Polyimide film with low thermal expansion coefficient and preparation method thereof

Abstract

The 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, the polyimide film comprises the following raw materials by mass: 6-10 parts of dianhydride, 6-10 parts of diamine, 3-5 parts of a composite reinforcing filler, and 80-120 parts of a polar solvent. The composite reinforcing filler contains a modified layered composite material, and the in-situ synthesized silicon carbide nanowire can be connected with the layered composite material in disordered distribution to form a three-dimensional network structure, so that a heat conduction path is remarkably enhanced, and the thermal expansion coefficient of the polyimide film is reduced; the formed three-dimensional network structure containing the silicon carbide nanowires can absorb and weaken gravitation generated by external force, the mechanical strength is improved, in addition, the composite reinforcing filler comprises bacterial cellulose and chitosan, and can be combined with polyimide resin through hydrogen bonds, so that the composite reinforcing filler is uniformly distributed in the polyimide resin, and the mechanical strength is improved. The prepared polyimide film has excellent heat-conducting property and lower thermal expansion coefficient.

Description

Technical Field

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

[0002] Polyimide is a highly regular polymer with imide rings in its main chain. It has excellent chemical stability, wear resistance, flame retardancy, high temperature resistance, low temperature resistance, corrosion resistance, radiation resistance, etc. Therefore, polyimide also exhibits excellent mechanical properties and dielectric properties. Due to these excellent characteristics, polyimide is used in the aerospace field to manufacture high-temperature structural components, thermal insulation materials and electronic components. In the fields of 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. In addition, polyimide is also applied to separation membranes, lasers, optical devices, etc.

[0003] The high regularity of the polyimide molecular chain results in strong intermolecular interactions inside, leading to a slow heat conduction rate, low thermal conductivity, and the highly regular structure of the polyimide molecular chain has a high coefficient of thermal expansion, causing large expansion or contraction under temperature changes. Summary of the Invention

[0004] The present invention provides a polyimide film with a low coefficient of thermal expansion and a preparation method thereof, solving the problem of high coefficient of thermal expansion of polyimide and easy occurrence of expansion and contraction.

[0005] Technical Solution of the Present Invention: A polyimide film with a low coefficient of thermal expansion, 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 filler, and 80 - 120 parts of polar solvent; A preparation method of a polyimide film with a low coefficient of thermal expansion, comprising the following preparation steps: S1. Mix the dianhydride, diamine and polar solvent evenly, and carry out a polycondensation reaction at 25 - 35 °C and a stirring rate of 60 - 80 r / min for 25 - 35 min under nitrogen protection to obtain a polyamic acid resin solution; S2. Add the reinforcing filler to the polyamic acid resin solution, stir at 60 - 80 r / min for 3 - 5 h, after ultrasonic degassing treatment, place it in a casting machine for casting film formation, and then carry out a curing treatment to obtain a polyimide film.

[0006] Further, the dianhydride is selected from any one of pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, and 2,2',3,3'-biphenyltetracarboxylic dianhydride.

[0007] Further, the diamine is selected from any one of 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, and p-phenylenediamine.

[0008] Further, the polar solvent is selected from any one of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone.

[0009] Further, the reinforcing filler is obtained by adhering a thermal conductive filler to graphene oxide through polydopamine, then forming a layered composite material with lamellar porous carbon. After the formed layered composite material is mixed and reacted with nickel chloride hexahydrate and methyltrichlorosilane, it is further mixed and reacted with bacterial cellulose, chitosan, and glutaraldehyde, and then freeze-dried.

[0010] Further, the composite reinforcing filler is specifically prepared by the following steps: A1. Add graphene oxide to Tris-HCl buffer (tris(hydroxymethyl)aminomethane hydrochloride buffer), stir evenly, add dopamine, and after the stirring reaction is completed, add the thermal conductive filler, continue to stir and mix, then filter, wash, and dry to obtain modified graphene oxide. A2. Add the modified graphene oxide to ethanol, stir evenly, add tannic acid, stir, then add lamellar porous carbon, continue to stir until the reaction is completed, then filter, wash, and dry to obtain a layered composite material. A3. Add nickel chloride hexahydrate, methyltrichlorosilane, and the layered composite material to ethanol, stir, then place it in a reaction kettle, introduce argon, react at 1000 - 1200 °C for 1.5 - 2.5 h, then cool to room temperature, take out, wash, and dry to obtain a modified layered composite material. A4. Add the modified layered composite material and chitosan to deionized water, perform ultrasonic treatment, then add acetic acid solution and bacterial cellulose, disperse them in a homogenizing mixer, add glutaraldehyde solution, stir until completed, then cool to room temperature, and obtain the composite reinforcing filler by freeze-drying.

