Curable dielectric coatings

Abstract

A method for forming a multiple-layer dielectric coating on a substrate includes (a) providing a coating composition having: (i) an actinic radiation curable material including at least one of a monomer and an oligomer, and (ii) a thermally conductive filler; (b) applying a first layer of the coating composition to the substrate; (c) exposing the first layer to a first dose of actinic radiation sufficient to partially cure the actinic radiation curable material of the first layer to a monomer conversion of between about 60% and about 95%; (d) applying a second layer of the coating composition to the partially-cured first layer; and (e) exposing the second layer of the coating composition to a second dose of actinic radiation sufficient to bond the first and second layers together and to cure the actinic radiation curable material of the second layer to a monomer conversion of at least 60%.

Description

CURABLE DIELECTRIC COATINGS TECHNICAL FIELD

[0001] The subject matter disclosed herein relates to thermally conductive materials and coatings and, in particular, to radiation curable dielectric coatings. The present invention further relates to methods for manufacturing and applying such thermally conductive constructs. BACKGROUND

[0002] Thermally conductive materials can be utilized for various heat dissipation applications, such as for dielectric coatings, thermal interface materials for computer processing chips, and for adhesives. Dielectric coatings can be utilized for various applications, including electronic devices, batteries, and motors. In high-speed battery production, battery cells are coated, and the coating is subsequently cured in seconds. Due to the speed of the process, many battery cells are either made with defects or the coating is applied with incorrect parameters, resulting in insufficient electrical insulation performance. Typically, batteries that do not pass the insulation requirements are either scrapped or re-worked. Unfortunately, the current re-work process is time consuming and high cost.

[0003] Conventionally, to re-work a coated battery, the batteries are typically partially or completely de-coated using various processes, such as a laser cleaning process. Other processes for re-working a coated battery include adding an additional tie-layer or primer prior to adding additional coating layers to ensure adhesion of the subsequent coatings. Conventionally, this additional tie-layer or primer is required to ensure sufficient insulation performance. These additional treatment methods, such as de-coating and / or applying additional layers prior to recoating, increase time and cost to battery production. SUMMARY

[0004] According to one aspect, a method for forming a multiple-layer dielectric coating on a substrate includes (a) providing a coating composition having: (i) an actinic radiation curable material including at least one of a monomer and an oligomer, and (ii) a thermally conductive filler; (b) applying a first layer of the coating composition to the substrate; (c) exposing the first layer to a first dose of actinic radiation sufficient to partially cure the actinicradiation curable material of the first layer to a monomer conversion of between about 60% and about 95%; (d) applying a second layer of the coating composition to the partially-cured first layer; and (e) exposing the second layer of the coating composition to a second dose of actinic radiation sufficient to bond the first and second layers together and to cure the actinic radiation curable material of the second layer to a monomer conversion of at least 60%.

[0005] According to another aspect, a method for forming a multiple-layer coating on a substrate includes (a) providing a first coating composition having: (i) an actinic radiation curable material including one or more acrylate monomers; and (ii) a thermally conductive filler, wherein a first component of the thermally conductive filler has a first refractive index, and the actinic radiation curable material has a second refractive index, the first refractive index being at least 10% different than the second refractive index, (b) applying a first layer of the first coating composition to the substrate; (c) exposing the first layer to a first dose of actinic radiation sufficient to partially cure the actinic radiation curable material of the first layer, wherein the first dose of actinic radiation includes actinic radiation between about 200 mJ / cm2and about 600 mJ / cm2in a range of between 100 nm and 250 nm; (d) applying a second layer of a second coating composition to the partially-cured first layer; and (e) exposing the second layer of the second coating composition to a second dose of actinic radiation sufficient to bond the first and second layers together.

[0006] According to another aspect, an actinic radiation curable composition for a dielectric coating includes an actinic radiation-curable resin material, wherein the actinic radiation-curable resin material includes a first material including at least one of isobornyl acrylate (IBOA) and dipropylene glycol diacrylate (DPGDA); a photoinitiator to initiate curing of the actinic radiation curable material on exposure to actinic radiation; and a thermally conductive filler, wherein a first component of the thermally conductive filler has a first refractive index, and the actinic radiation curable material has a second refractive index, the first refractive index being at least 10% different than the second refractive index, wherein a concentration of the first component ranges from about 2 parts per hundred of the actinicradiation-curable resin material to about 50 parts per hundred of the actinic radiation-curable resin material. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] FIG.1 illustrates method 100 for forming a multiple-layer dielectric coating on a substrate, according to some embodiments.

[0008] FIG.2 illustrates a multiple-layer dielectric coating 210 on a substrate 250, according to some embodiments. DETAILED DESCRIPTION

[0009] Embodiments of the present disclosure provide actinic radiation-curable compositions for dielectric coatings, and methods of forming multiple-layer dielectric coatings on substrates. For example, these multiple-layer dielectric coatings can be used for various electrical insulation applications, such as for battery cells. Conventionally, battery cells that are insufficiently coated and / or do not have the desired electrical insulation properties are either scrapped or re-worked. The re-work process conventionally requires coating removal or addition of tie-layers or primers prior to applying an additional coating layer. Therefore, it is desirable to form multiple-layer dielectric coatings without having to remove the initial coating layer or provide additional tie-layers or primers to ensure adequate adhesion of the multiple layers.

