Flexible substrate material, method for producing the same and use thereof

Abstract

This invention belongs to the field of flexible display materials technology, specifically relating to a flexible substrate material, its preparation method, and its application. The preparation method of the flexible substrate material includes the following steps: S1, dissolving a diamine monomer in an organic solvent, then adding a dianhydride monomer for a first reaction, followed by adding a 2-mercaptobenzoic acid-modified inorganic filler for a second reaction, to obtain a filler / PAA precursor composite solution; S2, filtering, degassing, and casting the filler / PAA precursor composite solution into a film, followed by hot stretching and winding to obtain the flexible substrate material. The prepared flexible substrate material exhibits excellent transparency, as well as excellent heat resistance, high modulus, and acid and alkali resistance.

Description

Technical Field

[0001] This invention belongs to the field of flexible display materials technology, specifically relating to a flexible substrate material, its preparation method, and its application. Background Technology

[0002] With the rapid development of flexible displays, flexible photovoltaics, and wearable electronic devices, the performance requirements for flexible substrate materials are increasing. While traditional polyimide (PI) materials possess excellent heat resistance, their typically dark color (yellow or brown) limits their application in transparent devices. The emergence of transparent polyimide (CPI) has improved transparency, but it still has some inherent drawbacks: 1) Insufficient dimensional stability at high temperatures, making it prone to thermal deformation in processes exceeding 250 feet; 2) Long-term exposure to high temperatures or strong ultraviolet (UV) environments can cause molecular chain breakage and degradation, leading to decreased mechanical properties; 3) Ester groups and other functional groups in the molecular structure are easily hydrolyzed in acidic and alkaline chemical environments, limiting its application in wet processes involving photolithography and etching. In existing technologies, modification methods through copolymerization, blending, or doping often only improve a single property and may lead to a decrease in other properties. CN110540643A describes a method that introduces dianhydrides containing naphthalene rings into polyimide to increase the content of benzene rings, thereby increasing its heat-resistant components and significantly improving its heat resistance. It also uses dianhydrides containing pyridine rings for end-capping to prevent excessive polymerization and reduced flexibility caused by group burst polymerization. The resulting polyimide exhibits excellent heat resistance and deformation resistance, making it suitable for use as a substrate material and encapsulation film material for flexible OLED panels. However, while increasing heat resistance and deformation resistance, its light transmittance decreases. CN118185309A describes a method that introduces flexible ether groups, side methyl groups, and biphenyl groups into the polyimide molecular chain through multi-component polymerization to improve the film's light transmittance and elastic modulus. It also adds hydroxylated ZnS nanoparticles to reduce the coefficient of thermal expansion, preparing a quaternary copolymer thermoplastic polyimide film with a low coefficient of thermal expansion and good mechanical properties. However, the interaction between hydroxylated ZnS and the polyimide matrix relies only on weak physical adsorption or hydrogen bonding. Under complex stress or thermal processes, the interface is prone to failure, leading to nanoparticle aggregation, which intensifies light scattering and stress concentration. As a result, it is difficult for the material to simultaneously achieve ultra-high light transmittance, high modulus, and high heat resistance.

[0003] Therefore, there is an urgent need to study a flexible substrate material with excellent temperature resistance, excellent acid and alkali resistance, good light transmittance and mechanical properties, and its preparation method. Summary of the Invention

[0004] The purpose of this invention is to overcome the problem that existing flexible substrate materials cannot simultaneously achieve high light transmittance, high heat resistance, high mechanical strength, and excellent chemical corrosion resistance. It provides a flexible substrate material, its preparation method, and its applications. This flexible substrate material exhibits excellent transparency, as well as excellent heat resistance, high modulus, and acid and alkali resistance.

[0005] To achieve the above objectives, in a first aspect, the present invention provides a method for preparing a flexible substrate material, comprising the following steps: S1. The diamine monomer is dissolved in an organic solvent, and then the dianhydride monomer is added to carry out the first reaction. Then, 2-mercaptobenzoic acid-modified inorganic filler is added to carry out the second reaction to obtain the filler / PAA precursor composite solution. S2. The filler / PAA precursor composite liquid is filtered, degassed, and cast into a film, followed by hot stretching and winding to obtain a flexible substrate material.

[0006] The flexible substrate material prepared in this invention exhibits excellent transparency, as well as superior heat resistance, high modulus, and acid and alkali resistance. This enables the flexible substrate material to withstand the high temperatures of the manufacturing process when used in electronic devices such as OLEDs, flexible displays, and flexible solar cells, while also possessing excellent optical properties, bendability, and acid and alkali resistance.

