JP7265864B2 - Polyimide precursor and polyimide - Google Patents

Description

TECHNICAL FIELD The present invention relates to a polyimide useful as a transparent resin substrate or the like and a precursor thereof.

Display devices such as organic EL devices and touch panels are used as constituent members of various displays, including large displays such as televisions and small displays such as mobile phones, personal computers, and smart phones. For example, in an organic EL device, a thin film transistor (TFT) is generally formed on a glass substrate, which is a supporting substrate, and electrodes, a light emitting layer and electrodes are sequentially formed thereon, and these are hermetically sealed with a glass substrate or a multilayer thin film. It is made by stopping. Further, the touch panel has a structure in which a first glass substrate on which a first electrode is formed and a second glass substrate on which a second electrode is formed are joined via an insulating layer (dielectric layer). there is

These constituent members are laminates in which various functional layers are formed on a glass substrate. By replacing this glass substrate with a resin substrate, it is possible to reduce the thickness, weight, and flexibility of a component using a conventional glass substrate. Utilizing this, it is expected to obtain flexible devices such as flexible displays. On the other hand, since resins are inferior to glass in dimensional stability, transparency, heat resistance, moisture resistance, film strength, etc., various studies have been made.

As a transparent resin film for this application, various studies have been made on polyimide films having excellent heat resistance and the like. Transparent resin films used for touch panels and touch sensors have various required physical properties, but they also need to have a low retardation (phase difference: R) in order to improve visibility.

For example, Patent Documents 1 and 2 and Non-Patent Document 1 disclose stretched polyimide films having repeating units of specific aliphatic or alicyclic tetracarboxylic acid structures. However, since it contains an alicyclic structure, its thermal decomposition temperature and discoloration temperature are low, and when heated during the panel manufacturing process, outgassing and discoloration occur, and the process temperature that it can withstand decreases.
Patent Document 3 discloses a polyimide obtained by copolymerizing a polymerization composition containing a dian-based monomer and a dianhydride-based monomer. However, it does not mention retardation.

Japanese Unexamined Patent Application Publication No. 2008-163107 WO2014/162733 JP 2018-515651 A High Perform. Polym, 13, S93 (2001)

Transparent resin films (substrates) used for touch panels and touch sensors need to have low retardation (phase difference: R) in order to improve visibility. Even if not only the retardation (Re) in the in-plane direction but also the retardation (Rth) in the thickness direction is high, light scattering occurs, the focus is lost, and the visibility of the image is lowered. Although the transparency of the film obtained from semi-alicyclic polyimide is relatively high, when considering its use as an optical material, the birefringence is large, so images appear doubled and colors are blurred. There was also a case of putting it away (Non-Patent Document 1). Therefore, as a transparent resin film, a transparent resin film having Rth≦50 nm is recently desired.
On the other hand, as a method for thinning a polyimide film, a polyimide precursor is directly coated on a supporting substrate (e.g. glass), imidized on the supporting substrate, and then the polyimide film is irradiated with a laser from the supporting substrate. However, the thin polyimide film obtained by the lift-off method has an Rth exceeding 50 nm. Therefore, it is an object of the present invention to provide a thin polyimide film having Rth≦50 nm even in the lift-off method, which is a general-purpose thin film manufacturing technique.
In particular, it is an object of the present invention to provide a polyimide precursor and a polyimide that can yield a thin polyimide film having a low Rth of Rth≦50 nm not only in the in-plane direction but also in the thickness direction.

The present invention proposes a polyimide precursor (varnish) formed by combining a specific diamine and an acid dianhydride, and using this polyimide precursor, a thin polyimide film obtained by a general-purpose lift-off method is , exhibiting excellent optical properties such as low Rth (≦50 nm) and excellent heat resistance.

式（２）中、ＸはＯ又は‐Ｃ（ＣＦ_３）_２‐である。
上記ポリイミド前駆体は、１，３－ビス（３－アミノフェノキシ）ベンゼンに由来する構造単位を、全ジアミンに由来する構造単位中５０モル％以上含むことが好適である。 That is, the present invention provides a polyimide precursor having a structural unit derived from a diamine and a structural unit derived from an acid dianhydride, wherein the structural unit derived from the diamine represented by the following formula (1) and the following formula (2 ) and a structural unit derived from the acid dianhydride shown in, containing 50 mol% or more of the total diamine derived from the following formula (1), the following formula (2) derived from the entire acid dianhydride It contains 50 mol% or more of structural units derived from acid dianhydride, and when the polyimide precursor is imidized to form a polyimide, the retardation in the thickness direction (Rth) at a thickness of 10 μm is 50 nm or less, and the retardation in the in-plane direction is The polyimide precursor has a (Re) of 10 nm or less and a 1% weight loss temperature of 450° C. or higher in a nitrogen atmosphere.

