JP2023038407A - Polyamide acid composition, polyimide, polyimide film, laminate and flexible device, and method for producing laminate - Google Patents

Abstract

To provide a polyamide acid composition that can give a polyimide having transparency, as well as high heat resistance and low residual stress.SOLUTION: Polyamide acid includes acid dianhydride represented by 5,5'-bis-2-norbornene-5,5',6,6'-tetracarboxylic acid-5,5',6,6'-dianhydride (BNBDA), and diamine represented by 4,4'-diaminobenzanilide (DABA). When the total acid dianhydride constituting the polyamide acid is 100 mol%, the proportion of BNBDA is preferably 40 mol% or more and 100 mol% or less.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to polyamic acid compositions, polyimides, polyimide films, laminates and flexible devices, and methods for producing laminates.

Electronic devices such as displays, touch panels, lighting devices, and solar cells are required to be thinner, lighter, and more flexible, and the use of resin film substrates instead of glass substrates is being investigated. In particular, for applications that require high heat resistance, dimensional stability, and high mechanical strength, the application of polyimide film as a substitute for glass is being investigated.

In the manufacturing process of electronic devices, electronic elements such as thin film transistors and transparent electrodes are formed on substrates. The formation of electronic elements requires high-temperature processes, and plastic film substrates are required to have heat resistance that can be adapted to high-temperature processes. Therefore, the use of polyimide as a material for plastic film substrates is being studied.

The manufacturing process of electronic devices can be divided into batch type and roll-to-roll type. In the batch process, a resin solution is applied onto a glass support and dried to form a laminate of the glass support and the film substrate. After forming and forming elements thereon, the film substrate can be peeled off from the glass support, and existing processing equipment for glass substrates can be used.
When the film substrate is polyimide, a polyamic acid solution as a polyimide precursor is applied onto the support, and the polyamic acid is heated together with the support for imidization, thereby forming a laminate of the support and the polyimide film. is obtained.

Transparency is not required for substrate materials in top-emission organic ELs and the like because light is emitted to the opposite side of the substrate. However, when light emitted from elements such as transparent displays and bottom-emission organic EL devices is emitted through the substrate, or when a sensor or camera module is installed on the back of the substrate to make the smartphone a full-screen display (notchless). , the substrate material is also required to have high transparency.
Against this background, materials having high heat resistance, dimensional stability, and high transparency are desired.

As a highly transparent polyimide, an alicyclic monomer is used to suppress coloration of the film (Patent Documents 1 and 2), improve heat resistance (Patent Document 3), and contain an imidazole compound. can improve the transmittance at 400 nm and have high transparency (Patent Document 4).

The polyimide described in Patent Document has high transparency, but the polyimide described in Patent Document 1 has a large weight loss value when kept at high temperature, and the polyimide described in Patent Document 3 has a high linear expansion coefficient (CTE). , not adaptable to the high temperature process of forming electronic devices.

JP 2017-160360 A JP 2017-66354 A WO2014-038714 JP 2019-108552 A

As a result of verification by the authors, Patent Documents 1 and 3 disclose polyimides obtained from acid dianhydrides and diamines having specific alicyclic structures. The polyimide described in Patent Document 2 has high transparency, but the residual stress and coefficient of linear expansion are high. The polyimide described in Patent Document 4 has high transparency and improved residual stress, but the problem is that the weight loss value under high temperature maintenance is large due to the alicyclic structure. However, there is room for improvement in the characteristics of the substrate material.

An object of the present invention is to obtain a polyimide having high heat resistance and low residual stress in addition to transparency. Furthermore, by developing a polyimide that satisfies these requirements, we will provide products or members that require high heat resistance and transparency. An object of the present invention is to provide a product and a member that are suitable for forming on the surface of an inorganic material such as crystalline silicon.

As a result of intensive studies, the present inventors found that a polyimide film using a polyamic acid composition having a specific composition has an excellent balance of characteristics as a substrate material. That is, the present invention has the following constructions.

1). A polyamic acid composition having a structure represented by the following formula (1),
A in formula (1) contains (A-1), B in formula (1) contains a structural unit represented by (B-1), and a structural unit represented by (A-1) Polyamic acid composition, characterized in that the is 40 mol% or more. (A in the formula is a tetravalent aromatic group or an aliphatic group, B is a divalent aromatic group or an aliphatic group, R ¹ is each independently a hydrogen atom or a monovalent aliphatic or an aromatic group.)

2). The polyamic acid composition according to 1), wherein A in the formula (1) contains a structural unit represented by (A-2).

3). The polyamic acid composition according to any one of 1) to 2) containing an imidazole compound.

4). The polyamic acid composition according to any one of 1) to 3), which further contains an organic solvent.

5). A polyimide which is a dehydrated cyclization product of the polyamic acid composition according to any one of 1) to 4).

6). 5) A polyimide film containing the polyimide described in 5).

7). The polyimide film according to 6), wherein the weight loss value when heated at 430 ° C. for 1 hour is 0.5% or less.

8). The polyimide film according to 6) or 7), wherein YI is 6 or less when the film thickness of the polyimide film is 10 μm.

9). A laminate of the polyimide film according to any one of 6) to 8) and a support.

10). 9) The polyimide laminate according to 9), wherein the residual stress at 25° C. is 20 MPa or less when the polyimide film of the laminate has a thickness of 10 μm.

