A polypropylene-based film material and a high energy storage density polypropylene-based ternary composite film and a preparation method thereof

Abstract

The application relates to the field of power capacitors, in particular to a polypropylene-based film material and a high-energy-density polypropylene-based ternary composite film and a preparation method thereof. The polypropylene-based film material provided by the application comprises chlorinated polypropylene and hydroxyl silane zirconium oxide. The polypropylene-based film material is formed into a film on the surface of a polypropylene film to obtain a composite film; after two pieces of the composite film are stacked and laminated, first bidirectional stretching, heat pressing and second bidirectional stretching are sequentially carried out to obtain a high-energy-density polypropylene-based ternary composite film. Experiments show that the ternary composite film has a discharge efficiency of not less than 90% under the condition of 120 DEG C high temperature and 600 kV / mm field intensity, and the breakdown field strength is increased from 639 kV / mm to 774 kV / mm, which is increased by 21%, compared with the composite film before the first bidirectional stretching, heat pressing and second bidirectional stretching.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power capacitors, and in particular to a polypropylene-based film material and a high-energy-density polypropylene-based ternary composite film and a preparation method thereof. BACKGROUND

[0002] The currently used energy storage devices are mainly batteries, supercapacitors, and power capacitors. Among the three, although batteries have the highest energy storage density, their lowest power density limits their application. The energy storage density and power density of supercapacitors are moderate, but their low voltage and high internal resistance also make them difficult to be widely used in power systems. Power capacitors have high power characteristics, self-healing, and high reliability, and play an important role in the technical fields of reactive power compensation, direct current filtering, pulse energy storage, etc. However, the energy storage density of power capacitors is relatively low, resulting in a large volume, which to a large extent limits their application in more fields. Therefore, developing dielectric materials with high energy storage density for manufacturing the next generation of smaller and larger capacity power capacitors has become an urgent problem to be solved.

[0003] The maximum energy storage density U of the dielectric material max is determined by the external electric field E and the maximum electric displacement strength D max , and the calculation method is as follows formula 1.

[0004]

[0005] For a linear dielectric, its energy storage density can be intuitively expressed as formula 2.

[0006]

[0007] In formula 2, ε0 is the vacuum permittivity, ε r is the relative permittivity, E b is the breakdown field strength of the dielectric material.

[0008] Modified dielectric materials have been widely used in the fields of electronics, communications, aerospace, etc. due to their excellent insulation performance, high dielectric constant, low dielectric loss, etc. Among them, biaxially oriented polypropylene (BOPP) has the advantages of high breakdown field strength, low dielectric loss and low production cost, and is often used as a dielectric film for capacitors. However, as a key component of capacitors, BOPP still has the disadvantage of low energy storage density due to its low dielectric constant, which seriously hinders the development of small and integrated capacitors. In addition to improving the intrinsic dielectric constant of polymers through molecular structure design, it has been found that adding ceramic or conductive nanofillers to polymers to make nanocomposite dielectrics can significantly improve the dielectric constant and obtain high energy storage density composites. However, in the process of studying nanocomposites, it was found that there were many problems such as serious agglomeration of nanofillers, decrease of electrical strength, increase of leakage current, increase of dielectric loss, decrease of flexibility, difficulty in film processing, and inability to achieve synergistic improvement of energy storage properties. SUMMARY

[0009] Therefore, the technical problem to be solved by the present application is to provide a polypropylene-based film material and a high energy storage density polypropylene-based ternary composite film and a preparation method thereof. The polypropylene-based film material provided by the present application can be prepared into a high energy storage density ternary composite film after multiple biaxial stretching and hot pressing.

[0010] The present application provides a polypropylene-based film material, comprising:

[0011] chlorinated polypropylene and hydroxyl silanized zirconium oxide.

[0012] The present application does not have special limitations on the chlorinated polypropylene (CPP), which is well known to those skilled in the art. The hydroxyl silanized zirconium oxide in the present application is nano zirconium oxide that has been hydroxylated and alkylated. In some embodiments of the present application, the mass ratio of the chlorinated polypropylene and the hydroxyl silanized zirconium oxide is (5-15):(10-15), preferably 5:15.

[0013] The present inventors have creatively found that the polypropylene-based composite film prepared from chlorinated polypropylene and hydroxyl silanized zirconium oxide as a film material can significantly improve the breakdown field strength and charge-discharge efficiency after multiple biaxial stretching and hot pressing, and can prepare a high energy storage density ternary composite film.

