Two-part hybrid epoxy-polyurethane coating systems and coatings formed therefrom

Abstract

A two-part coating system is provided. The system comprises a resin component and a crosslinking component. The resin component comprises a mixture of epoxy resin and polyurethane resin. The crosslinking component comprises a curing agent and a catalyst. The polyurethane resin comprises a donor for a Michael addition reaction and an acceptor for a Michael addition reaction. The catalyst is configured to promote a Michael addition reaction between the donor and acceptor of the polyurethane resin. The curing agent is configured to react with the epoxy resin.

Description

Cross-references to related applications

[0001] This application relates to and claims priority to U.S. Provisional Application Serial No. 63 / 556,619, filed on February 22, 2024, the contents of which are incorporated herein by reference in their entirety. Technical Field

[0002] This invention relates to a two-part coating system that forms a hybrid interpenetrating network of epoxy resin and polyurethane resin when reacting between a resin component and a crosslinking component; a coating formed therefrom; and a method for preparing the same. Background Technology

[0003] The U.S. paint and coatings industry comprises over 1,000 companies with a combined annual output exceeding $20 billion and continues to grow. Typical coatings used for interior applications, such as drywall in residences, are water-based latex paints. These water-based latex paints contain at least a polymer dispersed in water. When a water-based latex paint is applied to a substrate, the water evaporates, and the remaining polymer coalesces to form a continuous, cured film on the substrate. While water-based latex paints are inexpensive, easy to apply, easy to clean, and have low VOCs, their drying time varies depending on the humidity and temperature of the applied surface and the surrounding environment. Additionally, dried water-based latex paints are prone to scratching and cracking.

[0004] Polyurethane-based coatings are used to obtain coatings with high protective performance that are not easily scratched, cracked, or otherwise damaged by various environmental conditions (such as humidity, temperature, and light). For example, polyurethane-based coatings can be used on vehicles, wooden furniture, outdoor surfaces, interior decoration, marine applications, or other surfaces exposed to harsh conditions. Single-component polyurethane coatings cure through crosslinking upon exposure to water or heat. In two-component polyurethane coatings, the first component is mixed with the second component before the coating is applied to the surface. Two-component polyurethane coatings typically do not require water or heat to cure, but may cure depending on the specific ratio of the components mixed together and / or the crosslinking agent in the two-component polyurethane system. Although two-component polyurethane coatings may have higher mechanical properties than single-component polyurethane systems, there are associated environmental, health, and safety hazards related to the process of mixing and reacting the two components to form a cured two-component polyurethane coating. Summary of the Invention

[0005] Therefore, one object of the present invention is to provide a two-part coating system that is water-based and contains no or substantially no free isocyanates to improve the environmental impact of the two-part coating system during mixing and curing.

[0006] Another object of the present invention is to provide a two-part coating system formed of a resin component and a crosslinking component. The resin component comprises a polyurethane resin and an epoxy resin. The crosslinking component comprises a curing agent and a catalyst. The polyurethane resin comprises a donor for a Michael addition reaction and an acceptor for a Michael addition reaction. The catalyst is configured to promote the Michael addition reaction between the donor and the acceptor of the polyurethane resin. The curing agent is configured to react with the epoxy resin. When the resin component and the crosslinking component are mixed together and applied to a substrate, a cured coating is formed comprising a first polymer network of crosslinked polyurethane and a second polymer network of crosslinked epoxy resin. The first polymer network and the second polymer network are interwoven but not crosslinked to form an interpenetrating polymer network. In this way, the cured coating has advantageous properties from both the epoxy resin and the polyurethane, while still maintaining a controlled molecular weight for coating applications.

[0007] Another object of the present invention is to provide a method comprising mixing a resin component with a crosslinking component. The resin component comprises an epoxy resin and a polyurethane resin. The crosslinking component comprises a curing agent and a catalyst. The mixture of the resin component and the crosslinking component is then applied to a substrate. The mixture is cured to form a cured hybrid epoxy-polyurethane coating on the substrate. The mixture is cured when the curing agent reacts with the epoxy resin and the catalyst reacts with the polyurethane resin to form an interpenetrating polymer network on the substrate.

[0008] These and other objects of the present invention, individually or in combination, have been achieved by discovering a two-part hybrid epoxy-polyurethane system comprising a resin component and a crosslinking component. The hybrid epoxy-polyurethane system and coating compositions derived therefrom will be further described in the following detailed description and the appended claims. Attached Figure Description

[0009] The present invention may take the physical form of certain parts and arrangements of parts, the preferred embodiments of which will be described in detail in the specification and shown in the accompanying drawings which form part of the specification, and wherein:

[0010] Figure 1 Schematic diagrams illustrating some embodiments of interpenetrating polymer networks formed from a two-component system during the reaction between the resin component and the crosslinking component as described herein. Detailed Implementation

[0011] The range of values ​​expressed using endpoints includes all values ​​contained within that range (for example, 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc.).

[0012] To the extent used herein, the terms “comprising,” “having,” “with,” or variations thereof are intended to be inclusive in a manner similar to the term “comprising.” The singular forms “a,” “an,” and “the / that” include multiple referents unless the context clearly indicates otherwise. Furthermore, the terms “a,” “an,” “the / that,” “at least one,” and “one or more” are used interchangeably. Thus, for example, a coating composition containing “a” additive means that the coating composition may contain “one or more” additives. As used throughout this specification and claims, approximate language may be applied to modify quantitative expressions that can be permissibly varied without causing a change in the essential function associated with them. Therefore, values ​​modified by terms such as “about” are not limited to the specified precise values. In some cases, approximate language may correspond to the precision of the instrument used to measure the value. Moreover, unless otherwise specifically stated, the use of the terms “first,” “second,” etc., does not indicate order or importance, but rather the terms “first,” “second,” etc., are used to distinguish one element from another.

[0013] The term "comprising" and its variations are not intended to be limiting when they appear in the specification and claims.

[0014] As used herein, the terms “may” and “may” indicate a possibility of occurring within a set of circumstances; possessing the specified property, characteristic, or function; and / or defining one verb by expressing one or more of the properties, capabilities, or possibilities associated with the verb being defined. Thus, the use of “may” and “may” indicates that the modified term is clearly appropriate, capable, or suitable for the indicated capability, function, or use, while taking into account that in some cases the modified term may sometimes be inappropriate, incapable, or unsuitable. For example, in some cases an event or capability may be anticipated, while in others it may not occur—this distinction is captured by the terms “may” and “may”.