In formula (2), X is O or -C( _CF3 ) _2- .
The above polyimide precursor preferably contains structural units derived from 1,3-bis(3-aminophenoxy)benzene in an amount of 50 mol % or more of all structural units derived from diamine.

The present invention is a polyimide film obtained by imidizing the above polyimide precursor.
The polyimide film preferably has a light transmittance of 10% or less at 355 nm and a light transmittance of 70% or more at 430 nm at a thickness of 10 μm.
The polyimide film preferably has a yellowness index of 10 or less.
The above polyimide film is suitable as a transparent resin substrate material.

The present invention is a flexible device comprising a functional layer laminated on the polyimide film.

式（４）中、ＸはＯ又は‐Ｃ（ＣＦ_３）_２‐である。 The present invention is a polyimide having a structural unit derived from a diamine and a structural unit derived from an acid dianhydride, a structural unit derived from a diamine represented by the following formula (3), and an acid represented by the following formula (4) and a structural unit derived from a dianhydride, containing a diamine derived from the following formula (3) in an amount of 50 mol% or more of all diamines, and an acid dianhydride derived from the following formula (4) as a total acid dianhydride The thickness direction retardation (Rth) of a film having a thickness of 10 μm is 50 nm or less, the in-plane direction retardation (Re) is 10 nm or less, and 1 mass in a nitrogen atmosphere The polyimide is characterized by having a % weight loss temperature of 450° C. or higher.

In formula (4), X is O or -C( _CF3 ) _2- .

The present invention comprises a step of applying the polyimide precursor or its resin solution onto the surface of a supporting substrate, and imidizing the polyimide precursor or its resin solution by heating to form a polyimide layer on the surface of the supporting substrate. The step of forming and peeling the polyimide layer from the support, the thickness direction retardation (Rth) at a thickness of 10 μm is 50 nm or less, the in-plane direction retardation (Re) is 10 nm or less, and in a nitrogen atmosphere and obtaining a polyimide film having a 1 mass% weight loss temperature of 450° C. or higher.
In the method for producing the polyimide film of the present invention, it is preferable to irradiate the interface between the polyimide layer and the support substrate with a laser beam to peel the polyimide layer from the support.

In the present invention, it is possible to manufacture a thin polyimide film by a lift-off method using a general-purpose supporting substrate, and the thermal decomposition temperature is high, and the obtained thin polyimide film has a low retardation (Rth ≤ 50 nm) and excellent heat resistance. have sex. Therefore, it can be suitably used for touch panel transparent substrates and the like.

The polyimide precursor of the present invention is a polyimide precursor having a structural unit derived from a structural unit derived from a diamine and a structural unit derived from an acid dianhydride, the structural unit derived from the diamine represented by the above formula (1), (2) and a structural unit derived from the acid dianhydride shown in the above formula (1) containing 50 mol% or more of the total diamine, the acid dianhydride derived from the above formula (2) contains 50 mol% or more of the structural units derived from the total acid dianhydride. The polyimide obtained by imidizing the polyimide precursor of the present invention also retains these structural units as they are.
Since the structural units of the polyimide precursor and the polyimide and their proportions are determined by the types and proportions of the diamine and acid dianhydride used, the description of the structural units is based on the diamine and acid dianhydride. The usage ratio of diamine and acid dianhydride is the abundance ratio of structural units derived from each.

The diamine represented by the formula (1) is 1,3-bis(3-aminophenoxy)benzene (APB), 1,3-bis(4-aminophenoxy)benzene (TPE-R), 1,4-bis (4-aminophenoxy)benzene. A mixture of these may also be used.

From the viewpoint of heat resistance and low retardation, the diamine represented by the above formula (1) is contained in an amount of 50 mol% or more, preferably 70 mol% or more, and more preferably 90 mol% or more of the total diamine. In the prior art, as disclosed in Patent Document 3, when the content of the diamine represented by the above formula (1) is high, the arrangement of the polymer chains of the polyimide is disturbed, thereby improving optical properties and thermal properties. was perceived to be significantly reduced. On the other hand, in the present invention, as a result of intensive studies, a polyimide having a specific composition containing a certain amount or more of the diamine exhibits low retardation (Rth ≤ 50 nm) while ensuring general optical properties and thermal properties. This is what I discovered.

