High-temperature-resistant liquid crystal polymer substrate for ultra-thin flexible display

Abstract

This invention discloses a high-temperature resistant liquid crystal polymer substrate for ultra-thin flexible displays, belonging to the field of flexible display technology. The substrate of this invention comprises a modified liquid crystal polymer and functional additives dispersed therein. The modified liquid crystal polymer is polymerized from a monomer composition, specifically consisting of 38-42 parts of p-hydroxybenzoic acid, 28-30 parts of 4,4'-biphenylhydrazine, 5.6-6.0 parts of terephthalic acid, 4.4-5.0 parts of 2,6-naphthalenedicarboxylic acid, 2.7-3.3 parts of isophthalic acid, and 2,2-bis(3,5-difluoro-4-hydroxybenzene). The composition comprises 9-11 parts of hexafluoropropane, 4.5-5.5 parts of N,N'-dihydroxypyromellitic acid diamine, 9-11 parts of 9,9-bis[4-(4-methoxycarbonylphenoxy)phenyl]fluorene, and 5.5-6.5 parts of 1,4-cyclohexanediethanol; the functional additives include azobenzene derivatives, thermal acid generators, and hydrogen bond enhancers; the present invention overcomes the technical bottleneck of existing materials in achieving a balance between heat resistance, transparency, dimensional stability, and flexibility through the synergistic effect of specific monomer combinations, functional additives, and optimized processes.

Description

Technical Field

[0001] This invention relates to the field of flexible display technology, and in particular to high-temperature resistant liquid crystal polymer substrates for ultra-thin flexible displays. Background Technology

[0002] Ultra-thin flexible display technology, with its superior characteristics such as bendability, foldability, light weight, and small size, is leading the next wave of change in consumer electronics products and has become a core technology for high-end display products such as foldable phones and rollable TVs. As the supporting carrier of the entire display device, the flexible substrate must not only have excellent transparency, flexibility, and dimensional stability, but also be able to withstand the test of multiple high-temperature processes during the manufacturing of thin-film transistor arrays.

[0003] Due to its excellent heat resistance and mechanical properties, polyimide is the preferred material for flexible display substrates. Through molecular structure design, transparent polyimide has solved the problems of its dark color and poor light transmittance to some extent. However, achieving a balance between high heat resistance and high optical performance remains a challenge for this type of material. On the one hand, the intrinsic structure of aromatic polyimide makes it prone to forming charge-transfer complexes, resulting in a generally yellowish background color in the film even after optimization, affecting the display color accuracy. On the other hand, the introduction of non-conjugated structures such as alicyclic compounds to improve transparency often comes at the cost of heat resistance and mechanical strength, leading to a decrease in glass transition temperature and an increase in the coefficient of thermal expansion, making it prone to deformation and warping in subsequent high-temperature processes.

[0004] To overcome the inherent limitations of polyimide materials, other flexible substrates, such as polyethylene terephthalate (PET) and polyethylene naphthalate (PET), have been explored in this field. While these materials offer high transparency, their glass transition temperatures are too low to withstand temperatures exceeding 250°C, significantly limiting their applications.

[0005] Liquid crystal polymers are a class of high-performance polymers with highly ordered molecular chains. They inherently possess excellent high-temperature resistance, a low coefficient of thermal expansion, and superior dielectric properties, making them highly promising alternative materials. However, conventional liquid crystal polymers are typically opaque or milky white due to strong crystallization and scattering, making it difficult to directly meet the stringent high transparency requirements of display substrates. Existing technologies can control their properties through copolymerization and nanocompositing, but further research is needed on how to achieve high transparency, controllable flexibility, and good interfacial bonding with other functional layers while retaining their advantages of high temperature resistance and low coefficient of thermal expansion.

[0006] It is evident that existing flexible substrate materials cannot simultaneously meet the requirements of ultra-thin flexible displays for high heat resistance, high transparency, low coefficient of thermal expansion, and bendability. Therefore, there is an urgent need in this field to develop a novel substrate material system that can overcome the technical bottlenecks of existing materials and provide a high-performance carrier and platform for next-generation ultra-thin flexible displays. Summary of the Invention

[0007] The purpose of this invention is to provide a high-temperature resistant liquid crystal polymer substrate for ultra-thin flexible displays, in order to solve the technical problem that existing flexible substrate materials cannot simultaneously meet the requirements of high heat resistance, high transparency, low coefficient of thermal expansion and excellent flexibility, and to overcome the technical bottlenecks of polyimide materials in balancing heat resistance and transparency, as well as the inherent opacity of liquid crystal polymers.

[0008] To achieve the above objectives, the present invention provides the following solution:

[0009] The key to the high-temperature resistant liquid crystal polymer substrate for ultra-thin flexible displays is that the substrate contains a modified liquid crystal polymer and functional additives dispersed therein.

[0010] The modified liquid crystal polymer is polymerized from a monomer composition, which comprises 38-42 parts of p-hydroxybenzoic acid, 28-30 parts of 4,4'-biphenyl, 5.6-6.0 parts of terephthalic acid, 4.4-5.0 parts of 2,6-naphthalenedicarboxylic acid, 2.7-3.3 parts of isophthalic acid, 9-11 parts of 2,2-bis(3,5-difluoro-4-hydroxyphenyl)hexafluoropropane, 4.5-5.5 parts of N,N'-dihydroxypyromellitic acid diamine, 9-11 parts of 9,9-bis[4-(4-methoxycarbonylphenoxy)phenyl]fluorene, and 5.5-6.5 parts of 1,4-cyclohexanediethanol.

[0011] The aforementioned functional additives include 0.9 to 1.8 parts of azobenzene derivatives, 1.5 to 2.4 parts of thermal acid generators, and 2.1 to 4.2 parts of hydrogen bond enhancers.

