Composition containing hydroxy acrylic resin and two-component coating composition containing the same

Abstract

The present invention relates to a composition comprising a hydroxy acrylic resin and a two-component coating composition comprising the composition, wherein the hydroxy acrylic resin is formed by solution polymerization of a monomer mixture, wherein the monomer mixture comprises, relative to the total weight of the monomer mixture, a) 1-10% by weight of a multifunctional melamine-formaldehyde acrylic resin; b) 10-45% by weight of a hydroxy C1-C20 alkyl (meth)acrylate; and c) 45-80% by weight of other ethylenically unsaturated monomers other than a) and b); wherein the composition has a solids content of at least 75% by weight, based on the weight of the hydroxy acrylic resin. Furthermore, the present invention relates to a two-component coating composition comprising the above-mentioned composition comprising a hydroxy acrylic resin and a polyisocyanate crosslinker.

Description

Technical Field

[0001] The present invention relates to a high-solid, low-viscosity resin composition, in particular to a composition comprising a hydroxy acrylic resin and a two-component coating composition comprising the resin composition. Background Art

[0002] In recent years, as people have become more concerned about the environment, many countries have enacted environmental laws and regulations requiring further reductions in the amount of VOCs that coating compositions, particularly solvent-based coating compositions, are allowed to release into the air.

[0003] The coatings industry aims to develop a variety of green, environmentally friendly coatings to replace current solvent-based coatings. Current development focuses on the following areas: high-solids, low-viscosity coatings, water-based coatings, powder coatings, and UV-curable coatings. Compared to other environmentally friendly coating solutions, high-solids, low-viscosity coatings can be produced using existing traditional solvent-based coating production equipment and are compatible with traditional solvent-based coating systems. Consequently, they have experienced rapid growth both domestically and internationally in recent years.

[0004] Hydroxylated acrylic resins are a very important class of film-forming resins used in solvent-based coating compositions. They can be cured in a variety of ways, such as with isocyanate curing agents at low temperatures and with amino resin curing agents at high temperatures. They cure quickly without affecting gloss or color, and exhibit high hardness, weather resistance, color retention, adhesion, and water resistance. Consequently, hydroxylated acrylic resins are widely used in aviation, automotive, transportation, machinery, and light industrial products.

[0005] In recent years, the research and development of high-solids, low-viscosity (hereinafter referred to as "HSLV") hydroxylated acrylic resin compositions has rapidly developed. However, most of the HSLV hydroxylated acrylic resin compositions currently available on the market suffer from shortcomings such as slow curing speed and low hardness.

[0006] Therefore, the coatings industry still needs a hydroxy acrylic resin composition that has both high solid content, low viscosity, and high curing rate. Summary of the Invention

[0007] The present invention provides a composition comprising a hydroxy acrylic resin, wherein the hydroxy acrylic resin is formed by solution polymerization of a monomer mixture, the monomer mixture comprising, relative to the total weight of the monomer mixture,

[0008] a) 1-10% by weight of a multifunctional melamine formaldehyde acrylic resin;

[0009] b) 10 to 45% by weight of hydroxy C1-C20 alkyl (meth)acrylate; and

[0010] c) 45 to 80% by weight of other ethylenically unsaturated monomers different from a) and b);

[0011] The composition has a solid content of at least 75 wt % based on the weight of the hydroxy acrylic resin.

[0012] In an embodiment of the present invention, the viscosity of the composition comprising the hydroxy acrylic resin is in the range of 500 to 5000 mPa·s, and the viscosity is measured at 25° C. using a Brookfield viscometer.

[0013] In an embodiment according to the present invention, the hydroxy value of the hydroxy acrylic resin is in the range of 30-180 mg KOH / g.

[0014] According to another aspect of the present invention, there is provided a two-component coating composition comprising:

[0015] (i) a film-forming resin composition comprising the composition comprising a hydroxy acrylic resin according to the present invention; and

[0016] (ii) Polyisocyanate crosslinking agent.

[0017] In an embodiment of the present invention, the cured coating obtained from the two-component coating composition according to the present invention has a pencil hardness of at least 3B, preferably at least 2B, after baking at 60° for 20 minutes according to GB / T6739-2006.

[0018] In the present invention, the applicant uses a specific multifunctional melamine formaldehyde acrylic resin as a monomer, mixes it with other common acrylic resin monomers, and obtains a high-solid, low-viscosity composition containing a hydroxy acrylic resin after solution polymerization. Because the hydroxy acrylic resin has a three-dimensional, highly branched structure, its molecules do not form chain entanglements, and its viscosity is much lower than that of linear analogs with similar molecular weight. Therefore, the solid content of the composition can reach 75% by weight or higher, and the viscosity is as low as 500-5000mPa·s. The preparation process of the composition containing a hydroxy acrylic resin synthesized by the present invention is simple, low-cost, and has the characteristics of fast curing speed and high hardness. It can be applied to fields such as heavy machinery coating.