[0011] Further, during the above A1 reaction process, in the Tris-HCl buffer, dopamine can self-polymerize on the surface of graphene oxide to form polydopamine, enabling graphene oxide to carry a large number of phenolic hydroxyl groups and having excellent adhesion, thereby being able to adsorb the thermal conductive filler on graphene oxide to obtain modified graphene oxide.

[0012] Further, during the above A2 reaction process, tannic acid, as a cross-linking agent, can chemically bond with the hydroxyl groups on the modified graphene oxide and lamellar porous carbon, enabling the lamellar porous carbon to uniformly coat the surface of the modified graphene oxide to form a layered composite material.

[0013] Furthermore, in the above A3 reaction process, the layered composite material is mixed with nickel chloride hexahydrate and methyltrichlorosilane. Nickel chloride hexahydrate serves as a catalyst, and methyltrichlorosilane serves as a silicon source and a carbon source. Argon is introduced, and at 1100 °C, methyltrichlorosilane is thermally decomposed to form carbon and silicon elements. The carbon and silicon elements are combined through covalent bonds to form a silicon carbide crystal structure. Moreover, the carbon element provided by the lamellar porous carbon on the surface of the layered composite material can also combine with the silicon element, enabling the silicon carbide crystal to grow along the layered composite material to form silicon carbide nanowires. The formed silicon carbide nanowires are uniformly distributed on the surface of the randomly distributed layered composite material, presenting a network structure, and a modified layered composite material is obtained.

[0014] Furthermore, in the above A4 reaction process, bacterial cellulose and chitosan are used as the aerogel skeleton, and glutaraldehyde is used as a crosslinking agent to enable bacterial cellulose and chitosan to form a crosslinked structure aerogel, and the composite layered composite material is embedded in the aerogel structure as a composite reinforcing filler.

[0015] Furthermore, in step A1, the dosage ratio of graphene oxide, Tris-HCl buffer solution, dopamine, and thermal conductive filler is (1.4 - 1.6) g : (90 - 110) mL : (0.2 - 0.4) g : (0.2 - 0.4) g.

[0016] Furthermore, in step A2, the dosage 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.

[0017] Furthermore, in step A3, the dosage 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.

[0018] Furthermore, in step A4, the dosage 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.

[0019] Furthermore, the particle size of graphene oxide is 5 - 10 μm.

[0020] Furthermore, the pore size of the lamellar porous carbon is 80 - 120 nm, and the particle size is 4 - 6 μm.

[0021] Furthermore, the thermal conductive filler is selected from any one of boron nitride, aluminum nitride, and aluminum oxide.

[0022] Furthermore, the particle size of the thermal conductive filler is 200 - 300 nm.

[0023] The present invention has the following beneficial effects: (1) In the technical solution of the present invention, the thermal conductive filler is adsorbed on graphene oxide. The graphene oxide with a sheet structure serves as the carrier of the thermal conductive filler, which is conducive to loading more thermal conductive fillers on the graphene oxide. The combination of graphene oxide and the thermal conductive filler improves the thermal conductivity of the polyimide film, reduces the coefficient of thermal expansion of the polyimide film, and the graphene oxide and the thermal conductive filler can also enhance the mechanical properties of the polyimide film.

