Bending-resistant transparent polyamide-imide film with deformable structure as well as preparation method and application of bending-resistant transparent polyamide-imide film

Abstract

The invention relates to the technical field of flexible display materials, and discloses a bending-resistant transparent polyamide-imide film with a deformable structure and a preparation method and application thereof. The preparation method comprises the following steps: dissolving a diamine monomer in a polar organic solvent containing a cosolvent, adding a dianhydride monomer into the polar organic solvent, and carrying out a polymerization reaction to obtain a polyamide acid solution; adding an acyl chloride monomer into the polyamide acid solution in two times to carry out copolymerization reaction, then adding an end-capping reagent to carry out end-capping reaction, and then adding a dehydrating agent and a catalyst to carry out dehydration cyclization to obtain a polyamide-imide solution; adding a precipitator into the polyamide-imide solid resin for precipitation to obtain polyamide-imide solid resin; and dissolving in a polar organic solvent, then coating, carrying out staged programmed heating, and demolding to obtain the composite material. The prepared CPI / POSS composite film has a larger rebound angle and a larger elastic deformation range, and the bending deformation range of the film is expanded; and after being folded for 200,000 times under the bending radius of 0.5 mm, the film does not have creases.

Description

Technical Field

[0001] This application relates to the technical field of flexible display materials, and particularly relates to a bend-resistant transparent polyamide-imide film with a deformable structure, a preparation method thereof, and an application thereof. Background Art

[0002] With the continuous development of display technology, colorless transparent polyimide (CPI) has become one of the most promising thin film materials for flexible displays due to its excellent comprehensive properties and flexibility in structural design. The substrate material for flexible displays needs to withstand more than 200,000 cycles of cyclic folding during application. During the folding process, cyclic compressive / tensile stresses (σ xx ) and bending moments (M Z ) are respectively borne in the inner and outer sides of the film and in the direction perpendicular to the cross-section of the bending zone. However, during the bending process of the film, the CPI film with a rigid chain structure exhibits poor creep resistance, and the accumulation of plastic deformation caused by the slip of molecular chains leads to the formation of visible creases and wrinkles, affecting the reliability of flexible electronics.

[0003] How to broaden its range of tensile and compressive elastic deformation while maintaining a high glass transition temperature (Tg) and thermal dimensional stability is the key to the structural design and preparation of bend-resistant CPI films. Polyhedral oligomeric silsesquioxane (POSS) is a spatial cage-like small molecule, and its octahedral configuration is a great steric hindrance in the polymer confinement; at the same time, the chain segment structure of POSS appears like a football structure from a macroscopic perspective. When subjected to external force extrusion, due to its certain recoverable elasticity, it exhibits the characteristic of "softness". Modifying CPI with POSS to improve the bend resistance of CPI films is a feasible solution.

[0004] CN 116769170 A discloses the preparation and application of a modified polyimide self-lubricating composite material resistant to atomic oxygen irradiation. By introducing NH2-POSS copolymer into the molecular chain and in-situ introducing nano-silica, the resistance to atomic oxygen irradiation can be improved and the formation of a friction transfer film can be promoted. However, the prepared modified polyimide self-lubricating composite material cannot have both optical properties and good mechanical properties, which limits its application scenarios. Patent application CN 117430808 A discloses a polyamic acid resin and a transparent polyimide film using the same, which is copolymerized from diamine, acid dianhydride and polyhedral oligomeric silsesquioxane POSS. However, the POSS described therein is a multi-amino T8 configuration, but the multi-amino cross-linked POSS shows high brittleness, and the polyimide has both low shrinkage and high brittleness, and it is difficult to withstand the bending performance of the film exceeding 200,000 times. Patent application CN116179075 B discloses a POSS-modified polyimide insulating paint, a preparation method and an application thereof. It uses a single-reaction functional group POSS as a molecular chain end-capping agent to prepare a silicone-capped cured polyimide film. However, it is limited to improving the graft end-capping of POSS when the molecular weight is relatively low in the early stage, and it is difficult to be applied to the scenario of high molecular weight films; and the polyimide film cannot have both optical properties and good mechanical properties, especially the bending resistance.

[0005] The comprehensive performance of the bend-resistant polyimide film based on POSS prepared by the above existing methods is poor, and it cannot have both excellent bend resistance, mechanical properties and optical properties. There is an urgent need to develop a new polyimide-based film to meet the requirements of flexible displays. Summary of the Invention

[0006] The present application provides a bend-resistant transparent polyamide-imide film with a deformable structure, a preparation method and an application thereof, aiming to solve the technical problem that the existing bend-resistant polyimide films cannot have both excellent bend resistance, mechanical properties and optical properties.

[0007] In order to achieve the above object, the present application adopts the following technical solutions to be realized.

