboxylic acid dianhydride, etc., especially 1,2,4,5-cyclohexanetetracarboxylic dianhydride. Generally speaking, for polyimides that use aliphatic diamines as components, the intermediate polyamide acid and the diamine form a strong complex that is not easy to polymerize, so it is necessary to use the dissolution of the complex. Disposal of highly toxic solvents (such as cresol). However, polyamide imide, which contains 1,2,4,5-cyclohexanetetracarboxylic dianhydride and aliphatic diamine as its constituent components, is a weak complex of polyamide acid and diamine. It is bonded together, so it is easy to increase the molecular weight and obtain a flexible film. In addition, the above-mentioned tetracarboxylic acid component contains isomers.

Among the above-mentioned tetracarboxylic acid components, tetracarboxylic acids other than alicyclic tetracarboxylic acids or their derivatives can be used in combination within the scope of not impairing the solvent solubility of the polyimide, the flexibility and transparency of the film, and particularly can be used in combination. dianhydride.

Examples of tetracarboxylic acids other than alicyclic tetracarboxylic acids include aromatic tetracarboxylic acids and linear or branched aliphatic tetracarboxylic acids. Specific examples of aromatic tetracarboxylic acids include pyromellitic acid, 3,3',4,4'-biphenyltetracarboxylic acid, and 2,3,3',4'-biphenyltetracarboxylic acid. , 2,2-bis(3,4-dicarboxyphenyl)propane, 2,2-bis(2,3-dicarboxyphenyl)propane, 2,2-bis(3,4-dicarboxyphenyl) -1,1,1,3,3,3-hexafluoropropane, 2,2-bis(2,3-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane, bis (3,4-dicarboxyphenyl)terine, bis(3,4-dicarboxyphenyl) ether, bis(2,3-dicarboxyphenyl) ether, 3,3',4,4'-diphenyl Methyl ketone tetracarboxylic acid, 2,2',3,3'-benzophenone tetracarboxylic acid, 4,4-(p-phenylenedioxy)diphthalic acid, 4,4-(isophthalic acid) base) diphthalic acid, 1,1-bis(2,3-dicarboxyphenyl)ethane, bis(2,3-dicarboxyphenyl)methane, bis(3,4-dicarboxyphenyl) Methane and derivatives of these tetracarboxylic acids, especially dianhydrides, are at least one compound selected from these. Specific examples of linear or branched aliphatic tetracarboxylic acids include ethylenetetracarboxylic acid and the like.

Examples of the diamine-based component constituting the amide imine ring of formula [I] and Φ include diamine, diisocyanate, and diaminodisilanes, and a diamine is preferred. The diamine content in the diamine component is preferably 50 mol% or more, more preferably 70 mol% or more, and further preferably 90 mol% or more (including 100 mol%).

The diamine used in the synthesis of polyimide can be any one of aromatic diamine, aliphatic diamine or a mixture thereof. In addition, the "aromatic diamine" in the present invention refers to a diamine whose amine group is directly bonded to an aromatic ring, and may also contain an aliphatic group, an alicyclic group, or other substituents in a part of its structure. "Aliphatic diamine" refers to a diamine whose amine group is directly bonded to an aliphatic group or alicyclic group, and a part of its structure may also contain aromatic groups or other substituents.

