A polyimide dielectric film and its preparation method and application

Abstract

The present invention proposes a polyimide dielectric film and its preparation method and application, the preparation method of the polyimide dielectric film comprising: subjecting carboxylated multi-walled carbon nanotubes and 2,4-diaminophenol to a condensation reaction to obtain multi-walled carbon nanotubes bonded with aminobenzoxazole; then subjecting the multi-walled carbon nanotubes bonded with aminobenzoxazole to a polycondensation reaction with an aromatic diamine monomer and an aromatic dianhydride monomer, and then subjecting the film to a thermal imidization reaction to obtain the polyimide dielectric film. The present invention proposes a polyimide dielectric film and its preparation method and application, by introducing multi-walled carbon nanotubes bonded with aminobenzoxazole into polyimide synthesis, so that the resulting polyimide dielectric film has excellent mechanical properties while obtaining a high dielectric constant and low dielectric loss.

Description

Technical Field

[0001] The present invention relates to the technical field of dielectric films, and in particular to a polyimide dielectric film and a preparation method and application thereof. Background Art

[0002] Polyimide is a polymer material with superior overall properties, widely used in a variety of fields, including aerospace, electronics, shipbuilding, and chemical engineering. Due to its outstanding dielectric properties and easily designed and regulated molecular structure, polyimide has been used as a dielectric material in areas such as microelectronic packaging, insulated cables, electrothermal cooling, and energy storage capacitors. Previous research has largely focused on low-k polyimides for power electronics packaging. However, in recent years, with the increasing emphasis on global energy issues and technological advancements, various fields have placed new demands on the dielectric properties of energy storage materials. High-k polyimide films for dielectric energy storage are receiving increasing attention.

[0003] There are two main methods for preparing high-dielectric polyimide-based film materials. One method is to meet the requirements by compounding high-dielectric ceramic powder with polyimide. For example, Weng Ling et al. used in-situ polymerization and high-speed sand milling to prepare nano-barium titanate / polyimide high-dielectric constant composite films. When the volume fraction of the powder reached 50%, the dielectric constant of the composite film increased by 10 times compared to the pure film (Weng Ling et al., Preparation and Properties of Nano-barium Titanate Doped Polyimide-Based High-Dielectric Composite Films, Polymer Science and Engineering, 2012, 2:113-116). However, the disadvantage of this method is that due to the limitations of the material's own properties and the related mechanism for improving the dielectric constant, high-dielectric constant composite materials require a high content of ceramic filler, which greatly reduces the flexibility of the polymer-based composite material and easily damages the mechanical properties of the material. Another method is to add conductive fillers to the polyimide matrix and use the percolation effect to improve the dielectric constant of the composite material. For example, Fuan et al. added nanographite sheets to polyvinylidene fluoride to prepare a high-dielectric nanocomposite (Fuan He, High Dielectric Permittivity and Low Percolation Threshold in Nanocomposites Based on Poly(vinylidenefluoride)and Exfoliated Graphite Nanoplates, Advance Materials, 2009, 21:710-715). However, the conductive filler easily forms local conductive channels near the percolation threshold, resulting in excessive dielectric loss, thus limiting the application range of this type of high-dielectric constant composite film material. Summary of the Invention

[0004] Based on the technical problems existing in the background technology, the present invention proposes a polyimide dielectric film, a preparation method and application thereof. By introducing multi-walled carbon nanotubes bonded with aminobenzoxazole into the synthesis of polyimide, the obtained polyimide dielectric film has a high dielectric constant and low dielectric loss while also having excellent mechanical properties.

[0005] The present invention provides a method for preparing a polyimide dielectric film, comprising the following steps:

[0006] S1, condensing carboxylated multi-walled carbon nanotubes and 2,4-diaminophenol to obtain multi-walled carbon nanotubes bonded with aminobenzoxazole;

[0007] S2, subjecting the multi-walled carbon nanotubes bonded with aminobenzoxazole to a polycondensation reaction with aromatic diamine monomers and aromatic dianhydride monomers, and then subjecting the film to a thermal imidization reaction to obtain the polyimide dielectric film.

