Flexible polyimide display substrate and method of manufacturing the same

Abstract

This invention relates to the field of flexible display technology and discloses a flexible polyimide display substrate and its preparation method. The method includes: firstly, preparing a polyamic acid slurry containing specific functional fillers; coating it onto a carrier substrate and imidizing it via programmed temperature rise to obtain a flexible substrate; subjecting the substrate surface to plasma treatment to improve its surface energy; subsequently constructing a conductive layer and an encapsulation layer sequentially to form a multilayer composite structure; and finally, after annealing, peeling it off from the carrier substrate to obtain the final display substrate. The functional filler is composed of modified nano-silica and surface-modified two-dimensional boron nitride nanosheets. The resulting flexible polyimide display substrate exhibits high transparency, low coefficient of thermal expansion, high dimensional stability, flexibility, and water and oxygen barrier properties. This invention improves the overall uniformity, dimensional stability, and reliability of the final flexible substrate's mechanical and thermal properties.

Description

Technical Field

[0001] This invention relates to the field of flexible display technology, specifically to flexible polyimide display substrates and their preparation methods. Background Technology

[0002] Flexible display refers to display technology that uses flexible substrates to fabricate ultra-thin, ultra-light, and bendable products. Currently, it mainly refers to flexible AMOLED technology, which uses flexible substrates instead of traditional rigid glass substrates.

[0003] Currently, in the preparation process of flexible polyimide display substrates, the uniformity of functional filler dispersion in the polyimide matrix is ​​difficult to monitor and control in real time. This leads to microscopic differences in the mechanical and thermal properties of local areas of the final substrate, affecting its overall dimensional stability and reliability as a display substrate. At the same time, in the multi-step high-temperature processing, especially the imidization and annealing stages, the requirements for temperature and time control are extremely high. When there are slight deviations in the programmed temperature rise curve or uneven temperature field distribution in the furnace, it is easy to cause uneven distribution of residual stress in the substrate, resulting in substrate warping or a decrease in the bonding force with subsequent functional layers.

[0004] Therefore, a flexible polyimide display substrate and its preparation method are proposed to solve the above problems. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a flexible polyimide display substrate and its preparation method, which solves the problems mentioned in the background art, such as the difficulty in real-time monitoring and control of the uniformity of functional fillers in the polyimide matrix, which leads to microscopic differences in the mechanical and thermal properties of local areas of the final substrate, and the problem that uneven distribution of residual stress in the substrate is easily caused by slight deviations in the programmed temperature rise curve or uneven temperature field distribution in the furnace.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a flexible polyimide display substrate and a method for preparing the same, comprising the following steps: Step 1: Preparation of polyamic acid slurry, preparing a polyamic acid resin slurry containing functional fillers; Step 2: Flexible substrate preparation. The polyamic acid slurry is coated onto the carrier substrate and imidized by programmed temperature rise to form a flexible polyimide substrate. Step 3: Surface modification, the surface of the flexible polyimide substrate is subjected to plasma treatment; Step 4: Construction of multilayer composite structure, in which a conductive layer and an encapsulation layer are sequentially prepared on the surface-treated substrate; Step 5: Post-processing, the composite structure is annealed and then peeled off from the carrier substrate to obtain the flexible polyimide display substrate; In step one, the polyamic acid slurry is made from the following raw materials in parts by weight: 40-60 parts of aromatic dianhydride monomer, 35-55 parts of aromatic diamine monomer, 8-15 parts of functional filler, 1-3 parts of coupling agent, 0.5-2 parts of leveling agent, and 200-300 parts of organic solvent.

[0007] Preferably, step one specifically includes the following steps: under inert gas protection, the aromatic diamine monomer is dissolved in a portion of an organic solvent and stirred until completely dissolved to form a diamine solution. Under conditions of 0℃-10℃, the aromatic dianhydride monomer is added in batches to the diamine solution, the reaction temperature is controlled below 30℃, and the reaction is stirred for 8-16 hours to obtain a polyamic acid prepolymer solution. The functional filler, coupling agent, and leveling agent are mixed with the remaining organic solvent, ultrasonically dispersed for 30-60 minutes, and then mixed with the polyamic acid prepolymer solution. The mixture is stirred at a speed of 200r / min-500r / min for 2-4 hours and then vacuum degassing to obtain the polyamic acid slurry.

