Multilayer high temperature dielectric film

Abstract

The multilayer dielectric film comprises a plurality of nanolayers, with at least one first-type layer comprising a conventional dielectric film and at least one second-type layer comprising a high thermal stability polymer. The layered film exhibits an improved storage modulus and a reduced loss factor at elevated temperatures. The at least one first-type layer and the at least one second-type layer have dielectric constants that differ by about 0.5 to about 1.5 times.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application is related to and claims priority to the following U.S. patent applications: This application claims priority to U.S. patent application Ser. No. 2018 / 430,123, filed February 1, 2024, which claims priority to U.S. provisional application Ser. No. 63 / 443,194, filed February 3, 2023. This application claims priority to U.S. provisional application Ser. No. 63 / 443,194, filed February 3, 2023. The entire disclosure of each of the above applications is incorporated herein by reference.

[0002] 1. FIELD OF THE INVENTION

[0003] The present invention relates to thin films for use as dielectrics in capacitors, and in particular to nano-layered dielectric thin films capable of operating at high temperatures with relatively low dielectric losses. [Background technology]

[0004] (2. Description of the Prior Art)

[0005] In the prior art, it is generally known to provide thin films that function as dielectrics for capacitors, including materials such as polyethylene terephthalate (PET), polypropylene (PP), biaxially oriented polypropylene (BOPP), polyethylene naphthalate (PEN), polyphenylene sulfide (PPS), polytetrafluoroethylene (PTFE), polystyrene (PS), polycarbonate (PC), and the like.

[0006] Prior art patent documents include:

[0007] U.S. Patent No. 8,866,018, "Passive electrical devices and methods of fabricating passive electrical devices," filed January 12, 2009, and issued October 21, 2014, to inventors Pramanik et al., discloses a thin laminate passive electronic device, such as a capacitor, and a method for fabricating the same. The passive electronic device includes two conductors, such as copper foil conductors, separated by a dielectric having a first layer of a first material having a softening point temperature higher than a first temperature and a first layer of a second material having a softening point temperature lower than the first temperature. The first temperature can be at least 150°C or higher. The provision of the first layer having the higher softening point material prevents short circuits between the conductors that may be promoted during the fabrication process. A method for fabricating the passive electronic device is also disclosed.

[0008] U.S. Patent No. 6,594,134, "Polymer film capacitor," filed February 21, 2001, and issued July 15, 2003, to inventor Yializis, discloses a polymer film capacitor using a metallized film formed by a vacuum-formed plasma-treated first surface, a vacuum-deposited radiation-polymerized first acrylate monomer film having a first surface and a second surface, the first surface disposed on the first plasma-treated surface of a polymer substrate, and a metal layer disposed on the second surface of the first polymerized film. The metallized film is wound into a capacitor.

[0009] U.S. Patent Publication No. 2007 / 0108490, "Film capacitors with improved dielectric properties," filed November 14, 2005, and published May 17, 2007, by inventors Tan et al., discloses a film capacitor including a first electrode. The film capacitor also includes a first dielectric layer having a first dielectric constant disposed on the first electrode, and a second dielectric layer having a second dielectric constant disposed on the first dielectric layer, the second dielectric constant being at least 50% higher than the first dielectric constant. It further includes a second electrode disposed on the second dielectric layer.

[0010] U.S. Patent Publication No. 2021 / 0291499, "Multicomponent layered dielectric film with surface modification," filed July 18, 2019, and published September 23, 2021, by inventors Langhe et al., discloses a multicomponent dielectric film including overlapping dielectric layers and an outer layer having a higher surface energy than the overlapping dielectric layers, the overlapping dielectric layers including at least a first polymer material, a second polymer material, and optionally a third polymer material, adjacent dielectric layers defining generally planar interfaces generally located in the xy plane of an xyz coordinate system, and the interfaces between the layers delocalize charge accumulation within the layers.

[0011] U.S. Patent No. 10,614,958, "Multilayer polymer dielectric film," filed August 30, 2018, and issued April 7, 2020, by inventors Baer et al., discloses a multilayer polymer dielectric film that receives electrical charge and includes a stack of coextruded alternating first and second dielectric layers. The first dielectric layer includes a first polymer material, and the second dielectric layer includes a second polymer material that is different from the first polymer material. The first polymer material has a higher dielectric constant than the second polymer material. The second polymer material has a higher dielectric breakdown strength than the first polymer material. Adjacent first and second dielectric layers define an interface between the layers that delocalizes charge accumulation in the layers. The stack has substantial crystallographic symmetry before and during charge reception.

[0012] U.S. Patent No. 8,611,068, "Multilayer polymer dialectric film having a charge-delocalizing interface," filed October 16, 2009, and issued December 17, 2013, inventors Baer et al., discloses a multilayer polymer dielectric film including coextruded first and second dielectric layers. The first dielectric layer includes a first polymer material, and the second dielectric layer includes a second polymer material. The first and second dielectric layers define an interface that delocalizes charge within the layers.

[0013] U.S. Patent No. 9,558,888, "Multilayer polymer film having a charge-delocalizing interface," filed November 18, 2013, and issued January 31, 2017, by inventors Baer et al., discloses a multilayer polymer dielectric film including a stack of coextruded alternating first and second dielectric layers that receives electrical charge. The first dielectric layer includes a first polymer material, and the second dielectric layer includes a second polymer material that is different from the first polymer material. The first polymer material has a higher dielectric constant than the second polymer material. The second polymer material has a higher dielectric breakdown strength than the first polymer material. Adjacent first and second dielectric layers define an interface that delocalizes charge accumulation between the layers. The stack has substantial crystallographic symmetry before and during charge reception.

