Two-component polyurethane composition

Abstract

A two-component polyurethane composition contains: (A) an aqueous dispersion comprising: a hydroxyl group-containing acrylic emulsion polymer comprising 5 to 50 % by weight, based on the weight of the hydroxyl group-containing acrylic emulsion polymer, of structural units of a hydroxyl-functional (meth)acrylic alkyl ester; and 2 to 20 % by weight, based on the weight of the hydroxyl group-containing acrylic emulsion polymer, of a branched polyether polyol; wherein the branched polyether polyol has a hydroxyl functionality of 4 to 10 and a molecular weight per branch of 1200 to 2500 g / mol, and contains 20 to 40 % by weight, based on the weight of the branched polyether polyol, of ethylene oxide units; and (B) a polyisocyanate.

Description

Technical Field

[0001] This invention relates to a two-component polyurethane composition and its preparation method. Background Technology

[0002] Waterborne two-component polyurethane compositions are increasingly used in the coatings industry because they contribute zero or fewer volatile organic compounds (VOCs) compared to solvent-based polyurethane compositions. Two-component waterborne polyurethane compositions can provide coatings with acceptable appearances (such as gloss and fullness) and mechanical properties similar to solvent-based polyurethane compositions, but still do not offer sufficiently long pot life, as evidenced by foaming problems and / or loss of gloss after storage. Incorporating hydrophilically modified isocyanates (“hydrophilic isocyanates”) into two-component polyurethane coating compositions can extend pot life due to their better dispersibility in water compared to unmodified polyisocyanates. However, many consumers prefer unmodified isocyanates for better chemical and water resistance, greater bubble-free film thickness, and lower cost compared to hydrophilic isocyanates.

[0003] Therefore, there remains a need for an aqueous two-component polyurethane composition that has an extended pot life without compromising other properties such as appearance. Summary of the Invention

[0004] This invention provides an aqueous two-component polyurethane composition, particularly suitable for coatings, by combining an acrylic emulsion polymer containing hydroxyl groups and a specific branched polyether polyol with a polyisocyanate. The polyurethane composition of this invention exhibits excellent pot life, as demonstrated by a gloss level exceeding 75 at 60 degrees (°) after 3 hours of storage at 35°C, while providing acceptable initial gloss and DOI. These properties can be determined according to the test methods described in the Examples section below.

[0005] In a first aspect, the present invention is a two-component polyurethane composition comprising:

[0006] (A) An aqueous dispersion comprising:

[0007] A hydroxyl-containing acrylic emulsion polymer, the hydroxyl-containing acrylic emulsion polymer comprising 10% to 50% by weight of hydroxyl-functionalized alkyl (meth)acrylate structural units based on the weight of the hydroxyl-containing acrylic emulsion polymer; and

[0008] The branched polyether polyol comprises, by weight, 2% to 20% of a hydroxyl-containing acrylic emulsion polymer; wherein the branched polyether polyol has a hydroxyl functionality of 4 to 10 and a molecular weight of 1200 to 2500 g / mol per branch, and contains, by weight, 20% to 40% ethylidene units based on the branched polyether polyol; and

[0009] (B) Polyisocyanate.

[0010] In a second aspect, the present invention provides a method for preparing a two-component polyurethane composition according to the first aspect. The method comprises mixing an aqueous dispersion (A) with a polyisocyanate (B). Detailed Implementation

[0011] When a test method number is not used to indicate a date, the test method refers to the most recent test method as of the priority date of this document. References to test methods include references to both the testing association and the test method number. The following test method abbreviations and designations apply to this document: ASTM refers to the ASTM International Association Method.

[0012] Products identified by trade names refer to compositions available under those trade names as of the priority date of this document. "And / or" means "and, or as an alternative." Unless otherwise specified, all scopes include the endpoints.

[0013] In this document, "aqueous" dispersion refers to particles dispersed in an aqueous medium. "Aqueous medium" in this document refers to water and 0% to 30% by weight of a water-miscible compound, such as alcohols, glycols, glycol ethers, glycol esters, or mixtures thereof.

[0014] The "structural unit" (also called the "polymerization unit") of a named monomer refers to the residue of the monomer after polymerization; that is, the polymerized monomer or the monomer in polymerized form. For example, the structural unit of methyl methacrylate is shown below: The dashed lines represent the attachment points between the structural units and the polymer backbone.

[0015] As used herein, “acrylic emulsion polymer” refers to an emulsion homopolymer of acrylic monomers or an emulsion copolymer of acrylic monomers with different acrylic monomers or other monomers such as styrene and vinyl acetate. As used herein, “acrylic monomer” includes (meth)acrylic acid, (meth)alkyl acrylate, (meth)acrylamide, (meth)acrylonitrile, and their modified forms, such as (meth)hydroxyalkyl acrylate. Throughout this document, the word fragment “(meth)acryloyl” refers to both “methacryloyl” and “acryloyl”. For example, (meth)acrylic acid refers to both methacrylic acid and acrylic acid, and methyl methacrylate refers to both methyl methacrylate and methyl acrylate.

[0016] In this article, the "functionality" or "Fn" of polyols refers to the number of hydroxyl (OH) groups per molecule. This is determined by standard... 13 12C nuclear magnetic resonance (NMR) analysis was used to determine the functionality (Fn), concentrations of ethylene oxide, propylene oxide, and butyl oxide units of polyether polyols, as well as the chemical structure of the initiator used to prepare the polyether polyols.

[0017] In this article, "branched" polyether polyols refer to polyether polyols with a functionality greater than 2.

[0018] The two-component polyurethane composition of the present invention typically comprises part A and part B, wherein part A comprises an aqueous dispersion of an acrylic emulsion polymer containing hydroxyl groups and a branched polyether polyol, and part B comprises one or more polyisocyanates. The branched polyether polyol can be represented by formula (I).

[0019] R-[O-(AO) x -H] y (I)

[0020] Wherein R represents a polyvalent aliphatic hydrocarbon group, and each AO is independently selected from ethylene oxide unit (-CH2-CH2-O-), propylene oxide unit (-CH2-CH(CH3)-O-), butyl oxide unit (-CH2-CH(CH2CH3)-O-), or a combination thereof; provided that the ethylene oxide unit is present at a total concentration of 20% to 40% by weight based on the branched polyether polyol.

[0021] The subscript x refers to the average molar number of alkylene oxides and can be in the range of 20 to 55; and

[0022] The subscript y refers to the functionality of the polyether polyol, which can be in the range of 4 to 10.

[0023] Each AO in formula (I) can be block or random. The value of the subscript x is sufficient to provide a branched polyether polyol with the desired molecular weight for each branch as described below.

[0024] "Multivalent" groups include tetravalent or higher valence groups. The R group can be derived from an initiator having 4-10 hydroxyl groups used to prepare polyether polyols by removing the active hydrogen from the initiator. R can typically be a saturated hydrocarbon group having 4 to 10 carbon atoms. Examples of R groups can be pentaerythritolyl, sorbitolyl, or glycosyl.

[0025] Specific examples of branched polyether polyols have formula (II):

[0026]

[0027] in m is 5 to 23 and n is 12 to 35.

