Polyimide composite film with ultrahigh transmittance for flexible display

Abstract

The invention discloses a polyimide composite film with ultrahigh transmittance for flexible display. Belongs to the technical field of polyimide composite materials. A transparent polyimide film product doped with Al2O3 filler serves as a substrate, and silicon dioxide anti-reflection films are plated on the two faces of the transparent polyimide film product. The transparent polyimide film substrate is prepared by the following steps: uniformly polymerizing a diamine monomer containing a plurality of large-volume side groups and 6FDA, doping modified Al2O3 microspheres with different mass fractions, and casting on a treated glass substrate by a tape casting method; the silicon dioxide anti-reflection film is a SiO2-PI-SiO2 sandwich structure formed by preparing sol through a Stober method, aging the sol and uniformly plating the sol on a polyimide film substrate through a dip-coating method. The average transmittance of the polyimide composite film with the SiO2 anti-reflection films on the two sides and doped with the modified Al2O3 microspheres in the visible light range exceeds 97%, and meanwhile the polyimide composite film has excellent thermal performance and mechanical performance. The method can be used for large-scale production, and a new high-quality and sustainable substrate material selection is provided for the flexible display industry.

Description

Technical Field

[0001] The present invention belongs to the technical field of polyimide composite materials, and relates to a polyimide composite film with ultra-high transmittance for flexible display, which is mainly applied to the field of flexible display. Background Art

[0002] With the continuous upgrading of intelligent communication devices and intelligent wearable devices, the requirements for flexible display are getting higher and higher. At the same time, due to the excellent thermal stability, good mechanical properties, low density and light weight of polyimide films, they have attracted much attention in the field of flexible display. Compared with the use of traditional rigid glass substrates, flexible colorless transparent polyimide films have the characteristics of easy processing, good flexibility, and resistance to high and low temperatures, and also have excellent capabilities to cope with different processing and use environments, and can encapsulate devices of any shape. However, traditional polyimide films also have problems that need to be solved urgently, mainly the low optical transmittance, which seriously affects the use experience of flexible display devices. The reason is that charge transfer effects (CTC) are likely to occur within or between polyimide molecules, and this effect causes the polyimide film to absorb in the visible light region, resulting in a decrease in optical transmittance. Summary of the Invention

[0003] In view of the above problems, the object of the present invention is to provide a polyimide composite film with ultra-high transmittance for flexible display through chemical design and physical modification methods.

[0004] The technical solution of the present invention is as follows: A polyimide composite film with ultra-high transmittance for flexible display according to the present invention includes a transparent polyimide film product doped with Al 2 O 3 fillers as a substrate and antireflection films of silicon dioxide on both sides of the polyimide film substrate;

[0005] Among them, the substrate is shown as the following formula:

[0006]

[0007] In the above formula: 100 < n < 800;

[0008] The transparent polyimide film product doped with Al 2 O 3 fillers is obtained by uniformly mixing a polyimide solution and Al 2 O 3 powder modified by silane coupling agent KH560, and then through the casting method;

[0009] The antireflection films on both sides of the polyimide film substrate are prepared by dipping the polyimide film in silica sol and then controlling the pulling process. The pulling speed of the two layers of silica antireflection films is 1000 - 5000 μm / s, and after pulling, they are suspended in the air for 10 - 30 minutes. The silica antireflection films are uniformly combined with the polyimide matrix, and the thickness is about 160 - 210 nm.

[0010] Further, the preparation steps of the transparent polyimide film product doped with Al 2 O 3 fillers with the substrate are as follows:

[0011] Step (1): Put diamine monomers, aromatic dianhydride monomer hexafluoroisopropyl phthalic anhydride (6FDA), organic solvents such as m-cresol or N-methylpyrrolidone, and a small amount of isoquinoline or quinoline (usually 5 - 6 drops are added in the reaction) into a reaction vessel, introduce an inert gas (such as N 2 , Ar), and after a period of time, heat to 50°C to dissolve into a liquid containing a mixture of diamine monomers and aromatic dianhydride monomer hexafluoroisopropyl phthalic anhydride.

[0012] Step (2): Heat the completely dissolved viscous liquid obtained in step (1) to 120 - 160°C and react for 8 - 12 hours, then heat to 190 - 205°C and react for 16 - 20 hours to obtain a light yellow transparent polyimide solution, and wash it to remove impurities for purification purposes.

[0013] Wait for the reaction system to cool to 30 - 40°C, pour the obtained light yellow transparent polyimide solution into a large amount of vigorously stirred poor solvent, and then white fibrous polyimide solids will precipitate, and then filter by suction.