[0014] U.S. Patent No. 10,068,706, "Multilayer polymer dielectric film," filed January 11, 2017, and issued September 4, 2018, by inventors Baer et al., discloses a multilayer polymer dielectric film including a stack of coextruded alternating first and second dielectric layers that receives an electric charge. The first dielectric layer includes a first polymer material, and the second dielectric layer includes a second polymer material that is different from the first polymer material. The first polymer material has a higher dielectric constant than the second polymer material. The second polymer material has a higher dielectric breakdown strength than the first polymer material. Adjacent first and second dielectric layers define an interface between the layers that delocalizes charge accumulation in the layers. The stack has substantial crystallographic symmetry before and during charge reception.

[0015] U.S. Patent No. 10,759,139, "Multicomponent layered dielectric film and uses thereof," filed December 4, 2015, and issued September 1, 2020, to inventor Ponting, discloses a multicomponent dielectric film including separate, overlapping dielectric layers of at least a first polymer material, a second polymer material, and a third polymer material. Adjacent dielectric layers define generally planar interfaces that lie generally in the xy plane of an xyz coordinate system. The interfaces between the layers delocalize charge accumulation within the layers. At least one dielectric layer includes a stack of separate polymer layers, with the polymer layer interfaces extending transversely to the xy plane, and optionally at least one filler having a higher dielectric constant than the first, second, and / or third polymer materials.

[0016] U.S. Patent Publication No. 2021 / 0079179, "Film Capacitor," filed May 15, 2018, and published March 18, 2021, by inventors Alba et al., discloses a film capacitor. In one embodiment, the film capacitor includes a film comprising a blend of polypropylene and a cycloolefin copolymer, where the blend includes at least two-thirds by weight of polypropylene, and the cycloolefin copolymer includes 23% to 27% by weight of ethylene and 73% to 77% by weight of norbornene. Summary of the Invention

[0017] The present invention relates to thin films for use as dielectrics in capacitors, and in particular to nano-layered dielectric thin films capable of operating at high temperatures with relatively low dielectric losses.

[0018] It is an object of the present invention to provide a dielectric thin film that maintains a low dielectric loss tangent and a relatively high storage modulus at high temperatures, such as temperatures above about 100°C.

[0019] In one embodiment, the present invention relates to a high temperature performance dielectric film comprising coextruded layers including a plurality of A layers and a plurality of B layers, wherein the plurality of A layers comprise at least one high temperature polymer, the at least one high temperature polymer being a polymer having a glass transition temperature greater than 125°C or a melting point greater than 200°C, and the plurality of A layers having a dielectric constant 0.5 to 1.5 times higher than the plurality of B layers.

[0020] In another embodiment, the present invention relates to a high temperature performance dielectric film, comprising a coextruded plurality of layers including a plurality of A layers and a plurality of B layers, wherein the plurality of A layers comprise at least one high temperature polymer, the at least one high temperature polymer being a polymer having a glass transition temperature greater than 125°C or a melting point greater than 200°C, and the plurality of A layers consists of about 10% cyclic olefin copolymer and about 90% polypropylene.

[0021] In yet another embodiment, the present invention relates to a high temperature performance dielectric film comprising a coextruded and extrusion-stretched multi-layer structure comprising a plurality of A layers and a plurality of B layers, wherein the A layers have a dielectric constant that is 0.5 to 1.5 times higher than that of the B layers, at least one layer of the coextruded and / or extrusion-stretched multi-layer structure has a thickness of less than 150 nm, and the film has a total thickness of about 3 μm to about 15 μm.

[0022] These and other aspects of the present invention will become apparent to those skilled in the art after reading the following description of the preferred embodiments in light of the drawings supporting the claimed invention. [Brief explanation of the drawings]

[0023] [Figure 1] 1 shows a graph comparing the storage modulus of polyphenylsulfone (PPS) and a layered polymer structure of PPS and polysulfone (PSU) at different temperatures according to one embodiment of the present invention. [Figure 2]1 shows a graph comparing the storage modulus of polypropylene (PP) and a layered polymer structure of PP and cyclic olefin copolymer (COC) at different temperatures according to one embodiment of the present invention. [Figure 3] 1 shows a graph comparing the dielectric loss tangent of polyphenylsulfone (PPS) and a layered polymer structure of PPS and polysulfone (PSU) at different temperatures according to one embodiment of the present invention. [Figure 4] 1 shows a graph comparing the dielectric loss tangent of biaxially oriented polypropylene (BOPP) and a layered polymer structure of PP and cyclic olefin copolymer (COC) at different temperatures according to one embodiment of the present invention. [Figure 5] 1 shows a graph of experimental results showing the relative dielectric loss tangent at 1 kHz for several film materials at different temperatures. [Figure 6] 1 shows an experimental graph showing the relative dielectric loss tangent at 10 kHz for several film materials at different temperatures. [Figure 7] 1 shows an experimental graph showing the relative dielectric loss tangent at 1 kHz and different temperatures for several different film materials. [Figure 8] 1 shows an experimental graph showing the relative dielectric loss tangent at 10 kHz and different temperatures for several different film materials. [Figure 9] 1 shows an experimental graph illustrating storage modulus at different temperatures for several film materials. [Figure 10] 1 shows an experimental graph illustrating storage modulus at different temperatures for several different film materials. [Figure 11] 1 shows an experimental bar graph comparison of the temperatures at which storage moduli were 50% and 10% of the initial test value for several film materials. [Figure 12] 1 shows an experimental bar graph comparison of the temperatures at which storage moduli were 50% and 10% of the initial test value for several different film materials. [Figure 13]1 shows an experimental results graph showing a comparison of the relative dielectric loss tangent at 1 kHz at different temperatures for pure polyphenylene sulfide (PPS) film and layered PPS-polysulfone (PSU) film. [Figure 14] 1 shows an experimental results graph illustrating a comparison of storage modulus at different temperatures for pure polyphenylene sulfide (PPS) film and layered PPS-polysulfone (PSU) film. [Figure 15] 1 shows an experimental results graph comparing the storage modulus of pure polyphenylene sulfide (PPS) film and layered PPS-polysulfone (PSU) film at multiple film material temperatures at 50% and 10% of the initial test value. [Figure 16] 1 shows a graph of experimental results illustrating the relative percentage breakdown field strength at different temperatures for several film materials. [Figure 17] 1 shows a graph of experimental results illustrating the relative percentage breakdown field strength at different temperatures for several different film materials. DETAILED DESCRIPTION OF THE INVENTION

