JP2014026969A - Display device and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic EL device capable of being reduced in thickness, lightened in weight and made flexible, having no problem such as crack and peeling due to thermal stress, and excellent in dimensional stability or the like.SOLUTION: An organic EL device includes: a gas barrier layer on a support base material comprising a polyimide film; and further an organic EL light emitting layer formed therein. The polyimide film has a transmittance in a wavelength region of 440-780 nm of 80% or more, a thermal expansion coefficient of 15 ppm/K or less, and a difference between the thermal expansion coefficient of the polyimide film and that of the gas barrier layer of 10 ppm/K or less.

Description

  The present invention relates to a display device having a gas barrier layer on a support substrate made of a polyimide film.

  Organic EL devices used for various displays, including large displays such as televisions and small displays such as mobile phones, personal computers, and smartphones, are generally thin film transistors (hereinafter TFT) on a glass substrate that is a supporting substrate. The electrode, the light emitting layer, and the electrode are sequentially formed, and finally sealed by a glass substrate or a multilayer thin film. There are two types of organic EL device structures: a bottom emission structure that extracts light from the glass substrate side that is the support base material, and a top emission structure that extracts light from the opposite side of the glass substrate that is the support base material. ing. Moreover, since a structure in which external light passes as it is can be taken due to the structure, a transparent structure in which an electronic element such as a TFT can be seen from the outside has been proposed. Both can be realized by selecting transparent electrodes and substrate materials.

  In addition, by replacing the supporting base material of such an organic EL device with a resin from a conventional glass substrate, it is possible to reduce the thickness, weight, and flexibility of the organic EL device, and further expand the application of the organic EL device. However, since resin is generally inferior to glass in dimensional stability, transparency, heat resistance, moisture resistance, gas barrier property, etc., various studies have been made.

  For example, Japanese Patent Laid-Open No. 2008-231327 (Patent Document 1) relates to a polyimide useful as a plastic substrate for flexible display and an invention relating to a precursor thereof, and an alicyclic structure such as cyclohexylphenyltetracarboxylic acid. It has been reported that polyimides reacted with various diamines using tetracarboxylic acids containing benzene are excellent in transparency. However, the glass transition temperature of the polyimide obtained here is 337 ° C. at the maximum according to the examples (Table 1), and there is a problem that it cannot withstand the heat treatment temperature in the TFT annealing process which generally reaches about 400 ° C. is there. In addition, since the thermal expansion coefficient (CTE) of the obtained polyimide is about 50 to 60 ppm / K, when a gas barrier layer is provided to provide gas barrier properties as described in Patent Document 2 described later. In addition, it is difficult to obtain an organic EL device having excellent shape stability, such as peeling or cracking at the interface with the gas barrier layer.

  Japanese Patent Application Laid-Open No. 2011-238355 (Patent Document 2) describes a gas barrier film that is excellent in gas barrier properties and heat resistance, and is flexible and can be used as a base material of an organic EL device. The invention relates to a flexible film such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polycarbonate (PC), polyvinyl chloride (PVC), polyimide, etc., and a stress relaxation layer on one side thereof. In addition, by providing a gas barrier layer (inorganic barrier layer) containing at least a compound containing silicon and oxygen, penetration of water vapor and air is prevented, and the thermal expansion coefficient of the stress relaxation layer is 0.5 to 20 ppm / K. In the range, it is described that peeling and cracking due to a difference in thermal physical properties (thermal expansion coefficient, thermal contraction rate) between the resin base material and the inorganic barrier layer are prevented. However, in the case of a flexible film such as PET, PEN, PC, PVC, etc., mentioned here as the supporting substrate, heat resistance is insufficient and heat treatment temperature in the TFT annealing process generally reaching about 400 ° C. There is a problem that can not withstand. Further, the polyimide (gas barrier film 2-3) used in the comparative example is yellowish brown, has a low transmittance as compared with glass, and is not suitable as a glass substitute resin.

  Furthermore, Japanese Patent Application Laid-Open No. 2007-46054 (Patent Document 3) relates to an invention relating to a low-colored polyimide resin composition useful as a glass-type application in the field of electronic displays, and a polyimide film containing a perfluoro-imide moiety has a low thermal expansion. It has a coefficient, has a high glass transition temperature, and is excellent in transparency. However, most of the polyimide films actually obtained in the examples have a transmittance in the visible light region of less than 80%, and the glass transition temperature does not reach 400 ° C. In addition, a polyimide film satisfying both transparency and heat resistance has not been obtained.

  Similarly, JP-A-2-215564 (Patent Document 4) discloses that a fluorine-containing polyimide composition in which a fluorinated alkyl group is introduced into an acid anhydride and a diamine has a low dielectric constant, a low water absorption, and a low thermal expansion. It is disclosed that it can be applied to a printed board and a material for an optical waveguide. However, this Patent Document 4 does not describe the transmittance in the visible light region of the polyimide film. Moreover, when applying the transparent polyimide film which has a low thermal expansion coefficient to the support base material of a display apparatus, although a retardation becomes a problem, there is no description about the means for solving this.

  In addition to the above, attempts have been made to reduce the weight by using a flexible resin for the supporting substrate. For example, in the following Non-Patent Documents 1 and 2, an organic material in which highly transparent polyimide is applied to the supporting substrate. An EL device has been proposed. However, as described above, the polyimide films described in these documents cannot be said to have a sufficiently small difference in thermal expansion coefficient from the gas barrier layer of an inorganic compound provided for the purpose of supplementing the gas barrier property.

JP 2008-231327 A JP 2011-238355 A JP 2007-46054 A JP-A-2-215564

S. An et. Al., “2.8-inch WQVGA Flexible AMOLED Using High Performance Low Temperature Polysilicon TFT on Plastic Substrates”, SID 10 DIGEST, p706 (2010) Oishi et. Al., “Transparent PI for flexible display”, IDW’11 FLX2surasshuFMC4-1

  As described above, the organic EL device has low resistance to moisture, and the characteristics of the EL element that is the light-emitting layer are degraded by moisture. Therefore, when a resin is used as the support base, a gas barrier layer must be formed on at least one side of the support base in order to prevent moisture and oxygen from entering the organic EL device. In general, an inorganic material typified by silicon oxide or silicon nitride is used as the gas barrier layer having excellent gas barrier performance, and the coefficient of thermal expansion (CTE) thereof is usually 0 to 10 ppm / K. On the other hand, since transparent polyimide generally has a CTE of about 60 ppm / K, when the transparent polyimide is simply applied to the support substrate of the organic EL device, the gas barrier layer is cracked or peeled off due to thermal stress. Problems may occur.

  In addition, the formation of TFTs necessary for display applications requires an annealing process reaching about 400 ° C. In the case of a conventional glass substrate, there was no particular problem. However, when a resin is used as the support base, it is necessary to have heat resistance and dimensional stability at the heat treatment temperature of the TFT. On the other hand, a TFT may not be required unlike an organic EL device for illumination, but the resistance value of the transparent electrode is lowered by increasing the film formation temperature of the transparent electrode adjacent to the support substrate, and the organic EL device Since power consumption can be reduced, it is the same that heat resistance is required for the supporting base material in the case of lighting applications. In addition, metal oxides such as ITO are generally used as such transparent electrodes, and these are CTEs of 0 to 10 ppm / K, so that the same level can be avoided to avoid problems of cracks and peeling. CTE resin is required.

  In order to perform color display on an organic EL display device, materials capable of emitting light of the three primary colors of red (R), green (G), and blue (B) are vapor-deposited for each color using respective shadow masks. . However, this method has a problem that it is very difficult and expensive to manufacture a shadow mask. In addition, it is difficult to increase the definition and size of the shadow mask. In response to these problems, an organic EL display device has been proposed that performs color display by combining a white light-emitting organic EL with a color filter.