Examples of aromatic diamines used in the synthesis of polyimide include p-phenylenediamine, m-phenylenediamine, 2,4-diaminotoluene, 2,6-diaminotoluene, and diamine. Aniline, o-toluidine, m-toluidine, bis(trifluoromethyl)benzidine, octafluorobenzidine, 3,3'-dihydroxy-4,4'-diaminobiphenyl, 3,3' -Dimethoxy-4,4'-diaminobiphenyl, 3,3'-dichloro-4,4'-diaminobiphenyl, 3,3'-difluoro-4,4'-di Aminobiphenyl, 2,6-diaminonaphthalene, 1,5-diaminonaphthalene, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4 ,4'-Diaminodiphenylmethane, 4,4'-Diaminodiphenylsulfone, 3,4'-Diaminodiphenylsulfone, 4,4'-Diaminobenzophenone , 2,2-bis(4-(4-aminophenoxy)phenyl)propane, 2,2-bis(4-(2-methyl-4-aminophenoxy)phenyl)propane, 2,2-bis(4-(2,6-dimethyl-4-aminophenoxy)phenyl)propane, 2,2-bis(4-(4-aminophenoxy)phenyl) Hexafluoropropane, 2,2-bis(4-(2-methyl-4-aminophenoxy)phenyl)hexafluoropropane, 2,2-bis(4-(2,6-dimethyl- 4-Aminophenoxy)phenyl)hexafluoropropane, 4,4'-bis(4-aminophenoxy)biphenyl, 4,4'-bis(2-methyl-4-aminobenzene) Oxy)biphenyl, 4,4'-bis(2,6-dimethyl-4-aminophenoxy)biphenyl, 4,4'-bis(3-aminophenoxy)biphenyl, Bis(4-(4-aminophenoxy)phenyl)terine, bis(4-(2-methyl-4-aminophenoxy)phenyl)terine, bis(4-(2,6- Dimethyl-4-aminophenoxy)phenyl)terine, bis(4-(4-aminophenoxy)phenyl)ether, bis(4-(2-methyl-4-aminobenzene) Oxy)phenyl) ether, bis(4-(2,6-dimethyl-4-aminophenoxy)phenyl)ether, 1,4-bis(4-aminophenoxy)benzene, 1,4-bis(2-methyl-4-aminophenoxy)benzene, 1,4-bis(2,6-dimethyl-4-aminophenoxy)benzene, 1,3-bis (4-Aminophenoxy)benzene, 1,3-bis(2-methyl-4-aminophenoxy)benzene, 1,3-bis(2,6-dimethyl-4-amino) Phenoxy)benzene, 2,2-bis(4-aminophenyl)propane, 2,2-bis(2-methyl-4-aminophenyl)propane, 2,2-bis(2,6 -Dimethyl-4-aminophenyl)propane, 2,2-bis(4-aminophenyl)hexafluoropropane, 2,2-bis(2-methyl-4-aminophenyl)hexafluoropropane Fluoropropane, 2,2-bis(2,6-dimethyl-4-aminophenyl)hexafluoropropane, α,α'-bis(4-aminophenyl)-1,4-diisopropane Benzene, α,α'-bis(2-methyl-4-aminophenyl)-1,4-diisopropylbenzene, α,α'-bis(2,6-dimethyl-4- Aminophenyl)-1,4-diisopropylbenzene, α,α'-bis(3-aminophenyl)-1,4-diisopropylbenzene, α,α'-bis(4- Aminophenyl)-1,3-diisopropylbenzene, α,α'-bis(2-methyl-4-aminophenyl)-1,3-diisopropylbenzene, α,α' -Bis(2,6-dimethyl-4-aminophenyl)-1,3-diisopropylbenzene, α,α'-bis(3-aminophenyl)-1,3-diiso Propylbenzene, 9,9-bis(4-aminophenyl)fluorene, 9,9-bis(2-methyl-4-aminophenyl)fluorene, 9,9-bis(2,6-di Methyl-4-aminophenyl)fluorene, 1,1-bis(4-aminophenyl)cyclopentane, 1,1-bis(2-methyl-4-aminophenyl)cyclopentane , 1,1-bis(2,6-dimethyl-4-aminophenyl)cyclopentane, 1,1-bis(4-aminophenyl)cyclohexane, 1,1-bis(2 -Methyl-4-aminophenyl)cyclohexane, 1,1-bis(2,6-dimethyl-4-aminophenyl)cyclohexane, 1,1-bis(4-amino) Phenyl) 4-methyl-cyclohexane, 1,1-bis(4-aminophenyl)norbornane, 1,1-bis(2-methyl-4-aminophenyl)norbornane , 1,1-bis(2,6-dimethyl-4-aminophenyl)norbornane, 1,1-bis(4-aminophenyl)adamantane, 1,1-bis(2- Methyl-4-aminophenyl)adamantane, 1,1-bis(2,6-dimethyl-4-aminophenyl)adamantane, etc.

In addition, examples of aliphatic diamines used in the synthesis of polyimide include ethylene diamine, hexamethylene diamine, polyethylene glycol bis(3-aminopropyl) ether, and polyethylene glycol bis(3-aminopropyl) ether. Propylene glycol bis(3-aminopropyl) ether, 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, m-xylylenediamine, p-benzene Dimethylamine, 1,4-bis(2-amino-isopropyl)benzene, 1,3-bis(2-amino-isopropyl)benzene, isophoronediamine, norbornanediamine , siloxane diamines, etc.