[0024] The present invention relates to thin films for use as dielectrics in capacitors, and in particular to nano-layered dielectric thin films capable of operating at high temperatures with relatively low dielectric losses.

[0025] In one embodiment, the present invention relates to a high temperature performance dielectric film comprising coextruded layers including a plurality of A layers and a plurality of B layers, wherein the plurality of A layers comprise at least one high temperature polymer, the at least one high temperature polymer being a polymer having a glass transition temperature greater than 125°C or a melting point greater than 200°C, and the plurality of A layers having a dielectric constant 0.5 to 1.5 times higher than the plurality of B layers.

[0026] In another embodiment, the present invention relates to a high temperature performance dielectric film comprising coextruded layers including a plurality of A layers and a plurality of B layers, wherein the plurality of A layers comprise at least one high temperature polymer, the at least one high temperature polymer being a polymer having a glass transition temperature greater than 125°C or a melting point greater than 200°C, and the plurality of A layers consisting of about 10% cyclic olefin copolymer and about 90% polypropylene.

[0027] In yet another embodiment, the present invention relates to a high temperature performance dielectric film comprising a coextruded and post-extrusion stretched plurality of layers including a plurality of A layers and a plurality of B layers, wherein the plurality of A layers have a dielectric constant that is 0.5 to 1.5 times higher than the plurality of B layers, at least one layer of the coextruded and / or post-extrusion stretched plurality of layers has a thickness of less than 150 nm, and the film has a total thickness of about 3 μm to about 15 μm.

[0028] Thin-film capacitors are some of the most widely used capacitors today and offer particular advantages when used in high-frequency applications compared to other types of capacitors (e.g., supercapacitors, ceramic capacitors, etc.). They also tend to offer excellent long-term and high-temperature stability. However, while thin-film capacitors are known for their high-temperature stability, the limitations of these capacitors are being stretched by the need for new high-temperature applications, particularly in electric vehicle (EV) applications, oil and gas pipelines, and solar cell applications. These issues stem from the relaxation of polymer chains at high temperatures, resulting in a loss of dielectric properties through changes such as glass transitions or crystalline melting, and at even higher temperatures, the polymer layer often melts or deforms. As these high-temperature applications, such as EVs, become more prominent, improved thin-film materials are needed that operate with low losses at higher operating temperatures, enabling, for example, charging and discharging at higher frequencies than previously possible.

[0029] Currently, the materials used as dielectrics in thin-film capacitors are relatively limited. Five polymers dominate the market: polypropylene (PP) (including biaxially oriented PP, or BOPP), polyethylene terephthalate (PET) (including biaxially oriented PET, or BOPET), polyethylene naphthalate (PEN), polyphenylene sulfide (PPS), and polytetrafluoroethylene (PTFE), with PP and PET alone accounting for nearly 90% of the market share. Additionally, polystyrene (PS), polycarbonate (PC), and paper are occasionally used, though they are largely obsolete. However, polymers other than these are quite rare in the industry, and the focus is generally on the dielectric constant of the polymer.

[0030] Some prior art inventions apply nanolayered polymer mixes for thin-film capacitor applications. The central focus of prior art inventions, such as U.S. Pat. No. 10,759,139, is maximizing the electrical properties of the layered structure, such as energy density, breakdown strength, or dielectric constant, and maximizing the dielectric properties of the entire film at normal operating temperatures. For example, the '139 patent proposes optimizing one polymer in the layered structure for energy density while optimizing the other for breakdown strength, and also proposes varying the thickness and number of layers to maximize breakdown strength or energy density. U.S. Pat. No. 10,614,958 similarly attempts to maximize energy density by alternating layers with high and low dielectric constants (e.g., dielectric and insulating layers) and connecting the two layer types with tie layers. The '958 patent recognizes that the maximum energy density is proportional to the product of the effective dielectric constant and the square of the breakdown strength, allowing the entire system to have a higher energy density than either pure component. U.S. Patent No. 10,068,706 provides a system similar to that of the '958 patent, emphasizing the possibility of delocalization of charge storage due to adjacent layers having substantially different dielectric breakdown strengths. It is noteworthy that all of these prior art documents attempt to maximize energy density and other electrical properties, but do not provide for improving the high-temperature stability of the capacitor. Furthermore, while there are currently commercially available capacitors capable of high-temperature operation, these capacitors do not function properly, are impractical, or even usable, for high-frequency charge-discharge applications at these temperatures because the losses are too high or the breakdown strength is too low at these temperatures. Instead, these existing high-temperature capacitors are generally only usable for pulsed power or very low-frequency charge-discharge applications.