  In order to form the above color filter, it is necessary to heat treat the resist which generally reaches 230 ° C. or higher. Further, heat treatment at 300 ° C. or higher may be performed in order to reduce outgas from the resist, which may adversely affect the EL element. In addition, when the thermal expansion coefficient and humidity expansion coefficient of the support base of the display unit equipped with EL elements and the support base of the color filter do not match, there is a difference in the dimensional change of each substrate due to changes in temperature and humidity. This may cause warpage of the display device and peeling between the substrates. That is, the supporting substrate of the color filter needs to have heat resistance at the heat treatment temperature of the resist and dimensional stability equivalent to that of the supporting substrate of the display unit. In order to solve the above problem, it is desirable to use the same material for the support substrate of the organic EL display unit and the support substrate of the color filter.

  The polyimide film is generally colored yellow-brown. Therefore, when a minute foreign matter is mixed in the polyimide film, there is a problem that it is difficult to find it with the naked eye or an appearance inspection device. In particular, it is very difficult to find foreign matter such as rust of metal whose color is close to that of polyimide. If foreign matter exists in the polyimide film, it may cause defects such as a defect in the gas barrier layer formed on the polyimide film, a disconnection between electrodes, and a short circuit. By using a polyimide film having transparency, it becomes easy to find foreign matters, and contributes to prevention of yield reduction. For this reason, as a function of the display device, even in a display device such as electronic paper in which the support base material does not require transparency, using a transparent polyimide film leads to an improvement in productivity.

  The scratches on the surface of the polyimide film also cause defects such as a defect in the gas barrier layer, a disconnection between electrodes, and a short circuit, as in the case of foreign matter. When a polyimide film is applied to a supporting substrate of a display device, a defect of 1 μm or less which is allowed in a flexible printed wiring board which is the current main use of a polyimide film becomes a problem. A surface that can be applied to support substrates of display devices without problems, including polyimide films that are currently available on the market, including transparent polyimide films as well as general yellow-brown polyimide films (Kapton, Apical, Upilex, etc.) There is no state.

  Furthermore, the transmittance in the visible light region of glass is generally about 90%, and when a resin is used as a supporting base, it needs to be as close as possible to this. Since the wavelength of light emitted from the light emitting layer of the organic EL is mainly from 440 nm to 780 nm, the average transmittance in this wavelength region is at least 80% or more as a support substrate used in the organic EL device. Desired. In addition, it is desirable that the resin itself forming the support base material has moisture resistance.

  If the in-plane retardation of the supporting substrate exceeds 10 nm, there may be a case where uniform viewing angle characteristics cannot be obtained. When external light is incident on the organic EL device, the external light is reflected by the electrodes, thereby reducing the contrast. In this case, there is a method of preventing with a circularly polarizing plate, but if the retardation is large, the prevention effect is lowered. Therefore, in order to obtain high contrast, the retardation is preferably as small as possible.

  It is known that a polyimide film having a low thermal expansion coefficient can be obtained by orienting molecular chains by stretching a film using a tenter. However, there is a problem that the orientation of the molecular chain becomes non-uniform due to variations in stress applied to the film during stretching, thereby causing anisotropy in the refractive index and increasing the retardation.

  It is also known that a polyimide film having a low thermal expansion coefficient can be obtained without stretching by forming a film using polyimide having a rigid chemical structure under appropriate conditions such as heat treatment conditions, film thickness, and solvent type. It has been. However, since polyimides with a rigid chemical structure are easily oriented in molecular chains, the orientation of molecular chains becomes non-uniform due to in-plane variations in temperature, film thickness, etc. during heat treatment. There is a problem that the retardation is increased and the retardation is increased.

  That is, when replacing a glass substrate conventionally used in a display device with a resin film support base, it is necessary to use a resin that can simultaneously satisfy at least low CTE, heat resistance, and transparency. There was no resin film for the support substrate of the display device that could be used. In particular, it is important to control the physical property value at the interface between the resin film and the gas barrier layer in view of the particularity of the manufacturing process of the display device. Therefore, as a result of repeated studies by the present inventors, a polyimide containing a predetermined repetitive structure was produced under specific production conditions to obtain a polyimide film, and the difference in thermal expansion coefficient between the polyimide film and the gas barrier layer. It has been found that a display device excellent in dimensional stability can be obtained when the content is 10 ppm / K or less, and the present invention has been completed.

  Therefore, the object of the present invention is to be thin, light and flexible, free from cracking and peeling problems due to thermal stress, excellent in dimensional stability, and to prevent problems in the manufacturing process. An object of the present invention is to provide a display device such as an organic EL display, organic EL illumination, electronic paper, and liquid crystal display that can exhibit good element characteristics with a long lifetime.

  Another object of the present invention is to provide a manufacturing method of a display device or a member for a display device that can be made thin, light and flexible, can exhibit a long life and good characteristics. Here, the display device member is a member constituting the display device, and a thin film transistor, an electrode layer, an organic EL light emitting layer, electronic ink, a color filter, or two or more are formed on a polyimide film. It is a thing.

  That is, the present invention is a display device having a gas barrier layer on a support substrate made of a polyimide film, and the polyimide film has a transmittance of 80% or more in a wavelength region of 440 nm to 780 nm and a thermal expansion coefficient. The display device is characterized by being 15 ppm / K or less and having a difference in thermal expansion coefficient from the gas barrier layer of 10 ppm / K or less.

〔式中、Ａｒ₁は芳香環を有する４価の有機基を表し、Ａｒ₂は下記一般式（２）又は（３）で表される２価の有機基である。

〔ここで、一般式（２）又は一般式（３）におけるＲ₁〜Ｒ₈は、互いに独立に水素原子、フッ素原子、炭素数１〜５までのアルキル基若しくはアルコキシ基、又はフッ素置換炭化水素基であり、一般式（２）にあってはＲ₁〜Ｒ₄のうち、また、一般式（３）にあってはＲ₁〜Ｒ₈のうち、それぞれ少なくとも一つはフッ素原子又はフッ素置換炭化水素基である。〕 In addition, the present invention applies a polyimide or polyimide precursor resin solution on a base substrate so that the thickness of the polyimide film is 50 μm or less, completes the heat treatment, and forms a polyimide film on the base substrate. After the stress relaxation layer is formed on the polyimide film, the base substrate is removed in a state where the polyimide film and the stress relaxation layer are laminated, and the display device or the display device member is provided on the surface of the polyimide film opposite to the inorganic substrate. The polyimide film is composed of a single layer or a plurality of polyimide layers, and the polyimide constituting the main polyimide layer is 70 mol of the structural unit represented by the general formula (1). % Or more of the display device.

[In the formula, Ar ₁ represents a tetravalent organic group having an aromatic ring, and Ar ₂ represents a divalent organic group represented by the following general formula (2) or (3).

[Wherein, R _{1 to} R ₈ in the general formula (2) or the general formula (3) are each independently a hydrogen atom, a fluorine atom, an alkyl group or an alkoxy group having 1 to 5 carbon atoms, or a fluorine-substituted hydrocarbon. In the general formula (2), at least one of R _{1 to} R ₄ and R _{1 to} R _{8 in} the general formula (3) is a fluorine atom or a fluorine-substituted group. It is a hydrocarbon group. ]

  The polyimide film can be produced by polymerizing raw material diamine and acid anhydride in the presence of a solvent to obtain a polyimide precursor resin, and then imidizing by heat treatment. The molecular weight of the polyimide resin can be mainly controlled by changing the molar ratio of the raw material diamine and acid anhydride, but the molar ratio is usually 1: 1. Examples of the solvent include dimethylacetamide, dimethylformamide, n-methylpyrrolidinone, 2-butanone, diglyme, xylene and the like, and they can be used alone or in combination of two or more.