[0028] The branched polyether polyols used in this invention have a functionality (Fn) of 4 or greater, and can be 5 or greater or even 6 or greater, while typically 10 or less, 9 or less, 8 or less or even 6 or less. Ideally, each branch of the polyether polyol has one hydroxyl group. Mixtures of two or more polyether polyols can be used, which may differ in functionality, amount of ethylene oxide units, and / or molecular weight of each branch. When two or more polyols with different functionalities are used, Fn refers to the average functionality of these polyols. For example, for a mixture of 1 mole of a polyol with Fn = 6 and 2 moles of a polyol with Fn = 4, the average functionality = (1*6 + 2*4) / (1+2) = 4.67.

[0029] The branched polyether polyols used in this invention may contain ethylene oxide units (-(CH2CH2-O)-) with a concentration of 20% or more by weight based on the weight of the branched polyether polyol, and may be 22% or more, 24% or more, 25% or more, 26% or more, 28% or more, 30% or more, 32% or more or even 35% or more, while typically 40% or less, and may be 39% or less, 38% or less, 37% or less, 36% or less or even 35% or less.

[0030] The branched polyether polyols used in this invention may further comprise propylene oxide units, butyl oxide units, or mixtures thereof; the concentration, based on the weight of the branched polyether polyol, is 60% or greater, and may be 61% or greater, 62% or greater, 63% or greater, 64% or greater, or even 65% or greater, while typically 80% or less, and may be 78% or less, 76% or less, 75% or less, 74% or less, 72% or less, 70% or less, 68% or less, or even 65% or less. Ideally, based on the weight of the branched polyether polyol, the branched polyether polyol contains 20% to 40% ethylene oxide units and 60% to 80% propylene oxide units, and more ideally, contains 20% to 35% ethylene oxide units and 65% to 80% propylene oxide units.

[0031] Branched polyether polyols can have the following molecular weights (also referred to as "total MW"): 4,800 g / mol or greater, and can be 5,000 g / mol or greater, 5,200 g / mol or greater, 6,200 g / mol, 6,500 g / mol, 7,000 g / mol or greater, 8,000 g / mol or greater, 9,000 g / mol or greater, 10,000 g / mol or greater, 11,000 g / mol or greater, or even 12,000 g / mol or greater, while typically 25,000 g / mol or less, and can be 20,000 g / mol or less, 17,500 g / mol or less, 15,000 g / mol or less, or even 12,000 g / mol or less. The molecular weight of branched polyether polyols can be determined by the following equation:

[0032] Total MW = 56100 / (OHV×Fn)

[0033] Where total Mw represents the molecular weight of the polyol, OHV represents the hydroxyl value as determined by ASTM D4274, and Fn represents the functionality of the polyol.

[0034] The branched polyether polyols used in this invention can have the following molecular weights for each branch: 1,200 g / mol or greater, and can be 1,300 g / mol or greater, 1,400 g / mol or greater, 1,500 g / mol or greater, 1,600 g / mol or greater, 1,700 g / mol or greater, 1,800 g / mol or greater, 1,900 g / mol or greater, or even 2,000 g / mol or greater, while typically being 2,500 g / mol or less, 2,400 g / mol or less, 2,300 g / mol or less, 2,200 g / mol or less, 2,100 g / mol or less, or even 2,000 g / mol or less. The molecular weight of each branch (also referred to as “Mw / branch”) can be determined as follows:

[0035] Mw for each branch = [total MW - MW(initiator)] / Fn

[0036] As defined above, total MW and Fn represent the molecular weight of the initiator used to prepare the polyol. MW (initiator) can be based on... 13 The initiator structure was determined by C NMR analysis.

[0037] The branched polyether polyols usable in this invention can be obtained in a conventional manner by reacting an epoxide, such as ethylene oxide, propylene oxide, butane oxide, or combinations thereof, with an initiator in the presence of a catalyst for ring-opening polymerization of the epoxide. The polymerization can be bulk polymerization or solution polymerization. The initiator may have 4 to 10 active hydrogen atoms and is used to prepare branched polyether polyols with a hydroxyl functionality in the range of 4 to 10. Examples of suitable initiators include pentaerythritol, sorbitol, glucose, or mixtures thereof. The catalysts usable for polymerizing the epoxides can be anionic or cationic, including, for example, KOH, boron trifluoride, or dicyandiamide complex (DMC) catalysts such as zinc hexacyanocobaltate. Typically, the epoxide is fed into a reactor containing a dried initiator and catalyst at a temperature of 50°C to 140°C. Polymerization is generally considered complete when the pressure in the reactor returns to approximately the same pressure as before the epoxide was fed.

[0038] The branched polyether polyols used in this invention may be present in the following concentrations: 2% by weight or more based on the weight of the acrylic emulsion polymer containing hydroxyl groups, and may be 2.1% or more, 2.2% or more, 2.3% or more, 2.4% or more, 2.5% or more, 3% or more, 3.5% or more, 4% or more, 4.5% or more, 5% or more, 5.5% or more, 6% or more, 6.5% or more, 7% or more, 7.5% or more, or more than 2.5% by weight. Larger, 8% or larger, 8.5% or larger, 9% or larger, 9.5% or larger, or even 10% or larger, while typically 20% or smaller, and may be 19% or smaller, 18% or smaller, 17% or smaller, 16% or smaller, 15% or smaller, 14.5% or smaller, 14% or smaller, 13.5% or smaller, 13% or smaller, 12.5% ​​or smaller, 12% or smaller, 11.5% or smaller, 11% or smaller, or even 10.5% or smaller. "Weight of acrylic emulsion polymer containing hydroxyl groups" refers to the dry weight of the acrylic emulsion polymer.

[0039] The aqueous dispersion (A) in the polyurethane composition comprises one or more hydroxyl-containing acrylic emulsion polymers. Acrylic emulsion polymers are typically present as aqueous dispersions synthesized via emulsion polymerization (also referred to as "native dispersions"). Hydroxyl-containing acrylic emulsion polymers comprise one or more hydroxyl-functionalized alkyl (meth)acrylate structural units. Examples of suitable hydroxyl-functionalized alkyl (meth)acrylates include hydroxyethyl (meth)acrylates, such as 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate; hydroxypropyl (meth)acrylates, such as 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl acrylate, and 3-hydroxypropyl methacrylate; hydroxybutyl (meth)acrylates, such as 3-hydroxybutyl acrylate, 3-hydroxybutyl methacrylate, 4-hydroxybutyl acrylate, and 4-hydroxybutyl methacrylate; 6-hydroxyhexyl acrylate; 6-hydroxyhexyl methacrylate; 3-hydroxy-2-ethylhexyl acrylate; 3-hydroxy-2-ethylhexyl methacrylate; and mixtures thereof. Ideally, hydroxyl-functionalized alkyl (meth)acrylates include 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 3-hydroxypropyl acrylate, 3-hydroxypropyl methacrylate, or mixtures thereof. Based on the weight of the hydroxyl-containing acrylic emulsion polymer, the hydroxyl-containing acrylic emulsion polymer may contain the following concentrations of hydroxyl-functionalized alkyl (meth)acrylate structural units: 5% or greater, and may be 10% or greater, 12% or greater, 15% or greater, and may be greater than 15%, 17% or greater, 20% or greater, 23% or greater, 25% or greater, 27% or greater, or even 30% or greater, while typically 50% or less, and may be 48% or less, 45% or less, 42% or less, 40% or less, 38% or less, 36% or less, 35% or less, 34% or less, 32% or less, or even 30% or less.

