CN118005921A - High-transparency polyimide film material for flexible display and preparation method thereof - Google Patents

Abstract

The invention discloses a high-transparency polyimide film material for flexible display and a preparation method thereof, wherein a plurality of diamine and dianhydride monomers containing specific structures or groups are selected to prepare polyamide acid through a quaternary copolymerization mode, and finally polyimide for flexible display is prepared through chemical imidization; the polyimide has the advantages that the movement of a molecular chain can be restrained by introducing a crosslinking structure into polyimide, so that the CTE of the film is effectively reduced, the rigidity of the polyimide molecular chain is improved and the movement of the polyimide molecular chain is restrained by introducing a micro-branched crosslinking structure on the surface of the film, the amino grafted polyimide film and carboxyl of dicarboxymethyl phenyl phosphine oxide undergo condensation reaction, and then 4,4' -dimercapto diphenyl ether is added for amino-mercapto addition reaction, so that the CTE value of the polyimide film is effectively reduced; meanwhile, the introduction of the micro-branched cross-linked structure prevents the close packing of molecular chains, which is beneficial to the low dielectric property of the polyimide film.

Description

A highly transparent polyimide film material for flexible display and preparation method thereof

Technical Field

The present invention relates to the field of flexible display, and in particular to a highly transparent polyimide film material that can be used for flexible display and a preparation method thereof.

Background technique

With the continuous development of society, more and more electronic products are being used in all aspects of industrial production and life. With the continuous innovation of science and technology, many high-tech electronic products are gradually developing towards small-volume integration and lightweight. Most of these high-tech electronic products are equipped with intelligent display systems. Therefore, while these electronic products are gradually developing towards integrated intelligent innovation, they also put forward higher requirements for the performance of the display system in electronic equipment, especially the display screen. Traditional display screens are mostly made of inorganic glass. Such display screens have low mechanical strength and are very easy to be damaged during use. In addition, traditional glass screens cannot be made ultra-thin and are relatively bulky, which is not conducive to their application in lightweight, miniaturized and integrated electronic products. In addition, glass display screens are hard materials and cannot be made flexible, which also limits the application of glass display screens in some foldable electronic products and special-shaped displays. However, polyimide, as a new type of special polymer material, can perfectly overcome the above shortcomings of glass displays, thereby achieving a perfect replacement for traditional glass displays.

As a special polymer material, polyimide has the characteristics of high temperature resistance, corrosion resistance, high strength, etc., and it can be made into homogeneous ultra-thin films with different thickness requirements according to demand. In addition, by designing and modifying the molecular chain structure of polyimide, the high transparency and high flexibility of polyimide film materials can be effectively achieved, thereby preparing highly transparent polyimide that can be used for flexible displays, effectively replacing traditional glass screens and promoting the development of high-tech electronic products.

Chinese patent CN117343325A: discloses a polyimide, a transparent polyimide film and a preparation method thereof, wherein the polyimide is prepared by polymerization of a dianhydride and a diamine, the dianhydride is a fluorine-containing dianhydride or an alicyclic dianhydride, and the hydroxyl-containing diamine in the polyimide accounts for more than 10% of the total molar amount of the diamines involved in the polymerization, and the hydroxyl-containing diamine has a general formula shown in the following structural formula: The polyimide film material prepared by the present invention increases the glass transition temperature of the transparent polyimide material, and at the same time can reduce the thermal expansion coefficient of the material, improve the transparency of the material, so that it can better meet the application of downstream industries.

Chinese patent CN116675887A: discloses a method for preparing a transparent polyimide film, comprising the following steps: dissolving polyimide in a solvent to obtain a polyimide solution; casting the polyimide solution onto a flexible substrate film by slit coating, preliminarily drying at 100-180°C to obtain a primary film with a solvent content of 10%-25%, standing for 24 hours, peeling the primary film from the flexible substrate film, then stretching and tensioning the primary film and drying it for a second time at 200-300°C to remove the residual solvent in the film, and rolling it up to obtain a transparent polyimide film. The preparation method of the present invention first casts the polyimide solution onto a flexible substrate film for preliminarily drying to obtain a primary film, stands the primary film for a certain period of time and then peels it from the flexible substrate film, and then performs a second drying under stretching and tensioning, which can effectively avoid the warping problem of the film, and the obtained CPI film has low yellowness, high transparency and high flatness.

