JP6968008B2 - Method for manufacturing polyimide film for display device support base material - Google Patents

Description

The present invention relates to a method for manufacturing a display device for forming a display device or a member for a display device on a support base material made of a polyimide film. Specifically, the present invention relates to a polyimide film for a support base material used for obtaining this display device. Regarding the manufacturing method.

Organic EL devices used for various display applications, including large displays such as televisions and small displays such as mobile phones, personal computers, and smartphones, are generally thin film transistors (hereinafter referred to as TFTs) on a glass substrate that is a supporting base material. Is formed, an electrode, a light emitting layer, and an electrode are sequentially formed, and finally, the electrode, a light emitting layer, and an electrode are separately hermetically sealed with a glass substrate, a multilayer thin film transistor, or the like. The structure of the organic EL device includes 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. Further, since the structure allows external light to pass through as it is, a transparent structure in which an electronic element such as a TFT can be seen through 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 make the organic EL device thinner, lighter, and more flexible, and further expand the applications of the organic EL device. However, since resins are generally inferior in dimensional stability, transparency, heat resistance, moisture resistance, gas barrier properties, etc., as compared with glass, various studies have been made.

For example, Japanese Patent Application Laid-Open No. 2008-231327 (Patent Document 1) relates to an invention relating to a polyimide useful as a plastic substrate for a flexible display and a precursor thereof, and has an alicyclic structure such as cyclohexylphenyltetracarboxylic acid. It has been reported that polyimides reacted with various diamines using tetracarboxylic acids containing the above have excellent 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 annealing step of the TFT, which generally reaches about 400 ° C. be. In addition, since the coefficient of thermal expansion (CTE) of the obtained polyimide is about 50 to 60 ppm / K, when a gas barrier layer is provided to impart gas barrier properties as in Patent Document 2 described later. In addition, it is difficult to obtain an organic EL device having excellent shape stability, such as peeling and cracking at the interface with the gas barrier layer.

Further, Japanese Patent Application Laid-Open No. 2011-238355 (Patent Document 2) describes a gas barrier film having excellent gas barrier properties and heat resistance, which is flexible and can be used as a base material for organic EL devices. Regarding the present invention, a flexible film such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polycarbonate (PC), polyvinyl chloride (PVC), and polyimide is used as a base material, and a stress relaxation layer is provided on one side thereof. By providing a gas barrier layer (inorganic barrier layer) containing at least a compound having silicon and oxygen, permeation 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 the generation of peeling and cracks due to the difference in the thermal properties (thermal expansion coefficient, thermal shrinkage rate) between the resin base material and the inorganic barrier layer is prevented. However, in the case of flexible films such as PET, PEN, PC, and PVC listed as supporting base materials here, the heat resistance is insufficient, and the heat treatment temperature in the annealing step of the TFT generally reaches about 400 ° C. There is a problem that cannot be tolerated. Further, the polyimide (gas barrier film 2-3) used in the comparative example is yellowish brown and has a lower transmittance than glass, so that it is not suitable as a resin as a substitute for glass.

Further, Japanese Patent Application Laid-Open No. 2007-46054 (Patent Document 3) relates to an invention relating to a low-colored polyimide resin composition useful for glass-type applications in the field of electronic displays, wherein a polyimide film containing a perfluoro-imide moiety has low thermal swelling. It is described that 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 of less than 80% in the visible light region, and the glass transition temperature does not reach 400 ° C., resulting in low thermal expansion. , It has not been possible to obtain a polyimide film that satisfies both transparency and heat resistance at the same time.

Similarly, in Japanese Patent Application Laid-Open No. 2-251564 (Patent Document 4), 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 rate, and a low thermal expansion property. , Discloses that it is applicable to materials for printed plates and optical waveguides. However, this Patent Document 4 does not describe the transmittance of the polyimide film in the visible light region. Further, when a transparent polyimide film having a low coefficient of thermal expansion is applied to a supporting base material of a display device, retardation becomes a problem, but there is no description of a means for solving this problem.

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

Japanese Unexamined Patent Publication No. 2008-231327 Japanese Unexamined Patent Publication No. 2011-238355 Japanese Unexamined Patent Publication No. 2007-46054 Japanese Unexamined Patent Publication No. 2-251564

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 a weak resistance to moisture, and the characteristics of the EL element, which is a light emitting layer, are deteriorated by the moisture. Therefore, when a resin is used as the support base material, a gas barrier layer must be formed on at least one side of the support base material in order to prevent the intrusion of water and oxygen into 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) of these materials is usually 0 to 10 ppm / K. On the other hand, since the transparent polyimide generally has a CTE of about 60 ppm / K, if the transparent polyimide is simply applied to the supporting base material of the organic EL device, the gas barrier layer may be cracked or peeled off due to thermal stress. Problems such as shaving may occur.

Further, in order to form a TFT required for display applications, an annealing step of reaching about 400 ° C. is required. In the case of a conventional glass substrate, there is no particular problem, but when a resin is used as a supporting base material, it is necessary to have heat resistance and dimensional stability at the heat treatment temperature of the TFT. On the other hand, unlike an organic EL device for lighting, a TFT may not be required, but the resistance value of the transparent electrode can be lowered by raising the film formation temperature of the transparent electrode adjacent to the supporting substrate, and the organic EL device can be used. Since the power consumption can be reduced, the supporting base material is also required to have heat resistance in the case of lighting applications. Further, as such a transparent electrode, a metal oxide such as ITO is generally used, and since they have a CTE of 0 to 10 ppm / K, they are of the same degree in order to avoid the problem of cracking and peeling. CTE resin is required.

