Description:Field of the invention
[001] The present invention relates to the field of coating compositions. More particularly, it pertains to a single-component water-based coating composition comprising a polyester-polyurethane dispersion in combination with functional additives. The invention provides environmentally friendly, low-VOC coating suitable for various industrial and automotive applications.
Background of the invention
[002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[003] Coatings are protective or decorative layers applied to the surface of an object to enhance its appearance, improve surface properties, or extend the service life of the substrate. They are widely used in various industries including automotive, aerospace, construction, electronics, and consumer goods. Broadly, coatings can be classified into two main categories based on their solvent system: solvent-based and water-based. Solvent-based coatings contain a high proportion of organic solvents which evaporate during the curing process. These formulations have long been preferred for their superior durability, chemical resistance, and fast drying properties. However, they release significant quantities of volatile organic compounds (VOCs) into the atmosphere during application and drying. VOCs are not only hazardous to human health, contributing to respiratory issues and long-term chronic conditions, but are also known contributors to air pollution and smog formation. Due to these environmental and health concerns, regulatory agencies around the world have imposed strict limitations on VOC emissions, particularly in Europe, North America, and parts of Asia.
[004] As a result, water-based coatings have gained increasing attention as eco-friendly alternatives. In these formulations, water serves as the primary dispersing medium, greatly reducing VOC emissions. Besides being safer for both applicators and the environment, water-based coatings offer advantages such as ease of cleanup, lower flammability, and improved workplace safety. These systems are particularly attractive in automotive and industrial maintenance sectors where large-scale spray coating applications are common.
[005] Water-based coatings themselves can be further classified into single-component (1K) and two-component (2K) systems. While 2K systems, which require mixing a resin and a curing agent prior to use, tend to provide higher cross-linking density and better mechanical properties, they also suffer from several drawbacks. These include limited shelf life after mixing, greater formulation and application complexity, and increased waste due to leftover unmixed or expired material. On the other hand, 1K systems offer user-friendly application, longer shelf life, and reduced processing errors, making them ideal for Original Equipment Manufacturers (OEMs) and general maintenance tasks. However, existing 1K water-based systems often struggle to match the corrosion resistance, weatherability, and mechanical performance of their solvent-based or 2K counterparts.
[006] Despite advancements in 1K water-based polyurethane dispersions, challenges like water sensitivity, long drying times, poor film formation, and difficulty in incorporating multiple performance-enhancing additives without destabilizing the system still persist. These issues become more critical in automotive applications, where coatings must perform uniformly and durably across varied substrates such as steel, aluminium, plastics, and composites, without relying on primers or multi-layer systems.
[007] The practical demands of end-users including automotive OEMs and industrial maintenance operators further complicate the formulation space. These stakeholders require customized coating formulations addressing their requirements such as easy applicability, fast drying or curing, high gloss or matte finish, long shelf life as well as cost effective, while ensuring performance consistency across varied substrates like metal, plastic, and composite materials. Moreover, as there is a huge demand of high performance lightweight coated materials for incorporation in vehicles and machinery components, the coating formulation must adapt to different surface energies and provide uniform protection without the need for complex multi-layer systems.
[008] Thus, there exists a need for an improved water-based coating composition that addresses the limitations of conventional formulations. It should exhibit a broad spectrum of resistance properties, including but not limited to alkali resistance, acid resistance, water resistance, corrosion resistance, UV resistance, weather resistance, abrasion resistance, chemical resistance (e.g., solvents, oils, fuels), thermal resistance, scratch resistance, salt spray resistance, humidity resistance, and fungal or microbial resistance, depending on the application environment. The desired composition should offer a balanced combination of mechanical and chemical performance, exhibit excellent corrosion and UV resistance, remain stable over prolonged storage period, and be environment friendly.
Object of the invention
[009] An important object of the present invention is to provide a single-component, water-based polyurethane coating composition comprising a polyester-polyurethane dispersion.
[010] Another object of the invention is to provide a single-component, water-based polyurethane coating composition comprising a polyester-polyurethane dispersion in a combination with functional additives such as organic and inorganic pigments, coalescing solvents, wetting and dispersing agents, defoamers, rheology modifiers, and corrosion inhibitors, which offers enhanced performance for diverse applications.
[011] Another object of the present invention is to provide a coating composition that is free from lead, mercury, heavy metals, chromes, and free isocyanates, thereby enhancing environmental safety and user health without compromising performance.
[012] Yet another object of the invention is to develop an environmentally friendly coating formulation with low volatile organic compound (VOC) emissions, without compromising on critical performance attributes such as abrasion resistance, chemical resistance, and weatherability.
[013] It is a further object of the invention to provide a water-based coating system that exhibits excellent corrosion protection and UV stability on metal, plastic, wood and concrete substrates, thereby extending the service life of coated surfaces under harsh environmental conditions.
[014] Yet another object of the invention is to offer a stable, easy-to-apply, fast drying or curing, high gloss or matte finish, as well as cost effective, single-component water-based formulation that eliminates the need for mixing or external curing agents as required for two-component coating system, thus simplifying application, reducing processing time and costs, in end-use industries.
[015] It is also an object of the invention to enable uniform dispersion and compatibility of various performance-enhancing additives within the aqueous polyurethane matrix, ensuring long-term formulation stability and shelf life.
