JP2022068709A - Polyamic acid, polyamic acid solution, polyimide, polyimide film, laminate and flexible device, as well as production method of polyimide film - Google Patents

Abstract

To provide a polyimide which has high heat resistance (high glass transition temperature), low phase difference and high transparency, a polyamic acid used for formation of the polyimide, and the polyimide obtained therefrom.SOLUTION: A polyamic acid is a polyaddition reaction product of a diamine and a tetracarboxylic acid dianhydride, in which the diamine comprises 2, 2'-bis(trifluoromethyl)benzidine, the tetracarboxylic acid dianhydride comprises 3, 3',4, 4'-biphenyl tetracarboxylic acid dianhydride and 9, 9-bis(3, 4-dicarboxyphenyl)fluorene dianhydride, and an amount of 9, 9-bis(3, 4-dicarboxyphenyl)fluorene dianhydride to a total amount of the tetracarboxylic acid anhydride is 10-98 mol%. A polyimide film is obtained from the polyamic acid.SELECTED DRAWING: None

Description

The present invention relates to polyamic acids, polyamic acid solutions, polyimides, and polyimide films. Furthermore, the present invention relates to a laminate and a flexible device provided with a polyimide film.

Electronic devices such as displays and touch panels are required to be thinner, lighter, and more flexible, and the use of plastic film substrates in place of conventional glass substrates is being considered.

In the manufacturing process of these electronic devices, electronic elements such as thin film transistors and transparent electrodes are provided on the substrate. Since the formation of electronic devices requires a high temperature process, the plastic film substrate is required to have heat resistance suitable for the high temperature process. Further, along with the demand for thin film and flexibility of electronic devices, transparency and low phase difference of organic materials are required.

As a plastic material having high transparency and heat resistance and exhibiting low thermal expansion, polyimide using a monomer having a rigid structure is known (Patent Document 1). Patent Document 2 describes that a polyimide film having high transparency and a low coefficient of thermal expansion can be obtained by introducing a fluorene structure.

Japanese Unexamined Patent Publication No. 2007-046054 Japanese Unexamined Patent Publication No. 2019-503412

Polyimide, which has a high visible light transmittance by shortening the absorption wavelength by molecular design to make it transparent, has a large haze when formed into a film, and may be inferior in suitability as a substrate material for displays and the like. Further, in general, polyimide has a trade-off relationship between transparency and a coefficient of thermal expansion, and the coefficient of thermal expansion tends to increase as the transparency is increased. Patent Document 2 shows an example in which the thickness phase difference is reduced to 1000 nm while maintaining the transparency of polyimide by introducing a fluorene structure. However, for practical use as a substrate for a flexible electronic device, further low thermal expansion is shown. Properties and high heat resistance are required. In view of the above circumstances, an object of the present invention is to provide a polyimide having high heat resistance (high glass transition temperature), low phase difference and high transparency, and a polyamic acid used for forming the polyimide and a polyimide obtained from the polyimide.

As a result of diligent studies, the present inventors have found that the above problems can be solved by the following means.

The polyamic acid of the present invention is a double addition reaction product of diamine and tetracarboxylic acid dianhydride, and contains 2,2'-bistrifluoromethylbenzidine as a diamine component and 3, as a tetracarboxylic acid dianhydride component. Includes 3', 4,4'-biphenyltetracarboxylic acid dianhydride, and 9,9'-(3,4'-dicarboxyphenyl) fluorenic acid dianhydride. The amount of 9,9'-(3,4'-dicarboxyphenyl) fluorenic acid dianhydride with respect to the total amount of tetracarboxylic acid anhydride is 10 mol% or more and 10 mol% or more and 98 mol% or less.

As the tetracarboxylic acid anhydride component, pyromellitic acid anhydride may be further contained. The amount of pyromellitic anhydride with respect to the total amount of tetracarboxylic acid anhydride is, for example, 1 mol% or more and 80 mol% or less.

Polyimide can be obtained by imidizing the above polyamic acid. That is, it is a polyimide which is a polycondensation reaction product of diamine and tetracarboxylic acid dianhydride, wherein the diamine contains 2,2'-bistrifluoromethylbenzidine, and the tetracarboxylic acid dianhydride is 3,3'. , 4,4'-biphenyltetracarboxylic acid dianhydride, and 9,9'-(3,4'-dicarboxyphenyl) fluorenic acid dianhydride, 9,9'-based on the total amount of tetracarboxylic acid anhydride. (3,4'-Dicarboxyphenyl) A polyimide having a fluorenic acid dianhydride amount of 10 mol% or more and 98 mol% or less.

Further, the polyimide may further contain pyromellitic acid anhydride as the tetratracarboxylic acid anhydride, and the amount of pyromellitic acid anhydride may be 1 mol% or more and 80 mol% or less with respect to the total amount of the tetracarboxylic acid anhydride.