Other diamines can be used in addition to the diamines represented by formula (1) above. If other diamines are used, they are less than 50 mol%, preferably less than 30 mol%, more preferably less than 10 mol% of the total diamines.

Diamines having one or more aromatic rings are suitable as the other diamines. Examples of such diamines include 2,2'-dimethyl-4,4'-diaminobiphenyl (also known as 2,2'-dimethyl-benzidine), 3,3'-dimethyl-4,4'-diaminobiphenyl, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,6-dimethyl-m-phenylenediamine, 2,5-dimethyl-p-phenylenediamine, 2,4-diaminomesitylene, 4,4'- methylenedi-o-toluidine, 4,4'-methylenedi-2,6-xylidine, 4,4'-methylene-2,6-diethylaniline, 2,4-toluenediamine, m-phenylenediamine, p-phenylenediamine, 4,4'-diaminodiphenylpropane, 3,3'-diaminodiphenylpropane, 4,4'-diaminodiphenylethane, 3,3'-diaminodiphenylethane, 4,4'-diaminodiphenylmethane, 3,3'-diamino Diphenylmethane, 2,2-bis[4-(4-aminophenoxy)phenyl]propane 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl ether, 3,3'- Diaminodiphenyl ether, benzidine, 3,3' -diaminobiphenyl, 3,3' -dimethyl-4,4'-diaminobiphenyl, 3,3'-dimethoxybenzidine, 4,4'-diamino-p-terphenyl, 3, 3'-diamino-p-terphenyl, bis(p-β-amino-t-butylphenyl)ether, bis(p-β-methyl-δ-aminopentyl)benzene, p-bis(2-methyl-4- aminopentyl)benzene, p-bis(1,1-dimethyl-5-aminopentyl)benzene, 1,5-diaminonaphthalene, 2,6-diaminonaphthalene, 2,4-bis(β-amino-t-butyl) toluene, 2,4-diaminotoluene, m-xylene-2,5-diamine, p-xylene-2,5-diamine, m-xylylenediamine, p-xylylenediamine, 5-amino-2-(4- aminophenyl)benzimidazole and the like.

4,4'-Diaminodiphenyl ether, 4,6-dimethyl-m-phenylenediamine, 2,5-dimethyl-p-phenylenediamine, 2,4- with diaminomesitylene, 2,4-toluenediamine, m-phenylenediamine, 2,2′-dimethyl-4,4′-diaminobiphenyl, 5-amino-2-(4-aminophenyl)benzimidazole or p-phenylenediamine be.

The acid dianhydride represented by the above formula (2) is 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) or 4,4'-oxydiphthalic dianhydride ( ODPA). A mixture of these may also be used.

From the viewpoint of heat resistance and low retardation, the acid dianhydride represented by formula (2) is contained in an amount of 50 mol% or more, preferably 70 mol% or more, and more preferably 90 mol% or more of the total diamine.

Other acid dianhydrides can be used in addition to the acid dianhydride represented by the above formula (2). When other dianhydrides are used, they are less than 50 mol % of the total dianhydride, preferably less than 30 mol %.