Summary of the invention
[016] This summary is provided to introduce a selection of concepts in a simplified form that are further described below in detailed description section. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.
[017] The present invention primarily provides a single-component, water-based polyurethane coating composition for use in automotive and industrial applications. More particularly, it relates to a coating composition comprising a polyester-polyurethane dispersion and a combination of functional additives to enhance corrosion resistance, weatherability, and mechanical durability.
[018] In an aspect, the coating composition comprises a water-dispersible polyester-polyurethane resin as the primary binder, formulated with functional additives such as organic and inorganic pigments, coalescing solvents, wetting and dispersing agents, defoamers, rheology modifiers, and corrosion inhibitors.
[019] In an aspect of the present invention, the coating composition is substantially free from toxic substances including lead, mercury, heavy metals, chromates, and free isocyanates, thereby making it safer for human use.
[020] In yet another aspect, the present invention provides a stable, environmentally friendly coating composition that demonstrates excellent performance under demanding industrial conditions while eliminating the need for organic solvents and minimizing volatile organic compound (VOC) emissions.
[021] In yet another aspect, the invention provides a coating system that is applied directly onto metallic/non-metallic substrates or primer layers, without complex pre-treatment steps, and is suitable for applications involving metal parts, frames, and surfaces commonly found in automotive, transportation, and general manufacturing sectors.
[022] Other aspects of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learnt by the practice of the invention.
Detailed description of the invention
[023] The following is a detailed description of embodiments of the disclosure. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[024] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.
[025] In some embodiments, numbers have been used for quantifying weight percentages, angles, and so forth, to describe and claim certain embodiments of the invention and are to be understood as being modified in some instances by the term “about.” Accordingly, in some embodiments, the numerical parameters set forth in the written description and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable. The numerical values presented in some embodiments of the invention may contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.
[026] Various terms as used herein are shown below. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.
[027] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[028] Unless the context requires otherwise, throughout the specification which follow, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense that is as “including, but not limited to.”
[029] The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein.
[030] All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
[031] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified.
[032] The description that follows, and the embodiments described therein, is provided by way of illustration of an example, or examples, of particular embodiments of the principles and aspects of the present disclosure. These examples are provided for the purposes of explanation, and not of limitation, of those principles and of the disclosure.
[033] The headings and abstract of the invention provided herein are for convenience only and do not interpret the scope or meaning of the embodiments.
[034] The following discussion provides many example embodiments of the inventive subject matter. Although each embodiment represents a single combination of inventive elements, the inventive subject matter is considered to include all possible combinations of the disclosed elements. Thus, if one embodiment comprises elements A, B, and C, and a second embodiment comprises elements B and D, then the inventive subject matter is also considered to include other remaining combinations of A, B, C, or D, even if not explicitly disclosed.
[035] While a particular form of the invention has been illustrated and described, it will be apparent that various modifications can be made without departing from the spirit and scope of the invention.
[036] The present disclosure relates to an environment-friendly single-component water-based polyurethane coating composition for use in automotive and industrial applications.
[037] In an embodiment of the present invention, the coating composition comprises a water-based medium, a polyurethane dispersion (PUD) which acts as a main binder, a crosslinking agent, corrosion inhibitors, coalescing agents, rheology modifiers to maintain the right rheology of the suspension, surfactants, defoamers to eliminate air bubbles, and optional pigments or functional fillers.
[038] In an embodiment of the invention, the details of each type of formulation ingredient are discussed as below:
[039] Binders:
[040] Polyester–polyurethane dispersions (PUDs) are water-based systems comprising polyurethane polymers that are synthesized from polyester polyols and diisocyanates, dispersed in water with or without the use of organic solvents. These dispersions are environment-friendly alternatives to solvent-based polyurethanes due to their low volatile organic compound (VOC) content.
[041] Polyester-based PUDs are known for their excellent mechanical strength, flexibility, abrasion resistance, and chemical resistance, making them suitable for a wide range of industrial and consumer applications such as coatings, adhesives, paints, inks, and textile finishes. The polyester segment imparts superior toughness, hydrolysis resistance, and UV durability, making these dispersions particularly suitable for applications requiring long-term exposure to environmental stressors.
[042] The polyurethane dispersion is selected from, but not limited to, aliphatic or aromatic polyurethanes synthesized using polyisocyanates and polyols and dispersed in water using internal emulsifiers. Preferably, the dispersion is self-crosslinking or externally cross-linkable to enhance chemical and abrasion resistance.
[043] Examples of PUD:
[044] The polyester-polyurethane resin based on an aliphatic isocyanate and polyester polyol is commercially available, for example, the water-based polyurethane dispersions from the company Covestro, under different grades branded as Bayhydrol® A, Bayhydrol® U, Bayhydrol® UH, Bayhydrol® UA, Bayhydrol® UV, and Impranil®.
[045] Amongst these, Bayhydrol UH 2592 dispersion containing coatings formulations exhibit quick drying, high hardness upon drying, and very good water resistance after overnight curing. It is particularly suitable for high-gloss topcoats, primers, and effect coats, offering excellent anti-corrosion performance. It also demonstrates very good shear stability, making it suitable for dip application processes.
