2K varnish coating composition and application thereof

Abstract

The present invention provides a 2K varnish coating composition comprising component (I) comprising (A) a first resin having at least one primary hydroxyl group selected from the group consisting of hydroxyalkyl (meth) acrylate resins having C1-C10 and preferably C2-C6 alkyl groups, (B) a second resin having at least one secondary hydroxyl group selected from the group consisting of hydroxyalkyl (meth) acrylate resins having C1-C10 and preferably C2-C6 alkyl groups, and (C) a second resin having at least one secondary hydroxyl group selected from the group consisting of hydroxyalkyl (meth) acrylate resins having C1-C10 and preferably C2-C6 alkyl groups. A second resin selected from the group consisting of hydroxyalkyl (meth) acrylate resins having C2-C10, and (C) at least one amino resin; and a component (II) comprising (D) a cross-linking agent comprising at least one polyisocyanate wherein the first resin has a hydroxyl value in the range of 100 to 250 mg KOH / g and a weight average molecular weight in the range of 3,000 to 15,000 and the second resin has a hydroxyl value in the range of 150 to 500 mg KOH / g and a weight average molecular weight in the range of 500 to 2,500. The invention also provides an article coated with the coating composition of the invention.

Description

Technical Field

[0001] The present invention relates to a 2K clearcoat paint composition for automobiles. Background Art

[0002] The clearcoat, as the topcoat, provides both decoration and protection for automobiles, and thus it needs to have high initial gloss, good appearance, and sufficient hardness simultaneously. To achieve such performance requirements, the clearcoat must be highly crosslinked through a baking process. Currently, solvent-based 2K clearcoats generally need to be baked at a temperature higher than 140°C for at least 30 min to ensure sufficient crosslinking. Since reducing carbon emissions is becoming a trend in society and lowering the baking temperature can bring huge energy savings, it is necessary to lower the baking temperature as much as possible.

[0003] In addition, for environmental protection purposes, the paint composition forming the clearcoat is required to have low VOC, that is, to have a high solid content. However, low VOC or high solid content brings high viscosity to the paint composition, and it is difficult to obtain good appearance when applying a paint composition with high viscosity, let alone those specific requirements from OEM manufacturers.

[0004] WO2009 / 024351A1 discloses a paint composition comprising: a hydroxyl-containing resin (A) having a hydroxyl value of 80 to 220 mg KOH / g, a glass transition temperature of -50°C or above but below 0°C, and 25 to 55 mass% of (meth)acrylic acid 4-hydroxybutyl ester monomer units; a hydroxyl-containing resin (B) having a hydroxyl value of 80 to 220 mg KOH / g and a glass transition temperature of 0°C to 50°C; and a crosslinking agent (C) comprising a polyisocyanate compound. The paint composition of the present invention is applied as a topcoat paint in an uncrosslinked state and baked at 140°C for 30 min to prepare a sample. In this invention, it requires a relatively high baking temperature to crosslink the topcoat paint.

[0005] CN109476933A discloses a two-layer coating system comprising a first layer containing an aqueous paint composition and a second layer containing a solvent-based paint composition, wherein the catalyst in the aqueous paint composition catalyzes the crosslinking reaction of the solvent-based paint composition but does not catalyze the crosslinking reaction of the aqueous paint composition, and the catalyst in the solvent-based paint composition catalyzes the crosslinking reaction of the aqueous paint composition but does not catalyze the crosslinking reaction of the solvent-based paint composition, wherein the solvent-based and aqueous paint compositions can be cured within 20 minutes at a temperature of 80°C to 120°C. Although the paint composition of this invention can be cured at a relatively low temperature, the two-layer coating system is complex and requires the use of two different catalysts.

[0006] Accordingly, there is still a need to provide a coating composition having both a high solids content and a low viscosity, and the varnish layer obtained or obtainable from this coating composition can exhibit a high initial gloss, good appearance and sufficient hardness even when baked at a relatively low temperature. Summary of the Invention

[0007] In one aspect, the present invention provides a two-component (2K) varnish coating composition comprising

[0008] Component I, which comprises

[0009] (A) a first resin having at least one primary hydroxyl group, the first resin being selected from (meth)acrylic hydroxyalkyl ester resins having C1-C 10 and preferably C2-C6 alkyl groups,

[0010] (B) a second resin having at least one secondary hydroxyl group, the second resin being selected from (meth)acrylic hydroxyalkyl ester resins having C2-C 10 and preferably C2-C6 alkyl groups, and

[0011] (C) at least one amino resin, and

[0012] Component II, which comprises

[0013] (D) at least one polyisocyanate,

[0014] wherein the first resin has a hydroxyl value in the range of 100 to 250 mg KOH / g and a weight average molecular weight in the range of 3,000 to 15,000, and the second resin has a hydroxyl value in the range of 150 to 500 mg KOH / g and a weight average molecular weight in the range of 500 to 2,500.

[0015] In another aspect, the present invention provides an article coated with the coating composition of the present invention.

[0016] Surprisingly, it has been found that the coating composition of the present invention has both low VOC and low viscosity, and in addition the coating composition of the present invention is suitable for low baking temperatures (such as 110 °C). The varnish layer obtained or obtainable therefrom can exhibit a high initial gloss, good appearance and sufficient hardness even when baked at a relatively low temperature. Detailed Description of the Invention

[0017] The present invention will be described in detail hereinafter. It should be understood that the present invention can be implemented in many different ways and should not be construed as limited to the embodiments set forth herein.

[0018] Unless otherwise defined, all technical and scientific terms used herein have the meaning commonly understood by those skilled in the art to which this invention pertains. As used herein, unless otherwise specified, the following terms have the meanings given below.

[0019] As used herein, the article "a / an" refers to one or more than one (i.e., at least one) grammatical object of the article or component.

[0020] As used herein, terms such as "comprise / comprising" etc. are interchangeable with "contain / containing" etc. and should be interpreted in a non-restrictive, open manner. That is to say, for example, there may be additional components or elements. Expressions such as "consisting of" or "consisting essentially of" or cognates may be included in "comprises" or cognates.

[0021] Unless otherwise specified, all percentages (%) are "percentages by weight", and parts indicate parts by weight, and "%" and "wt.%" are used interchangeably in the text.

[0022] In the present invention, "(meth)acrylate" means acrylate and methacrylate, "(meth)acrylic acid" means acrylic acid and methacrylic acid, "(meth)acrylamide" means acrylamide and methacrylamide, "acrylic resin" includes acrylic resin and methacrylic resin, and "acrylic monomer" includes acrylic monomer and methacrylic monomer.

[0023] In the present invention, the acid value (AV) is determined according to DIN EN ISO 2114 (date: June 2002), the hydroxyl value (OH value or OHV) is determined according to DIN 53240-2 (date: November 2007), the solid content is determined according to DIN EN ISO 3251 (date: June 2008), and the weight-average molecular weight is determined according to DIN 55672-1 (date: August 2007).

