A polyimide film with low thermal expansion coefficient and preparation method thereof

Abstract

The present invention relates to the technical field of polyimide materials, and discloses a polyimide film with a low thermal expansion coefficient and a preparation method thereof, comprising the following raw materials in parts by mass: 6-10 parts of dianhydride, 6-10 parts of diamine, 3-5 parts of composite reinforcing fillers, and 80-120 parts of polar solvents. The composite reinforcing filler contains a modified layered composite material, and its in-situ synthesized silicon carbide nanowires can connect the randomly distributed layered composite materials to form a three-dimensional network structure, significantly enhancing the heat conduction path, reducing the thermal expansion coefficient of the polyimide film, and the formed three-dimensional network structure containing silicon carbide nanowires can absorb and weaken the gravitational force generated by external forces, thereby improving mechanical strength. In addition, the composite reinforcing filler includes bacterial cellulose and chitosan, which can be hydrogen-bonded with the polyimide resin so that the composite reinforcing filler is evenly distributed in the polyimide resin. The prepared polyimide film has excellent thermal conductivity and low thermal expansion coefficient.

Description

Technical Field

[0001] The present invention relates to the technical field of polyimide materials, in particular to a polyimide film with a low thermal expansion coefficient and a preparation method thereof. Background Art

[0002] Polyimide is a highly regular polymer containing imide rings in its main chain. It exhibits excellent chemical stability, wear resistance, flame retardancy, high-temperature resistance, low-temperature resistance, corrosion resistance, and radiation resistance. Consequently, polyimide also exhibits outstanding mechanical and dielectric properties. These excellent properties have led to its use in the aerospace industry for the manufacture of high-temperature structural parts, thermal insulation materials, and electronic components. In microelectronics and nanotechnology, polyimide can be used to manufacture high-performance electronic devices and nanomaterials. In the field of liquid crystal displays, polyimide is used as an alignment agent and encapsulation material. Polyimide is also used in separation membranes, lasers, optical devices, and other applications.

[0003] The highly regular nature of the polyimide molecular chain and the strong interaction between its internal molecules result in a slow heat conduction rate and low thermal conductivity. In addition, the highly regular structure of the polyimide molecular chain has a high thermal expansion coefficient, causing it to expand or contract significantly under temperature changes. Summary of the Invention

[0004] The present invention provides a polyimide film with a low thermal expansion coefficient and a preparation method thereof, which solves the problem that the polyimide has a high thermal expansion coefficient and is prone to expansion and contraction.

[0005] The technical solution of the present invention:

[0006] A polyimide film with a low thermal expansion coefficient comprises the following raw materials in parts by weight: 6-10 parts of dianhydride, 6-10 parts of diamine, 3-5 parts of composite reinforcing filler, and 80-120 parts of polar solvent;

[0007] A method for preparing a polyimide film with a low thermal expansion coefficient comprises the following steps:

[0008] S1. The dianhydride, diamine and polar solvent are mixed uniformly, and the polycondensation reaction is carried out under nitrogen protection at 25-35 ° C, a stirring rate of 60-80r / min for 25-35min to obtain a polyamic acid resin solution;

[0009] S2. Add the composite reinforcing filler to the polyamic acid resin solution, stir at 60-80 r / min for 3-5 hours, and after ultrasonic degassing, place it in a casting machine for film casting, and then perform curing treatment to obtain a polyimide film.

[0010] Furthermore, the dianhydride is selected from any one of pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride and 2,2',3,3'-biphenyltetracarboxylic dianhydride.

[0011] Furthermore, the diamine is selected from any one of 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, and p-phenylenediamine.

[0012] Furthermore, the polar solvent is selected from any one of N,N-dimethylformamide, N,N-dimethylacetamide and N-methylpyrrolidone.

[0013] Furthermore, the composite reinforcing filler is formed by adhering the thermal conductive filler to the graphene oxide through polydopamine, and then forming a layered composite material with the lamellar porous carbon. The formed layered composite material is mixed and reacted with nickel chloride hexahydrate and methyltrichlorosilane, and then mixed and reacted with bacterial cellulose, chitosan and glutaraldehyde, and freeze-dried to obtain the result.

[0014] Furthermore, the composite reinforced filler is specifically prepared by the following steps:

[0015] A1. Graphene oxide was added to Tris-HCl buffer (tris(hydroxymethyl)aminomethane hydrochloride buffer), stirred evenly, dopamine was added, and after stirring the reaction was complete, a thermally conductive filler was added, and stirring was continued. After mixing, the mixture was filtered, washed, and dried to obtain modified graphene oxide;

[0016] A2. The modified graphene oxide was added to ethanol, stirred evenly, tannic acid was added, stirred, and then the lamellar porous carbon was added. After stirring, the reaction was completed, filtered, washed, and dried to obtain a layered composite material.

