Metallized polypropylene film, preparation method thereof and capacitor

Abstract

The invention relates to a metallized polypropylene film, a preparation method thereof and a capacitor, and the preparation method comprises the following steps: putting a polypropylene film and metal into a vacuum chamber, and carrying out the vacuum pumping treatment; the metal is heated in a vacuum chamber for vacuum evaporation, and a metallized polypropylene film with the surface plated with a metal layer is obtained; wherein the evaporation rate of the metal ranges from 0.1 nm / s to 0.5 nm / s, and the thickness of the metal layer ranges from 40 nm to 200 nm. The metalized polypropylene film prepared by the preparation method disclosed by the invention is stable in performance, and has the advantages of good dielectric property stability, high breakdown strength, high discharge energy density, good self-healing performance and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of capacitors, and in particular relates to a metallized polypropylene film with excellent electrical properties, a preparation method thereof, and a capacitor comprising the same. Background Art

[0002] The consumption of fossil fuels and people's attention to environmental issues have made the grid connection of new energy an important research direction in recent years. Flexible DC transmission technology has shown better capabilities in the field of grid connection of new energy and interconnection of AC systems. The rectifier and inverter parts are important links in the flexible DC transmission system, and the capacitor is an extremely critical device in the converter valve. Its performance has an important impact on the safe and stable operation of the system. Metallized film capacitors do not have the problem of insulating oil leakage, and their size and weight are smaller than oil-immersed capacitors, which can better meet space requirements. At the same time, they also have the advantages of low noise and self-healing, and are widely used in flexible transmission, electric vehicles, rail transportation, etc.

[0003] Biaxially oriented polypropylene (BOPP) film is the main material for film capacitors at present. It has good mechanical tensile properties, low dielectric loss and high breakdown strength. The electrical properties of metallized polypropylene film, including breakdown strength, dielectric constant, self-healing properties, etc., affect the scope of use and working performance of film capacitors. Metallized polypropylene film is mainly composed of polypropylene film and evaporated metal layer. The properties of the metal layer directly affect the performance of metallized film and film capacitors. At present, the properties of the metal layer are mainly improved by optimizing the material type of the metal layer, thereby improving the performance of metallized polypropylene film and film capacitors. However, the optimization of the metal layer material has certain limitations. It is necessary to develop a new preparation method to provide a metallized polypropylene film with excellent electrical properties. Summary of the invention

[0004] The present invention aims to solve one of the technical problems in the related art at least to a certain extent. To this end, the purpose of the present invention is to provide a method for preparing a metallized polypropylene film with excellent electrical properties. The metallized polypropylene film prepared by the preparation method of the present invention has stable performance, good dielectric stability, high breakdown strength, high discharge energy density, good self-healing performance and the like.

[0005] In a first aspect, the present invention provides a method for preparing a metallized polypropylene film, comprising the following steps:

[0006] Put the polypropylene film and the metal into the vacuum chamber and perform vacuum treatment;

[0007] Heating the metal in a vacuum chamber to melt and evaporate it to perform vacuum evaporation to obtain a metallized polypropylene film with a metal layer coated on the surface;

[0008] Wherein, the evaporation rate of the metal is 0.1-0.5 nm / s, and the thickness of the metal layer is 40-200 nm.

[0009] In a second aspect, the present invention provides a metallized polypropylene film obtained by the preparation method of the first aspect of the present invention.

[0010] In a third aspect, the present invention provides a capacitor comprising the metallized polypropylene film according to the second aspect of the present invention.

[0011] Compared with the prior art, the present invention has the following beneficial effects:

[0012] The invention provides a method for preparing a metallized polypropylene film. By simultaneously regulating the metal evaporation rate and the metal layer thickness within the scope of the invention under high vacuum, the bonding ability between the metal layer and the polypropylene film can be improved, and the working stability of the metallized polypropylene film can be improved; meanwhile, a low-roughness surface can be formed, and the quality of the metallized polypropylene film can be improved, so as to prepare a metallized polypropylene film having the advantages of good dielectric property stability, high breakdown strength, high discharge energy density, good self-healing performance, and the like.

[0013] The preparation method of the present invention has a simple process, does not require the introduction of new steps or the addition of new substances, and is convenient and quick. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is an AFM morphology image of the metallized polypropylene film prepared in Example 1 of the present invention.

[0015] Figure 2 The dielectric constant and dielectric loss diagram of the metallized polypropylene films prepared in Examples 1, 2 and 3 of the present invention.

[0016] Figure 3 Graph showing the breakdown strength of the metallized polypropylene films obtained in Examples 1, 2 and 3 of the present invention.

