Radiation-curable dielectric coatings

Abstract

The invention is directed to radiation-curable liquid coating compositions for depositing thermally conductive dielectric coatings; intermediates comprising a substrate having a layer of radiation-curable, optionally dried, coating composition deposited thereon; an adherent layer of thermally conductive dielectric cured coating composition on a substrate, coated substrates and methods of producing the compositions, coatings, coating layers and coated substrates; and in an embodiment to a radiation-curable dielectric coating for adherence to low surface energy substrates which includes a resin matrix, an adhesion promoter, and an acid scavenger, and the coating may be adapted for dielectric protection and thermal diffusion for power conversion systems.

Description

2024P00019WDRADIATION-CURABLE DIELECTRIC COATINGSFIELD OF THE INVENTION

[0001] The present invention relates to dielectric coatings generally, and more particularly to radiation-curable coating compositions for producing thermally conductive dielectric coatings and methods of making and using them. The invention further relates to cured thermally conductive dielectric coatings that exhibit suitable adhesion to substrates with low surface energies and maintain dielectric properties over time and articles of manufacture comprising these coatings.BACKGROUND

[0002] Thermally conductive and dielectric coatings are highly desirable for various applications, including for power conversion in electric vehicles. In this application, battery packs generate significant excess heat that must be effectively dissipated in order to maintain specified battery performance. Additionally, electrical systems like inverters for power conversion use high voltages that require high electrical volume resistivity properties.

[0003] Dielectric coatings designed for electrical systems like battery cell applications must have excellent adhesion to respective substrates in order to ensure structural integrity between bonded cells in the battery module. Metal substrates used to form, for example, battery cells typically exhibit low surface energies that are not compatible with conventional coating compositions. To accomplish sufficient adhesion between the coatings and the substrate surface, pre-treatment of the substrate surface is often performed to increase surface energy and to remove contaminants that interfere with coating adhesion. However, chemical pre-treatment methods are not suitable for use with live battery cells since they often require immersion into a liquid solution. Moreover, laser-texturing pre-treatment methods are expensive. A need therefore exists for a dielectric coating that exhibits strong adhesion to low surface energy substrates, including those substrates which are exposed to only mild pre-treatment procedures prior to coating.2024P00019WGSUMMARY OF THE INVENTION

[0004] The invention is directed to radiation-curable liquid coating compositions for depositing thermally conductive dielectric coatings; intermediates comprising a substrate having a layer of radiation-curable, optionally dried, coating composition deposited thereon; an adherent layer of thermally conductive dielectric cured coating composition on a substrate, coated substrates and methods of producing the compositions, coatings, coating layers and coated substrates.

[0005] In one embodiment, a radiation-curable dielectric coating composition includes an acrylate resin, 1 - 3 parts per hundred resin (“phr”) of an adhesion promoter including a phosphate methacrylate, 0.1 - 2 phr of a polymeric carbodiimide, and a photo initiator.

[0006] In some embodiments, the radiation-curable dielectric coating composition includes 50-90 wt.% of the acrylate resin.

[0007] In some embodiments, the acrylate resin of the radiation-curable dielectric coating composition includes a di-functional acrylate monomer or oligomer, and a mono-functional acrylate monomer. At least one monomer or oligomer may preferably include an epoxy group.

[0008] In some embodiments, the mono-functional acrylate monomer of the radiation-curable dielectric coating composition includes about 10-30 wt.% of the total acrylate resin.

[0009] In some embodiments, the radiation-curable dielectric coating composition further includes a thermally conductive fdler at a concentration such that a cured coating of the coating composition on a substrate exhibits a thermal conductivity of at least 0.1 W / m*K. In some embodiments, the thermally conductive fdler is selected from aluminum oxide, aluminum nitride, aluminum trihydrate, silicon oxide, silicon carbide, zinc oxide, magnesium oxide, silicon carbide, boron nitride, and combinations thereof.

[0010] In another embodiment, an article of manufacture includes a metal substrate and a curable dielectric coating composition applied on the metal substrate. The curable dielectric coating composition includes a resin having thermally conductive fdler dispersed therein, about2024P00019WG1 - 3 phr of a free acid phosphate ester of a methacrylate, and about 0.1 - 2 phr of an acid scavenger including a polymeric carbodiimide.

[0011] In some embodiments, the resin of the article of manufacture is curable by exposure to actinic radiation, and the curable composition includes a photo initiator. In some embodiments, the resin includes an acrylate resin.

[0012] In some embodiments, the metal substrate of the article of manufacture is aluminum. In some embodiments, the metal substrate of the article of manufacture is a wall of a battery cell.

[0013] In another embodiment, an article of manufacture includes a metal substrate and a cured dielectric coating adhered to the metal substrate. The dielectric coating may have a thickness of about 10 - 250 pm, and the dielectric coating:(a) exhibits a cross-hatch adhesion rating of 5B by ASTM D3359;(b) passes HiPot testing under IEC 60950-1 at a voltage of 5 kV for 120 seconds; and / or(c) exhibits a thermal conductivity of at least 0.1 W / m*K.

[0014] In some embodiments, the dielectric coating of the article of manufacture includes acrylate polymer and thermally conductive filler selected from aluminum oxide, aluminum nitride, aluminum trihydrate, silicon oxide, silicon carbide, zinc oxide, magnesium oxide, silicon carbide, boron nitride, and combinations thereof.

[0015] In another embodiment, a method for forming a dielectric article of manufacture includes:(a) providing an aluminum substrate with a surface having a surface energy of about 60 - 70 mN / m;(b) applying a curable coating composition to the surface of the aluminum substrate to an uncured thickness of about 10 - 250 pm; and(c) exposing the curable coating composition to actinic radiation sufficient to form a cured polymeric coating on the surface of the aluminum substrate, wherein the cured polymeric coating exhibits:2024P00019WG(i) a cross-hatch adhesion rating of 5B by ASTM D3359;(ii) a successful HiPot test under IEC 60950-1 at a voltage of 5 kV for 120 seconds; and(iii) a thermal conductivity of at least 0.1 W / m*K.

[0016] In some embodiments of the method, the curable coating composition includes an acrylate resin, a thermally conductive filler, an adhesion promoter, an acid scavenger, and a photo initiator.

[0017] In some embodiments of the method, the acid scavenger is present in the curable coating composition in an amount of about 0.1 -2 phr, and the adhesion promoter is present in the curable coating composition in an amount of about 1 - 3 phr.

[0018] In some embodiments of the method, the acid scavenger of the curable coating composition includes a polymeric carbodiimide.

[0019] In some embodiments of the method, the adhesion promoter of the curable coating composition includes a phosphate methacrylate.

[0020] In some embodiments of the method, the acrylate resin of the curable coating composition includes a di-functional acrylate monomer or oligomer, and a mono-functional acrylate monomer.

[0021] In some embodiments of the method, the aluminum substrate surface is free of laser texture and / or wet chemical pre-treatment.

[0022] In another embodiment, a method for forming a dielectric article of manufacture includes:(a) conditioning a surface of a bare metal substrate by exposing the metal surface to a plasma environment or providing a bare metal substrate already comprising a plasma conditioned surface;(b) depositing a dielectric coating composition on the conditioned surface, wherein the dielectric coating composition includes:(i) a resin having thermally conductive filler dispersed therein;(ii) an adhesion promoter;(iii) an acid scavenger including a polymeric carbodiimide; and(iv) a photo initiator(c) exposing the dielectric coating composition to actinic radiation sufficient to form a cured polymeric, thermally conductive and dielectric coating on the conditioned surface.