[046] Bayhydrol® UH 2593/1, an aliphatic, fatty acid-modified, anionic polyurethane dispersion from the company Covestro is primarily used as a binder in water-reducible coatings and sealers for wood and wood-based materials. It has been specifically developed for one and two-component wood coating systems and is characterized by excellent wet film transparency, high hardness, and good resistance to black heel marks. When post-cured with suitable polyisocyanates such as Bayhydur® 305 or Bayhydur® 3100, the resulting water-based two-component coatings demonstrate significantly enhanced mechanical and chemical resistance. The typical mixing ratio of mill base to hardener solution is about 10:1. Owing to its good application properties and compatibility with cost-effective polyacrylate (PAC) dispersions, Bayhydrol® UH 2593/1 is also suitable for a wide range of coating applications. However, due to the wide variety of possible co-reactants, compatibility testing is recommended before use.
[047] Additional polymeric emulsions:
[048] The coating composition optionally further includes one or more additional polymeric emulsion (e.g., acrylics, silicones, polyesters) that can be used to tailor the coating's properties, allowing for customized solutions for specific applications. The polymeric emulsions can be selected from acrylic emulsion, self-crosslinking acrylic copolymers, polyester emulsion, silicone-modified polymer, polyether-based emulsions, styrene-butadiene emulsion, ethylene vinyl acetate emulsion, or a combination thereof. For example, acrylics are generally less expensive than polyurethanes and blending them with PUDs helps to lower the overall cost of the coating, provides a balance of the flexibility of PUDs with the hardness and gloss of acrylics, variable drying performance, creating an environmentally friendly, high-performance coating.
[049] Pigments:
[050] Inorganic pigments are stable, non-bleeding, and durable colorants commonly used in coatings, paints, plastics, and inks due to their excellent lightfastness, weather resistance, and thermal stability. Inorganic pigments are selected from the group consisting of titanium dioxide in rutile or anatase form, synthetic yellow iron oxide, natural red iron oxide, and nickel antimony titanate.
[051] Organic pigments are also included in the coating composition for their high tinting strength, excellent lightfastness, and thermal stability. Organic pigments selected from the group consisting of phthalocyanine blue, phthalocyanine green, quinacridone red, diketopyrrolopyrrole (DPP) pigments, and carbon black. Phthalocyanine pigments offer brilliant blue and green shades with high chemical resistance, while quinacridone and DPP pigments contribute deep red to maroon tones with superior weather and UV resistance. Carbon black provides deep black coloration with good dispersibility and durability. These organic pigments enhance the aesthetic appeal and long-term stability of the coating formulation, making them suitable for high-performance applications such as automotive and industrial coatings.
[052] Coalescing solvents:
[053] These solvents aid in film formation by temporarily softening the polymer particles in the dispersion during drying. Upon evaporation, they enable the polymer particles to fuse into a continuous, uniform film. Their inclusion enhances the mechanical properties, appearance, and durability of the final coating layer, particularly under ambient curing conditions. Coalescing solvents are selected from the group consisting of N-methyl-2-pyrrolidone (NMP), butyl cellosolve, butyl carbitol, dipropylene glycol methyl ether, and dipropylene glycol n-butyl ether.
[054] Wetting and dispersing agents:
[055] These are used in the present composition is selected from the group consisting of phosphate esters, polyacrylates, modified polyacrylates, and triethanolamine. For example, Evonik’s TEGO line dispersing agents for waterborne polyurethane dispersions (PUD) are typically based on modified polyethers or other polymeric structures. The company offers a wide range of additives, and the composition varies depending on the specific product and its intended application. These agents facilitate the uniform distribution and stabilization of pigments within the aqueous medium by reducing surface tension and preventing particle agglomeration. Their selection ensures improved pigment wetting, enhanced color development, and long-term dispersion stability, contributing to superior coating performance and visual consistency.
[056] Defoamers:
[057] Defoamers are additives used to reduce or eliminate foam during the manufacturing and application of water-based coating compositions. Suitable defoamers are selected from the group consisting of silicone-based defoamers (e.g., BYK grades), mineral oil-based defoamers, and polyether-modified polysiloxanes. Silicone-based defoamers are highly effective at low concentrations and are widely used due to their stability and compatibility with various coating systems. Mineral oil-based defoamers are economical options with good performance in water-based systems. Polyether-modified polysiloxanes offer a balance between defoaming and surface compatibility, enhancing the overall film quality without compromising gloss or leveling. These defoamers contribute to smooth application, improved surface appearance, and consistent film integrity by preventing air entrapment and microbubble formation during mixing and application.
[058] Rheology modifiers:
[059] These modifiers are an essential additive used to control the viscosity, flow behavior, and stability of coating formulations. Selected from the group consisting of fumed silica (e.g., Aerodisp wf 7620), organically modified hectorites, VOC- and APEO-free urea-modified polyurethanes, and polyamide waxes, these agents help maintain uniform dispersion of pigments and fillers, prevent sedimentation, and improve application properties such as sag resistance and leveling. Fumed silica offers thixotropic properties, enhancing viscosity under low shear and reducing dripping. Organically modified hectorites provide shear-thinning behavior and compatibility with water-based systems. Polyamide waxes aid in thickening, anti-settling, and improving surface smoothness. Together, these modifiers ensure a consistent and user-friendly coating formulation with desired application and film formation characteristics.
