Polypropylene capacitor film and preparation method and application thereof

Abstract

The invention belongs to the technical field of capacitor films, and relates to a polypropylene capacitor film and a preparation method and application thereof. The polypropylene capacitor film comprises a layer C, a layer B, a layer A, a layer B and a layer C. The layer A comprises, by mass, 94-98 wt% of polypropylene and 2-6 wt% of an olefin block copolymer; the layer B comprises the following components in percentage by weight: 98.5 to 99.5 percent of polypropylene and 0.5 to 1.5 percent of olefin block copolymer; the layer C is prepared from 87 to 98.7 weight percent of polypropylene, 1 to 10 weight percent of aliphatic-aromatic polycarbonate and 0.3 to 3 weight percent of compatilizer; the content of the olefin block copolymer is gradually reduced from the A layer to the B layer, and the C layer is not added with the olefin block copolymer. The prepared polypropylene capacitor film has excellent high and low temperature breakdown field strength and low thermal shrinkage rate, and meets the use requirements of high-end electric power equipment.

Description

Technical Field

[0001] This invention belongs to the field of capacitor film technology, and relates to a polypropylene capacitor film, its preparation method and application. Background Technology

[0002] As a core component in power electronic equipment, film capacitors are widely used in many key fields such as ultra-high voltage direct current transmission, new energy vehicles, rail transit, industrial frequency conversion, pulse power weapons, and flexible direct current transmission due to their excellent electrical performance, long service life, and good self-healing properties. Among them, biaxially oriented polypropylene (BOPP) film has become the core dielectric material of metallized film capacitors due to its core advantages such as high room temperature breakdown field strength, low dielectric loss, and excellent self-healing properties, and has always been the "gold standard" for metallized film capacitors.

[0003] With the global energy structure transformation and the rapid upgrading of power equipment technology, more stringent requirements have been placed on the thermal stability and high-temperature electrical performance of capacitor dielectric films. However, traditional polypropylene films suffer from increased risk of electrical breakdown and uneven thermal shrinkage under high-temperature and high-pressure operating conditions, affecting the stable operation of capacitors.

[0004] To overcome the aforementioned shortcomings, existing technologies have focused on two main approaches. First, they address the polypropylene raw material itself, optimizing polymerization processes and purification techniques to produce low-ash, high-isotacticity polypropylene resins, thereby improving the fundamental properties of polypropylene films. Currently, this direction has seen considerable research and reporting, and related polymerization and purification technologies are relatively mature. However, the potential for further performance improvement in the polypropylene raw material itself is limited, making it difficult to meet the performance requirements of high-end capacitor dielectric films. Second, adding nanofillers to the polypropylene matrix can improve the thermal stability and breakdown strength of polypropylene films with appropriate amounts, but a significant increase in dielectric loss has also been observed. Furthermore, existing technologies have attempted to improve film performance by blending polypropylene with other high-heat-resistant, high-dielectric polymers, but this often results in poor compatibility and phase separation, failing to effectively improve high-temperature electrical properties and potentially leading to overall film performance degradation.

[0005] Therefore, developing a polypropylene capacitor film that can simultaneously solve the problems of low breakdown field strength and high thermal shrinkage rate, while maintaining extremely low dielectric loss and taking into account processability, has become an urgent technical problem to be solved in this field. Summary of the Invention

[0006] In view of the problems existing in the prior art, the purpose of this invention is to provide a polypropylene capacitor film, its preparation method and application. Through multilayer structure design and precise matching of material components, the prepared polypropylene capacitor film has excellent high and low temperature breakdown field strength and low thermal shrinkage rate, which meets the needs of high-end power equipment.

[0007] The present invention employs the following technical solutions to achieve its objective: One aspect of the present invention provides a polypropylene capacitor film, comprising layers C, B, A, B, and C stacked sequentially, wherein layer A is an intermediate layer, layer B is a transition layer, and layer C is an outer layer, and the components of each layer by mass fraction are as follows: Layer A comprises: 94-98 wt% polypropylene and 2-6 wt% olefin block copolymer (OBC). The B layer comprises: 98.5~99.5 wt% polypropylene and 0.5~1.5 wt% olefin block copolymer; The C layer comprises: 87-98.7 wt% polypropylene, 1-10 wt% aliphatic-aromatic polycarbonate, and 0.3-3 wt% compatibilizer.

[0008] Preferably, the polypropylene is isotactic polypropylene with an isotactic index ≥ 97.5%, a melt flow index (MFR) of 3.0~4.2 g / 10 min (test conditions: 230℃, 2.16 kg), and an ash content ≤ 20 ppm. This invention uses polypropylene as the main polymer raw material because polypropylene itself has extremely low dielectric loss and excellent insulation properties, making it an ideal matrix for capacitor films. Furthermore, isotactic polypropylene with an isotactic index ≥ 97.5% has a regular molecular structure, which can improve the crystallinity and mechanical properties of the film and reduce the thermal shrinkage rate. Controlling the melt flow index at 3.0~4.2 g / 10 min ensures good melt blending processing performance of the material, facilitating subsequent extrusion and stretch molding, and avoiding problems caused by excessively high or low melt flow indices.

[0009] Preferably, the melt index of the olefin block copolymer is 2~20 g / 10 min (test conditions 2.16 kg, 190 °C), and Dow INFUSE is an example. TM OBC series copolymers, such as INFUSE TM OBC 9500, INFUSE TM OBC 9507, INFUSE TM OBC 9530, INFUSE TM OBC 9817 or INFUSE TM OBC 9807.

[0010] Further preferably, the melt index of the olefin block copolymer is 3~10 g / 10 min (test conditions: 2.16 kg, 190 °C), and the olefin block copolymer can be Dow INFUSE. TM OBC 9500, INFUSE TMOBC 9507, INFUSE TM One or more of OBC 9530.

[0011] Preferably, the content of the olefin block copolymer decreases from layer A to layer B, with the olefin block copolymer content being 2-6 wt% in layer A, 0.5-1.5 wt% in layer B, and 0 wt% in layer C.

[0012] Olefin block copolymers possess a unique block structure and exhibit excellent compatibility with polypropylene. During melt blending, they typically do not require additional compatibilizers and can be uniformly dispersed within the PP matrix in the molten state, ensuring thorough mixing and preventing phase separation. This guarantees the uniformity of the film structure and the stability of its performance. However, the content of olefin block copolymers in the A and B layers should not be excessive (maximum 6 wt%). Excessive addition of olefin block copolymers can interfere with the ordered arrangement and crystallization process of polypropylene molecular chains, disrupting the regularity of crystalline regions, thereby leading to decreased film breakdown strength and increased heat shrinkage.

[0013] This invention employs a multilayer structure design with decreasing olefin block copolymer content, achieving a breakthrough improvement in the overall performance of the capacitor film: Layer A, as the intermediate core layer, bears the main electrical insulation and withstand voltage functions. Adding an appropriate amount of OBC improves the toughness and thermal stability of Layer A without reducing the breakdown strength of polypropylene, increases the high-temperature breakdown field strength of the film, and reduces the thermal shrinkage rate. Layer B, as the transition layer, with 0.3~1wt% OBC added, enables a performance transition between Layer A and Layer C, reducing interlayer interface stress. Layer C, as the outer layer, does not contain OBC because its presence would interfere with the function of aliphatic-aromatic polycarbonate, affecting the surface roughness control of Layer C and thus impacting film performance. The olefin block copolymer content decreases from Layer A to Layer B. This layered design and content distribution effectively alleviates polarization stress concentration at the interlayer interface, extends the electrical breakdown path, and thus significantly improves the overall breakdown strength of the film. Furthermore, the inventors discovered that simply adding olefin block copolymers to polypropylene without a layered design or a decreasing content trend cannot achieve the aforementioned performance improvement effect. In fact, excessive OBC addition (especially in layers A and B) can lead to a decrease in the breakdown strength and an increase in the heat shrinkage rate of polypropylene.

[0014] Preferably, the aliphatic-aromatic polycarbonate is selected from one or more polycarbonates polymerized from alicyclic aliphatic diols, aromatic diphenols, and diphenyl carbonate (DPC).

