Flexible heterostructure polyimide film and preparation method thereof

Abstract

The application provides a flexible special-shaped structure polyimide film and a preparation method thereof, and belongs to the technical field of polymer film materials. The preparation method comprises the following steps: S1, reacting 4,4'-diamino diphenyl ether and pyromellitic anhydride to obtain a benzene type polyamide acid solution; S2, reacting 4,4'-diamino diphenyl ether and 3,3',4,4'-biphenyl tetracarboxylic dianhydride to obtain a biphenyl type polyamide acid solution; S3, mixing the benzene type polyamide acid solution and the biphenyl type polyamide acid solution to obtain a blended polyamide acid solution; and S4, performing desolvation curing and thermal imidization on the blended polyamide acid solution to obtain the flexible special-shaped structure polyimide film. The preparation method provided by the application is simple in process, and the prepared polyimide film has excellent temperature resistance and flexibility.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer film materials, and in particular relates to a flexible special-shaped polyimide film and a preparation method thereof. Background Art

[0002] Polyimide film is a new type of organic polymer film. Due to its excellent temperature resistance, mechanical properties, electrical properties and chemical stability, it has been widely used in various fields. However, the polyimide film prepared by existing preparation methods is difficult to achieve both temperature resistance and flexibility, which limits its application in special-shaped structures.

[0003] Therefore, there is an urgent need to provide a method for preparing polyimide to prepare polyimide having excellent temperature resistance and flexibility to meet different needs and broaden the application range of polyimide. Summary of the Invention

[0004] In response to one or more technical problems existing in the prior art, the present invention provides a flexible, special-shaped polyimide film and a preparation method thereof. The preparation method provided by the present invention has a simple process, and the prepared polyimide film has excellent temperature resistance and flexibility. The size and shape can be designed and selected according to actual conditions, thereby broadening the application scenarios and scope of the polyimide film.

[0005] In a first aspect, the present invention provides a method for preparing a flexible special-shaped polyimide film, the method comprising the following steps:

[0006] S1. The 4,4'-diaminodiphenyl ether and pyromellitic anhydride are reacted to obtain a pyromellitic polyamic acid solution;

[0007] S2. The 4,4'-diaminodiphenyl ether and 3,3',4,4'-biphenyltetracarboxylic dianhydride are reacted to obtain a biphenyl-type polyamic acid solution;

[0008] S3. The pyrophenyl polyamic acid solution and the biphenyl polyamic acid solution are mixed to obtain a blended polyamic acid solution;

[0009] S4. The blended polyamic acid solution is subjected to desolventizing, solidification, and thermal imidization to obtain the flexible special-shaped polyimide film.

[0010] Preferably, under nitrogen protection, 4,4'-diaminodiphenyl ether, pyromellitic anhydride and N,N-dimethylacetamide are mixed and reacted at 5-10° C. to obtain the pyromellitic polyamic acid solution.

[0011] Preferably, in step S1, the molar ratio of 4,4'-diaminodiphenyl ether to pyromellitic anhydride is (0.98-1):1; and the solid content of the pyromellitic polyamic acid solution is 10-15 wt%.

[0012] Preferably, under nitrogen protection, 4,4'-diaminodiphenyl ether, 3,3',4,4'-biphenyltetracarboxylic dianhydride and N,N-dimethylacetamide are mixed and reacted at 5-10° C. to obtain the biphenyl type polyamic acid solution.

[0013] Preferably, in step S2, the molar ratio of 4,4'-diaminodiphenyl ether to 3,3',4,4'-biphenyltetracarboxylic dianhydride is (0.98-1):1; and the solid content of the biphenyl type polyamic acid solution is 10-15 wt%.

[0014] Preferably, under nitrogen protection, at 5-10° C., the bisphenyl polyamic acid solution and the biphenyl polyamic acid solution are mixed to obtain a blended polyamic acid solution; the molar ratio of the bisphenyl polyamic acid in the bisphenyl polyamic acid solution to the biphenyl polyamic acid in the biphenyl polyamic acid solution is 3:7-7:3.

[0015] Preferably, the desolventizing curing includes six stages: the first stage: keeping warm at 80°C for 15 minutes, the second stage: keeping warm at 90°C for 15 minutes, the third stage: keeping warm at 100°C for 15 minutes, the fourth stage: keeping warm at 104-111°C for 30 minutes, the fifth stage: keeping warm at 117-119°C for 2 hours, and the sixth stage: keeping warm at 119-126°C for 30 minutes. The heating rate of the whole process is 2°C / min.

[0016] Preferably, before the desolventizing and curing, the method further comprises placing the blended polyamic acid solution in a vacuum oven for defoaming treatment.

