# US 2022/0033631 A1 · Biaxially oriented polypropylene film with improved breakdown strength > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2022/0033631 A1 - Document ID: US20220033631A1 - Status: Published application - Kind: A1 - Application number: 17/413,612 - Filed: 2019-12-20 - Published: 2022-02-03 - Earliest claimed: 2018-12-20 - Assignees: Borealis AG - Applicants: Borealis AG - Inventors: Dietrich GLOGER; Hermann BRAUN; Antonios GITSAS; Davide TRANCHIDA; Franciscus JACOBS; Wolfram STADLBAUER - Web page: https://patentgrep.com/patent/US20220033631A1 ## CPC - C08L 23/12: Polypropene - H01B 3/441: {from alkenes} - B29C 48/022: {characterised by the choice of material} - B29C 55/12: biaxial - B29C 55/16: simultaneously - C08J 5/18: Manufacture of films or sheets - C08L 23/142: {at least partially crystalline copolymers of propene with other olefins} - C08L 23/20: having four to nine carbon atoms - H01G 4/18: of synthetic material, e.g. derivatives of cellulose (H01G4/16 takes precedence) - H01G 4/32: Wound capacitors - B29K 2023/12: {PP, i.e. polypropylene} - B29K 2023/14: {Copolymers of polypropylene (B29K2023/16 takes precedence)} - B29K 2023/18: {Polymers of hydrocarbons having four or more carbon atoms, e.g. polymers of butylene, e.g. PB, i.e. polybutylene} - B29L 2009/003: {comprising a metal layer} - C08L 2203/16: used for films - C08L 2205/025: containing two or more polymers of the same hierarchy C08L, and differing only in parameters such as density, comonomer content, molecular weight, structure - C08L 2205/03: containing three or more polymers in a blend - C08L: COMPOSITIONS OF MACROMOLECULAR COMPOUNDS (compositions based on polymerisable monomers C08F, C08G; artificial filaments or fibres D01F; textile treating compositions D06) - H01B: CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES (selection for magnetic properties H01F1/00; waveguides H01P {; printed circuits H05K}) - B29C: SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING (making preforms B29B11/00; making laminated products by combining previously unconnected layers which become one product whose layers will remain together B32B37/00 - B32B41/00) - C08J: WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H (working, e.g. shaping, of plastics B29) - H01G: CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE (selection of specified materials as dielectric H01B3/00; capacitors having potential barriers H10D1/62, H10K10/10) - B29K: INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR {MOULDS, } REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS - B29L: INDEXING SCHEME ASSOCIATED WITH SUBCLASS B29C, RELATING TO PARTICULAR ARTICLES ## Abstract The present invention is directed to a biaxially oriented polypropylene (BOPP) film with improved breakdown strength and to a capacitor comprising an insulation film comprising a layer of the biaxially oriented polypropylene film of the present invention. The present invention is further directed to a process for producing a biaxially oriented polypropylene film. Finally, the present invention is further directed to the use of a biaxially oriented polypropylene film of the present invention as layer of an insulation film of a capacitor. The BOPP film comprises a polypropylene composition, wherein the polypropylene composition comprises a high isotactic homopolymer of propylene and a polymeric α-nucleating agent. The BOPP film has a dielectric breakdown field strength Eb63.2 of at least 595 kV/mm. The process for producing a biaxially oriented polypropylene film comprises the steps of extruding a polypropylene composition to a flat film and orienting the flat film simultaneously in the machine direction and in the transverse direction. ## Claims ### Claim 1 A biaxially oriented polypropylene film, comprising a polypropylene composition, wherein the polypropylene composition comprises: (i) from 90 to 99.99 wt %, based on the total weight of the polypropylene composition, of a homopolymer of propylene having a content of isotactic pentad fraction of from 93 to 98% and a melt flow rate MFR2 of from 0.4 to 10 g/10 min, and (ii) from 0.0000001 to 1 wt %, based on the total weight of the polypropylene composition, of a polymeric α-nucleating agent, wherein the biaxially oriented polypropylene film has a dielectric breakdown field strength Eb63.2 of at least 595 kV/mm, which is obtained as the Scale parameter