[0014] The present application provides a preparation method of the polypropylene-based film material, comprising: blending and homogenizing chlorinated polypropylene and hydroxyl-silane zirconium oxide to obtain the polypropylene-based film material. Specifically, the present application blends and homogenizes chlorinated polypropylene and hydroxyl-silane zirconium oxide in an organic solvent to obtain the polypropylene-based film material. In some embodiments of the present application, the blending time is 12-48 h, preferably 24 h; the homogenization time is 5-10 min, preferably 5 min.

[0015] The present application does not have special limitations on the chlorinated polypropylene (CPP), which is well known to those skilled in the art. Before blending and homogenizing the chlorinated polypropylene and hydroxyl-silane zirconium oxide, the present application also includes purifying the chlorinated polypropylene to remove additives. In some embodiments of the present application, the present application precipitates the chlorinated polypropylene in xylene with methanol and acetone, and then vacuum dries to constant weight, and the chlorinated polypropylene is purified.

[0016] The hydroxyl-silane zirconium oxide of the present application is nano zirconium oxide subjected to hydroxylation and alkylation. In some embodiments of the present application, the hydroxyl-silane zirconium oxide is obtained by reacting zirconium oxide with H2O2 and octyl triethyl oxy silane (OTS). Specifically, the hydroxyl-silane zirconium oxide is obtained by the following method: refluxing zirconium oxide nanoparticles and H2O2, and then heating the obtained product and octyl triethyl oxy silane in an organic solvent to obtain the hydroxyl-silane zirconium oxide. In one embodiment of the present application, the hydroxyl-silane zirconium oxide is obtained by the following method: mixing zirconium oxide nanoparticles and H2O2 and ultrasonic treatment, then refluxing, mixing the obtained product and an organic solvent and ultrasonic treatment, and then heating with octyl triethyl oxy silane to obtain the hydroxyl-silane zirconium oxide. The refluxing temperature of the present application is 100-120℃, preferably 105℃; the refluxing time is 3-10 h, preferably 6 h. The heating temperature of the present application is 80-100℃, preferably 80℃; the heating time is 5-18 h, preferably 12 h.

[0017] The present application provides a preparation method of a high energy storage density polypropylene-based ternary composite film, comprising the following steps:

[0018] S1) forming a film on the surface of a polypropylene film with a polypropylene-based film material to obtain a composite film; the polypropylene-based film material is the above-mentioned polypropylene-based film material or the polypropylene-based film material obtained by the above-mentioned preparation method;

[0019] S2) stacking and laminating two pieces of the composite film obtained in step S1), and then sequentially performing first biaxial stretching, hot pressing and second biaxial stretching to obtain a high energy storage density polypropylene-based ternary composite film.

[0020] The present application first forms a film on the surface of the polypropylene film with the polypropylene-based film material, to obtain a composite film. Specifically, the present application coats the polypropylene-based film material on the surface of the polypropylene film, and heats to evaporate the organic solvent in the film material, and forms a film on the surface of the polypropylene film with the polypropylene-based film material, to obtain a composite film. In some embodiments of the present application, the polypropylene-based film material is coated on the surface of the polypropylene film which has been pre-cleaned, and heated at 40-60°C for 6-10 hours to evaporate the organic solvent in the film material, and the film material is formed on the surface of the polypropylene film to obtain a composite film. The polypropylene-based film material of the present application is the polypropylene-based film material described above or obtained by the preparation method described above, and will not be described again.

[0021] After obtaining the composite film, the present application stacks and laminates two pieces of the composite film obtained above. Specifically, the present application stacks the two pieces of the composite film obtained above with the film-coated layers facing each other, so that the film-coated layers of the two pieces of the composite film are bonded together, and then laminates. The stacking temperature of the present application is 100-160°C, preferably 100°C; the stacking time is 5-80 min, preferably 15 min. The lamination temperature is 160-190°C, preferably 190°C; the lamination time is 5-10 min, preferably 8 min; the lamination pressure is 5-25 MPa, preferably 15 MPa. In some embodiments of the present application, the lamination process further includes venting.

[0022] After stacking and laminating the two pieces of the composite film obtained above, the present application sequentially performs first biaxial stretching, hot pressing and second biaxial stretching to obtain a high-energy-density polypropylene-based ternary composite film. The biaxial stretching of the present application is to stretch the composite material in the X and Y directions simultaneously, so that the material deforms and the thickness is reduced.