[0017] Preferably, the temperature of the thermal imidization is 340-360°C.

[0018] In a second aspect, the present invention provides a flexible special-shaped polyimide film, which is prepared by the preparation method described in the first aspect.

[0019] Compared with the prior art, the present invention has at least the following beneficial effects:

[0020] The present invention obtains a blended polyamic acid solution with excellent processing performance by mixing a homophenyl polyamic acid solution and a biphenyl polyamic acid solution, and then forms a polyimide film with a special structure having excellent temperature resistance and flexibility through desolvation, solidification and thermal imidization. The preparation process of the polyimide film of the present invention is simple, and the size and shape can be designed and selected according to actual conditions, thereby broadening the application scenarios and scope of the polyimide film. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0022] Figure 1 This is a physical picture of the special-shaped polyimide film provided in Example 2 of the present invention;

[0023] Figure 2 A physical image showing the flexibility of the special-shaped polyimide film provided in Example 2 of the present invention;

[0024] Figure 3 Physical pictures of polyimide films provided for Example 2 (left) and Comparative Example 4 (right) of the present invention;

[0025] Figure 4 The tan δ curves of the polyimides provided in Examples 1-3 of the present invention and Comparative Examples 1-2 are shown. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, not all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0027] In a first aspect, the present invention provides a method for preparing a flexible special-shaped polyimide film, the method comprising the following steps:

[0028] S1. The 4,4'-diaminodiphenyl ether and pyromellitic anhydride are reacted to obtain a pyromellitic polyamic acid solution;

[0029] S2. The 4,4'-diaminodiphenyl ether and 3,3',4,4'-biphenyltetracarboxylic dianhydride are reacted to obtain a biphenyl-type polyamic acid solution;

[0030] S3. The pyrophenyl polyamic acid solution and the biphenyl polyamic acid solution are mixed to obtain a blended polyamic acid solution;

[0031] S4. The blended polyamic acid solution is subjected to desolventizing, solidification, and thermal imidization to obtain the flexible special-shaped polyimide film.

[0032] The present invention obtains a blended polyamic acid solution with excellent processing performance by mixing a homophenyl polyamic acid solution and a biphenyl polyamic acid solution, and then forms a polyimide film with a special structure having excellent temperature resistance and flexibility through desolvation, solidification and thermal imidization. The preparation process of the polyimide film of the present invention is simple, and the size and shape can be designed and selected according to actual conditions, thereby broadening the application scenarios and scope of the polyimide film.

[0033] In order to ensure that the blended polyamic acid solution has better processability, the present invention determines the temperature range for synthesizing PAA-1 and PAA-2 based on the viscosity of the homophenyl polyamic acid solution (PAA-1) and the biphenyl polyamic acid solution (PAA-2) and the flexibility of the obtained polyimide film; in order to determine an optimal synthesis temperature range suitable for both PAA-1 and PAA-2, the inventors conducted a series of investigations: (1) The viscosities of PAA-1 and PAA-2 synthesized within different temperature ranges were selected for investigation. The results showed that the viscosities of PAA-1 and PAA-2 synthesized at 5-10°C were both low and had good processability; among them, the viscosity of PAA-1 was 768-2894 cP, and the viscosity of PAA-1 was the lowest at 10°C; the viscosity of PAA-2 was 334-1110 cP , and the viscosity of PAA-2 is the lowest at 10℃; (2) In order to examine the effect of the viscosity of polyamic acid solution on the mechanical properties of polyimide film, PAA-1 and PAA-2 synthesized in the range of 5-10℃ were prepared into phenylene polyimide film (PI-1 film) and biphenyl polyimide film (PI-2 film), and their properties were measured; it was found that the tensile strength and elastic modulus of the two polyimide films were at a high level, mainly because the molecular chains of both phenylene polyimide and biphenyl polyimide are relatively rigid and have high regularity, and there are strong intermolecular forces; the elongation at break of PI-1 film and PI-2 film prepared at 5-10℃ are both high, the elongation at break of PI-1 film can reach up to 18.9%, and the elongation at break of PI-2 film can reach up to 28.6%. In summary, in order to ensure low viscosities of the synthesized PAA-1 and PAA-2, and taking into account the mechanical properties of the resulting PI-1 and PI-2 films, the present invention selects the synthesis temperature of the homophenyl polyamic acid solution and the biphenyl polyamic acid solution to be 5-10°C, more preferably 10°C.

