Uv-curable thermally conductive dielectric coating

Abstract

The present invention provides a UV-curable liquid coating composition that can be spray applied to a substrate to form a thin, pinhole-free, thermally conductive, dielectric coating having a combination of improved dielectric strength and improved thermal conductivity. The liquid coating composition includes an organic resin, such as a polyester resin; a free-radical reactive diluent; a thermally conductive filler; a photoinitiator; an adhesion promoter; and at least one additive selected from a dispersant, a gas scavenger, a defoamer, an anti-foaming agent, an antioxidant, a pigment, an organic solvent, and a rheology modifier. Methods of making the composition, the UV-curable coating and the cured coating, and a substrate comprising the UV-curable or cured thermally conductive, dielectric coating are also provided.

Description

Technical Field

[0001] The present invention relates to a UV-curable liquid coating composition that can be used to deposit a thermally conductive dielectric coating on a substrate; an intermediate comprising a substrate having a UV-curable, optionally dried, coating composition layer deposited thereon; an adhesive layer of a cured thermally conductive dielectric coating composition on the substrate; a coated substrate; and a method for preparing said composition, coating, coating layer, and coated substrate. Background Technology

[0002] Electrical components are typically electrically insulated by applying a high-dielectric-strength material. While dielectric materials provide electrical insulation, they generally do not promote heat dissipation and may be thermally insulating. In many electrical components (particularly for vehicle OEMs), faster heat dissipation from battery operation is highly desirable to improve the driving range of battery-powered vehicles and the lifespan of the battery pack. Common battery electrical insulation in such vehicles is primarily achieved through powder coatings, thermosetting coatings, or the use of plastic insulating wraps or films; none of these methods adequately meet the heat dissipation requirements and the demands of rapid cryogenic production. Powder coatings have the disadvantages of requiring high-temperature curing (e.g., 10-15 minutes at 175-205°C) and a ramp time (approximately 30 minutes) for the component to reach curing temperature; thermosetting coatings share these disadvantages. Powder coatings are typically thick and require multiple layers to ensure a pinhole-free film. Therefore, powder coatings have the additional disadvantages of undesirably increased weight and high thermal resistance. Plastic wraps require complex handling and processing or installation and have unpredictable long-term reliability and a risk of delamination.

[0003] At least in part, due to the high coating thickness or multiple coatings required to ensure the necessary dielectric protection, conventional powder coatings and UV-curable coating options on the market do not offer enhanced thermal conductivity, making them unsuitable for the growing demand for efficient heat dissipation. Conventional UV-curable materials may also experience undesirable shrinkage during curing, leaving areas of reduced dielectric insulation that impact reliability. Typically, these options do not promote heat dissipation, which is crucial for rechargeable batteries that generate heat during charging and discharging. The proliferation of battery-powered vehicles and the like has increased the demand for lightweight, high-dielectric-strength, and heat-dissipating materials. Therefore, there is a need for thin dielectric coatings with high dielectric strength and high thermal conductivity or low thermal resistance, suitable for bake-free, higher-speed curing production line conditions for these and other applications.

[0004] There is also a desire to develop dielectric coatings that resist electrical conductivity but conduct heat to promote heat dissipation, particularly for battery cooling systems, prismatic cells, cold plates, power inverters, buses, and chargers. Improved dielectric coatings that provide good electrical insulation with low film thickness to reduce weight, can be applied through less complex processes, and use less time and energy are also desired. Therefore, there is a need for thermally conductive dielectric coatings that can be applied defect-free with a thinner coating thickness than previously available for vehicles, possessing a combination of improved dielectric strength and improved thermal conductivity or low thermal resistance. Summary of the Invention

[0005] This invention relates to UV-curable liquid coating compositions with reduced VOC content, preferably VOC-free, which can be used to deposit a thermally conductive dielectric coating that is photocurable within seconds by applied UV energy. The formulation of the VOC-free UV-curable coating composition typically comprises: at least one monomer, oligomer, or resin having one or more polymerizable groups capable of reacting upon exposure to UV irradiation; a radical reactive diluent, thermally conductive filler, photoinitiator, and optionally, an adhesion promoter, dispersant, and / or other additives for reacting the polymerizable groups under UV irradiation. The curing process of the applied liquid coating composition can be divided into two steps. First, under UV irradiation, the photoinitiator generates radicals or reactive cations. Second, the radicals or reactive cations induce polymerization of the monomer / oligomer / resin having polymerizable functional groups (e.g., unsaturated bonds or epoxy groups) and the radical reactive diluent. One advantage of the UV-curable coatings according to the present invention is that most or all of the components in the formulation can participate directly or indirectly in the curing reaction and become part of the solid film, thereby resulting in reduced or zero emissions of volatile organic compounds (VOCs) during curing. As used herein, “VOC” is defined according to 40 CFR 51.100 as any carbon compound (excluding carbon monoxide, carbon dioxide, carbonic acid, metal carbides or carbonates, and ammonium carbonate) that participates in atmospheric photochemical reactions.

[0006] Compared to powder coatings, UV-curable coatings offer faster curing rates and lower energy consumption. Unlike conventional plastic insulating films, the UV-curable liquid coating compositions disclosed herein can be readily sprayed onto all surfaces (e.g., battery cell cans and complex cooling plates) using conventional techniques, or alternatively, applied to specific portions of a substrate surface using any number of printing or masking methods known in the art. The UV-curable liquid coating compositions described herein have desired viscosities that allow them to form a thin, void-free coating on the coated surface. The UV-curable liquid coating compositions also provide good coverage at substrate edges, an improvement over some spray coatings that have poor edge coverage or shrink during curing, thus reducing edge coverage. As further described herein, cured polymer coatings with both high dielectric strength and high thermal conductivity are highly advantageous as electrical insulation in battery pack operation, where efficient heat dissipation is crucial for battery safety and lifespan. Furthermore, cured polymer coatings can provide additional protection against corrosion and abrasion, where condensation and continuous vibration are common during vehicle operation. The UV-curable liquid coating compositions, the cured polymer thermally conductive dielectric coatings on substrates, and the coated substrates according to various aspects of the present invention address one or more of the aforementioned disadvantages or requirements and exhibit high dielectric strength, heat dissipation, and good electrical insulation as further described herein.

[0007] Various embodiments of UV-curable liquid coating compositions may comprise, consist substantially of, or consist of: (a) an organic monomer, oligomer, or resin having one or more polymerizable functional groups (e.g., C=C double bonds, epoxy groups, etc.) for reaction under UV irradiation, preferably comprising an unsaturated polyester resin; (b) an organic radical reactive diluent different from (a) and having one or more polymerizable functional groups for reaction under UV irradiation, as described herein; (c) at least one thermally conductive filler; (d) at least one photoinitiator; and preferably at least one additive selected from adhesion promoters, degassing agents, defoamers, antifoaming agents, and dispersants. As used herein, antifoaming agents prevent foam formation, while defoaming agents reduce existing foam. Optionally, such compositions may also contain other additives, such as coupling agents, organic solvents, accelerators, optionally surface-modified rheology modifiers (also referred to herein as thixotropic agents), pigments and dyes, plasticizers, flexibleizers, flame retardants, impact modifiers / toughening agents, fillers other than (c), flow control agents, inhibitors, antioxidants, non-reactive diluents, extenders, or other auxiliaries. In some embodiments, the UV-curable liquid coating composition is free of volatile organic compounds (VOCs). Embodiments of the invention have been described throughout this disclosure, including: Implementation Scheme 1. A UV-curable liquid coating composition, said UV-curable liquid coating composition comprising: (a) At least one UV-curable monomer, oligomer, or resin having one or more polymerizable groups for reaction under UV irradiation, which is desired to be present in an amount ranging from 9% to 95%, preferably from 10% to 50%; (b) At least one functional or bifunctional radical reactive diluent, different from (a) and comprising one or more polymerizable groups for reaction under UV irradiation, which is preferably present in an amount ranging from 10% to 95%, preferably 15% to 80%, and preferably 25% to 50%; (c) At least one thermally conductive filler, which is preferably present in an amount ranging from 1% to 70%, preferably 5% to 60%, and more preferably 10% to 50%; (d) At least one photoinitiator, which is preferably present in an amount ranging from 0.1% to 7.0% or preferably from 0.75% to 5.0%; (e) at least one adhesion promoter; and (f) Any available dispersant. Wherein (a) is selected from unsaturated polyester monomers, oligomers, resins and combinations thereof, preferably from vinyl esters, more preferably from epoxy vinyl esters (e.g. epoxy acrylates and epoxy methacrylates and combinations thereof).

[0008] The UV-curable liquid coating composition of embodiment 1 may further comprise at least one additive, preferably selected from: organic solvents, accelerators, rheology modifiers (also referred to herein as thixotropic agents) that can optionally be surface-modified, degassing agents, defoamers, coupling agents, antifoaming agents, pigments and dyes, plasticizers, softeners, flame retardants, impact modifiers / toughening agents, additional fillers other than (c), flow control agents, inhibitors, antioxidants, non-reactive diluents, extenders, or other auxiliaries. In some aspects of this embodiment, the UV-curable liquid composition is formaldehyde-free.

[0009] Implementation Scheme 2. The UV-curable liquid coating composition of Implementation Scheme 1 is further characterized in that the components are or contain the following (all given in weight %): (a) At least one unsaturated polyester resin, preferably an epoxy vinyl ester resin, such as epoxy acrylate and epoxy methacrylate and combinations thereof, which is preferably present in the range of 9% to 95%, preferably 10% to 50%, more preferably 11% to 35%; (b) At least one free radical reactive diluent, which is preferably present in the range of 10% to 95%, preferably 15% to 80%, more preferably 25% to 50%; (c) At least one thermally conductive filler (e.g., boron nitride, alumina, aluminum trihydrate, and combinations thereof) is preferably present in the range of 1.0% to 70% or 5% to 60%, preferably 10% to 50%; (d) At least one photoinitiator, which is preferably present in the range of 0.1% to 5%, preferably 1% to 4%, and more preferably 1.5% to 3.5%; (e) at least one adhesion promoter, preferably present in the range of 0.1% to 10%, preferably 0.5% to 8.0%, more preferably 0.75% to 6.0%, and most preferably 1.0% to 5.0%; and Optional existence (f) At least one dispersant, ranging from 0.0% to, preferably, 7.0%, 6.0%, 5.0%, 4.0%, 3.0% in ascending order, or from 0.1% to 2.0%, and preferably present in an amount of 0.25% to 1.5%, preferably 0.5% to 1.25%; (g) Degassing agents, defoamers, antifoaming agents, or combinations thereof, preferably each present in the range of 0% to 2.0%; (h) At least one organic solvent, which is preferably present in the range of 0% to 20%; (i) At least one additive selected from rheology modifiers, softeners and plasticizers, each preferably present in the range of 0% to 5%; The weight percentage of each component is relative to the total weight of the composition, and the total amount of components does not exceed 100% by weight.

[0010] Implementation Scheme 3. A UV-curable liquid coating composition according to any one of the above embodiments, wherein, relative to the total weight of the composition, (a) at least one unsaturated polyester resin, epoxy vinyl ester resin, such as epoxy acrylate and epoxy methacrylate, and combinations thereof are present in the following ranges: 9% to 95%, 10% to 15% by weight, 15% to 20% by weight, 20% to 25% by weight, 25% to 30% by weight, 30% to 35% by weight, 35% to 40% by weight, 40% to 45% by weight, 45% to 50% by weight, 50% to 55% by weight, 55% to 60% by weight, 60% to 65% by weight, 65% to 70% by weight, 70% to 75% by weight, 75% to 80% by weight, 80% to 85% by weight, 85% to 90%, 90% to 95%, or any combination of two or more of the above ranges (e.g., 25% to 50% by weight), or any one of the above values.

[0011] Implementation Scheme 4. A UV-curable liquid coating composition according to any one of the above embodiments, wherein, relative to the total weight of the composition, (b) at least one free radical reactive diluent is present in the following ranges: 10 wt% to 15 wt%, 15 wt% to 20 wt%, 20 wt% to 25 wt%, 25 wt% to 30 wt%, 30 wt% to 35 wt%, 35 wt% to 40 wt%, 40 wt% to 45 wt%, 45 wt% to 50 wt%, 50 wt% to 55 wt%, 55 wt% to 60 wt%, 60 wt% to 65 wt%, 65 wt% to 70 wt%, 70 wt% to 75 wt%, 75 wt% to 80 wt%, 80 wt% to 85 wt%, 85% to 90%, 90% to 95%, or any combination of two or more of the above ranges (e.g., 25 wt% to 50 wt%), or any one of the above values.