[0019] The details of one or more embodiments of the invention are set forth in the description below. Other features, objects, and advantages of the invention will become apparent from the description and claims.

[0020] definition

[0021] As used herein, "a," "an," "the," "at least one," and "one or more" and the like, as well as the absence of quantifiers, are used interchangeably. Thus, for example, a component comprising "an" additive can be interpreted to mean that the component comprises "one or more" additives.

[0022] Where a composition is described as comprising or including specific components, it is contemplated that optional components not contemplated by the present invention are not excluded from the composition, and that the composition may consist of or be composed of the components contemplated; or where a method is described as comprising or including specific process steps, it is contemplated that optional process steps not contemplated by the present invention are not excluded from the method, and that the method may consist of or be composed of the process steps contemplated.

[0023] For simplicity, only some numerical ranges are explicitly disclosed herein. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, and similarly, any upper limit can be combined with any other upper limit to form an unspecified range. In addition, although not explicitly stated, each point or individual value between the endpoints of a range is included in the range. Thus, each point or individual value can serve as its own lower limit or upper limit and be combined with any other point or individual value, or with other lower limits or upper limits, to form an unspecified range.

[0024] In the context of the present invention, "hydroxy acrylic resin" refers to a type of resin obtained by polymerizing (meth)acrylic acid ester monomers and hydroxyalkyl (meth)acrylate monomers and optionally other ethylenically unsaturated monomers in the presence of an initiator.

[0025] The term "high solids content" when used in reference to a "resin composition" means that the resin composition has a solids content of at least 75 wt% or more, wherein the solids content is calculated based on the weight of the resin components in the resin composition.

[0026] In the context of the present invention, the term "solvent-based coating composition" refers to a coating composition with an organic solvent as a dispersion medium and containing less than 2 g / L of water, preferably substantially no water, more preferably substantially no water, and even more preferably no water.

[0027] When used with respect to a "solvent-borne coating composition," the term "substantially free" of water means that the solvent-borne coating composition of the present invention contains less than 1000 parts per million (ppm) of water; the term "essentially free" of water means that the solvent-borne coating composition of the present invention contains less than 100 ppm of water; the term "essentially completely free" of water means that the solvent-borne coating composition of the present invention contains less than 5 ppm of water; and the term "completely free" of water means that the solvent-borne coating composition of the present invention contains less than 20 parts per billion (ppb) of water.

[0028] In the context of the present invention, the term "ethylenically unsaturated monomer" refers to a monomer having ethylenically unsaturated groups, including reactive carbon-carbon double bond unsaturated groups in cis- or trans-configuration, but excluding aromatic unsaturated groups, carbon-carbon triple bonds, and carbon-heteroatom unsaturated groups.

[0029] In the context of the present invention, the term "monomer mixture" refers to a mixture consisting of reactive monomers, excluding solvents that do not participate in the reaction.

[0030] When used in this description and claims, the terms "comprises" and "includes" and variations thereof do not have a limiting meaning.

[0031] The terms "preferred" and "preferably" refer to embodiments of the invention that may offer certain benefits under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful and is not intended to exclude other embodiments from the scope of the invention. DETAILED DESCRIPTION

[0032] In one aspect, the present invention provides a composition comprising a hydroxy acrylic resin, wherein the hydroxy acrylic resin is formed by solution polymerization of a monomer mixture, wherein the monomer mixture comprises, relative to the total weight of the monomer mixture,

[0033] a) 1-10% by weight of a multifunctional melamine formaldehyde acrylic resin;

[0034] b) 10 to 45% by weight of hydroxy C1-C20 alkyl (meth)acrylate; and

[0035] c) 45 to 80% by weight of other ethylenically unsaturated monomers different from a) and b);

[0036] The composition has a solid content of at least 75 wt % based on the weight of the hydroxy acrylic resin.

[0037] The composition comprising a hydroxy acrylic resin according to the present invention not only has a high solid content but also has a very low viscosity and can thus be used to formulate solvent-based coating compositions without introducing excessive VOCs. In an embodiment according to the present invention, the composition comprising a hydroxy acrylic resin has a solid content of at least about 75% by weight, preferably at least 78% by weight, and more preferably at least 80% by weight, based on the weight of the hydroxy acrylic resin. The inventors were surprised to find that the composition of the hydroxy acrylic resin of the present invention has a significantly lower viscosity while maintaining a high solid content. In an embodiment according to the present invention, the hydroxy acrylic resin composition has a viscosity of 5000 mPa.s or less, more preferably 4000 mPa.s or less, and more preferably 3000 mPa.s or less, measured at 25°C using a BROOKFIELD viscometer.

[0038] Preferably, in some embodiments according to the present invention, the viscosity of the composition containing hydroxyl acrylic resin is in the range of 500 to 5000 mPa.s, preferably in the range of 600 to 3500 mPa.s, more preferably in the range of 800 to 2500 mPa.s, and the viscosity is measured using a BROOKFIELD viscometer at 25°C.

