Bopp capacitor film and preparation method thereof

Abstract

This invention relates to the field of thin films, and particularly to a BOPP capacitor film and its preparation method. The BOPP capacitor film comprises a heat-resistant layer, a phase change layer, a core layer, another phase change layer, and a heat-resistant layer arranged sequentially. The heat-resistant layer comprises polypropylene and 3-15 wt% PP-g-(DAP-co-GMA); the phase change layer comprises 25-35 wt% crosslinked SEBS, 58-72 wt% paraffin wax, and 3-7 wt% spherical mesoporous silica; the core layer comprises homopolymer polypropylene. The BOPP capacitor film of this invention enhances the heat resistance of the heat-resistant layer through PP-g-(DAP-co-GMA), and absorbs a large amount of latent heat by setting a special phase change layer, inhibiting the increase of free volume and the formation of voids in the film. Under the combined action of the heat-resistant layer and the phase change layer, it effectively improves the problem of a sharp decrease in breakdown strength and a sharp increase in dielectric loss of the BOPP capacitor film at temperatures above 100°C.

Description

Technical Field

[0001] This invention relates to the field of thin films, and in particular to a BOPP capacitor film and its preparation method. Background Technology

[0002] With the development of six major industries—3C consumer electronics, new energy storage, green lighting, electric vehicles, smart grid construction, and railway electrification—the demand for film capacitors is gradually increasing. BOPP capacitor film, due to its advantages such as dielectric loss, processability, and low cost, has become the dominant dielectric material in industrial applications.

[0003] BOPP capacitor film exhibits outstanding performance, primarily in the following aspects: excellent electrical insulation properties (high breakdown voltage), extremely low energy loss characteristics, excellent self-healing ability, superior film-forming processing performance, stable chemical resistance, excellent ultra-thinning potential, and high cost-effectiveness. These advantages make BOPP capacitor film the primary conductive dielectric material for film capacitors currently on the market. As film capacitors evolve towards miniaturization, increased capacitance, and higher voltage resistance, there are increasingly higher requirements for the heat resistance of BOPP capacitor film.

[0004] Currently, the long-term stable operating temperature of BOPP capacitor film is only 85℃. When the temperature rises to 100℃, the breakdown strength of the film drops sharply (by nearly 100kV / mm) and the dielectric loss increases sharply. Summary of the Invention

[0005] Based on this, the purpose of the present invention is to provide a BOPP capacitor film and its preparation method. The heat resistance of the heat-resistant layer is improved by grafting polypropylene (dally propylene phthalate-co-glycidyl methacrylate), and a special phase change layer is set to absorb a large amount of latent heat, suppress the increase of polypropylene free volume and the formation of voids. Under the combined action of the heat-resistant layer and the phase change layer, the problem of the BOPP capacitor film's breakdown strength dropping sharply and dielectric loss increasing sharply when the temperature is above 100°C is improved.

[0006] The technical solution of the present invention is achieved in the following ways:

[0007] A BOPP capacitor film includes a heat-resistant layer, a phase change layer, a core layer, and a heat-resistant layer arranged sequentially; the heat-resistant layer comprises polypropylene and 3-15 wt% polypropylene grafted (dallyl phthalate-co-glycidyl methacrylate); the phase change layer comprises 25-35 wt% crosslinked styrene-ethylene / butene-styrene block copolymer, 58-72 wt% paraffin wax, and 3-7 wt% spherical mesoporous silica; the core layer comprises homopolymer polypropylene.

[0008] Through extensive practical experience, the inventors discovered that the breakdown strength of existing BOPP capacitor films decreases significantly under high-temperature conditions, which is related to the linear molecular chain structure of polypropylene. As the temperature rises, the movement of polypropylene molecular chain segments intensifies, and relative slippage occurs between molecular chains. This process leads to an increase in the free volume within the film, and simultaneously, a significant increase in the average degree of freedom of charge carriers. Notably, due to the weak intermolecular forces within the amorphous region, the thermal motion effect of the molecular chains in this region is particularly prominent, ultimately becoming a key factor affecting the dielectric properties of polypropylene, resulting in a significant decrease in the breakdown strength of the BOPP capacitor film.

[0009] BOPP capacitor film is based on the melting point and structural characteristics of polypropylene (PP) material itself. At high temperatures, it will accelerate thermal aging, promote the migration and folding of PP molecular chains, increase the free volume and the number of high-energy charge carriers inside the film, making the polypropylene molecular chains easier to break, resulting in more voids inside the polypropylene, increasing the probability of partial discharge, and reducing the breakdown strength of BOPP capacitor film.

[0010] Under high-temperature conditions, the amount of charge injected into the BOPP capacitor film by the metal electrode increases, leading to an increase in the conductivity loss of polypropylene. At 120℃, the conductivity loss of polypropylene decreases sharply, causing the charging and discharging efficiency of the capacitor to drop by more than 30%. The BOPP capacitor film experiences thermal runaway, characterized by "temperature increase → increased conductivity → aggravated heating → temperature increase," ultimately leading to the failure of the BOPP capacitor film.

