JP2019098690A - Polyimide composite film and flexible device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyimide film which is excellent in transparency, dimensional stability and strength and can be applied to a roll-to-roll process. SOLUTION: A polyimide composite film having an average thickness of 5 to 50 μm and a total light transmittance of 85% or more, which is directed from both surfaces of the polyimide composite film to the inside in the thickness direction. In the range of 20% or less of the total thickness, the fibrous filler having an average fiber length of 200 nm or more and less than 1000 nm and an average diameter of 0.5 to 10 nm is dispersed and present in the polyimide composite. A polyimide composite film comprising 1 to 50 wt% of a filler. [Selection figure] None

Description

  The present invention relates to a polyimide composite film excellent in transparency, and a flexible device using the same. This film is suitable for a flexible device or the like in which a functional layer such as a liquid crystal display, an organic EL display, an organic EL illumination, electronic paper, a touch panel, or a color filter is formed on a film substrate.

  Display devices such as liquid crystal display devices and organic EL display devices are used for various display applications such as large displays such as televisions, small displays such as mobile phones, personal computers, and smartphones. For example, in an organic EL display device, thin film transistors (TFTs) are formed on a glass substrate which is a supporting substrate, an electrode, a light emitting layer and an electrode are sequentially formed, and finally airtight sealing is performed with another glass substrate or multilayer thin film It is made.

  Here, by replacing the glass substrate which is a supporting base material with a resin film substrate, it is possible to realize thinness, lightness and flexibility, and it is expected to further expand the application of the display device.

  For example, Non-Patent Documents 1 and 2 propose an organic EL display device in which a highly transparent polyimide is applied to a supporting substrate.

  Thus, it is known that a resin substrate such as polyimide is useful for a flexible substrate for a flexible display. However, since resin substrates generally have inferior dimensional stability, strength, surface hardness and the like compared to glass, further improvement is required.

In Patent Document 1, a polyimide film obtained by dispersing colloidal silica in a polyimide precursor solution obtained by reacting a fluorine atom-containing tetracarboxylic acid dianhydride and a fluorine atom-containing diamine is obtained. It is disclosed. By incorporating colloidal silica in a highly transparent polyimide, it is possible to obtain a polyimide which is excellent in transparency, and in particular, controlled to have a relatively low coefficient of linear expansion at high temperatures.
However, when a particulate filler such as colloidal silica is contained, there is a problem that the strength of the film is reduced.

  On the other hand, Patent Document 2 discloses a polyimide film containing needle-like titanium dioxide as a filler in a thermally and dimensionally stable polyimide film. However, it does not teach a transparent polyimide film.

  As a method of producing a flexible device using a transparent polyimide film substrate, a polyimide film is formed on a glass substrate which is a supporting substrate, and further a functional layer such as an electrode and a light emitting layer is formed thereon. Methods to peel off. However, due to the stress at the time of peeling the glass substrate, the polyimide film may be deformed, and the formed functional layer may be broken.

  Therefore, in the production of flexible devices such as liquid crystal display devices, organic EL displays, organic EL lighting, electronic paper, touch panels, color filters, etc., film strength that does not deform due to stress at the time of peeling from a supporting substrate is required.

WO 2013/1601970 WO 2009/142938

S. An et. al. , “2.8-inch WQVGA Flexible AMOLED Using High Performance Low Temperature Polysilicon TFT on Plastic Substrates”, SID 2010 DIGEST, p 706 (2010) Oishi et. al. , "Transparent PI for flexible display", IDW ‘11 FLX2 / FMC4-1

  Therefore, an object of the present invention is to provide a polyimide-based film which is excellent in transparency, dimensional stability (particularly, low thermal expansion) and strength and which can be applied to roll-to-roll process.

  MEANS TO SOLVE THE PROBLEM In order to solve the said subject, as a result of the present inventors earnestly examining, it discovered that the polyimide composite film which the fibrous filler disperse | distributed to transparent polyimide was suitable, and completed this invention.

  That is, the present invention is a polyimide composite film having an average thickness of 5 to 50 μm and a total light transmittance of 85% or more, and the inside in the thickness direction from both surfaces of the polyimide composite film. In the range of 20% or less of the total thickness towards the fiber length of 200 nm or more and less than 1000 nm of the average fiber length and 0.5 to 10 nm of the average diameter of the fibrous filler dispersed and present, 1 to 50 wt% of the fibrous filler It is a polyimide composite film characterized by containing.

  It is preferable to be composed of an outer layer on both sides on which a fibrous filler is dispersed and present, and an inner layer substantially free of a fibrous filler.