[0017] Figure 4 Graph showing the discharge energy density and charge-discharge efficiency of the metallized polypropylene films prepared in Examples 1, 2 and 3 of the present invention.

[0018] Figure 5 The circuit principle diagram of the self-healing energy testing circuit constructed for the present invention.

[0019] Figure 6 A schematic diagram of the structure of a film capacitor used in the self-healing energy test circuit constructed in the present invention.

[0020] Figure 7 The self-healing energy statistics of the metallized polypropylene films prepared in Examples 1, 2 and 3 of the present invention are shown.

[0021] Figure 8 This is a photograph of the single-sided evaporated metallized polypropylene film prepared in Comparative Example 3. DETAILED DESCRIPTION

[0022] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application clearer, the present application is further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not intended to limit the present application. Unless otherwise defined, the technical terms used in the following examples have the same meanings as those generally understood by those skilled in the art to which the present application belongs. In the embodiments, unless otherwise specified, the raw materials used are commercially available, and the methods used in the following embodiments are conventional methods in the art unless otherwise specified.

[0023] In a first aspect, the present invention provides a method for preparing a metallized polypropylene film, comprising the following steps:

[0024] Put the polypropylene film and the metal into the vacuum chamber and perform vacuum treatment;

[0025] Heating the metal in a vacuum chamber to melt and evaporate it to perform vacuum evaporation to obtain a metallized polypropylene film with a metal layer coated on the surface;

[0026] Wherein, the evaporation rate of the metal is 0.1-0.5 nm / s, and the thickness of the metal layer is 40-200 nm.

[0027] The present invention can improve the bonding ability between the metal layer and the polypropylene film and improve the working stability of the metalized polypropylene film by simultaneously regulating the metal evaporation rate and the metal layer thickness within the scope of the present invention under high vacuum; at the same time, it can also form a low-roughness surface and improve the quality of the metalized polypropylene film, thereby preparing a metalized polypropylene film with the advantages of good dielectric stability, high breakdown strength, high discharge energy density, good self-healing performance, etc. In addition, the preparation method of the present invention has a simple process, does not require the introduction of new steps or the addition of new substances, and is convenient and fast.

[0028] In some embodiments, the evaporation rate of the metal may be, for example, 0.1 nm / s, 0.2 nm / s, 0.3 nm / s, 0.4 nm / s, or 0.5 nm / s.

[0029] Preferably, the evaporation rate of the metal is 0.2-0.3 nm / s, for example, 0.22 nm / s, 0.24 nm / s, 0.26 nm / s, 0.28 nm / s or 0.3 nm / s.

[0030] In some embodiments, the thickness of the metal layer may be, for example, 40 nm, 60 nm, 80 nm, 100 nm, 120 nm, 140 nm, 160 nm, 180 nm, or 200 nm.

[0031] Preferably, the thickness of the metal layer is 50-100 nm, for example, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm or 100 nm.

[0032] It has been verified by experiments that the evaporation rate of the metal and the thickness of the metal layer need to be controlled within the numerical range of the present invention at the same time to improve the bonding ability between the metal layer and the polypropylene film, and to prepare a metallized polypropylene film having the advantages of good dielectric stability, high breakdown strength, high discharge energy density, good self-healing performance, etc. Any one of them not being within the numerical range of the present invention will lead to deterioration of the electrical properties of the polypropylene film. The metal evaporation rate and the thickness of the metal layer of the present invention synergistically improve the electrical properties of the metallized polypropylene film, so that the dielectric properties are stable, the breakdown strength is high, the discharge energy density is high, the self-healing performance is good, etc.

[0033] In some embodiments, after the vacuum treatment, the vacuum degree in the vacuum chamber is 3×10 -4 Pa or less; preferably, the vacuum degree is 1.5×10 -4 Below Pa.

[0034] In some specific embodiments, the vacuum degree in the vacuum chamber may be 3×10 -4 Pa or less, 2×10 -4 Pa or less or 1.5×10 -4 The vacuum degree affects the quality of metal layer deposition. If the vacuum degree is too high, metal atoms will collide with gas molecules frequently, and metal atoms will not be able to reach the film surface smoothly, thus failing to ensure the coating quality. If the vacuum degree is too low, the film performance will not be significantly improved and the film production efficiency will be low.