[0011] This invention adds 3-15 wt% polypropylene grafting (dally propylene phthalate-co-glycidyl methacrylate), i.e., PP-g-(DAP-co-GMA), to the heat-resistant layer, increasing the heat resistance and dielectric constant of the BOPP capacitor film. Specifically, DAP has two propylene groups. In PP-g-(DAP-co-GMA), after one propylene group of DAP is grafted onto the PP backbone, the other propylene group of DAP undergoes a free radical addition reaction with GMA through an olefin double bond (C=C), thereby introducing GMA into the polypropylene chain as well. This is equivalent to introducing a highly reactive epoxy group onto the PP chain. Under high-temperature conditions, the epoxy group of GMA in PP-g-(DAP-co-GMA) undergoes a ring-opening reaction, forming an ether cross-linked structure. This can suppress chain movement and chain segment relaxation of the PP molecular chain in the heat-resistant layer during heating, thus achieving better high-temperature performance. In addition, the nonlocalized π-electron cloud generated by the conjugated benzene ring configuration of DAP has a strong electron affinity, which can capture high-energy charge carriers during high field strength and high temperature breakdown, reduce damage to the main resin polypropylene of the film, and thus improve the breakdown resistance of BOPP capacitor film.

[0012] When the content of PP-g-(DAP-co-GMA) in the heat-resistant layer is less than 3wt%, the content of DAP and GMA introduced into the system is too low, and the improvement effect on the heat resistance and dielectric properties of the film is not significant. When the content of PP-g-(DAP-co-GMA) in the heat-resistant layer is higher than 15wt%, it will severely restrict the movement of PP molecular chains, resulting in poor flowability of the heat-resistant layer. Excessive PP-g-(DAP-co-GMA) cannot be fully compatible with the PP matrix resin of the heat-resistant layer and will agglomerate due to thermodynamic incompatibility, affecting the smoothness of production and processing.

[0013] This invention also introduces a phase change layer into the BOPP capacitor film. Please refer to the diagram for the structure of the phase change layer. Figure 1 By utilizing paraffin, a phase change material with a phase change temperature of 70~90℃, a large amount of latent heat is absorbed, which inhibits the increase of free volume and the formation of voids inside the film. At the same time, it helps to reduce the conductivity of the polypropylene body and reduce the amount of space charge injection, so that the conductivity loss of the capacitor film is always kept within a safe range, avoiding the rapid deterioration region near 120℃, thereby ensuring the charging and discharging efficiency.

[0014] Building upon this, to prevent the phase change material from leaking and losing its function after melting, the present invention further adds 25-35 wt% crosslinked styrene-ethylene / butene-styrene block copolymer (crosslinked SEBS) to the phase change layer. The crosslinked SEBS forms a crosslinked polymer network, confining the phase change material within the network. When paraffin cools, it crystallizes and solidifies within the crosslinked network, physically bound to the pores. When reheated above its melting point, the paraffin melts into a liquid, but its flow is prevented by the elastic binding force of the crosslinked network, thus achieving shape stability of the phase change material. It is important to note that this application uses cross-linked SEBS, rather than ordinary SEBS block copolymers. Although ordinary SEBS block copolymers can bind paraffin within a molecular chain network formed by the physical entanglement of molecular chains, the physical cross-linking points of the PS segments in the SEBS block copolymer will break down when the working temperature exceeds 100°C, causing the material to lose its shaping ability and failing to firmly bind the paraffin. In contrast, the EB segments of cross-linked SEBS form strong CC covalent bond cross-linking points through chemical cross-linking, which can ensure that the cross-linked SEBS maintains its complete elastic network structure even when the working temperature exceeds 100°C. If the content of cross-linked SEBS is less than 25wt%, the content of paraffin wax in the phase change material is too high. Excess paraffin wax cannot be confined in the spatial cross-linked network structure of the cross-linked SEBS, resulting in leakage and paraffin wax outflow. This reduces the amount of paraffin wax that actually produces effective temperature regulation, making it unable to effectively absorb or release latent heat. Consequently, the temperature control effect is compromised or even completely fails, affecting the normal use of the BOPP capacitor film. If the content of cross-linked SEBS is higher than 35wt%, the content of paraffin wax in the phase change layer is too low. This results in insufficient heat storage capacity of the phase change layer, reduced temperature regulation capability, and areas not filled with paraffin wax may develop microcracks inside the matrix due to repeated melting and crystallization. These cracks will expand during long-term use, which will weaken the fatigue life of the BOPP capacitor film.

[0015] Based on this, the present invention also adds 3-7 wt% spherical mesoporous silica to the phase change layer. Utilizing the porous structure and hydroxyl-rich properties of the surface of the mesoporous silica, the paraffin wax can enter the channels of the mesoporous silica after melting and form hydrogen bonds with the paraffin wax through the surface hydroxyl groups. Under the triple constraint of capillary force, surface tension and interfacial force, the liquid paraffin wax is prevented from flowing out. The paraffin wax can also crystallize in the channels after cooling, thereby further enhancing the binding force on the phase change material paraffin wax.