[0031] Referring now generally to the drawings, the illustrations are for purposes of illustrating one or more preferred embodiments of the present invention and are not intended to limit the invention thereto.

[0032] The present invention relates to a multilayer dielectric film for thin-film capacitor applications. The multilayer dielectric film includes multiple individual polymer layers. In one embodiment, the multiple individual polymer layers include one or more first-type layers, referred to herein as A layers, and one or more second-type layers, referred to herein as B layers. Those skilled in the art will understand that the multiple individual polymer layers are not limited to two types of layers, but can include any number of types (e.g., three types, four types, etc.). The layer types referred to herein describe layers made of substantially similar materials in substantially similar proportions, containing substantially similar additives, and having substantially similar thicknesses. By way of example and not limitation, an A layer is defined as comprising 10% by volume of cyclic olefin copolymer (COC) and 90% by volume of polypropylene (PP) and having a thickness of approximately 75 nm. In this embodiment, a layer made of pure polypropylene, for example, would not constitute an A layer but would constitute a second-type layer (i.e., a B layer).

[0033] In one embodiment, the layers of the multilayer dielectric film are arranged in a simple colloquial pattern (i.e., ABABABA, etc.). In another embodiment, the layers of the multilayer dielectric film are arranged in a double alternating pattern (i.e., ABBABBA, AABAABAA, etc.). In yet another embodiment, the layers of the multilayer dielectric film are arranged in a complex pattern (e.g., ABBABAABABBABAAB, etc.). In yet another embodiment, the layers of the multilayer dielectric film are not arranged in any repeating pattern.

[0034] In one embodiment, the layers are stacked as substantially parallel planar sheets, such that the interfaces between the layers lie approximately along the xy plane of an xyz coordinate system, while the layers of the multilayer dielectric film vary in depth along the z axis. Therefore, the thickness of each layer can be defined as the length of each layer in the z direction. Therefore, the total thickness of the entire multilayer dielectric film can be defined as the sum of the thicknesses of each individual layer. Those skilled in the art will appreciate that the length and width of the multilayer thin film along the x and y axes, respectively, are not intended to be limiting, and that the length and width of the multilayer thin film can be adapted to the size of the thin film capacitor required for the intended application. In one embodiment, each of the multiple layers has approximately the same thickness, while in another embodiment, the multiple layers include layer types with different thicknesses.

[0035] In one embodiment, the layers of the multilayer dielectric film are not bonded together by at least one tie layer. A tie layer is generally defined as a thin thermoplastic coating used as a melt-bondable surface for bonding adjacent layers. While tie layers are primarily concerned with maintaining the structural integrity of the layered structure, they typically degrade performance and, at least to some extent, reduce the overall volume occupied by the relevant polymer (i.e., the dielectric polymer or high-temperature polymer described herein) for its intended purpose. Prior art inventions, such as those described in U.S. Pat. No. 10,614,958, often require tie layers to create a stable layered structure. In one embodiment, the layers are each bonded together by at least one tie layer.

[0036] In one embodiment, a multilayer dielectric film is formed by coextrusion of a first polymer mix, a second polymer mix, and / or an additional polymer mix to form a first layer, a second layer, and / or an additional layer, respectively. In one embodiment, the first polymer mix, the second polymer mix, and / or the additional polymer mix are substantially incompatible, resulting in the formation of distinct, separate layers upon extrusion. Advantageously, the incompatibility of the polymer layers reduces energy losses across polymer phase boundaries within the film, enabling improved capacitor performance. In one embodiment, the coextruded layers are vertically multiplied by vertically cutting the flow with a first multiplier die, and the separated stacks are vertically stacked to form a vertically layered structure with twice the number of layers, as described, for example, in U.S. Patent Publications 2013 / 0194677 and 2017 / 0197348, each of which is incorporated herein by reference in its entirety. In one embodiment, the vertical layer multiplexing is repeated multiple times (e.g., two, four, eight, 32, etc.) to achieve the desired number of layers. Those skilled in the art will appreciate that the vertical layer multiplexing process doubles the number of horizontal layers, resulting in a layer count of 2n+1, where n represents the number of multiplexing steps. Thus, even a nine-multiplier die can produce structures with thousands of layers. By varying the volumetric flow rate of the polymer layers through the die, the thickness of the layers and the overall film thickness can be more precisely controlled. In one embodiment, after layer multiplexing is complete, at least one skin layer is extruded or otherwise disposed on the top and / or bottom surfaces of the layered structure. In one embodiment, the at least one skin layer comprises at least one metallized layer. In one embodiment, layers are simultaneously fabricated in a single multi-channel feedblock die, producing tens, hundreds, or thousands of layers without subsequent multiplexing.

[0037] In one embodiment of the present invention, a melt containing a high thermal stability polymer is co-extruded to form a layer containing a high thermal stability polymer. Similarly, a melt containing a dielectric polymer film is co-extruded to form a layer containing a dielectric polymer. Thus, in this embodiment, the high thermal stability polymer and the dielectric polymer are included in the co-extrusion process itself, rather than by post-treatment or inclusion. Alternatively, in another embodiment, the high thermal stability polymer and / or the dielectric polymer are included in one or more co-extruded layers after the co-extrusion layers are formed.

[0038] The multilayer dielectric films of the present invention are not limited to being formed by the above-described cast coextrusion method. In another embodiment, the multilayer dielectric films are formed by blow coextrusion, three-dimensional (3D) printing, lamination, spin coating, vapor deposition, and / or extrusion coating methods.

