Polypropylene uniaxially stretched film as well as preparation method and application thereof

Abstract

The invention discloses a polypropylene uniaxial stretching film as well as a preparation method and application thereof. Aiming at the physicochemical properties of polypropylene granules, the invention designs a process method suitable for producing a domestic polypropylene uniaxially stretched film, and the uniaxially stretched polypropylene film prepared by the method has the characteristics of stable performance, low dielectric loss, high breakdown strength, high discharge energy density and high charge-discharge efficiency; the method is suitable for preparing thin-film capacitors.

Description

Technical Field

[0001] The invention relates to the technical field of polypropylene films, and in particular to a uniaxially stretched polypropylene film and a preparation method and application thereof. Background Art

[0002] In recent years, human beings have paid more and more attention to environmental protection and sustainable development. How to use clean energy more efficiently is a key issue that the world is concerned about. For a long time, the power system has been mainly powered by fossil energy such as coal, which is not only non-renewable, but also causes a series of environmental pollution problems. How to better use clean and renewable energy to replace traditional fossil energy is a hot topic of research. However, clean energy such as solar energy and wind energy has the characteristics of temporal and spatial dispersion. For this, efficient energy storage systems such as capacitors and batteries are needed. Through the energy storage system, these decentralized clean energy can be converted into electrical energy, so that it can be used on a large scale in human production and life. As an energy node in the power system, capacitors have the functions of signal processing, energy storage, rectification and inversion, and are widely used in various links of power system generation, transmission, distribution and use. Among them, film capacitors made of polymers as raw materials have the advantages of lightweight, self-healing, surge resistance, etc., and are widely used in flexible power transmission, electric vehicles, aerospace and other fields.

[0003] Biaxially oriented polypropylene (BOPP) has always been the preferred material for preparing film capacitors. BOPP film has good tensile properties, and has the advantages of low dielectric loss and high breakdown strength. However, all film capacitors are currently developed using imported polypropylene raw materials, and the film capacitor industry faces monopoly and "stuck neck" problems. The reasons for this problem are as follows: Unlike packaging films and agricultural mulch films, capacitor films have higher requirements for film thickness, uniformity and electrical strength. These stringent requirements ultimately require the polypropylene raw materials used to prepare capacitors to have higher isotacticity and lower ash content. These ultra-clean polypropylene raw materials need to be imported from foreign manufacturers such as Borealis Chemical and Korea Petrochemical. At the same time, although ultra-clean polypropylene pellets suitable for capacitors have been prepared, the process of preparing film capacitors, including extrusion, biaxial stretching, slitting and winding, surface treatment, and evaporation electrodes, is very complicated, and the physical and chemical properties of polypropylene of different brands from different manufacturers are different. There are also differences in the specific process parameters in the process of film production. It is urgent to explore the production process suitable for domestic polypropylene films. Therefore, how to prepare high-performance domestic polypropylene films and domestic film capacitors has become an urgent problem to be solved in this field. 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.

[0005] To this end, an embodiment of the present invention provides a uniaxially stretched polypropylene film and a preparation method and application thereof.

[0006] In a first aspect, the present invention provides a method for preparing a uniaxially stretched polypropylene film, comprising the following steps:

[0007] (1) adding polypropylene pellets into a twin-screw extruder, preheating and melting, extruding and cooling to obtain polypropylene casting sheets;

[0008] (2) The polypropylene cast sheet is directly guided to the differential speed roller of a uniaxial stretching device for stretching and orientation, and then rolled up on a traction roller to obtain a uniaxially stretched polypropylene film.

[0009] In some embodiments, in the process of extruding and cooling to obtain the polypropylene casting sheet in step (1), cooling is performed using an air knife at the extrusion outlet, and in step (2), the uniaxial stretching equipment is the Netherlands Xplore.

[0010] Furthermore, the polypropylene pellets are domestically produced polypropylene with an isotacticity of more than 98%.

[0011] In some embodiments, the domestic pellets are LB03F domestic polypropylene pellets produced by PetroChina Lanzhou Petrochemical.

