KR101754573B1 - Flexible display substrate of plastic material - Google Patents

Abstract

The present invention provides a plastic substrate including a hard coating layer on one side of a transparent polyimide film substrate and a transparent electrode layer on the other side of the transparent polyimide film substrate, which has excellent light transmittance, satisfies high hardness characteristics, ITO processability and flexibility, The function of the window film and the electrode film can be performed together when the screen panel is applied. Accordingly, it is possible to provide a touch screen panel which can be thinned by reducing the number of films stacked including the plastic substrate.

Description

FLEXIBLE DISPLAY SUBSTRATE OF PLASTIC MATERIAL [0002]

The present invention relates to a plastic substrate and a touch screen panel including the plastic substrate.

In recent years, a plasma display panel (PDP), a liquid crystal display (LCD), an organic EL (Organic Light Emitting Diode), or the like, which is a flat panel display in a conventional CRT (Cathode Ray Tube) In particular, in the future, researches are being actively carried out in the world to realize such a flat panel display as a flexible display.

In such a flat panel display, a substrate is basically used as a glass substrate. In a typical flat panel display, a glass substrate is used as a most suitable material for a TFT (thin film transistor) because a high temperature heat treatment is required to form the TFT.

However, since the glass substrate has basically too rigid properties, it has poor flexibility and is not suitable as a substrate for a flexible display.

The flexible display substrate is excellent in weight, formability, non-destructiveness, and design compared to a glass substrate. In particular, it can be manufactured by a roll-to-roll production method, However, there has been no development of a flexible display substrate made of plastic suitable for commercialization.

Meanwhile, the touch screen panel TSP has various advantages such as an electronic notebook, a liquid crystal display device (LCD), a flat panel display device such as a plasma display panel (PDP), and an electroluminescence (EL), and a cathode ray tube (Flat-Panel-Display), and is a tool used to allow a user to select desired information through a display. Resistive type, capacitive type, Resistive-multi-type (Resistive-Multi Type).

Resistive type is made by putting a resistive substance on glass or plastic plate and covering it with a polyethylene film. Insulating bars are installed at regular intervals so that the two sides do not touch each other. The principle of operation is that if a constant current is applied at both ends of the resistive film, the resistive film acts like a resistive element having a resistive component, so that a voltage is applied across the resistive film. When the contact is made with the finger, the polyester film on the upper surface is bent and connected. Therefore, due to the two-sided resistance component, it becomes the same shape as the parallel connection of the resistors, and the resistance value changes. At this time, a voltage change occurs due to a current flowing at both ends, and the position of the finger that is touched can be known as the degree of change of the voltage. The resistance film method has a disadvantage that it is operated by the surface pressure and has a high resolution and the fastest response speed, but it can perform only one point and there is a great risk of breakage.

The capacitive type is made by coating a transparent special conductive metal (TAO) on both sides of the heat treated glass. When a voltage is applied to the four corners of the screen, the high frequency spreads to the front of the sensor. When the finger touches the screen, the flow of electrons changes and detects the change and finds the coordinates. The correction capacity method has the advantage of high resolution and high durability, but it has a disadvantage that the reaction rate is low and it is difficult to mount.

Lastly, the resistive-multi-touch type is a type that is implemented in such a manner that it can be practiced in the same manner as the corrected capacitance method by improving and improving the maximum disadvantage of the resistance film method which can be performed only by one point.

In addition, the touch screen panel (TSP) has a problem of signal amplification, a difference in resolution, difficulty in designing and processing techniques, as well as characteristic optical characteristics, electrical characteristics, mechanical characteristics, Resistive type and Capacitive type are widely used in electronic notebooks, PDAs, portable PCs and mobile phones, in particular, in consideration of durability and economy. do.

The future direction of the touch screen manufacturing technology is to make the thickness of the touch screen panel thinner so as to have a sufficient durability even if the conventional complicated process is reduced as much as possible. The reason for this is that even if the display brightness is lowered by increasing the light transmittance, the same performance as the existing product can be realized, thereby reducing the power consumption and increasing the battery usage time.

A general resistive type touch screen panel has been proposed.

The first and second ITO films are attached to the lower surface of the window film and electrically input information to the liquid crystal display module. , And the window film is provided to protect the first ITO film. It is made of general PET (Poly Ethylen Terephthalate) film, and the first ITO film is attached to window film (or Overlay Film) by OCA (Optical Clear Adhesive). The first ITO film and the second ITO film are printed with a first / second electrode layer using silver provided at an edge thereof, and a double-sided tape is attached between the first and second electrode layers for insulation And is spaced apart by a dot spacer and is electrically connected to each other at an external pressure (touch) using a finger or a touch pen, thereby detecting an accurate touch position.