11). 4) The polyamic acid composition containing the organic solvent described in 4) is applied to a support to form a film-like polyamic acid on the support, the polyamic acid is imidized by heating, and the polyimide is formed on the support. A method for manufacturing a laminate, which forms a film.

12). A flexible device having an electronic element formed on the polyimide film or laminate according to any one of 6) to 10).

A polyimide film obtained from the polyamic acid described above has a low residual stress in a laminate with an inorganic support, is excellent in heat resistance and transparency, and is suitable as a substrate material for electronic devices that require transparency. In addition, the polyimide film of the present invention is particularly excellent in heat resistance, with a very low weight loss value when kept at high temperatures as a polyimide having an alicyclic structure.

Embodiments of the present invention will be described below, but the present invention is not limited to these.

A polyamic acid is obtained by a polyaddition reaction of a tetracarboxylic dianhydride and a diamine, and a polyimide is obtained by a dehydration ring closure reaction of the polyamic acid. That is, polyimide is a polycondensation reaction product of tetracarboxylic dianhydride and diamine.

[Polyamide acid]
The polyamic acid composition according to an embodiment of the present invention includes a structural unit in which A in the following general formula (1) is represented by (A-1), and B in (1) is (B-1). A polyamic acid composition comprising the structural unit represented by (A-1), wherein the structural unit represented by (A-1) accounts for 40 mol% or more. (A in the formula is a tetravalent aromatic group or an aliphatic group, B is a divalent aromatic group or an aliphatic group, R ¹ is each independently a hydrogen atom or a monovalent aliphatic or an aromatic group.)

In the polyamic acid according to the embodiment of the present invention, the general formula (1) is 5,5′-bis-2-norbornene-5,5′,6,6′-tetracarboxylic acid-5,5′,6,6 containing an acid dianhydride represented by '-dianhydride (hereinafter sometimes referred to as BNBDA) and a diamine represented by 4,4'-diaminobenzanilide (hereinafter sometimes referred to as DABA) can obtain a polyamic acid for producing a polyimide film suitable as an electronic substrate material.

Further, decahydro-1H,3H-4,10:5,9-dimethanonaphtho[2,3-c:6,7-c′]difuran- represented by the general formula (A-2) is added to the formula (1). It may contain an acid dianhydride represented by 1,3,6,8-tetraone (hereinafter sometimes referred to as DNDA).

Although BNBDA and DNDA are alicyclic monomers, they have a rigid structure in which cyclohexane rings are crosslinked with methylene groups. , is a very effective monomer for imparting high heat resistance.

In the general formula (1), in order to highly combine the properties of transparency, heat resistance, and low residual stress, the proportion of BNBDA is 40 mol% when the total acid dianhydride constituting polyamic acid is 100 mol%. 100 mol % or less is preferable, 45 mol % or more and 90 mol % or less is more preferable, and 50 mol % or more and 80 mol % or less is even more preferable.

DNDA has a condensed polycyclic alicyclic structure and is effective in developing a higher Tg. From the viewpoint of high Tg and low residual stress, the proportion of DNDA is preferably 10 mol% or more and 60 mol% or less, more preferably 15 mol% or more and 55 mol% or less, when the total acid dianhydride constituting the polyamic acid is 100 mol%. , more preferably 20 mol % or more and 50 mol % or less.

The polyamic acid according to the embodiment of the present invention may contain a tetracarboxylic dianhydride component other than BNBDA and DNDA within a range that does not impair its performance. For example, 3,3′,4,4′-biphenyltetracarboxylic dianhydride, 2,3′,3,4′-biphenyltetracarboxylic dianhydride, pyromellitic anhydride, 3,3′,4 ,4'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 2,3 ,6,7-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 4,4′-oxydiphthalic anhydride, 9,9-bis(3,4-di Carboxyphenyl)fluorene dianhydride, spiro[11H-diflo[3,4-b:3′,4′-i]xanthene-11,9′-[9H]fluorene]-1,3,7,9-tetrone , 3,3′,4,4′-biphenyl ether tetracarboxylic dianhydride (BPAF), 2,3,5,6-pyridinetetracarboxylic dianhydride, 3,4,9,10-perylenetetracarboxylic acid dianhydride, 4,4′-sulfonyldiphthalic dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, 5-( Dioxotetrahydrofuryl-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride, 4-(2,5-dioxotetrahydrofuran-3-yl)-tetralin-1,2-dicarboxylic anhydride, tetrahydrofuran -2,3,4,5-tetracarboxylic dianhydride, bicyclo-3,3',4,4'-tetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,3-dimethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,4-dimethyl-1,2, 3,4-cyclobutanetetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, [1,1′-bi(cyclohexane)]-3,3′,4,4′- Tetracarboxylic dianhydride, [1,1′-bi(cyclohexane)]-2,3,3′,4′-tetracarboxylic dianhydride, [1,1′-bi(cyclohexane)]-2, 2',3,3'-tetracarboxylic dianhydride, bicyclo[2.2.2]octane-2,3,5,6-tetracarboxylic dianhydride, bicyclo[2.2.2]octa- 5-ene-2,3,7,8-tetracarboxylic dianhydride, tricyclo[4.2.2.02,5]deca n-3,4,7,8-tetracarboxylic dianhydride, tricyclo[4.2.2.02,5]dec-7-ene-3,4,9,10-tetracarboxylic dianhydride, 9-oxatricyclo[4.2.1.02,5]nonane-3,4,7,8-tetracarboxylic dianhydride, (4arH,8acH)-decahydro-1t,4t:5c,8c-di Methanonaphthalene-2c,3c,6c,7c-tetracarboxylic dianhydride, (4arH,8acH)-decahydro-1t,4t: 5c,8c-dimethanonaphthalene-2t,3t,6c,7c-tetracarboxylic acid dianhydride anhydride, 2′-oxodispiro[bicyclo[2.2.1]heptane-2,1′-cyclopentane-3′,2″-bicyclo[2.2.1]heptane]-5,6:5′ ',6''-tetracarboxylic dianhydrides and their analogues, which may be used singly or in combination of two or more.

