A method for modifying polypropylene dielectric films by melt blending and applications

Abstract

The application relates to a method for modifying polypropylene energy storage medium film through melt blending and application, and belongs to the field of manufacturing of medium materials for electrical component assemblies. The application aims to solve the problems of brittle cracking of existing polypropylene film in low-temperature environment, mechanical property deterioration and insulation failure. The application uses homopolymer polypropylene and terpolymer polypropylene resin as raw materials, and is prepared through melt blending extrusion combined with unidirectional stretching and winding processes. Due to the introduction of ethylene and butene in the terpolymer polypropylene, the regularity arrangement of the polypropylene segment is inhibited, the flexibility of the molecular chain is enhanced, and the glass transition temperature is reduced. On the other hand, the increase of the amorphous region proportion also provides sufficient free volume for the orientation polarization of the weak polar group methyl of the polypropylene molecular main chain, and the orientation polarization effect is enhanced. The blending polypropylene energy storage medium film prepared by the application can increase the elongation at break by 43.6% compared with the pure polypropylene energy storage medium film, and has application prospects under extreme working conditions.

Description

Technical Field

[0001] This invention belongs to the field of manufacturing dielectric materials for electrical components and assemblies, and specifically relates to a method and application of modifying polypropylene energy storage dielectric films through melt blending. Background Technology

[0002] Capacitors, as fundamental electrical components in electronic circuits, are widely used in high-voltage direct current (HVDC) transmission converter stations, electromagnetic weaponry, and electronic control systems for new energy vehicles. Among them, polymer film capacitors, with their superior power density, ultra-high cycle life, and excellent self-healing properties, have become indispensable components in modern power equipment. Currently, biaxially oriented polypropylene (BOPP), with its high insulation performance, low dielectric loss, and good processing properties, has become the mainstream energy storage dielectric material for commercial film capacitors. However, research on the degradation of mechanical properties in polypropylene films under low-temperature conditions, leading to a decrease in service life, is scarce. In my country's cold regions, winter temperatures can reach as low as -40 to -50°C. At these temperatures, polypropylene undergoes a transformation from a highly elastic state to a glassy state. The insulation failure caused by the degradation of its mechanical properties under low-temperature conditions urgently needs to be addressed.

[0003] While improving its low-temperature mechanical properties, it is crucial to ensure good compatibility with the "roll-to-roll" industrial production process of thin-film capacitor elements. Therefore, it is essential to develop a capacitor dielectric film that combines excellent mechanical properties and processing compatibility. Summary of the Invention

[0004] The purpose of this invention is to solve the problem of existing polypropylene films becoming brittle and cracking at low temperatures, resulting in insulation failure due to deterioration of mechanical properties, and to provide a method and application for modifying polypropylene energy storage medium films through melt blending.

[0005] A method for modifying polypropylene energy storage medium films through melt blending is specifically carried out according to the following steps:

[0006] 1. Mix the dried homopolymer polypropylene resin and the dried ternary copolymer polypropylene resin evenly to obtain the raw material;

[0007] 2. Set the heating zone temperature, die head extrusion temperature, and screw speed of the twin-screw extruder, and feed the raw material into the extruder hopper;

[0008] 3. The molten resin is drawn onto the surface of the cooling roller to cool, and then unidirectional stretching is performed;

[0009] Fourth, the stretched film is wound up to obtain a blended modified polypropylene energy storage medium film.

[0010] Application of blended modified polypropylene energy storage dielectric films in capacitors.

[0011] This invention provides a method for preparing and applying a polypropylene energy storage medium film using melt blending extrusion technology combined with unidirectional stretching and winding, enabling large-scale production. The blended modified polypropylene energy storage medium film prepared by this invention contains ethylene and butene segments, which effectively reduces the regular arrangement of polypropylene molecular chain segments, achieving a modification from rigid to flexible film. The elongation at break of the prepared blended modified polypropylene energy storage medium film reaches 950.24%, an increase of 43.6% compared to the unblended modified polypropylene film. Simultaneously, the increased free volume of the prepared blended modified polypropylene energy storage medium film provides sufficient free volume for the orientation polarization of the weakly polar methyl groups on the polypropylene molecular backbone. Furthermore, the discharge energy density and charge / discharge efficiency of the blended modified polypropylene energy storage medium film at 125℃ are 1.65 J / cm². 3 It has a high energy storage performance of 88.3% and excellent high-temperature energy storage performance, and it also exhibits excellent cycle stability during 50,000 charge-discharge tests.