[0008] In the present invention, multi-walled carbon nanotubes bonded with aminobenzoxazole are introduced into the synthesis of polyimide: (1) the amino groups of the multi-walled carbon nanotubes bonded with aminobenzoxazole can react with aromatic dianhydride monomers, thereby achieving grafting of the multi-walled carbon nanotubes onto the polyimide molecular chains, making the multi-walled carbon nanotubes difficult to approach due to the restriction of the movement of the polymer molecular chains, thereby promoting their uniform dispersion in the polyimide matrix; (2) aminobenzoxazole itself is a highly polar monomer, and its addition is conducive to further improving the dielectric properties of the obtained polyimide film; (3) the bonding of aminobenzoxazole also reduces the possibility of carbon nanotubes forming conductive channels, thereby improving the dielectric properties of the obtained polyimide while controlling the dielectric loss within an appropriate range, and finally preparing a polyimide dielectric film with excellent dielectric properties.

[0009] Preferably, the mass ratio of the carboxylated multi-walled carbon nanotubes to 2,4-diaminophenol is 1:1-3;

[0010] Preferably, the carboxylated multi-walled carbon nanotubes are obtained by adding multi-walled carbon nanotubes to concentrated acid and reacting at elevated temperature.

[0011] Preferably, the condensation reaction temperature is 120-160° C., and the time is 6-12 hours.

[0012] Preferably, the aromatic diamine monomer is at least one of 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, p-phenylenediamine or m-phenylenediamine.

[0013] Preferably, the aromatic dianhydride monomer is at least one of pyromellitic anhydride, 3,3',4,4'-biphenyltetracarboxylic anhydride, 3,3',4,4'-diphenyl ether tetracarboxylic anhydride, 3,3',4,4'-benzophenone tetracarboxylic anhydride or 3,3',4,4'-diphenyl sulfone tetracarboxylic anhydride.

[0014] Preferably, the molar ratio of the aromatic diamine monomer to the aromatic dianhydride monomer is 0.95-1.01:1;

[0015] Preferably, the amount of the aminobenzoxazole-bonded multi-walled carbon nanotubes is 1-5 wt % of the total weight of the aromatic diamine monomer and the aromatic dianhydride monomer.

[0016] Preferably, the polycondensation reaction is carried out at a temperature of 0-30° C. and for a time of 4-8 hours.

[0017] Preferably, the thermal imidization reaction comprises: heating to 50-100° C., keeping warm for 1-2 hours, then heating to 120-160° C., keeping warm for 1-2 hours, continuing to heat to 180-220° C., keeping warm for 1-2 hours, and then heating to 250-300° C., keeping warm for 1-2 hours.

[0018] The present invention also provides a polyimide dielectric film, which is prepared by the above preparation method.

[0019] The present invention also provides an application of the polyimide dielectric film in a dielectric capacitor.

[0020] In the method for preparing the polyimide dielectric film of the present invention, carboxylated multi-walled carbon nanotubes and 2,4-diaminophenol are subjected to a condensation reaction (the reaction route is schematically shown below), thereby bonding aminobenzoxazole groups to the surfaces of the multi-walled carbon nanotubes. The bonded aminobenzoxazole groups can act as diamine monomers to react with aromatic dianhydride monomers. This not only enhances the dispersion of the multi-walled carbon nanotubes in the polyimide matrix, but also fully utilizes the high dielectric properties of the aminobenzoxazole groups and the percolation effect of the conductive carbon nanotubes to improve the dielectric properties of the resulting polyimide dielectric film, reduce dielectric loss, and enhance mechanical properties.

[0021] DETAILED DESCRIPTION

[0022] Hereinafter, the technical solutions of the present invention will be described in detail through specific embodiments. However, it should be clearly stated that these embodiments are provided for illustration only and are not to be construed as limiting the scope of the present invention.