[0014] Step (3): Dissolve the white fibrous polyimide solids obtained in step (2) in an organic solvent, heat to 45 - 55°C and stir for 3 - 12 hours to obtain a purified light yellow transparent polyimide solution. Pour the purified light yellow transparent polyimide solution into another large amount of vigorously stirred poor solvent prepared, and white fibrous polyimide solids after purification will precipitate, and then filter by suction; repeat this twice, and then place the white fibrous polyimide solids in a vacuum oven at 110 - 120°C and dry for 24 - 36 hours to obtain purified and dried white fibrous polyimide solids.

[0015] Step (4): Dissolve the dried white fibrous polyimide solids obtained in step (3) in the prepared organic solvent, and incorporate Al 2 O 3The powder is stirred at 45 - 75 °C for 12 - 16 h, and the insoluble impurities are removed by filtration through a filter head. Then, it is cast into a film on a glass substrate by the casting method and peeled off in deionized water after the heating program ends.

[0016] Further, in step (1), the preparation steps of the diamine monomer are as follows:

[0017] Step (1.1): Different anilines and different benzaldehydes or cyclohexanecarboxaldehydes are added to a reactor, heated to 80 - 120 °C, then hydrochloric acid (37 wt%) is added to a dropping funnel, slowly dropped, and then the temperature is raised to 150 - 160 °C, and the reaction is carried out for 10 - 20 h to obtain a black-purple viscous liquid;

[0018] Among them, the molar ratio of aniline to benzaldehyde or cyclohexanecarboxaldehyde in the feed is 2.2 - 2.8:1, and the molar ratio of hydrochloric acid to aniline in the feed is 0.25 - 0.65:1;

[0019] Step (1.2): The obtained viscous liquid is added to a basic solution for neutralization, then an organic solvent is added for extraction, and after extraction and separation, an oily liquid is obtained, and it is further purified by silica gel column chromatography and recrystallization in ethanol, methanol or petroleum ether for further purification;

[0020] Among them, the basic solution is ammonia water (28 - 30 wt%); its molar ratio to hydrochloric acid is 2.5 - 3.5:1;

[0021] The organic solvent is one of dichloromethane, petroleum ether, ethanol, etc.;

[0022] The solvent for recrystallization is one of ethanol, methanol or petroleum ether.

[0023] Further, in step (1), the molar ratio of the diamine monomer, the aromatic dianhydride monomer hexafluoroisopropyl phthalic anhydride and m-cresol is 1:1:0.15 - 0.26;

[0024] The added isoquinoline or quinoline is 0.002 - 0.003 mol;

[0025] The inert gas is nitrogen or argon;

[0026] The period of introducing the inert gas is 10 - 30 min.

[0027] Further, in step (2), the poor solvent is one of methanol, ethanol or water, and its dosage is 400 - 1000 ml.

[0028] Further, in step (3), the organic solvent is one or a mixed solution of two of organic solvents such as N-methylpyrrolidone (NMP), N,N-dimethylacetamide (DMAc), and N,N-dimethylformamide (DMF);

[0029] The poor solvent is one of methanol, ethanol, or water.

[0030] Further, in step (4), the organic solvent is N,N-dimethylacetamide (DMAc);

[0031] The content of the white fibrous polyimide solid dissolved in the organic solvent is 45 - 80 mg / ml;

[0032] The filter head is a glass fiber filter head or an organic filter head with a size of 0.2 - 0.7 μm;

[0033] The heating program includes three stages. The first stage is in a non-vacuum state, with a temperature of 50 - 80 °C and maintained for 6 - 8 h. The second stage is in a vacuum state, with a temperature of 90 - 110 °C and maintained for 2 - 3 h. The third stage is in a vacuum state, with a temperature of 190 - 210 °C and maintained for 12 - 15 h.

[0034] Further, in step (4), the preparation steps of incorporating Al powder modified with silane coupling agent KH560 are as follows: 2 O 3 Step (4.1): Add 0.6 g of NaOH, 100 ml of deionized water, and 16 g of Al

[0035] O 2 O 3 to a beaker, stir at 70 °C for 12 h, then stir at room temperature for 12 h. Add acetic acid to neutralize in the uniformly mixed solution, then wash with ethanol, and vacuum dry in an oven for 12 h to obtain activated Al 2 O 3 powder;

[0036] Among them, the molar ratio of acetic acid to NaOH is 1:1;

[0037] Step (4.2): Add 0.1 - 5 g of silane coupling agent KH560, 10 - 100 ml of deionized water, and 10 - 100 ml of ethanol to a beaker, stir at 55 °C for 2 h, then add the activated Al 2 O 3 powder prepared in step (1) into the beaker, continuously stir for 8 h, filter and dry to obtain Al 2 O 3 powder modified with silane coupling agent KH560;