[0023] In some embodiments of the method, the plasma environment includes ionized air or nitrogen at a pressure of about 100 - 500 kPa. The plasma environment may be prepared by ionizing air or nitrogen with a voltage of about 200 - 500 volts at a frequency of about 3 - 100 kHz.

[0024] In some embodiments of the method, the conditioning is in the absence of laser treatment and / or wet chemical pre-treatment of the metal surface.

[0025] In some embodiments of the method, the conditioning establishes a surface energy of the metal surface of about 60 - 70 mN / m.

[0026] In some embodiments of the method, step (b) includes spraying a first layer of the dielectric coating composition onto the conditioned surface, followed by actinic radiation curing of the first layer and spraying a second layer of the dielectric coating composition on the cured first layer, followed by actinic radiation curing of the second layer of the dielectric coating composition. The first layer of the coating composition may have a thickness of about 5 - 125 pm.

[0027] In some embodiments of the method, the resin of the dielectric coating composition includes an acrylate resin having a di-functional acrylate monomer or oligomer, and a mono-functional acrylate monomer.

[0028] In some embodiments of the method, the dielectric coating composition includes about 1 - 3 phr of the adhesion promoter and about 0.1 -2 phr of the acid scavenger.

[0029] For a variety of reasons, it is preferred that radiation-curable liquid coating compositions, uncured layers of as-deposited coating compositions, optionally dried; and cured thermally conductive dielectric coatings disclosed herein may be made in the absence of certain ingredients, i.e. be free of certain materials, whether added or generated in situ, other than minor2024P00019WGamounts of contaminants; or may be substantially free from certain ingredients used for similar purposes in the prior art. Specifically, it is increasingly preferred in the order given, independently for each preferably minimized ingredient listed below, that at least some embodiments according to the invention contain no more than 1.0, 0.5, 0.35, 0.10, 0.08, 0.04, 0.02, 0.01, 0.001, or 0.0002 percent, more preferably said numerical values in grams per liter, more preferably said numerical values in ppm, of each of the following constituents: halogenated epoxy resins, nonylphenol, toluene, xylene, copper, gold, silver, oxidizing agents such as peroxides and peroxyacids, permanganate, perchlorate, chlorate, chlorite, hypochlorite, perborate, hexavalent chromium, trivalent chromium, sulfuric acid and sulfate, nitric acid and nitrate ions; as well as formaldehyde, formamide, hydroxylamines, cyanides, cyanates; dissolved or soluble boron species, e.g. borax, borate; strontium; and / or free halogen ions, e.g., fluoride, chloride, bromide or iodide.

[0030] In some embodiments, solid polymer / boron nitride composite particles, such as thermoset polymer / BN particles and / or thermoplastic polymer / BN particles, are absent from the coating composition or concentration is minimized to no more than 1.0, 0.5, 0.35, 0.10, 0.08, 0.04, 0.02, 0.01, 0.001, or 0.0002 percent, more preferably said numerical values in grams per liter, more preferably said numerical values in ppm.

[0031] As used herein, “actinic radiation” refers to electromagnetic radiation that can induce photochemical reactions. This type of radiation is primarily in the ultraviolet (UV) range but can also include certain wavelengths of visible, in the blue and violet end of the spectrum, and some infrared wavelengths.

[0032] As used herein, "dielectric coating" refers to a coating that is electrically insulating. As will be described in further detail herein, the dielectric coating of embodiments of the present invention remains electrically insulating, i.e. conducts little, preferably no electricity, at a dielectric withstand voltage of greater than 2.0 kV, desirably greater than 3.0 kV, preferably greater than 4.0 kV, most preferably greater than 5.0 kV, as measured by a HypotMAX 7720 or an Ikonix 3865 and in accordance with ASTM D 149-09 Hipot test. Dielectric withstand strength is calculated based upon the thickness of the sample and the dielectric withstand voltage.

[0033] As used herein, the term "polymer" refers to oligomers which typically have more than in increasing order of preference 3, 4, 5 or 6 monomer units or MW of at least 500, 1000,2024P00019WG5000 but less than 10,000 Daltons, and typically have between 4 and 10 repeating units;“polymer” also refers to macromolecules of MW greater than 10000, 50000 Daltons or higher molecular weights with many repeating units, such as homopolymers (e.g., polymers prepared from a single monomer species), copolymers (e.g., prepared from at least two monomer species), terpolymers, graft polymers and the like. The term "resin" as used herein refers to polymers having functional groups capable of further reactions, for example cross-linking, esterification, condensation and / or addition reactions. The term "lower alkyl" will be understood as a linear or branched chain of carbon atoms that are fully saturated with hydrogen atoms, generally having up to six carbon atoms, e.g. C1-C6 or C1-C4, or C2-C4 and the like. Further, the term "crosslinker" refers to a molecule comprising two or more functional groups reactive with polymer functional groups, and capable of linking two or more polymer molecules through chemical bonds. As used herein the term “radical reactive diluent” will be understood by the skilled person as a diluent that is reactive with radicals generated when components, such as the photoinitiator, in the composition are exposed to actinic radiation.

[0034] The transitional terms “comprising,” “consisting essentially of,” and “consisting of’ are intended to connote their generally accepted meanings in the patent lexicon; for those embodiments provided in terms of “consisting essentially of,” the basic and novel character! stic(s) is the facile operability of the methods or compositions / systems to provide compositions as exhibiting the claimed functional features using only those components listed.

[0035] When a list is presented, unless stated otherwise, it is to be understood that each individual element of that list, and every combination of that list, is a separate embodiment. For example, a list of embodiments presented as “A, B, or C” is to be interpreted as including the embodiments, “A,” “B,” “C,” “A or B,” “A or C,” “B or C,” or “A, B, or C,” as separate embodiments.

[0036] Unless otherwise specified, compositional percentages are in terms of weight percent, relative to the weight of the material or composition. Molecular weight is given in number average molecular weight.

[0037] It is to be appreciated that certain features of the disclosure which are, for clarity, described herein in the context of separate embodiments, may also be provided in combination in a single embodiment. That is, unless obviously incompatible or specifically excluded, eachindividual embodiment is deemed to be combinable with any other embodiment(s) and such a combination is another embodiment. Conversely, various features of the disclosure that are, for brevity, described in the context of a single embodiment, may also be provided separately or in any sub-combination. Finally, while an embodiment may be described as part of a series of steps or part of a more general structure, each said step may also be considered an independent embodiment, combinable with others.

[0038] Other than in any operating examples, or where otherwise indicated, all numbers expressing, for example, quantities of ingredients used in the specification and claims are to be understood as being modified in all instances by the term "about".BRIEF DESCRIPTION OF THE DRAWINGS

[0039] FIG. 1 is a cross-sectional view of a coated substrate in accordance with the present invention.

[0040] FIG. 2 is a schematic illustration of a battery module with dielectric coating in accordance with the present invention.

[0041] FIG. 3 shows 2 sets of test result photographs of cross-hatch adhesion performance of Control 1 composition after cure and after aging.

[0042] FIG. 4 shows 2 sets of test result photographs of cross-hatch adhesion performance of Control 2 composition after cure and after aging.