[0017] A3 nickel chloride hexahydrate, methyltrichlorosilane and the layered composite material were added to ethanol, stirred, placed in a reactor, introduced argon, reacted at 1000-1200 ℃ for 1.5-2.5h, cooled to room temperature, removed, washed, and dried to obtain a modified layered composite material;

[0018] A4. The modified layered composite material and chitosan were added to deionized water. After ultrasonic treatment, acetic acid solution and bacterial cellulose were added. After being dispersed in a homogenizer, glutaraldehyde solution was added. After stirring, the mixture was cooled to room temperature and freeze-dried to obtain a composite reinforced filler.

[0019] Furthermore, during the above-mentioned reaction A1, in the Tris-HCl buffer, dopamine can self-polymerize on the surface of graphene oxide to form polydopamine, so that the graphene oxide carries a large number of phenolic hydroxyl groups and has excellent adhesion, thereby being able to adsorb the thermal conductive filler on the graphene oxide to obtain modified graphene oxide.

[0020] Furthermore, during the above-mentioned reaction A2, tannic acid, as a cross-linking agent, can combine with the hydroxyl groups on the modified graphene oxide and the lamellar porous carbon through chemical bonds, so that the lamellar porous carbon is evenly coated on the surface of the modified graphene oxide to form a layered composite material.

[0021] Furthermore, in the above-mentioned reaction process A3, the layered composite material is mixed with nickel chloride hexahydrate and methyltrichlorosilane, nickel chloride hexahydrate is used as a catalyst, methyltrichlorosilane is used as a silicon source and a carbon source, argon is introduced, and at 1100°C, methyltrichlorosilane is thermally decomposed to form carbon elements and silicon elements. The carbon elements and silicon elements are combined by covalent bonds to form a silicon carbide crystal structure, and the carbon elements provided by the lamellar porous carbon on the surface of the layered composite material can also be combined with the silicon element, so that the silicon carbide crystals grow along the layered composite material to form silicon carbide nanowires. The formed silicon carbide nanowires are evenly distributed on the surface of the randomly distributed layered composite material, presenting a network structure, to obtain a modified layered composite material.

[0022] Furthermore, in the above-mentioned A4 reaction process, bacterial cellulose and chitosan are used as aerogel skeletons, and glutaraldehyde is used as a cross-linking agent, so that bacterial cellulose and chitosan form a cross-linked structure aerogel, and the composite layered composite material is embedded in the aerogel structure as a composite reinforcing filler.

[0023] Furthermore, in step A1, the ratio of graphene oxide, Tris-HCl buffer, dopamine and thermal conductive filler is (1.4-1.6) g: (90-110) mL: (0.2-0.4) g: (0.2-0.4) g.

[0024] Furthermore, in step A2, the ratio of modified graphene oxide, ethanol, tannic acid and lamellar porous carbon is (1.4-1.6) g: (140-160) mL: (1.1-1.3) g: (1.5-1.7) g.

[0025] Furthermore, in step A3, the ratio of nickel chloride hexahydrate, methyltrichlorosilane, layered composite material and ethanol is (0.8-1) g: (3.4-3.6) g: (2.4-2.6) g: (90-110) mL.

[0026] Furthermore, in step A4, the ratio of the modified layered composite material, chitosan, deionized water, acetic acid solution, bacterial cellulose and glutaraldehyde solution is (2-2.4) g: (1.3-1.7) g: (80-100) mL: (0.4-0.6) mL: (18-22) g: (45-55) mL.

[0027] Furthermore, the graphene oxide particle size is 5-10 μm.

[0028] Furthermore, the pore size of the lamellar porous carbon is 80-120 nm, and the particle size is 4-6 μm.

[0029] Furthermore, the thermally conductive filler is selected from any one of boron nitride, aluminum nitride and aluminum oxide.

[0030] Furthermore, the particle size of the thermal conductive filler is 200-300 nm.

[0031] The present invention has the following beneficial effects:

[0032] (1) In the technical solution of the present invention, a thermally conductive filler is adsorbed on graphene oxide. The lamellar structure of graphene oxide serves as a carrier of the thermally conductive filler, which is conducive to loading a large amount of thermally conductive filler on the graphene oxide. The graphene oxide and the thermally conductive filler are compounded to improve the thermal conductivity of the polyimide film and reduce the thermal expansion coefficient of the polyimide film. In addition, the graphene oxide and the thermally conductive filler can also enhance the mechanical properties of the polyimide film.