[0038] Further, the silica antireflection film (SiO 2 antireflection film) is prepared by the Stober method to prepare a sol, and after aging, it is uniformly coated on the substrate by the dip-coating method. The preparation steps are as follows:

[0039] Step (9.1): Add 90 - 120 g of ethanol, 12 - 20 g of tetraethyl orthosilicate, and 2 - 4 g of ammonia water (28 - 30 wt%) into the reactor. After stirring at 0 - 6 °C for 2 - 5 h, place it in an environment of 3 - 5 °C and age in the dark for 7 - 12 days to obtain a silica sol;

[0040] Step (9.2): Condense and reflux the silica sol obtained in step (9.1) at 80 °C for 24 - 36 h to obtain a treated silica sol;

[0041] Step (9.3): Immerse the substrate in the sol, and then slowly pull the substrate out of the sol to obtain a silica antireflection film on both sides of the substrate; the silica antireflection film on both sides of the substrate and the substrate form a polyimide composite film;

[0042] Among them, the slow pulling speed is 1000 - 5000 μm / s.

[0043] The beneficial effects of the present invention are as follows: 1. The polyimide composite film with large - volume side groups of the present invention has good flexibility and processability. At the same time, tert - butyl and isopropyl groups have large volumes, which can generate large steric hindrance to achieve the purpose of destroying high conjugation and improving the transmittance. At the same time, the large groups affect the rotational freedom of the groups in the polyimide main chain, thus maintaining high thermal stability, so that the polyimide film has high transmittance in the visible light region while maintaining good thermal and mechanical properties. The average transmittance of the obtained polyimide composite film in the visible light range exceeds 97%, and the 5% thermal decomposition temperature exceeds 515 °C; 2. The polyimide composite film with large - volume side groups of the present invention uses the dip - coating method to uniformly coat the film, with low synthesis cost, simple process flow, and can be industrially produced; 3. The polyimide composite film of the present invention has high transmittance in a wide range of wavelengths; 4. The refractive index of the SiO 2 antireflection film of the present invention can be adjusted by selecting different ratios of each reagent in the formula, and the thickness can be adjusted by the pulling speed during dip - coating, and it can be applied to the antireflection and antireflection enhancement of polyimide films with different repeating units; 5. The Al 2 O 3 powder modified by the silane coupling agent KH560, by incorporating different mass fractions, can improve the mechanical properties of the polyimide composite film and increase the number of bending resistance times while maintaining the ultra - high transmittance of the polyimide composite film. Description of the Drawings

[0044] Figure 1 is the ultraviolet-visible-infrared spectrum of the polyimide film obtained in Example 4 of the present invention;

[0045] Figure 2 is the infrared spectrum of the polyimide film obtained in Example 4 of the present invention;

[0046] Figure 3 is the ultraviolet-visible-infrared spectrum of the polyimide composite film obtained in Example 8 of the present invention;

[0047] Figure 4 is the infrared spectrum of the polyimide composite film obtained in Example 8 of the present invention;

[0048] Figure 5 is the schematic structural diagram of the polyimide composite film of the present invention. Detailed implementation manners

[0049] The following further elaborates on the specific technical solutions of the present invention in combination with specific examples.

[0050] In the first aspect of the present invention, the present invention provides a variety of diamine monomers with large-volume side groups, having the following structure:

[0051]

[0052] In the second aspect, the present invention provides a synthesis method of the diamine monomer described in the first aspect, including:

[0053] a step of reacting the corresponding aniline with the corresponding benzaldehyde or cyclohexanecarboxaldehyde under the action of concentrated hydrochloric acid to prepare the target diamine monomer,

[0054]

[0055]

[0056]

[0057] Further, add the corresponding aniline and the corresponding benzaldehyde or cyclohexanecarboxaldehyde into the reactor, heat to 80 - 120 °C, slowly dropwise add concentrated hydrochloric acid, and then heat up to 150 - 160 °C, and react for 10 - 20 h.

[0058] Further, the feeding molar ratio of the corresponding aniline to the corresponding benzaldehyde or cyclohexanecarboxaldehyde is 2.2 - 2.8:1, and the feeding molar ratio of concentrated hydrochloric acid to aniline is 0.25 - 0.65:1.

[0059] In the third aspect, the present invention provides a polyimide composite film with ultra-high transmittance for flexible display, including doped with modified Al 2 O 3A polyimide film substrate in powder form and antireflection silica films disposed on both sides of the polyimide film substrate. The polyimide film substrate is composed of the following repeating structural units:

[0060]

[0061] Wherein: 100 < n < 800.