The divalent organic group B contained in the formula (1) means an organic group other than the amino group of the diamine, and is 4,4'-diaminobenzanilide represented by the following (B-1) (hereinafter referred to as DABA).

DABA has a rigid structure and a hydrogen bond forming part, and is effective in high Tg, high heat resistance and low residual stress. From the viewpoint of high Tg, high heat resistance and low residual stress, the proportion of DABA is preferably 60 mol% or more, more preferably 70 mol% or more, more preferably 80 mol% when the total diamine constituting the polyamic acid is 100 mol%. It is more preferable to contain at least 100 mol %.

The polyamic acid according to the present embodiment may contain a diamine component other than DABA within a range that does not impair its performance. For example, 1,4-diaminocyclohexane, 1,4-phenylenediamine, 1,3-phenylenediamine, 9,9-bis(4-aminophenyl)fluorene, 4,4′-oxydianiline, 3,4′- oxydianiline, 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl ether, 4,4'-diaminobenzanilide, 4-aminophenyl 4-aminobenzoate, N,N'-bis( 4-aminophenyl)terephthalamide, N,N'-1,4-phenylenebis(4-aminobenzamide), 4,4'-diaminodiphenylsulfone, m-tolidine, o-tolidine, 4,4'-bis( aminophenoxy)biphenyl, 2-(4-aminophenyl)-6-aminobenzoxazole, 3,5-diaminobenzoic acid, 4,4'-diamino-3,3'dihydroxybiphenyl, 4,4'-methylenebis(cyclohexane amines), 1,3-bis(3-aminopropyl)tetramethyldisiloxane and analogs thereof, which may be used singly or in combination of two or more.

Commercially available monomer raw materials can be appropriately used for the polyamic acid of the present invention. Moreover, the polyamic acid of the present invention can be synthesized by a known general method, and the polyamic acid can be obtained by reacting a diamine and a tetracarboxylic dianhydride in an organic solvent. For example, a diamine is dissolved or dispersed in an organic solvent in the form of a slurry to obtain a diamine solution, and a tetracarboxylic dianhydride is dissolved in an organic solvent or dispersed in the form of a slurry in a solution or a solid state, and the diamine It may be added into the solution. A diamine may be added to the tetracarboxylic dianhydride solution.

When synthesizing a polyamic acid using a diamine and a tetracarboxylic dianhydride, one or both of the diamine and the tetracarboxylic dianhydride, using multiple species, the number of moles of the diamine and the total amount of the dianhydride By adjusting each, a polyamic acid copolymer having a plurality of types of structural units can be obtained. A polyamic acid containing a plurality of tetracarboxylic dianhydrides and diamines can also be obtained by blending two types of polyamic acid. In the present invention, polyamic acid synthesis may be random or block.

When synthesizing polyamic acid, the molar ratio of total acid dianhydride:total diamine is preferably 98:100 to 102:100 from the viewpoint of molecular weight. In addition, considering the transparency of polyimide, amine terminal groups may lead to deterioration of transparency due to oxidation, so the molar ratio of total acid dianhydride: total diamine is more preferably 100: 100 to 102: 100. .

The dissolution and reaction of diamine and tetracarboxylic dianhydride are preferably carried out in an inert gas atmosphere such as argon or nitrogen. The temperature conditions for the reaction between the diamine and the tetracarboxylic dianhydride are not particularly limited. ~80°C is more preferred. The reaction time may be arbitrarily set, for example, within the range of 10 minutes to 40 hours. As the reaction progresses, the molecular weight of the polyamic acid increases and the viscosity of the reaction solution increases. To increase the reaction rate, the concentration of tetracarboxylic dianhydride and diamine in the reaction solution may be increased. The concentration of raw materials (diamine and tetracarboxylic dianhydride) charged in the reaction solution is preferably 15 to 30% by weight.

When storing the polyamic acid solution after the completion of the reaction, the solid content concentration is preferably low from the viewpoint of storage stability. Specifically, it is preferably 25% by weight or less, more preferably 20% by weight or less, even more preferably 17% by weight or less, and particularly preferably 15% by weight or less. From the viewpoint of coatability, the solid content concentration is preferably 5% by weight or more, more preferably 7% by weight or more.

The organic solvent used in the polyamic acid synthesis reaction is not particularly limited. Any organic solvent may be used as long as it can be used when the tetracarboxylic dianhydride and diamine used are reacted, and preferably one capable of dissolving polyamic acid produced by polymerization.