[0016] If the content of spherical mesoporous silica is less than 3wt%, the spherical mesoporous silica has poor constraint on paraffin and poor ability to improve the thermal conductivity of the phase change layer, and its effect is not obvious. If the content of spherical mesoporous silica is higher than 7wt%, the spherical mesoporous silica has poor compatibility with SEBS and is prone to agglomeration, which will reduce the latent heat value of the phase change layer and weaken the thermal management ability.

[0017] Furthermore, the crosslinked styrene-ethylene / butene-styrene block copolymer is obtained by melt extrusion after crosslinking and blending styrene-ethylene / butene-styrene block copolymer with dicumyl peroxide.

[0018] Furthermore, the polypropylene graft (dally propyl phthalate-co-glycidyl methacrylate) is prepared by melt grafting polypropylene with glycidyl methacrylate and diallyl phthalate in a molar ratio of 1:1.5.

[0019] Furthermore, the paraffin wax has a melting point of 75~90℃, a latent heat of phase change of 230~260J / g, and a liquid density of 0.8~0.83g / cm³. 3 .

[0020] Furthermore, the styrene-ethylene / butene-styrene block copolymer contains 30-33 wt% styrene, and the melt index of the styrene-ethylene / butene-styrene block copolymer is 5-10 g / 10 min, measured at 230°C and 5 kg.

[0021] Furthermore, the spherical mesoporous silica has a D50 of 0.5~1μm and a pore size of 5~20nm.

[0022] Furthermore, the isotacticity of the homopolymer polypropylene is 97.5~98.5%, and the melt index of the homopolymer polypropylene measured at 230℃ and 2.16kg is 3.0~4.0g / 10min.

[0023] Furthermore, the total thickness of the BOPP capacitor film is 12~15μm, the thickness of the heat-resistant layer is 1~2.5μm, the thickness of the phase change layer is 2~2.5μm, and the thickness of the core layer is 5~6μm.

[0024] The present invention also provides a method for preparing any of the above-described BOPP capacitor films, comprising the following steps: Ingredient preparation and plasticizing: The raw materials of each layer are conveyed to each extruder for melting and plasticizing according to the formula. The melt enters the die head through the flow channel and distributor. Cast sheet: After being extruded through the die, the molten material immediately contacts the cooling roller to form a thick sheet; Longitudinal stretching: After the thick sheet is heated to the set temperature by the preheating roller, longitudinal stretching begins, followed by shaping. The longitudinal stretching ratio is 4.5 to 5.5 times. Lateral stretching: After the longitudinally stretched sheet is preheated to the set temperature, lateral stretching begins. After lateral stretching, it undergoes shaping and cooling. The lateral stretching ratio is 6 to 8 times. Traction and winding: The multi-layered film after transverse stretching enters the traction unit, and after thickness measurement and corona treatment, it enters the winding unit to obtain the master roll; Slitting: The aging-treated master roll is slitted to obtain BOPP capacitor film rolls of specified width and length.

[0025] Furthermore, the melt extrusion temperature of the heat-resistant layer is 200~260℃; the melt extrusion temperature of the phase change layer is 200~240℃; the melt extrusion temperature of the core layer is 230~260℃; in the process of melt contacting the cooling roller, the temperature of the quench water and the quench roller is 15~50℃; the longitudinal stretching temperature is 130~140℃; and the transverse stretching temperature is 155~165℃.

[0026] To better understand and implement this invention, the invention will be described in detail below. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the phase change layer of the BOPP capacitor film described in this invention. Detailed Implementation

[0028] It should be understood that the described embodiments are merely some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of the embodiments of this application.

[0029] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to limit the embodiments of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0030] In the following description, when referring to the accompanying drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims. In the description of this application, it should be understood that the terms "first," "second," "third," etc., are used only to distinguish similar objects and are not necessarily used to describe a specific order or sequence, nor should they be construed as indicating or implying relative importance. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0031] Furthermore, in the description of this application, unless otherwise stated, "multiple" means two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0032] It should be understood that the embodiments of this application are not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from their scope. The scope of the embodiments of this application is limited only by the appended claims.

[0033] This invention provides a BOPP capacitor film, comprising a heat-resistant layer, a phase change layer, a core layer, and a heat-resistant layer arranged sequentially; the heat-resistant layer comprises polypropylene and 3-15 wt% polypropylene grafted (dallyl phthalate-co-glycidyl methacrylate); the phase change layer comprises 25-35 wt% crosslinked styrene-ethylene / butene-styrene block copolymer, 58-72 wt% paraffin wax, and 3-7 wt% spherical mesoporous silica; the core layer comprises homopolymer polypropylene.

[0034] Further, the crosslinked styrene-ethylene / butene-styrene block copolymer is obtained by melt extrusion after crosslinking and blending the styrene-ethylene / butene-styrene block copolymer with dicumyl peroxide. Specifically, it includes the following steps: adding the styrene-ethylene / butene-styrene block copolymer (SEBS) and the initiator DCP at a mass ratio of 1:0.01 into a twin-screw extruder, processing at a temperature of 180~200℃, a mixing speed of 150~180 rpm, pelletizing, and drying. When SEBS is blended with DCP, DCP acts as a chemical crosslinking agent. DCP can chemically crosslink the EB segments of SEBS to form strong CC covalent bond crosslinking points, which helps to ensure that the SEBS crosslinked polymer network always maintains an intact elastic network structure.