[0008] In the first aspect of the present application, there is provided a bend-resistant transparent polyamide-imide film with a deformable structure, and its chemical structure is shown in formula (I):

[0009]

[0010] Among them, R is isobutyl, and R1 is -CH2- or -NH-;

[0011] m and n are positive integers, and m:n is 9:1 to 1:9.

[0012] In the second aspect of the present application, there is provided a method for preparing the above-mentioned bend-resistant transparent polyamide-imide film with a deformable structure, including:

[0013] S1, under a nitrogen atmosphere, dissolving diamine monomers in a polar organic solvent containing a co-solvent to obtain a diamine solution; adding dianhydride monomers to the diamine solution for a polymerization reaction to obtain a polyamic acid solution;

[0014] S2, adding acyl chloride monomers to the polyamic acid solution in two portions for a copolymerization reaction to obtain a polyamide-amic acid solution;

[0015] S3, adding a capping agent to the polyamide-amic acid solution for a capping reaction, and then adding a dehydrating agent and a catalyst for dehydration cyclization to obtain a polyamide-imide solution;

[0016] S4, adding a precipitating agent to the polyamide-imide solution for precipitation, washing and drying the precipitate to obtain a polyamide-imide solid resin;

[0017] S5, dissolving the polyamide-imide solid resin in a polar organic solvent, filtering and degassing to obtain a working solution;

[0018] S6, coating the working solution, and then performing stepwise programmed heating and demolding to obtain a bend-resistant transparent polyamide-imide film with a deformable structure.

[0019] Preferably, the capping agent is PSS-[3-(2-aminoethyl)amino]propyl-substituted heptaisobutyl or aminopropylheptyl-cage-like polyhedral oligomeric silsesquioxane;

[0020] The dehydrating agent is acetic anhydride;

[0021] The catalyst is pyridine, triethylamine or isoquinoline;

[0022] The precipitating agent is a mixture of deionized water and anhydrous ethanol / methanol with a volume ratio of (1-3):1.

[0023] Preferably, the diamine monomer is 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl;

[0024] The dianhydride monomer includes at least one of 2,2`-bis(3,4-dicarboxylic acid)hexafluoropropane dianhydride or 3,3',4,4'-biphenyltetracarboxylic dianhydride;

[0025] The acyl chloride monomer includes at least one of terephthaloyl chloride, isophthaloyl chloride or 4,4'-biphenyldicarbonyl chloride;

[0026] Preferably, the co-solvent is LiCl, and its mass ratio to the polar organic solvent is 0.035:1;

[0027] The polar organic solvent includes at least one of N-methylpyrrolidone, N,N-dimethylformamide, or N,N-dimethylacetamide, and its dosage accounts for 80-90 wt% of the total amount of the polyamic acid solution.

[0028] Preferably, the molar ratio of the diamine monomer, dianhydride monomer, and acyl chloride monomer is (m + n):m:(1-1.065)×n;

[0029] Wherein, m and n are positive integers, and m:n is 9:1-1:9.

[0030] More preferably, the first addition amount of the acyl chloride monomer is n×(99.5%-99.8%), and the second addition amount is n×(0.5%-6.5%).

[0031] More preferably, the dosage of the end-capping agent is (0.005:1-0.065:1)×n;

[0032] The molar ratio of the dehydrating agent to the dianhydride monomer is (2-2.5):1;

[0033] The molar ratio of the dehydrating agent to the catalyst is (1:0.001-2).

[0034] Preferably, the temperature of the dehydration cyclization is 55-65°C, and the time is 1-24 h;

[0035] The stepwise programmed temperature rise specifically includes:

[0036] First, raise the temperature to 50-80°C and keep it warm for 1-3 h, then raise the temperature to 150-180°C and keep it warm for 1-3 h, and finally raise the temperature to 220-250°C and keep it warm for 1-2 h.

[0037] In the third aspect of the present application, there is provided the use of the above-mentioned bend-resistant transparent polyamide-imide film having a deformable structure or the bend-resistant transparent polyamide-imide film having a deformable structure prepared by the above-mentioned preparation method in a flexible display.