[0062] Furthermore, the thickness of the single-layer antireflection silica film is 160 - 210 nm.

[0063] Fourthly, the present invention also provides a method for preparing the polyimide composite film with ultra-high transmittance for flexible display described in the third aspect. The antireflection silica film is combined with the polyimide film substrate by dip coating. The polyimide film substrate is prepared successively by steps of synthesizing a transparent polyimide solution, purification, doping, and film formation by casting method. Among them, synthesizing the transparent polyimide solution includes the following steps:

[0064] Adding a diamine monomer, an aromatic dianhydride monomer hexafluoroisopropyl phthalic anhydride (6FDA), organic solvents such as m-cresol, and a catalyst isoquinoline or quinoline into a reaction vessel. After introducing an inert gas for a period of time, heating to 50 °C for dissolution. Heating the obtained viscous liquid to 120 - 160 °C for reaction for 8 - 12 h, and then heating to 190 - 205 °C for reaction for 16 - 20 h to obtain a transparent polyimide solution;

[0065]

[0066] Furthermore, the molar ratio of the diamine monomer, the aromatic dianhydride monomer hexafluoroisopropyl phthalic anhydride, and m-cresol is 1:1:0.15 - 0.26; the added isoquinoline or quinoline is 0.002 - 0.003 mol; the period of introducing the inert gas is 10 - 30 min; the inert gas is nitrogen or argon.

[0067] Furthermore, when incorporating Al 2 O 3 powder modified by a silane coupling agent KH560, the mass fraction of the Al 2 O 3 powder is 5 - 10%.

[0068] Furthermore, the film formation step by casting method is specifically: After purification, incorporating Al 2 O 3The polyimide solution in powder form is cast on a glass substrate by the casting method, and the film is formed by programmed heating. After the film formation is completed, it is peeled off in deionized water to obtain a polyimide film substrate. The programmed heating is divided into three stages. The first stage is in a non-vacuum state, with a temperature of 50-80 °C and maintained for 6-8 h. The second stage is in a vacuum state, with a temperature of 90-110 °C and maintained for 2-3 h. The third stage is in a vacuum state, with a temperature of 190-210 °C and maintained for 12-15 h.

[0069] Further, the silica antireflection film is combined with the polyimide film substrate by the dip-coating method, and the pulling speed is 1000-5000 μm / s.

[0070] Further, the silica antireflection film is prepared by the following steps:

[0071] (1) Ethanol, tetraethyl orthosilicate and concentrated ammonia water (28-30 wt%) are added to a reactor, stirred at 0-6 °C for 2-5 h, and then placed in an environment at 3-5 °C for light-shielding aging for 7-12 days;

[0072] (2) The sol obtained in step (1) is placed at 80 °C for condensation reflux for 24-36 h;

[0073] Among them, the mass ratio of ethanol, tetraethyl orthosilicate and concentrated ammonia water is 30-40:4-7:1.

[0074] The polyimide composite film described in the present invention is composed of a polyimide film substrate doped with modified Al 2 O 3 powder and silica antireflection films provided on both sides of the polyimide film substrate.

[0075] In the following examples, except for the synthesis of diamine monomers, the remaining raw materials (such as hexafluoroisopropyl phthalic anhydride, isoquinoline, N,N-dimethylacetamide, tetraethyl orthosilicate, m-cresol, etc.) are all commercially available products. Among them, m-cresol is used after further purification by vacuum distillation.

[0076] The methods for testing the structure and performance of the samples obtained in the following examples are as follows:

[0077] Its polyimide structure is tested on a Fourier transform infrared spectrometer - infrared microscope Nicolet IS50. Under the ATR module, the resolution is 4 cm -1 , and scanned 32 times in total. The spectral range is 500-4000 cm -1 .

[0078] Its glass transition temperature (Tg) was tested by a differential scanning calorimeter TA Instruments Q2000 under a nitrogen atmosphere with a heating or cooling rate of 20 °C / min, a test range of 40 - 420 °C, and a sample weight of approximately 5 mg.

[0079] Its thermal decomposition temperature (T 5％ 、T 10％ and R 800℃ ) was tested by a thermogravimetric analyzer TG209F3 in an N 2 atmosphere with a temperature range of 50 °C to 800 °C and a heating rate of 20 °C / min.

[0080] Its optical transmittance was tested by an ultraviolet - visible - infrared spectrophotometer PerkinElmer Lambda 1050+ with a test range of 200 - 1200 nm.