[0015] Further preferably, the alicyclic aliphatic diol is cyclohexanediethanol, including one or more of 1,4-cyclohexanediethanol, 1,2-cyclohexanediethanol, and 1,3-cyclohexanediethanol. The aromatic diphenol is selected from one or more of bisphenol A (BPA), bisphenol F, and bisphenol S, preferably bisphenol A. The molecular weight (Mw) of the aliphatic-aromatic polycarbonate is 10,000~40,000 g / mol.

[0016] Aliphatic-aromatic polycarbonate combines the flexibility of aliphatic polycarbonate with the rigidity of aromatic polycarbonate. Its main function in the C layer is to control the surface roughness of the film. Aliphatic-aromatic polycarbonate forms island-like dispersed phases within the PP matrix. During film stretching, these dispersed phases exhibit different deformation rates than the PP matrix, resulting in uniform and minute protrusions on the film surface. By controlling the content of aliphatic-aromatic polycarbonate (1~10wt%) and subsequent stretching processes, the surface roughness (Ra) of the film can be controlled between 55~65nm. A moderately increased surface roughness (55~65nm) helps enhance the breakdown field strength of the film while maintaining the inherently low dielectric loss of polypropylene films, achieving the dual advantages of "high breakdown field strength + low dielectric loss." Furthermore, suitable roughness can improve thermal dimensional stability, further reducing the film's thermal shrinkage rate.

[0017] Further preferably, the preparation method of the aliphatic-aromatic polycarbonate includes the following steps: Aromatic diphenols, alicyclic aliphatic diols, diphenyl carbonate, and catalyst are added to a reaction vessel and heated to 170–190 °C in an inert gas atmosphere, and stirred for 10–30 min. Then, the vacuum is reduced to 10.0–30.0 kPa for 10–30 min, and the temperature is raised to 190–210 °C and held constant for 20–80 min. Subsequently, the temperature is increased to 230–250 °C and held constant for 5–20 min. After that, the pressure is reduced to 0.1–0.2 kPa for 40–100 min, and the reaction is stirred for 1–6 h. After the reaction is completed, heating and vacuum are stopped, and inert gas is introduced into the reactor to restore atmospheric pressure. The product is then discharged to obtain aliphatic-aromatic polycarbonate.

[0018] Preferably, the catalyst is sodium bicarbonate.

[0019] Preferably, the compatibilizer is selected from maleic anhydride-grafted polypropylene (PP-g-MAH).

[0020] Preferably, the thickness of layer B is less than the thickness of layer C, which is less than the thickness of layer A. More preferably, the thickness ratio of layer C, layer B, and layer A is (1.5~2.5):1:(3~5).

[0021] Preferably, the breakdown field strength attenuation of the polypropylene capacitor film at 80°C is ≤11%, the longitudinal thermal shrinkage rate measured at 120°C for 15 minutes is ≤2%, and the dielectric loss tanδ is ≤0.0001. The breakdown field strength attenuation at 80°C = (breakdown field strength at 25°C - breakdown field strength at 80°C) / breakdown field strength at 25°C * 100%.

[0022] A second aspect of this invention provides a method for preparing a polypropylene capacitor film, comprising the following steps: (1) After melting the A layer raw material, B layer raw material and C layer raw material respectively by independent screw extruder, co-extrusion casting is carried out by five-layer co-extrusion die head to form a casting sheet of C layer, B layer, A layer, B layer and C layer stacked in sequence. Then the casting sheet is cooled and shaped by chiller roller. (2) The casting sheet is first stretched longitudinally, with the stretching ratio controlled at 4 to 7 times; then it is stretched transversely, with the stretching ratio controlled at 8 to 10 times. (3) Then perform corona treatment, winding and cutting to obtain polypropylene capacitor film.

[0023] Preferably, the thickness of the cast sheet is 200~400 μm, and the thickness of each layer is 20~100 μm.

[0024] More preferably, in the casting, the thickness of layer B is less than the thickness of layer C, which is less than the thickness of layer A.

[0025] Further optimization is made to ensure that the thickness ratio of layer C, layer B and layer A in the casting is (1.5~2.5):1:(3~5).

[0026] Layer A, as the core layer, needs sufficient thickness to withstand pressure and provide insulation, hence its greatest thickness. Layer C, the surface layer, requires a moderate thickness while ensuring surface performance. Layer B, as the intermediate transition layer, primarily alleviates interfacial stress and has the smallest thickness. Adopting a design where layer B thickness < layer C thickness < layer A thickness, and limiting the thickness ratio of layers C, B, and A to (1.5~2.5):1:(3~5), allows for efficient functional synergy among the three layers, balancing the overall thermal stability and electrical performance of the film, and effectively avoiding performance defects caused by unreasonable layer thickness ratios.

[0027] Preferably, the cooling and shaping temperature of the chiller roller is 85~105℃.

[0028] Preferably, during the longitudinal stretching process, the preheating temperature is 100~135℃, the stretching temperature is 145~150℃, and the setting temperature is 150~153℃; during the transverse stretching process, the preheating temperature is 160~175℃, the stretching temperature is 160~165℃, and the setting temperature is 175~180℃.

[0029] Preferably, the corona treatment includes: simultaneous treatment on both sides, a voltage of 5~10 kV, an output power of 5~18 kW, and an electrode bombardment intensity of 10~18 W·min / m. 2 .

[0030] A third aspect of the present invention provides an application of a polypropylene capacitor film, wherein the polypropylene capacitor film is used as the dielectric layer of a capacitor, and the capacitor is suitable for one or more of the following fields: new energy vehicles, ultra-high voltage direct current transmission, rail transit, industrial frequency conversion, pulse power weapons, and flexible direct current transmission.

[0031] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention adopts a five-layer symmetrical structure (CBABC) design. Through the synergistic effect of core technical features such as the decreasing trend of olefin block copolymer (OBC) content in layer A > layer B, no OBC added to layer C, layer C compounded with aliphatic-aromatic polycarbonate, and specific layer thickness (layer B thickness < layer C thickness < layer A thickness), the polypropylene capacitor film achieves excellent high and low temperature breakdown field strength, low thermal shrinkage rate, and extremely low dielectric loss.

[0032] 2. This invention combines a specific amount of aliphatic-aromatic polycarbonate in the C layer and uses a stretching process to adjust the surface roughness of the film to 55~65nm. The appropriate surface roughness significantly improves the breakdown field strength and thermal dimensional stability while fully preserving the inherent low-loss characteristics of polypropylene.

[0033] 3. The present invention further preferably uses an olefin block copolymer with a melt index of 3-10 g / 10 min, wherein the olefin block copolymer may be Dow INFUSE. TM OBC 9500, INFUSE TM OBC 9507, INFUSE TM One or more of OBC 9530, working together to ensure that the film meets the following requirements: breakdown field strength attenuation ≤11% at 80℃, longitudinal thermal shrinkage ≤2%, and dielectric loss tanδ ≤0.0001.

[0034] 4. The film prepared by this invention combines high breakdown field strength, low thermal shrinkage rate and low dielectric loss, and its comprehensive performance meets the standards of high-end capacitor films. It can be used as a core dielectric layer in new energy vehicles, ultra-high voltage DC power transmission, rail transit, pulse power weapons and other fields, which greatly expands the high-end application scenarios of polypropylene capacitor films. Detailed Implementation

[0035] In the description of this invention, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, and includes both a and b. "Multiple" includes two or more types, and can be two, three, four, five, or more.

[0036] The technical solution of the present invention will be further described and illustrated below through specific embodiments. It should be understood that the specific embodiments described herein are only for the purpose of helping to understand the present invention and are not intended to limit the present invention. Unless otherwise specified, the raw materials used in the embodiments of the present invention are all commonly used raw materials in the art, and the methods used in the embodiments are all conventional methods in the art.

[0037] In the following examples and comparative examples, the sources of raw materials are as follows: Polypropylene: Borealis, model HC300BF, with an isotactic index of approximately 98.1%, a melt flow index (MFR) of approximately 3.8 g / 10 min (230℃, 2.16 kg), an ash content of approximately 10 ppm, a Mw of approximately 397610, and a Mw / Mn ratio of approximately 9.4.