[0038] Compared with the prior art, the beneficial effects of the present application are:

[0039] The present application introduces a monoamino POSS monomer containing a cage structure with Si-O at the end of the molecular chain containing interchain hydrogen bond interactions by a two-step gradient feeding method. Among them, the amount of acyl chloride added in the first stage is precisely regulated to be more than 99.5% of the theoretical value to ensure the acquisition of a high molecular weight polymer skeleton; in the second stage, a trace amount of excess acyl chloride is added at one time to accurately construct an active acyl chloride end group at the end of the molecular chain; on this basis, a POSS unit with a three-dimensional cage structure is successfully introduced at the end of the polymer chain by measuring the end-capping reaction of the monoamino POSS; the terminal POSS unit limits the molecular chain slip and inhibits the relaxation of the chain segment through the steric hindrance effect and the stress-induced deformation mechanism, while maintaining the mechanical and thermal properties of the matrix, achieving a synergistic improvement in the transmittance and bending life in the visible light region. In particular, by establishing a quantitative control model of the amount of POSS end-capping agent and material properties, the transmittance, flexibility and mechanical strength of the film can be programmably controlled over a wide range. In addition, in order to solve the solubility problem caused by the hydrogen bond network in polar solvents, this application innovatively constructs a LiCl dissolution-aiding system and a dynamic feeding sequence synergistic control strategy to effectively inhibit the gelation phenomenon.

[0040] The preparation method of the present application has the advantages of narrow molecular weight distribution, strong process controllability and raw material cost advantages (the price of monoamino POSS is only 1 / 5 of that of polyamino POSS), providing an innovative solution for flexible optoelectronic packaging materials.

[0041] The CPI / POSS composite film prepared in the present application has a larger rebound angle and elastic deformation range, which expands the bending deformation range of the film. No creases appear after folding 200,000 times at a bending radius of 0.5 mm. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments recorded in the present application, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0043] Figure 1 The figures are the physical pictures of the films of Examples 1-3 and Comparative Examples 1-2;

[0044] Figure 2 It is a static bending performance diagram of the films of Examples 1-3 and Comparative Examples 1-2;

[0045] Figure 3 This is a SEM image of the bending portion of the film of Example 1-3 after being bent 200,000 times at a bending radius of 0.5 mm. DETAILED DESCRIPTION

[0046] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts shall fall within the scope of protection of the present application.

[0047] In the following description of this embodiment, terms such as "include", "comprise", "have" and "contain" are all open-ended terms, that is, they are meant to include but not limited to.

[0048] In the following description of this embodiment, the term "and / or" is used to describe the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, B exists alone, and both A and B exist simultaneously. Wherein A and B can be singular or plural. The character " / " generally represents an "or" relationship between the associated objects before and after.

[0049] In the following description of this embodiment, the term "at least one" means one or more, and "a plurality" means two or more. "At least one of the following items (pieces)" or its similar expressions refer to any combination of these items, including any combination of single item (piece) or plural items (pieces). For example, "at least one of a, b or c", or, "at least one of a, b and c" can both represent: a, b, c, a - b (that is, a and b), a - c, b - c, or a - b - c, where a, b, and c can be single or multiple respectively.

[0050] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms of "a" and "the" used in the embodiments of the present application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0051] Those skilled in the art should understand that in the following description of the embodiments of the present application, the sequence number does not mean the sequence of execution. Some or all of the steps can be executed in parallel or sequentially. The execution sequence of each process should be determined by its function and internal logic, and should not constitute any limitation to the implementation process of the embodiments of the present application.

[0052] Those skilled in the art should understand that the numerical range in the embodiments of the present application should be understood as specifically disclosing each intermediate value between the upper and lower limits of the range. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present application. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0053] Unless otherwise specified, the technical / scientific terms used herein have the same meanings as commonly understood by those of ordinary skill in the art to which this application pertains. Although this application only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of this application. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the said documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0054] In a first aspect, this application provides a bend-resistant transparent polyamide-imide film with a deformable structure, whose chemical structure is shown in formula (I):

[0055]

[0056] Wherein, R is isobutyl, and R1 is -CH2- or -NH-;

[0057] m and n are positive integers, and m:n is 9:1 to 1:9.

[0058] In view of the two major technical bottlenecks of insufficient reaction activity of monoamino POSS as a polymer chain capping agent and gelation limitation in polar solvent systems, this application proposes an innovative solution. The preparation method of the bend-resistant transparent polyamide-imide film with a deformable structure of this application includes:

[0059] S1, under a nitrogen atmosphere, dissolve the diamine monomer in a polar organic solvent containing a co-solvent to obtain a diamine solution; add the dianhydride monomer to the diamine solution for a polymerization reaction to obtain a polyamic acid solution;

[0060] In this application, the diamine monomer is 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl; the dianhydride monomer can be selected from 2,2`-bis(3,4-dicarboxylic acid) hexafluoropropane dianhydride or 3,3',4,4'-biphenyltetracarboxylic dianhydride, or a mixture of the two.

[0061] In this application, the polar organic solvent can be selected from at least one of N-methylpyrrolidone, N,N-dimethylformamide or N,N-dimethylacetamide. The polar organic solvent contains a co-solvent LiCl, which can inhibit gelation; the mass ratio of LiCl to the polar organic solvent is 0.035:1.