Specific examples of organic solvents used in polyamic acid synthesis reactions include urea-based solvents such as tetramethylurea and N,N-dimethylethylurea; sulfoxide or sulfone-based solvents such as dimethylsulfoxide, diphenylsulfone, and tetramethylsulfone; N,N-dimethylacetamide (DMAC), N,N-dimethylformamide (DMF), N,N'-diethylacetamide, N-methyl-2-pyrrolidone (NMP), amide solvents such as hexamethylphosphoric triamide; Ester solvents such as γ-butyrolactone; Alkyl halide solvents such as chloroform and methylene chloride; Aromatic hydrocarbon solvents such as benzene and toluene; Phenolic solvents such as phenol and cresol; Ketone solvents such as cyclopentanone Ether solvents such as tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, dimethyl ether, diethyl ether, and p-cresol methyl ether. These solvents are usually used alone, but if necessary, two or more of them may be used in combination. In order to increase the solubility and reactivity of polyamic acid, the organic solvent used in the synthetic reaction of polyamic acid is preferably selected from amide solvents, ketone solvents, ester solvents and ether solvents, particularly DMF. , DMAC and NMP are preferred, and NMP is particularly preferred. An ether solvent such as diethylene glycol or tetrahydrofuran may be added to enhance the stability of the solution.

The weight average molecular weight of polyamic acid is, for example, 10,000 to 1,000,000, preferably 10,000 to 500,000, more preferably 10,000 to 100,000. If the weight average molecular weight is 10,000 or more, the mechanical strength of the polyimide film can be ensured. If the weight average molecular weight is 1,000,000 or less, the polyamic acid exhibits sufficient solubility in the solvent, and a coating or film having a smooth surface and a uniform thickness can be obtained. Further, if the molecular weight is 100,000 or less, the coatability is excellent even in a solution with a high solid content. The molecular weight is a value converted to polyethylene oxide by gel permeation chromatography (GPC).

The polyamic acid solution contains polyamic acid and a solvent. A solution obtained by reacting a diamine and a tetracarboxylic dianhydride can be used as it is as a polyamic acid solution. Also, the concentration of polyamic acid and the viscosity of the solution may be adjusted by removing part of the solvent from the polymerization solution or by adding a solvent. The solvent to be added may be different from the solvent used for polymerizing the polyamic acid. Alternatively, a solid polyamic acid resin obtained by removing the solvent from the polymerization solution may be dissolved in a solvent to prepare a polyamic acid solution. As the organic solvent for the polyamic acid solution, amide-based solvents, ketone-based solvents, ester-based solvents, and ether-based solvents are preferable. Among them, amide-based solvents such as DMF, DMAC, and NMP are preferable, and NMP is particularly preferable.

Polyimides are obtained by dehydration ring closure of polyamic acids. Dehydration ring closure can be carried out by azeotropic methods using azeotropic solvents, thermal methods or chemical methods. The imidization of polyamic acid to polyimide can take any ratio of 1 to 100%, and partially imidized polyamic acid may be synthesized.

In order to obtain a polyimide film, it is preferable to apply a polyamic acid solution to a support such as a glass plate, a metal plate, or a PET (polyethylene terephthalate) film in the form of a film, followed by dehydration and ring closure of the polyamic acid by heating. In order to adapt to a batch type device manufacturing process, it is preferable to use a glass substrate as a support, and alkali-free glass is preferably used. In order to shorten the heating time and develop properties, an imidizing agent containing a dehydrating agent and a dehydrating catalyst or a curing accelerator (imidazoles) is added to the polyamic acid solution, and this imidizing agent or curing accelerator (imidazoles) is added. The added polyamic acid solution may be imidized by heating by the above method.

Although the dehydration catalyst contained in the imidizing agent is not particularly limited, it is preferable to use a tertiary amine, and among these, a heterocyclic tertiary amine is preferable. Preferable specific examples of heterocyclic tertiary amines include pyridine, picoline, quinoline, isoquinoline and the like. Preferred specific examples of the dehydrating agent contained in the imidizing agent include acetic anhydride, propionic anhydride, n-butyric anhydride, benzoic anhydride, and trifluoroacetic anhydride.

The amount of dehydration agent and dehydration catalyst contained in the imidization agent is 0.5 to 5.0 times the molar equivalent of the dehydration catalyst, and further 0.7 to 2.5 times the amide group of the polyamic acid. Molar equivalents, particularly 0.8 to 2.0 times molar equivalents are preferred. Further, the dehydrating agent is 0.5 to 10.0-fold molar equivalents, further 0.7 to 5.0-fold molar equivalents, particularly 0.8 to 3.0-fold molar equivalents with respect to the amide group of polyamic acid. is preferred. When the imidizing agent or curing accelerator (imidazoles) is added to the polyamic acid solution, it may be added directly without being dissolved in an organic solvent, or may be added after being dissolved in an organic solvent. If the imidizing agent is directly added without being dissolved in an organic solvent, the reaction may proceed rapidly before the imidizing agent diffuses, resulting in the formation of a gel. More preferably, a solution obtained by dissolving an imidizing agent or curing accelerator (imidazoles) in an organic solvent is mixed with the polyamic acid solution.