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

In order to form the above-mentioned color filter, it is generally necessary to heat-treat the resist to reach 230 ° C. or higher. Further, in order to reduce the outgas from the resist, which may adversely affect the EL element, a heat treatment of 300 ° C. or higher may be performed. Further, when the thermal expansion coefficient and the humidity expansion coefficient of the support base material of the display unit provided with the EL element and the support base material of the color filter do not match, the dimensional change of each substrate is different due to the change of temperature and humidity. Will occur, causing warpage of the display device and peeling between the substrates. That is, it is necessary that the support base material of the color filter has heat resistance at the heat treatment temperature of the resist and dimensional stability equivalent to that of the support base material of the display portion. In order to solve the above problem, it is desirable that the support base material of the display portion of the organic EL and the support base material of the color filter are made of the same material.

The polyimide film is generally colored yellowish brown, and therefore, if a minute foreign substance is mixed in the polyimide film, there is a problem that it is difficult to find it with the naked eye or with a visual inspection device. In particular, it is extremely difficult to find foreign substances such as rust on metals that are similar in color to polyimide. The presence of foreign matter in the polyimide film causes defects such as defects in the gas barrier layer formed on the polyimide film, disconnection between electrodes, and short circuit. By using a transparent polyimide film, it becomes easy to find foreign substances, which contributes to the prevention of a decrease in yield. Therefore, even in a display device such as electronic paper, which does not require transparency in the supporting base material as a function of the display device, using a polyimide film having transparency leads to an improvement in productivity.

Similar to foreign matter, scratches on the surface of the polyimide film also cause defects such as defects in the gas barrier layer, disconnection between electrodes, and short circuits. When a polyimide film is applied to a supporting base material 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 application of the polyimide film, becomes a problem. Not only transparent polyimide film but also general yellowish brown polyimide film (Kapton, Apical, Upirex, etc.) is included in the polyimide film currently on the market, and the surface can be applied to the support base material of the display device without any problem. There is no state.

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

If the in-plane retardation of the supporting substrate exceeds 10 nm, it may not be possible to obtain a viewing angle characteristic with uniform contrast. When external light is incident on the organic EL device, the external light is reflected by the electrodes, which reduces the contrast. In this case, there is a method of preventing it with a circularly polarizing plate, but if the retardation is large, the preventive effect is reduced. Therefore, in order to obtain high contrast, the retardation should be as small as possible.

It is known that a polyimide film having a low coefficient of thermal expansion can be obtained by orienting a molecular chain by stretching a film using a tenter. However, there is a problem that the orientation of the molecular chains becomes non-uniform due to the variation in the stress applied to the film during stretching, which causes anisotropy in the refractive index and increases 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 a polyimide having a rigid chemical structure under appropriate conditions such as heat treatment conditions, film thickness, and solvent type. Has been done. However, since the molecular chains of polyimide having a rigid chemical structure are easily oriented, the orientation of the molecular chains becomes non-uniform due to in-plane variations in temperature, film thickness, etc. during heat treatment, and as a result, the refractive index differs. There is a problem that anisotropy is generated and the retardation becomes large.

That is, when replacing the glass substrate conventionally used in the display device with the supporting base material of the resin film, it is necessary to use a resin that can satisfy at least low CTE, heat resistance, and transparency at the same time, but all of these are satisfied. There was no resin film for the support substrate of the display device that could be used. Further, 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 peculiarity of the manufacturing process of the display device. Therefore, as a result of diligent research by the present inventors, a polyimide containing a predetermined repeating structure was produced under specific manufacturing conditions to form a polyimide film, and the difference in the coefficient of thermal expansion between the polyimide film and the gas barrier layer was obtained. It was found that a display device having excellent dimensional stability can be obtained when the coefficient is 10 ppm / K or less, and the present invention has been completed.

Therefore, an object of the present invention is that it can be made thin, lightweight, and flexible, has no problems of cracks and peeling due to thermal stress, has excellent dimensional stability, and prevents defects in the manufacturing process. It is an object of the present invention to provide a method for manufacturing a polyimide film for a supporting base material, which is used for obtaining a display device such as an organic EL display, an organic EL lighting, an electronic paper, and a liquid crystal display, which can exhibit good element characteristics in a long life.

In the present invention, the display device member is a member constituting the display device, and is a thin film transistor, an electrode layer, an organic EL light emitting layer, an electronic ink, a color filter, or two on a polyimide film. It forms one or more.

That is, in the present invention, a resin solution of polyimide or a polyimide precursor is applied onto a base substrate so that the thickness of the polyimide film is 3 to 40 μm, and the heat treatment is completed to form the polyimide film on the base substrate. It is a method for manufacturing a polyimide film for a display device support base material that separates the polyimide film from the base substrate (except when there is a thinning step of the polyimide film), and the polyimide film has a thickness of 440 nm to 780 nm. The average transmittance in the wavelength region is 80% or more, and the transmittance at 400 nm is 40% or less. In order to separate the polyimide film and the base substrate, UV laser light is applied to the bottom surface of the polyimide film through the base substrate. It is a method of manufacturing a polyimide film for a display device support base material, which is characterized by irradiating with.