[060] Anti-Corrosion Additives:
[061] Anti-corrosion additive for a coating composition is selected from the group consisting of zinc phosphate, organic zinc complexes, calcium ion-exchanged silica, organic acid amine complexes, and zero-VOC organic di-acids. These additives are known for their effectiveness in inhibiting corrosion on metal substrates. Zinc phosphate and its modified forms (e.g. Nalzin FA 179) act as anodic inhibitors, providing a passive protective layer that prevents the electrochemical reactions leading to rust. Calcium ion-exchanged silica functions as a corrosion-inhibiting pigment that neutralizes acidic by-products formed during environmental exposure. Together, these additives enhance the durability of the coating, improve long-term corrosion resistance, and are compatible with water-based formulations.
[062] The quantity of each ingredient in the composition is provided in percentages based on the total weight of the composition (100%).
[063] In an embodiment of the present invention, deionized water may be present in an amount ranging from about 1.5% to 5.0%, serving as a diluent and dispersion medium.
[064] In some embodiments, deaerators and defoamers may be present in an amount ranging from about 0.005% to 0.05%, to help minimize air entrapment and foaming during mixing and application.
[065] In another embodiment, dispersing agents for pigment stabilization may be included in an amount ranging from about 0.3% to 1.0%, aiding in uniform dispersion and stability of the colorants.
[066] In some embodiments, pH adjusters and emulsifiers, may be included in an amount ranging from about 0.05% to 0.5%, facilitating proper emulsification and pH control.
[067] In one embodiment, inorganic white pigments may be present in an amount ranging from about 2.0% to 8.0%, to impart opacity and resistance to ultraviolet radiation.
[068] In an embodiment, inorganic yellow pigments may be used in an amount ranging from about 0.3% to 1.5%, offering durable coloration.
[069] In some embodiments, organic blue pigments may be included in an amount ranging from about 0.2% to 0.8%, for achieving strong, stable blue coloration.
[070] In an embodiment of the invention, organic green pigments may be present in an amount ranging from about 0.2% to 1.0%, providing intense and durable green tones.
[071] In some embodiments, lead-free yellow pigments may be used in an amount ranging from about 0.5% to 2.0%, offering high chroma and brightness.
[072] In an embodiment, primary polyurethane dispersions (binders) may be present in an amount ranging from about 50.0% to 70.0%, contributing to film formation, adhesion, and mechanical performance.
[073] In another embodiment, secondary polyurethane dispersions may be included in an amount ranging from about 2.0% to 10.0%, enhancing flexibility, toughness, and weather resistance.
[074] In another embodiment, an optional, additional polymeric emulsion may be included in an amount ranging from about 10.0% to 20.0%, enhancing gloss, drying, and reduced cost.
[075] In some embodiments, a co-solvent system comprising water-miscible organic solvents and water may be used in an amount ranging from about 5.0% to 15.0%, to promote film formation and application smoothness.
[076] In one embodiment, rheology control agents may be present in an amount ranging from about 0.2% to 1.0%, helping to control viscosity and prevent sagging.
[077] In some embodiments, VOC-free defoamers may be included in an amount ranging from about 0.01% to 0.1%, minimizing foam generation during application.
[078] In one embodiment, surface-wetting and leveling agents may be present in an amount ranging from about 0.05% to 0.5%, ensuring uniform spreading and smooth finish.
[079] In some embodiments, rheology modifiers, such as urea-modified thickeners, may be included in an amount ranging from about 0.1% to 0.5%, improving handling and sag resistance.
[080] In an embodiment, additional deionized water may be added for final dilution in an amount ranging from about 5.0% to 20.0%, adjusted according to desired viscosity and solids content.
[081] In one embodiment, corrosion inhibitors (e.g., flash-rust inhibitors) may be present in an amount ranging from about 0.05% to 0.5%, to prevent early-stage rusting on metal substrates.
[082] In some embodiments of the present invention, the coating composition is formulated to be free from toxic and environmentally hazardous substances. Specifically, the composition is substantially free from lead, mercury, other heavy metals, chromium compounds (including hexavalent and trivalent chromes), and free isocyanates. This environmentally conscious formulation ensures reduced health risks to applicators and end-users, promotes safer handling during manufacturing and application, and complies with stringent environmental and safety regulations applicable in various jurisdictions. The absence of such substances also supports the composition's suitability for use in interior and exterior applications in automotive and related industries, where low-VOC and non-toxic coatings are increasingly preferred.
[083] Manufacturing process for coating composition:
[084] In accordance with one embodiment of the present invention, the method begins with the selection of a polyester–polyurethane dispersion that serves as the primary film-forming binder. The polyester–polyurethane dispersion is a hydroxyl-functional polyester–polyurethane having desired end-properties for the final coating. These dispersions provide excellent mechanical strength, adhesion, and flexibility, and their functionality allows for further cross-linking or interaction with other formulation components.
[085] Subsequently, one or more inorganic pigments and one or more organic pigments are selected and dispersed separately in deionized water to provide the desired color, opacity, and performance characteristics. The dispersion process is facilitated using at least one wetting and dispersing agent. These agents aid in breaking down pigment agglomerates and stabilizing the pigment particles in the aqueous medium.