α of a fitted two-parameter Weibull distribution based on 50 results, measured with active electrode area of 2.84 cm2 utilizing 250 V/s DC voltage ramp rate on films with a thickness of 3.8-4.2 μm, and a thickness of 2 to 5 μm, wherein further the film is stretched simultaneously in machine direction and transverse direction. ### Claim 2 (depends on 1) The biaxially oriented polypropylene film according to claim 1, wherein the polypropylene composition further comprises: (iii) up to 9.99 wt %, based on the total weight of the polypropylene composition, of a propylene homo- or copolymer other than the homopolymer of propylene (i). ### Claim 3 (depends on 1) The biaxially oriented polypropylene film according to claim 1, wherein the polypropylene composition further comprises: (iv) from 0.01 to 1 wt %, based on the total weight of the polypropylene composition, of additives. ### Claim 4 (depends on 1) The biaxially oriented polypropylene film according to claim 1, wherein the polypropylene composition has an ash content of not more than 30 ppm and/or the draw ratio in either TD or MD is at least 8.0. ### Claim 5 (depends on 1) The biaxially oriented polypropylene film according to claim 1, wherein the polymeric α-nucleating agent is selected from the group consisting of polyvinylcyclohexane, poly(3-methyl-1-butene) and mixtures thereof. ### Claim 6 (depends on 1) The biaxially oriented polypropylene film according to claim 1, wherein the additives are selected from the antioxidants, stabilisers, acid scavengers, and mixtures thereof. ### Claim 7 (depends on 1) The biaxially oriented polypropylene film according to claim 1, wherein the film comprises a layer consisting of the polypropylene composition and/or the film has a thickness between >2 and <5 μm. ### Claim 8 (depends on 1) The biaxially oriented polypropylene film according to claim 1, wherein the film also comprises a metal layer. ### Claim 9 (depends on 1) The biaxially oriented polypropylene film according to claim 1, having a dielectric breakdown field strength Eb10.0 of at least 535 kV/mm. ### Claim 10 (depends on 1) A capacitor comprising an insulation film comprising a layer of the biaxially oriented polypropylene film according to claim 1. ### Claim 11 A process for producing a biaxially oriented polypropylene film comprising the steps of: (A) providing a polypropylene composition comprising: (i) from 90 to 99.99 wt %, based on the total weight of the polypropylene composition, of a homopolymer of propylene having a content of isotactic pentad fraction of from 93 to 98% and a melt flow rate MFR2 of from 0.4 to 10 g/10 min, and (ii) from 0.0000001 to 1 wt %, based on the total weight of the polypropylene composition, of a polymeric α-nucleating agent, (B) extruding the polypropylene composition to a flat film, (C) orienting the flat film simultaneously in the machine direction and in the transverse direction to obtain the biaxially oriented polypropylene film, and (D) recovering the biaxially oriented polypropylene film. ### Claim 12 (depends on 11) The process according to claim 11, wherein the polypropylene composition further comprises: (iii) up to 9.99 wt %, based on the total weight of the polypropylene composition, of a propylene homo- or copolymer other than the homopolymer of propylene (i). ### Claim 13 (depends on 11) The process according to claim 11, wherein the polypropylene composition further comprises: (iv) from 0.01 to 1 wt %, based on the total weight of the polypropylene composition, of conventional additives. ### Claim 14 (depends on 11) The process according to claim 11, wherein simultaneous orientation of the flat film in the machine direction and in the transverse direction to obtain the biaxially oriented polypropylene film is conducted in a continuous process with a throughput of 20 kg/h to 900 kg/h, and the draw ratio in either TD or MD is at least 8.0. ### Claim 15 (depends on 11) The process according to claim 11, wherein the biaxially oriented polypropylene film has: a dielectric breakdown field strength Eb63.2 of at least 595 kV/mm, which is obtained as the Scale parameter α of a fitted two-parameter Weibull distribution based on 50 results, measured with active electrode area of 2.84 cm2 using 250 V/s DC voltage ramp rate on films with a thickness of 3.8-4.2 μm, a dielectric breakdown field strength Eb10.0 of at least 535 kV/mm, and a thickness of 2 to 5 μm.