In this case, the light transmittance is lowered between the window film (or Overlay Film) and the first ITO film by a lamination process using Optical Clear Adhesive (OCA), and a window film (or Overlay Film) And a separate process of attaching the first ITO film to the first ITO film by OCA must be performed. Therefore, the process is complicated and the process cost is increased.

In addition, this technique can not selectively coat ITO on a desired region of a window film (or PET film) because the ITO film on which ITO film is formed is patterned by laser wet etching.

In general, PET (polyethylene terephthalate) film is used most as a transparent substrate in the manufacture of a touch screen. In particular, although PET film is advantageous in terms of cost, it has a disadvantage that it is weak against heat to cause deformation at 130 ° C or higher.

Therefore, if the ITO (Indium Tin Oxide) thin film is deposited on the PET film and the subsequent heat treatment process is performed, the ITO thin film may expand or crack due to the expansion or contraction of the PET film. In order to prevent such a defective phenomenon as described above, there has recently been used a method in which a transparent substrate is exposed to a high temperature for a long time in a first step and then a subsequent step is performed. However, such a preprocessing process leads to a delay in the manufacturing time of the touch screen, which lowers the production rate.

The present invention provides a plastic substrate having excellent light transmittance, satisfying high hardness characteristics, ITO processability, and flexibility.

The present invention provides a plastic substrate which can perform the functions of a window film and an electrode film together.

The present invention is to provide a touch screen panel including a plastic substrate, which can be thinned by reducing the number of laminated films.

The plastic substrate according to the present invention comprises a polymer of dianhydride and diamine, an imide of polyimide resin precursor by polymerization of dianhydride and aromatic dicarbonyl compound and diamine, Of not more than 5 and a transmittance of not less than 80% at 550 nm when measured by a UV spectrometer; A hard coating layer formed on one side of the polyimide-based film; And a transparent electrode layer formed on the other surface of the polyimide-based film. This hard coating layer is a layer for high hardness of the plastic substrate, which can omit the window film when forming the touch screen panel. The hard coat layer may improve the chemical resistance together with the organic layer to be described later. Examples of the hard coating layer include tetramethylammonium hydroxide, magnesium sulfate, potassium hydroxide, N-methyl-2-pyrrolidone and methyl ethyl ketone The chemical resistance can be improved so that there is no visual change after dipping in an organic solvent.

The transmittance of 550 nm or more and the transmittance of 440 nm or more are preferably 70% or more when measured with a UV spectrometer based on the film thickness of 50-200 탆.

The polyimide film of the present invention satisfying the above-mentioned yellow color and transparency can be used in fields where transparency is required, such as optical windows and transmissive displays, for which applications have been limited due to the yellow of conventional polyimide films, In addition, it can be used for a flexible display substrate.

According to an embodiment of the present invention, the hard coating layer may include one or more resins selected from the group consisting of polysilazane series, acrylic series and polyurethane series.

According to an embodiment of the present invention, the transparent electrode layer may include at least one selected from the group consisting of ITO, IZO, Ag, and Ag nanowires.

According to one embodiment of the present invention, the polyimide-based film may be surface-modified, and an example of surface modification may be by plasma treatment or corona treatment. Through such surface modification, the surface adhesion with various layers exemplified in the present invention can be improved, and thus the light transmittance, surface hardness and moisture permeability can be further improved.

According to an embodiment of the present invention, one or more inorganic layers selected from silicon oxide or silicon nitride may be further formed between the polyimide-based film and the transparent electrode layer.

According to an embodiment of the present invention, a polyurethane (meth) acrylate obtained by reacting a (meth) acrylate compound containing (meth) acrylate having at least one hydroxyl group in one molecule on at least one surface of a transparent electrode layer. And an organic layer which is a cured layer of an active energy ray-curable composition containing a compound having one (meth) acryloyl group.

Such an organic layer may be formed on the hard coat layer.

Such an organic layer may have a thickness of 1 to 10 mu m.

The hard coating layer described above may be formed between the polyimide-based film and the transparent electrode layer.

According to a preferred embodiment of the present invention, the hard coating layer may have a thickness of 1 to 50 mu m.

According to a preferred embodiment of the present invention, the transparent electrode layer may have a thickness of 1 to 100 nm.

