Two-component polyurethane coating compositions, coatings formed therefrom, and coated articles thereof

Abstract

This application relates to a two-component polyurethane coating composition, a coating formed therefrom, and a coated article. The two-component polyurethane coating composition of this application comprises: component A, an aqueous dispersion comprising a hydroxyl-functionalized resin; and component B, comprising a non-hydrophilic isocyanate curing agent and a diluent, wherein the diluent comprises an alkyl diol ester, a cyclic carbonate, or a combination thereof, and the alkyl diol ester does not contain an ether bond. The coated article of this application comprises a coating formed from the above-described two-component polyurethane coating composition. The coating composition of the present invention uses a low-cost non-hydrophilic curing agent, and the formed coating has improved gloss or transparency.

Description

Technical Field

[0001] This application relates to a two-component polyurethane coating composition and a coated article. Specifically, this application relates to a coating composition comprising an aqueous dispersion and a non-hydrophilic curing agent, and a coated article comprising a coating formed from the coating composition. Background Technology

[0002] Traditional oil-based two-component polyurethane coatings are widely used due to their good acid resistance, high gloss, stain resistance, and scratch resistance. However, with increasing attention to environmental protection and the implementation of new environmental regulations, traditional oil-based two-component polyurethane coatings are facing limitations due to their high VOC content.

[0003] Waterborne two-component polyurethane coatings are gaining increasing attention as alternatives to traditional oil-based two-component polyurethane coatings. Current waterborne two-component polyurethane coatings utilize modified hydrophilic curing agents to form a stable dispersion between the curing agent and the film-forming resin. However, these modified hydrophilic curing agents typically involve complex synthesis processes and raw materials, significantly increasing the cost of the coatings and hindering their widespread application. Furthermore, coatings formed from current waterborne two-component polyurethane coatings often exhibit poor coating performance, such as reduced gloss. Summary of the Invention

[0004] Therefore, the coatings industry still needs a two-component polyurethane coating composition that has a lower cost and produces a coating with excellent coating properties after curing, especially gloss or transparency.

[0005] The above objectives can be achieved through the coating compositions described herein.

[0006] The first aspect of this application provides a two-component polyurethane coating composition comprising: component A, an aqueous dispersion comprising a hydroxyl-functionalized resin; and component B, comprising a non-hydrophilic isocyanate curing agent and a diluent, wherein the diluent comprises an alkyl diol ester, a cyclic carbonate, or a combination thereof, and the alkyl diol ester does not contain an ether bond.

[0007] The second aspect of this application is a coating formed by the two-component polyurethane coating composition described herein.

[0008] A third aspect of this application provides a coated article comprising a substrate and a coating or cured coating formed on the substrate by the two-component polyurethane coating composition described herein.

[0009] In the two-component polyurethane coating compositions described herein, alkyl diol esters, cyclic carbonates, or combinations thereof are used as diluents, and a low-cost, non-hydrophilic isocyanate curing agent is employed. The inventors have found that the cured coating exhibits excellent coating properties, particularly gloss and transparency. In some preferred embodiments, both excellent gloss and transparency are achieved simultaneously.

[0010] Furthermore, the coating composition of this application can form a stable dispersion by manually stirring components A and B during application, without the need for a strong dispersion process (e.g., high-speed stirring). This is quite surprising. Generally, non-hydrophilic curing agents have poor compatibility with aqueous dispersions and are prone to phase separation, requiring a strong dispersion process (e.g., high-speed stirring) to successfully disperse with the aqueous dispersion.

[0011] Furthermore, some embodiments of this application exhibit faster drying speeds and, preferably, improved pot life.

[0012] Details of one or more embodiments of this application are set forth in the following description. Other features, objectives, and advantages of this application will become clear from the description and claims.

[0013] definition

[0014] In this document, unless otherwise stated, the terms "a," "this," "at least one," and "one or more," as well as instances where no quantifier is used, are used interchangeably. Thus, for example, a coating composition containing "a" additive can be interpreted as meaning that the coating composition contains "one or more" additives. Unless otherwise stated herein, the use of the singular form is also intended to include the plural form.

[0015] When a composition is described as including or comprising specific components, it is anticipated that optional components not covered by the present invention are not excluded from the composition, and that the composition may be constituted or composed of the components involved. Similarly, when a method is described as including or comprising specific process steps, it is anticipated that optional process steps not covered by the present invention are not excluded from the method, and that the method may be constituted or composed of the process steps involved.

[0016] For simplicity, this document only explicitly discloses some numerical ranges. However, it should be understood that any range formed by combining any lower limit with any upper limit is included in the scope explicitly disclosed in this application; similarly, any range formed by combining any lower limit with other lower limits is also included in the scope explicitly disclosed in this application, and so on.

[0017] Unless otherwise stated, every point or individual value between the endpoints of a range is included within that range. For example, the range of 1 to 5 encompasses the values ​​1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc. Moreover, the disclosed numerical range includes all subsets of the wider range; for example, the range of 1 to 5 includes subranges 1 to 4, 1.5 to 4.5, 1 to 2, etc. Therefore, each point or individual value can be used as a lower or upper limit and combined with any other point or individual value, or combined with other lower or upper limits, to obtain a range that is explicitly disclosed in this application.