[0043] FIG. 5 shows 2 sets of test result photographs of cross-hatch adhesion performance of a dielectric coating from a composition of the present invention after cure and after aging.DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0044] The objects and advantages enumerated above together with other objects, features, and advances represented by the present invention are now described in terms ofdetailed embodiments. Other embodiments and aspects of the invention, however, are recognized as being within the grasp of those having ordinary skill in the art.

[0045] Embodiments of the present invention provide radiation-curable dielectric coating compositions that, as a cured coating, exhibit strong adhesion and durable dielectric properties. The coating compositions may therefore be applied to substrates without the use of wet chemical or laser texturing pre-treatment of the substrate surface. Conventional dielectric coatings, by contrast, require relatively high surface energy substrates in order to adequately adhere to the substrate. In applications involving metal substrates, surface pre-treatment is often necessary to sufficiently raise the surface energy to ensure adequate adhesion between the dielectric coating and the substrate. Because such surface pre-treatments may not be appropriate for all applications, especially for battery cell systems that are not compatible with immersion in liquid chemical pre-treatment compositions. The curable coating compositions of the invention are therefore useful in connection with, for example, battery cell coatings.

[0046] The radiation-curable coating compositions of the present invention also provide cured coatings that exhibit durable dielectric properties. Some solutions for enhanced coating adhesion come at the cost of dielectric properties, especially with time exposure to the ambient environment. Here, the cured coatings exhibit both enhanced adhesion properties and desired dielectric properties that do not significantly degrade over time.

[0047] The compositions of the present invention may include one or more curable resins that are capable of undergoing a cross-linking reaction to form a polymeric matrix. The cure reaction may occur upon the mixing of two initially separated reactable components, e.g. a so-called 2K product, and / or exposure of the curable resin to a cure initiator. Preferably, a cure reaction is initiated with exposure of the curable component s) and the cure initiator. In some embodiments, the compositions include one or more radiation-curable resins and a photo initiator for initiation of cross-linking reactions. The curable compositions are preferably exposed to actinic radiation to initiate cross-linking. Actinic radiation is electromagnetic radiation capable of initiating photochemical reactions. Accordingly, actinic radiation is capable of transmitting sufficient light energy to cause photo initiators to fracture into free radicals. These free radicals can initiate the curing or polymerization process to produce polymer chains from monomers and / or oligomers.

[0048] Generally, the radiation-curable composition includes one or more radiation-curable resins, an adhesion promoter, an acid scavenger, and a photo initiator. In some embodiments, the radiation-curable composition further includes a thermally conductive fdler.Resin

[0049] In some embodiments, one or more of the curable resins may be in liquid form at 20 °C and 1 bar pressure. In some embodiments, the liquid curable resins may exhibit a viscosity of less than 500 cP at 20 °C at a shear rate of 1 s-1. The one or more curable resins may be selected from a variety of monomers and oligomers wherein the term “resin” may include any natural or synthetic organic compound or mixture that is convertible into a polymer.

[0050] The curable resin may include an acrylate resin, including acrylate monomers and / or acrylate oligomers. In some embodiments, the one or more acrylate monomers and / or acrylate oligomers is free-radical curable to form a polymer network. Acrylates useful in the curable resin material may be selected from a host of different compounds. Acrylates contemplated for use in the present invention are known in the art. Exemplary acrylates contemplated for use herein include mono-functional (meth)acrylates, di-functional (meth)acrylates, tri -functional (meth)acrylates, polyfunctional (meth)acrylates, and the like.

[0051] Exemplary mono-functional (meth)acrylates include phenyl phenol acrylate, methoxypolyethylene acrylate, acryloyloxyethyl succinate, fatty acid acrylate, methacryloyloxy ethylphthalic acid, phenoxyethylene glycol methacrylate, fatty acid methacrylate, B-carboxyethyl acrylate, isobomyl acrylate, isobutyl acrylate, t-butyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, dihydrocyclopentadiethyl acrylate, cyclohexyl methacrylate, t-butyl methacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, t-butylaminoethyl methacrylate, 4-hydroxybutyl acrylate, tetrahydrofurfuryl acrylate, benzyl acrylate, ethyl carbitol acrylate, phenoxyethyl acrylate, methoxytriethylene glycol acrylate, monopentaerythritol acrylate, dipentaerythritol acrylate, tripentaerythritol acrylate, and polypentaerythritol acrylate.

[0052] Exemplary di-functional (meth)acrylates include hexane diol dimethacrylate, hydroxyacryloyloxypropyl methacrylate, hexanediol diacrylate, urethane acrylate, epoxy acrylate, Bisphenol A-type epoxy diacrylate, modified epoxy acrylate, fatty acid-modified epoxy2024P00019WGacrylate, amine-modified Bisphenol A-type epoxy acrylate, allyl methacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, ethoxylated Bisphenol A dimethacrylate, tricyclodecanedimethanol dimethacrylate, glycerin dimethacrylate, polypropylene glycol diacrylate, propoxylated ethoxylated Bisphenol A diacrylate, 9,9-bis(4-(2-acryloyloxyethoxy)phenyl) fluorene, tri cyclodecane diacrylate, dipropylene glycol diacrylate, polypropylene glycol diacrylate, PO-modified neopentyl glycol diacrylate, tricyclodecanedimethanol diacrylate, and 1,12-dodecanediol dimethacrylate.

[0053] Exemplary trifunctional (meth)acrylates include trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, trimethylolpropane ethoxy triacrylate, polyether triacrylate, and glycerin propoxy triacrylate.

[0054] Exemplary polyfunctional (meth)acrylates include dipentaerythritol polyacrylate, dipentaerythritol hexaacrylate, pentaerythritol tetraacrylate, pentaerythritol ethoxy tetraacrylate, and di(trimethylolpropane) tetraacrylate.

[0055] Further exemplary acrylates useful in the present compositions include cyanoacrylates, polyester acrylates, urethane acrylates, polyether acrylates, and silicone acrylates.

[0056] In some embodiments, the curable compositions comprise one or more acrylate resins in an amount of at least, in increasing order of preference, about 30, 40, 50, 60, or 70 and not more than in increasing order of preference about 95, 90, 85, or 80 wt.% of the composition.

[0057] The radiation curable resin component of the composition may comprise a difunctional acrylate monomer or oligomer, a mono-functional acrylate monomer or oligomer; or preferably, a combination thereof. The acrylate monomers and oligomers may each be linear, branched, alicyclic or aromatic. In some embodiments, the mono-functional acrylate monomer comprises an amount of at least, in increasing order of preference, about 1, 2, 5, 8, 10, 12, or 15 and not more than in increasing order of preference about 40, 35, 30, 25, or 20 wt.% of the composition. In some embodiments, the mono-functional acrylate monomer comprises a bridged alicyclic monomer, preferably isobornyl acrylate.

[0058] In some embodiments, the di-functional acrylate monomer or oligomer of the radiation curable resin component comprises an amount of at least, in increasing order of2024P00019WGpreference, about 1 , 2, 5, 8, 10, 12, 15, or 20 and not more than in increasing order of preference 50, 40, 35, or 30 wt.% of the composition. In some embodiments, the di-functional acrylate monomer or oligomer may be a linear or branched and preferably comprises dipropylene glycol di acrylate.