[0012] Furthermore, in step (1), the preheating temperature during the preheating and melting process is 200-220° C., the preheating time is 3-5 min, the stirring speed of the twin-screw extruder is 100-120 rpm, and the maximum torque is 11-14 N·m.

[0013] In some embodiments, the preheating temperature is 200°C, 210°C, 220°C, or a value within a range consisting of any two numerical values, the preheating time is 3 min, 4 min, 5 min, or a value within a range consisting of any two numerical values, and the stirring speed of the twin-screw extruder is 100 rpm, 110 rpm, 120 rpm, or a value within a range consisting of any two numerical values.

[0014] Furthermore, in step (1), the extrusion speed of the twin-screw extruder is 100-120 rpm, and the extrusion port temperature is 200-220°C.

[0015] In some embodiments, the extrusion speed of the twin-screw extruder is 100 rpm, 110 rpm, 120 rpm, or a value within a range consisting of any two values, and the extrusion port temperature is 200° C., 210° C., 220° C., or a value within a range consisting of any two values.

[0016] Furthermore, in step (2), the speed of the differential roller is 300 to 700 mm / min.

[0017] In some embodiments, the speed of the differential roller is 300 mm / min, 400 mm / min, 500 mm / min, 600 mm / min, 700 mm / min, or a value within a range consisting of any two values.

[0018] Furthermore, in step (2), the torque of the traction roller is 40 to 60 N·m.

[0019] In some embodiments, the torque of the pulling roller is 40 N·m, 50 N·m, 60 N·m, or a value within a range consisting of any two values.

[0020] Furthermore, the stretching ratio of the uniaxially stretched polypropylene film is 20-100.

[0021] In some embodiments, the stretching ratio of the uniaxially stretched polypropylene film is 20, 40, 60, 80, 100 or a value within a range consisting of any two of these values.

[0022] Furthermore, the thickness of the uniaxially stretched polypropylene film is 6 to 30 μm, and the overall thickness deviation of the uniaxially stretched polypropylene film is within ±200 nm.

[0023] In some embodiments, the thickness of the uniaxially stretched polypropylene film is 6 μm, 12 μm, 18 μm, 24 μm, 30 μm, or a value within a range consisting of any two of these values.

[0024] In a second aspect, the present invention provides a uniaxially stretched polypropylene film prepared by the method provided in the first aspect.

[0025] In a third aspect, the present invention proposes the use of a uniaxially stretched polypropylene film prepared by the method proposed in the first aspect or a uniaxially stretched polypropylene film proposed in the second aspect in the preparation of a film capacitor.

[0026] Compared with the prior art, the beneficial effects of the present invention are:

[0027] The present invention designs a process method suitable for producing domestic polypropylene uniaxially stretched film based on the physical and chemical properties of polypropylene pellets. The uniaxially stretched polypropylene film prepared by the method has stable performance, low dielectric loss, high breakdown strength, high discharge energy density, and high charge and discharge efficiency, and is suitable for preparing film capacitors. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0029] Figure 1This is a surface morphology image of the uniaxially stretched polypropylene film prepared in Example 1 of the present invention;

[0030] Figure 2 For Example 1 of the present invention and Comparative Example 1, the 4 Dielectric constant and dielectric loss curves at Hz frequency;

[0031] Figure 3 For Example 2 of the present invention and Comparative Example 2, the 4 Dielectric constant and dielectric loss curves at Hz frequency;

[0032] Figure 4 The Weibull distribution diagram of the breakdown strength of the polypropylene films of Example 1 and Comparative Example 1 of the present invention;

[0033] Figure 5 The Weibull distribution diagram of the breakdown strength of the polypropylene films of Example 2 of the present invention and Comparative Example 2 is shown. DETAILED DESCRIPTION

[0034] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0035] Unless otherwise specified, the test materials and reagents used in the following examples can be obtained from commercial sources.

[0036] If no specific techniques or conditions are specified in the examples, they can be carried out according to the techniques or conditions described in the literature in the art or according to the product instructions.