〔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。〕 Further, in the present invention, a polyimide or a resin solution of a polyimide precursor is applied onto a base substrate so that the thickness of the polyimide film is 50 μm or less, the heat treatment is completed, and the polyimide film is formed on the base substrate. After forming the stress relaxation layer 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 member for the display device is on the surface opposite to the inorganic substrate of the polyimide film. The polyimide film is composed of a single layer or a plurality of polyimide layers, and the polyimide constituting the main polyimide layer has a structural unit represented by the general formula (1) of 70 mol. % Or more, which is a method for manufacturing a display device.

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

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

The polyimide film can be produced by polymerizing a raw material diamine and an 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 the 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 one or more of them can be used in combination.

〔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 the polyimide film used in the present invention, the diamine and the acid dianhydride, which are the raw materials thereof, may each be composed of a single type of monomer or may be composed of a plurality of types of monomers. The polyimide film of the present invention is preferably made of a polyimide having a structural unit represented by the following general formula (1). Alternatively, it is preferable that the copolymer uses a plurality of types of monomers having the structural unit represented by the following general formula (1), and more preferably, the structural unit represented by the general formula (1) is 90 to 90 to. It is preferable that the polyimide resin contains 100 mol%.

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

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

The other polyimide resins which may be added in a maximum amount of 10 mol% other than 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 acid dianhydride, 3,3', 4,4'-biphenyltetracarboxylic acid dianhydride, 1,4-cyclohexanedicarboxylic acid, 1, Examples thereof include 2,3,4-cyclobutanetetracarboxylic acid dianhydride and 2,2'-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride, and 4,4'-diamino as a diamine. Diphenylsulfone, trans-1,4-diaminocyclohexane, 4,4'-diaminocyclohexylmethane, 2,2'-bis (4-aminocyclohexyl) -hexafluoropropane, 2,2'-bis (trifluoromethyl) -4, 4'-diaminobicyclohexane and the like can be mentioned.

As described above, the polyimide film in the present invention preferably has a fluorine atom or a fluorine-substituted hydrocarbon group as part of its 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 preferable form, in the above general formula (2), _{at least one of R 1 to} R ₄ is preferably a fluorine atom or a fluorine-substituted hydrocarbon group, and in the above general formula (3), R _{1 to} R _{8 are preferable.} At least one of them is preferably a fluorine atom or a fluorine-substituted hydrocarbon group.

Suitable specific examples of 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 −.} It should be either F or -CF _3.

_{Further, as a specific example of Ar 1 in} the general formula (1), for example, the following tetravalent acid anhydride residue can be mentioned.

_{Further, as a specific diamine residue giving Ar 2} in the general formula (1), for example, the following can be mentioned.

A particularly preferable configuration for constituting the polyimide film used in the present invention is a polyimide composed of the structural units of the following formulas (4) and (5). Here, the ratio of the formulas (4) and (5) in the polyimide is a molar ratio of (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 the formulas (4) and (5) may be contained in the range of less than 10 mol%. The raw material diamine or acid anhydride used therefor is 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 a raw material diamine and an 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 the acid anhydride, but the molar ratio is usually 1: 1.

As a production method, first, a diamine is dissolved in an organic solvent, and then an acid dianhydride is added to the solution to produce a 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 may be used alone or in combination of two or more. The subsequent imidization step can be performed by using thermal imidization by heat dehydration shown in the following method for producing a polyimide film, or chemical imidization using a condensing agent such as acetic anhydride.

As a method for producing a polyimide film, a gel film having self-supporting property is obtained by casting a polyamic acid or a resin solution of polyimide, which is a raw material of the polyimide film, on a base substrate such as a metal roll and heating and drying on the base substrate. After that, the method of peeling from the base substrate and heating it at a higher temperature while holding it with a tenter or the like is excellent in productivity and is the most widely used in industry. 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 the heat treatment, and the retardation is increased. Therefore, it is not preferable as the method for producing the polyimide film of the present invention.

In the method for producing a polyimide film in the present invention, for example, a resin solution of polyamic acid is cast-applied on an arbitrary base substrate such as a copper foil using an applicator, pre-dried, and then solvent-removed and imidized. Therefore, a method of heat-treating and removing the base substrate used for imidization by peeling or etching is preferable. When the resin solution is cast-coated on the base substrate, the viscosity of the resin solution is preferably in the range of 500 to 70,000 cps. Further, the surface of the base substrate to be the coated surface of the resin solution may be appropriately surface-treated and then coated. In the above, it is appropriate that the drying condition is 150 ° C. or lower for 2 to 30 minutes, and the heat treatment for imidization is performed at a temperature of about 130 to 360 ° C. for about 2 to 30 minutes.

In the above-mentioned method for producing a polyimide film in which a resin solution of polyamic acid is applied on a base substrate and the polyimide film is removed from the base substrate after the heat treatment is completed, in order to reduce the retardation in the in-plane direction, the heat treatment is performed. 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 lower, more preferably 2 ° C. or lower.