[0033] (2) In the technical solution of the present invention, lamellar porous carbon and modified graphene oxide form a layered composite material. On the one hand, the lamellar porous carbon adheres to the upper and lower surfaces of the modified graphene oxide to form a layered composite material, and then the thermal conductive filler forms a thermal conductive path between the layers of the layered composite material, which significantly improves the thermal conductivity of the polyimide film and reduces the thermal expansion coefficient of the polyimide film. On the other hand, the formed composite layered material can absorb and weaken the stress generated by external forces, thereby improving the mechanical strength of the polyimide film. In addition, the lamellar porous carbon contains a large number of porous structures and has excellent adsorption properties. It can adsorb and fix the thermal conductive filler on the modified graphene oxide, thereby increasing the structural stability of the layered composite material. The lamellar porous carbon has a high specific surface area and porosity, and has excellent thermal conductivity, thereby significantly reducing the thermal expansion coefficient of the polyimide film and avoiding large expansion or contraction of the polyimide film under temperature changes.

[0034] (3) In the technical solution of the present invention, silicon carbide crystals grow along the layered composite material to form silicon carbide nanowires. The formed silicon carbide nanowires are evenly distributed on the surface of the randomly distributed layered composite material, presenting a network structure, thereby obtaining a modified layered composite material. On the one hand, the synthesized silicon carbide nanowires have high thermal conductivity, which can significantly improve the thermal conductivity of the polyimide film and reduce the thermal expansion coefficient. In addition, the in-situ synthesized silicon carbide nanowires can connect the randomly distributed layered composite material to form a three-dimensional network structure, significantly enhance the heat conduction path, and further reduce the thermal expansion coefficient of the polyimide film. On the other hand, the formed three-dimensional network structure containing silicon carbide nanowires can also absorb and weaken the gravitational force generated by external forces, thereby improving the mechanical strength of the polyimide film.

[0035] (4) In the technical solution of the present invention, a modified layered composite material, bacterial cellulose, and chitosan are mixed and reacted to form an aerogel as a reinforcing filler. On the one hand, the modified layered composite material is embedded in the aerogel structure, increasing the crosslinking density, enhancing the mechanical strength of the aerogel, and improving the porosity of the aerogel, thereby improving the thermal conductivity of the polyimide film and reducing the thermal expansion coefficient. On the other hand, bacterial cellulose and chitosan are the aerogel skeleton, and their surfaces have abundant active groups such as hydroxyl and amine groups, which can be combined with the polyimide resin through hydrogen bonds, so that the reinforcing filler is evenly distributed in the polyimide resin, and the prepared polyimide film has excellent thermal conductivity and a low thermal expansion coefficient. DETAILED DESCRIPTION

[0036] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0037] The raw materials used in the examples of the present invention are as follows, and all reagents used are of analytical grade.

[0038] The dianhydride is pyromellitic dianhydride, the diamine is 4,4'-diaminodiphenyl ether, and the polar solvent is N,N-dimethylformamide.

[0039] The graphene oxide particle size is 8 μm.

[0040] The porous carbon sheets had a pore size of 100 nm and a particle size of 5 μm and were purchased from Xi'an Qiyue Biotechnology Co., Ltd.

[0041] The thermal conductive filler is selected from boron nitride, and the particle size is 200 nm.

[0042] Bacterial cellulose was purchased from Beijing Guanlan Technology Co., Ltd.

[0043] Example 1

[0044] A polyimide film with a low thermal expansion coefficient comprises the following raw materials in parts by weight: 6 parts of pyromellitic dianhydride, 6 parts of 4,4'-diaminodiphenyl ether, 3 parts of composite reinforcing filler, and 80 parts of N,N-dimethylformamide;

[0045] A method for preparing a polyimide film with a low thermal expansion coefficient comprises the following steps:

[0046] S1. Pyromellitic dianhydride, 4,4'-diaminodiphenyl ether and N,N-dimethylformamide were uniformly mixed and polycondensed at 25 ° C, 60 r / min stirring rate, under nitrogen protection for 25 min to obtain a polyamic acid resin solution;

[0047] S2. Add the composite reinforcing filler to the polyamic acid resin solution, stir at 60 r / min for 3 hours, perform ultrasonic degassing treatment at 40 kHz for 30 minutes, place it in a casting machine for film casting, and maintain the temperature at 100°C, 150°C, and 250°C for 2 hours at each point to obtain a polyimide film.

[0048] The composite reinforced filler is specifically prepared by the following steps:

[0049] A1. Add 1.4 g of graphene oxide to 90 mL of Tris-HCl buffer (pH 8.5) and stir until uniform. Then, add 0.2 g of dopamine and stir at 25°C for 3.5 h. Then, add 0.2 g of boron nitride and continue stirring for 1 h. The mixture is filtered, washed three times with deionized water, and dried in an oven at 70°C for 10 min to obtain modified graphene oxide.

[0050] A2. 1.4 g of modified graphene oxide was added to 140 mL of ethanol and stirred. 1.1 g of tannic acid was added and stirred at 40°C and 600 rpm for 10 h. 1.5 g of lamellar porous carbon was added and the mixture was stirred for another 20 min. The mixture was filtered, washed three times with deionized water, and dried in an oven at 70°C for 10 min to obtain a layered composite material.