[0008] Preferably, step two specifically includes the following steps: coating the polyamic acid slurry onto a clean glass or silicon wafer substrate using a slot coating method, controlling the wet film thickness to be 50 micrometers-150 micrometers; placing the coated substrate on a hot plate and sequentially performing a programmed temperature rise process of 80℃±5℃ for 30 minutes, 150℃±5℃ for 30 minutes, 250℃±10℃ for 60 minutes, and 350℃±10℃ for 120 minutes to complete imidization and solvent removal, ultimately forming the flexible polyimide substrate with a thickness of 10 micrometers-30 micrometers.

[0009] Preferably, in step three, the plasma treatment conditions are as follows: a mixture of argon and oxygen is used, wherein the oxygen volume percentage is 10%-30%, the treatment chamber pressure is 50Pa-200Pa, the radio frequency power is 100W-300W, and the treatment time is 30 seconds-120 seconds.

[0010] Preferably, the construction of the multilayer composite structure in step four specifically includes the following sub-steps: Sub-step 1: Conductive layer preparation. An indium tin oxide conductive layer is deposited on the surface of the treated flexible polyimide substrate using magnetron sputtering. The sputtering power is 100W-200W, the working pressure is 0.5Pa-1.0Pa, the substrate temperature is room temperature to 80℃, the sheet resistance of the conductive layer is 20Ω / sq-50Ω / sq, and the thickness is 100nm-200nm. Sub-step 2: Encapsulation layer preparation. A silicon nitride encapsulation layer is grown on the surface of the conductive layer using chemical vapor deposition. The reaction gases are silane and ammonia. The deposition temperature is 200℃-300℃, the chamber pressure is 100Pa-300Pa, and the encapsulation layer thickness is 500nm-1000nm.

[0011] Preferably, in step five, the annealing process is carried out under a nitrogen atmosphere, the annealing temperature is 200℃±10℃, and the annealing time is 1 hour to 2 hours.

[0012] Preferably, the functional filler is prepared by the following method: Modified nano-silica and two-dimensional boron nitride nanosheets are selected. The particle size of the modified nano-silica is 20-50 nanometers, and the lateral dimension of the two-dimensional boron nitride nanosheets is 1-5 micrometers, with a thickness of 1-5 nanometers. The two-dimensional boron nitride nanosheets are dispersed in deionized water, a silane coupling agent is added, and the mixture is stirred at 60-80°C for 2-4 hours. After the reaction is completed, the mixture is centrifuged, washed, and dried to obtain surface-modified boron nitride nanosheets. The modified nano-silica and the surface-modified boron nitride nanosheets are mixed at a mass ratio of 1:1 to 1:3, and ethanol solvent is added. The mixture is treated in an ultrasonic cell disruptor at 500-800W power for 30-60 minutes, followed by rotary evaporation at 40-60°C to remove the solvent, thus obtaining the functional filler.

[0013] Preferably, the coupling agent is γ-aminopropyltriethoxysilane or γ-(2,3-epoxypropoxy)propyltrimethoxysilane, the leveling agent is polyether-modified polydimethylsiloxane, and the organic solvent is at least one of N-methylpyrrolidone, N,N-dimethylacetamide, or dimethyl sulfoxide.

[0014] Preferably, the aromatic dianhydride monomer is at least one of pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, or 4,4'-oxobisphthalic anhydride, and the aromatic diamine monomer is at least one of p-phenylenediamine, 4,4'-diaminodiphenyl ether, or 2,2'-bis[4-(4-aminophenoxy)phenyl]propane.

[0015] Preferably, the display substrate comprises a flexible polyimide substrate, a surface modification layer formed on the substrate, a conductive layer disposed on the surface modification layer, and an encapsulation layer covering the conductive layer. The flexible polyimide substrate has a thickness of 10 micrometers to 30 micrometers and uniformly dispersed functional fillers therein. The substrate has a dielectric constant of 2.8-3.2 in the frequency range of 10Hz to 1MHz, a coefficient of thermal expansion of 10pm / ℃-20ppm / ℃, and a glass transition temperature higher than 350℃. The conductive layer is an indium tin oxide layer with a sheet resistance of 20Ω / sq-50Ω / sq. The encapsulation layer is a silicon nitride layer with a water vapor permeability of less than 10%. -4 g / (m 2 ·day).

[0016] Compared with the prior art, the present invention provides a flexible polyimide display substrate and its preparation method, which has the following beneficial effects: 1. In this invention, by employing specific functional fillers and their surface modification and pre-dispersion processes, and combining them with optimized polyamic acid synthesis and mixing processes, the functional fillers can achieve highly uniform and stable dispersion in the polyamic acid slurry. This avoids local performance differences in the substrate caused by filler agglomeration or uneven distribution, and improves the overall uniformity, dimensional stability and reliability of the final flexible substrate's mechanical and thermal properties.

