Polyamic acid resin, polyimide film and preparation method

Abstract

The invention belongs to the technical field of high polymer materials, and particularly relates to polyamide acid resin, a polyimide film and a preparation method thereof, and the polyamide acid resin is obtained by condensation polymerization of a diamine monomer and a dianhydride monomer in a molar ratio of 1: (0.8-1.2) in a polar aprotic solvent; the diamine monomer and the dianhydride monomer comprise a first type of diamine compound with a hydrophobic group and / or a first type of dianhydride compound with a rigid ester ring structure, and a second type of diamine compound and a second type of dianhydride compound. The low-grade and low-water-absorption special monomer is introduced into the formula, the molecular chain structure is changed, the dielectric constant is reduced, and therefore the short-time ghost phenomenon is reduced.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically relating to a polyamic acid resin, a polyimide film, and a preparation method thereof. Background Technology

[0002] Polyimide (PI) not only boasts excellent high-temperature resistance but also surpasses most specialty engineering plastics in optical transmittance, mechanical rigidity, and electrical stability, making it widely used in aerospace, insulation materials, and high-temperature components. In recent years, thanks to its ultra-thin and highly flexible properties, PI has become the preferred material to replace glass substrates in flexible displays, meeting the substrate requirements for bent and foldable displays. As display quality demands continue to rise, the image retention problem in AMOLED devices driven by low-temperature polycrystalline silicon thin-film transistors (LTPS-TFTs) remains a challenge that needs to be addressed under current material and process conditions.

[0003] Short-term image retention in AMOLED typically refers to recoverable residual images. The generation of short-term image retention is mainly caused by two coupled factors: Firstly, the pixel driving circuit and the LTPS-TFT itself have the ability to trap / release carriers, and the reversible hysteresis effect caused by bias stress leads to a drift in threshold voltage and mobility over time, resulting in pixel current deviations during grayscale switching. Secondly, the polyimide (PI) substrate contains polar groups, residual solvents, or adsorbed moisture, which easily generate and accumulate mobile or trapped charges. These charges are coupled to the TFT channel / electrode in an approximate "planar capacitor" manner, requiring charging and discharging during grayscale abrupt changes. Furthermore, the charge migration and release in PI have a relatively long time constant, causing a temporary shift in the effective gate voltage. The interaction of these two factors amplifies the recovery time, forming recoverable short-term image retention.

[0004] A Chinese invention patent with publication number CN 116715851A, entitled "A Polyimide Precursor and its Preparation Method, Polyimide Film and its Application," discloses a method to improve image retention by introducing fluorinated diamine monomers and fluorinated dianhydride monomers into diamine monomers and dianhydride monomers, thereby reducing the polarizability and dielectric constant of the entire molecular chain. However, fluorinated monomers typically refer to monomers with F or CF3 side groups on the main chain. Their large steric hindrance can affect the coefficient of thermal expansion (CTE) of the PI film. Furthermore, fluorinated monomers cannot meet the future requirements for PFAS-free polyimide.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and to propose a polyamic acid resin, a polyimide film and a preparation method thereof. By introducing special monomers with low virginity and low water absorption into the formulation, the molecular chain structure is changed and the dielectric constant is reduced, thereby reducing the generation of short-time image retention.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a polyamic acid resin for improving image retention in display devices, which is obtained by polycondensation reaction of a diamine monomer and a dianhydride monomer in a molar ratio of 1:(0.8~1.2) in a polar aprotic solvent; wherein the diamine monomer and the dianhydride monomer include a first type of diamine compound having a hydrophobic group and / or a first type of dianhydride compound having a rigid ester ring structure, as well as a second type of diamine compound and a second type of dianhydride compound; wherein the first type of diamine compound and the second type of diamine compound are diamine monomers, and the first type of dianhydride compound and the second type of dianhydride compound are dianhydride monomers.

[0008] Furthermore, the first type of diamine compound accounts for 0-20 mol% of the total molar number of diamine monomers; the first type of dianhydride compound accounts for 0-20 mol% of the total molar number of dianhydride monomers; and the first type of diamine compound and the first type of dianhydride compound are not both taken as 0.