[0012] The significant advantages of this invention compared to existing technologies are:

[0013] I. This invention differs from small-scale modification at the laboratory level. It can realize a roll-to-roll industrial production process. The preparation process is simple and environmentally friendly, and it can be used for large-scale preparation of polypropylene energy storage medium films with uniform thickness through blending modification.

[0014] II. Previous studies have mainly focused on suppressing the surge in conduction losses and the deterioration of insulation performance of capacitor films under high-temperature conditions, with little research on their low-temperature energy storage characteristics. When the ambient temperature is lower than the glass transition temperature of polypropylene films (-10℃~0℃), the amorphous regions in the film will change from a highly elastic state to a glassy state, leading to reduced toughness or even embrittlement, as well as microcrack defects and deterioration of electrical properties. This invention achieves the large-scale preparation of modified films through melt blending and extrusion of homopolymer polypropylene and ternary copolymer polypropylene resin (ternary copolymer polypropylene resin is a polypropylene material made by copolymerizing propylene, ethylene and 1-butene). Experimental results show that the successful introduction of ternary copolymer polypropylene resin reduces the energy storage modulus and glass transition temperature of the blended film in the low-temperature region. The elongation at break of the modified film is increased by 43.6% compared with the unmodified film, and the mechanical properties are significantly improved.

[0015] Third, by introducing a ternary copolymer polypropylene resin containing ethylene and butene segments, this invention effectively disrupts the regular arrangement of the polypropylene resin molecular chains, increases the free volume, and provides sufficient free volume for the orientation polarization of the weakly polar methyl groups on the polypropylene molecular backbone, thereby enhancing the polarization response and effectively improving the energy storage performance. Attached Figure Description

[0016] Figure 1The XRD patterns of the blended modified polypropylene energy storage medium films prepared in Examples 1 and 2 and the pure polypropylene energy storage medium film prepared in the control example are shown below.

[0017] Figure 2 Fourier transform infrared spectra of the blended modified polypropylene energy storage medium films prepared in Examples 1 and 2 and the pure polypropylene energy storage medium films prepared in the control example;

[0018] Figure 3 The DSC curves of the blended modified polypropylene energy storage medium film prepared in Examples 1 and 2 and the pure polypropylene energy storage medium film prepared in the control example are shown.

[0019] Figure 4 The energy storage modulus-temperature curves are shown for the blended modified polypropylene energy storage medium film prepared in Example 2 and the pure polypropylene energy storage medium film prepared in the control example.

[0020] Figure 5 The stress-strain curves of the blended modified polypropylene energy storage medium film prepared in Examples 1 and 2 and the pure polypropylene energy storage medium film prepared in the control example are shown.

[0021] Figure 6 The graph shows the energy storage characteristics of the blended modified polypropylene energy storage medium film prepared in Examples 1 and 2, and the pure polypropylene energy storage medium film prepared in the control example, as a function of electric field strength at 125°C.

[0022] Figure 7 The charge-discharge cycle test results at 125°C are shown for the blended modified polypropylene energy storage medium films prepared in Examples 1 and 2 and the pure polypropylene energy storage medium film prepared in the control example. Detailed Implementation

[0023] Specific Implementation Method 1: This implementation method is a method for modifying polypropylene energy storage medium films through melt blending, specifically carried out according to the following steps:

[0024] 1. Mix the dried homopolymer polypropylene resin and the dried ternary copolymer polypropylene resin evenly to obtain the raw material;

[0025] 2. Set the heating zone temperature, die head extrusion temperature, and screw speed of the twin-screw extruder, and feed the raw material into the extruder hopper;

[0026] 3. The molten resin is drawn onto the surface of the cooling roller to cool, and then unidirectional stretching is performed;

[0027] Fourth, the stretched film is wound up to obtain a blended modified polypropylene energy storage medium film.

[0028] This embodiment uses homopolymer polypropylene and ternary copolymer polypropylene resin as raw materials, and prepares the film through a melt blending extrusion combined with uniaxial stretching and winding process. The introduction of ethylene and butene into the ternary copolymer polypropylene suppresses the regular arrangement of polypropylene chain segments, enhancing the flexibility of the molecular chain. On the other hand, the increased proportion of amorphous regions provides sufficient free volume for the orientation polarization of the weakly polar methyl groups in the polypropylene molecular backbone, thus enhancing the orientation polarization effect. The results show that the blended polypropylene energy storage medium film prepared in this embodiment has a 43.6% higher elongation at break compared to the pure polypropylene energy storage medium film, significantly improving its mechanical properties. Furthermore, the blended modified polypropylene energy storage medium film showed no deterioration in energy storage performance after 50,000 charge-discharge cycles at 125℃ and 200MV / m, further validating the application prospects of blended polypropylene film capacitor elements under extreme conditions.