[0012] Specifically, the amount of isophthalic acid used is 27% to 30% of the sum of the mass fractions of terephthalic acid and 2,6-naphthalenedicarboxylic acid.

[0013] Specifically, the aforementioned azobenzene derivatives are selected from any one of 4-dimethylaminoazobenzene, 1-(2,4-dinitrophenyl)azo-2-naphthol, or 1-[(2,4-dimethylphenyl)azo]-2-naphthol; the aforementioned thermal acid generating agent is selected from any one of diphenyliodonium hexafluorophosphate, 4-methylphenyldiazotetrafluoroborate, or p-toluenesulfonic acid pyridine salt; and the aforementioned hydrogen bond reinforcing agent is selected from any one of polyvinylpyrrolidone, polyacrylamide, or aqueous polyurethane dispersion.

[0014] Furthermore, the surface of the substrate is also provided with a functional coating, which is formed by curing a coating composition of fluorinated polyurethane acrylate oligomer, modified nano-SiO2, photoinitiator and silane coupling agent, wherein the mass ratio of each component is 25-28:3-4:1:1.

[0015] Furthermore, the above-mentioned substrate preparation steps include S1, preparation and pretreatment of monomer composition raw materials, S2, prepolymerization reaction, S3, vacuum polycondensation and stabilization treatment to prepare modified LCP resin, S4, blending and molding of functional additives to prepare precursor film, S5, in-situ curing, orientation and annealing, and S6, coating of surface functional coating.

[0016] Furthermore, the prepolymerization reaction in step S2 specifically involves: in the presence of a compatibilizer, a composite antioxidant, and an acetylation system, the monomer composition is subjected to acetylation prepolymerization at 150°C–165°C for 60–90 min, followed by a stepwise temperature increase and further prepolymerization; the compatibilizer is a maleic anhydride-grafted hydrogenated styrene-butadiene block copolymer, added in an amount of 0.9–1.5 parts; the composite antioxidant is composed of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and tris(2,4-di-tert-butyl... The acetylation system is composed of trifluoroacetic anhydride, 0.02-0.05 parts potassium acetate, and 0.01-0.04 parts tetrabutyl titanate. The amount of trifluoroacetic anhydride added is 1.05-1.10 times the total mass of p-hydroxybenzoic acid, 4,4'-biphenyl, 2,2-bis(3,5-difluoro-4-hydroxyphenyl)hexafluoropropane, N,N'-dihydroxypyromellitic acid diamine, and 1,4-cyclohexanediethanol.

[0017] Furthermore, the aforementioned stepwise heating and prepolymerization reaction specifically involves raising the temperature at 1℃ / min to 180℃~190℃ and reacting for 50min~60min; then raising the temperature at 1℃ / min to 210℃~220℃ and reacting for 90min~120min.

[0018] Specifically, the vacuum polycondensation operation in step S3 is as follows: the reaction system is heated to 285℃ to 295℃ at a stirring speed of 60r / min to 80r / min at a rate of 0.5℃ / min. When the temperature reaches 240℃, a vacuum is drawn to steadily reduce the system pressure to below 80Pa. The system is then maintained at 285℃ to 295℃ under vacuum for 90min to 150min. The antioxidant stabilization operation is as follows: 10min to 15min before the end of the polycondensation reaction, 0.2 to 0.6 parts of liquid composite antioxidant are injected. The reaction continues for another 10min to 15min before the material is discharged to obtain the modified LCP resin.

[0019] Specifically, step S4 includes S41, melt blending, and S42, molding and quenching; the melt blending specifically involves melting the modified LCP resin using a twin-screw extruder at 265℃~280℃, adding functional additives and 0.4 to 0.7 parts of compatibilizer in the melting section; the molding and quenching specifically involves extruding the melt mixture at 275℃±3℃, and rapidly quenching it using a cooling roller at 30℃~40℃ to obtain a precursor film with a thickness of 25μm~50μm; the compatibilizer is a maleic anhydride-grafted hydrogenated styrene-butadiene block copolymer.

[0020] Preferably, step S5 specifically involves: passing the precursor film under a constant tension of 5 N / m to 15 N / m through a multi-temperature zone thermosetting oven, with the temperature zones set as follows: 160℃ to 165℃ for 3 min to 8 min, 190℃ to 195℃ for 100 min to 110 min, and 220℃ to 225℃ for 12 min to 18 min; and then performing an annealing treatment at 225℃ to 235℃ for 28 min to 35 min.

[0021] The present invention discloses the following technical effects:

[0022] The high-temperature resistant liquid crystal polymer substrate for ultra-thin flexible displays provided by this invention overcomes the technical bottleneck of existing materials in achieving a balance between heat resistance, transparency, dimensional stability, and flexibility through the synergistic effect of specific monomer combinations, functional additives, and optimized processes. Specific technical effects include:

[0023] First, the substrate of this invention achieves a balance between high heat resistance, low coefficient of thermal expansion, and excellent flexibility. This is because the specific monomer composition of this invention, in which rigid monomers such as p-hydroxybenzoic acid, 4,4'-biphenyl, and naphthalenedicarboxylic acid, and flexible monomers such as isophthalic acid and 1,4-cyclohexanediethanol, constitute the basic framework of the molecular skeleton, ensuring the material's inherent high glass transition temperature and low coefficient of thermal expansion. Simultaneously, the introduction of flexible monomers effectively disrupts the excessively rigid arrangement of the molecular chains, endowing the substrate with ultra-high bending resistance, resulting in a bending resistance of >100,000 cycles, overcoming the problem of high brittleness in traditional high heat-resistant materials.