[0018] As used herein, the term "or" is inclusive. That is, the phrase "A or (or) B" means "A, B, or both A and B," and can also be abbreviated as "A and / or B." More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist). In contrast, the exclusive "or" is used herein, for example, by terms such as "either A or B" and "one of A or B."

[0019] In the context of describing a composition as free from a certain ingredient, the term "free from" means that the composition does not contain that ingredient intentionally added. Given the complexity of the specific composition of each component in actual formulation, the phrase "free from a certain ingredient" can be understood as the composition containing less than 1% by weight of that ingredient based on the total weight of the composition, more preferably less than 0.5% by weight, even more preferably less than 0.2% by weight, and most preferably less than 0.1% by weight.

[0020] In this paper, the term “dispersion” conforms to the definition in the IUPAC Compendium of Chemical Terminology (2007), which defines a dispersion as a material comprising more than one phase, wherein at least one phase consists of subdivided phase domains distributed throughout a continuous phase domain, typically in the colloidal particle size range.

[0021] As used herein, the term "aqueous dispersion" means that the dispersion medium (solvent or carrier fluid) in the dispersion comprises primarily or predominantly water. For example, in some embodiments, the dispersion medium contains at least about 50% by weight, preferably at least about 60% by weight, more preferably at least 70% by weight, and at most about 99% by weight, and at most about 100% by weight of water, based on the total weight of the dispersion medium. For example, the dispersion medium contains about 80% by weight, about 85% by weight, or about 95% by weight of water, based on the total weight of the dispersion medium.

[0022] When used herein, the term "aqueous dispersion of resin" refers to a stable dispersion of resin (i.e., polymer) in particulate form in an aqueous liquid medium, optionally with the aid of suitable dispersing agents such as surfactants or cosolvents. Therefore, in this application, when referring to polymers, the terms "aqueous latex" and "aqueous dispersion" may be used interchangeably unless otherwise stated. Methods for preparing aqueous latexes are known in the art, for example, they can be prepared using emulsion polymerization processes known to those skilled in the art. Aqueous dispersions are also commercially available.

[0023] When used herein, the term "hydroxyl functional" means having at least one unreacted hydroxyl functional group.

[0024] As used herein, the terms "hydrophilic curing agent" and "non-hydrophilic curing agent" have the meanings known in the art. Typically, non-hydrophilic curing agents (also known as hydrophobic or oily curing agents) are difficult to mix homogeneously with water or an aqueous component A, and are prone to phase separation. For example, non-hydrophilic curing agents include most unmodified polyisocyanates. Hydrophilic curing agents are typically obtained by hydrophilic modification of the curing agent. Hydrophilic curing agents can be, for example, nonionic hydrophilically modified (e.g., Covestro's Bayhydur 3100), ionic modified, or a combination of nonionic and ionic modifications.

[0025] The workable time, pot life, or pot period is the time during which the reactive components of a coating composition can still be properly treated or applied to obtain a coating of unimpaired quality once the reactive components are mixed. In the treatment of two-component coating compositions, it is generally necessary to mix the reactive components shortly before application to prevent premature reaction. The term "shortly before application" is well known to those skilled in the art of working with two-component coating compositions. The time period during which the ready-to-use coating composition can be prepared before actual use or application depends, for example, on the pot life of the coating composition. Therefore, a sufficiently long pot life is required to provide a sufficient time window for preparing, mixing, and applying a two-component coating composition. Thus, the workable time can also be defined as the period during which the brushed film exhibits satisfactory performance. Generally, the viscosity of the coating doubles at the end of the workable time. Furthermore, since water-based resins differ from oil-based resins, viscosity alone cannot be used as a criterion for determining workable time. For water-based dispersions, the transparency, fullness, gloss, and hardness of the paint film should not decrease significantly after the application time ends.

[0026] As used herein, the term "cured" means, in the state of the liquid composition, that the applied film of the composition is cured to at least a set-to-touch state as defined in ASTM D5895 - Standard Test Methods for Evaluating Drying or Curing During Film Formation of Organic Coatings Using Mechanical Recorder, which is also incorporated herein by reference. As used herein, the terms "cure" and "curing" refer to the process by which an applied liquid composition changes from a liquid state to a solid state. The terms "cured," "cure," and "curing" encompass the drying process of the composition via solvent evaporation and chemical crosslinking of the components in the composition.

[0027] The terms “comprising,” “having,” “including,” “containing,” and their variations are not restrictive; rather, when these terms appear in the specification and claims, they are intended to be open-ended.

[0028] The terms "preferred" and "ideally" refer to embodiments of this application 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, nor is it intended to exclude other embodiments from the scope of this application. Detailed Implementation

[0029] According to a first aspect of this application, a two-component polyurethane coating composition is provided. The two-component polyurethane coating composition described herein typically comprises a component A (i.e., a resin component) and a component B (i.e., a curing agent component).

[0030] Component A comprises a compound having a functional group that is reactive with a curing agent, the functional group having active hydrogen. In the coating composition of this application, component A comprises an aqueous dispersion of a hydroxyl-functionalized resin. In some embodiments, the hydroxyl content of the hydroxyl-functionalized resin (calculated based on solid resin) is about 2 wt% or higher, preferably 3 wt% or higher. The hydroxyl content of the hydroxyl-functionalized resin (calculated based on solid resin) can be 6 wt% or lower, preferably 5 wt% or lower.