According to a preferred embodiment of the present invention, the thickness of the inorganic layer may be 10 to 100 nm.

In one preferred embodiment of the present invention, an example of a polyimide-based film that satisfies the physical properties is an aromatic dianhydride such as 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropanediamine hydride (6FDA ), 4- (2,5-dioxotetrahydrofuran-3-yl) -1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic anhydride (TDA) Bis (trifluoromethyl) -2,3,6,7-xanthenetetracarboxylic dianhydride (6FCDA), and 4,4 '- (4,4'-isopropylidene diphenoxy) bis (1) selected from among pyromellitic dianhydride (PMDA), biphenyltetracarboxylic dianhydride (BPDA), and oxydiphthalic dianhydride (ODPA) (4-aminophenoxy) -phenyl] propane (6HMDA), and 2,2'-bis (trifluoromethyl) -4 , 4'-diaminobiphenyl (2,2'-TFDB), 3,3'-bis (trifluoromethyl) -4,4'-diaminobiphenyl (3,3'- Bis (3-aminophenoxy) diphenylsulfone (DBSDA), bis (3-aminophenyl) sulfone (3DDS), bis (Aminophenoxy) benzene (APB-133), 1,4-bis (4-aminophenoxy) benzene (APB-134), 2,2'- (4-aminophenoxy) phenyl] hexafluoropropane (4-BDAF), 2,2'-bis (3-aminophenyl) hexafluoro (ODA) derived from at least one selected from propane (3,3'-6F), 2,2'-bis (4-aminophenyl) hexafluoropropane (4,4'-6F) and oxydianiline A unit structure; Terephthaloyl chloride (TPC), terephthalic acid, iso-phthaloyl dichloiride, and 4, 4-thiophenecarboxylic acid are used as the aromatic dicarbonyl compound and the unit structure derived from the aromatic dianhydride. (4,4'-benzoyl chloride) and a unit structure derived from the aromatic diamine. The polyimide-based resin may include a polyimide-based resin.

The polyimide-based film according to a preferred embodiment of the present invention may have an average coefficient of linear thermal expansion (CTE) of 30.0 ppm / ° C or less measured at 50 to 250 ° C by thermomechanical analysis based on a thickness of 50 to 200 μm.

The plastic substrate of the present invention can be used for a substrate on which a color filter is formed, an OLED TFT substrate, a PV substrate and an upper electrode layer substrate, wherein the polyimide film is formed by a process of forming a transparent electrode layer on a film, If the coefficient of linear expansion of a polyimide-based film is high, the film is stretched by a linear expansion coefficient in a high-temperature ITO process and shrinks again upon cooling at a normal temperature. If the expansion and shrinkage degree of the substrate and electrode materials are large, And the coefficient of linear expansion of the substrate is lower. The flexible plastic substrate according to the present invention has a thickness of 50 to 200 μm and a thickness of 50 to 200 μm according to the TMA-method (thermomechanical analysis) And an average linear expansion coefficient (CTE) measured at 250 deg. C is preferably 30.0 ppm / [deg.] C or less.

The plastic substrate having the structure of the present invention has a sheet resistance of 50? / Sq. As a result, it is possible to realize a low resistance.

In another embodiment of the present invention, the polymerization of dianhydrides and diamines or the imidization of polyimide-based resin precursors by polymerization of dianhydrides and aromatic dicarbonyl compounds with diamines, Forming a hard coating layer on a polyimide-based film having a degree of 5 or less and a transmittance of 550 nm at a transmittance of 80% or more when measured with a UV spectrometer; Forming a transparent electrode layer on the other surface of the polyimide-based film, wherein the step of forming the transparent electrode layer includes a step of depositing and heat-treating a transparent electrode layer on one side of the polyimide-based film, At a temperature ranging from 100 to 250 < RTI ID = 0.0 > C. < / RTI >

According to the plastic substrate satisfying these structural features, since the process of forming the transparent electrode layer can be performed at a high temperature, a substrate having a lower resistance can be provided.

The present invention ensures transparency, has no yellowing deformation even in the ITO process, has a high hardness property even at a thin thickness, can realize low surface resistance, and can achieve a simple structure when applied to a touch screen panel A plastic substrate was provided.

Hereinafter, the present invention will be described in more detail by way of examples.