[0081] Example 1

[0082] The preparation process of the diamine monomer FTTBP is as follows:

[0083] (1) Add 2 - tert - butylaniline (7.8 g, 0.0525 mol) and 3,5 - di - tert - butylbenzaldehyde (4.5 g, 0.0205 mol) into a 100 ml three - necked flask, heat to 80 °C under argon protection, and continuously stir for 30 min. Then, slowly drop hydrochloric acid (37 wt%, 1 ml) into the flask within 30 min. After uniform stirring, raise the reaction system temperature to 150 °C and continuously stir for 20 h;

[0084] (2) When the reaction solution in step (1) cools to 80 °C, slowly drop - add dichloromethane for extraction. When the reaction system cools to 60 °C, drop - add ammonia water (28 - 30 wt%, 2.5 ml) and stir for neutralization. Wash the organic phase with deionized water three times, and then dry it with anhydrous sodium sulfate to remove water; After standing for a period of time, filter out the organic phase, and purify it by a silica gel column chromatography using a mixed eluent of ethyl acetate and petroleum ether (1:20, V / V) to obtain a light yellow solid; Finally, recrystallize with ethanol twice to obtain 8.49 g of a colorless transparent solid.

[0085] Example 2

[0086] The preparation process of the diamine monomer 3,3′ - di - tert - butyl - 4,4′ - diaminodiphenyl - 4″ - tert - butylphenylmethane (TADBP) is as follows:

[0087] (1) Add 2-tert-butylaniline (10.7 g, 0.072 mol) to a 100-ml three-necked flask. Heat it to 120 °C under argon protection and stir continuously for 30 min. Then, slowly add a mixture of 4-tert-butylbenzaldehyde (4.5 g, 0.028 mol) and hydrochloric acid (37 wt%, 1 ml) to the flask within 40 min. After stirring evenly, raise the temperature of the reaction system to 150 °C and stir continuously for 15 h;

[0088] (2) When the reaction solution in step (1) cools to 80 °C, slowly add dichloromethane for extraction. When the reaction system cools to 60 °C, add ammonia water (28 - 30 wt%, 2.5 ml) and stir for neutralization. Wash the organic phase with deionized water, repeat three times, and then dry it with anhydrous sodium sulfate to remove water. After standing for a period of time, filter out the organic phase, and purify it by column chromatography on silica gel using a mixed eluent of ethyl acetate and petroleum ether (1:15, V / V) to obtain a light yellow solid. Finally, recrystallize it with ethanol twice to obtain 9.26 g of light yellow solid.

[0089] Example 3

[0090] The preparation process of Al 2 O 3 powder modified with silane coupling agent KH560 is as follows:

[0091] (1) Add 0.6 g of NaOH, 100 ml of deionized water, and 16 g of Al 2 O 3 to a beaker, stir at 70 °C for 12 h, then stir at room temperature for 12 h. Add acetic acid to neutralize in the uniformly mixed solution, then wash with ethanol, and vacuum dry in an oven for 12 h to obtain activated Al 2 O 3 powder;

[0092] (2) Add 1 g of silane coupling agent KH560, 50 ml of deionized water, and 50 ml of ethanol to a beaker, stir at 55 °C for 2 h. Then add 5 g of Al 2 O 3 powder obtained in step (1) to the beaker, continue to stir for 8 h, filter and dry to obtain Al 2 O 3 powder modified with silane coupling agent KH560.

[0093] Example 4

[0094] The preparation process of the polyimide film substrate in this example is as follows:

[0095]

[0096] (1) Under the protection of flowing argon gas, FTTBP (1.4952 g, 3 mmol), 6FDA (1.3327 g, 3 mmol) and 15.50 ml of m-cresol were poured into a 50 ml three-necked flask, mechanically stirred and refluxed with condensation. The system was heated to 50 °C. After dissolution, 6 drops of isoquinoline were added dropwise, the temperature was raised to 120 °C and maintained for 10 h, and then the temperature was raised to 195 °C and maintained for 16 h;

[0097] (2) The viscous liquid obtained in step (1) was cooled to room temperature and poured into vigorously stirred hot methanol to precipitate white fibrous polyimide solid. Subsequently, the PI fibrous solid was placed in a blast drying oven at 80 °C and dried overnight;

[0098] (3) The white fibrous polyimide solid obtained in step (2) was dissolved in DMAc, heated to 55 °C, stirred for 6 h, and then poured into hot methanol again for reprecipitation and washing. This step was repeated twice. Finally, the PI solid was placed in a vacuum drying oven and dried in a vacuum environment at 110 °C for 12 h;