〔式中、Ａｒ₁は芳香環を有する４価の有機基を表し、Ａｒ₂は下記一般式（２）又は（３）で表される２価の有機基である。

〔ここで、一般式（２）又は一般式（３）におけるＲ₁〜Ｒ₈は、互いに独立に水素原子、フッ素原子、炭素数１〜５までのアルキル基若しくはアルコキシ基、又はフッ素置換炭化水素基であり、一般式（２）にあってはＲ₁〜Ｒ₄のうち、また、一般式（３）にあってはＲ₁〜Ｒ₈のうち、それぞれ少なくとも一つはフッ素原子又はフッ素置換炭化水素基である。〕 As for the polyimide film used by this invention, the diamine and acid dianhydride which are the raw materials may each consist of a single type of monomer, and may consist of multiple types of monomers. The polyimide film of the present invention is preferably made of polyimide having a structural unit represented by the following general formula (1). Alternatively, the copolymer may be a copolymer using a plurality of types of monomers having a structural unit represented by the following general formula (1), and more preferably the structural unit represented by the general formula (1) is 90 to A polyimide resin containing 100 mol% is preferable.

[In the formula, Ar ₁ represents a tetravalent organic group having an aromatic ring, and Ar ₂ represents a divalent organic group represented by the following general formula (2) or (3).

[Wherein, R _{1 to} R ₈ in the general formula (2) or the general formula (3) are each independently a hydrogen atom, a fluorine atom, an alkyl group or an alkoxy group having 1 to 5 carbon atoms, or a fluorine-substituted hydrocarbon. In the general formula (2), at least one of R _{1 to} R ₄ and R _{1 to} R _{8 in} the general formula (3) is a fluorine atom or a fluorine-substituted group. It is a hydrocarbon group. ]

  Other polyimide resins that may be added at a maximum of 10 mol% in addition to the polyimide resin according to the general formula (1) are not particularly limited, and general acid anhydrides and diamines can be used. However, among the acid anhydrides preferably used, pyromellitic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, 1,4-cyclohexanedicarboxylic acid, 1, 2,3,4-cyclobutanetetracarboxylic dianhydride, 2,2′-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride, etc., and 4,4′-diamino as diamine Diphenylsulfone, trans-1,4-diaminocyclohexane, 4,4′-diaminocyclohexylmethane, 2,2′-bis (4-aminocyclohexyl) -hexafluoropropane, 2,2′-bis (trif Oromechiru) -4,4'-diamino-bi cyclohexane.

As above-mentioned, it is preferable that the polyimide film in this invention has a fluorine atom or a fluorine substituted hydrocarbon group in a part in the chemical structure. For that purpose, a fluorine atom or a fluorine-substituted hydrocarbon group may be contained in Ar ₁ in the general formula (1), may be contained in Ar ₂ , or may be contained in both. As a more preferred embodiment, in the general formula (2), at least one of R _{1 to} R ₄ may be a fluorine atom or a fluorine-substituted hydrocarbon group. In the general formula (3), R _{1 to} R ₈ At least one of these may be a fluorine atom or a fluorine-substituted hydrocarbon group.

Specific examples of suitable R _{1 to} R ₈ include —H, —CH ₃ , —OCH ₃ , —F, —CF ₃ , and more preferably, at least one of R _{1 to} R ₈ is — F, or may be from either -CF _3.

Moreover, specific examples of Ar _{1 in} the general formula (1) include the following tetravalent acid anhydride residues.

Further, as a specific diamine residue give Ar ₂ in the general formula (1), for example, include the following.

As a particularly preferable constitution constituting the polyimide film used in the present invention, a polyimide composed of structural units of the following formulas (4) and (5) is used. Here, the ratio of the formulas (4) and (5) in the polyimide is a molar ratio (4) :( 5) = 50: 50 to 100: 0, preferably (4) :( 5) = 70. : 30 to 95: 5, more preferably (4) :( 5) = 85: 15 to 95: 5, and these are contained in the polyimide in an amount of 90 to 100 mol%.

  In the above, in the present invention, structural units other than those represented by formulas (4) and (5) may be included in a range of less than 10 mol%. The raw material diamine and acid anhydride used there are not particularly limited, and one or more known diamines and acid anhydrides can be appropriately selected and used.

  The polyimide film can be produced by polymerizing raw material diamine and acid anhydride in the presence of a solvent to obtain a polyimide precursor resin, and then imidizing by heat treatment. The molecular weight of the polyimide resin is mainly controllable by changing the molar ratio of the raw material diamine and acid anhydride, but the molar ratio is usually 1: 1.

  As a production method, first, diamine is dissolved in an organic solvent, and then acid dianhydride is added to the solution to produce polyamic acid which is a polyimide precursor. Examples of the organic solvent include dimethylacetamide, dimethylformamide, n-methylpyrrolidinone, 2-butanone, diglyme, xylene and the like, and these can be used alone or in combination of two or more. The subsequent imidization step can be performed by chemical imidization using a condensing agent such as acetic anhydride in addition to thermal imidation by heat dehydration shown in the following method for producing a polyimide film.

  As a method for producing a polyimide film, a gel film having a self-supporting property is obtained by casting a polyamide acid or polyimide resin solution, which is a raw material of a polyimide film, onto a base substrate such as a metal roll and heating and drying on the base substrate After that, a method of peeling from the base substrate and heating at a higher temperature while being held by a tenter or the like to obtain a polyimide film is excellent in productivity and is most widely used industrially. However, in this method, the film is stretched due to the stress applied to the film when the gel film is peeled from the base substrate and the tension in the tenter during heat treatment, and the retardation increases. For this reason, it is unpreferable as a manufacturing method of the polyimide film of the present invention.

  The method for producing a polyimide film according to the present invention includes, for example, applying a polyamic acid resin solution onto an arbitrary base substrate such as a copper foil using an applicator, predrying, and further removing the solvent and imidizing. For this purpose, it is preferable to perform a heat treatment for removing the base substrate used at the time of imidation by peeling or etching. When the resin solution is cast applied to the base substrate, the viscosity of the resin solution is preferably in the range of 500 to 70000 cps. In addition, coating may be performed after appropriately performing a surface treatment on the surface of the base substrate to be the application surface of the resin solution. In the above, it is appropriate to perform the drying conditions at 150 ° C. or lower for 2 to 30 minutes, and the heat treatment for imidization at a temperature of about 130 to 360 ° C. for about 2 to 30 minutes.

  In the above polyimide film manufacturing method, in which the polyimide film is removed from the base substrate after the polyamide acid resin solution is applied on the base substrate and the heat treatment is completed, in order to reduce the in-plane direction retardation, It is preferable to reduce the in-plane variation of the film temperature. The in-plane variation of the film temperature during the heat treatment is preferably 6 ° C. or less, more preferably 2 ° C. or less.

  In order to reduce the in-plane variation of the film temperature, the polyamic acid resin and the base substrate are laminated by a forced convection oven with a sufficient time after reaching a predetermined temperature and a uniform furnace temperature. The body should be heat treated. In addition, when the laminate of the resin and the supporting base material is brought into direct contact with the inner surface of the furnace or the shelf board during heating, local temperature unevenness may occur. Furthermore, the laminate of the polyamic acid resin and the base substrate may be preheated before the heat treatment.

  If the thickness of the base substrate is large, the heat capacity becomes large, and further, the resin is not sufficiently heated from the base substrate side, which causes a temperature variation in the film surface, which is not preferable. The thickness of the support substrate is preferably 3 mm or less, more preferably 0.8 mm or less. In order to reduce the temperature variation, a metal having high thermal conductivity may be used for the base substrate.

  In order to reduce the retardation in the in-plane direction, it is preferable to reduce the in-plane variation of the film thickness. The in-plane variation in the thickness of the polyimide film after completion of the heat treatment is preferably 1/10 or less, more preferably 1/20 or less of the film thickness.