[0038] Olefin block copolymer OBC: Dow Chemical Company, INFUSE TM OBC 9010 (melt index 0.5 g / 10 min), INFUSE TM OBC 9507 (melt index 5g / 10min), INFUSE TM OBC 9500 (melt index 5g / 10min), INFUSE TM OBC 9817 (melt index 15g / 10min).

[0039] Ethylene-1-octene random copolymer: Dow Chemical Company, Engage TM 8200.

[0040] Aliphatic polycarbonates: Eastman Chemical Company, Tritan TM GX100.

[0041] Aromatic polycarbonates: Wanhua Chemical, CLARNATE TM A1105.

[0042] The aliphatic-aromatic polycarbonate was prepared in-house, and the specific preparation method is as follows: 0.05 mol bisphenol A, 0.10 mol 1,4-cyclohexanediol, 0.17 mol diphenyl carbonate, and 6.0 × 10⁻⁶... -6Sodium bicarbonate was added to a reactor equipped with a stirrer and a distillation apparatus, and then heated to 180°C and stirred for 20 minutes under a nitrogen atmosphere. The vacuum was then reduced to 20.0 kPa over 20 minutes, and the temperature was raised to 200°C and maintained for 40 minutes. The temperature was further increased to 240°C and maintained at this temperature for 10 minutes to further distill off residual phenol. The pressure was then reduced to 0.120 kPa over 1 hour, and the reaction proceeded for a total of 2 hours with stirring. After the reaction was complete, heating and vacuum were stopped, and nitrogen was introduced into the reactor to restore atmospheric pressure; the prepared aliphatic-aromatic polycarbonate was obtained. The Mw was measured to be 30000 g / mol.

[0043] Compatibilizer: Maleic anhydride-grafted polypropylene, ExxonMobil TM PO 1020.

[0044] Example 1

[0045] The polypropylene capacitor film of this embodiment is prepared by the following method: (1) Raw material preparation: Layer A is made of 96 wt% polypropylene and olefin block copolymer (INFUSE). TM OBC 9507) 4wt% Layer B is made of 99 wt% polypropylene and olefin block copolymer (INFUSE). TM OBC 9507) 1wt% The C layer is made of 96 wt% polypropylene, 3.2 wt% aliphatic-aromatic polycarbonate, and 0.8 wt% maleic anhydride-grafted polypropylene.

[0046] (2) Mix the A layer material in a high-speed mixer at 500 rpm for 5 min and feed it into a twin-screw extruder with a main screw speed of 80 rpm; mix the B layer material in a high-speed mixer at 500 rpm for 5 min and feed it into a twin-screw extruder with a main screw speed of 80 rpm; mix the C layer material in a high-speed mixer at 500 rpm for 5 min and feed it into a twin-screw extruder with a main screw speed of 80 rpm; melt the A layer material, B layer material and C layer material separately through an independent screw extruder, and then co-extrude and cast the material using a five-layer co-extrusion die to form a cast sheet with layers C, B, A, B and C stacked in sequence. The thickness of a single C layer is 50 μm (two layers have the same thickness), the thickness of a single B layer is 25 μm (two layers have the same thickness), and the thickness of a single A layer is 100 μm (two layers have the same thickness). The cast sheet is then cooled and shaped by a chilling roller (100℃).

[0047] (3) The casting sheet is first stretched longitudinally, with a preheating temperature of 120℃, a stretching temperature of 148℃, a setting temperature of 152℃, and a stretching ratio of 7 times; then it is stretched transversely, with a preheating temperature of 168℃, a stretching temperature of 162℃, a setting temperature of 178℃, and a stretching ratio of 9 times.

[0048] (4) Corona treatment is performed using a two-sided simultaneous treatment method, with a voltage range of 8 kV, an output power of 10 kW, and an electrode bombardment intensity of 12 W·min / m. 2 The film is then wound up and slit to obtain a polypropylene capacitor film.

[0049] The prepared polypropylene capacitor film comprises layers C, B, A, B, and C stacked sequentially, wherein layer A is the intermediate layer, layer B is the transition layer, and layer C is the outer layer. Layer A is composed of 96 wt% polypropylene and olefin block copolymer (INFUSE). TM The composition is 4 wt% OBC9507, and the B layer consists of 99 wt% polypropylene and olefin block copolymer (INFUSE). TM The composition is 1 wt% of OBC 9507, and the C layer is composed of 96 wt% polypropylene, 3.2 wt% aliphatic-aromatic polycarbonate, and 0.8 wt% maleic anhydride-grafted polypropylene.

[0050] Example 2

[0051] The polypropylene capacitor film of this embodiment is prepared by the following method: (1) Raw material preparation: Layer A is made of 94 wt% polypropylene and olefin block copolymer (INFUSE). TM OBC 9500) 6wt% Layer B is made of 98.5 wt% polypropylene and olefin block copolymer (INFUSE). TM OBC 9500) 1.5wt%; The C layer is made of 97.5 wt% polypropylene, 2 wt% aliphatic-aromatic polycarbonate, and 0.5 wt% maleic anhydride-grafted polypropylene.

[0052] (2) Mix the A layer material in a high-speed mixer at 600 rpm for 4 min and feed it into a twin-screw extruder with a main screw speed of 70 rpm; mix the B layer material in a high-speed mixer at 600 rpm for 4 min and feed it into a twin-screw extruder with a main screw speed of 70 rpm; mix the C layer material in a high-speed mixer at 600 rpm for 4 min and feed it into a twin-screw extruder with a main screw speed of 70 rpm; melt the A layer material, B layer material and C layer material separately through an independent screw extruder, and then co-extrude and cast the material using a five-layer co-extrusion die to form a cast sheet with layers C, B, A, B and C stacked in sequence. The thickness of a single C layer is 45 μm (two layers have the same thickness), the thickness of a single B layer is 30 μm (two layers have the same thickness), and the thickness of a single A layer is 90 μm (two layers have the same thickness). The cast sheet is then cooled and shaped by a chilling roller (90°C).

[0053] (3) The casting sheet is first stretched longitudinally, with a preheating temperature of 115℃, a stretching temperature of 146℃, a setting temperature of 150℃, and a stretching ratio controlled at 6 times; then it is stretched transversely, with a preheating temperature of 164℃, a stretching temperature of 160℃, a setting temperature of 176℃, and a stretching ratio controlled at 9 times.

[0054] (4) Corona treatment is performed using a two-sided simultaneous treatment method, with a voltage range of 8 kV, an output power of 10 kW, and an electrode bombardment intensity of 12 W·min / m. 2 The film is then wound up and slit to obtain a polypropylene capacitor film.

[0055] The prepared polypropylene capacitor film comprises layers C, B, A, B, and C stacked sequentially, wherein layer A is the intermediate layer, layer B is the transition layer, and layer C is the outer layer. Layer A is composed of 94 wt% polypropylene and olefin block copolymer (INFUSE). TM The composition is 6 wt% OBC9500, and the B layer consists of 98.5 wt% polypropylene and olefin block copolymer (INFUSE). TM The composition is 1.5wt% of OBC 9500, and the C layer is composed of 97.5wt% polypropylene, 2wt% aliphatic-aromatic polycarbonate, and 0.5wt% maleic anhydride-grafted polypropylene.

[0056] Example 3

[0057] The polypropylene capacitor film of this embodiment is prepared by the following method: (1) Raw material preparation: Layer A is made of 97 wt% polypropylene and olefin block copolymer (INFUSE). TM OBC 9507) 3wt% Layer B is made of 99.5 wt% polypropylene and olefin block copolymer (INFUSE). TM OBC 9507) 0.5wt% The C layer is made of 95 wt% polypropylene, 4 wt% aliphatic-aromatic polycarbonate, and 1 wt% maleic anhydride-grafted polypropylene.