[0009] Further, the first type of diamine compound is selected from any one of 4,4'-diaminodiphenyl sulfone (4,4-DDS), p-aminophenyl benzoate (APAB), 2,6-diaminoanthraquinone (2,6-DAAQ), 4,4'-diaminodiphenyl ether (ODA), 2,2'-bis(trifluoromethyl)benzyldiamine (TFMB), m-phenylenediamine (MPD), and 4,4'-diaminodiphenylmethane (MDA).

[0010] Furthermore, the second type of diamine compound is selected from any one of p-phenylenediamine (PDA), ethylenediamine (EDA), hexamethylenediamine (HMD), and 1,4-cyclohexanediamine (CHDA).

[0011] Further, the first type of dianhydride compound is selected from any one of 1,2,4,5-cyclohexanetetracarboxylic dianhydride (HPMDA), 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA), bicyclo[2.2.2]octane-2,3,5,6-tetracarboxylic dianhydride (BODA), cyclopentanetetracarboxylic dianhydride (CPDA), norbornane-2-spiro-α-cyclopentanone-α'-spiro-2''-norbornanetetracarboxylic dianhydride (NSDA), and 1,2,3,4-cyclopentanetetracarboxylic dianhydride (1,2,3,4-CPDA).

[0012] Furthermore, the second type of dianhydride compound is selected from any one of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), pyromellitic dianhydride (PMDA), and 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA).

[0013] Furthermore, the polar aprotic solvent is selected from one or more of N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), and dimethyl sulfoxide (DMSO).

[0014] Secondly, the present invention provides a method for preparing polyamic acid resin, which is used to prepare the polyamic acid resin as described above. The method involves adding a diamine monomer to a polar aprotic solvent in a certain proportion, stirring to dissolve the resin, then adding a dianhydride monomer, and performing a polycondensation reaction at a temperature of 10-60°C for 10-15 hours. The resin is then obtained by filtration and degassing.

[0015] Thirdly, the present invention provides a polyimide film, which is prepared by uniformly coating the polyamic acid resin onto a glass plate or glass substrate based on the polyamic acid resin as described above or the prepared polyamic acid resin, and then drying, gradient heating and heat preservation in sequence.

[0016] Fourthly, the present invention provides a method for preparing the polyimide film, comprising the following steps: Step 1: Coat the polyamic acid resin evenly onto the glass plate or glass substrate, and then place the whole thing in a vacuum drying oven at 80~100℃ for 5~9 minutes to pre-dry. Step 2: After pre-drying, the whole film is transferred to a nitrogen drying oven, heated to 400~500℃ in a gradient and held at that temperature for 20~40 minutes. After cooling to room temperature, the film is peeled off from the glass plate or glass substrate to obtain a polyimide film.

[0017] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention introduces a diamine monomer containing a hydrophobic group into the formulation. The hydrophobic group (sulfone group of 4,4'-diaminodiphenyl sulfone, ester group of p-aminobenzoic acid p-aminophenyl ester, carbonyl group of 2,6-diaminoanthraquinone, etc.) can improve the hydrophobicity of polyimide, reduce the migration of water in polyimide, thereby reducing the mobile charge source and improving short-time image retention.

[0018] (2) The present invention introduces a dianhydride monomer containing a rigid ester ring structure into the formulation. The ester ring is embedded in the main chain through rigid connection and is spatially restricted, so that the dipole cannot be effectively oriented, thus limiting the orientation polarization phenomenon. This can effectively reduce the polarizability of the molecular chain, thereby giving the material a lower and more stable intrinsic dielectric constant (Dk) and improving the short-time image retention problem in display devices.

[0019] (3) The present invention uses a rigid polymer backbone with no flexible branches or flexible side groups. After high-temperature curing, it forms a tight molecular chain arrangement, which effectively improves the thermal properties of polyimide. Detailed Implementation

[0020] Exemplary embodiments will now be described in detail. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples consistent with some aspects of the invention as detailed in the appended claims.