[0051] A3. 0.8 g of nickel chloride hexahydrate, 3.4 g of methyltrichlorosilane, and 2.4 g of the layered composite were added to 90 mL of ethanol, stirred, heated to 50°C, and stirred at 500 rpm for 40 min. The mixture was placed in a reactor and purged with argon. The reaction was incubated at 1100°C for 2 h, cooled to room temperature, removed, washed three times with deionized water, and dried in an oven at 70°C for 10 min to obtain a modified layered composite.

[0052] A4. 2 g of the modified layered composite material and 1.3 g of chitosan were added to 80 mL of deionized water, ultrasonically treated at 40 kHz for 30 min, 0.4 mL of acetic acid solution and 18 g of bacterial cellulose were added, and after being dispersed in a homogenizer, 45 mL of a 2% glutaraldehyde solution was added. The reaction was stirred at 55°C for 1.5 h, cooled to room temperature, and freeze-dried at -50°C for 24 h to obtain a composite reinforced filler.

[0053] Example 2

[0054] A polyimide film with a low thermal expansion coefficient comprises the following raw materials in parts by weight: 8 parts of pyromellitic dianhydride, 8 parts of 4,4'-diaminodiphenyl ether, 4 parts of composite reinforcing filler, and 100 parts of N,N-dimethylformamide;

[0055] A method for preparing a polyimide film with a low thermal expansion coefficient comprises the following steps:

[0056] S1. Pyromellitic dianhydride, 4,4'-diaminodiphenyl ether and N,N-dimethylformamide were uniformly mixed and polycondensed at 30 ° C, 70 r / min stirring rate, under nitrogen protection for 30 min to obtain a polyamic acid resin solution;

[0057] S2. Add the composite reinforcing filler to the polyamic acid resin solution, stir at 70 r / min for 4 hours, perform ultrasonic degassing treatment at 40 kHz for 30 minutes, place it in a casting machine for film casting, and maintain the temperature at 100°C, 150°C, and 250°C for 2 hours at each temperature point to obtain a polyimide film.

[0058] The composite reinforced filler is specifically prepared by the following steps:

[0059] A1. Add 1.5 g of graphene oxide to 100 mL of Tris-HCl buffer (pH 8.5) and stir until uniform. Then add 0.3 g of dopamine and stir at 25°C for 3.5 h. Then add 0.3 g of boron nitride and continue stirring for 1 h. The mixture is filtered, washed three times with deionized water, and dried in an oven at 70°C for 10 min to obtain modified graphene oxide.

[0060] A2. 1.5 g of modified graphene oxide was added to 150 mL of ethanol and stirred. 1.2 g of tannic acid was added and stirred at 40°C and 600 rpm for 10 h. 1.6 g of lamellar porous carbon was added and the mixture was stirred for another 20 min. The mixture was filtered, washed three times with deionized water, and dried in an oven at 70°C for 10 min to obtain a layered composite material.

[0061] A3. 0.9 g of nickel chloride hexahydrate, 3.5 g of methyltrichlorosilane, and 2.5 g of the layered composite were added to 100 mL of ethanol, stirred, heated to 50°C, and stirred at 500 rpm for 40 min. The mixture was placed in a reactor and purged with argon. The reaction was incubated at 1100°C for 2 h, cooled to room temperature, removed, washed three times with deionized water, and dried in an oven at 70°C for 10 min to obtain a modified layered composite.

[0062] A4. 2.2 g of the modified layered composite material and 1.5 g of chitosan were added to 90 mL of deionized water, ultrasonically treated at 40 kHz for 30 min, 0.5 mL of acetic acid solution and 20 g of bacterial cellulose were added, and after being dispersed in a homogenizer, 50 mL of a 2% glutaraldehyde solution was added. The reaction was stirred at 55°C for 1.5 h, cooled to room temperature, and freeze-dried at -50°C for 24 h to obtain a composite reinforced filler.

[0063] Example 3

[0064] A polyimide film with a low thermal expansion coefficient comprises the following raw materials in parts by weight: 10 parts of pyromellitic dianhydride, 10 parts of 4,4'-diaminodiphenyl ether, 5 parts of composite reinforcing filler, and 120 parts of N,N-dimethylformamide;

[0065] A method for preparing a polyimide film with a low thermal expansion coefficient comprises the following steps:

[0066] S1. Pyromellitic dianhydride, 4,4'-diaminodiphenyl ether and N,N-dimethylformamide were mixed uniformly and polycondensed at 35 ° C, 80 r / min stirring rate, under nitrogen protection for 35 min to obtain a polyamic acid resin solution;

[0067] S2. Add the composite reinforcing filler to the polyamic acid resin solution, stir at 80 r / min for 5 hours, perform ultrasonic degassing treatment at 40 kHz for 30 minutes, place it in a casting machine for film casting, and maintain the temperature at 100°C, 150°C, and 250°C for 2 hours at each point to obtain a polyimide film.