[0039] In one embodiment, at least one A layer of the multilayer dielectric film comprises at least one dielectric polymer film. Examples of dielectric polymers include, but are not limited to, polypropylene (PP) (including biaxially oriented PP, or BOPP), polyethylene terephthalate (PET) (including biaxially oriented PET, BOPET), polyethylene naphthalate (PEN), polyphenylene sulfide (PPS), polytetrafluoroethylene (PTFE), polystyrene (PS), acrylic, polyethylene (PE), polybutene, poly(propylene oxide), poly(ethyleneimine), thioalkane, polyvinyl alcohol (PVA), poly(vinylidene carbonate), polyacrylonitrile, polyvinyl sulfone, poly(p-phenylene terephthalamide), poly(vinylpyrrolidone), polyethylene-norbornene copolymers (e.g., TOPAS COC copolymer, ZEONOR, etc.), polyimide, and polycarbonate (PC). In a preferred embodiment, at least one A layer comprises polypropylene (PP) (e.g., BOPP) and / or polyethylene terephthalate (PET). In one embodiment, at least one B layer of the multilayer dielectric film comprises at least one high thermal stability polymer. For purposes of this application, a high thermal stability polymer is a polymer having a glass transition temperature above about 125°C or a melting point above about 200°C. In one embodiment, the at least one high thermal stability polymer comprises a polymer having a relatively low dielectric constant (and therefore not traditionally used as a dielectric). Examples of high thermal stability polymers include, but are not limited to, polyimide, polysulfone (PSU), polyethylene naphthalate (PEN), polyetherimide (PEI), polyetheretherketone (PEEK), polyphenylsulfone, cyclic olefin copolymer (COC), at least one high temperature fluorine-based polymer (e.g., polychlorotrifluoroethylene (PCTFE), ethylene chlorotrifluoroethylene (ECTFE), etc.), at least one liquid crystal polymer, borosilicate, polynorbornene, or any polymer containing these polymers as a copolymer.In one embodiment, at least one dielectric film is blended with a dielectric constant enhancing additive comprising barium titanate and / or carbon nanotubes. In one embodiment, both the at least one A layer and the at least one B layer comprise the same or different proportions of at least one dielectric polymer and / or at least one high thermal stability polymer.

[0040] In one embodiment, the present invention includes a film comprising about 10% to about 30% by volume of COC and about 70% to about 90% by volume of PP, while in a more specific embodiment, the present invention includes a film comprising about 10% by volume of COC and about 90% by volume of PP. In one embodiment, the present invention includes a film comprising about 50% by volume of PPS and about 50% by volume of PSU. In one embodiment, the present invention includes a film comprising about 10% by volume to about 30% by volume of PC and about 70% to about 90% by volume of PP, while in a more specific embodiment, the present invention includes a film comprising about 10% by volume of PC and about 90% by volume of PP.

[0041] In one embodiment, the multilayer dielectric film is stretched in at least one direction (i.e., uniaxially stretched, biaxially stretched, etc.). In one embodiment, the biaxial stretching process can produce a film that is about 5 to about 50 times thinner than before the stretching process began. In one embodiment, the stretching in at least one direction is substantially parallel to the surface of the multilayer dielectric film and at a rate effective to improve the dielectric breakdown strength of the film. In one embodiment, biaxial stretching of the film improves the dielectric breakdown strength of the film by about 20%.

[0042] In one embodiment, each layer of the multilayer dielectric film has a dielectric constant ratio of about 0.5 to about 1.5 times that of the adjacent layer. This contrasts significantly with prior art, including U.S. Patent Nos. 10,759,139 and 10,614,958, which assume a large dielectric constant contrast between layers to maximize energy density. However, the layer types of multilayer dielectric films differ significantly with respect to other properties, such as storage modulus, glass transition temperature, and melting point. In one embodiment, the combination of dielectric material layers and high thermal stability layers provides a multilayer dielectric film that exhibits a dielectric loss below a threshold of 0.5% at temperatures 10 to 15°C higher than conventional dielectric films (e.g., pure PPS or pure PP films). In one embodiment, the multilayer dielectric film experiences a storage modulus degradation of about 50% relative to the room temperature storage modulus at temperatures 10 to 15°C higher than the temperature at which a homogeneous film experiences a storage modulus degradation of about 50% relative to the room temperature storage modulus of a homogeneous film. The homogeneous film consists essentially of the polymer used in at least one A layer of the multilayer dielectric film. In one embodiment, the multilayer dielectric film has a higher dielectric breakdown strength than at least one of the constituent materials.

[0043] In one embodiment, each layer of the multilayer dielectric film has a thickness of less than 1 micron. In one embodiment, the multilayer dielectric film has a thickness of about 1 μm to about 50 μm. In one embodiment, the total thickness of the multilayer dielectric film is about 3 μm to about 15 μm (more specifically, about 12 μm to about 15 μm). In one embodiment, each layer has a thickness of less than about 1.2 μm. In a preferred embodiment, each layer has a thickness of about 150 nm to about 400 nm. In another embodiment, at least one layer has a thickness of less than about 150 nm. Those skilled in the art will understand that each layer need not have the same thickness within a given range (i.e., within the 150-400 nm range, one layer type has a thickness of about 200 nm and another layer type has a thickness of about 300 nm).

[0044] Those skilled in the art will appreciate that films made in accordance with the present invention can be used in a variety of capacitor configurations, including metallized film capacitors and film / foil capacitors.