[0021] Example 1 In a first aspect, this embodiment provides a method for preparing polyamic acid resin, comprising the following steps: Take a 500ml four-necked flask, add 200mL of ultra-dry N-methyl-2-pyrrolidone under continuous nitrogen purging, add 0.09mol PDA and 0.01mol 4,4-DDS (the first type of diamine compound 4,4-DDS accounts for 10mol% of the total molar number of diamine monomers) in batches, and add a total of 100mol% of diamine monomers. Stir for 30min to dissolve, and then slowly add 0.1mol BPDA (the first type of dianhydride compound accounts for 0 mol% of the total molar number of dianhydride monomers) in batches, and add a total of 100mol% of dianhydride monomers. React at 40℃ for 8 hours. After filtration and degassing in the four-necked flask, polyamic acid resin is obtained.

[0022] The four-necked flask is equipped with a mechanical stirrer, a 90° gas elbow, a red oil thermometer, and a heating plate.

[0023] Secondly, this embodiment provides a method for preparing a polyimide film, comprising the following steps: The polyamic acid resin prepared in this embodiment was cast onto a glass plate and pre-dried in a vacuum drying oven at 80°C for 5 minutes. Then, the glass plate was transferred to a high-temperature nitrogen drying oven and heated to 450°C in a gradient of 100°C for 1 hour, 150°C for 1 hour, 250°C for 1 hour, and 350°C for 1 hour, and held at that temperature for 30 minutes. After cooling to room temperature, the polyimide film was peeled off.

[0024] Example 2 In a first aspect, this embodiment provides a method for preparing polyamic acid resin, comprising the following steps: Take a 500ml four-necked flask, and under continuous nitrogen purging, add 100ml of ultra-dry N-methyl-2-pyrrolidone and 100ml of N,N-dimethylformamide. Then, add 0.085mol PDA and 0.015mol APAB (the first type of diamine compound APAB accounts for 15 mol% of the total molar number of diamine monomers) in batches, for a total of 100mol% of diamine monomers. Stir for 30min to dissolve, and then slowly add 0.1mol BPDA (the first type of dianhydride compound accounts for 0 mol% of the total molar number of dianhydride monomers) in batches, for a total of 100mol% of dianhydride monomers. React at 60℃ for 10 hours. After filtration and degassing in the four-necked flask, polyamic acid resin is obtained.

[0025] Secondly, this embodiment provides a method for preparing a polyimide film, comprising the following steps: The polyamic acid resin prepared in this embodiment was uniformly coated onto a glass plate using a slit coating device. The plate was then placed in a vacuum drying oven and pre-dried at 80°C for 7 minutes. The glass plate was then transferred to a high-temperature nitrogen drying oven and heated to 500°C in a gradient of 100°C for 1 hour, 200°C for 1 hour, 300°C for 1 hour, and 400°C for 1 hour, and held at that temperature for 20 minutes. After cooling to room temperature, the polyimide film was peeled off.

[0026] Example 3 In a first aspect, this embodiment provides a method for preparing polyamic acid resin, comprising the following steps: Take a 500ml four-necked flask, add 200mL of ultra-dry N,N-dimethylformamide under continuous nitrogen purging, then add 0.08mol PDA and 0.02mol 2,6-DAAQ (the first type of diamine compound 2,6-DAAQ accounts for 20 mol% of the total molar number of diamine monomers) in batches, for a total of 100mol% of diamine monomers. Stir for 30min to dissolve, then slowly add 0.1mol BPDA (the first type of dianhydride compound accounts for 0 mol% of the total molar number of dianhydride monomers) in batches, for a total of 100mol% of dianhydride monomers. React at 20℃ for 15 hours. After filtration and degassing in the four-necked flask, polyamic acid resin is obtained.

[0027] Secondly, this embodiment provides a method for preparing a polyimide film, comprising the following steps: The polyamic acid resin prepared in this embodiment was cast onto a glass plate and pre-dried in a vacuum drying oven at 100°C for 6 minutes. Then, the glass plate was transferred to a high-temperature nitrogen drying oven and heated to 400°C in a gradient of 100°C for 1 hour, 150°C for 1 hour, 200°C for 1 hour, and 250°C for 1 hour, and held at that temperature for 40 minutes. After cooling to room temperature, the polyimide film was peeled off.