[0017] 2. In this invention, by designing and strictly controlling the programmed temperature rise process from coating, drying to imidization and final annealing, and optimizing the temperature and time parameters at each stage, the polyamic acid can undergo imidization reaction smoothly and fully and release internal stress. This reduces the problems of substrate warping, deformation and uneven residual stress distribution caused by improper heat treatment process, and improves the flatness of the substrate and the interface bonding strength between it and subsequent functional layers.

[0018] 3. In this invention, by combining plasma treatment of the substrate surface with the precise deposition process of the subsequent conductive layer and encapsulation layer, and by synergistically controlling the key parameters of each layer preparation, the surface energy of the substrate, the interlayer adhesion, and the deposition quality of the functional film are optimized. This reduces performance degradation caused by interface defects, film inhomogeneity, or pinholes, and improves the photoelectric performance consistency and long-term reliability of the flexible polyimide display substrate as a device platform. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] Example 1: Flexible polyimide display substrate and its preparation method, including the following steps: Step 1: Preparation of polyamic acid slurry, preparing a polyamic acid resin slurry containing functional fillers; Step 2: Flexible substrate preparation. Polyamic acid slurry is coated onto the carrier substrate and imidized through programmed temperature rise to form a flexible polyimide substrate. Step 3: Surface modification, plasma treatment of the surface of the flexible polyimide substrate; Step 4: Construction of multilayer composite structure, in which a conductive layer and an encapsulation layer are sequentially prepared on the surface-treated substrate; Step 5: Post-processing, the composite structure is annealed and then peeled off from the carrier substrate to obtain the flexible polyimide display substrate; In step one, the polyamic acid slurry is made from the following raw materials in parts by weight: 40 parts aromatic dianhydride monomer, 35 parts aromatic diamine monomer, 8 parts functional filler, 1 part coupling agent, 0.5 parts leveling agent, and 200 parts organic solvent.

[0021] Step 1 specifically includes the following steps: Under inert gas protection, the aromatic diamine monomer is dissolved in a portion of the organic solvent and stirred until completely dissolved to form a diamine solution. At 0°C, the aromatic dianhydride monomer is added to the diamine solution in batches, and the reaction temperature is controlled below 30°C. The reaction is stirred for 8 hours to obtain a polyamic acid prepolymer solution. The functional filler, coupling agent, and leveling agent are mixed with the remaining organic solvent and ultrasonically dispersed for 30 minutes. Then, the mixture is mixed with the polyamic acid prepolymer solution and stirred at 200 r / min for 2 hours. After vacuum degassing, a polyamic acid slurry is obtained.

[0022] Step two specifically includes the following steps: applying polyamic acid slurry to a clean glass substrate using a slot coating method, controlling the wet film thickness to 50 micrometers; placing the coated substrate on a hot plate and sequentially performing a programmed temperature increase process of 75°C for 30 minutes, 145°C for 30 minutes, 240°C for 60 minutes, and 340°C for 120 minutes to complete imidization and solvent removal, ultimately forming a flexible polyimide substrate with a thickness of 10 micrometers.

[0023] In step three, the plasma treatment conditions are as follows: a mixture of argon and oxygen is used, with oxygen accounting for 10% of the volume; the treatment chamber pressure is 50 Pa; the radio frequency power is 100 W; and the treatment time is 30 seconds.

[0024] Step four, the construction of the multi-layered composite structure, specifically includes the following sub-steps: Sub-step 1: Preparation of conductive layer. An indium tin oxide conductive layer is deposited on the surface of the treated flexible polyimide substrate using magnetron sputtering. The sputtering power is 100W, the working pressure is 0.5Pa, the substrate temperature is room temperature to 80℃, the sheet resistance of the conductive layer is 20Ω / sq, and the thickness is 100nm. Sub-step 2: Encapsulation layer preparation. A silicon nitride encapsulation layer is grown on the surface of the conductive layer using chemical vapor deposition. The reaction gases are silane and ammonia. The deposition temperature is 200℃, the chamber pressure is 100Pa, and the encapsulation layer thickness is 500 nanometers.

[0025] In step five, the annealing process is carried out under a nitrogen atmosphere, at a temperature of 190°C, for a duration of 1 hour.