  The present invention is a flexible device characterized in that a functional layer is laminated on the surface of the above-mentioned polyimide composite film.

  According to the present invention, it is possible to provide a polyimide-based film which is excellent in transparency, dimensional stability and strength and to which a roll-to-roll process can be applied. The polyimide composite film of the present invention is less likely to be deformed, for example, by the stress at the time of peeling from the support substrate. Therefore, it can be suitably used as a substrate for a flexible device such as a liquid crystal display, an organic EL display, an organic EL illumination, electronic paper, a touch panel, a color filter, an electronic paper, a solar cell and the like.

  The polyimide composite film of the present invention has an average thickness of 5 to 50 μm, a total light transmittance of 85% or more, and an overall thickness from the both surfaces of the polyimide composite film toward the inside in the thickness direction. The fibrous filler is dispersed and present in the range of 20% or less of the length. The fibrous filler has an average fiber length of 200 nm or more and less than 1000 nm, and an average diameter of 0.5 to 10 nm, and is contained in the polyimide composite in an amount of 1 to 50 wt%.

A flexible device requiring transparency of a substrate such as a liquid crystal display device, an organic EL display, an organic EL illumination, an electronic paper, a touch panel, a color filter, an electronic paper, a solar cell, etc. by having a total light transmittance of 85% Can be used suitably. In the case of application to a bottom emission type organic EL display device, the wavelength of light emitted from the light emitting layer of the organic EL is mainly 440 nm to 780 nm, so the transmittance in the wavelength range of 440 nm to 780 nm is 80% or more Is preferred. More preferably, it is 85% or more. In addition, when the flexible device is a touch panel, the visibility of the display is required, so the average transmittance at 380 to 780 nm is preferably 90% or more. Moreover, it is preferable that the transmittance | permeability in 430 nm is 80% or more, More preferably, it is 90% or more from the reason of a blue wavelength.
The composite film of the present invention has an average thickness of 5 to 50 μm, preferably 5 to 30 μm. In this thickness range, it is preferable to satisfy the above-mentioned transmittance, but it is sufficient if the above-mentioned transmittance is satisfied in the thickness used. The measurement of the average thickness conforms to JIS K7130.

  By containing the above-mentioned fibrous filler in an amount of 1 to 50% by weight, it is possible to combine strength, transparency, low thermal expansion (low CTE) and smoothness. If the content of the fibrous filler is less than 1 wt%, the CTE is not sufficiently reduced, and if it exceeds 50 wt%, the optical properties are impaired. Preferably it is 1 to 30 wt%, more preferably 1 to 10 wt%.

  Although a fibrous filler can use a well-known fibrous filler, a transparent or colorless filler is preferable. The material is, for example, alumina, cellulose, barium titanate. More preferably, it is alumina from the viewpoint of dispersibility in transparent polyimide and heat resistance.

  The size of the fibrous filler preferably has an average diameter (median diameter) of 0.5 to 10 nm and an average fiber length of 200 to less than 1000 nm. The average diameter is more preferably 5 nm or less, still more preferably 1 nm or less. The average fiber length is preferably 200 to 450 nm. If the average diameter or average fiber length exceeds the upper limit, transparency is impaired.

The fibrous filler may be present on the outer layer side of the film. For example, they may be dispersed and present throughout the film, or may be localized at specific locations in the film, but are present on the outer layer side. Preferably, from the viewpoint of the dimensional stability of the film, it is dispersed in the range of 20% or less of the total thickness from the both surfaces of the film toward the inside in the thickness direction. In this case, it is preferable that the polyimide composite film is composed of an outer layer on both sides on which a fibrous filler is dispersed and present, and an inner layer on the center side. The outer layer may be in the range of 20% or less of the total thickness from the both surfaces of the film toward the inside in the thickness direction. The inner layer may have a fibrous filler, but preferably has a lower content or substantially no content than the outer layer. More preferably, the outer layer is a fibrous filler dispersed layer, and the inner layer is a non-filler dispersed polyimide layer.
If the fibrous filler is exposed from the surface of the film, the strength tends to decrease, the surface roughness increases, and the releasability from the supporting substrate tends to deteriorate, so from the surface on both sides of the film More preferably, no filler is present in the outermost layer within 1 nm in the thickness direction. The outermost layer is present on the surface side of the outer layer.
When the polyimide composite film comprises an outer layer on both sides on which fibrous fillers are dispersed and an inner layer substantially free of fibrous fillers, the thickness of each outer layer is 20% or less of the total thickness. is there. In the case of a three-layer structure of outer layer / inner layer / outer layer, the thickness of the inner layer is 60 to 98%, preferably 70 to 98%, and more preferably 75 to 98% of the total thickness. From another viewpoint, regardless of the film thickness, the thickness of the outer layer is preferably 1 μm or less. The inner layer preferably contains no fibrous filler (content 0%), and in the case of containing, the content of the fibrous filler is preferably less than the content in the outer layer from the viewpoint of transparency, which is preferable. Is 50% or less, more preferably 10% or less.