[0039] According to the composition comprising a hydroxylated acrylic resin of the present invention, its viscosity is related to the molecular weight and molecular weight distribution of the hydroxylated acrylic resin. Therefore, in some embodiments according to the present invention, the number average molecular weight (Mn) of the hydroxylated acrylic resin is in the range of 800-8000 g / mol, preferably in the range of 1000-3000 g / mol; and the molecular weight distribution coefficient (PDI=Mw / Mn) is in the range of 1.5-4. The molecular weight and the molecular weight distribution coefficient can be determined using gel permeation chromatography (GPC), for example, Agilent 1260.

[0040] In the composition according to the present invention comprising a hydroxylated acrylic resin, the hydroxylated acrylic resin is hydroxyl-functional. Thus, according to an embodiment of the present invention, the hydroxylated acrylic resin has a hydroxyl value greater than 30 mg KOH / g. In one embodiment of the present invention, the hydroxylated acrylic resin has a hydroxyl value of 30-180 mg KOH / g, preferably 70-120 mg KOH / g. The hydroxyl value is determined by titration according to ISO 4629-1998.

[0041] In the composition comprising a hydroxy acrylic resin according to the present invention, the hydroxy acrylic resin is formed by solution polymerization of a monomer mixture, and therefore the composition comprising a hydroxy acrylic resin according to the present invention contains a certain amount of organic solvent. However, the composition is high solid and low viscosity, and therefore contains a relatively small amount of organic solvent, for example, no more than 25% by weight of organic solvent, preferably no more than 23% by weight of organic solvent, relative to the total weight of the composition comprising a hydroxy acrylic resin.

[0042] The preparation process of the composition containing the hydroxylated acrylic resin requires the use of a solvent. The solvent can be selected from solvents commonly used in the art. Examples include, but are not limited to, aromatic hydrocarbons such as benzene, toluene, and xylene; alcohols such as ethanol, isopropyl alcohol, n-butanol, tert-butanol, and ethylhexanol; esters such as ethyl acetate, propyl acetate, butyl acetate, isobutyl acetate, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, and propylene glycol monomethyl ether acetate. Other suitable solvents include ketones such as methyl ethyl ketone, methyl n-amyl ketone, and methyl isobutyl ketone; glycols such as propylene glycol and diethylene glycol; and glycol ethers such as propylene glycol monomethyl ether and ethylene glycol monomethyl ether. Of course, various mixtures of solvents can be used. According to the present invention, the amount of organic solvent can be very low, for example, no more than 25% by weight of organic solvent, preferably no more than 23% by weight of organic solvent, relative to the total weight of the composition containing the hydroxylated acrylic resin, without affecting the preparation of the composition containing the hydroxylated acrylic resin.

[0043] According to the present invention, the monomer mixture comprises, relative to the total weight of the monomer mixture, a) 1-10 wt% of a multifunctional melamine formaldehyde acrylic resin; b) 10-45 wt% of a hydroxy C1-C20 alkyl (meth)acrylate; and c) 45-80 wt% of other ethylenically unsaturated monomers different from components a) and b).

[0044] The inventors of the present invention surprisingly discovered that, in the presence of an initiator and a very small amount of an organic solvent, a specific multifunctional melamine formaldehyde acrylic resin (hereinafter referred to as the "first monomer") is used as a monomer and mixed with other common acrylic monomers to obtain a high-solid, low-viscosity composition containing a hydroxy acrylic resin after solution polymerization. In an embodiment according to the present invention, the functionality of the multifunctional melamine formaldehyde acrylic resin is 3-6. The hydroxy acrylic resin produced by copolymerizing the multifunctional melamine formaldehyde acrylic resin with a (meth) hydroxy C1-C20 alkyl acrylate and other ethylenically unsaturated monomers has a high degree of branching. Since the molecule has a three-dimensional, highly branched structure, chain entanglement does not occur between its molecules, and its viscosity is much lower than that of linear analogs with similar molecular weights. Therefore, based on the weight of the hydroxy acrylic resin, the solid content of the composition containing the hydroxy acrylic resin can reach 75% by weight or more, and the viscosity is as low as 1000-5000 mPa·s.

[0045] Therefore, in the preparation of the composition comprising a hydroxy acrylic resin according to the present invention, a first monomer is essential. As described above, the inventors surprisingly discovered that by introducing the first monomer, i.e., a multifunctional melamine formaldehyde acrylic resin (preferably with a functionality of 3-6), during the preparation of the resin composition, the viscosity of the resin composition can be significantly reduced while maintaining a high solids content, thereby enabling the formulation of a solvent-based coating composition with low VOC emissions without the need for additional reactive diluents.

