Copolymerized polyamide-imide, film, preparation method and electronic device

Abstract

The invention provides copolymerized polyamide-imide, a film, a preparation method and an electronic device, and belongs to the field of flexible display materials. The copolymerized polyamide-imide is at least prepared from a reaction system containing the following monomers: a) a fluorine-containing aromatic dianhydride monomer; b) an aromatic diamine monomer containing ether bonds and fluorine; and c) an aromatic diacyl chloride monomer. The copolymerized polyamide-imide disclosed by the invention is prepared by carrying out polycondensation and chemical imidization on a dianhydride component, a diamine component and an acyl chloride component in a polar solvent; a rigid benzene ring structure and a hydrogen bond in a main chain can improve the modulus to be larger than or equal to 6 Gpa, the size stability is high, the thermal expansion coefficient is smaller than or equal to 10 ppm / DEG C, meanwhile, a large-steric-hindrance side group of a benzene ring on the main chain can effectively improve the optical performance of the thin film, light transmittance is prevented from being affected by low-temperature dropwise adding and step-by-step imidization (the light transmittance of the waveband of 360-780 nm is larger than or equal to 88%), the benzene ring structure containing an ether bond on the main chain, and the light transmittance of the thin film is larger than or equal to 80%. The tearing strength of the membrane material can be effectively improved.

Description

Technical Field

[0001] This invention belongs to the field of flexible display materials technology, and in particular to a copolyamide-imide, thin film, preparation method and electronic device. Background Technology

[0002] With the rapid development of flexible displays, wearable devices and 5G communication equipment, higher requirements are being placed on flexible substrate materials. These materials not only need excellent heat resistance and mechanical properties, but also high optical transparency, low dispersion and low coefficient of thermal expansion. Polyimide (PI) is one of the core candidate materials for flexible display substrates due to its excellent high temperature resistance, mechanical properties and dielectric properties.

[0003] However, traditional polyimides, due to their highly conjugated aromatic backbone and the formation of strong charge-transfer complexes between molecular chains, are typically dark yellow or brown, with insufficient transmittance in the visible light region, failing to meet the "colorless and transparent" requirements of flexible displays. Introducing alicyclic structures or fluorine-containing groups can improve transparency, but usually sacrifices the material's thermal stability and mechanical strength. While inorganic nanoparticle doping can improve the coefficient of thermal expansion and modulus, it often leads to decreased transmittance and increased haze, which limits its application in flexible optoelectronic devices.

[0004] A search revealed that Chinese invention application CN112500567A discloses a high-modulus transparent polyimide film material containing an amide structure. This material is prepared by polycondensation of a diamine containing an amide structure and a fluorinated aromatic diamine with a fluorinated dianhydride or a dianhydride monomer containing an alicyclic structure. It exhibits a high glass transition temperature (280-400℃) and a transmittance exceeding 90% at 450 nm. However, the dimensional stability and thermogravimetric properties of this material at high temperatures still have room for improvement. Chinese invention application CN108587163B provides a method for preparing a highly transparent, low-expansion polyimide film. This method involves mixing a polyimide resin solution and a perhydropolysilazane solution, followed by coating and in-situ hydrolysis of the perhydropolysilazane to silicon dioxide, resulting in a silicon dioxide-doped polyimide hybrid film. This method improves the coefficient of thermal expansion, but the introduction of the inorganic phase may affect the film's flexibility and surface smoothness. Summary of the Invention

[0005] To overcome the above-mentioned technical defects, the present invention provides a copolyamide imide, a thin film, a preparation method, and an electronic device to solve the problems involved in the background art.

[0006] According to a first aspect of the present invention, a copolyamide-imide is provided, comprising: the copolyamide-imide being prepared from a reaction system comprising at least the following monomers: a) Dianhydride monomers, said dianhydride monomers including fluorinated aromatic dianhydride monomers; b) Diamine monomers, said diamine monomers including aromatic diamine monomers containing ether bonds and aromatic diamine monomers containing fluorine and / or aromatic diamine monomers containing both ether bonds and fluorine; c) Aromatic diacyl chloride monomers; The polymer chain segment of the copolyamide imide includes an imide unit formed by the reaction of monomers a) and b), and an amide unit formed by the reaction of monomers b) and c), and the molar ratio of the imide unit to the amide unit is 1:9 to 9:1.

[0007] Preferably or optionally, the aromatic diamine monomer containing an ether bond accounts for 10-40 mol% of the total diamine monomer; the fluorinated aromatic diamine monomer accounts for 60-90 mol% of the total diamine monomer; the aromatic diamine monomer containing an ether bond includes at least one of 4,4'-diaminodiphenyl ether, 1,3-bis(4'-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, and 3,4'-diaminodiphenyl ether. Preferably or optionally, the aromatic diacyl chloride monomer includes at least one of terephthaloyl chloride, isophthaloyl chloride, and biphenyl diacyl chloride.

[0008] According to a second aspect of the present invention, a method for preparing a copolyamide-imide is provided, characterized in that it comprises: S1: A diamine monomer is dissolved in an organic solvent, and an aromatic diacyl chloride monomer is added to react and a first prepolymer solution is obtained; a dianhydride monomer is added to the first prepolymer solution to carry out a copolymerization reaction and a second prepolymer solution is obtained; the dianhydride monomer includes a fluorinated aromatic dianhydride monomer; the diamine monomer includes an aromatic diamine monomer containing an ether bond and / or a fluorinated aromatic diamine monomer and / or an aromatic diamine monomer containing both an ether bond and fluorine; S2: Perform an imidization reaction to obtain a solution containing copolyamide imide.

