Transparent polyamide acid syrup, transparent polyimide coating and preparation method and application thereof

Abstract

The present application relates to a kind of transparent polyamide acid slurry, transparent polyimide coating and its preparation method and application, belong to polyimide material technical field.The transparent polyamide acid slurry prepared by the present application is composed of polyamide acid resin and mixed solvent with different solubility parameters, and the transparent polyimide coating prepared after coating and heat treatment has high adhesion, solves the problems such as low adhesion, easy to fall off and easy to produce warping in the prior art when transparent polyimide is combined with glass substrate.The transparent polyimide coating provided by the present application can be applied to the manufacture of flexible display as transparent cover plate when combined with ultrathin glass or microcrystalline glass.

Description

Technical Field

[0001] This invention relates to the field of polyimide materials technology, and in particular to a transparent polyamic acid slurry, a transparent polyimide coating, and their preparation methods and applications. Background Technology

[0002] With the development of flexible display technology, foldable smartphones, laptops, and wearable electronic products using flexible displays are constantly being launched. In flexible display terminal products, the flexible cover material, which serves as the interface, must not only possess excellent optical transparency but also high strength, toughness, bending resistance, and impact resistance to meet the high reliability requirements of flexible display applications.

[0003] Currently, flexible cover materials mainly employ two technical routes: transparent polyimide (CPI) film and ultra-thin glass (UTG). CPI film boasts excellent flexibility and high impact resistance, but suffers from low surface hardness and susceptibility to creases, leading to localized deformation of the flexible display panel during long-term use. UTG combines the advantages of traditional rigid glass cover materials, such as high light transmittance, high surface hardness, and good bending resistance, but is brittle and has poor impact resistance. Utilizing the advantages of both polymer films and UTG to fabricate flexible composite substrates represents another compromise. Currently, this primarily involves bonding polymer films such as PET or CPI to the UTG surface using optically transparent adhesive (OCA) for protection, thus balancing the reliability requirements of flexible display panels in terms of bending resistance and impact resistance. However, this composite substrate structure inevitably increases the thickness of the display panel, failing to meet the application demands of increasingly ultra-thin and lightweight flexible terminal products.

[0004] Coating UTG surfaces with polymers such as CPI to prepare composite substrate materials is emerging as a new solution. However, because CPI materials are all fluorinated polyimide resin systems with low surface tension, they exhibit poor adhesion when directly coated onto UTG surfaces, easily leading to peeling, delamination, or even detachment. Furthermore, CPI coating on UTG surfaces requires a high-temperature heat treatment process, and the curing shrinkage of CPI can cause warping and deformation of the composite substrate, and even microcracks in the UTG. Summary of the Invention

[0005] Based on the above analysis, the present invention aims to provide a transparent polyamic acid slurry, a transparent polyimide coating, and the preparation method and application thereof, in order to solve the problems of low adhesion, easy peeling, warping deformation and microcracks of the composite substrate after the transparent polyimide coating is laminated with the ultrathin glass substrate in the prior art.

[0006] The objective of this invention is mainly achieved through the following technical solutions:

[0007] In a first aspect, the present invention provides a transparent polyamic acid slurry, the transparent polyamic acid slurry comprising a polyamic acid resin and a mixed solvent, wherein the polyamic acid resin is a block copolymer prepared by a fluorinated aromatic dianhydride or an alicyclic dianhydride with a fluorinated aromatic diamine and a siloxane-containing diamine, and the mixed solvent comprises two solvents A and B with different solubility parameters δ, wherein the solubility parameter of solvent A is greater than that of solvent B, the δ value of solvent A is 10.0 to 12.1, and the δ value of solvent B is 8.5 to 9.9.

[0008] Optionally, the polyamic acid resin has repeating units as shown in Formula IA or Formula IB:

[0009]

[0010]

[0011] In formula IA, Ar is selected from any one of the following groups:

[0012]

[0013] In the formula IB, Al is selected from any one of the following groups:

[0014]

[0015] In formulas IA and IB, R1 is selected from any one of the following groups:

[0016]

[0017] R2 is selected from any one of the following groups:

[0018]

[0019] The molar ratio of m to n in formulas IA and IB is (8:2) to (3:7).

[0020] Optionally, the fluorinated aromatic dianhydride comprises at least one of the following: 4,4'-(hexafluoroisopropyl)bisphthalic anhydride, 9,9-bis(trifluoromethyl)-2,3,6,7-oxanthracene tetracarboxylic anhydride, 4,4'-(2,2,2-trifluoro-1-phenyl-ethylidene)diphthalic anhydride, 4,4'-[2,2,2-trifluoro-1-(3-trifluoromethylphenyl)ethylidene]diphthalic anhydride, or 4,4'-[2,2,2-trifluoro-1-(3,5-bistrifluoromethylphenyl)ethylidene]diphthalic anhydride;

[0021] The alicyclic dianhydride comprises at least one of the following: 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,3,-dimethylcyclobutane-1,2,3,4-tetracarboxylic dianhydride, 1,2,4,5-cyclopentanetetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, bicyclo[2.2.1]hept-2,3,5,6-tetracarboxylic dianhydride, bicyclo[2.2.2]oct-2,3,5,6-tetracarboxylic dianhydride, and bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride;

[0022] The fluorinated aromatic diamine includes at least one of the following: 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether, 2,2-bis(4-aminophenyl)hexafluoropropane, 1,4-bis(2-trifluoromethyl-4-aminophenoxy)benzene, 4,4'-bis(4-amino-2-trifluoromethylphenoxy)biphenyl, and 2,2-bis[4-(4-aminophenoxybenzene)]hexafluoropropane;

[0023] The diamine containing a siloxane structure includes at least one of the following: 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane, bis(4-aminophenyl)tetramethyldisiloxane, bis(4-aminophenoxy)tetramethyldisiloxane, bis(3-aminophenoxy)tetramethyldisiloxane, bis(4-aminophenoxy)dimethylsilane, and bis(4-aminophenoxy)methylphenylsilane.

[0024] Optionally, solvent A includes at least one of N-methylpyrrolidone (NMP), N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and γ-butyrolactone (GBL);

[0025] Solvent B includes at least one of cyclohexanone, tetrahydrofuran, diethylene glycol dimethyl ether, xylene, and dioxane;

[0026] The mass ratio of solvent A to solvent B in the mixed solvent is (9:1) to (5:5).