  The coating method is not particularly limited, and a known method such as a spin coater, a spray coater, a bar coater, or a method of extruding from a slit nozzle can be applied as long as a predetermined thickness accuracy can be obtained. In general, when applying a highly oriented resin solution having a rigid molecular chain, it is known that retardation occurs due to shear stress generated during application, but surprisingly, in the present invention, The method of application does not affect the retardation. For this reason, the arbitrary application | coating method which balances film thickness precision and productivity can be selected.

  By the heat treatment, while having a low thermal expansion coefficient on the base substrate, a retardation in the in-plane direction is small, and a polyimide film having a transmittance in the wavelength region of 440 nm to 780 nm of 80% or more is obtained. In the present invention, the heating time in the high temperature heating temperature range from the temperature 20 ° C. lower than the maximum heating temperature (maximum reached temperature) at the time of temperature increase particularly in the thermal heat treatment (hereinafter referred to as high temperature holding time). It is preferable to make it within 15 minutes. When this high temperature holding time exceeds 15 minutes, the transparency of the polyimide film tends to be lowered due to coloring or the like. In order to maintain transparency, it is better that the high temperature holding time is short. However, if the time is too short, the effect of heat treatment may not be sufficiently obtained. The optimum high temperature holding time varies depending on the heating method, the heat capacity of the base substrate, the thickness of the polyimide film, etc., but is preferably 0.5 minutes or more and 5 minutes or less.

  In the above polyimide film manufacturing method in which the polyimide film is removed from the base substrate after the polyamic acid resin solution is applied on the base substrate and the heat treatment is completed, the base substrate is removed from the base film by etching. After the substrate is removed, washing with running water, removal of surface water droplets with an air knife, and drying by oven heating are usually performed. When the polyimide film is stretched due to the stress generated on the polyimide film during these steps, the in-plane retardation increases. This tendency is particularly noticeable because polyimide films having a low coefficient of thermal expansion have rigid molecular chains. For this reason, after etching the base substrate to form a single polyimide film, it is preferable to reduce the stress in the surface direction applied to the film.

  In order to prevent stretching of the polyimide film in a series of processes accompanying etching, after forming the stress relaxation layer on the polyimide film, the polyimide film and the stress relaxation layer are laminated, and the base substrate is etched. A method of dispersing the stress generated during the process in the polyimide film and the stress relaxation layer is also good. The method of forming the stress relaxation layer is not particularly limited. For example, a resin film or a metal foil having an appropriate thermal expansion coefficient as the stress relaxation layer is formed by a method such as bonding, coating, vapor deposition, sputtering, or the like using an adhesive. be able to.

  In the above polyimide film manufacturing method, in which the polyimide film is removed from the base substrate after the polyamic acid resin solution is applied on the base substrate and the heat treatment is completed, the polyimide film is removed when the base substrate is removed by peeling. When stress is applied to the film and the film is stretched in the plane direction, retardation in the in-plane direction increases. For this reason, it is preferable to peel so that the stress of the surface direction concerning a polyimide film may become small in the case of peeling.

  In order to prevent stretching when the polyimide film is peeled off from the base substrate, after the stress relaxation layer is formed on the polyimide film, the polyimide film and the stress relaxation layer are peeled off from the base substrate and peeled off. A method in which necessary stress is dispersed in the polyimide film and the stress relaxation layer is also good.

  The stress relaxation layer may be formed directly on the polyimide film, or after functional layers such as an electrode layer, a light emitting layer, a thin film transistor, a wiring layer, and a barrier layer are formed on the polyimide film, the stress relaxation layer is formed. May be formed.

  The stress relaxation layer may be a member constituting the display device in a state where the polyimide film is removed from the base substrate and then laminated without being separated from the polyimide film. Examples of members constituting the display device include a display unit such as an organic EL light emitting layer and electronic paper, an adhesive, a pressure-sensitive adhesive, a barrier film, a protective film, or a color filter. Here, in the case of a display device having a color filter, a color filter layer composed of a black matrix and colored portions such as R, G, and B is formed on the polyimide film before peeling the polyimide film from the base substrate. May be used as a stress relaxation layer.

  In addition, in order to facilitate the peeling of the polyimide film from the base substrate and prevent stretching, the polyimide film is fixed to another substrate and stripped in a state in which stretching in the surface direction of the polyimide film is prevented. A method of separating the film from the substrate may also be used. The method of fixing the polyimide film to the substrate is to use a substrate having pores connected from the inside of the substrate to the surface of the substrate, reduce the pressure inside the substrate, and fix the polyimide film on the surface of the substrate using vacuum. After peeling from the base substrate, a method of releasing the pressure reduction inside the substrate and separating the polyimide film from the substrate may be used. The substrate may be a resin or a metal such as stainless steel. The surface of the substrate on the polyimide film side may be a curved surface.

  In order to prevent stretching when the polyimide film is peeled from the base substrate, other known methods can also be applied. In JP-T-2007-512568, a yellow film such as polyimide is formed on glass, then a thin film electronic element is formed on the yellow film, and then the glass is irradiated with UV laser light through the glass to the bottom surface of the yellow film. And the yellow film can be peeled off. According to this method, since the polyimide film is separated from the glass by UV laser light, no stress is generated at the time of peeling, which is one of the preferable methods for the peeling process of the present invention. However, it is also disclosed that, unlike a yellow film, a transparent plastic does not absorb UV laser light, and therefore it is necessary to previously provide an absorption / release layer such as amorphous silicon under the film.

  JP-T-2012-511173 discloses that it is necessary to use a laser having a spectral range of 300 to 410 nm in order to separate the glass and the polyimide film by irradiation with UV laser light.

  Since the wavelength of light emitted from the light emitting layer of the organic EL is mainly from 440 nm to 780 nm, the average transmittance in this wavelength region is at least 80% or more as a support substrate used in the organic EL device. Desired. On the other hand, when the glass and polyimide film are peeled off by irradiation with the UV laser light described above, if the transmittance at the wavelength of the UV laser light is high, it is necessary to provide an absorption / peeling layer under the film, This reduces productivity. In order to perform peeling without providing an absorption / peeling layer, it is necessary that the polyimide film itself absorbs laser light. Therefore, the transmittance of the polyimide film at 400 nm is preferably 80% or less, more preferably. Is 60% or less, and more preferably 40% or less. Accordingly, it is possible to perform peeling by irradiation with UV laser light without providing an absorption / peeling layer while being transparent.

  Moreover, in this invention, the preferable thickness of a polyimide film is the range of 1 micrometer-50 micrometers, More preferably, it is the range of 3 micrometers-40 micrometers, Most preferably, it is the range of 5 micrometers-30 micrometers. If the thickness of the polyimide film is less than 1 μm, it is difficult to control with an applicator and the thickness tends to be non-uniform. Conversely, if it exceeds 50 μm, heat resistance and light transmittance may be reduced.

  Here, from the viewpoint of uniformly controlling the film thickness when coating using an applicator or the like, the polyamic acid used for forming the polyimide film and the degree of polymerization of the polyimide are within the viscosity range of the polyamic acid solution. When expressed, the solution viscosity is preferably in the range of 500 to 200,000 cP.

  The polyimide film used as the supporting substrate in the present invention has a transmittance of at least 80% in a wavelength region of 440 nm to 780 nm, a thermal expansion coefficient of 15 ppm / K or less, and a difference in thermal expansion coefficient from the gas barrier layer of 10 ppm. The polyimide film may be composed of a plurality of polyimide layers as long as it is less than / K. That is, since the polyimide having the structural unit represented by the general formula (1) described above has a relatively hard property with an elastic modulus of about 5 GPa to 10 GPa, a polyimide layer having a lower elastic modulus is used as a gas barrier. It may be arranged so as to be in contact with the layer so as to play a role of stress relaxation.