[0009] Preferably or optionally, the imidization reaction is a chemical imidization method or a thermal imidization method.

[0010] According to a third aspect of the present invention, a method for preparing a copolyamide-imide film is provided, comprising: S1: A diamine monomer is dissolved in an organic solvent, and an aromatic diacyl chloride monomer is added to react and a first prepolymer solution is obtained; a dianhydride monomer is added to the first prepolymer solution to carry out a copolymerization reaction and a second prepolymer solution is obtained; the dianhydride monomer includes a fluorinated aromatic dianhydride monomer; the diamine monomer includes an aromatic diamine monomer containing an ether bond and / or a fluorinated aromatic diamine monomer and / or an aromatic diamine monomer containing both an ether bond and fluorine; S2: Perform an imidization reaction to obtain a solution containing copolyamide imide; S3: The solution obtained in S2 is coated into a film, and after drying and heat treatment, a copolyamide-imide film is obtained.

[0011] Preferably or optionally, the dropping rate of the aromatic diacyl chloride monomer is 0.8-1.2 kg / min, and the mixture is kept warm and stirred for 1.5-2 h after the dropping is completed; the dropping rate of the fluorinated aromatic dianhydride monomer is 1.0-1.5 kg / min, and the reaction time is 2-5 h after the dropping is completed; the solid content of the second prepolymer solution is 12%-15%, and the viscosity is 8000-20000 mPa·s.

[0012] Preferably or optionally, the drying and heat treatment is a step-by-step heating process, and the specific parameters of the step-by-step heating process are: holding at 80-100℃ for 0.5-1 h, holding at 150-180℃ for 0.5-1 h, and holding at 290-310℃ for 0.5-1.5 h; the heating rate is controlled at 2-5℃ / min.

[0013] According to a third aspect of the present invention, a transparent flexible electronic device is provided comprising a thin film obtained by the copolyamide-imide or a thin film prepared by a method for preparing the copolyamide-imide thin film.

[0014] Compared with the prior art, the present invention provides a copolyamide-imide, a thin film, a preparation method, and an electronic device, which have the following beneficial effects: 1. One aspect of this invention involves copolymerizing a fluorinated dianhydride diamine monomer and an acyl chloride monomer with a diamine containing an ether-bonded triphenyl ring structure. The rigid benzene ring structure and hydrogen bonds in the main chain can increase the modulus by ≥6 GPa, while exhibiting high dimensional stability and a coefficient of thermal expansion ≤10 ppm / ℃. Simultaneously, the large steric hindrance side groups of the benzene ring on the main chain effectively enhance the optical properties of the thin film. Furthermore, low-temperature drop-addition and stepwise imidization avoid affecting light transmittance (transmittance ≥88% in the 360-780 nm band). The benzene ring structure containing ether bonds in the main chain effectively improves the tear strength of the film. Therefore, this thin film can be used as a flexible substrate, supporting the high-temperature fabrication of thin-film devices required for various microelectronic applications. Its tear resistance is particularly outstanding, making it especially suitable for secondary processing after being prepared into rolls. Currently, no other material possesses all these properties simultaneously.

[0015] 2. Another aspect of this invention introduces fluorinated dianhydrides or fluorinated diamines, utilizing their large -CF3 side groups to effectively inhibit the close packing of molecular chains. This not only significantly improves the solubility and transparency of the polymer but also reduces the dielectric constant. Simultaneously, the rigid imide ring and amide bond provide high modulus and heat resistance. The introduction of ether bonds imparts moderate flexibility to the molecular chains, which is beneficial for improving processability and film toughness. The synergistic effect of these three factors resolves the contradiction between "high modulus - high tear strength - high transparency - solubility".

[0016] 3. The polyamide-imide obtained by this invention has good solubility and can be formed into a film using a low-cost and high-efficiency solution coating method (such as slot coating). The process is simple, suitable for large-scale continuous production, and has high compatibility with existing display panel manufacturing processes. It can be widely used in flexible display panels, flexible electronic devices and other fields.

[0017] 4. The polymer in this invention possesses high tear strength, offers relatively wide processing conditions, and is easier to form films. It can be produced by intermittent solution casting or by continuous casting directly from its polymer mixture, followed by roll-to-roll curing to obtain transparent films with a thickness of 10-50 μm. Furthermore, the polymer solution can also be cast onto reinforcing substrates such as thin glass or microelectronic devices, curing to form films with a thickness of 30-35 μm.

[0018] 5. The polymer solution obtained by this invention produces a thin film that achieves a rare combination of high transparency, high modulus, extremely high tear strength, low coefficient of thermal expansion, and good solubility, fully meeting the core performance requirements of substrate / cover materials for next-generation foldable, rollable, transparent, and flexible displays.

[0019] 6. The thin film obtained by this invention has multiple advantages such as transparency, high mechanical strength, low coefficient of thermal expansion, and solubility. It can be used directly as a substrate for transparent flexible displays, or as a core component such as an encapsulation layer and a touch sensing layer, providing support for the performance improvement and structural optimization of flexible display devices.

[0020] 7. The polymer substrate film of the present invention possesses high modulus, tear strength, and optical properties. The substrate of the present invention will also drive the development of the flexible display market. Such flexible displays can be used in various scenarios, such as wearable displays that can be integrated into clothing, flexible electronic paper and e-book displays, and many other new application areas.