[0058] (2) Mix the A layer material in a high-speed mixer at 500 rpm for 6 min and feed it into a twin-screw extruder with a main screw speed of 90 rpm; mix the B layer material in a high-speed mixer at 500 rpm for 6 min and feed it into a twin-screw extruder with a main screw speed of 90 rpm; mix the C layer material in a high-speed mixer at 500 rpm for 6 min and feed it into a twin-screw extruder with a main screw speed of 90 rpm; melt the A layer material, B layer material and C layer material separately through an independent screw extruder, and then co-extrude and cast the material using a five-layer co-extrusion die to form a cast sheet with layers C, B, A, B and C stacked in sequence. The thickness of a single C layer is 50 μm (two layers have the same thickness), the thickness of a single B layer is 20 μm (two layers have the same thickness), and the thickness of a single A layer is 100 μm (two layers have the same thickness). The cast sheet is then cooled and shaped by a chilling roller (105℃).

[0059] (3) The casting sheet is first stretched longitudinally, with a preheating temperature of 125℃, a stretching temperature of 150℃, a setting temperature of 153℃, and a stretching ratio of 7 times; then it is stretched transversely, with a preheating temperature of 170℃, a stretching temperature of 164℃, a setting temperature of 180℃, and a stretching ratio of 10 times.

[0060] (4) Corona treatment is performed using a two-sided simultaneous treatment method, with a voltage range of 8 kV, an output power of 10 kW, and an electrode bombardment intensity of 12 W·min / m. 2 The film is then wound up and slit to obtain a polypropylene capacitor film.

[0061] The prepared polypropylene capacitor film comprises layers C, B, A, B, and C stacked sequentially, wherein layer A is the intermediate layer, layer B is the transition layer, and layer C is the outer layer. Layer A is composed of 97 wt% polypropylene and olefin block copolymer (INFUSE). TM The composition is 3 wt% OBC9507, and the B layer consists of 99.5 wt% polypropylene and olefin block copolymer (INFUSE). TM The composition is 0.5 wt% of OBC 9507, and the C layer is composed of 95 wt% polypropylene, 4 wt% aliphatic-aromatic polycarbonate, and 1 wt% maleic anhydride-grafted polypropylene.

[0062] Comparative Example 1 The polypropylene capacitor film of Comparative Example 1 was prepared by the following method: (1) Raw material preparation: 97.6 wt% polypropylene, olefin block copolymer (INFUSE) TM OBC 9507) 2.4 wt%.

[0063] (2) Mix polypropylene and INFUSE TM OBC 9507 was stirred and mixed in a high-speed mixer at 500 rpm for 5 minutes, and then fed into a twin-screw extruder with the main screw speed at 80 rpm. The mixture was melt-extruded to form a 350 μm thick sheet, which was then cooled and shaped by a chilling roller (100°C).

[0064] (3) The casting sheet is first stretched longitudinally, with a preheating temperature of 120℃, a stretching temperature of 148℃, a setting temperature of 152℃, and a stretching ratio of 7 times; then it is stretched transversely, with a preheating temperature of 168℃, a stretching temperature of 162℃, a setting temperature of 178℃, and a stretching ratio of 9 times.

[0065] (4) Corona treatment is performed using a two-sided simultaneous treatment method, with a voltage range of 8 kV, an output power of 10 kW, and an electrode bombardment intensity of 12 W·min / m. 2 The film is then wound up and slit to obtain a polypropylene capacitor film.

[0066] The prepared polypropylene capacitor film is a single-layer structure composed of polypropylene and olefin block copolymers.

[0067] Comparative Example 2 The polypropylene capacitor film of Comparative Example 2 was prepared by the following method: (1) Raw material preparation: 96.5 wt% polypropylene, olefin block copolymer (INFUSE) TM OBC 9507) 2.4 wt%, aliphatic-aromatic polycarbonate 0.9 wt%, maleic anhydride-grafted polypropylene 0.2 wt%.

[0068] (2) Add polypropylene and INFUSE TM OBC 9507, aliphatic-aromatic polycarbonate, and maleic anhydride-grafted polypropylene were mixed in a high-speed mixer at 500 rpm for 5 minutes and then fed into a twin-screw extruder with the main screw speed at 80 rpm. The mixture was melt-extruded to form a 350 μm thick cast sheet, which was then cooled and shaped by a chilling roller (100°C).

[0069] (3) The casting sheet is first stretched longitudinally, with a preheating temperature of 120℃, a stretching temperature of 148℃, a setting temperature of 152℃, and a stretching ratio of 7 times; then it is stretched transversely, with a preheating temperature of 168℃, a stretching temperature of 162℃, a setting temperature of 178℃, and a stretching ratio of 9 times.

[0070] (4) Corona treatment is performed using a two-sided simultaneous treatment method, with a voltage range of 8 kV, an output power of 10 kW, and an electrode bombardment intensity of 12 W·min / m. 2 The film is then wound up and slit to obtain a polypropylene capacitor film.

[0071] The prepared polypropylene capacitor film is a single-layer structure composed of polypropylene, olefin block copolymer, aliphatic-aromatic polycarbonate, and maleic anhydride-grafted polypropylene.

[0072] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that Comparative Example 3 does not have layer B, and its polypropylene capacitor film is specifically prepared by the following method: (1) Raw material preparation: Layer A is made of 96 wt% polypropylene and olefin block copolymer (INFUSE). TM OBC 9507) 4wt% The C layer is made of 96 wt% polypropylene, 3.2 wt% aliphatic-aromatic polycarbonate, and 0.8 wt% maleic anhydride-grafted polypropylene.

[0073] (2) Mix the A layer material in a high-speed mixer at 500 rpm for 5 min and feed it into a twin-screw extruder with a main screw speed of 80 rpm; mix the C layer material in a high-speed mixer at 500 rpm for 5 min and feed it into a twin-screw extruder with a main screw speed of 80 rpm; melt the A layer material and the C layer material separately through an independent screw extruder and then co-extrude them using a three-layer co-extrusion die to form a cast sheet with C layer, A layer and C layer stacked in sequence. The thickness of a single C layer is 75 μm (the thickness of the two layers is the same) and the thickness of a single A layer is 100 μm (the thickness of the two layers is the same). The cast sheet is then cooled and shaped by a chilling roller (100℃).

[0074] Steps (3)-(4) are the same as steps (3)-(4) in Example 1.

[0075] The prepared polypropylene capacitor film comprises layers C, A, and C3 stacked sequentially, wherein layer A is the intermediate layer, and layer C3 is the outer layer. Layer A is composed of 96 wt% polypropylene and olefin block copolymer (INFUSE). TM The composition is 4wt% OBC 9507, and the C layer is composed of 96wt% polypropylene, 3.2wt% aliphatic-aromatic polycarbonate, and 0.8wt% maleic anhydride-grafted polypropylene.

[0076] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that neither layer A nor layer B of Comparative Example 4 contains an olefin block copolymer, and its polypropylene capacitor film is specifically prepared by the following method: (1) Raw material preparation: Layer A is made of 100 wt% polypropylene. Layer B is made of 100% polypropylene. The C layer is made of 96 wt% polypropylene, 3.2 wt% aliphatic-aromatic polycarbonate, and 0.8 wt% maleic anhydride-grafted polypropylene.

[0077] Steps (2)-(4) are the same as steps (2)-(4) in Example 1.

[0078] The prepared polypropylene capacitor film comprises layers C, B, A, B and C stacked sequentially, wherein layer A is the intermediate layer, layer B is the transition layer and layer C is the outer layer. Layer A is composed of polypropylene, layer B is composed of polypropylene, and layer C is composed of 96 wt% polypropylene, 3.2 wt% aliphatic-aromatic polycarbonate and 0.8 wt% maleic anhydride-grafted polypropylene.

[0079] Comparative Example 5 The difference between Comparative Example 5 and Example 1 is that layer A of Comparative Example 5 does not contain an olefin block copolymer, and its polypropylene capacitor film is specifically prepared by the following method: (1) Raw material preparation: Layer A is made of 100 wt% polypropylene. Layer B is made of 99 wt% polypropylene and olefin block copolymer (INFUSE). TM OBC 9507) 1wt% The C layer is made of 96 wt% polypropylene, 3.2 wt% aliphatic-aromatic polycarbonate, and 0.8 wt% maleic anhydride-grafted polypropylene.