[0024] (2) In the technical solution of the present invention, the lamellar porous carbon and the 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 conduction path between the layers of the layered composite material, significantly improving the thermal conductivity of the polyimide film and reducing the coefficient of thermal expansion of the polyimide film. On the other hand, the formed composite layered material can absorb and weaken the stress generated by external forces, 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, which can adsorb and fix the thermal conductive filler on the modified graphene oxide, increasing the structural stability of the layered composite material. Moreover, the lamellar porous carbon has a high specific surface area and porosity and excellent thermal conductivity, thus significantly reducing the coefficient of thermal expansion of the polyimide film and avoiding large expansion or contraction of the polyimide film under temperature changes.

[0025] (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 uniformly distributed on the surface of the randomly distributed layered composite material, presenting a network structure to obtain 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 coefficient of thermal expansion. Moreover, the in-situ synthesized silicon carbide nanowires can connect the randomly distributed layered composite material to form a three-dimensional network structure, significantly enhancing the thermal conduction path and further reducing the coefficient of thermal expansion 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, improving the mechanical strength of the polyimide film.

[0026] (4) In the technical solution of the present invention, the 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 to increase the crosslinking density, enhance the mechanical strength of the aerogel, and improve 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 skeletons, and their surfaces have abundant 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. DETAILED DESCRIPTION

[0027] 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 described embodiments 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 creative work are within the scope of protection of the present invention.

[0028] The raw materials used in the examples of the present invention are as follows, and all reagents used are of analytical grade.

[0029] The dianhydride is pyromellitic dianhydride, the diamine is 4,4'-diaminodiphenyl ether, and the polar solvent is N,N-dimethylformamide.

[0030] The particle size of graphene oxide is 8 μm.

[0031] The porous carbon sheet has a pore size of 100 nm and a particle size of 5 μm and was purchased from Xi'an Qiyue Biotechnology Co., Ltd.

[0032] The thermal conductive filler is selected from boron nitride and has a particle size of 200 nm.

[0033] Bacterial cellulose was purchased from Beijing Guanlan Technology Co., Ltd.

[0034] Example 1 A polyimide film with a low thermal expansion coefficient comprises the following raw materials in parts by weight: 6 parts of pyromellitic anhydride, 6 parts of 4,4'-diaminodiphenyl ether, 3 parts of composite reinforcing filler, and 80 parts of N,N-dimethylformamide; A method for preparing a polyimide film with a low thermal expansion coefficient comprises the following preparation steps: S1. The pyromellitic anhydride, 4,4'-diaminodiphenyl ether and N,N-dimethylformamide were uniformly mixed, and polycondensed for 25 minutes at 25°C, a stirring rate of 60r / min, and nitrogen protection to obtain a polyamic acid resin solution; S2. Add the reinforcing filler into the polyamic acid resin solution, stir at 60 r / min for 3 h, conduct ultrasonic degassing treatment at 40 KHz for 30 min, place it in a casting machine for casting film formation, and conduct curing treatment at 100 °C, 150 °C, and 250 °C for 2 h at each temperature point to obtain the polyimide film.

[0035] The composite reinforcing filler is specifically prepared by the following steps: A1. Add 1.4 g of graphene oxide into 90 mL of Tris-HCl buffer solution with a pH of 8.5, stir evenly, add 0.2 g of dopamine, stir and react at 25 °C for 3.5 h, add 0.2 g of boron nitride, continue to stir and mix for 1 h, then filter, wash with deionized water 3 times, and dry in an oven at 70 °C for 10 min to obtain modified graphene oxide; A2. Add 1.4 g of modified graphene oxide into 140 mL of ethanol, stir evenly, add 1.1 g of tannic acid, stir at 40 °C and 600 r / min for 10 h, add 1.5 g of lamellar porous carbon, continue to stir and react for 20 min, then filter, wash with deionized water 3 times, and dry in an oven at 70 °C for 10 min to obtain the layered composite material; A3. Add 0.8 g of nickel chloride hexahydrate, 3.4 g of methyltrichlorosilane, and 2.4 g of the layered composite material into 90 mL of ethanol, stir evenly, heat up to 50 °C, stir at 500 r / min for 40 min, place it in a reaction kettle, introduce argon, react at 1100 °C for 2 h, then cool to room temperature, take out, wash with deionized water 3 times, and dry in an oven at 70 °C for 10 min to obtain the modified layered composite material; A4. Add 2 g of the modified layered composite material and 1.3 g of chitosan into 80 mL of deionized water, conduct ultrasonic treatment at 40 KHz for 30 min, add 0.4 mL of acetic acid solution and 18 g of bacterial cellulose, disperse it in a homogenizing mixer, then add 45 mL of 2% glutaraldehyde solution, stir and react at 55 °C for 1.5 h, cool to room temperature, and freeze-dry at -50 °C for 24 h to obtain the composite reinforcing filler.