[0007] Furthermore, compared to conventional coupling agent-modified inorganic fillers, the 2-mercaptobenzoic acid-modified inorganic filler in this invention exhibits π-carbonyl conjugation and hydrogen bonding interactions with the aromatic rings and carbonyl groups in the polyimide precursor. This creates a rigid-flexible balanced structure within the polyamide matrix, enabling better dispersion of the inorganic filler, thus improving stress transfer and reducing light scattering. This results in a better balance of the final material's optical, mechanical, and temperature resistance properties. Moreover, it forms a dense and stable interface layer, which, combined with the inertness of the fluorinated segments in the polymer, constructs an excellent chemical barrier, allowing the flexible substrate material to effectively protect sensitive chemical bonds in strong acid and alkali environments.

[0008] In this invention, the diamine monomer refers to a class of small organic molecule compounds containing two primary amine groups. Preferably, the diamine monomer is 6,6'-diamino-2,2'-bipyridine and 1,12-dodecanediamine in a molar ratio of 1:(0.3-0.4).

[0009] In this invention, experimental studies revealed that when the diamine monomers are 6,6'-diamino-2,2'-bipyridine and 1,12-dodecanediamine in a molar ratio of 1:(0.3-0.4), the resulting flexible substrate material exhibits superior overall performance. Specifically, when the proportion of 6,6'-diamino-2,2'-bipyridine is too high, although the flexible substrate material achieves a higher thermal decomposition temperature and tensile modulus, it leads to a decrease in light transmittance. Conversely, when the proportion of 1,12-dodecanediamine is too high, although the light transmittance of the flexible substrate material increases, its thermal decomposition temperature and tensile modulus decrease. Further analysis suggests that the aforementioned diamine monomers can better ensure the strong and tough backbone of the polymer molecular chain, while avoiding the defects of light scattering due to excessive rigidity or weak inter-chain interactions due to excessive flexibility. This results in a better balance between the material's transmittance, mechanical strength, and heat resistance. Furthermore, the aforementioned diamine monomers, combined with 2-mercaptobenzoic acid-modified fillers and dianhydride monomers, can jointly construct a dense and chemically inert bulk phase and interface, enabling the finally prepared flexible substrate material to exhibit excellent stability in strong acid and strong alkali environments.

[0010] Dianhydride monomers refer to a class of organic compounds containing two anhydride groups in their molecules. Preferably, the dianhydride monomer is selected from at least one of 4,4'-(hexafluoropropylene)bis-phthalic anhydride, dimethylcyclobutanetetracarboxylic dianhydride, and 4,4-carboxylic anhydride (hexafluoroisopropene)diphthalic anhydride, and more preferably 4,4'-at least hexafluoroisopropene)diphthalic anhydride. Using the aforementioned dianhydride monomers can better improve the overall performance of flexible substrate materials.

[0011] Preferably, the organic solvent is N,N-dimethylacetamide.

[0012] Preferably, the molar ratio of the diamine monomer to the dianhydride monomer is (0.98-1):1.

[0013] Preferably, the total mass ratio of the diamine monomer and the dianhydride monomer to the organic solvent is (15-20):100.

[0014] Preferably, the total mass ratio of the diamine monomer and the dianhydride monomer to the 2-mercaptobenzoic acid modified inorganic filler is (35-40):1. Controlling the amount of 2-mercaptobenzoic acid modified inorganic filler within the above range ensures that the flexible substrate material has excellent overall performance.

[0015] Preferably, in step S1, there are no special restrictions on the dissolution conditions; generally, stirring at 0-10 °C is sufficient for dissolution.

[0016] Preferably, in step S1, the conditions for the first reaction include: being carried out under a nitrogen atmosphere, a reaction temperature of 0-10 °C, a reaction time of 3-5 h, and a stirring speed of 300-400 pm.

[0017] Preferably, in step S1, the conditions for the second reaction include: being carried out under a nitrogen atmosphere, a reaction temperature of 0-10 h, a reaction time of 10-15 h, and a stirring speed of 600-800 rpm.

[0018] Preferably, the inorganic filler in the 2-mercaptobenzoic acid modified inorganic filler is selected from a combination of zinc aluminum oxide, lanthanum zirconate and yttrium-stabilized zirconium oxide, and the mass ratio of zinc aluminum oxide, lanthanum zirconate and yttrium-stabilized zirconium oxide is 1:(0.3-0.4):(0.3-0.4).

[0019] The present invention has found that when the proportion of inorganic fillers deviates from the above range or certain components are replaced, the performance of the flexible substrate material will decrease to varying degrees. It is speculated that this is because zinc oxide can serve as a high thermal conductivity rigid framework and has excellent surface activity, which can form a strong interfacial bond with 2-mercaptobenzoic acid. Lanthanum zirconate has a high melting point and low coefficient of thermal expansion, which can build a stable heat-resistant barrier in the matrix and significantly improve thermal stability. Yttrium-stabilized zirconium oxide can effectively dissipate stress through a phase transformation toughening mechanism. That is, when the three are used in a specific ratio, they can form a spatially interpenetrating and functionally complementary reinforcing network in the polymer matrix, thereby giving the flexible substrate material excellent comprehensive performance.