[0015] As used herein, the term "acrylic acid" includes (meth)acrylic acid, (meth)alkyl acrylate, (meth)acrylamide, (meth)acrylonitrile, and their modified forms, such as (meth)hydroxyalkyl acrylate. Throughout this document, the phrase "(meth)acryloyl" refers to both "methacryloyl" and "acryloyl". For example, (meth)acrylic acid refers to both methacrylic acid and acrylic acid, and methyl methacrylate refers to both methyl methacrylate and methyl acrylate.

[0016] When the term "aliphatic" is used in the context of carbon-carbon double bonds, it includes straight-chain (or open-chain) aliphatic carbon-carbon double bonds and cyclic aliphatic carbon-carbon double bonds, but excludes aromatic carbon-carbon double bonds of aromatic rings.

[0017] The term "aqueous" composition or dispersion as used herein means particles dispersed in an aqueous medium. An "aqueous medium" as used herein refers to a continuous phase comprising at least 50% by weight of water, wherein the remaining composition of the aqueous medium comprises particles and water-miscible compounds, such as, for example, alcohols, glycols, glycol ethers, and glycol esters.

[0018] Unless otherwise specified, the term “(co)polymer” as used herein includes both homopolymers (polymers containing units derived from a single monomer) and copolymers (polymers containing units derived from two or more different monomers).

[0019] As used herein, the terms “crosslinking agent” or “crosslinking component” refer to at least one molecule capable of forming covalent bonds between polymers or between two different regions of the same polymer.

[0020] When used in the context of coatings applied to a substrate, the term "on" includes both coatings applied directly or indirectly to the substrate. Thus, for example, a coating applied to a primer layer covering a substrate constitutes a coating applied to the substrate.

[0021] The terms "preferred" and "ideally" refer to embodiments of the invention that provide certain benefits in certain circumstances. However, other embodiments may also be preferred in the same or other circumstances. Furthermore, the description of one or more preferred embodiments does not imply that other embodiments are unavailable, and is not intended to exclude other embodiments from the scope of the invention.

[0022] As used in this article, the term “structural unit” (also known as a polymeric unit) for naming monomers refers to the residue of the monomer after polymerization, or the monomer in its polymerized form.

[0023] In the context of this invention, the term "waterborne" is intended to mean that the polymer component is in an aqueous medium. In some embodiments, waterborne coatings offer one or more of the following advantages: low toxicity and flammability due to low VOC levels and low HAP emissions; lower cost than solvent-based coatings and, in most cases, no additives, thinners, or hardeners required; less paint is needed to cover the same surface area compared to using solvent-based paint solutions; and the paint gun can be easily cleaned with water or water-based solutions without the need for paint thinners, acetone, or methyl acetate (making it more environmentally friendly and safer for users).

[0024] This invention relates to formulations of hybrid waterborne primer systems, methods for preparing primer coatings, and the use of these systems as coatings on substrates. The hybrid waterborne primers of this invention can be used alone as primers applied directly to substrates, or in combination with surface treatments (such as etching primers or other chemical surface treatments) on the substrate to be coated, so that the surface of the substrate can better receive and bond the hybrid waterborne primers of this invention.

[0025] The embodiments of the invention disclosed herein relate to a two-part coating system. This two-part coating system can be used for any desired end application, including but not limited to construction, automotive, building, marine, aerospace, and similar industries. As will be further described herein, the two-part coating system comprises a resin component and a crosslinking component. Each component provides various properties. The resin component comprises an epoxy resin and a polyurethane resin. The crosslinking component comprises a curing agent configured to react with the epoxy resin upon mixing and a catalyst configured to react with the polyurethane resin upon mixing. When the resin component and the crosslinking component are mixed together, the two components react to form a cured hybrid epoxy-polyurethane coating. This hybrid epoxy-polyurethane coating has a balance of advantageous properties attributable to both the polyurethane and epoxy resins, such as chemical resistance, mechanical properties, weather resistance, curing rate, pot life, corrosion resistance, etc. Furthermore, the hybrid epoxy-polyurethane coating cures without the use of isocyanates, thereby eliminating carbon dioxide byproducts. Without these carbon dioxide byproducts, the hybrid epoxy-polyurethane coating system has lower VOCs and also more advantageous mechanical properties compared to polyurethane coating systems containing isocyanates.

[0026] Polyurethane resins contain donors and acceptors for the Michael addition reaction within the polyurethane polymer chain. Epoxy resins can be blended with polyurethane resins to form resin components. Both epoxy and polyurethane resins can be water-based. Epoxy resins substantially do not react with polyurethane resins, or more preferably, do not react with polyurethane resins. "Substantially does not react with" means that if any reaction does occur after the two or more polymers are blended together, the amount of reaction between the polymers is so small and insignificant that the total viscosity of the mixture remains below 120 gRebs after storage at 40°C for 20 days. This viscosity limit indicates that gelation has not occurred, and therefore the resin component can still be used in coating applications with consistent performance properties.

[0027] Because polyurethane resins contain donors and acceptors for the Michael addition reaction, carbon dioxide production from polyurethane is reduced or more preferably eliminated. Therefore, few or no amine groups are present in the polyurethane resin, which act as catalysts to polymerize the epoxy resin when mixed with an epoxy resin to form a resin component. Thus, when a polyurethane resin containing donors and acceptors for the Michael addition reaction is mixed with an epoxy resin to form a resin component, the epoxy resin and polyurethane are substantially non-reactive to each other, or more preferably, do not react with each other. Therefore, substantially no crosslinking occurs between polyurethane polymer chains, between epoxy polymer chains, or between polyurethane polymer chains and epoxy polymer chains, or more preferably, no crosslinking occurs. "Substantially non-crosslinking" corresponds to an embodiment in which the epoxy resin and polyurethane resin substantially do not react with each other when mixed to form a resin component.