[0034] According to some preferred embodiments, under nitrogen protection, 4,4'-diaminodiphenyl ether (ODA), pyromellitic anhydride (PMAD) and N,N-dimethylacetamide (DMAc) are mixed and reacted at 5-10°C (for example, 5°C, 6°C, 7°C, 8°C, 9°C or 10°C) to obtain the pyromellitic polyamic acid solution.

[0035] In some specific embodiments, 4,4'-diaminodiphenyl ether is dissolved in N,N-dimethylacetamide, and under nitrogen protection, pyromellitic anhydride is added with stirring at a speed of 350 r / min, and the mixture is reacted at 5-10°C for 20-24 hours to obtain a transparent and viscous pyromellitic polyamic acid solution.

[0036] According to some preferred embodiments, in step S1, 4,4'-diaminodiphenyl ether (ODA) and pyromellitic anhydride ( PMAD ) The molar ratio is (0.98-1):1 (for example, it can be 0.98:1, 0.99:1 or 1:1); the solid content of the isophthalic polyamic acid solution is 10-15wt% (for example, it can be 10wt%, 11wt%, 12wt%, 13wt%, 14wt% or 15wt%).

[0037] In the present invention, N,N-dimethylacetamide mainly plays the role of dispersing and dissolving 4,4'-diaminodiphenyl ether (ODA) and pyromellitic anhydride. ( PMAD ) The effect of the reaction makes the reaction more complete, and a pyrophenyl polyamic acid solution with uniform performance is obtained; there is no special limitation on the amount of N,N-dimethylacetamide used, as long as the solid content of the pyrophenyl polyamic acid solution is 10 to 15 wt%.

[0038] According to some preferred embodiments, under nitrogen protection, 4,4'-diaminodiphenyl ether (ODA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) and N,N-dimethylacetamide are mixed and reacted at 5-10°C (for example, 5°C, 6°C, 7°C, 8°C, 9°C or 10°C) to obtain the biphenyl type polyamic acid solution.

[0039] In some specific embodiments, 4,4'-diaminodiphenyl ether is dissolved in N,N-dimethylacetamide, and under nitrogen protection, 3,3',4,4'-biphenyltetracarboxylic dianhydride is added with stirring at a speed of 350 r / min, and the mixture is reacted at 5-10° C. for 20-24 hours to obtain a transparent and viscous biphenyl polyamic acid solution.

[0040] The present invention controls the synthesis temperature of the bisphenyl polyamic acid solution and the biphenyl polyamic acid solution at 5-10° C., thereby ensuring that the obtained bisphenyl polyamic acid solution and the biphenyl polyamic acid solution have lower viscosity, stronger molecular chain mobility, better orientation during the film formation process, and improved processability of the blended polyamic acid solution, thereby obtaining a polyimide film with better temperature resistance and mechanical properties.

[0041] According to some preferred embodiments, in step S2, the molar ratio of 4,4'-diaminodiphenyl ether (ODA) and 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) is (0.98-1):1 (for example, it can be 0.98:1, 0.99:1 or 1:1); the solid content of the biphenyl type polyamic acid solution is 10-15wt% (for example, it can be 10wt%, 11wt%, 12wt%, 13wt%, 14wt% or 15wt%).

[0042] In the present invention, N,N-dimethylacetamide mainly plays the role of dispersing and dissolving 4,4'-diaminodiphenyl ether (ODA) and 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), so that the reaction is more complete and a biphenyl-type polyamic acid solution with uniform properties is obtained. There is no particular limitation on the amount of N,N-dimethylacetamide used, as long as the solid content of the homogeneous biphenyl-type polyamic acid solution is 10 to 15wt%.

[0043] According to some preferred embodiments, under nitrogen protection, the bisphenyl type polyamic acid solution and the biphenyl type polyamic acid solution are mixed at 5 to 10° C. (for example, 5° C., 6° C., 7° C., 8° C., 9° C. or 10° C.) to obtain a blended polyamic acid solution; the molar ratio of the bisphenyl type polyamic acid in the bisphenyl type polyamic acid solution to the biphenyl type polyamic acid in the biphenyl type polyamic acid solution is 3:7 to 7:3.