The polyimide may be formed as a polyimide film. For example, a polyamic acid solution containing a polyamic acid and an organic solvent is applied to a base material to form a laminate in which a film-shaped polyamic acid is provided on the base material, and the laminate is heated to obtain the polyamic acid. It may be formed as a polyimide film by imidization. The maximum heating temperature of the laminate is preferably, for example, 380 ° C. or higher and 500 ° C. or lower. The heating time in this temperature range is preferably 5 minutes or more and 60 minutes or less. Further, laser irradiation may be performed when the polyimide film is peeled off from the substrate.

The polyimide film preferably has a glass transition temperature of 350 ° C. or higher, a thermal expansion coefficient of 100 ppm / K or less at a temperature of 100 to 350 ° C., a light transmittance of 75% or more at a wavelength of 450 nm, and a haze. Is more preferably 1.2% or less.

One embodiment of the present invention is a laminate in which the above-mentioned polyimide film is provided on a base material. One embodiment of the present invention is a flexible device provided with an electronic element on the above-mentioned polyimide film.

The polyimide film of the present invention is excellent in thermal stability, low phase difference and high transparency, and is suitable for a substrate for a flexible device or the like.

Polyamic acid is obtained by the double addition reaction of tetracarboxylic acid dianhydride and diamine, and polyimide is obtained by the dehydration ring closure reaction of polyamic acid. That is, polyimide is a polycondensation reaction product of tetracarboxylic acid dianhydride and diamine. The polyamic acid and polyimide of the present invention contain 2,2'-bistrifluoromethylbenzidine (hereinafter, may be referred to as TFMB) as a diamine component, and 3,3,4 as a tetracarboxylic acid dianhydride component. 4-biphenyltetracarboxylic acid dianhydride (hereinafter, may be referred to as BPDA) and 9,9'-(3,4'-dicarboxyphenyl) fluorenic acid dianhydride (hereinafter, may be referred to as BPAF). including. The polyamic acid and the polyimide may further contain pyromellitic acid anhydride (hereinafter, may be referred to as PMDA) as a tetracarboxylic acid dianhydride component.

(Tetracarboxylic acid dianhydride component)
Polyimide containing BPDA as a tetracarboxylic acid dianhydride component exhibits low thermal expansion because BPDA has a rigid structure. The ratio of BPDA to 100 mol% of the total amount of the tetracarboxylic acid dianhydride component in the polyamic acid and the polyimide is preferably 10 mol% or more and 90 mol% or less, preferably 15 mol% or more and 80 mol% or less, more preferably 20 mol% or more and 70 mol% or less, and more preferably 20 mol. % Or more and 60 mol% or less are more preferable.

By including PMDA in addition to BPDA as the tetracarboxylic acid dianhydride component, the polyimide tends to exhibit higher heat resistance and lower thermal expansion. The ratio of PMDA to 100 mol% of the total amount of the tetracarboxylic acid dianhydride component in the polyamic acid and the polyimide is preferably 1 mol% or more and 80 mol% or less, and more preferably 5 mol% or more and 60 mol% or less. When the proportion of PMDA is 5 mol% or more, the polyimide film tends to show low thermal expansion, and when it is 60 mol% or less, the polyimide film tends to show high transparency. In order for the polyimide film to exhibit high transparency, the proportion of PMDA is preferably smaller than the proportion of BPDA.

Since BPDA and PMDA have a rigid structure, when a polyimide film is prepared from a polyamic acid containing only BPDA and PMDA as a tetracarboxylic acid dianhydride component, cloudiness due to crystallization or the like is likely to occur. By containing BPAF in addition to BPDA (and PMDA) as the tetracarboxylic acid dianhydride, white turbidity tends to be suppressed, and a polyimide film having excellent transparency can be obtained. The ratio of BPAF to 100 mol% of the total amount of the tetracarboxylic acid dianhydride component in the polyamic acid and the polyimide is preferably 10 mol% or more and 98 mol% or less, preferably 10 mol% or more and 90 mol% or less, more preferably 15 mol% or more and 80 mol% or less, and 15 mol. % Or more and 60 mol% or less are more preferable. When the ratio of BPAF is 10 mol% or more, the crystallization of the polyimide is suppressed, and the white turbidity of the polyimide film tends to be suppressed accordingly. By suppressing crystallization, dimensional changes due to phase transition during heating are unlikely to occur, and the coefficient of thermal expansion of the polyimide film tends to be small. When the ratio of BPAF is 80 mol% or less, the low thermal expansion characteristic can be maintained.

From the viewpoint of achieving both high transparency and low thermal expansion, the total amount of PMDA, BPDA and BPAF with respect to 100 mol% of the total amount of the tetracarboxylic acid dianhydride component in the polyamic acid and the polyimide is preferably 90 mol% or more, preferably 92% mol or more. More preferably, 95 mol% or more is further preferable.