≪ Examples 1-3 >

28.78 g of N, N-dimethylacetamide (DMAc) was charged into a 100 ml 3-neck round bottom flask equipped with a stirrer, a nitrogen inlet, a dropping funnel, a temperature controller and a condenser while passing nitrogen through the reactor, After the temperature was lowered to 0 캜, 3.2023 g (0.01 mol) of 2,2'-TFDB was dissolved and the solution was maintained at 0 캜. 0.88266 g (0.003 mol) of BPDA was added thereto, and the mixture was stirred for 1 hour to completely dissolve the BPDA. Then, 3.10975 g (0.007 mol) of 6FDA was added thereto to completely dissolve the BPDA. At this time, the solid content was 20 wt%, and then the solution was left at room temperature and stirred for 8 hours. At this time, a polyamic acid solution having a solution viscosity of 2100 poise at 23 占 폚 was obtained.

Acetic anhydride (Acetic Anhydride) and pyridine (pyridine) are added to the polyamic acid solution as a chemical hardener in an amount of 2 to 4 equivalents, respectively, and then the polyamic acid solution is heated to a temperature within a range of 20 to 180 ° C , The polyamic acid solution was imidated by heating for 1 to 10 hours while heating at a rate of 10 DEG C / min. Thereafter, 30 g of the imidized solution was added to 300 g of a non-polar solvent such as water or alcohol (methanol, ethanol) The precipitated solids were filtered and pulverized to fine powder and dried in a vacuum drying oven at 80 to 100 ° C for 6 hours to obtain about 8 g of polyimide resin solid powder. The polyimide resin solids thus obtained were dissolved in 32 g of DMAc or DMF solvent, which is a polymerization solvent, to obtain a 20 wt% polyimide solution. Using this, a polyimide film having a thickness of 100 탆 was obtained by heating for 1 to 8 hours while raising the temperature at a rate of 10 캜 / min in a temperature range from 40 to 400 캜 through a film forming process.

Using the obtained film as a base, a hard coat layer was formed on the upper side of the film by using an organic or inorganic hybrid hard coat including a polysilazane system or silica and an acrylic resin or a urethane resin.

Next, an ITO electrode layer was deposited on the other surface of the polyimide film by using a sputter and heat-treated by RTA (Rapid Thermal Annealing).

Examples 1 to 3 are examples in which the hard coating layer, ITO electrode layer thickness, and ITO process temperature are different, and are summarized in Table 1.

<Example 4>

28.78 g of N, N-dimethylacetamide (DMAc) was charged into a 100 ml 3-neck round bottom flask equipped with a stirrer, a nitrogen inlet, a dropping funnel, a temperature controller and a condenser while passing nitrogen through the reactor, After the temperature was lowered to 0 캜, 3.2023 g (0.01 mol) of 2,2'-TFDB was dissolved and the solution was maintained at 0 캜. 0.88266 g (0.003 mol) of BPDA was added thereto, and the mixture was stirred for 1 hour to completely dissolve BPDA, followed by addition of 1.33275 g (0.003 mol) of 6FDA to completely dissolve the BPDA. Then, 0.8121 g (0.004 mol) of TPC was added to obtain a polyamic acid solution having a solid content of 15 wt%.

Using the polyamic acid solution thus obtained, a plastic substrate film was prepared in the same manner as in Example 1 above.

The thickness of the polyimide film, the thickness of the hard coat layer and the thickness of the ITO electrode layer are shown in Table 1.

&Lt; Example 5 >

The polyamic acid solution was prepared in the same manner as in Example 1 except that 6FCDA (9,9-bis (trifluoromethyl) -2,3,6,7-xanthenetetracarboxylic dianhydride) was used instead of 6FDA to prepare a polyamic acid solution , And a plastic substrate film was prepared from the thus obtained film in the same manner as in Example 1 above.

The thickness of the polyimide film, the thickness of the hard coat layer and the thickness of the ITO electrode layer are shown in Table 1.

&Lt; Comparative Example 1 &

28.78 g of N, N-dimethylacetamide (DMAc) was charged into a 100 ml 3-neck round bottom flask equipped with a stirrer, a nitrogen inlet, a dropping funnel, a temperature controller and a condenser while passing nitrogen through the reactor, After the temperature was lowered to 0 캜, 3.2023 g (0.01 mol) of 2,2'-TFDB was dissolved and the solution was maintained at 0 캜. 0.88266 g (0.003 mol) of BPDA was added thereto, and the mixture was stirred for 1 hour to completely dissolve the BPDA. Then, 3.10975 g (0.007 mol) of 6FDA was added thereto to completely dissolve the BPDA. At this time, the solid content was 20 wt%, and then the solution was left at room temperature and stirred for 8 hours. At this time, a polyamic acid solution having a solution viscosity of 2100 poise at 23 占 폚 was obtained.