[0035] Furthermore, the polypropylene graft (dally propyl phthalate-co-glycidyl methacrylate) is prepared by melt grafting polypropylene with glycidyl methacrylate and diallyl phthalate in a molar ratio of 1:1.5.

[0036] Furthermore, paraffin wax has a melting point of 75–90°C, a latent heat of phase change of 230–260 J / g, and a liquid density of 0.8–0.83 g / cm³. 3 .

[0037] Furthermore, the styrene-ethylene / butene-styrene block copolymer contains 30~33wt% styrene, and the melt index of the styrene-ethylene / butene-styrene block copolymer is 5~10g / 10min when measured at 230℃ and 5kg.

[0038] Furthermore, the core layer also includes 0.05~0.2wt% antistatic agent.

[0039] Furthermore, the D50 of the spherical mesoporous silica is 0.5~1.0μm, and the pore size is 5~20nm.

[0040] Furthermore, the isotacticity of the homopolymer polypropylene is 97.5~98.5%, and the melt index of the homopolymer polypropylene measured at 230℃ and 2.16kg is 3.0~4.0g / 10min.

[0041] Furthermore, the homopolymer polypropylene is selected from one or more of the following: Borealis HC300BF, HC320BF, Singapore TPC FS3031, Korean Oil Chemicals 5104L-HPT-S, and Sinopec PPH-FC03.

[0042] Furthermore, the total thickness of the BOPP capacitor film is 12~15μm, the thickness of the heat-resistant layer is 1~2.5μm, the thickness of the phase change layer is 2~2.5μm, and the thickness of the core layer is 5~6μm.

[0043] The present invention also provides a method for preparing any of the above-mentioned BOPP capacitor films, comprising the following steps: Ingredient preparation and plasticizing: The raw materials of each layer are conveyed to each extruder for melting and plasticizing according to the formula. The melt enters the die head through the flow channel and distributor. Cast sheet: After being extruded through the die, the molten material immediately contacts the cooling roller to form a thick sheet; Longitudinal stretching: After the thick sheet is heated to the set temperature by the preheating roller, longitudinal stretching begins, followed by shaping. The longitudinal stretching ratio is 4.5 to 5.5 times. Lateral stretching: After the longitudinally stretched sheet is preheated to the set temperature, lateral stretching begins. After lateral stretching, it undergoes shaping and cooling. The lateral stretching ratio is 6 to 8 times. Traction and winding: The multi-layered film after transverse stretching enters the traction unit, and after thickness measurement and corona treatment, it enters the winding unit to obtain the master roll; Slitting: The aging-treated master roll is slitted to obtain BOPP capacitor film rolls of specified width and length.

[0044] Furthermore, the melt extrusion temperature of the heat-resistant layer is 200~260℃; the melt extrusion temperature of the phase change layer is 200~240℃; the melt extrusion temperature of the core layer is 230~260℃; in the process of melt contacting the cooling roller, the temperature of the quench water and the quench roller is 15~50℃; the longitudinal stretching temperature is 130~140℃; and the transverse stretching temperature is 155~165℃.

[0045] The physical properties and testing methods of the embodiments or comparative examples of the present invention are as follows: Breakdown strength: Tested in accordance with GB / T 1408.1-2016.

[0046] Latent heat value: tested using DSC.

[0047] Latent heat value after 100 temperature cycles: The BOPP capacitor film was placed in a test chamber at 80℃±20℃ and subjected to repeated temperature cycles of 100. After 100 cycles, its latent heat value was tested using DSC.

[0048] Thermal management capability test: The BOPP capacitor film was rolled into a thickness of 1 mm and placed in close contact with the ceramic heating element (resistance of 6Ω). The temperature of the heating element was recorded after heating for 3 minutes at 4V.

[0049] Shape stability test: Place the BOPP capacitor film, which is wound to a thickness of 1 mm, on weighing paper and place it on a heating platform. Set the temperature to 120℃ and observe whether the weighing paper in contact with the BOPP capacitor film is wetted. If wettation occurs, it indicates that the paraffin has leaked.

[0050] In the embodiments or comparative examples of this invention, polypropylene grafted (dallyl phthalate-co-glycidyl methacrylate) was prepared by melt grafting. The preparation method includes the following steps: PP 100g, GMA 2.8g, DAP 7.2g (controlling the molar ratio of GMA to DAP to 1:1.5), and DCP 0.2g were added to a torque rheometer for melt grafting at a temperature of 180℃, a rotation speed of 120 r / min, and a time of 10 min. 10g of the grafted product was heated under reflux for 4 h in a conical flask containing 200 mL of xylene, then 200 mL of acetone was added, the mixture was allowed to stand, precipitated, purified by vacuum filtration, and dried to obtain PP-g-(DAP-co-GMA) with a grafting rate of 0.5%. In the above preparation method, PP is homopolymer polypropylene, selected from one or more of the following: Borealis HC300BF, HC320BF, Singapore TPC FS3031, Korean Oil Chemicals 5104L-HPT-S, and Sinopec PPH-FC03.