The polyamic acid and the polyimide may contain a component other than PMDA, BPDA and BPAF as a tetracarboxylic acid dianhydride component. Other tetracarboxylic acid dianhydrides include 3,3', 4,4'-benzophenone tetracarboxylic acid dianhydride, 2,3,3', 4'-biphenyltetracarboxylic acid dianhydride, 3,3. ', 4,4'-Diphenylsulfone tetracarboxylic acid dianhydride, 1,4,5,8-naphthalenetetracarboxylic acid dianhydride, 2,3,6,7-naphthalenetetracarboxylic acid dianhydride, 1, 2,5,6-naphthalenetetracarboxylic acid dianhydride, 4,4'-oxydiphthalic acid anhydride, 9,9'-bis [4- (3,4-dicarboxyphenoxy) phenyl] fluorene dianhydride, 3 , 3', 4,4'-biphenyl ether tetracarboxylic acid dianhydride, 2,3,5,6-pyridinetetracarboxylic acid dianhydride, 3,4,9,10-perylenetetracarboxylic acid dianhydride, 4,4'-sulfonyldiphthalic acid dianhydride, paratelphenyl-3,4,3', 4'-tetracarboxylic acid dianhydride, metaterphenyl-3,3', 4,4'-tetracarboxylic Acid dianhydride, 3,3', 4,4'-diphenyl ether tetracarboxylic acid dianhydride, (1S, 2R, 4S, 5R) -cyclohexanetetracarboxylic acid dianhydride (cis, cis, cis-1,2) , 4,5-Cyclohexanetetracarboxylic acid dianhydride), (1S, 2S, 4R, 5R) -cyclohexanetetracarboxylic acid dianhydride, (1R, 2S, 4S, 5R) -cyclohexanetetracarboxylic acid dianhydride, Bicyclo [2.2.2] Octane-2,3,5,6-tetracarboxylic dianhydride, Bicyclo [2.2.2] Oct-7-en-2,3,5,6-tetracarboxylic acid Dianhydride, 5- (dioxotetrahydrofuryl-3-methyl-3-cyclohexene-1,2-dicarboxylic acid anhydride, 4- (2,5-dioxotetratetra-3-yl) -tetraline-1,2 -Dicarboxylic acid anhydride, tetrahydrofuran-2,3,4,5-tetracarboxylic acid dianhydride, bicyclo-3,3', 4,4'-tetracarboxylic acid dianhydride, 1,2,3,4- Cyclopentanetetracarboxylic acid dianhydride, 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride, 1,3-dimethyl-1,2,3,4-cyclobutanetetracarboxylic acid dianhydride, 1,4 -Dimethyl-1,2,3,4-cyclobutanetetracarboxylic acid dianhydride, etc. may be mentioned.

(Diamine component)
Polyimide films containing TFMB as a diamine component tend to exhibit high transparency and a low coefficient of linear expansion. From the viewpoint of achieving both high transparency and low thermal expansion, the amount of TFMB with respect to 100 mol% of the total amount of diamine components in polyamic acid and polyimide is preferably 90 mol% or more, more preferably 95 mol% or more, still more preferably 99 mol% or more.

The polyamic acid and the polyimide may contain a component other than TFMB as a diamine component. Diamines other than TFMB include 4,4'-diaminobenzanilide, p-phenylenediamine, m-phenylenediamine, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone. , 3,3'-diaminodiphenyl sulfone, 9,9'-(4-aminophenyl) fluorene, 9,9'-(4-amino-3-methylphenyl) fluorene, 1,4'-bis (4-amino) Phenoxy) benzene, 2,2'-bis (4-aminophenoxyphenyl) propane, 4,4'-bis (4-aminophenoxy) biphenyl, 4,4'-methylenebis (cyclohexaneamine), 3,3-diamino- Examples thereof include 4,4-dihydroxydiphenyl sulfone, 2,2-bis (3-amino4-hydroxyphenyl) hexafluoropropane, and the like.

When a flexible diamine such as silicone diamine is contained as the diamine component, the coefficient of linear expansion of the polyimide film tends to increase. Therefore, the amount of the flexible diamine with respect to the total amount of the diamine component in the polyamic acid and the polyimide is preferably 5 mol% or less, more preferably 1 mol% or less, and particularly preferably 0.5 mol% or less. From the viewpoint of reducing the coefficient of thermal expansion, it is preferable that the flexible diamine is not contained.