[0012] Implementation Scheme 5. A UV-curable liquid coating composition according to any one of the above embodiments, wherein, relative to the total weight of the composition, (c) at least one thermally conductive filler (which preferably comprises boron nitride filler) is present in the following ranges: 5% to 10% by weight, 10% to 15% by weight, 15% to 20% by weight, 20% to 25% by weight, 25% to 30% by weight, 30% to 35% by weight, 35% to 40% by weight, 40% to 45% by weight, 45% to 50% by weight, 50% to 55% by weight, 55% to 60% by weight, 60% to 65% by weight, 65% to 70% by weight, or any combination of two or more of the above ranges (e.g., 15% to 55% by weight, or 10% to 30% by weight), or any one of the above values.

[0013] Implementation Scheme 6. A UV-curable liquid coating composition according to any one of the above embodiments, wherein, relative to the total weight of the composition, (d) at least one photoinitiator is present in the following range: 0.1 wt% to 0.2 wt%, 0.2 wt% to 0.3 wt%, 0.3 wt% to 0.4 wt%, 0.4 wt% to 0.5 wt%, 0.5 wt% to 0.6 wt%, 0.6 wt% to 0.7 wt%, 0.7 wt% to 0.8 wt%, 0.8 wt% to 0.9 wt%, 0.9 wt% to 1.0 wt%, 1.0 wt% to 1.1 wt%. 1.1% to 1.2% by weight, 1.2% to 1.3% by weight, 1.3% to 1.4% by weight, 1.4% to 1.5% by weight, 1.5% to 1.6% by weight, 1.6% to 1.7% by weight, 1.7% to 1.8% by weight, 1.8% to 1.9% by weight, 1.9% to 2% by weight, 2% to 2.1% by weight, 2.1% to 2.2% by weight, 2.2% to 2.3% by weight, 2.3% to 2.4% by weight, 2.4% to 2.5% by weight, 2.5% to 2. 6 wt%, 2.6 wt% to 2.7 wt%, 2.7 wt% to 2.8 wt%, 2.8 wt% to 2.9 wt%, 2.9 wt% to 3 wt%, 3 wt% to 3.1 wt%, 3.1 wt% to 3.2 wt%, 3.2 wt% to 3.3 wt%, 3.3 wt% to 3.4 wt%, 3.4 wt% to 3.5 wt%, 3.5 wt% to 3.6 wt%, 3.6 wt% to 3.7 wt%, 3.7 wt% to 3.8 wt%, 3.8 wt% to 3.9 wt%, 3.9 wt% to 4 wt%, 4.0 wt% to 4.1% by weight, 4.1% to 4.2% by weight, 4.2% to 4.3% by weight, 4.3% to 4.4% by weight, 4.4% to 4.5% by weight, 4.5% to 4.6% by weight, 4.6% to 4.7% by weight, 4.7% to 4.8% by weight, 4.8% to 4.9% by weight, 4.9% to 5% by weight, or any combination of two or more of the above ranges (e.g., 0.1% to 5%, 1% to 4%, 1.5% to 3.5%, 0.3% to 0.7% by weight), or any of the above values.

[0014] Implementation Scheme 7. A UV-curable liquid coating composition according to any one of the above embodiments, wherein, relative to the total weight of the composition, (e) at least one adhesion promoter is present in the following range: 0.1 wt% to 0.2 wt%, 0.2 wt% to 0.3 wt%, 0.3 wt% to 0.4 wt%, 0.4 wt% to 0.5 wt%, 0.5 wt% to 0.6 wt%, 0.6 wt% to 0.7 wt%, 0.7 wt% to 0.8 wt%, 0.8 wt% to 0.9 wt%, 0.9 wt% to 1.0 wt%, 1.0 wt% to 1.1 wt%, 1.1 wt% to 1.2 wt%, 1.2 wt% to 1.3 wt%, 1.3 wt% to 1.4 wt%, 1 0.4 wt% to 1.5 wt%, 1.5 wt% to 1.6 wt%, 1.6 wt% to 1.7 wt%, 1.7 wt% to 1.8 wt%, 1.8 wt% to 1.9 wt%, 1.9 wt% to 2 wt%, 2 wt% to 2.1 wt%, 2.1 wt% to 2.2 wt%, 2.2 wt% to 2.3 wt%, 2.3 wt% to 2.4 wt%, 2.4 wt% to 2.5 wt%, 2.5 wt% to 2.6 wt%, 2.6 wt% to 2.7 wt%, 2.7 wt% to 2.8 wt%, 2.8 wt% to 2.9 wt%, 2.9 wt% to 3 wt%, 3 wt% to 3.1 wt%, 3.1 wt% to 3.2 wt%, 3.2 wt% 3.3% to 3.4% by weight, 3.4% to 3.5% by weight, 3.5% to 3.6% by weight, 3.6% to 3.7% by weight, 3.7% to 3.8% by weight, 3.8% to 3.9% by weight, 3.9% to 4% by weight, 4.0% to 4.1% by weight, 4.1% to 4.2% by weight, 4.2% to 4.3% by weight, 4.3% to 4.4% by weight, 4.4% to 4.5% by weight, 4.5% to 4.6% by weight, 4.6% to 4.7% by weight, 4.7% to 4.8% by weight, 4.8% to 4.9% by weight, 4.9% to 5% by weight, 5.0% by weight. 5.1% by weight, 5.1% by weight to 5.2% by weight, 5.2% by weight to 5.3% by weight, 5.3% by weight to 5.4% by weight, 5.4% by weight to 5.5% by weight, 5.5% by weight to 5.6% by weight, 5.6% by weight to 5.7% by weight, 5.7% by weight to 5.8% by weight, 5.8% by weight to 5.9% by weight, 5.9% by weight to 6% by weight, 6% by weight to 6.1% by weight, 6.1% by weight to 6.2% by weight, 6.2% by weight to 6.3% by weight, 6.3% by weight to 6.4% by weight, 6.4% by weight to 6.5% by weight, 6.5% by weight to 6.6% by weight, 6.6% by weight to 6.7% by weight, 6.7% by weight to 6.8% by weight, 6.8 wt% to 6.9 wt%, 6.9 wt% to 7 wt%, 7 wt% to 7.1 wt%, 7.1 wt% to 7.2 wt%, 7.2 wt% to 7.3 wt%, 7.3 wt% to 7.4 wt%, 7.4 wt% to 7.5 wt%, 7.5 wt% to 7.6 wt%, 7.6 wt% to 7.7 wt%, 7.7 wt% to 7.8 wt%, 7.8 wt% to 7.9 wt%, 7.9 wt% to 8 wt%, 8.0 wt% to 8.1 wt%, 8.1 wt% to 8.2 wt% %, 8.2% to 8.3% by weight, 8.3% to 8.4% by weight, 8.4% to 8.5% by weight, 8.5% to 8.6% by weight, 8.6% to 8.7% by weight, 8.7% to 8.8% by weight, 8.8% to 8.9% by weight, 8.9% to 9% by weight, or any combination of two or more of the above ranges (e.g., 0.3% to 0.7% by weight, 0.1% to 9%, 0.5% to 8.0%, 1.0% to 6.0%), or any of the above values.

[0015] Implementation Scheme 8. A UV-curable liquid coating composition according to any one of the above embodiments, wherein, relative to the total weight of the composition, (f) at least one dispersant is present in the following range: 0.1 wt% to 0.2 wt%, 0.2 wt% to 0.25 wt%, 0.25 wt% to 0.3 wt%, 0.3 wt% to 0.35 wt%, 0.35 wt% to 0.4 wt%, 0.4 wt% to 0.45 wt%, 0.45 wt% to 0.5 wt%, 0.5 wt% to 0.55 wt%, 0.55 wt% to 0.6 wt%, 0.6% to 0.65 wt%, 0.65 wt% to 0.7 wt%, 0.7 wt% to 0.75 wt%, 0.75 wt% to 0.8 wt%, 0.8 wt% to 0.85 wt%. %, 0.85 wt% to 0.9 wt%, 0.9 wt% to 1.0 wt%, 1.0 wt% to 1.1 wt%, 1.1 wt% to 1.2 wt%, 1.2 wt% to 1.25 wt%, 1.25 wt% to 1.3 wt%, 1.3 wt% to 1.4 wt%, 1.4 wt% to 1.5 wt%, 1.5 wt% to 1.6 wt%, 1.6 wt% to 1.7 wt%, 1.7 wt% to 1.8 wt%, 1.8 wt% to 1.9 wt%, 1.9 wt% to 2.0 wt%, or any combination of two or more of the above ranges (e.g., 0.1% to 2.0%; 0.3 wt% to 0.8 wt%, 0.25% to 1.5%, 0.5% to 1.25%), or any one of the above values.

[0016] Implementation Scheme 9. A UV-curable liquid coating composition according to any one of the above embodiments, wherein, relative to the total weight of the composition, (g) the degassing agent, defoamer, antifoaming agent, or combination thereof are each present in the following ranges: 0.1 wt% to 0.2 wt%, 0.2 wt% to 0.3 wt%, 0.3 wt% to 0.4 wt%, 0.4 wt% to 0.5 wt%, 0.5 wt% to 0.6 wt%, 0.6 wt% to 0.7 wt%, 0.7 wt% to 0.8 wt%, 0.8 wt% to 0.9 wt%, 0.9 wt% to 1.0 wt%. %, 1.0 wt% to 1.1 wt%, 1.1 wt% to 1.2 wt%, 1.2 wt% to 1.3 wt%, 1.3 wt% to 1.4 wt%, 1.4 wt% to 1.5 wt%, 1.5 wt% to 1.6 wt%, 1.6 wt% to 1.7 wt%, 1.7 wt% to 1.8 wt%, 1.8 wt% to 1.9 wt%, 1.9 wt% to 2.0 wt%, or any combination of two or more of the above ranges (e.g., 0% to 2.0%; 0.3 wt% to 0.7 wt%), or any of the above values.

[0017] Implementation Scheme 9. A UV-curable liquid coating composition according to any one of the above embodiments, wherein, relative to the total weight of the composition, (h) at least one organic solvent is present in the following ranges: 0.5 wt% to 1 wt%, 1 wt% to 2 wt%, 2 wt% to 3 wt%, 3 wt% to 4 wt%, 4 wt% to 5 wt%, 5 wt% to 6 wt%, 6 wt% to 7 wt%, 7 wt% to 8 wt%, 8 wt% to 9 wt%, 9 wt% to 10 wt%, 10 wt% to 11 wt%, 11 wt% to 12 wt%, 12 wt% to 13 wt%, 13 wt% to 14 wt%, 14 wt% to 15 wt%, 15 wt% to 16 wt%, 16 wt% to 17 wt%, 17 wt% to 18 wt%, 18 wt% to 19 wt%, 19 wt% to 20 wt%, or any combination of two or more of the above ranges (e.g., 0.5 wt% to 1.2 wt%), or any one of the above values.