[0023] The present application first performs first biaxial stretching; specifically, the first biaxial stretching is specifically: biaxial stretching at 140-170°C at a rate of 50-100 mm / s, preferably biaxial stretching at 140°C at a rate of 60 mm / s. The stretching ratio of the first biaxial stretching of the present application is (3-4) x (3-4), preferably 3 x 3 or 4 x 4. In one embodiment of the present application, the first biaxial stretching of the present application is biaxial stretching at a stretching ratio of 4 x 4 at 140°C at a rate of 60 mm / s. After the first biaxial stretching, the present application further includes heat preservation of the film after the first biaxial stretching for 60-120 s, preferably 100 s.

[0024] After the first biaxial stretching, the present application carries out heat pressing. The temperature of the heat pressing is 100-150 DEG C, preferably 120 DEG C; the pressure of the heat pressing is 5-25 MPa, preferably 15 MPa; and the time of the heat pressing is 20-100 min, preferably 30 min.

[0025] After the heat pressing, the present application carries out the second biaxial stretching to obtain the high energy storage density polypropylene-based ternary composite film. The second biaxial stretching is specifically carried out at 140-165 DEG C at a rate of 50-100 mm / s, preferably at 140 DEG C at a rate of 60 mm / s. The stretching ratio of the second biaxial stretching is (3-4) x (3-4), preferably 3 x 3 or 4 x 4. After the second biaxial stretching, the present application further comprises heat preservation of the film after the second biaxial stretching for 60-120 s, preferably 100 s.

[0026] The present application further provides a high energy storage density polypropylene-based ternary composite film obtained by the preparation method of the above-mentioned ternary composite film. The polypropylene-based ternary composite film provided by the present application is obtained by stacking and laminating two composite films after film formation of the above-mentioned film material on a polypropylene film and then carrying out multiple stretching and heat pressing. The multiple stretching and heat pressing adjust the interlayer structure of the film and homogenize the interface, thereby obtaining a ternary composite film with high energy storage density.

[0027] The present application provides a polypropylene-based film material, a high energy storage density polypropylene-based ternary composite film and a preparation method thereof. The polypropylene-based film material provided by the present application comprises chlorinated polypropylene and hydroxyl silanized zirconium oxide. The preparation method of the high energy storage density polypropylene-based ternary composite film provided by the present application comprises the following steps: S1) film formation of the polypropylene-based film material on the surface of a polypropylene film to obtain a composite film; the polypropylene-based film material is the polypropylene-based film material provided by the present application; S2) stacking and laminating two composite films obtained in step S1), and then sequentially carrying out first biaxial stretching, heat pressing and second biaxial stretching to obtain a high energy storage density polypropylene-based ternary composite film. Experiments show that the energy storage density of the composite film prepared from the film material provided by the present application and subjected to multiple biaxial stretching and heat pressing is significantly improved. Compared with the composite film not subjected to multiple biaxial stretching and heat pressing, the breakdown field strength is increased from 639 kV / mm to 774 kV / mm, an increase of 21%. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 The preparation method of the polypropylene-based ternary composite film of the present application is shown in the flow chart;

[0029] Figure 2 The Weibull distribution of the composite film material into different films of the present application is shown in the figure;

[0030] Figure 3 Charge-discharge efficiency graph of the BO (PP-CPP-PP) film prepared in the present application;

[0031] Figure 4 Weibull distribution graph of the BO (PP-CPP-PP) film prepared in the present application and other films prepared by different hot stretching processes. DETAILED DESCRIPTION

[0032] The application discloses a polypropylene-based film material and a high-energy-density polypropylene-based ternary composite film and a preparation method thereof. Those skilled in the art can refer to the content herein and appropriately improve process parameters to realize. It is particularly pointed out that all similar replacements and changes are obvious to those skilled in the art, and they are regarded as being included in the application. The method and application of the application have been described through preferred embodiments, and relevant personnel can obviously change or appropriately change and combine the method and application herein without departing from the content, spirit and scope of the application, to realize and apply the technology of the application.

[0033] The components and mass percentages of the polypropylene-based ternary composite film are as follows:

[0034] Biaxially stretched polypropylene: 70-80 wt.%;

[0035] Hydroxyl-silane nano zirconium oxide: 10-15 wt.%;

[0036] Chlorinated polypropylene: 5-15 wt.%.

[0037] In the embodiment 1 of the application, the components and mass percentages of the polypropylene-based ternary composite film are as follows:

[0038] Polypropylene: 80 wt.%;

[0039] Hydroxyl-silane nano zirconium oxide: 15 wt.%;

[0040] Chlorinated polypropylene: 5 wt.%.