[086] In the next stage, one or more coalescing solvents are added to enhance film formation and leveling properties. Additionally, one or more defoamers are incorporated to prevent foam formation during mixing and application. A rheology modifier is also added to control the flow behavior and ensure application suitability. To enhance corrosion resistance, an anti-corrosion additive is added to impart protection against alkali or acid mediated corrosion.
[087] Following the addition of all components, the pH of the composition is adjusted to a range of about 7 to 9 to ensure system stability and compatibility among ingredients. Likewise, the viscosity is adjusted to fall within a range of 20 to 60 seconds, measured using a DIN 4 cup at a temperature of 23°C. These adjustments are essential for optimal storage stability and ease of application through conventional methods.
[088] Finally, the entire mixture is subjected to high shear mixing at a speed of about 200 to 2000 revolutions per minute (rpm). This step ensures uniform dispersion of all components and results in a stable, homogeneous, and ready-to-use water-based polyurethane coating composition.
[089] In an embodiment of the present invention, the coating composition exhibits excellent performance characteristics. The composition is characterized by an abrasion resistance resulting in a weight loss of less than 30 milligrams, as measured in accordance with ASTM D4060. It further demonstrates superior UV durability, retaining at least 85% of its original gloss when tested under ASTM G154.
[090] The composition also offers effective corrosion protection, with a corrosion creep of less than 1 millimeter as per ASTM B117. Additionally, the volatile organic compound (VOC) content of the coating composition is maintained below 100 grams per liter, making it environmentally favorable and compliant with regulatory standards.
[091] In an embodiment, the coating composition exhibits excellent storage stability. Specifically, the composition remains stable for a period of at least 12 months under standard storage conditions without undergoing phase separation or significant change in viscosity. This ensures ease of application and consistent performance throughout its shelf life.
[092] Method of coating:
[093] In an embodiment, the present invention provides a method of coating a substrate using the water-based polyurethane coating composition as described. The method comprises applying the coating composition onto the surface of a desired substrate through conventional application techniques such as spraying, rolling, dipping, or brushing. Post application, the coated substrate is subjected to a curing or drying, which occur either at ambient temperature or under elevated temperature conditions, depending on the desired curing speed and application environment. The curing process results in the formation of a continuous, uniform, and protective film over the substrate surface, offering enhanced durability and performance characteristics.
[094] In some embodiments, the coating composition disclosed herein is suitable for application to a wide range of substrates. These substrates may include, but are not limited to, cold-rolled steel, electrogalvanized steel, aluminum, plastic materials, composite surfaces, and wood. The composition exhibits strong adhesion and compatibility with these materials, making it particularly advantageous for use in various industrial applications.
[095] In some embodiments, the coated article of the present invention comprises a substrate that may be a component of a wide range of end-use applications. Specifically, the substrate may be part of an automotive body or accessory, an aerospace structure such as an aircraft panel or internal component, an architectural element including but not limited to façades, window frames, or structural steel, or an industrial machine component subjected to environmental or mechanical wear. In further embodiments, the substrate may also be a part of a household appliance such as a refrigerator, washing machine, or microwave oven casing, or may constitute furniture elements including metal or wood surfaces of tables, chairs, cabinets, or shelving units. The coating composition applied to such substrates provides enhanced aesthetic and functional properties, including but not limited to corrosion resistance, environmental durability, and decorative finish, thereby meeting the performance requirements specific to each application.
[096] In an embodiment, the single-component, water-based polyurethane coating composition of the present invention may be used in any manner known to a person skilled in the art.
[097] Examples:
[098] The present disclosure is further explained in the form of following examples. However, it is to be understood that the foregoing examples are merely illustrative and are not to be taken as limitations upon the scope of the invention. Various changes and modifications to the disclosed embodiments will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the scope of the invention.
[099] Example 1: Single component water-based PU coating composition in Onan green color
[100] A water-based polyurethane coating composition prepared using the following components in the quantities (in weight percent) specified in Table 1 below. The batch was processed in accordance with standard industrial procedures and evaluated for dispersion and homogeneity.
COMPONENTS PERCENT (wt.%)
INORGANIC PIGMENT SOLUTION
DI WATER 2
TEGO AIROX 901 0.01
TEGO 757 0.57
TEA (20% SOLIN H2O: METHANOL 1:1) 0.15
TIO2 RUTILE 5
YELLOW OXIDE 0.75
ORGANIC PIGMENT SOLUTION
DI WATER 2
TEGO AIROX 901 0.01
TEGO 757 0.4
MONOLITE BLUE 0.4
MONOLITE GREEN 0.45
LEMON CHROME (LEAD FREE) 1.05
POLYMER AND SOLVENT SYSTEM
BAYHYDROL UH XP 2592 60
BAYHYDROL UH XP 2593 5
BC : NMP : DI WATER 9
AERODISP WF 7620 0.5
BYK 024 0.05
BYK 349 0.15
BYK 425 0.2
DI WATER 12.11
NALZIN FA 179 0.2
TOTAL 100
Table 1
[101] Method of preparation:
1. Premix I (Inorganic Pigment Dispersion)
a. 2 parts by weight of Deionized (DI) water was charged into a pre-cleaned bead mill, followed by addition of 0.01 parts of dispersing agents TEGO Airox 901 and 0.57 parts of TEGO 757;
b. 0.15 parts of neutralizing agent triethanolamine (TEA, 20% solution in H₂O: methanol 1:1) was introduced to adjust pH;
c. 6 parts of titanium dioxide rutile pigments and 0.75 parts of yellow oxide pigments were then added gradually;
d. The mixture was subjected to bead milling until a desired fineness was achieved, confirming uniform dispersion.