(Polyamic acid and polyamic acid solution)
The polyamic acid of the present invention can be synthesized by a known general method. For example, a polyamic acid solution can be obtained by reacting a diamine with a tetracarboxylic acid dianhydride in an organic solvent. The organic solvent used for the polymerization of the polyamic acid is preferably one that dissolves tetracarboxylic acid dianhydride and diamine as monomer components and dissolves the polyamic acid produced by double addition. Examples of the organic solvent include urea-based solvents such as tetramethylurea and N, N-dimethylethylurea; sulfonate-based solvents such as dimethylsulfoxide, diphenylsulfone and tetramethylsulfone; , N, N'-diethylacetamide, N-methyl-2-pyrrolidone, hexamethylphosphate triamide and other amide solvents; ester solvents such as γ-butyrolactone; chloroformated alkyl solvents such as chloroform and methylene chloride; benzene , Aromatic hydrocarbon solvents such as toluene; Phenolic solvents such as phenol and cresol; Ketone solvents such as cyclopentanone; tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, dimethyl ether, diethyl ether, p- Examples thereof include ether solvents such as cresol methyl ether. Usually, these solvents are used alone, but if necessary, two or more kinds may be used in combination as appropriate. In order to enhance the solubility and reactivity of polyamic acid, the organic solvent is preferably selected from the group consisting of amide-based solvents, ketone-based solvents, ester-based solvents and ether-based solvents, and particularly N, N-dimethylacetamide. , N, N-Dimethylformamide, N, N'-diethylacetamide, N-methyl-2-pyrrolidone and other amide solvents are preferred.

The molecular weight of the polyamic acid can be adjusted by adjusting the ratio of the number of moles of the total amount of the diamine component to the number of moles of the total amount of the tetracarboxylic acid dianhydride component. The monomer component used for the synthesis of polyamic acid may contain other than diamine and tetracarboxylic acid dianhydride. For example, a monofunctional amine or a monofunctional acid anhydride may be used for the purpose of adjusting the molecular weight.

The synthesis of polyamic acid by double addition of diamine and tetracarboxylic acid dianhydride is preferably carried out in an inert atmosphere such as argon or nitrogen. Polymerization proceeds by dissolving and mixing diamine and tetracarboxylic acid dianhydride in an organic solvent in an inert atmosphere. The order of addition of diamine and tetracarboxylic acid dianhydride is not particularly limited. For example, diamine may be dissolved in an organic solvent or dispersed in a slurry to form a diamine solution, and tetracarboxylic acid dianhydride may be added to the diamine solution. The tetracarboxylic acid dianhydride may be added in a solid state, or may be added in a state of being dissolved in an organic solvent or dispersed in a slurry.

The temperature conditions of the reaction are not particularly limited. The reaction temperature is preferably 80 ° C. or lower from the viewpoint of suppressing a decrease in the molecular weight of the polyamic acid due to depolymerization. From the viewpoint of appropriately advancing the polymerization reaction, the reaction temperature is more preferably 0 to 50 ° C. The reaction time may be arbitrarily set in the range of 10 minutes to 30 hours.

A polyamic acid solution is obtained by reacting a diamine with a tetracarboxylic acid dianhydride in an organic solvent. A solvent may be added to the polyamic acid solution to adjust the concentration of polyamic acid (solid content concentration of the solution). The polyamic acid solution may contain additives for the purpose of promoting imidization by dehydrating and closing the ring of polyamic acid, improving solution storage (pot life) by suppressing imidization, and the like.

Various organic or inorganic small molecule or high molecular weight compounds may be blended in order to impart processing properties and various functionalities to the polyamic acid and the polyimide. For example, the polyamic acid solution may contain a dye, a surfactant, a leveling agent, a plasticizer, fine particles, a sensitizer, a silane coupling agent, and the like. The fine particles may be either organic fine particles or inorganic fine particles, and may have a porous or hollow structure.

By blending the silane coupling agent with the polyamic acid solution, the adhesion between the polyimide film formed by the polyamic acid coating film and the dehydration ring closure and the substrate tends to be improved. The blending amount of the silane coupling agent is preferably 1.0 part by weight or less, more preferably 0.5 part by weight or less, still more preferably 0.1 part by weight or less with respect to 100 parts by weight of the polyamic acid. When the silane coupling agent is blended for the purpose of improving the adhesion to the substrate, the blending amount may be 0.01 parts by weight or more with respect to 100 parts by weight of the polyamic acid. The silane coupling agent may be added to the polyamic acid solution, or may be added to the solution before or during the polymerization reaction of the polyamic acid. For example, by using a silane coupling agent having an amino group, a structure derived from the silane coupling agent can be introduced at the end of the polyamic acid. When a silane coupling agent having an amino group is added to the polyamic acid polymerization system, in order to keep the molecular weight of the polyamic acid high, the silane cup with respect to 100 parts by weight of the polyamic acid (total of tetracarboxylic acid dianhydride and diamine) The blending ratio of the ring agent is preferably 1.0 part by weight or less.