[0044] The present invention is based on the fact that the homophenyl polyamic acid solution and the biphenyl polyamic acid solution have a low viscosity at 5-10°C. Mixing at this temperature can not only ensure that the obtained blended polyamic acid solution has a low viscosity and a stronger molecular chain movement ability, thereby improving the processability of the blended polyamic acid solution and being used for the molding of special-shaped polyimide films, but also ensure that the blended polyamic acid solution can be better oriented during the film-forming process, thereby obtaining a flexible special-shaped structure film with excellent mechanical properties and good temperature resistance, thereby broadening the application scenarios and scope of the polyimide film; if the temperature is too low, the viscosity of the blended polyamic acid solution is too high, the fluidity is poor, the processability is poor, and it is not conducive to degassing, and it is impossible to mold a structure and A polyimide film with uniform performance; in addition, the molar ratio of the isophenyl polyamic acid in the isophenyl polyamic acid solution to the biphenyl polyamic acid in the biphenyl polyamic acid solution is controlled within the above range, which can ensure that the obtained blended polyamic acid solution has good processability, and the obtained polyimide film has better flexibility and temperature resistance; within this range, it can be adjusted according to actual needs. If the scene requires higher temperature resistance, a blended polyamic acid solution with a higher proportion of isophenyl polyamic acid solution (the above 7:3) can be selected. If the scene requires higher flexibility, a blended polyamic acid solution with a higher proportion of biphenyl polyamic acid solution (the above 3:7) can be appropriately selected.

[0045] According to some preferred embodiments, the desolventizing curing includes six stages: the first stage: keeping warm at 80°C for 15 minutes, the second stage: keeping warm at 90°C for 15 minutes, the third stage: keeping warm at 100°C for 15 minutes, the fourth stage: keeping warm at 104-111°C for 30 minutes, the fifth stage: keeping warm at 117-119°C for 2 hours, and the sixth stage: keeping warm at 119-126°C for 30 minutes. The heating rate of the whole process is 2°C / min.

[0046] The desolventizing and curing process of the blended polyamic acid solution of the present invention is determined based on the starting curing temperature, peak curing temperature and ending curing temperature of the homophenyl polyamic acid solution and the biphenyl polyamic acid solution; in this way, the temperature and time of each stage in the desolventizing and curing process can be more accurately grasped, and the curing cycle is shortened. The temperature of the entire desolventizing and curing process is low (the maximum temperature does not exceed 130°C) and the time is short (does not exceed 4 hours), which greatly simplifies the curing process and improves the curing efficiency; it should be noted that the fourth stage is the starting curing stage, the fifth stage is the peak curing stage, and the sixth stage is the ending curing stage. In order to ensure the curing effect, the holding time of the peak curing stage is longer than that of other stages.

[0047] The blended polyamic acid solution of the present invention adopts the above-mentioned desolventizing and curing procedure to ensure the evaporation of the solvent in the blended polyamic acid solution without affecting the morphology of the resin, and finally obtains a polyimide with uniform performance and structure; if the temperature is too high, the obtained film will shrink; the present invention places the blended polyamic acid solution in a mold for desolventizing and curing, and thermal imidization molding to obtain a polyimide film; the present invention does not specifically limit the shape and size of the mold, and can be designed and selected according to the specific application scenario.

[0048] The present application determines the desolvation curing procedure based on the initial curing temperature, peak curing temperature and terminal curing temperature of the uniform benzene type polyamic acid solution (PAA-1) and the biphenyl type polyamic acid solution (PAA-2) obtained by extrapolation; the specific determination process is as follows: in order to determine the optimal procedure temperature of desolvation curing, the inventors use differential scanning calorimetry (DSC) to analyze PAA-1 and PAA-2 for thermal analysis to determine the curing process; in order to eliminate the influence of the constant heating rate method of thermal analysis, the temperature at the heating rate β = 0 is obtained by extrapolation, so as to determine the optimal curing process; the initial curing temperature of PAA-1 extrapolated to β = 0 is 104℃, the peak curing temperature is 119℃, and the terminal curing temperature is 126℃; the initial curing temperature of PAA-2 extrapolated to β = 0 is 111℃, the peak curing temperature is 117℃, and the terminal curing temperature is 119℃; considering that the polyamic acid solution system needs to evaporate the solvent during curing, in order to ensure the morphology of the resin, the curing process should be relatively slow, based on this, a certain holding step is given, the curing process of PAA-1 system is: the first stage: 80℃ for 15min, the second stage: 90℃ for 15min, the third stage: 100℃ for 15min, the fourth stage: 104℃ for 30min, the fifth stage: 119℃ for 2h, the sixth stage: 126℃ for 30min, the heating rate of the whole process is 2℃ / min; the curing process of PAA-2 system is: the first stage: 80℃ for 15min, the second stage: 90℃ for 15min, the third stage: 100℃ for 15min, the fourth stage: 111℃ for 30min, the fifth stage: 117℃ for 2h, the sixth stage: 119℃ for 30min, the heating rate of the whole process is 2℃ / min; based on this, in order to ensure the evaporation of the solvent of the blended polyamic acid solution during the desolvation curing process without affecting the morphology of the resin, a certain holding step is given, the desolvation curing procedure of the blended polyamic acid solution selected by the present application includes six stages, the first stage: 80℃ for 15min, the second stage: 90℃ for 15min, the third stage: 100℃ for 15min, the fourth stage: 104-111℃ for 30min, the fifth stage: 117-119℃ for 2h, the sixth stage: 119-126℃ for 30min, the heating rate of the whole process is 2℃ / min.