[0021] Experiments have demonstrated that the copolyamide-imide of this invention possesses a rigid backbone and hydrogen bonds, resulting in a polymer film with a tensile modulus exceeding 6 GPa. The benzene rings containing ether bonds in the backbone effectively enhance tear strength, surpassing that of currently commercially available films. The polymer film can be prepared via solution casting and cured at 250°C. The cured film exhibits high optical transparency (transmittance > 88%), low coefficient of thermal expansion (CTE < 10 ppm / °C), and high tear resistance (tear strength > 200 gf / mm) in the 360-780 nm wavelength range. When continuously bent 200,000 times at a bending radius R1.0 mm, the film shows no obvious creases or breakage, demonstrating excellent bending resistance. Detailed Implementation

[0022] In the following description, numerous specific details are set forth in order to provide a more thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention can be practiced without one or more of these details. In other instances, certain technical features well-known in the art have not been described in order to avoid obscuring the invention.

[0023]

Copolyamide imide

[0024] The fluorinated aromatic dianhydride monomer is 2,2'-bis(3,4-dicarboxylic acid phenyl)hexafluoropropane dianhydride. The aromatic diamine monomer containing an ether bond includes at least one of 1,3-bis(4'-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, and 3,4'-diaminodiphenyl ether. The aromatic diacyl chloride monomer includes one of terephthaloyl chloride, isophthaloyl chloride, and biphenyl dicarboxylate chloride.

[0025] [Preparation method of copolyamide imide] This embodiment provides a method for preparing copolyamide-imide, comprising the following steps: S1. Prepolymer solution synthesis: Under an inert atmosphere, ether-containing and fluorinated aromatic diamine monomers are dissolved in an organic solvent. At a low temperature (-10℃ to 10℃), propylene oxide (PO) is added first, followed by the addition of aromatic diacyl chloride monomers in batches, and the reaction is carried out for 1-4 hours to obtain the first prepolymer solution. The organic solvent is N-methylpyrrolidone (NMP), N,N-dimethylacetamide (DMAC), or dimethyl sulfoxide (DMSO), preferably N,N-dimethylacetamide (DMAC).

[0026] The addition of aromatic diacyl chloride monomers must be controlled under low temperature (-10℃ to 0℃) and low speed (0.8-1.2 kg / min) conditions to avoid local overheating and gelation due to excessive reactivity, which would affect the stability of the precursor solution. After the reagent propylene oxide (PO) is added, vacuum displacement is not performed to prevent the low-boiling-point PO from being removed by the vacuum system.

[0027] S2. Copolymerization and imidization: A fluorinated aromatic dianhydride monomer is added to the first prepolymer solution for copolymerization reaction. The reaction is carried out at 0~10℃ for 2-8 hours to obtain the second prepolymer solution. Subsequently, chemical imidization is used (acetic anhydride and pyridine are added as dehydrating agents) to cyclize and dehydrate the amyl acid to form a copolymer polyamide imide solution.

[0028] S3. Precipitation, washing and dissolution: The above solution is slowly dripped into an ethanol or methanol solution. The filamentous fibers are cut into powder using a high-speed cutting device. The powder is soaked in the ethanol or methanol solution for 12 hours and then dried in an oven at 105°C for 12 hours. The powdered resin is then dissolved in N,N-dimethylacetamide (DMAC) to obtain a copolyamide-imide solution with a solid content of 12-15% and a viscosity of 8000-20000 mPa·s.

[0029] Preparation method of copolyamide-imide film This embodiment provides a method for preparing a copolyamide-imide film, comprising the following steps: S4. Film forming: After filtration and degassing, the copolyamide-imide is coated onto a clean glass plate, release film or metal strip by casting or slot coating.

[0030] S5. Drying and Heat Treatment: The coated wet film is dried in sections at 80℃-180℃ to remove most of the solvent. Subsequently, it is subjected to high-temperature heat treatment under nitrogen or vacuum atmosphere at a temperature of 250℃-350℃ for 0.5-2 hours to completely remove residual solvent, promote molecular chain orientation and crystallization, and obtain the transparent copolyamide-imide film.

[0031] The drying and heat treatment are performed in steps, with the specific parameters as follows: holding at 80-100℃ for 0.5-1 h, holding at 150-180℃ for 0.5-1 h, and holding at 290-310℃ for 0.5-1.5 h, with the heating rate controlled at 2-5℃ / min. Especially during the transition from low-temperature drying to the medium-temperature stage, slow heating avoids rapid solvent evaporation and the generation of bubbles, ensuring the film's density. The maximum temperature during the high-temperature stage does not exceed 330℃ to prevent molecular chain degradation and ensure the film's mechanical properties and thermal stability.

[0032] Applications of Copolyamide-Imide Films The colorless polyamide-imide film obtained in this invention has a thickness of 30-35 μm. Under room temperature conditions, the relevant performance test results need to meet the following requirements: Tear strength: TPR > 200 gf / mm. Optical properties: Total transmittance (Y total) > 88%. Mechanical properties: Tensile modulus > 6 GPa. Thermal properties: Coefficient of thermal expansion (CTE) of the film < 10 ppm / ℃ in the range of 50-250℃. The film can withstand 200,000 bends at a bending radius of 1 mm without cracking, meeting the long-term use requirements of flexible displays.

[0033] The copolyamide-imide transparent film can be used in transparent flexible displays. Specifically, the film can be used as a substrate, encapsulation layer or touch sensing layer of a transparent flexible display device, and can also be used as a transparent flexible display cover, touch screen sensor substrate or flexible OLED encapsulation layer.

[0034] The present invention will be further described below with reference to the embodiments. The examples described are intended to explain the present invention and should not be construed as limiting the present invention.