[0027] Optionally, the transparent polyamic acid slurry has a solid content of 25-50 wt%, a rotational viscosity of 500-3000 mPa·s, a transmittance of >90% at 450 nm, and a turbidity of <1%, and features high solid content, low viscosity, and high transparency.

[0028] Secondly, the present invention provides a method for preparing a transparent polyamic acid slurry, which includes the following steps:

[0029] (1) Dissolve the fluorinated aromatic diamine in solvent A, cool the reaction system, add the fluorinated aromatic dianhydride or alicyclic dianhydride, stir the reaction, and obtain a homogeneous solution;

[0030] (2) Add solvent B to the homogeneous solution, cool the reaction system, add diamine containing siloxane structure, stir the reaction, and obtain transparent polyamic acid slurry.

[0031] In step (1), the reaction system is cooled to 5–20°C and the reaction time is 0.5–4 hours;

[0032] In step (2), the reaction system is cooled to -5 to 5°C and the reaction time is 8 to 24 hours.

[0033] Thirdly, the present invention provides a method for preparing a transparent polyimide coating, wherein the above-mentioned transparent polyamic acid slurry is coated on a substrate and heat-treated to obtain a transparent polyimide coating.

[0034] Optionally, the coating method includes blade coating, spin coating, dip coating, spray coating, or slot extrusion coating; the substrate is ultra-thin glass or microcrystalline glass; the heat treatment conditions are pre-drying at 60-80°C for 15-30 minutes, followed by heat treatment at 200-250°C for 0.5-3 hours.

[0035] Fourthly, the present invention provides a transparent polyimide coating, which is prepared by the above-mentioned preparation method. The thickness of the transparent polyimide coating is 10-50 μm, the average light transmittance in the wavelength range of 380-780 nm is >90%, the yellowness index is <2.0, the coating has excellent adhesion to the glass substrate, the cross-cut adhesion reaches 5B, and after aging for 240 hours in a humid heat environment of 60℃ / 90%RH, there is no blistering, no peeling, no warping, and no cracking.

[0036] Fifthly, the present invention provides an application of the above-mentioned transparent polyimide coating combined with ultrathin glass or microcrystalline glass as a transparent cover in a flexible display.

[0037] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0038] (1) The transparent polyamic acid slurry provided by the present invention is composed of polyamic acid resin and mixed solvent. The polyamic acid resin system is a block copolymer composed of alternating fluorinated aromatic segments or fluorinated alicyclic segments and flexible siloxane segments. The fluorinated aromatic segments or fluorinated alicyclic segments ensure that the coating has excellent optical transparency, while the introduction of flexible siloxane segments gives the coating good adhesion, solving the problem of low adhesion of traditional transparent fluorinated polyimide materials and easy peeling and falling off when combined with glass substrates.

[0039] (2) The transparent polyamic acid slurry provided by the present invention uses two mixed solvent systems with different solubility parameters (δ). Solvent A is a strong polar organic solvent with a higher δ value, and solvent B is a medium polar organic solvent with a relatively low δ value. By using solvents with different solubility parameters that are miscible, the problem of poor compatibility between strong polar fluorinated aromatic segments or fluorinated alicyclic segments and low polar siloxane segments, which easily leads to microphase separation during copolymerization, resulting in high turbidity of the slurry and thus affecting the optical performance of the coating is solved.

[0040] (3) The transparent polyamic acid slurry provided by this invention has the characteristics of high solid content (25-50 wt%) and low viscosity (rotational viscosity of 500-3000 mPa·s), which can meet the process requirements for preparing transparent coatings on glass substrates by various methods such as scraping, spin coating, dip coating, spraying, or slot extrusion coating. In addition, since the ultra-flexible siloxane segments in the resin system have good stress relaxation characteristics, it solves the problems of severe warping and deformation of the substrate and microcracks in the glass caused by large stress shrinkage during the preparation of coatings by polyamic acid thermal imidization.

[0041] (4) The transparent polyimide coating provided by the present invention not only has good optical transparency, but also has an average transmittance of >90% and a yellowness index of <2.0 in the wavelength range of 380-780nm after being combined with an ultra-thin glass substrate. At the same time, the coating has excellent adhesion to the glass substrate, with a cross-cut adhesion of 5B. After aging for 240 hours in a humid heat environment of 60℃ / 90%RH, there is no blistering, delamination, warping or cracking.

[0042] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages will become apparent from the description or may be learned by practicing the invention. Attached Figure Description

[0043] The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of the invention.

[0044] Figure 1 The ultraviolet-visible spectrum of the transparent polyamic acid slurry prepared in Example 1;

[0045] Figure 2 Infrared spectrum of the transparent polyimide coating prepared in Example 1;

[0046] Figure 3 Photographs showing the adhesion test results of the polyimide coating prepared in Example 1 to the coating on an ultrathin glass composite substrate using a cross-cut adhesion tester.

[0047] Figure 4 Photographs of the polyimide coating and ultrathin glass composite substrate prepared in Example 1 after damp heat aging. Detailed Implementation

[0048] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to the following embodiments.

[0049] Unless otherwise specified, all percentage contents in this invention refer to mass percentage contents. Unless otherwise specified, all methods described are conventional methods. Unless otherwise specified, all raw materials are commercially available.

[0050] In a first aspect, the present invention provides a transparent polyamic acid slurry, the transparent polyamic acid slurry being composed of polyamic acid resin and a mixed solvent, wherein the polyamic acid resin is a block copolymer prepared by fluorinated aromatic dianhydride or alicyclic dianhydride with fluorinated aromatic diamine and diamine containing siloxane structure, and the mixed solvent is composed of two solvents A and B with different solubility parameters (δ), wherein the solubility parameter of solvent A is greater than the solubility parameter of solvent B.

[0051] Specifically, solvent A is a highly polar organic solvent with a high δ value, and solvent B is a moderately polar organic solvent with a relatively low δ value. For example, the δ value of solvent A is 10.0 to 12.1, and the δ value of solvent B is 8.5 to 9.9.

[0052] Polyamic acid resins have repeating units as shown in Formula IA or Formula IB:

[0053]

[0054] In formula IA, Ar is selected from any one of the following groups:

[0055]

[0056] In the formula IB, Al is selected from any one of the following groups:

[0057]

[0058] In formulas IA and IB, R1 is selected from any one of the following groups:

[0059]

[0060] R2 is selected from any one of the following groups:

[0061]

[0062] The molar ratio of m to n in formulas IA and IB is (8:2) to (3:7).