[0059] In some embodiments, the acrylate resin component includes a modified Bisphenol-A epoxy diacrylate that is present in the curable composition in an amount of at least, in increasing order of preference, about 5, 10, 15, 20, 25 or 30 and not more than in increasing order of preference 50, 45, 40, or 36 wt.% of the composition. In some embodiments, the modified Bisphenol A epoxy diacrylate is formed from a mixture of Bisphenol-A epoxy diacrylate (50% in weight) and tripropylene glycol diacrylate (TPGDA). Suitable modified Bisphenol A epoxy acrylates are commercially available under the brand name Sartomer® CN series from Arkema Inc., Sinomer® EATM from Longchang Chemical, or the brand name Ebecryl® from Allnex Netherlands B.V.

[0060] The curable resin may include an epoxy resin. In some embodiments, the epoxy resin may be modified. In some embodiments, the epoxy resin has a flexible aliphatic or aliphatic / aromatic backbone, wherein the backbone includes straight or branched chain hydrocarbyl segments, wherein each hydrocarbyl segment has at least 20 carbon atoms.

[0061] In some embodiments, the curable resin comprises a rubber or elastomer-modified epoxy. Examples of rubber or elastomer-modified epoxies useful in the invention include epoxidized derivatives of:(a) homopolymers or copolymers of conjugated dienes having a weight average molecular weight (Mw) of 30,000 to 400,000 or higher, in which conjugated dienes contain from 4-11 carbon atoms per molecule (such as 1,3 -butadiene, isoprene, and the like);(b) epihalohydrin homopolymers, a copolymer of two or more epihalohydrin monomers, or a copolymer of an epihalohydrin monomer(s) with an oxide monomer(s) having a number average molecular weight (Mn) which varies from about 800 to about 50,000;(c) hydrocarbon polymers including ethylene / propylene copolymers and copolymers of ethylene / propylene and at least one nonconjugated diene, such as ethylene / propylene / hexadiene / norbomadiene; or(d) conjugated diene butyl elastomers, such as copolymers consisting of from 85 to 99.5% by weight of a C4-C5 olefin combined with about 0.5 to about 15% by weight of a conjugated multi-olefin having 4 to 14 carbon atoms, copolymers of isobutylene and isoprene where a major portion of the isoprene units combined therein have conjugated diene unsaturation.

[0062] In some embodiments, the epoxy resin is an epoxidized polybutadiene diglycidylether oligomer or polymer.

[0063] In some embodiments, epoxidized polybutadiene diglycidylether oligomers contemplated for use herein may have the general Formula I:wherein:R1and R2are each independently H or lower alkyl,R3is H, saturated or unsaturated hydrocarbyl, or epoxy,n falls in the range of 2-150,wherein at least one epoxy-containing repeating unit and at least one olefinic repeating unit is present in each oligomer; preferably present in a range of 1-10 of each repeating unit.

[0064] In certain embodiments, epoxidized polybutadiene diglycidylether oligomer or polymer contemplated for use in the practice of the present invention may have the general Formula II:2024P00019WDwherein:each R is, independently H, OH, lower alkyl, epoxy, oxirane-substituted lower alkyl, aryl, alkaryl, and the like.

[0065] A wide variety of epoxy-functionalized resins are contemplated for use in the curable compositions of the present invention. For example, liquid-type epoxy resins based on Bisphenol A, liquid-type epoxy resins based on Bisphenol F, multifunctional epoxy resins based on phenol novolac resin, dicyclopentadiene-type epoxy resins, naphthalene-type epoxy resins, and the like. Other examples of epoxy-functionalized resins contemplated for use herein include a di epoxide of a cycloaliphatic alcohol, hydrogenated Bisphenol A; and a difunctional cycloaliphatic glycidyl ester of hexahydrophthallic anhydride, both commercially available from Huntsman Corp, under brand name Epalloy or from Dai Nippon Ink & Chemicals, Inc., under the brand name Epicion , and similar epoxy-functionalized resins, as well as mixtures of any two or more thereof.

[0066] In some embodiments, the curable composition may include a combination of two or more different epoxy-functionalized resins, including two or more different Bisphenol-based epoxies. The bisphenol-based epoxies may be selected from Bisphenol A, Bisphenol F, or Bisphenol S epoxies, and combinations thereof. In addition, two or more different bisphenol epoxies within the same type of resin (such A, F, or S) may be used.

[0067] Commercially available examples of the bisphenol epoxies contemplated for use herein include Bisphenol-F-type epoxies (such as RE-404-S from Nippon Kayaku, Japan, and EPICLON from Dai Nippon Ink & Chemicals, Inc., and RSL 1738 and “JER”Tm epoxy YL-983U from Resolution) and Bisphenol-A-type epoxies (such as YL-979 and 980 from Resolution). Further examples of commercially available epoxy resins include Epon 828, Epon2024P00019WG826, Epon 862 (all from Hexion Co., Ltd.), also those sold under tradename DER (all from Dow Chemical Co.), and tradename JER (all from Japan Epoxy Resins Co).

[0068] The bisphenol epoxies available commercially from Dai Nippon and noted above are promoted as liquid undiluted epichlorohydrin-Bisphenol F epoxies having much lower viscosities than conventional epoxies based on Bisphenol A epoxies and have physical properties similar to liquid Bisphenol A epoxies. Bisphenol F epoxy has lower viscosity than Bisphenol A epoxies, all else being the same between the two types of epoxies. The Epoxy Equivalent Weight (EEW), which is the molecular weight divided by the number of epoxy groups of these four Bisphenol F epoxies is between 165 and 180. The viscosity at 25°C is between 3,000 and 4,500 cP (except for RE1801 whose upper viscosity limit is 4,000 cP). The hydrolyzable chloride content is reported as 200 ppm for RE1815 and 830W, and that for RE1826 as 100 ppm.

[0069] The bisphenol epoxies available commercially from Resolution and noted above are promoted as low chloride containing liquid epoxies. The Bisphenol A epoxies have an EEW (g / eq) of between 180 and 195 and a viscosity at 25°C of between 100 and 250 cP. The total chloride content for YL-979 is reported as between 500 and 700 ppm, and that for YL-980 as between 100 and 300 ppm. The Bisphenol F epoxies have an EEW (g / eq) of between 165 and 180 and a viscosity at 25°C of between 30 and 60. The total chloride content for RSL-1738 is reported as between 500 and 700 ppm, and that for YL-983U as between 150 and 350 ppm.

[0070] In addition to the bisphenol epoxies, other epoxy compounds are contemplated for use as the epoxy component of invention formulations. For instance, cycloaliphatic epoxies, such as 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexylcarbonate, can be used. Also, monofunctional, difunctional or multifunctional reactive diluents may be used to adjust the viscosity and / or lower the glass transition temperature (Tg) of the resulting resin material.Exemplary reactive diluents include butyl glycidyl ether, cresyl glycidyl ether, o-cresyl glycidyl ether, polyethylene glycol glycidyl ether, polypropylene glycol glycidyl ether, and the like.