[0035]

Detection Method

[0036] Solution viscosity test: The solution viscosity was measured at room temperature (25°C) using a Brookfield viscometer.

[0037] Thermal expansion coefficient test: measured by a thermomechanical analyzer (TMA) model TA-Q400, with the sample heated from 0°C to 350°C in a nitrogen atmosphere at a rate of 10°C / min.

[0038] Film formation performance test: The film was uniformly coated on the glass substrate using a DM slot coating equipment at a coating speed of 150 mm / min.

[0039] Modulus testing: Mechanical properties were measured using an INSTRON Instron 5944 series tensile testing machine. 30-micron film samples were stretched at room temperature at a rate of 10 mm / min, with an initial length of 100 mm.

[0040] Tear resistance test: Measured by INSTRON Instron 5944 series tensile testing machine, sample width 25mm.

[0041] Optical performance testing: Optical performance was measured using a Hunterlab UltraScan VIS series spectrophotometer for a 30-micron thin film sample, with a spectral resolution of 10 nm, a grating size of 8 nm, and a scanning range of 380-780 nm.

[0042] According to the monomer ratios specified in the following examples, polyamide-imide acid, the precursor of colorless polyimide, was prepared. The obtained polyamide-imide acid solution was uniformly coated into a thin film, and then the solvent was removed by drying and high-temperature heat treatment to obtain a colorless polyamide-imide film. The preparation of the colorless polyimide film requires film preparation according to specific requirements.

[0043] The tear strength and overall properties of the polyamide-polyimide films given in the following examples and the polyimide films in the comparative examples were prepared and studied. The composition and performance parameter test results of the multi-component copolymer polyamide-imide films and the high-tear-strength polyamide-imide films are shown below.

[0044] Comparative Example 1-1: A polyimide film was prepared from a 6FDA / BPDA / TFMB copolymer, comprising the following steps: In a dry three-necked flask equipped with a stirrer and a nitrogen inlet, 10 g (0.031 mol) of TFMB (2,2'-bis(trifluoromethyl)diaminobiphenyl) and 159.7 g of DMAC (N,N-dimethylacetamide) were added and stirred until dissolved. The mixture was cooled to below 5°C in an ice bath, and 13.87 g (0.031 mol) of 6FDA (4,4-hexafluoroisopropylphthalic anhydride) was added in portions. The mixture was reacted for 2 hours to obtain a transparent, viscous polyamic acid solution PI1. 6.17 g of pyridine and 15.93 g of acetic anhydride were added to the solution, and a chemical imidization reaction was carried out at 80°C for 6 hours.

[0045] The above reaction solution was poured into ethanol for precipitation, yielding a white fibrous polymer. After pulverization, washing, and drying, it was dissolved in DMAC (N,N-dimethylacetamide) to prepare a slurry with a solid content of 12 wt%. After filtering and degassing the slurry, it was cast onto a glass plate and dried at 80°C and 120°C for 0.5 hours each. Then, it was heat-treated at 250°C for 1 hour under nitrogen protection, and after natural cooling, it was peeled off to obtain a transparent film (PI-1) with a thickness of approximately 30 μm.

[0046] Comparative Examples 1-2A polyimide film was prepared from a 6FDA / BPDA / TFMB copolymer, comprising the following steps: In a dry three-necked flask equipped with a stirrer and a nitrogen inlet, 10 g (0.031 mol) of TFMB (2,2'-bis(trifluoromethyl)diaminobiphenyl) and 100 g of DMAC (N,N-dimethylacetamide) were added and stirred until dissolved. The mixture was cooled to below 5°C in an ice bath, and 9.71 g (0.022 mol) of 6FDA (4,4-hexafluoroisopropylphthalic anhydride) was added in portions, reacting for 2 hours. Then, 2.75 g (0.009 mmol) of BPDA (3,3',4,4'-biphenyltetracarboxylic acid dianhydride) was added to the solution, and the mixture was reacted at room temperature for 4 hours. Finally, the temperature was raised to 60°C and the reaction continued for 2 hours to obtain a transparent, viscous polyamic acid solution, PI2. 6.17 g of pyridine and 15.93 g of acetic anhydride were added to the solution, and the mixture was chemically imidized at 80 °C for 6 hours.

[0047] The above reaction solution was poured into ethanol for precipitation, yielding a white fibrous polymer. After pulverization, washing, and drying, it was dissolved in DMAC (N,N-dimethylacetamide) to prepare a slurry with a solid content of 12 wt%. After filtering and degassing the slurry, it was cast onto a glass plate and dried at 80°C and 120°C for 0.5 hours each. Then, it was heat-treated at 250°C for 1 hour under nitrogen protection, and after natural cooling, it was peeled off to obtain a transparent film (PI-2) with a thickness of approximately 30 μm.

[0048] Table 1. Properties of 6FDA / BPDA / TFMB copolymers .

[0049] discuss: As can be seen from the data in Table 1, the copolymers of PI1 and PI2 obtained by using Comparative Examples 1-1 and 1-2 have too low a modulus and too high CTE, which cannot meet the requirements of strength and dimensional stability of flexible display substrates.