[0029] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that: in step one, the homopolymer polypropylene resin and the ternary copolymer polypropylene resin are placed in a vacuum drying oven at a temperature of 50℃~80℃ and dried for 10h~12h to remove residual trace water in the resin, resulting in dried homopolymer polypropylene resin and dried ternary copolymer polypropylene resin. Other steps are the same as in Specific Implementation Method One.

[0030] Specific Implementation Method 3: This implementation method differs from Specific Implementation Methods 1 and 2 in that the mass fraction of the ternary copolymer polypropylene resin in the raw materials mentioned in step 1 is 5wt%~10wt%. The other steps are the same as in Specific Implementation Methods 1 and 2.

[0031] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the heating zone temperature in step two is 190℃~210℃, specifically divided into six zones with gradually increasing temperatures. The temperatures set for each zone are 190℃, 195℃, 200℃, 205℃, 210℃, and 210℃. The other steps are the same as in Specific Implementation Methods One to Three.

[0032] Specific Implementation Method Five: The difference between this implementation method and Specific Implementation Methods One to Four is that the extrusion temperature of the die head in step two is 210℃. The other steps are the same as those in Specific Implementation Methods One to Four.

[0033] Specific Implementation Method Six: The difference between this implementation method and Specific Implementation Methods One to Five is that the screw speed in step two is 80 r / min. The other steps are the same as in Specific Implementation Methods One to Five.

[0034] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that the temperature of the cooling roller in step three is 130℃~150℃. The other steps are the same as in Specific Implementation Methods One to Six.

[0035] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that the roller speed in the winding process described in step four is 90 r / min to 100 r / min, and the roller tension is 40 N to 50 N. The other steps are the same as in Specific Implementation Methods One to Seven.

[0036] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One through Eight in that the blended modified polypropylene energy storage medium film described in step four contains ethylene and butene segments, resulting in a significantly reduced low-temperature energy storage modulus, a high elongation at break of 950.24%, and a discharge energy density of 1.65 J / cm² at 125°C. 3 The charge / discharge efficiency can reach 88.3%, exhibiting excellent high-temperature energy storage performance and superior cycle stability. Other steps are the same as in specific implementation methods one through eight.

[0037] Specific Implementation Method 10: This implementation method is the application of blended modified polypropylene energy storage dielectric film in capacitors.

[0038] The beneficial effects of the present invention are verified using the following embodiments:

[0039] Example 1: A method for modifying polypropylene energy storage medium films through melt blending, specifically carried out according to the following steps:

[0040] 1. Place the homopolymer polypropylene resin and the ternary copolymer polypropylene resin in a vacuum drying oven at 80°C and dry for 10 hours to remove residual trace water in the resin, and obtain the dried homopolymer polypropylene resin and the dried ternary copolymer polypropylene resin.

[0041] II. Dry homopolymer polypropylene resin and dry ternary copolymer polypropylene resin are mixed evenly at a certain mass ratio to obtain the raw material:

[0042] The mass fraction of ternary copolymer polypropylene resin in the raw materials mentioned in step two is 5 wt%.

[0043] 3. Set the heating zone temperature, die head extrusion temperature and screw speed of the twin-screw extruder. After the temperature of each zone and the screw speed tend to stabilize, feed the raw material into the hopper of the extruder. The time from when the raw material enters the hopper to when it is extruded from the die head is 10 minutes.

[0044] The heating zone of the twin-screw extruder described in step three is divided into six zones, with the temperature set to increase in a gradient. The temperatures set for each zone are 190℃, 195℃, 200℃, 205℃, 210℃, and 210℃.

[0045] The extrusion temperature of the twin-screw extruder described in step three is 210℃, and the screw speed is 80 r / min.

[0046] 4. Adjust the temperature of the chilling roller, draw the molten modified polypropylene resin at the die head of the twin-screw extruder to the surface of the chilling roller for cooling, and then perform unidirectional stretching.

[0047] In step four, adjust the temperature of the quenching roller to 140℃;

[0048] 5. Set the roller speed and roller tension during the film winding process, and wind up the stretched film to obtain a blended modified polypropylene energy storage medium film.

[0049] In step five, the roller speed for the film winding process is set to 100 r / min and the roller tension to 40 N.

[0050] Example 2: The difference between this example and Example 1 is that the mass fraction of ternary copolymer polypropylene resin in the raw materials mentioned in step two is 10 wt%. Other steps and parameters are the same as in Example 1.