Chinese patent CN114231029B: belongs to the technical field of functional polymer materials, specifically relates to a cross-linked highly transparent polyimide film and its preparation method, which is obtained by polycondensation reaction of a novel alicyclic structure-containing tertiary amine monomer 1,3,5-tris(2-trifluoromethyl-4-aminobenzamide)cyclohexane and an aromatic dianhydride monomer, and introduces amide groups, alicyclic structures and fluorine-containing groups into the cross-linked polyimide molecular chain. The cross-linked highly transparent polyimide film prepared by the present invention has the characteristics of high transparency, low expansion, low dielectric, low expansion and high heat resistance, and its light transmittance at 400nm is greater than 85%, the yellowness index is less than 2, the thermal expansion coefficient is reduced to less than 20ppm/℃, the dielectric constant is less than 3, and the glass transition temperature is greater than 300℃, which has wide applications in optoelectronic fields such as electronic microelectronics. The preparation process of the present invention is simple, the processing performance is excellent, the film-forming process is simple, and it is suitable for industrial production.

Traditional aromatic polyimide is prepared by the polymerization of strongly electrophilic diamine and strongly nucleophilic dianhydride. The polymer molecular chains are tightly stacked and there is a strong conjugation between the aromatic rings. The strong interaction between the aromatic rings gives polyimide excellent properties, but also causes traditional aromatic polyimide to exhibit a characteristic yellow color and poor transmittance in the visible light region, which also limits the application of polyimide films in bottom-emitting flexible displays.

Summary of the invention

The present invention provides a highly transparent polyimide film material that can be used for flexible display and a preparation method thereof. The polyimide has high transparency, high solubility, high mechanical strength, high internal temperature, high chemical stability and film-forming properties, and can be used in the field of flexible display screens to solve the problem of replacing display screens for new integrated, special-shaped, lightweight and other electronic products.

A highly transparent polyimide that can be used for flexible display, its chemical structure is as follows:

In the formula, n is 0.1 to 0.9, m=1-n, and A1 is a diamine intermediate structure, which is any one of the following structures:

B1 is a dianhydride intermediate structure, which is any one of the following structures:

Another object of the present invention is to provide a method for preparing a highly transparent polyimide film material that can be used for flexible display, the operating steps of which are as follows:

S1: Weigh 100-200 parts of solvent and 6-12 parts of diamine monomer by weight in a reaction kettle, and stir to dissolve;

S2: Continue to add 10-15 parts of dianhydride monomer, react at 0-10°C for 4-8h to obtain a transparent and viscous polyamic acid slurry with a certain solid content;

S3: Continue to add 4-8 parts of catalyst and 5-10 parts of dehydrating agent, raise the temperature to 20-40°C, and react for 4-8 hours under stirring to obtain a transparent polyimide slurry;

S4: injecting the polyimide slurry into 800-1200 parts of the phase conversion solution and soaking for 8-10 hours;

S5: heating the soaked resin to 80-150° C. and drying for 6-12 hours to obtain a polyimide resin;

S6: Take 5-10 parts of polyimide resin, add it to 20-40 parts of solvent, prepare a slurry with a solid content of 20-30wt%, then pour it onto a clean glass plate, and use a scraper with an opening thickness of 10-50μm to evenly spread the polyimide slurry on the glass plate;

S7: placing the glass plate coated with polyimide obtained in S4 on a horizontal hot table, keeping it warm at 70-100°C for 4-10 hours, so as to preliminarily evaporate the solvent and form a solid film on the glass plate; then raising the temperature of the hot table to 120-160°C, and continuing to keep it warm for 4-8 hours, so as to form a film and remove most of the solvent contained in the film material; then transferring the glass plate coated with the polyimide film obtained in S6 to a vacuum oven, raising the temperature to 200-220°C, and keeping it warm for 4-8 hours, so as to completely remove the solvent in the film material, and solidify it into a film;

S8: naturally cooling the glass plate coated with the polyimide film obtained in S7 to room temperature, placing it in a plasma device, and performing plasma modification in an ammonia atmosphere for 20-40 minutes to obtain an amino-grafted polyimide film;

S9: Add 100-150 parts of amino-grafted polyimide film, 0.003-0.04 parts of dicarboxymethylphenylphosphine oxide, and 1000-2000 parts of toluene into a reaction kettle by mass, stir and react at 70-80°C for 10-20min, then add 0.03-0.4 parts of 4,4'-dimercaptodiphenyl ether and 0.6-2 parts of sodium tert-butoxide, stir and react at 70-80°C for 30-60min; after the reaction, take out, dry, and put into a plasma equipment for plasma modification in an argon atmosphere for 30-50min to obtain a phosphine-containing polytetrafluoroethylene filter; then soak it in distilled water for 3-6h; let the film material fall off naturally from the glass plate, carefully wipe the water stains on the surface of the film material with absorbent paper, and obtain a highly transparent polyimide film material that can be used for flexible display.