[0018] Implementation Scheme 10. A UV-curable liquid coating composition according to any one of the above embodiments, wherein, relative to the total weight of the composition, (i) the presence of at least one additive selected from rheology modifiers, softeners, and plasticizers ranges from: 0.1 wt% to 0.2 wt%, 0.2 wt% to 0.3 wt%, 0.3 wt% to 0.4 wt%, 0.4 wt% to 0.5 wt%, 0.5 wt% to 0.6 wt%, 0.6 wt% to 0.7 wt%, 0.7 wt% to 0.8 wt%, 0.8 wt% to 0.9 wt%, 0.9 wt% Up to 1.0 wt%, 1.0 wt% to 1.1 wt%, 1.1 wt% to 1.2 wt%, 1.2 wt% to 1.3 wt%, 1.3 wt% to 1.4 wt%, 1.4 wt% to 1.5 wt%, 1.5 wt% to 1.6 wt%, 1.6 wt% to 1.7 wt%, 1.7 wt% to 1.8 wt%, 1.8 wt% to 1.9 wt%, 1.9 wt% to 2.0 wt%, 2.1 wt% to 2.2 wt%, 2.2 wt% to 2.3 wt%, 2.3 wt% to 2.4 wt%, 2.4 wt% Up to 2.5 wt%, 2.5 wt% to 2.6 wt%, 2.6 wt% to 2.7 wt%, 2.7 wt% to 2.8 wt%, 2.8 wt% to 2.9 wt%, 2.9 wt% to 3.0 wt%, 3.1 wt% to 3.2 wt%, 3.2 wt% to 3.3 wt%, 3.3 wt% to 3.4 wt%, 3.4 wt% to 3.5 wt%, 3.5 wt% to 3.6 wt%, 3.6 wt% to 3.7 wt%, 3.7 wt% to 3.8 wt%, 3.8 wt% to 3.9 wt%, 3.9 wt% % to 4.0 wt%, 4.0 wt% to 4.1 wt%, 4.1 wt% to 4.2 wt%, 4.2 wt% to 4.3 wt%, 4.3 wt% to 4.4 wt%, 4.4 wt% to 4.5 wt%, 4.5 wt% to 4.6 wt%, 4.6 wt% to 4.7 wt%, 4.7 wt% to 4.8 wt%, 4.8 wt% to 4.9 wt%, 4.9 wt% to 5.0 wt%, or any combination of two or more of the above ranges (e.g., 0.3 wt% to 0.7 wt%), or any of the above values.

[0019] Implementation Scheme 11. A UV-curable liquid coating composition according to Implementation Scheme 10, wherein at least one additive comprises a rheology modifier present in the range of 0.05% to 5% according to any of the above embodiments.

[0020] For a variety of reasons, it is preferred that the UV-curable liquid coating compositions disclosed herein, the uncured layer (optionally dried) of the deposited coating compositions, and the cured thermally conductive dielectric coatings be prepared without certain components, i.e. without certain materials (whether added or generated in situ) except for a small amount of contaminants; or may be substantially free of certain components used in the prior art for similar purposes. Specifically, according to the order of preference given independently for each of the following preferred minimized components listed below, at least some embodiments of 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%, more preferably in g / L, more preferably in ppm, each of the following components: free bisphenol A, halogenated epoxy resin, nonylphenol, toluene, xylene, copper, gold, silver, oxidizing agents (e.g., peroxides and peroxyacids), permanganate, perchlorate, chlorate, chlorite, hypochlorite, perborate, hexavalent chromium, trivalent chromium, sulfuric acid and sulfate, nitric acid and nitrate ions; and formaldehyde, formamide, hydroxylamine, cyanide, cyanate; dissolved or soluble boron substances, such as borax, borate; strontium; and / or free halide ions, such as fluoride ions, chloride ions, bromide ions, or iodide ions. In some embodiments, the solid particles of the polymer / boron nitride composite material (e.g., thermosetting polymer / BN particles and / or thermoplastic polymer / BN particles) are not present in the coating composition, or the 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%, more preferably in grams per liter, and even more preferably in ppm.

[0021] As used herein, "dielectric coating" refers to an electrically insulating coating. As will be described in further detail herein, the dielectric coating of embodiments of the present invention maintains electrical insulation (i.e., virtually non-conductive, preferably non-conductive) at dielectric withstand voltages greater than 2.0 kV, preferably greater than 3.0 kV, preferably greater than 4.0 kV, and most preferably greater than 5 kV, as measured by HypotMAX 7720 or Ikonix 3865 and according to ASTM D 149-09 Hipot testing. The dielectric withstand strength is calculated based on the sample thickness and the dielectric withstand voltage.

[0022] As used herein, the term "polymer" refers to oligomers (having a molecular weight of MW greater than (preferably in ascending order) 3, 4, or 5 monomer units or at least 500, 1000, 5000 but less than 10000 Daltons, typically 4 to 10 repeating units), homopolymers (e.g., prepared from a single monomeric substance), copolymers (e.g., prepared from at least two monomeric substances), terpolymers, graft polymers, etc. The term "resin" as used herein refers to a polymer having functional groups capable of undergoing further reactions (e.g., crosslinking, esterification, condensation, and / or addition reactions). Furthermore, the term "crosslinking agent" refers to a molecule containing two or more functional groups that can react with polymer functional groups and are capable of linking two or more polymer molecules by chemical bonds. The term "radical reactive diluent" as used herein will be understood by those skilled in the art to be a diluent that reacts with the generated free radicals when a component in the composition (e.g., a photoinitiator) is exposed to UV light.

[0023] The transitional terms “comprising,” “substantially consisting of,” and “consisting of” are intended to indicate their generally accepted meanings in the patent dictionary; for those embodiments provided as “substantially consisting of,” one or more essential and novel features are the ease of operation of the method or composition / system to provide a composition that exhibits the claimed functional features using only those listed components.

[0024] When a list is provided, unless otherwise stated, it should be understood that each individual element of the list and each combination of the list is a separate implementation. For example, a list of implementations provided as “A, B, or C” should be interpreted as including implementations “A”, “B”, “C”, “A or B”, “A or C”, “B or C”, or “A, B, or C” as separate implementations.

[0025] Unless otherwise specified, composition percentages are expressed as weight percentages relative to the weight of the material or composition. Molecular weights are given as number average molecular weights.

[0026] It should be understood that certain features of this disclosure described herein in the context of individual embodiments for clarity may also be provided in combination in a single embodiment. That is, unless obviously incompatible or specifically excluded, each individual embodiment is considered to be combinable with one or more other embodiments, and such combination is another embodiment. Conversely, various features of this disclosure described herein in the context of individual embodiments for brevity may also be provided individually or in any sub-combination. Finally, while an embodiment may be described as part of a series of steps or a more general structure, each said step may also be considered as an independent embodiment that can be combined with other embodiments.

[0027] Except in any operational embodiment, or where otherwise stated, all figures used in the specification and claims that indicate, for example, the amount of ingredients, should be understood to be modified by the term “about” in all cases. Attached Figure Description

[0028] Figure 1 A scanning electron microscope (SEM) image of a cross-section of a corner of an aluminum battery cell container coated according to the present invention is shown. The image shows the metal of the container, the cured thermally conductive dielectric coating adhered thereto, and a mark indicating the measured thickness of the cured coating. It shows that the corner of the substrate is completely coated without gaps and retains more than 2 / 3 of the layer thickness compared to the maximum thickness shown.

[0029] Figure 2 A scanning electron microscope (SEM) image of a cross-section of a corner of an aluminum battery cell container coated according to the present invention is shown. The image shows the metal of the container, the cured thermally conductive dielectric coating adhered thereto, and a mark indicating the measured thickness of the cured coating. It shows that the corner of the substrate is completely coated without gaps and retains more than 3 / 4 of the layer thickness compared to the maximum coating thickness shown. Detailed Implementation

[0030] This disclosure can be more readily understood by referring to the following description, which is taken in conjunction with the appended summary, drawings, and embodiments (all of which form part of this disclosure). For the purposes of the following detailed description, it should be understood that the invention may take various alternative variations and sequences of steps unless expressly specified to the contrary.

[0031] The present invention, as described herein, provides an improved dielectric coating that promotes heat dissipation (particularly for vehicle battery systems) and provides good electrical insulation with a low film thickness to reduce weight. The deposition method for the dielectric coating is also more suitable for large-scale production lines, applied through less complex processes, and using less time and energy. Embodiments of the invention are described below. Some embodiments set forth in this disclosure include UV-curable liquid coating compositions comprising: (a) at least one polyester resin, (b) At least one free radical reactive diluent, (c) At least one thermally conductive filler; (d) At least one photoinitiator, (e) at least one adhesion promoter, and (f) At least one dispersant, At least one of the polyester resins may include, substantially consist of, or consist of: unsaturated polyester resins, preferably epoxy vinyl ester resins, such as epoxy acrylates and epoxy methacrylates, and combinations thereof.

[0032] In some embodiments, the UV-curable liquid coating composition comprises components as further described herein: (a) At least one unsaturated polyester resin, preferably an epoxy vinyl ester resin, such as epoxy acrylate and epoxy methacrylate, and combinations thereof, which are preferably present in the range of 9% to 95%, preferably 10% to 50%, more preferably 11% to 35%; (b) At least one free radical reactive diluent, which is preferably present in the range of 10% to 95%, preferably 15% to 80%, more preferably 25% to 50%; (c) At least one thermally conductive filler (e.g., boron nitride, alumina, aluminum trihydrate, and combinations thereof) is preferably present in the range of 1.0% to 70% or 5% to 60%, preferably 10% to 50%; (d) At least one photoinitiator, which is preferably present in the range of 0.1% to 5%, preferably 1% to 4%, and more preferably 1.5% to 3.5%; (e) at least one adhesion promoter, which is preferably present in the range of 0.1% to 10%, preferably 0.5% to 8.0%, more preferably 0.75% to 6.0%; and Optional existence (f) At least one dispersant, ranging from 0.0% to, preferably, 7.0%, 6.0%, 5.0%, 4.0%, 3.0% in ascending order, or from 0.1% to 2.0%, and preferably present in an amount of 0.25% to 1.5%, preferably 0.5% to 1.25%; (g) Degassing agents, defoamers, antifoaming agents, or combinations thereof, each preferably present in the range of 0% to 2.0%; (h) At least one organic solvent, which is preferably present in the range of 0.5% to 20%; (i) At least one additive selected from rheology modifiers, softeners and plasticizers, each of which is preferably present in the range of 0% to 5%; The weight percentage of each component is relative to the total weight of the composition, and the total amount of components does not exceed 100% by weight.

[0033] Polyester resin Generally, various polyester resins (preferably having one, two, or more unsaturated sites) are suitable as the polyester resin for (a) of the compositions of the present invention. Non-limiting examples include unsaturated polyester resins, epoxy vinyl ester resins (e.g., epoxy acrylates and epoxy methacrylates), etc. These resins have one or more olefinic unsaturated sites, preferably at least about two C=C functional groups per molecule, and may have other functional groups. Polyester oligomers and monomers with similar functionality may also be used.

[0034] Representative unsaturated polyester resins are described in U.S. Patent Nos. 4,742,121; 5,567,767; 5,571,863; 5,688,867; 5,777,053; 5,874,503 and 6,063,864 and PCT Publication Nos. WO94107674 A1, WO00123495 A1 and WO 031101918D (incorporated herein by reference).

[0035] Polyester resins can be prepared by the condensation of one or more carboxylic acids (e.g., monofunctional, difunctional, or polyfunctional unsaturated or saturated carboxylic acids) or their derivatives (e.g., acid anhydrides, C, alkyl esters, etc.) with one or more alcohols (including monofunctional, difunctional, and polyfunctional alcohols). The carboxylic acid or derivative reactants can, for example, be a mixture of unsaturated carboxylic acids or derivatives and saturated carboxylic acids or derivatives.

[0036] Unsaturated carboxylic acids or their derivatives may, for example, have about 3 to about 12, about 3 to about 8, or about 4 to about 6 carbon atoms. Representative unsaturated carboxylic acids and their derivatives include maleic acid, fumaric acid, chloromaleic acid, itaconic acid, citraconic acid, methylene glutaric acid, mesoconic acid, acrylic acid, methacrylic acid, and their esters or anhydrides. Desiredly, unsaturated carboxylic acids and their derivatives include maleic acid, fumaric acid, fumarate esters, and their anhydrides. The amount of unsaturated carboxylic acids or their derivatives may, for example, be about 20 to about 90 mol%, about 35 to about 75 mol%, or about 50 to about 65 mol% of the total carboxylic acids or acid derivatives used to prepare the unsaturated polyester resin.