[0062] Preferably, the dosage of the polar organic solvent accounts for 80-90 wt% of the total amount of the polyamic acid solution.

[0063] In this application, the polymerization reaction is carried out under stirring, and the stirring speed is preferably 350-500 rpm; the temperature of the polymerization reaction is room temperature, and the time is preferably 3-6 h.

[0064] S2, adding the acyl chloride monomer to the polyamic acid solution twice for copolymerization to obtain a polyamide-amic acid solution;

[0065] In the present application, the acyl chloride monomer includes at least one of terephthaloyl chloride, isophthaloyl chloride or 4,4'-biphenyl dichloride, preferably terephthaloyl chloride.

[0066] In the present application, the molar ratio of the diamine monomer, the dianhydride monomer and the acyl chloride monomer is preferably (m+n):m:(1-1.065)×n; wherein m and n are positive integers, and m:n is 9:1-1:9, and more preferably m:n=2:3.

[0067] In the present application, acyl chloride monomers are added by a two-step gradient feeding method to obtain a high molecular weight polymer backbone, and active acyl chloride end groups are precisely constructed at the ends of the molecular chains. Among them, the amount of acyl chloride is slightly excessive relative to the theoretical amount. The first addition of acyl chloride monomers close to the theoretical amount is 99.5% to 99.8% of the theoretical molar number n to obtain a high molecular weight polymer backbone; the second addition of the remaining slightly excessive acyl chloride is added at one time, and the addition amount is 0.5% to 6.5% of the theoretical molar number n, and the active acyl chloride end groups are precisely constructed at the ends of the molecular chains.

[0068] In the present application, the copolymerization reaction is preferably carried out under stirring; the stirring rate is preferably 200-350 rpm. The copolymerization reaction is carried out at room temperature or in an ice bath, and the reaction time is preferably 12-24 hours. The solid content of the polyamide-amic acid solution obtained by the copolymerization reaction is 5-20wt%, preferably 10-15wt%.

[0069] The present application further suppresses the gelation phenomenon through the synergistic regulation strategy of the LiCl dissolution system in S1 and the two-step gradient addition method of the acyl chloride monomer in S2.

[0070] S3, adding a capping agent to the polyamide-amic acid solution to perform a capping reaction, and then adding a dehydrating agent and a catalyst to perform dehydration cyclization to obtain a polyamide-imide solution;

[0071] In the present application, the end-capping agent is monoamino POSS, such as PSS-[3-(2-aminoethyl)amino]propyl-substituted heptaisobutyl or aminopropylheptyl-cage polysilsesquioxane, preferably PSS-[3-(2-aminoethyl)amino]propyl-substituted heptaisobutyl.

[0072] The end-capping reaction is preferably carried out under stirring, and the stirring rate is preferably 200-350 rpm. The end-capping reaction is carried out at room temperature or in an ice bath, and the reaction time is preferably 12-24 hours.

[0073] In this application, through the capping reaction of monoamino POSS, POSS units with a three-dimensional cage structure are successfully introduced at the polymer chain ends. The terminal POSS units limit the molecular chain slip and inhibit the segment relaxation through the steric hindrance effect and the stress-induced deformation mechanism, achieving a synergistic improvement in the light transmittance in the visible light region and the bending life while maintaining the mechanical and thermal properties of the matrix.

[0074] In particular, in this application, through the establishment of quantitative regulation of the amount of POSS capping agent and the material properties, the light transmittance, flexibility, and mechanical strength of the film can be programmed and regulated within a wide range. The amount of the capping agent is (0.005:1 - 0.065:1)×n.

[0075] In this application, the dehydrating agent is acetic anhydride; the catalyst is any one of pyridine, triethylamine, or isoquinoline, preferably anhydrous pyridine. The molar ratio of the dehydrating agent to the catalyst is (1:0.0001 - 2), more preferably 1:0.5; the molar ratio of the dehydrating agent to the dianhydride monomer is (2 - 2.5):1.

[0076] The temperature of the dehydration cyclization is 55 - 65°C, preferably 60°C; the time is 1 - 24 h.

[0077] S4, adding a precipitating agent to the polyamide-imide solution for precipitation, washing and drying the precipitate to obtain a polyamide-imide solid resin;

[0078] In this application, the precipitating agent is selected from methanol, ethanol, deionized water, a mixed solution of methanol and deionized water, or a mixed solution of ethanol and deionized water; the precipitating agent is preferably a mixed solution of deionized water and absolute ethanol or a mixed solution of methanol and deionized water, where the volume ratio of deionized water to absolute ethanol / methanol is (1 - 3):1, preferably 1:1.

[0079] The precipitate is washed with methanol or ethanol.