[0020] Preferably, the average particle size of the inorganic filler in the 2-mercaptobenzoic acid modified inorganic filler is 20-500 nm, for example, the average particle size of zinc aluminum oxide is 150-300 nm, the average particle size of yttrium stabilized zirconium oxide is 20-100 nm, and the average particle size of lanthanum zirconate is 300-400 nm.

[0021] The inorganic fillers in this invention can be obtained commercially. For example, zinc oxide aluminum was purchased from Zhejiang Yamei Nanotechnology Co., Ltd., with an average particle size of 200 nm; yttrium-stabilized zirconium oxide was purchased from Qinghe County Chaotai Metal Materials Co., Ltd., with a yttrium content of 5% and an average particle size of 50 nm; and lanthanum zirconate was purchased from Wuhan Kamik Technology Co., Ltd., with an average particle size of 350 nm.

[0022] Preferably, the preparation method of the 2-mercaptobenzoic acid modified inorganic filler includes the following steps: (1) The inorganic packing material was acid-treated in dilute nitric acid with a concentration of 0.05-0.1M, and then centrifuged, washed and dried to obtain an intermediate. (2) The intermediate was added to N-methylpyrrolidone and dispersed to obtain a suspension; (3) Add 2-mercaptobenzoic acid to the above suspension for modification reaction, then centrifuge, wash and dry to obtain 2-mercaptobenzoic acid modified inorganic filler.

[0023] More preferably, in step (1) above, the acid treatment conditions include: ultrasonic treatment for 20-40 minutes.

[0024] In step (1) above, there is no special limitation on the amount of dilute nitric acid used, as long as it can immerse the inorganic filler. This invention will not elaborate further on this point.

[0025] The purpose of washing in step (1) above is mainly to remove excess dilute nitric acid. In this invention, water can be used to wash repeatedly until the supernatant is neutral. In order to replace the water, after washing with water, anhydrous ethanol can be used to wash 2-3 times to replace the water. That is, in step (1), the washing method includes: washing the precipitate repeatedly with water until the supernatant is neutral, and then washing with anhydrous ethanol 2-3 times to obtain the precipitate.

[0026] There is no special limitation on the drying method in step (1), as long as the washing liquid (e.g., water, anhydrous ethanol) can be removed. More preferably, the drying conditions in step (1) include: drying under vacuum at 70-80°C for 8-24 hours.

[0027] More preferably, in step (2), the mass ratio of the intermediate to N-methylpyrrolidone is 1:(80-150).

[0028] More preferably, in step (2), the dispersion conditions include: being carried out in a nitrogen atmosphere and ultrasonically dispersed for 30-60 minutes.

[0029] More preferably, the mass ratio of 2-mercaptobenzoic acid to the intermediate is 1:(5-15), more preferably 1:(8-10).

[0030] More preferably, in step (3), the conditions for the modification reaction include: being carried out under a nitrogen atmosphere and reacting under reverse reflux at 120-130°C for 6-8 hours.

[0031] In step (3), centrifugation, washing, and drying can be conventional drying methods in the field. For example, N-methylpyrrolidone can be used for centrifugation and washing 2-5 times, followed by washing with anhydrous ethanol 2-3 times. Then, the solid modified material is dried under vacuum at 70-80°C for 8-24 hours to obtain 2-mercaptobenzoic acid modified inorganic filler.

[0032] More preferably, the preparation method of the 2-mercaptobenzoic acid modified inorganic filler includes the following steps: (1) Disperse zinc aluminum oxide, lanthanum zirconate and yttrium stabilized zirconium oxide in a mass ratio of 1:(0.3-0.4):(0.3-0.4) in dilute nitric acid with a concentration of 0.05-0.1M and sonicate for 20-40 minutes. Then centrifuge, remove the supernatant, wash the precipitate repeatedly with water until the supernatant is neutral, then wash with anhydrous ethanol 2-3 times, and dry the precipitate under vacuum at 70-80°C for 8-24 hours to obtain the intermediate. (2) Under a nitrogen atmosphere, the intermediate is added to N-methylpyrrolidone and ultrasonically dispersed for 30-60 minutes to obtain a suspension, wherein the mass ratio of the intermediate to N-methylpyrrolidone is 1:(80-150). (3) Under a nitrogen atmosphere, 2-mercaptobenzoic acid is added to the above suspension, and the reaction system is slowly heated to 120-130°C and refluxed for 6-8 hours. After the reaction is completed, heating is stopped, and the mixture is naturally cooled to room temperature. The reaction mixture is centrifuged and washed 2-5 times with N-methylpyrrolidone, and then washed 2-3 times with anhydrous ethanol. The solid modified material is then dried under vacuum at 70-80°C for 8-24 hours to obtain 2-mercaptobenzoic acid modified inorganic filler. The mass ratio of 2-mercaptobenzoic acid to the intermediate is 1:(8-10).

[0033] Preferably, in step S2, the filtration method includes: coarse filtration of the packing / PAA precursor composite liquid using a plate and frame filter with a pore size of 10-25, followed by fine filtration of the packing / PAA precursor composite liquid using a plate and frame filter with a composite pore size of 1-5.