[0028] Example 4 In a first aspect, this embodiment provides a method for preparing polyamic acid resin, comprising the following steps: Take a 500ml four-necked flask, add 200mL of ultra-dry N,N-dimethylacetamide under continuous nitrogen purging, add 0.1mol PDA (0 mol% of the total molar percentage of the diamine monomer) in batches, for a total of 100mol% of the diamine monomer, stir for 30min to dissolve, then slowly add 0.09mol BPDA and 0.01mol HPMDA (10 mol% of the total molar percentage of the dianhydride monomer) in batches, for a total of 100mol% of the dianhydride monomer, react at 50℃ for 7 hours, filter and degas in the four-necked flask to obtain polyamic acid resin.

[0029] Secondly, this embodiment provides a method for preparing a polyimide film, comprising the following steps: The polyamic acid resin prepared in this embodiment was cast onto a glass substrate and pre-dried in a vacuum drying oven at 90°C for 8 minutes. Then, the glass substrate was transferred to a high-temperature nitrogen drying oven and heated to 460°C in a gradient of 100°C for 1 hour, 160°C for 1 hour, 260°C for 1 hour, and 360°C for 1 hour, and held at that temperature for 25 minutes. After cooling to room temperature, the polyimide film was peeled off.

[0030] Example 5 In a first aspect, this embodiment provides a method for preparing polyamic acid resin, comprising the following steps: Take a 500ml four-necked flask, add 200mL of ultra-dry dimethyl sulfoxide under continuous nitrogen purging, add 0.1mol PDA (0 mol% of the total molar percentage of the diamine monomer) in batches, for a total of 100mol% of the diamine monomer, stir for 30min to dissolve, then slowly add 0.08mol BPDA and 0.02mol CBDA (20 mol% of the total molar percentage of the dianhydride monomer) in batches, for a total of 100mol% of the dianhydride monomer, react at 50℃ for 7 hours, filter and degas in the four-necked flask to obtain polyamic acid resin.

[0031] Secondly, this embodiment provides a method for preparing a polyimide film, comprising the following steps: The polyamic acid resin prepared in this embodiment was cast onto a glass plate and pre-dried in a vacuum drying oven at 90°C for 8 minutes. Then, the glass plate was transferred to a high-temperature nitrogen drying oven and heated to 450°C in a gradient of 100°C for 1 hour, 150°C for 1 hour, 250°C for 1 hour, and 350°C for 1 hour, and held at that temperature for 28 minutes. After cooling to room temperature, the polyimide film was peeled off.

[0032] Example 6 In a first aspect, this embodiment provides a method for preparing polyamic acid resin, comprising the following steps: Take a 500ml four-necked flask, add 200mL of ultra-dry N-methyl-2-pyrrolidone under continuous nitrogen purging, then add 0.09mol PDA and 0.01mol 4,4-DDS (the first type of diamine compound accounts for 10 mol% of the total molar number of diamine monomers) in batches, for a total of 100mol% of diamine monomers. Stir for 30min to dissolve, then slowly add 0.09mol BPDA and 0.01mol HPMDA (the first type of dianhydride compound accounts for 10 mol% of the total molar number of dianhydride monomers) in batches, for a total of 100mol% of dianhydride monomers. React at 40℃ for 8 hours. After filtration and degassing in the four-necked flask, polyamic acid resin is obtained.

[0033] Secondly, this embodiment provides a method for preparing a polyimide film, comprising the following steps: The polyamic acid resin prepared in this embodiment was cast onto a glass plate and pre-dried in a vacuum drying oven at 80°C for 5 minutes. Then, the glass plate was transferred to a high-temperature nitrogen drying oven and heated to 450°C in a gradient of 100°C for 1 hour, 150°C for 1 hour, 250°C for 1 hour, and 350°C for 1 hour, and held at that temperature for 30 minutes. After cooling to room temperature, the polyimide film was peeled off.

[0034] Example 7 The difference between this embodiment and Example 1 is that 0.09 mol of PDA and 0.01 mol of ODA (the first type of diamine compound ODA accounts for 10 mol% of the total molar number of diamine monomers) are added, for a total of 100 mol% of diamine monomers; BPDA 0.1 mol (0 mol% of the total moles of dianhydride compounds), totaling 100 mol% of dianhydride monomers were added.