[0051] In the embodiments or comparative examples of the present invention, the isotacticity of homopolymer polypropylene is 98.5%, and the melt index of homopolymer polypropylene measured at 230°C and 2.16 kg is 3.2 g / 10 min.

[0052] The preparation method of crosslinked SEBS in the embodiments or comparative examples of the present invention includes the following steps: styrene-ethylene / butene-styrene block copolymer (SEBS) (with a melt index of 10 g / 10 min measured at 230°C and 5 kg, and a styrene content of 30 wt%) and initiator DCP are added to a twin-screw extruder at a mass ratio of 1:0.01, the processing temperature is 200°C, the mixing speed is 180 rpm, the processing time is 10 min, and then the product is pelletized and dried.

[0053] In the embodiments or comparative examples of this invention, the paraffin wax has a melting point of 80°C, a latent heat of phase change of 260 J / g, and a liquid density of 0.82 g / cm³. 3 .

[0054] In the embodiments or comparative examples of this invention, the D50 of the spherical mesoporous silica is 0.5 μm, and the pore size is 10 nm.

[0055] In the embodiments or comparative examples of this invention, the antistatic agent used is Best AS2335PPTR.

[0056] It should be noted that the proportions mentioned in the embodiments or comparative examples of the present invention are all weight percentages. The components and contents of the heat-resistant layer and phase change layer in the embodiments and comparative examples of the present invention are shown in Table 1 below.

[0057] Table 1

[0058] Example 1 This embodiment provides a BOPP capacitor film, comprising a heat-resistant layer, a phase change layer, a core layer, another phase change layer, and a heat-resistant layer sequentially arranged; the preparation method of each resin layer of the BOPP capacitor film in this embodiment includes the following steps: Preparation of heat-resistant layer resin: Please refer to Table 1. Take 5 wt% polypropylene graft (diallyl phthalate-co-glycidyl methacrylate) and 95 wt% homopolymer polypropylene and mix them evenly to obtain the heat-resistant layer resin.

[0059] Preparation of phase change layer resin: Please refer to Table 1. Mix 27wt% crosslinked SEBS, 70wt% paraffin and 3wt% spherical mesoporous silica evenly to obtain phase change layer resin.

[0060] Core layer resin preparation: 99.9 wt% homopolymer polypropylene and 0.1 wt% antistatic agent are mixed evenly to obtain the core layer resin.

[0061] The method for preparing the BOPP film in this embodiment includes the following steps: Ingredient preparation and plasticizing: The raw materials of each layer are conveyed to each extruder for melting and plasticizing according to the formula. The melt enters the die head through the flow channel and distributor. Cast sheet: After being extruded through the die, the molten material immediately contacts the cooling roller to form a thick sheet; Longitudinal stretching: The thick sheet is heated to a set temperature by multiple sets of preheating rollers, and then longitudinal stretching begins, followed by shaping. The longitudinal stretching ratio is 4.5 times. Lateral stretching: After the longitudinally stretched thick sheet is preheated to the set temperature, lateral stretching begins. After lateral stretching, it undergoes shaping and cooling. The lateral stretching ratio is 8 times. Traction and winding: The multi-layered film after transverse stretching enters the traction unit, and after thickness measurement and corona treatment, it enters the winding unit to obtain the master roll; Slitting: The aging-treated master roll is slitted to obtain BOPP capacitor film rolls of specified width and length; During the preparation process, the melt extrusion temperature of the heat-resistant layer is 230℃; the melt extrusion temperature of the phase change layer is 200℃; the melt extrusion temperature of the core layer is 230℃; in the process of the melt contacting the cooling roller, the temperature of the quench water and the quench roller is 40℃; the temperature of the longitudinal stretching zone is 130℃; and the temperature of the transverse stretching zone is 160℃.

[0062] The total thickness of the film is 13µm, of which the heat-resistant layer is 1µm thick, the phase change layer is 2.5µm thick, and the core layer is 6µm thick.

[0063] Example 2 This embodiment provides a BOPP capacitor film, comprising a heat-resistant layer, a phase change layer, a core layer, another phase change layer, and a heat-resistant layer sequentially arranged; the preparation method of each resin layer of the BOPP capacitor film in this embodiment includes the following steps: Preparation of the heat-resistant layer resin: Please refer to Table 1. Mix 10 wt% of polypropylene grafted (dally propylene phthalate-co-glycidyl methacrylate) and 90 wt% of homopolymer polypropylene evenly to obtain the heat-resistant layer resin. Preparation of the phase change layer resin: Please refer to Table 1. Mix 30 wt% crosslinked SEBS, 65 wt% paraffin wax, and 5 wt% spherical mesoporous silica evenly to obtain the phase change layer resin.

[0064] Core layer resin preparation: The components and contents of the core layer are the same as in Example 1, so they will not be described again.

[0065] The preparation method of the BOPP capacitor film in this embodiment is the same as that in Embodiment 1, so it will not be described again.