[0034] In step S2, the degassing method is a conventional method in the art, generally static degassing.

[0035] Preferably, in step S2, the method of casting film formation includes: extruding from a casting die and flowing into a solidified steel plate for curing film formation, wherein the extrusion rate of the casting die is 2-5 cm3 / min, and the curing film formation conditions are 90°C for 3-8 min, 150°C for 3-8 min, and 200°C for 3-8 min.

[0036] Preferably, in step S2, the hot stretching method includes: a heat treatment temperature of 400-450°C, a longitudinal stretching ratio of 2-2.5 times, and a transverse stretching ratio of 1.5-2 times.

[0037] More preferably, the method for preparing the flexible substrate material includes the following steps: S1. Under nitrogen protection, 6,6'-diamino-2,2'-bipyridine and 1,12-dodecanediamine in a molar ratio of 1:(0.3-0.4) are dissolved in N,N-dimethylacetamide, and then 4,4-acetamide-hexafluoroisopropene phthalic anhydride is added. The stirring speed is adjusted to 300-400 rpm, and the reaction is carried out at 0-10°C under nitrogen protection for 3-5 hours. Then, 2-mercaptobenzoic acid modified inorganic filler is added, and the stirring speed is adjusted to 600-800 rpm. The reaction is carried out at 0-10°C under nitrogen protection for another 10-15 hours to obtain the filler / PAA precursor composite solution; wherein, 6,6'- The total molar mass of diamino-2,2'-bipyridine and 1,12-dodecanediamine, and the molar ratio of 4,4-diamine and hexafluoroisopropene phthalic anhydride are (0.98-1):100. The total mass of 1,6,6'-diamino-2,2'-bipyridine, 1,12-dodecanediamine, 4,4-diamine, and hexafluoroisopropene phthalic anhydride, and the mass ratio of N,N-dimethylacetamide are (15-20):100. The total mass of 6,6'-diamino-2,2'-bipyridine, 1,12-dodecanediamine, 4,4-diamine, and hexafluoroisopropene phthalic anhydride, and the mass ratio of 2-mercaptobenzoic acid modified inorganic filler are (35-40):1. S2. The filler / PAA precursor composite liquid is coarsely filtered using a plate and frame filter with a pore size of 10-25, and then finely filtered using a plate and frame filter with a pore size of 1-5. After standing to remove bubbles, the degassed filler / PAA precursor composite liquid is extruded from a casting die and flows into a cured steel plate for curing and film formation. The extrusion rate of the casting die is 2-5 cm³ / min, and the curing conditions are 90℃ for 3-8 min, 150℃ for 3-8 min, and 200℃ for 3-8 min. The cured film is then subjected to hot stretching at a heat treatment temperature of 400-450℃, with a longitudinal stretching ratio of 2-2.5 times and a transverse stretching ratio of 1.5-2 times. Finally, the film is wound up to obtain a flexible substrate material.

[0038] The second aspect of the present invention provides a flexible substrate material prepared by the method for preparing the flexible substrate material described in the first aspect of the present invention.

[0039] The third aspect of the present invention provides the application of the flexible substrate material described in the second aspect of the present invention in flexible displays.

[0040] Compared with the prior art, the present invention has at least the following beneficial effects: 1. The use of specific diamine monomers and dianhydride monomers in this invention can better enable the flexible substrate material to have a temperature resistance exceeding 220°C. Among them, 1,12-dodecanediamine, as a flexible amorphous component, can effectively suppress crystallization defects or stress concentration points that may be formed due to the over-ordered arrangement of rigid bipyridine units. 6,6'-diamino-2,2'-bipyridine and 4,4'-hexafluoroisopropene diazolic anhydride, during thermal imidization and subsequent thermal stretching, induce the formation of microcrystalline regions with uniform size and ordered orientation through the synergistic effect of aromatic heterocycles and imide rings, so as to form a crystallization synergistic effect during crystallization, enabling the flexible substrate material to have a temperature resistance exceeding 220°C.

[0041] 2. In this invention, by doping with a specific ratio of zinc aluminum oxide, lanthanum zirconate and yttrium-stabilized zirconium oxide, a stable inorganic heat-resistant network can be constructed in the polymer matrix, which can effectively inhibit the thermal stability of polymer chain segments at high temperatures, thereby improving the temperature resistance of the cast product to over 310°C.

[0042] 3. The introduction of lanthanum zirconate and yttrium-stabilized zirconium oxide in this invention enables the flexible substrate material to achieve ultra-high anti-aging ability, and the molecular chains do not break or undergo decomposition reaction under high temperature and ultraviolet light, thus maintaining the elastic modulus value.