[0063] Specifically, the fluorinated aromatic dianhydride includes at least one of the following: 4,4'-(hexafluoroisopropyl)bisphthalic anhydride, 9,9-bis(trifluoromethyl)-2,3,6,7-oxanthracene tetracarboxylic anhydride, 4,4'-(2,2,2-trifluoro-1-phenyl-ethylidene)diphthalic anhydride, 4,4'-[2,2,2-trifluoro-1-(3-trifluoromethylphenyl)ethylidene]diphthalic anhydride, or 4,4'-[2,2,2-trifluoro-1-(3,5-bistrifluoromethylphenyl)ethylidene]diphthalic anhydride;

[0064] The alicyclic dianhydride comprises at least one of the following: 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,3,-dimethylcyclobutane-1,2,3,4-tetracarboxylic dianhydride, 1,2,4,5-cyclopentanetetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, bicyclo[2.2.1]hept-2,3,5,6-tetracarboxylic dianhydride, bicyclo[2.2.2]oct-2,3,5,6-tetracarboxylic dianhydride, and bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride;

[0065] The fluorinated aromatic diamine includes at least one of the following: 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether, 2,2-bis(4-aminophenyl)hexafluoropropane, 1,4-bis(2-trifluoromethyl-4-aminophenoxy)benzene, 4,4'-bis(4-amino-2-trifluoromethylphenoxy)biphenyl, and 2,2-bis[4-(4-aminophenoxybenzene)]hexafluoropropane;

[0066] The diamine containing a siloxane structure includes at least one of the following: 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane, bis(4-aminophenyl)tetramethyldisiloxane, bis(4-aminophenoxy)tetramethyldisiloxane, bis(3-aminophenoxy)tetramethyldisiloxane, bis(4-aminophenoxy)dimethylsilane, and bis(4-aminophenoxy)methylphenylsilane.

[0067] In the mixed solvent, solvent A includes at least one of: N-methylpyrrolidone (NMP), N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and γ-butyrolactone (GBL);

[0068] Solvent B includes at least one of cyclohexanone, tetrahydrofuran, diethylene glycol dimethyl ether, xylene, and dioxane.

[0069] The mass ratio of solvent A to solvent B in the mixed solvent is (9:1) to (5:5).

[0070] The transparent polyamic acid slurry of the present invention has the characteristics of high solid content, low viscosity and high transparency. The solid content of the slurry is 25-50 wt%, the rotational viscosity is 500-3000 mPa·s, the transmittance at 450 nm is >90% and the turbidity is <1%.

[0071] Secondly, the present invention also provides a method for preparing a transparent polyamic acid slurry, which includes the following steps:

[0072] (1) Dissolve the fluorinated aromatic diamine in solvent A, cool the reaction system, then add the fluorinated aromatic dianhydride or alicyclic dianhydride, stir the reaction for a certain time to obtain a homogeneous solution;

[0073] (2) Add solvent B to the homogeneous solution, cool the reaction system, add diamine containing siloxane structure, and stir the reaction for a certain time to obtain transparent polyamic acid slurry.

[0074] In step (1), the reaction system is cooled to 5–20°C, for example, 5°C, 8°C, 10°C, 12°C, 15°C, 17°C, 18°C, or 20°C. The reaction time is 0.5–4 hours, for example, 0.5 hours, 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, or 4 hours.

[0075] In step (2), the reaction system is cooled to -5 to 5°C, for example, -5°C, -3°C, -1°C, 0°C, 1°C, 3°C, 5°C. The reaction time is 8 to 24 hours, for example, 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours, 24 hours.

[0076] Thirdly, the present invention also provides a method for preparing a transparent polyimide coating, comprising the following steps: coating a transparent polyamic acid slurry onto a glass substrate, and obtaining a transparent polyimide coating after heat treatment under certain conditions.

[0077] The coating methods include blade coating, spin coating, dip coating, spray coating, or slot extrusion coating;

[0078] The glass substrate is ultra-thin glass or microcrystalline glass with a thickness of 25-100μm, for example, 25μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm, 100μm.

[0079] The heat treatment includes: pre-drying at 60-80°C (e.g., 60°C, 65°C, 70°C, 75°C, 80°C) for 15-30 minutes (e.g., 15 minutes, 20 minutes, 25 minutes, 30 minutes), followed by heat drying at 200-250°C (e.g., 200°C, 210°C, 220°C, 230°C, 240°C, 250°C) for 0.5-3 hours (e.g., 0.5 hours, 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours).

[0080] Furthermore, this invention also provides a transparent polyimide coating, obtained using the above-described preparation method. The thickness of the transparent polyimide coating is 10–50 μm, for example, 10 μm, 20 μm, 30 μm, 40 μm, or 50 μm. When laminated with an ultrathin glass substrate, it exhibits an average light transmittance >90% in the wavelength range of 380–780 nm, a yellowness index <2.0, and excellent adhesion to the glass substrate, achieving a cross-cut adhesion of 5B. After 240 hours of aging in a humid heat environment of 60°C / 90% RH, it shows no blistering, delamination, warping, or cracking.

[0081] The present invention also provides the application of a transparent polyimide coating that can be combined with ultrathin glass or microcrystalline glass as a transparent cover in flexible displays.

[0082] Example 1

[0083] 9.61 g (0.03 mol) of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl and 192.85 g of N,N-dimethylacetamide DMAc (δ = 11.1) were added to a three-necked flask and stirred until completely dissolved under nitrogen protection. The reaction system was cooled to 5°C, and 44.42 g (0.1 mol) of 4,4'-(hexafluoroisopropyl)bisphthalic anhydride was added. The mixture was stirred for 1 hour to obtain a homogeneous solution. 21.43 g of tetrahydrofuran (δ = 9.5) was added to the reaction system, and after stirring until homogeneous, the reaction system was cooled to 5°C, and 17.40 g (0.07 mol) of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane was added. The mixture was stirred for another 8 hours to obtain a transparent polyamic acid slurry with a solid content of 25 wt% and a viscosity of 1155 mPa·s.