The polyamic acid solution of the present invention preferably contains imidazoles (imidazole compounds) as a curing accelerator for polyamic acid. When the polyamic acid solution contains imidazoles, there is a tendency that coloration during imidization by a thermal method is suppressed and the coefficient of linear expansion of the obtained polyimide film tends to be small. Imidazoles include 1H-imidazole, 2-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-phenyl -4-methylimidazole, 1-benzyl-2-methylimidazole, 1-benzyl-2-phenylimidazole, and other compounds containing a 1,3-diazole ring structure. Among them, 1H-imidazole, 1,2-dimethylimidazole, 1-benzyl-2-methylimidazole and 1-benzyl-2-phenylimidazole are preferred, and 1H-imidazole, 1,2-dimethylimidazole and 1-benzyl-2-methyl Imidazole is particularly preferred, and 1H-imidazole and 1,2-dimethylimidazole are more preferred.

The amount of imidazole added is preferably about 0.005 to 0.2 mol, more preferably 0.01 to 0.20 mol, and 0.02 to 0.15 mol per 1 mol of the amide group of the polyamic acid. More preferred.

“Amido group of polyamic acid” means an amide group produced by polyaddition reaction of diamine and tetracarboxylic dianhydride. When imidazoles are added, it is preferable to add polyamic acid after polymerization. The imidazole may be added to the polyamic acid solution as it is, or may be added to the polyamic acid solution as an imidazole solution.

The reason why the addition of imidazoles to polyamic acid solutions improves the thermal dimensional stability of polyimide films is unclear, but imidazoles promote imidization by dehydration ring closure of polyamic acid, and imidization proceeds at low temperatures. It is presumed that the fact that it is easy to do is involved in the improvement of thermal dimensional stability. When the solvent remains in the film at low temperature, the polymer chains have moderate mobility, and when imidization proceeds in this state, the orientation of the polymer is fixed in a highly stable and rigid conformation. One of the reasons for the improvement in thermal dimensional stability is that it is easy to be

The curing accelerator preferably has a boiling point exceeding 120° C., and preferably has a boiling point that does not exceed the upper limit temperature of the thermal treatment. If the boiling point exceeds the upper limit temperature, the percentage of residual in the polyimide tends to increase, which tends to affect properties such as heat resistance of the polyimide.

For the purpose of imparting processability and various functions to the polyamic acid and polyimide according to the present invention, the polyamic acid and polyimide may be compounded with an organic or inorganic low-molecular-weight or high-molecular-weight compound. Examples thereof include dyes, pigments, surfactants, leveling agents, plasticizers, silicones, silane coupling agents, sensitizers, fillers and fine particles. Fine particles include organic fine particles such as polystyrene and polytetrafluoroethylene, inorganic fine particles such as colloidal silica, carbon, and layered silicate, and the like, and they may have a porous or hollow structure. In addition, their functions or forms include pigments, fillers, fibers, and the like. A phosphate ester, a phosphite ester, a phthalate ester, or the like may be used as the plasticizer. The polyamic acid solution may contain a resin component such as a photocurable component, a thermosetting component, and a non-polymerizable resin, in addition to the polyamic acid.

As described above, the polyimide film produced from the polyamic acid according to the present embodiment is colorless and transparent, has a low degree of yellowness, and has a Tg and heat resistance that can withstand the TFT manufacturing process. Suitable for use on substrates.

When manufacturing a flexible display, an inorganic film such as glass is used as a support, a flexible substrate is formed thereon, and electronic elements such as TFTs are formed thereon (flexible device). The process of forming a TFT is generally performed in a wide temperature range of 150° C. to 650° C. However, in order to actually achieve desired performance, an oxide semiconductor or a-Si is formed at a temperature of 300° C. or higher. In some cases, a-Si or the like is further crystallized with a laser or the like to form LTPS (Low Temperature Polysilicon).

At this time, if the thermal decomposition temperature of the polyimide film is low, outgassing is generated from the polyimide film due to heating during element formation, which may cause performance deterioration or peeling of the element formed on the polyimide film. Therefore, the 1% weight loss temperature Td1 of the polyimide film is preferably 450° C. or higher, more preferably 480° C. or higher, even more preferably 500° C. or higher, and the higher the better.

To explain the TFT manufacturing process in detail, SiOx, SiNx, or the like is formed on a polyimide film as a barrier film before manufacturing a TFT. If the heat resistance of the polyimide is low or imidization has not progressed completely, volatile components such as the decomposition gas of the polyimide may cause the polyimide and the inorganic Delamination occurs at the film interface.

Therefore, although it depends on the device manufacturing process, it is required that the outgassing is small when isothermally held at 400°C to 500°C. Specifically, after forming an inorganic film such as SiOx on a polyimide film, it is desirable that there is no peeling between the polyimide film and the inorganic film when the film is held at 400° C. for 1 hour. The higher the processing temperature, the better the performance of the TFT. Therefore, it is more desirable that there is no peeling at 420°C, and it is even more desirable that there is no peeling at 430°C.

From the viewpoint of outgassing, the weight loss value when held isothermally at 430° C. is preferably 0.5% or less, more preferably 0.4% or less, and 0.3% or less. Especially preferred.