(Polyimide and polyimide film)
The above-mentioned polyamic acid and polyamic acid solution may be used as they are as a material for producing a product or a member, or a binder resin, an additive or the like may be blended to prepare a resin composition. Since it is excellent in heat resistance and mechanical properties, it is preferable to imidize the polyamic acid by dehydration ring closure and put it into practical use as a polyimide. Dehydration ring closure is performed by an azeotropic method using an azeotropic solvent, a thermal method, or a chemical method. When imidization is performed in the state of a solution, it is preferable to add an imidizing agent and / or a dehydration catalyst to the polyamic acid solution to perform chemical imidization. Thermal imidization is preferred when the solvent is removed from the polyamic acid solution to form a film-like polyamic acid and the film-like polyamic acid is imidized. For example, a polyamic acid solution may be applied to a glass, a silicon wafer, a metal plate such as a copper plate or an aluminum plate, or a film substrate such as PET (polyethylene terephthalate) to form a coating film, and then heat treatment may be performed.

The polyamic acid solution can be applied to the substrate by a known method such as a gravure coating method, a spin coating method, a silk screen method, a dip coating method, a bar coating method, a knife coating method, a roll coating method, and a die coating method. The heating temperature and heating time for imidization may be appropriately determined. The heating temperature is, for example, in the range of 80 ° C. to 500 ° C.

Since the polyimide of the present invention is excellent in transparency and thermal dimensional stability, it can be used as a transparent substrate for glass replacement, and is used as a TFT substrate material, a transparent electrode substrate material, printed matter, a color filter, a flexible display member, and an antireflection film. , Holograms, building materials, structures, etc. are expected to be used. In particular, since the polyimide film of the present invention is excellent in thermal dimensional stability, it is suitably used as a transparent substrate for electronic devices such as a TFT substrate and an electrode substrate. Examples of the electronic device include a liquid crystal display device, an image display device such as an organic EL and electronic paper, a touch panel, a solar cell, and the like. In these applications, the thickness of the polyimide film is about 1 to 200 μm, preferably about 5 to 100 μm.

In the process of manufacturing an electronic device, an electronic element such as a thin film transistor or a transparent electrode is provided on a substrate. The process of forming an element on a film substrate is divided into a batch type and a roll-to-roll type. In the roll-to-roll process, electronic devices are sequentially provided on the film substrate while conveying the long film substrate. In the batch process, a film substrate is formed on a rigid substrate such as non-alkali glass to form a laminate, an electronic element is provided on the film substrate of the laminate, and then the substrate is peeled off from the film substrate. The polyimide film of the present invention can be applied to any process. The batch process has a cost advantage because it can utilize the existing equipment for glass substrates. Hereinafter, an example of a method for manufacturing a polyimide film via a laminate in which a polyimide film is provided on a glass substrate will be described.

First, a polyamic acid solution is applied to a substrate to form a coating film of the polyamic acid solution, and the laminate of the substrate and the coating film is heated at a temperature of 40 to 200 ° C. for 3 to 120 minutes to dry the solvent. To obtain a polyamic acid film. For example, drying may be performed at a set temperature of two or more steps, such as at 50 ° C. for 30 minutes and then at 100 ° C. for 30 minutes. By heating the laminate of this base material and the polyamic acid film, imidization by dehydration ring closure of the polyamic acid is performed. The heating for imidization is carried out, for example, at a temperature of 200 to 500 ° C., and the heating time is, for example, 3 minutes to 300 minutes. It is preferable that the heating for imidization is gradually increased from a low temperature to a high temperature and then raised to the maximum temperature. The heating rate is preferably 2 to 10 ° C./min, more preferably 4 to 10 ° C./min. The maximum heating temperature is preferably 380 to 500 ° C, more preferably 400 to 480 ° C. When the maximum heating temperature is 380 ° C. or higher, imidization proceeds sufficiently, and a polyimide film suitable for a high temperature process can be obtained. When the maximum heating temperature is 500 ° C. or lower, thermal deterioration and coloring of the polyimide can be suppressed. The heating time at the maximum temperature is, for example, 5 minutes or more, and the heating time at a temperature of 380 ° C. or higher is preferably 5 to 60 minutes. It may be held at an arbitrary temperature for an arbitrary time until the maximum heating temperature is reached.

The imidization may be carried out under air, under reduced pressure, or in an inert gas such as nitrogen. In order to obtain a highly transparent polyimide film, heating under reduced pressure or in an inert gas such as nitrogen is preferable. As the heating device, a known device such as a hot air oven, an infrared oven, a vacuum oven, an inert oven, or a hot plate is used. In order to shorten the heating time and develop the characteristics, the polyamic acid solution to which the imidizing agent and the dehydration catalyst are added may be heated and imidized by the above method.

In the batch type device manufacturing process, when stress remains at the interface between the base material and the polyimide film formed on the base material, the laminate of the base material and the polyimide film is warped, and the element on the laminate is subjected to warp. It may interfere with the formation process. Therefore, it is preferable that the stress (internal stress) at the interface between the base material and the polyimide film is small. Specifically, the internal stress is preferably −30 MPa or more and 70 MPa or less, and more preferably −20 MPa or more and 65 MPa or less. The internal stress is calculated based on the change in the warp (radius of curvature) of the glass plate before and after forming the polyimide film on the glass plate.