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 in which the temperature inside the furnace becomes uniform after a sufficient time has passed after reaching the predetermined temperature. It is better to heat the body. Further, if the laminate of the resin and the supporting base material comes into direct contact with the inner surface of the furnace or the shelf plate during heating, local temperature unevenness may occur. Therefore, it is preferable to install the laminate so as not to come into contact with each other as much as possible. Further, 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 the resin is not sufficiently heated from the base substrate side, which is not preferable because it causes temperature variation in the film surface. The thickness of the base substrate is preferably 3 mm or less, more preferably 0.8 mm or less. Further, in order to reduce the temperature variation, it is also preferable to use a metal having high thermal conductivity for the base substrate.

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

The above-mentioned coating method is not particularly limited, and a known method, for example, a spin coater, a spray coater, a bar coater, or a method of extruding from a slit-shaped nozzle can be applied as long as a predetermined thickness accuracy can be obtained. In general, when a solution of a highly oriented resin having a rigid molecular chain is applied, it is known that shear stress generated at the time of application causes retardation. Surprisingly, in the present invention, it is known that retardation occurs. The method of application does not affect the retardation. Therefore, any coating method that achieves both film thickness accuracy and productivity can be selected.

By the above heat treatment, a polyimide film having a low coefficient of thermal expansion, small in-plane retardation, and a transmittance of 80% or more in the wavelength region of 440 nm to 780 nm can be obtained on the base substrate. In the present invention, in particular, the heating time (hereinafter referred to as high temperature holding time) in the high temperature heating temperature range from a temperature 20 ° C. lower than the maximum heating temperature (maximum ultimate temperature) at the time of temperature rise in the above thermal heat treatment to the maximum ultimate temperature is defined. It is preferably within 15 minutes. If this high temperature holding time exceeds 15 minutes, the transparency of the polyimide film tends to decrease due to coloring or the like. In order to maintain transparency, it is better to keep the high temperature for a short time, but if the time is too short, the effect of the 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, and the like, but is preferably 0.5 minutes or more and 5 minutes or less.

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

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

In the above-mentioned method for producing a polyimide film in which a resin solution of polyamic acid is applied on a base substrate and the polyimide film is removed from the base substrate after the heat treatment is completed, when the base substrate is removed by peeling, the polyimide film is peeled off. When stress is applied to the film and the film is stretched in the plane direction, the polyimide in the in-plane direction becomes large. Therefore, it is preferable to perform peeling so that the stress in the surface direction applied to the polyimide film at the time of peeling is small.

In order to prevent stretching when the polyimide film is peeled off from the base substrate, after forming a stress relaxation layer on the polyimide film, the polyimide film and the stress relaxation layer are peeled off from the base substrate in a laminated state for peeling. A method of dispersing the required stress in the polyimide film and the stress relaxation layer may also be used.

The stress relaxation layer may be formed directly on the polyimide film, or a functional layer such as an electrode layer, a light emitting layer, a thin film transistor, a wiring layer, and a barrier layer may be formed on the polyimide film, and then a stress relaxation layer may be 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 the members constituting the display device include a display unit such as an organic EL light emitting layer and electronic paper, an adhesive, an adhesive, a barrier film, a protective film, a color filter, and the like. 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 the polyimide film is peeled from the base substrate. May be used as a stress relaxation layer.

Further, 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, peeled in a state where the polyimide film is prevented from stretching in the surface direction, and then the polyimide is peeled off. A method of separating the film from the substrate may also be used. The method of fixing the polyimide film to the substrate uses a substrate having pores connecting from the inside of the substrate to the surface of the substrate, reduces the pressure inside the substrate, and uses vacuum to fix the polyimide film on the surface of the substrate. After peeling from the base substrate, the pressure inside the substrate may be released to separate the polyimide film from the substrate. The above-mentioned substrate may be a resin or a metal such as stainless steel. The surface of the substrate on the polyimide film side may be curved.

Further known other methods can also be applied to prevent stretching when the polyimide film is peeled from the base substrate. In Japanese Patent Publication No. 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 bottom surface of the yellow film is irradiated with UV laser light through the glass to form glass. It is disclosed that it is possible to peel off the yellow film. 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, unlike the yellow film, the transparent plastic does not absorb UV laser light, so it is also disclosed that an absorption / release layer such as amorphous silicon needs to be provided under the film in advance.

Japanese Patent Laid-Open No. 2012-511173 discloses that it is necessary to use a laser in the spectrum 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 the light emitted from the light emitting layer of the organic EL is mainly 440 nm to 780 nm, the average transmittance in this wavelength region is at least 80% or more for the supporting base material used in the organic EL device. Desired. On the other hand, when the glass and the polyimide film are peeled off by the irradiation of 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. Since the polyimide film itself needs to absorb laser light in order to perform peeling without providing an absorption / peeling layer, 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. This enables peeling by irradiation with UV laser light without providing an absorption / peeling layer while being transparent.