[0037] Saturated carboxylic acids and their derivatives may, for example, have about 8 to about 18, about 8 to about 15, or about 8 to about 12 carbon atoms. Representative saturated carboxylic acids and their derivatives may be aromatic, aliphatic, or combinations thereof, and include succinic acid, glutaric acid, d-methylglutaric acid, adipic acid, sebacic acid, pimelic acid, phthalic anhydride, phthalic acid, isophthalic acid, terephthalic acid, dihydrophthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid or anhydride, tetrachlorophthalic acid, chlorobenzic acid or anhydride, dodecanedicarboxylic acid, nadic anhydride, cis-5-norbornene-2,3-dicarboxylic acid or anhydride, dimethyl-2,6-cycloalkyldicarboxylic acid ester, dimethyl-2,6-cycloalkyldicarboxylic acid, cycloalkyldicarboxylic acid or anhydride, and 1,4-cyclohexanedicarboxylic acid. Other representative carboxylic acids include ethylhexanoic acid, propionic acid, phenyl-1,2,4-tricarboxylic acid, benzoic acid, 1,2,4-benzenetricarboxylic acid, 1,2,4,5-benzenetetracarboxylic acid, and their anhydrides. Representative aromatic saturated carboxylic acids include phthalic acid, isophthalic acid, and their derivatives. Representative aliphatic saturated carboxylic acids include 1,4-cyclohexanedicarboxylic acid, hexahydrophthalic acid, adipic acid, and their derivatives. The amount of saturated carboxylic acids or their derivatives may, for example, be about 10 to about 80 mol%, about 25 to about 65 mol%, or about 35 to about 50 mol% of the total carboxylic acids or acid derivatives used in the preparation of unsaturated polyester resins. Furthermore, the amount of aromatic carboxylic acids may, for example, be 0 to 100%, 0 to about 50%, or 0 to about 25% of the saturated carboxylic acids or acid derivatives used in the preparation of unsaturated polyester resins, and the amount of aliphatic carboxylic acids may, for example, be 0 to 100%, about 50 to 100%, or about 75 to 100% of the saturated carboxylic acids or acid derivatives used in the preparation of unsaturated polyester resins.

[0038] Representative alcohols used in the preparation of unsaturated polyester resins include alkyl glycols and oxaalkyl glycols, such as ethylene glycol, 1,2-propanediol, propane-3-diol, 1,3-butanediol, butene-1,4-diol, hexane-1,6-diol, diethylene glycol, triethylene glycol, polyethylene glycol, cyclohexane-1,2-diol, 2,2-bis-(p-hydroxycyclohexyl)-propane, 5-norbornene-2,2-dihydroxymethyl, 2,3-norbornene diol, cyclohexanediol, etc. Alcohols with novel structures can be preferred, such as 1,2-propanediol, 2-methyl-1,3-propanediol, 2,2-dimethylheptanediol, 2,2-dimethyloctanediol, 2,2-dimethyl-1,3-propanediol (also known as neopentyl glycol), pentaerythritol, dipentaerythritol, tripentaerythritol, trimethylolpropane, di-trimethylolpropane, 2,2,4-trimethyl-1,3-pentanediol, 2-butyl-2-ethyl-1,3-propanediol, and dimetphyrolpanate. Monofunctional alcohols can also be used to prepare unsaturated polyester resins. Representative monofunctional alcohols include benzyl alcohol, cyclohexanol, 2-ethylhexanol, 2-cyclohexylethanol, 2,2-dimethyl-1-propanol, and lauryl alcohol. When using monofunctional alcohols, the amount present can be a non-zero amount of less than about 10 mol% or less than about 5 mol% of the total alcohols used to prepare unsaturated polyester resins.

[0039] Unsaturated polyester resins can be prepared using esterification technology catalysts (e.g., esterification or transesterification catalysts) familiar to those skilled in the art. The esterification process is typically carried out until the polyester reaches an acid value corresponding to the desired molecular weight. For example, the final acid value can be from about 7 to about 30, the number-average molecular weight (Mn) can be from about 800 to about 3600, and the weight-average molecular weight (Mw) can be from about 1300 to about 11000. The acid value can be reduced by increasing the reaction temperature, conducting the reaction for a longer period, or by adding an acid neutralizer familiar to those skilled in the art.

[0040] Unsaturated polyester resins can also be formed by reacting a low-weight polyester (i.e., an ester oligomer chain containing a small number of repeating ester units) with a weight-average molecular weight of about 200 to about 4000 with a diisocyanate and a (meth)acrylate hydroxyalkyl ester to provide a polyurethane acrylate with terminal vinyl groups, as described in WO2006091446A1. The polyurethane acrylate resin can be used as is or blended with another unsaturated polyester resin (e.g., an aliphatic or aromatic unsaturated polyester resin).

[0041] In some embodiments, a free radical photoinitiator is used to react an unsaturated polyester resin with a free radical reactive diluent (e.g., styrene monomer). The double bonds on the polyester and the side-attached double bonds on the styrene diluent provide pathways for both chain extension and crosslinking.

[0042] The epoxy vinyl esters used in this invention are typically derived from epoxy resins, wherein the ethylene oxide group has been reacted to generate functional groups having side-attached double bonds. Desiredly, modification of the epoxy resin is achieved by reacting the ethylene oxide group with α,β-unsaturated groups (e.g., acrylates) to generate acrylic (double bond) end groups. For example, bisphenol A can react with methacrylic acid to form epoxy methacrylates. Examples of suitable epoxy resins include bisphenol A epoxy resins, alicyclic epoxy resins, epoxy linear phenolic resins, and epoxy cresol linear phenolic resins.

[0043] Typically, vinyl ester resin compositions can be prepared by dissolving the vinyl ester in a suitable compatible diluent to facilitate processing, curing, and provide excellent mechanical properties. Such compatible diluents can include, for example, styrene, chlorostyrene, vinyltoluene, α-methylstyrene, diallyl phthalate, triallyl cyanurate, acrylates and methacrylates (e.g., bisphenol A epoxy diacrylate and trimethylpropane triacrylate), and divinylbenzene. Styrene and mono(meth)acrylates, di(meth)acrylates and tri(meth)acrylates are preferred compatible diluents. However, when a low applied viscosity is required, but properties obtainable only with pure resin are desired, the resin can also be dissolved in a non-reactive diluent (e.g., acetone).

[0044] The vinyl ester resin of the present invention can be prepared by an addition reaction between an olefinically unsaturated monocarboxylic acid and an epoxy resin, wherein the epoxy resin comprises a plurality of ethylene oxide groups that react with the acid and an R group that does not participate in the reaction. The R group can be selected, for example, from alkylene, cycloalkylene, arylene, arylalkylene, oxyaryl, oxyarylalkyl, and cycloalkylene esters. Methods for preparing vinyl ester resins suitable for use in this invention include those disclosed by reference in the following patents incorporated herein by reference: U.S. Patent No. 3,256,226 to Fekete et al.; U.S. Patent No. 3,317,465 to Doyle et al.; U.S. Patent No. 3,345,401 to May; U.S. Patent No. 3,373,221 to May; U.S. Patent No. 3,377,406 to Newey; and U.S. Patent No. 3,432,478 to May; U.S. Patent No. 3,548,030 to Jernigan; U.S. Patent No. 3,564,074 to Swisser et al.; U.S. Patent No. 3,634,542 to Dowd et al.; and U.S. Patent No. 3,637,618 to May. Typically, the vinyl ester resins of this invention are prepared using suitable catalysts (e.g., tertiary amines, phosphine, alkali metal salts, or onium salts). Suitable components for several vinyl ester resins may include, but are not limited to, bisphenol A epoxy resins and linear phenolic epoxy resins that react with unsaturated acids (e.g., acrylic acid and methacrylic acid) and their derivatives.

[0045] A wider variety of vinyl ester resins can be obtained by selecting unsaturated monomer diluents as described below, which can be combined with and copolymerized with vinyl ester resins. Preferred vinyl ester resins for use in this invention are bisphenol A (BPA) epoxy resins. These resins can be used in resin compositions of this invention with or without reactive diluents (e.g., co-reactive monomers such as styrene).

[0046] Vinyl ester resins based on BPA epoxy resins offer processing properties similar to ambient temperature cured polyester systems, but exhibit excellent physical properties similar to cured epoxy systems upon curing. Therefore, the desired properties of these two different thermosetting resins can be combined into a single resin system.

[0047] Polyester resins can be co-cured with free radical photoinitiators and free radical reactive diluents (e.g., styrene monomers). The double bonds in the polyester backbone and the side double bonds in the styrene monomers provide pathways for both chain extension and crosslinking.

[0048] Free radical reactive diluent Desiredly, one or more radical reactive diluents can be used to reduce the viscosity of the composition and can at least partially replace the solvent. Typically, the radical reactive diluent copolymerizes with the aforementioned resin during curing and is incorporated into the coating. The one or more radical reactive diluents can be monofunctional, polyfunctional, or a mixture thereof. Monofunctional diluents can be selected to increase the stretchability of the cured coating, while polyfunctional diluents can be selected to increase the crosslinking density of the cured coating. In some embodiments, the radical reactive diluent is preferably one or more radical reactive diluents capable of participating in radical polymerization reactions; non-limiting examples are compounds having olefinic unsaturation. Representative examples include substituted and unsubstituted styrene, methyl methacrylate (MMA); monofunctional, difunctional, and polyfunctional esters of unsaturated monofunctional acids (e.g., acrylic acid and methacrylic acid) with alcohols or polyols having 1 to about 18 carbon atoms; and monofunctional, difunctional, and polyfunctional esters of unsaturated monofunctional alcohols with carboxylic acids or derivatives having 1 to about 18 carbon atoms. Other suitable free radical reactive diluents include, for example, acrylates, methacrylates, phthalates (e.g., diallyl phthalate); triallyl cyanurate; vinyl ethers, etc.

[0049] Representative acrylates and methacrylates include isobornyl acrylate (IBOA), isobornyl methacrylate (IBOMA), butanediol dimethacrylate, tripropylene glycol diacrylate (TPGDA), ethylene glycol dimethacrylate (EGDMA), polyethylene glycol dimethacrylate (PEGDMA), polypropylene glycol dimethacrylate (PPGDMA), trimethylolpropane triacrylate (TMPTA), trimethylolpropane trimethacrylate (TMPTMA), tetramethylolpropane trimethacrylate, dipropylene glycol dimethacrylate, and dipropylene glycol. Diacrylates (DPGDA), methyl 2-((allyloxy)meth)acrylate monomers, 1,4-cyclohexanediethanol divinyl ether (CHDM-di), monofunctional cyclic acrylates (e.g., aromatic polyether acrylates), isodecyl acrylate, isodecyl methacrylate, 1,3-butanediol dimethacrylate, 2-hydroxyethyl methacrylate (2-HEMA), 1,6-hexanediol dimethacrylate (HDODMA), triethylene glycol dimethacrylate (TEGDMA), acetylacetoxyethyl methacrylate (AAEM), and their acrylate counterparts. Isoborneol is preferred and is typically present in a ratio of about 2.2:1 to about 0.5:1 (a) to IBOA.

[0050] A mixture of free radical reactive diluents may be used. Preferred free radical reactive diluents include styrene, methyl methacrylate, TMPTMA, vinyltoluene, p-tert-butylstyrene, p-methylstyrene, EGDMA, 2-HEMA, and mixtures thereof. The total amount of free radical reactive diluent may, for example, be about 5 to about 60% by weight, about 15 to about 50% by weight, or about 25 to about 45% by weight of the total coating composition.

[0051] Thermally conductive filler The thermally conductive filler comprises boron nitride, preferably hexagonal boron nitride (h-BN). The thermally conductive filler may also comprise other particles selected from a variety of materials that provide thermal conductivity at the loading concentrations described herein. Examples of preferred thermally conductive particulate materials include alumina, alumina trihydrate (ATH), aluminum nitride, boron nitride, beryllium oxide, zinc oxide, magnesium oxide, and combinations thereof. Such particles impart significant thermal conductivity to the coating of the present invention and enhance dielectric strength. In some embodiments, when multiple of the above-described thermally conductive fillers are present, the ratio of BN thermally conductive filler to total thermally conductive filler may range from 0.1:1.0 to 0.99:1.0, preferably from 0.2:1.0 or 0.89:1. In a preferred embodiment, the total amount of thermally conductive filler typically ranges from about 5% to about 60% of the total composition.

[0052] Co-fillers (e.g., zirconium dioxide, titanium dioxide, silicon dioxide, silicon nitride, or calcium carbonate) have low thermal conductivity and can be used in coating compositions to replace part of the boron nitride, provided that the performance in the tests described herein is not unacceptably affected.