[0071] Other epoxies suitable for use herein include polyglycidyl derivatives of phenolic compounds, such as those available commercially under the tradename EPON from Resolution; tradename DER from Dow Chemical Co.; and BREN-S from Nippon Kayaku. Other suitable epoxies include polyepoxides prepared from polyols and the like and polyglycidyl derivatives of phenol-formaldehyde novolacs, the latter of such as sold under tradename DEN from Dow2024P00019WDChemical. Cresol analogs are also available commercially under the tradename ARALDITE from Ciba Specialty Chemicals Corporation. SU-8 is a Bisphenol-A-type epoxy novolac available from Resolution. Polyglycidyl adducts of amines, aminoalcohols and poly carboxylic acids are also useful in this invention, commercially available resins sold under the tradename GLYAMINE by EI.C. Corporation; ARALDITE by Ciba Specialty Chemicals and PGA-X and PGA-C from the Sherwin-Williams Co.Photo Initiator

[0072] Various photo initiators may be used in the curable compositions of the invention. Suitable photo initiators are capable of initiating substantial curing of the radiation curable composition on exposure to actinic radiation. In some embodiments, the photo initiator is capable of initiating curing of the radiation curable resin with exposure to ultra-violet (UV) radiation. In some embodiments, the photo initiator is capable of initiating chain growth polymerization and may undergo dissociation into a free radical upon exposure to sufficient UV radiation. In some embodiments, sufficient UV radiation for a partial cure of the curable composition may include about 0 - 500 mJ / cm2of UV-A radiation (315-400 nm), about 0 - 600 mJ / cm2of UV-B radiation (280-315 nm), and / or 0 - 2,500 mJ / cm2of UV-C radiation (100-280 nm) for up to about 0.5 seconds. In some embodiments, sufficient UV radiation for a full cure of the curable composition may include about 1,500 - 10,000 mJ / cm2of UV-A radiation (315-400 nm), 1,000 - 10,000 mJ / cm2UV-B radiation (280-315 nm) and / or 0 - 2,500 mJ / cm2UV-C radiation (100-280 nm) for up to about 5 seconds. In some embodiments, the UV radiation dosage may be delivered by a Type-D UVbulb.

[0073] The length of time for actinic radiation exposure is determinable by one skilled in the art, and depends upon the selected components in the radiation-curable composition.Exposure time may range for a period of at least, in increasing order of preference about 1, 2, 3, 4, or 5 and not more than, in increasing order of preference, about 60, 30, 20, or 10 seconds.

[0074] The photo initiator may be selected based on the absorbency characteristics and the spectral output of the actinic radiation source. Exemplary photo initiators useful in the present compositions include Type 1 photo initiators such as 2,4,6-trimethylbenzoyl-diphenyl phosphine oxide, commercially available under the trade name Omnirad® TPO, and 1-hydroxycyclohexyl-phenyl ketone, commercially available under the trade name Omnirad® 184.2024P00019WGOther example photo initiators include benzophenone, benzoin-ether, 2-(dimethylamino)ethanol (DMAE), hydroxy acetophenones, 2-hydroxy-2-methyl-l-phenylpropan-l-one, camphor derivatives, and hydroxyl-phenyl-ketone.

[0075] The curable compositions of the invention comprise one or more photo initiators in a total amount of at least, in increasing order of preference, about 0.1, 0.5, 1, 1.5 or 2 and not more than, in increasing order of preference 5, 4, 3.5, or 3 wt.% of the composition. The curable compositions of the invention comprise one or more photo initiators in a total amount of at least, in increasing order of preference, about 0.1, 0.5, 1, 1.5, 2, 2.5, or 3 and not more than, in increasing order of preference 5, 4.5, 4, or 3.5 phr of the curable resin.Adhesion Promoter and Acid Scavenger

[0076] Broadly, adhesion promoters aid in binding to a surface, and may be present in compositions in an amount effective for building chemical bonding at a joining location between the dielectric coating and a substrate. Examples of adhesion promoters include organosilanes, including mono-silanes, dipodal silanes, tripodal silanes, and oligomer silanes with methoxy, ethoxy, and / or propyloxy structure. An example alkoxysilane is an epoxy-functional alkoxysilane. Other adhesion promoters include organotitanates and mercapto-functional compounds. In some embodiments, methacrylates may be used as an adhesion promoter. An example methacrylate useful in the present compositions is phosphate methacrylate, such as mono- and di-phosphate esters of 2-hydroxyethylmethacrylate and mixtures thereof. An example phosphate methacrylate adhesion promoter includes those disclosed in US Patent No.8859098B2 and those commercially available from Johoku Chemical under the tradename JPA-514, from Harcros Chemicals Inc. under the trade name Harcryl, for example adhesion promoters which include bis(2-(methacryloyloxy)ethyl) phosphate and monomethacryloylethyl phosphate.

[0077] Applicant has found that use of certain adhesion promoters, while useful in improving adhesion characteristics of curable coating compositions, can detrimentally affect dielectric properties of the cured coating. Applicant has therefore discovered that use of an adhesion promoter within a specific concentration range of the curable coating composition provides beneficial improvement in coating adhesion while maintaining desired dielectric properties. Applicant has further discovered that use of an adhesion promoter together with an2024P00019WGacid scavenger, each within specific concentration ranges can provide unexpected mutual benefit in improving adhesion and maintaining dielectric properties. It is theorized that the complimentary use of an acid scavenger with an adhesion promoter within balanced concentration ranges stabilizes the acid functionality of the adhesion promoter to enhance its bonding potential with metal substrates, and to minimize free ion availability in a desired dielectric environment.

[0078] An example acid scavenger found to be useful in connection with the adhesion promoter of the present compositions is carbodiimide, which may be a monomeric or a polymeric carbodiimide. In preferred embodiments, polymeric carbodiimide is present alone or in combination with other acid scavengers. Commercially available examples of carbodiimides include those sold under tradename Stabaxol from RheinChemie, under tradename Lubio® from Schaefer-Additivsysteme GmbH, and under tradename Hymax from Langyi Functional Materials. The polymeric carbodiimide acid scavenger may preferably be used in connection with a phosphate methacrylate adhesion promoter.

[0079] The curable compositions of the present invention may comprise an adhesion promoter in an amount of at least, in increasing order of preference, about 0.1, 0.5, 1, or 1.5 and not more than, in increasing order of preference, about 5, 4, 3, or 2.5 phr of the curable resin in the curable composition. The curable compositions of the present invention may comprise an acid scavenger in an amount of at least, in increasing order of preference, about 0.1, 0.2, 0.3, or 0.4 and not more than, in increasing order of preference, about 3, 2.5, 2, 1.5, or 1.2 phr of the curable resin the curable composition. These concentrations of the adhesion promoter and the acid scavenger are particularly preferred for phosphate methacrylate adhesion promoter, preferably a free acid phosphate ester of methacrylate adhesion promoter, and a polymeric carbodiimide acid scavenger.Thermally Conductive Filler

[0080] In order to enhance the thermal conductivity of the dielectric coating, thermally conductive filler is preferably dispersed in the polymeric matrix formed by the curable composition. The thermally conductive fillers contemplated for use in the compositions of the present invention include electrically insulating particulates such as aluminum oxide, aluminumnitride, aluminum trihydrate, silicon oxide, silicon carbide, zinc oxide, magnesium oxide, silicon carbide, boron nitride, as well as mixtures of any two or more thereof.

[0081] In some embodiments, the thermally conductive filler may be substantially spherical, plate-like, rod-like, or combinations thereof. It is contemplated that a particle size distribution, including a multi-modal particle size distribution, may be employed to fit the parameters of any particular application, although certain particle size distributions may be found to be more effective than others. In some embodiments, the thermally conductive fillers may be substantially spherical, and have a mean particle size (dso) in a range of at least, in increasing order of preference, about 0.1, 0.2, 0.4, or 0.5 and not greater than, in increasing order of preference, about 20, 10, 8, 5, or 2 pm. In some embodiments, the thermally conductive filler may have a mean particle size (dso) of about 1 pm. Spherical particulate filler may have an aspect ratio of about 0.8 - 1.2.