Acetic anhydride (Acetic Anhydride) and pyridine (pyridine) are added to the polyamic acid solution as a chemical hardener in an amount of 2 to 4 equivalents, respectively, and then the polyamic acid solution is heated to a temperature within a range of 20 to 180 ° C , The polyamic acid solution was imidated by heating for 1 to 10 hours while heating at a rate of 10 DEG C / min. Thereafter, 30 g of the imidized solution was added to 300 g of a non-polar solvent such as water or alcohol (methanol, ethanol) The precipitated solids were filtered and pulverized to fine powder and dried in a vacuum drying oven at 80 to 100 ° C for 6 hours to obtain about 8 g of polyimide resin solid powder. The polyimide resin solids thus obtained were dissolved in 32 g of DMAc or DMF solvent, which is a polymerization solvent, to obtain a 20 wt% polyimide solution. Using this, a polyimide film having a thickness of 100 탆 was obtained by heating for 1 to 8 hours while raising the temperature at a rate of 10 캜 / min in a temperature range from 40 to 400 캜 through a film forming process.

&Lt; Comparative Example 2 &

A plastic substrate was prepared in the same manner as in Example 1 except that no hard coat layer was formed.

&Lt; Comparative Example 3 &

PET film used as substrate film of existing touch screen panel.

The physical properties of the plastic substrate films prepared in Examples and Comparative Examples were measured as follows and shown in Table 1 below.

(1) Coefficient of linear expansion (CTE, ppm / ° C)

The coefficient of linear expansion at 50 to 250 ° C was measured according to the TMA method using TMA (TA Instrument, Q400).

Specimen size: 20mm x 4mm

Temperature: Temperature rise from room temperature (30) to 250 ° C, temperature increase rate 10 ° C / min

Load: 10g (weight of hanging weight on specimen)

(2) Yellowness

The prepared film was measured for yellowness according to ASTM E313 standard using a UV spectrometer (Varian, Cary100).

(3) Transmittance (% @ 550 nm)

The visible light transmittance of the prepared film was measured using a UV spectrometer (Varian, Cary100).

(4) Surface Hardness (H)

The prepared film was measured using a pencil hardness meter according to ASTM D3363, and the measurement conditions were measured by moving a pencil with a 1 Kg load and a 45 degree inclination.

(5) Surface resistance (Ω / sq.)

The surface resistance was measured ten times using a low resistance meter (CMT-SR 2000N (Advanced Instrument Teshnology; AIT, 4-Point Probe System, measuring range: 10 × 10 ^-3 to 10 × 10 ⁵ ) Respectively.

division Furtherance Molar ratio Polyimide film thickness (占 퐉) H / C
(탆) Electrode layer
(Nm) Permeability
(% @ 550 nm) ITO process temperature CTE
(ppm / DEG C) Yellowness Surface hardness Sheet resistance
(Ω / sq.) Example One 6FDA + BPDA /
2,2-TFDB 7: 3: 10 100 5 100 87.51 100 17.22 2.78 5 30 2 6FDA + BPDA /
2,2-TFDB 7: 3: 10 100 30 100 86.81 150 17.22 2.82 9 21 3 6FDA + BPDA /
2,2-TFDB 7: 3: 10 100 30 100 85.43 250 17.22 3.01 9 13 4 (6FDA + BPDA +
TPC / 2,2-
TFDB) 3: 3: 4: 10 100 25 100 87.1 100 14.75 4.56 9 28 5 (6FCDA + BPDA
+ TPC / 2,2-
TFDB) 3: 3: 4: 10 102 25 100 86.4 100 15.68 4.35 8 30 Comparative Example One 6FDA + BPDA /
2,2-TFDB 7: 3: 10 100 - - 88.71 - 17.22 2.66 3 - 2 6FDA + BPDA /
2,2-TFDB 7: 3: 10 100 - ITO 100 nm 83.60 25 17.22 3.26 3 55 3 PET - 188 50 20 88.55 25 - 1.98 H 260

From the results shown in Table 1, it can be seen that the plastic substrates including the polyimide film layers of Examples 1 to 3, the hard coat layer and the transparent electrode layer have excellent surface hardness while maintaining transparency. The ITO process temperature is also stable up to 250 ° C. That is, even at such a high temperature, good results were obtained in yellowing. In contrast, the PET film useful as a plastic substrate for a conventional transparent electrode substrate causes yellowing at a process temperature of about 100 ° C., and furthermore, the sheet resistance value is too high when applied to an electrode substrate.