[0028] In some embodiments, about 5% to about 45% by weight, more preferably about 5% to about 40% by weight, about 5% to about 35% by weight, about 10% to about 45% by weight, about 10% to about 40% by weight, about 10% to about 35% by weight, about 10% to about 30% by weight, or even more preferably about 10% to about 25% by weight, of the resin component comprises epoxy resin, and the remainder of the resin component comprises polyurethane resin. As the amount of epoxy resin in the resin component increases, the viscosity of the resin component becomes greater. For example, in some embodiments where about 15% by weight of the resin component comprises epoxy resin, the resin component has a viscosity of about 75 gRebs after about 20 days at 40 degrees Celsius, measured using ASTM D562-10; while in some other embodiments where about 30% by weight of the resin component comprises epoxy resin, the resin component has a viscosity of about 100 gRebs after about 20 days at 40 degrees Celsius. In any embodiment, the resin component retains a viscosity of less than 120 gRebs after being stored at 40 degrees Celsius for 20 days, indicating that the epoxy and polyurethane resins are substantially unreactive or more preferably unreactive when mixed together to form the resin component.

[0029] In the crosslinking component, the curing agent and catalyst are substantially non-reactive to each other, or more preferably completely non-reactive. In some embodiments, the curing agent comprises an amine, and the catalyst comprises functional groups that promote a Michael addition reaction with the polyurethane resin. Because the polyurethane resins disclosed herein use a Michael addition reaction for crosslinking within the polyurethane resin, it is advantageous to eliminate free isocyanates from the system, as otherwise free isocyanates would react with the amine curing agent, thereby destabilizing the crosslinking component. Therefore, the catalyst does not contain isocyanates and thus is substantially non-reactive to the epoxy resin, or more preferably completely non-reactive, and the curing agent is substantially non-reactive to the polyurethane resin, or more preferably completely non-reactive. In some embodiments, the viscosity of the crosslinking component remains substantially constant over time after mixing and storage at 40 degrees Celsius for 36 days. For example, in some embodiments, the viscosity of the crosslinking component changes only within about 5 gRebs over time. In some embodiments, the viscosity of the crosslinking component can be in the range of, for example, about 35 gRebs and about 50 gRebs. If the viscosity of the crosslinking component is too high, water can be added to reduce it. Because the curing agent and catalyst are not consumed during mixing and storage of the crosslinking component, they are still available to react with the resin component when it is mixed with the resin component. When the resin component is mixed with the crosslinking component, the polyurethane resin crosslinks with itself, and the epoxy resin crosslinks with itself, thus forming an interpenetrating polymer network.

[0030] Figure 1 Schematic diagrams of some embodiments of the interpenetrating polymer network 100 are presented. The interpenetrating polymer network 100 comprises an interwoven network of crosslinked polyurethane resin 102 and crosslinked epoxy resin 104, wherein the crosslinked polyurethane resin 102 and crosslinked epoxy resin 104 are entangled and permeated with each other, but are substantially not crosslinked with each other, or more preferably not crosslinked with each other. In other words, although the crosslinked epoxy network 104 may be mechanically connected by entanglement with the crosslinked polyurethane network 102, the two networks are not chemically connected. This mechanical reinforcement between the crosslinked epoxy network 104 and the crosslinked polyurethane network 102 can provide better mechanical and chemical resistance properties than each crosslinked network alone. For example, in some embodiments, the interpenetrating polymer network 100 comprising the hybrid epoxy-polyurethane system disclosed herein may have better corrosion resistance than either the epoxy system alone or the polyurethane system alone. In some other embodiments, a partial interpenetrating polymer network 100 may be formed in which a small amount of crosslinking occurs between the crosslinked polyurethane resin and the crosslinked epoxy resin 104.

[0031] The reaction between the amine and the epoxy resin is based on a ring-opening reaction to produce a crosslinked epoxy network 104, while the reaction between the catalyst and the polyurethane resin is based on a Michael addition reaction to produce a crosslinked polyurethane network 102. Because these reaction mechanisms are very different from each other, when the resin component is mixed with the crosslinking component, crosslinking does not occur substantially or more preferably not between the crosslinked epoxy network 104 and the crosslinked polyurethane network 102. Because the two different reactions do not react substantially with each other, the final properties of the interpenetrating polymer network 100 and the coating formed therefrom can be more easily tuned, since when the reaction of one resin is tuned to achieve a specific property, the reactions of the other resins may not be changed or may not be significantly changed.

[0032] Furthermore, because the two reactions are essentially non-reactive, their reaction rates can differ. For example, in some embodiments, the ring-opening reaction between the epoxy resin and the amine curing agent occurs at a slower rate than the Michael addition reaction between the polyurethane resin and the catalyst. In some other embodiments, one of these reactions (Michael addition or ring-opening) may take longer to complete than the other, simply because more reactants are available for the reaction. Reaction rates can be measured, for example, by FTIR, by monitoring changes in the catalyst and the curing agent over time. This “change” can be a change in the structure or amount of reactants, functional groups, or byproducts (e.g., the transformation of double bonds in the acceptor for Michael addition in the polyurethane resin; the disappearance of ethylene oxide in the epoxy resin, etc.) or some other indicator of the progress of the reaction.

[0033] Because ring-opening and Michael addition reactions do not share reactants, there is no need to worry about one reaction occurring too quickly and consuming the reactants required for another reaction. Therefore, similarly, there is greater flexibility in adjusting properties attributable to one resin without affecting the reaction mechanisms of other resins. Because each reaction can be controlled individually, the crosslinking density of each resin network can also be increased and controlled based on, for example, the amount and structure of each resin (epoxy or polyurethane) and each crosslinking agent (curing agent or catalyst). Higher crosslinking densities can improve the mechanical and chemical properties of the two-part coating system.

[0034] For the Michael addition reaction to occur, the polyurethane resin within the resin component contains donors and acceptors for the Michael addition reaction before mixing with the crosslinking component. The donor may comprise an electron-rich malonate polyester, malonate, or some other suitable nucleophile or enol, and the acceptor may comprise an electron-deficient acryloyl monomer or oligomer, or some other suitable electrophile or acryloyl group. Additional non-limiting examples of donors that can be used in polyurethane resins include β-diketones; β-ketoesters; β-ketonitriles; β-nitroketones; α-nitroketones; nitro compounds; and ethyl acetoacetate. Additional non-limiting examples of acceptors that can be used in polyurethane resins include methyl acrylate; α,β-unsaturated aldehydes; α,β-unsaturated ketones; α,β-unsaturated esters; α,β-unsaturated amides; α,β-unsaturated nitriles; and nitroethylene.