[0036] Example 2 A polyimide film with a low coefficient of thermal expansion, comprising the following raw materials in parts by mass: 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; A preparation method of a polyimide film with a low coefficient of thermal expansion, comprising the following preparation steps: S1. Mix pyromellitic dianhydride, 4,4'-diaminodiphenyl ether, and N,N-dimethylformamide evenly, conduct polycondensation reaction at 30 °C and a stirring rate of 70 r / min under nitrogen protection for 30 min to obtain the polyamic acid resin solution; S2. Add reinforcing filler into the polyamic acid resin solution, stir at 70 r / min for 4 h, conduct ultrasonic degassing treatment at 40 KHz for 30 min, cast and form a film in a casting machine, and carry out curing treatment at 100 °C, 150 °C, and 250 °C for 2 h at each temperature point to obtain a polyimide film.

[0037] The composite reinforcing filler is specifically prepared by the following steps: A1. Add 1.5 g of graphene oxide into 100 mL of Tris-HCl buffer solution with a pH of 8.5, stir evenly, add 0.3 g of dopamine, stir and react at 25 °C for 3.5 h, add 0.3 g of boron nitride, continue to stir and mix for 1 h, then filter, wash with deionized water 3 times, and dry in an oven at 70 °C for 10 min to obtain modified graphene oxide; A2. Add 1.5 g of modified graphene oxide into 150 mL of ethanol, stir evenly, add 1.2 g of tannic acid, stir at 40 °C and 600 r / min for 10 h, add 1.6 g of lamellar porous carbon, continue to stir and react for 20 min, then filter, wash with deionized water 3 times, and dry in an oven at 70 °C for 10 min to obtain a layered composite material; A3. Add 0.9 g of nickel chloride hexahydrate, 3.5 g of methyltrichlorosilane, and 2.5 g of the layered composite material into 100 mL of ethanol, stir evenly, heat up to 50 °C, stir at 500 r / min for 40 min, place in a reaction kettle, introduce argon, react at 1100 °C for 2 h, then cool to room temperature, take out, wash with deionized water 3 times, and dry in an oven at 70 °C for 10 min to obtain a modified layered composite material; A4. Add 2.2 g of the modified layered composite material and 1.5 g of chitosan into 90 mL of deionized water, conduct ultrasonic treatment at 40 KHz for 30 min, add 0.5 mL of acetic acid solution and 20 g of bacterial cellulose, disperse in a homogenizing mixer, then add 50 mL of 2% glutaraldehyde solution, stir and react at 55 °C for 1.5 h, cool to room temperature, and freeze-dry at -50 °C for 24 h to obtain the composite reinforcing filler.

[0038] Example 3 A polyimide film with a low coefficient of thermal expansion, comprising the following raw materials in parts by mass: 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; A preparation method of a polyimide film with a low coefficient of thermal expansion, comprising the following preparation steps: S1. Mix pyromellitic dianhydride, 4,4'-diaminodiphenyl ether and N,N-dimethylformamide evenly, and carry out a polycondensation reaction for 35 min under nitrogen protection at a stirring rate of 80 r / min at 35 °C to obtain a polyamic acid resin solution; S2. Add the reinforcing filler to the polyamic acid resin solution, stir at 80 r / min for 5 h, perform ultrasonic degassing treatment at 40 KHz for 30 min, cast and form a film in a casting machine, and carry out a curing treatment by maintaining the temperature at 100 °C, 150 °C, and 250 °C for 2 h each to obtain a polyimide film.