[0049] According to some preferred embodiments, before the desolvation curing, a step of placing the blended polyamic acid solution in a vacuum oven for defoaming treatment is further included.

[0050] The present invention places the blended polyamic acid solution in a vacuum oven for defoaming treatment before desolventizing and curing to remove bubbles in the blended polyamic acid solution, so as to obtain a resin with uniform structure and performance after desolventizing and curing.

[0051] According to some preferred embodiments, the temperature of the thermal imidization is 340-360° C. (for example, 340° C., 345° C., 350° C., 355° C., or 360° C.).

[0052] The thermal imidization temperature of the present invention is determined based on the imidization temperature of the homophenyl type polyamic acid solution (PAA-1) and the biphenyl type polyamic acid solution (PAA-2); in order to determine the optimal thermal imidization temperature of the blended polyamic acid solution, the inventors used infrared analysis to analyze the imidization degree of the polyimide obtained from PAA-1 and PAA-2 at different thermal imidization temperatures; according to 734 cm -1 and 1500cm -1 The imidization rate was calculated by the peak area of ​​​​the imidization rate, and the imidization rate was calculated using the following formula;

[0053] Here, ID is the imidization rate (%) of PI, S is the peak area, and T is the imidization temperature (°C).

[0054] The imidization degree at 360°C is set as 100%. The calculation results show that PAA-1 is completely imidized at 340°C, and PAA-2 is completely imidized at 360°C. Based on this, in order to ensure the imidization of the blended polyamic acid, the thermal imidization temperature of the blended polyamic acid solution of the present invention is determined to be 340-360°C. If the temperature is too low, the imidization rate of the blended polyamic acid is low. If the temperature is too high, the blended polyamic acid is excessively cross-linked, and carbonization and shrinkage will occur on the surface of the obtained polyimide film, affecting the performance of the polyimide film.

[0055] In a second aspect, the present invention provides a flexible special-shaped polyimide film, which is prepared by the preparation method described in the first aspect.

[0056] The polyimide film provided by the present invention has a glass transition temperature higher than 300° C. and an elongation at break greater than 20%. It can be formed according to actual needs to obtain a special-shaped polyimide film with excellent temperature resistance and flexibility.

[0057] In order to more clearly illustrate the technical solutions and advantages of the present invention, the present invention is further described below with reference to embodiments.

[0058] The materials and reagents in the present invention can be purchased directly from the market or synthesized by themselves, and there is no limitation on the specific models.

[0059] Example 1

[0060] S1. 4,4'-diaminodiphenyl ether was added to N,N-dimethylacetamide and stirred until completely dissolved. Then, under nitrogen protection, pyromellitic anhydride was added with stirring at a speed of 350 r / min. The mixture was reacted at 10°C for 24 hours to obtain a transparent and viscous pyromellitic polyamic acid solution; wherein the molar ratio of 4,4'-diaminodiphenyl ether to pyromellitic anhydride was 1:1;

[0061] S2. 4,4'-diaminodiphenyl ether was added to N,N-dimethylacetamide and stirred until completely dissolved. Then, under nitrogen protection, 3,3',4,4'-biphenyltetracarboxylic dianhydride was added with stirring at a speed of 350 r / min, and the mixture was reacted at 10°C for 24 hours to obtain a transparent viscous biphenyl polyamic acid solution; wherein the molar ratio of 4,4'-diaminodiphenyl ether to 3,3',4,4'-biphenyltetracarboxylic dianhydride was 1:1;

[0062] S3. The bisphenyl polyamic acid solution and the biphenyl polyamic acid solution were mixed and mechanically stirred under nitrogen at 10 ° C for 6 h to obtain a blended polyamic acid solution; wherein the molar ratio of the bisphenyl polyamic acid in the bisphenyl polyamic acid solution to the biphenyl polyamic acid in the biphenyl polyamic acid solution was 3:7;

[0063] S4. The blended polyamic acid solution is transferred to a vacuum oven for defoaming for 10 minutes, and then the defoamed polyamic acid solution is placed in a mold for desolventizing and curing. The desolventizing and curing procedure includes six stages: the first stage: keeping warm at 80°C for 15 minutes, the second stage: keeping warm at 90°C for 15 minutes, the third stage: keeping warm at 100°C for 15 minutes, the fourth stage: keeping warm at 107°C for 30 minutes, the fifth stage: keeping warm at 117°C for 2 hours, and the sixth stage: keeping warm at 123°C for 30 minutes. The heating rate of the whole process is 2°C / min; finally, the desolventizing and curing polyamic acid solution is transferred to a muffle furnace and thermally imidized at 350°C. The mold is removed to obtain a polyimide film.

