Rare earth lanthanide complex for enhancing dielectric energy storage performance of polypropylene and dielectric composite film thereof
By adding rare earth lanthanide complexes to polypropylene to regulate the crystallization behavior, the dielectric composite film was prepared, and the problem of low dielectric constant of polypropylene was solved, which achieved an increase in dielectric constant and an increase in energy storage density, while maintaining low dielectric loss.
Patent Information
- Application Number
- CN202410138458.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-01-31
- Publication Date
- 2025-08-01
AI Technical Summary
The existing polypropylene film has a low dielectric constant, resulting in limited energy density, and the existing modification methods increase dielectric loss and cost, making it difficult to widely use in high energy storage performance.
The crystallization behavior of polypropylene is regulated to prepare dielectric composite membranes by adding rare earth lanthanide complexes, including lanthanide compounds, zinc or calcium compounds, dicarboxylic acid-type ligands and amide-type ligands to the polypropylene.
The dielectric constant and breakdown strength of polypropylene are improved, the energy storage density is increased, while maintaining the dielectric loss is low, achieving high-performance dielectric composite film preparation.
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Figure CN120398925A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of thin film materials, and particularly relates to a rare earth lanthanide complex for enhancing the dielectric energy storage performance of polypropylene and a dielectric composite film thereof. Background Art
[0002] In recent years, with the development of technology and the continuous advancement of informatization, dielectric energy storage thin film capacitors with advantages such as fast charge and discharge, anti-cycle aging, low loss, good self-healing property, and suitability for high-voltage environments have received extensive attention, especially in the filtering of new energy electric vehicles and power grids. The existing commercial capacitor films are mainly biaxially oriented polypropylene (BOPP). However, the dielectric constant of polypropylene is relatively low, resulting in limited energy density and increased volume, which greatly limits the wider application of polypropylene films. Therefore, it is particularly urgent to develop dielectric films with high energy storage performance.
[0003] Analysis shows that the key to improving the energy storage performance of dielectric energy storage capacitors is to develop dielectric materials with high dielectric constant, high energy storage density, high breakdown strength, and high discharge efficiency. At present, the research on polypropylene dielectric materials mainly focuses on improving the dielectric constant of the film by means of modification and adding functional fillers, but this inevitably leads to an increase in dielectric loss. More importantly, the corresponding cost and operation complexity also increase. In view of this, it is particularly important to improve the breakdown strength and energy storage density of polypropylene without significant increase in dielectric loss. Summary of the Invention
[0004] One object of the present invention is to provide a rare earth lanthanide complex, and the composition of the complex includes a lanthanide compound, a zinc or calcium compound, a dicarboxylic acid ligand, and an amide ligand.
[0005] Further, the lanthanide compound is specifically lanthanum stearate or lanthanum chloride, the zinc or calcium compound is specifically zinc stearate or calcium carbonate, the dicarboxylic acid ligand is specifically stearic acid or pimelic acid, and the amide ligand is specifically N,N'-dicyclohexyl terephthalamide or N,N'-dicyclohexyl-2,6-naphthalenedicarboxamide.
[0006] Further, the composition of the complex in terms of mass fraction is: lanthanide compound 4% - 6%, zinc or calcium compound 2% - 3%, dicarboxylic acid ligand 85% - 92%, amide ligand 2% - 4%, totaling 100%.
[0007] Another object of the present invention is to provide the application of the above rare earth lanthanide complex in regulating the crystallization performance and dielectric energy storage performance of polypropylene.
[0008] Further, the specific process of the above application is as follows: melt-mix the rare earth lanthanide complex with the polypropylene matrix, and then extrude and stretch the composite melt into a film to obtain the dielectric composite film.
[0009] Further, the above mixing process is carried out in at least two steps: first, mix the rare earth lanthanide complex with a small amount of polypropylene and heat to melt, then cool and pulverize to obtain small materials, then mix the small materials with the remaining polypropylene, and finally melt-extrude and stretch into a film.