[0050] Comparative Example 2-1:A method for preparing a polyamide-imide film from a 6FDA / TPC / TFMB copolymer includes the following steps: In a dry three-necked flask equipped with a stirrer and a nitrogen inlet, 10 g (0.031 mol) of TFMB (2,2'-bis(trifluoromethyl)diaminobiphenyl) and 154.7 g of DMAC (N,N-dimethylacetamide) are added and stirred until dissolved. The mixture is cooled to below -5°C in an ice bath, and 0.36 g (0.006 mol) of PO (propylene oxide) is added first, followed by 0.63 g (0.003 mol) of TPC (terephthaloyl chloride) in portions. The mixture is reacted for 2 hours. The mixture is then cooled to below 5°C in an ice bath, and 12.49 g (0.028 mol) of 6FDA (4,4-hexafluoroisopropylphthalic anhydride) is added in portions. The mixture is reacted for 2 hours to obtain a transparent, viscous polyamic acid solution PAI1. Add 5.56 g pyridine and 14.35 g acetic anhydride, and chemical imidize at 80 °C for 6 hours.

[0051] The above reaction solution was poured into deionized water for precipitation, yielding a white fibrous polymer. After washing and drying, it was dissolved in DMAC (N,N-dimethylacetamide) to prepare a slurry with a solid content of 12 wt%. After filtering and degassing, the slurry was cast onto a glass plate and dried at 80°C and 120°C for 0.5 hours each. Then, it was heat-treated at 250°C for 1 hour under nitrogen protection, and after natural cooling, it was peeled off to obtain a transparent film (PAI-1) with a thickness of approximately 30 μm.

[0052] Comparative Example 2-2 A method for preparing a polyamide-imide film from a 6FDA / TPC / TFMB copolymer includes the following steps: In a dry three-necked flask equipped with a stirrer and a nitrogen inlet, 10 g (0.031 mol) of TFMB (2,2'-bis(trifluoromethyl)diaminobiphenyl) and 144.6 g of DMAC (N,N-dimethylacetamide) are added and stirred until dissolved. The mixture is cooled to below -5°C in an ice bath, and 1.09 g (0.018 mol) of PO (propylene oxide) is added first, followed by 1.9 g (0.009 mol) of TPC (terephthaloyl chloride) in portions. The mixture is reacted for 2 hours. The mixture is then cooled to below 5°C in an ice bath, and 9.71 g (0.022 mol) of 6FDA (4,4-hexafluoroisopropylphthalic anhydride) is added in portions. The mixture is reacted for 2 hours to obtain a transparent, viscous polyamic acid solution PAI2. Add 4.32 g of pyridine and 11.16 g of acetic anhydride, and carry out chemical imidization reaction at 80 °C for 6 hours.

[0053] The above reaction solution was poured into deionized water for precipitation, yielding a white fibrous polymer. After washing and drying, it was dissolved in DMAC (N,N-dimethylacetamide) to prepare a slurry with a solid content of 12 wt%. After filtering and degassing the slurry, it was cast onto a glass plate and dried at 80°C and 120°C for 0.5 hours each. Then, it was heat-treated at 250°C for 1 hour under nitrogen protection, and after natural cooling, it was peeled off to obtain a transparent film (PAI-2) with a thickness of approximately 30 μm.

[0054] Comparative Examples 2-3 A method for preparing a polyamide-imide film from a 6FDA / TPC / TFMB copolymer includes the following steps: In a dry three-necked flask equipped with a stirrer and a nitrogen inlet, 10 g (0.031 mol) of TFMB (2,2'-bis(trifluoromethyl)diaminobiphenyl) and 139.6 g of DMAC (N,N-dimethylacetamide) are added and stirred until dissolved. The mixture is cooled to below -5°C in an ice bath, and 1.45 g (0.024 mol) of PO (propylene oxide) is added first, followed by 2.54 g (0.012 mol) of TPC (terephthaloyl chloride) in portions, reacting for 2 hours. The mixture is then cooled to below 5°C in an ice bath, and 8.32 g (0.019 mol) of 6FDA (4,4-hexafluoroisopropylphthalic anhydride) is added in portions, reacting for 2 hours to obtain a transparent, viscous polyamic acid solution PAI3. Add 371g of pyridine and 9.56g of acetic anhydride, and carry out chemical imidization reaction at 80℃ for 6 hours.

[0055] The above reaction solution was poured into deionized water for precipitation, yielding a white fibrous polymer. After washing and drying, it was dissolved in DMAC to prepare a slurry with a solid content of 12 wt%. The slurry was filtered and degassed, then cast onto a glass plate and dried at 80°C and 120°C for 0.5 hours each. It was then heat-treated at 250°C for 1 hour under nitrogen protection, and after natural cooling, it was peeled off to obtain a transparent film (PAI-3) with a thickness of approximately 30 μm.

[0056] Table 2. Properties of 6FDA / TPC / TFMB copolymers .

[0057] discuss: As shown in Table 2, the copolymers of PAI1, PAI2, and PAI3 obtained in Comparative Example 2 showed that PAI1 met the optical performance standards, but other properties did not; PAI2 failed to meet the tear strength standard, but all other properties met the standards; and PAI3 failed to meet both the tear strength and optical performance standards, but other properties met the standards. Based on these performance indicators, it can be seen that increasing the proportion of TPC copolymerization can improve the modulus and reduce the CTE, but excessive TPC addition will affect the optical performance. Furthermore, the introduction of TPC did not significantly improve the tear resistance of the film material.