[0024] In the present invention, the glass transition temperature of the copolymer is the value calculated using the equation indicated below:

[0025] 1 / Tg(K) = Σ(mi / Tgi)

[0026] Tg (°C) = Tg(K) - 273

[0027] Tg: The glass transition temperature of the copolymer

[0028] mi: The MoI fraction of monomer component i

[0029] Tgi: Glass transition temperature (K) of the homopolymer of monomer component i.

[0030] In addition, the glass transition temperature (K) of the homopolymer of monomer component i is based on the values obtained from the fourth edition of POLYMER HANDBOOK, edited by J. Brandrup, E. H. Immergut, and E. A. Grulke (1999). For homopolymers of monomers not described in this literature, the glass transition temperature can be determined by synthesizing a homopolymer of the monomer with a weight-average molecular weight of approximately 50,000 and measuring the glass transition temperature by differential scanning calorimetry.

[0031] First resin

[0032] The first resin has at least one primary hydroxyl group. Preferably, the first resin has at least 60 mol% of primary hydroxyl groups based on the total hydroxyl groups of the first resin, such as at least 70 mol%, at least 80 mol%, at least 90 mol%, and 100 mol% of primary hydroxyl groups.

[0033] The first resin has a Tg (glass transition temperature) in the range of 10°C to 80°C, preferably 10°C to 60°C, more preferably 12°C to 45°C, such as 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, and 75°C.

[0034] The first resin has a hydroxyl value in the range of 100 to 250 mg KOH / g, preferably 120 to 185 mg KOH / g, such as 110 mg KOH / g, 120 mg KOH / g, 130 mg KOH / g, 140 mg KOH / g, 160 mg KOH / g, 170 mg KOH / g, 180 mg KOH / g, 190 mg KOH / g, 210 mg KOH / g, 220 mg KOH / g, 230 mg KOH / g, and 240 mg KOH / g.

[0035] The first resin has a weight-average molecular weight in the range of 3,000 to 15,000, preferably 3,500 to 12,000, such as 3,000, 4,000, 5,000, 6,000, 7,000, 8,000, 9,000, 10,000, 11,000, 12,000, 13,000, and 14,000.

[0036] In a preferred embodiment of the present invention, the first resin is an acrylic resin containing at least one primary hydroxyl group in the molecule.

[0037] An acrylic resin containing at least one primary hydroxyl group can be synthesized by copolymerizing an acrylic monomer containing a primary hydroxyl group and other copolymerizable monomers by a conventional method (such as radical polymerization).

[0038] Examples of acrylic monomers containing a primary hydroxyl group include hydroxyalkyl (meth)acrylates having C1 to C 10 and preferably C2 to C6 alkyl groups, such as 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 7-hydroxyheptyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 7-methyl-8-hydroxyoctyl (meth)acrylate, 2-methyl-8-hydroxyoctyl (meth)acrylate, 9-hydroxynonyl (meth)acrylate; and ethylene oxide and / or propylene oxide adducts of the following: 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate or 4-hydroxybutyl (meth)acrylate, preferably 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 7-hydroxyheptyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 7-methyl-8-hydroxyoctyl (meth)acrylate, 2-methyl-8-hydroxyoctyl (meth)acrylate, 9-hydroxynonyl (meth)acrylate, or a combination thereof, more preferably 2-hydroxyethyl acrylate (2-HEA), 2-hydroxyethyl methacrylate (2-HEMA), 3-hydroxypropyl acrylate (3-HPA), 3-hydroxypropyl methacrylate (3-HPMA), 4-hydroxybutyl acrylate (4-HBA) and 4-hydroxybutyl methacrylate (4-HBMA). The acrylic monomers containing a primary hydroxyl group can be used alone or in combination of two or more monomers.

[0039] Examples of other copolymerizable monomers include C1-C 20 -alkyl (meth)acrylates, preferably C1-C 10-alkyl esters such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, lauryl (meth)acrylate, isobornyl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl methacrylate (CHMA); styrene; (meth)acrylic acid; maleic acid; caprolactone; maleic anhydride; N,N-dimethylaminoethyl (meth)acrylate; N,N-diethylaminoethyl (meth)acrylate; N,N-dimethylaminopropyl (meth)acrylate; aminoalkyl (meth)acrylates; (meth)acrylamide or its derivatives such as N,N-dimethylaminoethyl (meth)acrylamide, N,N-diethylaminoethyl (meth)acrylamide, N,N-dimethylaminopropyl (meth)acrylamide, N-hydroxymethylacrylamide, N-hydroxymethylacrylamide methyl ether, N-hydroxymethylacrylamide butyl ether. Other comonomers can be used alone or in combination with two or more monomers to react with the acrylic monomer containing a primary hydroxyl group in the polymerization.

[0040] Preferably, the other comonomer is at least one selected from the group consisting of methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, (meth)acrylic acid, caprolactone, styrene or a combination thereof, preferably methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, (meth)acrylic acid, caprolactone and styrene.

[0041] The first resin contains units derived from acrylic monomers in an amount of at least 60% by weight, preferably at least 70% and more preferably at least 80% by weight based on the total weight of the first resin, such as 60 wt.%, 65 wt.%, 70 wt.%, 75 wt.%, 80 wt.%, 85 wt.%, 90 wt.% and 95 wt.%. The acrylic monomers include any acrylic monomer having at least one primary hydroxyl group and other copolymerizable acrylic monomers.

[0042] In a preferred embodiment of the present invention, the first resin comprises units derived from acrylic monomers in an amount of 60% to 90% by weight, such as 65% to 85% by weight and 70% to 80% by weight, etc., based on the total weight of the first resin.

[0043] The first resin comprises units derived from acrylic monomers containing primary hydroxyl groups in an amount of 20% to 50% by weight, and preferably 25% to 45% by weight, such as 30 wt.%, 35 wt.%, and 40 wt.%, etc., based on the total weight of the first resin.

[0044] The first resin comprises units derived from other copolymerizable monomers in an amount of 50% to 80% by weight, and preferably 55% to 75% by weight, such as 60 wt.%, 65 wt.%, and 70 wt.%, etc., based on the total weight of the first resin.

[0045] Preferably, the first resin has an acid value in the range of 0 to 20 KOH / mg / g, preferably 2 to 20 KOH / mg / g, such as 5 KOH / mg / g, 10 KOH / mg / g, and 15 KOH / mg / g, etc.

[0046] The 2K coating composition comprises 10% to 70% by weight, and preferably 20% to 50% by weight, such as 10 wt.%, 20 wt.%, 30 wt.%, 40 wt.%, 50 wt.%, 60 wt.%, and 70 wt.%, etc., of the first resin based on the total weight of the coating composition.