[0099] (4) The polyimide was dissolved in DMAc (55 mg / ml), and 5 wt% of Al 2 O 3 powder modified with silane coupling agent KH560 was added, and stirred at 60 °C to obtain a homogeneous solution. The impurities were removed by filtering with a 0.7 μm glass fiber filter head; then it was cast into a film on a clean glass substrate by the casting method, placed in a vacuum drying oven, maintained at a temperature of 60 °C for a total of 6 h, evacuated to below 0.01 MPa, then the temperature was raised to 100 °C and maintained for 1 h, and 200 °C and maintained for 12 h; after the temperature dropped below 60 °C, the glass substrate was placed in deionized water and waited to peel off naturally to obtain a polyimide film, that is, a polyimide film substrate. Its ultraviolet-visible-infrared spectrum and infrared spectrum are shown in Figure 2 and Figure 3 .

[0100] It was measured that the glass transition temperature of this film was greater than 295 °C, the 5% thermal decomposition temperature was greater than 515 °C, the 10% thermal decomposition temperature was greater than 530 °C, the carbon residue rate at 800 °C was greater than 54%, and the average visible light transmittance of the film with a thickness of 25 - 35 μm was 91.0%.

[0101] Example 5

[0102] The preparation process of the polyimide film substrate in this example is as follows:

[0103] (1) Under the protection of flowing argon, TADBP (0.8847 g, 2 mmol), 6FDA (0.8885 g, 2 mmol) and 12.50 ml of m-cresol were poured into a 50 ml three-necked flask, mechanically stirred and refluxed with condensation. The system was heated to 60 °C. After dissolution, 5 drops of isoquinoline were added dropwise, the temperature was raised to 160 °C and maintained for 8 h, and then the temperature was raised to 200 °C and maintained for 18 h;

[0104] (2) The viscous liquid obtained in step (1) was cooled to room temperature and poured into vigorously stirred hot methanol to precipitate white fibrous polyimide solid. Subsequently, the PI fibrous solid was placed in a blast drying oven at 80 °C and dried overnight;

[0105] (3) The white fibrous polyimide solid obtained in step (2) was dissolved in DMAc, heated to 65 °C, stirred for 4 h, and then poured into hot methanol again for reprecipitation and washing. This step was repeated three times; finally, the PI solid was placed in a vacuum drying oven and dried in a vacuum environment at 115 °C for 24 h;

[0106] (4) The polyimide was dissolved in DMAc (60 mg / ml), and 8 wt% of Al powder modified with silane coupling agent KH560 was added, and stirred at 55 °C to obtain a uniform solution. The impurities were removed by filtering with a 0.22 μm organic filter head; then it was cast into a film on a clean glass substrate by the casting method, placed in a vacuum drying oven, maintained at 70 °C for 8 h, evacuated to below 0.01 MPa, then the temperature was raised to 105 °C and maintained for 4 h, and 200 °C and maintained for 14 h; after the temperature was lowered to room temperature, the glass substrate was placed in deionized water and waited for natural peeling to obtain a polyimide film. 2 O 3 It was measured that the glass transition temperature of this film was greater than 295 °C, the 5% thermal decomposition temperature was greater than 520 °C, the 10% thermal decomposition temperature was greater than 537 °C, the carbon residue rate at 800 °C was greater than 54%, and the average visible light transmittance of the film with a thickness of 25 - 35 μm was 90.8%.

[0107] Example 6

[0108] The preparation method of the anti-reflection film of silicon dioxide (silicon dioxide sol) is as follows:

[0109] (1) Weigh 120 g of ethanol, 15 g of TEOS and 2.75 g of ammonia water (28 - 30 wt%) and put them into a 250 ml round-bottomed flask, stir vigorously in an ice-water mixture (about 3 - 5 °C) for 2 h; then, seal it and place it in the refrigerator for refrigeration (about 5 °C) and age for 8 days;

[0110] (2) Seal it and place it in the refrigerator for refrigeration (about 5 °C) and age for 8 days;

[0111] (2), Subsequently, the sol obtained in step (1) was condensed and refluxed at 80 °C for 24 h. After the sol cooled down, the sol was filtered using a 0.7-μm glass fiber filter head.

[0112] Example 7

[0113] The preparation method of the anti-reflection film made of silica (silica sol) is as follows:

[0114] (1), Weigh 110 g of ethanol, 13 g of TEOS, and 3.25 g of ammonia water (28-30 wt%) and put them into a 250-ml round-bottom flask. Stir vigorously in an ice-water mixture (about 3-5 °C) for 4 h; then, seal it and put it in the refrigerator for cold storage (about 5 °C) and age for 12 days;

[0115] (2), Subsequently, the sol obtained in step (1) was condensed and refluxed at 80 °C for 36 h. After the sol cooled down, the sol was filtered using a 0.7-μm glass fiber filter head.