[0010] The actinic radiation curable composition (hereafter can be referred to as “coating composition”) can be used for dielectric coatings and can include at least one of an actinic radiation curable material, a photoinitiator, a thermally conductive filler, an adhesion promotor, a rheology modifier, pigment, and additives. The actinic radiation curable material can be an actinic radiation curable resin material, including one or more resins capable of at least partially curing upon exposure to sufficient actinic radiation. The actinic radiation curable material can include acrylate monomers and / or an oligomer. Acrylates may include reaction products of acrylic acid. In one example, acrylates include one or more of methacrylates, cyanoacrylates, and silicone acrylates. Additionally, or alternatively, the acrylate may include at least one of hydroxyethylacrylate, benzyl acrylate, and tetrahydrofurfuryl acrylate. Further examples of acrylates include acrylic acrylates, polyester acrylates, urethane acrylates, and polyether acrylates. In one non-limiting example, the actinic radiation curable material can include at leastone of an epoxy acrylate and a urethane acrylate. One suitable example of an acrylate is isobornyl acrylate (IBOA). For example, isobornyl acrylate 9 mPa‧s at about 25 °C can beutilized. Additionally, or alternatively, the actinic radiation curable material can include dipropylene glycol diacrylate (DPGDA). For example, dipropylene5 to about 15 mPa‧s at about 25 °C can be utilized.

[0011] The actinic radiation curable material may include cycloaliphatic epoxides and / or oxetanes. In one example, the actinic radiation curable material may include oligomers, such as a difunctional aliphatic urethane oligomer. In another example, the actinic radiation curable material includes an epoxy system. Epoxy resin may react with itself in the presence of a photoinitiator and sufficient actinic radiation to form a cured network. Generally, the epoxy system includes one or more epoxide groups, such as cycloaliphatic epoxies. These epoxides include organic three-membered cyclic oxygen compounds. One example of a cycloaliphatic epoxy is 3,4-epoxycyclohexylmethyl-3,4-epoxy-cyclohexanecarboxylate (EEC).

[0012] The actinic radiation curable material can include more than one resin, such as both isobornyl acrylate and dipropylene glycol diacrylate. In one non-limiting example, the use of both isobornyl acrylate and dipropylene glycol diacrylate can be beneficial for tuning the overall reactivity of the coating during exposure to actinic radiation and to enhance the adhesion of multiple-layers. In another example, the actinic radiation curable material includes a bisphenol A epoxy diacrylate. The bisphenol A epoxy diacrylate may be a modified bisphenol A epoxy diacrylate. For example, the modified bisphenol A epoxy diacrylate can have a viscosity of about 3500 mPa‧s at about 60 °C. In one non-limiting example, the actinic radiation curable material includes at least isobornyl acrylate, dipropylene glycol diacrylate, and a bisphenol A epoxy diacrylate. In another example, the actinic radiation curable material includes a material havingvinyl ether functional groups. For example, the material including vinyl ether functional groups can include 2-(2-vinyloxyethoxy)ethyl acrylate.

[0013] The weight percentage of isobornyl acrylate resin in the actinic radiation curable material may range from about 2 wt.% to about 40 wt.%. In one example, the weight percentage of isobornyl acrylate resin in the actinic radiation curable material ranges from about 5 wt.% to about 30 wt.%. In another example, the weight percentage of isobornyl acrylate resin in the actinic radiation curable material ranges from about 10 wt.% to about 20 wt.%. The weight percentage of dipropylene glycol diacrylate resin in the actinic radiation curable material may range from about 5 wt.% to about 50 wt.%. In one example, the weight percentage of dipropylene glycol diacrylate resin in the actinic radiation curable material ranges from about 10 wt.% to about 40 wt.%. In another example, the weight percentage of dipropylene glycol diacrylate resin in the actinic radiation curable material ranges from about 20 wt.% to about 30 wt.%.

[0014] The weight percentage of modified bisphenol A epoxy acrylate resin in the actinic radiation curable material may range from about 5 wt.% to about 40 wt.%. In one example, the weight percentage of modified bisphenol A epoxy acrylate resin in the actinic radiation curable material may range from about 15 wt.% to about 40 wt.%. The weight percentage of 2-(2- vinyloxyethoxy)ethyl acrylate in the actinic radiation curable material may be greater than about 10 wt.%. In one non-limiting example, using 2-(2-vinyloxyethoxy)ethyl acrylate in the actinic radiation curable material with a weight percentage above about 10 wt.% can enhance the multiple-layer adhesion properties. In one example, the weight percentage of 2-(2- vinyloxyethoxy)ethyl acrylate in the actinic radiation curable material ranges from about 10 wt.% to about 25 wt.%.

[0015] In one example, the weight percentage of the actinic radiation curable material in the coating composition ranges from about 50 wt.% to about 100 wt.%. In another example, the weight percentage of the actinic radiation curable material in the coating composition may range from about 30 wt.% to about 90 wt.%. In another example, the weight percentage of the actinic radiation curable material in the coating composition may range from about 50 wt.% to about 90 wt.%. In yet another example, the weight percentage of the actinic radiation curable material in the coating composition may range from about 60 wt.% to about 80 wt.%.

[0016] The photoinitiator is capable of initiating substantial curing of the actinic radiation curable material on exposure to actinic radiation. For example, the photoinitiator is capable of initiating chain growth polymerization and may undergo dissociation upon exposure to sufficient actinic radiation. In one example, the photoinitiator is selected based on the absorbency characteristics and the spectral output of an actinic radiation source. The polymerization and / or crosslinking effectiveness may be governed by the nature of monomers or oligomers used and the effectiveness of the photoinitiator. Examples of photoinitiators include benzophenone, benzoin-ether, 2-(dimethylamino)ethanol (DMAE), hydroxyacetophenones, 2-hydroxy-2- methyl-1-phenylpropan-1-one, camphor derivatives, and hydroxyl-phenyl-ketone. In one non- limiting example, the photoinitiator includes one or more of trimethylbenzoyl diphenylphosphine oxide and hydroxycyclohexyl-phenyl ketone. The weight percentage of photoinitiator in the coating composition may range from about 0.1 wt.% to about 10 wt.%. In one example, the weight percentage of photoinitiator in the coating composition ranges from about 1 wt.% to about 5 wt.%.

[0017] The thermally conductive filler can be dispersed / mixed with one or more components used for a cure reaction. The thermally conductive fillers contemplated for use in the preparations of the present invention include metals, metal oxides, ceramics, and combinations thereof. In one example, the thermally conductive filler is electrically insulating in order to promote an overall electrical resistivity of the coating composition. Example electrically insulating and thermally conductive fillers include boron nitride, aluminum nitride, alumina, and alumina trihydrate. In one example, the thermally conductive filler includes at least one of alumina and boron nitride.

