A low moisture-absorbing polyimide film and a method for producing the same

Abstract

The application relates to a low-hygroscopic polyimide film and a preparation method thereof, and belongs to the technical field of nanofiber membranes. The polyimide film is composed of the following components: a hydrophobic modifier 8.2-10.5 wt%, nano-zinc oxide 4.6-5.3 wt%, and the balance of polyimide resin; the main chain of the modifier molecule has the same imide ring structure as the base polyimide, good compatibility and dispersibility are achieved, the trifluoropropyl introduced in the side chain has high freedom, can cover the polar carbonyl and imide groups in the polyimide chain through dynamic rotation, form an effective space shielding effect, significantly reduce the adsorption sites of water molecules, and at the same time, the nano-zinc oxide forms an organic-inorganic hybrid reinforcing network through chelation, compensates for the loss of rigidity and thermal stability possibly caused by the introduction of flexible segments, and realizes the balance of hydrophobicity and mechanical / thermal properties.

Description

Technical Field

[0001] This invention belongs to the field of nanofiber membrane technology, specifically, it relates to a low-moisture-absorbing polyimide film and its preparation method. Background Technology

[0002] Nanofiber membranes, due to their high specific surface area, abundant microporous structure, and tunable pore size distribution, show broad application prospects in ultrafiltration, battery membranes, catalyst supports, and biomedical materials. Particularly in applications such as air filtration, water treatment, and lithium-ion battery membranes, nanofiber membranes can achieve highly efficient separation and barrier functions. Polyimide, as a high-performance polymer, possesses excellent thermal stability, outstanding mechanical strength, good chemical stability, and radiation resistance, and is therefore widely used as a substrate for high-temperature filtration materials, battery membranes, and flexible electronic devices.

[0003] However, the polar imide rings and carbonyl functional groups in the polyimide molecule give it a certain degree of hydrophilicity, making it prone to moisture absorption in real-world high-humidity environments. Moisture absorption not only causes dimensional changes but also reduces its insulation properties and mechanical strength. This is especially true in nanofiber membrane morphology, where the extremely high specific surface area further exacerbates moisture absorption, severely limiting its long-term application in precision electronic devices or high-humidity environments.

[0004] To improve the hygroscopicity of polyimide materials, existing technologies mainly employ two methods: First, physical blending with hydrophobic substances, such as introducing organosilicon or organofluoropolymers. While this improves hydrophobicity to some extent, these substances have poor compatibility with polyimide, especially prone to phase separation under high-temperature processing, resulting in insignificant improvement in hygroscopicity. Furthermore, excessive addition can disrupt the continuity and density of polyimide molecules, leading to a significant reduction in temperature resistance and strength. Second, chemical modification involves grafting hydrophobic groups onto the polyimide molecular chain, with fluorine modification being the mainstream approach. This involves synthesizing polymers from fluorine-containing raw materials, such as hexafluorodianhydride and trifluoromethyldiaminobiphenyl, uniformly introducing fluorine structures onto the polymer chain. Compared to blending, this method is more efficient at improving hygroscopicity. However, existing fluorine structures have low degrees of freedom, making it difficult to form a shielding effect between molecular chains. Moreover, the introduction of large amounts of fluorine structures leads to a decrease in molecular chain stacking density, which in turn causes a certain degree of deterioration in the mechanical strength and high-temperature stability of the membrane material. Summary of the Invention

[0005] In order to solve the technical problems mentioned in the background art, the purpose of this invention is to provide a low moisture absorption polyimide film and its preparation method.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A low-moisture-absorbing polyimide film, specifically comprising the following weight percentage components: 8.2-10.5 wt% hydrophobic modifier, 4.6-5.3 wt% nano zinc oxide, with the balance being polyimide resin.

