Preparation method of polypropylene film material for improving dielectric energy storage characteristic

Abstract

The invention discloses a preparation method of a polypropylene film material capable of improving dielectric energy storage characteristics, and relates to the technical field of polymer dielectric films. Norbornene anhydride is grafted to polypropylene, a polar group and a rigid structure are introduced into the polypropylene, then azobenzene is grafted, and the polypropylene film material capable of improving dielectric energy storage characteristics is obtained. The azobenzene can further react with norbornene dianhydride grafted to the polypropylene, then a cis-trans isomeric structure is introduced into the polypropylene, and then the modified polypropylene material is blended with the polypropylene. The prepared polypropylene film material can inhibit migration of carriers and improve the energy storage and release efficiency of the material, so that the material has excellent dielectric energy storage characteristics at room temperature and high temperature, is low in cost and has a very good application effect in the field of capacitors.

Description

Technical Field

[0001] This invention relates to the field of polymer dielectric thin film technology, and in particular to a method for preparing a polypropylene thin film material with improved dielectric energy storage properties. Background Technology

[0002] In power systems, high-voltage parallel capacitor banks play many irreplaceable and important roles, such as improving the power factor, stabilizing voltage, and reducing line losses. Polypropylene dielectric film, with its advantages of high breakdown field strength, low dielectric loss, low density, chemical stability, good insulation, and processability, has become the mainstream dielectric material for high-voltage parallel capacitors.

[0003] When nonlinear power equipment is connected to the power grid, high-voltage parallel capacitors will be subjected to high-frequency harmonics, causing their temperature to exceed 85°C. This leads to a sharp decline in the dielectric properties of the polypropylene dielectric film, severely affecting the reliability of the high-voltage parallel capacitors. The research and development and localization of new energy storage technologies and related products are key tasks in solving the problems of new energy generation and its volatility in new power systems. Dielectric film capacitors, possessing characteristics such as high voltage and high temperature resistance, rapid charge and discharge, and long cycle life, are key energy storage devices for improving the reliability and power quality of power systems.

[0004] To meet the needs of practical applications, polypropylene is often modified to improve its performance. Grafting monomers onto polypropylene is a common method of modification. Chinese patent (publication number CN102329405B) discloses a method for preparing continuous high melt strength polypropylene based on grafting reaction, which grafts vinyl silicone oil, cyclopentadiene, norbornene adienoic anhydride, oleic acid and styrene onto polypropylene to obtain high melt strength polypropylene with good performance containing long branches and no gel. However, this method is complex and does not explore the dielectric properties of the material. Chinese patent (publication number CN 118620260 B) discloses a method for preparing polypropylene capacitor film, which grafts cyclic olefin polymers onto polypropylene, enhancing the heat resistance and mechanical properties of polypropylene and improving the dielectric properties of polypropylene capacitor film, but it cannot improve the energy storage characteristics of polypropylene.

[0005] Therefore, there is an urgent need to explore a new high-performance polypropylene material that can have excellent energy storage properties at both room temperature and high temperature. Summary of the Invention

[0006] To address the above shortcomings, this invention provides a method for preparing a polypropylene film material with improved dielectric energy storage characteristics, exhibiting excellent energy storage properties at both room temperature and high temperature. The specific technical solution is as follows: A method for preparing a polypropylene thin film material with improved dielectric energy storage properties, comprising the following steps: (1) The polypropylene is placed in an oven and dried to obtain dried polypropylene; (2) Add norborneol olefinic anhydride, initiator and a certain amount of dried polypropylene obtained in step (1) to an organic solvent. After stirring and mixing, inert gas is introduced and the mixture is stirred at 100-110℃ for 2.5-3.5h. After the reaction is completed, cool to room temperature, filter, wash and dry to obtain polypropylene grafted norborneol olefinic anhydride granules. (3) Under the protection of inert gas, the polypropylene grafted norborneol anhydride granules obtained in step (2) are added to an organic solvent and refluxed at a certain temperature for a period of time. After the reaction is completed, the mixture is cooled to room temperature, filtered, washed and dried to obtain polypropylene grafted composite monomer granules. (4) A certain amount of the dried polypropylene obtained in step (1) and the polypropylene grafted composite monomer granules obtained in step (3) are melt-blended and placed in a torque rheometer for melt blending to obtain a mixture. The mixture is then hot-pressed, cooled, and stretched at a certain stretching rate and stretching ratio to obtain the polypropylene film material.