[0018] The thermally conductive filler can include a first component, wherein the first component of the thermally conductive filler has a first refractive index, and the actinic radiation curable material has a second refractive index. The first component can include fillers of the present disclosure. The thermally conductive filler can also include a second component, a distinct filler of the present disclosure. In one example, the first refractive index is at least 5% different than the second refractive index. In another example, the first refractive index is at least 10% different than the second refractive index. In another example, the first refractive index is at least 15% different than the second refractive index. The first refractive index can be at least 20% different than the second refractive index. In yet another example, the first refractive indexis between 10% and 60% greater than the second refractive index. In yet another example, the first refractive index is between 10% and 30% greater than the second refractive index.

[0019] The first refractive index can be greater than about 1.5. In one example, the first refractive index is greater than about 1.6, greater than about 1.7, greater than about 1.8, or greater than about 1.9. In another example, the first refractive index ranges from about 1.7 to about 2.6. In another example, the first refractive index ranges from about 1.7 to about 2.2. First refractive index values of the present disclosure can tune the monomer conversion percentage of the coating composition by diffracting incident actinic radiation, thereby limiting available actinic radiation to initiate polymerization of the curable composition. The presence of diffracting agents in the present compositions can render the actinic radiation as a limiting polymerization conversion reaction reagent. In the circumstance that the actinic radiation is limited, so too can be the extent of polymerization, which leaves unreacted monomer material available for subsequent bonding to a subsequent layer of curable material.

[0020] In one example, the first component includes boron nitride, and the first refractive index is about 1.8. In contrast, aluminum hydroxide has a refractive index of about 1.5 to about 1.6. Titanium oxide filler can exhibit a refractive index above about 2.5. The second refractive index of the curable resin may be less than the first refractive index. In one example, the second refractive index is less than 1.6. In another example, the second refractive index ranges from about 1.2 to about 1.6. For example, the second refractive index may be about 1.5. In one example, the actinic radiation curable material includes one or more UV curable acrylates with a second refractive index of about 1.5.

[0021] The concentration of the first component can range from about 2 parts per hundred of the actinic radiation curable material to about 50 parts per hundred of the actinic radiation curable material. In one example, the concentration of the first component ranges from about 5 parts per hundred of the actinic radiation curable material to about 50 parts per hundred of the actinic radiation curable material. In another example, the concentration of the first component ranges from about 5 parts per hundred of the actinic radiation curable material to about 30 parts per hundred of the actinic radiation curable material. The concentration of the first component can be greater than about 2 parts per hundred of the actinic radiation curable material.

[0022] In one example, the concentration of the thermally conductive filler ranges from about 5 parts per hundred of the actinic radiation curable material to about 50 parts per hundredof the actinic radiation curable material. In another example, the concentration of the thermally conductive filler ranges from about 10 parts per hundred of the actinic radiation curable material to about 50 parts per hundred of the actinic radiation curable material. In another example, the concentration of the thermally conductive filler ranges from about 15 parts per hundred of the actinic radiation curable material to about 40 parts per hundred of the actinic radiation curable material. In yet another example, the concentration of the thermally conductive filler ranges from about 20 parts per hundred of the actinic radiation curable material to about 35 parts per hundred of the actinic radiation curable material.

[0023] The weight percentage of thermally conductive filler in the coating composition can range from about 5 wt.% to about 60 wt.%. In one example, the weight percentage of thermally conductive filler in the coating composition ranges from about 10 wt.% to about 40 wt.%. In another example, the weight percentage of thermally conductive filler in the coating composition ranges from about 15 wt.% to about 30 wt.%. In one example, the thermally conductive filler includes boron nitride, wherein a weight percentage of boron nitride in the coating composition ranges from about 1 wt.% to about 30 wt.%. In another example, the thermally conductive filler includes boron nitride, wherein a weight percentage of boron nitride in the coating composition ranges from about 1 wt.% to about 20 wt.%. In yet another example, the thermally conductive filler includes boron nitride, wherein a weight percentage of boron nitride in the coating composition ranges from about 2 wt.% to about 10 wt.%.

[0024] The thermally conductive fillers may be of various shapes and size, and typically have a mean particle size (d50) in a range of between 0.1 and 200 µm. In some embodiments, the thermally conductive fillers have a mean particle size (d50) in a range of between 1 and 100 µm. In some embodiments, the distribution of thermally conductive filler particles is not a mono dispersion, but rather a particle size distribution. In some embodiments, the particle size distribution is multi-modal, including a mixture of relatively small particles and relatively large particles, within the size ranges described above. For the purposes hereof, the term “mean particle size” refers to a cumulative weight average value (d50) in which 50% of the particles are larger than the value, and 50% of the particles are smaller than the value, as determined by laser light diffraction. The shape of the thermally conductive filler may be spherical, aspherical, and combinations thereof. Example aspherical shapes include flake-like, plate-like, rod-like, and so on. Spherical thermally conductive filler may have an aspect ratio of between 0.8-1.2. In onenon-limiting example, the thermally conductive filler includes boron nitride platelets with a mean particle size ranging from about 0.5 µm to about 30 µm.

[0025] As discussed, the coating composition can include one or more of an adhesion promotor, rheology modifier, pigment, and additives. Adhesion promotors can be utilized for increasing / promoting the adhesion and / or compatibility of two or more components. One example of an adhesion promotor is methacryloylethyl phosphate. Rheology modifiers can alter the rheological properties, such as for tuning the viscosity and flow characteristics of coating compositions. One example of a rheology modifier is an organophilic phyllosilicate. Pigments can be utilized to alter the visual appearance of the coating composition. One example of a pigment includes ammonium iron(III) hexacyanoferrate(II). Various additives may be utilized, such as salts of unsaturated polyamine amides and low molecular acidic polyesters. Further examples of additives include polyolefin copolymers and pentaerythritol tetrakis(3-(3,5-di-tert- butyl-4-hydroxyphenyl)propionate. The coating composition can be formed by mixing various components of the present disclosure, with different mixing sequences possible. Dispersing machines may be utilized, such as milling equipment.