Polyimides are usually produced as organic solvent solutions (varnishes). The method of the present invention uses an organic solvent containing more than one organic solvent (S1) with a boiling point of 80°C or lower and more than one organic solvent (S2) with a boiling point of 130°C or higher. In the present invention, by using an organic solvent (S1) with a relatively low boiling point and an organic solvent (S2) with a relatively high boiling point in combination, the organic solvent (S1) can be efficiently volatilized in the drying step, thereby suppressing thin films. It turns yellow, and the organic solvent (S2) is deliberately left in the film to obtain a film with excellent optical isotropy.

The boiling point of the organic solvent (S1) is 80°C or lower, preferably 75°C or lower, more preferably 70°C or lower, further preferably 65°C or lower, further preferably 60°C or lower. The lower limit of the boiling point of the organic solvent (S1) is not particularly limited, but is preferably 30°C or higher from the viewpoint of work efficiency. By using an organic solvent (S1) with a lower boiling point of 80°C or less, the organic solvent (S1) can be volatilized at a lower drying temperature of about 120 to 150°C to obtain a resin film.

The organic solvent (S1) is not particularly limited, and for example, dichloromethane (DCM, boiling point 39.6°C), 1,3-dioxolane (boiling point 75°C), tetrahydrofuran (THF, boiling point 66°C) can be used , acetone (boiling point 56°C), chloroform (boiling point 61°C), ethyl acetate (boiling point 77°C), etc., and two or more types may be used in combination. Among these, the organic solvent (S1) is preferably at least one selected from the group consisting of methylene chloride and 1,3-dioxolane, considering the performance of the polyimide varnish. 1 species.

The boiling point of the organic solvent (S2) is 130°C or higher, preferably 140°C or higher, more preferably 150°C or higher, and further preferably 160°C or higher. The upper limit of the boiling point of the organic solvent (S2) is not particularly limited. For example, it may be 300°C or lower or 250°C or lower. By using an organic solvent (S2) with a relatively high boiling point of 130°C or higher, and drying the organic solvent solution of the resin at a drying temperature of about 120 to 150°C, a resin film with low retardation and excellent optical isotropy can be obtained. . Although the reason for this is not yet clear, it is presumed that by drying the organic solvent solution of the resin at a relatively low drying temperature of about 120 to 150°C, a level of organic solvent (S2) that is not problematic for use remains in the resin film, thereby Relax the alignment of polymer chains to achieve low latency.

The organic solvent (S2) is not particularly limited. For example, cyclopentanone (boiling point 131°C), cyclohexanone (boiling point 156°C), and N-methyl-2-pyrrolidone (boiling point 202°C) can be used. , N,N-dimethylacetamide (DMAc, boiling point 165°C), N,N-dimethylformamide (boiling point 153°C), γ-butyrolactone (GBL, boiling point 204°C), dimethyl Phosphate (boiling point: 189°C), dimethylisobutyric acid amide (boiling point: 179°C), etc. can also be used in combination. Among these, the organic solvent (S2) is preferably selected from the group consisting of N-methyl-2-pyrrolidone and N,N-dimethylethyl, taking into account the performance of the polyimide varnish. At least one kind from the group consisting of amide, γ-butyrolactone and dimethyl teroxide.

The mass ratio of the organic solvent (S1) and the organic solvent (S2) contained in the organic solvent solution of polyimide [(S1)/(S2)], consider drying the organic solvent solution of the resin at a lower drying temperature to inhibit The yellowing of the film should be 90/10~99/1, and more preferably 93/7~97/3.

Examples of methods for producing an organic solvent solution of polyimide include methods (1) to (3) below, but are not limited to these methods.

(1) When adding a tetracarboxylic acid component to an organic solvent solution of a diamine component, or adding a diamine component to an organic solvent solution of a tetracarboxylic acid component, the temperature should be below 80°C, especially near room temperature or higher. Maintain low temperature for 0.5~3 hours. Add an azeotropic dehydration solvent such as toluene or xylene to the obtained polyamide solution of the reaction intermediate, and perform a dehydration reaction while removing the generated water from the system through azeotropy to obtain an organic solvent solution of polyimide.

(2) After adding a dehydrating agent such as acetic anhydride to the polyamide acid solution of the reaction intermediate product obtained in the same manner as in (1) above, and then imidizing it, add a solvent such as methanol that lacks the ability to dissolve the polyimide. , to precipitate polyimide. After the solid is separated by filtration, cleaning and drying, it is dissolved in an organic solvent to obtain an organic solvent solution of polyimide.