[0041] The preparation method of the polypropylene-based ternary composite film is as shown in Figure 1 , Figure 1 The preparation method of the polypropylene-based ternary composite film is as shown in

[0042] The application is further described below in combination with embodiments:

[0043] Embodiment 1

[0044] a: Zr02particles (30 g, particle size 20 nm) and H202(220 mL) were added to a round bottom flask, the mixture was sonicated for 30 min, then refluxed in an oil bath at 105 °C for 6 h.

[0045] b: The nanoparticles were recovered by centrifugation at 4000 rpm for 5 min, and washed with deionized water and ethanol for 3 times.

[0046] c: The obtained Zr02nanoparticles were dried at 80 °C under vacuum for 12 h, and named as Z-OH.

[0047] d: Z-OH (10 g) and xylene (50 mL) were mixed in a round bottom flask, sonicated for 30 min, then 5 g of octyl triethyl oxysilane (OTS) was added to the flask. The mixture was heated to 80 °C, and kept under nitrogen atmosphere for 12 h.

[0048] e: The nanoparticles were recovered by centrifugation at 4000 rpm for 5 min, and washed with xylene for 3 times.

[0049] f: Finally dried to constant weight at 80 °C under vacuum, and named as OZ.

[0050] g: The chlorinated polypropylene film (CPP) was dissolved in xylene, precipitated with methanol and acetone, and then dried to constant weight at 80 °C under vacuum to remove additives.

[0051] h: The purified CPP was dissolved in xylene at 75 °C, and a certain amount of OZ particles was added at 10 wt% of CPP, respectively. Stirring for 24 h, homogenization for 5 min, the prepared coating material was used for subsequent solution casting.

[0052] i: The prepared coating material was uniformly treated for 5 min.

[0053] j: The coating material was coated on a PP film (thickness 1 mm) using a laboratory casting device, the surface was pre-cleaned, and the solvent was volatilized at 40 °C for 6 h to obtain a PP-OZ@CPP film.

[0054] k: The coating thickness was controlled by the height of the scraper. The coated two pieces of PP film were stacked at 100 °C (the coating layer was bonded together), and laminated by hot pressing for 15 min. The temperature of the flat press was set to 190 °C, the pressure was set to 15 MPa, the processing time was set to 8 min, the exhaust times were set to 6 times, and the exhaust time of each time was set to 10 s, to obtain a PP-CPP-PP film (thickness 2.1 mm).

[0055] l: The above PP-CPP-PP film (thickness 2.1 mm) was biaxially stretched at a ratio of 4x4, temperature 140℃, rate 60 mm / s, and holding time 100 s to obtain a BO (PP-CPP-PP) film with a thickness of 135 microns, which was recorded as BO (PP-CPP-PP)-1 (thickness 135 microns).

[0056] m: The above BO (PP-CPP-PP)-1 (thickness 135 microns) film was heat-pressed at 120℃, pressure 15 MPa, and time 30 min to adjust the interlayer structure of the film, and a heat-treated film was obtained, which was recorded as HT-BO (PP-CPP-PP)-1 (thickness 130 microns).

[0057] n: The above HT-BO (PP-CPP-PP)-1 (thickness 130 microns) film was biaxially stretched at a ratio of 4x4, temperature 140℃, rate 60 mm / s, and holding time 100 s to obtain a BO (PP-CPP-PP) film with a thickness of 8 microns, which was recorded as BO (PP-CPP-PP) (thickness 8 microns), i.e., the polypropylene-based ternary composite film after multiple heat-pressing and stretching interface homogenization according to the present application.

[0058] Comparative Example 1

[0059] Directly stretched film F1

[0060] The F1 film with a thickness of 150 microns was prepared by heat-pressing at a temperature of 180℃ and a pressure of 15 MPa.

[0061] The film was biaxially stretched once, and the steps were the same as the first stretching, to obtain a directly stretched film F1 with a thickness of about 10 microns.

[0062] Comparative Example 2

[0063] The preparation of the multiple-stretched double-layer composite film BO (PP-OZ) was as follows: after the j step of Example 1, no multiple heat-pressing was performed, and the same two stretching and one heat-pressing after the l step of Example 1 were directly performed to obtain a BO (PP-OZ) film with a thickness of about 4 microns.