[0068] The composite reinforced filler is specifically prepared by the following steps:

[0069] A1. Add 1.6 g of graphene oxide to 110 mL of Tris-HCl buffer (pH 8.5) and stir until uniform. Then add 0.4 g of dopamine and stir at 25°C for 3.5 h. Then add 0.4 g of boron nitride and continue stirring for 1 h. The mixture is filtered, washed three times with deionized water, and dried in an oven at 70°C for 10 min to obtain modified graphene oxide.

[0070] A2. 1.6 g of modified graphene oxide was added to 160 mL of ethanol and stirred. 1.3 g of tannic acid was added and stirred at 40°C and 600 rpm for 10 h. 1.7 g of lamellar porous carbon was added and the mixture was stirred for another 20 min. The mixture was filtered, washed three times with deionized water, and dried in an oven at 70°C for 10 min to obtain a layered composite material.

[0071] A3. 1 g of nickel chloride hexahydrate, 3.6 g of methyltrichlorosilane, and 2.6 g of the layered composite were added to 110 mL of ethanol, stirred, heated to 50°C, and stirred at 500 rpm for 40 min. The mixture was placed in a reactor and purged with argon. The reaction was continued at 1100°C for 2 h, cooled to room temperature, removed, washed three times with deionized water, and dried in an oven at 70°C for 10 min to obtain a modified layered composite.

[0072] A4. 2.4 g of the modified layered composite material and 1.7 g of chitosan were added to 100 mL of deionized water, ultrasonically treated at 40 kHz for 30 min, 0.6 mL of acetic acid solution and 22 g of bacterial cellulose were added, and after being dispersed in a homogenizer, 55 mL of a 2% glutaraldehyde solution was added. The reaction was stirred at 55°C for 1.5 h, cooled to room temperature, and freeze-dried at -50°C for 24 h to obtain a composite reinforced filler.

[0073] Comparative Example 1

[0074] A polyimide film with a low thermal expansion coefficient comprises the following raw materials in parts by weight: 10 parts of pyromellitic dianhydride, 10 parts of 4,4'-diaminodiphenyl ether, 5 parts of composite reinforcing filler, and 120 parts of N,N-dimethylformamide;

[0075] A method for preparing a polyimide film with a low thermal expansion coefficient comprises the following steps:

[0076] S1. Pyromellitic dianhydride, 4,4'-diaminodiphenyl ether and N,N-dimethylformamide were mixed uniformly and polycondensed at 35 ° C, 80 r / min stirring rate, under nitrogen protection for 35 min to obtain a polyamic acid resin solution;

[0077] S2. Add the composite reinforcing filler to the polyamic acid resin solution, stir at 80 r / min for 5 hours, perform ultrasonic degassing treatment at 40 kHz for 30 minutes, place it in a casting machine for film casting, and maintain the temperature at 100°C, 150°C, and 250°C for 2 hours at each point to obtain a polyimide film.

[0078] The composite reinforced filler is specifically prepared by the following steps:

[0079] A1. Add 1.6 g of graphene oxide to 160 mL of ethanol and stir until uniform. Then add 1.3 g of tannic acid and stir at 40°C and 600 rpm for 10 h. Then add 1.7 g of lamellar porous carbon and continue stirring for 20 min. The mixture is filtered, washed three times with deionized water, and dried in an oven at 70°C for 10 min to obtain a layered composite material.

[0080] A2. 1 g of nickel chloride hexahydrate, 3.6 g of methyltrichlorosilane, and 2.6 g of the layered composite were added to 110 mL of ethanol, stirred, heated to 50°C, and stirred at 500 rpm for 40 min. The mixture was placed in a reactor and purged with argon. The reaction was continued at 1100°C for 2 h, cooled to room temperature, removed, washed three times with deionized water, and dried in an oven at 70°C for 10 min to obtain a modified layered composite.

[0081] A3. 2.4 g of the modified layered composite material and 1.7 g of chitosan were added to 100 mL of deionized water, ultrasonically treated at 40 kHz for 30 min, 0.6 mL of acetic acid solution and 22 g of bacterial cellulose were added, and after being dispersed in a homogenizer, 55 mL of a 2% glutaraldehyde solution was added. The reaction was stirred at 55°C for 1.5 h, cooled to room temperature, and freeze-dried at -50°C for 24 h to obtain a composite reinforced filler.