[0031] Hydroxyl-functional resins include, for example, hydroxyl-functional acrylic resins, hydroxyl-functional polyurethane resins, hydroxyl-functional alkyd resins, hydroxyl-functional polyester resins, hydroxyl-functional polyether resins, or hydroxyl-functional epoxy resins.

[0032] Hydroxyl-functionalized acrylic resins can be prepared by free radical polymerization of polymerizable olefinically unsaturated monomers, optionally in the presence of oligomeric or polymerizable polyester or polyurethane resins. The free radically polymerizable olefinically unsaturated monomers that can be used are monomers containing functional groups other than at least one olefin double bond, and monomers that do not contain functional groups other than at least one olefin double bond. Other functional groups can be, for example, urea, hydroxyl, carboxyl, sulfonic acid, silane, amine, amide, acetoacetic acid, phosphate, phosphonic acid, heterocyclic, or epoxy groups. In the preparation of hydroxyl-functionalized acrylic resins, functional groups that do not tend to self-crosslink are suitably combined.

[0033] The hydroxyl groups are introduced into the (meth)acrylic copolymer using an olefinically unsaturated monomer having hydroxyl groups. Suitable hydroxyl-functionalized unsaturated monomers are, for example, hydroxyalkyl esters of α,β-olefinically unsaturated monocarboxylic acids having primary or secondary hydroxyl groups. Hydroxyl-functionalized unsaturated monomers may include, for example, hydroxyalkyl esters of acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, isocrotonic acid, or any combination thereof. Hydroxylalkyl esters of (meth)acrylic acid are preferred. Of course, other olefinically unsaturated monomers having hydroxyl groups or combinations thereof may also be used.

[0034] The carboxyl group is introduced into the (meth)acrylic copolymer using a carboxyl-functionalized olefinic unsaturated monomer. Examples of suitable olefinic unsaturated carboxylic acids include acrylic acid, methacrylic acid, crotonic acid and isocrotonic acid, itaconic acid, maleic acid, fumaric acid, and half-esters of these bifunctional acids. Acrylic acid and methacrylic acid are preferred.

[0035] An unsaturated monomer that does not contain any functional groups other than at least one olefin double bond is, for example, an aliphatic ester of an olefinic unsaturated carboxylic acid (such as (meth)acrylic acid), a vinyl ester, a vinyl aromatic hydrocarbon (such as styrene), or any combination thereof.

[0036] Furthermore, additional unsaturated monomers containing other functional groups besides olefin double bonds can be used.

[0037] Suitable hydroxyl-functionalized polyurethane resins can be prepared, for example, by reacting a compound reactive to isocyanate groups with a polyisocyanate having at least two free isocyanate groups per molecule. High molecular weight polyols can be used as the compounds reactive to isocyanate groups. Examples of polyols include polyacrylate polyols, polyester polyols, polyether polyols, polycarbonate polyols, and polyurethane polyols. Preferably, polyester polyols, polyether polyols, polycarbonate polyols, or any combination thereof having a molecular weight of, for example, 500 g / mol to 6000 g / mol are used. Examples of useful polyisocyanates include terephthalic diisocyanate, xylene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, and trimethylhexamethylene diisocyanate.

[0038] Other available hydroxyl-functional alkyd resins, hydroxyl-functional polyester resins, hydroxyl-functional polyether resins, and hydroxyl-functional epoxy resins are known in the art. Those skilled in the art can reasonably determine suitable resins that can be used in component A.

[0039] Particularly preferred, component A comprises a hydroxyacrylic acid dispersion. Suitable hydroxyacrylic acid dispersions may also be commercially available, for example, from Covestro. Series of products.

[0040] Based on the total weight of component A, component A may contain, for example, 30-70% by weight of water, such as about 45%, about 50%, or about 60% by weight of water. Optionally, component A may further contain at least one co-solvent. If present, the amount of the co-solvent is optionally low. For example, component A may contain up to 15% by weight, preferably up to 10% by weight of a co-solvent.

[0041] The co-solvent can be a commonly used organic solvent in the art. For example, the co-solvent can be a monohydric alcohol or polyhydric alcohol, such as propanol, butanol, hexanol; glycol ethers or esters, such as diethylene glycol dialkyl ethers, dipropylene glycol dialkyl ethers, ethoxypropanol, butylethylene glycol, each having a C1-C6 alkyl group; glycols, such as ethylene glycol, propylene glycol; and ketones, such as methyl ethyl ketone, acetone, cyclohexanone; N-methylpyrrolidone, N-ethylpyrrolidone; aromatic or aliphatic hydrocarbons, such as toluene, xylene, or straight-chain or branched aliphatic C6-C12 hydrocarbons. Preferably, the co-solvent is water-miscible. Examples of cosolvents include, but are not limited to, ethanol, isopropanol, butanol, butoxydiethylene glycol, butyl ethylene glycol, dipropylene glycol methyl ether (DPM), propylene glycol methyl ether, ethylene glycol butyl ether, dipropylene glycol butyl ether (DPnB), ethylene glycol ethyl ether, ethylene glycol monomethyl ether, ethylene glycol monohexyl ether, ethylene glycol mono-n-butyl ether, diethylene glycol monomethyl ether, ethylene glycol mono-n-butyl ether, tripropylene glycol monomethyl ether, ethylene glycol monoisobutyl ether, diethylene glycol monoisobutyl ether, propylene glycol monoisobutyl ether, ethylene glycol monophenyl ether, propylene glycol monophenyl ether, ethylene glycol monomethyl ether acetate, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, toluene, xylene, trimethylbenzene, 100# solvent naphtha, 150# solvent naphtha, 180# solvent naphtha, 200# solvent naphtha, 2-methylpropanol acetate and n-butyl acetate, and any combination thereof.