2. Premix II (Organic pigment dispersion)
a. Separately, 2 parts of DI water, 0.01 parts of TEGO Airox 901, and 0.70 parts of TEGO 757 were charged into a pre-cleaned bead mill;
b. 0.70 parts of Monolite blue pigment, 0.45 parts of Monolite green pigment, and 1.5 parts of lemon chrome pigment, were added gradually;
c. This dispersion was also processed in the bead mill until a desired fineness was achieved.
3. Combination of Premix I / II and Let-down
a. The premix I and premix II were combined under continuous stirring in a mixing vessel.
b. The resultant dispersion was passed once through a horizontal sand mill until a fineness ≥6 Hegman units was obtained.
4. Resin addition
a. The combined dispersion obtained in the preceding step is transferred to a mixing vessel, and 60 parts of BAYHYDROL UH XP 2592 was first added as the primary binder, with stirring maintained at 200–300 rpm;
b. 5 parts of BAYHYDROL UH XP 2593 was added to dispersion prepared in preceding step to improve flexibility and weathering resistance;
c. Subsequently, 9 parts of a co-solvent mixture comprising BC, NMP, and deionized water was incorporated with continuous stirring;
d. 0.5 parts of AERODISP WF 7620 was introduced to adjust the rheology of the dispersion;
e. 0.05 parts of BYK 024 was added to prevent and eliminate the foam formation;
f. 0.15 parts of BYK 349 was added as a surfactant, and 0.2 parts of BYK 425 (diluted 1:9 with deionized water) was added as a flow additive;
g. 0.2 parts of NALZIN FA 179 was added as a corrosion inhibitor;
h. Finally, the viscosity was adjusted by introducing 10.06 parts of deionized water.
5. Tinting and shade adjustment
After the base batch was finalized, the shade was adjusted to a desired standard by the addition of tinters under stirring at 600–700 rpm, ensuring uniform color development and homogeneity.
[102] The resulting product was a liquid, with an opaque appearance and Black-Matt Finish color, having a slight inherent odor. It had a pH of approximately 7.2 when diluted (1:4 with water), and no flash point applicable as it is water based. The specific gravity is about 1.15 ± 0.05 kg/L. It was miscible with water at 15 °C and remained stable under normal storage and usage conditions, with no hazardous decomposition products expected. The product as a paint exhibited uniform pigment dispersion, stable viscosity, and properties suitable for spray application.
[103] Example 2: Single component water-based PU coating composition in Black-Matt Finish
COMPONENTS PERCENT (wt.%)
Part 1
DE IONIZED WATER 8
TEGO AIROX 901 W 0.2
BYK 190 0.5
TRI ETHYL AMINE (20% SOLUTION IN H2O: METHANOL 1:1) 0.5
Z-PLEX 2
RAVEN 3000 ULTRA BLACK 1
Part 2
DE IONIZED WATER 5
TEGO AIROX 901 W 0.1
BYK 190 0.15
TRI ETHYL AMINE (20% SOLUTION IN H2O: METHANOL 1:1) 0.3
CALCIUM CARBONATE 15
TALC 5 MICRON 10
MICA 2
Part 3
DE IONIZED WATER 1
BAYHYDROL UH XP 2592 20
INDOFIL AC 261 30
BUTYL CELLOSOLVE : N-METHYL PYRROLIDONE : DI WATER (1:1:1) 3.4
AERODISP 7620 0.2
BYK 024 0.1
BYK 349 0.1
BYK 4509 0.2
BYK 425(10 % IN WATER) 0.1
NALZIN FA 179 0.15
TOTAL
100.00

Table 2

[104] Method of preparation:
The process of example 1 was followed, using RAVEN 3000 ULTRA BLACK pigment and other additives in respective quantities in partwise manner, as disclosed in Table 2.
[105] The resulting product was a liquid with an opaque appearance and Black-matt finish, having a slight inherent odor. It had a pH of approximately 7.2 when diluted (1:4 with water), and no flash point applicable as it is water based. It was miscible with water at 15 °C and remains stable under normal storage and usage conditions, with no hazardous decomposition products expected. The product as a paint exhibited uniform pigment dispersion, stable viscosity, and properties suitable for spray application.
[106] Example 3: Single component water-based PU coating composition in Grey
COMPONENTS PERCENT (wt.%)
Part 1
DE IONIZED WATER 10
TEGO AIROX 901W 0.1
BYK 190 0.4
TRI ETHYL AMINE (20% SOLUTION IN H2O: METHANOL 1:1) 0.3
ZINC PHOSPHATE 111 4
CARBON BLACK 1
TIO2 RUTILE RC 822 5
Part 2
DE IONIZED WATER 2
BAYHYDROL UHXP 2592 20
BAYHYDROL UHXP 2593 25
INDOFIL AC 261 10
BUTYL CELLOSOLVE : N-METHYL PYRROLIDONE : DI WATER (1:1:1) 10
AERODISP 7620 0.6
BYK 024 0.16
BYK 349 0.18
BYK 425 0.3
NALZIN FA 179 0.1
DE IONIZED WATER 10.86
TOTAL 100

Table 3
[107] Method of preparation:
The process of example 1 was followed, using a CARBON BLACK pigment and other additives in respective quantities in partwise manner, as disclosed in Table 3.