When an electronic element is formed on a substrate by a batch process, it is preferable to form the element on a laminate in which a polyimide film is provided on a substrate such as glass, and then peel the substrate from the polyimide film. The device may be formed on the polyimide film after peeling from the base material.

The method of peeling the polyimide film from the substrate is not particularly limited. For example, it may be peeled off by hand, or a peeling device such as a drive roll or a robot may be used. Peeling may be performed by reducing the adhesion between the substrate and the polyimide film. For example, a polyimide film may be formed on a substrate provided with a release layer. A silicon oxide film may be formed on a substrate having a large number of grooves and infiltrated with an etching solution to promote peeling. Peeling may be performed by irradiation with laser light.

When the base material and the polyimide are peeled off by laser irradiation, it is necessary for the polyimide film to absorb the laser light, so the cutoff wavelength of the polyimide film (wavelength with a transmittance of 0.1% or less) is used for the peeling. It is required to have a longer wavelength than the wavelength of the laser light to be used. For example, when a XeCl excimer laser having a wavelength of 308 nm is used, the cutoff wavelength of the polyimide film is preferably 310 nm or more, more preferably 320 nm or more. When a solid UV laser having a wavelength of 355 nm is used, the cutoff wavelength of the polyimide film is preferably 360 nm or more, more preferably 365 nm or more.

Generally, polyimide easily absorbs light on the short wavelength side, and when the cutoff wavelength moves to the long wavelength side, the film may be colored yellow due to absorption of visible light. In the polyimide of the present invention, the cutoff wavelength tends to shift to the long wavelength side when the ratio of PMDA in the tetracarboxylic acid dianhydride component is increased. By including PMDA as a tetracarboxylic acid dianhydride component in the range where the cutoff wavelength does not reach the visible light region, in addition to transparency and thermal dimensional stability, UV absorption characteristics suitable for the peeling process by UV laser are obtained. You can have it. The cutoff wavelength of the polyimide film is preferably 390 nm or less, more preferably 385 nm or less, and even more preferably 380 nm or less.

In transparent flexible substrate applications, the polyimide film is required to have high transmittance in the entire wavelength region of visible light. The polyimide film for a transparent flexible substrate preferably has a light transmittance of 75% or more, and more preferably 80% or more at a wavelength of 450 nm. The polyimide of the present invention preferably has a light transmittance in the above range when a film having a film thickness of 10 μm is formed.

The transparency of the polyimide film can also be evaluated, for example, by the total light transmittance and haze according to JIS K7105-1981. The total light transmittance of the polyimide film is preferably 80% or more, more preferably 85% or more. Further, the light transmittance at 450 nm is preferably 75% or more, more preferably 80% or more. The haze of the polyimide film is preferably 1.2% or less, more preferably 1.0% or less, still more preferably 0.8% or less. The polyimide of the present invention preferably has a total light transmittance and haze within the above ranges when a film having a film thickness of 10 μm is formed. As described above, by including BPAF as an anhydride component in the tetracarboxylic acid, the haze of the polyimide film tends to be reduced.

For application to high temperature processes, the polyimide membrane preferably has a high glass transition temperature. Specifically, the glass transition temperature of the polyimide film is preferably 380 ° C. or higher, more preferably 400 ° C. or higher. The glass transition temperature of the polyimide film is the temperature at which the loss tangent is maximized by the dynamic viscoelasticity measurement, and is measured by the method described in Examples described later. The polyimide film preferably has a small coefficient of thermal expansion (CTE) when the temperature rises. The CTE of the polyimide film is preferably −50 to 100 ppm / K, more preferably −30 to 90 ppm / K, and particularly preferably −20 to 80 ppm / K. The CTE may be 60 ppm / K or less, 50 ppm / K or less, 40 ppm / K or less, or 30 ppm / K or less, and may be -10 ppm / K or more or 0 ppm / K or more. CTE is the amount of strain of the sample per unit temperature in the range of 100 to 350 ° C. when the polyimide film is heated at a heating rate of 10 ° C./min, and is an example described later by thermomechanical analysis (TMA). It is measured by the method described in.

It is preferable that the phase difference in the thickness direction is low. The polyimide has a thickness direction retardation (Rth) of a film having a film thickness of 10 μm at 550 nm, preferably 500 nm or less, more preferably 300 nm or less, and particularly preferably 200 nm or less.

[Evaluation methods]
Material property values and the like were measured by the following evaluation methods.