[0116] Example 8

[0117] The preparation method of the polyimide multi-layer composite film is as follows:

[0118] (1), Place the polyimide film substrate obtained in Example 4 above the sol obtained in Example 6. Lower the polyimide film substrate completely into the sol at a speed of 5000 μm / s. Subsequently, pull out the film at a speed of 1000 μm / s;

[0119] (2), Hang the film obtained in step (1) in the air and let it stand for 15 min to obtain the polyimide multi-layer composite film. Its ultraviolet-visible-infrared spectrum and infrared spectrum are shown in Figure 4 and Figure 5 .

[0120] After testing, the glass transition temperature of this film is greater than 296 °C, the 5% thermal decomposition temperature is greater than 512 °C, the 10% thermal decomposition temperature is greater than 528 °C, the carbon residue rate at 800 °C is greater than 52%, and the average visible light transmittance of the 25-35-μm-thick film is 97.3%.

[0121] Example 9

[0122] (1), Place the polyimide film substrate obtained in Example 4 above the sol obtained in Example 7. Lower the polyimide film substrate completely into the sol at a speed of 5000 μm / s. Subsequently, pull out the film at a speed of 2000 μm / s;

[0123] (2), Hang the film obtained in step (1) in the air and let it stand for 30 min.

[0124] After testing, the glass transition temperature of the film is greater than 295 °C, the 5% thermal decomposition temperature is greater than 510 °C, the 10% thermal decomposition temperature is greater than 530 °C, the carbon residue rate at 800 °C is greater than 51%, and the average visible light transmittance of the film with a thickness of 25 - 35 μm is 97.2%.

Claims

1. A polyimide composite film with ultra-high transmittance for flexible display, characterized in that: The polyimide composite film comprises a transparent polyimide film product doped with Al2O3 filler as a substrate and a silicon dioxide anti-reflection film on both sides of the substrate; Wherein, the substrate is shown in the following formula: In the above formula: 100 <n<800; The substrate is a transparent polyimide film product doped with Al2O3 filler, which is obtained by uniformly mixing a polyimide solution and Al2O3 powder modified by a silane coupling agent KH560, and then using a casting method; The silicon dioxide anti-reflection films on both sides of the substrate are obtained by immersing the substrate in silicon dioxide sol and then pulling it up under control. The pulling speed is 1000-5000 μm / s and the substrate is suspended in the air for 10-30 minutes after pulling.

2. The polyimide composite film with ultra-high transmittance for flexible display according to claim 1, characterized in that: The preparation steps of the transparent polyimide film product doped with Al2O3 filler as the substrate are as follows: Step (1): adding a diamine monomer and an aromatic dianhydride monomer hexafluoroisopropylphthalic anhydride, m-cresol, isoquinoline or quinoline into a reaction container, introducing an inert gas for a period of time and then heating to 50° C. to dissolve the mixture into a liquid containing a mixture of the diamine monomer and the aromatic dianhydride monomer hexafluoroisopropylphthalic anhydride; Step (2): heating the liquid obtained in step (1) to 120-160° C. and reacting for 8-12 hours, and then heating to 190-205° C. and reacting for 16-20 hours to obtain a light yellow transparent polyimide solution; Wait for the reaction system to cool to 30-40°C, pour the obtained light yellow transparent polyimide solution into a continuously stirred poor solvent, and then precipitate a white fibrous polyimide solid, which is filtered; Step (3): dissolving the white fibrous polyimide solid obtained in step (2) in an organic solvent, heating to 45-55° C. and stirring for 3-12 hours to obtain a purified light yellow transparent polyimide solution, pouring the purified light yellow transparent polyimide solution into a separately prepared poor solvent, precipitating a purified white fibrous polyimide solid, and filtering; after repeating twice, placing the white fibrous polyimide solid in a vacuum oven at 110-120° C. and drying for 24-36 hours to obtain a purified and dried white fibrous polyimide solid; Step (4): dissolving the dry white fibrous polyimide solid obtained in step (3) in a prepared organic solvent, adding Al2O3 powder modified with silane coupling agent KH560, stirring at 45-75°C for 12-16h, filtering through a filter head to remove insoluble impurities, and then casting it into a film on a glass substrate by a casting method. After the heating program is completed, it is placed in deionized water for peeling.