[0040] Acrylic emulsion polymers containing hydroxyl groups may comprise structural units of one or more acid monomers, their salts, or mixtures thereof. Acid monomers may include carboxylic acid monomers, sulfonic acid monomers, phosphorus-containing acid monomers, or mixtures thereof. Examples of suitable phosphorus-containing acid monomers and their salts include alkyl phosphoacrylates of (meth)acrylate, such as ethyl phosphoacrylate, propyl phosphoacrylate, and butyl phosphoacrylate; their salts; or mixtures thereof, defined by a third part of the structural unit; CH2=C(R1)-C(O)-O-(R2O). q-P(O)(OH)2, wherein R1 = H or CH3, R2 = alkylene, such as an ethylene group, a propylene group, or a combination thereof; and q = 1-20, such as SIPOMER PAM-100, SIPOMER PAM-200, SIPOMER PAM-300, SIPOMER PAM-600, and SIPOMER PAM-4000, all obtained from Solvay; (meth)acrylate phosphonoalkoxy esters, such as ethylene glycol (meth)acrylate, diethylene glycol (meth)acrylate, triethylene glycol (meth)acrylate, propylene glycol (meth)acrylate, dipropylene glycol (meth)acrylate, or tripropylene glycol (meth)acrylate; their salts; or mixtures thereof. Ideally, the phosphorus-containing acid monomers and their salts are selected from ethyl phosphate (meth)acrylate, propyl phosphate (meth)acrylate, butyl phosphate (meth)acrylate, or allyl ether phosphate; their salts; or mixtures thereof. More ideally, the phosphorus-containing acid monomer is ethyl methacrylate (PEM). The carboxylic acid monomer can be an α,β-olefinically unsaturated carboxylic acid, a monomer with an acid-forming group that generates or is subsequently convertible into such an acid group (such as anhydrides, (meth)acrylic anhydrides, or maleic anhydrides); and mixtures thereof. Specific examples of carboxylic acid monomers include acrylic acid, methacrylic acid, maleic acid, itaconic acid, crotonic acid, fumaric acid, 2-carboxyethyl acrylate, and mixtures thereof. Sulfonic acid monomers and their salts may include sodium vinyl sulfonate (SVS), sodium styrene sulfonate (SSS), and sodium acrylamide-methyl-propane sulfonate (AMPS) or their salts; or mixtures thereof. The acid monomer can be a combination of a carboxylic acid monomer and / or its salt with a phosphorus-containing acid monomer and / or its salt. Ideally, the acid monomer is selected from acrylic acid, methacrylic acid, itaconic acid, or ethyl methacrylate; their salts; or mixtures thereof. Based on the weight of the hydroxyl-containing acrylic emulsion polymer, the hydroxyl-containing acrylic emulsion polymer may contain structural units of acid monomers and their salts in the following concentrations: 0.1% or greater, and may be 0.2% or greater, 0.3% or greater, 0.5% or greater, 0.8% or greater, 1.0% or greater, 1.3% or greater, 1.5% or greater, 1.7% or greater, 2.0% or greater or even 2.2% or greater, while typically 10% or less, and may be 8.0% or less, 7.0% or less, 6.0% or less, 5.0% or less, 4.5% or less, 4.0% or less, 3.5% or less, 3.0% or less or even 2.5% or less.

[0041] The hydroxyl-containing acrylic emulsion polymers used in this invention may contain or not contain structural units of one or more olefinically unsaturated functional monomers (other than those described above) having at least one functional group selected from the following: amide, acetoacetate, carbonyl, urea, silane, or amino groups. Suitable olefinically unsaturated functional monomers may include, for example, amino-functional monomers such as dimethylaminoethyl methacrylate, dimethylaminoethyl acrylate, dimethylaminopropyl methacrylate, and dimethylaminopropyl acrylate; and urea-functional monomers such as hydroxyethylvinyl urea methacrylate and hydroxyethylvinyl urea acrylate, such as SIPOMER from Solvay. WAMII; monomers with acetoacetyl acetate functional groups, such as acetoacetoxyethyl methacrylate (AAEM), acetoacetoxyethyl acrylate, acetoacetoxypropyl methacrylate, acetoacetoxypropyl acrylate, allyl acetoacetate, acetoacetoxybutyl methacrylate, acetoacetoxybutyl methacrylate, acetoacetamide ethyl methacrylate, acetoacetamide ethyl acrylate; monomers with carbonyl groups, such as diacetone acrylamide (DAAM), diacetone methacrylamide; monomers with amide functional groups, such as acrylamide and methacrylamide; vinyltrialkoxysilanes, such as vinyltrimethoxysilane, vinyltriethoxysilane, vinyltri(2-methoxyethoxy)silane, vinyldimethylethoxysilane, vinylmethyldiethoxysilane, or (meth)acryloyloxyalkyltrialkoxysilanes, such as (meth)acryloyloxyethyltrimethoxysilane and (meth)acryloyloxypropyltrimethoxysilane; or mixtures thereof. Based on the weight of the hydroxyl-containing acrylic emulsion polymer, the hydroxyl-containing acrylic emulsion polymer may contain structural units of olefinic unsaturated functional monomers in the following concentrations: zero or greater, and may be 0.1% or greater, 0.5% or greater, 1% or greater or even 2% or greater, while typically 10% or less, and may be 8% or less, 6% or less, 5% or less or even 3% or less.

[0042] The hydroxyl-containing acrylic emulsion polymers used in this invention may comprise structural units of one or more mono-olefin unsaturated nonionic monomers, in addition to the hydroxyl-functionalized alkyl (meth)acrylates and olefin unsaturated functional monomers described above. "Nonionic monomer" as used herein refers to a monomer that does not carry an ionic charge between pH 1 and 14. Mono-olefin unsaturated nonionic monomers may be selected from vinyl aromatic monomers, alkyl (meth)acrylates, acrylonitrile, or mixtures thereof. Suitable vinyl aromatic monomers may include, for example, styrene; substituted styrene, such as methylstyrene, α-methylstyrene, trans-β-methylstyrene, 2,4-dimethylstyrene, ethylstyrene, butylstyrene, and p-methoxystyrene; o-methoxystyrene, m-methoxystyrene, and p-methoxystyrene; and p-trifluoromethylstyrene; or mixtures thereof. Alkyl (meth)acrylates may be C1-C6 (meth)acrylates. 20 Alkyl, C1-C 18 Alkyl, C1-C 12 Alkyl or C1-C4 alkyl esters. Specific examples of (meth)acrylate alkyl esters include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, cyclohexyl methacrylate, cyclohexyl acrylate, tert-butylcyclohexyl methacrylate, trimethylcyclohexyl methacrylate, isobornyl methacrylate, isobornyl acrylate, tetrahydrofuran methacrylate, dicyclopentadienyl acrylate, dicyclopentadienyl methacrylate, and combinations thereof. Ideally, the mono-olefinic unsaturated nonionic monomer includes styrene combined with one or more (meth)acrylate alkyl esters. Ideally, the mono-olefinic unsaturated nonionic monomer is selected from styrene, methyl methacrylate, 2-ethylhexyl acrylate, butyl acrylate, or mixtures thereof. Based on the weight of the hydroxyl-containing acrylic emulsion polymer, the structural units of the mono-olefinic unsaturated nonionic monomer can be present in the following concentrations: 40% or more, and can be 45% or more, 50% or more, 55% or more, 60% or more or even 65% or more, while typically 94.9% or less, and can be 94.8% or less, 90% or less, 85% or less, 80% or less, 77% or less, 75% or less, 74% or less, 72% or less or even 70% or less.