[0039] The composite reinforcing filler is specifically prepared by the following steps: A1. Add 1.6 g of graphene oxide to 110 mL of Tris-HCl buffer solution with a pH of 8.5, stir evenly, add 0.4 g of dopamine, stir and react at 25 °C for 3.5 h, add 0.4 g of boron nitride, continue to stir and mix for 1 h, then filter, wash with deionized water 3 times, and dry in an oven at 70 °C for 10 min to obtain modified graphene oxide; A2. Add 1.6 g of modified graphene oxide to 160 mL of ethanol, stir evenly, add 1.3 g of tannic acid, stir at 40 °C and 600 r / min for 10 h, add 1.7 g of lamellar porous carbon, continue to stir and react for 20 min, then filter, wash with deionized water 3 times, and dry in an oven at 70 °C for 10 min to obtain a layered composite material; 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 up to 50 °C, stir at 500 r / min for 40 min, place in a reaction kettle, introduce argon, react at 1100 °C for 2 h, then cool to room temperature, take out, wash with deionized water 3 times, and dry in an oven at 70 °C for 10 min to obtain a modified layered composite material; A4. Add 2.4 g of the modified layered composite material and 1.7 g of chitosan to 100 mL of deionized water, perform ultrasonic treatment at 40 KHz for 30 min, add 0.6 mL of acetic acid solution and 22 g of bacterial cellulose, disperse in a homogenizing mixer, then add 55 mL of a 2% glutaraldehyde solution, stir and react at 55 °C for 1.5 h, cool to room temperature, and freeze-dry at -50 °C for 24 h to obtain the composite reinforcing filler.

[0040] Comparative Example 1 A polyimide film with a low coefficient of thermal expansion comprises the following raw materials in parts by mass: 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; A preparation method of a polyimide film with a low coefficient of thermal expansion, comprising the following preparation steps: S1. Mix pyromellitic dianhydride, 4,4'-diaminodiphenyl ether, and N,N-dimethylformamide evenly, and carry out a polycondensation reaction at 35 °C and a stirring rate of 80 r / min under nitrogen protection for 35 min to obtain a polyamic acid resin solution; S2. Add a reinforcing filler to the polyamic acid resin solution, stir at 80 r / min for 5 h, carry out ultrasonic degassing treatment at 40 KHz for 30 min, place it in a casting machine for casting film formation, and carry out curing treatment by maintaining the temperature at 100 °C, 150 °C, and 250 °C for 2 h each to obtain a polyimide film.

[0041] The composite reinforcing filler is specifically prepared by the following steps: A1. Add 1.6 g of graphene oxide to 160 mL of ethanol, stir evenly, add 1.3 g of tannic acid, stir at 40 °C and 600 r / min for 10 h, add 1.7 g of lamellar porous carbon, continue stirring and reacting for 20 min, filter, wash with deionized water 3 times, and dry in an oven at 70 °C for 10 min to obtain a layered composite material; A2. 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 up to 50 °C, stir at 500 r / min for 40 min, place it in a reaction kettle, introduce argon, react at 1100 °C for 2 h, cool to room temperature, take out, wash with deionized water 3 times, and dry in an oven at 70 °C for 10 min to obtain a modified layered composite material; A3. Add 2.4 g of the modified layered composite material and 1.7 g of chitosan to 100 mL of deionized water, carry out ultrasonic treatment at 40 KHz for 30 min, add 0.6 mL of acetic acid solution and 22 g of bacterial cellulose, disperse in a homogenizing mixer, add 55 mL of a 2% glutaraldehyde solution, stir and react at 55 °C for 1.5 h, cool to room temperature, and freeze-dry at -50 °C for 24 h to obtain a composite reinforcing filler.

[0042] Comparative Example 2 A polyimide film with a low coefficient of thermal expansion, comprising the following raw materials in parts by mass: 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; A preparation method of a polyimide film with a low coefficient of thermal expansion, comprising the following preparation steps: S1. Mix pyromellitic dianhydride, 4,4'-diaminodiphenyl ether and N,N-dimethylformamide evenly, and carry out a polycondensation reaction for 35 min under nitrogen protection at a stirring rate of 80 r / min at 35 °C to obtain a polyamic acid resin solution; S2. Add the reinforcing filler to the polyamic acid resin solution, stir at 80 r / min for 5 h, carry out ultrasonic degassing treatment at 40 KHz for 30 min, cast a film in a casting machine, and carry out curing treatment by heat preservation at 100 °C, 150 °C, and 250 °C for 2 h each to obtain a polyimide film.