[0064] The viscosity of the isophenyl polyamic acid solution in Example 1 is 768 cP, and the viscosity of the biphenyl polyamic acid solution is 334 cP. They have low viscosity, good fluidity, and strong processability. The obtained polyimide film has an elongation at break of 31.6%, a tensile strength of 124.7 MPa, and a glass transition temperature of 309°C.

[0065] Example 2

[0066] S1. 4,4'-diaminodiphenyl ether was added to N,N-dimethylacetamide, stirred until completely dissolved, then under the protection of nitrogen, stirring at a speed of 350 r / min, pyromellitic dianhydride was added, and reacted at 10 °C for 24 h to obtain a transparent viscous pyromellitic polyamic acid solution; wherein the molar ratio of 4,4'-diaminodiphenyl ether and pyromellitic dianhydride was 1:1;

[0067] S2. 4,4'-diaminodiphenyl ether was added to N,N-dimethylacetamide, stirred until completely dissolved, then under the protection of nitrogen, stirring at a speed of 350 r / min, 3,3',4,4'-biphenyl tetracarboxylic dianhydride was added, and reacted at 10 °C for 24 h to obtain a transparent viscous biphenyl polyamic acid solution; wherein the molar ratio of 4,4'-diaminodiphenyl ether and 3,3',4,4'-biphenyl tetracarboxylic dianhydride was 1:1;

[0068] S3. The pyromellitic polyamic acid solution and the biphenyl polyamic acid solution were mixed, and under the protection of nitrogen, mechanical stirring was carried out at 10 °C for 6 h to obtain a blended polyamic acid solution; wherein the molar ratio of the pyromellitic polyamic acid in the pyromellitic polyamic acid solution to the biphenyl polyamic acid in the biphenyl polyamic acid solution was 5:5;

[0069] S4. The blended polyamic acid solution was transferred to a vacuum oven for 10 min of defoaming, then the defoamed polyamic acid solution was placed in a mold for desolvation curing, the desolvation curing program included six stages, the first stage: 80 °C for 15 min, the second stage: 90 °C for 15 min, the third stage: 100 °C for 15 min, the fourth stage: 107 °C for 30 min, the fifth stage: 117 °C for 2 h, the sixth stage: 123 °C for 30 min, the whole process was at a heating rate of 2 °C / min; finally, the desolvation-cured polyamic acid solution was transferred to a muffle furnace and subjected to thermal imidization at 340 °C, the mold was removed, and a polyimide film was obtained.

[0070] The viscosity of the pyromellitic polyamic acid solution in Example 2 was 768 cP, and the viscosity of the biphenyl polyamic acid solution was 334 cP, which had good flowability and strong processability, and the elongation at break of the prepared polyimide film was 24.0%, the tensile strength was 95.1 MPa, and the glass transition temperature was 329 °C.

[0071] Example 3

[0072] S1. 4,4'-diaminodiphenyl ether was added to N,N-dimethylacetamide and stirred until completely dissolved. Then, under nitrogen protection, pyromellitic anhydride was added with stirring at a speed of 350 r / min. The mixture was reacted at 10°C for 24 hours to obtain a transparent and viscous pyromellitic polyamic acid solution; wherein the molar ratio of 4,4'-diaminodiphenyl ether to pyromellitic anhydride was 1:1;

[0073] S2. 4,4'-diaminodiphenyl ether was added to N,N-dimethylacetamide and stirred until completely dissolved. Then, under nitrogen protection, 3,3',4,4'-biphenyltetracarboxylic dianhydride was added with stirring at a speed of 350 r / min, and the mixture was reacted at 10°C for 24 hours to obtain a transparent viscous biphenyl polyamic acid solution; wherein the molar ratio of 4,4'-diaminodiphenyl ether to 3,3',4,4'-biphenyltetracarboxylic dianhydride was 1:1;

[0074] S3. The bisphenyl type polyamic acid solution and the biphenyl type polyamic acid solution were mixed to obtain a blended polyamic acid solution; wherein the molar ratio of the bisphenyl type polyamic acid solution to the biphenyl type polyamic acid solution was 7:3;

[0075] S4. The blended polyamic acid solution is transferred to a vacuum oven for defoaming for 10 minutes, and then the defoamed polyamic acid solution is placed in a mold for desolventizing and curing. The desolventizing and curing procedure includes six stages: the first stage: keeping warm at 80°C for 15 minutes, the second stage: keeping warm at 90°C for 15 minutes, the third stage: keeping warm at 100°C for 15 minutes, the fourth stage: keeping warm at 107°C for 30 minutes, the fifth stage: keeping warm at 117°C for 2 hours, and the sixth stage: keeping warm at 123°C for 30 minutes. The heating rate of the whole process is 2°C / min; finally, the desolventizing and curing polyamic acid solution is transferred to a muffle furnace and thermal imidized at 350°C, the mold is removed, and a polyimide film is obtained.