[0010] Further, when preparing the small materials, the mass ratio of the rare earth lanthanide complex to polypropylene is 80%-50%:20%-50%.
[0011] Further, the mass fraction of the rare earth lanthanide complex in the obtained dielectric composite film is 0.01%-5%.
[0012] Further, the equipment used for preparing the small materials is a torque rheometer. After feeding, pre-mix at room temperature first, and then heat to 190-240°C for melt mixing. During this period, the rotation speed of the torque rheometer is 30-60 rpm.
[0013] Further, the equipment used for melt extrusion is a single or twin-screw extruder. The temperature of the feeding section is 145°C-230°C, the temperature of the melting section is 165°C-250°C, the temperature of the homogenizing section is 195°C-250°C, the temperature of the die is 200°C-250°C, and the screw rotation speed is 5-30 rpm.
[0014] Further, use a winding machine to uniaxially stretch the melt output from the die to obtain a continuous and high-performance dielectric composite film. The winding speed of the winding machine is 7-15 rpm.
[0015] The third object of the present invention is to provide a rare earth lanthanide complex-polypropylene dielectric composite film prepared based on the above application method.
[0016] The present invention utilizes rare earth lanthanide complexes to regulate the crystallization behavior and crystalline structure of polypropylene, not only improving the crystallinity and β crystal content of polypropylene, reducing spherulite size, and improving the dielectric properties of the polypropylene matrix, while also increasing breakdown field strength and energy storage density. The principle of the present invention is as follows: a certain amount of lanthanide causes the crystallization mode of polypropylene to be mainly based on α crystal form, while β crystal has a spherulite size smaller than α crystal. On the one hand, β crystal has a spherulite size smaller than α crystal. On the other hand, after adding lanthanide, more nucleation points are distributed inside the polypropylene, so that the crystallinity is improved and has a higher spherulite density. Therefore, the advantages of the above β crystal jointly promote the improvement of the breakdown strength of the composite film. In addition, since lanthanide is mainly based on a variety of complexes, polarization will be generated inside the polypropylene, so that the dielectric constant of polypropylene is improved. It is worth noting that the improvement of the dielectric constant brought by rare earth lanthanide does not lead to a significant increase in dielectric loss and leakage current. This may be because after processes such as melt extrusion, a certain amount of lanthanide is evenly distributed inside the polypropylene, playing the role of heterogeneous nucleation, inducing the transformation of the α crystal of polypropylene to the β crystal.
[0017] Compared with existing similar technologies, the advantages of the present invention are embodied in the following aspects:
[0018] (1) The present invention proposes a novel method for industrial continuous and large-scale preparation of polypropylene dielectric composite films with excellent energy storage performance, which is relatively simple, low-cost and easy to implement;
[0019] (2) The dielectric composite film prepared according to the method of the present invention has outstanding performance. The dielectric constant increases from 2.2 of pure propylene to 3.2, the breakdown performance increases by 4%-6% relative to pure propylene, and the energy storage density increases by 10%-25% relative to pure propylene.
[0020] (3) The content of rare earth lanthanide complexes in the polypropylene dielectric composite film is low. On the one hand, it will not lead to a significant increase in the dielectric loss of polypropylene. On the other hand, the smaller addition amount also has more advantages in terms of cost and process complexity. BRIEF DESCRIPTION OF THE DRAWINGS
[0021] Figure 1 The figure is a flow chart of the preparation process of the polypropylene dielectric composite film of the present invention.
[0022] Figure 2 This is a diagram showing the element distribution results on the surface of the rare earth lanthanide complex in Example 1.
[0023] Figure 3 Graph showing the performance test results of the dielectric composite films prepared in Examples 1-3 and Comparative Example 1.
[0024] Figure 4 Schematic diagram of the crystallization process of the dielectric composite film in Examples 1-3 and Comparative Example 1. Detailed Embodiments
[0025] The present invention will be clearly and completely described below in conjunction with specific embodiments and the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.