[0080] S5, dissolving the polyamide-imide solid resin in a polar organic solvent, filtering and degassing to obtain a working solution;

[0081] In this application, it is preferred to prepare the working solution at room temperature, with a stirring rate of 150 - 250 rpm and a stirring time of 6 - 12 h.

[0082] This application has no special limitations on the operations of the filtration and degassing. The technical solutions of filtration and degassing well-known to those skilled in the art can be adopted. The equipment for the filtration is preferably a syringe filter or a sintered filter; the temperature for the degassing is preferably room temperature, and the degassing method is preferably vacuum degassing or static degassing.

[0083] S6. Coat the working solution, then perform stepwise programmed heating, and demold to obtain a bend-resistant transparent polyamide-imide film with a deformable structure.

[0084] In this application, the working solution is filtered and degassed, and then coated on a substrate; the substrate for coating is preferably a glass bottom plate.

[0085] The stepwise programmed heating specifically includes:

[0086] First, heat to 50 - 80 °C and hold for 1 - 3 h, then heat to 150 - 180 °C and hold for 1 - 3 h, and finally heat to 220 - 250 °C and hold for 1 - 2 h.

[0087] The preparation method of this application has the advantages of narrow molecular weight distribution, strong process controllability, and raw material cost advantages (the price of monoamino POSS is only 1 / 5 of that of polyamino type), and has great economic value.

[0088] The CPI / POSS composite film prepared in this application has a larger rebound angle and elastic deformation range, excellent anti-bending performance, and no creases appear after 200,000 folds at a bending radius of 0.5 mm, and is especially suitable for flexible displays.

[0089] The following further illustrates this application through examples.

[0090] In the examples of this application,

[0091] TFMB is 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl

[0092] 6FDA is 2,2`-bis(3,4-dicarboxylic acid) hexafluoropropane dianhydride

[0093] BPDA is 3,3',4,4'-biphenyltetracarboxylic dianhydride

[0094] TPC is terephthaloyl chloride

[0095] IPC is isophthaloyl chloride

[0096] NMP is N-methylpyrrolidone

[0097] DMF is N,N-dimethylformamide

[0098] DMAc is N,N-dimethylacetamide

[0099] Example 1

[0100] This example provides a preparation method of a bend-resistant transparent polyamide-imide film with a deformable structure, including:

[0101] S1. Under the nitrogen protection, 10 mmol of TFMB was dissolved in 40 mL of a mixed solution of DMAc and LiCl (DMAc / 3.5 wt% LiCl) to obtain a diamine solution. 4.0 mmol of 6FDA was added to the above diamine solution, and the mixture was stirred at a speed of 400 rpm for 3 h to obtain a polyamic acid solution.

[0102] S2. 5.988 mmol of TPC (99.8% of the theoretical amount) was first added to the polyamic acid solution, and the mixture was stirred at room temperature for 12 h. Then 0.042 mmol of TPC (0.7% of the theoretical amount) was added. The solid content of the resulting mixture after adding TPC was maintained at 10 wt% by dropping DMAc. After the addition was completed, the reaction was continued to stir at a rate of 250 rpm at room temperature for 6 h to obtain a polyamide-amido acid solution.

[0103] S3. 0.03 mmol of PSS-[3-(2-aminoethyl)amino]propyl-substituted heptaisobutyl was added to the polyamide-amido acid solution, and the reaction was continued to stir at a rate of 250 rpm at room temperature for 12 h. Then 8.0 mmol of acetic anhydride and 4.0 mmol of anhydrous pyridine were added, and the reaction was carried out at 60 °C for 4 h to obtain a polyamide-imide solution.

[0104] S4. A mixed solution of methanol and water (volume ratio of methanol to water is 1:1) was added to the polyamide-imide solution for precipitation, and then washed with deionized water to obtain a white fibrous polyamide-imide resin.

[0105] S5. The fibrous polyamide-imide resin was mixed with DMAc, and the mixture was stirred at a speed of 200 rpm at room temperature for 6 h, then filtered through a sintered filter, and then degassed under vacuum at room temperature to obtain a pure polyamide-imide solution with 0.2% POSS end-capping. Among them, the solid content of the polyamide-imide solution is 10%.

[0106] S6. The polyamide-imide solution with 0.2% POSS end-capping was uniformly coated on a glass substrate through a film coater, and then placed in a vacuum drying oven. It was first kept at 80 °C for 1 h, then at 180 °C for 1 h, and finally at 250 °C for 1 h. After cooling to room temperature, it was taken out and then placed in deionized water. After the film automatically peeled off, it was placed in a vacuum drying oven and dried at 80 °C for 2 h to obtain a bend-resistant transparent polyamide-imide film with a deformable structure, denoted as CPAI-0.2% POSS.