[0053] The preferred hexagonal boron nitride (“h-BN”) used in this invention is an inert, lubricating ceramic material having a graphite-like, plate-like hexagonal crystal structure, but with greater electrical insulation properties than graphite. In one embodiment, the invention relates to a mixture of at least two different boron nitride materials selected to provide synergistic effects (e.g., improved viscosity properties). The different boron nitride powder materials are selected from plate-like and non-plate-like morphologies. Non-plate-like boron nitride is defined herein as any boron nitride other than plate-like boron nitride. For example, non-plate-like boron nitride powder materials may include boron nitride agglomerates composed of boron nitride plates. The agglomerates of boron nitride powder materials may have spherical or irregular shapes and differ in size from one another. Other non-plate-like boron nitride powder materials include, but are not limited to, partially crystalline boron nitride, amorphous boron nitride, and nano-boron nitride powder materials with different properties (including, but not limited to, surface area, size, aspect ratio, and density). According to one embodiment, the two different boron nitride powder materials may be two different spherical agglomerates of boron nitride powder materials with different particle sizes.

[0054] To facilitate reactant viscosity control, the thermally conductive ceramic particles can have a specific particle size distribution within a controlled aspect ratio range. Therefore, the particle size can be from 0.01 to 100 micrometers. In another embodiment, the average particle size of the thermally conductive ceramic particles can be from 0.01 to 100 micrometers, or at least 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.75, 1.0, 1.5, or 2.0 micrometers, between 1 and 25 micrometers. The aspect ratio of the spherical, rod-shaped, or plate-shaped particles is preferably 1-50 or 1-10.

[0055] In one embodiment, at least one of the two different BN powder materials comprises crystalline or partially crystalline boron nitride particles prepared by methods known in the art, in the form of agglomerated or flake-like boron nitride. These may include spherical BN particles. In a preferred embodiment, the BN powder material comprises flakes, preferably at least 50%, 60%, or 70% flakes.

[0056] In one embodiment, the particle size distribution having a D50 can range from about 1, 1.2, 1.4, 1.6, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, or 5.0 micrometers to about 10.0, 9.5, 9.0, 8.5, 8.0, 7.5, 7.0, 6.5, or 6.0 micrometers. In another embodiment, the particle size distribution of the BN particles having a D90 is in the range of 12-25, 14-24, or 16-22 micrometers. The particle size distribution can be measured by dispersion in ethanol using laser scattering (e.g., Mastersizer 2000).

[0057] The surface area of ​​BN flake powder material is expected to be less than 20 m². 2 / g, and the surface area can be as low as less than 3.0 m². 2 / g. Preferably, the surface area and aspect ratio are selected such that the filler does not excessively increase the viscosity and the particles do not extend beyond the surface of the cured coating.

[0058] Photoinitiator The UV-curable liquid coating composition contains at least one photoinitiator. When the UV-curable composition is exposed to electromagnetic radiation (e.g., photochemical radiation, such as ultraviolet (UV) radiation), the photoinitiator enhances the speed of the curing process. After the composition is deposited on a substrate surface, the photoinitiator contained in the UV-curable liquid coating composition provided to the end user is activated by exposing the uncured coating composition to sufficient intensity of UV or other electromagnetic radiation for a sufficient time to initiate the process.

[0059] The initiator or crosslinking agent can be a photoinitiator. Examples of available photoinitiators include, but are not limited to, the photoinitiator "IRGACURE" and "DAROCUR" commercially available from Ciba Specialty Chemicals, specifically "IRGACURE". 184 (1-hydroxycyclohexylphenyl ketone), 907 (2-methyl-1-[4-(methylthio)phenyl]-2-morpholinylprop-1-one), 369 (2-benzyl-2-N,N-dimethylamino-1-(4-morpholinylphenyl)-1-butanone), 500 (a combination of 1-hydroxycyclohexylphenyl ketone and benzophenone), 651 (2,2-dimethoxy-2-phenylacetophenone), 1700 (a combination of bis(2,6-dimethoxybenzoyl-2,4,4-trimethylpentyl)phosphine oxide and 2-hydroxy-2-methyl-1-phenyl-prop-1-one), and 819 [bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide], and "DAROCUR" 1173 (2-hydroxy-2-methyl-1-phenyl-prop-1-one) and 4265 (a combination of 2,4,6-trimethylbenzoyl diphenylphosphine oxide and 2-hydroxy-2-methyl-1-phenyl-prop-1-one). Of course, combinations of these materials can also be used in this paper.

[0060] Other photoinitiators that may be used in this article include alkyl pyruvate esters (e.g., methyl pyruvate, ethyl pyruvate, propyl pyruvate and butyl pyruvate), aryl pyruvate esters (e.g. phenyl pyruvate, benzyl pyruvate), and their appropriately substituted derivatives. Photoinitiators particularly suitable for use herein include: ultraviolet photoinitiators such as 2,2-dimethoxy-2-phenylacetophenone (e.g., "IRGACURE" 651), and 2-hydroxy-2-methyl-1-phenyl-1-propane (e.g., "DAROCUR" 1173), bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (e.g., "IRGACURE" 819); and photoinitiator combinations of bis(2,6-dimethoxybenzoyl-2,4,4-trimethylpentyl)phosphine oxide and 2-hydroxy-2-methyl-1-phenyl-prop-1-one (e.g., "IRGACURE" 1700); and the photoinitiator bis(η5-2,4-cyclopentadien-1-yl)-bis[2,6-difluoro-3-(1H-pyrrolo-1-yl)phenyl]titanium (e.g., "IRGACURE" 784DC). Available photochemical radiation includes ultraviolet light, which may or may not be supplemented by other energy sources.

[0061] Ideally, the wavelength of the photochemical radiation used to cure the UV-curable liquid coating composition is from about 200 nm to about 400 nm. Available UV light includes, but is not limited to, UVA (from about 320 nm to about 400 nm), UVB (from about 290 nm to about 320 nm), UVC (from about 220 nm to about 290 nm), and combinations thereof. Available light supplementing the UV light can be visible light, including but not limited to violet, indigo, blue, green, and combinations thereof. The wavelength of such available visible light can be from about 450 nm to about 550 nm. The concentration of the photoinitiator used can effectively initiate the curing of the UV-curable liquid coating composition under the desired photochemical radiation exposure, and is typically used at a concentration from about 0.01% by weight to about 10% by weight of the composition.

[0062] Adhesion promoter The compositions of the present invention may include optional adhesion promoters to improve adhesion to metallic substrates (e.g., cross-hatch adhesion performance) and moisture resistance. Organosilane compounds may be used to promote adhesion, improve strength, and provide enhanced resistance to wet conditions. Other known adhesion promoters include organotitanates, zinc di(meth)acrylate, organozinc oligomers, organochromium, and zirconium complexes. If present, the adhesion promoter may contain one or more adhesion-promoting chemicals as described below, and, at least for economic reasons, the total amount of the adhesion promoter component may range from at least about 0.1, 0.3, 0.5, 0.75, 1.0, 1.5, 2, 2.5, 3, 3.5, 4, or 4.5% by weight to no more than about 10, 9, 8, 7, 6, or 5% by weight. In one embodiment, when the adhesion promoter is a silane having functional groups similar to those of a UV resin, more promoter may be used and incorporated into the coating.

[0063] In some embodiments, adhesion promoters are used and may comprise silanes, such as epoxy, vinyl / acrylate / methacrylate-functionalized silanes, desirably methacryl-functionalized silanes, such as Dynasylan products commercially available from Evonik Operations GmbH and some polyester-based products (e.g., TEGO Addbond products); and organophosphates, such as HEMA-phosphates. Examples of organozinc oligomers include organozinc acrylates, such as di(meth)acrylate-based oligomers, such as polyester zinc acrylate oligomers and polyurethane zinc acrylate oligomers.

[0064] Examples of silane adhesion promoters include, but are not limited to: aminosilanes, such as γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N-(aminoethyl)-γ-aminopropyltrimethoxysilane, N-(aminoethyl)-γ-aminopropyltrimethyldimethoxysilane, and N-phenyl-γ-aminopropyltrimethoxysilane; epoxysilanes, such as -(3,4-epoxycyclohexyl)-ethyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, and γ-glycidoxypropyltriethoxysilane; vinylsilanes, such as vinyltri(-methoxyethoxy)silane, vinyltriethoxysilane, vinyltrimethoxysilane, and γ-methacryloyloxypropyltrimethoxysilane; hexamethyldisilazane; and γ-mercaptopropyltrimethoxysilane.

[0065] Examples of titanate adhesion promoters include, but are not limited to, tetraisopropoxytitanium, tetra-n-butoxytitanium, tetrabutyl titanate dimer, tetrastearyl titanate, acetylacetone titanium, titanium lactate, tetraoctyl glycol titanate, titanium lactate, and tetrastearyloxytitanium.

[0066] wetting and dispersing agents The compositions of the present invention preferably contain a wetting and dispersing agent (also referred to herein as a "dispersant"), which is added to reduce the agglomeration and sedimentation of inorganic fillers (particularly BN and silica fillers) in the coating composition. In some embodiments, the ratio of the total amount of thermally conductive filler to the total amount of dispersant can be in the range of about 70:1 to 15:1, preferably about 60:1 to 20:1.

[0067] An important performance criterion for wetting and dispersing agents (f) is their ability to inhibit the thickening effect of inorganic fillers in the coating composition. Excessive thickening of the coating composition before application to the substrate negatively impacts sprayability, the surface roughness of the cured coating, and causes air pockets to remain within the coating. Wetting and dispersing agents (f) are components containing one or more groups X that have an affinity for fillers, and thus can covalently, ionicly, and / or through physical adsorption to bind to the filler surface. Wetting and dispersing agents also cause stabilization of filler particles and prevent agglomeration, which would otherwise lead to solid sedimentation and thus a non-uniform product. One or more groups Y in the wetting and dispersing agent (f) that ensure compatibility with the surrounding medium typically contribute to this stabilization.

[0068] The suitable wetting and dispersing agent (f) used is preferably a relatively high molecular weight wetting and dispersing agent (f), more particularly a polymeric wetting and dispersing agent (f). The suitable functional polymer preferably has a number average molecular weight (Mn) of at least 400 g / mol, preferably at least 800 g / mol, more preferably at least 2000 g / mol. The maximum molecular weight Mn is effectively 100,000 g / mol, preferably 50,000 g / mol, more preferably 25,000 g / mol. The number average molecular weight can be determined by gel permeation chromatography relative to a polystyrene standard.

[0069] More specifically, the wetting and dispersing agent (f) used according to the present invention may be selected from linear or branched polymers and copolymers that are compatible with the surrounding medium and functional groups and / or groups having filler affinity. Examples of lubricants and dispersants include alkylammonium salts of polymers and copolymers, polymers and copolymers having acidic groups, comb-shaped and block copolymers, such as block copolymers particularly having basic groups with filler affinity, optionally modified acrylate block copolymers, optionally modified polyurethanes, optionally modified and / or optionally salt-forming polyamines, epoxide-amine adducts, phosphate esters, especially phosphate esters of polyethers, polyesters and polyether-esters, basic or acidic ethoxylates, such as acidic 1,2-dicarboxylic anhydride monoesters of alkoxylated monoamines or polyamines or alkoxylated monools, reaction products of unsaturated fatty acids with maleic anhydride and / or monoamines, diamines and polyamines; and amino alcohols, and unsaturated 1,2-dicarboxylic acids and their anhydrides and their salts and their reaction products with alcohols and / or amines; polymers and copolymers having fatty acid residues, optionally modified polyacrylates, such as transesterified polyacrylates, optionally modified polyesters, such as acid-functionalized and / or amino-functionalized polyesters, polyphosphate esters, and mixtures thereof.

[0070] Polyisocyanate-based polymeric wetting and dispersing agents (f) can be prepared by addition reactions of monohydroxy compounds, diisocyanate functional compounds, and compounds having tertiary amino groups onto existing NCO groups of polyisocyanates containing isocyanurate, biuret, carbamate, and / or urethane groups. Amine-based wetting and dispersing agents (f) can be obtained by preparing amine salts of amine functional compounds using acids (salting).

[0071] The following wetting and dispersing agents (f) exhibit particularly good effects in the compositions of the present invention: (a) reaction products of unsaturated fatty acids with maleic anhydride and / or monoamines, diamines and polyamines, amino alcohols; and (b) unsaturated 1,2-dicarboxylic acids and their anhydrides and salts and their reaction products with alcohols and / or amines, unsaturated polyamine amides and their salts, and low molecular weight acidic polyesters.