Also, if Tg is significantly lower than the process temperature, there is a possibility that misalignment or the like may occur during element formation, which may cause warpage or breakage. Therefore, the Tg of the polyimide film used as the flexible substrate is preferably 300° C. or higher, more preferably 350° C. or higher, and even more preferably 400° C. or higher.

In general, since the coefficient of linear expansion of glass is smaller than that of resin, stress is generated at the interface of the laminate between the support and the polyimide film due to temperature changes during heating during electronic device formation and subsequent cooling. . If the glass substrate used as a support, the electronic element, and the polyimide film have high residual stress, the glass substrate will warp or break when it shrinks when cooled to room temperature after being expanded in the high-temperature TFT process. problems such as peeling of the Generally, since the coefficient of linear expansion of a glass substrate is smaller than that of resin, residual stress is generated between it and the flexible substrate. Therefore, the residual stress generated between the polyimide film and the glass substrate is preferably 20 MPa or less.

The polyimide of the present invention can be suitably used as a display substrate material such as a TFT substrate and a touch panel substrate. When used for the above applications, in many cases, a production method is used in which a laminate of a support and polyimide is produced, an electronic element is formed thereon, and finally the polyimide layer is peeled off. Also, alkali-free glass is preferably used as the support. Hereinafter, a method for producing a laminate of polyimide and a support and a method for producing polyimide via the laminate will be specifically described. These are examples of methods for producing polyimide, and are not limited to the following.

In forming a polyimide film on a support, first, a polyamic acid solution is applied to the support to form a coating film, and a laminate of the support and the polyamic acid coating film is heated at a temperature of 40 to 150°C. Heat for 3-120 minutes to remove solvent. For example, drying may be performed at two or more temperature steps, such as 50° C. for 30 minutes followed by 100° C. for 30 minutes.

By heating the laminate of the support and the polyamic acid at a temperature of 200 to 450° C. for 3 to 300 minutes, the polyamic acid undergoes dehydration ring closure to obtain a laminate having a polyimide film on the support. . At this time, it is preferable to gradually increase the temperature from a low temperature to the maximum temperature. The heating rate is preferably 2 to 10°C/min, more preferably 4 to 10°C/min. The maximum temperature is preferably 250-430°C. When the maximum temperature is 250° C. or higher, imidization proceeds sufficiently, and when the maximum temperature is 430° C. or lower, thermal deterioration and coloration of the polyimide can be suppressed. In the heating for imidization, any temperature may be maintained for any period of time until the maximum temperature is reached. The heating atmosphere may be under air, under reduced pressure, or in an inert gas such as nitrogen. Heating under reduced pressure or in an inert gas is preferred in order to develop higher transparency. Heating devices include hot air ovens, infrared ovens, vacuum ovens, inert ovens, hot plates, and the like. In addition, in order to shorten the heating time and develop properties, an imidizing agent and / or a dehydrating catalyst is added to the polyamic acid solution, and the imidizing agent and / or dehydrating catalyst is added to the polyamic acid solution by the above method. It may be imidized by heating at .

The method for peeling the polyimide film from the support is not particularly limited. For example, it may be peeled off by hand, or a peeling device such as a driving roll or robot may be used. Peeling may be performed by reducing the adhesion between the support and the polyimide film. For example, a polyimide film may be formed on a support provided with a release layer. A silicon oxide film may be formed on a substrate having a large number of grooves, and detachment may be accelerated by infiltrating the film with an etchant. Detachment may be performed by laser light irradiation.

In a batch type device fabrication process, it is more preferable that the adhesion between the support and the polyimide is good. Adhesion here means adhesion strength. In the production process of forming electronic elements on a polyimide film on a support to form a substrate and then peeling the polyimide substrate on which the electronic elements are formed from the support, excellent adhesion to the support is important. , electronic elements, etc. can be formed or mounted more accurately. From the viewpoint of the manufacturing process of laminating an electronic element or the like on a support, the higher the peel strength, the better. Specifically, it is preferably 0.05 N/cm or more, more preferably 0.1 N/cm or more.

In the manufacturing process as described above, when the polyimide layer is peeled off from the laminate of the support and polyimide, it is often peeled off from the support by laser irradiation. From the standpoint of this peeling workability, it is necessary to make the polyimide absorb the light of the laser wavelength. An excimer laser is often used for laser peeling, and since it is necessary to absorb light of the wavelength of the laser, the cut-off wavelength is preferably 312 nm or longer, more preferably 330 nm or longer. Further, when the cut-off wavelength is 390 nm or less, sufficient transparency can be exhibited. The term "cut-off wavelength" used herein means a wavelength at which the transmittance is 0.1% or less as measured by an ultraviolet-visible spectrophotometer.

The transparency of the polyimide film can be evaluated by total light transmittance and haze according to JIS K7361 and JIS K7136. The total light transmittance of the polyimide film is preferably 85% or higher, more preferably 86% or higher, even more preferably 87% or higher.

The haze of the polyimide film is preferably 1.5% or less, more preferably 1.2% or less, even more preferably 1.0% or less. In applications such as displays, high transmittance is required in the entire wavelength region of visible light. The yellowness index (YI) of the polyimide film is preferably 7 or less, more preferably 6 or less, and even more preferably 5 or less. YI can be measured according to JIS K7373-2006. Such a highly transparent polyimide film can be used as a transparent substrate for applications such as glass substitutes. can be suppressed.