[0058] Example 1-1: A method for preparing a polyamide-imide film from a 6FDA / TPC / TFMB / 1,3,4-APB copolymer includes the following steps: In a dry three-necked flask equipped with a stirrer and a nitrogen inlet, 9 g (0.028 mol) of TFMB (2,2'-bis(trifluoromethyl)diaminobiphenyl), 0.91 g (0.003 mol) of 1,3,4-APB (1,3-bis(4'-aminophenoxy)benzene), and 144.1 g of DMAC (N,N-dimethylacetamide) are added and stirred until dissolved. The mixture is cooled to below -5°C in an ice bath, and 1.09 g (0.018 mol) of PO (propylene oxide) is added first, followed by the addition of 1.9 g (0.009 mol) of TPC (terephthaloyl chloride) in portions. The reaction is carried out for 2 hours. The mixture was cooled to below 5°C in an ice bath, and 9.71 g (0.022 mol) of 6FDA (4,4-hexafluoroisopropylphthalic anhydride) was added in portions. The reaction was carried out for 2 hours to obtain a transparent, viscous polyamic acid solution, PAI4. 4.32 g of pyridine and 11.16 g of acetic anhydride were then added, and a chemical imidization reaction was carried out at 80°C for 6 hours.

[0059] The above reaction solution was poured into deionized water for precipitation, yielding a white fibrous polymer. After washing and drying, it was dissolved in DMAC to prepare a slurry with a solid content of 12 wt%. After filtering and degassing the slurry, it was cast onto a glass plate and dried at 80°C and 120°C for 0.5 hours each. Then, it was heat-treated at 250°C for 1 hour under nitrogen protection, and after natural cooling, it was peeled off to obtain a transparent film (PAI-4) with a thickness of approximately 30 μm.

[0060] Examples 1-2 A method for preparing a polyamide-imide film from a 6FDA / TPC / TFMB / 1,3,4-APB copolymer includes the following steps: In a dry three-necked flask equipped with a stirrer and a nitrogen inlet, add 7 g (0.022 mol) of TFMB (2,2'-bis(trifluoromethyl)diaminobiphenyl), 2.74 g (0.009 mol) of 1,3,4-APB (1,3-bis(4'-aminophenoxy)benzene), and 142.9 g of DMAC (N,N-dimethylacetamide), and stir to dissolve. Cool to below -5°C in an ice bath, first add 1.09 g (0.018 mol) of PO (propylene oxide), then add 1.9 g (0.009 mol) of TPC (terephthaloyl chloride) in portions, and react for 2 hours. The mixture was cooled to below 5°C in an ice bath, and 9.71 g (0.022 mol) of 6FDA (4,4-hexafluoroisopropylphthalic anhydride) was added in portions. The reaction was carried out for 2 hours to obtain a transparent, viscous polyamic acid solution, PAI5. 4.32 g of pyridine and 11.16 g of acetic anhydride were then added, and a chemical imidization reaction was carried out at 80°C for 6 hours.

[0061] The above reaction solution was poured into deionized water for precipitation, yielding a white fibrous polymer. After washing and drying, it was dissolved in DMAC to prepare a slurry with a solid content of 12 wt%. The slurry was filtered and degassed, then cast onto a glass plate and dried at 80°C and 120°C for 0.5 hours each. It was then heat-treated at 250°C for 1 hour under nitrogen protection, and after natural cooling, it was peeled off to obtain a transparent film (PAI-5) with a thickness of approximately 30 μm.

[0062] Examples 1-3 A method for preparing a polyamide-imide film from a 6FDA / TPC / TFMB / 1,3,4-APB copolymer includes the following steps: In a dry three-necked flask equipped with a stirrer and a nitrogen inlet, add 6 g (0.019 mol) of TFMB (2,2'-bis(trifluoromethyl)diaminobiphenyl), 3.65 g (0.012 mol) of 1,3,4-APB (1,3-bis(4'-aminophenoxy)benzene), and 142.9 g of DMAC (N,N-dimethylacetamide), and stir to dissolve. Cool to below -5°C in an ice bath, first add 1.09 g (0.018 mol) of PO (propylene oxide), then add 1.9 g (0.009 mol) of TPC (terephthaloyl chloride) in portions, and react for 2 hours. The mixture was cooled to below 5°C in an ice bath, and 9.71 g (0.022 mol) of 6FDA (4,4-hexafluoroisopropylphthalic anhydride) was added in portions. The reaction was carried out for 2 hours to obtain a transparent, viscous polyamic acid solution, PAI2. 4.32 g of pyridine and 11.16 g of acetic anhydride were then added, and a chemical imidization reaction was carried out at 80°C for 6 hours.

[0063] The above reaction solution was poured into deionized water for precipitation, yielding a white fibrous polymer. After washing and drying, it was dissolved in DMAC to prepare a slurry with a solid content of 12 wt%. After filtering and degassing the slurry, it was cast onto a glass plate and dried at 80°C and 120°C for 0.5 hours each. Then, it was heat-treated at 250°C for 1 hour under nitrogen protection, and after natural cooling, it was peeled off to obtain a transparent film (PAI-6) with a thickness of approximately 30 μm.

[0064] Table 3. Properties of 6FDA / TPC / TFMB / 1,3,4-APB copolymer .

[0065] discuss:As can be seen from the data in Table 3, the copolymers of PAI4, PAI5 and PAI6 used in Example 1 all met the standards for modulus and CTE, but their optical properties did not. With the increase of the 1,3,4-APB copolymerization ratio, the tear resistance of the film gradually increased. The introduction of 1,3,4-APB can significantly improve the tear resistance of the film.