[0072] These types of wetting and dispersing agents (f) are commercially available products, such as BYK-Chemie from Wesel, under the trade names BYK-220 S, BYK-P 9908, BYK-9076, BYK-9077, BYK-P 104, BYK-P 104 S, BYK-P 105, BYK-W 9010, BYK-W 920, BYK-W 935, BYK-W 940, BYK-W 960, BYK-W 965, BYK-W 966, BYK-W 975, BYK-W 980, BYK-W 990, BYK-W 995, and BYK-W 996 and trade names BYKUMEN, BYKJET, LACTIMON, ANTI-TERRA, and DISPERBYK. These commercially available products are desirable as solvent-free active materials when low levels of volatile organic compounds, particularly organic solvents, are required, and preferably do not contain volatile components.

[0073] organic solvents Optional organic solvents added to components can be used to reduce the viscosity of coating compositions. Added solvents (e.g., butyl acetate or acetone) are distinct from incidental solvents contained in the raw materials and incorporated into the coating composition together with the raw materials. Examples of incidental solvents contained in the raw materials include mineral spirits, naphtha, etc. Solvents as used herein refer to chemicals that are removed during manufacturing and are not contained in the final product (except in trace amounts).

[0074] rheology modifiers Optional rheology modifiers can be used to control the viscosity characteristics, bulk and hold-up characteristics of vinyl ester resins by imparting thixotropy to the vinyl ester resin composition. Suitable examples include modified and unmodified pyrolytic (fumed) amorphous silica or synthetic amorphous silica, preferably alkaline or hydrophobically modified silica. In one embodiment, the rheology modifier can be prepared by combining at least one unsaturated polyester resin with at least one fumed silica. Preferably, the rheology modifier is selected from those having one or more of the following properties: 150 to 210 m 2 / g BET surface area; SiO2 content greater than or equal to 98.5% by weight; and NaO content less than or equal to 0.5% by weight. These types of rheology modifiers are available as commercially available products, such as Cab-O-Sil M-5 (a fumed silica product manufactured by Cabot Corporation) and Aerosil®, which is commercially available from Evonik Operations GmbH.

[0075] Softener Optional component softeners may be included in embodiments of the invention. Suitable examples of softeners include methyl methacrylate-butadiene-styrene (MBS) and similar rubbers, one example being Clearstrength XT-100, commercially available from Arkema Inc.; and polysulfide resins, such as Thioplast resin, commercially available from Nouryon Chemicals LLC.

[0076] plasticizer In some embodiments of the invention, optional plasticizers may be used to increase the flexibility and toughness of the cured dielectric coating. Increased toughness of the dielectric coating can reduce cracking and contribute to longer battery life, particularly in batteries used in mobile vehicles. Examples of optional plasticizers include phthalates, benzoates, dibenzoates, phthalates, naphthalene sulfonates, trimellitates, adipates, sebacic acid esters, maleates, sulfonamides, organophosphates, and polybutene.

[0077] Degassing agent Another component that may be present is one or more degassing agents (so-called degassing agents). Degassing agents help degas UV-curable liquid coating compositions before they are fully cured, thereby reducing air entrainment and thus reducing the risk of weaknesses or porosity. Typical degassing agents include silicone or non-silicone materials, including solutions of polyalkylene ethers and / or polyolefins in petroleum distillates, silicone degassing agents, acrylic polymers, hydrophobic solids, vegetable oil-based paraffins, and mineral oil-based paraffins. Commercially available degassing agents include BYK-066, BYK-077, BYK-500, BYK-501, BYK-515, and BYK-555 degassing agents (from BYK-Chemie USA, Inc.). When used, the amount of degassing agent may be, for example, up to about 1.5% by weight, up to about 1% by weight, or about 0.1% to about 0.5% by weight of the UV-curable liquid coating composition.

[0078] Accelerator Another optional component that may be present is one or more accelerators. Representative accelerators for use in UV-curable liquid coating compositions are electron-donating substances that facilitate the activation of photoinitiators or catalysts and promote or accelerate the curing of the UV-curable liquid coating composition at relatively low temperatures (e.g., at temperatures from about 0 to about 30°C). Representative accelerators include metal compounds (e.g., cobalt, manganese, potassium, iron, vanadium, copper, and aluminum salts of organic acids); amines (e.g., dimethylaniline, diethylaniline, phenyldiethanolamine, dimethyl-p-toluidine, and 2-aminopyridine); Lewis acids (e.g., boron fluoride dihydrate and ferric chloride); bases (e.g., tetramethylammonium hydroxide); quaternary ammonium salts (e.g., trimethylbenzylammonium chloride and tetrahydroxymethylphosphonium chloride); sulfur compounds (e.g., dodecyl mercaptan and 2-mercaptoethanol); dimethylacetoacetamide; ethyl acetoacetate; methyl acetoacetate, and mixtures thereof. For example, cobalt salts of organic acids can be used to promote the low-temperature decomposition of peroxide catalysts and the curing of the disclosed UV-curable liquid coating compositions. Preferred accelerators include metal salts of organic acids as described above, particularly cobalt alkylates, such as cobalt 2-ethylhexanoate, cobalt octanoate, potassium octanoate, dimethyl acetoacetamide, ethyl acetoacetate, methyl acetoacetate, and mixtures thereof. Accelerators are typically used in amounts from about 0.05 to about 3% by weight, or from about 0.05 to about 2% by weight, of the UV-curable liquid coating composition.

[0079] Inhibitors Another optional component that may be present is an inhibitor. One or more inhibitors help extend or maintain the shelf life of the uncured UV-curable liquid coating composition by inhibiting premature polymerization. Suitable inhibitors may include free radical inhibitors and / or scavengers, such as quinones (e.g., hydroquinone (HQ), methyl hydroquinone (THQ), mono-tert-butyl hydroquinone (MTBHQ), di-tert-butyl hydroquinone (DTBHQ), naphthoquinone (NQ), and monomethyl ether hydroquinone (MEHQ)), butylated hydroxytoluene (BHT), tert-butylcatechol (TBC), etc. The amount of inhibitor present may be, for example, from about 0.01 to about 0.5% by weight, from about 0.01 to about 0.3% by weight, or from about 0.01 to about 0.1% by weight of the UV-curable liquid coating composition.

[0080] filler or extender In addition to the thermally conductive filler of component (c), additional fillers different from those in (c) as described in the following paragraphs may also be used, provided that they do not decrease the thermal conductivity of the cured coating to 0.20 W / mK or less, and / or do not decrease the dielectric withstand voltage of the cured coating to less than 2.0 kV. The UV-curable liquid coating may optionally contain at least one other extender filler, such as clay, heavy calcium carbonate, mica, talc, barium sulfate, precipitated silica, silica other than the rheology modifier, etc. The extender filler may also contribute to imparting thixotropy to the UV-curable liquid coating of the present invention. Although the UV-curable liquid coating compositions of the present invention containing the rheology modifiers disclosed herein can be prepared without the presence of additional extender fillers without diminishing their performance, such additional fillers may still be added if necessary. These amounts of such fillers are not limited, but they are typically added in amounts from about 0 to about 40% by weight of the UV-curable liquid coating composition.

[0081] In some embodiments where the UV-curable coating of the present invention may come into contact with moisture or aqueous materials in the environment of use, the UV-curable liquid coating composition preferably contains no more than 1.0%, 0.5%, 0.35%, 0.10%, 0.08%, 0.04%, 0.02%, 0.01%, 0.001%, or 0.0002%, more preferably in grams per liter, and even more preferably in ppm, or contains no extender fillers that readily react chemically or physically with moisture or aqueous materials (e.g., swelling, dissolution, or hydration). In this way, the cured coating does not exhibit whitening, delamination, or failure after prolonged contact with moisture or aqueous materials. Typical extender fillers in this case include chopped or ground glass fibers, talc, silica, titanium dioxide, wollastonite, mica, clay, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, magnesium sulfate, and barium sulfate. While small amounts of water-sensitive extender fillers are permissible, the use of water-sensitive extender fillers in UV-curable liquid coating compositions is preferably not more than about 2% by weight, more preferably not more than about 1% by weight (including not more than 0.8, 0.5, 0.3 and 0.1% by weight).

[0082] Other additives As described above, UV-curable liquid coating compositions may contain many other optional additives, such as coupling agents, defoamers, pigments and dyes, plasticizers, flame retardants, chelate-modified epoxy resins, auxiliary impact modifiers / toughening agents, flow control agents, antioxidants, non-reactive diluents, extenders, or other auxiliaries.

[0083] The UV-curable liquid coating composition of the present invention may contain additional auxiliary thermally conductive fillers. Examples of auxiliary thermally conductive fillers include aluminum nitride (AlN), magnesium oxide (MgO), zinc oxide (ZnO), silicon nitride (Si3N4), aluminum powder, and graphite. When the UV-curable liquid coating composition contains auxiliary thermally conductive fillers, the content of the auxiliary thermally conductive filler may be 0% by weight, but may be a non-zero amount of 1.0% by weight or more, more preferably 5.0% by weight or more, based on the UV-curable liquid coating composition. Based on the UV-curable liquid coating composition, the content of additional thermally conductive filler may be 20% by weight or less, preferably 15% by weight or less, more preferably 10% by weight or less, provided that the auxiliary material does not interfere with the desired dielectric or thermal conductivity benefits of the present invention.

[0084] Examples of flame retardants include antimony oxides, carbon halogens, halogenated esters, halogenated ethers, brominated flame retardants, and halogen-free compounds such as organophosphorus compounds, organonitrogen compounds, and intumescent flame retardants.

[0085] Examples of antioxidants include sodium sulfite, sodium metabisulfite, sodium bisulfite, sodium thiosulfate, and dibutylphenol, especially hindered substituted phenols such as pentaerythritol tetra(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate).

[0086] Examples of UV stabilizers include benzophenone, benzotriazole, substituted acrylates, aryl esters, and some compounds containing nickel or cobalt salts.

[0087] Examples of coupling agents include silane coupling agents, titanate coupling agents, zirconium coupling agents, magnesium coupling agents, and tin coupling agents.

[0088] Examples of pigments or dyes include sulfates, silicates, borates, molybdates, phosphates, vanadates, cyanates, sulfides, azo pigments, phthalocyanine pigments, anthraquinones, indigo, quinacridones, and dioxazine dyes.

[0089] Various embodiments of the invention are described throughout this disclosure. In each embodiment described herein, the UV-curable liquid coating composition is preferably a two-part coating composition, wherein the two parts are mixed together for a sufficient period of time prior to application, or optionally mixed together in a nozzle during or immediately prior to application. The preparation of the two-part composition is a conventional method to prevent premature reaction of the reactive components of the composition. Typically, part A comprises a resin and other components that react with the photoinitiator, as well as suitable carriers, additives, and auxiliaries; and part B comprises a photoinitiator and any carrier or additive suitable for packaging with the photoinitiator. Those skilled in the art will understand that embodiments listing all components together describe a partial A&B mixture and a two-part composition comprising parts A and B prior to their combination. This disclosure may also include single-part compositions that provide at least some of the benefits of the invention, wherein the reaction of the combined components is prevented or slowed by known means (e.g., reversible blocking of the photoinitiator and / or reactants).

[0090] method Methods for depositing UV-curable coating composition layers can include spraying, printing, dipping, and similar methods. UV-curable liquid coating compositions can be applied, for example, to the surface of all articles using conventional techniques, such that the component (e.g., vehicle parts or components, cooling devices, etc.) is completely encapsulated by, for example, dipping or spraying, with spraying being preferred for this purpose. Alternatively, UV-curable liquid coating compositions can be applied to specific portions of the component using any number of masking or printing methods known in the art. In some embodiments, the UV-curable liquid coating composition desirably has a viscosity suitable for spraying and / or printing, and is free of solvent or optionally has a low solvent content, which facilitates the deposition of a thin, void-free coating, thereby providing good substrate edge coverage through the uncured deposited coating composition layer. The low solvent content can be, for example (preferably in ascending order), less than 50, 40, 30, 20, 15, 10, 8, 6, 4, 2, or 1% by weight, more preferably values ​​in grams per liter or mg per liter.

[0091] After optional drying or solvent flash evaporation, the uncured layer can be cured or transported and / or incorporated into an assembly and then cured. The cured, preferably cross-linked, composition thus forms a thermally conductive dielectric layer, typically in the form of a coating adhered to a substrate.