[0047] The first resin can be produced by a conventional method such as radical polymerization. Examples of radical polymerization initiators include azo compounds such as 2,2'-azobisisobutyronitrile, 2,2'-azobis-2,4-dimethyl-pentanenitrile, 4,4'-azobis-4-cyanovaleric acid, 1-azobis-1-cyclohexanecarbonitrile, dimethyl-2,2'-azobisisobutyrate, etc., and organic peroxides such as methyl ethyl ketone peroxide, cyclohexanone peroxide, 3,5,5-trimethylhexanone peroxide, 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(tert-butylperoxy)-cyclohexane, 2,2-bis(tert-butylperoxy)octane, tert-butyl hydroperoxide, cumene hydroperoxide, dicumyl peroxide, di-tert-butyl peroxide (DTBP), tert-butyl cumyl peroxide, isobutyl peroxide, lauroyl peroxide, benzoyl peroxide, diisopropyl peroxydicarbonate, tert-butyl 2-ethylhexanoate (TBPEH), tert-butyl neodecanoate, tert-butyl laurate, tert-butyl benzoate, tert-butyl isopropyl carbonate, etc. One of these radical polymerization initiators can be used alone, or a combination of two or more types can be used.

[0048] The amount of the radical polymerization initiator is not particularly limited, but is preferably in an amount of 0.01% to 20% by weight based on the total weight of the radically polymerizable monomers.

[0049] Examples of suitable organic solvents that can be used to produce the first resin include aliphatic hydrocarbon-based solvents such as cyclohexane, ethylcyclohexane, etc.; aromatic hydrocarbon-based solvents such as toluene, xylene, ethylbenzene, aromatic naphtha, etc.; ketone-based solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, isophorone, etc.; ester-based solvents such as ethyl acetate, n-butyl acetate, isobutyl acetate, 3-methoxybutyl acetate, bis(2-ethylhexyl) adipate, etc.; ether-based solvents such as dibutyl ether, tetrahydrofuran, 1,4-dioxane, 1,3,5-trioxane, etc.; and nitrogen-containing solvents such as acetonitrile, valeronitrile, N,N-dimethylformamide, N,N-diethylformamide, etc. The organic solvent can be of one type, or it can be a mixed solvent containing two or more types.

[0050] The method of adding the organic solvent and the radical polymerization initiator during the production of the first resin is optional, but in order to control the polymerization heat and the reaction heat, the method of introducing the organic solvent into the reactor under stirring and dropwise feeding the radically polymerizable monomer or its organic solution from a dropping feed tank is preferred.

[0051] The polymerization temperature of the above polymerization reaction varies depending on the type of the radical polymerization initiator, but it is preferably in the range of 50°C to 200°C, more preferably 100°C to 160°C, and is carried out at temperatures such as 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, and 190°C.

[0052] Second resin

[0053] There is no specific definition for the Tg of the second resin. In one embodiment of the present invention, the second resin has a Tg in the range of -50°C to 150°C, such as -40°C, -30°C, -20°C, -10°C, 0°C, 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, and 140°C.

[0054] The second resin has a hydroxyl value in the range of 150 to 500 mg KOH / g, preferably 200 to 300 mg KOH / g, such as 150 mgKOH / g, 200 mg KOH / g, 250 mg KOH / g, 300 mg KOH / g, 350 mg KOH / g, 400 mg KOH / g, and 450 mg KOH / g.

[0055] The second resin has a weight average molecular weight of less than 3,000, preferably in the range of 500 to 2,500, such as 1,000, 1,500, and 2,000.

[0056] In a preferred embodiment of the present invention, the second resin is an acrylic resin containing at least one secondary hydroxyl group in the molecule.

[0057] The second resin contains monomer units derived from a (meth)acrylic acid hydroxyalkyl ester having C2-C 10 and preferably a C2-C6 alkyl group.

[0058] The acrylic resin containing at least one secondary hydroxyl group can be synthesized by copolymerizing a secondary hydroxyl group-containing acrylic monomer and optionally a primary hydroxyl group-containing acrylic monomer and other copolymerizable monomers by a conventional method (such as free radical polymerization).

[0059] Examples of the secondary hydroxyl group-containing acrylic monomer include (meth)acrylic acid hydroxyalkyl esters having an alkyl group with the number of carbon atoms in the range of 2 to 10, preferably in the range of 2 to 6, such as 1-hydroxyethyl (meth)acrylate, 1- or 2-hydroxypropyl (meth)acrylate, 1-, 2- or 3-hydroxybutyl (meth)acrylate, 1-, 2-, 3- or 4-hydroxypentyl (meth)acrylate, 1-, 2-, 3-, 4- or 5-hydroxyhexyl (meth)acrylate, 1-, 2-, 3-, 4-, 5- or 6-hydroxyheptyl (meth)acrylate, 1-, 2-, 3-, 4-, 5-, 6- or 7-hydroxyoctyl (meth)acrylate; and ethylene oxide and / or propylene oxide adducts of the following: 1-hydroxyethyl (meth)acrylate, 1- or 2-hydroxypropyl (meth)acrylate, 1-, 2- or 3-hydroxybutyl (meth)acrylate, preferably 1-hydroxyethyl (meth)acrylate, 1- or 2-hydroxypropyl (meth)acrylate, and 1-, 2- or 3-hydroxybutyl methacrylate. The secondary hydroxyl group-containing acrylic monomer can be used alone or in combination of two or more monomers.

[0060] Preferably, the secondary hydroxyl group-containing acrylic monomer is at least one selected from the group consisting of 1-hydroxyethyl acrylate (1-HEA), 1-hydroxyethyl methacrylate (1-HEMA), 1- or 2-hydroxypropyl acrylate (1- or 2-HPA), 1- or 2-hydroxypropyl methacrylate (1- or 2-HPMA), 1-, 2- or 3-hydroxybutyl acrylate (1-, 2- or 3-HBA), and 1-, 2- or 3-hydroxybutyl methacrylate (1-, 2- or 3-HBMA), and more preferably 2-hydroxypropyl methacrylate (2-HPMA).

[0061] Examples of the primary hydroxyl group-containing acrylic monomer include those having C1 to C 10And preferably hydroxyalkyl (meth)acrylates of C2 to C6 alkyl, such as 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 7-hydroxyheptyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 7-methyl-8-hydroxyoctyl (meth)acrylate, 2-methyl-8-hydroxyoctyl (meth)acrylate, 9-hydroxynonyl (meth)acrylate; and ethylene oxide and / or propylene oxide adducts of the following: 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, preferably 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 7-hydroxyheptyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 7-methyl-8-hydroxyoctyl (meth)acrylate, 2-methyl-8-hydroxyoctyl (meth)acrylate, 9-hydroxynonyl (meth)acrylate, or a combination thereof, more preferably 2-hydroxyethyl acrylate (2-HEA), 2-hydroxyethyl methacrylate (2-HEMA), 3-hydroxypropyl acrylate (3-HPA), 3-hydroxypropyl methacrylate (3-HPMA), 4-hydroxybutyl acrylate (4-HBA) and 4-hydroxybutyl methacrylate (4-HBMA). The acrylic monomers containing primary hydroxyl groups can be used alone or in combination of two or more monomers.