  When a plurality of polyimide layers are used, the polyimide layer in contact with the gas barrier layer preferably exhibits a lower elastic modulus than the polyimide layer (main polyimide layer) occupying the largest proportion of the polyimide film. Since the polyimide layer in contact with the gas barrier layer also functions as a stress relaxation layer that prevents stretching of the main polyimide layer having a low thermal expansion coefficient, the retardation of the polyimide film having low thermal expansion can be further reduced.

  Here, the elastic modulus of the polyimide layer in contact with the gas barrier layer is preferably less than 5 GPa, more preferably 0.1 GPa or more and less than 5 GPa, and particularly preferably 2 GPa or more and less than 5 GPa. A polyimide layer exhibiting such an elastic modulus can be formed of a widely known polyimide, but generally the transmittance in the visible light region of the polyimide is a structure represented by the general formula (1) described above. The thickness of the polyimide layer in contact with the gas barrier layer should be 0.5 μm to 10 μm, preferably 1 μm to 5 μm, since it is lower than the unitary polyimide and the CTE becomes relatively high. Is good. That is, when the polyimide film is formed from a plurality of polyimide layers, preferably, the polyimide layer (main polyimide layer) occupying the largest proportion of the thickness in the polyimide film is a structural unit represented by the above general formula (1). The polyimide layer which is formed in the above and has a lower elastic modulus on the gas barrier layer side so that the polyimide layer in contact with the gas barrier layer has a lower elastic modulus than other polyimide layers adjacent to the polyimide layer. To. The thickness ratio of the main polyimide layer and the polyimide layer exhibiting a low elastic modulus when the polyimide layer is composed of a plurality of polyimide layers (main polyimide layer / polyimide layer exhibiting a low elastic modulus) is preferably 3 to 50, and Preferably it is 5-20.

  The transmittance | permeability of the polyimide film used by this invention should just be 80% or more in the wavelength range of 440 nm to 780 nm by predetermined thickness, and the thickness range in particular is not restrict | limited. Preferably, it is preferably formed of polyimide that gives a transmittance of 80% or more in a wavelength region of 440 nm to 780 nm when a film having a thickness of 25 μm is formed. Composed. Particularly preferred polyimides are polyimides represented by the formulas (4) and (5).

  The present invention is an organic EL device having a gas barrier layer on a support substrate made of a polyimide film and further having an organic EL light emitting layer formed thereon, and as described above, an organic EL device using a resin as a support substrate. Then, in order to prevent moisture and oxygen from entering the organic EL light-emitting layer, it is common to provide a gas barrier layer on at least one side of the support substrate. Here, an inorganic oxide film such as silicon oxide, aluminum oxide, silicon carbide, silicon oxycarbide, silicon carbonitride, silicon nitride, silicon nitride oxide, etc. is suitably exemplified as a gas barrier layer having a barrier property against oxygen, water vapor, and the like. Is done. At that time, if the difference in CTE between the gas barrier layer of these inorganic oxides and the polyimide film of the supporting substrate is large, curling may occur during the subsequent TFT manufacturing process, dimensional stability may deteriorate, Occurrence may occur. In general, warpage is a problem when a large-area film is produced. However, in the case of the polyimide film of the present invention, since the difference in CTE from the gas barrier layer is small, problems such as these problems are solved. Table 1 shows typical inorganic films forming the gas barrier layer and their thermal expansion coefficients. Here, since the coefficient of thermal expansion varies depending on the manufacturing method even if the composition is the same, the values shown in Table 1 are approximate. Further, the gas barrier layer may be formed from one kind of the inorganic film as described above, or may be formed so as to include two or more kinds.

  When the gas barrier layer is formed on the support substrate made of the polyimide film, the gas barrier layer may be formed in a laminated state of the base substrate and the polyimide film, or may be formed on the polyimide film after the base substrate is removed. The thickness of the gas barrier layer is preferably 10 nm to 1 μm, more preferably 50 nm to 200 nm.

  As can be seen from Table 1, the CTE of the material forming the gas barrier layer is included in 0 to 10 ppm / K. Therefore, when the CTE of the polyimide film adjacent thereto is not a value close to this, warpage or the like occurs. Therefore, the polyimide film of the present invention has a thermal expansion coefficient of 15 ppm / K or less, preferably 0 to 10 ppm / K, and a difference in thermal expansion coefficient from the gas barrier layer is 10 ppm / K or less, preferably 0 to 5 ppm. / K. In addition, when a polyimide film is formed from a some polyimide layer, the thermal expansion coefficient in the whole polyimide film is represented (it is the same also about the characteristic of other polyimide films).

  The polyimide film in the present invention has a transmittance in the wavelength region of 440 nm to 780 nm of 80% or more, preferably 83% or more. If the transmittance in the above wavelength region is less than 80%, it is impossible to take out sufficient light (particularly in the case of a bottom emission structure). Furthermore, the polyimide film of the present invention has a heating weight reduction rate of 1.5% or less, preferably 1.3% or less when held at 460 ° C. for 90 minutes. If the heating weight reduction rate exceeds 1.5%, the TFT manufacturing process temperature cannot be withstood.

  In addition, the retardation in the in-plane direction of the polyimide film is 10 nm or less, preferably 5 nm or less. If the retardation in the in-plane direction exceeds 10 nm, a uniform contrast viewing angle characteristic may not be obtained. When external light is incident on the organic EL device, the external light is reflected by the electrodes, thereby reducing the contrast. In this case, there is a method of preventing with a circularly polarizing plate, but if the retardation is large, the prevention effect is lowered. Therefore, in order to obtain high contrast, the retardation is preferably as small as possible. Furthermore, the surface roughness Ra of the polyimide film is 5 nm or less, preferably 4 nm or less. When the surface roughness Ra exceeds 5 nm, the thickness of the organic EL layer becomes non-uniform, causing disconnection, uneven light emission, and color reproducibility. Furthermore, the polyimide film of the present invention has a humidity expansion coefficient of 15 ppm /% RH or less, preferably 0 to 10 ppm /% RH. If the humidity expansion coefficient exceeds 15 ppm /% RH, misalignment due to a dimensional change during the TFT process and a defect in a reliability test occur.

  According to the display device of the present invention, since a polyimide film having predetermined characteristics is used as a support base material, it can be made thin, light, and flexible, and is almost equivalent to a conventionally used glass substrate. Thus, a display device having performance equivalent to that of the conventional product can be realized.

FIG. 1 is a schematic cross-sectional view showing an example of an organic EL device having a bottom emission structure according to the present invention. FIG. 2 is a schematic cross-sectional view showing an example of an organic EL device having a top emission structure according to the present invention.

  The present invention will be described in more detail with reference to the drawings. In each drawing and each example, the same or similar components are denoted by the same reference numerals and description thereof is omitted.

  FIG. 1 is a schematic cross-sectional view of the organic EL device according to the present invention having a bottom emission structure. 1 in FIG. 1 represents a supporting substrate, and in the present invention, the supporting substrate 1 is formed from a polyimide film. A gas barrier layer 3-1 is provided on one surface (main surface) of the support substrate 1, and moisture permeability of the support substrate 1 is prevented by the gas barrier layer 3-1. Further, a circuit configuration layer 5 including a thin film transistor TFT (not shown) is formed on the upper surface of the gas barrier layer 3-1. The circuit configuration layer 5 is configured by forming an anode electrode 6 made of, for example, an ITO (Indium Tin Oxide) transparent conductive film for each of the pixel regions arranged in a matrix on the upper surface thereof.

  A light emitting layer 7 is formed on the upper surface of the anode electrode 6, and a cathode electrode 8 is formed on the upper surface of the light emitting layer 7. The cathode electrode 8 is formed in common for each pixel region. A gas barrier layer 3-2 is formed so as to cover the surface of the cathode electrode 8. Further, a sealing substrate 2 is disposed on the outermost surface of the organic EL device for surface protection. A gas barrier layer 3-3 is preferably formed on the surface of the sealing substrate 2 on the cathode electrode 8 side. The sealing substrate 2 is preferably attached to the cathode electrode 8 with an adhesive (adhesive layer) 9 containing a desiccant. As described above, in the organic EL device, each thin film is generally formed on the support base material 1 in the above order, and finally sealed with the sealing substrate 2. The sealing substrate 2 is generally attached with an adhesive containing a water absorbing material.