[0007] Furthermore, the initiator is benzoyl peroxide (BPO).

[0008] Furthermore, in the polypropylene grafted composite monomer granules, the raw material mass ratio of norbornene, initiator, dried polypropylene obtained in step (1), and azobenzene is (0.02-0.04):(0.003-0.007):1:(0.02-0.04).

[0009] Furthermore, in step (1), the drying temperature is 60-80 ℃ and the drying time is 6-8 h.

[0010] Furthermore, the organic solvent is dimethylacetamide and xylene in a volume ratio of 1:1.

[0011] Furthermore, in steps (2) and (3), the washing process is carried out sequentially with anhydrous ethanol and deionized water, the drying temperature is 60-80 ℃, and the drying time is 6-8 h.

[0012] Furthermore, in step (3), the reflux temperature is 100-120℃ and the reflux time is 3-5 h.

[0013] Furthermore, the content of the polypropylene grafted composite monomer granules in the polypropylene film material is 5-20%.

[0014] Furthermore, in step (4), the melt blending temperature is 190-200 ℃, the rotation speed is 20-40 rpm, and the time is 8-13 min.

[0015] Furthermore, the hot pressing process temperature is 195-205 ℃, the preheating time is 4-6 min, and the hot pressing adopts a stepped pressure increase, with hot pressing at 5, 10, and 15 MPa for 4-6 min respectively.

[0016] Further, in step (4), after the mixture is hot-pressed and cooled, it is placed in a biaxial stretching apparatus for stretching. The preheating temperature for stretching is 155-160℃, the preheating time is 1-2 min, the stretching rate is 50-100 mm / s, and the stretching ratio is 1.5-2.5.

[0017] Furthermore, the thickness of the polypropylene film material is 10-20 μm.

[0018] Compared with the prior art, the beneficial effects of the present invention are: The polypropylene film material of the present invention, which enhances dielectric energy storage characteristics, has good breakdown field strength at both room temperature and high temperature. When applied to capacitors, it has the characteristics of high voltage and high temperature resistance and high energy storage efficiency, which can improve the power quality of the material and thus improve the reliability of the power system.

[0019] This invention first grafts norbornene olefinic anhydride onto polypropylene, introducing polar groups and a rigid structure into the polypropylene. Then, azobenzene is grafted onto the polypropylene. The azobenzene can further react with the norbornene olefinic anhydride grafted onto the polypropylene, introducing a cis-trans isomer structure into the polypropylene to form a complex with cis-trans isomerism. This can suppress carrier migration, improve the energy storage and release efficiency of the material, and give it excellent energy storage characteristics at both room temperature and high temperature. Moreover, it is inexpensive and has good application effects in the field of capacitors. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 Fourier transform infrared spectrum of polypropylene grafted composite monomer granules in Example 1; Figure 2 The results are the DC breakdown field strength test results of the polypropylene grafted composite monomer films of Examples 1-4 and Comparative Example 1 at room temperature. Figure 3The DC breakdown field strength test results are for the polypropylene grafted composite monomer films of Examples 1-4 and Comparative Example 1 at 125 °C. Figure 4 The results show the energy storage efficiency test results of the polypropylene grafted composite monomer films of Examples 1-4 and Comparative Example 1 at room temperature. Figure 5 The results show the direct energy storage efficiency test results of the polypropylene grafted composite monomer films of Examples 1-4 and Comparative Example 1 at 125°C. Detailed Implementation

[0022] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. Unless otherwise defined, all technical terms used below have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of the present invention. Unless otherwise specifically stated, all raw materials, reagents, instruments, and equipment used in the present invention are commercially available or can be prepared by existing methods.