[0082] The curable compositions of the present invention may comprise thermally conductive fillers in an amount of at least, in increasing order of preference, about 5, 10, or 15 and not more than, in increasing order of preference, about 90, 80, 70, 60, 50, 40, 30, or 25 wt.% of the total curable composition. In some embodiments, the thermally conductive filler is present in an amount of about 20 wt.% of the curable composition.

[0083] The thermally conductive filler may be present in the curable compositions in an amount sufficient to provide the dielectric coating with a thermal conductivity of at least 0.1 W / m*K by ASTM 5470. In some embodiments, the thermally conductive filler may be present in the curable compositions in an amount sufficient to provide the dielectric coating with a thermal conductivity of at least 0.4 W / m*K by ASTM 5470.Other Additives

[0084] In some embodiments, optionally, suitable flow additives, dispersing agents, defoamers, anti-oxidants, colorants, and rheology modifiers may be added as desired. Optional flow additives include silicone polymers, ethyl acrylate / 2-ethylhexyl acrylate copolymers, alkylol ammonium salt of acid, phosphoric acid esters of ketoxime or mixtures thereof. Example rheology modifiers include organic and inorganic rheology modifiers, e.g. fumed silica, clays,2024P00019WGorganophilic clays, and / or phyllosilicates. Example stabilizers include sterically-hindered primary phenolic antioxidants.Cured Composition

[0085] The curable compositions of the present invention, when cured, may form a film-like coating. For the purposes hereof, the term “film” means a thin film having a thickness of less than or equal to 250 pm. Generally the cured coatings are solid and adhered to the substrate. The dielectric coatings of the present invention may have a thickness of at least, in increasing order of preference, about 1, 5, 10, 20, 25, 30, 40, or 50 and not greater than 250, 200, 175, 150, 125, or 100 pm. In some embodiments, the dielectric coatings may be one or more layers. In some embodiments, the dielectric coatings may be formed in more than one layer, and merged into a single layer upon full cure.

[0086] In some embodiments, the coating formed from the curable compositions of the present invention, alone or in combination, may be deposited on a surface of a substrate, such as a metal substrate. In a particular embodiment, the curable compositions may be employed to form a dielectric coating on an aluminum wall of a battery cell, and specifically as dielectric coatings between adjacent battery cells in a battery module made up of a plurality of minimally-spaced apart battery cells.

[0087] The curable compositions of the present invention exhibit good flowability at relatively low temperatures, such as below 80 °C, preferably below 50 °C, and more preferably below 30 °C. The curable compositions are preferably in liquid state at room temperature. This facilitates processing of the compositions through spray coating apparatus, die coating apparatus, and the like. In some embodiments, the compositions as described herein may be applied to a suitable substrate, then B-staged with exposure to actinic radiation, followed by a further layer of curable composition applied to the B-staged layer to form a laminate.

[0088] Dielectric coatings of the present invention preferably have excellent adhesion to metal substrates to ensure structural integrity between bonded cells in the battery module, and good dielectric properties to minimize risk of short-circuiting among the cells within the module. The dielectric coatings may be characterized with reference to cross-hatch adhesion, as tested by2024P00019WGASTM D3359. Preferably, the dielectric coatings exhibit a cross-hatch adhesion rating of at least 4B, more preferably 5B by ASTM D3359.

[0089] The dielectric coatings of the present invention may also be characterized by dielectric performance, both initially upon cure and subsequent to humidity aging, by HiPot (High Potential or Dielectric Withstand) testing under IEC 60950-1. The dielectric coatings of the present invention pass the HiPot test at a voltage of 5 kV for 120 seconds.

[0090] The dielectric coatings of the present invention may further be characterized by adhesion strength through lap shear strength testing in connection with ASTM D1002. As will be described in greater detail in the Examples section herein, the dielectric coatings of the present invention preferably exhibit a lap shear strength of at least 10 MPa.

[0091] Some embodiments of an article of manufacture 10 according to the invention are shown in the cross-sectional view of FIG. 1 which includes a substrate 12, having a first surface 16, and a cured dielectric coating 14 adhered on first surface 16 of the substrate 12. In some embodiments, the substrate 12 is metal. In some embodiments, the substrate 12 is aluminum.

[0092] As shown in FIG.2, article of manufacture 110 may comprise a battery module including a plurality of battery cells 120, wherein metal substrate 112 is a respective wall of each battery cell 120. Dielectric coating 114 is adhered to the metal substrate forming walls of the battery cell. The dielectric coating on the walls 112 provides a dielectric barrier between cells 120. The dielectric coating may bond adjacent cells 120 to one another, or may have insulative material sandwiched between the walls, isolating cells from each other.

[0093] Article of manufacture 10 may be formed by providing the substrate 12 and applying the curable coating composition to a first surface 16 of the substrate 12. The curable coating composition may be applied to the first surface 16 through a variety of coating techniques, including spray coating, roller coating, die coating, and the like, to an uncured coating thickness. In some embodiments, the uncured coating thickness is about 10-250 pm. The article of manufacture 10 is then exposed to sufficient actinic radiation to cure the radiation-curable composition into a cured dielectric coating.

[0094] In some embodiments, a first layer of the curable coating composition is applied to the first surface 16 to a first layer thickness, and the article of manufacture 10 exposed to a2024P00019WGpartial-cure dose of actinic radiation to partially cure the curable coating composition into a partially cured layer. The partial cure dose of actinic radiation may, in some embodiments, include about 0 - 500 mJ / cm2of UV-A radiation (315-400 nm), about 0 - 600 mJ / cm2of UV-B radiation (280 - 315 nm), and about 0 - 100 mJ / cm2of UV-C radiation (100-280 nm) with an exposure time of up to about 0.5 seconds. A second layer of the curable coating composition is then applied to the partially cured layer, and the article of manufacture 10 is then exposed to sufficient actinic radiation to fully cure the radiation-curable composition into a cured dielectric coating. The full cure dose of actinic radiation may, in some embodiments, include about 1,500 -10,000 mJ / cm2of UV-A radiation, about 1,000 - 10,000 mJ / cm2of UV-B radiation, and about 0 - 2,500 mJ / cm2of UV-C radiation with an exposure time of up to about 5s. The UV cure radiation may be applied by a Type-D UV bulb. Multiple layers of curable coating composition may be applied to the substrate 12 prior to exposure of a full dose of actinic radiation sufficient to fully cure the radiation-curable composition into a cured dielectric coating. By only partially curing each applied layer of radiation-curable composition to a gel state, subsequent applied layers can bond to the underlying partially cured layer prior to full cure.

[0095] An aspect of the dielectric coatings of the present invention is the property of adhesion to metal substrates that exhibit low surface energies. Conventional dielectric coatings require significant surface modification to increase substrate surface energy to a point at which adhesion levels are acceptable. Typical substrate surface modification techniques include laser texturing and wet chemical pretreatment. Chemical pretreatment methods and laser texturing can be effective methods for increasing surface energy (60-70 mN / m or higher); however, they both have limitations in battery cell applications. Chemical pretreatments are not feasible since cells cannot be immersed in the liquid bath. Laser texturing can also an effective pretreatment but the cost of implementing is very high. The present dielectric coatings, by contrast, may suitably adhere to relatively low surface energy surfaces. Untreated aluminum, for example, typically exhibits a surface energy of about 30 -50 milli-Newton / meter (mN / m), with a water contact angle exceeding 80°. To prepare the aluminum substrate surface for application of the curable coating compositions of the present invention, the substrate surface may undergo a conditioning process. In some embodiments, the conditioning process increases the surface energy to about 60 - 70 mN / m and a water contact angle of about 20-35°. Applicants have found that the dielectriccoatings of the present invention suitably adhere to substrates having a surface energy of about 60 - 70 mN / m.