[0043] The composite reinforcing filler is specifically prepared by the following steps: A1. Add 1.6 g of graphene oxide to 110 mL of Tris-HCl buffer solution with a pH of 8.5, stir evenly, add 0.4 g of dopamine, stir and react at 25 °C for 3.5 h, add 0.4 g of boron nitride, continue to stir and mix for 1 h, then filter, wash with deionized water 3 times, and dry in an oven at 70 °C for 10 min to obtain modified graphene oxide; A2. Add 1 g of nickel chloride hexahydrate, 3.6 g of methyltrichlorosilane and 2.6 g of modified graphene oxide to 110 mL of ethanol, stir evenly, heat up to 50 °C, stir at 500 r / min for 40 min, place in a reaction kettle, introduce argon, react at 1100 °C for 2 h, cool to room temperature, take out, wash with deionized water 3 times, and dry in an oven at 70 °C for 10 min to obtain a composite material; A3. Add 2.4 g of the composite material and 1.7 g of chitosan to 100 mL of deionized water, carry out ultrasonic treatment at 40 KHz for 30 min, add 0.6 mL of acetic acid solution and 22 g of bacterial cellulose, disperse in a homogenizing mixer, then add 55 mL of a 2% glutaraldehyde solution, stir and react at 55 °C for 1.5 h, cool to room temperature, and freeze-dry at -50 °C for 24 h to obtain the composite reinforcing filler.

[0044] Comparative Example 3 A polyimide film with a low coefficient of thermal expansion, comprising the following raw materials in parts by mass: 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; A preparation method of a polyimide film with a low coefficient of thermal expansion, comprising the following preparation steps: S1. Mix pyromellitic dianhydride, 4,4'-diaminodiphenyl ether and N,N-dimethylformamide evenly, and carry out a polycondensation reaction for 35 min under nitrogen protection at a stirring rate of 80 r / min at 35 °C to obtain a polyamic acid resin solution; S2. Add the reinforcing filler into the polyamic acid resin solution, stir at 80 r / min for 5 h, perform ultrasonic degassing treatment at 40 KHz for 30 min, place it in a casting machine for casting film formation, and carry out curing treatment by holding at each temperature point of 100 °C, 150 °C, and 250 °C for 2 h to obtain a polyimide film.

[0045] The composite reinforcing filler is specifically prepared by the following steps: A1. Add 1.6 g of graphene oxide into 110 mL of Tris-HCl buffer solution with a pH of 8.5, stir evenly, add 0.4 g of dopamine, stir and react at 25 °C for 3.5 h, then add 0.4 g of boron nitride, continue to stir and mix for 1 h, then filter, wash with deionized water 3 times, and dry in an oven at 70 °C for 10 min to obtain modified graphene oxide; A2. Add 1.6 g of modified graphene oxide into 160 mL of ethanol, stir evenly, add 1.3 g of tannic acid, stir at 40 °C and 600 r / min for 10 h, add 1.7 g of lamellar porous carbon, continue to stir and react for 20 min, then filter, wash with deionized water 3 times, and dry in an oven at 70 °C for 10 min to obtain a layered composite material; A3. Add 2.4 g of the layered composite material and 1.7 g of chitosan into 100 mL of deionized water, perform ultrasonic treatment at 40 KHz for 30 min, add 0.6 mL of acetic acid solution and 22 g of bacterial cellulose, disperse in a homogenizing mixer, then add 55 mL of a 2% glutaraldehyde solution, stir and react at 55 °C for 1.5 h, cool to room temperature, and freeze-dry at -50 °C for 24 h to obtain the composite reinforcing filler.