[0024] Secondly, the substrate of this invention possesses optical properties of high transparency and low chromaticity. The key components are the fluorinated monomer (2,2-bis(3,5-difluoro-4-hydroxyphenyl)hexafluoropropane) and the fluorene monomer (9,9-bis[4-(4-methoxycarbonylphenoxy)phenyl]fluorene). The fluorinated monomer effectively reduces light absorption and scattering by lowering the polarizability of the molecular chain and the formation of charge-transfer complexes; while the large-volume fluorene monomer increases the free volume of the molecular chain, further suppressing crystallization and the CTC effect. Thus, the substrate achieves high transmittance and a low yellowness index while maintaining high heat resistance.

[0025] Third, the substrate of this invention incorporates intelligent photothermal response characteristics, enhancing its mechanical reliability. This is thanks to the synergistic effect of functional additives. Azobenzene derivatives undergo cis-trans isomerization under ultraviolet light, resulting in a significant change in the macroscopic color of the substrate, which recovers rapidly under heat, achieving intelligent response. Hydrogen bond enhancers construct a dynamic physical cross-linking network in the polymer system, significantly improving the material's toughness and flexural strength. The thermal acid generator promotes specific reactions during processing, optimizing the network structure. The synergistic effect of these three components endows the substrate with additional functionality and mechanical reinforcement beyond its basic properties.

[0026] Fourth, the substrate of this invention exhibits excellent high-frequency electrical performance and overall application reliability. The introduction of fluorine-containing monomers not only benefits optical performance but also effectively reduces the dielectric constant and dielectric loss of the material, making it particularly suitable for high-frequency electronic circuits. The optimized stepped temperature polymerization process of this invention ensures the uniformity and integrity of the molecular structure, which is the basis for achieving various excellent performance characteristics and passing harsh application tests such as high-temperature storage and temperature and humidity cycling, proving that it fully meets the comprehensive requirements of next-generation ultra-thin flexible displays for substrate materials.

[0027] In summary, this invention integrates superior properties such as high heat resistance, low expansion, ultra-flexibility, high transparency, intelligent response, and low dielectric loss, providing a comprehensive substrate solution that can replace traditional polyimide and conventional liquid crystal polymers. It effectively solves the core problems in the prior art, such as difficulty in balancing performance, intrinsic opacity, and poor process adaptability. Detailed Implementation

[0028] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0029] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0030] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0031] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0032] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0033] Example 1

[0034] In this embodiment, the preparation of the liquid crystal polymer substrate of the present invention includes the following steps:

[0035] S1. Preparation and pretreatment of raw materials for monomer composition:

[0036] The monomer composition was vacuum dried at 80°C for 12 hours, and the moisture content was 48 ppm.

[0037] The monomer composition used in this embodiment includes 40 parts of p-hydroxybenzoic acid, 29 parts of 4,4'-biphenyl, 5.8 parts of terephthalic acid, 4.8 parts of 2,6-naphthalenedicarboxylic acid, 3.0 parts of isophthalic acid, 10 parts of 2,2-bis(3,5-difluoro-4-hydroxyphenyl)hexafluoropropane, 5.0 parts of N,N'-dihydroxypyromellitic acid diamine, 10 parts of 9,9-bis[4-(4-methoxycarbonylphenoxy)phenyl]fluorene, and 6.0 parts of 1,4-cyclohexanediethanol; wherein, in this embodiment, the amount of isophthalic acid used is 28.3% of the sum of the mass parts of terephthalic acid and 2,6-naphthalenedicarboxylic acid.

[0038] The functional additives were vacuum dried at 50°C for 6 hours.

[0039] The functional additives in this embodiment include 1.5 parts of an azobenzene derivative, 2.0 parts of a thermal acid generator, and 3.5 parts of a hydrogen bond enhancer; wherein, the azobenzene derivative is 4-dimethylaminoazobenzene; the thermal acid generator is diphenyliodonium hexafluorophosphate; and the hydrogen bond enhancer is polyvinylpyrrolidone.

[0040] S2, Prepolymerization reaction:

[0041] S21. Feeding and Initial Esterification:

[0042] The dried monomer composition was put into a reaction vessel, and 1.2 parts of maleic anhydride-grafted hydrogenated styrene-butadiene block copolymer were added.

[0043] S22, Mixed and Preliminary Antioxidant:

[0044] Under nitrogen protection and stirring speed of 90 r / min, the temperature was increased to 135℃ at a rate of 1.5℃ / min and stirred for 25 min.

[0045] When the reaction system reaches 98°C, inject 0.4 parts of liquid composite antioxidant;

[0046] In this embodiment, the liquid composite antioxidant is composed of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid] (antioxidant 1010) and tris(2,4-di-tert-butylphenyl) phosphite (antioxidant 168) in a mass ratio of 1.8:1.

[0047] S23, Acetylation reaction:

[0048] Continue heating to 160℃ at a rate of 1.5℃ / min, and add 97.2 parts of trifluoroacetic anhydride, the amount of which is 1.08 times the total mass of p-hydroxybenzoic acid, 4,4'-biphenyl, 2,2-bis(3,5-difluoro-4-hydroxyphenyl)hexafluoropropane, N,N'-dihydroxypyromellitic acid diamine and 1,4-cyclohexanediethanol.

[0049] Add 0.035 parts potassium acetate and 0.025 parts tetrabutyl titanate, maintain the temperature at 160℃, and carry out the acetylation reaction for 80 min.

[0050] S24, Stepped heating prepolymerization:

[0051] The temperature was increased to 185℃ at a rate of 1℃ / min and reacted for 55 min; then the temperature was increased to 215℃ at a rate of 1℃ / min and reacted for 110 min.

[0052] S3. Preparation of modified LCP resin by vacuum polycondensation and stabilization treatment:

[0053] S31. Vacuum extraction and polycondensation:

[0054] The reaction system was heated to 290℃ at a stirring speed of 70 r / min and a rate of 0.5℃ / min.

[0055] When the temperature reaches 240℃, vacuuming begins to reduce the system pressure to 75Pa.

[0056] The polycondensation reaction was carried out for 120 minutes under a high vacuum and temperature of 290°C.