[0066] The total thickness of the film is 13µm, of which the heat-resistant layer is 1µm thick, the phase change layer is 2.5µm thick, and the core layer is 6µm thick.

[0067] Example 3 This embodiment provides a BOPP capacitor film, comprising a heat-resistant layer, a phase change layer, a core layer, another phase change layer, and a heat-resistant layer sequentially arranged; the preparation method of each resin layer of the BOPP capacitor film in this embodiment includes the following steps: Preparation of the heat-resistant layer resin: Please refer to Table 1. Mix 15 wt% of polypropylene grafted (dally propylene phthalate-co-glycidyl methacrylate) and 85 wt% of homopolymer polypropylene evenly to obtain the heat-resistant layer resin. Preparation of the phase change layer resin: Please refer to Table 1. Mix 33 wt% crosslinked SEBS, 60 wt% paraffin wax, and 7 wt% spherical mesoporous silica evenly to obtain the phase change layer resin.

[0068] Core layer resin preparation: The components and contents of the core layer are the same as in Example 1, so they will not be described again.

[0069] The preparation method of the BOPP capacitor film in this embodiment is the same as that in Embodiment 1, so it will not be described again.

[0070] The total thickness of the film is 13µm, of which the heat-resistant layer is 1µm thick, the phase change layer is 2.5µm thick, and the core layer is 6µm thick.

[0071] Comparative Example 1 This comparative example provides a BOPP capacitor film, comprising a heat-resistant layer, a phase change layer, a core layer, another phase change layer, and a heat-resistant layer sequentially disposed therefrom; the preparation method of each resin layer of the BOPP capacitor film in this comparative example includes the following steps: Preparation of heat-resistant layer resin: Please refer to Table 1. Take 1 wt% polypropylene graft (diallyl phthalate-co-glycidyl methacrylate) and 99 wt% homopolymer polypropylene and mix them evenly to obtain the heat-resistant layer resin.

[0072] Preparation of phase change layer resin: The components and contents of the phase change layer are the same as in Example 2, so they will not be described again.

[0073] Core layer resin preparation: The components and contents of the core layer are the same as in Example 1, so they will not be described again.

[0074] The preparation method of the BOPP capacitor film in this comparative example is the same as that in Example 1, so it will not be described again.

[0075] The total thickness of the film is 13µm, of which the heat-resistant layer is 1µm thick, the phase change layer is 2.5µm thick, and the core layer is 6µm thick.

[0076] Comparative Example 2 This comparative example provides a BOPP capacitor film, comprising a heat-resistant layer, a phase change layer, a core layer, another phase change layer, and a heat-resistant layer sequentially disposed therefrom; the preparation method of each resin layer of the BOPP capacitor film in this comparative example includes the following steps: Preparation of heat-resistant layer resin: Please refer to Table 1. Take 20 wt% polypropylene graft (diallyl phthalate-co-glycidyl methacrylate) and 80 wt% homopolymer polypropylene and mix them evenly to obtain the heat-resistant layer resin.

[0077] Preparation of phase change layer resin: The components and contents of the phase change layer are the same as in Example 2, so they will not be described again.

[0078] Core layer resin preparation: The components and contents of the core layer are the same as in Example 1, so they will not be described again.

[0079] The preparation method of the BOPP capacitor film in this comparative example is the same as that in Example 1, so it will not be described again.

[0080] The total thickness of the film is 13µm, of which the heat-resistant layer is 1µm thick, the phase change layer is 2.5µm thick, and the core layer is 6µm thick.

[0081] Comparative Example 3 This comparative example provides a BOPP capacitor film, comprising a heat-resistant layer, a phase change layer, a core layer, another phase change layer, and a heat-resistant layer sequentially disposed therefrom; the preparation method of each resin layer of the BOPP capacitor film in this comparative example includes the following steps: Preparation of heat-resistant layer resin: The components and contents of the heat-resistant layer are the same as in Example 2, so they will not be described again.

[0082] Phase change layer resin preparation: Please refer to Table 1. Mix 95wt% crosslinked SEBS and 5wt% spherical mesoporous silica evenly to obtain the phase change layer resin.

[0083] Core layer resin preparation: The components and contents of the core layer are the same as in Example 1, so they will not be described again.

[0084] The preparation method of the BOPP capacitor film in this comparative example is the same as that in Example 1, so it will not be described again.

[0085] The total thickness of the film is 13µm, of which the heat-resistant layer is 1µm thick, the phase change layer is 2.5µm thick, and the core layer is 6µm thick.

[0086] Comparative Example 4 This comparative example provides a BOPP capacitor film, comprising a heat-resistant layer, a phase change layer, a core layer, another phase change layer, and a heat-resistant layer sequentially disposed therefrom; the preparation method of each resin layer of the BOPP capacitor film in this comparative example includes the following steps: Preparation of heat-resistant layer resin: The components and contents of the heat-resistant layer are the same as in Example 2, so they will not be described again.

[0087] Preparation of phase change layer resin: Please refer to Table 1. Mix 45wt% crosslinked SEBS, 50wt% paraffin and 5wt% spherical mesoporous silica evenly to obtain phase change layer resin.