[0062] Examples of other copolymerizable monomers include C1-C 20 -alkyl (meth)acrylates, preferably C1-C 10- Alkyl esters, such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, lauryl (meth)acrylate, isobornyl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl methacrylate (CHMA); styrene; (meth)acrylic acid; maleic acid; maleic anhydride; N,N-dimethylaminoethyl (meth)acrylate; N,N-diethylaminoethyl (meth)acrylate; N,N-dimethylaminopropyl (meth)acrylate; aminoalkyl (meth)acrylates; (meth)acrylamide or its derivatives, such as N,N-dimethylaminoethyl (meth)acrylamide, N,N-diethylaminoethyl (meth)acrylamide, N,N-dimethylaminopropyl (meth)acrylamide, N-hydroxymethylacrylamide, N-hydroxymethylacrylamide methyl ether, N-hydroxymethylacrylamide butyl ether. Other comonomers can be used alone or in combination with two or more monomers to react with the hydroxyl group-containing acrylic monomers in the polymerization.

[0063] Preferably, the other comonomers are at least one selected from the group consisting of methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, (meth)acrylic acid, styrene or combinations thereof, preferably methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, (meth)acrylic acid and styrene.

[0064] The second resin contains at least 70% by weight, preferably at least 80% and more preferably at least 90% by weight, such as 75 wt.%, 80 wt.%, 85 wt.%, 90 wt.% and 95 wt.% etc., of units derived from acrylic monomers based on the total weight of the second resin. The acrylic monomers include any hydroxyl group-containing acrylic monomers and other copolymerizable acrylic monomers.

[0065] In a preferred embodiment of the present invention, the second resin contains 85% to 95% by weight of units derived from acrylic monomers based on the total weight of the second resin.

[0066] The second resin contains 30% to 70% by weight, preferably 40% to 60% by weight, such as 50 wt.%, of units derived from a hydroxyl group-containing acrylic monomer, preferably a secondary hydroxyl group-containing acrylic monomer, based on the total weight of the second resin.

[0067] The second resin contains 30% to 70% by weight, preferably 40% to 60% by weight, such as 50 wt.%, of units derived from other copolymerizable monomers, based on the total weight of the second resin.

[0068] In one embodiment, the second resin is a resin having at least one secondary hydroxyl group and at least one primary hydroxyl group, wherein the molar ratio of the secondary hydroxyl group to the primary hydroxyl group in the second resin is in the range of 2:1 to 10:1, preferably 3:1 to 5:1, such as 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, and 9:1, etc.

[0069] Preferably, the second resin has an acid value in the range of 0 to 30 KOH / mg / g, such as 5 KOH / mg / g, 10 KOH / mg / g, and 15 KOH / mg / g, etc.

[0070] The coating composition contains 2% to 20% by weight, preferably 5% to 15% by weight, such as 5 wt.%, 10 wt.%, 15 wt.%, and 20 wt.%, etc., of the second resin based on the total weight of the coating composition.

[0071] The weight ratio between the first resin and the second resin in the coating composition is in the range of 2:1 to 10:1, preferably 3:1 to 5:1, such as 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, and 9:1, etc.

[0072] The second resin can be produced by a conventional method such as free radical polymerization, and the method for preparing the first resin is also applicable to the second resin.

[0073] Preferably, the sum of the first resin and the second resin is in the range of 40% to 80% by weight based on the total weight of the coating composition, such as 42 wt.%, 43 wt.%, 44 wt.%, 45 wt.%, 46 wt.%, 47 wt.%, 48 wt.%, 49 wt.%, 50 wt.%, 55 wt.%, 60 wt.%, 65 wt.%, 70 wt.%, and 75 wt.%, etc., based on the total weight of the coating composition.

[0074] Amino resin

[0075] Amino resins are condensation products of aldehydes, especially formaldehyde, with, for example, urea, melamine, guanamine and benzoguanamine. Amino resins contain alcohol groups, preferably methylol groups, which are usually partially or preferably completely etherified with alcohols. In particular, melamine-formaldehyde resins etherified with lower alcohols, especially with methanol or butanol, are used. Very particular preference is given to using melamine-formaldehyde resins etherified with lower alcohols, especially with methanol and / or ethanol and / or butanol, as crosslinkers.

[0076] In this context, any amino resin suitable for transparent topcoat or clearcoat materials, or a mixture of such resins, can be used. Particularly suitable are conventional amino resins, a portion of which methylol and / or methoxymethyl groups have been defunctionalized by urethane or allophanate groups.

[0077] Preferred amino resins are melamine resins as crosslinking agents. Such crosslinking agents are described in patents U.S. Pat. No. 4,710,542 A and EP 0 245 700 B1, and also in the article "Carbamylmethylated Melamines, Novel Crosslinkers for the Coatings Industry" by B. Singh and co-workers, Advanced Organic Coatings Science and Technology Series, 1991, Vol. 13, pp. 193-207. With regard to melamine resins, reference is also made to Rompp Lexikon Lacke und Druckfarben [Rompp Dictionary of Varnishes and Printing Inks], 1988, pages 374 and 375, “Melamine resins” and to Johan Bieleman’s book “Lackadditive” [Additives for Coatings], 1988, pages 242 to 250, in the section on “Melamine-resin-crosslinking systems”.

[0078] Melamine resins are well known to the skilled person and are supplied as commercial products by various companies. Examples of suitable low molecular weight, fully etherified melamine resins are Cytec® from Cytec. 301 and 303, from BASF Aktiengesellschaft 066. From Solutia and MF.

[0079] Examples of suitable relatively low molecular weight, highly etherified melamine resins containing free imino groups are those from Cytec Industries, 325 and 327 (methanol etherified), 202 and 203 (mixture of methanol and butanol etherified) and 1158 (butanol etherified), those from BASF Aktiengesellschaft, 062 (methanol etherified), 018 (butanol etherified) and 014 (butanol etherified, with relatively high viscosity), those from Solutia Inc., MF 927 and 3950 (methanol etherified), VMF 3611 and 3615 (butanol etherified) and 580 (isobutanol etherified) and also 717 and 718 (methanol etherified) and 750 and 5901 (butanol etherified) and also MB 9539, and those from Akzo Resins, US138 and US146 (butanol etherified).

[0080] Examples of suitable relatively low molecular weight, partially etherified melamine resins are those from BASF Aktiengesellschaft, 012, 016, 015, 018 and 010, those from Solutia Inc., MF 590 and 600, and those from Akzo Resins, US132 and 134.