[0084] After filtration and vacuum degassing, the above-mentioned transparent polyamic acid slurry is coated onto a clean and smooth ultrathin glass substrate (40 μm thick) by a scraping method. After pre-drying at 80°C for 30 minutes, it is then heat-dried at 250°C for 1 hour in an air and nitrogen mixed atmosphere to complete the imidization reaction. After cooling to room temperature, a coating and an ultrathin glass single-sided composite substrate are obtained, with a transparent polyimide coating thickness of 30 μm.

[0085] The main properties of the transparent polyamic acid slurry, transparent polyimide coating, and their composite substrate with ultrathin glass prepared in this embodiment are shown in Table 1.

[0086] Example 2

[0087] 17.13 g (0.04 mol) of 1,4-bis(2-trifluoromethyl-4-aminophenoxy)benzene and 129.72 g of N-methylpyrrolidone (NMP) (δ = 11.3) were added to a three-necked flask and stirred under nitrogen protection until completely dissolved. The reaction system was cooled to 10 °C, and 45.82 g (0.1 mol) of 9,9-bis(trifluoromethyl)-2,3,6,7-oxanthracene tetracarboxylic acid dianhydride was added. The mixture was stirred for 0.5 hours to obtain a homogeneous solution. 55.59 g of cyclohexanone (δ = 9.9) was added to the reaction system, and after thorough stirring, the reaction system was cooled to -5 °C, and 16.46 g (0.06 mol) of bis(4-aminophenoxy)dimethylsilane was added. The reaction was continued for 12 hours to obtain a transparent polyamic acid slurry with a solid content of 30 wt% and a viscosity of 1950 mPa·s.

[0088] After filtration and vacuum degassing, the above-mentioned transparent polyamic acid slurry is coated onto a clean and smooth ultrathin glass substrate (50 μm thick) by a scraping method. After pre-drying at 60°C for 15 minutes, it is then heat-dried at 250°C for 2 hours in an air and nitrogen mixed atmosphere to complete the imidization reaction. After cooling to room temperature, a coating and an ultrathin glass single-sided composite substrate are obtained, with a transparent polyimide coating thickness of 35 μm.

[0089] The main properties of the transparent polyamic acid slurry, transparent polyimide coating, and their composite substrate with ultrathin glass prepared in this embodiment are shown in Table 1.

[0090] Example 3

[0091] 25.22 g (0.05 mol) of 4,4'-bis(4-amino-2-trifluoromethylphenoxy)biphenyl and 102.53 g of γ-butyrolactone GBL (δ = 10.0) were added to a three-necked flask and stirred under nitrogen protection until completely dissolved. The reaction system was cooled to 20 °C, and 45.23 g (0.1 mol) of 4,4'-(2,2,2-trifluoro-1-phenyl-ethylidene)diphthalic anhydride was added. The mixture was stirred for 4 hours to obtain a homogeneous solution. 102.53 g of diethylene glycol dimethyl ether (δ = 8.5) was added to the reaction system, and after stirring until homogeneous, the reaction system was cooled to 5 °C, and 17.43 g (0.05 mol) of bis(3-aminophenoxy)tetramethyldisiloxane was added. The reaction was continued for 24 hours to obtain a transparent polyamic acid slurry with a solid content of 30 wt% and a viscosity of 500 mPa·s.

[0092] After filtration and vacuum degassing, the above-mentioned transparent polyamic acid slurry is spin-coated onto a clean and smooth ultrathin glass substrate (thickness of 30 μm). After pre-drying at 80°C for 30 minutes, it is heat-dried at 250°C for 3 hours in an air and nitrogen mixed atmosphere to complete the imidization reaction. After cooling to room temperature, a coating and an ultrathin glass single-sided composite substrate are obtained, with the thickness of the transparent polyimide coating being 20 μm.

[0093] The main properties of the transparent polyamic acid slurry, transparent polyimide coating, and their composite substrate with ultrathin glass prepared in this embodiment are shown in Table 1.

[0094] Example 4

[0095] 26.74 g (0.07 mol) of 2,2-bis(4-aminophenyl)hexafluoropropane and 101.12 g of dimethyl sulfoxide (DMSO) (δ = 12.0) were added to a three-necked flask and stirred under nitrogen protection until completely dissolved. The reaction system was cooled to 15 °C, and 52.03 g (0.1 mol) of 4,4'-[2,2,2-trifluoro-1-(3-trifluoromethylphenyl)ethylene]diphthalic anhydride was added. The mixture was stirred for 2 hours to obtain a homogeneous solution. 25.28 g of dioxane (δ = 9.9) was added to the reaction system, and after stirring until homogeneous, the reaction system was cooled to 5 °C, and 5.49 g (0.03 mol) of bis(4-aminophenoxy)dimethylsilane was added. The reaction was continued for 18 hours to obtain a transparent polyamic acid slurry with a solid content of 40 wt% and a viscosity of 1888 mPa·s.

[0096] After filtration and vacuum degassing, the above-mentioned transparent polyamic acid slurry is coated onto a clean and smooth ultrathin glass substrate (50 μm thick) by a scraping method. After pre-drying at 60°C for 15 minutes, it is then heat-dried at 200°C for 0.5 hours in an air and nitrogen mixed atmosphere to complete the imidization reaction. After cooling to room temperature, a coating and an ultrathin glass single-sided composite substrate are obtained, with the thickness of the transparent polyimide coating being 15 μm.

[0097] The main properties of the transparent polyamic acid slurry, transparent polyimide coating, and their composite substrate with ultrathin glass prepared in this embodiment are shown in Table 1.

[0098] Example 5

[0099] 20.17 g (0.06 mol) of 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether and 160.10 g of N,N-dimethylformamide DMF (δ = 12.1) were added to a three-necked flask and stirred under nitrogen protection until completely dissolved. The reaction system was cooled to 5 °C, and 58.83 g (0.1 mol) of 4,4'-[2,2,2-trifluoro-1-(3,5-bistrifluoromethylphenyl)ethylene]diphthalic anhydride was added. The mixture was stirred for 0.5 h to obtain a homogeneous solution. 106.74 g of xylene (δ = 8.8) was added to the reaction system and stirred until homogeneous. The reaction system was then cooled to 0 °C, and 9.94 g (0.04 mol) of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane was added. The reaction was continued for 18 hours to obtain a transparent polyamic acid slurry with a solid content of 25 wt% and a viscosity of 721 mPa·s.