[0043] The hydroxyl-containing acrylic emulsion polymers used in this invention may contain or not contain structural units of one or more polyene-bonded unsaturated monomers, including difunctional, trifunctional, tetrafunctional, or higher polyfunctional polyene-bonded unsaturated monomers. Examples of suitable polyene-bonded unsaturated monomers include butadiene, allyl (meth)acrylate, divinylbenzene, ethylene glycol dimethacrylate, butanediol dimethacrylate, and mixtures thereof. Based on the weight of the hydroxyl-containing acrylic emulsion polymer, the structural units of the polyene-bonded unsaturated monomers may be present in the following concentrations: 0 or greater, and may be 0.1% or greater or even 0.2% or greater, while typically 5% or less, and may be 3% or less, 1% or less, 1% or less, 0.5% or less or even 0.

[0044] Ideally, based on the weight of the hydroxyl-containing acrylic emulsion polymer, the hydroxyl-containing acrylic emulsion polymer used in this invention comprises 5% to 35% of structural units of hydroxyl-functionalized alkyl (meth)acrylates; 0.2% to 5% of structural units of acid monomers, their salts, or mixtures thereof; and 60% to 94.8% of structural units of monoolefinic unsaturated nonionic monomers other than hydroxyl-functionalized alkyl (meth)acrylates.

[0045] The hydroxyl-containing acrylic emulsion polymers used in this invention may have the following weight-average molecular weights: 50,000 g / mol or less, and may be 48,000 g / mol or less, 45,000 g / mol or less, 42,000 g / mol or less, 40,000 g / mol or less, 38,000 g / mol or less, 35,000 g / mol or less, 32,000 g / mol or less, 30,000 g / mol or less, 28,000 g / mol or less, 25,000 g / mol or less, 23,000 g / mol or less, 20,000 g / mol or less, 18,000 g / mol or less, or even 17,000 g / mol. / mol or less, while typically 3,000 g / mol, and can be 4,000 g / mol or greater, 5,000 g / mol or greater, 6,000 g / mol or greater, 7,000 g / mol or greater, 8,000 g / mol or greater, 9,000 g / mol or greater, 10,000 g / mol or greater, 11,000 g / mol or greater, 12,000 g / mol or greater, 13,000 g / mol or greater, 14,000 g / mol or greater, 15,000 g / mol or greater, or even 16,000 g / mol or greater, as determined by gel permeation chromatography (GPC) (further details are provided below under GPC analysis).

[0046] The hydroxyl-containing acrylic emulsion polymer particles dispersed in the aqueous dispersion (A) can have the following particle sizes: 30 nanometers (nm) or larger, and can be 50 nm or larger, 60 nm or larger, 70 nm or larger, or even 80 nm or larger, while typically 500 nm or smaller, and can be 300 nm or smaller, 200 nm or smaller, 150 nm or smaller, 120 nm or smaller, or even 100 nm or smaller. Particle size in this document refers to the number-average particle size measured using a Brookhaven BI-90Plus particle size analyzer.

[0047] Based on the total weight of the aqueous dispersion (A) on a dry or solid basis, the hydroxyl-containing acrylic emulsion polymers used in this invention may be present at concentrations of 20% to 70%, 30% to 55%, 35% to 50%, or 40% to 45%.

[0048] The hydroxyl-containing acrylic emulsion polymers used in this invention can be prepared by emulsion polymerization of the aforementioned monomers in an aqueous medium, preferably in the presence of a surfactant. The surfactant differs from the branched polyether polyols described above and can be added before, during, or in combination with the monomers. A portion of the surfactant may also be added after polymerization. These surfactants can be anionic or nonionic surfactants, and ideally anionic surfactants such as sulfate surfactants, sulfonate surfactants, or mixtures thereof. Based on the total weight of the monomers used to prepare the hydroxyl-containing acrylic emulsion polymers, these surfactants can be used in the following total amounts: 0.1% or more, and can be 0.3% or more, 0.5% or more, 0.7% or more, 0.9% or more, or even 1.2% or more, while typically 5% or less, and can be 4% or less, 3% or less, 2% or less, or even 1.5% or less.

[0049] Monomers can be added purely or in the form of an emulsion in water; or added in one or more forms, continuously, linearly, or non-linearly, during the reaction time for preparing the hydroxyl-containing acrylic emulsion polymer. The total weight concentration of the monomers used to prepare the hydroxyl-containing acrylic emulsion polymer is equal to 100% relative to the total weight of the monomers. The weight concentration of each monomer used to prepare the hydroxyl-containing acrylic emulsion polymer relative to the total weight of the monomers can be the same as the aforementioned weight concentration of the structural unit of that monomer relative to the weight of the hydroxyl-containing acrylic emulsion polymer. Suitable temperatures for polymerization of the monomers are below 100°C, in the range of 10°C to 95°C, or in the range of 50°C to 92°C. Multi-stage emulsion polymerization using the above-described monomers can be utilized, wherein at least two stages are formed sequentially, and typically an emulsion polymer comprising at least two polymer compositions is formed.

[0050] Free radical initiators can be used in polymerization methods. These methods can be thermally initiated or redox-initiated emulsion polymerization. Examples of suitable free radical initiators include hydrogen peroxide, tert-butyl hydroperoxide, cumene hydroperoxide, ammonium and / or alkali metal persulfates, sodium perborate, superphosphate and their salts; ammonium or alkali metal salts of potassium permanganate and peroxydisulfate. Based on the total weight of the monomers, free radical initiators can typically be used in amounts from 0.01% to 3.0% by weight. Redox systems comprising the above-mentioned initiators and suitable reducing agents can be used in the polymerization methods. Examples of suitable reducing agents include sodium formaldehyde sulfoxylate, ascorbic acid, isoascorbic acid, alkali metal salts and ammonium salts of sulfur-containing acids, such as sodium sulfite, bisulfite, thiosulfate, hyposulfite, sulfide, hydrosulfide, or dithionite; formadinesulfinic acid; acetone sulfite; glycolic acid; hydroxymethanesulfonic acid; glyoxylate hydrate; lactic acid; glyceric acid; malic acid; tartaric acid; and salts of the aforementioned acids. Metal salts of iron, copper, manganese, silver, platinum, vanadium, nickel, chromium, palladium, or cobalt can be used to catalyze redox reactions. Metal chelating agents may be used optionally.

[0051] One or more chain transfer agents can be used during polymerization to control the molecular weight of hydroxyl-containing acrylic emulsion polymers. Examples of suitable chain transfer agents include 3-mercaptopropionic acid, methyl 3-mercaptopropionic acid, butyl 3-mercaptopropionic acid, n-dodecyl mercaptan, n-hexadecyl mercaptan, tert-dodecyl mercaptan, n-octadecyl mercaptan, benzene mercaptan, nonanedialkyl mercaptan, hydroxyl-containing thiols (such as hydroxyethyl mercaptan), mercaptopropionic acid, and mixtures thereof. Based on the total weight of the monomers, chain transfer agents can be used at concentrations greater than 0.3%, and can be 0.4% or greater, 0.5% or greater, 0.6% or greater, 0.8% or greater, 1% or greater, 1.3% or greater, 1.5% or greater, or even 2.0%, while typically 20% or less, 15% or less, 13% or less, 10% or less, 8% or less, 6% or less, 4% or less, 3% or less, or even 2.5% or less.