[0076] The viscosity of the isophenyl polyamic acid solution in Example 3 is 768 cP, and the viscosity of the biphenyl polyamic acid solution is 334 cP. They have low viscosity, good fluidity, and strong processability. The obtained polyimide film has an elongation at break of 20.5%, a tensile strength of 163.5 MPa, and a glass transition temperature of 346°C.

[0077] Comparative Example 1

[0078] S1. 4,4'-diaminodiphenyl ether was added to N,N-dimethylacetamide and stirred until completely dissolved. Then, under nitrogen protection, pyromellitic anhydride was added with stirring at a speed of 350 r / min. The mixture was reacted at 10°C for 24 hours to obtain a transparent and viscous pyromellitic polyamic acid solution; wherein the molar ratio of 4,4'-diaminodiphenyl ether to pyromellitic anhydride was 1:1;

[0079] S2. The isophthalic acid polyamide solution is transferred to a vacuum oven for defoaming for 10 minutes, and then the defoamed polyamide acid solution is placed in a mold for desolventizing and curing. The desolventizing and curing procedure includes six stages: the first stage: keeping warm at 80°C for 15 minutes, the second stage: keeping warm at 90°C for 15 minutes, the third stage: keeping warm at 100°C for 15 minutes, the fourth stage: keeping warm at 104°C for 30 minutes, the fifth stage: keeping warm at 119°C for 2 hours, and the sixth stage: keeping warm at 126°C for 30 minutes. The heating rate of the whole process is 2°C / min; finally, the desolventizing and curing polyamide acid solution is transferred to a muffle furnace and subjected to thermal imidization at 360°C. The mold is removed to obtain a polyimide film.

[0080] The viscosity of the isophthalic polyamide acid solution prepared in Comparative Example 1 is 768 cP, and the elongation at break of the prepared polyimide film is 18.9%, the tensile strength is 79.2 MPa, and the glass transition temperature reaches 385°C; that is, although the temperature resistance of the polyimide film prepared in Comparative Example 1 is higher than that of Example 2, the mechanical properties are significantly worse than those of Example 2.

[0081] Comparative Example 2

[0082] S1. 4,4'-diaminodiphenyl ether was added to N,N-dimethylacetamide and stirred until completely dissolved. Then, under nitrogen protection, 3,3',4,4'-biphenyltetracarboxylic dianhydride was added with stirring at a speed of 350 r / min, and the mixture was reacted at 10°C for 24 hours to obtain a transparent and viscous biphenyl polyamic acid solution; wherein the molar ratio of 4,4'-diaminodiphenyl ether to 3,3',4,4'-biphenyltetracarboxylic dianhydride was 1:1;

[0083] S2. The biphenyl type polyamide acid solution is transferred to a vacuum oven for defoaming for 10 minutes, and then the defoamed polyamide acid solution is placed in a mold for desolventization and curing. The desolventization and curing procedure includes six stages: the first stage: keeping warm at 80°C for 15 minutes, the second stage: keeping warm at 90°C for 15 minutes, the third stage: keeping warm at 100°C for 15 minutes, the fourth stage: keeping warm at 111°C for 30 minutes, the fifth stage: keeping warm at 117°C for 2 hours, and the sixth stage: keeping warm at 119°C for 30 minutes. The heating rate of the whole process is 2°C / min; finally, the desolventized and cured polyamide acid solution is transferred to a muffle furnace and thermally imidized at 340°C. The mold is removed to obtain a polyimide film.

[0084] The viscosity of the biphenyl polyamic acid solution prepared in Comparative Example 2 was 334 cP, and the resulting polyimide film had an elongation at break of 28.5%, a tensile strength of 113.0 MPa, and a glass transition temperature of 299°C. That is, although the mechanical properties of the polyimide film prepared in Comparative Example 2 were higher than those of Example 2, its temperature resistance was significantly worse than that of Example 2.

[0085] Comparative Example 3

[0086] Comparative Example 3 is substantially the same as Example 2, except that the reaction temperatures in step S1 and step 2 are both 0°C.