[0023] The polypropylene used in this embodiment of the invention was purchased from Borealis, model HC-300BF. The melt flow rate was 3.3 g / 10 min as determined by ISO 1133 at 230°C and 2.16 kg.

[0024] Example 1 A method for preparing a polypropylene thin film material with improved dielectric energy storage properties includes the following steps: (1) Place the polypropylene in an oven to dry at a temperature of 80 °C for 8 h to obtain dried polypropylene for later use. (2) In a mixed solution of dimethylacetamide and xylene in a volume ratio of 1:1, norbornene, benzoyl peroxide (BPO) and the dried polypropylene obtained in step (1) are added sequentially. The mass ratio of norbornene, benzoyl peroxide (BPO) and dried polypropylene is 0.04:0.007:1. After stirring and mixing, nitrogen gas is introduced and the mixture is stirred at 105 °C for 3 h. After cooling to room temperature, the mixture is filtered and washed sequentially with anhydrous ethanol and deionized water. After drying at 60-80 °C for 6-8 h, polypropylene grafted with norbornene granules is obtained. (3) In a mixed solution of dimethylacetamide and xylene in a volume ratio of 1:1, the polypropylene grafted norbornenic anhydride granules and azobenzene obtained in step (2) are added sequentially. The mass ratio of the polypropylene grafted norbornenic anhydride granules to azobenzene is 1.047:0.04. After stirring and mixing, nitrogen gas is introduced and the mixture is refluxed at 100-120°C for 3-5 h. After filtration, the mixture is washed sequentially with anhydrous ethanol and deionized water, and dried at 60-80°C for 6-8 h to obtain polypropylene grafted composite monomer granules. (4) The dried polypropylene and the polypropylene grafted composite monomer granules obtained in step (3) are mixed at a mass ratio of 95:5 and melt-blended in a torque rheometer at a temperature of 200 ℃, a rotation speed of 30 rpm, and a blending time of 10 min. Then, the mixture is hot-pressed in a flat vulcanizing machine at a temperature of 200 ℃ and a preheating time of 5 min. Then, the pressure is increased in stages and hot-pressed at 5, 10, and 15 MPa for 5 min respectively. After cooling, polypropylene grafted composite monomer castings are obtained. (5) The polypropylene grafted composite monomer casting obtained in step (4) is placed in a biaxial stretching apparatus, preheated at 160 °C for 1 min, and then stretched synchronously at a stretching rate of 100 mm / s and a stretching ratio of 2.5 × 2.5 to obtain a polypropylene grafted film material, denoted as PP / 5% PP-g-CP.

[0025] Example 2 Compared with Example 1, the difference in this embodiment is that in step (3), polypropylene and polypropylene grafted composite monomer granules are mixed at a mass ratio of 90:10, while other steps remain unchanged, denoted as PP / 10% PP-g-CP.

[0026] Example 3 Compared with Example 1, the difference in this embodiment is that in step (3), polypropylene and polypropylene grafted composite monomer granules are mixed at a mass ratio of 85:15, while other steps remain unchanged, denoted as PP / 15% PP-g-CP.

[0027] Example 4 Compared with Example 1, the difference in this embodiment is that in step (3), polypropylene and polypropylene grafted composite monomer granules are mixed at a mass ratio of 80:20, while other steps remain unchanged, denoted as PP / 20% PP-g-CP.

[0028] Comparative Example 1 This comparative example uses commercially available Borealis HC-300BF polypropylene granules, which are hot-pressed in a flat vulcanizing apparatus at 200 ℃ for 5 min. Stepwise pressure is applied at 5, 10, and 15 MPa for 5 min each. After cooling, polypropylene sheets are obtained. The polypropylene sheets are then placed in a biaxial stretching apparatus and preheated at 160 ℃ for 1 min. They are then simultaneously stretched at a stretching rate of 100 mm / s and a stretching ratio of 2.5 × 2.5 to obtain a polypropylene film, denoted as PP.

[0029] Comparative Example 2 The difference between this comparative example and Example 1 is that no azobenzene was added to this comparative example.

[0030] The raw materials in this comparative example, by weight, consist of: 1 part polypropylene, 0.04 parts norbornene adiene anhydride, 0.04 parts azobenzene, and 0.007 parts initiator.