[0080] Steps (2)-(4) are the same as steps (2)-(4) in Example 1.

[0081] The prepared polypropylene capacitor film comprises layers C, B, A, B, and C stacked sequentially, wherein layer A is the intermediate layer, layer B is the transition layer, and layer C is the outer layer. Layer A is composed of polypropylene, and layer B is composed of 99 wt% polypropylene and an olefin block copolymer (INFUSE). TM The composition is 1 wt% of OBC 9507, and the C layer is composed of 96 wt% polypropylene, 3.2 wt% aliphatic-aromatic polycarbonate, and 0.8 wt% maleic anhydride-grafted polypropylene.

[0082] Comparative Example 6 The difference between Comparative Example 6 and Example 1 is that the B layer of Comparative Example 6 does not contain an olefin block copolymer, and its polypropylene capacitor film is specifically prepared by the following method: (1) Raw material preparation: Layer A is made of 96 wt% polypropylene and olefin block copolymer (INFUSE).TM OBC 9507) 4wt% Layer B is made of 100 wt% polypropylene. The C layer is made of 96 wt% polypropylene, 3.2 wt% aliphatic-aromatic polycarbonate, and 0.8 wt% maleic anhydride-grafted polypropylene.

[0083] Steps (2)-(4) are the same as steps (2)-(4) in Example 1.

[0084] The prepared polypropylene capacitor film comprises layers C, B, A, B, and C stacked sequentially, wherein layer A is the intermediate layer, layer B is the transition layer, and layer C is the outer layer. Layer A is composed of 96 wt% polypropylene and olefin block copolymer (INFUSE). TM The composition is 4wt% of OBC9507, with layer B consisting of polypropylene and layer C consisting of 96wt% polypropylene, 3.2wt% aliphatic-aromatic polycarbonate, and 0.8wt% maleic anhydride-grafted polypropylene.

[0085] Comparative Example 7 The difference between Comparative Example 7 and Example 1 is that the A-layer olefin block copolymer content of Comparative Example 7 is too high, and its polypropylene capacitor film is specifically prepared by the following method: (1) Raw material preparation: Layer A is made of 92 wt% polypropylene and olefin block copolymer (INFUSE). TM OBC 9507) 8wt% Layer B is made of 99 wt% polypropylene and olefin block copolymer (INFUSE). TM OBC 9507) 1wt% The C layer is made of 96 wt% polypropylene, 3.2 wt% aliphatic-aromatic polycarbonate, and 0.8 wt% maleic anhydride-grafted polypropylene.

[0086] Steps (2)-(4) are the same as steps (2)-(4) in Example 1.

[0087] The prepared polypropylene capacitor film comprises layers C, B, A, B, and C stacked sequentially, wherein layer A is the intermediate layer, layer B is the transition layer, and layer C is the outer layer. Layer A is composed of 92 wt% polypropylene and INFUSE. TM It consists of 8wt% OBC 9507, and layer B is composed of 99wt% polypropylene and INFUSE. TM OBC 9507 is composed of 1 wt% polypropylene, and the C layer is composed of 96 wt% polypropylene, 3.2 wt% aliphatic-aromatic polycarbonate, and 0.8 wt% maleic anhydride-grafted polypropylene.

[0088] Comparative Example 8 The difference between Comparative Example 8 and Example 1 is that the B-layer olefin block copolymer content of Comparative Example 8 is too high, and its polypropylene capacitor film is specifically prepared by the following method: (1) Raw material preparation: Layer A is made of 96 wt% polypropylene and olefin block copolymer (INFUSE). TM OBC 9507) 4wt% Layer B is made of 97 wt% polypropylene and olefin block copolymer (INFUSE). TM OBC 9507) 3wt% The C layer is made of 96 wt% polypropylene, 3.2 wt% aliphatic-aromatic polycarbonate, and 0.8 wt% maleic anhydride-grafted polypropylene.

[0089] Steps (2)-(4) are the same as steps (2)-(4) in Example 1.

[0090] The prepared polypropylene capacitor film comprises layers C, B, A, B, and C stacked sequentially, wherein layer A is the intermediate layer, layer B is the transition layer, and layer C is the outer layer. Layer A is composed of 96 wt% polypropylene and INFUSE. TM It consists of 4wt% OBC 9507, and layer B is composed of 97wt% polypropylene and INFUSE. TM OBC 9507 is composed of 3wt% polypropylene, and the C layer is composed of 96wt% polypropylene, 3.2wt% aliphatic-aromatic polycarbonate and 0.8wt% maleic anhydride-grafted polypropylene.

[0091] Comparative Example 9 The difference between Comparative Example 9 and Example 1 is that the content of olefin block copolymers in layers A and B of Comparative Example 9 is different from that in Example 1, and its polypropylene capacitor film is specifically prepared by the following method: (1) Raw material preparation: Layer A is made of 99 wt% polypropylene and olefin block copolymer (INFUSE). TM OBC 9507) 1wt% Layer B is made of 96 wt% polypropylene and olefin block copolymer (INFUSE). TM OBC 9507) 4wt% The C layer is made of 96 wt% polypropylene, 3.2 wt% aliphatic-aromatic polycarbonate, and 0.8 wt% maleic anhydride-grafted polypropylene.

[0092] Steps (2)-(4) are the same as steps (2)-(4) in Example 1.

[0093] The prepared polypropylene capacitor film comprises layers C, B, A, B, and C stacked sequentially, wherein layer A is the intermediate layer, layer B is the transition layer, and layer C is the outer layer. Layer A is composed of 99 wt% polypropylene and INFUSE. TM Composed of OBC 9507 1wt%, layer B consists of 96wt% polypropylene and INFUSE. TM OBC 9507 is composed of 4wt% polypropylene, and the C layer is composed of 96wt% polypropylene, 3.2wt% aliphatic-aromatic polycarbonate and 0.8wt% maleic anhydride-grafted polypropylene.

[0094] Comparative Example 10 The difference between Comparative Example 10 and Example 1 is that 0.5 wt% of an olefin block copolymer was added to the C layer of Comparative Example 10, and its polypropylene capacitor film was specifically prepared by the following method: (1) Raw material preparation: Layer A is made of 96 wt% polypropylene and olefin block copolymer (INFUSE). TM OBC 9507) 4wt% Layer B is made of 99 wt% polypropylene and olefin block copolymer (INFUSE). TM OBC 9507) 1wt% The C-layer material consists of 95.5 wt% polypropylene, 3.2 wt% aliphatic-aromatic polycarbonate, and olefin block copolymer (INFUSE). TM 0.5 wt% OBC 9507 and 0.8 wt% maleic anhydride-grafted polypropylene.

[0095] Steps (2)-(4) are the same as steps (2)-(4) in Example 1.

[0096] The prepared polypropylene capacitor film comprises layers C, B, A, B, and C stacked sequentially, wherein layer A is the intermediate layer, layer B is the transition layer, and layer C is the outer layer. Layer A is composed of 96 wt% polypropylene and INFUSE. TM OBC 9507 is composed of 4wt% polypropylene, and the B layer is composed of 99wt% polypropylene and olefin block copolymer INFUSE. TM OBC 9507 is composed of 1 wt% polypropylene, with the C layer consisting of 95.5 wt% polypropylene, 3.2 wt% aliphatic-aromatic polycarbonate, and INFUSE. TM Composed of 0.5 wt% OBC 9507 and 0.8 wt% maleic anhydride-grafted polypropylene.

[0097] Comparative Example 11 The difference between Comparative Example 11 and Example 1 is that the olefin block copolymer added to layers A and B of Comparative Example 11 is INFUSE. TMOBC 9010, its polypropylene capacitor film is specifically prepared by the following method: (1) Raw material preparation: Layer A is made of 96 wt% polypropylene and olefin block copolymer (INFUSE). TM OBC 9010) 4wt% Layer B is made of 99 wt% polypropylene and olefin block copolymer (INFUSE). TM OBC 9010) 1wt% The C layer is made of 96 wt% polypropylene, 3.2 wt% aliphatic-aromatic polycarbonate, and 0.8 wt% maleic anhydride-grafted polypropylene.