[0008] The hydrophobic modifier is prepared by the following method:

[0009] Step A1: Mix benzoin dimethyl ether and acetone, purge with nitrogen for protection, add allyl dimethyl silane and mercaptoethanol, mix well, and apply at room temperature at 35-45 mW / cm 2 Irradiate with ultraviolet light, stir the reaction for 6-8 hours, and remove acetone by rotary evaporation after the reaction is completed to obtain intermediate 1;

[0010] Furthermore, the molar ratio of allyl dimethylsilane, mercaptoethanol, benzoin dimethyl ether, and acetone is 0.1 mol: 0.1 mol: 0.12-0.15 g: 180-220 mL. Allyl dimethylsilane and mercaptoethanol undergo an addition reaction under ultraviolet irradiation. The specific reaction route is as follows:

[0011]

[0012] Step A2: Mix intermediate 1 with anhydrous toluene, purge with dry nitrogen for protection, slowly add trifluoropropylmethyldichlorosilane at room temperature and stir for 1.5-2 h, then add pyridine and mix, and heat to 60-70℃ to continue the reaction for 0.5-0.8 h. After the reaction is complete, remove toluene by rotary evaporation under reduced pressure, wash the substrate with water and dry to obtain intermediate 2.

[0013] Furthermore, the molar ratio of trifluoropropylmethyldichlorosilane, intermediate 1, pyridine, and anhydrous toluene is 0.1 mol: 0.2 mol: 15-22 mL: 330-400 mL. Trifluoropropylmethyldichlorosilane and intermediate 1 undergo a substitution reaction, and the specific reaction route is as follows:

[0014]

[0015] Step A3: Mix norborneol olefinic anhydride and carbon tetrachloride, then add intermediate 2 and chloroplatinic acid and mix well. Purge with dry nitrogen for protection, heat to 70-80℃ and reflux for 10-13 hours. After the reaction is complete, remove carbon tetrachloride by rotary evaporation to obtain the modified anhydride monomer.

[0016] Furthermore, the molar ratio of intermediate 2, norbornadiene anhydride, chloroplatinic acid, and carbon tetrachloride is 0.1 mol: 0.2 mol: 0.13-0.18 g: 350-500 mL. Intermediate 2 and norbornadiene anhydride undergo a hydrosilylation reaction, and the specific reaction route is as follows:

[0017]

[0018] Step A4: Mix the modified acid anhydride monomer, 4,4'-diaminodiphenyl ether and dimethylacetamide, purge with nitrogen for protection, heat to 40-50℃ and stir for 7-8 hours, then add acetic anhydride and triethylamine and mix, continue heating to 120-130℃ and react for 3.5-4 hours. After the reaction is complete, add water to wash, wash the precipitate with ethanol and dry, and finally dry at 220℃ under nitrogen atmosphere to constant weight to obtain the hydrophobic modifier;

[0019] Furthermore, the ratio of modified acid anhydride monomer, 4,4'-diaminodiphenyl ether, acetic anhydride, triethylamine and dimethylacetamide is 0.1 mol: 0.1 mol: 0.3-0.4 mL: 0.1-0.15 mL: 200-250 mL, and the modified acid anhydride monomer and 4,4'-diaminodiphenyl ether undergo an imidization reaction.

[0020] A method for preparing a low-moisture-absorbing polyimide film, specifically comprising:

[0021] Step S1: The hydrophobic modifier, polyimide resin and mixed solvent are heated and mixed, and then nano zinc oxide is added and ultrasonically dispersed evenly to prepare a spinning solution;

[0022] Step S2: The spinning solution is fed into the electrospinning equipment, the spinning voltage is controlled at 25kV, and a film is formed by electrospinning. Then it is sent into the hot pressing equipment for hot pressing and shaping to obtain a low moisture absorption polyimide film.

[0023] Preferably, the mixed solvent is composed of dimethylformamide, N-methylpyrrolidone and acetone in a volume ratio of 1:0.7-0.9:0.25-0.4. The mixture of the three forms a mixture with both gradient volatility and high solubility, balancing solubility and volatility, which makes the spinning of monofilaments more uniform and helps to improve the consistency of membrane material performance.

[0024] Preferably, the hot pressing temperature is 180-200℃, the pressure is 3-3.5MPa, and the hot pressing time is 5-8min; this improves the surface quality of the membrane material, makes the fibers more tightly packed, and enhances the stability of the membrane material.