  Here, driving of the organic EL device requires a thin film transistor having high mobility, and generally a low-temperature polysilicon TFT is used. The processing temperature is generally considered to be 450 ° C. or higher. In addition, although oxide semiconductor TFTs using IGZO having relatively high mobility in low temperature processing have been studied, recent findings indicate that high temperature processing at 400 ° C. or higher is necessary to increase TFT stability. I understand. Therefore, the polyimide film as the supporting base material needs to be able to withstand the heat treatment process of the TFT.

  The light-emitting layer 7 is formed of a multilayer film (anode electrode-light-emitting layer 7-cathode electrode) such as a hole injection layer-hole transport layer-light-emitting layer-electron transport layer. In particular, since the light emitting layer 7 is deteriorated by moisture or oxygen, it is generally formed by vacuum deposition and continuously formed in vacuum including electrode formation.

  FIG. 2 is a schematic cross-sectional view of an organic EL device having a top emission structure. Here, in FIG. 2, the support base material 1 is comprised from the transparent polyimide film. A gas barrier layer 3-1 is formed on one surface (main surface) of the support substrate 1. The support substrate 1 is prevented from moisture permeation by the gas barrier layer 3-1. On the upper surface of the gas barrier layer 3-1, a circuit component layer 5 including a thin film transistor 4 (not shown in detail) is formed. In the case of the top emission structure, light can be extracted also from above the thin film transistor 4, so that the light utilization efficiency is increased. The circuit component layer 5 includes, for example, a metal thin film as a reflective electrode and an ITO (Indium Tin Oxide) thin film for work function adjustment for each pixel region arranged in a matrix on the upper surface of the anode electrode 6. Is formed and configured. A light emitting layer 7 is formed on the upper surface of the anode electrode 6, and a cathode electrode 8 is formed on the upper surface of the light emitting layer 7. The cathode electrode 8 is formed in common for each pixel region. As the cathode electrode 8, a semi-transmissive thin film such as silver or an alloy thereof capable of adjusting the work function and partially transmitting light is generally used. In order to reduce the electrode resistance, a transparent electrode IZO (Indium Zinc Oxide) or the like is generally laminated.

  A gas barrier layer 3-2 is formed so as to cover the surface of the cathode electrode 8. Further, a sealing substrate 2 is disposed on the outermost surface of the organic EL device for surface protection. A barrier layer 3-3 is preferably formed on the surface of the sealing substrate 2 on the cathode electrode 8 side. The sealing substrate 2 is generally attached to the cathode electrode 8 with an adhesive 9 containing a desiccant. Gas barrier layer 3-2-adhesive 9-gas barrier layer 3-3-sealing substrate 2 needs to be transparent.

  In the case of the top emission structure, the support substrate 1 does not necessarily need to be transparent, but if it is transparent, there is another effect of the transparent support substrate, such as the TFT pattern can be observed from the surface on the support substrate side. . On the other hand, the sealing substrate 2 needs to be transparent, and if the polyimide film in the present invention is also used for the sealing substrate 2, the thermal expansion coefficient and the humidity expansion coefficient of the support base 1 and the sealing substrate 2 are increased. Since the same, it is possible to obtain an effect that there is little possibility of warping and destruction of the completed organic EL device.

  The organic EL device of the present invention can also be applied to organic EL lighting. Here, the organic EL illumination generally has a bottom emission structure excluding the four layers of the thin film transistor shown in FIG. However, since the thin film transistor 4 is not provided, it is necessary to reduce the resistance of the anode electrode 6. The anode electrode 6 is generally a transparent electrode such as ITO (Indium Tin Oxide), and the electrode resistance decreases as the temperature is increased. In the case of ITO, heat treatment at 200 to 300 ° C. is common. Note that organic EL illumination is in the direction of increasing size, and the ITO electrode is becoming insufficient in resistance, and various alternative electrode materials are being searched for. In this case, generally, there is a high possibility that a temperature higher than 200 to 300 ° C. is required, and the polyimide film according to the present invention can be preferably used.

  Hereinafter, the contents of the present invention will be described more specifically based on examples and the like, but the present invention is not limited to the scope of these examples.

(Formation method and characteristics of polyimide film as support substrate)
First, the abbreviations for monomers and solvents used in the synthesis of polyimide, and various physical property measurement methods and conditions in the examples are shown below.

TFMB: 2,2′-bis (trifluoromethyl) -4,4′-diaminobiphenyl PMDA: pyromellitic dianhydride DMAc: N, N-dimethylacetamide 6FDA: 2,2′-bis (3,4- Dicarboxyphenyl) hexafluoropropane dianhydride BPDA: 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride

"Thermal expansion coefficient (CTE)"
Tensile test of polyimide film with a size of 3mm x 15mm in a temperature range from 30 ° C to 260 ° C at a constant rate of temperature increase (20 ° C / min) while applying a 5.0 g load with a thermomechanical analysis (TMA) device The coefficient of thermal expansion (ppm / K) was measured from the amount of elongation of the polyimide film with respect to temperature.

"Transmissivity"
The average value of the light transmittance from 440 nm to 780 nm was determined for a polyimide film (50 mm × 50 mm) with a U4000 spectrophotometer.

"Thermal weight reduction rate"
Using TG / DTA7200 manufactured by SII Nanotechnology, the temperature was maintained at 460 ° C. for 90 minutes, and the weight loss before and after heating was measured.

"Retardation"
Retardation in the in-plane direction of the polyimide film was determined using a spectroscopic polarimeter “Poxy-spectra” manufactured by Tokyo Instruments. The measurement was performed in the range of 400 nm to 800 nm. Table 2 shows the measured value at 600 nm.

"Surface roughness"
About surface roughness Ra of the polyimide film of the surface which is not touching the base substrate at the time of film preparation, the surface observation was performed in tapping mode using the atomic force microscope (AFM) "Multi Mode8" by Bruker. Observation of a 10 μm square field of view was performed four times, and the average value thereof was obtained. The surface roughness (Ra) represents the arithmetic average roughness (JIS B0601-1991).

"Surface scratch"
The surface of the polyimide film was observed in the scan assist mode using a Bruker atomic force microscope (AFM) “Multi Mode 8” for the presence or absence of scratches on the air surface (the surface not touching the base substrate during film creation). . A 20 μm square visual field observation was performed four times, where “◯” was given when no flaws were observed, “Δ” when fine flaws were observed, and “X” when streak-like flaws were observed.

"Humidity expansion coefficient"
Cut into a size of 25 cm × 25 cm in the state of a laminated body of copper foil and polyimide film, an etching resist layer is provided on the copper foil side, and this has 16 square points of 16 mm on four sides of a square of 30 cm on one side. It was formed in a pattern to be placed in place. The exposed portion of the etching resist opening was etched to obtain a CHE measurement polyimide film having 16 copper foil remaining points. After drying this film at 120 ° C. for 2 hours, each film was allowed to stand for 24 hours at 23 ° C./30% RH / 50% RH / 70% RH constant temperature and humidity at 24 ° C. and measured with a two-dimensional measuring machine. The humidity expansion coefficient (ppm /% RH) was determined from the dimensional change between the copper foil points at humidity.

"crack"
A 50 nm silicon nitride film was formed by CVD, and the occurrence of cracks was observed with a microscope KH-7700 manufactured by Yamato Scientific Co., Ltd. In a 10 mm square field of view, when the number of cracks is 10 or more, the evaluation result is “X”, when the number is 1 or more and less than 9, the evaluation result is “◯”, and when there is no crack, the evaluation result is “◎”. It was.