[0098] Steps (2)-(4) are the same as steps (2)-(4) in Example 1.

[0099] The prepared polypropylene capacitor film comprises layers C, B, A, B, and C stacked sequentially, wherein layer A is the intermediate layer, layer B is the transition layer, and layer C is the outer layer. Layer A is composed of 96 wt% polypropylene and INFUSE. TM OBC 9010 consists of 4wt% polypropylene, and the B layer is composed of 99wt% polypropylene and olefin block copolymer INFUSE. TM OBC 9010 is composed of 1 wt% polypropylene, and the C layer is composed of 96 wt% polypropylene, 3.2 wt% aliphatic-aromatic polycarbonate, and 0.8 wt% maleic anhydride-grafted polypropylene.

[0100] Comparative Example 12 The difference between Comparative Example 12 and Example 1 is that the olefin block copolymer added to layers A and B of Comparative Example 12 is INFUSE. TM OBC 9817, its polypropylene capacitor film is specifically prepared by the following method: (1) Raw material preparation: Layer A is made of 96 wt% polypropylene and olefin block copolymer (INFUSE). TM OBC 9817) 4wt% Layer B is made of 99 wt% polypropylene and olefin block copolymer (INFUSE). TM OBC 9817) 1wt% The C layer is made of 96 wt% polypropylene, 3.2 wt% aliphatic-aromatic polycarbonate, and 0.8 wt% maleic anhydride-grafted polypropylene.

[0101] Steps (2)-(4) are the same as steps (2)-(4) in Example 1.

[0102] The prepared polypropylene capacitor film comprises layers C, B, A, B, and C stacked sequentially, wherein layer A is the intermediate layer, layer B is the transition layer, and layer C is the outer layer. Layer A is composed of 96 wt% polypropylene and INFUSE. TM OBC 9817 consists of 4 wt% polypropylene, and the B layer is composed of 99 wt% polypropylene and olefin block copolymer INFUSE. TM OBC 9817 is composed of 1 wt% polypropylene, and the C layer is composed of 96 wt% polypropylene, 3.2 wt% aliphatic-aromatic polycarbonate, and 0.8 wt% maleic anhydride-grafted polypropylene.

[0103] Comparative Example 13 The difference between Comparative Example 13 and Example 1 is that aliphatic polycarbonate Tritan is added to the C layer of Comparative Example 13. TM GX100, its polypropylene capacitor film is specifically prepared by the following method: (1) Raw material preparation: Layer A is made of 96 wt% polypropylene and olefin block copolymer (INFUSE). TM OBC 9507) 4wt% Layer B is made of 99 wt% polypropylene and olefin block copolymer (INFUSE). TM OBC 9507) 1wt% The C layer is made of 96 wt% polypropylene and Tritan aliphatic polycarbonate. TM GX100 3.2wt%, maleic anhydride-grafted polypropylene 0.8wt%.

[0104] Steps (2)-(4) are the same as steps (2)-(4) in Example 1.

[0105] The prepared polypropylene capacitor film comprises layers C, B, A, B, and C stacked sequentially, wherein layer A is the intermediate layer, layer B is the transition layer, and layer C is the outer layer. Layer A is composed of 96 wt% polypropylene and INFUSE. TM It consists of 4wt% OBC 9507, with layer B composed of 99wt% polypropylene and INFUSE. TM OBC 9507 is composed of 1wt% polypropylene, and the C layer is composed of 96wt% polypropylene and Tritan. TM The composition is 3.2 wt% GX100 and 0.8 wt% maleic anhydride-grafted polypropylene.

[0106] Comparative Example 14 The difference between Comparative Example 14 and Example 1 is that the C layer of Comparative Example 14 contains aromatic polycarbonate CLARNATE. TM A1105, its polypropylene capacitor film is specifically prepared by the following method: (1) Raw material preparation: Layer A is made of 96 wt% polypropylene and olefin block copolymer (INFUSE). TM OBC 9507) 4wt% Layer B is made of 99 wt% polypropylene and olefin block copolymer (INFUSE). TM OBC 9507) 1wt% The C layer material is 96 wt% polypropylene and CLARNATE aromatic polycarbonate. TM A1105 3.2wt%, maleic anhydride-grafted polypropylene 0.8wt%.

[0107] Steps (2)-(4) are the same as steps (2)-(4) in Example 1.

[0108] The prepared polypropylene capacitor film comprises layers C, B, A, B, and C stacked sequentially, wherein layer A is the intermediate layer, layer B is the transition layer, and layer C is the outer layer. Layer A is composed of 96 wt% polypropylene and INFUSE. TM It consists of 4wt% OBC 9507, with layer B composed of 99wt% polypropylene and INFUSE. TM OBC 9507 consists of 1 wt% polypropylene, and the C layer is composed of 96 wt% polypropylene and CLARNATE aromatic polycarbonate. TM Composed of 3.2 wt% A1105 and 0.8 wt% maleic anhydride-grafted polypropylene.

[0109] Comparative Example 15 The difference between Comparative Example 15 and Example 1 is that the C layer of Comparative Example 15 contains 15 wt% aliphatic-aromatic polycarbonate, and its polypropylene capacitor film is prepared by the following method: (1) Raw material preparation: Layer A is made of 96 wt% polypropylene and olefin block copolymer (INFUSE). TM OBC 9507) 4wt% Layer B is made of 99 wt% polypropylene and olefin block copolymer (INFUSE). TM OBC 9507) 1wt% The C layer is made of 83 wt% polypropylene, 15 wt% aliphatic-aromatic polycarbonate, and 2 wt% maleic anhydride-grafted polypropylene.

[0110] Steps (2)-(4) are the same as steps (2)-(4) in Example 1.

[0111] The prepared polypropylene capacitor film comprises layers C, B, A, B, and C stacked sequentially, wherein layer A is the intermediate layer, layer B is the transition layer, and layer C is the outer layer. Layer A is composed of 96 wt% polypropylene and INFUSE. TM It consists of 4wt% OBC 9507, with layer B composed of 99wt% polypropylene and INFUSE. TM OBC 9507 consists of 1 wt% polypropylene, and the C layer consists of 83 wt% polypropylene, 15 wt% aliphatic-aromatic polycarbonate, and 2 wt% maleic anhydride-grafted polypropylene.

[0112] Comparative Example 16 The difference between Comparative Example 16 and Example 1 is that no aliphatic-aromatic polycarbonate was added to the C layer of Comparative Example 16, and its polypropylene capacitor film was specifically prepared by the following method: (1) Raw material preparation: Layer A is made of 96 wt% polypropylene and olefin block copolymer (INFUSE). TM OBC 9507) 4wt% Layer B is made of 99 wt% polypropylene and olefin block copolymer (INFUSE). TM OBC 9507) 1wt% The raw material for layer C is 100wt% polypropylene.

[0113] Steps (2)-(4) are the same as steps (2)-(4) in Example 1.

[0114] The prepared polypropylene capacitor film comprises layers C, B, A, B, and C stacked sequentially, wherein layer A is the intermediate layer, layer B is the transition layer, and layer C is the outer layer. Layer A is composed of 96 wt% polypropylene and INFUSE. TM It consists of 4wt% OBC 9507, with layer B composed of 99wt% polypropylene and INFUSE. TM OBC 9507 is composed of 1 wt% and the C layer is composed of 100 wt% polypropylene.

[0115] Comparative Example 17 The difference between Comparative Example 17 and Example 1 is that the thickness of each layer in the casting of Comparative Example 17 is different from that of Example 1, and its polypropylene capacitor film is specifically prepared by the following method: Step (1) is the same as step (1) in Example 1. Step (2): Referring to step (2) of Example 1, the raw materials of layer A, layer B and layer C are mixed and melted respectively, and then co-extruded and cast using a five-layer co-extrusion die to form a cast sheet of layer C, layer B, layer A, layer B and layer C stacked in sequence. The thickness of each layer is 58μm. Then the cast sheet is cooled and shaped by a chilling roller (100℃).

[0116] Steps (3)-(4) are the same as steps (3)-(4) in Example 1.