[0100] After filtration and vacuum degassing, the above-mentioned transparent polyamic acid slurry is coated onto a clean and smooth ultrathin glass substrate (thickness of 30 μm) by a scraping method. After pre-drying at 80°C for 15 minutes, it is then heat-dried at 250°C for 0.5 hours in an air and nitrogen mixed atmosphere to complete the imidization reaction. After cooling to room temperature, a coating and an ultrathin glass single-sided composite substrate are obtained, with the thickness of the transparent polyimide coating being 50 μm.

[0101] The main properties of the transparent polyamic acid slurry, transparent polyimide coating, and their composite substrate with ultrathin glass prepared in this embodiment are shown in Table 1.

[0102] Example 6

[0103] 19.21 g (0.06 mol) of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl and 46.42 g of N,N-dimethylacetamide DMAc (δ = 11.1) were added to a three-necked flask and stirred under nitrogen protection until completely dissolved. The reaction system was cooled to 20 °C, and 22.42 g (0.1 mol) of 1,2,4,5-cyclohexanetetracarboxylic acid dianhydride was added. The mixture was stirred for 1 hour to obtain a homogeneous solution. 5.16 g of tetrahydrofuran (δ = 9.5) was added to the reaction system and stirred until homogeneous. The reaction system was then cooled to -5 °C, and 9.94 g (0.04 mol) of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane was added. The reaction was continued for 8 hours to obtain a transparent polyamic acid slurry with a solid content of 50 wt% and a viscosity of 3000 mPa·s.

[0104] After filtration and vacuum degassing, the above-mentioned transparent polyamic acid slurry is coated onto a clean and smooth ultrathin glass substrate (50 μm thick) using a slot extrusion coating method. After pre-drying at 60°C for 30 minutes, it is then heat-dried at 200°C for 3 hours in an air and nitrogen mixed atmosphere to complete the imidization reaction. After cooling to room temperature, a coating and an ultrathin glass single-sided composite substrate are obtained, with the thickness of the transparent polyimide coating being 15 μm.

[0105] The main properties of the transparent polyamic acid slurry, transparent polyimide coating, and their composite substrate with ultrathin glass prepared in this embodiment are shown in Table 1.

[0106] Example 7

[0107] 21.42 g (0.05 mol) of 1,4-bis(2-trifluoromethyl-4-aminophenoxy)benzene and 91.71 g of γ-butyrolactone GBL (δ = 10.0) were added to a three-necked flask and stirred under nitrogen protection until completely dissolved. The reaction system was cooled to 15 °C, and 21.01 g (0.1 mol) of 1,2,4,5-cyclopentanetetracarboxylic acid dianhydride was added. The mixture was stirred for 0.5 hours to obtain a homogeneous solution. 39.31 g of cyclohexanone (δ = 9.9) was added to the reaction system, and after thorough stirring, the reaction system was cooled to 5 °C, and 13.72 g (0.05 mol) of bis(4-aminophenoxy)dimethylsilane was added. The reaction was continued for 8 hours to obtain a transparent polyamic acid slurry with a solid content of 30 wt% and a viscosity of 985 mPa·s.

[0108] After filtration and vacuum degassing, the above-mentioned transparent polyamic acid slurry is spin-coated onto a clean and smooth ultrathin glass substrate (40 μm thick). After pre-drying at 60°C for 30 minutes, it is heat-dried at 200°C for 1 hour in a mixed atmosphere of air and nitrogen to complete the imidization reaction. After cooling to room temperature, a coating and an ultrathin glass single-sided composite substrate are obtained, with the thickness of the transparent polyimide coating being 10 μm.

[0109] The main properties of the transparent polyamic acid slurry, transparent polyimide coating, and their composite substrate with ultrathin glass prepared in this embodiment are shown in Table 1.

[0110] Example 8

[0111] 15.55 g (0.03 mol) of 2,2-bis[4-(4-aminophenoxybenzene)]hexafluoropropane and 111.18 g of N,N-dimethylacetamide DMAc (δ = 11.1) were added to a three-necked flask and stirred until completely dissolved under nitrogen protection. The reaction system was cooled to 10 °C, and 19.61 g (0.1 mol) of 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride was added. The mixture was stirred for 2 hours to obtain a homogeneous solution. 27.80 g of cyclohexanone (δ = 9.9) was added to the reaction system, and after thorough stirring, the reaction system was cooled to -5 °C, and 24.40 g (0.07 mol) of bis(4-aminophenoxy)tetramethyldisiloxane was added. The reaction was continued for 24 hours to obtain a transparent polyamic acid slurry with a solid content of 30 wt% and a viscosity of 1446 mPa·s.

[0112] After filtration and vacuum degassing, the above-mentioned transparent polyamic acid slurry is applied to a clean and smooth ultrathin glass substrate (40 μm thick) by dip coating. After pre-drying at 80°C for 30 minutes, it is subjected to heat treatment at 250°C for 3 hours in a mixed atmosphere of air and nitrogen to complete the imidization reaction. After cooling to room temperature, a double-sided composite substrate of coating and ultrathin glass is obtained, with the thickness of the double-sided transparent polyimide coating being 20 μm.

[0113] The main properties of the transparent polyamic acid slurry, transparent polyimide coating, and their composite substrate with ultrathin glass prepared in this embodiment are shown in Table 1.

[0114] By replacing the dianhydride used in this embodiment, namely 1,2,3,4-cyclobutanetetracarboxylic dianhydride, with 1,3,-dimethylcyclobutane-1,2,3,4-tetracarboxylic dianhydride, a transparent polyimide coating with comparable performance can be obtained using the same preparation conditions as in this embodiment.

[0115] Example 9

[0116] 12.81 g (0.04 mol) of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl and 78.32 g of N-methylpyrrolidone (NMP) (δ = 11.3) were added to a three-necked flask and stirred under nitrogen protection until completely dissolved. The reaction system was cooled to 5 °C, and 25.02 g (0.1 mol) of bicyclo[2.2.2]octyl-2,3,5,6-tetracarboxylic acid dianhydride was added. The mixture was stirred for 0.5 hours to obtain a homogeneous solution. 8.70 g of dioxane (δ = 9.9) was added to the reaction system, and after stirring until homogeneous, the reaction system was cooled to 5 °C, and 20.19 g (0.06 mol) of bis(4-aminophenoxy)methylphenylsilane was added. The reaction was continued for 24 hours to obtain a transparent polyamic acid slurry with a solid content of 40 wt% and a viscosity of 2140 mPa·s.