[0025] The beneficial effects of this invention are:

[0026] This invention synthesizes a novel hydrophobic modifier through molecular structure design, which has the following core advantages: First, the main chain of the modifier has the same imide ring structure as the matrix polyimide, achieving good compatibility and dispersibility, and avoiding the loss of mechanical properties caused by phase separation in traditional blending modification; Second, the trifluoropropyl group introduced into the molecular side chain of the hydrophobic modifier has high degree of freedom and can dynamically rotate to cover the polar carbonyl and imide groups in the polyimide chain, forming an effective spatial shielding effect and significantly reducing the adsorption sites of water molecules; At the same time, the sulfur-oxygen structure in the middle of the molecule forms a stable chelating effect with the nano zinc oxide filler, constructing an organic-inorganic hybrid reinforcement network, compensating for the possible loss of rigidity and thermal stability caused by the introduction of flexible segments, and achieving a balance between hydrophobicity and mechanical / thermal properties; In addition, the hydrophobic modifier is introduced through blending, making the method of preparing the membrane material compatible with traditional methods, and has good industrialization prospects.

[0027] In summary, this invention significantly reduces the hygroscopicity of polyimide nanofiber membranes while effectively maintaining their inherent high-performance characteristics, solving the key problem in the prior art where hydrophobic modification and performance maintenance are difficult to balance. Detailed Implementation

[0028] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0029] Example 1: Preparation of a low-moisture-absorbing polyimide film. The specific implementation process is as follows:

[0030] (1) Preparation of hydrophobic modifier

[0031] Step A1: Mix benzoin dimethyl ether and acetone, purge with nitrogen for protection, add allyl dimethyl silane and mercaptoethanol, mix well, and apply 35 mW / cm² ultraviolet light at room temperature. 2 The mixture was subjected to ultraviolet irradiation and stirred for 8 hours. The ratio of allyl dimethylsilane, mercaptoethanol, benzoin dimethyl ether and acetone was 0.1 mol: 0.1 mol: 0.12 g: 180 mL. After the reaction was completed, the acetone was removed by rotary evaporation to obtain intermediate 1.

[0032] Step A2: Mix intermediate 1 and anhydrous toluene, purge with dry nitrogen for protection, slowly add trifluoropropylmethyldichlorosilane at room temperature and stir for 2 h, then add pyridine and mix and heat to 60 °C to continue the reaction for 0.8 h. The ratio of trifluoropropylmethyldichlorosilane, intermediate 1, pyridine and anhydrous toluene is 0.1 mol: 0.2 mol: 15 mL: 330 mL. After the reaction is complete, remove toluene by rotary evaporation under reduced pressure. Wash the substrate with water and dry to obtain intermediate 2.

[0033] Step A3: Mix norbornadiene anhydride and carbon tetrachloride, then add intermediate 2 and chloroplatinic acid and mix well. Purge with dry nitrogen for protection and reflux at 70°C for 13 hours. The ratio of intermediate 2, norbornadiene anhydride, chloroplatinic acid and carbon tetrachloride is 0.1 mol: 0.2 mol: 0.13 g: 350 mL. After the reaction is complete, remove carbon tetrachloride by rotary evaporation to obtain the modified anhydride monomer.

[0034] Step A4: Mix the modified acid anhydride monomer, 4,4'-diaminodiphenyl ether, and dimethylacetamide, purge with nitrogen for protection, heat to 40°C and stir for 8 hours. Then add acetic anhydride and triethylamine and mix, continue heating to 120°C and react for 4 hours. The ratio of the modified acid anhydride monomer, 4,4'-diaminodiphenyl ether, acetic anhydride, triethylamine, and dimethylacetamide is 0.1 mol: 0.1 mol: 0.3 mL: 0.1 mL: 200 mL. After the reaction is complete, add water to wash the mixture, wash the precipitate with ethanol and dry it. Finally, dry it at 220°C under a nitrogen atmosphere to constant weight to obtain the hydrophobic modifier.

[0035] (2) Preparation of polyimide film

[0036] Raw materials are prepared by weight percentage as follows: 8.2 wt% hydrophobic modifier, prepared in this embodiment; 4.6 wt% nano zinc oxide, commercially available nano powder with an average particle size of 20 nm; the remainder is polyimide resin, P84 type resin powder; mixed solvent preparation: dimethylformamide, N-methylpyrrolidone and acetone are mixed in a volume ratio of 1:0.7:0.4.

[0037] Step S1: Mix the hydrophobic modifier and polyimide resin, add the mixed solvent intermittently and heat to 80°C, stir until completely dissolved, then add nano zinc oxide and ultrasonically disperse at 33 kHz for 20 min. No visible agglomeration is observed, forming a uniform dispersion, which is then used to prepare the spinning solution.