[0035] Example 8 The difference between this embodiment and Example 1 is that 0.085 mol of EDA and 0.015 mol of TFMB (TFMB, a type I diamine compound, accounts for 15 mol% of the total molar percentage of the diamine monomer) are added, for a total of 100 mol% of the diamine monomer. PMDA 0.1 mol (0 mol% of the total moles of dianhydride monomers, representing the first-order dianhydride compounds), was added in total, for a total of 100 mol% of dianhydride monomers.

[0036] Example 9 The difference between this embodiment and Example 1 is that 0.08 mol of HMD and 0.02 mol of MPD (MPD, a type I diamine compound, accounts for 20 mol% of the total molar percentage of the diamine monomer) are added, for a total of 100 mol% of the diamine monomer. BTDA 0.1 mol (0 mol% of the total moles of dianhydride monomers, representing the first-order dianhydride compound), was added in total, totaling 100 mol% of dianhydride monomers.

[0037] Example 10 The difference between this embodiment and Example 1 is that CHDA 0.09mol and MDA 0.01mol (the first type of diamine compound MDA accounts for 10 mol% of the total molar amount of diamine monomers) are added, for a total of 100mol% of diamine monomers; BPDA 0.1 mol (0 mol% of the total moles of dianhydride compounds), totaling 100 mol% of dianhydride monomers were added.

[0038] Example 11 The difference between this embodiment and Example 4 is that 0.1 mol of EDA (the first type of diamine compound EDA accounts for 0 mol% of the total moles of diamine monomers) is added, and a total of 100 mol% of diamine monomers are added; BPDA 0.09mol, BODA 0.01mol (the first type of dianhydride compound accounts for 10mol% of the total molar amount of dianhydride monomers), for a total of 100mol% of dianhydride monomers are added.

[0039] Example 12 The difference between this embodiment and Example 4 is that 0.1 mol of HMD (0 mol% of the total moles of the first type of diamine compound EDA) is added, and a total of 100 mol% of the diamine monomer is added. PMDA 0.08mol, CPDA 0.02mol (the first type of dianhydride compound accounts for 20mol% of the total molar amount of dianhydride monomers), for a total of 100mol% of dianhydride monomers added.

[0040] Example 13 The difference between this embodiment and Example 4 is that CHDA 0.1 mol (the first type of diamine compound EDA accounts for 0 mol% of the total molar number of diamine monomers), and a total of 100 mol% of diamine monomers are added; BTDA 0.08mol and NSDA 0.02mol (the first type of dianhydride compound accounts for 15mol% of the total molar amount of dianhydride monomers) were added, for a total of 100mol% of dianhydride monomers.

[0041] Comparative Example 1 The difference between this comparative example and Example 1 is that the polyamic acid resin is different, as detailed below: Take a 500ml four-necked flask, add 200mL of ultra-dry N-methyl-2-pyrrolidone to the flask, add 0.1mol PDA (0 mol% of the total molar percentage of the first type of diamine compound) in batches, and add a total of 100mol% of the diamine monomer. Stir for 30min to dissolve, and then slowly add 0.1mol BPDA (0 mol% of the total molar percentage of the first type of dianhydride compound) in batches. React at 40℃ for 8 hours. After filtration and degassing in the four-necked flask, polyamic acid resin is obtained.

[0042] Comparative Example 2 The difference between this comparative example and Example 1 is that the polyamic acid resin is different, as detailed below: Take a 500ml four-necked flask, add 200mL of ultra-dry N-methyl-2-pyrrolidone, add 0.075mol PDA and 0.025mol 4,4-DDS (the first type of diamine compound accounts for 25 mol% of the total molar number of diamine monomers) in batches, and add a total of 100mol% of diamine monomers. Stir for 30min to dissolve, and then slowly add 0.1mol BPDA (the first type of dianhydride compound accounts for 0 mol% of the total molar number of dianhydride monomers) in batches. React at 40℃ for 8 hours. After filtration and degassing in the four-necked flask, polyamic acid resin is obtained.

[0043] Comparative Example 3 The difference between this comparative example and Example 1 is that the polyamic acid resin is different, as detailed below: Take a 500ml four-necked flask, add 200mL of ultra-dry N-methyl-2-pyrrolidone to the flask, add 0.1mol PDA (0 mol% of the total molar percentage of the first-class diamine compound) in batches, and add a total of 100mol% of the diamine monomer. Stir for 30min to dissolve, and then slowly add 0.076mol BPDA and 0.024mol HPMDA (24 mol% of the total molar percentage of the first-class dianhydride compound) in batches. React at 40℃ for 8 hours. After filtration and degassing in the four-necked flask, polyamic acid resin is obtained.