[0096] A conditioning process for conditioning metal substrates to suitable surface energies includes exposing the substrate surface to a plasma environment. Plasma treatment processes may use different jet heads that produce different intensities of plasma. The plasma intensity is dependent at least in part on the width of the jet head and density of the plasma. The conditioning of the substrate surface is determined by several additional factors, including primarily the process gas, and the pressure and voltage used in plasma generation. As the plasma is produced, it can be expelled out of selected jet heads having different shapes and sizes to produce different intensities. Lower plasma intensity generally equates to milder conditioning of the substrate surface, and diminished increase in surface energy of the substrate surface.Although not required, prior to plasma treatment, substrate surfaces may optionally be cleaned using a solvent such as IPA or ethyl acetate.

[0097] In some embodiments, the conditioning process may utilize a plasma generator ionizing a process gas selected from air, nitrogen, argon, oxygen, and mixtures of hydrogen and nitrogen. The plasma generator may ionize the process gas at a pressure of at least, in increasing order of preference, about 50, 80, 100, 150, or 200 and not greater than, in increasing order of preference, about 1000, 800, 700, 650, or 600 kPa. The plasma generator may ionize the process gas with a voltage of at least, in increasing order of preference, about 100, 150, 200, or 250 and not greater than, in increasing order of preference, about 750, 600, 500, 400, or 350 volts at a frequency of at least, in increasing order of preference, about 1, 2, 3, 5, 10, 15, or 20 and not greater than, in increasing order of preference, about 100, 80, 60, 50, 40, 30, or 25 kHz.

[0098] In some embodiments, the conditioning process may utilize the plasma generator with a plasma jet rotation of about 2000 - 3000 rpm to apply the plasma environment to the substrate surface at a distance of about 0- 12 mm, with the substrate workpiece being moved through the plasma environment at a speed of up to 400 mm / s and a track pitch of about 1 - 50 mm, depending on the jet head diameter.

[0099] In some embodiments, the conditioning process is in the absence of laser treatment and / or wet chemical pretreatment of the metal substrate surface.2024P00019WGExamples

[0100] The following examples are intended to assist one skilled in the art to better understand and practice the present invention. The scope of the invention is not limited by the examples, but is defined in the appended claims. All parts and percentages are based on weight of solids unless otherwise stated, and do not include solvents or other liquid materials which may be present to facilitate storage and dispensing of the curable compositions.

[0101] Bare metal substrates were prepared from 2.5 cm x 10 cm panels of Aluminum 3003. Substrate surfaces of the panels were conditioned with exposure to a plasma environment generated by a Plasmatreat FG5001 plasma generator fitted with a RD1004 jet. The panels were conditioned by either plasma process A or B as set forth in Table 1 below.Table 1*D = Distance between jet head and the panel

[0102] The ingredients for Example 1, listed in Table 2 below were added into a mixing vessel and mixed at 600 rpm for 2 hours before milling for 30 minutes in a horizontal Eiger mill to generate the composition of Example 1, according to the invention. The process was repeated to generate comparative compositions, Control 1 and Control 2. Amounts in Table 2 are given in weight %.2024P00019WGTable 2

[0103] The individual compositions were then transferred to a Binks Trophy high volume, low pressure spray gun with a 1.2 mm tip, and each was applied onto separate sets of Aluminum 3003 preconditioned panels of Table 1, at an atomizing pressure of 12 psi for a time sufficient to form a first coating layer having a thickness of approximately 50 pm. The first layer-coated panels were passed through a UV conveyor oven with a Type-D mercury arc lamp for a UV pre-cure exposure of 0.5 seconds to immobilize the first coating layer. Immediately afterward, the sample composition was applied onto the first coating layer, as described above, forming a second coating layer having a thickness of approximately 50 pm, which resulted in a total coating thickness of about 100 pm. The coated panels were then passed through the UV conveyor oven for a UV final cure exposure of 5 seconds to fully cure the coating. Table 3 below sets forth the applied radiation dosage for each pass.2024P00019WGTable 3

[0104] The coated panels were tested for cross-hatch adhesion pursuant to ASTM D3359. A first set of panels was tested for each of Control 1, Control 2, and Example 1 shortly after completion of the final coating cure, as identified in Table 4 below as “Initial”. The first set of panels included two sample panels for each of Control 1, Control 2, and Example 1, one from plasma treatment process “A” in Table 1, and a second from plasma treatment process “B” in Table 1.

[0105] A second set of panels was tested for cross-hatch adhesion for each of Control 1, Control 2, and Example 1 after aging the panels for 1000 hours at 85 °C and 85% humidity, as identified in Table 4 below as “Post-Aging”. The second set of panels included two sample panels for each of Control 1, Control 2, and Example 1, one from plasma treatment process “A” in Table 1, and a second from plasma treatment process “B” in Table 1.Table 4: Cross-hatch adhesion tested according to ASTM D3359

[0106] A rating of 4 - 5B is the target minimum requirement before and after aging. The Control 1 formulation did not meet the minimum requirement, while both of the Control 2 and2024P00019WGExample 1 formulations did meet the minimum requirement. The enhanced adhesion for both of the Control 2 and Example 1 formulations may be attributed to the increased concentration of adhesion promoter.

[0107] FIG. 3 shows images of the cross-hatch adhesion test results for the Control 1 formulation. FIG. 4 shows images of the cross-hatch adhesion test results for the Control 2 formulation. FIG. 5 shows images of the cross-hatch adhesion test results for the Example 1 formulation.

[0108] Lap shear testing was performed on the coated panels by assembling the coated panels into test kits, with each test kit having two coated panels with the coated surfaces in facing relationship with one another, bonded with 2K polyurethane adhesive sandwiched between and cured in contact with both coated surfaces to a bond thickness of 0.25 mm. The test kits were tested for lap shear strength pursuant to ASTM DI 002 at a test pull speed of 10 mm / min.

[0109] A first set of panels was lap shear tested for each of Control 1, Control 2, and Example 1 shortly after completion of the final coating cure, as identified in Table 5 below as “Initial”. The first set of panels included two sample panels for each of Control 1, Control 2, and Example 1, one from plasma treatment process “A” in Table 1, and a second from plasma treatment process “B” in Table 1.

[0110] A second set of panels was lap shear tested for each of Control 1, Control 2, and Example 1 after aging the panels for 1000 hours at 85 °C and 85% humidity, as identified in Table 5 below as “Post-Aging”. The second set of panels included two sample panels for each of Control 1, Control 2, and Example 1, one from plasma treatment process “A” in Table 1, and a second from plasma treatment process “B” in Table 1.2024P00019WGTable 5[OHl] Table 5 shows that the Control 1 formulation did not consistently meet the target lap shear strength requirement of at least 10 MPa, either initially or post-aging. Table 5’s Example 1 panels from Process A were consistently better than Control 1 and 2 in both Initial and Post-Aging bond strength.