[0031] The preparation method of this comparative example includes the following steps: (1) The polypropylene was placed in an oven and dried at 80 °C for 8 h to obtain dried polypropylene; (2) In a mixed solution of dimethylacetamide and xylene in a volume ratio of 1:1, norborneol anhydride, benzoyl peroxide (BPO) and the dried polypropylene obtained in step (1) are added in sequence. After stirring and mixing, nitrogen gas is introduced and the mixture is stirred at 105 °C for 3 h. After cooling to room temperature, the mixture is filtered and washed with anhydrous ethanol and deionized water in sequence. After drying at 60-80 °C for 6-8 h, polypropylene grafted norborneol anhydride granules are obtained. (3) The polypropylene and the polypropylene-grafted norborneol anhydride granules obtained in step (2) are mixed at a mass ratio of 95:5 and melt-blended in a torque rheometer at a temperature of 200 ℃, a speed of 30 rpm, and a blending time of 10 min. Then, the mixture is hot-pressed in a flat vulcanizing machine at a temperature of 200 ℃ and a preheating time of 5 min. Then, the pressure is increased in stages and hot-pressed at 5, 10, and 15 MPa for 5 min respectively. After cooling, polypropylene-grafted composite monomer castings are obtained. (4) The polypropylene grafted composite monomer casting obtained in step (4) is placed in a biaxial stretching apparatus, preheated at 160 °C for 1 min, and then stretched synchronously at a stretching rate of 100 mm / s and a stretching ratio of 2.5 × 2.5 to obtain a polypropylene grafted film material, denoted as PP / 5% PP-g-NA.

[0032] Performance testing: 1. Fourier transform infrared spectroscopy was performed on the polypropylene grafted composite monomer granules prepared in Example 1. The transmission mode was selected for the test, and the test range was 3500-1000 cm⁻¹. -1 The test results are as follows: Figure 1 As shown.

[0033] 2. The films prepared in the above embodiments and comparative examples were placed in a DC breakdown test apparatus for testing. A 3mm diameter copper electrode was used, and the voltage ramp rate was 1kV / mm. Sixteen tests were performed on each sample at room temperature and 125℃, and the results were analyzed using a two-parameter Weibull distribution. The results are as follows: Figure 2 and Figure 3 As shown.

[0034] from Figure 1 It can be seen that, compared with pure polypropylene (PP), the polypropylene grafted composite monomer pellets have a thickness of 1744.37 cm⁻¹. -1 The presence of a distinct carbonyl characteristic peak indicates successful grafting.

[0035] from Figure 2 It can be seen that at room temperature, the DC breakdown field strength of Comparative Example 1 is 664.42 kV / mm, while the DC breakdown field strength of Examples 1-4 is improved to a certain extent compared with Comparative Example 1. The DC breakdown field strength of Example 2 is the largest, at 738.96 kV / mm, which is 11.2% higher than that of Comparative Example 1.

[0036] from Figure 3 It can be seen that at 125 ℃, the DC breakdown field strength of Comparative Example 1 is 281.27 kV / mm, while the DC breakdown field strength of Examples 1-4 is improved to a certain extent compared with Comparative Example 1. The DC breakdown field strength of Examples 2 and 3 is improved the most significantly, at 427.14 kV / mm and 429.95 kV / mm respectively, which are 51.9% and 52.9% higher than Comparative Example 1 respectively.

[0037] Therefore, the polypropylene grafted composite monomer film of the present invention exhibits high breakdown field strength at both room temperature and high temperature, according to the following formula for calculating the energy storage density of dielectric energy storage devices (where E is the breakdown field strength of the material). (where is the relative permittivity of the material), high breakdown field strength often results in high energy storage density.

[0038] 3. The films prepared in the above examples and comparative examples were gold-plated in a gold sputtering apparatus, and their discharge energy density and charge-discharge efficiency were analyzed using a ferromagnetic hysteresis loop (FERRO20B, USA).