[0107] Example 2

[0108] The difference between Example 2 and Example 1 is that steps S2 and S3 are different from those in Example 1, and the remaining steps are the same as those in Example 1.

[0109] S2, Add 5.988 mmol of TPC (accounting for 99.8%) to the polyamic acid solution for the first time, and stir at room temperature for 12 h; add 0.1995 mmol of TPC (accounting for 3.325%) for the second time, and maintain the solid content of the resulting mixture after adding TPC at 10 wt% by dropping DMAc. After the feeding is completed, continue to stir and react at a rate of 250 rpm at room temperature for 6 h to obtain a polyamide-amic acid solution;

[0110] S3, Add 0.1875 mmol of PSS-[3-(2-aminoethyl)amino]propyl-substituted heptaisobutyl to the polyamide-amic acid solution, and continue to stir and react at a rate of 250 rpm at room temperature for 12 h; then add 8.0 mmol of acetic anhydride and 4.0 mmol of anhydrous pyridine, and react at 60 °C for 4 h to obtain a polyamide-imide solution.

[0111] The bend-resistant transparent polyamide-imide film with a deformable structure prepared in Example 2 is denoted as CPAI-0.5% POSS.

[0112] Example 3

[0113] The difference between Example 3 and Example 1 is that steps S2 and S3 are different from those in Example 1, and the remaining steps are the same as those in Example 1.

[0114] S2, Add 5.988 mmol of TPC (accounting for 99.8%) to the polyamic acid solution for the first time, and stir at room temperature for 12 h; add 0.387 mmol of TPC (accounting for 6.45%) for the second time, and maintain the solid content of the resulting mixture after adding TPC at 10 wt% by dropping DMAc. After the feeding is completed, continue to stir and react at a rate of 250 rpm at room temperature for 6 h to obtain a polyamide-amic acid solution;

[0115] S3, Add 0.375 mmol of PSS-[3-(2-aminoethyl)amino]propyl-substituted heptaisobutyl to the polyamide-amic acid solution, and continue to stir and react at a rate of 250 rpm at room temperature for 12 h; then add 8.0 mmol of acetic anhydride (0.81680 g, 8.0 mmol) and 4.0 mmol of anhydrous pyridine, and react at 60 °C for 4 h to obtain a polyamide-imide solution.

[0116] The bend-resistant transparent polyamide-imide film with a deformable structure prepared in Example 3 is denoted as CPAI-1% POSS.

[0117] Comparative Example 1

[0118] S1. Under the protection of nitrogen, dissolve 10 mmol of TFMB in 20 mL of DMAc to obtain a diamine solution; add 10.0 mmol of 6FDA to the above diamine solution and mix and stir at a speed of 400 rpm for 3 h to obtain a polyamic acid solution.

[0119] S2. Add 20 mmol of acetic anhydride and 10 mmol of anhydrous pyridine to the polyamic acid solution and react at 60 °C for 4 h to obtain a polyimide solution;

[0120] S3. Add a mixed solution of methanol and water (the volume ratio of methanol to water is 1:1) to the polyimide solution for precipitation, and then wash with deionized water to obtain a white fibrous polyimide resin;

[0121] S4. Mix the fibrous polyimide resin with DMAc and mix and stir at a speed of 200 rpm at room temperature for 6 hours, filter it through a sintered filter, and then carry out vacuum degassing at room temperature to obtain a polyimide solution with a solid content of 10%;

[0122] S5. Uniformly coat the polyimide solution on a glass bottom plate through a film coater, then place it in a vacuum drying oven, keep it at 80 °C for 1 h first, then keep it at 180 °C for 1 h, and finally keep it at 250 °C for 1 h. After cooling to room temperature, take it out, then place it in deionized water, wait for the film to fall off automatically, and place it in a vacuum drying oven at 80 °C for drying for 2 h to obtain a polyimide film, denoted as CPI.

[0123] Comparative Example 2

[0124] S1. The same as in Example 1;

[0125] S2. Add 6 mmol of TPC to the polyamic acid solution at one time, and keep the solid content of the obtained mixed solution at 10 wt% after adding TPC by dropping DMAc. After the feeding is completed, continue to stir and react at a rate of 250 rpm at room temperature for 6 h to obtain a polyamide-amido acid solution;

[0126] S3. Add 8 mmol of acetic anhydride and 4 mmol of anhydrous pyridine to the polyamide-amido acid solution and react at 60 °C for 4 h to obtain a polyamide-imide solution;

[0127] S4. Add a mixed solution of methanol and water (the volume ratio of methanol to water is 1:1) to the polyamide-imide solution for precipitation, and then wash with deionized water to obtain a white fibrous polyamide-imide resin;

[0128] S5. Mix the fibrous polyamide-imide resin with DMAc, mix and stir at a speed of 200 rpm for 6 hours at room temperature, filter it through a sintered filter, and then carry out vacuum degassing at room temperature to obtain a pure polyamide-imide resin solution. The solid content of the polyamide-imide solution is 10%.