[0026] The functional filler was prepared by the following method: Modified nano-silica and two-dimensional boron nitride nanosheets were selected. The particle size of the modified nano-silica was 20 nm, and the lateral dimension of the two-dimensional boron nitride nanosheets was 1 μm and the thickness was 1 nm. The two-dimensional boron nitride nanosheets were dispersed in deionized water, a silane coupling agent was added, and the mixture was stirred at 60 °C for 2 hours. After the reaction was completed, the mixture was centrifuged, washed, and dried to obtain surface-modified boron nitride nanosheets. The modified nano-silica and the surface-modified boron nitride nanosheets were mixed at a mass ratio of 1:1, ethanol solvent was added, and the mixture was treated in an ultrasonic cell disruptor at a power of 500 W for 30 minutes. Subsequently, the solvent was removed by rotary evaporation at 40 °C to obtain the functional filler.

[0027] The coupling agent is γ-aminopropyltriethoxysilane or γ-(2,3-epoxypropoxy)propyltrimethoxysilane, the leveling agent is polyether-modified polydimethylsiloxane, and the organic solvent is N-methylpyrrolidone.

[0028] The aromatic dianhydride monomer is pyromellitic dianhydride, and the aromatic diamine monomer is p-phenylenediamine.

[0029] The display substrate includes a flexible polyimide substrate, a surface modification layer formed on the substrate, a conductive layer disposed on the surface modification layer, and an encapsulation layer covering the conductive layer. The flexible polyimide substrate has a thickness of 10 micrometers and uniformly dispersed functional fillers. The substrate has a dielectric constant of 2.8 at a frequency of 10 Hz, a coefficient of thermal expansion of 10 pm / ℃, a glass transition temperature higher than 350℃, an indium tin oxide (ITO) conductive layer with a sheet resistance of 20 Ω / sq, and a silicon nitride (SiN) encapsulation layer with a water vapor permeability of less than 10%. -4g / (m 2 ·day).

[0030] Example 2: Flexible polyimide display substrate and its preparation method, including the following steps: Step 1: Preparation of polyamic acid slurry, preparing a polyamic acid resin slurry containing functional fillers; Step 2: Flexible substrate preparation. Polyamic acid slurry is coated onto the carrier substrate and imidized through programmed temperature rise to form a flexible polyimide substrate. Step 3: Surface modification, plasma treatment of the surface of the flexible polyimide substrate; Step 4: Construction of multilayer composite structure, in which a conductive layer and an encapsulation layer are sequentially prepared on the surface-treated substrate; Step 5: Post-processing, the composite structure is annealed and then peeled off from the carrier substrate to obtain the flexible polyimide display substrate; In step one, the polyamic acid slurry is made from the following raw materials in parts by weight: 50 parts aromatic dianhydride monomer, 45 parts aromatic diamine monomer, 11.5 parts functional filler, 2 parts coupling agent, 1.25 parts leveling agent, and 250 parts organic solvent.

[0031] Step 1 specifically includes the following steps: Under inert gas protection, the aromatic diamine monomer is dissolved in a portion of the organic solvent and stirred until completely dissolved to form a diamine solution. At 5°C, the aromatic dianhydride monomer is added to the diamine solution in batches, and the reaction temperature is controlled below 30°C. The reaction is stirred for 12 hours to obtain a polyamic acid prepolymer solution. The functional filler, coupling agent, and leveling agent are mixed with the remaining organic solvent and ultrasonically dispersed for 45 minutes. Then, the mixture is mixed with the polyamic acid prepolymer solution and stirred at 350 r / min for 3 hours. After vacuum degassing, a polyamic acid slurry is obtained.

[0032] Step two specifically includes the following steps: applying polyamic acid slurry to a clean silicon wafer substrate using a slot coating method, controlling the wet film thickness to 100 micrometers, placing the coated substrate on a hot plate, and sequentially performing a programmed temperature increase process of 80°C for 30 minutes, 150°C for 30 minutes, 250°C for 60 minutes, and 350°C for 120 minutes to complete imidization and solvent removal, ultimately forming a flexible polyimide substrate with a thickness of 20 micrometers.

[0033] In step three, the plasma treatment conditions are as follows: a mixture of argon and oxygen is used, with oxygen accounting for 20% of the volume; the treatment chamber pressure is 125 Pa; the radio frequency power is 200 W; and the treatment time is 75 seconds.