3. The polyimide composite film with ultra-high transmittance for flexible display according to claim 2, characterized in that: In step (1), the preparation steps of the diamine monomer are as follows: Step (1.1): add different anilines and different benzaldehydes or cyclohexanecarboxaldehydes into a reactor, heat to 80-120°C, then add hydrochloric acid into a dropping funnel, raise the temperature to 150-160°C after dropwise addition, react for 10-20h, and obtain a black-purple viscous liquid; The molar ratio of aniline to benzaldehyde or cyclohexanecarboxaldehyde is 2.2-2.8:1, and the molar ratio of hydrochloric acid to aniline is 0.25-0.65:

1. Step (1.2): adding an alkaline solution to neutralize the obtained viscous liquid, then adding an organic solvent to extract, extracting and separating to obtain an oily liquid, separating and purifying by silica gel column chromatography, and finally purifying by recrystallization; Wherein, the alkaline solution is aqueous ammonia; The molar ratio of alkaline solution to hydrochloric acid is 2.5-3.5:1; The organic solvent is one of dichloromethane, petroleum ether and ethanol; The recrystallization solvent is one of ethanol, methanol or petroleum ether.

4. The polyimide composite film with ultra-high transmittance for flexible display according to claim 2, characterized in that: In step (1), the molar ratio of the diamine monomer, the aromatic dianhydride monomer hexafluoroisopropylphthalic anhydride and m-cresol is 1:1:0.15-0.26; The added isoquinoline or quinoline is 0.002-0.003 mol; The inert gas is nitrogen or argon; The period of time for introducing the inert gas is 10-30 minutes.

5. The polyimide composite film with ultra-high transmittance for flexible display according to claim 2, characterized in that: In step (2), the poor solvent is one of methanol, ethanol or water, and the dosage is 400-1000 ml.

6. The polyimide composite film with ultra-high transmittance for flexible display according to claim 2, characterized in that: In step (3), the organic solvent is a mixed solution of one or two of N-methylpyrrolidone, N,N-dimethylacetamide and N,N-dimethylformamide; The poor solvent is one of methanol, ethanol or water.

7. The polyimide composite film with ultra-high transmittance for flexible display according to claim 2, characterized in that: In step (4), the organic solvent is N,N-dimethylacetamide (DMAc); The content of the white fibrous polyimide solid dissolved in the organic solvent is 45-80 mg / ml; The filter head is a 0.2-0.7 μm glass fiber filter head or an organic filter head; The temperature rising program includes three stages. The first stage is a non-vacuum state with a temperature of 50-80°C and maintained for 6-8h. The second stage is a vacuum state with a temperature of 90-110°C and maintained for 2-3h. The third stage is a vacuum state with a temperature of 190-210°C and maintained for 12-15h.

8. The polyimide composite film with ultra-high transmittance for flexible display according to claim 2, characterized in that: In step (4), the preparation steps of the Al2O3 powder modified with the silane coupling agent KH560 are as follows: Step (4.1): add 0.6 g NaOH, 100 ml deionized water and 16 g Al2O3 into a beaker, stir at 70°C for 12 h, then stir at room temperature for 12 h, add acetic acid to the mixed solution for neutralization, then wash with ethanol, and vacuum dry in an oven for 12 h to obtain activated Al2O3 powder; Wherein, the molar ratio of acetic acid to NaOH is 1:1; Step (4.2): Add 0.1-5 g of silane coupling agent KH560, 10-100 ml of deionized water, and 10-100 ml of ethanol into a beaker, stir at 55°C for 2 h, then add the activated Al2O3 powder obtained in step (1) into the beaker, continue stirring for 8 h, filter and dry to obtain Al2O3 powder modified with silane coupling agent KH560.

9. The polyimide composite film with ultra-high transmittance for flexible display according to claim 1, characterized in that: The silicon dioxide anti-reflection film is prepared by the Stober method to prepare the sol, and after aging, it is uniformly plated on the substrate by the immersion and pulling method. The preparation steps are as follows: Step (9.1): 90-120 g of ethanol, 12-20 g of tetraethyl silicate and 2-4 g of aqueous ammonia are added into a reactor, stirred at 0-6° C. for 2-5 h, and then placed in an environment at 3-5° C. and protected from light for aging for 7-12 days to obtain a silica sol; Step (9.2): placing the silica sol obtained in step (9.1) under condensation reflux at 80° C. for 24-36 hours to obtain a treated silica sol; Step (9.3): immersing the substrate in the sol, and then pulling the substrate out of the sol at a uniform speed to obtain a silica anti-reflection film on both sides of the substrate; the silica anti-reflection film on both sides of the substrate and the substrate constitute a polyimide composite film.

10. The polyimide composite film with ultra-high transmittance for flexible display according to claim 9, characterized in that: In step (9.3), the uniform speed is 1000-5000 μm / s.

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