[0035] In some embodiments, the polyurethane resin further comprises a hydrophobic soft portion configured to prevent crystallization of other hard portions of the chain, and a hydrophilic portion configured to aid dispersion of the polymer chain in water, since the polyurethane resin is an aqueous system. In some embodiments, polyurethane functional groups may be arranged between the hydrophobic and hydrophilic portions of the polyurethane polymer chain. In some embodiments, a donor is arranged at a first end of the polyurethane polymer chain, while an acceptor is arranged at a second end of the polyurethane polymer chain. The polyurethane functional groups, hydrophobic portion, and hydrophilic portion of the polyurethane polymer chain may be arranged between the first and second ends of the polyurethane polymer chain. It should be understood that the polyurethane resin may contain other functional groups within the polyurethane polymer chain because these other functional groups do not react with the curing agent of the epoxy resin or crosslinking component. Furthermore, any additional functional groups in the polyurethane resin preferably do not react with the catalyst of the crosslinking component, such that the Michael addition reaction between the donor and acceptor in the polyurethane resin can still be controlled when mixed with the crosslinking component.

[0036] As a non-limiting example, in some embodiments, the polyurethane resin comprises deionized water as the primary solvent and an organic solvent as a co-solvent. Because water is the primary solvent, this means that the entire polyurethane resin is still considered aqueous because there is more water than organic solvent. In one exemplary embodiment, the co-solvent may be dipropylene glycol dimethyl ether. In some embodiments, the polyurethane resin also comprises various dispersants, deformants, pigments, rust inhibitors, corrosion inhibitors, fillers, leveling agents, epoxy latex, rheology modifiers, binders, etc.

[0037] In some embodiments, the catalyst in the crosslinking component comprises a base catalyst suitable for initiating the Michael addition reaction in the polyurethane resin. The catalyst may include, for example, tetramethylguanidine (TMG); 1,5-diazabicyclo(4,3,0)non-5-ene (DBN); 1,8-diazabicyclo(5,4,0)undec-7-ene (DBU); triphenylphosphine; titanium tetrachloride; chiral amino-amide organic catalysts; and dihalogen catalysts. To reduce the rate of the Michael addition reaction and thus extend the pot life of the two-part coating system, the catalyst in the crosslinking component may comprise a blocked base catalyst, such as, for example, a tetraalkylammonium hydroxide substance reacting with dialkyl carbonates in combination with a kinetic control additive. In some embodiments, the pot life may be further manipulated based on the amount of kinetic control additive included in the crosslinking component.

[0038] For the ring-opening reaction to occur, the epoxy resin contains epoxy groups prepared to react with the curing agent of the crosslinking groups. It should be understood that the epoxy resin may contain other functional groups within the epoxy polymer chain, as these other functional groups do not react with the polyurethane resin or the catalyst of the crosslinking component. Furthermore, any additional functional groups in the epoxy resin preferably do not react with the curing agent of the crosslinking component, such that the ring-opening reaction between the amine in the curing agent and the epoxy groups in the epoxy resin can still be controlled when the resin component is mixed with the crosslinking component.

[0039] As a non-limiting example, in some embodiments, the epoxy resin comprises deionized water as the primary solvent and an organic solvent as a co-solvent. Because water is the primary solvent, this means that the entire epoxy resin is still considered aqueous because there is more water than organic solvent. In one exemplary embodiment, the co-solvent may be dipropylene glycol dimethyl ether. In some embodiments, the epoxy resin also comprises various dispersants, deformants, pigments, rust inhibitors, corrosion inhibitors, fillers, leveling agents, epoxy latex, rheology modifiers, binders, etc.

[0040] In some embodiments, the curing agent contains amine functional groups. In some embodiments, the curing agent is aliphatic. In some other embodiments, the curing agent may be aromatic. Aliphatic amine curing agents provide a faster reaction with epoxy resins compared to aromatic amine curing agents. It should be understood that the curing agent may contain other functional groups within the amine polymer chain because these other functional groups do not react with the curing agent of the polyurethane resin or crosslinking component. Furthermore, any additional functional groups in the curing agent preferably do not react with the epoxy groups of the resin component, such that the ring-opening reaction between the amine of the curing agent and the epoxy groups in the epoxy resin can still be controlled when the resin component is mixed with the crosslinking component.

[0041] In some embodiments, the curing agent may include primary amines, secondary amines, tertiary amines, polyfunctional amines, polyamides, polyamides, aminosilanes, dimethylethanolamine, or combinations thereof. The amine may be, for example, aliphatic, alicyclic, aromatic, or dicyandiamide. Exemplary polyfunctional amines used as curing agents may be selected from aliphatic polyfunctional amines, aromatic polyfunctional amines, or combinations thereof. Exemplary aliphatic polyfunctional amines include polyethyleneamines, such as diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, 1,6-hexamethylenediamine, 3,3,5-trimethyl-1,6-hexamethylenediamine, 3,5,5-trimethyl-1,6-hexamethylenediamine, 2-methyl-1,5-pentamethylenediamine, di(3-aminopropyl)amine, N,N'-di(3-aminopropyl)-1,2-ethylenediamine, N,N-dimethyl-1,3-propanediamine, N,N-ethyl-1,3-propanediamine, aminoethylpiperazine, or combinations thereof. Exemplary aromatic polyfunctional amines include o-toluenediamine, m-toluenediamine, m-phenylenediamine, methylene-bridged di(phenylene)amine, and mixtures or combinations thereof. Additional non-limiting examples of possible curing agents include phenol-formaldehyde resins and amino-formaldehyde resins; carboxylic acid-functionalized polyesters, acid anhydrides, polysulfides, and polythiols. Additionally, the crosslinking component may also contain a catalyst for curing the epoxy resin, such as, for example, tertiary amines, imidazoles, ureas, hydrazides, and acylhydrazides. The aforementioned catalysts for epoxy curing may be used in addition to or in place of the curing agent in the crosslinking component. It should be understood that other curing agents and / or catalysts that react with epoxy resins but not with polyurethane resins and do not react with the catalyst are within the scope of this disclosure.