[0051] Comparative example: The preparation method of pure polypropylene energy storage medium film is carried out according to the following steps:

[0052] 1. Place the homopolymer polypropylene resin in a vacuum drying oven at 80℃ and dry for 10 hours to remove residual trace water in the resin, thereby obtaining dried homopolymer polypropylene resin.

[0053] 2. Set the heating zone temperature, die head extrusion temperature and screw speed of the twin-screw extruder. After the temperature of each zone and the screw speed tend to stabilize, put the dried homopolymer polypropylene resin into the hopper of the extruder. The time from when the dried homopolymer polypropylene resin enters the hopper to when it is extruded from the die head is 10 minutes.

[0054] The heating zone of the twin-screw extruder described in step two is divided into six zones, with the temperature set to increase in a gradient. The temperatures set for each zone are 190℃, 195℃, 200℃, 205℃, 210℃, and 210℃.

[0055] The extrusion temperature of the twin-screw extruder described in step two is 210℃, and the screw speed is 80 r / min.

[0056] 3. Adjust the temperature of the chilling roller, draw the molten polypropylene resin at the die head of the twin-screw extruder to the surface of the chilling roller for cooling, and then perform unidirectional stretching;

[0057] In step three, the temperature of the cooling roller is adjusted to 140℃;

[0058] IV. Set the roller speed and roller tension during the film winding process, and wind up the stretched film to obtain a blended modified polypropylene energy storage medium film.

[0059] In step four, the roller speed for the film winding process is set to 100 r / min and the roller tension to 40 N.

[0060] Figure 1 The XRD patterns of the blended modified polypropylene energy storage medium films prepared in Examples 1 and 2 and the pure polypropylene energy storage medium film prepared in the control example are shown below.

[0061] Depend on Figure 1 It is known that polypropylene is a semi-crystalline polymer. In the control example, Example 1, and Example 2, four diffraction peaks corresponding to the α-phase were observed at 14.31°, 17.16°, 18.70°, and 21.85°, respectively, corresponding to the (110), (040), (130), and (060) crystal planes of the α-phase. Furthermore, compared to the unblended polypropylene film in the control example, the peak intensity of the α-phase diffraction peaks in the blended modified polypropylene energy storage medium films prepared in Examples 1 and 2 was slightly reduced, demonstrating that the introduction of ethylene and butene segments successfully disrupted the regular arrangement of the polypropylene molecular chains, leading to a decrease in the crystallinity of the composite film.

[0062] Figure 2 Fourier transform infrared spectra of the blended modified polypropylene energy storage medium films prepared in Examples 1 and 2 and the pure polypropylene energy storage medium films prepared in the control example;

[0063] Depend on Figure 2 It can be seen that no new absorption peaks appeared in the blended modified polypropylene energy storage medium films prepared in Examples 1 and 2. This is mainly because no special functional groups were introduced into the ternary copolymer polypropylene, so its Fourier transform infrared spectrum is the same as that of the control example.

[0064] Figure 3 The DSC curves of the blended modified polypropylene energy storage medium film prepared in Examples 1 and 2 and the pure polypropylene energy storage medium film prepared in the control example are shown.

[0065] Depend on Figure 3 It can be seen that, compared with the control example, the melting temperature of the blended modified polypropylene energy storage film prepared in Examples 1 and 2 did not change significantly. This proves that the introduction of ethylene and butene segments did not degrade the heat resistance of the blended modified polypropylene energy storage film, and avoided the degradation of its insulation performance under high-temperature conditions due to the decrease in the melting temperature of the blended film.

[0066] Figure 4 The energy storage modulus-temperature curves are shown for the blended modified polypropylene energy storage medium film prepared in Example 2 and the pure polypropylene energy storage medium film prepared in the control example.

[0067] Depend on Figure 4It can be seen that, compared with the unmodified control polypropylene film, the storage modulus of the blend film prepared in Example 2 decreased significantly in the low-temperature range of -40℃ to 20℃. This is mainly because the molecular chains in the amorphous region are more prone to segmental movement under dynamic loads. The ternary copolymer polypropylene resin introduced flexible ethylene segments, allowing the molecular chains in the amorphous region of the composite film to move locally at lower temperatures. On the other hand, the introduction of flexible segments increased the proportion of amorphous regions, causing more energy to be dissipated through the viscous flow of molecular chains under stress, rather than stored in an elastic form, resulting in a decrease in storage modulus and effectively improving the embrittlement problem of the film at low temperatures. Meanwhile, the storage modulus of the blend film prepared in Example 2 in the high-temperature region is basically the same as that of the control polypropylene film, indicating that the introduction of the ternary copolymer polypropylene did not change its high-temperature mechanical properties.