[0046] Examples of suitable C1-C20 hydroxyalkyl (meth)acrylates include, but are not limited to, hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxybutyl methacrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, or any combination thereof. Preferably, the C1-C20 hydroxyalkyl (meth)acrylate is selected from at least one of hydroxyethyl methacrylate, hydroxypropyl methacrylate, and hydroxybutyl methacrylate, more preferably, from hydroxyethyl methacrylate.

[0047] In the present invention, a hydroxy C1-C20 alkyl (meth)acrylate is present to provide a hydroxy-functional final resin composition. Preferably, the hydroxy C1-C20 alkyl (meth)acrylate is present in an amount of 10-45 wt. %, preferably 15-40 wt. %, based on the total weight of the monomer mixture. The presence of the hydroxy C1-C20 alkyl (meth)acrylate monomer ensures that the resulting composition comprising the hydroxy acrylic resin according to the present invention can be used to formulate a two-component solvent-borne coating composition.

[0048] In the composition comprising a hydroxy acrylic resin according to the present invention, the monomer mixture further comprises other ethylenically unsaturated monomers other than the aforementioned multifunctional melamine formaldehyde acrylic resin and hydroxy C1-C20 alkyl (meth)acrylate. These monomers can be used to adjust the mechanical strength of the resulting resin composition. Examples of suitable other ethylenically unsaturated monomers other than a) and b) include, but are not limited to, C1-C20 alkyl (meth)acrylates, vinyl aromatic compounds having up to 20 carbon atoms, and optionally unsaturated carboxylic acids. The unsaturated carboxylic acid refers to an unsaturated carboxylic acid containing a double bond structure, preferably acrylic acid and / or methacrylic acid.

[0049] Therefore, according to one embodiment of the present invention, the monomer mixture comprises, relative to the total weight of the monomer mixture,

[0050] a) 1-10% by weight of a multifunctional melamine formaldehyde acrylic resin;

[0051] b) 10 to 45% by weight of hydroxy C1-C20 alkyl (meth)acrylate;

[0052] c1) 35 to 60% by weight of C1-C20 alkyl (meth)acrylate;

[0053] c2) 10 to 50% by weight of vinyl aromatic compounds having up to 20 carbon atoms; and

[0054] c3) 0 to 5% by weight of (meth)acrylic acid.

[0055] Examples of suitable C1-C20 alkyl methacrylates for use in the present invention include, but are not limited to, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, sec-butyl methacrylate, tert-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-octyl methacrylate, 2-ethylhexyl methacrylate (also known as isooctyl methacrylate), nonyl methacrylate, 2-methyloctyl methacrylate, 2-tert-butylheptyl methacrylate, 3-isopropylheptyl methacrylate, decyl methacrylate, undecyl methacrylate, 5-methylundecyl methacrylate, dodecyl methacrylate. methacrylate, 2-methyldodecyl methacrylate, tridecyl methacrylate, 5-methyltridecyl methacrylate, tetradecyl methacrylate, pentadecyl methacrylate, hexadecyl methacrylate, 2-methylhexadecyl methacrylate, heptadecyl methacrylate, 5-isopropylheptadecyl methacrylate, 5-ethyloctadecyl methacrylate, octadecyl methacrylate, nonadecyl methacrylate, eicosyl methacrylate, cycloalkyl methacrylates (e.g., cyclopentyl methacrylate, cyclohexyl methacrylate, 3-vinyl-2-butylcyclohexyl methacrylate, cycloheptyl methacrylate, cyclooctyl methacrylate), bornyl methacrylate, and isobornyl methacrylate. Preferred are methyl methacrylate, ethyl methacrylate, butyl methacrylate, tert-butyl methacrylate, or isobornyl methacrylate, and particularly preferred are methyl methacrylate or isobornyl methacrylate.

[0056] Examples of suitable C1-C20 alkyl acrylates for use in the present invention include, but are not limited to, methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, sec-butyl acrylate, tert-butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2-octyl acrylate, 2-ethylhexyl acrylate (also known as isooctyl acrylate), nonyl acrylate, 2-methyl-octyl acrylate, 2-tert-butylheptyl acrylate, 3-isopropylheptyl acrylate, decyl acrylate, undecyl acrylate, 5-methylundecyl acrylate, dodecyl acrylate, propyl acrylate, 1-octyl acrylate, 2-octyl acrylate, 2-ethylhexyl acrylate (also known as isooctyl acrylate), 1-octyl acrylate, 2-octyl acrylate, 2-octyl acrylate, 2-octyl acrylate, 3-isopropylheptyl acrylate, decyl acrylate, 1-octyl acrylate, 1-octyl acrylate, 2 ... The acrylates include 2-methyldodecyl acrylate, tridecyl acrylate, 5-methyltridecyl acrylate, tetradecyl acrylate, pentadecyl acrylate, hexadecyl acrylate, 2-methylhexadecyl acrylate, heptadecyl acrylate, 5-isopropylheptadecyl acrylate, 5-ethyloctadecyl acrylate, octadecyl acrylate, nonadecyl acrylate, eicosyl acrylate, cycloalkyl acrylates (e.g., cyclopentyl acrylate, cyclohexyl acrylate, 3-vinyl-2-butylcyclohexyl acrylate, cycloheptyl acrylate, cyclooctyl acrylate), bornyl acrylate, and isobornyl acrylate. Preferred are ethyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, or cyclohexyl acrylate, and particularly preferred are ethyl acrylate, n-butyl acrylate, or 2-ethylhexyl acrylate.