[0042] Based on the total weight of the coating composition, the amount of cosolvent can be about 4-10% by weight, preferably about 5-9% by weight, and more preferably about 6-8% by weight. For example, based on the total weight of the coating composition, the amount of cosolvent can be even more preferably about 6.5, 7, 7.5 or 8% by weight.

[0043] The coating composition of this application may optionally contain pigments, other additives, or any combination thereof.

[0044] In some preferred embodiments, the pigment can be a material having spherical, fibrous, flake-like, or other regular or irregular shapes with micron or even nanometer dimensions. Examples of pigments include metal oxides such as titanium dioxide, iron oxide, zinc oxide, zirconium oxide, and aluminum oxide; hybrid metal oxides of two or more metals, including manganese, nickel, titanium, chromium, antimony, magnesium, cobalt, iron, or aluminum; oxymetallic compounds such as bismuth vanadate, cobalt aluminate, cobalt zincate, and zinc chromate; pigments with metallic effects such as aluminum flakes, copper, and copper-zinc alloys; pearlescent pigments such as lead carbonate and bismuth oxychloride; talc; and any combination thereof. Preferably, the pigment is titanium dioxide, more preferably titanium dioxide in powder form. Particularly preferably, the pigment comprises rutile titanium dioxide. All types of thickeners are commercially available. For example, as an example of a pigment, BLR-688 titanium dioxide, available from Baililian, can be used.

[0045] Based on the total weight of the coating composition, the total amount of pigment can be from 0 wt% to 50 wt%, for example, 1 wt% to 45 wt%, 2 wt% to 40 wt%, 3 wt% to 35 wt%, 4 wt% to 30 wt%, 5 wt% to 25 wt%, or 10 wt% to 20 wt%. More preferably, based on the total weight of the coating composition, the amount of each pigment used independently is 0 wt% to 50 wt%, 1 wt% to 40 wt%, 2 wt% to 30 wt%, 3 wt% to 20 wt%, or 4 wt% to 15 wt%.

[0046] In the coating composition, optional other additives may be those commonly used in coating compositions. These additives will not adversely affect the coating composition or the cured coating obtained therefrom. Suitable additives include, for example, those agents that improve the processability or manufacturing properties of the composition, enhance the aesthetics of the composition, or improve specific functional properties or characteristics (such as adhesion to the substrate) of the coating composition or the cured composition obtained therefrom. Additives that may be included in the coating composition, depending on specific needs, include, but are not limited to, fillers, anti-skinning agents, driers, emulsifiers, anti-migration agents, antibacterial agents, chain extenders, lubricants, wetting agents, biocides, plasticizers, defoamers, colorants, waxes, antioxidants, corrosion inhibitors, antifreeze agents, rheology modifiers, thickeners, dispersants, pH adjusters, adhesion promoters, UV stabilizers, pH adjusters, leveling agents, or combinations thereof. The amounts of each optional component are sufficient to achieve their intended purpose, but preferably, such amounts will not adversely affect the coating composition or the cured coating obtained therefrom.

[0047] More preferably, based on the total weight of the coating composition, the coating composition further includes 0.1-1% by weight of other additives, said other additives including one or more of defoamers, leveling agents, thickeners and wetting agents.

[0048] As an example of a leveling agent, BYK 358, purchased from BYK Corporation, can be used. As an example of a defoamer, BYK-071, purchased from BYK Corporation, can be used.

[0049] Suitable thickeners include one or more of the following: cellulose thickeners, alkali-swellable thickeners, polyurethane thickeners, hydrophobically modified polyurethane thickeners, and inorganic thickeners. All types of thickeners are commercially available. For example, as an example of a cellulose thickener, HEC 250H4BR, a methyl hydroxyethyl cellulose ether thickener, can be used from ASHLAND, USA. As an example of an alkali-swellable thickener, ASE60, purchased from Dow Chemical, USA, can be used. As an example of a polyurethane thickener, RM-2050D, purchased from Dow Chemical, USA, or U902 and U903, purchased from Wanhua Chemical, USA, can be used. As an example of an inorganic thickener, bentonite can be used.

[0050] The coating composition according to this application may optionally include a defoamer. Suitable defoamers include one or more of organosiloxane defoamers, oil-based defoamers, polyether defoamers, and polyether-modified organosilicone defoamers. Preferably, nonionic mineral oil may be used. All types of defoamers are commercially available. As an example of a defoamer, CF-246, available from Blackburn, may be used.