Further, in the present invention, the thickness of the polyimide film is preferably in the range of 1 μm to 50 μm, more preferably in the range of 3 μm to 40 μm, and particularly preferably in the range of 5 μm to 30 μm. If the thickness of the polyimide film is less than 1 μm, it is difficult to control it with an applicator and the thickness tends to be non-uniform. On the contrary, if it exceeds 50 μm, heat resistance and light transmittance may decrease.

Here, from the viewpoint of uniformly controlling the film thickness when coating using an applicator or the like, the degree of polymerization of the polyamic acid and the polyimide used for forming the polyimide film is 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 base material in the present invention has a transmittance of at least 80% or more in the wavelength region of 440 nm to 780 nm, a coefficient of thermal expansion of 15 ppm / K or less, and a difference in coefficient of thermal expansion 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 satisfied that it is / K or less. That is, since the polyimide having the structural unit represented by the above-mentioned general formula (1) has an elastic modulus of about 5 GPa to 10 GPa and has a relatively hard property, a polyimide layer having a lower elastic modulus is used as a gas barrier. It may be arranged in contact with the layer to play a role of stress relaxation.

When a plurality of polyimide layers are used, it is preferable that the polyimide layer in contact with the gas barrier layer exhibits a lower elastic modulus than the polyimide layer (main polyimide layer) in which the thickness occupies the largest ratio among the polyimide films. Since the polyimide layer in contact with the gas barrier layer also functions as a stress relaxation layer for preventing the main polyimide layer having a low coefficient of thermal expansion from stretching, it is possible to further reduce the retardation of the polyimide film having low thermal expansion.

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 by a widely known polyimide, but in general, the transmittance of those polyimides in the visible light region is the structure represented by the above-mentioned general formula (1). Since it is lower than the polyimide having a unit and the CTE is relatively high, the thickness of the polyimide layer in contact with the gas barrier layer is preferably 0.5 μm to 10 μm, preferably 1 μm to 5 μm. Is good. That is, when the polyimide film is formed from a plurality of polyimide layers, the polyimide layer (main polyimide layer) in which the thickness occupies the largest ratio among the polyimide films is preferably a structural unit represented by the above general formula (1). A polyimide layer having an elasticity lower than this is arranged on the gas barrier layer side so that the polyimide layer in contact with the gas barrier layer has a lower elasticity than other polyimide layers adjacent to the polyimide layer. To. When the polyimide layer is composed of a plurality of pieces, the thickness ratio between the thickness of the main polyimide layer and the polyimide layer showing a low elastic modulus (main polyimide layer / polyimide layer showing a low elastic modulus) is preferably 3 to 50, and more preferably. It is preferably 5 to 20.

The transmittance of the polyimide film used in the present invention may be 80% or more in a wavelength region of 440 nm to 780 nm at a predetermined thickness, and the thickness range is not particularly limited. Preferably, it is often formed of a polyimide that gives a transmittance of 80% or more in the wavelength region of 440 nm to 780 nm when the film is formed on a film having a thickness of 25 μm, and such a polyimide is the polyimide shown above. It is composed. A particularly preferable polyimide is a polyimide represented by the formula (4) and the formula (5).

The present invention is an organic EL device in which a gas barrier layer is provided on a support base material made of a polyimide film and an organic EL light emitting layer is further formed. As described above, the organic EL device uses a resin as the support base material. Then, in order to prevent the invasion of moisture and oxygen into the organic EL light emitting layer, it is common to provide a gas barrier layer on at least one side of the BR> A supporting base material. Here, as the gas barrier layer having a barrier property against oxygen, water vapor, etc., an inorganic oxide film such as silicon oxide, aluminum oxide, silicon carbide, silicon oxide, silicon carbide, silicon nitride, silicon nitride, etc. is preferably exemplified. Will be 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 base material is large, curls occur during the subsequent TFT manufacturing process, dimensional stability deteriorates, and cracks occur. Occurrence may occur. In general, warpage becomes a problem when a large-area film is manufactured, but in the case of the polyimide film of the present invention, the difference in CTE from the gas barrier layer is small, so that the problem of such problems is solved. Table 1 shows a typical inorganic film forming the gas barrier layer and its coefficient of thermal expansion. 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 guidelines. Further, the gas barrier layer may be formed from one type of the inorganic film as described above, or may be formed so as to include two or more types.

When the gas barrier layer is formed on the support base material made of the polyimide film, it may be formed in the state of a laminate of the base substrate and the polyimide film, or it 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 contained in 0 to 10 ppm / K. Therefore, if the CTE of the polyimide film adjacent to this is not close to this value, warpage or the like will occur. Therefore, the polyimide film of the present invention has a coefficient of thermal expansion of 15 ppm / K or less, preferably 0 to 10 ppm / K, and the difference in coefficient of thermal expansion from the gas barrier layer is 10 ppm / K or less, preferably 0 to 5 ppm. Make it / K. When the polyimide film is formed from a plurality of polyimide layers, it represents the coefficient of thermal expansion of the entire polyimide film (the same applies to the characteristics of other polyimide films).

Further, the polyimide film in the present invention has a transmittance of 80% or more, preferably 83% or more in the wavelength region of 440 nm to 780 nm. If the transmittance in the above wavelength region is less than 80%, it becomes impossible to sufficiently extract light emission (particularly in the case of a bottom emission structure). Further, the polyimide film of the present invention preferably 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 this heating weight reduction rate exceeds 1.5%, it cannot withstand the temperature of the TFT manufacturing process.