  The thickness of the polyimide composite film is 5 to 50 μm from the viewpoint that the strength as a polyimide substrate is maintained and a thin flexible device can be produced. If it exceeds 50 μm, it will be difficult to make a thin flexible device, and if it is less than 5 μm, the strength of the flexible device tends to be insufficient. More preferably, it is 5-20 micrometers, More preferably, it is 5-15 micrometers.

  The polyimide constituting the polyimide composite film is not limited as long as it conforms to the object of the present invention, but from the viewpoint of heat resistance and transparency, preferably 4,4'-oxydiphthalic acid as a tetracarboxylic acid dianhydride monomer Anhydride (ODPA), pyromellitic anhydride (PMDA), 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride (CBDA) or 2,2-bis (3,4-anhydrodicarboxyphenyl) hexa As a diamine monomer, fluoropropane (6FDA) is used as 4,4'-diamino-2,2'-bis (trifluoromethyl) biphenyl (TFMB) or 2,2'-dimethyl-4,4'-diaminobiphenyl It is a polyimide obtained using mTB). More preferably, the tetracarboxylic acid dianhydride monomer is 6FDA, PMDA or CBDA, and the diamine monomer is TFMB.

Hereinafter, an embodiment of a method for producing a polyimide composite film will be illustrated.
One embodiment of the method for producing a polyimide composite of the present invention includes the following four steps.
Step 1: A step of forming a pre-fibrous filler dispersion layer 1 by coating and drying a polyimide precursor or a polyimide dispersion containing a fibrous filler on a continuously supplied coated substrate Step 2: The above-mentioned pre-fiber Forming a prepolyimide resin layer 2 by coating and drying a polyimide precursor or a polyimide solution on the fibrous filler layer 1 Step 3: a polyimide precursor or polyimide containing a fibrous filler on the prepolyimide resin layer A step of coating and drying the dispersion liquid to obtain a pre-fibrous filler layer 3, and forming a laminate in which the pre-fibrous filler dispersion layer 1, the pre-polyimide resin layer 2 and the pre-fibrillar filler dispersion layer 3 are sequentially laminated 4: A process of heating the laminate to form a polyimide composite

First, step 1 will be described.
A dispersion containing a fibrous filler and a polyimide or a precursor is coated and dried on a continuously supplied coating substrate (supporting substrate) to make the coating surface tack-free, thereby obtaining a pre-fibrous state. The filler dispersed layer 1 is formed.
As the dispersion medium in the dispersion containing the fibrous filler, known dispersion media such as water and organic solvents can be used.
Here, the coated substrate is continuously supplied. By continuously feeding, the laminate having the formed fibrous filler layer becomes a long film. Therefore, it becomes possible to convey by a roll-to-roll process after the process 2 and it becomes a long film as a whole. Therefore, multiple flexible devices, such as a touch panel and a flexible display, can be manufactured from one polyimide composite film.
The drying temperature for tack-free is 60 ° C. to 200 ° C., more preferably 70 ° C. to 180 ° C.
In addition, in this example, although the coated base material supplied continuously is demonstrated in detail, it is applicable also to the base materials which are not supplied continuously, such as a cut sheet-like base material.

  The coated substrate may be a cut sheet substrate, a roll substrate, an endless belt, or a metal drum, but preferably a cut sheet substrate capable of simple production, or a roll having excellent productivity. Base material. In the case of a roll-shaped substrate, the length may be such that two or more flexible devices can be produced from the polyimide composite film obtained in Step 4. However, the longer the one on the MD side, the more from one polyimide laminate. It is preferable because a flexible device can be manufactured. Preferably, (MD-side length) / (TD-side length) is 50 or more, more preferably 2000 or more. In the case of an endless belt, its shape is not limited.