[0088] Core layer resin preparation: The components and contents of the core layer are the same as in Example 1, so they will not be described again.

[0089] The preparation method of the BOPP capacitor film in this comparative example is the same as that in Example 1, so it will not be described again.

[0090] The total thickness of the film is 13µm, of which the heat-resistant layer is 1µm thick, the phase change layer is 2.5µm thick, and the core layer is 6µm thick.

[0091] Comparative Example 5 This comparative example provides a BOPP capacitor film, comprising a heat-resistant layer, a phase change layer, a core layer, another phase change layer, and a heat-resistant layer sequentially disposed therefrom; the preparation method of each resin layer of the BOPP capacitor film in this comparative example includes the following steps: Preparation of heat-resistant layer resin: The components and contents of the heat-resistant layer are the same as in Example 2, so they will not be described again.

[0092] Preparation of phase change layer resin: Please refer to Table 1. Mix 15wt% crosslinked SEBS, 80wt% paraffin and 5wt% spherical mesoporous silica evenly to obtain phase change layer resin.

[0093] Core layer resin preparation: The components and contents of the core layer are the same as in Example 1, so they will not be described again.

[0094] The preparation method of the BOPP capacitor film in this comparative example is the same as that in Example 1, so it will not be described again.

[0095] The total thickness of the film is 13µm, of which the heat-resistant layer is 1µm thick, the phase change layer is 2.5µm thick, and the core layer is 6µm thick.

[0096] Comparative Example 6 This comparative example provides a BOPP capacitor film, comprising a heat-resistant layer, a phase change layer, a core layer, another phase change layer, and a heat-resistant layer sequentially disposed therefrom; the preparation method of each resin layer of the BOPP capacitor film in this comparative example includes the following steps: Preparation of heat-resistant layer resin: The components and contents of the heat-resistant layer are the same as in Example 2, so they will not be described again.

[0097] Preparation of phase change layer resin: Please refer to Table 1. Mix 30wt% crosslinked SEBS and 70wt% paraffin evenly to obtain phase change layer resin.

[0098] Core layer resin preparation: The components and contents of the core layer are the same as in Example 1, so they will not be described again.

[0099] The preparation method of the BOPP capacitor film in this comparative example is the same as that in Example 1, so it will not be described again.

[0100] The total thickness of the film is 13µm, of which the heat-resistant layer is 1µm thick, the phase change layer is 2.5µm thick, and the core layer is 6µm thick.

[0101] Comparative Example 7 This comparative example provides a BOPP capacitor film, comprising a heat-resistant layer, a phase change layer, a core layer, another phase change layer, and a heat-resistant layer sequentially disposed therefrom; the preparation method of each resin layer of the BOPP capacitor film in this comparative example includes the following steps: Preparation of heat-resistant layer resin: The components and contents of the heat-resistant layer are the same as in Example 2, so they will not be described again.

[0102] Preparation of phase change layer resin: Please refer to Table 1. Mix 25wt% crosslinked SEBS, 65wt% paraffin and 10wt% spherical mesoporous silica evenly to obtain phase change layer resin.

[0103] Core layer resin preparation: The components and contents of the core layer are the same as in Example 1, so they will not be described again.

[0104] The preparation method of the BOPP capacitor film in this comparative example is the same as that in Example 1, so it will not be described again.

[0105] The total thickness of the film is 13µm, of which the heat-resistant layer is 1µm thick, the phase change layer is 2.5µm thick, and the core layer is 6µm thick.

[0106] The performance test results of the BOPP capacitor films of Examples 1-3 and Comparative Examples 1-7 are shown in Table 2 below.

[0107] Table 2

[0108] As can be seen from the above performance test data, the BOPP capacitor films of Examples 1 to 3 have superior breakdown strength, latent heat of phase change and thermal management capabilities, and do not leak paraffin.

[0109] Comparative Examples 1 to 7 are all based on Example 2, so they are mainly compared with Example 2.

[0110] In Comparative Example 1, the BOPP capacitor film had too little polypropylene graft (dallyl phthalate-co-glycidyl methacrylate) content in the heat-resistant layer, and the DAP and GMA content introduced into the system was too low. Therefore, the improvement effect on heat resistance and dielectric properties was not significant. Thus, compared with Example 2, Comparative Example 1 showed a worse breakdown strength, a significantly reduced latent heat of phase change, and a worse thermal management capability.

[0111] In Comparative Example 2, the BOPP capacitor film has an excessive amount of polypropylene grafted (dallyl phthalate-co-glycidyl methacrylate) in the heat-resistant layer. The excessive dielyl structure of DAP will form a dense cross-linked network, which severely restricts the movement of PP molecular chains, resulting in poor system fluidity. Excessive PP-g-(DAP-co-GMA) cannot be completely compatible with the PP matrix and will agglomerate due to thermodynamic incompatibility.

[0112] Compared with the BOPP capacitor film of Comparative Example 3, no paraffin was added to the phase change layer. The BOPP capacitor film does not have the ability to store heat or regulate temperature, and exhibits the worst thermal management ability. The film is at a higher temperature, and the breakdown strength at 100°C is even worse.