[0037] Example 1

[0038] 12 g of domestic polypropylene pellets LB03F from PetroChina Lanzhou Petrochemical Co., Ltd. were added into a twin-screw extruder (Xplore, the Netherlands). The pellets were a newly launched domestic polypropylene pellets and were preheated and melted at 200°C for 5 min. During this process, the twin screws were stirred at a speed of 100 and a maximum torque of 11 to 13 N·m. The maximum torque of the twin screws during the stirring process was a fluctuating value, so a range value was given here.

[0039] After preheating, the extrusion port of the twin-screw extruder is opened to extrude the preheated and stirred polypropylene melt. During extrusion, the speed of the twin screw is 100 rpm, the extrusion port temperature is 200°C, and the molten polypropylene is continuously extruded from the mold at the extrusion port and cooled by a wind knife at the extrusion port to obtain a polypropylene casting sheet with a thickness of about 600 μm.

[0040] The continuously extruded polypropylene cast sheet was guided to a uniaxial stretching device of the Netherlands Xplore model CPFL for uniaxial stretching and winding. The polypropylene cast sheet was pulled onto a differential roller for longitudinal stretching. The rotation speed of the differential roller was 700 mm / min, and then it was wound on a pulling roller with a torque of 50 N·m to obtain a uniaxially stretched polypropylene film with a thickness of 12 μm ± 200 nm. This film was recorded as A1.

[0041] Example 2

[0042] The difference from Example 1 was that the rotation speed of the differential roll was 500 mm / min. The thickness of the obtained uniaxially stretched polypropylene film was 15 μm±200 nm. This film was designated as A2.

[0043] Example 3

[0044] The difference from Example 1 is that the rotation speed of the differential roll is 300 mm / min. The thickness of the obtained uniaxially stretched polypropylene film is 18 μm±200 nm. This film is designated as A3.

[0045] Example 4

[0046] 12 g of domestic polypropylene pellets LB03F from PetroChina Lanzhou Petrochemical were added into a twin-screw extruder (Xplore, the Netherlands) and preheated and melted at 210°C for 5 min. During this process, the twin screws were stirred at a speed of 100 and a maximum torque of 11 to 13 N·m. The maximum torque of the twin screw during the stirring process was a fluctuating value, so a range value is given here.

[0047] After preheating, the extrusion port of the twin-screw extruder is opened to extrude the preheated and stirred polypropylene melt. During extrusion, the speed of the twin screw is 100 rpm, the extrusion port temperature is 210°C, and the molten polypropylene is continuously extruded from the mold at the extrusion port and cooled by an air knife at the extrusion port to obtain a polypropylene casting sheet with a thickness of about 600 μm.

[0048] The continuously extruded polypropylene cast sheet was guided to a uniaxial stretching device of the Netherlands Xplore model CPFL for uniaxial stretching and winding. The polypropylene cast sheet was pulled onto a differential roller for longitudinal stretching. The rotation speed of the differential roller was 700 mm / min, and then it was wound on a pulling roller with a torque of 50 N·m to obtain a uniaxially stretched polypropylene film with a thickness of 12 μm ± 200 nm. This film was recorded as B1.

[0049] Example 5

[0050] The difference from Example 4 is that the rotation speed of the differential roll is 500 mm / min. The thickness of the obtained uniaxially stretched polypropylene film is 15 μm±200 nm. This film is designated as B2.

[0051] Example 6

[0052] The difference from Example 4 is that the rotation speed of the differential roll is 300 mm / min. The thickness of the obtained uniaxially stretched polypropylene film is 18 μm±200 nm. This film is designated as B3.

[0053] Example 7

[0054] 12 g of domestic polypropylene pellets LB03F from PetroChina Lanzhou Petrochemical were added into a twin-screw extruder (Xplore, the Netherlands) and preheated and melted at 220°C for 5 min. During this process, the twin screws were stirred at a speed of 100 and a maximum torque of 11 to 13 N·m. The maximum torque of the twin screws during the stirring process was a fluctuating value, so a range value is given here.