[0023] Example 1

[0024] A method for preparing a polyimide dielectric film comprises the following steps:

[0025] (1) 0.5 g of multi-walled carbon nanotubes (outer diameter range 40-60 nm, length greater than 5 μm) were added to 25 mL of a mixture of concentrated sulfuric acid and concentrated nitric acid (3:1) and ultrasonically dispersed uniformly, the mixture was heated to 60°C and stirred for 3 h, the resulting reaction solution was cooled to room temperature, filtered, washed with water, and dried to obtain carboxylated multi-walled carbon nanotubes; the obtained carboxylated multi-walled carbon nanotubes were added to 10 mL of N,N-dimethylformamide (DMF), stirred and ultrasonically dispersed uniformly under nitrogen (N2) protection, and then 1 g of 2,4-diaminophenol was added, the mixture was heated to 140°C and stirred for 9 h, filtered, washed, and dried to obtain multi-walled carbon nanotubes bonded with aminobenzoxazole;

[0026] (2) Under nitrogen (N2) protection, 3.0 g (15 mmol) of 4,4'-diaminodiphenyl ether and 0.25 g of multi-walled carbon nanotubes bonded with aminobenzoxazole were added to 40 mL of N,N-dimethylformamide (DMF), stirred and ultrasonically dispersed uniformly, and then 3.3 g (15 mmol) of pyromellitic anhydride was added. After stirring and reacting at room temperature for 6 hours, a polyamide acid solution was obtained; the obtained polyamide acid solution was uniformly coated on a glass substrate, and the obtained coating film was first heated to 80°C and kept warm for 2 hours, then heated to 140°C and kept warm for 2 hours, and then heated to 200°C and kept warm for 1 hour, and then heated to 280°C and kept warm for 1 hour. After naturally cooling to room temperature, the film was placed in water for demolding, taken out and vacuum dried to obtain the polyimide dielectric film with a film thickness of 20 μm.

[0027] Example 2

[0028] A method for preparing a polyimide dielectric film comprises the following steps:

[0029] (1) 0.5 g of multi-walled carbon nanotubes (outer diameter range 40-60 nm, length greater than 5 μm) were added to 25 mL of a mixture of concentrated sulfuric acid and concentrated nitric acid (3:1) and ultrasonically dispersed uniformly, the mixture was heated to 60°C and stirred for 3 h, the resulting reaction solution was cooled to room temperature, filtered, washed with water, and dried to obtain carboxylated multi-walled carbon nanotubes; the obtained carboxylated multi-walled carbon nanotubes were added to 10 mL of N,N-dimethylformamide (DMF), stirred and ultrasonically dispersed uniformly under nitrogen (N2) protection, and then 1 g of 2,4-diaminophenol was added, the mixture was heated to 140°C and stirred for 9 h, filtered, washed, and dried to obtain multi-walled carbon nanotubes bonded with aminobenzoxazole;

[0030] (2) Under nitrogen (N2) protection, 3.0 g (15 mmol) of 4,4'-diaminodiphenyl ether and 0.25 g of multi-walled carbon nanotubes bonded with aminobenzoxazole were added to 40 mL of N,N-dimethylformamide (DMF), stirred and ultrasonically dispersed uniformly, and then 4.4 g (15 mmol) of 3,3',4,4'-biphenyltetracarboxylic dianhydride was added. After stirring and reacting at room temperature for 6 hours, a polyamide acid solution was obtained; the obtained polyamide acid solution was uniformly coated on a glass substrate, and the obtained coating film was first heated to 80°C and kept warm for 2 hours, then heated to 140°C and kept warm for 2 hours, and then heated to 200°C and kept warm for 1 hour, and then heated to 280°C and kept warm for 1 hour. After naturally cooling to room temperature, the film was placed in water for demolding, taken out and vacuum dried to obtain the polyimide dielectric film with a film thickness of 20 μm.