[0051] In the two-component polyurethane coating composition of this application, component B comprises a non-hydrophilic isocyanate curing agent. In some embodiments of this application, the non-hydrophilic isocyanate curing agent comprises aliphatic diisocyanates, aromatic diisocyanates, cycloaliphatic diisocyanates, or any combination thereof. Preferably, the non-hydrophilic isocyanate curing agent comprises an aliphatic diisocyanate.

[0052] Preferably, the NCO content of the non-hydrophilic isocyanate curing agent is in the range of 10 wt% to 30 wt%. More preferably, the NCO content is in the range of 15 wt% to 25 wt%. For example, the NCO content can be 18 wt%, 21 wt%, 22 wt%, 23 wt%, or 24 wt%. The NCO content is determined according to DIN EN ISO 11 909.

[0053] Preferably, a low-viscosity, non-hydrophilic isocyanate curing agent is used. For example, the viscosity of the non-hydrophilic isocyanate curing agent at 23°C is less than 4000 mPa·s. More preferably, the viscosity of the non-hydrophilic isocyanate curing agent at 23°C is between 600 and less than 3800 mPa·s. For example, the viscosity of the non-hydrophilic isocyanate curing agent at 23°C can be 730, 1000, 1500, 2000, or 3000 mPa·s. The above viscosities are determined according to DIN EN ISO 3219 / A.3.

[0054] The non-hydrophilic isocyanate curing agent can be in the form of oligomers or homopolymers. The oligomers or homopolymers can be oligomers or homopolymers containing 2-8 monomer units. For example, the non-hydrophilic isocyanate curing agent can be a trimer.

[0055] Examples of non-hydrophilic isocyanate curing agents include isocyanate curing agents based on hexamethylene diisocyanate (HDI), dicyclohexylmethane-4,4'-diisocyanate (HMDI), phenylenediethylene diisocyanate (XDI), or tetramethyl isophthalimethylene diisocyanate (TMXDI).

[0056] In some preferred embodiments, the aliphatic diisocyanate is an aliphatic diisocyanate based on hexamethylene diisocyanate (HDI), particularly preferably an HDI trimer. Preferably, the aliphatic diisocyanate may comprise one or more of HDI-based asymmetric trimers, symmetric trimers, and homopolymers. Commercially available isocyanate curing agents, such as DESMODUR N 3300, 3600, and 3900, can be used.

[0057] Each non-hydrophilic isocyanate curing agent can be used alone or in combination. In some embodiments, the non-hydrophilic isocyanate curing agent may also comprise a combination of two or more of the curing agents described above. For example, in an exemplary embodiment, DESMODUR N 3300, 3600, and 3900 in a 1:1:1 weight ratio can be used as a non-hydrophilic isocyanate curing agent.

[0058] Component B may or may not contain a hydrophilic isocyanate curing agent.

[0059] In some embodiments, component B comprises a hydrophilic isocyanate curing agent. The hydrophilic isocyanate curing agent can be prepared by modification in a manner known in the art. Examples of hydrophilic isocyanates include, but are not limited to, hydrophilic isocyanates based on isophorone diisocyanate (IPDI) and HDI types.

[0060] In some embodiments, the weight ratio of the non-hydrophilic isocyanate curing agent to the hydrophilic isocyanate curing agent is in the range of 99:1 to 5:95. Preferably, the weight ratio of the non-hydrophilic isocyanate curing agent to the hydrophilic isocyanate curing agent is in the range of 90:10 to 10:90, more preferably in the range of 80:20 to 20:80. For example, the weight ratio of the non-hydrophilic isocyanate curing agent to the hydrophilic isocyanate curing agent is 90:10, 70:30, 50:50, 30:70, or 10:90.

[0061] In the two-component polyurethane coating compositions described herein, component B comprises a diluent. The diluent includes alkyl diol esters, cyclic carbonates, or combinations thereof. In some preferred embodiments, the diluent comprises an alkyl diol ester.

[0062] It is worth noting that alkyl diol esters do not contain ether bonds. While not expected to be theoretically limited, it is generally accepted in the art that ether oxygen can promote the compatibility of the compound with water due to the formation of potential hydrogen bonds. However, the inventors surprisingly discovered that in the two-component polyurethane coating compositions of this application, using an organic solvent containing ether oxygen bonds as a diluent alone is detrimental to the stable dispersion of the aqueous dispersion and the curing agent, resulting in a decrease in the gloss or transparency of the obtained coating.

[0063] In some preferred embodiments, the weight ratio of the diluent to the non-hydrophilic curing agent is between 30:70 and 90:10. More preferably, the weight ratio is between 40:60 and 85:15. For example, the weight ratio of the diluent to the non-hydrophilic curing agent can be 45:65, 50:50, 55:45, 60:40, 70:30, or 80:20.

[0064] In component B, alkyl diol esters, cyclic carbonates, or combinations thereof can be used as diluents to thin the non-hydrophilic curing agent. In some preferred embodiments, the weight ratio of alkyl diol esters, cyclic carbonates, or combinations thereof (when both are present) to the non-hydrophilic curing agent is between 30:70 and 90:10. More preferably, the weight ratio of alkyl diol esters, cyclic carbonates, or combinations thereof (when both are present) to the non-hydrophilic curing agent is between 40:60 and 85:15. For example, the weight ratio of alkyl diol esters, cyclic carbonates, or combinations thereof (when both are present) to the non-hydrophilic curing agent can be 45:65, 50:50, 55:45, 60:40, 70:30, or 80:20.