[0064] Experimental Example 1

[0065] The BO (PP-CPP-PP) film prepared in step n of the above embodiment 1 was subjected to DC breakdown test (ball-ball electrode, voltage rise rate 500 V / s, test in silicone oil), and compared with the PP-CPP-PP film prepared in step k, the BO (PP-CPP-PP)-1 film prepared in step l and the HT-BO (PP-CPP-PP)-1 film prepared in step m of embodiment 1, and their Weibull distribution graphs were obtained as shown in Figure 2 , Figure 2 The Weibull distribution graphs of different films made of the composite film material of the present application were obtained. Figure 2 It can be seen that the breakdown field strength of the BO (PP-CPP-PP) film prepared in step n is increased from 639 kV / mm to 774 kV / mm, an increase of 21%, compared with the PP-CPP-PP film prepared by direct hot pressing.

[0066] Experimental Example 2

[0067] The BO (PP-CPP-PP) film prepared in step n of the above embodiment 1 was subjected to energy storage density and charge-discharge efficiency test (gold electrodes with a diameter of 3 mm were sprayed on the top and bottom, and the test was carried out in silicone oil using a ferroelectric workstation), and the results are shown in Figure 3 , Figure 3 The charge-discharge efficiency graph of the BO (PP-CPP-PP) film prepared in the present application is shown in Figure 3 It can be seen that the discharge efficiency is not less than 90% at a high temperature of 120℃ and a field strength of 600 kV / mm.

[0068] Experimental Example 3

[0069] The directly stretched film F1 prepared in the above comparative example 1 and the directly hot-pressed multiple-stretched double-layer composite film BO (PP-OZ) prepared in comparative example 2 were subjected to DC breakdown test according to the method of experimental example 1, and the experimental results of the BO (PP-CPP-PP) film in experimental example 1 were compared, as shown in Figure 4 , Figure 4 The Weibull distribution graphs of the BO (PP-CPP-PP) film of the present application and the films prepared by other hot-stretching processes are shown in Figure 4 It can be seen that the BO (PP-CPP-PP) film of the present application has the highest breakdown field strength, which is increased by nearly 15% compared with F1 and BO (PP-OZ) film. It can be shown that the performance of the composite film of this formula is significantly improved after multiple hot-stretching, which is superior to other materials.

[0070] The above merely describes preferred specific embodiments of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art, according to the technical solution and inventive concept of the present application, makes equivalent replacement or change within the technical range disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A method for preparing a high energy density polypropylene based ternary composite film, characterized in that, The method comprises the following steps: S1) coating a polypropylene-based film material on the surface of a polypropylene film to form a film, to obtain a composite film; the polypropylene-based film material comprises: chlorinated polypropylene and hydroxyl-silane zirconium oxide; the hydroxyl-silane zirconium oxide is obtained by reacting zirconium oxide, H2O2 and octyl triethyl oxy silane; the preparation method of the polypropylene-based film material comprises: blending and homogenizing the chlorinated polypropylene and the hydroxyl-silane zirconium oxide to obtain the polypropylene-based film material; the mass ratio of the chlorinated polypropylene to the hydroxyl-silane zirconium oxide is (5-15):(10-15); S2) stacking and laminating two pieces of the composite film obtained in step S1), wherein the stacking operation is to bond the film layers formed by the polypropylene-based film material in the two pieces of the composite film together, and then sequentially performing first biaxial stretching, hot pressing and second biaxial stretching to obtain a high energy storage density polypropylene-based ternary composite film.

2. The method for preparing a high energy storage density polypropylene-based ternary composite film according to claim 1, characterized in that, In step S2), the first biaxial stretching is specifically performed at 140-170°C at a rate of 50-100 mm / s. The second biaxial stretching is specifically performed at 140-165°C at a rate of 50-100 mm / s.

3. The method for preparing a high energy storage density polypropylene-based ternary composite film according to claim 2, characterized in that, In step S2), the stretching ratio of the first biaxial stretching is (3-4)×(3-4). The stretching ratio of the second biaxial stretching is (3-4)×(3-4).

4. The method for preparing a high energy storage density polypropylene-based ternary composite film according to claim 3, characterized in that, In step S2), the first biaxial stretching and the second biaxial stretching are both biaxial stretching at a stretching ratio of 4×4 at 140°C at a rate of 60 mm / s.

5. The method for preparing a high energy storage density polypropylene-based ternary composite film according to claim 1, characterized in that, In step S2), the temperature of the hot pressing is 100-150°C, the pressure of the hot pressing is 10-30 MPa, and the time of the hot pressing is 5-100 min.

6. The high energy storage density polypropylene-based ternary composite film obtained by the preparation method of any one of claims 1-5.

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