Other acid dianhydrides include, for example, 4,4'-(2,2'-hexafluoroisopropylidene)diphthalic dianhydride, naphthalene-2,3,6,7-tetracarboxylic dianhydride, naphthalene-1,2,5,6-tetracarboxylic dianhydride, naphthalene-1,2,6,7-tetracarboxylic dianhydride, pyromellitic dianhydride, 3,3',4,4' -biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 2,2',3,3'-benzophenonetetracarboxylic dianhydride, 2,3,3 ',4'-benzophenonetetracarboxylic dianhydride, naphthalene-1,2,4,5-tetracarboxylic dianhydride, naphthalene-1,4,5,8-tetracarboxylic dianhydride, naphthalene-1 ,2,6,7-tetracarboxylic dianhydride, 4,8-dimethyl-1,2,3,5,6,7-hexahydronaphthalene-1,2,5,6-tetracarboxylic dianhydride , 4,8-dimethyl-1,2,3,5,6,7-hexahydronaphthalene-2,3,6,7-tetracarboxylic dianhydride, 2,6-dichloronaphthalene-1,4,5 ,8-tetracarboxylic dianhydride, 2,7-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, 2,3,6,7-tetrachloronaphthalene-1,4,5, 8-tetracarboxylic dianhydride, 1,4,5,8-tetrachloronaphthalene-2,3,6,7-tetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic acid dianhydride, 2,3,3′,4′-biphenyltetracarboxylic dianhydride, 3,3″,4,4″-p-terphenyltetracarboxylic dianhydride, 2,2″ ,3,3''-p-terphenyltetracarboxylic dianhydride, 2,3,3'',4''-p-terphenyltetracarboxylic dianhydride, 2,2-bis(2,3 -dicarboxyphenyl)-propane dianhydride, 2,2-bis(3,4-dicarboxyphenyl)-propane dianhydride, bis(2,3-dicarboxyphenyl) ether dianhydride, bis(2, 3-dicarboxyphenyl)methane dianhydride, bis(3.4-dicarboxyphenyl)methane dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, 1,1-bis (3,4-dicarboxyphenyl)ethane dianhydride, perylene-2,3,8,9-tetracarboxylic dianhydride, perylene-3,4,9,10-tetracarboxylic dianhydride, perylene- 4,5,10,11-tetracarboxylic dianhydride, perylene-5,6,11,12-tetracarboxylic dianhydride, phenanthrene-1,2,7,8-tetracarboxylic dianhydride, phenanthrene -1,2,6,7-tetracarboxylic dianhydride, phenanthrene-1,2,9,10-tetracarboxylic dianhydride, cyclopentane-1,2,3,4-tetracarboxylic dianhydride , pyrazine-2,3,5,6-tetracarboxylic dianhydride, pyrrolidine-2,3,4,5-tetracarboxylic dianhydride, thiophene-2,3,4,5-tetracarboxylic dianhydride 4,4'-oxydiphthalic dianhydride, (trifluoromethyl) pyromellitic dianhydride, di (trifluoromethyl) pyromellitic dianhydride, di (heptafluoropropyl) pyromellitic dianhydride , pentafluoroethylpyromellitic dianhydride, bis{3,5-di(trifluoromethyl)phenoxy}pyromellitic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane di anhydride, 5,5'-bis(trifluoromethyl)-3,3',4,4'-tetracarboxybiphenyl dianhydride, 2,2',5,5'-tetrakis(trifluoromethyl)-3 ,3′,4,4′-tetracarboxybiphenyl dianhydride, 5,5′-bis(trifluoromethyl)-3,3′,4,4′-tetracarboxydiphenyl ether dianhydride, 5,5′- Bis(trifluoromethyl)-3,3',4,4'-tetracarboxybenzophenone dianhydride, bis{(trifluoromethyl)dicarboxyphenoxy}benzene dianhydride, bis{(trifluoromethyl)dicarboxyphenoxy }, trifluoromethylbenzene dianhydride, bis(dicarboxyphenoxy)trifluoromethylbenzene dianhydride, bis(dicarboxyphenoxy)bis(trifluoromethyl)benzene dianhydride, bis(dicarboxyphenoxy)tetrakis(tri fluoromethyl)benzene dianhydride, 2,2-bis{(4-(3,4-dicarboxyphenoxy)phenyl}hexafluoropropane dianhydride, bis{(trifluoromethyl)dicarboxyphenoxy}biphenyl dianhydride , bis {(trifluoromethyl) dicarboxyphenoxy} bis (trifluoromethyl) biphenyl dianhydride, bis {(trifluoromethyl) dicarboxyphenoxy} diphenyl ether dianhydride, bis (dicarboxyphenoxy) bis (trifluoromethyl ) and biphenyl dianhydride. Moreover, these may be used alone or in combination of two or more.

Preferably, pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 4,4'-oxydiphthalic dianhydride, which can impart strength and flexibility to the polyimide film. 4,4'-(2,2'-Hexafluoroisopropylidene)diphthalic dianhydride, 1,2,3,4- Cyclobutanetetracarboxylic dianhydride or 4,4'-oxydiphthalic dianhydride.

The polyimide precursor of the present invention can be produced by a known method of polymerizing in an organic polar solvent using the diamine and acid dianhydride at a molar ratio of 0.9 to 1.1. For example, after dissolving a diamine in an aprotic amide solvent such as N,N-dimethylacetamide or N-methyl-2-pyrrolidone under a nitrogen stream, an acid dianhydride is added and the mixture is stirred at room temperature for about 3 to 20 hours. It is obtained by reacting. In order to speed up the reaction, it may be heated at a temperature of 40° C. to 80° C. for 15 minutes to 5 hours. At this time, the molecular ends may be capped with an aromatic monoamine or an aromatic monocarboxylic acid dianhydride. Examples of the solvent include dimethylformamide, 2-butanone, diglyme, xylene, γ-butyrolactone, and the like, which may be used singly or in combination of two or more. Xylene, hexane, etc. can also be added to enhance solubility.