(3) In the above (1), use a high boiling point solvent such as cresol to prepare a polyamide solution, directly maintain it at 150~220°C for 3~12 hours to imidize the polyamide, and then add methanol, etc. to the polyamide solution. Solvents that lack the ability to dissolve the imine cause the polyimide to precipitate. After the solid is separated by filtration, cleaning and drying, it is dissolved in an organic solvent to obtain an organic solvent solution of polyimide.

In addition, when polyimide is produced by solution polymerization, it is appropriate to use a tertiary amine compound as a catalyst. Examples of these include trimethylamine, triethylamine (TEA), tripropylamine, tributylamine, triethanolamine, N,N-dimethylethanolamine, N,N-diethylethanolamine, and triethylenediamine. , N-methylpyrrolidine, N-ethylpyrrolidine, N-methylpiperidine, N-ethylpiperidine, imidazole, pyridine, quinoline, isoquinoline, etc. Among these tertiary amine compounds, TEA is particularly preferred.

In addition, the concentration of the polyimide organic solvent solution used in the present invention is preferably 4 to 45 mass % of the polyimide component, and more preferably 10 to 40 mass %. Specifically, the organic solvent solution of the resin is preferably in the range of 5 to 80 g, more preferably in the range of 10 to 70 g, relative to 100 g of the organic solvent. If it is within this range, the obtained polyimide film will have good surface smoothness.

The weight average molecular weight of the polyimide used in the present invention is preferably 10,000 or more, more preferably 50,000 or more, taking into account the flexibility and mechanical strength of the polyimide obtained. In addition, the weight average molecular weight of polyimide can be measured by a known method, for example, it can be measured by gel filtration chromatography. In addition, a method of measuring the absolute molecular weight using a light scattering detector using N,N-dimethylformamide in the eluent may also be used.

In the organic solvent solution of polyimide, surfactants such as fluorine series and polysiloxane series can also be added. By adding a surfactant, a film with good surface smoothness can be easily obtained.

In the organic solvent solution of polyimide, antioxidants such as phenol series, sulfur series, phosphoric acid series, and phosphorous acid series can also be added.

The manufacturing method of the polyimide film of the present invention is not particularly limited, and known methods can be used. For example, a solution containing the polyimide of the present invention or a solution containing the polyimide of the present invention and various additives described above is applied to a smooth support such as a glass plate, a metal plate, or plastic. Methods such as removing solvent components such as organic solvents contained in the solution, or after forming it into a film.

An example of a method for producing a colorless and transparent polyimide film is a solution casting method of casting an organic solvent solution of polyimide onto a support and drying the film. Specifically, after the organic solvent solution of polyimide is cast on the support, it is appropriate to use a film-making machine that blows a gas of 80°C or more and 250°C or less onto the support to make the cast product. The organic solvent evaporates and is peeled off from the support as a self-supporting film. It is advisable to dry once before blowing the gas. The conditions for primary drying are not particularly limited. For example, it is suitable to maintain the temperature at 80 to 120°C for 10 to 30 minutes.

The gas to be blown can be air or nitrogen. Air is preferred from the viewpoint of cost, and nitrogen is preferred from the viewpoint of preventing discoloration of the film. The temperature of the injection gas is more preferably 80°C or more and 250°C or less, and further preferably 100°C or more and 220°C or less. When the temperature of the blowing gas is lower than 80°C, the organic solvent may not be fully volatilized, and the film may stick to the support when peeling it off from the support. In addition, when the temperature of the gas is higher than 250°C, the solvent may evaporate rapidly, causing bubbling in the film, or the solvent may decompose and the film may be colored. The time for injecting gas varies depending on the temperature of the injected gas, and is preferably 15 to 30 minutes, more preferably 15 to 25 minutes. In addition, multiple regions with different temperatures of the gas sprayed on the cast object can also be provided.