[0031] Example 3

[0032] A method for preparing a polyimide dielectric film comprises the following steps:

[0033] (1) 0.5 g of multi-walled carbon nanotubes (outer diameter range 40-60 nm, length greater than 5 μm) were added to 25 mL of a mixture of concentrated sulfuric acid and concentrated nitric acid (3:1) and ultrasonically dispersed uniformly, the mixture was heated to 60°C and stirred for 3 h, the resulting reaction solution was cooled to room temperature, filtered, washed with water, and dried to obtain carboxylated multi-walled carbon nanotubes; the obtained carboxylated multi-walled carbon nanotubes were added to 10 mL of N,N-dimethylformamide (DMF), stirred and ultrasonically dispersed uniformly under nitrogen (N2) protection, and then 1 g of 2,4-diaminophenol was added, the mixture was heated to 140°C and stirred for 9 h, filtered, washed, and dried to obtain multi-walled carbon nanotubes bonded with aminobenzoxazole;

[0034] (2) Under nitrogen (N2) protection, 3.0 g (15 mmol) of 4,4'-diaminodiphenyl ether and 0.25 g of multi-walled carbon nanotubes bonded with aminobenzoxazole were added to 40 mL of N,N-dimethylformamide (DMF), stirred and ultrasonically dispersed uniformly, and then 4.7 g (15 mmol) of 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride was added. After stirring and reacting at room temperature for 6 hours, a polyamide acid solution was obtained; the obtained polyamide acid solution was uniformly coated on a glass substrate, and the obtained coating film was first heated to 80°C and kept warm for 2 hours, then heated to 140°C and kept warm for 2 hours, and then heated to 200°C and kept warm for 1 hour, and then heated to 280°C and kept warm for 1 hour. After naturally cooling to room temperature, the film was placed in water for demolding, taken out and vacuum dried to obtain the polyimide dielectric film with a film thickness of 20 μm.

[0035] Example 4

[0036] A method for preparing a polyimide dielectric film comprises the following steps:

[0037] (1) 0.5 g of multi-walled carbon nanotubes (outer diameter range 40-60 nm, length greater than 5 μm) were added to 25 mL of a mixture of concentrated sulfuric acid and concentrated nitric acid (3:1) and ultrasonically dispersed uniformly, the mixture was heated to 60°C and stirred for 3 h, the resulting reaction solution was cooled to room temperature, filtered, washed with water, and dried to obtain carboxylated multi-walled carbon nanotubes; the obtained carboxylated multi-walled carbon nanotubes were added to 10 mL of N,N-dimethylformamide (DMF), stirred and ultrasonically dispersed uniformly under nitrogen (N2) protection, and then 1 g of 2,4-diaminophenol was added, the mixture was heated to 140°C and stirred for 9 h, filtered, washed, and dried to obtain multi-walled carbon nanotubes bonded with aminobenzoxazole;

[0038] (2) Under nitrogen (N2) protection, 1.6 g (15 mmol) of p-phenylenediamine and 0.25 g of multi-walled carbon nanotubes bonded with aminobenzoxazole were added to 40 mL of N,N-dimethylformamide (DMF), stirred and ultrasonically dispersed uniformly, and then 4.8 g (15 mmol) of 3,3',4,4'-dibenzophenonetetracarboxylic dianhydride was added. After stirring and reacting at room temperature for 6 hours, a polyamide acid solution was obtained; the obtained polyamide acid solution was uniformly coated on a glass substrate, and the obtained coating film was first heated to 80°C and kept warm for 2 hours, then heated to 140°C and kept warm for 2 hours, and then heated to 200°C and kept warm for 1 hour, and then heated to 280°C and kept warm for 1 hour. After naturally cooling to room temperature, the film was placed in water for demolding, taken out and vacuum dried to obtain the polyimide dielectric film with a film thickness of 20 μm.

[0039] Comparative Example 1

[0040] A method for preparing a polyimide dielectric film comprises the following steps:

[0041] Under nitrogen (N2) protection, 3.0 g (15 mmol) of 4,4'-diaminodiphenyl ether and 0.25 g of multi-walled carbon nanotubes (outer diameter range 40-60 nm, length greater than 5 μm) were added to 40 mL of N,N-dimethylformamide (DMF), stirred and ultrasonically dispersed uniformly, and then 3.3 g (15 mmol) of pyromellitic anhydride was added. After stirring and reacting at room temperature for 6 hours, a polyamic acid solution was obtained; the obtained polyamic acid solution was uniformly coated on a glass substrate, and the obtained coating was first heated to 80°C and kept warm for 2 hours, then heated to 140°C and kept warm for 2 hours, and then heated to 200°C and kept warm for 1 hour, and then heated to 280°C and kept warm for 1 hour. After naturally cooling to room temperature, the film was placed in water for demolding, taken out and vacuum dried to obtain the polyimide dielectric film with a film thickness of 20 μm.