[0035] In some embodiments, the metal includes aluminum, zinc or aluminum-zinc alloy. Preferably, the metal is aluminum. Metal aluminum is plated on the polypropylene film to form an aluminum film layer, which is beneficial to improving the electrical properties of the metallized polypropylene film, so that the dielectric performance stability is better, the breakdown strength is higher, the discharge energy density is higher, and the self-healing performance is better. At the same time, the cost of aluminum is low, which is beneficial to the industrial production of metallized polypropylene film.

[0036] In some embodiments, the metal is in the form of particles. The granular metal is conducive to heating evaporation and maintaining a stable evaporation rate, thereby improving the quality of the evaporation film.

[0037] In some embodiments, the purity of the metal is above 99.9%. Preferably, the purity of the metal is above 99.99%. The purity of the metal affects the purity of the metal layer formed by vacuum evaporation, and further affects the stability of dielectric properties, breakdown strength, discharge energy density, self-healing properties, etc. By optimizing the purity of the metal, it is beneficial to improve the electrical properties of the metallized polypropylene film.

[0038] In some embodiments, the step of performing vacuum evaporation in a vacuum chamber to obtain the metallized polypropylene film includes: heating the metal, and performing vacuum evaporation after the metal evaporation rate is stable. The evaporation rate affects the internal structure and appearance of the metal layer. Maintaining a stable evaporation rate is conducive to improving the uniformity of the internal structure and appearance of the metal layer, and improving the electrical properties of the metallized polypropylene film.

[0039] In some embodiments, the step of heating the metal in the vacuum chamber for vacuum evaporation includes: heating the metal after the vacuum degree of the vacuum chamber reaches a predetermined value, and performing vacuum evaporation after the evaporation rate of the metal stabilizes.

[0040] In some embodiments, before placing the polypropylene film into the vacuum chamber, the preparation method further includes: performing corona treatment on the surface of the polypropylene film, and the corona treated surface of the polypropylene film is the evaporation surface. The corona treatment can enhance the adhesion between the metal layer and the polypropylene film; at the same time, the corona treatment can also reduce defects in the evaporation process; in addition, the corona treatment can also improve the surface morphology and roughness of the metal layer, and further optimize the electrical properties of the metallized polypropylene film.

[0041] In some embodiments, after the corona treatment, the preparation method further comprises: cleaning the polypropylene film and drying it.

[0042] The surface of the metallized polypropylene film prepared by the preparation method of the invention has an island structure of aluminum atoms, good flatness, and a surface roughness of less than or equal to 10 nm.

[0043] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited thereto.

[0044] Example 1

[0045] Take a 5.8μm thick polypropylene film and perform corona treatment on one surface. Use anhydrous ethanol to clean the surface, wipe it dry with dust-free paper, place it in the mask, and then put the mask into the vacuum coating machine (Shenyang Qihui Vacuum QHV-R76B), embed the tungsten metal boat into the fixture, place 2 high-purity aluminum particles (purity 99.99%) in the boat, and close the vacuum chamber for vacuum operation.

[0046] When the vacuum degree of the chamber reaches 1.5×10 -4Pa, turn on the heating source switch, increase the heating source current to about 50A to melt and evaporate the aluminum particles in the tungsten boat, and use a film thickness meter (STM-2XM) to measure the evaporation rate. When the evaporation rate stabilizes at 0.25nm / s, open the baffle between the mask and the metal boat, and the metal evaporates to the corona surface of the polypropylene film, starting the evaporation operation.

[0047] When the thickness of the evaporated metal layer reaches 50nm, the baffle between the mask and the metal boat is closed, the evaporation is stopped, the heating source is turned off, and the vacuum system is turned off. When the pressure in the chamber returns to the outside pressure and the temperature drops to room temperature, the metallized polypropylene film evaporated on one side is taken out and recorded as A1.

[0048] Example 2

[0049] A metallized polypropylene film was prepared according to Example 1. The difference between the preparation method and Example 1 is that the thickness of the evaporated metal layer was adjusted. The thickness of the metal layer was 80 nm, and a single-sided evaporated metallized polypropylene film was obtained. The film was recorded as A2.

[0050] Example 3

[0051] A metallized polypropylene film was prepared according to Example 1. The difference between the preparation method and Example 1 is that the thickness of the evaporated metal layer was adjusted. The thickness of the metal layer was 100 nm, and a single-sided evaporated metallized polypropylene film was obtained. The film was recorded as A3.

[0052] Example 4

[0053] A metallized polypropylene film was prepared according to Example 1. The difference between the preparation method and Example 1 is that the thickness of the evaporated metal layer was adjusted. The thickness of the metal layer was 200 nm, and a single-sided evaporated metallized polypropylene film was obtained. The film was recorded as A4.