[0117] Comparative Example 18 The difference between Comparative Example 18 and Example 1 is that the thickness of each layer in the casting of Comparative Example 18 is different from that of Example 1, and its polypropylene capacitor film is specifically prepared by the following method: Step (1) is the same as step (1) in Example 1. Step (2): Referring to step (2) of Example 1, the raw materials of layer A, layer B and layer C are mixed and melted respectively, and then co-extruded and cast using a five-layer co-extrusion die to form a cast sheet with layers C, B, A, B and C stacked in sequence. The thickness of a single layer C is 50μm (two layers have the same thickness), the thickness of a single layer B is 100μm (two layers have the same thickness), and the thickness of a single layer A is 25μm (two layers have the same thickness). Then the cast sheet is cooled and shaped by a chilling roller (100℃).

[0118] Steps (3)-(4) are the same as steps (3)-(4) in Example 1.

[0119] Comparative Example 19 The difference between Comparative Example 19 and Example 1 is that the thickness of each layer in the casting of Comparative Example 19 is different from that of Example 1, and its polypropylene capacitor film is specifically prepared by the following method: Step (1) is the same as step (1) in Example 1. Step (2): Referring to step (2) of Example 1, the raw materials of layer A, layer B and layer C are mixed and melted respectively, and then co-extruded and cast using a five-layer co-extrusion die to form a cast sheet with layers C, B, A, B and C stacked in sequence. The thickness of a single layer C is 100μm (two layers have the same thickness), the thickness of a single layer B is 50μm (two layers have the same thickness), and the thickness of a single layer A is 25μm (two layers have the same thickness). Then the cast sheet is cooled and shaped by a chilling roller (100℃).

[0120] Steps (3)-(4) are the same as steps (3)-(4) in Example 1.

[0121] Comparative Example 20 The difference between Comparative Example 20 and Example 1 is that the thickness of each layer in the casting of Comparative Example 20 is different from that of Example 1, and its polypropylene capacitor film is specifically prepared by the following method: Step (1) is the same as step (1) in Example 1. Step (2): Referring to step (2) of Example 1, the raw materials of layer A, layer B and layer C are mixed and melted respectively, and then co-extruded and cast using a five-layer co-extrusion die to form a cast sheet with layers C, B, A, B and C stacked in sequence. The thickness of a single layer C is 25μm (two layers have the same thickness), the thickness of a single layer B is 50μm (two layers have the same thickness), and the thickness of a single layer A is 100μm (two layers have the same thickness). Then the cast sheet is cooled and shaped by a chilling roller (100℃).

[0122] Steps (3)-(4) are the same as steps (3)-(4) in Example 1.

[0123] In the above embodiments and comparative examples, the performance testing methods include: (1) The test method for the breakdown field strength at 25℃ is as follows: Test equipment: The DC electrical strength test was performed using a CDI-20 withstand voltage strength tester (50-point electrode method).

[0124] Sample: Take three rectangular samples no smaller than 450mm × 650mm. The samples should be clean, flat, without wrinkles or damage.

[0125] electrode: The upper electrode is a brass cylindrical electrode with a diameter of 25mm, a chamfer radius of 2.5mm, and a height of 120mm. The surface roughness Ra of the working surface is less than 1.25μm.

[0126] A rubber sheet about 3mm thick with a Shore A hardness of (60-70)HA is laid on the platform, and an annealed aluminum foil is laid on the rubber as the lower electrode.

[0127] Ensure that the working surface of the electrode is flat, smooth, and free of scratches.

[0128] Breakdown device: The capacity of the high-voltage test transformer should ensure that the secondary rated current is not less than 0.1A. The voltage ripple factor of the DC power supply should not exceed 5%, and the protection resistor should be (0.2~0.5)Ω / V. The voltage regulator should be able to uniformly adjust the voltage. The overcurrent relay should have sufficient sensitivity to ensure that the power supply is cut off within 0.1s when the sample breaks down. The operating current should be selected with an appropriate value to avoid failure to operate after breakdown or false operation due to non-breakdown. The voltage measurement error should not exceed 4%.

[0129] Experimental steps: a) Place the sample on the lower electrode at 25°C and use the continuous pressure increase method.

[0130] b) Set the boost rate to 500V / s.

[0131] c) Measure 50 points evenly spaced on the sample.

[0132] d) Thickness test: Use a thickness gauge to test 40 points at equal intervals on the test sample, and take the arithmetic mean as the thickness of the sample.

[0133] result: From the 50 breakdown test values, remove the maximum and minimum values ​​(5 points each), and calculate the arithmetic mean of the remaining 40 points. Divide the average breakdown voltage by the sample thickness to obtain the average electrical strength of the batch of films.

[0134] (2) The test method for the breakdown field strength at 80℃ is the same as that at 25℃, except for the addition of a constant temperature control step: the sample and electrode are placed in a high-precision constant temperature test chamber, heated to the set 80℃ and kept at that temperature for 30 minutes to ensure that the sample and electrode reach thermal equilibrium; then the same 50-point continuous pressure increase method is used for testing, and the data processing method remains unchanged.

[0135] (3) The test method for heat shrinkage rate is as follows: Test equipment: Oven: Temperature control accuracy ±2℃; Timer; Steel ruler: Graduation value 0.5 mm.

[0136] Sample: Take five 100mm×100mm samples evenly along the film roll direction and mark them longitudinally and laterally. The sample surface should be smooth, the edges straight, and free from mechanical damage.

[0137] Test method: Measure the longitudinal and transverse dimensions of each piece separately. Then place the sample in an oven at a temperature of 120±2℃. Support the sample with A4 paper and bake in the oven for 15 minutes. After baking, remove the sample, cool it to room temperature, and remeasure the longitudinal and transverse dimensions of the sample.

[0138] result: Shrinkage rate is calculated using the following formula: X1= ×100% In the formula: X1 – Shrinkage rate; L0—The longitudinal or transverse dimension of the sample before baking, in mm; L1—The longitudinal or transverse dimension of the sample after baking, in mm.

[0139] The average of five measurements in the longitudinal and five in the transverse directions is taken as the test result for that direction.

[0140] (4) Dielectric loss tanδ (1 kHz) The dielectric loss (tanδ) of the thin film was measured at 25°C using a broadband dielectric spectrometer (NG-80, Novocontrol GmbH, Germany), with a test range of 10⁻¹⁰. 6 The dielectric loss value of the thin film was recorded at a frequency of 1 kHz. Before testing, conductive silver paste was applied to the surface of the thin film and allowed to dry at 40°C.

[0141] (5) Methods for measuring surface roughness Test equipment: Mahr M1 surface roughness tester; 50mm diameter flat mirror; cotton swabs; acetone Samples: Take five samples each longitudinally and transversely from the sample, with a size of 60 mm × 60 mm. The sample surface must be clean and free of damage or wrinkles.

[0142] Experimental steps: Clean the test surface of the plane mirror with a cotton swab soaked in acetone. Place the sample on the test surface of the plane mirror, ensuring the sample is completely flush against the surface and free of air bubbles. With the test surface of the sample facing the test probe, read the Ra values ​​of the five samples.

[0143] Results processing: The surface roughness of the film is expressed as the arithmetic mean of 10 Ra values ​​of five samples, in nm.

[0144] The test results for each performance aspect are shown in Table 1.

[0145] Table 1: Performance data of polypropylene films from examples and comparative examples

[0146] * Rate of change of breakdown field strength at high temperature = (breakdown field strength at 25℃ - breakdown field strength at 80℃) / breakdown field strength at 25℃ * 100%.

[0147] As can be seen from Table 1: Examples 1-3 are technical solutions within the protection scope, which can achieve excellent high and low temperature breakdown field strength, low thermal shrinkage rate, and low dielectric loss performance.

[0148] A comparison of Example 1 and Comparative Examples 1-2 shows that preparing a single-layer film by simply compounding OBC and / or aliphatic-aromatic polycarbonate, without a five-layer design, cannot achieve synergistic performance improvement of each component, resulting in defects such as high high-temperature breakdown attenuation, high thermal shrinkage, and high dielectric loss. The B layer is crucial as a transition layer; the absence of the B layer (Comparative Example 3) exacerbates interlayer stress, leading to a decrease in film performance.