Further, the diamine monomer is 2,6-diaminotrifluorotoluene, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (6FAP), 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl ether, 2,2'-bis(trifluoromethyl)diaminobiphenyl, 4,4'-diaminobenzanilide, 4,4'-diaminodiphenyl ether (ODA), 1,4-bis(2-trifluoromethyl-4-aminophenoxy)benzene, 2,7-diaminofluorene, 9,9-bis[4-(4-aminophenoxy)phenyl]fluorene (BAOFL), 9,9-bis[4-(4-aminomethoxycyclohexane)phenyl]fluorene, 9,9-bis[4-(2-trifluoromethyl-4-aminophenoxy)phenyl]fluorene, At least one of 9,9-bis[4-(2-trifluoromethyl-4-aminomethoxycyclohexane)phenyl]fluorene, 9,9-bis(4-amino-5-trifluoromethylcyclohexyl)fluorene, 9,9-bis(4-amino-5-trifluoromethylphenyl)fluorene, 9,9-bis(4-aminophenyl)fluorene and 9,9-bis(4-aminocyclohexyl)fluorene; the solvent is one or more of N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), tetrahydrofuran, p-chlorophenol (PCP), 1,3-dimethyl-2-imidazolidinone (DMI) and dimethyl sulfoxide (DMSO).

Further, the dianhydride monomer is 5,5'-oxybis-(cis-5-norbornane-exo-2,3'-dicarboxylic anhydride), exo-2,2',3,3'-bi(cis-5-norbornane) dicarboxylic anhydride, 5,5'-hexafluoroisopropylidenebis-(cis-5-norbornane-exo-2,3'-dicarboxylic anhydride), CPODA, hexafluorodianhydride (6FDA), 2,2'-difluoromethyl-4,4',5,5'-biphenyltetracarboxylic anhydride, 3,3',4,4'-biphenyltetracarboxylic anhydride (BPDA), cyclobutanetetracarboxylic anhydride (CBDA), 3,6-di(trifluoromethyl) ...3,6-di(trifluoromethyl) At least one of 1,2,4,5-tetracarboxylic acid dianhydride, 6-trifluoromethyl-1,2,4,5-benzenetetracarboxylic acid dianhydride, 4,4'-oxydiphthalic anhydride (ODPA), 4,4'-oxydi-o-(2-trifluoromethylphenyl)phthalic anhydride, 3,3',4,4'-tetracarboxylic acid-2,2'-bis(trifluoromethyl)diphenyl ether diamine, 1,2,4,5-cyclohexanetetracarboxylic acid dianhydride (HPMDA), dicyclohexyl-3,4,3',4'-tetracarboxylic acid dianhydride (HBPDA), bisphenol A diether dianhydride (BPADA), and bisphenol F diether dianhydride (BPFDA).

Furthermore, the catalyst is at least one of isoquinoline, pyridine, picoline and triethylamine.

Furthermore, the dehydrating agent is at least one of acetic anhydride, trifluoroacetic anhydride and propionic anhydride.

Furthermore, the phase conversion liquid is at least one of distilled water, methanol, ethanol and toluene.

Furthermore, the solvent is at least one of DMAc, DMF and NMP, and the solid content is 10-30wt%.

Furthermore, the plasma modification conditions of S8 and S9 are as follows: the frequency of the plasma radio frequency equipment is 100-200kHz, the output power is 100-150W; and the gas flow rate is 10-22ml/min.

Description of the drawings:

Fig. 1 is the infrared spectrum of embodiment 3;

FIG. 2 is a differential thermal scanning curve of Example 3.