[0043] 4. In this invention, 2-mercaptobenzoic acid-modified inorganic filler is used in conjunction with specific diamine and dianhydride monomers to introduce fluorine-containing groups, aromatic heterocycles, and chemically inert long-chain alkane segments into the molecular chain, forming a dense "protective layer." This protects the ester groups under strong acids and even strong bases, enabling the flexible substrate material to meet the requirements of photolithography processes and practical applications, providing it with acid and alkali resistance. Detailed Implementation

[0044] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] In the following embodiments: The zinc oxide aluminum was purchased from Zhejiang Yamei Nanotechnology Co., Ltd., with an average particle size of 200 nm.

[0046] The alumina was purchased from Zhejiang Yamei Nanotechnology Co., Ltd., with an average particle size of 200 nm.

[0047] Yttrium-stabilized zirconium oxide was purchased from Qinghe County Chaotai Metal Materials Co., Ltd., with a yttrium oxide molar content of 5% and an average particle size of 50 nm.

[0048] Lanthanum zirconate was purchased from Wuhan Camick Technology Co., Ltd., with an average particle size of 350 nm.

[0049] Example 1 Preparation of 2-mercaptobenzoic acid modified inorganic filler: (1) Disperse zinc aluminum oxide, lanthanum zirconate and yttrium stabilized zirconium oxide in a mass ratio of 1:0.32:0.38 in dilute nitric acid with a concentration of 0.06M and sonicate for 30 minutes. Then centrifuge, remove the supernatant, wash the precipitate repeatedly with water until the supernatant is neutral, then wash with anhydrous ethanol 3 times, and dry the precipitate under vacuum at 75 for 12 hours to obtain the intermediate. (2) Under a nitrogen atmosphere, the intermediate was added to N-methylpyrrolidone and ultrasonically dispersed for 50 minutes to obtain a suspension, wherein the mass ratio of the intermediate to N-methylpyrrolidone was 1:120; (3) Under a nitrogen atmosphere, 2-mercaptobenzoic acid was added to the above suspension, and the reaction system was slowly heated to 123°C and refluxed for 7 hours. After the reaction was completed, the heating was stopped, and the mixture was naturally cooled to room temperature. The reaction mixture was centrifuged and washed three times with N-methylpyrrolidone, and then washed three times with anhydrous ethanol. The solid modified material was then dried under vacuum at 75°C for 12 hours to obtain 2-mercaptobenzoic acid modified inorganic filler. The mass ratio of 2-mercaptobenzoic acid to the intermediate was 1:9.

[0050] Preparation of flexible substrate materials: S1. Under nitrogen protection, 6,6'-diamino-2,2'-bipyridine and 1,12-dodecanediamine in a molar ratio of 1:0.35 were dissolved in N,N-dimethylacetamide, and then 4,4-acetamide-hexafluoroisopropene phthalic anhydride was added. The stirring speed was adjusted to 350 rpm, and the reaction was carried out at a temperature under nitrogen protection for 4 hours. Then, the above-mentioned 2-mercaptobenzoic acid modified inorganic filler was added, and the stirring speed was adjusted to 700 rpm. The reaction was carried out at a temperature under nitrogen protection for another 12 hours to obtain the filler / PAA precursor composite solution; wherein, 6,6'-diamino-2,2'-bipyridine and 1,12-dodecanediamine were dissolved in N,N-dimethylacetamide. The total molar ratio of 6,6'-diamino-2,2'-bipyridine and 1,12-dodecanediamine to 4,4-diamine and hexafluoroisopropene phthalic anhydride is 1:1; the mass ratio of the total mass of 6,6'-diamino-2,2'-bipyridine, 1,12-dodecanediamine and 4,4-diamine and hexafluoroisopropene phthalic anhydride to N,N-dimethylacetamide is 18:100; and the mass ratio of the total mass of 6,6'-diamino-2,2'-bipyridine, 1,12-dodecanediamine and 4,4-diamine and hexafluoroisopropene phthalic anhydride to 2-mercaptobenzoic acid modified inorganic filler is 38:1. S2. The filler / PAA precursor composite liquid is coarsely filtered using a plate and frame filter with a 20mm pore size, and then finely filtered using a plate and frame filter with a 5mm pore size. After standing to remove bubbles, the degassed filler / PAA precursor composite liquid is extruded from a casting die and flows into a curing steel plate for curing and film formation. The extrusion rate of the casting die is 3 cm³ / min, and the curing conditions are 90°C for 5 min, 150°C for 5 min, and 200°C for 5 min. The cured film is then subjected to hot stretching at a temperature of 420°C, with a longitudinal stretching ratio of 2.2 times and a transverse stretching ratio of 1.8 times. Finally, the film is wound up to obtain a flexible substrate material.