[0045] Evaluation experiments were conducted on two different embodiments of the present invention: one layered structure of about 50% by volume PPS and about 50% by volume PSU, and a second layered structure of about 10% by volume COC and about 90% by volume PP. These layered polymers were compared to homogenous films containing only the constituent dielectric film materials (i.e., PPS and PP, respectively). The results of these experiments are shown in the graphs in Figures 1-4.

[0046] Figure 1 shows a graph comparing the storage modulus of polyphenylsulfide (PPS) and layered polymer structures of PPS and polysulfone (PSU) at different temperatures according to one embodiment of the present invention. As shown in Figure 1, the homogeneous PPS film exhibited a high storage modulus at low temperatures, but dropped off sharply around 100°C. On the other hand, the layered PPS / PSU material had a relatively low storage modulus at low temperatures, but maintained a consistent storage modulus up to about 165°C. Up to that point, the storage modulus remained above about 1000 MPa. In one embodiment, PSU, the high thermal stability polymer used in the present invention, has a glass transition temperature of about 180°C.

[0047] FIG. 2 shows a graph comparing the storage modulus of layered polymer structures of polypropylene (PP) and PP with cyclic olefin copolymer (COC) at different temperatures according to one embodiment of the present invention. In one embodiment, COC, the high-thermal stability polymer used in the present invention, has a glass transition temperature of about 180°C (substantially equivalent to that of PSU). In one embodiment, COC, when used as the high-thermal stability polymer in the present invention, has a glass transition temperature greater than about 120°C. Alternatively, a layered film having 10% by volume COC and 90% by volume PP exhibits a higher storage modulus at all test temperatures and does not exhibit significant mechanical degradation or strength loss up to about 160°C. In one embodiment, the present invention includes a film having about 10% by volume to about 30% by volume COC and about 70% by volume to about 90% by volume PP, and in a more specific embodiment, a film comprising about 10% by volume COC and about 90% by volume PP.

[0048] Figure 3 shows a graph comparing the dielectric loss tangent of polyphenylsulfide (PPS) and a layered polymer structure of PPS and polysulfone (PSU) at different temperatures, according to one embodiment of the present invention. As shown in Figure 3, the homogeneous PPS film exhibits a large increase in the dielectric loss tangent between about 100°C and about 140°C, while the layered polymer maintains a low dielectric loss tangent throughout this range, resulting in a significant increase in efficiency at higher temperatures.

[0049] Figure 4 shows a graph comparing the dielectric loss tangent of biaxially oriented polypropylene (BOPP) and a layered polymer structure of PP and cyclic olefin copolymer (COC) at different temperatures, according to one embodiment of the present invention. Figure 4 shows that the layered film exhibits a lower dielectric loss tangent than the homogeneous BOPP film over almost the entire temperature range, particularly around 90°C. Furthermore, while the BOPP film completely collapsed above 130°C, the layered polymer does not exhibit a sharp increase in dielectric loss tangent until about 160°C.

[0050] Table 1 below compares the dissipation factor for each test polymer at three different temperatures. As the graph shows, with the exception of the PPS film and layered PPS / PSU film, which were compared at low temperatures, the layered polymers exhibited lower dissipation factors, i.e., lower power losses. For the homogeneous BOPP, the dissipation factor at 160°C could not be measured because the film had completely destroyed, but the layered polymers continued to function.

[0051] [Table 1]

[0052] With respect to Figures 5 through 17 described below, the following polymer samples were used to compare relative dielectric loss tangent at different temperatures and frequencies, storage modulus at different temperatures, and breakdown field strength at different temperatures.

[0053] Example 1 (biaxial 10% COC / PP)

[0054] Example 1 was a film containing 10% by volume of cyclic olefin copolymer (COC) and 90% by volume of polypropylene (PP). The film of Example 1 contained 33 layers made by coextrusion of alternating nanolayered sheets of PP and COC with a melt flow rate (MFR) of 3 in a cast film process, with the COC having a glass transition temperature of 158°C. The extruded film was biaxially stretched 5 times in the machine direction (MD) and 8 times in the transverse direction (TD) at a temperature above the glass transition temperature of the COC.

[0055] Example 2 (10% PC / 90% PP 129 layers)

[0056] Example 2 was a film containing 10% by volume polycarbonate (PC) and 90% by volume PP. The film of Example 2 contained 129 layers made by co-extruding alternating nano-layered sheets of PP and PC at 3 melt flow rates (MFR) in a cast film process, with the PC having a glass transition temperature of 165°C.

[0057] Example 3 (50% PPS / PSU 33 layers)

[0058] Example 3 was a film containing 50% by volume of polyphenylene sulfide (PPS) and 50% by volume of polysulfone (PSU). The film of Example 3 contained 33 layers made by coextrusion of alternating nanolayered sheets of PPS and PSU at 3 melt flow rates (MFR) in a cast film process. The PSU had a glass transition temperature of 185-190°C, and the PPS grade had a melting point of 280°C and a glass transition temperature of 90°C.

[0059] Comparative example 1 (BOPP)

[0060] The sample of Comparative Example 1 was a commercially available biaxially stretched PP film.

[0061] Comparative Example 2 (100% PP extrusion)

[0062] The sample of Comparative Example 2 was a single layer dielectric film extruded from a 3MFR polypropylene (PP) grade using a cast film process.