[0082] Comparative Example 2

[0083] A polyimide film with a low thermal expansion coefficient comprises the following raw materials in parts by weight: 10 parts of pyromellitic dianhydride, 10 parts of 4,4'-diaminodiphenyl ether, 5 parts of composite reinforcing filler, and 120 parts of N,N-dimethylformamide;

[0084] A method for preparing a polyimide film with a low thermal expansion coefficient comprises the following steps:

[0085] S1. Pyromellitic dianhydride, 4,4'-diaminodiphenyl ether and N,N-dimethylformamide were mixed uniformly and polycondensed at 35 ° C, 80 r / min stirring rate, under nitrogen protection for 35 min to obtain a polyamic acid resin solution;

[0086] S2. Add the composite reinforcing filler to the polyamic acid resin solution, stir at 80 r / min for 5 hours, perform ultrasonic degassing treatment at 40 kHz for 30 minutes, place it in a casting machine for film casting, and maintain the temperature at 100°C, 150°C, and 250°C for 2 hours at each point to obtain a polyimide film.

[0087] The composite reinforced filler is specifically prepared by the following steps:

[0088] A1. Add 1.6 g of graphene oxide to 110 mL of Tris-HCl buffer (pH 8.5) and stir until uniform. Then add 0.4 g of dopamine and stir at 25°C for 3.5 h. Then add 0.4 g of boron nitride and continue stirring for 1 h. The mixture is filtered, washed three times with deionized water, and dried in an oven at 70°C for 10 min to obtain modified graphene oxide.

[0089] A2. 1 g of nickel chloride hexahydrate, 3.6 g of methyltrichlorosilane, and 2.6 g of modified graphene oxide were added to 110 mL of ethanol, stirred, heated to 50°C, and stirred at 500 rpm for 40 min. The mixture was placed in a reactor and purged with argon. The reaction was continued at 1100°C for 2 h, cooled to room temperature, removed, washed three times with deionized water, and dried in an oven at 70°C for 10 min to obtain a composite material.

[0090] A3. 2.4 g of the composite material and 1.7 g of chitosan were added to 100 mL of deionized water and ultrasonically treated at 40 kHz for 30 min. 0.6 mL of acetic acid solution and 22 g of bacterial cellulose were added and blended in a homogenizer. 55 mL of a 2% glutaraldehyde solution was added and the mixture was stirred at 55°C for 1.5 h. The mixture was cooled to room temperature and freeze-dried at -50°C for 24 h to obtain a composite reinforced filler.

[0091] Comparative Example 3

[0092] A polyimide film with a low thermal expansion coefficient comprises the following raw materials in parts by weight: 10 parts of pyromellitic dianhydride, 10 parts of 4,4'-diaminodiphenyl ether, 5 parts of composite reinforcing filler, and 120 parts of N,N-dimethylformamide;

[0093] A method for preparing a polyimide film with a low thermal expansion coefficient comprises the following steps:

[0094] S1. Pyromellitic dianhydride, 4,4'-diaminodiphenyl ether and N,N-dimethylformamide were mixed uniformly and polycondensed at 35 ° C, 80 r / min stirring rate, under nitrogen protection for 35 min to obtain a polyamic acid resin solution;

[0095] S2. Add the composite reinforcing filler to the polyamic acid resin solution, stir at 80 r / min for 5 hours, perform ultrasonic degassing treatment at 40 kHz for 30 minutes, place it in a casting machine for film casting, and maintain the temperature at 100°C, 150°C, and 250°C for 2 hours at each point to obtain a polyimide film.

[0096] The composite reinforced filler is specifically prepared by the following steps:

[0097] A1. Add 1.6 g of graphene oxide to 110 mL of Tris-HCl buffer (pH 8.5) and stir until uniform. Then add 0.4 g of dopamine and stir at 25°C for 3.5 h. Then add 0.4 g of boron nitride and continue stirring for 1 h. The mixture is filtered, washed three times with deionized water, and dried in an oven at 70°C for 10 min to obtain modified graphene oxide.

[0098] A2. 1.6 g of modified graphene oxide was added to 160 mL of ethanol and stirred. 1.3 g of tannic acid was added and stirred at 40°C and 600 rpm for 10 h. 1.7 g of lamellar porous carbon was added and the mixture was stirred for another 20 min. The mixture was filtered, washed three times with deionized water, and dried in an oven at 70°C for 10 min to obtain a layered composite material.

[0099] A3. 2.4 g of the layered composite material and 1.7 g of chitosan were added to 100 mL of deionized water, ultrasonically treated at 40 kHz for 30 min, 0.6 mL of acetic acid solution and 22 g of bacterial cellulose were added, and after being dispersed in a homogenizer, 55 mL of a 2% glutaraldehyde solution was added. The reaction was stirred at 55°C for 1.5 h, cooled to room temperature, and freeze-dried at -50°C for 24 h to obtain a composite reinforced filler.