[0039] from Figure 4 andFigure 5 It is evident that the discharge energy density increases when polypropylene grafted composite monomers are introduced into polypropylene. PP / 10% PP-g-CP maintains the highest discharge energy density at different temperatures, reaching 6.61 J / cm³ at room temperature and 2.49 J / cm³ at 125°C. Compared to PP / 5% PP-g-NA without azobenzene, PP / 10% PP-g-CP shows improvements of 38.3%, 109.4%, and 250.7%, respectively. Notably, the charge / discharge efficiency gradually decreases with increasing applied electric field; however, all films maintain an efficiency above 90% across the entire temperature range. Among them, PP / 10% PP-g-CP exhibits the highest charge / discharge efficiency: 93.8% at room temperature with an electric field of 750 kV / mm and 96.0% at 125°C with a magnetic field of 450 kV / mm. Therefore, the incorporation of polypropylene grafted composite monomers, particularly the PP / 10% PP-g-CP ratio, can effectively improve the energy storage performance of polypropylene.

[0040] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A method for preparing a polypropylene thin film material with improved dielectric energy storage properties, characterized in that, The preparation method includes: (1) The polypropylene is placed in an oven and dried to obtain dried polypropylene; (2) Add norborneol olefinic anhydride, initiator and a certain amount of dried polypropylene obtained in step (1) to an organic solvent. After stirring and mixing, inert gas is introduced and the mixture is stirred at 100-110℃ for 2.5-3.5h. After the reaction is completed, cool to room temperature, filter, wash and dry to obtain polypropylene grafted norborneol olefinic anhydride granules. (3) Under the protection of inert gas, the polypropylene grafted norborneol anhydride granules obtained in step (2) are added to an organic solvent and refluxed at a certain temperature for a period of time. After the reaction is completed, the mixture is cooled to room temperature, filtered, washed and dried to obtain polypropylene grafted composite monomer granules. (4) A certain amount of polypropylene obtained in step (1) and polypropylene grafted composite monomer granules obtained in step (3) are melt-blended to obtain a mixture. The mixture is hot-pressed, cooled, and then stretched at a certain stretching rate and stretching ratio to obtain the polypropylene film material.

2. The method for preparing a polypropylene film material with improved dielectric energy storage properties according to claim 1, characterized in that, The initiator is benzoyl peroxide.

3. The method for preparing a polypropylene film material with improved dielectric energy storage properties according to claim 1, characterized in that, In the polypropylene grafted composite monomer granules, the raw material mass ratio of norbornene, initiator, dried polypropylene obtained in step (1), and azobenzene is (0.02-0.04):(0.003-0.007):1:(0.02-0.04).

4. The method for preparing a polypropylene film material with improved dielectric energy storage properties according to claim 3, characterized in that, In step (1), the drying temperature is 60-80 ℃ and the drying time is 6-8 h.

5. The method for preparing a polypropylene film material with improved dielectric energy storage properties according to claim 3, characterized in that, The organic solvent is dimethylacetamide and xylene in a volume ratio of 1:

1.

6. The method for preparing a polypropylene film material with improved dielectric energy storage properties according to claim 3, characterized in that, In step (3), the reflux temperature is 100-120℃ and the reflux time is 3-5 h.

7. The method for preparing a polypropylene film material with improved dielectric energy storage properties according to claim 3, characterized in that, The content of the polypropylene grafted composite monomer granules in the polypropylene film material is 5-20%.

8. The method for preparing a polypropylene film material with improved dielectric energy storage properties according to claim 3, characterized in that, In step (4), the melt blending temperature is 190-200 ℃, the rotation speed is 20-40 rpm, and the time is 8-13 min.

9. The method for preparing a polypropylene film material with improved dielectric energy storage characteristics according to claim 3, wherein in step (4), the hot pressing process temperature is 195-205 ℃, the preheating time is 4-6 min, and the hot pressing adopts a stepped pressure increase, hot pressing at 5, 10, and 15 MPa for 4-6 min respectively.

10. The method for preparing a polypropylene film material with improved dielectric energy storage properties according to claim 3, characterized in that, The thickness of the polypropylene film material is 10-20 μm.

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