[0026] A rare earth lanthanide complex, which is a binuclear bimetallic complex formed by lanthanide metal and zinc or calcium with some specific ligands. Its specific composition is as follows (wt%): dicarboxylic acid type ligand (such as stearic acid, etc.) 85%-92%, lanthanum stearate or lanthanum chloride 4%-6%, zinc stearate or calcium carbonate 2%-3%, amide type ligand (such as N,N'-dicyclohexyl terephthalamide, etc.) 2%-4%, total 100%.
[0027] As Figure 1 shown, the method for regulating the crystallization performance of polypropylene and enhancing the dielectric energy storage performance of polypropylene by using the above rare earth lanthanide complex and the process for preparing the polypropylene dielectric composite film are as follows:
[0028] (1) According to the mass ratio of 80%-50%:20%-50%, polypropylene and the rare earth lanthanide complex are added to a torque rheometer. The temperature of the torque rheometer is set at 190°C - 240°C and the rotation speed is set at 20 - 50 rpm. Under these conditions, pre-mixing is carried out in segments for 5 - 30 minutes, and then the mixed melt is crushed to obtain small materials.
[0029] (2) The small materials and polypropylene are added to a single or twin-screw extruder in proportion and extruded into shape. The extruder adopts a segmented heating method, where the temperature of the feeding section is set at 145°C - 160°C, the temperature of the melting section is set at 165°C - 250°C, the temperature of the homogenizing section is set at 195°C - 250°C, the temperature at the die is set at 200°C - 250°C, and the screw rotation speed is 5 - 30 rpm.
[0030] (3) The melt at the die is uniaxially stretched by a winding machine at a winding speed of 7 - 15 rpm to obtain a continuous high-performance dielectric composite film. The mass fraction of the rare earth lanthanide complex in the composite film is 0.01% - 5%, and the rest is polypropylene.
[0031] Example 1
[0032] The components and their mass fractions in the rare earth lanthanide complex selected in this example are as follows: stearic acid 90%, lanthanum chloride 5%, zinc stearate 2%, N,N'-dicyclohexyl terephthalamide 3%. The morphology and element distribution of the rare earth lanthanide complex are as Figure 2As shown. It can be seen from the figure that the lanthanide complex contains elements such as C, O, Zn, La, and Cl, thus confirming its elements and components. In addition, it can also be seen that the lanthanide complex has a rod-like structure with a size of 200 - 400 nm.
[0033] The process of preparing a polypropylene dielectric composite film using the above rare earth lanthanide complex is as follows: The lanthanide complex powder and polypropylene pellets are premixed according to a mass ratio of 20%:80%, and then the mixture is put into a torque rheometer for heat melting and blending. The temperature is set at 190 °C and the torque is set at 50 rpm. After cooling the pre-prepared composite melt, it is crushed into small pieces, and then added to a twin-screw extruder together with polypropylene for extrusion molding. The screw speed is 5 rpm, and the temperatures of the feeding section, melting section, homogenizing section, and die are set at 145 °C, 165 °C, 195 °C, and 200 °C respectively. The melt coming out of the die head is uniaxially stretched by a winding machine with a winding speed of 12 rpm, and finally a polypropylene dielectric composite film with a uniform thickness (11 - 15 μm) is obtained, where the mass fraction of the rare earth lanthanide complex is 0.10%.
[0034] Example 2
[0035] The components and their mass fractions in the rare earth lanthanide complex selected in this example are as follows: stearic acid 90%, lanthanum chloride 5%, zinc stearate 2%, N,N'-dicyclohexyl terephthalamide 3%.