[0042] The two-part coating system of the present invention may also contain other optional components that will not adversely affect the two-part coating system or the cured coating produced therefrom. Such optional components include, for example, catalysts, dyes, pigments, toners, extenders, fillers, lubricants, preservatives, flow control agents, thixotropic agents, dispersants, antioxidants, adhesion promoters, light stabilizers, surfactants, and mixtures thereof. Each optional component is preferably contained in an amount sufficient for its intended purpose, but not in an amount that adversely affects the two-part coating system or the resulting cured coating. For example, these optional components preferably do not promote crosslinking between the epoxy and polyurethane resins in the resin component, such that the resin component remains storage stable and can be used for crosslinking to form an interpenetrating polymer network when mixed with the crosslinking component. Similarly, these optional components preferably do not promote reactions within the crosslinking component, such that the crosslinking component also remains storage stable and sufficient curing agent and catalyst remain available for reaction when mixed with the resin component.

[0043] After manufacturing the resin component and the crosslinking component, each component can be stored for a long time and remain stable for the aforementioned reasons (e.g., the epoxy resin substantially does not react with the polyurethane resin in the resin component, or more preferably, does not react with it; and the catalyst substantially does not react with the curing agent in the crosslinking component, or more preferably, does not react with it). When preparing to coat the substrate, the resin component and the crosslinking component are mixed in a predetermined ratio. For example, in some embodiments, the ratio between the equivalent amount of epoxy groups in the epoxy resin and amine groups in the curing agent may be in the range of preferably about 1:5 and about 2:1, more preferably about 2:5 and about 1.5:1, or even more preferably about 3:5 and about 1:1. Furthermore, in some embodiments, when mixing the crosslinking component and the resin component, the mixture may contain, for example, preferably about 2% to about 12% of catalyst, more preferably about 2% to about 10% of catalyst, even more preferably about 3% to about 10% of catalyst, or even more preferably about 4% to about 6% of catalyst. In some embodiments, the weight ratio of the catalyst to the polyurethane resin is in the range of, for example, about 1:30 to about 1:5. It should be understood that the ratio of functional groups and components in the two-part coating system can be adjusted during mixing to achieve desired properties, such as pot life, mechanical strength, adhesion, and corrosion resistance.

[0044] The resin and crosslinking components can be mixed together at room temperature using a mixing stick, bucket mixer, electric mixing attachment, or some other suitable tool. In some embodiments, the pot life of the mixture can be between about 1 hour and about 5 hours, which is significantly longer than that of ordinary polyurethane coatings cured by isocyanate. More preferably, in some embodiments, the pot life of the mixture is greater than 3 days. The resulting mixture of resin and crosslinking components can be applied as a coating to a prepared substrate via roller coating, brushing, spraying, or some other suitable coating method. The coating can be applied to a thickness, for example, between about 2 mils and about 5 mils. When room temperature air is blown onto the substrate, the coating can dry on the substrate at room temperature within 10 minutes and become almost tackless. After about 1 hour of blowing room temperature air onto the substrate, the coating can be cleaned and sanded. In some embodiments, the coating can be sanded using 320 grit and 600 grit sandpaper. Over time, the catalyst from the crosslinking agent promotes crosslinking between polymers in the polyurethane resin via Michael addition reaction, and the curing agent promotes crosslinking between polymers in the epoxy resin via ring-opening reaction. As these crosslinking reactions proceed, an interpenetrating polymer network begins to form, comprising a first polymer network of crosslinked epoxy resin entangled with a second polymer network of crosslinked polyurethane. This interpenetrating polymer network forms a hybrid epoxy-polyurethane coating on the substrate, and finally, once all reactions are complete, this hybrid epoxy-polyurethane coating cures on the substrate.

[0045] In some embodiments, the substrate is prepared to receive the hybrid epoxy-polyurethane coating by first applying an aqueous etching primer coating to the substrate. An aqueous etching primer can be used because the hybrid epoxy-polyurethane coating is also aqueous. In some embodiments, the etching primer coating comprises an epoxy-polysiloxane network. In some embodiments, the substrate may comprise a metal (e.g., steel, aluminum, etc.), a plastic (e.g., thermoplastic or thermoplastic), a ceramic, or some other suitable material or composite. In some embodiments, the hybrid epoxy-polyurethane coating may be applied directly to the substrate, while in other embodiments, an etching primer coating or some other pretreatment of the substrate is applied prior to the application of the hybrid epoxy-polyurethane coating.

[0046] In some embodiments, the hybrid epoxy-polyurethane coating acts as a primer layer configured to receive an overcoat. In some such embodiments, one or more overcoats (such as a base coat, varnish, etc.) may be applied to the hybrid epoxy-polyurethane coating when it is fully or partially cured. As a primer layer, the hybrid epoxy-polyurethane can be formulated to adhere to the underlying substrate or coating and the overcoat. In some embodiments, adhesion to the underlying substrate or coating, as well as adhesion to any overcoat, can be improved by adjusting the amount of hydrophilic portion in the polyurethane resin. For example, if the underlying coating or overcoat is also water-based, the hybrid epoxy-polyurethane coating, being hydrophilic, can wet and therefore adhere better to the underlying coating or overcoat.

[0047] As a non-limiting example, in some embodiments, the underlying etching primer layer, comprising, for example, an epoxy-polysiloxane network, is formed from an aqueous epoxy resin, an amine curing agent, a silane oligomer containing hydroxyl and amine functional groups, and other suitable additives. When these components are mixed, the etching primer layer is sprayed onto a substrate and can dry on the substrate at room temperature in about 1 minute to about 25 minutes, with minimal tackiness. The drying time of the etching primer layer can vary based on temperature and humidity conditions. In some embodiments, the substrate is prepared by cleaning and sanding to receive the epoxy-polysiloxane network. Additionally, in some embodiments, the etching primer layer containing the epoxy-polysiloxane network may be sanded before receiving a hybrid epoxy-polyurethane coating.

[0048] Other non-limiting examples of suitable organic solvents for the primary waterborne coating compositions of the present invention include aliphatic hydrocarbons (e.g., solvent oils, kerosene, VM&P naphtha solvent, etc.); aromatic hydrocarbons (e.g., benzene, toluene, xylene, naphtha series 100, 150, 200, etc.); alcohols (e.g., ethanol, n-propanol, isopropanol, n-butanol, isobutanol, etc.); ketones (e.g., acetone, 2-butanone, cyclohexanone, methyl aryl ketone, ethyl aryl ketone, methyl isopentyl ketone, etc.); esters (e.g., ethyl acetate, butyl acetate, etc.); glycols (e.g., butyl ethylene glycol); glycol ethers (e.g., ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, etc.); glycol ether esters (e.g., butyl ethylene glycol acetate, methoxypropyl acetate, etc.); and mixtures thereof.