[0034] Step four, the construction of the multi-layered composite structure, specifically includes the following sub-steps: Sub-step 1: Preparation of conductive layer. An indium tin oxide conductive layer is deposited on the surface of the treated flexible polyimide substrate using magnetron sputtering. The sputtering power is 150W, the working pressure is 0.75Pa, the substrate temperature is room temperature to 80℃, the sheet resistance of the conductive layer is 35Ω / sq, and the thickness is 150nm. Sub-step 2: Encapsulation layer preparation. A silicon nitride encapsulation layer is grown on the surface of the conductive layer using chemical vapor deposition. The reaction gases are silane and ammonia. The deposition temperature is 250℃, the chamber pressure is 200Pa, and the encapsulation layer thickness is 750 nanometers.

[0035] In step five, the annealing process is carried out under a nitrogen atmosphere, at a temperature of 200°C, for 1.5 hours.

[0036] The functional filler was prepared by the following method: Modified nano-silica and two-dimensional boron nitride nanosheets were selected. The particle size of the modified nano-silica was 35 nm, and the lateral dimension of the two-dimensional boron nitride nanosheets was 3 μm and the thickness was 3 nm. The two-dimensional boron nitride nanosheets were dispersed in deionized water, a silane coupling agent was added, and the mixture was stirred at 70 °C for 3 hours. After the reaction was completed, the mixture was centrifuged, washed, and dried to obtain surface-modified boron nitride nanosheets. The modified nano-silica and the surface-modified boron nitride nanosheets were mixed at a mass ratio of 1:12, ethanol solvent was added, and the mixture was treated in an ultrasonic cell disruptor at a power of 350 W for 45 minutes. Subsequently, the solvent was removed by rotary evaporation at 50 °C to obtain the functional filler.

[0037] The coupling agent is γ-aminopropyltriethoxysilane or γ-(2,3-epoxypropoxy)propyltrimethoxysilane, the leveling agent is polyether-modified polydimethylsiloxane, and the organic solvent is N,N-dimethylacetamide.

[0038] The aromatic dianhydride monomer is 3,3',4,4'-biphenyltetracarboxylic dianhydride, and the aromatic diamine monomer is 4,4'-diaminodiphenyl ether.

[0039] The display substrate includes a flexible polyimide substrate, a surface modification layer formed on the substrate, a conductive layer disposed on the surface modification layer, and an encapsulation layer covering the conductive layer. The flexible polyimide substrate has a thickness of 20 micrometers and contains uniformly dispersed functional fillers. The substrate has a dielectric constant of 3.0 at a frequency of 0.500005MHz, a coefficient of thermal expansion of 15ppm / ℃, a glass transition temperature higher than 350℃, an indium tin oxide (ITO) conductive layer with a sheet resistance of 35Ω / sq, and a silicon nitride (SiN) encapsulation layer with a water vapor permeability of less than 10%. -4 g / (m 2 ·day).

[0040] Example 3: Flexible polyimide display substrate and its preparation method, including the following steps: Step 1: Preparation of polyamic acid slurry, preparing a polyamic acid resin slurry containing functional fillers; Step 2: Flexible substrate preparation. Polyamic acid slurry is coated onto the carrier substrate and imidized through programmed temperature rise to form a flexible polyimide substrate. Step 3: Surface modification, plasma treatment of the surface of the flexible polyimide substrate; Step 4: Construction of multilayer composite structure, in which a conductive layer and an encapsulation layer are sequentially prepared on the surface-treated substrate; Step 5: Post-processing, the composite structure is annealed and then peeled off from the carrier substrate to obtain the flexible polyimide display substrate; In step one, the polyamic acid slurry is made from the following raw materials in parts by weight: 60 parts aromatic dianhydride monomer, 55 parts aromatic diamine monomer, 15 parts functional filler, 3 parts coupling agent, 2 parts leveling agent, and 300 parts organic solvent.

[0041] Step 1 specifically includes the following steps: Under inert gas protection, the aromatic diamine monomer is dissolved in a portion of the organic solvent and stirred until completely dissolved to form a diamine solution. At 10°C, the aromatic dianhydride monomer is added to the diamine solution in batches, and the reaction temperature is controlled below 30°C. The reaction is stirred for 16 hours to obtain a polyamic acid prepolymer solution. The functional filler, coupling agent, and leveling agent are mixed with the remaining organic solvent and ultrasonically dispersed for 60 minutes. Then, the mixture is mixed with the polyamic acid prepolymer solution and stirred at 500 r / min for 4 hours. After vacuum degassing, a polyamic acid slurry is obtained.

[0042] Step two specifically includes the following steps: applying polyamic acid slurry to a clean glass substrate using a slot coating method, controlling the wet film thickness to 150 micrometers; placing the coated substrate on a hot plate and sequentially performing a programmed temperature increase process of 85°C for 30 minutes, 155°C for 30 minutes, 260°C for 60 minutes, and 360°C for 120 minutes to complete imidization and solvent removal, ultimately forming a flexible polyimide substrate with a thickness of 30 micrometers.