"curl"
As a gas barrier layer, a 50 nm silicon oxide film was formed by CVD to prepare polyimide-gas barrier layer laminates having a size of 10 cm square and 100 cm square. The four corners that floated when placed on a flat surface with the convex surface down were visually observed.

  Next, manufacturing conditions in the examples are shown below.

"Application"
An applicator adjusted so that the in-plane variation in the thickness of the polyimide film after heat treatment was 1 μm or less was used.

"Heat treatment"
In heat treatment using a hot air oven, a forced convection type hot air oven equipped with a blower fan was used, and heat treatment was started one hour after reaching a predetermined temperature. The laminate of the base substrate and the resin was placed in the center of the hot air oven where the hot air hits the most, and was placed on a table made of stainless steel so as to prevent the hot air from circulating. The temperature variation at the position of the laminate was 2 ° C.

  In the heat treatment using a nitrogen oven, the heat treatment was performed by a general method without particularly considering the retardation. That is, using a nitrogen oven set to a predetermined temperature, a base substrate and a resin laminate were placed on a shelf board (stainless steel punching metal), and heat treatment was performed. The temperature variation of this nitrogen oven was 6 ° C.

[Example 1]
(Polyimide A)
Under a nitrogen stream, 25.2 g of TFMB was dissolved in the solvent DMAc while stirring in a 200 ml separable flask. Next, 14.5 g of PMDA and 5.2 g of 6FDA were added to this solution. Thereafter, the solution was stirred at room temperature for 5 hours to conduct a polymerization reaction, and kept for a whole day and night. A viscous polyamic acid solution was obtained, and it was confirmed that polyamic acid A having a high polymerization degree was produced.

  The polyamic acid solution obtained above was applied on an 18 μm thick copper foil (electrolytic copper foil “DFF” manufactured by Mitsui Mining & Smelting Co., Ltd.) using an applicator so that the film thickness after heat treatment was about 25 μm. Then, using a nitrogen oven, the temperature was raised from 90 ° C. to 360 ° C. at a rate of 22 ° C. per minute to obtain a laminate of copper foil and polyimide. Next, this laminate was immersed in a ferric chloride etching solution, and the copper foil was removed to obtain a film-like polyimide A. Table 2 shows the results of various evaluations of the obtained film-like polyimide A. Further, when the laminated body in which the gas barrier layer was formed by forming a silicon oxide film on the polyimide film A was observed, no curling was observed at a size of 10 cm square. On the other hand, slight curling occurred at a size of 100 cm square.

[Example 2]
(Polyimide B)
Under a nitrogen stream, 25.7 g of TFMB as diamine, 15.7 g of PMDA as acid anhydride, and 3.6 g of 6FDA while stirring in a 200 ml separable flask. Thereafter, the solution was stirred at room temperature for 5 hours to conduct a polymerization reaction, and kept for a whole day and night. A viscous polyamic acid solution was obtained, and it was confirmed that polyamic acid B having a high polymerization degree was produced.

  Using the polyamic acid solution obtained above, a film-like polyimide B was obtained in the same manner as in Example 1.

[Example 3]
(Polyimide C)
Under a nitrogen stream, 26.3 g of TFMB was dissolved in the solvent DMAc while stirring in a 200 ml separable flask. Next, 16.9 g of PMDA and 1.8 g of 6FDA were added to this solution. Thereafter, the solution was stirred at room temperature for 5 hours to conduct a polymerization reaction, and kept for a whole day and night. A viscous polyamic acid solution was obtained, and it was confirmed that polyamic acid C having a high polymerization degree was produced.

  Using the polyamic acid solution obtained above, the film thickness after heat treatment using an applicator on an 18 μm thick copper foil (electrolytic copper foil “DFF” manufactured by Mitsui Mining & Smelting Co., Ltd.) is about 25 μm. Using a hot air oven, the temperature was raised from 90 ° C. to 360 ° C. at a rate of 22 ° C. per minute to obtain a laminate of copper foil and polyimide film. Next, after sticking an adhesive film (PET film 100 μm, adhesive 33 μm) on the surface of the polyimide film, this laminate was immersed in a ferric chloride etchant to remove the copper foil, and from the adhesive film to the polyimide film Was obtained to obtain a film-like polyimide C.

[Comparative Example 1]
(Polyimide D)
A film-like polyimide D was obtained in the same manner as in Example 3 except that 23.4 g of TFMB was used as the diamine and 10.3 g of PMDA and 11.3 g of 6FDA were used as the acid anhydride.

[Comparative Example 2]
(Polyimide E)
A film-like polyimide E was obtained in the same manner as in Example 3 except that 23.0 g of TFMB was used as the diamine and 9.3 g of PMDA and 12.7 g of 6FDA were used as the acid anhydride.

[Comparative Example 3]
(Polyimide F)
A film-like polyimide F was obtained in the same manner as in Example 3 except that 23.5 g of TFMB was used as the diamine and 21.5 g of BPDA was used as the acid anhydride.

[Example 4]
Under a nitrogen stream, 18.9 g of TFMB was dissolved in the solvent DMAc while stirring in a 200 ml separable flask. Then 26.1 g of 6FDA was added to this solution. Thereafter, the solution was stirred at room temperature for 5 hours to conduct a polymerization reaction, and kept for a whole day and night. A viscous polyamic acid solution G was obtained, and it was confirmed that a polyamic acid having a high degree of polymerization was produced.

  Next, the polyamic acid solution C obtained in Example 3 was applied onto a rolled copper foil having a thickness of 18 μm using an applicator so that the film thickness after the heat treatment was about 25 μm, and from 90 ° C. using a hot air oven. Heated at 130 ° C. for 1 to 5 minutes. Thereafter, the polyamic acid solution G was further applied on the obtained polyamic acid and copper foil laminate so as to have a thickness of 5 μm, and from 90 ° C. at a rate of 22 ° C. per minute using a hot air oven. The temperature was raised to 360 ° C. to obtain a laminate composed of copper foil and two layers of polyimide.

  Next, this laminate was immersed in a ferric chloride etchant to remove the copper foil, and a polyimide laminate film composed of polyimide C and polyimide G was obtained. Separately, a single layer film of polyimide G was prepared by the same method, and the elastic modulus was measured, and it was 4.5 GPa.

[Example 5]
The polyamic acid solution C was applied on a glass with a thickness of 0.5 mm using an applicator so that the film thickness after the heat treatment was about 25 μm, and was dried by heating at 130 ° C. using a hot air oven to obtain a resin solution. The solvent in it was removed. Next, after heating at 150 ° C., 200 ° C., and 250 ° C. for 30 minutes, heating was performed at 360 ° C. for 1 minute to obtain a laminate of glass and a polyimide film. Next, an adhesive film (PET film 100 μm, adhesive 33 μm) was bonded to the surface of the polyimide film, the polyimide film was peeled off from the glass, and then the polyimide film was separated from the adhesive film to obtain a film-like polyimide C.

[Example 6]
A film-like polyimide C was obtained in the same manner as in Example 5 except that the heating time at 360 ° C. was 30 minutes.

[Example 7]
A film-like polyimide C was obtained in the same manner as in Example 5 except that the heat treatment was performed in a nitrogen oven.

[Example 8]
A film-like polyimide C was obtained in the same manner as in Example 5 except that the thickness of the glass was 3 mm.

[Example 9]
A film-like polyimide C was obtained in the same manner as in Example 5 except that the film thickness after the heat treatment was applied to be about 11 μm.

[Example 10]
A film-like polyimide C was obtained in the same manner as in Example 9 except that the heat treatment was performed in a nitrogen oven.