[0065] The inventors discovered that by changing the relative amounts of diluent and non-hydrophilic curing agent and selecting them within a suitable range, the transparency and gloss of the cured coating can be further improved.

[0066] Preferably, the alkyl diol ester has a low molecular weight, for example, less than 250 g / mol. More preferably, the alkyl diol ester has a molecular weight of 200 g / mol or lower. The alkyl diol ester particularly comprises dicarboxylic acid esters of alkyl diols. In some preferred embodiments, the alkyl diol ester includes one or more of propylene glycol diacetate (PGDA), ethylene glycol diacetate (EGDA), and ethylene glycol dipropionate (EGDP). Particularly preferably, the alkyl diol ester includes propylene glycol diacetate (PGDA), ethylene glycol diacetate (EGDA), or a combination of both. In some preferred embodiments, the alkyl diol ester is propylene glycol diacetate. In other preferred embodiments, the alkyl diol ester is ethylene glycol diacetate.

[0067] In some other preferred embodiments, the diluent comprises a cyclic carbonate. Generally, cyclic carbonates are a class of compounds as opposed to linear carbonates. Cyclic carbonates have a carbonate ring, preferably a five-membered ring. In some embodiments, the cyclic carbonate has a molecular weight of less than 200 g / mol, for example, less than 180 g / mol, less than 150 g / mol, or less than 120 g / mol. In some embodiments, the cyclic carbonate does not contain an ether bond. Preferably, the cyclic carbonate includes one or more of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, and 2,3-butylene carbonate.

[0068] The diluent may consist of alkyl diol esters, cyclic carbonates, or combinations thereof. For example, the diluent may consist of any one or more alkyl diol esters described herein. Similarly, the diluent may also consist of any one or more cyclic carbonates described herein.

[0069] In some embodiments, the diluent may also contain at least one low-boiling-point solvent. In this document, boiling point has the general meaning understood by those skilled in the art. "Boiling point" is understood as the temperature at which a liquid boils at atmospheric pressure (i.e., 1 bar), that is, the temperature at which the saturated vapor pressure of the liquid equals the external pressure. The boiling point value of a compound can be obtained from scientific literature or reference books.

[0070] The inventors also surprisingly discovered that adding a low-boiling-point solvent to a diluent containing alkyl diol esters, cyclic carbonates, or combinations thereof can shorten the curing time of the coating composition while maintaining good gloss. For example, compared to a diluent that does not contain an additional low-boiling-point solvent, using a diluent containing a low-boiling-point solvent can reduce the contact-drying time by approximately 25%, or even by half. This is highly desirable in applications requiring faster drying.

[0071] Preferably, the low-boiling-point solvent has a boiling point of 160°C or lower. For example, the low-boiling-point solvent comprises one or more of propylene glycol monomethyl ether acetate (PMA), dipropylene glycol dimethyl ether (DMM), methyl ethyl ketone (MEK), acetone, methyl isobutyl ketone, cyclohexanone, toluene, xylene, trimethylbenzene, naphtha (100# solvent), 2-methylpropanol acetate (MPA), and n-butyl acetate (BAC). More preferably, the low-boiling-point solvent is PMA, MEK, or a combination of both.

[0072] In some embodiments, the total amount of alkyl diol esters and cyclic carbonates (if present) is about 10-100% by weight based on the weight of the diluent, preferably about 20-90% by weight, more preferably about 30-80% by weight. For example, the total amount of alkyl diol esters and cyclic carbonates (if present) is about 25%, 40%, 50%, 60%, or 70% by weight based on the weight of the diluent.

[0073] To achieve excellent gloss or transparency of the paint film, the particle size of the composition obtained by mixing component A and component B is in the range of 10-1000 nm. Preferably, the particle size of the composition obtained by mixing component A and component B is less than 800 nm. The particle size refers to the hydrodynamic diameter obtained by dynamic light scattering testing. The inventors have discovered that when the particle size distribution of the composition obtained by mixing component A and component B shows a peak larger than 1 micrometer under dynamic light scattering, it may cause poor dispersion and affect the gloss and transparency of the paint film.

[0074] In some embodiments, during application, mixing component A and component B under low-speed stirring (e.g., hand stirring) yields an applyable coating composition. For example, mixing component A and component B at 10-10... 4 s -1 Stirring and mixing at a shear rate of 10 can yield an applyable coating composition, preferably, at 10 2 -10 3 s -1 The workable coating composition was obtained by stirring and mixing at a shear rate of [specific value].

[0075] Generally, non-hydrophilic curing agents have poor compatibility with aqueous dispersions, easily leading to phase separation. In some traditional studies of two-component coating compositions combining non-hydrophilic curing agents and aqueous dispersions, a strong dispersion process (e.g., high-speed stirring) is explicitly required to temporarily achieve stable dispersion of the non-hydrophilic curing agent and the aqueous dispersion. However, the inventors have surprisingly discovered that the coating composition of this application can form a stable dispersion simply by hand stirring, without the need for a strong dispersion process (e.g., high-speed stirring).