[0066] Example 2-1: A method for preparing a colorless polyamide-imide film from a 6FDA / TPC / TFMB / 1,3,3-APB copolymer includes the following steps: In a dry three-necked flask equipped with a stirrer and a nitrogen inlet, add 9 g (0.028 mol) of TFMB (2,2'-bis(trifluoromethyl)diaminobiphenyl), 0.91 g (0.003 mol) of 1,3,3-APB (1,3-bis(3-aminophenoxy)benzene), and 144.1 g of DMAC (N,N-dimethylacetamide), and stir to dissolve. Cool to below -5°C in an ice bath, first add 1.09 g (0.018 mol) of PO (propylene oxide), then add 1.9 g (0.009 mol) of TPC (terephthaloyl chloride) in portions, and react for 2 hours. The solution was cooled to below 5°C in an ice bath, and 9.71 g (0.022 mol) of 6FDA (4,4-hexafluoroisopropylphthalic anhydride) was added in portions. The reaction was carried out for 2 hours to obtain a transparent, viscous polyamic acid solution, PAI7. 4.32 g of pyridine and 11.16 g of acetic anhydride were then added, and a chemical imidization reaction was carried out at 80°C for 6 hours.

[0067] The above reaction solution was poured into deionized water for precipitation, yielding a white fibrous polymer. After washing and drying, it was dissolved in DMAC (N,N-dimethylacetamide) to prepare a slurry with a solid content of 12 wt%. After filtering and degassing the slurry, it was cast onto a glass plate and dried at 80°C and 120°C for 0.5 hours each. Then, it was heat-treated at 250°C for 1 hour under nitrogen protection, and after natural cooling, it was peeled off to obtain a transparent film (PAI-7) with a thickness of approximately 30 μm.

[0068] Example 2-2:A method for preparing a colorless polyamide-imide film from a 6FDA / TPC / TFMB / 1,3,3-APB copolymer includes the following steps: In a dry three-necked flask equipped with a stirrer and a nitrogen inlet, 7 g (0.022 mol) of TFMB (2,2'-bis(trifluoromethyl)diaminobiphenyl), 2.74 g (0.009 mol) of 1,3,3-APB (1,3-bis(3-aminophenoxy)benzene), and 142.9 g of DMAC (N,N-dimethylacetamide) are added and stirred until dissolved. The mixture is cooled to below -5°C in an ice bath, and 1.09 g (0.018 mol) of PO (propylene oxide) is added first, followed by the addition of 1.9 g (0.009 mol) of TPC (terephthaloyl chloride) in portions. The reaction is carried out for 2 hours. The solution was cooled to below 5°C in an ice bath, and 9.71 g (0.022 mol) of 6FDA (4,4-hexafluoroisopropylphthalic anhydride) was added in portions. The reaction was carried out for 2 hours to obtain a transparent, viscous polyamic acid solution, PAI8. 4.32 g of pyridine and 11.16 g of acetic anhydride were then added, and a chemical imidization reaction was carried out at 80°C for 6 hours.

[0069] The above reaction solution was poured into deionized water for precipitation, yielding a white fibrous polymer. After washing and drying, it was dissolved in DMAC (N,N-dimethylacetamide) to prepare a slurry with a solid content of 12 wt%. After filtering and degassing the slurry, it was cast onto a glass plate and dried at 80°C and 120°C for 0.5 hours each. Then, it was heat-treated at 250°C for 1 hour under nitrogen protection, and after natural cooling, it was peeled off to obtain a transparent film (PAI-8) with a thickness of approximately 30 μm.

[0070] Examples 2-3: A method for preparing a colorless polyamide-imide film from a 6FDA / TPC / TFMB / 1,3,3-APB copolymer includes the following steps: In a dry three-necked flask equipped with a stirrer and a nitrogen inlet, add 6 g (0.019 mol) of TFMB (2,2'-bis(trifluoromethyl)diaminobiphenyl), 3.65 g (0.012 mol) of 1,3,3-APB (1,3-bis(3-aminophenoxy)benzene), and 142.9 g of DMAC (N,N-dimethylacetamide), and stir to dissolve. Cool to below -5°C in an ice bath, first add 1.09 g (0.018 mol) of PO, then add 1.9 g (0.009 mol) of TPC (terephthaloyl chloride) in portions, and react for 2 hours. The solution was cooled to below 5°C in an ice bath, and 9.71 g (0.022 mol) of 6FDA (4,4-hexafluoroisopropylphthalic anhydride) was added in portions. The reaction was carried out for 2 hours to obtain a transparent, viscous polyamic acid solution, PAI9. 4.32 g of pyridine and 11.16 g of acetic anhydride were then added, and a chemical imidization reaction was carried out at 80°C for 6 hours.

[0071] The above reaction solution was poured into deionized water for precipitation, yielding a white fibrous polymer. After washing and drying, it was dissolved in DMAC (N,N-dimethylacetamide) to prepare a slurry with a solid content of 12 wt%. The slurry was filtered and degassed, then cast onto a glass plate and dried at 80°C and 120°C for 0.5 hours each. It was then heat-treated at 250°C for 1 hour under nitrogen protection, and after natural cooling, it was peeled off to obtain a transparent film (PAI-9) approximately 30 μm thick. Table 4. Properties of the 6FDA / TPC / TFMB / 1,3,3-APB copolymer .

[0072] As shown in Table 4, the copolymers of PAI7, PAI8, and PAI9 from Example 2 meet the requirements for modulus, CTE, and optical properties for PAI7; however, the tear strength does not meet the requirements. With the increase of the 1,3,3-APB copolymerization ratio, the tear strength of the film gradually increases. All properties of PAI8 meet the requirements, while the optical properties of PAI9 do not meet the requirements, and the remaining properties meet the requirements. The introduction of 1,3,3-APB can significantly improve the tear resistance of the film while ensuring its optical properties. In particular, the performance test data of the copolymer PAI8 obtained in Example 2-2 all meet the performance requirements for colorless transparent flexible display materials.