[0043] In step three, the plasma treatment conditions are as follows: a mixture of argon and oxygen is used, with oxygen accounting for 30% of the volume; the treatment chamber pressure is 200 Pa; the radio frequency power is 300 W; and the treatment time is 120 seconds.

[0044] Step four, the construction of the multi-layered composite structure, specifically includes the following sub-steps: Sub-step 1: Preparation of conductive layer. An indium tin oxide conductive layer is deposited on the surface of the treated flexible polyimide substrate using magnetron sputtering. The sputtering power is 200W, the working pressure is 1.0Pa, the substrate temperature is room temperature to 80℃, the sheet resistance of the conductive layer is 50Ω / sq, and the thickness is 200nm. Sub-step 2: Encapsulation layer preparation. A silicon nitride encapsulation layer is grown on the surface of the conductive layer using chemical vapor deposition. The reaction gases are silane and ammonia. The deposition temperature is 300℃, the chamber pressure is 300Pa, and the encapsulation layer thickness is 1000 nanometers.

[0045] In step five, the annealing process is carried out under a nitrogen atmosphere, at a temperature of 210°C, for a duration of 2 hours.

[0046] The functional filler was prepared by the following method: Modified nano-silica and two-dimensional boron nitride nanosheets were selected. The particle size of the modified nano-silica was 50 nm, and the lateral dimension of the two-dimensional boron nitride nanosheets was 5 μm and the thickness was 5 nm. The two-dimensional boron nitride nanosheets were dispersed in deionized water, a silane coupling agent was added, and the mixture was stirred at 80 °C for 4 hours. After the reaction was completed, the mixture was centrifuged, washed, and dried to obtain surface-modified boron nitride nanosheets. The modified nano-silica and the surface-modified boron nitride nanosheets were mixed at a mass ratio of 1:3, ethanol solvent was added, and the mixture was treated in an ultrasonic cell disruptor at 800 W power for 60 minutes. Subsequently, the solvent was removed by rotary evaporation at 60 °C to obtain the functional filler.

[0047] The coupling agent is γ-aminopropyltriethoxysilane or γ-(2,3-epoxypropoxy)propyltrimethoxysilane, the leveling agent is polyether-modified polydimethylsiloxane, and the organic solvent is dimethyl sulfoxide.

[0048] The aromatic dianhydride monomer is 4,4'-oxobisphthalic anhydride, and the aromatic diamine monomer is 2,2'-bis[4-(4-aminophenoxy)phenyl]propane.

[0049] The display substrate includes a flexible polyimide substrate, a surface modification layer formed on the substrate, a conductive layer disposed on the surface modification layer, and an encapsulation layer covering the conductive layer. The flexible polyimide substrate has a thickness of 30 micrometers and contains uniformly dispersed functional fillers. The substrate has a stable dielectric constant of 3.2 at a frequency of 1 MHz, a coefficient of thermal expansion of 20 ppm / ℃, and a glass transition temperature higher than 350℃. The conductive layer is an indium tin oxide layer with a sheet resistance of 50 Ω / sq. The encapsulation layer is a silicon nitride layer with a water vapor permeability of less than 10%. -4 g / (m 2 ·day).

[0050] Comparative Example 1 differs from Example 1 in that: no functional filler, a composite of modified nano-silica and two-dimensional boron nitride nanosheets, was added during the preparation of the polyamic acid slurry. Comparative Example 2 differs from Example 2 in that: in the process of preparing the flexible substrate in step two, imidization was not carried out by step-by-step temperature increase, but was directly cured at 350°C for the same time in one go. Comparative Example 3 differs from Example 3 in that: in the preparation of the conductive layer in step four, magnetron sputtering was not used, but screen printing was used to prepare the silver paste conductive layer. Comparative Example 4 differs from Example 3 in that the surface of the flexible polyimide substrate was not subjected to plasma treatment in step three.