[0100] Comparative Example 4

[0101] A polyimide film with a low thermal expansion coefficient comprises the following raw materials in parts by weight: 10 parts of pyromellitic dianhydride, 10 parts of 4,4'-diaminodiphenyl ether, 5 parts of composite reinforcing filler, and 120 parts of N,N-dimethylformamide;

[0102] A method for preparing a polyimide film with a low thermal expansion coefficient comprises the following steps:

[0103] S1. Pyromellitic dianhydride, 4,4'-diaminodiphenyl ether and N,N-dimethylformamide were mixed uniformly and polycondensed at 35 ° C, 80 r / min stirring rate, under nitrogen protection for 35 min to obtain a polyamic acid resin solution;

[0104] S2. Add the composite reinforcing filler to the polyamic acid resin solution, stir at 80 r / min for 5 hours, perform ultrasonic degassing treatment at 40 kHz for 30 minutes, place it in a casting machine for film casting, and maintain the temperature at 100°C, 150°C, and 250°C for 2 hours at each point to obtain a polyimide film.

[0105] The composite reinforced filler is specifically prepared by the following steps:

[0106] A1. Add 1.6 g of graphene oxide to 110 mL of Tris-HCl buffer (pH 8.5) and stir until uniform. Then add 0.4 g of dopamine and stir at 25°C for 3.5 h. Then add 0.4 g of boron nitride and continue stirring for 1 h. The mixture is filtered, washed three times with deionized water, and dried in an oven at 70°C for 10 min to obtain modified graphene oxide.

[0107] A2. 1.6 g of modified graphene oxide was added to 160 mL of ethanol and stirred. 1.3 g of tannic acid was added and stirred at 40°C and 600 rpm for 10 h. 1.7 g of lamellar porous carbon was added and the mixture was stirred for another 20 min. The mixture was filtered, washed three times with deionized water, and dried in an oven at 70°C for 10 min to obtain a layered composite material.

[0108] A3. Add 1 g of nickel chloride hexahydrate, 3.6 g of methyltrichlorosilane, and 2.6 g of the layered composite material to 110 mL of ethanol, stir evenly, heat to 50°C, and stir at 500 r / min for 40 min. Place the mixture in a reactor and introduce argon. After reacting at 1100°C for 2 h, cool to room temperature, remove the mixture, wash it three times with deionized water, and dry it in an oven at 70°C for 10 min to obtain a composite reinforced filler.

[0109] The properties of the polyimide films prepared in Examples 1-3 and Comparative Examples 1-4 were tested.

[0110] Thermal conductivity and thermal expansion coefficient test: The thermal conductivity and thermal expansion coefficient of the polyimide film prepared above were tested with reference to ASTM-D696 standard.

[0111] Mechanical properties test: A universal material testing machine was used to perform tensile tests at room temperature with a specimen gauge length of 20 mm and a speed of 10 mm / s.

[0112] As shown in Table 1 below.

[0113] Table 1 Performance test of polyimide films prepared in Examples 1-3 and Comparative Examples 1-4

[0114]

[0115]

[0116] It can be seen from the data in Table 1 that the polyimide films prepared in Examples 1-3 have lower thermal expansion coefficients and higher mechanical properties.

[0117] In Comparative Example 1, the modified graphene oxide was replaced with a composite reinforcing filler prepared by graphene oxide and added to the polyimide film. Its thermal expansion coefficient was high and the mechanical properties decreased, which proved that adsorbing the thermally conductive filler on the graphene oxide is conducive to loading more thermally conductive filler on the graphene oxide, and the thermally conductive filler can also form a thermal conductive path between the layers of the layered composite material, significantly improving the thermal conductivity of the polyimide film and reducing the thermal expansion coefficient of the polyimide film. In addition, the thermally conductive filler can also enhance the mechanical properties of the polyimide film.

[0118] In Comparative Example 2, the layered composite material is replaced with a composite reinforcing filler prepared by modified graphene oxide and added to the polyimide film. Its thermal expansion coefficient is high and the mechanical properties are reduced, which proves that the layered composite material formed by the lamellar porous carbon and the modified graphene oxide can significantly improve the thermal conductivity of the polyimide film, reduce the thermal expansion coefficient of the polyimide film, absorb and weaken the stress generated by external force, and improve the mechanical strength of the polyimide film. In addition, the lamellar porous carbon has a high specific surface area and porosity and has excellent thermal conductivity.

[0119] In Comparative Example 3, the modified layered composite material is replaced with a composite reinforcing filler prepared from the layered composite material and added to the polyimide film. Its thermal expansion coefficient is high and the mechanical properties are reduced, which proves that the silicon carbide nanowires formed by the growth of silicon carbide crystals along the layered composite material can connect the randomly distributed layered composite materials to form a three-dimensional network structure, significantly enhance the heat conduction path, further reduce the thermal expansion coefficient of the polyimide film, and the formed three-dimensional network structure can also absorb and weaken the gravitational force generated by external forces, thereby improving the mechanical strength of the polyimide film.