[0038] Step S2: The spinning solution is fed into an electrospinning device with a spinning needle inner diameter of 0.51 mm, a spinning voltage of 25 kV, an X-axis scanning rate of 0.25 cm / s, a Y-axis feed rate of 0.05 mm / s, and a receiving distance of 15 cm. The spinning solution is electrospinned to form a film, which is then fed into a flat plate hot press. The plate temperature is controlled at 180°C, the pressure at 3 MPa, and the hot pressing time at 5 min to obtain a polyimide film.

[0039] Example 2: Preparation of a low-moisture-absorbing polyimide film. The specific implementation process is as follows:

[0040] (1) Preparation of hydrophobic modifier

[0041] Step A1: Mix benzoin dimethyl ether and acetone, purge with nitrogen for protection, add allyl dimethyl silane and mercaptoethanol, mix well, and apply 45 mW / cm² ultraviolet light at room temperature using a 365 nm wavelength ultraviolet light source. 2 The mixture was subjected to ultraviolet irradiation and stirred for 6 hours. The ratio of allyl dimethylsilane, mercaptoethanol, benzoin dimethyl ether and acetone was 0.1 mol: 0.1 mol: 0.15 g: 220 mL. After the reaction was completed, the acetone was removed by rotary evaporation to obtain intermediate 1.

[0042] Step A2: Mix intermediate 1 and anhydrous toluene, purge with dry nitrogen for protection, slowly add trifluoropropylmethyldichlorosilane at room temperature and stir for 1.5 h, then add pyridine and mix, and heat to 70 °C to continue the reaction for 0.5 h. The ratio of trifluoropropylmethyldichlorosilane, intermediate 1, pyridine and anhydrous toluene is 0.1 mol: 0.2 mol: 22 mL: 400 mL. After the reaction is complete, remove toluene by rotary evaporation under reduced pressure. Wash the substrate with water and dry to obtain intermediate 2.

[0043] Step A3: Mix norbornadiene anhydride and carbon tetrachloride, then add intermediate 2 and chloroplatinic acid and mix well. Purge with dry nitrogen for protection and reflux at 80°C for 10 hours. The ratio of intermediate 2, norbornadiene anhydride, chloroplatinic acid and carbon tetrachloride is 0.1 mol: 0.2 mol: 0.18 g: 500 mL. After the reaction is complete, remove carbon tetrachloride by rotary evaporation to obtain the modified anhydride monomer.

[0044] Step A4: Mix the modified acid anhydride monomer, 4,4'-diaminodiphenyl ether, and dimethylacetamide, purge with nitrogen for protection, heat to 50°C and stir for 7 hours. Then add acetic anhydride and triethylamine and mix, continue heating to 130°C and react for 3.5 hours. The ratio of the modified acid anhydride monomer, 4,4'-diaminodiphenyl ether, acetic anhydride, triethylamine, and dimethylacetamide is 0.1 mol: 0.1 mol: 0.4 mL: 0.15 mL: 250 mL. After the reaction is complete, add water to wash the mixture, wash the precipitate with ethanol and dry it. Finally, dry it at 220°C under a nitrogen atmosphere to constant weight to obtain the hydrophobic modifier.

[0045] (2) Preparation of polyimide film

[0046] Raw materials are prepared by weight percentage as follows: 10.5 wt% hydrophobic modifier, prepared in this embodiment; 5.3 wt% nano zinc oxide, commercially available nano powder with an average particle size of 20 nm; the remainder is polyimide resin, P84 type resin powder; mixed solvent preparation: dimethylformamide, N-methylpyrrolidone and acetone are mixed in a volume ratio of 1:0.9:0.25.

[0047] Step S1: Mix the hydrophobic modifier and polyimide resin, add the mixed solvent intermittently and heat to 80°C, stir until completely dissolved, then add nano zinc oxide and ultrasonically disperse at 33 kHz for 20 min. No visible agglomeration is observed, forming a uniform dispersion, which is then used to prepare the spinning solution.

[0048] Step S2: The spinning solution is fed into an electrospinning device with a spinning needle inner diameter of 0.51 mm, a spinning voltage of 25 kV, an X-axis scanning rate of 0.25 cm / s, a Y-axis feed rate of 0.05 mm / s, and a receiving distance of 15 cm. The spinning solution is electrospinned to form a film, which is then fed into a flat plate hot press. The plate temperature is controlled at 200℃, the pressure at 3.5 MPa, and the hot pressing time at 5 min to obtain a polyimide film.