[0051] Example 2 Preparation of 2-mercaptobenzoic acid modified inorganic filler: (1) Disperse zinc oxide aluminum, lanthanum zirconate and yttrium stabilized zirconium oxide in a mass ratio of 1:0.3:0.4 in dilute nitric acid with a concentration of 0.06M and sonicate for 30 minutes. Then centrifuge, remove the supernatant, wash the precipitate repeatedly with water until the supernatant is neutral, then wash with anhydrous ethanol 3 times, and dry the precipitate under vacuum at 75 for 12 hours to obtain the intermediate. (2) Under a nitrogen atmosphere, the intermediate was added to N-methylpyrrolidone and ultrasonically dispersed for 50 minutes to obtain a suspension, wherein the mass ratio of the intermediate to N-methylpyrrolidone was 1:150; (3) Under a nitrogen atmosphere, 2-mercaptobenzoic acid was added to the above suspension, and the reaction system was slowly heated to 125°C and refluxed for 7 hours. After the reaction was completed, the heating was stopped, and the mixture was naturally cooled to room temperature. The reaction mixture was centrifuged and washed three times with N-methylpyrrolidone, and then washed three times with anhydrous ethanol. The solid modified material was then dried under vacuum at 75°C for 12 hours to obtain 2-mercaptobenzoic acid modified inorganic filler. The mass ratio of 2-mercaptobenzoic acid to the intermediate was 1:8.

[0052] Preparation of flexible substrate materials: S1. Under nitrogen protection, 6,6'-diamino-2,2'-bipyridine and 1,12-dodecanediamine in a molar ratio of 1:0.4 were dissolved in N,N-dimethylacetamide, and then 4,4-acetamide-hexafluoroisopropene phthalic anhydride was added. The stirring speed was adjusted to 350 rpm, and the reaction was carried out at a temperature under nitrogen protection for 4 hours. Then, the above-mentioned 2-mercaptobenzoic acid modified inorganic filler was added, and the stirring speed was adjusted to 700 rpm. The reaction was carried out at a temperature under nitrogen protection for another 12 hours to obtain the filler / PAA precursor composite solution; wherein, 6,6'-diamino-2,2'-bipyridine and 1,12-dodecanediamine were dissolved in N,N-dimethylacetamide. The total molar ratio of 6,6'-diamino-2,2'-bipyridine and 1,12-dodecanediamine to 4,4-diamine and hexafluoroisopropene phthalic anhydride is 1:1; the mass ratio of the total mass of 6,6'-diamino-2,2'-bipyridine, 1,12-dodecanediamine and 4,4-diamine and hexafluoroisopropene phthalic anhydride to N,N-dimethylacetamide is 20:100; and the mass ratio of the total mass of 6,6'-diamino-2,2'-bipyridine, 1,12-dodecanediamine and 4,4-diamine and hexafluoroisopropene phthalic anhydride to 2-mercaptobenzoic acid modified inorganic filler is 40:1. S2. The filler / PAA precursor composite liquid is coarsely filtered using a 20mm multi-pore plate and frame filter, and then finely filtered using a 5mm multi-pore plate and frame filter. After standing to remove bubbles, the degassed filler / PAA precursor composite liquid is extruded from a casting die and flows into a curing steel plate for curing and film formation. The extrusion rate of the casting die is 4 cm³ / min, and the curing conditions are 90°C for 5 min, 150°C for 5 min, and 200°C for 5 min. The cured film is then subjected to hot stretching at a temperature of 400°C, with a longitudinal stretching ratio of 2.5 times and a transverse stretching ratio of 1.5 times. Finally, the film is wound up to obtain a flexible substrate material.

[0053] Comparative Example 1 Preparation of coupling agent modified inorganic fillers: (1) Disperse zinc aluminum oxide, lanthanum zirconate and yttrium stabilized zirconium oxide in a mass ratio of 1:0.32:0.38 in dilute nitric acid with a concentration of 0.06M and sonicate for 30 minutes. Then centrifuge, remove the supernatant, wash the precipitate repeatedly with water until the supernatant is neutral, then wash with anhydrous ethanol 3 times, and dry the precipitate under vacuum at 75 for 12 hours to obtain the intermediate. (2) KH-550 coupling agent was added dropwise to anhydrous ethanol and deionized water to obtain a mixed solution. After the addition was completed, the mixture was stirred for 5 minutes. Then, glacial acetic acid was added dropwise until the pH of the solution reached and stabilized at 4.5. After the glacial acetic acid was added, the mixture was stirred at room temperature for 30 minutes. Then, the above intermediate was added and ultrasonically dispersed for 15 minutes to obtain a suspension. The volume ratio of anhydrous ethanol to deionized water was 9:1, the mass ratio of the mixed solution to the intermediate was 8:1, and the mass ratio of KH-550 coupling agent to the intermediate was 1.5:100. (3) The above suspension was refluxed at 60°C for 5 hours. After the reaction was completed, the reaction solution was cooled to room temperature and filtered. The filter cake was washed three times with anhydrous ethanol and then dried under vacuum at 75°C for 12 hours to obtain the coupling agent modified inorganic filler.

[0054] Preparation of flexible substrate materials: The procedure was carried out according to Example 1, except that the 2-mercaptobenzoic acid modified inorganic filler was replaced with the coupling agent modified inorganic filler in Comparative Example 1.