Technical effect:

The highly transparent polyimide film material for flexible display and the preparation method thereof of the present invention have the following significant effects compared with the prior art:

1. The dianhydride with norbornene structure and the diamine containing fluoromethyl with high electron-withdrawing effect and other monomers containing alicyclic ring are used to prepare polyimide. The introduction of alicyclic ring and fluoromethyl group effectively curbs the electron conjugation effect and electron transfer effect in the polyimide molecular chain, thereby effectively improving the light transmittance of polyimide;

2. The introduction of the bulky monomer containing fluorene groups of the present invention also increases the compatibility between molecular chains, further inhibits the electron transfer between molecular chains, and further improves the light transmittance of the polyimide;

3. The hydroxyl-containing monomer introduced into the polyimide of the present invention generates chemical hydrogen bonds between the polyimide molecules, which effectively reduces the thermal expansion coefficient of the polyimide film;

4. The present invention introduces monomers containing ether bond structures, which enhances the flexibility of the molecular chain, thereby greatly improving the flexibility of the final membrane material;

5. The highly transparent flexible polyimide of the present invention has very good application prospects and large-scale industrial promotion potential in cutting-edge flexible displays;

6. The introduction of cross-linking structure in polyimide can inhibit the movement of molecular chains, thereby effectively reducing the CTE of the film. The introduction of micro-branched cross-linking structure on the film surface improves the rigidity of the polyimide molecular chain and restricts its movement. The amino-grafted polyimide film undergoes a condensation reaction with the carboxyl group of dicarboxymethylphenylphosphine oxide, and then 4,4'-dithiol diphenyl ether is added for an amino-thiol addition reaction, which effectively reduces the CTE value of the polyimide film. At the same time, the introduction of micro-branched cross-linking structure hinders the close stacking of molecular chains, which is beneficial to the low dielectric properties of the polyimide film.

Detailed ways

The present invention will be further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.

Example test method:

1. Glass transition temperature test: The test was conducted using TA's Q800 dynamic mechanical analyzer (DMTA); a film stretching fixture was used, the test frequency was 1 Hz, the heating rate was 3 °C/min, the test temperature ranged from room temperature to 450 °C, and the temperature corresponding to the peak value of the loss angle tanδ curve was taken as the polymer glass transition temperature;

2. Use Instron electronic universal material testing machine to test the mechanical properties of the film;

3. Light transmittance test: Tested in accordance with standard GB/T2410-2008;

4. The linear thermal expansion coefficient of the polyimide resin layer was tested in a nitrogen atmosphere using a thermomechanical analyzer (TMA) at a heating rate of 10°C/min within a range of 50-250°C;

5. Dielectric constant test: Dielectric properties test was performed using a wideband dielectric impedance spectrometer (concept40); test temperature was 25°C, relative humidity was 30%; variable frequency test: test frequency range was 10 ⁰ -10 ⁶ Hz; variable temperature test: test temperature was 30-280°C (test frequency was 10 kHz).

Example 1

A highly transparent polyimide film material that can be used for flexible display and a preparation method thereof, wherein the operation steps are as follows:

S1: Weigh 100 g of solvent and 6 g of diamine monomer in a reaction kettle and stir to dissolve;

S2: Continue to add 10g of dianhydride monomer and react at 0°C for 4h to obtain a transparent and viscous polyamic acid slurry with a certain solid content;

S3: Continue to add 4g of catalyst and 5g of dehydrating agent, raise the temperature to 20°C, and react for 4h under stirring to obtain a transparent polyimide slurry;

S4: inject the polyimide slurry into 800 g of phase conversion solution and soak for 8 hours;

S5: heating the soaked resin to 80° C. and drying for 6 hours to obtain a polyimide resin;

S6: Take 5 g of polyimide resin, add it to 20 g of solvent, prepare a slurry with a solid content of 20 wt%, then pour it onto a clean glass plate, and use a scraper with an opening thickness of 10 μm to evenly spread the polyimide slurry on the glass plate;

S7: placing the glass plate coated with polyimide obtained in S4 on a horizontal hot stage, keeping it at 70°C for 4 hours to initially evaporate the solvent and form a solid film on the glass plate; then raising the temperature of the hot stage to 120°C, and continuing to keep it at this temperature for 4 hours to form a film and remove most of the solvent contained in the film material; then transferring the glass plate coated with the polyimide film obtained in S6 to a vacuum oven, raising the temperature to 200°C, and keeping it at this temperature for 4 hours to completely remove the solvent in the film material and solidify it into a film;

S8: The glass plate coated with the polyimide film obtained in S7 is naturally cooled to room temperature, placed in a plasma device, and subjected to plasma modification in an ammonia atmosphere for 20 minutes to obtain an amino-grafted polyimide film;

S9: Add 100g of amino-grafted polyimide film, 0.003g of dicarboxymethylphenylphosphine oxide, and 1000g of toluene into a reaction kettle, stir and react at 70°C for 10min, then add 0.03g of 4,4'-dimercaptodiphenyl ether and 0.6g of sodium tert-butoxide, stir and react at 70°C for 30min; after the reaction, take out, dry, and put into a plasma device for plasma modification in an argon atmosphere for 30min to obtain a phosphine-containing polytetrafluoroethylene filter; then soak it in distilled water for 3h; let the film material fall off naturally from the glass plate, carefully wipe off the water stains on the surface of the film material with absorbent paper, and obtain a highly transparent polyimide film material that can be used for flexible display.