[0026] The coating composition can be applied to a substrate for use as a dielectric coating. Dielectric coatings can be applied to a substrate to improve electrical insulation properties. For example, dielectric coatings can form a barrier for reducing or preventing the passage of electric charges through the coating. In one example, the dielectric strength of the dielectric coating is greater than 5 V / μm at 23 °C. In another example, the dielectric strength of the dielectric coating is greater than 15 V / μm at 23 °C. In another example, the dielectric strength of the dielectric coating is greater than 25 V / μm at 23 °C. In one example, the dielectric coating can insulate from voltages over about 3.0 kV. In another example, the dielectric coating can insulate from voltages over about 5.0 kV. The dielectric coating can be used to dissipate heat from a substrate. In one example, the dielectric coating has an overall thermal conductivity of greater than about 0.2 W / mK. In another example, the dielectric coating has an overall thermal conductivity of greater than about 1 W / mK. In yet another example, the dielectric coating has an overall thermal conductivity of greater than about 3 W / mK.

[0027] FIG.1 illustrates method 100 for forming a multiple-layer dielectric coating on a substrate, according to some embodiments. Method 100 includes one or more of the following steps (with various orders possible):

[0028] Referring to Step 110, a coating composition is provided. In one example, the coating composition includes at least one of an actinic radiation curable material and a thermally conductive filler of the present disclosure. The coating composition of Step 110 may include coating compositions of the present disclosure, and this coating composition may be termed “first coating composition”. In one example, the substrate includes at least a portion of a battery cell. In another example, the substrate includes a metallic surface.

[0029] Referring to Step 120, a first layer of the coating composition is applied to the substrate. Applying the coating composition to the substrate generally includes contacting at least a portion of the substrate with the coating composition. The coating composition can be applied to the substrate with various methods, such as by using a high volume low pressure (HVLP) spray gun. The coating composition may be applied sufficient to form various first layer thicknesses. In one example, the thickness of the first layer can range from about 50 μm to about 200 μm. In another example, the thickness of the first layer can range from about 75 μm to about 200 μm. In yet another example, the thickness of the first layer can range from about 75 μm to about 125 μm.

[0030] Referring to Step 130, the first layer is exposed to a first dose of actinic radiation sufficient to partially cure the actinic radiation curable material of the first layer. In some embodiments, the first layer is exposed to the first dose of actinic radiation sufficient to partially, but not fully cure the actinic radiation curable material of the first layer. Actinic radiation is electromagnetic radiation capable of initiating photochemical reactions. Accordingly, actinic radiation is capable of transmitting sufficient light energy to cause photoinitiators to fracture into free radicals. These free radicals can initiate the curing or polymerization process to produce long polymer chains from monomers. The production of long polymer chains at least partially begins or completes the curing process.

[0031] In one example, the first layer is exposed to a first dose of actinic radiation sufficient to partially cure the actinic radiation curable material of the first layer to a monomer conversion of less than 100%. In another example, the first layer is exposed to a first dose of actinic radiation sufficient to partially cure the actinic radiation curable material of the first layer to a monomer conversion of between about 50% and about 99%. In another example, the first layer is exposed to a first dose of actinic radiation sufficient to partially cure the actinic radiation curable material of the first layer to a monomer conversion of between about 60% and about95%. For the purposes hereof, the term “monomer conversion” is intended to mean the percentage (by mass or number) of actinic radiation-curable monomer molecules in the actinic radiation curable composition actually converted to polymer molecules, in comparison to the total (mass or number) of actinic radiation-curable monomer molecules available in the actinic radiation-curable composition prior to exposure to actinic radiation. The specific monomer conversions of the present disclosure can promote enhanced multiple-layer adhesion during the application of multiple-layers of the coating composition on a substrate. As described above, by providing less than complete (100%) conversion of monomer to polymer in the first layer, remaining monomer sites are available to polymerize with monomer sites in the second layer, which enhances the bonding of the first layer to the second layer.

[0032] In one example, actinic radiation of wavelengths between 100 nm and 250 nm can be utilized to tune the surface cure and / or monomer conversion of the first layer. Tuning the surface cure of the first layer can assist with obtaining the desired properties (such as shear strength) of multiple-layer dielectric coatings of the present disclosure. The first dose of actinic radiation can include actinic radiation of below about 700 mJ / cm2in a range of between 100 nm and 250 nm. The first dose of actinic radiation can include actinic radiation of below about 500 mJ / cm2in a range of between 100 nm and 250 nm. In one example, the first dose of actinic radiation includes actinic radiation between about 100 mJ / cm2and about 600 mJ / cm2in a range of between 100 nm and 250 nm. In another example, the first dose of actinic radiation includes actinic radiation between about 200 mJ / cm2and about 600 mJ / cm2in a range of between 100 nm and 250 nm. In yet another example, the first dose of actinic radiation includes actinic radiation between about 250 mJ / cm2and about 475 mJ / cm2in a range of between 100 nm and 250 nm. In one example, the first dose includes less than 500 mJ / cm2in a range of less than or equal to 280 nm.

[0033] In one example, actinic radiation of wavelengths between 250 nm and 315 nm can be utilized to tune the through layer (or internal) cure of the first layer. The first dose of actinic radiation can include actinic radiation of below about 4000 mJ / cm2in a range of between 250 nm and 315 nm. In one example, the first dose of actinic radiation includes actinic radiation between about 1000 mJ / cm2and about 4000 mJ / cm2in a range of between 250 nm and 315 nm. In another example, the first dose of actinic radiation includes actinic radiation between about 1000 mJ / cm2and about 3000 mJ / cm2in a range of between 250 nm and 315 nm. In yet anotherexample, the first dose of actinic radiation includes actinic radiation between about 1000 mJ / cm2and about 2000 mJ / cm2in a range of between 250 nm and 315 nm.