[0046] Comparative Example 4 A polyimide film with a low coefficient of thermal expansion, comprising the following raw materials in parts by mass: 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; A preparation method of a polyimide film with a low coefficient of thermal expansion, comprising the following preparation steps: S1. Mix pyromellitic dianhydride, 4,4'-diaminodiphenyl ether, and N,N-dimethylformamide evenly, carry out polycondensation reaction at 35 °C and a stirring rate of 80 r / min under nitrogen protection for 35 min to obtain a polyamic acid resin solution; S2. Add the reinforcing filler into the polyamic acid resin solution, stir at 80 r / min for 5 h, perform ultrasonic degassing treatment at 40 KHz for 30 min, place it in a casting machine for casting film formation, and carry out curing treatment by holding at each temperature point of 100 °C, 150 °C, and 250 °C for 2 h to obtain a polyimide film.

[0047] The composite reinforcing filler is specifically prepared by the following steps: A1. Add 1.6 g of graphene oxide to 110 mL of Tris-HCl buffer solution with a pH of 8.5, stir evenly, add 0.4 g of dopamine, stir and react at 25 °C for 3.5 h, then add 0.4 g of boron nitride, continue to stir and mix for 1 h, filter, wash with deionized water 3 times, and dry in an oven at 70 °C for 10 min to obtain modified graphene oxide; A2. Add 1.6 g of modified graphene oxide to 160 mL of ethanol, stir evenly, add 1.3 g of tannic acid, stir at 40 °C and 600 r / min for 10 h, add 1.7 g of lamellar porous carbon, continue to stir and react for 20 min, filter, wash with deionized water 3 times, and dry in an oven at 70 °C for 10 min to obtain a layered composite material; 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 up to 50 °C, stir at 500 r / min for 40 min, place it in a reaction kettle, introduce argon, react at 1100 °C for 2 h, cool to room temperature, take it out, wash with deionized water 3 times, and dry in an oven at 70 °C for 10 min to obtain the composite reinforcing filler.

[0048] Now, the polyimide films prepared in Examples 1-3 and Comparative Examples 1-4 are subjected to performance testing.

[0049] Testing of thermal conductivity and coefficient of thermal expansion: Refer to the ASTM-D696 standard to test the thermal conductivity and coefficient of thermal expansion of the above-prepared polyimide films.

[0050] Mechanical property testing: Use a universal material testing machine. At room temperature, with a specimen gauge length of 20 mm, conduct a tensile test at a speed of 10 mm / s.

[0051] As shown in Table 1 below.

[0052] Table 1 Performance testing of polyimide films prepared in Examples 1-3 and Comparative Examples 1-4

[0053] It can be seen from the data in Table 1 that the polyimide films prepared in Examples 1-3 have a lower coefficient of thermal expansion and higher mechanical properties.

[0054] In Comparative Example 1, the composite reinforcing filler prepared by replacing the modified graphene oxide with graphene oxide was added to the polyimide film, and its high coefficient of thermal expansion and decreased mechanical properties demonstrated that adsorbing the thermal conductive filler on graphene oxide was beneficial for loading more thermal conductive fillers on graphene oxide, and the thermal conductive filler could also form a thermal conduction path between the layers of the layered composite material, significantly improving the thermal conductivity of the polyimide film, reducing the coefficient of thermal expansion of the polyimide film. In addition, the thermal conductive filler could also enhance the mechanical properties of the polyimide film.

[0055] In Comparative Example 2, the composite reinforcing filler prepared by replacing the layered composite material with the modified graphene oxide was added to the polyimide film, and its high coefficient of thermal expansion and decreased mechanical properties demonstrated that forming a layered composite material with the sheet-like porous carbon and the modified graphene oxide could significantly improve the thermal conductivity of the polyimide film, reduce the coefficient of thermal expansion of the polyimide film, absorb and weaken the stress generated by external forces, and improve the mechanical strength of the polyimide film. In addition, the sheet-like porous carbon had a high specific surface area and porosity and excellent thermal conductivity.

[0056] In Comparative Example 3, the composite reinforcing filler prepared by replacing the modified layered composite material with the layered composite material was added to the polyimide film, and its high coefficient of thermal expansion and decreased mechanical properties demonstrated that the silicon carbide nanowires formed by the growth of silicon carbide crystals along the layered composite material could connect the randomly distributed layered composite materials to form a three-dimensional network structure, significantly enhancing the thermal conduction path, further reducing the coefficient of thermal expansion of the polyimide film, and the formed three-dimensional network structure could also absorb and weaken the gravitational force generated by external forces, improving the mechanical strength of the polyimide film.