[0076] Furthermore, the two-component polyurethane coating compositions described herein offer a longer workability time during application. For example, the workability of the coating composition is at least 4 hours. In some embodiments, the two-component polyurethane coating composition has a workability time of 4-6 hours. This is generally desirable, especially for wood coatings, as it provides painters with ample time to plan the application process more efficiently and achieve optimal coating results and efficiency.

[0077] Depending on the actual needs, the two-component polyurethane coating composition or component A may also contain additives such as, but not limited to, pigments, fillers, anti-skinning agents, driers, emulsifiers, anti-migration agents, antibacterial agents, chain extenders, lubricants, wetting agents, biocides, plasticizers, defoamers, colorants, waxes, antioxidants, corrosion inhibitors, antifreeze agents, rheology modifiers, thickeners, dispersants, pH adjusters, adhesion promoters, UV stabilizers, pH adjusters, leveling agents, or combinations thereof. The content of each optional component is sufficient to achieve its intended purpose, but preferably, such content will not adversely affect the coating composition or the cured coating obtained therefrom.

[0078] A second aspect of this application also relates to coatings formed by the two-component polyurethane coating compositions described herein. Preferably, the coatings described herein have a transparency of 95% or higher. For example, the transparency of the coating can be as high as 96%, 97%, 98%, or 100%. Even, in some particularly preferred embodiments, the transparency of the coating can exceed 100%. That is, after the coating described herein is formed on a substrate, the overall transparency of the substrate and the coating is better than the transparency of the substrate itself. This may be because the coating compositions described herein can further compensate for some minor defects on the surface of the substrate itself, allowing the substrate and the coating to adhere more tightly together, reducing the decrease in transparency caused by defects on the surface of the substrate itself. Transparency is expressed as a percentage of the light transmittance after the coating is applied to the substrate relative to the light transmittance of the substrate itself before coating.

[0079] The gloss of the coating described herein can be characterized by a 20° gloss, a 60° gloss, or both. Preferably, the 60° gloss is greater than 88, more preferably 89 or higher, and even more preferably 90 or higher. The gloss can be measured using methods and instruments known in the art.

[0080] Furthermore, it's important to note that when transparency reaches 95% or higher, or gloss reaches 80% or higher, the differences between the values ​​measured by experimental instruments become increasingly smaller relative to the actual differences observed by the human eye. In other words, when transparency reaches 95% or higher, or gloss reaches 80% or higher, even small differences between the values ​​measured by experimental instruments signify significant differences in actual coating performance. Therefore, when transparency reaches 95% or higher, or gloss reaches 80% or higher, even a difference of only 1% or 1% between the values ​​measured by experimental instruments will appear as a significant difference in transparency or gloss to the human eye. For example, a coating with a gloss of 87 at 60° is actually significantly inferior to a coating with a gloss of 90° at 60° in the eyes of the consumer; or, a coating with 90% transparency is actually far inferior to a coating with 95% transparency. In some applications, even a gloss below 87 at 60° and transparency below 93% are unacceptable.

[0081] A third aspect of this application provides a coated article comprising a substrate and a coating or cured coating formed on the substrate by the two-component polyurethane coating composition described herein. As an example, the substrate may be selected from one or more of wood, metal, plastic, interior wall, exterior wall, and cement board.

[0082] Particularly preferred is wood as the substrate. The two-component polyurethane coating compositions described herein exhibit particularly excellent suitability for application on wood. Typically, unlike coating compositions applied to metal substrates, coating compositions applied to wood require a longer application time. The two-component polyurethane coating compositions described herein are particularly suitable for application on wood due to their application time of up to 4-6 hours.

[0083] The waterborne coating compositions of this application can be applied using conventional methods known to those skilled in the art. Preferably, the coating compositions are applied by brushing, spraying, and other coating methods known in the art. In this way, a coating can be formed from the coating compositions of this application, which also falls within the protection scope of this application. Therefore, this application also provides coatings that can be obtained from the coating compositions described herein.

[0084] Unless otherwise stated, the various features and corresponding preferred methods described herein can be combined.

[0085] Example

[0086] The disclosure of this application is described in more detail through the examples below. These examples are merely illustrative and are not limited to these specific examples. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by weight. Moreover, all reagents used in the examples are commercially available and can be used directly without further processing. For example, Bayhydrol A XP 2770, an exemplary aqueous dispersion of a hydroxyl-functionalized resin, is commercially available from Covestro in the following examples. Those skilled in the art can readily obtain or prepare the raw materials used in the examples.

[0087] Test methods

[0088] transparency The sample was coated onto a 2 mm thick transparent glass substrate. The transmittance of the coating film at 550 nm, 430 nm, and 395 nm was measured using a transparency meter, and the percentage of transmittance relative to the substrate's own transmittance without the coating film was recorded. Three measurements were performed in parallel for each sample. The average value was expressed as a percentage.

[0089] gloss The gloss at 20° and 60° was measured using a gloss meter manufactured by BYK GmbH, Germany.

[0090] Contact drying time The time it takes for the coating to change from a liquid state to a state where the surface does not leave an indentation or feel sticky when lightly pressed with a finger.