[0073] discuss

[0074] As can be seen from the above comparative examples and embodiments, the transparent film prepared from the soluble aromatic copolymer polyamide-imide with high tear strength, high modulus, and low coefficient of thermal expansion provided by the present invention, especially the film material of Example 2-PAI8, achieves high tear strength (TPR > 200 gf / mm) while meeting the technical requirements of flexible displays. This is achieved through optimization and adjustment of the polymer monomers and processes, control of the polymer molecular weight, and optimization of the film-forming temperature conditions via multi-component copolymerization. Furthermore, the film material exhibits strong mechanical properties (modulus > 6 GPa), good thermal properties (CTE < 10 ppm / ℃), and good optical properties (Y total > 88%). The transparent film prepared from the soluble aromatic copolymer polyamide-imide with high tear strength, high modulus, and low coefficient of thermal expansion can be used as a substrate material for flexible display devices and other flexible substrate materials requiring these properties.

[0075] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

Claims

1. A copolyamide-imide, characterized in that, The copolyamide imide is prepared from a reaction system comprising at least the following monomers: a) Dianhydride monomers, said dianhydride monomers including fluorinated aromatic dianhydride monomers; b) Diamine monomers, said diamine monomers including aromatic diamine monomers containing ether bonds and aromatic diamine monomers containing fluorine and / or aromatic diamine monomers containing both ether bonds and fluorine; c) Aromatic diacyl chloride monomers; The polymer chain segment of the copolyamide imide includes an imide unit formed by the reaction of monomers a) and b), and an amide unit formed by the reaction of monomers b) and c), and the molar ratio of the imide unit to the amide unit is 1:9 to 9:

1.

2. The copolyamide-imide according to claim 1, characterized in that, The fluorinated aromatic dianhydride monomer accounts for 60-100 mol% of the total dianhydride monomers. The fluorinated aromatic dianhydride monomer is 2,2'-bis(3,4-dicarboxylic acid phenyl)hexafluoropropane dianhydride.

3. The copolyamide-imide according to claim 1, characterized in that, The aromatic diamine monomers containing ether bonds account for 10-40 mol% of the total diamine monomers; the fluorine-containing aromatic diamine monomers account for 60-90 mol% of the total diamine monomers. The aromatic diamine monomer containing an ether bond includes at least one of 4,4'-diaminodiphenyl ether, 1,3-bis(4'-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, and 3,4'-diaminodiphenyl ether; The fluorinated aromatic diamine monomer includes at least one of 4,4'-[1,4-phenylbis(oxy)]bis[3-(trifluoromethyl)aniline] or 2,2'-bis(trifluoromethyl)diaminobiphenyl.

4. The copolyamide-imide according to claim 1, characterized in that, The aromatic diacyl chloride monomer includes at least one of terephthaloyl chloride, isophthaloyl chloride, and biphenyl diacyl chloride.

5. A method for preparing a copolyamide-imide, characterized in that, include: S1: Dissolve the diamine monomer in an organic solvent, add an aromatic diacyl chloride monomer and react to obtain the first prepolymer solution; A dianhydride monomer is added to the first prepolymer solution to carry out a copolymerization reaction, thereby obtaining a second prepolymer solution; the dianhydride monomer includes a fluorinated aromatic dianhydride monomer; the diamine monomer includes an aromatic diamine monomer containing an ether bond and / or a fluorinated aromatic diamine monomer and / or an aromatic diamine monomer containing both an ether bond and fluorine. S2: Perform an imidization reaction to obtain a solution containing copolyamide imide.

6. The method for preparing the copolyamide-imide according to claim 5, characterized in that, The iminoization reaction is either chemical iminoization or thermal iminoization.

7. A method for preparing a copolyamide-imide film, characterized in that, The S1: A diamine monomer is dissolved in an organic solvent, and an aromatic diacyl chloride monomer is added to react and a first prepolymer solution is obtained; a dianhydride monomer is added to the first prepolymer solution to carry out a copolymerization reaction and a second prepolymer solution is obtained; the dianhydride monomer includes a fluorinated aromatic dianhydride monomer; the diamine monomer includes an aromatic diamine monomer containing an ether bond and / or a fluorinated aromatic diamine monomer and / or an aromatic diamine monomer containing both an ether bond and fluorine; S2: Perform an imidization reaction to obtain a solution containing copolyamide imide; S3: The solution obtained in S2 is coated into a film, and after drying and heat treatment, a copolyamide-imide film is obtained.

8. The method for preparing the copolyamide-imide film according to claim 7, characterized in that, The dropping rate of the aromatic diacyl chloride monomer is 0.8-1.2 kg / min, and after the dropping is completed, the mixture is kept warm and stirred for 1.5-2 h; the dropping rate of the dianhydride monomer is 1.0-1.5 kg / min, and the reaction time after the dropping is completed is 2-5 h; the solid content of the second prepolymer solution is 12%-15%, and the viscosity is 8000-20000 mPa·s.

9. The method for preparing the copolyamide-imide film according to claim 7, characterized in that, The drying and heat treatment are step-by-step heating processes, and the specific parameters of the step-by-step heating processes are: holding at 80-100℃ for 0.5-1 h, holding at 150-180℃ for 0.5-1 h, and holding at 290-310℃ for 0.5-1.5 h; the heating rate is controlled at 2-5℃ / min.

10. A transparent flexible electronic device, characterized in that, The thin film obtained by the copolyamide imide according to any one of claims 1 to 4 or the thin film prepared by the method according to any one of claims 7 to 9.