[0120] In Comparative Example 4, the composite reinforcing filler prepared without adding chitosan and bacterial cellulose was added to the polyimide film, and its thermal expansion coefficient was high and the mechanical properties decreased, which proved that the modified layered composite material, bacterial cellulose and chitosan were mixed and reacted to form an aerogel, whose surface has rich active groups hydroxyl and amine groups, which can be combined with the polyimide resin through hydrogen bonds, so that the reinforcing filler is evenly distributed in the polyimide resin, and the prepared polyimide film has excellent thermal conductivity and a low thermal expansion coefficient.

[0121] Throughout the specification, references to terms such as "one embodiment," "example," or "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these 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 any one or more embodiments or examples.

[0122] The above contents are merely examples and explanations of the present invention. Those skilled in the art may make various modifications or additions to the described specific embodiments or replace them in similar ways. As long as they do not deviate from the invention or exceed the scope defined by the claims, they should all fall within the scope of protection of the present invention.

Claims

1. A polyimide film with a low thermal expansion coefficient, characterized in that The method comprises the following raw materials in parts by weight: 6-10 parts of dianhydride, 6-10 parts of diamine, 3-5 parts of composite reinforcing filler, and 80-120 parts of polar solvent; The composite reinforced filler is specifically prepared by the following steps: A1. Graphene oxide was added to Tris-HCl buffer, stirred evenly, dopamine was added, and after the reaction was completed, a thermally conductive filler was added, and stirring was continued. After mixing, the mixture was filtered, washed, and dried to obtain modified graphene oxide. A2. The modified graphene oxide was added to ethanol, stirred evenly, tannic acid was added, stirred, and then the lamellar porous carbon was added. After stirring, the reaction was completed, filtered, washed, and dried to obtain a layered composite material. A3 nickel chloride hexahydrate, methyltrichlorosilane and the layered composite material were added to ethanol, stirred, placed in a reactor, introduced into an inert gas, reacted at 1000-1200 ℃ for 1.5-2.5h, cooled to room temperature, removed, washed, and dried to obtain a modified layered composite material; A4. The modified layered composite material and chitosan were added to deionized water. After ultrasonic treatment, acetic acid solution and bacterial cellulose were added. After homogenization, glutaraldehyde solution was added. After stirring, the mixture was cooled to room temperature and freeze-dried to obtain a composite reinforced filler.

2. A polyimide film with a low thermal expansion coefficient according to claim 1, characterized in that: In step A1, the ratio of the graphene oxide, Tris-HCl buffer, dopamine and thermal conductive filler is (1.4-1.6) g: (90-110) mL: (0.2-0.4) g: (0.2-0.4) g.

3. The polyimide film with low thermal expansion coefficient according to claim 1, characterized in that: In step A2, the ratio of the modified graphene oxide, ethanol, tannic acid and lamellar porous carbon is (1.4-1.6) g: (140-160) mL: (1.1-1.3) g: (1.5-1.7) g.

4. The polyimide film with low thermal expansion coefficient according to claim 1, characterized in that: In step A3, the nickel chloride hexahydrate, methyltrichlorosilane, layered composite material and ethanol are used in a ratio of (0.8-1) g: (3.4-3.6) g: (2.4-2.6) g: (90-111) mL.

5. The polyimide film with low thermal expansion coefficient according to claim 1, characterized in that: In step A4, the modified layered composite material, chitosan, deionized water, acetic acid solution, bacterial cellulose and glutaraldehyde solution are used in a ratio of (2-2.4) g: (1.3-1.7) g: (80-100) mL: (0.4-0.6) mL: (18-22) g: (45-55) mL.

6. The polyimide film with low thermal expansion coefficient according to claim 1, characterized in that: The dianhydride is selected from any one of pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride and 2,2',3,3'-biphenyltetracarboxylic dianhydride.

7. The polyimide film with low thermal expansion coefficient according to claim 1, characterized in that: The diamine is selected from any one of 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether and p-phenylenediamine.

8. The polyimide film with low thermal expansion coefficient according to claim 1, characterized in that: The polar solvent is selected from any one of N,N-dimethylformamide, N,N-dimethylacetamide and N-methylpyrrolidone.

9. A method for preparing a polyimide film with a low thermal expansion coefficient according to any one of claims 1 to 8, characterized in that: The method comprises the following preparation steps: S1. The dianhydride, diamine and polar solvent are mixed uniformly, and the polycondensation reaction is carried out under nitrogen protection at 25-35 ° C, a stirring rate of 60-80r / min for 25-35min to obtain a polyamic acid resin solution; S2. Add the composite reinforcing filler to the polyamic acid resin solution, stir at 60-80 r / min for 3-5 hours, and after ultrasonic degassing, place it in a casting machine for film casting, and then perform curing treatment to obtain a polyimide film.

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