[0092] Preferred curing methods include photochemical radiation, such as UV, as described herein. UV curing can be used alone or in combination with the application of heat, such as raising the temperature, flash evaporation of solvents, or other known methods.

[0093] The UV-curable liquid coating composition applied and cured as described herein produces a void-free, cured thin coating that provides good coverage at substrate edges and good overall electrical insulation. The thickness of the cured coating can be from about 1.75, 2.0, 2.5 to about 3.0, 3.5, 4 mils (meaning one-thousandth of an inch), i.e., from about 40, 50, 65 to about 75, 90, or 100 micrometers (also referred to herein as “μm” and “micrometer”). In contrast, cured UV and powder coatings require thicknesses greater than 5 mils (>127 μm) to greater than 10 mils (>254 μm) to provide a void-free cured coating, covering the substrate edges with the necessary thickness and without bare spots to achieve electrical insulation. Substrates containing the cured coating according to the invention are expected not to exhibit visible edge effects (e.g., excessive thickness at edges or picture frame effect), even at the lower coating thicknesses described above; these defects are typically present in contrast coatings.

[0094] The cured dielectric coating according to various aspects of the present invention provides both rapid heat dissipation and good electrical insulation with high dielectric strength.

[0095] Cured dielectric coatings can be used in applications requiring both heat dissipation and electrical insulation. They are suitable for high-energy-density power generation or storage, where significant amounts of heat are generated during operation, such as in battery packs in automobiles or aircraft. The combination of high dielectric strength and high thermal conductivity in cured dielectric coatings is advantageous as electrical insulation in battery pack operation, where effective heat dissipation is crucial for battery safety and lifespan.

[0096] The cured dielectric coating also provides additional protection against corrosion and abrasion during vehicle operation, where environmental factors such as water condensation, contaminants, vibration, etc., may damage the underlying substrate.

[0097] The UV curing of the applied coating composition can be enhanced or supplemented by optional additional steps, such as air drying, heat curing at relatively low temperatures (e.g., in the range of 10°C to 100°C, preferably at least (in ascending order) 15, 20 or 25°C and not exceeding (in ascending order) 100, 90, 80, 70, 65, 60, 50, 40, 30°C), or various combinations of curing steps and UV curing.

[0098] The benefits of using the coating compositions of the embodiments of the present invention to form a thermally conductive dielectric coating may include, but are not limited to: • Easily prepare coating compositions using standard or low-shear mixing (rather than high-shear mixing); reduce or eliminate complex filler grinding steps; simple application using techniques such as spraying or printing; and convenient transportation and handling of the uncured coated substrate if optional. • Single-layer deposition provides a thin coating with good edge coverage, thereby avoiding multiple deposition steps in the preferred embodiment; • For efficient and rapid curing times via UV curing, ranging from approximately 2 to 200 seconds, it is desirable to be within a small time range of 2, 4, 6, 8, 10, 12, 15, 20, 25, 30, 40, 50, or 60 seconds and not exceeding 200, 150, 120, 90, 80, 75, 70, 68, 66, 65, 64, 63, or 62 seconds; • The cured dielectric coating provides electrical insulation greater than 2.0, 3.0, 3.5, 4.0, 4.5 or 5.0 kV and reduced heat storage; • The cured dielectric coating exhibits high thermal conductivity and / or low thermal resistance as measured according to ASTM D5470, thus aiding in heat dissipation. In some embodiments, the cured dielectric coating of the present invention exhibits a thermal conductivity preferably greater than about 0.25, 0.30, 0.35, 0.40, 0.45, 0.50, or 0.55 watts per meter Kelvin (W / mK) in ascending order, which is significantly better than that of a powder coating of 0.20 W / mK.

[0099] Void test: Electrical insulation testing of cured coatings can be performed using the “Hipot test,” derived from the term high-potential testing, to reveal coating voids, which may include exposed edges, pinholes, and low-thickness areas on the substrate. In a Hipot test, a high voltage is applied directly to a component with the cured coating under test. The test voltage is typically much higher than the component's normal operating voltage to stress the dielectric properties of the coating under test. This test is designed to detect current leakage due to defects in the insulating cured coating, such as pinholes, cracks, voids, and even low-coating-weight areas. Breakdown in the insulating coating causes current to flow through the test point of the Hipot tester (i.e., current leakage). Hipot tests of cured coatings according to the invention show no voids, even around corners and edges of the coated substrate, indicating that edges are equally protected.

[0100] Electrical insulation test Electrical insulation properties are confirmed as “good,” meaning that no current flows through the test specimen when a high-voltage test (“Hipot test”) is performed, which detects current flow when a selected voltage is applied over a specific time period. “Dielectric withstand voltage” is the voltage that a dielectric material (insulator) will withstand without current flowing through it, i.e., the maximum voltage at which almost no or no current flows (as determined by test results). Desiredly, the electrical insulation properties of the cured dielectric coating according to the invention can exhibit dielectric withstand voltages greater than about 2.0, 2.5, 3.0, 3.5, 4.0, 4.2, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5.0, 5.1, 5.2, 5.3, 5.4, or 5.5 kV (preferably in ascending order) as measured according to the ASTM D 149-09 Hipot test. Alternatively, the dielectric withstand voltage can be increased incrementally, and the amount of current allowed to flow through the test specimen (also known as current leakage) can be recorded in microamperes (μA). The unaged, cured coating according to the invention typically limits current leakage at 3.5 kV and 5.0 kV to as low as 0 μA to about 5.0 μA.

[0101] Dielectric strength test Dielectric strength is a measure of the electrical strength of a material that acts as an insulator. It is defined as the maximum voltage required to induce dielectric breakdown through the material and is expressed in volts per unit thickness. Breakdown typically manifests as electrical burn-through or insulator decomposition. Higher dielectric strength indicates better insulator quality. This measurement allows for performance comparisons between different materials used at varying coating thicknesses. Ideally, cured dielectric coatings can exhibit dielectric strengths greater than approximately 80, 90, 100, 120, 130, 140, 150, or 160 kV / mm thickness (e.g., approximately 1.5, 2, 2.5, 3.0, 3.5, or 4.0 kV / mil thickness) (preferably in ascending order).

[0102] Throughout this document, it is recognized that the description relates to compositions and methods of preparing and using said compositions. That is, in cases where this disclosure describes or claims features or embodiments associated with a composition or a method of preparing or using the composition, it should be understood that such description or claims are intended to extend to embodiments in each of these contexts (i.e., compositions, methods of preparation, and methods of use).

[0103] The following examples are intended to supplement, rather than replace or supersede, the previous description.

[0104] Example The following examples provide experimental methods for preparing and testing liquid coating compositions for depositing thermally conductive dielectric coatings on substrates, their uncured properties, and cured properties and performance. While each example disclosed in the specification is intended to provide a specific individual embodiment of the composition, preparation, and use methods, the examples are not intended to limit the more general embodiments described herein.

[0105] In the following embodiments, efforts have been made to ensure the accuracy of the figures used (e.g., quantities, temperatures, etc.), but some experimental errors and biases should be taken into account. Unless otherwise stated, temperatures are in °C, ambient temperatures are approximately 22 °C, and pressures are at or near atmospheric pressure. High-shear mixing is not required unless otherwise stated.

[0106] Test method: Unless otherwise stated herein, the liquid coating composition of the examples is sprayed onto a commercially available metal test plate and cured as described below. The cured dielectric coating adhered to the metal test plate and the dielectric-coated test plate are tested according to the following standard test methods: • Dielectric withstand voltage strength / HiPot test: ASTM D149-09 • Thermal conductivity: ASTM D5470 • Thermal resistance: ASTM D5470 • Adhesion / Cross-cut test: ASTM D3359.

[0107] Example 1: Boron nitride only Add the ingredients listed in Table 1 sequentially to a mixing container. Mix the mixture at 600 RPM for 4 hours and then transfer it to an HVLP spray gun. Wipe a set of commercially available, contaminant-free aluminum 3003 alloy plates with isopropyl alcohol (IPA) solvent, allow them to air dry, and then spray to a thickness of 3 mils. Pass the plates through a UV conveyor oven equipped with H+ lamps (which provide total spectral emission covering a wide wavelength range (approximately 200 to 450 nm)) and allow the coating on the plates to cure.

[0108] Some of the boards with cured coatings were tested for dielectric withstand voltage strength / HiPot, and withstood 4.3 kV for 1 second (leakage current of 0.2 µA). Other boards with cured coatings on them scored 5 when tested for cross-cut adhesion according to ASTM D3359. The boards were aged in a Thermotron chamber at 85°C and 85% relative humidity for 500 hours and then tested again, and withstood 4.3 kV DC while maintaining a cross-cut adhesion score of 5.

[0109] Table 1

[0110] Example 2: Boron nitride only - different resin compositions The components listed in Table 2 were added sequentially to a mixing container, and the UV-curable liquid composition was prepared, applied, cured, and tested according to the procedure described in Example 1 above (unless otherwise specified). A 3-mil thick cured coating withstood 4.3 kV for 1 second (leakage current of 0.2 µA) and maintained a cross-cut adhesion of 5 according to ASTM D3359. The board was then kept in a Thermotron chamber at 85°C and 85% relative humidity for 500 hours and then tested again, maintaining a cross-cut adhesion of 5 at 4.3 kVDC.

[0111] Table 2

[0112] Example 3 (ATH only) The components listed in Table 3 were added sequentially to a mixing container, and the UV-curable liquid composition was prepared, applied, cured, and tested according to the procedure described in Example 1 above (unless otherwise specified). The cured coating had a thickness of 2.4 mils, withstood 4.3 kV for 1 second (leakage current of 0.6 µA), and had an adhesion of 5 according to the ASTM D3359 cross-cut adhesion test.

[0113] Table 3

[0114] Example 4: Boron nitride and ATH – ratio 2 / 7 Table 4

[0115] The components listed in Table 4 were added sequentially to a mixing container, and the UV-curable liquid composition was prepared, applied, cured, and tested according to the procedure described in Example 1 above (unless otherwise specified). The cured coating had a thickness of 2.7 mils, withstood 4.3 kV for 1 second (leakage current of 0.4 µA), and had an adhesion of 5 according to the ASTM D3359 cross-cut adhesion test.

[0116] Example 5: Boron nitride and ATH ratio 1 / 8 MO1791-58 The components listed in Table 5 were added sequentially to a mixing container, and the UV-curable liquid composition was prepared, applied, cured, and tested according to the procedure described in Example 1 above (unless otherwise specified). The cured coating had a thickness of 2.5 mils, withstood 4.3 kV for 1 second (leakage current of 0.6 µA), and had an adhesion of 5 according to the ASTM D3359 cross-cut adhesion test.

[0117] Table 5

[0118] Example 6: Boron nitride and ATH – ratio 2 / 7 with additional diluent The components listed in Table 6 were added sequentially to a mixing container. The mixture was mixed at 600 RPM for 4 hours, then transferred to an HVLP spray gun and applied to a set of aluminum 3003 alloy plates prepared according to the procedure of Example 1. Unless otherwise specified, the coated plates were cured and tested according to the procedure described in Example 1 above. The cured coating had a thickness of 2.7 mils, withstood 4.3 kV for 1 second (leakage current of 0.7 µA), and had an adhesion of 5 according to the ASTM D3359 cross-cut adhesion test.

[0119] Table 6

[0120] Example 7: Boron nitride and ATH ratio 2 / 7 and additional diluent The components listed in Table 7 were added sequentially to a mixing container, and the UV-curable liquid composition was prepared, applied, cured, and tested according to the procedure described in Example 1 above (unless otherwise specified). The cured coating had a thickness of 3.5 mils, withstood 4.3 kV for 1 second (leakage current of 0.6 µA), and had an adhesion of 5 according to the ASTM D3359 cross-cut adhesion test.

[0121] Table 7

[0122] Example 8 50% ATH - Additional Diluent Table 8

[0123] The components listed in Table 8 were added sequentially to a mixing container. The mixture was mixed at 2000 RPM for 8 minutes and then applied to a set of aluminum 3003 alloy plates using a coating applicator. Unless otherwise specified, the plates were prepared, cured, and tested according to the procedure described in Example 1 above. The cured coating had a thickness of 2.4 mils, withstood 4.3 kV for 1 second, and had an adhesion of 5 according to the ASTM D3359 cross-cut adhesion test.