In addition, in the production method of the colorless and transparent polyimide film of the present invention, the process of casting the organic solvent solution of the resin onto the support and drying it preferably includes the following steps: (i) using differential heat-thermogravimetry At the same time, measure the step of removing a part of the solvent so that the obtained weight reduction rate at 120 to 300°C becomes more than 1% and equal to or less than 10%, and (ii) the step of (i) removing a part of the solvent. ), when the glass transition temperature of the resin is Tg (°C), a heat treatment step is performed in the range of (Tg-50)°C to (Tg+100)°C. The weight reduction rate in the above step (i) is preferably more than 1% and equal to or less than 10%, more preferably 1% or more and 5% or less, further preferably 1% or more and 3% or less. As long as it is within this range, a colorless transparent resin film with excellent transparency and optical isotropy can be produced without taking too much time for drying. The heat treatment temperature in the above step (ii) is preferably (Tg-50)°C or above and (Tg+100)°C, more preferably (Tg-30)°C or above (Tg+80)°C, and further preferably (Tg- 10)℃ or above (Tg+60)℃ below. As long as it is within this range, a colorless transparent resin film excellent in transparency and optical isotropy can be produced.

The polyimide film may contain other components within the scope of not impairing the transparency and flexibility. Examples of other components include plasticizers, antioxidants, release agents, stabilizers, colorants such as blueing agents, flame retardants, lubricants, tackifiers, and smoothing agents. .

The thickness of the polyimide film obtained by this production method is appropriately adjusted according to the application, and is usually 10~500 μm, preferably 15~200 μm, and more preferably 20~100 μm.

When the thickness of the polyimide film is 20 to 50 μm, the total light transmittance according to JIS K7361-1 is preferably more than 85%, and more preferably more than 90%. In addition, when the thickness of the polyimide film is 20 to 50 μm, the haze according to JIS K7361-1 is preferably 2% or less, and more preferably 1% or less. In addition, when the thickness of the polyimide film is 20 to 50 μm, the yellow index (YI) according to JIS K7361-1 is preferably 5 or less, and more preferably 3 or less.

The polyimide film preferably has a retardation (Rth) in the thickness direction of 50 nm or less, more preferably 40 nm or less, further preferably 30 nm or less. The polyimide film preferably has an in-plane retardation (Re) of 20 nm or less, more preferably 15 nm or less.

The polyimide film obtained by this manufacturing method may contain additives and the like in terms of other components. For example, by containing titanium dioxide, etc., the reflectivity of white light can be improved. In addition, by containing nanofillers and the like, the apparent glass transition temperature of the resin composition molded body increases and the heat resistance is improved, the tensile elastic modulus becomes larger, and the mechanical strength increases.

The colorless transparent resin film obtained by the method of the present invention can be suitably used as a film for various components such as touch sensors, color filters, flexible displays, semiconductor components, and optical components. In addition, the colorless transparent resin film obtained by the method of the present invention can be used as a substrate for a transparent substrate of a liquid crystal display element, an organic EL display element, or a transparent conductive film of a touch panel. [Example]

Hereinafter, the present invention will be explained more specifically through examples. However, the present invention is not limited in any way by these embodiments. The method for measuring the physical properties of the films obtained in the following examples is as follows.

(1)Film thickness The film thickness was measured using a micrometer manufactured by Mitutoyo Corporation.

(2) Total light transmittance, haze, yellow index (YI) The measurement was performed in compliance with JIS K7361-1 using a color-turbidity simultaneous measuring instrument "COH400" manufactured by Nippon Denshoku Industries Co., Ltd.

(3) In-plane delay (Re) In-plane retardation (Re) was measured using an ellipsometer "M-220" manufactured by JASCO Corporation. The value of the in-plane phase difference measured at the measurement wavelength of 590 nm.

(4) Thickness direction retardation (Rth) The thickness retardation (Rth) was measured using an ellipsometer "M-220" manufactured by JASCO Corporation. The thickness retardation value is measured at a measurement wavelength of 590 nm. In addition, Rth is expressed by the following formula when the maximum refractive index in the plane of the polyimide film is nx, the minimum is ny, the refractive index in the thickness direction is nz, and the thickness of the film is d. Rth=[{(nx+ny)/2}-nz]×d

(5) Organic solvent content in the film Using the differential thermogravimetric simultaneous measurement device "TG/DTA6200" manufactured by Hitachi High-Tech Science Corporation., the measurement was carried out under nitrogen gas flow at a heating rate of 10°C/min, from 120°C to 300°C. Then maintain it at 300°C for 30 minutes, so that the mass reduced during this period is the organic solvent content in the film.