[0057] Examples of vinyl aromatic compounds having up to 20 carbon atoms include, but are not limited to, styrene, vinyltoluene, o-methylstyrene, p-methylstyrene, α-butylstyrene, 4-n-butylstyrene, 4-n-decylstyrene, halogenated styrenes (e.g., monochlorostyrene, dichlorostyrene, tribromostyrene or tetrabromostyrene), with styrene being preferred.

[0058] Therefore, the present invention also relates to a method for preparing a composition comprising a hydroxy acrylic resin according to the present invention, comprising: initiating polymerization of the monomer mixture with an initiator in the presence of an organic solvent in an amount of not more than 25% by weight, preferably not more than 23% by weight, relative to the total weight of the composition comprising the hydroxy acrylic resin, and a chain transfer agent, thereby forming the composition comprising the hydroxy acrylic resin. The composition thus obtained has a solids content of at least 75% by weight, based on the weight of the hydroxy acrylic resin.

[0059] The appropriate conditions for the above reaction depend on various factors, including the type of polymerizing monomer and the type of initiator, etc., which can be determined empirically by those skilled in the art.

[0060] Any known thermal initiator can be used to initiate the polymerization reaction. Examples of suitable thermal initiators include persulfates such as ammonium persulfate or alkali metal persulfates (including potassium, sodium or lithium); peroxides such as benzoyl peroxide, cumyl hydroperoxide, t-butyl hydroperoxide, di-t-butyl peroxide, di-t-amyl peroxide, 1,1-bis(t-amylperoxy)cyclohexane, dioctyl peroxide, t-butyl pervalerate, t-butyl peroxy-2-ethylhexanoate, t-butyl perisononanoate, t-butyl peroctoate, t-butyl perneodecanoate, di(2-ethylhexyl) peroxydicarbonate, di(isotridecyl) peroxydicarbonate; azo compounds such as azobisisobutyronitrile), azobisisovaleronitrile and azobis(4-cyanovaleric acid). Preferably, an oil-soluble thermal initiator such as azobisisobutyronitrile or peroxide is used, such as azobisisoheptanitrile, azobisisovaleronitrile, azobiscyclohexylcarbonitrile, dimethyl azobisisobutyrate, benzoyl peroxide, tert-butyl peroxy-2-ethylhexanoate, 1,1-bis(tert-amylperoxy)cyclohexane, di-tert-butyl peroxide, or di-tert-amyl peroxide. More specifically, azobisisobutyronitrile, di-tert-butyl peroxide, or di-tert-amyl peroxide is used as the thermal initiator. Preferably, the thermal initiator is present in an amount of 0.1-10% by weight relative to the total feed amount.

[0061] In particular, the initiator is added by uniformly mixing the initiator with the reactants to be reacted, and then adding the mixture to the solvent by dropwise addition, or the initiator and the reactants to be reacted are stored separately and added dropwise to the solvent at the same time, and the addition time is 1 to 8 hours, preferably 3 to 6 hours.

[0062] According to the present invention, during the preparation of the composition comprising the hydroxy acrylic resin, a chain transfer agent is added, wherein the chain transfer agent is selected from one or more of isopropyl alcohol, a halogenated compound, a linear or branched C2-C22 alkyl mercaptan, a mercaptoalkanol, a mercaptoalkanoic acid, and an alkyl mercaptoalkanoate, preferably one or more of n-dodecyl mercaptan, tert-dodecyl mercaptan, mercaptoethanol, and mercaptopropionic acid, and is preferably present in an amount of 0.1-10% by weight relative to the total feed amount. The chain transfer agent can be added once or in multiple times or continuously, linearly, or nonlinearly over most or all of the reaction period.

[0063] The inventors surprisingly discovered that the composition containing a hydroxyl acrylic resin according to the present invention can be used alone or as a film-forming resin composition in combination with a crosslinking agent capable of crosslinking therewith to produce a two-component coating composition that can be cured under high-temperature baking conditions. The present invention utilizes specific polymerizable monomers and process conditions to produce a composition containing a hydroxyl acrylic resin having a specific molecular weight, molecular weight distribution, and hydroxyl number. The two-component coating composition formed from this composition containing a hydroxyl acrylic resin exhibits high hardness after curing into a paint film, for example, a pencil hardness of at least 3B, preferably at least 2B, after baking at 60°C for 20 minutes according to GB / T 6739-2006.