[0087] The viscosity of the homophenyl polyamic acid solution obtained in Comparative Example 3 was 10610 cP, and the viscosity of the biphenyl polyamic acid solution was 3594 cP. The viscosity of the blended polyamic acid was too high and the fluidity was poor, and a polyamic acid film with uniform structure and performance could not be obtained.

[0088] Comparative Example 4

[0089] Comparative Example 4 is substantially the same as Example 2, except that the procedure for desolventizing and curing in step S4 is as follows: heating the temperature to 160° C. at a heating rate of 2° C. / min and keeping the temperature for 4 h.

[0090] like Figure 3 As shown, in Comparative Example 4, the polyimide film obtained was wrinkled and had bubbles on the surface due to the excessively high desolventizing and curing temperature.

[0091] Comparative Example 5

[0092] Comparative Example 5 is substantially the same as Example 2, except that the thermal imidization temperature is 320°C.

[0093] In Comparative Example 5, the temperature was too low, the imidization was not complete, and the temperature resistance of the material was poor.

[0094] Comparative Example 6

[0095] Comparative Example 6 is substantially the same as Example 2, except that the thermal imidization temperature is 370°C.

[0096] In Comparative Example 6, the temperature is too high, the degree of cross-linking inside the material is too high, and the flexibility of the material is poor.

[0097] Depend on Figures 1-3 It can be seen that the preparation method of the present invention can be used to form a polyimide film with a special-shaped structure having excellent flexibility and temperature resistance.

[0098] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for preparing a flexible special-shaped polyimide film, characterized in that: The preparation method comprises the following steps: S1. The 4,4'-diaminodiphenyl ether and pyromellitic anhydride are reacted to obtain a pyromellitic polyamic acid solution; S2. The 4,4'-diaminodiphenyl ether and 3,3',4,4'-biphenyltetracarboxylic dianhydride are reacted to obtain a biphenyl-type polyamic acid solution; S3. The pyrophenyl polyamic acid solution and the biphenyl polyamic acid solution are mixed to obtain a blended polyamic acid solution; S4. The blended polyamic acid solution is desolventized and cured, thermally imidized to obtain the flexible, shaped polyimide film; The desolventizing and curing process includes six stages: the first stage: keeping warm at 80°C for 15 minutes; the second stage: keeping warm at 90°C for 15 minutes; the third stage: keeping warm at 100°C for 15 minutes; the fourth stage: keeping warm at 104-111°C for 30 minutes; the fifth stage: keeping warm at 117-119°C for 2 hours; and the sixth stage: keeping warm at 119-126°C for 30 minutes. The heating rate of the whole process is 2°C / min.

2. The preparation method according to claim 1, characterized in that Under nitrogen protection, 4,4'-diaminodiphenyl ether, pyromellitic anhydride and N,N-dimethylacetamide are mixed and reacted at 5-10° C. to obtain the pyromellitic polyamic acid solution.

3. The preparation method according to claim 2, characterized in that In step S1, the molar ratio of 4,4'-diaminodiphenyl ether to pyromellitic anhydride is (0.98-1):1; and the solid content of the pyromellitic polyamic acid solution is 10-15 wt%.

4. The preparation method according to claim 1, characterized in that Under nitrogen protection, 4,4'-diaminodiphenyl ether, 3,3',4,4'-biphenyltetracarboxylic dianhydride and N,N-dimethylacetamide are mixed and reacted at 5-10° C. to obtain the biphenyl type polyamic acid solution.

5. The preparation method according to claim 4, characterized in that In step S2, the molar ratio of 4,4'-diaminodiphenyl ether to 3,3',4,4'-biphenyltetracarboxylic dianhydride is (0.98-1):1; and the solid content of the biphenyl type polyamic acid solution is 10-15 wt%.

6. The preparation method according to claim 1, characterized in that Under nitrogen protection, the bisphenyl polyamic acid solution and the biphenyl polyamic acid solution are mixed at 5-10° C. to obtain a blended polyamic acid solution; the molar ratio of the bisphenyl polyamic acid in the bisphenyl polyamic acid solution to the biphenyl polyamic acid in the biphenyl polyamic acid solution is 3:7-7:

3.

7. The preparation method according to claim 1, characterized in that Before the desolventizing and curing, the method further includes placing the blended polyamic acid solution in a vacuum oven for defoaming treatment.

8. The preparation method according to claim 1, characterized in that The temperature of the thermal imidization is 340-360°C.

9. A flexible special-shaped polyimide film prepared by the preparation method according to any one of claims 1 to 8.

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