[0063] Comparative Example 3 (10% COC / 90% PP blend)

[0064] The sample of Comparative Example 3 was a monolayer dielectric film that was dry blended with 3MF RPP grade and COC and extruded by a cast film process, with the COC having a glass transition temperature of 158° C. The blend contained 10% by volume of COC and 90% by volume of PP.

[0065] Comparative Example 4 (10% PC / 90% PP Blend)

[0066] The sample of Comparative Example 4 was a single-layer dielectric film extruded by a cast film process, dry blending 3MF RPP grade and PC, the latter having a glass transition temperature of 165° C. The blends each contained 10% by volume of PC and 90% by volume of PP.

[0067] Comparative example 5 (100%PPS)

[0068] The sample of Comparative Example 5 was a single layer dielectric film extruded from PPS using a cast film process. The PPS grade used had a melting point of 280°C and a glass transition temperature of 90°C.

[0069] To compare the samples, three different tests were performed. First, the film samples were subjected to dielectric breakdown strength testing in a silicone oil medium under a direct current (DC) electric field at a ramp rate of 500 V / s under increasing temperature conditions, according to ASTM D149. Next, the film samples were subjected to dynamic mechanical analysis (DMA) in tensile mode at 5°C / min, 1 Hz, and 0.1% strain from room temperature to 200°C. Finally, broadband dielectric spectroscopy (BDS) measurements were performed to evaluate the frequency- and temperature-dependent dielectric behavior of the materials. Each sample was sputter-coated with gold electrodes approximately 1 cm in diameter and 20 nm thick on both sides prior to testing. The temperature was varied from room temperature to 180°C in 20°C increments. At each temperature, the frequency was varied from 100 Hz to 100 kHz.

[0070] Figure 5 is a graph of experimental results showing the relative dielectric loss tangents at different temperatures at 1 kHz for several film materials. The relative dielectric loss tangents shown in the results in Figure 5 are measured as a percentage of the dielectric loss tangents exhibited at room temperature. Figure 5 shows that the layered example film (in this example, 33 layers of COC and PP) exhibited relatively low or even reduced dielectric loss tangents in the temperature range of 100-150°C, while the simple biaxially oriented (and unoriented) polypropylene and the comparative example, which simply blended the constituent polymer sample volumes, exhibited higher peaks than the baseline in this temperature range. This demonstrates the inherent improvement effect of layer orientation in addition to layer structuring.

[0071] Figure 6 is a graph of experimental results showing the relative dielectric loss tangents at different temperatures at 10 kHz for several film materials. Even at high frequencies, the experimental layered films showed reduced dielectric loss tangents above approximately 60°C compared to the homogeneous polypropylene and non-layered COC / PP blend samples. Furthermore, while the non-layered BOPP samples showed similar dielectric loss tangents between approximately 140 and 150°C, the experimental films showed significantly reduced dielectric loss tangents between 60 and 140°C.

[0072] Figure 7 is a graph of experimental results showing the relative dielectric loss tangents at different temperatures at 1 kHz for several different film materials. Compared to a simple polypropylene film, the experimental 129-layer PC / PP film exhibited a reduction in dielectric loss tangent at temperatures above approximately 120°C, demonstrating properties comparable to a non-layered blend using the same polymer ratio. The experimental film exhibited a higher dielectric loss tangent than the BOPP film in the temperature range of approximately 80–140°C, but the experimental film exhibited a significant reduction in dielectric loss tangent at temperatures above 140°C.

[0073] Figure 8 shows experimental results of the relative dielectric loss tangent at different temperatures at 10 kHz for several different film materials. For the 129-layer PC / PP film, the same behavior at 10 kHz as at 1 kHz was observed for the comparative sample.

[0074] Figure 9 is a graph of experimental results showing the storage modulus at different temperatures for several film materials. The experimental 33-layer COC / PP film showed an improvement in storage modulus over each of the comparative films tested at almost all temperatures, especially at higher temperatures, with the decrease in storage modulus occurring at higher temperatures (at about 160°C and disappearing at about 170°C) compared to the best-performing comparative sample (BOPP, which decreased at about 150°C and disappeared at about 165°C).

[0075] Figure 10 is a graph of experimental results showing the storage modulus at different temperatures for several different film materials. The experimental 129-layer PC / PP film also showed an improvement in storage modulus over all comparative samples at higher temperatures, i.e., above approximately 130°C. However, the layered film showed a significant improvement in storage modulus over the entire temperature range compared to the non-layered blend sample, demonstrating the inherent advantages of nanolayering.

[0076] Figure 11 shows an experimental bar graph comparison of the temperatures at which storage modulus values ​​reached 50% and 10% of the initial test value for several film materials. The results of the storage modulus graphs above can be easily visualized by the bar graph shown in Figure 11, which shows that the temperature at which the storage modulus reached half of the room temperature value was significantly elevated for the BOPP film, especially for the non-layered blend samples. Furthermore, the temperature at which the experimental films reached a storage modulus of only 10% of the room temperature value also showed a significant increase relative to the non-layered blends.

[0077] Figure 12 shows an experimental bar graph comparison of the temperatures at which 50% and 10% storage modulus values ​​were observed relative to the initial test value for several different film materials. The experimental 129-layer PC / PP film also showed a significant increase in the temperature at which the 10% storage modulus value was observed relative to all other samples, particularly the BOPP film. The 50% modulus temperature decreased for BOPP but also increased for the non-layered blend samples.

[0078] Figure 13 is an experimental result graph showing a comparison of the relative dielectric loss tangents at different temperatures at 1 kHz for pure polyphenylene sulfide (PPS) film and layered PPS-polysulfone (PSU) film. The 33-layer PPS / PSU sample showed a significant improvement in dielectric loss tangent over the pure PPS film, especially in the range of 90°C to 150°C, eliminating the large spike in the dielectric loss tangent of the pure PPS within that range.