[0044] To demonstrate the effectiveness of the present invention, the coefficient of thermal expansion, thermal decomposition temperature, and dielectric constant of all embodiments and comparative examples were tested with a polyimide film thickness of 10 μm. The test results are shown in Table 1.

[0045] The coefficient of thermal expansion was tested according to ASTM E831: the sample was a 10μm polyimide film with dimensions of 30mm×5mm, and the test direction was the longitudinal direction of the film; the test atmosphere was nitrogen (flow rate 50mL / min), the temperature range was 25~300℃, and the heating rate was 10℃ / min; a pusher-type thermal dilatometer was used to record the linear coefficient of thermal expansion (average CTE) in the range of 25~200℃.

[0046] The thermal decomposition temperature was tested according to ASTM D3850: the sample was vacuum dried at 80℃ for 2h (moisture content <0.5%), and the sample amount was 10±1mg; the test atmosphere was nitrogen (flow rate 60mL / min), the temperature range was 30~600℃, and the heating rate was 10℃ / min; a thermogravimetric analyzer (TGA) was used, and the thermal decomposition temperature (Td1%) was the temperature corresponding to a 1% mass loss.

[0047] Dielectric constant test setup: Using a precision impedance analyzer (4294A, Agilent Technologies): room temperature, Vdc=0V, Vac=100mV, test frequency range 40Hz~40MHz. Silver paint or gold plating was applied to both sides of the thermocured sample resin to form electrodes. The dielectric constant was calculated using the following formula: K 𝑟 = (C × d)⁄(C0 × S) where C, d, and S are the capacitance, thickness, and electrode area of ​​the material, respectively; e 0 represents the vacuum permittivity. e 0 = 8.854 × 10 -12 F / m.

[0048] Table 1 Within the range of no more than 20% of the total monomers, the introduction of diamine monomers containing hydrophobic groups or dianhydride monomers containing rigid ester ring structures can effectively reduce the dielectric constant of polyimide while maintaining good thermal stability, thereby helping to improve the short-term image retention problem of display devices.

[0049] Dielectric constant: The dielectric constants of all examples were below 3.0, while Comparative Example 1, without any added modified monomers (type I diamine compounds and type I dianhydrides), had a dielectric constant as high as 3.36. This demonstrates the effectiveness of introducing modified monomers in reducing the dielectric constant. Although Comparative Examples 2 and 3 (with modified monomer ratios exceeding 20 mol%) also had low dielectric constants (2.90, 2.82), their coefficients of thermal expansion deteriorated, proving that controlling the ratio within 0–20 mol% is key to balancing overall performance.

[0050] Thermal decomposition temperature: The thermal decomposition temperatures (552~578℃) of all embodiments did not show a significant decrease compared to the comparative examples, and some embodiments (such as Examples 3 and 5) were even slightly higher than that of Comparative Example 1. This indicates that at an addition ratio of 20 mol%, the introduction of the modified monomer did not affect the excellent thermal stability and strong compatibility of the material.

[0051] Coefficient of thermal expansion: Example 6, by introducing both epoxetine and hydrophobic diamine compounds, exhibits the lowest dielectric constant, a low coefficient of thermal expansion, and a high thermal decomposition temperature, demonstrating excellent overall performance. This proves the synergistic effect of "hydrophobic diamine + rigid epoxetine + rigid backbone," achieving a balanced optimization of multiple performance indicators.

[0052] Comparative Example 2 (when the 4,4-DDS ratio increased from 10 mol% to 25 mol%) showed a significant deterioration in the dimensional stability (CTE) of the polyimide film, with a 12.3% increase in the coefficient of thermal expansion. Simultaneously, the thermal stability (Td1%) also decreased. This indicates that the excessive introduction of hydrophobic diamine disrupts the rigidity and regularity of the polymer backbone, making the molecular chains more mobile upon heating, thus leading to a decrease in thermal stability.