[0064] Therefore, according to another aspect of the present invention, there is provided a two-component coating composition comprising:

[0065] (i) a film-forming resin composition comprising the composition comprising a hydroxy acrylic resin according to the present invention; and

[0066] (ii) Polyisocyanate crosslinking agent.

[0067] The cured coating obtained from the two-component coating composition according to the present invention has a pencil hardness of at least 3B, preferably at least 2B, after baking at 60° for 20 minutes according to GB / T 6739-2006.

[0068] Polyisocyanate crosslinker

[0069] The term "polyisocyanate crosslinker" as used herein refers to a polyisocyanate compound, an isocyanate oligomer, or a combination thereof. The polyisocyanate crosslinker contains two or more isocyanate functional groups, which can undergo chain extension and crosslinking reactions with the film-forming resin composition to form a three-dimensional network structure in the coating.

[0070] Examples of polyisocyanate crosslinking agents are blocked or unblocked aliphatic, cycloaliphatic or aromatic divalent, trivalent or polyvalent isocyanates such as hexamethylene diisocyanate, cyclohexyl 1,4-diisocyanate, etc. Other non-limiting examples of generally suitable blocked polyisocyanates include isophorone diisocyanate, dicyclohexylmethane diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, phenylene diisocyanate, tetramethylxylene diisocyanate, xylylene diisocyanate and isomers of mixtures thereof.

[0071] As examples of suitable isocyanate oligomers, polyurethane prepolymers of any of the polyisocyanate compounds listed above, polyester prepolymers of any of the polyisocyanate compounds listed above, or polyether prepolymers of any of the polyisocyanate compounds listed above, and any combination thereof, can be used. Polyurethane prepolymers, polyester prepolymers, or polyether prepolymers can be made by any suitable method known to those of ordinary skill in the art. For example, polyurethane prepolymers can be made by reacting a polyol monomer with one or more of the polyisocyanate compounds under suitable conditions; polyester prepolymers or polyether prepolymers can be made by reacting a polyester polyol or a polyether polyol with one or more of the polyisocyanate compounds under suitable conditions. Alternatively, any suitable commercial product can be used as the polyurethane prepolymer, polyester prepolymer, or polyether prepolymer.

[0072] Preferred polyisocyanate crosslinking agents are unblocked or blocked polyisocyanates, more preferably blocked polyisocyanates, and even more preferably polymeric.

[0073] Polymeric blocked polyisocyanates may be used in certain embodiments. Some examples of suitable polymeric blocked polyisocyanates include biuret or isocyanurate of diisocyanates, trifunctional "trimers," or mixtures thereof. Examples of suitable trimers may include trimerization products made from an average of three diisocyanate molecules, or trimers made by reacting an average of three moles of a diisocyanate (e.g., HDMI) with one mole of another compound, such as a triol (e.g., trimethylolpropane).

[0074] As an example of the polyisocyanate crosslinking agent, any suitable commercially available product may be used, such as DESMODUR N3600 (a polymeric blocked polyisocyanate based on hexamethylene diisocyanate (HDI) trimer) from Bayer.

[0075] According to the present invention, the amount of the polyisocyanate crosslinker and the film-forming resin composition is selected so that the molar ratio of hydroxyl (OH) to isocyanate (NCO) in the resulting system varies within the range of 1:1 to 1:2.5. Generally speaking, when the molar ratio of hydroxyl (OH) to isocyanate (NCO) is less than 1:2.5, the handling performance of the resulting two-component coating composition and / or the mechanical properties of the resulting coating may decrease. When the molar ratio of hydroxyl (OH) to isocyanate (NCO) is greater than 1:1, the curing performance of the resulting coating is poor. Depending on actual needs, an additional inert diluent that does not affect the reactivity of the above film-forming resin composition and polyisocyanate crosslinker may be added during the preparation of the film-forming resin composition and / or the polyisocyanate crosslinker, for example to reduce the viscosity of each component. Therefore, the amount of the film-forming resin composition and the polyisocyanate curing agent is not limited to the above range and can be adjusted according to actual needs.

[0076] In two-component coating compositions according to the present invention, the film-forming resin composition can also include conventional additives, and these additives do not adversely affect the two-component coating composition or the cured coating obtained therefrom. Suitable additives include, for example, those reagents that can improve the processing properties or manufacturing performance of the composition, enhance the aesthetic feeling of the composition, improve the specific functional properties or characteristics (such as adhesion to substrate) of the coating composition or the cured coating obtained therefrom or reduce costs. The additive that can include, for example, filler, lubricant, film-forming aid, wetting agent, plasticizer, defoamer, colorant, antioxidant, flow control agent, thixotropic agent, dispersant, adhesion promoter, thickening agent, pH adjusting agent, solvent, curing catalyst or its combination. The content of each optional component is enough to play its intention to achieve purpose, but preferably, such content does not adversely affect the two-component coating composition or the cured coating obtained therefrom. In a preferred embodiment, the film-forming resin composition can include catalyst (for example dialkyl tin salt of fatty acid), film-forming aid, leveling agent, solvent or its arbitrary combination as conventional additives. According to the present invention, the total amount of conventional additives is from 0.1 wt % to about 40 wt % relative to the total weight of the film-forming resin composition.