The polyimide of the present invention is obtained by imidating the polyimide precursor of the present invention. Imidization can be performed by a thermal imidization method, a chemical imidization method, or the like. Thermal imidization is performed by applying a polyimide precursor onto an arbitrary supporting substrate such as glass, metal, resin, etc. using an applicator, pre-drying at a temperature of 150 ° C. or less for 2 to 60 minutes, and then removing the solvent. For imidization, heat treatment is usually carried out at a temperature of about room temperature to 360° C. for about 10 minutes to 20 hours. When a desired polyimide film is obtained, the heat treatment temperature may be up to 280°C. It is also possible to vary the heat treatment temperature between 280° C. and 360° C., depending on the mechanical properties required. In chemical imidization, a dehydrating agent and a catalyst are added to a polyimide precursor (also called polyamic acid) solution, and chemical dehydration is carried out at 30 to 60°C. A typical dehydrating agent is acetic anhydride, and a typical catalyst is pyridine. Thermal imidization can be completed in a relatively short time by selecting a combination of acid dianhydride, diamine type, and solvent type, and heat treatment including preheating can be performed within 60 minutes. be. It may be applied as a polyimide precursor solution dissolved in a solvent.

The preferred degree of polymerization of the polyimide precursor and polyimide of the present invention is 1,000 to 100,000 cP as a viscosity measured by an E-type viscometer of the polyimide precursor solution, preferably in the range of 3,000 to 10,000 cP. be. The molecular weight of the polyimide precursor can be determined by the GPC method. The preferred molecular weight range of the polyimide precursor (in terms of polystyrene) is a number average molecular weight of 15,000 to 250,000 and a weight average molecular weight of 30,000 to 800,000. , outside this range may be acceptable. The preferred molecular weights of polyimides are also in the same range as the molecular weights of their precursors.

The polyimide obtained by imidizing the polyimide precursor of the present invention exhibits the following physical properties in the state of a polyimide film having a thickness of 10 μm as a reference thickness.

The retardation (Rth) in the thickness direction is less than 50 nm. It is preferably 40 nm or less, more preferably 30 nm or less. The retardation (Re) in the in-plane direction is less than 10 nm as a value (Re10) converted with a film thickness of 10 μm. It is preferably 5 nm or less. Within this range, the visibility that satisfies the recent requirements of touch panel substrates is achieved.

From the viewpoint of transparency, the total light transmittance in the visible region is preferably 70% or more. Preferably it is 80% or more. The light transmittance at 450 nm is preferably 70% or more. Preferably it is 80% or more. In addition, it is preferable that the light transmittance at 308 nm is 3% or less. It is preferably less than 1%, more preferably less than 0.1%.
Within these ranges, light in the near-ultraviolet region is absorbed, and transmittance of light in the ultraviolet region is high. It can absorb 308 nm laser light from an excimer laser or the like while maintaining transparency in the visible light region. As a result, in the production of flexible devices such as substrates for organic EL devices, touch panel substrates, and color filter substrates, by irradiating the flexible substrate with a laser, the supporting substrate can be peeled off without damaging the display device on the polyimide film. can be made A laser lift-off method can be preferably applied.
In addition, the laser lift-off method is, for example, forming a polyimide layer on glass as a supporting substrate, forming various functional layers on the polyimide layer to form a laminate, and then passing the polyimide layer through the supporting substrate. In this method, a polyimide film with a functional layer is produced by exfoliating the supporting substrate from the polyimide layer by irradiating the bottom surface with a laser.
As the supporting substrate, a known substrate can be used, and examples thereof include heat-resistant resins such as polyimide, and inorganic substrates such as metal foil and glass. Preferred are polyimide, copper foil, and glass, which have a good balance of releasability and adhesiveness between the polyimide layer and the support substrate, and excellent heat resistance. In particular, as one of the features of the present invention, it has been found that the polyimide precursor of the present invention exhibits a small value of Rth even when glass is used. From that point of view, it is preferable to use glass as the support substrate.