[0034] In one example, actinic radiation of wavelengths between 315 nm and 400 nm can be utilized to tune the through layer cure of the first layer, such as the bulk of the first layer. The first dose of actinic radiation can include actinic radiation of greater than about 2800 mJ / cm2in a range of between 315 nm and 400 nm. In one example, the first dose of actinic radiation includes actinic radiation between about 2800 and about 7000 mJ / cm2in a range of between 315 nm and 400 nm. In another example, the first dose of actinic radiation includes actinic radiation between about 3500 and about 7000 mJ / cm2in a range of between 315 nm and 400 nm. In yet another example, the first dose of actinic radiation includes actinic radiation between about 3800 and about 7000 mJ / cm2in a range of between 315 nm and 400 nm.

[0035] The first dose of actinic radiation can include actinic radiation of greater than about 2500 mJ / cm2in a range of between 400 nm and 450 nm. The first dose of actinic radiation can include actinic radiation of greater than about 3000 mJ / cm2in a range of between 400 nm and 450 nm. In one example, the first dose of actinic radiation can include actinic radiation of between about 3000 mJ / cm2and 6000 mJ / cm2in a range of between 400 nm and 450 nm. In another example, the first dose of actinic radiation can include actinic radiation of between about 3000 mJ / cm2and 5000 mJ / cm2in a range of between 400 nm and 450 nm.

[0036] The first dose of actinic radiation can be provided by a D type lamp. In other embodiments, the first dose of actinic radiation is provided by a V type lamp or an LED lamp. In one example, the first dose of actinic radiation is provided for less than 5 seconds. In another example, the first dose of actinic radiation is provided for about 1 second to about 5 seconds. In yet another example, the first dose of actinic radiation is provided for about 1 second to about 2 seconds. The first dose of actinic radiation can be applied multiple times to ensure adhesion to the substrate.

[0037] The first dose of actinic radiation can be sufficient to adhere the first layer to the substrate. For example, adhering the first layer to the substrate can ensure contact between the first layer and the substrate. In one example, the shear strength for the adhesion between the first layer and the substrate is greater than about 5 MPa. In another example, the shear strength for the adhesion between the first layer and the substrate is greater than about 10 MPa. In one example, the crosshatch adhesion classification is at least 4B according to ASTM D3359. In anotherexample, the crosshatch adhesion classification is 5B according to ASTM D3359. The crosshatch adhesion classification can be less than 1 according to ISO 2409. The crosshatch adhesion classification can be 0 according to ISO 2409.

[0038] Referring to Step 140, a second layer of the coating composition is applied to the partially-cured first layer. The coating composition of the second layer includes coating compositions of the present disclosure, and this coating composition may be termed “second coating composition”. The second layer may be the same coating composition as the first layer. Alternatively, the second layer may include alternative coating compositions of the present disclosure. In one example, the second layer can be applied to the first layer without any additional treatment or primers. During the application of the second layer, at least a portion of the second layer is contacted with at least a portion of the first layer. In one non-limiting example, the second layer is in contact with the first layer, but the second layer is substantially free of contact with the substrate.

[0039] The second layer may be applied to the partially-cured first layer immediately, or the second layer may be applied to the partially-cured first layer after a period of time. For example, a period of time of between 5 seconds and 5 hours can elapse between partially curing the first layer and applying the second layer. In one example, a period of time of between 5 minutes and 3 hours can elapse between partially curing the first layer and applying the second layer. The substrate and / or first layer may be inspected prior to applying the second layer. For example, if after inspection the substrate is not electrically insulated according to desired dielectric properties, then Step 140 can be performed.

[0040] The coating composition may be applied sufficient to form various second layer thicknesses. The thickness of the second layer may be less than, equal to, or greater than the thickness of the first layer. In one example, the thickness of the second layer is greater than the thickness of the first layer. In one example, the thickness of the second layer can range from about 50 μm to about 200 μm. In another example, the thickness of the second layer can range from about 75 μm to about 200 μm. In yet another example, the thickness of the second layer can range from about 75 μm to about 125 μm.

[0041] Referring to Step 150, the second layer of the coating composition is exposed to a second dose of actinic radiation sufficient to bond the first and second layers together. Bonding the first layer and the second layer together can ensure contact between the first layer and thesecond layer. Sufficient adhesion can promote efficient electrical insulation for the dielectric coating. Bonding the first layer and the second layer together can include a reaction between unreacted monomers of the first layer and monomers of the second layer. Both the first layer and the second layer can be exposed to the second dose of actinic radiation. The second dose may be greater in energy compared to the first dose. In one example, the second dose of actinic radiation is between 90-110% of the energy of the first dose of actinic radiation. In another example, the second dose of actinic radiation is greater than 110% of the energy of the first dose of actinic radiation. The second dose of actinic radiation can include various energies and wavelengths as discussed for the first dose of actinic radiation, such as below about 700 mJ / cm2in a range of between 100 nm and 250 nm, below about 4000 mJ / cm2in a range of between 250 nm and 315 nm, greater than about 2800 mJ / cm2in a range of between 315 nm and 400 nm, and / or greater than about 2500 mJ / cm2in a range of between 400 nm and 450 nm.

[0042] The second dose applied to the second layer may be sufficient for the monomer conversion of the second layer to be greater than the monomer conversion of the first layer using the first dose. In one example, the second layer is exposed to a second dose of actinic radiation sufficient to at least partially cure the actinic radiation curable material of the second layer to a monomer conversion greater than about 60%. In another example, the second layer is exposed to a second dose of actinic radiation sufficient to at least partially cure the actinic radiation curable material of the second layer to a monomer conversion of between about 60% and 100%. In another example, the second layer is exposed to a second dose of actinic radiation sufficient to partially cure the actinic radiation curable material of the second layer to a monomer conversion of greater than 70%.