[0117] After filtration and vacuum degassing, the above-mentioned transparent polyamic acid slurry is coated onto a clean and smooth ultrathin glass substrate (40 μm thick) by a scraping method. After pre-drying at 80°C for 30 minutes, it is then heat-dried at 250°C for 1 hour in an air and nitrogen mixed atmosphere to complete the imidization reaction. After cooling to room temperature, a coating and an ultrathin glass single-sided composite substrate are obtained, with the thickness of the transparent polyimide coating being 30 μm.

[0118] The main properties of the transparent polyamic acid slurry, transparent polyimide coating, and their composite substrate with ultrathin glass prepared in this embodiment are shown in Table 1.

[0119] Example 10

[0120] 10.09 g (0.03 mol) of 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether and 100.55 g of N,N-dimethylformamide DMF (δ = 12.1) were added to a three-necked flask and stirred until completely dissolved under nitrogen protection. The reaction system was cooled to 10 °C, and 23.62 g (0.1 mol) of bicyclo[2.2.1]hept-2,3,5,6-tetracarboxylic acid dianhydride was added. The mixture was stirred for 3 hours to obtain a homogeneous solution. 67.03 g of tetrahydrofuran (δ = 9.5) was added to the reaction system and stirred until homogeneous. The reaction system was then cooled to 0 °C, and 22.16 g (0.07 mol) of bis(4-aminophenyl)tetramethyldisiloxane was added. The reaction was continued for 12 hours to obtain a transparent polyamic acid slurry with a solid content of 25 wt% and a viscosity of 650 mPa·s.

[0121] After filtration and vacuum degassing, the above-mentioned transparent polyamic acid slurry is sprayed onto a clean and smooth ultrathin glass substrate (40 μm thick). After pre-drying at 60°C for 15 minutes, it is heat-dried at 200°C for 3 hours in an air and nitrogen mixed atmosphere to complete the imidization reaction. After cooling to room temperature, a coating and an ultrathin glass single-sided composite substrate are obtained, with the thickness of the transparent polyimide coating being 15 μm.

[0122] The main properties of the transparent polyamic acid slurry, transparent polyimide coating, and their composite substrate with ultrathin glass prepared in this embodiment are shown in Table 1.

[0123] Example 11

[0124] 23.40 g (0.07 mol) of 2,2-bis(4-aminophenyl)hexafluoropropane and 122.45 g of N,N-dimethylacetamide DMAc (δ = 11.1) were added to a three-necked flask and stirred until completely dissolved under nitrogen protection. The reaction system was cooled to 20 °C, and 24.82 g (0.1 mol) of bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic acid dianhydride was added. The mixture was stirred for 0.5 hours to obtain a homogeneous solution. 52.48 g of xylene (δ = 8.8) was added to the reaction system, and after stirring until homogeneous, the reaction system was cooled to 0 °C, and 10.09 g (0.03 mol) of bis(4-aminophenoxy)methylphenylsilane was added. The reaction was continued for 12 hours to obtain a transparent polyamic acid slurry with a solid content of 30 wt% and a viscosity of 2022 mPa·s.

[0125] After filtration and vacuum degassing, the above-mentioned transparent polyamic acid slurry is coated onto a clean and smooth ultrathin glass substrate (50 μm thick) by a scraping method. After pre-drying at 60°C for 15 minutes, it is then heat-dried at 200°C for 1 hour in an air and nitrogen mixed atmosphere to complete the imidization reaction. After cooling to room temperature, a coating and an ultrathin glass single-sided composite substrate are obtained, with the thickness of the transparent polyimide coating being 40 μm.

[0126] The main properties of the transparent polyamic acid slurry, transparent polyimide coating, and their composite substrate with ultrathin glass prepared in this embodiment are shown in Table 1.

[0127] Comparative Example 1

[0128] In a three-necked flask, 9.61 g (0.03 mol) of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 17.40 g (0.07 mol) of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane, 192.85 g of N,N-dimethylacetamide DMAc (δ = 11.1), and 21.43 g of tetrahydrofuran (δ = 9.1) were added and stirred under nitrogen protection until completely dissolved. The reaction system was cooled to 5 °C, and 44.42 g (0.1 mol) of 4,4'-(hexafluoroisopropyl)bisphthalic anhydride was added. The mixture was stirred for 1 hour to obtain a homogeneous solution. The reaction was continued for 8 hours to obtain a transparent polyamic acid slurry with a solid content of 25 wt% and a viscosity of 1310 mPa·s.

[0129] After filtration and vacuum degassing, the above-mentioned transparent polyamic acid slurry is coated onto a clean and smooth ultrathin glass substrate (40 μm thick) by a scraping method. After pre-drying at 80°C for 30 minutes, it is then heat-dried at 250°C for 1 hour in an air and nitrogen mixed atmosphere to complete the imidization reaction. After cooling to room temperature, a coating and an ultrathin glass single-sided composite substrate are obtained, with a transparent polyimide coating thickness of 30 μm.

[0130] The main properties of the transparent polyamic acid slurry, transparent polyimide coating, and their composite substrate with ultrathin glass prepared in this embodiment are shown in Table 1.

[0131] Comparative Example 2

[0132] 9.61 g (0.03 mol) of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl and 214.28 g of N,N-dimethylacetamide DMAc (δ = 11.1) were added to a three-necked flask and stirred under nitrogen protection until completely dissolved. The reaction system was cooled to 5 °C, and 44.42 g (0.1 mol) of 4,4'-(hexafluoroisopropyl)bisphthalic anhydride was added. The mixture was stirred for 1 hour to obtain a homogeneous solution. The reaction system was then cooled to 5 °C, and 17.40 g (0.07 mol) of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane was added. The mixture was stirred for another 8 hours to obtain a transparent polyamic acid slurry with a solid content of 25 wt% and a viscosity of 915 mPa·s.