[0081] The amount of the amino resin ranges from 1% to 30% by weight, preferably 5% to 15% by weight, based on the total weight of the coating composition, such as 3 wt.%, 8 wt.%, 10 wt.%, 12 wt.%, 16 wt.%, 18 wt.%, 20 wt.% and 25 wt.%, etc.

[0082] Polyisocyanate

[0083] Polyisocyanates having at least two and preferably at least three isocyanate groups can be used as crosslinking agents in the coating compositions of the present invention, and one type of polyisocyanate or a combination of two or more types of polyisocyanates can be used.

[0084] Examples of polyisocyanates having at least two isocyanate groups / molecule include aliphatic, cycloaliphatic, araliphatic and / or aromatic isocyanates such as 1,4-tetramethylene diisocyanate, hexamethylene diisocyanate (HDI), 2,2,4-trimethylhexane-1,6-diisocyanate, methylcyclohexyl-diisocyanate, p-phenylene diisocyanate, biphenyl diisocyanate, toluene diisocyanate, 3,3'-dimethyl-4,4'-biphenyl diisocyanate, methylene bis(phenyl isocyanate), lysine methyl ester diisocyanate, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (isophorone diisocyanate, IPDI), 2-isocyanatoethyl-2,6-diisocyanatohexanoate, 1,4- and / or 1,3-bis(isocyanatomethyl)cyclohexane (HXDI), cyclohexane 1,4-diisocyanate, 1-methylcyclohexane 2,4- and / or 2,6-diisocyanate and / or dicyclohexylmethane 4,4’-, 2,4’- and 2,2’-diisocyanate, diphenylmethane 2,2’-, 2,4’- and / or 4,4’-diisocyanate (MDI), polymeric MDI, naphthalene 1,5-diisocyanate (NDI), toluene 2,4- and / or 2,6-diisocyanate (TDI), 3,3’-dimethyldiphenyl diisocyanate, 1,2-diphenylethane diisocyanate and / or phenylene diisocyanate, the biuret form, isocyanurate form, oligomeric or polymeric isocyanates of these compounds, or mixtures thereof.

[0085] In a preferred embodiment, the polyisocyanate is an aliphatic polyisocyanate such as Desmodur N100, N75, N3200, N3400, N3600, Desmodur 3390 and Desmodur Z4470 from Covestro. In a preferred embodiment, the polyisocyanate is an oligomeric isocyanate compound such as an isocyanate dimer, an isocyanate trimer, etc. In a specific embodiment, the polyisocyanate is a trimer of HDI such as Desmodur 3390 from Covestro.

[0086] The molar ratio between the NCO groups in the polyisocyanate and the hydroxyl groups in both the first resin and the second resin is in the range of 0.7:1 to 1.6:1 and preferably 1.1:1 to 1.3:1.

[0087] In a specific embodiment according to the present invention, the 2K clearcoat coating composition comprises Component I which comprises

[0088] (A) 15% to 75% by weight and preferably 25% to 60% of a first resin having at least one primary hydroxyl group, the first resin being selected from those having C1-C 10and preferably a hydroxyalkyl (meth)acrylate resin having a C2-C6 alkyl group,

[0089] (B) 2% to 25% by weight and preferably 5% to 15% of a second resin having at least one secondary hydroxyl group, the second resin being selected from those having a C2-C 10 and preferably a hydroxyalkyl (meth)acrylate resin having a C2-C6 alkyl group, and

[0090] (C) at least one amino resin, and

[0091] Component II, which component contains

[0092] (D) at least one polyisocyanate,

[0093] wherein the first resin has a Tg of 10°C to 80°C, a hydroxyl value in the range of 100 to 190 mg KOH / g, and a weight average molecular weight in the range of 3,000 to 15,000, and the second resin has a hydroxyl value in the range of 150 to 500 mg KOH / g and a weight average molecular weight in the range of 500 to 2,500, and the total weight percentage of the first resin and the second resin is in the range of 40% to 80% by weight based on the total weight of the coating composition.

[0094] In another specific embodiment according to the present invention, the 2K clearcoat coating composition contains Component I, which component contains

[0095] (A) 15% to 75% by weight and preferably 25% to 60% of a first resin having at least one primary hydroxyl group, the first resin being selected from those having a C1-C 10 and preferably a hydroxyalkyl (meth)acrylate resin having a C2-C6 alkyl group,

[0096] (B) 2% to 25% by weight and preferably 5% to 15% of a second resin having at least one secondary hydroxyl group, the second resin being selected from those having a C2-C 10 and preferably a hydroxyalkyl (meth)acrylate resin having a C2-C6 alkyl group, and

[0097] (C) at least one amino resin, and

[0098] Component II, which component contains

[0099] (D) at least one polyisocyanate,

[0100] Wherein the first resin has a Tg of 10°C to 80°C, a hydroxyl value in the range of 120 to 140 mg KOH / g, and a weight average molecular weight in the range of 10,000 to 15,000, and the second resin has a hydroxyl value in the range of 150 to 500 mg KOH / g and a weight average molecular weight in the range of 500 to 2,500, and the total weight percentage of the first resin and the second resin is in the range of 40% to 80% by weight based on the total weight of the coating composition.

[0101] In another specific embodiment according to the present invention, the 2K clearcoat coating composition comprises Component I, which component comprises

[0102] (A) 15% to 75% by weight and preferably 25% to 60% by weight of a first resin having at least one primary hydroxyl group, the first resin being selected from (meth)acrylic hydroxyalkyl ester resins having C1-C 10 and preferably C2-C6 alkyl groups,

[0103] (B) 2% to 25% by weight and preferably 5% to 15% by weight of a second resin having at least one secondary hydroxyl group, the second resin being selected from (meth)acrylic hydroxyalkyl ester resins having C2-C 10 and preferably C2-C6 alkyl groups, and

[0104] (C) at least one amino resin, and

[0105] Component II, which component comprises

[0106] (D) at least one polyisocyanate,

[0107] Wherein the first resin has a Tg of 10°C to 80°C, a hydroxyl value in the range of 140 to 190 mg KOH / g, and a weight average molecular weight in the range of 10,000 to 15,000, and the second resin has a hydroxyl value in the range of 150 to 500 mg KOH / g and a weight average molecular weight in the range of 500 to 2,500, and the total weight percentage of the first resin and the second resin is in the range of 40% to 80% by weight based on the total weight of the coating composition.