[0077] In one specific embodiment of the present invention, the film-forming resin composition comprises, relative to the weight of the film-forming resin composition, 55-90 weight % of a composition comprising a hydroxy acrylic resin according to the present invention; 5-20 weight % of a solvent; 5-20 weight % of a film-forming aid; 0-5 weight % of a leveling agent; and 0-5 weight % of a catalyst.

[0078] Examples of film-forming aids include alcohols such as ethylene glycol, propylene glycol, hexylene glycol, and benzyl alcohol; alcohol esters such as dodecyl alcohol; alcohol ethers such as ethylene glycol butyl ether, propylene glycol methyl ether, propylene glycol ethyl ether, propylene glycol n-propyl ether, propylene glycol butyl ether, dipropylene glycol methyl ether, dipropylene glycol propyl ether, dipropylene glycol butyl ether, and tripropylene glycol n-butyl ether; and alcohol ether esters such as hexylene glycol monobutyl ether acetate and propylene glycol monomethyl ether acetate. Examples of leveling agents include BYK300 and BYK358N, available from BYK, Germany.

[0079] According to the present invention, the two-component coating composition can be prepared as follows: before application, the film-forming resin composition and the polyisocyanate crosslinking agent are simply mixed in a mixing device in a predetermined weight ratio. The mixed coating composition can be applied using various methods familiar to those skilled in the art, including spraying (e.g., air-assisted, airless or electrostatic spraying), brushing, roller coating, overflow coating and dipping. In one embodiment of the present invention, the mixed coating composition is applied by spraying. The coating composition can be applied to various wet film thicknesses. In an embodiment of the present invention, the wet film thickness preferably provides a dry film thickness of about 13 to about 260 μm, and more preferably about 75 to about 150 μm. The applied coating can be cured by air drying or by accelerating the curing using various drying devices familiar to those skilled in the art (e.g., ovens).

[0080] The two-component coating composition of the present invention has utility in a variety of applications. Therefore, embodiments of the present invention also include a coated article comprising a substrate having at least one major surface; and a coating applied directly or indirectly to the major surface of the substrate, the coating being formed from the two-component coating composition of an embodiment of the present invention.

[0081] In certain embodiments of the present invention, the two-component coating composition of the present invention may be used in conjunction with a primer. In this case, the coated article of the present invention comprises a substrate, a primer layer, and a coating layer formed from the two-component coating composition of the present invention.

[0082] In other embodiments of the present invention, the two-component coating composition of the present invention can be applied without a primer and directly coated on the major surface of the substrate.

[0083] Substrates that can benefit from having the two-component coating composition of the present invention applied to their surfaces are generally metal substrates, non-limiting examples of which include hot-rolled steel, cold-rolled steel, hot-dip galvanized sheet, electrogalvanized sheet, aluminum sheet, tin sheet, various grades of stainless steel, and aluminum-zinc alloy coated steel sheet (e.g., GALVALUME steel sheet or GAL panel).

[0084] The following examples more particularly describe the present disclosure, which are intended to be illustrative only, as various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by weight, and all reagents used in the examples are commercially available and can be used directly without further treatment.

[0085] Example

[0086] Test Method

[0087] Adhesion

[0088] The cross-cutting method is used according to GB / T 9286-1998, and the evaluation is based on a scale of 0-5, where 0 is the best and 5 is the worst.

[0089] Pencil hardness

[0090] This test is used to measure the hardness of a cured coating. The cured coating is baked at 60°C for 20 minutes or at 80°C for 30 minutes to evaluate the pencil hardness using GB / T 6739-2006, with a coating thickness of 30-40 microns.

[0091] Example

[0092] Below, the content disclosed in the present invention is described in more detail by examples. These examples are only for illustrative description and are not to be construed as limiting the scope of protection of the present invention, because it is obvious to those skilled in the art that various modifications and variations are made within the scope of the present invention.

[0093] Unless otherwise stated, all parts, percentages and ratios reported in the following examples are by weight, and all reagents used in the examples are commercially available and used directly without further treatment.

[0094] Preparation of compositions containing hydroxylated acrylic resins

[0095] The monomers for preparing the hydroxylated acrylic resin were mixed, and after adding an initiator and a chain transfer agent, the mixture was added dropwise to a reaction vessel containing a solvent over a period of 3 hours at a reaction temperature of 100°C. After the addition, the mixture was kept at 110°C for 1 hour, cooled, and discharged to obtain a high-solid, low-viscosity composition containing the hydroxylated acrylic resin.

[0096] According to the above steps and the formulations shown in Table 1, compositions containing hydroxy acrylic resins of samples 1 to 3 were prepared respectively.