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

According to the display device of the present invention, since a polyimide film having predetermined characteristics is used as a supporting base material, it is possible to make it thin, lightweight, and flexible, and it is almost the same as a glass substrate generally used in the past. It is possible to realize a display device having the same performance as the conventional product by the manufacturing method of.

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

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

FIG. 1 is a schematic cross-sectional view of the organic EL device according to the present invention when it has a bottom emission structure. 1 in FIG. 1 represents a supporting base material, and in the present invention, the supporting base material 1 is formed of a polyimide film. A gas barrier layer 3-1 is provided on one surface (main surface) of the support base material 1, and the support base material 1 is prevented from permeating by the gas barrier layer 3-1. Further, a circuit constituent 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 constituent layer 5 is configured by forming, for example, an anode electrode 6 made of a transparent conductive film of ITO (Indium Tin Oxide) for each of the pixel regions arranged in a matrix on the upper surface thereof.

Further, 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 commonly formed in each pixel region. Then, the gas barrier layer 3-2 is formed so as to cover the surface of the cathode electrode 8. Further, a sealing substrate 2 is arranged on the outermost surface of this organic EL device for surface protection. It is preferable that the gas barrier layer 3-3 is formed on the surface of the sealing substrate 2 on the cathode electrode 8 side. Further, it is desirable that the sealing substrate 2 is 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 by the sealing substrate 2. The sealing substrate 2 is generally attached with an adhesive containing a water absorbing material.

Here, a thin film transistor having high mobility is required to drive the organic EL device, and a low-temperature polysilicon TFT is generally used. It is generally said that the treatment temperature should be 450 ° C. or higher. In addition, oxide semiconductor TFTs using IGZO, which has relatively high mobility in low temperature treatment, have been studied, but recent findings indicate that high temperature treatment of 400 ° C or higher is required to increase the stability of the TFT. I'm starting to understand. Therefore, the polyimide film of the supporting base material needs to be able to withstand the heat treatment step of this TFT.

Further, 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 and 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 made of a transparent polyimide film. A gas barrier layer 3-1 is formed on one surface (main surface) of the support base material 1. Moisture permeability of the support base material 1 is blocked by the gas barrier layer 3-1. A circuit constituent layer 5 including a thin film transistor 4 (details are not shown) is formed on the upper surface of the gas barrier layer 3-1. In the case of the top emission structure, light can be taken out from above the thin film transistor 4, so that the efficiency of light utilization is increased. The circuit constituent layer 5 has, for example, a metal thin film as a reflective electrode and an ITO (Indium Tin Oxide) thin film for adjusting work functions as anode electrodes 6 for each of the pixel regions arranged in a matrix on the upper surface thereof. It is formed and configured as. 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 commonly formed in 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 this electrode resistance, transparent electrodes IZO (Indium Zinc Oxide) and the like are generally laminated.

Further, the gas barrier layer 3-2 is formed so as to cover the surface of the cathode electrode 8. Further, a sealing substrate 2 is arranged on the outermost surface of this organic EL device for surface protection. It is preferable that the barrier layer 3-3 is 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-sealed substrate 2 needs to be transparent.

In the case of the top emission structure, the support base material 1 does not necessarily have to be transparent, but if it is transparent, the TFT pattern or the like can be observed from the surface of the support base material side, and there is another effect of the transparent support base material. .. On the other hand, the encapsulating substrate 2 needs to be transparent, and if the polyimide film of the present invention is used for this encapsulating substrate 2, the coefficient of thermal expansion and the coefficient of thermal expansion between the supporting base material 1 and the encapsulating substrate 2 can be increased. Since they are the same, the effect of warping the completed organic EL device and the possibility of its destruction can be obtained.

Further, the organic EL device of the present invention can also be applied to organic EL lighting. Here, the organic EL lighting generally has a bottom emission structure excluding the four thin film transistor layers of FIG. However, since there is no thin film transistor 4, it is necessary to reduce the resistance of the anode electrode 6. A transparent electrode such as ITO (Indium Tin Oxide) is generally used for the anode electrode 6, and the electrode resistance becomes lower as the temperature is increased. In the case of ITO, heat treatment at 200-300 ° C. is common. It should be noted that organic EL lighting is in the direction of increasing size, and the resistance value of the ITO electrode is becoming insufficient, and various alternative electrode materials are being sought. In this case, it is generally likely that a temperature higher than 200-300 ° 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.

(Method of forming a polyimide film as a supporting base material and its characteristics)
First, abbreviations for monomers and solvents for synthesizing polyimide, and methods for measuring various physical properties in Examples and their conditions 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

"Coefficient of thermal expansion (CTE)"
A tensile test of a polyimide film with a size of 3 mm × 15 mm in a temperature range of 30 ° C to 260 ° C at a constant temperature rise rate (20 ° C / min) while applying a load of 5.0 g using 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.

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

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

"Ritaration"
In-plane retardation of the polyimide film was determined using a spectroscopic polarimeter "Poxi-spectra" manufactured by Tokyo Instruments. The measurement was performed in the range of 400 nm to 800 nm. Table 2 shows the measured values at 600 nm.