[0057] S32, Antioxidant Stabilization:

[0058] 12 minutes before the end of the polycondensation reaction, 0.4 parts of liquid composite antioxidant were injected; after continuing the reaction for another 12 minutes, the material was discharged to obtain the modified LCP resin.

[0059] S4. Preparation of precursor films by blending and molding with functional additives:

[0060] S41, Melt blending:

[0061] The modified LCP resin was melt-blended using a twin-screw extruder to obtain a melt mixture, wherein the screw temperature was controlled at 265℃~280℃.

[0062] The conveying section is 265°C, the melting section is 272°C, the mixing section is 280°C, and the homogenization section is 272°C.

[0063] A dried functional additive and 0.6 parts of maleic anhydride-grafted hydrogenated styrene-butadiene block copolymer were added to the melting section to obtain a melt mixture.

[0064] S42. Forming and Quenching:

[0065] The molten mixture is extruded through a T-die at a temperature of 275℃±3℃.

[0066] Rapid quenching was performed using a high-gloss cooling roller at 35°C to obtain a precursor film with a thickness of 35 μm.

[0067] S5, In-situ Curing, Orientation and Annealing:

[0068] The obtained precursor film was passed through a multi-temperature zone thermosetting oven under a constant tension of 10 N / m.

[0069] The specific temperature zones for the multi-zone thermosetting oven are: 162℃, maintained for 5 minutes; 192℃, maintained for 105 minutes; 222℃, maintained for 15 minutes.

[0070] The thin film was annealed at 230°C for 30 minutes to obtain an uncoated LCP substrate.

[0071] S6. Application of surface functional coatings:

[0072] Using a microgravure coating method, the coating solution was applied to the surface of the uncoated LCP substrate, and the wet film thickness was controlled to be 4μm. After preheating at 82℃ for 30s, it was cured by a UV curing device. After winding, the finished LCP substrate was obtained, which was denoted as Sample 1.

[0073] The coating solution used in this embodiment is composed of fluorinated polyurethane acrylate oligomers, modified nano-SiO2, photoinitiator, and silane coupling agent in a mass ratio of 26:3.5:1:1. The fluorinated polyurethane acrylate oligomers are fluorinated polyurethane acrylate resins; the photoinitiator is 2,4,6-trimethylbenzoyl-diphenylphosphine oxide; the silane coupling agent is 3-aminopropyltriethoxysilane; and the modified nano-SiO2 is silica nanoparticles modified with the silane coupling agent.

[0074] Example 2

[0075] In this embodiment, the preparation of the liquid crystal polymer substrate of the present invention includes the following steps:

[0076] S1. Preparation and pretreatment of raw materials for monomer composition:

[0077] The monomer composition was vacuum dried at 75°C for 14 hours, with a moisture content of 50 ppm.

[0078] The monomer composition used in this embodiment includes 38 parts of p-hydroxybenzoic acid, 30 parts of 4,4'-biphenyl, 6.0 parts of terephthalic acid, 5.0 parts of 2,6-naphthalenedicarboxylic acid, 3.3 parts of isophthalic acid, 10 parts of 2,2-bis(3,5-difluoro-4-hydroxyphenyl)hexafluoropropane, 5.0 parts of N,N'-dihydroxypyromellitic acid diamine, 10 parts of 9,9-bis[4-(4-methoxycarbonylphenoxy)phenyl]fluorene, and 6.0 parts of 1,4-cyclohexanediethanol; wherein, in this embodiment, the amount of isophthalic acid used is 30% of the sum of the mass parts of terephthalic acid and 2,6-naphthalenedicarboxylic acid.

[0079] The functional additives were vacuum dried at 55°C for 5 hours.

[0080] The functional additives in this embodiment include 0.9 parts of azobenzene derivatives, 2.4 parts of a thermal acid generator, and 4.2 parts of a hydrogen bond enhancer; wherein, the azobenzene derivative is 1-(2,4-dinitrophenyl)azo-2-naphthol; the thermal acid generator is 4-methylphenyldiazotetrafluoroborate; and the hydrogen bond enhancer is polyacrylamide.

[0081] S2, Prepolymerization reaction:

[0082] S21. Feeding and Initial Esterification:

[0083] The dried monomer composition was put into a reaction vessel, and 1.5 parts of maleic anhydride-grafted hydrogenated styrene-butadiene block copolymer were added.

[0084] S22, Mixed and Preliminary Antioxidant:

[0085] Under nitrogen protection and stirring speed of 80 r / min, the temperature was increased to 140℃ at a rate of 1.5℃ / min and stirred for 30 min.

[0086] When the reaction system reaches 98°C, inject 0.6 parts of liquid composite antioxidant;

[0087] In this embodiment, the liquid composite antioxidant is composed of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid] (antioxidant 1010) and tris(2,4-di-tert-butylphenyl) phosphite (antioxidant 168) in a mass ratio of 1.5:1.

[0088] S23, Acetylation reaction:

[0089] Continue heating to 165℃ at a rate of 1.5℃ / min, and add 93.45 parts of trifluoroacetic anhydride, the amount of which is 1.05 times the total mass of p-hydroxybenzoic acid, 4,4'-biphenyl, 2,2-bis(3,5-difluoro-4-hydroxyphenyl)hexafluoropropane, N,N'-dihydroxypyromellitic acid diamine and 1,4-cyclohexanediethanol.

[0090] Add 0.02 parts potassium acetate and 0.04 parts tetrabutyl titanate, maintain the temperature at 165℃, and carry out the acetylation reaction for 60 min.

[0091] S24, Stepped heating prepolymerization:

[0092] The temperature was increased to 190℃ at a rate of 1℃ / min and reacted for 50 min; then the temperature was increased to 220℃ at a rate of 1℃ / min and reacted for 90 min.