[0051] The performance of the flexible polyimide display substrates and their preparation methods in Examples 1-3 and Comparative Examples 1-4 were tested. The test items and methods are as follows: Dimensional stability test: In accordance with industry standards, a thermomechanical analyzer is used to measure the dimensional changes of the substrate in the temperature range of -50℃ to 300℃, calculate the average coefficient of thermal expansion, and observe the warpage radius of the substrate after high-temperature treatment. Conductivity test: The sheet resistance of the conductive layer at multiple points on the substrate surface is measured using a four-probe tester, and its uniformity is calculated. Barrier performance test: The water vapor transmission rate of the encapsulation layer was measured under conditions of 40℃ and 90% relative humidity. Mechanical flexibility and interfacial adhesion testing: The substrate was repeatedly bent around a mandrel of different diameters using a bending tester. The number of bends was recorded when the resistance of the conductive layer increased by 10% or the film layer cracked. The adhesion level between the encapsulation layer and the conductive layer, and between the conductive layer and the polyimide substrate was tested using the cross-cut adhesion test.

[0052] The test data of the flexible polyimide display substrates and their preparation methods in Examples 1-3 and Comparative Examples 1-4 are recorded in the table below:

[0053] Comparison and analysis of the data in the table show that the flexible polyimide display substrates and their preparation methods in Examples 1-3 exhibit superior performance compared to those in Comparative Examples 1-4. This indicates that by employing specific functional fillers and their surface modification and pre-dispersion processes, combined with optimized polyamic acid synthesis and mixing procedures, the functional fillers can achieve highly uniform and stable dispersion in the polyamic acid slurry. This avoids local performance differences in the substrate caused by filler agglomeration or uneven distribution, improving the overall uniformity, dimensional stability, and reliability of the final flexible substrate's mechanical and thermal properties. Furthermore, the process of designing and strictly controlling the programmed temperature rise from coating and drying to imidization and final annealing, and optimizing various parameters, demonstrates superior performance. The precise temperature and time parameters at each stage allow polyamic acid to undergo a stable and thorough imidization reaction and release internal stress, thereby reducing substrate warping, deformation, and uneven residual stress distribution caused by improper heat treatment. This improves the flatness of the substrate and the interfacial bonding strength between it and subsequent functional layers. By combining plasma treatment of the substrate surface with the precise deposition process of subsequent conductive and encapsulation layers, and by synergistically controlling the key parameters of each layer preparation, the surface energy of the substrate, interlayer adhesion, and deposition quality of the functional film are optimized. This reduces performance degradation caused by interface defects, film inhomogeneity, or pinholes, and enhances the photoelectric performance consistency and long-term reliability of the flexible polyimide display substrate as a device platform.

[0054] By comparing and analyzing the relevant data in the table, it can be seen that the flexible polyimide display substrate and its preparation method of the present invention have superior overall performance.

[0055] In the description of this specification, references to terms such as "an embodiment," "example," and "specific example" indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0056] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing a flexible polyimide display substrate, characterized in that, Includes the following steps: Step 1: Preparation of polyamic acid slurry, preparing a polyamic acid resin slurry containing functional fillers; Step 2: Flexible substrate preparation. The polyamic acid slurry is coated onto the carrier substrate and imidized by programmed temperature rise to form a flexible polyimide substrate. Step 3: Surface modification, the surface of the flexible polyimide substrate is subjected to plasma treatment; Step 4: Construction of multilayer composite structure, in which a conductive layer and an encapsulation layer are sequentially prepared on the surface-treated substrate; Step 5: Post-processing, the composite structure is annealed and then peeled off from the carrier substrate to obtain the flexible polyimide display substrate; In step one, the polyamic acid slurry is made from the following raw materials in parts by weight: 40-60 parts of aromatic dianhydride monomer, 35-55 parts of aromatic diamine monomer, 8-15 parts of functional filler, 1-3 parts of coupling agent, 0.5-2 parts of leveling agent, and 200-300 parts of organic solvent.

2. The method for preparing a flexible polyimide display substrate according to claim 1, characterized in that, Step one specifically includes the following steps: Under inert gas protection, the aromatic diamine monomer is dissolved in a portion of an organic solvent and stirred until completely dissolved to form a diamine solution. Under conditions of 0℃-10℃, the aromatic dianhydride monomer is added in batches to the diamine solution, the reaction temperature is controlled below 30℃, and the reaction is stirred for 8-16 hours to obtain a polyamic acid prepolymer solution. The functional filler, coupling agent, and leveling agent are mixed with the remaining organic solvent, ultrasonically dispersed for 30-60 minutes, and then mixed with the polyamic acid prepolymer solution. The mixture is stirred at a speed of 200r / min-500r / min for 2-4 hours and then vacuum degassing to obtain the polyamic acid slurry.