The diamine monomer is 2,6-diaminotrifluorotoluene.

The dianhydride monomer is 5,5'-oxybis-(cis-5-norbornane-exo-2,3'-dicarboxylic anhydride).

The catalyst is isoquinoline.

The dehydrating agent is acetic anhydride.

The phase conversion liquid is distilled water.

The solvent is DMAc, and the solid content is 10 wt%.

The plasma modification conditions of S8 and S9 are as follows: the frequency of the plasma radio frequency equipment is 100kHz, the output power is 100W; and the gas flow rate is 10ml/min.

Example 2

A highly transparent polyimide film material that can be used for flexible display and a preparation method thereof, wherein the operation steps are as follows:

S1: Weigh 140g of solvent and 8g of diamine monomer in a reaction kettle and stir to dissolve;

S2: Continue to add 12g of dianhydride monomer and react at 5°C for 5h to obtain a transparent and viscous polyamic acid slurry with a certain solid content;

S3: Continue to add 5g of catalyst and 6g of dehydrating agent, raise the temperature to 25°C, and react for 5h under stirring to obtain a transparent polyimide slurry;

S4: inject the polyimide slurry into 900 g of phase conversion solution and soak for 9 hours;

S5: heating the soaked resin to 100° C. and drying for 8 hours to obtain a polyimide resin;

S6: Take 6 g of polyimide resin, add it to 25 g of solvent, prepare a slurry with a solid content of 25 wt%, then pour it onto a clean glass plate, and use a scraper with an opening thickness of 20 μm to evenly spread the polyimide slurry on the glass plate;

S7: placing the glass plate coated with polyimide obtained in S4 on a horizontal hot stage, keeping it at 80°C for 6 hours to initially evaporate the solvent and form a solid film on the glass plate; then raising the temperature of the hot stage to 130°C, and continuing to keep it for 5 hours to form a film and remove most of the solvent contained in the film material; then transferring the glass plate coated with the polyimide film obtained in S6 to a vacuum oven, raising the temperature to 205°C, and keeping it for 5 hours to completely remove the solvent in the film material and solidify it into a film;

S8: The glass plate coated with the polyimide film obtained in S7 is naturally cooled to room temperature, placed in a plasma device, and subjected to plasma modification in an ammonia atmosphere for 25 minutes to obtain an amino-grafted polyimide film;

S9: Add 110g of amino-grafted polyimide film, 0.01g of dicarboxymethylphenylphosphine oxide, and 1300g of toluene into a reaction kettle, stir and react at 75°C for 15min, then add 0.1g of 4,4'-dimercaptodiphenyl ether and 1g of sodium tert-butoxide, stir and react at 75°C for 40min; after the reaction, take it out, dry it, and put it into a plasma equipment for plasma modification in an argon atmosphere for 35min to obtain a phosphine-containing polytetrafluoroethylene filter; then soak it in distilled water for 4h; let the film material fall off naturally from the glass plate, carefully wipe off the water stains on the surface of the film material with absorbent paper, and obtain a highly transparent polyimide film material that can be used for flexible display.

The diamine monomer is 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (6FAP).

The dianhydride monomer is exo-2,2',3,3'-bi-(cis-5-norbornane) dicarboxylic acid dianhydride.

The catalyst is pyridine.

The dehydrating agent is trifluoroacetic anhydride.

The phase conversion liquid is methanol.

The solvent is DMF, and the solid content is 15wt%.

The plasma modification conditions of S8 and S9 are as follows: the frequency of the plasma radio frequency equipment is 150kHz, the output power is 110W; and the gas flow rate is 15ml/min.