The yellowness index (YI) is preferably 10 or less. It is preferably 6 or less, more preferably 4 or less. Within this range, it can be suitably used for substrates that require high transparency and low coloring, such as TFT substrates for organic EL devices, touch panel substrates, and color filter substrates.
A low coefficient of thermal expansion (CTE) is also required, for example 70 ppm/K or less.

The flexible device substrate has a glass transition temperature (Tg) of 200° C. or higher, preferably 250° C. or higher, from the viewpoint of heat resistance. The thermal decomposition temperature (1% weight loss temperature, Td1) is 350° C. or higher, preferably 450° C. or higher.

The elastic modulus (E') is preferably 4 GPa or less. It is preferably 3.5 GPa or less. Here, the elastic modulus is the tensile elastic modulus at room temperature. Within this range, there is little residual stress in the substrate during the production of flexible devices such as TFT substrates for organic EL devices, touch panel substrates, and functional layer lamination in color filters and the like, and production yields of flexible devices are excellent.

A thin polyimide film satisfying the above properties is a diamine represented by the above formula (1) and an acid dianhydride represented by the above formula (2), which are contained as essential or preferable structural units in the polyimide precursor and polyimide of the present invention. It contains a predetermined amount of material and is obtained by the lift-off method.

The polyimide of the present invention is suitable as a polyimide film with a functional layer. The polyimide film in this case may be composed of a plurality of layers of polyimide. In the case of a single layer, the thickness is 3 μm to 50 μm. It is preferably 30 μm or less, more preferably 15 μm or less. In the case of multiple layers, the main polyimide layer may be a polyimide film having the above thickness. Here, the main polyimide layer refers to the polyimide layer having the largest thickness ratio among the multiple polyimide layers.

The polyimide of the present invention can be made into a laminate by forming an element layer or the like (functional layer) having various functions on the polyimide layer. Examples of the functional layer include display devices such as liquid crystal display devices, organic EL display devices, touch panels, color filters, and electronic paper, or components thereof. Various functional devices such as conductive films, films for touch panels, gas barrier films, and flexible circuit boards, which are used in conjunction with display devices, are also included. That is, the functional layer includes not only components such as a liquid crystal display device, an organic EL display device, and a color filter, but also an organic EL lighting device, a touch panel device, an electrode layer or a light emitting layer of an organic EL display device, a gas barrier film, and an adhesive layer. A film, a thin film transistor (TFT), a wiring layer of a liquid crystal display device, a transparent conductive layer, or the like, or a combination of two or more thereof is also included.

In forming a functional layer such as a display element on the polyimide film of the present invention, formation conditions are appropriately set according to the intended device.
After forming a metal film, an inorganic film, an organic film, or the like on a polyimide layer (film) by a known method, the film is patterned into a predetermined shape or heat-treated as necessary. That is, the method for forming the functional layer is not particularly limited, and can be appropriately selected from, for example, sputtering, vapor deposition, CVD, printing, exposure, immersion, and the like. If desired, these processes may be performed in a vacuum chamber or the like. The support substrate, for example, the glass substrate may be separated from the polyimide film immediately after forming the functional layer through various processing treatments, and the integrated state with the support substrate is maintained for a certain period after formation, For example, it may be peeled off and removed just before it is used as a display device.

As an example of the flexible device of the present invention, an outline of a method for manufacturing an organic EL display device having a bottom emission structure as a functional layer will be described below.

A gas barrier layer is provided on the polyimide film of the present invention to provide a structure capable of preventing the permeation of moisture and oxygen. Next, a circuit configuration layer including a thin film transistor (TFT) is formed on the upper surface of the gas barrier layer. In organic EL display devices, LTPS-TFTs are mainly selected as thin film transistors because of their high operating speed. Anode electrodes made of a transparent conductive film of, for example, ITO (Indium Tin Oxide) are formed on the upper surface of the circuit-constituting layer for each of a plurality of pixel regions arranged in a matrix. An organic EL light-emitting layer is formed on the upper surface of the anode electrode, and a cathode electrode is formed on the upper surface of the light-emitting layer. A cathode electrode is formed in common for each pixel region. A gas barrier layer is formed again so as to cover the surface of the cathode electrode, and a sealing substrate is placed on the outermost surface for surface protection. From the standpoint of reliability, it is desirable to laminate a gas barrier layer that prevents permeation of moisture and oxygen also on the surface of the sealing substrate on the cathode electrode side. The organic EL light-emitting layer is formed of a multilayer film (anode electrode-light-emitting layer-cathode electrode) such as hole injection layer-hole transport layer-light-emitting layer-electron transport layer. It is generally formed by vacuum deposition, and is continuously formed in vacuum, including electrode formation.