[0091] Example 1

[0092] Bayhydrol A XP 2770 was used as the aqueous dispersion of the base resin, i.e., component A. Desmodur N3600 was used as the curing agent, and the curing agent was diluted using the diluents and the weight ratio of curing agent to diluent shown in Table 1 below to obtain the curing agent component, i.e., component B. Component A and component B were mixed at an NCO / OH molar ratio of 1.5:1 by hand stirring (approximately 10 minutes). 2 -10 3 s -1 (by adjusting the shear rate), a stable dispersion is obtained. Water is added to adjust the viscosity to approximately 40s (Ford Cup 4), and then application is possible.

[0093] The dry film thickness is approximately 40 μm. The properties of the dry film (including 60° gloss, transparency, and touch-dry time) are shown in Table 1.

[0094] Table 1

[0095]

[0096]

[0097] As shown in Table 1, using PGDA alone as a diluent resulted in excellent transparency and gloss, especially a transparency of up to 100%. Samples 3-10 show that other solvents commonly used in coating compositions, when used alone as diluents, exhibited lower gloss. In fact, samples 7-10 even formed matte coatings.

[0098] In samples 11-14, using a mixture of PGDA and other solvents, excellent gloss was also achieved, while the transparency remained above 95%. More importantly, samples 11-12 and 14 exhibited significantly shorter touch-dry times.

[0099] Example 2

[0100] A two-component polyurethane coating composition was prepared in a manner similar to that of Sample 2 in Example 1, except that the diluents shown in Table 2 below were used.

[0101] Table 2

[0102]

[0103] As can be seen from Table 2, using EGDA and PC yielded a gloss comparable to PGDA, and even superior transparency. This demonstrates that using alkyl diol esters, cyclic carbonates, or combinations thereof as diluents as defined herein can produce coatings with excellent transparency and gloss.

[0104] Example 3

[0105] To further optimize the proportion of diluent in component B, the curing agent was diluted with 40% PGDA and 30% PGDA, respectively, while other parameters and experimental conditions were similar to those in Example 1. The results are shown in the table below:

[0106]

[0107] When diluted with 40% PGDA (i.e., a 40:60 weight ratio of diluent to curing agent), the coating exhibits significantly better transparency and gloss than when diluted with 30% PGDA. Furthermore, the inventors noted that the fullness of the coating with 40% PGDA dilution is also significantly better than that with 30% PGDA dilution. Therefore, using higher amounts (e.g., 40:60 or higher) of the diluent described herein further improves the transparency and gloss of the coating.

[0108] Although this application has been described with reference to numerous embodiments and examples, it will be readily apparent to those skilled in the art that modifications can be made to this application without departing from the principles disclosed in the foregoing specification. For example, combining multiple features or preferred embodiments described herein without departing from the principles disclosed in the foregoing specification should be understood as part of the content described herein. Such modifications are considered to be included in the following claims unless expressly specified otherwise. Accordingly, the embodiments detailed herein are merely exemplary and not intended to limit the scope of this application, which is the full scope of the appended claims and any and all equivalents.

Claims

1. A two-component polyurethane coating composition, comprising: Component A comprises an aqueous dispersion of a hydroxyl-functionalized resin; and Component B contains a non-hydrophilic isocyanate curing agent and a diluent, wherein... The diluent comprises alkyl diol esters, cyclic carbonates, or combinations thereof. The alkyl diol esters include one or more of propylene glycol diacetate, ethylene glycol diacetate, and ethylene glycol dipropionate. The alkyl diol esters do not contain ether bonds. The diluent also comprises at least one low-boiling solvent with a boiling point of 160°C or lower. The low-boiling solvent comprises propylene glycol monomethyl ether acetate, methyl ethyl ketone, or a combination thereof. The total amount of the alkyl diol esters and the cyclic carbonates is 10-60% by weight based on the weight of the diluent. The weight ratio of the diluent to the non-hydrophilic isocyanate curing agent is between 30:70 and 50:

50. Component B does not contain a hydrophilic isocyanate curing agent. During construction, component A and component B are mixed at a temperature of 10-10 ppm. 4 s -1 Stirring and mixing at a certain shear rate can yield an applyable coating composition.

2. The two-component polyurethane coating composition according to claim 1, wherein, The cyclic carbonates include one or more of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, and 2,3-butylene carbonate.

3. The two-component polyurethane coating composition according to claim 1, wherein, The non-hydrophilic isocyanate curing agent comprises aliphatic diisocyanates.

4. The two-component polyurethane coating composition according to claim 1, wherein, The particle size of the composition obtained by mixing component A and component B is in the range of 10-1000 nm.

5. The two-component polyurethane coating composition according to any one of claims 1 to 4, wherein, During construction, component A and component B are mixed at 10°C. 2 -10 3 s -1 The workable coating composition was obtained by stirring and mixing at a shear rate of [specific value].

6. The two-component polyurethane coating composition according to claim 1, wherein, The applyable coating composition has an applyability time of at least 4 hours.

7. A coating formed from the two-component polyurethane coating composition according to any one of claims 1 to 4, wherein, The coating has a transparency of 95% or higher.

8. A coated article comprising: The substrate, selected from one or more of wood, metal, plastic, interior wall panels, exterior wall panels, and cement board; and A coating according to claim 7 applied to the substrate or a cured coating formed from a two-component polyurethane coating composition according to any one of claims 1 to 4.

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