[0108] In another specific embodiment according to the present invention, the 2K clearcoat coating composition comprises Component I, which component comprises

[0109] (A) 15% to 75% by weight and preferably 25% to 60% by weight of a first resin having at least one primary hydroxyl group, the first resin being selected from (meth)acrylic hydroxyalkyl ester resins having C1-C 10 and preferably C2-C6 alkyl groups,

[0110] (B) 2% to 25% by weight, and preferably 5% to 15% by weight, of a second resin having at least one secondary hydroxyl group, the second resin being selected from (meth)acrylic hydroxyalkyl ester resins having C2-C 10 and preferably C2-C6 alkyl groups, and

[0111] (C) at least one amino resin, and

[0112] Component II, which component comprises

[0113] (D) at least one polyisocyanate,[

[0114] wherein the first resin has a Tg of 10°C to 80°C, a hydroxyl value in the range of 190 to 250 mg KOH / g, and a weight-average molecular weight in the range of 3,000 to 5,000, and the second resin has a hydroxyl value in the range of 150 to 500 mg KOH / g and a weight-average molecular weight in the range of 500 to 2,500, and the total weight percentage of the first resin and the second resin is in the range of 40% to 80% by weight based on the total weight of the coating composition.[

[0115] In another specific embodiment according to the present invention, the 2K clearcoat coating composition comprises Component I, which component comprises

[0116] (A) 15% to 75% by weight, and preferably 25% to 60% by weight, of a first resin having at least one primary hydroxyl group, the first resin being selected from (meth)acrylic hydroxyalkyl ester resins having C1-C 10 and preferably C2-C6 alkyl groups,

[0117] (B) 2% to 25% by weight, and preferably 5% to 15% by weight, of a second resin having at least one secondary hydroxyl group, the second resin being selected from (meth)acrylic hydroxyalkyl ester resins having C2-C 10 and preferably C2-C6 alkyl groups, and

[0118] (C) at least one amino resin, and

[0119] Component II, which component comprises

[0120] (D) at least one polyisocyanate,[

[0121] The first resin has a Tg of 10°C to 80°C, a hydroxyl value in the range of 190 to 250 mg KOH / g, and a weight-average molecular weight in the range of 5,000 to 10,000, and the second resin has a hydroxyl value in the range of 150 to 500 mg KOH / g and a weight-average molecular weight in the range of 500 to 2,500, and the total weight percentage of the first resin and the second resin is in the range of 40% to 80% by weight based on the total weight of the coating composition.

[0122] Various additives can be added as needed, such as leveling agents, sag control agents, defoaming agents, light stabilizers, ultraviolet absorbers, colorants, antioxidants, surfactants, surface control agents, hardening reaction catalysts, antistatic agents, fragrances, dehydrating agents, and rheology control agents such as polyethylene wax, polyamide wax, and fine particles of internally crosslinked resins, etc.

[0123] The coating composition of the present invention can be used as a varnish or a colored paint to which dyes and pigments are added, etc.

[0124] The application of the coating composition of the present invention is carried out by using any method in the prior art, such as an air sprayer, an electrostatic air sprayer, a roll coater, a flow coater or a dip coater, or a brush coater or a bar coater, or an applicator, etc. And spraying is preferred in the present invention.

[0125] The thickness of the paint film obtained by applying the coating composition of the present invention is not limited, but the thickness of the dried paint film is preferably in the range of 10 μm to 150 μm and more preferably 30 μm to 60 μm.

[0126] In addition, examples of the substrate materials for painting the coating composition of the present invention include both inorganic materials and organic materials, such as metals, woods, glasses, cloths, plastics, foams, elastomers, papers, ceramics, concretes, gypsum boards, etc., and metal substrates are preferred. These substrate materials may or may not be pretreated.

[0127] Examples of the coated articles obtained or obtainable include metal products, structural materials, wooden products, plastic products, rubber products, paper products, ceramic products, glass products, etc., and more specifically, they include automobiles and automobile parts (such as body, bumper, spoiler, mirror, wheel, interior decoration parts, etc., which are made of various materials), metal sheets (such as steel sheets), bicycles, bicycle parts, materials used on roads (such as guardrails, traffic signs, sound insulation walls, etc.), materials used in tunnels (such as side wall panels, etc.), ships, railway rolling stocks, aircrafts, furniture, musical instruments, household electrical appliances, building materials, containers, office accessories, sports accessories, toys, etc., and metal products are preferred.

[0128] Example

[0129] Although the following detailed description gives specific preferred embodiments, those skilled in the art will understand that these embodiments are by way of example only and that the invention may be practiced in alternative ways.

[0130] Example 1

[0131] A 2K varnish coating composition comprising

[0132] Component I, which comprises

[0133] (A) A first resin having at least one primary hydroxyl group, the first resin being selected from (meth)acrylic hydroxyalkyl ester resins having C1-C 10 and preferably C2-C6 alkyl groups,

[0134] (B) A second resin having at least one secondary hydroxyl group, the second resin being selected from (meth)acrylic hydroxyalkyl ester resins having C2-C 10 and preferably C2-C6 alkyl groups, and

[0135] (C) At least one amino resin, and

[0136] Component II, which comprises

[0137] (D) At least one polyisocyanate,

[0138] wherein the first resin has a hydroxyl value in the range of 100 to 250 mg KOH / g and a weight-average molecular weight in the range of 3,000 to 15,000, and the second resin has a hydroxyl value in the range of 150 to 500 mg KOH / g and a weight-average molecular weight in the range of 500 to 2,500.

[0139] Example 2

[0140] The coating composition according to Example 1, wherein the first resin has a Tg in the range of 10 °C to 80 °C and preferably 10 °C to 45 °C.

[0141] Example 3

[0142] The coating composition according to any one of Examples 1 to 2, wherein the first resin has an acid value in the range of 0 to 20 and preferably 2 to 20.

[0143] Example 4

[0144] The coating composition according to any one of Embodiments 1 to 3, wherein the first resin has a weight average molecular weight in the range of 3,500 to 12,000.

[0145] Example 5

[0146] The coating composition according to any one of Embodiments 1 to 4, wherein the first resin has a hydroxyl value in the range of 190 to 250 mg KOH / g and a weight average molecular weight in the range of 3,000 to 10,000.

[0147] Example 6

[0148] The coating composition according to any one of Embodiments 1 to 4, wherein the first resin has a hydroxyl value in the range of 100 to 190 mg KOH / g and a weight average molecular weight in the range of 3,000 to 15,000.

[0149] Example 7

[0150] The coating composition according to any one of Embodiments 1 to 6, wherein the second resin has a hydroxyl value in the range of 200 to 300 mg KOH / g.

[0151] Example 8

[0152] The coating composition according to any one of Embodiments 1 to 7, wherein the second resin further contains at least one primary hydroxyl group.

[0153] Example 9

[0154] The coating composition according to Embodiment 8, wherein the molar ratio of secondary hydroxyl groups to primary hydroxyl groups in the second resin is in the range of 2:1 to 10:1, preferably 3:1 to 5:1.

[0155] Example 10

[0156] The coating composition according to any one of Embodiments 1 to 9, wherein the molar ratio of the NCO groups in component (D) to the total hydroxyl groups in components (A) and (B) is in the range of 0.7:1 to 1.6:1 and preferably 1.1:1 to 1.3:1.