Example 3

A highly transparent polyimide film material that can be used for flexible display and a preparation method thereof, wherein the operation steps are as follows:

S1: Weigh 180g of solvent and 10g of diamine monomer in a reaction kettle and stir to dissolve;

S2: Continue to add 14 g of dianhydride monomer and react at 5° C. for 7 h to obtain a transparent and viscous polyamic acid slurry with a certain solid content;

S3: Continue to add 7g of catalyst and 9g of dehydrating agent, raise the temperature to 35°C, and react for 7h under stirring to obtain a transparent polyimide slurry;

S4: inject the polyimide slurry into 1100 g of phase conversion solution and soak for 9 hours;

S5: heating the soaked resin to 130° C. and drying for 10 hours to obtain a polyimide resin;

S6: Take 9g of polyimide resin, add it to 35g of solvent, prepare a slurry with a solid content of 25wt%, then pour it onto a clean glass plate, and use a scraper with an opening thickness of 40μm to flatten the polyimide slurry and evenly apply it on the glass plate;

S7: placing the glass plate coated with polyimide obtained in S4 on a horizontal hot stage, keeping it at 90°C for 8 hours to initially evaporate the solvent and form a solid film on the glass plate; then raising the temperature of the hot stage to 150°C, and continuing to keep it for 7 hours to form a film and remove most of the solvent contained in the film material; then transferring the glass plate coated with the polyimide film obtained in S6 to a vacuum oven, raising the temperature to 215°C, and keeping it for 7 hours to completely remove the solvent in the film material and solidify it into a film;

S8: The glass plate coated with the polyimide film obtained in S7 is naturally cooled to room temperature, placed in a plasma device, and subjected to plasma modification in an ammonia atmosphere for 35 minutes to obtain an amino-grafted polyimide film;

S9: Add 140g of amino-grafted polyimide film, 0.03g of dicarboxymethylphenylphosphine oxide, and 1800g of toluene into a reaction kettle, stir and react at 75°C for 15min, then add 0.3g of 4,4'-dimercaptodiphenyl ether and 1.5g of sodium tert-butoxide, stir and react at 75°C for 50min; after the reaction, take out, dry, and put into a plasma device for plasma modification in an argon atmosphere for 45min to obtain a phosphine-containing polytetrafluoroethylene filter; then soak it in distilled water for 5h; let the film material fall off naturally from the glass plate, carefully wipe off the water stains on the surface of the film material with absorbent paper, and obtain a highly transparent polyimide film material that can be used for flexible display.

The diamine monomer is 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl ether.

The dianhydride monomer is 5,5'-hexafluoroisopropylidene bis-(cis-5-norbornane-exo-2,3'-dicarboxylic anhydride).

The catalyst is picoline.

The dehydrating agent is trifluoroacetic anhydride.

The phase conversion liquid is ethanol.

The solvent is DMF, and the solid content is 25wt%.

The plasma modification conditions of S8 and S9 are as follows: the frequency of the plasma radio frequency equipment is 150kHz, the output power is 140W; and the gas flow rate is 20ml/min.

Example 4

A highly transparent polyimide film material that can be used for flexible display and a preparation method thereof, wherein the operation steps are as follows:

S1: Weigh 200 g of solvent and 12 g of diamine monomer in a reaction kettle and stir to dissolve;

S2: Continue to add 15g of dianhydride monomer and react at 10°C for 8h to obtain a transparent and viscous polyamic acid slurry with a certain solid content;

S3: Continue to add 8g of catalyst and 10g of dehydrating agent, raise the temperature to 40°C, and react for 8h under stirring to obtain a transparent polyimide slurry;

S4: inject the polyimide slurry into 1200 g of phase conversion solution and soak for 10 hours;

S5: heating the soaked resin to 150° C. and drying for 12 hours to obtain a polyimide resin;

S6: Take 10g of polyimide resin, add it to 40g of solvent, prepare a slurry with a solid content of 30wt%, then pour it onto a clean glass plate, and use a scraper with an opening thickness of 50μm to evenly spread the polyimide slurry on the glass plate;

S7: placing the glass plate coated with polyimide obtained in S4 on a horizontal hot stage, keeping it at 100°C for 10 hours to preliminarily evaporate the solvent and form a solid film on the glass plate; then raising the temperature of the hot stage to 160°C, and continuing to keep it for 8 hours to form a film and remove most of the solvent contained in the film material; then transferring the glass plate coated with the polyimide film obtained in S6 to a vacuum oven, raising the temperature to 220°C, and keeping it for 8 hours to completely remove the solvent in the film material and solidify it into a film;

S8: The glass plate coated with the polyimide film obtained in S7 is naturally cooled to room temperature, placed in a plasma device, and subjected to plasma modification in an ammonia atmosphere for 40 minutes to obtain an amino-grafted polyimide film;