[0149] A comparison of Example 1 with Comparative Examples 4-9 shows that adding an appropriate amount of OBC to layers A and B to form a decreasing trend in the content of OBC in layers A, B, and C is key to improving overall performance. The absence of OBC in layers A and / or B, excessive addition of OBC, or the lack of a decreasing trend in OBC content all lead to increased breakdown attenuation, increased thermal shrinkage, and increased dielectric loss.

[0150] The comparison between Example 1 and Comparative Example 10 shows that OBC should not be added to the C layer. OBC will interfere with the surface roughness control of aliphatic-aromatic polycarbonate, resulting in increased roughness and decreased breakdown performance and thermal dimensional stability.

[0151] By comparing Example 1 with Comparative Examples 11-12, it can be seen that OBC with a low or high melt flow index has poor compatibility with polypropylene matrix and cannot achieve better breakdown field strength and low dielectric loss.

[0152] By comparing Example 1 with Comparative Examples 13-16, it can be seen that the addition of aliphatic-aromatic polycarbonate to the C layer has better performance than aliphatic polycarbonate and aromatic polycarbonate. The content of aliphatic-aromatic polycarbonate should not exceed 10 wt%. Excessive addition will lead to excessive surface roughness, which will affect the film performance.

[0153] By comparing Example 1 with Comparative Examples 17-20, it can be seen that the thickness of layer C, layer B, and layer A must meet the following requirement: layer B thickness < layer C thickness < layer A thickness. Designing each layer to be of equal thickness or having each layer thickness that does not meet the protection range will damage the interlayer functional synergy, degrade the breakdown performance, reduce thermal dimensional stability, and increase dielectric loss.

[0154] This invention employs a five-layer symmetrical structure (CBABC), and through the synergistic effect of core technical features such as the olefin block copolymer (OBC) content decreasing from layer A to layer B and no OBC added to layer C, layer C being compounded with aliphatic-aromatic polycarbonate, a specific layer thickness ratio (C:B:A=1.5~2.5:1:3~5), and a specific melt index range for OBC, the film meets the requirements of high-end capacitor films, including a breakdown field strength attenuation of ≤11% at 80℃, a longitudinal thermal shrinkage rate of ≤2%, and a dielectric loss tanδ of ≤0.0001.

[0155] All aspects, embodiments, and features of this invention should be considered illustrative in all respects and not limiting of the invention; the scope of the invention is defined only by the claims. Other embodiments, modifications, and uses will become apparent to those skilled in the art without departing from the spirit and scope of the invention as claimed.

[0156] In the preparation method of this invention, the order of the steps is not limited to the listed order. For those skilled in the art, variations in the order of the steps without creative effort are also within the scope of protection of this invention. Furthermore, two or more steps or actions can be performed simultaneously.

[0157] Finally, it should be noted that the specific embodiments described herein are merely illustrative examples of the invention and are not intended to limit the implementation of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them; it is neither necessary nor possible to exemplify all embodiments here. However, these obvious variations or modifications derived from the essential spirit of the invention still fall within the scope of protection of the invention, and interpreting them as any additional limitation would contradict the spirit of the invention.

Claims

1. A polypropylene capacitor film, characterized in that, It comprises layers C, B, A, B, and C stacked sequentially, where layer A is the intermediate layer, layer B is the transition layer, and layer C is the outer layer. The components of each layer by mass fraction are as follows: The A layer comprises: 94-98 wt% polypropylene and 2-6 wt% olefin block copolymer; The B layer comprises: 98.5~99.5 wt% polypropylene and 0.5~1.5 wt% olefin block copolymer; The C layer comprises: 87-98.7 wt% polypropylene, 1-10 wt% aliphatic-aromatic polycarbonate, and 0.3-3 wt% compatibilizer; The content of the olefin block copolymer decreases from layer A to layer B, and no olefin block copolymer is added to layer C. The melt index of the olefin block copolymer is 2~20 g / 10 min, and the test conditions for the melt index are 2.16 kg and 190 °C.

2. The polypropylene capacitor film according to claim 1, characterized in that, The polypropylene is isotactic polypropylene with an isotactic index ≥97.5%, ash content ≤20ppm, melt flow index (MFR) of 3.0~4.2g / 10min, and MFR test conditions of 2.16kg and 230℃.

3. The polypropylene capacitor film according to claim 1, characterized in that, The melt index of the olefin block copolymer is 3~10 g / 10 min, and the test conditions for the melt index are 2.16 kg and 190 °C.

4. The polypropylene capacitor film according to claim 3, characterized in that, The olefin block copolymer is Dow INFUSE. TM OBC 9500, INFUSE TM OBC 9507, INFUSE TM One or more of OBC 9530.

5. The polypropylene capacitor film according to claim 1, characterized in that, The aliphatic-aromatic polycarbonate is selected from one or more polycarbonates polymerized from alicyclic aliphatic diols, aromatic diphenols, and diphenyl carbonate.

6. The polypropylene capacitor film according to claim 5, characterized in that, The alicyclic aliphatic diol is cyclohexanediethanol, including one or more of 1,4-cyclohexanediethanol, 1,2-cyclohexanediethanol, and 1,3-cyclohexanediethanol; The aromatic diphenol is selected from one or more of bisphenol A, bisphenol F, and bisphenol S.

7. The polypropylene capacitor film according to claim 5, characterized in that, The molecular weight (Mw) of the aliphatic-aromatic polycarbonate is 10,000 to 40,000 g / mol.

8. The polypropylene capacitor film according to claim 1, characterized in that, The surface roughness of the polypropylene capacitor film is 55~65nm.

9. The polypropylene capacitor film according to claim 1, characterized in that, The thickness ratio of layer C, layer B, and layer A is (1.5~2.5):1:(3~5).

10. The polypropylene capacitor film according to claim 1, characterized in that, The polypropylene capacitor film exhibits a breakdown field strength attenuation of ≤11% at 80℃, a longitudinal thermal shrinkage rate of ≤2% measured at 120℃ for 15 min, and a dielectric loss tanδ ≤0.0001.

11. A method for preparing a polypropylene capacitor film as described in claim 1, characterized in that, Includes the following steps: (1) After melting the A layer raw material, B layer raw material and C layer raw material respectively by independent screw extruder, co-extrusion casting is carried out by five-layer co-extrusion die head to form a casting sheet of C layer, B layer, A layer, B layer and C layer stacked in sequence. Then the casting sheet is cooled and shaped by chiller roller. (2) The casting sheet is first stretched longitudinally, with the stretching ratio controlled at 4 to 7 times; then it is stretched transversely, with the stretching ratio controlled at 8 to 10 times. (3) Then perform corona treatment, roll up and cut to obtain polypropylene capacitor film.

12. The preparation method according to claim 11, characterized in that, The thickness of the cast sheet is 200~400 μm, and the thickness of each layer is 20~100 μm, with the thickness of layer B < the thickness of layer C < the thickness of layer A.

13. The preparation method according to claim 12, characterized in that, In the casting, the thickness ratio of layer C, layer B and layer A is (1.5~2.5):1:(3~5).

14. The preparation method according to claim 11, characterized in that, During longitudinal stretching, the preheating temperature is 100~135℃, the stretching temperature is 145~150℃, and the setting temperature is 150~153℃; during transverse stretching, the preheating temperature is 160~175℃, the stretching temperature is 160~165℃, and the setting temperature is 175~180℃.

15. The preparation method according to claim 11, characterized in that, Corona treatment includes: simultaneous treatment on both sides, voltage of 5~10kV, output power of 5~18kW, and electrode bombardment intensity of 10~18W·min / m. 2 .

16. An application of the polypropylene capacitor film as described in claim 1, characterized in that, The polypropylene capacitor film is used as the dielectric layer of the capacitor, and the capacitor is suitable for one or more fields including new energy vehicles, ultra-high voltage direct current transmission, rail transit, industrial frequency conversion, pulse power weapons, and flexible direct current transmission.

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