[0129] S5. Uniformly coat the polyamide-imide resin solution on a glass substrate through a film coater, then place it in a vacuum drying oven, keep it at 80 °C for 1 h first, then keep it at 180 °C for 1 h, and finally keep it at 250 °C for 1 h. Take it out after cooling to room temperature, then place it in deionized water, wait for the film to fall off automatically, and place it in a vacuum drying oven at 80 °C for drying for 2 h to obtain a polyamide-imide film, denoted as CPAI.

[0130] Figure 1 are the physical pictures of the films of Examples 1-3 and Comparative Examples 1-2. From Figure 1 it can be seen that the above films are all colorless and transparent. The optical properties of the films of Examples 1-3 and Comparative Examples 1-2 were tested, and the test results are shown in Table 1.

[0131] Table 1 Test results of the optical properties of the films of Examples 1-3 and Comparative Examples 1-2

[0132] Embodiment CPIs <![CDATA[λ Cut-off > T400 / ％ T450 / ％ T550 / ％ YI <![CDATA[T d5 > Comparative Example 1 CPI 355 77.53 88.15 89.58 1.81 421 Comparative Example 2 CPAI 354 83.36 88.18 89.52 1.95 458 Example 1 CPAI - 0.2% POSS 354 80.84 88.37 90.34 1.53 461 Example 2 CPAI - 0.5% POSS 354 84.17 89.03 90.38 1.52 460 Example 3 CPAI - 1% POSS 354 84.7 89.12 90.42 1.55 462

[0133] As can be seen from Table 1, the above films all have good optical properties, and their yellowness values are all less than 2. In Comparative Example 2, an amide bond was introduced compared with Comparative Example 1, which did not have a great impact on the optical properties of the film; compared with Comparative Examples 1-2, Examples 1-3 have higher light transmittance, and the introduction of POSS brings greater steric hindrance, which improves the light transmittance.

[0134] The mechanical properties of the films of Examples 1-3 and Comparative Examples 1-2 were tested, and the test results are shown in Table 2.

[0135] Table 2 Test results of the mechanical properties of the films of Examples 1-3 and Comparative Examples 1-2

[0136]

[0137] As can be seen from Table 2, compared with Comparative Example 2 and Comparative Example 1, by introducing specific amide bond groups to form hydrogen bond interactions, the hydrogen bond interactions are beneficial for the formation of local regular arrangements of molecular chains, thereby effectively improving the mechanical properties of the CPI film. From the test results of Examples 1-3, it can be seen that by introducing a small amount of soluble monoamino POSS in the form of molecular chain capping, the purpose of restricting the slip of molecular chains due to the large steric hindrance between molecular chains can be achieved, and at the same time, the relaxation of chain segments can be inhibited to improve the mechanical properties of the film. The introduction of POSS molecules can improve the tensile strength / modulus and elongation at break of the film to a certain extent, however, if it is too high, it will lead to the transition of the film from toughness to brittleness.

[0138] The bending properties of the films of Examples 1-3 and Comparative Examples 1-2 were tested. By placing the film in a fixed fixture and placing it in a vacuum oven at 80 °C for 12 hours to simulate plastic accumulation, the static bending property diagram is as Figure 2 shown. From Figure 2 it can be seen that the large steric hindrance restricts the chain movement at the end of the molecular chain, resulting in high tensile strength, and the deformable large steric groups provide a space for rebound. The introduction of POSS molecules results in a larger rebound angle in static bending.

[0139] Figure 3 SEM images of the bending parts of the films of Examples 1-3 and Comparative Examples 1-2 after bending 200,000 times at a bending radius of 0.5 mm. From Figure 3 it can be seen that at a bending radius of 0.5 mm, after folding 200,000 times, the films of Examples 1-3 did not show creases, while the films of Comparative Examples 1-2 showed obvious creases after folding. The test results show that by introducing POSS capping, the large steric hindrance at the end of the molecular chain has a deformable rebound space, which can dissipate the energy of stress for the plastic deformation during the bending process of the film, and can effectively improve the bending properties of the film.

[0140] From the above test data, it can be seen that in this application, by introducing a cage-type structure POSS monomer containing Si-O at the end of the molecular chain with intermolecular hydrogen bond interactions, and utilizing the large steric hindrance of POSS itself and the deformable structure under stress, a CPI / POSS composite film with both high transparency and excellent bending resistance is obtained. On the premise of ensuring a high transmittance (T550>88%), by introducing a small amount of soluble monoamino POSS in the form of molecular chain capping, the purpose of restricting the slip of molecular chains due to the large steric hindrance between molecular chains can be achieved, and at the same time, the relaxation of chain segments can be inhibited to improve the mechanical properties of the film. At the same time, the existence of the deformable large steric hindrance makes the CPI / POSS composite film have a larger rebound angle and elastic deformation range, expanding the bending deformation range of the film. After folding 200,000 times at a bending radius of 0.5 mm, the film did not show creases.