3. The method for preparing a flexible polyimide display substrate according to claim 1, characterized in that, Step two specifically includes the following steps: applying the polyamic acid slurry onto a clean glass or silicon wafer substrate using a slot coating method, controlling the wet film thickness to be 50-150 micrometers; placing the coated substrate on a hot plate and sequentially performing a programmed temperature increase process of 80℃±5℃ for 30 minutes, 150℃±5℃ for 30 minutes, 250℃±10℃ for 60 minutes, and 350℃±10℃ for 120 minutes to complete imidization and solvent removal, ultimately forming the flexible polyimide substrate with a thickness of 10-30 micrometers.

4. The method for preparing a flexible polyimide display substrate according to claim 1, characterized in that, In step three, the plasma treatment conditions are as follows: a mixture of argon and oxygen is used, with oxygen accounting for 10%-30% of the volume; the treatment chamber pressure is 50Pa-200Pa; the radio frequency power is 100W-300W; and the treatment time is 30-120 seconds.

5. The method for preparing a flexible polyimide display substrate according to claim 1, characterized in that, The construction of the multi-layered composite structure in step four specifically includes the following sub-steps: Sub-step 1: Conductive layer preparation. An indium tin oxide conductive layer is deposited on the surface of the treated flexible polyimide substrate using magnetron sputtering. The sputtering power is 100W-200W, the working pressure is 0.5Pa-1.0Pa, the substrate temperature is room temperature to 80℃, the sheet resistance of the conductive layer is 20Ω / sq-50Ω / sq, and the thickness is 100nm-200nm. Sub-step 2: Encapsulation layer preparation. A silicon nitride encapsulation layer is grown on the surface of the conductive layer using chemical vapor deposition. The reaction gases are silane and ammonia. The deposition temperature is 200℃-300℃, the chamber pressure is 100Pa-300Pa, and the encapsulation layer thickness is 500nm-1000nm.

6. The method for preparing a flexible polyimide display substrate according to claim 1, characterized in that, In step five, the annealing process is carried out under a nitrogen atmosphere, with an annealing temperature of 200℃±10℃ and an annealing time of 1-2 hours.

7. The method for preparing a flexible polyimide display substrate according to claim 1, characterized in that, The functional filler is prepared by the following method: Modified nano-silica and two-dimensional boron nitride nanosheets are selected. The particle size of the modified nano-silica is 20-50 nm, and the lateral dimension of the two-dimensional boron nitride nanosheets is 1-5 μm, with a thickness of 1-5 nm. The two-dimensional boron nitride nanosheets are dispersed in deionized water, a silane coupling agent is added, and the mixture is stirred at 60-80°C for 2-4 hours. After the reaction is complete, the mixture is centrifuged, washed, and dried to obtain surface-modified boron nitride nanosheets. The modified nano-silica and surface-modified boron nitride nanosheets are mixed at a mass ratio of 1:1 to 1:3, and ethanol solvent is added. The mixture is then treated in an ultrasonic cell disruptor at 500-800W power for 30-60 minutes, followed by rotary evaporation at 40-60°C to remove the solvent, thus obtaining the functional filler.

8. The method for preparing a flexible polyimide display substrate according to claim 1, characterized in that, The coupling agent is γ-aminopropyltriethoxysilane or γ-(2,3-epoxypropoxy)propyltrimethoxysilane, the leveling agent is polyether-modified polydimethylsiloxane, and the organic solvent is at least one of N-methylpyrrolidone, N,N-dimethylacetamide, or dimethyl sulfoxide.

9. The method for preparing a flexible polyimide display substrate according to claim 1, characterized in that, The aromatic dianhydride monomer is at least one of pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, or 4,4'-oxobisphthalic anhydride, and the aromatic diamine monomer is at least one of p-phenylenediamine, 4,4'-diaminodiphenyl ether, or 2,2'-bis[4-(4-aminophenoxy)phenyl]propane.

10. A flexible polyimide display substrate, prepared by the method for preparing a flexible polyimide display substrate according to any one of claims 1 to 9, characterized in that, The display substrate includes a flexible polyimide substrate, a surface modification layer formed on the substrate, a conductive layer disposed on the surface modification layer, and an encapsulation layer covering the conductive layer. The flexible polyimide substrate has a thickness of 10-30 micrometers and uniformly dispersed functional fillers. The substrate has a dielectric constant of 2.8-3.2 in the frequency range of 10Hz to 1MHz, a coefficient of thermal expansion of 10pm / ℃-20ppm / ℃, and a glass transition temperature higher than 350℃. The conductive layer is an indium tin oxide layer with a sheet resistance of 20Ω / sq-50Ω / sq. The encapsulation layer is a silicon nitride layer with a water vapor permeability of less than 10%. -4 g / (m 2 ·day).

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