[0036] The process of preparing a polypropylene dielectric composite film using the above rare earth lanthanide complex is as follows: The lanthanide complex powder and polypropylene pellets are premixed according to a mass ratio of 25%:75%, and then the mixture is put into a torque rheometer for heat melting and blending. The temperature is set at 190 °C and the torque is set at 50 rpm. After cooling the pre-prepared composite melt, it is crushed into small pieces, and then added to a twin-screw extruder together with polypropylene for extrusion molding. The screw speed is 5 rpm, and the temperatures of the feeding section, melting section, homogenizing section, and die are set at 145 °C, 165 °C, 195 °C, and 200 °C respectively. The melt coming out of the die head is uniaxially stretched by a winding machine with a winding speed of 10 rpm, and finally a polypropylene dielectric composite film with a uniform thickness (10 - 15 μm) is obtained, where the mass fraction of the rare earth lanthanide complex is 0.15%.
[0037] Example 3
[0038] The components and their mass fractions in the rare earth lanthanide complex selected in this example are as follows: stearic acid 90%, lanthanum chloride 5%, zinc stearate 2%, N,N'-dicyclohexyl terephthalamide 3%.
[0039] The process for preparing the polypropylene dielectric composite film using the above rare earth lanthanide complex is as follows: The lanthanide complex powder and polypropylene pellets are premixed according to a mass ratio of 30%:70%, and then the mixture is put into a torque rheometer for heating and melt blending. The temperature is set at 190°C and the torque is set at 50 rpm. The prepared composite melt is cooled and then crushed into small pieces, and then added to a twin-screw extruder together with polypropylene for extrusion molding. The screw speed is 5 rpm, and the temperatures of the feeding section, melting section, homogenizing section, and die are set at 145°C, 165°C, 195°C, and 200°C respectively. The melt coming out of the die head is uniaxially stretched by a winding machine, and the winding speed is 7 rpm. Finally, a polypropylene dielectric composite film with a uniform thickness (10 - 15 μm) is obtained, and the mass fraction of the rare earth lanthanide complex is 0.20%.
[0040] Example 4
[0041] The components and their mass fractions in the rare earth lanthanide complex selected in this example are as follows: stearic acid 90%, lanthanum chloride 5%, calcium carbonate 2%, N,N'-dicyclohexyl terephthalamide 3%.
[0042] The process for preparing the polypropylene dielectric composite film using the above rare earth lanthanide complex is as follows: The lanthanide complex powder and polypropylene pellets are premixed according to a mass ratio of 40%:60%, and then the mixture is put into a torque rheometer for heating and melt blending. The temperature is set at 230°C and the torque is set at 30 rpm. The prepared composite melt is cooled and then crushed into small pieces, and then added to a twin-screw extruder together with polypropylene for extrusion molding. The screw speed is 10 rpm, and the temperatures of the feeding section, melting section, homogenizing section, and die are set at 155°C, 170°C, 210°C, and 220°C respectively. The melt coming out of the die head is uniaxially stretched by a winding machine, and the winding speed is 10 rpm. Finally, a polypropylene dielectric composite film with a uniform thickness (10 - 15 μm) is obtained, and the mass fraction of the rare earth lanthanide complex is 1.0%.
[0043] Example 5
[0044] The components and their mass fractions in the rare earth lanthanide complex selected in this example are as follows: stearic acid 88%, lanthanum chloride 6%, calcium carbonate 3%, N,N'-dicyclohexyl-2,6-naphthalenedicarboxamide 3%.
[0045] The process of preparing a polypropylene dielectric composite film using the above rare earth lanthanide complex is as follows: The lanthanide complex powder and polypropylene pellets are premixed in a mass ratio of 50%:50%, and then the mixture is put into a torque rheometer for heating and melt blending. The temperature is set at 230°C and the torque is set at 30 rpm. After cooling the prepared composite melt, it is crushed into small pieces, and then added to a twin-screw extruder together with polypropylene for extrusion molding. The screw speed is 10 rpm, and the temperatures of the feeding section, melting section, homogenizing section, and die are set at 155°C, 170°C, 210°C, and 220°C respectively. The melt coming out of the die head is uniaxially stretched by a winding machine, and the winding speed is 7 rpm. Finally, a polypropylene dielectric composite film with a uniform thickness (10 - 15 μm) is obtained, where the mass fraction of the rare earth lanthanide complex is 1.0%.