[0093] S3. Preparation of modified LCP resin by vacuum polycondensation and stabilization treatment:

[0094] S31. Vacuum extraction and polycondensation:

[0095] The reaction system was heated to 295℃ at a stirring speed of 80 r / min and a rate of 0.5℃ / min.

[0096] When the temperature reaches 240℃, a vacuum is drawn to steadily reduce the system pressure to 70Pa.

[0097] The polycondensation reaction was carried out at 295°C under high vacuum for 90 minutes.

[0098] S32, Antioxidant Stabilization:

[0099] Ten minutes before the end of the polycondensation reaction, 0.2 parts of liquid composite antioxidant were injected; after continuing the reaction for another 10 minutes, the material was discharged to obtain the modified LCP resin.

[0100] S4. Preparation of precursor films by blending and molding with functional additives:

[0101] S41, Melt blending:

[0102] The modified LCP resin was melt-blended using a twin-screw extruder to obtain a melt mixture, wherein the screw temperature was controlled at 265℃~280℃.

[0103] The conveying section is 265°C, the melting section is 270°C, the mixing section is 280°C, and the homogenization section is 275°C.

[0104] A dried functional additive and 0.4 parts of maleic anhydride-grafted hydrogenated styrene-butadiene block copolymer were added to the melting section to obtain a melt mixture.

[0105] S42. Forming and Quenching:

[0106] The molten mixture is extruded through a T-die at a temperature of 275℃±3℃.

[0107] Rapid quenching was performed using a high-gloss cooling roller at 40°C to obtain a precursor film with a thickness of 50 μm.

[0108] S5, In-situ Curing, Orientation and Annealing:

[0109] The obtained precursor film was passed through a multi-temperature zone thermosetting oven under a constant tension of 15 N / m.

[0110] The specific temperature zones for the multi-zone thermosetting oven are: 165℃, held for 3 minutes; 195℃, held for 100 minutes; 225℃, held for 12 minutes.

[0111] The thin film was annealed at 235°C for 35 minutes to obtain an uncoated LCP substrate.

[0112] S6. Application of surface functional coatings:

[0113] Using a microgravure coating method, the coating solution was applied to the surface of the uncoated LCP substrate, and the wet film thickness was controlled to be 3μm. After preheating at 80℃ for 35s, it was cured by a UV curing device. After winding, the finished LCP substrate was obtained, which was designated as sample 2.

[0114] The coating solution used in this embodiment is composed of fluorinated polyurethane acrylate oligomer, modified nano-SiO2, photoinitiator, and silane coupling agent in a mass ratio of 25:4:1:1. The fluorinated polyurethane acrylate oligomer is a fluorinated polyurethane acrylate resin; the photoinitiator is phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide; the silane coupling agent is 3-(2,3-epoxypropoxy)propyltrimethoxysilane; and the modified nano-SiO2 is silica nanoparticles modified with the silane coupling agent.

[0115] Example 3

[0116] In this embodiment, the preparation of the liquid crystal polymer substrate of the present invention includes the following steps:

[0117] S1. Preparation and pretreatment of raw materials for monomer composition:

[0118] The monomer composition was vacuum dried at 85°C for 10 hours, and the moisture content was 45 ppm.

[0119] The monomer composition used in this embodiment includes 42 parts of p-hydroxybenzoic acid, 28 parts of 4,4'-biphenyl, 5.6 parts of terephthalic acid, 4.4 parts of 2,6-naphthalenedicarboxylic acid, 2.7 parts of isophthalic acid, 11 parts of 2,2-bis(3,5-difluoro-4-hydroxyphenyl)hexafluoropropane, 4.5 parts of N,N'-dihydroxypyromellitic acid diamine, 11 parts of 9,9-bis[4-(4-methoxycarbonylphenoxy)phenyl]fluorene, and 5.5 parts of 1,4-cyclohexanediethanol; wherein, in this embodiment, the amount of isophthalic acid used is 27% of the sum of the mass parts of terephthalic acid and 2,6-naphthalenedicarboxylic acid.

[0120] The functional additives were vacuum dried at 45°C for 7 hours.

[0121] The functional additives in this embodiment include 1.8 parts of azobenzene derivatives, 1.5 parts of a thermal acid generator, and 2.1 parts of a hydrogen bond enhancer; wherein, the azobenzene derivative is 1-[(2,4-dimethylphenyl)azo]-2-naphthol; the thermal acid generator is pyridine salt of p-toluenesulfonate; and the hydrogen bond enhancer is an aqueous polyurethane dispersion.

[0122] S2, Prepolymerization reaction:

[0123] S21. Feeding and Initial Esterification:

[0124] The dried monomer composition was put into a reaction vessel, and 0.9 parts of maleic anhydride-grafted hydrogenated styrene-butadiene block copolymer were added as a compatibilizer.

[0125] S22, Mixed and Preliminary Antioxidant:

[0126] Under nitrogen protection and stirring speed of 100 r / min, the temperature was increased to 130℃ at a rate of 1.5℃ / min and stirred for 20 min.

[0127] When the reaction system reaches 98°C, inject 0.3 parts of liquid composite antioxidant;

[0128] In this embodiment, the liquid composite antioxidant is composed of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid] and tris(2,4-di-tert-butylphenyl) phosphite in a mass ratio of 2:1.

[0129] S23, Acetylation reaction:

[0130] Continue heating to 150℃ at a rate of 1.5℃ / min, and add 100.1 parts of trifluoroacetic anhydride, the amount of which is 1.10 times the total mass of p-hydroxybenzoic acid, 4,4'-biphenyl, 2,2-bis(3,5-difluoro-4-hydroxyphenyl)hexafluoropropane, N,N'-dihydroxypyromellitic acid diamine and 1,4-cyclohexanediethanol.