[108] The resulting product was a liquid with an opaque appearance and grey color, having a slight inherent odor. It shows a pH of approximately 7.2 when diluted (1:4 with water), and no flash point applicable as it is water based. It is miscible with water at 15 °C and remains stable under normal storage and usage conditions, with no hazardous decomposition products expected. The product as a paint exhibited uniform pigment dispersion, stable viscosity, and properties suitable for spray application.
[109] Example 4: Performance Evaluation of single component water-based PU coating composition
The coating compositions prepared in accordance with Examples 1–3 (Onan Green, Black matt finish, and Grey) were subjected to standardized performance testing. Across all shades, the compositions exhibited consistent durability and protective properties, indicating that pigment package and color variation did not adversely affect performance. The composition 1 to 3 were evaluated for wet paint properties, dry film characteristics, and environmental durability.
1. Wet paint properties (below properties are common across formulations)
a. Fineness of grind (Hegman gauge): ≥7, confirming uniform pigment dispersion.
b. Supply viscosity: 60–90 seconds at 30 °C (Ford Cup B4, IS 3994), within the range required for spray application.
c. Specific gravity: 1.05–1.10 kg/L (ASTM D1475).
d. Non-volatile matter (solids content): 35–45% by weight.
e. Settling: No settling observed after storage, confirming dispersion stability.
2. Dry film properties (uniform ASTM/ISO panel)
a. Abrasion resistance: Weight loss <30 mg after 1,000 cycles (ASTM D4060, CS-17 wheels, 1,000 g load).
b. Adhesion: ≥95% retention in cross-cut test (ASTM D3359, up to 50 µm DFT).
c. Impact resistance: No cracking under ASTM D2794 (0.908 kg load, 20" drop, 5/8" ball).
d. Flexibility: No cracking under ASTM D522 (¼ inch mandrel bend).
e. Hardness: Minimum 2B pencil hardness after ambient cure (ASTM D3363).
f. Gloss: Matt (10% at 60°) to high gloss (>80 at 60°), depending on formulation.
g. Dry film thickness: 40–50 µm per coat, uniform across all shades.
3. Environmental and chemical resistance
a. Corrosion resistance: Corrosion creep <1 mm after ≥250 h salt spray exposure (ASTM B117).
b. Humidity resistance: Passed ≥200 h (ASTM D2247) with no blistering or delamination.
c. UV durability: Retained ≥85% of original gloss after accelerated weathering (ASTM G154, QUV test).
d. Chemical resistance: No damage observed after exposure to diesel fuel, alkaline solution, ethylene glycol coolant, heavy-duty diesel engine oil, dilute battery acid, and tap water under specified conditions.
4. Environmental and storage profile
a. VOC content: Below 100 g/L, measured in accordance with ASTM D3960.
b. Storage stability: Stable for at least 12 months under standard storage conditions, with no phase separation or significant viscosity change.
[110] The above data demonstrate that the single-component water-based polyester–polyurethane coating compositions of the present invention deliver consistent performance across multiple shades and finishes. The coatings provide a balanced combination of abrasion resistance, chemical resistance, corrosion protection, weather durability, and environmental safety. It gives a high gloss exterior and interior coating and hence it is suitable for a coastal environment. It can be applied over any metal substrate with or without primer.
[111] Advantages of the Invention-
The present invention offers several technical and operational advantages, including but not limited to the following:
1. The coating composition facilitates substantial improvement in occupational safety by effecting a reduction of up to 98% in volatile organic compound (VOC) emissions during application, thereby minimizing inhalation exposure and health risks to applicators.
2. The use of de-ionized water as a primary diluent obviates the requirement for hazardous organic solvents, resulting in decreased environmental and toxicological impact.
3. The water-based formulation contributes to compliance with prevailing environmental and pollution control regulations by substantially reducing or eliminating the release of airborne pollutants during and after application.
4. The formulation provides simplified and environmentally benign disposal, thereby reducing the burden of hazardous waste management and associated regulatory compliance.
5. The elimination of solvent evaporation during curing enhances overall production efficiency and contributes to a measurable reduction in waste generation, estimated at approximately 30%.
6. The composition minimizes health-related discomfort such as respiratory irritation and suffocation typically encountered with solvent-based systems, thereby enhancing user comfort and workplace safety.
7. The non-flammable nature of the formulation mitigates fire and explosion hazards during storage, transportation, and application, thus improving overall operational safety.
[112] While the foregoing describes various embodiments of the disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof. The scope of the invention is determined by the claims that follow. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.