S9: Add 150g of amino-grafted polyimide film, 0.04g of dicarboxymethylphenylphosphine oxide, and 2000g of toluene into a reaction kettle, stir and react at 80°C for 20min, then add 0.4g of 4,4'-dimercaptodiphenyl ether and 2g of sodium tert-butoxide, stir and react at 80°C for 60min; after the reaction, take it out, dry it, and put it into a plasma equipment for plasma modification in an argon atmosphere for 50min to obtain a phosphine-containing polytetrafluoroethylene filter; then soak it in distilled water for 6h; let the film material fall off naturally from the glass plate, carefully wipe off the water stains on the surface of the film material with absorbent paper, and obtain a highly transparent polyimide film material that can be used for flexible display.

The diamine monomer is 2,2'-bis(trifluoromethyl)diaminobiphenyl.

The dianhydride monomer is hexafluorodianhydride (6FDA).

The catalyst is triethylamine.

The dehydrating agent is propionic anhydride.

The phase conversion liquid is toluene.

The solvent is NMP, and the solid content is 30wt%.

The plasma modification conditions of S8 and S9 are as follows: the frequency of the plasma radio frequency equipment is 200kHz, the output power is 150W; and the gas flow rate is 22ml/min.

Comparative Example 1

In this comparative example, no dicarboxymethylphenylphosphine oxide was added, and the other parts were the same as those in Example 1.

Comparative Example 2

In this comparative example, 4,4'-dimercaptodiphenyl ether was not added, and the other parts were the same as those in Example 1.

Comparative Example 3

In this comparative example, sodium tert-butoxide was not added, and the other parts were the same as those in Example 1.

Test Results

Through the analysis of the above examples and comparative data, the highly transparent polyimide film material for flexible display prepared by the present invention has the advantages of high light transmittance, low thermal expansion coefficient, good flexibility, low dielectric properties, etc.

The contents described in this specification are merely an enumeration of the implementation forms of the inventive concept. The protection scope of the present invention should not be regarded as limited to the specific forms described in the embodiments. The protection scope of the present invention is also limited to the equivalent technical means that can be thought of by those skilled in the art based on the inventive concept.

Claims (8)