[0043] In one example, the second dose of actinic radiation is provided for less than 5 seconds. In another example, the second dose of actinic radiation is provided for about 1 second to about 5 seconds. In yet another example, the second dose of actinic radiation is provided for about 1 second to about 2 seconds. The second dose of actinic radiation can be applied multiple times to ensure adhesion to the first layer. The shear strength (such as delamination shear strength) of the first layer bonded to the second layer can be greater than 5 MPa. In one example, the shear strength (such as delamination shear strength) of the first layer bonded to the second layer is greater than about 10 MPa. In another example, the shear strength (such as delamination shear strength) of the first layer bonded to the second layer is greater than about 12 MPa.

[0044] In one example, the total thickness of the multiple-layer coating can range from about 50 μm to about 400 μm. In another example, the thickness of the multiple-layer coating can range from about 100 μm to about 300 μm. In yet another example, the thickness of the multiple-layer coating can range from about 150 μm to about 250 μm. Additional coating applications of the coating composition may be applied to the second layer, and additional doses of actinic radiation can be applied to these additional coats to at least partially cure the additional coat.

[0045] The multiple-layers can provide the same or better performance as a single layer. The overall thermal conductivity of the multiple-layer coating can be at least about 0.2 W / mK. In one example, the overall thermal conductivity of the multiple-layer coating can be at least about 1 W / mK. In yet another example, the overall thermal conductivity of the multiple-layer coating can be at least about 3 W / mK. The multiple-layer coating can be a dielectric coating for various substrates. For example, the multiple-layer coating can be a dielectric coating for a battery cell. In one example, the dielectric strength of the dielectric coating is greater than 5 V / μm at 23 °C. In another example, the dielectric strength of the dielectric coating is greater than 15 V / μm at 23 °C.

[0046] FIG.2 illustrates a multiple-layer dielectric coating 210 on a substrate 250, according to some embodiments. In one example, multiple-layer dielectric coating 210 is formed by method 100. As shown, multiple-layer dielectric coating 210 can include first layer 212 and second layer 214. First layer 212 can correspond to the first layer of method 100, and second layer 214 can correspond to the second layer of method 100. Substrate 250 includes substrates of the present disclosure, such as a portion of a battery cell. As shown, first layer 212 is in contact with at least a portion of substrate 250 and at least a portion of second layer 214.

[0047] Importantly, multiple-layer dielectric coatings of the present disclosure can be formed without the use of an additional component such as an adhesive or primer to sufficiently adhere the first layer to the second layer. For battery cell applications, due to the unique formulations and methods of forming the coatings on substrates, the first layer does not need to be removed from the substrate during the rework process prior to applying the second layer. This improves the efficiency of the rework process by reducing production time and cost.

[0048] The presence of diffracting agents in the present compositions can assist in tuning monomer conversion by diffracting incident actinic radiation, thereby limiting available actinicradiation to initiate polymerization of the curable composition. The actinic radiation energy profiles of the present disclosure can be useful for tuning the specific monomer conversions of the present disclosure and can promote desired surface and through curing of the actinic radiation curable material. Tuning the specific monomer conversions and / or surface cure can promote enhanced multiple-layer adhesion during the application of multiple-layers of the coating composition on a substrate. The multiple-layer coatings of the present disclosure exhibit excellent adhesion to the substrate, heat dissipation properties, and electrical insulation. Example 1

[0049] The ingredients listed in Table 1 were added into a mixing vessel in sequence and mixed at 600 RPM for 4 hours before being passed through an Eiger mill for about 30 min. The product was then transferred to a HVLP Spray gun and applied on 3003 aluminum panels, and then cured through a UV conveyor oven equipped with D bulb. A set of panels of 3’’ x 6’’ size were coated in about 101.6 μm thickness and cured in a dosage shown in Table 2, then applied with a second coat in about 101.6 μm thickness and cured in a dosage listed in Table 2. These panels could withstand 5.0 kV for 120 seconds with no greater than 0.1 – 0.2 µA leakage current and had crosshatch adhesion of 5B to the substrate according to ASTM D3353, but the complete inter-coat delamination was observed between the two coats. Table 1. Formulation Example. Component Chemical Name Amount ) .0 .4 .8 .6 .5 .2 .1Additive Polymeric carbodiimide 0.5 Pigment Ammonium iron(III) hexacyanoferrate(II) 0.5 .5 .9 .4 .5Table 2. UV dosages. # of Coats Time in UVA UVB UVC UVV C t b t t2 2 2 2)Example 2

[0050] The ingredients listed in Table 3 were added into a mixing vessel in sequence, and mixed at 600 RPM for 4 hours before being passed through an Eiger mill for about 30 min. The product was then transferred to a HVLP Spray gun and applied on 3003 aluminum panels. The panels were passed through a UV conveyor oven equipped with D bulb to cure the coatings. Large panels of 3’’ x 6’’ size with 101.6 μm thickness could withstand 3.6 kV for 240 seconds with no greater than 0.1 µA leakage current, and had crosshatch adhesion of 5B according to ASTM D3353. A number of lap shear panels of 1’’ x 4’’ size were coated in either single coat or two coats and cured in different dosages as shown in Table 4. The coated panels were bonded with 2K polyurethane adhesive and tested on an Instron extensometer. The shear strength and failure mode, recorded in Table 5, showed no significant difference between single coat and two coats. Importantly, the inter-coat adhesion failure mode was not observed on fractured bonding surfaces.Table 3. Formulation Example. Component Chemical Name Amount (wt.%) .6 .0 .3 .8 .7 .5 .3 .1 .5 .8 .5 .4 .5Table 4. UV Dosages. # of Coats Time in UVA UVB UVC UVV 2)1st 4014 1398 321 3336 D 2 3 hrs. 2nd 3943 1338 302 3234 Table 5. Shear Strength and Failure Mode. Failure Mode % - nExample 3