[Example 11]
Under a nitrogen stream, 19.2 g of TFMB was dissolved in the solvent DMAc while stirring in a 200 ml separable flask. Next, 13.1 g of PMDA was added to this solution. Thereafter, the solution was stirred at room temperature for 5 hours to conduct a polymerization reaction, and kept for a whole day and night. A viscous polyamic acid solution was obtained, and it was confirmed that polyamic acid H having a high polymerization degree was produced.

  A film-like polyimide H was obtained in the same manner as in Example 5 except that the polyamic acid solution H was used.

[Example 12]
The polyamic acid solution was applied onto a copper foil having a thickness of 18 μm (electrolytic copper foil “DFF” manufactured by Mitsui Mining & Smelting Co., Ltd.) using an applicator so that the film thickness after the heat treatment was about 20 μm, The temperature was increased from 90 ° C. to 360 ° C. at a rate of 22 ° C. per minute to obtain a laminate of copper foil and polyimide. Without forming a stress relaxation layer, this laminate was immersed in a ferric chloride etchant, the copper foil was removed, and a film-like polyimide A was obtained.

[Example 13]
A film-like polyimide C was obtained in the same manner as in Example 7 except that the polyimide film was peeled from the glass without using an adhesive film.

[Example 14]
The polyamic acid solution C was applied onto a glass with a thickness of 0.5 mm using an applicator so that the film thickness after the heat treatment was about 11 μm, and was dried by heating at 130 ° C. using a nitrogen oven. The solvent was removed, and a laminate of glass and gel film was obtained. Next, the gel film was peeled off from the glass and fixed to a tenter clip, heated at 150 ° C., 200 ° C., and 250 ° C. for 30 minutes, and then heated at 360 ° C. for 1 minute to obtain polyimide C.

[Comparative Example 4]
A film-like polyimide G was obtained in the same manner as in Example 13 except that the polyamic acid solution G was used.

[Comparative Example 5]
Measurements were similarly made on a commercially available transparent polyimide film (Mitsubishi Gas Chemical Co., Ltd., Neoprim L, thickness 100 μm) (hereinafter referred to as polyimide I). The surface scratch was observed on both sides of the film.

  In addition, a 50 nm silicon nitride film was formed by CVD on polyimide films A to I and C and G polyimide laminate films, and cracks were observed with a microscope. No cracks were observed in A, B, C, and H. Further, many cracks were observed in D, E, F, G, and I.

  Table 2 shows the characteristic values of the obtained polyimide films A to I and C and G multilayer polyimide films (C / G films). As shown in Table 2, as is clear from the results obtained from Examples 1 to 14 and Comparative Examples 1 to 5, the polyimide satisfying the conditions of the present invention has excellent transparency and no warpage. The surface roughness and retardation of the polyimide resin layer surface were low. Moreover, curl when the gas barrier layer was formed was hardly confirmed, and the evaluation regarding the generation of cracks was also good. On the other hand, the polyimide resin layer that does not satisfy the conditions of the present invention has a large coefficient of thermal expansion, and curling is confirmed when the gas barrier layer is formed, and many cracks are generated.

  As described above, the present invention has been described using the embodiments. However, the configurations described in the respective embodiments so far are only examples, and the present invention can be appropriately changed without departing from the technical idea. .

DESCRIPTION OF SYMBOLS 1 ... Support base material, 2 ... Sealing substrate, 3-1, 3-2, 3-3 ... Gas barrier layer, 4 ... Thin film transistor, 5 ... Circuit composition layer containing a thin film transistor, 6 ... anode electrode, 7 ... light emitting layer, 8 ... cathode electrode, 9 ... adhesive layer, LT ... light extracted outside.

Claims (13)

A display device comprising a gas barrier layer on a support substrate made of a polyimide film,
The polyimide film has a transmittance in the wavelength region of 440 nm to 780 nm of 80% or more, a thermal expansion coefficient of 15 ppm / K or less, and a difference in thermal expansion coefficient from the gas barrier layer of 10 ppm / K or less. A display device.   The display device according to claim 1, wherein the polyimide film has an in-plane retardation of 10 nm or less and a surface roughness Ra of 5 nm or less.   The display device according to claim 1, wherein the polyimide film has a heating weight reduction rate of 1.5% or less when held at 460 ° C. for 90 minutes, and a humidity expansion coefficient of 15 ppm /% RH or less. .   The display device according to any one of claims 1 to 3, further comprising a gas barrier layer on a support substrate made of the polyimide film, and further an organic EL light emitting layer formed thereon.   The display device according to claim 4, wherein the display device has a bottom emission structure in which light is extracted from the surface of the support base material through the support base material made of the polyimide film.   The display device according to claim 4, wherein the display device has a top emission structure in which light is extracted from a surface opposite to the support base made of the polyimide film.   The display device according to claim 1, wherein the display device is an electronic paper in which an electronic ink layer is formed on a support substrate made of the polyimide film.   The display device according to claim 1, comprising a color filter, wherein a color filter layer is formed in advance on a support substrate made of the polyimide film.   The gas barrier layer is made of one or more selected from the group consisting of silicon oxide, silicon nitride, silicon nitride oxide, silicon carbide, silicon oxycarbide, silicon carbonitride, and aluminum oxide, and the heat of the gas barrier layer The display device according to claim 1, wherein an expansion coefficient is 0 ppm / K to 10 ppm / K.   The polyimide film has a plurality of polyimide layers having different elastic moduli, and the polyimide layer in contact with the gas barrier layer has a lower elastic modulus than other polyimide layers adjacent to the polyimide layer. The display device according to any one of 9.   The display device according to claim 10, wherein the elastic modulus of the polyimide layer in contact with the gas barrier layer is less than 5 GPa. A display device comprising a support substrate made of a polyimide film, wherein the polyimide film is composed of a single layer or a plurality of layers, and the polyimide constituting the main polyimide layer is 70 mol of the structural unit represented by the general formula (1) %, The thickness of the polyimide film is 50 μm or less, the in-plane retardation is 10 nm or less, and the surface roughness Ra is 5 nm or less.

[In the formula, Ar ₁ represents a tetravalent organic group having an aromatic ring, and Ar ₂ represents a divalent organic group represented by the following general formula (2) or (3).

[Wherein, R _{1 to} R ₈ in the general formula (2) or the general formula (3) are each independently a hydrogen atom, a fluorine atom, an alkyl group or an alkoxy group having 1 to 5 carbon atoms, or a fluorine-substituted hydrocarbon. In the general formula (2), at least one of R _{1 to} R ₄ and R _{1 to} R _{8 in} the general formula (3) is a fluorine atom or a fluorine-substituted group. It is a hydrocarbon group. ]] A polyimide or polyimide precursor resin solution is applied onto the base substrate so that the thickness of the polyimide film is 50 μm or less, heat treatment is completed, a polyimide film is formed on the base substrate, and stress relaxation is performed on the polyimide film. After forming the layer, the base substrate is removed in a state where the polyimide film and the stress relaxation layer are laminated, and the display device or the display device member is formed on the surface of the polyimide film opposite to the base substrate. It is a manufacturing method, Comprising: A polyimide film consists of a single layer or multiple layers of polyimide layers, and the polyimide which comprises the main polyimide layer is that the structural unit represented by General formula (1) is 70 mol% or more. A display device manufacturing method.

[In the formula, Ar ₁ represents a tetravalent organic group having an aromatic ring, and Ar ₂ represents a divalent organic group represented by the following general formula (2) or (3).

[Wherein, R _{1 to} R ₈ in the general formula (2) or the general formula (3) are each independently a hydrogen atom, a fluorine atom, an alkyl group or an alkoxy group having 1 to 5 carbon atoms, or a fluorine-substituted hydrocarbon. In the general formula (2), at least one of R _{1 to} R ₄ and R _{1 to} R _{8 in} the general formula (3) is a fluorine atom or a fluorine-substituted group. It is a hydrocarbon group. ]]

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