[0054] Example 5

[0055] A metallized polypropylene film was prepared according to Example 1. The difference between the preparation method and Example 1 is that the evaporation rate of the metal was adjusted to 0.2 nm / s, and a single-sided evaporated metallized polypropylene film was obtained. The film was recorded as A5.

[0056] Example 6

[0057] A metallized polypropylene film was prepared according to Example 1. The difference between the preparation method and Example 1 is that the evaporation rate of the metal was adjusted to 0.5 nm / s, and a single-sided evaporated metallized polypropylene film was obtained. The film was recorded as A6.

[0058] Example 7

[0059] The metallized polypropylene film was prepared according to Example 1. The difference between the preparation method and Example 1 is that the vacuum degree was adjusted to 1.0×10 -4 Pa, a single-sided vapor-deposited metallized polypropylene film was obtained, and this film was recorded as A7.

[0060] Example 8

[0061] The metallized polypropylene film was prepared according to Example 1. The difference between the preparation method and Example 1 is that the vacuum degree was adjusted to 5.0×10 -4 Pa, a single-sided vapor-deposited metallized polypropylene film was obtained, and this film was recorded as A8.

[0062] Comparative Example 1

[0063] A metallized polypropylene film was prepared according to Example 1. The difference between the preparation method and Example 1 is that the thickness of the evaporated metal layer was adjusted. The thickness of the metal layer was 30 nm, and a single-sided evaporated metallized polypropylene film was obtained. The film was recorded as D1.

[0064] Comparative Example 2

[0065] A metallized polypropylene film was prepared according to Example 1. The difference between the preparation method and Example 1 is that the thickness of the evaporated metal layer was adjusted. The thickness of the metal layer was 300 nm, and a single-sided evaporated metallized polypropylene film was obtained. The film was recorded as D2.

[0066] Comparative Example 3

[0067] A metallized polypropylene film was prepared according to Example 1. The difference between the preparation method and Example 1 is that the evaporation rate of the metal was adjusted to 0.05 nm / s, and a single-sided evaporated metallized polypropylene film was obtained. The film was recorded as D3.

[0068] Comparative Example 4

[0069] A metallized polypropylene film was prepared according to Example 1. The difference between the preparation method and Example 1 is that the evaporation rate of the metal was adjusted to 0.8 nm / s, and a single-sided evaporated metallized polypropylene film was obtained. The film was recorded as D4.

[0070] Test Case

[0071] The metallized polypropylene films prepared in Examples 1-8 and Comparative Examples 1-4 were subjected to performance tests, including surface morphology, dielectric properties, breakdown strength, energy density, and self-healing energy.

[0072] Surface topography test

[0073] The surface morphology of Example 1 was tested using an atomic force microscope at room temperature. The test area was 2 μm×2 μm. The atomic force microscope mode was selected as the Peak Force mode. The tip on the cantilever of the atomic force microscope interacted with the material surface to obtain the surface morphology of the material as shown in FIG. Figure 1 It can be seen that there is an island structure of aluminum atoms on the surface of the prepared metallized polypropylene film, the flatness is good, and the surface roughness is less than 10nm.

[0074] Dielectric properties test

[0075] The dielectric properties of the metallized polypropylene films of Examples 1-8 and Comparative Examples 1-4 were tested. The dielectric constant and dielectric loss of the materials at different frequencies were tested using a wideband dielectric spectrometer from Novocontrol, Germany, at room temperature. The dielectric constant and dielectric loss values ​​of Examples 1-8 and Comparative Examples 1-4 at 1 kHz are shown in Table 1. The dielectric constant of the polypropylene film prepared in Example 1-3 was basically stable at around 2.2 at 1 kHz, and the dielectric constant of Example 3 could reach 2.28; the dielectric constant of Examples 1-3 at 10 to 10 4 The dielectric constant and dielectric loss at Hz frequency are shown in Figure 2 The dielectric constant of the metallized polypropylene film prepared in Examples 1 to 3 is between 10 and 10 4 The frequency remains stable at Hz.

[0076] Breakdown strength test

[0077] The metallized polypropylene films prepared in Examples 1-8 and Comparative Examples 1-4 were subjected to a breakdown strength test. The samples were placed between the column-plate electrodes at room temperature, and a high voltage withstand tester was used to apply pressure between the column-plate electrodes under a DC voltage. In order to avoid surface flashover, the samples were placed in silicone oil for testing. The DC voltage boost rate was 500V / s. The breakdown was determined when the leakage current reached 50mA, and the results were expressed using a Weibull distribution. The expected values ​​of the breakdown strength of Examples 1-8 and Comparative Examples 1-4 are shown in Table 1. The breakdown strength of Examples 1-3 all exceeded 630kV / mm, and the insulation performance was excellent, see Table 1. Figure 3 The breakdown strength of Example 1 reaches 656 kV / mm. The improvement of the breakdown field strength can improve the working range of the film capacitor and the working reliability under high field strength.