1. A highly transparent polyimide film material that can be used for flexible display and a preparation method thereof, wherein the operation steps are as follows: S1: Weigh 100-200 parts of solvent and 6-12 parts of diamine monomer by weight in a reaction kettle, and stir to dissolve; S2: Continue to add 10-15 parts of dianhydride monomer, react at 0-10°C for 4-8h to obtain a transparent and viscous polyamic acid slurry with a certain solid content; S3: Continue to add 4-8 parts of catalyst and 5-10 parts of dehydrating agent, raise the temperature to 20-40° C., react for 4-8 hours under stirring, and obtain a transparent polyimide slurry; S4: injecting the polyimide slurry into 800-1200 parts of the phase conversion solution and soaking for 8-10 hours; S5: heating the soaked resin to 80-150° C. and drying for 6-12 hours to obtain a polyimide resin; S6: Take 5-10 parts of polyimide resin, add it to 20-40 parts of solvent, prepare a slurry with a solid content of 20-30wt%, then pour it onto a clean glass plate, and use a scraper with an opening thickness of 10-50μm to evenly spread the polyimide slurry on the glass plate; S7: placing the glass plate coated with polyimide obtained in S4 on a horizontal hot table, keeping it warm at 70-100°C for 4-10 hours, so as to preliminarily evaporate the solvent and form a solid film on the glass plate; then raising the temperature of the hot table to 120-160°C, and continuing to keep it warm for 4-8 hours, so as to form a film and remove most of the solvent contained in the film material; then transferring the glass plate coated with the polyimide film obtained in S6 to a vacuum oven, raising the temperature to 200-220°C, and keeping it warm for 4-8 hours, so as to completely remove the solvent in the film material, and solidify it into a film; S8: naturally cooling the glass plate coated with the polyimide film obtained in S7 to room temperature, placing it in a plasma device, and performing plasma modification in an ammonia atmosphere for 20-40 minutes to obtain an amino-grafted polyimide film; S9: Add 100-150 parts of amino-grafted polyimide film, 0.003-0.04 parts of dicarboxymethylphenylphosphine oxide, and 1000-2000 parts of toluene into a reaction kettle by mass, stir and react at 70-80°C for 10-20min, then add 0.03-0.4 parts of 4,4'-dimercaptodiphenyl ether and 0.6-2 parts of sodium tert-butoxide, stir and react at 70-80°C for 30-60min; after the reaction, take out, dry, and put into a plasma equipment for plasma modification in an argon atmosphere for 30-50min to obtain a phosphine-containing polytetrafluoroethylene filter; then soak it in distilled water for 3-6h; let the film material fall off naturally from the glass plate, carefully wipe the water stains on the surface of the film material with absorbent paper, and obtain a highly transparent polyimide film material that can be used for flexible display. 2. A highly transparent polyimide film material for flexible display and a preparation method thereof according to claim 1, characterized in that: the diamine monomer is 2,6-diaminotrifluorotoluene, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (6FAP), 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl ether, 2,2'-bis(trifluoromethyl)diaminobiphenyl, 4,4'-diaminobenzanilide, 4,4'-diaminodiphenyl ether (ODA), 1,4-bis(2-trifluoromethyl-4-aminophenoxy)benzene, 2,7-diaminofluorene, 9,9-bis[4-(4-aminophenoxy)phenyl]fluorene (BAOFL), 9,9-bis[4-(4-aminomethoxycyclohexane)phenyl]fluorene , 9,9-bis[4-(2-trifluoromethyl-4-aminophenoxy)phenyl]fluorene, 9,9-bis[4-(2-trifluoromethyl-4-aminomethoxycyclohexane)phenyl]fluorene, 9,9-bis(4-amino-5-trifluoromethylcyclohexyl)fluorene, 9,9-bis(4-amino-5-trifluoromethylphenyl)fluorene, 9,9-bis(4-aminophenyl)fluorene, 9,9-bis(4-aminocyclohexyl)fluorene; the solvent is one or more of N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), tetrahydrofuran, p-chlorophenol (PCP), 1,3-dimethyl-2-imidazolidinone (DMI), and dimethyl sulfoxide (DMSO). 3. A highly transparent polyimide film material for flexible display and a preparation method thereof according to claim 1, characterized in that: the dianhydride monomer is 5,5'-oxybis-(cis-5-norbornane-exo-2,3'-dicarboxylic anhydride), exo-2,2',3,3'-bi(cis-5-norbornane) dicarboxylic anhydride, 5,5'-hexafluoroisopropylidenebis-(cis-5-norbornane-exo-2,3'-dicarboxylic anhydride), CPODA, hexafluorodianhydride (6FDA), 2,2'-difluoromethyl-4,4',5,5'-biphenyltetracarboxylic anhydride, 3,3',4,4'-biphenyltetracarboxylic anhydride (BPDA), cyclobutanetetracarboxylic anhydride, At least one of formic dianhydride (CBDA), 3,6-bis(trifluoromethyl)-1,2,4,5-tetracarboxylic dianhydride, 6-trifluoromethyl-1,2,4,5-benzenetetracarboxylic dianhydride, 4,4'-oxydiphthalic anhydride (ODPA), 4,4'-oxydi-o-(2-trifluoromethylphenyl)phthalic anhydride, 3,3',4,4'-tetracarboxylic-2,2'-bis(trifluoromethyl)diphenyl ether diamine, 1,2,4,5-cyclohexanetetracarboxylic dianhydride (HPMDA), dicyclohexyl-3,4,3',4'-tetracarboxylic dianhydride (HBPDA), bisphenol A diether dianhydride (BPADA), and bisphenol F diether dianhydride (BPFDA). 4. A highly transparent polyimide film material for flexible display and a preparation method thereof according to claim 1, characterized in that the catalyst is at least one of isoquinoline, pyridine, picoline and triethylamine. 5. The highly transparent polyimide film material for flexible display and the preparation method thereof according to claim 1, characterized in that the dehydrating agent is at least one of acetic anhydride, trifluoroacetic anhydride and propionic anhydride. 6. The highly transparent polyimide film material for flexible display and the preparation method thereof according to claim 1, characterized in that the phase conversion liquid is at least one of distilled water, methanol, ethanol and toluene. 7. A highly transparent polyimide film material for flexible display and a preparation method thereof according to claim 1, characterized in that the solvent is at least one of DMAc, DMF, and NMP, and the solid content is 10-30wt%. 8. According to claim 1, a highly transparent polyimide film material that can be used for flexible display and a preparation method thereof are characterized in that: the plasma modification conditions of S8 and S9 are: the frequency of the plasma radio frequency equipment is 100-200kHz, the output power is 100-150W; the gas flow rate is 10-22ml/min.