<Internal stress>
A polyimide film was formed on Corning's non-alkali glass (thickness 0.7 mm, 100 mm × 100 mm) in which the amount of warpage was measured in the same manner as in Examples and Comparative Examples, and a polyimide film having a thickness of 10 μm was formed on the glass. Obtained a laminate to be provided. After allowing the laminate to stand in a desiccator for 10 minutes, it was set in a thin film stress measuring device (manufactured by Tencol) "FLX-2320-S"), and the amount of warpage of the laminate was measured under a nitrogen atmosphere at 25 ° C. The stress generated between the glass substrate and the polyimide film at 25 ° C. was calculated from the value of the amount of warpage.

<Light transmittance and YI of polyimide film>
The light transmittance of the polyimide film at 200 to 800 nm was measured using an ultraviolet-visible-near-infrared spectrophotometer (V-650) manufactured by JASCO Corporation. The transmittance was represented by the XYZ color system, and YI was calculated by the method described in JIS K7373.

<Haze of polyimide film>
It was measured by the method described in JIS K7105-1981 using an integrating sphere type haze meter 300A manufactured by Nippon Denshoku Kogyo.

<Double refraction of polyimide>
A phase difference meter manufactured by Shintec Co., Ltd .: The value of the thickness direction phase difference (Rth) at a measurement wavelength of 550 nm was measured by OPTIPRO.

<Glass transition temperature (Tg) of polyimide film>
Tg was measured using TMA / SS7100 manufactured by Hitachi High-Tech Science Co., Ltd. (sample size width 3 mm, length 10 mm, film thickness measured, film cross-sectional area calculated), load 98.0 mN, and 10 ° C / min. The temperature was raised from 10 ° C to 450 ° C. The inflection point of the amount of change in the strain of the sample in the temperature raising process was defined as the glass transition temperature.

<The coefficient of thermal expansion (CTE) of the polyimide film>
The coefficient of linear thermal expansion was measured using TMA / SS7100 manufactured by Hitachi High-Tech Science Co., Ltd. (sample size width 3 mm, length 10 mm, film thickness measured, film cross-sectional area calculated), load 29.4 mN, 10 The coefficient of linear expansion is based on the amount of change in the strain of the sample per unit temperature at 100 to 350 ° C. when the temperature is once raised from 10 ° C to 400 ° C at ° C / min and then lowered at 40 ° C / min. Asked.

[Synthesis of polyamic acid]
Polyamic acid solutions 1 to 4 were obtained according to the following Production Examples 1 to 4. The abbreviations of the reagents used in each production example are as follows.
NMP: 1-methyl-2-pyrrolidone BPDA: 3,3'-4,4'-biphenyltetracarboxylic acid dianhydride PMDA: pyromellitic acid dianhydride BPAF: 9,9'-(3,4'-di) Carboxyphenyl) fluorenic acid dianhydride TFMB: 2,2-bis (trifluoromethyl) benzidine

(Example 1)
425.00 g of N-methyl-2-pyrrolidone (hereinafter referred to as NMP) and 39.0 g of TFMB were charged in a 1 L glass separable flask equipped with a stirrer equipped with a stainless stir bar and a nitrogen introduction tube. After stirring and dissolving, while stirring the solution, 13.6 g of BPDA, 11.2 g of PMDA, and 11.2 g of BPAF were added in this order and stirred for 24 hours to obtain a polyamic acid solution. The concentration of the diamine component and the tetracarboxylic acid dianhydride component in this reaction solution was 15.0% by weight based on the total amount of the reaction solution.

(Example 2)
The amount of diamine charged was changed to 38.9 g of TFMB, and the amount of acid dianhydride charged was changed to 14.4 g of BPDA, 10.6 g of PMDA, and 11.1 g of BPAF. A solution was obtained.

(Example 3)
The amount of diamine charged was changed to 38.0 g of TFMB, the amount of acid dianhydride charged was changed to 20.9 g of BPDA, 5.2 g of PMDA, and 10.9 g of BPAF, and polymerization was carried out in the same manner as in Example 1 to carry out polymerization and polyamic acid. A solution was obtained.

(Example 4)
The amount of diamine charged was changed to 39.9 g of TFMB, and the amount of acid dianhydride charged was changed to 7.4 g of BPDA, 16.3 g of PMDA, and 11.4 g of BPAF. A solution was obtained.

(Comparative Example 1)
The amount of diamine charged was changed to 37.1 g of TFMB, the amount of acid dianhydride charged was changed to 27.3 g of BPDA and 10.6 g of BPAF, and polymerization was carried out in the same manner as in Example 1 to obtain a polyamic acid solution.

(Comparative Example 2)
The amount of diamine charged was changed to 41.0 g of TFMB, the amount of acid dianhydride charged was changed to 22.3 g of PMDA and 11.7 g of BPAF, and polymerization was carried out in the same manner as in Example 1 to obtain a polyamic acid solution.