[0052] The types and amounts of the monomers mentioned above can be selected to give the resulting hydroxyl-containing acrylic emulsion polymers glass transition temperatures (Tg) suitable for different applications. Hydroxyl-containing acrylic emulsion polymers may have the following Tg values: in the range of 0 to 80°C, and may be 0°C or greater, 10°C or greater, 15°C or greater, 20°C or greater, 25°C or greater, 30°C or greater, 35°C or greater, or even 40°C or greater, while typically 80°C or less, and may be 75°C or less, 70°C or less, 65°C or less, 60°C or less, 55°C or less, or even 50°C or less. As used herein, “Tg” can be determined by differential scanning calorimetry (DSC) (further details are provided below under DSC analysis).

[0053] After the polymerization process is completed, the resulting acrylic emulsion polymer dispersion containing hydroxyl groups can be neutralized by one or more bases to a pH value such as at least 5, i.e., 5.5 to 10, 6.0 to 9, 6.2 to 8, 6.4 to 7.5 or 6.6 to 7.2. Examples of suitable bases include ammonia; alkali metal or alkaline earth metal compounds, such as sodium hydroxide, potassium hydroxide, calcium hydroxide, zinc oxide, magnesium oxide, sodium carbonate; primary, secondary, and tertiary amines, such as triethylamine, ethylamine, propylamine, monoisopropylamine, monobutylamine, hexylamine, ethanolamine, diethylamine, dimethylamine, di-n-propylamine, tributylamine, triethanolamine, dimethoxyethylamine, 2-ethoxyethylamine, 3-ethoxypropylamine, dimethylethanolamine, diisopropanolamine, morpholine, ethylenediamine, 2-diethylaminoethylamine, 2,3-diaminopropane, 1,2-propenediamine, neopentyldiamine, dimethylaminopropylamine, hexamethylenediamine, 4,9-dioxododecane-1,12-diamine, polyethyleneimine, or polyethyleneamine; aluminum hydroxide; or mixtures thereof.

[0054] The polyurethane compositions of the present invention further comprise (B) one or more polyisocyanates as crosslinking agents. The polyisocyanate may comprise any molecule having two or more isocyanate (NCO) groups, or a mixture of two or more such molecules. The polyisocyanate may be aliphatic, alicyclic, or aromatic, or a mixture thereof. An aliphatic polyisocyanate is a polyisocyanate in which the NCO group is not directly attached to an aromatic ring. The polyisocyanate may be a biuret, isocyanurate trimer, urea diketone dimer, asymmetric iminooxadiazine diketone trimer, or urethane. The average functionality of the polyisocyanate may be greater than 2 (>2) or from 2.5 to 10. Examples of suitable polyisocyanates include aliphatic diisocyanates and their dimers and trimers, such as, for example, C2-C8 alkylene diisocyanates, such as tetramethylene diisocyanate and hexamethylene diisocyanate (HDI), 1,12-dodecane diisocyanate, 2,2,4-trimethyl-hexamethylene diisocyanate, 2,4,4-trimethyl-hexamethylene diisocyanate, 2-methyl-1,5-pentamethylene diisocyanate; alicyclic diisocyanates and their dimers and trimers, such as isophorone diisocyanate (IPDI) and dicyclohexylmethane diisocyanate (HMDI), 1,4-cyclohexane diisocyanate and 1,3-bis(isocyanomethyl)cyclohexane; aromatic diisocyanates and their dimers and trimers, such as toluene diisocyanate (TDI) and diphenylmethane diisocyanate (MDI). Ideally, the polyisocyanate comprises an aliphatic polyisocyanate. More ideally, the polyisocyanate is selected from hexamethylene diisocyanate homopolymers, hexamethylene diisocyanate adducts, isophorone diisocyanate homopolymers, isophorone diisocyanate adducts, or mixtures thereof. The trimer (or isocyanurate) in the polyisocyanate can be prepared, for example, by a method known in the art as disclosed in U.S. Patent Publication No. 2006 / 0155095A1 of Daussin et al., by trimerizing an alicyclic diisocyanate (e.g., isophorone diisocyanate) at a suitable high temperature in the presence of one or more trimerizing catalysts (such as, for example, tertiary amines or phosphine or heterogeneous catalysts) and, if necessary, in the presence of solvents and / or auxiliaries (such as co-catalysts), until the desired isocyanate (NCO) content has been reached, and then deactivating the catalyst using inorganic and organic acids, corresponding acyl halides and alkylating agents, preferably by heating. Isocyanurate compositions containing isocyanurates derived from aliphatic diisocyanates can also be formed by cyclizing the aliphatic diisocyanate in the presence of one or more trimerizing catalysts and then deactivating the catalyst. Any isocyanurate can be further modified by conventional methods to contain urethane, urea, imino-s-triazine, urea ketene imine, or carbodiimide moieties. Ideally, the polyisocyanate is selected from aliphatic diisocyanates, their dimers and trimers, or mixtures thereof.More ideally, the polyisocyanate is selected from aliphatic trimers, such as, in particular, HDI trimers or mixtures of HDI trimers and IPDI trimers.

[0055] Polyisocyanates used in this invention may comprise one or more polyisocyanate prepolymers, which can be formed by reacting an HDI trimer and / or another aliphatic diisocyanate / trimer with a monool, diol, diamine, or monoamine. Such prepolymers may further comprise polyalkoxy or polyether chains. Furthermore, suitable polyisocyanates may be modified with ionic compounds such as aminosulfonic acids. Commercially available polyisocyanates may include, for example, Desmodur... TM N3300, N3600 and N3900 polyisocyanates and Bayhydur TM XP 2655, 401-60 and 401-70 polyisocyanates (Covestro); Tolonate HDT, HDT-LV and HDT-LV2 and Easaqua L 600 polyisocyanate (Vencorex Chemicals); DURANATE TLA-100 and TMA-100 polyisocyanates (Asahi Kasei Corporation); and Aquolin 268, 269 and 270 polyisocyanates (Wanhua Chemicals).

[0056] The polyisocyanate used in this invention can be used alone or diluted with one or more solvents to form a polyisocyanate solution, which is then mixed with part A. Such solvents reduce the viscosity of the polyisocyanate and are non-reactive. Based on the weight of the polyisocyanate, the solvent can be used in amounts from 5% to 150% by weight, 15% to 130% by weight, 20% to 120% by weight, or 30% to 100% by weight. Suitable solvents may include, for example, propylene glycol diacetate, propylene glycol methyl ether acetate, dipropylene glycol dimethyl ether, or mixtures thereof.

[0057] The polyisocyanate may be present in an amount sufficient to provide a molar ratio of the total molar number of isocyanate groups in the polyisocyanate to the total molar number of hydroxyl groups in the hydroxyl-containing acrylic emulsion polymer and branched polyether polyol, wherein the polyisocyanate may contain two or more different polyisocyanates described above: 0.8:1 to 2.5:1, 0.9:1 to 2.0:1 or 1:1 to 1.5:1.