[0124] Example 9 50% ATH - Additional Diluent The components listed in Table 9 were added sequentially to a mixing container, and the UV-curable liquid composition was prepared, applied, cured, and tested according to the procedure described in Example 8 above (unless otherwise specified). The cured coating had a thickness of 2.4 mils, withstood 4.3 kV for 1 second, and had an adhesion of 5 according to the ASTM D3359 cross-cut adhesion test.

[0125] Table 9

[0126] Example 10: Boron nitride 10% and 40% ATH - Additional Diluent The components listed in Table 10 were added sequentially to a mixing container, and the UV-curable liquid composition was prepared, applied, cured, and tested according to the procedure described in Example 8 above (unless otherwise specified). The cured coating had a thickness of 2.4 mils, withstood 4.3 kV for 1 second, and had an adhesion of 5 according to the ASTM D3359 cross-cut adhesion test.

[0127] Table 10

[0128] Example 11: Boron nitride 5% and 45% ATH - Additional Diluent The components listed in Table 11 were added sequentially to a mixing container, and the UV-curable liquid composition was prepared, applied, cured, and tested according to the procedure described in Example 8 above (unless otherwise specified). The cured coating had a thickness of 2.4 mils, withstood 4.3 kV for 1 second, and had an adhesion of 5 according to the ASTM D3359 cross-cut adhesion test.

[0129] Table 11

[0130] Example 12 Boron nitride 5% and 35% ATH - Additional Diluent The components listed in Table 12 were added sequentially to a mixing container, and the UV-curable liquid composition was prepared, applied, cured, and tested according to the procedure described in Example 8 above (unless otherwise specified). The cured coating had a thickness of 2.4 mils, withstood 4.3 kV for 1 second, and had an adhesion of 5 according to the ASTM D3359 cross-cut adhesion test.

[0131] Table 12

[0132] Example 13 Boron nitride 9.5% and 38% ATH - Additional Diluent The components listed in Table 13 were added sequentially to a mixing container, and the UV-curable liquid composition was prepared, applied, cured, and tested according to the procedure described in Example 8 above (unless otherwise specified). The cured coating had a thickness of 2.4 mils, withstood 4.3 kV for 1 second, and had an adhesion of 3 according to the ASTM D3359 cross-cut adhesion test.

[0133] Table 13

[0134] Example 14 50% ATH - Additional Diluent The components listed in Table 14 were added sequentially to a mixing container, and the UV-curable liquid composition was prepared, applied, cured, and tested according to the procedure described in Example 8 above (unless otherwise specified). The cured coating had a thickness of 2.4 mils, withstood 4.3 kV for 1 second, and had an adhesion of 5 according to the ASTM D3359 cross-cut adhesion test.

[0135] Table 14

[0136] Example 15 50% ATH - Additional Diluent The components listed in Table 15 were added sequentially to a mixing container, and the UV-curable liquid composition was prepared, applied, cured, and tested according to the procedure described in Example 8 above (unless otherwise specified). The cured coating had a thickness of 2.4 mils, withstood 4.3 kV for 1 second, and had an adhesion of 5 according to the ASTM D3359 cross-cut adhesion test.

[0137] Table 15

[0138] 1000-hour humidity aging test: Cured coated boards from each of Examples 1-15 were aged for 1000 hours in a Thermotron chamber maintained at 85°C and 85% relative humidity, twice the exposure time of previous tests. After aging, the cross-cut adhesion and dielectric withstand voltage of the coated boards were tested according to the test methods disclosed above, and the results are as follows: Coating performance summary after 1000 hours of humidity aging: All coated boards maintained cross-cut adhesion after 1000 hours of aging and passed the dielectric withstand test at 5000 volts for 2 minutes (leakage current of 0.7 to 2.0 µA).

[0139] Example 16 The thermal conductivity of the newly coated and UV-cured boards according to each of Examples 1-15 was tested according to ASTM D5470. All tested boards exhibited a thermal conductivity of at least 0.25 watts per meter Kelvin (W / mK), with some exhibiting a thermal conductivity of at least 0.40 W / mK.

[0140] These results demonstrate that the thermal conductivity is increased by at least 25% compared to the performance of a conventional powder coating of 0.2 W / mK, thus indicating that the cured coating according to the invention provides improved heat dissipation.

[0141] The above exemplary embodiments demonstrate that the coating compositions of the present invention can be used to form a thin, void-free coating with good coverage at the edges of a substrate, while simultaneously providing rapid heat dissipation and good electrical insulation with high dielectric strength. Therefore, the cured coating offers significant advantages in applications where high energy density electricity is generated or stored, producing significant heat during operation, such as battery packs in vehicles (e.g., automobiles or aircraft). The coating can provide further protection against battery damage during vehicle operation, where condensation and continuous vibration are common sources of corrosion and abrasion. The coating can be cured with UV light.

Claims

1. A UV-curable liquid coating composition, said UV-curable liquid coating composition comprising: (a) At least one UV-curable monomer, oligomer, or resin having one or more polymerizable groups for reaction under UV irradiation; wherein (a) is selected from unsaturated polyester monomers, oligomers, resins, and combinations thereof, preferably from vinyl esters, more preferably from epoxy vinyl esters, said epoxy vinyl esters optionally including epoxy acrylates and epoxy methacrylates, and combinations thereof. (b) At least one radical reactive diluent, said radical reactive diluent being different from (a), and comprising one or more polymerizable groups for reaction under UV irradiation; (c) At least one thermally conductive filler; (d) At least one photoinitiator; (e) at least one adhesion promoter; and (f) Any available dispersant.

2. A UV-curable liquid coating composition, said UV-curable liquid coating composition comprising: (a) At least one UV-curable monomer, oligomer, or resin having one or more polymerizable groups for reaction under UV irradiation, which is desired to be present in an amount ranging from 9% to 95%, preferably from 10% to 50%; wherein (a) is selected from unsaturated polyester monomers, oligomers, resins, and combinations thereof, preferably from vinyl esters, more preferably from epoxy vinyl esters, said epoxy vinyl esters including epoxy acrylates and epoxy methacrylates, and combinations thereof. (b) At least one monofunctional or bifunctional radical reactive diluent, which is different from (a) and contains one or more polymerizable groups for reaction under UV irradiation, preferably in an amount ranging from 10% to 95%, preferably 15% to 80%, and preferably 25% to 50%. (c) At least one thermally conductive filler, which is preferably present in an amount ranging from 1% to 70%, preferably 5% to 60%, and more preferably 10% to 50%; (d) At least one photoinitiator, which is preferably present in the range of 0.1% to 5%, preferably 1% to 4%, and more preferably 1.5% to 3.5%; (e) at least one adhesion promoter, which is preferably present in the range of 0.1% to 10%, preferably 0.5% to 8.0%, more preferably 1.0% to 6.0%; and Optional existence (f) At least one dispersant, ranging from 0.0% to, preferably, 7.0%, 6.0%, 5.0%, 4.0%, 3.0% in ascending order, or from 0.1% to 2.0%, and preferably present in an amount of 0.25% to 1.5%, preferably 0.5% to 1.25%; (g) Degassing agents, defoamers, antifoaming agents, or combinations thereof, each preferably present in the range of 0% to 2.0%; (h) At least one organic solvent, which is preferably present in the range of 0.0% to 20%; (i) At least one additive selected from rheology modifiers, softeners and plasticizers, each of which is preferably present in the range of 0% to 5%; The weight percentage of each component is relative to the total weight of the composition, and the total amount of the components does not exceed 100% by weight.

3. The UV-curable liquid coating composition according to claim 1 or 2, wherein, Relative to the total weight of the composition, (a) at least one unsaturated polyester resin, epoxy vinyl ester resin, such as epoxy acrylate and epoxy methacrylate, and combinations thereof are present in the range of 10% by weight to 95% by weight.

4. The UV-curable liquid coating composition according to claim 1 or 2, wherein, (b) The at least one free radical reactive diluent is present in the range of 10% to 95% by weight relative to the total weight of the composition.

5. The UV-curable liquid coating composition according to claim 1 or 2, wherein, (c) the at least one thermally conductive filler is present in the range of 5% to 60% by weight relative to the total weight of the composition, and the thermally conductive filler preferably comprises boron nitride filler.

6. The UV-curable liquid coating composition according to claim 1 or 2, wherein, (d) The at least one photoinitiator is present in the range of 0.5% to 4% by weight relative to the total weight of the composition.

7. The UV-curable liquid coating composition according to claim 1 or 2, wherein (e) the at least one adhesion promoter is present in the range of 0.5% to 8.0%.

8. The liquid epoxy adhesive composition according to claim 1 or 2, wherein, (f) The at least one dispersant is included in the composition in an amount ranging from 0.1% to 7.0% relative to the total weight of the composition.

9. The UV-curable liquid coating composition according to claim 1 or 2, wherein (g) is present as a degassing agent, defoamer, or a combination thereof, in a range of 0.1% to 2.0% relative to the total weight of the composition.

10. The UV-curable liquid coating composition according to claim 1 or 2, wherein, The at least one organic solvent (h) is present in the range of 1% to 20% by weight relative to the total weight of the composition.

11. The UV-curable liquid coating composition according to claim 1 or 2, wherein, The amount of (i) the at least one additive is in the range of 0.1% by weight to 5.0% by weight relative to the total weight of the composition.

12. The UV-curable liquid coating composition according to claim 1 or 2, wherein, The at least one additive comprises a rheology modifier present in the range of 0.1% to 5% relative to the total weight of the composition.

13. The UV-curable liquid coating composition according to claim 1 or 2, wherein, The at least one softening agent is present in the range of 0.1% to 5% relative to the total weight of the composition.

14. The UV-curable liquid coating composition according to claim 1 or 2, wherein, The at least one plasticizer is present in the range of 0.1% to 5.0% relative to the total weight of the composition.

15. Intermediate products, said intermediate products comprising: Substrate surface, preferably metal surface; And an uncured layer of the UV-curable liquid coating composition according to claim 1 or 2 deposited on the surface of the substrate, the uncured layer optionally dried on the surface of the substrate having a thickness of about 40 to about 100 micrometers.

16. An article of manufacture, said article of manufacture comprising: Substrate surface, preferably metal surface; And the adhesiveness of the UV-curable liquid coating composition according to claim 1 or 2 deposited on the surface, which is a UV-curable layer.

17. A method for preparing a dielectric coating exhibiting thermal conductivity, the method comprising the steps of: Obtain a substrate containing a metal surface, clean the metal surface, and optionally reduce the amount of oxide scale on the metal surface; The UV-curable liquid coating composition according to claim 1 is applied to the metal surface to form an uncured layer, and the uncured layer is exposed to UV radiation for a time sufficient to form a cured dielectric coating of about 40 to about 100 micrometers in thickness, the cured coating exhibiting a dielectric strength greater than about 80 kV / mm of the cured coating thickness, and exhibiting a thermal conductivity of at least 0.25 watts per meter Kelvin (W / mK) as measured according to ASTM D5470.

18. The method of claim 17, wherein the UV radiation curing time ranges from about 2 to 200 seconds.

19. An article of manufacture, said article of manufacture comprising: Substrate surface, preferably metal surface; And an adhesive UV-cured layer deposited on the surface, the adhesive UV-cured layer comprising the free radical polymerization product of unsaturated polyester monomers, oligomers, resins, and combinations thereof; at least one free radical reactive diluent different from (a); and at least one adhesion promoter, wherein the cured layer is electrically insulating and thermally conductive, such that the cured layer exhibits a dielectric strength greater than about 80 kV / mm of the cured coating thickness, and exhibits a thermal conductivity greater than about 0.25 watts per meter Kelvin (W / mK) as measured according to ASTM D5470.

20. The article of manufacture according to claim 19, wherein, When tested according to ASTM D3359, the electrically insulating and thermally conductive cured layer on the substrate surface exhibits a cross-cut adhesion of "5".

21. The article of manufacture according to claim 20, wherein, When aged for 500 hours in a Thermotron chamber at 85°C and 85% relative humidity, the electrically insulating and thermally conductive cured layer on the substrate surface exhibits a cross-cut adhesion of "5" when tested according to ASTM D3359.

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