[0078] Discharge energy density and charge and discharge efficiency test

[0079] The discharge energy density and charge-discharge efficiency of Examples 1-8 and Comparative Examples 1-4 were tested using an American Radiant ferroelectric tester. The samples were placed in silicone oil for testing. The test results are shown in Table 1. Under a field strength of 600 kV / mm, the discharge energy density of Examples 1 to 3 exceeded 3 J / cm 3 The discharge energy density of Example 3 reaches 3.8 J / cm 3 . Figure 4 The discharge energy density and charge-discharge efficiency curves of the metallized polypropylene films prepared in Examples 1 to 3 at 350 to 700 kV / mm. As the electric field increases, the energy density of the examples increases steadily, while the charge-discharge efficiency remains above 85%. Examples 1 to 3 have excellent charge-discharge performance.

[0080] Self-healing energy test

[0081] The self-healing energy test circuit constructed was used to test the self-healing performance of Examples 1 to 3. The circuit schematic is shown in FIG. Figure 5 As shown, R c is the protection resistor, 10MΩ; C0 is the voltage stabilizing capacitor, 0.1μF; C s is the sample film capacitance, R s The sampling resistor is 1Ω. s The voltage on the capacitor reflects the current flowing through the embodiment. Two identical single-sided evaporated metallized polypropylene films prepared in the same embodiment are stacked up and down to form a sample film capacitor, such as Figure 6 As shown. Two metallized polypropylene films are stacked together in an offset manner, and electrodes are placed on both sides. The common area in the middle acts as a dielectric. The voltage and current waveforms when self-healing occurs are measured and integrated to obtain the self-healing energy. Figure 7 The scatter plot statistics of the self-healing energy of Examples 1 to 3 are shown. The self-healing energy of Examples 1 to 3 increases with the increase of voltage, but the self-healing energy is basically within a small range within the voltage range. The self-healing energy of the three examples does not exceed 15mJ, and the self-healing energy of Examples 1 and 2 is below 10mJ. The low self-healing energy makes the capacitance loss of the metallized polypropylene film smaller when self-healing occurs, and the probability of successful self-healing is higher, ensuring the long-term stable reliability of the metallized polypropylene film capacitor working under high field strength.

[0082] Table 1

[0083]

[0084] The terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0085] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, unless they are contradictory.

[0086] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A method for preparing a metallized polypropylene film, characterized in that: The following steps are involved: Put the polypropylene film and the metal into the vacuum chamber and perform vacuum treatment; Heating the metal in a vacuum chamber to melt and evaporate it to perform vacuum evaporation to obtain a metallized polypropylene film with a metal layer coated on the surface; Wherein, the evaporation rate of the metal is 0.1-0.5 nm / s, and the thickness of the metal layer is 40-200 nm.

2. The preparation method according to claim 1, characterized in that: The evaporation rate of the metal is 0.2-0.3 nm / s.

3. The preparation method according to claim 1 or 2, characterized in that: The thickness of the metal layer is 50-100 nm.

4. The preparation method according to claim 1 or 2, characterized in that: After vacuum treatment, the vacuum degree in the vacuum chamber is 3×10 -4 Pa or less; preferably, the vacuum degree is 1.5×10 -4 Below Pa.

5. The preparation method according to claim 1 or 2, characterized in that: The metal includes aluminum, zinc or an aluminum-zinc alloy.

6. The preparation method according to claim 1 or 2, characterized in that: The metal is in particle form; preferably, the purity of the metal is above 99.9%.

7. The preparation method according to claim 1 or 2, characterized in that: The step of performing vacuum evaporation in a vacuum chamber to obtain the metallized polypropylene film comprises: heating the metal and performing vacuum evaporation after the metal evaporation rate is stabilized.

8. The preparation method according to claim 1 or 2, characterized in that: Before placing the polypropylene film into the vacuum chamber, the preparation method further comprises: performing corona treatment on the surface of the polypropylene film, and the corona treated surface of the polypropylene film is the vapor deposition surface.

9. A metallized polypropylene film, characterized in that: The method is obtained by the preparation method according to any one of claims 1 to 8.

10. A capacitor, characterized in that: Comprising the metallized polypropylene film as described in claim 9.

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