[0042] The polyimide dielectric films obtained in Examples 1-4 and Comparative Example 1 were subjected to performance tests as shown in the following methods. The results are shown in Table 1.

[0043] The dielectric properties of the polyimide dielectric films were tested using an Agilent 4294A precision impedance analyzer to calculate the dielectric constant (ε) and dielectric loss (tan δ) at 150°C and a frequency of 1 MHz. Prior to the above tests, the polyimide dielectric films were sputter-coated with aluminum. The mechanical properties of the polyimide dielectric films were measured using a universal materials testing machine in accordance with GB / T1040.3-2006.

[0044] Table 1 Performance test results of polyimide films obtained in Examples and Comparative Examples

[0045] Dielectric constant Dielectric loss (%) Tensile strength (MPa) Example 1 13.71 0.013 146 Example 2 12.28 0.022 135 Example 3 11.85 0.039 141 Example 4 13.23 0.018 152 Comparative Example 1 4.76 0.25 109

[0046] As can be seen from the above table, the introduction of aminobenzoxazole-bonded multi-walled carbon nanotubes into the polyimide matrix enables the obtained polyimide dielectric film to have high dielectric constant and low dielectric loss as well as excellent mechanical properties.

[0047] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for preparing a polyimide dielectric film, characterized in that: The steps include: S1, condensing carboxylated multi-walled carbon nanotubes and 2,4-diaminophenol to obtain multi-walled carbon nanotubes bonded with aminobenzoxazole; S2, subjecting the multi-walled carbon nanotubes bonded with aminobenzoxazole to a condensation polymerization reaction with an aromatic diamine monomer and an aromatic dianhydride monomer, and then subjecting the film to a thermal imidization reaction to obtain the polyimide dielectric film; The mass ratio of the carboxylated multi-walled carbon nanotubes to 2,4-diaminophenol is 1:1-3; The condensation reaction temperature is 120-160° C., and the time is 6-12 hours; the molar ratio of the aromatic diamine monomer to the aromatic dianhydride monomer is 0.95-1.01:1; The amount of the aminobenzoxazole-bonded multi-walled carbon nanotubes is 1-5 wt % of the total weight of the aromatic diamine monomer and the aromatic dianhydride monomer.

2. The method for preparing a polyimide dielectric film according to claim 1, wherein: The carboxylated multi-walled carbon nanotubes are obtained by adding the multi-walled carbon nanotubes into concentrated acid and heating the reaction.

3. The method for preparing a polyimide dielectric film according to claim 1 or 2, characterized in that: The aromatic diamine monomer is at least one of 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, p-phenylenediamine or m-phenylenediamine.

4. The method for preparing a polyimide dielectric film according to claim 1 or 2, wherein: The aromatic dianhydride monomer is at least one of pyromellitic anhydride, 3,3',4,4'-biphenyltetracarboxylic anhydride, 3,3',4,4'-diphenyl ether tetracarboxylic anhydride, 3,3',4,4'-benzophenone tetracarboxylic anhydride or 3,3',4,4'-diphenyl sulfone tetracarboxylic anhydride.

5. The method for preparing a polyimide dielectric film according to claim 1 or 2, wherein: The temperature of the polycondensation reaction is 0-30° C., and the time is 4-8 hours.

6. The method for preparing a polyimide dielectric film according to claim 1 or 2, wherein: The thermal imidization reaction comprises: heating to 50-100° C., keeping warm for 1-2 hours, then heating to 120-160° C., keeping warm for 1-2 hours, continuing heating to 180-220° C., keeping warm for 1-2 hours, and then heating to 250-300° C., keeping warm for 1-2 hours.

7. A polyimide dielectric film, characterized in that: The invention is prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the polyimide dielectric film according to claim 7 in a dielectric capacitor.

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