  The material of the coating substrate is not limited as long as it has the shape of a roll-like substrate or an endless belt and the property does not change due to the heat treatment when making the coating surface tack-free in Step 1. In the case of a sheet-like substrate, it is preferably a polyimide film excellent in strength, heat resistance and flexibility, a SUS foil, a copper foil or a composite thereof. More preferably, it is a polyimide film. In the case of an endless belt, it is preferably made of SUS.

Next, step 2 will be described.
A solution of a polyimide precursor or polyimide is coated and dried on the pre-fibrillar filler dispersion layer 1 to obtain a pre-polyimide resin layer 2.
In order to obtain a pre-polyimide resin layer, it is dried by heat treatment to make it tack free. Here, the tack-free state refers to a state in which the object does not adhere to the contact when it contacts the surface of the object. For example, when it contacts with what applied the solution of the polyimide precursor on the pre-fibrous filler layer 1 with a finger, the state in which the composition of the solution of the polyimide precursor does not adhere to a finger is said.
In order to bring the pre-polyimide resin layer into a tack-free state, at least a part of the solvent contained in the pre-polyimide resin layer is volatilized and dried. In the case of a solution of a polyimide precursor, at least a part of the polyimide precursor may be imidized during drying. If the drying is not sufficient, it will not be tack free. In that case, when the laminate is heated in step 4, there is a risk that blisters may be generated in the formed polyimide composite film.
On the other hand, when drying is performed at high temperature, imidization proceeds only excessively on the surface, and there is a risk that the solvent inside will not be sufficiently volatilized and a large amount of solvent will remain in the polyimide composite film. Although the preferable drying conditions vary depending on the structure of the polyimide precursor and the polyimide, the preferable drying temperature is 60 ° C. to 200 ° C. so that the problem in step 4 does not occur. More preferable heat treatment conditions are a drying temperature of 130 ° C. to 200 ° C. when using a polyimide solution to form a polyimide layer, and a drying temperature of 60 ° C. to 180 ° C. when using a polyimide precursor or solution. . Moreover, preferable solid content concentration of the polyimide layer after drying is 95 wt%-99.5 wt%, More preferably, it is 99 wt%-99.5 wt%.

A known coating method can be used to form the pre-polyimide resin layer 2 on the pre-fibrous filler dispersion layer 1, and examples thereof include a knife coater, a die coater, a lip coater and the like, and are closed. Lip coaters are preferred because of the wide viscosity range they can handle.
The thickness of the pre-polyimide resin layer is adjusted to be the target thickness of the polyimide composite film formed in step 4.

  As a solvent for the polyimide precursor or the solution of the polyimide, N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAc), dimethylsulfoxide (DMSO), dimethyl sulfate, sulfolane, butyrolactone, cresol, Phenol, halogenated phenol, cyclohexanone, dioxane, tetrahydrofuran, diglyme type, triglyme type, carbonate type (for example, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate) and the like can be mentioned. Preferably, NMP and DMAc can be used to easily control the formation reaction of the polyimide precursor.

  In step 2, a polyimide precursor or polyimide solution to be a polyimide substrate film may be coated twice or more on the pre-fibrous filler dispersion layer 1 to form two or more pre-polyimide resin layers 2.

Next, step 3 will be described.
A dispersion containing a fibrous filler and a polyimide or a precursor is coated and dried on the pre-polyimide resin layer to make the surface tack free, thereby forming a pre-fibrous filler dispersion layer 3 and pre-fibrillar filler dispersion. A laminated body in which the layer 1, the pre-polyimide resin layer 2 and the pre-fibrous filler dispersion layer 3 are sequentially laminated is formed. The forming conditions such as the drying conditions for making the tack free and the type of the dispersion medium are the same as in the step 1.

Next, step 4 will be described.
The laminate obtained in step 3 is heated to form a polyimide composite layer. By heating, the polyimide precursor which comprises a laminated body imidizes and it becomes a polyimide. Alternatively, when the pre-fibrous filler dispersion layers 1 and 3 and the pre-polyimide resin layer 2 are made of polyimide, the residual solvent of the polyimide solution constituting the laminate is volatilized.
The heating conditions under which the imidization proceeds sufficiently are preferred. The heat treatment conditions vary depending on the type of polyimide precursor, but the maximum temperature is 100 ° C to 450 ° C. More preferably, the maximum temperature is 280 ° C to 400 ° C.
An imidation catalyst such as pyridine, acetic anhydride, N-methyl imidazole or the like may be added to the polyimide precursor for imidation. The addition of the imidation catalyst is preferable because the imidation proceeds even at a relatively low temperature.