The thickness of the electrode layer of the sheet resistance is influenced by the process temperature at the time of forming the electrode layer. According to the embodiments, the sheet resistance is gradually lowered as the process temperature is increased in forming the electrode layer of the same thickness. As a result of these results and the comparative example, it can be confirmed that the process of forming the transparent electrode layer can be performed at a high temperature according to the plastic substrate of the present invention, thereby realizing a lower sheet resistance.

Claims (13)

1. A flexible display substrate comprising a polyimide-based film, a hard coat layer and a transparent electrode layer,
The polyimide-based film contains an imide of a polyimide-based resin precursor by polymerization of an aromatic dianhydride, an aromatic diamine, and an aromatic dicarbonyl compound, and has a yellowness of 5 or less as measured using a UV spectrometer , The transmittance at 550 nm is 80% or more, and the average coefficient of linear expansion (CTE) measured at 50 to 250 占 폚 according to thermomechanical analysis is 30.0 ppm / 占 폚 or less on the basis of 50 to 200 占 퐉 in thickness,
The aromatic dianhydride is selected from the group consisting of 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropanediamine hydrate, 4- (2,5-dioxotetrahydrofuran- , 3,4-tetrahydronaphthalene-1,2-dicarboxylic anhydride, 9,9-bis (trifluoromethyl) -2,3,6,7-xanthenetetracarboxylic dianhydride and 4 , 4 '- (4,4'-isopropylidene diphenoxy) bis (phthalic anhydride) and at least one selected from pyromellitic dianhydride, biphenyltetracarboxylic dianhydride and oxy And a diphthalic dianhydride, wherein the unit structure is derived from at least one selected from diphthalic dianhydride,
The aromatic diamines may be selected from the group consisting of 2,2-bis [4- (4-aminophenoxy) -phenyl] propane, 2,2'-bis (trifluoromethyl) -4,4'- diaminobiphenyl, 3 , 3'-bis (trifluoromethyl) -4,4'-diaminobiphenyl, 4,4'-bis (3-aminophenoxy) diphenylsulfone, bis (4-aminophenoxy) benzene, 2,2'-bis [3 (3-aminophenoxy) benzene, ) Phenyl] hexafluoropropane, 2,2'-bis [4 (4-aminophenoxy) phenyl] hexafluoropropane, 2,2'- '- bis (4-aminophenyl) hexafluoropropane, and oxydianiline,
Wherein the aromatic dicarbonyl compound comprises a unit structure derived from at least one selected from terephthaloyl chloride, terephthalic acid, isophthaloyl dichloride and 4,4'-benzoyl chloride;
The hard coating layer being formed for hardness of the flexible display substrate;
The flexible display substrate has a sheet resistance of 50 OMEGA / sq. M, based on an average value measured 10 times using a low-resistance meter at a transparent electrode layer thickness of 100 nm. Or less. &Lt; / RTI &gt; The method according to claim 1,
Wherein the aromatic dianhydride is selected from the group consisting of 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropanediamine hydride, pyromellitic dianhydride, biphenyltetracarboxylic dianhydride and oxydiphthalic Dianhydride, and dianhydride. 2. A flexible display substrate comprising: a substrate; The method according to claim 1,
The sheet resistance is 30 Ω / sq. Or less. &Lt; / RTI &gt; The method according to claim 1,
Wherein the flexible display substrate has a surface hardness of 8H or more. The method according to claim 1,
Wherein the polyimide-based film is surface-modified. 6. The method of claim 5,
Wherein the surface modification is by plasma treatment or corona treatment. The method according to claim 1,
Wherein the transparent electrode layer comprises at least one selected from the group consisting of ITO, IZO, Ag and Ag nanowires. The method according to claim 1,
Wherein the transparent electrode layer has a thickness of 1 to 100 nm. delete The method according to claim 1,
Further comprising an inorganic layer formed between the polyimide-based film and the transparent electrode layer, the inorganic layer comprising at least one selected from silicon oxide or silicon nitride. 11. The method of claim 10,
Wherein the inorganic layer has a thickness of 10 to 100 nm. A touch screen panel comprising the flexible display substrate according to claim 1. The method according to claim 1,
Wherein the hard coating layer has a thickness of 1 to 50 mu m.