[0058] The polyurethane compositions of the present invention may contain or not contain one or more reinforcing and curing catalysts. The catalyst can be any suitable catalyst for a two-component polyurethane composition, including, for example, metal-based catalysts such as those containing tin, bismuth, zinc, aluminum, zirconium, or tertiary amine catalysts or mixtures thereof, said tertiary amine catalysts including aliphatic and alicyclic tertiary amine catalysts that are monoamines, diamines, or triamines. Examples of suitable metal-based catalysts include dibutyltin dilaurate, dibutyltin thiolate, dibutyltin sulfide, dimethyltin thiolate, mercaptodibutyltin ester, zirconium diketoate, aluminum diketoate, bismuth neodecanoate, and zinc amine compounds. Suitable tertiary amine catalysts may include, for example, triethylenediamine, triethyleneamine, 1,4-diazabicyclo[2.2.2]octane, 6-(dibutylamino)-1,8-diazabicyclo[5.4.0]undec-7-ene, dimethylcyclohexylamine, and mixtures thereof. The catalyst may be present in an amount of 0.01% to 2.5% or 0.1% to 1.0% by weight of the total weight of the polyisocyanate and the hydroxyl-containing component (e.g., hydroxyl-containing acrylic emulsion polymers and branched polyether polyols).

[0059] The polyurethane compositions of the present invention may contain or not contain one or more pigments, one or more extenders, or mixtures thereof. As used herein, “pigment” refers to particulate inorganic or organic materials capable of substantially contributing to the opacity, color, or hiding power of a coating. Inorganic pigments typically having a refractive index greater than 1.8 may include, for example, titanium dioxide (TiO2), zinc oxide, zinc sulfide, iron oxide, barium sulfate, barium carbonate, or mixtures thereof. Examples of suitable organic pigments include phthalocyanine blue, phthalocyanine green, monoazo yellow, carbon black, or mixtures thereof. TiO2 is a preferred pigment used in the present invention. The term “extender” refers to particulate materials with a refractive index less than or equal to 1.8 and greater than 1.3. Examples of suitable extenders include calcium carbonate, alumina (Al2O3), clay, calcium sulfate, aluminosilicates, silicates, zeolites, mica, diatomaceous earth, solid or hollow glass, ceramic beads, and opaque polymers (such as ROPAQUE from The Dow Chemical Company). TM Ultra E (ROPAQUE is a trademark of Dow Chemical Company) or mixtures thereof. Pigments and / or extenders are typically present in part A of the polyurethane composition. The polyurethane composition may have a pigment volume concentration (PVC) of 0 to 75%, 5% to 50%, or 10% to 30%. PVC can be determined according to the following equation: PVC = [volume(pigment + extender) / volume(pigment + extender + emulsion polymer + branched polyether polyol)] × 100%.

[0060] The polyurethane compositions of the present invention may or may not contain one or more coalescing agents. As used herein, "coalescing agent" refers to a solvent that fuses polymer particles into a continuous film under ambient conditions (10°C–30°C, relative humidity: 30%–80%). Examples of suitable coalescing agents include dipropylene glycol n-butyl ether, propylene glycol n-butyl ether, propylene glycol methyl ether, 2-butoxyethanol, dipropylene glycol methyl ether, propylene glycol n-propyl ether, diethylene glycol monobutyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, triethylene glycol monobutyl ether, dipropylene glycol n-propyl ether, n-butyl ether, aromatic hydrocarbons such as the Solvesso series from ExxonMobil, or 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate such as Eastman's Texanol ester alcohol, or mixtures thereof. The coalescing agent is typically present in part A of the polyurethane composition. The concentration of the coalescing agent, based on the total weight of the acrylic emulsion polymer containing hydroxyl groups, can be zero to 50%, 5% to 40%, or 10% to 25%.

[0061] The polyurethane compositions of the present invention may contain or not contain conventional additives, such as light stabilizers, ultraviolet (UV) absorbing compounds, leveling agents, wetting agents, dispersants, neutralizers, defoamers, or rheology modifiers, or mixtures thereof. These additives may be present in amounts from 0% to 20% or from 1% to 10% by weight of the polyurethane composition.

[0062] The polyurethane compositions of the present invention can be prepared using techniques known in the art. Methods for preparing polyurethane compositions generally include (i) providing a portion A comprising an aqueous dispersion containing a hydroxyl-containing acrylic emulsion polymer and a branched polyether polyol, and optionally pigments and other components described above; and (ii) mixing the portion A from step (i) with a polyisocyanate. The aqueous dispersion in portion A can be prepared by providing a hydroxyl-containing acrylic emulsion polymer and then mixing the resulting emulsion polymer with a branched polyether polyol, the acrylic emulsion polymer being prepared by causing the monomers described above to undergo hydroxyl-containing acrylic emulsion polymerization. Alternatively, the branched polyether polyol may be added before and / or during the polymerization of the monomers used to prepare the hydroxyl-containing acrylic polymer. Ideally, all the branched polyether polyols in the polyurethane composition are mixed with the hydroxyl-containing acrylic emulsion polymer after its polymerization. The polyisocyanate in portion B is preferably diluted with a solvent. Portions A and B may be mixed just before application. Polyurethane compositions can be cured at ambient temperatures (10°C–30°C) or at temperatures ranging from 4°C to 150°C, ideally from 25°C to 80°C. The curing temperature can vary depending on the substrate. Curing times typically range from 10 minutes at 50°C to 90°C to 1 to 14 days at 10°C to 35°C. Examples of suitable substrates include metals, wood, plastics, concrete, cementitious substrates, stone, asphalt, elastic substrates, glass, or fabrics.

[0063] The polyurethane compositions of the present invention can be used to produce coatings with or without pigments and / or extenders, adhesives, sealants, primers, or caulking agents. The polyurethane compositions can provide an expanded window for formulations with extended pot life. "Extended pot life" means that after storage at 35°C for 3 hours, the polyurethane composition can provide a coating prepared therefrom with a gloss level of 60° greater than 75 (further details are provided in the gloss test below). For example, the novel combination of an acrylic emulsion polymer containing hydroxyl groups in part A and a branched polyether polyol enables the use of various types of polyisocyanates, such as aliphatic polyisocyanates without polyalkoxy chain or ionic compound modification ("unmodified polyisocyanates"); or those with hydrophilic modification, such as aliphatic polyisocyanates with polyalkoxy chain or ionic compound modification (e.g., hydrophilic polyisocyanates); thereby forming a two-component polyurethane composition with the aforementioned extended pot life. The two-component polyurethane compositions can also provide coatings made therefrom with a Dot Image Scale (DOI) of 70 or greater. DOI measures the sharpness of a reflected image on a surface (e.g., a coated surface) and is an indicator of perfect reflection and the absence of haze or "orange peel" on the surface. Polyurethane compositions can provide coatings made from them with a gloss level of 75 or higher at 60°. DOI and gloss level can be measured according to the test methods described in the Examples section below.

[0064] The present invention further provides polyurethane coatings made from a two-component polyurethane composition on any of the substrates mentioned above. Such coatings can be multi-layer coatings over a primer layer and optionally a base coat or a colored coat. The coatings can be for agricultural, construction, and earthmoving equipment; architectural coatings; general industrial finishing coatings; marine and protective coatings; automotive coatings; self-repairing coatings; plastic coatings; wood coatings, roll coatings; and civil engineering coatings.

[0065] Examples

[0066] Some embodiments of the invention will now be described in the following examples. All percentage (%) values ​​are weight percentages relative to the weight of the composition. Table 1 lists the materials used to synthesize the polymer dispersions and coating compositions of the samples described below. OROTAN, DOWANOL, and ACRYSOL are trademarks of Dow Chemical Company.