[0157] Example 11

[0158] The coating composition according to any one of claims 1 to 10, wherein, based on the total weight of the coating composition, the weight percentage of component (A) is in the range of 15% to 75% and preferably 25% to 60%, and the percentage of component (B) is in the range of 2% to 25% and preferably 5% to 15%, and the total weight percentage of components (A) and (B) is in the range of 40% to 80% and preferably 44% to 60%.

[0159] Example 12

[0160] The coating composition according to any one of Examples 1 to 11, wherein the weight percentage of the amino resin is in the range of 1% to 30% and preferably 5% to 15% based on the total weight of the coating composition.

[0161] Example 13

[0162] The coating composition according to any one of Examples 1 to 12, wherein the amino resin is a melamine resin.

[0163] Example 14

[0164] An article coated with the coating composition according to any one of Examples 1 to 13.

[0165] Examples

[0166] The present invention will be described in a more practical manner by way of illustrative examples below, but the present invention is not limited in any way by these illustrative examples.

[0167] The properties of the paint film obtained with the coating composition of the present invention are determined in the manner indicated below.

[0168] Performance test of varnish

[0169] (1) Tukon hardness

[0170] The hardness of the coating is evaluated by Tukon hardness, which follows ASTM D1474, using a Wilson Tukon 1102 tester.

[0171] (2) Appearance

[0172] The appearance of the dried and cured varnish is evaluated by its surface texture, which is measured by a BYK wave-scan dual-functional instrument. The surface texture is a mixture of various textures ranging from very fine to very rough. The BYK wave-scan dual-functional instrument measures the surface texture at different scale levels, which are divided into six categories (Du, Wa, Wb, Wc, Wd, We) according to the wavelength. Based on the data measured, Lw, Sw, and DOI are calculated by the device and represent the appearance level of the paint layer. Lower Lw and Sw and higher DOI values indicate better appearance performance. Lw is mainly defined by the varnish layer, while Sw and DOI are defined not only by the varnish layer but also by the substrate and the primer coat. Generally, good appearance performance is defined by Lw < 5 and Sw < 15 simultaneously.

[0173] (3) Glossiness

[0174] The glossiness of the coating surface is measured at a 20° angle using a BYK Haze-Gloss meter according to the DIN 67530 method. Automotive coatings are a type of high-gloss coatings, and in such coatings, the higher the glossiness, the better the final application effect.

[0175] (4) VOC

[0176] The VOC is evaluated based on the measurement of the solid content according to the methods described in GB / T 38597 / 2020, GB / T 1725-2007, and GB / T 23985-2009. The solid content is measured by the following method: Weigh 1 g of the sample in an aluminum dish with a diameter of 75 mm, and then bake it at 105 °C for 1 h. The VOC is calculated according to the equation listed below. For all the samples and comparative samples listed in the present invention, the density ρ of the measured paint sample is 0.97 g / mL.

[0177] ρ(VOC) = (100 – NV) × ρ × 10

[0178] ρ(VOC) = Calculated value of sample VOC, g / L

[0179] NV = Solid content of the sample, expressed as a mass fraction (%)

[0180] ρ = Density of the paint sample measured at 23 °C, g / mL

[0181] Materials

[0182] 91756VS-60YA is a sag control agent from Allnex

[0183] 202 is an amino resin crosslinking agent from Allnex

[0184] 4045 is a catalyst from Allnex

[0185] 110 is a leveling agent from BYK Chemie

[0186] 325N is a leveling agent from BYK Chemie

[0187] 315N is a leveling agent from BYK Chemie

[0188] 355 is a leveling agent from BYK Chemie

[0189] ES 80 is a conductive additive from BYK Chemie

[0190] OX-883HF is an antifoaming agent from King Industries

[0191] 5248 is a light stabilizer from BASF

[0192] Desmodur 3390 is a polyisocyanate crosslinking agent from Covestro

[0193] The first resin in the following preparation examples was prepared according to the monomer composition and weight ratio shown in Table 1

[0194] Table 1: Monomer composition of the first resin

[0195] First resin St CHMA n-BA n-BMA 2-HEA 2-HEMA AA 1 24.4 20 5.8 19.8 29 0 0 2 24.4 35.8 0 3.6 35.2 0 0 3 24.4 30.7 0 0 20.7 23.2 0 4 24.4 28.3 0 15.1 14.5 16.2 1 5 24.4 15.8 0 23.6 35.2 0 1 6 24.4 33.2 0 0 35.2 6.2 1 7 24.4 29.8 0 14.8 29 0 2 8 24.4 27.8 0 8.5 17.6 19.7 2 9 24.4 18.8 0 13.4 41.4 0 2

[0196] Note: St: Styrene; 2-HEA: 2-Hydroxyethyl acrylate; 2-HEMA: 2-Hydroxyethyl methacrylate; n-BA: n-Butyl acrylate; n-BMA: n-Butyl methacrylate; CHMA: Cyclohexyl methacrylate; AA: Acrylic acid

[0197] Preparation example of First resin 1

[0198] Charge 25.492 parts by weight of solvent naphtha 160 / 180 (SN) into a stainless steel reactor equipped with a reflux condenser and an N2 inlet, and heat this initial charge to 160 °C while maintaining the pressure at 1.5 bar. Thereafter, over a period of 4.5 hours, meter in the initiator solution (6 parts by weight of di-tert-butyl peroxide (DTBP) in 1.42 parts by weight of solvent naphtha 160 / 180 (SN)) at a uniform rate with stirring. Meter in the monomer mixture containing 24.4 parts by weight of styrene (ST), 20 parts by weight of cyclohexyl methacrylate (CHMA), 5.8 parts by weight of n-butyl acrylate (n-BA), 19.8 parts by weight of n-butyl methacrylate (n-BMA) and 29 parts by weight of 2-hydroxyethyl acrylate (2-HEA) at a uniform rate over a period of 4 hours with stirring. Thereafter, maintain the reaction mixture at 150 °C at 1.5 bar pressure for 1.5 hours. Then cool the reaction mixture to 80 °C and dilute it by adding 0.913 parts by weight of solvent naphtha 160 / 180 (SN) and 7 parts by weight of n-butyl acrylate (BA).

[0199] Preparation examples of First resin 2 to First resin 9

[0200] The preparation examples of First Resin 2 to First Resin 9 are the same as those of First Resin 1, except for the monomer composition, as shown in Table 1.

[0201] The characteristics of the prepared First Resin are shown in Table 2.