[0112] Dielectric performance (HiPot) testing was performed on the coated panels pursuant to IEC 60950-1 testing procedure at both 3.6 kV for 240 seconds, and 5.0 kV for 120 seconds, and both shortly after final cure (“Initial”) and after 1000 hours aging at 85 °C and 85% humidity. The tests were performed on five sample coated panels for each of Control 1, Control 2, and Example 1, with the average values for each test set forth below in Table 6.Table 6

[0113] Importantly, only the Example 1 formulation consistently passed HiPot testing after aging. The balanced combination of the adhesion promoter and the acid scavenger of the Example 1 formulation provided the desired adhesion and durable dielectric properties.

[0114] Various modifications of the present invention, in addition to those shown and described herein, will be apparent to those skilled in the art of the above description. Such modifications are also intended to fall within the scope of the appended claims.

Claims

CLAIMS1. A radiation-curable dielectric coating composition, comprising:an acrylate resin;1 - 3 phr of an adhesion promoter comprising a phosphate methacrylate;0.1 - 2 phr of a carbodiimide; anda photo initiator.

2. The radiation-curable dielectric coating composition as in Claim 1, including 50-90 wt.% of the acrylate resin.

3. The radiation-curable dielectric coating composition as in Claim 2 wherein the acrylate resin includes a difunctional acrylate monomer or oligomer, and a monofunctional acrylate monomer, preferably wherein at least one monomer or oligomer comprises an epoxy group.

4. The radiation-curable dielectric coating composition as in Claim 3 wherein the monofunctional acrylate monomer comprises about 10-30 wt.% of the total acrylate resin.

5. The radiation-curable dielectric coating composition as in Claim 1, further comprising a thermally conductive fdler at a concentration such that a cured coating of the coating composition on a substrate exhibits a thermal conductivity of at least 0.1 W / m*K.

6. The radiation-curable dielectric coating composition as in Claim 5 wherein the thermally conductive fdler is selected from aluminum oxide, aluminum nitride, aluminum trihydrate, silicon oxide, silicon carbide, zinc oxide, magnesium oxide, silicon carbide, boron nitride, and combinations thereof, present in an amount of about 5 to 80 wt.%, preferably about 10 to about 50 wt.% .2024P00019WG7. An article of manufacture, comprising:a metal substrate; anda curable dielectric coating composition applied on the metal substrate, the curable dielectric coating composition including:a resin having thermally conductive filler dispersed therein;about 1 - 3 phr of a free acid phosphate ester of a methacrylate; andabout 0.1 -2 phr of an acid scavenger comprising a polymeric carbodiimide.

8. The article of manufacture as in Claim 7 wherein the resin is curable by exposure to actinic radiation, and the curable composition includes a photo initiator.

9. The article of manufacture as in Claim 8 wherein the resin includes an acrylate resin.

10. The article of manufacture as in Claim 7 wherein the metal substrate is aluminum.

11. The article of manufacture as in Claim 10 wherein the metal substrate is a wall of a battery cell.

12. An article of manufacture, comprising:a metal substrate; anda cured dielectric coating adhered to the metal substrate, wherein the dielectric coating has a thickness of about 10 - 250 pm, and the dielectric coating:(a) exhibits a cross-hatch adhesion rating of 5B by ASTM D3359;(b) passes HiPot testing under IEC 60950-1 at a voltage of 5 kV for 120 seconds; and / or(c) exhibits a thermal conductivity of at least 0.1 W / m*K.

13. The article of manufacture as in Claim 12 wherein the dielectric coating includes acrylate polymer and thermally conductive fdler selected from aluminum oxide,2024P00019WGaluminum nitride, aluminum trihydrate, silicon oxide, silicon carbide, zinc oxide, magnesium oxide, silicon carbide, boron nitride, and combinations thereof.

14. A method of forming a dielectric article of manufacture, the method comprising:(a) providing an aluminum substrate with a conditioned surface having a surface energy of about 60 - 70 mN / m;(b) applying a curable coating composition to the conditioned surface of the aluminum substrate to an uncured coating thickness of about 10 - 250 pm;(c) exposing the curable coating composition to actinic radiation sufficient to form a cured polymeric coating on the surface of the aluminum substrate, wherein the cured polymeric coating exhibits:(i) a cross-hatch adhesion rating of 5B by ASTM D3359;(ii) a successful HiPot test under IEC 60950-1 at a voltage of 5 kV for 120 seconds; and(iii) a thermal conductivity of at least 0.1 W7m*K.

15. The method as in Claim 14 wherein the curable coating composition comprises:an acrylate resin;a thermally conductive filler;an adhesion promoter;an acid scavenger; anda photo initiator.

16. The method as in Claim 15 wherein the acid scavenger is present in the curable coating composition in an amount of about 0.1 - 2 phr, and the adhesion promoter is present in the curable coating composition in an amount of about 1 -3 phr.

17. The method as in Claim 16 wherein the acid scavenger includes polymericcarbodiimide.2024P00019WG18. The method as in Claim 17 wherein the adhesion promoter includes a phosphate methacrylate.

19. The method as in Claim 16 wherein the acrylate resin includes a difunctional acrylate monomer or oligomer, and a monofunctional acrylate monomer.

20. The method as in Claim 14 wherein the aluminum substrate surface is free of laser texture and / or wet chemical pretreatment.

21. A method for forming a dielectric article of manufacture, the method comprising:(a) conditioning a surface of a bare metal substrate by exposing the metal surface to a plasma environment or providing a bare metal substrate already comprising a plasma conditioned surface;(b) depositing a dielectric coating composition on the conditioned surface, wherein the dielectric coating composition includes:(i) a resin having thermally conductive filler dispersed therein;(ii) an adhesion promoter(iii) an acid scavenger comprising a polymeric carbodiimide; and(iv) a photo initiator(c) exposing the dielectric coating composition to actinic radiation sufficient to form a cured polymeric coating on the conditioned surface.

22. The method as in Claim 21 wherein the plasma environment includes ionized process gas at a pressure of about 100 - 600 kPa.

23. The method as in Claim 22, including preparing the plasma environment by ionizing air, nitrogen, argon, oxygen, or mixtures of hydrogen and nitrogen with a voltage of about 200 - 500 volts at a frequency of about 3 - 100 kHz.

24. The method as in Claim 21 wherein the conditioning is in the absence of laser treatment and / or wet chemical pretreatment of the metal surface.2024P00019WG25. The method as in Claim 21 wherein the conditioning establishes a surface energy of the metal surface of about 60 - 70 mN / m.

26. The method as in Claim 21, wherein step (b) comprises spraying a first layer of the dielectric coating composition onto the conditioned surface, followed by partially radiation curing of the first layer and spraying a second layer of the dielectric coating composition on the partially cured first layer, followed by radiation curing of the second layer of the dielectric coating composition.

27. The method as in Claim 26 wherein the first layer of the dielectric coating composition has a thickness of about 5 - 125 pm, and the second layer of the dielectric coating composition has a thickness of about 5 - 125 pm.

28. The method as in Claim 21 wherein the resin of the dielectric coating composition includes an acrylate resin having a difunctional acrylate monomer or oligomer, and a monofunctional acrylate monomer.

29. The method as in Claim 21, wherein the dielectric coating composition comprises about 1 - 3 phr of the adhesion promoter and about 0.1 - 2 phr of the acid scavenger.

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