[0131] Add 0.05 parts potassium acetate and 0.01 parts tetrabutyl titanate, maintain the temperature at 150℃, and carry out the acetylation reaction for 90 min.

[0132] S24, Stepped heating prepolymerization:

[0133] The temperature was increased to 180℃ at a rate of 1℃ / min and reacted for 60 min; then the temperature was increased to 210℃ at a rate of 1℃ / min and reacted for 120 min.

[0134] S3. Preparation of modified LCP resin by vacuum polycondensation and stabilization treatment:

[0135] S31. Vacuum extraction and polycondensation:

[0136] The reaction system was heated to 285℃ at a stirring speed of 60 r / min and a rate of 0.5℃ / min.

[0137] When the temperature reaches 240℃, a vacuum is drawn to steadily reduce the system pressure to 80Pa.

[0138] The polycondensation reaction was carried out for 150 minutes under a high vacuum and temperature of 285°C.

[0139] S32, Antioxidant Stabilization:

[0140] 15 minutes before the end of the polycondensation reaction, 0.6 parts of liquid composite antioxidant were injected; after continuing the reaction for 16 minutes, the material was discharged to obtain the modified LCP resin.

[0141] S4. Preparation of precursor films by blending and molding with functional additives:

[0142] S41, Melt blending:

[0143] The modified LCP resin was melt-blended using a twin-screw extruder to obtain a melt mixture, wherein the screw temperature was controlled at 265℃~280℃.

[0144] The conveying section is 265°C, the melting section is 275°C, the mixing section is 280°C, and the homogenization section is 270°C.

[0145] A dried functional additive and 0.7 parts of maleic anhydride-grafted hydrogenated styrene-butadiene block copolymer were added to the melting section to obtain a melt mixture.

[0146] S42. Forming and Quenching:

[0147] The molten mixture is extruded through a T-die at a temperature of 275℃±3℃.

[0148] Rapid quenching was performed using a high-gloss cooling roller at 30°C to obtain a precursor film with a thickness of 25 μm.

[0149] S5, In-situ Curing, Orientation and Annealing:

[0150] The obtained precursor film was passed through a multi-temperature zone thermosetting oven under a constant tension of 5 N / m.

[0151] The specific temperature zones for the multi-zone thermosetting oven are: 160℃, held for 8 minutes; 190℃, held for 110 minutes; 220℃, held for 18 minutes.

[0152] The film was annealed at 225°C for 28 minutes to obtain an uncoated LCP substrate.

[0153] S6. Application of surface functional coatings:

[0154] Using a microgravure coating method, the coating solution was applied to the surface of the uncoated LCP substrate, and the wet film thickness was controlled to be 3μm. After preheating at 80℃ for 35s, it was cured by a UV curing device. After winding, the finished LCP substrate was obtained, which was designated as sample 3.

[0155] The coating solution used in this embodiment is composed of fluorinated polyurethane acrylate oligomer, modified nano-SiO2, photoinitiator and silane coupling agent in a mass ratio of 28:3:1:1; wherein, the fluorinated polyurethane acrylate oligomer is fluorinated polyurethane acrylate resin; the photoinitiator is 1-hydroxycyclohexylphenyl ketone; the silane coupling agent is 3-(methacryloyloxy)propyltrimethoxysilane; and the modified nano-SiO2 is silica nanoparticles modified with silane coupling agent.

[0156] Comparative Example 1

[0157] This comparative example provides a method for preparing a liquid crystal polymer substrate. The specific implementation method is the same as in Example 1, except that isophthalic acid and 1,4-cyclohexanediethanol are omitted.

[0158] In step S1, the monomer composition used includes 40 parts of p-hydroxybenzoic acid, 29 parts of 4,4'-biphenyl, 5.8 parts of terephthalic acid, 4.8 parts of 2,6-naphthalenedicarboxylic acid, 10 parts of 2,2-bis(3,5-difluoro-4-hydroxyphenyl)hexafluoropropane, 5.0 parts of N,N'-dihydroxypyromellitic acid diamine, and 10 parts of 9,9-bis[4-(4-methoxycarbonylphenoxy)phenyl]fluorene;

[0159] Meanwhile, the amount of trifluoroacetic anhydride used in step S23 is adjusted to 1.08 times that of p-hydroxybenzoic acid (40 parts), 4,4'-biphenyl (29 parts), N,N'-dihydroxypyromellitic acid diamine (5 parts) and 1,4-cyclohexanediethanol (6 parts), i.e., 86.4 parts.

[0160] The other steps are the same as in Example 1, and control sample 1 is prepared.

[0161] Comparative Example 2

[0162] This comparative example provides a method for preparing a liquid crystal polymer substrate. The specific implementation method is the same as in Example 1, except that the fluorine-containing monomer and the fluorene monomer are omitted, i.e.:

[0163] In step S1, the monomer composition used includes 40 parts of p-hydroxybenzoic acid, 29 parts of 4,4'-biphenyl, 5.8 parts of terephthalic acid, 4.8 parts of 2,6-naphthalenedicarboxylic acid, 3.0 parts of isophthalic acid, 5.0 parts of N,N'-dihydroxypyromellitic acid diamine, and 6.0 parts of 1,4-cyclohexanediethanol.

[0164] Meanwhile, the amount of trifluoroacetic anhydride used in step S23 is adjusted to 1.08 times that of p-hydroxybenzoic acid, 4,4'-biphenyl, N,N'-dihydroxypyromellitic acid diamine and 1,4-cyclohexanediethanol, i.e. 86.4 parts.

[0165] The other steps are the same as in Example 1, and control sample 2 is prepared.

[0166] Comparative Example 3

[0167] This comparative example provides a method for preparing a liquid crystal polymer substrate, with the specific implementation method being the same as in Example 1, except that all functional additives are omitted, i.e.:

[0168] In step S1, the functional additives are not dried;

[0169] In the melt blending process of step S4, no functional additives are added, that is, no azobenzene derivatives, hot acid generators and hydrogen bond enhancers are added.