  The adhesive strength between the coated base material and the pre-fibrous filler dispersed layer 1 and the adhesive strength between the coated base material and the polyimide composite film layer are not peeled off from the coated base material in steps 2 to 4. And after forming a polyimide composite film, or after forming a functional layer on a polyimide composite film, it is good if peeling of a coated substrate is possible, without damaging these. The adhesive strength is preferably 1 to 200 N / m, more preferably 1.5 to 50 N / m. Therefore, Ra of the coating surface of the coating substrate is preferably 1 nm to 100 nm, and more preferably 1 nm to 50 nm.

The arithmetic mean roughness (Ra) of the polyimide composite film is preferably 0.1 nm to 10 nm. More preferably, it is 0.1 nm to 5 nm. Within this range, the adhesion between the functional layer and the polyimide composite film and the performance as a flexible device can be secured.
It is preferable that back surface Ra of a coating base material is 10 nm-100 nm. More preferably, it is 50 nm to 100 nm. Within this range, it can be transported without blocking in the roll-to-roll process, and when the roll is wound it does not affect the Ra of the coated surface.
As a method of Ra control, the back surface may be processed by a method such as corona or plasma.

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

1. Various physical property measurement and performance test methods [Peeling strength]
The peel strength between the coated substrate and the polyimide composite film is processed into a strip having a width of 1 mm to 10 mm and a length of 10 mm to 25 mm for a laminate in which the polyimide composite film is laminated on the coated substrate. The polyimide composite film was peeled off in the direction of 180 ° using a Toyo Seiki Co., Ltd. tensile tester (Strograph-M1), and the peel strength was measured. In addition, the adhesion between the processed thin line and the resin interface is strong, and those which are difficult to peel are considered as “peelable”.
[Tensile strength]
A sample obtained by cutting a film into 20 mm wide strips was stretched at 10 mm / min using a strograph R-1 manufactured by Toyo Seiki Seisakusho Co., Ltd. The maximum point load was divided by the cross-sectional area to determine the tensile strength.
[Total light transmittance and 400 nm transmittance]
The film was cut into 5 cm squares, and this was measured for total light transmittance using HAZE METER NDH-5000 manufactured by Nippon Denshoku Kogyo.
Thermal linear expansion coefficient (CTE)
A 3 mm × 15 mm size film was subjected to a tensile test 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 with a thermomechanical analysis (TMA) device The thermal expansion coefficient (ppm / K) was measured from the amount of elongation of the film with respect to the temperature.
[Pencil hardness]
According to the pencil hardness method (JIS-K5400), pencils of various hardnesses were applied to the film surface at an angle of 45 degrees, scratched with a load of 750 kg, and indicated by the hardness of the pencil when scratched.
[Surface roughness Ra]
The surface roughness Ra of each of the carrier, the coated substrate, and the film was cut into 3 cm square, and the surface roughness Ra was measured using an AFM manufactured by Bruker AXS.

2. Synthesis of Polyamic Acid (Polyimide Precursor) Solution Raw Material Used for Synthesis of Polyamic Acid (Polyimide Precursor) Solution Handled in the Following Synthesis Examples, Examples, and Comparative Examples, Aromatic Diamino Compound, Acid of Aromatic Tetracarboxylic Acid The anhydrides and solvents are shown below.
[Aromatic diamino compound]
・ 4,4'-diamino-2,2'-bis (trifluoromethyl) biphenyl (TFMB)
・ 2,2'-Dimethyl-4,4'-diaminobiphenyl (mTB)
・ 1, 4- phenylene diamine (PPD)
・ 1, 3-bis (4-amino phenoxy) benzene (TPER)
・ 2,2-bis [4- (4-aminophenoxy) phenyl] propane (BAPP)
[Acid anhydride of aromatic tetracarboxylic acid]
-Pyromellitic anhydride (PMDA)
・ 2,2-bis (3,4-anhydrodicarboxyphenyl) hexafluoropropane (6FDA)
・ 2,3,2 ', 3'-biphenyltetracarboxylic acid dianhydride (BPDA)
〔solvent〕
・ N, N-Dimethylacetamide (DMAc)

Production Example 1
In a stream of nitrogen, 170 g of the solvent DMAc was placed in a 300 ml separable flask, and TFMB (12.65 g, 0.039 mol) was added and dissolved while stirring. Then 6FDA (17.35 g, 0.039 mol) was added. Then, the solution was continuously stirred at room temperature for 3 hours to carry out a polymerization reaction to obtain 200 g of pale white viscous polyamic acid (polyimide precursor) A varnish. In addition, polyimide resin A is obtained by hardening this polyimide precursor A varnish on the below-mentioned heating conditions.