(6) Glass transition temperature (Tg) Using the thermomechanical analysis device "TMA/SS6100" manufactured by Hitachi High-Tech Science Corporation., in the tensile mode, the sample size is 2mm×20mm, the load is 0.1N, and the temperature rise rate is 10°C/min. The temperature is raised to a level sufficient to remove residues. stress temperature to remove residual stress, and then cool to room temperature. Thereafter, the elongation of the test piece was measured under the same conditions as in the treatment for removing the above-mentioned residual stress, and the inflection point at which elongation was observed was determined as the glass transition temperature.

<Example 1> In a 2L, 5-mouth glass round-bottomed flask equipped with a stainless steel half-moon stirring blade, a nitrogen inlet pipe, a Dean-Stark apparatus equipped with a cooling pipe, a thermometer, and a glass end cap. , 239.772 g (0.696 mol) of α,α'-bis(4-aminophenyl)-1,3-diisopropylbenzene (manufactured by MITSUI FINE CHEMICALS, Inc.), 4,4-diamino Diphenyl ether (manufactured by Wakayama Seika Co., Ltd.) 34.842g (0.174 mol), γ-butyrolactone (manufactured by Mitsubishi Chemical Co., Ltd.) 376.453g, and triethylamine (Kanto) as a catalyst Chemical Co., Ltd.) 44.018 g and triethylenediamine (Tokyo Chemical Industry Co., Ltd.) 0.488 g were stirred at 200 rpm in a nitrogen atmosphere at a temperature of 70° C. in the reaction system to obtain a solution. To each of these, 195.028 g (0.870 mol) of 1,2,4,5-cyclohexanetetracarboxylic dianhydride (manufactured by Mitsubishi Gas Chemical Co., Ltd.) and γ-butyrolactone (Mitsubishi Chemical Co., Ltd.) were added. Co., Ltd.) 94.113 g, then heated with a heating pack, and it took about 20 minutes to raise the temperature in the reaction system to 200°C. Collect the distilled components, adjust the stirring speed according to the increase in viscosity, and maintain the temperature in the reaction system at 200°C for 5 hours. After adding 847.067g of N,N-dimethylacetamide, it was stirred at around 100° C. for about 1 hour to prepare a uniform solution, and a uniform polyimide varnish (a) with a solid content concentration of 25% by mass was obtained.

Then, the obtained polyimide varnish was added dropwise to methanol to precipitate the polyimide powder, and the solid was suction-filtered with a Kiriyama funnel, further washed with methanol, and dried at 200° C. for 30 minutes. The solvent is removed by treatment to obtain polyimide powder. The obtained polyvinyl alcohol was placed in a 300 mL 5-neck glass round-bottomed flask equipped with a stainless steel half-moon stirring blade, a nitrogen inlet pipe, a Dean-Stark device equipped with a cooling pipe, a thermometer, and a glass end cap. After adding 15g of imine powder, 80.75g of dichloromethane (DCM) and 4.25g of N,N-dimethylacetamide (DMAc) at once, stir at room temperature for 1 hour to prepare a uniform solution and obtain the solid content concentration. 15% by mass of uniform polyimide varnish (b).

Then, the obtained polyimide varnish (b) is coated on the PET substrate, maintained at room temperature for 5 minutes, maintained in an air environment of 50°C for 5 minutes, and finally sprayed in an air environment at 150°C for 30 minutes. Dry with hot air to obtain a film with a thickness of 35 μm. Table 1 shows the evaluation results of the polyimide film.

<Example 2> The polyimide film obtained in Example 1 was further dried by blowing hot air at 250°C for 20 minutes in an air environment to obtain a film with a thickness of 35 μm. Table 1 shows the evaluation results of the polyimide film.

＜Comparative example 1＞ The polyimide varnish (a) obtained in Example 1 was added dropwise to methanol to precipitate the polyimide powder and filtered by suction using a Kiriyama funnel. It was further washed with methanol and dried at 200°C for 30 minutes. The solvent is removed to obtain polyimide powder. The obtained polyvinyl alcohol was placed in a 300 mL 5-neck glass round-bottomed flask equipped with a stainless steel half-moon stirring blade, a nitrogen inlet pipe, a Dean-Stark device equipped with a cooling pipe, a thermometer, and a glass end cap. After adding 15 g of imine powder and 85 g of dichloromethane (DCM) at once, the mixture was stirred at room temperature for 1 hour to prepare a uniform solution, and a uniform polyimide varnish with a solid content concentration of 15 mass % was obtained.