[0170] The other steps are the same as in Example 1, and control standard 3 is prepared.

[0171] Comparative Example 4

[0172] This comparative example provides a method for preparing a liquid crystal polymer substrate. The specific implementation method is the same as in Example 1, except that the prepolymerization reaction process is changed, namely:

[0173] The stepwise heating prepolymerization in step S24 is cancelled; after the acetylation reaction in step S23 is completed, the reaction system is directly heated to 290°C at a rate of 5°C / min, and then the vacuum polycondensation in step S3 is started.

[0174] The other steps are the same as in Example 1, and control sample 4 is prepared.

[0175] Analysis and Testing

[0176] Samples 1-3 prepared in Examples 1-3 and control samples 1-4 prepared in Comparative Examples 1-4 were cut into standard sizes and then subjected to performance testing. The test environment was 23℃±2℃ and 50%±5% relative humidity.

[0177] I. Thermal and Mechanical Property Testing

[0178] Thermal and mechanical properties, including glass transition temperature (Tg), coefficient of thermal expansion (CTE), flexural strength, transmittance, and yellowness index, are shown in Table 1. The glass transition temperature was tested using a dynamic thermomechanical analyzer. The average coefficient of thermal expansion (CTE) within the temperature range of 50℃ to 200℃ was also tested and recorded using a thermomechanical analyzer. Flexural strength was tested using an in-house bending tester according to standard IEC 62715-6-1, where the substrate was bent 180° repeatedly with a bending radius of R=2mm. The number of bends at which electrical function failure or visible cracks appeared was recorded, with the higher number being considered. Transmittance at 550nm wavelength was measured using a UV-Vis spectrophotometer according to standard ASTM D1003, and the yellowness index was measured using a colorimeter, expressed as b* value.

[0179] Table 1: Test Results of Thermal and Mechanical Properties

[0180]

[0181] As can be seen from the results in Table 1, the liquid crystal polymer substrate samples of the present invention all exhibit excellent comprehensive performance. Among them, sample 1 has the most balanced performance, with high heat resistance, low coefficient of thermal expansion, ultra-high bending resistance (>100,000 times) and high transparency.

[0182] Control sample 1, using only rigid monomers, while exhibiting the highest Tg and lowest CTE, suffers from extreme brittleness and severely degraded bending resistance, failing to meet the requirements for flexible displays. This demonstrates the crucial role of introducing flexible monomers in ensuring substrate flexibility. Control sample 2, lacking fluorinated and fluorene monomers, shows significantly reduced heat resistance, increased CTE, and decreased transparency, proving the key role of these functional monomers in improving overall performance. Control sample 3, lacking functional additives, while maintaining acceptable basic properties, exhibits a significantly reduced number of bends, demonstrating the significant contribution of hydrogen bond reinforcement networks to mechanical properties. Control sample 4, due to changes in the polymerization process, shows a decline in all properties, highlighting the necessity of a stepped heating process for obtaining a uniform structure.

[0183] II. Optical Functional Performance Testing

[0184] Samples 1-3 and reference standards 1-4 were respectively placed under ultraviolet light (365nm, 100mW / cm²). 2 Irradiate the sample for 5 minutes in an ambient light environment and observe the color change; then heat it on an 85℃ hot stage and observe the color recovery. Record the color difference (ΔE) before and after irradiation and the time required for complete recovery. The results are shown in Table 2.

[0185] Table 2: Test Results of Photothermal Response Performance

[0186]

[0187] As shown in Table 2, samples 1-3 of this invention all exhibit significant photochromic properties and rapid thermal recovery, with samples 1 and 3 showing particularly outstanding performance. In contrast, controls 1-3, lacking key monomers or functional additives respectively, completely lost their photothermal response capabilities, demonstrating that the intelligent response characteristics of this invention originate from the synergistic effect of specific monomers and functional additives. Control 4, while showing some response, exhibited a significantly reduced effect and slow recovery, proving that the optimized polymerization process is crucial for ensuring the effective functioning of the functional additives.

[0188] III. Electrical Performance Testing

[0189] The dielectric constant (denoted as Dk) and dielectric loss (denoted as Df) were measured at a frequency of 10 GHz using an impedance analyzer. The results are shown in Table 3.

[0190] Table 3: High-Frequency Electrical Performance Test Results

[0191]

[0192] As shown in Table 3, samples 1-3 of this invention all exhibit low dielectric constants and low dielectric losses, making them particularly suitable for high-frequency applications. Reference 2, lacking a fluorinated monomer, shows a significant deterioration in dielectric properties, demonstrating the crucial role of the fluorinated monomer in reducing material polarity. References 1 and 4 also suffer negatively impacted dielectric properties due to their non-uniform molecular structures.

[0193] IV. Application Performance Testing

[0194] The substrates prepared from Sample 1 and Controls 1-4 were respectively applied to flexible display modules, and the following tests were performed:

[0195] 1. High-temperature storage test: Stored at 125℃ for 1000 hours. After the test, the module using sample 1 showed normal performance with no warping or yellowing; while the module using control 1 showed obvious warping, and the module using control 2 showed severe yellowing.

[0196] 2. Temperature and humidity cycling test: 500 cycles were performed at -40℃ to 85℃ and 85%RH. During the test, the module using sample 1 showed stability with no performance degradation; the module using control sample 3 showed microcracks in the bending area.

[0197] In summary, the liquid crystal polymer substrate prepared by this invention, especially sample 1, successfully integrates high heat resistance, low coefficient of thermal expansion, excellent flexibility, high transparency and intelligent response characteristics. Its comprehensive performance is far superior to that of the comparative samples, and it fully meets the application requirements of next-generation ultra-thin flexible displays.