[0202] Table 2: Characteristics of First Resin

[0203] First resin Tg OHV AV MW Solid content (wt%) 1 12 123 5.95 3788 59.5％ 2 45 147 2.6 6581 59.2％ 3 34 193 1.98 10556 55.0％ 4 26 121 9.49 5150 60.0％ 5 24 153 8.85 11329 60.0％ 6 34 161 11.97 4692 60.4％ 7 36 122 15.16 10014 59.5％ 8 39 150 17.7 3935 59.7％ 9 26 182 18.36 7495 59.8％

[0204] Preparation example of Second resin

[0205] Charge 27 parts by weight of solvent naphtha 160 / 180 (SN) into a stainless-steel reactor equipped with a reflux condenser and an N2 inlet, and heat this initial charge to 160 °C while maintaining the pressure at 2.5 bar. Subsequently, over a period of 4.75 hours, a solution of initiator (1 part by weight of di-tert-butyl peroxide (DTBP) in 2.02 parts by weight of solvent naphtha 160 / 180 (SN)) is metered in at a uniform rate with stirring. A monomer mixture containing 5 parts by weight of n-butyl methacrylate (n-BMA), 22 parts by weight of 2-ethylhexyl methacrylate (EHMA), 8 parts by weight of cyclohexyl methacrylate (CHMA), 12 parts by weight of styrene (ST), 42 parts by weight of 2-hydroxypropyl methacrylate (2-HPMA), 10 parts by weight of 4-hydroxybutyl acrylate (4-HBA), and 1 part by weight of acrylic acid (AA) is metered in at a uniform rate over a period of 4 hours with stirring. Thereafter, the reaction mixture is maintained at 110 °C under normal atmospheric pressure for 1.5 hours. Then the reaction mixture is cooled to 80 °C and diluted by adding 26.85 parts by weight of solvent naphtha 160 / 180 (SN). The resulting polyacrylate solution has a solids content of 65% by weight.

[0206] Preparation of 2K varnish coating composition

[0207] Table 3 describes the composition of Component I of the 2K varnish composition. Subsequently, all the components listed in the table are mixed to obtain Component I. To obtain Component II, Desmodur 3390 (from Covestro) is diluted to 80% by weight in a mixture of solvent naphtha and butyl acetate (1:1 by weight). The molar ratio of NCO in Component II to the total OH in Component I is 1.2:1.

[0208]

[0209] Preparation of dried and cured film

[0210] Mix Component I and Component II of each 2K coating composition, and stir the mixture uniformly; spray the mixture onto a steel plate and bake at 110 °C for 20 minutes. The coating composition in Comparative Example 2 is cured by using the polyisocyanate Desmodur 3390 alone in Component II without using an amino resin 202. The coating composition in Comparative Example 3 contains only Component I and no Component II, and thus this coating composition is cured only by the amino resin 202 in Component I.

[0211] Comparative example 4

[0212] Comparative Example 4 is a commercially available 2K clearcoat (trademark: ProGloss) from BASF, which was sprayed onto a steel sheet and baked at 140 °C for 20 minutes. ProGloss uses the same type of resin as Component B in the coating composition of the present invention, but uses a different resin from Component A in the coating composition of the present invention.

[0213] Comparative example 5

[0214] Comparative Example 5 is the same as Comparative Example 4, except that the baking temperature is 110 °C.

[0215] The evaluation of the clearcoat film was carried out in a multi-layer coating, which included a black aqueous primer coat (or white aqueous primer coat) produced from a commercial black (or white) aqueous primer coat material from BASF Shanghai Coatings Co., Ltd. The black primer coat and the white primer coat were selected because these two primer coats are basic and the most readily available. The results are shown in Table 4.

[0216]

[0217] As can be seen from Table 4, the examples of the present invention simultaneously show a high solid content (i.e., low VOC) and a low viscosity, and the obtained clearcoat layer exhibits a high initial gloss, good appearance, and sufficient hardness, while the comparative examples show one or more drawbacks.

[0218] It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. The embodiments and examples are intended to be considered only as exemplary. Accordingly, the present invention is intended to cover such modifications and variations within the scope of the appended claims and their equivalents.

Claims

1. A 2K varnish coating composition, which comprises Component I, which component comprises (A) A first resin having at least one primary hydroxyl group, the first resin being selected from (meth)acrylic hydroxyalkyl ester resins having C1-C 10 and preferably C2-C6 alkyl groups, (B) A second resin having at least one secondary hydroxyl group, the second resin being selected from (meth)acrylic acid hydroxyalkyl ester resins having C2-C 10 and preferably C2-C6 alkyl groups, and (C) at least one amino resin, and Component II, which component comprises (D) a crosslinking agent comprising at least one polyisocyanate, wherein the first resin has a hydroxyl value in the range of 100 to 250 mg KOH / g and a weight average molecular weight in the range of 3,000 to 15,000, and the second resin has a hydroxyl value in the range of 150 to 500 mg KOH / g and a weight average molecular weight in the range of 500 to 2,500.

2. The coating composition according to claim 1, wherein The first resin has a Tg in the range of 10 °C to 80 °C and preferably 10 °C to 45 °C.

3. The coating composition according to any one of claims 1 to 2, wherein, The first resin has an acid value in the range of 0 to 20 and preferably 2 to 20.

4. The coating composition according to any one of claims 1 to 3, wherein, The first resin has a weight average molecular weight in the range of 3,500 to 12,000.

5. The coating composition according to any one of claims 1 to 4, wherein, The first resin has a hydroxyl value in the range of 190 to 250 mg KOH / g and a weight average molecular weight in the range of 3,000 to 10,000.

6. The coating composition according to any one of claims 1 to 4, wherein, The first resin has a hydroxyl value in the range of 100 to 190 mg KOH / g and a weight average molecular weight in the range of 3,000 to 15,000.

7. The coating composition according to any one of claims 1 to 6, wherein The second resin has a hydroxyl value in the range of 200 to 300 mg KOH / g.

8. The coating composition according to any one of claims 1 to 7, wherein, The second resin further comprises at least one primary hydroxyl group.

9. The coating composition according to claim 8, wherein, The molar ratio of secondary hydroxyl groups to primary hydroxyl groups in the second resin is in the range of 2:1 to 10:1, preferably 3:1 to 5:

1.

10. The coating composition according to any one of claims 1 to 9, wherein, The molar ratio of NCO groups in component (D) to the total hydroxyl groups in components (A) and (B) is in the range of 0.7:1 to 1.6:1 and preferably 1.1:1 to 1.3:

1.

11. The coating composition according to any one of claims 1 to 10, wherein Based on the total weight of the coating composition, the weight percentage of component (A) is in the range of 15% to 75% and preferably 25% to 60%, and the percentage of component (B) is in the range of 2% to 25% and preferably 5% to 15%, and the total weight percentage of components (A) and (B) is in the range of 40% to 80% and preferably 44% to 60%.

12. The coating composition according to any one of claims 1 to 11, wherein, The weight percentage of the amino resin is in the range of 1% to 30% and preferably 5% to 15% based on the total weight of the coating composition.

13. The coating composition according to any one of claims 1 to 12, wherein, The amino resin is a melamine resin.

14. An article coated with the coating composition according to any one of claims 1 to 13.

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