[0049] Example 3: Preparation of a low-moisture-absorbing polyimide film. The specific implementation process is as follows:

[0050] (1) Preparation of hydrophobic modifier

[0051] Step A1: Mix benzoin dimethyl ether and acetone, purge with nitrogen for protection, add allyl dimethyl silane and mercaptoethanol, mix well, and apply 40 mW / cm² ultraviolet light at room temperature using a 365 nm wavelength ultraviolet light source. 2 The mixture was subjected to ultraviolet irradiation and stirred for 7 hours. The ratio of allyl dimethylsilane, mercaptoethanol, benzoin dimethyl ether and acetone was 0.1 mol: 0.1 mol: 0.13 g: 200 mL. After the reaction was completed, the acetone was removed by rotary evaporation to obtain intermediate 1.

[0052] Step A2: Mix intermediate 1 and anhydrous toluene, purge with dry nitrogen for protection, slowly add trifluoropropylmethyldichlorosilane at room temperature and stir for 1.8 h, then add pyridine and mix and heat to 65 °C to continue the reaction for 0.7 h. The ratio of trifluoropropylmethyldichlorosilane, intermediate 1, pyridine and anhydrous toluene is 0.1 mol: 0.2 mol: 20 mL: 360 mL. After the reaction is complete, remove toluene by rotary evaporation under reduced pressure. Wash the substrate with water and dry to obtain intermediate 2.

[0053] Step A3: Mix norbornadiene anhydride and carbon tetrachloride, then add intermediate 2 and chloroplatinic acid and mix well. Purge with dry nitrogen for protection and reflux at 75°C for 11 hours. The ratio of intermediate 2, norbornadiene anhydride, chloroplatinic acid and carbon tetrachloride is 0.1 mol: 0.2 mol: 0.15 g: 400 mL. After the reaction is complete, remove carbon tetrachloride by rotary evaporation to obtain the modified anhydride monomer.

[0054] Step A4: Mix the modified acid anhydride monomer, 4,4'-diaminodiphenyl ether, and dimethylacetamide, purge with nitrogen for protection, heat to 45°C and stir for 7.5 h. Then add acetic anhydride and triethylamine and mix, continue heating to 120°C and react for 4 h. The ratio of the modified acid anhydride monomer, 4,4'-diaminodiphenyl ether, acetic anhydride, triethylamine and dimethylacetamide is 0.1 mol: 0.1 mol: 0.3 mL: 0.15 mL: 220 mL. After the reaction is complete, add water to wash and the precipitate is washed with ethanol and dried. Finally, dry at 220°C under a nitrogen atmosphere to constant weight to obtain the hydrophobic modifier.

[0055] (2) Preparation of polyimide film

[0056] Raw materials are prepared by weight percentage as follows: 9.0 wt% hydrophobic modifier, prepared in this embodiment; 4.9 wt% nano zinc oxide, commercially available nano powder with an average particle size of 20 nm; the remainder is polyimide resin, P84 type resin powder; mixed solvent preparation: dimethylformamide, N-methylpyrrolidone and acetone are mixed in a volume ratio of 1:0.78:0.35.

[0057] Step S1: Mix the hydrophobic modifier and polyimide resin, add the mixed solvent intermittently and heat to 80°C, stir until completely dissolved, then add nano zinc oxide and ultrasonically disperse at 33 kHz for 20 min. No visible agglomeration is observed, forming a uniform dispersion, which is then used to prepare the spinning solution.

[0058] Step S2: The spinning solution is fed into an electrospinning device with a spinning needle inner diameter of 0.51 mm, a spinning voltage of 25 kV, an X-axis scanning rate of 0.25 cm / s, a Y-axis feed rate of 0.05 mm / s, and a receiving distance of 15 cm. The spinning solution is electrospinned to form a film, which is then fed into a flat plate hot press. The plate temperature is controlled at 190°C, the pressure at 3.5 MPa, and the hot pressing time at 6 min to obtain a polyimide film.