Since the wavelength of light emitted from the light-emitting layer of an organic EL display device is mainly 440 nm to 780 nm, the transparent resin film substrate used in the organic EL display device should have an average transmittance of at least 80% in this wavelength region. is required.
On the other hand, the support substrate is separated from the resin film by a lift-off method. In the case of the laser lift-off method, when the support substrate is peeled off from the polyimide layer by irradiation with UV laser light, if the transmittance at the wavelength of the UV laser light is high, it is necessary to provide a separate absorption/peeling layer, which reduces productivity. decreases. At present, a 308 nm laser device is generally used in this laser lift-off method. In order to perform peeling without providing an absorption/peeling layer, the polyimide itself must sufficiently absorb the 308 nm laser light, and it is desirable to transmit light in this wavelength region as little as possible.

The polyimide film of the present invention has small in-plane retardation, small haze, and high light transmittance. Furthermore, the retardation in the thickness direction can also be controlled to Rth≦50 nm. Therefore, it is particularly suitable for a panel substrate of a display device. Examples of display devices include touch panels, liquid crystal displays, organic EL displays, and the like.

A touch panel is generally a panel body composed of (i) a transparent substrate having a transparent electrode (detection electrode layer), (ii) an adhesive layer, and (iii) a transparent substrate having a transparent electrode (drive electrode layer). The aforementioned polyimide film can be applied to both the transparent substrate on the detection electrode layer side and the transparent substrate on the drive electrode layer side.

In addition, the liquid crystal cell of the liquid crystal display device is usually a laminate in which (i) a first transparent plate, (ii) a liquid crystal material sandwiched between transparent electrodes, and (iii) a second transparent plate are laminated in this order. It is a panel body having a structure. The aforementioned polyimide film can be applied to both the first transparent plate and the second transparent plate. The polyimide film described above can also be applied to substrates for color filters in liquid crystal display devices.

An organic EL panel is generally a panel in which a transparent substrate, an anode transparent electrode layer, an organic EL layer, a cathode reflective electrode layer, and a counter substrate are laminated in this order. The aforementioned polyimide film can be applied to both the transparent substrate and the counter substrate.

The present invention will be specifically described below based on examples and comparative examples. However, the present invention is not limited to these examples.

The abbreviations of raw materials used in Examples and the like are shown below.
・APB: 1,3-bis(3-aminophenoxy)benzene ・TPE-R: 1,3-bis(4-aminophenoxy)benzene ・TFMB: 2,2′-bis(trifluoromethyl)-4,4 '-diaminobiphenyl 6FDA: 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride ODPA: 4,4'-oxydiphthalic dianhydride BPDA: 3,3',4 , 4'-biphenyltetracarboxylic dianhydride NMP: N-methyl-2-pyrrolidone

The measurement method and evaluation method of each physical property in Examples etc. are shown below. [Light transmittance and yellowness index (YI)]
A polyimide film (50 mm×50 mm) was measured for light transmittance (T308, T355, T400, T430) at 308 nm, 355 nm, 400 nm and 430 nm using a SHIMADZU UV-3600 spectrophotometer. Also, YI (yellowness index) was calculated based on the following formula.
YI=100×(1.2879X−1.0592Z)/Y
X, Y, Z are the tristimulus values of the test piece, defined in JIS Z 8722.

[Coefficient of thermal expansion (CTE)]
A polyimide film having a size of 3 mm × 15 mm is heated from 30 ° C. to 280 ° C. at a constant heating rate (10 ° C./min) while applying a load of 5.0 g with a thermomechanical analysis (TMA) device, and then , the temperature was lowered from 250° C. to 100° C., and the thermal expansion coefficient was measured from the amount of elongation (linear expansion) of the polyimide film during the temperature drop.

[Thermal decomposition temperature (Td1)]
A polyimide film weighing 10 to 20 mg under a nitrogen atmosphere is heated from 30 ° C. to 550 ° C. at a constant rate with a thermogravimetric analysis (TG) device TG / DTA6200 manufactured by SEIKO, and the weight change is measured. The weight at 200° C. was assumed to be zero, and the temperature at which the weight reduction rate was 1% was defined as the thermal decomposition temperature (Td1).