[0055] Comparative Example 2 Preparation of 2-mercaptobenzoic acid modified inorganic filler: The method of Example 1 is the same, except that the zinc aluminum oxide, lanthanum zirconate and yttrium-stabilized zirconium oxide in a mass ratio of 1:0.32:0.38 are replaced with zinc aluminum oxide, lanthanum zirconate and yttrium-stabilized zirconium oxide in a mass ratio of 0.38:0.72:0.6.

[0056] Preparation of flexible substrate materials: The procedure was carried out according to Example 1, except that the 2-mercaptobenzoic acid modified inorganic filler was replaced with the 2-mercaptobenzoic acid modified inorganic filler in Comparative Example 2.

[0057] Comparative Example 3 Preparation of 2-mercaptobenzoic acid modified inorganic filler: The method of Example 1 is the same, except that the zinc aluminum oxide, lanthanum zirconate and yttrium-stabilized zirconium oxide in a mass ratio of 1:0.32:0.38 are replaced with zinc aluminum oxide, lanthanum zirconate and yttrium-stabilized zirconium oxide in a mass ratio of 1.4:0.12:0.18.

[0058] Preparation of flexible substrate materials: The procedure was carried out according to Example 1, except that the 2-mercaptobenzoic acid modified inorganic filler was replaced with the 2-mercaptobenzoic acid modified inorganic filler in Comparative Example 3.

[0059] Comparative Example 4 Preparation of 2-mercaptobenzoic acid modified inorganic filler: The method of Example 1 is the same, except that the zinc aluminum oxide, lanthanum zirconate and yttrium-stabilized zirconium oxide in a mass ratio of 1:0.32:0.38 are replaced with zinc aluminum oxide, lanthanum zirconate and yttrium-stabilized zirconium oxide in a mass ratio of 1:0.6:0.1.

[0060] Preparation of flexible substrate materials: The procedure was carried out according to Example 1, except that the 2-mercaptobenzoic acid modified inorganic filler was replaced with the 2-mercaptobenzoic acid modified inorganic filler in Comparative Example 4.

[0061] Comparative Example 5 Preparation of flexible substrate materials: The procedure was carried out according to Example 1, except that the molar ratio of 6,6'-diamino-2,2'-bipyridine to 1,12-dodecanediamine was replaced with the molar ratio of 1.25:0.1 for 6,6'-diamino-2,2'-bipyridine to 1,12-dodecanediamine.

[0062] Comparative Example 6 Preparation of flexible substrate materials: The procedure was carried out according to Example 1, except that the molar ratio of 6,6'-diamino-2,2'-bipyridine to 1,12-dodecanediamine was replaced with the molar ratio of 6,6'-diamino-2,2'-bipyridine to 1,12-dodecanediamine in a ratio of 0.35:1.

[0063] Comparative Example 7 Preparation of flexible substrate materials: The procedure was carried out according to Example 1, except that 6,6'-diamino-2,2'-bipyridine was replaced with 1,10-decanediamine.

[0064] Comparative Example 8 Preparation of 2-mercaptobenzoic acid modified inorganic filler: The method is the same as in Example 1, except that zinc oxide is replaced with aluminum oxide.

[0065] Preparation of flexible substrate materials: The procedure was carried out according to Example 1, except that the 2-mercaptobenzoic acid modified inorganic filler was replaced with the 2-mercaptobenzoic acid modified inorganic filler in Comparative Example 3.

[0066] Performance testing Decomposition temperature test: The flexible substrate materials prepared in the examples and comparative examples were subjected to TGA test in a nitrogen atmosphere. The temperature was increased to 800°C at a test rate of 5 rpm, and the temperature at which the thermal weight loss was 5 wt% was taken as the thermal decomposition temperature.

[0067] Transmittance test: The transmittance of the flexible substrate materials prepared in the examples and comparative examples at 450 nm was tested using a UV-Vis spectrophotometer.

[0068] Mechanical property testing: The flexible substrate materials prepared in the examples and comparative examples were cut into 50mm*10mm samples, and the tensile modulus of the samples was measured using a universal testing machine at a tensile rate of 5mm / min and a clamping distance of 2cm.

[0069] Acid resistance test: The flexible substrate materials prepared in the examples and comparative examples were immersed in 1M HCl solution for 24 hours. After being taken out, washed and dried, the surface showed no cracking, blistering or dissolution, and the weight loss rate was <0.5%, which was considered qualified; otherwise, it was considered unqualified.

[0070] Alkali resistance test: The flexible substrate materials prepared in the examples and comparative examples were immersed in 1M NaOH solution for 24 hours. After being taken out, washed and dried, the surface showed no cracking, blistering or dissolution, and the weight loss rate was <0.5%, which was considered qualified; otherwise, it was considered unqualified.

[0071] The performance test results are shown in Table 1.

[0072] Table 1 Performance Test Results As can be seen from the above performance test results, the flexible substrate materials prepared in Examples 1-2 have excellent light transmittance, mechanical properties, heat resistance and chemical corrosion resistance.