[0079] Figure 14 is an experimental graph showing a comparison of the storage modulus at different temperatures for pure polyphenylene sulfide (PPS) film and layered PPS-polysulfone (PSU) film. The 33-layer PPS / PSU sample exhibited a significantly increased storage modulus relative to the pure PPS film at high temperatures above approximately 100°C. This improvement can be easily seen in the bar graph shown in Figure 15, which shows an improvement at both the 50% storage modulus temperature and the 10% storage modulus temperature.

[0080] Figure 16 is a graph of experimental results showing the breakdown field strength at different temperatures for several film materials. One of the most obvious improvements in the experimental 33-layer COC / PP film is the relative breakdown strength, where the decrease in breakdown strength of the layered experimental film was much smaller than that of each of the comparative samples at temperatures above 100°C.

[0081] Figure 17 is a graph of experimental results showing the breakdown field strength at different temperatures for several different film materials. Similar to the 33-layer COC / PP film, the experimental PC / PP film also showed significantly improved breakdown strength not only at high temperatures, but also in the temperature range of 20°C to 90°C.

[0082] Certain modifications and improvements will occur to those skilled in the art upon reading the description of this specification. The above examples are provided for the purpose of clarifying aspects of the present invention, and it will be apparent to those skilled in the art that they are not intended to limit the scope of the present invention. All modifications and improvements have been omitted from this specification for the sake of brevity and readability, but are properly within the scope of the present invention. [Prior art documents] [Patent documents]

[0083] [Patent Document 1] U.S. Patent No. 8,866,018 [Patent Document 2] U.S. Patent No. 6,594,134 [Patent Document 3] U.S. Patent Publication No. 2007 / 0108490 [Patent Document 4] U.S. Patent Publication No. 2021 / 0291499 [Patent Document 5] U.S. Patent No. 10,614,958 [Patent Document 6] U.S. Patent No. 8,611,068 [Patent Document 7] U.S. Patent No. 9,558,888 [Patent Document 8] U.S. Patent No. 10,068,706 [Patent Document 9] U.S. Patent No. 10,759,139 [Patent Document 10] U.S. Patent Publication No. 2021 / 0079179

Claims

1. a plurality of coextruded layers including a plurality of A layers and a plurality of B layers in a simple alternating pattern; the plurality of A layers comprising at least one high temperature polymer; the plurality of B layers are made of polypropylene, the at least one high temperature polymer is a polymer having a glass transition temperature greater than 125°C or a melting point greater than 200°C; A high temperature performance dielectric film, wherein the plurality of A layers have a dielectric constant 0.5 to 1.5 times higher than that of the plurality of B layers.

2. The film of claim 1 , wherein the at least one high temperature polymer comprises a cyclic olefin copolymer (COC).

3. 3. The film of claim 2, wherein the plurality of A layers consists of about 10-30% COC and about 70-90% polypropylene.

4. 10. The film of claim 1, wherein the coextruded plurality of layers comprises at least 33 layers.

5. The film of claim 1 , wherein the film has a total thickness of from about 3 μm to about 15 μm.

6. 10. The film of claim 1, wherein at least one of the coextruded and / or extruded and stretched layers has a thickness of less than 150 nm.

7. 10. The film of claim 1, wherein the coextruded layers do not include any tie layers.

8. The film of claim 1 , wherein the film is incorporated into a capacitor.

9. a plurality of coextruded layers including a plurality of A layers and a plurality of B layers in a simple alternating pattern; the plurality of A layers comprising at least one high temperature polymer; the plurality of B layers are made of polypropylene, the at least one high temperature polymer is a polymer having a glass transition temperature greater than 125°C or a melting point greater than 200°C; The plurality of A layers are a high temperature performance dielectric film consisting of about 10-30% cyclic olefin copolymer and about 70-90% polypropylene.

10. 10. The film of claim 9, wherein each of the coextruded and / or extrusion-stretched layers has a thickness of less than 150 nm.

11. The film of claim 9, wherein the film has a total thickness of from about 3 μm to about 15 μm.

12. 10. The film of claim 9, wherein the coextruded plurality of layers comprises at least 33 layers.

13. 10. The film of claim 9, wherein the at least one high temperature polymer comprises a cyclic olefin copolymer (COC).

14. 10. The film of claim 9, wherein the coextruded layers do not include any tie layers.

15. 10. The film of claim 9, wherein the film comprises one or more skin or coating layers, the one or more skin or coating layers comprising at least one metallized layer.

16. The film of claim 9 , wherein the film is incorporated into a capacitor.

17. a plurality of coextruded layers including a plurality of A layers and a plurality of B layers in a simple alternating pattern; the plurality of B layers are made of polypropylene, the plurality of A layers have a dielectric constant 0.5 to 1.5 times higher than that of the plurality of B layers; at least one layer of the coextruded layers is less than 150 nm thick; The film is a high temperature performance dielectric film having a total thickness of about 3 μm to about 15 μm.

18. 20. The film of claim 17, wherein the plurality of A layers comprises at least one high temperature polymer, the at least one high temperature polymer being a polymer having a glass transition temperature greater than 125°C or a melting point greater than 200°C.

19. 20. The film of claim 17, wherein the plurality of A layers and the plurality of B layers are in a simple alternating pattern in the film.

20. 20. The film of claim 17, wherein the coextruded layers do not include any tie layers.

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