[0055] After preheating, the extrusion port of the twin-screw extruder is opened to extrude the preheated and stirred polypropylene melt. During extrusion, the speed of the twin screw is 100 rpm, the extrusion port temperature is 220°C, and the molten polypropylene is continuously extruded from the mold at the extrusion port and cooled by an air knife at the extrusion port to obtain a polypropylene casting sheet with a thickness of about 600 μm.

[0056] The continuously extruded polypropylene cast sheet was guided to a uniaxial stretching device of the Netherlands Xplore model CPFL for uniaxial stretching and winding. The polypropylene cast sheet was pulled onto a differential roller for longitudinal stretching. The rotation speed of the differential roller was 700 mm / min, and then it was wound on a pulling roller with a torque of 50 N·m to obtain a uniaxially stretched polypropylene film with a thickness of 12 μm ± 200 nm. This film was recorded as C1.

[0057] Example 8

[0058] The difference from Example 7 was that the rotation speed of the differential roll was 500 mm / min. The thickness of the obtained uniaxially stretched polypropylene film was 15 μm±200 nm. This film was designated as C2.

[0059] Example 9

[0060] The difference from Example 7 was that the rotation speed of the differential roll was 300 mm / min. The thickness of the obtained uniaxially stretched polypropylene film was 18 μm±200 nm. This film was designated as C3.

[0061] Comparative Example 1

[0062] The difference from Example 1 is that the polypropylene pellets are from Borealis HC300BF.

[0063] Comparative Example 2

[0064] The difference from Example 2 is that the polypropylene pellets are from Borealis HC300BF.

[0065] Test Example 1

[0066] The uniaxially stretched polypropylene film prepared in Example 1 was tested for surface morphology using an atomic force microscope at room temperature. The test area was 1 μm×1 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 surface of the material to obtain the surface morphology of the material as shown in the figure. Figure 1 shown.

[0067] Depend on Figure 1 It can be seen that the stretched polypropylene film has a structure of oriented crystals in a fixed direction, the film surface is relatively flat, the local thickness deviation is about ±20nm, and the thickness is uniform.

[0068] Test Example 2

[0069] The dielectric properties of the uniaxially stretched polypropylene films prepared in Examples 1 to 9 and Comparative Examples 1 and 2 were tested after gold plating in a small ion sputtering instrument. The dielectric constant and dielectric loss of the materials at different frequencies were tested using a broadband dielectric spectrometer from Novocontrol of Germany at room temperature.

[0070] The dielectric constant and dielectric loss of the polypropylene films prepared in Examples 1 to 9 at 1 kHz are shown in Table 1. According to Table 1, the dielectric constant of the polypropylene films prepared in Examples 1 to 9 at 1 kHz is stable at around 2.2. By comparing with Comparative Examples 1 and 2, the domestically produced polypropylene uniaxially stretched film prepared in the present invention has stable dielectric properties, and the dielectric loss factor is always maintained at a low level, and the performance is good.

[0071] Test Example 1, Example 2, Comparative Example 1 and Comparative Example 2 at 10 to 10 4 The dielectric constant and dielectric loss at Hz frequency, the test results are as follows Figure 2 and Figure 3 As shown. Figure 2 It can be seen that the dielectric constant of the uniaxially stretched polypropylene film prepared in Example 1 is between 10 and 10 4 Hz frequency is stable at 2.2. Compared with Comparative Example 1, the dielectric loss of the polypropylene film prepared in Example 1 is low (10-10 4 Hz frequency is less than 10 -3 ), has good dielectric properties; according to Figure 3 It can be seen that the dielectric constant of the uniaxially stretched polypropylene film prepared in Example 2 is between 10 and 10 4Hz frequency is stable at 2.16. Compared with Comparative Example 2, the dielectric loss of the polypropylene film prepared in Example 2 is low (10-10 4 Hz frequency is less than 10 -3 ), has good dielectric properties.