The polyimide may be directly subjected to coating and molding processes for making products and components. As noted above, the polyimide can also be a polyimide membrane molded into a film. Various inorganic thin films such as metal oxides and transparent electrodes may be formed on the surface of the polyimide film. The method for forming these inorganic thin films is not particularly limited, and examples thereof include PVD methods such as CVD, sputtering, vacuum deposition, and ion plating.

In addition to heat resistance, low thermal expansion, and transparency, the polyimide according to the present invention has little residual stress with the glass substrate. It is preferably used for displays, optical films, liquid crystal display devices, image display devices such as organic EL and electronic paper, 3-D displays, touch panels, transparent conductive film substrates or solar cells, and glass is currently used. It is more preferable to use a substitute material for the existing portion.

In addition, the polyamic acid, polyimide and polyamic acid solution according to the present invention are a batch type in which the polyamic acid solution is applied on a support, imidized by heating, electronic elements etc. are formed to form a substrate, and then peeled off. device manufacturing process. Therefore, in the present invention, a method for producing an electronic device includes a substrate forming step of applying a polyamic acid solution on a support, imidizing it by heating, and forming an electronic element or the like on a polyimide film formed on the support. is also included. Moreover, the method for manufacturing such an electronic device may further include a step of peeling off the polyimide substrate on which electronic elements and the like are formed from the support after the substrate forming step.

An organic EL display and an organic EL lighting are examples of flexible devices using a polyimide film as a substrate. There are two types of organic EL devices: a bottom emission type in which light is extracted from the substrate side, and a top emission type in which light is extracted from the opposite surface of the substrate. A transparent polyimide film with high visible light transmittance and low YI is also suitable as a substrate material for a bottom emission type organic EL device.

Examples will be described below in detail, but these are described for the sake of explanation and the present invention is not limited to the following examples.

[Evaluation method]
Material property values and the like described in this specification are obtained by the following evaluation methods.

<Light transmittance and YI of polyimide film>
Using a UV-visible near-infrared spectrophotometer (V-650) manufactured by JASCO Corporation, the light transmittance of the polyimide film at 200 to 800 nm is measured, and as an indicator of yellowness by the method described in JIS K7373-2006. A yellow index (YI) was calculated.

<Total light transmittance of polyimide film>
Measured by the method described in JIS K7361 using an integrating sphere type haze meter (HM-150N) manufactured by Murakami Color Research Laboratory.

<Haze>
Measured according to JIS K7136 using an integrating sphere haze meter (HM-150N) manufactured by Murakami Color Research Laboratory.

<Glass transition temperature (Tg)>
Using a thermomechanical analyzer ("TMA/SS7100" manufactured by Hitachi High-Tech Science), a load of 98.0 mN is applied to a sample with a width of 3 mm and a length of 10 mm, and the temperature is raised from 20 ° C. to 450 ° C. at 10 ° C./min, Temperature and strain amount (elongation) were plotted (TMA curve). The intersection point extrapolated from the tangent lines of the TMA curve before and after the change in slope was taken as the glass transition temperature.

<Residual stress>
The polyamic acid solution prepared in Examples and Comparative Examples was applied with a spin coater on Corning's alkali-free glass (thickness 0.7 mm, 100 mm × 100 mm) whose warpage amount had been measured in advance, and was applied at 80 ° C. in the air. After heating for 30 minutes at 430° C. for 30 minutes in a nitrogen atmosphere, a laminate having a polyimide film having a thickness of 10 μm on a glass substrate was obtained. In order to eliminate the influence of water absorption of the polyimide film, the laminate was dried at 120 ° C. for 10 minutes, and then the amount of warpage of the laminate at 25 ° C. in a nitrogen atmosphere was measured with a thin film stress measurement device (Tencor "FLX-2320- S”) was used to evaluate the residual stress generated between the glass substrate and the polyimide film.

<1% Weight Loss Temperature (Td1)>
Using "TG/DTA/7200" manufactured by Hitachi High-Tech Science Co., Ltd., the temperature was raised from 25 ° C. to 500 ° C. at 20 ° C./min under a nitrogen atmosphere, and the weight at 150 ° C. was reduced by 1%. The temperature at this time was taken as Td1 of the polyimide film.

<Weight loss value under isothermal holding at 430°C>
Using "TG / DTA / 7200" manufactured by Hitachi High-Tech Science Co., Ltd., the temperature was raised from 25 ° C. to 430 ° C. at 20 ° C./min under a nitrogen atmosphere, then held at 430 ° C. for 1 hour and reached 430 ° C. Based on the weight at that time, the weight loss value after 1 hour was determined.