[retardation]
A polyimide film (50 mm × 50 mm) is rotated using a birefringence/phase difference evaluation device (WPA-100, manufactured by Photonic Lattice Co., Ltd.) to change the incident angle of light incident on the sample. A rotating apparatus was attached to measure the incident angle dependency of the retardation of the polyimide film at a wavelength of 543 nm. The measurement data of the incident angle dependence of the retardation was numerically analyzed to obtain a retardation (Rth) of 90° in the thickness direction and a retardation (Re) of 0° in the in-plane direction.

[Haze and total light transmittance]
A polyimide film (50 mm×50 mm) was measured for haze and total light transmittance using a HAZE METER NDH500 manufactured by Nippon Denshoku Industries Co., Ltd.

Synthesis example 1
Under a nitrogen stream, 7.90 g of APB was dissolved in 80 g of NMP in a 200 ml separable flask. Then 12.10 g of 6FDA was added. The molar ratio (a/b) of acid dianhydride (a) and diamine (b) was set to 1.010. This solution is heated at 45° C. for 2 hours to dissolve the contents, and then the solution is stirred at room temperature for 10 hours to carry out a polymerization reaction, resulting in a polyimide precursor A (viscous solution) having a high degree of polymerization. Obtained.

Synthesis Examples 2-4, Comparative Synthesis Examples 1-2
A polyamic acid solution was prepared in the same manner as in Synthesis Example 1, except that the diamine and tetracarboxylic dianhydride as raw materials were changed to the compositions shown in Table 1 to obtain polyimide precursors B to F.

In addition, in Table 1, the unit of the amount of diamine and tetracarboxylic dianhydride is g.

Example 1
Add NMP to the polyimide precursor A to dilute it so that the viscosity becomes 4000 cP. was used to coat the polyimide so that the thickness of the cured polyimide was 10 μm. Subsequently, heating was performed at 100° C. for 15 minutes. Then, in a nitrogen atmosphere, the temperature was raised from room temperature to 380 ° C. (360 ° C. in Comparative Example 10) at a constant heating rate (4 ° C./min), and further held at 380 ° C. for 30 minutes, and then in a nitrogen atmosphere. It was gradually cooled to room temperature, taken out from the oven, and a polyimide layer (polyimide A) of 150 mm×150 mm was formed on the glass substrate to obtain a polyimide laminate A.

A rectangular cut (10 mm×10 mm) was formed in the polyimide layer of the polyimide laminate A with a cutter. Next, the polyimide laminate A was immersed in water and allowed to stand for one day, and after taking out from the water, the polyimide layer was peeled off from the polyimide laminate A using tweezers (lift-off method) to obtain a polyimide film A.
Various evaluations were performed on the polyimide film A. Table 2 shows the results.

Examples 2-4, Comparative Examples 1-2
Polyimide laminates B to F and polyimide films B to F were obtained in the same manner as in Example 1 except that polyimide precursors B to F were used instead of polyimide precursor A. The symbols of the polyimide precursor and the polyimide laminate correspond to each other. For example, from the polyimide precursor B, it means that the polyimide laminate B and the polyimide film B are obtained.

Claims (1)

A method for producing a polyimide film for a thin film flexible device transparent resin substrate, wherein a polyimide precursor is a structural unit derived from a diamine represented by the following formula (1) and an acid dianhydride represented by the following formula (2). and a structural unit derived from, containing 50 mol% or more of the total diamine derived from the following formula (1), an acid dianhydride derived from the following formula (2) a structure derived from the total acid dianhydride A step of applying a polyimide precursor solution containing 50 mol% or more of the units and dissolved in an organic solvent on the surface of the supporting substrate, and imidizing the polyimide precursor solution by heating to form the surface of the supporting substrate. A step of forming a polyimide layer on the top, and peeling the polyimide layer from the support substrate by a lift-off method so that the retardation in the thickness direction (Rth) in a film with a thickness of 10 μm is 50 nm or less, and the retardation in the in-plane direction (Re ) is 10 nm or less, and the 1% weight loss temperature in a nitrogen atmosphere is 450° C. or higher. .

In formula (2), X is O or -C( _CF3 ) _2- .
Here, the retardation is measured by using a polyimide film (50 mm × 50 mm) and a birefringence/phase difference evaluation device with a rotating device that rotates the sample to change the incident angle of light incident on the sample. At 543 nm, the incident angle dependence of the retardation of the polyimide film was measured. By numerically analyzing the measurement data of the incident angle dependency of retardation, the retardation (Rth) of 90° in the thickness direction and the retardation (Re) of 0° in the in-plane direction were obtained.