[0133] After filtration and vacuum degassing, the above-mentioned transparent polyamic acid slurry is coated onto a clean and smooth ultrathin glass substrate (40 μm thick) by a scraping method. After pre-drying at 80°C for 30 minutes, it is then heat-dried at 250°C for 1 hour in an air and nitrogen mixed atmosphere to complete the imidization reaction. After cooling to room temperature, a coating and an ultrathin glass single-sided composite substrate are obtained, with a transparent polyimide coating thickness of 30 μm.

[0134] The main properties of the transparent polyamic acid slurry, transparent polyimide coating, and their composite substrate with ultrathin glass prepared in this comparative example are shown in Table 1.

[0135] Comparative Example 3

[0136] 9.61 g (0.08 mol) of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl and 192.85 g of N,N-dimethylacetamide DMAc (δ = 11.1) were added to a three-necked flask and stirred under nitrogen protection until completely dissolved. The reaction system was cooled to 5°C, and 44.42 g (0.1 mol) of 4,4'-(hexafluoroisopropyl)bisphthalic anhydride was added. The mixture was stirred for 1 hour to obtain a homogeneous solution. 21.43 g of n-hexane (δ = 7.3) was added to the reaction system, and after stirring until homogeneous, the reaction system was cooled to 5°C, and 17.40 g (0.02 mol) of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane was added. The mixture was stirred for another 8 hours to obtain a transparent polyamic acid slurry with a solid content of 25 wt% and a viscosity of 675 mPa·s.

[0137] After filtration and vacuum degassing, the above-mentioned transparent polyamic acid slurry is coated onto a clean and smooth ultrathin glass substrate (40 μm thick) by a scraping method. After pre-drying at 80°C for 30 minutes, it is then heat-dried at 250°C for 1 hour in an air and nitrogen mixed atmosphere to complete the imidization reaction. After cooling to room temperature, a coating and an ultrathin glass single-sided composite substrate are obtained, with a transparent polyimide coating thickness of 30 μm.

[0138] The main properties of the transparent polyamic acid slurry, transparent polyimide coating, and their composite substrate with ultrathin glass prepared in this comparative example are shown in Table 1.

[0139] Comparative Example 4

[0140] 30.42 g (0.095 mol) of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl and 48.67 g of N,N-dimethylacetamide DMAc (δ = 11.1) were added to a three-necked flask and stirred under nitrogen protection until completely dissolved. The reaction system was cooled to 20 °C, and 22.42 g (0.1 mol) of 1,2,4,5-cyclohexanetetracarboxylic acid dianhydride was added. The mixture was stirred for 2 hours to obtain a homogeneous solution. 5.41 g of tetrahydrofuran (δ = 9.1) was added to the reaction system and stirred until homogeneous. The reaction system was then cooled to 5 °C, and 1.24 g (0.005 mol) of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane was added. The reaction was continued for 24 hours to obtain a transparent polyamic acid slurry with a solid content of 50 wt% and a viscosity of 2550 mPa·s.

[0141] After filtration and vacuum degassing, the above-mentioned transparent polyamic acid slurry is coated onto a clean and smooth ultrathin glass substrate (40 μm thick) by a scraping method. After pre-drying at 60°C for 30 minutes, it is then heat-dried at 200°C for 3 hours in a mixed atmosphere of air and nitrogen to complete the imidization reaction. After cooling to room temperature, a coating and an ultrathin glass single-sided composite substrate are obtained, with the thickness of the transparent polyimide coating being 15 μm.

[0142] The main properties of the transparent polyamic acid slurry, transparent polyimide coating, and their composite substrate with ultrathin glass prepared in this comparative example are shown in Table 1.

[0143] Table 1. Properties of transparent polyamic acid paste, transparent polyimide coating and their combination with ultrathin glass composite substrates

[0144]

[0145] *The viscosity of the transparent polyamic acid slurry was measured using a Brookfield rotational viscometer;

[0146] The optical properties of the transparent polyamic acid slurry and the transparent polyimide coating were measured using a UV-Vis spectrophotometer and a colorimeter. The transmittance of the slurry at 450 nm (denoted as T) was measured. 450 ) and turbidity (denoted as Haze), and the average transmittance of the coating in the 380–780 nm range (denoted as T) AV The yellowness index (YI) was tested according to ASTM D1003 and the YI value was calculated according to ASTM E313.

[0147] The thickness of the ultrathin glass used in the performance evaluation of the transparent polyimide coating and its composite substrate with ultrathin glass was 50 μm.

[0148] The adhesion of the transparent polyimide coating was evaluated using the cross-cut adhesion test according to ASTM D3359-2002.

[0149] The evaluation conditions for the damp heat aging performance of the transparent polyimide coating and ultra-thin glass composite substrate are as follows: the sample is placed in a constant temperature and humidity chamber at 60℃ / 90%RH for 240 hours, and then taken out and equilibrated at room temperature for 30 minutes. The sample is then observed for phenomena such as coating blistering or delamination, composite substrate warping and deformation, and microcracks in ultra-thin glass. If none of the above phenomena are observed, the sample is considered to have passed the test.

[0150] As shown in Table 1, the solid content of the polyamic acid slurry of the present invention is 25wt.%-50wt.%, the viscosity is 500-3000mPa·s, and the transmittance T at 450nm is... 450 >90%, specifically 90.2%-91.7%, turbidity Haze <1, specifically 0.21%-0.79%.

[0151] The thickness of the transparent polyimide coating is 10-50 μm, and the average transmittance T in the range of 380-780 nm is... AV >90%, specifically 90.8%-92.5%, and yellowness index YI <2, specifically 1.3-1.9, and the adhesion of the cross-cut adhesion tester all reached 5B, and all passed the wet heat aging evaluation.

[0152] Compared with Example 1, Comparative Example 1 uses random copolymerization to prepare polyamic acid slurry. Since the reactivity of fluorinated aromatic diamine is lower than that of diamine containing siloxane structure, the fluorinated aromatic segments and flexible siloxane chain sequence structure cannot form an orderly arrangement in the copolymerization system, resulting in a higher yellowness index of the coating.

[0153] Compared with Example 1, Comparative Example 2 only used a highly polar organic solvent with a δ value > 10 as the polymerization reaction solvent system. Since the low polarity of siloxane diamine cannot be completely dissolved in the solvent, the polyamic acid slurry has a large turbidity. The polyimide coating prepared from it has microphase separation and poor optical performance.