[0049] The following examples of improved properties of hybrid epoxy-polyurethane coatings are provided to illustrate the invention and its advantages, but should not be construed as limiting the scope of the invention.

[0050] In one embodiment, the following data are collected by comparing a conventional polyurethane coating with the hybrid epoxy-polyurethane coating disclosed herein. The hybrid epoxy-polyurethane coating samples used for testing were prepared by: sanding and cleaning a steel substrate; drying the steel substrate at room temperature; applying an aqueous epoxy-polysiloxane etch primer layer to the prepared substrate; applying the hybrid epoxy-polyurethane coating onto the aqueous epoxy-polysiloxane etch primer layer; drying the hybrid epoxy-polyurethane coating; polishing and cleaning the hybrid epoxy-polyurethane coating; applying a black base coat layer onto the hybrid epoxy-polyurethane coating; and applying a clear coat layer onto the black base coat layer. The control samples used for testing were prepared similarly to the hybrid epoxy-polyurethane coating samples, except that in the control samples, a solvent-based etch primer was used instead of the aqueous epoxy-polysiloxane etch primer layer; and a conventional solvent-based polyurethane coating was used instead of the aqueous hybrid epoxy-polyurethane coating.

[0051] In some embodiments, the dry film thickness of the waterborne epoxy-polysiloxane etch primer layer or solvent-based etch primer layer is in the range of about, for example, 0.5 mils to about 1.5 mils. In some embodiments, the dry film thickness of the waterborne hybrid epoxy-polyurethane coating or solvent-based polyurethane coating is in the range of about, for example, 3 mils to about 5 mils. In some embodiments, the dry film thickness of the black base coat layer is in the range of about, for example, 0.5 mils to about 1.2 mils. In some embodiments, the dry film thickness of the clear coat layer is in the range of about, for example, 3 mils to about 6 mils. It should be understood that other dry film thickness values ​​may be used, provided that sufficient drying time is allowed between layer applications. Additionally, for the following data collection, the corresponding layers in the hybrid epoxy-polyurethane coating samples and control samples had the same or similar dry film thickness to remove thickness as a variable from these test results.

[0052] In some implementations, the chemical resistance of hybrid epoxy-polyurethane coatings can be tested by rubbing a paper soaked in methyl ethyl ketone (MEK) solvent against a substrate according to ASTM D5402-19. If the substrate is not exposed after 300 cycles of rubbing with MEK solvent, the hybrid epoxy-polyurethane coating is considered "chemically resistant." Both hybrid epoxy-polyurethane samples and conventional samples can withstand at least 300 cycles and therefore both possess sufficient "chemical resistance."

[0053] In some implementations, the adhesive strength of hybrid epoxy-polyurethane coatings can be evaluated using crosshatch testing according to ASTM D3359. This test assesses adhesive strength by applying and removing pressure-sensitive adhesive tape over a cut formed in the coating. The substrate and coating are monitored to observe whether the coating peels off from the substrate and / or adheres to the tape. When performing this adhesive strength test, both hybrid epoxy-polyurethane samples and conventional samples exhibit the same adhesive strength values.

[0054] In some implementations, the impact resistance of hybrid epoxy-polyurethane coatings can be evaluated according to ASTM D5420. This test assesses the coating's direct and indirect impact strength. In this impact resistance test, both hybrid epoxy-polyurethane samples and conventional samples are able to withstand the same amount of pressure, both directly and indirectly. Stone chip testing is also performed to assess coating durability, and the results are similar between hybrid epoxy-polyurethane samples and conventional samples.

[0055] In some implementations, the film flexibility of the hybrid epoxy-polyurethane coating can be evaluated using the conical mandrel bending test disclosed in ASTM D522. When this flexibility test is performed, both the hybrid epoxy-polyurethane sample and the conventional sample achieve a passing score, meaning that both coatings exhibit sufficient film flexibility for their intended application.

[0056] In some implementations, the optical appearance of hybrid epoxy-polyurethane coatings can be evaluated based on gloss retention and / or DOI retention at 20 degrees. When performing these optical appearance tests, both hybrid epoxy-polyurethane samples and conventional samples exhibit similar gloss and DOI scores, with each test result being approximately 5% of the other.

[0057] In some embodiments, the behavior of hybrid epoxy-polyurethane coatings in humid and corrosive environments can be evaluated in humidity chambers and salt spray chambers. For example, in a humidity chamber, substrates coated with hybrid epoxy-polyurethane coatings and conventional solvent-based polyurethane coatings are evaluated after several days of exposure to elevated temperatures. Changes in optical appearance and adhesion strength can then be measured. In some embodiments, the optical appearance and adhesion loss of the hybrid epoxy-polyurethane coating are slightly less favorable than those of the conventional solvent-based polyurethane coating. This slightly worse behavior can be attributed to the fact that there is no chemical bonding between the layers in contact with the hybrid epoxy-polyurethane coating. Because the cured coating shrinks upon exposure to higher temperatures, the hybrid epoxy-polyurethane coating may lose more adhesion to surrounding layers in the absence of this chemical bonding. It has been observed that when the ratio between the equivalent of epoxy groups and amine groups in the hybrid epoxy-polyurethane coating increases from about 0.75:1 to about 1.5:1, the hybrid epoxy-polyurethane coating exhibits slightly more favorable optical appearance and / or adhesion loss after humidity testing compared to the conventional solvent-based polyurethane coating.

[0058] To test the behavior of coatings in corrosive environments, the substrate can be placed in a salt spray chamber at elevated temperatures for several weeks. Scratches can be intentionally created in both hybrid epoxy-polyurethane coatings and conventional solvent-based polyurethane coatings before loading the substrate into the salt spray chamber. In some embodiments, the salt spray chamber test is performed according to ASTM B117. After the substrate is removed from the salt spray chamber, the amount of delamination and corrosion occurring at the scratches is evaluated. The amount of delamination and corrosion in the hybrid epoxy-polyurethane coating is slightly less favorable than in the conventional solvent-based polyurethane coating. This can also be attributed to the small to no chemical bonding between the hybrid epoxy-polyurethane coating and the surrounding layers on the substrate. It has been observed that the corrosion of the hybrid epoxy-polyurethane coating is slightly more favorable than that of the conventional solvent-based polyurethane coating, at least after ASTM B117, as the ratio between the equivalent of epoxy groups and amine groups in the hybrid epoxy-polyurethane coating increases from about 0.75:1 to about 1.5:1.