[0097] Table 1: Preparation and characterization of compositions containing hydroxylated acrylic resins

[0098]

[0099] Preparation and performance testing of two-component coating compositions

[0100] The three compositions containing hydroxy acrylic resin prepared above and a commercially available hydroxy acrylic resin (Zhanxin SETALUX27-1550) were prepared into a two-component coating composition according to the following ratio.

[0101] The above-mentioned raw materials were mixed uniformly in a disperser to obtain a two-component coating composition. This was then applied to tinplate and dried at 60°C for 20 minutes and 80°C for 30 minutes. The composition was then tested for pencil hardness according to GB / T6739-2006. Furthermore, adhesion was tested using the cross-hatch method according to GB / T9286-1998. The test results are shown in the following table:

[0102] Table 2: Composition and test results of two-component coating compositions

[0103]

[0104] It can be seen from the results in Tables 1 and 2 that the hydroxyl acrylic resin composition according to the present invention is itself high-solid and low-viscosity. After being combined with a polyisocyanate crosslinker, the two-component coating composition formulated has both high curing rate and high hardness. The curing rate and hardness of the obtained two-component coating composition are comparable to or even better than those of a two-component coating composition formulated with a conventional commercial hydroxyl acrylic resin. Therefore, it can be used in fields such as heavy machinery coating.

[0105] The foregoing detailed description of the invention and examples are given for clarity of understanding only. No unnecessary limitations are to be understood therefrom. The invention is not limited to the precise details shown and described, and variations obvious to one skilled in the art are intended to be included within the invention as defined by the claims.

[0106] In some embodiments, the invention illustratively disclosed herein can be practiced in the absence of any element not explicitly disclosed herein. Although the invention has been described with reference to a number of embodiments and examples, one of ordinary skill in the art will recognize that other embodiments can be devised based on the present disclosure without departing from the scope and spirit of the invention.

Claims

1. A composition comprising a hydroxy acrylic resin, wherein the hydroxy acrylic resin is formed by solution polymerization of a monomer mixture, the monomer mixture comprising, relative to the total weight of the monomer mixture, a) 1-10% by weight of a multifunctional melamine formaldehyde acrylic resin; b) 10 to 45% by weight of hydroxy C1-C20 alkyl (meth)acrylate; and c) 45 to 80% by weight of other ethylenically unsaturated monomers different from a) and b); in, The composition has a solids content of at least 75% by weight based on the weight of the hydroxy acrylic resin; The viscosity of the composition comprising the hydroxy acrylic resin is in the range of 500 to 5000 mPa·s, as measured using a Brookfield viscometer at 25° C.; and The hydroxyl value of the hydroxy acrylic resin is in the range of 30-180 mg KOH / g.

2. The composition according to claim 1, characterized in that The multifunctional melamine formaldehyde acrylic resin has a functionality of 3-6.

3. The composition according to claim 1 or 2, characterized in that The other ethylenically unsaturated monomers include C1-C20 alkyl (meth)acrylates, vinyl aromatic compounds having up to 20 carbon atoms and optionally (meth)acrylic acid.

4. The composition according to claim 3, characterized in that The monomer mixture comprises, relative to the total weight of the monomer mixture, a) 1-10% by weight of a multifunctional melamine formaldehyde acrylic resin; b) 10 to 45% by weight of hydroxy C1-C20 alkyl (meth)acrylate; c1) 35 to 60% by weight of C1-C20 alkyl (meth)acrylate; c2) 10 to 50% by weight of (meth)acrylic acid or a vinylaromatic compound having up to 20 carbon atoms; and c3) 0 to 5% by weight of (meth)acrylic acid.

5. The composition according to claim 1 or 2, characterized in that The composition is prepared by initiating polymerization of the monomer mixture using an initiator in the presence of a chain transfer agent and a solvent, thereby forming the composition including the hydroxy acrylic resin.

6. The composition according to claim 5, characterized in that The chain transfer agent is selected from one or more of isopropyl alcohol, halogenated compounds, linear or branched C2-C22 alkyl mercaptans, mercaptoalkanols, mercaptoalkanoic acids and mercaptoalkanoic acid alkyl esters.

7. The composition according to claim 5, characterized in that The chain transfer agent is selected from one or more of n-dodecyl mercaptan, tert-dodecyl mercaptan, mercaptoethanol and mercaptopropionic acid.

8. A two-component coating composition comprising: (i) a film-forming resin composition comprising the composition comprising a hydroxy acrylic resin according to any one of claims 1 to 7; and (ii) Polyisocyanate crosslinking agent.

9. A cured coating obtained from the two-component coating composition of claim 8, having a pencil hardness of at least 3B after baking at 60°C for 20 minutes according to GB / T 6739-2006.

10. A cured coating obtained from the two-component coating composition of claim 8, having a pencil hardness of at least 2B after baking at 60°C for 20 minutes according to GB / T 6739-2006.

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