[0067] Table 1

[0068]

[0069] * "Secondary dispersion" refers to an aqueous dispersion prepared by a method including the following steps: solution polymerization of monomers in an organic solvent, neutralization of the obtained polymer, and phase inversion to obtain an aqueous dispersion.

[0070] Table 2

[0071]

[0072] *All polyether polyols listed in Table 2 are commercially available from Dow Chemical Company and can be prepared according to a procedure similar to that for the synthesis of polyether polyol 1 below, except for the order and / or amount of epoxide feed.

[0073] EO (ethylene oxide) represents And PO (propylene oxide) represents

[0074] Synthesis of polyether polyol 1

[0075] Branched polyether polyol 1 was prepared based on sorbitol as an initiator, followed by an alkoxylation step using KOH as a catalyst under known alkoxylation conditions. Sorbitol was added to a reactor along with KOH (2000 ppm active weight, 50% by weight aqueous solution). The reactor was shut off, and the contents were stirred at 250 rpm and heated to 80°C. A vacuum was applied while maintaining the contents at 80°C to remove residual water from the reactor. The contents were then heated to 120°C, and ethylene oxide was slowly added to the reactor while maintaining a reactor pressure less than 4.5 bar (450 kPa). After the addition of ethylene oxide (EO), the contents were maintained at 120°C for digestion; the reactor pressure was monitored until it approached the initial pressure (before EO addition). As a second feed step, propylene oxide (PO) was also slowly added to the reactor at 120°C while maintaining a reactor pressure less than 4.5 bar. The reactor contents were then maintained at 120°C for digestion; and the reactor pressure was monitored until it approached the pressure prior to the addition of PO and stabilized for 2 hours. The reactor was then purged three times with nitrogen and vacuum to remove any residual propylene oxide. The reactor contents were cooled to 60°C and neutralized with acetic acid to provide the polyether polyol represented by Formula I. The weight percentage of EO was approximately 35% and the weight percentage of PO was approximately 63% relative to the total weight of the components used to prepare polyether polyol 1.

[0076] Synthesis of polyether polyol 2

[0077] Polyether polyol 2 was prepared according to the same procedure as the synthesis of polyether polyol 1 described above, except that the order of EO and PO feeds was switched, and based on the total weight of the components used to prepare polyether polyol 2, the weight ratio of EO used was about 20% and the weight ratio of PO used was about 78%.

[0078] The following standard analytical equipment and methods were used in the embodiments and to determine the properties and characteristics described herein:

[0079] Particle size measurement

[0080] The particle size of polymer particles in an aqueous dispersion refers to the number-average particle size measured using a Brookhaven BI-90Plus particle size analyzer.

[0081] Tg measurement

[0082] Tg was measured by DSC. 5–10 mg samples were analyzed in a sealed aluminum disk on a TA Instrument DSC Q2000 equipped with an autosampler under a nitrogen atmosphere. Tg measurements by DSC were performed in three cycles: -40 °C to 180 °C, 10 °C / min (cycle 1, followed by a 5-minute hold to eliminate the thermal history of the sample); 180 °C to -40 °C, 10 °C / min (cycle 2); and -40 °C to 180 °C, 10 °C / min (cycle 3). Tg was obtained from cycle 3 by taking the midpoint of the heat flux relative to the temperature transition as the Tg value.

[0083] GPC analysis

[0084] GPC analysis of acrylic polymers is typically performed using an Agilent 1200. The sample is dissolved in a 2 mg / mL solution of tetrahydrofuran (THF) / formic acid (FA) (5%) and then filtered through a 0.45 μm polytetrafluoroethylene (PTFE) filter before GPC analysis. GPC analysis is performed under the following conditions:

[0085] Columns: One PLgel GUARD column (10 μm, 50 mm × 7.5 mm), two hybrid B columns in series (7.8 mm × 300 mm); Column temperature: 40 °C; Mobile phase: THF / FA (5%); Flow rate: 1.0 mL / min; Injection volume: 100 μL; Detector: Agilent refractive index detector, 40 °C; and Calibration curves: PL polystyrene I narrow standard, molecular weight in the range of 2,329,000 g / mol to 580 g / mol, using polynomial 3 fit.

[0086] Gloss test

[0087] • Initial gloss

[0088] Gloss was measured at a given angle (60 degrees (°)) using a BYK Gardener micro-TRI gloss meter (BYK-Gardner USA, Columbia, Md.) according to ASTM D523 (1999). Immediately after mixing all components of the two-component polyurethane composition, the composition was applied to an aluminum panel (Q-panel A-46) at a wet thickness of 150 μm. After drying at room temperature for 20 minutes, the coated panel was further dried at 60°C for 40 minutes, and then the gloss was measured. The average of three independent readings was reported as the “initial gloss.” An acceptable initial gloss (60°) was 84 or greater.

[0089] • Gloss after storage

[0090] Immediately after mixing all components, the two-component polyurethane composition was stored at 35°C for 1.5 hours and 3 hours, respectively. Then, after 1.5 hours or 3 hours of storage, coated panels were prepared using the resulting polyurethane composition according to the same procedure and drying conditions described above for determining the initial gloss. The 60° gloss of the obtained coated panels was then measured and denoted as "Gloss (35°C / 1.5 hours)" and "Gloss (35°C / 3 hours)," respectively. The average of three independent readings was reported. A gloss (60° gloss) of 75 or higher after 3 hours of storage indicates an acceptable pot life. Otherwise, if the gloss (60° gloss) is less than 75 after 3 hours of storage, it fails the pot life test.

[0091] Distinctness of image (DOI) test

[0092] DOI measurements were performed according to ASTM D5767-95 (2004) (Standard Test Method for Instrumental Measurement of Image Sharpness and Gloss of Coated Surfaces) using a BYK Gardener microwave scanner (BYK-Gartner, Columbia, ., USA). Immediately after mixing all components of the two-component polyurethane composition, the composition was applied to an aluminum panel (Q-panel A-36) at a wet thickness of 200 μm. After drying at room temperature for 20 minutes, the panel was further dried at 60°C for 40 minutes. For each panel, the average of three independent readings was reported as the DOI value. A sample passed the DOI test if the DOI was 70 or higher (≥70). Otherwise, samples with a DOI less than 70 failed.

[0093] Solid content

[0094] The solids content of the sample is measured by weighing 0.7 ± 0.1 g (wet weight of the sample, denoted as "W1") and placing it in an aluminum pan (weight of the aluminum pan, denoted as "W2") in a 150°C oven for 25 minutes. The aluminum pan containing the dried sample is then cooled, and the total weight is recorded as "W3". The solids content of the sample is calculated as (W3 - W2) / W1 * 100%.