[0113] Compared with Example 2, the BOPP capacitor film of Comparative Example 4 has too much cross-linked SEBS in the phase change layer and too little paraffin. The content of phase change material in the system is too low, the heat storage capacity of the material is insufficient, and the temperature regulation capacity is reduced. Overall, the performance of the BOPP capacitor film is worse than that of Example 2.

[0114] In Comparative Example 5, the BOPP capacitor film had too little cross-linked SEBS in the phase change layer, resulting in poor impact strength and low thermal management capability. Due to the increased paraffin content to 80wt% and the low cross-linked SEBS content, the excessive paraffin could not be bound in the spatial structure of SEBS, causing paraffin leakage to occur in the BOPP capacitor film at 120℃.

[0115] In Comparative Example 6, the BOPP capacitor film did not contain spherical mesoporous silica in the phase change layer, and the paraffin content was increased to 70 wt%. The BOPP capacitor film showed slight paraffin leakage at 120°C.

[0116] In Comparative Example 7, the BOPP capacitor film has an excessive amount of spherical mesoporous silica in the phase change layer. The spherical mesoporous silica has poor compatibility with SEBS and is prone to agglomeration, which will reduce the latent heat value of the phase change layer and weaken the thermal management capability.

[0117] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and the present invention also intends to include these modifications and variations.

Claims

1. A BOPP capacitive film characterized in that, The material comprises, in sequence, a heat-resistant layer, a phase change layer, a core layer, and another phase change layer; the heat-resistant layer comprises polypropylene and 3-15 wt% polypropylene grafted (dallyl phthalate-co-glycidyl methacrylate); the phase change layer comprises 25-35 wt% crosslinked styrene-ethylene / butene-styrene block copolymer, 58-72 wt% paraffin wax, and 3-7 wt% spherical mesoporous silica; the core layer comprises homopolymer polypropylene.

2. The BOPP capacitive film according to claim 1, characterized in that, The crosslinked styrene-ethylene / butene-styrene block copolymer is obtained by melt extrusion after crosslinking and blending styrene-ethylene / butene-styrene block copolymer with dicumyl peroxide.

3. The BOPP capacitor film according to claim 1, characterized in that, The polypropylene graft (dally propyl phthalate-co-glycidyl methacrylate) is prepared by melt grafting polypropylene with glycidyl methacrylate and diallyl phthalate in a molar ratio of 1:1.

5.

4. The BOPP capacitor film according to claim 1, characterized in that, The melting point of the paraffin is 75-90℃, the latent heat of phase transition is 230-260J / g, and the liquid density is 0.8-0.83g / cm 3 .

5. The BOPP capacitor film according to claim 2, characterized in that, The styrene-ethylene / butene-styrene block copolymer has a styrene content of 30-33 wt%, and the melt index of the styrene-ethylene / butene-styrene block copolymer was measured to be 5-10 g / 10 min at 230°C and 5 kg.

6. The BOPP capacitor film according to claim 1, characterized in that, The spherical mesoporous silica has a D50 of 0.5~1.0μm and a pore size of 5~20nm.

7. The BOPP capacitor film according to claim 1, characterized in that, The isotacticity of the homopolymer polypropylene is 97.5-98.5%, and the melt index of the homopolymer polypropylene measured at 230℃ and 2.16 kg is 3.0-4.0 g / 10 min.

8. The BOPP capacitor film according to claim 1, characterized in that, The total thickness of the BOPP capacitor film is 12~15μm, the thickness of the heat-resistant layer is 1~2.5μm, and the thickness of the phase change layer is 2~2.5μm.

9. A method for preparing a BOPP capacitor film as described in any one of claims 1 to 8, characterized in that, Includes the following steps: Ingredient preparation and plasticizing: The raw materials of each layer are conveyed to each extruder for melting and plasticizing according to the formula. The melt enters the die head through the flow channel and distributor. Cast sheet: After being extruded through the die, the molten material immediately contacts the cooling roller to form a thick sheet; Longitudinal stretching: The thick sheet is heated to a set temperature by a preheating roller and then longitudinally stretched, followed by shaping. The longitudinal stretching ratio is 4.5 to 5.5 times. Lateral stretching: After the longitudinally stretched sheet is preheated to the set temperature, lateral stretching begins. After lateral stretching, it undergoes shaping and cooling. The lateral stretching ratio is 6 to 8 times. Traction and winding: The multi-layered film after transverse stretching enters the traction unit, and after thickness measurement and corona treatment, it enters the winding unit to obtain the master roll; Slitting: The aging-treated master roll is slitted to obtain BOPP capacitor film rolls of specified width and length.

10. The method for preparing the BOPP capacitor film according to claim 9, characterized in that, The melt extrusion temperature of the heat-resistant layer is 200~260℃; the melt extrusion temperature of the phase change layer is 200~240℃; the melt extrusion temperature of the core layer is 230~260℃; in the process of melt contacting the cooling roller, the temperature of the quench water and the quench roller is 15~50℃; the longitudinal stretching temperature is 130~140℃; and the transverse stretching temperature is 155~165℃.

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