[0046] Example 6
[0047] This example is basically the same as Example 5, except that: the mass fraction of the rare earth lanthanide complex in the prepared polypropylene dielectric composite film is 5.0%.
[0048] Comparative Example 1
[0049] Polypropylene (from the same batch as the previous examples) is put into a torque rheometer for heating and melting. The temperature is set at 190°C and the torque is set at 50 rpm. After cooling the prepared melt, it is crushed into small pieces, and then added to a twin-screw extruder for extrusion molding. The screw speed is 5 rpm, and the temperatures of the feeding section, melting section, homogenizing section, and die are set at 145°C, 165°C, 195°C, and 200°C respectively. The melt coming out of the die head is uniaxially stretched by a winding machine, and the winding speed is 15 rpm. Finally, a polypropylene dielectric film with a uniform thickness (10 - 15 μm) is obtained.
[0050] To fully understand the performance of the dielectric films prepared in Examples 1 - 3 and Comparative Example 1 of the present invention, dielectric performance, breakdown performance, energy storage performance tests and crystallization behavior analysis were carried out on them respectively.
[0051] (1) Dielectric performance test
[0052] Using a high-vacuum resistance evaporation coating machine, copper electrodes (area 0.0707 cm 2 ) are respectively evaporated on both sides of the dielectric film sample, and then the dielectric film sample with copper electrodes is placed in a precision LCR meter (Agilent, E4980A, USA) and clamped with a fixture to test the dielectric performance in the range of 100 Hz - 20 MHz at room temperature. The results are shown in Figure 3 -a and 3-b.
[0053] From Figure 3It can be seen that after adding this rare earth lanthanide complex, the dielectric constant of the film increases from 2.25 to 3.24, and the dielectric loss remains at a low level. This indicates that this rare earth lanthanide complex increases the polarization of the polypropylene matrix and can significantly improve its dielectric properties.
[0054] (2) Breakdown performance test
[0055] The breakdown strength of the unmetallized dielectric film sample was measured using a DC withstand voltage test system (eec, 7474, China). The test conditions were: the voltage rise rate was 500 V / s, and the results are as Figure 3 shown in
[0056] As can be seen from Figure 3 , the breakdown performance of the film shows a trend of increasing first and then decreasing. This is mainly attributed to the fact that after adding the rare earth lanthanide complex, a unique β-crystal appears in the polypropylene. The lamellar structure and cross-arrangement of the β-crystal limit the transport of carriers inside it. However, as the content of the rare earth lanthanide complex increases, the breakdown strength decreases significantly, probably because the high-content rare earth lanthanide complex agglomerates inside the polypropylene. From the increase in the shape factor β compared with pure polypropylene, it can be seen that the breakdown strength of this composite film is more stable.
[0057] (3) Energy storage density test
[0058] First, copper electrodes (0.2827 cm 2 ) were respectively evaporated on both sides of the dielectric film sample using a high-vacuum resistance evaporation coating machine. Then, the dielectric film sample with copper electrodes was placed between the two electrodes of a ferroelectric tester (Polyk, CPE1901, USA) and clamped. The electrodes together with the dielectric film sample were immersed in highly insulating silicone oil, and the frequency was set to 100 Hz to test its energy storage density. The results are as Figure 3 shown in
[0059] As can be seen from the figure, the energy storage density of the dielectric composite film in Example 1 increased by 24.4% compared with Comparative Example 1. This is mainly due to the increase in the dielectric constant and breakdown strength. More importantly, the charge-discharge efficiency of this composite film is higher than 95%, which indicates that after adding the rare earth lanthanide complex, the stability of the film still remains at a high level.
[0060] (4) Crystal morphology observation
[0061] The crystal morphology of the sample was observed through a polarized optical microscope (POM, Zeiss, Axiolab 5, Germany) equipped with a heating platform. The results are as Figure 4 shown.