[0072] Test Example 3

[0073] The polypropylene uniaxially stretched films prepared in Examples 1 to 9 and Comparative Examples 1 and 2 were subjected to breakdown strength test after being gold plated in a small ion sputtering instrument. At room temperature, the sample was placed between the ball-plate electrodes, and a high voltage withstand tester was used to apply pressure between the ball-plate electrodes under a DC voltage. In order to avoid surface flashover, the sample was placed in silicone oil for testing, and the DC voltage step-up rate was 500V / m. The breakdown was judged when the leakage current reached 50mA, and the results were expressed using Weibull distribution, as shown in Table 1.

[0074] As can be seen from Table 1, the breakdown strength of Examples 1 to 9 as a whole is not much different from that of Comparative Examples 1 and 2, indicating that the insulation strength of the polypropylene film prepared in the examples of the present invention meets the use requirements.

[0075] The Weibull distribution of the breakdown strength of the polypropylene films of Example 1, Example 2, Comparative Example 1 and Comparative Example 2 is as follows: Figure 3 and Figure 4 As shown. Figure 3 It can be seen that there is no significant difference in the breakdown performance between Example 1 and Comparative Example 1; Figure 4 It can be seen that there is no significant difference in the breakdown performance between Example 2 and Comparative Example 2, indicating that the domestically produced polypropylene uniaxially stretched film prepared by the present invention has good insulation strength.

[0076] Test Example 4

[0077] The discharge energy density and charge-discharge efficiency of Examples 1 to 9 and Comparative Examples 1 and 2 were tested using an American Radiant ferroelectric tester, and the samples were placed in silicone oil for testing. The test results are shown in Table 1. The energy storage performance of the polypropylene films prepared in Examples 1 to 9 is relatively stable, and the charge-discharge efficiency is greater than 90% at 450 kV / mm. By comparing with Comparative Examples 1 and 2, the domestically produced polypropylene uniaxially stretched film prepared by the present invention has good discharge energy density and high charge-discharge efficiency, which meets the use requirements.

[0078] Table 1:

[0079]

[0080] 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 may be for different embodiments or examples. 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.

[0081] In addition, 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 the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0082] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A method for preparing a uniaxially stretched polypropylene film, characterized in that: The following steps are involved: (1) adding polypropylene pellets into a twin-screw extruder, preheating and melting, extruding and cooling to obtain polypropylene casting sheets; (2) The polypropylene cast sheet is directly guided to the differential speed roller of a uniaxial stretching device for stretching and orientation, and then rolled up on a traction roller to obtain a uniaxially stretched polypropylene film.

2. The method according to claim 1, characterized in that The polypropylene pellets are domestically produced polypropylene with an isotacticity of more than 98%.

3. The method according to claim 1, characterized in that In step (1), the preheating temperature during the preheating and melting process is 200-220° C., the preheating time is 3-5 min, the stirring speed of the twin-screw extruder is 100-120 rpm, and the maximum torque is 11-14 N·m.

4. The method according to claim 1, characterized in that In step (1), the extrusion speed of the twin-screw extruder is 100-120 rpm, and the extrusion port temperature is 200-220°C.

5. The method according to claim 1, characterized in that In step (2), the speed of the differential roller is 300-700 mm / min.

6. The method according to claim 1, characterized in that In step (2), the torque of the traction roller is 40 to 60 N·m.

7. The method according to claim 1, characterized in that The stretching ratio of the uniaxially stretched polypropylene film is 20-100.

8. The method according to claim 1, characterized in that The thickness of the uniaxially stretched polypropylene film is 6 to 30 μm, and the overall thickness deviation of the uniaxially stretched polypropylene film is within ±200 nm.

9. A uniaxially stretched polypropylene film, characterized in that: The method is prepared by any one of claims 1 to 8.

10. Use of the uniaxially stretched polypropylene film prepared by the method according to any one of claims 1 to 8 or the uniaxially stretched polypropylene film according to claim 9 in the preparation of film capacitors.

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