[0141] Although the present application has been described in detail in this specification with general descriptions and specific embodiments, modifications or improvements can be made to it based on the present application, which will be obvious to those skilled in the art. Therefore, these modifications or improvements made without departing from the spirit of the present application all fall within the scope of protection claimed by the present application.

Claims

1. A bend-resistant transparent polyamide-imide film with a deformable structure, characterized in that, Its chemical structure is shown in formula (I): Wherein, R is isobutyl, and R1 is -CH2- or -NH-; m and n are positive integers, and m:n is 9:1 to 1:

9.

2. The preparation method of the bend-resistant transparent polyamide-imide film with a deformable structure according to claim 1, characterized in that, It includes: S1. Under a nitrogen atmosphere, dissolve the diamine monomer in a polar organic solvent containing a co-solvent to obtain a diamine solution; Add a dianhydride monomer to the diamine solution for a polymerization reaction to obtain a polyamic acid solution; S2. Add the acyl chloride monomer to the polyamic acid solution in two portions for a copolymerization reaction to obtain a polyamide-amic acid solution; S3. Add a capping agent to the polyamide-amic acid solution for a capping reaction, and then add a dehydrating agent and a catalyst for dehydration cyclization to obtain a polyamide-imide solution; S4. Add a precipitating agent to the polyamide-imide solution for precipitation, wash and dry the precipitate to obtain a polyamide-imide solid resin; S5. Dissolve the polyamide-imide solid resin in a polar organic solvent, filter and defoam to obtain a working solution; S6. Coat the working solution, and then perform stepwise programmed heating, and demold to obtain a bend-resistant transparent polyamide-imide film with a deformable structure.

3. The preparation method according to claim 2, characterized in that, The capping agent is PSS-[3-(2-aminoethyl)amino]propyl-substituted heptaisobutyl or aminopropylheptyl-cage-like polyhedral oligomeric silsesquioxane; The dehydrating agent is acetic anhydride; The catalyst is pyridine, triethylamine or isoquinoline; The precipitating agent is a mixture of deionized water and anhydrous ethanol / methanol with a volume ratio of (1 to 3):

1.

4. The preparation method according to claim 2, characterized in that, The diamine monomer is 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl; The dianhydride monomer includes at least one of 2,2`-bis(3,4-dicarboxylic acid)hexafluoropropane dianhydride or 3,3',4,4'-biphenyltetracarboxylic dianhydride; The acyl chloride monomer includes at least one of terephthaloyl chloride, isophthaloyl chloride or 4,4'-biphenyldicarbonyl chloride.

5. The preparation method according to claim 2, wherein The co-solvent is LiCl, and its mass ratio to the polar organic solvent is 0.035:1; The polar organic solvent includes at least one of N-methylpyrrolidone, N,N-dimethylformamide or N,N-dimethylacetamide, and its dosage accounts for 80 to 90 wt% of the total amount of the polyamic acid solution.

6. The preparation method according to claim 2, wherein The molar ratio of the diamine monomer, dianhydride monomer and acyl chloride monomer is (m + n):m:(1 to 1.065)×n; Wherein, m and n are positive integers, and m:n is 9:1 to 1:

9.

7. The preparation method according to claim 6, characterized in that, The first addition amount of the acyl chloride monomer is n×(99.5% to 99.8%), and the second addition amount is n×(0.5% to 6.5%).

8. The preparation method according to claim 6, characterized in that, The dosage of the capping agent is (0.005:1 to 0.065:1)×n; The molar ratio of the dehydrating agent to the dianhydride monomer is (2 to 2.5):1; The molar ratio of the dehydrating agent and the catalyst is (1:0.001 to 2).

9. The preparation method according to claim 2, wherein, The temperature of the dehydration cyclization is 55 to 65 °C, and the time is 1 to 24 h; The stepwise programmed heating specifically includes: First, heat to 50 to 80 °C and keep warm for 1 to 3 h, then heat to 150 to 180 °C and keep warm for 1 to 3 h, and finally heat to 220 to 250 °C and keep warm for 1 to 2 h.

10. Use of the bend-resistant transparent polyamide-imide film with a deformable structure according to claim 1 or the bend-resistant transparent polyamide-imide film with a deformable structure prepared by the preparation method according to any one of claims 2 to 9 in a flexible display.

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