[0062] As can be seen from the figure, after the addition of the lanthanide complex, the crystal form of pure polypropylene changes from mainly typical α-spherulites to β-sheet crystals (as shown in Figure 4 -b2), and as the addition amount of the complex increases, the lamellar density of β-crystals gradually increases (as shown in Figure 4 b and Figure 4 c). The lanthanide complex regulates the crystallization behavior of polypropylene, converting the α-crystals of polypropylene into β-crystals, resulting in an increase in the density and a decrease in the size of the crystal form. These changes in crystallization behavior ultimately improve the electrical properties of the composite film.
[0063] The test results of the dielectric composite films prepared in different embodiments are specifically shown in the following table:
[0064]
[0065] As can be seen from the above table, adding a low content of rare earth lanthanide complex has no effect on the dielectric constant and dielectric loss of the polypropylene dielectric film. Since the β-crystals induced in polypropylene can effectively inhibit carrier transport, the loss when the addition amount of the rare earth lanthanide complex is less than 0.15 wt% is lower than that of pure polypropylene, and the charge-discharge cycle efficiency of the composite dielectric film is above 95% for 50,000 cycles.
Claims
1. A rare earth lanthanide complex, characterized in that: The composition of the rare earth lanthanide complex includes a lanthanide compound, a compound of zinc or calcium, a dicarboxylic acid ligand, and an amide ligand.
2. The rare earth lanthanide complex according to claim 1, wherein: The composition of the rare earth lanthanide complex by mass fraction is: lanthanide compound 4% - 6%, compound of zinc or calcium 2% - 3%, dicarboxylic acid ligand 85% - 92%, amide ligand 2% - 4%.
3. The rare earth lanthanide complex according to claim 1 or 2, characterized in that: The lanthanide compound is specifically lanthanum stearate or lanthanum chloride, the compound of zinc or calcium is specifically zinc stearate or calcium carbonate, the dicarboxylic acid ligand is specifically stearic acid or pimelic acid, and the amide ligand is specifically N,N'-dicyclohexyl terephthalamide or N,N'-dicyclohexyl-2,6-naphthalenedicarboxamide.
4. Application of the rare earth lanthanide complex according to any one of claims 1 - 3 in regulating the crystallization performance and dielectric energy storage performance of polypropylene.
5. The application according to claim 4, characterized in that The specific process of this application is as follows: The rare earth lanthanide complex is melt-mixed with the polypropylene matrix, and then the composite melt is extruded and stretched into a film, thereby obtaining a dielectric composite film.
6. The application according to claim 4, characterized in that The mixing is carried out in two steps: First, the rare earth lanthanide complex and polypropylene are mixed and heated to melt according to a mass ratio of 80% - 50%:20% - 50%, then cooled and pulverized to obtain small materials, then the small materials are mixed with polypropylene, and finally melt-extruded and stretched into a film.
7. The application according to claim 5, wherein: The mass fraction of the rare earth lanthanide complex in the prepared dielectric composite film is 0.01% - 5%.
8. The application according to claim 6, wherein: The equipment used for preparing the small materials is a torque rheometer. After the feeding is completed, pre-mixing is carried out at room temperature first, and then heated to 190 - 240 °C for melt-mixing. During this period, the rotation speed of the torque rheometer is 30 - 60 rpm.
9. The application according to claim 6, characterized in that: The equipment used for melt-extrusion is a single or twin-screw extruder. Among them, the temperature of the feeding section is 145 °C - 230 °C, the temperature of the melting section is 165 °C - 250 °C, the temperature of the homogenizing section is 195 °C - 250 °C, the temperature of the die is 200 °C - 250 °C, and the screw rotation speed is 5 - 30 rpm; The melt output from the die is uniaxially stretched by a winding machine, and the winding speed of the winding machine is 7 - 15 rpm.
10. A polypropylene dielectric composite film, characterized in that: The polypropylene dielectric composite film is prepared by any one of the methods according to claims 4 - 9.