, C , Claims:1. A single-component, water-based polyurethane coating composition, comprising:
a) a polyester-modified polyurethane dispersion as a primary film-forming binder present in the range of 50% to 70% based on the total weight of the composition, dispersed in deionized water;
b) one or more inorganic pigments present in the range of 15% to 20 % based on the total weight of the composition;
c) one or more organic pigments present in the range of 0.1% to 5.0% based on the total weight of the composition;
d) one or more coalescing solvents present in the range of 5.0% to 10.0% based on the total weight of the composition;
e) one or more wetting and dispersing agents present in the range of 0.1% to 2.0% based on the total weight of the composition;
f) one or more defoamers present in the range of 0.01% to 0.1% based on the total weight of the composition;
g) one or more rheology modifiers present in the range of 0.1% to 1.0% based on the total weight of the composition; and
h) one or more anti-corrosion additives present in the range of 0.1% to 0.5% based on the total weight of the composition;
wherein the coating composition is free from Lead, Mercury, Heavy Metals, Chromes and free isocyanates, and exhibits storage stability of at least 12 months without phase separation or significant viscosity change, and
characterized by an abrasion resistance of less than 30 milligrams weight loss when tested in accordance with ASTM D4060, an ultraviolet gloss retention of at least 85% when tested in accordance with ASTM G154, a corrosion creep of less than 1 millimeter when tested in accordance with ASTM B117, a volatile organic compound content of less than 100 grams per liter, no blisters or loss of adhesion when tested in accordance with D2247 for humidity Resistance, QUV Resistance, Chemical Resistance, Temperature Resistance up to 250°C.
2. The coating composition of claim 1, wherein the polyester–polyurethane dispersion is a hydroxyl-functional polyester–polyurethane selected from reaction products of isophorone diisocyanate with polyester polyols, reaction products of hexamethylene diisocyanate with polyester polyols, reaction products of isophorone diisocyanate with polycaprolactone polyols, or a combination thereof.
3. The coating composition of claim 1, wherein the inorganic pigments are selected from titanium dioxide in rutile form, synthetic yellow iron oxide, natural red iron oxide, nickel antimony titanate, chromium oxide green, or a combination thereof.
4. The coating composition of claim 1, wherein the organic pigments are selected from phthalocyanine blue, phthalocyanine green, quinacridone red, diketopyrrolopyrrole red pigments, or a combination thereof.
5. The coating composition of claim 1, wherein the coalescing solvent is selected from N-methyl-2-pyrrolidone, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, dipropylene glycol methyl ether, dipropylene glycol n-butyl ether, or a combination thereof.
6. The coating composition of claim 1, wherein the wetting and dispersing agent is selected from anionic high polymeric wetting and dispersing additives, phosphate ester surfactants, polyacrylate dispersants, modified polyacrylate dispersants, triethanolamine, or a combination thereof.
7. The coating composition of claim 1, wherein the defoamers are selected from silicone-based defoamers, polyether-modified polysiloxanes, mineral oil-based defoamers, or a combination thereof.
8. The coating composition of claim 1, wherein the rheology modifiers are selected from fumed silica, organically modified hectorites, VOC- and APEO- free urea-modified polyurethanes, or a combination thereof.
9. The coating composition of claim 1, wherein the anti-corrosion additive is selected from zinc phosphate, organic zinc complex, calcium ion-exchanged silica, organic acid amine complex, zero-VOC Organic Di-Acid, or a combination thereof.
10. The coating composition of claim 1, wherein the composition optionally further comprise one or more additional polymeric emulsion present in the range of 10% to 20% based on the total weight of the composition, selected from acrylic emulsion, self-crosslinking acrylic copolymers, polyester emulsion, silicone-modified polymer, polyether-based emulsions, styrene-butadiene emulsion, ethylene vinyl acetate emulsion, or a combination thereof.
11. The coating composition of claim 1, wherein the coating composition is suitable for application to a substrate selected from cold-rolled steel, electrogalvanized steel, aluminum, alloys, plastics, composites, acrylonitrile–butadiene–styrene (ABS), polycarbonate, fiber-reinforced composites or wood.
12. A method of manufacturing a single-component, water-based polyurethane coating composition as claimed in claim 1, comprising steps of:
a) separately dispersing one or more inorganic pigments and one or more organic pigments in deionized water with the aid of one or more defoamers, wetting and dispersing agents;
b) separately dispersing one or more polyester–polyurethane dispersion in deionized water with the aid of one or more defoamers, adding one or more coalescing solvents; adjusting pH to a range of 7 to 9.
c) blending the dispersions formed in step (a) and (b), adding one or more rheology modifiers and one or more anti-corrosion additives, to form a homogeneous mixture;
d) adjusting viscosity to a range of 60 to 100 seconds as measured using a Ford Cup B4 cup at 30°C; and
e) mixing under high shear at 200 to 2000 rpm to obtain a stable, uniform coating composition.
13. A method of coating a substrate, comprising steps of:
a) applying the coating composition of claim 1 to a surface of the substrate by spraying, rolling, dipping, or brushing; and
b) curing the coating at ambient temperature or at an elevated temperature to form a continuous stain-resistant, corrosion-resistant, chemical-resistant, and thermally stable protective film.
14. A coated article comprising a substrate selected from cold-rolled steel, electrogalvanized steel, aluminum, alloys, plastics, composites, acrylonitrile–butadiene–styrene (ABS), polycarbonate, fiber-reinforced composites and a cured film of the coating composition of claim 1 applied to at least one surface of the substrate, wherein the cured film has a dry film thickness of 50 to 100 micrometers depending upon application and number of coats.
15. The coated article of claim 14, wherein the substrate is selected from one or more component of an automotive, an aerospace, an industrial machine, or a home appliance.