[0051] The ingredients listed in Table 6 were added into a mixing vessel in sequence and mixed at 600 RPM for 4 hours before being passed through an Eiger mill for about 30 min. The product was then transferred to a HVLP Spray gun and applied on 3003 aluminum panels. The panels were passed through an UV conveyor oven equipped with D bulb to cure the coatings. Large panels of 3’’ X 6’’ size with 101.6 μm thickness could withstand 3.6 kV for 240 seconds with no more than 0.1 µA leakage current and had crosshatch adhesion of 5B according to ASTM D3353.Table 6. Formulation Example. Component Chemical Name Amount (wt.%) .8 .7 .6 .0 .8 .6 .5 .2 .1 .5 .0 .3 .4 .5Example 4

[0052] Example 2 and 3 formulations were applied on panels of 3” x 6” size in both single coat or two coats and cured with D lamp in similar dosages as listed in Table 4. The panels were put in a Thermotron chamber situated at 85 °C and 85% relative humidity and kept there for 6 weeks or 1000 hrs. The panels were taken out after the testing cycles and the crosshatch adhesion was performed on the panels. In one non-limiting example, the panels with single coats of both formulas maintained 5B adhesion according to ASTM D3353, however, the panel with two coats of Example 3 formulation showed partial inter-coat adhesion failure versus that of Example 2 which maintained adhesion of 5B.Example 5

[0053] The ingredients listed in Table 7 were added into a mixing vessel in sequence and mixed at 600 RPM for 4 hours before being passed through an Eiger mill for about 30 min. The product was then transferred to a HVLP Spray gun and applied on 3003 aluminum panels in both single coat and two coats. The panels were passed through an UV conveyor oven equipped with either H+ or D bulb to cure the coatings in dosages listed in Table 8. The panels were put in a Thermotron chamber situated at 85 °C and 85% relative humidity and remained there for 6 weeks or 1000 hrs. The panels were taken out after the testing cycles and the crosshatch adhesion was performed on the panels. The panels with single coats of both formulas maintained 5B adhesion according to ASTM D3353, however, the panel with two coats cured with H+ bulb showed severe inter-coat delamination versus the formulation cured with D bulb showing only very minor inter-coat adhesion failure. Accordingly, the actinic radiation energy profiles of the present disclosure can be useful for tuning the specific monomer conversions of the present disclosure and can promote desired surface and through curing of the actinic radiation curable material. Table 7. Formulation Example. Component Chemical Name Amount ) .0 .2 .9 .0 .7 .3 .4 .2 .1 .4Filler Aluminum hydroxide 20.0 Adhesion promoter Methacryloylethyl phosphate 0.4 Tabe . osages. # of Coats Time in UVA UVB UVC UVV Coats between (mJ / cm2) (mJ / cm2) (mJ / cm2) (mJ / cm2)Example 6

[0054] The ingredients listed in Table 9 were added into a mixing vessel in sequence and mixed at 600 RPM for 4 hours before being passed through an Eiger mill for about 30 min. The product was then transferred to a HVLP Spray gun and applied on 3003 aluminum panels. The panels were passed through an UV conveyor oven equipped with D bulb to cure the coatings. Large panels of 3’’ x 6’’ size with 101.6 μm thickness could withstand 5.0 kV for 120 seconds with no more than 0.1 µA leakage current and had crosshatch adhesion of 5B according to ASTM D3353. A number of lap shear panels of 1’’ x 4’’ size were coated in two coats and cured in dosages as shown in Table 10. The coated panels were bonded with 2K polyurethane adhesive and tested on Instron. The shear strength and failure mode are recorded in Table 11.

[0055] Four pairs of bonded panels were put in a Thermotron chamber situated at 85 °C and 85% relative humidity and remained there for 6 weeks or 1000 hrs. The panels were tested on Instron after the aging cycle and the results were recorded in Table 11 alongside the initial results. Initial panels had high shear strength and showed no inter-coat adhesion failure, therefore, indicated good initial inter-coat adhesion. Given the high shear strength after such asevere aging process, the inter-coat adhesion was sufficiently maintained for battery cell applications. Table 9. Formulation Example. Component Chemical Name Amount (wt.%) .5 .8 .1 .8 .7 .5 .3 .1 .5 .5 .2 .4 .5Table 10. UV Dosages. # of Coats Time in UVA UVB UVC UVV 2)Table 11. Shear Strength and Failure Mode. Failure Mode % - nExample 7

[0056] The ingredients listed in Table 12 were added into a mixing vessel in sequence and mixed at 600 RPM for 4 hours before being passed through an Eiger mill for about 30 min. The product was then transferred to a HVLP Spray gun and applied on 3003 aluminum panels. The panels were passed through an UV conveyor oven equipped with D bulb to cure the coatings. Large panels of 3’’ x 6’’ size with 101.6 μm thickness could withstand 5.0 kV for 120 seconds with no more than 0.1 µA leakage current and had crosshatch adhesion of 5B according to ASTM D3353. A number of lap shear panels of 1’’ x 4’’ size were coated in two coats and cured in dosages as shown in Table 13. The coated panels were bonded with 2K polyurethane adhesive and tested on Instron.

[0057] The shear strength and failure mode are recorded in Table 14. Four pairs of bonded panels were put in a Thermotron chamber situated at 85 °C and 85% relative humidity and remained there for 6 weeks or 1000 hrs. The panels were then tested on Instron after the aging cycle and the results were recorded in Table 14 alongside the initial results. Initial panels had high shear strength and showed no inter-coat adhesion failure, therefore, indicated good initial inter-coat adhesion. Given the high shear strength after such a severe aging process, the inter- coat adhesion was sufficiently maintained for the battery applications.Table 12. Formulation Example. Component Chemical Name Amount (wt.%)Table 13. UV Dosages. # of Coats Time in UVA UVB UVC UVV 2)Table 14. Shear Strength and Failure Mode. Failure Mode % - nExample 8