[Preparation of polyimide film]
NMP was added to each of the polyamic acid solutions obtained in the above Examples and Comparative Examples to dilute the polyamic acid concentration to 10.0% by weight. Using a spin coater, apply a polyamic acid solution on a 150 mm x 150 mm square non-alkali glass plate (Corning Eagle XG, thickness 0.7 mm) so that the thickness after drying is 10 μm, and use a hot air oven. It was dried at 80 ° C. for 30 minutes to form a polyamic acid film. After raising the temperature from 20 ° C to 350 ° C at 5 ° C / min under a nitrogen atmosphere, the temperature is maintained at 350 ° C for 30 minutes, the temperature is further raised to 420 ° C at 5 ° C / min, and then the temperature is heated at 420 ° C for 30 minutes. Imidization was performed to obtain a laminate of a polyimide film having a thickness of 10 μm and glass. The polyimide film was peeled off from the glass substrate of the obtained laminate, and the characteristics were evaluated.

The polyimide film of Comparative Example 1 containing no PMDA as a tetracarboxylic acid dianhydride component had a low glass transition temperature, a large CTE, and poor thermal dimensional stability.

The polyimide film of Comparative Example 2 containing no BPDA as a tetracarboxylic acid dianhydride component had a high YI and was inferior in transparency, and was significantly inferior in Rth.

In Examples 1, 3 and 4, the higher the proportion of PMDA of the tetracarboxylic acid dianhydride, the higher the Rth tended to be. On the other hand, in Comparative Example 1 containing no PMDA, a significant increase in CTE and a decrease in Tg were observed as compared with Examples 1 and 3. From these results, the inclusion of BPAF in addition to BPDA and PMDA as a tetracarboxylic acid dianhydride causes changes in the intramolecular and / or intramolecular interactions of the polymer, resulting in high transparency and thermal dimensional stability. It is thought that it exerts its sexuality.

Claims (14)

Polyamic acid, which is a double addition reaction product of diamine and tetracarboxylic acid dianhydride.
The diamine contains 2,2'-bistrifluoromethylbenzidine.
The tetracarboxylic acid dianhydride contains 3,3', 4,4'-biphenyltetracarboxylic acid dianhydride, and 9,9'-(3,4'-dicarboxyphenyl) fluorenic acid dianhydride. ,
A polyamic acid in which the amount of 9,9'-(3,4'-dicarboxyphenyl) fluorenic acid dianhydride is 10 mol% or more and 98 mol% or less with respect to the total amount of tetracarboxylic acid anhydride. The tetracarboxylic acid anhydride further contains pyromellitic acid anhydride and contains.
The polyamic acid according to claim 1, wherein the amount of pyromellitic acid anhydride is 1 mol% or more and 80 mol% or less with respect to the total amount of tetracarboxylic acid anhydride. A polyamic acid solution containing the polyamic acid according to claim 1 or 2 and an organic solvent. Polyimide, which is a polycondensation reaction product of diamine and tetracarboxylic acid dianhydride.
The diamine contains 2,2'-bistrifluoromethylbenzidine.
The tetracarboxylic acid dianhydride contains 3,3', 4,4'-biphenyltetracarboxylic acid dianhydride, and 9,9'-(3,4'-dicarboxyphenyl) fluorenic acid dianhydride. ,
A polyimide in which the amount of 9,9'-(3,4'-dicarboxyphenyl) fluorenic acid dianhydride is 10 mol% or more and 98 mol% or less with respect to the total amount of tetracarboxylic acid anhydride. The tetracarboxylic acid anhydride further contains pyromellitic acid anhydride and contains.
The polyimide according to claim 4, wherein the amount of pyromellitic acid anhydride is 1 mol% or more and 80 mol% or less with respect to the total amount of tetracarboxylic acid anhydride. A polyimide film containing the polyimide according to claim 4 or 5. The polyimide film according to claim 6, wherein the glass transition temperature is 350 ° C. or higher, and the coefficient of thermal expansion at temperature rise of 100 to 350 ° C. is 100 ppm / K or lower. The polyimide film according to claim 6 or 7, wherein the light transmittance at a wavelength of 450 nm is 75% or more and the haze is 1.2% or less. A laminate in which the polyimide film according to any one of claims 6 to 8 is provided on a substrate. A flexible device including an electronic element on the polyimide film according to any one of claims 6 to 9. A polyimide in which the polyamic acid solution according to claim 3 is applied to a substrate to form a laminate in which a film-shaped polyamic acid is provided on the substrate, and the laminate is heated to imidize the polyamic acid. Method of manufacturing the membrane. The method for producing a polyimide film according to claim 11, wherein the laminate is heated for 5 minutes or more and 60 minutes or less in a temperature range of 380 ° C. or higher and 500 ° C. or lower as the maximum heating temperature. A method for producing a polyimide film, which comprises forming a polyimide film by the production method according to claim 11 or 12 and peeling the base material from the polyimide film. The method for producing a polyimide film according to claim 13, wherein the substrate and the polyimide film are peeled off by laser irradiation.