[0059] Example 4: Preparation of a low-moisture-absorbing polyimide film. The specific implementation process is as follows:

[0060] (1) Preparation of hydrophobic modifier

[0061] Step A1: Mix benzoin dimethyl ether and acetone, purge with nitrogen for protection, add allyl dimethyl silane and mercaptoethanol, mix well, and apply 35 mW / cm² ultraviolet light at room temperature. 2 The mixture was subjected to ultraviolet irradiation and stirred for 7 hours. The ratio of allyl dimethylsilane, mercaptoethanol, benzoin dimethyl ether and acetone was 0.1 mol: 0.1 mol: 0.15 g: 200 mL. After the reaction was completed, the acetone was removed by rotary evaporation to obtain intermediate 1.

[0062] Step A2: Mix intermediate 1 and anhydrous toluene, purge with dry nitrogen for protection, slowly add trifluoropropylmethyldichlorosilane at room temperature and stir for 1.7 h, then add pyridine and mix and heat to 70 °C to continue the reaction for 0.7 h. The ratio of trifluoropropylmethyldichlorosilane, intermediate 1, pyridine and anhydrous toluene is 0.1 mol: 0.2 mol: 18 mL: 350 mL. After the reaction is complete, remove toluene by rotary evaporation under reduced pressure. Wash the substrate with water and dry to obtain intermediate 2.

[0063] Step A3: Mix norbornadiene anhydride and carbon tetrachloride, then add intermediate 2 and chloroplatinic acid and mix well. Purge with dry nitrogen for protection and reflux at 78°C for 102 h. The ratio of intermediate 2, norbornadiene anhydride, chloroplatinic acid and carbon tetrachloride is 0.1 mol: 0.2 mol: 0.16 g: 450 mL. After the reaction is complete, remove carbon tetrachloride by rotary evaporation to obtain the modified anhydride monomer.

[0064] Step A4: Mix the modified acid anhydride monomer, 4,4'-diaminodiphenyl ether, and dimethylacetamide, purge with nitrogen for protection, heat to 50°C and stir for 8 hours. Then add acetic anhydride and triethylamine and mix, continue heating to 125°C and react for 3.8 hours. The ratio of the modified acid anhydride monomer, 4,4'-diaminodiphenyl ether, acetic anhydride, triethylamine, and dimethylacetamide is 0.1 mol: 0.1 mol: 0.4 mL: 0.1 mL: 230 mL. After the reaction is complete, add water to wash the mixture, wash the precipitate with ethanol and dry it. Finally, dry it at 220°C under a nitrogen atmosphere to constant weight to obtain the hydrophobic modifier.

[0065] (2) Preparation of polyimide film

[0066] Raw materials are prepared by weight percentage as follows: 9.4 wt% hydrophobic modifier, prepared in this embodiment; 5.1 wt% nano zinc oxide, commercially available nano powder with an average particle size of 20 nm; the remainder is polyimide resin, P84 type resin powder; mixed solvent preparation: dimethylformamide, N-methylpyrrolidone and acetone are mixed in a volume ratio of 1:0.8:0.3.

[0067] Step S1: Mix the hydrophobic modifier and polyimide resin, add the mixed solvent intermittently and heat to 80°C, stir until completely dissolved, then add nano zinc oxide and ultrasonically disperse at 33 kHz for 20 min. No visible agglomeration is observed, forming a uniform dispersion, which is then used to prepare the spinning solution.

[0068] Step S2: The spinning solution is fed into an electrospinning device with a spinning needle inner diameter of 0.51 mm, a spinning voltage of 25 kV, an X-axis scanning rate of 0.25 cm / s, a Y-axis feed rate of 0.05 mm / s, and a receiving distance of 15 cm. The spinning solution is electrospinned to form a film, which is then fed into a flat plate hot press. The plate temperature is controlled at 200℃, the pressure at 3.2 MPa, and the hot pressing time at 7 min to obtain a polyimide film.

[0069] Comparative Example 1: This comparative example is a blank control of Example 4. No hydrophobic modifier was added, and the balance was made up to 100 wt% with polyimide resin.

[0070] Comparative Example 2, referring to Example 4, replaced the hydrophobic modifier with an equal amount of Avimid® N FPI-1 type fluorinated polyimide, and the rest of the implementation process was exactly the same.