[0073] The comparative examples, however, did not employ the necessary technical solutions, resulting in significantly inferior performance compared to the exemplary examples. Specifically, in Comparative Example 1, replacing the 2-mercaptobenzoic acid-modified inorganic filler with a coupling agent-modified inorganic filler led to a decrease in the transmittance, modulus, thermal decomposition temperature, and chemical resistance of the flexible substrate material. In Comparative Examples 2-4, the proportions of the three inorganic fillers varied. In Comparative Example 8, replacing zinc oxide with ordinary alumina resulted in a reduction in some properties of the flexible substrate material to a certain extent. This further illustrates that zinc oxide, lanthanum zirconate, and yttrium-stabilized zirconium oxide, when used in a specific ratio (1:0.3-0.5),... The ternary synergistic filler composed of 0.4:0.3-0.4 can better enhance the performance of the material. In Comparative Example 6, the proportion of dodecanediamine was too high, resulting in a decrease in the modulus and thermal decomposition temperature of the final flexible substrate material. In Comparative Example 7, replacing 6,6'-diamino-2,2'-bipyridine with 1,10-decanediamine resulted in a decrease in the modulus and thermal decomposition temperature of the final flexible substrate material. This further demonstrates that the diamine monomers of 6,6'-diamino-2,2'-bipyridine and 1,12-dodecanediamine in a molar ratio of 1:(0.3-0.4) can better achieve a performance balance between high light transmittance, high heat resistance and high modulus.

[0074] The above experimental results further demonstrate the importance of the technical solution defined in this invention to its technical effect.

[0075] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a flexible substrate material, characterized in that, Includes the following steps: S1. The diamine monomer is dissolved in an organic solvent, and then the dianhydride monomer is added to carry out the first reaction. Then, 2-mercaptobenzoic acid-modified inorganic filler is added to carry out the second reaction to obtain the filler / PAA precursor composite solution. S2. The filler / PAA precursor composite liquid is filtered, degassed, and cast into a film, followed by hot stretching and winding to obtain a flexible substrate material. The diamine monomer is 6,6'-diamino-2,2'-bipyridine and 1,12-dodecanediamine in a molar ratio of 1:(0.3-0.4); The molar ratio of the diamine monomer to the dianhydride monomer is (0.98-1):1; the mass ratio of the total mass of the diamine monomer and the dianhydride monomer to the mass of the organic solvent is (15-20):100; the mass ratio of the total mass of the diamine monomer and the dianhydride monomer to the mass of the 2-mercaptobenzoic acid modified inorganic filler is (35-40):

1. The inorganic filler in the 2-mercaptobenzoic acid modified inorganic filler is selected from a combination of zinc aluminum oxide, lanthanum zirconate, and yttrium-stabilized zirconium oxide, with a mass ratio of 1:(0.3-0.4):(0.3-0.4). The organic solvent is N,N-dimethylacetamide.

2. The method for preparing the flexible substrate material according to claim 1, characterized in that, In step S1, the conditions for the first reaction include: being carried out under a nitrogen atmosphere, with a reaction temperature of 0-10 °C, a reaction time of 3-5 h, and a stirring speed of 300-400 rpm; in step S1, the conditions for the second reaction include: being carried out under a nitrogen atmosphere, with a reaction temperature of 0-10 °C, a reaction time of 10-15 h, and a stirring speed of 600-800 rpm.

3. The method for preparing the flexible substrate material according to claim 1, characterized in that, The preparation method of the 2-mercaptobenzoic acid modified inorganic filler includes the following steps: (1) The inorganic packing material was acid-treated in dilute nitric acid with a concentration of 0.05-0.1M, and then centrifuged, washed and dried to obtain an intermediate. (2) The intermediate was added to N-methylpyrrolidone and dispersed to obtain a suspension; (3) Add 2-mercaptobenzoic acid to the above suspension for modification reaction, then centrifuge, wash and dry to obtain 2-mercaptobenzoic acid modified inorganic filler.

4. The method for preparing the flexible substrate material according to claim 1, characterized in that, In step S2, the filtration method includes: coarsely filtering the packing material / PAA precursor composite liquid using a plate and frame filter with a pore size of 10-25, and then finely filtering the packing material / PAA precursor composite liquid using a plate and frame filter with a composite pore size of 1-5.

5. The method for preparing the flexible substrate material according to claim 1, characterized in that, In step S2, the method of casting film formation includes: extruding from a casting die and flowing into a solidified steel plate for curing film formation, wherein the extrusion rate of the casting die is 2-5 cm³ / min, and the curing film formation conditions are 90°C for 3-8 min, 150°C for 3-8 min, and 200°C for 3-8 min; In step S2, the method of hot stretching includes: a heat treatment temperature of 400-450°C, a longitudinal stretching ratio of 2-2.5 times, and a transverse stretching ratio of 1.5-2 times.

6. A flexible substrate material prepared by the method for preparing the flexible substrate material according to any one of claims 1-5.

7. The application of the flexible substrate material according to claim 6 in a flexible display.

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