[0059] It is understood that other testing methods can be used to evaluate the above properties, as well as other properties of each of the hybrid epoxy-polyurethane coatings and conventional solvent-based polyurethane coatings. Furthermore, the above comparison between the properties of hybrid epoxy-polyurethane coatings and conventional solvent-based polyurethane coatings is exemplary and can be varied depending on the exact formulation and / or application method of the hybrid epoxy-polyurethane coating on the substrate.

[0060] As demonstrated by the exemplary data above, hybrid epoxy-polyurethane coatings exhibit faster drying times and better optical appearance compared to conventional solvent-based polyurethane coatings. Most other properties of hybrid epoxy-polyurethane coatings are comparable to those of conventional solvent-based polyurethane coatings. Therefore, the disclosed waterborne hybrid epoxy-polyurethane coatings have lower VOC levels while providing similar or better properties compared to conventional solvent-based polyurethane coatings.

[0061] The following are some non-limiting examples of embodiments of the present invention:

[0062] Implementation Scheme 1. A two-part system, the two-part system comprising:

[0063] The resin component comprises epoxy resin and polyurethane resin; and

[0064] The crosslinking component includes a curing agent and a catalyst.

[0065] The polyurethane resin comprises a donor for a Michael addition reaction and an acceptor for a Michael addition reaction, wherein the catalyst is configured to promote a Michael addition reaction between the donor and the acceptor of the polyurethane resin, and wherein the curing agent is configured to react with the epoxy resin.

[0066] Implementation Scheme 2. The two-part coating system according to Implementation Scheme 1, wherein the curing agent comprises an amine.

[0067] Implementation Scheme 3. A two-part coating system according to either Implementation Scheme 1 or Implementation Scheme 2, wherein the polyurethane resin comprises a hydrophobic portion and a hydrophilic portion.

[0068] Implementation Scheme 4. A two-part coating system according to any one of Implementation Schemes 1 to 3, wherein the resin component and the crosslinking component are configured to react without the use of isocyanate to form a hybrid epoxy-polyurethane coating.

[0069] Implementation Scheme 5. A two-part coating system according to any one of Implementation Schemes 1 to 4, wherein the epoxy resin is configured not to react with the catalyst, and wherein the polyurethane resin is configured not to react with the curing agent.

[0070] Implementation Scheme 6. A two-part coating system according to any one of Implementation Schemes 1 to 5, wherein about 5% by weight to about 25% by weight of the resin component comprises the epoxy resin.

[0071] Implementation Scheme 7. A two-part coating system according to any one of Implementation Schemes 1 to 6, wherein the resin component is water-based.

[0072] Implementation Scheme 8. A two-part coating system according to any one of Implementation Schemes 1 to 7, wherein the polyurethane resin is configured to react with the catalyst, and the epoxy resin is configured to react simultaneously with the curing agent to form a hybrid epoxy-polyurethane coating comprising an interpenetrating polymer network.

[0073] Implementation Scheme 9. The two-part coating system according to Implementation Scheme 8, wherein the interpenetrating polymer network comprises a first polymer network and a second polymer network, wherein the first polymer network comprises a crosslinked epoxy resin, and wherein the second polymer network comprises a crosslinked polyurethane.

[0074] Implementation Scheme 10. The two-part coating system according to Implementation Scheme 9, wherein the first polymer network and the second polymer network are interwoven but not cross-linked.

[0075] Implementation Scheme 11. A two-part coating system, said two-part coating system comprising:

[0076] The resin component comprises epoxy resin and polyurethane resin; and

[0077] The crosslinking component includes a curing agent and a catalyst.

[0078] The epoxy resin reacts with the curing agent but not with the catalyst.

[0079] The polyurethane resin reacts with the catalyst but not with the curing agent, and

[0080] When the resin component is mixed with the crosslinking component, the epoxy resin and the polyurethane resin are configured to react with the curing agent and the catalyst, respectively, to form an interpenetrating polymer network.

[0081] Implementation Scheme 12. The two-part coating system according to Implementation Scheme 11, wherein the resin component and the crosslinking component are water-based.

[0082] Implementation Scheme 13. A two-part coating system according to one of Implementation Scheme 11 or Implementation Scheme 12, wherein the polyurethane resin comprises a donor for a near-Michael addition reaction, an acceptor for a Michael addition reaction, a hydrophobic portion, a hydrophilic portion, and polyurethane functional groups.

[0083] Implementation Scheme 14. A two-part coating system according to any one of Implementation Schemes 11 to 13, wherein the curing agent comprises an amine.

[0084] Implementation Scheme 15. A two-part coating system according to any one of Implementation Schemes 11 to 14, wherein the epoxy resin does not react with the polyurethane resin, and wherein the catalyst does not react with the curing agent.

[0085] Implementation Scheme 16. A method for forming a coating, the method comprising:

[0086] A resin component is mixed with a crosslinking component to form a mixture, wherein the resin component comprises epoxy resin and polyurethane resin, and wherein the crosslinking component comprises a curing agent and a catalyst.

[0087] The mixture of the resin component and the crosslinking component is applied to a substrate; and

[0088] The mixture of the resin component and the crosslinking component is cured to form a cured hybrid epoxy-polyurethane coating on the substrate, wherein the mixture is cured when the curing agent reacts with the epoxy resin and the catalyst reacts with the polyurethane resin.

[0089] Implementation Scheme 17. The method according to Implementation Scheme 16, wherein the curing agent comprises an amine.

[0090] Implementation Scheme 18. The method according to one of Implementation Scheme 16 or Implementation Scheme 17, wherein the catalyst reacts with the polyurethane resin via a Michael addition reaction.

[0091] Implementation Scheme 19. The method according to any one of Implementation Schemes 16 to 18, wherein the substrate is metal, and wherein an aqueous etching primer coating is applied to the substrate prior to applying the mixture to the substrate, such that the mixture is applied directly to the aqueous etching primer coating on the substrate.

[0092] Implementation Scheme 20. The method according to Implementation Scheme 19, wherein the waterborne etching primer coating is formed from a waterborne epoxy-polysiloxane primer.

[0093] Implementation Scheme 21. The method according to any one of Implementation Schemes 16 to 20, wherein the mixture is aqueous.