[0071] Samples were taken from the films prepared above, and hygroscopicity tests were conducted according to ASTM D570-22 standard. The test environment was 25℃, 90%RH, and the cycle was 48h. Tensile tests were conducted according to GB / T 1040.3-2006 standard, with a tensile rate of 10mm / min. High-temperature stability tests were conducted, specifically including: placing the sample on a 320℃ hot table surface for 1h, then placing it at room temperature for 24h, and measuring the dimensional change rate, which is the static heat shrinkage rate; applying a tensile force of 0.5N to the sample, maintaining it at 200℃ for 24h, and then placing it at room temperature for 24h, measuring the dimensional change rate, which is the heat-bearing dimensional change rate. The specific test results are shown in Table 1.

[0072] Table 1

[0073] As can be seen from the test results in Table 1, the polyimide film prepared in the examples has extremely low hygroscopicity and good structural stability at high temperatures. In particular, under thermal conditions, the dimensional change rate of the film is significantly lower, resulting in higher structural stability.

[0074] In the description of this specification, the references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0075] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. A low moisture-absorbing polyimide film, characterized by comprising a polyimide film having a moisture absorption of 0.5% or less. Specific weight percentage components are: hydrophobic modifier 8.2-10.5wt%, nano zinc oxide 4.6-5.3wt%, and the rest is polyimide resin; The hydrophobic modifier is prepared by the following method: Step A1 : Dissolve benzoin dimethyl ether in acetone, add allyldimethylsilane and mercaptoethanol under nitrogen atmosphere, mix well, apply 35-45 mW / cm 2 of ultraviolet radiation at room temperature and stir the reaction for 6-8 h to produce intermediate 1; Step A2: intermediate 1 and anhydrous toluene are mixed, trifluoropropyl methyl dichlorosilane is slowly added under a nitrogen atmosphere at room temperature, and the reaction is stirred for 1.5-2h, then pyridine is added, mixed and heated to 60-70℃, and the reaction is continued for 0.5-0.8h to produce intermediate 2; Step A3: norbornene dianhydride and carbon tetrachloride are mixed, then intermediate 2 and chloroplatinic acid are added and mixed, protected by nitrogen and heated to 70-80℃ to reflux for 10-13h to produce modified anhydride monomer; Step A4: the modified anhydride monomer, 4,4'-diamino diphenyl ether and dimethylacetamide are mixed, heated to 40-50℃ under nitrogen protection, stirred for 7-8h, then acetic anhydride and triethylamine are added and mixed, and the temperature is further increased to 120-130℃ for 3.5-4h to produce the hydrophobic modifier.

2. The low moisture-absorption polyimide film according to claim 1, wherein The amount ratio of allyl dimethyl silane, mercaptoethanol, benzoin dimethyl ether and acetone is 0.1mol:0.1mol:0.12-0.15g:180-220mL.

3. The low moisture-absorption polyimide film according to claim 2, wherein The amount ratio of trifluoropropyl methyl dichlorosilane, intermediate 1, pyridine and anhydrous toluene is 0.1mol:0.2mol:15-22mL:330-400mL.

4. The low moisture-absorption polyimide film according to claim 3, wherein The amount ratio of intermediate 2, norbornene dianhydride, chloroplatinic acid and carbon tetrachloride is 0.1mol:0.2mol:0.13-0.18g:350-500mL.

5. The low moisture absorbing polyimide film according to claim 4, wherein The amount ratio of modified anhydride monomer, 4,4'-diamino diphenyl ether, acetic anhydride, triethylamine and dimethylacetamide is 0.1mol:0.1mol:0.3-0.4mL:0.1-0.15mL:200-250mL.

6. A method for preparing a low-moisture-absorbing polyimide film according to any one of claims 1-5, characterized in that, Specifically: Step S1: the hydrophobic modifier, polyimide resin and mixed solvent are heated and mixed, then nano zinc oxide is added and ultrasonically dispersed to produce a spinning solution; Step S2: the spinning solution is electrospun to form a film, then heat pressing is performed to form a low-hygroscopic polyimide film.

7. The method for preparing a low-moisture-absorbing polyimide film according to claim 6, characterized in that, The mixed solvent is prepared by mixing dimethylformamide, N-methyl pyrrolidone and acetone in a volume ratio of 1:0.7-0.9:0.25-0.

4.

8. The method for preparing a low-moisture-absorbing polyimide film according to claim 6, characterized in that, The heat pressing temperature is 180-200℃, the pressure is 3-3.5MPa, and the heat pressing time is 5-8min.

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