[0154] Compared with Example 1, although a dual solvent system with different polarities was used in the polymerization of Comparative Example 3, the resin was partially exuded during the polymerization process due to the low δ value of the second solvent system. The resulting slurry had high turbidity, and the coating prepared from it had poor adhesion to the ultrathin glass substrate.

[0155] Compared with Examples 1 and 6, Comparative Example 4 uses an alicyclic structure system to prepare a transparent polyimide coating. Although the fluorine content in the polymer is reduced compared with the fluorinated aromatic structure system, the low content of flexible siloxane leads to large stress shrinkage during the coating preparation process, resulting in severe warping deformation of the substrate after being laminated with ultrathin glass, and low adhesion.

[0156] In addition, by Figure 1 It can be seen that the transparent polyamic acid slurry prepared in Example 1 has a transmittance of 91.1% at 450 nm.

[0157] Depend on Figure 2 It can be seen that the transparent polyimide coating prepared in Example 1 is a polyimide containing a siloxane structure.

[0158] Depend on Figure 3 It can be seen that the adhesion test of the polyimide coating prepared in Example 1 to the coating of the ultrathin glass composite substrate reached 5B.

[0159] Depend on Figure 4 It can be seen that the polyimide coating and ultrathin glass composite substrate prepared in Example 1 showed no bubbling, delamination, warping, or cracking after aging in a humid and hot environment of 60℃ / 90%RH for 240 hours.

[0160] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A transparent polyamic acid slurry, characterized in that, The transparent polyamic acid slurry includes polyamic acid resin and a mixed solvent. The polyamic acid resin is a block copolymer prepared by fluorinated aromatic dianhydride or alicyclic dianhydride with fluorinated aromatic diamine and diamine containing siloxane structure. The mixed solvent includes two solvents, A and B, with different solubility parameters δ, wherein the solubility parameter of solvent A is greater than that of solvent B.

2. The polyamic acid slurry according to claim 1, characterized in that, The polyamic acid resin has repeating units as shown in Formula IA or Formula IB: In formula IA, Ar is selected from any one of the following groups: In the formula IB, Al is selected from any one of the following groups: In formulas IA and IB, R1 is selected from any one of the following groups: R2 is selected from any one of the following groups:

3. The polyamic acid slurry according to claim 1, characterized in that, The fluorinated aromatic dianhydride includes at least one of the following: 4,4'-(hexafluoroisopropyl)bisphthalic anhydride, 9,9-bis(trifluoromethyl)-2,3,6,7-oxanthracene tetracarboxylic anhydride, 4,4'-(2,2,2-trifluoro-1-phenyl-ethylidene)diphthalic anhydride, 4,4'-[2,2,2-trifluoro-1-(3-trifluoromethylphenyl)ethylidene]diphthalic anhydride, or 4,4'-[2,2,2-trifluoro-1-(3,5-bistrifluoromethylphenyl)ethylidene]diphthalic anhydride; The alicyclic dianhydride comprises at least one of the following: 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,3,-dimethylcyclobutane-1,2,3,4-tetracarboxylic dianhydride, 1,2,4,5-cyclopentanetetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, bicyclo[2.2.1]hept-2,3,5,6-tetracarboxylic dianhydride, bicyclo[2.2.2]oct-2,3,5,6-tetracarboxylic dianhydride, and bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride; The fluorinated aromatic diamine includes at least one of the following: 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether, 2,2-bis(4-aminophenyl)hexafluoropropane, 1,4-bis(2-trifluoromethyl-4-aminophenoxy)benzene, 4,4'-bis(4-amino-2-trifluoromethylphenoxy)biphenyl, and 2,2-bis[4-(4-aminophenoxybenzene)]hexafluoropropane; The diamine containing a siloxane structure includes at least one of the following: 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane, bis(4-aminophenyl)tetramethyldisiloxane, bis(4-aminophenoxy)tetramethyldisiloxane, bis(3-aminophenoxy)tetramethyldisiloxane, bis(4-aminophenoxy)dimethylsilane, and bis(4-aminophenoxy)methylphenylsilane.

4. The polyamic acid slurry according to claim 1, characterized in that, Solvent A includes at least one of N-methylpyrrolidone (NMP), N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and γ-butyrolactone (GBL); Solvent B includes at least one of cyclohexanone, tetrahydrofuran, diethylene glycol dimethyl ether, xylene, and dioxane; The mass ratio of solvent A to solvent B in the mixed solvent is (9:1) to (5:5).

5. The transparent polyamic acid slurry according to claim 1, characterized in that, The transparent polyamic acid slurry has a solid content of 25-50 wt%, a rotational viscosity of 500-3000 mPa·s, a light transmittance of >90% at 450 nm, and a turbidity of <1%, exhibiting the characteristics of high solid content, low viscosity, and high transparency.

6. A method for preparing a transparent polyamic acid slurry, characterized in that, The preparation of the transparent polyamic acid slurry according to any one of claims 1-5 comprises the following steps: (1) Dissolve the fluorinated aromatic diamine in solvent A, cool the reaction system, add the fluorinated aromatic dianhydride or alicyclic dianhydride, stir the reaction, and obtain a homogeneous solution; (2) Add solvent B to the homogeneous solution, cool the reaction system, add diamine containing siloxane structure, stir the reaction, and obtain transparent polyamic acid slurry.

7. A method for preparing a transparent polyimide coating, characterized in that, The transparent polyamic acid slurry according to any one of claims 1-6 is coated on a substrate and heat-treated to obtain a transparent polyimide coating.

8. The preparation method according to claim 7, characterized in that, The coating method includes blade coating, spin coating, dip coating, spray coating, or slot extrusion coating; the substrate is ultra-thin glass or microcrystalline glass; the heat treatment conditions are pre-drying at 60-80°C for 15-30 minutes, followed by heat treatment at 200-250°C for 0.5-3 hours.

9. A transparent polyimide coating, characterized in that, The transparent polyimide coating, prepared by the method of claim 7 or 8, has a thickness of 10–50 μm, an average transmittance of >90% in the wavelength range of 380–780 nm, a yellowness index of <2.0, excellent adhesion to the glass substrate, a cross-cut adhesion of 5B, and exhibits no blistering, peeling, warping, or cracking after 240 hours of aging in a humid and hot environment of 60°C / 90%RH.

10. The application of the transparent polyimide coating of claim 9, combined with ultrathin glass or microcrystalline glass, as a transparent cover in a flexible display.

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