Then, the obtained polyimide varnish is coated on the PET substrate, maintained at room temperature for 5 minutes, then maintained at 50°C in an air environment for 5 minutes, and finally by blowing hot air at 150°C for 20 minutes in an air environment. After drying, a film with a thickness of 35 μm was obtained. Table 1 shows the evaluation results of the polyimide film.

＜Comparative example 2＞ The polyimide film obtained in Comparative Example 1 was further dried by blowing hot air at 250°C for 20 minutes in an air environment to obtain a film with a thickness of 35 μm. Table 1 shows the evaluation results of the polyimide film.

[Table 1] organic solvent Drying temperature Film thickness(μm) Total light transmittance (%) Haze(%) YI Re(nm) Rth (nm) Tg(℃) Solvent content (mass %) Example 1 (S1)DCM (S2)DMAc 150℃ 35 90.2 0.3 1.2 15.6 40 195 6.0 Example 2 (S1)DCM (S2)DMAc 150℃/250℃ 35 90.0 0.7 1.8 11.8 26 195 0.8 Comparative example 1 (S1)DCM 150℃ 35 90.2 0.6 1.2 19.9 134 195 1.5 Comparative example 2 (S1)DCM 150℃/250℃ 35 91.0 0.5 2.3 12 62 195 0.005

As shown in Table 1, the polyimide films obtained in Examples 1 and 2 can obtain films with good optical properties such as total light transmittance, haze, and YI, low Rth, and excellent optical isotropic properties. In contrast, the polyimide films obtained in Comparative Examples 1 and 2 had a large Rth and poor optical isotropy.

Claims (7)

A method for producing a colorless transparent resin film by a solution casting method including a step of casting an organic solvent solution of a resin on a support and drying it, and the organic solvent contains one or more kinds An organic solvent with a boiling point below 80°C (S1) and one or more organic solvents with a boiling point above 130°C (S2). The organic solvent solution of the resin is an organic solvent solution of polyamide acid or an organic solvent of polyimide. Solution, the step of casting the organic solvent solution of the resin on the support and drying it includes the following steps: (i) making the weight at 120~300°C obtained by simultaneous measurement of differential heat and thermogravimetry The step of removing part of the solvent in such a manner that the reduction rate exceeds 1% and is equal to or less than 10%; and (ii) after the step (i) of removing part of the solvent, assuming that the glass transition temperature of the resin is Tg ( ℃), the heat treatment step is performed within the range of (Tg-50) ℃ ~ (Tg+100) ℃. The method for manufacturing a colorless transparent resin film according to claim 1, wherein when a film with a thickness of 20 to 50 μm is formed from an organic solvent solution of the resin, the total light transmittance of the film is more than 85%, and the yellow index (YI) is 5 or less, the haze is 2% or less, the in-plane retardation (Re) is 20nm or less, and the thickness direction retardation (Rth) is 50nm or less. The method for manufacturing a colorless transparent resin film according to claim 1 or 2, wherein the resin of the resin film is polyimide having repeating units represented by the following formula [I];

In the formula, R is a tetravalent alicyclic group with 4 to 39 carbon atoms, and Φ is a divalent aliphatic group with 2 to 39 carbon atoms in total, an alicyclic group, an aromatic group, or a combination thereof. The group, as a bonding group, may also have a group selected from the group consisting of -O-, -SO ₂ -, -CO-, -OSi(CH ₃ ) ₂ -, -C ₂ H ₄ O- and -S- At least one of the groups may have a bonding group selected from the group consisting of -CH ₂ - and -C(CH ₃ ) ₂ as an alicyclic group, an aromatic group, or a combination thereof. -At least one member of the group. The method for manufacturing a colorless transparent resin film according to claim 1 or 2, wherein the mass ratio of the organic solvent (S1) to the organic solvent (S2) contained in the organic solvent solution of the resin [(S1)/(S2) ] is 90/10~99/1. The method for manufacturing a colorless transparent resin film according to claim 1 or 2, wherein the organic solvent (S1) is at least one selected from the group consisting of methylene chloride and 1,3-dioxolane. The method for manufacturing a colorless transparent resin film according to claim 1 or 2, wherein the organic solvent (S2) is selected from the group consisting of N-methyl-2-pyrrolidinone, N,N-dimethylacetamide, At least one kind from the group consisting of γ-butyrolactone and dimethylstyrene. The method for manufacturing a colorless transparent resin film according to claim 1 or 2, wherein the content of the dissolved resin in the organic solvent solution of the resin is in the range of 5 to 80 g relative to 100 g of the organic solvent.