[0058] Both Example 2 and 6 formulations were applied on panels of 3” x 6” size in single coat or two coats and cured with a D lamp in dosages as listed in Table 15. The panels were immersed in a water bath maintained at 85 °C and kept there for 6 weeks or 1000 hrs. The panels were taken out after the testing cycles and the inter-coat adhesion was accessed by the severity of bubbling resulted from the inter-coat delamination after such a severe aging process. In one non- limiting example, the panels with single coats of both examples showed no loss of adhesion, while the panels of Example 6 showed higher degree of delamination than those of Example 2 as a result of lack of partial UV blocking from boron nitride. The presence of boron nitride in the present compositions can assist in tuning monomer conversion by diffracting incident actinic radiation, thereby limiting available actinic radiation to initiate polymerization of the curable composition.Table 15. UV Dosages. # of Coats Time in UVA UVB UVC UVV Coats between (mJ / cm2) (mJ / cm2) (mJ / cm2) (mJ / cm2)

[0059] While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims

CLAIMS What Is Claimed Is:

1. A method for forming a multiple-layer dielectric coating on a substrate, the method comprising: (a) providing a coating composition having: (i) an actinic radiation curable material including at least one of a monomer and an oligomer; and (ii) a thermally conductive filler, (b) applying a first layer of the coating composition to the substrate; (c) exposing the first layer to a first dose of actinic radiation sufficient to partially cure the actinic radiation curable material of the first layer to a monomer conversion of between about 60% and about 95%; (d) applying a second layer of the coating composition to the partially-cured first layer; and (e) exposing the second layer of the coating composition to a second dose of actinic radiation sufficient to bond the first and second layers together and to cure the actinic radiation curable material of the second layer to a monomer conversion of at least 60%.

2. The method of claim 1, including exposing the first and second layers of the coating composition to the second dose of actinic radiation.

3. The method of claim 1, wherein the first and second layers are bonded together with a delamination shear strength of at least 10 MPa.

4. The method of claim 1, wherein a first component of the thermally conductive filler has a first refractive index, and the actinic radiation curable material has a second refractive index, the first refractive index being at least 10% different than the second refractive index.

5. The method of claim 4, wherein the first refractive index is at least 20% greater than the second refractive index.

6. The method of claim 1, wherein the first dose of actinic radiation is between 3500 and 7000 mJ / cm2in a range of between 315 nm and 400 nm, and less than 500 mJ / cm2in a range of less than or equal to 280 nm.

7. The method of claim 6, wherein the second dose of actinic radiation is between 90-110% of the energy of the first dose of actinic radiation.

8. The method of claim 1, wherein the actinic radiation curable material is selected from one or more of an acrylate and an epoxy.

9. The method of claim 1, wherein the multiple-layer dielectric coating has a thermal conductivity of at least 0.2 W / mK.

10. The method of claim 1, wherein the substrate is a portion of a battery cell.

11. A method for forming a multiple-layer coating on a substrate, the method comprising: (a) providing a first coating composition having: (i) an actinic radiation curable material including one or more acrylate monomers; and (ii) a thermally conductive filler, wherein a first component of the thermally conductive filler has a first refractive index, and the actinic radiation curable material has a second refractive index, the first refractive index being at least 10% different than the second refractive index, (b) applying a first layer of the first coating composition to the substrate; (c) exposing the first layer to a first dose of actinic radiation sufficient to partially cure the actinic radiation curable material of the first layer, wherein the first dose of actinic radiation includes actinic radiation between about 200 mJ / cm2and about 600 mJ / cm2in a range of between 100 nm and 250 nm; (d) applying a second layer of a second coating composition to the partially-cured first layer; and(e) exposing the second layer of the second coating composition to a second dose of actinic radiation sufficient to bond the first and second layers together.

12. The method of claim 11, wherein the first dose of actinic radiation further includes actinic radiation between about 3500 mJ / cm2and 7000 mJ / cm2in a range of between about 315 nm and 400 nm, and actinic radiation between about 1000 mJ / cm2and 4000 mJ / cm2in a range of between about 250 nm and 315 nm.

13. The method of claim 11, wherein the first dose of actinic radiation includes actinic radiation between about 250 mJ / cm2and about 475 mJ / cm2in the range of between 100 nm and 250 nm.

14. The method of claim 11, wherein the first component includes boron nitride and the first refractive index is greater than about 1.

8.

15. The method of claim 11, wherein the actinic radiation curable material includes at least one of isobornyl acrylate (IBOA) and dipropylene glycol diacrylate (DPGDA).

16. The method of claim 11, wherein the first coating composition and the second coating composition are the same.

17. The method of claim 11, wherein the first dose of actinic radiation is provided for about 1 second to about 2 seconds.

18. An actinic radiation curable composition for a dielectric coating, the actinic radiation curable composition comprising: an actinic radiation curable material, wherein the actinic radiation curable material includes at least one of isobornyl acrylate (IBOA) and dipropylene glycol diacrylate (DPGDA); a photoinitiator to initiate curing of the actinic radiation curable material with exposure to actinic radiation; anda thermally conductive filler, wherein a first component of the thermally conductive filler has a first refractive index, and the actinic radiation curable material has a second refractive index, the first refractive index being at least 10% different than the second refractive index, wherein a concentration of the first component ranges from about 2 parts per hundred of the actinic radiation curable material to about 50 parts per hundred of the actinic radiation curable material.

19. The actinic radiation curable composition of claim 18, wherein the actinic radiation curable material further includes a bisphenol A epoxy acrylate.

20. The actinic radiation curable composition of claim 18, wherein the actinic radiation curable material further includes a material having vinyl ether functional groups, wherein a weight percentage of the material having vinyl ether functional groups in the actinic radiation curable composition is greater than about 10 wt.%.

21. The actinic radiation curable composition of claim 20, wherein the material having vinyl ether functional groups includes 2-(2-Vinyloxyethoxy)ethyl acrylate.

22. The actinic radiation curable composition of claim 18, wherein the first component includes boron nitride.

23. The actinic radiation curable composition of claim 18, wherein the thermally conductive filler further includes a second component including aluminum hydroxide.

Images