[0094] Implementation Scheme 22. The method according to any one of Implementation Schemes 16 to 21, wherein the mixture of the resin component and the crosslinking component is applied directly to the substrate.

[0095] Implementation Scheme 23. The method according to any one of Implementation Schemes 16 to 22, wherein the substrate is a metal, a plastic, or a combination thereof.

[0096] Unless otherwise indicated herein or clearly contradicted by the context, all methods described herein may be performed in any suitable order. The use of language (e.g., “such as”) in any examples or descriptions provided herein is intended to illustrate the invention and not to limit its scope. Any statements herein regarding the nature or benefits of the invention or preferred embodiments are not intended to be limiting. The invention includes all modifications and equivalents of the subject matter described herein as permitted by applicable law. Furthermore, unless otherwise indicated herein or clearly contradicted by the context, the invention covers any combination of the foregoing elements in all possible variations. Descriptions of any references or patent claims herein, even if marked “prior,” are not intended to constitute a concession by such references or patents to prior art. Unclaimed language should not be considered to limit the scope of the invention. Any statement or suggestion herein that certain features constitute part of the claimed invention, unless reflected in the appended claims, is not intended to be limiting. The marking of a patent number on any product or the identification of a patent number in connection with any service should not be construed as indicating that all embodiments described herein are incorporated into such product or service.

[0097] While the implementation schemes discussed herein involve the coatings and methods discussed above, these implementation schemes are intended to be illustrative only and are not intended to limit the applicability of these implementation schemes to those discussed only herein.

[0098] The above description illustrates only a few possible embodiments of various aspects of the invention, and equivalent changes and / or modifications will occur to those skilled in the art upon reading and understanding this specification and the accompanying drawings. Furthermore, while a particular feature of the invention may have been disclosed with respect to only one embodiment among several embodiments, such feature may be combined with one or more other features of other embodiments, as may be desired and advantageous for any given or particular application.

[0099] Based on the foregoing teachings, additional modifications and variations of the invention are possible. Therefore, it should be understood that, within the scope of the appended claims, the invention may be practiced in ways other than those specifically described herein.

Claims

1. A two-part coating system, said two-part coating system comprising: The resin component comprises epoxy resin and polyurethane resin; and The crosslinking component includes a curing agent and a catalyst. The polyurethane resin comprises a donor for a Michael addition reaction and an acceptor for a Michael addition reaction, wherein the catalyst is configured to promote a Michael addition reaction between the donor and the acceptor of the polyurethane resin, and wherein the curing agent is configured to react with the epoxy resin.

2. The two-part coating system according to claim 1, wherein the curing agent comprises an amine.

3. The two-part coating system according to claim 1 or claim 2, wherein the polyurethane resin comprises a hydrophobic portion and a hydrophilic portion.

4. The two-part coating system according to any one of claims 1 to 3, wherein the resin component and the crosslinking component are configured to react without the use of isocyanate to form a hybrid epoxy-polyurethane coating.

5. The two-part coating system according to any one of claims 1 to 4, wherein the epoxy resin is configured not to react with the catalyst, and wherein the polyurethane resin is configured not to react with the curing agent.

6. The two-part coating system according to any one of claims 1 to 5, wherein about 5% by weight to about 25% by weight of the resin component comprises the epoxy resin.

7. The two-part coating system according to any one of claims 1 to 6, wherein the resin component is water-based.

8. The two-part coating system according to any one of claims 1 to 7, wherein the polyurethane resin is configured to react with the catalyst, and the epoxy resin is configured to react simultaneously with the curing agent to form a hybrid epoxy-polyurethane coating comprising an interpenetrating polymer network.

9. The two-part coating system of claim 8, wherein the interpenetrating polymer network comprises a first polymer network and a second polymer network, wherein the first polymer network comprises a crosslinked epoxy resin, and wherein the second polymer network comprises a crosslinked polyurethane.

10. The two-part coating system of claim 9, wherein the first polymer network and the second polymer network are interwoven but not cross-linked.

11. A two-part coating system, said two-part coating system comprising: The resin component comprises epoxy resin and polyurethane resin; and The crosslinking component includes a curing agent and a catalyst. The epoxy resin reacts with the curing agent but not with the catalyst. The polyurethane resin reacts with the catalyst but not with the curing agent, and When the resin component is mixed with the crosslinking component, the epoxy resin and the polyurethane resin are configured to react with the curing agent and the catalyst, respectively, to form an interpenetrating polymer network.

12. The two-part coating system according to claim 11, wherein the resin component and the crosslinking component are water-based.

13. The two-part coating system according to claim 11 or claim 12, wherein the polyurethane resin comprises a donor for a Michael addition reaction, an acceptor for a Michael addition reaction, a hydrophobic portion, a hydrophilic portion, and polyurethane functional groups.

14. The two-part coating system according to any one of claims 11 to 13, wherein the curing agent comprises an amine.

15. The two-part coating system according to any one of claims 11 to 14, wherein the epoxy resin does not react with the polyurethane resin, and wherein the catalyst does not react with the curing agent.

16. A method of forming a coating, the method comprising: A resin component is mixed with a crosslinking component to form a mixture, wherein the resin component comprises epoxy resin and polyurethane resin, and wherein the crosslinking component comprises a curing agent and a catalyst. The mixture of the resin component and the crosslinking component is applied to the substrate; as well as The mixture of the resin component and the crosslinking component is cured to form a cured hybrid epoxy-polyurethane coating on the substrate, wherein the mixture is cured when the curing agent reacts with the epoxy resin and the catalyst reacts with the polyurethane resin.

17. The method of claim 16, wherein the curing agent comprises an amine.

18. The method according to claim 16 or any one of claim 17, wherein the catalyst reacts with the polyurethane resin via a Michael addition reaction.

19. The method according to any one of claims 16 to 18, wherein the substrate is metal, and wherein an aqueous etching primer coating is applied to the substrate prior to applying the mixture to the substrate, such that the mixture is applied directly to the aqueous etching primer coating on the substrate.

20. The method of claim 19, wherein the aqueous etching primer coating is formed from an aqueous epoxy-polysiloxane primer.

21. The method according to any one of claims 16 to 20, wherein the mixture is aqueous.

22. The method according to any one of claims 16 to 21, wherein the mixture of the resin component and the crosslinking component is applied directly to the substrate.

23. The method according to any one of claims 16 to 22, wherein the substrate is a metal, a plastic, or a combination thereof.

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