[0053] In Comparative Example 3, after significantly increasing the HPMDA ratio from 10 mol% to 24%, the decrease in dielectric constant was very limited (only 0.02), and the thermal decomposition temperature of the material decreased, indicating that excessive introduction of rigid ester ring structures would lead to a deterioration in the thermal stability of the polymer.

[0054] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention.

[0055] It should be understood that the present invention is not limited to the content already described above, and various modifications and changes can be made without departing from its scope. The scope of the present invention is limited only by the appended claims.

Claims

1. A polyamic acid resin for improving image retention in display devices, characterized in that, It is obtained by polycondensation reaction of diamine monomers and dianhydride monomers in a polar aprotic solvent at a molar ratio of 1:(0.8~1.2); the diamine monomers and dianhydride monomers include first-class diamine compounds having hydrophobic groups and / or first-class dianhydride compounds having rigid ester ring structures, as well as second-class diamine compounds and second-class dianhydride compounds; wherein the first-class diamine compounds and the second-class diamine compounds are diamine monomers, and the first-class dianhydride compounds and the second-class dianhydride compounds are dianhydride monomers.

2. The polyamic acid resin according to claim 1, characterized in that, The first type of diamine compound accounts for 0-20 mol% of the total molar amount of the diamine monomer; the first type of dianhydride compound accounts for 0-20 mol% of the total molar amount of the dianhydride monomer; the first type of diamine compound and the first type of dianhydride compound are not both taken as 0.

3. The polyamic acid resin according to claim 1, characterized in that, The first type of diamine compound is selected from any one of 4,4'-diaminodiphenyl sulfone, p-aminophenyl benzoate, 2,6-diaminoanthraquinone, 4,4'-diaminodiphenyl ether, 2,2'-bis(trifluoromethyl)biphenyldiamine, m-phenylenediamine, and 4,4'-diaminodiphenylmethane.

4. The polyamic acid resin according to claim 1, characterized in that, The second type of diamine compound is selected from any one of p-phenylenediamine, ethylenediamine, hexamethylenediamine, and 1,4-cyclohexanediamine.

5. The polyamic acid resin according to claim 1, characterized in that, The first type of dianhydride compound is selected from any one of 1,2,4,5-cyclohexanetetracarboxylic dianhydride, 1,2,3,4-cyclobutanetetracarboxylic dianhydride, bicyclo[2.2.2]octane-2,3,5,6-tetracarboxylic dianhydride, cyclopentanetetracarboxylic dianhydride, norbornane-2-spiro-α-cyclopentanone-α'-spiro-2''-norbornanetetracarboxylic dianhydride, and 1,2,3,4-cyclopentanetetracarboxylic dianhydride.

6. The polyamic acid resin according to claim 1, characterized in that, The second class of dianhydride compounds is selected from any one of 3,3',4,4'-biphenyltetracarboxylic dianhydride, pyromellitic dianhydride, and 3,3',4,4'-benzophenonetetracarboxylic dianhydride.

7. The polyamic acid resin according to claim 1, characterized in that, The polar aprotic solvent is selected from one or more of N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide.

8. A method for preparing a polyamic acid resin, characterized in that, To prepare the polyamic acid resin according to any one of claims 1 to 7, a diamine monomer is added to a polar aprotic solvent in a certain proportion, stirred and dissolved, and then a dianhydride monomer is added. The mixture undergoes a polycondensation reaction at a temperature of 10 to 60°C for 10 to 15 hours. After filtration and degassing, the polyamic acid resin is obtained.

9. A polyimide film, characterized in that, Based on the polyamic acid resin according to any one of claims 1 to 7 or the polyamic acid resin prepared according to claim 8, the polyamic acid resin is uniformly coated onto a glass plate or glass substrate, and then dried, heated in a gradient, and kept at a constant temperature to obtain the product.

10. A method for preparing the polyimide film of claim 8, characterized in that, Includes the following steps: Step 1: Coat the polyamic acid resin evenly onto the glass plate or glass substrate, and then place the whole thing in a vacuum drying oven at 80~100℃ for 5~9 minutes to pre-dry. Step 2: After pre-drying, the whole film is transferred to a nitrogen drying oven, heated to 400~500℃ in a gradient and held at that temperature for 20~40 minutes. After cooling to room temperature, the film is peeled off from the glass plate or glass substrate to obtain a polyimide film.

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