[0095] Synthesis of acrylic emulsion polymer dispersion with hydroxyl groups ("HA-01")

[0096] The monomer emulsion was prepared as follows :

[0097] 23 g of Disponil Fes 993 surfactant (30% active), 173 g of MMA, 306 g of ST, 204 g of EHA, 304 g of HEMA, 16 g of MAA, 16 g of PEM, and 21 g of n-DDM were added to 318 g of deionized (DI) water and mixed together to produce a stable monomer emulsion. Under a nitrogen atmosphere at 90°C, 42.6 g of Fes 993 surfactant (30% active) (42.6 g), 16.9 g of DI water containing ammonia (28%, 2.5 g), and 16.9 g of DI water containing 29 g of monomer emulsion and ammonium persulfate (APS) (2.03 g) were added to 600 g of DI water to form a reaction mixture. The remaining monomer emulsion was then added at 86°C over 160 minutes, followed by 30 g of DI water. At the end of the polymerization, a mixture of DI water (15.75 g) containing FeSO4·7H2O (0.005 g) and DI water (15.75 g) containing tetrasodium ethylenediaminetetraacetate (0.005 g), a solution of tert-butyl hydroperoxide (70%, 1.6 g) in DI water (32.76 g), a solution of isoascorbic acid (0.78 g) in DI water (34.32 g), a solution of tert-butyl hydroperoxide (0.78 g) in DI water (16.41 g), and a solution of isoascorbic acid (0.39 g) in DI water (17.19 g) were all added at 60 °C. Then, DI water (16.65 g) containing ammonia (28%, 7.02 g) was added at 50 °C to obtain an aqueous dispersion. The obtained aqueous dispersion was characterized according to the above test methods, and the characterization results are as follows: particle size: 76 nm, pH: 6.96, solids content: 42.75%, viscosity: 3589 centipoise, Tg measured by DSC at 25 °C using a Brookfield viscometer DV-IPrimer (60 RPM and spindle #2): 43 °C, number-average molecular weight (Mn) measured by GPC: 6,629 g / mol, and Mw measured by GPC: 16,586 g / mol.

[0098] IE 1 to IE4 and CE-A to CE-J paint formulation samples

[0099] Tables 3 and 4 list the formulations used to prepare the paint formulations (i.e., coating compositions) samples, with the amount of each component reported in grams (g). The molar ratio of NCO groups to OH groups in each paint formulation is 1.2:1. The components used to prepare the grinding media were mixed at 1,500 RPM for 30 minutes using a high-speed Cowles disperser to form a grinding media. Then, the components in the thinner (letdown) were added to the grinding media using a conventional laboratory mixer to obtain part A. Part A of each paint formulation sample was left to stand overnight, and then the components of part B were added to part A and mixed at 600 RPM for 10 minutes using a high-speed Cowles disperser to form the paint formulation sample. The solids content of each paint formulation sample is given in Tables 3 and 4. The obtained paint formulation samples were characterized according to the test methods described above, and the characterization results are given in Tables 3 and 4, respectively.

[0100] As shown in Table 3, the coating formulations of IE-1, IE-2, IE-3 and IE-4 all showed a long pot life (60° gloss ≥75 after 3 hours of storage at 35°), while providing high gloss (60° initial gloss ≥84) and passing the DOI test (initial DOI ≥70).

[0101] Conversely, as shown in Table 4, paint formulations without branched polyether polyol (CE-A) exhibited unacceptable initial gloss and pot life. Paint formulations containing branched polyether polyol (CE-B) with a lower MW per branch or branched polyether polyol (CE-C to CE-H) with a lower ethylene oxide unit concentration and / or lower functionality all showed shorter pot lives. Compared to the HA-01 emulsion polymer dispersion, the secondary dispersions of hydroxyl acrylic resins, with or without branched polyether polyol 1, provided paint formulations (CE-I and CE-J) with unacceptably short pot lives.

[0102] Table 3. Paint formulation of IE 1 to IE4 samples

[0103]

[0104]

[0105] 1 Polyol concentration: the weight of the branched polyether polyol relative to the solids of the hydroxyacrylic acid polymer dispersion.

[0106] Table 4. Paint formulation of CEA to CEJ samples Examples

[0107]

[0108]

[0109] 1 Polyol concentration: the weight of the branched polyether polyol relative to the solids of the hydroxyacrylic acid polymer dispersion.

Claims

1. A two-component polyurethane composition, said two-component polyurethane composition comprising: (A) An aqueous dispersion comprising: A hydroxyl-containing acrylic emulsion polymer, said hydroxyl-containing acrylic emulsion polymer comprising 5% to 50% by weight of a hydroxyl-functionalized alkyl (meth)acrylate structural unit based on the weight of said hydroxyl-containing acrylic emulsion polymer; and The branched polyether polyol comprises 2% to 20% by weight of the hydroxyl-containing acrylic emulsion polymer; wherein the branched polyether polyol has a hydroxyl functionality of 4 to 10 and a molecular weight of 1200 to 2500 g / mol per branch, and contains 20% to 40% by weight of ethylene oxide units based on the weight of the branched polyether polyol; and (B) Polyisocyanate; The molecular weight of each branch is determined as follows: Mw for each branch = [total MW - MW(initiator)] / Fn Where total MW represents the molecular weight of the polyol, Fn represents the functionality of the polyol, and MW (initiator) represents the molecular weight of the initiator used to prepare the polyol.

2. The two-component polyurethane composition according to claim 1, wherein the branched polyether polyol has the structure of formula (I), R-[O-(AO) x -H] y (I) Wherein R represents a polyvalent aliphatic hydrocarbon group, and each AO is independently selected from ethylene oxide unit, propylene oxide unit, butyl oxide unit, or a combination thereof; provided that the ethylene oxide unit is present at a total concentration of 20% to 40% by weight based on the branched polyether polyol; the subscript x is in the range of 20 to 55; and the subscript y is in the range of 4 to 10.

3. The two-component polyurethane composition according to claim 1, wherein the branched polyether polyol contains 20% to 40% by weight of the ethylene oxide unit and 60% to 80% by weight of the branched polyether polyol.

4. The two-component polyurethane composition according to any one of claims 1 to 3, wherein the polyisocyanate is an aliphatic diisocyanate trimer.

5. The two-component polyurethane composition according to any one of claims 1 to 3, wherein the aqueous dispersion (A) comprises 5% to 10% by weight of the branched polyether polyol based on the weight of the hydroxyl-containing acrylic emulsion polymer.

6. The two-component polyurethane composition according to any one of claims 1 to 3, wherein the hydroxyl-functionalized alkyl (meth)acrylate is selected from 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, or mixtures thereof.

7. The two-component polyurethane composition according to any one of claims 1 to 3, wherein the hydroxyl-containing acrylic emulsion polymer has a weight-average molecular weight of 50,000 g / mol or less.

8. The two-component polyurethane composition according to any one of claims 1 to 3, wherein the glass transition temperature of the acrylic emulsion polymer containing hydroxyl groups is from 10°C to 80°C.

9. The two-component polyurethane composition according to any one of claims 1 to 3, wherein, based on the weight of the hydroxyl-containing acrylic emulsion polymer, the hydroxyl-containing acrylic emulsion polymer comprises 5% to 35% of the structural units of the hydroxyl-functionalized alkyl (meth)acrylate; 0.2% to 5% of the structural units of an acid monomer, its salt, or mixtures thereof; and 60% to 94.8% of the structural units of a monoolefinic unsaturated nonionic monomer other than the hydroxyl-functionalized alkyl (meth)acrylate.

10. The two-component polyurethane composition according to any one of claims 1 to 3, wherein the molar ratio of total isocyanate groups to total hydroxyl groups in the aqueous dispersion (A) is in the range of 0.8:1 to 2.5:

1.

11. The two-component polyurethane composition according to any one of claims 1 to 3, wherein the branched polyether polyol has a molecular weight of 4800 to 15000 g / mol.

12. A method for preparing a two-component polyurethane composition according to any one of claims 1 to 11, the method comprising: The aqueous dispersion (A) is mixed with the polyisocyanate (B).

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