[0068] Figure 5 The stress-strain curves of the blended modified polypropylene energy storage medium film prepared in Examples 1 and 2 and the pure polypropylene energy storage medium film prepared in the control example are shown.

[0069] Depend on Figure 5 It can be seen that the elongation at break of the films prepared in the control example, Example 1, and Example 2 are 662.24%, 832.47%, and 950.24%, respectively. The mechanical properties of the blended modified polypropylene energy storage medium films prepared in Example 1 and Example 2 are significantly improved. Among them, the film prepared in Example 2 has an elongation at break that is 43.6% higher than that of the film prepared in the control example. This is because the introduction of ethylene and butene monomers into the ternary copolymer polypropylene forms a random copolymer structure, which disrupts the regular arrangement of propylene segments, enhances the mobility of molecular chains, and makes it easier for segment slip, orientation, and rearrangement to occur during stretching, thereby absorbing more energy and increasing the elongation at break.

[0070] Figure 6 The graph shows the energy storage characteristics of the blended modified polypropylene energy storage medium film prepared in Examples 1 and 2, and the pure polypropylene energy storage medium film prepared in the control example, as a function of electric field strength at 125°C.

[0071] Depend on Figure 6 It can be seen that the discharge energy density and charge / discharge efficiency of the pure polypropylene energy storage medium film prepared in the control example at 125℃ are 1.83 J / cm². 3 The discharge energy density and charge / discharge efficiency of the blended modified polypropylene energy storage medium film prepared in Example 1 at 125°C were 1.72 J / cm², 86.0%; 3 The discharge energy density and charge / discharge efficiency of the blended modified polypropylene energy storage medium film prepared in Example 2 at 125°C were 1.65 J / cm², 86.4%; 388.3%. The increase in charge and discharge efficiency helps to reduce energy loss of capacitor elements under actual operating conditions, reduce Joule heat conversion rate, and is conducive to the long-term reliable operation of capacitor elements.

[0072] Figure 7 Charge-discharge cycle test diagrams at 125°C for the blended modified polypropylene energy storage medium films prepared in Examples 1 and 2 and the pure polypropylene energy storage medium film prepared in the control example;

[0073] Depend on Figure 7 It can be seen that after 50,000 charge-discharge cycles at 125°C and 200 MV / m, the energy storage characteristics of all film samples did not deteriorate. Meanwhile, the charge-discharge efficiency of the film in Example 2 was significantly better than that of the control example, indicating that it has good long-term operational stability, further verifying the application prospects of blended polypropylene film capacitor elements under extreme conditions.

Claims

1. A method for modifying polypropylene energy storage medium films through melt blending, characterized in that... The method is specifically implemented according to the following steps:

1. Mix the dried homopolymer polypropylene resin and the dried ternary copolymer polypropylene resin evenly to obtain the raw material; The mass fraction of ternary copolymer polypropylene resin in the raw materials mentioned in step one is 5wt%~10wt%; The ternary copolymer polypropylene resin mentioned in step one is a polypropylene material made by copolymerizing three monomers: propylene, ethylene, and 1-butene.

2. Set the heating zone temperature, die head extrusion temperature, and screw speed of the twin-screw extruder, and feed the raw material into the extruder hopper; 3. The molten resin is drawn onto the surface of the cooling roller to cool, and then unidirectional stretching is performed; The temperature of the cooling roller mentioned in step three is 130℃~150℃; Fourth, the stretched film is wound up to obtain a blended modified polypropylene energy storage medium film.

2. The method for modifying polypropylene energy storage medium films by melt blending according to claim 1, characterized in that... The temperature of the heating zone mentioned in step two is 190℃~210℃.

3. The method for modifying polypropylene energy storage medium films by melt blending according to claim 1, characterized in that... The extrusion temperature of the die head mentioned in step two is 210℃.

4. The method for modifying polypropylene energy storage medium films by melt blending according to claim 1, characterized in that... The screw speed mentioned in step two is 80 r / min.

5. The method for modifying a polypropylene energy storage medium film by melt blending according to claim 1, characterized in that... In the winding process described in step four, the roller speed is 90 r / min to 100 r / min, and the roller tension is 40 N to 50 N.

6. The application of the blended modified polypropylene energy storage medium film prepared by the method according to any one of claims 1 to 5, characterized in that... The blended modified polypropylene energy storage dielectric film is used in capacitors.

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