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

[Abbreviation of compounds and reagents]
In the following, compounds and reagents are described with the following abbreviations.
<Solvent>
NMP: N-methyl-2-pyrrolidone <tetracarboxylic dianhydride>
BNBDA: 5,5'-bis-2-norbornene-5,5',6,6'-tetracarboxylic acid-5,5',6,6'-dianhydride DNDA: decahydro-1H,3H-4, 10: 5,9-dimethanonaphtho[2,3-c:6,7-c′]difuran-1,3,6,8-tetraone BzDA: 5,5′-(1,4-phenylene)bis(hexahydro- 4,7-methanoisobenzofuran-1,3-dione)
CpODA: 2′-oxodispiro[bicyclo[2.2.1]heptane-2,1′-cyclopentane-3′,2″-bicyclo[2.2.1]heptane]-5,6:5″ ,6''-tetracarboxylic dianhydride (also known as norbornane-2-spiro-α-cyclopentanone-α'-spiro-2''-norbornane-5,5'',6,6''-tetra carboxylic acid dianhydride)
<Diamine>
DABA: 4,4'-diaminobenzanilide DATA: N,N'-bis(4-aminophenyl)terephthalamide PDA: 1,4-phenylenediamine ODA: 4,4'-oxydianiline TFMB: 2,2' - Bis(trifluoromethyl)benzidine <imidazole>
DMI: 1,2-dimethylimidazole

(Example 1)
240 g of NMP and 33.277 g of DABA were charged into a 500 mL glass separable flask equipped with a stirrer equipped with a stainless steel stirring rod and a nitrogen inlet tube, and stirred for 1 hour or more, then BNBDA 29.793 g and DNDA 17.705 g were added. In addition, it was stirred at 40° C. and dissolved. After dissolution, the solution was stirred at room temperature (23° C.) for 24 hours to obtain a polyamic acid solution containing polyamic acid. The charged concentration of the diamine component and the tetracarboxylic dianhydride component in this reaction solution was 25.0% by weight with respect to the total amount of the reaction solution. To this polyamic acid solution, 4 parts by weight of DMI with respect to the polyamic acid solid content and 0.114 mol per 1 mol of amide groups were added, and the mixture was stirred for 5 minutes to obtain a uniform polyamic acid solution.

This polyamic acid solution was applied to Corning's alkali-free glass (thickness 0.7 mm, 100 mm × 100 mm) with a spin coater, heated at 80 ° C. in air for 30 minutes, and heated at 430 ° C. in a nitrogen atmosphere for 30 minutes. A laminate having a polyimide film having a thickness of 10 μm on a substrate was obtained. The polyimide film was peeled off from the glass base material of the obtained laminate, and the properties were evaluated.
Table 1 shows the evaluation results of the obtained polyimide film.

(Examples 2 to 6, Comparative Examples 1 to 8) A polyamic acid solution containing polyamic acid was obtained in the same manner as in Example 1, except that the charging ratio of the acid dianhydride and the diamine was changed as shown in Table 1. . The obtained polyamic acid solution was made into a polyimide film in the same manner as in Example 1.

As shown in Table 1, polyamic acid satisfying the following (1) to (3) is obtained in this example.
(1) Weight reduction value when heated at 430 ° C. for 1 hour is 0.5% or less (2) YI is 6 or less (3) Internal stress is 20 MPa or less

Comparative Examples 1 to 7 have a residual stress of 20 MPa or more, low dimensional stability, and cannot be applied to applications requiring low warpage of the glass substrate. Comparative Example 8 has low YI and residual stress, and is excellent in Tg, but the weight loss value is 1% or more when held at 430° C. for 1 hour, and the heat resistance is insufficient, and high temperatures such as TFT manufacturing processes are required. Not applicable for use.

From these results, the polyimide obtained from the polyamic acid composition composed of the specific polyamic acid according to the present invention is colorless and transparent, has a high thermal decomposition temperature, a high outgassing amount and a glass transition temperature, and has a small internal stress with the inorganic substrate. It was confirmed to have process heat resistance at high temperatures. It should be noted that the present invention is not limited to the above embodiments, and can be implemented with various modifications.

Claims (12)

A polyamic acid composition having a structure represented by the following formula (1),
A in formula (1) contains (A-1), B in formula (1) contains a structural unit represented by (B-1), and a structural unit represented by (A-1) Polyamic acid composition, characterized in that the is 40 mol% or more. (A in the formula is a tetravalent aromatic group or an aliphatic group, B is a divalent aromatic group or an aliphatic group, R ¹ is each independently a hydrogen atom or a monovalent aliphatic or an aromatic group.)

2. The polyamic acid composition according to claim 1, wherein A in formula (1) contains a structural unit represented by (A-2).

3. The polyamic acid composition according to any one of claims 1 and 2, which contains an imidazole compound. 4. The polyamic acid composition according to any one of claims 1 to 3, further comprising an organic solvent. A polyimide which is a dehydrated cyclization product of the polyamic acid composition according to any one of claims 1 to 4. A polyimide film comprising the polyimide of claim 5 . 7. The polyimide film according to claim 6, wherein the weight loss value when heated at 430° C. for 1 hour is 0.5% or less. 8. The polyimide film according to claim 6, wherein YI is 6 or less when the film thickness of the polyimide film is 10 μm. A laminate of the polyimide film according to any one of claims 6 to 8 and a support. 10. The polyimide laminate according to claim 9, wherein the residual stress at 25[deg.] C. is 20 MPa or less when the polyimide film of the laminate has a thickness of 10 [mu]m. The polyamic acid composition containing the organic solvent according to claim 4 is applied to a support to form a film-like polyamic acid on the support, the polyamic acid is imidized by heating, and is coated on the support. A method for manufacturing a laminate, comprising forming a polyimide film. A flexible device comprising an electronic element formed on the polyimide film or laminate according to any one of claims 6 to 10.