[0198] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A high-temperature resistant liquid crystal polymer substrate for ultra-thin flexible displays, characterized in that, The substrate comprises a modified liquid crystal polymer and functional additives dispersed therein; The modified liquid crystal polymer is polymerized from a monomer composition comprising 38-42 parts of p-hydroxybenzoic acid, 28-30 parts of 4,4'-biphenyl, 5.6-6.0 parts of terephthalic acid, 4.4-5.0 parts of 2,6-naphthalenedicarboxylic acid, 2.7-3.3 parts of isophthalic acid, 9-11 parts of 2,2-bis(3,5-difluoro-4-hydroxyphenyl)hexafluoropropane, 4.5-5.5 parts of N,N'-dihydroxypyromellitic acid diamine, 9-11 parts of 9,9-bis[4-(4-methoxycarbonylphenoxy)phenyl]fluorene, and 5.5-6.5 parts of 1,4-cyclohexanediethanol. The functional additives include 0.9 to 1.8 parts of azobenzene derivatives, 1.5 to 2.4 parts of a thermal acid generator, and 2.1 to 4.2 parts of a hydrogen bond enhancer.

2. The substrate according to claim 1, characterized in that, The amount of isophthalic acid used is 27% to 30% of the sum of the mass fractions of terephthalic acid and 2,6-naphthalenedicarboxylic acid.

3. The substrate according to claim 1, characterized in that, The azobenzene derivative is selected from any one of 4-dimethylaminoazobenzene, 1-(2,4-dinitrophenyl)azo-2-naphthol, or 1-[(2,4-dimethylphenyl)azo]-2-naphthol; the thermal acid generating agent is selected from any one of diphenyliodonium hexafluorophosphate, 4-methylphenyldiazotetrafluoroborate, or p-toluenesulfonic acid pyridine salt; the hydrogen bond reinforcing agent is selected from any one of polyvinylpyrrolidone, polyacrylamide, or aqueous polyurethane dispersion.

4. The substrate according to claim 1, characterized in that, The substrate surface is also provided with a functional coating, which is formed by curing a coating composition of fluorinated polyurethane acrylate oligomer, modified nano-SiO2, photoinitiator and silane coupling agent, wherein the mass ratio of each component is 25-28:3-4:1:

1.

5. The substrate according to any one of claims 1-4, characterized in that, The substrate preparation steps include S1, preparation and pretreatment of monomer composition raw materials, S2, prepolymerization reaction, S3, vacuum polycondensation and antioxidant stabilization treatment to prepare modified LCP resin, S4, blending and molding of functional additives to prepare precursor film, S5, in-situ curing, orientation and annealing, and S6, coating of surface functional coating.

6. The substrate according to claim 5, characterized in that, The prepolymerization reaction in step S2 specifically involves: in the presence of a compatibilizer, a composite antioxidant, and an acetylation system, the monomer composition is subjected to acetylation prepolymerization at 150℃~165℃ for 60min~90min, followed by a stepwise temperature increase and further prepolymerization. The compatibilizer is a maleic anhydride-grafted hydrogenated styrene-butadiene block copolymer, added in an amount of 0.9 parts to 1.5 parts. The composite antioxidant consists of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and tris(2,4-di-tert-butylphenyl) The phosphites are compounded in a mass ratio of 1.5 to 2:1, and the amount added is 0.3 to 0.6 parts; the acetylation system is composed of trifluoroacetic anhydride, 0.02 to 0.05 parts potassium acetate and 0.01 to 0.04 parts tetrabutyl titanate. The amount of trifluoroacetic anhydride added is 1.05 to 1.10 times the total mass of p-hydroxybenzoic acid, 4,4'-biphenyl, 2,2-bis(3,5-difluoro-4-hydroxyphenyl)hexafluoropropane, N,N'-dihydroxypyromellitic acid diamine and 1,4-cyclohexanediethanol.

7. The substrate according to claim 6, characterized in that, The stepwise heating and prepolymerization reaction specifically involves heating to 180℃~190℃ at a rate of 1℃ / min and reacting for 50min~60min; then heating to 210℃~220℃ at a rate of 1℃ / min and reacting for 90min~120min.

8. The substrate according to claim 5, characterized in that, The specific operation of vacuum polycondensation in step S3 is as follows: the reaction system is heated to 285℃ to 295℃ at a stirring speed of 60r / min to 80r / min at a rate of 0.5℃ / min. When the temperature reaches 240℃, vacuum is started to reduce the system pressure to below 80Pa. The system is then maintained at 285℃ to 295℃ under vacuum for 90min to 150min. The specific operation of antioxidant stabilization is as follows: 0.2 parts to 0.6 parts of liquid composite antioxidant are injected 10min to 15min before the end of the polycondensation reaction. The reaction is continued for another 10min to 15min before the material is discharged to obtain the modified LCP resin.

9. The substrate according to claim 5, characterized in that, Step S4 specifically includes S41, melt blending, and S42, molding and quenching; the melt blending specifically involves melt blending the modified LCP resin using a twin-screw extruder at 265℃~280℃, adding functional additives and 0.4 parts to 0.7 parts of compatibilizer in the melting section; the molding and quenching specifically involves extruding the melt mixture at 275℃±3℃, and rapidly quenching it using a cooling roller at 30℃~40℃ to obtain a precursor film with a thickness of 25μm~50μm; the compatibilizer is a maleic anhydride-grafted hydrogenated styrene-butadiene block copolymer.

10. The substrate according to claim 5, characterized in that, Step S5 specifically involves: passing the precursor film under a constant tension of 5 N / m to 15 N / m through a multi-temperature zone thermosetting oven, with the temperature zones set as follows: 160℃ to 165℃ for 3 min to 8 min, 190℃ to 195℃ for 100 min to 110 min, and 220℃ to 225℃ for 12 min to 18 min; and then annealing at 225℃ to 235℃ for 28 min to 35 min.

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