"Surface roughness"
The surface roughness Ra of the polyimide film on the surface not touching the base substrate at the time of film production was observed in the tapping mode using an atomic force microscope (AFM) "Multi Mode 8" manufactured by Bruker. The field of view of 10 μm square was observed four times, and the average value was obtained. Surface roughness (Ra) represents arithmetic mean roughness (JIS B0601-1991).

"Surface scratches"
The surface of the polyimide film was observed in scan assist mode using an atomic force microscope (AFM) "Multi Mode 8" manufactured by Bruker Co., Ltd. to check for scratches on the air surface (the surface that did not touch the base substrate when the film was made). .. The field of view of 20 μm square was observed four times, and when no scratches were observed, it was marked with ◯, when minute scratches were observed, it was marked with Δ, and when streaky scratches were observed, it was marked with x.

"Humidity expansion coefficient"
A laminated body of copper foil and polyimide film was cut into a size of 25 cm x 25 cm, and an etching resist layer was provided on the copper foil side, which was formed on four sides of a square with a side of 30 cm at intervals of 10 cm, with 16 points having a diameter of 1 mm. It was formed into a pattern to be arranged in places. The exposed portion of the etching resist opening was etched to obtain a polyimide film for CHE measurement having 16 remaining copper foil points. After drying this film at 120 ° C. for 2 hours, it was allowed to stand at a constant temperature and humidity chamber of 23 ° C./30% RH, 50% RH, and 70% RH for 24 hours at each humidity, and measured by a two-dimensional length measuring machine. The humidity expansion coefficient (ppm /% RH) was obtained from the dimensional change between the copper foil points due to 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 Kagaku Co., Ltd. In a 10 mm square field of view, if the number of cracks is 10 or more, the evaluation result is "x", if it is 1 or more and less than 9, the evaluation result is "○", and if there are no cracks, the evaluation result is "◎". And said.

"curl"
A silicon oxide film having a diameter of 50 nm was formed by CVD as a gas barrier layer to prepare a polyimide-gas barrier layer laminate having a size of 10 cm square and 100 cm square. The four floating corners when placed on a flat surface with the convex surface facing down were visually observed.

Next, the manufacturing conditions in the examples are shown below.

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

"Heat treatment"
In the heat treatment using a hot air oven, a forced convection type hot air oven equipped with a blower fan was used, and the 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 was most strongly applied, and was placed on a table made of stainless wire so as not to obstruct the circulation of the hot air and heat-treated. The temperature variation at the position of this laminated body was 2 ° C.

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

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

The polyamic acid solution obtained above is applied onto a copper foil with 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 heat treatment is 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 to remove the copper foil, and a film-shaped polyimide A was obtained. Table 2 shows the results of various evaluations of the obtained film-shaped polyimide A. Further, when the curled state of the laminate in which the silicon oxide film was formed on the polyimide film A to form the gas barrier layer was observed, there was no curl in the size of 10 cm square. On the other hand, a slight curl occurred in the size of 100 cm square.

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

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

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

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

[Comparative Example 1]
(Polyimide D)
The same procedure as in Example 3 was carried out except that 23.4 g of TFMB was used as the diamine, 10.3 g of PMDA and 11.3 g of PMDA were used as the acid anhydride, and a film-like polyimide D was obtained.

[Comparative Example 2]
(Polyimide E)
The same procedure as in Example 3 was carried out 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 to obtain a film-shaped polyimideE.

[Comparative Example 3]
(Polyimide F)
The same procedure as in Example 3 was carried out except that 23.5 g of TFMB was used as the diamine and 21.5 g of BPDA was used as the acid anhydride to obtain a film-shaped polyimide F.

[Example 4]
18.9 g of TFMB was dissolved in the solvent DMAc under a nitrogen stream with stirring in a 200 ml separable flask. Then, 26.1 g of 6FDA was added to this solution. Then, the solution was stirred at room temperature for 5 hours to carry out a polymerization reaction, and the solution was kept overnight. 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 heat treatment was about 25 μm, and from 90 ° C. using a hot air oven. It was heated at a temperature of 130 ° C. for 1 to 5 minutes. Then, a polyamic acid solution G was further applied onto the obtained laminate of the polyamic acid and the copper foil to a thickness of 5 μm, and the polyamic acid solution G was further applied 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 a copper foil and two layers of polyimide.

Next, this laminate was immersed in a ferric chloride etching solution to remove the copper foil, and a polyimide laminate film composed of polyimide C and polyimide G was obtained. A single-layer film of polyimide G was separately prepared by the same method, and the elastic modulus was measured and found to be 4.5 GPa.

[Example 5]
The polyamic acid solution C is applied onto a glass having a thickness of 0.5 mm using an applicator so that the film thickness after heat treatment is about 25 μm, and the resin solution is heated and dried at 130 ° C. using a hot air oven. The solvent inside was removed. Next, after heating at 150 ° C., 200 ° C. and 250 ° C. for 30 minutes, heating at 360 ° C. for 1 minute was performed to obtain a laminate of glass and a polyimide film. Next, an adhesive film (PET film 100 μm, adhesive 33 μm) was attached 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-shaped polyimide C.