Production Example 2
18.8 g of the polyimide precursor varnish A obtained in Production Example 1 is placed in a cylindrical container, 1.8 g of a 10 wt% DMAc solution of alumina fibers (average fiber length 400 nm, average fiber diameter 1 nm) is added, and a stirrer of rotation revolution type The mixture varnish 1 (alumina fiber content 10 wt%) was obtained.

Production Example 3
14 g of the polyimide precursor varnish A obtained in Production Example 1 is placed in a cylindrical container, 4.5 g of a 20 wt% solution of colloidal silica (average particle diameter 12.5 nm) is added, and mixed with the varnish by a rotation-revolution type stirrer , Mixed varnish 2 was obtained.

Each material handled in the following Examples and Comparative Examples is shown below.
Coating base material: Commercially available high heat resistance type polyimide film (UPILEX S manufactured by Ube Industries, thickness 0.75 mm)
Moreover, the polyimide precursor varnish apply | coated on the hard support body was dried and hardened on either of the following heating conditions.
Drying conditions [1]: 3 minutes and 120 ° C. 2 minutes Drying conditions [2]: 70 ° C. 10 minutes Drying and curing conditions [1]: 130 ° C. 10 minutes, 160 Temperature rising heating and curing conditions [2] ... 150 ° C 10 minutes, 150 ° C 5 minutes, 180 ° C 2 minutes, 220 ° C 2 minutes, 270 ° C 2 minutes, 320 ° C 2 minutes, 360 ° C 2 minutes in order After raising the temperature from 5 ° C to 400 ° C at a heating rate of 5 ° C / min, heating at 400 ° C for 60 minutes

Example 1
A coated substrate (230 × 320 mm) was attached to a metal mold (outside 240 × 330 mm, inner shape 220 × 310 mm) with a polyimide tape so that the surface became flat. 5 ml of a 10 wt% DMAc dispersion of alumina fibers (average fiber length 400 nm, average fiber diameter 1 nm) was flowed down onto this coated substrate surface, uniformly coated with a bar coater, and dried under drying conditions [2] After the free state, 10 ml of polyimide precursor A varnish is applied with a bar coater, dried under drying conditions [1], and after being made tack free, alumina fibers (average fiber length 400 nm, average fiber diameter 1 nm) are again obtained. 5 ml of the 10 wt% DMAc dispersion solution was poured down uniformly with a bar coater and dried under drying conditions [2]. This laminate is heated under curing conditions [1] to form a polyimide composite film having a thickness of 10 μm, and then the polyimide composite film is scored using a commercially available cutter to form a coated substrate. It peeled from and obtained the polyimide composite film (film A).
Here, the film A has a three-layer structure of fibrous filler dispersed layer / filler non-dispersed polyimide layer / fibrous filler dispersed layer, and each fibrous filler dispersed layer has a thickness of 1 μm and a fibrous filler content The filler non-dispersed polyimide layer had a thickness of 8 μm and a fibrous filler content of substantially 0%.
Various measurements were carried out on film A. The results are shown in Table 1.

Comparative Example 1
A polyimide film (a film was prepared in the same manner as in Example 1 except that the mixed varnish 1 was not used, the polyimide precursor A varnish was used so that the thickness was 10 μm, the drying condition 1 and the curing condition 1 were heated. I got B).
Next, as in Example 1, this film B was peeled off from the coated substrate, and various measurements were performed. The results are also shown in Table 1.

Comparative example 2
A polyimide composite film (film C) was obtained in the same manner as in Example 1, except that Mixed Varnish 2 was used instead of Mixed Varnish 1.
Next, as in Example 1, this film C was peeled off from the coated substrate, and various measurements were performed. The results are also shown in Table 1.

Claims (3)

  A polyimide composite film having an average thickness of 5 to 50 μm and a total light transmittance of 85% or more, wherein the total thickness from the both surfaces of the polyimide composite film toward the inside in the thickness direction In the range of 20% or less of the above, a fibrous filler having an average diameter of 200 nm or more and less than 1000 nm and having an average diameter of 0.5 to 10 nm is dispersed and present, and the fibrous filler is contained in 1 to 50 wt% Polyimide composite film.   2. The polyimide composite film according to claim 1, comprising an outer layer on both sides of the fibrous filler dispersed and present, and an inner layer substantially free of the fibrous filler. A flexible device comprising a functional layer laminated on the surface of the polyimide composite film according to claim 1.