[0057] In Comparative Example 4, the composite reinforcing filler prepared without adding chitosan and bacterial cellulose was added to the polyimide film, and its high coefficient of thermal expansion and decreased mechanical properties demonstrated that the modified layered composite material, bacterial cellulose, and chitosan reacted to form an aerogel, which had abundant active groups of hydroxyl and amine on its surface and could bind to the polyimide resin through hydrogen bonds, enabling the reinforcing filler to be evenly distributed in the polyimide resin, and thus the prepared polyimide film had excellent thermal conductivity and a low coefficient of thermal expansion.

[0058] In the description of the specification, the description referring to terms such as "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0059] The above content is only an example and illustration of the present invention. Those skilled in the art to which the present technology pertains may make various modifications or supplements to the described specific embodiments, or use similar means for substitution, as long as they do not deviate from the invention or exceed the scope defined by the claims of the present invention, and shall fall within the protection scope of the present invention.

Claims

1. A polyimide film with a low coefficient of thermal expansion, characterized in that, It includes the following raw materials in parts by mass: 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 reinforcing filler is obtained by adhering a thermal conductive filler to graphene oxide through polydopamine, and then forming a layered composite material with lamellar porous carbon. After the formed layered composite material is mixed and reacted with nickel chloride hexahydrate and methyltrichlorosilane, it is further mixed and reacted with bacterial cellulose, chitosan, and glutaraldehyde.

2. The polyimide film with a low coefficient of thermal expansion according to claim 1, wherein The composite reinforcing filler is specifically prepared by the following steps: A1. Add graphene oxide to Tris-HCl buffer solution, stir evenly, add dopamine, after the stirring reaction is completed, add the thermal conductive filler, continue to stir and mix, then filter, wash, and dry to obtain modified graphene oxide; A2. Add the modified graphene oxide to ethanol, stir evenly, add tannic acid, after stirring, add lamellar porous carbon, continue to stir until the reaction is completed, then filter, wash, and dry to obtain a layered composite material; A3. Add nickel chloride hexahydrate, methyltrichlorosilane, and the layered composite material to ethanol, stir, place it in a reaction kettle, introduce an inert gas, react at 1000-1200 °C for 1.5-2.5 h, then cool to room temperature, take out, wash, and dry to obtain a modified layered composite material; A4. Add the modified layered composite material and chitosan to deionized water, perform ultrasonic treatment, add acetic acid solution and bacterial cellulose, after homogenization, add glutaraldehyde solution, stir until completed, then cool to room temperature, and perform freeze-drying to obtain the composite reinforcing filler.

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

4. A polyimide film with a low coefficient of thermal expansion according to claim 2, characterized in that, In step A2, the dosage 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.

5. A polyimide film with a low coefficient of thermal expansion according to claim 2, characterized in that, In step A3, the dosage ratio of nickel chloride hexahydrate, methyltrichlorosilane, the layered composite material, and ethanol is (0.8-1) g : (3.4-3.6) g : (2.4-2.6) g : (90-111) mL.

6. A polyimide film with a low coefficient of thermal expansion according to claim 2, characterized in that, In step A4, the dosage 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.

7. A polyimide film with a low coefficient of thermal expansion 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.

8. A polyimide film with a low coefficient of thermal expansion 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.

9. A polyimide film with a low coefficient of thermal expansion 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.

10. A method for preparing a polyimide film with a low coefficient of thermal expansion according to any one of claims 1-9, characterized in that, It includes the following preparation steps: S1. Mix the dianhydride, diamine and polar solvent evenly, and carry out a polycondensation reaction for 25 - 35 min under nitrogen protection at a stirring rate of 60 - 80 r / min at 25 - 35 °C to obtain a polyamic acid resin solution; S2. Add the reinforcing filler into the polyamic acid resin solution, stir at 60 - 80 r / min for 3 - 5 h, after ultrasonic degassing treatment, place it in a casting machine for casting film formation, and then carry out a curing treatment to obtain a polyimide film.

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