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

[Example 7]
A film-shaped 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-shaped 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-shaped polyimide C was obtained in the same manner as in Example 5 except that the film was applied so that the film thickness after the heat treatment was about 11 μm.

[Example 10]
A film-shaped 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]
19.2 g of TFMB was dissolved in the solvent DMAc under a nitrogen stream with stirring in a 200 ml separable flask. Then 13.1 g of PMDA was added to this solution. Then, the solution was stirred at room temperature for 5 hours to carry out a polymerization reaction, and the solution was kept overnight. A viscous polyamic acid solution was obtained, and it was confirmed that the polyamic acid H having a high degree of polymerization was produced.

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

[Example 12]
A polyamic acid solution is applied onto a copper foil with 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 heat treatment is about 20 μm, and a nitrogen oven is used. Using, 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. This laminate was immersed in a ferric chloride etching solution without forming a stress relaxation layer, and the copper foil was removed to obtain a film-like polyimide A.

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

[Example 14]
The polyamic acid solution C was applied onto a glass having a thickness of 0.5 mm using an applicator so that the film thickness after heat treatment was about 11 μm, and the mixture was heated and dried at 130 ° C. using a nitrogen oven, and then in a resin solution. The solvent was removed to obtain a laminate of glass and gel film. 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-shaped polyimide G was obtained in the same manner as in Example 13 except that the polyamic acid solution G was used.

[Comparative Example 5]
The same measurement was performed on a commercially available transparent polyimide film (manufactured by Mitsubishi Gas Chemical Company, Inc., Neoprim L, thickness 100 μm) (hereinafter referred to as polyimide I). Observation of surface scratches was performed on both sides of the film.

Further, when a 50 nm silicon nitride film was formed by CVD on the polyimide films A to I and the polyimide laminate film of C and G and the occurrence of cracks was observed with a microscope, the cracks were observed in the C / G laminate. No cracks were observed in A, B, C and H. In addition, 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 the multilayer polyimide film (C / G film) of C and G. 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 is excellent in transparency and has no warp. , The surface roughness and retardation values of the polyimide resin layer surface were low. In addition, almost no curl was confirmed when the gas barrier layer was formed, and the evaluation of crack generation was also good. On the other hand, in the case of the polyimide resin layer not satisfying the conditions of the present invention, the coefficient of thermal expansion was large, curling was confirmed when the gas barrier layer was formed, and many cracks were further generated.

Although the present invention has been described above with reference to examples, the configurations described in the previous examples are merely examples, and the present invention can be appropriately modified without departing from the technical idea. ..

1 ... Supporting substrate, 2 ... Sealing substrate, 3-1, 3-2, 3-3 ... Gas barrier layer, 4 ... Thin film transistor, 5 ... Circuit constituent layer including thin film transistor, 6 ... Anode electrode, 7 ... Light emitting layer, 8 ... Cathode electrode, 9 ... Adhesive layer, LT ... Light taken out to the outside.

Claims (5)

A polyimide or a resin solution of a polyimide precursor is applied onto the base substrate so that the thickness of the polyimide film is 3 to 40 μm, the heat treatment is completed to form the polyimide film on the base substrate, and the polyimide is formed from the base substrate. It is a method for manufacturing a polyimide film for a display device supporting base material that separates the film (except when there is a thinning step of the polyimide film).
The base substrate is made of glass having a thickness of 3 mm or less.
The polyimide film is composed of a single layer or a plurality of layers of polyimide layers, and the polyimide constituting the main polyimide layer has a structural unit represented by the following general formula (1), and the polyimide film has a wavelength of 440 nm to 780 nm. The average transmittance in the region is 80% or more, the transmittance at 400 nm is 40% or less, and the polyimide in the in-plane direction is 10 nm or less.
A method for producing a polyimide film for a display device support base material, which comprises irradiating the bottom surface of the polyimide film with UV laser light through the base substrate in order to separate the polyimide film and the base substrate.

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

_{[Here, R 1 to} R ₈ in the general formula (2) or the general formula (3) are independent of each other, a hydrogen atom, a fluorine atom, an alkyl group or an alkoxy group having 1 to 5 carbon atoms, or a fluorine-substituted hydrocarbon. It is a group, and _{at least one of R 1 to} R _{4 in the general formula (2) and R 1 to} R _{8 in} the general formula (3) are each a hydrogen atom or a hydrogen substitution. It is a hydrocarbon group. ] The method for producing a polyimide film for a display device support base material according to claim 1, wherein the polyimide film has a coefficient of thermal expansion of 15 ppm / K or less. The display device according to claim 1 or 2, wherein the polyimide film has a heating weight reduction rate of 1.5% or less and a humidity expansion coefficient of 15 ppm /% RH or less when held at 460 ° C. for 90 minutes. A method for manufacturing a polyimide film for a supporting base material. The display device support base material according to any one of claims 1 to 3, wherein the polyimide film has an in-plane variation in the thickness of the polyimide film after the completion of the heat treatment is 1/10 or less of the film thickness. Method for manufacturing polyimide film. The polyimide for a display device support base material according to any one of claims 1 to 4, wherein the in-plane variation of the film temperature during the heat treatment when forming the polyimide film on the base substrate is 6 ° C. or less. Film manufacturing method.

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